The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Sanjay P. Bhat - One of the best experts on this subject based on the ideXlab platform.
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Time-Optimal Attitude Reorientation at Constant Angular Velocity Magnitude with Bounded Angular Acceleration
Proceedings of the 45th IEEE Conference on Decision and Control, 2006Co-Authors: Mrityunjay Modgalya, Sanjay P. BhatAbstract:This paper considers the problem of steering the orientation of an inertially symmetric rigid body of unit moment of inertia from an initial attitude and nonzero angular velocity to a specified terminal attitude in minimum time under an upper limit on the magnitude of angular acceleration with the magnitude of the angular velocity constrained to remain constant. Optimal control theory is used to show that singular optimal arcs are uniform eigenAxis rotations in which the body rotates at a uniform rate about a body-Fixed Axis, while nonsingular arcs are coning motions in which the body angular velocity vector rotates at a uniform rate about a body-Fixed Axis. Symmetries of the problem are exploited to further show that every optimal trajectory consists of at most one coning motion followed either by one uniform eigenAxis rotation or several coning motions of equal duration
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CDC - Time-Optimal Attitude Reorientation at Constant Angular Velocity Magnitude with Bounded Angular Acceleration
Proceedings of the 45th IEEE Conference on Decision and Control, 2006Co-Authors: Mrityunjay Modgalya, Sanjay P. BhatAbstract:This paper considers the problem of steering the orientation of an inertially symmetric rigid body of unit moment of inertia from an initial attitude and nonzero angular velocity to a specified terminal attitude in minimum time under an upper limit on the magnitude of angular acceleration with the magnitude of the angular velocity constrained to remain constant. Optimal control theory is used to show that singular optimal arcs are uniform eigenAxis rotations in which the body rotates at a uniform rate about a body-Fixed Axis, while nonsingular arcs are coning motions in which the body angular velocity vector rotates at a uniform rate about a body-Fixed Axis. Symmetries of the problem are exploited to further show that every optimal trajectory consists of at most one coning motion followed either by one uniform eigenAxis rotation or several coning motions of equal duration.
William T Coffey - One of the best experts on this subject based on the ideXlab platform.
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Thermally activated escape rate for the Brownian motion of a Fixed Axis rotator in an asymmetrical double-well potential for all values of the dissipation
The Journal of chemical physics, 2005Co-Authors: Yuri P Kalmykov, Sergey V Titov, William T CoffeyAbstract:The extension of the Kramers theory of the escape rate of a Brownian particle from a potential well to the entire range of damping proposed by Mel’nikov and Meshkov [J. Chem, Phys. 85, 1018 (1986)] is applied to the rotational Brownian motion of Fixed Axis rotators in a double well cosine potential. The procedure yields an expression for the Kramers escape rate valid for all values of the dissipation including the very low damping (VLD), very high damping (VHD), and crossover regimes. This equation provides a good asymptotic estimate of the correlation time τ∥ of the longitudinal dipole moment correlation function calculated by solving the underlying Langevin equation using the matrix-continued fraction method. Moreover, for low barriers, where the Mel’nikov and Meshkov approach is not applicable, analytic equations for τ∥ in the VLD and VHD limits are derived and a simple extrapolating equation that is valid for all values of the damping is proposed.
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Thermally activated escape rate for the Brownian motion of a Fixed Axis rotator in a double well potential for all values of the dissipation.
The Journal of chemical physics, 2004Co-Authors: William T Coffey, Yuri P Kalmykov, Sergey V TitovAbstract:The extension of the Kramers theory of the escape rate of a Brownian particle from a potential well to the entire range of damping proposed by Mel'nikov and Meshkov [J. Chem, Phys. 85, 1018 (1986)] is applied to the rotational Brownian motion of Fixed Axis rotators in a double well cosine potential. The procedure yields an expression for the Kramers escape rate valid for all values of the dissipation including the very low damping (VLD), very high damping (VHD), and crossover regimes. This equation provides a good asymptotic estimate of the correlation time tau per pendicular of the longitudinal dipole moment correlation function calculated by solving the underlying Langevin equation using the matrix-continued fraction method. Moreover, for low barriers, where the Mel'nikov and Meshkov approach is not applicable, analytic equations for tau in the VLD and VHD limits are derived and a simple extrapolating equation that is valid for all values of the damping is proposed.
Mrityunjay Modgalya - One of the best experts on this subject based on the ideXlab platform.
