Nonlinear Mode Research Articles

B-ROS re-balanced learning method for PS-A-RoF FWA communication

The enhanced remote area communication (eRAC) scenario is an important growth point in the communication market. In some remote areas where optical fiber access cannot be realized or the laying cost is too high, fixed wireless access (FWA) is an appropriate supplementary solution for eRAC. Adopting analog radio over fiber (A-RoF) technology to implement FWA can overcome the bandwidth limitation of electronic devices and realize high-frequency carrier communication economically to achieve high-capacity wireless communication. Also, probabilistic shaping (PS) technology can be combined with A-RoF to further improve the flexibility of the network and coverage of service provision. However, in the PS-A-RoF network, the high RF power introduces more undesired nonlinear effects into the network, and it is often necessary to deploy supervised machine learning (ML) compensation modules in wireless receivers (WRs). But the module performances are affected by the uneven probability distribution of PS-QAM constellation points. In this paper, we employ the PS-A-RoF nonlinear model to theoretically investigate the correlation between the distribution of training symbols and the wireless A-RoF system’s performance. Our analysis reveals that reducing the variance of training symbol power contributes to a lower BER in the A-RoF network. We introduce a borderline random over-sampling (B-ROS) that matches with the PS-A-RoF nonlinear model, instead of the mainstream ROS, which is only at the data level. Based on the B-ROS scheme, only the minority examples below the borderline are over-sampled to reach a better variance performance. Introducing the B-ROS method into the supervised complex value nonlinear compensation module can further improve the decision accuracy of WRs with the restoration of phase information, without increasing additional computational resource consumption. The vector noise power, training symbol power variance, and noise factor metrics have been calculated to optimize the borderline value of our ML-based approach. We also present experimental data on the proof-of-concept A-RoF experiment for PS-64QAM. The results demonstrate a promising nonlinear compensation performance of the B-ROS WR, and the optimal borderline agrees well with the one deduced from the theoretical model under certain transmission conditions. Our proposed B-ROS scheme lessens the training size demand and can improve the receiver sensitivity by 0.51 dB compared to the common ML-based WR and by 0.7 dB compared to the conventional ROS scheme.

Magnetization reversal and domain wall pinning in nanowires with nonlinear modulation of diameter

Micromagnetic simulation of magnetization reversal is studied on cylindrical tapered nanowire with radii 50nm and 10nm at wider and narrower end respectively. The radius decreases from wider end to the narrower end non-linearly as R-βzδ where δ is the degree of non-linearity. Value of δ is either an integer (n) or reciprocal of integer (1/n). At remanence, a vortex and flower state at the wider and narrower extremes respectively are exhibited combined with ferromagnetic ordering in the majority of volume. When δ is below 1/2, pinning and depinning of domain wall drives the hysteresis following a Modified Kondorsky model. Otherwise, the magnetization reversal proceeds with nucleation and propagation of vortex domain wall according to Kondorsky model. The propagation of domain wall is dependent upon the value of δ which suggests tunability of magnetic characteristics with modulation of diameter. For instance, large values of coercivity is observed for wires that have strong domain wall pinning which is considerably reduced when depinning and propagation of domain wall takes over. A large range (20kA/m to 130kA/m) of coercivity can be obtained by changing the modulation.

Unified nonlinear dynamic model for shells of revolution with arbitrary shaped meridians

The geometric design plays a significant role in achieving lightweight and high strength for spacecraft and aircraft fuselages. By introducing the general formulas for the curvature and Lamé coefficients in cylindrical coordinates, this work develops a unified nonlinear dynamic model for the shell of revolution with an arbitrary meridian. Based on Love’s theory with the von Kármán nonlinearity and the variational method, a system of high-dimensional nonlinear equations describing the motions of the shell of revolution is formulated. Subsequently, the natural frequencies are analyzed, and the nonlinear periodic responses are obtained with the harmonic balance method and the arc-length continuation technique. The effectiveness of the developed model has been verified by comparing with the available results in the literature and FEM. The numerical results demonstrate the crucial role of the shell meridian in determining dynamic responses. Furthermore, the results indicate that the natural frequencies of shells can be designed by meridian modifications without significant volume change. Meanwhile, the nonlinear mode coupling, which amplifies the response complexity, can be avoided. This feature facilitates the attainment of controllable response amplitude in the shell of revolution. The developed model offers an intuitive method to achieve high shell stiffness while minimizing mass by optimizing the meridian geometry.

