Polarization in a three-dimensional Fermi gas with Rabi coupling

We investigate the polarization of a two-component three-dimensional fermionic gas made of repulsive alkali-metal atoms. The two pseudo-spin components correspond to two hyperfine states which are Rabi coupled. The presence of Rabi coupling implies that only the total number of atoms is conserved and a quantum phase transition between states dominated by spin-polarization along different axses is possible. By using a variational Hartree-Fock scheme we calculate analytically the ground-state energy of the system and determine analytically and numerically the conditions under which there is this quantum phase transition. This scheme includes the well-known criterion for the Stoner instability. The obtained phase diagram clearly shows that the polarized phase crucially depends on the interplay among the Rabi coupling energy, the interaction energy per particle, and the kinetic energy per particle.Comment: 12 pages, 2 figure

To Give or Not To Give? Equity, Efficiency and Altruistic Behavior in a Survey-Based Experiment

This paper presents the results of a survey-based experiment on the role of equity and efficiency for altruistic behavior. Using simple binary decisions for a representative pool of subjects, we find that both equity and efficiency are relevant for the decision to give. However, contrary to the findings in several laboratory experiments, our results indicate that equity plays a major role for altruistic behavior. Differences in relative payoffs have a significant effect on the decision to give. When giving is not costly, more than half of the subjects prefer equal payoffs to a socially efficient but unequal allocation. When giving is Pareto-improving, half the subjects choose to sacrifice a higher payoff in order to avoid payoff inequality. We also find that preferences, as revealed by experimental choices, are largely consistent with reported pro-social activities, while only weakly related to self-reported well-being.Altruism, Inequality-Aversion, SocialWelfare, Envy, Large-Scale Experiment

Interactions in Electronic Mach-Zehnder Interferometers with Copropagating Edge Channels

We study Coulomb interactions in the finite bias response of Mach-Zehnder interferometers, which exploit copropagating edge states in the integer quantum Hall effect. Here, interactions are particularly important since the coherent coupling of edge channels is due to a resonant mechanism that is spoiled by inelastic processes. We find that interactions yield a saturation, as a function of bias voltage, of the period-averaged interferometer current, which gives rise to unusual features, such as negative differential conductance, enhancement of the visibility of the current, and nonbounded or even diverging visibility of the differential conductance.Comment: 5 pages, 2 figure

Strategies for fast convergence in semiotic dynamics

Semiotic dynamics is a novel field that studies how semiotic conventions spread and stabilize in a population of agents. This is a central issue both for theoretical and technological reasons since large system made up of communicating agents, like web communities or artificial embodied agents teams, are getting widespread. In this paper we discuss a recently introduced simple multi-agent model which is able to account for the emergence of a shared vocabulary in a population of agents. In particular we introduce a new deterministic agents' playing strategy that strongly improves the performance of the game in terms of faster convergence and reduced cognitive effort for the agents.Comment: 6 pages, 6 figure

Gaussian Discriminating Strength

We present a quantifier of non-classical correlations for bipartite, multi-mode Gaussian states. It is derived from the Discriminating Strength measure, introduced for finite dimensional systems in A. Farace et al., New. J. Phys. 16, 073010 (2014). As the latter the new measure exploits the Quantum Chernoff Bound to gauge the susceptibility of the composite system with respect to local perturbations induced by unitary gates extracted from a suitable set of allowed transformations (the latter being identified by posing some general requirements). Closed expressions are provided for the case of two-mode Gaussian states obtained by squeezing or by linearly mixing via a beam-splitter a factorized two-mode thermal state. For these density matrices, we study how non-classical correlations are related with the entanglement present in the system and with its total photon number.Comment: 11+6 pages, 4 figure

Experimental Investigation of Flow Condensation of Propylene in a horizontal Tube

