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Chris Flynn - One of the best experts on this subject based on the ideXlab platform.
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new solar twins and the metallicity and Temperature Scales of the geneva copenhagen survey
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: J Datson, Chris Flynn, Laura PortinariAbstract:We search for “solar twins” in the Geneva-Copenhagen Survey (GCS) using high resolution optical spectroscopy. We initially select Sun–like stars from the GCS by absolute magnitude, (b y) colour and metallicity close to the solar values. Our aim is to find the stars which are spectroscopically very close to the Sun using line depth ratios and the median equivalent widths and depths of selected lines with a range of excitation potentials. We present the ten best stars fulfilling combined photometric and spectroscopic criteria, of which six are new twins. We use our full sample of Sun–like stars to examine the calibration of the metallicity and Temperature scale in the GCS. Our results give rise to the conclusion that the GCS may be offset from the solar Temperature and metallicity for sun-like stars by 100K and 0.1dex, respectively.
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accurate fundamental parameters for lower main sequence stars
Monthly Notices of the Royal Astronomical Society, 2006Co-Authors: Luca Casagrande, Laura Portinari, Chris FlynnAbstract:We derive an empirical effective Temperature and bolometric luminosity calibration for G and K dwarfs, by applying our own implementation of the Infrared Flux Method to multiband photometry. Our study is based on 104 stars for which we have excellent BV(RI)CJHKS photometry, excellent parallaxes and good metallicities. Colours computed from the most recent synthetic libraries (ATLAS9 and MARCS) are found to be in good agreement with the empirical colours in the optical bands, but some discrepancies still remain in the infrared. Synthetic and empirical bolometric corrections also show fair agreement. A careful comparison to Temperatures, luminosities and angular diameters obtained with other methods in the literature shows that systematic effects still exist in the calibrations at the level of a few per cent. Our Infrared Flux Method Temperature scale is 100-K hotter than recent analogous determinations in the literature, but is in agreement with spectroscopically calibrated Temperature Scales and fits well the colours of the Sun. Our angular diameters are typically 3 per cent smaller when compared to other (indirect) determinations of angular diameter for such stars, but are consistent with the limb-darkening corrected predictions of the latest 3D model atmospheres and also with the results of asteroseismology. Very tight empirical relations are derived for bolometric luminosity, effective Temperature and angular diameter from photometric indices. We find that much of the discrepancy with other Temperature Scales and the uncertainties in the infrared synthetic colours arise from the uncertainties in the use of Vega as the flux calibrator. Angular diameter measurements for a well-chosen set of G and K dwarfs would go a long way to addressing this problem.
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accurate fundamental parameters for lower main sequence stars
arXiv: Astrophysics, 2006Co-Authors: Luca Casagrande, Laura Portinari, Chris FlynnAbstract:We derive an empirical effective Temperature and bolometric luminosity calibration for G and K dwarfs, by applying our own implementation of the InfraRed Flux Method to multi-band photometry. Our study is based on 104 stars for which we have excellent BVRIJHK photometry, excellent parallaxes and good metallicities. Colours computed from the most recent synthetic libraries (ATLAS9 and MARCS) are found to be in good agreement with the empirical colours in the optical bands, but some discrepancies still remain in the infrared. Synthetic and empirical bolometric corrections also show fair agreement. A careful comparison to Temperatures, luminosities and angular diameters obtained with other methods in literature shows that systematic effects still exist in the calibrations at the level of a few percent. Our InfraRed Flux Method Temperature scale is 100K hotter than recent analogous determinations in the literature, but is in agreement with spectroscopically calibrated Temperature Scales and fits well the colours of the Sun. Our angular diameters are typically 3% smaller when compared to other (indirect) determinations of angular diameter for such stars, but are consistent with the limb-darkening corrected predictions of the latest 3D model atmospheres and also with the results of asteroseismology. Very tight empirical relations are derived for bolometric luminosity, effective Temperature and angular diameter from photometric indices. We find that much of the discrepancy with other Temperature Scales and the uncertainties in the infrared synthetic colours arise from the uncertainties in the use of Vega as the flux calibrator. Angular diameter measurements for a well chosen set of G and K dwarfs would go a long way to addressing this problem.
