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ABSTRACT: Electrical properties of halogen-doped CdTe layers grown on Si substrates using iodine and chlorine dopants are presented.
No change in electrical properties of the layers was observed with chlorine as a dopant. However, doping with iodine resulted
in highly conductive n-type layers or highly resistive p-type layers depending upon the growth conditions, even though a similar amount of dopant was introduced into the growth chamber.
Layers grown at 560°C, with a vapor-phase Te/Cd precursor ratio of 3.0, were p-type. The resistivity of the layers remained unchanged for low dopant supply rates, but increased abruptly when the dopant
supply rate was increased beyond a certain value. On the other hand, layers grown at 325°C with Te/Cd ratios from 0.1 to 0.25
were n-type. A maximum free electron concentration of 1.3×1017cm−3 was obtained at room temperature. The types and conductivities of the grown layers were strongly dependent on the growth
conditions.
KeywordsCdTe epilayers-halogen doping-MOVPE-Si substrates-radiation detectors
Journal of Electronic Materials 05/2012; 39(7):1118-1123. · 1.47 Impact Factor
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ABSTRACT: As an inexpensive and scalable Internet access network, we have studied the architecture, protocols, and design optimizations of the Wireless Internet access Mesh Network (WIMNET). WIMNET is composed of multiple access points (APs) that are connected through wireless links. Previously, we have proposed the concept of the CSMA-based Fixed Back off-time Switching (CSMA-FBS) method for WIMNET to improve the performance by giving necessary link activation chances for multi-hop communications. In this paper, we propose a protocol for this CSMA-FBS method implement able on APs, and its actual implementation on the QualNet simulator for evaluations in realistic network environments. The simulation results in two network topologies confirm the effectiveness of our proposal.
26th International Conference on Advanced Information Networking and Applications Workshops (WAINA), 2012; 03/2012
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ABSTRACT: The wireless Internet-access mesh network (WIMNET) has been studied to offer an inexpensive, scalable Internet-access wireless network by adopting multiple access points (APs) connected by wireless links. WIMNET can improve the dependability to failures of links and/or APs by allocating APs redundantly in the network field. However, redundant APs may increase the operational cost and degrade the throughput due to increasing radio interferences. One solution to this problem is to activate only the necessary APs to provide the connectivity to the hosts while maximizing the throughput. In this paper, we first define this active AP selection problem of selecting the activated APs for communications, and propose its heuristic algorithm. The simulation results in three instances confirm the effectiveness of the proposed algorithm, and indicate the existence of an active AP selection that maximizes the throughput. Then, we present the average hop count and the traffic bias as the indices to seek the active AP selection with the maximal throughput, and the extension of our active AP selection algorithm using them.
Network-Based Information Systems (NBiS), 2011 14th International Conference on; 10/2011
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ABSTRACT: For busy persons such as working people, students, and nurturing parents, it is very hard to spend a long time in cooking foods by themselves at home after working for long hours on weekdays. As one solution, the cooking process can be divided into two phases, where the preparation steps for foods that they will eat on the following weekdays are performed on a weekend, and the final steps for some foods are finished on the eating day in a short time. Then, the task of generating a menu planning with this two-phase cooking becomes a complex problem to satisfy the limited cooking time. In this paper, we formulate this time-constrained menu planning problem with the two-phase cooking, and prove the NP-completeness of its decision problem through the reduction from the NP-complete knapsack problem. Then, we present its heuristic algorithm based on a simple greedy method for the knapsack problem, where foods are sequentially selected into the menu in descending order of food priorities. We apply the algorithm to the generation of one week menu plan from 53 food candidates, where the result verifies the effectiveness of our approach.
Complex, Intelligent and Software Intensive Systems (CISIS), 2011 International Conference on; 08/2011
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ABSTRACT: We have investigated thin film transistors (TFTs) with ultra-thin polycrystalline silicon (poly-Si) of 77 Å - 185 Å. The TFT charge transfer characteristics such as ON current and effective mobility are dominated not by the thickness itself but by the grain size of poly-Si channel. When the poly-Si channel thickness is decreased with the same grain size, the sub-threshold TFT characteristics are improved without degradation of ON current and reliability properties. These results give us appropriate criteria to establish an excellent poly-Si channel in vertical NAND flash memory.
