Results for "Hidefumi Ohsugi"

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Gorenstein cut polytopesFeb 12 2013Nov 01 2013An integral convex polytope ${\mathcal P}$ is said to be Gorenstein if its toric ring $K[{\mathcal P}]$ is normal and Gorenstein. In this paper, Gorenstein cut polytopes of graphs are characterized explicitly. First, we prove that Gorenstein cut polytopes ... More
Toric ideals and their circuitsOct 11 2012In this paper, we study toric ideals generated by circuits. For toric ideals which have squarefree quadratic initial ideals, a sufficient condition to be generated by circuits is given. In particular, squarefree Veronese subrings, the second Veronese ... More
Smooth Fano polytopes whose Ehrhart polynomial has a root with large real partSep 05 2011Nov 02 2011The symmetric edge polytopes of odd cycles (del Pezzo polytopes) are known as smooth Fano polytopes. In this paper, we show that if the length of the cycle is 127, then the Ehrhart polynomial has a root whose real part is greater than the dimension. As ... More
Simple polytopes arising from finite graphsApr 27 2008Let $G$ be a finite graph allowing loops, having no multiple edge and no isolated vertex. We associate $G$ with the edge polytope ${\cal P}_G$ and the toric ideal $I_G$. By classifying graphs whose edge polytope is simple, it is proved that the toric ... More
Reverse lexicographic squarefree initial ideals and Gorenstein Fano polytopesOct 17 2014Dec 30 2015Via the theory of reverse lexicographic squarefree initial ideals of toric ideals, we give a new class of Gorenstein Fano polytopes (reflexive polytopes) arising from a pair of stable set polytopes of perfect graphs.
Reflexive polytopes arising from bipartite graphs with $γ$-positivity associated to interior polynomialsOct 29 2018Apr 27 2019In this paper, we introduce polytopes ${\mathcal B}_G$ arising from root systems $B_n$ and finite graphs $G$, and study their combinatorial and algebraic properties. In particular, it is shown that ${\mathcal B}_G$ is a reflexive polytope with a regular ... More
Reverse lexicographic Gröbner bases and strongly Koszul toric ringsFeb 14 2014Jun 05 2014Restuccia and Rinaldo proved that a standard graded $K$-algebra $K[x_1, ... x_n]/I$ is strongly Koszul if the reduced Gr\"obner basis of $I$ with respect to any reverse lexicographic order is quadratic. In this paper, we give a sufficient condition for ... More
Non-very ample configurations arising from contingency tablesApr 23 2009Dec 08 2009In this paper, it is proved that, if a toric ideal possesses a fundamental binomial none of whose monomials is squarefree, then the corresponding semigroup ring is not very ample. Moreover, very ample semigroup rings of Lawrence type are discussed. As ... More
Roots of the Ehrhart polynomial of hypersimplicesApr 29 2013Aug 14 2013The Ehrhart polynomial of the $d$-th hypersimplex $\Delta(d,n)$ of order $n$ is studied. By computational experiments and a known result for $d=2$, we conjecture that the real part of every roots of the Ehrhart polynomial of $\Delta(d,n)$ is negative ... More
Toric ideals of finite graphs and adjacent 2-minorsAug 14 2011Oct 08 2012We study the problem when an ideal generated by adjacent 2-minors is the toric ideal of a finite graph.
Toric rings and ideals of nested configurationsJul 19 2009Feb 07 2010The toric ring together with the toric ideal arising from a nested configuration is studied, with particular attention given to the algebraic study of normality of the toric ring as well as the Gr\"obner bases of the toric ideal. One of the combinatorial ... More
Two way subtable sum problems and quadratic Groebner basesNov 19 2007Jun 12 2008Hara, Takemura and Yoshida discuss toric ideals arising from two way subtable sum problems and shows that these toric ideals are generated by quadratic binomials if and only if the subtables are either diagonal or triangular. In the present paper, we ... More
The $h^*$-polynomials of locally anti-blocking lattice polytopes and their $γ$-positivityJun 11 2019A lattice polytope $\mathcal{P} \subset \mathbb{R}^d$ is called a locally anti-blocking polytope if for any closed orthant $\mathbb{R}^d_{\varepsilon}$ in $\mathbb{R}^d$, $\mathcal{P} \cap \mathbb{R}^d_{\varepsilon}$ is unimodularly equivalent to an anti-blocking ... More
Integer decomposition property for Cayley sums of order and stable set polytopesJul 16 2018Apr 03 2019Lattice polytopes which possess the integer decomposition property (IDP for short) turn up in many fields of mathematics. It is known that if the Cayley sum of lattice polytopes possesses IDP, then so does their Minkowski sum. In this paper, the Cayley ... More
Strongly Koszul edge ringsOct 28 2013Jan 23 2014We classify the finite connected simple graphs whose edge rings are strongly Koszul. From the classification, it follows that if the edge ring is strongly Koszul, then its toric ideal possesses a quadratic Gr\"obner basis.
Ehrhart series of fractional stable set polytopes of finite graphsMar 31 2016Nov 29 2016The fractional stable set polytope ${\rm FRAC}(G)$ of a simple graph $G$ with $d$ vertices is a rational polytope that is the set of nonnegative vectors $(x_1,\ldots,x_d)$ satisfying $x_i+x_j\le 1$ for every edge $(i,j)$ of $G$. In this paper we show ... More
Toric rings and ideals of stable set polytopesMar 06 2016In this paper, we discuss the normality of the toric rings of stable set polytopes, and the set of generators and Gr\"obner bases of toric ideals of stable set polytopes by using the results on that of edge polytopes of finite nonsimple graphs. In particular, ... More
Markov chain Monte Carlo methods for the Box-Behnken designs and centrally symmetric configurationsFeb 09 2015We consider Markov chain Monte Carlo methods for calculating conditional p values of statistical models for count data arising in Box-Behnken designs. The statistical model we consider is a discrete version of the first-order model in the response surface ... More
Unmixed bipartite graphs and sublattices of the Boolean latticesJun 06 2008The correspondence between unmixed bipartite graphs and sublattices of the oolean lattice is discussed. By using this correspondence, we show the existence of squarefree quadratic initial ideals of toric ideals arising from minimal vertex covers of unmixed ... More
Ehrhart series of fractional stable set polytopes of finite graphsMar 31 2016The fractional stable set polytope ${\rm FRAC}(G)$ of a simple graph $G$ with $d$ vertices is a rational polytope that is the set of nonnegative vectors $(x_1,\ldots,x_d)$ satisfying $x_i+x_j\le 1$ for every edge $(i,j)$ of $G$. In this paper we show ... More
Powers of componentwise linear idealsApr 27 2009We give criteria for graded ideals to have the property that all their powers are componentwise linear. Typical examples to which our criteria can be applied include the vertex cover ideals of certain finite graphs.
Many toric ideals generated by quadratic binomials possess no quadratic Gröbner basesFeb 01 2013Jun 12 2013Let $G$ be a finite connected simple graph and $I_{G}$ the toric ideal of the edge ring $K[G]$ of $G$. In the present paper, we study finite graphs $G$ with the property that $I_{G}$ is generated by quadratic binomials and $I_{G}$ possesses no quadratic ... More
Normality of cut polytopes of graphs is a minor closed propertyJun 29 2009Oct 04 2009Sturmfels-Sullivant conjectured that the cut polytope of a graph is normal if and only if the graph has no K_5 minor. In the present paper, it is proved that the normality of cut polytopes of graphs is a minor closed property. By using this result, we ... More
Centrally symmetric configurations of order polytopesSep 15 2014Apr 04 2015It is shown that the toric ideal of the centrally symmetric configuration of the order polytope of a finite partially ordered set possesses a squarefree quadratic initial ideal. It then follows that the convex polytope arising from the centrally symmetric ... More
Groebner bases of nested configurationsJan 07 2008In this paper we introduce a new and large family of configurations whose toric ideals possess quadratic Groebner bases. As an application, a generalization of algebras of Segre-Veronese type will be studied.
