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Daniel Benjamin Berdichevsky - One of the best experts on this subject based on the ideXlab platform.
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correction to on fields and mass constraints for the uniform propagation of magnetic flux ropes undergoing Isotropic Expansion
Solar Physics, 2019Co-Authors: Daniel Benjamin BerdichevskyAbstract:Correction to: Solar Phys. (2013) 284:245 – 259 When expressing the steady current density
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on fields and mass constraints for the uniform propagation of magnetic flux ropes undergoing Isotropic Expansion
Solar Physics, 2013Co-Authors: Daniel Benjamin BerdichevskyAbstract:An analytical 3-D magnetohydrodynamic (MHD) solution of a magnetic-flux rope (FR) is presented. This FR solution may explain the uniform propagation, beyond ∼ 0.05 AU, of coronal mass ejections (CMEs) commonly observed by today’s missions like The Solar Mass Ejection Imager (SMEI), Solar and Heliospheric Observatory (SOHO) and Solar Terrestrial Relations Observatory (STEREO), tracked to tens of times the radius of the Sun, and in some cases up to 1 AU, and/or beyond. Once a CME occurs, we present arguments regarding its evolution based on its mass and linear momentum conservation. Here, we require that the gravitational and magnetic forces balance each other in the framework of the MHD theory for a simple model of the evolution of a CME, assuming it interacts weakly with the steady solar wind. When satisfying these ansatze we identify a relation between the transported mechanical mass of the interplanetary CME with its geometrical parameters and the intensity of the magnetic field carried by the structure. In this way we are able to estimate the mass of the interplanetary CME (ICME) for a list of cases, from the Wind mission records of ICME encountered near Earth, at 1 AU. We obtain a range for masses of ∼ 109 to 1013 kg, or assuming a uniform distribution, of ∼ 0.5 to 500 cm−3 for the hadron density of these structures, a result that appears to be consistent with observations.
Mitsuhiro Matsuura - One of the best experts on this subject based on the ideXlab platform.
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quasi static strain and stress fields due to a moment tensor in elastic viscoelastic layered half space
Pure and Applied Geophysics, 2014Co-Authors: Akinori Hashima, Yukitoshi Fukahata, Chihiro Hashimoto, Mitsuhiro MatsuuraAbstract:We derived explicit expressions in the time domain for 3-D quasi-static strain and stress fields, due to a point moment tensor source in an elastic surface layer overlying viscoelastic half-space under gravity. The expressions of strain in the elastic surface layer were directly obtained from the expressions of displacement in our previous paper. The conversion of strain into stress is easy, because the stress–strain relation of elastic material is linear. In the viscoelastic substratum, the expressions of strain were obtained by applying the correspondence principle of linear viscoelasticity to the associated elastic solution. The strain–stress conversion is not straightforward, as the stress–strain relation of viscoelastic material is usually given in a differential form. To convert strain into stress, we used an integral form of the stress–strain relation instead of the usual differential form. The expressions give the responses of elastic half-space at \( t = 0 \), and the responses of an elastic plate floating on non-viscous liquid at \( t = \infty \). The moment tensor is rationally decomposed into the three independent force systems, corresponding to Isotropic Expansion, shear faulting and crack opening, and so the expressions include the strain and stress fields for these force systems as special cases. As the first numerical example, we computed the temporal changes in strain and stress fields after the sudden opening of an infinitely long vertical crack cutting the elastic surface layer. Here, we observe that the stress changes caused by the sudden crack opening gradually decay with time and vanish at \( t = \infty \) everywhere. After the completion of stress relaxation, a characteristic pattern of shear strain remains in the viscoelastic substratum. Since the strain and stress fields at \( t = \infty \) can be read as the strain- and stress-rate fields caused by steady crack opening, respectively, this numerical example demonstrates the realization of a steady stress state supported by steady viscous flow in the asthenosphere, associated with steady seafloor spreading at mid-ocean ridges. For the second numerical example, we computed the temporal changes in strain and stress fields after the 2011 Tohoku-oki mega-thrust earthquake, which occurred at the North American-Pacific plate interface. In this numerical example, the stress changes caused by coseismic fault slip vanish at \( t = \infty \) in the viscoelastic substratum, but remain in the elastic surface layer. The coseismic stress changes (and also strain changes) in the elastic surface layer diffuse away from the source region with time, due to gradual stress relaxation in the viscoelastic substratum.
