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ABSTRACT: Understanding of interactions of proteins is important to reveal networks and functions of molecules. Many investigations have been conducted to analyze interactions and contacts between residues. It is supported that residues at interacting sites have co-evolved with those at the corresponding residues in the partner protein to keep the interactions between the proteins. Therefore, mutual information (MI) between residues calculated from multiple sequence alignments of homologous proteins is considered to be useful for identifying contact residues in interacting proteins. In our previous work, we proposed a prediction method for protein-protein interactions using mutual information and conditional random fields (CRFs), and confirmed its usefulness. The discriminative random field (DRF) is a special type of CRFs, and can recognize some specific characteristic regions in an image. Since the matrix consisted of mutual information between residues in two interacting proteins can be regarded as an image, we propose a prediction method for protein residue contacts using DRF models with mutual information. To validate our method, we perform computational experiments for several interactions between Pfam domains. The results suggest that the proposed DRF-based method with MI is useful for predicting protein residue contacts compared with that using the corresponding Markov random field (MRF) model.
Systems Biology (ISB), 2011 IEEE International Conference on; 10/2011
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ABSTRACT: In recent times, the web-based applications has grown rapidly and there has been an explosive increase in the number of users. Hence, it is necessary to develop technique to deal with several users. In this study, we particularly focus on web-based multiplayer online role-playing games (MORPGs), which have a large number of users and deal with high frequency of user requests. In our previous work, we introduced a method to deal with a large number of users using multiple web servers and a dynamic data allocation method to deal with dynamic change in the user request. Using our method, we achieved a user capacity of 320 for the web-based MORPG system as opposed to 200 user capacity of the single server MORPG system. However, we found some cases in which our dynamic data allocation role was not effective. In this paper, we propose three rules for our dynamic data allocation method to address various situations. We evaluate these rules using four web servers and investigate their properties and effectiveness.
Advanced Information Networking and Applications (AINA), 2011 IEEE International Conference on; 04/2011
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ABSTRACT: The recent spread of broadband Internet access, speeding up of JavaScript in Web browsers, and development of communications technology such as Ajax has led to the development of a variety of Web applications. The access congestion of Web servers and lower usability in the case of frequent requests are the major problems that affect the use of Web applications. In this study, we investigate the bottlenecks in single-server system and propose a technique to improve the usability of Web-based MORPG servers.
Communications, Computers and Signal Processing, 2009. PacRim 2009. IEEE Pacific Rim Conference on; 09/2009
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ABSTRACT: Energy spectra of X-rays emitted from the surface of a fiberglass-reinforced plastic (FRP) insulator were measured at three different positions and compared with those of the vacuum gap between electrodes. Near the anode, the X-ray spectrum was dominated by monoenergetic electrons. Near the cathode, the spectrum peak shifted to low energy as compared with that near the anode. This result showed that a large amount of low-energy electrons was generated on the surface of the FRP insulator near the cathode.
IEEE Transactions on Plasma Science 09/2009; · 1.17 Impact Factor
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ABSTRACT: Excess heat loads to accelerator grids limit extension of pulse length in operation of the large negative ion sources with multi aperture accelerator. Part of the heat loads is caused by interception of deflected beamlets due to their space charge repulsion. In this paper, a beamlet steering technique using aperture offset was examined for compensation of the beamlet deflections utilizing a three dimensional beam analysis simulating the D− negative ion source of JT‐60 U. The beamlet deflection was analyzed in detail using fifty beamlets, which were extracted from apertures arranged in a lattice pattern of 10×5. The simulation showed successful compensation of the beamlet deflection by aperture offsets defined according to the thin lens theory. Even if the beam energy was changed, the necessary aperture offset would not be changed maintaining the perveance and a ratio of extraction and acceleration voltage. In JT‐60 U, it was shown that the aperture offset of less than 1.0 mm would be enough to compensate the repulsion of all beamlets. When the magnetic field was applied for suppression of co‐extracted electrons, necessary aperture offset was estimated to be ±0.5 mm for 500 keV D− ion beam in JT‐60 U, in addition to the offset for the space charge repulsion. This result showed good agreements with the previous experimental results and design study of the JT‐60 U N‐NBI.
AIP Conference Proceedings. 03/2009; 1097(1):421-430.
