546 research outputs found
Coarse-Grained Probabilistic Automata Mimicking Chaotic Systems
Discretization of phase space usually nullifies chaos in dynamical systems.
We show that if randomness is associated with discretization dynamical chaos
may survive and be indistinguishable from that of the original chaotic system,
when an entropic, coarse-grained analysis is performed. Relevance of this
phenomenon to the problem of quantum chaos is discussed.Comment: 4 pages, 4 figure
Stochastic Resonance in Deterministic Chaotic Systems
We propose a mechanism which produces periodic variations of the degree of
predictability in dynamical systems. It is shown that even in the absence of
noise when the control parameter changes periodically in time, below and above
the threshold for the onset of chaos, stochastic resonance effects appears. As
a result one has an alternation of chaotic and regular, i.e. predictable,
evolutions in an almost periodic way, so that the Lyapunov exponent is positive
but some time correlations do not decay.Comment: 9 Pages + 3 Figures, RevTeX 3.0, sub. J. Phys.
Predictability: a way to characterize Complexity
Different aspects of the predictability problem in dynamical systems are
reviewed. The deep relation among Lyapunov exponents, Kolmogorov-Sinai entropy,
Shannon entropy and algorithmic complexity is discussed. In particular, we
emphasize how a characterization of the unpredictability of a system gives a
measure of its complexity. Adopting this point of view, we review some
developments in the characterization of the predictability of systems showing
different kind of complexity: from low-dimensional systems to high-dimensional
ones with spatio-temporal chaos and to fully developed turbulence. A special
attention is devoted to finite-time and finite-resolution effects on
predictability, which can be accounted with suitable generalization of the
standard indicators. The problems involved in systems with intrinsic randomness
is discussed, with emphasis on the important problems of distinguishing chaos
from noise and of modeling the system. The characterization of irregular
behavior in systems with discrete phase space is also considered.Comment: 142 Latex pgs. 41 included eps figures, submitted to Physics Reports.
Related information at this http://axtnt2.phys.uniroma1.i
DNA damage and repair following In vitro exposure to two different forms of titanium dioxide nanoparticles on trout erythrocyte
TiO(2) has been widely used to promote organic compounds degradation on waste aqueous solution, however, data on TiO(2) nanotoxicity to aquatic life are still limited. In this in vitro study, we compare the toxicity of two different families of TiO(2) nanoparticles on erythrocytes from Oncorhynchus mykiss trout. The crystal structure of the two TiO(2) nanoparticles was analyzed by XRD and the results indicated that one sample is composed of TiO(2) in the anatase crystal phase, while the other sample contains a mixture of both the anatase and the rutile forms of TiO(2) in a 2:8 ratio. Further characterization of the two families of TiO(2) nanoparticles was determined by SEM high resolution images and BET technique. The toxicity results indicate that both TiO(2) nanoparticles increase the hemolysis rate in a dose dependent way (1.6, 3.2, 4.8 μg mL(-1) ) but they do not influence superoxide anion production due to NADH addition measured by chemiluminescence. Moreover, TiO(2) nanoparticles (4.8 μg mL(-1) ) induce DNA damage and the entity of the damage is independent from the type of TiO(2) nanoparticles used. Modified comet assay (Endo III and Fpg) shows that TiO(2) oxidizes not only purine but also pyrimidine bases. In our experimental conditions, the exposure to TiO(2) nanoparticles does not affect the DNA repair system functionality. The data obtained contribute to better characterize the aqueous environmental risks linked to TiO(2) nanoparticles exposure. © 2011 Wiley Periodicals, Inc. Environ Toxicol, 2011
The method of global R* and its applications
The global R* operation is a powerful method for computing renormalisation
group functions. This technique, based on the principle of infrared
rearrangement, allows to express all the ultraviolet counterterms in terms of
massless propagator integrals. In this talk we present the main features of
global R* and its application to the renormalisation of QCD. By combining this
approach with the use of the program Forcer for the evaluation of the relevant
Feynman integrals, we renormalise for the first time QCD at five loops in
covariant gauges.Comment: 10 pages, 6 figures, contribution to the proceedings of the 13th
