The Search Coil Magnetometer for THEMIS

International audienceTHEMIS instruments incorporate a tri-axial Search Coil Magnetometer (SCM) designed to measure the magnetic components of waves associated with substorm breakup and expansion. The three search coil antennas cover the same frequency bandwidth, from 0.1 Hz to 4 kHz, in the ULF/ELF frequency range. They extend, with appropriate Noise Equivalent Magnetic Induction (NEMI) and sufficient overlap, the measurements of the fluxgate magnetometers. The NEMI of the searchcoil antennas and associated pre-amplifiers is smaller than 0.76 pT/ p Hz at 10 Hz.The analog signals produced by the searchcoils and associated preamplifiers are digitized and processed inside the IDPU, together with data from the EFI instrument. Searchcoil telemetry includes waveform transmission, FFT processed data, and data from a filter bank. The frequency range covered in waveform depends on the available telemetry. The searchcoils and their three axis structures have been precisely calibrated in a quiet site, and the calibration of the transfer function is checked on board usually once per orbit. The tri-axial searchcoils implemented on the five THEMIS spacecraft are working nominally

Hydrodynamic Interactions in Two Dimensions

We measure hydrodynamic interactions between colloidal particles confined in a thin sheet of fluid. The reduced dimensionality, compared to a bulk fluid, increases dramatically the range of couplings. Using optical tweezers we force a two body system along the eigenmodes of the mobility tensor and find that eigen-mobilities change logarithmically with particle separation. At a hundred radii distance, the mobilities for correlated and anti-correlated motions differ by a factor of two, whereas in bulk fluids, they would be practically indistinguishable. We derive the two dimensional counterpart of the Oseen hydrodynamic tensor which quantitatively reproduces the observed behavior. These results highlight the importance of dimensionality for transport and interactions in colloidal systems and proteins in biological membranes.Comment: 5 pages, 3 figure

Saddles in the energy landscape probed by supercooled liquids

We numerically investigate the supercooled dynamics of two simple model liquids exploiting the partition of the multi-dimension configuration space in basins of attraction of the stationary points (inherent saddles) of the potential energy surface. We find that the inherent saddles order and potential energy are well defined functions of the temperature T. Moreover, decreasing T, the saddle order vanishes at the same temperature (T_MCT) where the inverse diffusivity appears to diverge as a power law. This allows a topological interpretation of T_MCT: it marks the transition from a dynamics between basins of saddles (T>T_MCT) to a dynamics between basins of minima (T<T_MCT).Comment: 4 pages, 3 figures, to be published on PR

Delayed-type hypersensitivity in classic Kaposi sarcoma patients and controls

BACKGROUND: Immune perturbation likely affects the development of Kaposi sarcoma (KS) among people infected with the KS-associated herpesvirus (KSHV). We tested whether KSHV-seropositive individuals or cases of classic KS (cKS), which typically originates in the leg, had differing delayed-type hypersensitivity (DTH) in the forearm or leg. METHODS: Mantoux DTH with three antigens (Candida, tetanus, PPD) was performed on the forearm and leg of 15 cKS cases, 14 KSHV-positives without KS, and 15 KSHV-negative controls. The diameters of induration responses were compared by group and body site. RESULTS: Leg DTH was greater than forearm DTH among controls (mean difference 5.6 mm, P\ubc0.0004), whereas this was not observed in cKS cases ( 2.2 mm, P\ubc0.32) or KSHV-positives (0.5 mm, P\ubc0.56). Leg-minus-forearm DTH difference was greater in controls compared with cKS cases (P\ubc0.004) and KSHV-positives (P\ubc0.002). Leg-plus-forearm DTH was similar in controls (mean 28.2 mm) and cKS cases (24.5 mm, P\ubc0.60), but it was reduced in KSHV-positives (11.8 mm, P\ubc0.02), particularly in the leg (P\ubc0.004) and marginally in the forearm (P\ubc0.07). CONCLUSION: KS cases had weaker DTH only in the leg, whereas both body sites appeared weaker in KSHV-positives without KS. Both systemic and regional immune alterations may influence the development of this malignancy

