74 research outputs found
Generalized Complex Spherical Harmonics, Frame Functions, and Gleason Theorem
Consider a finite dimensional complex Hilbert space \cH, with dim(\cH)
\geq 3, define \bS(\cH):= \{x\in \cH \:|\: ||x||=1\}, and let \nu_\cH be
the unique regular Borel positive measure invariant under the action of the
unitary operators in \cH, with \nu_\cH(\bS(\cH))=1. We prove that if a
complex frame function f : \bS(\cH)\to \bC satisfies f \in \cL^2(\bS(\cH),
\nu_\cH), then it verifies Gleason's statement: There is a unique linear
operator A: \cH \to \cH such that for every u \in
\bS(\cH). is Hermitean when is real. No boundedness requirement is
thus assumed on {\em a priori}.Comment: 9 pages, Accepted for publication in Ann. H. Poincar\'
Density of states of the interacting two-dimensional electron gas
We study the influence of electron-electron interactions on the density of
states (DOS) of clean 2D electron gas. We confirm the linear cusp in the DOS
around the Fermi level, which was obtained previously. The cusp crosses over to
a pure logarithmic dependence further away from the Fermi surface.Comment: RevTeX, 3 pages, no figure
Quasiballistic correction to the density of states in three-dimensional metal
We study the exchange correction to the density of states in the
three-dimensional metal near the Fermi energy. In the ballistic limit, when the
distance to the Fermi level exceeds the inverse transport relaxation time
, we find the correction linear in the distance from the Fermi level.
By a large parameter this ballistic correction exceeds
the diffusive correction obtained earlier.Comment: 2 pages, 1 figur
Strong compensation of the quantum fluctuation corrections in clean superconductor
The theory of fluctuation conductivity for an arbitrary impurity
concentration including ultra-clean limit is developed. It is demonstrated that
the formal divergency of the fluctuation density of states contribution
obtained previously for the clean case is removed by the correct treatment of
the non-local ballistic electron scattering. We show that in the ultra-clean
limit () the density-of-states quantum
corrections are canceled by the Maki-Thompson term and only quasi-classical
paraconductivity remains.Comment: 7 pages 2 figure
Quantum magneto-oscillations in a two-dimensional Fermi liquid
Quantum magneto-oscillations provide a powerfull tool for quantifying
Fermi-liquid parameters of metals. In particular, the quasiparticle effective
mass and spin susceptibility are extracted from the experiment using the
Lifshitz-Kosevich formula, derived under the assumption that the properties of
the system in a non-zero magnetic field are determined uniquely by the
zero-field Fermi-liquid state. This assumption is valid in 3D but, generally
speaking, erroneous in 2D where the Lifshitz-Kosevich formula may be applied
only if the oscillations are strongly damped by thermal smearing and disorder.
In this work, the effects of interactions and disorder on the amplitude of
magneto-oscillations in 2D are studied. It is found that the effective mass
diverges logarithmically with decreasing temperature signaling a deviation from
the Fermi-liquid behavior. It is also shown that the quasiparticle lifetime due
to inelastic interactions does not enter the oscillation amplitude, although
these interactions do renormalize the effective mass. This result provides a
generalization of the Fowler-Prange theorem formulated originally for the
electron-phonon interaction.Comment: 4 pages, 1 figur
Magnetotunneling spectroscopy of mesoscopic correlations in two-dimensional electron systems
An approach to experimentally exploring electronic correlation functions in
mesoscopic regimes is proposed. The idea is to monitor the mesoscopic
fluctuations of a tunneling current flowing between the two layers of a
semiconductor double-quantum-well structure. From the dependence of these
fluctuations on external parameters, such as in-plane or perpendicular magnetic
fields, external bias voltages, etc., the temporal and spatial dependence of
various prominent correlation functions of mesoscopic physics can be
determined. Due to the absence of spatially localized external probes, the
method provides a way to explore the interplay of interaction and localization
effects in two-dimensional systems within a relatively unperturbed environment.
We describe the theoretical background of the approach and quantitatively
discuss the behavior of the current fluctuations in diffusive and ergodic
regimes. The influence of both various interaction mechanisms and localization
effects on the current is discussed. Finally a proposal is made on how, at
least in principle, the method may be used to experimentally determine the
relevant critical exponents of localization-delocalization transitions.Comment: 15 pages, 3 figures include
ARGONAUT-I: Activity of cefiderocol (s-649266), a siderophore cephalosporin, against gram-negative bacteria, including carbapenem-resistant nonfermenters and enterobacteriaceae with defined extended-spectrum β-lactamases and carbapenemases
The activity of the siderophore cephalosporin cefiderocol is targeted against carbapenem-resistant Gram-negative bacteria. In this study, the activity of cefiderocol against characterized carbapenem-resistant Acinetobacter baumannii complex, Stenotrophomonas maltophilia, Pseudomonas aeruginosa, and Enterobacteriaceae strains was determined by microdilution in iron-depleted Mueller-Hinton broth. The MIC90s against A. baumannii, S. maltophilia, and P. aeruginosa were 1, 0.25, and 0.5 mg/ liter, respectively. Against Enterobacteriaceae, the MIC90 was 1 mg/liter for the group harboring OXA-48-like, 2 mg/liter for the group harboring KPC-3, and 8 mg/liter for the group harboring TEM/SHV ESBL, NDM, and KPC-2
OqxAB, a quinolone and olaquindox efflux pump, is widely distributed among multidrug-resistant Klebsiella pneumoniae isolates of human origin
Use of antibiotics among livestock contributes to the selection and dissemination of multidrug resistant (MDR) bacteria. Olaquindox and carbadox are quinoxaline derivatives with antibacterial properties that prevent dysentery and enhance weight gain in suckling pigs. Resistance to quinoxalines is mediated by the efflux pump OqxAB, which also extrudes antibiotics such as chloramphenicol and fluoroquinolones. The gene encoding this efflux pump, oqxAB, was initially detected within plasmid pOLA52, which was found in Escherichia coli isolated from swine manure. Dissemination of oqxAB has been noted in Salmonella species, and the original genetic reservoir of oqxAB was traced to the chromosome of Klebsiella pneumoniae. Surprisingly, OqxAB has been reported only in clinical isolates of K. pneumoniae from China, South Korea, and Spain
Emergence of resistance to colistin during the treatment of bloodstream infection caused by Klebsiella pneumoniae carbapenemase-producing Klebsiella pneumoniae
We report the emergence of colistin resistance in Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella pneumoniae after 8 days of colistin-based therapy, resulting in relapse of bloodstream infection and death. Disruption of the mgrB gene by insertion of a mobile genetic element was found to be the mechanism, which was replicated in vitro after exposure to subinhibitory concentrations of colistin and meropenem
ARGONAUT II study of the in vitro activity of plazomicin against carbapenemase-producing klebsiella pneumoniae
Plazomicin was tested against 697 recently acquired carbapenemresistant Klebsiella pneumoniae isolates from the Great Lakes region of the United States. Plazomicin MIC50 and MIC90 values were 0.25 and 1 mg/liter, respectively; 680 isolates (97.6%) were susceptible (MICs of ≤2 mg/liter), 9 (1.3%) intermediate (MICs of 4 mg/liter), and 8 (1.1%) resistant (MICs of>32 mg/liter). Resistance was associated with rmtF-, rmtB-, or armA-encoded 16S rRNA methyltransferases in all except 1 isolate
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