Biodegradability and thermal stability of poly(propylene carbonate)/starch composites.

Poly(propylene carbonate)/starch (PPC/starch) composites with different starch contents were prepared by melt compounding. The biodegradability of the composites was studied by soil burial for a period of 6 months. FTIR study, thermal analysis and morphology observation indicated clearly the changes of the buried specimens. The weight loss curves and the molecular weight changes of the specimens revealed a three-stage biodegradation, corresponding to the propagation of microorganisms, the degradation of starch and the degradation of PPC. The experimental results showed that the addition of starch accelerated the degradation of PPC. Specimens with higher starch content exhibited greater weight loss in the second stage and smaller weight loss in the third stage.

Phase dependence of relativistic electron dynamics and emission spectra in the superposition of an ultraintense laser field and a strong uniform magnetic field.

The phase dependence of the dynamics and emission spectra of a fully relativistic electron in the superposition of an ultraintense plane wave laser field and a strong uniform magnetic field has been investigated. It is found that the effect of changing the initial laser phase is quite different for circularly and linearly polarized laser fields. For circular polarization only the axis of the helical trajectory is changed with variation of the initial laser field phase. However, for linear polarization, the effect of changing the initial phase is opposite in the two parameter regions divided by the resonance condition r=1 (r stands for the ratio between the reduced cyclotron frequency and laser frequency). When r<1, with increase in the initial laser field phase eta(0) from 0 to pi/2, both the radius of the electron's helical trajectory and the height of the peak related to the uniform magnetic field are decreased, and these two physical values are increased with an increase in the laser initial phase when r>1. The phase dependence of the electron's energy and velocity components was also studied. Some beat structure is found when eta(0)=0 and this structure is absent when eta(0)=pi/2.