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  • 1995-1999
  • 1985-1989  (458)
  • 1810-1819
  • 1987  (458)
  • Computational Chemistry and Molecular Modeling  (406)
  • Industrial Chemistry
Material
Years
  • 1995-1999
  • 1985-1989  (458)
  • 1810-1819
Year
  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 10 (1987) 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 10 (1987), S. 33-37 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: All the present experiments confirm that there is some liquid channelling on trays. Liquid channelling is extensive on trays of large diameters. It largely depends on the tilting of the plate, modifications of the inlet weirs and on non-uniform bubble cap spacing. Consequences of liquid channelling for plate efficiency are clear; the higher the degree of liquid channelling the lower the plate efficiency. However, own experimental and theoretical investigations indicate that plate efficiency never falls below the value of point efficiency. Therefore, liquid channelling only affects the crossflow on trays. Liquid channelling reduces the mass transfer performance to a similar extent as does the backmixing of liquid. Consequently, plate efficiency is not very sensitive to liquid channelling. Since the liquid is completely mixed in the downcomer, the effects of liquid channelling are restricted to a single tray. The behaviour of tray columns completely differs from that of packed columns, where the effects of liquid channelling are cumulative over the packed height. Consequently, trays represent a suitable design for columns of large diameters.
    Additional Material: 10 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 10 (1987), S. 16-27 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Although carbon dixoide is important as an abundant carbonaceous raw material, so far, its utilization in chemical processes has been rather limited. This review covers the reactions of CO2 employed in industry, such as the production of urea, the Kolbe-Schmitt reaction, the synthesis of cyclic organic carbonates and the use of CO2 in methanol synthesis. Interesting recent developments in CO2 chemistry, such as the reactions catalyzed by transition metals, are also described. Apart from the synthesis of polymers and hydrocarbons, the production of oxygen-containing substances appears to be very profitable and attractive for future industrial applications. Not only can derivatives of formic and carbonic acids be produced but also longer-chain carboxylic acids and their derivatives by reactions of carbon dioxide with hydrocarbons such as alkynes, alkenes and 1,3-dienes.
    Additional Material: 5 Ill.
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  • 4
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The present contribution illustrates a way of developing a continuous separation process for near critical fluid extraction, on the example of separation of soya oil from lecithin. First, a suitable solvent was selected. Phase equilibria were measured in autoclaves. Operating conditions for a pilot plant were derived from the phase equilibrium data. The pilot plant experiments provided the necessary data for designing a production plant. Computer programs for phase equilibrium, stage to stage and mass and heat balance calculations were used in order to minimize the number of experiments. A production plant with a capacity of 500 t/a of raw lecithin was designed on the basis of experimental and computational results. A cost estimation, based on tenders, showed that it is more economical to produce lecithin by near critical fluid extraction than by conventional acetone extraction.
    Additional Material: 7 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 10 (1987), S. 56-63 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Ideal flow conditions are generally assumed for the reactor design. If stoichiometry, reaction mechanism and kinetics are known, the balance equations for the ideal flow tube, the ideal steady-state continuous stirred tank reactor or the ideal, completely mixed stirred batch reactor are often applied. In many cases, formal kinetics, which forms the basis of reaction modelling, is so uncertain that the idealization of the flow field can be accepted. In practice, however, deviations from the ideally calculated conversions, yields and product qualities, often occur. In these cases, it is necessary to consider the real flow conditions. In general, a distinction is made between macroand micromixing processes.
    Additional Material: 9 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 10 (1987), S. 1-15 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Using pilot-scale test plant, the interfacial area per unit volume was investigated in different gasliquid reactors, i.e. packed column, bubble column and free jet reactor. The interfacial area was studied as a function of liquid viscosity and of operating parameters. As a rule, identical test conditions were maintained in all the measurements, in order to obtain comparable results. The interfacial area was determined by chemical means using the sulphite system (a solution of sodium sulphite in water as model liquid and air as gaseous medium). The viscosity of the solution can be increased by adding carboxymethyl cellulose without significantly affecting the reaction kinetics. The addition of a surfactant to the sulphite system allowed comparative measurements at reduced surface tension. Based on a large number of measurements, the correlations of the interfacial area are expressed as power laws. The inclusion of experiments with a jet tube reactor and a stirring vessel allows an extensive comparison of all reactors. All tests were carried out with the same material system and the same method was used to determine the interfacial area per unit volume. Therefore, a comparison with respect to mass transfer is possible.
    Additional Material: 21 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 10 (1987), S. 27-32 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new measurement method for determining the local liquid-phase velocities in multiphase flows is presented. It is based on a tracer technique, using heat introduced into the flow, seemingly at random, instead of a material tracer. The input of heat pulses and measurement of temperature at an adjacent point is performed by small probes. As an intermediate result, the flow time distribution of the heat-labelled fluid elements is calculated on-line as a cross-correlation function between the pseudo-random input and the measured output signals. This calculation and the automatic control of measurements is carried out by a simple microprocessor unit. The device produced excellent results in gas-liquid flows at high gas throughputs and high liquid-phase velocities.
    Additional Material: 6 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 10 (1987), S. 63-72 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Among other processes, adsorption is used for the removal of hydrogen sulphide from natural gases. Hereby, competitive adsorption of the different gas components plays an important role, e.g., that of carbon dioxide. Data of equilibrium loading and adsorption kinetics are required for the design of adsorbers, filled with molecular sieve. In order to obtain these data under the prevailing operating conditions, hydrogen sulphide was removed from gas mixtures H2S/CH4 and H2S/CO2/CH4, in a pilot plant, by adsorption on molecular sieve 5A. The equilibrium loading, the height of transfer zone, and the length of unused bed were determined from the measured breakthrough curves of H2S. With these data, the breakthrough time and the optimum process conditions were calculated for a practical example.
    Additional Material: 14 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 10 (1987), S. 43-55 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The oxidation of carbon monoxide by air in a turbulent flow was investigated under experimental conditions where the rates of turbulent mixing and of chemical reaction are comparable. For this purpose, carbon monoxide was admixed into the completely burnt gas of a natural gas flame operated with excess of air. Measurements of mean values of axial velocity, temperature and volume fractions of carbon monoxide and oxygen were compared with computational simulations involving the k - ∊ turbulence model and several turbulent reaction models for the oxidation of carbon monoxide. The comparison of measurements and numerical calculations demonstrated that the k - ∊ turbulence model is suitable for prediction of the turbulent flow field in the flow system investigated. Furthermore, it could be shown that one-variable turbulent reaction models, such as the flamesheet or the eddy-break-up model, cannot explain the measured carbon monoxide volume fraction profiles. Two-variable turbulent reaction models with a probability density function closure of the source term of the transport equation for the mass fraction of the chemical species result in a better agreement between the measured and simulated volume fraction profiles, particularly in predicting the clear influence of the initial temperature on carbon monoxide volume fractions. Weighting of the kinetic rate expression for the oxidation of carbon monoxide with different presumed probability density functions yields slightly different predictions of the carbon monoxide volume fractions, reflecting the assumed different character of turbulent fluctuations.
    Additional Material: 7 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 10 (1987), S. 92-98 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Distillation columns with vertical partitions can separate a feed mixture into 3 or 4 pure fractions. Compared to other column arrangements, their investment costs and energy consumption are lower. Production columns show good results and are easily controlled. Conventional distillation columns produce only 2 pure product streams at the top and at the bottom of the column. Side products are contaminated by light or heavy components, depending on the location of the side stream in the rectifying or stripping section. This disadvantage is set aside by using a distillation column with a vertical partition. The internal separation wall prevents lateral mixing of liquid and vapour in the central part of the column, forming there separate feed and outlet sections. In the presence of a vertical partition, 3 or 4 pure fractions can be obtained in a single distillation step. This is particularly advantageous when heat sensitive components are to be separated. On account of good thermodynamic properties, the energy consumption is 20 to 35% lower than that of other distillation arrangements. The control behaviour is similar or better than that of conventional distillation columns.
    Additional Material: 11 Ill.
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  • 11
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 10 (1987), S. 86-92 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The Carman-Arnell equation relates the rate of flow of a fluid through a packed bed to the pressure drop across the bed. This equation is the basis for surface area determination by permeametry. It is found that the surface area measured at sub-atmospheric pressure varies with the bed porosity, so a porosity was selected where the rate of change was at a minimum. The study suggests that, at reduced pressures, the gas flow rate is a linear function of the mean pressure.
    Additional Material: 3 Ill.
