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The 2 GB limit refers to a physical memory barrier for a process running on a 32-bit operating system, which can only use a maximum of 2 GB of memory. The problem mainly affects 32-bit versions of operating systems like Microsoft Windows and Linux, although some variants of the latter can overcome this barrier. It is also found in servers like FTP servers or embedded systems like Xbox. The use of Physical Address Extension (PAE) can overcome this barrier by extending the addresses used to represent mappings between virtual and physical memory.
The limit is created by the 32-bit integer limit (2,147,483,647), which is the largest possible integer that can be represented by 32 binary digits. In a computer with a 32-bit architecture, the memory address stored in one of the CPU registers will be limited to this number, thus the number of possible memory locations that can be addressed is limited to exactly 2 gibibytes, or roughly 2GB.
While Linux, FreeBSD, and most Unix-like operating systems support PAE so long as the hardware does, Windows needs this boot option enabled manually because many device drivers are incompatible with PAE. This is known as 4-gigabyte tuning (4GT), or the /3GB switch. Once enabled, executables can have the "large address aware" flag set to increase their memory limit to 3 GB. 32-bit processes on 64-bit Windows are also limited to 2 GB. However, they can use the "large address aware" flag as well, except that it doesn't require the /3GB switch and increases the limit to 4 GB.
== See also ==
640 KB barrier
3 GB barrier
== References ==

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The ACM Computing Classification System (CCS) is a subject classification system for computing devised by the Association for Computing Machinery (ACM). The system is comparable to the Mathematics Subject Classification (MSC) in scope, aims, and structure, being used by the various ACM journals to organize subjects by area.
== History ==
The system has gone through seven revisions, the first version being published in 1964, and revised versions appearing in 1982, 1983, 1987, 1991, 1998, and the now current version in 2012.
== Structure ==
It is hierarchically structured in four levels. For example, one branch of the hierarchy contains:
Computing methodologies
Artificial intelligence
Knowledge representation and reasoning
Ontology engineering
== See also ==
Computer Science Ontology
Physics and Astronomy Classification Scheme
arXiv, a preprint server allowing submitted papers to be classified using the ACM CCS
Physics Subject Headings
== References ==
Coulter, Neal (1997), "ACM's computing classification system reflects changing times", Communications of the ACM, 40 (12), New York, NY, USA: ACM: 111–112, doi:10.1145/265563.265579, S2CID 42548816.
Coulter, Neal (chair); French, James; Glinert, Ephraim; Horton, Thomas; Mead, Nancy; Ralston, Anthony; Rada, Roy; Rodkin, Craig; Rous, Bernard; Tucker, Allen; Wegner, Peter; Weiss, Eric; Wierzbicki, Carol (January 21, 1998), "Computing Classification System 1998: Current Status and Future Maintenance Report of the CCS Update Committee" (PDF), Computing Reviews, New York, NY, USA: ACM: 1–5.
Mirkin, Boris; Nascimento, Susana; Pereira, Luis Moniz (2008), "Representing a Computer Science Research Organization on the ACM Computing Classification System", in Eklund, Peter; Haemmerlé, Ollivier (eds.), Supplementary Proceedings of the 16th International Conference on Conceptual Structures (ICCS-2008) (PDF), CEUR Workshop Proceedings, vol. 354, RWTH Aachen University, pp. 57–65.
== External links ==
dl.acm.org/ccs is the homepage of the system, including links to four complete versions of the system:
the 1964 version Archived 2016-12-01 at the Wayback Machine
the 1991 version Archived 2017-09-21 at the Wayback Machine
the 1998 version
the current 2012 version.
The ACM Computing Research Repository uses a classification scheme that is much coarser than the ACM subject classification, and does not cover all areas of CS, but is intended to better cover active areas of research. In addition, papers in this repository are classified according to the ACM subject classification.
The ACM/IEEE/AAAI Computer Science Curriculum Guidance 2023 describes a body of knowledge for computer science divided into 17 knowledge areas, similar to the above classifications.

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ALF ("Another logical framework") is a structure editor for monomorphic Martin-Löf type theory developed at Chalmers University. It is a predecessor of the Alfa, Agda, Cayenne and Rocq proof assistants and dependently typed programming languages. It was the first language to support inductive families and dependent pattern matching.
== References ==
== Further reading ==
Lena Magnusson and Bengt Nordström. "The ALF proof editor and its proof engine".
Thorsten Altenkirch, Veronica Gaspes, Bengt Nordström and Björn von Sydow. "A user's guide to ALF".
== External links ==
Alfa

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In computer science, the terms TBox and ABox are used to describe two different types of statements in knowledge bases. TBox statements are the "terminology component", and describe a domain of interest by defining classes and properties as a domain vocabulary. ABox statements are the "assertion component" — facts associated with the TBox's conceptual model or ontologies.
Together ABox and TBox statements make up a knowledge base or a knowledge graph.
ABox statements must be TBox-compliant: they are assertions that use the vocabulary defined by the TBox.
TBox statements are sometimes associated with object-oriented classes and ABox statements associated with instances of those classes.
== Examples of ABox and TBox statements ==
ABox statements typically deal with concrete entities. They specify what category an entity belongs to, or what relation one entity has to another entity.
Item A is-an-instance-of Category C
Item A has-this-relation-to Item B
Examples:
Niger is-a country.
Chad is-a country
Niger is-next-to Chad.
Agadez is-a city.
Agadez is-located-in Niger.
TBox statements typically (or definitions of domain categories and implied relations) such as:
An entity X can be a country or a city
So Dagamanet is-a neighbourhood is not a fact you can specify, though it is a fact in real life.
A is-next-to B if B is-next-to A
So Niger is-next-to Chad implies Chad is-next-to Niger.
X is a place if X is-a city or X is-a country.
So Niger is-a country implies Niger is-a place.
place A contains place B if place B is-located-in A.
So Agadez is-located-in Niger implies Niger contains Agadez.
TBox statements tend to be more permanent within a knowledge base and are used and stored as a schema or a data model. In contrast, ABox statements are much more dynamic in nature and tend to be stored as instance data within transactional systems within databases. With the newer, NoSQL databases and especially with RDF databases (see Triplestore) the storage distinction may no longer apply. Data and models can be stored using the same approach. However, models continue to be more permanent, have a different lifecycle and are typically stored as separate graphs within such database.
== See also ==
Description logic § Modeling
Metadata
Web Ontology Language
Extensional and intensional definitions
== References ==

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The Abstract Rewriting Machine (ARM) is a virtual machine which implements term rewriting for minimal term rewriting systems.
Minimal term rewriting systems are left-linear term rewriting systems in which each rule takes on one of six forms:
Each of these six forms is mapped (in ARM) to one or a few processor instructions on most contemporary micro processors. Accordingly, minimal term rewriting is achieved at tens to hundreds of clock cycles per reduction step—millions of reduction steps per second.
ARM implements general term rewriting, in that every single-sorted unconditional left-linear term rewriting system can be transformed (compiled) into a minimal term rewriting system that gives rise to the same normal form relation.
An overview with references to this compilation process for innermost rewriting, as well as a detailed overview of ARM, can be found in "Within ARM's reach: compilation of left-linear rewrite systems via minimal rewrite systems". A description for lazy (non-innermost) rewriting can be found in "Lazy rewriting on eager machinery".
A documented implementation of ARM (with the term rewriting language Epic) is available here. Note that site and software are no longer being actively maintained.
== References ==
Giesl, J. R.; Middeldorp, A. (July 2004). "Transformation techniques for context-sensitive rewrite systems" (PDF). Journal of Functional Programming. 14 (4): 379–427. CiteSeerX 10.1.1.127.2817. doi:10.1017/S0956796803004945.
Lucas, Salvador (2002). "Lazy Rewriting and Context-Sensitive Rewriting" (PDF). Electronic Notes in Theoretical Computer Science. 64: 234–254. CiteSeerX 10.1.1.14.3470. doi:10.1016/S1571-0661(04)80353-0. Archived from the original (PDF) on 2006-05-16. Retrieved 2015-08-29.
Nguyen, Quang-Huy (2001). "Compact Normalisation Trace via Lazy Rewriting" (PDF). Electronic Notes in Theoretical Computer Science. 57: 87–108. CiteSeerX 10.1.1.24.771. doi:10.1016/S1571-0661(04)00269-5. S2CID 38634432.
Schernhammer, F.; Gramlich, B. (April 2008). "Termination of Lazy Rewriting Revisited" (PDF). Electronic Notes in Theoretical Computer Science. 204: 35–51. CiteSeerX 10.1.1.142.1957. doi:10.1016/j.entcs.2008.03.052.
Kirchner, C.; Kirchner, H. (2014). "Equational Logic and Rewriting" (PDF). Handbook of the History of Logic. 9: 255–282. doi:10.1016/B978-0-444-51624-4.50006-X. ISBN 9780444516244.
Antoy, S.; Johannsen, J.; Libby, S. (2015). "Needed Computations Shortcutting Needed Steps". Electronic Proceedings in Theoretical Computer Science. 183: 18–32. arXiv:1505.07162v1. doi:10.4204/EPTCS.183.2.

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Activity-centered design (ACD) is an extension of the Human-centered design paradigm in interaction design. ACD features heavier emphasis on the activities that a user would perform with a given piece of technology. ACD has its theoretical underpinnings in activity theory, from which activities can be defined as actions taken by a user to achieve a goal.
When working with activity-centered design, the designers use research to get insights of the users. Observations and interviews are typical approaches to learn more about the users' behavior. By mapping users' activities and tasks, the designer may notice missing tasks for the activity to become more easy to perform, and thus design solutions to accomplish those tasks.
== References ==
Saffer, Dan. 2010. Designing for interaction.
Gay, Geri and Helene Hembrooke. 2004. Activity-Centered Design: An Ecological Approach to Designing Smart Tools and Usable Systems.
Norman, Don. 2015. The Design of Everyday Things: Revised and Expanded Edition.
Niaz Mahmud " Activity Center Design"
== Notes ==

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In computing, an addressable cursor is a cursor which can, through use of either software or firmware, be moved (at least theoretically) to any given point on the computer screen.
== References ==

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title: "Adobe Content Server"
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Adobe Content Server is software developed by Adobe Systems to add digital rights management to e-books. It is designed to protect and distribute Adobe e-books in PDF or EPUB format through Adobe Digital Editions, or applications and devices developed using Adobe's Adobe Reader Mobile SDK, covering a wide range of tablets, smartphones, and dedicated devices. Adobe Content Server also works in conjunction with Adobe Digital Experience Protection Technology (ADEPT), Adobe's digital rights management scheme.
== See also ==
Digital library
Public library
Online shopping
Publishing
Adobe Digital Editions
== References ==

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Albert Charles Zettlemoyer (July 13, 1915 – January 27, 1991) was an American chemist, researcher and university professor.
== Life ==
He was born on 13 July 1915.
He died on 27 January 1991 in Bethlehem, Pennsylvania.
== Education ==
He attended the Lehigh University, where he completed his B.S. degree in chemical engineering in 1936 and an M.S. degree in 1938. He completed his Ph.D. in physical chemistry from Massachusetts Institute of Technology in 1941.
== Career ==
He became the president of the American Chemical Society in 1981. He also served as the provost and vice president of Lehigh University.
He published more than 230 technical articles and held 10 patents.
== References ==
== External links ==
https://mitmuseum.mit.edu/collections/object/GCP-00029663
https://www.findagrave.com/memorial/63798794/albert-c_-zettlemoyer
https://www.sciencedirect.com/author/24751529100/albert-c-zettlemoyer
https://pubs.acs.org/doi/10.1021/cen-v069n005.p005a

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Alewife was a cache coherent multiprocessor developed in the early 1990s by a group led by Anant Agarwal at the Massachusetts Institute of Technology. It was based on a network of up to 512 processing nodes, each of which used the Sparcle computer architecture, which was formed by modifying a Sun Microsystems SPARC CPU to include the APRIL techniques for fast context switches.
The Alewife project was one of two predecessors cited by the creators of the popular Beowulf cluster multiprocessor.
== References ==
== External links ==
MIT Alewife Project
Kubiatowicz, John. "The Alewife-1000 CMMU: Addressing the multiprocessor communications gap" (PDF). hotchips.org. Archived from the original (PDF) on April 23, 2016. Retrieved Feb 5, 2020.

