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Latex is the stable dispersion (emulsion) of polymer microparticles in an aqueous medium. Latexes may be natural or synthetic. Latex as found in nature is a milky sap-like fluid found in 10% of all flowering plants (angiosperms).[1] It is a complex emulsion consisting of proteins, alkaloids, starches, sugars, oils, tannins, resins, and gums that coagulates on exposure to air. It is usually exuded after tissue injury. In most plants, latex is white, but some have yellow, orange, or scarlet latex. Since the 1600s, latex has been used as a term for the fluid substance in plants.[2] It serves mainly as defense against small insects.[1]
The word is also used to refer to natural latex rubber; particularly for non-vulcanized rubber. Such is the case in products like latex gloves, latex condoms and latex clothing. It can also be made synthetically by polymerizing a monomer that has been emulsified with surfactants.
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The cells or vessels in which latex is found make up the laticiferous system, which forms in two very different ways. In many plants, the laticiferous system is formed from rows of cells laid down in the meristem of the stem or root. The cell walls between these cells are dissolved so that continuous tubes, called latex vessels, are formed. This method of formation is found in the poppy family, in the rubber trees (Para rubber tree and Castilla elastica), and in the Cichorieae, a section of the Family Asteraceae distinguished by the presence of latex in its members. Dandelion, lettuce, hawkweed, and salsify are members of the Cichorieae. It is also present in another member of the Asteraceae, the guayule plant.
In the milkweed and spurge families, on the other hand, the laticiferous system is formed quite differently. Early in the development of the seedling latex cells differentiate, and as the plant grows these latex cells grow into a branching system extending throughout the plant. In the mature plant, the entire laticiferous system is descended from a single cell or group of cells present in the embryo.
The laticiferous system is present in all parts of the mature plant, including roots, stems, leaves, and sometimes the fruits. It is particularly noticeable in the cortical tissues. Latex may squirt out as a white glue or be difficult to see due to it being clear or not exuding very much. It can be red such as in Cannabaceae.[1]
Latex is produced by 20,000 species from over 40 families occurring in multiple lineages in both dicotyledonous and monocotyledonous of plant. It is also found in conifers and pteridophytes. Several members of the fungal kingdom also produce latex upon injury. Notable are the milk-caps such as Lactarius deliciosus. This suggests it is the product of convergent evolution and has been selected for on many separate occasions.[1]
14% of tropical plant species create latex but only 6% of temperate ones.[3]
Latex functions to protect the plant from herbivores. The idea was first proposed in 1887 by Joseph F. James who noted that latex
“. . .it carries with it at the same time such disagreeable properties that it becomes a better protection to the plant from enemies than all the thorns, prickles, or hairs that could be provided. In this plant, so copious and so distasteful has the sap become that it serves a most important purpose in its economy.”[4]
Evidence showing this defense function include the finding that slugs will eat of leaves drained of their latex but not intact ones, that many insects sever the veins carrying latex before they feed, and that the latex of Asclepias humistrata kills by trapping 30% of newly hatched monarch butterfly caterpillars.[1]
Other evidence is that latex contains 50–1000 higher concentrations of defense substances than other plant tissues. These toxins include ones that are also toxic to the plant and consist of a diverse range of chemicals that are either poisonous or "antinutritive". Latex is actively moved to the area of injury in the case of Cryptostegia grandiflora this can be more than 70 cm.[1]
The clotting latex is functional in this defenses since it prevents it being wasted and its stickiness traps insects and their mouthparts.[1]
It has been noted that while there exist other explanations for the existence of latex including storage and movement of plant nutrients, waste, and maintenance of water balance that "Essentially none of these functions remain credible and none have any empirical support."[1]
The latex of many species can be processed to produce other materials.
Natural rubber is the most important product obtained from latex; more than 12,000 plant species yield latex containing rubber, though in the vast majority of those species the rubber is not suitable for commercial use.[5]. This latex is used to make many other products as well, including gloves, swim caps, condoms, catheters, balloons, and heavy duty dog toys. The latter are considered a safer alternative to vinyl toys as latex is difficult for the animal to break apart and small ingested pieces are unlikely to harm the dog.
Balatá and gutta percha latex contain an inelastic polymer related to rubber.
Latex from the chicle and jelutong trees is used in chewing gum.
Dried latex from the opium poppy is opium, the source of many useful opiates and other alkaloids of high value.
