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Working ubiquitous chemicals

The ubiquitous electron was discoveied by J. J. Thompson in 1897 some 25 y after the original work on chemical periodicity by D. I. Mendeleev and Lothar Meyer however, a further 20 y were to pass before G. N. Lewis and then I. Langmuir connected the electron with valency and chemical bonding. Refinements continued via wave mechanics and molecular Orbital theory, and the symbiotic relation between experiment and theory still continues... [Pg.21]

Chemicals are ubiquitous. They are used in virtually all occupations, and everyone will encounter chemicals of one type or another in his or her lifetime (Table 12.1). Many chemicals can be hazardous, especially if used improperly. Laboratory research in the biomedical laboratory deals with a wide variety of chemicals. Flammable and toxic chemicals are hazards most frequently encountered in the laboratory a recent survey reported that 82 percent of biologists work with toxic chemicals (241). Unlike the chemist, however, the biomedical researcher usually does not work with chemicals specifically to study chemical phenomena, such as chemical interactions or molecular structure, or to develop techniques. [Pg.140]

It is this type of work that is ubiquitous in chemical themiodynamics, principally because of changes of the volume of the system under the external pressure of the atmosphere. The negative sign of the work done on the system is, of course, because the application of excess pressure produces a decrease in volume. (The negative sign in the two-dimensional case is analogous.)... [Pg.327]

The four process control parameters are temperature, pressure, flow, and level. Modem process level detection systems are varied and ubiquitous in modem chemical plants there are thousands of processes requiring Hquid level indication and Hquid level control. From accumulators to wet wells, the need for level devices is based on the need for plant efficiency, safety, quaUty control, and data logging. Unfortunately, no single level measurement technology works rehably on all chemical plant appHcations. This fact has spawned a broad selection of level indication and control device technologies, each of which operates successfully on specific appHcations. [Pg.206]

The examples of ex situ steady-state X-ray photodiffraction utihzed to follow the photodimerizations of olefin bonds in a single-crystal-to-single-crystal (or nearly so) manner are ubiquitous in the chemical literature. The interest of sohd-state chemists in this reaction dates back to the work of Cohen and Schmidt [30, 31], and it has become much of a guinea pig in organic solid-state photochemistry. In 1993, Enkelmann and collaborators published two seminal papers in the Journal of the American Chemical Society [32] and in Angewandte Chemie [33], where they presented a series of structures of a-tra s-cinnamic acid crystals reacted to various extents. These reports laid the way for a plethora of later studies on the olefin photodimerization reaction. The convenience of the high conversion and the simple mechanism, combined with the relatively small structural perturbation that it requires, has turned this reaction into a very useful tool to probe intermolecular... [Pg.121]

The acid-base couple is the most known because of the massive and ubiquitous use of the acids and bases in work environment as well as in homelife during chemical assaults. But it is not the only cause of ocular irritations or corrosions. An oxidizer or a reducing agent can also generate lesions to tissues. [Pg.32]

Dioxins in food and the environment have been intensively studied over the past twenty years (see for example Steering Group on Chemical Aspects of Food Surveillance, 1992a). The term dioxins has come to be used for polychlorinated dibenzo-p-dioxins and in some cases also polychlorinated dibenzofurans. Both of these are ubiquitous environmental contaminants. They are highly resistant to breakdown in the environment. They are particularly difficult to study because of the large number of substances involved and the very low levels of detection needed. Nevertheless, much surveillance work has been done on polychlorinated dibenzo-p-dioxins, particularly 2,3,7,8-tetrachlorodibenzo-p-... [Pg.6]

I have such sympathy for women who have to spend their pregnancies working in factories or hair salons where chemical smells are ubiquitous. I don t know how they do it—and I know they shouldn t have to. [Pg.5]

ATP has a ubiquitous and dominant role in cellular metabolism. This role can be appreciated more fully if cognizance is extended to the energy requirements of cells, to the regulation of cellular activity and metabolism imposed by ATP, and to what interference with ATP production means to the growth of a chloro-phyllous plant. Plants store oxidative and photochemical energy in the terminal phosphate bonds of ATP. The terminal bond energy is used subsequently to perform the chemical, mechanical, and osmotic work of the cell. [Pg.76]

Numerous investigations of the pheromone communication systems of Lepidoptera have been conducted during the last two decades, probably because Lepidoptera are ubiquitous phytophagous pests and because, superficially, their pheromones and related behavior appear simple. Most of these investigations have involved the chemical identification of the pheromone or pheromone blend obtained from the females and subsequent evaluation of synthesized pheromones to determine whether or not they "work" as trap baits for males, or communication disruptants in the field. However, in the last five years there has been a growing body of evidence that lepidopteran pheromones and pheromone mediated behavior is much more complex than first believed. It is now clear that information regarding the chemical composition of the pheromone and the pheromone elicited behavior... [Pg.2]

With the obvious effects being regulated and assessments and approaches harmonised, it is natural that attention be turned even further to ubiquitous environmental contamination with chemicals. The most obvious substances with persistent, toxic and bioaccumulating properties have been addressed in the Stockholm Convention, and there is a working process to review additional substances for possible inclusion. Such additions may not come easily, as shown by the example from the Rotterdam Convention with contention around inclusion of additional live chemicals, such as... [Pg.203]

The extreme sensitivity of RNA to the ubiquitous inter- and intracellular nudeases (for example on the skin of the investigator) makes special precautions necessary for effective RNA preparations. The use of disposable containers is recommended, or glassware that has been soaked in dilute hydrochloric acid and rinsed with autoclaved distilled water. Disposable gloves must be worn in all procedures where RNA is handled, or is likely to come into contact with RNA, such as solutions, chemicals, glassware, spatulas etc. Buffers for RNA work should be prepared from reagents reserved for this purpose, and stored separately. Buffers can be treated with 0.2 % (v/v) diethylpyrocarbonate (care - this is carcinogenic) and autodaved to inactivate RNases, or at least those with adive site histidines. Since most nucleases require Mg2 for activity, the addition of EDTA in mM concentrations to solutions is also recommended. [Pg.52]

This study focuses on the effect of water on the variations of surface characteristics of the drug substance and how these surfaces manifest themselves in terms of measurable physico-chemical quantities. Water plays a central role in many pharmaceutical and food situations, not only because of its unique interactive properties and behavior, but also because its importance, ubiquitous nature, and common use in pharmaceutical and food processing. In this study, the working hypothesis is that the surface energetics of the two polymorphs can be distinguished through the study of their interactions with a common probe, water, and that such differences can, in turn, be related to differences in the corresponding powder properties. [Pg.640]

In these examples, the metastable H2 does not actually undergo electron loss because the Na or Mg Ion "retrieves the electron as the complex dissociates leaving the H2 vlbratlonally excited and the Na or Mg atom In Its ground state. Recent work on electron transmission spectroscopy studies of unsaturated hydrocarbons (24) demonstrates that electronic shape resonances may be essentially ubiquitous In chemical systems which possess low-energy vacant orbitals and the availability of electron density to enter such orbitals. [Pg.9]


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See also in sourсe #XX -- [ Pg.171 ]




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Chemical work

Ubiquitous

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