Higher order delta-sigma (ΔΣ) modulator with one bit quantizer is known as one of the easiest method to gain a high resolution A/D converter without the need of accurately matched components. However, stability of higher order ΔΣ modulator is still a problem during the design and implementation process. Stabilizing higher order modulator requires the proper choice of integrator gains. In this paper, a new approach on ΔΣ modulator stability analysis which based on the system auto-correlation function is proposed, and equation of NTF power integration is derived out. The specification of equation related to input signal amplitude and output quantization level is discussed. Combining with system control theory, the stability of higher order modulator (2nd and 3rd order) is evaluated. Matlab simulation confirm the proposed method. It offers an evaluation method for the choice of the in-loop integrator gains which ensure the modulator operates under the stable status, and is able to be used for designing stable higher order ΔΣ analog-to-digital converters.

There are many public key cryptosystems that require random inputs to encrypt messages and their security is always discussed assuming that random objects are ideally generated. Since cryptosystems run on computers, it is quite natural that these random objects are computationally generated. One theoretical solution is the use of pseudorandom generators in the Yao's sense. Informally saying, the pseudorandom generators are polynomial-time algorithms whose outputs are computationally indistinguishable from the uniform distribution. Since if we use the Yao's generators then it takes much more time to generate pseudorandom objects than to encrypt messages in public key cryptosystems, we relax the conditions of pseudorandom generators to fit public key cryptosystems and give a minimal requirement for pseudorandom generators within public key cryptosystems. As an example, we discuss the security of the ElGamal cryptosystem with some well-known generators (e. g. , the linear congruential generator). We also propose a new pseudorandom number generator, for random inputs to the ElGamal cryptosystem, that satisfies the minimal requirement. The newly proposed generator is based on the linear congruential generator. We show some evidence that the ElGamal cryptosystem with the proposed generator is secure.

Investigations were carried out on metalorganic-chemical-vapor-deposition (MOCVD)-grown strained AlGaN/ GaN/sapphire structures using X-ray diffratometry. While AlGaN with lower AlN molar fraction (< 0.1) is under the in-plane compressive stress, it is under the in-plane tensile stress with high AlN molar fraction (> 0.1). Though tensile stress caused the cracks in AlGaN layer with high AlN molar fraction, we found that the cracks dramatically reduced when the GaN layer quality was not good. Using this technique, we fabricated a GaInN multi-quantum-well (MQW) surface emitting diodes were fabricated on 15 pairs of AlGaN/GaN distributed Bragg reflector (DBR) structures. The reflectivity of 15 pairs of AlGaN/GaN DBR structure has been shown as 75% at 435 nm. Considerably higher output power (1.5 times) has been observed for DBR based GaInN MQW LED when compared with non-DBR based MQW structures.

This paper proposes an intelligent image interpolation method based on Cubic Hermite procedure for improving digital images. Image interpolation has been used to create high-resolution effects in digitized image data, providing sharpness in high frequency image data and smoothness in low frequency image data. Most interpolation techniques proposed in the past are centered on determining pixel values using the relationship between neighboring points. As one of the more prevalent interpolation techniques, Cubic Hermite procedure attains the interpolation with a 3rd order polynomial fit using derivatives of points and adaptive smoothness parameters. Cubic Hermite features many forms of a curved shape, which effectively reduce the problems inherent in interpolations. This paper focuses on a method that intelligently determines the derivatives and adaptive smoothness parameters to effectively contain the interpolation error, achieving significantly improved images. Derivatives are determined by taking a weighted sum of the neighboring points whose weighting function decreases as the intensity difference of neighboring points increases. Smoothness parameter is obtained by training an exemplar image to fit into the Cubic Hermite function such that the interpolation error is minimized at each interpolating point. The simulations indicate that the proposed method achieves improved image results over that of conventional methods in terms of error and image quality performance.

