著者

Aoki S. Fukugita M. Hashimoto S. Ishizuka N. Iwasaki Y. Kanaya K. Kuramashi Y. Okawa M. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.60, no.3, pp.034511, 1999-07

被引用文献数

24 47

---

A lattice QCD calculation of the kaon B parameter BK is carried out with the Wilson quark action in the quenched approximation at β=6/g2=5.9–6.5. The mixing problem of the Δs=2 four-quark operators is solved nonperturbatively with full use of chiral Ward identities employing four external quarks with an equal off-shell momentum in the Landau gauge. This method, without invoking any effective theory, enables us to construct the weak four-quark operators exhibiting good chiral behavior. Our results for BK with the nonperturbative mixing coefficients show small scaling violation beyond the lattice cutoff a-1∼2.5 GeV. Our estimate concludes BK(NDR,2 GeV)=0.69(7) at a-1=2.7–4.3 GeV, which agrees with the value obtained with the Kogut-Susskind quark action. For comparison we also calculate BK with one-loop perturbative mixing coefficients. While this yields incorrect values at finite lattice spacing, a linear extrapolation to the continuum limit as a function of a leads to a result consistent with those obtained with the Ward identity method.

著者

Aoki S. Fukugita M. Hashimoto S. Ishizuka N. Iwasaki Y. Kanaya K. Kuramashi Y. Okawa M. Ukawa A. Yoshié T.

出版者

American Physical Society

雑誌

Physical review D (ISSN:05562821)

巻号頁・発行日

vol.58, no.5, pp.054503, 1998-07

被引用文献数

13 39

---

We present a calculation for the K+→π+π0 decay amplitude using a quenched simulation of lattice QCD with the Wilson quark action at β=6/g2=6.1. The decay amplitude is extracted from the ratio, the K→ππ three-point function divided by either K and π meson two-point functions or K meson two-point function and I=2 ππ four-point function; the two different methods yield consistent results. Finite size effects are examined with calculations made on 243×64 and 323×64 lattices, and are shown that they are explained by one-loop effects of chiral perturbation theory. The lattice amplitude is converted to the continuum value by employing a one-loop calculation of chiral perturbation theory, yielding a value in agreement with experiment if extrapolated to the chiral limit. We also report on the K meson B parameter BK obtained from the K+→π+π0 amplitude using chiral perturbation theory.

著者

Sato T. Matsui H. Takahashi T. Ding H. Yang H.-B. Wang S.-C. Fujii T. Watanabe T. Matsuda A. Terashima T. Kadowaki K.

出版者

American Physical Society

雑誌

Physical review letters (ISSN:00319007)

巻号頁・発行日

vol.91, no.15, pp.157003, 2003-10

被引用文献数

99 110

---

We report a systematic high-resolution angle-resolved photoemission spectroscopy on high-Tc superconductors Bi2Sr2Can-1CunO2n+4 (n=1–3) to study the origin of many-body interactions responsible for superconductivity. For n=2 and 3, a sudden change in the energy dispersion, so called “kink”, becomes pronounced on approaching (π,0) in the superconducting state, while a kink appears only around the nodal direction in the normal state. For n=1, the kink shows no significant temperature dependence even across Tc. This could suggest that the coupling of electrons with Q=(π,π) magnetic mode is dominant in the superconducting state for multilayered cuprates, while the interactions at the normal state and that of single-layered cuprates have a different origin.

著者

Aoki S. Fukugita M. Hashimoto S. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Onogi T. Tsutsui N. Ukawa A. Yamada N. Yoshié T.

