著者
Saigusa Tetsu Tero Atsushi Nakagaki Toshiyuki Kuramoto Yoshiki
出版者
American Physical Society
雑誌
Physical Review Letters (ISSN:00319007)
巻号頁・発行日
vol.100, no.1, pp.018101, 2008-01-11
被引用文献数
139 130

When plasmodia of the true slime mold Physarum were exposed to unfavorable conditions presented as three consecutive pulses at constant intervals, they reduced their locomotive speed in response to each episode. When the plasmodia were subsequently subjected to favorable conditions, they spontaneously reduced their locomotive speed at the time when the next unfavorable episode would have occurred. This implied the anticipation of impending environmental change. We explored the mechanisms underlying these types of behavior from a dynamical systems perspective.
著者
Hattori T. Ihara Y. Nakai Y. Ishida K. Tada Y. Fujimoto S. Kawakami N. Osaki E. Deguchi K. Sato N. Satoh I.
出版者
American Physical Society
雑誌
Physical Review Letters (ISSN:00319007)
巻号頁・発行日
vol.108, no.6, 2012-02
被引用文献数
71

磁石でありながら超伝導にもなる物質の超伝導発現の新しい仕組みを解明 -磁石が生み出す超伝導-. 京都大学プレスリリース. 2012-02-07.
著者
Ozawa Misaki Kuroiwa Takeshi Ikeda Atsushi Miyazaki Kunimasa
出版者
American Physical Society
雑誌
Physical review letters (ISSN:00319007)
巻号頁・発行日
vol.109, no.20, pp.205701, 2012-11
被引用文献数
28 6

Recent studies show that volume fractions φJ at the jamming transition of frictionless hard spheres and disks are not uniquely determined but exist over a continuous range. Motivated by this observation, we numerically investigate the dependence of φJ on the initial configurations of the parent fluid equilibrated at a volume fraction φeq, before compressing to generate a jammed packing. We find that φJ remains constant when φeq is small but sharply increases as φeq exceeds the dynamic transition point which the mode-coupling theory predicts. We carefully analyze configurational properties of both jammed packings and parent fluids and find that, while all jammed packings remain isostatic, the increase of φJ is accompanied with subtle but distinct changes of local orders, a static length scale, and an exponent of the finite-size scaling. These results are consistent with the scenario of the random first-order transition theory of the glass transition.
著者
Chiba Ayano Funamori Nobumasa Nakayama Kazuya Ohishi Yasuo Bennington Stephen Rastogi Sanjay Shukla Anuj Tsuji Kazuhiko Takenaka Mikihito
出版者
American Physical Society
雑誌
Physical Review E (ISSN:15393755)
巻号頁・発行日
vol.85, no.2, 2012-02
被引用文献数
10

溶融高分子の新しい構造変化を発見-加圧によるナノスケールの構造変化-. 京都大学プレスリリース. 2012-02-28.
著者
Sasaki Misao Suyama Teruaki Tanaka Takahiro Yokoyama Shuichiro
出版者
American Physical Society
雑誌
Physical Review Letters (ISSN:00319007)
巻号頁・発行日
vol.117, no.6, 2016-08-02
被引用文献数
123

初検出された重力波の起源は原始ブラックホール? : 宇宙の始まりに迫る新理論. 京都大学プレスリリース. 2016-08-09.
著者
Charbonneau P. Ikeda A. Meel J. A. van Miyazaki K.
出版者
American Physical Society
雑誌
Physical review E (ISSN:15393755)
巻号頁・発行日
vol.81, no.04, pp.040501, 2010-04
被引用文献数
24 13

There exists a variety of theories of the glass transition and many more numerical models. But because the models need built-in complexity to prevent crystallization, comparisons with theory can be difficult. We study the dynamics of a deeply supersaturated monodisperse four-dimensional (4D) hard-sphere fluid, which has no such complexity, but whose strong intrinsic geometrical frustration inhibits crystallization, even when deeply supersaturated. As an application, we compare its behavior to the mode-coupling theory (MCT) of glass formation. We find MCT to describe this system better than any other structural glass formers in lower dimensions. The reduction in dynamical heterogeneity in 4D suggested by a milder violation of the Stokes-Einstein relation could explain the agreement. These results are consistent with a mean-field scenario of the glass transition.
著者
Nakayama K. Sato T. Dobashi T. Terashima K. Souma S. Matsui H. Takahashi T. Campuzano J. C. Kudo K. Sasaki T. Kobayashi N. Kondo T. Takeuchi T. Kadowaki K. Kofu M. Hirota K.
出版者
American Physical Society
雑誌
Physical review B (ISSN:10980121)
巻号頁・発行日
vol.74, pp.054505, 2006-08
被引用文献数
18

