Criteria for selecting cure cycles in autoclave processing of graphite/epoxy composites

Room temperature mechanical properties, such as flexural strength and impact resistance, of epoxies and graphite/epoxy composites go through a maximum as a function of epoxy conversion. For tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM)-4,4′-diamlnodiphenylsulfone (DDS) formulations, the recommended cure cycle prescribes a maximum temperature close to 177°C. The maximum extent of reaction that may be obtained at this temperature is determined from the vitrification curve. At this maximum conversion, balanced mechanical and physical properties are attained in the partially cured specimen. However, if the standard cycle is used to cure thick parts, the maximum temperature inside the sample increases beyond 177°C. This leads to a complete conversion in most of the part and a consequent impairment of resulting physical and mechanical properties. It is shown how numerical solutions of differential energy and mass balances may be used to propose alternative cure cycles such that the maximum conversion at every point remains bounded by the vitrification curve. An illustration for a particular thickness is provided.     

Rigid polyurethane foams: A model of the foaming process

A model of the manufacture of rigid polyurethane foams by free rising is presented. The extent of cream and rise periods as well as the amount of blowing agent necessary to give the desired foam density are theoretically predicted. The rate of blowing agent evaporation is calculated from an experimental boiling temperature vs. composition curve. Experimental runs were carried out with a formulation consisting of a polymeric isocyanate, a polyether polyol based on sorbitol, a silicone-polyol block-copolymer as surfactant, dibutyltin dilaurate as catalyst, and trichlorofluoromethane as blowing agent. Mixing was performed in situ in the mold using a commercial foaming machine. Experimental results gave a satisfactory agreement with model predictions. A diagram containing all the relevant information may be theoretically built and used for the selection of adequate operating parameters for a given formulation.     

Assessing detergent safety: A comparison of a nonphosphate laundry detergent with phosphate detergents

The potential hazard of a carbonate-based, phosphate-free detergent was compared with that of a variety of granular and liquid phosphate detergents. Evaluations were made using methods prescribed by the Federal Hazardous Substances Act (FHSA) and others designed to more closely approximate exposure in actual use. Some phosphate products produced esophageal and gastric mucosal irritation similar to that produced by the nonphosphate detergent, while others caused varying, lesser degrees of injury. The nonphosphate detergent, as well as several phosphate products, was seriously irritating to the unwashed eye at required FHSA test levels. Under more realistic conditions, eye irritation was reduced significantly. Skin irritation by the nonphosphate product was comparable to that by phosphate detergents, and in some cases was lower. In skin irritation tests with human subjects, results with the carbonate detergent were equal to or lower than those obtained with phosphate detergents. The carbonate detergent was found not to be phototoxic, nor a contact- nor photo-sensitizer. Total alkalinity was shown not to correlate with the severity of tissue injury in either test animals or in man. Presented at the AOCS Short Course, “Update on Detergents and Raw Materials,” Lake Placid, New York, June 1971.     

On guiding the augmentation of an automated test suite via mutation analysis

Mutation testing has traditionally been used as a defect injection technique to assess the effectiveness of a test suite as represented by a “mutation score.” Recently, mutation testing tools have become more efficient, and industrial usage of mutation analysis is experiencing growth. Mutation analysis entails adding or modifying test cases until the test suite is sufficient to detect as many mutants as possible and the mutation score is satisfactory. The augmented test suite resulting from mutation analysis may reveal latent faults and provides a stronger test suite to detect future errors which might be injected. Software engineers often look for guidance on how to augment their test suite using information provided by line and/or branch coverage tools. As the use of mutation analysis grows, software engineers will want to know how the emerging technique compares with and/or complements coverage analysis for guiding the augmentation of an automated test suite. Additionally, software engineers can benefit from an enhanced understanding of efficient mutation analysis techniques. To address these needs for additional information about mutation analysis, we conducted an empirical study of the use of mutation analysis on two open source projects. Our results indicate that a focused effort on increasing mutation score leads to a corresponding increase in line and branch coverage to the point that line coverage, branch coverage and mutation score reach a maximum but leave some types of code structures uncovered. Mutation analysis guides the creation of additional “common programmer error” tests beyond those written to increase line and branch coverage. We also found that 74% of our chosen set of mutation operators is useful, on average, for producing new tests. The remaining 26% of mutation operators did not produce new test cases because their mutants were immediately detected by the initial test suite, indirectly detected by test suites we added to detect other mutants, or were not able to be detected by any test.

An RFID Attacker Behavior Taxonomy

A taxonomy of system attacker behavior reveals security vulnerabilities in RFID authorization and monitoring systems. RFID systems are classified by their informational goals-typically, authorization and monitoring. Authorization systems replace the more traditional approaches of granting an entity access to a particular zone, whereas monitoring systems establish an entity's location in that zone. Although their informational goals differ, the underlying hardware is identical for both types of systems; consequently, attacks at the hardware level are the same. However, because attacker behavior invalidates each subsystem's informational goals differently, RFID security requirements should consider these goals individually.     

Calming fears, easing pain. Children's anesthesia tricky

To a child, pain and fear are inseparable. How to safely relieve both is a subject of growing debate and research. Only recently has a narcotic drug been approved specifically for children, and its use is controversial.     

Photometer for measuring intensity and rhodopsin distributions in intact eyes

We describe a photometer that measures light transmitted through excised eyes. The instrument, an ocular transmission photometer, employs sensitive single photon-counting techniques, and its usefulness has been tested by the study of the absorbance of rhodopsin in retinal rod cells in situ. We find that absorbances of rat rods agree well with those predicted by microspectrophotometry without making corrections for cellular mosaics. Additional tests of the ocular transmission photometer show that (a) the instrument is sensitive to subtle differences in rhodopsin absorbance, known to exist in specific locations in the rat retina, and (b) using the rate of rhodopsin bleaching as the measure of intensity, we can determine the intensity distribution at several locations across the rat retina.     

Recovered memories of abuse in women with documented child sexual victimization histories

This study provides evidence that some adults who claim to have recovered memories of sexual abuse recall actual events that occurred in childhood. One hundred twenty-nine women with documented histories of sexual victimization in childhood were interviewed and asked about abuse history. Seventeen years following the initial report of the abuse, 80 of the women recalled the victimization. One in 10 women (16% of those who recalled the abuse) reported that at some time in the past they had forgotten about the abuse. Those with a prior period of forgetting--the women with "recovered memories"--were younger at the time of abuse and were less likely to have received support from their mothers than the women who reported that they had always remembered their victimization. The women who had recovered memories and those who had always remembered had the same number of discrepancies when their accounts of the abuse were compared to the reports from the early 1970s.