Hollow fine fiber vs. flat sheet membranes - a comparison of structures and performance

The reverse osmosis performance of polymeric membranes depends not only on the chemical structure of the polymer but also on the physical structure of the membrane. Percolation theory is used to describe water flux and salt passage as functions of the polymer density, or porosity, of the membrane. Water permeability increases with increasing porosity, or decreasing polymer density in the membrane. Salt passage is controlled primarily by the membrane polymer density in the surface layer on the feed side of the membrane. Experimental data on both hollow fine fiber and flat sheet membranes are consistent with the basic concepts of percolation theory.     

Miller Analogies Test: A note on permissive retesting.

Mean scores on the Miller Analogies Test (MAT) were computed for 84 graduate students (UW group) who took the MAT twice—Form K followed by Form J. Retest scores were significantly higher (p     

Time-dependent failure in poly(methyl methacrylate) and polyethylene

Time-dependent failure of PMMA and polyethylene are characterized within the framework of a cumulative damage model for failure. It is found that the mean failure times in constant rate of stress experiments can be successfully predicted from the model using a time to fail function determined from constant stress experiments. For zero-tension sinusoidal fatigue tests, differences of up to an order of magnitude are observed between predicted and experimental failure times. PMMA and polyethylene data deviate from the predictions in different ways. In PMMA, the distribution of failure times in constant stress tests is moderately broad, as measured by the coefficient of variation, and symmetric about the mean, while in the fatigue tests the distribution is considerably broader, has a high positive skewness and shows evidence of being bimodal. For polyethylene, the distribution changes from being moderately broad and positively skewed in constant stress tests to a moderately broad, symmetric distribution in the fatigue tests. The model also predicts the total lifetime in sinusoidal fatigue tests to be independent of test frequency. Experimental results show that the lifetime of PMMA decreases with increasing frequency, although less rapidly than if the fatigue process were cycle dependent. The lifetime of polyethylene increases with increasing test frequency.     

The powder metallurgy of n-type Bi2Te2.55Se0.45 thermoelectric material

The effects of fabrication by powder processes on the density and thermoelectric properties of an n-type pseudo-binary Bi₂Te_2.55Se_0.45 alloy have been examined. The large effects on the thermoelectric properties are ascribed primarily to the generation and removal of point defects, together with the doping effects of atmospheric contamination in finer powders (–50 mesh).     

The role of performance antecedents and consequences in work motivation.

Assessed the effects of both antecedents and consequences while keeping supervisory involvement and stimulus changes constant. The safety performance of 200 employees in 4 departments of a processing plant was monitored 3 times/wk over 46 wks. A multiple baseline design was used in which the phases were introduced in steps. Following baseline, the antecedent condition was presented, in which safety rules were explained and safety meetings held, along with frequent supervisor interaction and stimulus changes. Then the performance consequence, feedback, in which a feedback graph was maintained and feedback meetings held, was added. The antecedent condition, even when bolstered by fairly extensive supervisor involvement, resulted in improvements in only 2 out of 4 departments. Only during the consequent condition did performance significantly improve in all departments over baseline and antecedent conditions. Furthermore, employees reported that they preferred obtaining information following their performance. The results confirm that performance consequences such as feedback play a critical role in work motivation and that antecedents alone may not be effective in all cases, even with fairly extensive supervisor involvement. (8 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Efficient transitive closure of sparse matrices over closed semirings

This paper surveys several alternative data structures and algorithms for multiplying sparse upper-triangular matrices over closed semirings, and evaluates their efficiency in computing transitive closures of matrices over the Boolean semiring. Two new variants are introduced that outperform previously known methods on a collection of large data-sets drawn from linguistic applications.     

探索空间的前沿 ——比尔·希列尔(1937—2019)

通过该文,艾伦·佩恩向比尔·希列尔(1937—2019)致敬.比尔是空间句法的创始人,创造了空间模式的分析方法.作为学术大师,比尔在科学领域中建立空间句法,整合了理论探索与规划设计实践.艾伦描述了空间句法的发展历史,以及比尔对建筑设计和城市规划学科的贡献.     

Strain rate effect in the single‐fiber‐fragmentation test

The single fiber fragmentation test (SFVU) has been widely used to characterize the interface it fiber‐reinforced polymers. The purpose of the work reported here was to determine the effect of strain rate on the fiber fragment lengths obtained in the SFFT. Three materials systems were used to make single‐fiber‐composite specimens: E‐glass fiber/polycarbonate matrix, AS4‐carbon fiber/polycarbonate matrix, and AS4‐carbon fiber/polycarbonate matrix. The fiber‐matrix adhesion in all three systems is based on physisorption rather than chemisorption. Each system was tested at strain rates ranging over four orders of magnitude. Results are reported in terms of fragment length, the dependent variable in this study, which is inversely related to the quality of the Interface. It was expected that the fragment length would show a systematic decrease with Increasing strain rate, but the expected trend was not found. Although the polycarbonate matrix exhibited rate‐dependent viscoelastic behavior typical of amorphous polymers below T_g, the fragment length at saturation did not show a statistically significant variation with strain rate for any of the three materials systems. A major contributor to the lack of observed effect was the inherent random variability associated with the SFFT; random variability in average fragment length was equal or greater than the 19% effect of rate predicted for ideal elastic systems with no debonding at the interface. In addition, considerable interfacial debonding occurred during the SFFT, not surprising for Interfaces based on physisorption alone. Debonding Interferes with transfer of applied load from matrix to fiber, and would thus interfere with transfer of the effect of rate from matrix to fiber. A tensile Impact test developed previously was also performed on single‐fiber composite specimens made from the same three materials systems. The results of the Impact tests differed from those obtained at controlled strain‐rates for only two of the materials systems.     

Impact of electromagnetic field management on the design of 500 kV transmission lines

The electric and magnetic field (EMF) issue has become an area of increasing public concern. There is a heightened sensitivity among the public to the siting and construction of new, and the upgrading of existing electric facilities. There is substantial scientific uncertainty and no widespread agreement among scientists as to how the presently available information regarding the possible health effects of electric and magnetic fields should be interpreted. Animal and epidemiological studies are inconclusive on whether exposure to EMF can cause human health effects.

Minimizing electric and magnetic field strength is one of the many factors to consider in the planning and design of a transmission system. It must be considered along with other issues such as safety, environmental concerns, reliability, insulation and electrical clearance requirements, aesthetics, cost, operations and maintenance. The field reduction techniques described in this paper are proven methods, and the new techniques are explained thoroughly and incorporated taking into consideration the percentage field reduction, maintenance, and operational reliability.

The constraints for electric and magnetic field reduction by line compaction and optimization of bundles configuration are studied taking into consideration the international accepted minimum clearances. The importance of the phase configuration and sequence is also demonstrated. Novel-field cancellation methods are presented. Systematic comparisons of the effectiveness of different line designs in reducing the EMF are included.