Journal of the Physical Society of Japan
Online ISSN : 1347-4073
Print ISSN : 0031-9015
ISSN-L : 0031-9015
Volume 76, Issue 11
Displaying 1-50 of 68 articles from this issue
  • Sachio Komamiya, Yoshitaka Kuno
    2007 Volume 76 Issue 11 Pages 111001
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    Near the end of the last century, remarkable progress was made in elementary particle physics both experimentally and theoretically, which led to the development of the Standard Model. However, we consider the model as a realization of a more fundamental theory at low energies, since there are so many unexplained physics in the model. Now, elementary particle physics is entering an exciting period in which a new paradigm of the field will be opened by the new discoveries expected in experiments at high-energy frontier colliders. The Higgs boson and supersymmetry are the main targets in these experiments. In parallel to energy frontier physics, experimental and theoretical studies attack the mystery of quark and lepton flavors. The combined efforts in cosmology and particle physics give synergy effects in understanding the history and the current state of the Universe.
    Download PDF (400K)
  • Yoichiro Nambu
    2007 Volume 76 Issue 11 Pages 111002
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    An overview is given of the development of particle physics since the 1930s to the 1960s when the concept of spontaneous symmetry breaking (SSB) was established as an essential component of particle theory and eventually led to the Standard Model. A brief account of SSB as a general phenomenon in physics is also added.
    Download PDF (95K)
  • Tatsuo Kawamoto
    2007 Volume 76 Issue 11 Pages 111003
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    Progress in the electroweak physics at the e+e colliders are reviewed, focusing mainly on the latest and highest energy colliders LEP and SLC. The results on the Z and W boson properties are discussed, and the implications of these precision results in the standard model are shown.
    Download PDF (297K)
  • Beate Heinemann
    2007 Volume 76 Issue 11 Pages 111004
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    Hadron colliders have played a pivotal role in establishing the electroweak sector of the standard model at high precision. Highlights were the discovery of the W and Z bosons in 1983, the discovery of the top quark in 1995 and the high precision measurements of the mass of the W boson and the top quark. The Higgs boson is the final missing piece in the theory of electroweak interactions. In this article the discoveries and precision measurements of the W boson and top quark are reviewed, and the status of searches for the Higgs boson at hadron colliders is presented.
    Download PDF (258K)
  • A. I. Sanda
    2007 Volume 76 Issue 11 Pages 111005
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    Without flavor physics, we would not have the standard model of elementary particles today. The goal of flavor physics is to get at the most fundamental theory of nature. This is done by looking for phenomena which can not be explained by the standard model. To do this, we need to study flavor physics from every angle possible. In support of this, we review how flavor physics has contributed to our understanding of nature over the past 60 years.
    Download PDF (364K)
  • Laurence S. Littenberg
    2007 Volume 76 Issue 11 Pages 111006
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    Selected recent results on rare kaon decays are reviewed and prospects for on-going and future experiments are discussed.
    Download PDF (2391K)
  • Robin Devenish
    2007 Volume 76 Issue 11 Pages 111007
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    A brief introduction is given to high energy electron–proton interactions at the HERA collider. The article focuses on deep-inelastic scattering at high momentum transfers, electroweak interactions of neutral and charged current processes with polarised e± beams and one example of a search for signals beyond the standard model of particle physics.
    Download PDF (343K)
  • Kenzo Nakamura
    2007 Volume 76 Issue 11 Pages 111008
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    This paper reviews the current understanding of neutrino mass and mixing parameters in the framework of three active neutrino species and experimental results which established neutrino oscillations. Future prospects are also discussed.
    Download PDF (417K)
  • Bradley Lee Roberts
    2007 Volume 76 Issue 11 Pages 111009
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    Since its discovery in the 1930s, the muon has played an important role in our quest to understand the sub-atomic theory of matter. The muon was the first second-generation standard-model particle to be discovered, and its decay has provided information on the (VectorAxial Vector) structure of the weak interaction, the strength of the weak interaction, GF, and the conservation of lepton number (flavor) in muon decay. The muon’s anomalous magnetic moment has played an important role in restricting theories of physics beyond the standard standard model, where at present there is a 3.4σ difference between the experiment and standard-model theory. Its capture on the atomic nucleus has provided valuable information on the modification of the weak current by the strong interaction which is complementary to that obtained from nuclear β decay.
