An x-ray detector using PIN photodiodes for the axion helioscope

An x-ray detector for a solar axion search was developed. The detector is operated at 60K in a cryostat of a superconducting magnet. Special care was paid to microphonic noise immunity and mechanical structure against thermal contraction. The detector consists of an array of PIN photodiodes and tailor made preamplifiers. The size of each PIN photodiode is $11\times 11\times 0.5\ {\rm mm^3}$ and 16 pieces are used for the detector. The detector consists of two parts, the front-end part being operated at a temperature of 60K and the main part in room temperature. Under these circumstances, the detector achieved 1.0 keV resolution in FWHM, 2.5 keV threshold and 6\times 10^{-5} counts sec^{-1} keV^{-1} cm^{-2} background level.Comment: 8 pages, 5 figures, submitted to Nucl. Instr. Meth.

Four-electron shell structures and an interacting two-electron system in carbon nanotube quantum dots

Low-temperature transport measurements have been carried out on single-wall carbon nanotube quantum dots in a weakly coupled regime in magnetic fields up to 8 Tesla. Four-electron shell filling was observed, and the magnetic field evolution of each Coulomb peak was investigated, in which magnetic field induced spin flip and resulting spin polarization were observed. Excitation spectroscopy measurements have revealed Zeeman splitting of single particle states for one electron in the shell, and demonstrated singlet and triplet states with direct observation of the exchange splitting at zero-magnetic field for two electrons in the shell, the simplest example of the Hund's rule. The latter indicates the direct analogy to an artificial He atom.Comment: 4 pages, 3 figures, submitted to Physical Review Letter

Stability Analysis of Optimal Velocity Model for Traffic and Granular Flow under Open Boundary Condition

We analyzed the stability of the uniform flow solution in the optimal velocity model for traffic and granular flow under the open boundary condition. It was demonstrated that, even within the linearly unstable region, there is a parameter region where the uniform solution is stable against a localized perturbation. We also found an oscillatory solution in the linearly unstable region and its period is not commensurate with the periodicity of the car index space. The oscillatory solution has some features in common with the synchronized flow observed in real traffic.Comment: 4 pages, 6 figures. Typos removed. To appear in J. Phys. Soc. Jp

A Search For Solar Hadronic Axions Using Kr-83

We introduce a new experimental method for solar hadronic axions search. It is suggested that these axions are created in the Sun during M1 transition between the first thermally excited level at 9.4 keV and the ground state in $^{83}Kr$. Our method is based on axion detection via resonant absorption process by the same nucleus in the laboratory. We use proportional gas counter filled with krypton to detect signals for axions. With this setup, target and detector are the same which increases the efficiency of the experiment. At present, an upper limit on hadronic axion mass of 5.5 keV at the 95% confidence level is obtained.Comment: 3 pages, contribution to ISRP9 Conference in Cape Town 2003. Version accepted by Radiat. Phys. Che

Fluctuation of the Top Location and Avalanches in the Formation Process of a Sandpile

We investigate the formation processes of a sandpile using numerical simulation. We find a new relation between the fluctuation of the motion of the top and the surface state of a sandpile. The top moves frequently as particles are fed one by one every time interval T. The time series of the top location has the power spectrum which obeys a power law, S(f)~f^{\alpha}, and its exponent \alpha depends on T and the system size w. The surface state is characterized by two time scales; the lifetime of an avalanche, T_{a}, and the time required to cause an avalanche, T_{s}. The surface state is fluid-like when T_{a}~T_{s}, and it is solid-like when T_{a}<<T_{s}. Our numerical results show that \alpha is a function of T_{s}/T_{a}.Comment: 15 pages, 13 figure

Classical Exchange Algebra of the Superstring on S^5 with the AdS-time

A classical exchange algebra of the superstring on S^5 with the AdS-time is shown on the light-like plane. To this end we use the geometrical method of which consistency is guaranteed by the classical Yang-Baxter equation. The Dirac method does not work, there being constraints which contain first-class and second-class and one can disentangle with each other keeping the isometry hardly.Comment: 12 pages, v2: argument on alternative representation of S^5 spherical functions added, typos corrected, one reference added, matches journal versio

The Tokyo Axion Helioscope

The Tokyo Axion Helioscope experiment aims to detect axions which are produced in the solar core. The helioscope uses a strong magnetic field in order to convert axions into X-ray photons and has a mounting to follow the sun very accurately. The photons are detected by an X-ray detector which is made of 16 PIN-photodiodes. In addition, a gas container and a gas regulation system is adopted for recovering the coherence between axions and photons in the conversion region giving sensitivity to axions with masses up to 2 eV. In this paper, we report on the technical detail of the Tokyo Axion Helioscope

Comments on Supersymmetry Algebra and Contact Term in Matrix String Theory

Following hep-th/0309238 relating the matrix string theory to the light-cone superstring field theory, we write down two supercharges in the matrix string theory explicitly. After checking the supersymmetry algebra at the leading order, we proceed to discuss higher-order contact terms.Comment: 17 pages, no figures, v2: eq. (5.1) and related appendices corrected, v3: final version to appear in JHE

InP solid state detector and the observation of low energy solar neutrinos

A large volume radiation detectors using a semi-insulating Indium Phosphide (InP) wafer have been developed for Indium Project on Neutrino Observation for Solar interior (IPNOS) experiment. The volume has achieved to 20mm3 , and this is world largest size among the detector observed gammas at hundred keV region. Although the depletion layer, most of charge are generated by an induction, and the charge collection efficiency achieves 50 to 60%, which is determined by the detector thickness and the carrier drift length (Ld = 120μm). The energy resolution is obtained by 25%. We measured actual backgrounds from 115 In beta decay, and also the effect of radiative Bremsstrahlung from those betas. No significant event was found in the measurement and the radiation such as Bremsstrahlung from InP detector could be negligible