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  • 12
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 10 (1987), S. 104-112 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A 0.5 MW spray-dry scrubbing FGD pilot plant was used in the study of spray dryer performance over a wide range of operating conditions. Experimental findings were compared with a spray dryer model. During operation with large excesses of lime, the SO2 absorption was limited by gas phase diffusion. At operation with a shortage of lime, the rate limiting step was the dissolution rate of lime. In addition, the flow regime in a spray dryer can be best described as well mixed. The SO2 level in the flue gas was found to exert no direct effect on the efficiency of SO2 removal. The observed effects are attributed solely to the changes in the drying process, due to the inter-dependence of slurry composition and SO2 concentration.
    Additional Material: 9 Ill.
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  • 13
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 10 (1987), S. 73-86 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: As a part of a research project on the mass transfer in liquid pulsed sieve-tray extraction columns (PSE), the diameters and hold-ups of the drops were measured: the drop size using a suction technique, with photoelectric detection, which was adapted to the special boundary conditions of the PSE; the integral hold-up by the pressure difference between the lower and upper parts of the column. Since experimental results cannot be described by known calculation formulae for the Sauter mean diameter and the hold-up, a new method of calculation was developed. It is phenomenologically based on high-speed photographs of the drop motion on a sieve tray. The mathematical-physical model allows the prediction of drop size and hold-up within certain limits, while the possible different operating regimes of the PSE, i.e. the mixer-settler and dispersion regimes can also be estimated.
    Additional Material: 12 Ill.
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  • 14
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 10 (1987), S. 125-131 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: When crude oil is vacuum distilled, about 30% of the feed remain as low value residue. Hydrocracking can upgrade this residue into valuable light hydrocarbons. The hydrocracking could be optimized catalytically, if the residue were not to contain the metals vanadium and nickel that poison the catalyst. This contribution shows that continuous extraction of the residue with ethyl acetate yields a fraction with low metal content, while an asphaltene fraction with the remaining metal content is filtered off.
    Additional Material: 14 Ill.
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  • 15
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A one-stage model of the formation of primary bubbles is presented in which the bubble volume is deduced from an equilibrium of buoyancy, viscosity, inertia and surface tension forces. In contrast to the two-stage model, presented by Kumar and Kuloor, it was not assumed that the drag coefficient in bubble expansion can be described by the same constants as in the steady-state bubble ascent. The constants were adapted in such a way that the introduction of an additional bubble volume was not necessary. It was demonstrated that this model describes the bubble formation in gravitational and centrifugal fields equally well and, furthermore, is also applicable to structurally viscous liquids, provided that the effective shear gradient \documentclass{article}\pagestyle{empty}\begin{document}$$ \mathop {\rm \gamma }\limits^. = \frac{1}{6}({\rm \Delta \rho }gzd_{\rm B} /{\rm \eta }) $$\end{document} is calculated from the equilibrium of shearing and buoyancy forces. The model is based on the assumption of a constant volumetric flow rate during bubble formation and, for this reason, a minimum Froude number is necessary in analogy to the weeping limit for sieve plates. The normalized presentation permits simple operation. The possibility of applying the model to drop formation was confirmed by comparison of experimental values with those, predicted by the model.
    Additional Material: 9 Ill.
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  • 16
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new equipment for the measurement of virial coefficients of pure substances and binary mixtures is described. It consists of an improved modification of the set-up proposed by Eucken and Meyer in 1929. The development is based on a critical review of the existing methods particularly with respect to adsorption effects. In order to reduce the influence of adsorption on the accuracy of virial coefficients, an optimum range for gas density is recommended. The accuracy of the virial coefficients is better than 20 cm3 mol-1. The set-up was employed for the measurement of virial coefficients of acetone and hexane in the range from 352.95 to 393.85 K. The results are in excellent agreement with data published in literature. Furthermore, cross-virial coefficients of the binary system acetone/hexane were measured and interpreted.
    Additional Material: 13 Ill.
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  • 17
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 10 (1987), S. 113-125 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Fouling and/or scaling of heat transfer surfaces causes serious problems in industry. Prevention of fouling is therefore essential for technical (considerable deterioration of heat transfer) and also economic reasons (increased costs). In order to provide successful countermeasures, it is, however, necessary to obtain more detailed information on the physical, chemical and biological processes which produce fouling. Based on the already known fouling mechanisms, it is shown that a satisfactory prediction of fouling behaviour of heat exchangers is not yet possible. This contribution presents a physical model for the description of fouling, caused by sedimentation and crystallization. It is assumed that, during fouling, deposition and removal processes overlap. In order to verify the theoretical considerations, experiments were carried out on a test rig, which could also be used for field experiments. Aqueous CaSO4 solutions served as experimental liquids. A comparison of experimental and calculated fouling factors shows a satisfactory agreement.
    Additional Material: 23 Ill.
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  • 18
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 10 (1987), S. 157-164 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Based on a paper by Hein, a dimensioning program for tube-bundle heat exchangers with straight tubes and fixed tube sheets has been developed. The equipment to be dimensioned is tested at 14 critical points, with regard to permissible stresses. The optimum thickness of the tube sheet, the shell and channel are subsequently selected on the basis of economic criteria. Compared to dimensioning according to AD-data sheet, it is possible to save between 10 and 25% of production costs. With the aid of a finite-element (FE) program, complex structures such as heat exchangers can be calculated accurately. Several mesh-generation programs were written for the data input. The structure of a tube-bundle heat exchanger with straight tubes is generated with 3/D elements with only some geometrical data. An FE-calculation of a heat exchanger is explained with the aid of an example and stress analysis is presented.
    Additional Material: 19 Ill.
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  • 19
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The present contribution reports on a new method for the simulation of the dispersed phase behaviour in liquid-liquid extraction columns. The fluid dynamic description is based on a mathematical model which explicitly takes into account drop transport, break-up and coalescence mechanisms, via a drop population balance along the column. Application of the model requires some simple measurements on single drops in order to determine transport and break-up laws, which are required by the model, and possibly also coalescence parameters. In this study the model is applied to pulsed sieve plate columns. The specific example considered here is based on systematic studies on the determination of break-up rates from the corresponding probabilities of break-up and the generated daughter drop size distributions by means of high-speed photography. The validity of the model was subsequently tested by comparison with some experimental results from studies on two different pulsed columns 80 and 225 mm in diameter for the water/toluene system without mass transfer. The satisfactory agreement between the results justifies the use of such a method for the description of the behaviour of liquid-liquid extraction columns in a wide range of operating conditions. Furthermore, application of the model may help to dispense with long and expensive pilot tests.
    Additional Material: 12 Ill.
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  • 20
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Microbial desulphurization of coal by pyrite oxidizing enrichment cultures containing predominantly Thiobacillus ferrooxidans was performed in an air-agitated slurry reactor, 20 l in volume. A model of microbiological and chemical reactions, occurring at various points within the coal, was set up taking into account the pore structure of the coal. The influence of parameters relevant to industrial processes, such as superficial gas velocity, particle size, initial pyrite concentration, and slurry density of the coal, on the conversion of pyrite was examined. Variation of the superficial gas velocity in the range of 0.01 to 0.04 m/s confirmed that the reaction is not controlled by oxygen transfer from gaseous to liquid phase. The rate of pyrite oxidation depends mainly on the accessibility of pyrite to micro-organisms which is determined by the particle size of the coal as well as the distribution of pyrite crystals in the coal matrix. The accessibility of pyrite to the micro-organisms is described by the ratio of effective to maximum microbial activity, measured as oxygen consumption. Starting with higher initial concentration of pyrite in the coal increases the oxidation rate, according to first order kinetics. Enhanced slurry densities lead to a decrease of pyrite conversion, in spite of higher pyrite concentration. The maximum pyrite oxidation rate was measured at 15% (v/v) slurry density and 25°C as 1800 mg Spyr/kg coal per day, or 360 mg Spyr/l reactor volume per day.
    Additional Material: 13 Ill.
