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  • 1990-1994  (1,063)
  • 1993  (1,063)
  • Engineering General  (629)
  • Atomic, Molecular and Optical Physics  (301)
  • Industrial Chemistry and Chemical Engineering  (133)
Material
Years
  • 1990-1994  (1,063)
Year
Keywords
  • 101
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 16 (1993), S. 119-124 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The hydrodynamic behaviour of a cocurrent gas-liquid-solid fluidized bed was studied by using the bed collapse technique. The key parameters, k and x, of the generalized wake model were estimated. Compared with other existing methods for evaluating the parameters k and x, the bed collapse technique shows some distinct advantages. Parameters are derived directly from experiments in a three-dimensional three-phase fluidized bed and there is no need to assume that a bubble and its wake form a perfect sphere. Hold-up data of the three-phase fluidized bed predicted by the generalized wake model with k and x estimated by the bed collapse technique are in good agreement with those obtained via the traditional pressure-drop method.
    Additional Material: 7 Ill.
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  • 102
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 16 (1993), S. 147-152 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The influence of solids concentration and static mixers on the hydrodynamics of the gas phase was studied for a three-phase fluidized bed bioreactor (air, nutrient solution, biocatalyst Ca alginate beads). Axial gas hold-up profiles, radial gas velocity profiles, mean bubble diameter and gas/liquid interfacial area per unit volume were measured in a bubble column (DR = 0.142 m, HR = 1.748 m). The influence of solids concentration on the gas hold-up is insignificant; static mixers enhance the gas hold-up in the reactor volume element in which they are installed. Axial gas velocity decreases with increasing solids concentration. At high solids concentrations, static mixers exert little influence on the gas phase but, at low concentrations, they do. A model is suggested to describe the influence of solids concentration (characterized by turbulent viscosity vt) and static mixers (characterized by profile parameter n) on the gas velocity profile.
    Additional Material: 5 Ill.
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  • 103
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 16 (1993), S. 180-185 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Acidianus brierleyi was demonstrated to remove pyritic sulphur from coal. A. brierleyi was also found capable of catalyzing the removal of what is normally reported as organic sulphur from coal 171US34. A kinetic analysis was performed by assuming a first order reaction. The first order kinetics allowed a comparison with literature data for Thiobacillus ferrooxidans. Also, formation of jarosite was taken into account in the analysis. The simple first order kinetics was observed to fit the data on removal of sulphur satisfactorily.
    Additional Material: 4 Ill.
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  • 104
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 16 (1993) 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    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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  • 105
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 16 (1993), S. 229-233 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper presents a very simple model of liquid homogenization in a mixing tank. The model, based on the pumping capacity of impellers and the degree of homogeneity, is valid for turbulent mixing; however, it has been extended to transient regime of mixing (Re = 100 to 1000).
    Additional Material: 7 Ill.
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  • 106
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 16 (1993), S. 260-262 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: It was established by using double impulse method that the transmission time of an ultrasonic wave, which passes near a bubble, is either shorter or longer than that in the liquid system. This is attributed to the fluid vortex originated by the bubble rising ahead of the wave. The longitudinal distribution of gas hold-up in a three-phase system, measured by analyzing wave shape and reduction of transmission time is in good agreement with that obtained by using the static pressure method. This indicates the possibility of application of ultrasonic techniques to the simultaneous measurement of phase hold-ups in the three-phase system.
    Additional Material: 4 Ill.
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  • 107
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 16 (1993), S. 263-269 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The effects of gas velocity (0.32 to 0.67 m/s), inlet gas temperature (25 to 100 °C) and the mass ratio of starch to inert particles (0.1 to 0.4) on the drying rate of starch in a 0.083 m-ID × 0.80 m-high inert medium fluidized bed were investigated. The drying mechanism in an inert medium fluidized bed can be classified into adhesion-dispersion, evaporation and disintegration steps. The drying rate increases with the increasing inlet gas temperature and velocity; the rates being about 10 times those reported for an agitated pan dryer. However, the drying rate decreases slightly as the mass ratio of starch to inert particles increases. Also, the drying rate exhibits a maximum at an optimum bed porosity. The drying rate data obtained in an inert medium fluidized bed have been correlated with the relevant dimensionless groups, i.e. Stefan and particle Reynolds numbers based on the theory of isotropic turbulence.
    Additional Material: 10 Ill.
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  • 108
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 16 (1993), S. 275-278 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Ozonization of water in a cooling tower was investigated. A laboratory experimental set-up was employed to study changes in water quality during ozonization. Measured data were analyzed in the context of cooling water's resistance to corrosion, scaling and biofouling. A method is proposed for determining the suitable dosage of ozone for maintaining the necessary water quality. It has been found that ozonization is very effective in maintaining the correct water quality for the required purpose and provides an attractive alternative to the conventional multiple chemical method of cooling water treatment.
    Additional Material: 8 Ill.
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  • 109
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 16 (1993), S. 291-295 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Fuzziness is quite a different notion from probability. Probability describes the objective uncertainty obtained on the basis of a large number of observations. Fuzziness describes the uncertainity that has a subjective meaning. Fuzzy notions describe the degrees of possession of a given property. The popularity of fuzzy set theory in solving control problems results from its ability to treat some situations which are difficult to deal with by the classical control theory. Fuzzy sets are used to control ill-defined, complex, non-linear systems. There are two aspects of this phenomenon. The first aspect concerns the descriptive ability of fuzzy sets. The second important feature is the applicability of fuzzy sets to work with incomplete, contradictory and subjective information. Fuzzy set theory is becoming increasingly important tool in the new fast developing disciplines of artificial intelligence: expert systems and neural networks. It creates completely new opportunities for the application of fuzzy sets in chemical engineering.
    Additional Material: 6 Ill.
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  • 110
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 16 (1993), S. 318-324 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Heat accumulation in batch reactors may eventually lead to a temperature runaway. Critical values of process parameters were used to investigate process safety. Parameter sensitivity is discussed for a wide range of operating conditions. Two criteria for safe operation are presented, based on critical values of process parameters.
    Additional Material: 8 Ill.
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  • 111
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 16 (1993), S. 341-346 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: High temperature oxidation of some metals contained in special alloys has been studied. Defect models for pure an doped CoO and pure NiO were developed and fitted to electrical conductivity data. The models involve different kinds of theoretically possible complex defects with different numbers of vacancies and interstitials forming a cluster. Equilibrium constants for defects formation have been estimated using an algorithm based on the constrained variation method that allows fitting of data to implicit models involving errors in all the measured variables. Results indicate the presence of a significant concentration of complex defects in CoO at high temperatures, while confirming the rather small concentration of these defects in NiO.
    Additional Material: 2 Ill.
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  • 112
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 16 (1993), S. 370-375 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This contribution presents the determination of liquid hold-up in gas/liquid two-phase countercurrent columns filled with random or structured packings. The equations resulting from the established physical relationships are varified against the values for liquid hold-up determined experimentally on 56 different column packings and 16 gas/liquid systems. The experimental and calculated results agree well, with only slight deviations. This also applies to the range between the loading and flooding points for two-phase countercurrent flow.
