arXiv subjects

M. Tanaka

Publications and source records attributed to M. Tanaka.

At least 235 records · Page 13Linked to original sources

arXiv2006

Asymmetric Explosion of Type Ia Supernovae as Seen from Near Infrared Observations

We present near-infrared spectra of late phase (>200 d) Type Ia supernovae (SNe Ia) taken at the Subaru telescope. The [Fe II] line of SN 2003hv shows a clear flat-topped feature, while that of SN 2005W show less prominent flatness. In addition, a large shift in their line center, varying from -3000 to 1000 (km/s) with respect to the host galaxies, is seen. Such a shift suggests the occurrence of an off-center, non-spherical explosion in the central region, and provides important, new constraints on the explosion models of SNe Ia.

astro-ph↗

arXiv2006

Quantum-size effect and tunneling magnetoresistance in ferromagnetic-semiconductor quantum heterostructures

We report on the resonant tunneling effect and the increase of tunneling magnetoresistance (TMR) induced by it in ferromagnetic-semiconductor GaMnAs quantum-well heterostructures. The observed quantum levels of the GaMnAs quantum well were successfully explained by the valence-band kp model with the p-d exchange interaction. It was also found that the Fermi level of the electrode injecting carriers is important to observe resonant tunneling in this system.

cond-mat.mtrl-sci↗

arXiv2006

Japanese Virtual Observatory (JVO) as an advanced astronomical research enviroment

We present the design and implementation of the Japanese Virtual Observatory (JVO) system. JVO is a portal site to various kinds of astronomical resources distributed all over the world. We have developed five components for constructing the portal: (1) registry, (2) data service, (3) workflow system, (4) data analysis service (5) portal GUI. Registry services are used for publishing and searching data services in the VO, and they are constructed using an OAI-PMH metadata harvesting protocol and a SOAP web service protocol so that VO standard architecture is applied. Data services are developed based on the Astronomical Data Query Language (ADQL) which is an international VO standard and an extension of the standard SQL. The toolkit for building the ADQL-based service is released to the public on the JVO web site. The toolkit also provides the protocol translation from a Simple Image Access Protocol (SIAP) to ADQL protocol, so that both the VO standard service can be constructed using our toolkit. In order to federate the distributed databases and analysis services, we have designed a workflow language which is described in XML and developed execution system of the workflow. We have succeeded to connect to a hundred of data resources of the world as of April 2006. We have applied this system to the study of QSO environment by federating a QSO database, a Subaru Suprim-Cam database, and some analysis services such a SExtractor and HyperZ web services. These experiences are described is this paper.

astro-ph↗

arXiv2005

Magneto-optical properties of a new group-IV ferromagnetic semiconductor Ge1-xFex grown by low-temperature molecular beam epitaxy

A new group-IV ferromagnetic semiconductor, Ge1-xFex, was successfully grown by low-temperature molecular beam epitaxy (LT-MBE) without precipitation of ferromagnetic Ge-Fe intermetallic compounds. The ferromagnetism of Ge1-xFex films was investigated by magnetic circular dichroism (MCD). In particular, the influence of the Fe content (FFe/FGe =1 - 10%) and growth temperature (100, 200OC) on the ferromagnetism was carefully studied. The MCD measurements revealed that the band structure of the Ge1-xFex films was identical with that of bulk Ge, and that the large spin splitting of the band structure was induced by the incorporation of Fe atoms into the Ge matrix, indicating the existence of s,p-d exchange interactions. The Ge1-xFex films showed ferromagnetic behavior and the ferromagnetic transition temperature linearly increased with increasing the Fe composition. These results indicate that the epitaxially grown Ge1-xFex is an intrinsic ferromagnetic semiconductor.

cond-mat.mtrl-sci↗

arXiv2005

The Unique Type Ib Supernova 2005bf: A WN Star Explosion Model for Peculiar Light Curves and Spectra

