Proton acceleration from picosecond-laser interaction with a hydrocarbon target

As an intense picosecond laser pulse irradiates a hydrocarbon target,the protons therein can be accelerated by the radiation pressure as well as the sheath field behind the target.We investigate the effect of the laser and hydrocarbon target parameters on proton acceleration with two/threedimensional particle-in-cell simulations.It is found that the resulting two-ion species plasma can generate a multiple peaked charge-separation field that accelerates the protons.In particular,a smaller carbon-to-hydrogen ratio,as well as the thinner and/or lower density of the target,leads to a larger sheath field and thus proton beams with a larger cutoff energy and smoother energy spectrum.These results may be useful in achieving high-flux quasi-monoenergetic proton beams by properly designing the hydrocarbon target.

A Low Complexity VCS Method for PAPR Reduction in Multicarrier Code Division Multiple Access

This paper investigates a peak to average power ratio （PAPR） reduction method in multicarrier code division multiple access （MC-CDMA） system. Variable code sets （VCS）, a spreading codes selection scheme, can improve the PAPR property of the MC-CDMA signals, but this technique requires an exhaustive search over the combinations of spreading code sets. It is observed that when the number of active users increases, the search complexity will increase exponentially. Based on this fact, we propose a low complexity VCS （LC-VCS） method to reduce the computational complexity. The basic idea of LC-VCS is to derive new signals using the relationship between candidature signals. Simulation results show that the proposed approach can reduce PAPR with lower comtational pucomplexity. In addition, it can be blindly received without any side information.

MODELING THE STRESS-STRAIN CURVES UNDER DYNAMIC RECRYSTALLIZATION

An analytical model for dynamic recrystallization (DRX) is studied based on the relative grain size model proposed by Sakai and Jonas, and the characteristic flow behaviors under DRX are analyzed and simulated. Introducing the variation of dynamic grain size and the heterogeneous distribution of disolo- cation densities densities under DRX,a simple method for modeling and simulating DRX processes is developed by using Laplace transformation theory. The results derived from the present model agree well with the experimental results in literatures. This simulation can reproduce a number of features in DRX flow behaviors, for example,single and multiple peak flow behaviors followed by a steady state flow, the transition between them, and so on.

Energy spectrum of multi-radiation of X-rays in a low energy Mather-type plasma focus device

The multi-radiation of X-rays was investigated with special attention to their energy spectrum in a Mather-type plasma focus device （operated with argon gas）. The analysis is based on the effect of anomalous resistances. To study the energy spectrum, a four-channel diode X-ray spectrometer was used along with a special set of filters. The filters were suitable for detection of medium range X-rays as well as hard X-rays with energy exceeding 30 keV. The results indicate that the anomalous resistivity effect during the post pinch phase may cause multi-radiation of X-rays with a total duration of 300 ± 50 ns. The significant contribution of Cu-Kα was due to the medium range X-rays, nonetheless, hard X-rays with energies greater than 15 keV also participate in the process. The total emitted X-ray energy in the forms of Cu-K and Cu-K/3 was around 0.14 ± 0.02 （J/Sr） and 0.04 ±0.01 （J/Sr）, respectively. The total energy of the emitted hard X-ray （〉 15 keV） was around 0.12± 0.02 （J/Sr）.

Numerical Investigation on the Flow Mechanism of Multi-Peak Frequency Feature of Rotating Instability

In this paper,the rotating instability(RI)in an axial compressor has been investigated numerically in order to examine the capability of URANS method to simulate its typical characteristics of RI broadband humps with multi-peak frequencies(MPFs)and further to uncover the underlying flow mechanism.A full-annulus modeling solution has been adopted to fully capture the wide range of different length-scale flow disturbances that circumferentially propagating around the compressor rotor.During the transient computing process,long-term monitoring up to 50 revolutions has been carried out to achieve a fine frequency resolution,and that would be essential for resolving the MPFs with small frequency interval.It is shown that the MPFs feature of RI has been successfully captured by the full-annulus URANS approach,and also its frequency range and spectral feature agree well with the experimental results.Further,with a circumferential mode decomposition on the MPFs characteristics of RI,it has been found that the MPFs result from the interaction between long-and short-scale flow disturbances which circumferentially propagate around the compressor rotor near the clearance region.zDetailed examination on the numerical three dimensional flow field indicates that the short-scale disturbance is induced by the unsteady oscillation of tip clearance vortexes with inter-passage phase delay.The long-scale disturbance is caused by the mistuning of the wave number of the short-scale disturbance and the blade number within the whole annulus.