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Christopher F Mckee - One of the best experts on this subject based on the ideXlab platform.

  • the expulsion of stellar envelopes in core collapse supernovae
    1999
    Co-Authors: Christopher D Matzner, Christopher F Mckee
    Abstract:

    We examine the relation between presupernova stellar structure and the distribution of ejecta in core-collapse supernovae of Types Ib, Ic, and II, under the approximations of adiabatic, spherically symmetric flow. We develop a simple yet accurate analytical formula for the velocity of the initial forward shock that traverses the stellar envelope. For material that does not later experience a strong reverse shock, the entropy deposited by this forward shock persists into the Final, freely expanding state. We demonstrate that the Final density distribution can be approximated with simple models for the Final Pressure distribution, in a way that matches the results of simulations. Our results indicate that the distribution of density and radiation Pressure in a star's ejecta depends on whether the outer envelope is radiative or convective, and if convective, on the composition structure of the star. Our models are most accurate for the high-velocity ejecta cast away from the periphery of a star. For stellar structures that limit to a common form in this region, the resulting ejecta limit to a common distribution at high velocities because the blast wave forgets its history as it approaches the stellar surface. We present formulae for the Final density distribution of this material as a function of mass, for both radiative and efficiently convective envelopes. These formulae limit to the well-known planar, self-similar solutions for mass shells approaching the stellar surface. However, the assumption of adiabatic flow breaks down for shells of low optical depth, so this planar limit need not be attained. The event of shock emergence, which limits adiabatic flow, also produces a soft X-ray burst of radiation. Formulae are given for the observable properties of this burst and their dependence on the parameters of the explosion. Motivated by the relativistic expansion recently inferred by Kulkarni et al. for the synchrotron shell around SN 1998bw, we estimate the criterion for relativistic mass ejection and the rest mass of relativistic ejecta. We base our models for the entire ejecta distribution on the high-velocity solution, on our shock-velocity formula, and on realistic radiation Pressure distributions. We also present simpler, but less flexible, analytical approximations for ejecta distributions. We survey the ejecta of the polytropic hydrogen envelopes of red supergiants. Our models will be useful for studies of the light curves and circumstellar or interstellar interactions of core-collapse supernovae, and of the birth of pulsar nebulae in their ejecta.

  • the expulsion of stellar envelopes in core collapse supernovae
    1998
    Co-Authors: Christopher D Matzner, Christopher F Mckee
    Abstract:

    We examine the relation between presupernova stellar structure and the distribution of ejecta in core-collapse supernovae, assuming adiabatic, spherically symmetric flow. We develop a simple yet accurate formula for the blastwave shock velocity, and demonstrate that the entire Final density distribution can be approximated with simple models for the Final Pressure distribution, along with the approximate shock-deposited entropy, in a way that matches the results of simulations. We find that the distribution of density in a star's ejecta depends on whether its outer envelope is radiative or convective, and if convective, on the composition structure of the star; simple approximate forms are presented for red and blue supergiant ejecta. Our models are most accurate for the high-velocity ejecta from the periphery of a star, where the shock dynamics are predictable. We present formulae for the Final density distribution of this material, for both radiative and efficiently convective envelopes. These formulae limit to the well-known planar, self-similar solutions for mass shells approaching the stellar surface. But, the assumption of adiabatic flow fails at low optical depth, so this planar limit need not be attained. Formulae are given for the observable properties of the X-ray burst accompanying shock emergence, and their dependence on the parameters of the explosion. Motivated by the relativistic expansion recently inferred by Kulkarni et al. (1998) for the synchrotron shell around SN1998bw, we estimate the criterion for relativistic mass ejection and the rest mass of relativistic ejecta.

Chatzievangelou Damianos - One of the best experts on this subject based on the ideXlab platform.

  • Quality Control and Pre-Analysis Treatment of the Environmental Datasets Collected by an Internet Operated Deep-Sea Crawler during Its Entire 7-Year Long Deployment (2009–2016)
    2020
    Co-Authors: Chatzievangelou Damianos, Aguzzi Jacopo, Scherwath Martin, Thomsen Laurenz
    Abstract:

    Deep-sea environmental datasets are ever-increasing in size and diversity, as technological advances lead monitoring studies towards long-term, high-frequency data acquisition protocols. This study presents examples of pre-analysis data treatment steps applied to the environmental time series collected by the Internet Operated Deep-sea Crawler “Wally” during a 7-year deployment (2009–2016) in the Barkley Canyon methane hydrates site, off Vancouver Island (BC, Canada). Pressure, temperature, electrical conductivity, flow, turbidity, and chlorophyll data were subjected to different standardizing, normalizing, and de-trending methods on a case-by-case basis, depending on the nature of the treated variable and the range and scale of the values provided by each of the different sensors. The Final Pressure, temperature, and electrical conductivity (transformed to practical salinity) datasets are ready for use. On the other hand, in the cases of flow, turbidity, and chlorophyll, further in-depth processing, in tandem with data describing the movement and position of the crawler, will be needed in order to filter out all possible effects of the latter. Our work evidences challenges and solutions in multiparametric data acquisition and quality control and ensures that a big step is taken so that the available environmental data meet high quality standards and facilitate the production of reliable scientific results

