Theoretical Analysis Research Articles

A comprehensive study of optical resonances in metals, dielectrics, and excitonic materials in double interface structures

From an optical perspective, depending on the relationship between the real (n) and imaginary (k) parts of its refractive index, three broad categories of materials can be distinguished: metals (k ≫ n), dielectrics (n ≫ k), and materials in which n ≈ k (termed here excitonic materials). The modes and optical resonances that appear in a thin film bounded by two dielectrics with similar refractive index, what we call here a double interface structure, have been widely studied in the case of metals, but not for dielectrics, or materials with n ≈ k. In this work, we propose a new approach, based on employing the phase matching condition to correlate the resonances that appear in the wavelength versus incident angle color maps of the reflected power with the modal analysis of the cross section of the structure. This analysis is performed, using an attenuated total reflection (ATR) setup, for thin film materials that belong to each of the mentioned categories: a metal (gold, Au), a dielectric (titanium dioxide, TiO2), and a material with n ≈ k (chromium, Cr). The theoretical analysis is supported with experimental results. It is demonstrated that this method enables to identify any resonance at any wavelength or incident angle, being valid for all three types of materials. Therefore, it is considered the suggested approach will help the research in these materials and in the double interface structure in the optics and photonics field.

Tunable Properties of New Cyano‐Substituent Heptahelicenes for Optoelectronic Devices: A Combined Experimental and DFT Computational Study

AbstractHere, we describe a set of coupled experimental and theoretical analyses. The introduction of one and two additional cyano groups in the carboheptahelicene backbone enhance its electron‐accepting properties. New carboheptahelicene derivatives are synthesized, and relevant characterizations of structural features, photophysical and electrochemical properties, and structure‐property relationships are described. This present work concerns the use of the density functional theory (DFT) to highlight the structural and the optoelectronic properties of carboheptahelicene derivatives and comparing the obtained findings with the experimental ones. The experimental and theoretical spectra (UV‐Vis absorption and photoluminescence) provide excellent concurrence. Afterward, molecular structures, structural parameters, molecular electrostatic potential (MEP), highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies of frontier molecular orbitals (FMOs) are constructed. Some other optoelectronic parameter including electron affinity (EA), ionization potential (IP), and some reactive descriptor such as chemical potential (μ), global hardness (η), electronegativity (χ) and the overall electrophilicity index (ω) are determined and indicating its potential uses as an active layer in optoelectronic efficient devices. The topological methods such as electron localization function (ELF), localization orbital locator (LOL) and the reduced density gradient method (RDG) were also conducted to clarify the strengths and kinds of interactions.

Geometrical incompatibility regulated pattern selection and morphological evolution in growing spherical soft tissues

Surface morphological patterns are widely observed in natural systems, which are closely correlated to vital biological functions and inspire surface morphology designs in soft matter systems. Geometrical incompatibility widely exists in biological tissues across different length scales and plays an important role in growth-induced pattern selection and morphological evolution of soft tissues. However, the underlying physical mechanism of growth-induced pattern formation and post-buckling evolution in geometrically incompatible spherical soft tissues remain elusive. Here, the effect of geometrical incompatibility on the growth-induced pattern selection and post-buckling evolution are investigated through swelling experiment, theoretical analysis and numerical simulation. The results show that not only the instability pattern but also the instability threshold can be regulated by manipulating geometric incompatibility. Notably, when the geometrical incompatibility parameter exceeds a critical value, spontaneous instability is observed before growth. With continuous growth, the core–shell soft sphere buckles into a periodic buckyball pattern and evolves toward a bean-shaped pattern, and then undergoes a wrinkle-to-fold transition into a labyrinth topography. Our results demonstrate, both experimentally and theoretically, that geometrical incompatibility can guide the growth-induced pattern formation and morphological evolution effectively. This study not only enhances our understanding of the growth-induced pattern selection and morphological evolution in spherical soft tissues, but also provides an inspiring insight for the fabrication of morphological patterns on curved surfaces.

