The Relationship between Epidemiologic Factors and Usage Pattern of Hair Care Products in Korea.

BACKGROUND: For hair care products that are used almost everyday, it is important to estimate the cumulative dosage of long-term exposure and to assess the effects on the human body. Little data are available to evaluate actual daily usage in Asian populations. OBJECTIVE: Reliable exposure data for hair care products is essential to conduct safety assessments. METHODS: We evaluated the actual usage pattern and amounts by checking the daily log over a 2-week period, to obtain all the data regarding the participants' hair care preferences. And, statistical analyses were conducted to analyze the daily use amount (g/d) and daily usage per hair length (g/cm/d), and other variables by sex, age group, and hair oiliness. RESULTS: Throughout this study, we found that female users consumed significantly larger daily amounts of shampoo and rinse. Male groups used more hair gel and spray than female groups. Interestingly, all the hair care products studied scored higher levels of usage among men when calibrated per unit length. Koreans tend to use lesser amount of rinse although their hairs are usually thicker than the Western hairs. CONCLUSION: This study provides exposure information for commonly used hair care products, which will be useful for risk assessment purposes.

Long-time simulations of the Kelvin-Helmholtz instability using an adaptive vortex method.

The nonlinear evolution of an interface subject to a parallel shear flow is studied by the vortex sheet model. We perform long-time computations for the vortex sheet in density-stratified fluids by using the point vortex method and investigate late-time dynamics of the Kelvin-Helmholtz instability. We apply an adaptive point insertion procedure and a high-order shock-capturing scheme to the vortex method to handle the nonuniform distribution of point vortices and enhance the resolution. Our adaptive vortex method successfully simulates chaotically distorted interfaces of the Kelvin-Helmholtz instability with fine resolutions. The numerical results show that the Kelvin-Helmholtz instability evolves a secondary instability at a late time, distorting the internal rollup, and eventually develops to a disordered structure.