Relation between crack growth behaviour and crack front morphology under hold-time conditions in DA Inconel 718

The crack growth behaviour of Direct Aged Inconel 718 was studied at 550 °C. Experiments were carried out under pure fatigue cycles, hold-time cycles of different durations and a mix of both. Hold-time cycles were systematically associated with complex crack front morphologies. A new numerical approach was developed to assess the effect of crack front morphology on the direct current potential drop technique, mechanical fields at the crack tip and ultimately, measured crack growth rates. Using this approach, a clear relation was established between crack front morphology and its evolution, and the crack growth behaviour under hold-time conditions. Complex crack front morphologies are demonstrated to be responsible for increased crack growth rates. From this, a crack growth mechanism under hold-time conditions is proposed. Finally, the numerical framework here presented is to be considered as a new, easily reproducible, way to properly analyse experimental data when dealing with complex loading cycles and complex crack front morphologies

Stable chromium isotopic composition of meteorites and metal-silicate experiments: Implications for fractionation during core formation

We present new mass independent and mass dependent Cr isotope compositions for meteorites measured by double spike thermal ionisation mass spectrometry. Small differences in both mass independent 53Cr and 54Cr relative to the Bulk Silicate Earth are reported and are very similar to previously published values. Carbonaceous chondrites are characterised by an excess in 54Cr compared to ordinary and enstatite chondrites which make mass independent Cr isotopes a useful tool for distinguishing between meteoritic groups. Mass dependent stable Cr isotope compositions for the same samples are also reported. Carbonaceous and ordinary chondrites are identical within uncertainty with average δ53Crδ53Cr values of −0.118±0.040‰−0.118±0.040‰ and −0.143±0.074‰−0.143±0.074‰ respectively. The heaviest isotope compositions are recorded by an enstatite chondrite and a CO carbonaceous chondrite, both of which have relatively reduced chemical compositions implying some stable Cr isotope fractionation related to redox processes in the circumstellar disk. The average δ53Crδ53Cr values for chondrites are within error of the estimate for the Bulk Silicate Earth (BSE) also determined by double spiking. The lack of isotopic difference between chondritic material and the BSE provides evidence that Cr isotopes were not fractionated during core formation on Earth. A series of high-pressure experiments was also carried out to investigate stable Cr isotope fractionation between metal and silicate and no demonstrable fractionation was observed, consistent with our meteorites data. Mass dependent Cr isotope data for achondrites suggest that Cr isotopes are fractionated during magmatic differentiation and therefore further work is required to constrain the Cr isotopic compositions of the mantles of Vesta and Mars.

A polyphasic approach to study the dynamics of microbial population of an organic wheat sourdough during its conversion to gluten-free sourdough

To develop a method for organic gluten-free (GF) sourdough bread production, a long-term and original wheat sourdough was refreshed with GF flours. The dynamics of the sourdough microbiota during five months of back-slopping were analyzed by classical enumeration and molecular methods, including PCR-temporal temperature gel electrophoresis (PCR-TTGE), multiplex PCR, and pulsed field gel electrophoresis (PFGE). The results showed that the yeast counts remained constant, although Saccharomyces cerevisiae, present in the initial wheat sourdough, was no longer detected in the GF sourdough, while lactic acid bacteria (LAB) counts increased consistently. In the first phase, which was aimed at obtaining a GF sourdough from wheat sourdough, Lactobacillus sanfranciscensis, L. plantarum, and L. spicheri were the main LAB species detected. During the second phase, aimed at maintaining the GF sourdough, the L. plantarum and L. spicheri populations decreased whereas L. sanfranciscensis persisted and L. sakei became the predominant species. Multiplex PCRs also revealed the presence of several L. sakei strains in the GF sourdough. In a search for the origin of the LAB species, PCR-TTGE was performed on the flour samples but only L. sanfranciscensis was detected, suggesting a flour origin for this typical sourdough species. Thus, while replacement of the wheat flour by GF flour influenced the sourdough microbiota, some of the original sourdough LAB and yeast species remained in the GF sourdough. [Int Microbiol 2014; 17(1):1-9]Keywords: Lactobacillus spp. · Saccharomyces · Candida ·  sourdough · gluten-free food · organic · lactic acid bacteria · yeas

Realization of low-loss mirrors with sub-nanometer flatness for future gravitational wave detectors

The second generation of gravitational wave detectors will aim at improving by an order of magnitude their sensitivity versus the present ones (LIGO and VIRGO). These detectors are based on long-baseline Michelson interferometer with high finesse Fabry-Perot cavity in the arms and have strong requirements on the mirrors quality. These large low-loss mirrors (340 mm in diameter, 200 mm thick) must have a near perfect flatness. The coating process shall not add surface figure Zernike terms higher than second order with amplitude >0.5 nm over the central 160 mm diameter. The limits for absorption and scattering losses are respectively 0.5 and 5 ppm. For each cavity the maximum loss budget due to the surface figure error should be smaller than 50 ppm. Moreover the transmission matching between the two inputs mirrors must be better than 99%. We describe the different configurations that were explored in order to respect all these requirements. Coatings are done using IBS. The two first configurations based on a single rotation motion combined or not with uniformity masks allow to obtain coating thickness uniformity around 0.2 % rms on 160 mm diameter. But this is not sufficient to meet all the specifications. A planetary motion completed by masking technique has been studied. With simulated values the loss cavity is below 20 ppm, better than the requirements. First experimental results obtained with the planetary system will be presented

