Rival

The capillary rise method is generally considered to be the most accurate means to measure 7, partly because the theory has been worked out with considerable exactitude and partly because the experimental variables can be closely controlled. This is to some extent a historical accident, and other methods now rival or surpass the capillary rise one in value. 

The first point to remark is that methods that are to be incorporated in MD, and thus require frequent updates, must be both accurate and efficient. It is likely that only semi-empirical and density functional (DFT) methods are suitable for embedding. Semi-empirical methods include MO (molecular orbital) [90] and valence-bond methods [89], both being dependent on suitable parametrizations that can be validated by high-level ab initio QM. The quality of DFT has improved recently by refinements of the exchange density functional to such an extent that its accuracy rivals that of the best ab initio calculations [91]. DFT is quite suitable for embedding into a classical environment [92]. Therefore DFT is expected to have the best potential for future incorporation in embedded QM/MD. 

By systematically applying a series of corrections to approximate solutions of the Schroedinger equation the Pople group has anived at a family of computational protocols that include an early method Gl, more recent methods, G2 and G3, and their variants by which one can anive at themiochemical energies and enthalpies of formation, Af and that rival exper imental accuracy. The important thing... 

The disadvantage of ah initio methods is that they are expensive. These methods often take enormous amounts of computer CPU time, memory, and disk space. The HF method scales as N, where N is the number of basis functions. This means that a calculation twice as big takes 16 times as long (2" ) to complete. Correlated calculations often scale much worse than this. In practice, extremely accurate solutions are only obtainable when the molecule contains a dozen electrons or less. However, results with an accuracy rivaling that of many experimental techniques can be obtained for moderate-size organic molecules. The minimally correlated methods, such as MP2 and GVB, are often used when correlation is important to the description of large molecules. 

Evil "No. we used to have an account with Rival Scientific Company but they couldn t seem to get our orders on time."... 

From the colorless state it can be switched with light of short wavelength (A = 380 nm) via an electrocycHc ring opening and cis/trans rotation of one half of the molecule into a state with violet/purple color. The reverse reaction is effected by visible light (A = 580 nm). Since the system is metastable, one of the two reaction directions is matched by a rival thermal reaction, the thermoreversion. This progresses, however, in the case of benzospiropyran, at room temperature by a factor of 10 slower than the light-induced reaction. 

One of the most vexing aspects of pilot-plant work can be feed and product handling as a pilot plant is neither designed nor operated as a closed-loop system like a commercial plant. Indeed, the problems involved in handling and storing feed and product materials can sometimes seem to rival the pilot-plant process problems in difficulty. 

Siace the mid 1950s, tall oil fatty acids (TOFA) have become available ia good quaUties and large quantities (see Carboxylic acids, fatty acids from TALL oil). Refined grades of TOFA have degrees of unsaturation rivaling that of soya acids. Siace it is a year-rouad by-product from the paper iadustry, its... 

Humectants and low vapor pressure cosolvents are added to inhibit drying of ink in the no22les. Surfactants or cosolvents that lower surface tension are added to promote absorption of ink vehicle by the paper and to prevent bleed. For improvements in durabiUty, additional materials such as film-forming polymers have been added. Ink developments are providing ink-jet prints with improved lightfastness, waterfastness, and durabiUty. As a result, such prints are beginning to rival the quaUty of electrophotographic prints. 

Allyl Complexes. Allyl complexes of thorium have been known since the 1960s and are usually stabilized by cyclopentadienyl ligands. AEyl complexes can be accessed via the interaction of a thorium haUde and an aHyl grignard. This synthetic method was utilized to obtain a rare example of a naked aHyl complex, Th(Tj -C2H )4 [144564-74-9] which decomposes at 0°C. This complex, when supported on dehydroxylated y-alumina, is an outstanding heterogeneous catalyst for arene hydrogenation and rivals the most active platinum metal catalysts in activity (17,18). 

So, Sulfolane and Carom, ca 1997, are two current rival processes. Sulfolane has a slight advantage over Carom ia energy consumption, while Carom has 6—8% less capital for the same capacity Sulfolane unit. In 1995, Exxon (37) commercialized the most recent technology for aromatics recovery when it used copolymer hoUow-fiber membrane ia concentration-driven processes, pervaporation and perstraction, for aromatic—paraffin separation. Once the non aromatic paraffins and cycloparaffins are removed, fractionation to separate the C to C aromatics is relatively simple. 

These acids (51) are organic molecules that contain a plurality of cyano groups and are readily ionized to hydrogen ions and resonance-stabilized anions. Typical cyanocarbon acids are cyanoform, methanetricarbonitrile (5) 1,1,3,3-tetracyanopropene [32019-26-4] l-propene-l,l,3,3-tetracarbonitrile (52) 1,1,2,3,3-pentacyanopropene [45078-17-9], l-propene-l,l,2,3,3-pentacarbonitrile (51) l,l,2,6,7,7-hexacyano-l,3,5-heptatriene [69239-39-0] (53) 2-dicyanomethylene-l,l,3,3-tetracyanopropane [32019-27-5] (51) and l,3-cyclopentadiene-l,2,3,4,5-pentacarbonitrile [69239-40-3] (54,55). Many of these acids rival mineral acids in strength (56) and are usually isolable only as salts with metal or ammonium ions. The remarkable strength of these acids results from resonance stabilization in the anions that is not possible in the protonated forms. 