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general expressions for internal deformation due to a moment tensor in an elastic viscoelastic multilayered half space
Geophysical Journal International, 2008Co-Authors: Akinori Hashima, Youichiro Takada, Yukitoshi Fukahata, Mitsuhiro MatsuuraAbstract:SUMMARY In the framework of elasticity theory any indigenous source can be represented by a moment tensor. We have succeeded in obtaining general expressions for internal deformation due to a moment tensor in an elastic/viscoelastic multilayered half-space under gravity. First, starting from Stokes’ classical solution, we obtained the expressions for static displacement fields due to a moment tensor in an infinite elastic medium. Then, performing the Hankel transformation of the static solution in Cartesian coordinates, we derived static displacement potentials for a moment tensor in cylindrical coordinates. Second, representing internal deformation fields by the superposition of a particular solution calculated from the displacement potentials and the general solution for an elastic multilayered half-space without sources, and using the generalized propagator matrix method, we obtained exact expressions for internal elastic deformation fields due to a moment tensor. Finally, applying the correspondence principle of linear viscoelasticity to the elastic solution, we obtained general expressions for quasi-static internal deformation fields due to a moment tensor in an elastic/viscoelastic multilayered half-space. The moment tensor can be generally decomposed into the three independent force systems corresponding to Isotropic Expansion, crack opening and shear faulting, and so the general expressions include internal deformation fields for these force systems as special cases. As numerical examples we computed the quasi-static internal displacement fields associated with dyke intrusion, episodic segmental ridge opening and steady plate divergence in an elastic‐viscoelastic two-layered half-space. We also demonstrated the usefulness of the source representation with moment tensor through the numerical simulation of deformation cycles associated with the periodic occurrence of interplate earthquakes in a ridge-transform fault system.
Toshihiko Fujimori - One of the best experts on this subject based on the ideXlab platform.
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Isotropic Expansion of external environment induces tissue elongation and collective cell alignment.
Journal of theoretical biology, 2020Co-Authors: Hiroshi Koyama, Toshihiko FujimoriAbstract:Abstract Cell movement is crucial for morphogenesis in multicellular organisms. Growing embryos or tissues often expand Isotropically, i.e., uniformly, in all dimensions. On the surfaces of these expanding environments, which we call “fields,” cells are subjected to frictional forces and move passively in response. However, the potential roles of Isotropically expanding fields in morphogenetic events have not been investigated well. Our previous mathematical simulations showed that a tissue was elongated on an Isotropically expanding field ( Imuta et al., 2014 ). However, the underlying mechanism remains unclarified, and how cells behave during tissue elongation was not investigated. In this study, we mathematically analyzed the effect of Isotropically expanding fields using a vertex model, a standard type of multi-cellular model. We found that cells located on fields were elongated along a similar direction each other and exhibited a columnar configuration with nearly single-cell width. Simultaneously, it was confirmed that the cell clusters were also elongated, even though field Expansion was absolutely Isotropic. We then investigated the mechanism underlying these counterintuitive phenomena. In particular, we asked whether the dynamics of elongation was predominantly determined by the properties of the field, the cell cluster, or both. Theoretical analyses involving simplification of the model revealed that cell clusters have an intrinsic ability to asymmetrically deform, leading to their elongation. Importantly, this ability is effective only under the non-equilibrium conditions provided by field Expansion. This may explain the elongation of the notochord, located on the surface of the growing mouse embryo. We established the mechanism underlying tissue elongation induced by Isotropically expanding external environments, and its involvement in collective cell alignment with cell elongation, providing key insight into morphogenesis involving multiple adjacent tissues.
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Isotropic Expansion of external environment induces tissue elongation and collective cell alignment
2019Co-Authors: Hiroshi Koyama, Toshihiko FujimoriAbstract:Abstract Cell movement is crucial for morphogenesis in multicellular organisms. Growing embryos or tissues often expand Isotropically, i.e., uniformly, in all dimensions. On the surfaces of these expanding environments, which we call “fields,” cells are subjected to frictional forces and move passively in response. However, the potential roles of Isotropically expanding fields in morphogenetic events have not been investigated well. In this study, we mathematically analyzed the effect of Isotropically expanding fields using a vertex model, a standard type of multi-cellular model. We found that cells located on fields were elongated along a similar direction each other. Simultaneously, the cell clusters were also elongated, even though field Expansion was absolutely Isotropic. We then investigated the mechanism underlying these counterintuitive phenomena. In particular, we asked whether elongation was caused by the properties of the field, the cell cluster, or both. Theoretical analyses involving simplification of the model revealed that cell clusters have an intrinsic ability to asymmetrically deform, leading to their elongation. Importantly, this ability is effective only under the non-equilibrium conditions provided by field Expansion. This may explain the elongation of the notochord, located on the surface of the growing mouse embryo. We established that passive cell movement induced by Isotropically expanding external environments can contribute to both cell and tissue elongation, as well as collective cell alignment, providing key insight into morphogenesis involving multiple adjacent tissues. Statement of Significance It is a central question of developmental biology how the symmetric shapes of eggs can develop the asymmetric structures of embryos. Embryos expand through their growth. Simultaneously, elongation of tissues such as the notochord occurs, which is fundamental phenomena of morphogenesis. However, possible relationships between tissue elongation and the Expansion of embryos have not been investigated well. Here we mathematically present that, even if the Expansion is Isotropic, tissues located on the embryos are asymmetrically deformed by the Expansion, resulting in elongation. We generalize the effect of expanding environments on tissue elongation through model reduction and uncover the mechanism underlying elongation. This process can be a novel key piece for symmetry breaking of embryos, together with previously established morphogenetic processes.
