ABSTRACT
A bifurcation criterion for the transition from straight to oscillatory quasistatic crack propagation in an isotropic material is derived from the requirement of pure mode I stress fields at the crack tip (K_{II}=0) on the entire crack path, henceforth called global bifurcation criterion. For a small-amplitude sine-shaped crack path which is observed in experiments at the transition, it is shown to be sufficient to postulate K_{II}=0 only for two phases of the crack path instead, which simplifies calculations. By using the measured temperature fields to solve the thermoelastic problem of dipping a hot thin glass slab into cold water, critical wavelengths of the oscillating crack growth obtained with the derived global bifurcation criterion agree remarkably well with those observed in experiments by Ronsin and Perrin. It is also shown that local bifurcation criteria, which do not take into account K_{II}=0 on the entire crack path, lead to incorrect results for the oscillatory crack path instability.
ABSTRACT
416 people (females 82.7%) living in Ho Chi Minh city was studied about reasons of using private clinics in January 2005. Among them, 50.6% was from 30 to 39 years old. 74.5% was living in urban district 4; 6.7% in urban district 7 and 9.1% in urban district 1. 44% of them had health insurance and 56% had not. 9 reasons of out-working time surgery choosing are self control in time (69%), have no impact to work (66.3%), simple procedure (78.6%), thoughful welcome (78.8%), clear explanation on disease 78.8%, having right to discuss about disease and treatment (58.9%), free in choosing doctor (72.1%), mild disease (64.9%), affordable (76.4%). Older people had higher awareness in choosing doctor