出版者

American Physical Society

雑誌

Physical review letters (ISSN:00319007)

巻号頁・発行日

vol.91, no.21, pp.212001, 2003-11

被引用文献数

63 155

---

We present an unquenched lattice calculation for the B0-B̅ 0 transition amplitude. The calculation, carried out at an inverse lattice spacing 1/a=2.22(4)  GeV, incorporates two flavors of dynamical quarks described by the O(a)-improved Wilson fermion action and heavy quarks described by nonrelativistic QCD. Particular attention is paid to the uncertainty that arises from the chiral extrapolation, especially the effect of pion loops, for light quarks, which we find could be sizable for the leptonic decay constant, whereas it is small for the B parameters. We obtain fBd=191(10)(-22+12)   MeV, fBs/fBd=1.13(3)(-2+13), BBd(mb)=0.836(27)(-62+56), BBs/BBd=1.017(16)(-17+56), and ξ=1.14(3)(-2+13), where the first error is statistical, and the second is systematic, including uncertainties due to chiral extrapolation, finite lattice spacing, heavy quark expansion, and perturbative operator matching.

著者

Umeda T. Son N. T. Isoya J. Janzén E. Ohshima T. Morishita N. Itoh H. Gali A. Bockstedte M.

出版者

American Physical Society

雑誌

Physical review letters (ISSN:00319007)

巻号頁・発行日

vol.96, pp.145501, 2006-04

被引用文献数

70

---

The metastability of vacancies was theoretically predicted for several compound semiconductors alongside their transformation into the antisite-vacancy pair counterpart; however, no experiment to date has unambiguously confirmed the existence of antisite-vacancy pairs. Using electron paramagnetic resonance and first principles calculations we identify the SI5 center as the carbon antisite-vacancy pair in the negative charge state (CSiV_C^-) in 4H-SiC. We suggest that this defect is a strong carrier-compensating center in n-type or high-purity semi-insulating SiC.

著者

Ito T. Katanuma I.

出版者

American Institute of Physics

雑誌

Physics of Plasmas (ISSN:1070664X)

巻号頁・発行日

vol.12, no.8, pp.082512, 2005-08-16

被引用文献数

5 4

---

The neoclassical resonant plateau transport in a mirror cell is studied theoretically. The analytical expression for a non-square-well magnetic field is obtained. The analytical result is applied to the GAMMA10 tandem mirror [T. Cho, M. Yoshida, J. Kohagura et al., Phys. Rev. Lett. 94, 085002-1 (2005)], which consists of several mirror cells in it, and the confinement time due to the neoclassical resonant plateau transport is determined in each mirror cell. It is found that the neoclassical resonant transport of ions trapped in the nonaxisymmetric anchor mirror cell and transition mirror cells is significantly smaller than those trapped in the central cell.

著者

Sasagawa Y. Katanuma I. Mizoguchi Y. Cho T. Pastukhov V. P.

出版者

American Institute of Physics

雑誌

Physics of Plasmas (ISSN:1070664X)

巻号頁・発行日

vol.13, no.12, pp.122506, 2006-12-18

被引用文献数

9 9

---

Magnetohydrodynamic stabilization of an axisymmetric mirror plasma with a magnetic divertor is studied. An equation is found for the flute modes, which includes the stabilizing influence of ion temperature anisotropy and nonparaxial magnetic fields, as well as a finite ion Larmor radius. It is shown that if the density profile is sufficiently gentle, then the nonparaxial configuration can stabilize all modes as long as ion temperature is radially uniform. This can be demonstrated even when the density vanishes on the separatrix and even for small ion Larmor radii. It is found, however, that the ion temperature gradient makes the unstable region wider; high ion temperature is required to stabilize the flute mode.

著者

Katanuma I. Yagi K. Nakashima Y. Ichimura M. Imai T.

出版者

American Institute of Physics

雑誌

Physics of Plasmas (ISSN:1070664X)

巻号頁・発行日

vol.17, no.3, pp.032303, 2010-03

被引用文献数

8 7

---

The computer code by reduced magnetohydrodynamic equations were made which can simulate the flute interchange modes (similar to the Rayleigh–Taylor instability) and the instability associated with the presence of nonuniform plasma flows (similar to the Kelvin–Helmholtz instability). This code is applied to a model divertor and the GAMMA10 [ M. Inutake et al., Phys. Rev. Lett. 55, 939 (1985) ] with divertor in order to investigate the flute modes in these divertor cells. The linear growth rate of the flute instability determined by the nonlocal linear analysis agrees with that in the linear phase of the simulations. There is a stable nonlinear steady state in both divertor cells, but the nonlinear steady state is different between the model divertor and the GAMMA10 with divertor.

