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  • 1
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Stationary phase optimization ; Mobile phase optimization ; Column temperature optimization ; Multifactor optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A computer-assisted method is presented for the simultaneous multifactor optimization (stationary phase loading, column temperature and carrier gas flow rate) of the analytical conditions for the optimum separation of multicomponent samples in gas chromatography. The optimization of the separation over the experimental region is based on a special polynomial from twelve preliminary experiments using the resolution as the selection criterion. Computer scanning technique was used for optimum selection in three dimensions. Excellent agreement was obtained between the predicted data and the experimental results.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of fusion energy 13 (1994), S. 275-280 
    ISSN: 1572-9591
    Keywords: Spherical pinch ; inertial confinement fusion ; Rayleigh-Taylor instability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The spherical pinch (SP) concept is an outgrowth of the inertial confinement model (ICF). Unlike the ICF, where instabilities, especially the Rayleigh-Taylor instability, have been studied extensively, the instability study of the spherical pinch has just begun. The Rayleigh-Taylor instability is investigated for the first time in the SP in the present work. By using the simple condition for the Rayleigh-Taylor instability ∇p·∇ρ〈0 (density and pressure gradients have opposite direction), we have qualitatively identified the regions for development of instabilities in the SP. It is found that the explosion phase (central discharge) is stable and instabilities take place in the imploding phase. However, the growth rate for the instability is not in exponential form, and the appearance of the Rayleigh-Taylor instability does not prevent the main shock wave from converging to the center of the sphere.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of fusion energy 14 (1995), S. 389-392 
    ISSN: 1572-9591
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The stability of spherically imploding shock waves is systematically investigated in this letter. The basic state is Guderley and Landau's unsteady self-similar solution of the implosion of a spherical shock wave. The stability analysis is conducted by combining Chandrasekhar's approach to the stability of a viscous liquid drop with Zel'dovich's approach to the stability of spherical flames. The time-dependent amplitudes of the perturbations are obtained analytically by using perturbation method. The relative amplification and decay of the amplitudes of perturbations decides the stability/instability of the spherical imploding shock waves. It is found that the growth rate of perturbations is not in exponential form and near the collapse phase of the shocks, the spherically imploding shock waves are relatively stable.
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  • 4
    ISSN: 0271-2091
    Keywords: rotating flow ; three-dimensional rectangular channel ; pseudospectral matrix method ; eigenvalue decomposition ; two- and four-cell flow pattern ; 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 Fourier-Chebyshev pseudospectral method is used for the numerical simulation of incompressible flows in a three-dimensio nal channel of square cross-section with rotation. Realistic, non-periodic boundary conditions that impose no-slip conditions in two directions (spanwis e and vertical directions) are used. The Navier-Stokes equations are integrated in time using a fractional step method. The Poisson equations for pressure and the Helmholtz equation for velocity are solved using a matrix diagonalization (eigenfunction decomposition) method, through which we are able to reduce a three-dimensional matrix problem to a simple algebraic vector equation. This results in signficant savings in computer storage requirement, particularly for large-scale computations. Verification of the numerical algorithm and code is carried out by comparing with a limiting case of an exact steady state solution for a one-dimensional channel flow and also with a two-dimensional rotating channel case. Two-cell and four-cell two-dimensional flow patterns are observed in the numerical experiment. It is found that the four-cell flow pattern is stable to symmetri cal disturbances but unstable to asymmetrical disturbances.
    Additional Material: 17 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    ISSN: 0271-2091
    Keywords: Instability ; Non-parallel flow ; Fourier-rational Chebyshev mode ; Vortex street ; 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: The local instability of a full non-parallel flow is investigated. The basic flow is a horizontal uniform flow about a vertical array of periodic bound eddies. This flow was found by Kovasznay as an exact solution to the Navier-Stokes equations. The problem is formulated as an initial value problem with two sets of complete orthogonal functions. A new approach to the problem with semi-infinite domain is given computationally with a new modified rational Chebyshev function. The linear stability analysis of the Kovasznay flow is performed with respect to the odd-rational Chebyshev mode and the even-rational Chebyshev mode for the evolution of disturbances. While symmetrical vortex sheets appeared through the process of big eddies breaking into small eddies in the odd-rational Chebyshev mode, the von Kármán vortex street phenomena is found in the even-rational Chebyshev mode. The mode corresponding to antisymmetric velocity perturbation is found to be far more unstable than symmetric disturbance. An organized structure is developed after the onset of instability. Several general characteristics of non-parallel flow stability are discussed.
    Additional Material: 18 Ill.
