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Smith Eiamsaard - One of the best experts on this subject based on the ideXlab platform.
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friction and heat transfer characteristics of laminar swirl flow through the round tubes inserted with alternate Clockwise and counter Clockwise twisted tapes
International Communications in Heat and Mass Transfer, 2011Co-Authors: Khwanchit Wongcharee, Smith EiamsaardAbstract:Abstract The thermohydraulic characteristics of the circular tubes equipped with alternate Clockwise and counter-Clockwise twisted-tapes (TA) for the Reynolds number ranging from 830 to 1990, are reported. In the experiments, the twisted tapes with three different twist ratios (y/W = 3, 4 and 5) were inserted individually into the uniform wall heat flux tubes where water was utilized as the working fluid. The plain tube and the tube inserted with twisted tape (TT) were also tested, for comparison. The obtained results reveal that, Nusselt number, friction factor and thermal performance factor associated by TA are higher than those associated by TT. Among the tapes examined, the one with the smallest twist ratio of y/W = 3 is found to be the most efficient for heat transfer enhancement. For the range studied, the applications of both TT and TA for heat transfer enhancement are found to be promising since the thermal performance factors determined under the same pumping power are all above unity. In addition, the empirical correlations for Nusselt number, friction factor and thermal performance factor have also been developed. The consequential results obtained from the correlations are found to be in good agreement with the experimental results within ± 8% variation for Nusselt number (Nu), ± 8% for thermal performance factor (η) and ± 5% for friction factor (f).
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performance assessment in a heat exchanger tube with alternate Clockwise and counter Clockwise twisted tape inserts
International Journal of Heat and Mass Transfer, 2010Co-Authors: Smith Eiamsaard, Pongjet PromvongeAbstract:Abstract The article presents an experimental study of turbulent heat transfer and flow friction characteristics in a circular tube equipped with two types of twisted tapes: (1) typical twisted tapes and (2) alternate Clockwise and counterClockwise twisted tapes (C–CC twisted tapes). Nine different C–CC twisted tapes are tested in the current work; they included the tapes with three twist ratios, y/w = 3.0, 4.0 and 5.0, each with three twist angles, θ = 30o, 60o and 90o. The experiments have been performed over a Reynolds number range of 3000–27,000 under uniform heat flux conditions, using water as working fluid. The obtained results reveal that the C–CC twisted-tapes provide higher heat transfer rate, friction factor and heat transfer enhancement index than the typical twisted-tapes at similar operating conditions. The results also show that the heat transfer rate of the C–CC tapes increases with the decrease of twist ratio and the increase of twist angle values. Depending on Reynolds number, twist ratio and twist angle values, the mean Nusselt numbers in the tube fitted with the C–CC twisted tapes are higher than those with the typical ones and the plain tube around 12.8–41.9% and 27.3–90.5%, respectively. The maximum heat transfer enhancement indexes of the C–CC twisted tapes with θ = 90o for y/w = 3.0, 4.0 and 5.0, are 1.4, 1.34 and 1.3, respectively. In addition, correlations of the Nusselt number and the friction factor for using the C–CC twisted tapes are also determined. Both predicted Nusselt number and friction factor are within ±15% and ±15% deviation compared to the experimental data.
Pongjet Promvonge - One of the best experts on this subject based on the ideXlab platform.
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performance assessment in a heat exchanger tube with alternate Clockwise and counter Clockwise twisted tape inserts
International Journal of Heat and Mass Transfer, 2010Co-Authors: Smith Eiamsaard, Pongjet PromvongeAbstract:Abstract The article presents an experimental study of turbulent heat transfer and flow friction characteristics in a circular tube equipped with two types of twisted tapes: (1) typical twisted tapes and (2) alternate Clockwise and counterClockwise twisted tapes (C–CC twisted tapes). Nine different C–CC twisted tapes are tested in the current work; they included the tapes with three twist ratios, y/w = 3.0, 4.0 and 5.0, each with three twist angles, θ = 30o, 60o and 90o. The experiments have been performed over a Reynolds number range of 3000–27,000 under uniform heat flux conditions, using water as working fluid. The obtained results reveal that the C–CC twisted-tapes provide higher heat transfer rate, friction factor and heat transfer enhancement index than the typical twisted-tapes at similar operating conditions. The results also show that the heat transfer rate of the C–CC tapes increases with the decrease of twist ratio and the increase of twist angle values. Depending on Reynolds number, twist ratio and twist angle values, the mean Nusselt numbers in the tube fitted with the C–CC twisted tapes are higher than those with the typical ones and the plain tube around 12.8–41.9% and 27.3–90.5%, respectively. The maximum heat transfer enhancement indexes of the C–CC twisted tapes with θ = 90o for y/w = 3.0, 4.0 and 5.0, are 1.4, 1.34 and 1.3, respectively. In addition, correlations of the Nusselt number and the friction factor for using the C–CC twisted tapes are also determined. Both predicted Nusselt number and friction factor are within ±15% and ±15% deviation compared to the experimental data.