    Download PDF (346K)
  • Eugene D. Commins
    2007 Volume 76 Issue 11 Pages 111010
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    The significance of particle and nuclear electric dipole moments is explained in the broader context of elementary particle physics and the charge–parity (CP) violation problem. The present status and future prospects of various experimental searches for electric dipole moments are surveyed.
    Download PDF (182K)
  • Yasuhiro Okada
    2007 Volume 76 Issue 11 Pages 111011
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    The Higgs particle is a new elementary particle predicted in the Standard Model of the elementary particle physics. It plays a special role in the theory of mass generation of quarks, leptons, and gauge bosons. In this article, theoretical issues on the Higgs mechanism are first discussed, and then experimental prospects on the Higgs particle study at the future collider experiments, LHC and ILC, are reviewed. The Higgs coupling determination is an essential step to establish the mass generation mechanism, which could lead to a deeper understanding of particle physics.
    Download PDF (164K)
  • Masahiro Yamaguchi
    2007 Volume 76 Issue 11 Pages 111012
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    Despite the success of the standard model of particle physics, there are reasons to expect new physics beyond it. Supersymmetric extension is a promising possibility, which solves the fine-tuning problem inherent to the origin of the electroweak scale in the standard model. It also provides a promising candidate for dark matter. The verification of low-energy supersymmetry in forthcoming experiments will lead us to a new paradigm of particle physics, in particular, it may open up the road to the unification of forces.
    Download PDF (121K)
  • Shoji Asai
    2007 Volume 76 Issue 11 Pages 111013
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    Physics potential of the LHC (Large Hadron Collider) is summarized in this report, focusing especially on two major topics, the Higgs boson and Supersymmetry. ATLAS and CMS collaborations have excellent potential to discover them, if they exist at the mass scale less than about 1 and 3 TeV, respectively. Methods and their expected performances, to determine the properties of these new particles, are summarized.
    Download PDF (851K)
  • Hitoshi Yamamoto
    2007 Volume 76 Issue 11 Pages 111014
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    International Linear Collider (ILC) is an electron–positron collider with the initial center-of-mass energy of 500 GeV which is upgradable to about 1 TeV later on. Its goal is to study the physics at TeV scale with unprecedented high sensitivities. The main topics include precision measurements of the Higgs particle properties, studies of supersymmtric particles and the underlying theoretical structure if supersymmetry turns out to be realized in nature, probing alternative possibilities for the origin of mass, and the cosmological connections thereof. In many channels, Higgs and leptonic sector in particular, ILC is substantially more sensitive than LHC, and is complementary to LHC overall. In this short article, we will have a quick look at the capabilities of ILC.
    Download PDF (624K)
  • Michael S. Turner, Dragan Huterer
    2007 Volume 76 Issue 11 Pages 111015
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    A web of interlocking observations has established that the expansion of the Universe is speeding up and not slowing, revealing the presence of some form of repulsive gravity. Within the context of general relativity the cause of cosmic acceleration is a highly elastic (p∼−ρ), very smooth form of energy called “dark energy” accounting for about 75% of the Universe. The “simplest” explanation for dark energy is the zero-point energy density associated with the quantum vacuum; however, all estimates for its value are many orders-of-magnitude too large. Other ideas for dark energy include a very light scalar field or a tangled network of topological defects. An alternate explanation invokes gravitational physics beyond general relativity. Observations and experiments underway and more precise cosmological measurements and laboratory experiments planned for the next decade will test whether or not dark energy is the quantum energy of the vacuum or something more exotic, and whether or not general relativity can self consistently explain cosmic acceleration. Dark energy is the most conspicuous example of physics beyond the standard model and perhaps the most profound mystery in all of science.
    Download PDF (345K)
  • Neil J. C. Spooner
    2007 Volume 76 Issue 11 Pages 111016
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    For many working in particle physics and cosmology successful discovery and characterisation of the new particles that most likely explain the non-baryonic cold dark matter, known to comprise the majority of matter in the Universe, would be the most significant advance in physics for a century. Reviewed here is the current status of direct searches for such particles, in particular the so-called weakly interacting massive particles (WIMPs), together with a brief overview of the possible future direction of the field extrapolated from recent advances. Current best limits are at or below 10−7 pb for spin-independent neutralino coupling, sufficient that experiments are already probing SUSY models. However, new detectors with tonne-scale mass and/or capability to correlate signal events to our motion through the Galaxy will likely be needed to determine finally whether WIMPs exist.
