Impact of trans-Planckian excitations on black-hole radiation in dipolar condensates

We consider a quasi-one-dimensional dipolar condensate in an analogue black hole setup. It is shown that the existence of a roton minimum in the condensate dispersion relation leaves deep imprints onto the Hawking radiation spectrum. In particular, the emitted radiation can be either more intense or suppressed, depending on the depth of the roton minimum in the excitation spectrum. In addition, we find that spontaneous particle creation occurs even when the horizon is removed. Our results establish that dipolar condensates offer a richer and more versatile environment for the simulation of particle production from the quantum vacuum in the presence of horizon-interfaces than their contact-interaction counterparts.Comment: 6+4 pages, 2 figure

Number-conserving solution for dynamical quantum backreaction in a Bose-Einstein condensate

We provide a number-conserving approach to the backreaction problem of small quantum fluctuations onto a classical background for the exactly soluble dynamical evolution of a Bose-Einstein condensate, experimentally realizable in the ultracold gas laboratory. A force density exerted on the gas particles which is of quantum origin is uniquely identified as the deviation from the classical Eulerian force density. The backreaction equations are then explored for the specific example of a finite size uniform density condensate initially at rest. By assuming that the condensate starts from a non-interacting regime, and in its ground state, we fix a well-defined initial vacuum condition, which is driven out-of-equilibrium by instantaneously turning on the interactions. The assumption of this initial vacuum accounts for the ambiguity in choosing a vacuum state for interacting condensates, which is due to phase diffusion and the ensuing condensate collapse. As a major finding, we reveal that the time evolution of the condensate cloud leads to condensate density corrections that cannot in general be disentangled from the quantum depletion in measurements probing the power spectrum of the total density. Furthermore, while the condensate is initially at rest, quantum fluctuations give rise to a nontrivial condensate flux, from which we demonstrate that the quantum force density attenuates the classical Eulerian force. Finally, the knowledge of the particle density as a function of time for a condensate at rest determines, to order $N^0$, where $N$ is the total number of particles, the quantum force density, thus offering a viable route for obtaining experimentally accessible quantum backreaction effects.Comment: 15 pages, 6 figure

Rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART): Study protocol for a randomized controlled trial

Background: Acute respiratory distress syndrome (ARDS) is associated with high in-hospital mortality. Alveolar recruitment followed by ventilation at optimal titrated PEEP may reduce ventilator-induced lung injury and improve oxygenation in patients with ARDS, but the effects on mortality and other clinical outcomes remain unknown. This article reports the rationale, study design, and analysis plan of the Alveolar Recruitment for ARDS Trial (ART). Methods/Design: ART is a pragmatic, multicenter, randomized (concealed), controlled trial, which aims to determine if maximum stepwise alveolar recruitment associated with PEEP titration is able to increase 28-day survival in patients with ARDS compared to conventional treatment (ARDSNet strategy). We will enroll adult patients with ARDS of less than 72 h duration. The intervention group will receive an alveolar recruitment maneuver, with stepwise increases of PEEP achieving 45 cmH(2)O and peak pressure of 60 cmH2O, followed by ventilation with optimal PEEP titrated according to the static compliance of the respiratory system. In the control group, mechanical ventilation will follow a conventional protocol (ARDSNet). In both groups, we will use controlled volume mode with low tidal volumes (4 to 6 mL/kg of predicted body weight) and targeting plateau pressure <= 30 cmH2O. The primary outcome is 28-day survival, and the secondary outcomes are: length of ICU stay; length of hospital stay; pneumothorax requiring chest tube during first 7 days; barotrauma during first 7 days; mechanical ventilation-free days from days 1 to 28; ICU, in-hospital, and 6-month survival. ART is an event-guided trial planned to last until 520 events (deaths within 28 days) are observed. These events allow detection of a hazard ratio of 0.75, with 90% power and two-tailed type I error of 5%. All analysis will follow the intention-to-treat principle. Discussion: If the ART strategy with maximum recruitment and PEEP titration improves 28-day survival, this will represent a notable advance to the care of ARDS patients. Conversely, if the ART strategy is similar or inferior to the current evidence-based strategy (ARDSNet), this should also change current practice as many institutions routinely employ recruitment maneuvers and set PEEP levels according to some titration method.Hospital do Coracao (HCor) as part of the Program 'Hospitais de Excelencia a Servico do SUS (PROADI-SUS)'Brazilian Ministry of Healt

