Research Progress in Nonlinear Ultrasonic Testing for Early Damage in Metal Materials.

There are some limitations when conventional ultrasonic testing methods are used for testing early damage in metal parts. With the continuous development of acoustics and materials science, nonlinear ultrasonic nondestructive testing technology has been used for testing of early damage in metal materials. In order to better understand the basic theory and research progress of the nonlinear ultrasonic testing technology, the classical nonlinear ultrasonic theoretical models, including the dislocation monopole model, dislocation dipole model, precipitate-dislocation pinning model, and contact nonlinear ultrasonic theory-microcrack model, are analyzed in depth. This paper introduces the application and research progress of nonlinear ultrasonic detection technology, which is derived from different acoustic nonlinear effects, such as higher harmonic, wave mixing and modulation, sub-harmonic, resonance frequency spectrum analysis, and non-linear ultrasonic phased array imaging. The key technologies and problems are summarized to provide a reference for the further development and promotion of nonlinear ultrasonic non-destructive testing technology.

Patients having haemodialysis: physical activity and associated factors.

AIM: This paper is a report of a study exploring the physical activity status of Beijing patients having haemodialysis and its associated factors. BACKGROUND: Inactivity is widely regarded as a risk factor for the development and progression of chronic diseases. Patients having dialysis could obtain important health benefits by participating in a moderate amount of physical activity. METHODS: A cross-sectional survey using convenience sampling was conducted in 2008 at outpatient haemodialysis centres of two tertiary Peking University-affiliated hospitals. Physical activity status and health status were assessed using the International Physical Activity Questionnaire and the medical outcomes study Short Form 36-Item Questionnaire respectively. RESULT: The participants were 95 men and 92 women aged from 18 to 86 years (median 59 years). Transport-related walking and household work were the main types of physical activity. Median of metabolic equivalent-minutes/week was 1743.0 (0-13482.0); 26.7% of participants were inactive and 73.3% were minimally active or active. Factors associated with physical activity energy expenditure were age (rho = -0.334 P < 0.001), serum albumin concentration (rho = 0.155 P < 0.05), physical function (rho = 0.469 P < 0.001) and physical component summary (rho = 0.315 P < 0.001) scores on the Short Form 36-Item Questionnaire. CONCLUSION: Advice on exercise is needed for patients having haemodialysis, especially for young patients. Individualized physical activity programmes are strongly recommended for patients having haemodialysis, according to their physical capacity.