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title: "Algebraic Logic Functional programming language"
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Algebraic Logic Functional (ALF) programming language combines functional and logic programming techniques. Its foundation is Horn clause logic with equality, which consists of predicates and Horn clauses for logic programming, and functions and equations for functional programming.
ALF was designed to be genuine integration of both programming paradigms, and thus any functional expression can be used in a goal literal and arbitrary predicates can occur in conditions of equations. ALF's operational semantics is based on the resolution rule to solve literals and narrowing to evaluate functional expressions. To reduce the number of possible narrowing steps, a leftmost-innermost basic narrowing strategy is used which, it is claimed, can be efficiently implemented. Terms are simplified by rewriting before a narrowing step is applied and equations are rejected if the two sides have different constructors at the top. Rewriting and rejection are supposed to result in a large reduction of the search tree and produce an operational semantics that is more efficient than Prolog's resolution strategy. Similarly to Prolog, ALF uses a backtracking strategy corresponding to a depth-first search in the derivation tree.
The ALF system was designed to be an efficient implementation of the combination of resolution, narrowing, rewriting, and rejection. ALF programs are compiled into instructions of an abstract machine, which is based on the Warren Abstract Machine (WAM) with several extensions to implement narrowing and rewriting. In the current ALF implementation programs of this abstract machine are executed by an emulator written in C.
In the Carnegie Mellon University Artificial Intelligence Repository, ALF is included as an AI programming language, more so as a functional/logic programming language Prolog implementation. A user manual describing the language and the use of the system is available. The ALF System runs on Unix and is available under a custom proprietary software license that grants the right to use for "evaluation, research and teaching purposes" but not commercial or military use.
== References ==
== External links ==
Publications of Michael Hanus, including many articles relevant to the design and theory of ALF
Information about getting and installing the ALF system

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The algebraic reconstruction technique (ART) is an iterative reconstruction technique used in computed tomography. It reconstructs an image from a series of angular projections (a sinogram). Gordon, Bender and Herman first showed its use in image reconstruction; whereas the method is known as Kaczmarz method in numerical linear algebra.
An advantage of ART over other reconstruction methods (such as filtered backprojection) is that it is relatively easy to incorporate prior knowledge into the reconstruction process.
ART can be considered as an iterative solver of a system of linear equations
A
x
=
b
{\displaystyle Ax=b}
, where:
A
{\displaystyle A}
is a sparse
m
×
n
{\displaystyle m\times n}
matrix whose values represent the relative contribution of each output pixel to different points in the sinogram (
m
{\displaystyle m}
being the number of individual values in the sinogram, and
n
{\displaystyle n}
being the number of output pixels);
x
{\displaystyle x}
represents the pixels in the generated (output) image, arranged as a vector, and:
b
{\displaystyle b}
is a vector representing the sinogram. Each projection (row) in the sinogram is made up of a number of discrete values, arranged along the transverse axis.
b
{\displaystyle b}
is made up of all of these values, from each of the individual projections.
Given a real or complex matrix
A
{\displaystyle A}
and a real or complex vector
b
{\displaystyle b}
, respectively, the method computes an approximation of the solution of the linear systems of equations as in the following formula,
x
k
+
1
=
x
k
+
λ
k
b
i
−
⟨
a
i
,
x
k
⟩
‖
a
i
‖
2
a
i
T
{\displaystyle x^{k+1}=x^{k}+\lambda _{k}{\frac {b_{i}-\langle a_{i},x^{k}\rangle }{\|a_{i}\|^{2}}}a_{i}^{T}}
where
i
=
k
mod
m
+
1
{\displaystyle i=k{\bmod {m}}+1}
,
a
i
{\displaystyle a_{i}}
is the i-th row of the matrix
A
{\displaystyle A}
,
b
i
{\displaystyle b_{i}}
is the i-th component of the vector
b
{\displaystyle b}
.
λ
k
{\displaystyle \lambda _{k}}
is an optional relaxation parameter, of the range
0
<
λ
k
≤
1
{\displaystyle 0<\lambda _{k}\leq 1}
. The relaxation parameter is used to slow the convergence of the system. This increases computation time, but can improve the signal-to-noise ratio of the output. In some implementations, the value of
λ
k
{\displaystyle \lambda _{k}}
is reduced with each successive iteration.
A further development of the ART algorithm is the simultaneous algebraic reconstruction technique (SART) algorithm.
== References ==

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Analog image processing is the use of an optical computer to process physical, optical images formed by light waves coming from an object, as opposed to the digital image processing and its use of digital computers to process pixelated, digital images. Correspondingly, a range of digital image processing techniques possess direct physical analogs. For example, fast Fourier transform algorithms are commonly implemented in digital phase correlation and other digital image processing techniques. These digital Fourier transforms can be considered to be the digitized approximation of methods utilizing Fourier transforming properties of an ideal lens.
== References ==

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The Apple Worm is a computer program written by Apple Computer, and especially for the 6502 microprocessor, which performs dynamic self-relocation. The source code of the Apple Worm is the first program printed in its entirety in Scientific American. The Apple Worm was designed and developed by James R. Hauser and William R. Buckley. Other example Apple Worm programs are described in the cover story of the November 1986 issue of Call_A.P.P.L.E. Magazine.
Because the Apple Worm performs dynamic self-relocation within the one main memory of one computer, it does not constitute a computer virus, an apt if somewhat inaccurate description. Although the analogous behavior of copying code between memories is exactly the act performed by a computer virus, the virus has other characters not present in the worm. Such programs do not necessarily cause collateral damage to the computing systems upon which their instructions execute; there is no reliance upon a vector to ensure subsequent execution. This extends to the computer virus; it need not be destructive in order to effect its communication between computational environments.
== Programs ==
A typical computer program manipulates data which is external to the corporeal representation of the computer program. In programmer-ese, this means the code and data spaces are kept separate. Programs which manipulate data which is internal to its corporeal representation, such as that held in the code space, are self-relational; in part at least, its function is to maintain its function. In this sense, a dynamic self-relocator is a self-referential system, as defined by Douglas R. Hofstadter.
== Other examples ==
The instruction set of the PDP-11 computer includes an instruction for moving data, which when constructed in a particular form causes itself to be moved from higher addresses to lower addresses; the form includes an automatic decrement of the instruction pointer register. Hence, when this instruction includes autodecrement of the instruction pointer, it behaves as a dynamic self-relocator.
A more current example of a self-relocating program is an adaptation of the Apple Worm for the Intel 80x86 microprocessor and its derivatives, such as the Pentium, and corresponding AMD microprocessors.
== See also ==
Worm memory test
== References ==
== External links ==
The Apple Worm source code
Video of executing Apple Worm program
Cover Story: The Contiguous Traveler / Simple Worms

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Application discovery and understanding (ADU) is the process of automatically analyzing artifacts of a software application and determining metadata structures associated with the application in the form of lists of data elements and business rules. The relationships discovered between this application and a central metadata registry is then stored in the metadata registry itself.
== Business benefits of ADU ==
On average, developers are spending only 5% of their time writing new code, 20% modifying the legacy code and up to 60% understanding the existing code.
Thus, ADU saves a great deal of time and expense for organizations that are involved in the change control and impact analysis of complex computer systems. Impact analysis allows managers to know that if specific structures are changed or removed altogether, what the impact of those changes might be to enterprise-wide systems. This process has been largely used in the preparation of Y2K changes and validations in software.
Application Discovery and Understanding is part of the process enabling development teams to learn and improve themselves by providing information on the context and current state of the application.
The process of gaining application understanding is greatly accelerated when the extracted metadata is displayed using interactive diagrams.
When a developer can browse the metadata, and drill down into relevant details on demand, then application understanding is achieved in a way that is natural to the developer. Significant reductions in the effort and time required to perform full impact analysis have been reported when ADU tools are implemented.
ADU tools are especially beneficial to newly hired developers. A newly hired developer will be productive much sooner and will require less assistance from the existing staff when ADU tools are in place.
== ADU process ==
ADU software is usually written to scan the following application structures:
Data structures of all kinds
Application source code
User interfaces (searching for labels of forms)
Reports
The output of the ADU process frequently includes:
Lists of previously registered data elements discovered within an application
List of unregistered data elements discovered
Note that a registered data element is any data element that already exists within a metadata registry.
== See also ==
metadata
metadata registry
data element
== Related ==
Configuration Management
== References ==

19
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---
title: "Association for Automated Reasoning"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Association_for_Automated_Reasoning"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:30:54.154891+00:00"
instance: "kb-cron"
---
The Association for Automated Reasoning (AAR) is a non-profit corporation that serves as an association of researchers working on automated theorem proving, automated reasoning, and related fields. It organizes the CADE and IJCAR conferences and publishes a roughly quarterly newsletter.
The website of the association is maintained by Valentin Montmirail and Geoff Sutcliffe in Jekyll.
== References ==
== External links ==
AAR web page

169
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---
title: "Asymptotic decider"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Asymptotic_decider"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:30:55.353541+00:00"
instance: "kb-cron"
---
In scientific visualization the asymptotic decider is an algorithm developed by Nielson and Hamann in 1991 that creates isosurfaces from a given scalar field. It was proposed as an improvement to the marching cubes algorithm, which can produce some "bad" topology, but can also be considered an algorithm in its own right.
== Principle ==
The algorithm first divides the scalar field into uniform cubes. It draws topologically correct contours on the sides (interface) of the cubes. These contours can then be connected to polygons and triangulated. The triangles of all cubes form the isosurfaces and are thus the output of the algorithm. Sometimes there is more than one way to connect adjacent constructs. This algorithm describes a method for resolving these ambiguous configurations in a consistent manner.
Ambiguous cases often occur if diagonally opposing points are found on the same side of the isoline, but on a different side to the other points in the square (for 2D systems) or cube (for 3D systems). In a 2D case this means that there are two possibilities. If we suppose that we mark the corners as positive if their value is greater than that of the isoline, or negative if it is less, then either the positive corners are separated by two isolines, or the positive corners are in the main section of the square and the negative corners are separated by two isolines. The correct situation depends on the value at the asymptote of the isolines. Isolines are hyperbolae which can be described using the following formula:
f
(
α
,
β
)
=
γ
(
α
−
α
0
)
(
β
−
β
0
)
+
δ
{\displaystyle f(\alpha ,\beta )=\gamma (\alpha -\alpha _{0})(\beta -\beta _{0})+\delta }
where
α
{\displaystyle \alpha }
is the normalised distance in the square from the left-hand side, and
β
{\displaystyle \beta }
is the normalised distance in the square from the bottom. The values
α
0
{\displaystyle \alpha _{0}}
and
β
0
{\displaystyle \beta _{0}}
are therefore the coordinates of the asymptotes, and
δ
{\displaystyle \delta }
is the value at the position
(
α
0
,
β
0
)
{\displaystyle (\alpha _{0},\beta _{0})}
. This point ought to belong to the section which contains two corners. Therefore, if
δ
{\displaystyle \delta }
is greater than the value of the isoline the positive corners are in the main section of the square and the negative corners are separated by two isolines, and if
δ
{\displaystyle \delta }
is less than the value of isoline the negative corners are in the main section of the square and the positive corners are separated by two isolines. A similar solution is used the 3D version.
== See also ==
Isosurface
Marching cubes
Science portal
== References ==
Notes
Bibliography
== Further reading ==
Charles D. Hansen; Chris R. Johnson (2004). Visualization Handbook. Academic Press. pp. 7–12. ISBN 978-0-12-387582-2.
A. Lopes; K. Brodlie (2005). "Interactive approaches to contouring and isosurfaces for geovisualization". In Jason Dykes; Alan M. MacEachren; M. J. Kraak (eds.). Exploring Geovisualization. Elsevier. pp. 352–353. ISBN 978-0-08-044531-1.