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Y. Ikeda,
M. Hanada, M. Kamada,
K. Kobayashi,
N. Umeda,
N. Akino,
N. Ebisawa,
T. Inoue,
A. Honda,
M. Kawai, [......],
S. Sasaki,
T. Simizu,
T. Takenouchi,
Y. Tanai,
K. Usui,
K. Watanabe,
L.R. Grisham,
S. Kobayashi,
Y. Yamano,
M. Takahashi
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ABSTRACT: The JT-60 Super Advanced (JT-60SA) tokamak aims to perform the ITER support and to demonstrate steady-state high-beta plasma project with the collaboration between Japan and EU. To attain these objectives, the negative-ion-based NBI (N-NBI) system is required to inject 10 MW for 100 s at the beam energy of 500 keV. On JT-60U, the present N-NBI ion source has injected 3.2 MW for 21 s at 320 keV; however, three key issues should be solved for the JT-60SA N-NBI ion source. One is to improve the voltage holding capability of the large negative ion source, where the available acceleration voltage has been limited to less than ~400 kV due to breakdowns. The accelerator of the JT-60U ion source is composed of large three-stage grids and three fiberglass reinforced plastic (FRP) insulators. Recent R&D tests suggested that the FRP insulators were not the main factor to trigger the breakdowns at the early conditioning stage. The accelerator with a large area of grids and their supporting structure may need a high margin in the design of electric field and a long time for conditioning. The second issue is to reduce the power loading of the acceleration grids. It was found that some beamlets were strongly deflected due to beamlet-beamlet interaction and strike on the grounded grid in the accelerator. Moreover, the electrons generated in the accelerator caused the grid loading and the overheating of the beamline components. The acceleration grids for JT-60SA are to be designed by taking account of the beamlet-beamlet interaction and the applied magnetic field in 3-D simulation. Third is to maintain the D production for 100 s. Although a constant D<sup>-</sup> beam power was confirmed on JT-60U for 21 s, an active cooling system is required to keep the temperature of the plasma grid (PG) under optimum condition during 100-s operation. A simple cooling structure is proposed for the active cooled PG, where a key is the temperature gradient on the PG for uniform D<sup>-</sup> p-
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roduction. In the present schedule, design work, reflecting the latest R&D progress, will continue until ~2011. The modified N-NBI ion source will start on JT-60SA in 2015.
IEEE Transactions on Plasma Science 09/2008; · 1.17 Impact Factor
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ABSTRACT: The power loading of electrons ejected from the negative ion accelerator to the beamline was first measured in the negative-ion-based neutral beam injector on JT-60U. At 0.3 Pa of the operating pressure in the arc chamber, the heat flux and the total power load for the single segment were ~8 W/cm<sup>2</sup> and 27 kW for the D ion beam of 300 keV and 3.4 A, respectively. The normalized total power loading on the electron dump was no more than 2.6% of the electric power in the acceleration power supply. About 70% of the total power is originated by the electrons stripped from D ions due to collisions with residual gas molecules in the accelerator. The calculation of the stripped electron trajectories shows that the electrons stripped in the second acceleration gap are the main origin of the power loading in the beamline.
IEEE Transactions on Plasma Science 09/2008; · 1.17 Impact Factor
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M Hanada, M Kamada,
N Akino,
N Ebisawa,
A Honda,
M Kawai,
M Kazawa,
K Kikuchi,
M Komata,
K Mogaki,
K Noto,
K Ohshima,
T Takenouchi,
Y Tanai,
K Usui,
H Yamazaki,
Y Ikeda,
L R Grisham
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ABSTRACT: The first long pulse production of high power D(-) ion beams has been demonstrated in the JT-60 U negative ion sources, each of which was designed to produce 22 A, 500 keV D(-) ion beams. Voltage holding capability and the grid power loading were examined for long pulse production of high power D(-) ion beams. From the correlation between voltage holding and the light intensity of cathodoluminescence from the Fiber Reinforced Plastic insulators, the acceleration voltage for stable voltage holding capability was found to be less than 320-340 kV where the light was sufficiently suppressed. By tuning the extraction voltage, the grid power loadings in the ion sources were decreased to the allowable levels for long pulse injection without a significant reduction of the beam power. After tuning the acceleration and extraction voltages, D(-) ion beams of 12.5 and 9.8 A were produced at 340 keV with cesium seeding at a rate of approximately 14 microg/s into the ion sources. The pulse duration of these D(-) ion beams was extended step by step, and then was successfully extended up to 18 s without degradation of the negative ion production. The D(-) ion beams were neutralized to yield 3.6 MW D(0) beams by a gas cell, and then injected into the JT-60 U plasma. Further, a slight reduction of D(-) ion beam power allowed the longer injection duration of 21 s at a D(0) beam power of 3.2 MW. The success in the long pulse production of a high power D(-) ion beam shows that negative ion beams can be produced during a few tens of seconds without degradations of negative ion production and the voltage holding in a large Cs-seeded negative ion source.
