Quantum molecular dynamics simulations for the nonmetal-to-metal transition in fluid helium

We have performed quantum molecular dynamics simulations for dense helium to study the nonmetal-to-metal transition at high pressures. We present new results for the equation of state and the Hugoniot curve in the warm dense matter region. The optical conductivity is calculated via the Kubo-Greenwood formula from which the dc conductivity is derived. The nonmetal-to-metal transition is identified at about 1 g/ccm. We compare with experimental results as well as with other theoretical approaches, especially with predictions of chemical models.Comment: 4 pages, 5 figure

XUV Opacity of Aluminum between the Cold-Solid to Warm-Plasma Transition

We present calculations of the free-free XUV opacity of warm, solid-density aluminum at photon energies between the plasma frequency at 15 eV and the L-edge at 73 eV, using both density functional theory combined with molecular dynamics and a semi-analytical model in the RPA framework with the inclusion of local field corrections. As the temperature is increased from room temperature to 10 eV, with the ion and electron temperatures equal, we calculate an increase in the opacity in the range over which the degree of ionization is constant. The effect is less pronounced if only the electron temperature is allowed to increase. The physical significance of these increases is discussed in terms of intense XUV-laser matter interactions on both femtosecond and picosecond time-scales.Comment: 4 pages, 3 figure

Probing the interiors of the ice giants: Shock compression of water to 700 GPa and 3.8 g/ccm

Recently there has been tremendous increase in the number of identified extra-solar planetary systems. Our understanding of their formation is tied to exoplanet internal structure models, which rely upon equations of state of light elements and compounds like water. Here we present shock compression data for water with unprecedented accuracy that shows water equations of state commonly used in planetary modeling significantly overestimate the compressibility at conditions relevant to planetary interiors. Furthermore, we show its behavior at these conditions, including reflectivity and isentropic response, is well described by a recent first-principles based equation of state. These findings advocate this water model be used as the standard for modeling Neptune, Uranus, and "hot Neptune" exoplanets, and should improve our understanding of these types of planets.Comment: Accepted to Phys. Rev. Lett.; supplementary material attached including 2 figures and 2 tables; to view attachments, please download and extract the gzipped tar source file listed under "Other formats

Sensitivity of Low Sloped Roofs Designs to Initial Water and Air Leakage

Liquid water in low sloped roofs almost always causes problems. Roofs are designed only to control the migration of vapor, if at all. Small amounts of water leakage/penetration, may cause mold growth or catastrophic corrosion in current roofs systems. In a recent paper by the authors the effect of exterior surface emissive and absorptive properties was found to have a significant effect on the moisture performance of a roof that had a leak. Depending on the surface characteristics, roof systems can be designed to effectively manage water penetration, but at an energy cost. In the roofs system examined previously, air leakage was not included. In the present study, the authors reinvestigated the effect of water penetration and the influence of air leakage on the hygrothermal performance of a few selected roofs. The drying potential of a groove ventilated roof is examined. The performance concept is based on the fact that warming up of air in the groove increases it's ability to transport moisture to the outside. Solar radiation raises the temperature of air in the grooves and on average, during a sunny summer day 0.5 L of water can be ventilated out of the roof per 1m width of the roof. In this paper, one climatic condition was investigated; a hot and humid Climate representative of Houston, TX. The specific questions that the paper addresses are: What are the vapor and liquid control dynamic involved in the moisture migration of a roof in Houston TX? and how does airflow influence the performance of a roof that is initially wet ? A state-of-the-art numerical model was used to address these issues. Results showed that the drying potential depends on the ventilation rates. The roof system with ventilation grooves dried out faster from the initially wet stage than the roof without the ventilation grooves. The total increase in heat loss of the roof was found to be between 0 - 5 % depending on the thickness of the insulation. The ventilation can cool down the temperature of the roof in the middle of a hot and sunny day thus reducing the heat load to the inside

Homeless street children in Nepal : use of allostatic load to assess the burden of childhood adversity.

As challenges to child well-being through economic disadvantage, family disruption, and migration or displacement escalate world wide, the need for cross-culturally robust understanding of childhood adversity proportionately increases. Toward this end, developmental risk was assessed in four contrasting groups of 107 Nepali children ages 10–14 years that represent distinctive, common conditions in which contemporary children grow up. Relative cumulative burden (allostatic load) indexed by multiple dimensions of physical and psychosocial stress was ascertained among homeless street boys and three family-based groups, from poor urban squatter settlements, urban middle class, and a remote rural village. Biomarkers of stress and vulnerability to stress included growth status, salivary cortisol, antibodies to Epstein–Barr virus, acute phase inflammatory responses (alpha1-antichymotrypsin), and cardiovascular fitness and reactivity (flex heart rate and pressor response). Individual biomarkers of risk and allostatic load differed markedly among groups, were highest in villagers, and varied by components of allostatic load. Such data suggest a need for critical appraisal of homelessness and migration as a risk factor to youth, given prevailing local conditions such as rural poverty, and represents the only multidimensional study of childhood allostatic load and developmental risk in non-Western settings

Integrated Hygrothermal Performance of Building Envelopes and Systems in Hot and Humid Climates

In hot and humid climates the interior and exterior environmental loads that building envelopes must respond to are larger than many other climatic conditions. Moisture-originated failures in low-rise residential buildings have put a significant pressure to change construction codes in North America. Solutions to moisture induced problems may be difficult when several interacting mechanisms of moisture transport are present. A new approach to building envelope durability assessment has been introduced in North America; a moisture engineering approach. This requires system information about the wall systems as constructed along with aging characteristics coupled with advanced modeling that 0 term allow the designer to predict the Iong-term performances of building envelope systems. This permits the comparison and ranking of individual building envelope systems with respect to total hygrothermal performance. Critical information can be obtained by investigating the one to one relationships of a building envelope to interior and exterior environments, however, the total behavior of the actual whole building is not accounted for. This paper goes one step further, by incorporating the individual hygrothermal performances of all walls, roof, floor and mechanical systems. The direct and indirect coupling of the building envelope and indoor environment with HVAC system are included in the analysis. The full house hygrothermal performance of an aerated concrete wall system are examined for a hot and humid climate. The hour by hour drying potential of each system was then numerically analyzed using weather conditions of Miami (hot and humid climate). The results clearly demonstrate the limited drying potential for the wall system in that climate. Furthermore, the selected exterior thermal insulation strategies and interior vapor control strategies in this study clearly show the critical behavior of the full house with respect to drying initial construction moisture. The results show the importance of the total hygrothermal behavior of the whole house to the coupling between the various envelope parts, interior and exterior environments and HVAC system. From these results moisture control strategies are identified for the whole house hygrothermal performance