Reliability Physics Symposium (IRPS), 2011 IEEE International; 05/2011
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ABSTRACT: UBIF having compressive residual stress at cladding surface without additional layer is newly developed, which realizes both 13 times longer lifetime at 1.3mm-radius bending and 100 times lower 25-years failure probability at 5mm-radius bending compared with those of conventional UBIF.
Optical Communication (ECOC), 2010 36th European Conference and Exhibition on; 10/2010
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ABSTRACT: Recently, Web-page browsings at various terminals have become popular due to deployments of small mobile devices and large flat displays. To deal with this recent trend, we have proposed a Web-page layout optimization method for multimodal browsing sizes. It dynamically changes box locations and font sizes by switching CSS files for different browsing sizes, so that the main content can be accessed without the screen scroll operation even at a small size whereas the blank space is avoided at a large size. However, in this method, any box location must be specified by the absolute value in HTML/CSS files, which is not easy under a variety of browsing sizes. In this paper, we propose the extension of this method for flexible Web-page designs using the normal flow, the liquid layout, and the float property, where the browser automatically arranges the boxes. Using Ajax, the box location and the font size is switched to fit to the current browsing size by our method. The effectiveness of our proposal is verified through a usability test using sample Web-pages at small sizes.
Network-Based Information Systems (NBiS), 2010 13th International Conference on; 10/2010
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ABSTRACT: This paper presents the design and experimental verification of a sensorless-oriented interior permanent magnet (IPM) synchronous motor intended for a general industrial application. A concentrated-winding IPM motor is designed by the proposed design procedure so as to meet torque ripple requirements with wide sensorless operating region. Special features of the resulting motor include its V-shape-magnets and circular flux-barriers at the rotor-yoke in the center of the N-pole and S-pole. This makes significant reduction of the torque ripple under heavy load conditions. The IPMSM designed is built and tested experimentally. As a result, it is demonstrated that the test machine realizes low-torque ripple under the frequent operating conditions while satisfying the required maximum torque under the sensorless drive.
Electrical Machines (ICEM), 2010 XIX International Conference on; 10/2010
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ABSTRACT: Recently, the number of users who use search engines for not only retrieving Web pages but also understanding or learning an arbitrary concept has been increasing. However, it is difficult to understand and learn an arbitrary concept by using the existing search engines. This paper presents a method for the interconnection of heterogeneous knowledge bases on Knowledge Grid for knowledge sharing and provision. In this paper, for realizing the proposed method, we introduce two types of services—intra-operation services and inter-operation services—on Knowledge Grid. The system dynamically creates a semantic associative network that connects the user's interests and concepts, and provides correlation views that represent various relationships for connecting related resources. In addition, we employ a link-free browsing system by this method called correlation browsing, which represents the semantic association utilizing collective knowledge by connecting various knowledge bases. The current web browsing has two actions—browsing and jumping by static hyperlinks. It is difficult to understand the relationship between each page that is connected by static hyperlink. The system navigates the related contents while repeatedly switching between a content browsing mode and a correlation browsing mode. Therefore, a user can access various contents while understanding the relationships. Copyright © 2010 John Wiley & Sons, Ltd.
Concurrency and Computation Practice and Experience 09/2010; 23(9):940 - 955. · 0.64 Impact Factor
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ABSTRACT: Recently, a learning management system (LMS) using the Web technology has been used at many educational institutions. To support educational activities in our department, we have independently developed an LMS called NOBASU (NetwOrk-Based Assistant System for University education) to improve the quality while reducing costs. Besides conventional functions in LMS, NOBASU has incorporated several original ones such as the keyword submission function for preparing and reviewing class contents. In this paper, we present two new characteristic functions for the Java programming education in NOBASU. The Java code test function verifies the specifications in source codes from students using the test-driven development (TDD) method. The Java test code submission function requests students to submit test codes so that they can generate detailed program specifications by themselves.
Applications and the Internet (SAINT), 2010 10th IEEE/IPSJ International Symposium on; 08/2010
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ABSTRACT: This paper proposes a new flux-barrier design to reduce the torque ripple of the concentrated-winding interior permanent magnet (IPM) motor under saliency-based sensorless drive. It is based on the combinations of the V-shape-magnet and the circular flux-barrier at the rotor-yoke in the center of the N-pole and S-pole. It is applied to 45 Nm-5.5 kW industrial drive IPM motor to fulfill the torque ripple requirement with a large operating region under the sensorless drive. The design result is validated by FEA, confirming the expected performance.
