Single-particle vs. pair superfluidity in a bilayer system of dipolar bosons

We consider the ground state of a bilayer system of dipolar bosons, where dipoles are oriented by an external field in the direction perpendicular to the parallel planes. Quantum Monte Carlo methods are used to calculate the ground-state energy, the one-body and two-body density matrix, and the superfluid response as a function of the separation between layers. We find that by decreasing the interlayer distance for fixed value of the strength of the dipolar interaction, the system undergoes a quantum phase transition from a single-particle to a pair superfluid. The single-particle superfluid is characterized by a finite value of both the atomic condensate and the super-counterfluid density. The pair superfluid phase is found to be stable against formation of many-body cluster states and features a gap in the spectrum of elementary excitations.Comment: 4 figure

Low-dimensional weakly interacting Bose gases: non-universal equations of state

The zero-temperature equation of state is analyzed in low-dimensional bosonic systems. In the dilute regime the equation of state is universal in terms of the gas parameter, i.e. it is the same for different potentials with the same value of the s-wave scattering length. Series expansions of the universal equation of state are reported for one- and two- dimensional systems. We propose to use the concept of energy-dependent s-wave scattering length for obtaining estimations of non-universal terms in the energy expansion. We test this approach by making a comparison to exactly solvable one-dimensional problems and find that the generated terms have the correct structure. The applicability to two-dimensional systems is analyzed by comparing with results of Monte Carlo simulations. The prediction for the non-universal behavior is qualitatively correct and the densities, at which the deviations from the universal equation of state become visible, are estimated properly. Finally, the possibility of observing the non-universal terms in experiments with trapped gases is also discussed.Comment: 11 pages, 4 figure

Ground-State Properties of a One-Dimensional System of Hard Rods

A quantum Monte Carlo simulation of a system of hard rods in one dimension is presented and discussed. The calculation is exact since the analytical form of the wavefunction is known, and is in excellent agreement with predictions obtained from asymptotic expansions valid at large distances. The analysis of the static structure factor and the pair distribution function indicates that a solid-like and a gas-like phases exist at high and low densities, respectively. The one-body density matrix decays following a power-law at large distances and produces a divergence in the low density momentum distribution at k=0 which can be identified as a quasi-condensate.Comment: 4 pages, 4 figure

Zero-temperature phase diagram of Yukawa bosons

We study the zero-temperature phase diagram of bosons interacting via screened Coulomb (Yukawa) potential by means of the diffusion Monte Carlo method. The Yukawa potential is used as a model interaction in the neutron matter, dusty plasmas and charged colloids. As shown by D. S. Petrov et al. [Phys. Rev. Lett. 99, 130407 (2007)], interactions between weakly bound molecules of heavy and light fermionic atoms are described by an effective Yukawa potential with a strength related to the heavy-light mass ratio M/m which might lead to crystallization in a two-dimensional geometry if the mass ratio of heavy-light fermions exceeds a certain critical value. In the present work we do a thorough study of the quantum three-dimensional Yukawa system. For strong interactions (equivalently, large mass ratios) the system experiences several phase transitions as the density is increased, passing from gas to solid and to gas phase again. Weakly interacting Yukawa particles do not crystallize at any density. We find the minimal interaction strength at which the crystallization happens. In terms of the two-component fermionic system, this strength corresponds to a heavy-light mass ratio of M/m ~ 180, so that it is impossible to realize the gas-crystal transition in a conventional bulk system. For the Yukawa model of fermionic mixtures we also analyze the possibility of building molecular systems with very large effective mass ratios by confining the heavy component to a sufficiently deep optical lattice. We show how the effective mass of the heavy component can be made arbitrarily large by increasing the lattice depth, thus leading to a tunable effective mass ratio that can be used to realize a molecular superlattice.Comment: added figure with finite-size dependence of the energy; comments and references added; title change

La coltura della Reseda Biondella. Un primato nell'area di Mutina?

The Ex Cassa di Risparmio site is a reclaimed channel - first Imperial age - located in the center of the city of Modena and it is unique in Emilia Romagna for the archaeobotanical information provided on urban area. The study of seeds/fruits remains produced a framework which can be considered representative for reconstructing the vegetal environment of Mutina at the moment of maximum splendor of the Roman empire and of the city; some species appeared particularly worthy of insights, such as weld - Reseda luteola L., grass species that produces a very stable yellow pigment used since ancient times for dyeing fabrics like wool, linen and silk. The abundance of seeds found in the drained canal suggests agricultural practices implemented in peri-urban area of the city and presumably related to the economy of this prosperous Roman colony. Agriculture should have been a strong element of its economy in addition to ceramic production, sheep farming and the textile industry

Thermal conductivity of clay bricks

In the present work the thermal conductivity of 29 samples of clay bricks was measured and the correlations of the thermal performance with the compositional, physical, and microstructural features of products were investigated. The results obtained directed our attention toward a better understanding of the role played by some parameters (i.e., mineralogical components and pore size distribution), other than bulk density, in improving or depressing the insulating properties of bricks. Among them, the unfavorable role of quartz, Ca-rich silicates, and amorphous phase came out, while the role of pore size and specific surface should be more accurately evaluated in the structural design of materials