A Gröbner basis characterization for chordal comparability graphsJan 31 2016Aug 04 2016In this paper, we study toric ideals associated with multichains of posets. It is shown that the comparability graph of a poset is chordal if and only if there exists a quadratic Gr\"obner basis of the toric ideal of the poset. Strong perfect elimination ... More
Special simplices and Gorenstein toric ringsMar 29 2005Christos Athanasiadis studies an effective technique to show that Gorenstein sequences coming from compressed polytopes are unimodal. In the present paper we will use such the technique to find a rich class of Gorenstein toric rings with unimodal $h$-vectors ... More
Centrally symmetric configurations of integer matricesMay 22 2011The concept of centrally symmetric configurations of integer matrices is introduced. We study the problem when the toric ring of a centrally symmetric configuration is normal as well as is Gorenstein. In addition, Gr\"obner bases of toric ideals of centrally ... More
Enriched order polytopes and Enriched Hibi ringsMar 03 2019Stanley introduced two classes of lattice polytopes associated to posets, which are called the order polytope ${\mathcal O}_P$ and the chain polytope ${\mathcal C}_P$ of a poset $P$. It is known that, given a poset $P$, the Ehrhart polynomials of ${\mathcal ... More
Enriched chain polytopesDec 05 2018Jun 17 2019Stanley introduced a lattice polytope $\mathcal{C}_P$ arising from a finite poset $P$, which is called the chain polytope of $P$. The geometric structure of $\mathcal{C}_P$ has good relations with the combinatorial structure of $P$. In particular, the ... More
Reflexive polytopes arising from bipartite graphs with $γ$-positivity associated to interior polynomialsOct 29 2018Nov 01 2018In this paper, we introduce polytopes ${\mathcal B}_G$ arising from root systems $B_n$ and finite graphs $G$, and study their combinatorial and algebraic properties. In particular, it is shown that ${\mathcal B}_G$ is a reflexive polytope with a regular ... More
Enriched chain polytopesDec 05 2018Stanley introduced a lattice polytope $\mathcal{C}_P$ arising from a finite poset $P$, which is called the chain polytope of $P$. The geometric structure of $\mathcal{C}_P$ has good relations with the combinatorial structure of $P$. In particular, the ... More
Roots of Ehrhart polynomials of Gorenstein Fano polytopesJan 23 2010Given arbitrary integers $k$ and $d$ with $0 \leq 2k \leq d$, we construct a Gorenstein Fano polytope $\Pc \subset \RR^d$ of dimension $d$ such that (i) its Ehrhart polynomial $i(\Pc, n)$ possesses $d$ distinct roots; (ii) $i(\Pc, n)$ possesses exactly ... More
Markov chain Monte Carlo methods for the regular two-level fractional factorial designs and cut idealsFeb 12 2013It is known that a Markov basis of the binary graph model of a graph $G$ corresponds to a set of binomial generators of cut ideals $I_{\widehat{G}}$ of the suspension $\widehat{G}$ of $G$. In this paper, we give another application of cut ideals to statistics. ... More
Integer decomposition property for Cayley sums of order and stable set polytopesJul 16 2018Lattice polytopes which possess the integer decomposition property (IDP for short) turn up in many fields of mathematics. It is known that if the Cayley sum of lattice polytopes possesses IDP, then so does their Minkowski sum. In this paper, the Cayley ... More
The face vector of a half-open hypersimplexSep 20 2013Sep 29 2014The half-open hypersimplex $\Delta'_{n,k}$ consists of those $x = (x_{1}, \ldots, x_{n}) \in[0,1]^n$ with $k-1<x_1+\cdots+x_n\le k$, where $0 < k \leq n$. The $f$-vector of a half-open hypersimplex and related generating functions are explicitly studied. ... More
The number of $4$-cycles and the cyclomatic number of a finite simple graphJan 18 2018Let $G$ be a finite connected simple graph with $d$ vertices and $e$ edges. The cyclomatic number $e-d+1$ of $G$ is the dimension of the cycle space of $G$. Let $c_4(G)$ denote the number of $4$-cycles of $G$ and $k_4(G)$ that of $K_4$, the complete graph ... More
Markov basis and Groebner basis of Segre-Veronese configuration for testing independence in group-wise selectionsApr 09 2007Feb 06 2008We consider testing independence in group-wise selections with some restrictions on combinations of choices. We present models for frequency data of selections for which it is easy to perform conditional tests by Markov chain Monte Carlo (MCMC) methods. ... More