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  • 21
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 10 (1987), S. 131-142 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The influence of electrolytes, which are dissolved in the aqueous absorbent and do not react with nitrogen oxides, on the absorption kinetics of both these components was investigated experimentally. In addition to demineralized water, various salt solutions of different concentrations as well as sodium hydroxide solution were used as absorbents. The term H \documentclass{article}\pagestyle{empty}\begin{document}$ H\sqrt {k_1 D} $\end{document} for N2O4 and N2O3, which is important for the design of industrial absorbers, was determined as a function of composition and concentration of the absorbents. In the case of N2O4, the chosen measuring and evaluation methods permitted a separate determination of the rate constant k of the pseudo first order reaction and of the solubility H. The diffusion coefficient D of the gas in the absorbent can be obtained only by calculation. Experimental results showed that \documentclass{article}\pagestyle{empty}\begin{document}$(H\sqrt {k_1 D} )\,_{{\rm N}_{\rm 2} {\rm O}_{\rm 4} } $\end{document} decreases with increasing ionic strength I, however, without a clear indication of any ion-specific effects. This decrease does not appear to be caused simply by a reduction in solubility (salting out effect), or in diffusion coefficient, but at least, to the same extent, through a decrease of the rate constant k with increasing electrolyte content in the absorbent. The measurements permitted the determination of the gas-based salting out parameter for N2O4. The investigations on the absorption of N2O3 in water and in an Na2SO4 solution showed no experimentally detectable influence of dissolved salts on \documentclass{article}\pagestyle{empty}\begin{document}$(H\sqrt {k_1 D} )\,_{{\rm N}_{\rm 2} {\rm O}_{\rm 3} } $\end{document}. The numerical value of \documentclass{article}\pagestyle{empty}\begin{document}$(H\sqrt {k_1 D} )\,_{{\rm N}_{\rm 2} {\rm O}_{\rm 3} } $\end{document} is six times that of \documentclass{article}\pagestyle{empty}\begin{document}$(H\sqrt {k_1 D} )\,_{{\rm N}_{\rm 2} {\rm O}_{\rm 4} } $\end{document}.
    Additional Material: 12 Ill.
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  • 22
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Slurry bubble columns are widely used in biotechnology. Therefore, the effects of solid particles on fluidization characteristics, gas hold-up and volumetric liquid-side mass transfer coefficient were measured in a slurry bubble column (i.d. 0.14 m). The density and diameter of the suspended particles were similar to those applied in biotechnology with immobilized bacteria. Based on models of turbulence and of liquid circulation induced by rising gas bubbles, equations for critical gas velocity, gas hold-up and volumetric liquid-side mass transfer coefficient were obtained by dimensional analysis.
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  • 23
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The detailed dynamic simulation of coupled process units in chemical plants is gaining an increasing importance as a useful tool in plant engineering and operation. The outline of the program package DIVA (Dynamische Simulation verfahrenstechnischer Anlagen) which is currently under development is presented in the following. The dynamic plant equations and the corresponding Jacobian matrix are generated automatically. The full exploitation of sparse matrix techniques in combination with stiff ODE (ordinary differential equation) solvers allows an efficient solution of all the equations simultaneously. The possibilities offered by the simulator are demonstrated by the simulation of two laboratory plants.
    Additional Material: 9 Ill.
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  • 24
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 10 (1987), S. 190-203 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Spatially resolved oxygen concentration measurements were performed in premixed hydrocarbon flames by using laser induced spontaneous Raman scattering. The measurements demonstrate the performance of a relatively simple pulsed laser Raman probe for fundamental combustion studies and also for the control of the equivalence ratio in flames (best spatial resolution: 0.2 mm3; theoretical detection limit: 0.8% of O2). Comparison of the results with those obtained by a mechanical suction probe (Magnos 2 T) confirmed a good agreement. At present, control of different stoichiometric conditions is possible at a minimum O2 concentration of 1.3%.
    Additional Material: 25 Ill.
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  • 25
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: During the sudden unheated vessel top venting of initially saturated two-component gas/liquid mixtures, in which the gas is also extensively dissolved in the non-evaporating liquid phase, a solubility inequilibrium develops between the phases; re-equilibration can set in only after a so-called desorption delay time. Laboratory measurements of this delay time were under-taken with model mixtures of CO2 and water and viscous aqueous (Newtonian) solutions by high speed cinematography. The parameters of the experiments are relief cross-section, initial liquid level, pressure, temperature, and concentration. The shortest deley time obtained lasts approximately 75 ms. It differs substantially from the minimum boiling delay time previously measured with various refrigerants in the same test facility. The experimental results are correlated by a semi-empirical dimensionless power relationship, which includes all independent primary design variables generally availble in a physically consistent interrelationship. Reasonable extrapolations to other test conditions and aqueous two-component systems with an acceptable accuracy systems can therefore be expected.
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  • 26
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Correlations for pressure drop and upper capacity limit (flooding) are useful for the design of packed columns. Available correlations are based on the results of measurements made at atmospheric pressure. Extrapolation to higher pressures is not recommended. Therefore, systematic experimental investigations were carried out in a pilot plant at pressures of up to 100 bar. The experimental equipment and techniques, evaluation methods, and some characteristic experimental results are presented.
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  • 27
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    Chemical Engineering & Technology - CET 10 (1987), S. 224-230 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper describes a pilot plant for entrainment measurements on various types of column trays. The data obtained from different trays differ by up to a factor of 10. The measurements were compared with the theoretical model of Stichlmair. The Stichlmair entrainment diagram permits a fairly accurate prediction for most types of trays if the height of the two-phase layer is known. Prediction of the height and relative liquid hold-up in this two-phase system should be modified by a term reflecting the vapour flow profile, which requires further testing. These tests should examine the effect of tray spacing, fractional free area and, in particular, the influence of different media.
    Additional Material: 9 Ill.
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  • 28
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    Chemical Engineering & Technology - CET 10 (1987), S. 204-215 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In three-phase systems, where the liquid constitutes the continuous phase, solid is the catalyst and gas represents the dispersed phase, there are decisive criteria which have to be observed in reactor design. These are e.g. the interfacial area per unit volume between gas and liquid, the volumetric mass transfer coefficient and the mass transfer coefficient. The basic aim of the present work was therefore the investigation of these parameters in relation to the main influencing parameters. Process parameters stirrer speed and superficial gas velocity were varied as well as the physical properties such as liquid viscosity, solids concentration, particle diameter and a geometrical parameter, i.e. reactor diameter. The sulphite method was employed for the determination of these values. The test results confirmed the known relationships of power consumption and superficial gas velocity. An increase in the liquid viscosity leads to a decrease in all the tested values. In most cases, suspended solid particles lead to a lowering of the test values. The influence of the tank diameter on the plots of the test values against specific power consumption turned out to be invariant so that a scale-up of geometrically similar systems can be carried out at constant power consumption, superficial gas velocity and liquid viscosity.
    Additional Material: 27 Ill.
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  • 29
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    Chemical Engineering & Technology - CET 10 (1987), S. 242-248 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Pool boiling data of multicomponent mixtures show that the heat transfer coefficients can be considerably lower than those of a corresponding pure fluid with the same physical properties as the mixture. The proposed model, which assumes maximum mass transfer resistance in the liquid boundary layer, is confirmed by the comparison between calculated and experimental data. The model allows the prediction of heat transfer coefficients in pool boiling of mixtures using only single component properties and vapour-liquid equilibrium data. Judging by experience with a number of different systems, the method should be sufficiently accurate for most practical applications.
    Additional Material: 10 Ill.
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  • 30
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    Chemical Engineering & Technology - CET 10 (1987), S. 248-255 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The development of heat resistant permeation membranes has opened up new possibilities for the conversion of fossil energy resources. In steam reforming of natural gas, such membranes even permit a direct production of hydrogen at high temperatures during the conversion of feed hydrocarbons. Further gas processing, such as required for reformer gas in existing hydrogen production processes, is not necessary. Due to continuous hydrogen discharge directly in the reformer tube, the chemical equilibrium of the occurring reactions becomes displaced towards the products, resulting in more favourable process conditions and, consequently, in improved by 36% utilization of the feed hydrocarbons. At the same time, the hydrogen yield increases by 44%. The heat required, which is provided by a high temperature reactor, is 17% in excess of that in conventional plants. It can be expected that the simplified process design will produce substantial cost advantages over the existing processes for the production of hydrogen.
    Additional Material: 14 Ill.
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  • 31
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In the present paper, models are developed for the description of coalescence and splitting of bubbles in gas fluidized beds. The distinction between slow and fast bubbles, which originates from the Davidson model of gas flow in and around a rising bubble, was found to be decisive for the modelling of coalescence processes. On the basis of the respective models, it is shown that a change in bed temperature does influence the mechanisms of both bubble coalescence and splitting. In cases of both slow and fast bubbles undergoing splitting, the theory predicts a decrease of bubble size with temperature whereas in the case of a non-splitting system with fast bubbles, typically encountered with Geldart type B particles, no significant temperature effect on bubble size is expected. The theoretical predictions are shown to be in agreement with own measurements as well as with the results of other workers.
