Nitrogen isotopic fractionation during abiotic synthesis of organic solid particles

The formation of organic compounds is generally assumed to result from abiotic processes in the Solar System, with the exception of biogenic organics on Earth. Nitrogen-bearing organics are of particular interest, notably for prebiotic perspectives but also for overall comprehension of organic formation in the young solar system and in planetary atmospheres. We have investigated abiotic synthesis of organics upon plasma discharge, with special attention to N isotope fractionation. Organic aerosols were synthesized from N2-CH4 and N2-CO gaseous mixtures using low-pressure plasma discharge experiments, aimed at simulating chemistry occurring in Titan s atmosphere and in the protosolar nebula, respectively. Nitrogen is efficiently incorporated into the synthesized solids, independently of the oxidation degree, of the N2 content of the starting gas mixture, and of the nitrogen speciation in the aerosols. The aerosols are depleted in 15N by 15-25 permil relative to the initial N2 gas, whatever the experimental setup is. Such an isotopic fractionation is attributed to mass-dependent kinetic effect(s). Nitrogen isotope fractionation upon electric discharge cannot account for the large N isotope variations observed among solar system objects and reservoirs. Extreme N isotope signatures in the solar system are more likely the result of self-shielding during N2 photodissociation, exotic effect during photodissociation of N2 and/or low temperature ion-molecule isotope exchange. Kinetic N isotope fractionation may play a significant role in the Titan s atmosphere. We also suggest that the low delta15N values of Archaean organic matter are partly the result of abiotic synthesis of organics that occurred at that time

A Variance-Expected Compliance Model for Structural Optimization

t The goal of this paper is to find robust structures for a given main load and its perturbations. In the first part, we show the mathematical formulation of an original variance-expected compliance model used for structural optimization. In the second part, we study the interest of this model on two 3D benchmark test cases and compare the obtained results with those given by an expected compliance mode

First performance of the gems + gmos system. Part1. Imaging

During the commissioning of the Gemini MCAO System (GeMS), we had the opportunity to obtain data with the Gemini Multi-Object Spectrograph (GMOS), the most utilised instrument at Gemini South Observatory, in March and May 2012. Several globular clusters were observed in imaging mode that allowed us to study the performance of this new and untested combination. GMOS is a visible instrument, hence pushing MCAO toward the visible.We report here on the results with the GMOS instruments, derive photometric performance in term of Full Width Half Maximum (FWHM) and throughput. In most of the cases, we obtained an improvement factor of at least 2 against the natural seeing. This result also depends on the Natural Guide Star constellation selected for the observations and we then study the impact of the guide star selection on the FWHM performance.We also derive a first astrometric analysis showing that the GeMS+GMOS system provide an absolute astrometric precision better than 8mas and a relative astrometric precision lower than 50 mas.Comment: 13 pages, 11 figures, accepted for publication in MNRAS on March 23rd 201

Variation in surface energy and reduction drive of a metal oxide lithium-ion anode with stoichiometry:a DFT study of lithium titanate spinel surfaces

Li4Ti5O12 is a “zero-strain” lithium-ion anode material that shows excellent stability over repeated lithium insertion–extraction cycles. Although lithium (de)intercalation in the bulk material has been well characterised, our understanding of surface atomic-scale–structure and the relationship with electrochemical behaviour is incomplete. To address this, we have modelled the Li4Ti5O12 (111) , Li7Ti5O12 (111) and a-Li2TiO3 (100), (110), and (111) a-Li2TiO3 surfaces using Hubbard-corrected density-functional theory (GGA+U), screening more than 600 stoichiometric Li4Ti5O12 and Li7Ti5O12 (111) surfaces. For Li4Ti5O12 and Li7Ti5O12 we find Li-terminated surfaces are more stable than mixed Li/Ti-terminated surfaces, which typically reconstruct. For a-Li2TiO3, the (100) surface energy is significantly lower than for the (110) and (111) surfaces, and is competitive with the pristine Li7Ti5O12 (111) surface. Using these stoichiometric surfaces as reference, we also model variation in Li surface coverage as a function of lithium chemical potential. For Li4Ti5O12, the stoichiometric surface is most stable across the full chemical potential range of thermodymamic stability, whereas for Li7Ti5O12, Li deficient surfaces are stablised at low Li chemical potentials. The highest occupied electronic state for Li7Ti5O12 (111) is 2:56eV below the vacuum energy. This is 0.3 eV smaller than the work function for metallic lithium, indicating an extreme thermodynamic drive for reduction. In contrast, the highest occupied state for the a-Li2TiO3 (100) surface is 4.71eV below the vacuum level, indicating a substantially lower reduction drive. This result demonstrates how stoichiometry can strongly affect the thermodynamic drive for reduction at metal-oxide–electrode surfaces. In this context, we conclude by discussing the design of highly-reducible metal-oxide electrode coatings, with the potential for controlled solid-electrolyte–interphase formation via equilibrium chemistry, by electrode wetting in the absence of any applied bias