Roots of Ehrhart polynomials arising from graphsMar 29 2010Dec 29 2010Several polytopes arise from finite graphs. For edge and symmetric edge polytopes, in particular, exhaustive computation of the Ehrhart polynomials not merely supports the conjecture of Beck {\it et al.}\ that all roots $\alpha$ of Ehrhart polynomials ... More
The number of edges of the edge polytope of a finite simple graphAug 16 2013Jan 07 2016Let $d \geq 3$ be an integer. It is known that the number of edges of the edge polytope of the complete graph with $d$ vertices is $d(d-1)(d-2)/2$. In this paper, we study the maximum possible number $\mu_d$ of edges of the edge polytope arising from ... More
Continuous area spectrum in regular black holeApr 07 2005May 23 2005We investigate highly damped quasinormal modes of regular black hole coupled to nonlinear electrodynamics. Using the WKB approximation combined with complex-integration technique, we show that the real part of the frequency disappears in the highly damped ... More
Ambiguity of black hole entropy in loop quantum gravityAug 19 2005Nov 17 2005We reexmine some proposals of black hole entropy in loop quantum gravity (LQG) and consider a new possible choice of the Immirzi parameter which has not been pointed out so far. We also discuss that a new idea is inevitable if we regard the relation between ... More
The universal area spectrum in single-horizon black holesMay 22 2004Jun 16 2004We investigate highly damped quasinormal mode of single-horizon black holes motivated by its relation to the loop quantum gravity. Using the WKB approximation, we show that the real part of the frequency approaches the value $T_{\rm H}\ln 3$ for dilatonic ... More
Theoretical study of metal-encapsulating Si cage clusters: Revealing the nature of their peculiar geometriesAug 12 2002We present a density-functional (DF) study of structures of Si cage clusters that encapsulate metal atoms. As a prototypical example, the case of WSi$_{n}$ clusters is shown. To obtain the low-energy clusters in efficient and unbiased ways, genetic-like ... More
Topology and Energetics of Metal-Encapsulating Si Fullerene-Like Cage ClustersJul 27 2001Aug 09 2001On the basis of a topological discussion as well as an {\it ab initio} calculation, we show that it is possible to construct a fullerene-like Si cage by doping of a transition metal atom. The cage is a simple 3-polytope which maximizes the number of its ... More
Determination of the Number of Graphene Layers: Discrete Distribution of the Secondary Electron Intensity Derived from Individual Graphene LayersAug 12 2010Sep 28 2010Using a scanning electron microscope, we observed a reproducible, discrete distribution of secondary electron intensity stemming from an atomically thick graphene film on a thick insulating substrate. The discrete distribution made it possible to uniquely ... More
Fourier imaging study of efficient near-field optical coupling in solid immersion fluorescence microscopyMay 02 2002We measured images and Fourier images of fluorescence for 0.11- and 0.22-$\mu$m-diameter dye-doped polystyrene micro-sphere beads on a solid immersion lens, and experimentally verified strongly-angle-dependent fluorescence intensities due to efficient ... More
Enhanced thermopower via spin-state modificationJul 02 2018We investigated the effect of pressure on the magnetic and thermoelectric properties of Sr$_{3.1}$Y$_{0.9}$Co$_{4}$O$_{10+\delta }$. The magnetization is reduced with the application of pressure, reflecting the spin-state modification of the Co$^{3+}$ ... More
Shear viscosity of classical fields in scalar theoryApr 04 2019We investigate the shear viscosity of classical scalar fields in the $\phi^4$ theory on a lattice by using the Green-Kubo formula. Equilibrium expectation value of the time correlation function of the energy-momentum tensor is evaluated as the ensemble ... More
Intersubband absorption linewidth in GaAs quantum wells due to scattering by interface roughness, phonons, alloy disorder, and impuritiesAug 09 2002We calculate the intersubband absorption linewidth in quantum wells (QWs) due to scattering by interface roughness, LO phonons, LA phonons, alloy disorder, and ionized impurities, and compare it with the transport energy broadening that corresponds to ... More
Shear viscosity of classical fields in scalar theoryApr 04 2019Apr 25 2019We investigate the shear viscosity of classical scalar fields in the $\phi^4$ theory on a lattice by using the Green-Kubo formula. Equilibrium expectation value of the time correlation function of the energy-momentum tensor is evaluated as the ensemble ... More
