The Southern Vilnius Photometric System. IV. The E Regions Standard Stars

This paper is the fourth in a series on the extension of the Vilnius photometric system to the southern hemisphere. Observations were made of 60 stars in the Harvard Standard E regions to increase a set of standard stars.Comment: 6 pages, TeX, requires 2 macros (baltic2.tex, baltic4.tex) included no figures, to be published in Baltic Astronomy, Vol 6, pp1-6 (1997

Ellipsoidally Referenced Surveys: Issues and Solutions

One of the most significant issues in hydrography today is the use of the ellipsoid as a vertical reference for surveying measurements. High-accuracy GPS is used to vertically position hydrographic data collection platforms, relating bathymetric observations directly to the ellipsoid. Models are used to translate those observations to another datum. The use of high-accuracy vertical GPS and translation models to replace traditional tidal correctors is relatively new to the hydrographic community and, as such, requires some discussion. Even though individual components of the process are well understood in their particular field, it is their amalgamation and application to hydrography that requires explanation, clarification and evaluation.Many hydrographic organizations around the world are using Global Navigation Satellite Systems (GNSS) derived heights in their data collection and processing stream. The International Federation of Surveyors (FIG) has recognized the importance of these new developments and has established a new working group under Commission 4, tasked to developing best practices for Ellipsoidally Referenced Surveys (ERS). Over twenty groups from academia, industry and government who are engaged in some form of ERS have provided the working group with a summary of their practices and experiences. This paper outlines the issues related to ERS and summarizes the solutions being employed.Uno de los temas más significativos en la hidrografía actual es el uso del elipsoide como referencia vertical para las medidas hidrográficas. El GPS de alta precisión se utiliza para posicionar verticalmente las plataformas para la recogida de datos hidrográficos, relacionando las observaciones batimétricas directamente al elipsoide. Se utilizan modelos para traducir esas observaciones a otro plano de referencia. El uso de un GPS vertical de alta precisión y de modelos de traducción para sustituir a los correctores de mareas tradicionales es relativamente nuevo para la comunidad hidrográfica y, como tal, requiere una cierta discusión. Aunque se entienden bien las componentes individuales del proceso en su campo particular, lo que requiere una explicación, una aclaración y una evaluación es su amalgama y su aplicación a la hidrografía.Muchas organizaciones hidrográficas del mundo entero están utilizando en la recogida y el flujo de tratamiento de sus datos las alturas derivadas mediante los Sistemas Mundiales de Navegación por Satélite (GNSS). La Federación Internacional de Geodestas (FIG) ha reconocido la importancia de estos nuevos desarrollos y ha creado un nuevo grupo de trabajo en la Comisión 4, a la que se ha atribuido la tarea de desarrollar las mejores prácticas para los Levantamientos Referenciados Elipsoidalmente (ERS). Más de veinte grupos de la enseñanza, la industria y el gobierno, que están implicados en alguna forma de ERS, han proporcionado al grupo de trabajo un resumen de sus prácticas y experiencias. Este artículo destaca los temas relativos a los ERS y resume las soluciones que se están empleando.Une des questions les plus importantes en hydrographie aujourd‘hui est l‘utilisation de l‘ellipsoïde comme référence verticale pour le mesurage des levés. Le GPS à haute précision est utilisé pour positionner verticalement les plates formes de collecte des données hydrographiques, rapportant les observations bathymétriques directement à l‘ellipsoïde. Les modèles sont utilisés pour convertir ces observations dans un autre système. L‘utilisation du GPS vertical à haute précision et des modèles de conversion pour remplacer les correcteurs de marée traditionnels est relativement nouvelle pour la communauté hydrographique et, en tant que telle, nécessite une certaine discussion. Même si les composantes individuelles du processus sont bien comprises dans leur domaine spécifique, c‘est leur fusion et leur application à l‘hydrographie qui nécessite des explications, des éclaircissements et une évaluation.De nombreux organismes hydrographiques dans le monde utilisent les hauteurs dérivées des systè-mes globaux de navigation par satellite (GNSS) dans leur collecte et flux de traitement des données. La Fédération internationale des géomètres (FIG) a reconnu l‘importance de ces nouveaux dévelop-pements et a établi un nouveau groupe de travail dans le cadre de la Commission 4, chargé de déve-lopper de meilleures pratiques pour l‘ERS (Ellipsoidally Referenced Survey). Plus de vingt groupes du milieu universitaire, de l‘industrie et du gouvernement engagés dans une quelconque forme d‘ERS ont fourni au groupe de travail un résumé de leurs pratiques et expériences. Cet article passe en revue les questions liées à l‘ERS et résume les solutions mises en oeuvre

