104 research outputs found
ModĂ©lisation de l'injection de gaz sous vide poussĂ© pour des applications en Ă©pitaxie par jets chimiques : Ă©tude des performances dâun injecteur conique
Ce projet de recherche sâest intĂ©ressĂ© Ă la modĂ©lisation fine du transport dâespĂšces gazeuses en rĂ©gime molĂ©culaire en vue de lâappliquer Ă des technologies de dĂ©pĂŽt sous vide poussĂ© (VP), et plus particuliĂšrement Ă la technique dâĂ©pitaxie par jets chimiques (ĂJC). Un modĂšle spĂ©cifique a Ă©tĂ© Ă©tabli et une mĂ©thode de calcul a Ă©tĂ© implĂ©mentĂ©e sous la forme dâun logiciel MATLABTM.
Les profils angulaires de densitĂ© de flux obtenus via le logiciel ont Ă©tĂ© comparĂ©s Ă ceux mesurĂ©s Ă lâaide dâun banc de test mis au point durant ce projet. Le banc de test est constituĂ© dâune chambre Ă VP dans laquelle on peut conditionner et faire circuler un gaz neutre Ă travers un injecteur et mesurer avec prĂ©cision les flux Ă©mis le long dâun arc de cercle.
Un excellent accord entre les distributions de densitĂ© de flux simulĂ©e et mesurĂ©e a Ă©tĂ© obtenu pour chacun des injecteurs testĂ©s lorsque le dĂ©bit utilisĂ© Ă©tait suffisamment faible. Pour des dĂ©bits plus forts, une dĂ©gradation progressive de lâaccord entre mesures et simulations a Ă©tĂ© observĂ©e de façon systĂ©matique. Les profils de densitĂ© de flux tendent Ă sâaplatir et Ă sâĂ©largir et les zones anguleuses Ă sâĂ©mousser, puis Ă sâarrondir. Cette Ă©volution est attribuĂ©e Ă la perte graduelle du rĂ©gime molĂ©culaire dans lâinjecteur. Cela impose donc une limite haute, liĂ©e Ă la gĂ©omĂ©trie de lâinjecteur, sur le dĂ©bit utilisable dans le cadre du modĂšle choisi.
Le logiciel ainsi validĂ© a Ă©tĂ© utilisĂ© pour Ă©tudier les performances dâun injecteur tronc-conique Ă©mettant vers un disque (substrat) en fonction de la gĂ©omĂ©trie dâinjection (dimensions de lâinjecteur et configuration spatiale source-cible). Les critĂšres de performances Ă©taient, en premier, lâuniformitĂ© des flux sur le substrat, et ensuite, la fraction des flux atteignant la cible (efficacitĂ© dâinjection). Plusieurs gĂ©omĂ©tries dâinjection optimales ont Ă©tĂ© trouvĂ©es aussi bien pour un disque fixe que pour un disque en rotation autour de son axe. NĂ©anmoins, pour la plupart dâentre elles, une sĂ©vĂšre limite sur le dĂ©bit est imposĂ©e par la nĂ©cessitĂ© de maintenir le rĂ©gime molĂ©culaire dans lâinjecteur.
Au vu de ces rĂ©sultats, il est suggĂ©rĂ© de se tourner vers des gĂ©omĂ©tries dâinjecteur prĂ©sentant de plus fortes conductances ou bien dâutiliser ou de dĂ©velopper un logiciel de simulation applicable au rĂ©gime de transition
Carbon-rich dust in comet 67P/Churyumov-Gerasimenko measured by COSIMA/Rosetta
Cometary ices are rich in CO2, CO and organic volatile
compounds, but the carbon content of cometary dust was only measured for
the Oort Cloud comet 1P/Halley, during its flyby in 1986. The COmetary
Secondary Ion Mass Analyzer (COSIMA)/Rosetta mass spectrometer
analysed dust particles with sizes ranging from 50 to 1000Â ÎŒm, collected
over 2 yr, from 67P/Churyumov-Gerasimenko (67P), a Jupiter family
comet. Here, we report 67P dust composition focusing on the elements C
and O. It has a high carbon content (atomic | |â )
close to the solar value and comparable to the 1P/Halley data. From
COSIMA measurements, we conclude that 67P particles are made of nearly
50 per cent organic matter in mass, mixed with mineral phases that are
mostly anhydrous. The whole composition, rich in carbon and non-hydrated
minerals, points to a primitive matter that likely preserved its
initial characteristics since the comet accretion in the outer regions
of the protoplanetary disc.</p
Nitrogen-to-carbon atomic ratio measured by COSIMA in the particles of comet 67P/ChuryumovâGerasimenko
The COmetary Secondary Ion Mass Analyzer (COSIMA) on board the Rosetta mission has analysed numerous cometary dust particles collected at very low velocities (a few m sâ1)
in the environment of comet 67P/ChuryumovâGerasimenko (hereafter 67P).
