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Martinus A J S Van Boekel - One of the best experts on this subject based on the ideXlab platform.
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melanoidins Extinction Coefficient in the glucose glycine maillard reaction
Food Chemistry, 2003Co-Authors: Sara I F S Martins, Martinus A J S Van BoekelAbstract:Melanoidins (brown, nitrogenous polymers and co-polymers) are the final products of the Maillard reaction. The glucose/glycine melanoidins Extinction Coefficient was determined using C-14-labelled glucose at three different reaction conditions. The absorbance was measured at different wavelengths (420, 450, 470 and 490 nm) and the Extinction Coefficient determined for each. The value of the Extinction Coefficient can be used to recalculate browning, measured as absorbance units, into melanoidins concentration in terms of sugar molecules incorporated. The amount of C-14-labelled sugar molecules was estimated in melanoidins separated via dialysis with a cut-off value of 3500 Da. These melanoidins only represented approximate to12% of the total colour formed. The Extinction Coefficient of the melanoidins remained constant during the observation period. At 470 nm, values of 0.65 (+/-0.02) 1 mmol(-1) cm(-1); 0.66 (+/-0.02) 1 mmol(-1) cm(-1) and 0.62 (+/-0.05) 1 mmol(-1) cm(-1), were obtained at 120 degreesC pH 6.8, 100 degreesC pH 6.8 and 100 degreesC pH 5.5, respectively. The difference is not significant. The Extinction Coefficient appeared to not to vary within the pH and temperature range studied. From the elemental analysis, the nondialysable melanoidins elementary composition seemed to be influenced by the reaction conditions, which was supposed to be related to the presence of side-chains on the melanoidin backbone. A trend was observed in the melanoidins C/N ratio: it decreased with increasing reaction pH as well as it changed to a lower level, of about 8, as the extent of browning increased. (C) 2003 Elsevier Ltd. All rights reserved.
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Melanoidins Extinction Coefficient in the glucose/glycine Maillard reaction
Food Chemistry, 2003Co-Authors: Sara I F S Martins, Martinus A J S Van BoekelAbstract:Melanoidins (brown, nitrogenous polymers and co-polymers) are the final products of the Maillard reaction. The glucose/glycine melanoidins Extinction Coefficient was determined using C-14-labelled glucose at three different reaction conditions. The absorbance was measured at different wavelengths (420, 450, 470 and 490 nm) and the Extinction Coefficient determined for each. The value of the Extinction Coefficient can be used to recalculate browning, measured as absorbance units, into melanoidins concentration in terms of sugar molecules incorporated. The amount of C-14-labelled sugar molecules was estimated in melanoidins separated via dialysis with a cut-off value of 3500 Da. These melanoidins only represented approximate to12% of the total colour formed. The Extinction Coefficient of the melanoidins remained constant during the observation period. At 470 nm, values of 0.65 (+/-0.02) 1 mmol(-1) cm(-1); 0.66 (+/-0.02) 1 mmol(-1) cm(-1) and 0.62 (+/-0.05) 1 mmol(-1) cm(-1), were obtained at 120 degreesC pH 6.8, 100 degreesC pH 6.8 and 100 degreesC pH 5.5, respectively. The difference is not significant. The Extinction Coefficient appeared to not to vary within the pH and temperature range studied. From the elemental analysis, the nondialysable melanoidins elementary composition seemed to be influenced by the reaction conditions, which was supposed to be related to the presence of side-chains on the melanoidin backbone. A trend was observed in the melanoidins C/N ratio: it decreased with increasing reaction pH as well as it changed to a lower level, of about 8, as the extent of browning increased. (C) 2003 Elsevier Ltd. All rights reserved.
David M. Bartels - One of the best experts on this subject based on the ideXlab platform.
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solvated electron Extinction Coefficient and oscillator strength in high temperature water
Journal of Physical Chemistry A, 2010Co-Authors: Patrick M. Hare, Erica A. Price, Christopher M Stanisky, Ireneusz Janik, David M. BartelsAbstract:The decadic Extinction Coefficient of the hydrated electron is reported for the absorption maximum from room temperature to 380 °C. The Extinction Coefficient is established by relating the transient absorption of the hydrated electrons in the presence of a scavenger to the concentration of stable product produced in the same experiment. Scavengers used in this report are SF6, N2O, and methyl viologen. The room temperature value is established as 22 500 M−1 cm−1, higher by 10−20% than values used over the last several decades. We demonstrate how previous workers arrived at a low value by incorrect choice of a radiolysis yield value. With this revision, the integrated oscillator strength, corrected by refractive index, is definitely (ca. 10%) larger than unity. This result is fully consistent with EPR and resonance Raman results which indicate mixing of the hydrated electron wave function with solvent electronic orbitals. Oscillator strength appears to be conserved vs temperature.
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Hydrated electron Extinction Coefficient revisited.
The journal of physical chemistry. A, 2008Co-Authors: Patrick M. Hare, Erica A. Price, David M. BartelsAbstract:The Extinction Coefficient of the hydrated electron (e−)aq generated by pulse radiolysis is evaluated relative to the methyl viologen radical cation •MV+, whose Extinction Coefficient at 605 nm has been carefully measured in the past. We find that the room temperature (e−)aq Extinction Coefficients reported in the literature are underestimated by 10−20%. We obtain ϵ = 22 700 M−1 cm−1 for the 20 °C hydrated electron at 720 nm, assuming the •MV+ Extinction is 13 700 M−1 cm−1 at 605 nm. This has implications both for second-order reaction rate measurements of (e−)aq and for the estimate of its integrated oscillator strength.
Sara I F S Martins - One of the best experts on this subject based on the ideXlab platform.
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melanoidins Extinction Coefficient in the glucose glycine maillard reaction
Food Chemistry, 2003Co-Authors: Sara I F S Martins, Martinus A J S Van BoekelAbstract:Melanoidins (brown, nitrogenous polymers and co-polymers) are the final products of the Maillard reaction. The glucose/glycine melanoidins Extinction Coefficient was determined using C-14-labelled glucose at three different reaction conditions. The absorbance was measured at different wavelengths (420, 450, 470 and 490 nm) and the Extinction Coefficient determined for each. The value of the Extinction Coefficient can be used to recalculate browning, measured as absorbance units, into melanoidins concentration in terms of sugar molecules incorporated. The amount of C-14-labelled sugar molecules was estimated in melanoidins separated via dialysis with a cut-off value of 3500 Da. These melanoidins only represented approximate to12% of the total colour formed. The Extinction Coefficient of the melanoidins remained constant during the observation period. At 470 nm, values of 0.65 (+/-0.02) 1 mmol(-1) cm(-1); 0.66 (+/-0.02) 1 mmol(-1) cm(-1) and 0.62 (+/-0.05) 1 mmol(-1) cm(-1), were obtained at 120 degreesC pH 6.8, 100 degreesC pH 6.8 and 100 degreesC pH 5.5, respectively. The difference is not significant. The Extinction Coefficient appeared to not to vary within the pH and temperature range studied. From the elemental analysis, the nondialysable melanoidins elementary composition seemed to be influenced by the reaction conditions, which was supposed to be related to the presence of side-chains on the melanoidin backbone. A trend was observed in the melanoidins C/N ratio: it decreased with increasing reaction pH as well as it changed to a lower level, of about 8, as the extent of browning increased. (C) 2003 Elsevier Ltd. All rights reserved.