    Additional Material: 4 Ill.
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  • 113
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 16 (1993), S. 399-404 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A lattice-gas model is used for calculating the solubilities of light gases in heavy complex hydrocarbons. For waxes, the model gives a good prediction of the solubilities on using the molecular weight of the liquid to describe the solvent. For crude oils and coal-derived liquids, the prediction is of only modest quality. However, it does improve on using experimental Henry's constants.
    Additional Material: 4 Ill.
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  • 114
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The practical performances of single and multi-angle photon correlation spectroscopy (PCS) for resolving bimodal distributions of industrial poly (methyl methacrylate) samples was investigated in a comparative study by several users affiliated to academic and industrial groups and by two suppliers of commercial equipment. The results for the harmonic intensity averaged diameters obtained by cumulants analysis reported by the different laboratories are in agreement, in addition to the results for the normalized second cumulants. The uncertainty on the latter quantities is large, however. For the bimodal samples with two populations with average diameters in a ratio of about 2.5 : 1, not all users were able to resolve the distribution in its components by single-angle PCS. Some slight improvement was obtained by multi-angle PCS. Other indirect techniques (polarization intensity differential scattering, static light scattering data and disc photosedimentometer) appeared to be superior for resolving the bimodal distributions.
    Additional Material: 10 Ill.
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  • 115
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 10 (1993), S. 156-156 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 116
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 10 (1993), S. 138-145 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Essentially the laser two-focus (L2F) and laser Doppler anemometer (LDA) are time-of-flight anemometers. The velocity of particles in the micrometre range is determined within the limits of an optically fixed measurement distance. For this only one optoelectronic receiver for the detection of the scattered light is required [1, 2]. With an arrangement of two receiving optics, positioned under an off-axis angle ϕ and an elevation angle ± ψ to the optical axis of the measurement system, a resolution of three-dimensional structures can be achieved and with regard to spherical particles it is possible to determine the dimensions by means of the temporal or phase shift of the signals in the receiving optics. A particle size-dependent distance inside the measurement volume can be fixed, which has to be passed in order to change the signal from one receiving optics to the other. An LDA with an arrangement of two receiving optics for particle sizing is known as a phase Doppler anemometer (PDA); an L2F designed with two receiving optics can be termed a pulse-displacement two-focus anemometer (P2F). The physical analysis of the two methods with respect to a temporal signal displacement in the receivers yielded new results.
    Additional Material: 11 Ill.
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  • 117
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 10 (1993), S. 229-233 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Several solid-liquid suspensions containing submicron particles at moderate to high concentrations (5 to 50 volume percent) are encountered in industrial slurry processing. Measurements of ultrasonic attenuation spectra are used in a newly developed AcoustoPhor particle analysis system to get particle size distributions of such colloidal suspensions. This paper deals with the performance evaluation of the AcoustoPhor system. The automated ultrasonic spectrometer component of the AcoustoPhor system was tested using a reference silicone liquid for its accuracy and precision. The particle size distribution (PSD) estimation capabilities were evaluated using a set of well-dispersed slurries covering a wide range of particle concentrations. Sensitivity to process variations was evaluated in field tests at a pigment manufacturing plant. The AcoustoPhor system appears to be capable of providing reliable PSD data for inorganic pigment slurries with particle diameters ranging from 0.01 to 100 micrometers at particle concentrations as high as 50 volume percent.
    Additional Material: 6 Ill.
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  • 118
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 10 (1993), S. 222-225 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Dry test sieving results given by woven wire cloths with a square mesh and by round electroformed apertures were compared using sands of various origin. The difference has been found to be constant and independent of substance and quantile. The quantile obtained on a square mesh was converted into the corresponding quantile on an electroformed sheet of the same nominal aperture by multiplication by a constant factor of 1.21 ± 0.04.
    Additional Material: 2 Ill.
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  • 119
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 10 (1993), S. 201-211 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The transmission and diffraction of radiation through dense monolayers of monodisperse opaque spheres were studied for the Fraunhofer domain. Theoretical considerations, numerical calculations and experiments on ultrasonic transmission and on laser light transmission and diffraction yielded corresponding results. Complementary studies included the cases of sterically non-interacting particles (by numerical simulation) and of small particle size parameters (by ultrasonic extinction). Transmission was found to be, in general, a non-linear function of the monolayer density. Secondary effects on the transmission can be attributed to the effect of the monolayer structure (characterized by the pair correlation function) on the angular distribution of diffracted intensity. The results were found to be in accordance with experimental results on extinction in three-dimensional systems.
    Additional Material: 18 Ill.
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  • 120
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 10 (1993), S. 228-228 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 121
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 10 (1993), S. 275-278 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An investigation is presented concerning the ability of neural nets to classify particles using contour data. Different nets were trained to classify limestone, quartz and coffee particles by their outer boundaries. The contour lines of the analysed particles were similar and differed only in a complex way. A new method of interpreting the Fourier coefficients is shown, which might lead to a possibility of defining particle shape classes by examples. Information is given concerning the selection and design of the appropriate neural net, e.g. back-propagation, and self-organizing maps. In addition, a possibility of interpreting the trained neural nets is demonstrated.
    Additional Material: 5 Ill.
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  • 122
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    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 10 (1993), S. 308-312 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper describes preliminary work carried out on the applicability of fractal geometry for differentiating between wear and contaminant particles found in mining machinery lubrication systems.Coal dust, stone dust and roadstone dust from a granite quarry were used as the contaminant particles and the particles from two crushers, which had failed whilst in service, were used to provide the wear particles.Two differing populations appeared with the wear particles having higher boundary fractals than the contaminant, but tending to spread across a wide range of fractal numbers, whereas the contaminants were lower and fairly tightly grouped.The underfractal distributions of the two populations of particles, generate straight lines when plotted on Gaussian probability paper. This leads to the probability of being able to predict the distribution of particles, in fractal terms between wear and contaminant particles.
    Additional Material: 9 Ill.
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  • 123
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    Electronic Resource
    Weinheim : Wiley-Blackwell
    Particle and Particle Systems Characterization 10 (1993), S. 321-331 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A combined theoretical and experimental study has been conducted to evaluate the effectiveness of using large, hollow micro-balloons as LDV seed particles. The study has focused on the ability of phase Doppler systems to size hollow microballoons, the ability of large micro-balloons to respond to high frequency spatial and temporal flow field variations, and the overall advantages and disadvantages of using large microballoons instead of conventional LDV seed particles, such as very small water droplets or polystyrene latex (PSL) particles. This paper discusses the development of a theoretical phase Doppler response model for stratified spheres, the experimental facility, and the theoretical and experimental results.
    Additional Material: 26 Ill.
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  • 124
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: With progress in the advancement of measuring techniques and information processing, it is increasingly possible to analyse even complex signals with on-line methods. After fundamental considerations concerning the evaluation of such signals, digital Fourier spectroscopy is explained as an example of a new development. With this method the image of a particle collection will be transformed by the Fourier transformation. Methods such as used with laser diffraction spectrometry are applied to calculate back to the particle size distribution. After a description of the principles of the procedure, its application is demonstrated by different examples. It can be shown that digital Fourier spectroscopy is superior to conventional image analysis methods especially if the particle density in the image is high and the particles overlap. In a further development step it should be possible to determine the particle size distribution of the bulk from an image of its surface.
    Additional Material: 14 Ill.
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  • 125
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    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 16 (1993), S. 125-129 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Any process engineering scale-up procedure is a source of uncertainties and risk. This paper presents an algorithm that completely eliminates the traditional scale-up procedure using a direct application of “large-scale” industrial knowledge. The large-scale knowledge base is represented by fuzzy descriptions of 489 existing suspension mixing tanks. A fuzzy reasoning algorithm is used to answer different queries. Therefore, a flexible user-computer dialogue is possible. A practical example is given in full detail.
    Additional Material: 1 Ill.
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  • 126
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    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 16 (1993), S. 172-179 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Operating characteristics of an agitator in a tube are necessary for the calculation of its pumping capacity and power consumption in a given configuration. General dimensionless equations for pumping and power characteristics are presented which were derived by inspection analysis of basic equations. Experimental procedure for the determination of these characteristics is put forward. This procedure is based on the measurement of flow rate or pressure rise and power consumption for an agitator in a draft tube, calandria or closed tube. The measurements and their evaluation are illustrated on the example of a three-blade screw agitator.
    Additional Material: 13 Ill.
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  • 127
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    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 16 (1993), S. 191-199 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A mathematical model of dehydroisomerization of methylcyclopentane in presence of bifunctional catalysts under industrial operating conditions is presented. The model consists of six differential equations. The rate constants are expressed as polynomial functions of the catalyst blend, and coefficients of these polynomials were determined from numerous measurements, taken along the axis of a tubular reactor. The resulting polynomial coefficients led to reaction rate constants which yielded results close to the actual process.
    Additional Material: 5 Ill.
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  • 128
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Countercurrent-flow columns are widely used in production processes in the chemical industry and their application in ecological engineering is of increasing importance. A theoretical model is presented here that allows mass transfer to be described in terms of packing geometry and physical properties which influence the gas-liquid or vapour-liquid systems in absorption, desorption and rectification columns. The relationships derived from the model can be applied to all countercurrent-flow columns, regardless of whether the packing has been dumped at random or arranged in a geometric pattern.
    Additional Material: 4 Ill.
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  • 129
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    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 16 (1993), S. 26-34 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A disturbance control scheme for the concentration control of differential recycle reactors is developed which is based on the learning feedforward control strategy. Steady-state decoupling eliminates interactions between the closed loops of this non-linear, multivariable control system, thereby significantly improving the response to disturbances. Since the process model is iteratively updated, the control strategy can be regarded as a model identification adaptive control. Simulation experiments show the performance of the overall control concept.
    Additional Material: 8 Ill.
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  • 130
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    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 16 (1993), S. 363-369 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Pellet heat transfer coefficients in a packed bed have been obtained, both for specific individual pellets and for the entire bed. They are referred to as local and global values, respectively. It appears that the local values are scattered around the global value. This is due to the heat transfer coefficient of individual pellets being statistically distributed, as a result of the randomnes of the packing. At low Reynolds numbers, both global and local values fall well below Nu = 2, which is the lower limit for a single sphere in absence of convection. In the literature, this behaviour has been attributed i.a. to axial dispersion and fluid maldistribution. However, these phenomena cannot explain why the same behaviour is observed in slurries. The fact that the local values fall below Nu = 2 would suggest that neither of these explanations is valid for packed beds.
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  • 131
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    Chemical Engineering & Technology - CET 16 (1993), S. 395-398 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Vibrating capillary apparatus (VCA) was designed and constructed for the preparation of sulphamethoxazole (SMZ) microcapsules using gelatin as a coating polymer. The microcapsules were characterized by physico-chemical methods. The apparent diffusion coefficient Da and diffusion rate constant KBL of the drug were measured at pH of 1.2 and 7.2. Better controlled release products were obtained in the VCA.
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  • 132
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    Chemical Engineering & Technology - CET 16 (1993), S. 429-432 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The mechanism of free-radical chain reaction of tetrachloroethene photochlorination in a homogeneous liquid system is discussed and three kinetic models based on the reaction mechanism are presented. The parameters of these three models have been evaluated on the basis of experimental data presented in [1].
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  • 133
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    Chemical Engineering & Technology - CET 16 (1993) 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 134
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    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Distributions of pressure and velocity in the main channels were studied in a radial flow cold model of a moving bed reactor, 500 mm in diameter, in four different gas flow modes, inward Z gas flow, inward Π gas flow, outward Z gas flow, outward Π gas flow. It has been found that, in outward Π gas flow mode, the axial non-uniformity of the gas is at a minimum. The following correlations are proposed for the momentum recovery factors Ka and Kb: Ka = 0.684 + 0.0128 (du/dx)/u, Kb = 1.135 + 0.0158 (du/dx)/u. Pressure distributions in the main channels can be accurately predicted using Ka and Kb.
    Additional Material: 9 Ill.
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  • 135
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    Chemical Engineering & Technology - CET 16 (1993), S. 405-412 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Enzymes are of growing interest to the chemical and pharmaceutical industries as highly specific biocatalysts. An obstacle to a large-scale application of such proteins is the expenditure on recovery operations which can amount up to 80% of the total production costs. Therefore, it is necessary to investigate in detail the individual stages of downstream processing in order to obtain high product yields without loss of quality. After a survey of recovery operations and information on some special features of proteins which are relevant to downstream processing, this paper deals with the methods of precipitation, chromatography and foam fractionation. Several results obtained with a real, multicomponent system, namely the supernatant of lipase fermentation, are presented and compared with one another.
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  • 136
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    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Acid catalyzed cracking and bifunctional cracking of n-heptane were investigated on HZSM-5 catalysts. At a reaction temperature of 543 K, the cracking on metal-free zeolite was found to be directly proportional to hydrogen partial pressure. Hydrogen influences the hydrogenation of product olefins and carbon deposits and therefore enhances the overall activity. Under the same conditions, in the presence of platinum, the hydrocracking rate reaches a maximum with increasing hydrogen partial pressure. The reaction can be formally described by a Langmuir Hinshewood mechanism: hydrogen is adsorbed on Pt in competition with hydrocarbons. The maximum reaction rate depends on a favourable ratio of the two adsorbed reactants. The energy of activation of hydrocracking was over 100 kJ/mol higher than that of acid cracking.
