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1.
The results of the metal-insulator transition (MIT) induced by impurity concentration are presented in the case of metallic and insulating samples 70Ge:Ga p-type. The eight samples studied have Ga concentrations N ranging from 1.848 × 1017 to 1.912 × 1017cm-3. The conductivity measurements were carried out at low temperature in the range 1 to 0.019 K. We provide physical explanations to explain the behaviors of the temperature dependence of the electrical conductivity in both sides of the MIT. The data are for a 70Ge:Ga sample prepared and reported by Itoh et al. in Ref. [Itoh K M, Watanabe M, Ootuka Y, et al. J Phys Soc Jpn, 2004, 73(1): 173]. 相似文献
2.
Xiang-dong Hou 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1997,43(3):1025-1027
Let ρ(1,m) and N(1,m) be the covering radius and norm of the first-order Reed-Muller code R(1,m), respectively. It is known that ρ(1,2k+1)⩽lower bound [22k-2(2k-1/2)] and N(1,2k+1)⩽2 lower bound [22k-2(2k-1/2)] (k>0). We prove that ρ(1,2k+1)⩽2 lower bound [22k-1-2(2k-3/2)] and N(1,2k+1)⩽4 lower bound [22k-1-2(2k-3/2)] (k>0). We also discuss the connections of the two new bounds with other coding theoretic problems 相似文献
3.
Square-root QR inverse iteration for tracking the minor subspace 总被引:1,自引:0,他引:1
A new algorithm for tracking the eigenvectors associated with the r smallest eigenvalues of an N×N covariance matrix is introduced. The method is sequential inverse iteration based on a recursive square-root QR factor updating of the covariance matrix with O(N2 r) operations per time update. The principal operations count of this new tracker is justified by a significantly better performance compared with the fast O(Nr2) minor subspace tracker of Douglas et al. (1998) 相似文献
4.
Canali C. Paccagnella A. Zanoni E. Lanzieri C. Cetronio A. 《Electron Device Letters, IEEE》1991,12(2):80-81
In the above-named work (see ibid., vol.11, p.113-15, March 1990), Hui et al. proposed a method to measure impact ionization current in GaAs MESFETs and evaluated the impact ionization coefficient αn in GaAs. For electric fields greater than approximately 1.5×105 V-cm-1, αn can be fitted to the equation αn=4.0×10 6×exp (-2.3×106/E). In the present work, the commenters performed careful measurements of gate current I g in GaAs MESFET devices similar to those used by Hui et al., and they show that the ionization coefficient still fits the above equation down to αn=10-4 cm-1 . These results extend the previous data by three orders of magnitude. In a reply, the original authors affirm that the commenters have significantly improved the accuracy of the data previously presented 相似文献
5.
Beach R. Shinn M.D. Davis L. Solarz R.W. Krupke W.F. 《Quantum Electronics, IEEE Journal of》1990,26(8):1405-1412
A spectroscopic investigation of the biaxial crystal yttrium orthosilicate doped with Nd3+(Nd3+:Y2SiO5) has been performed. Spectrally and orientationally resolved emission cross sections necessary for the evaluation of laser performance on the Nd3+ 4F 3/2-4I 9/2 and 4F 3/2-4I 11/2 transitions have been determined. The Judd-Ofelt theory has been applied to measured values of optical absorption line strengths to obtain the orientation averaged intensity parameters: Ω2-3.34×10-20 cm2, Ω 4=4.35×10-20 cm2, and Ω6=5.60×10-20 cm2. These Judd-Ofelt intensity parameter values are significantly different from those previously reported by A.M. Tkachuk et al. Using these intensity parameters, the Nd3+ 4F 2 metastable state lifetime is predicted to be 225 μs. Measured low Nd concentration 4F 3/2 lifetimes of 214 μs indicate a high radiative quantum efficiency. Because of the Stark level splitting of the Nd3+ 4F 3/2 and 4I 9/2 manifolds, laser operation at twice one of the Cs atomic resonance filter acceptance wavelengths is possible 相似文献
6.