We have performed systematic angle-resolved photoemission spectroscopy (ARPES) on single-layered cuprate superconductor Bi2Sr2CuO6+delta to elucidate the origin of shadow band. We found that the shadow band is exactly the c(2×2) replica of the main band irrespective of the carrier concentration and its intensity is invariable with respect to temperature, doping, and substitution constituents of block layers. This result rules out the possibility of antiferromagnetic correlation and supports the structural origin of shadow band. ARPES experiments on optimally doped La1.85Sr0.15CuO4 also clarified the existence of the c(2×2) shadow band, demonstrating that the shadow band is not a unique feature of Bi-based cuprates. We conclude that the shadow band is related to the orthorhombic distortion at the crystal surface.
著者
Aoki S. Fukugita M. Hashimoto S. Ishikawa K.-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneda T. Kaya S. Kuramashi Y. Okawa M. Onogi T. Tominaga S. Tsutsui N. Ukawa A. Yamada N. Yoshié T.
出版者
American Physical Society
雑誌
Physical review D (ISSN:05562821)
巻号頁・発行日
vol.62, no.9, pp.094501, 2000-10
被引用文献数
12 18

We present a study for the pion decay constant fπ in the quenched approximation to lattice QCD with the Kogut-Susskind (KS) quark action, with the emphasis given to the renormalization problems. Numerical simulations are carried out at the couplings β=6.0 and 6.2 on 323×64 and 483×64 lattices, respectively. The pion decay constant is evaluated for all KS flavors via gauge invariant and noninvariant axial vector currents with the renormalization constants calculated by both the nonperturbative method and perturbation theory. We obtain fπ=89(6) MeV in the continuum limit as the best value using the partially conserved axial vector current, which requires no renormalization. From a study for the other KS flavors we find that the results obtained with the nonperturbative renormalization constants are well convergent among the KS flavors in the continuum limit, confirming restoration of SU(4)A, flavor symmetry, while perturbative renormalization still leaves an apparent flavor breaking effect even in the continuum limit.
著者
Kiyono Ken Konno Hidetoshi
出版者
American Physical Society
雑誌
Physical review E (ISSN:15393755)
巻号頁・発行日
vol.87, no.5, pp.052104, 2013-05
被引用文献数
5 3

As a possible generalization of Beck-Cohen superstatistical processes, we study non-Gaussian processes with temporal heterogeneity of local variance. To characterize the variance heterogeneity, we define log-amplitude cumulants and log-amplitude autocovariance and derive closed-form expressions of the log-amplitude cumulants for χ2, inverse χ2, and log-normal superstatistical distributions. Furthermore, we show that χ2 and inverse χ2 superstatistics with degree 2 are closely related to an extreme value distribution, called the Gumbel distribution. In these cases, the corresponding superstatistical distributions result in the q-Gaussian distribution with q=5/3 and the bilateral exponential distribution, respectively. Thus, our finding provides a hypothesis that the asymptotic appearance of these two special distributions may be explained by a link with the asymptotic limit distributions involving extreme values. In addition, as an application of our approach, we demonstrated that non-Gaussian fluctuations observed in a stock index futures market can be well approximated by the χ2 superstatistical distribution with degree 2.
著者
Sasa Shin-Ichi Yokokura Yuki
出版者
American Physical Society
雑誌
Physical review letters (ISSN:10797114)
巻号頁・発行日
vol.116, no.14, 2016-04-08
被引用文献数
5

乱雑さを決める時間の対称性を発見-100年前の物理と数学の融合が築くミクロとマクロの架け橋-. 京都大学プレスリリース. 2016-05-24.
著者
Tsujimoto M. Kambara H. Maeda Y. Yoshioka Y. Nakagawa Y. Kakeya I.
出版者
American Physical Society
雑誌
Physical Review Applied (ISSN:23317019)
巻号頁・発行日
vol.2, no.4, 2014-10-29
被引用文献数
28

高温超伝導体を用いた新しいテラヘルツ光源における温度分布の可視化と制御に成功 -小型コヒーレントテラヘルツ光源の実現につながる重要な手がかり-. 京都大学プレスリリース. 2014-10-22.
著者
Tsutsui N. Aoki S. Fukugita M. Hashimoto S. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneko T. Kuramashi Y. Okawa M. Onogi T. Taniguchi Y. Ukawa A. Yoshié T.
出版者
American Physical Society
雑誌
Physical review D (ISSN:15507998)
巻号頁・発行日
vol.70, no.11, pp.111501, 2004-12
被引用文献数
13 15

