Laser-Induced Plasma Analysis for Surrogate Nuclear Debris

This work identifies analytical lines in laser-induced plasma for chemical analyses of major elements found in surrogate nuclear debris. These lines are evaluated for interferences and signal strength to insure they would be useful to measure relative concentrations. Compact, portable instruments are employed and can be included as part of a mobile nuclear forensics laboratory for field screening of nuclear debris and contamination. The average plasma temperature is measured using the well-established Boltzmann plot technique, and plasma\u27s average electron density is determined using empirical formulae based on Stark broadening of the H-alpha line. These measurements suggest existence of partial local thermal equilibrium

On the measurement of laser-induced plasma breakdown thresholds

The breakdown threshold of a gas exposed to intense laser-radiation is a function of gas and laser properties. Breakdown thresholds reported in the literature often vary greatly and these differences can partially be traced back to the method that is typically used to determine breakdown thresholds. This paper discusses the traditional method used to determine breakdown thresholds and the potential errors that can arise using this approach, and presents an alternative method which can yield more accurate data especially when determining breakdown thresholds as functions of gas pressure

Specific Cationic Antimicrobial Peptides Enhance the Recovery of Low-Load Quiescent Mycobacterium tuberculosis in Routine Diagnostics.

The culture confirmation of Mycobacterium tuberculosis (MTB) remains the gold standard for the diagnosis of Tuberculosis (TB) with culture conversion representing proof of cure. However, over 40% of TB samples fail to isolate MTB even though many patients remain infectious due to the presence of viable non-culturable forms. Previously, we have shown that two short cationic peptides, T14D and TB08L, induce a hormetic response at low concentrations, leading to a stimulation of growth in MTB and the related animal pathogen Mycobacterium bovis (bTB). Here, we examine these peptides showing they can influence the mycobacterial membrane integrity and function through membrane potential reduction. We also show this disruption is associated with an abnormal reduction in transcriptomic signalling from specific mycobacterial membrane sensors that normally monitor the immediate cellular environment and maintain the non-growing phenotype. We observe that exposing MTB or bTB to these peptides at optimal concentrations rapidly represses signalling mechanisms maintaining dormancy phenotypes, which leads to the promotion of aerobic metabolism and conversion into a replicative phenotype. We further show a practical application of these peptides as reagents able to enhance conventional routine culture methods by stimulating mycobacterial growth. We evaluated the ability of a peptide-supplemented sample preparation and culture protocol to isolate the MTB against a gold standard routine method tested in parallel on 255 samples from 155 patients with suspected TB. The peptide enhancement increased the sample positivity rate by 46% and decreased the average time to sample positivity of respiratory/faecal sampling by seven days. The most significant improvements in isolation rates were from sputum smear-negative low-load samples and faeces. The peptide enhancement increased sampling test sensitivity by 19%, recovery in samples from patients with a previously culture-confirmed TB by 20%, and those empirically treated for TB by 21%. We conclude that sample decontamination and culture enhancement with D-enantiomer peptides offer good potential for the much-needed improvement of the culture confirmation of TB

Measurement and Analysis of C₂ Swan Spectra Following Breakdown of Nitro Compound Simulants

Recent measurements of micro-plasma following laser-induced optical breakdown on 3-nitrobenzoic acid show well developed molecular spectra during the first several hundreds of nanoseconds. Analysis of Carbon Swan spectra for well-above breakdown threshold energy/pulse is accomplished using an accurate line strength file. Moreover, presence of hydrogen-beta allows us to infer electron density in the plasma evolution. Computational challenges include accounting for background variation and appropriate modeling of hydrogen embedded in molecular spectra. Recorded and computed spectra agree nicely for time delays on the order of 1600 ns from optical breakdown when using a single temperature for local thermodynamic equilibrium plasma