Quantum wells with atomically smooth interfacesMay 09 2002By a cleaved-edge overgrowth method with molecular beam epitaxy and a (110) growth-interrupt-anneal, we have fabricated a GaAs quantum well exactly 30 monolayers thick bounded by atomically smooth AlGaAs hetero-interfaces without atomic roughness. Micro-photoluminescence ... More
Dwarf Novae in the Shortest Orbital Period Regime: II. WZ Sge Stars as the Missing Population near the Period MinimumMar 04 2010Mar 09 2010WZ Sge-type dwarf novae are characterized by long recurrence times of outbursts (~10 yr) and short orbital periods (<~ 85 min). A significant part of WZ Sge stars may remain undiscovered because of low outburst activity. Recently, the observed orbital ... More
A Simple but Effective Method to Incorporate Multi-turn Context with BERT for Conversational Machine ComprehensionMay 30 2019Conversational machine comprehension (CMC) requires understanding the context of multi-turn dialogue. Using BERT, a pre-training language model, has been successful for single-turn machine comprehension, while modeling multiple turns of question answering ... More
Room-temperature excitonic absorption in quantum wiresMay 20 2005Jun 17 2005We measured absorption spectra of T-shaped quantum wires at room temperature using waveguide-transmission spectroscopy. Strong and narrow room-temperature one-dimensional-exciton absorption peak was observed, which shows peak modal absorption coefficient ... More
Multiple Rabi Splittings under Ultra-Strong Vibrational CouplingSep 06 2016From the high vibrational dipolar strength offered by molecular liquids, we demonstrate that a molecular vibration can be ultra-strongly coupled to multiple IR cavity modes, with Rabi splittings reaching $24\%$ of the vibration frequencies. As a proof ... More
Enhanced Logic Performance with Semiconducting Bilayer Graphene ChannelsDec 15 2010Realization of logic circuits in graphene with an energy gap (EG) remains one of the main challenges for graphene electronics. We found that large transport EGs (>100 meV) can be fulfilled in dual-gated bilayer graphene underneath a simple alumina passivation ... More
Evolution of excitons via biexcitons to an electron-hole plasma without level crossing between band edge and exciton in a quantum wireFeb 20 2004Mar 14 2005A recent single quantum wire is of sufficient quality to reveal new details of the photoluminescence (PL) evolution with increasing electron--hole (e--h) pair density. At a pair density of 3.6 $\times$ 10$^{3}$ cm$^{-1}$, the PL is characteristic of biexcitons ... More
Determination and Spectroscopy of Quantum Yields in Bio/Chemiluminescence via Novel Light-Collection-Efficiency Calibration: Reexamination of The Aqueous Luminol Chemiluminescence StandardOct 17 2006We have developed a luminescence-measurement system for liquid bio/chemiluminescence that can obtain quantitative luminescence spectra as the absolute total number of luminescence photons at each wavelength or photon energy and quantum yields. Calibration ... More
Intrinsic effects of substitution and intercalation on thermal transport in two-dimensional TiS$_2$ single crystalsApr 16 2015The promising thermoelectric material TiS$_2$ can be easily chemically doped and intercalated. We present here studies of single crystals that are intercalated with excess Ti or Co, or substituted with Ta. We demonstrate the intrinsic impact of these ... More
Strong photo-absorption by a single quantum wire in waveguide-transmission spectroscopyFeb 15 2005We measured the absorption spectrum of a single T-shaped, 14x6 nm lateral-sized quantum wire embedded in an optical waveguide using waveguide-transmission spectroscopy at 5 K. In spite of its small volume, the one-dimensional-exciton ground state shows ... More
One-dimensional continuum and exciton states in quantum wiresSep 10 2002High-quality T-shaped quantum wires are fabricated by cleaved-edge overgrowth with the molecular beam epitaxy on the interface improved by a growth-interrupt high-temperature anneal. Characterization by micro-photoluminescence (PL) and PL excitation (PLE) ... More
Observation of large many-body Coulomb interaction effects in a doped quantum wireApr 14 2002We demonstrate strong one dimensional (1-D) many-body interaction effects in photoluminescence (PL) in a GaAs single quantum wire of unprecedented optical quality, where 1-D electron plasma densities are controlled via electrical gating. We observed PL ... More
