302 research outputs found
The amalgamated duplication of a ring along a multiplicative-canonical ideal
After recalling briefly the main properties of the amalgamated duplication of
a ring along an ideal , denoted by R\JoinI, we restrict our attention
to the study of the properties of R\JoinI, when is a multiplicative
canonical ideal of \cite{hhp}. In particular, we study when every regular
fractional ideal of is divisorial
Correlations between eigenvalues of large random matrices with independent entries
We derive the connected correlation functions for eigenvalues of large
Hermitian random matrices with independently distributed elements using both a
diagrammatic and a renormalization group (RG) inspired approach. With the
diagrammatic method we obtain a general form for the one, two and three-point
connected Green function for this class of ensembles when matrix elements are
identically distributed, and then discuss the derivation of higher order
functions by the same approach. Using the RG approach we re-derive the one and
two-point Green functions and show they are unchanged by choosing certain
ensembles with non-identically distributed elements. Throughout, we compare the
Green functions we obtain to those from the class of ensembles with unitary
invariant distributions and discuss universality in both ensemble classes.Comment: 23 pages, RevTex, hard figures available from [email protected]
Non-universality of compact support probability distributions in random matrix theory
The two-point resolvent is calculated in the large-n limit for the generalized fixed and bounded trace ensembles. It is shown to disagree with that of the canonical Gaussian ensemble by a nonuniversal part that is given explicitly for all monomial potentials V(M)=M2p. Moreover, we prove that for the generalized fixed and bounded trace ensemble all k-point resolvents agree in the large-n limit, despite their nonuniversality
Melting of Flux Lines in an Alternating Parallel Current
We use a Langevin equation to examine the dynamics and fluctuations of a flux
line (FL) in the presence of an {\it alternating longitudinal current}
. The magnus and dissipative forces are equated to those
resulting from line tension, confinement in a harmonic cage by neighboring FLs,
parallel current, and noise. The resulting mean-square FL fluctuations are
calculated {\it exactly}, and a Lindemann criterion is then used to obtain a
nonequilibrium `phase diagram' as a function of the magnitude and frequency of
. For zero frequency, the melting temperature of the
mixed phase (a lattice, or the putative "Bose" or "Bragg Glass") vanishes at a
limiting current. However, for any finite frequency, there is a non-zero
melting temperature.Comment: 5 pages, 1 figur
Contraceptive methods and knowledge of sexually transmitted diseases in nursing students. Results from a survey conducted at the University of Palermo
Background: The main purpose of the study was to evaluatesexual habits, sexual relations and knowledge of sexually transmitted infections (STIs) among the students in the nursing science course of University of Palermo, and to evaluate the use of contraceptive methods.
Methods: In April 2019, a survey was provided to students who attend daily lessons in the nursing science course of University of Palermo, that investigate primarily about sexual habits, sexual relations and knowledge of sexually transmitted diseases. A multivariable logistic regression was performed.
Results: The sample size consists of 405 students. The average age of the sample is 21.65 years, 69.63% of the interviewees are women. In relation to the question âDo you think you are sufficiently informed to be able to avoid risks of infection from sexually transmitted diseases? Noâ, the analysis shows that this independent variable is significantly associated with the following independent variables: female gender (aOR 3.11, 95% CI 1.01 - 9.65); âhow would you define your knowledge about contraceptive methods? - Poorâ (aOR 5.38, 95% CI 1.79 - 16.20); âhave you ever received information on sex education and/or sexually transmitted diseases? - Noâ (aOR 11.59, 95% CI 2.26 - 59.42); âdo you know the human papillomavirus (HPV) vaccination? - yes, but Iâm not vaccinatedâ (aOR 3.09, 95% CI 1.12 - 8.51); âdo you know that men can also undergo HPV vaccination? - Noâ (aOR 2.67, 95% CI 1.01 - 7.04).
Conclusion: Based on our findings, it is necessary to implement sexual education programs for the improvement of knowledge in terms of STIs and the promotion of health. Improving sexual health outcomes for young people is a priority for the public health. 
