Pickoff and spin-conversion quenchings of ortho-positronium in oxygen

The quenching processes of the thermalized ortho-positronium(o-Ps) on an oxygen molecule have been studied by the positron annihilation age-momentum correlation techinique(AMOC). The Doppler broadening spectrum of the 511 keV gamma-rays from the 2gamma annihilation of o-Ps in O_2 has been measured as a function of the o-Ps age. The rate of the quenching, consisting of the pickoff and the spin-conversion, is estimated from the positron lifetime spectrum. The ratio of the pickoff quenching rate to the spin-conversion rate is deduced from the Doppler broadening of the 511 keV gamma-rays from the annihilation of the o-Ps. The pickoff parameter ^1Z_eff, the effective number of the electrons per molecule which contribute to the pickoff quenching, for O_2 is determined to be 0.6 +- 0.4. The cross-section for the elastic spin-conversion quenching is determined to be (1.16 +- 0.01) * 10^{-19} cm^2.Comment: 4 pages with 5 eps figures, LaTeX2e(revtex4

Damped Lyman alpha Absorbing Galaxies At Low Redshifts z<1 From Hierarchical Galaxy Formation Models

We investigate Damped Ly-alpha absorbing galaxies (DLA galaxies) at low redshifts z<1 in the hierarchical structure formation scenario to clarify the nature of DLA galaxies because observational data of such galaxies mainly at low redshifts are currently available. We find that our model well reproduces distributions of fundamental properties of DLA galaxies such as luminosities, column densities, impact parameters obtained by optical and near-infrared imagings. Our results suggest that DLA systems primarily consist of low luminosity galaxies with small impact parameters (typical radius about 3 kpc, surface brightness from 22 to 27 mag arcsec^{-2}) similar to low surface brightness (LSB) galaxies. In addition, we investigate selection biases arising from the faintness and from the masking effect which prevents us from identifying a DLA galaxy hidden or contaminated by a point spread function of a background quasar. We find that the latter affects the distributions of DLA properties more seriously rather than the former, and that the observational data are well reproduced only when taking into account the masking effect. The missing rate of DLA galaxies by the masking effect attains 60-90 % in the sample at redshift 0<z<1 when an angular size limit is as small as 1 arcsec. Furthermore we find a tight correlation between HI mass and cross section of DLA galaxies, and also find that HI-rich galaxies with M(HI) \sim 10^{9} M_sun dominate DLA systems. These features are entirely consistent with those from the Arecibo Dual-Beam Survey which is a blind 21 cm survey. Finally we discuss star formation rates, and find that they are typically about 10^{-2} M_sun yr^{-1} as low as those in LSB galaxies.Comment: 21 pages, 13 figures, Accepted for publication in Astrophsical Journa

The abundance of high-redshift objects as a probe of non-Gaussian initial conditions

The observed abundance of high-redshift galaxies and clusters contains precious information about the properties of the initial perturbations. We present a method to compute analytically the number density of objects as a function of mass and redshift for a range of physically motivated non-Gaussian models. In these models the non-Gaussianity can be dialed from zero and is assumed to be small. We compute the probability density function for the smoothed dark matter density field and we extend the Press and Schechter approach to mildly non-Gaussian density fields. The abundance of high-redshift objects can be directly related to the non-Gaussianity parameter and thus to the physical processes that generated deviations from the Gaussian behaviour. Even a skewness parameter of order 0.1 implies a dramatic change in the predicted abundance of z\gap 1 objects. Observations from NGST and X-ray satellites (XMM) can be used to accurately measure the amount of non-Gaussianity in the primordial density field.Comment: Minor changes to match the accepted ApJ version (ApJ, 539

The Modified Weighted Slab Technique: Models and Results

In an attempt to understand the source and propagation of galactic cosmic rays we have employed the Modified Weighted Slab technique along with recent values of the relevant cross sections to compute primary to secondary ratios including B/C and Sub-Fe/Fe for different galactic propagation models. The models that we have considered are the disk-halo diffusion model, the dynamical halo wind model, the turbulent diffusion model and a model with minimal reacceleration. The modified weighted slab technique will be briefly discussed and a more detailed description of the models will be given. We will also discuss the impact that the various models have on the problem of anisotropy at high energy and discuss what properties of a particular model bear on this issue.Comment: LaTeX - AASTEX format, Submitted to ApJ, 8 figures, 20 page