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  • 137
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    Particle and Particle Systems Characterization 10 (1993), S. 56-61 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An aerosol measurement instrument is presented which allows for the simultaneous measurement of the size distribution, number concentration and velocities of particles. A commercial optical particle counter (OPC) was modified in terms of optics and signal evaluation to provide the required measurement information. The design of this instrument allows the definition of a cubic measuring volume by purely optical means. This is achieved by an aperture/lens system which projects a sharply defined light beam into a stream of aerosol flow. Light scattered from single particles at average angles of 90° is collected by two opposite receiver units, each projecting light on to a separate photomultiplier. The intensity of the scattered light with this instrument is found to be an unambiguous function of the particle size. The total number of particles detected per unit time results in the particle flux. The particle velocity can be calculated, in principle, through the correlation of the signal length and the optical length of the measuring volume, provided that the particles have a straight trajectory through the measuring volume and the measuring volume length in the mean flow direction is well defined. The absence of sharpness in real optical projections effects a border zone of definite length, in which the illumination declines to zero. This leads, together with the low-pass filtering of the particle signals, to an increase in the length of the signal slopes, causing some difficulties in the determination of the signal length. A digital signal evaluation technique was developed that renders possible the clear differentiation between the slope and the kernel region of the signal. The latter represents the motion of particles through the completely illuminated region, which can be a more accurate parameter to define the signal length. In addition to the signal length determination, a cross-correlation technique was tested for its potential to obtain particle velocity. the instrument has two interlaced measuring volumes of nearly the same size, which are shifted for this special application in the main flow direction by 20 μm. The phase difference between the signals from the two photomultipliers, together with the optical distance, yields the particle velocity.
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  • 138
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    Particle and Particle Systems Characterization 10 (1993), S. 74-78 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In jet agglomeration plants, powders are agglomerated to obtain good instant properties. The free-falling initial material is wetted in a spray cone by droplets or in a steam jet by condensation at the particle surface. In a subsequent region of high particle concentration, collision between particles occurs and agglomerates form, if the forces of adhesion are strong enough. A commercial measurement device, working according to the principle of Fraunhofer diffraction, was modified for in-line application. It was used to measure particle size distributions and concentrations of solid particles and droplets in jets. A model is presented to calculate local particle sizes by means of mass balances from integral measurements over large volumes. The results of in-line particle size and agglomerate size analyses show the practical importance of dry agglomeration during transport and lead to a better understanding of the subsequent wet agglomeration process.
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  • 139
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    Particle and Particle Systems Characterization 10 (1993), S. 92-94 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 140
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    Particle and Particle Systems Characterization 10 (1993) 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 141
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    Particle and Particle Systems Characterization 10 (1993), S. 99-110 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Fractal Geometry developed in 1977 by B. Mandelbrot describes the structure of rugged systems by extending the concepts of classical dimensional analysis to include a fractional addendum to the topological dimension of a system in order to describe the space filling properties of the rugged system. In the 15 years since the publication of Mandelbrot's book describing his seminal ideas fractal geometry has found many applications in fineparticle science and technology. This body of applied knowledge is now known as Applied Fractal Geometry. The purpose of this review is to focus on the various branches of applied fractal geometry of interest to the fineparticle specialist in a systematic manner. The first part is concerned with ruggedness of fineparticle boundaries, the structure of simple porous bodies, fragmentation and powder production, the assessment of the properties of such materials as paper, and the characterization of rough surfaces. The second part will explore the use of fractal dimensions to describe mixing operations, composite bodies, such as synthetic bones, and paint films.
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  • 142
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    Particle and Particle Systems Characterization 10 (1993), S. 158-158 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 143
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    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The drawback of conventional sedimentation methods, mainly their extremely long sedimentation time for small particles, can be overcome in two phase flow systems. In this paper several principles which permit the rapid determination of settling rate distributions are discussed. Settling rate distributions can be determined from the accelerated particle movement in a flow of constant velocity at low and high solids concentrations. Another system uses accelerated flow at low solids concentrations. The best utilisation of settling rate applications have socalled cross flow systems as set up in a stagnation point flow, in a flow round a bend, or in the decelerated particle movement perpendicular to a flow of constant velocity.
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  • 144
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    Particle and Particle Systems Characterization 10 (1993), S. 191-200 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Fractal dimensions in data space are being used to describe fineparticle systems. The relationship between these new parametric descriptions of fineparticle systems and a more classical description of such system using the classical hyperbolic function is discussed. It is shown that fractal dimensions in data space are useful for presenting data for such diverse systems as pigment clusters in composite materials, avalanching powder systems, ballistically fractured material and pore size distribution of porous bodies as determined by mercury intrusion methods. In particular new data is presented on the usefulness of fractal dimensions for describing the flow properties of powders with and without silica flow agents.
    Additional Material: 12 Ill.
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  • 145
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The effect of the geometry of the fiber ends on the scattered intensities is considered. A new modification of the Rayleighdebye-Gans (RDG) approximate theory, the Mie Substitution Theory (MST) theory, is introduced. The Boundary Value Method (BVM) for the infinite cylinder, the RDG theory, the Shifrin (SFR) modification of the RDG theory and the MST theory are compared with the EBCM theory for various values of fiber diameter, length, refractive index and for various fiber orientations, including random orientation. Scattering from suspensions of fibers, typical of UICC crocidolite and anthophyllite asbestos fibers, is considered using the BVM, the MST and the RDG theories when the fibers are assumed to be aligned and the MST and the RDG theories when the fibers are assumed to be randomly oriented.
    Additional Material: 8 Ill.
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  • 146
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    Particle and Particle Systems Characterization 10 (1993) 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 147
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    Particle and Particle Systems Characterization 10 (1993), S. 347-352 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Pellets of sintered Al2O3 of approximately 3 mm diameter and length were broken in the Brazilian mode and the distribution of strength obtained. It was found that there was also a distribution of Young's modulus E. Hertzian theory implies that the maximum impact force of a pellet fired against a rigid target would depend on E. However, since the pellets can strike in different geometries there is a distribution of impact force for a fixed E. Comparison of theory with data obtained with a force-time transducer as the target showed that the major variation of maximum recorded force could be assigned to the variation of E. The median of the maximum recorded force varied with velocity as v6/5, implying that the pellets behaved approximately as impacting spheres. An attempt was made to predict the probability of breakage in one impact from convoluting the distribution of impact force with the strength distribution from the Brazilian test converted to the equivalent strength distribution expected for impacting spheres. This gave the correct order of magnitude but did not accurately predict the experimental values.
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  • 148
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    Particle and Particle Systems Characterization 10 (1993), S. 353-356 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Investigations on the size control of pneumatically conveyed coarse particles were carried out using a microphone which detects the structure-borne sound caused by the impact of the particles on the pipe wall. Modes of eigenvibrations of the pipes are excited up to a maximum frequency, which decreases with increasing particle size. In an assembly of different sized particles, the lower frequencies are more stimulated as the fraction of larger particles increases. Changes in the particle size distribution are detected by analysing the intensities of the vibration modes which are set up in the walls of the tube by particle impact. One application is the monitoring of the upper range of a particle size distribution.
