arXiv subjects

K. Sato

Publications and source records attributed to K. Sato.

At least 127 records · Page 7Linked to original sources

arXiv2010

Existence of a phase transition under finite magnetic field in the long-range RKKY Ising spin glass Dy$_{x}$Y$_{1-x}$Ru$_{2}$Si$_{2}$

A phase transition of a model compound of the long-range Ising spin glass (SG) Dy$_{x}$Y$_{1-x}$Ru$_{2}$Si$_{2}$, where spins interact via the RKKY interaction, has been investigated. The static and the dynamic scaling analyses reveal that the SG phase transition in the model magnet belongs to the mean-field universality class. Moreover, the characteristic relaxation time in finite magnetic fields exhibits a critical divergent behavior as well as in zero field, indicating a stability of the SG phase in finite fields. The presence of the SG phase transition in field in the model magnet strongly syggests that the replica symmetry is broken in the long-range Ising SG.

cond-mat.dis-nn↗

arXiv2010

A multipixel silicon APD with ultralow dark count rate at liquid nitrogen temperature

The dark count rate of a multipixel photon counter (MPPC) was reduced to less than 0.2 cps by cooling the counter to 78.5 K. Characteristics of the MPPC other than the dark count rate were also detemined at 78.5 K and 295 K. The photodetection efficiency and the timing jitter at 78.5 K were comparable to those at 295 K. The MPPC had a count rate of up to 50 MHz at 78.5 K and above 100 MHz at 295 K. Detailed measurements were performed for detemining the afterpulse probability.

quant-ph↗

arXiv2010

X-ray Temperature and Mass Measurements to the Virial Radius of Abell 1413 with Suzaku

We present X-ray observations of the northern outskirts of the relaxed galaxy cluster A1413 with Suzaku, whose XIS instrument has the low intrinsic background needed to make measurements of these low surface brightness regions. We excise 15 point sources superimposed on the image above a flux of $1\times 10^{-14}$ \fluxunit (2--10keV) using XMM-Newton and Suzaku images of the cluster. We quantify all known systematic errors as part of our analysis, and show our statistical errors encompasses them for the most part. Our results extend previous measurements with Chandra and XMM-Newton, and show a significant temperature drop to about 3keV at the virial radius, $r_{200}$. Our entropy profile in the outer region ($> 0.5 r_{200}$) joins smoothly onto that of XMM-Newton, and shows a flatter slope compared with simple models, similar to a few other clusters observed at the virial radius. The integrated mass of the cluster at the virial radius is approximately $7.5\times10^{14}M_{\odot}$ and varies by about 30% depending on the particular method used to measure it.

astro-ph.CO↗

arXiv2010

Open problems in microscopic theory of large-amplitude collective motion

Construction of the microscopic theory of large-amplitude collective motion, capable of describing a wide variety of quantum collective phenomena in nuclei, is a long-standing and fundamental subject in the study of nuclear many-body systems. Present status of the challenge toward this goal is discussed taking the shape coexistence/mixing phenomena as typical manifestations of the large-amplitude collective motion at zero temperature. Some open problems in rapidly rotating cold nuclei are also briefly discussed in this connection.

nucl-th↗

arXiv2009

Detecting individual gravity modes in the Sun: Chimera or reality?

Over the past 15 years, our knowledge of the interior of the Sun has tremendously progressed by the use of helioseismic measurements. However, to go further in our understanding of the solar core, we need to measure gravity (g) modes. Thanks to the high quality of the Doppler-velocity signal measured by GOLF/SoHO, it has been possible to unveil the signature of the asymptotic properties of the solar g modes, thus obtaining a hint of the rotation rate in the core. However, the quest for the detection of individual g modes is not yet over. In this work, we apply the latest theoretical developments to guide our research using GOLF velocity time series. In contrary to what was thought till now, we are maybe starting to identify individual low-frequency g modes...

astro-ph.SR↗

arXiv2009

Suzaku measurement of Abell 2204's intracluster gas temperature profile out to 1800 kpc