Constitutively Active Canonical NF-κB Pathway Induces Severe Bone Loss in Mice

Physiologic osteoclastogenesis entails activation of multiple signal transduction pathways distal to the cell membrane receptor RANK. However, atypical osteoclastogenesis driven by pro-inflammatory stimuli has been described. We have reported recently a novel mechanism whereby endogenous mutational activation of the classical NF-κB pathway is sufficient to induce RANKL/RANK-independent osteoclastogenesis. Here we investigate the physiologic relevance of this phenomenon in vivo. Using a knock-in approach, the active form of IKK2, namely IKK2SSEE, was introduced into the myeloid lineage with the aid of CD11b-cre mice. Phenotypic assessment revealed that expression of IKK2SSEE in the myeloid compartment induced significant bone loss in vivo. This observation was supported by a dramatic increase in the number and size of osteoclasts in trabecular regions, elevated levels of circulating TRACP-5b, and reduced bone volume. Mechanistically, we observed that IKK2SSEE induced high expression of not only p65 but also p52 and RelB; the latter two molecules are considered exclusive members of the alternative NF-κB pathway. Intriguingly, RelB and P52 were both required to mediate the osteoclastogenic effect of IKK2SSEE and co-expression of these two proteins was sufficient to recapitulate osteoclastogenesis in the absence of RANKL or IKK2SSEE. Furthermore, we found that NF-κB2/p100 is a potent inhibitor of IKK2SSEE-induced osteoclastogenesis. Deletion of p52 enabled more robust osteoclast formation by the active kinase. In summary, molecular activation of IKK2 may play a role in conditions of pathologic bone destruction, which may be refractory to therapeutic interventions targeting the proximal RANKL/RANK signal

Equilibration times in numerical simulation of structural glasses: Comparing parallel tempering and conventional molecular dynamics

Generation of equilibrium configurations is the major obstacle for numerical investigation of the slow dynamics in supercooled liquid states. The parallel tempering (PT) technique, originally proposed for the numerical equilibration of discrete spin-glass model configurations, has recently been applied in the study of supercooled structural glasses. We present an investigation of the ability of parallel tempering to properly sample the liquid configuration space at different temperatures, by mapping the PT dynamics into the dynamics of the closest local potential energy minima (inherent structures). Comparing the PT equilibration process with the standard molecular dynamics equilibration process we find that the PT does not increase the speed of equilibration of the (slow) configurational degrees of freedom.Comment: 5 pages, 3 figure

Non-Equilibrium Thermodynamic Description of the Coupling between Structural and Entropic Modes in Supercooled Liquids

The density response of supercooled glycerol to an impulsive stimulated thermal grating (q=0.63 micron^-1) has been studied in the temperature range (T=200-340 K) where the structure rearrangement (alpha-relaxation) and thermal diffusion occur on the same time scale. A strong interaction between the two modes occurs giving rise to a dip in the T-dependence of the apparent thermal conductivity and a flattening of the apparent alpha-relaxation time upon cooling. A non-equilibrium thermodynamic (NET) model for the long time response of relaxing fluids has been developed. The model is capable to reproduce the experimental data and to explain the observed phenomenology.Comment: to be published in PRE Rapid Commu

Trophic niche partitioning of five skate species of genus Bathyraja in northern and central Patagonia, Argentina

Overexploitation of marine communities can lead to modifications in the structure of the food web and can force organisms like elasmobranchs to change their feeding habits. To evaluate the impact that fisheries have on food webs and on the interactions between species, it is necessary to describe and quantify the diet of the species involved and follow it through time. This study compares the diet of five skate species using the data obtained from the by-catch of the Argentine hake (Merluccius hubbsi) fishery in north and central Patagonia, Argentina. Diet composition was assessed by analysing the digestive tract contents and trophic overlapping between species of the genus Bathyraja: Bathyraja albomaculata, Bathyraja brachyurops, Bathyraja macloviana, Bathyraja magellanica and Bathyraja multispinis. A total of 184 stomachs were analysed. The diets of B. albomaculata and B. macloviana mainly comprised annelids, whereas that of B. brachyurops primarily comprised fish, including hake heads discarded by the fishery. The diets of B. magellanica and B. multispinis were largely based on crustaceans. Despite the morphological similarities and their shared preference for benthic habitats, no complete diet overlaps were found between the different species. These results suggest that these skate species have undergone a process of diet specialisation. This is a common feeding strategy that occurs to successfully eliminate competition when resources are limited, which corresponds to the conditions found in an environment being affected by the pressures of overfishing.Fil: Tschopp, Ayelen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Cristiani, Franco. Universidad Nacional de la Patagonia "San Juan Bosco". Facultad de Ciencias Naturales y Ciencias de la Salud - Sede Puerto Madryn. Departamento de Biología y Ambiente; ArgentinaFil: Garcia, Nestor Anibal. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Crespo, Enrique Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco". Facultad de Ciencias Naturales y Ciencias de la Salud - Sede Puerto Madryn. Departamento de Biología y Ambiente; ArgentinaFil: Coscarella, Mariano Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco". Facultad de Ciencias Naturales y Ciencias de la Salud - Sede Puerto Madryn. Departamento de Biología y Ambiente; Argentin