Experimental study on the compressive behavior of UHPC filled stainless steel tubes subjected to monotonic and cyclic loading

Ultra-High Performance Concrete Filled Stainless Steel Tubular (UHPCFSST) column is a novel type of composite columns appealing to be adopted in corrosive and marine environment. To explore the axial performance of UHPCFSST columns, this paper initiates an experimental program containing 14 UHPCFSST columns subjected to either monotonic or cyclical axial compressive loading. The test variables in this program mainly include the column dimension, tube thickness and the loading schemes. Based on the test results, the damage evolution process, ultimate failure mode, load-deformation response and the typical mechanical performance indexes inclusive of loading-carrying capacity, stiffness degradation, as well as ductility coefficient are thoroughly examined. After that, theoretical analysis is carried out to explore the interaction behavior between UHPC and stainless-steel tube and hence judge the degree of confinement effect. To assess the applicability of the code equations stipulated in current international design guidelines and the empirical formulas proposed by other researchers, a small-scale dataset containing 41 UHPCFSST columns was compiled to make comparison of axial capacity between test results and analytical predictions. In view of the limited accuracy or the burdensome calculation process, a new formula considering actual loading carrying mechanism was proposed to calculate the axial capacity of UHPCFSST columns, which exhibits enhanced accuracy and efficiency than the current formulas.

Influence of nitrogen exchange in the core-shell structure of naphthalenediimide molecules on the advancement of quantum electronic properties

This study explores how nitrogen substitution and gold electrodes collectively influence the electronic characteristics of naphthalenediimide (NDI) molecules (M = 1, 2, and 3) through theoretical analysis. Utilizing ELF, LOL, QTAIM, and NCI analyses, we reveal significant alterations in NDI's electronic structure and interactions upon bonding with gold electrodes (Au-M-Au). Both ELF and LOL analyses demonstrate increased electron localization and delocalization on the NDI surface due to gold electrodes, with a stronger effect on nitrogen-doped molecules (M = 2, 3). QTAIM analysis confirms favorable non-covalent interactions, including evident hydrogen bonding, between NDI molecules and gold electrodes, notably intensified in doped molecules, especially the Au…O interaction. NCI analysis provides insight into the diverse interactions within the molecular system. Overall, this research highlights the crucial role of gold electrodes and nitrogen substitution in fine-tuning NDI molecules' electronic properties. The observed modulation of electron behavior and formation of beneficial interactions with gold electrodes hint at promising applications for doped NDI-gold systems requiring efficient charge transport mechanisms.

Theoretical Analysis, Simulation and Optimization of Electric Field on the Three-Phase Electrodynamic Screen

Theoretical Analysis, Simulation and Optimization of Electric Field on the Three-Phase Electrodynamic Screen

Trojan-horse attack on a real-world quantum key distribution system: Theoretical and experimental security analysis

Trojan-horse attack on a real-world quantum key distribution system: Theoretical and experimental security analysis

Iterative-Weighted Thresholding Method for Group-Sparsity-Constrained Optimization With Applications.

Taking advantage of the natural grouping structure inside data, group sparse optimization can effectively improve the efficiency and stability of high-dimensional data analysis, and it has wide applications in a variety of fields such as machine learning, signal processing, and bioinformatics. Although there has been a lot of progress, it is still a challenge to construct a group sparse-inducing function with good properties and to identify significant groups. This article aims to address the group-sparsity-constrained minimization problem. We convert the problem to an equivalent weighted lp,q -norm ( , ) constrained optimization model, instead of its relaxation or approximation problem. Then, by applying the proximal gradient method, a solution method with theoretical convergence analysis is developed. Moreover, based on the properties proved in the Lagrangian dual framework, the homotopy technique is employed to cope with the parameter tuning task and to ensure that the output of the proposed homotopy algorithm is an L -stationary point of the original problem. The proposed weighted framework, with the central idea of identifying important groups, is compatible with a wide range of support set identification strategies, which can better meet the needs of different applications and improve the robustness of the model in practice. Both simulated and real data experiments demonstrate the superiority of the proposed method in terms of group feature selection accuracy and computational efficiency. Extensive experimental results in application areas such as compressed sensing, image recognition, and classifier design show that our method has great potential in a wide range of applications. Our codes will be available at https://github.com/jianglanfan/HIWT-GSC.

