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1.
The scattering from an infinite elliptic metallic cylinder coated by a circular dielectric one is considered. The electromagnetic field is expressed in terms of both circular and elliptical cylindrical wave functions, which are connected with one another by well-known expansion formulas. In the special case of small h =ka /2 (a being the interfocal distance of the elliptic conductor and k the wavenumber of the dielectric coating), exact, closed-form expressions of the form S (h )=S (0)[1+g "h 2+O (h 4)] are obtained for the scattered field and the various scattering cross sections of the problem. Both polarizations are considered for normal incidence. Graphical results for various values of the parameters are given 相似文献
2.
Two theorems on lattice expansions 总被引:1,自引:0,他引:1
Daubechies I. Janssen A.J.E.M. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1993,39(1):3-6
It is shown that there is a tradeoff between the smoothness and decay properties of the dual functions, occurring in the lattice expansion problem. More precisely, it is shown that if g and g ¯ are dual, then (1) at least one of H 1/2 g and H 1/2 g ¯ is n in L 2(R), and (2) at least one of Hg and g ¯ is not in L 2(R). Here, H is the operator -1/(4π2)d 2/(dt 2 )+t 2. The first result is a generalization of a theorem first stated by R.C. Balian (1987). The second result is new and relies heavily on the fact that, when G ∈W2,2(S ) with S =[-1/2, 1/2]×[-1/2, 1/2] and G (0), than 1/G ∉L 2(S ) 相似文献
3.
Scattering by an infinite circular dielectric cylinder coatingeccentrically an elliptic metallic one
The scattering of a plane electromagnetic wave by an infinite-circular dielectric cylinder, containing eccentrically an elliptic metallic one is considered. The electromagnetic field is expressed in terms of both circular and elliptical-cylindrical wave functions, connected with one another by well-known expansion formulas. Translational addition theorems for circular cylindrical wave functions are also used for the satisfaction of the boundary conditions in the dielectric cylinder. When the solution is specialized to small values of h=k1c/2, with k1 the wavenumber of the dielectric cylinder and c the interfocal distance of the elliptic conductor, semianalytical expressions of the form S(h)=S(0)[1+gh2+O(h 4)] are obtained for the scattered field and the various scattering cross sections of this configuration. Both polarizations are considered for normal incidence. Numerical results are given for various values of the parameters 相似文献
4.
Energy transfer from selectively formed metastable states of SiO is used to pump sodium-atom laser amplifiers at λ≈569 nm (4d 2D -3p 2P ), λ≈616 nm (5s 2S -3p 2 P ), and λ≈819 nm (3d 2D -3p 2P ). The a 3Σ+ and b 3Π states of SiO are generated in high yield from the Si+N2O→SiO+N2 reaction. The energy stored in the triplet states is transferred in a highly efficient collisional process to pump sodium atoms to their lowest excited 3d 2 D , 4d 2D , and 5s 2S states. Adopting a sequence in which high concentrations of silicon and sodium atoms are mixed and oxidized, a continuous amplification (gain condition) is monitored which suggests the creation of a population inversion among the receptor sodium-atom energy levels and forms the basis for full cavity oscillation on the Na4 d 2D -3p 2P transition at 569 nm 相似文献
5.
Janssen A.J.E.M. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1992,38(1):168-171
It is shown how the Zak transform can be used to find nontrivial examples of functions f , g ∈L 2(R ) with f ×g ≡0≡F ×G , where F , G are the Fourier transforms of f , g , respectively. This is then used to exhibit a nontrivial pair of functions h , k ∈L2(R ), h ≠k , such that |h |=|k |, |H |=|K |. A similar construction is used to find an abundance of nontrivial pairs of functions h , k ∈L2 (R ), h ≠k , with |A h |=|A k| or with |W h|=|W k| where A h, A k and W h, W k are the ambiguity functions and Wigner distributions of h , k , respectively. One of the examples of a pair of h , k ∈L 2(R ), h ≠k , with |A h|=|A k| is F.A. Grunbaum's (1981) example. In addition, nontrivial examples of functions g and signals f 1≠f 2 such that f 1 and f 2 have the same spectrogram when using g as window have been found 相似文献
6.
Chew W.C. Friedrich J.A. Geiger R. 《Geoscience and Remote Sensing, IEEE Transactions on》1990,28(2):207-214
A recursive algorithm for calculating the exact solution of a random assortment of spheres is described. In this algorithm, the scattering from a single sphere is expressed in a one-sphere T matrix. The scattering from two spheres is expressed in terms of two-sphere T matrices, which are related to the one-sphere T matrix. A recursive algorithm to deduce the (n +1)-sphere T matrix from the n -sphere T matrix is derived. With this recursive algorithm, the multiple scattering from a random assortment of N spheres can be obtained. This results in an N 2 algorithm rather than the normal N 3 algorithm. As an example, the algorithm is used to calculate the low-frequency effective permittivity of a random assortment of 18 dielectric spheres. The effective permittivity deviates from the Maxwell-Garnett result for high contrast and high packing fraction. With a high packing fraction, dielectric enhancement at low frequency is possible 相似文献
7.
