Magnetic structures of Mn3-xFexSn2: an experimental and theoretical study

We investigate the magnetic structure of Mn3-xFexSn2 using neutron powder diffraction experiments and electronic structure calculations. These alloys crystallize in the orthorhombic Ni3Sn2 type of structure (Pnma) and comprise two inequivalent sites for the transition metal atoms (4c and 8d) and two Sn sites (4c and 4c). The neutron data show that the substituting Fe atoms predominantly occupy the 4c transition metal site and carry a lower magnetic moment than Mn atoms. Four kinds of magnetic structures are encountered as a function of temperature and composition: two simple ferromagnetic structures (with the magnetic moments pointing along the b or c axis) and two canted ferromagnetic arrangements (with the ferromagnetic component pointing along the b or c axis). Electronic structure calculations results agree well with the low-temperature experimental magnetic moments and canting angles throughout the series. Comparisons between collinear and non-collinear computations show that the canted state is stabilized by a band mechanism through the opening of a hybridization gap. Synchrotron powder diffraction experiments on Mn3Sn2 reveal a weak monoclinic distortion at low temperature (90.08 deg at 175 K). This lowering of symmetry could explain the stabilization of the c-axis canted ferromagnetic structure, which mixes two orthorhombic magnetic space groups, a circumstance that would otherwise require unusually large high-order terms in the spin Hamiltonian.Comment: 11 pages, 13 figure

Influence de l'origine et de la nature des substances humiques sur l'adsorption de l'atrazine sur charbon actif en poudre

Les essais d'adsorption sur charbon actif en poudre, de sept acides humiques (H) ou fulviques (F) et pour trois pH (5,6 ; 7,0 ; 8,8) marquent que ces acides ont un comportement différent suivant leur origine.Lorsque le pH de la suspension de charbon est basique, l'adsorption des différentes fractions humiques diminue, ce qui est en relation avec l'augmentation de leur solubilité. Pour un même pH de la suspension, les acides humiques et fulviques d'origine aqueuse s'adsorbent mieux que ceux d'origine commerciale ou que ceux extraits de sol.La capacité maximale d'adsorption de l'atrazine sur charbon actif en poudre : 260 mg.g-1 (Langmuir), est plus fortement diminuée en présence d'acides fulviques que d'acides humiques d'une part, et plus inhibée (jusqu'à 40 %) par les acides fulviques extraits d'eau (F1, F2) que par ceux extraits de sol (F3) d'autre part.Par contre, les acides humiques provenant de substances commerciales (H4, H5) influencent moins l'adsorption de l'atrazine.L'ensemble des essais montre que l'origine et la nature des substances humiques joue un rôle prépondérant sur l'adsorption de l'atrazine sur charbon actif, le pH ayant une influence limitée.Enfin l'étude de l'influence de l'atrazine sur l'adsorption des substances humiques sur charbon actif en poudre indique également une différence de comportement entre les acides fulviques, pour lesquels on note peu de variation, et les acides humiques, pour lesquels on note à la fois une promotion de l'adsorption et une meilleure affinité d'adsorption sur le charbon actif en poudre en présence d'atrazine.Ce travail met en évidence l'importance du choix des substances humiques pour des essais d'évaluation des interactions substances humiques - pesticides lors de l'adsorption sur charbon actif en poudre.Though the subject was copiously and oldly studied, this work is bringing a new contribution to the study of the influence of the origin and the nature upon their properties and in particular with atrazine, the more used herbicide these fast years.In order to study this influence of the origin and nature of various humic substances upon the removal of atrazine by adsorption onto powdered activated carbon (PAC), humic substances were obtained from different sources :- Natural aquatic fulvic (F1) and humic (H1) acids isolated from Beaune Lake (Limoges, France).- Natural aquatic fulvic (F2) and humic (H2) acids extracted from hydroxyde sludges of the water treatment plant of La Bastide (Limoges, France).- Soil fulvic acids (F3) extracted from a canadian top soil horizon.- Commercial humic acids (Aldrich. H4 and Jansen H5) obtained from commercial sodium humates.The results of adsorption test of humic acids, fulvic acids and atrazine (alone or together) onto powdered activated carbon (PAC) at three different pH (5,6 ; 7,0 ; 8,8) were expressed by Freundlich's and Langmuir’s models and permitted us to note that :- According to the increasing of water solubility of humic substances with basic pH, their adsorption was better in acidic medium.- Natural aquatic humic substances (H1, H2, F1, F2) were more adsorbed onto PAC than humic substances tram soil (H3) or commercial origines (H4, H5).- Atrazine adsorption capacity was 260 mg.g-1 according to Langmuir's model.- Atrazine adsorption decreased with F1 for all pH ; the same result was also observed with the other natural aquatic humic substances.- Commercial humic acids didn’t importantly affect atrazine adsorption. These differences appeared to be derived from the nature and the origin of fulvic and humic acids. The rose of atrazine on the humic substances adsorption showed a difference between humic and fulvic acids whose adsorption was not influenced by atrazine even humic acids only presented an increasing of adsorption.All these results showed the importance of the selection of humic substances to evaluate the interaction SH-Pesticides during adsorption onto PAC and let us think to a competitive adsorption between fulvic acids and atrazine onto PAC

