Mechanical Flip-Chip for Ultra-High Electron Mobility Devices

Electrostatic gates are of paramount importance for the physics of devices based on high-mobility two-dimensional electron gas (2DEG) since they allow depletion of electrons in selected areas. This field-effect gating enables the fabrication of a wide range of devices such as, for example, quantum point contacts (QPC), electron interferometers and quantum dots. To fabricate these gates, processing is usually performed on the 2DEG material, which is in many cases detrimental to its electron mobility. Here we propose an alternative process which does not require any processing of the 2DEG material other than for the ohmic contacts. This approach relies on processing a separate wafer that is then mechanically mounted on the 2DEG material in a flip-chip fashion. This technique proved successful to fabricate quantum point contacts on both GaAs/AlGaAs materials with both moderate and ultra-high electron mobility.Comment: 5 pages, 3 figure

Recurring Necrotic Enteritis Outbreaks in Commercial Broiler Chicken Flocks Strongly Influence Toxin Gene Carriage and Species Richness in the Resident Clostridium perfringens Population

Extensive use of antibiotic growth promoters (AGPs) in food animals has been questioned due to the globally increasing problem of antibiotic resistance. For the poultry industry, digestive health management following AGP withdrawal in Europe has been a challenge, especially the control of necrotic enteritis. Much research work has focused on gut health in commercial broiler chicken husbandry. Understanding the behavior of Clostridium perfringens in its ecological niche, the poultry barn, is key to a sustainable and cost-effective production in the absence of AGPs. Using polymerase chain reaction and pulsed-field gel electrophoresis, we evaluated how the C. perfringens population evolved in drug-free commercial broiler chicken farms, either healthy or affected with recurring clinical necrotic enteritis outbreaks, over a 14-month period. We show that a high genotypic richness was associated with an increased risk of clinical necrotic enteritis. Also, necrotic enteritis-affected farms had a significant reduction of C. perfringens genotypic richness over time, an increase in the proportion of C. perfringens strains harboring the cpb2 gene, the netB gene, or both. Thus, necrotic enteritis occurrence is correlated with the presence of an initial highly diverse C. perfringens population, increasing the opportunity for the selective sweep of particularly virulent genotypes. Disease outbreaks also appear to largely influence the evolution of this bacterial species in poultry farms over time

Selection of coals of different maturities for CO2 Storage by modelling of CH4 and CO2 adsorption isotherms

International audienceCO2 injection in unmineable coal seams could be one interesting option for both storage and methane recovery processes. The objective of this study is to compare and model pure gas sorption isotherms (CO2 and CH4) for well-characterised coals of different maturities to determine the most suitable coal for CO2 storage. Carbon dioxide and methane adsorption on several coals have been investigated using a gravimetric adsorption method. The experiments were carried out using both CO2 and CH4 pure gases at 25 °C from 0.1 to 5 MPa (1 to 50 bar). The experimental results were fitted using Temkin's approach but also with the corrected Langmuir's and the corrected Tóth's equations. The two last approaches are more accurate from a thermodynamical point of view, and have the advantage of taking into account the fact that experimental data (isotherms) correspond to excess adsorption capacities. These approaches allow better quantification of the adsorbed gas. Determined CO2 adsorption capacities are from 0.5 to 2 mmol/g of dry coal. Modelling provides also the affinity parameters of the two gases for the different coals. We have shown these parameters determined with adsorption models could be used for classification and first selection of coals for CO2 storage. The affinity ratio ranges from a value close to 1 for immature coals to 41 for high rank coals like anthracites. This ratio allows selecting coals having high CO2 adsorption capacities. In our case, the modelling study of a significant number of coals from various ranks shows that anthracites seem to have the highest CO2 storage capacities. Our study provides high quality affinity parameters and values of CO2 and CH4 adsorption capacities on various coals for the future modelling of CO2 injection in coal seams

Analysis of transitions at two-fold redundant sites in mammalian genomes. Transition redundant approach-to-equilibrium (TREx) distance metrics