著者

Katanuma I. Yagi K. Haraguchi Y. Ichioka N. Masaki S. Ichimura M. Imai T.

出版者

American Institute of Physics

雑誌

Physics of plasmas (ISSN:1070664X)

巻号頁・発行日

vol.17, no.11, pp.112506, 2010-11

被引用文献数

8 7

---

The flute instability and the associated radial transport are investigated in the tandem mirror with a divertor mirror cell (the GAMMA10 A-divertor) with help of computer simulation, where GAMMA10 is introduced [ Inutake et al., Phys. Rev. Lett. 55, 939 (1985) ]. The basic equations used in the simulation were derived on the assumption of an axisymmetric magnetic field. So the high plasma pressure in a nonaxisymmetric minimum-B anchor mirror cell, which is important for the flute mode stability, is taken into account by redefining the specific volume of a magnetic field line. It is found that the flute modes are stabilized by the minimum-B magnetic field even with a divertor mirror although its stabilizing effects are weaker than that without the divertor mirror. The flute instability enhances the radial transport by intermittently repeating the growing up and down of the Fourier amplitude of the flute instability in time.

著者

Turkoglu F Koseoglu H Demirhan Y Ozyuzer L Preu S Malzer S Simsek Y Müller P Yamamoto T Kadowaki K

出版者

IOP Publishing

雑誌

Superconductor science & technology (ISSN:09532048)

巻号頁・発行日

vol.25, no.12, pp.125004, 2012-10

被引用文献数

39 16

---

We fabricated rectangular mesa structures of superconducting Bi2Sr2CaCu2O8+d (Bi2212) using e-beam lithography and Ar ion beam etching techniques for terahertz (THz) emission. c-axis resistance versus temperature (R–T), current–voltage (I–V) characteristics and bolometric THz power measurements were performed to characterize Bi2212 mesas. The emission frequency of mesas was determined using a Michelson interferometer setup which also demonstrates polarized emission. Interference patterns of THz radiation from Bi2212 mesas were detected by various detectors such as a liquid helium cooled silicon composite bolometer, a Golay cell and a pyroelectric detector. An emitted power as high as 0.06 mW was detected from Bi2212 mesas. For the first time, most of the pumped power was extracted as THz emission from a Bi2212 mesa. The radiation at 0.54 THz was detected using the Michelson interferometric setup.

著者

Umeda T Ohno H Kanaya K

出版者

IOP Publishing Ltd

雑誌

Journal of physics. G, Nuclear and particle physics (ISSN:09543899)

巻号頁・発行日

vol.35, no.10, pp.104157, 2008-10

被引用文献数

1 1

---

Dissociation temperatures of J/ψ, ψ' and χc states play key roles in the sequential J/ψ suppression scenario for high-energy heavy-ion collisions. We report on a study of charmonium dissociation temperatures in quenched lattice QCD. On anisotropic lattices, we first subtract the effects of the constant mode in finite temperature meson correlators, which have led to unphysical results in previous studies. We then extract ground and first exited state masses by diagonalizing correlation functions among different source and sink operators. To distinguish bound states from scattering states, we first compare the charmonium mass spectra under different spatial boundary conditions, and examine the shape and the volume dependence of their Bethe–Salpeter wavefunctions. From these studies, we found, so far, no sign of scattering states up to about 2.3Tc.

著者

Ohno H Umeda T Kanaya K WHOT-QCD Collaboration

出版者

IOP Publishing Ltd

雑誌

Journal of physics. G, Nuclear and particle physics (ISSN:09543899)

巻号頁・発行日

vol.36, no.6, pp.064027, 2009

被引用文献数

4

---

Dissociation of charmonia in hot QCD is studied on a quenched anisotropic lattice using standard plaquette gauge action and O(a) improved Wilson fermion action. Simulations are carried out at temperatures in the range 0.88 TC to 2.3 TC. We calculate effective masses and Bethe–Salpeter wavefunctions for the ground state (1S, 1P) and some excited states (2S, 2P) with variational analysis. To distinguish between bound states and scattering states, we apply two methods: first, we compare effective masses for charmonium correlation functions under different spatial boundary conditions. Because the scattering states are sensitive to the boundary conditions, finite volume effects are expected when a charmonium dissociates. Second, we study if the wavefunctions show a sign of scattering states which will be characterized by a broad wavefunction. We find no clear evidence of dissociation for the charmonium states up to 2.3 TC so far.

