The Experts below are selected from a list of 177 Experts worldwide ranked by ideXlab platform
Bing-ming Cheng - One of the best experts on this subject based on the ideXlab platform.
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Photolysis of O2 dispersed in solid neon with Far-Ultraviolet Radiation
Physical chemistry chemical physics : PCCP, 2018Co-Authors: Sheng-lung Chou, Yu-chain Peng, Bing-ming Cheng, John F. OgilvieAbstract:IrRadiation at 173 or 143 nm of samples of 16O2 or 18O2 in solid Ne near 4 K produced many new spectral lines in absorption and emission from the mid-infrared to the near-Ultraviolet regions. The major product was ozone, O3, that was identified with its mid-infrared and near-Ultraviolet absorption lines. Oxygen atoms were formed on photolysis of O2 and stored in solid neon until the temperature of a sample was increased to 9 K, which enabled their migration and combination to form O3 and likely also O2. O2 in five excited states and O in two excited states detected through the emission spectra indicate that complicated processes occurred in solid Ne after Far-Ultraviolet excitation. For the transition 1D2 → 3P1,2 of O, the lifetime was determined to be 5.87 ± 0.10 s; the lifetime of the upper state of an unidentified transition associated with an emission feature at 701.7 nm was determined to be 2.34 ± 0.07 s.
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THE EMISSION, LIFETIMES, AND FORMATION THRESHOLD OF THE VEGARD–KAPLAN TRANSITION OF SOLID NITROGEN EXPOSED TO Far-Ultraviolet Radiation
The Astrophysical Journal, 2016Co-Authors: Yu-chain Peng, Sheng-lung Chou, Meng-yeh Lin, Bing-ming ChengAbstract:IrRadiation of solid nitrogen at 4 K with Far-Ultraviolet light from a synchrotron caused excitation to the upper state of the Vegard–Kaplan (VK) system; the emission in that system was simultaneously recorded in wavelength region 200–440 nm. The lifetimes of emission lines for VK (0, 1) to (0, 12) transitions were measured in the range of 2.12 ~ 2.65 s. The threshold wavelength to observe the VK emission was 175.0 ± 3.5 nm, corresponding to energy 7.08 ± 0.14 eV. This investigation of the generation of icy VK nitrogen enhances our understanding of its photochemistry in space.
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the emission lifetimes and formation threshold of the vegard kaplan transition of solid nitrogen exposed to Far Ultraviolet Radiation
The Astrophysical Journal, 2016Co-Authors: Yu-chain Peng, Sheng-lung Chou, Meng-yeh Lin, Bing-ming ChengAbstract:IrRadiation of solid nitrogen at 4 K with Far-Ultraviolet light from a synchrotron caused excitation to the upper state of the Vegard–Kaplan (VK) system; the emission in that system was simultaneously recorded in wavelength region 200–440 nm. The lifetimes of emission lines for VK (0, 1) to (0, 12) transitions were measured in the range of 2.12 ~ 2.65 s. The threshold wavelength to observe the VK emission was 175.0 ± 3.5 nm, corresponding to energy 7.08 ± 0.14 eV. This investigation of the generation of icy VK nitrogen enhances our understanding of its photochemistry in space.
Yu-chain Peng - One of the best experts on this subject based on the ideXlab platform.
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Photolysis of O2 dispersed in solid neon with Far-Ultraviolet Radiation
Physical chemistry chemical physics : PCCP, 2018Co-Authors: Sheng-lung Chou, Yu-chain Peng, Bing-ming Cheng, John F. OgilvieAbstract:IrRadiation at 173 or 143 nm of samples of 16O2 or 18O2 in solid Ne near 4 K produced many new spectral lines in absorption and emission from the mid-infrared to the near-Ultraviolet regions. The major product was ozone, O3, that was identified with its mid-infrared and near-Ultraviolet absorption lines. Oxygen atoms were formed on photolysis of O2 and stored in solid neon until the temperature of a sample was increased to 9 K, which enabled their migration and combination to form O3 and likely also O2. O2 in five excited states and O in two excited states detected through the emission spectra indicate that complicated processes occurred in solid Ne after Far-Ultraviolet excitation. For the transition 1D2 → 3P1,2 of O, the lifetime was determined to be 5.87 ± 0.10 s; the lifetime of the upper state of an unidentified transition associated with an emission feature at 701.7 nm was determined to be 2.34 ± 0.07 s.