BACKGROUND: The exchange of nucleotides at synonymous sites in a gene encoding a protein is believed to have little impact on the fitness of a host organism. This should be especially true for synonymous transitions, where a pyrimidine nucleotide is replaced by another pyrimidine, or a purine is replaced by another purine. This suggests that transition redundant exchange (TREx) processes at the third position of conserved two-fold codon systems might offer the best approximation for a neutral molecular clock, serving to examine, within coding regions, theories that require neutrality, determine whether transition rate constants differ within genes in a single lineage, and correlate dates of events recorded in genomes with dates in the geological and paleontological records. To date, TREx analysis of the yeast genome has recognized correlated duplications that established a new metabolic strategies in fungi, and supported analyses of functional change in aromatases in pigs. TREx dating has limitations, however. Multiple transitions at synonymous sites may cause equilibration and loss of information. Further, to be useful to correlate events in the genomic record, different genes within a genome must suffer transitions at similar rates. RESULTS: A formalism to analyze divergence at two fold redundant codon systems is presented. This formalism exploits two-state approach-to-equilibrium kinetics from chemistry. This formalism captures, in a single equation, the possibility of multiple substitutions at individual sites, avoiding any need to "correct" for these. The formalism also connects specific rate constants for transitions to specific approximations in an underlying evolutionary model, including assumptions that transition rate constants are invariant at different sites, in different genes, in different lineages, and at different times. Therefore, the formalism supports analyses that evaluate these approximations. Transitions at synonymous sites within two-fold redundant coding systems were examined in the mouse, rat, and human genomes. The key metric (f(2)), the fraction of those sites that holds the same nucleotide, was measured for putative ortholog pairs. A transition redundant exchange (TREx) distance was calculated from f(2 )for these pairs. Pyrimidine-pyrimidine transitions at these sites occur approximately 14% faster than purine-purine transitions in various lineages. Transition rate constants were similar in different genes within the same lineages; within a set of orthologs, the f(2 )distribution is only modest overdispersed. No correlation between disparity and overdispersion is observed. In rodents, evidence was found for greater conservation of TREx sites in genes on the X chromosome, accounting for a small part of the overdispersion, however. CONCLUSION: The TREx metric is useful to analyze the history of transition rate constants within these mammals over the past 100 million years. The TREx metric estimates the extent to which silent nucleotide substitutions accumulate in different genes, on different chromosomes, with different compositions, in different lineages, and at different times

A convenient category of locally preordered spaces

As a practical foundation for a homotopy theory of abstract spacetime, we extend a category of certain compact partially ordered spaces to a convenient category of locally preordered spaces. In particular, we show that our new category is Cartesian closed and that the forgetful functor to the category of compactly generated spaces creates all limits and colimits.Comment: 26 pages, 0 figures, partially presented at GETCO 2005; changes: claim of Prop. 5.11 weakened to finite case and proof changed due to problems with proof of Lemma 3.26, now removed; Eg. 2.7, statement before Lem. 2.11, typos, and other minor problems corrected throughout; extensive rewording; proof of Lem. 3.31, now 3.30, adde

Litoestratigrafía, Bioestratigrafía y Correlaciones de las Sucesiones Sedimentarias del Neoproterozoico-Cámbrico del cratón del Río de la Plata (Uruguay y Argentina)