openLa condensazione durante deflusso è un processo fisico molto diffuso, utilizzato nei condensatori adottati per diverse applicazioni come pompe di calore, impianti di condizionamento e nell’industria chimica. L'esigenza dell'industria della refrigerazione di trovare refrigeranti alternativi a HFC, caratterizzati da un ODP quasi nullo ma da un GWP troppo elevato, rende molto importante lo studio degli idrocarburi per le applicazioni a ciclo inverso. L'obiettivo del presente lavoro è studiare la condensazione del flusso di propilene all'interno di un tubo orizzontale liscio. La condensazione in flusso è un meccanismo di trasferimento del calore molto complesso che attualmente non può essere descritto da equazioni analitiche. Pertanto, l'analisi sperimentale diventa uno strumento importante per convalidare le correlazioni presentate in letteratura. Il lavoro sperimentale è stato condotto sfruttando un impianto di prova su scala industriale, il KIIR, che consente di impostare le condizioni termodinamiche all'ingresso della sezione di prova, dove avviene la condensazione parziale. La sezione di prova consiste in uno scambiatore di calore a fascio tubiero. Il propilene viene raffreddato da un olio in configurazione di flusso controcorrente. Il tubo sperimentale è stato dotato di sensori di temperatura e installato all’interno dell'apparato sperimentale. Ciascun test è stato eseguito in condizioni operative costanti in termini di pressione p, flusso di massa G e titolo di vapore x. L'analisi dei risultati a livello locale ha permesso di dimostrare la dipendenza del coefficiente di trasferimento di calore α dalla posizione radiale φ del tubo. In particolare, nelle condizioni di prova associate al verificarsi di un flusso stratificato, il coefficiente di trasferimento di calore α varia notevolmente in funzione della posizione radiale φ. Nelle condizioni di alta turbolenza e flusso anulare, il coefficiente di trasferimento di calore α è approssimativamente costante in funzione della posizione radiale φ. A causa delle incertezze del set-up sperimentale, queste osservazioni sono state più chiare nelle condizioni di prova in cui la differenza di temperatura media tra la sostanza in esame e l'olio di raffreddamento era più elevata. Inoltre, è stato possibile verificare sperimentalmente che il coefficiente di trasferimento del calore α aumenta all'aumentare del flusso di massa G. Allo stesso modo, è stato possibile verificare che il coefficiente di trasferimento di calore α diminuisce con l'aumento della pressione p. Confrontando i risultati relativi al trasferimento di calore complessivo e alle perdite di carico, si è dedotto che un elevato coefficiente di trasferimento di calore è sempre abbinato a un alto valore di perdite di carico.Flow condensation is a very widely spread physical process, used in condensers adopted for several applications like heat pumps, air conditioning systems, and the chemical industry. The urge of the refrigeration industry to find alternative refrigerants to HFC, characterized by null ODP but too high GWP, makes the study of hydrocarbons for inverse cycle applications very important. The goal of the present work is to study flow condensation of propylene inside a horizontal smooth tube. Flow condensation is a very complex heat transfer mechanism that currently, cannot be described by analytical equations. Therefore, experimental analysis becomes an important tool to validate the correlations presented in the literature. The present experimental work has been conducted exploiting an industrial scale test rig, KIIR, that allows to set the thermodynamics conditions at the inlet of the test section, where partial condensation occurs. The test section consists in a tube-shell-heat exchanger. Propylene is cooled down by an oil in counter-current flow configuration. The test tube has been equipped with temperature sensors and installed in the experimental apparatus and the measurement plan has been conducted. Each test has been executed under constant operating conditions in terms of pressure p, mass flux G and vapor quality x. The analysis of the local experimental results has allowed to observe the dependency of the heat transfer coefficient α on the radial position φ of the test tube. Specifically, under test conditions associated with the occurrence of stratified flow, the heat transfer coefficient α varies considerably as function of the radial position φ. Under the conditions associated with high turbulence and annular flow, the heat transfer coefficient α is approximately constant as function of the radial position φ. Because of the uncertainties of the experimental set up, these observations were clearer under the test conditions in which the average temperature difference between the test substance and the cooling oil was higher. Moreover, it was observed that the overall heat transfer coefficient α increases as the mass flux G increases. In the same way, it was possible to observe that the overall heat transfer coefficient α decreases as the pressure p increases. By comparing the results regarding overall heat transfer and pressure drops, it was verified that a high heat transfer coefficient is always coupled with a high value of pressure drops

The Step-Harmonic Potential

We analyze the behavior of a quantum system described by a one-dimensional asymmetric potential consisting of a step plus a harmonic barrier. We solve the eigenvalue equation by the integral representation method, which allows us to classify the independent solutions as equivalence classes of homotopic paths in the complex plane. We then consider the propagation of a wave packet reflected by the harmonic barrier and obtain an expression for the interaction time as a function of the peak energy. For high energies we recover the classical half-period limit.Comment: 19 pages, 7 figure

Unified Fock space representation of fractional quantum Hall states

Many bosonic (fermionic) fractional quantum Hall states, such as Laughlin, Moore-Read and Read-Rezayi wavefunctions, belong to a special class of orthogonal polynomials: the Jack polynomials (times a Vandermonde determinant). This fundamental observation allows to point out two different recurrence relations for the coefficients of the permanent (Slater) decomposition of the bosonic (fermionic) states. Here we provide an explicit Fock space representation for these wavefunctions by introducing a two-body squeezing operator which represents them as a Jastrow operator applied to reference states, which are in general simple periodic one dimensional patterns. Remarkably, this operator representation is the same for bosons and fermions, and the different nature of the two recurrence relations is an outcome of particle statistics.Comment: 10 pages, 3 figure