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  • 149
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    Particle and Particle Systems Characterization 10 (1993), S. 364-365 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 150
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    Particle and Particle Systems Characterization 10 (1993), S. 300-300 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
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  • 151
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    Particle and Particle Systems Characterization 10 (1993), S. 301-307 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The apparent fractal dimension of normalized rugged compressive force-deformation curves of two types of brittle particulates was determined using the blanket algorithm. Although the shape of the original force-deformation relationships of the individual specimens was irreproducible, the apparent fractal dimension of the normalized data was fairly constant and characteristic of the material. The applicability of the algorithm and the validity of the results were tested with computer simulated relationships generated with a set of Weierstrass functions whose fractal dimension was known a-priori. It is demonstrated that as long as the resolution along the two axes is the same, the fractal dimension so calculated provides an absolute rather than a relative measure of the relationship's jaggedness.
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  • 152
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    Particle and Particle Systems Characterization 10 (1993), S. 313-320 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The development and change of surface ruggedness in chars was studied at conditions typical in a pulverized coal furnace. The fractal dimension, a measure of surface ruggedness, of chars was measured using physisorption techniques. By adjusting the temperature encountered (1173 to 1773 K) and residence time (0.1 to 1.5 s) of the synthetic coal (sized to 46-106 μm diameter), chars at different stages of combustion were prepared in a laminar flow (drop-tube) furnace. The particles were quickly cooled and quenched in an inert atmosphere. The samples were examined using a scanning electron microprobe, and their fractal dimensions were determined using gas physisorption. The adsorption data were used to test if the char surface was fractal on a molecular scale, to determine the fractal dimension, and to quantify changes in the fractal dimension during combustion. The fractal dimension of the unburned synthetic coal was approximately 2. The fractal dimension increased as high as 2.85 as the carbon matrix burned away and exposed mineral moieties. However, as combustion continued the carbon burned completely away leaving a mineral fly ash particle with a fractal dimension as low as 2.47.
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  • 153
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    Particle and Particle Systems Characterization 10 (1993), S. 332-338 
    ISSN: 0934-0866
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The effects of the particle trajectories on phase Doppler measurements were explored numerically using generalized Lorenz-Mie theory. Computations were performed for a commercial phase Doppler system and various schemes for elimination of the trajectory effects were examined. It is shown that these effects cannot be completely suppressed if the ratio of the two measured phase shifts from a single receiving unit is used to validate the measurements. On the other hand, the errors due to particle trajectories can be eliminated satisfactorily by employing an additional receiving unit, which allows one to detect the asymmetry of the scattered light pattern due to displacement of the particle trajectory from the centre of the measuring volume. A preliminary experimental evaluation of this method is presented and discussed.
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  • 154
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    International Journal of Quantum Chemistry 47 (1993), S. 405-423 
    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 numerical method is developed to obtain sequences of functions converging to the eigenfunctions of a Schrödinger operator in the Hilbert space L2(-∞, ∞), whose norm is used to introduce the criterion of convergence in the norm and we show that it guarantees the accurate computation of expected values of a symmetric operator. The method consists in solving the Dirichlet problem associated to the eigenvalue problem in the interval [-n, n] by the Ritz method, whose convergence to both eigenvalues and eigenfunctions is guaranteed by the compactness criterion. Using the asymptotic perturbation theory in L2(-∞, ∞), we prove the convergence of both eigenvalues and eigenfunctions of the Dirichlet problem to those of the unbounded system when the interval [-n, n] is expanded. The method is applied to the harmonic oscillator, the Mitra potential, as well as to the potential V(r) = r and the Coulomb and Yukawa potentials; in each case, the convergence of eigenvalues and eigenfunctions is shown. © 1993 John Wiley & Sons, Inc.
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  • 155
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    International Journal of Quantum Chemistry 47 (1993), S. 425-435 
    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 relativistic theory for the nuclear spin-spin coupling tensor within the polarization propagator approach using the particle-hole Dirac-Coulomb-Breit Hamiltonian and the full four-component wave function. We give explicit expressions for the coupling tensor in the random-phase approximation, neglecting the Breit interaction. A purely relativistic perturbative electron-nuclear Hamiltonian is used and it is shown how the single relativistic contribution to the coupling tensor reduces to Ramsey's three second-order terms (Fermi contact, spin-dipole, and paramagnetic spin-orbit) in the nonrelativistic limit. The principal propagator becomes complex and the leading property integrals mix atomic orbitals of different parity. The well-known propagator expressions for the coupling tensor in the nonrelativistic limit is obtained neglecting terms of the order c-n (n ≥ 1). © 1993 John Wiley & Sons, Inc.
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  • 156
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    International Journal of Quantum Chemistry 47 (1993), S. 437-448 
    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 this paper, we present a symmetrical and adiabatic reaction path for hydrogen transfer from methane by methyl by an ab initio method using the 6-31G** basis set with the MP2 corrections for UHF/6-31G** optimized geometries. The theoretical barrier is fitted with the symmetric Eckart function. We, then, take thermal averages of the rate constant (k) considering the discrete nature of the C-H oscillators and the continuous character of the various low-frequency modes of the composite system. Finally, we present a linear relation between log k and temperature. It is shown that this relation gives a good description of the kinetic results of both thermal and photochemical H-transfer reactions in the region of low temperatures. © 1993 John Wiley & Sons, Inc.
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  • 157
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    International Journal of Quantum Chemistry 48 (1993) 
    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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  • 158
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    International Journal of Quantum Chemistry 48 (1993), S. 151-159 
    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 regime of the molecular-orbital theory, a new approach beyond of the Hartree-Fock approximations is proposed. By an appropriate introduction of the quantum fluctuation into the molecular electronic ground state, the Hartree-Fock equations plus Gaussian fluctuation are obtained. Basically, the procedure proposed consists of an adequate utilization of the Gaussian approximation of the Ising model on a lattice (K.G. Wilson et al., Phys. Rep. C 12, 76 (1974)). It leads to an effective nonlinear Hamiltonian for the molecule for studying nonlinear problems in the molecular electronic structure. © 1993 John Wiley & Sons, Inc.
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  • 159
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    International Journal of Quantum Chemistry 48 (1993), S. 185-200 
    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 review and update a recently developed one-particle theory of N-electron systems that bears a certain resemblance to density functional (DF) theory and has been put forward by the present author. As distinct from DF theory, the new one-particle scheme applies to any N-electron eigenstate including the ground state. For the latter case, the key equations become identical to those familiar from the Kohn-Sham version of DF theory. The theory given here constitutes the basis for a consistent treatment of normal conductivity and superconductivity, which will be discussed in Part II of this article. © 1993 John Wiley & Sons, Inc.