In this paper, we present a class of combinatorial-logical classifiers called test feature classifiers. These are polynomial functions that can be used as pattern classifiers of binary-valued feature vectors. The method is based on so-called tests, sets of features, which are sufficient to distinguish patterns from different classes of training samples. Based on the concept of test we propose a new distance-based test feature classifiers. To test the performance of the classifiers, we apply them to a well-known phoneme database and to a textual region location problem where we propose a new effective textual region searching system that can locate textual regions in a complex background. Experimental results show that the proposed classifiers yield a high recognition rate than conventional ones, have a high ability of generalization, and suggest that they can be used in a variety of pattern recognition applications.

This paper proposes a Space-Time Object Model, an object oriented model that possesses space and time management mechanisms. The goal of this object model is to provide a common software infrastructure for implementing large-scale moving object simulations efficiently, such as car traffic simulations and disaster evacuation simulations, using a direct mapping scheme on a parallel and distributed computing environment. In this object model, the software infrastructure provides two principal functions, "Space Management" and "Time Management," which allows programmers to focus on application programming instead of parallel programming. Although there are several known infrastructure software, which provide the environment needed to develop and execute parallel and distributed simulations, they only provide a "Time Management" mechanism. In this paper, we present a Space-Time Object Model and an overview of a program called OSim, which is an implementation of the Space-Time Object Model. Then, we demonstrate the applicability and efficiency of this model by introducing the overview and evaluation results of a parallel car traffic simulation system using OSim.

Distributed shared memory (DSM) systems on top of network of workstations are especially vulnerable to the impact of false sharing because of their higher memory transaction overheads and thus higher false sharing penalties. In this paper we develop a dynamic-granularity shared memory management scheme that eliminates false sharing without sacrificing the transparency to conventional shared-memory applications. Our approach utilizes a special threaded splay tree (TST) for shared memory information management, and a dynamic token-based path-compression synchronization algorithm for data transferring. The combination of the TST and path compression is quite efficient; asymptotically, in an n-processor system with m shared memory segments, synchronizing at most s segments takes O(s log m log n) amortized computation steps and generates O(s log n) communication messages, respectively. Based on the proposed scheme we constructed an experimental DSM prototype which consists of several Ethernet-connected Pentium-based computers running Linux. Preliminary benchmark results on our prototype indicate that our scheme is quite efficient, significantly outperforming traditional schemes and scaling up well.

We present efficient all-to-all personalized communication algorithms for a 2D torus in wormhole-routed networks. Our complete exchange algorithms reduce the number of start-up by a factor of up to 2, which is a good metric for network performance in wormhole networks. Our algorithms divide the whole network into 22 networks, giving two contention-free networks with N/2N/2. After specially designated nodes called master nodes have collected messages, whose destinations are the rest of the basic cells, only master nodes perform complete exchange with a reduced network size. When finished with this complete exchange among master nodes, these nodes distribute messages to the rest of the master nodes, which results in the desired complete exchange. Then, we present a modified algorithm that further reduces the data transmission time sacrificing the start-up time. After we present our new algorithms, we analyze time complexities and compare several algorithms. We show that our practical algorithm is efficient by a factor of 2 in the required start-up time which means that our algorithms are suitable for wormhole-routed networks.

We propose a learning algorithm for simple deterministic languages from queries and a priori knowledge. To the learner, a special finite subset of the target language, called a representative sample, is provided at the beginning and two types of queries, equivalence queries and membership queries, are available. This learning algorithm constructs nonterminals of a hypothesis grammar based on Ishizaka(1990)'s idea. In Ishizaka(1990)'s algorithm, the learner makes rules as many as possible from positive counterexamples, and diagnoses wrong rules from negative counterexamples. In contrast, our algorithm guesses a simple deterministic grammar and diagnoses them using positive and negative counterexamples based on Angluin(1987)'s algorithm.

