The Experts below are selected from a list of 110793 Experts worldwide ranked by ideXlab platform
M Kozak - One of the best experts on this subject based on the ideXlab platform.
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ultrafast scanning Electron microscope applied for studying the interaction between free Electrons and optical near fields of periodic nanostructures
Journal of Applied Physics, 2018Co-Authors: M Kozak, Joshua Mcneur, Norbert Schonenberger, J Illmer, Alexander Tafel, Peyman Yousefi, T Eckstein, Peter HommelhoffAbstract:In this paper, we describe an ultrafast scanning Electron microscope setup developed for the research of inelastic scattering of Electrons at optical near-fields of periodic dielectric nanostructures. Electron emission from the Schottky cathode is controlled by ultraviolet femtosecond laser pulses. The Electron pulse duration at the interaction site is characterized via cross-correlation of the Electrons with an infrared laser pulse that excites a synchronous periodic near-field on the surface of a silicon nanostructure. The lower limit of 410 fs is found in the regime of a single Electron per pulse. The role of pulse broadening due to Coulomb interaction in multiElectron pulses is investigated. The setup is used to demonstrate an increase in the interaction distance between the Electrons and the optical near-fields by introducing a pulse-front-tilt to the infrared laser beam. Furthermore, we show the dependence of the Final Electron spectra on the resonance condition between the phase velocity of the optical near-field and the Electron propagation velocity. The resonance is controlled by adjusting the initial Electron energy/velocity and by introducing a linear chirp to the structure period allowing the increase of the Final Electron energy gain up to a demonstrated value of 3.8 keV.
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ultrafast scanning Electron microscope applied for studying the interaction between free Electrons and optical near fields of periodic nanostructures
arXiv: Applied Physics, 2018Co-Authors: M Kozak, Joshua Mcneur, Norbert Schonenberger, J Illmer, Alexander Tafel, Peyman Yousefi, T Eckstein, Peter HommelhoffAbstract:In this paper we describe an ultrafast scanning Electron microscope setup developed for the research of inelastic scattering of Electrons at optical near-fields of periodic dielectric nanostructures. Electron emission from the Schottky cathode is controlled by ultraviolet femtosecond laser pulses. The Electron pulse duration at the interaction site is characterized via cross-correlation of the Electrons with an infrared laser pulse that excites a synchronous periodic near-field on the surface of a silicon nanostructure. The lower limit of 410 fs is found in the regime of a single Electron per pulse. The role of pulse broadening due to Coulomb interaction in multiElectron pulses is investigated. The setup is used to demonstrate an increase of the interaction distance between the Electrons and the optical near-fields by introducing a pulse-front-tilt to the infrared laser beam. Further we show the dependence of the Final Electron spectra on the resonance condition between the phase velocity of the optical near-field and the Electron propagation velocity. The resonance is controlled by adjusting the initial Electron energy/velocity and by introducing a linear chirp to the structure period allowing to increase the Final Electron energy gain up to a demonstrated 3.8 keV.
Dieter Breitschwerdt - One of the best experts on this subject based on the ideXlab platform.
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Temperature-averaged and total free-free Gaunt factors for κ and Maxwellian distributions of Electrons
Astronomy & Astrophysics, 2015Co-Authors: Miguel A. De Avillez, Dieter BreitschwerdtAbstract:Aims. Optically thin plasmas may deviate from thermal equilibrium and thus, Electrons (and ions) are no longer described by the Maxwellian distribution. Instead they can be described by -distributions. The free-free spectrum and radiative losses depend on the temperature-averaged (over the Electrons distribution) and total Gaunt factors, respectively. Thus, there is a need to calculate and make available these factors to be used by any software that deals with plasma emission. Methods. We recalculated the free-free Gaunt factor for a wide range of energies and frequencies using hypergeometric functions of complex arguments and the Clenshaw recurrence formula technique combined with approximations whenever the di erence between the initial and Final Electron energies is smaller than 10 10 in units of z 2 Ry. We used double and quadruple precisions. The temperatureaveraged and total Gaunt factors calculations make use of the Gauss-Laguerre integration with 128 nodes. Results. The temperature-averaged and total Gaunt factors depend on the parameter, which shows increasing deviations (with respect to the results obtained with the use of the Maxwellian distribution) with decreasing . Tables of these Gaunt factors are provided.
