Organic field-effect transistors (FETs) which employ (BEDT-TTF)(TCNQ) films for active layer have been fabricated and characterized. Their FET characteristics exhibited both p-channel and n-channel operation by changing the gate and drain voltages. For a particular bias condition, the I-V curves revealed behavior where both electrons and holes simultaneously are injected from source and drain electrodes. These bipolar type characteristics are strongly related to the structure of donor and acceptor molecular layers. The degree of charge transfer of approximately 0.2 was estimated by Raman spectroscopy.

A stability of the cascade two-stage Power-Factor-Correction converter is investigated. The first stage is boost PFC converter to achieve a near unity power factor and the second stage is forward converter to regulate the output voltage. Previous researches studied the system using linear analysis. However, PFC boost converter is a nonlinear circuit due to the existence of the multiplier and the large variation of the duty cycle. Moreover, the effect of the second stage DC/DC converter on the first stage PFC converter adds more complexity to the nonlinear circuit. In this issue, low-frequency instability has been detected in the two-stage PFC converter assuring the limitation of the prior linear models. Therefore, nonlinear model is proposed to detected and explain these instabilities. The borderlines between stable and unstable operation has been made clear. It is cleared that feedback gains of the first stage PFC and the second stage DC/DC converters are the main affected parts to the total system stability. Then, a simplified nonlinear model is provided. Experiment confirm the two models with a good agreement. These nonlinear models have introduced new PFC design scheme by choosing the minimum required output capacitor and the feedback loop design.

This paper proposes a new simulation algorithm for analyzing large power distribution networks, modeled as linear RLC circuits, based on a novel partial random walk concept. The random walk simulation method has been shown to be an efficient way to solve for voltages of small number of nodes in a large power distribution network, but the algorithm becomes expensive to solve for voltages of nodes that are more than a few with high accuracy. In this paper, we combine direct methods like LU factorization with the random walk concept to solve power distribution networks when voltage waveforms from a large number of nodes are required. We extend the random walk algorithm to deal with general RLC networks and show that Norton companion models for capacitors and self-inductors are more amenable for transient analysis by using random walks than Thevenin companion models. We also show that by nodal analysis (NA) formulation for all the voltage sources, LU-based direct simulations of subcircuits can be speeded up. Experimental results demonstrate that the resulting algorithm, called partial random walk (PRW), has significant advantages over the existing random walk method especially when the VDD/GND nodes are sparse and accuracy requirement is high.

Analysing and modeling of traffic play a vital role in designing and controlling of networks effectively. To construct a practical traffic model that can be used for various networks, it is necessary to characterize aggregated traffic and user traffic. This paper investigates these characteristics and their relationship. Our analyses are based on a huge number of packet traces from five different networks on the Internet. We found that: (1) marginal distributions of aggregated traffic fluctuations follow positively skewed (non-Gaussian) distributions, which leads to the existence of "spikes", where spikes correspond to an extremely large value of momentary throughput, (2) the amount of user traffic in a unit of time has a wide range of variability, and (3) flows within spikes are more likely to be "elephant flows", where an elephant flow is an IP flow with a high volume of traffic. These findings are useful in constructing a practical and realistic Internet traffic model.

We have demonstrated radio-over-fiber transmission of wireless signals at millimeter-wave bands. The system incorporated 25 km of an optical intermediate frequency feeder and 60 GHz OFDM signal transmission at 155 Mbps with a BER of less than 10-6 was achieved within the system cell of a radius of 2.6 m under the channel condition of Line-of-Sight.

This paper presents a method for improving the performance of syntactic analysis by using accurate temporal expression processing. Temporal expression causes parsing errors due to its syntactic duality, but its resolution is not trivial since the syntactic role of temporal expression is understandable in the context. In our work, syntactic functions of temporal words are decisively identified based on local contexts of individual temporal words acquired from a large corpus, which are represented by a finite state method. Experimental results show how the proposed method, incorporated with parsing, improves the accuracy and efficiency of the syntactic analysis.

