10,605 research outputs found
Magnet Laboratory Research
Contains research objectives and reports on three research projects
Electrical and Optical Performance Characteristics of p/n InGaAs Monolithic Interconnected Modules
There has been a traditional trade-off in ThermoPhotoVoltaic (TPV) energy conversion development between system efficiency and power density. This trade-off originates from the use of front surface spectral controls such as selective emitters and various types of filters. A Monolithic Interconnected Module (MIM) structure has been developed which allows for both high power densities and high system efficiencies. The MIM device consists of many individual Indium Gallium Arsenide (InGaAs) devices series-connected on a single semi-insulating Indium Phosphide (InP) substrate. The MIMs are exposed to the entire emitter output, thereby maximizing output power density. An InfraRed (IR) reflector placed on the rear surface of the substrate returns the unused portion of the emitter output spectrum back to the emitter for recycling, thereby providing for high system efficiencies. Initial MIM development has focused on a 1 sq cm device consisting of eight (8) series interconnected cells. MIM devices, produced from 0.74eV InGaAs, have demonstrated V(sub infinity) = 3.2 volts, J(sub sc) = 70 mA/sq cm and a fill factor of 66% under flashlamp testing. IR reflectance measurements (greater than 2 microns) of these devices indicate a reflectivity of greater than 82%. MIM devices produced from 0.55 eV InGaAs have also been demonstrated. In addition, conventional p/n InGaAs devices with record efficiencies (11.7% AM0) have been demonstrated
Nuclear Magnetic Resonance and Hyperfine Structure
Contains reports on three research projects
Magnet Laboratory Research
Contains reports on five research projects.United States Atomic Energy Commission (Contract AT(30-1)-1283
Chandra Orion Ultradeep Project: Observations and Source Lists
We present a description of the data reduction methods and the derived
catalog of more than 1600 X-ray point sources from the exceptionally deep
January 2003 Chandra X-ray Observatory observation of the Orion Nebula Cluster
and embedded populations around OMC-1. The observation was obtained with
Chandra's Advanced CCD Imaging Spectrometer (ACIS) and has been nicknamed the
Chandra Orion Ultradeep Project (COUP). With an 838 ks exposure made over a
continuous period of 13.2 days, the COUP observation provides the most uniform
and comprehensive dataset on the X-ray emission of normal stars ever obtained
in the history of X-ray astronomy.Comment: 52 pages, 11 figures, 12 tables. Accepted for publication in ApJS,
special issue dedicated to Chandra Orion Ultradeep Project. A version with
high quality figures can be found at
http://www.astro.psu.edu/users/gkosta/COUP_Methodology.pd
Chandra X-ray Observation of the Orion Nebula Cluster. II Relationship between X-ray activity indicators and stellar parameters
Using the results of our first paper on the Chandra HRC observation of the
Orion Nebula Cluster (ONC), here we explore the relation between the coronal
activity of its 1-Myr-old pre-main sequence population and stellar parameters.
We find that median X-ray luminosities of low mass stars (M/M_sun < 3) increase
with increasing mass and decreasing stellar age. Brown dwarfs (0.03 < M/M_sun <
0.08) follow the same trend with mass. From M~0.1 to M~0.5M_sun, median
L_X/L_bol values increase by about half an order of magnitude and then remain
constant at ~10^-3.5 for the mass range from 0.5 to 3.0 M/M_sun. In these same
two mass ranges, L_X/L_bol remains roughly constant with age, until it drops by
more than two orders of magnitudes at the epoch when ~2-4M_sun stars are
expected to become fully radiative.
We find a dependence of L_X and L_X/L_bol on circumstellar accretion
indicators and suggest three possible hypotheses for its origin. In spite of
improved X-ray and rotational data, correlations between activity indicators
and rotation remain elusive for these stars, possibly indicating that stars for
which rotational periods have been measured have reached some saturation level.
Our study of X-ray activity vs. stellar mass leads us to propose that the few
HRC X-ray sources not associated with any optical/infrared counterpart trace a
yet to be discovered stellar population of deeply embedded, relatively massive
ONC members.Comment: 31 pages, 17 figures; to be published in Ap
Neighbourhood, Route and Workplace-Related Environmental Characteristics Predict Adults' Mode of Travel to Work
Commuting provides opportunities for regular physical activity which can reduce the risk of chronic disease. Commuters' mode of travel may be shaped by their environment, but understanding of which specific environmental characteristics are most important and might form targets for intervention is limited. This study investigated associations between mode choice and a range of objectively assessed environmental characteristics.Participants in the Commuting and Health in Cambridge study reported where they lived and worked, their usual mode of travel to work and a variety of socio-demographic characteristics. Using geographic information system (GIS) software, 30 exposure variables were produced capturing characteristics of areas around participants' homes and workplaces and their shortest modelled routes to work. Associations between usual mode of travel to work and personal and environmental characteristics were investigated using multinomial logistic regression.Of the 1124 respondents, 50% reported cycling or walking as their usual mode of travel to work. In adjusted analyses, home-work distance was strongly associated with mode choice, particularly for walking. Lower odds of walking or cycling rather than driving were associated with a less frequent bus service (highest versus lowest tertile: walking OR 0.61 [95% CI 0.20–1.85]; cycling OR 0.43 [95% CI 0.23–0.83]), low street connectivity (OR 0.22, [0.07–0.67]; OR 0.48 [0.26–0.90]) and free car parking at work (OR 0.24 [0.10–0.59]; OR 0.55 [0.32–0.95]). Participants were less likely to cycle if they had access to fewer destinations (leisure facilities, shops and schools) close to work (OR 0.36 [0.21–0.62]) and a railway station further from home (OR 0.53 [0.30–0.93]). Covariates strongly predicted travel mode (pseudo r-squared 0.74).Potentially modifiable environmental characteristics, including workplace car parking, street connectivity and access to public transport, are associated with travel mode choice, and could be addressed as part of transport policy and infrastructural interventions to promote active commuting
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