Energy Conversion Congress and Exposition, 2009. ECCE 2009. IEEE; 10/2009
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ABSTRACT: A new technique is proposed to reduce the torque-ripple of the concentrated-winding interior permanent magnet motor (IPMSM) under saliency-based sensorless drive. It is based on the combination of circular-flux-barriers at the rotor-yoke and the V-shape-magnets. It is applied to 45 Nm-5.5 kW industrial drive IPMSM to fulfill the torque-ripple requirement with a large region for sensorless rotor position detection.
Power Electronics and Applications, 2009. EPE '09. 13th European Conference on; 10/2009
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M. Niraula,
K. Yasuda,
A. Watanabe,
Y. Kai,
H. Ichihashi,
W. Yamada,
H. Oka,
K. Matsumoto,
T. Yoneyama, T. Nakanishi,
D. Katoh,
H. Nakashima,
Y. Agata
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ABSTRACT: We studied the effect of iodine doping of CdTe films on Si substrates grown by MOVPE at different growth conditions. A high resistivity film was obtained by adjusting the growth temperature, Te/Cd precursor flow ratio and the dopant flow-rate. Our results show the film resistivity does not change linearly with the dopant flow-rate. The resistivity remains low and similar to that of undoped value for low dopant flow-rate, but increases abruptly when the dopant flow-rate is increased beyond certain value. Photoluminescence measurements of the films confirmed the dopant incorporation in the crystal. We explained the result of resistivity change due to the compensation of excess shallow acceptors by deep intrinsic donors.
IEEE Transactions on Nuclear Science 09/2009; · 1.45 Impact Factor
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ABSTRACT: We have obtained Eu<sup>2+</sup>-doped glass-ceramic phosphors, where the two-phosphor crystals of green and red were precipitated by novel GC preparation "frozen sorbet" method and postceraming process. The as-made GC consisted of glass and spherical beta-Ca<sub>2</sub>SiO<sub>4</sub>:Eu<sup>2+</sup> crystal phases with size of about 20-40 mum. After ceramization, Ca<sub>3</sub>Si<sub>2</sub>O<sub>7</sub>:Eu<sup>2+</sup> crystals were also precipitated in addition to the beta-Ca<sub>2</sub>SiO<sub>4</sub> crystal. The photoluminescence had two broad emission bands: at 515 nm from Eu<sup>2+</sup> :beta-Ca<sub>2</sub>SiO<sub>4</sub> and at 600 nm from Eu<sup>2+</sup> :Ca<sub>3</sub>Si<sub>2</sub>O<sub>7</sub>. Judging from the cathodoluminescence mapping images of microstructure, two emission bands peaked at 515 and 600 nm were observed from different parts in the GC. With increasing heat-treatment temperature, the color coordinates shifted from green range to center region, which corresponds to pure white in the International Commission on Illumination chromaticity diagram. Eu<sup>2+</sup>-doped calcium silicate GC containing beta-Ca<sub>2</sub>SiO<sub>4</sub> and Ca<sub>3</sub>Si<sub>2</sub>O<sub>7</sub> are suitable phosphor as the use of phosphor converting white LED with high color rendering.
IEEE Journal of Selected Topics in Quantum Electronics 09/2009; · 3.78 Impact Factor
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ABSTRACT: We show that application of hydrostatic pressure makes the ferromagnetic insulating phase of La <sub>0.79</sub> Ca <sub>0.21</sub> MnO <sub>3</sub> metallic at a pressure of ∼1 GPa . On further increase in pressure (∼6 GPa ) the high temperature polaronic state also crosses over to a metallic behavior. The application of the pressure also shifts the ferromagnetic T<sub>C</sub> of the material to higher temperature. We also find that in the process of pressure induced metallization, the material shows a coherence temperature where a highly resistive incoherent metal crosses over to a less resistive band type metal. The metallic phase so created under pressure has no appreciable magnetoresistance.
