3,948 research outputs found
Reviewing past environments in a historic house using building simulation
This paper reviews different heatingregimes applied to the same space,using building simulation. Theconstruction of a computer simulationmodel to investigate past and presentenvironments in a historic house libraryis described. The model simulated fourhypothetical scenarios, based on realdata. The simulation outputs werereviewed in terms of the risk ofphysical and chemical deterioration,and their relationship with an existingnational standard for archives. Thepossibility of simulating pastenvironments to investigate naturalageing is also discussed
Population inversion in optically pumped asymmetric quantum well terahertz lasers
Intersubband carrier lifetimes and population ratios are calculated for three- and four-level optically pumped terahertz laser structures. Laser operation is based on intersubband transitions between the conduction band states of asymmetric GaAs-Ga(1 – x)Al(x)As quantum wells. It is shown that the carrier lifetimes in three-level systems fulfill the necessary conditions for stimulated emission only at temperatures below 200 K. The addition of a fourth level, however, enables fast depopulation of the lower laser level by resonant longitudinal optical phonon emission and thus offers potential for room temperature laser operation. © 1997 American Institute of Physics
Global MHD simulations of Saturns's magnetosphere at the time of Cassini approach
We present the results of a 3D global magnetohydrodynamic simulation of the magnetosphere of Saturn for the period of Cassini's initial approach and entry into the magnetosphere. We compare calculated bow shock and magnetopause locations with the Cassini measurements. In order to match the measured locations we use a substantial mass source due to the icy satellites (\sim1 x 10^{28} s^{-1} of water product ions). We find that the location of bow shock and magnetopause crossings are consistent with previous spacecraft measurements, although Cassini encountered the surfaces further from Saturn than the previously determined average location. In addition, we find that the shape of the model bow shock and magnetopause have smaller flaring angles than previous models and are asymmetric dawn-to-dusk. Finally, we find that tilt of Saturn's dipole and rotation axes results in asymmetries in the bow shock and magnetopause and in the magnetotail being hinged near Titan's orbit (\sim20 R _S)
Fatty-acid uptake in prostate cancer cells using dynamic microfluidic raman technology
It is known that intake of dietary fatty acid (FA) is strongly correlated with prostate cancer progression but is highly dependent on the type of FAs. High levels of palmitic acid (PA) or arachidonic acid (AA) can stimulate the progression of cancer. In this study, a unique experimental set-up consisting of a Raman microscope, coupled with a commercial shear-flow microfluidic system is used to monitor fatty acid uptake by prostate cancer (PC-3) cells in real-time at the single cell level. Uptake of deuterated PA, deuterated AA, and the omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) were monitored using this new system, while complementary flow cytometry experiments using Nile red staining, were also conducted for the validation of the cellular lipid uptake. Using this novel experimental system, we show that DHA and EPA have inhibitory effects on the uptake of PA and AA by PC-3 cells
Suppression of electron relaxation and dephasing rates in quantum dots caused by external magnetic fields
An external magnetic field has been applied in laterally coupled dots (QDs)
and we have studied the QD properties related to charge decoherence. The
significance of the applied magnetic field to the suppression of
electron-phonon relaxation and dephasing rates has been explored. The coupled
QDs have been studied by varing the magnetic field and the interdot distance as
other system parameters. Our numerical results show that the electron
scattering rates are strongly dependent on the applied external magnetic field
and the details of the double QD configuration.Comment: 13 pages, 6 figure
Establishing Social Work Practices in England: The Early Evidence
Social Work Practices (SWPs) were established in England in 2009 to deliver social work services to looked after children and care leavers. The introduction of independent social work-led organisations generated controversy focused on issues such as the privatisation of children's services and social workers' conditions of employment. This paper reports early findings from the evaluation of four of these pilots, drawing on interviews with children and young people, staff, and local authority and national stakeholders. The SWPs assumed a variety of organisational forms. The procurement process was demanding, with protracted negotiations over matters such as budgetary control and providing a round-the-clock service. Start-up was facilitated by an established relationship between the SWP provider and the local authority. Once operational, SWPs continued to rely on local authorities for various functions; in most cases, local authorities retained control of placement budgets. Levels of consultation and choice offered to children and young people regarding the move to an SWP varied considerably. Children's understanding about SWPs was generally low except in the pilot where most children retained their original social worker. These early findings show some dilution of the original SWP model, while the pilots' diversity allows the benefits of particular models to emerge
Cooling of cryogenic electron bilayers via the Coulomb interaction
Heat dissipation in current-carrying cryogenic nanostructures is problematic
because the phonon density of states decreases strongly as energy decreases. We
show that the Coulomb interaction can prove a valuable resource for carrier
cooling via coupling to a nearby, cold electron reservoir. Specifically, we
consider the geometry of an electron bilayer in a silicon-based
heterostructure, and analyze the power transfer. We show that across a range of
temperatures, separations, and sheet densities, the electron-electron
interaction dominates the phonon heat-dissipation modes as the main cooling
mechanism. Coulomb cooling is most effective at low densities, when phonon
cooling is least effective in silicon, making it especially relevant for
experiments attempting to perform coherent manipulations of single spins.Comment: 9 pages, 5 figure
Polar optical phonon scattering and negative Kromer-Esaki-Tsu differential conductivity in bulk GaN
Cataloged from PDF version of article.GaN is being considered as a viable alternative semiconductor for high-power solid-state electronics. This creates a demand for the characterization of the main scattering channel at high electric fields. The dominant scattering mechanism for carriers reaching high energies under the influence of very high electric fields is the polar optical phonon (POP) emission. To highlight the directional variations, we compute POP emission rates along high-symmetry directions for the zinc-blende and wurtzite crystal phases of GaN. Our treatment relies on the empirical pseudopotential energies and wave functions. The scattering rates are efficiently computed using the Lehmann-Taut Brillouin zone integration technique. For both crystal phases, we also consider the negative differential conductivity possibilities associated with the negative effective mass part of the band structure. (C) 2001 Elsevier Science B.V. All rights reserved
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