5,571 research outputs found
Effects of low energy proton, electron, and simultaneously combined proton and electron environments in silicon and GaAs solar cells
Degradation of silicon and GaAs solar cells due to exposures to low energy proton and electron environments and annealing data for these cells are discussed. Degradation of silicon cells in simultaneously combined electron and low energy proton environments and previous experimental work is summarized and evaluated. The deficiencies in current solar array damage prediction techniques indicated by these data and the relevance of these deficiencies to specific missions such as intermediate altitude orbits and orbital transfer vehicles using solar electric propulsion systems are considered
Radioisotope thermal photovoltaic application of the GaSb solar cell
An examination of a RTVP (radioisotopic thermophotovoltaic) conceptual design has shown a high potential for power densities well above those achievable with radioisotopic thermoelectric generator (RTG) systems. An efficiency of 14.4 percent and system specific power of 9.25 watts/kg were predicted for a system with sixteen GPHS (general purpose heat source) sources operating at 1100 C. The models also showed a 500 watt system power by the strontium-90 isotope at 1200 C at an efficiency of 17.0 percent and a system specific power of 11.8 watts/kg. The key to this level of performance is a high-quality photovoltaic cell with narrow bandgap and a reflective rear contact. Recent work at Boeing on GaSb cells and transparent back GaAs cells indicate that such a cell is well within reach
Interference and complementarity for two-photon hybrid entangled states
In this work we generate two-photon hybrid entangled states (HES), where the
polarization of one photon is entangled with the transverse spatial degree of
freedom of the second photon. The photon pair is created by parametric
down-conversion in a polarization-entangled state. A birefringent double-slit
couples the polarization and spatial degrees of freedom of these photons and
finally, suitable spatial and polarization projections generate the HES. We
investigate some interesting aspects of the two-photon hybrid interference, and
present this study in the context of the complementarity relation that exists
between the visibilities of the one- and two-photon interference patterns.Comment: 10 pages, 4 figures. Accepted in Physical Review
A search for starlight reflected from HD 75289 b
We have used a doppler tomographic analysis to conduct a deep search for the
starlight reflected from the planetary companion to HD 75289. In 4 nights on
VLT2/UVES in January 2003, we obtained 684 high resolution echelle spectra with
a total integration time of 26 hours. We establish an upper limit on the
planet's geometric albedo p < 0.12 (to the 99.9% significance level) at the
most probable orbital inclination i ~ 60 degrees, assuming a grey albedo, a
Venus-like phase function and a planetary radius R_p = 1.6 R_Jup. We are able
to rule out some combinations of the predicted planetary radius and atmospheric
albedo models with high, reflective cloud decks.Comment: 5 pages, 5 figures, MNRAS accepted 12 Oct 200
Proposal to demonstrate the non-locality of Bohmian mechanics with entangled photons
Bohmian mechanics reproduces all statistical predictions of quantum
mechanics, which ensures that entanglement cannot be used for superluminal
signaling. However, individual Bohmian particles can experience superluminal
influences. We propose to illustrate this point using a double double-slit
setup with path-entangled photons. The Bohmian velocity field for one of the
photons can be measured using a recently demonstrated weak-measurement
technique. The found velocities strongly depend on the value of a phase shift
that is applied to the other photon, potentially at spacelike separation.Comment: 6 pages, 4 figure
Contamination in complex healthcare trials:the falls in care homes (FinCH) study experience
BACKGROUND: Trials are at risk of contamination bias which can occur when participants in the control group are inadvertently exposed to the intervention. This is a particular risk in rehabilitation studies where it is easy for trial interventions to be either intentionally or inadvertently adopted in control settings. The Falls in Care Homes (FinCH) trial is used in this paper as an example of a large randomised controlled trial of a complex intervention to explore the potential risks of contamination bias. We outline the FinCH trial design, present the potential risks from contamination bias, and the strategies used in the design of the trial to minimise or mitigate against this. The FinCH trial was a multi-centre randomised controlled trial, with embedded process evaluation, which evaluated whether systematic training in the use of the Guide to Action Tool for Care Homes reduced falls in care home residents. Data were collected from a number of sources to explore contamination in the FinCH trial. Where specific procedures were adopted to reduce risk of, or mitigate against, contamination, this was recorded. Data were collected from study e-mails, meetings with clinicians, research assistant and clinician network communications, and an embedded process evaluation in six intervention care homes. During the FinCH trial, there were six new falls prevention initiatives implemented outside the study which could have contaminated our intervention and findings. Methods used to minimise contamination were: cluster randomisation at the level of care home; engagement with the clinical community to highlight the risks of early adoption; establishing local collaborators in each site familiar with the local context; signing agreements with NHS falls specialists that they would maintain confidentiality regarding details of the intervention; opening additional research sites; and by raising awareness about the importance of contamination in research among participants. CONCLUSION: Complex rehabilitation trials are at risk of contamination bias. The potential for contamination bias in studies can be minimized by strengthening collaboration and dialogue with the clinical community. Researchers should recognise that clinicians may contaminate a study through lack of research expertise
A Prototype for the PASS Permanent All Sky Survey
A prototype system for the Permanent All Sky Survey (PASS) project is
presented. PASS is a continuous photometric survey of the entire celestial
sphere with a high temporal resolution. Its major objectives are the detection
of all giant-planet transits (with periods up to some weeks) across stars up to
mag 10.5, and to deliver continuously photometry that is useful for the study
of any variable stars. The prototype is based on CCD cameras with short focal
length optics on a fixed mount. A small dome to house it at Teide Observatory,
Tenerife, is currently being constructed. A placement at the antarctic Dome C
is also being considered. The prototype will be used for a feasibility study of
PASS, to define the best observing strategies, and to perform a detailed
characterization of the capabilities and scope of the survey. Afterwards, a
first partial sky surveying will be started with it. That first survey may be
able to detect transiting planets during its first few hundred hours of
operation. It will also deliver a data set around which software modules
dealing with the various scientific objectives of PASS will be developed. The
PASS project is still in its early phase and teams interested in specific
scientific objectives, in providing technical expertise, or in participating
with own observations are invited to collaborate.Comment: Accepted for Astronomische Nachrichten (special issue for 3rd Potsdam
Thinkshop 'Robotic Astronomy' in July 2004). 4 pages, 4 fig
Demonstration of the Complementarity of One- and Two-Photon Interference
The visibilities of second-order (single-photon) and fourth-order
(two-photon) interference have been observed in a Young's double-slit
experiment using light generated by spontaneous parametric down-conversion and
a photon-counting intensified CCD camera. Coherence and entanglement underlie
one-and two-photon interference, respectively. As the effective source size is
increased, coherence is diminished while entanglement is enhanced, so that the
visibility of single-photon interference decreases while that of two-photon
interference increases. This is the first experimental demonstration of the
complementarity between single- and two-photon interference (coherence and
entanglement) in the spatial domain.Comment: 21 pages, 7 figure
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