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---
title: "Asynchrony (computer programming)"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Asynchrony_(computer_programming)"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:30:56.586693+00:00"
instance: "kb-cron"
---
Asynchrony, in computer programming, refers to the occurrence of events independent of the main program flow and ways to deal with such events. These may be "outside" events such as the arrival of signals, or actions instigated by a program that take place concurrently with program execution, without the program hanging to wait for results. Asynchronous input/output is an example of the latter case of asynchrony, and lets programs issue commands to storage or network devices that service these requests while the processor continues executing the program. Doing so provides a degree of concurrency.
A common way for dealing with asynchrony in a programming interface is to provide subroutines that return a future or promise that represents the ongoing operation, and a synchronizing operation that blocks until the future or promise is completed. Some programming languages, such as Cilk, have special syntax for expressing an asynchronous procedure call.
Examples of asynchrony include the following:
Asynchronous procedure call, a method to run a procedure concurrently, a lightweight alternative to threads.
Ajax is a set of client-side web technologies used by the client to create asynchronous I/O web applications.
Asynchronous method dispatch (AMD), a data communication method used when there is a need for the server side to handle a large number of long lasting client requests. Using synchronous method dispatch (SMD), this scenario may turn the server into an unavailable busy state resulting in a connection failure response caused by a network connection request timeout. The servicing of a client request is immediately dispatched to an available thread from a pool of threads and the client is put in a blocking state. Upon the completion of the task, the server is notified by a callback. The server unblocks the client and transmits the response back to the client. In case of thread starvation, clients are blocked waiting for threads to become available.
== See also ==
Asynchronous system
Asynchronous circuit
== References ==

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---
title: "Attentive user interface"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Attentive_user_interface"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:30:57.799642+00:00"
instance: "kb-cron"
---
Attentive user interfaces (AUI) are user interfaces that manage the user's attention. For instance, an AUI can manage notifications, deciding when to interrupt the user, the kind of warnings, and the level of detail of the messages presented to the user.
Attentive user interfaces, by generating only the relevant information, can in particular be used to display information in a way that increase the effectiveness of the interaction.
According to Roel Vertegaal, there are four main types of attentive user interfaces:
Visual attention
Turn management
Interruption decision interfaces
Visual detail management interfaces
== See also ==
Adaptive hypermedia
Attention management
== References ==

23
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---
title: "Automated exception handling"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Automated_exception_handling"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:30:58.974069+00:00"
instance: "kb-cron"
---
Automated exception handling is a computing term referring to the computerized handling of errors. Runtime systems (engines) such as those for the Java programming language or .NET Framework lend themselves to an automated mode of exception or error handling. In these environments, software errors do not crash the operating system or runtime engine, but rather generate exceptions. Recent advances in these runtime engines enables specialized runtime engine add-on products to provide automated exception handling that is independent of the source code and provides root-cause information for every exception of interest.
== How it works ==
Upon exception, the runtime engine calls an error interception tool that is attached to the runtime engine (e.g., Java virtual machine (JVM)). Based on the nature of the exception, such as its type and the class and method in which it occurred, and based on user preferences, an exception can be either handled or ignored.
If the preference is to handle the exception, then based on handling preferences such as memory search depth, the error interception utility extracts memory values from heap and stack memories. This snapshot then produces the equivalent of a debugger screen (as if there had been a debugger) at the moment of the exception.
== Effects ==
This mechanism enables the automated handling of software errors independent of the application source code and of its developers. It is a direct artifact of the runtime engine paradigm and it enables unique advantages to the software life cycle that were unavailable before.
== References ==

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---
title: "Automatic layout"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Automatic_layout"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:31:00.236258+00:00"
instance: "kb-cron"
---
Automatic layout is an option in graph drawing toolkits that allow to lay out the Graph according to specific rules, such as:
reducing the length of the arcs between the Graph vertices
reduce the number of edges crossing (to improve the graph readability)
== See also ==
Methods in graph drawing
== References ==

18
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---
title: "Automatic mutual exclusion"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Automatic_mutual_exclusion"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:31:01.443703+00:00"
instance: "kb-cron"
---
Automatic mutual exclusion is a parallel computing programming paradigm in which threads are divided into atomic chunks, and the atomic execution of the chunks automatically parallelized using transactional memory.
== References ==
== See also ==
Bulk synchronous parallel

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---
title: "Available expression"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Available_expression"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:31:02.661923+00:00"
instance: "kb-cron"
---
In the field of compiler optimizations, available expressions is an analysis algorithm that determines for each point in the program the set of expressions that need not be recomputed. Those expressions are said to be available at such a point. To be available on a program point, the operands of the expression should not be modified on any path from the occurrence of that expression to the program point.
The analysis is an example of a forward data flow analysis problem. A set of available expressions is maintained. Each statement is analysed to see whether it changes the operands of one or more available expressions. This yields sets of available expressions at the end of each basic block, known as the outset in data flow analysis terms. An expression is available at the start of a basic block if it is available at the end of each of the basic block's predecessors. This gives a set of equations in terms of available sets, which can be solved by an iterative algorithm.
Available expression analysis is used to do global common subexpression elimination (CSE). If an expression is available at a point, there is no need to re-evaluate it.
== References ==
Aho, Sethi & Ullman: Compilers – Principles, Techniques, and Tools Addison-Wesley Publishing Company 1986

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---
title: "OPA mixture"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/OPA_mixture"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:29:01.534092+00:00"
instance: "kb-cron"
---
OPA is a mixture of isopropyl alcohol and isopropylamine that is used in the production of the sarin nerve agent. The mixture reacts with methylphosphonyl difluoride to produce sarin.
== References ==

21
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---
title: "Organoastatine chemistry"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Organoastatine_chemistry"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:29:02.727135+00:00"
instance: "kb-cron"
---
Organoastatine chemistry describes the synthesis and properties of organoastatine compounds, chemical compounds containing a carbon to astatine chemical bond.
Astatine is extremely radioactive, with the longest-lived isotope (210At) having a half-life of only 8.1 hours. Consequently, organoastatine chemistry can only be studied by tracer techniques on extremely small quantities. The problems caused by radiation damage as well as difficulties in separation and identification are worse for organic astatine derivatives than for inorganic compounds. Most studies of organoastatine chemistry focus on 211At (half-life 7.21 hours), which is the subject of ongoing studies in nuclear medicine: it is better than 131I at destroying abnormal thyroid tissue.
Astatine-labelled iodine reagents have been used to synthesise RAt, RAtCl2, R2AtCl, and RAtO2 (R = phenyl or p-tolyl). Alkyl and aryl astatides are relatively stable and have been analysed at high temperatures (120 °C) with radio gas chromatography. Demercuration reactions have produced with good yields trace quantities of 211At-containing aromatic amino acids, steroids, and imidazoles, among other compounds.
Astatine has both halogen-like and metallic properties, so that analogies with iodine sometimes hold, but sometimes do not. Astatine can be incorporated into organic molecules via halogen exchange, halodediazotation (replacing a diazonium group), halodeprotonation, or halodemetallation. Initial attempts to radiolabel proteins with 211At exemplify its intermediate behaviour, as astatination (analogous to radioiodination) produces unstable results and it is instead AtO+ (or a hydrolysed species) that probably bonds to proteins. Two-step procedures are used today, first synthesising stable astatoaryl prosthetic groups before incorporating them into the protein. Not only is the C–At bond the weakest of all carbon–halogen bonds (following periodic trends), but also the bond easily breaks as the astatine is oxidised back to free astatine.
== References ==
== Further reading ==
Berei, K.; Vasáros, L. (1983). "Organic Chemistry of Astatine" (PDF). inis.iaea.org. Retrieved 19 December 2022.

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---
title: "Organokrypton chemistry"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Organokrypton_chemistry"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:29:03.899962+00:00"
instance: "kb-cron"
---
Organokrypton chemistry describes the synthesis and properties of organokrypton compounds, chemical compounds containing a carbon to krypton chemical bond.
Far fewer such compounds are known than organoxenon compounds. The first organokrypton compound, HKrCCH, was reported in 2003 and made by photolytic insertion of a krypton atom into acetylene. Similar work was then done on diacetylene and cyanoacetylene, producing HKrC4H and HKrC3N. All these were made in matrix isolation and are stable up to 40 K. HKrCCF and HCCKrF have also been experimentally produced in matrix isolation.
Dications generated by dissociative electron ionisation of 2,4,6-trimethylpyridine react with krypton to form the organokrypton cations C8H7NKr2+ and C8H8NKr2+. Reaction of acetylene dications with krypton produced HCCKr2+.
== References ==

18
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---
title: "Organoneptunium chemistry"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Organoneptunium_chemistry"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:29:05.061465+00:00"
instance: "kb-cron"
---
Organoneptunium chemistry is the chemical science exploring the properties, structure, and reactivity of organoneptunium compounds, which are organometallic compounds containing a carbon to neptunium chemical bond. Several such compounds exist even though the element itself, neptunium, is man-made and highly radioactive: tricyclopentadienylneptunium-chloride, tetrakis(cyclopentadienyl)neptunium(IV) and neptunocene Np(C8H8)2.
== See also ==
Organoactinide chemistry
== References ==

17
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---
title: "Organopolonium chemistry"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Organopolonium_chemistry"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:29:06.335197+00:00"
instance: "kb-cron"
---
Organopolonium chemistry describes the synthesis and properties of chemical compounds containing a carbon to polonium chemical bond.
As polonium is a highly radioactive element (its most commonly used isotope, 210Po, has a half-life of about 138 days), organopolonium chemistry is mostly unexplored, and what is known is mostly confined to tracer-level studies due to self-destruction and charring of the compounds by the energetic alpha decay of polonium. Moreover, the C–Po bond is even weaker than the C–Te and C–Se bonds; compounds with those bonds tend to decompose over time to form elemental tellurium and selenium respectively.
Identification of such compounds has mostly been accomplished using chromatography, with analogous tellurium compounds as references, as classical chemical methods cannot be applied. Their production is often accomplished by the beta decay of 210Bi-containing organobismuth compounds. Some compounds have been claimed but not securely identified.
Relatively well-characterised derivatives are mostly restricted to dialkyl and diaryl polonides (R2Po), triarylpolonium halides (Ar3PoX), and diarylpolonium dihalides (Ar2PoX2). Polonium also forms soluble compounds with some ligands, such as 2,3-butanediol and thiourea.
== References ==

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---
title: "Overlayer"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Overlayer"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:29:07.516612+00:00"
instance: "kb-cron"
---
An overlayer is a layer of adatoms adsorbed onto a surface, for instance onto the surface of a single crystal.
== On single crystals ==
Adsorbed species on single crystal surfaces are frequently found to exhibit long-range ordering; that is to say that the adsorbed species form a well-defined overlayer structure. Each particular structure may only exist over a limited coverage range of the adsorbate, and in some adsorbate/substrate systems a whole progression of adsorbate structure are formed as the surface coverage is gradually increased.
The periodicity of the overlayer (which often is larger than that of the substrate unit cell) can be determined by low-energy electron diffraction (LEED), because there will be additional diffraction beams associated with the overlayer.
== Types ==
There are two types of overlayers: commensurate and incommensurate. In the former the substrate-adsorbate interaction tends to dominate over any lateral adsorbate-adsorbate interaction, while in the latter the adsorbate-adsorbate interactions are of similar magnitude to those between adsorbate and substrate.
== Notation ==
An overlayer on a substrate can be notated in either Wood's notation or matrix notation.
=== Wood's notation ===
Wood's notation takes the form
M
(
h
k
ℓ
)
−
(
|
a
0
|
|
a
s
|
×
|
b
0
|
|
b
s
|
)
−
R
α
∘
−
A
{\displaystyle {\text{M}}(hk\ell )-\left({\tfrac {|{\textbf {a}}_{0}|}{|{\textbf {a}}_{s}|}}\times {\tfrac {|{\textbf {b}}_{0}|}{|{\textbf {b}}_{s}|}}\right)-{\text{R}}\alpha ^{\circ }-{\text{A}}}
where M is the chemical symbol of the substrate, A is the chemical symbol of the overlayer,
(
h
k
ℓ
)
{\displaystyle (hk\ell )}
are the Miller indices of the surface plane, R and
α
{\displaystyle \alpha }
correspond to the rotational difference between the substrate and overlayer vectors, and the vector magnitudes shown are those of the substrate (
s
{\displaystyle s}
subscripts) and of the overlayer (
0
{\displaystyle 0}
subscripts). This notation can only describe commensurate overlayers however, while matrix notation can describe both.
=== Matrix notation ===
Matrix notation differs from Wood's notation in the second term, which is replaced by the
G
{\displaystyle G}
matrix that describes the overlayer primitive vectors in terms of the substrate primitive vectors:
(
a
0
b
0
)
=
G
(
a
s
b
s
)
{\displaystyle {\begin{pmatrix}{\textbf {a}}_{0}\\{\textbf {b}}_{0}\end{pmatrix}}=G{\begin{pmatrix}{\textbf {a}}_{s}\\{\textbf {b}}_{s}\end{pmatrix}}}
, where
G
=
(
G
11
G
12
G
21
G
22
)
{\displaystyle G={\begin{pmatrix}G_{11}&G_{12}\\G_{21}&G_{22}\\\end{pmatrix}}}
and so hence matrix notation has the form
M
(
h
k
ℓ
)
−
G
−
R
α
∘
−
A
{\displaystyle {\text{M}}(hk\ell )-G-{\text{R}}\alpha ^{\circ }-{\text{A}}}
== See also ==
Surface reconstruction
Superstructure
LEED#Superstructures
== Citations ==
== References ==
=== Textbooks ===
Kolasinski, Kurt W. (2012). Surface Science: Foundations of Catalysis and Nanoscience (3 ed.). Wiley. ISBN 978-1119990352.
Attard, Gary; Barnes, Colin (1998). Surfaces. Oxford Chemistry Primers. ISBN 978-0198556862.
=== Websites ===
"6.1: Classification of Overlayer Structures". chem.libretexts.org. 11 February 2015. Retrieved 2019-03-12.

