From numerical simulations,we study the generation of quasi-monoenergetic MeV proton beams from a laserilluminated funnel-like target.We show that,when passing through such a target,the laser beam can be focused and constricted within a cylindrical bore at the funnel apex from which proton beams are produced.Accompanied by a much-enhanced laser intensity,the proton beams experience more acceleration time than with normal funnel targets.Constriction from the cylinder bore,combined with an enhancement of a separated charge field from Al electrons,protons can attain higher energies up to several tens of MeV.At the same time,strong suppression of the transverse divergence of the laser and proton beams yields a localized,collimated,mono-energetic proton beam.
In this paper, we derive a universal function from a model based on statistical mechanics developed recently, and show that the function is well fitted to all the available experimental data which cannot be described by any function previously established. With the function predicting creep rate, it is unnecessary to consider which creep mechanism dominates the process, but only perform several experiments to determine the three constants in the function. It is expected that the new function would be widely used in industry in the future.
Based on a lognormal particle size distribution, this paper makes a model analysis on the polydispersity effects on the magnetization behaviour of diluted ferrofluids. Using a modified Langevin relationship for the lognormal dis- persion, it first performs reduced calculations without material parameters. From the results, it is extrapolated that for the ferrofluid of lognormal polydispersion, in comparison with the corresponding monodispersion, the saturation magnetization is enhanced higher by the particle size distribution. It also indicates that in an equivalent magnetic field, the lognormally polydispersed ferrofluid is magnetically saturated faster than the corresponding monodispersion. Along the theoretical extrapolations, the polydispersity effects are evaluated for a typical ferrofluid of magnetite, with a dispersity of σ = 0.20. The results indicate that the lognormal polydispersity leads to a slight increase of the saturation magnetization, but a noticeable increase of the speed to reach the saturation value in an equivalent magnetic field.