Lasing from a single quantum wireSep 18 2002A laser with an active volume consisting of only a single quantum wire in the 1-dimensional (1-D) ground state is demonstrated. The single wire is formed quantum-mechanically at the T-intersection of a 14 nm Al_{0.07}Ga_{0.93}As quantum well and a 6 nm ... More
Studies of Impurity-Doping Effects and NMR Measurement5s of La1111 and/or Nd 1111 Fe-Pnictide SuperconductorsJul 17 2009Nov 01 2009Measurements of the electrical resistivities, Hall coefficients, thermoelectric powers, electronic specific heat coefficients have been carried out for samples of LnFe1-yMyAsO1-xFx (Ln=La, Nd; M=Co, Mn; x=0.11) obtained by M atom dopings to the superconducting ... More
Imaging of emission patterns in a T-shaped quantum wire laserMar 18 2003Spatially and spectrally resolved microscopic images of spontaneous and stimulated emissions are imaged at the mirror facets of a GaAs T-shaped quantum wire laser with high uniformity. Laser emission from the one-dimensional ground state reveals a circular ... More
Intersubband electronic Raman scattering in narrow GaAs single quantum wells dominated by single-particle excitationsJun 08 2004We measured resonant Raman scattering by intersubband electronic excitations in GaAs/AlAs single quantum wells (QWs) with well widths ranging from 8.5 to 18 nm. In narrow (less than 10 nm) QWs with sufficiently high electron concentrations, only single-particle ... More
Polarization-dependent photoluminescence-excitation spectra of one-dimensional exciton and continuum states in T-shaped quantum wiresMar 17 2003Jul 09 2003We measured polarization-dependent photoluminescence-excitation spectra of highly uniform T-shaped quantum wires at 5 K. We attribute one peak to the 1D-exciton ground state and the continuous absorption band to 1D continuum states. These had similar ... More
Studying the High-Energy Gamma-Ray Sky with GlastJan 14 1999Building on the success of the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory, the Gamma-ray Large Area Space Telescope (GLAST) will make a major step in the study of such subjects as blazars, gamma-ray bursts, the ... More
Quantum-dot single-photon source on a CMOS silicon photonic chip integrated using transfer printingDec 31 2018Silicon photonics is a powerful platform for implementing large-scale photonic integrated circuits (PICs), because of its compatibility with mature complementary-metal-oxide-semiconductor (CMOS) technology. Exploiting silicon-based PICs for quantum photonic ... More
Gain in a quantum wire laser of high uniformityJun 08 2002A multi-quantum wire laser operating in the 1-D ground state has been achieved in a very high uniformity structure that shows free exciton emission with unprecedented narrow width and low lasing threshold. Under optical pumping the spontaneous emission ... More
"Visible" 5d orbital states in a pleochroic oxychlorideApr 12 2019Transition metal compounds sometimes exhibit beautiful colors. We report here on a new oxychloride Ca3ReO5Cl2 which shows unusually distinct pleochroism; that is, the material exhibits different colors depending on viewing directions. This ple-ochroism ... More
Photopolarimetric monitoring of 41 blazars in the optical and near-infrared bands with the Kanata telescopeDec 18 2009Blazars are a kind of active galactic nuclei (AGN) in which a relativistic jet is considered to be directed along the line of sight. They are characterized by strong and rapid variability of the flux and high polarization. We performed a monitoring of ... More
Photopolarimetric Monitoring of Blazars in the Optical and Near-Infrared Bands with the Kanata Telescope. I. Correlations between Flux, Color, and PolarizationMay 02 2011May 13 2011We report on the correlation between the flux, color and polarization variations on time scales of days--months in blazars, and discuss their universal aspects. We performed monitoring of 42 blazars in the optical and near-infrared bands from 2008 to ... More
Outburst of a WZ Sge-type dwarf nova, AL Com in 2007Jan 31 2008We report photometric observations of AL Com during its rare outburst in 2007. The light curve is reminiscent of its past superoutbursts in 1995 and 2001, except for the rebrightening phase after the main superoutburst. During the rebrightening phase ... More