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Time-Optimal Attitude Reorientation at Constant Angular Velocity Magnitude with Bounded Angular Acceleration
Proceedings of the 45th IEEE Conference on Decision and Control, 2006Co-Authors: Mrityunjay Modgalya, Sanjay P. BhatAbstract:This paper considers the problem of steering the orientation of an inertially symmetric rigid body of unit moment of inertia from an initial attitude and nonzero angular velocity to a specified terminal attitude in minimum time under an upper limit on the magnitude of angular acceleration with the magnitude of the angular velocity constrained to remain constant. Optimal control theory is used to show that singular optimal arcs are uniform eigenAxis rotations in which the body rotates at a uniform rate about a body-Fixed Axis, while nonsingular arcs are coning motions in which the body angular velocity vector rotates at a uniform rate about a body-Fixed Axis. Symmetries of the problem are exploited to further show that every optimal trajectory consists of at most one coning motion followed either by one uniform eigenAxis rotation or several coning motions of equal duration
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CDC - Time-Optimal Attitude Reorientation at Constant Angular Velocity Magnitude with Bounded Angular Acceleration
Proceedings of the 45th IEEE Conference on Decision and Control, 2006Co-Authors: Mrityunjay Modgalya, Sanjay P. BhatAbstract:This paper considers the problem of steering the orientation of an inertially symmetric rigid body of unit moment of inertia from an initial attitude and nonzero angular velocity to a specified terminal attitude in minimum time under an upper limit on the magnitude of angular acceleration with the magnitude of the angular velocity constrained to remain constant. Optimal control theory is used to show that singular optimal arcs are uniform eigenAxis rotations in which the body rotates at a uniform rate about a body-Fixed Axis, while nonsingular arcs are coning motions in which the body angular velocity vector rotates at a uniform rate about a body-Fixed Axis. Symmetries of the problem are exploited to further show that every optimal trajectory consists of at most one coning motion followed either by one uniform eigenAxis rotation or several coning motions of equal duration.
Sergey V Titov - One of the best experts on this subject based on the ideXlab platform.
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Thermally activated escape rate for the Brownian motion of a Fixed Axis rotator in an asymmetrical double-well potential for all values of the dissipation
The Journal of chemical physics, 2005Co-Authors: Yuri P Kalmykov, Sergey V Titov, William T CoffeyAbstract:The extension of the Kramers theory of the escape rate of a Brownian particle from a potential well to the entire range of damping proposed by Mel’nikov and Meshkov [J. Chem, Phys. 85, 1018 (1986)] is applied to the rotational Brownian motion of Fixed Axis rotators in a double well cosine potential. The procedure yields an expression for the Kramers escape rate valid for all values of the dissipation including the very low damping (VLD), very high damping (VHD), and crossover regimes. This equation provides a good asymptotic estimate of the correlation time τ∥ of the longitudinal dipole moment correlation function calculated by solving the underlying Langevin equation using the matrix-continued fraction method. Moreover, for low barriers, where the Mel’nikov and Meshkov approach is not applicable, analytic equations for τ∥ in the VLD and VHD limits are derived and a simple extrapolating equation that is valid for all values of the damping is proposed.
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Thermally activated escape rate for the Brownian motion of a Fixed Axis rotator in a double well potential for all values of the dissipation.
The Journal of chemical physics, 2004Co-Authors: William T Coffey, Yuri P Kalmykov, Sergey V TitovAbstract:The extension of the Kramers theory of the escape rate of a Brownian particle from a potential well to the entire range of damping proposed by Mel'nikov and Meshkov [J. Chem, Phys. 85, 1018 (1986)] is applied to the rotational Brownian motion of Fixed Axis rotators in a double well cosine potential. The procedure yields an expression for the Kramers escape rate valid for all values of the dissipation including the very low damping (VLD), very high damping (VHD), and crossover regimes. This equation provides a good asymptotic estimate of the correlation time tau per pendicular of the longitudinal dipole moment correlation function calculated by solving the underlying Langevin equation using the matrix-continued fraction method. Moreover, for low barriers, where the Mel'nikov and Meshkov approach is not applicable, analytic equations for tau in the VLD and VHD limits are derived and a simple extrapolating equation that is valid for all values of the damping is proposed.
Joseph L Kirschvink - One of the best experts on this subject based on the ideXlab platform.