International Symposium on Radiative Corrections (RADCOR 2017
The Flat Phase of Crystalline Membranes
We present the results of a high-statistics Monte Carlo simulation of a
phantom crystalline (fixed-connectivity) membrane with free boundary. We verify
the existence of a flat phase by examining lattices of size up to . The
Hamiltonian of the model is the sum of a simple spring pair potential, with no
hard-core repulsion, and bending energy. The only free parameter is the the
bending rigidity . In-plane elastic constants are not explicitly
introduced. We obtain the remarkable result that this simple model dynamically
generates the elastic constants required to stabilise the flat phase. We
present measurements of the size (Flory) exponent and the roughness
exponent . We also determine the critical exponents and
describing the scale dependence of the bending rigidity () and the induced elastic constants (). At bending rigidity , we find
(Hausdorff dimension ), and . These results are consistent with the scaling relation . The additional scaling relation implies
. A direct measurement of from the power-law decay of
the normal-normal correlation function yields on the
lattice.Comment: Latex, 31 Pages with 14 figures. Improved introduction, appendix A
and discussion of numerical methods. Some references added. Revised version
to appear in J. Phys.
Reactive oxygen species, health and longevity
Reactive oxygen species (ROS) are considered responsible of ageing in animal and humans. Mitochondria are both source and target of ROS. Various strategies to reduce ROS production have been considered to extend lifespan. Caloric restriction, exercise, and antioxidants are thought to be able to protect cells from structural and functional damage. However, there is evidence that ROS production has a detrimental effect on health, but at physiological levels are necessary to stimulate longevity. They play an important effect on secondary signal transduction stimulating innate immunology and mitochondriogenesis. During exercise at moderate intensity, skeletal muscles generate ROS that are necessary for the remodelling of the muscular cells. Physical inactivity determines excessive ROS production and muscle atrophy. Caloric restriction (CR) can reduce ROS generation and improve longevity while antioxidant supplementation has shown a negative effect on longevity reducing the muscle adaptation to exercise and increasing mortality risk in patients with chronic diseases. The role of ROS in chronic diseases in also influenced by sex steroids that decrease in aging. The physiology of longevity is the result of integrated biological mechanisms that influence mitochondrial function and activity. The main objective of this review is to evaluate the effects of ROS on mitochondriogenesis and lifespan extension
Glue Ball Masses and the Chameleon Gauge
We introduce a new numerical technique to compute mass spectra, based on
difference method and on a new gauge fixing procedure. We show that the method
is very effective by test runs on a lattice gauge theory.Comment: latex format, 10 pages, 4 figures added in uufiles forma
The Heavy Quark Form Factors at Two Loops
We compute the two-loop QCD corrections to the heavy quark form factors in
case of the vector, axial-vector, scalar and pseudo-scalar currents up to
second order in the dimensional parameter . These terms are
required in the renormalization of the higher order corrections to these form
factors.Comment: 131 pages, 3 figure
Four-loop splitting functions in QCD -- The gluon-to-quark case
We have computed the even- moments of the gluon-to-quark
splitting function at the fourth order of perturbative QCD via the
renormalization of off-shell operator matrix elements. Our results, derived
analytically for a general gauge group, agree with all results obtained for
this function so far, in particular with the lowest five moments obtained via
physical cross sections. Using our new moments and all available endpoint
constraints, we construct approximations for the four-loop that
should be sufficient for a wide range of collider-physics applications. The
NLO corrections resulting from these and the corresponding quark-quark
splitting functions lead to a marked improvement of the perturbative accuracy
for the scale derivative of the singlet quark distribution, with effects of 1%
or less at at a standard reference scale with .Comment: 17 pages latex, 3 figures, 2 ancillary files (FORM file with results
and FORTRAN subroutine
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