Undoped, Dy^3＋ doped and Dy^3＋, K^＋ codoped calcium molybdate phosphors have been synthesized by solid-state reaction method. X-ray diffraction studies reveal the tetragonal structure of the prepared phosphors havi...Undoped, Dy^3＋ doped and Dy^3＋, K^＋ codoped calcium molybdate phosphors have been synthesized by solid-state reaction method. X-ray diffraction studies reveal the tetragonal structure of the prepared phosphors having crystallite size 15-50 nm. Scanning electron microscopy （SEM） studies reveal the morphology and crystallite size of the prepared phosphors. Photoluminescence studies indicate that there are blue and yellow emissions at 489 and 576 nm, respectively corresponding to Dy^3＋ ion. The introduction of K＋ ion significantly influences the blue and yellow emissions which causes the near white light emission from this codoped phosphor. The intense absorption peak of the codoped phosphor at 210 nm is attributed to the band gap and a shoulder at 240 nm appears due to charge transfer from oxygen ions to neighbouring molybdenum ions. The band gap of the codoped phosphor is calculated as 5.5 eV from the absorption studies. The dielectric properties such as permittivity and dielectric loss are studied as a function of frequency.Acknowledgement The authors are thankful to the Department of Science and Technology, New Delhi （Government of India） for funding this work under the Project SR/FTP/PS-087/2010.展开更多
Practical simulations of turbulent processes are generally cutoff, with a grid resolution that stops within the inertial range, meaning that multiple active regions and length scales occur below the grid level and are...Practical simulations of turbulent processes are generally cutoff, with a grid resolution that stops within the inertial range, meaning that multiple active regions and length scales occur below the grid level and are not resolved. This is the regime of large eddy simulations （LES）, in which the larger but not the smaller of the turbulent length scales are resolved. Solutions of the fluid Navier-Stokes equations, when considered in the inertial regime, are conventionally regarded as solutions of the Euler equations. In other words, the viscous and diffusive transport terms in the Navier-Stokes equations can be neglected in the inertial regime and in LES simulations, while the Euler equation becomes fundamental. For such simulations, significant new solution details emerge as the grid is refined. It follows that conventional notions of grid convergence are at risk of failure, and that a new, and weaker notion of convergence may be appropriate. It is generally understood that the LES or inertial regime is inherently fluctuating and its description must be statistical in nature. Here we develop such a point of view systematically, based on Young measures, which are measures depending on or indexed by space time points. In the Young measure du（ξ）x,t, the random variable ξ of the measure is a solution state variable, i.e., a solution dependent variable, representing momentum, density, energy and species concentrations, while the space time coordinates, x, t, serve to index the measure.Theoretical evidence suggests that convergence via Young measures is suifficiently weak to encompass the LES/inertial regime; numerical and theoretical evidence suggests that this notion may be required for passive scalar concentration and therm degrees of freedom. Our objective in this research is twofold： turbulent simulations without recourse to ad- justable parameters （calibration） and extension to more complex physics, without use of additional models or parameters, in both cases with validation through comparison to experimental data.展开更多
Nuclear reaction studies on unstable isotopes can strongly help in improving our understanding of nucleosynthesis in stars.Indirect approaches to determining astrophysical reaction rates are increasingly common-place ...Nuclear reaction studies on unstable isotopes can strongly help in improving our understanding of nucleosynthesis in stars.Indirect approaches to determining astrophysical reaction rates are increasingly common-place and undergoing continuous refinement.Of particular interest is the use of such indirect techniques at storage rings,which,among other aspects,allow to recycle rare unstable beams.We propose to investigate the reaction rates of astrophysical interest using indirect methods(surrogate,Trojan horse,etc.)in reverse kinematics at the IMP-CAS storage ring.Long lived radioactive ion beams,produced remotely,can be accelerated,and made to interact with light targets.The proposed reactions are^(85)Kr(p,p’γ),^(85)Kr(d,pγ),constraining the neutron flux in an s-process branching point,^(79)Se(p,p’γ),^(79)Se(d,pγ),constraining the temperature in s-process nucleosyntheses,and^(59)Fe(d,pγ),constraining core collapse supernovae.展开更多
基金the Department of Science and Technology,New Delhi(Government of India) for funding this work under the Project SR/FTP/PS-087/2010
文摘Undoped, Dy^3＋ doped and Dy^3＋, K^＋ codoped calcium molybdate phosphors have been synthesized by solid-state reaction method. X-ray diffraction studies reveal the tetragonal structure of the prepared phosphors having crystallite size 15-50 nm. Scanning electron microscopy （SEM） studies reveal the morphology and crystallite size of the prepared phosphors. Photoluminescence studies indicate that there are blue and yellow emissions at 489 and 576 nm, respectively corresponding to Dy^3＋ ion. The introduction of K＋ ion significantly influences the blue and yellow emissions which causes the near white light emission from this codoped phosphor. The intense absorption peak of the codoped phosphor at 210 nm is attributed to the band gap and a shoulder at 240 nm appears due to charge transfer from oxygen ions to neighbouring molybdenum ions. The band gap of the codoped phosphor is calculated as 5.5 eV from the absorption studies. The dielectric properties such as permittivity and dielectric loss are studied as a function of frequency.Acknowledgement The authors are thankful to the Department of Science and Technology, New Delhi （Government of India） for funding this work under the Project SR/FTP/PS-087/2010.
