In this study, a novel phoswich detector for beta–gamma coincidence detection is designed. Unlike the triple crystal phoswich detector designed by researchers at the University of Missouri, Columbia, this phoswich de...In this study, a novel phoswich detector for beta–gamma coincidence detection is designed. Unlike the triple crystal phoswich detector designed by researchers at the University of Missouri, Columbia, this phoswich detector is of the semi-well type, so it has a higher detection efficiency. The detector consists of BC-400 and NaI:Tl with decay time constants of 2.4 and 230 ns, respectively.The BC-400 scintillator detects beta particles, and the Na I:Tl cell is used for gamma detection. Geant4 simulations of this phoswich detector find that a 2-mm-thick BC-400 scintillator can absorb nearly all of the beta particles whose energies are below 700 keV. Further, for a 2.00-cmthick NaI:Tl crystal, the gamma source peak efficiency for photons ranges from a maximum of nearly 90% at 30 keV to 10% at 1 MeV. The self-absorption effect is also discussed in this paper in order to determine the carrier gas' s influence.展开更多
The treatment and disposal of radioactive waste are presently facing great challenges.Spent ion exchange resins have become a focus of attention due to their high production and serious environmental risks.In this pap...The treatment and disposal of radioactive waste are presently facing great challenges.Spent ion exchange resins have become a focus of attention due to their high production and serious environmental risks.In this paper,a simplified model of cationic exchange resin is proposed,and the degradation processes of cationic resin monomer initiated by hydroxyl radicals(·OH)are clarified by combining statistical molecular fragmentation(SMF)model and density functional theory(DFT)calculations.The prediction of active sites indicates that the S-O bonds and the C-S bond of the sulfonic group are more likely to react during the degradation.The meta-position of the sulfonic group on the benzene ring is the most active site,and the benzene ring without the sulfonic group has a certain reactivity.The C11-C14 and C17-C20 bonds,on the carbon skeleton,are the most easily broken.It is also found that dihydroxy addition and elimination reactions play a major role in the process of desulfonation,carbon skeleton cleavage and benzene ring separation.The decomposition mechanisms found through the combination of physical models and chemical calculations,provide theoretical guidance for the treatment of complex polycyclic aromatic hydrocarbons.展开更多
To improve the adsorption and catalytic performance of heterogeneous Fenton-like catalysts for oil wastes,amino acids were used to modify nanoscale zero-valent iron(AA@Fe^(0)),which were applied in the Fenton-like deg...To improve the adsorption and catalytic performance of heterogeneous Fenton-like catalysts for oil wastes,amino acids were used to modify nanoscale zero-valent iron(AA@Fe^(0)),which were applied in the Fenton-like degradation of organic solvents(tributyl phosphate and n-dodecane,named TBP and DD).Twelve amino acids,i.e.,glycine(Gly),alanine(Ala),leucine(Leu),proline(Pro),phenylalanine(Phe),methionine(Met),cysteine(Cys),asparagine(Asn),serine(Ser),glutamic acid(Glu),lysine(Lys)and arginine(Arg),were selected and calculated by density functional theory(DFT).The optimized structure,charge distribution,the highest occupied molecular orbital(HOMO),the lowest unoccupied molecular orbital(LUMO),interaction region indicator(IRI)isosurface map and adsorption energy of AA@Fe^(0),AA@Fe^(0)-TBP and AA@Fe^(0)-DD were studied,which indicated that Fe is more likely to approach and charge transfer with-COO and-NH_(3) on theα-carbon of amino acids.There is strong attraction between Fe and–COO,and Van der Waals force between Fe and-NH_(3),respectively.In the interaction of AA@Fe^(0)with TBP and DD,Van der Waal force plays an important role.AA@Fe^(0)was synthesized in laboratory and characterized to investigate physicochemical properties.In Fenton-like degradation of organic solvents,the change of COD in water phase during the degradation process as well as the volume of the organic phase after the reaction were investigated.The results of calculations combined with experiments showed that Ser-modified Fe^(0)performed the best in these amino acids,with 98%removal of organic solvents.A possible catalytic mechanism was proposed in which amino acids acted a linking role between Fe and organic solvents,activating H_(2)O_(2)to generate hydroxyl radicals for the degradation of organic solvents.展开更多