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  • 32
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    Chemical Engineering & Technology - CET 10 (1987), S. 262-271 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Pressure pulsations in hydraulic systems, generated by reciprocating pumps, can cause serious problems with regard to plant safety and reliability. In particular, fatigue problems arise in high-pressure piping systems. The available knowledge is not sufficient for an accurate computation of pressure peaks in the piping of reciprocating pumps. A number of calculation models are available which, however, neglect both fluid compressibility and friction. This contribution presents a calculation method which allows a precise modelling of various pump installations. Comparison of calculated and experimental data shows a good agreement and provides a validation of the computational model.
    Additional Material: 18 Ill.
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  • 33
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    Chemical Engineering & Technology - CET 10 (1987), S. 256-261 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In the separation of gaseous mixtures by gas permeation, it is in some cases impossible to achieve the desired product quality in a single stage and, therefore, several stages may be necessary. Multistage processes can be implemented by membrane modules arranged in the form of a cascade or by a membrane column design. On the basis of an economic analysis, this paper discusses different possible module arrangements for 2 cases, i.e. the enrichment of oxygen from air and the separation of methane from biogas. Present calculations indicate that, in the first case, two-stage cascades with or without recycle and, in the second case, one-stage cascade without recycle constitute the optimum module arrangements. However, depending on the selling price of the methane enriched gas, one- or two-stage cascades with recycle have to be considered. Finally, It was shown that, in the permeation of non-ideal gases, the Joule-Thomson effect has to be taken into account.
    Additional Material: 10 Ill.
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  • 34
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    Chemical Engineering & Technology - CET 10 (1987), S. 281-289 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Fundamental investigations of coalescence processes in settlers with plate packages for the separation of liquid-liquid dispersions prompted an analysis of the drop motion on the interface of a stratified two-phase flow. Therefore, a physical model was developed, which permits the calculation of drop velocity along the interface of an inclined trickling film. Starting from a balance of forces around a single particle, the model provides the equation of motion for a steady motion of single particles in a stratified two-phase flow. Several assumptions and considerations were necessary to solve this equation, such as taking into account the influence of the wall and of flow resistance. The model calculation assumes Newtonian liquids and laminar, smooth trickling films. A comparison with experimental results confirms that the drop motion behaviour is well reproduced.
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  • 35
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    Chemical Engineering & Technology - CET 10 (1987), S. 291-296 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The kinetics of extraction processes with chemical reaction was studied experimentally on the system copper/Acorga PT 5050 and quantified according to meaningful kinetic models. These were coupled with other models describing the behaviour of dispersions in columns in order to permit a computer aided simultation of reactive extraction. Thus, a better prediction of column performance is achieved.
    Additional Material: 8 Ill.
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  • 36
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    Chemical Engineering & Technology - CET 10 (1987), S. 312-322 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Existing heat exchanger design criteria do not satisfy the continually increasing requirements for greater efficiency or mass flux and energy throughput. Occasionally, failures appear even after only a few hours of operation, as shown in section 3. A long series of experiments, often carried out on original scale, did lead to the derivation of a large number of empirical expressions; however, physical explanations of the complex tube-failure interactions could not as yet be found. In contrast, experiments with a well defined simple model, whereby the tube deflections were recorded digitally and, at the same time, tube-fluid interactions were registered on a high-speed film, show that elementary “fluid transport mechanisms” control the stability behaviour of the heat exchanger tubes. Vibration excitation mechanisms such as “galloping”, “jet switching” and “whirling” (fluid elastic coupling) proved, with their characteristics, as typical for the vibration behaviour of single rows within the tube array, but not for the vibration phenomena of tube bundles.
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  • 37
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    Chemical Engineering & Technology - CET 10 (1987), S. 297-305 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Against the background of long-term availability of natural gas, its present technology and future prospects are described. Particular emphasis is put on the oxidative coupling of methane to C2+ hydrocarbons: (1) Catalyst development, activity, selectivity and deactivation as well as reactor operation are discussed; (2) a tentative process scheme is put forward and its economics evaluated with respect to ethylene production.
    Additional Material: 8 Ill.
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  • 38
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    Chemical Engineering & Technology - CET 10 (1987), S. 323-329 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The conversion of a number of alcohols, ethers, ketones, aldehydes, carboxylic acids, esters, and cyclic compounds and their mixtures on H-ZSM-5 at 673 K was investigated. These compounds can be easily converted to aromatic hydrocarbons if the C/H ratio of the molecule fragment, remaining after elimination of oxygen as water, is less than 0.62. At higher C/H ratios, coking of the catalyst increases, thus reducing its lifetime, a difficulty which can be overcome by hydrogenation of these compounds prior to their conversion over H-ZSM-5. A procedure is proposed for converting at least a part of organic waste chemicals to valuable products instead of burning them.
    Additional Material: 8 Ill.
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  • 39
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An experimental study of the flow of phosphate mine tailings was carried out in order to characterize these suspensions of fine particles for pipeline transport. Rheological measurements with a rotating cylinder viscometer indicate a viscoplastic behaviour which can be represented by a Herschell-Bulkley or by a Casson model. The variation of the parameters of these models with solids concentration reveals a change in the behaviour at a concentration of 10 to 15%. The pressure drops were measured during flow in capillary tubes, in both laminar and turbulent regimes. The variation of the pressure drop coefficient (Fanning friction factor) as a function of the generalized Reynolds number confirms the validity of the employed rheological models. The results are in good agreement with measurements made in pipes of industrial size. The velocity profiles measured with a novel ultrasonic velocimeter demonstrate the influence of the rheological behaviour on the yield and wall stresses.
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  • 40
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    Chemical Engineering & Technology - CET 10 (1987), S. 330-337 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The aim of this investigation is to show the demarcation of two possible mechanisms for surface deposition of fine particles on the rear surface of single spheres. By means of single particle trajectory computation, based on numerically determined flow fields (Remax = 103), it is shown that the mere existence of a wake is not in itself sufficient to produce eddy deposition. In addition, the particle's motion must undergo a lateral transfer promoted by fluid trubulence, in order to effect eddy deposition commencing at a Reynolds number of about 100. On the other hand, rear deposition, influenced by electrostatic forces, especially by the Coulomb force, is possible at any Reynolds number. Consequently, for Reynolds numbers of less than 100, only electrostatic effects can produce rear surface deposition. In the range of high Reynolds numbers, the coexistence of both mechanisms is possible. Very high Reynolds numbers (Re 〉 103) and low Stokes numbers indicated the predominance of the electrostatic effect over eddy deposition, whereas at very high Reynolds numbers and medium to high Stokes numbers the electrostatic effect is only predominant in presence of high electrostatic charges.
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  • 41
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    Chemical Engineering & Technology - CET 10 (1987), S. 349-352 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A simplified reactor model can be used for predicting the performance of an industrial VGO-treater. Laboratory-scale experiments performed on the same feed and catalyst as those in the industrial unit lead to a reactor simulation which agrees well with the data from this unit. In the laboratory experiments, it is possible to overcome the specific hydrodynamic problems of tricklebed reactors by appllying the catalyst dilution technique. Results obtained by this technique allowed the development of a reactor model which enables the user to simulate the adiabatic behaviour of the industrial reactor. In this way, the significant gap between the reaction temperature in the isothermal laboratory reactor and the WABT of the industrial adiabatic reactor can be bridged.
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  • 42
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    Chemical Engineering & Technology - CET 10 (1987), S. 361-367 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The rate behaviour of multi-step reaction systems is difficult to model. Concentration-controlled investigations in a recycle reactor provide new tools for this purpose, e.g. the possibility to decompose a network into single reaction steps. Methanation of carbon monoxide over a supported Ni catalyst could be shown to be accompanied to a considerable extent by the shift reaction, and to a lesser extent by direct hydrogenation of carbon dioxide. Deactivation of the catalyst was measured at definite gas compositions. The two main steps show different responses to deactivation: Separable kinetics was found only for the methanation step. Power law rate equations were fitted to the rate data of the individual reaction steps to represent the main features of their kinetic behaviour. Some aspects of deactivation kinetics are also discussed.
    Additional Material: 8 Ill.
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  • 43
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    Chemical Engineering & Technology - CET 10 (1987), S. 368-375 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This contribution presents the measurements of bubble behaviour in presence of A, B and D powders in a semi-industrial scale pressurized fluidized bed. Local measurements were taken at static pressures of 0.2, 1.0 and 2.5 MPa, using capacitance probes. Quartz sand with mean particle diameter of 157 μm was fluidized in small “two-dimensional” transparent equipment with Frigen R 115. In addition, pressure fluctuations in the bulk of the fluidized bed with inner diameter of 0.4 m were studied experimentally.