Tal Alexander - One of the best experts on this subject based on the ideXlab platform.
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evidence for warped disks of young stars in the galactic center
The Astrophysical Journal, 2009Co-Authors: H Bartko, F Martins, T K Fritz, R Genzel, Y Levin, Hagai B Perets, Thibaut Paumard, Sergei Nayakshin, Ortwin Gerhard, Tal AlexanderAbstract:The central parsec around the supermassive black hole in the Galactic center (GC) hosts more than 100 young and massive stars. Outside the central cusp (R ~ 1'') the majority of these O and Wolf-Rayet (W-R) stars reside in a main Clockwise system, plus a second, less prominent disk or streamer system at large angles with respect to the main system. Here we present the results from new observations of the GC with the AO-assisted near-infrared imager NACO and the integral field spectrograph SINFONI on the ESO/VLT. These include the detection of 27 new reliably measured W-R/O stars in the central 12'' and improved measurements of 63 previously detected stars, with proper motion uncertainties reduced by a factor of 4 compared to our earlier work. Based on the sample of 90 well measured W-R/O stars, we develop a detailed statistical analysis of their orbital properties and orientations. We show that half of the W-R/O stars are compatible with being members of a Clockwise rotating system. The rotation axis of this system shows a strong transition from the inner to the outer regions as a function of the projected distance from Sgr A*. The main Clockwise system either is either a strongly warped single disk with a thickness of about 10°, or consists of a series of streamers with significant radial variation in their orbital planes. Eleven out of 61 Clockwise moving stars have an angular separation of more than 30° from the local angular momentum direction of the Clockwise system. The mean eccentricity of the Clockwise system is 0.36 ± 0.06. The distribution of the counterClockwise W-R/O star is not isotropic at the 98% confidence level. It is compatible with a coherent structure such as stellar filaments, streams, small clusters or possibly a disk in a dissolving state: 10 out of 29 counterClockwise moving W-R/O stars have an angular separation of more than 30° from the local angular momentum direction of the counterClockwise system. The observed disk warp and the steep surface density distribution favor in situ star formation in gaseous accretion disks as the origin of the young massive stars.
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evidence for warped disks of young stars in the galactic center
arXiv: Astrophysics, 2008Co-Authors: H Bartko, F Martins, T K Fritz, R Genzel, Y Levin, Hagai B Perets, Thibaut Paumard, Sergei Nayakshin, Ortwin Gerhard, Tal AlexanderAbstract:The central parsec around the super-massive black hole in the Galactic Center hosts more than 100 young and massive stars. Outside the central cusp (R~1") the majority of these O and Wolf-Rayet (WR) stars reside in a main Clockwise system, plus a second, less prominent disk or streamer system at large angles with respect to the main system. Here we present the results from new observations of the Galactic Center with the AO-assisted near-infrared imager NACO and the integral field spectrograph SINFONI on the ESO/VLT. These include the detection of 27 new reliably measured WR/O stars in the central 12" and improved measurements of 63 previously detected stars, with proper motion uncertainties reduced by a factor of four compared to our earlier work. We develop a detailed statistical analysis of their orbital properties and orientations. Half of the WR/O stars are compatible with being members of a Clockwise rotating system. The rotation axis of this system shows a strong transition as a function of the projected distance from SgrA*. The main Clockwise system either is either a strongly warped single disk with a thickness of about 10 degrees, or consists of a series of streamers with significant radial variation in their orbital planes. 11 out of 61 Clockwise moving stars have an angular separation of more than 30 degrees from the Clockwise system. The mean eccentricity of the Clockwise system is 0.36+/-0.06. The distribution of the counter-Clockwise WR/O star is not isotropic at the 98% confidence level. It is compatible with a coherent structure such as stellar filaments, streams, small clusters or possibly a disk in a dissolving state. The observed disk warp and the steep surface density distribution favor in situ star formation in gaseous accretion disks as the origin of the young stars.
Y Levin - One of the best experts on this subject based on the ideXlab platform.
