科研成果

This paper reports that Coulomb explosions taken place in the experiment of heteronuclear deuterated methane clusters ((CD4)2) in a gas jet subjected to intense femtosecond laser pulses (170mJ, 70fs) have led to table-top laser driven DD nuclear fusion. The clusters produced in supersonic expansion had an average size of about 5nm in radius and the laser intensity used was 3×1017W/cm2.The measured maximum and average energies of deuterons produced in the laser--cluster interaction were 60 and 13.5keV, respectively. From DD collisions of energetic deuterons, a yield of 2.5(±0.4)×104 fusion neutrons of 2.45MeV per shot was realized, giving rise to a neutron production efficiency of about 1.5×105 per joule of incident laser pulse energy. Theoretical calculations were performed and a fairly good agreement of the calculated neutron yield with that obtained from the present experiment was found.

Simplicity of mesh generation and robustness against mesh entanglement during large deformations are key attractive features of particle based methods. These features can be exploited in number of engineering problems where traditional techniques suffer due to aforementioned limitations. Numerical modelling of particulate composites is one of such ideal engineering applications where particle based methods can be effectively used due to their simplicity and robustness. Complicated geometrical configurations of particulate composites obtained from techniques such as scanning electron microscopy (SEM) can be easily converted to particle based mesh without loosing much information. This enables more accurate analysis of the chosen composite materials. Therefore, a smooth particle hydrodynamics (SPH) based numerical technique is developed here to investigate the mechanical properties and evolution of debonding process in particulate composites. To perform the numerical study, a Lagrangian corrected SPH (CSPH) method is presented together with an appropriate numerical model for treating material interface discontinuity within the particulate composites. The material interface discontinuity is enforced using an innovative method which combines penalty formulation with a bilinear interface cohesive model for SPH method. The proposed SPH methodology is used in a number of numerical examples involving composite materials and related interface problems. The effect of penalty value on the interface model and of the smoothing length of the SPH method are also analysed during these simulations. The results illustrate the effectiveness, robustness and potential of the developed methodology. It is concluded that the proposed numerical techniques can be easily and effectively applied to simulate multi-phase composites with various interface conditions and, can provide useful information regarding the inherent mechanism of damage evolution and fracture of particulate or fibre reinforced composites. (C) 2009 Elsevier B.V. All rights reserved.

Simplicity of mesh generation and robustness against mesh entanglement during large deformations are key attractive features of particle based methods. These features can be exploited in number of engineering problems where traditional techniques suffer due to aforementioned limitations. Numerical modelling of particulate composites is one of such ideal engineering applications where particle based methods can be effectively used due to their simplicity and robustness. Complicated geometrical configurations of particulate composites obtained from techniques such as scanning electron microscopy (SEM) can be easily converted to particle based mesh without loosing much information. This enables more accurate analysis of the chosen composite materials. Therefore, a smooth particle hydrodynamics (SPH) based numerical technique is developed here to investigate the mechanical properties and evolution of debonding process in particulate composites. To perform the numerical study, a Lagrangian corrected SPH (CSPH) method is presented together with an appropriate numerical model for treating material interface discontinuity within the particulate composites. The material interface discontinuity is enforced using an innovative method which combines penalty formulation with a bilinear interface cohesive model for SPH method. The proposed SPH methodology is used in a number of numerical examples involving composite materials and related interface problems. The effect of penalty value on the interface model and of the smoothing length of the SPH method are also analysed during these simulations. The results illustrate the effectiveness, robustness and potential of the developed methodology. It is concluded that the proposed numerical techniques can be easily and effectively applied to simulate multi-phase composites with various interface conditions and, can provide useful information regarding the inherent mechanism of damage evolution and fracture of particulate or fibre reinforced composites. (C) 2009 Elsevier B.V. All rights reserved.

1-Chloro-2,2-bis(4-chlorophenyl)ethene(p,p'-DDMU),a metabolite of either 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane (pp'-DDD) or 1,1-dichloro-2,2-bis(4-chlorophenyl)ethene (p,p'-DDE), which is degraded from 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (p,p'-DDT), was detected in a variety of environmental matrices of the Pearl River Delta (PRD), South China, including fish, fish feeds, semidigested fish stomach contents, marine surface sediment, surface soil, atmospheric gaseous phase, and particulates, rainwater, and coastal rainwater. For fish species,the concentrations of p,p'-DDMU were significantly higher in farmed fish than in marine wild fish, with the highest value obtained in seawater farmed fish species (mean/median values of 262/173 ng/g lipid). The relative abundance of p,p'-DDMU to total DDTs (sum of o,p'-and p,p'-DDT, DDD, and DDE) was higher in samples of marine origin (similar to 5%) than in those of terrestrial origin (similar to 2%). Because p,p'-DDD was considerably abundant in all samples and a negative linear correlation was found between p,p'-DDD/(p,p'-DDD + p,p'-DDE) and p,p'-DDMU/DDTs in the marine sediments (r(2) = 0.73) and seawater farmed fish (r(2) = 0.29) under investigation, it is possible that DDMU was partially dehydrochlorinated from DDD in the environment of the PRD. A fugacity-based assessment suggested that p,p'-DDMU is likely to transport from sediment to seawater and then to air and from soil to air. The ubiquity of p,p'-DDMU in the PRD indicates that it may also be widespread worldwide particularly in countries with large amounts of DDT used currently and/or historically. Given the potential risk of p,p'-DDMU to human health, more efforts should be directed toward to this previously overlooked contaminant.