Vortex-Peierls States in Optical Lattices

We show that vortices, induced in cold atom superfluids in optical lattices, may order in a novel vortex-Peierls ground state. In such a state vortices do not form a simple lattice but arrange themselves in clusters, within which the vortices are partially delocalized, tunneling between classically degenerate configurations. We demonstrate that this exotic quantum many-body state is selected by an order-from-disorder mechanism for a special combination of the vortex filling and lattice geometry that has a macroscopic number of classically degenerate ground states.Comment: 4 pages, 4 figures. Published versio

Observation of Vortex Pinning in Bose-Einstein Condensates

We report the observation of vortex pinning in rotating gaseous Bose-Einstein condensates (BEC). The vortices are pinned to columnar pinning sites created by a co-rotating optical lattice superimposed on the rotating BEC. We study the effects of two different types of optical lattice, triangular and square. With both geometries we see an orientation locking between the vortex and the optical lattices. At sufficient intensity the square optical lattice induces a structural cross-over in the vortex lattice.Comment: 4 pages, 6 figures. Replaced by final version to appear in Phys. Rev. Let

Preparación de nuevas nanoemulsiones a partir de aceite rico en omega-3

This work aimed to produce stabilized omega-3-rich oil in a water nanoemulsion using a high-pressure homogenizer (HPH). Studies were carried out on the effects of the type of the emulsifier and its con­centration, HPH conditions (pressure and number of passes inside the homogenization chamber) as well as continuous phase viscosity on the polydispersity index (PDI) and mean droplet size of the nanoemulsion were carried out. The impact of rosemary extract on the oxidative stability of the emulsion was also monitored. Results showed that small molecular weight emulsifiers gave small droplet size and vice versa. In addition, the results revealed that a parallel decrease in mean droplet diameter was observed with increases in emulsifier concentra­tion, homogenization cycles (passes) and homogenization pressure. Furthermore, when the viscosity of the aque­ous phase increased, a slight non-significant and irregular fluctuation in the droplet size was detected. The results demonstrated that rosemary extract enhanced the oxidative stability of this nanoemulsion. Our results could help in formulating stabilized omega-3-enriched nanoemulsions that could be applied in different food stuffs.Este trabajo tuvo como objetivo producir nanoemulsiones de aceite rico en omega-3 estabilizado en agua usando un homogeneizador de alta presión (HPH). Estudiando los efectos del tipo de emulsionante y su concentración, se llevaron a cabo las condiciones de HPH (presión y número de pasadas dentro de la cámara de homogeneización), así como la viscosidad de fase continua en el índice de polidispersidad (PDI) y el tamaño medio de gota de la nanoemulsión. También se siguió el impacto de la adición de extracto de romero sobre la estabilidad oxidativa de la emulsión. Los resultados mostraron que los emulsionantes de peso molecular pequeño dieron un tamaño de gota pequeño y viceversa. Los resultados también revelaron que hay una disminución paralela en el diámetro medio de las gotitas con el aumento de la concentración de emulsionante, los ciclos de homogeneización (pases) y la presión de homogeneización. Además, cuando aumentó la viscosidad de la fase acuosa, se observó una ligera fluctua­ción no significativa e irregular en el tamaño de la gota. Además, los resultados demostraron que el extracto de romero mejoró la estabilidad oxidativa de esta nanoemulsión. Nuestros resultados podrían ayudar a formular nanoemulsiones enriquecidas con omega-3 estabilizadas que podrían aplicarse en diferentes alimentos

Influence of a Hybrid MPPT Technique, SA-P&O, on PV System Performance under Partial Shading Conditions

