The Experts below are selected from a list of 47439 Experts worldwide ranked by ideXlab platform
Robert P Kirshner - One of the best experts on this subject based on the ideXlab platform.
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metallicity differences in type ia supernova progenitors inferred from ultraviolet spectra
The Astrophysical Journal, 2013Co-Authors: R J Foley, Robert P KirshnerAbstract:Two ''twin'' Type Ia supernovae (SNe Ia), SNe 2011by and 2011fe, have extremely similar optical light-curve shapes, colors, and spectra, yet have different ultraviolet (UV) continua as measured in Hubble Space Telescope spectra and measurably different peak luminosities. We attribute the difference in the UV continua to significantly different progenitor metallicities. This is the first robust detection of different metallicities for SN Ia progenitors. Theoretical Reasoning suggests that differences in metallicity also lead to differences in luminosity. SNe Ia with higher progenitor metallicities have lower {sup 56}Ni yields and lower luminosities for the same light-curve shape. SNe 2011by and 2011fe have different peak luminosities ({Delta}M{sub V} Almost-Equal-To 0.6 mag), which correspond to different {sup 56}Ni yields: M{sub 11fe}({sup 56}Ni) / M{sub 11by}({sup 56}Ni) = 1.7{sup +0.7}{sub -0.5}. From Theoretical models that account for different neutron-to-proton ratios in progenitors, the differences in {sup 56}Ni yields for SNe 2011by and 2011fe imply that their progenitor stars were above and below solar metallicity, respectively. Although we can distinguish progenitor metallicities in a qualitative way from UV data, the quantitative interpretation in terms of abundances is limited by the present state of Theoretical models.
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metallicity differences in type ia supernova progenitors inferred from ultraviolet spectra
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: R J Foley, Robert P KirshnerAbstract:Two "twin" Type Ia supernovae (SNe Ia), SNe 2011by and 2011fe, have extremely similar optical light-curve shapes, colors, and spectra, yet have different ultraviolet (UV) continua as measured in Hubble Space Telescope spectra and measurably different peak luminosities. We attribute the difference in the UV continua to significantly different progenitor metallicities. This is the first robust detection of different metallicities for SN Ia progenitors. Theoretical Reasoning suggests that differences in metallicity also lead to differences in luminosity. SNe Ia with higher progenitor metallicities have lower 56Ni yields, and lower luminosities, for the same light-curve shape. SNe 2011by and 2011fe have different peak luminosities (Delta M_V = 0.6 mag), which correspond to different 56Ni yields: M_11fe(56Ni)/M_11by(56Ni) = 1.7^+0.7_-0.5. From Theoretical models that account for different neutron to proton ratios in progenitors, the differences in 56Ni yields for SNe 2011by and 2011fe imply that their progenitor stars were above and below solar metallicity, respectively. Although we can distinguish progenitor metallicities in a qualitative way from UV data, the quantitative interpretation in terms of abundances is limited by the present state of Theoretical models.
Johan Wiklund - One of the best experts on this subject based on the ideXlab platform.
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an operationalization of stevenson s conceptualization of entrepreneurship as opportunity based firm behavior
Australian Centre for Entrepreneurship; QUT Business School, 2001Co-Authors: Terrence Brown, Per Davidsson, Johan WiklundAbstract:Stevenson (1983) holds that entrepreneurial management, defined as a set of opportunity-based man-agement practices, can help firms remain vital and contribute to firm and societal level value creation. While his conceptualization has received much attention, little progress has been made because of a lack of empirical tools to examine his propositions. This article seeks to resolve this by describing a new instrument that was developed specifically for operationalizing Stevenson’s conceptualization. After two pre-tests, the instrument was tested full scale on a very large (1200+ cases) stratified random sample of firms with different size, governance struc-ture, and industry affiliation. The results show that both in the full sample and in various sub-samples it was pos-sible to identify six sub-dimensions with high discriminant validity and moderate to high reliability, which rep-resent dimensions of Stevenson’s Theoretical Reasoning. We label these Strategic Orientation, Resource Orienta-tion, Management Structure, Reward Philosophy, Growth Orientation and Entrepreneurial Culture. We were further able to show that these dimensions only partly overlap with ‘Entrepreneurial Orientation’, the hitherto best established empirical instrument for assessing a firm’s degree of entrepreneurship. Our instrument should open up opportunities for researchers to further evaluate entrepreneurship in existing firms.
