Nanoindentation tests were conducted to investigate the near-surface mechanical properties of the individual components(fiber and matrix) for three-dimensional reinforced carbon/carbon composites(3D C/C).Optical micro...Nanoindentation tests were conducted to investigate the near-surface mechanical properties of the individual components(fiber and matrix) for three-dimensional reinforced carbon/carbon composites(3D C/C).Optical microscope and polarizing light microscope were used to characterize the microstructure of 3D C/C.The microscopy results show that large number of pores and cracks exist at both bundle/matrix interface and pitch carbon matrix.These defects have important effect on the mechanical behavior of 3D C/C.The in situ properties for components of 3D C/C were acquired by nanoindentation technique.Relative to the matrix sample,the fiber samples have more larger values for modulus,stiffness and hardness.However,there is no significant difference of modulus and stiffness among fiber samples with different directions.展开更多
The resolution characteristic of GaAs/GaAlAs transmission photocathode is an important parameter in third generation intensifiers. The modulation transfer function of GaAs/GaAlAs transmission photo...The resolution characteristic of GaAs/GaAlAs transmission photocathode is an important parameter in third generation intensifiers. The modulation transfer function of GaAs/GaAlAs transmission photocathode is derived from a simple two-dimensional diffusion equation. The theoretical resolution characteristic of a 2 μm thick GaAs/GaAlAs transmission photocathode is calculated. The relationship between resolution and parameters in GaAs/GaAlAs transmission photocathode is discussed. A conclusion is shown that one can design the GaAs/GaAlAs transmission photocathode for maximum quantum efficiency, since the sacrifice in the resolution doesn't limit system performances.展开更多
Polyelectrolyte becomes more and more popular in electrocatalysis.The understanding of electrode/polyelectrolyte interfaces at the molecular level is important for guiding further the polyelectrolyte-based electrocata...Polyelectrolyte becomes more and more popular in electrocatalysis.The understanding of electrode/polyelectrolyte interfaces at the molecular level is important for guiding further the polyelectrolyte-based electrocatalysis.Herein,we demonstrate an in-situ surface-enhanced Raman spectroscopic method by using a three-electrode spectroelectrochemical cell towards characterizing the electrode/polyelectrolyte interfaces.The Ag/AgCl and Ag/Ag_(2)O electrodes are used as the reference electrode in the acidic and the alkaline systems,respectively.The working electrode is made of a transparent carbon thin film which loads the electrocatalysts.The applications of this method are demonstrated through the in-situ characterizations of the p-methylthiophenol adsorbed on the Au and Pt and the electrochemical oxidation of Au on polyelectrolyte membranes.The potential-dependent spectral features of these two systems show that this method is a powerful tool for investigating the electrode/polyelectrolyte interfaces in electrocatalysis.展开更多
A series of aromatic acids has been tested as additives for the platinum-catalyzed hydrosilylation of styrene with triethoxysilane. Both excellent conversion of styrene and selectivity in favor of the ,β-adduct were ...A series of aromatic acids has been tested as additives for the platinum-catalyzed hydrosilylation of styrene with triethoxysilane. Both excellent conversion of styrene and selectivity in favor of the ,β-adduct were achieved using aminobenzoic acids as additive. Moreover, the use of 4-aminobenzoic acid led to significantly superior enhancement in both catalytic activity and selectivity among the tested aminobenzoic acids. Indeed, 100% conversion of styrene and 98.4% selectivity in favor of the β-adduct were obtained. Additionally, hydrosilylations of various alkenes with a variety of platinum catalysts have also been tested, and in each case the conversion of substrate and the selectivity of the β-adduct were promoted by using 4-aminobenzoic acid as additive.展开更多
The potential of externally applied FRP （fiber-reinforced plastic） sheets, being employed in retrofitting schemes aimed to repair and strengthen RC （reinforced concrete） structural elements damaged by prototype st...The potential of externally applied FRP （fiber-reinforced plastic） sheets, being employed in retrofitting schemes aimed to repair and strengthen RC （reinforced concrete） structural elements damaged by prototype strong earthquakes, is presented and discussed in this study. The limitation of the debonding mode of failure of these FRP sheets is highlighted and the necessity to develop efficient anchoring devices for these FRP sheets is underlined. The behavior of such a novel HAD （hybrid anchoring device） capable of anchoring CFRP （carbon fiber reinforcing plastic） sheets to RC structural elements, is presented and discussed. The behavior of the device itself was studied through a 3D non-linear numerical simulation at the preliminary design stage in order to establish certain desired features such as the ductile behavior of the device itself as well as the satisfactory performance of the FRP sheets wrapped around this device. This HAD was next applied as part of a strengthening scheme aimed to upgrade the flexural capacity of an RC bridge-type pier specimen subjected to a cyclic seismic-type loading sequence. The obtained results demonstrated an increase in the specimen＇s flexural capacity by 100% as well as a similar increase in its capability of dissipating energy in a ductile manner during the cyclic load sequence. Moreover, the employed 3D non-linear numerical simulation yielded reasonably good agreement between the measured and the predicted cyclic response of this specimen strengthened by CFRP layers, which were anchored by the novel HAD. The successful behavior of this novel HAD, which has been patented with No. WO2011073696, is currently being tried with a number of other retrofitting schemes employing FRP sheets externally attached on RC structural elements.展开更多
Using nanosecond pulse near-infrared and mid-infrared laser pulses as the pump source, we obtain terahertz wave sources via four-wave difference frequency mixing. From the coupled wave theory, we analyze the four-wave...Using nanosecond pulse near-infrared and mid-infrared laser pulses as the pump source, we obtain terahertz wave sources via four-wave difference frequency mixing. From the coupled wave theory, we analyze the four-wave mixing process of GaSe crystal and alkali metal vapor in detail, get the analytical expression of terahertz wave output power, and discuss the conditions for achieving phase matching. By adjusting the pump frequency, the third-order nonlinear polarization of alkali metal vapor is resonance-enhanced. This program offers a new type of high-power terahertz radiation source.展开更多
基金Project(61391) supported by the National Security Basic Research Program of ChinaProject (91016029) supported by the National Natural Science Foundation of China
文摘Nanoindentation tests were conducted to investigate the near-surface mechanical properties of the individual components(fiber and matrix) for three-dimensional reinforced carbon/carbon composites(3D C/C).Optical microscope and polarizing light microscope were used to characterize the microstructure of 3D C/C.The microscopy results show that large number of pores and cracks exist at both bundle/matrix interface and pitch carbon matrix.These defects have important effect on the mechanical behavior of 3D C/C.The in situ properties for components of 3D C/C were acquired by nanoindentation technique.Relative to the matrix sample,the fiber samples have more larger values for modulus,stiffness and hardness.However,there is no significant difference of modulus and stiffness among fiber samples with different directions.