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---
title: "Ox gall"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Ox_gall"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:29:08.721408+00:00"
instance: "kb-cron"
---
Ox gall (also spaced oxgall) is bile, also known as "gall", usually obtained from the gallbladder of cows, it is an ingredient in bile soap and mixed with alcohol and used as the wetting agent in paper marbling, engraving, lithography, and watercolor painting. It is a greenish-brown liquid mixture containing cholesterol, lecithin, taurocholic acid, and glycocholic acid.
== References ==
== External links ==
http://www.neogen.com/acumedia/pdf/ProdInfo/7216_PI.pdf
http://www.usbio.net/item/O8175

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---
title: "Oxazosulfyl"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Oxazosulfyl"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:29:09.945834+00:00"
instance: "kb-cron"
---
Oxazosulfyl is an insecticide that was developed by Sumitomo and introduced to the market in Japan in 2021 for use against insect pests on rice. The molecule has two different sulfonyl groups.
Oxazosulfyl works by inhibiting the vesicular acetylcholine transporter (VAChT) and was allocated to IRAC group 37. This inhibition results in rapid paralysis of the insect, which onsets a few minutes after application, and lasts for several days.
Oxazosulfyl is the first and until now only insecticide in the IRAC group 37. The class has not been given a name by IRAC, but Sumitomo propose the name "sulfyl" for the class.
Oxazosulfyl is used mainly in rice seed boxes. It controls a broad spectrum of rice pests in the orders of hemiptera, lepidoptera, and coleoptera. Some of the target insects are the brown planthopper (Nilaparvata lugens), the white-backed planthopper (Sogatella furcifera), the small brown planthopper (Laodelphax striatellus) and the rice leaf beetle (Oulema oryzae).
== References ==

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---
title: "PG5"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/PG5"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:29:14.956232+00:00"
instance: "kb-cron"
---
PG5 is the largest stable synthetic molecule ever made up to 2010. PG5 is a dendrimer designed by the organic chemistry research group working at the Federal Institute of Technology in Zürich.
== Properties ==
PG5 has a molecular mass of about 200 MDa or 200,000,000 grams (200,000 kg)/mol. It has roughly 17 million atoms and a diameter of about 10 nm. Its length is up to a few micrometers. It is similar in size to a tobacco mosaic virus with comparable length and diameter. PG5 was shown to be resistant against attempts to flatten its structure, and it is one of the heaviest compounds in the world.
== References ==

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---
title: "PSB-SB-487"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/PSB-SB-487"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:29:23.445372+00:00"
instance: "kb-cron"
---
PSB-SB-487 is an experimental drug which is used as a pharmacological research tool. It is a coumarin derivative which is an antagonist at the former orphan receptor GPR55. Unlike older GPR55 antagonists such as O-1918, PSB-SB-487 has good selectivity over the related receptor GPR18, with an IC50 of 113nM at GPR55 vs 12500nM at GPR18. However it has poorer selectivity over other related receptors, acting as a weak antagonist at CB1 with a Ki of 1170nM, and a partial agonist at CB2 with a Ki of 292nM.
== See also ==
CID-16020046
PSB-SB-1202
== References ==

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---
title: "Partial specific volume"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Partial_specific_volume"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:29:11.323030+00:00"
instance: "kb-cron"
---
The partial specific volume
v
i
¯
,
{\displaystyle {\bar {v_{i}}},}
express the variation of the extensive volume of a mixture in respect to composition of the masses. It is the partial derivative of volume with respect to the mass of the component of interest.
V
=
∑
i
=
1
n
m
i
v
i
¯
,
{\displaystyle V=\sum _{i=1}^{n}m_{i}{\bar {v_{i}}},}
where
v
i
¯
{\displaystyle {\bar {v_{i}}}}
is the partial specific volume of a component
i
{\displaystyle i}
defined as:
v
i
¯
=
(
∂
V
∂
m
i
)
T
,
P
,
m
j
≠
i
.
{\displaystyle {\bar {v_{i}}}=\left({\frac {\partial V}{\partial m_{i}}}\right)_{T,P,m_{j\neq i}}.}
The PSV is usually measured in milliLiters (mL) per gram (g), proteins > 30 kDa can often be assumed to have a partial specific volume of 0.708 mL/g, though this estimate varies depending on the amount of volume accessible by solvent or bound molecules. Experimental determination is possible by measuring the natural frequency of a U-shaped tube filled successively with air, buffer and protein solution.
== Properties ==
The weighted sum of partial specific volumes of a mixture or solution is an inverse of density of the mixture namely the specific volume of the mixture.
v
=
∑
i
w
i
⋅
v
i
¯
=
1
ρ
{\displaystyle v=\sum _{i}w_{i}\cdot {\bar {v_{i}}}={\frac {1}{\rho }}}
∑
i
ρ
i
⋅
v
i
¯
=
1
{\displaystyle \sum _{i}\rho _{i}\cdot {\bar {v_{i}}}=1}
== See also ==
Partial molar property
Apparent molar property
== References ==

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title: "Pensky–Martens closed-cup test"
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The Pensky–Martens closed-cup flash-point test is a test for the determination of the flash point of flammable liquids. It is standardized as ASTM D93, EN ISO 2719 and IP 34 The United States Environmental Protection Agency (EPA) has also published Method 1010A: Test Methods for Flash Point by Pensky-Martens Closed Cup Tester, part of Test Methods for Evaluating Solid Waste, Physical/Chemical Methods, which references the ASTM standard series D93. The Pensky-Martens test is a closed-cup method as opposed to the Cleveland open-cup method.
== Test Procedure ==
A brass test cup is filled with a test specimen and closed with a lid, through which an ignition source can be introduced periodically. The sample is heated and stirred at specified rates depending on the material that is being tested. This allows the development of an equilibrium between the liquid and the air volume. The ignition source is directed into the cup at regular intervals with simultaneous interruption of stirring. The test concludes upon observation of a flash that spreads throughout the inside of the cup. The corresponding temperature is the liquid's flash point.
== Critique of test method ==
The different flash point methods depend on the controlled conditions in the laboratory and do not determine an intrinsic property of the material tested. They are however useful to compare different substances and is therefore widely used in road transportation and environmental safety regulations.
Closed cup testers give lower values for the flashpoint than open-cup testers (typically 5–10 K) and are a better approximation to the temperature at which the vapour pressure reaches the "Lower flammable limit" (LFL).
== References ==

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The peptization of a liquid mixture is the process of converting the mixture into a colloid by shaking it with a suitable electrolyte called a peptizing agent. That is, the insoluble solid particles which have settled out of the mixture (i.e. the precipitate) are reformed into microscopic particles suspended in the mixture. Peptization is the reverse of flocculation, the aggregation of colloidal particles into precipitate; as such, it is also known as deflocculation.
This is particularly important in colloid chemistry or for precipitation reactions in an aqueous solution. When colloidal particles bear a same sign electric charge, they mutually repel each other and cannot aggregate together. Freshly precipitated aluminium or iron hydroxide is extremely difficult to filter because the very fine colloidal particles directly pass through a paper filter. To facilitate the filtration, the colloidal suspension must be first flocculated by adding a concentrated solution of salt to the system. Multivalent cations are more efficient flocculants than monovalent cations: AlCl3 > CaCl2 > NaCl. The electrical charges present at the surface of the particles are so "neutralised" and disappear. More correctly speaking, the electrical double layer existing at the surface of the particles is compressed by the added electrolyte and collapses at high ionic strength. The electrical repulsion no longer hinders the aggregation of particles and they can then coalesce to form a flocculent precipitate that is easy to filter. If the precipitate is washed with an excessive volume of deionised water, the electrical double layer present at the surface of the particles expands again and the electrical repulsion reappears: the precipitate peptizes and the particles pass again through the filter.
Peptization is also used in nanoparticle synthesis to make a large grouping of particles split into many primary particles. This is done by changing the surface properties, applying a charge, or by adding a surfactant.
In the synthesis of titania (titanium dioxide) nanoparticles, peptization involves adsorption of quaternary ammonium cation on the titania surface. This causes the surface to become positively charged. Electrostatic repulsion of the primary particles in the agglomerated titania breaks up the agglomerate into primary particles. The efficacy of adsorbates or suspension modification in imparting interparticle electrostatic repulsion is most commonly studied in terms of zeta potential.
== See also ==
Colloid
Suspension
Zeta potential
Dispersion
== References ==

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---
In photochemistry, photohydrogen is hydrogen produced with the help of artificial or natural light. This is how the leaf of a tree splits water molecules into protons (hydrogen ions), electrons (to make carbohydrates) and oxygen (released into the air as a waste product). Photohydrogen may also be produced by the photodissociation of water by ultraviolet light.
Photohydrogen is sometimes discussed in the context of obtaining renewable energy from sunlight, by using microscopic organisms such as bacteria or algae. These organisms create hydrogen with the help of hydrogenase enzymes which convert protons derived from the water splitting reaction into hydrogen gas which can then be collected and used as a biofuel.
== See also ==
Solar hydrogen panel
Photofermentation
Biological hydrogen production (Algae)
Photoelectrochemical cell
Photosynthesis
Hydrogen cycle
Hydrogen economy
== References ==

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Picotiter plates are flat plates with multiple wells used as small test tubes. It is a miniaturised version of the microtiter and nanotiter plates that are standard tools in analytical research. Picotiter plates are used in the DNA sequencing strategy first exploited by a spin-off company (454 Life Sciences) and commercially available on the market. The picotiter plate platform enables parallel sequence analysis of 1.7 million of separate DNA fragments and thus is capable of sequencing entire genomes within a couple of hours. Titerplates can be produced from photosensitive glass, such as Foturan from SCHOTT Corporation.
== References ==

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A pipeclay triangle is a piece of laboratory apparatus that is used to support a crucible or other object being heated by a Bunsen burner or other heat source. It is made of wires strung in an equilateral triangle on which are strung hollow ceramic, normally fire clay, tubes. The triangle is usually supported on a tripod or iron ring. Unlike wire gauze, which primarily supports glassware such as beakers, flasks, or evaporating dishes and provides indirect heat transfer to the glassware, the pipeclay triangle normally supports a crucible and allows the flame to heat the crucible directly. The triangular shape allows rounded crucibles of various sizes to rest in a stable way.
== References ==

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The polar surface area (PSA) or topological polar surface area (TPSA) of a molecule is defined as the surface sum over all polar atoms or molecules, primarily oxygen and nitrogen, also including their attached hydrogen atoms.
PSA is a commonly used medicinal chemistry metric for the optimization of a drug's ability to permeate cells. Molecules with a polar surface area of greater than 140 angstroms squared (Å2) tend to be poor at permeating cell membranes. For molecules to penetrate the blood–brain barrier (and thus act on receptors in the central nervous system), a PSA less than 90 Å2 is usually needed.
TPSA is a valuable tool in drug discovery and development. By analyzing a drug candidate's TPSA, scientists can predict its potential for oral bioavailability and ability to reach target sites within the body. This prediction hinges on a drug's ability to permeate biological barriers.
Permeating these barriers, such as the Blood-Brain Barrier (BBB), the Placental Barrier (PB), and the Blood-Mammary Barrier (BM), is crucial for many drugs to reach their intended targets.
The BBB, for example, protects the brain from harmful substances. Drugs with a lower TPSA (generally below 90 Ų) tend to permeate the BBB more easily, allowing them to reach the brain and exert their therapeutic effects (Shityakov et al., 2013).
Similarly, for drugs intended to treat the fetus, a lower TPSA (below 60 Ų) is preferred to ensure they can pass through the placenta (Augustiño-Roubina et al., 2019).
Breastfeeding mothers also need consideration. Here, an optimal TPSA for a drug is around 60-80 Ų to allow it to reach the breast tissue for milk production, while drugs exceeding 90 Ų are less likely to permeate the Blood-Mammary Barrier.
== See also ==
Biopharmaceutics Classification System
Cheminformatics
Chemistry Development Kit
JOELib
Implicit solvation
Lipinski's rule of five
== References ==
== Literature ==
Pajouhesh, Hassan; Lenz, George R (2005). "Medicinal chemical properties of successful central nervous system drugs". NeuroRx. 2 (4): 541–553. doi:10.1602/neurorx.2.4.541. PMC 1201314. PMID 16489364.
Clark, David E (1999). "Rapid calculation of polar molecular surface area and its application to the prediction of transport phenomena. 1. Prediction of intestinal absorption". Journal of Pharmaceutical Sciences. 88 (8): 807–14. doi:10.1021/js9804011. PMID 10430547.
Palm, Katrin; Stenberg, Patric; Luthman, Kristina; Artursson1, Per (1997). "Polar molecular surface properties predict the intestinal absorption of drugs in humans". Pharmaceutical Research. 14 (5): 568–71. doi:10.1023/A:1012188625088. PMID 9165525. S2CID 7178582.{{cite journal}}: CS1 maint: numeric names: authors list (link)
Ertl, Peter; Rohde, Bernhard; Selzer, Paul (2000). "Fast Calculation of Molecular Polar Surface Area as a Sum of Fragment-Based Contributions and Its Application to the Prediction of Drug Transport Properties". Journal of Medicinal Chemistry. 43 (20): 3714–3717. doi:10.1021/jm000942e. PMID 11020286.
Ertl, P. Polar Surface Area, in Molecular Drug Properties, R. Mannhold (ed), Wiley-VCH, pp. 111–126, 2007
Shityakov, Sergey; Neuhaus, Winfried; Dandekar, Thomas; Förster, Carola (2013). "Analysing molecular polar surface descriptors to predict blood-brain barrier permeation". International Journal of Computational Biology and Drug Design. 6 (1–2): 146–56. doi:10.1504/IJCBDD.2013.052195. PMID 23428480.
== External links ==
Interactive Polar Surface Area calculator
Free, Programmable TPSA Calculator

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Polycide is a silicide formed over polysilicon. Widely used in DRAMs. In a polycide MOSFET transistor process, the silicide is formed only over the polysilicon film as formation occurs prior to any polysilicon etch. Polycide processes contrast with salicide processes in which silicide is formed after the polysilicon etch. Thus, with a salicide process, silicide is formed over both the polysilicon gate and the exposed monocrystalline terminal regions of the transistor in a self-aligned fashion.
== References ==

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In the United States, the Emergency Management Issues Special Interest Group (EMI SIG) state that "Protective Action Criteria (PACs) are essential components for planning and response to uncontrolled releases of hazardous chemicals. These criteria, combined with estimates of exposure, provide the information necessary to evaluate chemical release events for the purpose of taking appropriate protective actions. During an emergency response, these criteria may be used to evaluate the severity of the event, to identify potential outcomes, and to decide what protective actions should be taken".
PAC values are based on the following exposure limit values:
Acute Exposure Guideline Levels (AEGL) values published by the U.S. Environmental Protection Agency (EPA)
Emergency Response Planning Guideline (ERPG) values produced by the American Industrial Hygiene Association (AIHA)
Temporary Emergency Exposure Limit (TEEL) values developed by SCAPA
AEGL, ERPG and TEEL benchmark values are not available for all chemicals as the clinical effects are still an active research area. Consequently, when defining PAC values the following procedure is followed.
Use AEGLs (including final or interim values) if they are available.
If AEGLs are not available, use ERPGs.
If neither AEGLs or ERPGs are available, use TEELs.
There are three levels of PAC value (1 to 3) where each successive value is associated with an increasingly severe effect from a higher level of exposure. Each level is defined as follows:
PAC-1 : Mild, transient health effects.
PAC-2 : Irreversible or other serious health effects that could impair the ability to take protective action.
PAC-3 : Life-threatening health effects.
== References ==

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The Platinum-Cobalt Scale (Pt/Co scale or Apha-Hazen Scale) is a color scale that was introduced in 1892 by chemist Allen Hazen (1869–1930). The index was developed as a way to evaluate pollution levels in waste water. It has since expanded to a common method of comparison of the intensity of yellow-tinted samples. It is specific to the color yellow and is based on dilutions of a 500 ppm platinum cobalt solution. The colour produced by one milligram of platinum cobalt dissolved in one liter of water is fixed as one unit of colour in platinum-cobalt scale. The ASTM has detailed description and procedures in ASTM Designation D1209, "Standard Test Method for Color of Clear Liquids (Platinum-Cobalt Scale)".
Colour may be reported on a water quality report using this scale.
== See also ==
APHA color
== References ==

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Pulsed columns are a type of liquid-liquid extraction equipment; examples of this class of extraction equipment is used at the BNFL plant THORP.
Special use in nuclear industries for fuel reprocessing, where spent fuel from reactors is subjected to solvent extraction. A pulsation is created using air by a pulse leg. The feed is aqueous solution containing radioactive solutes, and the solvent used is TBP (Tri-Butyl Phosphate) in suitable hydrocarbon. To create turbulence for dispersion of one phase in other, a mechanical agitator is used in conventional equipments. But, because of radioactivity, and frequent maintenance required for mechanical agitators, pulsing is used in extraction columns.
== References ==

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The Randić index, also known as the connectivity index, of a graph is the sum of bond contributions
1
/
(
d
i
d
j
)
1
/
2
{\displaystyle 1/(d_{i}d_{j})^{1/2}}
where
d
i
{\displaystyle d_{i}}
and
d
j
{\displaystyle d_{j}}
are
the degrees of the vertices making bond i ~ j.
== History ==
This graph invariant was introduced by Milan Randić in 1975. It is often used in chemoinformatics for investigations of organic compounds.
== Notes ==
== References ==
Roberto Todeschini, Viviana Consonni (2009) "Molecular Descriptors for Chemoinformatics", Wiley-VCH, ISBN 978-3-527-31852-0
Li, Xueliang; Shi, Yongtang (2008), "A survey on the Randić index", MATCH Communications in Mathematical and in Computer Chemistry, 59 (1): 127–156.

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Rat Ice is a trademarked version of dry ice approved by the U.S. Environmental Protection Agency for use in suffocating rat nests. The trademark is owned by Bell Laboratories, Inc. of Windsor, Wisconsin.
== References ==
== External links ==
Bell Laboratories, Inc: Rat Ice Archived 2023-10-02 at the Wayback Machine

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The Reichert value (also Reichert-Meissl number, Reichert-Meissl-Wollny value or Reichert-Meissl-Wollny number) is a value determined when examining fats and oils. The Reichert value is an indicator of how much volatile fatty acid can be extracted from a particular fat or oil through saponification. It is equal to the number of millilitres of 0.1 normal hydroxide solution necessary for the neutralization of the water-soluble volatile fatty acids distilled and filtered from 5 grams of a given saponified fat. (The hydroxide solution used in such a titration is typically made from sodium hydroxide, potassium hydroxide, or barium hydroxide.)
This number is a useful indicator of non-fat compounds in edible fats, and is especially high in butter.
The value is named for the chemists who developed it, Emil Reichert and Emerich Meissl.
The Polenske value and Kirschner value are related numbers based on similar tests.
The Reichert-Meissel value for milk ranges between 28.5 and 33.
== References ==
== External links ==
"Untersuchung einer Margarine" (PDF) (in German). Archived from the original (PDF) on June 11, 2007.

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Retrogradation is a process in which the amylose and amylopectin chains in cooked, gelatinized starch realign themselves as the cooked starch cools.
When native starch is heated and dissolved in water, the crystalline structure of amylose and amylopectin molecules is lost and they hydrate to form a viscous solution. If the viscous solution is cooled or left at lower temperature for a long enough period, the linear molecules, amylose, and linear parts of amylopectin molecules recrystallize. The linear chains place themselves parallel and form hydrogen bonds.
At temperatures between −8 °C (18 °F) and 8 °C (46 °F), the aging process is enhanced drastically. Amylose crystallization occurs much faster than crystallization of the amylopectin. The crystal melting temperature of amylose is much higher (about 150 °C (302 °F)) than amylopectin (about 50–60 °C (122–140 °F)). The temperature range between cooking starch and storing in room temperature is optimum for amylose crystallization, and therefore amylose crystallization is responsible for the development of the initial hardness of the starch gel. On the other hand, amylopectin has a narrower temperature range for crystallization as crystallization does not occur at a temperature higher than its melting temperature. Therefore, amylopectin is responsible for development of the long-term crystallinity and gel structure.
Retrogradation can expel water from the polymer network. This process is known as syneresis. A small amount of water can be seen on top of the gel.
Retrogradation is directly related to the staling or aging of bread. Retrograded starch is a type of resistant starch.
Chemical modification of starches can reduce or enhance the retrogradation. Waxy, high amylopectin, starches also have much less of a tendency to retrograde. Additives such as fat, glucose, sodium nitrate and emulsifier can reduce retrogradation of starch.
== See also ==
Retrograde (disambiguation)
Retrogradation – Movement of the front of a river delta inland over time
== References ==
== External links ==
"Dietary Carbohydrate Composition". FAO.org. FAO Corporate Document Repository.

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A ribonucleoside is a type of nucleoside including ribose as a component. They are analogous to the nucleosides that, along with a phosphate group, form nucleotides that are the functional units of DNA; however, ribonucleosides are principal components of RNA. These form ribonucleotides with the addition of a phosphate group, which chain to form a molecule of RNA.
Deoxyribonucleosides (or simply nucleosides) are synthesised from ribonucleosides through a series of reactions. It is possible for ribonucleosides to be converted to their deoxy form through a reaction catalysed by ribonucleoside disphosphate reductase. The enzyme itself provides reducing equivalents by having its sulfhydryl groups oxidised through the course of the reaction.
One example of a ribonucleoside is cytidine.
== References ==

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Rovibronic coupling, also known as rotation/vibration-electron coupling, denotes the simultaneous interactions between rotational, vibrational, and electronic degrees of freedom in a molecule. When a rovibronic transition occurs, the rotational, vibrational, and electronic states change simultaneously, unlike in rovibrational coupling. The coupling can be observed using spectroscopy, and is most easily seen in the Renner–Teller effect in which a linear polyatomic molecule is in a degenerate electronic state and bending vibrations will cause a large rovibronic coupling.
== See also ==
Afterglow plasma
Vibronic coupling
== References ==

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date_saved: "2026-05-05T11:29:34.456557+00:00"
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date_saved: "2026-05-05T11:29:33.198946+00:00"
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SEAgel (Safe Emulsion Agar gel) is one of a class of high-tech foam materials known as aerogels. It is an excellent thermal insulator and among the least dense solids known. SEAgel was invented by Robert Morrison at the Lawrence Livermore National Laboratory in 1992. SEAgel is made of agar, a carbohydrate material that comes from kelp and red algae, and has a density of 200 mg/cm3.
SEAgel can be made lighter than air using hydrogen, causing it to float or hang in the air. It insulates against temperature, noise, and electric current. SEAgel is also completely biodegradable, as it is made entirely of biological material and can even be eaten.
Initially, SEAgel starts out as a gelatin-like mixture of agar and water. After it is freeze-dried to remove the water, it is left as a honeycomb of dried agar filled with air, with cell sizes two to three micrometers (2–3 μm) in diameter.
SEAgel can have many different uses. Laboratory scientists use SEAgel as targets for X-ray laser experiments because it can be doped with other materials, such as selenium. In order to eliminate the volatile hydrodynamics that occur when a solid-density target explodes before it reaches the density required for lasing, scientists are trying to develop an X-ray laser target with a density that is less than the critical density of laser light (4×1021 electrons/cm3 for 0.53-μm light). SEAgel can help them achieve a more uniform plasma, which will ultimately improve the quality of the X-ray laser beam.
SEAgel could also be used as food packaging or the encapsulating material of timed-release medical pills, as it is safe to digest. SEAgel could also replace balsa wood, to insulate supertankers, and to provide sound damping in high-speed trains.
SEAgel was covered under U.S. patents 5,382,285 ("Biofoam") and 5,360,828 ("Biofoam II").
== References ==
== External links ==
Physics News Update — (Story #4), August 19, 1992 by Phillip F. Schewe and Ben Stein
MadSci Network — Re: What exactly are SEAgels?

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source: "https://en.wikipedia.org/wiki/Salting_in"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:29:36.905377+00:00"
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Salting in refers to the effect where increasing the ionic strength of a solution increases the solubility of a solute, such as a protein. This effect tends to be observed at lower ionic strengths.
Protein solubility is a complex function of physicochemical nature of the protein, pH, temperature, and the concentration of the salt used. It also depends on whether the salt is kosmotropic, whereby the salt will stabilize water. The solubility of proteins usually increases slightly in the presence of salt, referred to as "salting in". However, at high concentrations of salt, the solubility of the proteins drop sharply and proteins can precipitate out, referred to as "salting out".
== Anionic interactions ==
Initial salting in at low concentrations is explained by the Debye–Huckel theory. Proteins are surrounded by the salt counterions (ions of opposite net charge) and this screening results in decreasing electrostatic free energy of the protein and increasing activity of the solvent, which in turn leads to increasing solubility. This theory predicts that the logarithm of solubility is proportional to the square root of the ionic strength.
The behavior of proteins in solutions at high salt concentrations is explained by John Gamble Kirkwood. The abundance of the salt ions decreases the solvating power of salt ions, resulting in the decrease in the solubility of the proteins and precipitation results.
At high salt concentrations, the solubility is given by the following empirical expression.
log S = B − KI
where S is the solubility of the protein, B is a constant (function of protein, pH and temperature), K is the salting out constant (function of pH, mixing and salt), and I is the ionic strength of the salt. This expression is an approximation to that proposed by Long and McDevit.
== See also ==
Salting out
Solvation shell
== References ==
== Further reading ==
Perron, Gérald; Joly, Daniel; Desnoyers, Jacques E.; Avédikian, Lévon; Morel, Jean-Pierre (15 February 1978). "Thermodynamics of the salting effect; free energies, enthalpies, entropies, heat capacities, and volumes of the ternary systems electrolyte–alcohol–water at 25 °C". Canadian Journal of Chemistry. 56 (4): 552–559. doi:10.1139/v78-089.
Kramer, Ryan M.; Shende, Varad R.; Motl, Nicole; Pace, C. Nick; Scholtz, J. Martin (18 April 2012). "Toward a Molecular Understanding of Protein Solubility: Increased Negative Surface Charge Correlates with Increased Solubility". Biophysical Journal. 102 (8): 1907–1915. Bibcode:2012BpJ...102.1907K. doi:10.1016/j.bpj.2012.01.060. PMC 3328702. PMID 22768947.

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The double bond rule, postulated by Otto Schmidt in 1932, relates to the enhanced reactivity of sigma bonds attached to an atom adjacent to a double bond. Examples of this phenomenon include the difference in reactivity of allyl bromides as compared to bromoalkenes and benzyl bromides are compared to bromobenzenes. The first to observe the phenomenon was Conrad Laar in 1885.
== References ==

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Scoopula is a brand name of a spatula-like scoop utensil used primarily in experimental laboratories to transfer solids: to a weighing paper for weighing, to a cover slip to measure melting point, or a graduated cylinder, or to a watch glass from a flask or beaker through scraping. "Scoopula" is a registered trademark owned by Thermo Fisher Scientific. They are very often made of metal.
== References ==

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Selenite refers to the anion with the chemical formula SeO2−3. It is the oxyanion of selenium. It is the selenium analog of the sulfite ion, SO2−3. Thus selenite is pyramidal and selenium is assigned oxidation state +4. Selenite also refers to compounds that contains this ion, for example sodium selenite Na2SeO3 which is a common source of selenite. Selenite also refers to the esters of selenous acid, for example dimethyl selenite (CH3)2SeO3.
== Synthesis and reactions ==
Selenite salts can be prepared by neutralizing solutions of selenous acid, which is generated by dissolving selenium dioxide in water. The process proceeds via the hydrogenselenite ion, HSeO−3.
Most selenite salts can be formed by heating the metal oxide with selenium dioxide, e.g.:
Na2O + SeO2 → Na2SeO3
== References ==

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Silicone resins are a type of silicone material which is formed by branched, cage-like oligosiloxanes with the general formula of RnSiXmOy, where R is a non-reactive substituent, usually methyl (Me = −CH3) or phenyl (Ph = −C6H5), and X is a functional group: hydrogen (−H), hydroxyl (−OH), chlorine (−Cl) or alkoxy (−O−). These groups are further condensed in many applications, to give highly crosslinked, insoluble polysiloxane networks.
When R is methyl, the four possible functional siloxane monomeric units are described as follows:
"M" stands for trimethylsilanol, Me3SiO;
"D" for Me2SiO2;
"T" for MeSiO3;
"Q" for SiO4.
Note that a network of only Q groups becomes fused quartz.
The most abundant silicone resins are built of D and T units (DT resins) or from M and Q units (MQ resins); however, many other combinations (MDT, MTQ, QDT) are also used in industry.
Silicone resins represent a broad range of products. Materials of molecular weight in the range of 1000–10,000 are very useful in pressure-sensitive adhesives, silicone rubbers, coatings, and additives. Polysiloxane polymers with reactive side group functionality such as vinyl, acrylate, epoxy, mercaptan, or amine, are used to create thermoset polymer matrix composites, coatings, and adhesives.
Silicone resins are prepared by hydrolytic condensation of various silicone precursors. In early processes of preparation of silicone resins, sodium silicate and various chlorosilanes were used as starting materials. Although the starting materials were the least expensive ones (something typical for industry), structural control of the product was very difficult. More recently, a less reactive tetraethoxysilane - (TEOS) or ethyl polysilicate and various disiloxanes are used as starting materials.
== Microbial deterioration ==
The algae Stichococcus bacillaris and certain fungal species have been seen to colonize silicone resins used at archaeological sites.
== See also ==
Water glass (Sodium silicate, .e.g Na2SiO3 etc.)
Silicone rubber
== References ==

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Silicynes are allotropes of silicon.
1-dimensional silicyne is analogous to the carbon allotrope carbyne, being a long chain of silicons, instead of carbons. It is amorphous silicon with sp hybridization of the valence electrons. Silicyne is a single linear molecule composed of just silicon atoms. One of the manners they are bonded to each other in a succession of double-bonded silicons, analogous to the situation of carbon found in cumulene. The other manner they may be bonded to each other is a succession of alternating single and triple-bonded silicons, analogous to the situation of carbon found in polyyne.
2-dimensional silicyne is analogous to the carbon allotrope graphyne, and similar to the silicon allotrope silicene, being a sheet of silicon atoms. In this form, the silicyne chains that link the silicene hexagons use disilyne bonding alternating with disilane bonding, analogous to polyyne.
== References ==

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Sinner's circle is a concept used in the field of cleaning and detergents. It was introduced by the German chemist Herbert Sinner in 1959, who was working for the detergent manufacturer Henkel at the time. This model, represented as a circle with four quadrants, describes the four main factors that influence cleaning effectiveness.
The four elements of the Sinner circle are:
Chemistry: This refers to the solvents or detergents used for cleaning. Chemical agents play a crucial role in helping to dissolve dirt and facilitate its removal.
Temperature: Heat can speed up chemical reactions and help dissolve grease and other residues more effectively.
Mechanical: This involves mechanical agitation or rubbing used to dislodge dirt.
Time: The length of time the cleaning agents are in contact with the surface to be cleaned.
According to Sinner, cleaning efficiency can be improved by optimizing these four factors. For example, if one cannot use a very strong detergent for safety or cost reasons, one can compensate by increasing the temperature, extending the cleaning time, or using more mechanical agitation.
Later research has helped to more clearly describe the interactions between Sinner's four factors in real cleaning scenarios.
A fifth element, water, is sometimes added as an inner circle.
== References ==

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date_saved: "2026-05-05T11:29:46.480158+00:00"
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A sol is a colloidal solution made out of tiny solid particles in a continuous liquid medium. Sols are stable, so that they do not settle down when left undisturbed, and exhibit the Tyndall effect, which is the scattering of light by the particles in the colloid. The size of the particles can vary from 1 nm - 100 nm. Examples include blood, pigmented ink, cell fluids, paint, antacids and mud.
Artificial sols can be prepared by two main methods: dispersion and condensation. In the dispersion method, solid particles are reduced to colloidal dimensions through techniques such as ball milling and Bredig's arc method. In the condensation method, small particles are formed from larger molecules through a chemical reaction.
The stability of sols can be maintained through the use of dispersing agents, which prevent the particles from clumping together or settling out of the suspension. Sols are often used in the sol-gel process, in which a sol is converted into a gel through the addition of a crosslinking agent.
In a sol, solid particles are dispersed in a liquid continuous phase, while in an emulsion, liquid droplets are dispersed in a liquid or semi-solid continuous phase.
== References ==

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Solid film lubricants are paint-like coatings of very fine particles of lubricating pigment blended with a binder and other additives. The lubricant is applied to a substrate by spray, dip or brush methods and, once cured, creates a solid film which repels water, reduces friction and increases the wear life of the substrate to which it has been applied. Certain film lubricants also offer additional properties such as corrosion inhibition. Solid film lubricants are used in the automotive, transportation and aerospace industries. 2 commonly used ones are graphite and molybdenum disulfide.
== References ==

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In a chemistry laboratory a solvent cabinet is a chemical storage cabinet or cupboard which is properly labeled and equipped, for the storage of solvents (especially those that are combustible). A solvent cabinet should be positioned separately from acid cabinet or base cabinet (used for storing acids and caustic bases respectively, as solvents are not compatible with these substances. (Some carts for transporting containers of chemicals come equipped with a built in solvent cabinet).
A solvent cabinet must incorporate a number of safety features. It should be adequately ventilated, preventing the release of excessive fumes (being either sealed or vented). It should be equipped to contain fires and isolate the contents from sources of ignition, be grounded (to prevent sparks and static discharge).
== References ==
PETER URBEN (22 October 2013). Bretherick's Handbook of Reactive Chemical Hazards. Academic Press. p. 381. ISBN 978-0-08-052340-8.

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title: "Solvent casting and particulate leaching"
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In solvent casting and particulate leaching (SCPL), a polymer is dissolved in an organic solvent. Particles, mainly salts, with specific dimensions are then added to the solution. The mixture is shaped into its final geometry. For example, it can be cast onto a glass plate to produce a membrane or in a three-dimensional mold to produce a scaffold. When the solvent evaporates, it creates a structure of composite material consisting of the particles together with the polymer. The composite material is then placed in a bath which dissolves the particles, leaving behind a porous structure.
== References ==

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Solvent exposure occurs when a chemical, material, or person comes into contact with a solvent. Chemicals can be dissolved in solvents, materials such as polymers can be broken down chemically by solvents, and people can develop certain ailments from exposure to solvents both organic and inorganic.
Some common solvents include acetone, methanol, tetrahydrofuran, dimethylsulfoxide, and water among countless others.
In biology, the solvent exposure of an amino acid in a protein measures to what extent the amino acid is accessible to the solvent (usually water) surrounding the protein. Generally speaking, hydrophobic amino acids will be buried inside the protein and thus shielded from the solvent, while hydrophilic amino acids will be close to the surface and thus exposed to the solvent. However, as with many biological rules exceptions are common and hydrophilic residues are frequently found to be buried in the native structure and vice versa.
Solvent exposure can be numerically described by several measures, the most popular measures being accessible surface area and relative accessible surface area. Other measures are for example:
Contact number: number of amino acid neighbors within a sphere around the amino acid.
Residue depth: distance of the amino acid to the molecular surface.
Half sphere exposure: number of amino acid neighbors within two half spheres around the amino acid.
== References ==
Lee B, Richards F. (1971) The interpretation of protein structures: estimation of static accessibility. J. Mol. Biol. 55:379-400
Greer J, Bush B. (1978) Macromolecular shape and surface maps by solvent exclusion. Proc. Natl. Acad. Sci. USA 75:303-307.
Connolly M. (1983) Solvent-accessible surfaces of proteins and nucleic acids. Science 221:709-713
Chakravarty S, Varadarajan R. (1999) Residue depth: a novel parameter for the analysis of protein structure and stability. Structure Fold. Des. 7:723-732.
Pintar A, Carugo O, Pongor S. (2003) Atom depth in protein structure and function. Trends Biochem. Sci. 28:593-597.
Hamelryck T. (2005) An amino acid has two sides: A new 2D measure provides a different view of solvent exposure. Proteins Struct. Func. Bioinf. 59:38-48.

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A spectator ion is an ion that exists both as a reactant and a product in a chemical equation of an aqueous solution.
For example, in the reaction of aqueous solutions of sodium carbonate and copper(II) sulfate:
2 Na+(aq) + CO2−3(aq) + Cu2+(aq) + SO2−4(aq) → 2 Na+(aq) + SO2−4(aq) + CuCO3(s)
The Na+ and SO2−4 ions are spectator ions since they remain unchanged on both sides of the equation. They simply "watch" the other ions react and does not participate in any reaction, hence the name. They are present in total ionic equations to balance the charges of the ions. Whereas the Cu2+ and CO2−3 ions combine to form a precipitate of solid CuCO3. In reaction stoichiometry, spectator ions are removed from a complete ionic equation to form a net ionic equation. For the above example this yields:
So: 2 Na+(aq) + CO2−3(aq) + Cu2+(aq) + SO2−4(aq) → 2 Na+(aq) + SO2−4(aq) + CuCO3(s) (where x = spectator ion)
⇒ CO2−3(aq) + Cu2+(aq) → CuCO3(s)
Spectator ion concentration only affects the Debye length. In contrast, potential determining ions, whose concentrations affect surface potential (by surface chemical reactions) as well the Debye length.
== Net ionic equation ==
A net ionic equation ignores the spectator ions that were part of the original equation. So, the net ionic equation only shows the ions which reacted to produce a precipitate. Therefore, the total ionic reaction is different from the net reaction.
== See also ==
Catalysis
== References ==

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The Speeter–Anthony route, also known as the Speeter–Anthony tryptamine synthesis (STS), is a well-known and widely used chemical synthesis route used in the synthesis of tryptamines, including psychedelic tryptamines like psilocin and 5-MeO-DiPT. It starts with indole or a ring-substituted indole. The scheme of the route is as follows:
The route was first described by Merrill E. Speeter and William C. Anthony in 1954.
Other tryptamine synthesis routes have also been described, for instance starting with tryptamine rather than indole.
== References ==

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Spill kits are typically single-use kits containing chemicals used for absorption of (hazardous) wastes. Ready-for-use kits typically contain personal protective equipment, decontamination or neutralizing agents, disposal containers, and signage markers. Sometimes, spill containment material will also be included.
== Types ==
Specialized kits are available for specific spills:
Infectious body fluids
Cooking oil and food waste
Sewage
Corrosive and hazardous chemicals
Carcinogens
Irritants
Toxic substances
Solvents
Petroleum (see oil spill) and p. products like
Fossil fuels
== References ==
== External links ==
Rashid, Adeel (2024-11-04). "What's A Spill Kit? Types, Uses, Benefits and Components". Occupational Health and Safety Blog. Retrieved 2025-03-31.
Lee, Evie (2021-11-03). "Types Of Spills Kits, What Are They Used For?". CPD Online College. Retrieved 2025-03-31.

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The stannite ion is [Sn(OH)3]−. It can be formed by adding strong base to stannous hydroxide. The stannite ion is a strong reducing agent; also, it may disproportionate to tin metal plus stannate ion.
There are stannite compounds, for example, sodium stannite, Na2SnO2.
== See also ==
Stannate
== References ==

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For chemical solutions, a Steric exclusion occurs when a solute molecule in water has a relatively larger hydrodynamic radius than water leading to a deficiency of the solute molecule in the vicinity of a second solute molecule (which must have some hydrophilic surfaces) of interest.
== References ==

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Stigmasterol-rich plant sterols is a food additive. It is a mixture derived from soybeans that consists of the plant sterols stigmasterol, β-sitosterol, campesterol, and brassicasterol, with stigmasterol representing >85% of the mixture. Its E number is E499 and it is used as a stabiliser in ready-to-freeze alcoholic cocktails.
== References ==

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title: "Structural unit"
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In polymer chemistry, a structural unit is a building block of a polymer chain. It is the result of a monomer which has been polymerized into a long chain.
There may be more than one structural unit in the repeat unit. When different monomers are polymerized, a copolymer is formed. It is a routine way of developing new properties for new materials.
== Example ==
Consider the example of polyethylene terephthalate (PET or "polyester"). The monomers which could be used to create this polymer are ethylene glycol and terephthalic acid:
HO-CH2-CH2-OH
and
HOOC-C6H4-COOH
In the polymer, there are two structural units, which are
-O-CH2-CH2-O-
and
-CO-C6H4-CO-
The repeat unit is
-CH2-CH2-O-CO-C6H4-CO-O-
== Functionality of structural units ==
The functionality of a monomeric structural unit is defined as the number of covalent bonds which it forms with other reactants. A structural unit in a linear polymer chain segment forms two bonds and is therefore bifunctional, as for the PET structural units above.
Other values of functionality exist. Unless the macromolecule is cyclic, it will have monovalent structural units at each end of the polymer chain. In branched polymers, there are trifunctional units at each branch point. For example, in the synthesis of PET, a small fraction of the ethylene glycol can be replaced by glycerol which has three alcohol groups. This trifunctional molecule inserts itself in the polymeric chain and bonds to three carboxylic acid groups forming a branch point.
Finally, the formation of cross-linked polymers involves tetrafunctional structural units. For example, in the synthesis of cross-linked polystyrene, a small fraction of monomeric styrene (or vinylbenzene) is replaced by 1,4-divinylbenzene (or para-divinylbenzene). Each of the two vinyl groups is inserted into a polymeric chain, so that the tetravalent unit is inserted into both chains, linking them together.
== See also ==
Repeat unit
== References ==

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The Sulfurozador was a popular name for a device that emits sulfur dioxide in closed spaces for sanitation purposes, used extensively in South America, especially in Buenos Aires, to kill rat populations. The device was originally invented in France by René Marot, and found more widespread use in times of epidemics, such as the plague epidemic in San Francisco. It was used extensively for fumigation of ships.
== References ==

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A sulphobe is a film composed of formaldehyde and thiocyanates alleged to have lifelike properties. The name is a portmanteau of sulphur microbe. Sulphobes were a subject in the researches of Alfonso L. Herrera, a biologist who studied the origin of life.
== References ==
== Further reading ==
Bedau, Mark A.; et al. (2009). Protocells: Bridging Nonliving and Living Matter. MIT Press. p. 4. ISBN 978-0-262-28209-3. OCLC 939059014.
Ponnamperuma, Cyril; Chela-Flores, Julián (1995). Chemical Evolution: The Structure and Model of the First Cell. Kluwer Academic Publishers. pp. 13–15. ISBN 978-0-7923-3562-7. OCLC 492364104. OL 1279293M.

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---
title: "Synthome"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Synthome"
category: "reference"
tags: "science, encyclopedia"
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The synthome comprises the set of all reactions that are available to a chemist for the synthesis of small molecules. The word was coined by Stephen F. Martin.
== References ==

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title: "Tashiro's indicator"
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category: "reference"
tags: "science, encyclopedia"
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instance: "kb-cron"
---
Tashiro's indicator is a pH indicator (pH value: 4.4–6.2), mixed indicator composed of a solution of methylene blue (0.1%) and methyl red (0.03%) in ethanol or in methanol.
It can be used for the titration of ammonia in Kjeldahl analysis.
== Colours ==
In acids: violet
At equivalence point (pH 5.2): grey
In bases: green
Methylene blue functions to change the red-yellow shift of methyl red to a more distinct violet-green shift.
== See also ==
Litmus
pH Indicator
== References ==

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title: "Thermotropic crystal"
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category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:30:07.051684+00:00"
instance: "kb-cron"
---
A liquid crystal phase is thermotropic if its order parameter is determined by temperature. At high temperatures, liquid crystals become an isotropic liquid and at low temperatures, they tend to glassify. In a thermotropic crystal, those phase transitions occur only at temperature extremes; the phase is insensitive to concentration.
Most thermotropic liquid crystals are composed of rod-like molecules, and admit nematic, smectic, or cholesterolic phases.
== See also ==
Thermochromism
Thermotropic liquid crystals
== References ==
Chandrasekhar, S. (1977). Liquid Crystals (2nd ed.). Cambridge, UK: Cambridge University Press (published 1992). ISBN 0-521-42741-X.
== External links ==
What are Liquid Crystals?

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title: "Thiadiazine"
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category: "reference"
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date_saved: "2026-05-05T11:30:08.269904+00:00"
instance: "kb-cron"
---
In organosulfur chemistry, thiadiazine is a heterocyclic compound containing a six-membered ring composed of three carbon atoms, one sulfur atom, and two nitrogen atoms. It exists in several isomeric forms, each characterized by the different arrangement of the sulfur and nitrogen atoms in the ring structure. Common isomers include 1,2,4-thiadiazine, 1,2,6-thiadiazine, and 1,3,4-thiadiazine. Thiadiazines have gained significant interest in organic and medicinal chemistry research due to their diverse potential biological activities, including antimicrobial, anti-inflammatory, and muscle relaxant properties. They have been explored their potential applications in treating conditions such as Huntington's disease, rheumatoid arthritis, and type 2 diabetes.
== References ==

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title: "Third phase (chemistry)"
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category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:30:09.435611+00:00"
instance: "kb-cron"
---
Third phase is the term for a stable emulsion which forms in a liquid–liquid extraction when the original two phases (aqueous and organic) are mixed.
The third phase can be caused by a detergent (surfactant) or a fine solid. While third phase is a term for an unwanted emulsion, a stable emulsion is wanted in emulsion polymerization all the things which can be used to make a stable 'emulsion' for a latex synthesis can prove to encourage a third phase to form.
One term for the third phase found in PUREX plants is crud (Chalk River Unknown Deposit). One common crud is formed by the reaction of zirconium salts (from fission) with degraded tributyl phosphate (TBP). The TBP degrades into dibutyl hydrogen phosphate and then into butyl dihydrogen phosphate. The dibutyl hydrogen phosphate and the zirconium can form polymeric solid which is very insoluble.

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title: "Thistle tube"
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instance: "kb-cron"
---
A thistle tube is a piece of laboratory glassware consisting of a shaft of tube, with a reservoir and funnel-like section at the top. Thistle tubes are typically used by chemists to add liquid to an existing system or apparatus. Thistle funnels are used to add small volumes of liquids to an exact position. Thistle funnels are found with or without taps.
The thistle tube shaft is designed to allow insertion through a small hole present in some stoppers, permitting the tube to be inserted into a container such as an Erlenmeyer flask.
== References ==

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title: "Tilting pan filter"
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category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:30:11.882721+00:00"
instance: "kb-cron"
---
A tilting pan filter is a chemical equipment used in continuous solid-liquid filtration.
It is formed by a number of trapezoidal pans arranged in circle. At the center of the equipment there is the main valve which is connected to every pan through pipes. The pans are rotating continuously around the main valve, which provides the air or the vacuum necessary for the operation. In each pan it is carried out the filtration in a cyclic process that involves these stages:
feed is poured in the pan; the material to be filtered formed in this way a "cake";
cake is washed out;
cake is dried through the aspiration of the liquid;
cake is washed out again;
cake is dried again;
pan is tilted in order to discharge the solid;
pan is sprayed with water to be cleaned;
pan is tilted back to the initial angle and the process continues with the feeding stage.
== See also ==
Filtration
Filter cake
== References ==

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title: "Total carbon"
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source: "https://en.wikipedia.org/wiki/Total_carbon"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:30:13.061149+00:00"
instance: "kb-cron"
---
Total carbon (TC) is an analytical parameter representing the concentration of carbon in a sample. TC includes carbon in any form, whether organic or inorganic, volatile or fixed, dissolved or suspended. In many application areas, rather than TC, a parameter representing of subset of TC is measured; examples include Total organic carbon (TOC), Particulate inorganic carbon (PIC), and Dissolved organic carbon (DOC).

