118 research outputs found
COMPETING MECHANISMS OF MOLECULAR HYDROGEN FORMATION IN CONDITIONS RELEVANT TO THE INTERSTELLAR MEDIUM
International audienceThe most efficient mechanism of the formation of molecular hydrogen in the current universe is by association of hydrogen atoms on the surface of interstellar dust grains. The details of the processes of its formation and release from the grain are of great importance in the physical and chemical evolution of the space environmentswhere it takes place. Themain puzzle is still the fate of the 4.5 eV released in H2 formation and whether it goes into internal energy (rovibrational excitation), translational kinetic energy, or heating of the grain. The modality of the release of this energy affects the dynamics of the ISM and its evolution toward star formation.We present results of the detection of the rovibrational states of the just-formed H2 as it leaves the surface of a silicate.We find that rovibrationally excited molecules are ejected into the gas phase immediately after formation over a much wider range of grain temperatures than anticipated. Our results can be explained by the presence of twomechanisms ofmolecule formation that operate in partially overlapping ranges of grain temperature. A preliminary analysis of the relative importance of these two mechanisms is given. These unexpected findings, which will be complemented with experiments on the influence of factors such as silicate morphology, should be of great interest to the astrophysics and astrochemistry communities
Procedures and Frequencies of Embalming and Heart Extractions in Modern Period in Brittany. Contribution to the Evolution of Ritual Funerary in Europe.
The evolution of funeral practices from the Middle Ages through the Modern era in Europe is generally seen as a process of secularization. The study, through imaging and autopsy, of two mummies, five lead urns containing hearts, and more than six hundred skeletons of nobles and clergymen from a Renaissance convent in Brittany has led us to reject this view. In addition to exceptional embalming, we observed instances in which hearts alone had been extracted, a phenomenon that had never before been described, and brains alone as well, and instances in which each spouse's heart had been placed on the other's coffin. In some identified cases we were able to establish links between the religious attitudes of given individuals and either ancient Medieval practices or more modern ones generated by the Council of Trent. All of these practices, which were a function of social status, were rooted in religion. They offer no evidence of secularization whatsoever
Water formation at low temperatures by surface O2 hydrogenation II: the reaction network
Water is abundantly present in the Universe. It is the main component of
interstellar ice mantles and a key ingredient for life. Water in space is
mainly formed through surface reactions. Three formation routes have been
proposed in the past: hydrogenation of surface O, O2, and O3. In a previous
paper [Ioppolo et al., Astrophys. J., 2008, 686, 1474] we discussed an
unexpected non-standard zeroth-order H2O2 production behaviour in O2
hydrogenation experiments, which suggests that the proposed reaction network is
not complete, and that the reaction channels are probably more interconnected
than previously thought. In this paper we aim to derive the full reaction
scheme for O2 surface hydrogenation and to constrain the rates of the
individual reactions. This is achieved through simultaneous H-atom and O2
deposition under ultra-high vacuum conditions for astronomically relevant
temperatures. Different H/O2 ratios are used to trace different stages in the
hydrogenation network. The chemical changes in the forming ice are followed by
means of reflection absorption infrared spectroscopy (RAIRS). New reaction
paths are revealed as compared to previous experiments. Several reaction steps
prove to be much more efficient (H + O2) or less efficient (H + OH and H2 + OH)
than originally thought. These are the main conclusions of this work and the
extended network concluded here will have profound implications for models that
describe the formation of water in space.Comment: 1 page, 1 figur
Local delivery of tacrolimus using electrospun poly-ε-caprolactone nanofibres suppresses the T-cell response to peripheral nerve allografts
OBJECTIVE: Repair of nerve gap injuries can be achieved through nerve autografting, but this approach is restricted by limited tissue supply and donor site morbidity. The use of living nerve allografts would provide an abundant tissue source, improving outcomes following peripheral nerve injury. Currently this approach is not used due to the requirement for systemic immunosuppression, to prevent donor-derived cells within the transplanted nerve causing an immune response, which is associated with severe adverse effects. The aim of this study was to develop a method for delivering immunosuppression locally, then to test its effectiveness in reducing the immune response to transplanted tissue in a rat model of nerve allograft repair. APPROACH: A coaxial electrospinning approach was used to produce poly-ε-caprolactone fibre sheets loaded with the immunosuppressant tacrolimus. The