Observations and modeling for the light curve (LC) and spectra of supernova (SN) 2005bf are reported. This SN showed unique features: the LC had two maxima, and declined rapidly after the second maximum, while the spectra showed strengthening He lines whose velocity increased with time. The double-peaked LC can be reproduced by a double-peaked $^{56}$Ni distribution, with most $^{56}$Ni at low velocity and a small amount at high velocity. The rapid post-maximum decline requires a large fraction of the $γ$-rays to escape from the $^{56}$Ni-dominated region, possibly because of low-density ``holes''. The presence of Balmer lines in the spectrum suggests that the He layer of the progenitor was substantially intact. Increasing $γ$-ray deposition in the He layer due to enhanced $γ$-ray escape from the $^{56}$Ni-dominated region may explain both the delayed strengthening and the increasing velocity of the He lines. The SN has massive ejecta ($\sim6-7\Msun$), normal kinetic energy ($\sim 1.0-1.5\times 10^{51}$ ergs), high peak bolometric luminosity ($\sim 5\times 10^{42}$ erg s$^{-1}$) for an epoch as late as $\sim$ 40 days, and a large $^{56}$Ni mass ($\sim0.32\Msun$). These properties, and the presence of a small amount of H suggest that the progenitor was initially massive (M$\sim 25-30 \Msun$) and had lost most of its H envelope, and was possibly a WN star. The double-peaked $^{56}$Ni distribution suggests that the explosion may have formed jets that did not reach the He layer. The properties of SN 2005bf resemble those of the explosion of Cassiopeia A.

astro-ph↗

arXiv2005

The peculiar type Ib supernova 2005bf: explosion of a massive He star with a thin hydrogen envelope?

We present BVRI photometry and optical spectroscopy of SN 2005bf near light maximum. The maximum phase is broad and occurred around 2005 May 7, about forty days after the shock breakout. SN 2005bf has a peak bolometric magnitude M_{bol}=-18.0\pm 0.2: while this is not particularly bright, it occurred at an epoch significantly later than other SNe Ibc, indicating that the SN possibly ejected ~0.31 M_{sun} of 56Ni, which is more than the typical amount. The spectra of SN 2005bf around maximum are very similar to those of the Type Ib SNe 1999ex and 1984L about 25-35 days after explosion, displaying prominent He I, Fe II, Ca II H & K and the near-IR triplet P Cygni lines. Except for the strongest lines, He I absorptions are blueshifted by <~6500 km/s, and Fe II by \~7500-8000 km/s. No other SNe Ib have been reported to have their Fe II absorptions blueshifted more than their He I absorptions. Relatively weak H-alpha and very weak H-beta may also exist, blueshifted by ~15,000 km/s. We suggest that SN 2005bf was the explosion of a massive He star, possibly with a trace of a hydrogen envelope.

astro-ph↗

arXiv2005

The Discovery Potential of a Super B Factory

The Proceedings of the 2003 SLAC Workshops on flavor physics with a high luminosity asymmetric e+e- collider. The sensitivity of flavor physics to physics beyond the Standard Model is addressed in detail, in the context of the improvement of experimental measurements and theoretical calculations.

hep-ph↗

arXiv2005

High Temperature Ferromagnetism in GaAs-based Heterostructures with Mn Delta Doping

We show that suitably-designed magnetic semiconductor heterostructures consisting of Mn delta-doped GaAs and p-type AlGaAs layers, in which the locally high concentration of magnetic moments of Mn atoms are controllably overlapped with the 2-dimensional hole gas wavefunction, realized remarkably high ferromagnetic transition temperatures (TC). Significant reduction of compensative Mn interstitials by varying the growth sequence of the structures followed by low temperature annealing led to high TC up to 250 K. The heterostructure with high TC exhibited peculiar anomalous Hall effect behavior, whose sign depends on temperature.

cond-mat.mtrl-sci↗

arXiv2005

IRTS observation of the near-infrared extragalactic background light

We searched for near-infrared extragalactic background light (EBL) in the data from the Near-InfraRed Spectrometer (NIRS) on the Infrared Telescope in Space (IRTS). After subtracting the contribution of faint stars and the zodiacal component based on modeling, a significant isotropic emission is obtained in the wavelength bands from 1.4 micron to 4.0 micron. The in-band flux amounts to ~ 35 nW m-2 sr-1 which is too bright to be explained by the integrated light from faint galaxies. Significant fluctuations in sky brightness were also detected which can not be explained by fluctuations due to faint stars, zodiacal components and normal galaxies. The excess fluctuation amounts to ~ 1/4 of the excess emission over the integrated light of galaxies. A two-point correlation analysis shows that IRTS/NIRS data has an angular scale of fluctuations of a few degrees. Recent WMAP results of CMB polarization indicate that the reionization of the Universe occurred at z ~ 17 or earlier. The observed near infrared background light could be redshifted UV light from the first generation of massive stars (Pop.III stars) which caused the reionization of the Universe. The spectral jump around 1 micron over the optical EBL suggests that massive star formation terminated at z~9. The observed fluctuations, however, are considerably larger than the theoretical predictions and require a new scenario for the Pop.III era.