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  • 160
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    International Journal of Quantum Chemistry 48 (1993), S. 161-183 
    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: An explicitly connected commutator expansion for the average value of an observable in the coupled-cluster theory is derived. Specifically, it is shown that the expectation value of an operator for the state Ψ, related to the Fermi vacuum Φ by the exponential Ansatz ψ = eT Φ, is expressed as a finite commutator series containing the cluster operator T and an auxiliary operator S, defined by a linear equation involving again a finite commutator series in T. The above result is applied to derive the explicitly connected commutator form of the order-by-order many-body perturbation theory (MBPT) expansion for the expectation values and density matrices. We also show how the commutator expansion derived by us can be used as a basis for size-extensive infinite-order summation techniques. An operator technique of eliminating the nonlocal, “off-energy shell” denominators from MBPT expressions is proposed and applied to obtain compact commutator formulas for the expectation values of one- and two-electron operators through the fourth and third order, respectively, and for the correlation energy through the fifth order of perturbation theory. © 1993 John Wiley & Sons, Inc.
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  • 161
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    International Journal of Quantum Chemistry 48 (1993), S. 201-209 
    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 show that a consistent N-electron theory of a solid can within the Born-Oppenheimer (BO) approximation lead only to normal conductivity or to an insulating state. If one leaves the BO approximation by turning on electron-phonon interaction, one can establish a lower-lying new ground state that has the characteristic properties of the Bardeen-Cooper-Schrieffer (BSC) ground state. We demonstrate that an (N + Nn)-particle Schrödinger equation that describes the motion of N electrons and Nn nuclei of a solid can lead only to phonon-induced superconductivity. © 1993 John Wiley & Sons, Inc.
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  • 162
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
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  • 163
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    International Journal of Quantum Chemistry 48 (1993), S. 219-224 
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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 energy levels in sodium atoms with quarks attached to the nucleus are obtained using the configuration interaction method. It is found that the calculated 3p (2P) → 3s (2S) electronic transition in the Na-1/3 quark-atom system is in agreement with that predicted by extrapolation of experimental data. Also, ionization potentials of fractionally charged sodium atoms are discussed. © 1993 John Wiley & Sons, Inc.
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  • 164
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    International Journal of Quantum Chemistry 48 (1993), S. 225-232 
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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: A survey is given of the resemblance theorems associated with various types of orthonormalization procedures having different kinds of symmetry properties appearing in the current literature. It is shown that the proofs for the minimum properties are closely connected with the fact that the Hilbert-Schmidt norm of an operator is always nonnegative and has the lowest value equal to zero. © 1993 John Wiley & Sons, Inc.
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  • 165
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    International Journal of Quantum Chemistry 48 (1993), S. 233-238 
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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: Electric-field maps of certain anions and cations of adenine and guanine have been studied. The results are compared with those of neutral adenine and guanine. In all cases, the geometries were fully optimized using the MNDO molecular orbital method and the fields were computed using Mulliken charges. Reactivities and hydrogen-bonding pattern predicted by electric fields, including those of cations, are in satisfactory agreement with experiment. © 1993 John Wiley & Sons, Inc.
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  • 166
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    International Journal of Quantum Chemistry 48 (1993), S. 239-247 
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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, a general method is presented that allows the derivation of the expansion coefficients of the product of two orthogonal functions provided the generating function is known. For the three classical orthogonal polynomials, the Laguerre, the Hermite, and the Legendre polynomials, the coefficients blmn with φmφn = ∑lblmnφl are derived. © 1993 John Wiley & Sons, Inc.
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  • 167
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    International Journal of Quantum Chemistry 48 (1993), S. 211-218 
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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: When second-order Jahn-Teller couplings become strong along “streambeds” on potential energy surfaces, instability reflected in negative curvature along a symmetry-lowering distortion coordinate can take place. The point where such negative curvature sets in is usually not a transition state because the gradient of the potential is usually large there. In this paper, it is demonstrated how to use the local energy, local gradient, local Hessian, and knowledge of how quickly the curvature for the symmetry-breaking mode evolves along the streambed (i.e., the derivative of this curvature) to predict how far to move in the symmetry-breaking mode in search of the desired transition state. It is shown that the Hessian matrix evaluated at the symmetry-broken geometry suggested by this analysis has only one negative eigenvalue. Because this analysis is based on a local approximation to the potential, its predictions are, of course, approximate. As such, they only “suggest” the proper direction and magnitude that one should “step” to move toward a transition state. © 1993 John Wiley & Sons, Inc.
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  • 168
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    International Journal of Quantum Chemistry 48 (1993), S. 249-256 
    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 electronegativity perturbation theory up to the fourth order has been used to study the preferred isomer of linear triatomic molecules. Systems with 10-16 valence-electron systems are discussed and our results are in good agreement with the experiment. The only exception is the isomers of PNO. The usefulness of the perturbation theory is briefly discussed. © 1993 John Wiley & Sons, Inc.
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  • 169
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    International Journal of Quantum Chemistry 48 (1993), S. 257-265 
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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: Recurrence relations are derived for the evaluation of two-electron repulsion integrals (ERIs) over Hermite and spherical Gaussian functions. Through such relations, a generic ERI or ERI derivative may be reduced to “basic” integrals, i.e., true and auxiliary integrals involving only zero angular momentum functions. Extensive use is made of differential operators, in particular, of the spherical tensor gradient Ylm(∇). Spherical Gaussians, being nonseparable in the x, y, and z coordinates, were not included in previous formulations. The advantages of using spherical Gaussians instead of Cartesian or Hermite Gaussians are briefly discussed. © 1993 John Wiley & Sons, Inc.
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  • 170
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    International Journal of Quantum Chemistry 48 (1993), S. 267-276 
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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 chain-length dependencies of 2Ag and 1Bu excitation energies as well as their unexpected inversion observed experimentally in trans-polyenes have so far been explained satisfactorily only in terms of configuration interactions within the standard Pariser-Parr-Pople (PPP) parametrization scheme with at least double excitations involving prohibitively large computational labor for long polyenes. A simpler calculation allowing nonzero differential overlap and employing restricted (first-order) single-excitation configuration interaction with chain-length-dependent screened potential is shown to provide an adequate alternative for the studies of those basic spectroscopic features of polyene excited states. The screening factor is parametrized in accordance with the chain-length-dependent behavior of the electrical polarizabilities of polyenes derived within the standard PPP approximation scheme. © 1993 John Wiley & Sons, Inc.
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  • 171
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    International Journal of Quantum Chemistry 45 (1993), S. 225-225 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
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    Topics: Chemistry and Pharmacology
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  • 172
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    International Journal of Quantum Chemistry 45 (1993), S. 189-207 
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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 atomic statement of the principle of stationary action determines the theorems that establish the mechanics of an atom in a molecule. The atomic torque, power, and current theorems are derived. They, along with the atomic force, virial, and continuity theorems, provide a complete description of the behavior of matter at the atomic level, including the effects of electric and magnetic fields. The atomic power theorem, for example, enables one to determine the atomic or molecular source of the creation and dissipation of power in combustion or in an explosion. An atom in a molecule is an open system and an atomic equation of motion for an observable contains a component corresponding to the flux in its current density through the atomic surface. The differential form of each theorem yields an equation of motion for the corresponding property density in which the same surface flux appears as a divergence of the current density. The differential and integrated atomic theorems complement those for the total system, enabling one to relate the property to its atomic components and ultimately to a local contribution from each element in real space. © 1993 John Wiley & Sons, Inc.
