588 research outputs found
Aging after shear rejuvenation in a soft glassy colloidal suspension: evidence for two different regimes
The aging dynamics after shear rejuvenation in a glassy, charged clay
suspension have been investigated through dynamic light scattering (DLS). Two
different aging regimes are observed: one is attained if the sample is
rejuvenated before its gelation and one after the rejuvenation of the gelled
sample. In the first regime, the application of shear fully rejuvenates the
sample, as the system dynamics soon after shear cessation follow the same aging
evolution characteristic of normal aging. In the second regime, aging proceeds
very fast after shear rejuvenation, and classical DLS cannot be used. An
original protocol to measure an ensemble averaged intensity correlation
function is proposed and its consistency with classical DLS is verified. The
fast aging dynamics of rejuvenated gelled samples exhibit a power law
dependence of the slow relaxation time on the waiting time.Comment: 7 pages, 6 figure
Phonon-like and single particle dynamics in liquid lithium
The dynamic structure factor, S(Q,E), of liquid lithium (T=475 K) has been
determined by inelastic x-ray scattering (IXS) in the momentum transfer region
(Q = 1.4-110 nm-1). These data allow to observe how, in a simple liquid, a
phonon-like collective mode evolves towards the single particle dynamics. As a
function of Q, one finds: i) at low Q's, a sound mode with a positive
dispersion of the sound velocity, ii) at intermediate Q's, excitations whose
energy oscillates similarly to phonons in the crystal Brillouin zones, and iii)
at high Q's, the S(Q,E) approaches a Gaussian shape, indicating that the single
particle dynamics has been reached.Comment: 3 pages and 5 figure
Liquid-like behavior of supercritical fluids
The high frequency dynamics of fluid oxygen have been investigated by
Inelastic X-ray Scattering. In spite of the markedly supercritical conditions
(, ), the sound velocity exceeds the hydrodynamic
value of about 20%, a feature which is the fingerprint of liquid-like dynamics.
The comparison of the present results with literature data obtained in several
fluids allow us to identify the extrapolation of the liquid vapor-coexistence
line in the (, ) plane as the relevant edge between liquid- and
gas-like dynamics. More interestingly, this extrapolation is very close to the
non metal-metal transition in hot dense fluids, at pressure and temperature
values as obtained by shock wave experiments. This result points to the
existence of a connection between structural modifications and transport
properties in dense fluids.Comment: 4 pages, 3 figures, accepted by Phys. Rev. Let
Topological Signature of First Order Phase Transitions
We show that the presence and the location of first order phase transitions
in a thermodynamic system can be deduced by the study of the topology of the
potential energy function, V(q), without introducing any thermodynamic measure.
In particular, we present the thermodynamics of an analytically solvable
mean-field model with a k-body interaction which -depending on the value of k-
displays no transition (k=1), second order (k=2) or first order (k>2) phase
transition. This rich behavior is quantitatively retrieved by the investigation
of a topological invariant, the Euler characteristic, of some submanifolds of
the configuration space. Finally, we conjecture a direct link between the Euler
characteristic and the thermodynamic entropy.Comment: 6 pages, 2 figure
A spectroscopic cell for fast pressure jumps across the glass transition line
We present a new experimental protocol for the spectroscopic study of the
dynamics of glasses in the aging regime induced by sudden pressure jumps
(crunches) across the glass transition line. The sample, initially in the
liquid state, is suddenly brought in the glassy state, and therefore out of
equilibrium, in a four-window optical crunch cell which is able to perform
pressure jumps of 3 kbar in a time interval of ~10 ms. The main advantages of
this setup with respect to previous pressure-jump systems is that the pressure
jump is induced through a pressure transmitting fluid mechanically coupled to
the sample stage through a deformable membrane, thus avoiding any flow of the
sample itself in the pressure network and allowing to deal with highly viscous
materials. The dynamics of the sample during the aging regime is investigated
by Brillouin Light Scattering (BLS). For this purpose the crunch cell is used
in conjunction with a high resolution double monochromator equipped with a CCD
detector. This system is able to record a full spectrum of a typical glass
forming material in a single 1 s shot. As an example we present the study of
the evolution toward equilibrium of the infinite frequency longitudinal elastic
modulus (M_infinity) of a low molecular weight polymer (Poly(bisphenol
A-co-epichlorohydrin), glycidyl end capped). The observed time evolution of
M_infinity, well represented by a single stretched exponential, is interpreted
within the framework of the Tool-Narayanaswamy theory.Comment: 9 pages, 11 figure
An approximate model for optimizing Bernoulli columns against buckling
International audienceProposed herein is a simple but powerful method for optimization of inhomogeneous, elastically restrained columns against buckling when subjected to both compressive concentrated and distributed axial loads that include self-weight. Unlike previously published studies on the subject, we do not have to specify any prescribed geometrical variation and analysis may be readily performed on columns with any complex geometrical shape. In the proposed method, the differential equation governing the buckling of Euler columns is discretized by adopting the Hencky bar-chain model, and critical buckling loads are evaluated by seeking the lowest eigenvalue of the resulting system of algebraic equations. The discrete nature of the formulation, as well as the reduced number of parameters to be optimized, is well suited for the adopted optimization process that is based on evolutionary algorithms. We propose an optimization scheme based on a parallel genetic algorithm. A comparisori study between the obtained optimal column shape and buckling loads on homogeneous and isotropic columns with circular cross section, and the numerical and analytical solutions found in the open literature shows fast convergence, high accuracy and flexibility of the proposed method
Glassy behavior of light
We study the nonlinear dynamics of a multi-mode random laser using the
methods of statistical physics of disordered systems. A replica-symmetry
breaking phase transition is predicted as a function of the pump intensity. We
thus show that light propagating in a random non-linear medium displays glassy
behavior, i.e. the photon gas has a multitude of metastable states and a non
vanishing complexity, corresponding to mode-locking processes in random lasers.
