Radi Radi | Defence Services Medical Academy (DSMA), Yangon, Myanmar (Burma) (original) (raw)

Papers by Radi Radi

Research paper thumbnail of Effect of lateral radiative losses on radiative shock propagation

High Energy Density Physics, 2007

Experimental and numerical studies of radiative shocks, of interest as scaled astrophysical objec... more Experimental and numerical studies of radiative shocks, of interest as scaled astrophysical objects, have been performed. Experiments were conducted at the PALS facility in Prague with a xenon filled mini-shock tube using a laser accelerated plastic pusher. Numerical simulations of the hydrodynamics including radiation effects have been performed with the 3D code HERACLES. Measurements have been made of the electronic density of the shocked gas and of the time history of the position of the radiative precursor. Simulations and experimental results show good agreement when lateral radiative losses are taken into account, including a wall albedo of 40%.

Research paper thumbnail of The effects of core structure on radiative and non-radiative recombinations at metal ion substituents in semiconductors and phosphors

Advances in Physics, 1978

Abstract Carrier binding and recombination processes at transition metal (TM) and post-transition... more Abstract Carrier binding and recombination processes at transition metal (TM) and post-transition metal impurities in solids are reviewed. The presence of low-lying empty core orbitals in these impurities introduces novel binding and recombination phenomena and ...

Research paper thumbnail of Radiative and non radiative spectroscopic properties of Er 3+ ion in tellurite glass

Optics Communications, 2006

We have investigated in detail the mechanism of infrared emission and upconversion emission of Er... more We have investigated in detail the mechanism of infrared emission and upconversion emission of Er 3+ in tellurite glass as a function of the dopant concentration. Both the infrared and upconversion emissions are competing processes and the efficiency of infrared emission at 1534 nm is 100% at the lowest Er content (0.5 mol%) and reduces to 50% at higher dopant concentration (>2 mol%). The green upconversion emission at 548 nm is mainly due to the excited state absorption (ESA) from 4 I 11/2 , which populate the 4 F 7/2 level. In addition to this, the possible energy transfer (ET) through Er 3+ ( 4 I 11/2 ) + Er 3+ ( 4 I 11/2 ) ! Er 3+ ( 4 F 7/2 ) + Er 3+ ( 4 I 15/2 ) can also results in the green emission as is noticed from the concentration dependent efficiency change of the green emission. The fluorescence quenching of green emission with Er concentration may be related with the cross relaxation (CR) process 2 H 11/2 + 4 I 15/2 ! 4 I 9/2 + 4 I 13/2 . The red emission is due to the combined effect of the ESA from level 4 I 13/2 to 4 F 9/2 , the energy transfer process described by Er 3+ ( 4 I 13/2 ) + Er 3+ ( 4 I 11/2 ) ! Er 3+ ( 4 F 9/2 ) + Er 3+ ( 4 I 15/2 ) and the cross relaxation process.

Research paper thumbnail of On-Line Processing of Unidirectional Fiber Composites Using Radiative Heating: II. Radiative Properties, Experimental Validation and Process Parameter Selection

Journal of Composite Materials, 2002

ABSTRACT

Research paper thumbnail of Radiative and non-radiative decay of a single molecule close to a metallic nanoparticle

Optics Communications, 2006

We study the spontaneous emission of a single emitter close to a metallic nanoparticle, with the ... more We study the spontaneous emission of a single emitter close to a metallic nanoparticle, with the aim to clarify the distance dependence of the radiative and non-radiative decay rates. We derive analytical formulas based on a dipole-dipole model, and show that the nonradiative decay rate follows a R À6 dependence at short distance, where R is the distance between the emitter and the center of the nanoparticle, as in Fö rster's energy transfer. The distance dependence of the radiative decay rate is more subtle. It is chiefly dominated by a R À3 dependence, a R À6 dependence being visible at plasmon resonance. The latter is a consequence of radiative damping in the effective dipole polarizability of the nanoparticle. The different distance behavior of the radiative and non-radiative decay rates implies that the apparent quantum yield always vanishes at short distance. Moreover, non-radiative decay is strongly enhanced when the emitter radiates at the plasmon-resonance frequency of the nanoparticle.

