Distribution of Snow and Maximum Snow Water Equivalent Obtained by LANDSAT Data and Degree Day Method

Maximum snow water equivalence and snowcover distribution are estimated using several LANDSAT data taken in snowmelting season over a four year period. The test site is Okutadami-gawa Basin located in the central position of Tohoku-Kanto-Chubu District. The year to year normalization for snowmelt volume computation on the snow line is conducted by year to year correction of degree days using the snowcover percentage within the test basin obtained from LANDSAT data. The maximum snow water equivalent map in the test basin is generated based on the normalized snowmelt volume on the snow line extracted from four LANDSAT data taken in a different year. The snowcover distribution on an arbitrary day in snowmelting of 1982 is estimated from the maximum snow water equivalent map. The estimated snowcover is compared with the snowcover area extracted from NOAA-AVHRR data taken on the same day. The applicability of the snow estimation using LANDSAT data is discussed

Nucleon strange quark content from two-flavor lattice QCD with exact chiral symmetry

Strange quark content of the nucleon is calculated in dynamical lattice QCD employing the overlap fermion formulation. For this quantity, exact chiral symmetry guaranteed by the Ginsparg-Wilson relation is crucial to avoid large contamination due to a possible operator mixing with $\bar{u}u+\bar{d}d$. Gauge configurations are generated with two dynamical flavors on a 16^3 x 32 lattice at a lattice spacing a \simeq 0.12fm. We directly calculate the relevant three-point function on the lattice including a disconnected strange quark loop utilizing the techniques of all-to-all quark propagator and low-mode averaging. Our result f_{T_s} = 0.032(8)(22), is in good agreement with our previous indirect estimate using the Feynman-Hellmann theorem.Comment: 31 pages, 22 figures; version published in PR

Anisotropy and Ising-like transition of the S=5/2 two-dimensional Heisenberg antiferromagnet Mn-formate di-Urea

Recently reported measurements of specific heat on the compound Mn-formate di-Urea (Mn-f-2U) by Takeda et al. [Phys. Rev. B 63, 024425 (2001)] are considered. As a model to describe the overall thermodynamic behavior of such compound, the easy-axis two-dimensional Heisenberg antiferromagnet is proposed and studied by means of the 'pure quantum self-consistent harmonic approximation' (PQSCHA). In particular it is shown that, when the temperature decreases, the compound exhibits a crossover from 2D-Heisenberg to 2D-Ising behavior, followed by a 2D-Ising-like phase transition, whose location allows to get a reliable estimate of the easy-axis anisotropy driving the transition itself. Below the critical temperature T_N=3.77 K, the specific heat is well described by the two-dimensional easy-axis model down to a temperature T*=1.47 K where a T^3-law sets in, possibly marking a low-temperature crossover of magnetic fluctuations from two to three dimensions.Comment: 3 pages, 2 figures, 47th Annual Conference on Magnetism and Magnetic Materials (Tampa, FL, USA, 11-15/11/2002

Behavior of Li abundances in solar-analog stars II. Evidence of the connection with rotation and stellar activity

We previously attempted to ascertain why the Li I 6708 line-strengths of Sun-like stars differ so significantly despite the superficial similarities of stellar parameters. We carried out a comprehensive analysis of 118 solar analogs and reported that a close connection exists between the Li abundance A_Li and the line-broadening width (v_r+m; mainly contributed by rotational effect), which led us to conclude that stellar rotation may be the primary control of the surface Li content. To examine our claim in more detail, we study whether the degree of stellar activity exhibits a similar correlation with the Li abundance, which is expected because of the widely believed close connection between rotation and activity. We measured the residual flux at the line center of the strong Ca II 8542 line, r_0(8542), known to be a useful index of stellar activity, for all sample stars using newly acquired spectra in this near-IR region. The projected rotational velocity (v_e sin i) was estimated by subtracting the macroturbulence contribution from v_r+m that we had already established. A remarkable (positive) correlation was found in the A_Li versus (vs.) r_0(8542) diagram as well as in both the r_0(8542) vs. v_e sin i and A_Li vs. v_e sin i diagrams, as had been expected. With the confirmation of rotation-dependent stellar activity, this clearly shows that the surface Li abundances of these solar analogs progressively decrease as the rotation rate decreases. Given this observational evidence, we conclude that the depletion of surface Li in solar-type stars, probably caused by effective envelope mixing, operates more efficiently as stellar rotation decelerates. It may be promising to attribute the low-Li tendency of planet-host G dwarfs to their different nature in the stellar angular momentum.Comment: 12 pages, 9 figures; accepted for publication in Astron. Astrophys