Adsorption du pentachlorophenol sur divers matériaux : Influence de co-adsorbats organiques (Substances humiques et lindane)

Nous avons réalisé, pour de faibles concentrations, l'étude de l'adsoprtion d'un pesticide le pentachlorophénol, sur plusieurs matériaux adsorbants : le charbon actif, la kaolinite et la bentone. Les résultats montrent que l'adsorption du pentachlorophénol sur la kaolinite reste négligeable tandis que la bentone SD-3 (argile traitée) permet d'obtenir des résultats intéressants avec toutefois une capacité maximale d'adsorption 10 à 100 fois plus faible que celle du charbon actif. Le charbon actif reste le meilleur matériau adsorbant pour le pentachlorophénol. La solubilité de ce composé étant très variable en fonction du pH du milieu on constate que l'adsorption du pentachlorophénol-pentachlorophénate (5 mg.l-1) diminue pour des valeurs de pH supérieures au pKa du couple acide-base que nous avons déterminé expérimentalement, égal à 5,9 ± 0,1. L'adsorption du pentachlorophénol n'est pas affectée par la présence d'acides humiques (obtenus à partir de substances commerciales) utilisés comme coadsorbats (10 mg.l-1) alors que les acides fulviques (20 mg.l-1) extraits de sols semblent provoquer une promotion de l'adsorption. On observe d'autre part que le pentachlorophénol n'affecte pas l'adsorption des acides humiques mais augmente légèrement celle des acides fulviques. Ces remarques suggèrent la possible formation d'un complexe acides fulviques-pentachlorophénol. Lorsqu'on utilise le lindane, pesticide hydrophobe comme coadsorbat (165 mg.l-1), on observe encore d'une façon systématique pour tous les nombreux essais une légère promotion de l'adsorption.Adsorption studies for the removal of the pesticide pentachlorophenol found in a number of water supplies (BELAMIE and GIROUD, 1986) were carried out using various materials including kaolinite, bentone SD-3 and powdered activated carbon (WEBER and GOULD, 1966; WEBER and JODELHAH, 1985). It was found that adsorption on kaolinite was negligible, whereas bentone SD-3 presented and adsorption efficiency from 10 to 100-fold less than equivalent quantities of powdered activated carbon (LOTSE et al., 1968; SHAROM et al., 1980). The effect of the pH on the removal of pentachlorophenol by activated carbon was studied. The removal efficiency of pentachlorophenol by activated carbon is better in acidic media. A clear dependence of adsorption on the pH appeared to be the result of a marked variation of the pesticide solubility as a function of the pH (fig. 3). Adsorption of pentachlorophenol/phenate (5mg.l-1) diminishes markedly at pH values above the pKa of this weak acid (that we found equal to 5,9 ± 0,1) when the pentachlorophenol exists almost entirely in ionic form in aqueous solution, and is enhanced at low pH when the percentage of molecular species (whose concentration can be determined from pKa value) becomes significant (WARD and GETZEN, 1970). These remarks and the adsorptive capacities (163 mg.g-1= 0,6 mmol.g-1 at pH = 5,2 and 79 mg.g-1 0,3 mmol.g-1 at pH =12,7), suggest a П-П interaction between pentachlorophenol and activated carbon which seems to be confirmed by the results with bentone SD-3 (tables 1 to 4), and the values of the electrokinetic potential of these materials. This study emphasizes the effect of organic coadsorbates (e.g., dissolved humic substances and the pesticide lindane) on the adsorption capacity of activated carbon for pentachlorophenol. Two different natural organic matters were studied as coadsorbates : purified humic acids from a commercial source (at 10 mg.l-1) and fulvic acids extracted from a top soil horizon (et 20 mg.l-1) (SCHNITZER and SKINNER, 1963; THURMAN and MALCOLM, 1981). Pentachlorophenol adsorption was not affected by humic acids, whereas an increase of adsorption seemed to be observed in the presence of fulvic acids (fig. 6). Pentachlorophenol does not affect the adsorption of humic acids, but improves slightly the removal of fulvic acids. This suggests an association between the two kinds of organic compounds (WERSNAW et al., 1969; KHAN, 1972; OGNER and SCHNITZER, 1970), the resulting « complex », fulvic acids/pentachlorophenol, being more adsorbed than the compounds themselves. The coadsorbate lindane (0,65 mg.l-1) which is easily adsorbed by activated carton (GOMELLA and BELLE, 1975...) seemed also to Improve slightly the removal efficiency of pentachlorophenol by activated carton (fig. 7)