Thurairaj M. Das M.B. Ballingall J.M. Ho P. Chao P.C. Kao M.-Y. 《Electron Device Letters, IEEE》1991,12(8):410-412
Experimental data are presented on equivalent gate noise voltage from 1 to 105 Hz obtained from lattice-matched and strained InGaAs quantum-well modulation-doped field effect transistors (MODFETs). In both types of devices excess generation-recombination (g-r) noise is observed at or below 100 Hz above an `apparent' background 1/f noise with spectral intensity ranging from 0.5×10-17 to 2×10-17 V2-Hz-1-cm2 at 1 Hz. These results are comparable to those reported by S.M.J. Liu et al. (1986) for the pseudomorphic MODFETs 相似文献
7.
Adaptive recovery of a chirped signal using the RLS algorithm 总被引:1,自引:0,他引:1
This paper studies the performance of the recursive least squares (RLS) algorithm in the presence of a general chirped signal and additive white noise. The chirped signal, which is a moving average (MA) signal deterministically shifted in frequency at rate ψ, can be used to model a frequency shift in a received signal. General expressions for the optimum Wiener-Hopf coefficients, one-step recovery and estimation errors, noise and lag misadjustments, and the optimum adaptation constant (βopt) are found in terms of the parameters of the stationary MA signal. The output misadjustment is shown to be composed of a noise (ξ0Mβ/2) and lag term (κ/(β2ψ2)), and the optimum adaptation constant is proportional to the chirp rate as ψ2/3 . The special case of a chirped first-order autoregressive (AR1) process with correlation (α) is used to illustrate the effect the bandwidth (1/α) of the chirped signal on the adaptation parameters. It is shown that unlike for the chirped tone, where the βopt increases with the filter length (M), the adaptation constant reaches a maximum for M near the inverse of the signal correlation (1/α). Furthermore, there is an optimum filter length for tracking the chirped signal and this length is less than (1/α) 相似文献
8.
The method of infrared microwave sideband laser spectroscopy developed by G. Magerl, et al. (ibid, vol.18, p.1214-20, 1982) for application in the 9-11-μm region with a CO2 laser has been extended to application in the 5-6-μm region with a CO laser. The experimental details, performance of the system, and typical spectra are described. Frequency measurements of spectra in the 0111←0000 band of 14N2 16O and the 200←0000 band of 16O12C32S are compared to the results of previous precise measurements by heterodyne techniques to show that the accuracy is limited mainly by the resettability of the CO laser frequency 相似文献
9.
Multicast connections are used in broad-band switching networks as well as in parallel processing. We consider wide-sense and strict-sense nonblocking conditions for multi-log2 N switching networks with multicast connections. We prove that such networks are wide-sense nonblocking if they are designed by vertically stacking at least t · 2n-t-1 + 2 n-2t-1 planes of a log2 N networks together, where 1 ⩽ t ⩽ [n/2] and t defines the size of a blocking window K = 2t. For t = [n/2] and n even, and for [n/2] ⩽ t ⩽ n the number of planes must be at least t · 2n-t-1 + 1 and 2t + (n - t - 1) · 2n-t-1 - 22t-n-1 + 1, respectively. In the case of strict-sense nonblocking switching networks, the number of planes is at least N/2. The results obtained in this paper show that in many cases number of planes in wide-sense nonblocking switching networks is less than those for t = [n/2] considered by Tscha and Lee (see ibid., vol.47, p.1425-31, Sept. 1999). The number of planes given in the paper is the minimum number of planes needed for wide-sense nonblocking operation provided that Algorithm 1 is used for setting up connections. The minimum number of planes for such operation in general is still open issue 相似文献
10.
