Experimental Investigation of Gully Formation Under Low Pressure and Low Temperature Conditions

International audienceIntroduction: A large morphological diversity of gullies is observed on Earth and on Mars. Debris flow – a non-newtonian flow comprising a sediment-water mix – is a common process attributed to gully formation on both planets [1, 2]. Many variables can influence the morphology of debris flows (grainsizes, discharge , slope, soil moisture, etc) and their respective influences are difficult to disentangle in the field. Furthermore effects specific to the martian environment have not yet been explored in detail. Some preliminary laboratory simulations have already been performed that isolate some of these variables. Cold room experiments [3] were already perfomed to test the effect of a melted surface layer on the formation of linear gullies over sand dunes. Low pressure experiments [4] were performed to test the effect of the atmospheric pressure on erosional capacity and runout distance of the flows. Our aim is to develop a new set of experiments both under Martian atmospheric pressure and terrestrial atmospheric pressure in order to reproduce the variability of the observed morphologies under well constrained experimental conditions

Approach to equilibrium of diffusion in a logarithmic potential

The late-time distribution function P(x,t) of a particle diffusing in a one-dimensional logarithmic potential is calculated for arbitrary initial conditions. We find a scaling solution with three surprising features: (i) the solution is given by two distinct scaling forms, corresponding to a diffusive (x ~ t^(1/2)) and a subdiffusive (x ~ t^{\gamma} with a given {\gamma} < 1/2) length scale, respectively, (ii) the overall scaling function is selected by the initial condition, and (iii) depending on the tail of the initial condition, the scaling exponent which characterizes the scaling function is found to exhibit a transition from a continuously varying to a fixed value.Comment: 4 pages, 3 figures; Published versio

Comparison of precipitated calcium carbonate/polylactic acid and halloysite/polylactic acid nanocomposites

PLA nanocomposites with stearate coated precipitated calcium carbonate (PCC) and halloysite natural nanotubes (HNT) were prepared by melt extrusion. The crystallization behavior, mechanical properties, thermal dynamical mechanical analysis (DMTA), and the morphology of the PCC/PLA, HNT/PLA, and HNT/PCC/PLA composites were discussed. Compared to halloysite nanotubes, PCC nanoparticles showed a better nucleating effect, which decreased both the glass transition and cold crystallization temperatures. The tensile performance of PLA composites showed that the addition of inorganic nanofillers increased Young’s modulus but decreased tensile strength. More interestingly, PLA composites with PCC particles exhibited an effectively increased elongation at break with respect to pure PLA, while HNT/PLA showed a decreased ultimate deformation of composites. DMTA results indicated that PLA composites had a similar storage modulus at temperatures below the glass transition and the addition of nanofillers into PLA caused to shift to lower temperatures by about 3°C. The morphological analysis of fractures surface of PLA nanocomposites showed good dispersion of nanofillers, formation of microvoids, and larger plastic deformation of the PLA matrix when the PCC particles were added, while a strong aggregation was noticed in composites with HNT nanofillers, which has been attributed to a nonoptimal surface coating

Local connectedness "with respect to''

In this article, a certain new concept of connectedness in frames is introduced, namely, local connectedness with respect to. We show that whenever h : L --&gt; M is a dense homomorphism with M locally connected with respect to h; then h preserves connectedness. (And this provides a "partial" converse to a result of Baboolal and Banaschewski.) Also, under the hypothesis, the right adjoint preserves pairwise disjoint joins. In this article, a certain new concept of connectedness in frames is introduced, namely, local connectedness with respect to. We show that whenever h : L --&gt; M is a dense homomorphism with M locally connected with respect to h; then h preserves connectedness. (And this provides a "partial" converse to a result of Baboolal and Banaschewski.) Also, under the hypothesis, the right adjoint preserves pairwise disjoint joins

Black Strings and Classical Hair

We examine the geometry near the event horizon of a family of black string solutions with traveling waves. It has previously been shown that the metric is continuous there. Contrary to expectations, we find that the geometry is not smooth, and the horizon becomes singular whenever a wave is present. Both five dimensional and six dimensional black strings are considered with similar results.Comment: 14 pages, harvma

