Harmonic State Research Articles

Thermal generation of droplet soliton in chiral magnet

Controlled creation of localized magnetic textures beyond conventional $\ensuremath{\pi}$-skyrmions is an important problem in the field of magnetism. Here, by means of spin dynamics simulations, Monte Carlo simulations, and harmonic transition state theory we demonstrate that an elementary chiral magnetic soliton with zero topological charge---the chiral droplet---can be created by thermal fluctuations in the presence of the tilted magnetic field. The proposed protocol relies on an unusual kinetics combining the effects of the entropic stabilization and low-energy barrier for the nucleation of a topologically trivial state. Following this protocol by varying temperature and the tilt of the external magnetic field, one can selectively generate chiral droplets or $\ensuremath{\pi}$-skyrmions in a single system. The coexistence of two distinct magnetic solitons establishes a basis for a rich magnetization dynamics and opens up the possibility for the construction of more complex magnetic textures such as skyrmion bags and skyrmions with chiral kinks.

M252 Routine serum creatinine measurement state of accuracy and inter-laboratory harmonization in China

M252 Routine serum creatinine measurement state of accuracy and inter-laboratory harmonization in China

Dual-wavelength harmonic mode-locked dissipative soliton resonance of Yb fiber laser

Dissipative soliton resonance (DSR) mode-locked fiber lasers have stimulated great interest recent years due to their unique pulse-breaking-free advantage for scaling soliton pulse energy. However, the mechanism accounting for pulse breaking to generate multipulses in DSR fiber lasers has not reached a consensus. Here, we show that harmonic mode-locked DSR 1-μm Yb-doped fiber laser in the dual-wavelength regime can be realized with a semiconductor saturable absorber mirror (SESAM). In the fundamental frequency (3.5 MHz) mode-locked state, the pulse width continuously broadens from 2 to 8.9 ns as the output power increases from 1.26 to 5.1 mW (pulse energy being from 0.36 to 1.46 nJ), while the pulse peak power is clamped at 0.17 W, highlighting the typical characteristics of DSR mode-locking operation. Through simply adjusting the SESAM’s feedback conditions, the DSR fiber laser can transits from the fundamental-frequency mode locking to harmonic mode-locked states. Harmonic states from the 2nd to 9th order have been observed, with pulse repetition rate enhanced from 7 to 31.5 MHz. Under fixed pump power, increasing harmonic orders leads to reduction of the pulse width and pulse energy but does not change the unique quantization feature of the peak power. The status of the SESAM also guarantees the generation of dual wavelengths centered at 1072.5 and 1079.5 nm with spectral widths of 2.7 and 1.9 nm, respectively. This dual-wavelength harmonic mode-locked DSR Yb fiber laser can find applications in various areas.

Harmonic state estimation based on discrete exponential expansion, singular value decomposition and a variable measurement model

In this contribution, a method for harmonic state estimation (HSE) of electrical systems using the discrete exponential expansion (DEE), singular value decomposition (SVD) and a variable measurement model is presented. Variable harmonics, interharmonics, and subharmonics can be estimated using this DEE-SVD time-domain methodology, depending on the number of state variables in the system model and the measurements related through a variable measurement equation, which is proposed as a function of a variable number of measurements and their derivatives to define over, normal and under-determined conditions, respectively. The observability analysis can be verified using the SVD and the resulting null-space vectors, if the electrical system is not completely observable; this analysis can define observable system areas. The HSE regularly receives a limited number of measurements from the system, performs the state estimation and evaluates the global state of the actual harmonic condition. The discrete exponential expansion Newton method determines the periodic steady-state under a particular harmonic condition, obtains a convenient initial steady-state condition to apply the SVD and performs the HSE with a small state estimation error. Noisy measurements adversely affect the state estimation and may increase the state estimation error. The time-domain DEE-HSE can be used to enhance the operation and control of electrical systems under harmonic distortion conditions, e.g., to control active and passive harmonic filters. The state estimation results have been validated through direct comparison against the response obtained with the PSCAD/EMTDC® simulator.

