Noise and diffusion of particles obeying asymmetric exclusion processes

The relation between noise and Fick's diffusion coefficient in barrier limited transport associated with hopping or tunneling mechanisms of particles obeying the asymmetric simple exclusion processes (ASEP) is physically assessed by Monte Carlo simulations. For a closed ring consisting of a large number of barriers the diffusion coefficient is related explicitly to the current noise thus revealing the existence of a generalized Nyquist-Einstein relation. Both diffusion and noise are confirmed to decrease as the square root of the number of barriers as a consequence of the correlation induced by ASEP. By contrast, for an open linear chain of barriers the diffusion coefficient is found to be no longer related to current noise. Here diffusion depends on particle concentration but is independent of the number of barriers

Shot-noise suppression in Schottky barrier diodes

We give a theoretical interpretation of the noise properties of Schottky barrier diodes based on the role played by the long range Coulomb interaction. We show that at low bias Schottky diodes display shot noise because the presence of the depletion layer makes negligible the effects of the Coulomb interaction on the current fluctuations. When the device passes from barrier to flat band conditions, the Coulomb interaction becomes active, thus introducing correlation between different current fluctuations. Therefore, the cross-over between shot and thermal noise represents the suppression due to long range Coulomb interaction of the otherwise full shot-noise. Similar ideas can be used to interpret the noise properties of others semiconductor devices.Comment: 3 page

Large mixing angle solution to the solar neutrino problem and random matter density perturbations

There are reasons to believe that mechanisms exist in the solar interior which lead to random density perturbations in the resonant region of the Large Mixing Angle solution to the solar neutrino problem. We find that, in the presence of these density perturbations, the best fit point in the (sin^2(2\theta), Delta_m^2) parameter space moves to smaller values, compared with the values obtained for the standard LMA solution. Combining solar data with KamLAND results, we find a new compatibility region, which we call VERY-LOW LMA, where sin^2(2\theta) ~ 0.6 and Delta_m^2~2e-5 eV^2, for random density fluctuations of order 5% < \xi< 8%. We argue that such values of density fluctuations are still allowed by helioseismological observations at small scales of order 10 - 1000 km deep inside the solar core.Comment: References and discussion added, with some small numerical corrections implemente

Teams or Tournaments? A Field Experiment on Cooperation and Competition in Academic Achievement

This paper assesses the effect of two stylized and antithetic non-monetary incentive schemes on students’ effort. We collect data from a field experiment where incentives are exogenously imposed, performance is monitored and individual characteristics are observed. Students are randomly assigned to a tournament scheme that fosters competition between coupled students, a cooperative scheme that promotes information sharing and collaboration between students and a control treatment in which students can neither compete, nor cooperate. In line with theoretical predictions, we find that competition induces higher effort with respect to cooperation and cooperation does not increase effort with respect to the baseline. However, this is true only for men, while women do not seem to react to non-monetary incentives.

Noise suppression due to long-range Coulomb interaction: Crossover between diffusive and ballistic transport regimes

We present a Monte Carlo analysis of shot-noise suppression due to long-range Coulomb interaction in semiconductor samples under a crossover between diffusive and ballistic transport regimes. By varying the mean time between collisions we find that the strong suppression observed under the ballistic regime persists under quasi-ballistic conditions, before being washed out when a complete diffusive regime is reached.Comment: RevTex, 3 pages, 4 figures, minor correction

Effects of magnetohydrodynamics matter density fluctuations on the solar neutrino resonant spin-flavor precession

Taking into account the stringent limits from helioseismology observations on possible matter density fluctuations described by magnetohydrodynamics theory, we find the corresponding time variations of solar neutrino survival probability due to the resonant spin-flavor precession phenomenon with amplitude of order O(10%). We discuss the physics potential of high statistics real time experiments, like as Superkamiokande, to observe the effects of such magnetohydrodynamics fluctuations on their data. We conclude that these observations could be thought as a test of the resonant spin-flavor precession solution to the solar neutrino anomaly.Comment: 16 pages, 3 figure

Religious attitudes and home bias: theory and evidence from a pilot study

This paper examines the relationship between religion and home bias. We propose a simple theoretical framework that suggests that countries interacting via their representative individuals might show a certain degree of religion-driven international altruism that in turn affects trade. We test these predictions exploiting data from a survey on religious attitudes and individuals' preferences over consumption of home-produced versus foreign goods that we designed and carried out in 15 different countries. We find evidence that religious openness and home bias are negatively correlated. This appears to provide some support to the hypothesis that religious openness, through trust and altruism, may have a pro-trade effect.

