Vafa-Witten Estimates for Compact Symmetric Spaces

We give an optimal upper bound for the first eigenvalue of the untwisted Dirac operator on a compact symmetric space G/H with rk G-rk H\le 1 with respect to arbitrary Riemannian metrics. We also prove a rigidity statement.Comment: LaTeX, 11 pages. V2: Rigidity statement added, minor changes. To appea

Characterization of elastic scattering near a Feshbach resonance in rubidium 87

The s-wave scattering length for elastic collisions between 87Rb atoms in the state |f,m_f>=|1,1> is measured in the vicinity of a Feshbach resonance near 1007 G. Experimentally, the scattering length is determined from the mean-field driven expansion of a Bose-Einstein condensate in a homogeneous magnetic field. The scattering length is measured as a function of the magnetic field and agrees with the theoretical expectation. The position and the width of the resonance are determined to be 1007.40 G and 0.20 G, respectively.Comment: 4 pages, 2 figures minor revisions: added Ref.6, included error bar

Pumping Metallic Nanoparticles with Spatial Precision within Magnetic Mesoporous Platforms: 3D Characterization and Catalytic Application

The present work shows an efficient strategy to assemble two types of functional nanoparticles onto mesoporous MCM-41 silica nanospheres with a high degree of spatial precision. In a first stage, magnetite nanoparticles are synthesized with a size larger than the support pores and grafted covalently through a peptide-like bonding onto their external surface. This endowed the silica nanoparticles with a strong superparamagnetic response, while preserving the highly ordered interior space for the encapsulation of other functional guest species. Second, we report the finely controlled pumping of preformed Pt nanoparticles (1.5 nm) within the channels of the magnetic MCM-41 nanospheres to confer an additional catalytic functionality to the multiassembled nanoplatform. The penetration depth of the metallic nanoparticles can be explained as a result of the interplay between the particle-wall electrostatic attraction and the repulsive forces between neighboring Pt nanoparticles. A detailed transmission electron microscopy and a 3D high-resolution high-angle annular dark-field detector electron tomography study were carried out to characterize the material and to explain the assembly mechanism. Finally, the performance of these multifunctional nanohybrids as magnetically recoverable catalysts has been evaluated in the selective hydrogenation of p-nitrophenol, a well-known pollutant and intermediate in multiple industrial processes

Advances in single crystal growth and annealing treatment of electron-doped HTSC

High quality electron-doped HTSC single crystals of $\rm Pr_{2-x}Ce_{x}CuO_{4+\delta}$ and $\rm Nd_{2-x}Ce_{x}CuO_{4+\delta}$ have been successfully grown by the container-free traveling solvent floating zone technique. The optimally doped $\rm Pr_{2-x}Ce_{x}CuO_{4+\delta}$ and $\rm Nd_{2-x}Ce_{x}CuO_{4+\delta}$ crystals have transition temperatures $T_{\rm c}$ of $25$\,K and $23.5$\,K, respectively, with a transition width of less than $1$\,K. We found a strong dependence of the optimal growth parameters on the Ce content $x$. We discuss the optimization of the post-growth annealing treatment of the samples, the doping extension of the superconducting dome for both compounds as well as the role of excess oxygen. The absolute oxygen content of the as-grown crystals is determined from thermogravimetric experiments and is found to be $\ge 4.0$. This oxygen surplus is nearly completely removed by a post-growth annealing treatment. The reduction process is reversible as demonstrated by magnetization measurements. In as-grown samples the excess oxygen resides on the apical site O(3). This apical oxygen has nearly no doping effect, but rather influences the evolution of superconductivity by inducing additional disorder in the CuO$_{2}$ layers. The very high crystal quality of $\rm Nd_{2-x}Ce_{x}CuO_{4+\delta}$ is particularly manifest in magnetic quantum oscillations observed on several samples at different doping levels. They provide a unique opportunity of studying the Fermi surface and its dependence on the carrier concentration in the bulk of the crystals.Comment: 19 pages, 7 figures, submitted to Eur. Phys. J.

Unzipping Dynamics of Long DNAs

The two strands of the DNA double helix can be `unzipped' by application of 15 pN force. We analyze the dynamics of unzipping and rezipping, for the case where the molecule ends are separated and re-approached at constant velocity. For unzipping of 50 kilobase DNAs at less than about 1000 bases per second, thermal equilibrium-based theory applies. However, for higher unzipping velocities, rotational viscous drag creates a buildup of elastic torque to levels above kBT in the dsDNA region, causing the unzipping force to be well above or well below the equilibrium unzipping force during respectively unzipping and rezipping, in accord with recent experimental results of Thomen et al. [Phys. Rev. Lett. 88, 248102 (2002)]. Our analysis includes the effect of sequence on unzipping and rezipping, and the transient delay in buildup of the unzipping force due to the approach to the steady state.Comment: 15 pages Revtex file including 9 figure

The low-lying excitations of polydiacetylene

The Pariser-Parr-Pople Hamiltonian is used to calculate and identify the nature of the low-lying vertical transition energies of polydiacetylene. The model is solved using the density matrix renormalisation group method for a fixed acetylenic geometry for chains of up to 102 atoms. The non-linear optical properties of polydiacetylene are considered, which are determined by the third-order susceptibility. The experimental 1Bu data of Giesa and Schultz are used as the geometric model for the calculation. For short chains, the calculated E(1Bu) agrees with the experimental value, within solvation effects (ca. 0.3 eV). The charge gap is used to characterise bound and unbound states. The nBu is above the charge gap and hence a continuum state; the 1Bu, 2Ag and mAg are not and hence are bound excitons. For large chain lengths, the nBu tends towards the charge gap as expected, strongly suggesting that the nBu is the conduction band edge. The conduction band edge for PDA is agreed in the literature to be ca. 3.0 eV. Accounting for the strong polarisation effects of the medium and polaron formation gives our calculated E(nBu) ca. 3.6 eV, with an exciton binding energy of ca. 1.0 eV. The 2Ag state is found to be above the 1Bu, which does not agree with relaxed transition experimental data. However, this could be resolved by including explicit lattice relaxation in the Pariser- Parr-Pople-Peierls model. Particle-hole separation data further suggest that the 1Bu, 2Ag and mAg are bound excitons, and that the nBu is an unbound exciton.Comment: LaTeX, 23 pages, 4 postscript tables and 8 postscript figure