We present a quenched lattice QCD calculation of the alpha and beta parameters of the proton decay matrix element. The simulation is carried out using the Wilson quark action at three values of the lattice spacing in the range a[approximate]0.1-0.064 fm to study the scaling violation effect. We find only mild scaling violation when the lattice scale is determined by the nucleon mass. We obtain in the continuum limit,
著者
Aoki S. Fukugita M. Hashimoto S. Ishikawa K-I. Ishizuka N. Iwasaki Y. Kanaya K. Kaneda T. Kaya S. Kuramashi Y. Okawa M. Onogi T. Tominaga S. Tsutsui N. Ukawa A. Yamada N. Yoshié T.
出版者
American Physical Society
雑誌
Physical review D (ISSN:05562821)
巻号頁・発行日
vol.62, no.1, pp.014506, 2000-06
被引用文献数
57 95

We present a model-independent calculation of hadron matrix elements for all dimension-6 operators associated with baryon number violating processes using lattice QCD. The calculation is performed with the Wilson quark action in the quenched approximation at β=6/g2=6.0 on a 282×48×80 lattice. Our results cover all the matrix elements required to estimate the partial lifetimes of (proton,neutron)→(π,K,η)+(ν̅ ,e+,μ+) decay modes. We point out the necessity of disentangling two form factors that contribute to the matrix element; previous calculations did not make the separation, which led to an underestimate of the physical matrix elements. With a correct separation, we find that the matrix elements have values 3–5 times larger than the smallest estimates employed in phenomenological analyses of the nucleon decays, which could give strong constraints on several GUT models. We also find that the values of the matrix elements are comparable with the tree-level predictions of the chiral Lagrangian.
著者
Shintani E. Aoki S. Ishizuka N. Kanaya K. Kikukawa Y. Kuramashi Y. Okawa M. Taniguchi Y. Ukawa A. Yoshié T.
出版者
American Physical Society
雑誌
Physical review D (ISSN:15507998)
巻号頁・発行日
vol.72, no.1, pp.014504, 2005-07
被引用文献数
39 51

We carry out a feasibility study for the lattice QCD calculation of the neutron electric dipole moment (NEDM) in the presence of the theta term. We develop the strategy to obtain the nucleon EDM from the CP- odd electromagnetic form factor F-3 at small theta, in which NEDM is given by lim(q2 -> 0 theta)F(3)(q(2))/(2m(N)), where q is the momentum transfer and m(N) is the nucleon mass. We first derive a formula which relates F-3, a matrix element of the electromagnetic current between nucleon states, with vacuum expectation values of nucleons and/ or the current. In the expansion of theta, the parity-odd part of the nucleon- current- nucleon three-point function contains contributions not only from the parity-odd form factors but also from the parity-even form factors multiplied by the parity-odd part of the nucleon two- point function, and, therefore, the latter contribution must be subtracted to extract F-3. We then perform an explicit lattice calculation employing the domain- wall quark action with the renormalization group improved gauge action in quenched QCD at a(-1) similar or equal to 2 GeV on a 16(3) x 32 x 16 lattice. At the quark mass m(f)a = 0: 03, corresponding to m(pi)/m(rho) similar or equal to 0:63, we accumulate 730 configurations, which allow us to extract the parityodd part in both two- and three- point functions. Employing two different Dirac gamma matrix projections, we show that a consistent value for F-3 cannot be obtained without the subtraction described above. We obtain F-3(q(2) similar or equal to 0:58 GeV2)/(2m(N))= -0:024(5) e . fm for the neutron and F-3(q(2) similar or equal to 0: 58 GeV2)/(2mN) = 0:021(6)e . fm for the proton.
著者
Shinohara Satoshi Ohta Hirofumi Nakatsukasa Takashi Yabana Kazuhiro
出版者
American Physical Society
雑誌
Physical review C (ISSN:05562813)
巻号頁・発行日
vol.74, pp.054315, 2006-11
被引用文献数
7 8

We propose a new theoretical approach to ground and low-energy excited states of nuclei extending the nuclear mean-field theory. It consists of three steps: stochastic preparation of many Slater determinants, the parity and angular-momentum projection, and diagonalization of the generalized eigenvalue problems. The Slater determinants are constructed in the three-dimensional Cartesian coordinate representation capable of describing arbitrary shape of nuclei. We examine feasibility and usefulness of the method by applying the method with the Bonche-Koonin-Negele interaction to light 4N nuclei, 12C, 16O, and 20Ne. We discuss difficulties of keeping linear independence for basis states projected on good parity and angular momentum and present a possible prescription.
著者
Okada Susumu Miyamoto Yoshiyuki Saito Mineo
出版者
American Physical Society
雑誌
Physical review B (ISSN:10980121)
巻号頁・発行日
vol.64, no.24, pp.245405, 2001-11
被引用文献数
34 46

