The Jmol applet, among other abilities, offers an alternative to the Chime plug-in, no longer under active development. While Jmol has many features that Chime lacks, it does not claim to reproduce all Chime functions, most notably, the Sculpt mode. Chime requires plug-in installation and Internet Explorer 6.0 or Firefox 2.0 on Microsoft Windows, or Netscape Communicator 4.8 on Mac OS 9. Jmol operates on a wide variety of platforms. For example, Jmol is functional in Mozilla Firefox, Internet Explorer, Google Chrome, Safari. Chemistry Development Kit Comparison of software for molecular mechanics modeling Jmol extension for MediaWiki List of molecular graphics systems Molecular graphics Molecule editor Proteopedia PyMOL SAMSON Official website Wiki with listings of websites and moodles Willighagen, Egon. "Fast and Scriptable Molecular Graphics in Web Browsers without Java3D". Doi:10.1038/npre.2007.50.1
Immediately dangerous to life or health
The term dangerous to life or health is defined by the US National Institute for Occupational Safety and Health as exposure to airborne contaminants, "likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment." Examples include smoke or other poisonous gases at sufficiently high concentrations. It is calculated using the LD50 or LC50; the Occupational Safety and Health Administration regulation defines the term as "an atmosphere that poses an immediate threat to life, would cause irreversible adverse health effects, or would impair an individual's ability to escape from a dangerous atmosphere."IDLH values are used to guide the selection of breathing apparatus that are made available to workers or firefighters in specific situations. The NIOSH definition does not include oxygen deficiency although atmosphere-supplying breathing apparatus is required. Examples unventilated, confined spaces; the OSHA definition is arguably broad enough to include oxygen-deficient circumstances in the absence of "airborne contaminants", as well as many other chemical, thermal, or pneumatic hazards to life or health.
It uses the broader term "impair", rather than "prevent", with respect to the ability to escape. For example, blinding but non-toxic smoke could be considered IDLH under the OSHA definition if it would impair the ability to escape a "dangerous" but not life-threatening atmosphere; the OSHA definition is part of a legal standard, the minimum legal requirement. Users or employers are encouraged to apply proper judgment to avoid taking unnecessary risks if the only immediate hazard is "reversible", such as temporary pain, nausea, or non-toxic contamination. If the concentration of harmful substances is IDLH, the worker must use the most reliable respirators; such respirators should not use cartridges or canister with the sorbent, as their lifetime is too poorly predicted. In addition, the respirator must maintain positive pressure under the mask during inspiration, as this will prevent the leakage of unfiltered air through the gaps. Textbook NIOSH recommended for use in IDLH conditions only pressure-demand self-contained breathing apparatus with a full facepiece, or pressure-demand supplied-air respirator equipped with a full facepiece in combination with an auxiliary pressure-demand self-contained breathing apparatus.
The following examples are listed in reference to IDLH values. Legend: Ca NIOSH considers this substance to be a potential occupational carcinogen. Revised values may follow in parentheses. N. D. Not determined; that is, the level is unknown, not non-existent. 10%LEL The IDLM value has been set at 10% of the lower explosive limit although other irreversible health effects or impairment of escape due to toxicology exist only at higher levels. NIOSH air filtration rating NIOSH IDLH site 1910.134 Respiratory protection definitions
Plaster is a building material used for the protective or decorative coating of walls and ceilings and for moulding and casting decorative elements. In English "plaster" means a material used for the interiors of buildings, while "render" refers to external applications. Another imprecise term used for the material is stucco, often used for plasterwork, worked in some way to produce relief decoration, rather than flat surfaces; the most common types of plaster contain either gypsum, lime, or cement, but all work in a similar way. The plaster is manufactured as a dry powder and is mixed with water to form a stiff but workable paste before it is applied to the surface; the reaction with water liberates heat through crystallization and the hydrated plaster hardens. Plaster can be easily worked with metal tools or sandpaper, can be moulded, either on site or to make pre-formed sections in advance, which are put in place with adhesive. Plaster is not a strong material. Forms of plaster have several other uses.
