Interpolation formula for the electrical conductivity of nonideal plasmas

On the basis of a quantum-statistical approach to the electrical conductivity of nonideal plasmas we derive analytical results in the classical low-density regime, in the degenerate Born limit, and for the contribution of the Debye-Onsager relaxation effect. These explicit results are used to construct an improved interpolation formula of the electrical conductivity valid in a wide range of temperature and density which allows to compare with available experimental data of nonideal plasmas.Comment: 7 pages, 1 tabl

The causes for geographical variations in OS187/OS186 at the Cretaceous-Tertiary boundary

Researchers at Yale has approached the problem of the osmium isotopic composition of marine deposits formed in contact with both oxidized and reduced bottom waters. The measured (187) Os/(186) Os ratios of modern bulk sediment can be explained using mixing equations involving continental detrital, volcaniclastic, cosmogenic and hydrogeneous components. These studies show that sediments deposited under reducing marine conditions contain a hydrogenous component which is enriched in Re and has a radiogenic (187) Os/(186) Os ratio. The presence of such a hydrogenous component in the marine fish clay at Stevns Klint can account for the elevation of its (187) Os/(186) Os ration above the expected meteoritic value. Mass balance considerations require the Re/Os ratio of the phase precipitated from the terminal Cretaceous sea at Stevns Klint to have been about one tenth the value observed in contemporary deposits in the Black Sea, assuming Re has not been lost (or Os gained) subsequent to precipitation. In continental sections, the elevation of the (187) Os/(186) Os ratio in boundary layers may be due to precipitation from continental waters of crustally-derived radiogenic osmium either contemporaneous with the meteoritic (or mantle) osmium deposition or later during diagenesis

Report on a visit to Indonesia to conduct a review of the post harvest fisheries sector

A review of post-harvest fisheries in Indonesia was undertaken for the Overseas Development Administration, by a fisheries technologist, a biologist, and an economist, during a five week visit in June and July 1988. The terms of reference were: to review post-harvest fisheries and donors' activities in the sector, and to identify a strategy for future ODA inputs. The marine fishery is the most important in terms of value, followed by tambak aquaculture (mostly shrimps and milkfish), and the inland capture fishery. Most of the harvest is sold in the domestic market as wet fish, dried fish, and pindang (fish cooked in brine). Exports of frozen shrimp, from the tambaks and the marine fishery, are becoming increasingly important. Additionally, there are exports of wet fish on ice to Singapore. The team considered that the greatest problem facing the sector is overfishing of the South Java Sea, resulting in operational fishing grounds being located at an ever increasing distance from the main markets on Java. This poses a challenge to resource management, both pre- and post-harvest. The former requiring resource surveys, and the latter, the identification of low-cost improvements to on-board handling, to ensure the supply of fish to Java's predominantly low income population. A study encompassing these aspects is proposed by the EC in collaboration with France; ODNRI, in consultation with ODA HO, will liase with the French technical agency (ORSTOM) to determine whether complementary inputs from ODNRI would be useful. A second area in which action is proposed is in reducing losses from insect infestation of sun-dried fish. Dried fish is an important protein source for low-income groups in Indonesia, and an area in which ODA could make an effective contribution. The use of household insecticides on drying fish in Indonesia has been widely publicised and the practice banned. The problem persists though, and the team recommends a follow-up programme to an existing project. The existing project has provided training to the staff of provincial quality control laboratories in loss assessment and reduction, including the use of a safe (and approved) insecticide - Minawet. Financial analysis of the use of Minawet and adoption trials will be undertaken during the final stages of the existing project. Subject to satisfactory results from these, a large-scale extension project is proposed, aimed at adoption of Minawet by fish processors. An additional element will be the provision of the necessary training and equipment in pesticide residue analysis, for the National Centre for Quality Control and Fish Processing

Brands in international and multi‐platform expansion strategies: economic and management issues

Powerful media branding has historically facilitated successful international expansion on the part of magazine and other content forms including film and TV formats. Multi-platform expansion is now increasingly central to the strategies of media companies and, as this chapter argues, effective use of branding in order to engage audiences effectively and to secure a prominent presence across digital platforms forms a core part of this. Drawing on original research into the experience of UK media companies, this chapter highlights some of the key economic, management and socio-cultural issues raised by the ever-increasing role of brands and branding in the strategies of international and multi-platform expansion that are increasingly common- place across media