Digital halftoning is used to quantize a grayscale image to a binary image. Error diffusion halftoning generates a high-quality binary image, but also generates some defects such as the warm effect, sharpening, and so forth. To reduce these defects, Kite proposed a modified threshold modulation method that utilizes a multiplicative parameter for controlling sharpening. Nevertheless, some degradation was observed near the edges of objects with a large luminance change. In this paper, we propose a method of controlling the multiplicative parameter in proportion to the magnitude of the local edge slope. The results of computer simulation show a greater reduction of sharpening in the halftone image. In particular, there is a great improvement in the quality of the edges of objects with a large luminance change.

In this paper, we propose a probabilistic feature-based parsing model for head-final languages, which can lead to an improvement of syntactic disambiguation while reducing the parsing cost related to lexical information. For effective syntactic disambiguation, the proposed parsing model utilizes several useful features such as a syntactic label feature, a content feature, a functional feature, and a size feature. Moreover, it is designed to be suitable for representing word order variation of non-head words in head-final languages. Experimental results show that the proposed parsing model performs better than previous lexicalized parsing models, although it has much less dependence on lexical information.

This study proposes an edge-based single-resolution compression scheme for triangular mesh connectivity. The proposed method improves upon EdgeBreaker. Nearly all of these algorithms are either multiple traversals or operate in reverse order. Operating in reverse order should work only off-line in the EdgeBreaker decompression process. Many restrictions on applications will be caused by these factors. To overcome these restrictions, the algorithm developed here can both encode and decode 3D models in a straightforward manner by single traversal in sequential order. Most algorithms require complicated operations when the triangular mesh is split. This study investigates spatial locality to minimize costs in split operations. Meanwhile, some simplification rules are proposed by considering geometric characteristics which ignore the last triangle when a split occurs. The proposed method improves not only the compression ratio but also the execution time.

This paper proposes a cell layout synthesis method via Boolean Satisfiability (SAT). Cell layout synthesis problems are first transformed into SAT problems by our formulations. Our method realizes a high-speed layout synthesis for CMOS logic cells and guarantees to generate the minimum-width cells with routability under our layout styles. It considers complementary P-/N-MOSFETs individually during transistor placement, and can generate smaller width layout compared with pairing the complementary P-/N-MOSFETs case. To demonstrate the effectiveness of our SAT-based cell synthesis, we present experimental results which compare it with the 0-1 ILP-based transistor placement method and a commercial cell generation tool. The experimental results show that our SAT-based method can generate minimum-width placements in much shorter run time than the 0-1 ILP-based transistor placement method, and can generate the cell layouts of 32 static dual CMOS logic circuits in 54% run time compared with the commercial tool. Area increase of our method without compaction is only 3% compared with the commercial tool with compaction.

In this paper, we present a test data compression technique to reduce test data volume for multiscan-based designs. In our method the internal scan chains are divided into equal sized groups and two dictionaries were build to encode either an entire slice or a subset of the slice. Depending on the codeword, the decompressor may load all scan chains or may load only a group of the scan chains, which can enhance the effectiveness of dictionary-based compression. In contrast to previous dictionary coding techniques, even for the CUT with a large number of scan chains, the proposed approach can achieve satisfied reduction in test data volume with a reasonable smaller dictionary. Experimental results showed the proposed test scheme works particularly well for the large ISCAS'89 benchmarks.

In this letter, we propose an approach to incorporate a statistical model for the voiced/unvoiced (V/UV) speech decision under background noise environments. Our approach consists of splitting the input noisy speech into two separate bands and applying a statistical model for each band. We compute and compare the likelihood ratio (LR) for each band based on the statistical model and estimated noise statistics for the V/UV decision. According to the simulation test, the proposed V/UV decision shows a better performance compared with the selectable mode vocoder (SMV) V/UV decision algorithm, particularly in clean and white noise environments.

In recent years the size of transformer in a DC-DC converter becomes smaller and thinner for power module type application. It results in the increase of the leakage inductances because the number of turns of the secondary winding becomes smaller. This paper presents the analysis of static and dynamic characteristics of the novel flyback converter proposed before, and clarifies that the transformer's leakage inductances deteriorate the static load regulation, but improve the dynamic stability by increasing the dumping factor.

