A Gapless Theory of Bose-Einstein Condensation in Dilute Gases at Finite Temperature

In this paper we develop a gapless theory of BEC which can be applied to both trapped and homogeneous gases at zero and finite temperature. The many-body Hamiltonian for the system is written in a form which is approximately quadratic with higher order cubic and quartic terms. The quadratic part is diagonalized exactly by transforming to a quasiparticle basis, while the non-quadratic terms are dealt with using first and second order perturbation theory. The conventional treatment of these terms, based on factorization approximations, is shown to be inconsistent. Infra-red divergences can appear in individual terms of the perturbation expansion, but we show analytically that the total contribution beyond quadratic order is finite. The resulting excitation spectrum is gapless and the energy shifts are small for a dilute gas away from the critical region, justifying the use of perturbation theory. Ultra-violet divergences can appear if a contact potential is used to describe particle interactions. We show that the use of this potential as an approximation to the two-body T-matrix leads naturally to a high-energy renormalization. The theory developed in this paper is therefore well-defined at both low and high energy and provides a systematic description of Bose-Einstein condensation in dilute gases. It can therefore be used to calculate the energies and decay rates of the excitations of the system at temperatures approaching the phase transition.Comment: 39 pages of Revtex. 1 figur

Global Magellan-image map of Venus at full resolution

During its first 243-day mapping cycle, the Magellan spacecraft succeeded in imaging 84 percent of the surface of Venus at resolutions on the order of 100 meters; subsequent cycles have increased the total coverage to over 97 percent and provided redundant coverage of much of the planet with differing viewing geometries. Unfortunately, this full-resolution global dataset is in the form of thousands of individual orbit tracks (F-BIDR's) whose length-to-width ratio of nearly 1000:1 makes them minimally useful unless mosaicked. The Magellan project produced full-resolution mosaics (F-MIDR's) only for selected regions on the planet, whereas a global set of mosaics was made only at threefold degraded resolution (C1-MIDR's). Furthermore, although the F-MIDR's, which are approximately equidimensional, are much better suited for scientific interpretation than the F-BIDR's, they are still an unwieldy dataset: over 1500 quadrangles, each showing a region only about 600 km on a side, would be required to cover the entire planet. The USGS has therefore undertaken to produce and distribute a global, full resolution set of mosaics of the Magellan image data in a format that will be efficient for both hardcopy and digital use. The initial motivation was that it would provide an efficient means of verifying the integrity of the F-BIDR's to be archived on computer-compatible tape at the USGS Flagstaff facility. However, the resulting product, known as the FMAP, should also serve as an important resource for future scientific interpretation. It will offer several advantages beyond global coverage at full resolution. The first, alluded to above, is its division of the planet's surface to minimize the number of quadrangles and maximize their area, subject to the limits on the number of pixels imposed by state-of-the-art digital recording media and hardcopy output devices. The second, the use of improved 'cosmetic' processing techniques, will greatly reduce tonal discontinuities between component F-BIDR's in the FMAP compared to the standard Magellan mosaic products. Finally, wherever possible, the FMAP will incorporate data that were unavailable (e.g., because of processing delays) when the standard MIDR products were created, as well as data that were reprocessed to improve their radiometric or geometric quality

Survey of parasite control practices in sheep and cattle

Farms in the Albany, Esperance, Jerramungup and Katanning districts were surveyed to determine parasite control strategies currently used, to evaluate the adoption of recommended control practices and to detect areas of ineffective parasite control. For cattle, the number of drenches given in the low rainfall zone was higher than the number given in the high rainfall zone

Phenomenological damping in trapped atomic Bose-Einstein condensates

The method of phenomenological damping developed by Pitaevskii for superfluidity near the $\lambda$ point is simulated numerically for the case of a dilute, alkali, inhomogeneous Bose-condensed gas near absolute zero. We study several features of this method in describing the damping of excitations in a Bose-Einstein condensate. In addition, we show that the method may be employed to obtain numerically accurate ground states for a variety of trap potentials.Comment: 5 pages including 2 figures. To appear in Phys. Rev. A as a Brief Repor

Derived electron densities from linear polarization observations of the visible-light corona during the 14 December 2020 total solar eclipse