Numerical Galaxy Catalog -I. A Semi-analytic Model of Galaxy Formation with N-body simulations

We construct the Numerical Galaxy Catalog ($\nu$GC), based on a semi-analytic model of galaxy formation combined with high-resolution N-body simulations in a $\Lambda$-dominated flat cold dark matter ($\Lambda$CDM) cosmological model. The model includes several essential ingredients for galaxy formation, such as merging histories of dark halos directly taken from N-body simulations, radiative gas cooling, star formation, heating by supernova explosions (supernova feedback), mergers of galaxies, population synthesis, and extinction by internal dust and intervening HI clouds. As the first paper in a series using this model, we focus on basic photometric, structural and kinematical properties of galaxies at present and high redshifts. Two sets of model parameters are examined, strong and weak supernova feedback models, which are in good agreement with observational luminosity functions of local galaxies in a range of observational uncertainty. Both models agree well with many observations such as cold gas mass-to-stellar luminosity ratios of spiral galaxies, HI mass functions, galaxy sizes, faint galaxy number counts and photometric redshift distributions in optical pass-bands, isophotal angular sizes, and cosmic star formation rates. In particular, the strong supernova feedback model is in much better agreement with near-infrared (K'-band) faint galaxy number counts and redshift distribution than the weak feedback model and our previous semi-analytic models based on the extended Press-Schechter formalism. (Abridged)Comment: 26 pages including 27 figures, accepted for publication in ApJ, full-resolution version is available at http://grape.astron.s.u-tokyo.ac.jp/~yahagi/nugc

Inclusive dileptonic rare B decays with an extra generation of vector-like quarks

We investigate the leading effects of extending the Standard Model of electroweak interactions by an extra iso-singlet up- and down- type quark pair on various distributions and total branching ratio of the inclusive B-> X_s l^+ l^- (l =e,\mu) rare B decays. The presence of the extra vector-like down quark $D$ results in the non-unitarity of the extended quark mixing matrix V, which in turn leads to b-> s FCNC at the tree level proportional to (V^\dagger V)_{sb}. On the other hand, the effective penguin and box vertex functions are sensitive to the mass of the extra iso-singlet up quark m_U. The experimental upper bound on BR(B-> X_s \mu^+ \mu^-) is used to constrain the parameters of the model. It is shown that the shapes of the differential branching ratio and forward-backward asymmetry distribution are very sensitive to the value of the model parameters. We also calculate the CP aymmetry distribution of the dileptonic decay in the vector-like quark model. It is shown that, for a typical choice of the model parameters, asymmetries up to around 10% can be achieved for certain values of the dilepton invariant mass.Comment: 15 pages, 2 figure

Ac transport studies in polymers by a resistor network and transfer matrix approaches: application to polyaniline

A statistical model of resistor network is proposed to describe a polymer structure and to simulate the real and imaginary components of its ac resistivity. It takes into account the polydispersiveness of the material as well as intrachain and interchain charge transport processes. By the application of a transfer matrix technique, it reproduces ac resistivity measurements carried out with polyaniline films in different doping degrees and at different temperatures. Our results indicate that interchain processes govern the resistivity behavior in the low frequency region while, for higher frequencies, intrachain mechanisms are dominant.Comment: LaTeX file, 15 pages, 5 ps figures, to appear in Phys. Rev.

41Ca in tooth enamel. part I: A biological signature of neutron exposure in atomic bomb survivors

