Aim To improve the dissolution rate and bioavailability of silybin. Methods Sustained-release silybin microspheres were prepared by the spherical crystallization technique with soliddispersing and release-retarding po...Aim To improve the dissolution rate and bioavailability of silybin. Methods Sustained-release silybin microspheres were prepared by the spherical crystallization technique with soliddispersing and release-retarding polymers. A differential scanning calorimeter and an X-ray diffractometer were used to investigate the dispersion state of silybin in the microspheres. The shape, surface morphology, and internal structure of the microspheres were observed using a scanning electron microscope. Characterization of the microspheres, such as average diameter, size distribution and bulk density of the microspheres was investigated. Results The particle size of the microspheres was determined mainly by the agitation speed. The dissolution rate of silybin from microspheres was enhanced by increasing the amount of the dispersing agents, and sustained by the retarding agents. The release rate of microspheres was controlled by adjusting the combination ratio of the dispersing agents to the retarding agents. The resuits of X-ray diffraction and differential scanning calorimetry analysis indicated that silybin was highly dispersed in the microspheres in amorphous state. The release profiles and content did not change after a three-month accelerated stability test at 40 ℃ and 75% relative humidity. Conclusion Sustained-release silybin microspheres with a solid dispersion structure were prepared successfully in one step by a spherical crystallization technique combined with solid dispersion technique. The preparation process is simple, reproducible and inexpensive. The method is efficient for designing sustained-release microspheres with water-insoluble drugs.展开更多
The microstructure formation and grains refinement of two Mg-based alloys,i.e.AZ31 and AZ91D,were reported using an electromagnetic vibration(EMV) technique.These two alloys were solidified at various vibration freque...The microstructure formation and grains refinement of two Mg-based alloys,i.e.AZ31 and AZ91D,were reported using an electromagnetic vibration(EMV) technique.These two alloys were solidified at various vibration frequencies and the microstructures were observed.The average size of grains was quantitatively measured as a function of vibration frequencies. Moreover,the grain size distribution was outlined versus number fraction.A novel model was proposed to account for the microstructure formation and grain refinement when considering the significant difference of the electrical resistivity properties of the solid and the liquid during EMV processing in the semisolid state.The remarkable difference originates uncoupled movement between the mobile solid and the sluggish liquid,which can activate melt flow.The microstructure evolution can be well explained when the fluid flow intensity versus vibration frequency is taken into account.Moreover,the influence of the static magnetic field on texture formation is also considered,which plays an important role at higher vibration frequencies.展开更多
Efficiency and power loss in the microelectronic devices is a major issue in power electronics applications. The engineers are challenged every year to increase power density and at the same time reduce the amount of ...Efficiency and power loss in the microelectronic devices is a major issue in power electronics applications. The engineers are challenged every year to increase power density and at the same time reduce the amount of power dissipated in the applications to keep the maximum temperatures under specifications. This situation drives a constant demand for better efficiencies in smaller packages. Traditional approaches to improve efficiency in DC/DC synchronous buck converters include reducing conduction losses in the MOSFETs （metal oxide semiconductor field effect transistors） through lower RDS （ON） （resistance drain to source in the ON state） devices and lowering switching losses through low-frequency operation. However, the incremental improvements in RDS （ON） are at a point of diminishing returns and low RDS （ON） devices have large parasitic capacitances that do not facilitate the high-frequency operation required to improve power density. The drive for higher efficiency and increased power in smaller packages is being addressed by advancements in both silicon and packaging technologies. The NexFET power block combines these two technologies to achieve higher levels of performance, and in half the space versus discrete MOSFETs. This article explains these new technologies and highlights their performance advantage.展开更多
The DS(directional solidification) polycrystalline silicon ingot is the most important photovoltaic material today,and the conversion efficiency of solar cells is affected by the morphology and organization of the cry...The DS(directional solidification) polycrystalline silicon ingot is the most important photovoltaic material today,and the conversion efficiency of solar cells is affected by the morphology and organization of the crystal.Uniform grains with larger size are conducive to get high-quality wafer,so improving the cell conversion efficiency.However,grains sizes that are less than 1 mm2 can be observed frequently in the central district of mc-Si ingots,which bring negative effect to the quality of the mc-Si ingot and decrease the electrical performance of wafer.In this paper,we make an attempt to explain the formation mechanism and influence factors of microcrystal in mc-Si ingot with computer simulation technology and theory of component supercooling.It was found that:to avoid production of microcrystal,it's better to increase the value of G/V(V is the growth rate and G is the near-interface temperature gradient),strengthen the melt convection front in the solidification interface and keep a fairly flat solid/melt interface in producing mc-Si ingot.展开更多
The investigation of multi-crystalline silicon （mc-Si） surface etching technology is a key point in solar cell research. In this paper, mc-Si surface was etched in the common alkaline solution modified by an additiv...The investigation of multi-crystalline silicon （mc-Si） surface etching technology is a key point in solar cell research. In this paper, mc-Si surface was etched in the common alkaline solution modified by an additive for 20 minutes at 78-80~C. Samples＇ surface morphology was observed by scanning electron microscope （SEM）. It is firstly found that the etched mc-Si surface has the uniform distribution of trap pits although the morphologies of trap pits are slightly different on different crystallographic planes. Si （100） plane was covered with many small Si-mountaln ranges or long V-shape channels arranged in a crisscross pat- tern. For （110） plane and （111） plane, they were full of a lot of triangle pit-traps （or quadrilateral holes） and twisted earthworm trap pits, respectively. The measured reflectance of the sample was 20.5% at wavelength range of 400--900 nm. These results illustrate that alkaline solution modified by an additive can effectively etch out trap pits with a good trapping light effect on mc-Si surfaces. This method should be very valuable for mc-Si solar cells.展开更多