Review of Scientific Instruments 03/2008; 79(2 Pt 2):02A519. · 1.37 Impact Factor
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ABSTRACT: The JT-60U negative ion source has been designed to produce high current beams of 22 A through grids of 1080 apertures (five segments with nine rows of 24 apertures). One of the key issues is to steer such a high current beam through the multiaperture grids in order to focus the overall beam envelope because the beamlet-beamlet interaction may deflect the outer beamlets outward due to unbalanced space charge repulsion. To clarify the beam deflection in the JT-60U negative ion source, the beamlet trajectory in a multiaperture ion source was calculated by a three-dimensional simulation code. The measured angles of the outmost beamlets were in agreement with the calculated results where space charge of the beamlets was taken into account. It is noticed that the deflection of the outermost beamlet due to the beamlet-beamlet interaction is saturated at 5.2 mrad outward for beamlets more than ten.
Review of Scientific Instruments 03/2008; 79(2 Pt 2):02C114. · 1.37 Impact Factor
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ABSTRACT: A large orbit gyrotron (LOG) has been developed for generation of high-power far-infrared radiation. It uses pulsed relativistic electron beam with maximum electron energy of 400 kV. The studies were carried out through both experimental and simulation approaches. The objective is to demonstrate high-power radiation in terahertz range by using LOG.
Pulsed Power Conference, 2007 16th IEEE International; 07/2007
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ABSTRACT: Voltage holding capability in a 500 keV electrostatic accelerator with large FRP insulators was examined without the beam acceleration. When high voltage was applied, the light with a broad peak at a wavelength of 420 nm was mostly emitted inside the accelerator even though breakdown did not occur. The voltage holding capability has a strong correlation with the light intensity. Stable voltage holding was realized under the conditions in which light emission was well suppressed.
IEEE Transactions on Dielectrics and Electrical Insulation 07/2007; · 1.09 Impact Factor
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ABSTRACT: The paper discusses the construction of UWB pulses on the basis of B-splines under the following conditions: (i) the B-splines are time-limited piecewise polynomials; (ii) the pulses are rectangular when their order is one and they converge to band-limited functions at the limit that their order tends to infinity; (iii) an analog circuit and a fast digital filter exist for the generation of B-splines. A constrained minimization technique is proposed for designing pulses so as to comply with the FCC spectral mask and satisfy basic requirements for UWB pulses.
Circuits and Systems, 2005. ISCAS 2005. IEEE International Symposium on; 06/2005
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ABSTRACT: Preliminary design of cavity for high power submillimeter large orbit gyrotron has been described. Time-dependent, multi-mode calculation gives us the possibility to achieve output power of up to 1.5 MW with a frequency 420.8 GHz at third harmonic. The most important advantages of LOG are possibility of selective excitation of high harmonic number. However, due to low efficiency of this devices (typically a few percents), high output power needs powerful electron beams.
Infrared and Millimeter Waves, 2004 and 12th International Conference on Terahertz Electronics, 2004. Conference Digest of the 2004 Joint 29th International Conference on; 11/2004
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ABSTRACT: In this paper, the nonorthogonal multilevel spread ALOHA system, which combines the spread ALOHA system with the nonorthogonal multilevel system is investigated. In particular, the throughput performance of the nonorthogonal multilevel spread ALOHA system is evaluated by theoretical analysis. It is found that the throughput performance of the nonorthogonal multilevel spread ALOHA system is greater than that of the conventional spread ALOHA systems when the network traffic is not busy. It is found that application of the traffic control to the nonorthogonal multilevel spread ALOHA system is effective in improvement of the performance.
Global Telecommunications Conference, 2002. GLOBECOM '02. IEEE; 12/2002
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ABSTRACT: The 10th anniversary of UVSOR was celebrated on December 3, 1993. During the past 10 years the number of users has been increasing and is now at about 600, including scientists from foreign countries. The stability and the lifetime of the SR light were improved by introducing a double rf cavity system. The free‐electron laser experiment in the short‐wavelength region has been carried out and the UV lasing at 300 nm was successfully obtained in July 1993. Eighteen experimental stations are now operational, which cover the wide energy range from far infrared to soft x rays. Two new beamlines are now under construction, which are expected to be useful in the extreme ultraviolet region. © 1995 American Institute of Physics.
