Dielectric constant of glasses: first observation of a two-dimensional behavior

The 1kHz real part $\chi'$ of the dielectric constant of a structural glass was measured at low temperature $T$ down to 14 mK. Reducing the sample thickness $h$ to 10 nm suppresses the usual minimum of $\chi'$ for measuring fields $E<.5$ MV/m. This contradicts the Two Level System (TLS) model but is well accounted for by including TLS-TLS interactions where excitations delocalize between TLS's through a $E$-induced mechanism recently designed: for small $h$'s this interaction is reduced, which explains the two-dimensional behavior of $\chi'(T)$. Hence, interactions play a key role in standard thick samples.Comment: latex finesse3.tex, 5 files, 4 figures, 4 pages [SPEC-S02/050], submitted to Phys. Rev. Let

Estimating age composition for multiple years when there are gaps in the ageing data: the case of western Atlantic bluefin tuna

Age–length key (ALK) methods generally perform well when length samples and age samples are representative of the underlying population. It is unclear how well these methods perform when lengths are representative but age samples are sparse (i.e. age samples are small or missing in many years, and some length groups do not have any age observations). With western Atlantic bluefin tuna, the available age data are sparse and have been, for the most part, collected opportunistically. We evaluated two methods capable of accommodating sparse age data: a novel hybrid ALK (combining forward ALKs and cohort slicing) and the combined forward-inverse ALK. Our goal was to determine if the methods performed better than cohort slicing, which has traditionally been used to obtain catch-at-age for Atlantic bluefin tuna, given the data limitations outlined above. Simulation results indicated that the combined forward-inverse ALK performed much better than the other methods. When applied to western Atlantic bluefin tuna data, the combined forward-inverse ALK approach was able to track cohorts and identified an inconsistency in the ageing of some samples

Glancing at host adaptation in <em>Ralstonia solanacearum</em> through comparative genomics of highly host-adapted lineages

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Probing overheatings under microprobe irradiation via Zn vaporisation

International audienceA thin layer of ZnO 0.3 deposited on a SiO 2 glass substrate was irradiated with a 2 MeV α microbeam. The disappearance of ZnO 0.3 in the neighbourhood of the beam was registered in situ. We quantitatively account for this behaviour in the framework of a very simple vaporisation model based both upon the local temperature increase resulting from the microbeam itself and upon the variation of the Zn vapour pressure with the local temperature. Other possible explanations are briefly discussed

In Vivo Genome and Methylome Adaptation of cag-Negative Helicobacter pylori during Experimental Human Infection

Exceptional genetic diversity and variability are hallmarks of Helicobacter pylori, but the biological role of this plasticity remains incompletely understood. Here, we had the rare opportunity to investigate the molecular evolution during the first weeks of H. pylori infection by comparing the genomes and epigenomes of H. pylori strain BCS 100 used to challenge human volunteers in a vaccine trial with those of bacteria reisolated from the volunteers 10 weeks after the challenge. The data provide molecular insights into the process of establishment of this highly versatile pathogen in 10 different human individual hosts, showing, for example, selection for changes in host-interaction molecules as well as changes in epigenetic methylation patterns. The data provide important clues to the early adaptation of H. pylori to new host niches after transmission, which we believe is vital to understand its success as a chronic pathogen and develop more efficient treatments and vaccines.Multiple studies have demonstrated rapid bacterial genome evolution during chronic infection with Helicobacter pylori. In contrast, little was known about genetic changes during the first stages of infection, when selective pressure is likely to be highest. Using single-molecule, real-time (SMRT) and Illumina sequencing technologies, we analyzed genome and methylome evolution during the first 10 weeks of infection by comparing the cag pathogenicity island (cagPAI)-negative H. pylori challenge strain BCS 100 with pairs of H. pylori reisolates from gastric antrum and corpus biopsy specimens of 10 human volunteers who had been infected with this strain as part of a vaccine trial. Most genetic changes detected in the reisolates affected genes with a surface-related role or a predicted function in peptide uptake. Apart from phenotypic changes of the bacterial envelope, a duplication of the catalase gene was observed in one reisolate, which resulted in higher catalase activity and improved survival under oxidative stress conditions. The methylomes also varied in some of the reisolates, mostly by activity switching of phase-variable methyltransferase (MTase) genes. The observed in vivo mutation spectrum was remarkable for a very high proportion of nonsynonymous mutations. Although the data showed substantial within-strain genome diversity in the challenge strain, most antrum and corpus reisolates from the same volunteers were highly similar to each other, indicating that the challenge infection represents a major selective bottleneck shaping the transmitted population. Our findings suggest rapid in vivo selection of H. pylori during early-phase infection providing adaptation to different individuals by common mechanisms of genetic and epigenetic alterations

Tag-shedding rates for tropical tuna species in the Atlantic Ocean estimated from double-tagging data

An objective of the Atlantic Ocean Tropical tuna Tagging Programme (AOTTP) was to estimate Type-I (immediate) and Type-II (long-term) tag-shedding rates for tropical Atlantic tunas from double-tagging experiments. Historical information on tuna tag-shedding studies conducted in different parts of the world was incorporated as prior distributions using a Bayesian approach to estimate the new tag-shedding parameters. Type-I and Type-II tag-shedding rates were respectively estimated at 0.007 and 0.084/yr for bigeye tuna, 0.021 and 0.051/yr for skipjack and 0.021 and 0.088/yr for yellowfin tuna. Using realizations derived from the MCMC posterior distributions, the shedding rate was estimated to reach 50% of the tags after seven and a half years at sea for yellowfin and after eight years at sea for bigeye tuna. The loss rate of conventional tags is lower for skipjack. Our results suggested that continuous Type-II shedding rate is size-dependant for yellowfin and bigeye (i.e., showing a three-fold increase between individuals less than 45 cm fork length (FL) at release and fishes larger than 65 cm FL). This study reinforces the need to account for tag-shedding along with other sources of uncertainty, such as reporting rate, in order to accurately estimate the exploitation and mortality rates derived from tagging data

Tag-shedding rates for tropical tuna species in the Atlantic Ocean estimated from double-tagging data

International audienceAn objective of the Atlantic Ocean Tropical tuna Tagging Programme (AOTTP) was to estimate Type-I (immediate) and Type-II (long-term) tag-shedding rates for tropical Atlantic tunas from double-tagging experiments. Historical information on tuna tag-shedding studies conducted in different parts of the world was incorporated as prior distributions using a Bayesian approach to estimate the new tag-shedding parameters. Type-I and Type-II tag-shedding rates were respectively estimated at 0.007 and 0.084/yr for bigeye tuna, 0.021 and 0.051/yr for skipjack and 0.021 and 0.088/yr for yellowfin tuna. Using realizations derived from the MCMC posterior distributions, the shedding rate was estimated to reach 50% of the tags after seven and a half years at sea for yellowfin and after eight years at sea for bigeye tuna. The loss rate of conventional tags is lower for skipjack. Our results suggested that continuous Type-II shedding rate is size-dependant for yellowfin and bigeye (i.e., showing a three-fold increase between individuals less than 45 cm fork length (FL) at release and fishes larger than 65 cm FL). This study reinforces the need to account for tag-shedding along with other sources of uncertainty, such as reporting rate, in order to accurately estimate the exploitation and mortality rates derived from tagging data