14,127 research outputs found
Constraints on Lorentz Invariance Violation using INTEGRAL/IBIS observations of GRB041219A
One of the experimental tests of Lorentz invariance violation is to measure
the helicity dependence of the propagation velocity of photons originating in
distant cosmological obejcts. Using a recent determination of the distance of
the Gamma-Ray Burst GRB 041219A, for which a high degree of polarization is
observed in the prompt emission, we are able to improve by 4 orders of
magnitude the existing constraint on Lorentz invariance violation, arising from
the phenomenon of vacuum birefringence.Comment: 5 pages, 3 figures, accepted for publication as a Rapid Communication
in Physical Review
Multiple sclerosis and the risk of infection: considerations in the threat of the novel coronavirus, COVID-19/SARS-CoV-2
ZEN2: a narrow J-band search for z∼ 9 Lyα emitting galaxies directed towards three lensing clusters
We present the results of a continuing survey to detect Lyα emitting galaxies at redshifts z∼ 9: the ‘z equals nine' (ZEN) survey. We have obtained deep VLT Infrared Spectrometer and Array Camera observations in the narrow J-band filter NB119 directed towards three massive lensing clusters: Abell clusters 1689, 1835 and 114. The foreground clusters provide a magnified view of the distant Universe and permit a sensitive test for the presence of very high redshift galaxies. We search for z∼ 9 Lyα emitting galaxies displaying a significant narrow-band excess relative to accompanying J-band observations that remain undetected in Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) optical images of each field. No sources consistent with this criterion are detected above the unlensed 90 per cent point-source flux limit of the narrow-band image, FNB= 3.7 × 10−18erg s−1cm−2. To date, the total coverage of the ZEN survey has sampled a volume at z∼ 9 of approximately 1700 comoving Mpc3 to a Lyα emission luminosity of 1043erg s−1. We conclude by considering the prospects for detecting z∼ 9 Lyα emitting galaxies in light of both observed galaxy properties at z
Airborne measurements of cloud-forming nuclei and aerosol particles in stabilized ground clouds produced by solid rocket booster firings
Airborne measurements of cloud volumes, ice nuclei and cloud condensation nuclei, liquid particles, and aerosol particles were obtained from stabilized ground clouds (SGCs) produced by Titan 3 launches at Kennedy Space Center, 20 August and 5 September 1977. The SGCs were bright, white, cumulus clouds early in their life and contained up to 3.5 g/m3 of liquid in micron to millimeter size droplets. The measured cloud volumes were 40 to 60 cu km five hours after launch. The SGCs contained high concentrations of cloud condensation nuclei active at 0.2%, 0.5%, and 1.0% supersaturation for periods of three to five hours. The SGCs also contained high concentrations of submicron particles. Three modes existed in the particle population: a 0.05 to 0.1 micron mode composed of aluminum-containing particles, a 0.2 to 0.8 micron mode, and a 2.0 to 10 micron mode composed of particles that contained primarily aluminum
Gas Purity effect on GEM Performance in He and Ne at Low Temperatures
The performance of Gas Electron Multipliers (GEMs) in gaseous He, Ne, He+H2
and Ne+H2 was studied at temperatures in the range of 3-293 K. This paper
reports on previously published measurements and additional studies on the
effects of the purity of the gases in which the GEM performance is evaluated.
In He, at temperatures between 77 and 293 K, triple-GEM structures operate at
rather high gains, exceeding 1000. There is an indication that this high gain
is achieved through the Penning effect as a result of impurities in the gas. At
lower temperatures the gain-voltage characteristics are significantly modified
probably due to the freeze-out of these impurities. Double-GEM and single-GEM
structures can operate down to 3 K at gains reaching only several tens at a gas
density of about 0.5 g/l; at higher densities the maximum gain drops further.
In Ne, the maximum gain also drops at cryogenic temperatures. The gain drop in
Ne at low temperatures can be re-established in Penning mixtures of Ne+H2: very
high gains, exceeding 104, have been obtained in these mixtures at 30-77 K, at
a density of 9.2 g/l which corresponds to saturated Ne vapor density at 27 K.
The addition of small amounts of H2 in He also re-establishes large GEM gains
above 30 K but no gain was observed in He+H2 at 4 K and a density of 1.7 g/l
(corresponding to roughly one-tenth of the saturated vapor density). These
studies are, in part, being pursued in the development of two-phase He and Ne
detectors for solar neutrino detection.Comment: 4 pages, 7 figure
Applications of ethylene vinyl acetate as an encapsulation material for terrestrial photovoltaic modules
Terrestrial photovoltaic modules must undergo substantial reductions in cost in order to become economically attractive as practical devices for large scale production of electricity. Part of the cost reductions must be realized by the encapsulation materials that are used to package, protect, and support the solar cells, electrical interconnects, and other ancillary components. As many of the encapsulation materials are polymeric, cost reductions necessitate the use of low cost polymers. The performance and status of ethylene vinyl acetate, a low cost polymer that is being investigated as an encapsulation material for terrestrial photovoltaic modules, are described
ZEN and the search for high-redshift galaxies
We present the ZEN (z equals nine) survey: a deep, narrow J-band search for
proto-galactic Lya emission at redshifts z=9. In the first phase of the survey,
dubbed ZEN1, we combine an exceptionally deep image of the Hubble Deep Field
South, obtained using a narrow band filter centred on the wavelength 1.187
microns, with existing deep, broad band images covering optical to near
infrared wavelengths. Candidate z=9 Lya-emitting galaxies display a significant
narrow band excess relative to the Js-band that are undetected at optical
wavelengths. We detect no sources consistent with this criterion to the 90%
point source flux limit of the NB image, F_NB = 3.28e-18 ergs/s/cm2. The survey
selection function indicates that we have sampled a volume of approximately 340
h^{-3} Mpc3 to a Lya emission luminosity of 10e43 h^{-2} ergs/s. When compared
to the predicted properties of z=9 galaxies based upon no evolution of observed
z=6 Lya-emitting galaxies, the `volume shortfall' of the current survey, i.e.
the volume required to detect this putative population, is a factor of at least
8 to 10. We also discuss continuing narrow J-band imaging surveys that will
reduce the volume shortfall factor to the point where the no-evolution
prediction from z=6 is probed in a meaningful manner.Comment: To appear in proceedings of UC Irvine May 2005 workshop on "First
Light & Reionization", eds. E. Barton & A. Cooray, New Astronomy Reviews, in
pres
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