This work presents the results of an extensive DC current aging and failure analysis carried out on blue InGaN/GaN LEDs which identify failure mechanisms related to package degradation, changes in effective doping profile, and generation of deep levels. DLTS and ElectroLuminescence (EL) spectra indicate the creation of extended defects in devices aged at very high current density.

We consider the problem of constructing nonlinear dynamical systems that realize an arbitrary prescribed tree sources. We give a construction of dynamical systems by using piecewise-linear maps. Furthermore, we examine the obtained dynamical system to show that the structure of the memory of tree sources is characterized with some geometrical property of the constructed dynamical systems. Using a similar method, we also construct a dynamical system generating an arbitrary prescribed reverse tree source and show that the obtained dynamical system has some interesting geometrical property explicitly reflecting the tree structure of the memory of the reverse tree source.

This paper proposes a technique for indexing, clustering and retrieving images based on their edge features. In this technique, images are decomposed into several frequency bands using the Haar wavelet transform. From the one-level decomposition sub-bands an edge image is formed. Next, the higher order auto-correlation function is applied on the edge image to extract the edge features. These higher order autocorrelation features are normalized to generate a compact feature vector, which is invariant to shift, image size. We used direction cosine as measure of distance not to be influenced by difference of each image's luminance. Then, these feature vectors are clustered by a self-organizing map (SOM) based on their edge feature similarity. The performed experiments show higher precision and recall of this technique than traditional ways in clustering and retrieving images in a large image database environment.

We report the investigation of major dispersion mechanisms such as self-heating, trapping, current collapse, and floating-body effects present in AlGaN/GaN HFETs. These effects are analyzed using DC/Pulsed IV, load-pull, low-frequency noise systems, and a cryogenic probe station. This study leads to a better understanding of the device physics, which is critical for accurate large-signal modeling and device optimization.

We propose a new detection method of a 2-dimensional pH image to measure the pH distribution of test materials by illuminating a frequency modulated light to LAPS using a chopping wheel. It could simultaneously measure signals in one line by applying a modulated light with a different frequency for each pixel, using a chopping wheel for modulating the frequency, and calculating an amplitude with respect to a frequency component by the light source. To test the proposed method, we implement a chopping wheel in consideration of a LAPS's characteristic, and reconstructed an image by frequency analysis using the implemented chopping wheel and 4 mm test pattern image. As a result, we verified that the proposed method using the chopping wheel was able to detect 30 times faster a 3030 pixels pH image having a PSNR more than 22 dB above the conventional method.

In many distributed systems, tokens are fundamental tools to manage resources shared by processes. Thus, monitoring tokens has become a significant problem in developing the distributed programs. This paper formulates the problems of monitoring tokens in terms of detecting the special global predicates, called summative global predicates. In this paper, several algorithms to detect various summative global predicates are developed and their time complexities are discussed.

This paper addresses the system throughput maximization problem for HAPS third generation cellular systems. We assume that the Stratospheric Platform is able to perform a perfect link gain estimation for all mobile terminals, such that a centralized resource allocation strategy is made possible. A classical 3G wireless scenario is considered, where traffics characterized by different bit rates coexist with Best Effort Traffic services without stringent bit rate constraints. In this scenario, we firstly envisage three Rate Assignment schemes for best effort terminals which aim at achieving the maximum system throughput subject to different bit rate constraints. For the second envisaged rate assignment scheme, which represents the best compromise between service fairness and throughput, we then propose a simplified approach that allows to noticeably decrease the implementation complexity with a slight performance degradation.

By a worst input (for the selection phase of Heapsort) of size n, we mean a heap of size n such that, if it is given to the selection phase of Heapsort, the number of movements of data is maximum among the numbers of movements for all heaps of size n. D. E. Knuth showed a special type of worst inputs which we will call the K-type heaps. His definition of K-type heaps was by the induction on the size n. We give one characterization of K-type worst heaps that is based on their tree structure. This characterization gives more information on the tree structure of K-type heaps than the Knuth's definition.

