The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
V F Suleimanov - One of the best experts on this subject based on the ideXlab platform.
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evidence for the photoionization absorption edge in a photospheric radius expansion x ray burst from grs 1747 312 in terzan 6
arXiv: High Energy Astrophysical Phenomena, 2018Co-Authors: V F Suleimanov, Juri Poutanen, Tuomo Salmi, M Falanga, Joonas NattilaAbstract:Thermonuclear X-ray bursts on the surface of neutron stars (NSs) can enrich photosphere with metals, which may imprint the photoionization edges on the burst spectra. We report here the discovery of absorption edges in the spectra of the type I X-ray burst from the NS low-mass X-ray binary GRS 1747$-$312 in Terzan 6 during observations by the Rossi X-ray Timing Explorer. We find that the edge energy evolves from $9.45\pm0.51$ keV to $\sim6$ keV and then back to $9.44\pm0.40$ keV during the photospheric radius expansion phase and remains at $8.06\pm0.66$ keV in the Cooling tail. The photoionization absorption edges of hydrogen-like Ni, Fe or Fe/Ni mixture and the bound-bound transitions of metals may be responsible for the observed spectral features. The ratio of the measured absorption edge energy in the Cooling tail to the laboratory value of hydrogen-like Ni(Fe) edge energy allows us to estimate the gravitational redshift factor $1+z=1.34\pm0.11$($1+z=1.15\pm0.09$). The evolution of the spectral parameters during the Cooling tail are well-described by the metal-rich atmosphere models. The combined constraints on the NS mass and radius from the Direct Cooling method and the tidal deformability strongly suggest very high atmospheric abundance of the iron group elements and limit the distance to the source to $11\pm1$ kpc.
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the Direct Cooling tail method for x ray burst analysis to constrain neutron star masses and radii
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: V F Suleimanov, Juri Poutanen, Joonas Nattila, J J E Kajava, M Revnivtsev, K WernerAbstract:Determining neutron star (NS) radii and masses can help to understand the properties of matter at supra-nuclear densities. Thermal emission during thermonuclear X-ray bursts from NSs in low-mass X- ...
Ananthanarayanan Veeraragavan - One of the best experts on this subject based on the ideXlab platform.
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comparison of Direct and inDirect natural draft dry Cooling tower Cooling of the sco2 brayton cycle for concentrated solar power plants
Applied Thermal Engineering, 2018Co-Authors: Sam Duniam, Yuanshen Lu, Kamel Hooman, Ingo Jahn, Ananthanarayanan VeeraragavanAbstract:Abstract This study investigates the performance of Direct and inDirect Cooling in conjunction with natural draft dry Cooling towers (NDDCT) for the heat rejection of a supercritical carbon dioxide (sCO2) recompression Brayton cycle. One dimensional models were developed for Direct and inDirect Cooling NDDCTs. The inlet conditions to the heat rejection system that correspond to the peak cycle efficiency for the scenario considered were identified and used to determine the minimum NDDCT size for Direct and inDirect Cooling. The Direct Cooling configuration requires a smaller tower than inDirect Cooling, due to the much higher temperature difference between the two fluid streams. When analysed in isolation the Direct Cooling NDDCT is found to over cool at both high and low inlet temperatures. The Direct and inDirect dry cooled recompression cycles were analysed at a range of ambient temperatures, using a coupled NDDCT and cycle model approach, in order to represent daily and annual variances. In both Direct and inDirect configurations, the cycle is overcooled at low ambient temperature, reducing cycle efficiency. A novel bypass arrangement was proposed that allows control of the compressor inlet temperature by reducing heat rejection from the tower, and allows both cycles to maintain peak efficiency at low ambient temperatures. At the design point ambient temperature of 20 °C the cycle efficiency is 49.6%. This is maintained down to 0 °C for both configurations, and drops to 44.7% and 43.8% at 50 °C ambient for Direct and inDirect respectively.
Juri Poutanen - One of the best experts on this subject based on the ideXlab platform.
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evidence for the photoionization absorption edge in a photospheric radius expansion x ray burst from grs 1747 312 in terzan 6
arXiv: High Energy Astrophysical Phenomena, 2018Co-Authors: V F Suleimanov, Juri Poutanen, Tuomo Salmi, M Falanga, Joonas NattilaAbstract:Thermonuclear X-ray bursts on the surface of neutron stars (NSs) can enrich photosphere with metals, which may imprint the photoionization edges on the burst spectra. We report here the discovery of absorption edges in the spectra of the type I X-ray burst from the NS low-mass X-ray binary GRS 1747$-$312 in Terzan 6 during observations by the Rossi X-ray Timing Explorer. We find that the edge energy evolves from $9.45\pm0.51$ keV to $\sim6$ keV and then back to $9.44\pm0.40$ keV during the photospheric radius expansion phase and remains at $8.06\pm0.66$ keV in the Cooling tail. The photoionization absorption edges of hydrogen-like Ni, Fe or Fe/Ni mixture and the bound-bound transitions of metals may be responsible for the observed spectral features. The ratio of the measured absorption edge energy in the Cooling tail to the laboratory value of hydrogen-like Ni(Fe) edge energy allows us to estimate the gravitational redshift factor $1+z=1.34\pm0.11$($1+z=1.15\pm0.09$). The evolution of the spectral parameters during the Cooling tail are well-described by the metal-rich atmosphere models. The combined constraints on the NS mass and radius from the Direct Cooling method and the tidal deformability strongly suggest very high atmospheric abundance of the iron group elements and limit the distance to the source to $11\pm1$ kpc.
