Orbitally Driven Spin Pairing in the 3D Non-Magnetic Mott Insulator BaVS3: Evidence from Single Crystal Studies

Static electrical and magnetic properties of single crystal BaVS_3 were measured over the structural (T_S=240K), metal-insulator (T_MI=69K), and suspected orbital ordering (T_X=30K) transitions. The resistivity is almost isotropic both in the metallic and insulating states. An anomaly in the magnetic anisotropy at T_X signals a phase transition to an ordered low-T state. The results are interpreted in terms of orbital ordering and spin pairing within the lowest crystal field quasi-doublet. The disordered insulator at T_X<T<T_MI is described as a classical liquid of non-magnetic pairs.Comment: 4 pages, 5 figures, revtex, epsf, and multicol style. Problem with figures fixed. To appear in Phys. Rev. B Rap. Com

Evidence for discrimination between feeding sounds of familiar fish and unfamiliar mammal-eating killer whale ecotypes by long-finned pilot whales

Research funding was provided by the US Office of Naval Research, the DGA/TN (France), the UK Natural Environmental Research Council, and the Ministries of Defence of Norway and The Netherlands. PLT acknowledges funding received from the MASTS pooling initiative (The Marine Alliance for Science and Technology for Scotland). MASTS is funded by the Scottish Funding Council (Grant reference HR09011) and contributing institutions. CC acknowledges statistical support provided by the Multi-study OCean acoustics Human effects Analysis (MOCHA) project funded by the United States Office of Naval Research (Grant N00014-12-1-0204).Killer whales (KW) may be predators or competitors of other cetaceans. Since their foraging behavior and acoustics differ among populations ('ecotypes'), we hypothesized that other cetaceans can eavesdrop on KW sounds and adjust their behavior according to the KW ecotype. We performed playback experiments on long-finned pilot whales (Globicephala melas) in Norway using familiar fish-eating KW sounds (fKW) simulating a sympatric population that might compete for foraging areas, unfamiliar mammal-eating KW sounds (mKW) simulating a potential predator threat, and two control sounds. We assessed behavioral responses using animal-borne multi-sensor tags and surface visual observations. Pilot whales barely changed behavior to a broadband noise (CTRL-), whereas they were attracted and exhibited spyhops to fKW, mKW, and to a repeated-tonal upsweep signal (CTRL+). Whales never stopped nor started feeding in response to fKW, whereas they reduced or stopped foraging to mKW and CTRL+. Moreover, pilot whales joined other subgroups in response to fKW and CTRL+, whereas they tightened individual spacing within group and reduced time at surface in response to mKW. Typical active intimidation behavior displayed to fKW might be an antipredator strategy to a known low-risk ecotype or alternatively a way of securing the habitat exploited by a heterospecific sympatric population. Cessation of feeding and more cohesive approach to mKW playbacks might reflect an antipredator behavior towards an unknown KW ecotype of potentially higher risk. We conclude that pilot whales are able to acoustically discriminate between familiar and unfamiliar KW ecotypes, enabling them to adjust their behavior according to the perceived disturbance type.PostprintPeer reviewe

Effect of a serogroup A meningococcal conjugate vaccine (PsA-TT) on serogroup A meningococcal meningitis and carriage in Chad: a community study [corrected].

BACKGROUND: A serogroup A meningococcal polysaccharide-tetanus toxoid conjugate vaccine (PsA-TT, MenAfriVac) was licensed in India in 2009, and pre-qualified by WHO in 2010, on the basis of its safety and immunogenicity. This vaccine is now being deployed across the African meningitis belt. We studied the effect of PsA-TT on meningococcal meningitis and carriage in Chad during a serogroup A meningococcal meningitis epidemic. METHODS: We obtained data for the incidence of meningitis before and after vaccination from national records between January, 2009, and June, 2012. In 2012, surveillance was enhanced in regions where vaccination with PsA-TT had been undertaken in 2011, and in one district where a reactive vaccination campaign in response to an outbreak of meningitis was undertaken. Meningococcal carriage was studied in an age-stratified sample of residents aged 1-29 years of a rural area roughly 13-15 and 2-4 months before and 4-6 months after vaccination. Meningococci obtained from cerebrospinal fluid or oropharyngeal swabs were characterised by conventional microbiological and molecular methods. FINDINGS: Roughly 1·8 million individuals aged 1-29 years received one dose of PsA-TT during a vaccination campaign in three regions of Chad in and around the capital N'Djamena during 10 days in December, 2011. The incidence of meningitis during the 2012 meningitis season in these three regions was 2·48 per 100,000 (57 cases in the 2·3 million population), whereas in regions without mass vaccination, incidence was 43·8 per 100,000 (3809 cases per 8·7 million population), a 94% difference in crude incidence (p<0·0001), and an incidence rate ratio of 0·096 (95% CI 0·046-0·198). Despite enhanced surveillance, no case of serogroup A meningococcal meningitis was reported in the three vaccinated regions. 32 serogroup A carriers were identified in 4278 age-stratified individuals (0·75%) living in a rural area near the capital 2-4 months before vaccination, whereas only one serogroup A meningococcus was isolated in 5001 people living in the same community 4-6 months after vaccination (adjusted odds ratio 0·019, 95% CI 0·002-0·138; p<0·0001). INTERPRETATION: PSA-TT was highly effective at prevention of serogroup A invasive meningococcal disease and carriage in Chad. How long this protection will persist needs to be established. FUNDING: The Bill & Melinda Gates Foundation, the Wellcome Trust, and Médecins Sans Frontères

