Spinning particles in the vacuum C metric

The motion of a spinning test particle given by the Mathisson-Papapetrou equations is studied on an exterior vacuum C metric background spacetime describing the accelerated motion of a spherically symmetric gravitational source. We consider circular orbits of the particle around the direction of acceleration of the source. The symmetries of this configuration lead to the reduction of the differential equations of motion to algebraic relations. The spin supplementary conditions as well as the coupling between the spin of the particle and the acceleration of the source are discussed.Comment: IOP macros used, eps figures n.

Glycopeptide resistance in Enterococcus spp. and coagulase-negative staphylococci from hospitalised patients in Germany: occurrence, characteristics and dalbavancin susceptibility

Objectives: The aim of this study was to evaluate the occurrence of glycopeptide resistance in enterococci and coagulase-negative staphylococci (CoNS) and to determine the susceptibilities of the identified glycopeptide-resistant isolates to dalbavancin. Methods: Twenty-two medical laboratories participated in the study conducted in 2016/17 by the Paul-Ehrlich-Society for Chemotherapy. Each laboratory was asked to collect 30 Enterococcus spp. (limited to Enterococcus faecalis and Enterococcus faecium) and 30 CoNS isolates consecutively from hospitalised patients with a proven or suspected infection. Results: A total of 1285 isolates were collected, comprising 364 E. faecalis, 291 E. faecium and 630 CoNS. No E. faecalis isolates (0%) but 76 E. faecium isolates (26.1%) were vancomycin-resistant, of which 21 showed the VanA type and 55 the VanB type. The proportion of vancomycin-resistant strains among E. faecium isolates from patients in intensive care units (21.6%) was significantly lower than that from patients on regular wards (30.5%). Among the CoNS, 67 isolates (10.6%) were teicoplanin-resistant but none were vancomycin-resistant, with resistance only detected in Staphylococcus epidermidis (12.2%), Staphylococcus haemolyticus (17.9%) and Staphylococcus hominis (13.2%). Dalbavancin at ≤0.25 mg/L inhibited all VanB-type enterococci and 95.5% of teicoplanin-resistant CoNS. Conclusion: The level of glycopeptide resistance in E. faecalis remains very low in Germany but achieved 26% in E. faecium and was >10% in CoNS. Dalbavancin appears to be a feasible option for treating infections caused by VanB-type vancomycin-resistant E. faecium and teicoplanin-resistant CoNS.Peer Reviewe

Quantum nucleation in ferromagnets with tetragonal and hexagonal symmetries

The phenomenon of quantum nucleation is studied in a ferromagnet in the presence of a magnetic field at an arbitrary angle. We consider the magnetocrystalline anisotropy with tetragonal symmetry and that with hexagonal symmetry, respectively. By applying the instanton method in the spin-coherent-state path-integral representation, we calculate the dependence of the rate of quantum nucleation and the crossover temperature on the orientation and strength of the field for a thin film and for a bulk solid. Our results show that the rate of quantum nucleation and the crossover temperature depend on the orientation of the external magnetic field distinctly, which provides a possible experimental test for quantum nucleation in nanometer-scale ferromagnets.Comment: 19 pages and 3 figures, Final version and accepted by Phys. Rev. B (Feb. B1 2001

Phase Space Analysis of Quintessence Cosmologies with a Double Exponential Potential

We use phase space methods to investigate closed, flat, and open Friedmann-Robertson-Walker cosmologies with a scalar potential given by the sum of two exponential terms. The form of the potential is motivated by the dimensional reduction of M-theory with non-trivial four-form flux on a maximally symmetric internal space. To describe the asymptotic features of run-away solutions we introduce the concept of a `quasi fixed point.' We give the complete classification of solutions according to their late-time behavior (accelerating, decelerating, crunch) and the number of periods of accelerated expansion.Comment: 46 pages, 5 figures; v2: minor changes, references added; v3: title changed, refined classification of solutions, 3 references added, version which appeared in JCA

Random-phase approximation and its applications in computational chemistry and materials science

The random-phase approximation (RPA) as an approach for computing the electronic correlation energy is reviewed. After a brief account of its basic concept and historical development, the paper is devoted to the theoretical formulations of RPA, and its applications to realistic systems. With several illustrating applications, we discuss the implications of RPA for computational chemistry and materials science. The computational cost of RPA is also addressed which is critical for its widespread use in future applications. In addition, current correction schemes going beyond RPA and directions of further development will be discussed.Comment: 25 pages, 11 figures, published online in J. Mater. Sci. (2012

Surfactants with colloids: Adsorption or absorption?

The interaction of Aerosol OT (AOT) surfactant with systems of model colloids in nonaqueous solvents (water-in-oil microemulsions, surfactant-stabilized silica organosols, and sterically-stabilized PMMA latexes) is expected to be system specific. Two limiting cases are expected: adsorption, with surfactant located at the particle surfaces, or absorption, with surfactant incorporated into the particle cores. Experiments: Two approaches have been used to determine how AOT is distributed in the colloidal systems. The stability of the colloids in different alkanes (heptane to hexadecane, including mixtures) has been studied to determine any effects on the colloid surfaces. Contrast-variation small-angle neutron scattering (SANS) measurements of the colloid cores and of AOT-colloid mixtures in colloid-matched solvent have also been performed. Normalization to account for the different scattering intensities and different particle radii have been used to enable a system-independent comparison. Findings: AOT in water-in-oil microemulsions and surfactant-stabilized silica organosols is determined to be adsorbed, whereas, surprisingly, AOT in sterically-stabilized PMMA latexes is found to be absorbed. Possible origins of these differences are discussed

Dose equivalence of two commercial preparations of botulinum neurotoxin type A: time for a reassessment?

International audienceBACKGROUND: The units of different preparations of botulinum neurotoxin type A (BoNT-A) have different potencies, and dosing recommendations for each product are not interchangeable. Historically, there has been debate concerning the dose-equivalence ratio that should be used in clinical practice. METHODS: Published evidence was considered to establish an appropriate dose-conversion ratio for the two main commercially available preparations of BoNT-A--Dysport (Dp) and Botox (Bx). RESULTS: Four key areas of evidence were identified: nonclinical and preclinical studies; studies exploring the diffusion characteristics and effects of complexing proteins; comparative experimental data from human studies; and clinical studies. Nonclinical data indicate that the principal reasons for differences in unit potency between the two products are dilution artefacts in the mouse assay. Use of saline as a diluent, at high dilutions, results in significant loss of potency in the Bx assay, whereas use of gelatin phosphate buffer in the Dp assay procedure protects the toxin during dilution. The published data on mouse assays show a Dp : Bx unit ratio range of 2.3-2.5 : 1 in saline and 1.8-3.2 : 1 in gelatin phosphate buffer. Data indicate that complexing proteins or size of the complex, which is highly pH sensitive, play no role in toxin diffusion and that Dp and Bx have similar diffusion characteristics when used at comparable doses. Randomized, controlled clinical studies indicate that 3 : 1 is more appropriate than 4 : 1, but the two products are not equivalent at this ratio. Comparative human experimental studies using the extensor digitorum brevis test, facial lines and anhidrotic action halo tests support dose-conversion ratios less than 3 : 1. LIMITATIONS: Data comparing dose equivalence ratios from the non-clinical setting should be extrapolated into the clinical setting with some caution. CONCLUSIONS: Dose-conversion ratios between Dp and Bx of 4 : 1 and greater are not supported by the recent literature