In these particles, carbon and nitrogen are expected mainly to be part
of the organic matter. We have measured the nitrogen-to-carbon (N/C)
atomic ratio of 27 cometary particles. It ranges from 0.018 to 0.06 with
an averaged value of 0.035 ± 0.011. This is compatible with the
measurements of the particles of comet 1P/Halley and is in the lower
range of the values measured in comet 81P/Wild 2 particles brought back
to Earth by the Stardust mission. Moreover, the averaged value
found in 67P particles is also similar to the one found in the insoluble
organic matter extracted from CM, CI and CR carbonaceous chondrites and
to the bulk values measured in most interplanetary dust particles and
micrometeorites. The close agreement of the N/C atomic ratio in all
these objects indicates that their organic matters share some
similarities and could have a similar chemical origin. Furthermore,
compared to the abundances of all the detected elements in the particles
of 67P and to the elemental solar abundances, the nitrogen is depleted
in the particles and the nucleus of 67P as was previously inferred also
for comet 1P/Halley. This nitrogen depletion could constrain the
formation scenarios of cometary nuclei.</p
Hydrolyzed eggshell membrane immobilized on phosphorylcholine polymer supplies extracellular matrix environment for human dermal fibroblasts
We have found that a water-soluble alkaline-digested form of eggshell membrane (ASESM) can provide an extracellular matrix (ECM) environment for human dermal fibroblast cells (HDF) in vitro. Avian eggshell membrane (ESM) has a fibrous-meshwork structure and has long been utilized as a Chinese medicine for recovery from burn injuries and wounds in Asian countries. Therefore, ESM is expected to provide an excellent natural material for biomedical use. However, such applications have been hampered by the insolubility of ESM proteins. We have used a recently developed artificial cell membrane biointerface, 2-methacryloyloxyethyl phosphorylcholine polymer (PMBN) to immobilize ASESM proteins. The surface shows a fibrous structure under the atomic force microscope, and adhesion of HDF to ASESM is ASESM-dose-dependent. Quantitative mRNA analysis has revealed that the expression of type III collagen, matrix metalloproteinase-2, and decorin mRNAs is more than two-fold higher when HDF come into contact with a lower dose ASESM proteins immobilized on PMBN surface. A particle-exclusion assay with fixed erythrocytes has visualized secreted water-binding molecules around the cells. Thus, HDF seems to possess an ECM environment on the newly designed PMBN-ASESM surface, and future applications of the ASESM-PMBN system for biomedical use should be of great interest
Genetic Association Study Identifies HSPB7 as a Risk Gene for Idiopathic Dilated Cardiomyopathy
Dilated cardiomyopathy (DCM) is a structural heart disease with strong genetic background. Monogenic forms of DCM are observed in families with mutations located mostly in genes encoding structural and sarcomeric proteins. However, strong evidence suggests that genetic factors also affect the susceptibility to idiopathic DCM. To identify risk alleles for non-familial forms of DCM, we carried out a case-control association study, genotyping 664 DCM cases and 1,874 population-based healthy controls from Germany using a 50K human cardiovascular disease bead chip covering more than 2,000 genes pre-selected for cardiovascular relevance. After quality control, 30,920 single nucleotide polymorphisms (SNP) were tested for association with the disease by logistic regression adjusted for gender, and results were genomic-control corrected. The analysis revealed a significant association between a SNP in HSPB7 gene (rs1739843, minor