Se compara la lito- bio- y quimioestratigrafía de sucesiones sedimentarias del Neoproterozoico del Cratón del Río de la Plata, a saber: Grupo Arroyo del Soldado (GAS), Uruguay y Grupo Sierras Bayas - Formación Cerro Negro (GSB-FmCN) de Tandilia (Argentina). Ambas sucesiones se caracterizan por la intercalación de unidades carbonáticas y siliciclásticas, así como por un ambiente geotectónico correspondiente a un margen continental pasivo. Las formaciones Yerbal, Polanco y Cerro Espuelitas inferior se correlacionan litoestratigráficamente con las formaciones Cerro Largo, Loma Negra y Cerro Negro de Tandilia. Las formaciones siliciclásticas Yerbal y Cerro Largo representan la ingresión del mar Vendiano (Ediacarense) sobre el Cratón del Río de La Plata. Las sobreyacentes formaciones Polanco y Loma Negra se caracterizan por importantes depósitos carbonáticos, culminando con una expresiva superficie kárstica indicando regresión y exposición subaérea de la plataforma. La parte inferior de la Formación Cerro Espuelitas y la Formación Cerro Negro se caracterizan por depósitos margosos en la base, pasando a pelitas y facies heterolíticas hacia el tope. Se comunica el hallazgo de Cloudina cf. C. riemkeae de calizas micríticas de la Formación Loma Negra, apoyando la correlación de esta unidad con la parte inferior de la Formación Polanco y la asignación de ambas unidades al Ediacarense superior. Una microflora de acritarcas de baja diversidad ocurre en el GAS y en el GSB-FmCN. En el GAS se distinguen dos asociaciones de microfósiles de pared orgánica: una dominada por Bavlinella faveolata y Soldadophycus que ocurre en las formaciones siliciclásticas, y una de diversidad algo mayor denominada de Leiosphaeridia- Lophosphaeridium, característica de la Formación Polanco. En el GSB-FmCN la asociación está dominada por esferomorfos, principalmente Leiosphaeridia, siendo comparable a la asociación de Leiosphaeridia-Lophosphaeridium del GAS. Se reportan por primera vez para la Formación Villa Mónica las siguientes especies de acritarcas: Leiosphaeridia minutissima, Leiosphaeridia tenuissima y Synsphaeridium sp. Trátase de los fósiles más antiguos que se conocen en territorio de Argentina. En la Formación Cerro Largo superior aparece Leiosphaeridia tenuissima como elemento dominante y una sola vesícula de Leiosphaeridia minutissima, sumándose a previas descripciones de acritarcas de esta unidad. En la Formación Cerro Negro pudieron aislarse acritarcas asignables a Leiosphaeridia tenuissima. Se verifica una disminución del diámetro máximo de las acritarcas hacia el tope: de 450 µm para la Formación Villa Mónica a 380 µm para la Formación Cerro Largo y finalmente 200 µm para la Formación Cerro Negro. La asociación de acritarcas del GSB-FmCN puede correlacionarse con la Palinoflora de Leiosferas Simples o con la asociación Kotlin-Rovno del Ediacarense. La asociación de acritarcas del GAS inferior y medio ha sido asignada a la asociación Kotlin-Rovno y por tanto apoya una correlación entre las formaciones Cerro Largo, Loma Negra y Cerro Negro con la mitad inferior del GAS. Los datos quimioestratigráficos disponibles apoyan esta correlación, verificándose valores de 87Sr/86Sr entre 0.7069 y 0.7087 y variaciones seculares de d13C para los carbonatos entre -3.5 y +5.8 ‰ PDB. Respecto a la Formación Villa Mónica, los datos disponibles son ambiguos en cuanto a su edad y posibles correlaciones. Mientras la asociación de estromatolitos que ocurre en esa unidad sugiere una edad Neoproterozoico temprano, la similitud de la microflora allí preservada con la de las unidades suprayacentes sugiere que no existe un hiato temporal muy importante entre las mismas. Desde el punto de vista paleogeográfico, las correlaciones arriba planteadas implican el desarrollo de una extensa plataforma en el Ediacarense tardío y en condiciones tropicales, que abarcaba una gran parte del Cratón del Río de la Plata e incluía posiblemente al Grupo Corumbá en Mato Grosso, Brasil

Surfactin Protects Wheat against Zymoseptoria tritici and Activates Both Salicylic Acid- and Jasmonic Acid-Dependent Defense Responses

