For rebooting economic activities in the ongoing COVID-19 pandemic scenario, it is important to pay detailed attention to infection transfer mechanisms during interaction of people in enclosed environments. Utmost concern is the possibility of aerosol mediated infection transfer, which is largely governed by the size distributions of virus laden droplets, termed as virusols in this work, ejected from humans. We expand on the well-known theory of Poisson fluctuations which acts as statistical barrier against formation of virusols. Analysis suggests that for viral loads < 2 × 105 RNA copies/mL, often corresponding to mild-to-moderate cases of COVID-19, droplets of diameter < 20 µm at the time of emission (equivalent to ~ 10 µm desiccated residue diameter) are unlikely to be of consequence in carrying infections. Cut-off diameters below which droplets will be practically free of contamination, are presented as a function of viral loading. The median diameters of virus laden polydisperse droplet distributions will be 1.5 to 20 times higher depending upon the geometric standard deviation. The studies have implications to risk assessment as well as residence time estimates of airborne infections in indoor environments. Additionally, it will be also helpful for performance evaluation of sanitization and control technologies to mitigate infection risks in workplaces.

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We report on the temperature tuning of the optical properties of planar Photonic Crystal (PhC) microcavities. Studies were made on one and two dimensional PhCs that were etched in InP and GaAs vertical waveguides. Two dimensional (hexagonal) and one-dimensional (Fabry-Pérot) cavities were optically investigated by an internal light source technique. The samples were mounted on a Peltier-stage which allowed temperature variation from T = 20 °C up to T = 76 °C. A linear dependence of the resonance wavelengths with respect to temperature is observed. A gradient of dλ/dT = 0.09 nm/°C and 0.1 nm/°C for the GaAs and InP based cavities was observed, respectively. These results are in agreement with the theoretical calculations based on the thermal dependence of the refractive index of the PhC semiconductor component.

An investigation of coherently grown InP quantum dots embedded in Ga0.5In0.5P by conventional space charge spectroscopy methods is reported. Deep level transient spectroscopy (DLTS) is used to obtain quantitative information on the electron emission from the dots. The applied field is found to significantly enhance the electron emission rates as seen by shifts in the peaks towards lower temperatures with increased field. Taking the field induced barrier lowering into account, the emission energy for the one electron ground state of the dot is determined as 240±10 meV. The correlation between the measured signal and the observed electron accumulation in capacitance–voltage measurements is clearly demonstrated. Further, studies of the electron emission when the average electron population in the dots was varied show that the emission energies are modified by the coulomb charging energy. Admittance measurements as a function of temperature, bias and frequency were also performed, and the results are qualitatively explained in terms of response from the dots. These observations are consistent with the effect of the signal frequency on the measured carrier concentration profile. To complete the picture and in order to distinguish the DLTS signature of the dots from that of the deep levels in GaInP, electron traps in the barrier material were also characterized. Two main electron traps, one with an activation energy of about 950 meV and the other having an activation energy of 450 meV, were present in all the samples.