    Download PDF (422K)
  • Michael E. Peskin
    2007 Volume 76 Issue 11 Pages 111017
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    Astrophysicists now know that 80% of the matter in the universe is “dark matter”, composed of neutral and weakly interacting elementary particles that are not part of the Standard Model of particle physics. I will summarize the evidence for dark matter. I will explain why I expect dark matter particles to be produced at the CERN LHC. We will then need to characterize the new weakly interacting particles and demonstrate that they the same particles that are found in the cosmos. I will describe how this might be done.
    Download PDF (451K)
  • Motohiko Yoshimura
    2007 Volume 76 Issue 11 Pages 111018
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    The advent of the standard gauge theory of particle physics is a story of remarkable suceess. Yet it is the view of most particle physicists that it is not the end for the quest of the ultimate microscopic world. Direct experimental hints for physics beyond the standard theory have recently been provided by the discovery of neutrino oscillation. On the theoretical side, there are many unsolved problems, one of which we will explain in this article.
    Download PDF (117K)
  • Paul Mackenzie
    2007 Volume 76 Issue 11 Pages 111019
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    Modern lattice gauge theory calculations are making it possible for lattice QCD to play an increasingly important role in the quantitative investigation of the Standard Model. The fact that QCD is strongly coupled at large distances has required the development of nonperturbative methods and large-scale computer simulations to solve the theory. The development of successful numerical methods for QCD calculations puts us in a good position to be ready for the possible discovery of new strongly coupled forces beyond the Standard Model in the era of the Large Hadron Collider.
    Download PDF (747K)
  • Tamiaki Yoneya
    2007 Volume 76 Issue 11 Pages 111020
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    This article is devoted to a nontechnical review on the present status of string theory towards an ultimate unification of all fundamental interactions including gravity. In particular, we emphasize the importance of string theory as a new theoretical framework in which the long-standing conflict between quantum theory and general relativity is resolved.
    Download PDF (167K)
  • Andrei Smolyakov, Patrick Diamond, Masatoshi Yagi, Kimitaka Itoh, Sana ...
    2007 Volume 76 Issue 11 Pages 113501
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    Effect of turbulence on neoclassical tearing modes (NTM) is studied assuming the scale separation between the small scale turbulence and large scale magnetic island. The modified Ohms law taking into account the bootstrap current and the current diffusion due to the small scale turbulence is used. It is shown that the turbulent spreading of the current reduces the pressure gradient drive for NTM and provides an amplitude threshold for NTM excitation.
    Download PDF (86K)
  • Isao Maruyama, Yasuhiro Hatsugai
    2007 Volume 76 Issue 11 Pages 113601
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    Quantized Berry phases used as local order parameters in tJ models are studied. A texture pattern of the local order parameters is topologically stable due to the quantization of non-Abelian Berry phases defined by low-energy states below a spin gap, which exists in the large Jt case with a few electrons. We have confirmed that the itinerant singlets in the wide class of tJ models carry the nontrivial Berry phase π. In the large Jt case for the one-dimensional tJ model, the Berry phases are uniformly π when the number of electrons is N=4n+2 (n=0,1,2,…).
    Download PDF (224K)
  • Koichiro Sadakane, Hideki Seto, Hitoshi Endo, Mitsuhiro Shibayama
    2007 Volume 76 Issue 11 Pages 113602
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    The effect of adding sodium tetraphenylborate (NaBPh4) on a LCST type phase separation of a mixture of D2O and 3-methylpyridine is investigated by visual observation and small-angle neutron scattering (SANS). In the case that the amount of salt is smaller than 50 mM, the mixture colors below the phase separation temperature. When the amount of salt is increased, the phase separation disappears and a single peak profile is observed at finite-Q by SANS. These results indicate that a periodic structure is induced in one phase region by the addition of NaBPh4.
