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

Exploring the efficacy of different electric field models in driving a model of the plasmasphere

The dynamics of the plasmasphere are strongly controlled by the inner magnetospheric electric field. In order to capture realistically the erosion of the nightside plasmapause and the formation of the drainage plume in a model of the plasmasphere, the electric field must be accurate. This study investigates how well five different electric field models drive the Dynamic Global Core Plasma Model during eight storm periods. The five electric field models are the Volland‐Stern analytic formula with Maynard‐Chen Kp dependence, two versions of the Weimer statistical models (96 and 05), and two versions of the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) technique using magnetometer and DMSP satellite data. Manually extracted plasmapause locations from images taken by the EUV instrument on the Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) satellite, as described by Goldstein et al. (2005), were compared to the simulation results throughout the main phase of the eight events. Three methods of calculating the plasmapause were employed to determine the best fit to EUV data, using the maximum gradient, a constant density contour (fit method), and the location in which the modeled density fell significantly below the specified saturation density for the given radial position (saturation method). It was found that the simulations driven by the Weimer (1996) model produced the best fit overall and that the fit and saturation methods worked best for matching the model results to the observations. Key Points The Weimer [1996] model works quite well for driving the plasmasphere A saturation technique for determining the plasmapause location in introduced Plasmapause determined by IMAGE may not be the steepest gradient in densityPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108010/1/jgra51094.pd

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 0.5$-$1 eV excess energy, holes take a significantly shorter time ($\sim$0.1 ps) to relax to the band edge compared to electrons, which take $\sim$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

What controls the recent changes in African mineral dust aerosol across the Atlantic?

Dust from Africa strongly perturbs the radiative balance over the Atlantic, with emissions that are highly variable from year to year. We show that the aerosol optical depth (AOD) of dust over the mid-Atlantic observed by the AVHRR satellite has decreased by approximately 10% per decade from 1982 to 2008. This downward trend persists through both winter and summer close to source and is also observed in dust surface concentration measurements downwind in Barbados during summer. The GEOS-Chem model, driven with MERRA re-analysis meteorology and using a new dust source activation scheme, reproduces the observed trend and is used to quantify the factors contributing to this trend and the observed variability from 1982 to 2008. We find that changes in dustiness over the east mid-Atlantic are almost entirely mediated by a reduction in surface winds over dust source regions in Africa and are not directly linked with changes in land use or vegetation cover. The global mean all-sky direct radiative effect (DRE) of African dust is −0.18 Wm−2 at top of atmosphere, accounting for 46% of the global dust total, with a regional DRE of −7.4 ± 1.5 Wm−2 at the surface of the mid-Atlantic, varying by over 6.0 Wm−2 from year to year, with a trend of +1.3 Wm−2 per decade. These large interannual changes and the downward trend highlight the importance of climate feedbacks on natural aerosol abundance. Our analysis of the CMIP5 models suggests that the decreases in the indirect anthropogenic aerosol forcing over the North Atlantic in recent decades may be responsible for the observed climate response in African dust, indicating a potential amplification of anthropogenic aerosol radiative impacts in the Atlantic via natural mineral dust aerosol.Massachusetts Institute of Technology (Charles E. Reed Faculty Initiative Fund)National Science Foundation (U.S.) (AGS-1238109)National Science Foundation (U.S.) (AGS- 0962256)National Science Foundation (U.S.) (NASA NNX12AP45G

The effect of ring current electron scattering rates on magnetosphere‐ionosphere coupling

This simulation study investigated the electrodynamic impact of varying descriptions of the diffuse aurora on the magnetosphere‐ionosphere (M‐I) 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 storm‐dependent electrodynamic impacts of the diffuse aurora were analyzed using a comparison between a new self‐consistent 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 cross‐track plasma velocity observations. It was found that changing the maximum lifetime of electrons in the ring current by 2–6 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 self‐consistent 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 self‐electric 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

Spin Readout and Initialization in a Semiconductor Quantum Dot

Electron spin qubits in semiconductors are attractive from the viewpoint of long coherence times. However, single spin measurement is challenging. Several promising schemes incorporate ancillary tunnel couplings that may provide unwanted channels for decoherence. Here, we propose a novel spin-charge transduction scheme, converting spin information to orbital information within a single quantum dot by microwave excitation. The same quantum dot can be used for rapid initialization, gating, and readout. We present detailed modeling of such a device in silicon to confirm its feasibility.Comment: Published versio

Energy bands, conductance and thermoelectric power for ballistic electrons in a nanowire with spin-orbit interaction

We calculated the effects of spin-orbit interaction (SOI) on the energy bands, ballistic conductance and the electron-diffusion thermoelectric power of a nanowire by varying the temperature, electron density and width of the wire. The potential barriers at the edges of the wire are assumed to be very high. A consequence of the boundary conditions used in this model is determined by the energy band structure, resulting in wider plateaus when the electron density is increased due to larger energy-level separation as the higher subbands are occupied by electrons. The nonlinear dependence of the transverse confinement on position with respect to the well center excludes the "pole-like feature" in the conductance which is obtained when a harmonic potential is employed for confinement. At low temperature, the electron diffusion thermoelectric power increases linearly with T but deviates from the linear behavior for large values of T.Comment: Updated corrected version of the original submissio

Conceptualising ethical capital in social enterprises

Purpose – In popular culture, ethics and morality are topical (Giroux 1994), heightened by recent attention to the banking industry and pay awards, monopoly capitalism, global warming and sustainability. Yet, surprisingly, little attention is given to these in the narrative of the conceptualisation of social enterprise or social entrepreneurship – nor in the academic research on the sector. Current conceptualisations of social enterprise fail to fully satisfy the spirit of the movement which advances a narrative that social enterprises: are more like businesses than voluntary organisations; are more entrepreneurial than public service delivery; use business models but are not just in it for the money. A focus on the economic implies a business model where deep tensions lie. A focus on social capital offers a different frame of reference, yet both these conceptualisations fail to fully identify the phenomenon that is social enterprise. The objective of this paper is to fill that gap. Ethical capital is offered here as an alternative and unrecognised conceptualisation in the field of social enterprise. Design/methodology/approach – This paper is exploratory in nature - a tentative piece of theorising that brings together the authors‟ perspectives on ethical capital to offer a new frame of reference on social enterprise. It sets out to investigate some of the issues in order to provoke further research. As authors, we felt it important to theoretically explore the concept and discuss several themes to provoke a response. All need further research to tease out the detail. We start by outlining the current conceptualisations of social enterprise, then move on to theorising ethical capital using three broad themes; theme 1 discusses the levels of ethical capital, bridging from the private sector into the social sector. Theme 2 deconstructs the ethics of social enterprise and theme 3 questions moral agency through a conventional and enforcing enterpriser or the greater good through a critical and creative moral enterpriser. Findings – This paper very much aims at starting the process of intellectual debate about the notion of ethical capital in social enterprises. The conclusions of this paper outline further research questions that need to be addressed in order to fully develop this concept. Originality/value – It is argued that the current ideology of the neo-classical economic paradigm pursues interests towards the self and erodes the moral basis of association. The outcome leaves society with a problem of low ethical virtue. The implications of this paper are that social enterprises maximise ethical virtue beyond any other form of organisation and as such create value beyond their missions and values. This paper offers value in the understanding of social enterprise through fresh insight into its conceptualisation. A critical perspective is adopted toward the current literature. This paper sheds new light on our understanding of the sector, providing practitioners, business support agencies and academics alike with a conceptualisation that has not been explored before