Obtaining cloud top height from WRF model vertical profiles: application to the EUSO program

The objective of the Extreme Universe Space Observatory (EUSO) program is detection and measurement of high-energy particles that reach earth?s atmosphere from space. Clouds at mid and upper levels of the troposphere can interfere with such detection. Therefore, determining cloud top height with high accuracy is crucial to estimating the effect of clouds on these measurements.With this aim, we developed a method to extract that height using cloud temperature via vertical profiles predicted by the WRF model

Levosimendan for resuscitating the microcirculation in patients with septic shock: A randomized controlled study

__Introduction:__ The purpose of the present study was to investigate microcirculatory blood flow in patients with septic shock treated with levosimendan as compared to an active comparator drug (i.e. dobutamine). The primary end point was a difference of ≥ 20% in the microvascular flow index of small vessels (MFIs) among groups. __Methods:__ The study was designed as a prospective, randomized, double-blind clinical trial and performed in a multidisciplinary intensive care unit. After achieving normovolemia and a mean arterial pressure of at least 65 mmHg, 40 septic shock patients were randomized to receive either levosimendan 0.2 μg·kg-1·min-1(n = 20) or an active comparator (dobutamine 5 μg·kg-1·min-1; control; n = 20) for 24 hours. Sublingual microcirculatory blood flow of small and medium vessels was assessed by sidestream dark-field imaging. Microcirculatory variables and data from right heart catheterization were obtained at baseline and 24 hours after randomization. Baseline and demographic data were compared by means of Mann-Whitney rank sum test or chi-square test, as appropriate. Microvascular and hemodynamic variables were analyzed using the Mann-Whitney rank sum test. __Results:__ Microcirculatory flow indices of small and medium vessels increased over time and were significantly higher in the levosimendan group as compared to the control group; P = .02; MFIs 2.9. The relative increase of perfused vessel density vs. baseline was significantly higher in the levosimendan group than in the control group. In addition, the heterogeneity index decreased only in the levosimendan group. There was no statistically significant correlation between systemic and microcirculatory flow variables within each group. __Conclusions:__ Compared to a standard dose of 5 μg·kg-1·min-1of dobutamine, levosimendan at 0.2 μg·kg-1·min-1improved sublingual microcirculatory blood flow in patients with septic shock, as reflected by changes in microcirculatory flow indices of small and medium vessels.Trial registration: NCT00800306

Social capital in Russian agricultural production co-operatives

When the Soviet kolkhozy and sovkhozy were converted, a large number of agricultural production co-operatives was created. Most of these co-operatives still exist in Russia and some of them have a strong market position, accounting for almost one-third of the aggregate volume produced by large farms. This study explores whether social capital might be the explanation for this relative success, i.e. that members support their co-operative because they trust their fellow members as well as the leadership. Interviews with co-operative members resulted in 1401 usable answers. The results from an ordered logit model indicate that social capital plays a partial role. Members who consider co-operatives to be an efficient business form value social ties to other members, even though the leadership does not enjoy much social capital

A hypoperfusion context may aid to interpret hyperlactatemia in sepsis-3 septic shock patients: a proof-of-concept study

__Background:__ Persistent hyperlactatemia is particularly difficult to interpret in septic shock. Besides hypoperfusion, adrenergic-driven lactate production and impaired lactate clearance are important contributors. However, clinical recognition of different sources of hyperlactatemia is unfortunately not a common practice and patients are treated with the same strategy despite the risk of over-resuscitation in some. Indeed, pursuing additional resuscitation in non-hypoperfusion-related cases might lead to the toxicity of fluid overload and vasoactive drugs. We hypothesized that two different clinical patterns can be recognized in septic shock patients through a multimodal perfusion monitoring. Hyperlactatemic patients with a hypoperfusion context probably represent a more severe acute circulatory dysfunction, and the absence of a hypoperfusion context is eventually associated with a good outcome. We performed a retrospective analysis of a database of septic shock patients with persistent hyperlactatemia after initial resuscitation. __Results:__ We defined hypoperfusion context by the presence of a ScvO2 < 70%, or a P(cv-a)CO2 ≥6 mmHg, or a CRT ≥4 s together with hyperlactatemia. Ninety patients were included, of whom seventy exhibited a hypoperfusion-related pattern and 20 did not. Although lactate values were comparable at baseline (4.8 ± 2.8 vs. 4.7 ± 3.7 mmol/L), patients with a hypoperfusion context exhibited a more severe circulatory dysfunction with higher vasopressor requirements, and a trend to longer mechanical ventilation days, ICU stay, and more rescue therapies. Only one of the 20 hyperlactatemic patients without a hypoperfusion context died (5%) compared to 11 of the 70 with hypoperfusion-related hyperlactatemia (16%). __Conclusions:__ Two different clinical patterns among hyperlactatemic septic shock patients may be identified according to hypoperfusion context. Patients with hyperlactatemia plus low ScvO2, or high P(cv-a)CO2, or high CRT values exhibited a more severe circulatory dysfunction. This provides a starting point to launch further prospective studies to confirm if this approach can lead to a more selective resuscitation strategy