Search Results (202)

Electroencephalography (EEG) helps to assess the electrical activities of the brain so that the neuronal activities of the brain are captured effectively. EEG is used to analyze many neurological disorders, as it serves as a low-cost equipment. To diagnose and treat every neurological disorder, lengthy EEG signals are needed, and different machine learning and deep learning techniques have been developed so that the EEG signals could be classified automatically. In this work, five ensemble models are proposed for EEG signal classification, and the main neurological disorder analyzed in this paper is epilepsy. The first proposed ensemble technique utilizes an equidistant assessment and ranking determination mode with the proposed Enhance the Sum of Connection and Distance (ESCD)-based feature selection technique for the classification of EEG signals; the second proposed ensemble technique utilizes the concept of Infinite Independent Component Analysis (I-ICA) and multiple classifiers with majority voting concept; the third proposed ensemble technique utilizes the concept of Genetic Algorithm (GA)-based feature selection technique and bagging Support Vector Machine (SVM)-based classification model. The fourth proposed ensemble technique utilizes the concept of Hilbert Huang Transform (HHT) and multiple classifiers with GA-based multiparameter optimization, and the fifth proposed ensemble technique utilizes the concept of Factor analysis with Ensemble layer K nearest neighbor (KNN) classifier. The best results are obtained when the Ensemble hybrid model using the equidistant assessment and ranking determination method with the proposed ESCD-based feature selection technique and Support Vector Machine (SVM) classifier is utilized, achieving a classification accuracy of 89.98%. Full article

A spatial problem of elasticity theory is solved for a layer located on two bearings embedded in it. The bearings are represented as thick-walled pipes embedded in the layer parallel to its boundaries. The pipes are rigidly connected to the layer, and contact-type conditions (normal displacements and tangential stresses) are specified on the insides of the pipes. Stresses are set on the flat surfaces of the layer. The objective of this study is to obtain the stress–strain state of the body of the layer under different geometric characteristics of the model. The solution to the problem is presented in the form of the Lamé equation, whose terms are written in different coordinate systems. The generalized Fourier method is used to transfer the basic solutions between coordinate systems. By satisfying the boundary and conjugation conditions, the problem is reduced to a system of infinite linear algebraic equations of the second kind, to which the reduction method is applied. After finding the unknowns, using the generalized Fourier method, it is possible to find the stress–strain state at any point of the body. The numerical study of the stress state showed high convergence of the approximate solutions to the exact one. The stress–strain state of the composite body was analyzed for different geometric parameters and different pipe materials. The results obtained can be used for the preliminary determination of the geometric parameters of the model and the materials of the joints. The proposed solution method can be used not only to calculate the stress state of bearing joints, but also of bushings (under specified conditions of rigid contact without friction on the internal surfaces). Full article

A novel and efficient modeling approach has been developed for simulating the responses of triaxial induction logging (TIL) in layered biaxial anisotropic (BA) formations. The core of this innovative technique lies in analytically calculating the primary fields within a homogeneous medium and approximating the scattered fields within layered formations. The former involves employing a two-level subtraction technique. Initially, the first-level subtraction entails altering the direction of the Fourier transform to mitigate the integral singularity of the spectral fields, particularly in high-angle and horizontal wells. Conversely, the second-level subtraction aims to further optimize integral convergence by creating an equivalent unbounded transverse isotropic (TI) formation and eliminating the corresponding spectral fields. With the two-level subtractions, the convergence of the spectral field has been enhanced by more than six orders of magnitude. Additionally, a strict recursive algorithm and approximation method are developed to compute the scattered fields in layered biaxial anisotropic media. The rigorous algorithm is based on a modified amplitude propagator matrix (MAPM) approach and serves as the benchmark for the approximation method. In contrast, the approximation method exploits the similarity between the spectral scattered field of the TI medium and the BA medium, establishing corresponding equivalent layered TI models for each magnetic component. Since the scattered field in TI models only involves a one-dimensional semi-infinite integral, the computational complexity is significantly reduced. Numerical simulation examples demonstrate that the new simulation method is at least two orders of magnitude faster than the current modeling approach while maintaining computational precision error within 0.5%. This significantly improved simulation efficiency provides a solid foundation for expediting the logging data processing. Full article

