Modeling ambient temperature and relative humidity sensitivity of respiratory droplets and their role in Covid-19 outbreaks

One of the many unresolved questions that revolves around the Covid-19 pandemic is whether local outbreaks can depend on ambient conditions like temperature and relative humidity. In this paper, we develop a model that tries to explain and describe the temperature and relative humidity sensitivity of respiratory droplets and their possible connection in determining viral outbreaks. The model has two parts. First, we model the growth rate of the infected population based on a reaction mechanism - the final equations of which are similar to the well-known SIR model. The advantage of modeling the pandemic using the reaction mechanism is that the rate constants have sound physical interpretation. The infection rate constant is derived using collision rate theory and shown to be a function of the respiratory droplet lifetime. In the second part, we have emulated the respiratory droplets responsible for disease transmission as salt solution droplets and computed their evaporation time accounting for droplet cooling, heat and mass transfer and finally crystallization of the salt. The model output favourably compares with the experimentally obtained evaporation characteristics of levitated droplets of pure water and salt solution, respectively, ensuring fidelity of the model. Droplet evaporation/desiccation time is indeed dependent on ambient temperature and relative humidity, considered at both outdoor and indoor conditions. Since the droplet evaporation time determines the infection rate constant, ambient temperature and relative humidity are shown to impact the outbreak growth rates.Comment: Revised Equations 7 and 24. This resulted in a minor change in Figure

Thermally induced secondary atomization of droplet in an acoustic field

We study the thermal effects that lead to instability and break up in acoustically levitated vaporizing fuel droplets. For selective liquids, atomization occurs at the droplet equator under external heating. Short wavelength [Kelvin-Helmholtz (KH)] instability for diesel and bio-diesel droplets triggers this secondary atomization. Vapor pressure, latent heat, and specific heat govern the vaporization rate and temperature history, which affect the surface tension gradient and gas phase density, ultimately dictating the onset of KH instability. We develop a criterion based on Weber number to define a condition for the inception of secondary atomization

Analyzing the dominant SARS-CoV-2 transmission routes towards an ab initio SEIR model

Identifying the relative importance of the different transmission routes of the SARS-CoV-2 virus is an urgent research priority. To that end, the different transmission routes, and their role in determining the evolution of the Covid-19 pandemic are analyzed in this work. Probability of infection caused by inhaling virus-laden droplets (initial, ejection diameters between $0.5-750\mu m$) and the corresponding desiccated nuclei that mostly encapsulate the virions post droplet evaporation, are individually calculated. At typical, air-conditioned yet quiescent indoor space, for average viral loading, cough droplets of initial diameter between $10-50 \mu m$ have the highest infection probability. However, by the time they are inhaled, the diameters reduce to about $1/6^{th}$ of their initial diameters. While the initially near unity infection probability due to droplets rapidly decays within the first $25s$, the small yet persistent infection probability of desiccated nuclei decays appreciably only by $\mathcal{O} (1000s)$, assuming the virus sustains equally well within the dried droplet nuclei as in the droplets. Combined with molecular collision theory adapted to calculate frequency of contact between the susceptible population and the droplet/nuclei cloud, infection rate constants are derived ab-initio, leading to a SEIR model applicable for any respiratory event - vector combination. Viral load, minimum infectious dose, sensitivity of the virus half-life to the phase of its vector and dilution of the respiratory jet/puff by the entraining air are shown to mechanistically determine specific physical modes of transmission and variation in the basic reproduction number $\mathcal{R}_0$, from first principle calculations

PcrG protects the two long helical oligomerization domains of PcrV, by an interaction mediated by the intramolecular coiled-coil region of PcrG

PcrV is a hydrophilic translocator of type three secretion system (TTSS) and a structural component of the functional translocon. C-terminal helix of PcrV is essential for its oligomerization at the needle tip. Conformational changes within PcrV regulate the effector translocation. PcrG is a cytoplasmic regulator of TTSS and forms a high affinity complex with PcrV. C-terminal residues of PcrG control the effector secretion

CLINICAL INSIGHT ON PATTERNS OF CARE AND PROGNOSTIC FACTORS IN ADULT HIGH GRADE GLIOMA: EXPERIENCE FROM A TERTIARY CANCER HOSPITAL FROM EASTERN INDIA

Objective: The Central Nervous System Tumors account for 2.4% of all malignancies in India, but are associated with high mortality in high-grade tumors which result in poor death-adjusted life years. This study focuses on patterns of care and prognostic factors of adult high-grade glioma to explore the unaddressed nuances in treating such patients. Methods: It was a retrospective single institutional study from June 2018 to July 2021 with an age group between 16 to 70 years. All histopathologically or clinicoradiologically proven cases of high-grade (World Health Organization Grades III and IV) gliomas were assessed. Defaulters and recurrent glioma at presentation were excluded from the analysis. Baseline characteristics were analyzed by Chi-square and unpaired t-test, and the Kaplan– Meir test was used for survival analysis. p<0.05 was considered significant. Results: 41 patients were accrued for final analysis with a median follow-up period of 18 months. The most common histology was Astrocytoma, followed by Glioblastoma with a female preponderance. The Frontal and Temporal lobe was the predominant site in the study population. A majority (82%) of the patients underwent maximal safe resection followed by chemoradiation therapy (63.4%). Median progression free survival was 24 months and 8 months for Grades III and IV gliomas, respectively. The median overall survival for Grade IV gliomas was 7 months. Conclusion: Resection status, Grade IV, IDH and 1p19q codeletion status were significant prognostic factors, while intensity modulated radiotherapy showed better dosimetry. More prospective randomized studies with larger sample sizes and longer follow-ups are required for validation and drafting an outcome nomogram

Insights on drying and precipitation dynamics of respiratory droplets in the perspective of Covid-19

We isolate a nano-colloidal droplet of surrogate mucosalivary fluid to gain fundamental insights into the infectivity of air borne nuclei during the Covid-19 pandemic. Evaporation experiments are performed with salt-water solutions seeded with a viral load of inactive nanoparticles in an acoustic levitator. We seek to emulate the drying, flow and precipitation dynamics of such air borne mucosalivary droplets. Observations with the surrogate fluid are validated by similar experiments with actual samples from a healthy subject. A unique feature emerges with regards to the final crystallite dimension; it is always 20-30% of the initial droplet diameter for different sizes and ambient conditions. The preserved precipitates from levitated droplets show that 15% of the total virion population remain dispersed on the outer surface of air-desiccated air borne nuclei. This fraction increases to ~90% if the respiratory droplets (of larger initial size) settle on a surface and then evaporate in the sessile mode.Comment: 4 Figure