1,721,132 research outputs found
Inherent structures and Kauzmann temperature of confined liquids
No full textCalculations of the thermodynamical properties of a supercooled liquid confined in a matrix are performed with an inherent structure analysis. The liquid entropy is computed by means of a thermodynamical integration procedure. The contributions to the free energy of the liquid can be decoupled also in confinement in the configurational and the vibrational parts. We show that the vibrational entropy can be calculated in the harmonic approximation as in the bulk case. The Kauzmann temperature of the confined system is estimated from the behavior of the configurational entropy
Mode Coupling behaviour of a Lennard Jones binary mixture: a comparison between bulk and confined phases
No full textWe present a quantitative comparison at equivalent thermodynamical conditions of bulk and confined dynamical properties of a Lennard-Jones binary mixture upon supercooling. Both systems had been previously found to display a behavior in agreement with the mode coupling theory of the evolution of glassy dynamics. Differences and analogies of behavior are discussed focusing, in particular, on the role of hopping in reducing spatially correlated dynamics in the confined system with respect to the bulk
Acinetobacter baumannii: Its Clinical Significance in Human and Veterinary Medicine
Get PDFAcinetobacter baumannii is a Gram-negative, opportunistic pathogen, causing severe infections difficult to treat. The A. baumannii infection rate has increased year by year in human medicine and it is also considered as a major cause of nosocomial infections worldwide. This bac-terium, also well known for its ability to form biofilms, has a strong environmental adaptability and the characteristics of multi-drug resistance. Indeed, strains showing fully resistant profiles represent a worrisome problem in clinical therapeutic treatment. Furthermore, A. baumannii-associated veterinary nosocomial infections has been reported in recent literature. Particularly, carbapenem-resistant A. baumannii can be considered an emerging opportunistic pathogen in human medicine as well as in veterinary medicine
Slow dynamics of a confined supercooled binary mixture in comparison with the bulk phase
No full textDynamic properties of a liquid Lennard-Jones binary mixture embedded in an off-lattice matrix of soft spheres and the corresponding bulk phase are studied upon supercooling close to the crossover temperature of mode-coupling theory by molecular dynamics simulations. The model con. ning system is designed to mimic the properties of silica xerogels. In spite of the strong confinement the dynamic behaviour of the mixture is consistent with the mode-coupling predictions. The parameters of the theory are compared for bulk and confined phases. The range of validity of the theory shrinks in confinement. Consistently with the hypothesis of a growing length scale in supercooled liquids, the dynamics of the confined mixture are faster than those of the equivalent bulk phase
Glass Transition in confinement: a Lennard-Jones binary mixture study
No full textWe present results from an extensive study upon cooling on the behavior of a model glass former, a liquid Lennard-Jones binary mixture, confined in a model for Xerogels. Modification of the dynamical and thermodynamical behavior on approaching the glass transition with respect to the bulk are studied. The Mode Coupling Theory is able to account for the behavior of the liquid mixture also in confinement, but with important differences with respect to the bulk. A study of the thermodynamic behavior via inherent structure analysis is also performed and the Kauzmann temperature is evaluated from the behavior of the configurational entropy
Scale interaction in a mixing layer: The role of the large-scale gradients
No full textThe interaction between scales is investigated in a turbulent mixing layer. The large-scale amplitude modulation of the small scales already observed in other works depends on the crosswise location. Large-scale positive fluctuations correlate with a stronger activity of the small scales on the low speed-side of the mixing layer, and a reduced activity on the high speed-side. However, from physical considerations we would expect the scales to interact in a qualitatively similar way within the flow and across different turbulent flows. Therefore, instead of the large-scale fluctuations, the large-scale gradients modulation of the small scales has been additionally investigated
Methicillin-resistant staphylococci in clinical bovine mastitis: occurrence, molecular analysis, and biofilm production
No full textStaphylococcus aureus is an important pathogen that causes mastitis in cattle, and the emergence of methicillin-resistant S. aureus (MRSA) poses a threat to veterinary and human medicine. The aims of the study were to investigate the prevalence of MRSA and methicillin-resistant coagulase-negative staphylococci (MR-CoNS) isolated from clinical mastitis, their ability to form biofilms, and the antimicrobial susceptibility of S. aureus strains. In addition, the Staphylococcal Cassette Chromosome mec (SCCmec) type, spa type and the presence of Panton-Valentine Leucocidin in MRSA were evaluated. A total of 326 staphylococcal strains were screened by multiplex-PCR for S. aureus and Staphylococcus intermedius group (SIG) identification. The S. aureus strains (n = 163) were subjected to phenotypic testing for antimicrobial susceptibility and biofilm formation. Molecular analysis was performed on MRSA mecA-positive strains. Of 163 S. aureus isolates, 142 strains (87.1%) were resistant to at least one antibiotic, and all 19 MRSA strains were resistant to at least four out of five antibiotics tested. All S. aureus strains harboured the icaA gene and were biofilm producers. Nineteen MR-CoNS strains were also isolated. The most prevalent spa types among MRSA were t001 (57.9%) and t037 (31.6%), while one MRSA was type t008 and one was type t041. Most MRSA were SCCmec type I (63.2%) and III (31.6%) and only one strain was type IV. None of the MRSA isolates had the PVL gene. The prevalence of multidrug-resistant S. aureus in bovine mastitis is a serious concern. The finding of MRSA with spa types predominant in humans and infrequent in Italian cows and with SCCmec infrequently found in bovine milk or cheese suggest a human origin of these strains. The ability of MRSA and MR-CoNS involved in bovine mastitis to be transferred to humans and vice versa poses a public health concern
Mode-coupling behavior of a Lennard-Jones binary mixture upon increasing confinement
No full textMolecular dynamics simulations are performed on a Lennard Jones binary mixture confined in off lattice matrices of soft spheres with increasing radius. We focus on dynamics upon supercooling and in particular on testing the mode coupling theory properties of the confined mixture. Parameters of mode coupling theory in going from bulk to weak confinement, and from weak to strong confinement are extracted from simulations and analyzed. We focus on the study of the behavior of the single particle density correlators. We find that the mode coupling theory retains its validity also in the case of strong confinement, with a reduction of range of validity. The role of hopping is discussed in relation with the differences between the results obtained from the diffusion coefficients and the mode coupling theory predictions
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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