Juncture stress fields in multicellular shell structures. Volume IV - Stresses and deformations of fixed-edge segmental spherical shells Final report

Equations for thin elastic spherical shells and digital program for analysis of stresses and deformation of fixed edge segmental spherical shells - solution by finite difference techniqu

Changing Snowmelt Conditions in the Western Canadian Arctic

Multidecadal Changes in Spring Snowmelt in the Western Canadian Arctic This study investigates the changes in key aspects of snowmelt in the western Canadian Arctic. Specifically, we will look at changes in the onset of snowmelt and the duration of snowmelt between 1999 and 2019, and extended air temperature between 1957 and 2019. In addition, we will look at changes in eight meteorological variables during the melt period. It was found that the onset of snowmelt occurred 14 days earlier, while the melt period ends 20 days earlier than 20 years ago. As a result, the duration of melt period has decreased by 5 days. During this earlier and shorter melt period, the air temperature and relative humidity have both increased. While these changes were statistically significant, there were no statistically significant changes in SWE, precipitation, wind speed, downward shortwave and longwave radiation, or refreeze events. Future research will consider the effects and the variability of these changes on the snowmelt energy balance. Changing Snowmelt Energy Balance in the Western Canadian Arctic The hydrology of the of the Arctic is dominated by the accumulation of snow over the long winter, and the rapid melt of this snow over a few weeks in the spring. This aspect of the Arctic water cycle is especially sensitive to a warming climate. The timing and the rate of snow melt during the spring period has implications for aquatic ecosystems and communities that depend on melt water. As shown in Chapter 2, the western Canadian Arctic has experienced an earlier onset of snowmelt compared to earlier decades, a warmer and shorter melt period. The changes in the energy balance components are tied to climate warming, and therefore, controlling the rate of snowmelt. In this paper we will use a physically based snowmelt model to investigate changes in the energy transfers between the snow surface and the atmosphere during the snowmelt period over the last 21 years. Model runs demonstrate that radiation plays a decisive role, followed by turbulent fluxes of sensible heat and latent heat. A shorter duration of melt is due to a combination of changes in the end of winter SWE and meteorological conditions. As net radiation and warmer air temperatures increased, we found an increase to the rate of snowmelt by 0.7 mm/day per decade

Universality at integer quantum Hall transitions

We report in this paper results of experimental and theoretical studies of transitions between different integer quantum Hall phases, as well as transition between the insulating phase and quantum Hall phases at high magnetic fields. We focus mainly on universal properties of the transitions. We demonstrate that properly defined conductivity tensor is universal at the transitions. We also present numerical results of a non-interacting electron model, which suggest that the Thouless conductance is universal at integer quantum Hall transitions, just like the conductivity tensor. Finite temperature and system size effects near the transition point are also studied.Comment: 20 pages, 15 figure

Valley splitting of Si/SiGe heterostructures in tilted magnetic fields

We have investigated the valley splitting of two-dimensional electrons in high quality Si/Si$_{1-x}$Ge$_x$ heterostructures under tilted magnetic fields. For all the samples in our study, the valley splitting at filling factor $\nu=3$ ($\Delta_3$) is significantly different before and after the coincidence angle, at which energy levels cross at the Fermi level. On both sides of the coincidence, a linear density dependence of $\Delta_3$ on the electron density was observed, while the slope of these two configurations differs by more than a factor of two. We argue that screening of the Coulomb interaction from the low-lying filled levels, which also explains the observed spin-dependent resistivity, is responsible for the large difference of $\Delta_3$ before and after the coincidence.Comment: REVTEX 4 pages, 4 figure

Novel Properties of The Apparent Metal-Insulator Transition in Two-Dimensional Systems

The low-temperature conductivity of low-density, high-mobility, two-dimensional hole systems in GaAs was studied. We explicitly show that the metal-insulator transition, observed in these systems, is characterized by a well-defined critical density, p_0c. We also observe that the low-temperature conductivity of these systems depends linearly on the hole density, over a wide density range. The high-density linear conductivity extrapolates to zero at a density close to the critical density.Comment: 4 Figure

Josephson Plasma Resonance as a Structural Probe of Vortex Liquid

Recent developments of the Josephson plasma resonance and transport c-axis measurements in layered high T$_{c}$ superconductors allow to probe Josephson coupling in a wide range of the vortex phase diagram. We derive a relation between the field dependent Josephson coupling energy and the density correlation function of the vortex liquid. This relation provides a unique opportunity to extract the density correlation function of pancake vortices from the dependence of the plasma resonance on the $ab$-component of the magnetic field at a fixed $c$-axis component.Comment: 4 pages, 1 fugure, accepted to Phys. Rev. Let

Acceptability of A/H1N1 vaccination during pandemic phase of influenza A/H1N1 in Hong Kong: population based cross sectional survey

Objective To investigate the intention of the Hong Kong general population to take up vaccination against influenza A/H1N1

Josephson Plasma Resonance in Bi2Sr2CaCu2O8+yBi_2 Sr_2 Ca Cu_2 O_{8+y} with Spatially Dependent Interlayer-Phase Coherence

We study the Josephson plasma resonance (JPR) in Bi$_2$Sr$_2$CaCu$_2$O$_{8+y}$ (BSCCO) with spatially dependent interlayer-phase coherence (IPC). The half-irradiated BSCCO (HI-BSCCO), in which columnar defects are introduced only in a half of the sample, shows several resonance peaks, which are not simple superposition of the peaks in irradiated- and pristine-parts. JPR in HI-BSCCO changes its character from irradiated- to pristine-type at a crossover frequency ($\omega_{cr}$). We demonstrate that the one-dimensional \LSGE, which takes into account the spatial dependence of IPC, can reproduce most of the experimental findings including the presence of $\omega_{cr}$.Comment: 4 figure