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An operationalization of Stevenson's conceptualization of entrepreneurship as opportunity-based firm behavior
Strategic Management Journal, 2001Co-Authors: Terrence E. Brown, Per Davidsson, Johan WiklundAbstract:Stevenson (1983) holds that entrepreneurial management, defined as a set of opportunity-based management practices, can help firms remain vital and contribute to firm and societal level value creation. Mule his conceptualization has received much attention, little progress has been made because of a lack of empirical tools to examine his propositions. This article seeks to resolve this by describing a new instrument that was developed specifically for operationalizing Stevenson's conceptualization. After two pre-tests, the instrument was tested full scale on a very large (1200+ cases) stratified random sample of firms with different size, governance structure, and industry affiliation. The results show that both in the full sample and in various sub-samples it was possible to identify six sub-dimensions with high discriminant validity and moderate to high reliability, which represent dimensions of Stevenson's Theoretical Reasoning. We label these Strategic Orientation, Resource Orientation, Management Structure, Reward Philosophy, Growth Orientation and Entrepreneurial Culture. We were further able to show that these dimensions only partly overlap with 'Entrepreneurial Orientation', the hitherto best established empirical instrument for assessing a firm's degree of entrepreneurship. Our instrument should open tip opportunities for researchers to further evaluate entrepreneurship in existing firms. Copyright (C) 2001 John Wiley & Sons, Ltd.
R J Foley - One of the best experts on this subject based on the ideXlab platform.
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metallicity differences in type ia supernova progenitors inferred from ultraviolet spectra
The Astrophysical Journal, 2013Co-Authors: R J Foley, Robert P KirshnerAbstract:Two ''twin'' Type Ia supernovae (SNe Ia), SNe 2011by and 2011fe, have extremely similar optical light-curve shapes, colors, and spectra, yet have different ultraviolet (UV) continua as measured in Hubble Space Telescope spectra and measurably different peak luminosities. We attribute the difference in the UV continua to significantly different progenitor metallicities. This is the first robust detection of different metallicities for SN Ia progenitors. Theoretical Reasoning suggests that differences in metallicity also lead to differences in luminosity. SNe Ia with higher progenitor metallicities have lower {sup 56}Ni yields and lower luminosities for the same light-curve shape. SNe 2011by and 2011fe have different peak luminosities ({Delta}M{sub V} Almost-Equal-To 0.6 mag), which correspond to different {sup 56}Ni yields: M{sub 11fe}({sup 56}Ni) / M{sub 11by}({sup 56}Ni) = 1.7{sup +0.7}{sub -0.5}. From Theoretical models that account for different neutron-to-proton ratios in progenitors, the differences in {sup 56}Ni yields for SNe 2011by and 2011fe imply that their progenitor stars were above and below solar metallicity, respectively. Although we can distinguish progenitor metallicities in a qualitative way from UV data, the quantitative interpretation in terms of abundances is limited by the present state of Theoretical models.
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metallicity differences in type ia supernova progenitors inferred from ultraviolet spectra
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: R J Foley, Robert P KirshnerAbstract:Two "twin" Type Ia supernovae (SNe Ia), SNe 2011by and 2011fe, have extremely similar optical light-curve shapes, colors, and spectra, yet have different ultraviolet (UV) continua as measured in Hubble Space Telescope spectra and measurably different peak luminosities. We attribute the difference in the UV continua to significantly different progenitor metallicities. This is the first robust detection of different metallicities for SN Ia progenitors. Theoretical Reasoning suggests that differences in metallicity also lead to differences in luminosity. SNe Ia with higher progenitor metallicities have lower 56Ni yields, and lower luminosities, for the same light-curve shape. SNe 2011by and 2011fe have different peak luminosities (Delta M_V = 0.6 mag), which correspond to different 56Ni yields: M_11fe(56Ni)/M_11by(56Ni) = 1.7^+0.7_-0.5. From Theoretical models that account for different neutron to proton ratios in progenitors, the differences in 56Ni yields for SNe 2011by and 2011fe imply that their progenitor stars were above and below solar metallicity, respectively. Although we can distinguish progenitor metallicities in a qualitative way from UV data, the quantitative interpretation in terms of abundances is limited by the present state of Theoretical models.
