The Experts below are selected from a list of 193908 Experts worldwide ranked by ideXlab platform
H.-g. Ludwig - One of the best experts on this subject based on the ideXlab platform.
-
stellar granulation as seen in disk integrated intensity i simplified Theoretical Modeling
Astronomy and Astrophysics, 2013Co-Authors: R. Samadi, K. Belkacem, H.-g. LudwigAbstract:Context. Solar granulation has been known for a long time to be a surface manifestation of convection. The space-borne missions CoRoT and Kepler enable us to observe the signature of this phenomena in disk-integrated intensity on a large number of stars. Aims. The space-based photometric measurements show that the global brightness fluctuations and the lifetime associated wit h granulation obeys characteristic scaling relations. We thus ai med at providing simple Theoretical Modeling to reproduce these scaling relations, and subsequently at inferring the physical prop erties of granulation across the HR diagram. Methods. We developed a simple 1D Theoretical model. The input parameters were extracted from 3D hydrodynamical models of the surface layers of stars, and the free parameters involve d in the model were calibrated with solar observations. Two different prescriptions for representing the Fourier transform of the ti me-correlation of the eddy velocity were compared: a Lorentzian and an exponential form. Finally, we compared our Theoretical pre diction with 3D radiative hydrodynamical (RHD) numerical Modeling of stellar granulation (hereafter ab initio approach). Results. Provided that the free parameters are appropriately adjust ed, our Theoretical model reproduces the observed solar gra nulation spectrum quite satisfactorily ; the best agreement is obtai ned for an exponential form. Furthermore, our model results in granulation spectra that agree well with the ab initio approach using two 3D RHD models that are representative of the surface layers of an F-dwarf and a red-giant star. Conclusions. We have developed a Theoretical model that satisfactory reproduces the solar granulation spectrum and gives results consistent with the ab initio approach. The model is used in a companion paper as Theoretical framework for interpretating the observed scaling relations.
-
stellar granulation as seen in disk integrated intensity i simplified Theoretical Modeling
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: R. Samadi, K. Belkacem, H.-g. LudwigAbstract:The solar granulation is known for a long time to be a surface manifestation of convection. Thanks to the current space-borne missions CoRoT and Kepler, it is now possible to observe in disk-integrated intensity the signature of this phenomena in a growing number of stars. The space-based photometric measurements show that the global brightness fluctuations and the lifetime associated with granulation obeys characteristic scaling relations. We thus aim at providing a simple Theoretical Modeling to reproduce these scaling relations and subsequently at inferring the physical properties of granulation properties across the HR diagram. We develop a simple 1D Theoretical model that enable us to test any prescription concerning the time-correlation between granules. The input parameters of the model are extracted from 3D hydrodynamical models of the surface layers of stars, and the free parameters involved in the model are calibrated with solar observations. Two different prescriptions for representing the eddy time-correlation in the Fourier space are compared: a Lorentzian and an exponential form. Finally, we compare our Theoretical prediction with a 3D radiative hydrodynamical (RHD) numerical Modeling of stellar granulation (ab-initio approach). Provided that the free parameters are appropriately adjusted, our Theoretical model satisfactorily reproduces the shape and the amplitude of the observed solar granulation spectrum. The best agreement is obtained with an exponential form. Furthermore, our Theoretical model results in granulation spectra that consistently agree with the these calculated on the basis of the ab-initio approach with two 3D RHD models. Comparison between Theoretical granulation spectra calculated with the present model and high precision photometry measurements of stellar granulation is undertaken in a companion paper.
J Trevena - One of the best experts on this subject based on the ideXlab platform.
