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  • Analytical Chemistry and Spectroscopy  (13)
  • Engineering  (4)
  • 1
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    International Journal for Numerical Methods in Engineering 26 (1988), S. 2279-2304 
    ISSN: 0029-5981
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An important limiting factor in the accurate modelling of fluid flow problems is the numerical representation of the convection terms in the Navier-Stokes equations. This paper reviews several approaches used to approximate the convection terms and reduce the so-called false-diffusion errors, within the context of finite-difference and finite-volume methods. Numerical errors are characterized as those due to discretization of the differential terms and those due to the influence of the multidimensional nature of the flow. Necessary criteria are identified which a numerical scheme must satisfy, if it is to be a candidate, at least in terms of accuracy and practicality, for the successful solution of the Navier-Stokes equations. One of the criteria is the need of the scheme to account explicitly for the multidimensionality of the flow in the transport of scalar variables. All schemes except Raithby's SKEW approximation are deficient in this respect. However, the SKEW scheme does not satisfy some of the other criteria and does not always perform well. A new scheme called CUPID (Corner UPwInDing), which is based on the ideas of the SKEW scheme, yet obeys more of the criteria identified above, is described. The scheme is tested on a series of discriminating test problems which, the authors contend, demonstrate its potential for practical use in solving accurately the Navier-Stokes equations.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 11 (1982), S. 64-65 
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Finely divided metal particles, formed in the interlayer space of montmorillonite, have been identified by a x-ray microprobe technique and their dimensions measured by scanning electron microscopy. The dimensions of Ni0 and Cu0 obtained on reduction of the respective metal ions by H2 have been shown to be ∼ 100 Å.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 17 (1988), S. 181-185 
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Pyrophyllite was heat treated up to 1000°C in the presence of fluxes such as Li2CO3, Na2CO3, K2CO3 and CaCO3 and the products were examined by scanning electron microscopy (SEM). It is shown that the surface morphology of the mineral varies with both temperature and flux. The dehydroxylation reaction in the mineral commences at 500°C and continues above 900°C. Dehydroxylated phases are observed even at 950-1000°C. The formation of free Al2O3, cristobalite, mullite and other phases from pyrophyllite was detected by the SEM examination.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 12 (1983), S. 42-46 
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The usual method of polishing the surface of a solid sample for examination using the x-ray microprobe technique cannot be adopted for clay minerals. A modified method is suggested and its validity is tested using vermiculite mineral. It is observed that precision of quantitative elemental analysis increases significantly according to the present pretreatment procedure; variation from values obtained by wet chemical method is 〈 1% for SiO2, MgO and Fe2O3 and 2-3% for the rest. However, values obtained with the x-ray microprobe technique vary enormously from point to point and this non-uniformity is explained in terms of the structural characteristics of the clay mineral. The variation increases with the rise in temperature of treatment due to structural modifications occurring during heat treatment. The x-ray microprobe technique has been found to be quite effective in determination of trace elements such as K and Ti.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 16 (1987), S. 57-60 
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The Silica structural framework in plant materials can be separated from the organic part by acid leaching and can be examined by SEM. Scanning electron micrographs characterizing the bonding and distribution patterns of silica in rice husk, rice straw and sugarcane leaves are presented. The differences in the surface morphology of the three plant products are discussed.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 18 (1989), S. 215-218 
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The surface structure of silicon carbide whiskers, produced from rice husk at 1500-1800°C, was examined by x-ray photoelectron spectroscopy. An ESCA survey scan of the surface showed Si, C, O and F to be present; Si in the form of SiCx and SiOx and C in the form of SiCx and CHx. On sputtering the sample, the SiOx and CHx species were reduced and the SiCx level increased. The photoelectron spectra are presented.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 18 (1989), S. 219-224 
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The structural characterization of alumina fibres obtained from an aluminium salt and three natural fibres (jute, sisal and coir) was examined by EDXRF and XRD. Elemental composition spectra from EDXRF of fibres pyrolysed at 1200 and 1400°C are presented and the results are compared with those obtained by wet chemical analysis and atomic absorption spectrometry. XRD diffractograms of the same samples are also shown. The evolution of the α phase of alumina with increase in pyrolysis temperature was examined. Scanning electron micrographs of alumina fibre with jute fibre are also presented.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 18 (1989), S. 267-269 
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Rice husk was heat treated up to 1300°C and the products were examined by scanning electron microscopy. The fibrous structure of the initial rice husk persisted throughout. Cristobalite and tridymite were detected in the product at 1250°C by x-ray diffraction. The fibrous structures were characterized and shown to have a bearing on the formation of SiC whiskers as substrates.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 6 (1986), S. 129-153 
    ISSN: 0271-2091
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A comparative study of eight discretization schemes for the equations describing convection-diffusion transport phenomena is presented. The (differencing) schemes considered are the conventional central, upwind and hybrid difference schemes,1,2 together with the quadratic upstream,3,4 quadratic upstream extended4 and quadratic upstream extended revised difference4 schemes. Also tested are the so called locally exact difference scheme5 and the power difference scheme.6 In multi-dimensional problems errors arise from ‘false diffusion’ and function approximations. It is asserted that false diffusion is essentially a multi-dimensional source of error. Hence errors associated with false diffusion may be investigated only via two- and three-dimensional problems. The above schemes have been tested for both one- and two-dimensional flows with sources, to distinguish between ‘discretization’ errors and ‘false diffusion’ errors.7 The one-dimensional study is reported in Reference 7. For 2D flows, the quadratic upstream difference schemes are shown to be superior in accuracy to the others at all Peclet numbers, for the test cases considered. The stability of the schemes and their CPU time requirements are also discussed.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 15 (1984), S. 211-216 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A design of a high-temperature cell (used with a Spex-1403 Ramalog spectrophotometer) for Raman studies with 90° geometry is given. Raman spectra of normal (d0) and denteriated (d12) tetramethylammonium chlorides in phases III and II are reported, together with their assignments. On the basis of the temperature dependence of the thermosensitive bands, the III → II phase transition was found at 367 ± 2 K for normal (d0) tetramethylam monium chloride and at 407±5 K for deuteriated (d12) tetramethylammonium chloride. It is observed that the III → II phase transition is irreversible if the samples are kept under vacuum during the investigation. Traces of moisture present in the samples are responsible for the stability of the room-temperature phase III.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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