著者

Islam M. M. Yamada A. Sakurai T. Kubota M. Ishizuka S. Matsubara K. Niki S. Akimoto K.

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.110, no.1, pp.014903, 2011

被引用文献数

8 6

---

The Cu-dependent phase transition in polycrystalline CuGaSe2 thin films has been studied by an electron probe micro-analyzer (EPMA) and the synchrotron x-ray diffraction method. A Cu-deficiency parameter, Z, defined as (1 − Cu/Ga) was used to study the phase transition. Upon increasing the Z-value, the composition of the films on the Cu2Se-Ga2Se3 pseudo binary tie line was found to shift from the stoichiometric CuGaSe2 (1:1:2) (Z = 0) to the Ga-rich composition through the formation of several ordered defect compounds.The structural modification in the Cu-poor CuGaSe2 film has been investigated by the synchrotron x-ray diffraction method. The existence of the Cu-poor surface phase over the near-stoichiometric bulk CuGaSe2 film was confirmed by the fitting of the accelerated voltage dependent EPMA data.

著者

Huré J.-M. Hersant F. Surville C. Nakai N. Jacq T.

出版者

EDP Sciences

雑誌

Astronomy and astrophysics (ISSN:00046361)

巻号頁・発行日

vol.530, pp.A145, 2011-06

被引用文献数

16 6

---

We exploit our formula for the gravitational potential of finite size, power-law disks to derive a general expression linking the mass of the black hole in active galactic nuclei (AGN), the mass of the surrounding disk, its surface density profile (through the power index s), and the differential rotation law. We find that the global rotation curve v(R) of the disk in centrifugal balance does not obey a power law of the cylindrical radius R (except in the confusing case s = −2 that mimics a Keplerian motion), and discuss the local velocity index. This formula can help to understand how, from position-velocity diagrams, mass is shared between the disk and the black hole. To this purpose, we checked the idea by generating a sample of synthetic data with different levels of Gaussian noise, added in radius. It turns out that, when observations are spread over a large radial domain and exhibit low dispersion (standard deviation σ ≲ 10% typically), the disk properties (mass and s-parameter) and black hole mass can be deduced from a non linear fit of kinematic data plotted on a (R,Rv2)-diagram. For σ ≳ 10%, masses are estimated fairly well from a linear regression (corresponding to the zeroth-order treatment of the formula), but the power index s is no longer accessible. We have applied the model to 7 AGN disks whose rotation has already been probed through water maser emission. For NGC 3393 and UGC 3789, the masses seem well constrained through the linear approach. For IC 1481, the power-law exponent s can even be deduced. Because the model is scale-free, it applies to any kind of star/disk system. Extension to disks around young stars showing deviation from Keplerian motion is thus straightforward.

著者

Takakura K. Ohyama H. Takarabe K. Suemasu T. Hasegawa F.

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.97, no.09, pp.093716, 2005-04

被引用文献数

24 13

---

The hole mobility of intentionally undoped p-type beta-FeSi2 thin films grown by a multilayer method was investigated. With increasing annealing temperature and time, the hole mobility increased to approximately 450 cm2/V s at room temperature (RT). The observed hole mobility was analyzed by considering various carrier scatterings such as acoustic-phonon and polar-optical-phonon scatterings, intervalley scattering, ionized impurity scattering, and grain-boundary scattering. The nice fit of the mobility to the experimental results reveals that the polar-optical-phonon scattering determines the hole mobility at RT.

著者

Li Cheng Lai Hongkai Chen Songyan Suemasu T. Hasegawa F.