Prediction and prevention of the next pandemic zoonosis.

Most pandemics--eg, HIV/AIDS, severe acute respiratory syndrome, pandemic influenza--originate in animals, are caused by viruses, and are driven to emerge by ecological, behavioural, or socioeconomic changes. Despite their substantial effects on global public health and growing understanding of the process by which they emerge, no pandemic has been predicted before infecting human beings. We review what is known about the pathogens that emerge, the hosts that they originate in, and the factors that drive their emergence. We discuss challenges to their control and new efforts to predict pandemics, target surveillance to the most crucial interfaces, and identify prevention strategies. New mathematical modelling, diagnostic, communications, and informatics technologies can identify and report hitherto unknown microbes in other species, and thus new risk assessment approaches are needed to identify microbes most likely to cause human disease. We lay out a series of research and surveillance opportunities and goals that could help to overcome these challenges and move the global pandemic strategy from response to pre-emption

One Health proof of concept: Bringing a transdisciplinary approach to surveillance for zoonotic viruses at the human-wild animal interface.

As the world continues to react and respond inefficiently to emerging infectious diseases, such as Middle Eastern Respiratory Syndrome and the Ebola and Zika viruses, a growing transdisciplinary community has called for a more proactive and holistic approach to prevention and preparedness - One Health. Such an approach presents important opportunities to reduce the impact of disease emergence events and also to mitigate future emergence through improved cross-sectoral coordination. In an attempt to provide proof of concept of the utility of the One Health approach, the US Agency for International Development's PREDICT project consortium designed and implemented a targeted, risk-based surveillance strategy based not on humans as sentinels of disease but on detecting viruses early, at their source, where intervention strategies can be implemented before there is opportunity for spillover and spread in people or food animals. Here, we share One Health approaches used by consortium members to illustrate the potential for successful One Health outcomes that can be achieved through collaborative, transdisciplinary partnerships. PREDICT's collaboration with partners around the world on strengthening local capacity to detect hundreds of viruses in wild animals, coupled with a series of cutting-edge virological and analytical activities, have significantly improved our baseline knowledge on the zoonotic pool of viruses and the risk of exposure to people. Further testament to the success of the project's One Health approach and the work of its team of dedicated One Health professionals are the resulting 90 peer-reviewed, scientific publications in under 5 years that improve our understanding of zoonoses and the factors influencing their emergence. The findings are assisting in global health improvements, including surveillance science, diagnostic technologies, understanding of viral evolution, and ecological driver identification. Through its One Health leadership and multi-disciplinary partnerships, PREDICT has forged new networks of professionals from the human, animal, and environmental health sectors to promote global health, improving our understanding of viral disease spillover from wildlife and implementing strategies for preventing and controlling emerging disease threats

Wildlife Trade and Human Health in Lao PDR: An Assessment of the Zoonotic Disease Risk in Markets.

