Practical method for the determination of time step in non-orthogonal FDTD

The Non-Orthogonal FDTD algorithm is well-suited to the modelling of curved structures, however users of the technique frequently have difficulty determining an appropriate time step for the algorithm. This contribution presents a new method which is shown to be both a practical and reliable technique for determining the time step

Quantifying numerical dispersion in non-orthogonal FDTD meshes

Numerical electromagnetic models such as FDTD are widely used for the design and analysis of structures, including antennas. Numerical dispersion is one of the main sources of error that degrade the accuracy of the results-for each structure of interest, the users of the model must attempt to generate a mesh that will avoid introducing high levels of dispersion. This is, however, especially difficult for non-orthogonal meshes since little information is available on the dispersion properties of the non-orthogonal FDTD algorithm on complex meshes. For the first time, the dispersion in realistic non-orthogonal FDTD models of microstrip structures is quantified directly through numerical simulations. A test structure is considered, discretised using a number of nonorthogonal mesh configurations, including single and multiple skew angles. A numerical analysis of reflections generated at the transition between two mesh regions with different skew angles is also presented. These results give a practical guide to mesh generation for users of the algorith

Modelling metallic discontinuities with the non-orthogonal finite difference time domain method

Numerical electromagnetic models, such as the finite difference time domain (FDTD) method, have many applications. The authors focus on the non-orthogonal FDTD method, which offers an improved geometric flexibility compared to other standard techniques. Results from numerical electromagnetic analysis methods, such as the FDTD method, are often degraded by an error known as numerical dispersion. For metallic structures this dispersion error is often higher than expected from theoretical considerations. The source of this additional error is due to the reciprocal field interpolation scheme used in the non-orthogonal FDTD algorithm. The error is illustrated by means of a microstrip waveguide and a microstrip antenna. Techniques for reducing this error are evaluated; careful construction of the mesh at the metallic boundary being the most reliable solution

How children access antiretroviral treatment at Kgapane District Hospital, Limpopo, South Africa

Background: At Kgapane Hospital, Limpopo Province, only 20% of eligible children initiated antiretroviral treatment (ART) in 2007. The aim of this study was to improve the ART programme by assessing how children were accessing ART, and to explore the factors that facilitate or obstruct this access.Method: Mixed methods were used in a descriptive study of human immunodeficiency virus (HIV)-infected children admitted to the hospital over a seven-month period and their caregivers. Children’s subsequent attendance for ART was tracked and caregivers were interviewed about factors influencing access and attendance.Results: Of 132 children initially admitted, 14 (10.6%) subsequently died and 13 (9.8%) relocated. Sixty of the remaining 105 (57.1%) returned within one month to the antiretroviral clinic, three (2.9%) attended later and 42 (40.0%) did not return at all. Quantitative data associated with poor attendance were younger age, higher CD4 count, maternal caregiver, no income and participation in the prevention of mother-to-child transmission program. Qualitative factors included a lack of money for transport, poor social support, and mothers who struggled to accept their diagnosis, had poor understanding of HIV and strong traditional beliefs. Primary care providers delayed HIV testing and referral, displayed poor attitudes, and were insufficient in number. Quantitative factors significantly associated with good attendance were prior knowledge of the child/mother’s HIV status, mother’s ART treatment and referral to the dietician.Conclusion: There are serious deficiencies in the prevention, diagnosis and treatment of HIV in children. Factors were identified to improve health services and these highlight the need for broader strategies aimed at addressing poverty, stigma and education

Reply to Justin D’Arms

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43371/1/11098_2005_Article_2319.pd

The Right Wrong‐Makers

Right- and wrong-making features ("moral grounds") are widely believed to play important normative roles, e.g. in morally apt or virtuous motivation. This paper argues that moral grounds have been systematically misidentified. Canonical statements of our moral theories tend to summarize, rather than directly state, the full range of moral grounds posited by the theory. Further work is required to "unpack" a theory's criterion of rightness and identify the features that are of ground-level moral significance. As a result, it is not actually true that maximizing value is the relevant right-making feature even for maximizing consequentialists. Focusing on the simple example of utilitarianism, I show how careful attention to the ground level can drastically influence how we think about our moral theories