    Download PDF (170K)
  • Shinji Watanabe, Masatoshi Imada
    2007 Volume 76 Issue 11 Pages 113603
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    We show theoretically that the second layer of 3He adsorbed on graphite and solidified at 4/7 of the first-layer density is close to the fluid–solid boundary with substantial density fluctuations on the third layer. The solid shows a translational symmetry breaking as in charge-ordered insulators of electronic systems. We construct a minimal model beyond the multiple-exchange Heisenberg model. An unexpectedly large magnetic field required for the measured saturation of magnetization is well explained by the density fluctuations. The emergence of quantum spin liquid is understood from the same mechanism as in the Hubbard model and in κ-(ET)2Cu2(CN)3 near the Mott transitions.
    Download PDF (173K)
  • Kazuhiro Sano, Yoshiaki Ono
    2007 Volume 76 Issue 11 Pages 113701
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    Using the numerical diagonalization method, we examine the one-dimensional t1t2J1J2 model (zigzag-chain tJ model) which is an effective model for metallic CuO double chains in the superconductor Pr2Ba4Cu7O15−δ. Based on the Tomonaga–Luttinger liquid theory, we calculate the Luttinger liquid parameter Kρ as a function of the electron density n. It is found that superconductivity is realized in the parameter region, which is in accordance with experimental results. We show the phase diagram of a spin gap in the t2⁄|t1|–n plane by analyzing the expectation value of the twist operator Zσ in the spin sector. The spin gap appears in the region with a large t2⁄|t1|, where the phase boundary at half filling is consistent with that of the known frustrated quantum spin system. The analysis also suggests that the estimated value of the spin gap reaches ∼100 K in the realistic parameter region of Pr2Ba4Cu7O15−δ.
    Download PDF (200K)
  • Toru Kakiuchi, Yusuke Wakabayashi, Hiroshi Sawa, Toshihiro Takahashi, ...
    2007 Volume 76 Issue 11 Pages 113702
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    The spatial charge arrangement of a typical quasi-two-dimensional organic conductor α-(BEDT-TTF)2I3 is revealed by single crystal structure analysis using synchrotron radiation. The results show that the horizontal-stripe-type structure, which was suggested by the mean field theory, is established. We also find the charge disproportionation above the metal–insulator transition temperature and a significant change in the transfer integrals caused by the phase transition. Our result elucidates the insulating phase of this material as the 2kF charge density localization.
    Download PDF (153K)
  • Yuji Aoki, Shotaro Sanada, Daisuke Kikuchi, Hitoshi Sugawara, Hideyuki ...
    2007 Volume 76 Issue 11 Pages 113703
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    We measured specific heat in the anomalous ordered phase (T<16.5 K) of filled skutterudite SmRu4P12. From the hyperfine-enhanced Sm nuclear contribution, the ordered Sm dipole moment has been accurately determined to be 0.29±0.01 μB, which is strongly reduced for usual dipolar ordering. We demonstrate that this finding along with other physical quantities provide strong evidence that the primary order parameter is Γ4u-type octupole. The ordered state provides the first example of an octupolar ordering accompanied by nonzero parasitic dipole moments.
    Download PDF (443K)
  • Makoto Yoshida, Yumiko Kitano, Yuji Inagaki, Takahiro Sakurai, Motoi K ...
    2007 Volume 76 Issue 11 Pages 113704
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    High-field electron spin resonance (ESR) measurements of single crystals of (CH3)2NH2CuCl3 (DMACuCl3) have been performed in the frequency range of 50 to 550 GHz in the paramagnetic region. In addition to the electron paramagnetic resonance, we have observed four ESR modes ω1, ω2, ω3, and ω4. The modes ω2 and ω3 have a frequency gap of 325 GHz (15.6 K), while the mode ω1 has a gap of 420 GHz (20 K) at 0 T. The modes ω2 and ω3 are attributed to the transitions between the singlet and the triplet of the antiferromagnetic (AF) dimer. We found that the large spin-gap for the AF dimer still remains at the critical field Bc2 = 3.5 T determined by magnetization and specific heat measurements.
    Download PDF (236K)
  • Sogo Kuroiwa, Akiyoshi Nakashima, Shin Miyahara, Nobuo Furukawa, Jun A ...
