The luminescent properties of ZnSe, ZnSe：Cr（0.05 at.% Cr）, ZnSe：Yb（0.03 at.% Yb） and ZnSe：Cr：Yb（0.05 at.% Cr, 0.05 at.% Yb） crystals, doped during the growth process by the chemical vapor transport method, w...The luminescent properties of ZnSe, ZnSe：Cr（0.05 at.% Cr）, ZnSe：Yb（0.03 at.% Yb） and ZnSe：Cr：Yb（0.05 at.% Cr, 0.05 at.% Yb） crystals, doped during the growth process by the chemical vapor transport method, were studied within the temperature interval of 6–300 K. At the 6 K temperature in the visible spectral range 2 bands were observed： a band in the excitonic spectral region and a band of self-activated luminescence. It was shown that co-doping of zinc selenide crystals with the chromium and ytterbium led to the combination of the impurities influence on the photoluminescent properties. At the liquid helium temperature in the middle infrared range of the spectra of the ytterbium and chromium co-doped crystal a band with the maximum localized at 1.7μm was observed, which was overlapped with a complex band in the middle-IR spectral range, characteristic for the chromium doped ZnSe crystals. On the basis of obtained data an interaction mechanism of the chromium and ytterbium co-doping impurities was proposed. Guided by the existent model of the ytterbium ion incorporation in the selenide sublattice of the ZnSe crystals, an assumption about stabilization of single charged chromium ions in the zinc sublattice crystal nodes, by means of formation of the local charge compensating clusters, was made. It was assumed that the resonant energy transfer from one chromium ion to another,which led to the concentration quenching of the IR emission in the ZnSe：Cr PL spectra, would lead to the broadening of the IR emission in the spectra of ytterbium and chromium co-doped zinc selenide crystals.g展开更多
The nuclear mean-field potential built up during the ^(12)C+^(12)C and ^(16)O+^(16)O collisions at low energies relevant for the carbon-and oxygen-burning processes is constructed within the double-folding model(DFM) ...The nuclear mean-field potential built up during the ^(12)C+^(12)C and ^(16)O+^(16)O collisions at low energies relevant for the carbon-and oxygen-burning processes is constructed within the double-folding model(DFM) using the realistic ground-state densities of^(12)C and^(16)O, and CDM3Yn density-dependent nucleon–nucleon(NN) interaction. The rearrangement term, indicated by the Hugenholtz–van Hove theorem for the single-particle energy in nuclear matter, is properly considered in the DFM calculation. To validate the use of the density-dependent NN interaction at low energies, an adiabatic approximation was suggested for the dinuclear overlap density. The reliability of the nucleus–nucleus potential predicted through this low-energy version of the DFM was tested in the optical model(OM) analysis of the elastic^(12)C+^(12)C and ^(16)O+^(16)O scattering data at energies below 10 MeV/nucleon.These OM results provide a consistently good description of the elastic angular distributions and 90 excitation function. The dinuclear mean-field potential predicted by the DFM is further used to determine the astrophysical S factor of the ^(12)C+^(12)C and ^(16)O+^(16)O fusions in the barrier penetration model. Without any adjustment of the potential strength, our results reproduce the non-resonant behavior of the S factor of the ^(12)C+^(12)C and ^(16)O+^(16)O fusions very well over a wide range of energies.展开更多
Calculation of the neutron noise induced by fuel assembly vibrations in two pressurized water reactor(PWR) cores has been conducted to investigate the effect of cycle burnup on the properties of the ex-core detector n...Calculation of the neutron noise induced by fuel assembly vibrations in two pressurized water reactor(PWR) cores has been conducted to investigate the effect of cycle burnup on the properties of the ex-core detector noise. An extension of the method and the computational models of a previous work have been applied to two different PWR cores to examine a hypothesis that fuel assembly vibrations cause the corresponding peak in the auto power spectral density(APSD) increase during the cycle. Stochastic vibrations along a random two-dimensional trajectory of individual fuel assemblies were assumed to occur at different locations in the cores. Two models regarding the displacement amplitude of the vibrating assembly have been considered to determine the noise source. Then, the APSD of the ex-core detector noise was evaluated at three burnup steps. The results show that there is no monotonic tendency of the change in the APSD of ex-core detector; however, the increase in APSD occurs predominantly for peripheral assemblies. When assuming simultaneous vibrations of a number of fuel assemblies uniformly distributed over the core, the effect of the peripheral assemblies dominates the ex-core neutron noise.This behaviour was found similar in both cores.展开更多
Cosmological models of a scalar field with dynamical equations containing fractional derivatives or derived from the Einstein-Hilbert action of fractional order, are constructed. A number of exact solutions to those e...Cosmological models of a scalar field with dynamical equations containing fractional derivatives or derived from the Einstein-Hilbert action of fractional order, are constructed. A number of exact solutions to those equations of fractional cosmological models in both eases is given.展开更多
