Shock tube measurements of growth constants in the branched chain formaldehyde-carbon monoxide-oxygen system

Exponential free radical growth constants were measured for formaldehyde carbon monoxide-oxygen systems by monitoring the growth of oxygen atom concentration as manifested by CO flame band emission. Data were obtained over the temperature range of 1200 to 2000 K. The data were analyzed using a formaldehyde oxidation mechanism involving 12 elementary reaction steps. The computed growth constants are roughly in accord with experimental values, but are much more temperature dependent. The data was also analyzed assuming formaldehyde is rapidly decomposed to carbon monoxide and hydrogen. Growth constants computed for the resulting carbon monoxide hydrogen oxygen mixtures have a temperature dependence similar to experiments; however, for most mixtures, the computed growth constants were larger than experimental values

Ignition delay times of benzene and toluene with oxygen in argon mixtures

The ignition delay times of benzene and toluene with oxygen diluted in argon were investigated over a wide range of conditions. For benzene the concentration ranges were 0.42 to 1.69 percent fuel and 3.78 to 20.3 percent oxygen. The temperature range was 1212 to 1748 K and the reflected shock pressures were 1.7 to 7.89 atm. Statistical evaluation of the benzene experiments provided an overall equation which is given. For toluene the concentration ranges were 0.5 to 1.5 percent fuel and 4.48 to 13.45 percent oxygen. The temperature range was 1339 to 1797 K and the reflected shock pressures were 1.95 to 8.85 atm. The overall ignition delay equation for toluene after a statistical evaluation is also given. Detailed experimental information is provided

Fuel-rich catalytic combustion: A soot-free technique for in situ hydrogen-like enrichment

An experimental program on the catalytic oxidation of iso-octane demonstrated the feasibility of the two-stage combustion system for reducing particulate emissions. With a fuel-rich (phi = 4.8 to 7.8) catalytic combustion preburner as the first stage the combustion process was soot free at reactor outlet temperatures of 1200 K or less. Although soot was not measured directly, its absence was indicated. Reaction products collected at two positions downstream of the catalyst bed were analyzed on a gas chromatograph. Comparison of these products indicated that pyrolysis of the larger molecules continued along the drift tube and that benzene formation was a gas-phase reaction. The effective hydrogen-carbon ratio calculated from the reaction products increased by 20 to 68 percent over the range of equivalence ratios tested. The catalytic partial oxidation process also yielded a large number of smaller-containing molecules. The fraction of fuel carbon in compounds having two or fewer carbon atoms ranged from 30 percent at 1100 K to 80 percent at 1200 K

Fuel rich catalytic comustion: The first stage of a two-stage combustor

An experimental program demonstrated that fuel-rich catalytic combustion can be accomplished soot free as long as the combustion temperature is less than the temperature at the rich limit of combustion. Although soot was not measured directly, three pieces of data strongly suggest that it was not present: (1) the product gases were completely transparent and produced no radiation characteristic of soot, (2) measured reaction temperatures followed closely those calculated for equilibrium with no soot present, and (3) over 99 percent of the carbon was accounted for in the measured reaction products. Data for two catalyst configurations were taken along with gas samples at two locations downstream of the catalyst bed

Shock tube measurements of growth constants in the branched-chain ethane-carbon monoxide-oxygen system

Exponential free radical growth constants have been measured for ethane carbon monoxide oxygen mixtures by monitoring the growth of oxygen atom concentration as manifested by CO flame band emission. Data were obtained over the temperature range of 1200 to 1700 K. The data were analyzed using an ethane oxidation mechanism involving seven elementary reaction steps. Calculated growth constants were close to experimental values at lower temperatures, up to about 1400 K, but at higher temperatures computed growth constants were considerably smaller than experiment. In attempts to explain these results additional branching reactions were added to the mechanism. However, these additional reactions did not appreciably change calculated growth constants

Methane oxidation behind reflected shock waves: Ignition delay times measured by pressure and flame band emission

