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Bayesian optimization (BO) based on Gaussian process regression (GPR) is applied to different CFD (computational fluid dynamics) problems which can be of practical relevance. The problems are i) shape optimization in a lid-driven cavity to minimize or maximize the energy dissipation, ii) shape optimization of the wall of a channel flow in order to obtain a desired pressure-gradient distribution along the edge of the turbulent boundary layer formed on the other wall, and finally, iii) optimization of the controlling parameters of a spoiler-ice model to attain the aerodynamic characteristics of the airfoil with an actual surface ice. The diversity of the optimization problems, independence of the optimization approach from any adjoint information, the ease of employing different CFD solvers in the optimization loop, and more importantly, the relatively small number of the required flow simulations reveal the flexibility, efficiency, and versatility of the BO-GPR approach in CFD applications. It is shown that to ensure finding the global optimum of the design parameters of the size up to 8, less than 90 executions of the CFD solvers are needed. Furthermore, it is observed that the number of flow simulations does not significantly increase with the number of design parameters. The associated computational cost of these simulations can be affordable for many optimization cases with practical relevance.

In graphene superlattices, bulk topological currents can lead to long-range charge-neutral flow and non-local resistance near Dirac points. A ballistic version of these phenomena has never been explored. Here, we report transport properties of ballistic graphene superlattices. This allows us to study and exploit giant non-local resistances with a large valley Hall angle without a magnetic field. In the low-temperature regime, a crossover occurs toward a new state of matter, referred to as a quantum valley Hall state (qVHS), which is an analog of the quantum Hall state without a magnetic field. Furthermore, a non-local resistance plateau, implying rigidity of the qVHS, emerges as a function of magnetic field, and the collapse of this plateau is observed, which is considered as a manifestation of valley/pseudospin magnetism., Comment: 23 pages, 9 figures

We report an approach to confine the carriers in single-layer graphene, which leads to quantum devices with field-induced quantum confinement. We demonstrated that the Coulomb-blockade effect evolves under a uniform magnetic field perpendicular to the graphene device. Our experimental results show that field-induced quantum dots are realized in graphene, and a quantum confinement-deconfinement transition is switched by the magnetic field.

The Belle detector at the KEKB electron-positron collider has collected almost 1 billion Y(4S) events in its decade of operation. Super-KEKB, an upgrade of KEKB is under construction, to increase the luminosity by two orders of magnitude during a three-year shutdown, with an ultimate goal of 8E35 /cm^2 /s luminosity. To exploit the increased luminosity, an upgrade of the Belle detector has been proposed. A new international collaboration Belle-II, is being formed. The Technical Design Report presents physics motivation, basic methods of the accelerator upgrade, as well as key improvements of the detector., Comment: Edited by: Z. Dole\v{z}al and S. Uno

The critical current densities of polycrystalline bulk SmFeAsO$_{1-x}$F$_x$ prepared by the powder-in-tube (PIT) method and by a conventional solid-state reaction were investigated using the remnant magnetic moment method and Campbell's method. Two types of shielding current, corresponding to global and local critical current densities $J_{\rm c}$ were observed using both measurement methods. The global and local $J_{\rm c}$ were on the order of $10^7$ A/m$^2$ and $10^{10}$ A/m$^2$ at 5 K, respectively. The local $J_{\rm c}$ decreased slightly with increasing magnetic field. The global $J_{\rm c}$ was independent of the preparation method, while the local $J_{\rm c}$ was larger for samples prepared by PIT than for those prepared by solid-state reaction., Comment: 20 pages, 5 figures. to be published in Physica C

Crab cavities have been installed in the KEKB B--Factory rings to compensate the crossing angle at the collision point and thus increase luminosity. The beam operation with crab crossing has been done since February 2007. This is the first experience with such cavities in colliders or storage rings. The crab cavities have been working without serious issues. While higher specific luminosity than the geometrical gain has been achieved, further study is necessary and under way to reach the prediction of simulation., Comment: Submitted to Particle Accelerator Conference 2007, MOZAKI01, Albuquerque