Positron annihilation in TiO2 rutile crystal is studied by an assumption that a positron binds with valance electrons of a titanium dioxide to form a pseudo TiO2-positron molecule before it annihilates with these elec...Positron annihilation in TiO2 rutile crystal is studied by an assumption that a positron binds with valance electrons of a titanium dioxide to form a pseudo TiO2-positron molecule before it annihilates with these electrons. The orbital modification consisting of explicit electron-positron and electron-electron correlation in each electronic orbital is used for the electrons and positron wave functions. By these wave functions, the calculation results of the positron lifetimes in unmitigated and defective TiO2 crystals are about 170 ps, 266 ps and 243 ps, respectively. These results are in good agreement with experimental data of the positron lifetimes in vacancies of TiO2 from 180 ps to 300 ps.展开更多
For the first time the moss biomonitoring technique was used to assess the environmental situation in the area affected by a lead zinc plant as one of the most hazardous enterprises in Bulgaria. 77 Hypnum cupressiform...For the first time the moss biomonitoring technique was used to assess the environmental situation in the area affected by a lead zinc plant as one of the most hazardous enterprises in Bulgaria. 77 Hypnum cupressiforme moss samples were collected in the Kardzhali municipality, in the summer and autumn of 2011. The concentrations of a total of 47 elements were determined by means of instrumental epithermal neutron activation analysis (ENAA), atomic absorption spectrometry (AAS) and inductively coupled plasma-atomic emission spectrometry (ICP-AES). Multivariate statistics was applied to characterize the sources of elements detected in the samples. Four groups of elements were found. In comparison to the data averaged for the area outside of the town, the atmospheric deposition loads for the elements of industrial origin in Kardzhali, where the smelter chimney is located, were found to be much higher. Median levels of the measured concentrations for the most toxic metals (Pb, Zn, Cd, As, Cu, In, Sb) were extremely high in this hot spot when compared to the median Bulgarian cross-country data from the 2010/2011 European moss survey. GIS technology was used to produce element distribution maps illustrating deposition patterns of element pollutants in the study area. The results obtained contribute to the Bulgarian environmental research used to study and control the manufacturing processes of a lead-zinc smelter in the town of Kardzhali.展开更多
Mangrove forest is always considered an effective barrier to protect habitats from high waves,especially tsunami.Therefore,the estimation of wave energy dissipation is required for disater warning.The aim of this stud...Mangrove forest is always considered an effective barrier to protect habitats from high waves,especially tsunami.Therefore,the estimation of wave energy dissipation is required for disater warning.The aim of this study is to calculate wave attenuation in mangrove areas by combining field survey method and mathematical modeling method.The application area is Cu Lao Dung mangrove forest,Soc Trang,Vietnam.From data measurements of hydrodynamics and mangrove characteristics,the wave attenuation coefficient r,the drag coefficient Cd were determined in mud area,mud-mangrove area and mangrove area.In addition,using WAPROMAN model,the attenuation of wave height is simulated in different cases such as without mangrove,with mangrove,breaking wave effect and wave trunk interaction effect.Both the results from the measured method and the model method show the role of mangroves in reducing wave energy.The results from modeling are smaller than the calculated results.However,both methods tend to be suitable.Such difference required more considerations not only on calculation formulas but also on modeling adjustment.The research clearly demonstrated the effectiveness of mangroves in coastal protection,with wave-trunk interaction becoming the dominant factor in energy dissipation deeper into the forest.For future,extending the study to different mangrove forests and longer time scales could provide a more comprehensive understanding of the role of mangroves in coastal protection across various geographical and temporal contexts.展开更多
Conductivity s and thermal conductivity k are directly related to carrier concentration while Seebeck coefficient S is inversely proportional to carrier concentration.Therefore,improving thermoelectric(TE)performance ...Conductivity s and thermal conductivity k are directly related to carrier concentration while Seebeck coefficient S is inversely proportional to carrier concentration.Therefore,improving thermoelectric(TE)performance is challenging.Here,the first-time analysis of secondary phase-controlled TE performance in terms of density-of-state effective mass m*d,weighted mobility mw and quality factor B is discussed in ZnO system.The results show that the secondary spinel phase Ga2O_(3)(ZnO)9 not only impacts on k but also on s and S at high temperature,while the effect of carrier concentration seem to be dominant at low temperature.For the high-spinel-segregation sample,a compensation of dopant atoms from the spinel to substitutional sites in the ZnO matrix at high temperature leads to a low decreased rate of temperaturedependent m*d.The compensation process also induces a band sharpening,a small mw reduction,and a large B enhancement.As a result,In and Ga co-doped ZnO bulk with the highest spinel segregation achieves the greatest PF improvement by 112.8%,owing to enhanced Seebeck coefficient by 110%as compared to the good Zn-substitution sample.展开更多