Context: Measurements of intracluster gas temperatures out to large radii are important for the use of clusters for precision cosmology and for studies of cluster physics. Previous attempts to measure robust temperatures at cluster virial radii failed. Aims: The goal of this work is to measure the temperature profile of the very relaxed galaxy cluster Abell 2204 out to large radii, possibly reaching the virial radius. Methods: Taking advantage of its low particle background due to its low-Earth orbit, Suzaku data are used to measure the outer temperature profile of Abell 2204. These data are combined with Chandra and XMM-Newton data of the same cluster in order to make the connection to the inner regions, unresolved by Suzaku, and to determine the smearing due to Suzaku's PSF. Results: The temperature profile of Abell 2204 is determined from 10 kpc to 1800 kpc, close to an estimate of r200 (the approximation to the virial radius). The temperature rises steeply from below 4 keV in the very center up to more than 8 keV in the intermediate range and then decreases again to about 4 keV at the largest radii. Varying the measured particle background normalization artificially by +-10 percent does not change the results significantly. Predictions for outer temperature profiles based on hydrodynamic simulations show good agreement. In particular, we find the observed temperature profile to be slightly steeper but consistent with a drop of a factor of 0.6 from 0.3 r200 to r200, as predicted by simulations. Conclusions: Temperature measurements up to the virial radius seem feasible with Suzaku, when a careful analysis of the different background components and the effects of the PSF is performed. The result obtained here indicates that numerical simulations capture the intracluster gas physics well in cluster outskirts.

astro-ph↗

arXiv2009

Spontaneous magnetization in QCD and non-Fermi-liquid effects

Magnetic properties of quark matter at finite temperature are discussed by evaluating the magnetic susceptibility. Combining the microscopic calculation of the self-energy for quarks as well as the screening effects for gluons with Fermi-liquid theory in a consistent way, we study the temperature dependence of the magnetic susceptibility. The longitudinal gluons have the static screening given by the Debye mass, and have a standard temperature dependence of $O(T^2)$. An anomalous $T^2\ln T$ term arises in the magnetic susceptibility as a novel non-Fermi-liquid effect due to the anomalous self-energy for quarks given by the dynamic screening for transverse gluons. We then extract the critical(Curie) temperature and present the magnetic phase diagram on the density-temperature plane.

hep-ph↗

arXiv2008

Non-Fermi-liquid effect in magnetic susceptibility

Taking into account the anomalous self-energy for quarks due to the dynamic screening effect for the transverse gluon propagator, we study the temperature dependence of the magnetic susceptibility in detail. It is shown that there does not exist the $T\ln T$ term in the susceptibility, different from the specific heat, but an anomalous $T^2\ln T$ term arises instead as a novel non-Fermi-liquid effect.

hep-ph↗

arXiv2008

Study of the internal mechanisms of Pixelized Photon Detectors operated in Geiger-mode

In the 1990s, a novel semiconductor photon-sensor operated in Geiger-mode was invented in Russia (Silicon PhotoMultiplier), which consists of many tiny pixels and has a single photon level sensitivity. Since then, various types of the sensor with this scheme, Pixelized Photon Detectors (PPD), have been developed in many places in the world. For instance, Hamamatsu Photonics K.K. in Japan produces the PPD as a Multi-Pixel Photon Counter. While the internal mechanisms of the PPD have been intensively studied in recent years, the existing models do not succeeded to fully reproduce the output characteristic, such as waveforms at low temperature. We have developed a new model with the transient multiplication and quenching of the realistic avalanche process and have succeeded in reproducing the output waveform of the PPD at various temperature. In this paper, we discuss our improved model.

physics.ins-det↗

arXiv2008

An Isotopic Fingerprint of Electron-Phonon Coupling in High-Tc Cuprates

Angle-resolved photoemission spectroscopy with low-energy tunable photons along the nodal direction of oxygen isotope substituted Bi2Sr2CaCu2O8+delta reveals a distinct oxygen isotope shift near the electron-boson coupling "kink" in the electronic dispersion. The magnitude (a few meV) and direction of the kink shift are as expected due to the measured isotopic shift of phonon frequency, which are also in agreement with theoretical expectations. This demonstrates the participation of the phonons as dominant players, as well as pinpointing the most relevant of the phonon branches.