The pressure-dependent Sellmeier coefficients are essential to characterize the optical design parameters for the optical fiber communication systems under deep sea environmental conditions. These coefficients are calculated for densified silica glass for the first time to compute the pressure dependence of material dispersion at any wavelength from the ultraviolet (UV) to 1.71 μm. The zero dispersion wavelength λ0 (1.2725 μm at 0.1 106 N m -2) varies linearly with pressure, and dλ0/dP is 0.0027 nm/(106 N m-2). The calculated value is approximately one-third of the experimental value of 0.0076 nm/(106 N m-2) for a germanium-doped dispersion shifted fiber having λ0=1.5484 μm and -0.0070 nm/(106 N m-2) for a pure silica-core fiber cable having λ0 =1.2860 μm. Since, the refractive indexes are increased with pressure, the negative value of shift of the zero-dispersion wavelength is erroneous. The explanations are due to Ge-doping in silica glass, a possible temperature fluctuation of 0.16°C in the pressure-dependent measurement system of the zero dispersion wavelength and different experimental conditions of the silica glass and the optical fibers. This anomaly can also be attributed to the internal strain development at the core-cladding and fiber-jacketing boundaries due to pressure, which shows a larger experimental value. It accounts for the experimental values satisfactorily 相似文献
11.
M. Y. Simmons A. R. Hamilton A. Kurobe S. J. Stevens D. A. Ritchie M. Pepper 《Microelectronics Journal》1997,28(8-10):795-801
This paper reports the fabrication of an in situ back-gated hole gas on the (311)A surface of GaAs. The hole density can be varied from fully depleted to ps = 2.1 × 1011 cm−2 with mobilities of up to μ = 1.1 × 106 cm2V−1 s−1. It is seen that for carrier densities down to ps = 4 × 1010 cm−2 the mobility in the [
] direction is greater than that in the [
] direction. Using a combination of front- and back-gates we are able to keep the carrier density constant and deform the hole gas wavefunction such that the holes are pushed up against or moved further away from the heterointerface. Thus we are able to separately investigate the various scattering mechanisms that determine the mobility, and compare the experimental data with theoretical calculations based on the shape of the wavefunction. 相似文献
12.
Rectangular Pisarenko method applied to source localization 总被引:1,自引:0,他引:1
Most high-resolution (HR) direction-of-arrival (DOA) estimation schemes require the extraction of a low-dimensional subspace: a task that takes O(N3) flops for an order S matrix. Different techniques have been recently proposed to reduce this computational load. For those working on blocks of data, the number of flops required is generally O(N2P), where P, which is the dimension of the subspace (the number of sources), is often quite small as compared with N, which is the number of sensors. The method we propose is a HR technique that requires O(NP2)+O(P3) flops, i.e., that is linear in the number of sensors. The price to be paid for this drastic computational saving is a reduction in performance. Although the Cramer-Rao lower bound (CRLB) on the variance of the direction estimates is of the order T-1 N-3 (with T the number of snapshots), this variance is of order T-1 N-2 for the proposed procedure. The idea behind the method is to apply a Pisarenko method to a rectangular matrix extracted from the Toeplerized estimated covariance matrix, and it is this Toeplerization that allows preservation of the O(T-1 N-2) level of performance 相似文献
13.
Two efficient time slot assignment algorithms, called the two-phase algorithm for the nonhierarchical and the three-phase algorithm for the hierarchical time-division multiplex (TDM) switching systems, are proposed. The simple idea behind these two algorithms is to schedule the traffic on the critical lines/trunks of a traffic matrix first. The time complexities of these two algorithms are found to be O(LN2) and O(LM2), where L is the frame length, N is the switch size, and M is the number of input/output users connected to a hierarchical TDM switch. Unlike conventional algorithms, they are fast, iterative and simple for hardware implementation. Since no backtracking is used, pipelined packet transmission and packet scheduling can be performed for reducing the scheduling complexity of a transmission matrix to O(N2) and O(M2), respectively. Extensive simulations reveal that the two proposed algorithms give close-to-optimal performance under various traffic conditions 相似文献
14.
