Viscous heating has a substantial influence on the extrusion forming process and product quality of powder materials.This study selected the MUZL420 ring die pellet mill as the research object,from which a 3D flow phy...Viscous heating has a substantial influence on the extrusion forming process and product quality of powder materials.This study selected the MUZL420 ring die pellet mill as the research object,from which a 3D flow physical model was established.The numerical simulation of 3D nonisothermal flow in the extrusion pelletizing process of granulated alfalfa was performed with POLYFLOW.The distribution laws of pressure,velocity,shear rate,viscosity,viscous heating and temperature in the flow field were revealed to thoroughly investigate the pelletizing process and provide a reference for structural optimization and process control.The results showed that two extrusion zones in the pelleting chamber were symmetrical with respect to the center,and the significant pressure gradient along the rotating direction of the ring die and the roller caused the material to flow back in the opposite direction.There were larger velocity gradients,shear rates and viscous heating levels in the deformation and compaction zone,the negative pressure zone behind the extrusion zone and the die holes.The distribution of viscosity was opposite to that of the shear rate.The temperature increase area caused by viscous heating gradually expanded from the material inlet to the bottom of the extrusion chamber along the Z-axis direction,and the temperature increased accordingly.The extrusion force and the forming temperature in the extrusion forming zone were captured in the numerical simulation.The extrusion forming density was calculated with the regression prediction model established through the simulation experiment of pelletizing with a ring die.Through a comparison with the results of mean alfalfa pellet density from the ring die pellet mill experiment,the relative error was less than 5%,which indicated that the numerical simulation method was reliable.展开更多
Aim: To evaluate the effects of 60 Hz extremely low frequency (ELF) elelctromagnetic field (EMF) exposure on germ cell apoptosis in the testis of mice. Methods: Adult male BALB/c mice (7 weeks of age) were exposed to ...Aim: To evaluate the effects of 60 Hz extremely low frequency (ELF) elelctromagnetic field (EMF) exposure on germ cell apoptosis in the testis of mice. Methods: Adult male BALB/c mice (7 weeks of age) were exposed to a 60 Hz EMF of 0.1 mT or 0.5 mT for 24 h/day. A sham-exposed group served as the control. After 8 weeks of exposure, the mice were sacrificed. Germ cell apoptosis in the testis was assessed by histopathological examination, the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling assay (TUNEL) and flow cytometric examination of isolated spermatogenic cells stained with 7 aminoactinomycin D (7-AAD). Results: EMF exposure did not significantly affect the body and testis weights, but significantly increased the incidence of germ cell death. The distinguishing morphological feature of EMF exposure was a decrement in the number of well organized seminiferous tubules. Quantitative analysis of TUNEL-positive germ cells showed a significantly higher apoptotic rate in the 0.5 mT exposed mice than that in the sham controls (P<0.05), while the difference between the two exposed groups was insignificant. The TUNEL-positive cells were mainly spermatogonia. In flow cytometry analysis, the percentage of live cells [forward scatter count (FSC)high7-AAD-] was lower in the exposed groups than that in the controls (Figure 5A), but the decrease in viability was not statistically significant. Conclusion: Continuous exposure to ELF EMF may induce testicular germ cell apoptosis in mice.展开更多
基金funded by the National Natural Science Foundation of China(NSFC)(51365002)the Gansu Agricultural University Youth Tutor Foundation(GAUQNDS-201204).
文摘Viscous heating has a substantial influence on the extrusion forming process and product quality of powder materials.This study selected the MUZL420 ring die pellet mill as the research object,from which a 3D flow physical model was established.The numerical simulation of 3D nonisothermal flow in the extrusion pelletizing process of granulated alfalfa was performed with POLYFLOW.The distribution laws of pressure,velocity,shear rate,viscosity,viscous heating and temperature in the flow field were revealed to thoroughly investigate the pelletizing process and provide a reference for structural optimization and process control.The results showed that two extrusion zones in the pelleting chamber were symmetrical with respect to the center,and the significant pressure gradient along the rotating direction of the ring die and the roller caused the material to flow back in the opposite direction.There were larger velocity gradients,shear rates and viscous heating levels in the deformation and compaction zone,the negative pressure zone behind the extrusion zone and the die holes.The distribution of viscosity was opposite to that of the shear rate.The temperature increase area caused by viscous heating gradually expanded from the material inlet to the bottom of the extrusion chamber along the Z-axis direction,and the temperature increased accordingly.The extrusion force and the forming temperature in the extrusion forming zone were captured in the numerical simulation.The extrusion forming density was calculated with the regression prediction model established through the simulation experiment of pelletizing with a ring die.Through a comparison with the results of mean alfalfa pellet density from the ring die pellet mill experiment,the relative error was less than 5%,which indicated that the numerical simulation method was reliable.
文摘Aim: To evaluate the effects of 60 Hz extremely low frequency (ELF) elelctromagnetic field (EMF) exposure on germ cell apoptosis in the testis of mice. Methods: Adult male BALB/c mice (7 weeks of age) were exposed to a 60 Hz EMF of 0.1 mT or 0.5 mT for 24 h/day. A sham-exposed group served as the control. After 8 weeks of exposure, the mice were sacrificed. Germ cell apoptosis in the testis was assessed by histopathological examination, the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling assay (TUNEL) and flow cytometric examination of isolated spermatogenic cells stained with 7 aminoactinomycin D (7-AAD). Results: EMF exposure did not significantly affect the body and testis weights, but significantly increased the incidence of germ cell death. The distinguishing morphological feature of EMF exposure was a decrement in the number of well organized seminiferous tubules. Quantitative analysis of TUNEL-positive germ cells showed a significantly higher apoptotic rate in the 0.5 mT exposed mice than that in the sham controls (P<0.05), while the difference between the two exposed groups was insignificant. The TUNEL-positive cells were mainly spermatogonia. In flow cytometry analysis, the percentage of live cells [forward scatter count (FSC)high7-AAD-] was lower in the exposed groups than that in the controls (Figure 5A), but the decrease in viability was not statistically significant. Conclusion: Continuous exposure to ELF EMF may induce testicular germ cell apoptosis in mice.