Ignition delay data were recorded for three methane-oxygen-argon mixtures (phi = 0.5, 1.0, 2.0) for the temperature range 1500 to 1920 K. Quiet pressure trances enabled us to obtain delay times for the start of the experimental pressure rise. These times were in good agreement with those obtained from the flame band emission at 3700 A. The data correlated well with the oxygen and methane dependence of Lifshitz, but showed a much stronger temperature dependence (phi = 0.5 delta E = 51.9, phi = 1.0 delta = 58.8, phi = 2.0 delta E = 58.7 Kcal). The effect of probe location on the delay time measurement was studied. It appears that the probe located 83 mm from the reflecting surface measured delay times which may not be related to the initial temperature and pressure. It was estimated that for a probe located 7 mm from the reflecting surface, the measured delay time would be about 10 microseconds too short, and it was suggested that delay times less than 100 microsecond should not be used. The ignition period was defined as the time interval between start of the experimental pressure rise and 50 percent of the ignition pressure. This time interval was measured for three gas mixtures and found to be similar (40 to 60 micro sec) for phi = 1.0 and 0.5 but much longer (100 to 120) microsecond for phi = 2.0. It was suggested that the ignition period would be very useful to the kinetic modeler in judging the agreement between experimental and calculated delay times

Norwich COVID-19 testing initiative pilot: evaluating the feasibility of asymptomatic testing on a university campus

Background: There is a high prevalence of COVID-19 in university-age students, who are returning to campuses. There is little evidence regarding the feasibility of universal, asymptomatic testing to help control outbreaks in this population. This study aimed to pilot mass COVID-19 testing on a university research park, to assess the feasibility and acceptability of scaling up testing to all staff and students. Methods: This was a cross-sectional feasibility study on a university research park in the East of England. All staff and students (5625) were eligible to participate. All participants were offered four PCR swabs, which they self-administered over two weeks. Outcome measures included uptake, drop-out rate, positivity rates, participant acceptability measures, laboratory processing measures, data collection and management measures. Results: 798 (76%) of 1053 who registered provided at least one swab; 687 (86%) provided all four; 792 (99%) of 798 who submitted at least one swab had all negative results and 6 participants had one inconclusive result. There were no positive results. 458 (57%) of 798 participants responded to a post-testing survey, demonstrating a mean acceptability score of 4.51/5, with five being the most positive. Conclusions: Repeated self-testing for COVID-19 using PCR is feasible and acceptable to a university population

Mechanical loading: biphasic osteocyte survival and targeting of osteoclasts for bone destruction in rat cortical bone

Bone is removed or replaced in defined locations by targeting osteoclasts and osteoblasts in response to its local history of mechanical loading. There is increasing evidence that osteocytes modulate this targeting by their apoptosis, which is associated with locally increased bone resorption. To investigate the role of osteocytes in the control of loading-related modeling or remodeling, we studied the effects on osteocyte viability of short periods of mechanical loading applied to the ulnae of rats. Loading, which produced peak compressive strains of -0.003 or -0.004, was associated with a 78% reduction in the resorption surface at the midshaft. The same loading regimen resulted in a 40% relative reduction in osteocyte apoptosis at the same site 3 days after loading compared with the contralateral side (P = 0.01). The proportion of osteocytes that were apoptotic was inversely related to the estimated local strain (P < 0.02). In contrast, a single short period of loading resulting in strains of -0.008 engendered both tissue microdamage and subsequent bone remodeling and was associated with an eightfold increase in the proportion of apoptotic osteocytes (P = 0.02) at 7 days. This increase in osteocyte apoptosis was transient and preceded both intracortical remodeling and death of half of the osteocytes (P < 0.01). The data suggest that osteocytes might use their U-shaped survival response to strain as a mechanism to influence bone remodeling. We hypothesize that this relationship reflects a causal mechanism by which osteocyte apoptosis regulates bone's structural architecture