In the case where the knowledge of goal states is not known, the controllers are constructed to stabilize unstable steady states for a coupled dynamos system. A delayed feedback control technique is used to suppress c...In the case where the knowledge of goal states is not known, the controllers are constructed to stabilize unstable steady states for a coupled dynamos system. A delayed feedback control technique is used to suppress chaos to unstable focuses and unstable periodic orbits. To overcome the topological limitation that the saddle-type steady state cannot be stabilized, an adaptive control based on LaSalle＇s invariance principle is used to control chaos to unstable equilibrium （i.e. saddle point, focus, node, etc.）. The control technique does not require any computer analysis of the system dynamics, and it operates without needing to know any explicit knowledge of the desired steady-state position.展开更多
Recently torsion fields were introduced in CP-violating cosmic axion a2-dynamos [Garcia de Andrade, Mod Phys Lett A, (2011)] in order to obtain Lorentz violating bounds for torsion. Here instead, oscillating axion sol...Recently torsion fields were introduced in CP-violating cosmic axion a2-dynamos [Garcia de Andrade, Mod Phys Lett A, (2011)] in order to obtain Lorentz violating bounds for torsion. Here instead, oscillating axion solutions of the dynamo equation with torsion modes [Garcia de Andrade, Phys Lett B (2012)] are obtained taking into account dissipative torsion fields. Magnetic helicity torsion oscillatory contribution is also obtained. Note that the torsion presence guarantees dynamo efficiency when axion dynamo length is much stronger than the torsion length. Primordial axion oscillations due to torsion yield a magnetic field of 109 G at Nucleosynthesis epoch. This is obtained due to a decay of BBN magnetic field of 1015 G induced by torsion. Since torsion is taken as 10–20 s–1, the dynamo efficiency is granted over torsion damping. Of course dynamo efficiency is better in the absence of torsion. In the particular case when the torsion is obtained from anomalies it is given by the gradient of axion scalar [Duncan et al., Nuclear Phys B 87, 215] that a simpler dynamo equation is obtained and dynamo mechanism seems to be efficient when the torsion helicity, is negative while magnetic field decays when the torsion is positive. In this case an extremely huge value for the magnetic field of 1015 Gauss is obtained. This is one order of magnitude greater than the primordial magnetic fields of the domain wall. Actually if one uses tDW ~ 10-4 s one obtains BDW ~ 1022 G which is a more stringent limit to the DW magnetic primordial field.展开更多
The high‐temperature superconducting(HTS)dynamo enables injection of large DC currents into a superconducting coil,without the need for thermally‐inefficient current leads.Because of this important advantage,there i...The high‐temperature superconducting(HTS)dynamo enables injection of large DC currents into a superconducting coil,without the need for thermally‐inefficient current leads.Because of this important advantage,there is significant interest in using such technology to energise superconducting coils in superconducting rotating machines and NMR/MRI magnets.Despite the extensive experimental work carried out over the past decade,there was–until very recently–considerable confusion and debate regarding the physical origin of the HTS dynamo’s DC output voltage.Numerical modelling has played a key role in elucidating the underlying physics of such devices and several different numerical models have now been developed as useful and cost‐effective tools to not only explain and further examine experimental results,but also optimise and improve dynamo designs.This review summarises all of the developments in this important area over recent years,including modelling the open‐circuit voltage behaviour in 2D and 3D,the definition of a new benchmark problem for the HTS modelling community,investigating key dynamo parameters,modelling dynamic coil charging behaviour and calculating losses.A view towards the future is provided,including the outstanding challenges and the developments required to address these.展开更多
基金supported by the Doctoral Foundation of North China Electric Power University (Grant No. kH0433)the International Science and Technology Cooperation Program (Grant No. 2007DFA71250)
文摘In the case where the knowledge of goal states is not known, the controllers are constructed to stabilize unstable steady states for a coupled dynamos system. A delayed feedback control technique is used to suppress chaos to unstable focuses and unstable periodic orbits. To overcome the topological limitation that the saddle-type steady state cannot be stabilized, an adaptive control based on LaSalle＇s invariance principle is used to control chaos to unstable equilibrium （i.e. saddle point, focus, node, etc.）. The control technique does not require any computer analysis of the system dynamics, and it operates without needing to know any explicit knowledge of the desired steady-state position.
文摘Recently torsion fields were introduced in CP-violating cosmic axion a2-dynamos [Garcia de Andrade, Mod Phys Lett A, (2011)] in order to obtain Lorentz violating bounds for torsion. Here instead, oscillating axion solutions of the dynamo equation with torsion modes [Garcia de Andrade, Phys Lett B (2012)] are obtained taking into account dissipative torsion fields. Magnetic helicity torsion oscillatory contribution is also obtained. Note that the torsion presence guarantees dynamo efficiency when axion dynamo length is much stronger than the torsion length. Primordial axion oscillations due to torsion yield a magnetic field of 109 G at Nucleosynthesis epoch. This is obtained due to a decay of BBN magnetic field of 1015 G induced by torsion. Since torsion is taken as 10–20 s–1, the dynamo efficiency is granted over torsion damping. Of course dynamo efficiency is better in the absence of torsion. In the particular case when the torsion is obtained from anomalies it is given by the gradient of axion scalar [Duncan et al., Nuclear Phys B 87, 215] that a simpler dynamo equation is obtained and dynamo mechanism seems to be efficient when the torsion helicity, is negative while magnetic field decays when the torsion is positive. In this case an extremely huge value for the magnetic field of 1015 Gauss is obtained. This is one order of magnitude greater than the primordial magnetic fields of the domain wall. Actually if one uses tDW ~ 10-4 s one obtains BDW ~ 1022 G which is a more stringent limit to the DW magnetic primordial field.
文摘The high‐temperature superconducting(HTS)dynamo enables injection of large DC currents into a superconducting coil,without the need for thermally‐inefficient current leads.Because of this important advantage,there is significant interest in using such technology to energise superconducting coils in superconducting rotating machines and NMR/MRI magnets.Despite the extensive experimental work carried out over the past decade,there was–until very recently–considerable confusion and debate regarding the physical origin of the HTS dynamo’s DC output voltage.Numerical modelling has played a key role in elucidating the underlying physics of such devices and several different numerical models have now been developed as useful and cost‐effective tools to not only explain and further examine experimental results,but also optimise and improve dynamo designs.This review summarises all of the developments in this important area over recent years,including modelling the open‐circuit voltage behaviour in 2D and 3D,the definition of a new benchmark problem for the HTS modelling community,investigating key dynamo parameters,modelling dynamic coil charging behaviour and calculating losses.A view towards the future is provided,including the outstanding challenges and the developments required to address these.
