Jet A Explosion Experiments: Laboratory Testing

This report describes a series of experiments and analyses on the flammability of Jet A (aviation kerosene) in air. This is a progress report on ongoing work. The emphasis so far has been on measuring basic explosion parameters as a function of fuel amount and temperature. These parameters include vapor pressure, flammability limits, peak explosion pressure and pressure as a function of time during the explosion. These measurements were undertaken in order to clear up some fundamental issues with the existing data. The report is organized as follows: First, we give some background with data from previous studies and discuss the fuel weathering issues. Second, we describe the facility used to do combustion experiments, the combustion test procedures and the results of the combustion experiments. Third, we give estimates of peak pressure, review the standard analysis of pressure histories and discuss the application to the present data. Fourth, we review the standard approach to flammability limits and the issues in determining Jet A flammability. Fifth, we discuss the problems associated with measuring vapor pressure and describe our results for Jet A. Sixth, we present a model for Jet A which illustrates the issues in analyzing multicomponent fuels. Finally, we apply these results to TWA 800 and summarize our conclusions to date

Spark Ignition Energy Measurements in Jet A

Experiments have been carried out to measure the spark ignition energy of Jet A vapor in air. A range of ignition energies from 1 mJ to 100 J was examined in these tests. The test method was validated by first measuring ignition energies for lean mixtures of the fuels hexane (C6H6) and propane (C3H8) in air at normal temperature (295 K) and pressure (1 atm). These results agree with existing data and provide new results for compositions between the lean flame limit and stoichiometric mixtures. Jet A (from LAX, flashpoint 45–48 [degress] C) vapor mixtures with air have been tested at temperatures between 30 and 60 [degrees] C at two fuel mass loadings, 3 and 200 kg/m3, in an explosion test vessel with a volume of 1.8 liter. Tests at 40, 50, and 60 [degrees] C have been performed at a mass loading of 3 kg/m3 in an 1180-liter vessel. Experiments with Jet A have been carried out with initial conditions of 0.585 bar pressure to simulate altitude conditions appropriate to the TWA 800 explosion. Ignition energies and peak pressures vary strongly as a function of initial temperature, but are a weak function of mass loading. The minimum ignition energy varies from less than 1 mJ at 60 [degrees] C to over 100 J at 30 [degrees] C. At temperatures less than 30 [degrees] C, ignition was not possible with 100 J or even a neon sign transformer (continuous discharge). The peak pressure between 40 and 55 [degrees] C was approximately 4 bar. Peak pressures in the 1180-liter vessel were slightly lower and the ignition energy was higher than in the 1.8-liter vessel. The following conclusions were reached relative to the TWA 800 crash: (a) spark ignition sources with energies between 5 mJ and 1 J are sufficient to ignite Jet A vapor, resulting in a propagating flame; (b) the peak pressure rise was between 1.5 and 4 bar (20 and 60 psi). (c) a thermal ignition source consisting of a hot filament created by discharging electrical energy into a metal wire is also sufficient to ignite Jet A vapor, resulting in a propagating flame; (d) laminar burning speeds are between 15 and 45 cm/s; and (e) the limited amount of fuel available in the CWT (about 50 gal) did not significantly increase the flammability limit. The rapid decrease in spark ignition energy with increasing temperature demonstrates that hot fuel tanks are significantly more hazardous than cool ones with respect to spark ignition sources. A systematic effort is now needed in order to utilize these results and apply spark ignition energy measurements to future analyses of fuel tank flammability. Some key issues that need to be addressed in future testing are: (a) effect of flashpoint on the ignition energy-temperature relationship; (b) ignition energy vs. temperature as a function of altitude; (c) effect of fuel weathering on ignition energy; and (d) the effect of ignition source type on ignition limits

Expansion of the Knockdown Resistance Frequency Map for Human Head Lice (Phthiraptera: Pediculidae) in the United States Using Quantitative Sequencing

Pediculosis is a prevalent parasitic infestation of humans, which is increasing due, in part, to the selection of lice resistant to either the pyrethrins or pyrethroid insecticides by the knockdown resistance (kdr) mechanism. To determine the extent and magnitude of thekdr-type mutations responsible for this resistance, lice were collected from 138 collection sites in 48 U.S. states from 22 July 2013 to 11 May 2015 and analyzed by quantitative sequencing. Previously published data were used for comparisons of the changes in the frequency of thekdr-type mutations over time. Mean percent resistance allele frequency (mean % RAF) values across the three mutation loci were determined from each collection site. The overall mean % RAF (+/-SD) for all analyzed lice was 98.3 +/- 10%. 132/138 sites (95.6%) had a mean % RAF of 100%, five sites (3.7%) had intermediate values, and only a single site had no mutations (0.0%). Forty-two states (88%) had a mean % RAF of 100%. The frequencies ofkdr-type mutations did not differ regardless of the human population size that the lice were collected from, indicating a uniformly high level of resistant alleles. The loss of efficacy of the Nix formulation (Prestige Brand, Tarrytown, NY) from 1998 to 2013 was correlated to the increase inkdr-type mutations. These data provide a plausible reason for the decrease in the effectiveness of permethrin in the Nix formulation, which is the parallel increase ofkdr-type mutations in lice over time

PMN J1632-0033: A new gravitationally lensed quasar

We report the discovery of a gravitationally lensed quasar resulting from our survey for lenses in the southern sky. Radio images of PMN J1632-0033 with the VLA and ATCA exhibit two compact, flat-spectrum components with separation 1.47" and flux density ratio 13.2. Images with the HST reveal the optical counterparts to the radio components and also the lens galaxy. An optical spectrum of the bright component, obtained with the first Magellan telescope, reveals quasar emission lines at redshift 3.42. Deeper radio images with MERLIN and the VLBA reveal a faint third radio component located near the center of the lens galaxy, which is either a third image of the background quasar or faint emission from the lens galaxy.Comment: 21 pp., including 4 figures; thoroughly revised in light of new MERLIN/HST data; accepted for publication in A

Overview and application of the Mitscherlich equation and its extensions to estimate the soil nitrogen pool fraction associated with crop yield and nitrous oxide emission.