The antenna properties of optical heterodyne receivers 总被引:1,自引:0,他引:1
《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1966,54(10):1350-1356
An optical heterodyne receiver is, in effect, both a receiver and an antenna. As an antenna it has an effective aperture or capture cross section AR (Ω) for plane wave signals arriving from any direction Ω. The wavefront alignment between signal and local-oscillator (LO) beams required for effective optical heterodyning may be summarized in the "antenna theorem" ∫∫AR (Ω)dΩ = [η2/η2]λ2where the moments of the quantum efficiency η are evaluated over the photosensitive surface. Thus, an optical heterodyne having effective aperture AR for signals arriving within a single main antenna lobe or field of view of solid angle ΩR is limited by the constraint AR ΩR ≈ λ2. Optical elements placed in the signal and/or LO beam paths can vary the trade-off between AR and ΩR but cannot change their product. It is also noted that an optical heterodyne is an insensitive detector for thermal radiation, since a thermal source filling the receiver's field of view must have a temperature T ≈ [In (1 + η)]-1hf/k to be detected with S/N ≈ 1. Optical heterodyning can be useful in practical situations, however, for detecting Doppler shifts in coherent light scattered by liquids, gases, or small particles. Another antenna theorem applicable to this problem says that in a scattering experiment the received power will be ≲ Nσλ/4π times the transmitted power, where N is the density of scatterers and σ is the total scattering cross section of a single scatterer. The equality sign is obtained only when a single aperture serves as both. transmitting and receiving aperture, or when two separate apertures are optimally focused at short range onto a common volume. 相似文献
15.
“特洛伊”消息攻击是Andreeva等针对MD结构杂凑函数提出的一种攻击方法,首次将其应用于不同于MD结构的一类杂凑函数,即联接杂凑。结合联接杂凑的特点,综合利用Joux的多碰撞和深度为n?l的“钻石树”结构多碰撞,构造出了2n-bit联接杂凑函数的长度为 块的“特洛伊”消息,并据此首次提出了对其的固定前缀“特洛伊”消息攻击,其存储复杂性为 块消息,时间复杂性为 次压缩函数运算,远低于理想的时间复杂性 。 相似文献
16.
《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1977,65(7):1079-1080
It is proposed that pulse delay, in the presence of distortion, be defined as ∫TX(T) dT/∫X(T) dT where X(T) = ∫|m1 (t - T)|2|m2 (t)|2dt is the cross correlation of the squares of the magnitudes of the transmitted and received pulse modulation. In the absence of the distortion, the definition reduces to the group delay. 相似文献
17.
This paper is about the eigenvalues and eigenvectors of (↓2)H. The ordinary FIR filter H is a convolution with a vector h=(h(O),...,h(N)), which is the impulse response. The operator (↓2) downsamples the output y=h*x, keeping the even-numbered components y(2n). Where H is represented by a constant-diagonal matrix, this is a Toeplitz matrix with h(k) on its kth diagonal, the odd-numbered rows are removed in (↓2)H. The result is a double shift between rows, yielding a block Toeplitz matrix with 1×2 blocks. Iteration of the filter is governed by the eigenvalues. If the transfer function H(z)=Σh(k)z-k has a zero of order p at z=-1, corresponding to ω=π, then (↓2)H has p special eigenvalues ½,¼...,(½)p. We show how each additional “zero at π” divides all eigenvalues by 2 and creates a new eigenvector for λ=½. This eigenvector solves the dilation equation φ(t)=2Σh(k)φ(2t-k) at the integers t=n. The left eigenvectors show how 1,t,...,tp-1 can be produced as combinations of φ(t-k). The dilation equation is solved by the cascade algorithm, which is an infinite iteration of M=(↓2)2H. Convergence in L2 is governed by the eigenvalues of T=(↓2)2HHT corresponding to the response 2H(z)H(z-1 ). We find a simple proof of the necessary and sufficient condition for convergence 相似文献
18.
