New Bounds on the Size of Optimal Meshes

The theory of optimal size meshes gives a method for analyzing the output size (number of simplices) of a Delaunay refinement mesh in terms of the integral of a sizing function over the input domain. The input points define a maximal such sizing function called the feature size. This paper presents a way to bound the feature size integral in terms of an easy to compute property of a suitable ordering of the point set. The key idea is to consider the pacing of an ordered point set, a measure of the rate of change in the feature size as points are added one at a time. In previous work, Miller et al. showed that if an ordered point set has pacing ?, then the number of vertices in an optimal mesh will be O(?^dn), where d is the input dimension. We give a new analysis of this integral showing that the output size is only θ(n+nlog?). The new analysis tightens bounds from several previous results and provides matching lower bounds. Moreover, it precisely characterizes inputs that yield outputs of size O(n).     

Impact of an organizational control policy on absenteeism, performance, and satisfaction.

Examined the impact of an organizational control policy based on the concept of "legal compliance" with established organizational norms on 2 behavioral measures--absenteeism and performance--and 2 attitudinal measures of satisfaction. The control policy was experimentally manipulated in each of 2 experimental groups totaling 297 undergraduates. In one group, a compulsory attendance policy followed by a noncompulsory policy was employed, while in the other the sequence of administering the policies was reversed. Attendance, performance, and satisfaction measures were used as criteria in analyses of variance. Results indicate that a control policy based on legal compliance significantly improved attendance and performance and did not alter satisfaction levels. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A Computer-Based Brain Stimulation System to Investigate Sensory Prostheses for the Blind and Deaf

Electrical stimulation of the visual cortex of the brain results in punctate photic sensations called ``phosphenes.' This suggests the concept of producing artificial vision for the blind by implanting arrays of electrodes, producing scoreboard-like displays. Electrical stimulation of the cochlea, VIIIth nerve, and auditory cortex produces analogous auditory sensations called ``audenes,' which might be used to provide artificial hearing for the deaf.     

Engineering better wheelchairs to enhance community participation.

With about 2.2 million Americans currently using wheeled mobility devices, wheelchairs are frequently provided to people with impaired mobility to provide accessibility to the community. Individuals with spinal cord injuries, arthritis, balance disorders, and other conditions or diseases are typical users of wheelchairs. However, secondary injuries and wheelchair-related accidents are risks introduced by wheelchairs. Research is underway to advance wheelchair design to prevent or accommodate secondary injuries related to propulsion and transfer biomechanics, while improving safe, functional performance and accessibility to the community. This paper summarizes research and development underway aimed at enhancing safety and optimizing wheelchair design.     

Electrically small antenna elements using negative permittivity resonators

We show how resonators composed of negative permittivity materials can form the basis of effective small antenna elements. A quasi-static analysis of the resonant properties of a sub-wavelength negative permittivity sphere predicts that such a resonator will have a Q-factor that is only 1.5 times the Chu limit, matching the performance of other known electrically small spherical antenna designs, such as the folded spherical helix and the spherical capped dipole. Finite element simulation is used to demonstrate an impedance-matched radiating structure formed by coupling the resonator (a half-sphere above a ground plane) to a 50 ohm coaxial transmission line, where the coupling is mediated by a small conducting stub extending partially into the half-sphere. The resulting antenna has a ka<0.5, and its bandwidth and efficiency performance corresponds well to that predicted by the quasi-static analysis of the resonator.     

球化处理对氢化脱氢钛粉特性及其注射成形喂料流变性能的影响

氢化脱氢(HDH)钛粉形状不规则、流动性较差,不利于注射成形和提高其制品性能。本文通过PCS系统对HDH钛粉末进行球化处理,考察了球化处理对HDH钛粉特性及其注射成形喂料流变性能的影响。结果表明:球化处理后的HDH钛粉末变为近球形,粉末的流动性显著提高,其注射成形喂料的流变性能得到明显改善;同时,球化处理后钛粉的烧结组织明显细化,致密度大幅度提高。     

Comparison of Oxygen Transfer Parameters Determined from the Steady State Oxygen Uptake Rate and the Non-Steady-State Changing Power Level Methods

In this study, a laboratory scale Univ. of Cape Town enhanced biological phosphorus removal process was operated under controlled conditions at a solids retention time of 15 days. Results are presented for the process performance and oxygen transfer parameters determined by applying the steady state oxygen uptake rate (OUR) and the changing power level (CPL) techniques, as per ASCE standard guidelines. The testing periods were temporally separated to eliminate interference of the tests. During the application of the CPL method, the sludge volume index gradually increased and higher values of the oxygen transfer rate and alpha were measured, in comparison to the data from the steady state OUR method, under similar process performance. Furthermore, the mass transfer rate decreased as the CPL method of testing continued. In contrast, the oxygen transfer parameters remained uniform during the time when the OUR method was applied. The data indicated that the CPL method resulted in higher and variable oxygen transfer parameters, even though the process performance remained unchanged. Therefore, a more rigorous evaluation of the CPL method is recommended to clarify the validity of the test.     

Obituaries: Leo Joseph Postman (1918-2004).

Presents the obituary of Leo Joseph Postman, one of the most prolific psychologists of the last century. With over 250 publications to his credit, Postman died on April 22, 2004, of heart failure in Marblehead, Massachusetts, at the age of 85. His life and career accomplishments are discussed. Postman is best known for his interests in perception, serial learning, memory, and interference theory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Description of Structural Damage Caused by the Terrorist Attack on the Pentagon

On September 11, 2001, an airliner was intentionally crashed into the Pentagon. It struck at the first elevated slab on the west wall, and slid approximately 310?ft (94.5?m) diagonally into the building. The force of the collision demolished numerous columns and the fa?ade of the exterior wall, and induced damage to first-floor columns and the first elevated slab over an area approximately 90?ft (27.4?m) wide and 310?ft (94.5?m) long. None of the building collapsed immediately. The portion that remained standing, even after an intense fire, sustained substantial damage at the first-floor level.     

Toughness of the Pentagon Structure

On September 11, 2001, the reinforced concrete structure of the Pentagon Building was able to resist, without collapse, the impact of a large commercial airliner despite the total loss of 26 columns and severe damage to 15 columns at the ground level. The ensuing fire and related fire-fighting activities led to the collapse of a portion of the building approximately one-half hour after the impact. In this paper, the reasons for the demonstrated toughness of the reinforced concrete structure are examined and attributed to use of spiral columns, effective splicing of reinforcing bars, strong girders, and short span lengths.