Transition from the Couette-Taylor system to the plane Couette system

We discuss the flow between concentric rotating cylinders in the limit of large radii where the system approaches plane Couette flow. We discuss how in this limit the linear instability that leads to the formation of Taylor vortices is lost and how the character of the transition approaches that of planar shear flows. In particular, a parameter regime is identified where fractal distributions of life times and spatiotemporal intermittency occur. Experiments in this regime should allow to study the characteristics of shear flow turbulence in a closed flow geometry.Comment: 5 pages, 5 figure

Alfven Wave Reflection and Turbulent Heating in the Solar Wind from 1 Solar Radius to 1 AU: an Analytical Treatment

We study the propagation, reflection, and turbulent dissipation of Alfven waves in coronal holes and the solar wind. We start with the Heinemann-Olbert equations, which describe non-compressive magnetohydrodynamic fluctuations in an inhomogeneous medium with a background flow parallel to the background magnetic field. Following the approach of Dmitruk et al, we model the nonlinear terms in these equations using a simple phenomenology for the cascade and dissipation of wave energy, and assume that there is much more energy in waves propagating away from the Sun than waves propagating towards the Sun. We then solve the equations analytically for waves with periods of hours and longer to obtain expressions for the wave amplitudes and turbulent heating rate as a function of heliocentric distance. We also develop a second approximate model that includes waves with periods of roughly one minute to one hour, which undergo less reflection than the longer-period waves, and compare our models to observations. Our models generalize the phenomenological model of Dmitruk et al by accounting for the solar wind velocity, so that the turbulent heating rate can be evaluated from the coronal base out past the Alfven critical point - that is, throughout the region in which most of the heating and acceleration occurs. The simple analytical expressions that we obtain can be used to incorporate Alfven-wave reflection and turbulent heating into fluid models of the solar wind.Comment: 9 pages, 9 figures, accepted for publication in Ap

Limiter lock systems at TEXTOR: flexible tools for plasma-wall investigation

Limiter lock systems on the top and the bottom of the TEXTOR vessel are essential elements for experimental investigations of plasma-wall interaction in a tokamak. The lock systems are designed as user facilities that allow the insertion of wall elements (limiter) and tools for diagnostic (electrical probes, gas injection) without breaking the TEXTOR vacuum. The specially designed holder on top of the central carrier and a powerful vacuum pump system permit the exchange of components within similar to1 h. Up to ten electrical signals, four thermocouples, and a gas supply can be connected at the holder interface. Between discharges, the inserted component can be positioned radially and turned with respect to the toroidal magnetic field. Additionally, the central carrier is electrically isolated to apply bias voltages and currents up to 1 kV and 1 kA, respectively.An important feature of the lock system is the good access for optical spectroscopic observation of the inserted components in the vicinity of the edge plasma. The whole spectrum from ultraviolet to infrared is covered by spectrometers and filters combined with cameras. Toroidally and poloidally resolved measurements are obtained front the view on top of the probes while the tangential poloidal view delivers radially and toroidally resolved information.A programmable logic controller (Simatic S5) that is operated inside the TEXTOR bunker and from remote locations outside the concrete wall drives all possible features of the lock system

Class Attendance and Students’ Evaluations of Teaching: Do No-Shows Bias Course Ratings and Rankings?

Background: Many university departments use students’ evaluations of teaching (SET) to compare and rank courses. However, absenteeism from class is often nonrandom and, therefore, SET for different courses might not be comparable. Objective: The present study aims to answer two questions. Are SET positively biased due to absenteeism? Do procedures, which adjust for absenteeism, change course rankings? Research Design: The author discusses the problem from a missing data perspective and present empirical results from regression models to determine which factors are simultaneously associated with students’ class attendance and course ratings. In order to determine the extent of these biases, the author then corrects average ratings for students’ absenteeism and inspect changes in course rankings resulting from this adjustment. Subjects: The author analyzes SET data on the individual level. One or more course ratings are available for each student. Measures: Individual course ratings and absenteeism served as the key outcomes. Results: Absenteeism decreases with rising teaching quality. Furthermore, both factors are systematically related to student and course attributes. Weighting students’ ratings by actual absenteeism leads to mostly small changes in ranks, which follow a power law. Only a few, average courses are disproportionally influenced by the adjustment. Weighting by predicted absenteeism leads to very small changes in ranks. Again, average courses are more strongly affected than courses of very high or low in quality. Conclusions: No-shows bias course ratings and rankings. SET are more appropriate to identify high- and low-quality courses than to determine the exact ranks of average courses