Quasi-ballistic transport in HgTe quantum-well nanostructures

The transport properties of micrometer scale structures fabricated from high-mobility HgTe quantum-wells have been investigated. A special photoresist and Ti masks were used, which allow for the fabrication of devices with characteristic dimensions down to 0.45 $\mu$m. Evidence that the transport properties are dominated by ballistic effects in these structures is presented. Monte Carlo simulations of semi-classical electron trajectories show good agreement with the experiment.Comment: 3 pages, 3 figures; minor revisions: replaced "inelastic mean free path" with "transport mean free path"; corrected typing errors; restructered most paragraphs for easier reading; accepted for publication in AP

In Situ Investigation of Iron Meteorites at Meridiani Planum Mars

The Mars Exploration Rover Opportunity has encountered four iron meteorites at its landing site in Meridiani Planum. The first one, informally named "Heat Shield Rock", measuring approx.30 by 15 cm, was encountered in January 2005 [1, 2] and officially recognized as the first iron meteorite on the martian surface with the name "Meridiani Planum" after the location of its find [3]. We will refer to it as "Heat Shield Rock" to avoid confusion with the site. Between July and October 2009, separated approx.10 km from Heat Shield Rock, three other iron meteorite fragments were encountered, informally named "Block Island" (approx.60 cm across), "Shelter Island" (approx.50 by 20 cm), and "Mackinac Island" (approx.30 cm across). Heat Shield Rock and Block Island, the two specimens investigated in detail, are shown in Figure 1. Here, we focus on the meteorites chemistry and mineralogy. An overview in the mission context is given in [4]; other abstracts discuss their morphology [5], photometric properties [6], and their provenance [7]

Broad-line radio galaxies: old and feeble?

Far-infrared photometry of broad-line radio galaxies shows this class of AGN to consist of many hot and some cool infrared emitters, with peaks in their spectral energy distributions around 25 micron or longward of 60 micron, respectively. Quantitative analysis indicates that this distribution relates to a substantial dispersion in the strength of the cool dust component: broad-line radio galaxies are relatively poor in large-scale dust. Possibly they have undergone a different merger evolution, or are relatively old AGN.Comment: Accepted for publication in A&A Letter

ExoMars entry, descent and landing science

The entry, descent and landing of ExoMars offer a rare (once-per-mission) opportunity to perform in situ investigation of the martian environment over a wide altitude range. Entry, Descent and Landing System (EDLS) measurements can provide essential data for atmospheric scientific investigations. We intend to perform atmospheric science measurements by exploiting data from EDLS engineering sensors and exploiting their readings beyond the expected engineering information

Amazonian chemical weathering rate derived from stony meteorite finds at Meridiani Planum on Mars

© The Author(s) 2016.Spacecraft exploring Mars such as the Mars Exploration Rovers Spirit and Opportunity, as well as the Mars Science Laboratory or Curiosity rover, have accumulated evidence for wet and habitable conditions on early Mars more than 3 billion years ago. Current conditions, by contrast, are cold, extremely arid and seemingly inhospitable. To evaluate exactly how dry today's environment is, it is important to understand the ongoing current weathering processes. Here we present chemical weathering rates determined for Mars. We use the oxidation of iron in stony meteorites investigated by the Mars Exploration Rover Opportunity at Meridiani Planum. Their maximum exposure age is constrained by the formation of Victoria crater and their minimum age by erosion of the meteorites. The chemical weathering rates thus derived are ~1 to 4 orders of magnitude slower than that of similar meteorites found in Antarctica where the slowest rates are observed on Earth

TThermodynamics of the thermoelectric working fluid close to the superconducting phase transition

The bottleneck in state-of-the-art thermoelectric power generation and cooling is the low performance of thermoelectric materials. While the adverse effects of lattice phonons on performance can be mitigated, the main difficulty remains to obtain a large thermoelectric power factor as the Seebeck coefficient and the electrical conductivity cannot be increased independently. Here, relating the thermoelastic properties of the electron gas that performs the thermoelectric energy conversion, to its transport properties, we analyze theoretically whether an electronic phase transition can enhance thermoelectric conversion and at what cost. More precisely, we consider the metal-to-superconductor phase transition in a model two-dimensional system, and we seek to quantify the contribution of the 2D fluctuating Cooper pairs to the power factor in the close vicinity of the critical temperature $T_{\rm c}$. In addition, we provide experimental evidence of the rapid increase of the Seebeck coefficient without decreasing the electrical conductivity near $T_{\rm c}$ in a 100-nm Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ thin film with high structural quality resulting in a power factor enhancement of approximately 300. This level of performance cannot be achieved in a system with low structural quality as shown experimentally with our sample degraded by ion bombardment as defects preclude the strong enhancement of the Seebeck coefficient near the phase transition. Finally, we theoretically discuss the ideal thermoelectric conversion efficiency (i.e. disregarding adverse phonon effects) and show that driving the electronic system to the vicinity of a phase transition may be an innovative path towards a strong performance increase but at the cost of a narrow temperature range of use of such materials.Comment: Submission to SciPos

