Search Results (223)

Complex phase diagrams are a generic feature of quantum materials that display high-temperature superconductivity. In addition to d-wave superconductivity (or other unconventional states), these phase diagrams typically include various forms of charge-ordered phases, including charge-density waves and/or spin-density waves, as well as electronic nematic states. In most cases, these phases have critical temperatures comparable in magnitude to that of the superconducting state and appear in a “pseudo-gap” regime. In these systems, the high temperature state does not produce a good metal with well-defined quasiparticles but a ”strange metal”. These states typically arise from doping a strongly correlated Mott insulator. With my collaborators, I have identified these behaviors as a problem with “Intertwined Orders”. A pair-density wave is a type of superconducting state that embodies the physics of intertwined orders. Here, I discuss the phenomenology of intertwined orders and the quantum materials that are known to display these behaviors. Full article

This article uses the sailfish outline as an airfoil profile to create a dual vertical-axis water turbine model for capturing wave and tidal current energy. A parametric water turbine model is built with the shape function perturbation and characteristic parameter description methods. Optimized by the multi-island genetic algorithm on the Isight platform, a CNC sample of the optimized model is made. Its torque and pressure are measured in a wind tunnel and compared with CFD numerical analysis results. The results show small differences between the numerical and experimental results. Both indicate that the relevant performance parameters of the turbine improved after optimization. During constant flow velocity measurement, the optimized axial-flow turbine has a pressure increase of 55% and a torque increase of 40%, while for the centrifugal turbine, the pressure increases by 60% and the torque by 12.5%. During constant rotational speed measurement, the axial-flow turbine’s pressure increases by 16.7%, with an unobvious torque increase. The Q-criterion diagram shows more vortices after optimization. This proves the method can quickly and effectively optimize the dual vertical-axis water turbine. Full article

In this research paper, we study symmetry groups, soliton solutions, and the dynamical behavior of the Ivancevic Option Pricing Model (IOPM). First, we find the Lie symmetries of the considered model; next, we use them to determine the corresponding symmetry groups. Then, we attempt to solve IOPM by means of two methods. We provide some wave solutions and give further details of the solution using 2D and 3D graphs. These results are interpreted as important clarifications in financial mathematics and deepen our understanding of the dynamics involved during the pricing of options. Secondly, the quasi-periodic behavior of the two-dimensional dynamical system and its perturbed system are plotted using Python software (Python 3.13.5 version). Various frequencies and amplitudes are considered to confirm the quasi-periodic behavior via the Lyapunov exponent, bifurcation diagram, and multistability analysis. These findings are particularly in consonance with current research that investigates IOPM as a nonlinear wave alternate for normal models and the importance of graphical representations in the understanding of financial derivative dynamics. We, therefore, hope to fill in the gaps in the literature that currently exist about the use of multi-solution methods and their effects on financial modeling through the employment of sophisticated graphical techniques. This will be helpful in discussing matters in the field of financial mathematics and open up new directions of investigation. Full article

This paper investigates the bifurcation dynamics and optical soliton solutions of the integrable quintic Kundu–Eckhaus (QKE) equation with an M-fractional derivative. By adding quintic nonlinearity and higher-order dispersion, this model expands on the nonlinear Schrödinger equation, which makes it especially applicable in explaining the propagation of high-power optical waves in fiber optics. To comprehend the behavior of the connected dynamical system, we categorize its equilibrium points, determine and analyze its Hamiltonian structure, and look at phase diagrams. Moreover, integrating along periodic trajectories yields soliton solutions. We achieve this by using the simplest equation approach and the modified extended Tanh method, which allow for a thorough investigation of soliton structures in the fractional QKE model. The model provides useful implications for reducing internet traffic congestion by including fractional temporal dynamics, which enables directed flow control to avoid bottlenecks. Periodic breather waves, bright and dark kinky periodic waves, periodic lump solitons, brilliant-dark double periodic waves, and multi-kink-shaped waves are among the several soliton solutions that are revealed by the analysis. The establishment of crucial parameter restrictions for soliton existence further demonstrates the usefulness of these solutions in optimizing optical communication systems. The theoretical results are confirmed by numerical simulations, highlighting their importance for practical uses. Full article

