226 research outputs found
Statistical equilibrium in simple exchange games I
Simple stochastic exchange games are based on random allocation of finite
resources. These games are Markov chains that can be studied either
analytically or by Monte Carlo simulations. In particular, the equilibrium
distribution can be derived either by direct diagonalization of the transition
matrix, or using the detailed balance equation, or by Monte Carlo estimates. In
this paper, these methods are introduced and applied to the
Bennati-Dragulescu-Yakovenko (BDY) game. The exact analysis shows that the
statistical-mechanical analogies used in the previous literature have to be
revised.Comment: 11 pages, 3 figures, submitted to EPJ
Relaxation in statistical many-agent economy models
We review some statistical many-agent models of economic and social systems
inspired by microscopic molecular models and discuss their stochastic
interpretation. We apply these models to wealth exchange in economics and study
how the relaxation process depends on the parameters of the system, in
particular on the saving propensities that define and diversify the agent
profiles.Comment: Revised final version. 6 pages, 5 figure
Gamma-distribution and wealth inequality
We discuss the equivalence between kinetic wealth-exchange models, in which
agents exchange wealth during trades, and mechanical models of particles,
exchanging energy during collisions. The universality of the underlying
dynamics is shown both through a variational approach based on the minimization
of the Boltzmann entropy and a complementary microscopic analysis of the
collision dynamics of molecules in a gas. In various relevant cases the
equilibrium distribution is the same for all these models, namely a
gamma-distribution with suitably defined temperature and number of dimensions.
This in turn allows one to quantify the inequalities observed in the wealth
distributions and suggests that their origin should be traced back to very
general underlying mechanisms: for instance, it follows that the smaller the
fraction of the relevant quantity (e.g. wealth or energy) that agents can
exchange during an interaction, the closer the corresponding equilibrium
distribution is to a fair distribution.Comment: Presented to the International Workshop and Conference on:
Statistical Physics Approaches to Multi-disciplinary Problems, January 07-13,
2008, IIT Guwahati, Indi
Heterogeneous nucleation and heat flux avalanches in La(Fe, Si)13 magnetocaloric compounds near the critical point
The phase transformation kinetics of LaFe11.41Mn0.30Si1.29-H1.65 magnetocaloric compound is
addressed by low rate calorimetry experiments. Scans at 1 mK/s show that its first order phase
transitions are made by multiple heat flux avalanches. Getting very close to the critical point, when
the transition becomes of the second order type, the step-like discontinuous behaviour associated
with avalanches is smoothed out and the thermal hysteresis disappears. This result is confirmed by
magneto-resistivity measurements and allows to obtain accurate values of the temperature hysteresis
(DThyst = 0.37 K) at zero external magnetic field and of the critical field (Hc = 1.19 T). The number
and magnitude of heat flux avalanches change as the magnetic field strength is increased,
showing the interplay between the intrinsic energy barrier between phases and the microstructural
disorder of the sample
Collective privacy recovery: Data-sharing coordination via decentralized artificial intelligence
Collective privacy loss becomes a colossal problem, an emergency for personal freedoms and democracy. But, are we prepared to handle personal data as scarce resource and collectively share data under the doctrine: as little as possible, as much as necessary? We hypothesize a significant privacy recovery if a population of individuals, the data collective, coordinates to share minimum data for running online services with the required quality. Here, we show how to automate and scale-up complex collective arrangements for privacy recovery using decentralized artificial intelligence. For this, we compare for the first time attitudinal, intrinsic, rewarded, and coordinated data sharing in a rigorous living-lab experiment of high realism involving real data disclosures. Using causal inference and cluster analysis, we differentiate criteria predicting privacy and five key data-sharing behaviors. Strikingly, data-sharing coordination proves to be a win–win for all: remarkable privacy recovery for people with evident costs reduction for service providers
Surprises in the Orbital Magnetic Moment and g-Factor of the Dynamic Jahn-Teller Ion C_{60}^-
We calculate the magnetic susceptibility and g-factor of the isolated
C_{60}^- ion at zero temperature, with a proper treatment of the dynamical
Jahn-Teller effect, and of the associated orbital angular momentum, Ham-reduced
gyromagnetic ratio, and molecular spin-orbit coupling. A number of surprises
emerge. First, the predicted molecular spin-orbit splitting is two orders of
magnitude smaller than in the bare carbon atom, due to the large radius of
curvature of the molecule. Second, this reduced spin-orbit splitting is
comparable to Zeeman energies, for instance, in X-band EPR at 3.39KGauss, and a
field dependence of the g-factor is predicted. Third, the orbital gyromagnetic
factor is strongly reduced by vibron coupling, and so therefore are the
effective weak-field g-factors of all low-lying states. In particular, the
ground-state doublet of C_{60}^- is predicted to show a negative g-factor of
\sim -0.1.Comment: 19 pages RevTex, 2 postscript figures include
Basic kinetic wealth-exchange models: common features and open problems
We review the basic kinetic wealth-exchange models of Angle [J. Angle, Social
Forces 65 (1986) 293; J. Math. Sociol. 26 (2002) 217], Bennati [E. Bennati,
Rivista Internazionale di Scienze Economiche e Commerciali 35 (1988) 735],
Chakraborti and Chakrabarti [A. Chakraborti, B. K. Chakrabarti, Eur. Phys. J. B
17 (2000) 167], and of Dragulescu and Yakovenko [A. Dragulescu, V. M.
