Topoclimatic Zones and Ice Dynamics in the Caves of the Northern Yukon, Canada

In the upper basin of the Porcupine River, the subhorizontal caves of Bear Cave and Tsi-it-toh-Choh mountains are characterized by a very rich ice zone. The authors propose a model for the build-up of ice based on the formation of hexagonal ice sublimation crystals on the cold walls of underground passages. In this model, water freezes and thaws many times, causing a series of different forms from the ceiling to the floor of the caves. This process will sometimes provoke total obstruction of a passage due to particular topoclimatic conditions or a change of climate, notably an increase in atmospheric humidity. During the summer the passage where the ice is located is preceded by a warm and humid passage and is followed by a cold and extremely dry passage, in which are preserved fragments of wood, animal faeces and remains of small mammals.Key words: Yukon, Porcupine River, Bear Cave and Tsi-it-toh-Choh mountains, caves, climate, cave iceMots clés: Yukon Rivière Porcupine, massifs de Bear Cave et de Tsi-it-toh-Choh, cavernes, climat, glaces de caverne

H008 Le blocage des récepteurs AT1 de L′angiotensine II inhibe L′hypertrophie ventriculaire gauche et L′activation de FHL1 chez la souris hétérozygote déficiente en cMyBP-C

Les mutations de la protéine C cardiaque (cMyBP-C) sont une cause de cardiomyopathies hypertrophiques (CMH). Les souris transgéniques hétérozygotes défi cientes en cMyBP-C (HET) présentent une CMH d′apparition tardive à fonction systolique conservée. Le système rénine angiotensine (SRA) cardiaque joue un rôle important dans l′hypertrophie, mais son rôle dans le développement d′une CMH génétiquement déterminée a été peu étudié.Cette étude évaluait le rôle du SRA dans l′induction de la CMH chez la souris HET. Des souris HET et sauvages (WT), âgées de 5 mois, ont été traitées par irbésartan (50mg/kg/jour) ou placebo pendant 8 semaines. L′expression dans le ventricule gauche (VG) des gènes de l′enzyme de conversion de l′angiotensine I (ACE), du récepteur AT1 de l′angiotensine II (AGTR1), de la calcineurine A (PPP3CB) de la calcipressin 1 (RCAN1), et de FHL1 (four and a half LIM domains 1, une protéine associée à cMyBP-C au sein du sarcomère) a été analysée par RT-qPCR.Après 8 semaines de traitement, la pression artérielle est normale dans tous les groupes. Le poids du VG/poids du corps des souris HET est augmenté par rapport aux WT (3,9±0,3 vs. 3,3±0,4mg/g; p<0.01) dans le groupe placebo. Dans les groupes traités par irbésartan, ce rapport est comparable pour les souris HET (3,4±0,5mg/g) et WT (3,2±0,4mg/g; p=ns). L′expression des gènes de l′ACE, PPP3CB et RCAN1 est comparable entre les souris HET et WT et n′est pas affectée par le traitement par irbésartan. L′expression d′AGTR1 est similaire chez les souris HET et WT traitées par placebo mais augmente après traitement par irbésartan uniquement chez les souris HET. A l′inverse, l′expression de FHL1 est activée chez les souris HET par rapport aux souris WT mais cette augmentation est prévenue par le traitement par irbésartan.En conclusion, chez la souris cMyBP-C, le développement de l′hypertrophie est accompagné par une augmentation de l′expression du gène FHL1 dans le VG. Le traitement par irbésartan inhibe l′hypertrophie et l′activation de l′expression de FHL1 don′t le mécanisme reste à déterminer

Proteasome inhibition slightly improves cardiac function in mice with hypertrophic cardiomyopathy

A growing line of evidence indicates dysfunctional ubiquitin-proteasome system (UPS) in cardiac diseases. Anti-hypertrophic effects and improved cardiac function have been reported after treatment with proteasome inhibitors in experimental models of cardiac hypertrophy. Here we tested whether proteasome inhibition could also reverse the disease phenotype in a genetically-modified mouse model of hypertrophic cardiomyopathy (HCM), which carries a mutation in Mybpc3, encoding the myofilament protein cardiac myosin-binding protein C. At 7 weeks of age, homozygous mice (KI) have +39% higher left ventricular mass and -29% lower fractional area shortening (FAS) than wild-type (WT) mice. Both groups were treated with epoxomicin (0.5 mg/kg/day) or vehicle for 1 week via osmotic minipumps. Epoxomicin inhibited the chymotrypsin-like activity by ~50% in both groups. All parameters of cardiac hypertrophy (including the fetal gene program) were not affected by epoxomicin treatment in both groups. In contrast, FAS was +12% and 35% higher in epoxomicin-treated than vehicle-treated WT and KI mice, respectively. To identify which genes or pathways could be involved in this positive effect, we performed a transcriptome analysis in KI and WT neonatal cardiac myocytes, treated or not with the proteasome inhibitor MG132 (1 {mu}M, 24 h). This revealed 103 genes (4-fold difference; 5% FDR) which are commonly regulated in both KI and WT cardiac myocytes. Thus, even in genetically-modified mice with manifest HCM, proteasome inhibition showed beneficial effects, at least with regard to cardiac function. Targeting the UPS in cardiac diseases remains therefore a therapeutic option