Power-law singularities in string theory and M-theory

We extend the definition of the Szekeres-Iyer power-law singularities to supergravity, string and M-theory backgrounds, and find that are characterized by Kasner type exponents. The near singularity geometries of brane and some intersecting brane backgrounds are investigated and the exponents are computed. The Penrose limits of some of these power-law singularities have profiles $A\sim {\rm u}^{-\gamma}$ for $\gamma\geq 2$. We find the range of the exponents for which $\gamma=2$ and the frequency squares are bounded by 1/4. We propose some qualitative tests for deciding whether a null or timelike spacetime singularity can be resolved within string theory and M-theory based on the near singularity geometry and its Penrose limits.Comment: 32 page

Self force on particle in orbit around a black hole

We study the self force acting on a scalar charge in uniform circular motion around a Schwarzschild black hole. The analysis is based on a direct calculation of the self force via mode decomposition, and on a regularization procedure based on Ori's mode-sum regularization prescription. We find the four self-force at arbitrary radii and angular velocities (both geodesic and non-geodesic), in particular near the black hole, where general-relativistic effects are strongest, and for fast motion. We find the radial component of the self force to be repulsive or attractive, depending on the orbit.Comment: RevTeX, 4 pages, 4 Encapsulated PostScript figures. Submitted to Phys. Rev. Let

The association of sex, age and FKBP5 genotype with common somatic symptoms:A replication study in the lifelines cohort study

OBJECTIVE: Our aim was to replicate a recent study that reported an association between the rs9470080 CC-genotype and common somatic symptoms in women, but not in men. Additionally, we quantified the genetic contribution to phenotypic variation in common somatic symptom levels. METHODS: We used data from the Lifelines Cohort Study, including 28,299 participants (60.0% female; 44.2% CC-genotype; mean age 42.9 (14.2) years). Common somatic symptoms were measured with the SCL-90 SOM subscale. To assess the association between the rs9470080 genotype and SCL-90 SOM scores we applied similar analyses as the original study, including independent t-tests, two-way ANOVAs and a mixed ANOVA. To estimate the proportion of phenotypic variance in SCL-90 SOM scores explained by single nucleotide polymorphisms (SNPs), we used a genomic-relatedness-based restricted maximum-likelihood method. RESULTS: We could not replicate the original study's findings. We found no association between the rs9470080 genotype and common somatic symptom levels in either female or male participants (F(1, 8775) = 1.07, p = 0.30 and F(1,13,903) = 0.01, p = 0.93, respectively). Genome-wide heritability analyses show that 12.1% (p = 2.1e-08) of the phenotypic variance in common somatic symptom levels in Lifelines can be explained by SNPs. The genetic contribution to common somatic symptom levels was higher in male participants (SNP-h2 = 20.5%; p = 9.1e-08) than in female participants (SNP-h2 = 12.0%, p = 2.8e-05). CONCLUSION: Our findings of significant SNP-h2 and the sex-specific differences herein, does warrant further sex-stratified research of individual genetic variants associated with common somatic symptoms. Preferably, further research should be performed within the analytic framework of a genome-wide association study

Life in the Atacama — Year 2: Geologic reconnaissance through long-range roving and implications on the search for life

The Life in the Atacama-2004 project, which included geological, morphological, and mineralogical mapping through combined satellite, field-based, and microscopic perspectives and long-range roving, led to the localization of potential habitats

The late-time singularity inside non-spherical black holes

It was long believed that the singularity inside a realistic, rotating black hole must be spacelike. However, studies of the internal geometry of black holes indicate a more complicated structure is typical. While it seems likely that an observer falling into a black hole with the collapsing star encounters a crushing spacelike singularity, an observer falling in at late times generally reaches a null singularity which is vastly different in character to the standard Belinsky, Khalatnikov and Lifschitz (BKL) spacelike singularity. In the spirit of the classic work of BKL we present an asymptotic analysis of the null singularity inside a realistic black hole. Motivated by current understanding of spherical models, we argue that the Einstein equations reduce to a simple form in the neighborhood of the null singularity. The main results arising from this approach are demonstrated using an almost plane symmetric model. The analysis shows that the null singularity results from the blueshift of the late-time gravitational wave tail; the amplitude of these gravitational waves is taken to decay as an inverse power of advanced time as suggested by perturbation theory. The divergence of the Weyl curvature at the null singularity is dominated by the propagating modes of the gravitational field. The null singularity is weak in the sense that tidal distortion remains bounded along timelike geodesics crossing the Cauchy horizon. These results are in agreement with previous analyses of black hole interiors. We briefly discuss some outstanding problems which must be resolved before the picture of the generic black hole interior is complete.Comment: 16 pages, RevTeX, 3 figures included using psfi