Analysis of room temperature magnetic regenerative refrigeration

Results of a room temperature magnetic refrigeration test bed and an analysis using a computational model are presented. A detailed demonstration of the four sequential processes in the transient magnetocaloric regeneration process of a magnetic material is presented. The temperature profile during the transient approach to steady state operation was measured in detail. A 5 °C evolution of the difference of temperature between the hot end and the cold end of the magnetocaloric bed due to regeneration is reported. A model is developed for the heat transfer and fluid mechanics of the four sequential processes in each cycle of thermal wave propagation in the regenerative bed combined with the magnetocaloric effect. The basic equations that can be used in simulation of magnetic refrigeration systems are derived and the design parameters are discussed.     

The three-dimensional X-ray crystal microscope: A new tool for materials characterization

The three-dimensional (3-D) X-ray crystal microscope is a new nondestructive tool for the 3-D characterization of the mesoscopic and nanoscopic materials structure. A prototype microscope is installed on beamline 34-ID at the advanced photon source and has begun initial operation. The prototype microscope has a routine spatial resolution of approximately 0.5 × 0.5 × 1 μm³ and can probe tens to hundreds of microns below a sample surface, depending on the composition of the sample. For each volume element measured, the microscope can determine between 10 and 16 parameters. The measured parameters are the local crystallographic phase (1 deg of freedom), the Eulerian angles of crystal orientation (3 deg of freedom), and the plastic and/or elastic strain-tensor elements (6 to 12 deg of freedom). The time required to collect each volume element varies between 1 and 14 seconds, depending on the precision of the parameters and the sample complexity. Much faster data acquisition and much better spatial resolution are certain in the near future. Some initial results are presented to illustrate how the 3-D X-ray crystal microscope can provide unprecedented information about the 3-D structure of materials. This article is based on a presentation made at the symposium “Characterization and Representation of Material Microstructures in 3-D” held October 8–10, 2002, in Columbus, OH, under the auspices of ASM International’s Phase Transformations committee.     

Moderators of the Relationships Between Coworkers' Organizational Citizenship Behavior and Fellow Employees' Attitudes.

The authors developed and tested the prediction that the relationship hetween coworkers' organizational citizenship behaviors (OCBs) and fellow employees' attitudes depends on the supervisors' abusiveness. Results of a longitudinal study using data collected from 173 supervised employees at 2 points in time (separated by 7 months) suggested that coworkers' OCB was positively related to fellow employees' job satisfaction and affective commitment when abusive supervision was low. However, when abusive supervision was high, coworkers' OCB was negatively related to job satisfaction and was unrelated to organizational commitment. The results of a 2nd study were consistent with the idea that the attributions employees make for their coworkers' OCB explains the moderating effect of abusive supervision on the relationship between coworkers' OCB and job satisfaction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Quantal transmitter release at somatic motor-nerve terminals: stochastic analysis of the subunit hypothesis

Here we analyze the problem of determining whether experimentally measured spontaneous miniature end-plate currents (MEPCs) indicate that quanta are composed of subunits. The properties of MEPCs at end plates with or without secondary clefts at the neuromuscular junction are investigated, using both stochastic and deterministic models of the action of a quantum of transmitter. It is shown that as the amount of transmitter in a quantum is increased above about 4000 acetylcholine (ACh) molecules there is a linear increase in the size of the MEPC. It is possible to then use amplitude-frequency histograms of such MEPCs to detect a subunit structure, as there is little potentiation effect above 4000 ACh molecules. Autocorrelation and power spectral analyses of such histograms establish that their subunit structure can be detected if the coefficient of variation of the subunit size is less than about 0.12 or, if electrical noise is added, about 0.1. Positive gradients relate the rise time and half-decay times of MEPCs to their amplitude, even in the absence of potentiating effects; these gradients are shallower at motor nerve terminals that possess secondary clefts. The effect of asynchronous release of subunits is also investigated. The criteria determined by this analysis for identifying a subunit composition in the quantum are applied to an amplitude-frequency histogram of MEPCs recorded from a small group of active zones at a visualized amphibian motor-nerve terminal. This did not provide evidence for a subunit structure.     

The stability of supply chains

A continuous time version of the well-known beer game model is derived and its stability and robust stability properties are investigated. Novelty originates from the treatment of pure process delays rather than exponential lags and it is shown that this can lead to diametrically different dynamics to the exponential lag case. The stability properties of the system are shown to support and quantify the qualitative empirical results of the beer game. Additional insight into the influence of certain model parameters is attained by their interpretation as the degree of mismatch in a Smith predictor regulator. The transient inability to supply all that is demanded is mimicked and shown to constitute an influential source of demand amplification. The analytical nature of these calculations engenders the capacity to improve supply chain dynamics through the synthesis and calibration of strategic supply chain trade-off problems.     

Production-inventory system controller design and supply chain dynamics

The paper deals with the modelling and control of aggregated production-inventory systems as described by differential equations. Hitherto, research in the area has been characterized by the approximation of production delays by first-order lags rather than more realistic pure delays. We demonstrate the substantial qualitative differences between these two approaches and thus generate the motivation for the rest of the paper, which tackles pure delay systems. The application of some relatively new design methodologies for delay systems yields four design choices that are tested for their performance over a range of criteria including stability robustness. The investigation is then extended to the model of a supply chain comprising many such productioninventory systems. The mechanism by which disturbances can be transmitted along the supply chain causing disruption and incurring costs to other supply chain echelons is elucidated. A heuristic feedback policy designed adaptively to tune the individual system designs in response to such disturbances is presented.     

Brick and mortar treatment by cream emulsion for improved water repellence and thermal insulation

A novel polymer cream was applied to brick and mortar in an attempt to reduce water absorption and to improve thermal insulation for household heating energy saving. Tests were carried out on surface energy, water contact angle, thermal conductivity and sorptivity of brick and mortar with and without cream treatment. A model house was built and a heating and monitoring system was developed to quantitatively evaluate the heating energy consumption in different conditions before and after cream treatment. It was found out that cream treatment can successfully impart good water repellence and enhanced the thermal insulation of the brick and mortar. The results from contact angle and surface energy measurements showed that the materials became highly hydrophobic. Experimental results from the model house showed approximately 9% heating energy consumption reduction in dry conditions and approximately 50% in wet conditions. In addition, the internal humidity typically was reduced to almost 1/3 of that of the control. It has been demonstrated that the novel cream treatment on masonry buildings can help reduce damp problems and save household heating energy consumption which can make a significant contribution to addressing social, environmental, ecological and economic problems resulting from climate change and global warming.     

Decision rules for determining terrestrial movement and the consequences for filtering high-resolution global positioning system tracks: a case study using the African lion (Panthera leo)

The combined use of global positioning system (GPS) technology and motion sensors within the discipline of movement ecology has increased over recent years. This is particularly the case for instrumented wildlife, with many studies now opting to record parameters at high (infra-second) sampling frequencies. However, the detail with which GPS loggers can elucidate fine-scale movement depends on the precision and accuracy of fixes, with accuracy being affected by signal reception. We hypothesized that animal behaviour was the main factor affecting fix inaccuracy, with inherent GPS positional noise (jitter) being most apparent during GPS fixes for non-moving locations, thereby producing disproportionate error during rest periods. A movement-verified filtering (MVF) protocol was constructed to compare GPS-derived speed data with dynamic body acceleration, to provide a computationally quick method for identifying genuine travelling movement. This method was tested on 11 free-ranging lions (Panthera leo) fitted with collar-mounted GPS units and tri-axial motion sensors recording at 1 and 40 Hz, respectively. The findings support the hypothesis and show that distance moved estimates were, on average, overestimated by greater than 80% prior to GPS screening. We present the conceptual and mathematical protocols for screening fix inaccuracy within high-resolution GPS datasets and demonstrate the importance that MVF has for avoiding inaccurate and biased estimates of movement.