Latexes are used in coatings (e.g. latex paint) and glues because they solidify by coalescence of the polymer particles as the water evaporates, and therefore can form films without releasing potentially toxic organic solvents in the environment. Other uses include cement additives.
Latex, usually styrene based, is also used in immunoassays.
Latex is used in many types of clothing. Worn on the body (or applied directly by painting) it tends to be skin-tight, producing a "second skin" effect.
Some people have a serious latex allergy, and exposure to latex products such as latex gloves can cause anaphylactic shock. Guayule latex is hypoallergenic and is being researched as a substitute to the allergy-inducing Hevea latexes. Additionally, chemical processes may be employed to reduce the amount of antigenic protein in Hevea latex, yielding alternative materials such as Vytex Natural Rubber Latex which provide significantly reduced exposure to latex allergens.
Many people with spina bifida are also allergic to natural latex rubber, as well as people who have had multiple surgeries, and people who have had prolonged exposure to natural latex.
| Original author(s) | Leslie Lamport |
|---|---|
| Platform | Cross-platform |
| Type | Typesetting |
| License | LaTeX Project Public License (LPPL) |
| Website | latex-project.org |
LaTeX (pronounced /ˈleɪtɛk/, /ˈleɪtɛx/, /ˈlɑːtɛx/, or /ˈlɑːtɛk/) is a document markup language and document preparation system for the TeX typesetting program. Within the typesetting system, its name is styled as . The term LaTeX refers only to the language in which documents are written, not to the editor used to write those documents. In order to create a document in LaTeX, a .tex file must be created using some form of text editor. While most text editors can be used to create a LaTeX document, a number of editors have been created specifically for working with LaTeX.
LaTeX is most widely used by mathematicians, scientists, engineers, philosophers, lawyers, linguists, economists, researchers, and other scholars in academia.[1][2] As a primary or intermediate format, e.g., translating DocBook and other XML-based formats to PDF, LaTeX is used because of the high quality of typesetting achievable by TeX. The typesetting system offers programmable desktop publishing features and extensive facilities for automating most aspects of typesetting and desktop publishing, including numbering and cross-referencing, tables and figures, page layout and bibliographies.
LaTeX is intended to provide a high-level language that accesses the power of TeX. LaTeX essentially comprises a collection of TeX macros and a program to process LaTeX documents. Because the TeX formatting commands are very low-level, it is usually much simpler for end-users to use LaTeX.
LaTeX was originally written in the early 1980s by Leslie Lamport at SRI International.[3] It has become the dominant method for using TeX—relatively few people write in plain TeX anymore. The current version is LaTeX2e (styled ).
As it is distributed under the terms of the LaTeX Project Public License (LPPL), LaTeX is free software.
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LaTeX is based on the idea that authors should be able to focus on the content of what they are writing without being distracted by its visual presentation. In preparing a LaTeX document, the author specifies the logical structure using familiar concepts such as chapter, section, table, figure, etc., and lets the LaTeX system worry about the presentation of these structures. It therefore encourages the separation of layout from content while still allowing manual typesetting adjustments where needed. This is similar to the mechanism by which many word processors allow styles to be defined globally for an entire document or the use of Cascading Style Sheets to style HTML.
LaTeX can be arbitrarily extended by using the underlying macro language to develop custom formats. Such macros are often collected into packages, which are available to address special formatting issues such as complicated mathematical content or graphics. Indeed, in the example below, the align environment is provided by the amsmath package.
The example below shows the LaTeX input and corresponding output:
\documentclass[12pt]{article} \usepackage{amsmath} \title{\LaTeX} \date{} \begin{document} \maketitle
\LaTeX{} is a document preparation system for the \TeX{}
typesetting program. It offers programmable desktop publishing
features and extensive facilities for automating most aspects of
typesetting and desktop publishing, including numbering and
cross-referencing, tables and figures, page layout, bibliographies,
and much more. \LaTeX{} was originally written in 1984 by Leslie
Lamport and has become the dominant method for using \TeX; few
people write in plain \TeX{} anymore. The current version is
\LaTeXe.
% This is a comment; it is not shown in the final output.
% The following shows a little of the typesetting power of LaTeX
\begin{align}
E &= mc^2 \\
m &= \frac{m_0}{\sqrt{1-\frac{v^2}{c^2}}}
\end{align}
\end{document} |
.]]