Nonlocal field theory of quasiparticle scattering in dipolar Bose-Einstein condensates

We consider the propagation of quasiparticle excitations in a dipolar Bose-Einstein condensate, and derive a nonlocal field theory of quasiparticle scattering at a stepwise inhomogeneity of the sound speed, obtained by tuning the contact coupling part of the interaction on one side of the barrier. To solve this problem ab initio, i.e., without prior assumptions on the form of the solutions, we reformulate the dipolar Bogoliubov-de Gennes equation as a singular integral equation. The latter is of a novel hypersingular type, in having a kernel which is hypersingular at only two isolated points. Deriving its solution, we show that the integral equation reveals a continuum of evanescent channels at the sound barrier which is absent for a purely contact-interaction condensate. We furthermore demonstrate that by performing a discrete approximation for the kernel, one achieves an excellent solution accuracy for already a moderate number of discretization steps. Finally, we show that the non-monotonic nature of the system dispersion, corresponding to the emergence of a roton minimum in the excitation spectrum, results in peculiar features of the transmission and reflection at the sound barrier which are nonexistent for contact interactions

Quantum vacuum fluctuations near a partially reflecting boundary: Brownian motion of a test charge as probe

International audienceThe modified vacuum fluctuations of quantum fields in the presence of a perfectly reflecting mirror lead to divergent velocity dispersions of a charged test particle. Here, it is shown that when the mirror is modeled by a material medium described by a Drude-like susceptibility, these dispersions become regular, thus elucidating that the origin of the divergences that appear in the previous treatments is related to the assumption of idealized boundary conditions. As a consequence of implementing this more realistic description, the dispersion curves acquire an oscillatory behavior caused by the effective mass of the field modes inside the dispersive medium. Additionally, it is found that the effects over the particle are delayed when compared to the perfect mirror limit, a phenomenon attributed to the imperfect reflection of field modes on the mirror. Therefore, although idealized boundary conditions are simplifying hypotheses, their usage might hide or significantly modify relevant physical phenomena

Bois-bumbás de Parintins: síntese metafórica da realidade? Bois-bumbás of Parintins: metaphoric synthesis of reality?

Este artigo analisa como os atores sociais internos percebem o evento dos bois-bumbás da cidade de Parintins, tendo em vista o valor que tal fenômeno representa para a comunidade local nos aspectos culturais, econômicos e sociais, e por criar um espaço onde os seus integrantes possam refletir, falar e produzir conhecimento sobre sua realidade. Procurou-se identificar a percepção dos atores sociais internos sobre a influência desse fenômeno cultural nas dimensões sistêmica e cultural do desenvolvimento local sustentável (DLS) da cidade de Parintins. Os pressupostos que orientaram o estudo foram: elementos da cultura brasileira estão presentes na cultura local representada pelo contexto dos bois-bumbás; a cultura indígena amazônica dá significado aos elementos que possibilitam a construção dos bois-bumbás; e o boi-bumbá está se transformando em mercadoria subsumida às necessidades do capital. O referencial de análise baseou-se principalmente nos conceitos de DLS, modo de produção capitalista e cultura. A metodologia utilizada foi de natureza qualitativa. As conclusões sinalizam para a confirmação dos pressupostos.<br>This article investigates on how the inside social actors perceive the boi-bumbá celebrations in the town of Parintins, Brazil, considering the value that such phenomenon represents to the local community in its cultural, economic and social aspects, as well as the opportunity for the participants to reflect on, speak about and produce knowledge on their own reality. The investigation identified how such actors perceive the influence of this social phenomenon in the systemic and cultural dimensions of the town's sustainable local development (SLD). The hypotheses that guided the study were: elements of the Brazilian culture are present in the local culture represented by the boi-bumbá context; the native Amazonian culture gives signification to the elements that allow the construction of the bois-bumbás; the boi-bumbá is becoming a merchandise submitted to the capital's demands. The analytical framework was based mostly in the concepts of SLD, capitalist production system and culture. The investigation adopted a quantitative method. The conclusions confirm the hypotheses