Effects of temperature upon the collapse of a Bose-Einstein condensate in a gas with attractive interactions

We present a study of the effects of temperature upon the excitation frequencies of a Bose-Einstein condensate formed within a dilute gas with a weak attractive effective interaction between the atoms. We use the self-consistent Hartree-Fock Bogoliubov treatment within the Popov approximation and compare our results to previous zero temperature and Hartree-Fock calculations The metastability of the condensate is monitored by means of the $l=0$ excitation frequency. As the number of atoms in the condensate is increased, with $T$ held constant, this frequency goes to zero, signalling a phase transition to a dense collapsed state. The critical number for collapse is found to decrease as a function of temperature, the rate of decrease being greater than that obtained in previous Hartree-Fock calculations.Comment: 4 pages LaTeX, 3 eps figures. To appear as a letter in J. Phys.

Skeleton weed : how serious a threat in Western Australia?

Skeleton weed is probably the most serious weed ever to threaten the Australian wheat industry. It interferes with wheat cropping at two stages: through competition with the growing crop, particularly for nitrogen and water during the crop\u27s development: and later through the production of a tall, wiry flowering stem which tangles in harvesting machinery and can make harvesting difficult, if not impossible. The weed is a major problem in eastern Australia although a combination of cultural, chemical and biological control programmes is helping to reduce its impact. In Western Australia, skeleton weed is being contained mainly by eradication efforts. Weed Agronomy Research Officers, F.D. Panetta and J. Dodd, are studying the ecology of skeleton weed to determine why it hasn\u27t spread further and how current control methods can be more effectively applied

Localized matter-waves patterns with attractive interaction in rotating potentials

We consider a two-dimensional (2D) model of a rotating attractive Bose-Einstein condensate (BEC), trapped in an external potential. First, an harmonic potential with the critical strength is considered, which generates quasi-solitons at the lowest Landau level (LLL). We describe a family of the LLL quasi-solitons using both numerical method and a variational approximation (VA), which are in good agreement with each other. We demonstrate that kicking the LLL mode or applying a ramp potential sets it in the Larmor (cyclotron) motion, that can also be accurately modeled by the VA.Comment: 13 pages, 11 figure

Long-range sound-mediated dark soliton interactions in trapped atomic condensates

A long-range soliton interaction is discussed whereby two or more dark solitons interact in an inhomogeneous atomic condensate, modifying their respective dynamics via the exchange of sound waves without ever coming into direct contact. An idealized double well geometry is shown to yield perfect energy transfer and complete periodic identity reversal of the two solitons. Two experimentally relevant geometries are analyzed which should enable the observation of this long-range interaction

Vortices in attractive Bose-Einstein condensates in two dimensions

The form and stability of quantum vortices in Bose-Einstein condensates with attractive atomic interactions is elucidated. They appear as ring bright solitons, and are a generalization of the Townes soliton to nonzero winding number $m$. An infinite sequence of radially excited stationary states appear for each value of $m$, which are characterized by concentric matter-wave rings separated by nodes, in contrast to repulsive condensates, where no such set of states exists. It is shown that robustly stable as well as unstable regimes may be achieved in confined geometries, thereby suggesting that vortices and their radial excited states can be observed in experiments on attractive condensates in two dimensions.Comment: 4 pages, 3 figure