基金supported by Erasmus Mundus(BMUMID2011238)Moldavian Academy of Science(11.817.05.11F)Jenny and AnttiWihuri Foundation
文摘The luminescent properties of ZnSe, ZnSe：Cr（0.05 at.% Cr）, ZnSe：Yb（0.03 at.% Yb） and ZnSe：Cr：Yb（0.05 at.% Cr, 0.05 at.% Yb） crystals, doped during the growth process by the chemical vapor transport method, were studied within the temperature interval of 6–300 K. At the 6 K temperature in the visible spectral range 2 bands were observed： a band in the excitonic spectral region and a band of self-activated luminescence. It was shown that co-doping of zinc selenide crystals with the chromium and ytterbium led to the combination of the impurities influence on the photoluminescent properties. At the liquid helium temperature in the middle infrared range of the spectra of the ytterbium and chromium co-doped crystal a band with the maximum localized at 1.7μm was observed, which was overlapped with a complex band in the middle-IR spectral range, characteristic for the chromium doped ZnSe crystals. On the basis of obtained data an interaction mechanism of the chromium and ytterbium co-doping impurities was proposed. Guided by the existent model of the ytterbium ion incorporation in the selenide sublattice of the ZnSe crystals, an assumption about stabilization of single charged chromium ions in the zinc sublattice crystal nodes, by means of formation of the local charge compensating clusters, was made. It was assumed that the resonant energy transfer from one chromium ion to another,which led to the concentration quenching of the IR emission in the ZnSe：Cr PL spectra, would lead to the broadening of the IR emission in the spectra of ytterbium and chromium co-doped zinc selenide crystals.g
基金supported,in part,by the National Foundation for Scientific and Technological Development(NAFOSTED Project No.103.04-2017.317)
文摘The nuclear mean-field potential built up during the ^(12)C+^(12)C and ^(16)O+^(16)O collisions at low energies relevant for the carbon-and oxygen-burning processes is constructed within the double-folding model(DFM) using the realistic ground-state densities of^(12)C and^(16)O, and CDM3Yn density-dependent nucleon–nucleon(NN) interaction. The rearrangement term, indicated by the Hugenholtz–van Hove theorem for the single-particle energy in nuclear matter, is properly considered in the DFM calculation. To validate the use of the density-dependent NN interaction at low energies, an adiabatic approximation was suggested for the dinuclear overlap density. The reliability of the nucleus–nucleus potential predicted through this low-energy version of the DFM was tested in the optical model(OM) analysis of the elastic^(12)C+^(12)C and ^(16)O+^(16)O scattering data at energies below 10 MeV/nucleon.These OM results provide a consistently good description of the elastic angular distributions and 90 excitation function. The dinuclear mean-field potential predicted by the DFM is further used to determine the astrophysical S factor of the ^(12)C+^(12)C and ^(16)O+^(16)O fusions in the barrier penetration model. Without any adjustment of the potential strength, our results reproduce the non-resonant behavior of the S factor of the ^(12)C+^(12)C and ^(16)O+^(16)O fusions very well over a wide range of energies.
基金supported by Vietnam National Foundation for Science and Technology Development(NAFOSTED)(No.103.04-2014.79)
文摘Calculation of the neutron noise induced by fuel assembly vibrations in two pressurized water reactor(PWR) cores has been conducted to investigate the effect of cycle burnup on the properties of the ex-core detector noise. An extension of the method and the computational models of a previous work have been applied to two different PWR cores to examine a hypothesis that fuel assembly vibrations cause the corresponding peak in the auto power spectral density(APSD) increase during the cycle. Stochastic vibrations along a random two-dimensional trajectory of individual fuel assemblies were assumed to occur at different locations in the cores. Two models regarding the displacement amplitude of the vibrating assembly have been considered to determine the noise source. Then, the APSD of the ex-core detector noise was evaluated at three burnup steps. The results show that there is no monotonic tendency of the change in the APSD of ex-core detector; however, the increase in APSD occurs predominantly for peripheral assemblies. When assuming simultaneous vibrations of a number of fuel assemblies uniformly distributed over the core, the effect of the peripheral assemblies dominates the ex-core neutron noise.This behaviour was found similar in both cores.