The detection of 41Ca atoms in tooth enamel using accelerator mass spectrometry is suggested as a method capable of reconstructing thermal neutron exposures from atomic bomb survivors in Hiroshima and Nagasaki. In general, 41Ca atoms are produced via thermal neutron capture by stable 40Ca. Thus any 41Ca atoms present in the tooth enamel of the survivors would be due to neutron exposure from both natural sources and radiation from the bomb. Tooth samples from five survivors in a control group with negligible neutron exposure were used to investigate the natural 41Ca content in tooth enamel, and 16 tooth samples from 13 survivors were used to estimate bomb-related neutron exposure. The results showed that the mean 41Ca/Ca isotope ratio was (0.17 ± 0.05) × 10-14 in the control samples and increased to 2 × 10-14 for survivors who were proximally exposed to the bomb. The 41Ca/Ca ratios showed an inverse correlation with distance from the hypocenter at the time of the bombing, similar to values that have been derived from theoretical free-in-air thermal-neutron transport calculations. Given that γ-ray doses were determined earlier for the same tooth samples by means of electron spin resonance (ESR, or electron paramagnetic resonance, EPR), these results can serve to validate neutron exposures that were calculated individually for the survivors but that had to incorporate a number of assumptions (e.g. shielding conditions for the survivors).Fil: Wallner, A.. Ludwig Maximilians Universitat; Alemania. Universitat Technical Zu Munich; Alemania. Universidad de Viena; AustriaFil: Ruhm, W.. Helmholtz Center Munich German Research Center For Environmental Health; Alemania. Ludwig Maximilians Universitat; AlemaniaFil: Rugel, G.. Ludwig Maximilians Universitat; Alemania. Universitat Technical Zu Munich; AlemaniaFil: Nakamura, N.. Radiation Effects Research Foundation; JapónFil: Arazi, Andres. Universitat Technical Zu Munich; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Faestermann, T.. Universitat Technical Zu Munich; AlemaniaFil: Knie, K.. Universitat Technical Zu Munich; Alemania. Ludwig Maximilians Universitat; AlemaniaFil: Maier, H. J.. Ludwig Maximilians Universitat; AlemaniaFil: Korschinek, G.. Universitat Technical Zu Munich; Alemani

Two-Dimensional Helioseismic Power, Phase, and Coherence Spectra of {\it Solar Dynamics Observatory} Photospheric and Chromospheric Observables

While the {\it Helioseismic and Magnetic Imager} (HMI) onboard the {\it Solar Dynamics Observatory} (SDO) provides Doppler velocity [$V$], continuum intensity [$I_C$], and line-depth [$Ld$] observations, each of which is sensitive to the five-minute acoustic spectrum, the {\it Atmospheric Imaging Array} (AIA) also observes at wavelengths -- specifically the 1600 and 1700 Angstrom bands -- that are partly formed in the upper photosphere and have good sensitivity to acoustic modes. In this article we consider the characteristics of the spatio--temporal Fourier spectra in AIA and HMI observables for a 15-degree region around NOAA Active Region 11072. We map the spatio--temporal-power distribution for the different observables and the HMI Line Core [$I_L$], or Continuum minus Line Depth, and the phase and coherence functions for selected observable pairs, as a function of position and frequency. Five-minute oscillation power in all observables is suppressed in the sunspot and also in plage areas. Above the acoustic cut-off frequency, the behaviour is more complicated: power in HMI $I_C$ is still suppressed in the presence of surface magnetic fields, while power in HMI $I_L$ and the AIA bands is suppressed in areas of surface field but enhanced in an extended area around the active region, and power in HMI $V$ is enhanced in a narrow zone around strong-field concentrations and suppressed in a wider surrounding area. The relative phase of the observables, and their cross-coherence functions, are also altered around the active region. These effects may help us to understand the interaction of waves and magnetic fields in the different layers of the photosphere, and will need to be taken into account in multi-wavelength local helioseismic analysis of active regions.Comment: 18 pages, 15 figures, to be published in Solar Physic

Dispersion Effects in Nucleon Polarisabilities

We present a formalism to extract the dynamical nucleon polarisabilities defined via a multipole expansion of the structure amplitudes in nucleon Compton scattering. In contradistinction to the static polarisabilities, dynamical polarisabilities gauge the response of the internal degrees of freedom of a composed object to an external, real photon field of arbitrary energy. Being energy dependent, they therefore contain additional information about dispersive effects induced by internal relaxation mechanisms, baryonic resonances and meson production thresholds of the nucleon. We give explicit formulae to extract the dynamical electric and magnetic dipole as well as quadrupole polarisabilities from low energy nucleon Compton scattering up to the one pion production threshold and discuss the connection to the definition of static nucleon polarisabilities. As a concrete example, we examine the results of leading order Heavy Baryon Chiral Perturbation Theory for the four leading spin independent iso-scalar polarisabilities of the nucleon. Finally, we consider the possible r{\^o}le of energy dependent effects in low energy extractions of the iso-scalar dipole polarisabilities from Compton scattering on the deuteron.Comment: 17 pages LaTeX2e with 2 figures, using includegraphicx (5 .eps files). Minor corrections, references updated. Contents identical to version to appear in Phys. Rev. C 65, spelling differen