210 research outputs found
Detection of Acetylene toward Cepheus A East with Spitzer
The first map of interstellar acetylene (C2H2) has been obtained with the
infrared spectrograph onboard the Spitzer Space Telescope. A spectral line map
of the vibration-rotation band at 13.7 microns carried out toward the
star-forming region Cepheus A East, shows that the C2H2 emission peaks in a few
localized clumps where gas-phase CO2 emission was previously detected with
Spitzer. The distribution of excitation temperatures derived from fits to the
C2H2 line profiles ranges from 50 to 200 K, a range consistent with that
derived for gaseous CO2 suggesting that both molecules probe the same warm gas
component. The C2H2 molecules are excited via radiative pumping by 13.7 microns
continuum photons emanating from the HW2 protostellar region. We derive column
densities ranging from a few x 10^13 to ~ 7 x 10^14 cm^-2, corresponding to
C2H2 abundances of 1 x 10^-9 to 4 x 10^-8 with respect to H2. The spatial
distribution of the C2H2 emission along with a roughly constant N(C2H2)/N(CO2)
strongly suggest an association with shock activity, most likely the result of
the sputtering of acetylene in icy grain mantles.Comment: 11 pages, 5 figures, accepted for publication in ApJ Letter
Protein crystals in adenovirus type 5-infected cells: requirements for intranuclear crystallogenesis, structural and functional analysis
Intranuclear crystalline inclusions have been observed in the nucleus of epithelial cells infected with Adenovirus serotype 5 (Ad5) at late steps of the virus life cycle. Using immuno-electron microscopy and confocal microscopy of cells infected with various Ad5 recombinants modified in their penton base or fiber domains, we found that these inclusions represented crystals of penton capsomers, the heteromeric capsid protein formed of penton base and fiber subunits. The occurrence of protein crystals within the nucleus of infected cells required the integrity of the fiber knob and part of the shaft domain. In the knob domain, the region overlapping residues 489–492 in the FG loop was found to be essential for crystal formation. In the shaft, a large deletion of repeats 4 to 16 had no detrimental effect on crystal inclusions, whereas deletion of repeats 8 to 21 abolished crystal formation without altering the level of fiber protein expression. This suggested a crucial role of the five penultimate repeats in the crystallisation process. Chimeric pentons made of Ad5 penton base and fiber domains from different serotypes were analyzed with respect to crystal formation. No crystal was found when fiber consisted of shaft (S) from Ad5 and knob (K) from Ad3 (heterotypic S5-K3 fiber), but occurred with homotypic S3K3 fiber. However, less regular crystals were observed with homotypic S35-K35 fiber. TB5, a monoclonal antibody directed against the Ad5 fiber knob was found by immunofluorescence microscopy to react with high efficiency with the intranuclear protein crystals in situ. Data obtained with Ad fiber mutants indicated that the absence of crystalline inclusions correlated with a lower infectivity and/or lower yields of virus progeny, suggesting that the protein crystals might be involved in virion assembly. Thus, we propose that TB5 staining of Ad-infected 293 cells can be used as a prognostic assay for the viability and productivity of fiber-modified Ad5 vectors
Distributional and classical solutions to the Cauchy Boltzmann problem for soft potentials with integrable angular cross section
This paper focuses on the study of existence and uniqueness of distributional
and classical solutions to the Cauchy Boltzmann problem for the soft potential
case assuming integrability of the angular part of the collision
kernel (Grad cut-off assumption). For this purpose we revisit the
Kaniel--Shinbrot iteration technique to present an elementary proof of
existence and uniqueness results that includes large data near a local
Maxwellian regime with possibly infinite initial mass. We study the propagation
of regularity using a recent estimate for the positive collision operator given
in [3], by E. Carneiro and the authors, that permits to study such propagation
without additional conditions on the collision kernel. Finally, an
-stability result (with ) is presented assuming the
aforementioned condition.Comment: 19 page
Laboratory evidence for efficient water formation in interstellar ices
Even though water is the main constituent in interstellar icy mantles, its
chemical origin is not well understood. Three different formation routes have
been proposed following hydrogenation of O, O2, or O3, but experimental
