We show that under some conditions an attacker can break the public-key cryptosystem proposed by J. Schwenk and J. Eisfeld at Eurocrypt '96 which is based on the difficulty of factoring over the ring Z/nZ [x], even though its security is as intractable as the difficulty of factoring a rational integer. We apply attacks previously reported against RSA-type cryptosystems with a low exponent to the Schwenk-Eisfeld cryptosystem and show a method of breaking the Schwenk-Eisfeld signature with a low exponent.

We present an experimental and theoretical study of multiple diffraction rings of a cw Ar+ laser beam from a nitrobenzene solution of BDN (bis-(4-dimethylaminodithiobenzil)-nickel) caused by the spatial self-phase modulation. We examine in detail the effect of the intensity and phase shift profiles of the beam in the nonlinear medium by comparing the measured ring patterns with the theoretical results based on the Fraunhofer diffraction. Although the thickness of the sample is only 180 µm in our experiment, it is found that the intensity and phase shift profiles are broadened owing to the self-defocusing effect. It is also found that the phase shift profile is further broadened by the thermal diffusion. These two effects become remarkable when the focused beam is used.

The showering arc waveforms generated when contact is being separate have poor reproducibility whose causes are not sufficiently clear. This paper describes that the contact surface conditions which change with the number of contact operations are deeply related to the showering arc waveforms. First, it is experimentally shown that the contacts' surface roughness increases with the number of contact operations, and the growth model of contact surface roughness is proposed based on the change of contact resistance for the number of contact operations. Second, the growth model of molten metal bridge is proposed based on the fact that the showering arc waveforms change with the number of contact operations and the evaluation indexes of showering arc are proposed.

A more judicious choice of trial functions to implement the Improved Circuit Theory (ICT) application to multi-element antennas is achieved. These new trial functions, based on Tai's modified variational implementation for single element antennas, leads to an ICT implementation applicable to much longer co-planar dipole arrays. The accuracy of the generalized impedance formulas is in good agreement with the method of moments. Moreover, all these generalized formulas including the radiation pattern expressions are all in closed-form. This leads to an ICT implementation which still requires much shorter CPU time and lesser computer storage compared to method of moments. Thus, for co-planar dipole arrays, the proposed implementation presents a relatively very efficient method and would therefore be found useful in applications such as CAD/CAE systems.

Although the performance degradation for TCP/IP over plain ATM during congestion can be reduced if switch buffer management techniques such as Early Packet Discarding (EPD) and Partial Packet Discarding (PPD) schemes are employed. However, we show via simulation that fairness among connections remains a problem. For example, the fairness among packets of different length is a well known unsolved issue for EPD. To improve fairness of TCP and UDP over an Internet backbone, we propose a new technique called the Age Priority Packet Discarding (APPD) scheme to be used along with EPD and PPD. We employ two simulation scenarios to examine the performance of APPD; the MPEG-I video over UDP protocol and the FTP over TCP protocol. The simulation shows that with APPD combined with EPD and PPD, fairness can be well maintained against different packet length, order of connections, as well as different propagation delays. In addition, packet loss probability can be reduced with APPD in all scenarios, and the improvement is especially significant for video over UDP protocol. Finally we discuss the hardware implementation technique of the APPD scheme.

While active researches have been continuously made on the ATM switch architectures and the QoS service guarantees, most of them have been treated independently in the past. In this paper, we first explain the architectural requirement on the ATM switches to implement the mechanism of QoS guarantees in the context of ATM congestion control. Then we discuss how a vital link between two should be built, and remaining problems are pointed out.

It is shown from the Hilberts theory that if the real function Π(θ) has no zeros over the interval [0, 2π], it can be factorized into a product of the factor π+(θ) and its complex conjugate π-(θ)(=). This factorization is tested to decompose a real far-zone field pattern having zeros. To this end, the factorized factors are described in terms of bicomplex mathematics. In our bicomplex mathematics, the temporal imaginary unit "j" is newly defined to distinguish from the spatial imaginary unit i, both of which satisfy i2=-1 and j2=-1.