Slow dynamics and aging of a confined granular flow
We present experimental results on slow flow properties of a granular
assembly confined in a vertical column and driven upwards at a constant
velocity V. For monodisperse assemblies this study evidences at low velocities
() a stiffening behaviour i.e. the stress necessary to obtain
a steady sate velocity increases roughly logarithmically with velocity. On the
other hand, at very low driving velocity (), we evidence a
discontinuous and hysteretic transition to a stick-slip regime characterized by
a strong divergence of the maximal blockage force when the velocity goes to
zero. We show that all this phenomenology is strongly influenced by surrounding
humidity. We also present a tentative to establish a link between the granular
rheology and the solid friction forces between the wall and the grains. We base
our discussions on a simple theoretical model and independent grain/wall
tribology measurements. We also use finite elements numerical simulations to
confront experimental results to isotropic elasticity. A second system made of
polydisperse assemblies of glass beads is investigated. We emphasize the onset
of a new dynamical behavior, i.e. the large distribution of blockage forces
evidenced in the stick-slip regime
"Single Ring Theorem" and the Disk-Annulus Phase Transition
Recently, an analytic method was developed to study in the large limit
non-hermitean random matrices that are drawn from a large class of circularly
symmetric non-Gaussian probability distributions, thus extending the existing
Gaussian non-hermitean literature. One obtains an explicit algebraic equation
for the integrated density of eigenvalues from which the Green's function and
averaged density of eigenvalues could be calculated in a simple manner. Thus,
that formalism may be thought of as the non-hermitean analog of the method due
to Br\'ezin, Itzykson, Parisi and Zuber for analyzing hermitean non-Gaussian
random matrices. A somewhat surprising result is the so called "Single Ring"
theorem, namely, that the domain of the eigenvalue distribution in the complex
plane is either a disk or an annulus. In this paper we extend previous results
and provide simple new explicit expressions for the radii of the eigenvalue
distiobution and for the value of the eigenvalue density at the edges of the
eigenvalue distribution of the non-hermitean matrix in terms of moments of the
eigenvalue distribution of the associated hermitean matrix. We then present
several numerical verifications of the previously obtained analytic results for
the quartic ensemble and its phase transition from a disk shaped eigenvalue
distribution to an annular distribution. Finally, we demonstrate numerically
the "Single Ring" theorem for the sextic potential, namely, the potential of
lowest degree for which the "Single Ring" theorem has non-trivial consequences.Comment: latex, 5 eps figures, 41 page
Vibration-induced "thermally activated" jamming transition in granular media
The quasi-static frequency response of a granular medium is measured by a
forced torsion oscillator method, with forcing frequency in the range
Hz to 5 Hz, while weak vibrations at high-frequency , in the
range 50 Hz to 200 Hz, are generated by an external shaker. The intensity of
vibration, , is below the fluidization limit. A loss factor peak is
observed in the oscillator response as a function of or . In a
plot of against , the position of the peak follows an
Arrhenius-like behaviour over four orders of magnitude in . The data can
be described as a stochastic hopping process involving a probability factor
with a -dependent characteristic
vibration intensity. A -independent description is given by
, with an intrinsic characteristic time, and
, n=0.5-0.6, an empirical control parameter with
unit of time. is seen as the effective average time during which the
perturbed grains can undergo structural rearrangement. The loss factor peak
appears as a crossover in the dynamic behaviour of the vibrated granular
system, which, at the time-scale , is solid-like at low , and
the oscillator is jammed into the granular material, and is fluid-like at high
, where the oscillator can slide viscously.Comment: Final version to appear in PR
Rheology of a confined granular material
We study the rheology of a granular material slowly driven in a confined
geometry. The motion is characterized by a steady sliding with a resistance
force increasing with the driving velocity and the surrounding relative
humidity. For lower driving velocities a transition to stick-slip motion
occurs, exhibiting a blocking enhancement whith decreasing velocity. We propose
a model to explain this behavior pointing out the leading role of friction
properties between the grains and the container's boundary.Comment: 9 pages, 3 .eps figures, submitted to PR
A thermodynamic unification of jamming
Fragile materials ranging from sand to fire-retardant to toothpaste are able
to exhibit both solid and fluid-like properties across the jamming transition.
Unlike ordinary fusion, systems of grains, foams and colloids jam and cease to
flow under conditions that still remain unknown. Here we quantify jamming via a
thermodynamic approach by accounting for the structural ageing and the
shear-induced compressibility of dry sand. Specifically, the jamming threshold
is defined using a non-thermal temperature that measures the 'fluffiness' of a
granular mixture. The thermodynamic model, casted in terms of pressure,
temperature and free-volume, also successfully predicts the entropic data of
five molecular glasses. Notably, the predicted configurational entropy avoids
the Kauzmann paradox entirely. Without any free parameters, the proposed
equation-of-state also governs the mechanism of shear-banding and the
associated features of shear-softening and thickness-invariance.Comment: 16 pgs double spaced. 4 figure
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