A Conceptual Design Study on the Application of Liquid Metal Heat Transfer Technology to the Solar Thermal Power Plant

Alkali metal heat transfer technology was used in the development of conceptual designs for the transport and storage of sensible and latent heat thermal energy in distributed concentrator, solar Stirling power conversion systems at a power level of 15 kWe per unit. Both liquid metal pumped loop and heat pipe thermal transport were considered; system configurations included: (1) an integrated, focal mounted sodium heat pipe solar receiver (HPSR) with latent heat thermal energy storage; (2) a liquid sodium pumped loop with the latent heat storage, Stirling engine-generator, pump and valves located on the back side of the concentrator; and (3) similar pumped loops serving several concentrators with more centralized power conversion and storage. The focus mounted HPSR was most efficient, lightest and lowest in estimated cost. Design confirmation testing indicated satisfactory performance at all angles of inclination of the primary heat pipes to be used in the solar receiver

Self-Regulation in a Web-Based Course: A Case Study

Little is known about how successful students in Web-based courses self-regulate their learning. This descriptive case study used a social cognitive model of self-regulated learning (SRL) to investigate how six graduate students used and adapted traditional SRL strategies to complete tasks and cope with challenges in a Web-based technology course; it also explored motivational and environmental influences on strategy use. Primary data sources were three transcribed interviews with each of the students over the course of the semester, a transcribed interview with the course instructor, and the students’ reflective journals. Archived course documents, including transcripts of threaded discussions and student Web pages, were secondary data sources. Content analysis of the data indicated that these students used many traditional SRL strategies, but they also adapted planning, organization, environmental structuring, help seeking, monitoring, record keeping, and self-reflection strategies in ways that were unique to the Web-based learning environment. The data also suggested that important motivational influences on SRL strategy use—self-efficacy, goal orientation, interest, and attributions—were shaped largely by student successes in managing the technical and social environment of the course. Important environmental influences on SRL strategy use included instructor support, peer support, and course design. Implications for online course instructors and designers, and suggestions for future research are offered

Knowledge and Awareness Among Patients with Chronic Kidney Disease Stage 3

Knowledge is a prerequisite for changing behavior, and is useful for improving outcomes and reducing mortality rates in patients diagnosed with chronic kidney disease (CKD). The purpose of this article is to describe baseline CKD knowledge and awareness obtained as part of a larger study testing the feasibility of a self-management intervention. Thirty patients were recruited who had CKD Stage 3 with coexisting diabetes and hypertension. Fifty-four percent of the sample were unaware of their CKD diagnosis. Participants had a moderate amount of CKD knowledge. This study suggests the need to increase knowledge in patients with CKD Stage 3 to aid in slowing disease progression

Failure mechanisms and surface roughness statistics of fractured Fontainebleau sandstone

In an effort to investigate the link between failure mechanisms and the geometry of fractures of compacted grains materials, a detailed statistical analysis of the surfaces of fractured Fontainebleau sandstones has been achieved. The roughness of samples of different widths W is shown to be self affine with an exponent zeta=0.46 +- 0.05 over a range of length scales ranging from the grain size d up to an upper cut-off length \xi = 0.15 W. This low zeta value is in agreement with measurements on other sandstones and on sintered materials. The probability distributions P(delta z,delta h) of the variations of height over different distances delta z > d can be collapsed onto a single Gaussian distribution with a suitable normalisation and do not display multifractal features. The roughness amplitude, as characterized by the height-height correlation over fixed distances delta z, does not depend on the sample width, implying that no anomalous scaling of the type reported for other materials is present. It is suggested, in agreement with recent theoretical work, to explain these results by the occurence of brittle fracture (instead of damage failure in materials displaying a higher value of zeta = 0.8).Comment: 7 page

A touch and pair system for battery-free 802.15.4/ZigBee home automation networks

In this paper, 2 problems affecting the acceptance of wireless devices by a wider public are introduced, and possible solutions are suggested. The first obstacle is linked to the necessity of changing the batteries of autonomous wireless nodes after. Although this problem can be solved to a certain extent by using battery-less devices, the energy need of flexible protocols such as ZigBee increases the complexity of such a device autonomously joining a network (including association and binding). A solution based on RFID components that allow the transfer of pairing information using a “Touch and Pair” system is presented. It is shown that a consumer device such as an iPod/iPhone can be modified to serve as a user friendly pairing device. Using ultra low power components, battery-less switches sending ZigBee compatible frames are built. Key network parameters can be transferred from the iPod/iPhone to the switch or other endpoints and thus allow a fast and simple configuration of battery-less elements on the network

GaAs Quantum Dot Thermometry Using Direct Transport and Charge Sensing

We present measurements of the electron temperature using gate defined quantum dots formed in a GaAs 2D electron gas in both direct transport and charge sensing mode. Decent agreement with the refrigerator temperature was observed over a broad range of temperatures down to 10 mK. Upon cooling nuclear demagnetization stages integrated into the sample wires below 1 mK, the device electron temperature saturates, remaining close to 10 mK. The extreme sensitivity of the thermometer to its environment as well as electronic noise complicates temperature measurements but could potentially provide further insight into the device characteristics. We discuss thermal coupling mechanisms, address possible reasons for the temperature saturation and delineate the prospects of further reducing the device electron temperature.Comment: 8 pages, 3 (color) figure

Concerning the Charging of an Exploration Craft on and near a Small Asteroid

Introduction: An object immersed in an airless plasma environment will experience a natural process of surface charging in order to acheieve current balance, or zero net electric current to the object. It has been shown in recent computer simulations that the small-body plasma environment is very complex [1], considering effects of photoemission, topography, and formation of a plasma wake. For this work we consider an exploration craft (or astronaut) immersed within a plasma environment near an asteroid, which exhibits widely varying solar wind and photoelectric particle fluxes and continuously evolving illumination conditions. Objective: We aim to determine how an explo-ration craft or astronaut suit accumulates charge while located in the "nightside" asteroid wake where the particle fluxes are reduced, and in the dayside near-surface photoelectron sheath, by combining an object charging model [2] with kinetic simulations of a near-asteroid plasma environment [1]. We consider an astronaut floating near the asteroid while not in contact with the surface, as well as an astronaut moving along the surface using their hands/gloves to crawl along. Results: The modeling results suggest that remediation of triboelectric charge via accumulation of plasma currents is an important factor to consider when designing future NEA mission infrastructure, especially if repeated and frequent contact with the surface is planned. In shadowed regions such as the location shown in Fig. 1a, the plasma currents are so low (and the effective charge-remediation timescale so long, e.g. minutes to hours) that repeated contact with the surface tribocharges the glove in an uncontrollable fashion, as shown for two representative electron temperatures in Fig. 2a. The resulting buildup of significant negative charge would eventually initiate some other "current of last resort" [4] such as transport of positively-charged dust, field-emission from the glove, or significant alteration of environmental ion currents within the wake. In contrast, the few-meters-thick dayside photoelectron sheath in which the astronaut of Fig. 1b is immersed in is so rich in electrons (and hence so electrically conductive) that accumulated tribocharge dissipates almost instantaneously (e.g. in less than a ms) as shown in Fig. 2b. As our model astronaut orbits the NEA they would experience plasma currents and associated charge re-mediation times spanning many orders of magnitude, and the fusion between our numerical models provides a detailed understanding of the charging hazards possibly associated with contact-based NEA exploration