Modeling Spinal Muscular Atrophy in Drosophila

Spinal Muscular Atrophy (SMA), a recessive hereditary neurodegenerative disease in humans, has been linked to mutations in the survival motor neuron (SMN) gene. SMA patients display early onset lethality coupled with motor neuron loss and skeletal muscle atrophy. We used Drosophila, which encodes a single SMN ortholog, survival motor neuron (Smn), to model SMA, since reduction of Smn function leads to defects that mimic the SMA pathology in humans. Here we show that a normal neuromuscular junction (NMJ) structure depends on SMN expression and that SMN concentrates in the post-synaptic NMJ regions. We conducted a screen for genetic modifiers of an Smn phenotype using the Exelixis collection of transposon-induced mutations, which affects approximately 50% of the Drosophila genome. This screen resulted in the recovery of 27 modifiers, thereby expanding the genetic circuitry of Smn to include several genes not previously known to be associated with this locus. Among the identified modifiers was wishful thinking (wit), a type II BMP receptor, which was shown to alter the Smn NMJ phenotype. Further characterization of two additional members of the BMP signaling pathway, Mothers against dpp (Mad) and Daughters against dpp (Dad), also modify the Smn NMJ phenotype. The NMJ defects caused by loss of Smn function can be ameliorated by increasing BMP signals, suggesting that increased BMP activity in SMA patients may help to alleviate symptoms of the disease. These results confirm that our genetic approach is likely to identify bona fide modulators of SMN activity, especially regarding its role at the neuromuscular junction, and as a consequence, may identify putative SMA therapeutic targets

Large-scale profiling of noncoding RNA function in yeast

Noncoding RNAs (ncRNAs) are emerging as key regulators of cellular function. We have exploited the recently developed barcoded ncRNA gene deletion strain collections in the yeast Saccharomyces cerevisiae to investigate the numerous ncRNAs in yeast with no known function. The ncRNA deletion collection contains deletions of tRNAs, snoRNAs, snRNAs, stable unannotated transcripts (SUTs), cryptic unstable transcripts (CUTs) and other annotated ncRNAs encompassing 532 different individual ncRNA deletions. We have profiled the fitness of the diploid heterozygous ncRNA deletion strain collection in six conditions using batch and continuous liquid culture, as well as the haploid ncRNA deletion strain collections arrayed individually onto solid rich media. These analyses revealed many novel environmental-specific haplo-insufficient and haplo-proficient phenotypes providing key information on the importance of each specific ncRNA in every condition. Co-fitness analysis using fitness data from the heterozygous ncRNA deletion strain collection identified two ncRNA groups required for growth during heat stress and nutrient deprivation. The extensive fitness data for each ncRNA deletion strain has been compiled into an easy to navigate database called Yeast ncRNA Analysis (YNCA). By expanding the original ncRNA deletion strain collection we identified four novel essential ncRNAs; SUT527, SUT075, SUT367 and SUT259/691. We defined the effects of each new essential ncRNA on adjacent gene expression in the heterozygote background identifying both repression and induction of nearby genes. Additionally, we discovered a function for SUT527 in the expression, 3’ end formation and localization of SEC4, an essential protein coding mRNA. Finally, using plasmid complementation we rescued the SUT075 lethal phenotype revealing that this ncRNA acts in trans. Overall, our findings provide important new insights into the function of ncRNAs

