Representation of effective facial mask design as a novel dimensionless number—Implications for COVID 19 pandemic

A dimensionless number Nr for the effective design of facial masks was derived and compared with other dimensionless numbers of fluid mechanics. Nr is found to closely resemble Euler's number (Eu). Nr is equal to the logarithmic function of the ratio of inertial force (Fi) of the air to the pressure force (Fp) of the air through the porous membrane of the mask. Nr is then introduced as a novel dimensionless number (Habib number) Ha in which the air flow through a facial mask is derived with parameters for an effective barrier from the COVID-19 virus (SARS COV 2). The introduction of Ha was not only for a comparison reason with other dimensionless numbers of fluid mechanics but also the number Ha is an essential extension of an early work on "Fluid mechanics of facial masks as personal protection equipment (PPE) of COVID-19 virus"[Rev. Sci. Instrum. 92, 074101 (2021)], in which the air flow through the mask is in its optimum design conditions to shield against the COVID-19 virus. As a result, an optimum Nr of expressing the flow of the O2 and N2 gases through the porous membrane was determined (Nr = NO2 = NN2 = Ha = -4.4). This was obtained when the N95 mask with specifications of a = 20 nm, l = 30 μm, and ϵ = 30% was used, with respect to the pressure gradient of the human lungs during exhaled and inhaled conditions, PAverage = 20 mm Hg (g cm-1 S-2), and to the size of the COVID-19 virus of about 125 nm (0.125 μm). In addition, a range of values of Nr was analyzed with respect to the optimum (Ha) value of Nr. On the one hand, when the range value of Nr falls between 0 ≥ Nr ≥ Ha, the mask has less resistance than Nr < -4.4, but not necessarily its optimum design conditions. On the other hand, when Nr = 0, the flow through the mask has no resistance at all, as if the mask does not exist. © 2023 Author(s).

Neonatal necrotizing enterocolitis due to COVID-19. A case report.

Digestive symptoms have been reported in an important proportion of children with COVID-19, and the clinical expression of critical patients with COVID-19 is thought to result from progressive increase of inflammation and an unusual trend of hypercoagulation. We report a newborn received with abdominal distension, green vomiting and imaging suggestive for enterocolitis. He had a close contact with COVID-19 and the PCR for SARS-CoV-2 came back positive. Despite the supportive measures, his condition deteriorated and a surgery was decided. The surgical exploration found an ischemic bowel. The therapeutic measures were ineffective as the child passed away a few hours after surgery despite the resuscitation treatment performed. The confirmed enterocolitis happening within the period of acute infection by SARS-CoV-2, the NEC was likely a manifestation of COVID-19.

From technology to community: the role of artefacts in teaching and learning during and beyond pandemic times

This article explores lecturers' experience of adapting, shaping and transforming teaching and learning during the COVID-19 pandemic. The study focuses on understanding the challenges and opportunities that are afforded by pandemic-induced changes in terms of digital teaching and learning and their post-pandemic implications. Empirical data were collected through 16 semi-structured interviews with teaching staff at a Norwegian university. The article draws on Max W. Wartofsky's work on artefacts, and uses the categorisation of primary, secondary and tertiary artefacts as a theoretical lens. The data indicates that designing and delivering courses that combine online and in-site teaching is a complex process requiring flexibility and creativity, which needs to be acknowledged by management and budget-allocating entities. Career development is an incentive to invest time in developing digital teaching. Finally, building a community of peers can support course quality and the professional welfare of the teaching staff.

Fluid mechanics of facial masks as personal protection equipment (PPE) of COVID-19 virus.

A fluid mechanics model of inhaled air gases, nitrogen (N2) and oxygen (O2) gases, and exhaled gas components (CO2 and water vapor particles) through a facial mask (membrane) to shield the COVID-19 virus is established. The model was developed based on several gas flux contributions that normally take place through membranes. Semiempirical solutions of the mathematical model were predicted for the N95 facial mask accounting on several parameters, such as a range of porosity size (i.e., 1-30 nm), void fraction (i.e., 10-3%-0.3%), and thickness of the membrane (i.e., 10-40 µm) in comparison to the size of the COVID-19 virus. A unitless number (Nr) was introduced for the first time to describe semiempirical solutions of O2, N2, and CO2 gases through the porous membrane. An optimum Nr of expressing the flow of the inhaled air gases, O2 and N2, through the porous membrane was determined (NO2 = NN2 = -4.4) when an N95 facial mask of specifications of a = 20 nm, l = 30 µm, and ε = 30% was used as a personal protection equipment (PPE). The concept of the optimum number Nr can be standardized not only for testing commercially available facial masks as PPEs but also for designing new masks for protecting humans from the COVID-19 virus.