Byrd et al.

To avoid these problems, refiners commonly use additives called detergents" (Hall et al., 1976), (Bert et al., 1983). These are in reality surfactants made from molecules having hydrocarbon chains long enough to ensure their solubility in the fuel and a polar group that enables them to be absorbed on the walls and prevent deposits from sticking. The most effective chemical structures are succinimides, imides, and fatty acid amines. The required dosages are between 500 and 1000 ppm of active material.  [c.243]

The Octane Requirement Increase, ORI, is a phenomenon manifested by the appearance of knocking and is due to the increase in engine octane demand with time. This phenomenon is correlated with the increase of solid deposits in the combustion chamber. Although the causes have not been determined with certainty, some companies have patented additives which modify the deposits. The effect is to limit the increase in octane demand (Bert et al., 1983 Chevron, 1988 Nelson et al., 1989).  [c.347]

A. J. Bard et al J. Phys. Chem., 97, 7147 (1993).  [c.223]

The effect of the bundle of capillaries picture is to stress the use of the desorption branch to obtain a pore-size distribution. The basic procedure stems from those of Barrett et al. [201] and Pierce [196] see also Ref. 58 wherein the effective meniscus curvature is regarded as given by the capillary radius minus the thickness of ordinary multilayer adsorption expected at that P/P. This last can be estimated from adsorption data on similar but nonporous material, and for this de Boer s t-curve (see Table XVII-4) is widely used. The general calculation is as follows. After each stepwise decrease in (pressure on desorption), an effective capillary radius is calculated from Eq. XVII-135, and the true radius is obtained by adding the estimated multilayer thickness. The exposed pore volume and pore area can then be calculated from the volume desorbed in that step. For all steps after the first, the desorbed volume is first corrected for that from multilayer thinning on the sum of the areas of previously exposed pores. In this way a tabulation of cumulative pore volume of pores of radius greater than a given r is obtained and, from the slopes of the corresponding plot, a pore-size distribution results. Such a distribution was compared in Fig. XVI-2  [c.666]

Chapman-Enskog (Bird et al.) and Wilke-Lee The inherent assumptions of these equations are quite restrictive (i.e., low density.  [c.594]

For this case, the need for a molecular theory is cleverly avoided. The Stokes-Einstein equation is (Bird et al.)  [c.596]

T. C. Huang and W. Parrish. In Advances in X-Ray Analysis. (C. S. Barrett, et al., Eds.) Plenum, New York, 1986, Vol. 29, p. 395.  [c.348]

Y. Kataoka and T. Arai. In Advances in X-Ray Analysis. (C. S. Barrett et al., Eds.) Plenum, New York, 1990, Vol. 33, p. 220.  [c.348]

Another theory of liquid-liquid explosion comes from Board et al. (1975). They noticed that when an initial disturbance, for example, at the vapor-liquid interface, causes a shock wave, some of the liquid is atomized, thus enhancing rapid heat transfer to the droplets. This action produces further expansion and atomization. When the droplets are heated to a temperature equal to the superheat temperature limit, rapid evaporation (flashing liquid) may cause an explosion. In fact, this theory resembles the theory of Reid (1979), except that only droplets, and not bulk liquid, have to be at the superheat temperature limit of atmospheric pressure (McDevitt et al. 1987).  [c.160]

The method used here is based on a general application of the maximum-likelihood principle. A rigorous discussion is given by Bard (1974) on nonlinear-parameter estimation based on the maximum-likelihood principle. The most important feature of this method is that it attempts properly to account for all measurement errors. A discussion of the background of this method and details of its implementation are given by Anderson et al. (1978).  [c.97]

J. A. Board, Jr. et al.. Scalable variants of Multipole-Accelerated Algorithms for Molecular Dynamics Applications, Proceedings, Seventh SIAM Conference on Parallel Processing for Scientific Computing, SIAM, Philadelphia (1995), pp. 295-300.  [c.470]