In this paper, a multi-transmitting formula (MTF) was integrated into ANSYS software through secondary development, enabling dynamic finite element simulation of wave propagation in infinite domains. The numerical reliability and accuracy of the MTF were verified through a plane wave problem involving a homogeneous elastic half-space, as well as 3D scattering and source problems in a three-layered soil site. Additionally, a comparative analysis of various artificial boundaries was conducted to highlight the advantages of the MTF. Field observations of environmental vibrations caused by high-speed railway operations revealed localized amplification of vibrations along the depth direction at the Kunshan segment of the Beijing–Shanghai high-speed railway. Based on these observations, a series of numerical analyses were conducted using the customized ANSYS integrated with the MTF to investigate the underlying causes and mechanisms of this phenomenon, as well as the spatial variation characteristics of foundation vibrations induced by bridge vibrations during high-speed train operations. This study reveals the mechanism by which the combined effect of bridge piles and soft soil layers influences the depth variation in peak ground accelerations during site vibrations. It also demonstrates that the presence of bridge piers and pile foundations effectively reduces vibration intensity in the vicinity of the railway, playing a crucial role in mitigating vibrations induced by high-speed train operations. Full article

This study develops a one-dimensional analytical solution for contaminant advection, diffusion and adsorption through a soil–bentonite (SB)/geosynthetic clay liner (GCL)/SB–aquifer composite cutoff wall (CCW) system. The solution agrees well with an existing double-layer model. Adopting toluene as a representative contaminant, using the present solution, the analysis systematically investigates the impact of hydraulic gradient (i) and the hydraulic conductivities of GCL (k_gcl) and SB (k_sb). The results show the following: (1) Increasing i from 0.1 to 1 reduces the concentration breakthrough time (t_cb) from 20 to 11 years and mass flux breakthrough time (t_fb) from infinite to 11 years, indicating lower i significantly extend both t_cb and t_fb, which is crucial for optimizing CCW barrier performance; (2) lowering k_gcl from 5.0 × 10⁻¹¹ m/s to 1 × 10⁻¹² m/s and reducing k_sb from 1.0 × 10⁻⁹ m/s to 1.0 × 10⁻¹¹ m/s, would increase the t_cb by 36% and 100%, respectively. It demonstrates that reducing k_gcl and k_sb could enhance barrier performance. (3) To achieve equivalent barrier performance, soil–bentonite cutoff wall (SBCW) requires greater thickness compared to SB/GCL/SB CCW, indicating that GCL reduces the required amount of bentonite; and (4) CCWs can use SB with lower adsorption capacity to achieve equivalent performance, further reducing bentonite requirements. The present solution can aid in the design and optimization of GCL-enhanced CCWs. Full article