Intramolecular Structural Heterogeneity altered by Long-range Contacts in an Intrinsically Disordered Protein

Short-range interactions and long-range contacts drive the 3D folding of structured proteins. The proteins' structure has a direct impact on their biological function. However, nearly 40% of the eukaryotes proteome is composed of intrinsically disordered proteins (IDPs) and protein regions that fluctuate between ensembles of numerous conformations. Therefore, to understand their biological function, it is critical to depict how the structural ensemble statistics correlate to the IDPs' amino acid sequence. Here, using small-angle x-ray scattering (SAXS) and time-resolved F\"orster resonance energy transfer (trFRET), we study the intra-molecular structural heterogeneity of the neurofilament low intrinsically disordered tail domain (NFLt). Using theoretical results of polymer physics, we find that the Flory scaling exponent of NFLt sub-segments correlates linearly with their net charge, ranging from statistics of ideal to self-avoiding chains. Surprisingly, measuring the same segments in the context of the whole NFLt protein, we find that regardless of the peptide sequence, the segments' structural statistics are more expanded than when measured independently. Our findings show that while polymer physics can, to some level, relate the IDP's sequence to its ensemble conformations, long-range contacts between distant amino acids play a crucial role in determining intra-molecular structures. This emphasizes the necessity of advanced polymer theories to fully describe IDPs ensembles with the hope it will allow us to model their biological function

A Model for Multidimensional Delayed Detonations in SN Ia Explosions

We show that a flame tracking/capturing scheme originally developed for deflagration fronts can be used to model thermonuclear detonations in multidimensional explosion simulations of type Ia supernovae. After testing the accuracy of the front model, we present a set of two-dimensional simulations of delayed detonations with a physically motivated off-center deflagration-detonation-transition point. Furthermore, we demonstrate the ability of the front model to reproduce the full range of possible interactions of the detonation with clumps of burned material. This feature is crucial for assessing the viability of the delayed detonation scenario.Comment: 7 pages, accepted by A&

Mineralogy and chemistry of cobbles at Meridiani Planum, Mars, investigated by the Mars Exploration Rover Opportunity

Numerous loose rocks with dimensions of a few centimeters to tens of centimeters and with no obvious physical relationship to outcrop rocks have been observed along the traverse of the Mars Exploration Rover Opportunity. To date, about a dozen of these rocks have been analyzed with Opportunity’s contact instruments, providing information about elemental chemistry (Alpha Particle X‐ray Spectrometer), iron mineralogy and oxidation states (Mössbauer Spectrometer) and texture (Microscopic Imager). These “cobbles” appear to be impact related, and three distinct groups can be identified on the basis of chemistry and mineralogy. The first group comprises bright fragments of the sulfate‐rich bedrock that are compositionally and texturally indistinguishable from outcrop rocks. All other cobbles are dark and are divided into two groups, referred to as the “Barberton group” and the “Arkansas group,” after the first specimen of each that was encountered by Opportunity. Barberton group cobbles are interpreted as meteorites with an overall chemistry and mineralogy consistent with a mesosiderite silicate clast composition. Arkansas group cobbles appear to be related to Meridiani outcrop and contain an additional basaltic component. They have brecciated textures, pointing to an impact‐related origin during which local bedrock and basaltic material were mixed

Fluvial organic carbon composition regulated by seasonal variability in lowland river migration and water discharge

Identifying drivers of seasonal variations in fluvial particulate organic carbon (POC) composition can aid sediment provenance and biogeochemical cycling studies. We evaluate seasonal changes in POC composition in the Río Bermejo, Argentina, a lowland river running ∼1,270 km without tributaries. Weekly POC concentration and isotopic composition from 2016 to 2018 show that during the wet season, increased lateral channel migration generates an influx of 13C-enriched and 14C-enriched floodplain-sourced material, overprinting the 13C-depleted and 14C-depleted headwater signature that is observed during the dry season. These findings demonstrate how channel morphodynamics can drive variability of POC composition in lowland rivers, and may modulate the composition of POC preserved in sedimentary archives