Glassy dynamics of a binary Voronoi fluid: a mode-coupling analysis.

The binary Voronoi mixture is a fluid model whose interactions are derived from the Voronoi-Laguerre tessellation of the configurations of the system. The resulting interactions are local and many-body. Here we perform molecular-dynamics (MD) simulations of an equimolar mixture that is weakly polydisperse and additive. For the first time we study the structural relaxation of this mixture in the supercooled-liquid regime. From the simulations we determine the time- and temperature-dependent coherent and incoherent scattering functions for a large range of wave vectors, as well as the mean-square displacements of both particle species. We perform a detailed analysis of the dynamics by comparing the MD results with the first-principles-based idealized mode-coupling theory (MCT). To this end, we employ two approaches: fits to the asymptotic predictions of the theory, and fit-parameter-free binary MCT calculations based on static-structure-factor input from the simulations. We find that many-body interactions of the Voronoi mixture do not lead to strong qualitative differences relative to similar analyses carried out for simple liquids with pair-wise interactions. For instance, the fits give an exponent parameter λ ≈ 0.746 comparable to typical values found for simple liquids, the wavevector dependence of the Kohlrausch relaxation time is in good qualitative agreement with literature results for polydisperse hard spheres, and the MCT calculations based on static input overestimate the critical temperature, albeit only by a factor of about 1.2. This overestimation appears to be weak relative to other well-studied supercooled-liquid models such as the binary Kob-Andersen Lennard-Jones mixture. Overall, the agreement between MCT and simulation suggests that it is possible to predict several microscopic dynamic properties with qualitative, and in some cases near-quantitative, accuracy based solely on static two-point structural correlations, even though the system itself is inherently governed by many-body interactions.

Composition fluctuations in polydisperse liquids: Glasslike effects well above the glass transition.

We study a two-dimensional glass-forming system of slightly polydisperse (LJ) particles using molecular dynamics simulations and demonstrate that in the liquid regime (well above the vitrification temperature) this model shows a number of features typical of the glass transition: (i) the relation between compressibility and structure factor S(q) is strongly violated; (ii) the dynamical structure factor S(q,t) at low q shows a two-step relaxation; (iii) the time-dependent heat capacity c_{v}(t) shows a long-time power-law tail. We show that these phenomena can be rationalized with the idea of composition fluctuations and provide a quantitative theory for the effects (i) and (ii). It implies that such effects must be inherent in all polydisperse colloidal models, including binary LJ mixtures.

Voronoi glass-forming liquids: A structural study.

We introduce a 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.

Prevalence and risk factors for colonization by Clostridium difficile and extended-spectrum ß-lactamase-producing Enterobacteriaceae in rehabilitation clinics in Germany.

BACKGROUND: Rehabilitation clinics may vary widely in terms of type of care provided, duration of hospital stay, and case severity. Few data are available on prevalence of Clostridium difficile or extended-spectrum ß-lactamase-producing Enterobacteriaceae (ESBL-E) colonization in rehabilitation clinics in Germany. AIM: This study investigated the frequency of intestinal colonization by these pathogens among patients in rehabilitation clinics of different specialization. METHODS: In the scope of a point prevalence study, faecal samples and demographic and clinical data were collected in five rehabilitation clinics. Samples were screened for C. difficile and ESBL-E by culture. Isolates were characterized by polymerase chain reaction for C. difficile toxins A and B, for ß-lactamase genes, and by molecular typing including pulsed-field gel electrophoresis and PCR-based ribotyping. FINDINGS: Of 305 patients screened, 11.1% were colonized by toxigenic C. difficile and 7.5% by ESBL-E. Colonization rates differed markedly between facilities, ranging from 1.6% to 26.3% for C. difficile and from zero to 23.7% for ESBL-E. Prevalence of colonization by C. difficile and ESBL-E was higher in neurological rehabilitation clinics than in clinics with other specialties (P<0.001). Molecular typing revealed six patients from one neurological rehabilitation clinic harbouring a unique C. difficile strain (ribotype 017). CTX-M-15 was the most prevalent ESBL type. We detected several indistinguishable pairs of ESBL-E isolates within some facilities. CONCLUSION: Significant differences were found in the prevalence of C. difficile and ESBL-E between rehabilitation clinics. Facilities providing specialized medical care for critically ill patients had higher prevalence rates. These results may help to delineate the requirements for infection prevention and control in rehabilitation clinics.

Anomalous sound attenuation in Voronoi liquid.

The physics of simple fluids in the hydrodynamic limit and notably the connection between the proper microscopic scales and the macroscopic hydrodynamical description are nowadays well understood. In particular, the three peak shape of the dynamical structure factor S(k,ω) is a universal feature, as well as the k-dependence of the peak position (∝k) and width ∝k2, the latter accounting for the sound attenuation rate. In this paper, we present a theoretical model of monodisperse fluid, whose interactions are defined via the Voronoi tessellations of the configurations [called the Voronoi liquid and first studied in Ruscher et al., Europhys. Lett. 112, 66003 (2015)], which displays at low temperatures a marked violation of the universal features of S(k,ω) with a sound attenuation rate only ∝k. This anomalous behaviour, which apparently violates the basic symmetries of the liquid state, is traced back to the existence of a time scale which is both short enough for the viscoelastic features of the liquid to impact the relaxational dynamics and however long enough for the momentum diffusion to be substantially slower than the sound propagation on that characteristic time.

[The challenge of infections and multiresistant bacteria among the elderly living in long-term care facilities]. / Herausforderungen durch Infektionen und mehrfach-resistente Bakterien bei alten Menschen in Heimen.

Healthcare-associated infections not only affect patients in acute care hospitals but also patients in need of long-term care. As the elderly are generally most affected, the demographic change in Germany faces a range of increasing challenges in the field of infection control. The ageing process itself is accompanied by several physiological and pathological changes which may result in an increase in the risk of infectious diseases. Elderly living in long-term care facilities (LTCFs) may in addition be exposed to further risks due to their everyday life in a community, nursing care and the, to some extent, inappropriate use of antibiotics. Bacteria that have become resistant to commonly used antimicrobial agents are meanwhile prevalent in nursing homes. Caregivers often feel left alone when facing the task of achieving a balance between the need for a comfortable familiar environment and the application of infection control measures according to a resolute prevention strategy. This review aims to give an overview about the characteristics of infections among the elderly, especially with respect to long-term care.