In medicine plaster orthopedic casts are still used for supporting set broken bones. In dentistry plaster is used to make dental impressions. Various types of models and moulds are made with plaster. In art, lime plaster is the traditional matrix for fresco painting. In the ancient world, as well as the sort of ornamental designs in plaster relief that are still used, plaster was widely used to create large figurative reliefs for walls, though few of these have survived. Clay plaster is a mixture of clay and water with the addition of plant fibers for tensile strength over wood lath. Clay plaster has been used since antiquity. Settlers in the American colonies used clay plaster on the interiors of their houses: “Interior plastering in the form of clay antedated the building of houses of frame, must have been visible in the inside of wattle filling in those earliest frame houses in which …wainscot had not been indulged. Clay continued in the use long after the adoption of laths and brick filling for the frame."
Where lime was not available or accessible it was rationed or substituted with other binders. In Martin E. Weaver’s seminal work he says, “Mud plaster consists of clay or earth, mixed with water to give a “plastic” or workable consistency. If the clay mixture is too plastic it will shrink and distort on drying, it will probably drop off the wall. Sand and fine gravels were added to reduce the concentrations of fine clay particles which were the cause of the excessive shrinkage.” Straw or grass was added sometimes with the addition of manure. In the Earliest European settlers’ plasterwork, a mud plaster was used or more a mud-lime mixture. McKee writes, of a circa 1675 Massachusetts contract that specified the plasterer, “Is to lath and siele the four rooms of the house betwixt the joists overhead with a coat of lime and haire upon the clay. 5. To lath and plaster partitions of the house with clay and lime, to fill and plaister them with lime and haire besides. 6. The said Daniel Andrews is to find lime, clay, haire, together with laborers and workmen….”
Records of the New Haven colony in 1641 mention hay as well as lime and hair also. In German houses of Pennsylvania the use of clay persisted.” Old Economy Village is one such German settlement. The early Nineteenth-Century utopian village in present-day Ambridge, used clay plaster substrate in the brick and wood frame high architecture of the Feast Hall, Great House and other large and commercial structures as well as in the brick and log dwellings of the society members; the use of clay in plaster and in laying brickwork appears to have been a common practice at that time not just in the construction of Economy village when the settlement was founded in 1824. Specifications for the construction of, “Lock keepers houses on the Chesapeake and Ohio Canal, written about 1828, require stone walls to be laid with clay mortar, excepting 3 inches on the outside of the walls…which to be good lime mortar and well pointed.” The choice of clay was because of its low cost, but the availability. At Economy, root cellars dug under the houses yielded clay and sand, or the nearby Ohio river yielded washed sand from the sand bars.
Other required building materials were sourced locally. The surrounding forests of the new village of Economy provided straight grain, old-growth oak trees for lath. Hand split lath starts with a log of straight grained wood of the required length; the log is spit into quarters and smaller and smaller bolts with wedges and a sledge. When small enough, a froe and mallet were used to split away narrow strips of lath - unattainable with field trees and their many limbs. Farm animals pastured in the fields cleared of trees provided the hair and manure for the float coat of plaster. Fields of wheat and grains provided straw and other grasses for binders for the clay plaster, but there was no uniformity in clay plaster recipes. Straw or grass was added sometimes with the addition of manure providing fiber for tensile strength as well as protein adhesive. Proteins in the manure act as binders; the hydrogen bonds of p
European Chemicals Agency
The European Chemicals Agency is an agency of the European Union which manages the technical and administrative aspects of the implementation of the European Union regulation called Registration, Evaluation and Restriction of Chemicals. ECHA is the driving force among regulatory authorities in implementing the EU's chemicals legislation. ECHA helps companies to comply with the legislation, advances the safe use of chemicals, provides information on chemicals and addresses chemicals of concern, it is located in Finland. The agency headed by Executive Director Bjorn Hansen, started working on 1 June 2007; the REACH Regulation requires companies to provide information on the hazards and safe use of chemical substances that they manufacture or import. Companies register this information with ECHA and it is freely available on their website. So far, thousands of the most hazardous and the most used substances have been registered; the information is technical but gives detail on the impact of each chemical on people and the environment.
This gives European consumers the right to ask retailers whether the goods they buy contain dangerous substances. The Classification and Packaging Regulation introduces a globally harmonised system for classifying and labelling chemicals into the EU; this worldwide system makes it easier for workers and consumers to know the effects of chemicals and how to use products safely because the labels on products are now the same throughout the world. Companies need to notify ECHA of the labelling of their chemicals. So far, ECHA has received over 5 million notifications for more than 100 000 substances; the information is available on their website. Consumers can check chemicals in the products. Biocidal products include, for example, insect disinfectants used in hospitals; the Biocidal Products Regulation ensures that there is enough information about these products so that consumers can use them safely. ECHA is responsible for implementing the regulation; the law on Prior Informed Consent sets guidelines for the import of hazardous chemicals.