Mg_(3)Sb_(2) as a Zintl compound is a promising thermoelectric material with the intrinsically low lattice thermal conductivity and excellent n-type electrical properties,but its p-type electrical transport properties...Mg_(3)Sb_(2) as a Zintl compound is a promising thermoelectric material with the intrinsically low lattice thermal conductivity and excellent n-type electrical properties,but its p-type electrical transport properties are poor.Here,the thermoelectric performance of Mg_(3)Sb_(2) under the effect of biaxial strain is investigated by using first-principles method and Boltzmann transport theory.The application of biaxial strain enables tuning the band structure of Mg_(3)Sb_(2) in such a way that the band degeneracy of both the conduction band and valence band increases.As the biaxial strain increases,the Seebeck coefficient of ptype Mg_(3)Sb_(2) has a remarkable increase,leading to a significant improvement in power factor.This is mainly ascribed to the achievement of valence band orbital degeneracy.Meanwhile,the lattice thermal conductivity exhibits very slight biaxial strain dependence within the strain range considered in this work,which increases from 1.28 to 1.62 W m^(-1) K^(-1) at 300 K.Finally,the highest ZT of p-type Mg_(3)Sb_(2) at 700 K can be up to 2.6 along the in-plane direction under-2.5%biaxial strain,which is almost three times that of the unstrained counterpart.The realization of high thermoelectric performance of p-type Mg_(3)Sb_(2) will promote its practical applications as thermoelectric generators.展开更多
Tungsten,a leading candidate for plasma-facing materials(PFM) in future fusion devices,will be exposed to high-flux low-energy helium plasma under the anticipated fusion operation conditions.In the past two decades,ex...Tungsten,a leading candidate for plasma-facing materials(PFM) in future fusion devices,will be exposed to high-flux low-energy helium plasma under the anticipated fusion operation conditions.In the past two decades,experiments have revealed that exposure to helium plasma strongly modifies the surface morphology and hence the sputtering,thermal and other properties of tungsten,posing a serious danger to the performance and lifetime of tungsten and the steadystate operation of plasma.In this article,we provide a review of modeling and simulation efforts on the long-term evolution of helium bubbles,surface morphology,and property changes of tungsten exposed to low-energy helium plasma.The current gap and outstanding challenges to establish a predictive modeling capability for dynamic evolution of PFM are discussed.展开更多
In this work,a discrete unified gas kinetic scheme(DUGKS)is developed for radiative transfer in anisotropic scattering media.The method is an extension of a previous one for isotropic radiation problems[1].The present...In this work,a discrete unified gas kinetic scheme(DUGKS)is developed for radiative transfer in anisotropic scattering media.The method is an extension of a previous one for isotropic radiation problems[1].The present scheme is a finite-volume discretization of the anisotropic gray radiation equation,where the anisotropic scattering phase function is approximated by the Legendre polynomial expansion.With the coupling of free transport and scattering processes in the reconstruction of the flux at cell interfaces,the present DUGKS has the nice unified preserving properties such that the cell size is not limited by the photon mean free path even in the optical thick regime.Several one-and two-dimensional numerical tests are conducted to validate the performance of the present DUGKS,and the numerical results demonstrate that the scheme is a reliable method for anisotropic radiative heat transfer problems.展开更多
基金supported by the National Natural Science Foundation of China(Nos.11205108,11475121,and 11575145)the Excellent Youth Fund of Sichuan University(No.2016SCU04A13)
文摘In this study, a novel phoswich detector for beta–gamma coincidence detection is designed. Unlike the triple crystal phoswich detector designed by researchers at the University of Missouri, Columbia, this phoswich detector is of the semi-well type, so it has a higher detection efficiency. The detector consists of BC-400 and NaI:Tl with decay time constants of 2.4 and 230 ns, respectively.The BC-400 scintillator detects beta particles, and the Na I:Tl cell is used for gamma detection. Geant4 simulations of this phoswich detector find that a 2-mm-thick BC-400 scintillator can absorb nearly all of the beta particles whose energies are below 700 keV. Further, for a 2.00-cmthick NaI:Tl crystal, the gamma source peak efficiency for photons ranges from a maximum of nearly 90% at 30 keV to 10% at 1 MeV. The self-absorption effect is also discussed in this paper in order to determine the carrier gas' s influence.
基金supported by the National Natural Science Foundation of China (No.22176067).
文摘The treatment and disposal of radioactive waste are presently facing great challenges.Spent ion exchange resins have become a focus of attention due to their high production and serious environmental risks.In this paper,a simplified model of cationic exchange resin is proposed,and the degradation processes of cationic resin monomer initiated by hydroxyl radicals(·OH)are clarified by combining statistical molecular fragmentation(SMF)model and density functional theory(DFT)calculations.The prediction of active sites indicates that the S-O bonds and the C-S bond of the sulfonic group are more likely to react during the degradation.The meta-position of the sulfonic group on the benzene ring is the most active site,and the benzene ring without the sulfonic group has a certain reactivity.The C11-C14 and C17-C20 bonds,on the carbon skeleton,are the most easily broken.It is also found that dihydroxy addition and elimination reactions play a major role in the process of desulfonation,carbon skeleton cleavage and benzene ring separation.The decomposition mechanisms found through the combination of physical models and chemical calculations,provide theoretical guidance for the treatment of complex polycyclic aromatic hydrocarbons.