LaTeX is usually pronounced /ˈlɑːtɛk/ or /ˈleɪtɛk/ in English (that is, not with the /ks/ pronunciation English speakers normally associate with X, but with a /k/). The characters T, E, X in the name come from capital Greek letters tau, epsilon, and chi, as the name of TeX derives from the Greek: τέχνη (skill, art, technique); for this reason, TeX's creator Donald Knuth promotes a pronunciation of /tɛx/ (tekh)[4] (that is, with a voiceless velar fricative as in Modern Greek, similar to the last sound of the German word "Bach", the Spanish "j" sound, or as ch in loch). Lamport, on the other hand, has said he does not favor or discourage any pronunciation for LaTeX.
The name is traditionally printed with the special typographical logo shown at the top of this page. In media where the logo cannot be precisely reproduced in running text, the word is typically given the unique capitalization LaTeX. The TeX, LaTeX [5] and XeTeX [6] logos can be rendered via pure CSS and XHTML for use in graphical web browsers following the specifications of the internal \LaTeX macro.[7]
LaTeX is typically distributed along with plain TeX. It is distributed under a free software license, the LaTeX Project Public License (LPPL). The LPPL is not compatible with the GNU General Public License, as it requires that modified files must be clearly differentiable from their originals (usually by changing the filename); this was done to ensure that files that depend on other files will produce the expected behavior and avoid dependency hell. The LPPL is DFSG compliant as of version 1.3. As free software, LaTeX is available on most operating systems including Unix (Linux, BSDs, Mac OS X), Windows, RISC OS and AmigaOS.
As a macro package, LaTeX provides a set of macros for TeX to interpret. There are many other macro packages for TeX, including Plain TeX, GNU Texinfo, AMSTeX, and ConTeXt.
When TeX "compiles" a document, the processing sequence (from the user's point of view) goes like this: Macros > TeX > Driver > Output. Different implementations of each of these steps are typically available in TeX distributions. Traditional TeX will output a DVI file, which is usually converted to a PostScript file. More recently, Hàn Thế Thành and others have written a new implementation of TeX called pdfTeX, which also outputs to PDF and takes advantage of features available in that format. The XeTeX engine developed by Jonathan Kew merges modern font technologies and Unicode with TeX.
The default font for LaTeX is Knuth's Computer Modern, which gives default documents created with LaTeX the same distinctive look as those created with plain TeX. XeTeX allows the use of OpenType and TrueType (that is, outlined) fonts for output files.
There are also many editors for LaTeX, listed in section See also.
LaTeX2e is the current version of LaTeX. As of 2010[update], a future version called LaTeX3, started in the early 1990s, is still in development.[8] Planned features include improved syntax, hyperlink support, a new user interface, access to arbitrary fonts, and new documentation.[9]
There are numerous commercial implementations of the entire TeX system. System vendors may add extra features like additional typefaces and telephone support. LyX is a free, WYSIWYM visual document processor that uses LaTeX for a back-end. TeXmacs is a free, WYSIWYG editor with similar functionalities as LaTeX but a different typesetting engine. Other WYSIWYG editors that produce LaTeX include Scientific Word on MS Windows.
A number of TeX distributions are available, including TeX Live (multiplatform), teTeX (deprecated in favour of TeX Live, Unix), fpTeX (deprecated), MiKTeX (Windows), MacTeX (TeX Live with the addition of Mac specific programs), gwTeX (Mac OS X), OzTeX (Mac OS Classic), AmigaTeX (no longer available) and PasTeX (AmigaOS, available on the Aminet repository).
LaTeX documents can be shared with people who only use Microsoft Word or OpenOffice.org Writer, converting the LaTeX file (.tex) to Rich Text Format (.rtf). This can be done using the free software program LaTeX2RTF.
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LaTeX is a markup language (as is MediaWiki!) for producing mathematical texts of the highest quality. Its use is widespread in the mathematics world. It is built on plain TeX developed by Donald Knuth. You can embed LaTeX markups in MediaWiki by the <math></math> tags, e.g. <math> e = m c^2</math> is rendered as e = mc2.
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A good editing environment helps! A useful and free option is the LaTeX editor (LEd) (see their home page).
This is a guide to the LaTeX markup language. It is intended that this can serve as a useful resource for everyone from new users who wish to learn, to old hands who need a quick reference.
Latex is found in the sap of the Para rubber tree. The tree takes its name from the state of Pará, Brazil. Latex is used to make rubber. Brazil, in particular the city of Manaus grew rich on latex. Today, much natural latex comes from Southeast Asia, particularly Malaysia and Indonesia. Rubber can be produced synthetically (this means that it can be made in factories).
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