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Peter H Yoon - One of the best experts on this subject based on the ideXlab platform.
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high frequency waves driven by agyrotropic electrons near the electron diffusion region
Geophysical Research Letters, 2020Co-Authors: Kyunghwan Dokgo, K J Hwang, J L Burch, Peter H Yoon, Daniel B GrahamAbstract:National Aeronautics and Space Administration's Magnetosphere Multiscale mission reveals that agyrotropic electrons and intense waves are prevalently present in the electron diffusion region. Prompted by two distinct Magnetosphere Multiscale observations, this letter investigates by theoretical means and the properties of agyrotropic electron beam-plasma instability and explains the origin of different structures in the wave spectra. The difference is owing to the fact that in one instance, a continuous beam Mode is excited, while in the other, discrete Bernstein Modes are excited, and the excitation of one Mode versus the other depends on physical input parameters, which are consistent with observations. Analyses of dispersion relations show that the Growing Mode becomes discrete when the maximum growth rate is lower than the electron cyclotron frequency. Making use of particle-in-cell simulations, we found that the broadening angle Δ in the gyroangle space is also an important factor controlling the growth rate. Ramifications of the present finding are also discussed.
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a purely Growing electromagnetic Mode operative in the geomagnetic tail
Journal of Geophysical Research, 1992Co-Authors: C S Wu, Peter H Yoon, L F Ziebell, Chialie Chang, H K WongAbstract:This paper discusses a purely Growing Mode driven by a cross-field current. The study was motivated by a recent article by Chang et al. (1990). The present discussion pays special attention to two aspects. One is to generalize the analysis by Chang et al. (1990) so that the unmagnetized-ion approximation used by these authors is removed, and the other is to apply the theory to several regions in the magnetotail where the value of the plasma beta is in general very high. The present analysis is restricted to waves propagating along the ambient magnetic field. The high ion beta limit is discussed by considering two different situations. The first is to fix the strength of the ambient magnetic field but to increase the plasma temperature, and the second is to maintain the plasma temperature but to decrease the ambient magnetic field strength. It is found that in the former case the Mode stabilizes when βi → ∞, but in the latter case the instability persists even if βi → ∞ (although the growth rate is significantly reduced). The present theory is applied to three regions in the magnetotail. These are: (1) the inner edge region, (2) the midtail region, and (3) the neutral sheet of a distant magnetotail. It is found that, among these three regions, for a given value of υ0 / αi, where υ0 is the net cross-field drift speed between the electrons and the ions and αi is the ion thermal speed, the growth rate in the neutral sheet is found to be the largest.
Jean-claude Mollet - One of the best experts on this subject based on the ideXlab platform.
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Table_1_Evolution of Cell Wall Polymers in Tip-Growing Land Plant Gametophytes: Composition, Distribution, Functional Aspects and Their ReModeling.pdf
2019Co-Authors: Jérémy Dehors, Alain Mareck, Marie-christine Kiefer-meyer, Laurence Menu-bouaouiche, Arnaud Lehner, Jean-claude MolletAbstract:During evolution of land plants, the first colonizing species presented leafy-dominant gametophytes, found in non-vascular plants (bryophytes). Today, bryophytes include liverworts, mosses, and hornworts. In the first seedless vascular plants (lycophytes), the sporophytic stage of life started to be predominant. In the seed producing plants, gymnosperms and angiosperms , the gametophytic stage is restricted to reproduction. In mosses and ferns, the haploid spores germinate and form a protonema, which develops into a leafy gametophyte producing rhizoids for anchorage, water and nutrient uptakes. The basal gymnosperms (cycads and Ginkgo) reproduce by zooidogamy. Their pollen grains develop a multi-branched pollen tube that penetrates the nucellus and releases flagellated sperm cells that swim to the egg cell. The pollen grain of other gymnosperms (conifers and gnetophytes) as well as angiosperms germinates and produces a pollen tube that directly delivers the sperm cells to the ovule (siphonogamy). These different gametophytes, which are short or long-lived structures, share a common tip-Growing Mode of cell expansion. Tip-growth requires a massive cell wall deposition to promote cell elongation, but also a tight spatial and temporal control of the cell wall reModeling in order to modulate the mechanical properties of the cell wall. The growth rate of these cells is very variable depending on the structure and the species, ranging from very slow (protonemata, rhizoids, and some gymnosperm pollen tubes), to a slow to fast-growth in other gymnosperms and angiosperms. In addition, the structural diversity of the female counterparts in angiosperms (dry, semi-dry vs wet stigmas, short vs long, solid vs hollow styles) will impact the speed and efficiency of sperm delivery. As the evolution and diversity of the cell wall polysaccharides accompanied the diversification of cell wall structural proteins and reModeling enzymes, this review focuses on our current knowledge on the biochemistry, the distribution and reModeling of the main cell wall polymers (including cellulose, hemicelluloses, pectins, callose, arabinogalactan-proteins and extensins), during the tip-expansion of gametophytes from bryophytes, pteridophytes (lycophytes and monilophytes), gymnosperms and the monocot and eudicot angiosperms.
