507 research outputs found
Anderson Localization Phenomenon in One-dimensional Elastic Systems
The phenomenon of Anderson localization of waves in elastic systems is
studied. We analyze this phenomenon in two different set of systems: disordered
linear chains of harmonic oscillators and disordered rods which oscillate with
torsional waves. The first set is analyzed numerically whereas the second one
is studied both experimentally and theoretically. In particular, we discuss the
localization properties of the waves as a function of the frequency. In doing
that we have used the inverse participation ratio, which is related to the
localization length. We find that the normal modes localize exponentially
according to Anderson theory. In the elastic systems, the localization length
decreases with frequency. This behavior is in contrast with what happens in
analogous quantum mechanical systems, for which the localization length grows
with energy. This difference is explained by means of the properties of the re
ection coefficient of a single scatterer in each case.Comment: 15 pages, 10 figure
Positive changes in the continuous desaturation index during mechanical ventilation are associated with mortality due to acute respiratory failure
Wannier-Stark ladders in one-dimensional elastic systems
The optical analogues of Bloch oscillations and their associated
Wannier-Stark ladders have been recently analyzed. In this paper we propose an
elastic realization of these ladders, employing for this purpose the torsional
vibrations of specially designed one-dimensional elastic systems. We have
measured, for the first time, the ladder wave amplitudes, which are not
directly accessible either in the quantum mechanical or optical cases. The wave
amplitudes are spatially localized and coincide rather well with theoretically
predicted amplitudes. The rods we analyze can be used to localize different
frequencies in different parts of the elastic systems and viceversa.Comment: 10 pages, 6 figures, accepted in Phys. Rev. Let
Critical properties of the optical field localization in a three-dimensional percolating system: Theory and experiment
We systematically study the optical field localization in an active
three-dimensional (3D) disordered percolating system with light nanoemitters
incorporated in percolating clusters. An essential feature of such a hybrid
medium is that the clusters are combined into a fractal radiation pattern, in
which light is simultaneously emitted and scattered by the disordered
structures. Theoretical considerations, based on systematic 3D simulations,
reveal nontrivial dynamics in the form of propagation of localized field
bunches in the percolating material. We obtain the length of the field
localization and dynamical properties of such states as functions of the
occupation probability of the disordered clusters. A transition between the
dynamical states and narrow point-like fields pinned to the emitters is found.
The theoretical analysis of the fractal field properties is followed by an
experimental study of the light generation by nanoemitters incorporated in the
percolating clusters. The experimental results corroborate theoretical
predictions.Comment: 10 pages, 14 figures, to be published Chaos, Solitons & Fractal
Coutilization of glucose and glycerol enhances the production of aromatic compounds in an Escherichia coli strain lacking the phosphoenolpyruvate: carbohydrate phosphotransferase system
<p>Abstract</p> <p>Background</p> <p><it>Escherichia coli </it>strains lacking the phosphoenolpyruvate: carbohydrate phosphotransferase system (PTS) are capable of coutilizing glucose and other carbon sources due to the absence of catabolite repression by glucose. In these strains, the lack of this important regulatory and transport system allows the coexistence of glycolytic and gluconeogenic pathways. Strains lacking PTS have been constructed with the goal of canalizing part of the phosphoenolpyruvate (PEP) not consumed in glucose transport to the aromatic pathway. The deletion of the <it>ptsHIcrr </it>operon inactivates PTS causing poor growth on this sugar; nonetheless, fast growing mutants on glucose have been isolated (PB12 strain). However, there are no reported studies concerning the growth potential of a PTS<sup>- </sup>strain in mixtures of different carbon sources to enhance the production of aromatics compounds.</p> <p>Results</p> <p>PB12 strain is capable of coutilizing mixtures of glucose-arabinose, glucose-gluconate and glucose-glycerol. This capacity increases its specific growth rate (Ό) given that this strain metabolizes more moles of carbon source per unit time. The presence of plasmids pRW300<it>aroG</it><sup><it>fbr </it></sup>and pCL<it>tktA </it>reduces the Ό of strain PB12 in all mixtures of carbon sources, but enhances the productivity and yield of aromatic compounds, especially in the glucose-glycerol mixture, as compared to glucose or glycerol cultures. No acetate was detected in the glycerol and the glucose-glycerol batch fermentations.</p> <p>Conclusion</p> <p>Due to the lack of catabolite repression, PB12 strain carrying multicopy plasmids containing <it>tktA </it>and <it>aroG</it><sup><it>fbr </it></sup>genes is capable of coutilizing glucose and other carbon sources; this capacity, reduces its Ό but increases the production of aromatic compounds.</p
