3,285 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
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
A structural study of PrCrO3 under extreme conditions: a comparison with the effects of doping
Ultrafast Hot Carrier Dynamics in GaN and its Impact on the Efficiency Droop
GaN is a key material for lighting technology. Yet, the carrier transport and
ultrafast dynamics that are central in GaN light emitting devices are not
completely understood. We present first-principles calculations of carrier
dynamics in GaN, focusing on electron-phonon (e-ph) scattering and the cooling
and nanoscale dynamics of hot carriers. We find that e-ph scattering is
significantly faster for holes compared to electrons, and that for hot carriers
with an initial 0.51 eV excess energy, holes take a significantly shorter
time (0.1 ps) to relax to the band edge compared to electrons, which take
1 ps. The asymmetry in the hot carrier dynamics is shown to originate
from the valence band degeneracy, the heavier effective mass of holes compared
to electrons, and the details of the coupling to different phonon modes in the
valence and conduction bands. We show that the slow cooling of hot electrons
and their long ballistic mean free paths (over 3 nm) are a possible cause of
efficiency droop in GaN light emitting diodes. Taken together, our work sheds
light on the ultrafast dynamics of hot carriers in GaN and the nanoscale origin
of efficiency droop.Comment: Submitted, 10 pages, 4 figure
Anisotropic charge transport in non-polar GaN QW: polarization induced charge and interface roughness scattering
Charge transport in GaN quantum well (QW) devices grown in non-polar
direction has been theoretically investigated . Emergence of anisotropic line
charge scattering mechanism originating as a result of anisotropic rough
surface morphology in conjunction with in-plane built-in polarization has been
proposed. It has shown that in-plane growth anisotropy leads to large
anisotropic carrier transport at low temperatures. At high temperatures, this
anisotropy in charge transport is partially washed out by strong isotropic
optical phonon scattering in GaN QW.Comment: 4 pages, 4 figure
The effect of ring current electron scattering rates on magnetosphereâionosphere coupling
This simulation study investigated the electrodynamic impact of varying descriptions of the diffuse aurora on the magnetosphereâionosphere (MâI) system. Pitch angle diffusion caused by waves in the inner magnetosphere is the primary source term for the diffuse aurora, especially during storm time. The magnetic local time (MLT) and stormâdependent electrodynamic impacts of the diffuse aurora were analyzed using a comparison between a new selfâconsistent version of the Hot Electron Ion Drift Integrator with varying electron scattering rates and real geomagnetic storm events. The results were compared with Dst and hemispheric power indices, as well as auroral electron flux and crossâtrack plasma velocity observations. It was found that changing the maximum lifetime of electrons in the ring current by 2â6Â h can alter electric fields in the nightside ionosphere by up to 26%. The lifetime also strongly influenced the location of the aurora, but the model generally produced aurora equatorward of observations.Key PointsA ring current model is updated to include selfâconsistent auroral precipitation in its electric field solverThe electron scattering rate controls where conductance producing aurora is altering the entire electrodynamic systemFor best results, ring current models should include a selfâelectric field, including both diffuse and discrete auroraPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137355/1/jgra53401_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137355/2/jgra53401.pd
Breast biopsy pathology request forms: are the radiologists completing them correctly and legibly?
Surface scattering velocities in III-nitride quantum well laser structures via the emission of hybrid phonons
We have theoretically and numerically studied nitride-based quantum well (QW)
laser structures. More specifically, we have used a QW made with III-nitride
where the width of the barrier region is large relative to the electron mean
free path, and we have calculated the electron surface capture velocities by
considering an electron flux which is captured into the well region. The
process is assisted by the emission of the longitudinal optical phonons as
predicted by the hybrid (HB) model. The results of surface capture velocities
via the emission of HB phonons are compared to the emission of the dielectric
continuum phonons (Zakhleniuk et al 1999 Phys. Status Solidi a 176 79). Our
investigation shows that the two different phonon models predict almost the
same results for the non-retarded limit. Furthermore, the surface capture
velocities strongly depend on the size of the structure and the heterostructure
materials. Lastly, a comparison to the recent experimental values shows that
our model could accurately describe the experimentally measured parameters of
the quantum capture processes
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