Sheer amount of petabyte scale data foreseen in the LHC experiments require a careful consideration of the persistency design and the system design in the world-wide distributed computing. Event parallelism of the HENP data analysis enables us to take maximum advantage of the high performance cluster computing and networking when we keep the parallelism both in the data processing phase, in the data management phase, and in the data transfer phase. A modular architecture of FADS/ Goofy, a versatile detector simulation framework for Geant4, enables an easy choice of plug-in facilities for persistency technologies such as Objectivity/DB and ROOT I/O. The framework is designed to work naturally with the parallel file system of Grid Datafarm (Gfarm). FADS/Goofy is proven to generate 10^6 Geant4-simulated Atlas Mockup events using a 512 CPU PC cluster. The data in ROOT I/O files is replicated using Gfarm file system. The histogram information is collected from the distributed ROOT files. During the data replication it has been demonstrated to achieve more than 2.3 Gbps data transfer rate between the PC clusters over seven participating PC clusters in the United States and in Japan., Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics (CHEP03), La Jolla, Ca, USA, March 2003, 4 pages, PDF. PSN TUDT010

The roles of aliovalent Ca(II)-for-Y(III) substitution and high-pressure-oxygen annealing in the process of "superconducterizing" the Co-based layered copper oxide, CoSr2(Y1-xCax)Cu2O7+d (Co-1212), were investigated. The as-air-synthesized samples up to x = 0.4 were found essentially oxygen stoichiometric (-0.03 <= d <= 0.00). These samples, however, were not superconductive, suggesting that the holes created by the divalent-for-trivalent cation substitution are trapped on Co in the charge reservoir. Ultra-high-pressure heat treatment carried out at 5 GPa and 500C for 30 min in the presence of Ag2O2 as an excess oxygen source induced bulk superconductivity in these samples. The highest Tc was obtained for the high-oxygen-pressure treated x = 0.3 sample at ~40 K., Comment: 16 pages, 6 figures, submitted to Solid State Communications

Here results of a systematic study on oxygen stoichiometry are reported for the first three members of the novel CoSr2(Y,Ce)sCu2O5+2s or Co-12s2 homologous series, i.e. Co-1212, Co-1222 and Co-1232 phases with a SrO-CoO1-SrO-CuO2-(Y,Ce)-[O2-(Y,Ce)]s-1-CuO2 layered structure. The oxygen content was precisely determined by two independent chemical techniques: coulometric Cu+/Cu2+ titration and iodometric titration. Furthermore, oxygen stability/tunability was investigated by means of oxygenative and reductive an-nealings carried out in a thermobalance. It was revealed that all the three phases are rather stoichiometric in oxygen content and stable against both oxygenative and reductive an-nealings. The present results for the Co-12s2 homologous series suggest that not only the CoO1 charge reservoir but also the nominally oxygen-stoichiometric B-[O2-B]s-1 fluo-rite block, that is the characteristic structural element for the Co-12s2 (s > 1) phases and all other layered copper oxides of category-B [H. Yamauchi and M. Karppinen, Superlatt. Microstructr. 21A (1997) 128] is non-tunable in terms of the oxygen content., Comment: 10 pages text, 3 pages Figs. For ISS-2002(Yokohama)in Physica C

Effects of electron correlation on the Fermi surface is investigated for the two-dimensional Hubbard model by the quantum Monte Carlo method. At first, an infinitesimal doping from the half filling is focused on and the momentum dependent charge susceptibility $\kappa(k)=\frac {dn(k)}{d\mu}$ is calculated at a finite temperature. At the temperature $T \sim \frac {t^2} U$, it shows peak structure at $(\pm \pi/2,\pm \pi/2)$ on the Fermi surface (line). It is consistent with the mean-field prediction of the d-wave pairing state or the staggerd flux state. This momentum dependent structure disappears at the high temperature $T \approx U$. After summarizing the results of the half filling case, we also discuss the effects of the doping on the momentum dependent charge susceptibility. The anisotropic structure at half filling fades out with sufficient doping., Comment: 6 pages, 3 figures; proceedings of ISSP8

