Fast Energy Exchange Research Articles

Persistent Nonlinear Phase-Locking and Nonmonotonic Energy Dissipation in Micromechanical Resonators.

Many nonlinear systems are described by eigenmodes with amplitude-dependent frequencies, interacting strongly whenever the frequencies become commensurate at internal resonances. Fast energy exchange via the resonances holds the key to rich dynamical behavior, such as time-varying relaxation rates and signatures of nonergodicity in thermal equilibrium, revealed in the recent experimental and theoretical studies of micro- and nanomechanical resonators. However, a universal yet intuitive physical description for these diverse and sometimes contradictory experimental observations remains elusive. Here we experimentally reveal persistent nonlinear phase-locked states occurring at internal resonances and demonstrate that they are essential for understanding the transient dynamics of nonlinear systems with coupled eigenmodes. The measured dynamics of a fully observable micromechanical resonator system are quantitatively described by the lower-frequency mode entering, maintaining, and exiting a persistent phase-locked period-tripling state generated by the nonlinear driving force exerted by the higher-frequency mode. This model describes the observed phase-locked coherence times, the direction and magnitude of the energy exchange, and the resulting nonmonotonic mode energy evolution. Depending on the initial relative phase, the system selects distinct relaxation pathways, either entering or bypassing the locked state. The described persistent phase locking is not limited to particular frequency fractions or types of nonlinearities and may advance nonlinear resonator systems engineering across physical domains, including photonics as well as nanomechanics.

Interaction between magnon and skyrmion: Toward quantum magnonics

In recent years, magnon and spin texture are attracting great interest in condensed matter physics and magnetism. Magnonics is aiming to use magnon as information carriers to realize functions for storage, transmission, and processing. Magnetic skyrmion is representative spin texture due to its topologically nontrivial properties. Since skyrmions are topologically protected, their transformation to other spin configurations requires overcoming additional topological energy barriers. Therefore, skyrmions are more stable than other trivial spin textures. In addition, the characters of nanoscale size, quasiparticle properties, and various excitation modes make them a potential candidate for spintronic application. Magnon and skyrmion, as two fundamental excitations, can coexist in magnetic systems and interplay with each other through direct exchange interactions. In this review, we provide an overview of recent theoretical and experimental studies on magnon–skyrmion interactions. We mainly focus on three kinds of magnon–skyrmion interactions: (i) magnon scattering by skyrmion, (ii) skyrmion motion driven by magnon, and (iii) coupling between magnon and skyrmion modes. The first two kinds of interactions could be clearly explained by the wave-particle interaction model on the classical level. Alternatively, the last kind of interaction could be understood by the coupled harmonic oscillator model on the quantum level, which indicates fast energy exchange and hybrid magnon states. The exploration focused on quantum phenomena of magnon has led to the emerging field of quantum magnonics and promoted applications of magnon in quantum information storage and processing. In the end, we give a perspective on the exploration of magnon–skyrmion interaction in quantum magnonics.

Energy balance and synchronization via inductive-coupling in functional neural circuits

A reliable functional neural circuit can estimate the information encoding and signal exchange between neurons, and thus the recognition of electric activities in biological issues can be considered with problems on functional networks connected by neural circuits because more biophysical factors can be taken into account. Neurons communicate with each other via synaptic connections, besides the electric synapse connection via resistor coupling, inductor is effective to perform function as chemical synapses by activating similar inductive field coupling. In this paper, two kinds of neural circuits (light-sensitive and thermosensitive circuits) are connected by an induction coil, and external stimuli are applied to detect the adaptive synchronization approach when the coupling intensity is controlled by energy diversity between neurons. The two neurons hold different intrinsic energy values and then the synaptic connection is created for fast energy exchange along the coupling channel with increasing coupling intensity adaptively. When the energy of two neural circuits/neurons reaches perfect balance, the coupling intensity terminates its further increase and maintains a constant value. In case of phase synchronization/lock between neurons, desynchronization occurs accompanied by continuous energy pumping along the coupling channel without energy balance. Indeed, external energy injection can enhance the field coupling between neurons for decreasing the energy diversity. The involvement of memristive function as induction current for discerning electromagnetic induction in one neuron can increase the energy diversity between neurons, and then bursting synchronization can be suppressed. For the same and identical neural circuits, adaptive growth of synaptic connection can realize perfect energy balance and complete synchronization. For different neural circuits, synchronization is corrupted even the field coupling is further enhanced in the intensity. As a result changeable energy diversity is helpful to induce desynchronization and potential neural disorders and diseases can be blocked.