Yakovenko, Eur. Phys. J. B 17 (2000) 723]. Analytical fitting forms for the
equilibrium wealth distributions are proposed. The influence of heterogeneity
is investigated, the appearance of the fat tail in the wealth distribution and
the relaxation to equilibrium are discussed. A unified reformulation of the
models considered is suggested.Comment: Updated version; 9 pages, 5 figures, 2 table
Multipurpose High Frequency Electron Spin Resonance Spectrometer for Condensed Matter Research
We describe a quasi-optical multifrequency ESR spectrometer operating in the
75-225 GHz range and optimized at 210 GHz for general use in condensed matter
physics, chemistry and biology. The quasi-optical bridge detects the change of
mm wave polarization at the ESR. A controllable reference arm maintains a mm
wave bias at the detector. The attained sensitivity of 2x10^10 spin/G/(Hz)1/2,
measured on a dilute Mn:MgO sample in a non-resonant probe head at 222.4 GHz
and 300 K, is comparable to commercial high sensitive X band spectrometers. The
spectrometer has a Fabry-Perot resonator based probe head to measure aqueous
solutions, and a probe head to measure magnetic field angular dependence of
single crystals. The spectrometer is robust and easy to use and may be operated
by undergraduate students. Its performance is demonstrated by examples from
various fields of condensed matter physics.Comment: submitted to Journal of Magnetic Resonanc
Prevalence of Tuberculosis infection among teen-agers in Tuscany
Introduction. In Tuscany, Tuberculosis incidence is more thantriplicate from 1982 to the beginning of the third millennium.The impact of this trend on open population is not known, asupdated studies on Tuberculosis prevalence are not available.Tuberculin skin test provides the currently most widely used toolfor assessing Tuberculosis transmission in a community and theprevalence of infection as well.The objective of this investigation was the evaluation of tuberculin index by means of the Mantoux test in adolescents eighteen-years old.Results. The study was carried out in 21 secondary schools ofSiena and its Province; 1,138 students participated to this survey.The overall prevalence of subjects with a skin reaction size >5 mm was 1.6%; if the standard cut-off of 10 mm was used, the overall prevalence of a positive skin reaction was 0.4%. Riskfactors for a doubtful or positive reaction were previous immunization with BCG and migration from high-endemicity countries. Discussion. In Italy, studies on tuberculin index in young adultsare scanty and controversial: our results show a very low Tuberculosis prevalence and an epidemiological pattern typical ofcountries with low Tuberculosis endemicity.Conclusions. The slightly increase in Tuberculosis incidencehas no impact on the prevalence of latent Tuberculosis infection on our geographical area. We conclude that skin-test screening for Tuberculosis should be addressed to high risk population as migrants from Countries reporting high transmissionrate, those recently exposed to an infectious case and healthworkers
Hydrogeology of Stromboli volcano, Aeolian Islands (Italy) from the interpretation of resistivity tomograms, self-potential, soil temperature and soil CO2 concentration measurements
International audienceTo gain a better insight of the hydrogeology and the location of the main tectonic faults of Stromboli volcano in Italy, we collected electrical resistivity measurements, soil CO2 concentrations, temperature and self-potential measurements along two profiles. These two profiles started at the village of Ginostra in the southwest part of the island. The first profile (4.8 km in length) ended up at the village of Scari in the north east part of the volcano and the second one (3.5 km in length) at Forgia Vecchia beach, in the eastern part of the island. These data were used to provide insights regarding the position of shallow aquifers and the extension of the hydrothermal system. This large-scale study is complemented by two high-resolution studies, one at the Pizzo area (near the active vents) and one at Rina Grande where flank collapse areas can be observed. The Pizzo corresponds to one of the main degassing structure of the hydrothermal system. The main degassing area is localized along a higher permeability area corresponding to the head of the gliding plane of the Rina Grande sector collapse. We found that the self-potential data reveal the position of an aquifer above the villages of Scari and San Vincenzo. We provide an estimate of the depth of this aquifer from these data. The lateral extension of the hydrothermal system (resistivity ∼15-60 ohm m) is broader than anticipated extending in the direction of the villages of Scari and San Vincenzo (in agreement with temperature data recorded in shallow wells). The lateral extension of the hydrothermal system reaches the lower third of the Rina Grande sector collapse area in the eastern part of the island. The hydrothermal body in this area is blocked by an old collapse boundary. This position of the hydrothermal body is consistent with low values of the magnetization (<2.5 A m−1) from previously published work. The presence of the hydrothermal body below Rina Grande raises questions about the mechanical stability of this flank of the edifice
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