Terrence E. Brown - One of the best experts on this subject based on the ideXlab platform.
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An operationalization of Stevenson's conceptualization of entrepreneurship as opportunity-based firm behavior
Strategic Management Journal, 2001Co-Authors: Terrence E. Brown, Per Davidsson, Johan WiklundAbstract:Stevenson (1983) holds that entrepreneurial management, defined as a set of opportunity-based management practices, can help firms remain vital and contribute to firm and societal level value creation. Mule his conceptualization has received much attention, little progress has been made because of a lack of empirical tools to examine his propositions. This article seeks to resolve this by describing a new instrument that was developed specifically for operationalizing Stevenson's conceptualization. After two pre-tests, the instrument was tested full scale on a very large (1200+ cases) stratified random sample of firms with different size, governance structure, and industry affiliation. The results show that both in the full sample and in various sub-samples it was possible to identify six sub-dimensions with high discriminant validity and moderate to high reliability, which represent dimensions of Stevenson's Theoretical Reasoning. We label these Strategic Orientation, Resource Orientation, Management Structure, Reward Philosophy, Growth Orientation and Entrepreneurial Culture. We were further able to show that these dimensions only partly overlap with 'Entrepreneurial Orientation', the hitherto best established empirical instrument for assessing a firm's degree of entrepreneurship. Our instrument should open tip opportunities for researchers to further evaluate entrepreneurship in existing firms. Copyright (C) 2001 John Wiley & Sons, Ltd.
Per Davidsson - One of the best experts on this subject based on the ideXlab platform.
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an operationalization of stevenson s conceptualization of entrepreneurship as opportunity based firm behavior
Australian Centre for Entrepreneurship; QUT Business School, 2001Co-Authors: Terrence Brown, Per Davidsson, Johan WiklundAbstract:Stevenson (1983) holds that entrepreneurial management, defined as a set of opportunity-based man-agement practices, can help firms remain vital and contribute to firm and societal level value creation. While his conceptualization has received much attention, little progress has been made because of a lack of empirical tools to examine his propositions. This article seeks to resolve this by describing a new instrument that was developed specifically for operationalizing Stevenson’s conceptualization. After two pre-tests, the instrument was tested full scale on a very large (1200+ cases) stratified random sample of firms with different size, governance struc-ture, and industry affiliation. The results show that both in the full sample and in various sub-samples it was pos-sible to identify six sub-dimensions with high discriminant validity and moderate to high reliability, which rep-resent dimensions of Stevenson’s Theoretical Reasoning. We label these Strategic Orientation, Resource Orienta-tion, Management Structure, Reward Philosophy, Growth Orientation and Entrepreneurial Culture. We were further able to show that these dimensions only partly overlap with ‘Entrepreneurial Orientation’, the hitherto best established empirical instrument for assessing a firm’s degree of entrepreneurship. Our instrument should open up opportunities for researchers to further evaluate entrepreneurship in existing firms.
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An operationalization of Stevenson's conceptualization of entrepreneurship as opportunity-based firm behavior
Strategic Management Journal, 2001Co-Authors: Terrence E. Brown, Per Davidsson, Johan WiklundAbstract:Stevenson (1983) holds that entrepreneurial management, defined as a set of opportunity-based management practices, can help firms remain vital and contribute to firm and societal level value creation. Mule his conceptualization has received much attention, little progress has been made because of a lack of empirical tools to examine his propositions. This article seeks to resolve this by describing a new instrument that was developed specifically for operationalizing Stevenson's conceptualization. After two pre-tests, the instrument was tested full scale on a very large (1200+ cases) stratified random sample of firms with different size, governance structure, and industry affiliation. The results show that both in the full sample and in various sub-samples it was possible to identify six sub-dimensions with high discriminant validity and moderate to high reliability, which represent dimensions of Stevenson's Theoretical Reasoning. We label these Strategic Orientation, Resource Orientation, Management Structure, Reward Philosophy, Growth Orientation and Entrepreneurial Culture. We were further able to show that these dimensions only partly overlap with 'Entrepreneurial Orientation', the hitherto best established empirical instrument for assessing a firm's degree of entrepreneurship. Our instrument should open tip opportunities for researchers to further evaluate entrepreneurship in existing firms. Copyright (C) 2001 John Wiley & Sons, Ltd.
