310 research outputs found
Über die Moderation schenller Neutronen in Polyätheylen und ihre Anwendung in der Neotronendosimetrie. EUR 4540. = The moderation of fast neutrons in polyethylene and their use in neutron dosimetry. EUR 4540.
PANIC: the new panoramic NIR camera for Calar Alto
PANIC is a wide-field NIR camera, which is currently under development for
the Calar Alto observatory (CAHA) in Spain. It uses a mosaic of four Hawaii-2RG
detectors and covers the spectral range from 0.8-2.5 micron(z to K-band). The
field-of-view is 30x30 arcmin. This instrument can be used at the 2.2m
telescope (0.45arcsec/pixel, 0.5x0.5 degree FOV) and at the 3.5m telescope
(0.23arcsec/pixel, 0.25x0.25 degree FOV). The operating temperature is about
77K, achieved by liquid Nitrogen cooling. The cryogenic optics has three flat
folding mirrors with diameters up to 282 mm and nine lenses with diameters
between 130 mm and 255 mm. A compact filter unit can carry up to 19 filters
distributed over four filter wheels. Narrow band (1%) filters can be used. The
instrument has a diameter of 1.1 m and it is about 1 m long. The weight limit
of 400 kg at the 2.2m telescope requires a light-weight cryostat design. The
aluminium vacuum vessel and radiation shield have wall thicknesses of only 6 mm
and 3 mm respectively.Comment: This paper has been presented in the SPIE of Astronomical Telescopes
and Instrumentation 2008 in Marseille (France
GRAVITY: getting to the event horizon of Sgr A*
We present the second-generation VLTI instrument GRAVITY, which currently is
in the preliminary design phase. GRAVITY is specifically designed to observe
highly relativistic motions of matter close to the event horizon of Sgr A*, the
massive black hole at center of the Milky Way. We have identified the key
design features needed to achieve this goal and present the resulting
instrument concept. It includes an integrated optics, 4-telescope, dual feed
beam combiner operated in a cryogenic vessel; near infrared wavefront sensing
adaptive optics; fringe tracking on secondary sources within the field of view
of the VLTI and a novel metrology concept. Simulations show that the planned
design matches the scientific needs; in particular that 10 microarcsecond
astrometry is feasible for a source with a magnitude of K=15 like Sgr A*, given
the availability of suitable phase reference sources.Comment: 13 pages, 11 figures, to appear in the conference proceedings of SPIE
Astronomical Instrumentation, 23-28 June 2008, Marseille, Franc
Modification of a conventional photolytic converter for improving aircraft measurements of NO via chemiluminescence
Nitrogen oxides (NO≡NO+NO) are centrally involved in the photochemical processes taking place in the Earth\u27s atmosphere. Measurements of NO, particularly in remote areas where concentrations are of the order of parts per trillion by volume (pptv), are still a challenge and subject to extensive research. In this study, we present NO measurements via photolysis–chemiluminescence during the research aircraft campaign CAFE Africa (Chemistry of the Atmosphere – Field Experiment in Africa) 2018 around Cabo Verde and the results of laboratory experiments to characterize the photolytic converter used. We find the NO reservoir species MPN (methyl peroxy nitrate) to produce the only relevant thermal interference in the converter under the operating conditions during CAFE Africa. We identify a memory effect within the conventional photolytic converter (type 1) associated with high NO concentrations and rapidly changing water vapor concentrations, accompanying changes in altitude during aircraft measurements, which is due to the porous structure of the converter material. As a result, NO artifacts, which are amplified by low conversion efficiencies, and a varying instrumental background adversely affect the NO measurements. We test and characterize an alternative photolytic converter (type 2) made from quartz glass, which improves the reliability of NO measurements in laboratory and field studies
Characterizing Exoplanets in the Visible and Infrared: A Spectrometer Concept for the EChO Space Mission
Transit-spectroscopy of exoplanets is one of the key observational techniques
to characterize the extrasolar planet and its atmosphere. The observational
challenges of these measurements require dedicated instrumentation and only the
space environment allows an undisturbed access to earth-like atmospheric
features such as water or carbon-dioxide. Therefore, several exoplanet-specific