    2007 Volume 76 Issue 11 Pages 113705
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    The full-potential linear augmented plane-wave calculations have been applied to investigate the systematic change of electronic structures in CaAlSi due to different stacking sequences of AlSi layers. The present ab-initio calculations have revealed that the multistacking, buckling and 60° rotation of AlSi layer affect the electronic band structure in this system. In particular, such a structural perturbation gives rise to the disconnected and cylindrical Fermi surface along the M–L lines of the hexagonal Brillouin zone. This means that multistacked CaAlSi with the buckling AlSi layers increases degree of two-dimensional electronic characters, and it gives us qualitative understanding for the quite different upper critical field anisotropy between specimens with and without superstructure as reported previously.
    Download PDF (556K)
  • Yoichi Tanabe, Tadashi Adachi, Keisuke Omori, Hidetaka Sato, Takashi N ...
    2007 Volume 76 Issue 11 Pages 113706
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    In order to investigate the inhomogeneity of the superconducting (SC) state in the overdoped high-Tc cuprates, we have measured the magnetic susceptibility, χ, of La2−xSrxCuO4 (LSCO) single crystals in the overdoped regime in magnetic fields parallel to the c-axis up to 7 T on warming after zero-field cooling. It has been found for x=0.198 and 0.219 that the temperature dependence of χ in 1 T shows a plateau, that is, χ is almost independent of temperature in a moderate temperature-range in the SC state. Moreover, a so-called second peak in the magnetization curve has markedly appeared in these crystals. These results indicate an anomalous enhancement of the vortex pinning and strongly suggest the occurrence of a microscopic phase separation into SC and normal-state regions in the overdoped high-Tc cuprates.
    Download PDF (820K)
  • Kazuaki Kobayashi, Shojiro Komatsu
    2007 Volume 76 Issue 11 Pages 113707
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    We calculated the electronic and lattice properties of 5H-BN and related phases. 5H-BN is an sp3 bonded compound as 2H-BN (wurtzite BN) and 3C-BN (cubic BN). This is a hexagonal layered structure which is determined uniquely. The lattice properties were optimized automatically by the first-principles molecular dynamics (FPMD) method. The calculated lattice properties agree well with experimental results. A calculated electronic band structure of 5H-BN is non-metallic and its band gap is indirect. Valence band maximum (VBM)–conduction band minimum (CBM) of 5H-BN is Γ–L.
    Download PDF (114K)
  • Takeshi Aimi, Masatoshi Imada
    2007 Volume 76 Issue 11 Pages 113708
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    We reexamine whether the essence of high-Tc superconductivity is contained in doped Hubbard models on the square lattice by using recently developed pre-projected Gaussian-basis Monte Carlo method. The superconducting correlations of the dx2y2 wave symmetry in the ground state at distance r decays essentially as r−3. The upper bound of the correlation at long distances estimated by this unbiased method is 10−3, indicating that recent extensions of dynamical mean-field theories and variational methods yielded at least an order of magnitude overestimates of it. The correlations are too weak for the realistic account of the cuprate high-Tc superconductivity.
    Download PDF (201K)
  • Hiromi Taniguchi, Takahiro Okuhata, Takuya Nagai, Kazuhiko Satoh, Nobu ...
    2007 Volume 76 Issue 11 Pages 113709
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    The PT phase diagram and transport properties of a layered organic superconductor, κ-(BEDT-TTF)4Hg2.89Br8, which can be viewed as a nealy half-filled band system, are reported. Through careful resistivity measurements under pressures of up to 4.5 GPa, we uncovered anomalous pressure dependence of Tc of this superconductor, including a peak structure at approximatly 0.7 GPa and a minimum structure at higher pressure. The normal-state resistivity showed T-linear behavior at low pressures and this behavior gradually transformed into T-squared behavior with increasing pressure. The pressure, Pc≈2 GPa, at which Tc has a turning value, corresponds to the onset of the T-squared behavior.
    Download PDF (507K)
  • Hideto Utsumi, Seiji Miyoshi, Masato Okada
    2007 Volume 76 Issue 11 Pages 114001
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    We analyze the generalization performance of a student in a model composed of nonlinear perceptrons: a true teacher, ensemble teachers, and the student. We calculate the generalization error of the student analytically or numerically using statistical mechanics in the framework of on-line learning. We treat two well-known learning rules: Hebbian learning and perceptron learning. As a result, it is proven that the nonlinear model shows qualitatively different behaviors from the linear model. Moreover, it is clarified that Hebbian learning and perceptron learning show qualitatively different behaviors from each other. In Hebbian learning, we can analytically obtain the solutions. In this case, the generalization error monotonically decreases. The steady value of the generalization error is independent of the learning rate. The larger the number of teachers is and the more variety the ensemble teachers have, the smaller the generalization error is. In perceptron learning, we have to numerically obtain the solutions. In this case, the dynamical behaviors of the generalization error are nonmonotonic. The smaller the learning rate is, the larger the number of teachers is; and the more variety the ensemble teachers have, the smaller the minimum value of the generalization error is.
