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Oleg Smirnov - One of the best experts on this subject based on the ideXlab platform.
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revisiting the radio interferometer measurement equation ii calibration and direction dependent effects
Astronomy and Astrophysics, 2011Co-Authors: Oleg SmirnovAbstract:Context. Paper I of the series re-derived the radio interferometry measurement equation (Rime) from first principles, and extended the Jones formalism to the full-sky case, incorporating direction-dependent effects (DDEs). Aims. This paper aims to describe both classical radio interferometric calibration (selfcal and related methods), and the recent developments in the treatment of DDEs, using the Rime-based mathematical framework developed in Paper I. It also aims to demonstrate the ease with which the various effects can be described and understood. Methods. The first section of this paper uses the Rime formalism to describe self-calibration, both with a full Rime, and with the approximate equations of older software packages, and shows how this is affected by DDEs. The second section gives an overview of real-life DDEs and proposed methods of dealing with them. Results. A formal Rime-based description and comparison of existing and proposed approaches to the problem of DDEs.
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revisiting the radio interferometer measurement equation i a full sky jones formalism
Astronomy and Astrophysics, 2011Co-Authors: Oleg SmirnovAbstract:Context. Since its formulation by Hamaker et al., the radio interferometer measurement equation (Rime) has provided a rigorous mathematical basis for the development of novel calibration methods and techniques, including various approaches to the problem of direction-dependent effects (DDEs). However, acceptance of the Rime in the radio astronomical community at large has been slow, which is partially due to the limited availability of software to exploit its power, and the sparsity of practical results. This needs to change urgently. Aims. This series of papers aims to place recent developments in the treatment of DDEs into one Rime-based mathematical framework, and to demonstrate the ease with which the various effects can be described and understood. It also aims to show the benefits of a Rime-based approach to calibration. Methods. Paper I re-derives the Rime from first principles, extends the formalism to the full-sky case, and incorporates DDEs. Paper II then uses the formalism to describe self-calibration, both with a full Rime, and with the approximate equations of older software packages, and shows how this is affected by DDEs. It also gives an overview of real-life DDEs and proposed methods of dealing with them. Finally, in Paper III some of these methods are exercised to achieve an extremely high-dynamic range calibration of WSRT observations of 3C 147 at 21 cm, with full treatment of DDEs. Results. The Rime formalism is extended to the full-sky case (Paper I), and is shown to be an elegant way of describing calibration and DDEs (Paper II). Applying this to WSRT data (Paper III) results in a noise-limited image of the field around 3C 147 with a very high dynamic range (1.6 million), and none of the off-axis artifacts that plague regular selfcal. The resulting differential gain solutions contain significant information on DDEs and errors in the sky model. Conclusions. The Rime is a powerful formalism for describing radio interferometry, and underpins the development of novel calibration methods, in particular those dealing with DDEs. One of these is the differential gains approach used for the 3C 147 reduction. Differential gains can eliminate DDE-related artifacts, and provide information for iterative improvements of sky models. Perhaps most importantly, sources as faint as 2 mJy have been shown to yield meaningful differential gain solutions, and thus can be used as potential calibration beacons in other DDE-related schemes.
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revisiting the radio interferometer measurement equation ii calibration and direction dependent effects
arXiv: Instrumentation and Methods for Astrophysics, 2011Co-Authors: Oleg SmirnovAbstract:Paper I of the series re-derived the radio interferometry measurement equation (Rime) from first principles, and extended the Jones formalism to the full-sky case, incorporating direction-dependent effects (DDEs). This paper aims to describe both classical radio interferometric calibration (selfcal and related methods), and the recent developments in the treatment of DDEs, using the Rime-based mathematical framework developed in Paper I. It also aims to demonstrate the ease with which the various effects can be described and understood. The first section of this paper uses the Rime formalism to describe self-calibration, both with a full Rime, and with the approximate equations of older software packages, and shows how this is affected by DDEs. The second section gives an overview of real-life DDEs and proposed methods of dealing with them. This results in a formal Rime-based description and comparison of existing and proposed approaches to the problem of DDEs.
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revisiting the radio interferometer measurement equation i a full sky jones formalism
arXiv: Instrumentation and Methods for Astrophysics, 2011Co-Authors: Oleg SmirnovAbstract:Since its formulation by Hamaker et al., the radio interferometer measurement equation (Rime) has provided a rigorous mathematical basis for the development of novel calibration methods and techniques, including various approaches to the problem of direction-dependent effects (DDEs). This series of papers aims to place recent developments in the treatment of DDEs into one Rime-based mathematical framework, and to demonstrate the ease with which the various effects can be described and understood. It also aims to show the benefits of a Rime-based approach to calibration. Paper I re-derives the Rime from first principles, extends the formalism to the full-sky case, and incorporates DDEs. Paper II then uses the formalism to describe self-calibration, both with a full Rime, and with the approximate equations of older software packages, and shows how this is affected by DDEs. It also gives an overview of real-life DDEs and proposed methods of dealing with them. Applying this to WSRT data (Paper III) results in a noise-limited image of the field around 3C 147 with a very high dynamic range (1.6 million), and none of the off-axis artifacts that plague regular selfcal. The resulting differential gain solutions contain significant information on DDEs, and can be used for iterative improvements of sky models. Perhaps most importantly, sources as faint as 2 mJy have been shown to yield meaningful differential gain solutions, and thus can be used as potential calibration beacons in other DDE-related schemes.
Michael A Cotta - One of the best experts on this subject based on the ideXlab platform.
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lime pretreatment enzymatic saccharification and fermentation of rice hulls to ethanol
Biomass & Bioenergy, 2008Co-Authors: Badal C. Saha, Michael A CottaAbstract:Rice hulls used in this study contained 35.6±0.1% cellulose and 12.0±0.7% hemicellulose. The maximum yield of monomeric sugars from rice hulls (15.0%, w/v) by lime pretreatment (100 mg g−1 hulls, 121 °C, 1 h) and enzymatic saccharification (45 °C, pH 5.0, 72 h) using a cocktail of three commercial enzyme preparations (cellulase, β-glucosidase and hemicellulase) at the dose level of 0.15 ml of each enzyme preparation g−1 hulls was 154±1 mg g−1 (32% yield). The lime pretreatment did not generate any detectable furfural and hydroxymethyl furfural in the hydrolyzate. The concentration of ethanol from lime-pretreated enzyme-saccharified rice hull (138 g) hydrolyzate by recombinant Escherichia coli strain FBR5 at pH 6.5 and 35 °C in 19 h was 9.8±0.5 g l−1 with a yield of 0.49 g g−1 available sugars. The ethanol concentration was 11.0±1.0 g l−1 in the case of simultaneous saccharification and fermentation by the E. coli strain at pH 6.0 and 35 °C in 53 h.
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lime pretreatment enzymatic saccharification and fermentation of rice hulls to ethanol
Biomass & Bioenergy, 2008Co-Authors: Badal C. Saha, Michael A CottaAbstract:Rice hulls used in this study contained 35.6±0.1% cellulose and 12.0±0.7% hemicellulose. The maximum yield of monomeric sugars from rice hulls (15.0%, w/v) by lime pretreatment (100 mg g−1 hulls, 121 °C, 1 h) and enzymatic saccharification (45 °C, pH 5.0, 72 h) using a cocktail of three commercial enzyme preparations (cellulase, β-glucosidase and hemicellulase) at the dose level of 0.15 ml of each enzyme preparation g−1 hulls was 154±1 mg g−1 (32% yield). The lime pretreatment did not generate any detectable furfural and hydroxymethyl furfural in the hydrolyzate. The concentration of ethanol from lime-pretreated enzyme-saccharified rice hull (138 g) hydrolyzate by recombinant Escherichia coli strain FBR5 at pH 6.5 and 35 °C in 19 h was 9.8±0.5 g l−1 with a yield of 0.49 g g−1 available sugars. The ethanol concentration was 11.0±1.0 g l−1 in the case of simultaneous saccharification and fermentation by the E. coli strain at pH 6.0 and 35 °C in 53 h.
O Smirnov - One of the best experts on this subject based on the ideXlab platform.
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revisiting the radio interferometer measurement equation iii addressing direction dependent effects in 21 cm wsrt observations of 3c 147
Astronomy and Astrophysics, 2011Co-Authors: O SmirnovAbstract:Context. Papers I and II of this series have extended the radio interfe rometry measurement equation (Rime) formalism to the full-sky case, and provided a Rime-based description of calibration and the problem of direction-dependent effects (DDEs). Aims. This paper aims to provide a practical demonstration of a Rime-based approach to calibration, via an example of extremely high-dynamic range calibration of WSRT observations of 3C 147 at 21 cm, with full treatment of DDEs. Methods. A version of the Rime incorporating differential gains has been implemented in MeqTrees, and applied to the 3C 147 data. This was used to perform regular selfcal, then solve for interferometer-based errors and for differential gains. Results. The resulting image of the field around 3C 147 is thermal noise -limited, has a very high dynamic range (1.6 million), and none of the off-axis artefacts that plague regular selfcal. The differential gain solutions show a high signal-to-noise ratio, and may be used to extract information on DDEs and errors in the sky model. Conclusions. The differential gain approach can eliminate DDE-related artefacts, and provide information for iterative improvements of sky models. Perhaps most importantly, sources as faint as 2 mJy have been shown to yield meaningful differential gain solutions, and thus can be used as potential calibration beacons in other DDE-related schemes.