Natural elicitors induce plant resistance against a broad spectrum of diseases, and are currently among the most promising biocontrol tools. The present study focuses on the elicitor properties of the cyclic lipopeptide surfactin on wheat, in order to stimulate the defenses of this major crop against the challenging fungal pathogen Zymoseptoria tritici. The protection efficacy of surfactin extracted from the strain Bacillus amyloliquefaciens S499 was investigated through greenhouse trials. Surfactin protected wheat by 70% against Z. tritici, similarly to the chemical reference elicitor Bion®50WG. In vitro biocidal assays revealed no antifungal activities of surfactin towards the pathogen. A biomolecular RT-qPCR based low-density microarray tool was used to study the relative expression of 23 wheat defense genes. Surfactin significantly induced wheat natural defenses by stimulating both salicylic acid- and jasmonic acid-dependent signaling pathways. Surfactin was successfully tested as an elicitor on the pathosystem wheat–Z. tritici. These results promote further sustainable agricultural practices and the reduction of chemical inputs

Effects of habitat and land use on breeding season density of male Asian Houbara Chlamydotis macqueenii

Landscape-scale habitat and land-use influences on Asian Houbara Chlamydotis macqueenii (IUCN Vulnerable) remain unstudied, while estimating numbers of this cryptic, low-density, over-hunted species is challenging. In spring 2013, male houbara were recorded at 231 point counts, conducted twice, across a gradient of sheep density and shrub assemblages within 14,300 km² of the Kyzylkum Desert, Uzbekistan. Four sets of models related male abundance to: (1) vegetation structure (shrub height and substrate); (2) shrub assemblage; (3) shrub species composition (multidimensional scaling); (4) remote-sensed derived land-cover (GLOBCOVER, 4 variables). Each set also incorporated measures of landscape rugosity and sheep density. For each set, multi-model inference was applied to generalised linear mixed models of visit-specific counts that included important detectability covariates and point ID as a random effect. Vegetation structure received strongest support, followed by shrub species composition and shrub assemblage, with weakest support for the GLOBCOVER model set. Male houbara numbers were greater with lower mean shrub height, more gravel and flatter surfaces, but were unaffected by sheep density. Male density (mean 0.14 km-2, 95% CI, 0.12‒0.15) estimated by distance analysis differed substantially among shrub assemblages, being highest in vegetation dominated by Salsola rigida (0.22 [CI, 0.20‒0.25]), high in areas of S. arbuscula and Astragalus (0.14 [CI, 0.13‒0.16] and 0.15 [CI, 0.14‒0.17] respectively), lower (0.09 [CI, 0.08‒0.10]) in Artemisia and lowest (0.04 [CI, 0.04‒0.05]) in Calligonum. The study area was estimated to hold 1,824 males (CI: 1,645‒2,030). The spatial distribution of relative male houbara abundance, predicted from vegetation structure models, had the strongest correspondence with observed numbers in both model-calibration and the subsequent year’s data. We found no effect of pastoralism on male distribution but potential effects on nesting females are unknown. Density differences among shrub communities suggest extrapolation to estimate country- or range-wide population size must take account of vegetation composition

Evaluation of λ-carrageenan, CpG-ODN, glycine betaine, Spirulina platensis and ergosterol as elicitors for the control of Zymoseptoria tritici in wheat

Wheat crops are constantly challenged by the pathogen Zymoseptoria tritici responsible for Septoria tritici Blotch (STB) disease. The present study reports the identification of five biocontrol compounds (λ-carrageenan, CpG-ODN, glycine betaine, Spirulina platensis and ergosterol) for the protection of wheat against STB in order to offer new alternative tools to farmers for sustainable crop protection. Screening of elicitors of wheat defenses was carried out through a succession of experiments: biocidal in vitro tests enabled to check for any fungicidal activities; glasshouse experiments allowed to determine the efficacy of a given compound in protecting wheat against STB; qRT-PCR biomolecular tests investigated the relative expression of 23 defense genes in treated versus untreated plants. We therefore demonstrated that λ-carrageenan, CpG-ODN, glycine betaine, Spirulina platensis and ergosterol are potential elicitors of wheat defenses. Foliar treatments with these compounds conferred protection of wheat by up to approximately 70 % against Z. tritici under semi-controlled conditions and induced both SA- and/or JA-dependent signaling pathways in the plant. These findings contribute to extend the narrow list of potential elicitors of wheat defenses against Z. tritici