Donald G Archer - One of the best experts on this subject based on the ideXlab platform.
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thermodynamic properties of synthetic sapphire α al2o3 standard reference material 720 and the effect of Temperature scale differences on thermodynamic properties
Journal of Physical and Chemical Reference Data, 1993Co-Authors: Donald G ArcherAbstract:Comparison of the National Institute of Standards and Technology’s Standard Reference Material 720 certificate values for heat capacity with those obtained from recent experimental determinations indicated the possibility of a systematic error in the certificate values. Selected experimental determinations of enthalpy increments and heat capacities were fitted in order to obtain a representation of the thermodynamic properties of α‐Al2O3, a sample of which is the standard reference material (SRM‐720) for calibration of some types of calorimeters. The fitted equation and calculated values of the heat capacity, the relative enthalpy, and the entropy are given. The new values are more accurate and result from a better representation of the experimental values than did the 1982 SRM‐720 certificate values. Additionally, the general problem of the effect of changes in practical Temperature Scales on thermodynamic properties is briefly discussed, using the results for α‐Al2O3. A recent report from the I.U.P.A.C. Commission on Thermodynamics gave a method for the conversion of thermodynamic properties for changes in practical Temperature scale. The I.U.P.A.C. method is shown to be not generally correct. A better method for estimation of these changes is given.
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thermodynamic properties of synthetic sapphire α al2o3 standard reference material 720 and the effect of Temperature scale differences on thermodynamic properties
Journal of Physical and Chemical Reference Data, 1993Co-Authors: Donald G ArcherAbstract:Comparison of the National Institute of Standards and Technology’s Standard Reference Material 720 certificate values for heat capacity with those obtained from recent experimental determinations indicated the possibility of a systematic error in the certificate values. Selected experimental determinations of enthalpy increments and heat capacities were fitted in order to obtain a representation of the thermodynamic properties of α‐Al2O3, a sample of which is the standard reference material (SRM‐720) for calibration of some types of calorimeters. The fitted equation and calculated values of the heat capacity, the relative enthalpy, and the entropy are given. The new values are more accurate and result from a better representation of the experimental values than did the 1982 SRM‐720 certificate values. Additionally, the general problem of the effect of changes in practical Temperature Scales on thermodynamic properties is briefly discussed, using the results for α‐Al2O3. A recent report from the I.U.P.A.C....
Fabien Baron - One of the best experts on this subject based on the ideXlab platform.
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chara mirc observations of two m supergiants in perseus ob1 Temperature bayesian modeling and compressed sensing imaging
arXiv: Solar and Stellar Astrophysics, 2014Co-Authors: Matthew D. Anderson, Fabien Baron, J D Monnier, L L Kiss, Hilding R Neilson, Ming Zhao, Alicia Aarnio, E PedrettiAbstract:Two red supergiants of the Per OB1 association, RS Per and T Per, have been observed in H band using the MIRC instrument at the CHARA array. The data show clear evidence of departure from circular symmetry. We present here new techniques specially developed to analyze such cases, based on state-of-the-art statistical frameworks. The stellar surfaces are first modeled as limb-darkened discs based on SATLAS models that fit both MIRC interferometric data and publicly available spectrophotometric data. Bayesian model selection is then used to determine the most probable number of spots. The effective surface Temperatures are also determined and give further support to the recently derived hotter Temperature Scales of red su- pergiants. The stellar surfaces are reconstructed by our model-independent imaging code SQUEEZE, making use of its novel regularizer based on Compressed Sensing theory. We find excellent agreement between the model-selection results and the reconstructions. Our results provide evidence for the presence of near-infrared spots representing about 3-5% of the stellar flux.