The present work reveals the existence of new physical phenomena, and
demonstrates how nonlinear optics and random lasers can be a benchmark for the
modern theory of complex systems and glasses.Comment: 5 pages, 1 figur
Genomic analysis of the nomenclatural type strain of the nematode-associated entomopathogenic bacterium Providencia vermicola
Background: Enterobacteria of the genus Providencia are mainly known as opportunistic human pathogens but have been isolated from highly diverse natural environments. The species Providencia vermicola comprises insect pathogenic bacteria carried by entomoparasitic nematodes and is investigated as a possible insect biocontrol agent. The recent publication of several genome sequences from bacteria assigned to this species has given rise to inconsistent preliminary results. Results: The genome of the nematode-derived P. vermicola type strain DSM_17385 has been assembled into a 4.2 Mb sequence comprising 5 scaffolds and 13 contigs. A total of 3969 protein-encoding genes were identified. Multilocus sequence typing with different marker sets revealed that none of the previously published presumed P. vermicola genomes represents this taxonomic species. Comparative genomic analysis has confirmed a close phylogenetic relationship of P. vermicola to the P. rettgeri species complex. P. vermicola DSM_17385 carries a type III secretion system (T3SS-1) with probable function in host cell invasion or intracellular survival. Potentially antibiotic resistance-associated genes comprising numerous efflux pumps and point-mutated house-keeping genes, have been identified across the P. vermicola genome. A single small (3.7 kb) plasmid identified, pPVER1, structurally belongs to the qnrD-type family of fluoroquinolone resistance conferring plasmids that is prominent in Providencia and Proteus bacteria, but lacks the qnrD resistance gene. Conclusions: The sequence reported represents the first well-supported published genome for the taxonomic species P. vermicola to be used as reference in further comparative genomics studies on Providencia bacteria. Due to a striking difference in the type of injectisome encoded by the respective genomes, P. vermicola might operate a fundamentally different mechanism of entomopathogenicity when compared to insect-pathogenic Providencia sneebia or Providencia burhodogranariea. The complete absence of antibiotic resistance gene carrying plasmids or mobile genetic elements as those causing multi drug resistance phenomena in clinical Providencia strains, is consistent with the invertebrate pathogen P. vermicola being in its natural environment efficiently excluded from the propagation routes of multidrug resistance (MDR) carrying genetic elements operating between human pathogens. Susceptibility to MDR plasmid acquisition will likely become a major criterion in the evaluation of P. vermicola for potential applications in biological pest control
Novel Approaches to the Development and Application of Informetric and Scientometric Tools Special Issue of Journal of Data and Information Science on ISSI2019 Conference-Part II
This is the second part of the Journal of Data and Information Science (JDIS)
Special Issue on ISSI 2019, the 17th International Conference on Scientometrics
and Informetrics (ISSI2019) held in Rome, on 2–5 September 2019 and includes
additional 10 selected posters presented during the conference largely expanded by
the authors afterwards.
The papers included in this volume have been grouped in three broad themes:
- Indicators & Databases (4 papers);
- Social context, Innovation, and Policy (3 papers);
- Application domains (3 papers)
Novel Approaches to the Development and Application of Informetric and Scientometric Tools Special Issue of Journal of Data and Information Science on ISSI2019 Conference-Part i
[No abstract available
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