Orbital magnetism in the half-metallic Heusler alloys

Using the fully-relativistic screened Korringa-Kohn-Rostoker method I study the orbital magnetism in the half-metallic Heusler alloys. Orbital moments are almost completely quenched and they are negligible with respect to the spin moments. The change in the atomic-resolved orbital moments can be easily explained in terms of the spin-orbit strength and hybridization effects. Finally I discuss the orbital and spin moments derived from X-ray magnetic circular dichroism experiments

Spectroscopy of a narrow-line laser cooling transition in atomic dysprosium

The laser cooling and trapping of ultracold neutral dysprosium has been recently demonstrated using the broad, open 421-nm cycling transition. Narrow-line magneto-optical trapping of Dy on longer wavelength transitions would enable the preparation of ultracold Dy samples suitable for loading optical dipole traps and subsequent evaporative cooling. We have identified the closed 741-nm cycling transition as a candidate for the narrow-line cooling of Dy. We present experimental data on the isotope shifts, the hyperfine constants A and B, and the decay rate of the 741-nm transition. In addition, we report a measurement of the 421-nm transition's linewidth, which agrees with previous measurements. We summarize the laser cooling characteristics of these transitions as well as other narrow cycling transitions that may prove useful for cooling Dy.Comment: 6+ pages, 5 figures, 5 table

Extensive spatiotemporal analyses of surface ozone and related meteorological variables in South Korea for the period 1999–2010

Spatiotemporal characteristics of surface ozone (O₃) variations over South Korea are investigated with consideration of meteorological factors and timescales based on the Kolmogorov–Zurbenko filter (KZ filter), using measurement data at 124 air quality monitoring sites and 72 weather stations for the 12 yr period of 1999–2010. In general, O₃ levels at coastal cities are high due to dynamic effects of the sea breeze while those at the inland and Seoul Metropolitan Area (SMA) cities are low due to the NO_x titration by local precursor emissions. We examine the meteorological influences on O₃ using a combined analysis of the KZ filter and linear regressions between O₃ and meteorological variables. We decomposed O₃ time series at each site into short-term, seasonal, and long-term components by the KZ filter and regressed on meteorological variables. Impact of temperature on the O₃ levels is significantly high in the highly populated SMA and inland region, but low in the coastal region. In particular, the probability of high O₃ occurrence doubles with 4 °C of temperature increase in the SMA during high O₃ months (May–October). This implies that those regions will experience frequent high O₃ events in a future warming climate. In terms of short-term variation, the distribution of high O₃ probability classified by wind direction shows the effect of both local precursor emissions and long-range transport from China. In terms of long-term variation, the O₃ concentrations have increased by +0.26 ppbv yr⁻¹ (parts per billion by volume) on nationwide average, but their trends show large spatial variability. Singular value decomposition analyses further reveal that the long-term temporal evolution of O₃ is similar to that of nitrogen dioxide, although the spatial distribution of their trends is different. This study will be helpful as a reference for diagnostics and evaluation of regional- and local-scale O₃ and climate simulations, and as a guide to appropriate O₃ control policy in South Korea

Modelling stochastic bivariate mortality

Stochastic mortality, i.e. modelling death arrival via a jump process with stochastic intensity, is gaining increasing reputation as a way to represent mortality risk. This paper represents a first attempt to model the mortality risk of couples of individuals, according to the stochastic intensity approach. On the theoretical side, we extend to couples the Cox processes set up, i.e. the idea that mortality is driven by a jump process whose intensity is itself a stochastic process, proper of a particular generation within each gender. Dependence between the survival times of the members of a couple is captured by an Archimedean copula. On the calibration side, we fit the joint survival function by calibrating separately the (analytical) copula and the (analytical) margins. First, we select the best fit copula according to the methodology of Wang and Wells (2000) for censored data. Then, we provide a sample-based calibration for the intensity, using a time-homogeneous, non mean-reverting, affine process: this gives the analytical marginal survival functions. Coupling the best fit copula with the calibrated margins we obtain, on a sample generation, a joint survival function which incorporates the stochastic nature of mortality improvements and is far from representing independency.On the contrary, since the best fit copula turns out to be a Nelsen one, dependency is increasing with age and long-term dependence exists

Upper critical fields and thermally-activated transport of Nd(O_0.7F_0.3)FeAs single crystal

We present measurements of the resistivity and the upper critical field H_c2 of Nd(O_0.7F_0.3)FeAs single crystals in strong DC and pulsed magnetic fields up to 45 T and 60 T, respectively. We found that the field scale of H_c2 is comparable to ~100 T of high T_c cuprates. H_c2(T) parallel to the c-axis exhibits a pronounced upward curvature similar to what was extracted from earlier measurements on polycrystalline samples. Thus this behavior is indeed an intrinsic feature of oxypnictides, rather than manifestation of vortex lattice melting or granularity. The orientational dependence of H_c2 shows deviations from the one-band Ginzburg-Landau scaling. The mass anisotropy decreases as T decreases, from 9.2 at 44K to 5 at 34K. Spin dependent magnetoresistance and nonlinearities in the Hall coefficient suggest contribution to the conductivity from electron-electron interactions modified by disorder reminiscent that of diluted magnetic semiconductors. The Ohmic resistivity measured below T_c but above the irreversibility field exhibits a clear Arrhenius thermally activated behavior over 4-5 decades. The activation energy has very different field dependencies for H||ab and H\perp ab. We discuss to what extent different pairing scenarios can manifest themselves in the observed behavior of H_{c2}, using the two-band model of superconductivity. The results indicate the importance of paramagnetic effects on H_c2(T),which may significantly reduce H_c2(0) as compared toH_c2(0)~200-300 T based on extrapolations of H_c2(T) near T_c down to low temperatures.Comment: 11 pages, 16 figure