astro-ph↗

arXiv2004

Carbon stars in the IRTS survey

We have identified 139 cool carbon stars in the near-infrared spectro-photometric survey of the InfraRed Telescope in Space (IRTS) from the conspicuous presence of molecular absorption bands at 1.8, 3.1 and 3.8 microns. Among them 14 are new, bright (K ~ 4.0-7.0), carbon stars. We find a trend relating the 3.1 microns band strength to the K-L' color index, which is known to correlate with mass-loss rate. This could be an effect of a relation between the depth of the 3.1 microns feature and the degree of development of the extended stellar atmosphere where dust starts to form.

astro-ph↗

arXiv2004

Physics at Super B Factory

This report presents the results of studies that investigate the physics reach at a Super B factory, an asymmetric-energy e^+e^- collider with a design luminosity of 5 x 10^35 cm^-2s^-1, which is around 40 times as large as the peak luminosity achieved by the KEKB collider. The studies focus on flavor physics and CP violation measurements that could be carried out in the LHC era. The physics motivation, key observables, measurement methods and expected precisions are presented. The sensitivity studies are a part of the activities associated with the preparation of a Letter of Intent for SuperKEKB, which has been submitted recently.

hep-ex↗

arXiv2004

Nuclear Transparency in 90 Degree c.m. Quasielastic A(p,2p) Reactions

We summarize the results of two experimental programs at the Alternating Gradient Synchrotron of BNL to measure the nuclear transparency of nuclei measured in the A(p,2p) quasielastic scattering process near 90 Deg .in the pp center of mass. The incident momenta varied from 5.9 to 14.4 GeV/c, corresponding to 4.8 < Q^2 < 12.7 (GeV/c)^2. First, we describe the measurements with the newer experiment, E850, which had more complete kinematic definition of quasielastic events. In E850 the angular dependence of the nuclear transparency near 90 Deg. c.m., and the nuclear transparency for deuterons was studied. Second, we review the techniques used in an earlier experiment, E834, and show that the two experiments are consistent for the Carbon data. E834 also determines the nuclear transparencies for Li, Al, Cu, and Pb nuclei as well as for C. We find for both E850 and E834 that the A(p,2p) nuclear transparency, unlike that for A(e,e'p) nuclear transparency, is incompatible with a constant value versus energy as predicted by Glauber calculations. The A(p,2p) nuclear transparency for C and Al increases by a factor of two between 5.9 and 9.5 GeV/c incident proton momentum. At its peak the A(p,2p) nuclear transparency is about 80% of the constant A(e,e'p) nuclear transparency. Then the nuclear transparency falls back to the Glauber level again. This oscillating behavior is generally interpreted as an interplay between two components of the pN scattering amplitude; one short ranged and perturbative, and the other long ranged and strongly absorbed in the nuclear medium. We suggest a number of experiments for further studies of nuclear transparency effects.

nucl-ex↗

arXiv2004

Wide-Area Mapping of 155 Micron Continuum Emission from the Orion Molecular Cloud Complex

We present the results of a wide-area mapping of the far-infrared continuum emission toward the Orion complex by using a Japanese balloon-borne telescope. The 155-um continuum emission was detected over a region of 1.5 deg^2 around the KL nebula with 3' resolution similar to that of the IRAS 100-um map. Assuming a single-temperature model of the thermal equilibrium dust, maps of the temperature and the optical depth were derived from the 155 um intensity and the IRAS 100 um intensity. The derived dust temperature is 5 - 15 K lower and the derived dust optical thickness were derived from the 155-um intensity and the IRAS 100-um intensity. The derived dust temperature is 5 - 15 K lower and the derived dust optical depth is 5 - 300 times larger than those derived from the IRAS 60 and 100-um intensities due to the significant contribution of the statistically heated very small grains to the IRAS 60-um intensity. The optical-thickness distribution shows a filamentary dust ridge that has a 1.5 degrees extent in the north - south direction and well resembles the Integral-Shaped Filament (ISF) molecular gas distribution. The gas-to-dust ratio derived from the CO molecular gas distribution along the ISF is in the range 30 - 200, which may be interpreted as being an effect of CO depletion due to the photodissociation and/or the freezing on dust grains.