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Fixed Axis magnetic orientation by an amphibian non shoreward directed compass orientation misdirected homing or positioning a magnetite based map detector in a consistent alignment relative to the magnetic field
The Journal of Experimental Biology, 2002Co-Authors: John B Phillips, Michael J Freake, Jacques Brassart, Chris S Borland, Joseph L KirschvinkAbstract:Experiments were carried out to investigate the earlier prediction that prolonged exposure to long-wavelength (>500 nm) light would eliminate homing orientation by male Eastern red-spotted newts Notophthalmus viridescens. As in previous experiments, controls held in outdoor tanks under natural lighting conditions and tested in a visually uniform indoor arena under full-spectrum light were homeward oriented. As predicted, however, newts held under long-wavelength light and tested under either full-spectrum or long-wavelength light (>500 nm) failed to show consistent homeward orientation. The newts also did not orient with respect to the shore directions in the outdoor tanks in which they were held prior to testing. Unexpectedly, however, the newts exhibited bimodal orientation along a more-or-less ‘Fixed’ northnortheast‐south-southwest magnetic Axis. The orientation exhibited by newts tested under full-spectrum light was indistinguishable from that of newts tested under longwavelength light, although these two wavelength conditions have previously been shown to differentially affect both shoreward compass orientation and homing orientation. To investigate the possibility that the ‘FixedAxis’ response of the newts was mediated by a magnetoreception mechanism involving single-domain particles of magnetite, natural remanent magnetism (NRM) was measured from a subset of the newts. The distribution of NRM alignments with respect to the head‐body Axis of the newts was indistinguishable from random. Furthermore, there was no consistent relationship between the NRM of individual newts and their directional response in the overall sample. However, under full-spectrum, but not long-wavelength, light, the alignment of the NRM when the newts reached the 20 cm radius criterion circle in the indoor testing arena (estimated by adding the NRM alignment measured from each newt to its magnetic bearing) was non-randomly distributed. These findings are consistent with the earlier suggestion that homing newts use the light-dependent magnetic compass to align a magnetite-based ‘map detector’ when obtaining the precise measurements necessary to derive map information from the magnetic field. However, aligning the putative map detector does not explain the Fixed-Axis response of newts tested under long-wavelength light. Preliminary evidence suggests that, in the absence of reliable directional information from the magnetic compass (caused by the 90° rotation of the response of the magnetic compass under long-wavelength light), newts may resort to a systematic sampling strategy to identify alignment(s) of the map detector that yields reliable magnetic field measurements.
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'Fixed-Axis' magnetic orientation by an amphibian: non-shoreward-directed compass orientation, misdirected homing or positioning a magnetite-based map detector in a consistent alignment relative to the magnetic field?
The Journal of experimental biology, 2002Co-Authors: John B Phillips, S Chris Borland, Michael J Freake, Jacques Brassart, Joseph L KirschvinkAbstract:Experiments were carried out to investigate the earlier prediction that prolonged exposure to long-wavelength (>500 nm) light would eliminate homing orientation by male Eastern red-spotted newts Notophthalmus viridescens. As in previous experiments, controls held in outdoor tanks under natural lighting conditions and tested in a visually uniform indoor arena under full-spectrum light were homeward oriented. As predicted, however, newts held under long-wavelength light and tested under either full-spectrum or long-wavelength light (>500 nm) failed to show consistent homeward orientation. The newts also did not orient with respect to the shore directions in the outdoor tanks in which they were held prior to testing. Unexpectedly, however, the newts exhibited bimodal orientation along a more-or-less 'Fixed' north-northeast-south-southwest magnetic Axis. The orientation exhibited by newts tested under full-spectrum light was indistinguishable from that of newts tested under long-wavelength light, although these two wavelength conditions have previously been shown to differentially affect both shoreward compass orientation and homing orientation. To investigate the possibility that the 'Fixed-Axis' response of the newts was mediated by a magnetoreception mechanism involving single-domain particles of magnetite, natural remanent magnetism (NRM) was measured from a subset of the newts. The distribution of NRM alignments with respect to the head-body Axis of the newts was indistinguishable from random. Furthermore, there was no consistent relationship between the NRM of individual newts and their directional response in the overall sample. However, under full-spectrum, but not long-wavelength, light, the alignment of the NRM when the newts reached the 20 cm radius criterion circle in the indoor testing arena (estimated by adding the NRM alignment measured from each newt to its magnetic bearing) was non-randomly distributed. These findings are consistent with the earlier suggestion that homing newts use the light-dependent magnetic compass to align a magnetite-based 'map detector' when obtaining the precise measurements necessary to derive map information from the magnetic field. However, aligning the putative map detector does not explain the Fixed-Axis response of newts tested under long-wavelength light. Preliminary evidence suggests that, in the absence of reliable directional information from the magnetic compass (caused by the 90 degrees rotation of the response of the magnetic compass under long-wavelength light), newts may resort to a systematic sampling strategy to identify alignment(s) of the map detector that yields reliable magnetic field measurements.