799 research outputs found
Microscopic dynamics of a phase transition: equilibrium vs out-of-equilibrium regime
We present for the first time to the nuclear physics community the
Hamiltonian Mean Field (HMF) model. The model can be solved analytically in the
canonical ensemble and shows a second-order phase transition in the
thermodynamic limit. Numerical microcanonical simulations show interesting
features in the out-of-equilibrium regime: in particular the model has a
negative specific heat. The potential relevance for nuclear multifragmentation
is discussed.Comment: 9 pages, Latex, 4 figures included, invited talk to the Int. Conf.
CRIS2000 on "Phase transitions in strong interactions: status and
perspectives", Acicastello (Italy) May 22-26 2000, submitted to Nucl Phys.
Chaos in the thermodynamic limit
We study chaos in the Hamiltonian Mean Field model (HMF), a system with many
degrees of freedom in which classical rotators are fully coupled. We review
the most important results on the dynamics and the thermodynamics of the HMF,
and in particular we focus on the chaotic properties.We study the Lyapunov
exponents and the Kolmogorov--Sinai entropy, namely their dependence on the
number of degrees of freedom and on energy density, both for the ferromagnetic
and the antiferromagnetic case.Comment: 10 pages, Latex, 4 figures included, invited talk to the Int.
school/Conf. on "Let's face Chaos Through Nonlinear Dynamics" Maribor
(Slovenia) 27 june - 11 july 1999, submitted to Prog. Theor. Physics supp
Widening use of dexamethasone implant for the treatment of macular edema
Sustained-release intravitreal 0.7 mg dexamethasone (DEX) implant is approved in Europe for the treatment of macular edema related to diabetic retinopathy, branch retinal vein occlusion, central retinal vein occlusion, and non-infectious uveitis. The implant is formulated in a biodegradable copolymer to release the active ingredient within the vitreous chamber for up to 6 months after an intravitreal injection, allowing a prolonged interval of efficacy between injections with a good safety profile. Various other ocular pathologies with inflammatory etioÂpathogeneses associated with macular edema have been treated by DEX implant, including neovascular age-related macular degeneration, Irvine–Gass syndrome, vasoproliferative retinal tumors, retinal telangiectasia, Coats’ disease, radiation maculopathy, retinitis pigmentosa, and macular edema secondary to scleral buckling and pars plana vitrectomy. We undertook a review to provide a comprehensive collection of all of the diseases that benefit from the use of the sustained-release DEX implant, alone or in combination with concomitant therapies. A MEDLINE search revealed lack of randomized controlled trials related to these indications. Therefore we included and analyzed all available studies (retrospective and prospective, comÂparative and non-comparative, randomized and nonrandomized, single center and multicenter, and case report). There are reports in the literature of the use of DEX implant across a range of macular edema-related pathologies, with their clinical experience supporting the use of DEX implant on a case-by-case basis with the aim of improving patient outcomes in many macular pathologies. As many of the reported macular pathologies are difficult to treat, a new treatÂment option that has a beneficial influence on the clinical course of the disease may be useful in clinical practice
Analysis of Self-Organized Criticality in the Olami-Feder-Christensen model and in real earthquakes
We perform a new analysis on the dissipative Olami-Feder-Christensen model on
a small world topology considering avalanche size differences. We show that
when criticality appears the Probability Density Functions (PDFs) for the
avalanche size differences at different times have fat tails with a q-Gaussian
shape. This behaviour does not depend on the time interval adopted and is found
also when considering energy differences between real earthquakes. Such a
result can be analytically understood if the sizes (released energies) of the
avalanches (earthquakes) have no correlations. Our findings support the
hypothesis that a self-organized criticality mechanism with long-range
interactions is at the origin of seismic events and indicate that it is not
possible to predict the magnitude of the next earthquake knowing those of the
previous ones.Comment: 5 pages, 3 figures. New version accepted for publication on PRE Rapid
Communication
- …