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.

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

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

Theory of ω−4/3\omega^{-4/3} law of the power spectrum in dissipative flows

It is demonstrated that $\omega^{-4/3}$ law of the power spectrum with the angular frequency $\omega$ in dissipative flows is produced by the emission of dispersive waves from the antikink of an congested domain. The analytic theory predicts the spectrum is proportional to $\omega^{-2}$ for relatively low frequency and $\omega^{-4/3}$ for high frequency.Comment: 11 pages, 2 figure

Nonstructural Carbohydrate Reserves of Temperate Perennial Grasses in Autumn Early Growth

The objective of this study was to determine levels of nonstructural carbohydrate reserves of four temperate perennial grasses: Orchardgrass (Dactylis glomerata L.), Timothy (Phleum pratense L.), Perennial ryegrass (Lolium perenne L.), and Reed canarygrass (Phalaris arundinacea L.) in their early growth stages during the cool autumn temperatures in northern Japan. At the time of sampling, all grasses were in their vegetative stage, and Reed canarygrass was not forming rhizomes. Fructosan concentration in reed canarygrass roots (8.04%) was 22 times that of the leaf blade (0.36%) and twice that of the stem (3.40%); the concentration in reed canarygrass root was the highest of the four grasses. Timothy stored fructosan in the root at a significantly higher concentration (1.65%) than did the orchardgrass (0.58%) and perennial ryegrass (0.83%). The concentration of fructosan in the timothy was the highest in the stem, the lowest in the leaf blade and intermediate in the root. On the other hand, orchardgrass and perennial ryegrass stored the highest amount of fructosan in the stem, the lowest amount in the root, and an intermediate amount in the leaf blade. In addition, the root dry weight and the ratio of the root dry weight to the total dry weight were significantly higher in reed canarygrass than in the other three grasses. Timothy was in second place surpassing orchardgrass and perennial ryegrass. We considered that winter survival is the highest in reed canarygrass and second highest in timothy over orchard grass and perennial ryegrass

Measurement of the thickness of an insensitive surface layer of a PIN photodiode

We measured the thickness of an insensitive surface layer of a PIN photodiode, Hamamatsu S3590-06, used in the Tokyo Axion Helioscope. We made alpha-particles impinge on the PIN photodiode in various incidence angles and measured the pulse height to estimate the thickness of the insensitive surface layer. This measurement showed its thickness was $0.31 \pm 0.02 \mu m$ on the assumption that the insensitive layer consisted of Si. We calculated the peak detection efficiency for low energy x-rays in consideration of the insensitive layer and escape of x-rays and Auger electrons. This result showed the efficiency for 4-10keV x-rays was more than 95%.Comment: 7 pages, 7 figure

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