We investigate the transport properties of Dirac fermions through velocity-modulation structures,with the Fermi velocity inside the barriers larger than the one outside.It is shown that the transmission exhibits pseud...We investigate the transport properties of Dirac fermions through velocity-modulation structures,with the Fermi velocity inside the barriers larger than the one outside.It is shown that the transmission exhibits pseudo-periodicity with the incident angle below the critical transmission angle,but attenuates exponentially in the opposite situation.It is found that in the transmission,(1)the pseudo-periodicity turns to periodicity with suitable modulation;(2)line-type peaks appear in the exponential attenuation region for multiple velocity barriers;(3)peak splitting occurs with the number of the velocity barriers increasing.Some sharp oscillations with the falling-edge slopes close to infinity exist in the conductance profile.These novel transport properties suggest significant potential applications in graphene-based devices.展开更多
Two kinds of approaches are built to solve the fission products diffusion models(Fick's equation)based on sphere fuel particles and sphere fuel elements exactly.Two models for homogenous TRISO-coated fuel particle...Two kinds of approaches are built to solve the fission products diffusion models(Fick's equation)based on sphere fuel particles and sphere fuel elements exactly.Two models for homogenous TRISO-coated fuel particles and fuel elements used in pebble-bed high temperature gas-cooled reactors are presented,respectively.The analytical solution of Fick's equation for fission products diffusion in fuel particles is derived by variables separation.In the fuel element system,a modification of the diffusion coefficient from D to D/Гis made to characterize the difference of diffusion rates in distinct areas and it is shown that the Laplace and Hankel transformations are effective as the diffusion coefficient in Fick's equation is dependant on the radius of the fuel element.Both the solutions are useful for the prediction of the fission product behaviors and could be programmed in the corresponding engineering calculations.展开更多
An algorithm is employed to calculate molecular bond polarizabilities of p-hydroxybenzoic acid,which supplies essential electronic information of the nonresonant Raman excited virtual states.The main dynamical behavio...An algorithm is employed to calculate molecular bond polarizabilities of p-hydroxybenzoic acid,which supplies essential electronic information of the nonresonant Raman excited virtual states.The main dynamical behavior of the excited virtual states of p-hydroxybenzoic acid with 514.5 nm excitation is such that the Raman excited electrons tend to flow to the C–C connected with–OH and–COOH from the benzene ring because of the electronic repulsion effect.The distribution of the electrons at the final stage of relaxation is given out through the comparison between the bond electronic densities of the ground states and the bond polarizabilities after de-excitation.Furthermore,the relaxation characteristic times of bond polarizabilities shows that the transport of electrons on–COOH is distinct.展开更多
The adsorption behaviors of radioactive strontium and silver nuclides on the graphite surface in a high-temperature gas-cooled reactor are studied by first-principles theory using generalized gradient approximation(GG...The adsorption behaviors of radioactive strontium and silver nuclides on the graphite surface in a high-temperature gas-cooled reactor are studied by first-principles theory using generalized gradient approximation(GGA)and local density approximation(LDA)pseudo-potentials.It turns out that Sr prefers to be absorbed at the hollow of the carbon hexagonal cell by 0.54 eV(GGA),while Ag likes to sit right above the carbon atom with an adsorption energy of almost zero(GGA)and 0.45 eV(LDA).Electronic structure analysis reveals that Sr donates its partial electrons of the 4𝑝and 5𝑠states to the graphite substrate,while Ag on graphite is a physical adsorption without any electron transfer.展开更多
基金the National Natural Science Foundation of China under Grant Nos 11104156 and 21271114the Postdoctoral Science Foundation of China under Grant No 2012M510405+1 种基金the Independent Research and Development Fund of Tsinghua University under Grant Nos 20121087948 and 20111080982the Beijing Key Lab of Fine Ceramics Opening Fund under Grant No 2012200110.
文摘We investigate the transport properties of Dirac fermions through velocity-modulation structures,with the Fermi velocity inside the barriers larger than the one outside.It is shown that the transmission exhibits pseudo-periodicity with the incident angle below the critical transmission angle,but attenuates exponentially in the opposite situation.It is found that in the transmission,(1)the pseudo-periodicity turns to periodicity with suitable modulation;(2)line-type peaks appear in the exponential attenuation region for multiple velocity barriers;(3)peak splitting occurs with the number of the velocity barriers increasing.Some sharp oscillations with the falling-edge slopes close to infinity exist in the conductance profile.These novel transport properties suggest significant potential applications in graphene-based devices.
基金Supported by the National S&T Major Project of China under Grant No ZX06901.
文摘Two kinds of approaches are built to solve the fission products diffusion models(Fick's equation)based on sphere fuel particles and sphere fuel elements exactly.Two models for homogenous TRISO-coated fuel particles and fuel elements used in pebble-bed high temperature gas-cooled reactors are presented,respectively.The analytical solution of Fick's equation for fission products diffusion in fuel particles is derived by variables separation.In the fuel element system,a modification of the diffusion coefficient from D to D/Гis made to characterize the difference of diffusion rates in distinct areas and it is shown that the Laplace and Hankel transformations are effective as the diffusion coefficient in Fick's equation is dependant on the radius of the fuel element.Both the solutions are useful for the prediction of the fission product behaviors and could be programmed in the corresponding engineering calculations.
基金Supported by the National Natural Science Foundation under Grant No 11104156.
文摘An algorithm is employed to calculate molecular bond polarizabilities of p-hydroxybenzoic acid,which supplies essential electronic information of the nonresonant Raman excited virtual states.The main dynamical behavior of the excited virtual states of p-hydroxybenzoic acid with 514.5 nm excitation is such that the Raman excited electrons tend to flow to the C–C connected with–OH and–COOH from the benzene ring because of the electronic repulsion effect.The distribution of the electrons at the final stage of relaxation is given out through the comparison between the bond electronic densities of the ground states and the bond polarizabilities after de-excitation.Furthermore,the relaxation characteristic times of bond polarizabilities shows that the transport of electrons on–COOH is distinct.
基金Supported by the National Science and Technology Major Project of China under Grant No 2008ZX06901the National Natural Science Foundation of China under Grant No 50871057+1 种基金the Independent Research and Development Fund of Tsinghua University under Grant No 20111080982the Beijing Key Lab of Fine Ceramics Opening Fund under Grant No 2012200110.
文摘The adsorption behaviors of radioactive strontium and silver nuclides on the graphite surface in a high-temperature gas-cooled reactor are studied by first-principles theory using generalized gradient approximation(GGA)and local density approximation(LDA)pseudo-potentials.It turns out that Sr prefers to be absorbed at the hollow of the carbon hexagonal cell by 0.54 eV(GGA),while Ag likes to sit right above the carbon atom with an adsorption energy of almost zero(GGA)and 0.45 eV(LDA).Electronic structure analysis reveals that Sr donates its partial electrons of the 4𝑝and 5𝑠states to the graphite substrate,while Ag on graphite is a physical adsorption without any electron transfer.