-
Theoretical Modeling of starburst galaxies
The Astrophysical Journal, 2001Co-Authors: Lisa J Kewley, Michael A Dopita, Ralph S Sutherland, C A Heisler, J TrevenaAbstract:We have modeled a large sample of infrared starburst galaxies using both the PEGASE v2.0 and STARBURST99 codes to generate the spectral energy distribution (SED) of the young star clusters. PEGASE utilizes the Padova group tracks, while STARBURST99 uses the Geneva group tracks, allowing comparison between the two. We used our MAPPINGS III code to compute photoionization models that include a self-consistent treatment of dust physics and chemical depletion. We use the standard optical diagnostic diagrams as indicators of the hardness of the EUV radiation field in these galaxies. These diagnostic diagrams are most sensitive to the spectral index of the ionizing radiation field in the 1-4 ryd region. We find that warm infrared starburst galaxies contain a relatively hard EUV field in this region. The PEGASE ionizing stellar continuum is harder in the 1-4 ryd range than that of STARBURST99. As the spectrum in this regime is dominated by emission from Wolf-Rayet (W-R) stars, this discrepancy is most likely due to the differences in stellar atmosphere models used for the W-R stars. The PEGASE models use the Clegg & Middlemass planetary nebula nuclei (PNN) atmosphere models for the W-R stars, whereas the STARBURST99 models use the Schmutz, Leitherer, & Gruenwald W-R atmosphere models. We believe that the Schmutz et al. atmospheres are more applicable to the starburst galaxies in our sample; however, they do not produce the hard EUV field in the 1-4 ryd region required by our observations. The inclusion of continuum metal blanketing in the models may be one solution. Supernova remnant (SNR) shock Modeling shows that the contribution by mechanical energy from SNRs to the photoionization models is 20%. The models presented here are used to derive a new Theoretical classification scheme for starbursts and active galactic nucleus (AGN) galaxies based on the optical diagnostic diagrams.
-
Theoretical Modeling of starburst galaxies
arXiv: Astrophysics, 2001Co-Authors: Lisa J Kewley, Michael A Dopita, Ralph S Sutherland, C A Heisler, J TrevenaAbstract:We have modeled a large sample of infrared starburst galaxies using both the PEGASE v2.0 and STARBURST99 codes to generate the spectral energy distribution of the young star clusters. PEGASE utilizes the Padova group tracks while STARBURST99 uses the Geneva group tracks, allowing comparison between the two. We used our MAPPINGS III code to compute photoionization models which include a self-consistent treatment of dust physics and chemical depletion. We use the standard optical diagnostic diagrams as indicators of the hardness of the EUV radiation field in these galaxies. These diagnostic diagrams are most sensitive to the spectral index of the ionizing radiation field in the 1-4 Rydberg region. We find that warm infrared starburst galaxies contain a relatively hard EUV field in this region. The PEGASE ionizing stellar continuum is harder in the 1-4 Rydberg range than that of STARBURST99. As the spectrum in this regime is dominated by emission from Wolf-Rayet (W-R) stars, this difference is most likely due to the differences in stellar atmosphere models used for the W-R stars. We believe that the stellar atmospheres in STARBURST99 are more applicable to the starburst galaxies in our sample, however they do not produce the hard EUV field in the 1-4 Rydberg region required by our observations. The inclusion of continuum metal blanketing in the models may be one solution. Supernova remnant (SNR) shock Modeling shows that the contribution by mechanical energy from SNRs to the photoionization models is << 20%. The models presented here are used to derive a new Theoretical classification scheme for starbursts and AGN galaxies based on the optical diagnostic diagrams.
Zhong Lin Wang - One of the best experts on this subject based on the ideXlab platform.
-
Theoretical Modeling of triboelectric nanogenerators (TENGs)
Journal of Applied Physics, 2020Co-Authors: Jiajia Shao, Morten Willatzen, Zhong Lin WangAbstract:Triboelectric nanogenerators (TENGs), using Maxwell's displacement current as the driving force, can effectively convert mechanical energy into electricity. In this work, an extensive review of Theoretical models of TENGs is presented. Based on Maxwell's equations, a formal physical model is established referred to as the quasi-electrostatic model of a TENG. Since a TENG is electrically neutral at any time owing to the low operation frequency, it is conveniently regarded as a lumped circuit element. Then, using the lumped parameter equivalent circuit theory, the conventional capacitive model and Norton's equivalent circuit model are derived. Optimal conditions for power, voltage, and total energy conversion efficiency can be calculated. The presented TENG models provide an effective Theoretical foundation for understanding and predicting the performance of TENGs for practical applications.
