共查询到20条相似文献,搜索用时 31 毫秒
1.
We propose an all-optical in-fiber ultra-broadband fractional differentiator. We numerically demonstrate that a long-period grating inherently performs the temporal fractional differentiation on an optical pulse propagating in the fundamental fiber mode, within a certain spectral bandwidth around the resonance frequency. The device shows a good accuracy calculating the fractional time derivatives of the complex field of THz-bandwidth optical pulses. 相似文献
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《Nuclear Physics B》1998,529(3):737-762
The concept of discrepancy plays an important rôle in the study of uniformity properties of point sets. For sets of random points, the discrepancy is a random variable. We apply techniques from quantum field theory to translate the problem of calculating the probability density of (quadratic) discrepancies into that of evaluating certain path integrals. Both their perturbative and non-perturbative properties are discussed. 1998 Elsevier Science B.V. 相似文献
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M.T. Grisaru 《Physics letters. [Part B]》1978,79(3):225-230
We examine at the one-loop level the equivalence between SU(4) and SO(4) supergravity by calculating some amplitudes which are zero in SO(4) theory but may not be zero in SU(4) theory. The results of the calculation show that the theories are not equivalent and global supersymmetry is violated unless certain finite counter terms are introduced. 相似文献
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E. V. Shepilko 《Radiophysics and Quantum Electronics》2010,53(3):201-206
We formulate and solve the problem of scattering of a plane electromagnetic wave by an infinite, perfectly conducting wedge
with a truncated, perfectly conducting circular cylinder which is coated coaxially with a magnetodielectric layer and located
along the wedge edge. The rigorous solution is obtained and reduced to a system of linear algebraic equations of the second
kind for unknown coefficients of Fourier expansions of the scattered field. The results of calculating the scattered field
in the far zone with a specified accuracy are presented for the case of an H-polarized wave. It is shown that for certain
values of the electric radius of the cylinder, the backscattering cross section of such a structure has pronounced maxima. 相似文献
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D. Kreimer 《Zeitschrift fur Physik C Particles and Fields》1992,54(4):667-671
We present a new calculation of the well-known one-loop two-point scalar and tensor functions. We also present a systematic reduction to a certain class of functions which minimizes the effort for calculating tensor integrals drastically. We avoid standard techniques such as Feynman parametrization and Wick rotation. 相似文献
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We present several approximate arguments for calculating the wind force of electromigration. By considering simple models and making many intercomparisons we try to clarify the physics in these arguments. It is concluded that the arguments allow considerable qualitative insight and calculational ability in certain situations, but that they lack a general validity and quantitative rigor. 相似文献
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We investigate the direction-dependent Andreev reflection of normal state-superconductor junctions both in monolayer and bilayer graphene with a single magnetic barrier by means of the Green?s function formalism. Such a barrier is capable of tuning the preferred angles of incidence for the Andreev retro-reflection. It enhances the specular reflection probability for certain angles of incidence in bilayer-based hybrid structures. We further study the impacts of magnetic barriers on the monolayer and bilayer hybrid structures by calculating the differential conductances within the Blonder–Tinkham–Klapwijk formula for experimental comparisons. 相似文献
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The theory and parametrization of an iterative method of calculating the electron structure of molecules are presented. Use is made of the modified Mulliken equation for calculating the population of the atomic orbits, while group theory is employed for estimating the parameters. A comparison between the calculated and experimental ionization potentials of certain molecules confirms that the simple computing method here proposed yields reasonably satisfactory results. 相似文献
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We present a practical method for calculating the local gravitational self-force (often called "radiation-reaction force") for a pointlike particle orbiting a Schwarzschild black hole. This is an implementation of the method of mode-sum regularization, in which one first calculates the (finite) contribution to the force due to each individual multipole mode of the perturbation, and then applies a certain regularization procedure to the mode sum. Here we give the values of all the "regularization parameters" required for implementing this regularization procedure, for any geodesic orbit in Schwarzschild spacetime. 相似文献
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É. Z. Kuchinskii M. V. Sadovskii 《Journal of Experimental and Theoretical Physics》1999,88(5):968-979
We analyze several almost exactly solvable models of the electronic spectrum of two-dimensional systems with well-developed
short-range-order dielectric (e.g., antiferromagnetic) or superconducting fluctuations that give rise to an anisotropic pseudogap
state in certain segments of the Fermi surface. We develop a recurrence procedure for calculating the one-electron Green’s
function that is equivalent to summing all Feynman diagrams. The procedure is based on an approximate ansatz for higher order
terms in the perturbation series. We do detailed calculations of the spectral densities and the one-electron density of states.