Atmospheric parameters and chemical properties of red giants in the CoRoT asteroseismology fields

A precise characterisation of the red giants in the seismology fields of the CoRoT satellite is a prerequisite for further in-depth seismic modelling. High-resolution FEROS and HARPS spectra were obtained as part of the ground-based follow-up campaigns for 19 targets holding great asteroseismic potential. These data are used to accurately estimate their fundamental parameters and the abundances of 16 chemical species in a self-consistent manner. Some powerful probes of mixing are investigated (the Li and CNO abundances, as well as the carbon isotopic ratio in a few cases). The information provided by the spectroscopic and seismic data is combined to provide more accurate physical parameters and abundances. The stars in our sample follow the general abundance trends as a function of the metallicity observed in stars of the Galactic disk. After an allowance is made for the chemical evolution of the interstellar medium, the observational signature of internal mixing phenomena is revealed through the detection at the stellar surface of the products of the CN cycle. A contamination by NeNa-cycled material in the most massive stars is also discussed. With the asteroseismic constraints, these data will pave the way for a detailed theoretical investigation of the physical processes responsible for the transport of chemical elements in evolved, low- and intermediate-mass stars.Comment: Accepted for publication in A&A, 25 pages, 13 colour figures (revised version after language editing

Using apparent activation energy as a reactivity criterion for biomass pyrolysis

The reactivity of chemically isolated lignocellulosic blocks, namely, α-cellulose, holocellulose, and lignin, has been rationalized on the basis of the dependence of the effective activation energy (Eα) upon conversion (α) determined via the popular isoconversional kinetic analysis, Friedman’s method. First of all, a detailed procedure for the thermogravimetric data preparation, kinetic calculation, and uncertainty estimation was implemented. Resulting Eα dependencies obtained for the slow pyrolysis of the extractive-free Eucalyptus grandis isolated α-cellulose and holocellulose remained constant for 0.05 < α < 0.80 and equal to 173 ± 10, 208 ± 11, and 197 ± 118 kJ/mol, thus confirming the single-step nature of pyrolysis. On the other hand, large and significant variations in Eα with α from 174 ± 10 to 322 ± 11 kJ/mol in the region of 0.05 and 0.79 were obtained for the Klason lignin and reported for the first time. The non-monotonic nature of weight loss at low and high conversions had a direct consequence on the confidence levels of Eα. The new experimental and calculation guidelines applied led to more accurate estimates of Eα values than those reported earlier. The increasing Eα dependency trend confirms that lignin is converted into a thermally more stable carbonaceous material

Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints

Context. The availability of asteroseismic constraints for a large sample of red giant stars from the CoRoT and Kepler missions paves the way for various statistical studies of the seismic properties of stellar populations. Aims. We use the first detailed spectroscopic study of 19 CoRoT red-giant stars (Morel et al 2014) to compare theoretical stellar evolution models to observations of the open cluster NGC 6633 and field stars. Methods. In order to explore the effects of rotation-induced mixing and thermohaline instability, we compare surface abundances of carbon isotopic ratio and lithium with stellar evolution predictions. These chemicals are sensitive to extra-mixing on the red-giant branch. Results. We estimate mass, radius, and distance for each star using the seismic constraints. We note that the Hipparcos and seismic distances are different. However, the uncertainties are such that this may not be significant. Although the seismic distances for the cluster members are self consistent they are somewhat larger than the Hipparcos distance. This is an issue that should be considered elsewhere. Models including thermohaline instability and rotation-induced mixing, together with the seismically determined masses can explain the chemical properties of red-giants targets. However, with this sample of stars we cannot perform stringent tests of the current stellar models. Tighter constraints on the physics of the models would require the measurement of the core and surface rotation rates, and of the period spacing of gravity-dominated mixed modes. A larger number of stars with longer times series, as provided by Kepler or expected with Plato, would help for ensemble asteroseismology.Comment: Accepted 03/05/201