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THE EMISSION, LIFETIMES, AND FORMATION THRESHOLD OF THE VEGARD–KAPLAN TRANSITION OF SOLID NITROGEN EXPOSED TO Far-Ultraviolet Radiation
The Astrophysical Journal, 2016Co-Authors: Yu-chain Peng, Sheng-lung Chou, Meng-yeh Lin, Bing-ming ChengAbstract:IrRadiation of solid nitrogen at 4 K with Far-Ultraviolet light from a synchrotron caused excitation to the upper state of the Vegard–Kaplan (VK) system; the emission in that system was simultaneously recorded in wavelength region 200–440 nm. The lifetimes of emission lines for VK (0, 1) to (0, 12) transitions were measured in the range of 2.12 ~ 2.65 s. The threshold wavelength to observe the VK emission was 175.0 ± 3.5 nm, corresponding to energy 7.08 ± 0.14 eV. This investigation of the generation of icy VK nitrogen enhances our understanding of its photochemistry in space.
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the emission lifetimes and formation threshold of the vegard kaplan transition of solid nitrogen exposed to Far Ultraviolet Radiation
The Astrophysical Journal, 2016Co-Authors: Yu-chain Peng, Sheng-lung Chou, Meng-yeh Lin, Bing-ming ChengAbstract:IrRadiation of solid nitrogen at 4 K with Far-Ultraviolet light from a synchrotron caused excitation to the upper state of the Vegard–Kaplan (VK) system; the emission in that system was simultaneously recorded in wavelength region 200–440 nm. The lifetimes of emission lines for VK (0, 1) to (0, 12) transitions were measured in the range of 2.12 ~ 2.65 s. The threshold wavelength to observe the VK emission was 175.0 ± 3.5 nm, corresponding to energy 7.08 ± 0.14 eV. This investigation of the generation of icy VK nitrogen enhances our understanding of its photochemistry in space.
Kazuyuki Omukai - One of the best experts on this subject based on the ideXlab platform.
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primordial star formation under the influence of Far Ultraviolet Radiation 1540 cosmological haloes and the stellar mass distribution
Monthly Notices of the Royal Astronomical Society, 2015Co-Authors: Shingo Hirano, Takashi Hosokawa, Kazuyuki Omukai, Naoki Yoshida, Harold W YorkeAbstract:We perform a large set of cosmological simulations of early structure formation and follow the formation and evolution of 1540 star-forming gas clouds to derive the mass distribution of primordial stars. The star formation in our cosmological simulations is characterized by two distinct populations, the so-called Population III.1 stars and primordial stars formed under the influence of Far Ultraviolet (FUV) Radiation (Population III.2D stars). In this work, we determine the stellar masses by using the dependences on the physical properties of star-forming cloud and/or the external photodissociating intensity from nearby primordial stars, which are derived from the results of two-dimensional Radiation hydrodynamic simulations of protostellar feedback. The characteristic mass of the Pop III stars is found to be a few hundred solar masses at z ~ 25, and it gradually shifts to lower masses with decreasing redshift. At high redshifts z > 20, about half of the star-forming gas clouds are exposed to intense FUV Radiation and thus give birth to massive Pop III.2D stars. However, the local FUV Radiation by nearby Pop III stars becomes weaker at lower redshifts, when typical Pop III stars have smaller masses and the mean physical separation between the stars becomes large owing to cosmic expansion. Therefore, at z < 20, a large fraction of the primordial gas clouds host Pop III.1 stars. At z =< 15, the Pop III.1 stars are formed in relatively cool gas clouds due to efficient radiative cooling by H_2 and HD molecules; such stars have masses of a few x 10 Msun. Since the stellar evolution and the final fate are determined by the stellar mass, Pop III stars formed at different epochs play different roles in the early universe.