Through this mechanism, countries due to receive hazardous chemicals are informed in advance and have the possibility of rejecting their import. Substances that may have serious effects on human health and the environment are identified as Substances of Very High Concern 1; these are substances which cause cancer, mutation or are toxic to reproduction as well as substances which persist in the body or the environment and do not break down. Other substances considered. Companies manufacturing or importing articles containing these substances in a concentration above 0,1% weight of the article, have legal obligations, they are required to inform users about the presence of the substance and therefore how to use it safely. Consumers have the right to ask the retailer whether these substances are present in the products they buy. Once a substance has been identified in the EU as being of high concern, it will be added to a list; this list is available on ECHA's website and shows consumers and industry which chemicals are identified as SVHCs.
Substances placed on the Candidate List can move to another list. This means that, after a given date, companies will not be allowed to place the substance on the market or to use it, unless they have been given prior authorisation to do so by ECHA. One of the main aims of this listing process is to phase out SVHCs where possible. In its 2018 substance evaluation progress report, ECHA said chemical companies failed to provide “important safety information” in nearly three quarters of cases checked that year. "The numbers show a similar picture to previous years" the report said. The agency noted that member states need to develop risk management measures to control unsafe commercial use of chemicals in 71% of the substances checked. Executive Director Bjorn Hansen called non-compliance with REACH a "worry". Industry group CEFIC acknowledged the problem; the European Environmental Bureau called for faster enforcement to minimise chemical exposure. European Chemicals Bureau Official website
A desiccant is a hygroscopic substance that induces or sustains a state of dryness in its vicinity. Encountered pre-packaged desiccants are solids that absorb water. Desiccants for specialized purposes may be in forms other than solid, may work through other principles, such as chemical bonding of water molecules, they are encountered in foods to retain crispness. Industrially, desiccants are used to control the level of water in gas streams. Although some desiccants are chemically inert, others are reactive and require specialized handling techniques; the most common desiccant is silica, an otherwise inert, water-insoluble white solid. Tens of thousands of tons are produced annually for this purpose. Other common desiccants include activated charcoal, calcium sulfate, calcium chloride, molecular sieves. One measure of desiccant efficiency is the ratio of water storable in the desiccant relative to the mass of desiccant. Another measure is the residual relative humidity of the air or other fluid being dried.
The performance of any desiccant varies with temperature and both relative humidity and absolute humidity. To some extent, desiccant performance can be described, but most the final choice of which desiccant best suits a given situation, how much of it to use, in what form, is made based on testing and practical experience. Sometimes a humidity indicator is included in the desiccant to show, by color changes, the degree of water-saturation of the desiccant. One used indicator is cobalt chloride. Anhydrous cobalt chloride is blue; when it bonds with two water molecules, it turns purple. Further hydration results in the pink hexaaquacobalt chloride complex Cl2. One example of desiccant usage is in the manufacture of insulated windows where zeolite spheroids fill a rectangular spacer tube at the perimeter of the panes of glass; the desiccant helps to prevent the condensation of moisture between the panes. Another use of zeolites is in the dryer component of air conditioning systems to help maintain the efficacy of the refrigerant.
Desiccants are commonly used to protect goods in shipping containers against moisture damage. Hygroscopic cargo, such as cocoa and various nuts and grains, are susceptible to mold and rot when exposed to condensation and humidity; because of this, shippers take precautionary measures to protect against cargo loss. Desiccants reduce the amount of moisture present in air. Desiccants come in various forms and have found widespread use in the food, packing and many manufacturing industries. Air conditioning systems can be made based on desiccants. Desiccants are used in different kinds of livestock farming to dry newborn animals, such as piglets; the use of a good desiccant can help them dry quicker and save energy, which can be crucial for the animal's development. Another use is to reduce bacteria and pathogens that thrive in wet surfaces, reducing bacteria pressure. However, some desiccants have a high pH-level, which can be harmful for an animal's skin. Desiccants are used to remove water from solvents required by chemical reactions that do not tolerate water, e.g. the Grignard reaction.
