We investigate the Landau-Zener tunnelling of two-component Bose-Einstein condensates （BECs） in optical lattices. In the neighborhood of the Brillouin zone edge, the system can be reduced to two coupled nonlinear tw...We investigate the Landau-Zener tunnelling of two-component Bose-Einstein condensates （BECs） in optical lattices. In the neighborhood of the Brillouin zone edge, the system can be reduced to two coupled nonlinear two-level models. From the models, we calculate the change of the tunnelling probability for each component with the linear sweeping rate. It is found that the probability for each component exhibits regular oscillating behavior for the larger sweeping rate, but for smaller rate the oscillation is irregular. Moreover, the asymmetry of the tunnelling between the two components can be induced by the unbalanced initial populations or the inequality of the two self-interactions when the cross-interaction between the components exists. The result can not be found in the single component BECs.展开更多
Microwave sintering is being developed as a novel technique for the preparation of dense structural ceramics,but the mature theory has not been established due to the technical difficulties.The synchrotron radiation X...Microwave sintering is being developed as a novel technique for the preparation of dense structural ceramics,but the mature theory has not been established due to the technical difficulties.The synchrotron radiation X-ray computed tomography(SR-CT) technique was introduced for the first time into the study of microwave sintering to in-situ observe the microstructure evolution of silicon carbide(SiC) material in this paper.By applying the SR-CT technique,the reconstructed 2D and 3D images of the specimen were obtained and the double logarithm curve of mean neck size and time(Ln(x)-Ln(t)) were obtained from these reconstructed images.Various sintering phenomena including sintering neck growth during microwave treatment were observed from the reconstructed images.Furthermore,the differences in microstructure evolution and sintering kinetics between microwave and conventional sintering were analyzed based on the reconstructed images and the Ln(x)-Ln(t) curve.1) The sharp surface of grains near the contact region distinctly grew blunt and the sintering neck growth between these grains were obviously observed at the early stage.Besides,the larger particles grew faster than smaller ones.The main reason for these phenomena may be the micro-focusing effect of electric fields.2) During each of the three sintering stages,the sintering kinetics curve of double logarithm relationship between mean neck size and time shows a good linear relationship,but at the middle stage the slope of the curve increases dramatically,which is quite larger than conventional sintering.The preliminary interpretation for these extraordinary phenomena has been discussed in details.展开更多
基金Supported by Natural Science Foundation of Shaanxi University of Science and Technology under Grant No.SUST-ZX08-27
文摘We investigate the Landau-Zener tunnelling of two-component Bose-Einstein condensates （BECs） in optical lattices. In the neighborhood of the Brillouin zone edge, the system can be reduced to two coupled nonlinear two-level models. From the models, we calculate the change of the tunnelling probability for each component with the linear sweeping rate. It is found that the probability for each component exhibits regular oscillating behavior for the larger sweeping rate, but for smaller rate the oscillation is irregular. Moreover, the asymmetry of the tunnelling between the two components can be induced by the unbalanced initial populations or the inequality of the two self-interactions when the cross-interaction between the components exists. The result can not be found in the single component BECs.
基金supported by the National Natural Science Foundation of China (Grant Nos 10902108, 10732080, 10872190)the National Basic Research Program of China ("973" Project) (Grant No 2007CB936800)
文摘Microwave sintering is being developed as a novel technique for the preparation of dense structural ceramics,but the mature theory has not been established due to the technical difficulties.The synchrotron radiation X-ray computed tomography(SR-CT) technique was introduced for the first time into the study of microwave sintering to in-situ observe the microstructure evolution of silicon carbide(SiC) material in this paper.By applying the SR-CT technique,the reconstructed 2D and 3D images of the specimen were obtained and the double logarithm curve of mean neck size and time(Ln(x)-Ln(t)) were obtained from these reconstructed images.Various sintering phenomena including sintering neck growth during microwave treatment were observed from the reconstructed images.Furthermore,the differences in microstructure evolution and sintering kinetics between microwave and conventional sintering were analyzed based on the reconstructed images and the Ln(x)-Ln(t) curve.1) The sharp surface of grains near the contact region distinctly grew blunt and the sintering neck growth between these grains were obviously observed at the early stage.Besides,the larger particles grew faster than smaller ones.The main reason for these phenomena may be the micro-focusing effect of electric fields.2) During each of the three sintering stages,the sintering kinetics curve of double logarithm relationship between mean neck size and time shows a good linear relationship,but at the middle stage the slope of the curve increases dramatically,which is quite larger than conventional sintering.The preliminary interpretation for these extraordinary phenomena has been discussed in details.