evidence is largely lacking. We present a solid state astrochemical laboratory
study in which one of these routes is tested. For this purpose O2 ice is
bombarded by H- or D-atoms under ultra high vacuum conditions at astronomically
relevant temperatures ranging from 12 to 28 K. The use of reflection absorption
infrared spectroscopy (RAIRS) permits derivation of reaction rates and shows
efficient formation of H2O (D2O) with a rate that is surprisingly independent
of temperature. This formation route converts O2 into H2O via H2O2 and is found
to be orders of magnitude more efficient than previously assumed. It should
therefore be considered as an important channel for interstellar water ice
formation as illustrated by astrochemical model calculations.Comment: 15 pages, 4 figures. ApJ, in pres
Boltzmann and Fokker-Planck equations modelling the Elo rating system with learning effects
In this paper we propose and study a new kinetic rating model for a large number of players, which is motivated by the well-known Elo rating system. Each player is characterised by an intrinsic strength and a rating, which are both updated after each game. We state and analyse the respective Boltzmann type equation and derive the corresponding nonlinear, nonlocal Fokker-Planck equation. We investigate the existence of solutions to the Fokker-Planck equation and discuss their behaviour in the long time limit. Furthermore, we illustrate the dynamics of the Boltzmann and Fokker-Planck equation with various numerical experiments
ISO spectroscopy of gas and dust: from molecular clouds to protoplanetary disks
Observations of interstellar gas-phase and solid-state species in the 2.4-200
micron range obtained with the spectrometers on board the Infrared Space
Observatory are reviewed. Lines and bands due to ices, polycyclic aromatic
hydrocarbons, silicates and gas-phase atoms and molecules (in particular H2,
CO, H2O, OH and CO2) are summarized and their diagnostic capabilities
illustrated. The results are discussed in the context of the physical and
chemical evolution of star-forming regions, including photon-dominated regions,
shocks, protostellar envelopes and disks around young stars.Comment: 56 pages, 17 figures. To appear in Ann. Rev. Astron. Astrophys. 2004.
Higher resolution version posted at
http://www.strw.leidenuniv.nl/~ewine/araa04.pd
EMC ASPECTS OF TURBULENCE HEATING OBSERVER (THOR) SPACECRAFT
Turbulence Heating ObserveR (THOR) is a spacecraft mission dedicated to the study of plasma turbulence in near-Earth space. The mission is currently under study for implementation as a part of ESA Cosmic Vision program. THOR will involve a single spinning spacecraft equipped with state of the art instruments capable of sensitive measurements of electromagnetic fields and plasma particles. The sensitive electric and magnetic field measurements require that the spacecraft-generated emissions are restricted and strictly controlled; therefore a comprehensive EMC program has been put in place already during the study phase. The THOR study team and a dedicated EMC working group are formulating the mission EMC requirements state of its EMC requirements
The multiplicity of malaria transmission: a review of entomological inoculation rate measurements and methods across sub-Saharan Africa
Plasmodium falciparum malaria is a serious tropical disease that causes more than one million deaths each year, most of them in Africa. It is transmitted by a range of Anopheles mosquitoes and the risk of disease varies greatly across the continent. The "entomological inoculation rate" is the commonly-used measure of the intensity of malaria transmission, yet the methods used are currently not standardized, nor do they take the ecological, demographic, and socioeconomic differences across populations into account. To better understand the multiplicity of malaria transmission, this study examines the distribution of transmission intensity across sub-Saharan Africa, reviews the range of methods used, and explores ecological parameters in selected locations. It builds on an extensive geo-referenced database and uses geographical information systems to highlight transmission patterns, knowledge gaps, trends and changes in methodologies over time, and key differences between land use, population density, climate, and the main mosquito species. The aim is to improve the methods of measuring malaria transmission, to help develop the way forward so that we can better assess the impact of the large-scale intervention programmes, and rapid demographic and environmental change taking place across Africa
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