Research paper thumbnail of An approximate calculation of radiative heating and radiative equilibrium in the Martian atmosphere

Planetary and Space Science, 1967

... 1. INTRODUCTION Numerical computations of the radiative equilibrium state of the Martian atmo... more ... 1. INTRODUCTION Numerical computations of the radiative equilibrium state of the Martian atmosphere by various authors have shown a satisfactory degree of agreement (Goody, 1957; Ohring, 1963; Ohring and Mariano, 1965; Prabhakara and Hogan, 1965). ...

Research paper thumbnail of Deuterium isotope effect on single vibronic level photochemistry of formaldehyde ?, 1A2): Fluorescence quantum yields, radiative and non-radiative transitions

Chemical Physics Letters, 1976

Research paper thumbnail of Radiative and non-radiative processes of Ce related transitions in CaGa 2S 4 and SrGa 2S 4

Journal of Physics and Chemistry of Solids, 2003

The Ce emission appearing in the blue-green region was investigated for CaGa 2 S 4 and SrGa 2 S 4... more The Ce emission appearing in the blue-green region was investigated for CaGa 2 S 4 and SrGa 2 S 4 . The room temperature quantum efficiency as high as 73% was observed for a 0.4 wt% Ce-doped CaGa 2 S 4 single crystal grown by the melt method. The quantum efficiency decreased for a 0.8 wt% Ce-doped CaGa 2 S 4 crystal and clear photoacoustic signal was detected in this sample, indicating an increase of non-radiative transition. For each of these compounds, ultraviolet (UV) excitation produced a hitherto unreported new UV emission which is thought to originate from 5d(E g ) level of the Ce ion. Temperature dependent intensity changes observed in this UV emission and in the blue-green emission suggest temperature dependent population transfer from the upper level of E g to the lower level of T 2g in the excited state of 5d electrons. q

Research paper thumbnail of Dysprosium-doped YAl 3(BO 3) 4 (YAB) crystals: an investigation of radiative and non-radiative processes

Journal of Alloys and Compounds, 2003

The absorption, emission spectra and lifetime of the F fluorescent level of Dy in YAl (BO ) cryst... more The absorption, emission spectra and lifetime of the F fluorescent level of Dy in YAl (BO ) crystal were investigated. Energy 9 / 2 3 3 4 level structure was constructed from absorption and emission spectra recorded at 5 K. The measured oscillator strengths of the transitions between the J manifolds at 300 K were compared with those derived from the Judd-Ofelt theory. The radiative transition rates and 4 radiative lifetimes were calculated. Although there are several transitions originating in the F level a major part of emission intensity 9 / 2 4 6 4 is contained in the F → H transition. Measurement of selfquenching of the F luminescence provided a parameter 9 / 2 13 / 2 9 / 2 31 characterizing an activator-activator interaction, which may be used to predict an optimal Dy concentration. The narrow and 4 polarization dependent emission lines, relatively long lifetime of the F metastable level (t5520 ms) and its high quantum efficiency 9 / 2 are advantageous for low threshold laser action in both CW and pulsed operation. The emission cross-section of a potential laser line at 4 6 570 nm connected with F → H transition was estimated. 9 / 2 13 / 2

Research paper thumbnail of Comparison of different global information sources used in surface radiative flux calculation: Radiative properties of the surface

