ABBA models

As for detergent range alcohols, extensive use of capillary gas chromatography is also made for composition and purity determination of the plasticizer range materials. For those products that are a broad mixture of various isomers, however, distillation range and Hydroxyl Value are more useful characterizations. From the HV the combining weight can be calculated for subsequent chemical reactions. Carbonyl content is important, especially for those alcohols manufactured from aldehydes by the oxo process. It is often expressed similarly to HV as the mg of KOH equivalent to the carbonyl oxygen in 1 g of sample. Acidity, expressed in terms of the equivalent weight percent of acetic acid, is used to determine the quaUty of the alcohol, as are moisture and APHA color. As with the detergent range alcohols, tests which measure color stabiUty in the presence of sulfuric acid are employed to predict the color changes that may occur in subsequent reactions utilizing acid catalysts. Additionally, analytical determinations such as odor, chloride level, hydrocarbon content, and trace metal content, are required for specific uses.  [c.444]

Other important breakthroughs include the discovery of shock-induced electronic transitions, as reported by Royce in 1967 and by Al tshuler and Bakanova in 1969 the introduction in 1970, by Barker and Hollenbach, of the fused quartz buffer to generate ramp waves the shock-induced anisotropy in ferromagnetic materials by Grady, Duvall, and Royce in 1972 the measurement of physical properties under shock loading by Graham in 1972 and 1977 the observation of shock-induced insulator-to-metal transitions in iodine in 1977 by McMahan, Hard, and Ross the acquisition of numerous thermodynamic data for shock-compressed solids in 1977 by Van Thiel, Shaner, and Salina the introduction of superposed shear waves by Abou-Sayed and Clifton and Gupta in 1976 and the publication of a comprehensive review on shock compression solids by Davison and Graham in 1979.  [c.400]

The crystal structure of CgK is shown in Fig. 8.15(a) the graphite layers remain intact but are stacked vertically above each other instead of in the sequence ABAB found in a-graphite itself. Each graphite layer is interleaved by a layer of K atoms having a commensurate lattice in which the spacing between each K is twice the spacing between the centres of the graphite hexagons (Fig. 8.15(b)). The stoichiometries of the other stages can then be achieved by varying the frequency of occurrence of the intercalated M layers in the host lattice. An idealized representation of this model is shown in Fig. 8.16. Difficulties are encountered in devising a plausible mechanistic route to the formation of these compounds since the direct preparation of one stage from an adjacent stage apparently requires both the complete emptying and the complete filling of inserted layers. It may be that the situation is more complex, with distributions of stages rather than a single uniform arrangement for each stoichiometry. Very recently a new metal-rich phase has been prepared by reacting graphite with molten potassium the composition is very close to C4K and the structure comprises double planes of K atoms intercalated between each graphite sheet, with a consequent increase in the interplanar spacing to 850 pm.  [c.293]

Abbau-mittel, n. decomposing or disintegrating agent, -produkt, n. decomposition product, degradation product, -stufe, /. step or stage in decomposition or degradation.  [c.1]

Quantitative measurements of flocculation rates have provided estimates of Hamaker constants in qualitative agreement with theory. One assumes diffusion-limited flocculation where the probability to aggregate decreases with the exponential of the potential energy barrier height of the type illustrated in Fig. Vl-5. The barrier height is estimated from the measured flocculation rate other measurements (see Section V-6) give the surface (or zeta) potential leaving the Hamaker constant to be determined from Equations like VI-36 [47 9]. Complications arise from the assumption of constant surface potential during aggregation, double-layer relaxation during aggregation [50-52], and nonuniform charge distribution on the particles [53-55], In studies of the stability of ZnS sols in NaCl and CaC Duran and co-workers [56] found they had to add the Lewis acid-base interactions developed by van Oss [57] to the DLVO potential to model their measurements. Alternatively, the initial flocculation rate may be measured at an ionic strength such that no barrier exists. By this means Apwp was found to be about 0.7 x 10 erg for aqueous suspensions of polystyrene latex [58]. The hydrodynamic resistance between particles in a viscous fluid must generally be recognized to obtain the correct flocculation rates [3].  [c.242]

We restrict ourselves again to symmetric tetraatomic molecules (ABBA) with linear eqnilibrium geometi7. After integrating over electronic spatial and spin coordinates we obtain for A elecbonic states in the lowest order (quartic) approximation the effective model Hamiltonian H — Hq+ H, which zeroth-order part is given by Eq. (A.4) and the perturbative part of it of the form  [c.539]