Pure green ZnTe light-emitting diodes (LEDs) were first realized reproducibly based on high quality ZnTe substrates and a simple thermal diffusion process. This success which overcomes the compensation effect in II-VI materials is due to the use of high quality p-type ZnTe single crystals with low dislocation densities of the level of 2000 cm-2 grown by the vertical gradient freezing (VGF) method and the suppression of as compensating point defects by low temperature annealing with covering the surface of the substrates by the deposition of n-type dopant, Al. The thermal diffusion coefficient and the activation energy of Al were determined from the pn interface observed by scanning electron spectroscopy (SEM). The formation of the intrinsic pn junctions was confirmed from the electron-beam induced current (EBIC) observation and I-V measurement. The bright 550 nm electroluminescence (EL) from these pn-junctions was reproducibly observed under room light at room temperature, with the lifetime exceeding 1000 hrs.

We describe an index for estimating the level of interest in Web pages. This "time-based interest" (TBI) index combinates an equation reflecting page accesses and an equation reflecting the decrease in interest over time. These equations work simultaneously by using a parameter that is based on the time since the last access. We experimentally estimated the decrease ratio of the TBI index and evaluated the characteristics of the TBI equation. We found that the index follows Zipf's distribution, indicating that reflects the change in popularity. We also introduce an access-log analysis system called CyberRanking that includes TBI analysis. CyberRanking analyzes the access logs of Web servers and presents the results in 2-D or 3-D graph on a Web browser.

The quality of an architectural design of a software system has a great influence on achieving non-functional requirements to the system, so formal evaluation and validation techniques to designed architectures are necessary in the early phase of development processes. In this paper, we present a technique for describing software architectures formally based on Coloured Petri Nets (CPNs) and a technique for reusing architectural constituents. Architectural descriptions are essentially written with a CPN language, so that the evaluation and analysis on the architectural descriptions can be made in architectural design phrase. We extract reusable architectural parts from standard architecture styles and architectural patterns so that a designer can construct an architecture by only retrieving the parts and combine them. We also designed the language for describing the combination of the architectural parts. To show the effectiveness of our techniques, we illustrate how a blackboard architecture can be composed of reusable parts and be simulated on a CPN tool (Design/CPN).

We introduce the characteristics for continuous wave operation at room temperature of InGaN laser diodes fabricated on SiC substrates. The threshold current was 60 mA, the threshold voltage was 8.3 V, and the oscillation wavelength was 404.4 nm. The lifetime of the laser diodes with a constant light output of 1 mW at 25 was 57 hours. The heat dissipation of the devices mounted p-side-up on a stem without using a heat sink was shown to be as good as that of devices mounted p-side-down with an external heat sink, owing to the high thermal conductivity of SiC substrates.

In a software maintenance phase, since quality assurance engineers frequently only change source codes, the consistency between the source codes and their specification documents cannot be kept. In this paper we propose a supporting technique for changing specification documents automatically so that the specifications can be consistent with the source codes. In our technique, we represent a program with multiple graphs and we consider the changes on programs as the modification of the graphs. The modification of the graphs is formalized with a sequence of the operation on the graphs. We design the rules of how to relate the operations on program graphs to the operations on graphs that represent specification documents. By applying these rules, we can detect what modification and which parts of the specification document should be made to maintain the consistency between the specification and the program, when the program is modified.

A software requirements specification (SRS) is a document at the first phase of software development. Since it is difficult to make an accurate SRS at the beginning of software development, we propose a supporting method to detect and interpret the inconsistency of SRS. First, we classify and define the inconsistency of SRS. Next, we describe how to detect and interpret the inconsistency of SRS. We use the Requirements Frame Model to detect the inconsistency of SRS. We apply the Dempster and Shafer's theory to interpret the inconsistency of SRS. We illustrate our method with an example.

This paper proposes a method of automatically eliciting knowledge which is used to detect feature interactions in telecommunication services. With conventional methods, the knowledge is provided manually. With the proposed method, the knowledge is automatically elicited as service constraints. In telecommunication systems, when a new service is added, new state transitions are created. In case of new service, the new state should be reached in the state transitions. On the other hand, some states of existing services should not be reached. These constraints can be considered as knowledge for detecting feature interactions. This paper also proposes a scenario for detecting feature interactions using elicited knowledge. This scenario was confirmed as effective.

