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T. Matsumoto

Publications and source records attributed to T. Matsumoto.

At least 91 records · Page 5Linked to original sources
arXiv2003

Determination of $S_{17}$ from systematic analyses on $^8$B Coulomb breakup with the Eikonal-CDCC method

A new version of the method of Continuum-Discretized Coupled-Channels method (CDCC) is proposed, that is, the Eikonal-CDCC method (E-CDCC). The E-CDCC equation, for Coulomb dissociation in particular, can easily and safely be solved, since it is a first-order differential equation and contains no huge angular momentum in contrast to the CDCC one. The scattering amplitude calculated by E-CDCC has a similar form to that by CDCC. Then one can construct hybrid amplitude in an intuitive way, i.e., CDCC amplitude is adopted for a smaller angular momentum $L$ and E-CDCC one for a larger $L$ related to an impact parameter $b$. The hybrid calculation is found to perfectly reproduce the quantum mechanical result for $^{58}$Ni($^8$B,$^7$Be$+p$)$^{58}$Ni at 240 MeV, which shows its applicability to systematic analysis of $^8$B dissociation to extract the astrophysical factor $S_{17}$ with high accuracy.

nucl-th↗
arXiv2003

Singularities of Euler flow? Not out of the blue!

Does three-dimensional incompressible Euler flow with smooth initial conditions develop a singularity with infinite vorticity after a finite time? This blowup problem is still open. After briefly reviewing what is known and pointing out some of the difficulties, we propose to tackle this issue for the class of flows having analytic initial data for which hypothetical real singularities are preceded by singularities at complex locations. We present some results concerning the nature of complex space singularities in two dimensions and propose a new strategy for the numerical investigation of blowup.(A version of the paper with higher-quality figures is available at http://www.obs-nice.fr/etc7/complex.pdf)

nlin.CD↗
arXiv2003

A deep 6.7um survey in the SSA13 field with ISO

We present results of a deep mid-infrared survey in the SSA13 field with the Infrared Space Observatory (ISO). In order to probe the near-infrared light at high redshifts, we surveyed the field with the broad band LW2 (5-8.5um) filter of the mid-infrared camera ISOCAM. Adopting a highly redundant imaging strategy for the 23 hour observation and carefully treating gradual changes in the detector responsivity caused by a very high rate of cosmic ray impacts, we succeeded in reaching an 80% completeness limit of 16uJy in the central 7 arcmin2 region. Utilizing the signal-to-noise ratio map, we detected 65 sources down to 6uJy in the 16 arcmin2 field. Integral galaxy number counts at 6.7um are then derived, reaching 1.3e4/deg2 at the faint limit with a slope of -1.6 between 13uJy and 130uJy. Integrating individual sources in this flux range, the resolved fraction of the extragalactic background light at 6.7um is estimated to be 0.56nW/m2/sr. These results, which reach a flux limit three times fainter than those in the Hubble Deep Fields, are in fairly good agreement with a model prediction by Franceschini et al. (1997). Finally, we discuss the relation of distant massive E/S0 galaxies to the faint 6.7um galaxy population.

astro-ph↗
arXiv2003

New treatment of breakup continuum in the method of continuum discretized coupled channels

A new method of pseudo-state discretization is proposed for the method of continuum discretized coupled channels (CDCC) to deal with three-body breakup processes. We propose real- and complex-range Gaussian bases for the pseudo-state wave functions, and show that they form in good approximation a complete set in the configuration space which is important for breakup processes. Continuous S-matrix elements are derived with the approximate completeness from discrete ones calculated by CDCC. Accuracy of the method is tested quantitatively for two realistic examples, d+$^{58}$Ni scattering at 80 MeV and $^{6}$Li+$^{40}$Ca scattering at 156 MeV with the satisfactory results. Possibility of application of the method to four-body breakup processes is also discussed.

nucl-th↗
arXiv2003

Spin Susceptibility and Superexchange Interaction in the Antiferromagnet CuO

Evidence for the quasi one-dimensional (1D) antiferromagnetism of CuO is presented in a framework of Heisenberg model. We have obtained an experimental absolute value of the paramagnetic spin susceptibility of CuO by subtracting the orbital susceptibility separately from the total susceptibility through the $^{63}$Cu NMR shift measurement, and compared directly with the theoretical predictions. The result is best described by a 1D $S=1/2$ antiferromagnetic Heisenberg (AFH) model, supporting the speculation invoked by earlier authors. We also present a semi-quantitative reason why CuO, seemingly of 3D structure, is unexpectedly a quasi 1D antiferromagnet.