Having built a hidden Markov model for a particular family of proteins, it can then b< used to search a database. A score is computed for each sequence in the database anc those sequences that score significantly more than other sequences of a similar length ar( identified. This was demonstrated for two key families of proteins, globins and kinases ii the original paper [Krogh et al. 1994]. For the kinases, 296 sequences with a Z score abov<  [c.553]

Once you make a set of approximations and introduce a set of parameters, you have an aphoh method (a model of chemistry) for exploring arbitrary molecular systems. The input to these calculations is relatively straightforward it consists of describing the number of nuclei, atomic number and position or configuration of the nuclei, and indicating how many electrons are to be added to the system of nuclei. This last input essentially describes the total charge of the system. For example, in a singly charged anion, there is one more electron than there is total nuclear charge thus the charge on the system is -1. The charge of the system is a principal input quantity.  [c.218]

The common structural element in the crystal lattice of fluoroaluminates is the hexafluoroaluminate octahedron, AIF. The differing stmctural features of the fluoroaluminates confer distinct physical properties to the species as compared to aluminum trifluoride. For example, in A1F. all corners are shared and the crystal becomes a giant molecule of very high melting point (13). In KAIF, all four equatorial atoms of each octahedron are shared and a layer lattice results. When the ratio of fluorine to aluminum is 6, as in cryoHte, Na AlF, the AIFp ions are separate and bound in position by the balancing metal ions. Fluorine atoms may be shared between octahedrons. When opposite corners of each octahedron are shared with a corner of each neighboring octahedron, an infinite chain is formed as, for example, in TI AIF [33897-68-6]. More complex relations exist in chioUte, wherein one-third of the hexafluoroaluminate octahedra share four corners each and two-thirds share only two corners (14).  [c.142]

In its general sense, multiphase flow is not currently solvable by computational fluid dynamics. However, in certain cases reasonable solutions are possible. These include well-separated flows where the phases are confined to relatively well-defined regions separated by one or a few interfaces and flows in which a second phase appears as discrete particles of known size and shape whose motion may be approximately computed with drag coefficient formulations, or rigorously computed with refined meshes applying boundary conditions at the particle surface. Two-fluid modeling, in which the phases are treated as overlapping continua, with each phase occupying a volume fraction that is a continuous function of position (and time) is a useful approximation which is becoming available in commercial software. See Elghobashi and Abou-Arab (I. Physics Fluids, 26, 931-938 [1983]) for a /c— model for two-fluid systems.  [c.673]

An RTD, however, does not represent the mixing behavior in a vessel uniquely, because several arrangements of the internals of a vessel may give the same tracer response, for example, any series arrangements of reactor elements sucm as plug flow or complete mixing. This is a consequence of the fac t that tracer behavior is represented by linear differential equations. The lack of uniqueness hmits direct apph-cation of tracer studies to first-order reac tions with constant specific rates. For other reactions, the tracer curve may determine the upper and lower hmits of reactor performance. When this range is not too broad, the result can be useful. Tracer data also may be taken at several representative positions in the vessel in order to develop a reahs-tic model of the reactor.  [c.2081]

Further improvement in the seleetion of the best linear reetifieation model ean be performed by eomparing the uneertainty in model fit as determined from the standard error of the data (Nelson, 1982). Also, the use of confidence limits in determining the uneertainty in the estimates from linear regression is useful for assessing the nature of the data, partieularly when small samples are taken and/or when outlying data points eontrol the gradient of the regression line. Confidenee limits are generally wider than some inexperieneed data analysts expeet, so they help avoid thinking that estimates are eloser to the true value than they really are. A diseussion of their applieation in data analysis ean be found in Ayyub and MeCuen (1997), Comer and Kjerengtroen (1996), Nelson (1982), and Riee (1997).  [c.145]

At 318 K the methyl signals coalesce. The half-width Avof the coalescence signal is approximately equal to the frequency separation of the methyl signals at 308 K its value is ASff = 3.14 - 2.86 = 0.28, which at 250 MHz corresponds to Av = 70 Hz. The following exchange or rotation frequency of the A,A-dlmethylamino group is calculated at the coalescence temperature  [c.189]

Persons, D. D., Hess, G. D., Muller, W. J., and 5>cheret, P. W. (1987). Airway deposition of hygroscopic heterodispersed aerosols results of a computer model. ]. Appi. Physiol. 63, 1195-1204.  [c.232]

