The microstructure, dielectric properties and chemical state of Ti element on BaTi_4O_9 (f)/(0.64 BaTi_4O_9-0.36BaPr_2Ti_4O_(12)) composites sample surface were characterized by X-ray diffraction (XRD), Transmission e...The microstructure, dielectric properties and chemical state of Ti element on BaTi_4O_9 (f)/(0.64 BaTi_4O_9-0.36BaPr_2Ti_4O_(12)) composites sample surface were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), LCR meter method and X-ray photoelectron spectroscopy (XPS). The results show that the system is composed of BaTi_4O_9 and BaPr_2Ti_4O_(12) two phases. Pr ions are distributed in the BaWi_4O_9 grains and the segregation of Pr ions was observed on the grain boundaries of BaTi_4O_9/BaTi_4O_9. The content of Ti^(3+) and Ti^(2+) decrease in the BPT system composites due to the addition of BaTi_4O_9 fibers, which improved the dielectric properties of the system. BPT10 sample with 10% BaTi_4O_9 fibers, has the best dielectric properties in the system, its ε_r = 64, tan δ= 1×10^(-4)(at 1 MHz) , and it may be a potential candidate for microwave dielectric ceramics.展开更多
Gas diffusion layers(GDLs)are an important component of polymer electrolyte membrane(PEM)fuel cells.They are around 100–400μm thick in typical fuel cell design,which contribute a considerable volume in fuel cell and...Gas diffusion layers(GDLs)are an important component of polymer electrolyte membrane(PEM)fuel cells.They are around 100–400μm thick in typical fuel cell design,which contribute a considerable volume in fuel cell and influence the stack’s volumetric power density.Thus,thin GDLs are considered a viable strategy to increase fuel cell power per volume,which is crucial to fuel cell automobile application.The impacts of the GDL physical processes on cell performance are investigated,with a focus on thin GDLs,through advanced three-dimensional(3-D)non-isothermal two-phase modeling.The 3-D model is based on the conservation equations for mass,momentum,heat,species(oxygen,hydrogen,water,etc.),electron,and proton,coupled with the electrochemical kinetics.It is found that thin GDLs can deteriorate oxygen starvation under the land,reducing local and overall cell performances.In addition,the temperature spatial variation in fuel cell increases when reducing GDL thickness,which can lead to dryout of local GDL and hence electrode in the cathode.For the 25μm thick GDL,the temperature variation can be as high as 17°C at 1.3 A/cm2,raising a major concern of local hot spot formation.Analysis is presented to explain a few important physical processes in GDLs,including the in-plane heat removal by GDL,vapor diffusion driven by temperature gradient,and gas flow in GDLs.The 3-D distributions of reactant and product species and temperature are disclosed,showing that advanced modeling is important to assist thin GDL design for fuel cells.展开更多
In the present study, dot-blot hybridization, serial dilution analysis and densitomctric scanning were used to detect amplification of proto- oncogenes including c-erbB2, c-myc, int-2 and c-Ha-ras in 104 paraffin-embe...In the present study, dot-blot hybridization, serial dilution analysis and densitomctric scanning were used to detect amplification of proto- oncogenes including c-erbB2, c-myc, int-2 and c-Ha-ras in 104 paraffin-embedded breast cancers. Expression of c-erbB2 was also examined by immunohistochemistry. Amplification of c-erbB2. c-myc and int-2 genes was found in 34.7%, 17.8% and 11.9% of breast cancers respectively. However amplification of c-Ha-ras was not detected in all cases. In 11.9% of cases co-amplification of two or more oncogenes was observed. Positive immunostain-ing of c-erbB2 was seen in 23.8% of the cases and it was significantly associated, but not always corresponding to the amplification of the gene. There was no difference between primary and metastatic breast cancer in the alterations of proto-oncogenes examined in this study, which suggested that the amplification and overexpression of these proto-oncogenes occured prior to and maintained in the process of metastasis of breast cancer. Statistical analysis showed that high-scale of immunopositive staining of c-erbB2 and high-fold co-amplification of proto-oncogenes were significantly correlated with large size of the tumour and the number of involved lymph nodes. Our results indicate that the alterations of multiple oncogenes are involved in the development of breats cancer and some of them may have prognostic importance for breast cancer patients.展开更多