A marine plasmid hitchhiking vast phylogenetic and geographic distances

Horizontal gene transfer (HGT) plays an important role in bacterial evolution and serves as a driving force for bacterial diversity and versatility. HGT events often involve mobile genetic elements like plasmids, which can promote their own dissemination by associating with adaptive traits in the gene pool of the so-called mobilome. Novel traits that evolve through HGT can therefore lead to the exploitation of new ecological niches, prompting an adaptive radiation of bacterial species. In this study, we present phylogenetic, biogeographic, and functional analyses of a previously unrecognized RepL-type plasmid found in diverse members of the marine Roseobacter group across the globe. Noteworthy, 100% identical plasmids were detected in phylogenetically and geographically distant bacteria, revealing a so-far overlooked, but environmentally highly relevant vector for HGT. The genomic and functional characterization of this plasmid showed a completely conserved backbone dedicated to replication, stability, and mobilization as well as an interchangeable gene cassette with highly diverse, but recurring motifs. The majority of the latter appear to be involved in mechanisms coping with toxins and/or pollutants in the marine environment. Furthermore, we provide experimental evidence that the plasmid has the potential to be transmitted across bacterial orders, thereby increasing our understanding of evolution and microbial niche adaptation in the environment

Potential of Chromium Isotopes as a Tracer of Past Ocean Oxygenation

Levels of atmospheric oxygen (O2) have increased from 53Cr analysis in low concentration samples has been developed. In addition, the Cr isotopic composition of modern and Phanerozoic carbonates, and seawater, have been determined to provide new constraints of the environmental behaviour of Cr isotopes. Modern seawater is characterised by heavy δ53Cr values (+0.55-1.55%) relative to the continental crust (-0.12%), which indicates that Cr isotopes are fractionated during oxidative weathering. Importantly, the Cr isotopic composition of modern carbonates, precipitated in shallow water, is within the range of seawater. This suggests that fractionation of Cr isotopes during carbonate precipitation is minimal, and carbonates should provide a record of seawater δ53Cr. Carbonate samples of Phanerozoic age also have high δ53Cr values (0.737-1.994%), consistent with oxidative weathering on the continents at this time. Most of the Neoproterozoic carbonates have significantly lower δ53Cr values than the modern and Phanerozoic carbonates. However, oolitic limestones deposited just prior to the first Cryogenian glaciations, have higher δ53Cr (+0.571-1.004%). Together, the δ53Cr and REE data suggest that the operation of the Cr cycle was significantly different in the Neoproterozoic. Changes in δ53Cr reflect either a shift in the relative importance of riverine and hydrothermal sources, and/or changes in levels of atmospheric O2 . Modelling indicates that shallow waters were either dysoxic or suboxic during the Cryogenian, and levels of atmospheric O2 must have been less than 30-40% PAL

There\u27s a Librarian in My Living Room! Teaching Information Literacy Skills with Web Conferencing

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Reconstruction of the gravitational wave signal h(t)h(t) during the Virgo science runs and independent validation with a photon calibrator

The Virgo detector is a kilometer-scale interferometer for gravitational wave detection located near Pisa (Italy). About 13 months of data were accumulated during four science runs (VSR1, VSR2, VSR3 and VSR4) between May 2007 and September 2011, with increasing sensitivity. In this paper, the method used to reconstruct, in the range 10 Hz-10 kHz, the gravitational wave strain time series $h(t)$ from the detector signals is described. The standard consistency checks of the reconstruction are discussed and used to estimate the systematic uncertainties of the $h(t)$ signal as a function of frequency. Finally, an independent setup, the photon calibrator, is described and used to validate the reconstructed $h(t)$ signal and the associated uncertainties. The uncertainties of the $h(t)$ time series are estimated to be 8% in amplitude. The uncertainty of the phase of $h(t)$ is 50 mrad at 10 Hz with a frequency dependence following a delay of 8 $\mu$s at high frequency. A bias lower than $4\,\mathrm{\mu s}$ and depending on the sky direction of the GW is also present.Comment: 35 pages, 16 figures. Accepted by CQ

Characterization of the LIGO detectors during their sixth science run

31 pages, 13 figures - See paper for full list of authorsInternational audienceIn 2009-2010, the Laser Interferometer Gravitational-wave Observatory (LIGO) operated together with international partners Virgo and GEO600 as a network to search for gravitational waves of astrophysical origin. The sensitiv- ity of these detectors was limited by a combination of noise sources inherent to the instrumental design and its environment, often localized in time or frequency, that couple into the gravitational-wave readout. Here we review the performance of the LIGO instruments during this epoch, the work done to characterize the de- tectors and their data, and the effect that transient and continuous noise artefacts have on the sensitivity of LIGO to a variety of astrophysical sources

Search for gravitational waves associated with the InterPlanetary Network short gamma ray bursts

We outline the scientific motivation behind a search for gravitational waves associated with short gamma ray bursts detected by the InterPlanetary Network (IPN) during LIGO's fifth science run and Virgo's first science run. The IPN localisation of short gamma ray bursts is limited to extended error boxes of different shapes and sizes and a search on these error boxes poses a series of challenges for data analysis. We will discuss these challenges and outline the methods to optimise the search over these error boxes.Comment: Methods paper; Proceedings for Eduardo Amaldi 9 Conference on Gravitational Waves, July 2011, Cardiff, U