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chara mirc observations of two m supergiants in perseus ob1 Temperature bayesian modeling and compressed sensing imaging
The Astrophysical Journal, 2014Co-Authors: Matthew D. Anderson, Fabien Baron, J D Monnier, L L Kiss, Hilding R Neilson, Ming Zhao, Alicia Aarnio, E PedrettiAbstract:Two red supergiants (RSGs) of the Per OB1 association, RS Per and T Per, have been observed in the H band using the Michigan Infra-Red Combiner (MIRC) instrument at the CHARA array. The data show clear evidence of a departure from circular symmetry. We present here new techniques specially developed to analyze such cases, based on state-of-the-art statistical frameworks. The stellar surfaces are first modeled as limb-darkened disks based on SATLAS models that fit both MIRC interferometric data and publicly available spectrophotometric data. Bayesian model selection is then used to determine the most probable number of spots. The effective surface Temperatures are also determined and give further support to the recently derived hotter Temperature Scales of RSGs. The stellar surfaces are reconstructed by our model-independent imaging code SQUEEZE, making use of its novel regularizer based on Compressed Sensing theory. We find excellent agreement between the model-selection results and the reconstructions. Our results provide evidence for the presence of near-infrared spots representing about 3%-5% of the stellar flux.
Patrick Gervais - One of the best experts on this subject based on the ideXlab platform.
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Cellular Injuries in Cronobacter sakazakii CIP 103183T and Salmonella enterica Exposed to Drying and Subsequent Heat Treatment in Milk Powder
Frontiers in Microbiology, 2018Co-Authors: Emilie Lang, Stéphane Guyot, Caroline Peltier, Pablo Alvarez-martin, Jean-marie Perrier-cornet, Patrick GervaisAbstract:Because of the ability of foodborne pathogens to survive in low-moisture foods, their decontamination is an important issue in food protection. This study aimed to clarify some of the cellular mechanisms involved in inactivation of foodborne pathogens after drying and subsequent heating. Individual strains of Salmonella Typhimurium, Salmonella Senftenberg, and Cronobacter sakazakii were mixed into whole milk powder and dried to different water activity levels (0.25 and 0.58); the number of surviving cells was determined after drying and subsequent thermal treatments in closed vessels at 90 and 100 degrees C, for 30 and 120 s. For each condition, the percentage of unculturable cells was estimated and, in parallel, membrane permeability and respiratory activity were estimated by flow cytometry using fluorescent probes. After drying, it was clearly observable that the percentage of unculturable cells was correlated with the percentage of permeabilized cells (responsible for 20-40% of the total inactivated bacteria after drying), and to a lesser degree with the percentage of cells presenting with loss of respiratory activity. In contrast, the percentages of unculturable cells observed after heat treatment were strongly correlated with the loss of respiratory activity and weakly with membrane permeability (for 70-80% of the total inactivated bacteria after heat treatment). We conclude that cell inactivation during drying is closely linked to membrane permeabilization and that heat treatment of dried cells affects principally their respiratory activity. These results legitimize the use of time-Temperature Scales and allow better understanding of the cellular mechanisms of bacterial death during drying and subsequent heat treatment. These results may also allow better optimization of the decontamination process to ensure food safety by targeting the most deleterious conditions for bacterial cells without denaturing the food product.
