Electrical properties of teflon and ceramic capacitors at high temperatures

Space power systems and components are often required to operate efficiently and reliably in harsh environments where stresses, such as high temperature, are encountered. These systems must, therefore, withstand exposure to high temperature while still providing good electrical and other functional properties. Experiments were carried out to evaluate Teflon and ceramic capacitors for potential use in high temperature applications. The capacitors were characterized in terms of their capacitance and dielectric loss as a function of temperature, up to 200 C. At a given temperature, these properties were obtained in a frequency range of 50 Hz to 100 kHz. DC leakage current measurements were also performed in a temperature range from 25 to 200 C. The results obtained are discussed and conclusions are made concerning the suitability of the capacitors studied for high temperature applications

Electrical characterization of glass, teflon, and tantalum capacitors at high temperatures

Dielectric materials and electrical components and devices employed in radiation fields and the space environment are often exposed to elevated temperatures among other things. Therefore, these systems must withstand the high temperature exposure while still providing good electrical and other functional properties. Experiments were carried out to evaluate glass, teflon, and tantalum capacitors for potential use in high temperature applications. The capacitors were characterized in terms of their capacitance and dielectric loss as a function of temperature up to 200 C. At a given temperature, these properties were obtained in a frequency range of 50 Hz to 100 kHz. The DC leakage current measurements were also performed in a temperature range from 20 to 200 C. The obtained results are discussed and conclusions are made concerning the suitability of the capacitors investigated for high temperature applications

On the action potential as a propagating density pulse and the role of anesthetics

The Hodgkin-Huxley model of nerve pulse propagation relies on ion currents through specific resistors called ion channels. We discuss a number of classical thermodynamic findings on nerves that are not contained in this classical theory. Particularly striking is the finding of reversible heat changes, thickness and phase changes of the membrane during the action potential. Data on various nerves rather suggest that a reversible density pulse accompanies the action potential of nerves. Here, we attempted to explain these phenomena by propagating solitons that depend on the presence of cooperative phase transitions in the nerve membrane. These transitions are, however, strongly influenced by the presence of anesthetics. Therefore, the thermodynamic theory of nerve pulses suggests a explanation for the famous Meyer-Overton rule that states that the critical anesthetic dose is linearly related to the solubility of the drug in the membranes.Comment: 13 pages, 8 figure

Optimizing Resistance Coefficients for Large Bed Element Streams

This is a report of a comparison of Darcy resistance coefficients calculafed for previously reported laboratory data and those calculated for large bed element streams. Large bed element (LBE) streams exist frequently in nature where rocks derived from valley walls or from channels cutting through ancient glacial or fluvial deposits are moved only under conditions of extreme flood. The height of bed elements is a significant part of the mean depth of flow. The stream gradients are high and are quite stable for all but the highest flows

High temperature dielectric properties of Apical, Kapton, Peek, Teflon AF, and Upilex polymers

Reliable lightweight systems capable of providing electrical power at the magawatt level are a requirement for future manned space exploration missions. This can be achieved by the development of high temperature insulating materials which are not only capable of surviving the hostile space environment but can contribute to reducing the mass and weight of the heat rejection system. In this work, Apical, Upilex, Kapton, Teflon AF, and Peek polymers are characterized for AC and DC dielectric breakdown in air and in silicone oil at temperatures up to 250 C. The materials are also tested in terms of their dielectric constant and dissipation factor at high temperatures with an electrical stress of 60 Hz, 200 V/mil present. The effects of thermal aging on the properties of the films are determined after 15 hours of exposure to 200 and 250 C, each. The results obtained are discussed and conclusions are made concerning the suitability of these dielectrics for use in capacitors and cable insulations in high temperature environments

Combining education and science outcomes : the marine studies programme and Tūhua marine reserve monitoring

Tūhua (Mayor Island) lies 35 kilometres off shore in the Bay of Plenty, New Zealand. It has a long history of Māori occupation and is of high cultural significance to these traditional owners. Tūhua was once world-renowned for big game fishing, but after incremental declines in local fish populations, in 1993 a no-take marine reserve was gazetted and has been the subject of annual marine monitoring surveys since that time. Continued monitoring has only been possible because of the creation of an innovative science/education partnership between the Tūhua Trust Board, representing the indigenous Māori owners of the island, the Department of Conservation (DOC), responsible for managing the reserve, and the Marine Studies Department of Bay of Plenty Polytechnic (BOPP). The Polytechnic\u27s Marine Studies course is a successful undergraduate diploma/degree education programme, combining strong practical elements with academic rigour. Second year Marine Studies students and staff members undertake the marine monitoring surveys at Tūhua on an annual extended field trip. Managers expected the marine reserve would demonstrate growth in fish numbers in comparison to the adjacent less protected areas. However little change in key indicator species was apparent after ten years of protection and this precipitated a review of the methodology and marine management policies. Twenty years after protection, there are now clear differences. Interwoven with this hard science discourse are the perceptions of the students involved in the annual monitoring programme. On the extended monitoring field trip, the students and staff members live on the island for ten days in basic conditions and are immersed in a natural learning environment. Results of a series of questionnaires suggest that the students involved increase not only their skill sets but also have increased self-confidence, motivation and conservation awareness. Science and education outcomes have been successfully combined into a readily transferable model over twenty years at this ecologically and culturally significant island location.Keith E. Gregor: Marine Studies Department, Bay of Plenty PolytechnicKim D. Youg: Conservation Ecology Research Unit, Department of Zoology and Entomology, University of PretoriaDaniel C. Rapson: Tauranga Management Area, Department of ConservationJacob McC. Overton: Landcare Researc

Using mental-modelling to explore how irrigators in the Murray-Darling Basin make water-use decisions

Study region: Water stress and over-allocation are at the forefront of water management and policy challenges in Australia, especially in the Murray–Darling Basin (MDB). Because irrigated agriculture is a major social and economic component of the MDB, farmer decision-making plays a major role in water sustainability in the region. Study focus: This study used a fuzzy cognitive mapping methodology, ‘mental modeling’, to understand the perceived constraints of irrigator water-use decisions in the MDB, for two different types of irrigation: permanent and annual crops. The approach elicits and documents irrigator insights into the complex and networked nature of irrigation water use decisions in relation to farm-based dynamics. New hydrological insights for the region: Results suggest support for greater local and irrigator involvement in water management decisions. Many, if not most, of the irrigators understood the need for, or at least the inevitability of, governmental policies and regulations. However, a lack of accountability, predictability, and transparency has added to the uncertainty in farm-based water decision-making. Irrigators supported the concept of environmental sustainability, although they might not always agree with how the concept is implemented. The mental modelling approach facilitated knowledge sharing among stakeholders and can be used to identify common goals. Future research utilizing the mental modelling approach may encourage co-management and knowledge partnerships between irrigators, water managers and government officials.Ellen M. Douglas, Sarah Ann Wheeler, David J. Smith, Ian C. Overton, Steven A. Gray, Tanya M. Doody, Neville D. Crossma

Propagation modes of 3D scour below a submarine pipeline in oblique steady currents and waves

This paper presents experimental results on 3D scour propagation along a pipeline under oblique-incidence currents and waves. Different modes of 3D scour propagation were discovered after the local scour was initiated below the pipeline. These modes include scour propagation throughout the whole pipeline, onset of scour at multiple locations due to piping, termination of scour propagation induced by backfill and no scour propagation. The critical conditions for these scour propagation modes were determined in terms of flow incident angle, embedment depth and Shields parameter (or KC number). © 2016 Taylor & Francis Group, London