Chi hotspots trigger a conformational change in the helicase-like domain of AddAB to activate homologous recombination

In bacteria, the repair of double-stranded DNA breaks is modulated by Chi sequences. These are recognised by helicase-nuclease complexes that process DNA ends for homologous recombination. Chi activates recombination by changing the biochemical properties of the helicase-nuclease, transforming it from a destructive exonuclease into a recombination-promoting repair enzyme. This transition is thought to be controlled by the Chi-dependent opening of a molecular latch, which enables part of the DNA substrate to evade degradation beyond Chi. Here, we show that disruption of the latch improves Chi recognition efficiency and stabilizes the interaction of AddAB with Chi, even in mutants that are impaired for Chi binding. Chi recognition elicits a structural change in AddAB that maps to a region of AddB which resembles a helicase domain, and which harbours both the Chi recognition locus and the latch. Mutation of the latch potentiates the change and moderately reduces the duration of a translocation pause at Chi. However, this mutant displays properties of Chi-modified AddAB even in the complete absence of bona fide hotspot sequences. The results are used to develop a model for AddAB regulation in which allosteric communication between Chi binding and latch opening ensures quality control during recombination hotspot recognition

High-Level Design of a Data Carousel for the Basic Fusion Files

Sometimes data is large enough that the resources needed to merely hold the data can severely strain budgets. When resource constraints are severe, and the alternative is not having access to the data at all, an alternative is to 1) use a cheaper storage solution and 2) mitigate any problems that arise from the use of this type of storage. 3) deal with the restrictions that are present in the solution. We present a white paper based on limited prototyping, reflecting our current thinking on the high-level design and operational model using the Data Carousel Access pattern, applied in the context of Amazon Web services, for the 2.4 PB Basic Fusion Dataset.Ope

A bright, spatially extended lensed galaxy at z = 1.7 behind the cluster RCS2 032727-132623

We present the discovery of an extremely bright and extended lensed source from the second Red Sequence Cluster Survey (RCS2). RCSGA 032727-132609 is spectroscopically confirmed as a giant arc and counter-image of a background galaxy at $z=1.701$, strongly-lensed by the foreground galaxy cluster RCS2 032727-132623 at $z=0.564$. The giant arc extends over $\sim 38$\,\arcsec and has an integrated $g$-band magnitude of 19.15, making it $\sim 20$ times larger and $\sim 4$ times brighter than the prototypical lensed galaxy MS1512-cB58. This is the brightest distant lensed galaxy in the Universe known to date. Its location in the `redshift desert' provides unique opportunities to connect between the large samples of galaxies known at $z\sim3$ and $z\sim1$. We have collected photometry in 9 bands, ranging from $u$ to $K_s$, which densely sample the rest-frame UV and optical light, including the age-sensitive 4000\AA\ break. A lens model is constructed for the system, and results in a robust total magnification of $2.04 \pm 0.16$ for the counter-image; we estimate an average magnification of $17.2 \pm 1.4$ for the giant arc based on the relative physical scales of the arc and counter-image. Fits of single-component spectral energy distribution (SED) models to the photometry result in a moderately young age, $t = 115 \pm 65$\,Myr, small amounts of dust, $E(B-V) \le 0.035$, and an exponentially declining star formation history with \textit{e}-folding time $\tau = 10-100$\,Myr. After correcting for the lensing magnification, we find a stellar mass of $\log(\mathrm{M}/\mathrm{M}_\odot)=10.0 \pm 0.1$. Allowing for episodic star formation, an underlying old burst could contain up to twice the mass inferred from single-component modeling. This stellar mass estimate is consistent with the average stellar mass of a sample of `BM' galaxies ($1.4 < z < 2.0$) studied by Reddy et al. (2006).Comment: 13 pages, 8 figures, abstract abridge

Yield perfomance of forage shubs and effects on milk production and chemical composition under the tropical climatic conditions of Peru

Forage shrubs have the potential to substantially contribute to pasture and increase the milk production of cows in tropical environments. The yield performance of forage shrubs and its effects on the production and chemical composition of milk in Bos indicus and Bos taurus crossbred cows in the tropics of Peru were studied. Fifteen cows were divided into M. alba, L. leucocephala, M. oleifera, and C. argentea treatments and only one of B. brizantha (control). Analysis of variance (p < 0.05) and comparison of means with Tukey’s test were performed. The highest plant height, stem diameter, fresh forage, and dry matter were observed in L. leucocephala and M. oleifera. The highest milk production was observed in cows fed B. brizantha with M. alba, and the highest milk production was in the rainy season. The highest concentration of fat and total solids was observed in milk from cows fed B. brizantha with L. leucocephala. The highest utility was observed in cows fed B. brizantha with M. alba; however, the highest operational profitability was observed in the treatment of only B. brizantha and B. brizantha with L. leucocephala. The use of forage shrubs can contribute to cattle feeding, especially in the dry season when there is a shortage of pastures, and possibly contribute to improving the soil and overcoming climate change