-
Theoretical Modeling of triboelectric nanogenerators
2016Co-Authors: Zhong Lin Wang, Long Lin, Jun Chen, Simiao NiuAbstract:In the previous Chaps. 2– 5, we have extensively discussed the fundamental working principle, Theoretical analysis, and device configurations of the fundamental working modes of triboelectric nanogenerators (TENGs). In this chapter, we will try to discuss the Modeling and fundamental output characteristics of TENGs. The TENG has intrinsic capacitive behavior since it is based on a conjugation of contact electrification and electrostatic induction. After examining the Theoretical basis and fundamental physics of the TENG, its governing equation is its V-Q-x relationship and its first-order equivalent model is a series of a voltage source and a capacitor. We have developed Theoretical calculation method for TENGs and studied their load characteristics. When TENGs are connected with resistive loads, a three-working-region behavior is shown due to the impedance match mechanism. An optimum resistance is observed to maximize the TENG output on the load. When TENGs are utilized to charge a capacitor through bridge rectifier, it has a saturation charging behavior and is equivalent to the first-order resistor-capacitor charging. An optimum capacitive load is also observed to maximize the energy storage. Our systematic analysis provides guidance to the design of nanogenerator based systems for maximum utilization of output power.
R. Samadi - One of the best experts on this subject based on the ideXlab platform.
-
stellar granulation as seen in disk integrated intensity i simplified Theoretical Modeling
Astronomy and Astrophysics, 2013Co-Authors: R. Samadi, K. Belkacem, H.-g. LudwigAbstract:Context. Solar granulation has been known for a long time to be a surface manifestation of convection. The space-borne missions CoRoT and Kepler enable us to observe the signature of this phenomena in disk-integrated intensity on a large number of stars. Aims. The space-based photometric measurements show that the global brightness fluctuations and the lifetime associated wit h granulation obeys characteristic scaling relations. We thus ai med at providing simple Theoretical Modeling to reproduce these scaling relations, and subsequently at inferring the physical prop erties of granulation across the HR diagram. Methods. We developed a simple 1D Theoretical model. The input parameters were extracted from 3D hydrodynamical models of the surface layers of stars, and the free parameters involve d in the model were calibrated with solar observations. Two different prescriptions for representing the Fourier transform of the ti me-correlation of the eddy velocity were compared: a Lorentzian and an exponential form. Finally, we compared our Theoretical pre diction with 3D radiative hydrodynamical (RHD) numerical Modeling of stellar granulation (hereafter ab initio approach). Results. Provided that the free parameters are appropriately adjust ed, our Theoretical model reproduces the observed solar gra nulation spectrum quite satisfactorily ; the best agreement is obtai ned for an exponential form. Furthermore, our model results in granulation spectra that agree well with the ab initio approach using two 3D RHD models that are representative of the surface layers of an F-dwarf and a red-giant star. Conclusions. We have developed a Theoretical model that satisfactory reproduces the solar granulation spectrum and gives results consistent with the ab initio approach. The model is used in a companion paper as Theoretical framework for interpretating the observed scaling relations.
-
stellar granulation as seen in disk integrated intensity i simplified Theoretical Modeling
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: R. Samadi, K. Belkacem, H.-g. LudwigAbstract:The solar granulation is known for a long time to be a surface manifestation of convection. Thanks to the current space-borne missions CoRoT and Kepler, it is now possible to observe in disk-integrated intensity the signature of this phenomena in a growing number of stars. The space-based photometric measurements show that the global brightness fluctuations and the lifetime associated with granulation obeys characteristic scaling relations. We thus aim at providing a simple Theoretical Modeling to reproduce these scaling relations and subsequently at inferring the physical properties of granulation properties across the HR diagram. We develop a simple 1D Theoretical model that enable us to test any prescription concerning the time-correlation between granules. The input parameters of the model are extracted from 3D hydrodynamical models of the surface layers of stars, and the free parameters involved in the model are calibrated with solar observations. Two different prescriptions for representing the eddy time-correlation in the Fourier space are compared: a Lorentzian and an exponential form. Finally, we compare our Theoretical prediction with a 3D radiative hydrodynamical (RHD) numerical Modeling of stellar granulation (ab-initio approach). Provided that the free parameters are appropriately adjusted, our Theoretical model satisfactorily reproduces the shape and the amplitude of the observed solar granulation spectrum. The best agreement is obtained with an exponential form. Furthermore, our Theoretical model results in granulation spectra that consistently agree with the these calculated on the basis of the ab-initio approach with two 3D RHD models. Comparison between Theoretical granulation spectra calculated with the present model and high precision photometry measurements of stellar granulation is undertaken in a companion paper.