Finally, we analyze the limits of the adopted approximations and some important points concerning the substantiation of these
approximations.
Zh. éksp. Teor. Fiz. 115, 1765–1785 (May 1999) 相似文献
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The partition functions of quantum Yang-Mills theory have an expansion in powers of the coupling constant; the leading order term in this expansion is called the semiclassical approximation. We study the semiclassical approximation for Yang-Mills theory on a compact Riemannian 4-manifold using geometric techniques, and do explicit calculations for the case when the manifold is the 4-sphere. This involves calculating the Riemannian measure and certain functional determinants on the moduli space of self-dual connections. The main result is that the contribution to the semiclassical partition functions coming from thek=1 connections on the 4-sphere isfinite andcalculable. We also discuss a renormalization procedure in which the radius of the 4-sphere is allowed to tend to infinity.Partially supported by N.S.F. grant DMS-8905211Partially supported by N.S.F. grant DMS-8802885 相似文献
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Hernando Quevedo 《General Relativity and Gravitation》1992,24(8):799-819
A method of calculating the metric from the curvature is presented. Assuming that a tensor with the symmetry properties of a type D curvature tensor is given in an orthonormal tetrad, we use the Bianchi identities and the relationship between the connection and the tetrad in order to calculate, under certain assumptions, the corresponding metric. Some well-known metrics are derived from the curvature by using the method given here. 相似文献
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We show the existence of the only procedure ensuring the absolute minimum of an arithmetic mean covariance in a certain parameter-variation range and coinciding identically with the algorithm for calculating the estimate minimizing the mean risk for a quadratic loss function and a uniform a priory distribution of parameters. This procedure is compared with the standard method for obtaining maximum likely estimates. In particular, it is shown that the procedure ensures a significantly smaller random scatter of estimates during the estimation of deterministic-signal parameters against the background of Gaussian interference. In the case where the estimate covariance is independent of the parameter estimated for physical reasons, the use of the above procedure with an arbitrary sample size allows us to reach the actual attainable variance bound. 相似文献
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A. S. Chernoskutov L. M. Martyushev 《Journal of Experimental and Theoretical Physics》2020,130(4):523-527
We perform linear analysis of morphological stability of a circular bubble growing nonstationary in a 2D liquid disregarding the variation of temperature and viscosity. The media are treated as incompressible, and the pressure in the bubble is assumed to be constant. Beginning from a certain critical size (kinetic spinodal), a transition from stable to unstable growth is observed, which differs in principle from the known solution for the 3D case. An approximate equation is derived for calculating the spinodal. 相似文献
19.
Kurt E. Shuler 《Physica A》1979,95(1):12-34
We have developed a new technique for calculating certain asymptotic random walk properties on sparsely periodic and related random lattices in two and three dimensions. This technique is based on an ansatz which relates the number of lattice bonds in “irreducible lattice fragments” to the number of steps along these bonds. We show that certain random walk properties can be calculated very simply on the basis of this ansatz and that they depend only on the density of bonds and not on the arrangement of the bonds within the lattice. The random walk properties calculated here (mean square displacements, number of distinct sites visited, probability of return to the origin) are in complete agreement with results obtained earlier via generating function techniques. A subsequent paper contains generating function calculations which verify a number of new results presented here, such as mean occupation frequency of lattice sites, and a proof of our basic assumption on the relation between the number of lattice bonds and random walk steps. 相似文献
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长干涉腔波长移相计算的自适应相位筛选法 总被引:1,自引:0,他引:1
波长移相干涉仪可用于大口径光学元件的测试。其移相量需经过标定方可采用定步长移相算法计算相位分布。在长腔长测试条件下,由于激光器的波长调谐驱动源的精度有限,采用定步长移相算法求解相位分布的精度不高。在分析干涉腔长和波面计算误差的基础上,提出了一种自适应相位筛选计算方法。根据电压-相位标定曲线采集多组周期干涉图,对干涉图中的光强值进行均匀分布抽样后,对其进行随机移相计算,求取每帧干涉图精确的步进移相量,从中筛选出移相量为π/2的四帧干涉图,利用四步移相计算公式求得精确的相位分布。实验结果表明,在波长移相干涉仪中运用该方法,可以很好地解决长腔长测试条件下的相位计算问题,与未进行筛选的计算结果比较,其测试精度得到了显著提高。 相似文献