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the Direct Cooling tail method for x ray burst analysis to constrain neutron star masses and radii
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: V F Suleimanov, Juri Poutanen, Joonas Nattila, J J E Kajava, M Revnivtsev, K WernerAbstract:Determining neutron star (NS) radii and masses can help to understand the properties of matter at supra-nuclear densities. Thermal emission during thermonuclear X-ray bursts from NSs in low-mass X- ...
Sam Duniam - One of the best experts on this subject based on the ideXlab platform.
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comparison of Direct and inDirect natural draft dry Cooling tower Cooling of the sco2 brayton cycle for concentrated solar power plants
Applied Thermal Engineering, 2018Co-Authors: Sam Duniam, Yuanshen Lu, Kamel Hooman, Ingo Jahn, Ananthanarayanan VeeraragavanAbstract:Abstract This study investigates the performance of Direct and inDirect Cooling in conjunction with natural draft dry Cooling towers (NDDCT) for the heat rejection of a supercritical carbon dioxide (sCO2) recompression Brayton cycle. One dimensional models were developed for Direct and inDirect Cooling NDDCTs. The inlet conditions to the heat rejection system that correspond to the peak cycle efficiency for the scenario considered were identified and used to determine the minimum NDDCT size for Direct and inDirect Cooling. The Direct Cooling configuration requires a smaller tower than inDirect Cooling, due to the much higher temperature difference between the two fluid streams. When analysed in isolation the Direct Cooling NDDCT is found to over cool at both high and low inlet temperatures. The Direct and inDirect dry cooled recompression cycles were analysed at a range of ambient temperatures, using a coupled NDDCT and cycle model approach, in order to represent daily and annual variances. In both Direct and inDirect configurations, the cycle is overcooled at low ambient temperature, reducing cycle efficiency. A novel bypass arrangement was proposed that allows control of the compressor inlet temperature by reducing heat rejection from the tower, and allows both cycles to maintain peak efficiency at low ambient temperatures. At the design point ambient temperature of 20 °C the cycle efficiency is 49.6%. This is maintained down to 0 °C for both configurations, and drops to 44.7% and 43.8% at 50 °C ambient for Direct and inDirect respectively.
Joonas Nattila - One of the best experts on this subject based on the ideXlab platform.
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evidence for the photoionization absorption edge in a photospheric radius expansion x ray burst from grs 1747 312 in terzan 6
arXiv: High Energy Astrophysical Phenomena, 2018Co-Authors: V F Suleimanov, Juri Poutanen, Tuomo Salmi, M Falanga, Joonas NattilaAbstract:Thermonuclear X-ray bursts on the surface of neutron stars (NSs) can enrich photosphere with metals, which may imprint the photoionization edges on the burst spectra. We report here the discovery of absorption edges in the spectra of the type I X-ray burst from the NS low-mass X-ray binary GRS 1747$-$312 in Terzan 6 during observations by the Rossi X-ray Timing Explorer. We find that the edge energy evolves from $9.45\pm0.51$ keV to $\sim6$ keV and then back to $9.44\pm0.40$ keV during the photospheric radius expansion phase and remains at $8.06\pm0.66$ keV in the Cooling tail. The photoionization absorption edges of hydrogen-like Ni, Fe or Fe/Ni mixture and the bound-bound transitions of metals may be responsible for the observed spectral features. The ratio of the measured absorption edge energy in the Cooling tail to the laboratory value of hydrogen-like Ni(Fe) edge energy allows us to estimate the gravitational redshift factor $1+z=1.34\pm0.11$($1+z=1.15\pm0.09$). The evolution of the spectral parameters during the Cooling tail are well-described by the metal-rich atmosphere models. The combined constraints on the NS mass and radius from the Direct Cooling method and the tidal deformability strongly suggest very high atmospheric abundance of the iron group elements and limit the distance to the source to $11\pm1$ kpc.
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the Direct Cooling tail method for x ray burst analysis to constrain neutron star masses and radii
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: V F Suleimanov, Juri Poutanen, Joonas Nattila, J J E Kajava, M Revnivtsev, K WernerAbstract:Determining neutron star (NS) radii and masses can help to understand the properties of matter at supra-nuclear densities. Thermal emission during thermonuclear X-ray bursts from NSs in low-mass X- ...