On Matroids and Nonideal Secret Sharing

Secret-sharing schemes are a tool used in many cryptographic protocols. In these schemes, a dealer holding a secret string distributes shares to the parties such that only authorized subsets of participants can reconstruct the secret from their shares. The collection of authorized sets is called an access structure. An access structure is ideal if there is a secret-sharing scheme realizing it such that the shares are taken from the same domain as the secrets. Brickell and Davenport (Journal of Cryptology, 1991) have shown that ideal access structures are closely related to matroids. They give a necessary condition for an access structure to be ideal-the access structure must be induced by a matroid. Seymour (Journal of Combinatorial Theory B, 1992) has proved that the necessary condition is not sufficient: There exists an access structure induced by a matroid that does not have an ideal scheme. The research on access structures induced by matroids is continued in this work. The main result in this paper is strengthening the result of Seymour. It is shown that in any secret-sharing scheme realizing the access structure induced by the Vamos matroid with domain of the secrets of size k, the size of the domain of the shares is at least k + Omega(radic(k)). The second result considers nonideal secret-sharing schemes realizing access structures induced by matroids. It is proved that the fact that an access structure is induced by a matroid implies lower and upper bounds on the size of the domain of shares of subsets of participants even in nonideal schemes (as long as the shares are still relatively short). This generalized results of Brickell and Davenport for ideal schemes. Finally, an example of a nonideal access structure that is nearly ideal is presented.     

High-Rate Interpolation of Random Signals From Nonideal Samples

We address the problem of reconstructing a random signal from samples of its filtered version using a given interpolation kernel. In order to reduce the mean squared error (MSE) when using a nonoptimal kernel, we propose a high rate interpolation scheme in which the interpolation grid is finer than the sampling grid. A digital correction system that processes the samples prior to their multiplication with the shifts of the interpolation kernel is developed. This system is constructed such that the reconstructed signal is the linear minimum MSE (LMMSE) estimate of the original signal given its samples. An analytic expression for the MSE as a function of the interpolation rate is provided, which leads to an explicit condition such that the optimal MSE is achieved with the given nonoptimal kernel. Simulations confirm the reduction in MSE with respect to a system with equal sampling and reconstruction rates.      

Maximum Frequency Indication: Minima Counting Versus Zero-Crossing Counting

Certain Doppler blood flow measurements are well done by extracting the greatest momentarily present frequency; an alternative method involving counting of minima is presented, along with a circuit type that directly produces a volume-indicating integral.     

非理想DDS输出信号分析及滤波处理

直接数字频率合成(DDS)技术广泛应用于可变时钟发生电路中,文中介绍了直接数字频率合成(DDS)技术的基本原理和非理想情况下DDS输出频谱结构,然后分析了工程实际中杂散对时钟信号的影响,最后解释了以滤波器和锁相环(PLL)改善输出时钟信号质量的原理,并给出了实验结果。     

Frequency Counting Modulator

One modulation method called the frequency counting modulator (FCM), which can produce various constant envelope signals, is proposed. The FCM is materialized by only digital circuits and, therefore, is easily implemented in a large scale integrated circuit (LSI). From analytical study of the FCM, design formulas are derived for MSK-type modulation, and modulated signal performance features are clarified in terms of minimum signal distance, the effect of a Gaussian receiving filter, and spectral power concentration.     

Correcting Radiated EM Emission Data Measured in Nonideal Environments

The Federal Communications Commission (FCC) requires that all computing devices meet radiated electromagnetic (EM) emission limits before they are marketed in the United States. EM emission measurements must be made in an environment where the results can be correlated with the results of tests made in an open field. Although the FCC does not specify a method of correlation, it is not uncommon to add or subtract correction factors to the measured results. These correction factors are usually arrived at by comparing data taken in the nonideal environment with theoretical or open-field data. However, when correction factors are applied without regard to the characteristics of the EM source, the corrected value may be more in error than the uncorrected value.     

