Positron is an excellent probe of lattice defects in solids. A thermallized positron delocalized in lattice can be trapped at open volume defects, e.g. vacancies, dislocations, grain boundaries etc. Positron anni- hil...Positron is an excellent probe of lattice defects in solids. A thermallized positron delocalized in lattice can be trapped at open volume defects, e.g. vacancies, dislocations, grain boundaries etc. Positron anni- hilation spectroscopy is a non-destructive technique lattice defects in solids on the atomic scale. Positron which enables characterization of open volume lifetime and Doppler broadening of annihilation photo-peak are the most common observables related to positron annihilation process. Positron lifetime spectroscopy enables to identify defects in solids and to determine their concentrations while coinci- dence measurement of Doppler broadening provides information about local chemical environment of defects. This article provides a review of the state-of-art of defect characterization in bulk metallic mate- rials by positron annihilation spectroscopy. Advanced analysis of positron annihilation data and recent developments of positron annihilation methodology are described and discussed on examples of defect studies of metallic materials. Future develonment in the field in proposed as well.展开更多
We studied the excitation spectra in the case of Xe@(p-H2)n embedded in a solid-state parahydrogen, making use of the ab initio molecular orbital method (QMO), in order to seek the possibility of the radiative emissio...We studied the excitation spectra in the case of Xe@(p-H2)n embedded in a solid-state parahydrogen, making use of the ab initio molecular orbital method (QMO), in order to seek the possibility of the radiative emission of the neutrino pair (RENP) process that may be associated with the E1 × M1 transition processes. By means of a QMO calculation, the remarkable matrix effect was found in the structure of the electronic states. Three E1-type excitation bands (ε1, ε2, ε3, in the order of increasing energy) in the UV absorption were found. In the present preliminary calculation, the second was too close to be clearly/well distinguished as an independent peak observed in the last experiment. Nevertheless, across the second (ε2) band, two associated bands that may link to the M1-type transition were found. Therefore, the M1-type de-excitation process may be probable with the help of intensity borrowing from the ε2 band, which may support the probability of the RENP process.展开更多
The elastic constants of Al single crystal were calculated by ab initio method for calibration. Three deformation directions were selected in order to obtain the different constants of c 11 , c 12 and c 44 . The cohes...The elastic constants of Al single crystal were calculated by ab initio method for calibration. Three deformation directions were selected in order to obtain the different constants of c 11 , c 12 and c 44 . The cohesion energy curves of the three deformation directions were calculated. The results of the second order partial differential at the equilibrium point of the cohesion energy curve provide the elastic constants of the Al single crystal. The changes of crystal symmetry and lattice can lead to the deviations of the calculated cohesion energy curves and the accurate elastic constants can not be obtained, but when the correction is taken into calculation, the calculated results are very close to the literature data. It is very difficult to obtain the elastic constants of thin films by experiment and the data from the handbook are scattered in a large scale. However, the elastic constants calculated by this method can be served as a standard. Though the errors of TiN elastic constants calculated by this method are a little higher than that for Al, the results are acceptable. [展开更多
5-Amino-3-methylthio-1H-pyrazoles are very important building blocks from which a wide variety of pyrazole de-rivatives can be prepared. When substituted 5-amino-3-methylthio-1H-pyrazole was treated with CH3I, the met...5-Amino-3-methylthio-1H-pyrazoles are very important building blocks from which a wide variety of pyrazole de-rivatives can be prepared. When substituted 5-amino-3-methylthio-1H-pyrazole was treated with CH3I, the methy-lation occurres at endocyclic two nitrogens at the same time. The ratio of isomers in products was depended upon the nature of 4-position substituent in the pyrazole ring. The products were characterized by X-ray diffraction analysis, and the ratios of isomer were explained by means of the results of ab inito calculation.展开更多
基金Financial support by the Czech Science Agency(project 1612828S)
文摘Positron is an excellent probe of lattice defects in solids. A thermallized positron delocalized in lattice can be trapped at open volume defects, e.g. vacancies, dislocations, grain boundaries etc. Positron anni- hilation spectroscopy is a non-destructive technique lattice defects in solids on the atomic scale. Positron which enables characterization of open volume lifetime and Doppler broadening of annihilation photo-peak are the most common observables related to positron annihilation process. Positron lifetime spectroscopy enables to identify defects in solids and to determine their concentrations while coinci- dence measurement of Doppler broadening provides information about local chemical environment of defects. This article provides a review of the state-of-art of defect characterization in bulk metallic mate- rials by positron annihilation spectroscopy. Advanced analysis of positron annihilation data and recent developments of positron annihilation methodology are described and discussed on examples of defect studies of metallic materials. Future develonment in the field in proposed as well.
文摘We studied the excitation spectra in the case of Xe@(p-H2)n embedded in a solid-state parahydrogen, making use of the ab initio molecular orbital method (QMO), in order to seek the possibility of the radiative emission of the neutrino pair (RENP) process that may be associated with the E1 × M1 transition processes. By means of a QMO calculation, the remarkable matrix effect was found in the structure of the electronic states. Three E1-type excitation bands (ε1, ε2, ε3, in the order of increasing energy) in the UV absorption were found. In the present preliminary calculation, the second was too close to be clearly/well distinguished as an independent peak observed in the last experiment. Nevertheless, across the second (ε2) band, two associated bands that may link to the M1-type transition were found. Therefore, the M1-type de-excitation process may be probable with the help of intensity borrowing from the ε2 band, which may support the probability of the RENP process.
文摘The elastic constants of Al single crystal were calculated by ab initio method for calibration. Three deformation directions were selected in order to obtain the different constants of c 11 , c 12 and c 44 . The cohesion energy curves of the three deformation directions were calculated. The results of the second order partial differential at the equilibrium point of the cohesion energy curve provide the elastic constants of the Al single crystal. The changes of crystal symmetry and lattice can lead to the deviations of the calculated cohesion energy curves and the accurate elastic constants can not be obtained, but when the correction is taken into calculation, the calculated results are very close to the literature data. It is very difficult to obtain the elastic constants of thin films by experiment and the data from the handbook are scattered in a large scale. However, the elastic constants calculated by this method can be served as a standard. Though the errors of TiN elastic constants calculated by this method are a little higher than that for Al, the results are acceptable. [
基金Project supported by the National Natural Science Foundation of China (No. 20172031) and the Research Fund for the Doctoral Program of Higher Education China.
文摘5-Amino-3-methylthio-1H-pyrazoles are very important building blocks from which a wide variety of pyrazole de-rivatives can be prepared. When substituted 5-amino-3-methylthio-1H-pyrazole was treated with CH3I, the methy-lation occurres at endocyclic two nitrogens at the same time. The ratio of isomers in products was depended upon the nature of 4-position substituent in the pyrazole ring. The products were characterized by X-ray diffraction analysis, and the ratios of isomer were explained by means of the results of ab inito calculation.