material was characterised in terms of structure and tacrolimus release, then tested in vivo through implantation in a rat sciatic nerve allograft model with immunologically mismatched host and donor tissue. MAIN RESULTS: Following successful drug encapsulation, the fibre sheets showed nanofibrous structure and controlled release of tacrolimus over several weeks. Materials containing tacrolimus (and blank material controls) were implanted around the nerve graft at the time of allograft or autograft repair. The fibre sheets were well tolerated by the animals and tacrolimus release resulted in a significant reduction in lymphocyte infiltration at three weeks post-transplantation. SIGNIFICANCE: These findings demonstrate proof of concept for a novel nanofibrous biomaterial-based targeted drug delivery strategy for immunosuppression in peripheral nerve allografting
Water formation at low temperatures by surface O2 hydrogenation I: characterization of ice penetration
Water is the main component of interstellar ice mantles, is abundant in the
solar system and is a crucial ingredient for life. The formation of this
molecule in the interstellar medium cannot be explained by gas-phase chemistry
only and its surface hydrogenation formation routes at low temperatures (O, O2,
O3 channels) are still unclear and most likely incomplete. In a previous paper
we discussed an unexpected zeroth-order H2O production behavior in O2 ice
hydrogenation experiments compared to the first-order H2CO and CH3OH production
behavior found in former studies on hydrogenation of CO ice. In this paper we
experimentally investigate in detail how the structure of O2 ice leads to this
rare behavior in reaction order and production yield. In our experiments H
atoms are added to a thick O2 ice under fully controlled conditions, while the
changes are followed by means of reflection absorption infrared spectroscopy
(RAIRS). The H-atom penetration mechanism is systematically studied by varying
the temperature, thickness and structure of the O2 ice. We conclude that the
competition between reaction and diffusion of the H atoms into the O2 ice
explains the unexpected H2O and H2O2 formation behavior. In addition, we show
that the proposed O2 hydrogenation scheme is incomplete, suggesting that
additional surface reactions should be considered. Indeed, the detection of
newly formed O3 in the ice upon H-atom exposure proves that the O2 channel is
not an isolated route. Furthermore, the addition of H2 molecules is found not
to have a measurable effect on the O2 reaction channel.Comment: 1 page, 1 figur
Water formation on bare grains: When the chemistry on dust impacts interstellar gas
Context. Water together with O2 are important gas phase ingredients to cool
dense gas in order to form stars. On dust grains, H2 O is an important
constituent of the icy mantle in which a complex chemistry is taking place, as
revealed by hot core observations. The formation of water can occur on dust
grain surfaces, and can impact gas phase composition. Aims. The formation of
molecules such as OH, H2 O, HO2, H2 O2, as well as their deuterated forms and
O2 and O3 is studied in order to assess how the chemistry varies in different
astrophysical environments, and how the gas phase is affected by grain surface
chemistry. Methods. We use Monte Carlo simulations to follow the formation of
molecules on bare grains as well as the fraction of molecules released into the
gas phase. We consider a surface reaction network, based on gas phase
reactions, as well as UV photo-dissociation of the chemical species. Results.
We show that grain surface chemistry has a strong impact on gas phase
chemistry, and that this chemistry is very different for different dust grain
temperatures. Low temperatures favor hydrogenation, while higher temperatures
favor oxygenation. Also, UV photons dissociate the molecules on the surface,
that can reform subsequently. The formation-destruction cycle increases the
amount of species released into the gas phase. We also determine the time
scales to form ices in diffuse and dense clouds, and show that ices are formed
only in shielded environments, as supported by observations.Comment: Accepted in A&
Contamination of common spices by aflatoxigenic fungi and aflatoxin B1 in Algeria
Spices are usually produced in areas where the climatic conditions are favourable to growth of toxigenic fungi and production of mycotoxins. This study assesses the occurrence of aflatoxigenic fungi and aflatoxin B1 (AFB1) in spices marketed in Algeria. A total of 44 spice samples (4 for each type of spice) composed of aniseed, black pepper, caraway, cinnamon, coriander, cumin, ginger, red pepper, saffron, sweet cumin, and sweet pepper were collected from four popular markets located in Algeria. Mycological analysis of the spice was by dilution plating while AFB1 contamination levels were determined by high-performance liquid chromatography coupled with fluorescence detection (HPLC-FLD) after post-column derivatisation. The commonly isolated fungi were species of Aspergillus (56.4%), Penicillium (25.1%), Mucor (12.8%) and Eurotium (5.7%). Species belonging to Aspergillus section Flavi represented 28.9% of the total Aspergilli. The aflatoxin producing ability of isolates belonging to Aspergillus section Flavi was determined on coconut agar medium and confirmed by thin layer chromatography and HPLC-FLD. Ninety-four isolates (38.4%) of the 245 Aspergillus section Flavi examined produced aflatoxins. The most frequent chemotypes (84%) correspond to isolates able to produce both aflatoxin B and cyclopiazonic acid followed by the producers of only aflatoxin B. Twenty-three (63.9%) of the 36 spices contained AFB1 at levels ranging from 0.10 to 26.50 μg/kg. Two saffron (24.34 and 26.50 μg/kg) and two sweet cumin (14.65 and 19.07 μg/kg) samples were above the Algerian regulatory limit of 10 μg/kg. This work represents the first report about the occurrence of aflatoxigenic fungi and AFB1 in the common spices in Algeria
Enhanced H2O formation through dust grain chemistry in X-ray exposed environments
The ULIRG Mrk 231 exhibits very strong water rotational lines between \lambda
= 200-670\mu m, comparable to the strength of the CO rotational lines. High
redshift quasars also show similar CO and H2O line properties, while starburst
galaxies, such as M82, lack these very strong H2O lines in the same wavelength
range, but do show strong CO lines. We explore the possibility of enhancing the
gas phase H2O abundance in X-ray exposed environments, using bare interstellar
carbonaceous dust grains as a catalyst. Cloud-cloud collisions cause C and J
shocks, and strip the grains of their ice layers. The internal UV field created
by X-rays from the accreting black hole does not allow to reform the ice. We
determine formation rates of both OH and H2O on dust grains, having temperature
T_dust=10-60 K, using both Monte Carlo as well as rate equation method
simulations. The acquired formation rates are added to our X-ray chemistry
code, that allows us to calculate the thermal and chemical structure of the
interstellar medium near an active galactic nucleus. We derive analytic
expressions for the formation of OH and H2O on bare dust grains as a catalyst.
Oxygen atoms arriving on the dust are released into the gas phase under the
form of OH and H2O. The efficiencies of this conversion due to the chemistry
occurring on dust are of order 30 percent for oxygen converted into OH and 60
percent for oxygen converted into H_2O between T_dust=15-40 K. At higher
temperatures, the efficiencies rapidly decline. When the gas is mostly atomic,
molecule formation on dust is dominant over the gas-phase route, which is then
quenched by the low H2 abundance. Here, it is possible to enhance the warm (T>
200 K) water abundance by an order of magnitude in X-ray exposed environments.
This helps to explain the observed bright water lines in nearby and
high-redshift ULIRGs and Quasars.Comment: 13 pages, 8 figures, accepted by A&
Peeling the astronomical onion
Water ice is the most abundant solid in the Universe. Understanding the formation, structure and multiplicity of physicochemical roles for water ice in the cold, dense interstellar environments in which it is predominantly observed is a crucial quest for astrochemistry as these are regions active in star and planet formation. Intuitively, we would expect the mobility of water molecules deposited or synthesised on dust grain surfaces at temperatures below 50 K to be very limited. This work delves into the thermally-activated mobility of H2O molecules on model interstellar grain surfaces. The energy required to initiate this process is studied by reflection-absorption infrared spectroscopy of small quantities of water on amorphous silica and highly oriented pyrolytic graphite surfaces as the surface is annealed. Strongly non-Arrhenius behaviour is observed with an activation energy of 2 kJ mol-1 on the silica surface below 25 K and 0 kJ mol-1 on both surfaces between 25 and 100 K. The astrophysical implication of these results is that on timescales shorter than that estimated for the formation of a complete monolayer of water ice on a grain, aggregation of water ice will result in a non-uniform coating of water, hence leaving bare grain surface exposed. Other molecules can thus be formed or adsorbed on this bare surface
Effect of organic tomato (Lycopersicon esculentum) extract on the genotoxicity of doxorubicin in the Drosophila wing spot test
The consumption of organic tomatoes (ORTs) reduces the risk of harmful effects to humans and the environment caused by exposure to toxic agrochemicals. In this study, we used the somatic mutation and recombination test (SMART) of wing spots in Drosophila melanogaster to evaluate the genotoxicity of ORT and the effect of cotreatment with ORT on the genotoxicity of Doxorubicin® (DXR, a cancer chemotherapeutic agent) that is mediated by free radical formation. Standard (ST) cross larvae were treated chronically with solutions containing 25%, 50% or 100% of an aqueous extract of ORT, in the absence and presence of DXR (0.125 mg/mL), and the number of mutant spots on the wings of emergent flies was counted. ORT alone was not genotoxic but enhanced the toxicity of DXR when administered concomitantly with DXR. The ORT-enhanced frequency of spots induced by DXR may have resulted from the interaction of ORT with the enzymatic systems that catalyze the metabolic detoxification of this drug
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