Nonideal behaviour of singlemode fibre-optic 3×3 directionalcouplers

The phase shifts of 3×3 singlemode couplers deviate from 120° because of losses and asymmetries. The dependence of the phase shifts on the input states of polarisation is shown. Furthermore, the phase shift deviations due to power splitting asymmetries can be predicted numerically to some extent without phase sensitive measurements     

Nonideal sampling and interpolation from noisy observations in shift-invariant spaces

Digital analysis and processing of signals inherently relies on the existence of methods for reconstructing a continuous-time signal from a sequence of corrupted discrete-time samples. In this paper, a general formulation of this problem is developed that treats the interpolation problem from ideal, noisy samples, and the deconvolution problem in which the signal is filtered prior to sampling, in a unified way. The signal reconstruction is performed in a shift-invariant subspace spanned by the integer shifts of a generating function, where the expansion coefficients are obtained by processing the noisy samples with a digital correction filter. Several alternative approaches to designing the correction filter are suggested, which differ in their assumptions on the signal and noise. The classical deconvolution solutions (least-squares, Tikhonov, and Wiener) are adapted to our particular situation, and new methods that are optimal in a minimax sense are also proposed. The solutions often have a similar structure and can be computed simply and efficiently by digital filtering. Some concrete examples of reconstruction filters are presented, as well as simple guidelines for selecting the free parameters (e.g., regularization) of the various algorithms.     

Birth-Death and Bug Counting

Many software reliability time-domain bug-counting models are, as fault counters, special cases of the stochastic process known as the death process. Generalization to a nonhomogeneous birth-death process achieves three ends: stochastic fault introduction, the synthesis of a time-dependent failure rate with imperfect debugging and fault introduction, and the mathematical unification of much bug-counting theory. Often, the price for generalization is mathematical intractability. Yet useful and tractable reliability measures with strong intuitive appeal are derived. The paper opens with a brief general discussion of software reliability and a selective review of some bug-counting models. Thereafter, the fundamental concepts and equations of a birth-death process are presented and applied to software reliability modeling. Assumptions for this application are then dealt with at some length. Reliability measures-initial, present, and future - are developed. Finally. the practical application of the model in the reliability assessment of a software package is discussed.     

非理想相位调制边带锁腔系统的理论分析

本文阐述了用相位调制边带系统获取光学参量振荡腔信息的原理,并在此基础上分别讨论了内腔、腔镜损耗以及调制频率对该锁腔系统的影响,这对提高锁频技术的精度和稳定度有一定的指导意义。     

System Stimulation for Dispersion Compensation with Nonideal Chirped Fiber Bragg Grating

Chirped fiber Bragg grating (CBG) has been used to compensate the dispersion in the optical fiber communication system. We substitute dispersion compensation fiber (DCF) with CBG in the 10Gbit/s disperion-managed system over 1100km. In order to get system performance in the nonideal situation, the parameters of CBG are varied from the designed optimum in some extent. Post-, pre- and dual-compensation methods are compared.     

Theoretical Efficiency for Triplers Using Nonideal Varistor Diodes at Submillimeter Wavelengths

The theoretical efficiency for frequency triplers multiplying from 300 to 900 GHz has been calculated for nonideal GaAs Schottky diodes operating in the varistor mode. The maximum efficiency is determined to be about 7 percent, only slightly smaller than that for ideal varistors. Guidelines for optimum bias conditions and embedding network impedances have been determined using the large-signal analysis computer program of Siegel and Kerr.     

Analysis of a Negative Conductance Amplifier Operated with a Nonideal Circulator

Negative conductance amplifiers are usually operated with a circulator in order to achieve greater gain-bandwidth products and stable operation. Typical circulators differ from ideal circulators in that the forward loss between ports is not zero, and the reverse isolation between ports is not intinite. The main effects of nonintinite isolation are shown to be a modified gain-bandwidth product and a assumed to exist between ports 3 and 2. No other dechange in output admittance of the circulator output port. These effects result principally from the finite isolation between the output and amplifier ports. The main effect of incidental dissipation has previously been shown to be an increase in system noise figure. This paper considers only the effects caused by noninfinite isolation. A model of a lossless three-port circulator with noninfinite isolation is set up, and a negative conductance amplifier is considered to be limited to ensure a positive output conductance at the output port of the circulator (that is, the combination of negative conductance amplifier and nonideal circulator is assumed to be open-circuit stable). Subject to this assumption, the combination of negative conductance amplifier and nonideal circulator is then analyzed for its output admittance, available power gain, and effective input noise temperature.     

