Dynamical instability and dispersion management of an attractive condensate in an optical lattice

We investigate the stability of an attractive Bose-Einstein condensate in a moving 1D optical lattice in the presence of transverse confinement. By means of a Bogoliubov linear stability analysis we find that the system is dynamically unstable for low quasimomenta and becomes stable near the band edge, in a specular fashion with respect to the repulsive case. For low interactions the instability occurs via long wavelength excitations that are not sufficient for spoiling the condensate coherence, producing instead an oscillating density pattern both in real and momentum space. This behaviour is illustrated by simulations for the expansion of the condensate in a moving lattice.Comment: 5 pages, 4 figure

Beyond Perrault's experiments: repeatability, didactics and complexity

Abstract. The naturalistic and philosophical studies conducted in the second half of the 17th century were crucial both for the birth of modern hydrological science and modern epistemology. Thanks to quantitative observations and to the new experiment-based scientific approach, the Sun was about to be fully recognized as the engine of the hydrological cycle. In this context of great vitality and rapid cultural changes, Pierre Perrault published his classical opus De l'origine des fontaines (On the origin of springs) in 1674. The opus presents a discussion on the origin of springs and contains the report of a set of experiments of water flow through a soil column, which may be considered the first of modern hydrology. In assessing the importance of Perrault's opus, we will discuss his epistemological relevance by looking at the novelty of his approach, at the repeatability of the experiments, at the intriguing didactic aspects for the modern teaching of hydrology and at his attitude in facing the complexity of hydrological processes. Perrault places himself in the context of a novel experimental epistemology. On the basis of our analyses he seems to be aware that the processes involved in the hydrological cycle and in soil hydrology are hardly reproducible by means of a controlled laboratory model. This circumstance put the modern scientific approach to a severe test at its very beginning. It is suggested that some of Perrault's epistemological and methodological reflections are precursors of the modern epistemology of complexity. Thus even if Perrault's conclusions followed an ancient opinion, his work is not only seminal for hydrology, but also helps to enlighten some features of the scientific revolution of the 17th century

Estimate of turbulent fluxes with eddy-covariance technique in a complex topography: A case study in the Italian Alps

A sensitivity analysis to different eddy—covariance data processing algorithms is presented for a dataset collected in an Alpine environment with complex topography. In Summer 2012 a micrometeorological station was installed at Cividate Camuno (274 m a.s.l., Oglio river basin, Central Italian Alps), in a flat and rectangular grass-covered lawn. The grass was 0.6 m tall during most of the field campaign. The station is equipped with traditional devices, four multiplexed TDR probes, and an eddy--covariance apparatus sampling at 20 Hz (Gill WindMaster Sonic Anemometer and Licor Li7500 Gas Analyzer), at about 3 m above the ground. The local winds regime is strongly affected by the morphology of the valley, and the topography is complex also due to the heterogeneity of the surrounding-areas land—cover. Using EddyPro software, the sensitivity of the turbulent fluxes estimate was assessed addressing three major issues of the data processing procedure, i.e. the choice of the computational averaging period, of the axis rotation method and of the data detrending criterion. Once identified three test periods of consecutive days without rainfall, the fluxes of momentum, sensible heat and latent heat were computed at the averaging period of 30, 60 and 120 min respectively. At each averaging period, both the triple rotation method, the double rotation method and the planar fit method were applied. Particularly the latter was applied both fitting a unique plane for all the wind directions and fitting multiple planes, one for each sector of the wind rose. Regarding the detrending criteria, data were processed with a block average and a linear detrend, the latter with time constant of 5, 30, 60 and 120 min respectively. Therefore, for each test period about 50 estimates of the fluxes were provided. As a result the obtained fluxes were compared. Even if with different flux quality, their pattern is quite stable with regard to the applied estimate procedures, but with sensitively different average values

Universality in Three- and Four-Body Bound States of Ultracold Atoms

Under certain circumstances, three or more interacting particles may form bound states. While the general few-body problem is not analytically solvable, the so-called Efimov trimers appear for a system of three particles with resonant two-body interactions. The binding energies of these trimers are predicted to be universally connected to each other, independent of the microscopic details of the interaction. By exploiting a Feshbach resonance to widely tune the interactions between trapped ultracold lithium atoms, we find evidence for two universally connected Efimov trimers and their associated four-body bound states. A total of eleven precisely determined three- and four-body features are found in the inelastic loss spectrum. Their relative locations on either side of the resonance agree well with universal theory, while a systematic deviation from universality is found when comparing features across the resonance.Comment: 16 pages including figures and Supplementary Online Materia

Development and demonstration of an HBIM framework for the preventive conservation of cultural heritage

Building Information Modelling (BIM) methodology is becoming widespread with many potential uses, such as facility and asset management for new buildings. Recently, it has also been applied for the maintenance of built heritage, within the so-called Historical BIM (HBIM) field. A BIM model, empowered by detailed embedded information, is an excellent tool to monitor and infer on the behaviour, performance, and deterioration of heritage buildings, collecting and classifying diverse data that can co-exist in an asset model. However, three main issues must be tackled: lack of standardization, insufficient interoperability and inherent complexity of the information. It is essential to balance model’s geometrical and non-geometrical features, such as the level of detail accuracy and the quantity of linked information, to make the methodology cost-effective and hence more attractive for end-users. The present work focuses on the development of easy-to-implement strategy to report and monitor damage evolution over time. Standardization and simplification of the procedures are pursued by using Product Data Templates (PDTs) and focusing on interoperability of information through specific provisions of export/import definitions for Industry Foundation Classes (IFC). The developed methodology is tested on the Ducal Palace in Guimarães, Portugal, one of the most prominent monuments of the country.This work was partly financed by the HeritageCare project (Interreg-Sudoe/FEDER, SOE1/P5/P0258), with FEDER funds through the Competitivity Factors Operational Programme -COMPETE and by national funds through FCT Foundation for Science and Technology within the scope of the project POCI-01-0145-FEDER-007633. This work was also partly financed by FCT/MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB / 04029/2020. The authors acknowledge the support of the Northern Regional Directorate of Culture through Dr. Isabel Fernandes, Director of the Ducal Palace of Bragança, for making accessible all parts of the Palace and for kindly sharing her knowledge about the building. The authors would like also to acknowledge Nuno Moreira (TopArcos) for carrying out the laser scanner survey

Entropy exchange in a mixture of ultracold atoms

We investigate experimentally the entropy transfer between two distinguishable atomic quantum gases at ultralow temperatures. Exploiting a species-selective trapping potential, we are able to control the entropy of one target gas in presence of a second auxiliary gas. With this method, we drive the target gas into the degenerate regime in conditions of controlled temperature by transferring entropy to the auxiliary gas. We envision that our method could be useful both to achieve the low entropies required to realize new quantum phases and to measure the temperature of atoms in deep optical lattices. We verified the thermalization of the two species in a 1D lattice.Comment: 5 pages, 4 figure

Resonant Atom-Dimer Relaxation in Ultracold Atoms

Three-body systems with large scattering length display universal phenomena associated with a discrete scaling symmetry. These phenomena include resonant enhancement of three-body loss rates when an Efimov three-body resonance is at the scattering threshold. In particular, there can be resonant peaks in the atom-dimer relaxation rate for large positive scattering length. We improve upon earlier studies and calculate the atom-dimer relaxation rate as a function of temperature using a Bose-Einstein distribution for the thermal average. As input, we use calculations of the atom-dimer scattering phase shifts from effective field theory.Comment: 5 pages, 2 figures, published version, minor change in result