共查询到20条相似文献,搜索用时 15 毫秒
1.
D. Batic N. G. Kelkar M. Nowakowski 《The European Physical Journal C - Particles and Fields》2011,71(12):1831
A massless field propagating on spherically symmetric black hole metrics such as the Schwarzschild, Reissner–Nordström and Reissner–Nordström–de Sitter backgrounds is considered. In particular, explicit formulae in terms of transcendental functions for the scattering of massless scalar particles off black holes are derived within a Born approximation. It is shown that the conditions on the existence of the Born integral forbid a straightforward extraction of the quasi normal modes using the Born approximation for the scattering amplitude. Such a method has been used in literature. We suggest a novel, well defined method, to extract the large imaginary part of quasinormal modes via the Coulomb-like phase shift. Furthermore, we compare the numerically evaluated exact scattering amplitude with the Born one to find that the approximation is not very useful for the scattering of massless scalar, electromagnetic as well as gravitational waves from black holes. 相似文献
2.
3.
It has recently been demonstrated that the Born approximation for predicting the scattering response of flaws can be improved through the use of simple modifications called the "doubly distorted Born approximation". In this paper the doubly distorted Born approximation itself is modified with phase and amplitude corrections that further improve the Born scattering results for isotropic elastic media. The reliability of this new modification of the Born approximation has been evaluated by comparison with the exact solution for spherical inclusions obtained with the method of separation of variables. Unlike the ordinary Born approximation which works well only for very weak scattering inclusions, our modification of the doubly distorted Born approximation gives improved scattering results for both weak and strong scattering inclusions. 相似文献
4.
Experimental three-dimensional fluorescence reconstruction of diffuse media by use of a normalized Born approximation 总被引:5,自引:0,他引:5
We present a normalized Born expansion that facilitates fluorescence reconstructions in turbid, tissuelike media. The algorithm can be particularly useful for tissue investigations of fluorochrome distributionin vivo, since it does not require absolute photon-field measurements or measurements before contrast-agent administration. This unique advantage can be achieved only in fluorescence mode. We used this algorithm to three-dimensionally image and quantify an indocyanine fluorochrome phantom, using a novel fluorescence tomographic imager developed for animals. 相似文献
5.
To improve the Coulomb-Born approximation (CBA) theory of ionization in positronium (Ps) and atom scattering, the effect of
exchange is introduced. The nine-dimensional exchange amplitude for ionization of Ps in Ps—H scattering is reduced to a two-dimensional
integral using the present Coulomb-Born-Oppenheimer approximation (CBOA). The methodology is extremely useful to evaluate
ionization parameters for different target systems and for different types of ionization processes. It is then applied to
evaluate the Ps-ionization cross-section and to estimate the effect of exchange on Psionization in Ps-H system. We establish
the importance of exchange at lower energy region. 相似文献
6.
The correction factors for Coulomb effects in inelastic electron scattering are given for electric quadrupole transitions. The cross sections in Born approximation and distorted wave Born approximation are calculated in the liquid drop model for electron energies between 20 and 80 MeV and nuclei up toZ=26. 相似文献
7.
D. Khalil A. Makhoute A. Maquet G. Rahali M. Zitane 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(2):287-295
The dynamics of laser-assisted elastic collisions in
helium is studied using the second-order Born approximation.
Detailed calculations of the scattering amplitudes are performed
by using the Sturmian basis expansion. Differential cross sections
for elastic scattering with the net absorption/emission of up to
two photons are calculated for collision energies of 5 eV, 10 eV,
and 20 eV. We discuss the influence of the low-energy electrons on
the differential cross section (DCS) as a function of the
scattering angle for selected choices of the laser frequency and
the number of photons exchanged between the external field and
electron-helium system. 相似文献
8.
M. Zarcone 《Il Nuovo Cimento D》1991,13(6):749-756
Summary The total cross-section for potential scattering in the presence of a strong magnetic field presents singularities and exhibits
giant growth (cyclotron resonances) at values of the incident particle energy exactly matching the differences between the
initial-and final-state Landau levels. In this paper (in cylindrical coordinates) a higher-order modified Born series has
been derived that can be summed at all orders giving a nondivergent total cross-section at the Landau thresholds. 相似文献
9.
A new approximation for the elastic scattering transition matrix is suggested. This approximation satisfies the unitarity condition. A modified Born series is introduced which has this unitarized Born approximation as the leading term. The series is applied to the solvable case of scattering by a separable potential and is found to converge in a wider region of energies than that of the conventional Born series. 相似文献
10.
C. S. Singh S. N. Rai R. Srivastava D. K. Rai 《Zeitschrift für Physik A Hadrons and Nuclei》1984,319(1):9-11
Total cross-sections for electron impact excitation of 11 S – 23 S transition in helium have been calculated using variable-charge Coulomb-projected Born approximation and also using a distorted wave model in which the prior form of theT-matrix is used. The comparison of the two sets of results enables us to make certain observations about the suitability of the variable-charge Coulomb-projected Born approximation. 相似文献
11.
