An examination of the relationship between workload and fatigue within and across consecutive days of work: Is the relationship static or dynamic?

Cognitive–energetical theories of information processing were used to generate predictions regarding the relationship between perceived workload and fatigue within and across consecutive days of work. Repeated measures were taken aboard a naval vessel from a sample of 20 Navy patrol vessel crew members during nonroutine and routine patrols. The hypotheses were tested through growth curve modeling. There was a nonmonotonic relationship between workload and fatigue in the routine patrol; moderate workload was associated with the lowest fatigue. The relationship between workload and fatigue changed over consecutive days in the nonroutine patrol. At the beginning of the patrol, low workload was associated with fatigue. At the end of the patrol, high workload was associated with fatigue. These results suggest that the optimal level of workload can change over time and thus have implications for the management of fatigue, particularly where prolonged operations are involved. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Critical wall thickness in electrical discharge machining

Electrical discharge machining (EDM) is capable of fabricating thin wall structures due to the absence of physical contact between the tool and workpiece. However, the presence of impulsive force does exist during the sparking process, which could give rise to limitations in fabricating small features. The L9 Taguchi method together with the analysis of variance was used to determine the significance of various machining parameters on the specific impulsive force. Through the statistical analysis, it was observed that discharge energy was the most significant factor that influenced the specific impulsive force. Hence, it is important to understand the effects of specific impulsive force in EDM and to investigate its influence that limits the fabrication of thin wall structures. The limit in which the machined part is able to maintain its geometrical integrity is described as the critical wall thickness. The effects of specific impulsive force on thin wall structure were studied through determining the critical wall thickness for various discharge energies. The experimental work showed that both electrothermal erosion and brink erosion, which is attributed by the specific impulsive force was responsible for the loss of geometrical integrity of the wall structure. As the wall thickness falls below a critical value in a given discharge energy setting, the brink erosion was observed. The limit that established the critical wall thickness was elucidated by conflating the thermal erosion and brink erosion.     

An Endosymbiotic Evolutionary Algorithm for Optimization

This paper proposes a new symbiotic evolutionary algorithm to solve complex optimization problems. This algorithm imitates the natural evolution process of endosymbionts, which is called endosymbiotic evolutionary algorithm. Existing symbiotic algorithms take the strategy that the evolution of symbionts is separated from the host. In the natural world, prokaryotic cells that are originally independent organisms are combined into an eukaryotic cell. The basic idea of the proposed algorithm is the incorporation of the evolution of the eukaryotic cells into the existing symbiotic algorithms. In the proposed algorithm, the formation and evolution of the endosymbionts is based on fitness, as it can increase the adaptability of the individuals and the search efficiency. In addition, a localized coevolutionary strategy is employed to maintain the population diversity. Experimental results demonstrate that the proposed algorithm is a promising approach to solving complex problems that are composed of multiple sub- problems interrelated with each other.     

A taxonomy of market‐based resource management systems for utility‐driven cluster computing

In utility‐driven cluster computing, cluster Resource Management Systems (RMSs) need to know the specific needs of different users in order to allocate resources according to their needs. This in turn is vital to achieve service‐oriented Grid computing that harnesses resources distributed worldwide based on users' objectives. Recently, numerous market‐based RMSs have been proposed to make use of real‐world market concepts and behavior to assign resources to users for various computing platforms. The aim of this paper is to develop a taxonomy that characterizes and classifies how market‐based RMSs can support utility‐driven cluster computing in practice. The taxonomy is then mapped to existing market‐based RMSs designed for both cluster and other computing platforms to survey current research developments and identify outstanding issues. Copyright © 2006 John Wiley & Sons, Ltd.     

Novel Approach to Integration of Numerical Modeling and Field Observations for Deep Excavations

Precedent and observation of performance are an essential part of the design and construction process in geotechnical engineering. For deep urban excavations designers rely on empirical data to estimate potential deformations and impact on surrounding structures. Numerical simulations are also employed to estimate induced ground deformations. Significant resources are dedicated to monitor construction activities and control induced ground deformations. While engineers are able to learn from observations, numerical simulations have been unable to fully benefit from information gained at a given site or prior excavation case histories in the same area. A novel analysis method, self-learning in engineering simulations (SelfSim), is introduced to integrate precedent into numerical simulations. SelfSim is an inverse analysis technique that combines finite element method, biologically inspired material models, and field measurements. SelfSim extracts relevant constitutive soil information from field measurements of excavation response such as lateral wall deformations and surface settlement. The resulting soil model, used in a numerical analysis, provides correct ground deformations and can be used in estimating deformations of similar excavations. The soil model can continuously evolve using additional field information. SelfSim is demonstrated using two excavation case histories in Boston and Chicago.     

Comparison of left anterior oblique, anterior, and geometric mean methods in gastric emptying assessment of postpancreaticoduodenectomy patients

Although left anterior oblique (LAO) gastric emptying studies appear to be an adequate alternative to geometric mean (GM) measurements in patients with normal gastric anatomy, it is not clear whether they can be used after gastric or duodenal surgery. In this study, dual-phase gastric emptying studies with combined solid-liquid meal were performed in 54 patients who had undergone pancreaticoduodenectomy (Whipple procedure). Gastric emptying was studied with GM, LAO, and anterior (ANT) methods. T1/2 and percent gastric retention at 10, 30, 60, 90, and 120 minutes were calculated. Results from the three methods were compared using correlation analysis and the t test. The t test showed no significant difference in T1/2 and percent retention values between the GM and LAO or ANT views. The solid emptying T1/2 showed a better correlation between GM and LAO values (r = 0.824) than between GM and ANT (r = 0.589). For the liquid T1/2, the reverse was true. Correlation between GM and ANT (r = 0.939) was better than between GM and LAO (r = 0.839); however, both LAO and ANT views correlated well with GM liquid emptying. It is concluded that the LAO view can replace GM gastric emptying methods in postpancreaticoduodenectomy patients for evaluation of both solid and liquid emptying, although the ANT view appears completely adequate for the study of liquid emptying.     

Effects of dietary amino acid balance on the response of dairy cows to an increase of milking frequency from twice to three times daily

An experiment was conducted to examine how the response of dairy cows to a change from twice to three times-daily milking is affected by deficiencies in the dietary supplies of three amino acids, His, Met, and Lys. Six cows were used in a 6 x 6 Latin square with 14-d periods. The three dietary treatments were: grass silage and a cereal-based supplement containing feather meal as the sole protein supplement; the same silage-cereal diet supplying similar amounts of metabolizable and rumen-undegradable protein but with additional amounts of His, Met, and Lys in the form of fish meal; and the fish meal diet with additional metabolizable energy in the form of an additional 2 kg/d of sugar beet pulp. Within each of these dietary treatments, the cows were milked twice and three times daily, making a total of six treatments. When cows were given the feather meal diet, even though dietary metabolizable energy was in considerable excess, a deficiency of specific amino acids prevented any increase in milk yield in response to increasing the frequency of milking from twice to three times daily. In contrast, when cows consumed a similar level of excess metabolizable energy and a similar level of rumen-undegradable protein for which the protein was of better amino acid balance (fish meal), the increased frequency of milking led to increased yield of milk and milk protein.