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  • 173
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  • 174
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    International Journal of Quantum Chemistry 45 (1993), S. 235-250 
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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 1940, Kramers derived an expression for the rate constant of chemical reactions in viscous media. In this theory, chemical reactions are modeled as Brownian processes in the presence of potential barriers. The derivation of the rate constant is based on the solution of the Smoluchowski equation, a Fokker-Planck-type equation in position space. Kramers' theory has been confirmed for reactions in systems ranging from nuclear processes to biochemical problems. The reaction rate can be obtained from the diffusion currents appearing in the Smoluchowski equation. A Smoluchowski-type equation in position space, similar to the one applied by Kramers, has been used to find a nonlinear Schrödinger equation (NLSE) for dissipative, frictionally damped systems, taking into account wave-particle duality. For several potentials, the NLSE can be solved exactly, and analytic expressions for the currents, appearing in the Smoluchowski equation and necessary to determine the rate constants, can be obtained. These currents are not only stationary, but can also be time-dependent. It will be shown that, essentially, the determination of the time-dependence of the currents can be reduced to the solution of Newton-type equations of motion. © 1993 John Wiley & Sons, Inc.
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  • 175
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    International Journal of Quantum Chemistry 45 (1993), S. 263-294 
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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: This paper considers a Husimi representation of quantum mechanics in which the (stationary) state of a system or ensemble is described by a Husimi function and an observable is described by a phase space function or distribution such that the expectation value of the observable is given by an integral over phase space of the product of that function or distribution and the Husimi function. The density matrix, Wigner function, and Husimi function are considered to be alternative ways of describing the state of a system or ensemble, and methods of recovering the Wigner function or density matrix from the Husimi function are discussed. The classical limits of the Wigner and Husimi functions and of the relationship between them are considered. © 1993 John Wiley & Sons, Inc.
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  • 176
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  • 177
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    International Journal of Quantum Chemistry 45 (1993), S. 333-347 
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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 nonlocal weighted density approximation (WDA) to the exchange and kinetic energy functionals of many-electron systems proposed several years ago by Alonso and Girifalco in the context of density functional theory is used to compute, within the framework of the spherical jellium model, the ground-state electronic density, chemical potential, and total energy of neutral and negatively and positively charged sodium clusters containing up to N = 800 atoms. From these calculations, we study the behavior of the total energies per atom, chemical potentials, ionization potentials, I(N), and electron affinities, A(N). These results are compared with analogous calculations using the well-known Thomas-Fermi-Weizsäcker-Dirac (TFWD) approximation for the kinetic (TFW) and exchange (D) energy functionals. Calculations including the local density approximation (LDA) to the correlation energy in both WDA and TFWD functionals are also presented. © 1993 John Wiley & Sons, Inc.
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  • 178
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    International Journal of Quantum Chemistry 45 (1993), S. 363-383 
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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: We derived the necessary conditions to which the vector coupling coefficients (VCC) amn and bmn, describing atomic L, S-multiplets of pMdN and dNs1 configurations (1 ≤ N ≤ 9, 1 ≤ M ≤ 5), should satisfy. It is shown that for two-open-shell systems under consideration the unknown VCC should satisfy not only usual restrictions resulting from the spheric symmetry, but also some additional equation introduced in the present paper in the form of a postulate. VCC obtained were used for the ab initio calculations (by the general SCF coupling operator method) of several transitionmetal atoms and ions with electronic configurations 3d14p1, 3p43d3, and 3p53d3. To check the presented theory, we carried out a detailed comparison between these results and analogous data, obtained by the atomic Roothaan-Hartree-Fock method [2]. © 1993 John Wiley & Sons, Inc.
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  • 179
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    International Journal of Quantum Chemistry 45 (1993), S. 385-390 
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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 Schrödinger equation for an atom or molecule is expressed in terms of hyperspherical coordinates. The eigenfunction is expanded in a series of orthonormal complete sets: Yλ,μ(Ω), eigenfunctions of generalized angular momentum scalar operator, and Lvn, generalized Laguerre polynomials. The recurrence relation of the expansion coefficients are derived and the eigenvalues can be obtained from the secular equation. © 1993 John Wiley & Sons, Inc.
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  • 180
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    Topics: Chemistry and Pharmacology
    Notes: We have calculated certain dynamic polarizabilities (for both real and imaginary frequencies) for H, He, and H2 and the dispersion-energy coefficients for long-range interactions between them. We have done so in a sum-over-states formalism with explicitly electron-correlated wave functions to describe the states. To be precise, we have determined the dipole (α1), quadrupole (α2), and octupole (α3) polarizabilities of H and He for real frequencies (ω) in a range between zero and the first electronic-transition frequency and for imaginary frequencies (iω) on a 32-point Gauss-Legendre grid running from zero to ħω = 20 Eh, and for H2, we have found the dipole (α), quadrupole (C), and dipole-octupole (E) polarizability tensors for the same real and imaginary frequencies. The dispersion-energy coefficients, obtained by combining the sum-over-states for-malism for the polarizabilities with analytic integration over ω, gave values of C6, C8, and C10 for the atom-atom systems; C06, C26, C08, C28, and C48 for the atom-diatom systems; and C6, C′6 and C″6 for the H2—H2 system. Nearly all the results are considered to be more reliable than those hitherto published and some have been obtained for the first time, e.g., C(iω), E(ω), and E(iω) for H2 and C08, C48, and C48 for the H—H2 system. © 1993 John Wiley & Sons, Inc.
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    International Journal of Quantum Chemistry 45 (1993), S. 403-403 
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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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  • 182
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  • 183
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    International Journal of Quantum Chemistry 45 (1993), S. 445-470 
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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, the efficient evaluation of the atomic integrals I =∫r1ar2br3cr23λr13μr12νe-αr1-βr2-γr3dτ with one or two factors rij-2 is described. These integrals are necessary for a lower-bound calculation for Li-like systems using the method of variance minimization or Temple's formula. © 1993 John Wiley & Sons, Inc.
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  • 184
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    International Journal of Quantum Chemistry 45 (1993), S. 409-431 
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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: Coupled-cluster equations for the calculation of the nonexpanded (fully damped) dispersion energy are derived. These equations are solved in the ring approximation using the Møller-Plesset expansion in terms of the fluctuation potentials WA and WB for the individual molecules. Numerical results of high-order perturbative calculations for the He, H2, LiH, H2O, and HF dimers are presented and compared with the converged results computed using the same basis sets. It is found that the convergence of the Møller-Plesset expansion of the dispersion energy in the ring approximation is very fast. The padé approximants still accelerate this already good convergence. For all complexes studied in this paper, the sum of the corrections through the second-order in WA + WB reproduces over 99% of the converged value. The sum of third- and higher-order corrections in the ring approximation is found to be one or two orders of magnitude smaller than the sum of second-order terms not included in the ring approximation and, therefore, may be safely neglected. Thus, it appears that a second-order calculation, which does not require iterating coupled-cluster equations or solving random phase approximation equations, offers the best compromise between accuracy and computational requirements. © 1993 John Wiley & Sons, Inc.