  • Quality Control and Pre-Analysis Treatment of the Environmental Datasets Collected by an Internet Operated Deep-Sea Crawler during Its Entire 7-Year Long Deployment (2009-2016)
    2020
    Co-Authors: Chatzievangelou Damianos, Aguzzi Jacopo, Scherwath Martin, Thomsen L.
    Abstract:

    Special issue Selected Papers from the 2019 IMEKO TC-19 International Workshop on Metrology for the Sea.-- 20 pages, 8 figures, 2 tables, 1 appendix, supplementary materials at http://www.mdpi.com/1424-8220/20/10/2991/s1Deep-sea environmental datasets are ever-increasing in size and diversity, as technological advances lead monitoring studies towards long-term, high-frequency data acquisition protocols. This study presents examples of pre-analysis data treatment steps applied to the environmental time series collected by the Internet Operated Deep-sea Crawler “Wally” during a 7-year deployment (2009–2016) in the Barkley Canyon methane hydrates site, off Vancouver Island (BC, Canada). Pressure, temperature, electrical conductivity, flow, turbidity, and chlorophyll data were subjected to different standardizing, normalizing, and de-trending methods on a case-by-case basis, depending on the nature of the treated variable and the range and scale of the values provided by each of the different sensors. The Final Pressure, temperature, and electrical conductivity (transformed to practical salinity) datasets are ready for use. On the other hand, in the cases of flow, turbidity, and chlorophyll, further in-depth processing, in tandem with data describing the movement and position of the crawler, will be needed in order to filter out all possible effects of the latter. Our work evidences challenges and solutions in multiparametric data acquisition and quality control and ensures that a big step is taken so that the available environmental data meet high quality standards and facilitate the production of reliable scientific resultsThis research was developed within the framework of Ocean Networks Canada and NEPTUNE Canada, an initiative of the University of Victoria, and primarily funded by the Canadian Foundation for Innovation, Transport Canada, Fisheries and Oceans Canada, and the Canadian Province of British Columbia; Helmholtz Alliance and Tecnoterra (ICM-CSIC/UPC) and the following project activities: ROBEX (HA-304); ARIM (Autonomous Robotic sea-floor Infrastructure for benthopelagic Monitoring; MartTERA ERA-Net Cofound); ARCHES (Autonomous Robotic Networks to Help Modern Societies; German Helmholtz Association) and RESBIO (TEC2017-87861-R; Ministerio de Ciencia, Innovación y Universidades

Christopher D Matzner - One of the best experts on this subject based on the ideXlab platform.

  • the expulsion of stellar envelopes in core collapse supernovae
    1999
    Co-Authors: Christopher D Matzner, Christopher F Mckee
    Abstract:

    We examine the relation between presupernova stellar structure and the distribution of ejecta in core-collapse supernovae of Types Ib, Ic, and II, under the approximations of adiabatic, spherically symmetric flow. We develop a simple yet accurate analytical formula for the velocity of the initial forward shock that traverses the stellar envelope. For material that does not later experience a strong reverse shock, the entropy deposited by this forward shock persists into the Final, freely expanding state. We demonstrate that the Final density distribution can be approximated with simple models for the Final Pressure distribution, in a way that matches the results of simulations. Our results indicate that the distribution of density and radiation Pressure in a star's ejecta depends on whether the outer envelope is radiative or convective, and if convective, on the composition structure of the star. Our models are most accurate for the high-velocity ejecta cast away from the periphery of a star. For stellar structures that limit to a common form in this region, the resulting ejecta limit to a common distribution at high velocities because the blast wave forgets its history as it approaches the stellar surface. We present formulae for the Final density distribution of this material as a function of mass, for both radiative and efficiently convective envelopes. These formulae limit to the well-known planar, self-similar solutions for mass shells approaching the stellar surface. However, the assumption of adiabatic flow breaks down for shells of low optical depth, so this planar limit need not be attained. The event of shock emergence, which limits adiabatic flow, also produces a soft X-ray burst of radiation. Formulae are given for the observable properties of this burst and their dependence on the parameters of the explosion. Motivated by the relativistic expansion recently inferred by Kulkarni et al. for the synchrotron shell around SN 1998bw, we estimate the criterion for relativistic mass ejection and the rest mass of relativistic ejecta. We base our models for the entire ejecta distribution on the high-velocity solution, on our shock-velocity formula, and on realistic radiation Pressure distributions. We also present simpler, but less flexible, analytical approximations for ejecta distributions. We survey the ejecta of the polytropic hydrogen envelopes of red supergiants. Our models will be useful for studies of the light curves and circumstellar or interstellar interactions of core-collapse supernovae, and of the birth of pulsar nebulae in their ejecta.