The paper presents a novel small-footprint varactor diode-based reconfigurable reflectarray (RRA) design and investigates its power reflection efficiency theoretically and experimentally in a real-life indoor environment. The surface is designed to operate at 865.5 MHz and is intended for simultaneous use with other wireless power transfer (WPT) efficiency-improving techniques that have been recently reported in the literature. To the best of the authors’ knowledge, no RRA intended to improve the performance of antenna-based WPT systems operating in the sub-GHz range has been designed and studied both theoretically and experimentally so far. The proposed RRA is a two-layer structure. The top layer contains electronically tunable phase shifters for the local phase control of an incoming electromagnetic wave, while the other one is fully covered by metal to reduce the phase shifter size and RRA’s backscattering. Each phase shifter is a pair of diode-loaded 8-shaped metallic patches. Extensive numerical studies are conducted to ascertain a suitable set of RRA unit cell parameters that ensure both adequate phase agility and reflection uniformity for a given varactor parameter. The RRA design parameter finding procedure followed in this paper comprises several steps. First, the phase and amplitude responses of a virtual infinite double periodic RRA are computed using full-wave solver Ansys HFSS. Once the design parameters are found for a given set of physical constraints, the phase curve of the corresponding finite array is retrieved to estimate the side lobe level due to the finiteness of the RRA aperture. Then, a diode reactance combination is found for several different RRA reflection angles, and the corresponding RRA radiation pattern is computed. The numerical results show that the side lobe level and the deviation of the peak reflected power angles from the desired ones are more sensitive to the reflection coefficient magnitude uniformity than to the phase agility. Furthermore, it is found that for scanning angles less than 50°, satisfactory reflection efficiency can be achieved by using the classical reactance profile synthesis approach employing the generalized geometrical optics (GGO) approximation, which is in accord with the findings of other studies. Additionally, for large reflection angles, an alternative synthesis approach relying on the Floquet mode amplitude optimization is utilized to verify the maximum achievable efficiency of the proposed RRA at large angles. A prototype consisting of 36 elements is fabricated and measured to verify the proposed reflectarray design experimentally. The initial diode voltage combination is found by applying the GGO-based phase profile synthesis method to the experimentally obtained phase curve. Then, the voltage combination is optimized in real time based on power measurement. Finally, the radiation pattern of the prototype is acquired using a pair of identical 4-director printed Yagi antennas with a gain of 9.17 dBi and compared with the simulated. The calculated results are consistent with the measured ones. However, some discrepancies attributed to the adverse effects of biasing lines are observed. Full article

The layered orthorhombic quaternary tellurides EuRECuTe₃ (RE = Ho, Tm, Sc) with Cmcm symmetry were first synthesized. Single crystals of the compounds up to 500 μm in size were obtained by the halide-flux method at 1120 K from elements taken in a ratio of Eu/RE/Cu/Te = 1:1:1:3. In the series of compounds, the changes in lattice parameters were in the ranges a = 4.3129(3)–4.2341(3) Å, b = 14.3150(9)–14.1562(9) Å, c = 11.2312(7)–10.8698(7) Å, V = 693.40(8)–651.52(7) ų. In the structures, the cations Eu²⁺, RE³⁺ (RE = Ho, Tm, Sc), and Cu⁺ occupied independent crystallographic positions. The structures were built with distorted copper tetrahedra forming infinite chains [CuTe₄]⁷⁻ and octahedra [RETe₆]⁹⁻ forming two-dimensional layers along the a-axis. These coordination polyhedra formed parallel two-dimensional layers ${}_{\infty }{}^2\left\{{\left[\mathrm{C}\mathrm{u}RE{\mathrm{T}\mathrm{e}}_3\right]}^{2-}\right\}$. Between the layers, along the a-axis, chains of europium trigonal prisms [EuTe₆]¹⁰⁻ were located. Regularities in the variation of structural parameters and the degree of distortion of coordination polyhedra depending on the ionic radius of the rare-earth metal in the compounds EuRECuCh₃ (RE = Ho, Er, Tm, Lu, Sc; Ch = S, Se, Te) were established. It is shown that with a decrease in the ionic radius r_i(RE³⁺) in the compounds EuRECuTe₃, the unit-cell volume, bond length d(RE–Te), distortion degree [CuTe₄]⁷⁻, and crystallographic compression of layers [RECuTe₃]²⁻ decreased. The distortion degree of tetrahedral polyhedra [CuCh₄]⁷⁻, as well as the structural parameters in europium rare-earth copper tellurides EuRECuTe₃, were higher than in isostructural quaternary chalcogenides. Ab initio calculations of the crystalline structure, phonon spectrum, and elastic properties of compounds EuRECuTe₃ (RE = Ho, Tm, and Sc) ere conducted. The types and wave numbers of fundamental modes were determined, and the involvement of ions in IR and Raman modes was assessed. The calculated data of the crystal structure correlated well with the experimental results. Full article