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Melanoidins Extinction Coefficient in the glucose/glycine Maillard reaction
Food Chemistry, 2003Co-Authors: Sara I F S Martins, Martinus A J S Van BoekelAbstract:Melanoidins (brown, nitrogenous polymers and co-polymers) are the final products of the Maillard reaction. The glucose/glycine melanoidins Extinction Coefficient was determined using C-14-labelled glucose at three different reaction conditions. The absorbance was measured at different wavelengths (420, 450, 470 and 490 nm) and the Extinction Coefficient determined for each. The value of the Extinction Coefficient can be used to recalculate browning, measured as absorbance units, into melanoidins concentration in terms of sugar molecules incorporated. The amount of C-14-labelled sugar molecules was estimated in melanoidins separated via dialysis with a cut-off value of 3500 Da. These melanoidins only represented approximate to12% of the total colour formed. The Extinction Coefficient of the melanoidins remained constant during the observation period. At 470 nm, values of 0.65 (+/-0.02) 1 mmol(-1) cm(-1); 0.66 (+/-0.02) 1 mmol(-1) cm(-1) and 0.62 (+/-0.05) 1 mmol(-1) cm(-1), were obtained at 120 degreesC pH 6.8, 100 degreesC pH 6.8 and 100 degreesC pH 5.5, respectively. The difference is not significant. The Extinction Coefficient appeared to not to vary within the pH and temperature range studied. From the elemental analysis, the nondialysable melanoidins elementary composition seemed to be influenced by the reaction conditions, which was supposed to be related to the presence of side-chains on the melanoidin backbone. A trend was observed in the melanoidins C/N ratio: it decreased with increasing reaction pH as well as it changed to a lower level, of about 8, as the extent of browning increased. (C) 2003 Elsevier Ltd. All rights reserved.
Patrick Minnis - One of the best experts on this subject based on the ideXlab platform.
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Extinction Coefficient 1 μm properties of high altitude clouds from solar occultation measurements 1985 1990 evidence of volcanic aerosol effect
Journal of Geophysical Research, 1995Co-Authors: Pi-huan Wang, Patrick MinnisAbstract:The properties of the l-μm volume Extinction Coefficient of two geographically different high-altitude cloud systems have been examined for the posteruption period (1985–1990) of the April 1982 El Chichon volcanic event with emphasis on the effect of volcanic aerosols on clouds. These two high-altitude cloud systems are the tropical clouds in the tropopause region observed by the Stratospheric Aerosol and Gas Experiment (SAGE) II and the polar stratospheric clouds (PSCs) sighted by the Stratospheric Aerosol Measurement (SAM) II. The results indicate that volcanic aerosols alter the frequency distributions of these high-altitude clouds in such a manner that the occurrence of clouds having high Extinction Coefficients (6×10−3 – 2×10−2 km−1) is suppressed, while that of clouds having low Extinction Coefficients (2×10−3 – 6×10−2 km−1) is enhanced. This influence of the volcanic aerosols appears to be opposite to the increase in the Extinction Coefficient of optically thick clouds observed by the Earth Radiation Budget Experiment (ERBE) during the initial posteruption period of the June 1991 Pinatubo eruption. A plausible explanation of this difference, based on the Mie theory, is presented. The Mie calculation indicates that there are two possible types of response of cloud Extinction Coefficient to changes in aerosol concentration depending on the primary effective radius (re) of cloud systems observed by the instrument. These two types of response are separated by the cloud particle effective radius of about 0.8 μm. When re is smaller than 0.8 μm, the cloud Extinction Coefficient decreases in response to increases of aerosol concentration, and when re is greater than 0.8 μm, the opposite happens. As a consequence, the effective radius of most, if not all, of the high-altitude clouds, measured by the SAGE series of satellite instruments must be less than about 0.8 μm. This mean cloud particle size implied by the satellite Extinction-Coefficient data at a single wavelength (1 μm) is further substantiated by the particle size analysis based on cloud Extinction Coefficient at two wavelengths (0.525 and 1.02 μm) obtained by the SAGE II observations. Most of the radiation measured by ERBE is reflected by cloud systems comprised of particles having effective radii much greater than 1 μm. A reduction in the effective radius of these clouds due to volcanic aerosols is expected to increase their Extinction-Coefficient values, opposite the effect observed by SAGE II and SAM II. This work further illustrates the capability of the solar occultation satellite sensor to provide particulate Extinction-Coefficient measurements important to the study of the aerosol-cloud interactions. Finally, the June 1991 Mount Pinatubo major eruption put 3 times more material into the stratosphere than that of the 1982 El Chichon volcanic event. It is important to examine the variations of the Extinction Coefficient of these two high-altitude cloud systems for the posteruption years of the Pinatubo volcanic event for further evidence of the impact of volcanic aerosols on high-altitude clouds.
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Extinction Coefficient (1 μm) properties of high‐altitude clouds from solar occultation measurements (1985–1990): Evidence of volcanic aerosol effect
Journal of Geophysical Research, 1995Co-Authors: Pi-huan Wang, Patrick Minnis, Glenn K. YueAbstract:The properties of the l-μm volume Extinction Coefficient of two geographically different high-altitude cloud systems have been examined for the posteruption period (1985–1990) of the April 1982 El Chichon volcanic event with emphasis on the effect of volcanic aerosols on clouds. These two high-altitude cloud systems are the tropical clouds in the tropopause region observed by the Stratospheric Aerosol and Gas Experiment (SAGE) II and the polar stratospheric clouds (PSCs) sighted by the Stratospheric Aerosol Measurement (SAM) II. The results indicate that volcanic aerosols alter the frequency distributions of these high-altitude clouds in such a manner that the occurrence of clouds having high Extinction Coefficients (6×10−3 – 2×10−2 km−1) is suppressed, while that of clouds having low Extinction Coefficients (2×10−3 – 6×10−2 km−1) is enhanced. This influence of the volcanic aerosols appears to be opposite to the increase in the Extinction Coefficient of optically thick clouds observed by the Earth Radiation Budget Experiment (ERBE) during the initial posteruption period of the June 1991 Pinatubo eruption. A plausible explanation of this difference, based on the Mie theory, is presented. The Mie calculation indicates that there are two possible types of response of cloud Extinction Coefficient to changes in aerosol concentration depending on the primary effective radius (re) of cloud systems observed by the instrument. These two types of response are separated by the cloud particle effective radius of about 0.8 μm. When re is smaller than 0.8 μm, the cloud Extinction Coefficient decreases in response to increases of aerosol concentration, and when re is greater than 0.8 μm, the opposite happens. As a consequence, the effective radius of most, if not all, of the high-altitude clouds, measured by the SAGE series of satellite instruments must be less than about 0.8 μm. This mean cloud particle size implied by the satellite Extinction-Coefficient data at a single wavelength (1 μm) is further substantiated by the particle size analysis based on cloud Extinction Coefficient at two wavelengths (0.525 and 1.02 μm) obtained by the SAGE II observations. Most of the radiation measured by ERBE is reflected by cloud systems comprised of particles having effective radii much greater than 1 μm. A reduction in the effective radius of these clouds due to volcanic aerosols is expected to increase their Extinction-Coefficient values, opposite the effect observed by SAGE II and SAM II. This work further illustrates the capability of the solar occultation satellite sensor to provide particulate Extinction-Coefficient measurements important to the study of the aerosol-cloud interactions. Finally, the June 1991 Mount Pinatubo major eruption put 3 times more material into the stratosphere than that of the 1982 El Chichon volcanic event. It is important to examine the variations of the Extinction Coefficient of these two high-altitude cloud systems for the posteruption years of the Pinatubo volcanic event for further evidence of the impact of volcanic aerosols on high-altitude clouds.
Tobias Hertel - One of the best experts on this subject based on the ideXlab platform.
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molar Extinction Coefficient of single wall carbon nanotubes
Journal of Physical Chemistry C, 2011Co-Authors: Friedrich Schoppler, Christoph Mann, Tilman C Hain, Felix M Neubauer, G Privitera, Francesco Bonaccorso, Daping Chu, Andrea Ferrari, Tobias HertelAbstract:The molar Extinction Coefficient of single-wall carbon nanotubes (SWNTs) is determined using fluorescence tagging, as well as atomic force microscopy (AFM) imaging, which facilitate the correlation of nanotube concentrations with absorption spectra. Tagging of SWNTs is achieved using fluorescence-labeled single-strand DNA oligomers as the dispersion additive, while AFM imaging is used to determine the mass of SWNTs in the retentate of vacuum-filtered colloidal SWNT suspensions. The resulting absorption cross section for the first exciton transition of (6,5) nanotubes of 1.7 × 10–17 cm2 per C-atom corresponds to an Extinction Coefficient of (4400 ± 1000) M–1·cm–1, which is equivalent to an oscillator strength of 0.010 per carbon atom.
