Incoherence of Bose-Einstein condensates at supersonic speeds due to quantum noise

We calculate the effect of quantum noise in supersonic transport of Bose-Einstein condensates. When an obstacle obstructs the flow of atoms, quantum fluctuations cause atoms to be scattered incoherently into random directions. This suppresses the propagation of Cherenkov radiation, creating quantum turbulence and a crescent of incoherent atoms around the obstacle. We observe similar dynamics if the BEC is stirred by a laser beam: crescents of incoherent atoms are emitted from the laser's turning-points. Finally, we investigate supersonic flow through a disordered potential, and find that the quantum fluctuations generate an accumulation of incoherent atoms as the condensate enters the disorder.Comment: 6 pages, 5 figure

Data documentation for the bare soil experiment at the University of Arkansas

The reflectivities of several controlled moisture test plots were investigated. These test plots were of a similar soil texture which was clay loam and were prepared to give a desired initial soil moisture and density profile. Measurements were conducted on the plots as the soil water redistributed for both long term and diurnal cycles. These measurements included reflectivity, gravimetric and volumetric soil moisture, soil moisture potential, and soil temperature

Student perceptions of their autonomy at University

© 2017, The Author(s). Learner autonomy is a primary learning outcome of Higher Education in many countries. However, empirical evaluation of how student autonomy progresses during undergraduate degrees is limited. We surveyed a total of 636 students’ self-perceived autonomy during a period of two academic years using the Autonomous Learning Scale. Our analysis suggests that students do not perceive themselves as being any more autonomous as they progress through University. Given the relativity of self-perception metrics, we suggest that our results evince a “red queen” effect. In essence, as course expectations increase with each year, each student’s self-perceived autonomy relative to their ideal remains constant; we term this the “moving goalpost” hypothesis. This article corroborates pedagogical literature suggesting that providing students with opportunities to act autonomously and develop confidence is key to developing graduates who have the independence that they need in order to be successful in the workplace

The use of aerial photographs for estimating school sizes of cetaceans

ENGLISH: The accuracy and precision of dolphin school size estimates based on aerial photograph counts were examined using data collected on recent aerial and ship surveys. These estimates were found to be accurate during a 1979research cruise aboard a tuna purse-seiner; dolphin schools were photographed from the ship’s helicopter, encircled with the purse-seine, and then counted as the dolphins were released from the net. A comparison of photographic estimates with these counts indicated that the relationship was fairly close and gave no indication of significantly differing from 1:1. During a 1980 aerial study, photographic estimates from different schools, passes, and camera formats were compared and were found to be quite precise with a standard deviation of approximately 60/0 of school size. Photographic estimates were also compared with estimates made by aerial observers. Most observers tended to underestimate school size, particularly for large schools. The variability among observers was high, indicating that observers should be individually calibrated. SPANISH: Se examinó la exactitud y la precisión de las estimaciones de la magnitud de los cardúmenes de delfines basadas en el cálculo de las fotografías aéreas, usando los datos obtenidos en los últimos reconocimientos aéreos y de los barcos. En 1979, durante un crucero de investigación en un cerquero atunero, se encontró que estas estimaciones eran acertadas; se fotografiaron los cardúmenes de delfines desde un helicóptero del barco, cercados con la red y luego se contaron a medida que se libraban los delfines de la red. Una comparación de las estimaciones fotográficas con estos cálculos indicó que la relación era bastante aproximada y no hubo indicación que se diferenció significativamente de la razón 1:1. Durante un estudio aéreo en 1980, se compararon las estimaciones fotográficas de diferentes del cardúmenes, en los pases y los formatos de las cámaras y se encontró que eran bastante precisos, con una desviación normal de cerca del 60/0 de la magnitud cardumen. Se compararon también las estimaciones fotográficas con las estimaciones realizadas por los observadores aéreos. La mayoría de los observadores tienden a subestimar la magnitud de los cardúmenes, especialmente los cardúmenes grandes. La variabilidad entre los observadores fue elevada, lo que indica que se deben calibrar individualmente los datos de observadores. (PDF contains 39 pages.