Potassium-ion batteries (PIBs) have been widely studied owing to the abundant reserves, widespread distribution, and easy extraction of potassium (K) resources. Molybdenum disulfide (MoS₂) has received a great deal of attention as a key anode material for PIBs owing to its two-dimensional diffusion channels for K⁺ ions. However, due to its poor electronic conductivity and the huge influence of embedded K⁺ ions (with a large ionic radius of 3.6 Å) on MoS₂ layer, MoS₂ anodes exhibit a poor rate performance and easily collapsed structure. To address these issues, the common strategies are enlarging the interlayer spacing to reduce the mechanical strain and increasing the electronic conductivity by adding conductive agents. However, simultaneous implementation of the above strategies by simple methods is currently still a challenge. Herein, MoS₂ anodes on reduced graphene oxide (MoS₂/rGO) composite were prepared using one-step hydrothermal methods. Owing to the presence of rGO in the synthesis process, MoS₂ possesses a unique scaled structure with large layer spacing, and the intrinsic conductivity of MoS₂ is proved. As a result, MoS₂/rGO composite anodes exhibit a larger rate performance and better cycle stability than that of anodes based on pure MoS₂, and the direct mixtures of MoS₂ and graphene oxide (MoS₂-GO). This work suggests that the composite material of MoS₂/rGO has infinite possibilities as a high-quality anode material for PIBs. Full article

Na_1.36(Si_0.86Ga_0.14)₂As_2.98 and Li_1.5Ga_0.9Si_3.1As₄ were synthesized by heating mixtures of the elements at 950 °C. The crystal structures were determined by single crystal X-ray diffraction (Na_1.36(Si_0.86Ga_0.14)₂As_2.98: I4₁/a, Z = 100, a = 19.8772(4) Å, c = 37.652(1) Å; Li_1.5Ga_0.9Si_3.1As₄: C2/c, Z = 8, a = 10.8838(6) Å, b = 10.8821(6) Å, c = 13.1591(7) Å). Na_1.36(Si_0.86Ga_0.14)₂As_2.98 crystallizes similar to NaSi₂P₃ with interpenetrating networks of vertex-sharing T4 and T5 supertetrahedra. Gallium substitution at the silicon sites increases the charge of the cluster network, which is compensated for by a 36% higher sodium content. Since in contrast to NaSi₂P₃, all sodium sites are now fully occupied, there is no significant ion mobility, as indicated by ²³Na-NMR. Consequently, the total sodium-ion conductivity of Na_1.36(Si_0.86Ga_0.14)₂As_2.98 amounts to only 1.6(1) × 10⁻⁷ S cm⁻¹ and is therefore three orders of magnitude lower than in NaSi₂P₃. Li_1.5Ga_0.9Si_3.1As₄ crystallizes in a new structure type with layers of edge-sharing (Si_1−xGa_x)As₄ tetrahedra alternating with layers that contain infinite Si_n zigzag chains. Lithium ions reside in channels between the chains, and thus, the structure does not provide three dimensional pathways for ion conduction and the measured total Li-ion conductivity amounts to only 1.3(1) × 10⁻⁷ S cm⁻¹. Full article

Machines operate under increasingly harsher contact conditions, causing significant wear and contact fatigue. Sub-surface stresses are responsible for the premature contact fatigue of rolling element bearings, meshing gears, and cam–follower pairs. Surface protection measures include hard, wear-resistant coatings. Traditionally, contact integrity has been predicted using classical Hertzian contact mechanics. However, the theory is only applicable when the contact between a pair of ellipsoidal solids of revolution may be considered as a rigid indenter penetrating a semi-infinite elastic half-space. Many coatings act as thin bonded elastic layers that undergo considerably higher pressures than those predicted by the classical theory. Furthermore, inelastic deformation of bonded solids can cause plastic flow, work-hardening, and elastoplastic behaviour. This paper presents a comprehensive, integrated contact mechanics analysis that includes induced sub-surface stresses in concentrated counterformal finite line contacts for all the aforementioned cases. Generated pressures and deformation are predicted for hard coated surfaces, for which there is a dearth of relevant analysis. The contact characteristics, which are of particular practical significance, of many hard, wear-resistant advanced coatings are also studied. The paper clearly demonstrates the importance of using efficient semi-analytical, detailed holistic contact mechanics rather than the classical idealised methods or empirical numerical ones such as FEA. The novel approach presented for the finite line contact of thin-layered bonded solids has not hitherto been reported in the open literature. Full article