    Download PDF (161K)
  • Norio Inui
    2007 Volume 76 Issue 11 Pages 114002
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    We regularize an infinite summation of the zero-point energy for the massless scalar field obeying the Dirichlet boundary condition on the surface of an equilateral triangular domain, and we calculate the Casimir energy for the relevant field configuration. To evaluate the infinite summation over two distinct nonzero integers, we generalize the Abel–Plana formula so that the finite summation in which the upper bound is a variable integer is expressed in terms of integrals. The obtained approximate value of the Casimir energy density in the equilateral triangular domain with side length L is 0.4681h⁄L3.
    Download PDF (174K)
  • Masayuki Ohzeki
    2007 Volume 76 Issue 11 Pages 114003
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    We predict the locations of several multicritical points of the Potts spin glass model on the triangular lattice. In particular, continuous multicritical lines, which consist of multicritical points, are obtained for two types of two-state Potts (i.e., Ising) spin glasses with two- and three-body interactions on the triangular lattice. These results provide us with numerous examples to further verify the validity of the conjecture, which has succeeded in deriving highly precise locations of multicritical points for several spin glass models. The technique, called the direct triangular duality, a variant of the ordinary duality transformation, directly relates the triangular lattice with its dual triangular lattice in conjunction with the replica method.
    Download PDF (151K)
  • Yoshiaki Rikitake, Hiroshi Imamura, Hideo Kosaka
    2007 Volume 76 Issue 11 Pages 114004
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    We analyzed the yield and fidelity of the quantum state transfer (QST) from a photon polarization qubit to an electron spin qubit in a spin-coherent photodetector consisting of a semiconductor quantum dot. We used a model consisting of the quantum dot, where the QST is carried out, coupled with a photonic cavity. We determined the optimal conditions that allow the realization of both high-yield and high-fidelity QST.
    Download PDF (242K)
  • Jeong-Bo Shim, Sang-Bum Lee, Juhee Yang, Songky Moon, Jai-Hyung Lee, K ...
    2007 Volume 76 Issue 11 Pages 114005
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    We have investigated quasi-eigenmodes of a quadrupolar deformed microcavity by extensive numerical calculations. The spectral structure is found to be quite regular, which can be explained on the basis of the fact that the microcavity is an open system. The far-field emission directions of different modes show unexpected similarity irrespective of their distinct shapes in phase space. This universal directionality is ascribed to the influence from the geometry of the unstable manifolds in the corresponding ray dynamics.
    Download PDF (1827K)
  • Tatsuya Uezu, Seiji Miyoshi, Mika Izuo, Masato Okada
    2007 Volume 76 Issue 11 Pages 114006
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    We analyze the time domain ensemble on-line learning of a Perceptron under the existence of external noise. We adopt three typical learning rules, Hebbian, Perceptron, and AdaTron rules. We treat the input and output noises. In order to improve the learning when it does not succeed in the sense that the student vector does not converge to the teacher vector, we use an averaging method and give theoretical analysis of the method. We obtain the precise formula for the overlap between the teacher vector and the time averaged student vector for t→∞ limit as a function of the number of student vectors to be averaged. We compare the theoretical results with numerical simulations and find that the theoretical results agree quite well with the numerical simulations.
    Download PDF (166K)
  • Robabeh Rahimi, Akira SaiToh, Mikio Nakahara
    2007 Volume 76 Issue 11 Pages 114007
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    A linear coupling model of a spin system with bosonic modes is a typical model to theoretically evaluate decoherence. In this contribution, we consider a dynamical control of decoherence of entanglement in a spin system consisting of an electron spin and nuclear spins (namely, a spin bus system) coupled with bosons whose modes are in resonance with individual spins. Numerical simulations show that bang-bang pulses with a realistic duty ratio can suppress decoherence considerably in an entangled two-qubit system. Simulation results indicate one phenomenon: a very large, as well as very small, dissipation rate of bosons results in a small decoherence.