A siphon-trap of a Petri net N is defined as a place set S with S = S, where S = { u| N has an edge from u to a vertex of S} and S = { v| N has an edge from a vertex of S to v}. A minimal siphon-trap is a siphon-trap such that any proper subset is not a siphon-trap. The following polynomial-time algorithms are proposed: (1) FDST for finding, if any, a minimal siphon-trap or even a maximal class of mutually disjoint minimal siphon-traps of a given Petri net; (2) FDSTi that repeats FDST i times in order to extract more minimal siphon-traps than FDST. (3) STFM_T (STFM_Ti, respectively) which is a combination of the Fourier-Motzkin method and FDST (FDSTi) and which has high possibility of finding, if any, at least one minimal-support nonnegative integer invariant.

The plan of High Altitude Platform Station (HAPS) is considered as a revolutionary wireless system plan with several economic and technological advantages over both space- or ground-based counterparts. In this paper, we propose a joint system of terrestrial and HAPS cellular for Wideband-CDMA mobile communication. This system makes the conventional terrestrial W-CDMA cellular area smaller and the remainder area covered by HAPS to increase the total capacity. Furthermore in down link channel, we introduce the polarized wave and doughnut-like radiation. However, in the proposed system, the performance would be dependent on the terminal position especially near the boundary of doughnut-like cell zone. To overcome this, site diversity that uses both signals from terrestrial Base Station and HAPS Base Station is also introduced. To confirm the availability of the proposed system, we evaluate the system performance by computer simulation.

There are several attempts to generate chaotic binary sequences by using one-dimensional maps. From the standpoint of engineering applications, it is necessary to evaluate statistical properties of sample sequences of finite length. In this paper we attempt to evaluate the statistics of chaotic binary sequences of finite length. The large deviation theory for dynamical systems is useful for investigating this problem.

Recently binary or real-valued sequences generated by Chebyshev maps are proposed as spreading sequences in DS/CDMA systems. In this article, we consider sequences of real-valued functions of bounded variation, which include binary functions, of iterates generated by Chebyshev maps, and evaluate explicitly the upper bound of mixing rate of such sequences by defining the modified Perron-Frobenius operator associated with the Chebyshev maps.

Recently, feature maps have been applied to various problem domains. The success of some of these applications critically depends on whether feature maps are topologically ordered. Several different approaches have been proposed to improve the conventional self-organizing feature map (SOM) algorithm. However, these approaches do not guarantee that a topologically-ordered feature map can be formed at the end of a simulation. Therefore, the trial-and-error procedure still dominates the procedure of forming feature maps. In this paper, we propose a healing mechanism to repair feature maps that are not well topologically ordered. The healed map is then further fine-tuned by the conventional SOM algorithm with a small learning rate and a small-sized neighborhood set so as to improve the accuracy of the map. Two data sets were tested to illustrate the performance of the proposed method.

We consider only P-invariants that are nonnegative integer vectors in this paper. An P-invariant of a Petri net N=(P,T,E,α,β) is a |P|-dimensional vector Y with Yt A = for the place-transition incidence matrix A of N. The support of an invariant is the set of elements having nonzero values in the vector. Since any invariant is expressed as a linear combination of minimal-support invariants (ms-invariants for short) with nonnegative rational coefficients, it is usual to try to obtain either several invariants or the set of all ms-invariants. The Fourier-Motzkin method (FM) is well-known for computing a set of invariants including all ms-invariants. It has, however, critical deficiencies such that, even if invariants exist, none of them may be computed because of memory overflow caused by storing candidate vectors for invariants and such that, even when a set of invariants are produced, many non-ms invariants may be included. We are going to propose the following two methods: (1) FM1_M2 that finds a smallest possible set of invariants including all ms-invariants; (2) STFM that necessarily produces one or more invariants if they exist. Experimental results are given to show their superiority over existing ones.

In this paper we consider a tensor-based approach to the analytical computation of higher-order expectations of quantized trajectories generated by Piecewise Affine Markov (PWAM) maps. We formally derive closed-form expressions for expectations of trajectories generated by three families of maps, referred to as (n,t)-tailed shifts, (n,t)-broken identities and (n,t,π)-mixing permutations. These families produce expectations with asymptotic exponential decay whose detailed profile is controlled by map design. In the (n,t)-tailed shift case expectations are alternating in sign, in the (n,t)-broken identity case they are constant in sign, and the (n,t,π)-mixing permutation case they follow a dumped periodic trend.

