189 research outputs found
First results on Martian carbon monoxide from Herschel/HIFI observations
We report on the initial analysis of Herschel/HIFI carbon monoxide (CO)
observations of the Martian atmosphere performed between 11 and 16 April 2010.
We selected the (7-6) rotational transitions of the isotopes ^{13}CO at 771 GHz
and C^{18}O at 768 GHz in order to retrieve the mean vertical profile of
temperature and the mean volume mixing ratio of carbon monoxide. The derived
temperature profile agrees within less than 5 K with general circulation model
(GCM) predictions up to an altitude of 45 km, however, show about 12-15 K lower
values at 60 km. The CO mixing ratio was determined as 980 \pm 150 ppm, in
agreement with the 900 ppm derived from Herschel/SPIRE observations in November
2009.Comment: Accepted for publication in Astronomy and Astrophysics (special issue
on HIFI first results); minor changes to match published versio
Soil erosion processes in european vineyards: a qualitative comparison of rainfall simulation measurements in Germany, Spain and France
Small portable rainfall simulators are considered a useful tool to analyze soil erosion processes in cultivated lands. European research groups in Spain (Valencia, Málaga, Lleida, Madrid and La Rioja), France (Reims) and Germany (Trier) have used different rainfall simulators (varying in drop size distribution and fall velocities, kinetic energy, plot forms and sizes, and field of application) to study soil loss, surface flow, runoff and infiltration coefficients in different experimental plots (Valencia, Montes de Málaga, Penedès, Campo Real and La Rioja in Spain, Champagne in France and Mosel-Ruwer valley in Germany). The measurements and experiments developed by these research teams give an overview of the variety of methodologies used in rainfall simulations to study the problem of soil erosion and describe the erosion features in different climatic environments, management practices and soil types. The aims of this study are: (i) to investigate where, how and why researchers from different wine-growing regions applied rainfall simulations with successful results as a tool to measure soil erosion processes; (ii) to make a qualitative comparison about the general soil erosion processes in European terroirs; (iii) to demonstrate the importance of the development of standard method for measurement of soil erosion processes in vineyards, using rainfall simulators; and (iv) and to analyze the key factors that should be taken into account to carry out rainfall simulations. The rainfall simulations in all cases allowed infiltration capacity, susceptibility of the soil to detachment and generation of sediment loads to runoff to be determined. Despite using small plots, the experiments were useful to analyze the influence of soil cover to reduce soil erosion, to make comparisons between different locations, and to evaluate the influence of different soil characteristics. The comparative analysis of the studies performed in different study areas points out the need to define an operational methodology to carry out rainfall simulations, which allows us to obtain representative and comparable results and to avoid errors in the interpretation in order to achieve comparable information about runoff and soil los
The origin of GEMS in IDPs as deduced from microstructural evolution of amorphous silicates with annealing
We present laboratory studies of the micro-structural evolution of an
amorphous ferro-magnesian silicate, of olivine composition, following thermal
annealing under vacuum. Annealing under vacuum was performed at temperatures
ranging from 870 to 1020 K. After annealing spheroidal metallic nano-particles
(2-50 nm) are found within the silicate films. We interpret this microstructure
in terms of a reduction of the initial amorphous silicate FeO component,
because of the carbon-rich partial pressure in the furnace due to pumping
mechanism. Annealing in a controlled oxygen-rich atmosphere confirms this
interpretation. The observed microstructures closely resemble those of the GEMS
(Glass with Embedded Metal and Sulphides) found in chondritic IDPs
(Interplanetary Dust Particles). Since IDPs contain abundant carbonaceous
matter, a solid-state reduction reaction may have occurred during heating in
the hot inner regions of the proto-solar disc. Related to this, the presence of
forsterite grains grown from the amorphous precursor material clearly
demonstrates that condensation from gaseous species is not required to explain
the occurrence of forsterite around young protostars and in comets. Forsterite
grains in these environments can be formed directly in the solid phase by
thermal annealing of amorphous ferro-magnesian silicates under reducing
conditions.Comment: 4 pages, 2 figures. Accepted for publication A&A Letter to the Edito
The Main Belt Comets and ice in the Solar System
We review the evidence for buried ice in the asteroid belt; specifically the questions around the so-called Main Belt Comets (MBCs). We summarise the evidence for water throughout the Solar System, and describe the various methods for detecting it, including remote sensing from ultraviolet to radio wavelengths. We review progress in the first decade of study of MBCs, including observations, modelling of ice survival, and discussion on their origins. We then look at which methods will likely be most effective for further progress, including the key challenge of direct detection of (escaping) water in these bodies
Water production in comet 81P/Wild 2 as determined by Herschel/HIFI
The high spectral resolution and sensitivity of Herschel/HIFI allows for the detection of multiple rotational water lines and accurate determinations of water production rates in comets. In this Letter we present HIFI observations of the fundamental 1(10)-1(01) (557 GHz) ortho and 1(11)-0(00) (1113 GHz) para rotational transitions of water in comet 81P/Wild 2 acquired in February 2010. We mapped the extent of the water line emission with five point scans. Line profiles are computed using excitation models which include excitation by collisions with electrons and neutrals and solar infrared radiation. We derive a mean water production rate of 1.0 x 10(28) molecules s(-1) at a heliocentric distance of 1.61 AU about 20 days before perihelion, in agreement with production rates measured from the ground using observations of the 18-cm OH lines. Furthermore, we constrain the electron density profile and gas kinetic temperature, and estimate the coma expansion velocity by fitting the water line shapes.</p