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evidence for warped disks of young stars in the galactic center
The Astrophysical Journal, 2009Co-Authors: H Bartko, F Martins, T K Fritz, R Genzel, Y Levin, Hagai B Perets, Thibaut Paumard, Sergei Nayakshin, Ortwin Gerhard, Tal AlexanderAbstract:The central parsec around the supermassive black hole in the Galactic center (GC) hosts more than 100 young and massive stars. Outside the central cusp (R ~ 1'') the majority of these O and Wolf-Rayet (W-R) stars reside in a main Clockwise system, plus a second, less prominent disk or streamer system at large angles with respect to the main system. Here we present the results from new observations of the GC with the AO-assisted near-infrared imager NACO and the integral field spectrograph SINFONI on the ESO/VLT. These include the detection of 27 new reliably measured W-R/O stars in the central 12'' and improved measurements of 63 previously detected stars, with proper motion uncertainties reduced by a factor of 4 compared to our earlier work. Based on the sample of 90 well measured W-R/O stars, we develop a detailed statistical analysis of their orbital properties and orientations. We show that half of the W-R/O stars are compatible with being members of a Clockwise rotating system. The rotation axis of this system shows a strong transition from the inner to the outer regions as a function of the projected distance from Sgr A*. The main Clockwise system either is either a strongly warped single disk with a thickness of about 10°, or consists of a series of streamers with significant radial variation in their orbital planes. Eleven out of 61 Clockwise moving stars have an angular separation of more than 30° from the local angular momentum direction of the Clockwise system. The mean eccentricity of the Clockwise system is 0.36 ± 0.06. The distribution of the counterClockwise W-R/O star is not isotropic at the 98% confidence level. It is compatible with a coherent structure such as stellar filaments, streams, small clusters or possibly a disk in a dissolving state: 10 out of 29 counterClockwise moving W-R/O stars have an angular separation of more than 30° from the local angular momentum direction of the counterClockwise system. The observed disk warp and the steep surface density distribution favor in situ star formation in gaseous accretion disks as the origin of the young massive stars.
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evidence for warped disks of young stars in the galactic center
arXiv: Astrophysics, 2008Co-Authors: H Bartko, F Martins, T K Fritz, R Genzel, Y Levin, Hagai B Perets, Thibaut Paumard, Sergei Nayakshin, Ortwin Gerhard, Tal AlexanderAbstract:The central parsec around the super-massive black hole in the Galactic Center hosts more than 100 young and massive stars. Outside the central cusp (R~1") the majority of these O and Wolf-Rayet (WR) stars reside in a main Clockwise system, plus a second, less prominent disk or streamer system at large angles with respect to the main system. Here we present the results from new observations of the Galactic Center with the AO-assisted near-infrared imager NACO and the integral field spectrograph SINFONI on the ESO/VLT. These include the detection of 27 new reliably measured WR/O stars in the central 12" and improved measurements of 63 previously detected stars, with proper motion uncertainties reduced by a factor of four compared to our earlier work. We develop a detailed statistical analysis of their orbital properties and orientations. Half of the WR/O stars are compatible with being members of a Clockwise rotating system. The rotation axis of this system shows a strong transition as a function of the projected distance from SgrA*. The main Clockwise system either is either a strongly warped single disk with a thickness of about 10 degrees, or consists of a series of streamers with significant radial variation in their orbital planes. 11 out of 61 Clockwise moving stars have an angular separation of more than 30 degrees from the Clockwise system. The mean eccentricity of the Clockwise system is 0.36+/-0.06. The distribution of the counter-Clockwise WR/O star is not isotropic at the 98% confidence level. It is compatible with a coherent structure such as stellar filaments, streams, small clusters or possibly a disk in a dissolving state. The observed disk warp and the steep surface density distribution favor in situ star formation in gaseous accretion disks as the origin of the young stars.
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the two young star disks in the central parsec of the galaxy properties dynamics and formation
Web Science, 2006Co-Authors: T Paumard, F Martins, R Genzel, Y Levin, Sergei Nayakshin, Andrei M Beloborodov, Sascha Trippe, F EisenhauerAbstract:We report the definite spectroscopic identification of 40 OB supergiants, giants and main sequence stars in the central parsec of the Galaxy. Detection of their absorption lines have become possible with the high spatial and spectral resolution and sensitivity of the adaptive optics integral Held spectrometer SPIFFI/SINFONI on the ESO VLT. Several of these OB stars appear to be helium and nitrogen rich. Almost all of the 80 massive stars now known in the central parsec (central arcsecond excluded) reside in one of two somewhat thick (|/R 0.14) rotating disks. These stellar disks have fairly sharp inner edges (R 1'') and surface density profiles that scale as R−2. We do not detect any OB stars outside the central 0.5 pc. The majority of the stars in the Clockwise system appear to be on almost circular orbits, whereas most of those in the 'counter-Clockwise' disk appear to be on eccentric orbits. Based on its stellar surface density distribution and dynamics we propose that IRS 13E is an extremely dense cluster (ρcore 3 × 108M⊙ pc−3), which has formed in the counter-Clockwise disk. The stellar contents of both systems are remarkably similar, indicating a common age of 6±2 Myr. The K-band luminosity function of the massive stars suggests a top-heavy mass function and limits the total stellar mass contained in both disks to 1.5 × 104 M⊙. Our data strongly favor in situ star formation from dense gas accretion disks for the two stellar disks. This conclusion is very clear for the Clockwise disk and highly plausible for the counter-Clockwise system.