Groups of algebraic integers used for coding QAM signals 总被引:2,自引:0,他引:2
Xue-dong Dong Cheong Boon Soh Gunawan E. Li-zhong Tang 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1998,44(5):1848-1860
Linear block codes over Gaussian integers and Eisenstein integers were used for coding over two-dimensional signal space. A group of Gaussian integers with 22n elements was constructed to code quadrature amplitude modulation (QAM) signals such that a differentially coherent method can be applied to demodulate the QAM signals. This paper shows that one subgroup of the multiplicative group of units in the algebraic integer ring of any quadratic number field with unique factorization, modulo the ideal (Pn), can be used to obtain a QAM signal space of 2p2n-2 points, where p is any given odd prime number. Furthermore, one subgroup of the multiplicative group of units in the quotient ring Z[ω]/(pn) can be used to obtain a QAM signal space of 6p2n-2 points; one subgroup of the multiplicative group of units in the quotient ring Z[i](pn) can be used to obtain a QAM signal space of 4p2n-2 points which is symmetrical over the quadrants of the complex plane and useful for differentially coherent detection of QAM signals; the multiplicative group of units in the quotient ring Z[ω]/(2n) can be used to obtain a QAM signal space of 3·22n-2 points, where i=√-1, ω=(-1+√-3)/2=(-1+i√3)/2, p is any given odd prime number, Z[i] and Z[ω] are, respectively, the Gaussian integer ring and the Eisenstein integer ring. These multiplicative groups can also be used to construct block codes over Gaussian integers or Eisenstein integers which are able to correct some error patterns 相似文献
19.
Minimum bias multiple taper spectral estimation 总被引:10,自引:0,他引:10
Two families of orthonormal tapers are proposed for multitaper spectral analysis: minimum bias tapers, and sinusoidal tapers {υ (k/)}, where υsub n//sup (k/)=√(2/(N+1))sin(πkn/N+1), and N is the number of points. The resulting sinusoidal multitaper spectral estimate is Sˆ(f)=(1/2K(N+1))Σj=1K |y(f+j/(2N+2))-y(f-j/(2N+2))|2, where y(f) is the Fourier transform of the stationary time series, S(f) is the spectral density, and K is the number of tapers. For fixed j, the sinusoidal tapers converge to the minimum bias tapers like 1/N. Since the sinusoidal tapers have analytic expressions, no numerical eigenvalue decomposition is necessary. Both the minimum bias and sinusoidal tapers have no additional parameter for the spectral bandwidth. The bandwidth of the jth taper is simply 1/N centered about the frequencies (±j)/(2N+2). Thus, the bandwidth of the multitaper spectral estimate can be adjusted locally by simply adding or deleting tapers. The band limited spectral concentration, ∫-ww|V(f)|2df of both the minimum bias and sinusoidal tapers is very close to the optimal concentration achieved by the Slepian (1978) tapers. In contrast, the Slepian tapers can have the local bias, ∫-½½f 2|V(f)|2df, much larger than of the minimum bias tapers and the sinusoidal tapers 相似文献
20.
Yiu-Wing Leung 《Selected Areas in Communications, IEEE Journal on》1994,12(9):1481-1487
In an N×N time-multiplex switch, transmission conflict arises when two or more input adaptors transmit packets to the same output adaptor simultaneously. To resolve transmission conflict, we propose two neural-based scheduling algorithms which use a large number of simple processing elements to perform scheduling in parallel. The first algorithm uses N2 hysteresis McCulloch-Pitts (1943) neurons to determine conflict-free transmission schedules with maximum throughput. The second algorithm resolves transmission conflict among the first M packets in each input queue. It determines suboptimal transmission schedules using only NM neurons (M2=250000 to NM=5000 相似文献