Hardcastle N - One of the best experts on this subject based on the ideXlab platform.
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A robust VMAT delivery solution for single-fraction lung SABR utilizing FFF beams minimizing dosimetric compromise
'Wiley', 2020Co-Authors: Burton A, Offer K, Hardcastle NAbstract:Peripheral lung lesions treated with a single fraction of stereotactic ablative body radiotherapy (SABR) utilizing volumetric modulated arc therapy (VMAT) delivery and flattening filter-free (FFF) beams represent a potentially high-risk scenario for clinically significant dose blurring effects due to interplay between the respiratory motion of the lesion and dynamic multi-leaf collimators (MLCs). The aim of this study was to determine an efficient means of developing low-modulation VMAT plans in the Eclipse treatment planning system (v15.5, Varian Medical Systems, Palo Alto, USA) in order to minimize this risk, while maintaining dosimetric quality. The study involved 19 patients where an internal target volume (ITV) was contoured to encompass the entire range of tumor motion, and a planning target volume (PTV) created using a 5-mm Isotropic Expansion of this contour. Each patient had seven plan variations created, with each rescaled to achieve the clinical planning goal for PTV coverage. All plan variations used the same field arrangement, and consisted of one dynamic conformal arc therapy (DCAT) plan, and six VMAT plans with varying degrees of modulation restriction, achieved through utilizing different combinations of the aperture shape controller (ASC) in the calculation parameters, and monitor unit (MU) objective during optimization. The dosimetric quality was assessed based on RTOG conformity indices (CI100/CI50), as well as adherence to dose-volume metrics used clinically at our institution. Plan complexity was assessed based on the modulation factor (MU/cGy) and the field edge metric. While VMAT plans with the least modulation restriction achieved the best dosimetry, it was found that there was no clinically significant trade-off in terms of dose to organs at risk and conformity by reducing complexity. Furthermore, it was found that utilizing the ASC and MU objective could reduce plan complexity to near-DCAT levels with improved dosimetry, which may be sufficiently robust to overcome the interplay effect
Hardcastle, Nicholas G - One of the best experts on this subject based on the ideXlab platform.
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A robust VMAT delivery solution for single-fraction lung SABR utilizing FFF beams minimizing dosimetric compromise
'Sociological Research Online', 2020Co-Authors: Burton Alex, Offer Keith, Hardcastle, Nicholas GAbstract:© 2020 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine. Peripheral lung lesions treated with a single fraction of stereotactic ablative body radiotherapy (SABR) utilizing volumetric modulated arc therapy (VMAT) delivery and flattening filter-free (FFF) beams represent a potentially high-risk scenario for clinically significant dose blurring effects due to interplay between the respiratory motion of the lesion and dynamic multi-leaf collimators (MLCs). The aim of this study was to determine an efficient means of developing low-modulation VMAT plans in the Eclipse treatment planning system (v15.5, Varian Medical Systems, Palo Alto, USA) in order to minimize this risk, while maintaining dosimetric quality. The study involved 19 patients where an internal target volume (ITV) was contoured to encompass the entire range of tumor motion, and a planning target volume (PTV) created using a 5-mm Isotropic Expansion of this contour. Each patient had seven plan variations created, with each rescaled to achieve the clinical planning goal for PTV coverage. All plan variations used the same field arrangement, and consisted of one dynamic conformal arc therapy (DCAT) plan, and six VMAT plans with varying degrees of modulation restriction, achieved through utilizing different combinations of the aperture shape controller (ASC) in the calculation parameters, and monitor unit (MU) objective during optimization. The dosimetric quality was assessed based on RTOG conformity indices (CI100/CI50), as well as adherence to dose–volume metrics used clinically at our institution. Plan complexity was assessed based on the modulation factor (MU/cGy) and the field edge metric. While VMAT plans with the least modulation restriction achieved the best dosimetry, it was found that there was no clinically significant trade-off in terms of dose to organs at risk and conformity by reducing complexity. Furthermore, it was found that utilizing the ASC and MU objective could reduce plan complexity to near-DCAT levels with improved dosimetry, which may be sufficiently robust to overcome the interplay effect