基金supported by the National Natural Science Foundation of China (No.22176067)。
文摘To improve the adsorption and catalytic performance of heterogeneous Fenton-like catalysts for oil wastes,amino acids were used to modify nanoscale zero-valent iron(AA@Fe^(0)),which were applied in the Fenton-like degradation of organic solvents(tributyl phosphate and n-dodecane,named TBP and DD).Twelve amino acids,i.e.,glycine(Gly),alanine(Ala),leucine(Leu),proline(Pro),phenylalanine(Phe),methionine(Met),cysteine(Cys),asparagine(Asn),serine(Ser),glutamic acid(Glu),lysine(Lys)and arginine(Arg),were selected and calculated by density functional theory(DFT).The optimized structure,charge distribution,the highest occupied molecular orbital(HOMO),the lowest unoccupied molecular orbital(LUMO),interaction region indicator(IRI)isosurface map and adsorption energy of AA@Fe^(0),AA@Fe^(0)-TBP and AA@Fe^(0)-DD were studied,which indicated that Fe is more likely to approach and charge transfer with-COO and-NH_(3) on theα-carbon of amino acids.There is strong attraction between Fe and–COO,and Van der Waals force between Fe and-NH_(3),respectively.In the interaction of AA@Fe^(0)with TBP and DD,Van der Waal force plays an important role.AA@Fe^(0)was synthesized in laboratory and characterized to investigate physicochemical properties.In Fenton-like degradation of organic solvents,the change of COD in water phase during the degradation process as well as the volume of the organic phase after the reaction were investigated.The results of calculations combined with experiments showed that Ser-modified Fe^(0)performed the best in these amino acids,with 98%removal of organic solvents.A possible catalytic mechanism was proposed in which amino acids acted a linking role between Fe and organic solvents,activating H_(2)O_(2)to generate hydroxyl radicals for the degradation of organic solvents.
基金This work was supported by the National Natural Science Foundation of China under Grant Nos.11775163,12175166,12175079the National Key R&D Program of China(2019YFA0210003).
文摘Mg_(3)Sb_(2) as a Zintl compound is a promising thermoelectric material with the intrinsically low lattice thermal conductivity and excellent n-type electrical properties,but its p-type electrical transport properties are poor.Here,the thermoelectric performance of Mg_(3)Sb_(2) under the effect of biaxial strain is investigated by using first-principles method and Boltzmann transport theory.The application of biaxial strain enables tuning the band structure of Mg_(3)Sb_(2) in such a way that the band degeneracy of both the conduction band and valence band increases.As the biaxial strain increases,the Seebeck coefficient of ptype Mg_(3)Sb_(2) has a remarkable increase,leading to a significant improvement in power factor.This is mainly ascribed to the achievement of valence band orbital degeneracy.Meanwhile,the lattice thermal conductivity exhibits very slight biaxial strain dependence within the strain range considered in this work,which increases from 1.28 to 1.62 W m^(-1) K^(-1) at 300 K.Finally,the highest ZT of p-type Mg_(3)Sb_(2) at 700 K can be up to 2.6 along the in-plane direction under-2.5%biaxial strain,which is almost three times that of the unstrained counterpart.The realization of high thermoelectric performance of p-type Mg_(3)Sb_(2) will promote its practical applications as thermoelectric generators.
基金supported by National Natural Science Foundation of China(No.11905071)the National MCF Energy R&D Program(No.2018YFE0308103)
文摘Tungsten,a leading candidate for plasma-facing materials(PFM) in future fusion devices,will be exposed to high-flux low-energy helium plasma under the anticipated fusion operation conditions.In the past two decades,experiments have revealed that exposure to helium plasma strongly modifies the surface morphology and hence the sputtering,thermal and other properties of tungsten,posing a serious danger to the performance and lifetime of tungsten and the steadystate operation of plasma.In this article,we provide a review of modeling and simulation efforts on the long-term evolution of helium bubbles,surface morphology,and property changes of tungsten exposed to low-energy helium plasma.The current gap and outstanding challenges to establish a predictive modeling capability for dynamic evolution of PFM are discussed.
基金The National Key R&D Program of China(No.2018YFE0180900)the Fundamental Research Funds for the Central Universities(No.2019kfyXMBZ040).
文摘In this work,a discrete unified gas kinetic scheme(DUGKS)is developed for radiative transfer in anisotropic scattering media.The method is an extension of a previous one for isotropic radiation problems[1].The present scheme is a finite-volume discretization of the anisotropic gray radiation equation,where the anisotropic scattering phase function is approximated by the Legendre polynomial expansion.With the coupling of free transport and scattering processes in the reconstruction of the flux at cell interfaces,the present DUGKS has the nice unified preserving properties such that the cell size is not limited by the photon mean free path even in the optical thick regime.Several one-and two-dimensional numerical tests are conducted to validate the performance of the present DUGKS,and the numerical results demonstrate that the scheme is a reliable method for anisotropic radiative heat transfer problems.
