Voronoi Glass-Forming Liquids : A Structural Study

We introduce a new theoretical model of simple fluid, whose interactions, defined in terms of the Voronoi cells of the configurations, are local and many-body. The resulting system is studied both theoretically and numerically. We show that the fluid, though sharing the global features of other models of fluids with soft interactions, has several unusual characteristics, which are investigated and discussed.Comment: 19 pages, 9 figure

The notion of persistence applied to breathers in thermal equilibrium

We study the thermal equilibrium of nonlinear Klein-Gordon chains at the limit of small coupling (anticontinuum limit). We show that the persistence distribution associated to the local energy density is a useful tool to study the statistical distribution of so-called thermal breathers, mainly when the equilibrium is characterized by long-lived static excitations; in that case, the distribution of persistence intervals turns out to be a powerlaw. We demonstrate also that this generic behaviour has a counterpart in the power spectra, where the high frequencies domains nicely collapse if properly rescaled. These results are also compared to non linear Klein-Gordon chains with a soft nonlinearity, for which the thermal breathers are rather mobile entities. Finally, we discuss the possibility of a breather-induced anomalous diffusion law, and show that despite a strong slowing-down of the energy diffusion, there are numerical evidences for a normal asymptotic diffusion mechanism, but with exceptionnally small diffusion coefficients.Comment: submitted to Physica

Trotter Derivation of Algorithms for Brownian and Dissipative Particle Dynamics

This paper focuses on the temporal discretization of the Langevin dynamics, and on different resulting numerical integration schemes. Using a method based on the exponentiation of time dependent operators, we carefully derive a numerical scheme for the Langevin dynamics, that we found equivalent to the proposal of Ermak, and not simply to the stochastic version of the velocity-Verlet algorithm. However, we checked on numerical simulations that both algorithms give similar results, and share the same ``weak order two'' accuracy. We then apply the same strategy to derive and test two numerical schemes for the dissipative particle dynamics (DPD). The first one of them was found to compare well, in terms of speed and accuracy, with the best currently available algorithms.Comment: to be published in J.Chem.Phy

New conserved structural fields for supercooled liquids

By considering Voronoi tessellations of the configurations of a fluid, we propose two new conserved fields, which provide structural information not fully accounted for by the usual 2-point density field fluctuations (structure factor). One of these fields is scalar and associated to the Voronoi cell volumes, whereas the other one, termed the "geometrical polarisation", is vectorial, related to the very local anisotropy of the configurations. We study the static and dynamical properties of these fields in the supercooled regime of a model glass-forming liquid. We show in particular that the geometrical polarisation is both statically correlated to the force field and contrary to it develops a plateau regime when the temperature is lowered. We attribute this behaviour to the microsopic disorder of the underlying inherent structures (IS) which dictate the dynamics on time scales larger than the true microscopic time, in the strong supercooled regime. In this respect, this work raises the issue of to what extent the inter IS dynamics, intrinsically anisotropic and collective (cf. T.B. Schr{\o}der et al. {\it J. of Chem. Phys.}, {\bf 112}, 9834 (2000)), could be related to their polarisation field.Comment: submitted to EPJE the 09/30/201

Injected Power Fluctuations in 1D dissipative systems : role of ballistic transport

This paper is a generalization of the models considered in [J. Stat. Phys. 128,1365 (2007)]. Using an analogy with free fermions, we compute exactly the large deviation function (ldf) of the energy injected up to time $t$ in a one-dimensional dissipative system of classical spins, where a drift is allowed. The dynamics are T=0 asymmetric Glauber dynamics driven out of rest by an injection mechanism, namely a Poissonian flipping of one spin. The drift induces anisotropy in the system, making the model more comparable to experimental systems with dissipative structures. We discuss the physical content of the results, specifically the influence of the rate of the Poisson injection process and the magnitude of the drift on the properties of the ldf. We also compare the results of this spin model to simple phenomenological models of energy injection (Poisson or Bernoulli processes of domain wall injection). We show that many qualitative results of the spin model can be understood within this simplified framework.Comment: 23 pages, 8 figure

Power fluctuations in stochastic models of dissipative systems

We consider different models of stochastic dissipative equations and theoretically compute the probability distribution functions (actually the associated large deviation functions) of the time averaged injected power required to sustain a nontrivial stationary state. We discuss the results and in particular draw from our results some general features shared by these distributions in realistic dissipative systems

Injected Power Fluctuations in 1D Dissipative Systems

Using fermionic techniques, we compute exactly the large deviation function (ldf) of the time-integrated injected power in several one-dimensional dissipative systems of classical spins. The dynamics are T=0 Glauber dynamics supplemented by an injection mechanism, which is taken as a Poissonian flipping of one particular spin. We discuss the physical content of the results, specifically the influence of the rate of the Poisson process on the properties of the ldf.Comment: 18 pages, 8 figure

Colistin-sparing regimens against Klebsiella pneumoniae carbapenemase-producing K. pneumoniae isolates: Combination of tigecycline or doxycycline and gentamicin or amikacin

AbstractBackground/PurposeIn vitro studies of the combination of an aminoglycoside with tigecycline or doxycycline against Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae isolates are rarely published. The goal of this study was to evaluate the antibacterial activity of the combination regimens.MethodsThirteen genetically different KPC-producing K. pneumoniae isolates were randomly selected. Drug concentrations of amikacin, gentamicin, tigecycline, and doxycycline were adjusted to 1-, 1/2-, and 1/4-fold of respective minimum inhibitory concentrations (MICs). Each drug alone or the combinations of amikacin or gentamicin with tigecycline or doxycycline were tested by combination studies.ResultsTreatment with the 1× MIC concentration in combinations of amikacin or gentamicin and tigecycline or doxycycline for 24 hours resulted in bactericidal activity of 84–100% in the isolates. Treatment with 1/2× MIC combinations resulted in synergism of 69–100% in the isolates. Notably, doxycycline plus gentamicin or amikacin was synergistic for all tested isolates. However, bactericidal or synergistic effect was barely evident following 1/4× MIC combinations. There was no antagonism in any of the combination regimens.ConclusionEnhanced activity was noted following treatment with doxycycline combined with gentamicin or amikacin against KPC-producing K. pneumoniae isolates, warranting further in vitro and animal investigations before clinical application