ALBERT — All Library Books, journals and Electronic Records Telegrafenberg

1

Electronic Resource

A model cylindrical magnetron Vlasov distribution function (1994)

Kaup, D. J. ; Choudhury, S. Roy

[S.l.] : American Institute of Physics (AIP)

Physics of Plasmas 1 (1994), S. 3437-3443

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ISSN: 1089-7674

Source: AIP Digital Archive

Topics: Physics

Notes: The analysis of the planar magnetron Vlasov distribution function [Phys. Fluids 31, 2362 (1988)] is extended to the cylindrical case. In momentum space, the model distribution function is f(w,pθ) =Ne−βwwe−(Ωβθ/4p0)(pθ−p0)2 where w(pθ) is the single particle energy (angular momentum), βw(βθ) is the inverse of the thermal energy associated with variations in w(pθ), p0 is the angular momentum at the cathode, and Ω is the electron cyclotron frequency (=eB0/mc). The problem is shown to be too "stiff'' numerically to permit a pure numerical solution even using very high accuracy and state-of-the-art numerical schemes. It is shown that one may use a global singular perturbation expansion, similar to, but significantly more complex than the one used in the planar case, to solve the resulting nonlinear ordinary differential equation for the spatial dependence of the distribution function, density, electrostatic potential, and drift velocity.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.870492

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2

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Invariant Painlevé analysis and coherent structures of two families of reaction-diffusion equations (1999)

Tanriver, Ugur ; Choudhury, S. Roy

College Park, Md. : American Institute of Physics (AIP)

Journal of Mathematical Physics 40 (1999), S. 3643-3653

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ISSN: 1089-7658

Source: AIP Digital Archive

Topics: Mathematics , Physics

Notes: Exact closed-form coherent structures (pulses/fronts/domain walls) having the form of complicated traveling waves are constructed for two families of reaction–diffusion equations by the use of invariant Painlevé analysis. These analytical solutions, which are derived directly from the underlying PDE's, are investigated in the light of restrictions imposed by the ODE that any traveling wave reduction of the corresponding PDE must satisfy. In particular, it is shown that the coherent structures (a) asymptotically satisfy the ODE governing traveling wave reductions, and (b) are accessible to the PDE from compact support initial conditions. The solutions are compared with each other, and with previously known solutions of the equations. © 1999 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.532914

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3

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Linear stability analysis of the Vlasov–Poisson equations in high density plasmas in the presence of crossed fields and density gradients (1986)

Kaup, D. J. ; Hansen, P. J. ; Choudhury, S. Roy ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Physics of Fluids 29 (1986), S. 4047-4054

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ISSN: 1089-7666

Source: AIP Digital Archive

Topics: Physics

Notes: A method is presented for the linear stability analysis of the Vlasov–Poisson equations in high density, finite temperature plasmas in the presence of inhomogeneous crossed fields and density gradients. The method is more general than earlier studies of high-β inhomogeneous plasmas in that various approximations employed therein such as the local approximation (JWKB), low-frequency, or small wavelength restrictions are not employed here. Although only the nonrelativistic electrostatic planar case is treated, the method, with due modification, could be extended into the relativistic electromagnetic regime. The method uses a singular perturbation expansion to construct the unperturbed single particle orbits. Then with these orbits the "integration over the unperturbed orbits'' necessary for determining the perturbed distribution function is performed. The initial distribution function may be quite general, but the expansions used do assume a distribution close to that of a sheared laminar flow. The perturbed distribution function is obtained as a singular perturbation expansion also. Lastly, the application of the method is demonstrated by reducing the linearized Vlasov–Poisson equations, with inhomogeneous electric fields and density gradients, to a second-order ordinary differential equation where the frequency is an eigenvalue. Similarities to and differences from the cold-fluid equations are pointed out.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.865747

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4

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A note on axisymmetric thermoelastic interactions in an unbounded body with cylindrical cavity (1994)