基金supported in part by the Nuclear Energy University Program of the Department of Energy,project NEUP-09-349Battelle Energy Alliance LLC 00088495 (subaward with DOE as prime sponsor)+2 种基金Leland Stanford Junior University 2175022040367A (subaward with DOE as prime sponsor)Army Research Office W911NF0910306supported by the US Department of Energy under Contract DEAC 5206NA25396,supported by the Office of Science of the U.S. Department of Energy under contract DE-AC02-06CH11357
文摘Practical simulations of turbulent processes are generally cutoff, with a grid resolution that stops within the inertial range, meaning that multiple active regions and length scales occur below the grid level and are not resolved. This is the regime of large eddy simulations （LES）, in which the larger but not the smaller of the turbulent length scales are resolved. Solutions of the fluid Navier-Stokes equations, when considered in the inertial regime, are conventionally regarded as solutions of the Euler equations. In other words, the viscous and diffusive transport terms in the Navier-Stokes equations can be neglected in the inertial regime and in LES simulations, while the Euler equation becomes fundamental. For such simulations, significant new solution details emerge as the grid is refined. It follows that conventional notions of grid convergence are at risk of failure, and that a new, and weaker notion of convergence may be appropriate. It is generally understood that the LES or inertial regime is inherently fluctuating and its description must be statistical in nature. Here we develop such a point of view systematically, based on Young measures, which are measures depending on or indexed by space time points. In the Young measure du（ξ）x,t, the random variable ξ of the measure is a solution state variable, i.e., a solution dependent variable, representing momentum, density, energy and species concentrations, while the space time coordinates, x, t, serve to index the measure.Theoretical evidence suggests that convergence via Young measures is suifficiently weak to encompass the LES/inertial regime; numerical and theoretical evidence suggests that this notion may be required for passive scalar concentration and therm degrees of freedom. Our objective in this research is twofold： turbulent simulations without recourse to ad- justable parameters （calibration） and extension to more complex physics, without use of additional models or parameters, in both cases with validation through comparison to experimental data.
文摘Nuclear reaction studies on unstable isotopes can strongly help in improving our understanding of nucleosynthesis in stars.Indirect approaches to determining astrophysical reaction rates are increasingly common-place and undergoing continuous refinement.Of particular interest is the use of such indirect techniques at storage rings,which,among other aspects,allow to recycle rare unstable beams.We propose to investigate the reaction rates of astrophysical interest using indirect methods(surrogate,Trojan horse,etc.)in reverse kinematics at the IMP-CAS storage ring.Long lived radioactive ion beams,produced remotely,can be accelerated,and made to interact with light targets.The proposed reactions are^(85)Kr(p,p’γ),^(85)Kr(d,pγ),constraining the neutron flux in an s-process branching point,^(79)Se(p,p’γ),^(79)Se(d,pγ),constraining the temperature in s-process nucleosyntheses,and^(59)Fe(d,pγ),constraining core collapse supernovae.