cond-mat.str-el↗
arXiv2002

Meausurement of Sky Suface Brightness Fluctuations at lambda = 4 micron

We present a Monte-Carlo technique to probe the cosmic Infrared background radiation (CIB) with faint source confusion in deep, wide-field 4 micron images. We report a detection of surface brightness fluctuations using an ensemble of 5000 pixels. The brightness fluctuations do not show correlated structure and appear to be dominated by galaxies. We estimate a lower limit (95% C.L.) on CIB by modeling the number-count behavior of contributing sources to the detected fluctuations.

astro-ph↗
arXiv2002

ASTRO-F - Super IRAS - The All Sky Infra-Red Survey

We review the next generation Japanese infrared space mission, ASTRO-F. ASTRO-F will be the first survey of the entire sky at infrared wavelengths since the IRAS mission almost 20 years ago. ASTRO-F will survey the entire sky in 4 far-infrared bands from 50-200microns and 2 mid-infrared bands at 9 and 20microns to sensitivities of 10-1000 times deeper than the IRAS satellite at angular resolutions of 25-45arcsec (c.f. IRAS 2-5arcmins). ASTRO-F can be considered a SUPER-IRAS. Using the galaxy evolution model of Pearson (2001) we produce expected numbers of sources under 3 different cosmological world models. We predict that ASTRO-F will detect of the order of 10's millions of sources in the far-infrared wavelength bands, most of which will be dusty LIG/ULIGs of which as many as half will lie at redshifts greater than unity. We produce number-redshift distributions, flux-redshift and colour-colour diagrams for the survey and discuss various segregation and photometric redshift techniques. Furthermore, we investigate the large scale structure scales that will be accessed by ASTRO-F, discovering that ASTRO-F and SIRTF-SWIRE probe both different scales and redshift domains and concluding that the 2 missions will supplement rather than supplant one another.

astro-ph↗
arXiv2002

On multifractality and fractional derivatives

It is shown phenomenologically that the fractional derivative $ξ=D^αu$ of order $α$ of a multifractal function has a power-law tail $\propto |ξ| ^{-p_\star}$ in its cumulative probability, for a suitable range of $α$'s. The exponent is determined by the condition $ζ_{p_\star} = αp_\star$, where $ζ_p$ is the exponent of the structure function of order $p$. A detailed study is made for the case of random multiplicative processes (Benzi {\it et al.} 1993 Physica D {\bf 65}: 352) which are amenable to both theory and numerical simulations. Large deviations theory provides a concrete criterion, which involves the departure from straightness of the $ζ_p$ graph, for the presence of power-law tails when there is only a limited range over which the data possess scaling properties (e.g. because of the presence of a viscous cutoff). The method is also applied to wind tunnel data and financial data.

nlin.CD↗
arXiv2002

Ionic Ordering in Thiospinel CuIr$_{2}$S$_{4}$

Crystal structure of spinel compound CuIr$_{2}$S$_{4}$ was examined by powder X-ray diffraction for the insulating phase below the metal-insulator transition at $T_{MI}$ = 230 K. The superstructure spots are reproduced by considering the displacement of Ir atoms. A model for the ionic ordering of Ir$^{4+}$ and Ir$^{3+}$ with the same number is proposed for the insulating phase on the basis of the structural analysis. The model suggests that the structural change at $T_{MI}$ is driven by the formation Ir$^{4+}$ dimers. In addition, we found that the superstructure spots becomes significantly weak below 60 K, without any significant effects on electric and magnetic properties. Possible mechanism for the transition is discussed.

cond-mat.str-el↗
arXiv2002

The Magnetic Phase Diagram and the Pressure and Field Dependence of the Fermi Surface in UGe$_2$

The ac susceptibility and de Haas-van Alphen (dHvA) effect in UGe$_2$ are measured at pressures {\it P} up to 17.7 kbar for the magnetic field {\it B} parallel to the {\it a} axis, which is the easy axis of magnetization. Two anomalies are observed at {\it B$_x$}({\it P}) and {\it B}$_m$({\it P}) ({\it B$_x$} $>$ {\it B}$_m$ at any {\it P}), and the {\it P}-{\it B} phase diagram is presented. The Fermi surface and quasiparticle mass are found to vary smoothly with pressure up to 17.7 kbar unless the phase boundary {\it B$_x$}({\it P}) is crossed. The observed dHvA frequencies may be grouped into three according to their pressure dependences, which are largely positive, nearly constant or negative. It is suggested that the quasiparticle mass moderately increases as the boundary {\it B$_x$}({\it P}) is approached. DHvA effect measurements are also performed across the boundary at 16.8 kbar.

cond-mat.str-el↗
arXiv2001

ASTRO-F - The next generation of mid-infrared surveys

We present basic observational strategies for ASTRO-F (also known as the Imaging Infra Red Surveyor (IRIS)) to be launched in 2004 by the Japanese Institute of Space and Astronautical Science (ISAS). We examine 2 survey scenarios, a deep ~1sq.deg. survey reaching sensitivities an order of magnitude below than the deepest surveys performed by ISO in the mid-IR, and a shallow \~18sq.deg mid-infrared (7-25um in 6 bands) covering an area greater than the entire area covered by all ISO mid-IR surveys. Using 2 cosmological models the number of galaxies predicted for each survey is calculated. The first model uses an enhancement of the pure luminosity evolution model of Pearson & Rowan-Robinson while the new models incorporate a strongly evolving ULIG component. For the deep survey, between 20,000-30,000 galaxies should be detected in the shortest wavebands and ~5000 in the longest (25um) band. The shallow survey would be expected to detect of the order of 100,000 - 150,000 sources.

astro-ph↗
arXiv2000

Beam Switching and Beam Feedback Systems at KEKB Linac

The KEK 8-GeV electron / 3.5-GeV positron linac has been operated with very different beam specifications for downstream rings, KEKB, PF and PF-AR. For the reliable operation among these beam modes intelligent beam switching and beam feedback systems have been developed and used since its commissioning. A software panel is used to choose one of four beam modes and a switching sequence is executed in about two minutes. Most items in a sequence are simple operations followed by failure recoveries. The magnet standardization part consumes most of the time. The sequence can be re-arranged easily by accelerator operators. Linac beam modes are switched about fifty times a day using this software. In order to stabilize linac beam energy and orbits, as well as some accelerator equipment, about thirty software beam feedback loops have been installed. They have been utilized routinely in all beam modes, and have improved its beam quality. Since its software interfaces are standardized, it is easy to add new feedback loops simply defining monitors and actuators.

physics.acc-ph↗
arXiv2000

[Ne II] 12.8 Micron Images of Four Galactic Ultracompact H II Regions: Ionized Neon Abundance as a Tracer of the Ionizing Stars

We present the results of ground-based imaging spectroscopy of the [Ne II] 12.8 micron line emitted from the ultracompact (UC) H II regions; W51d, G45.12+0.13, G35.20-1.74 and Monoceros R2, with 2arcsec spatial resolution. We found that the overall distribution of the [Ne II] emission is generally in good agreement with the radio (5 or 15 GHz) VLA distribution for each source. The Ne+ abundance ([Ne+/H+]) distributions are also derived from the [Ne II] and the radio maps. As for G45.12+0.13 and W51d, the Ne+ abundance decreases steeply from the outer part of the map toward the radio peak. On the other hand, the Ne+ abundance distributions of G35.20-1.74 and Mon R2 appear rather uniform. These results can be interpreted by the variation of ionizing structures of neon, which is primarily determined by the spectral type of the ionizing stars. We have evaluated the effective temperature of the ionizing star by comparing the Ne+ abundance averaged over the whole observed region with that calculated by H II region models based on recent non-LTE stellar atmosphere models: 39,100 (+1100, -500) K (O7.5V-O8V) for W51d, 37,200 (+1000, -700) K (O8V-O8.5V) for G45.12+0.13, 35,000-37,600 (+1500, -600) K (O8V-O9V) for G35.20-1.74, and < 34,000 K (< B0V) for Mon R2. These effective temperatures are consistent with those inferred from the observed Ne+ abundance distributions.