Searching for gas giant planets on Solar System scales - A NACO/APP L'-band survey of A- and F-type Main Sequence stars

We report the results of a direct imaging survey of A- and F-type main sequence stars searching for giant planets. A/F stars are often the targets of surveys, as they are thought to have more massive giant planets relative to solar-type stars. However, most imaging is only sensitive to orbital separations $>$30 AU, where it has been demonstrated that giant planets are rare. In this survey, we take advantage of the high-contrast capabilities of the Apodizing Phase Plate coronagraph on NACO at the Very Large Telescope. Combined with optimized principal component analysis post-processing, we are sensitive to planetary-mass companions (2 to 12 $M_{\rm Jup}$) at Solar System scales ($\leq$30 AU). We obtained data on 13 stars in L'-band and detected one new companion as part of this survey: an M$6.0\pm0.5$ dwarf companion around HD 984. We re-detect low-mass companions around HD 12894 and HD 20385, both reported shortly after the completion of this survey. We use Monte Carlo simulations to determine new constraints on the low-mass ($<$80 $M_{\rm Jup}$) companion frequency, as a function of mass and separation. Assuming solar-type planet mass and separation distributions, normalized to the planet frequency appropriate for A-stars, and the observed companion mass-ratio distribution for stellar companions extrapolated to planetary masses, we derive a truncation radius for the planetary mass companion surface density of $<$135 AU at 95% confidence.Comment: Accepted for publication in MNRAS, 8 pages, 4 figure

Statistics and quantum maximum entropy principle

By using the reduced Wigner formalism we consider a kinetic theory for a quantum gas. We introduce a set of generalized kinetic fields and obtain a hierarchy of Quantum Hydrodynamic (QHD) equations for the corresponding macroscopic variables. To close the QHD system a maximum entropy principle is asserted, and to explicitly incorporate particles indistinguishability a proper quantum entropy is analyzed in terms of the reduced density matrix. This approach implies a quantum generalization of the corresponding Lagrange multipliers. Quantum contributions are expressed in powers of ¯h2

Scuola, Università e Mercato del lavoro dopo la Riforma Biagi. Le politiche per la transizione dai percorsi educativi e formativi al mercato del lavoro

Quale ruolo per i percorsi di educazione e formazione nella riforma del mercato del lavoro? Se ne è parlato poco, in questi ultimi tempi. Eppure, nell’impianto della legge Biagi, proprio il sistema di istruzione e quello della formazione professionale rappresentano, assieme al nuovo contratto di apprendistato, il principale canale di sviluppo e valorizzazione delle risorse umane. Un canale attraverso cui avvicinare, grazie a investimenti in ricerca, innovazione e capitale umano, le performances del nostro sistema economico-produttivo a quelle degli altri Paesi europei. E non poteva essere diversamente, in una Europa che, da Lisbona in poi, dichiara enfaticamente di voler diventare l’economia basata sulla conoscenza più competitiva e dinamica del mondo. Il ritardo dell’Italia rispetto agli altri Stati europei è, da questo punto di vista, ancora impressionante. È sufficiente ricordare, al riguardo, come i tradizionali percorsi didattici e formativi abbiano sin qui determinato alti tassi di dispersione e, quel che più è grave, un ingresso tardivo nel mercato del lavoro. Le rilevazioni statistiche parlano di 28 anni, quando la media europea è attestata intorno ai 22-23 anni. È da tempo che se ne discute, senza tuttavia approdare a esiti concreti: gli istituti scolastici e le università italiane devono accelerare i processi volti a rafforzare la coerenza tra formazione erogata e fabbisogni del mercato del lavoro. La riforma universitaria che prevede la laurea triennale è entrata in vigore con l’anno accademico 2001/2002, i primi laureati tuttavia in minima parte si sono avvicinati al mondo del lavoro ma hanno proseguito il corso di studi verso la laurea specialistica e quindi se questa tendenza verrà confermata, difficilmente nel nostro Paese ci avvicineremo alla media europea e continueremo ad avere laureati in cerca di prima occupazione ad un’età troppo elevata per rispondere ai bisogni del mercato del lavoro