Theoretical and practical differences between creep and relaxation Poisson's ratios in linear viscoelasticity

International audiencePoisson's ratio is a well-defined parameter in elasticity. For time-dependent materials , multiple definitions based on the ratios between lateral and axial deformations are available. Here, we focus ourselves on the two most widely used definitions in the time domain, which define time-dependent functions that we call relaxation Poisson's ratio and creep Poisson's ratio. Those two ratios are theoretically different, but are linked in an exact manner through an equation we derive. We show that those two functions are equal at both initial and large times and that their derivatives with respect to time also are. Based on simple rheological models for both the deviatoric and volumetric creep behaviors, we perform a parametric study and show that the difference between those two time-dependent Poisson's ratios can be significant. However, based on creep data available in the literature, we show that, for cementitious materials, this difference can be negligible or not, depending on the case

Nutrient-Dense Orange-Fleshed Sweetpotato: Advances in Drought-Tolerance Breeding and Understanding of Management Practices for Sustainable Next-Generation Cropping Systems in Sub-Saharan Africa

Almost half of children < 5 years old living in sub-Saharan Africa (SSA) suffer from vitamin A deficiency and 60% suffer from iron deficiency. Thus, there has been a strong commitment to breeding for, promoting awareness of, and delivering adapted pro-vitamin A rich orange-fleshed sweetpotato (OFSP) in SSA during the past two decades and for enhanced iron content since 2014. This review article focuses on major breeding efforts in SSA to enhance the drought tolerance of OFSP and reviews integrated crop management practices for improved and sustained sweetpotato production in SSA farming systems. Under climate change, the frequency and severity of droughts is expected to increase. Technical issues are presented in the context of addressing challenges along the entire value chain to ensure adoption. First, the use of an accelerated breeding scheme reduced the breeding cycle from 8–10 to 4–5 years. Since 2010, 19 drought-tolerant OFSP cultivars have been released in Mozambique, 7 in Malawi, and 2 in South Africa. Moreover, research in four breeding populations using the heterosis exploiting breeding scheme (HEBS) demonstrated that within one breeding cycle of 5 years, clones with significantly higher root yield, abiotic tolerance, host plant resistance to pests and diseases, and early maturity can be produced. In the future, HEBS will be combined with greater use of modern genomic tools, new phenotyping tools, and CRISPR/Cas9-mediated gene editing. Second, beyond genetic enhancements, evidence is presented that using improved crop management systems, existing sweet potato yields can be increased 2–4 times. Current knowledge is reviewed concerning sweetpotato’s role in diverse farming systems, but integrated crop management is clearly under researched. Third, the outlook for drought tolerance breeding indicates that two distinct classes of nutrient-rich cultivars are emerging: (1) Early maturing cultivars (< 4 month growing period) that escape drought but also serve humid environments with small landholding size per capita; and (2) Medium maturing (4–6 month growing period) cultivars that avoid drought, are drought tolerant and exhibit continuous root formation. Increasing commercialization of the crop and climate change will drive demand, and the willingness of farmers to invest in improved sweetpotato crop management

Decreasing population selection rates of resistance mutation K65R over time in HIV-1 patients receiving combination therapy including tenofovir

Objectives The use of tenofovir is highly associated with the emergence of mutation K65R, which confers broad resistance to nucleoside/nucleotide analogue reverse transcriptase inhibitors (NRTIs), especially when tenofovir is combined with other NRTIs also selecting for K65R. Although recent HIV-1 treatment guidelines discouraging these combinations resulted in reduced K65R selection with tenofovir, updated information on the impact of currently recommended regimens on the population selection rate of K65R is presently lacking. Methods In this study, we evaluated changes over time in the selection rate of resistance mutation K65R in a large population of 2736 HIV-1-infected patients failing combination antiretroviral treatment between 2002 and 2010. Results The K65R resistance mutation was detected in 144 patients, a prevalence of 5.3%. A large majority of observed K65R cases were explained by the use of tenofovir, reflecting its wide use in clinical practice. However, changing patterns over time in NRTIs accompanying tenofovir resulted in a persistent decreasing probability of K65R selection by tenofovir-based therapy. The currently recommended NRTI combination tenofovir/emtricitabine was associated with a low probability of K65R emergence. For any given dual NRTI combination including tenofovir, higher selection rates of K65R were consistently observed with a non-nucleoside reverse transcriptase inhibitor than with a protease inhibitor as the third agent. Discussion Our finding of a stable time trend of K65R despite elevated use of tenofovir illustrates increased potency of current HIV-1 therapy including tenofovi

Diagnostic approach for detection and identification of emerging enteric pathogens revisited : the (Ali)arcobacter lanthieri case

An immunocompetent patient without a history of recent travel or animal exposure developed persistent abdominal bloating and cramps without diarrhoea or fever. Negative additional investigations excluded gastritis, infectious colitis, inflammatory bowel disease and neoplasia, but routine stool culture detected a Campylobacter-like organism. The isolate was obtained with use of a polycarbonate filter technique, emphasizing the importance of culture to support and validate the occurrence of emerging and new bacterial enteric pathogens. The ensuing extensive laboratory examinations proved challenging in identifying this potential pathogen. Phylogenetic marker analysis based on the 16S ribosomal RNA and rpoB gene sequences revealed that the isolate was most closely related to Arcobacter lanthieri and Arcobacter faecis. Subsequent analysis of a draft whole genome sequence assigned the isolate to A. lanthieri. We report the presence of five virulence genes, cadF, ciaB, mviN, hecA and iroE, indicating a possible pathogenic nature of this organism. This case demonstrated the importance of the use of agnostic methods for the detection of emerging pathogens in cases of enteric disease with a wide array of gastrointestinal symptoms