Review of Scientific Instruments 03/1995; · 1.37 Impact Factor
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ABSTRACT: At the UVSOR Facility, a 750‐MeV storage ring has been operated with an initial current of 200 mA. It has two undulators and a superconducting wiggler. A computer control system with two VAXs was introduced. The bunch length at the single‐bunch operation was studied. A gain measurement for free electron laser study was successfully done. The number of beam lines is 19. By the use of these beam lines, about 140 programs have been accomplished in the fiscal year 1990. Among them, a photoelectron coincidence study on Xe atoms, a Te 4d absorption study in p‐ and n‐type SnTe, and a photostimulated desorption study of Na atoms from sodium halides are demonstrated as topics. The Department of Vacuum Ultraviolet Photoscience has been newly approved at IMS to impel the researches by using UVSOR.
Review of Scientific Instruments 02/1992; · 1.37 Impact Factor
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ABSTRACT: Sputtering of excited‐state potassium atoms from electron‐bombarded KBr crystals has been investigated at 300 and 443 K by measuring simultaneously the optical emission, Auger, and mass spectra. The beam current dependences of the intensities of the ground‐state and excited‐state potassium atoms at 443 K are nearly linear and quadratic, respectively, indicating that excited‐state potassium atoms are produced by gas‐phase collisions of potassium atoms desorbed from the surface. On the other hand, the room‐temperature data show complicated dependences, which can be divided into three current regions. In the low‐current region (≪13 μA), electronic excitation followed by Auger‐induced Coulomb repulsion produces the excited‐state potassium atoms. In the high‐current region (≫25 μA), effects due to sample decomposition, nonstoichiometry, and gas‐phase collisions play important roles in the production of excited‐state potassium atoms. The nonlinear sputtering yield of excited‐state potassium atoms in the intermediate‐current region may be due to secondary effects including the formation of defects and cluster ions.
Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 08/1990; · 1.25 Impact Factor
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ABSTRACT: We established that the contact resistance to the two‐dimensional electron gas (2DEG) in selectively doped n‐AlGaAs/GaAs heterostructure is crystal orientation dependent. The contact resistance in the [011] direction is the lowest and that in the [01¯1] direction is the highest. The contact resistance monotonically changes between the [011] and [01¯1] directions. We also find the sheet resistance dependence of the contact resistance.
Applied Physics Letters 12/1986; · 3.84 Impact Factor
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ABSTRACT: Origin of a nonradiative center in AlGaAs grown by molecular‐beam epitaxy was investigated by secondary ion mass spectroscopy and deep‐level transient spectroscopy, from the change of photoluminescence intensity with anneal treatment, and from its comparison with GaAs. Aluminum‐oxygen complex is a most probable defect which acts as a nonradiative center in AlGaAs, and the oxygen would evaporate as Al 2 O from the surface, which would be a reason why the photoluminescence intensity increases under higher substrate temperature and lower V/III flux ratio. The electron‐trap level at 0.76 eV from the conduction band would be the recombination center, and the photoluminescence intensity is inversely proportional to the trap concentration.
Journal of Applied Physics 05/1986; · 2.17 Impact Factor
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Y. Ikeda,
N. Akino,
N. Ebisawa,
M. Hanada,
T. Inoue,
A. Honda, M. Kamada,
M. Kawai,
M. Kazawa,
K. Kikuchi, [......],
F. Okano,
T. Ohga,
K. Oshima,
T. Takenouchi,
H. Tamai,
Y. Tanai,
N. Umeda,
K. Usui,
K. Watanabe,
H. Yamazaki
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ABSTRACT: Modification of JT-60U to a superconducting device (so called JT-60SA) has been planned to contribute to ITER and DEMO. The NBI system is required to inject D0 beams of 34 MW for 100 s. The upgraded NBI system for JT-60SA consists of 12 positive-ion-based NBI (P-NBI) units and one negative-ion-based NBI (N-NBI) unit. The injection powers of each P-NBI and N-NBI units are 2 MW at 85 keV and 10 MW at 500 keV, respectively. On JT-60U, the long pulse operations of 30 s at 2 MW and 20 s at 3.2 MW have been achieved on the P-NBI and N-NBI units, respectively. Both units have demonstrated no injection power degradation for long pulse operation. It has been also found that the thermal time constants of the main key components with active cooling, such as the ion source of the present NBI system, are less than ∼20 s. Therefore, the pulse extension up to 100 s is expected to need some modifications mainly the power supply system. In addition, the voltage-holding capability of the negative ion source is required to be improved. The detailed technical design of the NBI system for JT-60SA is presented.
Fusion Engineering and Design.