PRIMI RISULTATI DI UN INDAGINE SULLO STATO DELLE SISTEMAZIONI IDRAULICO-FORESTALI NEL BACINO DELL’ARNO

Il presente lavoro è relativo ai risultati ottenuti con il primo stato d’avanzamento di una ricerca sullo stato delle Sistemazioni Idraulico-Forestali per assegnate aree di indagine comprese nel bacino del fiume Arno affidata dall’ Autorità di Bacino del Fiume Arno al Dipartimento di Ingegneria Agraria e Forestale dell’Università degli Studi di Firenze. Innanzi tutto, è stata condotta un’analisi preventiva, mediante un database, di documentazione relativa alle opere idrauliche già censite in precedenti lavori (prof. Grazi) con identificazione della posizione geografica delle opere stesse con l’ausilio di software GIS. A questa prima fase sono seguiti la predisposizione di una opportuna scheda di rilievo (sia cartacea sia elettronica) e quindi sopralluoghi in campo condotti mediante l’ausilio di un GPS collegato a computer palmare per il supporto cartografico di base. Rilievi di dettaglio sono stati condotti nei torrenti dell’area del Mugello, già oggetto di studi risalenti a una trentina di anni fa per la valutazione delle pendenze di compensazione (Falciai et al.) che sono stati utilizzati spesso in letteratura (Ferro et al., Pica et al., etc.). Con riferimento ad altre zone campione del bacino (es. Casentino e Area Fiorentina), la documentazione storica ed il sopralluogo in campo (su base statistica) ha avuto lo scopo di rintracciare le opere esistenti e verificare l’attendibilità e la confrontabilità dei vari censimenti eseguiti anche da altri Enti preposti. In particolare si è analizzato il dimensionamento delle opere ed il loro stato attuale di conservazione ed efficienza, confrontandolo con quanto riportato in eventuali elaborati progettuali e nei censimenti precedenti. Eventuali danneggiamenti dei manufatti possono essere derivati dalle valutazioni in sede progettuale, da scarsa o inesistente manutenzione o da mutate caratteristiche in alveo e nel bacino. Per avere qualche indicazione in proposito si è valutata la portata di progetto a partire dalle dimensioni delle gavete considerate come stramazzi in parete grossa e se ne è stimato il tempo di ritorno, mediante i modelli AlTo (Regione Toscana) e Idrarno (Autorità di Bacino). Questa fase ha richiesto un lavoro preventivo di queries spaziali che hanno lo scopo di attribuire il codice dell’asta a cui appartengono le opere idrauliche in esame (all’interno del reticolo idrografico del modello AlTo e all’interno del reticolo “Sistema Acque” dell’Autorità di Bacino dell’Arno). Questa operazione consente, inoltre, il collegamento tra il contenuto informativo del geodatabase dell’Autorità di Bacino con il sistema di regionalizzazione delle portate di piena della Regione Toscana. Mediante la misura delle caratteristiche dimensionali dell’opera si sono cercate di ricavare anche indicazioni statistiche riguardo alla pendenza di compensazione dei corsi d’acqua in esame. Le verifiche in campo ha permesso anche una descrizione delle condizioni generali dell’alveo in cui sono situate le opere e dei versanti siti in prossimità delle opere stesse. I dati raccolti sono stati immessi in un geodatabase opportunamente costruito secondo lo standard di quello esistente presso l’Autorità di Bacino del Fiume Arno e quindi elaborati per la ricerca delle relazioni tra le caratteristiche delle opere e la pendenza attuale dell’alveo nonché la stima della necessità, per i corsi d’acqua esaminati, di opere atte a garantire la continuità fluviale per la ittiofauna (Pini Prato e Barneschi)

JET ANALYSIS BY NEURAL NETWORKS IN HIGH ENERGY HADRON-HADRON COLLISIONS

We study the possibility to employ neural networks to simulate jet clustering procedures in high energy hadron-hadron collisions. We concentrate our analysis on the Fermilab Tevatron energy and on the $k_\bot$ algorithm. We consider both supervised multilayer feed-forward network trained by the backpropagation algorithm and unsupervised learning, where the neural network autonomously organizes the events in clusters.Comment: 9 pages, latex, 2 figures not included

Azimuthal Correlation in Lepton-Hadron Scattering via Charged Weak-Current Processes

We consider the azimuthal correlation of the final-state particles in charged weak-current processes. This correlation provides a test of perturbative quantum chromodynamics. The azimuthal asymmetry is large in the semi-inclusive processes in which we identify a final-state hadron, say, a charged pion compared to that in the inclusive processes in which we do not identify final-state particles and use only the calorimetric information. In semi-inclusive processes the azimuthal asymmetry is more conspicuous when the incident lepton is an antineutrino or a positron than when the incident lepton is a neutrino or an electron. We analyze all the possible charged weak-current processes and study the quantitative aspects of each process. We also compare this result to the ep scattering with a photon exchange.Comment: 25 pages, 2 Postscript figures, uses RevTeX, fixes.st

Explorations of the Extended ncKP Hierarchy

A recently obtained extension (xncKP) of the Moyal-deformed KP hierarchy (ncKP hierarchy) by a set of evolution equations in the Moyal-deformation parameters is further explored. Formulae are derived to compute these equations efficiently. Reductions of the xncKP hierarchy are treated, in particular to the extended ncKdV and ncBoussinesq hierarchies. Furthermore, a good part of the Sato formalism for the KP hierarchy is carried over to the generalized framework. In particular, the well-known bilinear identity theorem for the KP hierarchy, expressed in terms of the (formal) Baker-Akhiezer function, extends to the xncKP hierarchy. Moreover, it is demonstrated that N-soliton solutions of the ncKP equation are also solutions of the first few deformation equations. This is shown to be related to the existence of certain families of algebraic identities.Comment: 34 pages, correction of typos in (7.2) and (7.5