CONVERSION ELECTRON MÖSSBAUER SPECTROSCOPY DOWN TO LIQUID HELIUM TEMPERATURE

On a réalisé un spectromètre Mössbauer à électrons de conversion qui permet d'effectuer des mesures jusqu'à la température de l'hélium liquide. Le détecteur d'électrons de conversion fonctionne sous vide ; il comporte un analyseur d'électrons à champ longitudinal et un multiplicateur tubulaire d'électrons (channeltron). Des mesures Mössbauer à 4,2 K et à la température ambiante, effectuées sur des couches minces d'alliages amorphes FexGe1-x sont présentées.A conversion Electron Mössbauer Spectrometer is described which allows measurements to be performed down to liquid helium temperature. The conversion electron detector operates under vacuum. It is made of a longitudinal field electron analyser and a tubular electron multiplier (channeltron). Mössbauer measurements at room temperature and 4.2 K, made on thin films, 1000 Å, of amorphous FexGe1-x alloys are presented

ELECTRIC FIELD GRADIENT AT Fe2+ SITES IN TRIOCTAHEDRAL LAYER SILICATES

Nous avons étudié une série de silicates en feuillets aussi bien en cristaux et sous champ magnétique (biotite, chlorite, vermiculite) qu'en poudre dans l'état antiferromagnétique (greenalite et berthiérine). On trouve que dans les minéraux 1 : 1 l'axe Z du gradient de champ électrique est proche de l'axe c des silicates, que VZZ est négatif et que η ≤ 0,2, résultats cohérents avec un état |0> de Fe2+. Ceci implique un plan c de facile aimantation. Dans les minéraux 2 : 1, au contraire, η = 0,9(1), le signe de VZZ est indéterminé, mais l'axe Z est encore proche de l'axe c.We have examined a series of sheet silicates, both in single crystal form in an applied magnetic field (biotite, chlorite, vermiculite) and as powders in the magnetically ordered state (greenalite, berthierine). It is found that VZZ is negative in the 1 : 1 minerals, that η ≤ 0,2 and that the Z-axis is close to the c-axis of the silicate. These results indicate a |0> ground state for the Fe2+ ion and a c-plane of easy magnetization. In the 2 : 1 minerals however, η = 0.9(1). The sign of VZZ was not determined, but the Z axis is again close to the c-axis

MAGNETIC ORDERING AND MAGNETIZATION IN AMORPHOUS Fe-Ge FILMS

Des couches minces amorphes d'alliages Fe-Ge dont la composition varie de 0 à 75 at. % de Fe ont été préparées, le germanium se comportant comme une matrice diamagnétique amorphe pour les atomes de Fe. L'analyse des diagrammes de diffraction électronique montre que les couches sont amorphes pour toutes les concentrations, une interprétation est donnée en utilisant un modèle de sphères rigides. La conductivité électrique a été mesurée de 20 K à 300 K ; pour tous les films jusqu'a environ 25 at. % de Fe, la loi de Mott σ(T) = σ0 exp–(T0/T)¼ est vérifiée. Des mesures magnétiques ont été réalisées pour établir la nature des interactions magnétiques. Un ordre magnétique à longue distance (ferromagnétique) apparaît pour une concentration critique d'environ 25 at. % de Fe. La température de Curie Tc croît très rapidement avec la quantité de fer au voisinage de la concentration critique. Les cycles d'hystérésis mesurés par effet Kerr sont rectangulaires, ce qui suppose une aimantation relativement uniforme des films. La concentration critique de percolation des atomes magnétiques implique un nombre de coordination d'environ 8 à cette concentration. Des mesures en microscopie Lorentz ont aussi été effectuées.Amorphous thin films alloys of Fe-Ge ranging from 0 to 75 at. % iron have been prepared in which germanium serves as an amorphous diamagnetic matrix for iron atoms. Analysis of electron diffraction rings show the films to be amorphous for all compositions and can be interpreted on the basis of hard sphere models. Electrical conductivity from 20 K to 300 K has been performed, and for all films up to 25 at. % Fe, the Mott power law σ(T) = σ0 exp–(T0/T)¼ is obeyed. Magnetic measurements have been performed to establish the nature and range of magnetic interactions. Long range magnetic order (ferromagnetic) appears at around a critical concentration of about 25 at. % Fe. Curie temperature as a function of increasing Fe concentration shows extremely rapid increase of Tc around the critical concentration. The hysteresis loop measured by Kerr effect is square and implies uniform magnetization in the films. The critical percolation concentration of magnetic atoms implies a coordination number of ~ 8 for the amorphous matrix at this concentration. Measurements by Lorentz electron microscopy are also performed