If the number of lattice sites is odd, a quantum particle hopping on a bipartite lattice with random hopping between the two sublattices only is guaranteed to have an eigenstate at zero energy. We show that the localization length of this eigenstate depends strongly on the boundaries of the lattice, and can take values anywhere between the mean free path and infinity. The same dependence on boundary conditions is seen in the conductance of such a lattice if it is connected to electron reservoirs via narrow leads. For any nonzero energy, the dependence on boundary conditions is removed for sufficiently large system sizes., Comment: 12 pages, 11 figures

We investigate anisotropic charge fluctuations in the two-dimensional Hubbard model at half filling. By the quantum Monte Carlo method, we calculate a momentum-resolved charge compressibility $\kappa (\bm{k}) = {d < n(\bm{k}) >}/{d \mu}$, which shows effects of an infinitesimal doping. At the temperature $T \sim {t^2}/{U}$, $\kappa (\bm{k})$ shows peak structure at the $(\pm \pi/2,\pm \pi/2)$ points along the $|k_x| + |k_y| = \pi$ line. A similar peak structure is reproduced in the mean-filed calculation for the d-wave pairing state or the staggered flux state., Comment: 5 pages, 3 figures, figures and presentation are modified

A single-parameter family of lattice-fermion model is constructed. It is a deformation of the Azbel-Hofstadter problem by a parameter $h={$B%((BDelta}/t$ (quantum parameter). A topological number is attached to each energy band. A duality between the classical limit ($h=+0$) and the quantum limit ($h=1$) is revealed in the energy spectrum and the topological number. The model has a close relation to the two-dimensional d-wave superconductivity with a magnetic field. Making use of the duality and a topological argument, we shed light on how the quasiparticles with a magnetic field behave especially in the quantum limit., Comment: 3 pages with 5 postscript figures, RevTeX

Transitions between the quantum Hall state and the Anderson insulator are studied in a two dimensional tight binding model with a uniform magnetic field and a random potential. By the string (anyon) gauge, the weak magnetic field regime is explored numerically. The regime is closely related to the continuum model. The change of the Hall conductance and the trajectoy of the delocalized states are investigated by the topological arguments and the Thouless number study., Comment: 10 pages RevTeX, 14 postscript figures

Based on the two-dimensional lattice fermion model, we discuss transitions between different pairing states. Each phase is labeled by an integer which is a topological invariant and characterized by vortices of the Bloch wavefunction. The transitions between phases with different integers obey a selection rule. Basic properties of the edge states are revealed. They reflect the topological character of the bulk. Transitions driven by randomness are also discussed numerically., Comment: 8 pages with 2 postscript figures, RevTeX

The Hall conductance $\sigma_{xy}$ of two-dimensional {\it lattice} electrons with random potential is investigated. The change of $\sigma_{xy}$ due to randomness is focused on. It is a quantum phase transition where the {\it sum rule} of $\sigma_{xy}$ plays an important role. By the {\it string} (anyon) gauge, numerical study becomes possible in sufficiently weak magnetic field regime which is essential to discuss the floating scenario in the continuum model. Topological objects in the Bloch wavefunctions, charged vortices, are obtained explicitly. The anomalous plateau transitions ($\Delta \sigma_{xy}= 2,3,... >1$) and the trajectory of delocalized states are discussed., Comment: 7 pages RevTeX, 4 postscript figures, to appear in Physical Review Letters

Effects of randomness on interacting fermionic systems in one dimension are investigated by quantum Monte-Carlo techniques. At first, interacting spinless fermions are studied whose ground state shows charge ordering. Quantum phase transition due to randomness is observed associated with the collapse of the charge ordering. We also treat random Hubbard model focusing on the Mott gap. Although the randomness closes the Mott gap and low-lying states are created, which is observed in the charge compressibility, no (quasi-) Fermi surface singularity is formed. It implies localized nature of the low-lying states., Comment: RevTeX with 3 postscript figures