Research on renewable energy power demand forecasting method based on IWOA-SA-BILSTM modeling

This paper introduces a novel coupling method to enhance the precision of short- and medium-term renewable energy power load demand forecasting. Firstly, the Tent chaotic mapping incorporates the standard WOA and modifies its internal convergence factor to a nonlinear convergence mode, resulting in an improved IWOA. It is used for the weight optimization part of BILSTM. Then, the SA is introduced to optimize the learning rate, the number of nodes in hidden layers 1 and 2, and the number of iterations of BILSTM, constructing an IWOA-SA-BILSTM prediction model. Finally, through case analysis, the prediction model proposed in this paper has the highest improvement of 76.7%, 74.5%, and 45.9% in terms of Mean Absolute Error, Root Mean Square Error, and R2, respectively, compared to other optimal benchmark models, proving the effectiveness of the model.

Non-linear modes of global sea surface temperature variability and their relationships with global precipitation and temperature

Sea surface temperature (SST) modes are comprised of variability that arises from inherently nonlinear processes. Historically, a limitation arises from applying linear statistics to define these modes. Accurate depiction of the complex, non-linear nature of SST modes of variability necessitates the specification of a model capable of producing nonlinear patterns. In this study, we apply an artificial neural network algorithm integrated with autoencoders to analyze the seasonal non-linear global SST modes allowing for improved characterization of the modes and their large-scale temperature and precipitation teleconnections. Our results show that during boreal summer, SST cooling over the central to eastern tropical Pacific co-occurs with the Arctic amplification. In recent decades, the negative SST trend in the central to eastern tropical Pacific, combined with the positive trend in the western tropical Pacific is linked to an increase in the amplitude of SST modes associated with the Arctic warming, resulting in warmer temperatures over large portions of the global land, particularly over Greenland. In boreal winter, El Niño Southern Oscillation (ENSO) is the prominent global SST mode. The distinct spatiotemporal patterns of ENSO modes are associated with unique effects on regional land temperature and precipitation. The central Pacific El Niño is more associated with the combination of warm and dry conditions over Western Australia, and the northern part of South America. Conversely, the central to eastern El Niño is more associated with the combination of warm and dry conditions over parts of Southern Africa, and the northern part of South America. The spatiotemporal patterns and trends in the amplitude of the analyzed non-linear global SST modes alongside their regional influences on temperature and precipitation are discussed. The broader impact of this study is on the potential of neural networks in effectively delineating non-linear global SST modes and their associations with regional climates.

Interfacial Charge Transfer for Enhancing Nonlinear Saturable Absorption in WS2/graphene Heterostructure.

Interlayer charge-transfer (CT) in 2D atomically thin vertical stacks heterostructures offers an unparalleled new approach to regulation of device performance in optoelectronic and photonics applications. Despite the fact that the saturable absorption (SA) in 2D heterostructures involves highly efficient optical modulation in the space and time domain, the lack of explicit SA regulation mechanism at the nanoscale prevents this feature from realizing nanophotonic modulation. Here, the enhancement of SA response via CT in WS2/graphene vertical heterostructure is proposed and the related mechanism is demonstrated through simulations and experiments. Leveraging this mechanism, CT-induced SA enhancement can be expanded to a wide range of nonlinear optical modulation applications for 2D materials. The results suggest that CT between 2D heterostructures enables efficient nonlinear optical response regulation.

Delocalized nonlinear vibrational modes and discrete breathers in β-FPUT simple cubic lattice.

The problem of finding various discrete breathers (DBs) in the β-Fermi-Pasta-Ulam-Tsingou simple cubic lattice is addressed. DBs are obtained by imposing localizing functions on delocalized nonlinear vibrational modes (DNVMs) having frequencies above the phonon spectrum of the lattice. Among 27 DNVMs with the wave vector at the boundary of the first Brillouin zone there are three satisfying this condition. Seven robust DBs of different symmetries are found using this approach.