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the two young star disks in the central parsec of the galaxy properties dynamics and formation
arXiv: Astrophysics, 2006Co-Authors: T Paumard, F Martins, R Genzel, Y Levin, Sergei Nayakshin, Andrei M Beloborodov, Sascha Trippe, F EisenhauerAbstract:We report the definite spectroscopic identification of 41 OB supergiants, giants and main sequence stars in the central parsec of the Galaxy. Detection of their absorption lines have become possible with the high spatial and spectral resolution and sensitivity of the adaptive optics integral field spectrometer SPIFFI/SINFONI on the ESO VLT. Several of these OB stars appear to be helium and nitrogen rich. Almost all of the ~80 massive stars now known in the central parsec (central arcsecond excluded) reside in one of two somewhat thick ( ~0.14) rotating disks. These stellar disks have fairly sharp inner edges (R~1") and surface density profiles that scale as R^{-2}. We do not detect any OB stars outside the central 0.5 pc. The majority of the stars in the Clockwise system appear to be on almost circular orbits, whereas most of those in the `counter-Clockwise' disk appear to be on eccentric orbits. Based on its stellar surface density distribution and dynamics we propose that IRS 13E is an extremely dense cluster (core density > 3x10^8 sunmass/pc^3), which has formed in the counter-Clockwise disk. The stellar contents of both systems are remarkably similar, indicating a common age of ~6+/-2 Myr. The K-band luminosity function of the massive stars suggests a top-heavy mass function and limits the total stellar mass contained in both disks to ~1.5x10^4 sunmass. Our data strongly favor in situ star formation from dense gas accretion disks for the two stellar disks. This conclusion is very clear for the Clockwise disk and highly plausible for the counter-Clockwise system.
Meldrum R Robertson - One of the best experts on this subject based on the ideXlab platform.
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persistent one way walking in a circular arena in drosophila melanogaster canton s strain
Behavior Genetics, 2018Co-Authors: Chengfeng Xiao, Shuang Qiu, Meldrum R RobertsonAbstract:We describe persistent one-way walking of Drosophila melanogaster in a circular arena. Wild-type Canton-S adult flies walked in one direction, counter-Clockwise or Clockwise, for minutes, whereas white-eyed mutant [Formula: see text] changed directions frequently. Locomotion in the circular arena could be classified into four components: counter-Clockwise walking, Clockwise walking, nondirectional walking and pausing. Genetic analysis revealed that while wild-type genetic background was associated with reduced directional change and reduced numbers of one-way (including counter-Clockwise and Clockwise) and nondirectional walks, the white ([Formula: see text]) locus promoted persistent one-way walking by increasing the maximal duration of one-way episodes. The promoting effect of [Formula: see text] was further supported by the observations that (1) [Formula: see text] duplicated to the Y chromosome, (2) four genomic copies of mini-white inserted on the autosomes, and (3) pan-neuronal overexpression of the White protein increased the maximal duration of one-way episodes, and that RNAi knockdown of [Formula: see text] in the neurons decreased the maximal duration of one-way episodes. These results suggested a pleiotropic function of [Formula: see text] in promoting persistent one-way walking in the circular arena.
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persistent one way walking in a circular arena in drosophila melanogaster canton s strain
bioRxiv, 2017Co-Authors: Chengfeng Xiao, Shuang Qiu, Meldrum R RobertsonAbstract:We describe persistent one-way walking of Drosophila melanogaster in a circular arena. Wild-type Canton-S adult flies walked in one direction, counter-Clockwise or Clockwise, for minutes, whereas white-eyed mutant w 1118 changed directions frequently. Computational analysis of locomotor behavior showed that counter-Clockwise walking and Clockwise walking were the two main components of locomotion, and that pausing was more frequently associated with directional persistence but not directional change. Genetic analysis revealed that while wild-type genetic background primarily controlled the number of counter-Clockwise walking and Clockwise walking during five minutes of locomotion, the white ( w + ) gene promoted persistent one-way walking by increasing the number of pauses, increasing the maximal duration of one-way walking, and reducing the path length in five minutes. These results support a pleiotropic function of w + in promoting persistent one-way walking in addition to eye pigmentation.