ABSTRACT
The surface interaction between substrates and block copolymers is one of the most important factors that control the alignment of self-assembled domains under thin film confinement. Most previous studies simply modeled substrates modified by grafting polymers as a hard wall with a specified surface energy, leading to an incomplete understanding of the role of grafted polymers. In this study, we propose a general model of surface interactions where the role of grafted polymers is decomposed into two independent contributions: the surface preference and the surface softness. Based on this model, we perform a numerical analysis of the stability competition between perpendicular and parallel lamellae of symmetric diblock copolymers on substrates modified by homopolymers using self-consistent field theory. The effects of the surface preference and the surface softness on the alignment of lamellar domains are carefully examined. A phase diagram of the alignment in the plane of the surface preference parameter and the surface softness parameter is constructed, which reveals a considerable parameter window for preparing stable perpendicular lamellae even on highly preferential substrates.
ABSTRACT
OBJECTIVE: To study the human immunodeficiency virus (HIV) status through heterosexual transmission in Yining city and to provide information on effective intervention measures. METHODS: Cohort of HIV sero-discordant couples identified from 1997 to 2000 was formed. Proportional risk model was used to analyze the time of HIV sero-conversion and the related factors. All the recruiters were under informed consent. RESULTS: Through following on 22 sero-discordant couples, we found that the incidence density (ID) of HIV sero-conversion was 32.49/100 person-year (PY) with 33.74/100 PY for women. In the proportional hazard model, the course of sero-conversion was only 2.43 years and the frequency of sexual contact was statistically significant (>or= 3 times/week vs. < 3 time/week: RR = 1.984, 95% CI: 1.045 - 3.767), indicating this factor was related to the hazard of HIV sero-conversion. However, the viral load of HIV infections has no such effect on HIV sero-conversion of their spouses. In addition, the ratio of CD4(+)/CD8(+) was lower in spouses of HIV sero-conversion than that in spouses of HIV non-sero conversion (t test: t = 4.77, P < 0.01). CONCLUSION: In order to control HIV transmission among general population, we suggested that HIV/AIDS counseling and testing be developed for pre-marital people in the region with high HIV prevalence.