Recently the existence of a random critical line in two dimensional Dirac fermions is confirmed. In this paper, we focus on its scaling properties, especially in the critical region. We treat Dirac fermions in two dimensions with two types of randomness, a random site (RS) model and a random hopping (RH) model. The RS model belongs to the usual orthogonal class and all states are localized. For the RH model, there is an additional symmetry expressed by ${\{}{\cal H},{\gamma}{\}}=0$. Therefore, although all non-zero energy states localize, the localization length diverges at the zero energy. In the weak localization region, the generalized Ohm's law in fractional dimensions, $d^{*}(<2)$, has been observed for the RH model., Comment: RevTeX with 4 postscript figures, To appear in Physical Review B

A full quantum-mechanical treatment of the Bogoliubov-de Gennes equation for a single vortex in a d-wave superconductor is presented. First, we find low-energy states extended in four diagonal directions, which have no counterpart in a vortex of s-wave superconductors. The four-fold symmetry is due to 'quantum effect', which is enhanced when $p_{F}\xi $ is small. Second, for $p_{F}\xi \sim 1$, a peak with a large energy gap $E_{0}\sim \Delta $ is found in the density of states, which is due to the formation of the lowest bound states., Comment: 7pages, Revtex

Using the Bogoliubov-de Gennes equation, we study quasi-particle spectra around a single vortex in a d-wave superconductor, where a magnetic field is parallel to the c-axis. In the temperature region where the Ginzburg-Landau theory is valid, we find that the local density of states preserves a circular symmetry when the symmetry of the superconducting order parameter is {\it pure} d-wave. It, however, exhibits a four-fold symmetry when the mixing of a s-wave component occurs. A peak with a {\it large energy gap} is found in the local density of states at the center of the vortex, which corresponds to the lowest bound state. Our results are consistent with a recent scanning tunneling microscopy experiment in an YBa$_{2}$Cu$_{3}$O$_{7-{\delta}}$ (YBCO) monocrystal. The breakdown of the Eilenberger theory in YBCO in particular and in the high-T$_{c}$ superconductors in generalis discussed., Comment: 9 pages, REV TeX file

Primary fields of the $q$-deformed Virasoro algebra are constructed. Commutation relations among the primary fields are studied. Adjoint actions of the deformed Virasoro current on the primary fields are represented by the shift operator $\Theta_{\xi} f(x)=f(\xi x)$. Four point functions of the primary fields enjoy the connection formula associated with the Boltzmann weights of the fusion Andrews-Baxter-Forrester model., Comment: 9 pages, LaTex file

A variant of the one-dimensional $t$-$J$ model with anisotropic spin interaction and broken parity is studied by the nested algebraic Bethe-ansatz method. The gapless charge excitations and the gapful spin excitations are obtained. It is shown that the singlet-superconducting correlation dominates in the low-density region by applying the finite-size scaling analysis in the conformal field theory., Comment: REVTeX

We present a family of exactly solvable models at arbitrary filling in any dimensions which exhibit novel superconductivity with interband pairing. By the use of the hidden $SU(2)$ algebra the Hamiltonians were diagonalized explicitly. The zero-temperature phase diagrams and the thermodynamic properties are discussed. Several new properties are revealed which are different from those of the BCS-type superconductor.

We study the correlations between eigenvalues of the large random matrices by a renormalization group approach. The results strongly support the universality of the correlations proposed by Br\'ezin and Zee. Then we apply the results to the ground state of the 1D particles with long range interactions in a confinement potential. We obtain the exact ground state. We also show the existence of a transition similar to a phase separation. Before and after the transition, we obtain the density-density correlation explicitly. The correlation shows nontrivial universal behavior., Comment: (second revision: authors added)