The spin wave renormalization processes in two-dimensional van der Waals ferromagnetic monolayers are investigated using an established non-bosonic diagram technique based on the drone-fermion perturbation method. The aim is to evaluate the damping of the long-wavelength spin wave modes at temperatures below the Curie temperature. In addition to the multi-magnon scattering processes, which typically dominate at low temperatures, an additional mechanism is found here that becomes important at elevated temperatures. This spin disorder damping mechanism, which was mainly studied previously in bulk magnetic materials and thicker films, features a spin wave or magnon being scattered by the magnetic disorder that is present when a longitudinal spin component undergoes large thermal fluctuations. The magnetic ordering in the monolayers is stabilized by an out-of-plane single-ion or Ising-type anisotropy, which influences the damping properties. Numerical results are derived for monolayer films of the van der Waals ferromagnet Cr₂Ge₂Te₆. Full article

Multiband and nodal-like superconductivity (SC) with s- + d-wave pairing symmetry have implied that tetragonal iron sulphide (FeS) is a distinctive testbed for exploring unexpected electronic correlations. In particular, the low-moment disordered static magnetism originating from the Fe moment leads to the possibility of the coexistence of magnetic orders (MOs) in the superconducting ground state via the tuning of electronic configurations. Here, guided by density functional theory (DFT) calculations, we found that slightly substitutionally doped chromium (Cr) atoms in tetragonal FeS single crystals can induce both considerable d-orbital reconstruction around the Fermi surface and a local magnetic moment of 2.4 µ_B at each doping site, which could highly modulate the SC ground states of the host. On this basis, a clear magnetic transition and reduced anisotropy of SC were experimentally observed. In particular, SC can survive with a doping content below 0.05. This coexistence of SC and MOs suggests strong spin correlations between Cr dopants and the host through exchange coupling. Further, an electronic temperature-related phase diagram of FeS with Cr doping contents from 0 to 0.07 is also provided. These results demonstrate that the continuous injection of local moments can be a controllable method to use to tune collective orders in unconventional iron-based superconductors. Full article

This article investigates the qualitative analysis and traveling wave solutions of a (3 + 1)-dimensional generalized nonlinear Konopelchenko-Dubrovsky-Kaup-Kupershmidt system. This equation is commonly used to simulate nonlinear wave problems in the fields of fluid mechanics, plasma physics, and nonlinear optics, as well as to transform nonlinear partial differential equations into nonlinear ordinary differential equations through wave transformations. Based on the analysis of planar dynamical systems, a nonlinear ordinary differential equation is transformed into a two-dimensional dynamical system, and the qualitative behavior of the two-dimensional dynamical system and its periodic disturbance system is studied. A two-dimensional phase portrait, three-dimensional phase portrait, sensitivity analysis diagrams, Poincaré section diagrams, and Lyapunov exponent diagrams are provided to illustrate the dynamic behavior of two-dimensional dynamical systems with disturbances. The traveling wave solution of a Konopelchenko-Dubrovsky-Kaup-Kupershmidt system is studied based on the complete discriminant system method, and its three-dimensional, two-dimensional graphs and contour plots are plotted. These works can provide a deeper understanding of the dynamic behavior of Konopelchenko-Dubrovsky-Kaup-Kupershmidt systems and the propagation process of waves. Full article

Background: Absence epilepsy is a non-convulsive form of genetic generalized epilepsy characterized by spontaneous bilateral spike-and-wave discharges (SWDs) in EEG. In contrast to grand-mal epilepsy, absence epilepsy without greatly expressed motor and interictal EEG abnormalities is difficult to detect, especially at the early stages. The WAG/Rij rat strain is a well-validated animal model of childhood absence epilepsy. At the early, preclinical stage, precursors or immature SWDs appear. Then, with age, immature discharges gradually turn into mature ones and mature SWDs prevail at the clinical stage. Mature SWDs, with an amplitude several times higher than the background EEG, can be easily distinguished visually. However, the amplitude of immature discharges is significantly lower than that of mature SWDs and is comparable to the amplitude of sleep spindles. Therefore, it is quite a difficult problem to distinguish immature discharges from sleep spindles. The task is further complicated by the fact that absence seizures mainly appear in a state of drowsiness and slow-wave (non-REM) sleep, when a lot of sleep spindles occur. The purpose of the present study was to develop a diagnostic method that allows us to precisely distinguish immature forms of epileptic seizures from background EEG and sleep spindles. Methods: The idea of analyzing wave-train electrical activity is to investigate the wavelet spectrum, find local peculiarities in this spectrum, and estimate generalized time-frequency peculiarities of the signal in terms of the found local peculiarities. Results: The criteria for diagnosis of the immature form of epileptic discharges and sleep spindles have been developed based on the analysis of wave-train activity with the construction of AUC diagrams (area under the curve diagrams). Conclusions: The method of wave-train analysis with the construction of AUC diagrams can be used for extracting the diagnostic features necessary for the diagnosis of absence epilepsy at the early stages of the disease in people with a genetic predisposition. Full article

