			Home About us Contact

Analytical Treatment (analytical + treatment)

Distribution by Scientific Domains

Physics and Astronomy	40%

Selected Abstracts

Effect of Oscillating Sheath on Near-Wall Electron Current Profile in Hall Thrusters

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 9-10 2008
D. R. Yu
Abstract The radial profile of the axial electron current in Hall thrusters was measured; however, the significant decay of the current density peak in the near-wall region can't be explained effectively by the steady sheath theory. As the sheath exhibits an oscillating character when the thruster is in operation, its effect on the near-wall current profile has been studied in this paper. To obtain a comprehensive knowledge, we have considered a wide sheath oscillation frequency span which includes two asymptotic frequency cases at high and low ends. Based on the case studied, either an analytical treatment or a numerical simulation is applied. The results show that the current density peak has a fastest damping speed away from the wall at the asymptotic low frequency. With the increase of the frequency, both the decay and the spatial "wavelength" of the current profile decrease. The decay finally disappears at the asymptotic high frequency with a constant spatial "wavelength". Moreover, the sheath oscillation amplitude can enhance the decay and enlarge the spatial "wavelength". Taking into account of the realistic situation in Hall thrusters, the significant impact of the oscillating sheath on the near-wall electron current profiles can be anticipant. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Transform Analysis and Asset Pricing for Affine Jump-diffusions

ECONOMETRICA, Issue 6 2000
Darrell Duffie
In the setting of ,affine' jump-diffusion state processes, this paper provides an analytical treatment of a class of transforms, including various Laplace and Fourier transforms as special cases, that allow an analytical treatment of a range of valuation and econometric problems. Example applications include fixed-income pricing models, with a role for intensity-based models of default, as well as a wide range of option-pricing applications. An illustrative example examines the implications of stochastic volatility and jumps for option valuation. This example highlights the impact on option ,smirks' of the joint distribution of jumps in volatility and jumps in the underlying asset price, through both jump amplitude as well as jump timing. [source]

Symplectic molecular dynamics integration using normal mode analysis

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2001
anka Jane
Abstract The split integration symplectic method (SISM) for molecular dynamics (MD) integration using normal mode analysis based on a factorization of the Liouville propagator is presented. This approach is quite distinct from others that use fractional-step methods, owing to the analytical treatment of high-frequency motions. The method involves splitting the total Hamiltonian of the system into a harmonic part and the remaining part. Then the Hamilton equations are solved using a second-order generalized leapfrog integration scheme in which the purely harmonic Hamiltonian (which represents the main contribution of the chemical bonds and angles) is treated analytically, i.e., independent of the step size of integration, by a normal mode analysis that is carried out only once, at the beginning of calculation. The whole integration step combines analytical evolution of the harmonic part of the Hamiltonian with a correction arising from the remaining part. The proposed algorithm requires only one force evaluation per integration step. The algorithm was tested on a simple system of linear chain molecules. Results demonstrate the method makes possible the integration of the MD equations over larger time steps without loss of stability while being economical in computer time. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 84: 2,12, 2001 [source]

Diffractive optical elements with square concentric rings of equal width

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2010
Javier Alda
Abstract A diffractive optical element having equal-width concentric square rings is analyzed in this article. This constant width makes possible its realization using spatial light modulators or square pixels phase screens. It allows a simple analytical treatment, and the element is also simulated using the Rayleigh-Sommerfeld approach. An experimental verification of its performance has been compared with the simulated results. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:930,934, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25065 [source]

An upper limit to the central density of dark matter haloes from consistency with the presence of massive central black holes

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2010
X. Hernandez
ABSTRACT We study the growth rates of massive black holes in the centres of galaxies from accretion of dark matter from their surrounding haloes. By considering only the accretion due to dark matter particles on orbits unbound to the central black hole, we obtain a firm lower limit to the resulting accretion rate. We find that a runaway accretion regime occurs on a time-scale which depends on the three characteristic parameters of the problem: the initial mass of the black hole, the volume density and velocity dispersion of the dark matter particles in its vicinity. An analytical treatment of the accretion rate yields results implying that, for the largest black hole masses inferred from quasi-stellar object (QSO) studies (>109 M,), the runaway regime would be reached on time-scales which are shorter than the lifetimes of the haloes in question for central dark matter densities in excess of 250 M, pc,3. Since reaching runaway accretion would strongly distort the host dark matter halo, the inferences of QSO black holes in this mass range lead to an upper limit on the central dark matter densities of their host haloes of ,0 < 250 M, pc,3. This limit scales inversely with the assumed central black hole mass. However, thinking of dark matter profiles as universal across galactic populations, as cosmological studies imply, we obtain a firm upper limit for the central density of dark matter in such structures. [source]