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  • 44
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    Chemical Engineering & Technology - CET 10 (1987), S. 353-360 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Correlation flowmeters have been used in the scientific field for many years and are actually gaining greater commercial importance due to an increasing number of applications in industrial plants. The importance of the correlation method is based on the fact that essentially no alternatives exist for measuring velocity and mass flow rate in pneumatic conveyors. However, the hitherto employed transit time correlation method leads to results which are clouded by uncertainties. The commonly used theoretical model of the measurement process does not explain these effects satisfactorily. Therefore, the theory of non-intrusive flow sensors is reinvestigated from a physical standpoint. The derived model permits a discussion of the transit time correlation method in some detail. Furthermore, this model leads to an alternative sensor arrangement and signal processing scheme which makes it possible to measure the true mean velocities. Examples of experimental results are given.
    Additional Material: 13 Ill.
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  • 45
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: For the simulation of steady- and non-steady-state behaiour of separation columns, a simulation program was developed and employed for the calculation and optimization of methanol-water separation. The demand for increasingly higher purities and energy-saving optimization of plants results in complex column configurations and thus in complex control schemes. The number of possible control schemes was reduced on the basis of heuristic rules. By simulating the process, the optimum control and manipulative variables and measuring points were determined from the reduced number of control concepts. A control scheme was introduced. The model was verified by simulation of the dynamic behaviour of the process. The investigation included the effects of computing technique, time interval, model reduction and tray hold-up on the results. Thus, various effects and interactions were verified theoretically with respect to the robustness of the model. This was followed by a simulation of the non-ontrolled and controlled column. By implementing the controllers in the existing column program, the computer can predict the control parameters. These parameters were checked and corrected when the metahnol-ater column was put in operation. In the start-up phase, major problems were caused by the sensitivity and failure rate of density, throughput and pump measuring sensors. Feed impurities were another source of problems. Operation with high product purities is possible, with a side stream to discharge impurities.
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  • 46
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    Chemical Engineering & Technology - CET 10 (1987), S. 382-389 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Phase equilibria in the n-hexadecane-water-hydrogen and n-hexadecane-benzene-water-hydrogen systems were determined experimentally at temperatures between 200 and 350°C and pressures between 100 and 300 bar. At high water concentrations, three-phase equilibria were observed. Two-phase regions could be correlated with a modified Redlich-Kwong equation of state. The influence of interaction parameters on the calculated miscibility gaps was investigated. On application of mean interaction parameters, it is possible to calculate phase equilibria at different pressures or temperatures with the same set of parameters. In the ternary system, the three-phase regions could be calculated from the correlated binodal curves of two-phase regions. In the quaternary system, cross-sections through the vapour-liquid miscibility gap could be successfully correlated.
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  • 47
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    Chemical Engineering & Technology - CET 10 (1987), S. 375-382 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In the extraction literature, no attention has been given so far to differential calculation models for countercurrent extraction columns which take into account the changes in flow rates of the phases as a result of transferred mass, and which also reflect the variations in interfacial area per unit volume and in axial dispersion coefficients since these depend on the flow rates. The present contribution puts forward a formulation of such a model; this results in a set of non-linear differential equations with separated boundary conditions, representing the feeds at either side of the extraction column. This set of differential equations must be solved numerically. The model is illustrated by a sample calculation on the extraction of benzene with furfural. In this (realistic) example, the interfacial area per unit volume varies from bottom to top by a factor of 3. Ignoring this effect would obviously result in serious under- or overdesign.
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  • 48
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    Chemical Engineering & Technology - CET 10 (1987), S. 405-410 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Starting from the assumption that the growth of desublimed layers is governed mainly by heat and mass transfer, the authors present a model based on conditions in the diffusion boundary layer and suggest that the “hoarfrost”Hereafter the term frost will be used instead of hoarfrost. density depends on only one parameter. The discussion accounts for the process determining factors, i.e. the growth rate, mass transfer and gas concentration. The theoretical relationship is confirmed by the authors' own experiments on two systems and data from literature. The relationship can be established by a few laboratory experiments and permits the calculation of frost density and of associated variables, thus facilitating the optimization of desublimator design.
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  • 49
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    Chemical Engineering & Technology - CET 10 (1987), S. 411-419 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This contribution reviews the work performed mainly at Bergbau-Forschung during the past few years. First, it deals with the quantitative description of gasification kinetics, taking into account the pressure of the gasifying agent and partial pressures of product gases. Thereby, a method and quantitative data are provided for the calculation of reaction rates for uncatalyzed and potassium-catalyzed gasification, on the example of chars from high volatile bituminous coals. In addition, a method for characterization of internal surface area by oxygen chemisorption with respect to char reactivity has been improved. Progress has also been achieved in the assessment of the impact of pyrolysis conditions, especially the time-temperature profile during char formation, on its chemical activity during subsequent use.
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  • 50
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    Chemical Engineering & Technology - CET 10 (1987), S. 398-404 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Previous investigations have shown that the specific energy input is the overall parameter of influence on product size during communition in agitated ball mills, from laboratory up to industrial scale. The specific energy input is the introduced energy related to the amount of comminuted material. This parameter can be used for mill scale-up. Consequently, a method had to be found of introducing power into the mill so as to obtain a given specific energy input. For this purpose, stirring tests with purely Newtonian liquids were carried out in absence of solids and hence, without comminution. Mathematical models are presented which describe the power consumption in agitated ball mills in absence of grinding beads. In addition, tests with grinding beads filling were also performed, leading to scale-up guidelines with respect to power consumption. Finally, the influence of size and material of grinding beads was investigated.
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  • 51
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A pressure swing adsorption process for hydrogen recovery from coke oven gases comprises the steps of adsorption at pressures above 6 bar, cocurrent and countercurrent depressurization, purging with hydrogen at ambient pressure and repressurization. The process was investigated in the cyclic mode, on a laboratory scale, using an adsorber filled with 1.3 litres of carbon molecular sieve. Based on the test results of concentrations and pressures within the adsorber during complete cycles, a pseudo-homogeneous model was developed for the adsorption step. Adsorption equilibrium parameters were determined by separate measurements, while the transport parameters were evaluated by fitting the experiments of the fixed bed adsorber. It was possible to consider the residual load, resulting from an incomplete regeneration, by the assumption of a load distribution in the inlet region of the adsorber.
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  • 52
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An important aspect of nuclear and chemical reactor safety is the ability to predict the maximum or critical mass flow rate from a break or leak in a pipe system. At the beginning of such a blowdown, if the stagnation condition of the fluid is subcooled or slightly saturated thermodynamic non-equilibrium exists in the downstream, e.g. the fluid becomes superheated to a degree determined by the liquid pressure. A simplified non-equilibrium model, explained in this report, is valid for rapidly decreasing pressure along the flow path. It presumes that fluid has to be superheated by an amount governed by physical principles before it starts to flash into steam. The flow is assumed to be homogeneous, i.e. the steam and liquid velocities are equal. An adiabatic flow calculation mode (Fanno lines) is employed to evaluate the critical flow rate for long pipes. The model is found to satisfactorily describe critical flow tests. Good agreement is obtained with the large scale Marviken tests as well as with small scale experiments.
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  • 53
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    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 1-1 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 54
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    International Journal of Quantum Chemistry 31 (1987), S. 33-44 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The theory of MCSCF and CI energy derivatives with respect to geometrical variations is briefly reviewed with special attention given to the MCSCF and MRCI energy gradients. A computational procedure is proposed for MRCI energy gradients that does not require the solution to any “coupled-perturbed MCSCF” equations, it does not require any expensive direct-CI matrix-vector products involving derivative integrals, and it does not require any derivative integrals to be transformed from the AO basis to the MO basis. An additional feature is that it does not require any changes to existing MCSCF gradient evaluation programs in order to compute MRCI gradients. The only difference in the two cases is the exact nature of the data passed to the gradient evaluation program from the previous steps in the computational procedure. The additional effort required to compute the entire MRCI energy gradient vector is approximately that required for one additional iteration of the MRCI diagonalization procedure and for one additional MCSCF iteration. For large scale MRCI wave functions, the MRCI energy gradient evaluation should only require about 10% of the effort of computing the wave function itself. This computational procedure removes a major computational botleneck of potential energy surface evaluation.
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  • 55
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    International Journal of Quantum Chemistry 31 (1987), S. 65-71 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Preliminary results are presented for transition probabilities in the H + H2 system derived from an adiabatic representation in terms of surface functions on hyperspheres. Special attention is given to the resonance structure for transition probabilities in the first vibrational level.