Onboard Energy Storage System Based on Interleaved High-Conversion-Ratio Quasi-Resonant Converter With Small Characteristic Impedance

An onboard energy storage system (OESS) withfast-energy-exchange capability is needed to enable future grid-to-vehicle (G2V) and vehicle-to-grid (V2G) operations. To facilitate the fast energy exchange, the OESS normally interfaces between a high voltage (HV) bus on the grid side and a low voltage (LV) bus on the vehicle side. The HV bus can be up to 1200 V, while the LV bus is as low as 48 V, which means a high conversion ratio is needed. Resonant converters are commonly used for OESS and designed with large characteristic impedance for wide-range output power and zero-voltage-switching operation. However, such a design leads to large volume and complex customization of the magnetic components. In this paper, a high-conversion-ratio OESS is proposed, which is based on interleaved quasi-resonant converters with small characteristic impedance. The resonant converters are of modular design with a small characteristic impedance to achieve small volume, low cost, and simple customization. Interleaved in LV-side-parallel and HV-side-series configuration, a high conversion ratio can be achieved. Moreover, modulated in quasi-resonant operations, all the switches can realize soft switching even at light load conditions for high efficiency. Burst control for output regulation is implemented in each modular quasi-resonant converter, while interleaved control is implemented between them to minimize the current ripple. The proposed design and control are validated by a compact 5 kW prototype with a charging/discharging current of 100 A, high power efficiency of 98.91%, a high power density of 3.86 W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , and high-conversion-ratio (up to 20: 1) power flow between a 1000 VDC HV bus and a 48 VDC LV bus.

Colloidal Assembly of Au-Quantum Dot-Au Sandwiched Nanostructures with Strong Plasmon-Exciton Coupling.

Strong plasmon-exciton coupling could occur in hybrid metal-dye/semiconductor nanostructures, where the fast energy exchange between plasmons and excitons leads to two new eigenmodes of the system, known as Rabi splitting. In experiments, strongly coupled nanosystems are difficult to obtain because they require some strict conditions, such as low plasmonic damping, small plasmon mode volume, and good spectral overlap. This work demonstrates strongly coupled metal-semiconductor nanostructures can be constructed using colloidal assembly. Specifically, sandwiched Au-quantum dot-Au nanostructures were created through the assembly of Au nanoparticles and colloidal quantum dots (QDs). The sizes of the QDs and the assembly conditions were varied to control the mode volume of the plasmonic cavity formed between the two Au nanoparticles. With a decreased gap size, Rabi splitting was observed in both dark-field scattering and fluorescence spectra of single Au-QD-Au nanostructures. Theoretical simulations revealed that the strong coupling occurred between the excitons and the octupolar plasmon modes.

Fast Energy Exchange between Fixed Supercapacitor and On-board Supercapacitor

Fast Energy Exchange between Fixed Supercapacitor and On-board Supercapacitor

Intelligent Vehicle-to-Vehicle Charging Navigation for Mobile Electric Vehicles via VANET-Based Communication

A direct vehicle-to-vehicle (V2V) charging scheme supplies flexible and fast energy exchange way for electric vehicles (EVs) without the supports of charging stations. Main technical challenges in cooperative V2V charging may include the efficient charging navigation structure designs with low communication loads and computational complexities, the decision-making intelligence for the selection of stopping locations to operate V2V charging services, and the optimal matching issue between charging EVs and discharging EVs. In this paper, to solve the above problems, we propose an intelligent V2V charging navigation strategy for a large number of mobile EVs. Specifically, by means of a hybrid vehicular ad-hoc networks (VANETs) based communication paradigm, we first study a mobile edge computing (MEC) based semi-centralized charging navigation framework to ensure the reliable communication and efficient charging coordination. Then, based on the derived charging models, we propose an effective local charging navigation scheme to adaptively select the optimal traveling route and appropriate stopping locations for mobile EVs via the designed Q-learning based algorithm. After that, an efficient global charging navigation mechanism is proposed to complete the best charging-discharging EV pair matching based on the constructed weighted bipartite graph. A series of simulation results and theoretical analyses are presented to demonstrate the feasibility and effectiveness of the proposed V2V charging navigation strategy.

An Energy Management Strategy for a DC Distribution System for Power System Integration of Plug-In Electric Vehicles

This paper proposes an energy management strategy (EMS) for a dc distribution system for power system integration of plug-in electric vehicles (PEVs). The dc distribution system is intended to integrate electric vehicles in a parking lot with an ac grid through bidirectional dc–dc converters (battery chargers) and a central voltage-sourced converter. Using an online constrained optimization algorithm, the proposed EMS manages the power flow within the dc system. Thus, the PEV owners can charge or discharge their batteries based on the state-of-charge of the batteries and their upcoming trip plans. The EMS offers two energy exchange options to the PEV owners: 1) the fast energy exchange option for the owners wishing to minimize the energy exchange time; and 2) the optimal energy exchange option for the owners intend to either minimize their costs of charging or maximize their revenues through selling their stored energy. The proposed EMS seamlessly handles all charging/discharging requests from the PEV owners with different options and, at the same time, it takes into account the power demand and power generation limits of the ac grid to preclude under-voltage, over-voltage, and reverse power flow issues. Various energy exchange scenarios are simulated to demonstrate the effectiveness of the proposed EMS.

Nonlocal effects in energy balance in an equilibrium plasma during its fast heating/cooling in tokamaks and stellarators

The long-standing problem of nonlocal energy transfer observed in a number of fast heating/cooling experiments in tokamaks and stellarators is discussed. The most representative and still unexplained are the results from cold-pulse experiments that demonstrate a rapid transient increase in the electron temperature in the plasma core in response to an abrupt cooling of the edge. This occurs on a timescale much faster than the diffusive one, which is incompatible with conventional local transport models. This paper contains a review of the most enigmatical observations and theoretical efforts to describe them, and offers an alternative theoretical approach to the problem. Its essential element is the incorporation of the induction effects and fast energy exchange between the plasma and the magnetic field into the traditional transport model. This makes an emphasis on the magnetic field as the main carrier of the interaction, which naturally explains the fast and nonlocal character of the process. The approach uses the ideas recently applied to the analysis of a closely related problem of ‘missing power’. Accordingly, the flux-conserving evolution of the plasma equilibrium and evaluation of the integral energy balance are parts of the analysis.

Influence of oxygen on the resonant photoacoustic signal from methane excited at the ν 3 mode

This paper shows that, when samples of methane in dry air are irradiated with an OPO tuned at the ν 3 mode at 3019 cm−1, the photoacoustic signal is lower than in mixtures in pure nitrogen. In order to explain this change, we developed a rate-equation-based model which describes the methane excitation and relaxation to heat by collisions with the buffer. In particular, we reduced the problem to a system of six energy levels taking into account the fast energy exchange between methane and oxygen resonant states and the slow relaxation rate of oxygen. Thus, the photoacoustic signal is calculated for methane–nitrogen and methane–air systems and a very good agreement is found with the experimental results.

Dimension reduction for extracting geometrical structure of multidimensional phase space: Application to fast energy exchange in the reactionO(D1)+N2O→NO+NO

One of the most fundamental problems in studying general Hamiltonian systems with many degrees of freedom is to extract a low-dimensional subsystem including the essential dynamics. In this paper, a new partial normal form (PNF) method is developed to reduce the number of coupling terms in the Hamiltonian and to simplify the dynamics analyses. The PNF method allows one to decouple many unimportant bath modes as well as the reactive mode from the system by assessing the significance of the coupling terms. The method is applied to the chemical reaction $\mathrm{O}(^{1}D)+{\mathrm{N}}_{2}\mathrm{O}\ensuremath{\rightarrow}\mathrm{NO}+\mathrm{NO}$, which was found to exhibit efficient energy exchange between the two $\mathrm{NO}$ stretching modes despite the short lifetime of the reaction intermediate [S. Kawai et al., J. Chem. Phys. 124, 184315 (2006)]. Through the analysis of the two-dimensional PNF Hamiltonian subsystem, it is found that the motion of the subsystem preserves the ``normal mode picture'' of the symmetric and antisymmetric $\mathrm{NO}$ stretching modes despite its high energy. Then the vibrational energy, initially localized in the newly formed $\mathrm{NO}$ bond, is transferred to the reactants' $\mathrm{NO}$ bond through the beating between the symmetric and antisymmetric stretching modes. The preservation of the normal mode picture and the short period of the beating explain the fast energy exchange between the two $\mathrm{NO}$ bonds. This successful application proves that the PNF method can extract the essential small subspace from many-degrees-of-freedom Hamiltonian systems.

Quantum-mechanical wave packet calculation of photoinduced surface reaction: O2/Pt(111)

We present a two-dimensional quantum-mechanical wave packet study of photoinduced reaction of O2 on Pt(111) within a mechanism of hot electron/hole excitation of a molecular resonance. Based on three constructed potential energy surfaces including the molecule-surface and intra-molecular coordinates, photoexcitation is simulated by nonadiabatic electronic transitions between the ground state (the chemisorbed O2−) and a negative ion resonance state (the O22− shape resonance) or a neutral O2 state. The wave packet dynamics exhibits a fast energy exchange between the two bonds, giving a comparable yield for desorption and dissociation. The calculated branching ratio, BR=0.5–1.0, between desorption and dissociation and the mean kinetic energy of the desorbed molecules 〈Ekin〉/2kB= 990 K are comparable with the reported experimental data measured in desorption by nanosecond laser pulses, while the vibrational temperature is first predicted by this calculation. In addition our results indicate the importance of a proper treatment of damping effect in a coherent wave packet after deexcitation.

Two-stage feature of Hartmann-Hahn cross relaxation in magic-angle sample spinning.

In magic-angle sample-spinning experiments the Hartmann-Hahn cross relaxation between protonated $^{13}\mathrm{C}$ and protons usually proceeds in two stages, except in fast internal rotating $^{13}\mathrm{CH}_{3}$. The protonated $^{13}\mathrm{C}$ magnetization of powder samples changes very rapidly during the first tens of microseconds due to the fast energy exchange between each protonated $^{13}\mathrm{C}$ and its directly bonded $^{1}\mathrm{H}$ spins; then it approaches at a much slower rate to a quasiequilibrium value via the energy exchange between these $^{13}\mathrm{C}{\mathrm{H}}_{n}$ subsystems and the remaining $^{1}\mathrm{H}$ spins. This fact means that the whole $^{1}\mathrm{H}$ spin system is not in a quasiequilibrium state and is not describable by a single spin temperature at least during the first stage of the cross relaxation. The two-stage feature has been obviously revealed by the depolarization experiment for $^{13}\mathrm{C}$ magnetization. The expression for protonated $^{13}\mathrm{C}$ magnetization as a function of depolarization time has been deduced, which reaches agreement with the experiments semiquantitatively. The depolarization experiment offers a reliable approach to distinguishing between $^{13}\mathrm{C}$H and $^{13}\mathrm{CH}_{2}$ signals in organic solids.