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

Comparison of experimental and analytical methods to evaluate thermal bridges in wall systems

Twelve ASTM C0236 guarded hot box experiments have been performed on wall systems containing a variety of thermal bridges. All of the wall systems included steel framing. Six walls also had a concrete block wall system and a concrete slab to simulate a wall/floor intersection. Thermal bridges included in the wall systems included steel studs, steel tracks, steel stud/track joints, fasteners (steel framing system), concrete slab, metal bolts and angle iron, and brick ties (concrete block wall). Two-dimensional finite difference modeling was also employed to characterize the wall systems. The experimental test data was used to tune and ultimately validate the computer simulation model. The average variation between the tested and simulated wall system R-Values was 3.3% and ranged from {minus}3.4 to +7.4%. The model was then used to determine the thermal impact of each individual thermal bridge. Beside the standard complement of temperature sensors that are traditionally used for these laboratory experiments, additional sensors were installed near each thermal bridge to define the area and magnitude of the thermal distortion caused by the thermal bridge. These thermal bridges were analytically simulated and the additional heat flux due to each thermal bridge was computed. This paper summarizes the experimental and analytical analyses used to characterize the wall systems and concentrate on the thermal impact each type of thermal bridge has on the overall performance of the wall systems

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

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

Prevalence of Depression among Households in Three Capital Cities of Pakistan: Need to Revise the Mental Health Policy

BACKGROUND: Pakistan, among the other developing countries, has a higher prevalence rate of depression because of the current social adversities. There is, thus, a great need for systematic studies on prevalence of depression. The current study aims at exploring the prevalence of depression among households in three capital cities of Pakistan. METHODOLOGY AND PRINCIPAL FINDINGS: A sample of N = 820 was randomly selected, and a cross sectional telephone-based study was conducted for a duration of six months. It was found that there was a regional variation in prevalence rates for depression among the three cities. Lahore had the highest number of depressives (53.4%), as compared to Quetta (43.9%) and Karachi (35.7%). Middle age, female gender and secondary school level of education were significantly associated with depression among the study group. CONCLUSIONS/SIGNIFICANCE: The different rates of prevalence among the three cities could be attributed to local cultural influence, geographical locations and social adversities. There is a need for revision of existing health policy by the government

Anthropology, Brokerage and Collaboration in the development of a Tongan Public Psychiatry: Local Lessons for Global Mental Health

The Global Mental Health (GMH) movement has revitalised questions of the translatability of psychiatric concepts and the challenges of community engagement in countries where knowledge of the biomedical basis for psychiatric diagnosis is limited or challenged by local cultural codes. In Tonga, the local psychiatrist Dr Puloka has successfully established a publicly accessible psychiatry that has raised admission rates for serious mental illness and addressed some of the stigma attached to diagnosis. On the basis of historical analysis and ethnographic fieldwork with healers, doctors and patients since 1998, this article offers an ethnographic contextualization of the development and reception of three key interventions during the 1990s inspired by traditional healing and reliant on the translation of psychiatric terms and diagnosis. Dr Puloka’s use of medical anthropological and transcultural psychiatry research informed a community engaged brokerage between the implications of psychiatric nosologies and local needs. As such it reveals deficiencies in current polarised positions on the GMH project and offers suggestions to address current challenges of the Global Mental Health movement

Role of lattice structure and low temperature resistivity on fast electron beam filamentation in carbon

The influence of low temperature (eV to tens-of-eV) electrical resistivity on the onset of the filamentation instability in fast-electron transport is investigated in targets comprising of layers of ordered (diamond) and disordered (vitreous) carbon. It is shown experimentally and numerically that the thickness of the disordered carbon layer influences the degree of filamentation of the fast-electron beam. Strong filamentation is produced if the thickness is of the order of 60 μm or greater, for an electron distribution driven by a sub-picosecond, mid-1020 Wcm-2 laser pulse. It is shown that the position of the vitreous carbon layer relative to the fast-electron source (where the beam current density and background temperature are highest) does not have a strong effect because the resistive filamentation growth rate is high in disordered carbon over a wide range of temperatures up to the Spitzer regime

Thermal and electrical conductivity of iron at Earth's core conditions

The Earth acts as a gigantic heat engine driven by decay of radiogenic isotopes and slow cooling, which gives rise to plate tectonics, volcanoes, and mountain building. Another key product is the geomagnetic field, generated in the liquid iron core by a dynamo running on heat released by cooling and freezing to grow the solid inner core, and on chemical convection due to light elements expelled from the liquid on freezing. The power supplied to the geodynamo, measured by the heat-flux across the core-mantle boundary (CMB), places constraints on Earth's evolution. Estimates of CMB heat-flux depend on properties of iron mixtures under the extreme pressure and temperature conditions in the core, most critically on the thermal and electrical conductivities. These quantities remain poorly known because of inherent difficulties in experimentation and theory. Here we use density functional theory to compute these conductivities in liquid iron mixtures at core conditions from first principles- the first directly computed values that do not rely on estimates based on extrapolations. The mixtures of Fe, O, S, and Si are taken from earlier work and fit the seismologically-determined core density and inner-core boundary density jump. We find both conductivities to be 2-3 times higher than estimates in current use. The changes are so large that core thermal histories and power requirements must be reassessed. New estimates of adiabatic heat-flux give 15-16 TW at the CMB, higher than present estimates of CMB heat-flux based on mantle convection; the top of the core must be thermally stratified and any convection in the upper core driven by chemical convection against the adverse thermal buoyancy or lateral variations in CMB heat flow. Power for the geodynamo is greatly restricted and future models of mantle evolution must incorporate a high CMB heat-flux and explain recent formation of the inner core.Comment: 11 pages including supplementary information, two figures. Scheduled to appear in Nature, April 201