Modelling a high-mass red giant observed by CoRoT

The G6 giant HR\,2582 (HD\,50890) was observed by CoRoT for approximately 55 days. Mode frequencies are extracted from the observed Fourier spectrum of the light curve. Numerical stellar models are then computed to determine the characteristics of the star (mass, age, etc...) from the comparison with observational constraints. We provide evidence for the presence of solar-like oscillations at low frequency, between 10 and 20\,$\mu$Hz, with a regular spacing of $(1.7\pm0.1)\mu$Hz between consecutive radial orders. Only radial modes are clearly visible. From the models compatible with the observational constraints used here, We find that HR\,2582 (HD\,50890) is a massive star with a mass in the range (3--\,5\,$M_{\odot}$), clearly above the red clump. It oscillates with rather low radial order ($n$ = 5\,--\,12) modes. Its evolutionary stage cannot be determined with precision: the star could be on the ascending red giant branch (hydrogen shell burning) with an age of approximately 155 Myr or in a later phase (helium burning). In order to obtain a reasonable helium amount, the metallicity of the star must be quite subsolar. Our best models are obtained with a mixing length significantly smaller than that obtained for the Sun with the same physical description (except overshoot). The amount of core overshoot during the main-sequence phase is found to be mild, of the order of 0.1\,$H_{\rm p}$.Comment: Accepted in A&

Mars sample return – a proposed mission campaign whose time is now

The analysis in Earth laboratories of samples that could be returned from Mars is of extremely high interest to the international Mars exploration community. IMEWG (the International Mars Exploration Working Group) has been evaluating options, by means of a working group referred to as iMOST, to refine the scientific objectives of MSR. The Mars 2020 sample-caching rover mission is the first component of the Mars Sample Return campaign, so its existence constitutes a critical opportunity. Finally, on April 26, 2018, NASA and ESA signed a Statement of Intent to work together to formulate, by the end of 2019, a joint plan for the retrieval missions that are essential to the completion of the MSR Campaign. All of these converged April 25-27, 2018 in Berlin, Germany, at the 2nd International Mars Sample Return Conference

Optical properties of structurally-relaxed Si/SiO2_2 superlattices: the role of bonding at interfaces

We have constructed microscopic, structurally-relaxed atomistic models of Si/SiO$_2$ superlattices. The structural distortion and oxidation-state characteristics of the interface Si atoms are examined in detail. The role played by the interface Si suboxides in raising the band gap and producing dispersionless energy bands is established. The suboxide atoms are shown to generate an abrupt interface layer about 1.60 \AA thick. Bandstructure and optical-absorption calculations at the Fermi Golden rule level are used to demonstrate that increasing confinement leads to (a) direct bandgaps (b) a blue shift in the spectrum, and (c) an enhancement of the absorption intensity in the threshold-energy region. Some aspects of this behaviour appear not only in the symmetry direction associated with the superlattice axis, but also in the orthogonal plane directions. We conclude that, in contrast to Si/Ge, Si/SiO$_2$ superlattices show clear optical enhancement and a shift of the optical spectrum into the region useful for many opto-electronic applications.Comment: 11 pages, 10 figures (submitted to Phys. Rev. B

Solar-like oscillations in red giants observed with Kepler: comparison of global oscillation parameters from different methods

The large number of stars for which uninterrupted high-precision photometric timeseries data are being collected with \textit{Kepler} and CoRoT initiated the development of automated methods to analyse the stochastically excited oscillations in main-sequence, subgiant and red-giant stars. Aims: We investigate the differences in results for global oscillation parameters of G and K red-giant stars due to different methods and definitions. We also investigate uncertainties originating from the stochastic nature of the oscillations. Methods: For this investigation we use Kepler data obtained during the first four months of operation. These data have been analysed by different groups using already published methods and the results are compared. We also performed simulations to investigate the uncertainty on the resulting parameters due to different realizations of the stochastic signal. Results: We obtain results for the frequency of maximum oscillation power (nu_max) and the mean large separation () from different methods for over one thousand red-giant stars. The results for these parameters agree within a few percent and seem therefore robust to the different analysis methods and definitions used here. The uncertainties for nu_max and due to differences in realization noise are not negligible and should be taken into account when using these results for stellar modelling.Comment: 11 pages, 9 Figures and 7 tables, accepted for publication in Astronomy and Astrophysic