allele frequency 39%) and idiopathic DCM (pâ=â1.06Ă10â6, ORâ=â0.67 [95% CI 0.57â0.79] for the minor allele T). Three more SNPs showed p < 2.21Ă10â5. De novo genotyping of these four SNPs was done in three independent case-control studies of idiopathic DCM. Association between SNP rs1739843 and DCM was significant in all replication samples: Germany (nâ=â564, nâ=â981 controls, pâ=â2.07Ă10â3, ORâ=â0.79 [95% CI 0.67â0.92]), France 1 (nâ=â433 cases, nâ=â395 controls, pâ=â3.73Ă10â3, ORâ=â0.74 [95% CI 0.60â0.91]), and France 2 (nâ=â249 cases, nâ=â380 controls, pâ=â2.26Ă10â4, ORâ=â0.63 [95% CI 0.50â0.81]). The combined analysis of all four studies including a total of nâ=â1,910 cases and nâ=â3,630 controls showed highly significant evidence for association between rs1739843 and idiopathic DCM (pâ=â5.28Ă10â13, ORâ=â0.72 [95% CI 0.65â0.78]). None of the other three SNPs showed significant results in the replication stage
COVID-19 symptoms at hospital admission vary with age and sex: results from the ISARIC prospective multinational observational study
Background:
The ISARIC prospective multinational observational study is the largest cohort of hospitalized patients with COVID-19. We present relationships of age, sex, and nationality to presenting symptoms.
Methods:
International, prospective observational study of 60â109 hospitalized symptomatic patients with laboratory-confirmed COVID-19 recruited from 43 countries between 30 January and 3 August 2020. Logistic regression was performed to evaluate relationships of age and sex to published COVID-19 case definitions and the most commonly reported symptoms.
Results:
âTypicalâ symptoms of fever (69%), cough (68%) and shortness of breath (66%) were the most commonly reported. 92% of patients experienced at least one of these. Prevalence of typical symptoms was greatest in 30- to 60-year-olds (respectively 80, 79, 69%; at least one 95%). They were reported less frequently in children (â€â18 years: 69, 48, 23; 85%), older adults (â„â70 years: 61, 62, 65; 90%), and women (66, 66, 64; 90%; vs. men 71, 70, 67; 93%, each Pâ<â0.001). The most common atypical presentations under 60 years of age were nausea and vomiting and abdominal pain, and over 60 years was confusion. Regression models showed significant differences in symptoms with sex, age and country.
Interpretation:
This international collaboration has allowed us to report reliable symptom data from the largest cohort of patients admitted to hospital with COVID-19. Adults over 60 and children admitted to hospital with COVID-19 are less likely to present with typical symptoms. Nausea and vomiting are common atypical presentations under 30 years. Confusion is a frequent atypical presentation of COVID-19 in adults over 60 years. Women are less likely to experience typical symptoms than men
ModĂ©lisation de l'injection de gaz sous vide poussĂ© pour des applications en Ă©pitaxie par jets chimiques : Ă©tude des performances dâun injecteur conique
Ce projet de recherche sâest intĂ©ressĂ© Ă la modĂ©lisation fine du transport dâespĂšces gazeuses en rĂ©gime molĂ©culaire en vue de lâappliquer Ă des technologies de dĂ©pĂŽt sous vide poussĂ© (VP), et plus particuliĂšrement Ă la technique dâĂ©pitaxie par jets chimiques (ĂJC). Un modĂšle spĂ©cifique a Ă©tĂ© Ă©tabli et une mĂ©thode de calcul a Ă©tĂ© implĂ©mentĂ©e sous la forme dâun logiciel MATLABTM.
Les profils angulaires de densitĂ© de flux obtenus via le logiciel ont Ă©tĂ© comparĂ©s Ă ceux mesurĂ©s Ă lâaide dâun banc de test mis au point durant ce projet. Le banc de test est constituĂ© dâune chambre Ă VP dans laquelle on peut conditionner et faire circuler un gaz neutre Ă travers un injecteur et mesurer avec prĂ©cision les flux Ă©mis le long dâun arc de cercle.