Choudhury, S. Roy

Springer

Acta mechanica 104 (1994), S. 91-96

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ISSN: 1619-6937

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics

Notes: Summary Thermoelastic interactions in a linear, homogeneous and transversely isotropic unbounded body containing a cylindrical cavity due to a time-dependent stress or temperature applied to the boundary of the cavity are studied. A unified system of governing equations that includes among its particular cases the governing equations of the conventional and generalized thermoelasticity theories is employed. By the use of the Laplace transform technique, discontinuities experienced by the temperature, displacement, radial stress and hoop stress fields at the wavefronts are computed under a small-time approximation. Comparison with the corresponding results obtained in earlier work is made.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01170278

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5

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Enzyme histochemistry of basal ganglia in the septally cannulated rat (1978)

Choudhury, S. Roy

Springer

Journal of molecular histology 10 (1978), S. 229-237

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ISSN: 1573-6865

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Medicine

Notes: Synopsis Stereotaxic septal cannulation in one hemisphere of the rat results in displacement of the ipsilateral basal ganglion along its rostrocaudal axis. In an attempt to elucidate any metabolic changes in the ganglion due to possible alteration in its vascular supply in the displaced position, enzyme histochemical studies were undertaken on the forebrain of septally cannulated rats. A survey of hydrolases (acid and alkaline phosphatases, ATPase, cholinesterase and non-specific esterases), dehydrogenases (succinate and lactate) and diaphorases (NADH- and NADPH- tetrazolium reductases) revealed no difference in activity between the ganglia of the two sides. Cortical activity appeared to be enhanced with a rostral shift of the ganglion and decreased with a caudal shift. In the light of available histoenzymatic data on ischaemic brain damages, the present results rule out the existence of any major metabolic difference between the two basal ganglia. This underlines the extraordinary degree of functional plasticity of subcortical nuclear masses, despite considerable physical displacement.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01003308

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6

Electronic Resource

Multi-rate numerical methods for diffusion problems (1993)

Choudhury, S. Roy

Chichester : Wiley-Blackwell

Communications in Numerical Methods in Engineering 9 (1993), S. 1-8

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ISSN: 1069-8299

Keywords: Engineering ; Engineering General

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Mathematics , Technology

Notes: The one-dimensional diffusion equation is solved using a recent class of multi-rate numerical algorithms collectively referred to as waveform relaxation methods. The methods enable different parts or blocks in the system to take widely different time steps by decoupling the blocks in the time domain. Significant speed-up is obtained over the results using a composite trapezoidal rule/second-order backward Euler time-stepping scheme without blocking. Possible implementation strategies for two-dimensional diffusion are briefly discussed.

Additional Material: 2 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/cnm.1640090103

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7

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Some results on the stability and dynamics of finite difference approximations to nonlinear partial differential equations (1993)

Choudhury, S. Roy

New York, NY [u.a.] : Wiley-Blackwell

Numerical Methods for Partial Differential Equations 9 (1993), S. 117-133

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ISSN: 0749-159X

Keywords: Mathematics and Statistics ; Numerical Methods

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Mathematics

Notes: A miscellany of results on the nonlinear instability and dynamics of finite difference discretizations of the Burgers and Kortweg de Vries equations is obtained using a variety of phase-plane, functional analytic, and regularity methods. For the semidiscrete (space-discrete, time-continuous) schemes, large-wave-numer instabilities occurring in special exact solutions are investigated, and parameter values for which the semidiscrete scheme is monotone are considered. For fully discrete schemes (space and time discrete), large-wave-number instabilities introduced by various time-stepping schemes such as forward Euler, leapfrog, and Runge-Kutta schemes are analyzed. Also, a time step restriction for the monotonicity of the forward-Euler time-stepping scheme, and regularity of a 4-stage monotone/conservative Runge-Kutta time stepping are investigated. The techniques used here may be employed, in conjunction with bifurcation-theoretic and weakly nonlinear analyses, to analyze the stability of numerical schemes for other nonlinear partial differential equations of both dissipative and dispersive varieties. © 1993 John Wiley & Sons, Inc.

Additional Material: 2 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/num.1690090203

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