Microstructures and properties of materials under repeated laser irradiation

This research program has explored the stability of alloys under pulsed laser irradiation. Two primary directions were investigated: (i) phase transitions during a single laser pulse, and (ii) phase stability under repeated laser irradiation. The first theme was primarily concerned with both the crystalline to amorphous phase transition and the transition of liquids and glasses to crystalline matter. The second project examined the phase evolution during laser pulsing in situations where plastic deformation was prevalent (high-energy laser pulses). Both computer simulation and experimental programs were undertaken. Our work using computer simulations had several notable successes. For the work connected with multiple pulsing, we used molecular dynamics (MD) to simulate the behavior of alloys under severe plastic deformation. We found that during high strain-rate deformation atomic mixing of chemical species is random, independent of the detailed thermochemical properties of the system. This result contrasts with recent reports. In this work, we also developed two new methods of analyzing atomic mixing, one is based on relative mean square displacements (RMSD) of atoms and the other, Burgers vector analysis (BVA), on nearest neighbor displacements. The RMSD analysis is valuable in that it specifies the length scales over which deformation processes take place, and we applied it to understand deformation in nanocrystalline, amorphous and large-grained systems. The BVA analysis, on the other hand, reveals if the damage is homogeneous. Finally we showed that at elevated temperatures, the phase stability is not determined from a simple competition between shearing events and vacancy diffusion, which has long been assumed, but rather atomic mixing in the shearing events is temperature dependent. This work is significant in that it elucidates the fundamental mechanisms that underlie high strain rate deformation, and it provides computational tools for other researchers to perform related work. Our work on MD simulation also examined shock-induced spall. We showed that as voids develop in the early stage of spall, an amorphous region forms around them and that voids coalescence via mass transfer through this amorphous medium. Finally the MD work began examining solidification at deep undercoolings; we found the surprising result that solidification was limited by defects in the liquid and that these defects have virtually identical properties as interstitialcy atoms in the crystalline state. This work is being continued in the renewal project since it offers new insight into the melting and solidification processes under extreme conditions. The experimental work began looking at plastic deformation and liquid-state diffusion using nanosecond laser pulses, but taking advantage of an NSF equipment award, we switched to study solidification at deep undercooling using a femtosecond laser system. We have developed in this program the first application of non-linear reflectivity using third harmonic generation (THG) of light to monitor the solid-liquid/liquid-solid (or any phase transition with 10 fs time resolution). THG decreases by three orders of magnitude on melting whereas the change in linear reflectivity in metals is only 5%. We have also showed that THG can be used as an ultrafast (sub picosecond) thermometer for systems such as Si

Simultaneous and accurate measurement of the dielectric constant at many frequencies spanning a wide range

We present an innovative technique which allows the simultaneous measurement of the dielectric constant of a material at many frequencies, spanning a four orders of magnitude range chosen between 10 --2 Hz and 10 4 Hz. The sensitivity and accuracy are comparable to those obtained using standard single frequency techniques. The technique is based on three new and simple features: a) the precise real time correction of the amplication of a current amplier; b) the specic shape of the excitation signal and its frequency spectrum; and c) the precise synchronization between the generation of the excitation signal and the acquisition of the dielectric response signal. This technique is useful in the case of relatively fast dynamical measurements when the knowledge of the time evolution of the dielectric constant is needed

Relações entre agricultura orgânica e agroecologia: desafios atuais em torno dos princípios da agroecologia.

Neste artigo, exploramos a relação entre Agroecologia e Agricultura Orgânica. O debate na comunidade científica em alguns países e a análise das posições ou discursos de pesquisadores e artigos apontam para distintas combinações, trocas e interações entre a Agricultura Orgânica e Agroecologia. Nesse sentido, primeiramente, com base na revisão de literatura, mostramos distintas interações entre esses estilos de agricultura. Além disto, analisamos as controvérsias das agriculturas em foco, bem como apresentamos uma síntese de dois estudos de caso para ilustrar a aplicação prática de princípios da agroecologia, ava¬liando práticas e valores éticos, relacionando-as com as lógicas familiares ou patronais de funcionamento da produção. Concluímos que as relações entre os estilos de agricultura não podem ser reduzidas a uma simples oposição entre um campo científico e um domínio prático. Diversos elementos devem ser tomados em conta, entre os quais o grau de integração sociocultural (valores) à sociedade, as práticas e a inserção no mercado. Estudos no território brasileiro exemplificam a diversidade de relações existentes, seja in¬clusiva ou exclusiva, observando-se uma fluidez entre conceitos de agroecologia e agricultura orgânica

Mechanical Properties of Molybdenum Disulfide and the Effect of Doping: An in Situ TEM Study

Direct observations on nanopillars composed of molybdenum disulfide (MoS₂) and chromium-doped MoS₂ and their response to compressive stress have been made. Time-resolved transmission electron microscopy (TEM) during compression of the submicrometer diameter pillars of MoS₂- and Cr-doped MoS₂ (Cr: 0, 10, and 50 at %) allow the deformation process of the material to be observed and can be directly correlated with mechanical response to applied load. The addition of chromium to the MoS₂ changed the failure mode from plastic deformation to catastrophic brittle fracture, an effect that was more pronounced as chromium content increased

Farmer seed networks make a limited contribution to agriculture? Four common misconceptions

