The epitaxial lateral overgrowth (ELO) of GaN with a stripe tungsten (W) mask pattern is performed by hydride vapor phase epitaxy (HVPE) and the crystalline and optical properties are investigated compared with ELO GaN using SiO2 mask by characterizations of X-ray rocking curve (XRC), transmission electron microscopy (TEM) and low temperature cathodoluminescence (CL). A buried ELO structure of the W mask with a smooth surface is successfully obtained. The tilt of c-axis on the W mask in the ELO GaN is not observed, but in the case of the SiO2 mask, c-axis tilts on the mask region at 1 to 10 together with small angle grain boundaries. Half the way from the ELO interface to the surface, the luminescence becomes excitonic over the whole lateral extension region, which indicates the optically high crystalline quality of the material. On the other hand, different kinds of luminescence are observed depending on the position. The difference of these luminescence is caused by the defects and/or impurity incorporation on the mask region due to the tilting of c-axis.

Electron-cyclotron-resonance plasma-excited molecular beam epitaxial (ECR-MBE) growth of GaN using hydrogen-nitrogen mixed gas plasma was investigated. The growth rate of GaN was drastically increased by addition of hydrogen to nitrogen plasma. The transition of reflection high energy electron diffraction (RHEED) patterns, from streaked patterns created without the presence of hydrogen to spotted patterns in the presence of hydrogen, indicated that the effective V/III ratio was increased by the addition of hydrogen. NHx radical families were detected in hydrogen-nitrogen mixed gas plasma by quadrupole mass spectroscopy and optical emission spectroscopy. These radicals were considered to be responsible for the observed increase in growth rate. Transmission electron microscope observation showed that the surface morphology of GaN without hydrogen was relatively flat and that with hydrogen was columnar with {1 0 ~1 1} facets. It seems likely that the columnar structure of the GaN layers grown with hydrogen were strongly related to initial island growth.

This paper presents a non-interactive and optimally resilient distributed multiplication scheme. By non-interactive we mean that the players need to use outgoing communication channels only once without the need to synchronize with the other players as long as no disruption occurs. Our protocol withstands corrupt players up to less than the half of the players, so it provides optimal resiliency. Furthermore, the shared secrets are secure even against infinitely powerful adversaries. The security is proven under the intractability assumption of the discrete logarithm problem. Those properties are achieved by using an information theoretically secure non-interactive verifiable secret sharing as a kind of non-interactive proof system between a single prover and distributed verifiers. Compared to a former interactive solution in the same setting, the cost is an increase in local computation and communication complexity that is determined by the factor of the threshold used in the verifiable secret sharing.

A per-connection end-to-end call admission control (CAC) problem is solved in this paper to allocate network resources to an input session to guarantee its quality of service (Qos) requirements. In conjunction with the solution of the CAC problem, a traffic descriptor is proposed to describe the loss rate and the delay bound Qos requirements of the connection to be set up as well as the statistical characteristics of the associated input traffic which is modeled as a linear mean function plus a (zero-mean) fractional Brownian motion. The information in the traffic descriptor is sufficient to determine the allocation of channel bandwidth and buffer space to the input traffic in a network which employs leaky bucket shapers and scheduling algorithms to guarantee the Qos requirements. The CAC problem is solved by an iterative algorithm of which there are two stages in each iteration: one is responsible for the search of a candidate end-to-end routing path and the other for the verification of the legitimacy of this candidate path to meet the Qos requirements and for the allocation of resources in such a legitimate path.

This paper studies the "usefulness" of initial conditions for distributed algorithms on anonymous networks. In the literature, several initial conditions such as making one vertex a leader, giving the number of vertex to each vertices, and so on, have been considered. In this paper, we study a relation between the initial condition by considering transformation algorithm from one initial condition to another. For such transformation algorithms, we consider in this paper, both deterministic and randomized distributed algorithms. For each deterministic and randomized transformation type, we show that the relation induces an infinite lattice structure among equivalence classes of initial conditions.

Mathematical proof for the equivalent edge currents for physical optics (POEECs) is given for plane wave incidence and the observer in far zone; the perfect accuracy of POEECs for plane wave incidence as well as the degradation for the dipole source closer to the scatterer is clearly explained for the first time. POEECs for perfectly conducting plates are extended to those for impedance plates.