Stimulated anti-Stokes Raman scattering at 145.7 nm in inverted Se is generated by photolysis of OCSe at 193 nm and the subsequent up-conversion of 205.1-nm pump radiation. The tuning profile is characterized with OCSe pressure, the energies and relative timing of the pump and photodissociation lasers, and CO and Ar buffer-gas pressure. The use of CO as a buffer gas is discovered to be detrimental to the anti-Stokes output. Sixteen competing stimulated emission channels are found to suppress anti-Stokes emission on exact 4p 4 1S 0-4p 3 5s 3 P 01 pump resonance 相似文献
8.
Ashley J. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1993,39(4):1303-1309
The construction of finite-state codes between constrained systems called sofic systems introduced by R. Karabed and B. Marcus (1988) is continued. It is shown that if Σ is a shift of finite type and S is a sofic system with k /n =h (S )/h (Σ), where h denotes entropy, there is a noncatastrophic finite-state invertible code from Σ to S at rate k :n if Σ and S satisfy a certain algebraic condition involving dimension groups, and Σ and S satisfy a certain condition on their periodic points. Moreover, if S is an almost finite type sofic system, then the decoder can be sliding block 相似文献
9.
Yiqi Zhuang Qing Sun 《Electron Devices, IEEE Transactions on》1991,38(11):2540-2547
Accelerated life tests with high-temperature storage and electric aging for n+-p-n silicon planar transistors were carried out. Current gain h FE increases monotonously with time during the tests, and the h FE drift is correlated with initial measured 1/f noise in the transistors, i.e. the drift amount significantly increases with the increase of noise level. The correlation coefficient of relative drift Δh FE /h FE and 1/f noise spectral density S iB(f ) is far larger than that of Δ h FE/h FE and initial DC parameters of the transistors. A quantitative theory model for the h FE drift has been developed and explains the h FE drift behavior in the tests, which suggests that the h FE drift and 1/f noise can be attributed to the same physical origin, and both are caused by the modulation of the oxide traps near the Si-SiO2 interface to Si surface recombination. 1/f noise measurement, therefore, may be used as a fast and nondestructive means to predict the long-term instability in bipolar transistors 相似文献
10.
Peransin J.-M. Vignaud P. Rigaud D. Vandamme L.K.J. 《Electron Devices, IEEE Transactions on》1990,37(10):2250-2253
The 1/f noise in normally-on MODFETs biased at low drain voltages is investigated. The experimentally observed relative noise in the drain current S I/I 2 versus the effective gate voltage V G=V GS-V off shows three regions which are explained. The observed dependencies are S I/I 2∝V G m with the exponents m =-1, -3, 0 with increasing values of V G. The model explains m =-1 as the region where the resistance and the 1/f noise stem from the 2-D electron gas under the gate electrode; the region with m =0 at large V G or V GS≅0 is due to the dominant contribution of the series resistance. In the region at intermediate V G , m =-3, the 1/f noise stems from the channel under the gate electrode, and the drain-source resistance is already dominated by the series resistance 相似文献
11.
Jen-Shyan Wu Rong-Jaye Chen 《Reliability, IEEE Transactions on》1993,42(1):163-164
The time complexities of previously published algorithms for circular consecutive-k -out-of-n :F systems are O (nk 2) and O (nk ). The authors propose a method to improve the original O (nk 2 ) algorithm, and hence derive an O (nk ) algorithm 相似文献
12.
Time-hopping patterns can be constructed from simple difference sets. By studying such constructions, it has been proven that whenever n -2, n -1, or n +1 is a prime power, then time-hopping patterns that have n terms can be constructed and are of length less than n 2. By computation it is shown that such patterns can have length less than n 2-n 1.44 for all n ⩽150. It is also shown that time-hopping patterns for n terms can have length less than n 2+O(n 1.55) for all n 相似文献
13.
Optimality property of the Gaussian window spectrogram 总被引:1,自引:0,他引:1
It is shown that for any signal x (t ) the minimum of ∫-∞∞∫-∞ ∞ [(t -t x)2+(f -f x)2] S x(w)(t , f ) dt df over all normalized time-windows w (t ) is achieved by the Gaussian window w (t )=21/4 exp (-πt 2). Here (t x, f x) is the center of gravity of the signal x (t ), S x(w) (t , f ) is the spectrogram of x (t ) due to the window w ( t ), and the double integral is a measure of the spread of S x(w) (t , f ) around (t x, f X) in the time-frequency plane 相似文献
14.
Two recursive T -matrix algorithms are presented and their reduced computational complexities and reduced memory requirements are demonstrated. These algorithms are applied to the problem of electromagnetic scattering from conducting strips and patches with canonical geometries. The geometries are reminiscent of finite-sized frequency selective surfaces. Computational complexities of O ( N 2) and O (N 7/3) and memory requirements of O (N ) and O (N 4/3) are shown to be feasible for two-dimensional and three-dimensional geometries, respectively. The formulation uses only two components of the electric field. Therefore, the vector electromagnetic problem of scattering from three-dimensional patch geometries can be solved using scalar addition theorems for spherical harmonic wave functions. For a two-dimensional strip problem, both TM and TE polarizations can be solved simultaneously using this formulation. Numerical scattering results in the form of radar cross sections (RCS) are validated by comparison with the method of moments 相似文献
15.