Current state of harmonization of domestic legislation in the field of protection of consumer rights with the legislation of the European Union

The current state of harmonization of Ukrainian legislation, which protects the rights and legitimate interests of consumers in distance trade is analyzed. The current state of electronic communication (interaction) between public authorities, businesses and consumers.
 Approaches to the formation of EU secondary legislation in the field of consumer policy are revealed. The first approach, based on the principle of full harmonization, increases the level of consumption, provides a high degree of consumers protection. Another one provides Member States with the right to go beyond consumer protection, and to maintain more strict national rules, which must comply with primary EU law.
 The expediency of creating an "E-buyer" platform for sellers who carry out business activities in online stores is argued.
 It is noted that the procedure of e-seller identification will simplify the identification of the seller at the stage of online shopping, should be free and carried out by the consumer himself online.
 The innovations of draft laws on consumer protection in the remote conclusion of contracts are described.
 Amendments to the legislation on establishing the right to apply to the competent authority on restrictions, restoring access to the website of the provider (owner or owner) of electronic communications services, where the information is posted, are proposed.
 The necessity to provide a warning mechanism in case of restriction of access to e-sellers' websites and to set a deadline for providing sellers with additional time (within two days) to correct their data is considered.
 It is suggested that requests to block websites should be sent to the provider (owner or owner) of electronic communications services.
 It is noted that the procedure for restricting and restoring access to information resources should be provided only by law.

Analytical theory of frequency-modulated combs: generalized mean-field theory, complex cavities, and harmonic states.

Frequency-modulated (FM) combs with a linearly-chirped frequency and nearly constant intensity occur naturally in certain laser systems; they can be most succinctly described by a nonlinear Schrödinger equation with a phase potential. In this work, we perform a comprehensive analytical study of FM combs in order to calculate their salient properties. We develop a general procedure that allows mean-field theories to be constructed for arbitrary sets of master equations, and as an example consider the case of reflective defects. We derive an expression for the FM chirp of arbitrary Fabry-Perot cavities-important for most realistic lasers-and use perturbation theory to show how they are affected by finite gain bandwidth and linewidth enhancment in fast gain media. Lastly, we show that an eigenvalue formulation of the laser's dynamics can be useful for characterizing all of the stable states of the laser: the fundamental comb, the continuous-wave solution, and the harmonic states.

Harmonic state estimation based on graph signal processing

This paper presents a novel harmonic state estimation (HSE) methodology based on graph signal processing. The proposed approach can perform HSE without calculating harmonic impedance. The proposed methodology involves graph signal theory for constructing a graph Laplacian matrix and an unconstrained optimization function, the adaptive K-means algorithm for building a prior information model of the target bus, as well as data fuzzification and the domain averaging method for state estimation. Simulations are carried out using a 30-bus power distribution system, and results are presented and discussed to prove the efficiency of the proposed method. The practical application further verifies the availability of the proposed method.

Carbon-induced strengthening of bcc iron at the atomic scale

In steels, the interaction between screw dislocations and carbon solutes has a great influence on the yield strength. Fe-C potentials used in molecular dynamics (MD) simulations yield a poor description of screw dislocation properties---their core structure and Peierls barrier---compared to ab initio calculations. Here we combine two EAM potentials from the literature, which greatly improves dislocation property accuracy in FeC alloys. Using this hybrid potential, MD simulations of dislocation glide in random solid solutions confirm a powerful solute strengthening, caused by complex interaction processes. We analyze these processes in a model geometry, where a row of carbon atoms is inserted in the dislocation core with varying separations. We use a combination of MD simulations, minimum-energy path calculations, and a statistical model based on the harmonic transition state theory to explain the strengthening induced by carbon. We unveil that carbon disrupts the glide process, as unpinning requires the successive nucleation of two kink pairs. When solute separation is below about 100 Burgers vectors, the activation enthalpy of both kink pairs are markedly increased compared to pure iron, resulting in a strong dependence of the unpinning stress on solute spacing. Our simulations also suggest an effect of carbon spacing on the kink-pair activation entropy. This work provides elementary processes and parameters that will be useful for larger-scale models and, in particular, kinetic Monte Carlo simulations.

Supermode noise suppression with polarization-multiplexed dual-loop for active mode-locking optoelectronic oscillator.

