1,692 research outputs found
Critical behavior of plastic depinning of vortex lattices in two dimensions: Molecular dynamics simulations
Using molecular dynamics simulations, we report a study of the dynamics of
two-dimensional vortex lattices driven over a disordered medium. In strong
disorder, when topological order is lost, we show that the depinning transition
is analogous to a second order critical transition: the velocity-force response
at the onset of motion is continuous and characterized by critical exponents.
Combining studies at zero and nonzero temperature and using a scaling analysis,
two critical expo- nents are evaluated. We find v\sim (F-F_c)^\beta with
\beta=1.3\pm0.1 at T=0 and F>F_c, and v\sim T^{1/\delta} with
\delta^{-1}=0.75\pm0.1 at F=F_c, where F_c is the critical driving force at
which the lattice goes from a pinned state to a sliding one. Both critical
exponents and the scaling function are found to exhibit universality with
regard to the pinning strength and different disorder realizations.
Furthermore, the dynamics is shown to be chaotic in the whole critical region.Comment: 8 pages, 6 figure
Non-Markovian dissipative dynamics of two coupled qubits in independent reservoirs: a comparison between exact solutions and master equation approaches
The reduced dynamics of two interacting qubits coupled to two independent
bosonic baths is investigated. The one-excitation dynamics is derived and
compared with that based on the resolution of appropriate non-Markovian master
equations. The Nakajima-Zwanzig and the time-convolutionless projection
operator techniques are exploited to provide a description of the non-Markovian
features of the dynamics of the two-qubits system. The validity of such
approximate methods and their range of validity in correspondence to different
choices of the parameters describing the system are brought to light.Comment: 6 pages, 3 figures. Submitted to PR
The elastic depinning transition of vortex lattices in two dimensions
Large scale numerical simulations are used to study the elastic dynamics of
two-dimensional vortex lattices driven on a disordered medium in the case of
weak disorder. We investigate the so-called elastic depinning transition by
decreasing the driving force from the elastic dynamical regime to the state
pinned by the quenched disorder. Similarly to the plastic depinning transition,
we find results compatible with a second order phase transition, although both
depinning transitions are very different from many viewpoints. We evaluate
three critical exponents of the elastic depinning transition. is found for the velocity exponent at zero temperature, and from the
velocity-temperature curves we extract the critical exponent . Furthermore, in contrast with charge-density waves, a
finite-size scaling analysis suggests the existence of a unique diverging
length at the depinning threshold with an exponent , which
controls the critical force distribution, the finite-size crossover force
distribution and the intrinsic correlation length. Finally, a scaling relation
is found between velocity and temperature with the and
critical exponents both independent with regard to pinning strength and
disorder realizations.Comment: 17 pages, 10 figure
Polar Actions on Berger Spheres
The object of this article is to study a torus action on a so-called Berger sphere. We also make some comments on polar actions on naturally reductive homogeneous spaces. Finally, we prove a rigidity-type theorem for Riemannian manifolds carrying a polar action with a fix point
experimental and numerical analyses of a spark ignition engine firing with n butanol gasoline blends at high load operation
Abstract In this paper, the potential of alcohol-gasoline blends as fuels for spark-ignition engines has been evaluated. The general purpose of the work is to verify the possibility of incrementing the bio-fuels penetration in the market of transportation fuels. As it is well known, bio-mass derived fuels, in fact, could significantly reduce the CO2 emissions of energy thermal systems. The behavior of a small, turbocharged spark-ignition engine, firing with gasoline-butanol blends, has been analyzed. Analyses have been carried out by means of both experimental tests and numerical simulations. In previous works, engine main performances have been illustrated and discussed. Here, experimental tests have been carried out in order to compare the engine knock resistance and the obtainable fuel conversion efficiency when the engine is fueled by pure gasoline or gasoline-butanol blends at high load operation. Furthermore, one dimensional numerical analyses have been utilized in order to compare the engine behavior, at different operating points, when it is firing with pure gasoline or pure butanol. In general, the obtained results seem to indicate that butanol (produced by bio-masses) is a viable alternative to fossil fuels in the way of CO2 emission reduction
Global symplectic coordinates on gradient Kaehler-Ricci solitons
A classical result of D. McDuff asserts that a simply-connected complete
Kaehler manifold with non positive sectional curvature admits
global symplectic coordinates through a symplectomorphism (where is the complex dimension of ), satisfying the following
property (proved by E. Ciriza): the image of any complex totally
geodesic submanifold through the point such that ,
is a complex linear subspace of . The aim of this paper is
to exhibit, for all positive integers , examples of -dimensional complete
Kaehler manifolds with non-negative sectional curvature globally
symplectomorphic to through a symplectomorphism satisfying Ciriza's
property.Comment: 8 page
On the validity of non-Markovian master equation approaches for the entanglement dynamics of two-qubit systems
In the framework of the dissipative dynamics of coupled qubits interacting with independent reservoirs, a comparison between non-Markovian master equation techniques and an exact solution is presented here. We study various regimes in order to find the limits of validity of the Nakajima\u2013Zwanzig and the time-convolutionless master equations in the description of the
entanglement dynamics. A comparison between the performances of the concurrence and the
negativity as entanglement measures for the system under study is also presented
Neuronal nitric oxide synthase (NOS I) in the buffalo epididymis
The localization of neuronal nitric oxide (NOS I) in the buffalo epididymis have been investigated by nicotinamide adenite dinucleotide phosphatase-diaphorase (NADPH-d) histochemichemistry to the light microscope (LM) and NOS immunoistochemistry to the scanning electron microscope (SEM), respectively. Histochemistry: examination of epididymis specimens revealed an intense NADPH-d staining in the basal cell epithelium and endothelium cells of blood vessel. The NADPH diaphorase staining was diffuse and granular only along the caput epididymal epithelium. NADPH diaphorase staining was less intense or absent in the corpus and in the cauda of epididymis. Dense NADPH diaphorase is labeling in the endothelium of blood vessels along the whole buffalo epididymis. Immunoistochemistry: intense NOS I immunoreactivity was detected in the caput epididymis specimen by immuno-SEM. The basal epithelium showed intense and wide-spread immunoreactivity. In the corpus and in the cauda of the epididymis not observed NOS I immunoreactivity. The specific localization of NOS I in buffalo epididymis suggest that nitric oxide may be involved to explain epididymal function: maturation and storage
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