The differential cross-sections forē-helium elastic scattering are calculated by using Yateshigh-energy higher order Born approximations, through 0 (K
i
Emphasis>−2
) of the incident electron momentum, and comparisons have been made with the recent theoretical and experimental results. 相似文献
12.
We study the elastic scattering of atomic argon by electron in the presence of a bichromatic laser field in the second Born
approximation. The target atom is approximated by a simple screening potential and the continuum states of the impinging and
emitting electrons are described as Volkov states. We evaluate the S-matrix elements numerically. The dependence of differential
cross-section on the relative phase between the two laser components is presented. The results obtained in the first and second
Born approximations are compared and analysed. 相似文献
13.
When deriving the Fourier diffraction theorem based on the first-order Born approximation,the difference between wave number of the scattering object and that of the surrounding medium is ignored,causing substantial errors in sound scattering prediction.This paper modifies the Born approximation by taking into account the amplitude and phase changes between the scattering object and the water due to the wave number difference.By changing the radius and center position of the sampling circle in the Fourier domain,accuracy of the predicted sound scattering is improved.With the modified Born approximation,the computed far-field directional pattern of the scattered sound from a circular cylinder is in good agreement with the rigorous solution.Numerical calculations for several objects with different shapes are used to show applicability and effectiveness of the proposed method. 相似文献
14.
在推导Fourier衍射定理中运用一阶Born近似时忽略了弱散射体内外的波数差异,使散射声场方向特性的预报产生较大误差,针对这一问题,对一阶Born近似进行修正。考虑散射体内外波数差异引起的幅度和相位误差,通过调整频域采样圆弧半径并移动圆心位置得到了修正的一阶Born近似解。由于更准确地反映了目标与周围水介质的声学性质,有效提高了散射声场的预报精度。根据修正的Born近似计算了弱散射条件下无限长圆柱目标的散射远场指向性,结果与严格解相吻合,对其它形状截面的柱状目标也得到了合理的计算结果。 相似文献
15.
This work is concerned with the reconstruction, from measured (synthetic or real) data, of a 2D penetrable fluid-like object of arbitrary cross-section embedded in a fluid of infinite extent and insonified by a plane acoustic wave. Green's theorem is used to provide a domain integral representation of the scattered field. The introduction therein of the Born approximation gives rise to a linearized form of the inverse problem. The actual inversion is carried out by two methods. The first diffraction tomography (DT), exhibits the contrast function very conveniently and explicitly in the form of a wave number/incident angle Fourier transform of the far backscattered field and thus requires measurements of this field for incident waves all around the object and at all frequencies. The second discretized domain integral equation with Born approximation method, is numerically more intensive, but enables a wider choice of configurations and requires less measurements (one or several frequencies, one or several incident waves, choice of measurement points) than the DT method. A comparison of the two methods is carried out by inversion of both simulated and experimental scattered field data. 相似文献
16.
17.
18.
This paper intends to identify the validity of the orn approximation by
a new universal criterion, which is ultimately reduced to the
calculation of an operator norm. With the purpose of enabling the
criterion to be applicable to general scattering problems, a method is
proposed to estimate the norm of the operator concerned. Compared
with the conventional criterion, this method excels in its ability
to acquire a quantificational upper bound of the relative error by
Born approximation as well as to extend its valid frequency to a
wider range. Two canonical scattering examples are given as evidence
for the validity of the criterion. 相似文献
19.
A systematic study is made to find out the differential scattering cross-section in the case of electron-atom collisions.
The first and the second Born terms ofO(1/k
i
) are calculated in the framework of Yates high energy higher order Born approximation. The second Born term ofO(1/k
i
2
) is calculated using the second order Wallace term, the third term is calculated using the Glauber-eikonal series of Yates.
The method is applied to the elastic scattering of electrons by atomic hydrogen in the energy range 100–400 eV and by helium
for energies 200 eV and 400 eV. Comparison is made with other theoretical results and the experimental data. 相似文献
20.
The nuclear Overhauser effect (NOE) is undoubtedly one of the most useful tools in NMR spectroscopy and is widely used in solving structural and conformational problems of small organic molecules and macromolecular systems alike. In particular, measurement of the kinetics of the NOE, often facilitated by selective 1D NOE buildup experiments, can generate invaluable quantitative distance information for the molecule being investigated. In practice, analysis of such kinetic NOE data routinely assumes a first-order approximation of the initial buildup rate. However, often times such an approximation holds true only for the shortest mixing times. As shown by Macura and others, the linear range of the NOE buildup obtained from 2D NOESY and exchange experiments can be substantially extended by simply scaling the NOE cross-peaks against the corresponding diagonal peaks. In this note, we demonstrate through a detailed analysis that the same approach can be applied to the analysis of 1D NOE data obtained with the DPFGSE NOE pulse sequence, one of the most widely used selective 1D NOE experiments today. We show that this approach allows the inclusion of data points acquired with much longer mixing times in the analysis and thus considerably improves the accuracy of the measured cross-relaxation rates and internuclear distances, while considerably simplifying the data analysis. Similar results can be obtained for the rotating frame DPFGSE ROE experiment. 相似文献