Stress Superposition in High-Strength Glass

The introduction of surface compression via alkali-ion exchange is frequently used to strengthen alkali-containing glass. However, previous investigators found that when starting with high-strength glass, the strength measured after exchange was significantly less than the sum of the residual compression and the starting fracture strength. Results are presented which suggest that the source of this discrepancy is surface damage produced during the heat treatment accompanying the ion-exchange process. Further, when the surface damage was removed by shallow hydrofluoric acid etching, the resulting fracture strength did approximately equal the sum of the residual stress and the high starting strength.     

Rapid determination of double bond configuration and position along the hydrocarbon chain in cyclic fatty acid monomers

This study reports the structural elucidation of diunsaturated 5- or 6-membered ring cyclic fatty acid monomers (CFAM) isolated from heated flaxseed oil by complementary gas chromatography (GC)-mass spectrometry (MS) and GC-matrix isolation-Fourier transform infrared spectroscopy (MI-FTIR). Infrared measurements of CFAM were carried out on methyl ester derivatives as well-resolved chromatograms were obtained on a polar 100% cyanopropyl polysiloxane capillary GC column. By contrast, electron ionization MS of methyl ester derivatives was of limited value because of double bond migration during the ionization process in the mass spectrometer. This communication reports definitive MS fragmentation patterns that can confirm ring position and double bond position along the fatty acid chain in 1,2-disubstituted CFAM determined as 2-alkenyl-4,4-dimethyloxazoline derivatives. Double bond configuration (cis, trans, or conjugatedcis,cis) in CFAM was confirmed by GC-MI-FTIR. The presence of CFAM, degradation products found in used frying oils, is a potential source of dietary toxicity. This work was presented in part at the 84th American Oil Chemists' Society Annual Meeting held in Anaheim, CA, in April 1993.     

Defensive steroids from a carrion beetle (Silpha novaboracensis)

Two novel steroids, 3,7-dihydroxy-14-pregn-4-en-15,20-dione (1) and 3,7, 20-trihydroxy-14-pregn-4-en-15-one (4), have been characterized from the rectal gland ofSilpha novaboracensis (Coleoptera: Silphidae). Judging from the function of comparable pregnanes in another species ofSilpha, the compounds may play an antipredator role.Paper No. 81 of the seriesDefense Mechanisms of Arthropods. Paper No. 80 is Eisner, T., Deyrup, M., Jacobs, R., and Meinwald, J.,J. Chem. Ecol. 12:1407–1415.     

Eucapnic voluntary hyperventilation as a bronchoprovocation technique: development of a standarized dosing schedule in asthmatics

A variety of dosing schedules have been reported for the hyperventilation method of broncho-provocation testing. To evaluate the effect of challenge technique on the bronchoconstrictive response, we had 16 subjects perform eucapnic voluntary hyperventilation (EVH) with dry, room temperature gas using four different dosing schedules. The hyperventilation challenge dosages included the following: (1) a target minute ventilation (VE) of 20 x FEV1 for 6 min; (2) a target VE of 15 x FEV1 for 12 min; (3) an interrupted challenge with a target VE of 30 x FEV1 for 2 min repeated 3 times; and (4) a target VE of 30 x FEV1 for 6 min. Challenges 2, 3, and 4 gave identical absolute ventilatory challenges (identical factor FEV1 x minutes) but at different VE dosages or time. Challenges 1 and 4 were of identical length, but different target VE. The mean postchallenge fall in FEV1 was 16.6 +/- 10.9%, 11.0 +/- 8.1%, 19.6 +/- 9.9%, and 26.7 +/- 11.3% for challenges 1, 2, 3, and 4, respectively. The response to an identical EVH challenge (FEV1 x 30 for 6 min) was reproducible when performed on separate days. We conclude that the challenge technique used for hyperventilation testing will have a significant impact on the bronchoconstrictive response and must be taken into account when interpreting study results. Tests may be quantitatively comparable over a narrow range of challenge time and VE. We recommend that a 6-min uninterrupted EVH challenge using dry, room temperature gas at a target VE of 30 x FEV1 be adopted as the "standard" challenge.     

The effects of different roster schedules on sleep in miners

Shiftwork involving early morning starts and night work can affect both sleep and fatigue. This study aimed to assess the impact of different rostering schedules at an Australian mine site on sleep and subjective sleep quality. Participants worked one of four rosters;

4 × 4 (n = 14) 4D4O4N4O

7 × 4 (n = 10) 7D4O7N40

10 × 5 (n = 17) 5D5N50

14 × 7 (n = 12) 7D7N70

Sleep (wrist actigraphy and sleep diaries) was monitored for a full roster cycle including days off. Total sleep time (TST) was longer on days off (7.0 ± 1.9) compared to sleep when on day (6.0 ± 1.0) and nightshifts (6.2 ± 1.6). Despite an increase in TST on days off, this may be insufficient to recover from the severe sleep restriction occurring during work times. Restricted sleep and quick shift-change periods may lead to long-term sleep loss and associated fatigue.     

DynaMICs: Comprehensive Support for Run-Time Monitoring

Software engineering strives to enable the economic construction of software systems that behave reliably, predictably, and safely. In other engineering disciplines, safety is assured in part by detailed monitoring of processes. In software, we may achieve some level of confidence in the operation of programs by monitoring their execution. DynaMICs is a software tool that facilitates the collection and use of constraints for software systems. In addition, it supports traceability by mapping constraints to system artifacts. Constraint specifications are stored separately from code; constraint-monitoring code is automatically generated from the specifications and inserted into the program at appropriate places; and constraints are verified at execution time. These constraint checks are triggered by changes made to variable values. We describe the architecture of DynaMICs, discuss alternative verification techniques, and outline research directions for the DynaMICs project.     

Simulated train driving: fatigue, self-awareness and cognitive disengagement

Fatigue is a serious issue for the rail industry, increasing inefficiency and accident risk. The performance of 20 train drivers in a rail simulator was investigated at low, moderate and high fatigue levels. Psychomotor vigilance (PVT), self-rated performance and subjective alertness were also assessed. Alertness, PVT reaction times, extreme speed violations (>25% above the limit) and penalty brake applications increased with increasing fatigue level. In contrast, fuel use, draft (stretch) forces and braking errors were highest at moderate fatigue levels. Thus, at high fatigue levels, errors involving a failure to act (errors of omission) increased, whereas incorrect responses (errors of commission) decreased. The differential effect of fatigue on error types can be explained through a cognitive disengagement with the virtual train at high fatigue levels. Interaction with the train reduced dramatically, and accident risk increased. Awareness of fatigue-related performance changes was moderate at best. These findings are of operational concern.     

Computer tracking of objects moving in space

A method is developed to represent movement of convex blocks in three-dimensional space from a sequence of two-dimensional camera images. The goals are to determine the objects' movement toward or away from the camera as well as left/right and up/down movement in the image plane and to build models of the blocks. The movement information is used as part of a hierarchical matching process that determines the correspondence of blocks between scenes.