Availability of network access "anytime and anywhere" will impose new requirements to presence services - server load sharing and privacy protection. In such cases, presence services would have to deal with sensor device information with maximum consideration of user's privacy. In this paper, we propose FieldCast: peer-to-peer system architecture for presence information exchange in ubiquitous computing environment. According to our proposal, presence information is exchanged directly among user's own computing resources. We illustrate our result of evaluation that proves the feasibility of our proposal.

Performance measurements are indispensable for managing the Internet. Among the performance measurement techniques known, passive measurement is attractive because of its accuracy; user traffic is observed without inserting additional test traffic. However, the technique is handicapped by its large storage and bandwidth costs. This paper proposes a passive packet loss measurement technique that effectively avoids the difficulty of the conventional passive measurement approaches. Its key advance is utilizing the packet feature computed by a hash function. Since the feature can identify a packet with a short length of data, it becomes possible to greatly decrease the storage and bandwidth costs of passive measurements. The paper details the measurement procedure and assesses the design parameters used in the method. In addition, the validity of the proposed method is confirmed through experiments. The experiments also show the advantage of the method over the conventional active measurement.

The partial projection filter gives optimal signal restoration in the presence of both the signal space and the observation space noises. In this paper, the filter has been characterized from the point of view of its signal restoration and noise suppression capabilities. The filter is shown to suppress the noise component in the restored signal while retaining the signal component, thus maximizing the signal-to-noise ratio. Further, a digital implementation of the filter is presented in matrix form in contrast to its original operator based derivation, for practical applications.

Replication to mask the effects of failures is a basic technique for improving reliability of a file system. Consistency control protocols are implemented to ensure the consistency among these replicas. The native token-based mechanism which merely sequences the distributed requests suffered from the poor system utilization due to the lack of dependence checking between writes and management of out-of-ordered requests. Hence, in this paper, by utilizing the idempotent property of NFS and executing ahead most of independent WRITE requests, the new consistency control scheme is proposed to improve the performance of operations and failure recovery. Finally, a numeric case shows the efficiency of the new scheme.

This study investigates the effect of the method of time division in frequency domain ICA on estimation accuracy of ICA. We show that source signals expressed in the frequency domain lose non-Gaussianity and independence because of the long and overlapping window function, respectively, in time division. Consequently, the estimation accuracy of ICA decreases.

The IEEE 802.11 protocol is one of the most important standards for Wireless Local Area Networks. The primary MAC protocol of 802.11 is the distributed coordination function (DCF), which is Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) with binary slotted exponential backoff scheme. The basic access and the RTS/CTS access mechanisms are the two channel access methods defined in DCF. In real work environments, the common channel access method of 802.11 is the coexistence of the above two mechanisms, i.e., packets longer than a given threshold RTSthreshold are transmitted according to the RTS/CTS mechanism, otherwise, they are transmitted by means of basic mechanism. The common mechanism is called as hybrid access mechanism in this paper. Few analytical models have been proposed to evaluate the hybrid access mechanism up to now. The necessary condition which enables the hybrid mechanism to work is that the packets must be variable. But, almost all analytical models proposed for 802.11 DCF assume that the packet size is fix, so they can not study the hybrid access method. In this paper, we propose a detailed analytical model to evaluate the saturation performance of the hybrid access mechanism, in the assumption that the packet lengthes are sampled from a general distribution function f(x). Both the throughput and the delay performances are concerned. Our model is validated by extensive simulations. By means of the proposed model, we compare the performances of the above three mechanisms, i.e., basic, RTS/CTS and hybrid, under different network scenarios. Numerical results show that the hybrid access mechanism is the best choice in almost all scenarios.

With the growing design complexity of contemporary embedded systems, real-time operating systems (RTOSs) have become one of important components of such complex embedded systems. This paper presents an RTOS-centric hardware/software cosimulator which we have developed for embedded system design. One of the most remarkable features in our cosimulator is that it has a complete simulation model of an RTOS which is widely used in industry, so that application tasks including RTOS service calls are natively executed on a host computer. Our cosimulator also features cosimulation with functional simulation models of hardware written in C/C++ and cosimulation with HDL simulators. A case study with a JPEG decoder application demonstrates the effectiveness of our cosimulator.