Search

Sampling at appropriate spatial scales in the Southern Ocean is logistically challenging and may influence estimates of diversity by missing intermediate representatives. With the assistance of sampling efforts especially influenced by the International Polar Year 2007-2008, we gathered nearly 1500 specimens of the crinoid species Promachocrinus kerguelensis from around Antarctica. We used phylogeographic and phylogenetic tools to assess its genetic diversity, demographic history and evolutionary relationships. Six phylogroups (A-F) identified in an earlier study are corroborated here, with the addition of one new phylogroup (E2). All phylogroups are circumpolar, sympatric and eurybathic. The phylogeny of Promachocrinus phylogroups reveals two principal clades that may represent two different cryptic species with contrasting demographic histories. Genetic diversity indices vary dramatically within phylogroups, and within populations, suggesting multiple glacial refugia in the Southern Ocean: on the Kerguelen Plateau, in the East Weddell Sea and the South Shetland Islands (Atlantic sector), and on the East Antarctic continental shelf in the Dumont d'Urville Sea and Ross Sea. The inferences of gene flow vary among the phylogroups, showing discordant spatial patterns. Phylogroup A is the only one found in the Sub-Antarctic region, although without evident connectivity between Bouvet and Kerguelen populations. The Scotia Arc region shows high levels of connectivity between populations in most of the phylogroups, and barriers to gene flow are evident in East Antarctica.

The formation of porous silica microstructures (frits) in capillaries with an internal diameter of 500 µm has been examined for inducing electroosmotic flow (EOF). Capillaries with this internal diameter are normally considered too large to support efficient EOF, but the discrete pumping devices reported here are able to overcome this limitation. The formation of these structures in the capillaries has been examined, with particular emphasis on identifying parameters within the preparation stage that might give rise to variation in the porosity of the frit. The initial results showed that the induced electroosmotic flow rate increased with frit length (to an optimum of 50 mm) with an applied potential of 700 V. The work offers an opportunity to extend electroosmotic pumping to capillaries of larger internal diameter than was previously thought ideal. It offers a number of potential advantages in the area of fluid propulsion, including the electric control of flow rates, the plug like nature of the flow, and the absence of moving parts. When this technology is applied to micro-reactors, the silica structures offer the dual advantages of providing a pumping mechanism while also retaining the catalyst in the micro-reactor.

Dans le monde byzantin, la demande de textes bibliques, theologiques et liturgiques etait persistante. Jusqu'a ce que le papier devienne disponible a bas prix, tout vieux livre ecrit sur du parchemin et contenant des textes d'une importance relative risquait d'etre converti en palimpseste. Le texte d'Archimede a ete une cible facile pour un pretre ayant besoin d'un nouveau livre de service. Le palimpseste est un livre liturgique grec, ecrit dans la seconde moitie du 12e siecle ou dans la premiere moitie du 13e siecle. L'A. decrit ce document tout en presentant ce qu'a pu etre celui d'Archimede.

A cost-effective method of experimentally determining rail vehicle dynamic parameters for use in analytical dynamic models has been developed by the Association of American Railroads (AAR). In this method, the rail vehicle’s rigid body modes of vibration are manually excited and the corresponding resonant frequencies are measured. Using these frequencies, the equations of motion for the system are solved for the vehicle’s mass moments of inertias, center of gravity location, and suspension stiffness. This method of dynamic parameter identification was developed at AAR’s Transportation Technology Center, Pueblo, Colorado. Compared to competing experimental methods, the AAR method offers the advantage of cost-effectiveness; it requires no expensive equipment and can be executed at remote locations. This paper describes the AAR method for rail vehicle parameter identification. An example of its use in the characterization of an iron ore rail vehicle is presented. In addition, dynamic simulation results for a transit vehicle, characterized using the AAR method, are compared to track test data for validation.

A vacuum system utilizing two 25 000 l/s (H2O) two‐stage (20 and 70 K) helium refrigerator (cold gas) cryopumps and a 1500 l/s turbomolecular pump has been provided for a 25 000‐l‐volume stainless steel chamber as a part of the Helios Laser Facility. Design goals for the performance of the vacuum system are to produce a chamber pressure of less than 1.33×10−4 Pa after two hours pumping from atmospheric pressure. Details of the vacuum system configuration, and typical operating conditions are described. Observations made during operation indicate the cryopumps utilized initially produce expected pumping performance followed by variable performance (pumping speed and ultimate pressure) depending upon pumping history. The turbomolecular pump utilized has demonstrated reproducible pump speed and ultimate pressure. Both pumps produce some vibration which can cause interference with critical components in the target chamber; vibration damping/attenuation has been successfully employed for the turbomolecular pum...

A trailer-mounted two-stage booster mechanical pumping system has been constructed for use in evacuation of large vacuum vessels in remote locations. The pumping system is composed of three nominal 1500-cm air-cooled Roots blowers and four nominal 150-cfm mechanical pumps. It includes a high conductance cryogenic baffle, a self-contained helium leak detection station with a high speed oil diffusion pump, a liquid cryogenic system for supply of cryogenic fluids to the two cryogenic traps, and dry gas for use in backfilling of vessels as required. A programmed start-up and run-down control is provided for simplified, safe operation of the pumping system. A simplified method of presenting pumping system performance and a design analysis procedure for matching of mechanical pumps to the boosters are described.