Let l be a positive integer, and let G be a graph with nonnegative integer weights on edges. Then a generalized vertex-coloring, called an l-coloring of G, is an assignment of colors to the vertices of G in such a way that any two vertices u and v get different colors if the distance between u and v in G is at most l. In this paper we give an algorithm to find an l-coloring of a given graph G with the minimum number of colors. The algorithm takes polynomial time if G is a partial k-tree and both l and k are bounded integers.

The three dimensional (3D) packing problem is to arrange given rectangular boxes in a rectangular box of the minimum volume without overlapping each other. As an approach, this paper introduces the system of three sequences of the box labels, the sequence-triple, to encode the topology of the 3D-packing. The topology is the system of relative relations in pairs of boxes such as right-of, above, front-of, etc. It will be proved that the sequence-triple represents the topology of the tractable 3D-packings which is a 3D-packing such that there is an order of the boxes along which all the boxes are extracted one by one in a certain fixed direction without disturbing other remaining boxes. The idea is extended to the system of five ordered sequences, the sequence-quintuple. A decoding rule is given by which any 3D-packing is represented. These coding systems are applied to design heuristic algorithms by simulated annealing which search the codes for better 3D-packings. Experimental results were very convincing its usefulness as automated packing algorithms.

In order to get a perspective to the future of GaN materials, theoretical and experimental knowledge of the optoelectronic activities of dislocations in hexagonal GaN have been reviewed. Although the dislocations in GaN have been thought to be not quite harmful, a growing number of evidences have been accumulated for the intrinsic noxiousness of the dislocations. There are some inconsistencies between experimental data reported by different groups or at different dates, which can be reconciled by a proposed simple model that takes into account the trapping of free excitons. A transmission electron microscopic study revealed that some type of dislocations exhibit the recombination enhanced dislocation glide effect, suggesting the non-radiative recombination activity of the fresh dislocations. Such intrinsic activities of dislocations in GaN, in both electronical and mechanical respects, will possibly cause great difficulties in optoelectronic devices based on this material when the crystal quality becomes improved.

This paper describes a jitter suppression technique for a clock multiplier IC that uses a phase-locked loop (PLL). It is shown that the jitter cutoff frequency of the jitter transfer function can be greatly improved by adding a surface acoustic wave (SAW) filter whose center frequency equals the input frequency. The jitter transfer function is mainly determined by the characteristics of the SAW filter. Therefore, the clock multiplier IC can be set at a high loop gain to minimize the jitter generation without increasing the jitter cutoff frequency. The use of a clock multiplier IC that was fabricated with Si bipolar technology and a SAW filter with the center frequency of 155.52 MHz and a quality (Q) factor of 1500 results in a very low jitter generation of 3.5 mUI rms and an extremely low jitter cutoff frequency of about 50 kHz when the clock multiplier converts a clock frequency of 155.52 MHz into a 2.48832-GHz signal.

This paper proposes a reference model of CAD system generation, and describes its prototype implementation. The problems encountered in using CAD systems in industry involve complicated data handling and unsatisfied demands for domain knowledge because of the lack of a way of extracting and adopting it in the system. In the example domain of architecture, the authors have already defined domain-specific BDL (Building Design Language) for architecture experts to describe modelers of architectural structure in CAD systems by themselves. Moreover, the authors have developed a CAD system generator based on BDL descriptions. However, the different domain-specific languages required for individual domains create difficulty in developing various CAD system generators. The proposed reference model solves this problem by applying a common intermediate language based on the object model. Moreover, the model allows the creation of an integrated CAD system which contains multiple domains required by a field of industry. Its prototype implementation demonstrates its feasibility.

This paper describes the architecture to implement an application in network environments, which adapts to unexpected change in the development phase. In this architecture, an application is expressed as an agent which consists of two layers: base level and meta level. The base level program is an application program and the meta level program is the program that controls the execution of the base level and changes the base level program. Virtual places are also provided in the network. They are used for the release of programs and information which agents retrieve to change their own base level program. An application (or an agent), when a change is required, moves from places to places for the retrieval of programs to adapt to the change. A program search strategy is introduced to adapt to changes by using distributed thesauri of released programs, which realizes an agent's program retrieval method in network environments.

