Mass Transfer in a closed stirred gas/liquid contactor: Part 2: The liquid phase mass transfer coefficient kL

The liquid phase mass transfer coefficient kL for the absorption of oxygen in tap water and in ionic solutions has been calculated from the quotien\ud \ud It is concluded that the liquid phase mass transfer coefficient is roughly proportional to the stirrer speed. The gas fraction e apparently has littl

Mass Transfer in a closed stirred gas/liquid contactor: Part 1: The mass transfer rate kLS

Liquid phase mass transfer rates kLS for the absorption of oxygen in tap water and in aqueous ionic solutions have been determined in two closed stirred tank contactors for a power input between 3 and 70 W/kg and (impeller diameter)f(tank diameter) ratios DifT of 0.3, 0.35 and 0.4. The contactors had diameters\ud of 0. I9 and 0.6 m. The dispersed phase fraction was 1% by volume in all experiments. The values of kLS were determined using two different techniques:\ud (1) a transient physical absorption method; and (2) the sulphite method

Grid infrastructures for secure access to and use of bioinformatics data: experiences from the BRIDGES project

The BRIDGES project was funded by the UK Department of Trade and Industry (DTI) to address the needs of cardiovascular research scientists investigating the genetic causes of hypertension as part of the Wellcome Trust funded (£4.34M) cardiovascular functional genomics (CFG) project. Security was at the heart of the BRIDGES project and an advanced data and compute grid infrastructure incorporating latest grid authorisation technologies was developed and delivered to the scientists. We outline these grid infrastructures and describe the perceived security requirements at the project start including data classifications and how these evolved throughout the lifetime of the project. The uptake and adoption of the project results are also presented along with the challenges that must be overcome to support the secure exchange of life science data sets. We also present how we will use the BRIDGES experiences in future projects at the National e-Science Centre

DyVOSE project: experiences in applying privilege management infrastructures

Privilege Management Infrastructures (PMI) are emerging as a necessary alternative to authorization through Access Control Lists (ACL) as the need for finer grained security on the Grid increases in numerous domains. The 2-year JISC funded DyVOSE Project has investigated applying PMIs within an e-Science education context. This has involved establishing a Grid Computing module as part of Glasgow University’s Advanced MSc degree in Computing Science. A laboratory infrastructure was built for the students realising a PMI with the PERMIS software, to protect Grid Services they created. The first year of the course centered on building a static PMI at Glasgow. The second year extended this to allow dynamic attribute delegation between Glasgow and Edinburgh to support dynamic establishment of fine grained authorization based virtual organizations across multiple institutions. This dynamic delegation was implemented using the DIS (Delegation Issuing) Web Service supplied by the University of Kent. This paper describes the experiences and lessons learned from setting up and applying the advanced Grid authorization infrastructure within the Grid Computing course, focusing primarily on the second year and the dynamic virtual organisation setup between Glasgow and Edinburgh

Single sign-on and authorization for dynamic virtual organizations

The vision of the Grid is to support the dynamic establishment and subsequent management of virtual organizations (VO). To achieve this presents many challenges for the Grid community with perhaps the greatest one being security. Whilst Public Key Infrastructures (PKI) provide a form of single sign-on through recognition of trusted certification authorities, they have numerous limitations. The Internet2 Shibboleth architecture and protocols provide an enabling technology overcoming some of the issues with PKIs however Shibboleth too suffers from various limitations that make its application for dynamic VO establishment and management difficult. In this paper we explore the limitations of PKIs and Shibboleth and present an infrastructure that incorporates single sign-on with advanced authorization of federated security infrastructures and yet is seamless and targeted to the needs of end users. We explore this infrastructure through an educational case study at the National e-Science Centre (NeSC) at the University of Glasgow and Edinburgh

BEC-BCS crossover in an optical lattice

We present the microscopic theory for the BEC-BCS crossover of an atomic Fermi gas in an optical lattice, showing that the Feshbach resonance underlying the crossover in principle induces strong multiband effects. Nevertheless, the BEC-BCS crossover itself can be described by a single-band model since it occurs at magnetic fields that are relatively far away from the Feshbach resonance. A criterion is proposed for the latter, which is obeyed by most known Feshbach resonances in ultracold atomic gases.Comment: 4 pages, 3 figure