cond-mat.supr-con↗

arXiv2008

Magnetic Susceptibility of Quark Matter

Magnetic properties of quark matter is discussed by evaluating the spin susceptibility within Fermi-liquid theory. We take into account the dynamical and static screening effects. At finite temperature, an anomalous T^2 ln T term for susceptibity is shown as a non-Fermi-liquid effect due to the dynamical screening of transverse gluons.

hep-ph↗

arXiv2008

Magnetic susceptibility of quark matter within Fermi-liquid theory

Possibility of spontaneous magnetization in QCD and magnetic properties of quark matter is discussed by evaluating the magnetic susceptibility within Fermi-liquid theory. The screening effects for gluons are taken into account to figure out the specific properties of the magnetic transition in gauge theories. It is shown that the static screening effect in terms of the Debye mass does not necessarily work against the magnetic instability; it promotes the instability, depending on the coupling constant and the number of flavors.

hep-ph↗

arXiv2007

Local density of states at zigzag edge of carbon nanotubes and graphene

The electron-phonon matrix element for edge states of carbon nanotubes and graphene at zigzag edges is calculated for obtaining renormalized energy dispersion of the edge states. Self-energy correction by electron-phonon interaction contributes to the energy dispersion of edge states whose energy bandwidth is similar to phonon energy. Since the energy-uncertainty of the edge state is larger than temperature, we conclude that the single-particle picture of the edge state in not appropriate when the electron-phonon interaction is taken into account. The longitudinal acoustic phonon mode contributes to the matrix element through the on-site deformation potential because the wavefunction of the edge state has an amplitude only on one of the two sublattices. The on-site deformation potentials for the longitudinal and in-plane tangential optical phonon modes are enhanced at the boundary. The results of local density of states are compared with the recent experimental data of scanning tunneling spectroscopy.

cond-mat.mes-hall↗

arXiv2006

Dispersal and dive patterns in gravid leatherback turtles during the nesting season in French Guiana

We present the first combined analysis of diving behaviour and dispersal patterns in gravid leatherback turtles during 3 consecutive nesting seasons in French Guiana. In total 23 turtles were fitted with Argos satellite transmitters and 16 individuals (including 6 concurrently satellite-tracked) were equipped with an electronic time-depth recorder for single inter-nesting intervals, i.e. between two consecutive ovi-positions. The leatherbacks dispersed over the continental shelf, ranging from the coastal zone to the shelf break and moved over 546.2 $\pm$ 154.1 km (mean $\pm$ SD) in waters of French Guiana and neighbouring Surinam. They mostly performed shallow (9.4 $\pm$ 9.2 m) and short (4.4 $\pm$ 3.4 min) dives with a slight diurnal pattern. They dived deeper as they moved away from the coast suggesting that they were predominantly following the seabed. Inter-nesting intervals could be divided into two phases: during the first 75% of the time turtles spent at sea, they dived on average 47 min h-1 before showing a lower and more variable diving effort as they came back to the shore. The extended movements of leatherbacks and the fine analysis of dive shapes suggest that in French Guiana leatherbacks may feed during the inter-nesting interval, probably to compensate for the energy costs associated with reproduction. This results in this endangered species being exposed to high risks of interactions with local fisheries throughout the continental shelf.

q-bio.PE↗

arXiv2006

Monte-Carlo Simulator and Ancillary Response Generator of Suzaku XRT/XIS System for Spatially Extended Source Analysis