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Primordial Star Formation under Far-Ultraviolet Radiation
The Astrophysical Journal, 2001Co-Authors: Kazuyuki OmukaiAbstract:Thermal and chemical evolution of primordial gas clouds irradiated with Far-Ultraviolet (FUV; hν < 13.6 eV) Radiation is investigated. In clouds irradiated by intense FUV Radiation, sufficient hydrogen molecules to be important for cooling are never formed. However, even without molecular hydrogen, if the clouds are massive enough, they start collapsing via atomic hydrogen line cooling. Such clouds continue to collapse almost isothermally owing to successive cooling by H- free-bound emission up to the number density of 1016 cm-3. Inside the clouds, the Jeans mass eventually falls well below a solar mass. This indicates that hydrogen molecules are dispensable for low-mass primordial star formation, provided that fragmentation of the clouds occurs at sufficiently high density.
Sheng-lung Chou - One of the best experts on this subject based on the ideXlab platform.
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Photolysis of O2 dispersed in solid neon with Far-Ultraviolet Radiation
Physical chemistry chemical physics : PCCP, 2018Co-Authors: Sheng-lung Chou, Yu-chain Peng, Bing-ming Cheng, John F. OgilvieAbstract:IrRadiation at 173 or 143 nm of samples of 16O2 or 18O2 in solid Ne near 4 K produced many new spectral lines in absorption and emission from the mid-infrared to the near-Ultraviolet regions. The major product was ozone, O3, that was identified with its mid-infrared and near-Ultraviolet absorption lines. Oxygen atoms were formed on photolysis of O2 and stored in solid neon until the temperature of a sample was increased to 9 K, which enabled their migration and combination to form O3 and likely also O2. O2 in five excited states and O in two excited states detected through the emission spectra indicate that complicated processes occurred in solid Ne after Far-Ultraviolet excitation. For the transition 1D2 → 3P1,2 of O, the lifetime was determined to be 5.87 ± 0.10 s; the lifetime of the upper state of an unidentified transition associated with an emission feature at 701.7 nm was determined to be 2.34 ± 0.07 s.
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THE EMISSION, LIFETIMES, AND FORMATION THRESHOLD OF THE VEGARD–KAPLAN TRANSITION OF SOLID NITROGEN EXPOSED TO Far-Ultraviolet Radiation
The Astrophysical Journal, 2016Co-Authors: Yu-chain Peng, Sheng-lung Chou, Meng-yeh Lin, Bing-ming ChengAbstract:IrRadiation of solid nitrogen at 4 K with Far-Ultraviolet light from a synchrotron caused excitation to the upper state of the Vegard–Kaplan (VK) system; the emission in that system was simultaneously recorded in wavelength region 200–440 nm. The lifetimes of emission lines for VK (0, 1) to (0, 12) transitions were measured in the range of 2.12 ~ 2.65 s. The threshold wavelength to observe the VK emission was 175.0 ± 3.5 nm, corresponding to energy 7.08 ± 0.14 eV. This investigation of the generation of icy VK nitrogen enhances our understanding of its photochemistry in space.
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the emission lifetimes and formation threshold of the vegard kaplan transition of solid nitrogen exposed to Far Ultraviolet Radiation
The Astrophysical Journal, 2016Co-Authors: Yu-chain Peng, Sheng-lung Chou, Meng-yeh Lin, Bing-ming ChengAbstract:IrRadiation of solid nitrogen at 4 K with Far-Ultraviolet light from a synchrotron caused excitation to the upper state of the Vegard–Kaplan (VK) system; the emission in that system was simultaneously recorded in wavelength region 200–440 nm. The lifetimes of emission lines for VK (0, 1) to (0, 12) transitions were measured in the range of 2.12 ~ 2.65 s. The threshold wavelength to observe the VK emission was 175.0 ± 3.5 nm, corresponding to energy 7.08 ± 0.14 eV. This investigation of the generation of icy VK nitrogen enhances our understanding of its photochemistry in space.
