Real-Time Measurement of Xenon Concentration in a Binary Gas Mixture Using a Modified Ultrasonic Time-of-Flight Anesthesia Gas Flowmeter

Background: Xenon (Xe) is an anesthetic gas which may have potential as a neuroprotectant. To measure each gas in a xenon/oxygen mixture one would typically use a thermal conductivity meter and a fuel cell respectively. The speed of sound in a binary gas mixture like this is related to fractional concentration, temperature, pressure, and masses of the gases present. We assessed the feasibility of developing a novel single sterilizable device which used the time of flight of ultrasound through the gas to measure both real-time gas flow and also the concentration of Xe in O2.Method: We adapted an ultrasonic time-of-flight flow meter from a conventional anesthetic machine to also measure the real time fractional concentration of Xe in O2. A total of 5 095 readings of were taken in the range 5 % to 95 % xenon, and compared with simultaneous measurements from a commercially available thermal conductivity xenon analyser.Results: Ultrasonic measurements of Xe (%) showed agreement with thermal conductivity meter measurements but there was marked discontinuity in the central region of the measurement range. Bland-Altman analysis (95% CI): Mean Difference (Bias) 3.1 (2.9 % to 3.2 %); lower 95 % Limit of Agreement -4.6 % (-4.8 % to -4.4 %); upper 95 % Limit of Agreement 10.8 % (10.5 % to 11.0 %).Conclusions: The modified ultrasonic flow meter estimated the Xe (%) however at present the accuracy is not sufficient for clinical use. With further work it may be possible to improve the accuracy sufficiently for potential clinical use

Implementation of ultrasonic sensing for high resolution measurement of binary gas mixture fractions

We describe an ultrasonic instrument for continuous real-time analysis of the fractional mixture of a binary gas system. The instrument is particularly well suited to measurement of leaks of a high molecular weight gas into a system that is nominally composed of a single gas. Sensitivity < 5 × 10−5 is demonstrated to leaks of octaflouropropane (C3F8) coolant into nitrogen during a long duration (18 month) continuous study. The sensitivity of the described measurement system is shown to depend on the difference in molecular masses of the two gases in the mixture. The impact of temperature and pressure variances on the accuracy of the measurement is analysed. Practical considerations for the implementation and deployment of long term, in situ ultrasonic leak detection systems are also described. Although development of the described systems was motivated by the requirements of an evaporative fluorocarbon cooling system, the instrument is applicable to the detection of leaks of many other gases and to processes requiring continuous knowledge of particular binary gas mixture fractions

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements