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The three dimensional vibration of the rotor in the HTSC-permanent magnet flywheel system is studied. The magnetic levitation using pining force of the HTSC bulk material has an advantage to achieve stable levitation without control. However the transient characteristics of the levitation is not clearly understood. We have developed the flywheel system which can revolve up to 12,000rpm, and the three dimensional vibration of the rotor are measured with laser displacement sensors. The vibration of the rotor around the mechanical resonance frequency is investigated. The rotor shows both columnar and conical behavior in the mechanical resonant state. Index Terms--Bulk superconductor, magnetic levitation, mechanical resonance, flywheel.

Power electronics is a major candidate in the ongoing research of electrical power grids because they can provide better control with more information (voltage ratio, efficiency, power flow direction, etc.) than the all-passive solutions such as transformers and so forth. Power electronic transformer has the possibility to replace the conventional one by ac/ac matrix converter with high-frequency compact electronic transformers. In this work, a dynamic model of matrix converter is studied and issues such as efficiency, voltage ratio limitation, and transient behavior are discussed and the equivalent numerical calculations are presented. Moreover, an experimental converter is built to validate the numerical results and also to describe the switching frequency impact on the operation. It is concluded that the control creates voltage ratio saturation and high-switching frequency results in lower efficiency values. On the other hand, efficiency can be increased by using resonances of the circuit, which can also provide higher operating frequencies. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This article discusses the effects of DC power flow on the transient dynamics of an AC/DC power system, based on a non-symmetrical swing equation system. The non-symmetry implies a unidirectional component of external forcing, which corresponds to both DC power and exciting power swing. The dynamical behavior when affected by a DC external force, however, has not been solved for these systems, although some studies on the Duffing equation with unsymmetrical force were reported. The dynamical behavior now remains an open problem in power system dynamics and also in nonlinear oscillation theory. As an important aspect of the dynamical behavior, one consider a stability boundary and its qualitative change in the swing equation system.

The density matrix renormalization group theory is reviewed as a numerical variational method. The variational state, expressed as a product of local tensors, is improved through locally tuning each tensor. The first section is a tutorial with simplified discussions. Details are discussed in the subsequent sections. The review concludes with some recent developments and future directions. [ABSTRACT FROM AUTHOR]

In this article, we propose a model for a stand-alone hybrid distributed generation system. In this model, the input sources are distributed DC sources like solar panels or batteries. The idea behind this network framework is to introduce a hybrid DC/AC network, feasible for small and remotely located areas with stand-alone DC grids, in the vicinity of larger towns requiring a functional AC connection. The behaviour of the system in the steady state is analysed, and the network is mathematically represented with port-controlled Hamiltonian modelling. Stabilization to the desired voltage, both AC as well as DC, is attained with nonlinear passivity-based control taking into consideration not only the energy characteristics but also the inherent physical structure., Competing Interests: We declare we have no competing interests., (© 2024 The Authors.)

This article presents an application of the recently proposed logic operation of power based on power packetization. In a power packet despatching system, the power supply can be considered as a sequence of power pulses, where the occurrence of pulses follows a probability that corresponds to the capacity of the power sources or power lines. In this study, we propose a processing scheme to reshape a stream of power packets from such stochastic sequences to satisfy the load demand. The proposed scheme is realized by extending the concept of stochastic computing to the power domain. We demonstrate the operation of the proposed scheme through experiments and numerical simulations by implementing it as a function of a power packet router, which forms a power packet despatching network. The stochastic framework proposed in this study provides a new design foundation for low-power distribution networks as an embodiment of the close connection between the cyber and physical components., Competing Interests: We declare we have no competing interests., (© 2023 The Authors.)

We study the scale dependence of effective diffusion of fluid tracers, specifically, its dependence on the Péclet number, a dimensionless parameter of the ratio between advection and molecular diffusion. Here, we address the case that length and time scales on which the effective diffusion can be described are not separated from those of advection and molecular diffusion. For this, we propose an alternate method for characterizing the effective diffusivity without relying on the scale separation. For a given spatial domain inside which the effective diffusion can emerge, a time constant related to the diffusion is identified by considering the spatiotemporal evolution of a test advection-diffusion equation, where its initial condition is set at a pulse function. Then, the value of effective diffusivity is identified by minimizing the L_{∞} distance between solutions of the above test equation and the diffusion one with mean drift. With this method, for time-independent gyre and time-periodic shear flows, we numerically show the scale dependence of the effective diffusivity and its discrepancy from the classical limits that were derived on the assumption of the scale separation. The kinematic origins of the discrepancy are revealed as the development of the molecular diffusion across flow cells of the gyre and as the suppression of the drift motion due to a temporal oscillation in the shear.

In this study, electric power is processed using the logic operation method and the error correction algorithms to meet load demand. Electric power was treated as the physical flow through the distribution network, which was governed by circuit configuration and efficiency. The hardware required to digitize or packetize electric power, which is called power packet router, was developed in this research work for low power distribution. It provides an opportunity for functional electric power dispatching while disregarding the power flow in the circuit. This study proposes a new design for the network, which makes the logic operation of electric power possible and provides an algorithm to correct the inaccuracies caused by dissipation and noise. Phase shift of the power supply network is resulted by implementing the introduced design., (© 2021 The Authors.)

Cluster formation has been observed in many organisms in nature. It has the desirable properties for designing energy efficient protocols for Wireless Sensor Networks (WSNs). In this paper, we present a new approach for energy efficient WSN protocols that investigates how the cluster formation of sensors responds to the external time-invariant energy potential. In this approach, the necessity for data transmission to the Base Station is eliminated, thereby conserving energy for WSNs. We define swarm formation topology and estimate the curvature of an external potential manifold by analyzing the change of the swarm formation in time. We also introduce a dynamic formation control algorithm for maintaining defined swarm formation topology in the external potential.

An investigation of air-core toroidal transformers has been undertaken to enable power converters to achieve megahertz operation. The characteristics of the air-core toroidal transformer govern the behaviors of the internal magnetic flux of the transformer. Understanding the behaviors at an above-megahertz level is a key issue in the design of the air-core toroidal transformer. This paper discusses the internal magnetic flux density distribution in the air-core toroidal transformer under high-frequency excitation. We propose a measurement method for the distribution and show the obtained results under a sinusoidal excitation with an amplitude of 1.5 A and a frequency of 1 MHz. The results reveal a non-uniform distribution in the tangential and normal directions. The cause of this non-uniformity was found to be the structure of the air-core toroidal transformer. In addition, the validity of the proposed measurement method was confirmed by comparing the experimentally obtained results with a numerical estimation using the Biot-Savart law. These results suggest that the proposed measurement method is capable of investigating the distributed characteristics of air-core toroidal transformers under megahertz excitation.

A power packet distribution network is expected to be one of the advanced power distribution systems, providing high controllability in both energy management and failure management. Regarding network operations, the power packet transmission is governed by switching operation within each of the routers. Here, the power distribution through power packets exhibits consensus-like dynamical behaviors. These features lead to the question of a consensus dynamics on switching topology and routing controls for appropriate power flows. Our approach to the above subjects is based on the dynamical modeling and the emulation of dynamics through the decentralized control of routers. The simulations on a ring-structure network, of the power distribution, reveal that the dynamical solution of the unbiased distribution is feasible via the decentralized control, while in the biased case, the result shows two behavioral fragments, which is quite different from the dynamical solution. In this discussion, we propose a decentralized algorithm that contains only fundamental functions for the packet transmission and is able to be redesigned or extended for further applications.

A power packet is a unit of electric power composed of a power pulse and an information tag. In Shannon's information theory, messages are represented by symbol sequences in a digitized manner. Referring to this formulation, we define symbols in power packetization as a minimum unit of power transferred by a tagged pulse. Here, power is digitized and quantized. In this paper, we consider packetized power in networks for a finite duration, giving symbols and their energies to the networks. A network structure is defined using a graph whose nodes represent routers, sources and destinations. First, we introduce the concept of a symbol propagation matrix (SPM) in which symbols are transferred at links during unit times. Packetized power is described as a network flow in a spatio-temporal structure. Then, we study the problem of selecting an SPM in terms of transferability, that is, the possibility to represent given energies at sources and destinations during the finite duration. To select an SPM, we consider a network flow problem of packetized power. The problem is formulated as an M-convex submodular flow problem which is a solvable generalization of the minimum cost flow problem. Finally, through examples, we verify that this formulation provides reasonable packetized power., Competing Interests: We declare we have no competing interests.

Edge magnetism in graphene sparks intense theoretical and experimental interests. In the previous study, we demonstrated the existence of collective excitations at the zigzag edge of the honeycomb lattice with long-ranged Néel order. By employing the Schwinger-boson approach, we show that the edge magnons remain robust even when the long-ranged order is destroyed by spin fluctuations. Furthermore, in the effective field-theory limit, the dynamics of the edge magnon is captured by the one-dimensional relativistic Klein-Gordon equation. It is intriguing that the boundary field theory for the edge magnon is tied up with its bulk counterpart. By performing density-matrix renormalization group calculations, we show that the robustness may be attributed to the closeness between the ground state and the Néel state. The existence of edge magnon is not limited to the honeycomb structure, as demonstrated in the rotated-square lattice with zigzag edges as well. The universal behavior indicates that the edge magnons may attribute to the uncompensated edges and can be detected in many two-dimensional materials.

We develop a microscopic theory of finite-temperature spin-nematic orderings in three-dimensional spatially anisotropic magnets consisting of weakly coupled frustrated spin-1/2 chains with nearest-neighbor and next-nearest-neighbor couplings in a magnetic field. Combining a field theoretical technique with density-matrix renormalization group results, we complete finite-temperature phase diagrams in a wide magnetic-field range that possess spin-bond-nematic and incommensurate spin-density-wave ordered phases. The effects of a four-spin interaction are also studied. The relevance of our results to quasi-one-dimensional edge-shared cuprate magnets such as LiCuVO(4) is discussed.