文摘Aim To improve the dissolution rate and bioavailability of silybin. Methods Sustained-release silybin microspheres were prepared by the spherical crystallization technique with soliddispersing and release-retarding polymers. A differential scanning calorimeter and an X-ray diffractometer were used to investigate the dispersion state of silybin in the microspheres. The shape, surface morphology, and internal structure of the microspheres were observed using a scanning electron microscope. Characterization of the microspheres, such as average diameter, size distribution and bulk density of the microspheres was investigated. Results The particle size of the microspheres was determined mainly by the agitation speed. The dissolution rate of silybin from microspheres was enhanced by increasing the amount of the dispersing agents, and sustained by the retarding agents. The release rate of microspheres was controlled by adjusting the combination ratio of the dispersing agents to the retarding agents. The resuits of X-ray diffraction and differential scanning calorimetry analysis indicated that silybin was highly dispersed in the microspheres in amorphous state. The release profiles and content did not change after a three-month accelerated stability test at 40 ℃ and 75% relative humidity. Conclusion Sustained-release silybin microspheres with a solid dispersion structure were prepared successfully in one step by a spherical crystallization technique combined with solid dispersion technique. The preparation process is simple, reproducible and inexpensive. The method is efficient for designing sustained-release microspheres with water-insoluble drugs.
文摘The microstructure formation and grains refinement of two Mg-based alloys,i.e.AZ31 and AZ91D,were reported using an electromagnetic vibration(EMV) technique.These two alloys were solidified at various vibration frequencies and the microstructures were observed.The average size of grains was quantitatively measured as a function of vibration frequencies. Moreover,the grain size distribution was outlined versus number fraction.A novel model was proposed to account for the microstructure formation and grain refinement when considering the significant difference of the electrical resistivity properties of the solid and the liquid during EMV processing in the semisolid state.The remarkable difference originates uncoupled movement between the mobile solid and the sluggish liquid,which can activate melt flow.The microstructure evolution can be well explained when the fluid flow intensity versus vibration frequency is taken into account.Moreover,the influence of the static magnetic field on texture formation is also considered,which plays an important role at higher vibration frequencies.
文摘Efficiency and power loss in the microelectronic devices is a major issue in power electronics applications. The engineers are challenged every year to increase power density and at the same time reduce the amount of power dissipated in the applications to keep the maximum temperatures under specifications. This situation drives a constant demand for better efficiencies in smaller packages. Traditional approaches to improve efficiency in DC/DC synchronous buck converters include reducing conduction losses in the MOSFETs （metal oxide semiconductor field effect transistors） through lower RDS （ON） （resistance drain to source in the ON state） devices and lowering switching losses through low-frequency operation. However, the incremental improvements in RDS （ON） are at a point of diminishing returns and low RDS （ON） devices have large parasitic capacitances that do not facilitate the high-frequency operation required to improve power density. The drive for higher efficiency and increased power in smaller packages is being addressed by advancements in both silicon and packaging technologies. The NexFET power block combines these two technologies to achieve higher levels of performance, and in half the space versus discrete MOSFETs. This article explains these new technologies and highlights their performance advantage.
基金supported by the Natural Science Foundation of Jiangsu Province of China (Grant No BK2008548)
文摘The DS(directional solidification) polycrystalline silicon ingot is the most important photovoltaic material today,and the conversion efficiency of solar cells is affected by the morphology and organization of the crystal.Uniform grains with larger size are conducive to get high-quality wafer,so improving the cell conversion efficiency.However,grains sizes that are less than 1 mm2 can be observed frequently in the central district of mc-Si ingots,which bring negative effect to the quality of the mc-Si ingot and decrease the electrical performance of wafer.In this paper,we make an attempt to explain the formation mechanism and influence factors of microcrystal in mc-Si ingot with computer simulation technology and theory of component supercooling.It was found that:to avoid production of microcrystal,it's better to increase the value of G/V(V is the growth rate and G is the near-interface temperature gradient),strengthen the melt convection front in the solidification interface and keep a fairly flat solid/melt interface in producing mc-Si ingot.
基金supported by the Shanghai Aerospace Foundation (Grant No. GC072003)
文摘The investigation of multi-crystalline silicon （mc-Si） surface etching technology is a key point in solar cell research. In this paper, mc-Si surface was etched in the common alkaline solution modified by an additive for 20 minutes at 78-80~C. Samples＇ surface morphology was observed by scanning electron microscope （SEM）. It is firstly found that the etched mc-Si surface has the uniform distribution of trap pits although the morphologies of trap pits are slightly different on different crystallographic planes. Si （100） plane was covered with many small Si-mountaln ranges or long V-shape channels arranged in a crisscross pat- tern. For （110） plane and （111） plane, they were full of a lot of triangle pit-traps （or quadrilateral holes） and twisted earthworm trap pits, respectively. The measured reflectance of the sample was 20.5% at wavelength range of 400--900 nm. These results illustrate that alkaline solution modified by an additive can effectively etch out trap pits with a good trapping light effect on mc-Si surfaces. This method should be very valuable for mc-Si solar cells.