astro-ph↗

arXiv2004

Development of a multi-pixel hybrid photo-detector with high quantum efficiency and gain

A hybrid photo-detector (HPD) consisting of a photocathode and a multi-pixel avalanche diode (MP-AD) was developed a few years ago. Our previous studies showed that its inherent potential for high resolution photon counting could be further enhanced by reducing fluctuations in charge loss in the dead layer at the entrance of the MP-AD. In this paper, we report on the improvement with the newly developed HPD whose encapsulated MP-AD has a thinner dead layer than before. It is demonstrated that the new HPD has much better energy resolution, which enables clearer counting up to nine photoelectrons. Further enhancement of the photocathode sensitivity of the HPD is also discussed.

physics.ins-det↗

arXiv2003

A spin metal-oxide-semiconductor field-effect transistor using half-metallic-ferromagnet contacts for the source and drain

We propose and theoretically analyze a novel metal-oxide-semiconductor field-effect-transistor (MOSFET) type of spin transistor (hereafter referred to as a spin MOSFET) consisting of a MOS gate structure and half-metallic-ferromagnet (HMF) contacts for the source and drain. When the magnetization configuration between the HMF source and drain is parallel (antiparallel), highly spin-polarized carriers injected from the HMF source to the channel are transported into (blocked by) the HMF drain, resulting in the magnetization-configuration-dependent output characteristics. Our two-dimensional numerical analysis indicates that the spin MOSFET exhibits high (low) current drive capability in the parallel (antiparallel) magnetization, and that extremely large magnetocurrent ratios can be obtained. Furthermore, the spin MOSFET satisfies other important requirements for "spintronic" integrated circuits, such as high amplification capability, low power-delay product, and low off-current.

cond-mat.mtrl-sci↗

arXiv2003

External Control of Magnetism in Semiconductors at High Temperature (~100K)

We demonstrate the electrical and optical control of ferromagnetism in semiconductor heterostructures at high temperatures of 100-117 K. The heterostructures consist of Mn delta-doped GaAs and p-type AlGaAs, where the overlap of the hole wavefunction with the Mn delta-doping profile leads to high ferromagnetic transition temperature TC of over 100 K (max. 172 K). We are able to isothermally change the paramagnetic state to the ferromagnetic state and vice versa, by applying a gate electric-field or by light irradiation. The large modulation of TC (DTC ~15 K) at high temperatures (> ~100 K) demonstrated here may pave the way to functional device applications compatible with the present semiconductor technology.

cond-mat.mtrl-sci↗

arXiv2003

Development of a pipeline CAMAC controller with PC/104-Plus single board computer

A pipeline CAMAC controller with PC/104-Plus single board computer has been developed. The architecture of the pipeline CAMAC controller is completely different from that of traditional CAMAC controller. The pipeline CAMAC controller adopted truly pipelined command and data paths from/to computer memory to/from CAMAC. The pipeline method enabled the controller maximum speed of CAMAC, approximately up to 3 MB/sec with 24-bit data. The controller also has a DAQ function such as event numbering for co-existence with other equipment such as VME. Not only the functionality and the performance but also the pipeline architecture and the design concept are described.

physics.ins-det↗

arXiv2003

The Data Acquisition System Based on PMC Bus

High energy physics experiments in KEK/Japan rush into over KHz trigger stage. Thus, we need a successor of the data acquisition(DAQ) system that replaces the CAMAC or FASTBUS systems. To meet these needs, we have developed a DAQ system which includes a crate, base-board modules, daughter cards for front-end A/D or T/D conversion, and back-end communication cards for data transfer and timing control. The size of the crate is for the 9U Euro-cards with the standard VME32 bus and extension connectors for power supply. The base-board comprises of a local bus with the sequencer connected to the front-end daughter cards via event buffering FIFOs, and the standard PMC (PCI mezzanine card) bus to be set a PMC processor unit to reduce data size from the front-end daughter cards. A data transfer module, which is connected to the event building system, and a trigger control unit, which communicates with the central timing controller are installed on the back-end communication card connected to the rear end of the base-board. We describe the design of this DAQ system and evaluate the performance of it.

physics.ins-det↗