In a study to assess the importance of the 3j -acetoxy group and epoxide stereochemistry in determining the course of boron trifluoride catalyzed rearrangement of 5,6-epoxy-6-methyl steroids, Kirk and co-workers examined reactions of boron trifluoride etherate with epimeric 5,6-epoxy-6-methyl-cholestanes with and without a C3-substituent. Reaction of boron trifluoride etherate with the 6l5-methyl-5a,6a-epoxide (110b) gives the 6l5-methyl-A-homo--B-nor-5-one (111b). Brief reaction (2 min) of 3j -acetoxy-5/5,6j -epoxide (112a) with boron trifluoride etherate in benzene gives the fluoro-hydrin (113) in 60% yield, but longer reaction times rapidly deerease the yield of fluorohydrin (113) and give 3j -hydroxy-6-methyl-10(5 -> 6)abeo-  [c.391]

Boron trifluoride catalyzed rearrangement of 5a,6a-epoxy-6j5-methyl steroids to give 10(56)fl6eo-6jS-methyl-5-ones (6)5-methyl-A-homo-B-nor-4a-ones) can be carried out under sufficiently mild conditions so that a variety of unprotected functional groups such as double bonds, ketones, esters, ethers, halogens, ketals and the like may be present. A possible disadvantage is the presence of a 6)5-methyl group in the product. If this must be avoided, room temperature pinacol rearrangement of 5a-hydroxy-6-tosylates provides a general method for preparing 10(5 6pH)abeo-5-ketones (A-homo-B-nor-4a-ones). The sole limitation is that additional functional groups must be stable under basic conditions (e.g., calcium carbonate in dimethylformamide). The latter procedure is not limited to steroids but is a general method for perhydroazulene synthesis.  [c.394]

Hydroxy-6-methyl-10 (5 6) abeo-cholestan-5-one acetate, 391 3 a-Hydroxy-16a-methyl-11,20-dioxo-5/3-pregnane-21-glyoxylic acid, 191 17 -Hydroxy-l-niethyl-A-homo-5a-androst-l-en-3-one acetate, 362 17 /3-Hy droxy-5a, 1 Oa-methy lene-A-norestran-3-one, 429 17 3-Hydroxy-17 a-methyl-10 ( 5 4) -fl( < o-estrane-3,5-dione, 314 3a-Hydroxy-16a-methyl-5/3-pregnane-11,20-dione, lyl  [c.460]

Fig. 13. Simulated diffraction space of a 10-layer monochiral MWCNT with Hamada indices (40+8/ , 5+k) with / =0,...,9. In (a), (a ) and (02) the initial stacking at ( q was ABAB. whereas in (b), (b[) and (b2) the initial stacking was random, (a) The normal incidence pattern has a centre of symmetry only. (3 )(a2) The cusps are of two different types. The arc length separating the cusps is c (b) The normal incidence pattern now exhibits 2mm symmetry. (b )(b2) The cusps are distributed at random along the generating circles of the evolutes. These sections represent the diffuse coronae referred to in the "disordered stacking model" [17]. Fig. 13. Simulated diffraction space of a 10-layer monochiral MWCNT with Hamada indices (40+8/ , 5+k) with / =0,...,9. In (a), (a ) and (02) the initial stacking at ( q was ABAB. whereas in (b), (b[) and (b2) the initial stacking was random, (a) The normal incidence pattern has a centre of symmetry only. (3 )(a2) The cusps are of two different types. The arc length separating the cusps is c (b) The normal incidence pattern now exhibits 2mm symmetry. (b )(b2) The cusps are distributed at random along the generating circles of the evolutes. These sections represent the diffuse coronae referred to in the "disordered stacking model" [17].
Decomposition in the presence of styrene at 60°C or with a tertiary amine in the presence of methyl methacrylate gives the corresponding ABA active block copolymer or ABBA active block copolymer, respectively. When both active block copolymers are used as polymeric initiators in another vinyl polymerization, an ABCBA type multiblock copolymer is obtained [34].  [c.729]

See pages that mention the term ABBA models : [c.533]    [c.104]    [c.600]    [c.192]    [c.244]    [c.2435]    [c.447]    [c.341]    [c.101]    [c.315]    [c.460]    [c.251]    [c.144]    [c.379]    [c.522]    [c.756]    [c.684]    [c.175]    [c.274]    [c.716]   
The role of degenerate states in chemistry (0) -- [ c.631 , c.632 ]