Vortical control of forced two-dimensional turbulence

A new numerical technique for the simulation of forced two-dimensional turbulence (Dritschel and Fontane, 2010) is used to examine the validity of Kraichnan-Batchelor scaling laws at higher Reynolds number than previously accessible with classical pseudo-spectral methods,making use of large simulation ensembles to allow a detailed consideration of the inverse cascade in a quasi-steady state. Our results support the recent finding of Scott (2007), namely that when a direct enstrophy cascading range is well-represented numerically, a steeper energy spectrum proportional to k^(−2) is obtained in place of the classical k^(−5/3) prediction. It is further shown that this steep spectrum is associated with a faster growth of energy at large scales, scaling like t^(−1) rather than Kraichnan’s prediction of t^(−3/2). The deviation from Kraichnan’s theory is related to the emergence of a population of vortices that dominate the distribution of energy across scales, and whose number density and vorticity distribution with respect to vortex area are related to the shape of the enstrophy spectrum. An analytical model is proposed which closely matches the numerical spectra between the large scales and the forcing scale

Topology of the polarization field in ferroelectric nanowires from first principles

The behaviour of the cross-sectional polarization field is explored for thin nanowires of barium titanate from first-principles calculations. Topological defects of different winding numbers have been obtained, beyond the known textures in ferroelectric nanostructures. They result from the inward accommodation of the polarization patterns imposed at the surface of the wire by surface and edge effects. Close to a topological defect the polarization field orients out of the basal plane in some cases, maintaining a close to constant magnitude, whereas it virtually vanishes in other cases.Comment: 4 pages, 3 figure

Reduced Energy and Maintenance Costs Using Polyurethane as a Replacement Roof System

Reduction in maintenance and allied costs was the number one priority when Texas A&M University first considered polyurethane foam as a replacement roof for existing buildings. An investigation revealed that when properly applied, this system would solve most of the maintenance problems associated with built-up roofs. Standard specifications for this replacement roof were developed, requiring the application of 2 inches of polyurethane foam and 45 mils of a urethane coating. The result being a monolithic weatherproof cover for the roof. Additionly, with the application of polyurethane foam, a reduction in the energy used to air condition the building was noted. A method was developed for estimating maximum roof temperatures. Using the Heat Transfer Equation, Q = U x A x dT, roof loads before and after the application of the foam were calculated. With these loads, annual energy used was calculated and the savings resulting from the use of the foam were determined. 27 buildings were reroofed using polyurethane foam, totalling some 593,000 square feet at a total cost of $1,694,000. Annual energy savings were$327,500, for a payback of 5 years, 2 months, using the Simple Payback Method

Immunohistological studies of connective tissues

This thesis is concerned with immunohistological studies of adult human connective tissues and with connective tissues in the adult and embryonic rat.The concept that the constitution of connective tissues represents a response by synthesising cells to their environment, provides a basis for conjecture concerning the processes involved in ageing and rheumatoid disease.The concept that a mutual interplay between a cell and its environment is involved in the maintenance of the integrity of connective tissues has, it is suggested, relevance to rheumatoid disease. Alterations in the representation of any one constituent of connective tissue, whether attributable to abnormal genetic endowment or somatic mutation in the relevant synthesizing cell, are likely to initiate changes in the environment, and therefore the function of cells synthesizing related constituents of connective tissue. Although this concept takes into account the view that rheumatoid disease involves a restricted number of somatic mutations, responsible perhaps for the formation of a tissue constituent which is abnormally susceptible to damage by trauma or infection, a major difficulty arises. The present concept appears to require that to the rheumatoid factors be ascribed a role in the metabolism, or in the control of the synthesis of one or other of the constituents of adult connective tissue. This view is hardly tenable, It may be, however, that the rheumatoid factors reflect the activity of a gene- enzyme system which is responsible for the synthesis of a constituent of connective tissue peculiarly susceptible to degradation by trauma or micro -organisms. It is not necessary, however, to deny immune mechanisms as a role in the production of rheumatoid factors. The view that rheumatoid factors reflect intense immunological activity in rheumatoid disease is not necessarily irreconcilable with the proposition that one of the initiating events in rheumatoid disease may be the synthesis of a constituent of connective tissue which is abnormally susceptible to degradation by the action of micro -organisms or trauma.In connection with ageing, the possibility is considered that subtle changes in the structure of the collagen molecule may contribute to the age associated alterations in the rheological properties of collagen. This is not to deny the proposition that the increased structural stability of aged collagen is to be attributed to an increase in the number and strength of cross links between and within collagen macromolecules, but merely to suggest that the nature of the intra- and inter-molecular cross links, the rate at which they can form, and the ease with which cross linking agents can react with adjacent collagen macromolecules, are governed by the subtle structure of the collagen molecule. The proposition that ageing is associated with changes in the subtle structure of the collagen molecule may be open to investigation by means of a study of the patterns of immunological reactivity manifested by neutral salt-soluble, acetic acid-soluble and insoluble collagen obtained from subjects of different ages