Journal of Geophysical Research, 2007

1] Direct estimates of surface radiative fluxes that resolve regional and weather-scale variabili... more 1] Direct estimates of surface radiative fluxes that resolve regional and weather-scale variability over the whole globe with reasonable accuracy have only become possible with the advent of extensive global, mostly satellite, data sets within the past couple of decades. The accuracy of these fluxes, estimated to be about 10-15 W/m 2 , is largely limited by the accuracy of the input data sets. The leading uncertainties in the surface fluxes are no longer predominantly induced by clouds but are now as much associated with uncertainties in the surface and near-surface atmospheric properties. This study presents a fuller, more quantitative evaluation of the uncertainties for the surface albedo and emissivity and surface skin temperatures by comparing the main available global data sets from the Moderate-Resolution Imaging Spectroradiometer product, the NASA Global Energy and Water Cycle Experiment Surface Radiation Budget project, the European Centre for Medium-Range Weather Forecasts, the National Aeronautics and Space Administration, the National Centers for Environmental Prediction, the International Satellite Cloud Climatology Project (ISCCP), the Laboratoire de Météorologie Dynamique, NOAA/NASA Pathfinder Advanced Very High Resolution Radiometer project, and the NOAA Optimum Interpolation Sea Surface Temperature Analysis and the Tropical Rainfall Measuring Mission (TRMM) Microwave Image project. The data sets are, in practice, treated as an ensemble of realizations of the actual climate such that their differences represent an estimate of the uncertainty in their measurements because we do not possess global ''truth'' data sets for these quantities. The results are globally representative and may be taken as a generalization of our previous ISCCP-based uncertainty estimates for the input data sets. Surface properties have the primary role in determining the surface upward shortwave (SW) and longwave (LW) flux.From this study the following conclusions are obtained. Although land surface albedos in the near-infrared remain poorly constrained (highly uncertain), they do not cause too much error in total surface SW fluxes; the more subtle regional and seasonal variations associated with vegetation and snow are still in doubt. The uncertainty of the broadband black-sky SW albedo for land surface from this study is about 7%, which can easily induce 5-10 W/m 2 uncertainty in (upwelling) surface SW flux estimates. Even though available surface (broadband) LW emissivity data sets differ significantly (3-5% uncertainty), this disagreement is confined to wavelengths >20 mm so that there is little practical effect (1-3 W/m 2 ) on the surface upwelling LW fluxes. The surface skin temperature is one of two leading factors that cause problems with surface LW fluxes. Even though the differences among the various data sets are generally only 2-4 K, this can easily cause 10-15 W/m 2 uncertainty in calculated surface (upwelling) LW fluxes. Significant improvements could be obtained for surface LW flux calculations by improving the retrievals of (in order of decreasing importance): (1) surface skin temperature, (2) surface air and near-surface-layer temperature, (3) column precipitable water amount, and JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, D01102, doi:10.

Research paper thumbnail of Effect of lateral radiative losses on radiative shock propagation

High Energy Density Physics, 2007

Experimental and numerical studies of radiative shocks, of interest as scaled astrophysical objec... more Experimental and numerical studies of radiative shocks, of interest as scaled astrophysical objects, have been performed. Experiments were conducted at the PALS facility in Prague with a xenon filled mini-shock tube using a laser accelerated plastic pusher. Numerical simulations of the hydrodynamics including radiation effects have been performed with the 3D code HERACLES. Measurements have been made of the electronic density of the shocked gas and of the time history of the position of the radiative precursor. Simulations and experimental results show good agreement when lateral radiative losses are taken into account, including a wall albedo of 40%.

Research paper thumbnail of The effects of core structure on radiative and non-radiative recombinations at metal ion substituents in semiconductors and phosphors

Advances in Physics, 1978

Abstract Carrier binding and recombination processes at transition metal (TM) and post-transition... more Abstract Carrier binding and recombination processes at transition metal (TM) and post-transition metal impurities in solids are reviewed. The presence of low-lying empty core orbitals in these impurities introduces novel binding and recombination phenomena and ...

Research paper thumbnail of Radiative and non radiative spectroscopic properties of Er 3+ ion in tellurite glass