Harold W Yorke - One of the best experts on this subject based on the ideXlab platform.
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primordial star formation under the influence of Far Ultraviolet Radiation 1540 cosmological haloes and the stellar mass distribution
Monthly Notices of the Royal Astronomical Society, 2015Co-Authors: Shingo Hirano, Takashi Hosokawa, Kazuyuki Omukai, Naoki Yoshida, Harold W YorkeAbstract:We perform a large set of cosmological simulations of early structure formation and follow the formation and evolution of 1540 star-forming gas clouds to derive the mass distribution of primordial stars. The star formation in our cosmological simulations is characterized by two distinct populations, the so-called Population III.1 stars and primordial stars formed under the influence of Far Ultraviolet (FUV) Radiation (Population III.2D stars). In this work, we determine the stellar masses by using the dependences on the physical properties of star-forming cloud and/or the external photodissociating intensity from nearby primordial stars, which are derived from the results of two-dimensional Radiation hydrodynamic simulations of protostellar feedback. The characteristic mass of the Pop III stars is found to be a few hundred solar masses at z ~ 25, and it gradually shifts to lower masses with decreasing redshift. At high redshifts z > 20, about half of the star-forming gas clouds are exposed to intense FUV Radiation and thus give birth to massive Pop III.2D stars. However, the local FUV Radiation by nearby Pop III stars becomes weaker at lower redshifts, when typical Pop III stars have smaller masses and the mean physical separation between the stars becomes large owing to cosmic expansion. Therefore, at z < 20, a large fraction of the primordial gas clouds host Pop III.1 stars. At z =< 15, the Pop III.1 stars are formed in relatively cool gas clouds due to efficient radiative cooling by H_2 and HD molecules; such stars have masses of a few x 10 Msun. Since the stellar evolution and the final fate are determined by the stellar mass, Pop III stars formed at different epochs play different roles in the early universe.
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Photoevaporation of Protostellar Disks. V. Circumstellar Disks under the Influence of Both Extreme-Ultraviolet and Far-Ultraviolet Radiation
The Astrophysical Journal, 2000Co-Authors: Sabine Richling, Harold W YorkeAbstract:The evolution and appearance of protostellar disks can be significantly altered by their UV environment. We investigate numerically the photoevaporation of protostellar disks under the influence of an external Radiation field with both EUV (h? > 13.6 eV) and FUV (6 eV < h? < 13.6 eV) components. Our two-dimensional axisymmetric Radiation hydrodynamics calculations begin with star-disk configurations resulting from previously published collapse simulations. We follow the evolution after the external UV Radiation source has been turned on. We consider the transfer of both direct (from the UV point source) as well as diffuse Radiation fields simultaneously with the ionization of hydrogen and carbon. A simplified cooling function is employed which assumes that the carbon ionization front separates the molecular region from the region in atomic or ionized form. For some simulations an isotropic stellar wind has been included at the position of the disk's central star. At selected evolutionary times a frequency-dependent ray-tracing diagnostic code is used to calculate emission line spectra and emission line maps over the volume of interest. The interaction of the FUV-induced neutral flow at the disk surface with the direct and diffuse EUV Radiation fields leads to the typical head-tail objects with bright emission line crescents and tails pointing away from the external Radiation source. The properties of the head-tail objects are in agreement with the properties of the proplyds in the Orion Nebula, M8, NGC 2024, and?in a more extreme UV environment?of the newly discovered proplyds in NGC 3603. After losing material via photoevaporation over a time 105 yr, our initially rather massive disks are reduced to typical observed disk masses. At this time the radius of the disk, the radius of the hydrogen ionization front, and the length of the tail are compatible to observed proplyds. Our model disks can be either silhouetted or nonsilhouetted in the emission line maps, depending on orientation. The [O III] 5007 ? emission appears more diffuse than [O II] 3726 ?, because the abundance of O III is low near the hydrogen ionization front and in the shadow regions along the tail. Monopolar and bipolar microjets emerging from the proplyds can be explained by spherically symmetric stellar winds hydrodynamically focused by the neutral evaporating flow from the disk surface.