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  • 56
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    International Journal of Quantum Chemistry 31 (1987), S. 99-112 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Low-lying excitation energies from the ground state of Be were calculated using a basis set of 61 Cartesian Gaussian functions. Three approximations were employed: the time-dependent Hartree-Fock (TDHF), second-order equations-of-motion (EOM), and multiconfigurational time-dependent Hartree-Fock (MCTDHF). The TDHF excitation energies are 0.5-1.1 eV lower than experiment, and the EOM values are 0.3-1.2 eV lower than experiment, whereas the MCTDHF excitation energies deviate on the absolute average from experiment by only 0.03 eV. We found that in an MCTDHF calculation, any proper MCSCF stationary point is a good reference (i.e., initial) state, not just the ground state. Experimental values for oscillator strength are accurately known only for the 2s2X1S → 2s2p1P0 transition. The TDHF value and the MCTDHF value agree with experiment, but the EOM value does not. The agreement of the TDHF value with experiment seems to be coincidental, because for higher lying transitions the TDHF values differ by approximately a factor of two or more from the more accurate MCTDHF. Frequency independent polarizabilities, α(0), were also calculated with the TDHF, HRPA, and MCTDHF and frequency dependent polarizabilities, β(ω), were calculated with the MCTDHF. No experimental data for Be polarizabilities exist, but we expect the MCTDHF values to be among the most accurate calculations available.
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  • 57
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cellular spin resonance (CSR) or electrorotation is the spinning of cells or other particulate matter in rotating electric fields. The spin rate of the (bio)particle varies markedly with the applied frequency and often is seen to have rather sharp maxima as the frequency is varied. In certain frequency ranges, living cells often are observed to undergo a striking inversion of their spin rate and then spin counter-clockwise (CCW) while the direction of rotation of the applied electric field is clockwise (CW).The CSR spectra are presumably due to dipolar interactions with the applied field, as are the spectra obtained by straightforward dielectrophoresis (DEP) techniques. The two spectra, however, differ radically in the low frequency ranges (below about 1 MHz). It is our objective to explain this apparently anomalous behavior.We believe that the anomaly appears primarily because one is comparing rotational with translational force responses. In the DEP techniques, the simpler translational force arising from the comparative polarizability of cell versus medium (water) gives a straightforward measure of the differential polarizability owing to volume and surface effects pro forma. In the CSR techniques the spin rate reflects the torque on the cells and hence emphasizes polarization at the outer periphery of the cells rather than that of the average overall polarizability.The problem is considered in terms of a living or dead cell rotating with an angular velocity Ω in a fluid medium of viscosity η when it is subject to an electric field rotating at angular frequency ω. It is observed in many experiments that Ω ≪ ω, and also that the sign of Ω for the same cell can change from CW to CCW and back to CW as the applied frequency ω of the CW electric field is increased. Moreover, the sign and magnitude of the CSR spectra differ for living and dead cells. All of these experimental results can be explained quantitatively by using Maxwell's equations and the dielectric properties of a lossy dielectric sphere in an ionically conductive dielectric fluid.
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  • 58
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    International Journal of Quantum Chemistry 32 (1987), S. 181-191 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It has been shown that an easier procedure to the study of molecular electrostatic potentials than the prevalent monopole isopotential approach is to use a dipole as the mapping device: allow the dipole to move on a geometrical surface enclosing the molecule such that the distance between the surface and the nearest atoms of the molecule (closest distance of approach) is fixed, say at 2 Å, calculate the electrostatic interaction energy between the molecule and the dipole at different points of the surface, and let the dipole orient itself along the minimum energy direction and treat these minimum energies as the desired electrostatic potentials. Thus the favorable binding sites of a given molecule for other species along with their relative orientations can be obtained. This procedure has been applied to the nucleic acid bases using the necessary input data from two independent sources. Thus success of the procedure in predicting important features of molecular electrostatic potentials has been demonstrated.
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  • 59
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    International Journal of Quantum Chemistry 32 (1987), S. 149-164 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Hartree-Fock (HF) equations for the (He)2 system are solved using a suitable exchange perturbation technique. The HF interaction energy is then obtained directly from a rapidly convergent iteration procedure. The method remains convergent for short interatomic distances, where the interaction energy surpasses the energy of intraatomic excitations. The fast convergence of the method is a result of the proper treatment of the exchange-deformation effects. In the region of the van der Waals minimum, these effects account for 50% of the HF deformation energy.
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  • 60
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    International Journal of Quantum Chemistry 32 (1987), S. 249-264 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The algorithm to derive symmetry orbitals for one-electron band-structure calculations of one-dimensional crystals presented by Božović and Delhalle [1] has been applied to extend the explicit formulation of symmetry-adapted linear combinations of Bloch sums to any line group isogonal to Cn or Cnv. We also point out how the transformation matrices that block-diagonalize the one-electron eigenvalue equation H(k)C(k) = S(k)C(k)E(k) can be determined. Finally, the extended-Hückel block-matrix dimensions of some typical quasi-one-dimensional transition metal compounds have been tabulated in order to give a measure for computational savings achievable by this technique.
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  • 61
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    International Journal of Quantum Chemistry 32 (1987) 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 62
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    International Journal of Quantum Chemistry 32 (1987), S. 313-347 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Neutral, ionic, and complete alternant systems are studied using the alternancy symmetry adapted (ASA) approach. This approach is based on an explicit construction of ASA operators that are up to the sign invariant with respect to the particle-hole symmetry transformation. These operators serve as building blocks of alternant systems, and they determine their characteristic properties. All Hamiltonians describing neutral alternant systems are explicitly constructed. Up to some minor restrictions, all Hamiltonians describing ionic and complete alternant systems are also explicitly constructed. Inversely, given a Hamiltonian Ĥ in a second quantization notation, one can easily check whether or not this Hamiltonian describes a neutral (ionic, complete) alternant system. All linear properties characteristic to neutral (ionic, complete) alternant systems are obtained. In particular, all one- and two-particle properties are derived in an explicit form. The properties obtained substantially generalize “classical” properties of alternant systems such as, in the case of neutral alternant systems, uniform charge density distribution, vanishing bond orders between atomic sites of the same parity, and alternancy selection rules for the electric dipole transitions.
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    International Journal of Quantum Chemistry 32 (1987), S. 397-397 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 64
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    International Journal of Quantum Chemistry 32 (1987) 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 65
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    International Journal of Quantum Chemistry 32 (1987), S. 451-456 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The entity of generalized Rayleigh's quotient is introduced. A formalism involving calculation of the functional gradient and Hessian of the quotient reveals several properties that lean on the variational approach to the direct optimization of the ground state wave function. In particular, the link between a minimization of the generalized quotient and the solution to the “nonlinear Schrödinger equation” is elucidated. The concept of functional derivatives enables us to perform a direct optimization of the trial ket through the Newton-Raphson or the augmented Hessian method. Eventually, a “universal” perturbation theory is derived.
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  • 66
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    International Journal of Quantum Chemistry 32 (1987), S. 491-499 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The investigations on nonclassical polymers [4, 6, 12] have been extended to a new class of quasi-one-dimensional hydrocarbons. The latter are characterized by the occurrence of an infinitely narrow nonbonding band, originating from a new type of structural peculiarity. In contrast to the systems considered so far, the new polymers exhibit a strictly localized nonbonding band.
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    International Journal of Quantum Chemistry 32 (1987), S. 549-549 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 68
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    International Journal of Quantum Chemistry 32 (1987), S. 551-562 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pair-excitation multiconfigurational self-consistent field (PEMCSCF) treatment of 11 small molecules (LiH, BeH2, BH3, BF, CH4, C2H4, C2H2, CH2O, NH3, H2O, and HF) has been carried out in a minimum basis set of Slater Transform Preuss functions as fitted by six cartesian gaussians (STP-6G). The advantages of accuracy without using a split basis are shown by comparison to familiar 4-31G and 6-31G calculations using molecular geometries optimized with STO-6G basis sets. A benefit is shown for the use of minimum basis fitted to STP functions: they overemphasize long-tail radial dependence to achieve long range basis sensitivity without increasing the basis size at the AO-to-MO transformation step in the configuration interaction portion of the MCSCF algorithm. Fully optimized STP-6G parameters are given and appear to be transferable as shown for acrolein. A FORTRAN listing of the full least squares fitting algorithm is available* for in situ generation of STP-6G orbitals energetically superior to 4-31G, or a less accurate STP-6G 1S, 2S, and 2P basis may be scaled directly as if they were STO-6G functions, but with considerably lower energy that with an STO-6G basis.
