a Public health classicsThis section looks back on a ground-breaking contribution to public health, reproduces an extract of the original text and adds a commentary on its significance from a modern perspective. To complement the theme of this month's issue, John R Williams looks at the Declaration of Helsinki and how it has evolved over time. The original declaration is reproduced here in full with permission of the World Medical Association.

Over the last two decades, lattice Boltzmann methods have become an increasingly popular tool to compute the flow in complex geometries such as porous media. In addition to single phase simulations allowing, for example, a precise quantification of the permeability of a porous sample, a number of extensions to the lattice Boltzmann method are available which allow to study multiphase and multicomponent flows on a pore scale level. In this article, we give an extensive overview on a number of these diffuse interface models and discuss their advantages and disadvantages. Furthermore, we shortly report on multiphase flows containing solid particles, as well as implementation details and optimization issues.

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Results of capacitance-voltage measurements are reported for metal-oxide-semiconductor capacitors fabricated using the 4H polytype of silicon carbide doped with either nitrogen ͑n͒ or aluminum ͑p͒. Annealing in nitric oxide after a standard oxidation/reoxidation process results in a slight increase in the defect state density in the lower portion of the band gap for p-SiC and a significant decrease in the density of states in the upper half of the gap for n-SiC. Theoretical calculations provide an explanation for these results in terms of N passivating C and C clusters at the oxide-semiconductor interface.

BackgroundPatterns of person-to-person contacts relevant for infectious diseases transmission are still poorly quantified in Sub-Saharan Africa (SSA), where socio-demographic structures and behavioral attitudes are expected to be different from those of more developed countries.Methods and FindingsWe conducted a diary-based survey on daily contacts and time-use of individuals of different ages in one rural and one peri-urban site of Manicaland, Zimbabwe. A total of 2,490 diaries were collected and used to derive age-structured contact matrices, to analyze time spent by individuals in different settings, and to identify the key determinants of individuals’ mixing patterns. Overall 10.8 contacts per person/day were reported, with a significant difference between the peri-urban and the rural site (11.6 versus 10.2). A strong age-assortativeness characterized contacts of school-aged children, whereas the high proportion of extended families and the young population age-structure led to a significant intergenerational mixing at older ages. Individuals spent on average 67% of daytime at home, 2% at work, and 9% at school. Active participation in school and work resulted the key drivers of the number of contacts and, similarly, household size, class size, and time spent at work influenced the number of home, school, and work contacts, respectively. We found that the heterogeneous nature of home contacts is critical for an epidemic transmission chain. In particular, our results suggest that, during the initial phase of an epidemic, about 50% of infections are expected to occur among individuals younger than 12 years and less than 20% among individuals older than 35 years.ConclusionsWith the current work, we have gathered data and information on the ways through which individuals in SSA interact, and on the factors that mostly facilitate this interaction. Monitoring these processes is critical to realistically predict the effects of interventions on infectious diseases dynamics.

A modified Deal Grove model for the oxidation of 4H-SiC is presented, which includes the removal of the carbon species. The model is applied to data on the oxidation rates for the (0001) Si, (0001̄) C, and (112̄0) a faces, which are performed in 1 atm dry oxygen and in the temperature range 950–1150 °C. Analysis within the model provides a physical explanation for the large crystal-face dependent oxidation rates observed.

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The specific contact resistance of an ohmic contact will be discussed including ways to calculate and measure this parameter. Ohmic contacts to n‐ and p‐type hexagonal SiC will then be detailed. Low resistance n‐type ohmic contacts are predominately fabricated by annealing a refractory metal, thereby forming a silicide with a lowered Schottky barrier height at the metal–SiC interface. P‐type contacts on the other hand generally use Al or Al alloys which upon annealing enable Al to diffuse into the SiC thus resulting in ohmic properties. Aluminium alloys however suffer from many problems which will be discussed. Other novel contacting schemes to p‐type SiC will also be reviewed.