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Revisiting the radio interferometer measurement equation. III. Addressing direction-dependent effects in 21 cm WSRT observations of 3C 147
Astronomy & Astrophysics, 2011Co-Authors: O SmirnovAbstract:Papers I and II of this series have extended the radio interferometry measurement equation (Rime) formalism to the full-sky case, and provided a Rime-based description of calibration and the problem of direction-dependent effects (DDEs). This paper aims to provide a practical demonstration of a Rime-based approach to calibration, via an example of extremely high-dynamic range calibration of WSRT observations of 3C 147 at 21 cm, with full treatment of DDEs. A version of the Rime incorporating differential gains has been implemented in MeqTrees, and applied to the 3C 147 data. This was used to perform regular selfcal, then solve for interferometer-based errors and for differential gains. The resulting image of the field around 3C 147 is thermal noise-limited, has a very high dynamic range (1.6 million), and none of the off-axis artefacts that plague regular selfcal. The differential gain solutions show a high signal-to-noise ratio, and may be used to extract information on DDEs and errors in the sky model. The differential gain approach can eliminate DDE-related artefacts, and provide information for iterative improvements of sky models. Perhaps most importantly, sources as faint as 2 mJy have been shown to yield meaningful differential gain solutions, and thus can be used as potential calibration beacons in other DDE-related schemes.
Badal C. Saha - One of the best experts on this subject based on the ideXlab platform.
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lime pretreatment enzymatic saccharification and fermentation of rice hulls to ethanol
Biomass & Bioenergy, 2008Co-Authors: Badal C. Saha, Michael A CottaAbstract:Rice hulls used in this study contained 35.6±0.1% cellulose and 12.0±0.7% hemicellulose. The maximum yield of monomeric sugars from rice hulls (15.0%, w/v) by lime pretreatment (100 mg g−1 hulls, 121 °C, 1 h) and enzymatic saccharification (45 °C, pH 5.0, 72 h) using a cocktail of three commercial enzyme preparations (cellulase, β-glucosidase and hemicellulase) at the dose level of 0.15 ml of each enzyme preparation g−1 hulls was 154±1 mg g−1 (32% yield). The lime pretreatment did not generate any detectable furfural and hydroxymethyl furfural in the hydrolyzate. The concentration of ethanol from lime-pretreated enzyme-saccharified rice hull (138 g) hydrolyzate by recombinant Escherichia coli strain FBR5 at pH 6.5 and 35 °C in 19 h was 9.8±0.5 g l−1 with a yield of 0.49 g g−1 available sugars. The ethanol concentration was 11.0±1.0 g l−1 in the case of simultaneous saccharification and fermentation by the E. coli strain at pH 6.0 and 35 °C in 53 h.
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lime pretreatment enzymatic saccharification and fermentation of rice hulls to ethanol
Biomass & Bioenergy, 2008Co-Authors: Badal C. Saha, Michael A CottaAbstract:Rice hulls used in this study contained 35.6±0.1% cellulose and 12.0±0.7% hemicellulose. The maximum yield of monomeric sugars from rice hulls (15.0%, w/v) by lime pretreatment (100 mg g−1 hulls, 121 °C, 1 h) and enzymatic saccharification (45 °C, pH 5.0, 72 h) using a cocktail of three commercial enzyme preparations (cellulase, β-glucosidase and hemicellulase) at the dose level of 0.15 ml of each enzyme preparation g−1 hulls was 154±1 mg g−1 (32% yield). The lime pretreatment did not generate any detectable furfural and hydroxymethyl furfural in the hydrolyzate. The concentration of ethanol from lime-pretreated enzyme-saccharified rice hull (138 g) hydrolyzate by recombinant Escherichia coli strain FBR5 at pH 6.5 and 35 °C in 19 h was 9.8±0.5 g l−1 with a yield of 0.49 g g−1 available sugars. The ethanol concentration was 11.0±1.0 g l−1 in the case of simultaneous saccharification and fermentation by the E. coli strain at pH 6.0 and 35 °C in 53 h.
Kwing-so Choi - One of the best experts on this subject based on the ideXlab platform.
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Mixed ice accretion on aircraft wings
Physics of Fluids, 2018Co-Authors: Zaid A. Janjua, Barbara Turnbull, Stephen Hibberd, Kwing-so ChoiAbstract:Ice accretion is a problematic natural phenomenon that affects a wide range of engineering applications including power cables, radio masts, and wind turbines. Accretion on aircraft wings occurs when supercooled water droplets freeze instantaneously on impact to form Rime ice or runback as water along the wing to form glaze ice. Most models to date have ignored the accretion of mixed ice, which is a combination of Rime and glaze. A parameter we term the “freezing fraction” is defined as the fraction of a supercooled droplet that freezes on impact with the top surface of the accretion ice to explore the concept of mixed ice accretion. Additionally we consider different “packing densities” of Rime ice, mimicking the different bulk Rime densities observed in nature. Ice accretion is considered in four stages: Rime, primary mixed, secondary mixed, and glaze ice. Predictions match with existing models and expeRimental data in the limiting Rime and glaze cases. The mixed ice formulation however provides additio...
