No abstract

The laser drilling process is a complex phenomenon. This is especially true after the evaporation process starts. It is experimentally evident that liquid ejection occurs due to drag forces developed around the solid cavity and/or explosion resulting from nucleation of vapour bubbles in the liquid zone. Therefore, study into the ejection of liquid due to vapour bubble formation is necessary. Consequently, the present study examines the liquid ejection mechanism experimentally and possible saturated nucleate boiling is treated theoretically. In the experimental study, streak photography is introduced while a kinetic theory is adopted for the heat transfer model. This enables us to obtain the surface and internal temperature rise due to the laser heating pulse. It is found that the time measured for the liquid expulsion from the heated zone is identical with the time computed corresponding to possible saturated nucleate boiling.

COVID-19 has been declared a global pandemic which has brought the world economy and the society to a standstill. The current emphasis of testing is on detection of genetic material of SARS-CoV-2. Such tests are useful for assessing the current state of a subject: Infected or not infected. In addition to such tests, antibody testing is necessary to stratify the population into three groups: never exposed, infected, and immune. Such a stratification is necessary for safely reopening the society and remobilizing the economy. The aim of this review article is to inform the audience of the current diagnostic and surveillance technologies that are being employed for the detection of SARS-CoV-2 antibodies along with their shortcomings, and to highlight microfluidic sensors and devices that show promise of being commercialized for detection and quantification of SARS-CoV-2 antibodies in low-resource and Point-of-Care (POC) settings. Index Terms-Antibody, biosensors, chemical and biological sensors, enzyme linked immunosorbent assay (ELISA), protein. I. INTRODUCTIONC OVID-19 is an infectious disease caused by SARS-CoV-2 virus; a virus closely related to the SARS virus. The disease surfaced in late 2019 in the city of Wuhan, capital of Hubei province in mainland China. According to the most recent statistics, as of October 2020, coronavirus has spread across the world, by infecting more than 38 million people and has claimed about 1,089,000 lives [1]. In the United States alone, almost 8 million cases of coronavirus have been reported and the fatalities have amounted to approximately 214,000 and these numbers keep on increasing with each

Silver nanoparticles (AgNPs) exhibit strong antimicrobial properties against many pathogens. Traditionally employed chemical methods for AgNPs synthesis are toxic for the environment. Here, we report a quicker, simpler, and environmentally benign process to synthesize AgNPs by using an aqueous ‘root extract’ of Salvadora persica (Sp) plant as a reducing agent. The synthesized Salvadora persica nano particles (SpNPs) showed significantly higher antimicrobial efficacy compared to earlier reported studies. We characterized SpNPs using UV–Vis spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM), Field Emission Scanning Electron Microscopy (FE-SEM), Dynamic Light Scattering (DLS) and X-ray powder diffraction (P-XRD). UV–Vis spectrum showed the highest absorbance at 420 nm. FTIR analysis depicts presence of bond stretching including OH– (3300 cm−1), C=N– (2100 cm−1) and NH– (1630 cm−1) which are attributed in the involvement of phenolics, proteins or nitrogenous compounds in reduction and stabilization of AgNPs. TEM, FE-SEM and DLS analysis revealed the spherical and rod nature of SpNPs and an average size of particles as 37.5 nm. XRD analysis showed the presence of the cubic structure of Ag which confirmed the synthesis of silver nanoparticles. To demonstrate antimicrobial efficacy, we evaluated SpNPs antimicrobial activity against two bacterial pathogens (Escherichia coli (ATCC 11229) and Staphylococcus epidermidis (ATCC 12228)). SpNPs showed a significantly high inhibition for both pathogens and minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were found to be 0.39 µg/mL and 0.78 µg/mL for E. coli while 0.19 µg/mL and 0.39 µg/mL for S. epidermidis respectively. Further, Syto 16 staining of bacterial cells provided a supplemental confirmation of the antimicrobial efficacy as the bacterial cells treated with SpNPs stop to fluoresce compared to the untreated bacterial cells. Our highly potent SpNPs will likely have a great potential for many antimicrobial applications including wound healing, water purification, air filtering and other biomedical applications.

The laser processing of engineering materials requires an in-depth analysis of the applicable heating mechanism. The modelling of the laser heating process offers improved understanding of the machining mechanism. In the present study, a closed-form solution for a step input laser heating pulse is obtained and a numerical scheme solving a three-dimensional heat transfer equation is introduced. The numerical solution provides a comparison of temperature profiles with those obtained from the analytical approach. To validate the analytical and numerical solutions, an experiment is conducted to measure the surface temperature and evaporating front velocity during the Nd-YAG laser heating process. It is found that the temperature profiles resulting from both theory and experiment are in a good agreement. However, a small discrepancy in temperatures at the upper end of the profiles occurs. This may be due to the assumptions made in both the numerical and the analytical approaches. In addition, the equilibrium time, based on the energy balance among the internal energy gain, conduction losses and latent heat of fusion, is introduced.of evaporation (kJ/kg) I power intensity ( W/m2) I 0 peak power intensity ( W/m2) k thermal conductivity ( W/m K) 1 INTRODUCTION k B Boltzmann's constant m atomic weight (kg)The laser finds increasing commercial use as a machine p pressure (Pa) tool. However, for its use to be consolidated, it is necesp s recoil pressure (Pa) sary to explore the laser workpiece interaction mechanp z axial pressure (Pa) ism. Therefore, modelling the physical process can yield r radial distance (m) much insight into the complex phenomena occurring s, x distance from the surface (m) within the region activated by the laser beam. t time (s) Furthermore, modelling can substantially reduce the t eq equilibrium time (s) time required for process optimization, scale-up and T temperature ( K ) control. T s surface temperature ( K ) The modelling of temperature distribution induced by T sup superheat temperature ( K ) laser radiation in solids was previously investigated by V instantaneous velocity (m/s) several researchers (1-3) for stationary beam and for V liq liquid front velocity (m/s) moving beam interaction. In laser interaction mechan-V r evaporating surface velocity in the radial ism, the laser energy is absorbed at the surface by Fresnel direction (m/s) as well as surface plasma absorption (4). As the absorp-V vap vapour front velocity (m/s) tion is substantiated, the metal vapour reaches tempera-V z evaporating surface velocity in the axial tures much higher than the evaporation temperature, direction (m/s) resulting in strong ionization. The resulting plasma absorbs the laser radiation mainly by the effect of inverseThe MS was