Comparable efforts are needed to master the flood of information and accumulated knowledge in chemistry today. While until 1960 the number of natural and laboratory-produced compounds had almost linearly increased to roughly one million in about 150 years, its growth expanded exponentially from then on, reaching 18 million in 2000. This is just one aspect of the revolution in chemistry brought about by the rapid advancement of computer technology since 1965. Methods of physics, mathematics and information science entered chemistry to an unprecedented extent, which furnished laboratories with powerful new instrumental techniques. Also, a broad variety of model-based or quantum-mechanical computations became feasible, which were thought impossible a few decades ago. For example, the computer modeling of water transport through membranes mediated by aqua-porins yields the time dependence of the spatial position of typically 10 atoms on a picosecond scale up to 10 ns Grubmuller et al., MPl Gottingen). Such huge data arrays can be searched for and accessed via computer networks and then evaluated in a different context ( data mining"). Furthermore, new chemical techniques, such as combinatorial synthesis, have high data output. Overall it can be stated that, particularly for the chemical and pharmaceutical industries, researchers  [c.655]

The one-center two-electron integrals used in MINDO/3 are derived from an analysis of atomic spectra [see, e.g., N. C. Baird and M. J. S. Dewar, J. Chem. Phys. 50, 1262(1969)]. Following Pople et al.[J. A. Pople, D. L. Beveridge, and P. A. Dobosh, J. Chem. Phys., 47, 2026(1967)], the one-center two-electron integrals are written  [c.282]

R. I. Edwards, W. A. M. te Riele, and G. J. Bemfeld, in A. J. Bird, ed., Gmelin Handbook of Inorganic Chemist, Platinum Supplement, Springer-Vedag, New York, 1986, Sect. Al, pp. 1—23.  [c.185]

Apart from the prediction of a variable viscosity, generalized Newtonian constitutive models cannot explain other phenomena such as recoil, stress relaxation, stress overshoot and extrudate swell which are commonly observed in polymer processing flows. These effects have a significant impact on the product quality in polymer processing and they should not be ignored. Theoretically, all of these phenomena can be considered as the result of the material having a combination of the properties of elastic solids and viscous fluids. Therefore mathematical modelling of polymer processing flows should, ideally, be based on the use of viscoelastic constitutive equations. Formulation of the constitutive equations for viscoelastic fluids has been the subject of a considerable amount of research over many decades. Details of the derivation of the viscoelastic constitutive equations and their classification are covered in many textbooks and review papers (see Tanner, 1985 Bird et al, 1977 Mitsoulis, 1990). Despite these efforts and the proliferation of proposed viscoelastic constitutive equations in recent years, the problem of selecting one which can yield verifiable results for a fluid under all types of flow condition.s is still unresolved (Pearson, 1994). In practice, therefore, the remaining option is to choose a constitutive viscoela.stic model that can predict the most dominant features of the fluid behaviour for a given flow situation. It should also be mentioned here that the use of a computationally costly and complex viscoelastic model in situations that are different from those assumed in the formulation of that model will in general yield unreliable predictions and should be avoided.  [c.9]

Both the binder solution viscosity [L and the granule density are largely properties of the feed. Binder viscosity is also a function of local temperature, collisional strain rate (for non-Newtonian binders) and binder concentration. It can be controlled as discussed above through judicious selection of binding and surfactant agents and measured by standard rheological techniques. [Bird et al., Dynamics of Polymeric Liquids, vol. 1, John Wiley Sons, Inc. (1977)]. The coUi-sional velocity is a function of process design and operating variables, and is related to bed agitation intensity and mixing. Possible choices of Uq are summarized in Fig. 20-71. Note that Uq is an interparticle collisional velocity, which is not necessarily the local average granular flow velocity.  [c.1883]

Trifluoromethanesulfonic anhydride (triflic anhydride) [358-23-6] M 282.1, b 82-85°, 84°, d 1.71, n 1.322. Distil through a short Vigreux column. Could be freshly prepd from the anhydrous acid (11.5g) and P2O5 (11.5g, or half this weight) by setting aside at room temp for Ih, distilling off volatile products then through a short Vigreux column. Readily hydrolysed by HjO and decomposes appreciably after a few days to liberate SO2 and produce a viscous liquid. Store dry at low low temp. [Burdon et al. J Chem Soc 2514 1957 Beard et al. J Org Chem 38 373 1973.] Highly TOXIC vapour.  [c.377]

Triphenylarsine [603-32-7] M 306.2, m 60-62°. Recrystd from EtOH or aqueous EtOH [Dahlinger et al. J Chem Soc, Dalton Trans 2145 1986 Boert et al. J Am Chem Soc 109 7781 1987].  [c.492]

Reynolds (1839 1939) postulated first that a relationship exists between momentum and heat transfer. He did not deal with mass transfer. Bird et al (1960) set up criteria for a direct analogy between mass and heat transfer. Gupta and Thodos (1963) investigated this analogy for packed beds and concluded that the Colburn factor ratio of jh/jd = 1.076 is valid only for shallow beds. At deeper beds, jd is significantly larger and that deviation increases as rates get higher. An exhaustive review was published by Gomezplata and Regan (1970). This review and the book of Bird et al (1960) serve as general references.  [c.23]

Edison s lamps were primitive, and their life was limited because of the fragility of the carbon filaments, the expense of hand manufacture and the inadequacy of contemporary vacuum pumps. The extraordinary lengths to which Edison went to find the best organic precursor for filaments, including the competitive trying-out of beard-hairs from two men, is retailed in a racy essay by Jehl (1995). Many alternatives, notably platinum and osmium, were tried, especially after Edison s patents ran out in the mid-1890s, until in 1911 General Electric put on sale lamps made with the non-sag tungsten filaments developed by William Coolidge and they swept all before them. These filaments are still, today, made essentially by the same elaborate methods as used in 1911, using sintering of doped metal powder (see Section 9.4). An entire book was recently devoted to the different stages and aspects of manufacture of tungsten filaments (Bartha et al. 1995). Many manufacturers tried to break GE s patents and the lawyers and their advisers had a splendid time my wife s father, a metallurgist, to whose memory this book is dedicated, sent his three children to boarding school on the proceeds of his work as expert witness in one such trial over lamp patents.  [c.365]

Bertho et al. have shown that geissospermine is hydrolysed by cold, strong hydrochloric acid to two isomeric bases, CgoHagOaNj, presumably by the scission of an ether linkage between the two halves of the molecule. Base A discolours at 155°, m.p. —- 205° (dec.), [a]a — 101° (EtOH), and shows colour reactions similar to those of the parent base, which resemble those of yohimbine and it is suggested that base A, the corresponding half of geissospermine, and the minor alkaloid pereirine (p. 736) probably have the same ring system as yohimbine. Base B, isolated as the hydrochloride, m.p. 159-160°, is crystalline, m.p. 160° (dec.), gives no colour  [c.735]

Conkurchine, C21HJJN2, was first isolated by Bertho et al. The base  [c.745]

For the [021] orientation, where the resolved shear stress for <110] ordinary slip is twice that for <101] superlattice slip, <110] ordinary slip is observed in the whole temperature range. Hence the profile of the CRSS versus temperature curve for this orientation, including the strength anomaly, is solely associated with <110] ordinary slip. TTie peak in CRSS is observed at 900°C. However, the peak height is seen to be very small when compared to those for other orientations where the anomaly is associated with <101] superlattice slip. Ordinary dislocations with b = 1/2<110] tend to be parallel to their screw and 60° orientations at low temperatures, whereas they are roughly in the screw orientation and accompanied by many cusps near the peak temperature [13]. Tilting experiments have indicated that cusps are not on the primary slip plane but are bowed-out on different planes, indicating the frequent occurrence of cross-slip. Such dislocation structures seem to be in agreement with those observed by Viguier et al. [11] and Bird et al. [10].  [c.316]

