Effects of processing parameters and molecular weight distribution on the tensile properties of polypropylene fibers

The tensile properties of polypropylene fibers, produced in a short-spin line, are correlated with the parameters of the three processing stages (spinning, drawing, and annealing), and with the molecular weight distribution. In general, tensile stiffness and strength increase with increasing molecular orientation, while the elongation at break decreases. The degree of orientation is determined by the deformation ratios and temperatures of the first two stages. Tensil modulus and strength also increase with increasing annealing stage shrinkage ratio. All the tensile properties, including the elongation at break, increase with increasing average molecular weight. The mechanisms of crystallization and deformation are related to the molecular weight distribution in different ways. Hence, the tensile modulus is highest for broad distributions when the draw ratio is low, and for narrow distributions when the draw ratio is high. The tensile strength increases and the elongation at break decreases as the width of the molecular weight distribution decreases, for all combinations of processing parameters. The distribution of tensile strength, for fibers with high draw ratios, broadens as the molecular weight distribution narrows. The total draw ratio of fibers, as experienced during processing and testing, and the true stress at break, are discussed in terms of deformation rates and relaxation times. © 1994 John Wiley & Sons, Inc.     

Effectiveness of Monazite Coatings in Oxide/Oxide Composites after Long-Term Exposure at High Temperature

The effectiveness of monazite (LaPO₄) in providing an oxidation-resistant weak fiber/matrix interface was evaluated in a fiber roving/thin coating/ceramic-matrix composite with >20% fiber volume fraction. Nextel™ 610/monazite/alumina composites were fabricated and tensile tested after isothermal exposures of up to 1000 h. Some strength loss was seen after short-term exposures (1100°–1200°C/5–250 h); however, no further loss was observed after 1000 h at 1200°C. Conversely, control samples containing uncoated fiber displayed >70% strength losses after only 5 h at 1200°C. Fiber pullout was seen in monazite-containing samples even after 1000 h at 1200°C. Debonding was predominantly in the coating or at either the fiber/coating or coating/matrix interface. Push-out testing confirmed the weakness of the monazite coating interface.     

Nonuniform cooling in multifilament melt spinning of polypropylene fibers: Cooling air speed limits and fiber-to-fiber variations

The cooling of the spinning stage in a commercial compact-spinning line has been studied. A rectangular fiber bundle is extruded from the spinneret and cooled by air entering from one side. The speed of the cooling air is considerably reduced through the fiber bundle. There are practical lower and upper limits for the cooling air entrance speed, corresponding to filament breakage at the leeward and windward sides, respectively. These limits are functions of the material and processing parameters. Due to the nonuniform cooling, fibers sampled at the windward side generally have higher molecular orientation, lower amorphous fraction, higher density, and higher tensile modulus and strength. For most combinations of spinning and material parameters, the structure is either bimodally oriented α-crystalline or uniaxially oriented mesomorphic at all spinneret positions. Fibers with different structure types show opposite windward/leeward side trends with regard to local order and melting behavior. The structure may be mesomorphic at the leeward side and α-crystalline at the windward side, if the average spin-line stress is close to a critical value for orientation-induced crystallization, and the air speed difference across the spinneret is large. The cooling air speed affects the spin-line stress. Hence, the fiber-to-fiber variations due to nonuniform cooling are discussed in terms of the molecular orientation in the melt and the effective time available for arranging molecules into ordered structures. © 1995 John Wiley & Sons, Inc.     

A comparative evaluation of viewing metaphors on psychophysical skills education in an interactive virtual environment

In an empirical evaluation, we examined the effect of viewing condition on psychophysical skills education in an interactive 3D simulation to train users in electrical circuitry. We compared an immersive head-mounted display (HMD)-based viewing metaphor versus a limited, desktop-based virtual reality (DVR) viewing metaphor with interaction using a spatial user interface. Psychophysical skills education involves the association of cognitive functions with motor functions to make the task autonomous with repeated practice. In electrical circuitry, this is demonstrated by the fine movements involved in handling and manipulating components on the electrical circuit, particularly while measuring electrical parameters. We created an interactive circuitry simulation (IBAS) where participants could learn about electrical measurement instruments such as the ammeter, voltmeter and multimeter, in a simulated breadboard VR system. Twenty-four participants utilized the simulation (12 in each condition), and the quantitative and qualitative aspects of psychophysical skills education with respect to the viewing metaphor were examined. Each viewing condition in IBAS was head-tracked and non-stereoscopic. Perspective correction was coupled with head-tracking in the DVR condition. The key quantitative measures were cognitive questionnaires addressing different levels of Bloom’s cognitive taxonomy and a real-world psychophysical task addressing various levels of Dave’s psychomotor taxonomy. The qualitative measures were the Witmer–Singer sense of presence questionnaire and self-report. Results suggest that there was a significant increase in cognition post-experiment in both DVR and HMD viewing conditions in levels of knowledge, application, analysis and evaluation. Results also revealed a significant learning benefit with respect to the higher level concepts pertaining to evaluation in the HMD condition as compared to DVR. Participants seem to have enjoyed a greater level of affordance in task performance and spent a larger amount of time to complete the simulated exercises as well as manually maneuvered to further distances in the HMD viewing condition as compared to DVR viewing.     