space missions are currently being studied. One of them is EChO, the Exoplanet
Characterization Observatory, which is part of ESA's Cosmic Vision 2015-2025
program, and which is one of four candidates for the M3 launch slot in 2024. In
this paper we present the results of our assessment study of the EChO
spectrometer, the only science instrument onboard this spacecraft. The
instrument is a multi-channel all-reflective dispersive spectrometer, covering
the wavelength range from 400 nm to 16 microns simultaneously with a moderately
low spectral resolution. We illustrate how the key technical challenge of the
EChO mission - the high photometric stability - influences the choice of
spectrometer concept and drives fundamentally the instrument design. First
performance evaluations underline the fitness of the elaborated design solution
for the needs of the EChO mission.Comment: 20 pages, 8 figures, accepted for publication in the Journal of
Astronomical Instrumentatio
Identification of Contractile Vacuole Proteins in Trypanosoma cruzi
Contractile vacuole complexes are critical components of cell volume regulation
and have been shown to have other functional roles in several free-living
protists. However, very little is known about the functions of the contractile
vacuole complex of the parasite Trypanosoma cruzi, the
etiologic agent of Chagas disease, other than a role in osmoregulation.
Identification of the protein composition of these organelles is important for
understanding their physiological roles. We applied a combined proteomic and
bioinfomatic approach to identify proteins localized to the contractile vacuole.
Proteomic analysis of a T. cruzi fraction enriched for
contractile vacuoles and analyzed by one-dimensional gel electrophoresis and
LC-MS/MS resulted in the addition of 109 newly detected proteins to the group of
expressed proteins of epimastigotes. We also identified different peptides that
map to at least 39 members of the dispersed gene family 1 (DGF-1) providing
evidence that many members of this family are simultaneously expressed in
epimastigotes. Of the proteins present in the fraction we selected several
homologues with known localizations in contractile vacuoles of other organisms
and others that we expected to be present in these vacuoles on the basis of
their potential roles. We determined the localization of each by expression as
GFP-fusion proteins or with specific antibodies. Six of these putative proteins
(Rab11, Rab32, AP180, ATPase subunit B, VAMP1, and phosphate transporter)
predominantly localized to the vacuole bladder. TcSNARE2.1, TcSNARE2.2, and
calmodulin localized to the spongiome. Calmodulin was also cytosolic. Our
results demonstrate the utility of combining subcellular fractionation,
proteomic analysis, and bioinformatic approaches for localization of organellar
proteins that are difficult to detect with whole cell methodologies. The CV
localization of the proteins investigated revealed potential novel roles of
these organelles in phosphate metabolism and provided information on the
potential participation of adaptor protein complexes in their biogenesis
PSPACE-completeness of Modular Supervisory Control Problems*
In this paper we investigate computational issues associated with the supervision of concurrent processes modeled as modular discrete-event systems. Here, modular discrete-event systems are sets of deterministic finite-state automata whose interaction is modeled by the parallel composition operation. Even with such a simple model process model, we show that in general many problems related to the supervision of these systems are PSPACE-complete. This shows that although there may be space-efficient methods for avoiding the state-explosion problem inherent to concurrent processes, there are most likely no time-efficient solutions that would aid in the study of such “large-scale” systems. We show our results using a reduction from a special class of automata intersection problem introduced here where behavior is assumed to be prefix-closed. We find that deciding if there exists a supervisor for a modular system to achieve a global specification is PSPACE-complete. We also show many verification problems for system supervision are PSPACE-complete, even for prefix-closed cases. Supervisor admissibility and online supervision operations are also discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45090/1/10626_2004_Article_6210.pd
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