Bayesian Approach to Find a Long-Term Trend in Erratic Polarization Variations Observed in BlazarsNov 16 2009We developed a method to separate a long-term trend from observed temporal variations of polarization in blazars using a Bayesian approach. The temporal variation of the polarization vector is apparently erratic in most blazars, while several objects ... More
Optical Behavior of GRB 061121 around its X-Ray Shallow Decay PhaseNov 11 2010Aims. We report on a detailed study of the optical afterglow of GRB 061121 with our original time-series photometric data. In conjunction with X-ray observations, we discuss the origin of its optical and X-ray afterglows. Methods. We observed the optical ... More
Tohoku-Hiroshima-Nagoya planetary spectra library: A method for characterizing planets in the visible to near infraredSep 15 2009There has not been a comprehensive framework for comparing spectral data from different planets.Such a framework is needed for the study of extrasolar planets and objects within the solar system. We have undertaken observations to compile a library of ... More
Detection of Polarimetric Variations Associated with the Shortest Time-Scale Variability in S5 0716$ + $714Dec 08 2008We present the result of near-infrared and optical observations of the BL Lac object S5 0716$ + $714 carried out by the KANATA telescope. S5 0716$ + $714 has both a long term high-amplitude variability and a short-term variability within a night. The ... More
Prominent Polarized Flares of the Blazars AO 0235+164 and PKS 1510-089Feb 09 2011We report on multi-band photometric and polarimetric observations of the blazars AO 0235+164 and PKS 1510-089. These two blazars were active in 2008 and 2009, respectively. In these active states, prominent short flares were observed in both objects, ... More
Spectropolarimetric Study on Circumstellar Structure of Microquasar LS I +61deg 303Oct 05 2006We present optical linear spectropolarimetry of the microquasar LS I +61$^{\circ}$ 303. The continuum emission is mildly polarized (up to 1.3 %) and shows almost no temporal change. We find a distinct change of polarization across the H$\alpha$ emission ... More
The Fate of a Five-Dimensional Rotating Black Hole via Hawking RadiationFeb 21 2005Aug 23 2005We study the evolution of a five-dimensional rotating black hole emitting scalar field radiation via the Hawking process for arbitrary initial values of the two rotation parameters $a$ and $b$. It is found that any such black hole whose initial rotation ... More
The intrinsic abundance ratio and X-factor of CO isotopologues in L1551 shielded from FUV photodissociationMay 11 2016L1551 is chosen because it is relatively isolated in the Taurus molecular cloud shielded from FUV photons, providing an ideal environment for studying the target properties. Our observations cover ~40'x40' with resolution ~30", which are the maps with ... More
Early Spectroscopy of the 2010 Outburst of U ScorpiiAug 17 2010We present early spectroscopy of the recurrent nova U~Sco during the outburst in 2010. We successfully obtained time-series spectra at $t_{\rm d}=$0.37--0.44~d, where $t_{\rm d}$ denotes the time from the discovery of the present outburst. This is the ... More
Extremely high polarization in 2010 outburst of blazar 3C 454.3Feb 25 2014The gamma-ray-detected blazar 3C 454.3 exhibits dramatic flux and polarization variations in the optical and near-infrared bands. In December 2010, the object emitted a very bright outburst. We monitored it for approximately four years (including the ... More
Infrared/optical - X-ray simultaneous observations of X-ray flares in GRB 071112C and GRB 080506Jun 04 2010Jun 08 2010We investigate the origin of short X-ray flares which are occasionally observed in early stages of afterglows of gamma-ray bursts (GRBs). We observed two events, GRB 071112C and GRB 080506, before the start of X-ray flares in the optical and near-infrared ... More
Multiband Photopolarimetric Monitoring of the Outburst of the Blazar 3C~454.3 in 2007Mar 10 2010We report on optical-near-infrared photopolarimetric observations of a blazar 3C 454.3 over 200 d. The object experienced an optical outburst in July 2007. This outburst was followed by a short state fainter than $V=15.2$ mag lasting $\sim 25$ d. The ... More
Minute-Scale Rapid Variability of Optical Polarization in Narrow-Line Seyfert 1 Galaxy: PMN J0948+0022Aug 21 2013We report on optical photopolarimetric results of the radio-loud narrow line Seyfert 1 (RL-NLSy1) galaxy PMN J0948+0022 on 2012 December to 2013 February triggered by flux enhancements in near infrared and gamma-ray bands. Thanks to one-shot polarimetry ... More