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    International Journal of Quantum Chemistry 45 (1993), S. 471-484 
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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 integrity bases for representations of the nuclear permutation groups Sn (n = 3,4) in the space of internal coordinates describing AXn molecules are determined. This allows optimal expressions of the molecular potential energy functions in terms of internal coordinates that are totally symmetric with respect to permutations of indistinguishable nuclei. © 1993 John Wiley & Sons, Inc.
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  • 186
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  • 187
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    International Journal of Quantum Chemistry 45 (1993), S. 491-505 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
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  • 188
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    International Journal of Quantum Chemistry 45 (1993), S. 489-490 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
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  • 189
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    International Journal of Quantum Chemistry 45 (1993), S. 563-572 
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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: A p-version finite element method has been used to calculate second-order pair and total correlation energies for closed-shell Mg and Ar. Comparison with the best results found in the literature suggests that the present values are the most accurate and that the method should perform comparatively better for heavier elements. © 1993 John Wiley & Sons, Inc.
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  • 190
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    Topics: Chemistry and Pharmacology
    Notes: Some topics in relativistic quantum chemistry are reviewed with special emphasis on 4-currents and 4-potentials. It is shown that, both in molecular quantum theory and in solid-state physics, calculations can include relativistic and magnetic effects by means of 4-currents without an excessive increase in complication, provided that 4-component Dirac spinors are used rather than the Pauli approximation. © 1993 John Wiley & Sons, Inc.
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    International Journal of Quantum Chemistry 45 (1993), S. 587-590 
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Consider two orbital sets χk, k = 1…m and η1, 1 = 1…n, which are mutually nonorthogonal. Provided that n 〉 m, at least n - m orbitals of the set {η} can be orthogonalized to the set {χ} by a transformation within the set {η}. The orthogonalization of the remaining orbitals of {η} to the set {χ} requires a transformation in which the χk appear explicitly. The orthogonalization of one orbital set to another is relevant for SCF optimizations in a truncated basis set, in the presence of frozen occupied orbitals. Examples are frozen core calculations, ECP calculations, and embedded cluster calculations, where the cluster is embedded in a frozen environment. A simple orthogonalization scheme, which makes use of a corresponding orbital transformation, is presented. It is suggested that with a small, well-defined extension of the set {η} the complete orthogonalization can be done with a transformation in which the {χ} do not appear explicitly. © 1993 John Wiley & Sons, Inc.
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    International Journal of Quantum Chemistry 48 (1993), S. 67-80 
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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: Ground state electron correlation is introduced into the one-particle propagator via coupled cluster theory. This defines a similarity transformation of the Hamiltonian, which leads to the complete separation of the ionization and electron attachment aspects of the propagator. The latter makes it possible to solve for each property independently. Furthermore, the frequency (or energy) dependence which characterizes propagator theory is eliminated by introducing a wave operator formalism. It is shown that this procedure is equivalent to the summation of certain types of terms in the electron propagator perturbation expansion to infinite order. Finally, the resulting equations are found to be equivalent to those of the Fock-space coupled-cluster (or equivalently the equation of motion coupled-cluster) method, which provides an explicit wave function for each state, demonstrating the connection between these different approaches for the calculation of ionization potentials and electron affinities. Understanding this relationship permits new and powerful approximations to be proposed. © 1993 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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  • 193
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    International Journal of Quantum Chemistry 48 (1993), S. 155-162 
    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: 7 Tab.
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  • 194
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    International Journal of Quantum Chemistry 45 (1993), S. 71-85 
    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 variational principle for the transition matrix is considered. Conception of the MC SCF (in particular, CASSCF) approach for the transition matrix is proposed as a solution of the variational problem on the optimal evolution of a packet of two stationary states with some additional conditions. An ordinary MC SCF method for a single state is a special case of the proposed approach. Some aspects of the solving of the equations for the optimal transition matrix are treated. The method can be used in atomic and molecular calculations of transition energies, oscillator strengths, and other properties. © 1993 John Wiley & Sons, Inc.
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  • 195
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    International Journal of Quantum Chemistry 45 (1993), S. 105-114 
    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: Some operators considered conventionally as Hermitian are not strictly Hermitian for the freeelectron states known especially in the case of solids. The consequences of this fact on the closure property are examined. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Tab.
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  • 196
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    International Journal of Quantum Chemistry 45 (1993), S. 115-117 
    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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  • 197
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    International Journal of Quantum Chemistry 45 (1993), S. 123-132 
    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 barriers to internal rotation about the N—C bond of formamide and the formamide-H2O complex have been examined by ab initio quantum chemistry methods. Both self-consistent field and correlated approaches have been utilized to determine the geometries, energies, and local harmonic vibrational frequencies of the minimum-energy and transition-state structures of these two systems. We find that formamide's rotation barrier of 14-15 kcal/mol is increased to 16-18 kcal/mol when a single H2O molecule is attached. This result contrasts with the effect of a single H2O solvent molecule on the barrier to tautomerization of formamide (to form formamidic acid HN—CHOH) for which a barrier lowering of ca. 20 kcal/mol has been observed. The rotation barriers obtained for formamide and for its H2O complex are compared with barriers obtained experimentally in various solvents. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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  • 198
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    International Journal of Quantum Chemistry 45 (1993), S. 167-176 
    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 new formulation of the eigenvector equations for certain polymeric molecules is given. The electronic bands for the infinite molecules are deduced. For the finite molecules, the use of ghost molecules allows an exact specialization of the infinite to the finite eigenvector equations. The complete solution of the equations depends on the solution of a simple transcendental equation. Approximate solutions of this equation are given that bracket the accurate solutions so that, for molecules with many repeated moieties, the approximations become good. The general theory is illustrated by applications to the chrysene series and to the polyphenyls. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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  • 199
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    International Journal of Quantum Chemistry 48 (1993), S. 269-285 
    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 exploit the unitary group formalism in formulating a multiconfigurational single-reference coupled cluster method for cases involving one or two electrons in open shells. The linear version of CCSD theory for the simple open shell case and for low lying singlet states of closed shell systems are considered in detail. The entire formalism is related to the unitary group based CISD method, and explicit expressions for size-extensivity corrections, leading to the L-CCSD formalism, are given. An illustrative example of the minimum basis set model of the BeH radical is also presented. © 1993 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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  • 200
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    International Journal of Quantum Chemistry 48 (1993), S. 303-308 
    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: This article gives an improved derivation for U(n1 + n2) ⊃ U(n1) × U(n2), SN1+N2 ⊃ SN1 × SN2, and other transformation coefficients by using a series of elementary Racah transformations. These transformation coefficients can be expressed generally in terms of a product of segments containing 6j symbols and easily calculated. Possible segment factors are given in Table I. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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