晶体中光电子涨落的影响因素

针对晶体中光电子涨落的特点,分析了光吸收激发和热激发中影响光电子产生的因素.在光电子的衰减阶段,不同的电子陷阱所起的作用不同,浅电子陷阱由于延长了光电子在导带的弛豫时间,使光电子的衰减变缓;而深电子陷阱由于对光电子形成强束缚或作为复合中心加速了光电子的衰减.     

Negative Impedance Converter With Reduced Nonideal Gain and Parasitic Impedance Effects

In this paper, two novel negative impedance converter (NIC) structures are proposed. One of the introduced NICs exhibits the property of both simultaneously reduced nonideal gain and parasitic impedance effects. Also, the other one shows the property of reducing only parasitic impedance effects and employs only second-generation current conveyors; accordingly, it can be realized with commercially available active devices such as AD844s. In order to show the performance of the introduced NICs, a versatile circuit employing a minimum number of active and passive elements for all the analog filters and lossy inductor simulators is developed. The proposed topology with appropriate component and input port selections gives four kinds of lossy grounded simulated inductors as well. Further, the presented multipurpose circuit is the first one that provides both of the current-mode and voltage-mode standard universal filter responses as well as synthetic inductors from the same topology. The developed topology employing only grounded capacitors can also realize transimpedance-mode low-pass and bandpass responses simultaneously; thus, it is convenient for integrated circuit (IC) realization. Likewise, positive lossy inductor simulators consist of a grounded capacitor. Nevertheless, the realized circuit requires a single resistive component-matching condition. Simulation results using SPICE program and experimental results are included to verify the theoretical ones.      

Nonideal battery and main memory effects on CPU speed-setting forlow power

This paper explores the system-level power-performance tradeoffs of dynamically varying CPU speed. Previous work in CPU speed-setting considered only the power of the CPU and only CPUs that vary supply voltage with frequency. This work takes a broader approach, considering total system power, battery capacity, and main memory bandwidth. The results, which are up to a factor of four less than ideal, show that all three must be considered when setting the CPU speed     

器件的非理想化对光纤陀螺精度的影响

为了提高开环光纤陀螺的测量精度,研究了干涉式开环光纤陀螺系统中元器件的非理想化对陀螺精度的影响.根据光纤陀螺系统的结构特点,给出了陀螺系统不同元器件的矩阵模型,导出了开环陀螺的输出表达式,重点分析了光源偏振度和输出光功率波动、耦合器分光比波动以及系统中光纤尾纤熔接点对轴误差造成的偏振误差.研究结果表明,在诸多影响因素中,光源波动对陀螺系统的影响最大,耦合器分光比波动次之,熔接点对轴误差的影响最小.     

支撑RoF技术的新型光电子器件及技术

在高频的微波光子学研究的领域中,光载无线（RoF）技术已经成为下一代宽带无线通信技术的发展热点。近年来,支撑RoF技术的新型光电子器件的关键技术有毫米波副载波光学产生技术和接收技术,其中包括外调制器方法、射频上转换法、光学外差法、毫米波调制光脉冲发生器等等。这些技术的突破将促进RoF技术市场化的步伐。     

硫化镉薄膜的XPS研究

用XPS分析了CdS薄膜的结构。硫化镉薄膜是用化学沉积法制备的胶体颗粒,然后再通过真空蒸发法在平面玻璃上形成的多晶薄膜。XPS分析表明CdS薄膜中的Cd3d和S2p峰值均比块状CdS向高能方向偏移了10eV。这主要是由于表面效应所致。