Underwater spark discharges are used in multiple practical applications including plasma closing switches, water treatment, plasma channel drilling and mineral processing, waste recycling, treatment of metals, and medical lithotripsy. Spark discharges in water have been studied for several decades, however, despite significant research efforts and progress in this area, further investigation into the efficiency of plasma-acoustic sources and their optimisation is required in order to expand their practical application. This paper is aimed at investigation of the electrical and hydrodynamic parameters of underwater plasma-generated cavities, including plasma resistance, energy delivered into the plasma cavity, period of cavity oscillations and characteristics of pressure impulses. Different energy levels, breakdown voltages and gap distances were used in the present study to allow systematic analysis of these electrical and hydrodynamic parameters. Empirical scaling relations which link the maximum acoustic pressure and the period of cavity oscillations with the energisation parameters and the resistance of plasma have been obtained. These empirical functions can be used for optimisation of the plasma-acoustic sources and for tailoring their parameters for specific practical applications. Index Terms-Underwater spark discharges, plasma resistance, hydrodynamic parameters of period of cavity, acoustic impulses I. INTRODUCTION N recent years, significant research efforts have been focused on investigation of high-voltage spark discharges in water. Such discharges have found practical application in different technological areas, including water-filled plasma closing switches used in high-voltage, pulsed-power systems [1], medical lithotripters [2], minerals engineering [3], recycling of solid materials [4, 5, 6], in water cleaning and remediation operations, and water-well cleaning operations [7]. An important area of potential practical applications of underwater spark discharges is generation of wide-band ultrasound impulses [8, 9]. Underwater, high-voltage spark discharges

Timely deployment of contaminant warning systems requires on‐line sensors and advancement of data analysis and decision support systems to accurately detect water quality changes. As a demonstration of event detection in water quality data, three water quality change‐detection algorithms were developed and used to detect changes in water quality observed at four locations within a distribution system. Each data set was “spiked” with simulated anomalous water quality values of 1 h duration and 10 levels of spike strength. The receiver operating characteristic (ROC) curve is proposed as an objective means of assessing and comparing water quality change‐detection algorithm results that is also able to provide the tradeoff between missed detections and false alarms on a single plot. The area under the ROC curve provides a measure of the sensitivity and specificity of each algorithm for each spike strength and location. Resulting areas under the ROC curve range from 0.46 for spike strengths of 1.0 (background) to 0.98 for strengths of 3.5 standard deviations from the mean, where an ROC curve area of 1.0 indicates perfect detection.

Objective: This study investigates possible advantages in pulsed over continuous 405-nm light-emitting diode (LED) light for bacterial inactivation and energy efficiency. Background: Alternative nonantibiotic methods of disinfection and infection control have become of significant interest. Recent studies have demonstrated the application of systems using 405-nm LEDs for continuous disinfection of the clinical environment, and also for potential treatment of contaminated wounds. Methods: Liquid suspensions of 103 colony-forming units/mL populations of Staphylococcus aureus were subject to pulsed 405-nm light of different frequencies, duty cycles, and intensities and for different lengths of time. Results: Pulsed exposures with the same average irradiance of 16 mW/cm2 and varying duty cycle (25%, 50%, 75%) showed very similar performance compared with continuous exposures, with 95–98% reduction of S. aureus achieved for all duty cycles. The pulsing frequency was varied in intervals from 100 Hz to 10 kHz and appeared to have little effect on antimicrobial efficacy. However, when comparing pulsed with continuous exposure, an improvement in inactivation per unit optical energy was achieved, with results showing an increase of approximately 83% in optical efficiency. Conclusions: These results suggest that under pulsed conditions, a lower energy consumption and lower perceived brightness could be achieved, thus potentially providing improved operating conditions for medical/infection control applications without compromising antimicrobial efficacy.

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This paper explores the possibilities of using impulsive and steady-state corona discharges for biodecontamination operations. A high tension tubular corona electrode was stressed with positive or negative dc voltage with magnitude up to 26 kV, and a grounded mesh was used as an opposite electrode. Different operational regimes of this corona generator were investigated for the production of ozone in air flow and the inactivation of microorganisms. The test microorganisms used in this work were Escherichia coli and Staphylococcus aureus, populations of which were seeded onto agar plates. These bacterial plates were located behind the grounded mesh electrode to assess bactericidal efficacy. The results show that corona discharges have a strong bactericidal effect, for example, positive flashing corona discharges were able to reduce populations of the test microorganism by ∼94% within a 30-60-s time interval. Negative steady-state corona discharges also produce noticeable bactericidal effect, reducing population of E. coli and S. aureus by more than 97% within a 120-s energization interval. The bactericidal efficiency of different corona discharge modes and its correlation with ozone levels produced by these discharges are discussed. The results obtained in this work will help in the design and development of compact plasma systems for environmental applications. IndexTerms-Corona discharges, inactivation of microorganisms.