Development of an autonomous bridge deck inspection robotic system

The threat to safety of aging bridges has been recognized as a critical concern to the general public due to the poor condition of many bridges in the United States. Currently, the bridge inspection is conducted manually, and it is not efficient to identify bridge condition deterioration in order to facilitate implementation of appropriate maintenance or rehabilitation procedures. In this paper, we report a new development of the autonomous mobile robotic system for bridge deck inspection and evaluation. The robot is integrated with several nondestructive evaluation (NDE) sensors and a navigation control algorithm to allow it to accurately and autonomously maneuver on the bridge deck to collect visual images and conduct NDE measurements. The developed robotic system can reduce the cost and time of the bridge deck data collection and inspection. For efficient bridge deck monitoring, the crack detection algorithm to build the deck crack map is presented in detail. The impact‐echo (IE), ultrasonic surface waves (USW), and electrical resistivity (ER) data collected by the robot are analyzed to generate the delamination, concrete elastic modulus, corrosion maps of the bridge deck, respectively. The presented robotic system has been successfully deployed to inspect numerous bridges in more than ten different states in the United States.     

Sustaining Data Archives over Time: Lessons from the Organizational Studies Literature

This article will explore how organizational theoretic approaches to understanding institutional sustainability could be applied to contemporary data archives and archival practices, with the aim of raising larger questions about data sustainability. The article is part of a larger study in progress of how one particular example of long-lived archives, Social Science Data Archives (SSDAs), have maintained themselves over time. SSDAs predate both computers and the Internet and provide a unique opportunity to examine perceptions about what makes an archive sustainable, through the ups and downs of funding cycles and massive changes in technical and organizational infrastructure.     

Using Genetic Algorithms for Tasking Teams of Raven UAVs

Control of multiple unmanned aerial vehicles is of importance given that so many have been deployed in the field. This work discusses how genetic algorithms (GA) have been applied to the cooperative tasking of the AeroVironment’s Raven unmanned aerial vehicle (UAV) engaged in an intelligence, reconnaissance, and surveillance (ISR) mission. Mission assumptions, development of the GA, the method used to test for convergence, and the outcome of preliminary testing are all discussed.     

Drug abuse risk and protective factors among black urban adolescent girls: A group-randomized trial of computer-delivered mother-daughter intervention.

A group-randomized design tested a mother-daughter intervention in which researchers aimed to increase protective factors in a community sample of Black urban adolescent girls. Girls and their mothers at 2 community agencies were pretested and, by agency, were randomized to either an intervention arm or a control arm. Intervention arm girls and their mothers received a program for improving mother- daughter rapport. Posttest data collected 3 weeks after program delivery revealed that intervention arm mothers and daughters improved more than did control arm mothers and daughters on measures of communication and closeness. At 3-month follow-up, intervention arm mothers, relative to control arm mothers, continued to report better communication with and closeness to their daughters. Girls and mothers in the intervention arm rated the computer program favorably on parameters of enjoyment, comfort, relevance, usefulness of information, improvements to their relationship with one another, and whether they would recommend the computer program to friends. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The moderating roles of self-esteem and neuroticism in the relationship between group and individual undermining behavior.

The authors developed and tested a multilevel interactive model of the relationship between group undermining and individual undermining behavior in 2 multiwave studies of group members. Integrating the literature on group influences on individual behavior with the individual difference literature, the authors predicted a 3-way Group Undermining × Self-Esteem × Neuroticism interaction, such that the relationship between group and individual undermining would be strongest among those simultaneously high in self-esteem and neuroticism. The 3-way interaction was supported in Study 1 (457 participants in 103 groups) and replicated in Study 2 (415 participants in 93 groups) with additional controls and alternative measures of key constructs. The authors discuss the implications of the research and identify future research directions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Write/erase cycling endurance of memory cells with SiO/sub 2//HfO/sub 2/ tunnel dielectric

The write/erase cycling endurance of low voltage floating-gate memory cells programmed and erased by tunneling through a SiO/sub 2//HfO/sub 2/ dual layer tunnel dielectric stack is investigated. The use of fixed single pulse program and erase conditions leads to fast shifting (after /spl sim/1000 cycles) of the threshold voltage window, so that only a limited number of write/erase cycles can be achieved. Increasing the write and erase duration quickly leads to an excessive erase time so that a different erase method has to be used. Improvement of the erase behavior and cycling endurance has been obtained by a combination of two methods. Inclusion of soft write pulses between the erase pulses reduces the amount of charge trapped in the tunnel dielectric and therefore limits the increase in erase time. Also, the erase voltage can progressively be raised in order to further limit the erase time, leading to an endurance of 10 000 cycles on the considered cells. When combining the SiO/sub 2//HfO/sub 2/ stack with channel hot electron injection so that tunneling is only required in one direction, 100 000 write/erase cycles are demonstrated with minimal change of the memory window.