There are the following three targets to be achieved in a software project from the three viewpoints of process management (or progress management), cost management, and quality management for software project to be successful: (a) drafting a software development plan based on accurate estimation, (b) early detection of risks that the project includes based on correct situation appraisal, (c) early avoidance of risks that the project includes. In this paper, the authors propose a method and facilities to project risks in a software project through Kepner-Tregoe program, and propose schedule re-planning by using genetic algorithm for avoiding the projected risks. Furthermore the authors show, from the results of execution of the system, that the system is effective in early avoidance of risks that the software project includes.

Knowledge-based program understanding is widely known as one of the key issues in programming education support systems and environments for novices. Most program understanders, however, have limitations. One of them is an ability to deal with a single programming language, while human tutors can comprehend plural languages by means of generalized knowledge on programming languages and techniques. This paper proposes the concepts and methodology of the knowledge-based program understander ALPUS II, which deals with plural programming languages, i. e. , Pascal and C, by means of generalized abstract syntax AL and knowledge representations based on it. ALPUS II is an extension of ALPUS, which dealt with a single programming language Pascal, and is a sub-system of an intelligent programming environment INTELLITUTOR. The INTELLITUTOR system consists of a guided programming editor GUIDE and a knowledge-based program understander ALPUS II, and is available on the Internet. In the process of comprehension source statements written in Pascal or C are translated into AL representation first. Since the contents of the programming knowledge bases are adjusted to deal with the AL representations the program comprehension procedure is available for both Pascal and C. It is possible to append other programming languages by simply attaching a transformation module for each additional procedural language. It is noted that knowledge acquisition tasks for additional languages are not needed since the contents of the knowledge base are generalized for multiple use. The INTELLITUTOR system was implemented in the frame-based knowledge engineering environment ZERO on a UNIX server machine in the Internet environment. ALPUS II demonstrates interesting features in program comprehension for the C language by means of the transformed knowledge from the already available knowledge for Pascal, which was developed for ALPUS, in a feasibility study. The current version of ALPUS II supports almost full specifications for Pascal and a Pascal-associated subset for C. This limitation should be reasonable for programming practice at freshmen classes of a university.

To bridge a wide gap between the end users and the requirements engineers, we propose a business flow diagram for acquiring users' requirements of the object oriented software development in the business application domain. Each field of this diagram shows either a role or a responsibility of a particular person or an organization. This paper proposes a development method that the engineers acquire the requirements by using our diagrams. We have implemented a supporting tool based on this study for collaborating the requirements engineers with their users. At first, the end users of an information system to be developed draw diagrams representing the flows of information and physical objects in their work from their own points of view. Sometimes the engineers write them with the users. If all users submit their diagrams, then our tool collects them and constructs a total diagram. The requirements engineers analyze the total diagram for improving the business flow. After the engineers complete this diagram, our tool can automatically transform it into an initial version of the class diagram. We show the effectiveness of our approach with some experiments. Comparing the related works, we discuss some issues of the practical aspects of this proposal.

Dislocation properties in InGaN/GaN Quantum Wells and GaN grown on bulk GaN and sapphire substrates by metalorganic chemical vapor deposition (MOCVD) were characterized using cathodoluminescnece (CL), transmission electron microscopy (TEM), atomic force microscopy (AFM) and photoluminescence (PL). It was clearly demonstrated that dislocations act as nonradiative recombination centers in both n-type (undoped and Si-doped) GaN and InGaN layers. Furthermore the very short-minority carrier diffusion length was a key parameter to explain the high light emission efficiency in GaN-based light emitting diodes (LEDs) prepared on sapphire substrates. On the other side band-tail states were detected in the heteroepitaxial InGaN layers only by temperature dependence PL measurement. Additionally InGaN phase separation, which consists of few micron domains, has been produced under growth conditions which favors the spiral growth. These results indicate that the dislocations in the InGaN layers act as triggering centers for the InGaN phase separation which cause both a compositional fluctuation and the formation of few micron phase separated domains. The homoepitaxial InGaN layers showed however quite normal behaviors for all characterizations.