We have developed a framework for the Monte-Carlo simulation of the X-Ray Telescopes (XRT) and the X-ray Imaging Spectrometers (XIS) onboard Suzaku, mainly for the scientific analysis of spatially and spectroscopically complex celestial sources. A photon-by-photon instrumental simulator is built on the ANL platform, which has been successfully used in ASCA data analysis. The simulator has a modular structure, in which the XRT simulation is based on a ray-tracing library, while the XIS simulation utilizes a spectral "Redistribution Matrix File" (RMF), generated separately by other tools. Instrumental characteristics and calibration results, e.g., XRT geometry, reflectivity, mutual alignments, thermal shield transmission, build-up of the contamination on the XIS optical blocking filters (OBF), are incorporated as completely as possible. Most of this information is available in the form of the FITS (Flexible Image Transport System) files in the standard calibration database (CALDB). This simulator can also be utilized to generate an "Ancillary Response File" (ARF), which describes the XRT response and the amount of OBF contamination. The ARF is dependent on the spatial distribution of the celestial target and the photon accumulation region on the detector, as well as observing conditions such as the observation date and satellite attitude. We describe principles of the simulator and the ARF generator, and demonstrate their performance in comparison with in-flight data.

astro-ph↗

arXiv2005

Heavy Element Production in Inhomogeneous Big Bang Nucleosynthesis

We present a new astrophysical site of the big bang nucleosynthesis (BBN) that are very peculiar compared with the standard BBN. Some models of the baryogenesis suggest that very high baryon density regions were formed in the early universe. On the other hand, recent observations suggest that heavy elements already exist in high red-shifts and the origin of these elements become a big puzzle. Motivated by these, we investigate BBN in very high baryon density regions. BBN proceeds in proton-rich environment, which is known to be like the p-process. However, by taking very heavy nuclei into account, we find that BBN proceeds through both the p-process and the r-process simultaneously. P-nuclei such as 92Mo, 94Mo, 96Ru, 98Ru whose origin is not well known are also synthesized.

astro-ph↗

arXiv2005

XMM-Newton Observation of IC 310 in the Outer Region of the Perseus Cluster of Galaxies

We present results from an XMM-Newton observation of the head-tail radio galaxy IC 310 located in the southwest region of the Perseus cluster. The spectrum is well-fitted by an absorbed power-law model with a photon index of $2.50 \pm 0.02$ with no significant absorption excess. The X-ray image shows a point-like emission at IC 310 without any signs of a structure correlated with the radio halo tail. The temperature of the intracluster medium surrounding IC 310 declines as a function of distance from the cluster center, from $ kT \sim 6$ keV in the northeast corner of the field of view to about 3 keV in the southwest region. Although we do not find any sharp edges in the surface brightness profile, a brightness excess over a smooth $β$ model by about 20% is seen. The temperature also rises by about 10% in the same region. This indicates that the IC 310 region is a subcluster probably infalling into the Perseus cluster, and the gas in front of IC 310 towards the Perseus cluster is likely to be compressed by the large-scale motion, which supports the view that the IC 310 system is undergoing a merger.

astro-ph↗

arXiv2005

Multi-epoch VERA Observations of H2O masers in OH 43.8-0.1

We report on the multi-epoch observations of H2O maser emission in star forming region OH 43.8-0.1 carried out with VLBI Exploration of Radio Astrometry (VERA). The large-scale maser distributions obtained by single-beam VLBI mapping reveal new maser spots scattered in area of 0.7 x 1.0 arcsec, in addition to a `shell-like' structure with a scale of 0.3 x 0.5 arcsec which was previously mapped by Downes et al.(1979). Proper motions are also obtained for 43 spots based on 5-epoch monitoring with a time span of 281 days. The distributions of proper motions show a systematic outflow in the north-south direction with an expansion velocity of ~8 km/s, and overall distributions of maser spots as well as proper motions are better represented by a bipolar flow plus a central maser cluster with a complex structure, rather than a shell with a uniform expansion such as those found in Cep A R5 and W75N VLA2. The distance to OH 43.8-0.1 is also estimated based on the statistical parallax, yielding D = 2.8 +/- 0.5 kpc. This distance is consistent with a near kinematic distance and rules out a far kinematics distance (~9 kpc), and the LSR velocity of OH 43.8-0.1 combined with the distance provides a constraint on the flatness of the galactic rotation curve, that there is no systematic difference in rotation speeds at the Sun and at the position of OH 43.8-0.1, which is located at the galacto-centric radius of ~6.3 kpc.

astro-ph↗