The importance of seed provisioning in food security and nutrition, agricultural development and rural livelihoods, and agrobiodiversity and germplasm conservation is well accepted by policy makers, practitioners and researchers. The role of farmer seed networks is less well understood and yet is central to debates on current issues ranging from seed sovereignty and rights for farmers to GMOs and the conservation of crop germplasm. In this paper we identify four common misconceptions regarding the nature and importance of farmer seed networks today. (1) Farmer seed networks are inefficient for seed dissemination. (2) Farmer seed networks are closed, conservative systems. (3) Farmer seed networks provide ready, egalitarian access to seed. (4) Farmer seed networks are destined to weaken and disappear. We challenge these misconceptions by drawing upon recent research findings and the authors’ collective field experience in studying farmer seed systems in Africa, Europe, Latin America and Oceania. Priorities for future research are suggested that would advance our understanding of seed networks and better inform agricultural and food policy

Intestinal Protists in Captive Non-human Primates and Their Handlers in Six European Zoological Gardens. Molecular Evidence of Zoonotic Transmission

We assessed the occurrence, genetic diversity, and zoonotic potential of four protozoan (Cryptosporidium spp., Entamoeba histolytica, Entamoeba dispar, Giardia duodenalis), one stramenopile (Blastocystis sp.), one microsporidia (Enterocytozoon bieneusi), and two ciliate (Balantioides coli, Troglodytella abrassarti) intestinal parasite or commensal protist species in captive non-human primates (NHP) and their zookeepers from six European zoological gardens in France (n = 1), Germany (n = 1), and Spain (n = 4). Faecal samples from NHP (n = 454) belonging to 63 species within 35 genera and humans (n = 70) were collected at two sampling periods in each participating institution between October 2018-August 2021. Detection and species identification was accomplished by PCR and Sanger sequencing of the ssu rRNA and/or ITS genes. Sub-genotyping analyses using specific markers were conducted on isolates positive for G. duodenalis (gdh, bg, tpi) and Cryptosporidium spp. (gp60). Overall, 41.0% (186/454) and 30.0% (21/70) of the faecal samples of NHP and human origin tested positive for at least one intestinal protist species, respectively. In NHP, Blastocystis sp. was the most prevalent protist species found (20.3%), followed by G. duodenalis (18.1%), E. dispar (7.9%), B. coli and T. abrassarti (1.5% each), and Cryptosporidium spp. and E. bieneusi (0.9% each). Occurrence rates varied largely among NHP host species, sampling periods, and zoological institutions. The predominant protist species found in humans was Blastocystis sp. (25.7%), followed by Cryptosporidium spp. (2.9%), E. dispar (1.4%), and G. duodenalis (1.4%). Sequencing of PCR-positive amplicons in human and/or NHP confirmed the presence of Cryptosporidium in six isolates (C. hominis: 66.7%, C. parvum: 33.3%), G. duodenalis in 18 isolates (assemblage A: 16.7%, assemblage B: 83.3%), Blastocystis in 110 isolates (ST1:38.2%, ST2:11.8%, ST3: 18.2%, ST4: 9.1%, ST5: 17.3%, ST8: 2.7%, ST13: 0.9%), and E. bieneusi in four isolates (CM18: 75.0%, Type IV: 25.0%). Zoonotic transmission events involving Blastocystis ST1-ST4 were identified in four zoological institutions. Zoonotic transmission of C. hominis was highly suspected, but not fully demonstrated, in one of them. Monitoring of intestinal protist species might be useful for assessing health status of captive NHP and their zookeepers, and to identify transmission pathways of faecal-orally transmitted pathogens.This study was funded by the Health Institute Carlos III (ISCIII), Spanish Ministry of Economy and Competitiveness under project PI16CIII/00024. DG-B was recipient of a Sara Borrell Postdoctoral Fellowship (CD19CIII/00011) funded by the Spanish Ministry of Science, Innovation and Universities. AD was recipient of a PFIS contract (FI20CIII/00002) funded by the Spanish Ministry of Science and Innovation and Universities.S

Hierarchy of lesion processing governs the repair, double-strand break formation and mutability of three-lesion clustered DNA damage

Ionising radiation induces clustered DNA damage sites which pose a severe challenge to the cell’s repair machinery, particularly base excision repair. To date, most studies have focussed on two-lesion clusters. We have designed synthetic oligonucleotides to give a variety of three-lesion clusters containing abasic sites and 8-oxo-7, 8-dihydroguanine to investigate if the hierarchy of lesion processing dictates whether the cluster is cytotoxic or mutagenic. Clusters containing two tandem 8-oxoG lesions opposing an AP site showed retardation of repair of the AP site with nuclear extract and an elevated mutation frequency after transformation into wild-type or mutY Escherichia coli. Clusters containing bistranded AP sites with a vicinal 8-oxoG form DSBs with nuclear extract, as confirmed in vivo by transformation into wild-type E. coli. Using ung1 E. coli, we propose that DSBs arise via lesion processing rather than stalled replication in cycling cells. This study provides evidence that it is not only the prompt formation of DSBs that has implications on cell survival but also the conversion of non-DSB clusters into DSBs during processing and attempted repair. The inaccurate repair of such clusters has biological significance due to the ultimate risk of tumourigenesis or as potential cytotoxic lesions in tumour cells

Contribution a l'etude des equilibres contraints en science des materiaux : couches heteroepitaxiees, couches implantees dans le GaAs : critere de stabilite de composes sollicites

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc