Determining the load-time history of fibre composite materials by acoustic emission

Acoustic emission was monitored during the axial loading of unidirectional fibre composite tensile specimens. The material consisted of strong, brittle fibres (E glass) embedded in a viscoelastic matrix (epoxy). It was found that when the load was held constant the acoustic emission output continued, but at a decreasing rate with time at load. As the load level was increased, the acoustic emission output at load continued for a longer period. It is suggested that the acoustic emission under constant load is a result of fibre fracture which continues after loading ceases because of the viscoelastic nature of the matrix which allows stress redistribution with time. The experimental results from acoustic emission are compared with computer calculations for fibre fracture based on theoretical considerations. Good agreement is noted between the theoretical and experimental results.     

Accelerated fatigue testing method

A method for accelerated fatigue testing of materials, based on a cumulative damage rule, is developed and examined. The method is based on monotonically increasing the stress amplitude with the number of cycles, until failure. When the initial stress amplitude is above the endurance limit, two tests are needed to determine the S/N curve; another test, with an initial stress amplitude below the endurance limit, is needed to determine the fatigue endurance limit. It is shown how to choose the right loading rate and starting level. This method minimizes the number of tests needed for the determination of the fatigue strength endurance limit, and also shortens these tests by reducing the number of cycles, (as each test ends with specimen failure).     

Gradient Clock Synchronization in Dynamic Networks

Over the last years, large-scale decentralized computer networks such as peer-to-peer and mobile ad hoc networks have become increasingly prevalent. The topologies of many of these networks are often highly dynamic. This is especially true for ad hoc networks formed by mobile wireless devices.     

1,25-Dihydroxyvitamin D3 enhances degranulation of mast cells

Copper sulfate is one of the most widely used algicides for the control of phytoplankton in lakes, reservoirs, and ponds. It is also used for aquatic weed control. To study the toxic effects of copper on carp (Cyprinus carpio L.), toxicity tests were carried out. Fish recovery in copper-free water was followed. After a 14-day period of exposure to five concentrations of copper sulfate (0.25-4.0 mg/L CuSO4, values ranging from approximately 5 to 70% of the 96-h LC-50) and a recovery period of the same duration, activities of the functional enzymes alkaline phosphatase (AP), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) in the blood serum and gills were determined. Because the gills are the known target organ for copper, changes in gill structure were investigated as well. In all exposure groups for all the enzymes studied, an increase in activity was noted after 14 days. The increase in AP activity was the most pronounced in both gills and serum of carp exposed to the highest concentration tested (4 mg/L). After a "recovery" period, compared with the end of treatment, a decrease in enzyme activities was recorded, indicating eventual recovery from the Cu-induced stress (the only exception being the ALT activity in gills in the highest CuSO4 concentration). The results of biochemical analysis were confirmed by histopathology. Lesions such as epithelial hyperplasia, curling of secondary lamellae, and changes in chloride cells were observed on the gills, and their severity increased with increased toxicant concentration. Most of the changes were reversible, as exhibited by gill histopathology after the recovery period.     

Finding the best compromise in compiling compound loops to Verilog

In this work we consider a special optimization problem involved with compiling compound loops (combining nested and consecutive sub-loops) to Verilog. Each sub-loop of the compound loop may require a different optimized hardware configuration (OHC) for optimized execution times. For example, one loop requires at least two memory ports and one multiplier for an optimized execution time, while another loop may require only one memory port but two multipliers, yet one OHC should be selected for both loops. The goal is to compute a minimal OHC which, based on the different heat levels (expected number of iterations) of the sub-loops, is a good compromise between all the conflicting requirements of each sub-loop. Though synthesis of nested loops has been implemented in quite a few systems this aspect has not been considered so far. We avoid the use of time consuming integer linear programming (ILP) techniques and instead use a fast space exploration technique combined with an efficient variant of list scheduling.Another novel aspect of the proposed system is the observation that the real latencies of the hardware units should be considered as variables of the OHC rather than fixed real values as is usually done in high-level synthesis systems. Experimental results show a significant improvement in the OHC without a significant increase in the execution time due to the use of this search procedure.¹     

iPACS: Power-aware covering sets for energy proportionality and performance in data parallel computing clusters

Energy consumption in datacenters has recently become a major concern due to the rising operational costs and scalability issues. Recent solutions to this problem propose the principle of energy proportionality, i.e., the amount of energy consumed by the server nodes must be proportional to the amount of work performed. For data parallelism and fault tolerance purposes, most common file systems used in MapReduce-type clusters maintain a set of replicas for each data block. A covering subset is a group of nodes that together contain at least one replica of the data blocks needed for performing computing tasks. In this work, we develop and analyze algorithms to maintain energy proportionality by discovering a covering subset that minimizes energy consumption while placing the remaining nodes in low-power standby mode in a data parallel computing cluster. Our algorithms can also discover covering subset in heterogeneous   computing environments. In order to allow more data parallelism, we generalize our algorithms so that it can discover k$k$-covering subset, i.e., a set of nodes that contain at least k$k$ replicas of the data blocks. Our experimental results show that we can achieve substantial energy saving without significant performance loss in diverse cluster configurations and working environments.     

The three cultures in American science: publication productivity in physics,history and economics

Scientometrics - In 1959 Lord Charles Percy Snow delivered a scathing critique of the bifurcation of scientists into two cultures: The humanists and the natural scientists. Five decades later,...