    Download PDF (560K)
  • Nao Sato, Ko Okumura
    2007 Volume 76 Issue 11 Pages 114008
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    We investigated a model of a nematic–isotropic (NI) transition, whose mean-field approximation coincides with Maier–Saupe (MS) theory, by Fukuda’s inversion method (IM), which is based on the Legendre transformation and is similar to a method of symmetry-breaking potential. The first-order approximation of this nonperturbative method neglects fluctuations and reproduces the MS theory, predicting a weakly discontinuous phase transition at the MS transition temperature TMS. The second-order IM approximation allows us to include fluctuations, which suppress the phase transition.
    Download PDF (121K)
  • Hidehito Nakamura, Peter J. Doe, Hiroyasu Ejiri, Steven R. Elliott, Jo ...
    2007 Volume 76 Issue 11 Pages 114201
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    An ensemble of multilayer scintillators is discussed as an option of the high-sensitivity detector MOON (Mo Observatory of Neutrinos) for spectroscopic measurements of neutrinoless double beta decays. A prototype detector MOON-1, which consists of 6-layer plastic scintillator plates, was built to study the photon responses of the MOON-type detector. The photon responses, i.e., the number of scintillation photons collected and the energy resolution, which are key elements for high-sensitivity experiments, are found to be 1835±30 photoelectrons for 976 keV electrons and σ=2.9±0.1% (ΔEE=6.8±0.3% in FWHM) at the Qββ∼3 MeV region, respectively. The multilayer plastic scintillator structure with high energy resolution as well as a good signal for the background suppression of β–γ rays is crucial for the MOON-type detector to achieve inverted-hierarchy neutrino-mass sensitivity. It will also be useful for medical and other rare-decay experiments as well.
    Download PDF (262K)
  • Yasuo Wakabayashi, Tomonori Fukuchi, Yasuyuki Gono, Atsuko Odahara, Sh ...
    2007 Volume 76 Issue 11 Pages 114202
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    The high-spin states of 93Nb are studied by the 82Se(16O, p4n)93Nb reaction at a beam energy of 100 MeV. The in-beam γ-ray spectroscopic techniques are used. The γt-, γγt-coincidence, γ-ray angular distributions, and linear polarizations are measured. The configurations of the resultant levels are assigned by comparing them with those of the deformed independent particle model (DIPM) calculation. A high-spin isomer with a half life of 1.5(5) μs is found above the 37/2(−) state at 7436 keV. A possible M1 rotational band is found to start from the 37/2(−) state. This band shows the characteristics of an oblate collective rotational band.
    Download PDF (199K)
  • Young-Tak Chough
    2007 Volume 76 Issue 11 Pages 114301
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    We present an in-depth study on the behavior of an atomic wave packet which is placed in a standing wave cavity prepared in various states of light. We extract a simple classical oscillator model out of the dynamics of the quantum system. We quantitatively resolve the states of the spatially reorganized wave packet by the dressed state spatial probability distribution functions we developed. We also report a novel type of the “quantum collapse and revival” behavior of the Rabi nutation which is originated from the effect of the quantized atomic center-of-mass motion on the atomic internal motion.
    Download PDF (1376K)
  • Demet Demir, Yusuf Sahin
    2007 Volume 76 Issue 11 Pages 114302
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    The L shell x-ray intensity ratios Lα⁄Ll, Lα⁄Lβ, and Lα⁄Lγ for Ta, W, Au, Hg, Tl, Pb, Bi, Th, and U have been measured using the 59.54 keV incident photon energy in the external magnetic field of intensities ±0.15, ±0.45, and ±0.75 T. A comparison is made of the experimental values obtained for B=0 with calculated values using theoretical x-ray emission rates, subshell ionization cross sections, subshell fluorescence yields and Coster–Kronig transitions probabilities. In the absence of external magnetic field, a fairly agreement is observed between experimental and theoretical values.
