科研成果 by Year: 2012

Studies on the macroscopic and microscopic packing properties of nonconvex particles are scarce. As a common concave form, the curved spherocylinder is used in the simulations, and its bending and elongation effects on the random packings are investigated numerically with sphere assembly models and a relaxation algorithm. The aspect ratio is demonstrated to be the main factor regarding the packing density. However, at certain aspect ratios of low densities around 0.3–0.4, the density of curved spherocylinders may increase by 15% more than that of the straight ones, indicating that bending is also a contributor to the packing density. The excluded volume of the curved spherocylinder decreases with the increase of the bending angle, indicating that the excluded volume is applicable in explaining the bending effect on the packing density variation of nonconvex particles. The packings are verified to be randomly distributed in orientation with no significant layering or in-plane order. The local arrangements are further analyzed from the radial distribution function and contact results. The results show that the random packings of nonconvex particles have significant differences and richer characteristics on both the macroscopic and microscopic properties compared with convex objects.

We explore the feasibility of accelerating electron beams up to energies much beyond 1 TeV in a realistic scale and evolution of the beam qualities such as emittance and energy spread at the final beam energy on the order of 100 TeV, using the newly formulated coupled equations describing the beam dynamics and radiative damping of electrons. As an example, we present a design for a 100 TeV laser-plasma accelerator in the operating plasma density n(p) = 10(15) cm(-3) and numerical solutions for evolution of the normalized emittance as well as their analytical solutions. We show that the betatron radiative damping causes very small normalized emittance that promises future applications for the high-energy frontier physics.

The fine particles serving as cloud condensation nuclei in pristine Amazonian rainforest air consist mostly of secondary organic aerosol. Their origin is enigmatic, however, because new particle formation in the atmosphere is not observed. Here, we show that the growth of organic aerosol particles can be initiated by potassium-salt-rich particles emitted by biota in the rainforest. These particles act as seeds for the condensation of low- or semi-volatile organic compounds from the atmospheric gas phase or multiphase oxidation of isoprene and terpenes. Our findings suggest that the primary emission of biogenic salt particles directly influences the number concentration of cloud condensation nuclei and affects the microphysics of cloud formation and precipitation over the rainforest.

A novel biodegradable polymer composed of PHBV and PLA was prepared for advanced wastewater treatment. It could serve as both biofilm carrier and carbon source for denitrification. Results of batch test showed the average denitrification rate was 0.07 mg NO3-N/(g h). The kinetic study demonstrated that when nitrate concentration was above 10.00 mg/L, DOC could not be detected in the effluent. In continuous packed-bed reactor, the average nitrogen removal efficiency was 94.11%. Nitrite concentration throughout the experiment was below 0.15 mg/L. The formation of NH4-N was observed, though small. DOC released in the effluent did not exceed 16.00 mg/L in the whole process, and it finally dropped below 1.20 mg/L. (C) 2012 Elsevier Ltd. All rights reserved.

For sustainable geologic CO2 sequestration (GCS), it is important to understand the effects of temperature and CO2 pressure on mica’s dissolution and surface morphological changes under saline hydrothermal conditions. Batch experiments were conducted with biotite (Fe-end member mica) under conditions relevant to GCS sites (35–95 °C and 75–120 atm CO2), and 1 M NaCl solution was used to mimic the brine. With increasing temperature, a transition from incongruent to congruent dissolution of biotite was observed. The dissolution activation energy based on Si release was calculated to be 52 ± 5 kJ mol–1. By comparison with N2 experiments, we showed that CO2 injection greatly enhanced biotite’s dissolution and its surface morphology evolutions, such as crack formation and detachment of newly formed fibrous illite. For biotite’s dissolution and morphological evolutions, the pH effects of CO2 were differentiated from the effects of bicarbonate complexation and CO2 intercalation. Bicarbonate complexation effects on ion release from biotite were found to be minor under our experimental conditions. On the other hand, the CO2 molecules in brine could get into the biotite interlayer and cause enhanced swelling of the biotite interlayer and hence the observed promotion of biotite surface cracking. The cracking created more reactive surface area in contact with brine and thus enhanced the later ion release from biotite. These results provide new information for understanding CO2–brine–mica interactions in saline aquifers with varied temperatures and CO2 pressures, which can be useful for GCS site selection and operations.