Ship operability diagrams are commonly defined based on the seakeeping analysis, showing which course and speed can safely be taken at the sea state to satisfy pre-defined seakeeping limiting values. Although ship operability diagrams are inherently probabilistic, because of the random nature of the environmental loads, their outcome is deterministic, showing if the seakeeping criteria are satisfied or not for a certain combination of environmental and operational parameters. In the present study, uncertainties in seakeeping predictions and limiting values, which are usually neglected, are integrated into the ship operability analysis. This results in probabilistic operability diagrams, where the seakeeping criteria are exceeded with certain probabilities. The approach is demonstrated in the example of the passenger ship on a route in the Adriatic Sea. Semi-analytical closed-form expressions are used for seakeeping analysis, while limiting values for vertical bow acceleration, pitch, slamming, roll, and propeller emergence are analyzed. The second-order reliability method is used to calculate probabilities of the exceedance of the seakeeping criteria, and the results are presented as probabilistic operability diagrams. The method enables the determination of a new probabilistic operability index applicable to the ship design and represents a prerequisite for risk-based decision making in ship operation. It is also presented how the method can be validated for the existing shipping route using numerical wave databases. Full article

The precoder obtained using the traditional singular value decomposition (SVD) method for legitimate user’s channel, while achieving the highest spectral efficiency for the legitimate user, cannot defend against eavesdropping attacks, thus posing a security vulnerability. This paper investigates the millimeter wave (mmWave) secure beam hybrid precoding technology and proposes a generalized singular value decomposition (GSVD)-based secure beam hybrid precoding algorithm, termed GSVD-Sparsity, leveraging the sparsity of the mmWave beamspace channel. The algorithm selects the most powerful paths from the legitimate user’s beamspace channel representation and utilizes their corresponding angle information to construct a radio frequency (RF) precoder. It then constructs a hybrid precoder that closely approximates the optimal digital precoder derived from the GSVD-based scheme in a fully digital system. The simulation results indicate that, compared to the SVD-based scheme that focuses on spectral efficiency, the GSVD-based precoding scheme can form secure beams in a fully digital system. Under the condition that the legitimate user experiences a certain loss in the received signal-to-noise ratio (SNR), the eavesdropper is unable to correctly reconstruct the original constellation diagram, ensuring the scheme has strong anti-eavesdropping capabilities. In a hybrid precoding system, the low-complexity GSVD-Sparsity algorithm can achieve a spectral efficiency close to that of the GSVD-based scheme in a fully digital system while maintaining anti-eavesdropping capabilities. Full article

We propose a wide field-of-view (FOV) refractive and meta-optics hybrid imaging system designed for the mid-wave infrared spectrum (3–5 μm) to address the challenge of high-quality imaging in wide FOV applications. The system consists of only three refractive lenses and two metasurfaces (one functioning as a circular polarizer and the other as a phase element), with a total length of 29 mm. Through a detailed analysis of modulation transfer function curves and spot diagrams, the system achieves 178° FOV while maintaining exceptional imaging performance across a temperature range of −40 °C to 60 °C. The system demonstrates the potential for extending applications to other wavelengths and scenarios, thereby contributing to the advancement of high-performance compact optical systems. Full article

When two axisymmetric stress waves of the same strength propagate radially at the same velocity, the stress wave wavefronts collide and interact along a specific locus, which is the perpendicular bisector between the two sources. The maximum principal stress occurs along this perpendicular bisector, and the tensile stresses result in crack bridging between the two source points. This symmetric wave propagation behavior allows us to use the Voronoi tessellation diagram and its symmetric dual graph, the Delaunay triangulation, to gain first-order insight into complex wave propagation phenomena for an arbitrary distribution of wave propagation sources. The inherent symmetry of these simultaneous wave propagation mechanics allows us to rapidly visualize and predict the stress wave propagation and interactions, and the resultant crack bridging patterns that arise from random blast sources. The current work is focused on rock blast fracture mechanics, but the visualization scheme can be implemented for any application where waves propagate axisymmetrically and interact. Full article