The active mode-locking (AML) technique has been widely used in erbium-doped fiber lasers to generate picosecond pulse trains. Here we propose a novel active mode-locking dual-loop optoelectronic oscillator (AML-DL-OEO), which can generate microwave frequency comb (MFC) signals with adjustable comb spacings. Based on this scheme, the order of harmonic mode-locking is dramatically decreased for a certain AML driving frequency compared with a single-loop AML-OEO. Thus, the supermode noise caused by harmonic mode-locking can be efficiently suppressed. In addition, the sidemodes are well suppressed by the dual-loop architecture. An experiment is performed. MFC signals with different comb spacings are generated under fundamental or harmonic mode-locking states. AML-DL-OEO systems with different length differences between two loops are implemented to evaluate supermode noise suppression capability. The performance of the generated MFC signals is recorded and analyzed.

Lifetime of skyrmions in discrete systems with infinitesimal lattice constant

Topological protection of chiral magnetic structures is investigated by taking a two-dimensional magnetic skyrmion as an example. The skyrmion lifetime is calculated based on harmonic transition state theory for a discrete lattice model using various values of the ratio of the lattice constant and the skyrmion size. Parameters of the system corresponding to exchange, anisotropy and Dzyaloshinskii–Moriya interaction are chosen in such a way as to keep the energy and size of the skyrmion unchanged for small values of the lattice constant, using scaling relations derived from continuous micromagnetic description. The number of magnetic moments included in the calculations reaches more than a million. The results indicate that in the limit of infinitesimal lattice constant, the energy barrier for skyrmion collapse approaches the Belavin–Polyakov lower bound of the energy of a topological soliton in the σ-model, the entropy contribution to the pre-exponential factor in the Arrhenius rate expression for collapse approaches a constant and the skyrmion lifetime can, for large enough number of spins, correspond to thermally stable skyrmion at room temperature even without magnetic dipole–dipole interaction.

Nonlinear liquid sloshing in an upright circular container: Modal responses and higher-order harmonics

Nonlinear sloshing in an upright circular container near the lowest natural frequency is analyzed by using a fully nonlinear overset-mesh-based harmonic polynomial cell method, two weakly nonlinear Narimanov–Moiseev-type multimodal models and a linear multimodal method. Modal responses are extracted from the fully nonlinear results based on a simple but accurate least-square procedure using the time series of free-surface wave elevations, which provides new ways to delve into the underlying modal responses and energy transfer between modes, as well as to verify the validity of ordering assumptions in the weakly nonlinear models. Wavelet analyses are also performed for the wave elevations and generalized coordinates of the modes to better understand the time-frequency information of the higher harmonics of the sloshing responses and energy transfer in a nonlinear process. Planar harmonic sloshing state, swirling harmonic sloshing state, and periodically modulated sloshing state are analyzed. It is found that the energy is more dispersed among different modes in the periodically modulated sloshing state, which means higher natural modes are consequential. In general, energies are found to transfer from lower to higher natural modes and between symmetric and antisymmetric natural modes. The results also show that the O(ε1/3) and O(ε2/3) responses are dominated by only first and second harmonics, respectively, while the O(ε) response contains non-negligible first and third harmonic contribution. At last, the influence of initial disturbance is examined, demonstrating that different initial disturbances may lead to the different rotation direction of the swirling waves and the sloshing-wave responses in the transient stage, while the main characteristics of the sloshing waves are robust and independent of initial conditions.

СТАТИСТИКА ОСВІТИ УКРАЇНИ В КОНТЕКСТІ ЄВРОІНТЕГРАЦІЇ

The paper examines the current state of harmonization of state statistical activity with the requirements of the European Statistical System. The purpose of the article is to determine the state of integration of the education statistics system of Ukraine into the European Union to ensure comparability of education data at the international level. The research was carried out on the basis of general scientific methods such as analysis and synthesis, comparison, time-series analysis, structural analysis, graphical method, etc. The legal framework for the implementation of obligations in the field of statistics and information exchange between Ukraine and the European Union was analyzed. The Law of Ukraine on amendments to certain laws of Ukraine related to the activity of state statistics was reviewed with regard to amendments to the Law of Ukraine "On Education". The main aspects and processes of education systems at the global level were outlined. Special attention is given to creating the necessary conditions for international comparability of education data and indicators. The International Standard Classification of Education is described to provide internationally comparable statistics. The compliance of coverage of relevant age groups by educational programs of Ukraine with international standards was analyzed. Student enrolment has been studied in comparison with European Union member and candidate countries. It was noted that Ukraine had completed a significant amount of work on the commitments towards European integration, despite the emergency situation in Ukraine as a result of the attack by the russian federation. The article draws conclusions about the state of integration of the system of education statistics of Ukraine into the European Union. The task of integrating the system of education statistics of Ukraine into the European space can be carried out effectively only on the condition of consensus, systematic, and compre­hensive consideration.

