Upper critical field in {Ba1−x_{1-x}Kx_xBiO3_3}: magnetotransport versus magnetotunneling

Elastic tunneling is used as a powerful direct tool to determine the upper critical field $H_{c2}(T)$ in the high-$T_c$ oxide Ba$_{1-x}$K$_x$BiO$_3$. The temperature dependence of $H_{c2}$ inferred from the tunneling follows the Werthamer-Helfand-Hohenberg prediction for type-II superconductors. A comparison will be made with resistively determined critical field data.Comment: 4 pages incl. 5 figure

Field and angular dependence of the Sommerfeld coefficient in Al-doped MgB2 single crystals

International audienceThe angular and field dependence of the Sommerfeld coefficient = lim Cel /T T→0 Cel being the electronic contribution to the specific heat has been measured in Al-doped MgB2 single crystals for x=0, x=0.1, and x 0.2 . We show that the decomposition previously introduced to describe H, where is the angle between the applied field and the c axis in pure samples Phys. Rev. Lett. 98, 137001 2007 is well adapted to doped samples: e.g., the contribution of the band to the specific heat is proportional to B/Bc2 whereas the contribution of the band is isotropic but highly nonlinear in field. We hence present the evolution of the coherence lengths of the two bands and corresponding Fermi velocities with doping

Anisotropic Enhancement of Superconductivity in Heavy-Ion Irradiated KBa BiO3

International audienceWe have measured the specific heat, resistivity, and ac susceptibility of K; Ba BiO3 single crystals before and after introduction of either point or columnar defects by electron (EI) or heavy-ion irradiation (HII).While the magnetic field dependence of these properties remains mainly unaffected by EI, the irreversibility line and the location of the specific heat anomaly are both shifted up in temperature after HII. The shift is apparent only if the magnetic field is applied parallel to the ion tracks. For perpendicularly applied fields, both lines lie at the same field as in the pristine sample. These experiments call the nature of the vortex liquid state into question

String Loop Corrections to Kahler Potentials in Orientifolds

We determine one-loop string corrections to Kahler potentials in type IIB orientifold compactifications with either N=1 or N=2 supersymmetry, including D-brane moduli, by evaluating string scattering amplitudes.Comment: 80 pages, 4 figure

Direct Transition from Bose Glass to Normal State in the (K,Ba)BiO3 Superconductor

International audienceThe introduction of columnar defects in K; Ba BiO3 single crystals shifts both the irreversibility and thermodynamic transition lines, respectively, deduced from ac susceptibility (and/or transport) and specific heat measurements, upwards. This shift can be attributed to the defect-induced decrease of the difference ( F) between the free energies in the superconducting and the normal states, assuming that the position of the superconducting transition is given by the condition j Fj kBT= 3. This criterion also perfectly reproduces the influence of the angle between the tracks and the external field. This result suggests that no vortex liquid phase exists in this system

Evidence for Two Superconducting Energy Gaps in MgB2 by Point-Contact Spectroscopy

International audienceExperimental support is found for the multiband model of the superconductivity in the recently discovered system MgB2 with the transition temperature Tc 39 K. By means of Andreev reflection, evidence is obtained for two distinct superconducting energy gaps. The sizes of the two gaps (DS 2.8 meV and DL 7 meV) are, respectively, smaller and larger than the expected weak coupling value. Because of the temperature smearing of the spectra the two gaps are hardly distinguishable at elevated temperatures, but when a magnetic field is applied the presence of two gaps can be demonstrated close to the bulk Tc in the raw data

Geometrical barriers and lower critical field in MgB2 single crystals

International audienceThe first penetration field sHpd has been deduced from local magnetization and specific heat measurements in magnesium diboride single crystals. For Ha ic, the geometrical barriers (GB) play a dominant role in the irreversibility mechanism. In thin samples, neglecting the GB in this direction would then lead to a large overestimation of Hc1 deduced from Hp through the standard elliptical formula. The lower critical field is found to be isotropic at low temperature (0.11±0.01 T)

Coordinating Role of RXR alpha in Downregulating Hepatic Detoxification during Inflammation Revealed by Fuzzy-Logic Modeling

During various inflammatory processes circulating cytokines including IL-6, IL-1 beta, and TNF alpha elicit a broad and clinically relevant impairment of hepatic detoxification that is based on the simultaneous downregulation of many drug metabolizing enzymes and transporter genes. To address the question whether a common mechanism is involved we treated human primary hepatocytes with IL-6, the major mediator of the acute phase response in liver, and characterized acute phase and detoxification responses in quantitative gene expression and (phospho-)proteomics data sets. Selective inhibitors were used to disentangle the roles of JAK/STAT, MAPK, and PI3K signaling pathways. A prior knowledge-based fuzzy logic model comprising signal transduction and gene regulation was established and trained with perturbation-derived gene expression data from five hepatocyte donors. Our model suggests a greater role of MAPK/PI3K compared to JAK/STAT with the orphan nuclear receptor RXR alpha playing a central role in mediating transcriptional downregulation. Validation experiments revealed a striking similarity of RXRa gene silencing versus IL-6 induced negative gene regulation (r(s) = 0.79;P<0.0001). These results concur with RXRa functioning as obligatory heterodimerization partner for several nuclear receptors that regulate drug and lipid metabolism

Simple heuristics for the assembly line worker assignment and balancing problem

We propose simple heuristics for the assembly line worker assignment and balancing problem. This problem typically occurs in assembly lines in sheltered work centers for the disabled. Different from the classical simple assembly line balancing problem, the task execution times vary according to the assigned worker. We develop a constructive heuristic framework based on task and worker priority rules defining the order in which the tasks and workers should be assigned to the workstations. We present a number of such rules and compare their performance across three possible uses: as a stand-alone method, as an initial solution generator for meta-heuristics, and as a decoder for a hybrid genetic algorithm. Our results show that the heuristics are fast, they obtain good results as a stand-alone method and are efficient when used as a initial solution generator or as a solution decoder within more elaborate approaches.Comment: 18 pages, 1 figur

Anisotropy of the Sommerfeld Coefficient in Magnesium Diboride Single Crystals

International audienceThe anisotropic field dependence of the Sommerfeld coefficient has been measured down to B ! 0 by combining specific heat and Hall probe magnetization measurements in MgB2 single crystals. We find that B; is the sum of two contributions arising from the and band, respectively. We show that B; B=Bc2 where Bc2 Bab c2= si n 2 2cos2 p with 5:4 ( being the angle between the applied field and the c axis) and B; B B=B B . The ''critical field'' of the band B is fully isotropic but field dependent increasing from 0:25 T for B 0:1 T up to 3 T Bcc 2 for B ! 3 T. Because of the coupling of the two bands, superconductivity survives in the band up to 3 T but is totally destroyed above for any orientation of the field