Epidemic reproduction numbers and herd immunity

In this educational article, we explore the meanings and the applications of the reproductive numbers, namely the basic reproductive number R0, and the effective reproductive number R. We also give examples of how these numbers may be affected by the values of β, κ and D, and we go on to explore the relationship of the R0 value to the concept of herd immunity. Finally, we discuss how these concepts may contribute to the control of infectious disease outbreaks.http://www.samj.org.za/index.php/samjam2021School of Health Systems and Public Health (SHSPH

$p+^{4,6,8}He elastic scattering at intermediate energies

Using a relativistic nuclear optical potential consisting of a Lorentz scalar, $V_{s}$, and the time-like component of a four-vector potential, $V_{0}$, we calculate elastic scattering differential cross sections and polarizations for $p+^{4}$He at intermediate energies for which experimental data are available. We also calculate the differential cross sections and analyzing powers for $p+^{6,8}$He at intermediate energies and compare with the few available experimental data.Comment: 09 pages, 04 figure

Parametric hypothesis tests for the difference between two population means

When one wishes to perform a statistical-hypothesis test, the first important step is to select the correct, most appropriate, test to perform. This article aims, firstly, to outline the test-selection criteria when one wishes to obtain statistical evidence about the equality of population means. Thereafter, Stata statistical software (StataCorp, USA) commands will be given for the various tests. If the population means of interest are numerical and have known probability-sampling distributions, then the standard recommended statistical-hypothesis test, with data from samples, is either the classic t-test, or a variant of it. In this article, the first part concentrates on the selection of the appropriate test to perform when using sample data to determine whether two population means are likely to differ. The selection criteria/steps are illustrated by a diagram (Fig. 1). The second part describes how to perform the tests using Stata. In that section, some Stata output is also presented, and the interpretation of the output is explained.http://www.shsjournal.org/index.php/shsjam2018School of Health Systems and Public Health (SHSPH

Comparison of exact and approximate cross-sections in relativistic Coulomb excitation

We present a new method of obtaining time-dependent matrix elements of the electromagnetic pulse produced by a highly-relativistic projectile. These matrix elements are used in a coupled-channel calculation to predict the cross-sections for population of 1- and 2-phonon states of the giant dipole resonance. Comparisons are made with the predictions of the long-wavelength and Born approximations.Comment: 26 pages, LaTex2

D' Production in Heavy Ion Collisions

The production of d' dibaryons in heavy ion collisions due to the elementary process NN -> d' + pion is considered. The cross section NN -> d' + pion is estimated using the vacuum d' width = 0.5 MeV extracted from data on the double charge exchange reactions on nuclei. The d' production rate per single collision of heavy ions is estimated at an incident beam energy of 1 A GeV within the framework of the Quantum Molecular Dynamics transport model. We suggest to analyse the invariant mass spectrum of the NN + pion system in order to search for an abundance of events with the invariant mass of the d' dibaryon. The d' peak is found to exceed the statistical fluctuations of the background at a level of 6 standard deviations for 2 10^5 A central collisions of heavy ions with the atomic number A.Comment: 29 pages including 7 figures, REVTe

Temperature dependence of the Casimir effect between metallic mirrors

We calculate the Casimir force and free energy for plane metallic mirrors at non-zero temperature. Numerical evaluations are given with temperature and conductivity effects treated simultaneously. The results are compared with the approximation where both effects are treated independently and the corrections simply multiplied. The deviation between the exact and approximated results takes the form of a temperature dependent function for which an analytical expression is given. The knowledge of this function allows simple and accurate estimations at the % level.Comment: 8 pages, 4 figures, uses RevTe

Screening programmes and the evaluation of screening tests using Stata and R

This article describes the commonly recognised criteria for establishing a mass screening programme. In addition, the article describes commonly used parameters for assessing the performance of public health screening tests. The calculation of the parameters is described. Stata commands, and R code, are also supplied to assist readers with the estimation of these parameters using Stata or R. This article does not include the evaluation of diagnostic tests.http://www.shsjournal.org/index.php/shsjam2020School of Health Systems and Public Health (SHSPH

Effects of friction on cosmic strings

We study the evolution of cosmic strings taking into account the frictional force due to the surrounding radiation. We consider small perturbations on straight strings, oscillation of circular loops and small perturbations on circular loops. For straight strings, friction exponentially suppresses perturbations whose co-moving scale crosses the horizon before cosmological time $t_*\sim \mu^{-2}$ (in Planck units), where $\mu$ is the string tension. Loops with size much smaller than $t_*$ will be approximately circular at the time when they start the relativistic collapse. We investigate the possibility that such loops will form black holes. We find that the number of black holes which are formed through this process is well bellow present observational limits, so this does not give any lower or upper bounds on $\mu$. We also consider the case of straight strings attached to walls and circular holes that can spontaneously nucleate on metastable domain walls.Comment: 32 pages, TUTP-93-

The impact of the South African antiretroviral treatment programme on the age-standardised incidence rate of Kaposi sarcoma, 1999-2016 : an interrupted time series analysis

OBJECTIVE : The objective of this study was to quantify the impact of the South African antiretroviral treatment programme on the age-standardised incidence rate of Kaposi sarcoma among black South African residents of all ages. METHODS : We performed an interrupted time series analysis using routinely collected, histologically confirmed surveillance data from the South African National Cancer Registry for the years 1999 to 2016. The analysis was performed using R statistical software. The total number of cases was 29,623 (12,475 females and 17,166 males). The background antiretroviral treatment coverage was less than 1% at the time that the antiretroviral programme was introduced and increased to over 50% in 2016. RESULTS : In 1999, the age-standardised rates were 1.48 and 2.82 cases per 100,000 per year for black females and males, respectively. These rates increased to 5.52 and 7.46 in 2008 before declining. The antiretroviral treatment programme was started in 2004. Five years after 2008 (nine years after the antiretroviral programme was introduced), the predicted standardised rates were 58.3% and 50.3% lower for females and males, respectively, than what they would have been without the treatment programme. CONCLUSION : Introduction of the antiretroviral treatment programme was associated with a decrease of over 50% in the predicted age-standardised incidence rates of Kaposi sarcoma. © 2020 The Authors. Published by Elsevier Ltd on behalf of International Society for Infectious Diseases.www.elsevier.com/locate/ijidam2022School of Health Systems and Public Health (SHSPH