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Cellular Injuries in Cronobacter sakazakii CIP 103183T and Salmonella enterica Exposed to Drying and Subsequent Heat Treatment in Milk Powder
Frontiers Media S.A., 2018Co-Authors: Emilie Lang, Stéphane Guyot, Caroline Peltier, Pablo Alvarez-martin, Jean-marie Perrier-cornet, Patrick GervaisAbstract:Because of the ability of foodborne pathogens to survive in low-moisture foods, their decontamination is an important issue in food protection. This study aimed to clarify some of the cellular mechanisms involved in inactivation of foodborne pathogens after drying and subsequent heating. Individual strains of Salmonella Typhimurium, Salmonella Senftenberg, and Cronobacter sakazakii were mixed into whole milk powder and dried to different water activity levels (0.25 and 0.58); the number of surviving cells was determined after drying and subsequent thermal treatments in closed vessels at 90 and 100°C, for 30 and 120 s. For each condition, the percentage of unculturable cells was estimated and, in parallel, membrane permeability and respiratory activity were estimated by flow cytometry using fluorescent probes. After drying, it was clearly observable that the percentage of unculturable cells was correlated with the percentage of permeabilized cells (responsible for 20–40% of the total inactivated bacteria after drying), and to a lesser degree with the percentage of cells presenting with loss of respiratory activity. In contrast, the percentages of unculturable cells observed after heat treatment were strongly correlated with the loss of respiratory activity and weakly with membrane permeability (for 70–80% of the total inactivated bacteria after heat treatment). We conclude that cell inactivation during drying is closely linked to membrane permeabilization and that heat treatment of dried cells affects principally their respiratory activity. These results legitimize the use of time–Temperature Scales and allow better understanding of the cellular mechanisms of bacterial death during drying and subsequent heat treatment. These results may also allow better optimization of the decontamination process to ensure food safety by targeting the most deleterious conditions for bacterial cells without denaturing the food product
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Image_1.tif
2018Co-Authors: Emilie Lang, Stéphane Guyot, Caroline Peltier, Pablo Alvarez-martin, Jean-marie Perrier-cornet, Patrick GervaisAbstract:Because of the ability of foodborne pathogens to survive in low-moisture foods, their decontamination is an important issue in food protection. This study aimed to clarify some of the cellular mechanisms involved in inactivation of foodborne pathogens after drying and subsequent heating. Individual strains of Salmonella Typhimurium, Salmonella Senftenberg, and Cronobacter sakazakii were mixed into whole milk powder and dried to different water activity levels (0.25 and 0.58); the number of surviving cells was determined after drying and subsequent thermal treatments in closed vessels at 90 and 100°C, for 30 and 120 s. For each condition, the percentage of unculturable cells was estimated and, in parallel, membrane permeability and respiratory activity were estimated by flow cytometry using fluorescent probes. After drying, it was clearly observable that the percentage of unculturable cells was correlated with the percentage of permeabilized cells (responsible for 20–40% of the total inactivated bacteria after drying), and to a lesser degree with the percentage of cells presenting with loss of respiratory activity. In contrast, the percentages of unculturable cells observed after heat treatment were strongly correlated with the loss of respiratory activity and weakly with membrane permeability (for 70–80% of the total inactivated bacteria after heat treatment). We conclude that cell inactivation during drying is closely linked to membrane permeabilization and that heat treatment of dried cells affects principally their respiratory activity. These results legitimize the use of time–Temperature Scales and allow better understanding of the cellular mechanisms of bacterial death during drying and subsequent heat treatment. These results may also allow better optimization of the decontamination process to ensure food safety by targeting the most deleterious conditions for bacterial cells without denaturing the food product.
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Table_1.XLSX
2018Co-Authors: Emilie Lang, Stéphane Guyot, Caroline Peltier, Pablo Alvarez-martin, Jean-marie Perrier-cornet, Patrick GervaisAbstract:Because of the ability of foodborne pathogens to survive in low-moisture foods, their decontamination is an important issue in food protection. This study aimed to clarify some of the cellular mechanisms involved in inactivation of foodborne pathogens after drying and subsequent heating. Individual strains of Salmonella Typhimurium, Salmonella Senftenberg, and Cronobacter sakazakii were mixed into whole milk powder and dried to different water activity levels (0.25 and 0.58); the number of surviving cells was determined after drying and subsequent thermal treatments in closed vessels at 90 and 100°C, for 30 and 120 s. For each condition, the percentage of unculturable cells was estimated and, in parallel, membrane permeability and respiratory activity were estimated by flow cytometry using fluorescent probes. After drying, it was clearly observable that the percentage of unculturable cells was correlated with the percentage of permeabilized cells (responsible for 20–40% of the total inactivated bacteria after drying), and to a lesser degree with the percentage of cells presenting with loss of respiratory activity. In contrast, the percentages of unculturable cells observed after heat treatment were strongly correlated with the loss of respiratory activity and weakly with membrane permeability (for 70–80% of the total inactivated bacteria after heat treatment). We conclude that cell inactivation during drying is closely linked to membrane permeabilization and that heat treatment of dried cells affects principally their respiratory activity. These results legitimize the use of time–Temperature Scales and allow better understanding of the cellular mechanisms of bacterial death during drying and subsequent heat treatment. These results may also allow better optimization of the decontamination process to ensure food safety by targeting the most deleterious conditions for bacterial cells without denaturing the food product.
Ryan O Milligan - One of the best experts on this subject based on the ideXlab platform.
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the thermal properties of solar flares over three solar cycles using goes x ray observations
Astrophysical Journal Supplement Series, 2012Co-Authors: Daniel Ryan, Ryan O Milligan, Peter T Gallagher, Brian R Dennis, Kim A Tolbert, Richard A Schwartz, Alex C YoungAbstract:Solar flare X-ray emission results from rapidly increasing Temperatures and emission measures in flaring active region loops. To date, observations from the X-Ray Sensor (XRS) on board the Geostationary Operational Environmental Satellite (GOES) have been used to derive these properties, but have been limited by a number of factors, including the lack of a consistent background subtraction method capable of being automatically applied to large numbers of flares. In this paper, we describe an automated Temperature and Emission measure-Based Background Subtraction method (TEBBS), that builds on the methods of Bornmann. Our algorithm ensures that the derived Temperature is always greater than the instrumental limit and the pre-flare background Temperature, and that the Temperature and emission measure are increasing during the flare rise phase. Additionally, TEBBS utilizes the improved estimates of GOES Temperatures and emission measures from White et al. TEBBS was successfully applied to over 50,000 solar flares occurring over nearly three solar cycles (1980-2007), and used to create an extensive catalog of the solar flare thermal properties. We confirm that the peak emission measure and total radiative losses scale with background subtracted GOES X-ray flux as power laws, while the peak Temperature Scales logarithmically. As expected, the peak emission measure shows an increasing trend with peak Temperature, although the total radiative losses do not. While these results are comparable to previous studies, we find that flares of a given GOES class have lower peak Temperatures and higher peak emission measures than previously reported. The TEBBS database of flare thermal plasma properties is publicly available at http://www.SolarMonitor.org/TEBBS/.
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the thermal properties of solar flares over three solar cycles using goes x ray observations
arXiv: Solar and Stellar Astrophysics, 2012Co-Authors: Daniel Ryan, Ryan O Milligan, Peter T Gallagher, Brian R Dennis, Kim A Tolbert, Richard A Schwartz, Alex C YoungAbstract:Solar flare X-ray emission results from rapidly increasing Temperatures and emission measures in flaring active region loops. To date, observations from the X-Ray Sensor (XRS) onboard the Geostationary Operational Environmental Satellite (GOES) have been used to derive these properties, but have been limited by a number of factors, including the lack of a consistent background subtraction method capable of being automatically applied to large numbers of flares. In this paper, we describe an automated Temperature and emission measure-based background subtraction method (TEBBS), which builds on the methods of Bornmann (1990). Our algorithm ensures that the derived Temperature is always greater than the instrumental limit and the pre-flare background Temperature, and that the Temperature and emission measure are increasing during the flare rise phase. Additionally, TEBBS utilizes the improved estimates of GOES Temperatures and emission measures from White et al. (2005). TEBBS was successfully applied to over 50,000 solar flares occurring over nearly three solar cycles (1980-2007), and used to create an extensive catalog of the solar flare thermal properties. We confirm that the peak emission measure and total radiative losses scale with background subtracted GOES X-ray flux as power-laws, while the peak Temperature Scales logarithmically. As expected, the peak emission measure shows an increasing trend with peak Temperature, although the total radiative losses do not. While these results are comparable to previous studies, we find that flares of a given GOES class have lower peak Temperatures and higher peak emission measures than previously reported. The resulting TEBBS database of thermal flare plasma properties is publicly available on Solar Monitor (this http URL) and will be available on Heliophysics Integrated Observatory (this http URL).
