9,946 research outputs found
Special Pyrheliometer Shroud Development
To insure that the insolation values accurately represent the input power to a power conversion unit the field of view (FOV) of the concentrator aperture and the insolation radiometer must be the same. The calculations, implementation, and results of this approach are covered. Three instruments were used to measure the insolation: an Eppley Normal Incidence Radiometer (NIP) and two versions of the kendall cavity radiometer. The shrouds used to limit the FOV of the radiometers were designed to simulate the FOV of the PDC-1 concentrater with the cold water cavity calorimeter. This technique of matching the FOV of an insolation radiometer to the FOV of a specific concentrater and receiver aperture appears to be both practical and effective. The efficiency of a power conversion unit will be too low if the insolation is measured with a radiometer which has a FOV which is larger than the FOV of the concentrator
Radiowave scattering and ultra-long-baseline interferometry
Interstellar scattering can irretrievably blur the images of compact radio sources when examined with extremely high resolution. Because of this effect, diffraction limited observations of extragalactic sources with an Earth-Moon baseline will only be possible at frequencies above about 7 GHz, in which case the resolution will be approx. = to or less than 20 microarcsec. Preliminary observations to determine the potential usefulness of such resolving power are discussed. The simplest of these would consist of a search for interstellar scintillations in compact sources at 10 GHz, which would provide an effective resolution about equal to that of an Earth-Moon baseline at this frequency. Also important in this context is the development of very long baseline interferometry in near-Earth orbit, as any ultra high resolution observations, if appropriate, would require intermediate baselines for mapping
On the infrared polarization of the Orion Nebula
The implications of the 10 micron polarization of the Orion Nebula were re-examined. The polarization was produced by preferential extinction in one of the well studied regions of the Kleinman-Low Nebula and/or its surroundings. In particular, the need for abnormally low temperatures in the polarizing medium was obviated. The most likely candidate for the polarizing medium was the extended region surrounding the Kleinman-Low Nebula. The degree of polarization produced by emission in the far infrared was estimated to be as large as 8 percent, although other factors could reduce the observable value
Memory systems for signal generating photoelectric image detectors
Digital systems are discussed which have the capacity to handle the large amounts of information contained in a typical image. It was used with a high gain pulse counting television camera tube, with a silicon target image detector and an analog to digital converter between the detector and the memory
Active galactic nuclei at gamma-ray energies
Active Galactic Nuclei can be copious extragalactic emitters of MeV-GeV-TeV
gamma rays, a phenomenon linked to the presence of relativistic jets powered by
a super-massive black hole in the center of the host galaxy. Most of gamma-ray
emitting active galactic nuclei, with more than 1500 known at GeV energies, and
more than 60 at TeV energies, are called "blazars". The standard blazar
paradigm features a jet of relativistic magnetized plasma ejected from the
neighborhood of a spinning and accreting super-massive black hole, close to the
observer direction. Two classes of blazars are distinguished from observations:
the flat-spectrum radio-quasar class (FSRQ) is characterized by strong external
radiation fields, emission of broad optical lines, and dust tori. The BL Lac
class (from the name of one of its members, BL Lacertae) corresponds to weaker
advection-dominated flows with gamma-ray spectra dominated by the inverse
Compton effect on synchrotron photons. This paradigm has been very successful
for modeling the broadband spectral energy distributions of blazars. However,
many fundamental issues remain, including the role of hadronic processes and
the rapid variability of those BL Lac objects whose synchrotron spectrum peaks
at UV or X-ray frequencies. A class of gamma-ray--emitting radio galaxies,
which are thought to be the misaligned counterparts of blazars, has emerged
from the results of the Fermi-Large Area Telescope and of ground-based
Cherenkov telescopes. Blazars and their misaligned ounterparts make up most of
the >100 MeV extragalactic gamma ray background (EGB), and are uspected of
being the sources of ultra-high energy cosmic rays. The future "Cherenkov
Telescope Array", in synergy with the Fermi-Large Area Telescope and a wide
range of telescopes in space and on he ground, will write the next chapter of
blazar physics.Comment: 27 pages, 28 figures, in a topical review on gamma-ray astronomy
above 100 MeV, to be published in Comptes Rendus Physique de l'Acad\'emie des
Sciences (CRAS
The role of C-terminal amidation in the membrane interactions of the anionic antimicrobial peptide, maximin H5
Maximin H5 is an anionic antimicrobial peptide from amphibians, which carries a C-terminal amide moiety, and was found to be moderately haemolytic (20%). The α-helicity of the peptide was 42% in the presence of lipid mimics of erythrocyte membranes and was found able to penetrate (10.8mNm(-1)) and lyse these model membranes (64 %). In contrast, the deaminated peptide exhibited lower levels of haemolysis (12%) and α-helicity (16%) along with a reduced ability to penetrate (7.8mNm(-1)) and lyse (55%) lipid mimics of erythrocyte membranes. Taken with molecular dynamic simulations and theoretical analysis, these data suggest that native maximin H5 primarily exerts its haemolytic action via the formation of an oblique orientated α-helical structure and tilted membrane insertion. However, the C-terminal deamination of maximin H5 induces a loss of tilted α-helical structure, which abolishes the ability of the peptide's N-terminal and C-terminal regions to H-bond and leads to a loss in haemolytic ability. Taken in combination, these observations strongly suggest that the C-terminal amide moiety carried by maximin H5 is required to stabilise the adoption of membrane interactive tilted structure by the peptide. Consistent with previous reports, these data show that the efficacy of interaction and specificity of maximin H5 for membranes can be attenuated by sequence modification and may assist in the development of variants of the peptide with the potential to serve as anti-infective
Schwarzschild-de Sitter Spacetimes, McVittie Coordinates, and Trumpet Geometries
Trumpet geometries play an important role in numerical simulations of black
hole spacetimes, which are usually performed under the assumption of asymptotic
flatness. Our Universe is not asymptotically flat, however, which has motivated
numerical studies of black holes in asymptotically de Sitter spacetimes. We
derive analytical expressions for trumpet geometries in Schwarzschild-de Sitter
spacetimes by first generalizing the static maximal trumpet slicing of the
Schwarzschild spacetime to static constant mean curvature trumpet slicings of
Schwarzschild-de Sitter spacetimes. We then switch to a comoving isotropic
radial coordinate which results in a coordinate system analogous to McVittie
coordinates. At large distances from the black hole the resulting metric
asymptotes to a Friedmann-Lemaitre-Robertson-Walker metric with an
exponentially-expanding scale factor. While McVittie coordinates have another
asymptotically de Sitter end as the radial coordinate goes to zero, so that
they generalize the notion of a "wormhole" geometry, our new coordinates
approach a horizon-penetrating trumpet geometry in the same limit. Our
analytical expressions clarify the role of time-dependence, boundary conditions
and coordinate conditions for trumpet slices in a cosmological context, and
provide a useful test for black hole simulations in asymptotically de Sitter
spacetimes.Comment: 7 pages, 3 figures, added referenc
Micro-Perspectives on 19th-century Russian Living Standards
Russia, livings standards, economic history
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