Molecular dynamics study of the nucleation behavior and lamellar mergence in polyethylene globule crystallization

The site order parameter (SOP) has been adopted to analyze various orders of structure formation and distribution during the crystallization of a polyethylene globule simulated by molecular dynamics. The SOP not only identifies different orders among the structures but also different phases. The results showed that intermediate structures with medium order exist unevenly in the early stage of nucleation, which differs from traditional models. We found that the nucleation relies on crystallinity fluctuations with increasing amplitude, and a baby nucleus with different shape and increasing size suddenly appears in the fluctuations. Once its size is large enough, the baby nucleus becomes the nucleus. In the growth stage, a number of lamellar mergences were observed and their selective behaviors were related to the orientation differences between the lamellae to be merged. The SOP distribution of all atoms in the system during crystallization had two peaks: one for the amorphous phase and the other for the crystalline phase. The intermediate structures with medium orders are located between the two peaks as an order promotion pathway. The data show that the medium order structure fluctuates at the growth front and is not always available, and that the medium order structure existing at the front is not always good for development. It is possibly caused by chain entanglement. Structure fluctuation at the growth front enables the system showing thousands of the most probable configurations to approach the precursor. The growth front is thus active for a while and inactive at other times.

The Korean Mergence

More South Koreans are heading to China for better lives and business and academic

The brief introduction of China International Water and Electric Corporation(CWE)

China International Water and Electric Cor-poration (CWE) was formed by mergence offormer Hydraulic Engineering Corporation ofChina (HECC) and former China NationalComplete Plant Export Corporation ElectricEngineering Company (CEEC) on August 4,1983.It has a history of more than 30 years inundertaking hydraulic and electric engineeringprojects counted from the beginning of its formerbodies.The corporation has 600 staff members.Under the corporation,there are 2 branches and15 oversea organizations.CWE possesses acapital fund of 500 million Yuan RMB.CWE is a national corporation establishedspecially for economic and technical coopera-tion with foreign countries and contracting hy-draulic and electric engineering projects andother civil engineering projects abroad.Themain business lines are as follows:1.contracting hydraulic,electric and

A randomized double-blind multicenter study on comparing levonorgestrel and mifepristone for emergency contraception

Objective: To compare the efficacy and side effects of levonorgestrel and low dose mifepristone in emergency contraception. Method: The study is a randomized double--blind multicenter comparative trial. A total of 1, 276 women with unprotected intercourse within 72 hours were allocated to one of the two study groups. In the levonorgestrel (LNG) group, 0. 75 mg LNG was taken twice, 12 hours apart, whereas in the mifepristone (Mife) group, a single dose of 10 mg mifepristone was taken and a placebo 12 hours after. Follow--up visit was paid on the seventh day of the expected next menstruation to evaluate the contraceptive efficacy and side effects. Contraceptive efficacy was calculated by Dixon’s method. Result:In the LNG group 20 pregnancies occurred among 643 women, while in the Mife group 9 pregnancies occurred among 633 women. The pregnancy rates were 3. 10% and 1. 43% respectively. Contraceptive efficacy rate of preventing pregnancy was 59. 16% and 79. 73%, the difference was statistically significant (P<O. 05). The incidence of various side effects, which were mild, was less than 10%. There was no statistical difference between the two groups. The percentage of subjects who had their next menstruation 3 days earlier or later than their expected menstruation in LNG group and Mife group was 77. 7% and 78. 5% respectively. Conclusion: Use of levonorgestrel or low dose mifepristone for emergency contraception is effective and safe.

Study on the Interaction of Non-axisymmetric Binary Vortices

In the context of advection dynamics, 19 experiments （Exps.） are performed using a quasi-geostrophic barotropic vorticity equation model to explore the condition for the mergence of binary vortices and the self-organization of the larger scale vortex. Results show that the initial distance between the centers of binary vortices and the non-axisymmetric distributions of their initial vorticity are two factors affecting the mergence of binary vortices. There is a critical distance for the mergence of initial symmetric binary vortices, however, the mergence of initial non-axisymmetric binary vortices is also affected by the asymmetric structure of initial vortices. The self-organization processes in 19 experiments can be classified into two types： one is the merging of identical, axisymmetric binary vortices in which the interaction of the two vortices undergoes slowly change, rapid change, and the formation, stretching, and development of the filaments of vorticity, and the two vortices merge into a symmetric vortex, with its vorticity piled up in the inner region coming from the two initial vortices, and the vorticity of the spiral band in the outer region from the stretching of the filaments of the two initial vortices. And the other type is the merging of the two non-axisymmetric initial vortices of an elliptic vortex and an eccentric vortex in which the elliptic vortex, on the one hand, mutually rotates, and on the other hand moves towards the center of the computational domain, at the same time expands its vorticity area, and at last forms the inner core of resultant state vortex; and the eccentric vortex mutually rotates, meanwhile continuously stretches, and finally forms the spiral band of resultant state vortex. The interaction process is characteristic of the vorticity piled up in the inner core region of resultant state vortex originating from the elliptic vortex and the vorticity in spiral band mainly from the successive stretch and rupture of the eccentric vortex.