850 research outputs found
Telavancin activity when tested by a revised susceptibility testing method against uncommonly isolated Gram-positive pathogens responsible for documented infections in hospitals worldwide (2011–2013)
AbstractThe broth microdilution method for telavancin susceptibility testing was revised and now utilises DMSO as solvent for stock solution preparation and diluent for stock solution dilution, following CLSI guidelines for water-insoluble agents. The revised method also incorporates polysorbate 80 in the test medium to mitigate drug binding to plastics. This revised methodology provides more accurate and reproducible MIC determinations, which results in values lower than the previously established method. This study was conducted to re-establish telavancin potencies and susceptibility profiles (using updated interpretive criteria) against a collection of uncommon clinical pathogens (3821 isolates). Telavancin showed MIC50 values of 0.06mg/L against tested staphylococcal species (MIC50/90, 0.03/0.06mg/L; 98.1–100.0% susceptible), with lower results for Staphylococcus hominis (MIC50, ≤0.015mg/L), Staphylococcus lugdunensis (MIC50, ≤0.015mg/L) and Staphylococcus simulans (MIC50, 0.03mg/L). Vancomycin (MIC50, 1mg/L), daptomycin (MIC50, 0.12–1mg/L) and linezolid (MIC50, 0.25–1mg/L) had MIC50 results at least four-fold higher than telavancin against CoNS. Streptococci (99.2–100.0% susceptible) displayed telavancin MIC50 values of ≤0.015–0.03mg/L. Vancomycin (MIC50, 0.25–0.5mg/L) and linezolid (MIC50, 0.5–1mg/L) had higher MIC50 results against streptococci, whilst daptomycin MIC50 values varied from ≤0.06mg/L to 0.5mg/L. Micrococcus, Listeria and Corynebacterium spp. were inhibited by telavancin at ≤0.015, ≤0.03 and ≤0.06mg/L, respectively. Telavancin exhibited potent in vitro activity against this collection, greater than comparators (daptomycin, linezolid, vancomycin). This study provides new baseline MIC results for telavancin and confirms the spectrum and potency of telavancin against less commonly encountered Gram-positive species
Axially symmetric rotating traversable wormholes
This paper generalizes the static and spherically symmetric traversable
wormhole geometry to a rotating axially symmetric one with a time-dependent
angular velocity by means of an exact solution. It was found that the violation
of the weak energy condition, although unavoidable, is considerably less severe
than in the static spherically symmetric case. The radial tidal constraint is
more easily met due to the rotation. Similar improvements are seen in one of
the lateral tidal constraints. The magnitude of the angular velocity may have
little effect on the weak energy condition violation for an axially symmetric
wormhole. For a spherically symmetric one, however, the violation becomes less
severe with increasing angular velocity. The time rate of change of the angular
velocity, on the other hand, was found to have no effect at all. Finally, the
angular velocity must depend only on the radial coordinate, confirming an
earlier result.Comment: 17 pages, AMSTe
Meson Mass Splittings in the Nonrelativistic Model
Mass splittings between isodoublet meson pairs and between and
mesons of the same valence quark content are computed in a detailed
nonrelativistic model. The field theoretic expressions for such splittings are
shown to reduce to kinematic and Breit-Fermi terms in the nonrelativistic
limit. Algebraic results thus obtained are applied to the specific case of the
linear-plus-Coulomb potential, with resultant numbers compared to experiment.Comment: 29 pages with 2 tables and 4 figures, LBL-32872 and UCB-PTH-92/3
Bohr-Sommerfeld quantization and meson spectroscopy
We use the Bohr-Sommerfeld quantization approach in the context of
constituent quark models. This method provides, for the Cornell potential,
analytical formulae for the energy spectra which closely approximate numerical
exact calculations performed with the Schrodinger or the spinless Salpeter
equations. The Bohr-Sommerfeld quantization procedure can also be used to
calculate other observables such as r.m.s. radius or wave function at the
origin. Asymptotic dependence of these observables on quantum numbers are also
obtained in the case of potentials which behave asymptotically as a power-law.
We discuss the constraints imposed by these formulae on the dynamics of the
quark-antiquark interaction.Comment: 13 page
Ground state energy in a wormhole space-time
The ground state energy of the massive scalar field with non-conformal
coupling on the short-throat flat-space wormhole background is calculated
by using zeta renormalization approach. We discuss the renormalization and
relevant heat kernel coefficients in detail. We show that the stable
configuration of wormholes can exist for . In particular case of
massive conformal scalar field with , the radius of throat of stable
wormhole . The self-consistent wormhole has radius of throat
and mass of scalar boson ( and
are the Planck length and mass, respectively).Comment: revtex, 18 pages, 3 eps figures. accepted in Phys.Rev.
Vector Positronium States in QED3
The homogeneous Bethe-Salpeter equation is solved in the quenched ladder
approximation for the vector positronium states of 4-component quantum
electrodynamics in 2 space and 1 time dimensions. Fermion propagator input is
from a Rainbow approximation Dyson-Schwinger solution, with a broad range of
fermion masses considered. This work is an extension of earlier work on the
scalar spectrum of the same model. The non-relativistic limit is also
considered via the large fermion mass limit. Classification of states via their
transformation properties under discrete parity transformations allows
analogies to be drawn with the meson spectrum of QCD.Comment: 24 pages, 2 encapsulated postscript figure
Statistical mechanics of secondary structures formed by random RNA sequences
The formation of secondary structures by a random RNA sequence is studied as
a model system for the sequence-structure problem omnipresent in biopolymers.
Several toy energy models are introduced to allow detailed analytical and
numerical studies. First, a two-replica calculation is performed. By mapping
the two-replica problem to the denaturation of a single homogeneous RNA in
6-dimensional embedding space, we show that sequence disorder is perturbatively
irrelevant, i.e., an RNA molecule with weak sequence disorder is in a molten
phase where many secondary structures with comparable total energy coexist. A
numerical study of various models at high temperature reproduces behaviors
characteristic of the molten phase. On the other hand, a scaling argument based
on the extremal statistics of rare regions can be constructed to show that the
low temperature phase is unstable to sequence disorder. We performed a detailed
numerical study of the low temperature phase using the droplet theory as a
guide, and characterized the statistics of large-scale, low-energy excitations
of the secondary structures from the ground state structure. We find the
excitation energy to grow very slowly (i.e., logarithmically) with the length
scale of the excitation, suggesting the existence of a marginal glass phase.
The transition between the low temperature glass phase and the high temperature
molten phase is also characterized numerically. It is revealed by a change in
the coefficient of the logarithmic excitation energy, from being disorder
dominated to entropy dominated.Comment: 24 pages, 16 figure
Non-perturbative Gluons and Pseudoscalar Mesons in Baryon Spectroscopy
We study baryon spectroscopy including the effects of pseudoscalar meson
exchange and one gluon exchange potentials between quarks, governed by
. The non-perturbative, hyperspherical method calculations show that
one can obtain a good description of the data by using a quark-meson coupling
constant that is compatible with the measured pion-nucleon coupling constant,
and a reasonably small value of .Comment: 12 pages; Submitted to Phys. Rev. C. Rapid Communication
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