A new instrument was designed to take visible-light (VL) polarized brightness ($pB$) observations of the solar corona during the 14 December 2020 total solar eclipse. The instrument, called the Coronal Imaging Polarizer (CIP), consisted of a 16 MP CMOS detector, a linear polarizer housed within a piezoelectric rotation mount, and an f-5.6, 200 mm DSLR lens. Observations were successfully obtained, despite poor weather conditions, for five different exposure times (0.001 s, 0.01 s, 0.1 s, 1 s, and 3 s) at six different orientation angles of the linear polarizer (0\de, 30\de, 60\de, 90\de, 120\de, and 150\de). The images were manually aligned using the drift of background stars in the sky and images of different exposure times were combined using a simple signal-to-noise ratio cut. The polarization and brightness of the local sky is also estimated and the observations were subsequently corrected. The $pB$ of the K-corona was determined using least squares fitting and radiometric calibration was done relative to the Mauna Loa Solar Observatory (MLSO) K-Cor $pB$ observations from the day of the eclipse. The $pB$ data was then inverted to acquire the coronal electron density, $n_e$, for an equatorial streamer and a polar coronal hole, which agreed very well with previous studies. The effect of changing the number of polarizer angles used to compute the $pB$ is also discussed and it is found that the results vary by up to $\sim$ 13\% when using all six polarizer angles versus only a select three angles

The importance of the weak: Interaction modifiers in artificial spin ices

The modification of geometry and interactions in two-dimensional magnetic nanosystems has enabled a range of studies addressing the magnetic order, collective low-energy dynamics, and emergent magnetic properties, in e.g. artificial spin ice structures. The common denominator of all these investigations is the use of Ising-like mesospins as building blocks, in the form of elongated magnetic islands. Here we introduce a new approach: single interaction modifiers, using slave-mesospins in the form of discs, within which the mesospin is free to rotate in the disc plane. We show that by placing these on the vertices of square artificial spin ice arrays and varying their diameter, it is possible to tailor the strength and the ratio of the interaction energies. We demonstrate the existence of degenerate ice-rule obeying states in square artificial spin ice structures, enabling the exploration of thermal dynamics in a spin liquid manifold. Furthermore, we even observe the emergence of flux lattices on larger length-scales, when the energy landscape of the vertices is reversed. The work highlights the potential of a design strategy for two-dimensional magnetic nano-architectures, through which mixed dimensionality of mesospins can be used to promote thermally emergent mesoscale magnetic states.Comment: 17 pages, including methods, 4 figures. Supplementary information contains 16 pages and 15 figure

Potential Alzheimer’s Disease Therapeutics Among Weak Cysteine Protease Inhibitors Exhibit Mechanistic Differences Regarding Extent of Cathepsin B Up-Regulation and Ability to Block Calpain

Cysteine protease inhibitors have long been part of drug discovery programs for Alzheimer's disease (AD), traumatic brain injury (TBI), and other disorders. Select inhibitors reduce accumulating proteins and AD pathology in mouse models. One such compound, Z-Phe-Aladiazomethylketone (PADK), exhibits a very weak IC50 (9-11 μM) towards cathepsin B (CatB), but curiously PADK causes marked up-regulation of the Aβ-degrading CatB and improves spatial memory. Potential therapeutic and weak inhibitor E64d (14 μM IC50) also up-regulates CatB. PADK and E64d were compared regarding the blockage of calcium-induced cytoskeletal deterioration in brain samples, monitoring the 150-kDa spectrin breakdown product (SBDP) known to be produced by calpain. PADK had little to no effect on SBDP production at 10-100 μM. In contrast, E64d caused a dosedependent decline in SBDP levels with an IC50 of 3-6 μM, closely matching its reported potency for inhibiting μ-calpain. Calpain also cleaves the cytoskeletal organizing protein gephyrin, producing 49-kDa (GnBDP49) and 18-kDa (GnBDP18) breakdown products. PADK had no apparent effect on calcium-induced gephyrin fragments whereas E64d blocked their production. E64d also protected the parent gephyrin in correspondence with reduced BDP levels. The findings of this study indicate that PADK’s positive and selective effects on CatB are consistent with human studies showing exercise elevates CatB and such elevation correlates with improved memory. On the other hand, E64d exhibits both marginal CatB enhancement and potent calpain inhibition. This dual effect may be beneficial for treating AD. Alternatively, the potent action on calpain-related pathology may explain E64d’s protection in AD and TBI models

Investıgatıon of Removal of Dye from Aqueous Solutıon by Advanced Treatment

The textile dyeing and finishing industry use a significant amount of water and produce water pollution. Conventional biological treatment processes have some difficulties for degradation of nonbiodegradable compounds. Dye-bearing wastewaters have high COD and colour. In this study, a photo reactor process was used to remove color from aqueous solution.Effects of pH on Reactive Red 4 and cationic dye removal using 1g/L TiO2, as catalyst were studied at constant inital dye concentration (25 mg/l). Cationic dye removal efficiency is better than Reactive dye removal efficiency for photocatalytic oxidation in this stud