  • the expulsion of stellar envelopes in core collapse supernovae
    1998
    Co-Authors: Christopher D Matzner, Christopher F Mckee
    Abstract:

    We examine the relation between presupernova stellar structure and the distribution of ejecta in core-collapse supernovae, assuming adiabatic, spherically symmetric flow. We develop a simple yet accurate formula for the blastwave shock velocity, and demonstrate that the entire Final density distribution can be approximated with simple models for the Final Pressure distribution, along with the approximate shock-deposited entropy, in a way that matches the results of simulations. We find that the distribution of density in a star's ejecta depends on whether its outer envelope is radiative or convective, and if convective, on the composition structure of the star; simple approximate forms are presented for red and blue supergiant ejecta. Our models are most accurate for the high-velocity ejecta from the periphery of a star, where the shock dynamics are predictable. We present formulae for the Final density distribution of this material, for both radiative and efficiently convective envelopes. These formulae limit to the well-known planar, self-similar solutions for mass shells approaching the stellar surface. But, the assumption of adiabatic flow fails at low optical depth, so this planar limit need not be attained. Formulae are given for the observable properties of the X-ray burst accompanying shock emergence, and their dependence on the parameters of the explosion. Motivated by the relativistic expansion recently inferred by Kulkarni et al. (1998) for the synchrotron shell around SN1998bw, we estimate the criterion for relativistic mass ejection and the rest mass of relativistic ejecta.

Cavus Falamaki - One of the best experts on this subject based on the ideXlab platform.

  • The effect of reliable prediction of Final Pressure during Pressure equalization steps on the performance of PSA cycles
    2011
    Co-Authors: Milad Yavary, Habib Ale-ebrahim, Cavus Falamaki
    Abstract:

    Abstract The present work aims at modeling the performance of isothermal PSA cycles for the production of H 2 from refinery fuel gas by introducing a more reliable calculation of the Final Pressure during the Pressure equalization steps. The latter calculation is performed based on the law of conservation of mass in a system comprehending the depressurizing and pressurizing beds in contact. Single adsorbent (zeolite 5A) dual and six-bed PSA processes have been considered. The PSA cycle performance is compared with a conventional model considering an arithmetic mean for the Final Pressure during the Pressure equalization steps (old model). It is shown that the new model predicts lower values for product purity and recovery when compared with the old model. The error in the estimation of the product recovery is larger than the corresponding value for product purity and may exceed 9%. It is shown that the error in the calculation of purity and recovery strongly depends on the number of beds. The error in the calculation of product recovery increases approximately two-fold increasing the number of beds from 2 to 6. Therefore, the present study shows that implementation of a more robust method for the evaluation of Final Pressure during the equalization steps is imperative for the development of new models of industrial PSA processes, especially for the number of beds exceeding 2.

Thomsen Laurenz - One of the best experts on this subject based on the ideXlab platform.

  • Quality Control and Pre-Analysis Treatment of the Environmental Datasets Collected by an Internet Operated Deep-Sea Crawler during Its Entire 7-Year Long Deployment (2009–2016)
    2020
    Co-Authors: Chatzievangelou Damianos, Aguzzi Jacopo, Scherwath Martin, Thomsen Laurenz
    Abstract:

    Deep-sea environmental datasets are ever-increasing in size and diversity, as technological advances lead monitoring studies towards long-term, high-frequency data acquisition protocols. This study presents examples of pre-analysis data treatment steps applied to the environmental time series collected by the Internet Operated Deep-sea Crawler “Wally” during a 7-year deployment (2009–2016) in the Barkley Canyon methane hydrates site, off Vancouver Island (BC, Canada). Pressure, temperature, electrical conductivity, flow, turbidity, and chlorophyll data were subjected to different standardizing, normalizing, and de-trending methods on a case-by-case basis, depending on the nature of the treated variable and the range and scale of the values provided by each of the different sensors. The Final Pressure, temperature, and electrical conductivity (transformed to practical salinity) datasets are ready for use. On the other hand, in the cases of flow, turbidity, and chlorophyll, further in-depth processing, in tandem with data describing the movement and position of the crawler, will be needed in order to filter out all possible effects of the latter. Our work evidences challenges and solutions in multiparametric data acquisition and quality control and ensures that a big step is taken so that the available environmental data meet high quality standards and facilitate the production of reliable scientific results