文摘The resolution characteristic of GaAs/GaAlAs transmission photocathode is an important parameter in third generation intensifiers. The modulation transfer function of GaAs/GaAlAs transmission photocathode is derived from a simple two-dimensional diffusion equation. The theoretical resolution characteristic of a 2 μm thick GaAs/GaAlAs transmission photocathode is calculated. The relationship between resolution and parameters in GaAs/GaAlAs transmission photocathode is discussed. A conclusion is shown that one can design the GaAs/GaAlAs transmission photocathode for maximum quantum efficiency, since the sacrifice in the resolution doesn't limit system performances.
文摘Polyelectrolyte becomes more and more popular in electrocatalysis.The understanding of electrode/polyelectrolyte interfaces at the molecular level is important for guiding further the polyelectrolyte-based electrocatalysis.Herein,we demonstrate an in-situ surface-enhanced Raman spectroscopic method by using a three-electrode spectroelectrochemical cell towards characterizing the electrode/polyelectrolyte interfaces.The Ag/AgCl and Ag/Ag_(2)O electrodes are used as the reference electrode in the acidic and the alkaline systems,respectively.The working electrode is made of a transparent carbon thin film which loads the electrocatalysts.The applications of this method are demonstrated through the in-situ characterizations of the p-methylthiophenol adsorbed on the Au and Pt and the electrochemical oxidation of Au on polyelectrolyte membranes.The potential-dependent spectral features of these two systems show that this method is a powerful tool for investigating the electrode/polyelectrolyte interfaces in electrocatalysis.
基金Supported by the National High Technology Research and Development Program of China (2006AA03A134)Zhejiang Province Program (2008C14041)
文摘A series of aromatic acids has been tested as additives for the platinum-catalyzed hydrosilylation of styrene with triethoxysilane. Both excellent conversion of styrene and selectivity in favor of the ,β-adduct were achieved using aminobenzoic acids as additive. Moreover, the use of 4-aminobenzoic acid led to significantly superior enhancement in both catalytic activity and selectivity among the tested aminobenzoic acids. Indeed, 100% conversion of styrene and 98.4% selectivity in favor of the β-adduct were obtained. Additionally, hydrosilylations of various alkenes with a variety of platinum catalysts have also been tested, and in each case the conversion of substrate and the selectivity of the β-adduct were promoted by using 4-aminobenzoic acid as additive.
文摘The potential of externally applied FRP （fiber-reinforced plastic） sheets, being employed in retrofitting schemes aimed to repair and strengthen RC （reinforced concrete） structural elements damaged by prototype strong earthquakes, is presented and discussed in this study. The limitation of the debonding mode of failure of these FRP sheets is highlighted and the necessity to develop efficient anchoring devices for these FRP sheets is underlined. The behavior of such a novel HAD （hybrid anchoring device） capable of anchoring CFRP （carbon fiber reinforcing plastic） sheets to RC structural elements, is presented and discussed. The behavior of the device itself was studied through a 3D non-linear numerical simulation at the preliminary design stage in order to establish certain desired features such as the ductile behavior of the device itself as well as the satisfactory performance of the FRP sheets wrapped around this device. This HAD was next applied as part of a strengthening scheme aimed to upgrade the flexural capacity of an RC bridge-type pier specimen subjected to a cyclic seismic-type loading sequence. The obtained results demonstrated an increase in the specimen＇s flexural capacity by 100% as well as a similar increase in its capability of dissipating energy in a ductile manner during the cyclic load sequence. Moreover, the employed 3D non-linear numerical simulation yielded reasonably good agreement between the measured and the predicted cyclic response of this specimen strengthened by CFRP layers, which were anchored by the novel HAD. The successful behavior of this novel HAD, which has been patented with No. WO2011073696, is currently being tried with a number of other retrofitting schemes employing FRP sheets externally attached on RC structural elements.
基金supported by the National Natural Science Foundation of China (No.60801017)the Tianjin Municipal Primary Application and Frontier Technology Research Plan (No.11JCYBJC01100)the Key Technology Research and Development Program of Tianjin (No.09ZCKFSF00200)
文摘Using nanosecond pulse near-infrared and mid-infrared laser pulses as the pump source, we obtain terahertz wave sources via four-wave difference frequency mixing. From the coupled wave theory, we analyze the four-wave mixing process of GaSe crystal and alkali metal vapor in detail, get the analytical expression of terahertz wave output power, and discuss the conditions for achieving phase matching. By adjusting the pump frequency, the third-order nonlinear polarization of alkali metal vapor is resonance-enhanced. This program offers a new type of high-power terahertz radiation source.