Small-Signal Modeling and Interaction Analysis of LCC-HVDC Systems Based on Harmonic State Space Theory

High-voltage direct current (HVDC) technology based on Line Commutated Converter (LCC) is widely used in modern power systems due to its numerous benefits. However, as a typical power electronic device, LCC-HVDC has caused significant changes in the dynamic behavior of modern power systems due to largely replaced conventional power supplies in power systems. The interactions among sending-terminal and receiving-terminal system become stronger and have caused some stability issues, but the mechanism behind this has yet to be fully revealed. In order to analyze the interactions among sending-terminal and receiving-terminal system of LCC-HVDC, a small-signal model of modular HSS modeling is proposed based on Harmonic State Space (HSS) theory. Comparison of time-domain response with detailed switching model shows that the proposed can well reflect the dynamic behavior of the detailed switching model. Based on the model, the influence of controller’s parameters on system stability is analyzed, as well as the dynamic interactions of LCC-HVDC among sending-terminal and receiving-terminal system are investigated. Analytical results demonstrate that there exists interactions among sending-terminal and receiving-terminal system which have an influence on the stability of the system.

Modeling of Power Electronics Systems and PWM Modulators in Harmonic-State Space

Modeling and simulation of the converter dominated systems have recently emerged as a monumental challenge. These simulations are useful for predicting instability and system's harmonic content, consequently assisting in developing better control and filters. But, as more and more converters are incorporated into the system, time-domain simulation models have a tradeoff of either limited accuracy or fewer simulated converters. On the contrary, frequency-domain modeling methods like linear time-invariant models cannot capture the system's time-varying nature and complex converter interactions. The recently developed harmonic state space (HSS) modeling approach has emerged to provide an alternate avenue to model and simulate these converter-dominated systems. HSS models, while accurate, until recently have not been able to reliably model the non-linear pulse width modulator. This paper solves this challenge and develops a new modulator model for harmonic domain models, including HSS. The proposed large-signal modulator is computationally less demanding and can reliably capture the harmonic spectrum of complex multi-converter systems till converter switching frequencies. Several optimization methods are introduced to utilize the unique multi-harmonic nature of HSS, making simulations faster than conventional time-domain methods. Results are verified with extensive simulations and experiments. The application, challenges, and future scope for this method are also highlighted.

Bad data correction in harmonic state estimation for power distribution systems: an approach based on generalised pattern search algorithm

This paper presents a novel methodology for bad data correction in harmonic state estimation for power distribution systems. An optimisation model is formulated considering an objective function to be minimised based on the weighted least squares. Inequality constraints are incorporated to the problem for those buses which are not monitored in real time by any dedicated meter, being their corresponding active and reactive powers considered between upper and lower bounds in order to provide supplementary information about the current system state. In this paper, a measurement calibration vector is introduced into the optimisation model, assuming that a correction factor is associated with the measurements gathered from the network. GPSA (Generalized Pattern Search Algorithm) is used to determine the optimal values of each calibration factor to provide correct state estimation results. A 69-bus test system is used for the computational simulations considering different case studies with multiple bad data to be identified and corrected proving the efficiency and viability of the proposed method. The main contribution of this work is the automatic detection of bad data, identification of the corrupted measurements and correction of the bad data ensuring that the system states are estimated with errors lower than 1%.

Toward robust and practical interband cascade laser frequency combs: A perspective

Multimode emission from a semiconductor laser can sometimes take the form of a low-noise frequency comb with equidistant separation between the modes. Two general types of “passive” comb operation have been explored experimentally: (1) the periodic short-pulse mode achieved by intracavity mode locking, usually obtained by incorporating a saturable absorber section into the cavity, and (2) the so-called frequency-modulated (FM) mode in which the output intensity can vary within wide bounds but does not completely turn off between pulses, and the instantaneous frequency is linearly chirped over a round trip. The FM mode sometimes manifests as a “sparse” harmonic state, with individual modes spaced by multiples of the cavity free spectral range. This Perspective reviews the current understanding of these modes, along with the conditions under which they may arise in practical devices. We then consider in detail the case of type-II mid-infrared interband cascade laser (ICL) frequency combs. Our simulations clarify the roles of carrier dynamics and group velocity dispersion and identify design modifications that may substantially improve the device performance. We find no fundamental roadblocks to the development of practical mode-locked ICL frequency combs that emit short pulses with broad spectral bandwidth for dual comb spectroscopy and other applications, alongside the FM combs that have already been demonstrated experimentally.