Although ATM networks support various traffic requirements, but many data applications are unable to precisely specify traffic parameters such as bit rate. These applications generally require a dynamic share of the available bandwidth among all active connections, they are called available-bit-rate (ABR) service. Due to bursty and unpredictable pattern of an ABR data stream, its traffic control is more challenging than other services. In this paper, we present an improved ABR traffic control approach, called Offset Proportional Rate Control Algorithm (OPRCA). The proposed approach achieves high link utilization, low delay and weighted fair sharing among contenting sources according to the predefined OPR. The implementation is much simpler than that of existing schemes. OPRCA combines an end-to-end rate control with link-by-link feedback control, and employs a buffering scheme that avoids Head-of-Line (HOL) blocking. It can dynamically regulate the transmission rate of source traffic and maintain the real fairness among all active connections. Simulation results have shown the effectiveness of OPRCA in several performance aspects.

A traffic engineering method has been developed to meet the requirements for efficient bandwidth dimensioning and for a practical and consolidated network design method. It characterizes the offered-traffic burstiness on a transit link by using time-series measurement of the aggregate traffic. It estimates future traffic characteristics based on the average traffic volume at that time which is easily derived from trend analysis, i. e. , an x% increase in bandwidth each year and gives the required link capacity. Simulation showed that the parameters estimated using this method fit the actual behavior of a network well. This method enables an appropriate bandwidth to be allocated to a transit link without having to estimate the specific traffic characteristics for each connection over the link. Once the burstiness parameter and its trend have been identified based on this method, it is possible to use a simple traffic measurement method to detect changes in network traffic and feed them back to the engineering procedure.

This paper proposes a design method of feature spaces in a two-stage image recognition method that improves the recognition accuracy and efficiency in statistical image recognition. The two stages are (1) image screening and (2) image recognition. Statistical image recognition methods require a lot of calculations for spatially matching between subimages and reference patterns of the specified objects to be detected in input images. Our image screening method is effective in lowering the calculation load and improving recognition accuracy. This method selects a candidate set of subimages similar to those in the object class by using a lower dimensional feature vector, while rejecting the rest. Since a set of selected subimages is recognized by using a higher dimensional feature vector, overall recognition efficiency is improved. The classifier for recognition is designed from the selected subimages and also improves recognition accuracy, since the selected subimages are less contaminated than the originals. Even when conventional recognition methods based on linear transformation algorithms, i. e. principal component analysis (PCA) and projection pursuit (PP), are applied to the recognition stage in our method, recognition accuracy and efficiency may be improved. A new criterion, called a screening criterion, for measuring overall efficiency and accuracy of image recognition is introduced to efficiently design the feature spaces of image screening and recognition. The feature space for image screening are empirically designed subject to taking the lower number of dimensions for the feature space referred to as LS and the larger value of the screening criterion. Then, the recognition feature space which number of dimensions is referred to as LR is designed under the condition LSLR. The two detection tasks were conducted in order to examine the performance of image screening. One task is to detect the eye- and-mouth-areas in a face image and the other is to detect the text-area in a document image. The experimental results demonstrate that image screening for these two tasks improves both recognition accuracy and throughput when compared to the conventional one-stage recognition method.

In this paper, we present an analytic model to study the reliability of some important disk array organizations that have been proposed by others in the literature. These organizations are based on the combination of two options for the data layout, regular RAID-5 and block designs, and three alternatives for sparing, hot sparing, distributed sparing and parity sparing. Uncorrectable bit errors have big effects on reliability but are ignored in traditional reliability analysis of disk arrays. We consider both disk failures and uncorrectable bit errors in the model. The reliability of disk arrays is measured in terms of MTTDL (Mean Time To Data Loss). A unified formula of MTTDL has been derived for these disk array organizations. The MTTDLs of these disk array organizations are also compared using the analytic model. By numerical experiments, we show that the data losses caused by uncorrectable bit errors may dominate the data losses of disk array systems though only the data losses caused by disk failures are traditionally considered. The consideration of uncorrectable bit errors provides a more realistic look at the reliability of the disk array systems.

We describe an algorithm for efficiently compositing partial images generated during parallel volume rendering on a distributed memory parallel computer. In this object space partitioning algorithm, each PE is assigned to several subvolumes where each subvolume has a corresponding local frame buffer. After volume rendering is performed independently for each subvolume, the partial images stored in the local frame buffers are combined to generate a complete image. During this compositing process, the communication of partial image data between the PEs is kept minimal by assigning PEs to subvolumes in an interleaved manner. This assignment makes possible a reduction in communication in the axis direction in which there is the most communication. Experimental results indicate that a 9% to 35% reduction in the total rendering time can be attained with no additional data structures and no memory overhead.

This paper proposes practical escrow cash schemes with particular emphasis on countermeasures against social crimes such as money laundering and extortion. The proposed cash schemes restrict "unconditional" privacy in order to prevent these social crimes while preserving off-line-ness, divisibility and transferability, properties listed in [25] as criteria for ideal cash schemes.