Application of synchro spline-kernelled chirplet transformation in nonlinear ultrasonic wave modulation: self-sensing method with temperature protection

The purpose of this work is to investigate the synchro spline-kernelled chirplet extracting transformation (SSCET) method for defect detection in the nonlinear ultrasonic wave modulation (NUWM) method. To implement the NUWM method using only one piezoelectric transducer, the self-sensing method is used. Self-sensing has many advantages, but it is sensitive to temperature changes. To reduce the temperature effects, a novel circuit has been designed and implemented. A sandwich beam with bolt loosening and an aluminum beam with boundary loosening damages are used to test the results of the SSCET method on the signal received from the self-sensing circuit. First, an aluminum beam with a loosened boundary is modeled based on beam theory including self-sensing circuits with temperature effects. In this study, SSCET results are compared with those of other time–frequency methods for the detection of the loosened boundary. Based on the temperature effects, the theoretical results are compared with the experimental results of the circuit. To quantify defect detection, a damage index calculated based on instantaneous frequency is provided. Three piezoelectric configurations are also compared with the self-sensing method damage index results. SSCET is then used to check bolt loosening in a sandwich beam for further investigation. The proposed method is compared to a previous self-sensing temperature compensation method. Based on the SSCET method, the severity of the bolt loosening is determined.

Nonlinear frequency modulation for Fourier transform ion mobility mass spectrometry improves experimental efficiency

Through optimization of terminal frequencies and effective sampling rates, we have developed nonlinear sawtooth-shaped frequency sweeps for efficient Fourier transform ion mobility mass spectrometry (FT-IM-MS) experiments. This is in contrast to conventional FT-IM-MS experiments where ion gates are modulated according to a linear frequency sweep. Linear frequency sweeps are effective but can be hindered by the amount of useful signal obtained using a single sweep over a large frequency range imposed by ion gating inefficiencies, particularly small ion packets, and gate depletion. These negative factors are direct consequences of the inherently low gate pulse widths of high-frequency ion gating events, placing an upper bound on FT-IM-MS performance. Here, we report alternative ion modulation strategies. Sawtooth frequency sweeps may be constructed for the purpose of either extending high-SNR transients or conducting efficient signal-averaging experiments for low-SNR transients. The data obtained using this approach show high-SNR signals for a set of low-mass tetraalkylammonium salts (<1000 m/z) where resolving powers in excess of 500 are achieved. Data for low-SNR obtained for multimeric protein complexes streptavidin (53 kDa) and GroEL (800 kDa) also reveal large increases in the signal-to-noise ratio for reconstructed arrival time distributions.

New dynamical analysis of the exact traveling wave solutions to a (3+1)-dimensional Gardner-KP equation by three efficient architecture

In this research article, the (3 + 1) dimensional nonlinear Gardner- Kadomtsov–Petviashvili (Gardner-KP) equation, demonstrating the nonlinear modulation of periodic waves, has been analyzed using G′G, G′G2, and the generalized improved G′G methods and a large number of traveling wave solutions have been generated. These solutions exhibit structures with physical properties of hyperbolic, trigonometric, and rational solution types. Numerical simulations were performed for the obtained solutions at different values of the parameters. The stability property of the obtained solutions was tested to demonstrate their reliability. Our novelty in this study lies in obtaining distinct and enriched solutions compared to existing literature, conducting a comparative analysis of three methods, and investigating the stability property of solutions for the Gardner-KP equation, which has not been explored in the existing literature.

Infinite $\mathrm{T\bar T}$-like symmetries of compactified LST

We show that the three-dimensional asymptotically linear dilaton background that arises in the near-horizon decoupling region of NS5-branes compactified on T^4T4 admits boundary conditions that lead to an infinite set of symmetries. The associated conserved charges, which implement field-dependent coordinate transformations, are found to be identical to the corresponding generators in a symmetric product orbifold of T\bar TTT‾ - deformed CFTs. Their algebra is a non-linear modification of the Virasoro × Virasoro algebra, which precisely coincides with the algebra of the “unrescaled” symmetry generators in T\bar TTT‾-deformed CFTs. This further strengthens a previously proposed link between the single-trace T\bar TTT‾ deformation and compactified little string theory.

Weakly nonlinear modulation of interfacial gravity-capillary waves

Weakly nonlinear modulation of interfacial gravity-capillary waves

Adaptive sparse estimation of nonlinear chirp signals using Laplace priors.

The identification of nonlinear chirp signals has attracted notable attention in the recent literature, including estimators such as the variational mode decomposition and the nonlinear chirp mode estimator. However, most presented methods fail to process signals with close frequency intervals or depend on user-determined parameters that are often non-trivial to select optimally. In this work, we propose a fully adaptive method, termed the adaptive nonlinear chirp mode estimation. The method decomposes a combined nonlinear chirp signal into its principal modes, accurately representing each mode's time-frequency representation simultaneously. Exploiting the sparsity of the instantaneous amplitudes, the proposed method can produce estimates that are smooth in the sense of being piecewise linear. Furthermore, we analyze the decomposition problem from a Bayesian perspective, using hierarchical Laplace priors to form an efficient implementation, allowing for a fully automatic parameter selection. Numerical simulations and experimental data analysis show the effectiveness and advantages of the proposed method. Notably, the algorithm is found to yield reliable estimates even when encountering signals with crossed modes. The method's practical potential is illustrated on a whale whistle signal.

Nonlinear regimes of spin wave propagation in a waveguide with a one-dimensional hole array

Purpose. Investigation of spin-wave signal passage in a system of magnetic microwaves separated from each other by a one-dimensional array of holes. Using numerical and experimental methods to show controlled spatial-frequency selection of the signal in linear and nonlinear modes of operation. Methods. Micromagnetic modeling of the spatial intensity distributions of spin waves. Obtaining S-parameters of spin waves propagating in a tangentially magnetized structure using a vector circuit analyzer. Results. The spatially selective properties of the structure in linear and nonlinear modes are demonstrated using micromagnetic modeling. A mechanism for controlling the frequency range of the Bragg zone is revealed using a vector analyzer. Conclusion. The proposed structure can be used as a functional element in planar topologies of magnon networks and parallel signal processing devices based on them.

Research Advances on Femtosecond Laser Modulation of Optical Nonlinearity in Crystal Materials (Invited)

Research Advances on Femtosecond Laser Modulation of Optical Nonlinearity in Crystal Materials (Invited)

Сравнительный анализ технических характеристик гидроакустических средств профилирования донного грунта

Provides a comparative analysis of the main technical characteristics of some of the most popular foreign and domestic hydroacoustic means for profiling bottom soil. A number of promising samples are considered for each manufacturer. The comparison included hydroacoustic profilers operating in linear mode, as well as in parametric (nonlinear) mode. Hydroacoustic bottom soil profilers operating using tonal and linear frequency modulated signals are presented. Among the parameters that are of the greatest interest are the frequency of bottom soil probing, profiling depth, working depth, resolution, etc.

Tailoring linear and nonlinear plasmons of metal/MoS2/metal nanostructures.

We investigated the linear and nonlinear response of the localized surface plasmons (LSPs) and surface plasmon polaritons (SPPs) in metal and MoS2 nanostructures. The results show that the response of LSPs and SPPs has an important influence on the energy exchange. SPPs with unique non-radiative characteristics can be used as energy recovery tanks to reuse the radiated energy of LSPs and promote the production of hot carriers. The energy exchange through plasmon modes can promote the transfer of hot electrons in the Au grating, the MoS2 layer, and the metal film. The fundamental field induces the increase of the second harmonic wave by introducing the second-order nonlinear source. In addition, the evolution of the lifetime of linear and nonlinear plasmonic modes is also investigated to study the underlying mechanism of the micro process in the plasmonic-photonic interaction. The plasmonic energy exchanging configuration overcomes the challenge by utilizing hot carriers. It is instructive in terms of improving the linear and nonlinear performance of plasmonic opto-electronic devices.

Selective reflection study of excitation-dependent dipole-dipole interaction in dense rubidium vapour

We conducted a comprehensive study of excitation dependent dipole-dipole interaction in dense rubidium gas using the resonant selective reflection of weak probe radiation from the dielectric-rubidium vapor interface. The excitation was created by the pump laser beam. The study involved exploring a diverse range of pumping radiation intensity and detuning for the number density of the rubidium vapour 2.8 × 1016 cm-3. We have measured experimental selective reflection spectra in both linear and nonlinear pumping modes.

Optimal α-Variable Model-Free Adaptive Barrier Function Fractional Order Nonlinear Sliding Mode Control for Four Area Interconnected Hybrid Power System With Nonlinearities

Optimal α-Variable Model-Free Adaptive Barrier Function Fractional Order Nonlinear Sliding Mode Control for Four Area Interconnected Hybrid Power System With Nonlinearities

A Novel Nonlinear Frequency Scanning SAR Imaging Mode

A Novel Nonlinear Frequency Scanning SAR Imaging Mode