Nonlinear Wave Synchronization in a Dusty Plasma Under Microgravity on the International Space Station (ISS)

In a plasma containing micrometer-size dust particles, nonlinear wave synchronization was investigated experimentally under microgravity conditions on board the International Space Station (ISS). These dust particles were confined into a 3-D cloud, in the vicinity of a diffuse edge of the plasma, which was generated by an inductively coupled radio frequency (RF) glow discharge. A cross-sectional slab of the cloud was imaged using a video camera. The dust-density fluctuations in the slab were characterized using the video image data. A steady and long-lived dust acoustic wave (DAW) was observed to be spontaneously generated in the cloud; it propagated through the dust cloud, which had a gradually varying density distribution. Two kinds of spectral analyses of the wave motion were performed, using Fourier transforms and Hilbert transforms, respectively; these revealed two distinctive spatial domains in the cloud, termed frequency clusters. Within each cluster, waves were found to oscillate at a dominant frequency that remained constant, manifesting mutual synchronization throughout the cluster. Across the two clusters, the dominant frequency exhibited a step-wise change, with a frequency ratio of 2:1, which is consistent with phase-lock conditions for a harmonic synchronization state.

Coherent States for Fractional Powers of the Harmonic Oscillator Hamiltonian

Inspired by special and general relativistic systems that can have Hamiltonians involving square roots or more general fractional powers, in this article, we address the question of how a suitable set of coherent states for such systems can be obtained. This becomes a relevant topic if the semiclassical sector of a given quantum theory is to be analysed. As a simple setup, we consider the toy model of a deparametrised system with one constraint that involves a fractional power of the harmonic oscillator Hamiltonian operator, and we discuss two approaches to finding suitable coherent states for this system. In the first approach, we consider Dirac quantisation and group averaging, as have been used by Ashtekar et al., but only for integer powers of operators. Our generalisation to fractional powers yields in the case of the toy model a suitable set of coherent states. The second approach is inspired by coherent states based on a fractional Poisson distribution introduced by Laskin, which however turn out not to satisfy all properties to yield good semiclassical results for the operators considered here and in particular do not satisfy a resolution of identity as claimed. Therefore, we present a generalisation of the standard harmonic oscillator coherent states to states involving fractional labels, which approximate the fractional operators in our toy model semiclassically more accurately and satisfy a resolution of identity. In addition, motivated by the way the proof of the resolution of identity is performed, we consider these kind of coherent states also for the polymerised harmonic oscillator and discuss their semiclassical properties.

Weak- and strong-expansions of coherent states eigenfunctions for the generalized q-deformed harmonic oscillator and their completeness relations

The explicit expressions for generalized q-deformed harmonic oscillator coherent states (q-DHO CS) obtained in terms of a weak- and strong-behavior expansions are investigated. We first employ the weak-deformed version () of q-boson annihilation operator to solve Barut-Girardello’s eigenvalues coherent states equation for generalized q-deformed harmonic oscillator, using for this some lemmas directly related to the resolution of Riccati differential equation. The similarity with the perturbation theory is established. In strong-behavior limit, (), the previous results are resumed using the variational perturbation theory, and the corresponding q-DHO CS are deduced. We also construct, in both limits, their associated completeness relations which turns out to be the elliptic Jacobi -function.

Ultrafast dynamics of exciton–polariton in optically tailored potential landscapes at room temperature

In this work, by using femtosecond angle-resolved spectroscopic imaging technique, the ultrafast dynamics of confined exciton–polaritons in an optical induced potential well based on a ZnO whispering-gallery microcavity is explicitly visualized. The sub-picosecond transition between succeeding quantum harmonic oscillator states can be experimentally distinguished. The landscape of the potential well can be modified by the pump power, the spatial distance and the time delay of the two input laser pulses. Clarifying the underlying mechanism of the polariton harmonic oscillator is interesting for the applications of polariton-based optoelectronic devices and quantum information processing.