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temperature averaged and total free free gaunt factors for kappa and maxwellian distributions of Electrons
arXiv: High Energy Astrophysical Phenomena, 2015Co-Authors: Miguel A. De Avillez, Dieter BreitschwerdtAbstract:Aims. Optically thin plasmas may deviate from thermal equilibrium and thus, Electrons (and ions) are no longer described by the Maxwellian distribution. Instead they can be described by $\kappa$-distributions. The free-free spectrum and radiative losses depend on the temperature-averaged (over the Electrons distribution) and total Gaunt factors, respectively. Thus, there is a need to calculate and make available these factors to be used by any software that deals with plasma emission. Methods. We recalculated the free-free Gaunt factor for a wide range of energies and frequencies using hypergeometric functions of complex arguments and the Clenshaw recurrence formula technique combined with approximations whenever the difference between the initial and Final Electron energies is smaller than $10^{-10}$ in units of $z^2Ry$. We used double and quadruple precisions. The temperature- averaged and total Gaunt factors calculations make use of the Gauss-Laguerre integration with 128 nodes. Results. The temperature-averaged and total Gaunt factors depend on the $\kappa$ parameter, which shows increasing deviations (with respect to the results obtained with the use of the Maxwellian distribution) with decreasing $\kappa$. Tables of these Gaunt factors are provided.
Peter Hommelhoff - One of the best experts on this subject based on the ideXlab platform.
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ultrafast scanning Electron microscope applied for studying the interaction between free Electrons and optical near fields of periodic nanostructures
Journal of Applied Physics, 2018Co-Authors: M Kozak, Joshua Mcneur, Norbert Schonenberger, J Illmer, Alexander Tafel, Peyman Yousefi, T Eckstein, Peter HommelhoffAbstract:In this paper, we describe an ultrafast scanning Electron microscope setup developed for the research of inelastic scattering of Electrons at optical near-fields of periodic dielectric nanostructures. Electron emission from the Schottky cathode is controlled by ultraviolet femtosecond laser pulses. The Electron pulse duration at the interaction site is characterized via cross-correlation of the Electrons with an infrared laser pulse that excites a synchronous periodic near-field on the surface of a silicon nanostructure. The lower limit of 410 fs is found in the regime of a single Electron per pulse. The role of pulse broadening due to Coulomb interaction in multiElectron pulses is investigated. The setup is used to demonstrate an increase in the interaction distance between the Electrons and the optical near-fields by introducing a pulse-front-tilt to the infrared laser beam. Furthermore, we show the dependence of the Final Electron spectra on the resonance condition between the phase velocity of the optical near-field and the Electron propagation velocity. The resonance is controlled by adjusting the initial Electron energy/velocity and by introducing a linear chirp to the structure period allowing the increase of the Final Electron energy gain up to a demonstrated value of 3.8 keV.
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ultrafast scanning Electron microscope applied for studying the interaction between free Electrons and optical near fields of periodic nanostructures
arXiv: Applied Physics, 2018Co-Authors: M Kozak, Joshua Mcneur, Norbert Schonenberger, J Illmer, Alexander Tafel, Peyman Yousefi, T Eckstein, Peter HommelhoffAbstract:In this paper we describe an ultrafast scanning Electron microscope setup developed for the research of inelastic scattering of Electrons at optical near-fields of periodic dielectric nanostructures. Electron emission from the Schottky cathode is controlled by ultraviolet femtosecond laser pulses. The Electron pulse duration at the interaction site is characterized via cross-correlation of the Electrons with an infrared laser pulse that excites a synchronous periodic near-field on the surface of a silicon nanostructure. The lower limit of 410 fs is found in the regime of a single Electron per pulse. The role of pulse broadening due to Coulomb interaction in multiElectron pulses is investigated. The setup is used to demonstrate an increase of the interaction distance between the Electrons and the optical near-fields by introducing a pulse-front-tilt to the infrared laser beam. Further we show the dependence of the Final Electron spectra on the resonance condition between the phase velocity of the optical near-field and the Electron propagation velocity. The resonance is controlled by adjusting the initial Electron energy/velocity and by introducing a linear chirp to the structure period allowing to increase the Final Electron energy gain up to a demonstrated 3.8 keV.
Miguel A. De Avillez - One of the best experts on this subject based on the ideXlab platform.
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Temperature-averaged and total free-free Gaunt factors for κ and Maxwellian distributions of Electrons
Astronomy & Astrophysics, 2015Co-Authors: Miguel A. De Avillez, Dieter BreitschwerdtAbstract:Aims. Optically thin plasmas may deviate from thermal equilibrium and thus, Electrons (and ions) are no longer described by the Maxwellian distribution. Instead they can be described by -distributions. The free-free spectrum and radiative losses depend on the temperature-averaged (over the Electrons distribution) and total Gaunt factors, respectively. Thus, there is a need to calculate and make available these factors to be used by any software that deals with plasma emission. Methods. We recalculated the free-free Gaunt factor for a wide range of energies and frequencies using hypergeometric functions of complex arguments and the Clenshaw recurrence formula technique combined with approximations whenever the di erence between the initial and Final Electron energies is smaller than 10 10 in units of z 2 Ry. We used double and quadruple precisions. The temperatureaveraged and total Gaunt factors calculations make use of the Gauss-Laguerre integration with 128 nodes. Results. The temperature-averaged and total Gaunt factors depend on the parameter, which shows increasing deviations (with respect to the results obtained with the use of the Maxwellian distribution) with decreasing . Tables of these Gaunt factors are provided.