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Evolution of Cell Wall Polymers in Tip-Growing Land Plant Gametophytes: Composition, Distribution, Functional Aspects and Their ReModeling
Frontiers in Plant Science, 2019Co-Authors: Jérémy Dehors, Alain Mareck, Marie-christine Kiefer-meyer, Laurence Menu-bouaouiche, Arnaud Lehner, Jean-claude MolletAbstract:During evolution of land plants, the first colonizing species presented leafy-dominant gametophytes, found in non-vascular plants (bryophytes). Today, bryophytes include liverworts, mosses, and hornworts. In the first seedless vascular plants (lycophytes), the sporophytic stage of life started to be predominant. In the seed producing plants, gymnosperms and angiosperms , the gametophytic stage is restricted to reproduction. In mosses and ferns, the haploid spores germinate and form a protonema, which develops into a leafy gametophyte producing rhizoids for anchorage, water and nutrient uptakes. The basal gymnosperms (cycads and Ginkgo) reproduce by zooidogamy. Their pollen grains develop a multi-branched pollen tube that penetrates the nucellus and releases flagellated sperm cells that swim to the egg cell. The pollen grain of other gymnosperms (conifers and gnetophytes) as well as angiosperms germinates and produces a pollen tube that directly delivers the sperm cells to the ovule (siphonogamy). These different gametophytes, which are short or long-lived structures, share a common tip-Growing Mode of cell expansion. Tip-growth requires a massive cell wall deposition to promote cell elongation, but also a tight spatial and temporal control of the cell wall reModeling in order to modulate the mechanical properties of the cell wall. The growth rate of these cells is very variable depending on the structure and the species, ranging from very slow (protonemata, rhizoids, and some gymnosperm pollen tubes), to a slow to fast-growth in other gymnosperms and angiosperms. In addition, the structural diversity of the female counterparts in angiosperms (dry, semi-dry vs wet stigmas, short vs long, solid vs hollow styles) will impact the speed and efficiency of sperm delivery. As the evolution and diversity of the cell wall polysaccharides accompanied the diversification of cell wall structural proteins and reModeling enzymes, this review focuses on our current knowledge on the biochemistry, the distribution and reModeling of the main cell wall polymers (including cellulose, hemicelluloses, pectins, callose, arabinogalactan-proteins and extensins), during the tip-expansion of gametophytes from bryophytes, pteridophytes (lycophytes and monilophytes), gymnosperms and the monocot and eudicot angiosperms.
Kohji Tomisaka - One of the best experts on this subject based on the ideXlab platform.
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structure and stability of filamentary clouds supported by lateral magnetic field
The Astrophysical Journal, 2015Co-Authors: Tomoyuki Hanawa, Kohji TomisakaAbstract:We have constructed two types of analytical Models for an isothermal filamentary cloud supported mainly by magnetic tension. The first one describes an isolated cloud while the second considers filamentary clouds spaced periodically. Both Models assume that the filamentary clouds are highly flattened. The former is proved to be the asymptotic limit of the latter in which each filamentary cloud is much thinner than the distance to the neighboring filaments. We show that these Models reproduce the main features of the 2D equilibrium Model of Tomisaka for a filamentary cloud threaded by a perpendicular magnetic field. It is also shown that the critical mass to flux ratio is , where M, Φ and G denote the cloud mass, the total magnetic flux of the cloud, and the gravitational constant, respectively. This upper bound coincides with that for an axisymmetric cloud supported by poloidal magnetic fields. We apply the variational principle for studying the Jeans instability of the first Model. Our Model cloud is unstable against fragmentation as well as the filamentary clouds threaded by a longitudinal magnetic field. The fastest Growing Mode has a wavelength several times longer than the cloud diameter. The second Model describes quasi-static evolution of a filamentary molecular cloud by ambipolar diffusion.