A self-similar behavior characterizes the traffic in many real-world communication networks. This traffic is traditionally modeled as an ON/OFF discrete-time second-order self-similar random process. The self-similar processes are identified by means of a polynomially decaying trend of the autocovariance function. In this work we concentrate on two criteria to build a chaotic system able to generate self-similar trajectories. The first criterion relates self-similarity with the polynomially decaying trend of the autocovariance function. The second one relates self-similarity with the heavy-tailedness of the distributions of the sojourn times in the ON and/or OFF states. A family of discrete-time chaotic systems is then devised among the countable piecewise affine Pseudo-Markov maps. These maps can be constructed so that the quantization of their trajectories emulates traffic processes with different Hurst parameters and average load. Some simulations are reported showing how, according to the theory, the map design is able to fit those specifications.

This paper discusses recognition up to intensities of mix of primary facial expressions in real time. The proposed recognition method is compatible with the MPEG-4 high level expression Facial Animation Parameter (FAP). In our method, the whole facial image is considered as a single pattern without any block segmentation. As model features, an expression vector, viz. low global frequency coefficient (DCT) changes relative to neutral facial image of a person is used. These features are robust and good enough to deal with real time processing. To construct a person specific model, apex images of primary facial expression categories are utilized as references. Personal facial expression space (PFES) is constructed by using multidimensional scaling. PFES with its generalization capability maps an unknown input image relative to known reference images. As PFES possesses linear mapping characteristics, MPEG-4 high level expression FAP can be easily calculated by the location of the input face on PFES. Also, temporal variations of facial expressions can be seen on PFES as trajectories. Experimental results are shown to demonstrate the effectiveness of the proposed method.

This paper presents the effect of stress on device degradation in metal-oxide-semiconductor field-effect transistors (MOSFETs) due to stud bumping. Stud bumping above the MOSFET region generates interface traps at the Si/SiO2 interface and results in the degradation of transconductance in N-channel MOSFETs. The interface traps are apparently eliminated by both nitrogen and hydrogen annealing. However, the hot-carrier immunity after hydrogen annealing is one order of magnitude stronger than that after nitrogen annealing. This effect is explained by the termination of dangling bonds with hydrogen atoms.

Since river levee collapse causes great damage, it is socially very important to prevent such disasters by using a monitoring system which can detect changes in the state of a river levee. To investigate the possibility of detecting the collapse of a levee slope at an early stage, we performed an experiment in which we used artificial rainfall and penetration to collapse a full-scale levee model, and measured the change in the levee state using a detection system during collapse. The system consists of sensor plates, a distributed fiber optic strain sensor, and a personal computer. With this system, the stretching produced in the sensor plates by the force resulting from the movement of the soil on the levee slope face is detected as strain by a sensing optical fiber fixed to the plates. Since the distributed fiber optic strain sensor can measure strain continuously and for a long distance along a fiber, it is suitable for monitoring civil structures such as river levees. The experiment confirmed that a change in a levee can be clearly detected when the slope face collapse progresses near the place where the sensor plates are buried. The results suggest the feasibility of being able to foresee the collapse of a levee slope.

Multimedia service users can require multi-services according to their own environment for accessing to public networks. For copying with customer-oriented service requirements, network providers have to prepare multi-layer service networks. This paper deals with frame relay, ATM and IP networking services on multi-layer networks. In order to provide multiple data services, network provider needs to define and make use of client-server and interworking relationships between these networks. In this paper, we propose a service management architecture in order to efficiently manage multiple services and network resources from service point of view. The proposed service management architecture includes functionalities such as subscription management, customer-network management, communication session management, and business layer support management. Especially, it describes an information model for managing multi-layer networks by way of the interworking or client-server relationship. The proposed functionalities are modeled in accordance with the object-oriented modeling concept and implemented on a CORBA platform. The applications on the proposed architecture include VPN services and various statistical services for customers and the carrier. The realized system is to be used for Koera Telecom's high speed networks mainly for supporting Internet services.