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title: "Total fatty matter"
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source: "https://en.wikipedia.org/wiki/Total_fatty_matter"
category: "reference"
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date_saved: "2026-05-05T11:30:14.253447+00:00"
instance: "kb-cron"
---
Total fatty matter (TFM) is one of the most important characteristics describing the quality of soap and is always specified in commercial transactions. It is defined as the total amount of fatty matter, mostly fatty acids, that can be separated from a sample after splitting with a mineral acid, usually hydrochloric acid.
The fatty acids most commonly present in soap are oleic, stearic and palmitic acids, and pure, dry, sodium oleate has a TFM of 92.8%, while top quality soap noodles, now increasingly used for making soap tablets in small and medium-sized factories, are typically traded with a specification of TFM of 78% min., moisture 14% max. But besides moisture, finished commercial soap, especially laundry soap, also contains fillers used to lower its cost or confer special properties, plus emollients, preservatives, etc., making the TFM go as low as 50%. Fillers, which are usually dry powders, also make the soap harder, harsher on the skin, and with a greater tendency to become 'mushy' in water, so low TFM is usually associated with lower quality and hardness. In the past, and still in some countries today, soap with a TFM of 75% minimum was called Grade 1, 65% minimum was called Grade 2, and less than 60% was called Grade 3.
== References ==

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title: "Toxophore"
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source: "https://en.wikipedia.org/wiki/Toxophore"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:30:15.460565+00:00"
instance: "kb-cron"
---
A toxophore is the chemical group that produces the toxic effect in a toxin molecule: commonly used in pharmaceutical and pesticide sciences.
== References ==

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category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T10:53:34.363641+00:00"
date_saved: "2026-05-05T11:30:16.718142+00:00"
instance: "kb-cron"
---

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title: "Trichlorogermanate"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Trichlorogermanate"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:30:17.922134+00:00"
instance: "kb-cron"
---
Trichlorogermanate is the inorganic anion with the formula GeCl−3. It is the chloride adduct of germanium dichloride:
GeCl2 + Cl− → GeCl−3
The anion can be isolated as a quaternary ammonium salt. The anion is similar to trichlorostannate (SnCl−3).
The anion is pyramidal according to X-ray crystallography with Cl-Ge-Cl angle of about 95° and Ge-Cl distance of 232 pm.
== References ==

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date_saved: "2026-05-05T09:00:20.364378+00:00"
date_saved: "2026-05-05T11:30:19.196110+00:00"
instance: "kb-cron"
---

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title: "Unica (material)"
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category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:30:20.430311+00:00"
instance: "kb-cron"
---
Unica is a vulcanised lump paper material. It was (and to some extent still is) used to make boxes. The most famous product is probably a lunch box. But unica has also been used to make suitcases, helmets, buttons, shoes and, during the Second World War it was even used to make fuel tanks for Swedish aeroplanes. Many unica products were made by AB Tidan in Mariestad. Nowadays unica boxes are made by Alstermo Bruk in Småland, Sweden.
== References ==

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title: "Unit process"
chunk: 1/1
source: "https://en.wikipedia.org/wiki/Unit_process"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:30:21.649551+00:00"
instance: "kb-cron"
---
A unit process is one or more grouped unit operations in a manufacturing system that can be defined and separated from others.
In life-cycle assessment (LCA) and ISO 14040, a unit process is defined as "smallest element considered in the life cycle inventory analysis for which input and output data are quantified".
== See also ==
Unit operation
== References ==

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title: "Viehland–Mason theory"
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date_saved: "2026-05-05T11:30:22.818395+00:00"
instance: "kb-cron"
---
The Viehland–Mason theory is a two-temperature theory for charged and neutral atoms, which explains how trace ions can have a substantially different temperature than dilute gas atoms. It is one of any of a number of kinetic theories of the transport of trace amounts of molecular ions through neutral gases under the influence of a uniform electrostatic field. Larry Viehland and Edward A. Mason developed it in the late 1970s. They later extended this theory into a three-temperature theory that allowed for different ion temperatures parallel and perpendicular to the electric field. Current work for atomic ion-neutral systems uses a Gram–Charlier probability function as a zero-order approximation to the ion velocity distribution function.
The Gram–Charlier theory has been remarkably successful in producing calculated mobilities and diffusion coefficients that are in excellent agreement with experimental results if the microscopic force between the ion and atom is accurately known over a wide range of separation. The Viehland–Mason theories for molecular ions in molecular gases are more elaborate than those for atoms, since the forces are angle-dependent and since internal degrees of freedom must be included. Theories have been developed using quantum-mechanical and semi-classical approaches, but there have been no numerical applications because it is extremely difficult to calculate the necessary cross-sections. To circumvent this difficulty, completely classical kinetic theories for atomic ions in non-vibrating (rigid rotor) diatomic gases and for non-vibrating diatomic ions in atomic or non-vibrating diatomic gases have been developed.
== References ==
Mason, Edward A. and Earl W. MacDaniel. 1988. Transport Properties of Ions in Gases. John Wiley & Sons.
Viehland, L. A. 2003. “Mobilities.” In Armentrout, Peter B. (ed.) The Encyclopedia of Mass Spectrometry. Elsevier. pp. 491–498

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title: "Vitamin C2"
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category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T11:30:24.052523+00:00"
instance: "kb-cron"
---
Vitamin C2 or Vitamin C2 is not a widely recognized term in modern scientific classification. However, it has been historically or erroneously used to refer to various substances, including:
A proprietary trademarked name for a combination of calcium ascorbate and ascorbyl palmitate, marketed as a blend of "water-soluble" and "fat-soluble" vitamin C.
Vitamin P, a historical term once used for certain bioflavonoids, though they are not classified as true vitamins. This term was used circa 1948 or earlier.
Vitamin J which was used circa 1935. Vitamin J was an earlier term for choline.
Aesculin (also known as Esculin), a compound sometimes referred to as "Vitamin C2" in older databases, though this designation is not widely accepted.
== References ==

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title: "Von Baeyer nomenclature"
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tags: "science, encyclopedia"
date_saved: "2026-05-05T11:30:25.246609+00:00"
instance: "kb-cron"
---
In organic chemistry, the von Baeyer nomenclature is a system for describing polycyclic (i.e. multi-ringed) hydrocarbons. The system was originally developed in 1900 by German chemist Adolf von Baeyer for bicyclic systems and in 1913 expanded by Eduard Buchner and Wilhelm Weigand for tricyclic systems. The system has been adopted and extended by the IUPAC as part of its nomenclature for organic chemistry. The modern version has been extended to cover more cases of compounds including an arbitrary number of cycles, heterocyclic compounds and unsaturated compounds.
== Extended Von Baeyer ==
== See also ==
Clar's rule
== References ==

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title: "Water conditioner"
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tags: "science, encyclopedia"
date_saved: "2026-05-05T11:30:26.432346+00:00"
instance: "kb-cron"
---
Water conditioners are chemical formulations designed to be added to tap water to improve water quality.
== Aquariums ==
If the tap water is chlorinated then a simple conditioner containing a dechlorinator may be used in an aquarium. These products contain sodium thiosulfate which reduces chlorine to chloride which is less harmful to fish. However, chloramine is now often used in water disinfection and simple dechlorinators only deal with the chlorine portion, releasing free ammonia that is very harmful to fish. More complex products employ sulfonates that are able to deal with both chlorine and ammonia. The most sophisticated products also contain chelators such as ethylenediaminetetraacetic acid to bind and remove heavy metals. Some water conditioners also contain slime coat protectors such as polyvinylpyrrolidones or Aloe vera extracts, which can reduce stress behaviour of fish.
== Waterbeds ==
Waterbeds commonly use water conditioners to inhibit the growth of algae, bacteria, and fungi within the mattress water. These conditioners help prevent unpleasant odors and discoloration caused by microbial activity. They may also contain additives that protect the vinyl liner by maintaining its flexibility and reducing the risk of cracking or degradation. Furthermore, conditioners help minimize mineral buildup inside the mattress, contributing to prolonged water clarity and overall mattress longevity.
== References ==

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title: "Weldon mud"
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tags: "science, encyclopedia"
date_saved: "2026-05-05T11:30:27.586582+00:00"
instance: "kb-cron"
---
Weldon mud is a precipitation of manganese used in the production of chlorine.
Walter Weldon developed a process in the chlorine production process for reuse of manganese by treating the manganese chloride with milk of lime and blowing air through the mixture to form a precipitation of manganese known as Weldon mud, which was used to generate more chlorine.
== References ==

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title: "Wiswesser line notation"
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date_saved: "2026-05-05T11:30:28.824092+00:00"
instance: "kb-cron"
---
Wiswesser line notation (WLN), invented by William J. Wiswesser in 1949, was the first line notation capable of precisely describing complex molecules. It was the basis of ICI Ltd's CROSSBOW database system developed in the late 1960s. WLN allowed for indexing the Chemical Structure Index (CSI) at the Institute for Scientific Information (ISI). It was also the tool used to develop the CAOCI (Commercially Available Organic Chemical Intermediates) database, the datafile from which Accelrys' (successor to MDL) ACD file was developed. WLN is still being extensively used by BARK Information Services. Descriptions of how to encode molecules as WLN have been published in several books.
== Examples ==
1H : methane
2H : ethane
3H : propane
1Y : isobutane
1X : neopentane
Q1 : methanol
1R : toluene
1V1 : acetone
2O2 : diethyl ether
1VR : acetophenone
ZR CVQ : 3-aminobenzoic acid
QVYZ1R : phenylalanine
QX2&2&2 : 3-ethylpentan-3-ol
QVY3&1VQ : 2-propylbutanedioic acid
L66J BMR& DSWQ IN1&1 : 6-dimethylamino-4-phenylamino-naphthalene-2-sulfonic acid
QVR-/G 5 : pentachlorobenzoic acid
T5NN DNJ AVN3&2 CSW3 : Epronaz
== References ==
== External links ==
Everything Old is New Again: Wiswesser Line Notation (WLN)

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title: "World Cell Race"
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date_saved: "2026-05-05T11:30:30.000988+00:00"
instance: "kb-cron"
---
The World Cell Race is a competition among labs to see which biological cell type can travel 600 microns the fastest. The idea is to promote research into how to make cells move faster to aid immune system response or slow metastatic cancers. A fork with a dead end was added to the course in 2013 to assess responses to growth-factor protein. The race was broadcast live online. A Dicty World Race "to find the fastest and smartest Dicty cells" took place on May 16, 2014, in Boston.
== References ==
== External links ==
World Cell Race 2014 website
World Cell Race 2013 website
World Cell Race 2012 website

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title: "Zenker's fixative"
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tags: "science, encyclopedia"
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instance: "kb-cron"
---
Zenker's fixative is a rapid-acting fixative for animal tissues. It is employed to prepare specimens of animal or vegetable tissues for microscopic study. It provides excellent fixation of nuclear chromatin, connective tissue fibers and some cytoplasmic features, but does not preserve delicate cytoplasmic organelles such as mitochondria. Helly's fixative is preferable for traditional dye staining of mitochondria. Zenker's fixative permeabilises the plasma, but not the nuclear membrane. It can therefore be used to selectively stain mitotic cells (where the nuclear membrane has dissolved) with antibodies against chromatin
Zenker's fixative contains mercuric chloride ("corrosive sublimate"), potassium dichromate, sodium sulfate, water, and acetic acid. Fixatives containing mercuric chloride or potassium dichromate are toxic, making disposal as hazardous waste costly. Mercuric chloride can be replaced with the same weight of less toxic zinc chloride, but the resulting "zinc-Zenker" may not give the same quality of fixation as the original mixture.
This fixative is named after Konrad Zenker, a German histologist, who died in 1894 (Baker 1958).
== Stock solution ==
Zenker is usually made with 50g of mercuric chloride, 25g of potassium dichromate, 10g of sodium sulfate (decahydrate) and distilled water to complete 1000 ml.
Before use, 5 ml glacial acetic acid is added to 100 ml of the solution. Both the stock solution and the complete Zenker fixative are stable for many years.
=== Helly's fixative ===
If the glacial acetic acid is replaced by 5 ml of formalin (37–40% formaldehyde), the resulting solution is Helly's fixative, also sometimes called "formol-Zenker". Helly is stable for only a few hours because the formaldehyde and dichromate components react, producing formic acid and chromium(III) ions; the orange solution becomes greenish.
== See also ==
Fixation (histology)
Dorland's Medical Dictionary
== References ==
Barszcz CA (1976) Use of zinc chloride in Zenker-type fixatives. Histo-Logic 6: 87.[1]
Baker JR (1958) Principles of Biological Microtechnique. London: Methuen, p. 344.
Gabe M (1976) Histological Techniques (Transl. E. Blakith and A. Kavoor). Paris: Masson.
Kiernan JA (2008) Histological and Histochemical Methods. 4th ed. Bloxham, UK: Scion. p. 40–41.
Lillie RD & Fullmer HM (1976) Histopathologic Technic and Practical Histochemistry. 4th ed. New York: McGraw-Hill. p. 54–57.
www.whonamedit.com

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