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structure and stability of filamentary clouds supported by lateral magnetic field
arXiv: Astrophysics of Galaxies, 2015Co-Authors: Tomoyuki Hanawa, Kohji TomisakaAbstract:We have constructed two types of analytical Models for an isothermal filamentary cloud supported mainly by magnetic tension. The first one describes an isolated cloud while the second considers filamentary clouds spaced periodically. Both the Models assume that the filamentary clouds are highly flattened. The former is proved to be the asymptotic limit of the latter in which each filamentary cloud is much thinner than the distance to the neighboring filaments. We show that these Models reproduce main features of the 2D equilibrium Model of Tomisaka (2014) for filamentary cloud threaded by perpendicular magnetic field. It is also shown that the critical mass to flux ratio is $ M /\Phi = (2 \pi \sqrt{G}) ^{-1} $, where $ M $, $ \Phi $ and $ G $ denote the cloud mass, the total magnetic flux of the cloud, and the gravitational constant, respectively. This upper bound coincides with that for an axisymmetric cloud supported by poloidal magnetic fields. We applied the variational principle for studying the Jeans instability of the first Model. Our Model cloud is unstable against fragmentation as well as the filamentary clouds threaded by longitudinal magnetic field. The fastest Growing Mode has a wavelength several times longer than the cloud diameter. The second Model describes quasi-static evolution of filamentary molecular cloud by ambipolar diffusion.
Dominic Dold - One of the best experts on this subject based on the ideXlab platform.
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unstable Mode solutions to the klein gordon equation in kerr anti de sitter spacetimes
Communications in Mathematical Physics, 2017Co-Authors: Dominic DoldAbstract:For any cosmological constant \({\Lambda = -3/\ell^{2} |a|\ell}\). We obtain an analogous result for Neumann boundary conditions if \({5/4 < \alpha < 9/4}\). Moreover, in the Dirichlet case, one can prove that, for any Kerr-AdS spacetime violating the Hawking–Reall bound, there exists an open family of masses \({\alpha}\) such that the corresponding Klein–Gordon equation permits exponentially Growing Mode solutions. Our result adopts methods of Shlapentokh-Rothman developed in (Commun. Math. Phys. 329:859–891, 2014) and provides the first rigorous construction of a superradiant instability for negative cosmological constant.
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unstable Mode solutions to the klein gordon equation in kerr anti de sitter spacetimes
arXiv: General Relativity and Quantum Cosmology, 2015Co-Authors: Dominic DoldAbstract:For any cosmological constant $\Lambda=-3/\ell^2 |a|\ell$. We obtain an analogous result for Neumann boundary conditions if $5/4<\alpha<9/4$. Moreover, in the Dirichlet case, one can prove that, for any Kerr-AdS spacetime violating the Hawking-Reall bound, there exists an open family of masses $\alpha$ such that the corresponding Klein-Gordon equation permits exponentially Growing Mode solutions. Our result adopts methods of Shlapentokh-Rothman (see arXiv:1302.3448) and provides the first rigorous construction of a superradiant instability for negative cosmological constant.
Jérémy Dehors - One of the best experts on this subject based on the ideXlab platform.