Multi-Wavelength Photometric and Polarimetric Observations of the Outburst of 3C 454.3 in Dec. 2009Dec 20 2011In December 2009, the bright blazar, 3C 454.3 exhibited a strong outburst in the optical, X-ray and gamma-ray regions. We performed photometric and polarimetric monitoring of this outburst in the optical and near-infrared bands with TRISPEC and HOWPol ... More
A Luminous and Fast-Expanding Type Ib Supernova SN 2012auJun 24 2013We present a set of photometric and spectroscopic observations of a bright Type Ib supernova SN 2012au from -6d until ~+150d after maximum. The shape of its early R-band light curve is similar to that of an average Type Ib/c supernova. The peak absolute ... More
Observation of Tunneling Current in Semiconducting Graphene p-n JunctionsNov 15 2011We demonstrate a tunneling and rectification behavior in bilayer graphene. A stepped dielectric top gate creates a spatially modulated electric field, which opens the band gap in the graphene and produces an insulating region at the p-n interface. A current-voltage ... More
A Study of the Long-term Spectral Variations of 3C 66A Observed with the Fermi and Kanata TelescopesJan 12 20133C 66A is an intermediate-frequency-peaked BL Lac object detected by the Large Area Telescope onboard the Fermi Gamma-ray Space Telescope. We present a study of the long-term variations of this blazar seen over 2 years at GeV energies with Fermi and in ... More
Systematic Study of Gamma-ray bright Blazars with Optical Polarization and Gamma-ray VariabilityOct 14 2016Blazars are highly variable active galactic nuclei which emit radiation at all wavelengths from radio to gamma-rays. Polarized radiation from blazars is one key piece of evidence for synchrotron radiation at low energies and it also varies dramatically. ... More
Dwarf Novae in the Shortest Orbital Period Regime: I. A New Short Period Dwarf Nova, OT J055717+683226Dec 22 2009We report the observation of a new dwarf nova, OT J055717+683226, during its first-ever recorded superoutburst in December 2006. Our observation shows that this object is an SU UMa-type dwarf nova having a very short superhump period of 76.67+/- 0.03 ... More
GRB 091208B: First Detection of the Optical Polarization in Early Forward Shock Emission of a Gamma-Ray Burst AfterglowMay 10 2012May 16 2012We report that the optical polarization in the afterglow of GRB 091208B is measured at t = 149 - 706 s after the burst trigger, and the polarization degree is P = 10.4% +/- 2.5%. The optical light curve at this time shows a power-law decay with index ... More
Science with UT's Dichroic-Mirror Camera (DMC), 15-band simultaneous imagerOct 31 2008We introduce the Dichroic-Mirror Camera (DMC), an instrument developed at the University of Tokyo which is capable of performing simultaneous imaging in fifteen bands. The main feature of the DMC is the dichroic mirrors, which split incoming light into ... More
Discovery of a WZ Sge-Type Dwarf Nova, SDSS J102146.44+234926.3: Unprecedented Infrared Activity during a Rebrightening PhaseNov 19 2007Several SU UMa-type dwarf novae, in particular, WZ Sge-type stars tend to exhibit rebrightenings after superoutbursts. The rebrightening phenomenon is problematic for the disk instability theory of dwarf novae since it requires a large amount of remnant ... More
Testing the External Shock Model of Gamma-Ray Bursts using the Late-Time Simultaneous Optical and X-ray AfterglowsJul 19 2007Sep 03 2007We study the ``normal'' decay phase of the X-ray afterglows of gamma-ray bursts (GRBs), which follows the shallow decay phase, using the events simultaneously observed in the R-band. The classical external shock model -- in which neither the delayed energy ... More
Anti-Correlation of the Near-Infrared and X-Ray Variations of the Microquasar GRS 1915+105 in Soft StateApr 06 2009We report detailed, long term near-infrared (NIR) light curves of GRS 1915+105 in 2007-2008, covering its long "soft state" for the first time. From our NIR monitoring and the X-ray data of the All Sky Monitor (ASM) onboard Rossi X-ray Timing Explorer ... More
Optical and Near-Infrared Photometry of Nova V2362 Cyg : Rebrightening Event and Dust FormationAug 03 2010We present optical and near-infrared (NIR) photometry of a classical nova, V2362 Cyg (= Nova Cygni 2006). V2362 Cyg experienced a peculiar rebrightening with a long duration from 100 to 240 d after the maximum of the nova. Our multicolor observation indicates ... More