37,402 research outputs found
Local light-ray rotation
We present a sheet structure that rotates the local ray direction through an
arbitrary angle around the sheet normal. The sheet structure consists of two
parallel Dove-prism sheets, each of which flips one component of the local
direction of transmitted light rays. Together, the two sheets rotate
transmitted light rays around the sheet normal. We show that the direction
under which a point light source is seen is given by a Mobius transform. We
illustrate some of the properties with movies calculated by ray-tracing
software.Comment: 9 pages, 6 figure
Impact of thermal energy storage properties on solar dynamic space power conversion system mass
A 16 parameter solar concentrator/heat receiver mass model is used in conjunction with Stirling and Brayton Power Conversion System (PCS) performance and mass computer codes to determine the effect of thermal energy storage (TES) material property changes on overall PCS mass as a function of steady state electrical power output. Included in the PCS mass model are component masses as a function of thermal power for: concentrator, heat receiver, heat exchangers (source unless integral with heat receiver, heat sink, regenerator), heat engine units with optional parallel redundancy, power conditioning and control (PC and C), PC and C radiator, main radiator, and structure. Critical TES properties are: melting temperature, heat of fusion, density of the liquid phase, and the ratio of solid-to-liquid density. Preliminary results indicate that even though overalll system efficiency increases with TES melting temperature up to 1400 K for concentrator surface accuracies of 1 mrad or better, reductions in the overall system mass beyond that achievable with lithium fluoride (LiF) can be accomplished only if the heat of fusion is at least 800 kJ/kg and the liquid density is comparable to that of LiF (1880 kg/cu m
Bandwidth in bolometric interferometry
Bolometric Interferometry is a technology currently under development that
will be first dedicated to the detection of B-mode polarization fluctuations in
the Cosmic Microwave Background. A bolometric interferometer will have to take
advantage of the wide spectral detection band of its bolometers in order to be
competitive with imaging experiments. A crucial concern is that interferometers
are presumed to be importantly affected by a spoiling effect known as bandwidth
smearing. In this paper, we investigate how the bandwidth modifies the work
principle of a bolometric interferometer and how it affects its sensitivity to
the CMB angular power spectra. We obtain analytical expressions for the
broadband visibilities measured by broadband heterodyne and bolometric
interferometers. We investigate how the visibilities must be reconstructed in a
broadband bolometric interferometer and show that this critically depends on
hardware properties of the modulation phase shifters. Using an angular power
spectrum estimator accounting for the bandwidth, we finally calculate the
sensitivity of a broadband bolometric interferometer. A numerical simulation
has been performed and confirms the analytical results. We conclude (i) that
broadband bolometric interferometers allow broadband visibilities to be
reconstructed whatever the kind of phase shifters used and (ii) that for
dedicated B-mode bolometric interferometers, the sensitivity loss due to
bandwidth smearing is quite acceptable, even for wideband instruments (a factor
2 loss for a typical 20% bandwidth experiment).Comment: 13 pages, 14 figures, submitted to A&
Symptom lead time distribution in lung cancer:natural history and prospects for early diagnosis
A new method to search for a cosmic ray dipole anisotropy
We propose a new method to determine the dipole (and quadrupole) component of
a distribution of cosmic ray arrival directions, which can be applied when
there is partial sky coverage and/or inhomogeneous exposure. In its simplest
version it requires that the exposure only depends on the declination, but it
can be easily extended to the case of a small amplitude modulation in right
ascension. The method essentially combines a minimization of the
distribution in declination to obtain the multipolar components along the
North-South axis and a harmonic Rayleigh analysis for the components involving
the right ascension direction
Impacts of energy efficiency retrofitting measures on indoor PM concentrations across different income groups in England: a modelling study
As part of an effort to reduce carbon emissions in the UK, policies encouraging the energy-efficient retrofit of domestic properties are being implemented. Typical retrofits, including installation of insulation and double glazing can cause tightening of the building envelope which may affect indoor air quality (IAQ) impacting occupant health. Using the example of PM (an airborne pollutant with known health impacts), this study considers the influence of energy-efficient retrofits on indoor PM concentrations in domestic properties both above and below the low-income threshold (LIT) for a range of tenancies across England. Simulations using EnergyPlus and its integrated Generic Contaminant model are employed to predict indoor PM exposures from both indoor and outdoor sources in building archetypes representative of (i) the existing housing stock and (ii) a retrofitted English housing stock. The exposures of occupants for buildings occupied by groups above and below the LIT are then estimated under current conditions and following retrofits. One-way ANOVA tests were applied to clarify results and investigate differences between the various income and tenure groups. Results indicate that all tenures below the LIT experience greater indoor PM concentrations than those above, suggesting possible social inequalities driven by housing, leading to consequences for health
HST Images and Spectra of the Remnant of SN 1885 in M31
Near UV HST images of the remnant of SN 1885 (S And) in M31 show a 0"70 +-
0"05 diameter absorption disk silhouetted against M31's central bulge, at SN
1885's historically reported position. The disk's size corresponds to a linear
diameter of 2.5 +- 0.4 pc at a distance of 725 +- 70 kpc, implying an average
expansion velocity of 11000 +- 2000 km/s over 110 years. Low-dispersion FOS
spectra over 3200-4800 A; reveal that the absorption arises principally from Ca
II H & K (equivalent width ~215 A;) with weaker absorption features of Ca I
4227 A; and Fe I 3720 A;. The flux at Ca II line center indicates a foreground
starlight fraction of 0.21, which places SNR 1885 some 64 pc to the near side
of the midpoint of the M31 bulge, comparable to its projected 55 pc distance
from the nucleus. The absorption line profiles suggest an approximately
spherically symmetric, bell-shaped density distribution of supernova ejecta
freely expanding at up to 13100 +- 1500 km/s. We estimate Ca I, Ca II, and Fe I
masses of 2.9(+2.4,-0.6) x 10^-4 M_o, 0.005(+0.016,-0.002) M_o, and
0.013(+0.010,-0.005) M_o respectively. If the ionization state of iron is
similar to the observed ionization state of calcium, M_CaII/M_CaI = 16(+42,-5),
then the mass of Fe II is 0.21(+0.74,-0.08) M_o, consistent with that expected
for either normal or subluminous SN Ia.Comment: 8 pages, including 4 embedded EPS figures, emulateapj.sty style file.
Color image at http://casa.colorado.edu/~mcl/sand.shtml . Submitted to Ap
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