With the fast development and miniaturization of acoustic and electric smart devices, micro and nanoscale piezoelectric semiconductor materials are gradually being used to manufacture information communication, energy conversion, and nondestructive testing technologies. As the core components of the above piezoelectric semiconductor devices, homo- and hetero-junctions have an evident influence on the propagation performance of high-frequency and short-wavelength elastic waves inside the bulk piezoelectric semiconductor materials. Based on the Gurtin–Murdoch theory, a theoretical model of interface effect originating from homo- and hetero-junctions is established to investigate the propagation properties of Love waves in a piezoelectric semiconductor semi-infinite medium considering the electrical open circuit (insulation) and short circuit (metalized ground) surface boundary conditions and biasing electric fields. Four interface characteristic lengths are introduced to describe the electrical imperfect interface of homo- and hetero-junctions, which are legitimately confirmed through comparisons of the dispersion and attenuation curves of Love waves. The influence of homo- and hetero-junctions on the dispersion and attenuation characteristics of Love waves are elaborated in detail. Numerical results show that the interface characteristic lengths are independent of the electrical surface boundary conditions, acceptor and donor concentrations, thickness of the upper piezoelectric semiconductor layer, and biasing electric fields in the piezoelectric semiconductor semi-infinite medium. Moreover, the propagation characteristics of Love waves can be manipulated by changing the biasing electric field parallel to the homo- and hetero-junctions. Since the high-frequency and short-wavelength Love wave is an important class of surface acoustic waves propagating in micro- and nano-scale piezoelectric semiconductor materials, the establishment of mathematical models and the revelation of physical mechanisms are fundamental to the analysis and optimization of the above piezoelectric semiconductor devices. Full article

A study concerning the influence of flow on the Herschel–Quincke duct is presented here, which includes the numerical model, the acoustic source and the absorption condition called the Perfectly Matched Layer. For the excitation of a sound field, a normal mode wave is placed at the inlet of the tube. The function of PML is to simulate the infinite tube and avoid the reflection of acoustic wave. To investigate the influence of flow field on sound field, a coupled calculation method combining the finite element method and computational fluid dynamics is used to solve the linearized Euler equation, named the Galbrun equation. Firstly, the influence of the cross-section of the tube on the acoustic field is considered. Secondly, the effects of flow on the acoustic field is also investigated. Lastly, a comparative analysis of the simulation results reveals the influence of flow and other parameters of the tube on sound propagation. Both the Mach number and the cross-section ratio have an influence on the acoustic resonance, and the resonance frequency decreases with the increase in the cross-section ratio. Full article

Numerical seismic wave field simulation is essential for studying the dynamic responses in semi-infinite space, and the absorbing boundary setting is critical for simulation accuracy. This study addresses spherical waves incident from the free boundary by applying dynamic equations and Rayleigh damping. A new multi-directional viscous damping absorbing boundary (MVDB) method is proposed based on regional attenuation. An approximate formula for the damping value is established, which can achieve absorbing the boundary setting by only solving the mass damping coefficients without increasing the absorbing region grid cells or depending on the spatial and temporal walking distance. The validity and stability of the proposed method are proven through numerical calculations with seismic sources incident from different angles. Meanwhile, the key parameters affecting the absorption of the MVDB are analyzed, and the best implementation scheme is provided. In order to meet the requirements of mediums with different elastic parameters for boundary absorption and ensure the high efficiency of numerical calculations, the damping amplitude control coefficients k can be set between 1.02 and 1.12, the thickness of the absorbing region L is set to 2–3 times of the wavelength of the incident transverse wave, and the thickness of the single absorbing layer is set to the size of the discrete mesh of the model Δl. Full article