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temperature averaged and total free free gaunt factors for kappa and maxwellian distributions of Electrons
arXiv: High Energy Astrophysical Phenomena, 2015Co-Authors: Miguel A. De Avillez, Dieter BreitschwerdtAbstract:Aims. Optically thin plasmas may deviate from thermal equilibrium and thus, Electrons (and ions) are no longer described by the Maxwellian distribution. Instead they can be described by $\kappa$-distributions. The free-free spectrum and radiative losses depend on the temperature-averaged (over the Electrons distribution) and total Gaunt factors, respectively. Thus, there is a need to calculate and make available these factors to be used by any software that deals with plasma emission. Methods. We recalculated the free-free Gaunt factor for a wide range of energies and frequencies using hypergeometric functions of complex arguments and the Clenshaw recurrence formula technique combined with approximations whenever the difference between the initial and Final Electron energies is smaller than $10^{-10}$ in units of $z^2Ry$. We used double and quadruple precisions. The temperature- averaged and total Gaunt factors calculations make use of the Gauss-Laguerre integration with 128 nodes. Results. The temperature-averaged and total Gaunt factors depend on the $\kappa$ parameter, which shows increasing deviations (with respect to the results obtained with the use of the Maxwellian distribution) with decreasing $\kappa$. Tables of these Gaunt factors are provided.
Aloysius G M Tielens - One of the best experts on this subject based on the ideXlab platform.
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lipids are the preferred substrate of the protist naegleria gruberi relative of a human brain pathogen
Cell Reports, 2018Co-Authors: Michiel L Bexkens, Maarten J Sarink, Jaap J Van Hellemond, Johan F De Jonckheere, Verena Zimorski, Hans Wienk, Jos F Brouwers, William Martin, Fred R Opperdoes, Aloysius G M TielensAbstract:Summary Naegleria gruberi is a free-living non-pathogenic amoeboflagellate and relative of Naegleria fowleri, a deadly pathogen causing primary amoebic meningoencephalitis (PAM). A genomic analysis of N. gruberi exists, but physiological evidence for its core energy metabolism or in vivo growth substrates is lacking. Here, we show that N. gruberi trophozoites need oxygen for normal functioning and growth and that they shun both glucose and amino acids as growth substrates. Trophozoite growth depends mainly upon lipid oxidation via a mitochondrial branched respiratory chain, both ends of which require oxygen as Final Electron acceptor. Growing N. gruberi trophozoites thus have a strictly aerobic energy metabolism with a marked substrate preference for the oxidation of fatty acids. Analyses of N. fowleri genome data and comparison with those of N. gruberi indicate that N. fowleri has the same type of metabolism. Specialization to oxygen-dependent lipid breakdown represents an additional metabolic strategy in protists.
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lipids are the preferred substrate of the protist naegleria gruberi relative of a human brain pathogen
bioRxiv, 2018Co-Authors: Michiel L Bexkens, Maarten J Sarink, Jaap J Van Hellemond, Johan F De Jonckheere, Verena Zimorski, Hans Wienk, Jos F Brouwers, William Martin, Fred R Opperdoes, Aloysius G M TielensAbstract:Naegleria gruberi is a free-living non-pathogenic amoeboflagellate and relative of Naegleria fowleri, a deadly pathogen causing primary amoebic meningoencephalitis (PAM). A genomic analysis of N. gruberi exists, but physiological evidence for its core energy metabolism or in vivo growth substrates is lacking. Here we show that N. gruberi trophozoites need oxygen for normal functioning and growth and that they furthermore shun both glucose and amino acids as growth substrates. Trophozoite growth depends mainly upon lipid oxidation via a mitochondrial branched respiratory chain, both ends of which require oxygen as Final Electron acceptor. Growing N. gruberi trophozoites thus have a strictly aerobic energy metabolism with a marked substrate preference for the oxidation of fatty acids. Analyses of N. fowleri genome data and comparison with those of N. gruberi indicate that N. fowleri has the same type of metabolism. Specialization to oxygen-dependent lipid breakdown represents a hitherto unprecedented metabolic strategy in protists.