Dynamics of apparent horizons in quantum gravitational collapse

We study the gravitational collapse of a massless scalar field within the effective scenario of loop quantum gravity. Classical singularity is avoided and replaced by a quantum bounce in this model. It is shown that, quantum gravity effects predict a threshold scale below which no horizon can form as the collapse evolves towards the bounce.Comment: Contribution to the Spanish Relativity Meeting in Portugal 2012 (ERE2012), Guimaraes, Portuga

Phase Fluctuations in Bose-Einstein Condensates

We demonstrate the existence of phase fluctuations in elongated Bose-Einstein Condensates (BECs) and study the dependence of those fluctuations on the system parameters. A strong dependence on temperature, atom number, and trapping geometry is observed. Phase fluctuations directly affect the coherence properties of BECs. In particular, we observe instances where the phase coherence length is significantly smaller than the condensate size. Our method of detecting phase fluctuations is based on their transformation into density modulations after ballistic expansion. An analytic theory describing this transformation is developed.Comment: 11 pages, 7 figure

Biodegradable Polymers: Opportunities and Challenges

The overuse of polymer materials from fossil sources has generated a large volume of waste that causes environmental impacts due to the degradation time. The technological advance has stimulated the search for alternatives that can contribute to sustainability. In this context, the use of biodegradable polymers, that use raw materials from renewable sources stand out because they have that ability to form films and come from abundant sources. Also, in the expectation of optimizing the environmental benefits in this process, it is possible to value the agroindustrial residues, using them as raw material in the synthesis of the polymer, the physical, chemical and mechanical properties of these polymers are important to evaluate the possible applications. The proposal of this chapter is to present current research on renewable sources, including agricultural and industrial residues, to obtain biodegradable polymers, highlighting their properties and possibilities of application

Trans-Dimensional Geoacoustic Inversion of Wind-Driven Ambient Noise

This letter applies trans-dimensional Bayesian geoacoustic inversion to quantify the uncertainty due to model selection when inverting bottom-loss data derived from wind-driven ambient-noise measurements. A partition model is used to represent the seabed, in which the number of layers, their thicknesses, and acoustic parameters are unknowns to be determined from the data. Exploration of the parameter space is implemented using the Metropolis–Hastings algorithm with parallel tempering, whereas jumps between parameterizations are controlled by a reversible-jump Markov chain Monte Carlo algorithm. Sediment uncertainty profiles from inversion of simulated and experimental data are presented

Ramos do Cooperativismo: cenário da região centro oeste do Brasil.

O cooperativismo é um modelo econômico com características próprias, baseado em princípios definidos pela Aliança Cooperativa Internacional - ACI. Está presente no Brasil desde o final do século XIX, contemplando hoje seus diferentes ramos, e em todos os Estados brasileiros e Distrito Federal. Na região centro oeste do país, temos hoje 575 cooperativas ativas, sendo 178 do ramo agropecuário, em Mato Grosso do Sul das 71 cooperativas, 26 são deste ramo. O desenvolvimento de forma sustentável é um desafio para as instituições e governos, assim, devido a sua natureza, o cooperativismo pode ser uma alternativa de promover o crescimento da economia, o desenvolvimento local de maneira sustentável? O que percebemos é que o crescente número de negócios de natureza cooperativa que vêm se firmando no país pode ser um sinal de que o caminho para alcançar tal desenvolvimento foi encontrado, uma vez que a maior parte das cooperativas do país já existem a mais de 20 anos, algumas mais de 40 demonstrando a solidez e sustentabilidade do negócio. Também evidenciando que ainda há espaço para crescimento.Anais do VI EIGEDIN

Agricultura e inovação: estudo sobre a viabilidade de uso do 'pó de rocha' em sistemas de produção agrícola.