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  • 6
    ISSN: 1572-8935
    Keywords: Polyurethane ; Phenylbis(hydroxyalkyl)phosphonate ; Thermal stability ; Char yield
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Phenylbis(hydroxyalkyl)phosphonates were prepared by treating excess glycol(ethylene glycol or diethylene glycol) with phenylphosphonic dichloride (PPD). Phosphorus-containing homopolyurethanes were synthesized by low temperature solution polyaddition by phenylbis (hydroxyalkyl)phosphonates with tolylene diisocyanate (TDI). Copolyurethanes with various phosphorus content were prepared by copolymerization of tolylene diisocyanate with polypropylene glycol (PPG, MW = 3000), and phenylbis(hydroxyalkyl)phosphonate. All polymers were characterized by elemental analysis, infrared (IR), differential scanning calorimeter (DSC), differential thermal analysis (DTA), and thermogravimetric analysis (TGA). Thermal properties of the polyurethane were compared with that of the common polyurethane. Phosphorus containing homopolyurethanes and copolyurethanes had lower decomposition temperatures and higher char yield residue than the corresponding common polyurethane.
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  • 7
    ISSN: 1572-8935
    Keywords: Polysiloxane ; Side-chain liquid crystal ; Dilution ; Activation energy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The synthesis and characterization are described for a series of side-chain liquid crystal polysiloxanes using polyhydrosilylation reaction between a poly(hydrogen methyl-co-dimethylsiloxanes),-(OSiHMe)x,-(OSiMe2)y-, where x/y was 13/87, 30/70, 55/45, 73/27 and 98/2, and [4-(allyloxy)benzoyll biphenyl mesogenic group. The side-chain liquid crystal polysiloxanes were characterized by1H NMR,13C NMR, IR, gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and optical polarizing microscopy. The dimethylsiloxane segment factors governing thermal transition temperatures and activation energy (Ea) of the nematic-to-isotropic phase transition are discussed.
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  • 8
    ISSN: 1572-9591
    Keywords: Inertial confinement fusion ; spherical pinch ; shock wave ; implosion and explosion ; hightemperature hydrodynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The spherical pinch concept is an outgrowth of the inertial confinement model. The salient feature of the spherical pinch concept is the creation of a hot plasma in the center of a sphere.(1,2) This plasma is then compressed by a strong shock wave launched from the periphery of the vessel by an imploded plasma acting as a driver. This scheme, reveals that convergence of the shock, which is the main feature of all inertial confinement schemes, is a component of the spherical pinch model. The reasons for classifying the spherical pinch as a particular ICF model and designating it as a ICF-SP are given here. The fluid mechanics and high-temperature hydrodynamics of the spherical pinch can be briefly described as an explosion within an implosion. The structure of the shock wave for such explosion within an implosion and for, an implosion alone is determined by solving numerically the governing equations of the phenomena. We present here a detailed computational comparison of the inertial confinement model and the spherical pinch in terms of density, pressure, temperature, confinement time, total accumulated number of neutrons, and time-resolved neutron flux from reactions in deuterium-tritium mixture. It is shown that temperature, confinement time, and total number of neutrons for the ICF-Spherical Pinch improve upon the classical ICF.
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  • 9
    ISSN: 0887-624X
    Keywords: polymethylphenylsilane ; polymeric photoinitiator ; rate constants ; monomer dipole moment ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rates of photochemical polymerization of styrene (St), p-chlorostyrene (Cl-St), methyl methacrylate (MMA), and butyl methacrylate (BMA) with polymethylphenylsilane (PMPS) as an initiator were measured. Polymethylphenylsilane is photodegrated to form silyl radicals that may initiate polymerization of vinyl monomers. Rate constants kp and kt have been determined for these systems. A good correlation (log P = α + βμ) of the resonance stabilization (P) of the chain radicals and the dipole moment (μ) of the monomers is observed for these polymerization systems. This equation may be used to estimate the resonance stabilization (P) of a monomer and the polymerization rate constant (kp). © 1996 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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  • 10
    ISSN: 0887-624X
    Keywords: polydimethylsiloxane ; poly(methyl methacrylate) ; block copolymer ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Azo group-containing polydimethylsiloxanes (PDMS-ACP), macroazoinitiators, were prepared by polycondensation reaction of 4,4′-azobis-4-cyanopentanoyl chloride (ACPC) with hydroxybutyl-terminated polydimethylsiloxane (PDMS) of varying molecular weights. The activation energy (Ea), activation enthalpy (ΔH
    Additional Material: 9 Ill.
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