A Shibboleth-protected privilege management infrastructure for e-science education

Simplifying access to and usage of large scale compute resources via the grid is of critical importance to encourage the uptake of e-research. Security is one aspect that needs to be made as simple as possible for end users. The ESP-Grid and DyVOSE projects at the National e-Science Centre (NeSC) at the University of Glasgow are investigating security technologies which will make the end-user experience of using the grid easier and more secure. In this paper, we outline how simplified (from the user experience) authentication and authorization of users are achieved through single usernames and passwords at users' home institutions. This infrastructure, which will be applied in the second year of the grid computing module part of the advanced MSc in Computing Science at the University of Glasgow, combines grid portal technology, the Internet2 Shibboleth Federated Access Control infrastructure, and the PERMS role-based access control technology. Through this infrastructure inter-institutional teaching can be supported where secure access to federated resources is made possible between sites. A key aspect of the work we describe here is the ability to support dynamic delegation of authority whereby local/remote administrators are able to dynamically assign meaningful privileges to remote/local users respectively in a trusted manner thus allowing for the dynamic establishment of virtual organizations with fine grained security at their heart

An Irrigation Canal as a Lotic Mesocosm: Examining the Relationship Between Macroinvertebrate Benthos and Drift

We explored the notion that small canals could be good experimental proxies of streams by documenting physiochemical parameters and macroinvertebrate community development in an aridland irrigation canal. Further, we tested the production-compensation hypothesis between benthic invertebrates and invertebrates in the water column (drift). If the hypothesis held, invertebrates in the drift would be low until the benthic carrying capacity was reached; then organisms in the drift would increase as individuals avoided overcrowded conditions in the substrate. In a small, naturalized freshwater canal, we sampled macroinvertebrates in the substrate and those in the drift once every 2 weeks over 170 days (May–October). We placed macroinvertebrates into functional feeding groups (FFG) and examined these groups along with total density and taxa richness. We found no density-dependent relationship either in FFG or total density between the benthos and invertebrates in the drift. Our negative results might indicate that the stream benthos did not reach carrying capacity (partially affected by adult emergence in the autumn), the invertebrate dynamics in the canal did not adequately represent those occurring in a natural stream, or the duration of our study was too short. However, the invertebrate community in the canal did follow community buildup patterns for small streams reported in the literature, and it also resembled the community in a nearby natural stream. We suggest that naturalized canals could be used as “mesocosms,” mimicking small natural streams, in which highly manipulative experiments could be conducted. In addition, the effects of temporary and permanent canals across the arid western landscape have been understudied and represent a new area of ecological research

The imbalanced antiferromagnet in an optical lattice

We study the rich properties of the imbalanced antiferromagnet in an optical lattice. We present its phase diagram, discuss spin waves and explore the emergence of topological excitations in two dimensions, known as merons, which are responsible for a Kosterlitz-Thouless transition that has never unambiguously been observed.Comment: 4 pages, 5 figures, RevTe

Present Effects of Past Wildfires on the Diets of Stream Fish

We investigated present indirect effects from a decade-old burn on the diets of stream fish. Based on soil instability and burn patterns from a 12–14-year-old wildfire complex, we separated 9 streams into 3 conditions: unburned, burned, and burned/scoured (i.e., experiencing a massive scour event 1 year post-burn). In the streams, we measured light levels and water temperatures, and we estimated fish density and biomass. We removed the digestive tracts from 9–15 rainbow trout (Oncorhynchus mykiss) from each stream and used a gravimetric procedure to analyze gut contents. Canopy cover development may dictate the composition of dietary items. Greater amounts of aquatic invertebrates and inorganic material were found in trout from streams with reduced overhead canopy. Further, these streams had lower amounts of terrestrial invertebrates and organic materials in the diets of fish. Although trout abundance was not different among the stream treatments, fire-induced, indirect effects on fish diets were still evident more than a decade after the burn. This suggests that recovery rates for trout assemblages may take longer than predicted and may depend on riparian recovery