The discovery of deterministic chaos in the late nineteenth century, its subsequent study, and the development of mathematical and computational methods for its analysis have substantially influenced the sciences. Chaos is, however, only one phenomenon in the larger area of dynamical systems theory. This Focus Issue collects 13 papers, from authors and research groups representing the mathematical, physical, and biological sciences, that were presented at a symposium held at Kyoto University from November 28 to December 2, 2011. The symposium, sponsored by the International Union of Theoretical and Applied Mechanics, was called 50 Years of Chaos: Applied and Theoretical. Following some historical remarks to provide a background for the last 50 years, and for chaos, this Introduction surveys the papers and identifies some common themes that appear in them and in the theory of dynamical systems.

Extraction and deposition of single atoms using an atomic force microscope tip is a promising technique for building nanostructures. Previous theoretical models for this technique, based on adiabatic atom motion in either classical or quantum mechanics settings, encountered an apparent difficulty in explaining atom extraction and deposition for the same experimental conditions. We resolve that difficulty by showing that both extraction and deposition of atoms can be formulated in terms of pure classical mechanics as a resonance effect, arising from a combination of interatomic forces and vibrations of individual atoms.

A method to manipulate intrinsic localized mode (ILM) is numerically discussed in a nonlinear coupled oscillator array, which is obtained by modeling a microcantilever array. Prior to the manipulation, coexistence and dynamical stability of standing ILMs are first investigated. The stability of coexisting ILMs is determined by a nonlinear coupling coefficient of the array. In addition, the global phase structure, which dominates traveling ILMs, is also changed with the stability. It makes possible to manipulate a traveling ILM by adjusting the nonlinear coupling coefficient. The capture and release manipulation of the traveling ILM is shown numerically.

This paper analyzes frequency entrainment described by van der Pol and phase-locked loop (PLL) equations. The PLL equation represents the dynamics of a PLL circuit that appear in typical phase-locking phenomena. These two equations describe frequency entrainment by a periodic force. The entrainment originates from two different types of limit cycles: libration for the van der Pol equation and rotation for the PLL one. To explore the relationship between the geometry of limit cycles and the mechanism of entrainment, we investigate the entrainment using an energy balance relation. This relation is equivalent to the energy conservation law of dynamical systems with dissipation and input terms. We show response curves for the dc component, harmonic amplitude, phase difference, and energy supplied by a periodic force. The obtained curves indicate that the entrainments for the two equations have different features of supplied energy, and that the entrainment for the PLL equation possibly has the same mechanism as does the regulation of the phase difference for the van der Pol equation.

This paper concerns global phase structures of a time-delayed-feedback controlled two-well Duffing system. The remains of a global stretch and fold structure along an unstable manifold, which develops from an unstable fixed point in function space, reveals that the global chaotic dynamics is inherited from the original system by the controlled system. The remains of the original chaotic dynamics causes a highly complicated domain of attraction for target orbits and a long chaotic transient before convergence.

Time delayed feedback control is well known as a practical method for stabilizing unstable periodic orbits embedded in chaotic attractors. However, this control method still has an open problem of estimating domain of attraction for target unstable periodic orbits. In this paper, we numerically discuss the domain of attraction in Duffing systems under the control method. The disturbance to initial conditions reveals that the domain of attraction possibly exhibits self-similar structures in its boundaries.

Using gauge transformations on electron bond operators, we derive exact duality relations between various order parameters for correlated electron systems. Applying these transformations, we find two duality relations in the generalized two-leg Hubbard ladder at arbitrary filling. The relations show that unconventional density-wave orders such as staggered flux or circulating spin current are dual to conventional density-wave orders and there are direct mappings between dual phases. Several exact results on the phase diagram are also concluded.

Effect of four-spin cyclic exchange on magnetism is studied in the two-leg S=1/2 ladder. We develop an exact spin-chirality duality transformation, under which the system is self-dual when the four-spin exchange J4 is half of the two-spin exchange. Using the density-matrix renormalization-group method and the duality relation, we find that the four-spin exchange makes the vector-chirality correlation dominant. A "chirality short-range resonating-valence-bond" phase is identified for the first time at large J4.

Time delayed feedback control is well known as an effective continuous control method for stabilizing the unstable periodic orbit embedded in chaotic attractors. As for the system with time delay, the solution is in a function space and shows characteristics governed by an infinite dimension. Therefore it is difficult to understand the system behavior analytically. In this paper, it is shown that, when the state space for the system with time delay is expanded into the spatio-temporal state space, the solution propagates in the space as a wave theoretically and numerically. The dynamic behavior experimentally obtained in the sinusoidally excited magneto-elastic beam system under time delayed feedback control is also discussed by the transformation into the expanded spatio-temporal state space. (c) 1999 American Institute of Physics.

In this paper the vibration and the traveling wave in a coupled magneto-elastic beam system are discussed experimentally. The vibration excited by the periodical forcing at the beam system propagates to another as a wave through the coupling elastic beams. Each magneto-elastic beam shows the variety of vibrations caused by the nonlinearity of the potential well and the wave propagation with time delay. The temporal vibration of the magneto-elastic beam is explained with relations to the spatial state transition based on the experimental results. (c) 1997 American Institute of Physics.