We investigate collision characteristics of micro-sized particles (diameter less than 100 microns) via numerical simulations and experiments. Discrete element method (DEM) simulations, based on improved hard-sphere model, are performed to explore effect of initial velocity, surface energy, size, mass concentration, and wind speed on cohesive collisions and non-cohesive collisions between micro-sized particles. Aggregation and settlement process are considered as well. It is found that simulated cohesive collision rate agrees with experimental results of self-settlement of micro-sized particles.

In large eddy simulations (LES), a flat ground model and rough wedge ground models with different wedge heights were adopted to investigate near-surface wind field characteristics under condition of time-varying upstream inflows. In both flat ground model and rough wedge ground models, simulated results show that there is downdraft in peak period of gusty wind and updraft in valley period, respectively. Intensity of downdraft/updraft flows are related to ground roughness in upwind areas and amplitude of inflows. It follows that wind velocity and direction in atmospheric boundary layer always change over time in time-varying upstream inflows, which enhances transportation of mass and energy in actual atmospheric boundary layer.

Dose coefficients for external photon radiation are widely used for assessment of radiation dose to public and workers due to ground surface contamination and air immersion of radionuclides released in nuclear accidents. Dose coefficients based on Chinese reference voxel phantom were presented. Photons that incident into the cylinder, which is slightly larger than phantom, is simulated using Geant4, including distributions of angle, height and energy of photons; Secondly, photons are sampled on surface of cylinder around Chinese Reference Male/Female Voxel Phantom with MCNPX 2.4.k from the above source, dose coefficients of 20 initial gamma ray energies, from 15keV to 10 MeV, are calculated. Thirdly, dose coefficients of 68 important nuclides are evaluated by combining of decay data from ICRP 107 and photon coefficients using cubic-spline fitting. GB/T 17982-2000 shows an overestimation for ground contamination while an underestimation of high Z nuclides for air immersion compared to our results.

We simulate radiation effects of solar cosmic protons on spacecraft and satellites with a Monte Carlo software GEANT4.Damage induced by proton irradiation and shielding of Al layer are calculated.Linear energy transfer and range in materials agree well with referenced data. Energy deposited in incident direction shows a Bragg curve and nonelastic interactions show important impact.In Si recoil atoms are mainly distributed along incident proton trajectory and isolated recoils distribute along lateral direction with lower concentration. Al shielding layer shows a shielding on high energetic protons.Shielding is hardly changed as layer thickness is larger than 10mm.On the contrary,secondary production increases obviously.

Photoelectron outgoing wave emitted from core state of excited atom will be scattered by near neighbor atoms.Scattered waves (object waves) which contain structural information of the environment around the excited atom interfere with the original one(reference wave)which propagates directly to the detector,and then a diffraction pattern,i.e.a photoelectron hologram,will be created.A complete 3 D image of the structure surrounding the emitter with at omic resolution can be reconstructed.This paper gives computer simulation for ca lculat ing photoelectron holograms of small atomic clusters on c(2×2) S/Ni(100) surface,in metal copper,and on puckered Cu2O plane of superconductor YBCO.

It investigates the application of solid crystallization process in the optimization algorithm.A special way is also proposed for the parameter "stirring" for the target function to get minimum value of the target function in the whole parameters' region.Meanwhile,the optimization algorithm is independent on the initial value of parameters without the larger calculation time.