Controlling the dynamics of an open many-body quantum system with localized dissipation

We experimentally investigate the action of a localized dissipative potential on a macroscopic matter wave, which we implement by shining an electron beam on an atomic Bose-Einstein condensate (BEC). We measure the losses induced by the dissipative potential as a function of the dissipation strength observing a paradoxical behavior when the strength of the dissipation exceeds a critical limit: for an increase of the dissipation rate the number of atoms lost from the BEC becomes lower. We repeat the experiment for different parameters of the electron beam and we compare our results with a simple theoretical model, finding excellent agreement. By monitoring the dynamics induced by the dissipative defect we identify the mechanisms which are responsible for the observed paradoxical behavior. We finally demonstrate the link between our dissipative dynamics and the measurement of the density distribution of the BEC allowing for a generalized definition of the Zeno effect. Due to the high degree of control on every parameter, our system is a promising candidate for the engineering of fully governable open quantum systems

Association of ultracold double-species bosonic molecules

We report on the creation of heterospecies bosonic molecules, associated from an ultracold Bose-Bose mixture of 41K and 87Rb, by using a resonantly modulated magnetic field close to two Feshbach resonances. We measure the binding energy of the weakly bound molecular states versus the Feshbach field and compare our results to theoretical predictions. We observe the broadening and asymmetry of the association spectrum due to thermal distribution of the atoms, and a frequency shift occurring when the binding energy depends nonlinearly on the Feshbach field. A simple model is developed to quantitatively describe the association process. Our work marks an important step forward in the experimental route towards Bose-Einstein condensates of dipolar molecules.Comment: 5 pages, 4 figure

Double species condensate with tunable interspecies interactions

We produce Bose-Einstein condensates of two different species, $^{87}$Rb and $^{41}$K, in an optical dipole trap in proximity of interspecies Feshbach resonances. We discover and characterize two Feshbach resonances, located around 35 and 79 G, by observing the three-body losses and the elastic cross-section. The narrower resonance is exploited to create a double species condensate with tunable interactions. Our system opens the way to the exploration of double species Mott insulators and, more in general, of the quantum phase diagram of the two species Bose-Hubbard model.Comment: 4 pages, 4 figure

Collisional properties of sympathetically cooled 39^{39}K

We report the experimental evidence of the sympathetic cooling of $^{39}$K with $^{87}$Rb down to 1 $\mu$K, obtained in a novel tight confining magnetic trap. This allowed us to perform the first direct measurement of the elastic cross section of $^{39}$K below 50 $\mu$K. The result obtained for the triplet scattering length, $a_T = -51(7)$ Bohr radii, agrees with previous results derived from photoassociation spectra and from Feshbach spectroscopy of $^{40}$K.Comment: 7 pages, 4 figures, submitted to Phys. Rev.

Observation of heteronuclear atomic Efimov resonances

The Efimov effect represents a cornerstone in few-body physics. Building on the recent experimental observation with ultracold atoms, we report the first experimental signature of Efimov physics in a heteronuclear system. A mixture of $^{41}$K and $^{87}$Rb atoms was cooled to few hundred nanoKelvins and stored in an optical dipole trap. Exploiting a broad interspecies Feshbach resonance, the losses due to three-body collisions were studied as a function of the interspecies scattering length. We observe an enhancement of the three-body collisions for three distinct values of the interspecies scattering lengths, both positive and negative. We attribute the two features at negative scattering length to the existence of two kind of Efimov trimers, namely KKRb and KRbRb.Comment: 4 pages, 4 figure

Collisional and molecular spectroscopy in an ultracold Bose-Bose mixture

The route toward a Bose-Einstein condensate of dipolar molecules requires the ability to efficiently associate dimers of different chemical species and transfer them to the stable rovibrational ground state. Here, we report on recent spectroscopic measurements of two weakly bound molecular levels and newly observed narrow d-wave Feshbach resonances. The data are used to improve the collisional model for the Bose-Bose mixture 41K87Rb, among the most promising candidates to create a molecular dipolar BEC.Comment: 13 pages, 3 figure

