118 research outputs found
Nos\'e-Hoover and Langevin thermostats do not reproduce the nonequilibrium behavior of long-range Hamiltonians
We compare simulations performed using the Nos\'e-Hoover and the Langevin
thermostats with the Hamiltonian dynamics of a long-range interacting system in
contact with a reservoir. We find that while the statistical mechanics
equilibrium properties of the system are recovered by all the different
methods, the Nos\'e-Hoover and the Langevin thermostats fail in reproducing the
nonequilibrium behavior of such Hamiltonian.Comment: Contribution to the proceeding of the "International Conference on
the Frontiers of Nonlinear and Complex Systems" in honor of Prof. Bambi Hu,
Hong Kong, May 200
Hamiltonian dynamics reveals the existence of quasi-stationary states for long-range systems in contact with a reservoir
We introduce a Hamiltonian dynamics for the description of long-range
interacting systems in contact with a thermal bath (i.e., in the canonical
ensemble). The dynamics confirms statistical mechanics equilibrium predictions
for the Hamiltonian Mean Field model and the equilibrium ensemble equivalence.
We find that long-lasting quasi-stationary states persist in presence of the
interaction with the environment. Our results indicate that quasi-stationary
states are indeed reproducible in real physical experiments.Comment: Title changed, throughout revision of the tex
Anomalous scaling due to correlations: Limit theorems and self-similar processes
We derive theorems which outline explicit mechanisms by which anomalous
scaling for the probability density function of the sum of many correlated
random variables asymptotically prevails. The results characterize general
anomalous scaling forms, justify their universal character, and specify
universality domains in the spaces of joint probability density functions of
the summand variables. These density functions are assumed to be invariant
under arbitrary permutations of their arguments. Examples from the theory of
critical phenomena are discussed. The novel notion of stability implied by the
limit theorems also allows us to define sequences of random variables whose sum
satisfies anomalous scaling for any finite number of summands. If regarded as
developing in time, the stochastic processes described by these variables are
non-Markovian generalizations of Gaussian processes with uncorrelated
increments, and provide, e.g., explicit realizations of a recently proposed
model of index evolution in finance.Comment: Through text revision. 15 pages, 3 figure
Incomplete equilibrium in long-range interacting systems
We use a Hamiltonian dynamics to discuss the statistical mechanics of
long-lasting quasi-stationary states particularly relevant for long-range
interacting systems. Despite the presence of an anomalous single-particle
velocity distribution, we find that the Central Limit Theorem implies the
Boltzmann expression in Gibbs' -space. We identify the nonequilibrium
sub-manifold of -space characterizing the anomalous behavior and show
that by restricting the Boltzmann-Gibbs approach to this sub-manifold we obtain
the statistical mechanics of the quasi-stationary states.Comment: Title changed, throughout revision of the tex
Microcanonical quasi-stationarity of long-range interacting systems in contact with a heat bath
On the basis of analytical results and molecular dynamics simulations we
clarify the nonequilibrium dynamics of a long-range interacting system in
contact with a heat bath. For small couplings with the bath, we show that the
system can first be trapped in a Vlasov quasi-stationary state, then a
microcanonical one follows, and finally canonical equilibrium is reached at the
bath temperature. We compare a Langevin mesoscopic thermostat with Hamiltonian
reservoirs microscopically coupled with the system and demonstrate the
equivalence of the two descriptions. Our identification of the parameters
determining the quasi-stationary lifetimes could be exploited to control
experimental systems such as the Free Electron Laser, in the presence of
external noise or inherent imperfections
The impact of acute intoxications in a toxicological unit care in North East Italy
Retrospective study in a Toxicological Unit Care (TUC) performed
to know the epidemiology of acute intoxication (AI) in
Verona (Italy) during years 2008-2009.
All data regarding patients with a diagnosis of certain/suspected
AI were collected and evaluated: some demographic information,
the characteristics of the agent involved, the pattern of exposure,
the triage at the admission to TUC and the outcome.