Kermisic Acid. Many accounts claim that kermisic acid [476-35-7] (Cl Natural Red 3 Cl 75460) is the oldest dyestuff ever recorded (23). The name kermes is derived from an Armenian word meaning Httle worm for which the later Latin equivalent was vermiculus, the basis of the Knglish word Vermillion. The dye was obtained from an oriental shield louse, K. ilicis which infest the holm o5kQuercus ilex and the shmb oak. coccifera. The dye produces a brilliant scarlet color with an alum mordant. Although expensive, it was cheaper than its rival Tyrian Purple. It was in great demand until the sixteenth century when it was displaced by carminic acid. 

Regulatory Control For most batch processes, the discrete logic reqmrements overshadow the continuous control requirements. For many batch processes, the continuous control can be provided by simple loops for flow, pressure, level, and temperature. However, very sophisticated advanced control techniques are occasionally apphed. As temperature control is especially critical in reactors, the simple feedback approach is replaced by model-based strategies that rival if not exceed the sophistication of advanced control loops in continuous plants. 

STEM can provide image resolution of thin specimens rivaling TEM, but in addition can provide simultaneous crystallographic and compositional analysis at a higher spatial resolution than any other widely-used technique. Any solid material may be examined, provided that a specimen can be prepared that is less than about 100 nm in thickness. 

Staeking faults and sometimes proper polytypism are found in many inorganic compounds - to pick out just a few, zinc sulphide, zinc oxide, beryllium oxide. Interest in these faults arises from the present-day focus on electron theory of phase stability, and on eomputer simulation of lattice faults of all kinds investigators are attempting to relate staeking-fault concentration on various measurable character-isties of the compounds in question, such as ionicity , and thereby to cast light on the eleetronic strueture and phase stability of the two rival structures that give rise to the faults. 

This approach is an alternative to quantitative metallography and in the hands of a master gives even more accurate results than the rival method. A more recent development (Chen and Spaepen 1991) is the analysis of the isothermal curve when a material which may be properly amorphous or else nanocrystalline (e.g., a bismuth film vapour-deposited at low temperature) is annealed. The form of the isotherm allows one to distinguish nucleation and growth of a crystalline phase, from the growth of a preexisting nanocrystalline structure. 

The electronic theory of metallic superconduction was established by Bardeen, Cooper and Schrieffer in 1957, but the basis of superconduction in the oxides remains a battleground for rival interpretations. The technology of the oxide ( high-temperature ) superconductors is currently receiving a great deal of attention the central problem is to make windable wires or tapes from an intensely brittle material. It is in no way a negative judgment on the importance and interest of these materials that they do not receive a detailed discussion here it is simply that they do not lend themselves to a superficial account, and there is no space here for a discussion in the detail that they intrinsically deserve. 

It is perhaps not too fanciful to compare the stormy history of liquid crystals to that of colour centres in ionic crystals resolute empiricism followed by fierce strife between rival theoretical schools, until at last a systematic theoretical approach led to understanding and then to widespread practical application. In neither of these domains would it be true to say that the empirical approach sufficed to generate practical uses such uses in fact had to await the advent of good theory. 

The 32-year interval between 1879 and 1911 saw a classic instance of challenge and response, in the battle between electric and gas lighting, and between two rival... 

Batteries, both primary and secondary, have become very big business indeed, which moreover is growing rapidly. Salkind (1998) in a concise overview of the entire domain of battery types and technologies, estimates that in 1996, the world market in the two types of battery combined totalled ss 33 billion dollars, and that the ratio of secondary to primary battery sales is steadily edging upwards. In spite of its poor charge density per unit mass, the lead-acid battery still accounts for more than a quarter of the total, because it costs so much less than its rivals and lasts well. 

Several methods of quantitative description of molecular structure based on the concepts of valence bond theory have been developed. These methods employ orbitals similar to localized valence bond orbitals, but permitting modest delocalization. These orbitals allow many fewer structures to be considered and remove the need for incorporating many ionic structures, in agreement with chemical intuition. To date, these methods have not been as widely applied in organic chemistry as MO calculations. They have, however, been successfully applied to fundamental structural issues. For example, successful quantitative treatments of the structure and energy of benzene and its heterocyclic analogs have been developed. It remains to be seen whether computations based on DFT and modem valence bond theory will come to rival the widely used MO programs in analysis and interpretation of stmcture and reactivity. 

The concept of chemical periodicity is central to the study of inorganic chemistry. No other generalization rivals the periodic table of the elements in its ability to systematize and rationalize known chemical facts or to predict new ones and suggest fruitful areas for further study. Chemical periodicity and the periodic table now find their natural interpretation in the detailed electronic structure of the atom indeed, they played a major role at the turn of the century in elucidating the mysterious phenomena of radioactivity and the quantum effects which led ultimately to Bohr s theory of the hydrogen atom. Because of this central position it is perhaps not surprising that innumerable articles and books have been written on the subject since the seminal papers by Mendeleev in 1869, and some 700 forms of the periodic table (classified into 146 different types or subtypes) have been proposed. A brief historical survey of these developments is summarized in the Panel opposite. 

Boron (like silicon) invariably occurs in nature as 0X0 compounds and is never found as the element or even directly bonded to any other element than oxygen. The structural chemistry of B-O compounds is characterized by an extraordinary complexity and diversity which rivals those of the borides (p. 145) and boranes (p. 151). In addition, vast numbers of predominantly organic compounds containing B-O are known. 

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