文摘The microstructure, dielectric properties and chemical state of Ti element on BaTi_4O_9 (f)/(0.64 BaTi_4O_9-0.36BaPr_2Ti_4O_(12)) composites sample surface were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM), LCR meter method and X-ray photoelectron spectroscopy (XPS). The results show that the system is composed of BaTi_4O_9 and BaPr_2Ti_4O_(12) two phases. Pr ions are distributed in the BaWi_4O_9 grains and the segregation of Pr ions was observed on the grain boundaries of BaTi_4O_9/BaTi_4O_9. The content of Ti^(3+) and Ti^(2+) decrease in the BPT system composites due to the addition of BaTi_4O_9 fibers, which improved the dielectric properties of the system. BPT10 sample with 10% BaTi_4O_9 fibers, has the best dielectric properties in the system, its ε_r = 64, tan δ= 1×10^(-4)(at 1 MHz) , and it may be a potential candidate for microwave dielectric ceramics.
文摘Gas diffusion layers(GDLs)are an important component of polymer electrolyte membrane(PEM)fuel cells.They are around 100–400μm thick in typical fuel cell design,which contribute a considerable volume in fuel cell and influence the stack’s volumetric power density.Thus,thin GDLs are considered a viable strategy to increase fuel cell power per volume,which is crucial to fuel cell automobile application.The impacts of the GDL physical processes on cell performance are investigated,with a focus on thin GDLs,through advanced three-dimensional(3-D)non-isothermal two-phase modeling.The 3-D model is based on the conservation equations for mass,momentum,heat,species(oxygen,hydrogen,water,etc.),electron,and proton,coupled with the electrochemical kinetics.It is found that thin GDLs can deteriorate oxygen starvation under the land,reducing local and overall cell performances.In addition,the temperature spatial variation in fuel cell increases when reducing GDL thickness,which can lead to dryout of local GDL and hence electrode in the cathode.For the 25μm thick GDL,the temperature variation can be as high as 17°C at 1.3 A/cm2,raising a major concern of local hot spot formation.Analysis is presented to explain a few important physical processes in GDLs,including the in-plane heat removal by GDL,vapor diffusion driven by temperature gradient,and gas flow in GDLs.The 3-D distributions of reactant and product species and temperature are disclosed,showing that advanced modeling is important to assist thin GDL design for fuel cells.
文摘In the present study, dot-blot hybridization, serial dilution analysis and densitomctric scanning were used to detect amplification of proto- oncogenes including c-erbB2, c-myc, int-2 and c-Ha-ras in 104 paraffin-embedded breast cancers. Expression of c-erbB2 was also examined by immunohistochemistry. Amplification of c-erbB2. c-myc and int-2 genes was found in 34.7%, 17.8% and 11.9% of breast cancers respectively. However amplification of c-Ha-ras was not detected in all cases. In 11.9% of cases co-amplification of two or more oncogenes was observed. Positive immunostain-ing of c-erbB2 was seen in 23.8% of the cases and it was significantly associated, but not always corresponding to the amplification of the gene. There was no difference between primary and metastatic breast cancer in the alterations of proto-oncogenes examined in this study, which suggested that the amplification and overexpression of these proto-oncogenes occured prior to and maintained in the process of metastasis of breast cancer. Statistical analysis showed that high-scale of immunopositive staining of c-erbB2 and high-fold co-amplification of proto-oncogenes were significantly correlated with large size of the tumour and the number of involved lymph nodes. Our results indicate that the alterations of multiple oncogenes are involved in the development of breats cancer and some of them may have prognostic importance for breast cancer patients.
