There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Metal-based nanoenergetic materials: Synthesis, properties, and applications

This paper describes the production of thin, focused microjets with velocities of up to 850??m/s by the rapid vaporization of a small mass of liquid in an open liquid-filled capillary. The vaporization is caused by the absorption of a low-energy laser pulse. A likely explanation of the observed phenomenon is based on the impingement of the shock wave caused by the nearly instantaneous vaporization on the free surface of the liquid. We conduct an experimental study of the dependence of the jet velocity on several parameters and develop a semiempirical relation for its prediction. The coherence of the jets and their high velocity, good reproducibility, and controllability are unique features of the system. A possible application is to development of needle-free drug-injection systems that would be of great importance for health care worldwide.

Highly Focused Supersonic Microjets

The paper describes the production of thin, focused microjets with velocities up to 850 m/s by the rapid vaporization of a small mass of liquid in an open liquid-filled capillary. The vaporization is caused by the absorption of a low-energy laser pulse. A likely explanation of the observed phenomenon is based on the impingement of the shock wave caused by the nearly-instantaneous vaporization on the free surface of the liquid. An experimental study of the dependence of the jet velocity on several parameters is conducted, and a semi-empirical relation for its prediction is developed. The coherence of the jets, their high velocity and good reproducibility and controllability are unique features of the system described. A possible application is to the development of needle-free drug injection systems which are of great importance for global health care.

Highly focused supersonic microjets

Shortages in the availability of personal protective face masks during the COVID-19 pandemic required many to fabricate masks and filter inserts from available materials. While the base filtration efficiency of a material is of primary importance when a perfect seal is possible, ideal fit is not likely to be achieved by the average person preparing to enter a public space or even a healthcare worker without fit-testing before each shift. Our findings suggest that parameters including permeability and pliability can play a strong role in the filtration efficiency of a mask fabricated with various filter media, and that the filtration efficiency of loosely fitting masks/respirators against ultrafine particulates can drop by more than 60% when worn compared to the ideal filtration efficiency of the base material. Further, a test method using SARS-CoV-2 virion-sized silica nanoaerosols is demonstrated to assess the filtration efficiency against nanoparticulates that follow air currents associated with mask leakage.

Testing of Commercial Masks and Respirators and Cotton Mask Insert Materials using SARS-CoV-2 Virion-Sized Particulates: Comparison of Ideal Aerosol Filtration Efficiency versus Fitted Filtration Efficiency.

The growth and collapse of laser-induced vapor cavities inside axisymmetric free-falling liquid water jets have been studied. Bubbles of different size are generated at various distances from the jet axis and the effects on the jet interface are recorded by means of ultrafast cinematography. The configuration is characterized by two dimensionless parameters: the bubble to jet diameter ratio δ and the eccentricity coefficient e defined as the radius of bubble generation divided by the jet radius. For high δ and e, microjets and droplets are ejected from the liquid jet at speeds exceeding 100m∕s. The observed jet fragmentation shows similarities with experiments conducted on a liquid mercury jet hit by a pulsed proton beam, a candidate configuration for future accelerator based facilities.

/pdf/cavitation-bubble-behavior-inside-a-liquid-jet-59aijxcp1l.pdf

Cavitation bubble behavior inside a liquid jet

A quadrupole mass spectrometer (QMS) is used to measure the mixture composition of gas samples gathered in a novel burner configuration used to generate unstretched diffusion flames. The large variations of species concentration in the mixtures found in the burning chamber lead to accuracy problems due to the nonlinearities inherent to the instrument mode of operation. To obtain precise and real-time measurements, the sensitivity of the instrument is mapped to account for important changes in the sample composition. The implemented calibration procedure accounts for the concentration of the various species of interest in the burner (H2, He, H2O, CH4, O2, Ar, CO2) in mixtures containing up to five constituents, using up to one hundred reference mixtures. When necessary, calibration adjustments are performed using a small set of measurements to account for the effect of the drift of instrument sensitivity resulting from instrument wear or fouling. This procedure allows us to keep the relative error on the concentration of every species of interest below 5% for most of the mixtures while a classical calibration based on a limited number of reference mixtures often resulted in relative errors in excess of 50%.

https://iopscience.iop.org/article/10.1088/0957-0233/21/2/025102/pdf

Mass spectrometer calibration over wide concentration ranges in multicomponent gas mixtures

Thermal-diffusive instabilities in unstretched, planar diffusion flames

The novel species injector of a recently developed research burner, consisting of an array of hypodermic needles, which allows to produce quasi one-dimensional unstrained diffusion flames has been improved. It is used in a new symmetric design with fuel and oxidizer injected through needle arrays which allows to independently choose both the magnitude and direction of the bulk flow through the flame. A simplified theoretical model for the flame position with variable bulk flow is presented which accounts for the transport properties of both reactants. The model results are compared to experiments with a CO2-diluted H-2-O-2 flame and variable bulk flow. The mixture composition-throughout the burning chamber is monitored by mass spectrometry. The resulting concentration profiles and also compared to the simplified theory and demonstrate that the new burner configuration produces a good approximation of the I D chambered diffusion flame, which has been used extensively for the stability analysis of diffusion flames. Hence, the new research burner opens up new possibilities for the experimental validation of theoretical models developed in the idealized unstrained I D chambered flame configuration, in particular models concerning the effect of bulk flow magnitude and direction on flame stability. Some preliminary results are presented on the effect of bulk flow direction on the thermal-diffusive cellular flame instability. (C) 2009 The Combustion Institute. Published by Elsevier Inc.-All rights reserved.

Etienne Robert

Papers

Cavitation bubble behavior inside a liquid jet

Mass spectrometer calibration over wide concentration ranges in multicomponent gas mixtures

Thermal-diffusive instabilities in unstretched, planar diffusion flames

Experiments in a novel quasi-1D diffusion flame with variable bulk flow

Experimental Methods in Chemical Engineering: Mass Spectrometry—MS