244 cases were analyzed: 45.9% males and 54.9% females, mean
age respectively 45.1 and 43.9 years. The monthly distribution of
admitted patients resulted fairly constant, except from a light rising
prevalence in autumn, with a majority of yellow (45.9%) and green
(43.4%) triage code. The pattern of exposure resulted: ingestion
(82.7% of cases; age peaks: 18-34 and 35-51 years old; mostly due
to food (as mushrooms), drinks, detergents, soap, pharmaceutical,
drugs of abuse, caustics substances), contact (10.2% of cases; age
peak 18-51) and inhalation (6.9% of cases). In 17.2% of cases the
poisoning exposure was intentional. In 63.5% the patients were
sent to their general practitioners (45.5% of the yellow and 81.1%
of the green coded patients) and in 22.1% of cases they were admitted
to clinical rooms (44.6% of the yellow coded patients).
In most cases the triage code assigned to the studied patients
resulted yellow and green. Considering that the seriousness of
the symptoms can appear after several hours from the exposure
to toxic substances, a quick and specific intervention to obtain the
best therapeutical effectiveness is suitable, in order to save lives
or to avoid irremediable health damages
Mapping dynamical systems onto complex networks
A procedure to characterize chaotic dynamical systems with concepts of
complex networks is pursued, in which a dynamical system is mapped onto a
network. The nodes represent the regions of space visited by the system, while
edges represent the transitions between these regions. Parameters used to
quantify the properties of complex networks, including those related to higher
order neighborhoods, are used in the analysis. The methodology is tested for
the logistic map, focusing the onset of chaos and chaotic regimes. It is found
that the corresponding networks show distinct features, which are associated to
the particular type of dynamics that have generated them.Comment: 13 pages, 8 eps files in 5 figure
Classical Infinite-Range-Interaction Heisenberg Ferromagnetic Model: Metastability and Sensitivity to Initial Conditions
A N-sized inertial classical Heisenberg ferromagnet, which consists in a
modification of the well-known standard model, where the spins are replaced by
classical rotators, is studied in the limit of infinite-range interactions. The
usual canonical-ensemble mean-field solution of the inertial classical
-vector ferromagnet (for which recovers the particular Heisenberg
model considered herein) is briefly reviewed, showing the well-known
second-order phase transition. This Heisenberg model is studied numerically
within the microcanonical ensemble, through molecular dynamics.Comment: 18 pages text, and 7 EPS figure
Infinite ergodic theory and Non-extensive entropies
We bring into account a series of result in the infinite ergodic theory that
we believe that they are relevant to the theory of non-extensive entropie
High-Resolution Chandra X-Ray Imaging And Spectroscopy Of The Sigma Orionis Cluster
We present results of a 90 ks Chandra X-ray observation of the young sigma Orionis cluster ( age similar to 3 Myr) obtained with the HETGS. We use the high-resolution grating spectrum and moderate-resolution CCD spectrum of the massive central star sigma Ori AB (O9.5 V + B0.5 V) to test wind shock theories of X-ray emission and also analyze the high spatial resolution zero-order ACIS-S image of the central cluster region. Chandra detected 42 X-ray sources on the primary CCD (ACIS-S3). All but five have near-IR or optical counterparts and about one-fourth are variable. Notable high-mass stellar detections are sigma Ori AB, the magnetic B star sigma Ori E, and the B5 V binary HD 37525. Most of the other detections have properties consistent with lower mass K- or M-type stars. We present the first X-ray spectrum of the unusual infrared source IRS 1, located approximate to 3 \u27\u27 north of sigma Ori AB. Its X-ray properties and elongated mid-IR morphology suggest that it is an embedded low-mass T Tauri star whose disk/envelope is being photoevaporated by sigma Ori AB. We focus on the radiative wind shock interpretation of the soft luminous X-ray emission from sigma Ori AB, but also consider possible alternatives including magnetically confined wind shocks and colliding wind shocks. Its emission lines show no significant asymmetries or centroid shifts and are moderately broadened to HWHM approximate to 264 km s(-1), or one-fourth the terminal wind speed. Forbidden lines in He-like ions are formally undetected, implying strong UV suppression. The Mg XI triplet forms in the wind acceleration zone within one stellar radius above the surface. These X-ray properties are consistent in several respects with the predictions of radiative wind shock theory for an optically thin wind, but explaining the narrow line widths presents a challenge to the theory
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