Continuous-wave operation at room-tempera-ture has been demonstrated for InGaN multi-quantum-well (MQW) laser diodes (LDs) grown on FIELO GaN substrates with a backside n-contact. This was made possible by introducing important new concept of reducing threading dislocations that occur during the growth of the GaN substrates. We found that InGaN active layers grown on FIELO GaN are superior to those grown on conventional sapphire substrates in terms of their growth mode and the resultant In compositional fluctuation. The fabricated laser diode shows the threshold current, the threshold current density and the threshold voltage were 36 mA, 5.4 kA/cm2 and 7.5 V, respectively, with the lasing wavelength of 412 nm and internal quantum efficiency as high as 98%.

In this paper, we propose a method for detecting conserved domains from a set of amino acid sequences that belong to a protein family. This method detects the domains as follows: first, generate fixed-length subsequences from the sequences; second, construct a weighted graph that connects any two of the subsequences (vertices) having higher similarity than a pre-defined threshold; third, search for the maximum-density subgraph for each connected component of the graph; finally, explore conserved domains in the sequences by combining the results of the previous step. From the performance results obtained by applying the method to several protein families that have complex conserved domains, we found that our method was able to detect those domains even though some domains were weakly conserved.

Formal description techniques (FDTs) such as VDM, Z, LOTOS, etc are powerful to develop safety-critical systems since they have strict semantics and mathematical reasoning basis. However, they have no methods or guides how to construct specifications unlike specification and design methods such as Object-Oriented Modeling and Technique (OMT), and that makes it difficult for practitioners to compose formal specifications. One of the solutions is to connect formal description techniques with some existing methods. This paper discusses a technique how to integrate FDTs with specification and design methods such as OMT so that we can have new methods to support writing formal specifications. The integration mechanism is based on transformation rules of specification documents produced following methods into the descriptions written in formal description techniques. The transformation rules specify the correspondences on two meta models; of methods and of formal description techniques, and are described as graph rewriting rules. As an example, we pick up OMT as a method and LOTOS as a FDT and define the transformation rule on their meta models.

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.

In order to maintain the communications quality at a target level, signal-to-interference ratio (SIR)-based transmission power control methods have been developed in CDMA cellular systems. These power control methods, however, do not necessarily improve system efficiency when there is a large geographic deviation in traffic because they only control power levels. A shift in the cell boundary can control traffic balance between cells. In this paper, we evaluate the optimum location of the cell boundary and the power levels when a mobile station adaptively selects a base station (BS) for each of uplink and downlink under non-uniform traffic. Because of the asymmetry in system structure between uplink and downlink, the optimum cell boundaries are not always coincident for both the two links; the location of the cell boundary is found to migrate according to the loss in orthogonality in the downlink.

We survey recent developments in the study of approximation algorithms for NP-hard geometric optimization problems. We focus on those problems which, given a set of points, ask for a graph of a specified type on those points with the minimum total edge length, such as the traveling salesman problem, the Steiner minimum tree problem, and the k-minimum spanning tree problem. In a recent few years, several polynomial time approximation schemes are discovered for these problems. All of them are dynamic programming algorithms based on some geometric theorems that assert the existence of a good approximate solution with a simple recursive decomposition structure. Our emphasis is on these geometric theorems, which have potential uses in the design and analysis of heuristic algorithms.

The invariant polynomials of discrete systems such as graphs, matroids, hyperplane arrangements, and simplicial complexes, have been theoretically investigated actively in recent years. These invariants include the Tutte polynomial of a graph and a matroid, the chromatic polynomial of a graph, the network reliability of a network, the Jones polynomial of a link, the percolation function of a grid, etc. The computational complexity issues of computing these invariants have been studied and most of them are shown to be #P-complete. But, these complexity results do not imply that we cannot compute the invariants of a given instance of moderate size in practice. To meet large demand of computing these invariants in practice, there have been proposed a framework of computing the invariants by using the binary decision diagrams (BDD for short). This provides mildly exponential algorithms which are useful to solve moderate-size practical problems. This paper surveys the BDD-based approach to computing the invariants, together with some computational results showing the usefulness of the framework.

The vehicle routing and facility location fields are well-developed areas in management science and operations research application. There is an increasing recognition that effective decision-making in these fields requires the adoption of optimization software that can be embedded into a decision support system. In this paper, we describe the implementation details of our software components for solving the vehicle routing and facility location problems.