The electricity sector has been undergoing profound transformations. In particular, the Portuguese self-consumer regime has allowed customers of the medium and low voltage electricity grid to be producers/consumers of electricity, actively contributing to greater energy efficiency. In this context, the energy that comes from the sun is not used to its maximum. In addition, photovoltaic cells have a characteristic operating curve (voltage vs. current), in which any operating point is reflected. Within this curve, there is a particular point known as the maximum power point (MPP) at which the cell supplies the maximum power output to a load. If the cell does not operate at this point, it has lower efficiency values. To harness maximum power under standard and dynamic shading conditions, there are various techniques of low complexity for capturing maximum power. We present a maximum power point tracking (MPPT) algorithm capable of dealing with the problem of partial shading. This algorithm involves modifying one of the most used algorithms within photovoltaic systems, known as P&O, using a simulated annealing (SA) algorithm. P&O is often used due to its straightforward implementation, but it is susceptible to partial shade conditions. Sampling was added to this algorithm to a better approach to the point of maximum power using the SA, and then to attain a more precise convergence with P&O. Implementing a maximum power point tracking method under partial shading was the major goal of this study

Response of an atomic Bose-Einstein condensate to a rotating elliptical trap

We investigate numerically the response of an atomic Bose-Einstein condensate to a weakly-elliptical rotating trap over a large range of rotation frequencies. We analyse the quadrupolar shape oscillation excited by rotation, and discriminate between its stable and unstable regimes. In the latter case, where a vortex lattice forms, we compare with experimental observations and find good agreement. By examining the role of thermal atoms in the process, we infer that the process is temperature-independent, and show how terminating the rotation gives control over the number of vortices in the lattice. We also study the case of critical rotation at the trap frequency, and observe large centre-of-mass oscillations of the condensate.Comment: 14 pages, 8 figure

Two-dimensional Bose gas under extreme rotation

We show that a Bose-condensed gas under extreme rotation in a 2D anisotropic trap, forms a novel elongated quantum fluid which has a roton-maxon excitation spectrum. For a sufficiently large interaction strength, the roton energy reaches zero and the system undergoes a second order quantum transition to the state with a periodic structure - rows of vortices. The number of rows increases with the interaction, and the vortices eventually form a triangular Abrikosov lattice.Comment: typos corrected, ref. added, minor changes in the pape

Vortex Lattices in Rotating Atomic Bose Gases with Dipolar Interactions

We show that dipolar interactions have dramatic effects on the groundstates of rotating atomic Bose gases in the weak interaction limit. With increasing dipolar interaction (relative to the net contact interaction), the mean-field, or high filling fraction, groundstate undergoes a series of transitions between vortex lattices of different symmetries: triangular, square, ``stripe'', and ``bubble'' phases. We also study the effects of dipolar interactions on the quantum fluids at low filling fractions. We show that the incompressible Laughlin state at filling fraction $\nu=1/2$ is replaced by compressible stripe and bubble phases.Comment: 4 pages, 2 figure

Formulating an Efficient Statistical Test Using the Goodness of Fit Approach with Applications to Real-life Data

Statistical tests are very important for researchers to make decisions. In particular, when the tests are non- parametric, they are of greater importance because they can be applied to a wide range of data sets regardless of knowing the distribution of these data. Researchers are therefore racing to obtain efficient tests for making good decisions based on the results of these tests. In this study, NBU (2)L was used based on the goodness of fit approach to present an efficient statistical test. The efficiency of the proposed test was computed, and the results were compared to those of other tests. Critical values were computed and tabulated, and the power of this test was estimated. Finally, this test was applicable to both real, complete data and censored data

Measuring the condensate fraction of rapidly rotating trapped boson systems: off-diagonal order from the density

We demonstrate a direct connection between the density profile of a system of ultra-cold trapped bosonic particles in the rapid-rotation limit and its condensate fraction. This connection can be used to probe the crossover from condensed vortex-lattice states to uncondensed quantum fluid states that occurs in rapidly rotating boson systems as the particle density decreases or the rotation frequency increases. We illustrate our proposal with a series of examples, including ones based on models of realistic finite trap systems, and comment on its application to freely expanding boson density profile measurements.Comment: 4 pages, 3 figures, version accepted for publication in Phys. Rev. Let