astro-ph↗
arXiv2000

ISO deep far-infrared survey in the "Lockman Hole" II. Power spectrum analysis: evidence of a strong evolution in number counts

We investigate the characteristics of FIR brightness fluctuations at 90 micron and 170 micron in the Lockman Hole, which were surveyed with ISOPHOT aboard the Infrared Space Observatory(ISO). We first calculated the angular correlation function of each field and then its Fourier transform(the angular Power Spectral Density: PSD) over the spatial frequency range of f=0.05 - 1 arcmin^-1. The PSDs are found to be rather flat at low spatial frequencies (f <= 0.1 arcmin^-1), slowly decreasing toward higher frequencies. These spectra are unlike the power-law ones seen in the IR cirrus fluctuations, and are well explained by randomly distributed point sources. Furthermore, point-to-point comparison between 90 micron and 170 micron brightness shows a linear correlation between them, and the slope of the linear fit is much shallower than that expected from the IR cirrus color, and is consistent with the color of galaxies at low or moderate redshift(z < 1). We conclude that the brightness fluctuations in the Lockman Hole are not caused by the IR cirrus, but are most likely due to faint star-forming galaxies. We also give the constraints on the galaxy number counts down to 35 mJy at 90 micron and 60 mJy at 170 micron, which indicate the existence of a strong evolution down to these fluxes in the counts. The galaxies responsible for the fluctuations also significantly contribute to the cosmic infrared background radiation.

astro-ph↗
arXiv2000

A Search for Near-Infrared Emission From the Halo of NGC 5907 at Radii of 10 kpc to 30 kpc

We present a search for near-infrared (3.5-5 micron) emission from baryonic dark matter in the form of low-mass stars and/or brown dwarfs in the halo of the nearby edge-on spiral galaxy NGC 5907. The observations were made using a 256 by 256 InSb array with a pixel scale of 17" at the focus of a liquid-helium-cooled telescope carried above the Earth's atmosphere by a sounding rocket. In contrast to previous experiments which have detected a halo around NGC 5907 in the V, R, I, J and K bands at galactic radii 6kpc < r < 10kpc, our search finds no evidence for emission from a halo at 10kpc < r < 30kpc. Assuming a halo mass density scaling as r^(-2), which is consistent with the flat rotation curves that are observed out to radii of 32kpc, the lower limit of the mass-to-light ratio at 3.5-5 microns for the halo of NGC 5907 is 250 (2 sigma) in solar units. This is comparable to the lower limit we have found previously for NGC 4565 (Uemizu et al. 1998). Based on recent models, our non-detection implies that hydrogen- burning stars contribute < 15% of the mass of the dark halo of NGC 5907. Our results are consistent with the previous detection of extended emission at r < 10kpc if the latter is caused by a stellar population that has been ejected from the disk because of tidal interactions. We conclude that the dark halo of NGC 5907, which is evident from rotation curves that extend far beyond 10kpc, is not comprised of hydrogen burning stars.

astro-ph↗
arXiv2000

[OII]3727 Emission from the Companion to the Quasar BR 1202-0725 at z=4.7

Results of a narrow-band imaging for the redshifted [OII]3727 emission around a quasar at z=4.7 obtained with the Subaru telescope and CISCO (a Cassegrain near infrared camera) are presented. A significant emission line is detected in the narrow-band H_2 (v=1-0 S(1)) filter at a location 2.4" northwest from the quasar, where the presence of a companion has been reported in Lyman alpha emission and the rest-frame UV continuum. We identify this line as [OII]3727 emission and confirm that the source really is a companion at z=4.7. The [OII]3727 flux from the companion is estimated to be 2.5 x 10^{-17} erg s^{-1} cm^{-2}. If the companion is a star forming object, the inferred star formation rate is as high as 45-230 M_{solar} yr^{-1} even without assuming the extinction correction. This value is higher than those derived from the Lyman alpha emission or from the UV continuum. Thus, provided that the difference is caused by dust extinction, the extinction corrected star formation rate is calculated to be 45 to 2300 M_{solar} yr^{-1} depending on the assuming extinction curves.

astro-ph↗