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  • 69
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    International Journal of Quantum Chemistry 32 (1987), S. 575-589 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to avoid the determination of the perturbed wave function in the susceptibility calculation of closed shell molecules, several authors have developed gauge-variation methods based on Rebane's work. The present work illustrates that introduction of a certain restriction in the gauge-variation method makes the susceptibility calculations exceptionally simple. The restriction involves the use of the Coulomb gauge so that the gauge-function satisfies Laplace's equation. The restriction was dictated by the demonstration of gauge-invariance of the Rayleigh-Schrouml;dinger perturbation theory of diamagnetism. The method with the prescribed restriction has been applied to the H2O molecule, as an example, to demonstrate the advantages.
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    International Journal of Quantum Chemistry 32 (1987), S. 621-653 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Spin-independent alternant systems are analyzed using the alternancy symmetry adapted (ASA) approach. This approach is based on an explicit construction of ASA operators that either commute (altemant) or anticommute (antialternant) with the particle-hole symmetry operator K̂. The method yields an explicit construction and identification of all spin-independent Hamiltonians that describe altemant systems (neutral and/or ionic) as well as an explicit identification of all linear properties characteristic to these systems. It also establishes the connection between the spin-eigenstates and the particle-hole symmetry.
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    International Journal of Quantum Chemistry 32 (1987), S. 685-697 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A complete description of the rotational isomerism of monothioformic acid is presented. Ab initio results concerning the barrier heights and the energy difference between the stable isomers are in good agreement with the experimental data. A reduced potential function deduced from our calculations has been used to characterize the kinetics and thermodynamics of the rotational isomerization. The reported ab initio values of equilibrium constants are in good agreement with the experimental ones. From the analysis of the available experimental data, we have found that the free energy and enthalpy behavior are quite similar and that no noticeable entropy contributions are involved in the internal rotation, in agreement with previous studies on unimolecular isomerization processes.
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    International Journal of Quantum Chemistry 32 (1987), S. 723-723 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 73
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    International Journal of Quantum Chemistry 32 (1987), S. 1-1 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 74
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    International Journal of Quantum Chemistry 32 (1987), S. 85-103 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The equilibrium geometry, stabilization energy, and electric polarizability of formic acid, formamide, and the three possible cyclic hydrogen-bonded pairs are obtained by ab initio calculations using the STO-3G, 4-31G, and 6-31G** bases. These three properties are found to be very much dependent on the basis set extension. The polarizability of the dimers is found to be basically additive in contribution from the monomeric moieties.
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    International Journal of Quantum Chemistry 32 (1987), S. 133-147 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the course of conformational motions of molecules the changes in shapes of electronic charge distributions follow that of the nuclear framework. However, this coupling between the changes in the nuclear geometry and electron density may depend on the actual nuclear displacement; the coupling may be weak or strong for a given conformational motion. It is of some interest to analyze how faithfully the charge density variations follow the nuclear displacements in a family of conformational rearrangements. In certain cases small conformational changes may induce large changes in the shape of charge density distributions, while in other cases large and qualitatively important conformational changes may involve qualitatively inessential distortions in the shape of electron distributions. In this article we describe a new classification of conformations based on those domains of nuclear configuration space within which the „shape groups“ (symmetry independent homology groups) of the electric charge density remain invariant. Such an analysis might be valuable when seeking correlations between molecular structure and certain biological or biochemical activities.
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    International Journal of Quantum Chemistry 31 (1987), S. 565-567 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two-center Coulomb and hybrid integrals are combined into a single expression by use of the formulas given by the author for the expansion of real and complex STO's about a point displaced from the orbital center. The final results are expressed in terms of the overlap integrals between STO's. Analytical formulas for the evaluation of these integrals have been established recently by the author.
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  • 77
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    International Journal of Quantum Chemistry 31 (1987), S. 581-590 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The spectral density operator technique is proved to be a convenient tool for derivation of approximate topological formulae for total pi-electron energy (Epi) of benzenoid hydrocarbons (BHs). Developed mathematical formalism points out a common origin of three different measures for the stability of BHs, namely: resonance energy (RE), number of Kekule structures (K) and HOMO-LUMO separation (XHL). In turn, a novel topological invariant corresponding to “normalized” RE is derived. Numerical calculations for a representative set of BHs demonstrate effectiveness of the present approach. Various approaches to an estimation of BH stabilities are discussed.
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    International Journal of Quantum Chemistry 31 (1987), S. 569-579 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: There is considerable evidence indicating that the primary in vivo DNA alkylation product of vinyl chloride, believed to be responsible for its carcinogenicity, is the 7-N-(2-oxoethyl) derivative of guanine. Using a representative keto-enol system, we have studied computationally two possible equilibria involving this adduct. The first is between the 2-oxoethyl derivatives of the keto and enol forms of the representative system, whereas the second is between the 2-oxoethyl derivative of the keto form and the corresponding hemiacetal. In the case of the analogous guanine derivatives, such equilibria could lead to disruption of the hydrogen bonding between guanine and cytosine in DNA and could cause miscoding and replicational and transcriptional errors. An ab initio self-consistent field molecular orbital study has been carried out using the GAUSSIAN 82 system of programs. Optimized structures and energies have been calculated at the 2-21G level for the representative keto-enol system and its 2-oxoethyl and hemiacetal forms. The formation of the 2-oxoethyl adduct was found to have no significant effect upon this keto-enol equilibrium, which strongly favors the keto form. Our calculations further show hemiacetal formation to be an unlikely possibility for this system. On the basis of these results and recent data on guanine tautomers, we speculate about the analogous equilibria involving the guanine derivatives.
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    International Journal of Quantum Chemistry 31 (1987), S. 591-603 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The CI space Xn generated by n electrons moving over 2n spin orbitals is considered. It is shown that the transitions between different eigenstates ψi ∊ Xn of alternant and weakly alternant Hamiltonians are governed by some special selection rules. These selection rules are characteristic to alternant systems, and they do not apply to nonalternant systems. The set of all such selection rules can be easily derived from the splitting theorem. In particular, the selection rules associated with spin independent alternant systems are considered. As an example, the PPP Hamiltonian Ĥp describing netural alternant hydrocarbons is treated. In the case of electron dipole transitions between eigenstates ψi ∊ Xn of the Hamiltonian Ĥp, the selection rules obtained are in agreement with the selection rules derived previously by Pariser and McLachlan.
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    International Journal of Quantum Chemistry 31 (1987), S. 605-609 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An asymptotic formula describing a dependence of the algebraic structure count (ASC) of the even-membered rotagraphs on its size (N) is derived from the backfolding theorem for the electronic band structure. This new result imposes very strict constrains on ASC as a function of N.
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    International Journal of Quantum Chemistry 31 (1987), S. 625-638 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper we study the unitary transformations on the model space in quasidegenerate many body perturbation theory (QDMBPT). From this point of view we compare Brandow's and Kirtman's versions of QDMBPT up to the fifth order of perturbation expansion. We show that, starting from Brandow's QDMBPT, we can derive various versions of effective Hamiltonians order by order, of which the Kirtman's version is the simplest one. The operator of unitary transformation we express through the correlation operator.
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    International Journal of Quantum Chemistry 31 (1987), S. 639-647 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the Xα method a generalized Hellmann-Feynman theorem has been derived, and its most important applications are presented. A formula for electronegativity using the definition of electronegativity given by Iczkowski and Margrave and the magnetic nuclear shielding factor and its relation to the electronegativity have been obtained. The virial theorem of the Xα method has also been derived with the aid of the Hellmann-Feynman theorem.
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    International Journal of Quantum Chemistry 31 (1987), S. 611-623 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conformational preferences of modified nucleic acid base N6-(N-glycylcarbonyl) adenine, gc6Ade, have been investigated using the quantum chemical PCILO (Perturbative configuration interaction using localized orbitals) method. The multidimensional conformational space has been searched using selected grid points formed by combining various torsion angles that take favored values derived from energy variation with respect to each torsion angle individually. The theoretically predicted most stable, minimum energy conformation of the molecule is such that the substituent on N(6) spreads away from the imidazole moiety of the adenine ring, thus keeping distal orientation. The preferred molecular orientation is stabilized by an intramolecular hydrogen bond from N(11)H of the amino acid to N(1) of the adenine. The carboxylic group of the substituent is trurned away in relation to N(11)H…N(1) and is perpendicular to the plane through the rest of the moleculeThe alternative stable conformation corresponding to an 0.8 kcal/mol higher energy has a coplanar carboxylic group turned towards the same side as N(11)H…N(1) and is exhibited in the crystal structure of the nucleoside derivative, gc6A. Energetically, the carboxyl group may change its orientation over a wide range, without much destabilization. This suggests probing by the carboxyl group of the molecular environment in the vicinity of the anticodon in tRNA.
    Additional Material: 6 Ill.
