3,498 research outputs found
Systematic investigation of the effects of disorder at the lowest order throughout the BCS-BEC crossover
A systematic investigation of the effects of disorder on the BCS-BEC
crossover at the lowest order in the impurity potential is presented for the
normal phase above the critical temperature Tc. Starting with the t-matrix
approach for the clean system, by which pairing correlations between
opposite-spin fermions evolve from the weak-coupling (BCS) to the
strong-coupling (BEC) limits by increasing the strength of the attractive
inter-particle interaction, all possible diagrammatic processes are considered
where the effects of a disordered potential are retained in the self-energy at
the lowest order. An accurate numerical investigation is carried out for all
these diagrammatic terms, to determine which of them are mostly important
throughout the BCS-BEC crossover. Explicit calculations for the values of Tc,
the chemical potential, and the Tan's contact are carried out. In addition, the
effect of disorder on the single-particle spectral function is analyzed, and a
correlation is found between an increase of Tc and a widening of the pseudo-gap
energy at Tc on the BCS side of unitarity in the presence of disorder, while on
the BEC side of unitarity the presence of disorder favors the collapse of the
underlying Fermi surface. The present investigation is meant to orient future
studies when the effects of disorder will be considered at higher orders, with
the purpose of limiting the proliferation of diagrammatic terms in which
interaction and disorder are considered simultaneously.Comment: 20 pages, 21 figure
Density and spin response of a strongly-interacting Fermi gas in the attractive and quasi-repulsive regime
Recent experimental advances in ultra-cold Fermi gases allow for exploring
response functions under different dynamical conditions. In particular, the
issue of obtaining a "quasi-repulsive" regime starting from a Fermi gas with an
attractive inter-particle interaction while avoiding the formation of the
two-body bound state is currently debated. Here, we provide a calculation of
the density and spin response for a wide range of temperature and coupling both
in the attractive and quasi-repulsive regime, whereby the system is assumed to
evolve non-adiabatically toward the "upper branch" of the Fermi gas. A
comparison is made with the available experimental data for these two
quantities.Comment: 8 pages, 7 figures, to appear on Phys. Rev. Let
Pairing effects in the normal phase of a two-dimensional Fermi gas
In a recent experiment [M. Feld et al., Nature 480, 75 (2011); B. Froehlich
et al., Phys. Rev. Lett. 109,130403 (2012)], a pairing gap was detected in a
two-dimensional (2D) Fermi gas with attractive interaction at temperatures
where superfluidity does not occur. The question remains open as to whether
this gap is a pseudogap phenomenon or is due to a molecular state. In this
paper, by using a t-matrix approach, we reproduce quite well the experimental
data for a 2D Fermi gas, and set the boundary between the pseudogap and
molecular regimes. We also show that pseudogap phenomena occurring in 2D and 3D
can be related through a variable spanning the BCS-BEC crossover in a universal
way.Comment: 10 pages, 9 figures; final versio
GEOMATICS AS A SURVEY TOOL TO DOCUMENT AND ENHANCE THE CULTURALAND LANDSCAPED HERITAGE OF THE MONUMENTAL COMPLEXES IN THEMOUNTAINS OF ABRUZZO
Abstract. The themes of the conference provide an opportunity to exchange views on topics of study in which multidisciplinary contributions of geomatics and restoration contribute to the cognitive process aimed at the conservation of cultural Heritage. In this regard, the contribution exposes research aimed at understanding the documentation and the enhancement of unique architectural – landscape patrimony kept in the Abruzzo mountains. It is about the numerous spiritual retreats established by Pietro da Morrone, Pope Celestino V, mounted among unpassable rocky walls, where the architecture blends with its natural environment camouflaging with it. The analysis refers, specifically to the aspects of survey conducted during the years with the aid of integrated methodologies, able to allow the acquisition, management and comparison of the data. The analysis refers, specifically, to recent digital acquisitions involving the development of San Bartolomeo in Legio, on the slopes of Majella near Roccamorice detected with the use of comparative Agisoft Photoscan and Pix4d software, with shots taken with drones of different sizes, able to mount professional photographic cameras and associate to each picture the coordinates Gps of the point of shooting. Follows a confrontation between a survey carried out with 3d laser scanner, Faro Ls1105, and described acquisitions, obtained from ground and from drone with Photoscan, in order to compare the two scans and the metric differences obtained with the two methods
Temperature and coupling dependence of the universal contact intensity for an ultracold Fermi gas
Physical properties of an ultracold Fermi gas in the temperature-coupling
phase diagram can be characterized by the contact intensity C, which enters the
pair-correlation function at short distances and describes how the two-body