A36 Prevalence of HIV-1 subtypes in Slovenia with an emphasis on molecular and phylogenetic investigation of subtype A

21st International BioInformatics Workshop on Virus Evolution and Molecular EpidemiologyIn Slovenia, a small country in Central Europe, less than 1 per 1,000 inhabitants are estimated to be infected with HIV-1. As in most of the Central and Western European countries, the majority of patients diagnosed with HIV-1 are infected with subtype B. However, due to migration, other subtypes can become more prevalent in the country. The aim of this study was to determine HIV-1 subtypes circulating in Slovenia and to further examine the molecular epidemiology of subtype A. A total of 367 Slovenian HIV-1 sequences were included in the study, representing 58% of all patients diagnosed in Slovenia until the end of the year 2013. Subtype was assigned by employing different HIV subtyping tools coupled with Maximum likelihood phylogenetic analysis. The latter was performed to examine the molecular epidemiology of subtype A as well. Identified clusters of Slovenian subtype A sequences were further analyzed for the determination of the time of the most recent common ancestor (tMRCA) by using Monte Carlo Markov chain (MCMC) method available in BEAST 2.1.3 software. We determined the prevalence of subtype B to be 85.3%, while subtype A was the most prevalent non-B subtype found in 18 patients (4.9%), followed by CRF02_AG (2.4%), subtype C (1.1%), subtypes D, G and CRF01_AE (0.8% each) and subtypes F1 and CRF22_01A1 (0.3% each). Subtypes could not be assigned to 12 sequences (3.3%). The phylogenetic tree obtained by ML analysis of the subtype A and subtype A related recombinants revealed that Slovenian sequences were part of 6 major international clusters. Two clusters consisting only of Slovenian sequences were identified and thus additional MCMC analysis was employed. Results of a Slovenian cluster of 4 subtype A sequences showed a posterior probability value of 1 and a tMRCA between the years 1985 and 2008, with a mean in the year 2001. In conclusion, in a Central European country, where subtype B predominates, the second most common subtype was found to be subtype A. Non-B subtypes were observed in one out of seven patients in Slovenia, a fraction that is not negligible, thus proving importance of surveillance of HIV subtype diversity and corresponding molecular epidemiology of non-B subtypes.publishersversionpublishe

New <i>Methyloceanibacter</i> diversity from North Sea sediments includes methanotroph containing solely the soluble methane monooxygenase

Marine methylotrophs play a key role in the global carbon cycle by metabolizing reduced one-carbon compounds that are found in high concentrations in marine environments. Genome, physiology and diversity studies have been greatly facilitated by the numerous model organisms brought into culture. However, the availability of marine representatives remains poor. Here, we report the isolation of four novel species from North Sea sediment enrichments closely related to the Alphaproteobacterium Methyloceanibacter caenitepidi. Each of the newly isolated Methyloceanibacter species exhibited a clear genome sequence divergence which was reflected in physiological differences. Notably one strain R-67174 was capable of oxidizing methane as sole source of carbon and energy using solely a soluble methane monooxygenase and represents the first marine Alphaproteobacterial methanotroph brought into culture. Differences in maximum cell density of >1.5 orders of magnitude were observed. Furthermore, three strains were capable of producing nitrous oxide from nitrate. Together, these findings highlight the metabolic and physiologic variability within closely related Methyloceanibacter species and provide a new understanding of the physiological basis of marine methylotrophy

HIV-1 gp120 N-linked glycosylation differs between plasma and leukocyte compartments

<p>Abstract</p> <p>Background</p> <p>N-linked glycosylation is a major mechanism for minimizing virus neutralizing antibody response and is present on the Human Immunodeficiency Virus (HIV) envelope glycoprotein. Although it is known that glycosylation changes can dramatically influence virus recognition by the host antibody, the actual contribution of compartmental differences in N-linked glycosylation patterns remains unclear.</p> <p>Methodology and Principal Findings</p> <p>We amplified the <it>env </it>gp120 C2-V5 region and analyzed 305 clones derived from plasma and other compartments from 15 HIV-1 patients. Bioinformatics and Bayesian network analyses were used to examine N-linked glycosylation differences between compartments. We found evidence for cellspecific single amino acid changes particular to monocytes, and significant variation was found in the total number of N-linked glycosylation sites between patients. Further, significant differences in the number of glycosylation sites were observed between plasma and cellular compartments. Bayesian network analyses showed an interdependency between N-linked glycosylation sites found in our study, which may have immense functional relevance.</p> <p>Conclusion</p> <p>Our analyses have identified single cell/compartment-specific amino acid changes and differences in N-linked glycosylation patterns between plasma and diverse blood leukocytes. Bayesian network analyses showed associations inferring alternative glycosylation pathways. We believe that these studies will provide crucial insights into the host immune response and its ability in controlling HIV replication <it>in vivo</it>. These findings could also have relevance in shielding and evasion of HIV-1 from neutralizing antibodies.</p

Assessing transmissibility of HIV-1 drug resistance mutations from treated and from drug-naive individuals (AIDS (2015) 29 (2045-2052))

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