The fifth and final chapter, on Parallel Force Field Evaluation, takes account of the fact that the bulk of CPU time spent in MD simulations is required for evaluation of the force field. In the first paper, BOARD and his coworkers present a comparison of the performance of various parallel implementations of Ewald and multipole summations together with recommendations for their application. The second paper, by Phillips et AL., addresses the special problems associated with the design of parallel MD programs. Conflicting issues that shape the design of such codes are identified and the use of features such as multiple threads and message-driven execution is described. The final paper, by Okunbor Murty, compares three force decomposition techniques (the checkerboard partitioning method.  [c.499]

Mathematically speaking, two chicken halves give one chicken. This is true with respect to mass. Such a chicken, however, is not a living one. Moreover, the two halves must be mirror images to form the shape of a chicken. Obviously, numbers are only half of the story, information comes in disparate guises. Chemistry, the science of materials and theii transformations, exhibits a broad diversity of information, which by now encompasses an enormous body of knowledge about chemical structures, properties, and reactions. However, despite all the achievements during the last two centuries, which changed early chemical craftsmanship into a sophisticated natural science, chemistry is still devoid of the all-round theory, having, for examples the potential to predict precise structure-activity or structure-function relationships. It would explain, for instance, why palytoxin C129H223N3O54, being isolated from a Hawaiian coral in 1979, is one of the most poisonous natural substances. With its 64 chiral carbon atoms and six olefinic bonds, offering more than 10 possible isomers, the total synthesis of palytoxin carboxylic acid may be compared with the first climbing of Mount Everest Kishi, et al. at Harvard University, 1989).  [c.655]

Jhh spin-coupling results in first-order coupling figures that are easy to interpret. Only the long-range couplings of protons a- to nitrogen are uncertain because of their broad signals. Besides the already mentioned systematic studies concerning signal assignments, where the coupling constants are usually given, three studies are particularly devoted to the determination of homonuclear couplings Bojesen et al. (113), Jacobsen, et al. (252), and Bildsoe and Schaumburg (251). There is a Jhh coupling of approximately 3.2 Hz between H(4) and H(5), a Jhh coupling of approximately 2 Hz between H(2) and H(5), and a very low Jhh coupling of 0.4 to 0.5 Hz between H(2) and H(4). This last coupling does not usually appear because of the signal broadening due to the nitrogen atom, but could be revealed by certain solvents (235) or by nitrogen decoupling (255). Some attempts to calculate these couplings based on results of theoretical approaches have been performed using the method of finite perturbations or that of state summation (256). The results have not been very convincing (251, 252). Only in the case of Jhh in fluorinated derivatives of thiazole (253) was it possible to obtain, by CNDO calculations, Jfh coupling constants in reasonable agreement with the experimental values (251).  [c.76]

Experimental confirmation of the metal-nitrogen coordination of thiazole complexes was recently given by Pannell et al. (472), who studied the Cr(0), Mo(0), and W(0) pentacarbonyl complexes of thiazole (Th)M(CO)5. The infrared spectra are quite similar to those of the pyridine analogs the H-NMR resonance associated with 2- and 4-protons are sharper and possess fine structure, in contrast to the broad, featureless resonances of free thiazole ligands. This is expected since removal of electron density from nitrogen upon coordination reduces the N quad-rupole coupling constant that is responsible for the line broadening of the a protons.  [c.129]

Axial dispersion occurs in both the liquid and the gas phases. The degree of axial dispersion is affected by vessel diameter, vessel internals, gas superficial velocity, and surface-active agents that retard coalescence. For systems with coalescence-retarding surfactants the initial bubble size produced by the gas sparger is also significant. The gas and hquid physical properties nave only a slight effect on the degree of axial dispersion, except that liquid viscosity oecomes important as the flow regime becomes laminar. With pure liquids, in the absence of coalescence-inhibiting, surface-active agents, the nature of the sparger has little effect on the axial dispersion, and experimental results are reasonably well correlated by the dispersion model. For the liquid phase the correlation recommended by Deckwer et al. (op. cit.), alter the original work by Baird and Rice [Chem. Eng. J., 9, 171(1975)] is as follows  [c.1426]

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