The method though not always, involves mixing the solvent with the solid desiccant. Studies show that molecular sieves are superior as desiccants relative to chemical drying reagents such as sodium-benzophenone. Sieves offer the advantages of being recyclable. Desiccator Humidity buffering Humidity indicator card Hygroscopy Moisture sorption isotherm Solar air conditioning Oxygen scavenger Sorbent Volatile Corrosion Inhibitor Lavan, Z.. "Second Law Analysis of Desiccant Cooling Systems". Journal of Solar Energy Engineering. 104: 229–236. Doi:10.1115/1.3266307. S. Sadik. "True potato seed drying over rice". Potato Research. 25: 269. Doi:10.1007/BF02357312
In optics, the refractive index or index of refraction of a material is a dimensionless number that describes how fast light propagates through the material. It is defined as n = c v, where c is the speed of light in vacuum and v is the phase velocity of light in the medium. For example, the refractive index of water is 1.333, meaning that light travels 1.333 times as fast in vacuum as in water. The refractive index determines how much the path of light is bent, or refracted, when entering a material; this is described by Snell's law of refraction, n1 sinθ1 = n2 sinθ2, where θ1 and θ2 are the angles of incidence and refraction of a ray crossing the interface between two media with refractive indices n1 and n2. The refractive indices determine the amount of light, reflected when reaching the interface, as well as the critical angle for total internal reflection and Brewster's angle; the refractive index can be seen as the factor by which the speed and the wavelength of the radiation are reduced with respect to their vacuum values: the speed of light in a medium is v = c/n, the wavelength in that medium is λ = λ0/n, where λ0 is the wavelength of that light in vacuum.
This implies that vacuum has a refractive index of 1, that the frequency of the wave is not affected by the refractive index. As a result, the energy of the photon, therefore the perceived color of the refracted light to a human eye which depends on photon energy, is not affected by the refraction or the refractive index of the medium. While the refractive index affects wavelength, it depends on photon frequency and energy so the resulting difference in the bending angle causes white light to split into its constituent colors; this is called dispersion. It can be observed in prisms and rainbows, chromatic aberration in lenses. Light propagation in absorbing materials can be described using a complex-valued refractive index; the imaginary part handles the attenuation, while the real part accounts for refraction. The concept of refractive index applies within the full electromagnetic spectrum, from X-rays to radio waves, it can be applied to wave phenomena such as sound. In this case the speed of sound is used instead of that of light, a reference medium other than vacuum must be chosen.
The refractive index n of an optical medium is defined as the ratio of the speed of light in vacuum, c = 299792458 m/s, the phase velocity v of light in the medium, n = c v. The phase velocity is the speed at which the crests or the phase of the wave moves, which may be different from the group velocity, the speed at which the pulse of light or the envelope of the wave moves; the definition above is sometimes referred to as the absolute refractive index or the absolute index of refraction to distinguish it from definitions where the speed of light in other reference media than vacuum is used. Air at a standardized pressure and temperature has been common as a reference medium. Thomas Young was the person who first used, invented, the name "index of refraction", in 1807. At the same time he changed this value of refractive power into a single number, instead of the traditional ratio of two numbers; the ratio had the disadvantage of different appearances. Newton, who called it the "proportion of the sines of incidence and refraction", wrote it as a ratio of two numbers, like "529 to 396".
Hauksbee, who called it the "ratio of refraction", wrote it as a ratio with a fixed numerator, like "10000 to 7451.9". Hutton wrote it as a ratio with a fixed denominator, like 1.3358 to 1. Young did not use a symbol for the index of refraction, in 1807. In the next years, others started using different symbols: n, m, µ; the symbol n prevailed. For visible light most transparent media have refractive indices between 1 and 2. A few examples are given in the adjacent table; these values are measured at the yellow doublet D-line of sodium, with a wavelength of 589 nanometers, as is conventionally done. Gases at atmospheric pressure have refractive indices close to 1 because of their low density. All solids and liquids have refractive indices above 1.3, with aerogel as the clear exception. Aerogel is a low density solid that can be produced with refractive index in the range from 1.002 to 1.265. Moissanite lies at the other end of the range with a refractive index as high as 2.65. Most plastics have refractive indices in the range from 1.3 to 1.7, but some high-refractive-index polymers can have values as high as 1.76.