Optics Communications, 2006

We have investigated in detail the mechanism of infrared emission and upconversion emission of Er... more We have investigated in detail the mechanism of infrared emission and upconversion emission of Er 3+ in tellurite glass as a function of the dopant concentration. Both the infrared and upconversion emissions are competing processes and the efficiency of infrared emission at 1534 nm is 100% at the lowest Er content (0.5 mol%) and reduces to 50% at higher dopant concentration (>2 mol%). The green upconversion emission at 548 nm is mainly due to the excited state absorption (ESA) from 4 I 11/2 , which populate the 4 F 7/2 level. In addition to this, the possible energy transfer (ET) through Er 3+ ( 4 I 11/2 ) + Er 3+ ( 4 I 11/2 ) ! Er 3+ ( 4 F 7/2 ) + Er 3+ ( 4 I 15/2 ) can also results in the green emission as is noticed from the concentration dependent efficiency change of the green emission. The fluorescence quenching of green emission with Er concentration may be related with the cross relaxation (CR) process 2 H 11/2 + 4 I 15/2 ! 4 I 9/2 + 4 I 13/2 . The red emission is due to the combined effect of the ESA from level 4 I 13/2 to 4 F 9/2 , the energy transfer process described by Er 3+ ( 4 I 13/2 ) + Er 3+ ( 4 I 11/2 ) ! Er 3+ ( 4 F 9/2 ) + Er 3+ ( 4 I 15/2 ) and the cross relaxation process.

Research paper thumbnail of On-Line Processing of Unidirectional Fiber Composites Using Radiative Heating: II. Radiative Properties, Experimental Validation and Process Parameter Selection

Journal of Composite Materials, 2002

ABSTRACT

Research paper thumbnail of Radiative and non-radiative decay of a single molecule close to a metallic nanoparticle

Optics Communications, 2006

We study the spontaneous emission of a single emitter close to a metallic nanoparticle, with the ... more We study the spontaneous emission of a single emitter close to a metallic nanoparticle, with the aim to clarify the distance dependence of the radiative and non-radiative decay rates. We derive analytical formulas based on a dipole-dipole model, and show that the nonradiative decay rate follows a R À6 dependence at short distance, where R is the distance between the emitter and the center of the nanoparticle, as in Fö rster's energy transfer. The distance dependence of the radiative decay rate is more subtle. It is chiefly dominated by a R À3 dependence, a R À6 dependence being visible at plasmon resonance. The latter is a consequence of radiative damping in the effective dipole polarizability of the nanoparticle. The different distance behavior of the radiative and non-radiative decay rates implies that the apparent quantum yield always vanishes at short distance. Moreover, non-radiative decay is strongly enhanced when the emitter radiates at the plasmon-resonance frequency of the nanoparticle.

Research paper thumbnail of An approximate calculation of radiative heating and radiative equilibrium in the Martian atmosphere

Planetary and Space Science, 1967

... 1. INTRODUCTION Numerical computations of the radiative equilibrium state of the Martian atmo... more ... 1. INTRODUCTION Numerical computations of the radiative equilibrium state of the Martian atmosphere by various authors have shown a satisfactory degree of agreement (Goody, 1957; Ohring, 1963; Ohring and Mariano, 1965; Prabhakara and Hogan, 1965). ...

Research paper thumbnail of Deuterium isotope effect on single vibronic level photochemistry of formaldehyde ?, 1A2): Fluorescence quantum yields, radiative and non-radiative transitions

Chemical Physics Letters, 1976

Research paper thumbnail of Radiative and non-radiative processes of Ce related transitions in CaGa 2S 4 and SrGa 2S 4

Journal of Physics and Chemistry of Solids, 2003

The Ce emission appearing in the blue-green region was investigated for CaGa 2 S 4 and SrGa 2 S 4... more The Ce emission appearing in the blue-green region was investigated for CaGa 2 S 4 and SrGa 2 S 4 . The room temperature quantum efficiency as high as 73% was observed for a 0.4 wt% Ce-doped CaGa 2 S 4 single crystal grown by the melt method. The quantum efficiency decreased for a 0.8 wt% Ce-doped CaGa 2 S 4 crystal and clear photoacoustic signal was detected in this sample, indicating an increase of non-radiative transition. For each of these compounds, ultraviolet (UV) excitation produced a hitherto unreported new UV emission which is thought to originate from 5d(E g ) level of the Ce ion. Temperature dependent intensity changes observed in this UV emission and in the blue-green emission suggest temperature dependent population transfer from the upper level of E g to the lower level of T 2g in the excited state of 5d electrons. q

Research paper thumbnail of Dysprosium-doped YAl 3(BO 3) 4 (YAB) crystals: an investigation of radiative and non-radiative processes

