Breather lattice and its stabilization for the modified Korteweg-de Vries equation

We obtain an exact solution for the breather lattice solution of the modified Korteweg-de Vries (MKdV) equation. Numerical simulation of the breather lattice demonstrates its instability due to the breather-breather interaction. However, such multi-breather structures can be stabilized through the concurrent application of ac driving and viscous damping terms.Comment: 6 pages, 3 figures, Phys. Rev. E (in press

Excitation and Propagation of Negative-Potential Solitons in an Electronegative Plasma

The excitation, propagation, and interaction of planar negative-potential solitary waves in a plasma containing positive ions, negative ions, and electrons (i.e., an electronegative plasma) are studied using a hybrid simulation with kinetic, particle ions, and Boltzmann electrons. Solitary waves are launched into the plasma when the potential on an initially unbiased electrode is stepped downward. They then propagate self-consistently through the ambient plasma. Results are shown for excitation and propagation as well as for overtaking collisions. During overtaking collisions, the solitons preserve their shape and speed, though they are not necessarily described by the Korteweg-deVries theory. These solitons may provide a useful diagnostic of the negative ion concentration in electronegative plasmas

Excitation of Ion Acoustic Solitons from Grids

Using a particle-in-cell code, we are able to simulate the excitation of ion acoustic solitons from a grid whose potential is suddenly increased. The numerical results are in substantial agreement with previous laboratory experiments

Modelling the risk-benefit impact of H1N1 influenza vaccines

BACKGROUND: Shortly after the H1N1 influenza virus reached pandemic status in June 2009, the benefit-risk project team at the European Medicines Agency recognized this presented a research opportunity for testing the usefulness of a decision analysis model in deliberations about approving vaccines soon based on limited data or waiting for more data. Undertaken purely as a research exercise, the model was not connected to the ongoing assessment by the European Medicines Agency, which approved the H1N1 vaccines on 25 September 2009. METHODS: A decision tree model constructed initially on 1 September 2009, and slightly revised subsequently as new data were obtained, represented an end-of-September or end-of-October approval of vaccines. The model showed combinations of uncertain events, the severity of the disease and the vaccines' efficacy and safety, leading to estimates of numbers of deaths and serious disabilities. The group based their probability assessments on available information and background knowledge about vaccines and similar pandemics in the past. RESULTS: Weighting the numbers by their joint probabilities for all paths through the decision tree gave a weighted average for a September decision of 216 500 deaths and serious disabilities, and for a decision delayed to October of 291 547, showing that an early decision was preferable. CONCLUSIONS: The process of constructing the model facilitated communications among the group's members and led to new insights for several participants, while its robustness built confidence in the decision. These findings suggest that models might be helpful to regulators, as they form their preferences during the process of deliberation and debate, and more generally, for public health issues when decision makers face considerable uncertainty