A genetic algorithm is presented for the blind-deconvolution problem of image restoration without any a priori information about object image or blurring function. The restoration problem is modeled as an optimization problem, whose cost function is to be minimized based on mechanics of natural selection and natural genetics. The applicability of GA for blind-deconvolution problem was demonstrated.

This letter proposes and investigates a method of estimating the direction of arrival (DOA) of wideband signals such as spread spectrum signals, in a multipath channel. The DOA estimation method can reduce the effect of signal distortion due to bandwidth of signals by creating a spatial spectrum wihch satisfies the sampling theory in the time domain. The DOA estimate calculated from this spatial spectrum is robust against signal distortion due to multipath. Computer simulations numerically evaluate the proposed method. In comparison with conventional MUSIC algorithm, the proposed method achieves superior performance in a multipath channel.

A rigorous radar cross section (RCS) analysis is carried out for two-dimensional rectangular and circular cavities with double-layer material loading by means of the Wiener-Hopf (WH) technique and the Riemann-Hilbert problem (RHP) technique, respectively. Both E and H polarizations are treated. The WH solution for the rectangular cavity and the RHP solution for the circular cavity involve numerical inversion of matrix equations. Since both methods take into account the edge condition explicitly, the convergence of the WH and RHP solutions is rapid and the final results are valid over a broad frequency range. Illustrative numerical examples on the monostatic and bistatic RCS are presented for various physical parameters and the far field scattering characteristics are discussed in detail. It is shown that the double-layer lossy meterial loading inside the cavities leads to the significant RCS reduction.

Scattering data from radar targets are analyzed in the time-frequency domain by using wavelet transform, and the scattering mechanisms are investigated. The wavelet transform used here is a powerful tool for the analysis of scattering data, because it can provide better insights into scattering mechanisms that are not immediately apparent in either the time or frequency domain. First, two types of wavelet transforms that are applied to the time domain data and to the frequency domain data are defined, and the multi-resolution characteristics of them are discussed. Next, the scattering data from a conducting cylinder, two parallel conducting cylinders, a parallel-plate waveguide cavity, and a rectangular cavity in the underground are analyzed by using these wavelet transforms to reveal the scattering mechanisms. In the resulting time-frequency displays, the scattering mechanisms including specular reflection, creeping wave, resonance, and dispersion are clearly observed and identified.

This paper deals with a probabilistic formulation of the diffraction and scattering of a plane wave from a periodic surface randomly deformed by a binary sequence. The scattered wave is shown to have a stochastic Floquet's form, that is a product of a periodic stationary random function and an exponential phase factor. Such a periodic stationary random function is then represented in terms of a harmonic series representation similar to Fourier series, where `Fourier coefficients' are mutually correlated stationary processes rather than constants. The mutually correlated stationary processes are written by binary orthogonal functionals with unknown binary kernels. When the surface deformations are small compared with wavelength, an approximate solution is obtained for low-order binary kernels, from which the scattering cross section, coherently diffracted power and the optical theorem are numerically calculated and are illustrated in figures.

Switching device used on digital and inverter circuits such as a stabilizer of fluorescent lamp is one of main sources of electromagnetic noise. To make such noise characteristics clear, using a simple printed line model with a TTL IC as a switching device, electric far field noise radiating from that model is measured in an anechoic chamber. It is shown typical results and that noise characteristics can be evaluated by comparing the spectrum and spectrum change of the harmonics of 3 MHz switching pulse using the same switching device. And the characteristics of the electric field noise with PCB thickness and strip line width changed are compared with the magnetic near-field noise measured by a small shielded loop antenna. The results indicate that the electric field noise strength, on the case where the width is 7 mm and the thickness is 0.51 mm, is larger than that on other cases in the range from 50 to 150 MHz. And it is confirmed that the magnetic near-field noise increases as the loop antenna approaches the IC and varies depending on the PCB thickness and the line width. However, the spectral profile of the electric field noise is different from the magnetic near-field noise.

The redundancy of universal lossy data compression for discrete memoryless sources is considered in terms of type and d-ball covering. It is shown that there exists a universal d-semifaithful code whose rate redundancy is upper bounded by (A-1/2)n-1ln n+o(n-1ln n), where A is the cardinality of source alphabet and n is the block length of the code. This new bound is tighter than known ones, and moreover, it turns out to be the attainable minimum of the universal coding proposed by Davisson.