O uso dos chamados remineralizadores de solo, "pó de rocha" (rochagem / ?rocks-for-crops?), é uma técnica que vem se expandindo com o passar dos anos. O trabalho visa observar o comportamento das culturas anuais de soja e milho durante três safras consecutivas, utilizando pó de rocha (remineralizador), como fonte principal da adubação verificando viabilidade econômica e técnica de uso da técnica. O projeto está sendo conduzido na Fazenda Campanário município de Itaquiraí, estado de Mato Grosso do Sul, Brasil, a partir da safra de soja 2018/2019. São três tratamentos sendo T1, utilizando adubo químico solúvel na base de plantio, T2 e T3 utilizando 12 e 6 toneladas de pó de rocha de origem basáltica respectivamente, 30 dias após o plantio. O acompanhamento da área para tomada dos dados e observações é semanal, com visitas in loco, tendo maior frequência a partir do período de implantação da cultura até sua colheita. Foram coletadas informações como: datas de plantio, emergência e colheita da cultura Tipos de manejos efetuados para o controle das pragas, doenças e plantas invasoras. A coleta do solo para análise é realizada depois da retirada de cada cultura. Análises foliares são realizadas durante o desenvolvimento da cultura.EIGEDIN 2019

Breakdown of superfluidity of an atom laser past an obstacle

The 1D flow of a continuous beam of Bose-Einstein condensed atoms in the presence of an obstacle is studied as a function of the beam velocity and of the type of perturbing potential (representing the interaction of the obstacle with the atoms of the beam). We identify the relevant regimes: stationary/time-dependent and superfluid/dissipative; the absence of drag is used as a criterion for superfluidity. There exists a critical velocity below which the flow is superfluid. For attractive obstacles, we show that this critical velocity can reach the value predicted by Landau's approach. For penetrable obstacles, it is shown that superfluidity is recovered at large beam velocity. Finally, enormous differences in drag occur when switching from repulsive to attractive potential.Comment: 15 pages, 6 figure

Extension of Bogoliubov theory to quasi-condensates

We present an extension of the well-known Bogoliubov theory to treat low dimensional degenerate Bose gases in the limit of weak interactions and low density fluctuations. We use a density-phase representation and show that a precise definition of the phase operator requires a space discretisation in cells of size $l$. We perform a systematic expansion of the Hamiltonian in terms of two small parameters, the relative density fluctuations inside a cell and the phase change over a cell. The resulting macroscopic observables can be computed in one, two and three dimensions with no ultraviolet or infrared divergence. Furthermore this approach exactly matches Bogoliubov's approach when there is a true condensate. We give the resulting expressions for the equation of state of the gas, the ground state energy, the first order and second order correlations functions of the field. Explicit calculations are done for homogeneous systems.Comment: 32 pages, 2 figures; typos corrected in revised versio

Radio-frequency dressed state potentials for neutral atoms

Potentials for atoms can be created by external fields acting on properties like magnetic moment, charge, polarizability, or by oscillating fields which couple internal states. The most prominent realization of the latter is the optical dipole potential formed by coupling ground and electronically excited states of an atom with light. Here we present an experimental investigation of the remarkable properties of potentials derived from radio-frequency (RF) coupling between electronic ground states. The coupling is magnetic and the vector character allows to design state dependent potential landscapes. On atom chips this enables robust coherent atom manipulation on much smaller spatial scales than possible with static fields alone. We find no additional heating or collisional loss up to densities approaching $10^{15}$ atoms / cm$^3$ compared to static magnetic traps. We demonstrate the creation of Bose-Einstein condensates in RF potentials and investigate the difference in the interference between two independently created and two coherently split condensates in identical traps. All together this makes RF dressing a powerful new tool for micro manipulation of atomic and molecular systems

Violation of self-similarity in the expansion of a 1D Bose gas

The expansion of a 1D Bose gas is investigated employing the Lieb-Liniger equation of state within the local density approximation. We show that during the expansion the density profile of the gas does not follow a self-similar solution, as one would expect from a simple scaling Ansatz. We carry out a variational calculation, which recovers the numerical results for the expansion, the equilibrium properties of the density profile, and the frequency of the lowest compressional mode. The variational approach allows for the analysis of the expansion in all interaction regimes between the mean field and the Tonks-Girardeau limits, and in particular shows the range of parameters for which the expansion violates self-similarity.Comment: 6 pages, 5 eps figure