Board of Directors' characteristics and environmental SDGs adoption: an international study

Drivers of environmentally conscious firm behaviour have gained increasing attention over past decades. The Board of Directors holds a central role in corporate decision-making, and previous empirical evidence suggests that its characteristics could influence corporate environmental performance. This paper contributes to the literature with the first evidence of the influence certain board characteristics have on whether a firm ulti-mately supports one or more environmental SDGs. Our focus is on board size, gender diversity, board independence and CEO duality. Logistic and fractional regressions on 4417 globally listed firms highlight that board size, the share of female directors, and the share of independent directors are significant drivers of support for environmental SDGs. The results and insights revealed in this study should be helpful to policymakers, investors and corporations in evaluating the effectiveness of corporate governance characteristics and fostering corporate contributions to the 2030 Agenda

An Experimental Investigation on the Effect of Exhaust Gas Recirculation in a Small-Scale Fixed Bed Biomass Boiler

Exhaust gas recirculation is a technique that allows for controlling the combustion chamber temperature and reducing the NOx and particle matter emissions. Moreover, it helps to mitigate soot formation and ash agglomeration in combustion systems. The present study investigated the effect of exhaust gas recirculation on combustion temperatures of a 140 kW underfed stoker biomass boiler. To this purpose, a wide range of operating conditions were used, collecting data regarding flue gas and fixed bed temperatures. It turned out that the recirculating ratio has a significant effect on the temperatures in the primary combustion zone, affecting the thermal gradient and the main thermal zones of the biomass combusting bed. The obtained results can be useful for lumped parameter modeling, or CFD validation purposes

Woodchip size effect on combustion temperatures and volatiles in a small-scale fixed bed biomass boiler

Biomass combustion performance is greatly affected by the particle size distribution, which influences heat and mass transport phenomena. The present work investigates the effect of woodchip size distribution on combustion in a 140 kW underfeed stoker boiler. Three different fuel sizes were prepared, and their combustion performance was measured by monitoring temperatures inside and above the fire pit and the gas composition above the fuel bed. The gas composition was then correlated to the particle mean diameter. Although minor effects could be detected in the temperature and composition of the flue gases, a more uniform spatial distribution of volatiles was observed when employing bigger woodchips. The present results can improve the understanding of the impact of fuel size on the performance of woodchip-fired boilers and can be valuably used for numerical model validation

Particle Swarm Optimization for damage identification in beam-like structures

The main objectives of Structural Health Monitoring (SHM) are the characterization and the assessment of the health condition of structural systems. Combined with appropriate Damage Identification (DI) strategies, SHM aims to provide reliable information about the localization and quantification of the structural damage by using an inverse formulation approach, with the damage parameters being estimated from parametric changes in dynamic properties. Mathematically, an inverse problem consists of the optimization of a function which represents the "distance" between the experimental and the numerically-simulated features of the system. Such process requires the development of a mock-up numerical model fairly representative of the system and iteratively updated until a response, as close as possible to the experimental one, is provided. The minimization of the difference between measured and predicted features' values is the objective function, whose global minimum corresponds to the best adjustment of the model variables. Metaheuristics represent a large class of global methods for optimization purposes able to outperformtraditional methods in the following aspects: ease of implementation, time consumption, suitability for non-linear phenomena, black-box and high-dimensional problems. The present paper analyses, through a numerical experimentation approach, the suitability of one of the best-known metaheuristics, i.e. the Particle Swarm Optimization (PSO) algorithm, for DI of beam-like structures. Modal properties are used to define the objective function and various algorithm instances are tested across different problem instances to assess robustness and influence of the algorithm parameters.This work was supported by FCT (Portuguese Foundation for Science and Technology), within ISISE, scholarship SFRH/BD/115188/2016. This work was also financed by 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