For infrared light refractive indices can be higher. Germanium is transparent in the wavelength region from 2 to 14 µm and has a refractive index of about 4. A type of new materials, called topological insulator, was found holding higher refractive index of up to 6 in near to mid infrared frequency range. Moreover, topological insulator material are transparent; these excellent properties make them a type of significant materials for infrared optics. According to the theory of relativity, no information can travel faster than the speed of light in vacuum, but this does not mean that the refractive index cannot be lower than 1; the refractive index measures the phase velocity of light. The phase velocity is the speed at which the crests of the wave move and can be faster than the speed of light in vacuum, thereby give a refractive index below 1; this can occur close to resonance frequencies, for absorbing media, in plasmas, for X-rays. In the X-ray regime the refractive indices are
Simplified molecular-input line-entry system
The simplified molecular-input line-entry system is a specification in the form of a line notation for describing the structure of chemical species using short ASCII strings. SMILES strings can be imported by most molecule editors for conversion back into two-dimensional drawings or three-dimensional models of the molecules; the original SMILES specification was initiated in the 1980s. It has since been extended. In 2007, an open standard called. Other linear notations include the Wiswesser line notation, ROSDAL, SYBYL Line Notation; the original SMILES specification was initiated by David Weininger at the USEPA Mid-Continent Ecology Division Laboratory in Duluth in the 1980s. Acknowledged for their parts in the early development were "Gilman Veith and Rose Russo and Albert Leo and Corwin Hansch for supporting the work, Arthur Weininger and Jeremy Scofield for assistance in programming the system." The Environmental Protection Agency funded the initial project to develop SMILES. It has since been modified and extended by others, most notably by Daylight Chemical Information Systems.
In 2007, an open standard called "OpenSMILES" was developed by the Blue Obelisk open-source chemistry community. Other'linear' notations include the Wiswesser Line Notation, ROSDAL and SLN. In July 2006, the IUPAC introduced the InChI as a standard for formula representation. SMILES is considered to have the advantage of being more human-readable than InChI; the term SMILES refers to a line notation for encoding molecular structures and specific instances should be called SMILES strings. However, the term SMILES is commonly used to refer to both a single SMILES string and a number of SMILES strings; the terms "canonical" and "isomeric" can lead to some confusion when applied to SMILES. The terms are not mutually exclusive. A number of valid SMILES strings can be written for a molecule. For example, CCO, OCC and CC all specify the structure of ethanol. Algorithms have been developed to generate the same SMILES string for a given molecule; this SMILES is unique for each structure, although dependent on the canonicalization algorithm used to generate it, is termed the canonical SMILES.
These algorithms first convert the SMILES to an internal representation of the molecular structure. Various algorithms for generating canonical SMILES have been developed and include those by Daylight Chemical Information Systems, OpenEye Scientific Software, MEDIT, Chemical Computing Group, MolSoft LLC, the Chemistry Development Kit. A common application of canonical SMILES is indexing and ensuring uniqueness of molecules in a database; the original paper that described the CANGEN algorithm claimed to generate unique SMILES strings for graphs representing molecules, but the algorithm fails for a number of simple cases and cannot be considered a correct method for representing a graph canonically. There is no systematic comparison across commercial software to test if such flaws exist in those packages. SMILES notation allows the specification of configuration at tetrahedral centers, double bond geometry; these are structural features that cannot be specified by connectivity alone and SMILES which encode this information are termed isomeric SMILES.
A notable feature of these rules is. The term isomeric SMILES is applied to SMILES in which isotopes are specified. In terms of a graph-based computational procedure, SMILES is a string obtained by printing the symbol nodes encountered in a depth-first tree traversal of a chemical graph; the chemical graph is first trimmed to remove hydrogen atoms and cycles are broken to turn it into a spanning tree. Where cycles have been broken, numeric suffix labels are included to indicate the connected nodes. Parentheses are used to indicate points of branching on the tree; the resultant SMILES form depends on the choices: of the bonds chosen to break cycles, of the starting atom used for the depth-first traversal, of the order in which branches are listed when encountered. Atoms are represented by the standard abbreviation of the chemical elements, in square brackets, such as for gold. Brackets may be omitted in the common case of atoms which: are in the "organic subset" of B, C, N, O, P, S, F, Cl, Br, or I, have no formal charge, have the number of hydrogens attached implied by the SMILES valence model, are the normal isotopes, are not chiral centers.
All other elements must be enclosed in brackets, have charges and hydrogens shown explicitly. For instance, the SMILES for water may be written as either O or. Hydrogen may be written as a separate atom; when brackets are used, the symbol H is added if the atom in brackets is bonded to one or more hydrogen, followed by the number of hydrogen atoms if greater than 1 by the sign + for a positive charge or by - for a negative charge. For example, for ammonium. If there is more than one charge, it is written as digit.