Focusing on an energy-saving winch-type heave compensation system applicable to real working conditions, with the objective of enhancing compensation accuracy, a wavelet neural network was employed for platform velocity prediction, and the prediction results were applied to velocity disturbance compensation control. Initially, the ITTC two-parameter spectrum was utilized to generate wave spectral diagrams under different sea conditions, along with displacement and velocity data of the floating platform’s heave motion. Subsequently, a time-series-based wavelet neural network velocity prediction model was developed, trained, and tested. Comparative analyses were performed on prediction performance differences across varying prediction steps and sea condition levels. Then, the effectiveness of the time-series-based wavelet neural network prediction model was validated through a valve-controlled hydraulic cylinder heave motion simulation system. Experimental results indicated that the wavelet neural network-based velocity prediction method effectively improved the compensation accuracy of the winch-type heave compensation system. Finally, after verifying the effectiveness of the wavelet neural network prediction model based on time series, the compensation performance of the system after adding the velocity prediction module was tested and verified using the winch-type heave compensation simulation test bench built by the research team. After experimental verification, after adding velocity prediction, the compensation accuracy of the system was improved by 19% compared with that without velocity prediction. Full article

Ta₂AlC is an emerging ceramic material characterized by its high melting point, high hardness, excellent thermal stability, and superior mechanical properties, which allow for broad application prospects in aerospace and defense fields. This paper investigates the physical mechanisms underlying the modulation of the mechanical and photoelectric properties of Ta₂AlC through doping using the first-principles pseudopotential plane-wave method. We specifically calculated the geometric structure, mechanical properties, electronic structure, Mulliken population analysis, and optical properties of Ta₂AlC doped with V, Ga, or Si. The results indicate that doping induces significant changes in the structural parameters of Ta₂AlC. By applying the Born’s criterion as the standard for mechanical stability, we have calculated that the structures of Ta₂AlC, both before and after doping, are stable. The mechanical property calculations revealed that V and Si doping weaken the material’s resistance to deformation while enhancing its plasticity. In contrast, Ga doping increases the material’s resistance to lateral deformation and brittleness. Doping also increases the anisotropy of Ta₂AlC. Electronic structure calculations confirmed that Ta₂AlC is a conductor with excellent electrical conductivity, which is not diminished by doping. The symmetric distribution of spin-up and spin-down electronic state densities indicates that the Ta₂AlC system remains non-magnetic after doping. The partial density of states diagrams successfully elucidated the influence of dopant atoms on the band structure and electronic state density. Mulliken population analysis revealed that V and Ga doping enhance the covalent interactions between C-Ta and Al-Ta atoms, whereas Si doping weakens these interactions. Optical property calculations showed that V and Si doping significantly enhance the electromagnetic energy storage capacity and dielectric loss of Ta₂AlC, while Ga doping has minimal effect. The reflectivity of doped and undoped Ta₂AlC reaches over 90% in the ultraviolet region, indicating its potential as an anti-ultraviolet coating material. In the visible light region, both doped and undoped Ta₂AlC exhibit a similar metallic gray appearance, suggesting its potential as a temperature control coating material. The light loss of Ta₂AlC is limited to a narrow energy range, indicating that doping does not affect its use as a light storage material. These results demonstrate that different dopants can effectively modulate the mechanical and photoelectric properties of Ta₂AlC. Full article

This paper presents a new methodology for localizing impact events on plate-like structures using a proposed two-dimensional convolutional neural network (CNN) and received impact signals. A network of four piezoelectric wafer active sensors (PWAS) was installed on the tested plate to acquire impact signals. These signals consisted of reflection waves that provided valuable information about impact events. In this methodology, each of the received signals was divided into several equal segments. Then, a wavelet transform (WT)-based time-frequency analysis was used for processing each segment signal. The generated WT diagrams of these segments’ signals were cropped and resized using MATLAB code to be used as input image datasets to train, validate, and test the proposed CNN model. Two scenarios were adopted from PAWS transducers. First, two sensors were positioned in two corners of the plate, while, in the second scenario, four sensors were used to monitor and collect the signals. Eight datasets were collected and reshaped from these two scenarios. These datasets presented the signals of two, three, four, and five impacts. The model’s performance was evaluated using four metrics: confusion matrix, accuracy, precision, and F1 score. The proposed model demonstrated exceptional performance by accurately localizing all of the impact points of the first scenario and 99% of the second scenario. The main limitation of the proposed model is how to differentiate the data samples that have similar features. From our point of view, the similarity challenge arose from two factors: the segmentation interval and the impact distance. First, applying the segmenting procedure to the PWAS signals led to an increase in the number of data samples. The procedure segmented each PWAS signal to 30 samples with equal intervals, regardless of the features of the signal. Segmenting and transforming different PWAS signals into image-based data points led to data samples that had similar features. Second, some of the impacts had a close distance to the PWAS sensors, which resulted in similar segmented signals. Therefore, the second scenario was more challenging for the proposed model. Full article