Journal of Alloys and Compounds, 2003

The absorption, emission spectra and lifetime of the F fluorescent level of Dy in YAl (BO ) cryst... more The absorption, emission spectra and lifetime of the F fluorescent level of Dy in YAl (BO ) crystal were investigated. Energy 9 / 2 3 3 4 level structure was constructed from absorption and emission spectra recorded at 5 K. The measured oscillator strengths of the transitions between the J manifolds at 300 K were compared with those derived from the Judd-Ofelt theory. The radiative transition rates and 4 radiative lifetimes were calculated. Although there are several transitions originating in the F level a major part of emission intensity 9 / 2 4 6 4 is contained in the F → H transition. Measurement of selfquenching of the F luminescence provided a parameter 9 / 2 13 / 2 9 / 2 31 characterizing an activator-activator interaction, which may be used to predict an optimal Dy concentration. The narrow and 4 polarization dependent emission lines, relatively long lifetime of the F metastable level (t5520 ms) and its high quantum efficiency 9 / 2 are advantageous for low threshold laser action in both CW and pulsed operation. The emission cross-section of a potential laser line at 4 6 570 nm connected with F → H transition was estimated. 9 / 2 13 / 2

Research paper thumbnail of Comparison of different global information sources used in surface radiative flux calculation: Radiative properties of the surface

Journal of Geophysical Research, 2007

1] Direct estimates of surface radiative fluxes that resolve regional and weather-scale variabili... more 1] Direct estimates of surface radiative fluxes that resolve regional and weather-scale variability over the whole globe with reasonable accuracy have only become possible with the advent of extensive global, mostly satellite, data sets within the past couple of decades. The accuracy of these fluxes, estimated to be about 10-15 W/m 2 , is largely limited by the accuracy of the input data sets. The leading uncertainties in the surface fluxes are no longer predominantly induced by clouds but are now as much associated with uncertainties in the surface and near-surface atmospheric properties. This study presents a fuller, more quantitative evaluation of the uncertainties for the surface albedo and emissivity and surface skin temperatures by comparing the main available global data sets from the Moderate-Resolution Imaging Spectroradiometer product, the NASA Global Energy and Water Cycle Experiment Surface Radiation Budget project, the European Centre for Medium-Range Weather Forecasts, the National Aeronautics and Space Administration, the National Centers for Environmental Prediction, the International Satellite Cloud Climatology Project (ISCCP), the Laboratoire de Météorologie Dynamique, NOAA/NASA Pathfinder Advanced Very High Resolution Radiometer project, and the NOAA Optimum Interpolation Sea Surface Temperature Analysis and the Tropical Rainfall Measuring Mission (TRMM) Microwave Image project. The data sets are, in practice, treated as an ensemble of realizations of the actual climate such that their differences represent an estimate of the uncertainty in their measurements because we do not possess global ''truth'' data sets for these quantities. The results are globally representative and may be taken as a generalization of our previous ISCCP-based uncertainty estimates for the input data sets. Surface properties have the primary role in determining the surface upward shortwave (SW) and longwave (LW) flux.From this study the following conclusions are obtained. Although land surface albedos in the near-infrared remain poorly constrained (highly uncertain), they do not cause too much error in total surface SW fluxes; the more subtle regional and seasonal variations associated with vegetation and snow are still in doubt. The uncertainty of the broadband black-sky SW albedo for land surface from this study is about 7%, which can easily induce 5-10 W/m 2 uncertainty in (upwelling) surface SW flux estimates. Even though available surface (broadband) LW emissivity data sets differ significantly (3-5% uncertainty), this disagreement is confined to wavelengths >20 mm so that there is little practical effect (1-3 W/m 2 ) on the surface upwelling LW fluxes. The surface skin temperature is one of two leading factors that cause problems with surface LW fluxes. Even though the differences among the various data sets are generally only 2-4 K, this can easily cause 10-15 W/m 2 uncertainty in calculated surface (upwelling) LW fluxes. Significant improvements could be obtained for surface LW flux calculations by improving the retrievals of (in order of decreasing importance): (1) surface skin temperature, (2) surface air and near-surface-layer temperature, (3) column precipitable water amount, and JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, D01102, doi:10.