problem merges into its surrounding. We show that the local order established
by pairing fluctuations about the critical temperature Tc of the superfluid
transition considerably enhances the contact C in a temperature range where
pseudogap phenomena are maximal. Our ab initio results for C in a trap compare
well with recently available experimental data over a wide coupling range. An
analysis is also provided for the effects of trap averaging on C.Comment: 5 pages, 5 figure
INTEGRATED PHOTOGRAMMETRIC SURVEY AND BIM MODELLING FOR THE PROTECTION OF SCHOOL HERITAGE, APPLICATIONS ON A CASE STUDY
The contribution, considering the use of low-cost photogrammetric detection methodologies and the use of asset Historical-BIM, has as its aim the theme of knowledge and the adaptation of safety in school buildings, a topic brought to attention by the many situations of seismic risk that have interested the central Apennines in Italy. The specific investigation is referred to the Abruzzo region, hit by the recent earthquakes of 2016 and 2009 that have highlighted the vulnerability of the building structures involved in a large seismic crater covering large areas of the territory. The need to consider in advance the performance standards of building components, especially concerning the strategic ways of the functions contained in them, starts here. In this sense, the school buildings have emerged among the types on which to pay attention, a study theme to be promptly considered, considering the functions performed within them and the possible criticality of such constructions, often dated, enlarged or readjusted without appropriate seismic adaptation plans. From here derives the purpose of the research that is directed towards a systematic recognition of the scholastic heritage, deriving from objective and rapid surveys at low cost, taking into consideration the as-built and the different formal and structural aspects that define the architectural organisms to analyse and manage through three-dimensional models that can be interrogated using HBIM connected to databases containing information of a structural and functional nature. In summary, through the implementation of information in the BIM model, it will be possible to query and obtain in real time all the necessary information to optimize, in terms of efficiency, costs, and future maintenance operations
Dispersions, weights, and widths of the single-particle spectral function in the normal phase of a Fermi gas
The dispersions, weights, and widths of the peaks of the single-particle
spectral function in the presence of pair correlations, for a Fermi gas with
either attractive or repulsive short-range inter-particle interaction, are
determined in the normal phase over a wide range of wave vectors, with a
twofold purpose. The first one is to determine how these dispersions identify
both an energy scale known as the pseudo-gap near the Fermi wave vector, as
well as an additional energy scale related to the contact C at large wave
vectors. The second one is to differentiate the behaviors of the repulsive gas
from the attractive one in terms of crossing versus avoided crossing of the
dispersions near the Fermi wave vector. An analogy will also be drawn between
the occurrence of the pseudo-gap physics in a Fermi gas subject to pair
fluctuations and the persistence of local spin waves in the normal phase of
magnetic materials.Comment: 18 pages, 21 figure
THE PALLADIOLIBRARY GEO-MODELS: AN OPEN 3D ARCHIVE TO MANAGE AND VISUALIZE INFORMATION-COMMUNICATION RESOURCES ABOUT PALLADIO
Abstract. The paper describes objectives, methods, procedures and outcomes of the development of the digital archive of Palladio works and documentation: the PALLADIOLibrary of Centro Internazionale di Studi di Architettura Andrea Palladio di Vicenza (CISAAP). The core of the application consists of fifty-one reality-based 3D models usable and navigable within a system grounded on GoogleEarth. This information system, a collaboration of four universities bearers of specific skills returns a comprehensive, structured and coherent semantic interpretation of Palladian landscape through shapes realistically reconstructed from historical sources and surveys and treated for GE with Ambient Occlusion techniques, overcoming the traditional display mode
Evolution of the Normal State of a Strongly Interacting Fermi Gas from a Pseudogap Phase to a Molecular Bose Gas
Wave-vector resolved radio frequency (rf) spectroscopy data for an ultracold
trapped Fermi gas are reported for several couplings at Tc, and extensively
analyzed in terms of a pairing-fluctuation theory. We map the evolution of a
strongly interacting Fermi gas from the pseudogap phase into a fully gapped
molecular Bose gas as a function of the interaction strength, which is marked
by a rapid disappearance of a remnant Fermi surface in the single-particle
dispersion. We also show that our theory of a pseudogap phase is consistent
with a recent experimental observation as well as with Quantum Monte Carlo data
of thermodynamic quantities of a unitary Fermi gas above Tc.Comment: 9 pages, 9 figures. Substantially revised version (to appear in Phys.
Rev. Lett.
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