Journal of Applied Physics 08/2009; · 2.17 Impact Factor
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M. Niraula,
K. Yasuda,
A. Watanabe,
Y. Kai,
H. Ichihashi,
W. Yamada,
H. Oka,
T. Yoneyama,
H. Nakashima, T. Nakanishi,
K. Matsumoto,
D. Katoh,
Y. Agata
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ABSTRACT: High crystalline quality thick films of single crystal CdTe were grown directly on (211) Si substrates using MOVPE growth technique for gamma ray detector fabrication. A highest growth-rate of 65 mum/h was achieved at a substrate temperature of 600<sup>deg</sup>C. Films were monocrystalline as confirmed from the X-ray diffraction pattern. Results from the 4.2 K photoluminescence measurement showed films were of good crystalline quality. The gamma detector was fabricated in a p-CdTe/n-CdTe/n<sup>+</sup>-Si heterojunction diode structure, which exhibited clear rectifying behavior with a low value of room-temperature reverse bias leakage current, typically 0.11 muA/cm<sup>2</sup> at 100 V bias. The detector leakage current was reduced by three orders of magnitude from the room-temperature value at -30<sup>deg</sup>C. The detector clearly demonstrated its spectroscopy capability by resolving energy peaks from the <sup>241</sup>Am gamma isotope.
IEEE Transactions on Nuclear Science 07/2009; · 1.45 Impact Factor
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ABSTRACT: The intermodulation distortion (IMD) of a 5-GHz HTS resonator is precisely measured and a nonlinear analysis is conducted. When designing a radio communication system that uses an HTS microwave device, the device's IMD characteristic is one of the most important problems that must be quantitatively evaluated. The amplitudes of third-order IMD (IMD3) and higher-order IMD, which are generated in an HTS resonator given a two-tone fundamental signal, are measured in detail using a fundamental signal cancellation circuit. Moreover, the relative phase of IMD3 is obtained by using a novel measurement system constructed around a reference IMD3 generator. The measured IMD3 phase shows a drastic change in a relatively low IMD3 amplitude region. In addition, the measured resonator exhibits strong higher-order IMD. A nonlinear evaluation using complex power series representation confirms that the drastic phase change may be due to the higher-order distortions present in IMD3.
IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
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ABSTRACT: This paper shows an implementation of the anonymous authentication system for Web services. This system uses privacy-enhancing digital signatures, called group signatures, which allow the user to be anonymously authenticated. Since the adopted group signature scheme utilizes novel cryptographic algorithms, the simple introduction of the authentication to the Web browsers and servers needs modifications of them. Thus, we use proxies in our implementation to avoid the modifications. We show that the authentication time is practical by the experiments.
Consumer Electronics, 2009. ISCE '09. IEEE 13th International Symposium on; 06/2009
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ABSTRACT: Recently, Web-page browsing opportunities at multimodal browsing sizes have increased due to developments of various terminals. Meanwhile, most Web pages have been designed to fit to the standard size. As a result, the screen scroll operation is necessary to access the main content at a small size, whereas the blank space becomes large at a large size. In this paper, we propose a Web-page layout optimization method for multimodal browsing sizes by focusing on the standard Web design style with the separation of the document structure description by an XHTML file and the appearance description by a CSS file. Our method automatically generates a set of CSS files fit to different sizes from the files designed for the standard size by a user. Then, it dynamically switches to the CSS file fit to the current browsing size using JavaScript. We confirm the practicality of our proposal through experiments of the Web page generation and access at various sizes.
Consumer Electronics, 2009. ISCE '09. IEEE 13th International Symposium on; 06/2009
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ABSTRACT: Currently, several streaming servers are available to provide a variety of multimedia applications such as VoD (Video-on-Demand), IP-phone, and IP-TV. As a result, the provision of multiple streaming servers on a single machine using the virtualization technology has become important in order to save the operational/management costs while enhancing the performance and the reliability of the system. In this paper, we show the performance evaluation of two representative open source softwares for the virtualization technology, Xen and OpenVZ, in various configurations of applications on three open source streaming servers, Red5, Darwin, and VLC. Our experimental results indicate that OpenVZ provides the better performance for streaming applications with Darwin and VLC whereas Red5 can run only on Xen.
Consumer Electronics, 2009. ISCE '09. IEEE 13th International Symposium on; 06/2009