Detection of exposed H2O ice on the nucleus of comet 67P/Churyumov-Gerasimenko: As observed by Rosetta OSIRIS and VIRTIS instruments
Context. Since the orbital insertion of the Rosetta spacecraft, comet 67P/Churyumov-Gerasimenko (67P) has been mapped by OSIRIS camera and VIRTIS spectro-imager, producing a huge quantity of images and spectra of the comet's nucleus. Aims. The aim of this work is to search for the presence of H2O on the nucleus which, in general, appears very dark and rich in dehydrated organic material. After selecting images of the bright spots which could be good candidates to search for H2O ice, taken at high resolution by OSIRIS, we check for spectral cubes of the selected coordinates to identify these spots observed by VIRTIS. Methods. The selected OSIRIS images were processed with the OSIRIS standard pipeline and corrected for the illumination conditions for each pixel using the Lommel-Seeliger disk law. The spots with higher I/F were selected and then analysed spectrophotometrically and compared with the surrounding area. We selected 13 spots as good targets to be analysed by VIRTIS to search for the 2 μm absorption band of water ice in the VIRTIS spectral cubes. Results. Out of the 13 selected bright spots, eight of them present positive H2O ice detection on the VIRTIS data. A spectral analysis was performed and the approximate temperature of each spot was computed. The H2O ice content was confirmed by modeling the spectra with mixing (areal and intimate) of H2O ice and dark terrain, using Hapke's radiative transfer modeling. We also present a detailed analysis of the detected spots
Attraction Basins as Gauges of Robustness against Boundary Conditions in Biological Complex Systems
One fundamental concept in the context of biological systems on which researches have flourished in the past decade is that of the apparent robustness of these systems, i.e., their ability to resist to perturbations or constraints induced by external or boundary elements such as electromagnetic fields acting on neural networks, micro-RNAs acting on genetic networks and even hormone flows acting both on neural and genetic networks. Recent studies have shown the importance of addressing the question of the environmental robustness of biological networks such as neural and genetic networks. In some cases, external regulatory elements can be given a relevant formal representation by assimilating them to or modeling them by boundary conditions. This article presents a generic mathematical approach to understand the influence of boundary elements on the dynamics of regulation networks, considering their attraction basins as gauges of their robustness. The application of this method on a real genetic regulation network will point out a mathematical explanation of a biological phenomenon which has only been observed experimentally until now, namely the necessity of the presence of gibberellin for the flower of the plant Arabidopsis thaliana to develop normally
The nucleus and coma of 67P/Churyumov-Gerasimenko: highlights of the Rosetta-VIRTIS results
This paper will describe the major results obtained so far during the prelanding and initial escort phases (July 2014–February 2015) by the VIRTIS (Visible, Infrared and Thermal Imaging Spectrometer) dual channel spectrometer onboard Rosetta.
The scientific goals of the VIRTIS instrument are related to the study of the nucleus surface composition and of
its temperature and to the study of the gaseous and dust components of the coma. These are achieved by studying
the reflected and emitted radiance of the comet in the spectral range 0.25-5.0 μm with a Mapping Spectrometer
(VIRTIS-M) and a High Resolution Spectrometer (VIRTIS-H). The nucleus observations were performed
with spatial resolution varying from the initial 500m down to 2.5m and have generated compositional maps of the
illuminated areas. The nucleus integrated normal albedo has been calculated as 0.060 ± 0.003 at 0.55 μm,
and reflectance spectra display distinct gradients in the VIS and IR regions (5-25 and 1.5-5 % kÅ-1 respectively).
These results suggest a surface made of an association of carbon bearing species and opaque minerals such as
sulfides. In addition a broad absorption feature in the 2.9-3.6μm range has been observed; this band is present
across the entire illuminated surface and, its shape and width are compatible with absorptions due to non-volatile
organic macromolecular materials, complex mixture of various types of C-H and/or O-H chemical groups.
Ice rich regions of very limited extent, have also been observed. The surface temperature has been measured
since the first distant observations of the nucleus in thermal emission. The highest surface temperature seen so
far is 220K, which is an indication of a surface structure largely covered by a porous crust, mainly devoid of
water ice. Water vapour and carbon dioxide molecules have been observed in the coma and their variability,
as a function of altitude and geographic location has been studied. The molecules display an anti-correlated
behaviour in their spatial distribution, which could suggest either intrinsic differences in the nucleus composition
or insolation induced variability, which most probably will imply seasonal changes
Low CD4+ T Cell Counts among African HIV-1 Infected Subjects with Group B KIR Haplotypes in the Absence of Specific Inhibitory KIR Ligands
Natural killer (NK) cells are regulated by interactions between polymorphic
killer immunoglobulin-like receptors (KIR) and human leukocyte antigens (HLA).
Genotypic combinations of KIR3DS1/L1 and HLA
Bw4-80I were previously shown to influence HIV-1 disease
progression, however other KIR genes have not been well
studied. In this study, we analyzed the influence of all activating and
inhibitory KIR, in association with the known HLA inhibitory KIR ligands, on
markers of disease progression in a West African population of
therapy-naïve HIV-1 infected subjects. We observed a significant
association between carriage of a group B KIR haplotype and
lower CD4+ T cell counts, with an additional effect for
KIR3DS1 within the frame of this haplotype. In contrast, we
found that individuals carrying genes for the inhibitory KIR ligands
HLA-Bw4 as well as HLA-C1 showed
significantly higher CD4+ T cell counts. These associations were
independent from the viral load and from individual HIV-1 protective HLA
alleles. Our data suggest that group B KIR haplotypes and lack
of specific inhibitory KIR ligand genes, genotypes considered to favor NK cell
activation, are predictive of HIV-1 disease progression
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