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  • 84
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    International Journal of Quantum Chemistry 31 (1987), S. 649-662 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Energies and geometries for a number of small hydrogen bonded dimers have been calculated by semiempirical method based on a perturbation approach. Results have been compared with experimental and the best theoretical data. A quite good description of equilibrium configurations has been obtained in every case when local multipoles from sufficiently accurate wave functions have been used. Hydrogen bond lengths have not been predicted with sufficient precision. Results indicate, however, that it should be possible to achieve improvement in the framework of the applied calculation scheme by modification of the parameter values.
    Additional Material: 4 Ill.
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  • 85
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    International Journal of Quantum Chemistry 32 (1987), S. 131-136 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Most band structure calculations approximate the integral over the Brillouin zone of momentum (i.e., wave vector) dependent properties with an appropriately weighted sum over a discrete set of points in the Brillouin zone. The best choice for such a set of points has long been a point of discussion in crystalline band structure calculations. For one-dimensionally periodic systems, however, the usual choice of points has been evenly spaced points in the one-dimensional Brillouin zone with equal weights. We have analyzed the exact error for the integral over the π band of a tight-binding model of trans-polyacetylene as a function of bond alternation. We find that the error in π band energy decreases in magnitude as q-2, where q is the total number of points treated in the Brillouin zone, for the metallic polyacetylene system with equal bond lengths. As bond alternation increases, however, we find that the error in π band energy decreases in magnitude roughly exponentially as a function of bond alternation for any given value of q. We find that this systematic change in error as a function of bond alternation can lead to either apparent overestimation or underestimation of the equilibrium dimerization and stabilization energy of Peierls distorted systems using first-principles total energy calculations.
    Additional Material: 1 Ill.
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  • 86
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    International Journal of Quantum Chemistry 32 (1987), S. 321-339 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A time-dependent approach to molecular dynamics involving both electrons and nuclei is formulated to study the interaction between electronic structure and nuclear geometry during electron transfer processes. The formulation uses the time-dependent variational principle to obtain a Hamiltonian system of first-order ordinary differential equations for wave function parameters from the quantum mechanical Schrödinger equation. We apply the formulation to a two-level model. In this first application, the nuclei are treated classically. The electron transfer process in both the “normal” and the “abnormal” case is studied and discussed. The role of the nuclear motion in the electron transfer process is clearly exhibited in both two and three moiety systems. For small coupling the difference in evolution between the dynamics using adiabatic and diabatic basis states shows the importance of nuclear motion in the process. Then various aspects of applications to realistic systems are discussed, and the techniques to treat those applications are outlined.
    Additional Material: 3 Ill.
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  • 87
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    International Journal of Quantum Chemistry 32 (1987), S. 377-387 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We describe a procedure to calculate resonance energies that is based on the addition of a complex perturbation to a one-channel or multichannel description of a quantum system. The perturbation has the effect of modifying the boundary conditions so that the perturbed problem leads to the search of the eigenvalues of a bound system. The energies cannot be exploited directly. A point Padé procedure is subsequently applied to remove the perturbation. Tests are made on a well-known one-channel example. Another application is made to two simple photofragmentation processes: photoionization of the ground state hydrogen atom and photodissociation of the HBr molecule. The complex perturbation in this instance is the change of the photon frequency into a complex quantity.
    Additional Material: 6 Tab.
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  • 88
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    International Journal of Quantum Chemistry 32 (1987), S. 425-433 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Direct evaluation of momentum space Hartree-Fock wave functions require accurate numerical integrations. The purpose of this computer experimentation with the Gauss-Legendre method is to examine the sensitivity of calculated properties on the truncation of the interval of integration for the radial variable.
    Additional Material: 1 Ill.
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  • 89
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    International Journal of Quantum Chemistry 32 (1987), S. 475-485 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present a coupled-cluster polarization propagator method based on a coupled cluster singles and doubles reference state. Applications to the Be atom show that we may calculate electronic excitation energies with an average absolute error of about 0.08 eV using this method. We have also calculated the nuclear spin-spin coupling constant of 1H19F to be 524.4 cps, in good agreement with experiment. For Be there is a large effect of using coupled-cluster rather than a low-order Rayleigh-Schrödinger expansion, whereas the coupling constant of HF is less sensitive to this improvement in the reference state.
    Additional Material: 8 Tab.
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  • 90
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    International Journal of Quantum Chemistry 32 (1987), S. 513-521 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A symmetric group approach is presented for performing large scale, direct configuration interaction (CI) studies of electronic correlation effects in molecules. Two alternative graphical methods are described for representing very large sets of lexically ordered orbital configurations. One is suited for truncations in the number of core orbitals and the other for changes in the number of virtual orbitals. The Hamiltonian matrix elements are constructed using a graphical approach for localizing the one-and two-electron contributions. Compact and direct algorithms are given for calculating the irreducible representation matrices of S(N) for the “line-up” permutations. The program implementation of the CI procedure, PEDICI, calculates directly firstorder molecular one-electron properties and transition probabilities from a multireference space for general excitation schemes.
    Additional Material: 4 Ill.
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  • 91
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    International Journal of Quantum Chemistry 31 (1987), S. 747-753 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A concept is advanced explaining how low resolution studies of chaotic spectral regions can result in assignable regular spectra. The concept draws on ideas from resonance scattering theory, and application is made to interpretation of vibrational spectra in the quasicontinuum.
    Additional Material: 2 Ill.
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  • 92
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    International Journal of Quantum Chemistry 31 (1987), S. 795-821 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The notion of resonances in different settings is discussed. Two methods for localizing the resonances in the complex plane are given and applied to model potentials.
    Additional Material: 3 Ill.
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  • 93
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    International Journal of Quantum Chemistry 32 (1987), S. 573-587 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The quantum path integral molecular dynamics method was utilized to explore the compositional, structural, and size dependence of localization mode of an excess electron in ionic and hydrogen-bonded clusters, providing information on the nature of surface states and on isomerization induced by electron attachment in large finite systems.
    Additional Material: 4 Ill.
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  • 94
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    International Journal of Quantum Chemistry 32 (1987), S. 503-512 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Total geometry optimizations are reported for Cr(CO)6, HMn(CO)5, Fe(CO)5, Ni(CO)4, Cr(C6H6)2, Fe(C5H5)2, Ni(C4H4)2, Cr(NO)4, (C5H5)Mn(CO)3, and (C6H6)Cr(CO)3. A variety of basis sets were examined, and, based on the results, a relatively compact and accurate basis set is proposed. The differences between the calculated and experimental metal-carbonyl, metal-benzene, and metal-nitrosyl bond distances average 0.03, 0.08, and 0.07 Å, respectively. Calculated metal-cyclopentadienyl bond lengths were found to be an average of 0.15 Å longer than experimental bond lengths. Addition of electron correlation at the perfect pairing GVB level reduced the average difference in the metal-cyclopentadienyl bond length to 0.08 Å.
    Additional Material: 4 Tab.
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  • 95
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The analytic energy gradient method that we have recently implemented for CCSD wave functions is applied to fully optimize the pyramidal C3v and planar D3h structures of ammonia. Using a double-zeta plus polarization basis set, results for harmonic vibrational frequencies, infrared intensities, and dipole moments have been obtained. Comparison with different levels of truncated configuration interaction suggests that CCSD values are of better than CISD quality and generally closer to CISDTQ results.
    Additional Material: 3 Tab.
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  • 96
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    International Journal of Quantum Chemistry 32 (1987), S. 539-545 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Effective core potentials are utilized in conjunction with polarization propagator calculations of excited state properties. The propagator method employed is based on an antisymmetrized geminal power wave function as the reference state. Calculations are presented on the low-lying excited states of HF and NaH. All-electron and valence-electron results are compared for HF. The choice of basis set is found to be very important for obtaining good results.
    Additional Material: 6 Ill.
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  • 97
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    International Journal of Quantum Chemistry 32 (1987), S. 569-572 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nonadiabatic energy correction term of the hydrogen molecule at large separation is discussed to determine whether or not the nuclear motion induces the inter-atomic interaction potential. Nonadiabatic vibrational motion of nuclei induces the internal charge polarization of atoms to give the novel correction term to the London R-6 force. The correction term is (4/M) (1/R3), which is important at large R despite the overwhelming magnitude of nuclear mass.
    Additional Material: 1 Ill.
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  • 98
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    International Journal of Quantum Chemistry 32 (1987), S. 603-612 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 99
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    International Journal of Quantum Chemistry 32 (1987), S. 765-766 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 100
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    International Journal of Quantum Chemistry 32 (1987), S. 763-764 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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