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.100, no.2, pp.023506, 2006-07

被引用文献数

5 4

---

The temperature dependence of electroluminescence from silicon p-i-n light-emitting diodes with a layer of beta-FeSi2 particles inserted in intrinsic silicon was investigated. Anomalous blueshift of the peak energy and enhanced electroluminescence intensity of the silicon band-edge emission were observed at temperatures from 50 to 200 K. The electroluminescence intensity was enhanced due to longer diffusion paths of the injected electrons at elevated temperature, as well as thermal escape of the electrons from the beta-FeSi2 particles. The low peak energy compared to that from bulk silicon at low temperature is due to the bound electron-hole pairs induced by the strain potential at the interface between silicon and beta-FeSi2 particles. The blueshift of the peak is ascribed to the transition of bound electron-hole pairs into free excitons at elevated temperature. Room temperature electroluminescence from such a silicon light-emitting diode can be obtained at a low current density of 0.3 A/cm2.

著者

Fukata N. Oshima T. Okada N. Murakami K. Kizuka T. Tsurui T. Ito S.

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.100, no.2, pp.024311, 2006-07

被引用文献数

44 33

---

The phonon confinement and self-limiting oxidation effects of silicon nanowires (SiNWs) synthesized by laser ablation were investigated. The size of SiNWs was controlled by the synthesis parameters during laser ablation and the subsequent thermal oxidation. Thermal oxidation increases the thickness of the SiNWs' surface oxide layer, resulting in a decrease in their crystalline Si core diameter. This effect causes a downshift and asymmetric broadening of the Si optical phonon peak due to phonon confinement, while excess oxidation causes an upshift due to compressive stress. The compressive stress retarded the oxidation of the SiNWs by self-limiting oxidation effect. This result shows that the Si core diameter can be controlled by compressive stress.

著者

Koyano T. Nomiyama T. Kanoh N. Numata H. Ohba T. Kita E. Ohtsuka H.

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.100, no.3, pp.033906, 2006-08

被引用文献数

7

---

The gamma iron nitride (nitrogen austenite) was subjected to high magnetic field process in order to drive the fcc-->bct martensitic transformation. Molar fraction of martensite monotonically increased with increasing the magnetic field and reached 94% at 35 T. With a combination of magnetization and 57Fe Mössbauer spectroscopy data, magnetization of bulk processed alpha[prime] phase with 9.6 at. % N is determined to be 229 emu/g, the same as that for dc sputtered thin films.

著者

Aoki M. Toyoshima S. Kamada T. Sogo M. Masuda S. Sakurai T. Akimoto K.

出版者

American Institute of Physics

雑誌

Journal of applied physics (ISSN:00218979)

巻号頁・発行日

vol.106, no.4, pp.043715, 2009-08

被引用文献数

11 7

---

Electron emission spectra resulting from thermal collision of He*(23S) atoms with 2,9-demethyl-4,7-diphenyl-1,10-phenanthroline (BCP) films deposited on metal substrates were measured to characterize gap states emerged at the organic-metal interface. For BCP on Au, the gap state is originated from weak chemisorption and serves as a mediator of metal wave functions to the first layer. For BCP on K, organic-metal complex is formed by spontaneous diffusion, yielding the gap states delocalized over the film. In the interfacial region, all the gap state reveals an incommensurate shift with the valence band top of the film, indicating the breakdown of the Schottky–Mott model as evaluating the transport characteristics in organic-metal system.

著者

Umeda T. Isoya J. Ohshima T. Onoda S. Morishita N. Okonogi K. Shiratake S.

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.97, no.4, pp.041911, 2010-07

被引用文献数

5

---

An electron paramagnetic resonance (EPR) study on fluorine-vacancy defects (FnVm) in fluorine-implanted silicon is demonstrated. Fluorine implantation is an important technology for Si microdevices and EPR measurements showed that this process created a variety of FnVm defects of different sizes (V2, V4, and V5). In FnVm, a Si–F bond exhibited a different chemical nature compared to a Si–H bond in hydrogen-vacancy complexes. The most primitive defect was FV2 (F0 center) and the final types were FnV5 (F1 center) and FnV2 (F2 center) which increased in annealing processes as low temperature as 200 °C.