Although the majority of emerging infectious diseases can be linked to wildlife sources, most pathogen spillover events to people could likely be avoided if transmission was better understood and practices adjusted to mitigate risk. Wildlife trade can facilitate zoonotic disease transmission and represents a threat to human health and economies in Asia, highlighted by the 2003 SARS coronavirus outbreak, where a Chinese wildlife market facilitated pathogen transmission. Additionally, wildlife trade poses a serious threat to biodiversity. Therefore, the combined impacts of Asian wildlife trade, sometimes termed bush meat trade, on public health and biodiversity need assessing. From 2010 to 2013, observational data were collected in Lao PDR from markets selling wildlife, including information on volume, form, species and price of wildlife; market biosafety and visitor origin. The potential for traded wildlife to host zoonotic diseases that pose a serious threat to human health was then evaluated at seven markets identified as having high volumes of trade. At the seven markets, during 21 observational surveys, 1,937 alive or fresh dead mammals (approximately 1,009 kg) were observed for sale, including mammals from 12 taxonomic families previously documented to be capable of hosting 36 zoonotic pathogens. In these seven markets, the combination of high wildlife volumes, high risk taxa for zoonoses and poor biosafety increases the potential for pathogen presence and transmission. To examine the potential conservation impact of trade in markets, we assessed the status of 33,752 animals observed during 375 visits to 93 markets, under the Lao PDR Wildlife and Aquatic Law. We observed 6,452 animals listed by Lao PDR as near extinct or threatened with extinction. The combined risks of wildlife trade in Lao PDR to human health and biodiversity highlight the need for a multi-sector approach to effectively protect public health, economic interests and biodiversity

Electronic structure and magnetic properties of RMnX (R= Mg, Ca, Sr, Ba, Y; X= Si, Ge) studied by KKR method

Electronic structure calculations, using the charge and spin self-consistent Korringa- Kohn-Rostoker (KKR) method, have been performed for several $R$Mn$X$ compounds ($R$ = Mg, Ca, Sr, Ba, Y; $X$ = Si, Ge) of the CeFeSi-type structure. The origin of their magnetic properties has been investigated emphasizing the role of the Mn sublattice. The significant influence of the Mn-Mn and Mn-$X$ interatomic distances on the Mn magnetic moment value is delineated from our computations, supporting many neutron diffraction data. We show that the marked change of $\mu_{Mn}$ with the Mn-Mn and Mn-$X$ distances resulted from a redistribution between spin-up and spin-down $d$-Mn DOS rather than from different fillings of the Mn 3$d$-shell. Bearing in mind that the neutron diffraction data reported for the $R$Mn$X$ compounds are rather scattered, the KKR computations of $\mu_{Mn}$ are in fair agreement with the experimental values. Comparing density of states near $E_{F}$ obtained in different magnetic orderings, one can notice that the entitled $R$Mn$X$ systems seem to 'adapt' their magnetic structures to minimize the DOS in the vicinity of the Fermi level. Noteworthy, the SrMnGe antiferromagnet exhibits a pseudo-gap behaviour at $E_{F}$, suggesting anomalous electron transport properties. In addition, the F-AF transition occurring in the disordered La$_{1-x}$Y$_{x}$MnSi alloy for the $0.8<x<1$ range is well supported by the DOS features of La$_{0.2}$Y$_{0.8}$MnSi. In contrast to the investigated $R$Mn$X$ compounds, YFeSi was found to be non-magnetic, which is in excellent agreement with the experimental data.Comment: 10 pages + 14 figures, to appear in Eur. Phys. Jour.

Analyse non-linéaire des instabilités mécaniques induites par le frottement dans les systèmes de freinage aéronautique: effets de l'amortissement sur le comportement transitoire et les cycles limites

Cet article porte sur l'analyse non-linéaire des instabilités mécaniques induites par le frottement dans les systèmes de freinage aéronautique. L'étude est réalisée sur un modèle non-linéaire complet du frein capable de reproduire les principaux phénomènes vibratoires observés au cours d'essais expérimentaux. Le contact non-linéaire frottant entre disques stators et rotors du frein responsable de l'apparition de vibrations est considéré. L'étude a pour but de déterminer l'effet de l'amortissement sur le comportement transitoire et les niveaux vibratoires du frein, dans le cas d'une vibration générée par le couplage de deux modes propres du frein. En particulier on s'attachera à déterminer s'il existe une répartition optimale en amortissement qui permette de réduire les niveaux vibratoires engendrés lors de l'apparition de l'instabilité. Une meilleure compréhension des effets de l'amortissement sur le comportement transitoire et les niveaux vibratoires stationnaires du frein pour des points d'équilibre instable permettra de définir des précautions à prendre lors de la conception du système de freinage afin d'en limiter les risques vibratoires