Un excellent accord entre les distributions de densitĂ© de flux simulĂ©e et mesurĂ©e a Ă©tĂ© obtenu pour chacun des injecteurs testĂ©s lorsque le dĂ©bit utilisĂ© Ă©tait suffisamment faible. Pour des dĂ©bits plus forts, une dĂ©gradation progressive de lâaccord entre mesures et simulations a Ă©tĂ© observĂ©e de façon systĂ©matique. Les profils de densitĂ© de flux tendent Ă sâaplatir et Ă sâĂ©largir et les zones anguleuses Ă sâĂ©mousser, puis Ă sâarrondir. Cette Ă©volution est attribuĂ©e Ă la perte graduelle du rĂ©gime molĂ©culaire dans lâinjecteur. Cela impose donc une limite haute, liĂ©e Ă la gĂ©omĂ©trie de lâinjecteur, sur le dĂ©bit utilisable dans le cadre du modĂšle choisi.
Le logiciel ainsi validĂ© a Ă©tĂ© utilisĂ© pour Ă©tudier les performances dâun injecteur tronc-conique Ă©mettant vers un disque (substrat) en fonction de la gĂ©omĂ©trie dâinjection (dimensions de lâinjecteur et configuration spatiale source-cible). Les critĂšres de performances Ă©taient, en premier, lâuniformitĂ© des flux sur le substrat, et ensuite, la fraction des flux atteignant la cible (efficacitĂ© dâinjection). Plusieurs gĂ©omĂ©tries dâinjection optimales ont Ă©tĂ© trouvĂ©es aussi bien pour un disque fixe que pour un disque en rotation autour de son axe. NĂ©anmoins, pour la plupart dâentre elles, une sĂ©vĂšre limite sur le dĂ©bit est imposĂ©e par la nĂ©cessitĂ© de maintenir le rĂ©gime molĂ©culaire dans lâinjecteur.
Au vu de ces rĂ©sultats, il est suggĂ©rĂ© de se tourner vers des gĂ©omĂ©tries dâinjecteur prĂ©sentant de plus fortes conductances ou bien dâutiliser ou de dĂ©velopper un logiciel de simulation applicable au rĂ©gime de transition
Point-to-source path tracing Monte Carlo to compute the Clausing and distribution functions in high-vacuum systems
International audienceThis paper presents an approach to simulate the free molecular flow in vacuum systems by using a Monte Carlo method for solving the Boltzmann particle transport equation with no intermolecular collisions. Sometimes referred to as a point-to-source Monte Carlo path tracing in image rendering, in this paper the name is borrowed from the thermal radiation and heat transfer field, reverse Monte Carlo path tracing. It is shown that this method provides better accuracy and stability when computing the Clausing function when compared to the standard test particle Monte Carlo method used for free molecular flow. The Clausing function leads to the distribution function of positions and velocities from which the particle density map, pressure gradient, energy flux, and other local quantities can be computed. Using reverse path tracing, the particle concentration in a conical segment is computed, and the maximal flow input is determined by calculating the mean free path at the maximum density position
How did the ultramafic soils shape the flora of the New Caledonian hotspot?
International audienceNew Caledonia is renowned as one of the world's most significant biodiversity hotpots. The nutrient-deficiency and cations imbalances of ultramafic soils, which cover a third of the island, harbor a disproportionally high proportion of the plant diversity and endemism of New Caledonia. This review explores how ultramafic soils have influenced the exceptional endemism and richness of New Caledonia trough the concomitant occurrences of habitat patchiness, climatic instability, environmental gradient, and edaphic heterogeneity of ultramafic soils. We focus on the unique `maquis' vegetation where selective pressures by nutrient deficiency and trace element surplus are at their acme. We aim to synthesize our current understanding of diversification and speciation of lineages that have been phylogenetically studied to date. Fragmentation of the peridotite mantle in isolated massifs, and as such spatial heterogeneity of ultramafic soils types, appear to promote plant endemism and speciation. Repeated independent dispersal events of pre-adapted species and persistence of paleo-endemic lineages have contributed to the phylogenetic diversity and the endemism of the ultramafic flora. Finally, historical climatic instability has caused shifts of rain forest species in refugia thereby favoring the extension of maquis species
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