    Download PDF (304K)
  • Ju Tae Seo, Seung Hoon Yoo, Sang June Hahn
    2007 Volume 76 Issue 11 Pages 114501
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    High-energy proton generation from the interaction of an ultraintense femtosecond laser pulse with an overdense plasma slab combined with an underdense preplasma has been studied by using two-dimensional, fully electromagnetic and relativistic particle-in-cell simulations. With a proper condition of the preplasma, it was observed that the forwardly directed proton acceleration from the rear side of the plasma slab was surely enhanced and the resulting proton beams had a better directionality compared to those in case of no preplasma. For the detailed analysis, the proton momentum distribution, and the angular distribution of the accelerated protons were investigated with the variation of target thickness, laser intensity, and preplasma scale length.
    Download PDF (174K)
  • Yosio Hiki, Tomohiko Aida, Shin Takeuchi
    2007 Volume 76 Issue 11 Pages 114601
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    The internal friction (IF) of binary, ternary, quaternary, and quinary metallic glasses with widely different glass-forming ability (GFA) has been studied. A single-roller melt-spinning apparatus was used for preparing ribbon specimens. An inverted torsion pendulum was used in the IF measurement. The measurements were performed from room temperature, through the glass transition temperature, up to the crystallization temperature. The background IF monotonously increases with increasing temperature. The increase is of the thermal-activation type, and the activation energy E is determined. For alloys with higher GFA, the E value tends to be higher. IF is inversely proportional to the measurement frequency. The viscosity relaxation based on the Maxwell model is considered, and the relaxation time τ is determined. A linear relationship is seen between the logarithm of pre-exponential factor τo and the activation energy E. Explanations of these results and discussions concerned are presented.
    Download PDF (125K)
  • Vo Van Hoang, Nguyen Ngoc Linh
    2007 Volume 76 Issue 11 Pages 114602
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    Finite size effects on static and dynamic properties of Al2O3·2SiO2 spherical models with different diameters of 2, 3, 4, and 5 nm have been studied via molecular dynamics (MD) simulation under non-periodic boundary conditions (NPBC). Models have been obtained by cooling from the melts at constant density of 2.60 g/cm3. We found strong finite size effects on both static and dynamic properties of the system. Static properties have been studied via partial radial distribution function (PRDF), mean atomic distances and coordination number distributions. Dynamic properties of the system with different sizes have been found and discussed via the mean-squared displacement (MSD) of atoms and temperature dependence of diffusion constant. Moreover, size dependence of glass transition temperature has been found and discussed.
    Download PDF (222K)
  • Xianglian, Hiroyuki Honda, Khairul Basar, Sainer Siagian, Takashi Sak ...
    2007 Volume 76 Issue 11 Pages 114603
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    The γ–β phase transition and crystal structure of the superionic conductor Ag3SBrxI1−x are investigated by the X-ray diffraction and thermal analysis methods. The room temperature β-phase of Ag3SBrxI1−x (0≤x≤1) belongs to the cubic system with the space group Pm3m. In the range 0≤x<0.29, the low-temperature γ-phase of Ag3SBrxI1−x shows an ordered arrangement of Ag atoms, which are located at one of the four positions obeying the symmetry of the rhombohedral space group R3. A new low-temperature γ-phase of Ag3SBrxI1−x is found in the range 0.29≤x≤0.83. This phase belongs to the orthorhombic system, and the space group is Pnm21 or Pnmm. Another new low-temperature γ-phase of Ag3SBrxI1−x, which belongs to the monoclinic or triclinic system, is also found in the range 0.83<x<1.
    Download PDF (217K)
  • Hao Ran Gong, Asok K. Ray
    2007 Volume 76 Issue 11 Pages 114701
    Published: November 15, 2007
    Released on J-STAGE: August 12, 2010
    JOURNAL RESTRICTED ACCESS
    Full-potential linearized augmented plane-wave calculations indicate that the antiferromagnetic states including spin–orbit coupling effect is the ground state of bulk α-Pu with the atomic volume of 128.9 a.u.3 and bulk modulus of 58.8 GPa, which are in good agreements with experimental values in the literature. Density of states shows that the majority of 5f electrons of bulk α-Pu are above the Fermi level, which is different from our previous result that the 5f electrons of bulk δ-Pu are mainly located below the Fermi level. It implies that 5f electrons of bulk α-Pu might be probably on the delocalized side of the localization-delocalization transition.
    Download PDF (142K)
feedback
Top