Development of a photofragmentation laser-induced-fluorescence laser sensor for detection of 2, 4, 6-trinitrotoluene in soil and groundwater

Laser photofragmentation (PF) and subsequent nitric oxide (NO) laser-induced fluorescence (LIF) have been developed to measure the concentration of energetic materials (EM's), such as 2, 4, 6-trinitrotoluene (TNT), in soil and other media. Gas-phase EM's photodissociate, releasing NO(2), when exposed to laser radiation near 226 nm. Laser-excited NO(2) predissociates to form NO that gives an intense fluorescence when excited near 226 nm. The EM concentration is inferred from the intensity of the NO fluorescence. A PF-LIF laser-based sensor is being developed to be used with the U.S. Army Corps of Engineers' Waterways Experiment Station's cone penetrometer to measure in situ the concentration of subsurface TNT. Several factors that affect the PF-LIF signal waveforms, such as sample temperature, laser power, and heating time, were investigated. Also, effects on the PF-LIF signal of adding water and fertilizer to the TNT mixtures were studied. Decay times were determined by least-squares fitting of the exponential PF-LIF signal waveforms. The use of PF-LIF waveforms promises to enable diagnostics of the sample's characteristics that would otherwise not be possible in situ.     

Noise equivalent count measurements in a neuro-PET scanner with retractable septa

The noise-equivalent count-rate (NEC) performance of a neuro-positron emission tomography (PET) scanner has been determined with and without interplane septa on uniform cylindrical phantoms of differing radii and in human studies to assess the optimum count rate conditions that realize the maximum gain. In the brain, the effective gain in NEC performance for three-dimensions (3-D) ranges from >5 at low count rates to approximately 3.3 at 200 kcps (equivalent to 37 kcps in 2-D). The gains of the 3-D method assessed by this analysis are significant, and are shown to be highly dependent on count rate and object dimensions.     

Comparison of M. longissimus dorsi pigment concentration from implanted and control Angus and Limousin bulls and steers

M. longissimus dorsi total pigment concentration, visual color score and 24-h pH values were evaluated in a 2(3) factorial design that included bulls versus steers, Zeranol implants versus control and Angus versus Limousin comparisons. Bulls had greater total pigment concentration than steers (3.25 versus 2·90 mg/g; P < 0·01) and darker colored lean (P < 0·01). Twenty-four hour pH values did not differ between bulls and steers. Zeranol implanting and breed had no effect on total pigment concentration or visual color score; however, Limousin had higher (P < 0·05) 24-h pH values than Angus. The initial slaughter group (N = 10; average age = 256 days) had 34% less total pigment than the final slaughter group (N = 48; average age = 458 days). The correlation between visual color score and total pigment concentration was -0·65. These results indicate that the darker colored lean from bulls is due in part to an increase in pigment concentration.     

Keeping up with the neighbours--measuring the bystander response

Ionising radiation can induce responses within non-exposed neighbouring (bystander) cells, which potentially have important implications on the estimates of risk at environmentally relevant doses. Using human skin fibroblasts (AG1522), a range of methods were used to investigate the nature of the signal(s) arising from the exposed cells. The signal(s) can be transmitted by direct cell-cell communication (investigated by using partial dish irradiations) or by medium-borne factors (a co-culture system where two monolayers share the same medium but only one monolayer is exposed to ionising radiation). CDKN1A was found to be up-regulated in both directly exposed and non-exposed cells. The data suggest that direct cell-cell communication dominates for these confluent cells, with medium-borne factors also contributing.     

Bioremediation of Pb-contaminated soil by incubating with Phanerochaete chrysosporium and straw

The bioremediation of the simulated lead (Pb)-contaminated soils by incubating with Phanerochaete chrysosporium and straw was studied at laboratory-scale. The soil pH, Pb concentration, soil microbial biomass, microbial metabolic quotient, microbial quotient and microbial biomass C-to-N ratios were monitored. The above indicators were to study the stress of Pb on soil and the microbial effects during the bioremediation process. It was found that the soils treated with P. chrysosporium and straw showed a much lower concentration of soluble-exchangeable Pb, lower metabolic quotient and biomass C-to-N ratios (0mgkg(-1) dry weight soil, 1.9mg CO(2)-Cmg(-1) biomass carbon and 4.9 on day 60, respectively) and higher microbial biomass and microbial quotient (2258mgkg(-1) dry weight soil and 7.86% on day 60, respectively) compared with the controls. In addition, the kinetic parameters in the model based on logistic equation were calculated by the BIOLOG data. By analyzing those kinetic parameters some information on the metabolic capacity of the microbial community could be obtained. All the results indicated that the bioavailability of Pb in contaminated soil was reduced so that the potential stress of Pb was alleviated, and also showed that the soil microbial effects and the metabolic capacity of microbial community were improved.     

Inverse scattering for rotationally scanned optical coherence tomography

Optical coherence tomography of luminal structures, such as for intravascular or gastrointestinal imaging, is performed by using a fiber-optic catheter as a beam-delivery probe. The interrogating beam is scanned angularly by rotating the fiber around a fixed central axis. Because the beam is focused only at a fixed distance from the center of the fiber, only scatterers near this distance are resolved. We present a solution of the inverse scattering problem that provides an estimate of the susceptibility of the sample for an angularly scanned Gaussian beam focused at a fixed distance from the origin. This solution provides quantitatively meaningful reconstructions while also extending the volume of the sample that is resolvable by the instrument.