The Holstein Polaron
We describe a variational method to solve the Holstein model for an electron
coupled to dynamical, quantum phonons on an infinite lattice. The variational
space can be systematically expanded to achieve high accuracy with modest
computational resources (12-digit accuracy for the 1d polaron energy at
intermediate coupling). We compute ground and low-lying excited state
properties of the model at continuous values of the wavevector in
essentially all parameter regimes. Our results for the polaron energy band,
effective mass and correlation functions compare favorably with those of other
numerical techniques including DMRG, Global Local and exact diagonalization. We
find a phase transition for the first excited state between a bound and unbound
system of a polaron and an additional phonon excitation. The phase transition
is also treated in strong coupling perturbation theory.Comment: 24 pages, 11 figures submitted to PR
N-cadherin: A new player in neuronal polarity
Comment on: GĂ€rtner A, et al. EMBO J 2012; <span class="b">31</span>:1893-90
Transport properties and Kondo correlations in nanostructures: the time-dependent DMRG method applied to quantum dots coupled to Wilson chains
We apply the adaptive time-dependent Density Matrix Renormalization Group
method (tDMRG) to the study of transport properties of quantum-dot systems
connected to metallic leads. Finite-size effects make the usual tDMRG
description of the Kondo regime a numerically demanding task. We show that such
effects can be attenuated by describing the leads by "Wilson chains", in which
the hopping matrix elements decay exponentially away from the impurity (). For a given system size and in the linear response
regime, results for show several improvements over the undamped,
case: perfect conductance is obtained deeper in the strongly
interacting regime and current plateaus remain well defined for longer time
scales. Similar improvements were obtained in the finite-bias regime up to bias
voltages of the order of the Kondo temperature. These results show that, with
the proposed modification, the tDMRG characterization of Kondo correlations in
the transport properties can be substantially improved, while it turns out to
be sufficient to work with much smaller system sizes. We discuss the numerical
cost of this approach with respect to the necessary system sizes and the
entanglement growth during the time-evolution.Comment: 10 pages, 9 figures. Updated: new section on finite bias adde
Safety and efficacy of ceftolozane/tazobactam plus metronidazole versus meropenem from a phase 2, randomized clinical trial in pediatric participants with complicated intra-abdominal infection
BACKGROUND: Ceftolozane/tazobactam, a cephalosporin-ÎČ-lactamase inhibitor combination, is approved for the treatment of complicated urinary tract infections and complicated intra-abdominal infections (cIAI). The safety and efficacy of ceftolozane/tazobactam in pediatric participants with cIAI were assessed.
METHODS: This phase 2 study (NCT03217136) randomized participants to either ceftolozane/tazobactam+metronidazole or meropenem for treatment of cIAI in pediatric participants (\u3c18 years). The primary objective was to assess the safety and tolerability of intravenous ceftolozane/tazobactam+metronidazole. Clinical cure at end of treatment (EOT) and test of cure (TOC) visits were secondary end points.
RESULTS: The modified intent-to-treat (MITT) population included 91 participants (ceftolozane/tazobactam+metronidazole, n = 70; meropenem, n = 21). Complicated appendicitis was the most common diagnosis (93.4%); Escherichia coli was the most common pathogen (65.9%). Adverse events (AEs) occurred in 80.0% and 61.9% of participants receiving ceftolozane/tazobactam+metronidazole and meropenem, drug-related AEs occurred in 18.6% and 14.3% and serious AEs occurred in 11.4% and 0% of participants receiving ceftolozane/tazobactam+metronidazole and meropenem, respectively. No drug-related serious AEs or discontinuations due to drug-related AEs occurred. Rates of the clinical cure for ceftolozane/tazobactam+metronidazole and meropenem at EOT were 80.0% and 95.2% (difference: -14.3; 95% confidence interval: -26.67 to 4.93) and at TOC were 80.0% and 100.0% (difference: -19.1; 95% confidence interval: -30.18 to -2.89), respectively; 6 of the 14 clinical failures for ceftolozane/tazobactam+metronidazole at TOC were indeterminate responses imputed as failures per protocol.
CONCLUSION: Ceftolozane/tazobactam+metronidazole was well tolerated in pediatric participants with cIAI and had a safety profile similar to the established safety profile in adults. In this descriptive efficacy analysis, ceftolozane/tazobactam+metronidazole appeared efficacious
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