文摘Cosmological models of a scalar field with dynamical equations containing fractional derivatives or derived from the Einstein-Hilbert action of fractional order, are constructed. A number of exact solutions to those equations of fractional cosmological models in both eases is given.
文摘Positron annihilation in TiO2 rutile crystal is studied by an assumption that a positron binds with valance electrons of a titanium dioxide to form a pseudo TiO2-positron molecule before it annihilates with these electrons. The orbital modification consisting of explicit electron-positron and electron-electron correlation in each electronic orbital is used for the electrons and positron wave functions. By these wave functions, the calculation results of the positron lifetimes in unmitigated and defective TiO2 crystals are about 170 ps, 266 ps and 243 ps, respectively. These results are in good agreement with experimental data of the positron lifetimes in vacancies of TiO2 from 180 ps to 300 ps.
文摘For the first time the moss biomonitoring technique was used to assess the environmental situation in the area affected by a lead zinc plant as one of the most hazardous enterprises in Bulgaria. 77 Hypnum cupressiforme moss samples were collected in the Kardzhali municipality, in the summer and autumn of 2011. The concentrations of a total of 47 elements were determined by means of instrumental epithermal neutron activation analysis (ENAA), atomic absorption spectrometry (AAS) and inductively coupled plasma-atomic emission spectrometry (ICP-AES). Multivariate statistics was applied to characterize the sources of elements detected in the samples. Four groups of elements were found. In comparison to the data averaged for the area outside of the town, the atmospheric deposition loads for the elements of industrial origin in Kardzhali, where the smelter chimney is located, were found to be much higher. Median levels of the measured concentrations for the most toxic metals (Pb, Zn, Cd, As, Cu, In, Sb) were extremely high in this hot spot when compared to the median Bulgarian cross-country data from the 2010/2011 European moss survey. GIS technology was used to produce element distribution maps illustrating deposition patterns of element pollutants in the study area. The results obtained contribute to the Bulgarian environmental research used to study and control the manufacturing processes of a lead-zinc smelter in the town of Kardzhali.
基金funded by Vietnam National University Ho Chi Minh City(VNU-HCM)under grant number B2019-18-09.
文摘Mangrove forest is always considered an effective barrier to protect habitats from high waves,especially tsunami.Therefore,the estimation of wave energy dissipation is required for disater warning.The aim of this study is to calculate wave attenuation in mangrove areas by combining field survey method and mathematical modeling method.The application area is Cu Lao Dung mangrove forest,Soc Trang,Vietnam.From data measurements of hydrodynamics and mangrove characteristics,the wave attenuation coefficient r,the drag coefficient Cd were determined in mud area,mud-mangrove area and mangrove area.In addition,using WAPROMAN model,the attenuation of wave height is simulated in different cases such as without mangrove,with mangrove,breaking wave effect and wave trunk interaction effect.Both the results from the measured method and the model method show the role of mangroves in reducing wave energy.The results from modeling are smaller than the calculated results.However,both methods tend to be suitable.Such difference required more considerations not only on calculation formulas but also on modeling adjustment.The research clearly demonstrated the effectiveness of mangroves in coastal protection,with wave-trunk interaction becoming the dominant factor in energy dissipation deeper into the forest.For future,extending the study to different mangrove forests and longer time scales could provide a more comprehensive understanding of the role of mangroves in coastal protection across various geographical and temporal contexts.
基金supported by the Vietnam Ministry of Science and Technology under grant numberÐTÐL.CN-23/18.
文摘Conductivity s and thermal conductivity k are directly related to carrier concentration while Seebeck coefficient S is inversely proportional to carrier concentration.Therefore,improving thermoelectric(TE)performance is challenging.Here,the first-time analysis of secondary phase-controlled TE performance in terms of density-of-state effective mass m*d,weighted mobility mw and quality factor B is discussed in ZnO system.The results show that the secondary spinel phase Ga2O_(3)(ZnO)9 not only impacts on k but also on s and S at high temperature,while the effect of carrier concentration seem to be dominant at low temperature.For the high-spinel-segregation sample,a compensation of dopant atoms from the spinel to substitutional sites in the ZnO matrix at high temperature leads to a low decreased rate of temperaturedependent m*d.The compensation process also induces a band sharpening,a small mw reduction,and a large B enhancement.As a result,In and Ga co-doped ZnO bulk with the highest spinel segregation achieves the greatest PF improvement by 112.8%,owing to enhanced Seebeck coefficient by 110%as compared to the good Zn-substitution sample.