A formalism for improving the convergence of the method of lines is presented. This formalism was developed for analyzing waveguide structures used in integrated optics and reduces the discretization error to O (h 4). The interface conditions between different dielectrics are taken into account. Excellent convergence is demonstrated for the slab waveguide 相似文献
16.
Woodward J.R. Cobb S.H. Shen K. Gole J.L. 《Quantum Electronics, IEEE Journal of》1990,26(9):1574-1587
Evidence is obtained which demonstrates the potential for developing purely chemical visible lasers based on rapid near-resonant energy transfer from metastable excited triplet states of germanium and silicon monoxide (a 3Σ+,b 3Π) to select metal atoms. In this study, the Group IIIA metal atoms were chosen as the energy receptors for the energy transfer-pump sequence. Excited triplet states were generated from the Ge-O3, Ge-N2, Si-N2O, and Si-NO2 reactions; the bulk of the experimental results was obtained with a germanium-based system. The energy stored in the long-lived triplet states is transferred to pump X 2P 1/2 thallium, indium, and gallium atoms to their lowest lying 2 S 1/2 states. The authors observe a system of temporal behavior which suggests the creation of a population inversion producing a gain condition and forming the basis for full cavity oscillation on the Tl 72S 1/2-6P 3/2 transition at 535 nm 相似文献
17.
Fast decoding of codes from algebraic plane curves 总被引:2,自引:0,他引:2
Justesen J. Larsen K.J. Jensen H.E. Hoholdt T. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1992,38(1):111-119
Improvement to an earlier decoding algorithm for codes from algebraic geometry is presented. For codes from an arbitrary regular plane curve the authors correct up to d */2-m 2 /8+m /4-9/8 errors, where d * is the designed distance of the code and m is the degree of the curve. The complexity of finding the error locator is O (n 7/3 ), where n is the length of the code. For codes from Hermitian curves the complexity of finding the error values, given the error locator, is O (n 2), and the same complexity can be obtained in the general case if only d */2-m 2/2 errors are corrected 相似文献
18.
Engheta N. Murphy W.D. Rokhlin V. Vassiliou M.S. 《Antennas and Propagation, IEEE Transactions on》1992,40(6):634-641
The fast multipole method (FMM) developed by V. Rokhlin (1990) to efficiently solve acoustic scattering problems is modified and adapted to the second-kind-integral-equation formulation of electromagnetic scattering problems in two dimensions. The present implementation treats the exterior Dirichlet problem for two-dimensional, closed, conducting objects of arbitrary geometry. The FMM reduces the operation count for solving the second-kind integral equation from O (n 3) for Gaussian elimination to O (n 4/3) per conjugate-gradient iteration, where n is the number of sample points on the boundary of the scatterer. A sample technique for accelerating convergence of the iterative method, termed complexifying k , the wavenumber, is also presented. This has the effect of bounding the condition number of the discrete system; consequently, the operation count of the entire FMM (all iterations) becomes O (n 4/3). Computational results for moderate values of ka , where a is the characteristic size of the scatterer, are given 相似文献
19.
Nakamura Y. Ohzu H. Miyawaki M. Ishizaki A. Kochi T. Ohmi T. 《Electron Devices, IEEE Transactions on》1992,39(6):1341-1349
A design methodology for a bipolar imaging device, the base-stored image sensor (BASIS), has been established by theoretical analysis and experimental verification for random noise. The random noise in BASIS is dominated by the shot noise in readout and transient reset operation. The theoretical analysis has been carried out by introducing the probability density functions for these operations. The readout noise depends on the base-to-collector junction capacitance C bc , the emitter common current gain h FE, the storage capacitor C T, and the emitter voltage V E. The reset noise has been confirmed to be given by thermal noise. The theoretical results coincide well with the experimental results obtained by TEG devices. An expression for the S /N ratio has been derived theoretically. It is found that h FE should be made as large as possible and ( C bc+C be) as small as possible to improve the S /N ratio for random noise, where C be is the base-to-emitter junction capacitance 相似文献
20.
Sadowsky J.S. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1993,39(1):119-128
Estimation of the large deviations probability p n =P (S n⩾γn ) via importance sampling is considered, where S n is a sum of n i.i.d. random variables. It has been previously shown that within the nonparametric candidate family of all i.i.d. (or, more generally, Markov) distributions, the optimized exponentially twisted distribution is the unique asymptotically optimal sampling distribution. As n →∞, the sampling cost required to stabilize the normalized variance grows with strictly positive exponential rate for any suboptimal sampling distribution, while this sampling cost for the optimal exponentially twisted distribution is only O (n 1/2). Here, it is established that the optimality is actually much stronger. As n →∞, this solution simultaneously stabilizes all error moments of both the sample mean and the sample variance estimators with sampling cost O (n 1/2 ). In addition, it is shown that the embedded parametric family of exponentially twisted distributions has a certain uniform asymptotic stability property. The technique is stable even if the optimal twisting parameter(s) cannot be precisely determined 相似文献