Constructing a Space from the System of Geodesic Equations

Given a space it is easy to obtain the system of geodesic equations on it. In this paper the inverse problem of reconstructing the space from the geodesic equations is addressed. A procedure is developed for obtaining the metric tensor from the Christoffel symbols. The procedure is extended for determining if a second order quadratically semi-linear system can be expressed as a system of geodesic equations, provided it has terms only quadratic in the first derivative apart from the second derivative term. A computer code has been developed for dealing with larger systems of geodesic equations

Friction in metal-on-metal total disc arthroplasty: effect of ball radius

Total Disc Arthroplasty (TDA) can be used to replace a degenerated intervertebral disc in the spine. There are different designs of prosthetic discs, but one of the most common is a ball-and-socket combination. Contact between the bearing surfaces can result in high frictional torque, which can then result in wear and implant loosening. This study was designed to determine the effects of ball radius on friction. Generic models of metal-on-metal TDA were manufactured with ball radii of 10, 12, 14 and 16 mm, with a radial clearance of 0.015 mm. A simulator was used to test each sample in flexion-extension, lateral bending and axial rotation at frequencies of 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75 and 2 Hz under loads of 50, 600, 1200 and 2000 N, in new born calf serum. Frictional torque was measured and Stribeck curves were plotted to illustrate the lubrication regime in each case. It was observed that implants with a smaller ball radius showed lower friction and showed boundary and mixed lubrication regimes, whereas implants with larger ball radius showed boundary lubrication only. This study suggests designing metal-on-metal TDAs with ball radius of 10 or 12 mm, in order to reduce wear and implant loosening

Conditional linearizability criteria for a system of third-order ordinary differential equations

We provide linearizability criteria for a class of systems of third-order ordinary differential equations (ODEs) that is cubically semi-linear in the first derivative, by differentiating a system of second-order quadratically semi-linear ODEs and using the original system to replace the second derivative. The procedure developed splits into two cases, those where the coefficients are constant and those where they are variables. Both cases are discussed and examples given

Biobank research: Time for discussion and debate

The establishment of biobanks is gaining prominence globally. The open and evolving nature of biobanks has profound ethical, legal and social implications for individual and group autonomy, informed consent, privacy, confidentiality, secondary use of samples and data over time, return of results, data sharing, benefit sharing with communities, and premature or unplanned closure. Complexities also emerge  because of increasing international collaborations, and differing national positions. Public consultation and involvement are very necessary to the success of biobanks. Implementing national laws in an internationally consistent manner is problematic

Biobank research: Time for discussion and debate

The establishment of biobanks is gaining prominence globally. The open and evolving nature of biobanks has profound ethical, legal and social implications for individual and group autonomy, informed consent, privacy, confidentiality, secondary use of samples and data over time, return of results, data sharing, benefit sharing with communities, and premature or unplanned closure. Complexities also emerge because of increasing international collaborations, and differing national positions. Public consultation and involvement are very necessary to the success of biobanks. Implementing national laws in an internationally consistent manner is problematic

Nurses at risk for occupationally acquired blood-borne virus infection at a South African academic hospital

Aim. We aimed to ascertain if there had been any improvement in thenumber of nurses being immunised against hepatitis B virus (HBV) infection in a large academic hospital in which, 10 years previously,only 30.6% of the nurses were immune to infection with the virus,and to ascertain the incidence of infection with hepatitis C virus(HCV) and human immunodeficiency virus (HIV) in these nurses.Methods. We studied 170 predominantly black nurses.Their blood was tested for the presence of active or past HBVinfection using appropriate immunoassays, HCV infection bychromatographic immunoassays confirmed by polymerase chainreaction assays, and HIV using a rapid test confirmed by enzymelinkedimmunosorbent assays.Results. Serum of 89 (52.4%) nurses was positive for hepatitisB surface antibody (anti-HBs). Of these nurses 18 said that theyhad not received the vaccine; the serum of 9 of these was positivefor anti-hepatitis B core antibody (anti-HBc) as well as anti-HBs,indicating natural infection with the virus. Of the nurses positivefor anti-HBs, 89 were tested for anti-HBc; 28.2% tested positive foranti-HBc. Three nurses gave dates of immunisation that fell outsideof their nursing careers; 3 (1.8%) were actively infected with thevirus; 2 (1.8%) were infected with HCV; 10 nurses (5.9%) werepositive for HIV.Conclusion. Nurses at this academic hospital remain at high riskof work-related HBV infection