Lisa J Kewley - One of the best experts on this subject based on the ideXlab platform.
-
Theoretical Modeling of starburst galaxies
The Astrophysical Journal, 2001Co-Authors: Lisa J Kewley, Michael A Dopita, Ralph S Sutherland, C A Heisler, J TrevenaAbstract:We have modeled a large sample of infrared starburst galaxies using both the PEGASE v2.0 and STARBURST99 codes to generate the spectral energy distribution (SED) of the young star clusters. PEGASE utilizes the Padova group tracks, while STARBURST99 uses the Geneva group tracks, allowing comparison between the two. We used our MAPPINGS III code to compute photoionization models that include a self-consistent treatment of dust physics and chemical depletion. We use the standard optical diagnostic diagrams as indicators of the hardness of the EUV radiation field in these galaxies. These diagnostic diagrams are most sensitive to the spectral index of the ionizing radiation field in the 1-4 ryd region. We find that warm infrared starburst galaxies contain a relatively hard EUV field in this region. The PEGASE ionizing stellar continuum is harder in the 1-4 ryd range than that of STARBURST99. As the spectrum in this regime is dominated by emission from Wolf-Rayet (W-R) stars, this discrepancy is most likely due to the differences in stellar atmosphere models used for the W-R stars. The PEGASE models use the Clegg & Middlemass planetary nebula nuclei (PNN) atmosphere models for the W-R stars, whereas the STARBURST99 models use the Schmutz, Leitherer, & Gruenwald W-R atmosphere models. We believe that the Schmutz et al. atmospheres are more applicable to the starburst galaxies in our sample; however, they do not produce the hard EUV field in the 1-4 ryd region required by our observations. The inclusion of continuum metal blanketing in the models may be one solution. Supernova remnant (SNR) shock Modeling shows that the contribution by mechanical energy from SNRs to the photoionization models is 20%. The models presented here are used to derive a new Theoretical classification scheme for starbursts and active galactic nucleus (AGN) galaxies based on the optical diagnostic diagrams.
-
Theoretical Modeling of starburst galaxies
arXiv: Astrophysics, 2001Co-Authors: Lisa J Kewley, Michael A Dopita, Ralph S Sutherland, C A Heisler, J TrevenaAbstract:We have modeled a large sample of infrared starburst galaxies using both the PEGASE v2.0 and STARBURST99 codes to generate the spectral energy distribution of the young star clusters. PEGASE utilizes the Padova group tracks while STARBURST99 uses the Geneva group tracks, allowing comparison between the two. We used our MAPPINGS III code to compute photoionization models which include a self-consistent treatment of dust physics and chemical depletion. We use the standard optical diagnostic diagrams as indicators of the hardness of the EUV radiation field in these galaxies. These diagnostic diagrams are most sensitive to the spectral index of the ionizing radiation field in the 1-4 Rydberg region. We find that warm infrared starburst galaxies contain a relatively hard EUV field in this region. The PEGASE ionizing stellar continuum is harder in the 1-4 Rydberg range than that of STARBURST99. As the spectrum in this regime is dominated by emission from Wolf-Rayet (W-R) stars, this difference is most likely due to the differences in stellar atmosphere models used for the W-R stars. We believe that the stellar atmospheres in STARBURST99 are more applicable to the starburst galaxies in our sample, however they do not produce the hard EUV field in the 1-4 Rydberg region required by our observations. The inclusion of continuum metal blanketing in the models may be one solution. Supernova remnant (SNR) shock Modeling shows that the contribution by mechanical energy from SNRs to the photoionization models is << 20%. The models presented here are used to derive a new Theoretical classification scheme for starbursts and AGN galaxies based on the optical diagnostic diagrams.