Postprin

Blood pressure variability and cardiovascular risk in the PROspective study of pravastatin in the elderly at risk (PROSPER)

Variability in blood pressure predicts cardiovascular disease in young- and middle-aged subjects, but relevant data for older individuals are sparse. We analysed data from the PROspective Study of Pravastatin in the Elderly at Risk (PROSPER) study of 5804 participants aged 70–82 years with a history of, or risk factors for cardiovascular disease. Visit-to-visit variability in blood pressure (standard deviation) was determined using a minimum of five measurements over 1 year; an inception cohort of 4819 subjects had subsequent in-trial 3 years follow-up; longer-term follow-up (mean 7.1 years) was available for 1808 subjects. Higher systolic blood pressure variability independently predicted long-term follow-up vascular and total mortality (hazard ratio per 5 mmHg increase in standard deviation of systolic blood pressure = 1.2, 95% confidence interval 1.1–1.4; hazard ratio 1.1, 95% confidence interval 1.1–1.2, respectively). Variability in diastolic blood pressure associated with increased risk for coronary events (hazard ratio 1.5, 95% confidence interval 1.2–1.8 for each 5 mmHg increase), heart failure hospitalisation (hazard ratio 1.4, 95% confidence interval 1.1–1.8) and vascular (hazard ratio 1.4, 95% confidence interval 1.1–1.7) and total mortality (hazard ratio 1.3, 95% confidence interval 1.1–1.5), all in long-term follow-up. Pulse pressure variability was associated with increased stroke risk (hazard ratio 1.2, 95% confidence interval 1.0–1.4 for each 5 mmHg increase), vascular mortality (hazard ratio 1.2, 95% confidence interval 1.0–1.3) and total mortality (hazard ratio 1.1, 95% confidence interval 1.0–1.2), all in long-term follow-up. All associations were independent of respective mean blood pressure levels, age, gender, in-trial treatment group (pravastatin or placebo) and prior vascular disease and cardiovascular disease risk factors. Our observations suggest variability in diastolic blood pressure is more strongly associated with vascular or total mortality than is systolic pressure variability in older high-risk subjects

The end of the world, or just 'goodbye to all that'? Contextualising the red deer heap from Links of Noltland, Westray, within late 3rd-millennium cal BC Orkney

As part of a major international research project, The Times of Their Lives, a programme of radiocarbon dating and Bayesian modelling was undertaken to refine the chronology of activities in one small but important part of the extensive Late Neolithic and Bronze Age settlement on Links of Noltland on the island of Westray, Orkney. The selected area (Trench D) is well known for having produced, next to a wall, the remains of a heap of at least 15 red deer carcasses, on top of which had been placed a large cod, a gannet’s wing along with part of a greater black-backed gull, and a pair of large antlers. This remarkable deposit had been preceded by, and was followed by, periods of cultivation and the deposition of domestic refuse. Refined date estimates have been produced, based on 18 radiocarbon determinations obtained from 16 samples from Trench D (including nine newly obtained dates, three from individual deer in the heap). These clarify when, during this long sequence of activities, the deer were heaped up: probably in the 22nd century cal bc, around the same time as Beaker pottery was deposited elsewhere on the Links. This allows comparison between the dated activities in this part of the site with activity elsewhere on the Links and also with other episodes of deer deposition in 3rd-millennium cal bc Orkney. It encourages exploration of the possible reasons for what appears to be a remarkable act of structured deposition. The significance of an earlier, much larger scale deposit featuring cattle remains at Ness of Brodgar is discussed in exploring the nature of Orcadian society and practices during the second half of the 3rd millennium cal bc

A near IR imaging survey of intermediate and high-mass young stellar outflow candidates

We have carried out a near-infrared imaging survey of luminous young stellar outflow candidates using the United Kingdom Infrared Telescope. Observations were obtained in the broad band K (2.2 mu) and through narrow band filters at the wavelengths of H_2 v=1--0 S(1) (2.1218 mu) and Br gamma (2.166 mu) lines. Fifty regions were imaged with a field of view of 2.2 X 2.2 arcmin^2. Several young embedded clusters are unveiled in our near-infrared images. 76% of the objects exhibit H_2 emission and 50% or more of the objects exhibit aligned H_2 emission features suggesting collimated outflows, many of which are new detections. These observations suggest that disk accretion is probably the leading mechanism in the formation of stars, at least up to late O spectral types. The young stellar objects responsible for many of these outflows are positively identified in our images based on their locations with respect to the outflow lobes, 2MASS colours and association with MSX, IRAS, millimetre and radio sources. The close association of molecular outflows detected in CO with the H_2 emission features produced by shock excitation by jets from the young stellar objects suggests that the outflows from these objects are jet-driven. Towards strong radio emitting sources, H_2 jets were either not detected or were weak when detected, implying that most of the accretion happens in the pre-UCHII phase; accretion and outflows are probably weak when the YSO has advanced to its UCHII stage.Comment: 64 pages, 53 figures, Accepted for publication in the MNRA