A magnetic nozzle calculation of the force on a plasma

The measured axial force imparted from a magnetically expanding current-free plasma has been shown recently [Takahashi, Phys. Rev. Lett. 107, 235001 (2011)] to equal the axial force on that plasma calculated by a two-dimensional fluid model. Here, we calculate the same axial force on the plasma by a quasi one-dimensional model of a magnetic nozzle. The quasi one-dimensional magnetic nozzle model provides us with an estimate of the force on the plasma that is similar to that found by the more accurate two-dimensional model.This research has been partially supported by the Israel Science Foundation (Grants 864/07 and 765/11)

Measurement of the energy distribution of trapped and free electrons in a current-free double layer

In the high potential plasma, upstream of the double layer, the measuredelectron energy distribution function(EEDF) shows a very clear change in slope at energies (εbreak) corresponding to the double layer potential drop. Electrons with lower energy are Maxwellian with a temperature of 8eV, whereas those with higher energy have a temperature of 5eV. The EEDF in the downstream plasma has a temperature of 5eV. Over the range of pressures wherein the double layer and accelerated ion beam are detected by analysis of a retarding field energy analyzer, the strength of the double layer corresponds to the energy where the slope changes in the EEDF(εbreak). We deduce that the downstream electrons come from upstream electrons that have sufficient energy to overcome the potential of the double layer, and that only a single upstream plasma source is required to maintain this phenomenon.This work was supported by Tohoku University 21st COE program, System Construction of GlobalNetwork Oriented Information Electronics, and by the Japan Society for the Promotion of Science for Young Scientists. It was also supported by a Visiting Fellowship of the Research School of Physical Sciences and Engineering

Comorbidity in context: Part 1. Medical considerations around HIV and tuberculosis during the COVID-19 pandemic in South Africa

Infectious diseases pandemics have devastating health, social and economic consequences, especially in developing countries such as South Africa. Scarce medical resources must often be rationed effectively to contain the disease outbreak. In the case of COVID-19, even the best-resourced countries will have inadequate intensive care facilities for the large number of patients needing admission and ventilation. The scarcity of medical resources creates the need for national governments to establish admission criteria that are evidence-based and fair. Questions have been raised whether infection with HIV or tuberculosis (TB) may amplify the risk of adverse COVID-19 outcomes and therefore whether these conditions should be factored in when deciding on the rationing of intensive care facilities. In light of these questions, clinical evidence regarding inclusion of these infections as comorbidities relevant to intensive care unit admission triage criteria is investigated in the first of a two-part series of articles. There is currently no evidence to indicate that HIV or TB infection on their own predispose to an increased risk of infection with SARS-CoV-2 or worse outcomes for COVID-19. It is recommended that, as for other medical conditions, validated scoring systems for poor prognostic factors should be applied. A subsequent article examines the ethicolegal implications of limiting intensive care access of persons living with HIV or TB

Comorbidity in context: Part 2. Ethicolegal considerations around HIV and tuberculosis during the COVID-19 pandemic in South Africa

The COVID-19 pandemic has brought discussions around the appropriate and fair rationing of scare resources to the forefront. This is of special importance in a country such as South Africa (SA), where scarce resources interface with high levels of need. A large proportion of the SA population has risk factors associated with worse COVID-19 outcomes. Many people are also potentially medically and socially vulnerable secondary to the high levels of infection with HIV and tuberculosis (TB) in the country. This is the second of two articles. The first examined the clinical evidence regarding the inclusion of HIV and TB as comorbidities relevant to intensive care unit (ICU) admission triage criteria. Given the fact that patients with HIV or TB may potentially be excluded from admission to an ICU on the basis of an assumption of lack of clinical suitability for critical care, in this article we explore the ethicolegal implications of limiting ICU access of persons living with HIV or TB. We argue that all allocation and rationing decisions must be in terms of SA law, which prohibits unfair discrimination. In addition, ethical decision-making demands accurate and evidence-based strategies for the fair distribution of limited resources. Rationing decisions and processes should be fair and based on visible and consistent criteria that can be subjected to objective scrutiny, with the ultimate aim of ensuring accountability, equity and fairness