In this paper, a theoretical model of the propagation of a shear horizontal wave in a piezoelectric semiconductor semi-infinite medium is established using the optimized spectral method. First, the basic equations of the piezoelectric semiconductor semi-infinite medium are derived with the consideration of biased electric fields. Then, considering the propagation of a shear horizontal wave in the piezoelectric semiconductor semi-infinite medium, two equivalent mathematical models are established. In the first mathematical model, the Schottky junction is theoretically treated as an electrically imperfect interface, and an interface characteristic length is utilized to describe the interface effect of the Schottky junction. To legitimately confirm the interface characteristic length, a second mathematical model is established, in which the Schottky junction is theoretically treated as an electrical gradient layer. Finally, the dispersion and attenuation curves of shear horizontal waves are numerically calculated using these two mathematical models to discuss the influence of the Schottky junction on the dispersion and attenuation characteristics of shear horizontal waves. Utilizing the equivalence of these two mathematical models and the above numerical results, the numerical value of the interface characteristic length is reliably legitimately confirmed; this value is independent of the thickness of the upper metal layer, the doping concentration of the lower n-type piezoelectric semiconductor substrate, and biasing electric fields. Only the biasing electric field parallel to the Schottky junction can provide an evident influence on the attenuation characteristics of shear horizontal waves and enhance the interface effect of the Schottky junction. Since the second mathematical model is also a validation of our previous mathematical model established through the state transfer equation method, some numerical results calculated using these two mathematical models are compared with those obtained using the previous method to verify the correctness and superiority of the research work presented in this paper. Since these two mathematical models can better calculate the dispersion and attenuation curves of high-frequency waves in micro- and nano-scale piezoelectric semiconductor materials, the establishment of mathematical models and the revelation of physical mechanisms are fundamental to the analysis and optimization of micro-scale resonators, energy harvesters, and amplifications. Full article

The cis- and trans-isomers of 6-(3-(3,4-dichlorophenyl)-1,2,4-oxadiazol-5-yl)cyclohex-3-ene-1-carboxylic acid (cis-A and trans-A) were obtained by the reaction of 3,4-dichloro-N′-hydroxybenzimidamide and cis-1,2,3,6-tetrahydrophthalic anhydride. Cocrystals of cis-A with appropriate solvents (cis-A‧½(1,2-DCE), cis-A‧½(1,2-DBE), and cis-A‧½C₆H₁₄) were grown from 1,2-dichloroethane (1,2-DCE), 1,2-dibromoethane (1,2-DBE), and a n-hexane/CHCl₃ mixture and then characterized by X-ray crystallography. In their structures, cis-A is self-assembled to give a hybrid 2D supramolecular organic framework (SOF) formed by the cooperative action of O–H⋯O hydrogen bonding, Cl⋯O halogen bonding, and π⋯π stacking. The self-assembled cis-A divides the space between the 2D SOF layers into infinite hollow tunnels incorporating solvent molecules. The energy contribution of each noncovalent interaction to the occurrence of the 2D SOF was verified by several theoretical approaches, including MEP and combined QTAIM and NCIplot analyses. The consideration of the theoretical data proved that hydrogen bonding (approx. −15.2 kcal/mol) is the most important interaction, followed by π⋯π stacking (approx. −11.1 kcal/mol); meanwhile, the contribution of halogen bonding (approx. −3.6 kcal/mol) is the smallest among these interactions. The structure of the isomeric compound trans-A does not exhibit a 2D SOF architecture. It is assembled by the combined action of hydrogen bonding and π⋯π stacking, without the involvement of halogen bonds. A comparison of the cis-A structures with that of trans-A indicated that halogen bonding, although it has the lowest energy in cis-A-based cocrystals, plays a significant role in the crystal design of the hybrid 2D SOF. The majority of the reported porous halogen-bonded organic frameworks were assembled via iodine and bromine-based contacts, while chlorine-based systems—which, in our case, are structure-directing—were unknown before this study. Full article