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Table_1_Evolution of Cell Wall Polymers in Tip-Growing Land Plant Gametophytes: Composition, Distribution, Functional Aspects and Their ReModeling.pdf
2019Co-Authors: Jérémy Dehors, Alain Mareck, Marie-christine Kiefer-meyer, Laurence Menu-bouaouiche, Arnaud Lehner, Jean-claude MolletAbstract:During evolution of land plants, the first colonizing species presented leafy-dominant gametophytes, found in non-vascular plants (bryophytes). Today, bryophytes include liverworts, mosses, and hornworts. In the first seedless vascular plants (lycophytes), the sporophytic stage of life started to be predominant. In the seed producing plants, gymnosperms and angiosperms , the gametophytic stage is restricted to reproduction. In mosses and ferns, the haploid spores germinate and form a protonema, which develops into a leafy gametophyte producing rhizoids for anchorage, water and nutrient uptakes. The basal gymnosperms (cycads and Ginkgo) reproduce by zooidogamy. Their pollen grains develop a multi-branched pollen tube that penetrates the nucellus and releases flagellated sperm cells that swim to the egg cell. The pollen grain of other gymnosperms (conifers and gnetophytes) as well as angiosperms germinates and produces a pollen tube that directly delivers the sperm cells to the ovule (siphonogamy). These different gametophytes, which are short or long-lived structures, share a common tip-Growing Mode of cell expansion. Tip-growth requires a massive cell wall deposition to promote cell elongation, but also a tight spatial and temporal control of the cell wall reModeling in order to modulate the mechanical properties of the cell wall. The growth rate of these cells is very variable depending on the structure and the species, ranging from very slow (protonemata, rhizoids, and some gymnosperm pollen tubes), to a slow to fast-growth in other gymnosperms and angiosperms. In addition, the structural diversity of the female counterparts in angiosperms (dry, semi-dry vs wet stigmas, short vs long, solid vs hollow styles) will impact the speed and efficiency of sperm delivery. As the evolution and diversity of the cell wall polysaccharides accompanied the diversification of cell wall structural proteins and reModeling enzymes, this review focuses on our current knowledge on the biochemistry, the distribution and reModeling of the main cell wall polymers (including cellulose, hemicelluloses, pectins, callose, arabinogalactan-proteins and extensins), during the tip-expansion of gametophytes from bryophytes, pteridophytes (lycophytes and monilophytes), gymnosperms and the monocot and eudicot angiosperms.
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Evolution of Cell Wall Polymers in Tip-Growing Land Plant Gametophytes: Composition, Distribution, Functional Aspects and Their ReModeling
Frontiers in Plant Science, 2019Co-Authors: Jérémy Dehors, Alain Mareck, Marie-christine Kiefer-meyer, Laurence Menu-bouaouiche, Arnaud Lehner, Jean-claude MolletAbstract:During evolution of land plants, the first colonizing species presented leafy-dominant gametophytes, found in non-vascular plants (bryophytes). Today, bryophytes include liverworts, mosses, and hornworts. In the first seedless vascular plants (lycophytes), the sporophytic stage of life started to be predominant. In the seed producing plants, gymnosperms and angiosperms , the gametophytic stage is restricted to reproduction. In mosses and ferns, the haploid spores germinate and form a protonema, which develops into a leafy gametophyte producing rhizoids for anchorage, water and nutrient uptakes. The basal gymnosperms (cycads and Ginkgo) reproduce by zooidogamy. Their pollen grains develop a multi-branched pollen tube that penetrates the nucellus and releases flagellated sperm cells that swim to the egg cell. The pollen grain of other gymnosperms (conifers and gnetophytes) as well as angiosperms germinates and produces a pollen tube that directly delivers the sperm cells to the ovule (siphonogamy). These different gametophytes, which are short or long-lived structures, share a common tip-Growing Mode of cell expansion. Tip-growth requires a massive cell wall deposition to promote cell elongation, but also a tight spatial and temporal control of the cell wall reModeling in order to modulate the mechanical properties of the cell wall. The growth rate of these cells is very variable depending on the structure and the species, ranging from very slow (protonemata, rhizoids, and some gymnosperm pollen tubes), to a slow to fast-growth in other gymnosperms and angiosperms. In addition, the structural diversity of the female counterparts in angiosperms (dry, semi-dry vs wet stigmas, short vs long, solid vs hollow styles) will impact the speed and efficiency of sperm delivery. As the evolution and diversity of the cell wall polysaccharides accompanied the diversification of cell wall structural proteins and reModeling enzymes, this review focuses on our current knowledge on the biochemistry, the distribution and reModeling of the main cell wall polymers (including cellulose, hemicelluloses, pectins, callose, arabinogalactan-proteins and extensins), during the tip-expansion of gametophytes from bryophytes, pteridophytes (lycophytes and monilophytes), gymnosperms and the monocot and eudicot angiosperms.