We report on a first-principles total-energy calculation that provides the energetics and electronic structure of stable polymerized fullerites consisting of the smallest fullerene C20. We find that the C20 fullerene has periodic three-dimensional covalent networks with orthorhombic and tetragonal symmetries. Both are found to be energetically stable and to be elemental semiconductors with a moderate energy gap of about 1.5 eV. Substantially high peaks of the density of states are found to appear below the top of the valence band, suggesting that these materials under hole-doped conditions are candidates for superconductors.
著者
Okada Susumu Saito Susumu Oshiyama Atsushi
出版者
American Physical Society
雑誌
Physical review B (ISSN:10980121)
巻号頁・発行日
vol.64, no.20, pp.201303, 2001-10
被引用文献数
28 39

We report first-principles total-energy electronic-structure calculations that provide energetics of encapsulation of C60 in nanotubes consisting of boron and nitrogen atoms and electronic structures of resulting “BNC peapods.” We find that the encapsulating process is exothermic for (10,10) and (9,9) nanotubes. The energy gain upon the encapsulation is larger than that for carbon peapods, so that the BN nanotube is a promising candidate to accommodate the fullerenes inside. The material is predicted to be a new form of ternary semiconductor with interesting structural hierarchy.
著者
Ishida Masahiko Takeuchi Osamu Mori Takehiko Shigekawa Hidemi
出版者
American Physical Society
雑誌
Physical review B (ISSN:01631829)
巻号頁・発行日
vol.64, no.15, pp.153405, 2001-09
被引用文献数
7 10

In addition to the intermolecular symmetry breaking which is generally observed during the surface relaxation/reconstruction of atomic crystals, intramolecular relaxation is expected to exist in the case of molecular crystals, which was confirmed on the surface of β-(BEDT-TTF)2PF6 [BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene] by using scanning tunneling microscopy (STM). Two types of molecular images obtained by STM were comprehensively explained by the spatial distributions of the highest-occupied molecular orbital calculated for the two types of the molecular structures. One is the structure appearing in the crystal that is derived from the x-ray diffraction measurement, which was used in the previous calculations to reproduce the STM images. The other is the relaxed molecular structure calculated by optimization of the molecular structure.
著者
Umeda T. Isoya J. Morishita N. Ohshima T. Kamiya T. Gali A. Deák P. Son N. T. Janzén E.
出版者
American Physical Society
雑誌
Physical review B (ISSN:10980121)
巻号頁・発行日
vol.70, pp.235212, 2004-12
被引用文献数
32

The carbon vacancy is a dominant defect in 4H-SiC, and the "EI5" electron-paramagnetic-resonance (EPR) spectrum originates from positively charged carbon vacancies (VC+) at quasicubic sites. The observed state for EI5, however, has been attributed to a motional-averaged state with the C3v symmetry, and its true atomic structure has not been revealed so far. We here report low temperature (<40 K) EPR measurements on EI5 and show that this center has a C1h-symmetric structure due to Jahn-Teller distortion. We also performed ab inito calculations of the hyperfine tensors for EI5, and obtained a good agreement between experiment and theory in not only their principal values but also their principal axis directions. A good agreement was also demonstrated for the EI6 center (hexagonal-site VC+) in this paper. The transition from EI5(C1h) to EI5(C3v) was found to be thermally activated and its activation energy was measured as 0.014 eV.
著者
Okada Susumu Saito Susumu Oshiyama Atsushi
出版者
American Physical Society
雑誌
Physical review B (ISSN:10980121)
巻号頁・発行日
vol.65, no.16, pp.165410, 2002-04
被引用文献数
61 83

We report first-principles total-energy electronic-structure calculations that provide energetics and electronic structures of double-walled BN nanotubes, (n,0)@(15,0) and (m,0)@(20,0). We find that the most favorable double-walled nanotubes studied here are (7,0)@(15,0) and (12,0)@(20,0) in which the interwall distances are about 3 Å. The electronic energy bands around the Fermi energy depend interestingly on the tube radii due to the hybridization between σ and π states. We also find that the nearly-free-electron states of the nanotubes induce peculiar charge redistribution in the interwall region.