Design and performance analysis of an embedded amplified piezoelectric jetting dispensing valve

Abstract In order to satisfy the market's demand for high-consistency, micro-dispensing of colloids, an embedded lever-amplified piezoelectric dispensing valve based on flexure hinge is designed. This structure has stable jetting performance, strong reliability, and can achieve micro-dispensing of medium and low viscosity glue. Theoretical analysis shows that the output displacement of the piezoelectric stack can meet the displacement requirement of dispensing after being amplified by this amplification mechanism. And the output displacement and mode of the amplification mechanism are calculated and analyzed by simulation. The rationality of the simulation model is verified by experiments, and the effect law of driving voltage, signal duty cycle and working frequency on the mass of glue droplets is obtained. The results show that under the conditions of driving voltage 100 V, duty cycle 50%, glue supply pressure 0.6 MPa, working frequency 100 Hz, the consistency deviation of single dispensing amount is ± 2.01%, as a whole, 0.34-0.38 mg of uniform tiny glue dots can be obtained. The experimental results have verified the stability and micro-dispensing performance of the embedded lever amplification piezoelectric dispensing valve, providing reference for the subsequent application and research of jet dispensing.

Assessing the impact of disease incidence and immunization on the resilience of complex networks during epidemics

Disease severity through an immunized population ensconced on a physical network topology is a key technique for preventing epidemic spreading. Its influence can be quantified by adjusting the common (basic) methodology for analyzing the percolation and connectivity of contact networks. Stochastic spreading properties are difficult to express, and physical networks significantly influence them. Visualizing physical networks is crucial for studying and intervening in disease transmission. The multi-agent simulation method is useful for measuring randomness, and this study explores stochastic characteristics of epidemic transmission in various homogeneous and heterogeneous networks. This work thoroughly explores stochastic characteristics of epidemic propagation in homogeneous and heterogeneous networks through extensive theoretical analysis (positivity and boundedness of solutions, disease-free equilibrium point, basic reproduction number, endemic equilibrium point, stability analysis) and multi-agent simulation approach using the Gilespie algorithm. Results show that Ring and Lattice networks have small stochastic variations in the ultimate epidemic size, while BA-SF networks have disease transmission starting before the threshold value. The theoretical and deterministic aftermaths strongly agree with multi-agent simulations (MAS) and could shed light on various multi-dynamic spreading process applications. The study also proposes a novel concept of void nodes, Empty nodes and disease severity, which reduces the incidence of contagious diseases through immunization and topologies.

High efficiency femtosecond laser ablation of alumina ceramics under the filament induced plasma shock wave

Femtosecond laser filament enables energy transfer over long distances, which is of great value for studying long-range ablation. However, the energy coupling of filament with the plasma generated by the ablation process leads to a very complex behavior which limits the ablation efficiency. This study systematically investigated the ablation mechanism of laser-induced filament in alumina ceramic. The plasma shock wave was initially investigated using spectral detection techniques combined with Sedov-Taylor theory. The results indicated that the maximum plasma shock wave reached 30 MPa under the irradiated by a 1 mJ fs laser. The theoretical analysis confirmed the effectiveness of the filament-induced plasma shock wave in enhancing the ablation rate of alumina ceramic. In this context, the experimental studies were conducted with varying filament positions and pulse energies, and the corresponding ablation rates for each parameter were investigated. The filament in the ablation process was found to has a secondary sputtering effect, which is an effective contributor to enhance the ablation rate. The corresponding ablation depth reach to 550 μm while achieving an ablation rate of 3.1 μm3/μJ. Finally, the coupling mechanism between the femtosecond laser filament and the plasma shock wave was systematically revealed. This research will facilitate future laser remote ablation applications with high efficiency.

Research on FBG curvature sensor based on PET substrate and silicone package

To address the low repeatability and accuracy in single package form and lack of strain transfer theory analysis in composite material form of fiber Bragg grating (FBG) curvature sensors, a flexible curvature sensing test scheme for FBG based on polyethylene terephthalate (PET) substrate and silicone package is proposed. Firstly, the factors affecting the strain response of the FBG are obtained through the analysis of the multilayer strain transfer theory, and the relationship between different material encapsulation forms and the strain response of the FBG is explored through finite element simulation. Secondly, the FBG curvature sensor with optimized simulation parameters is fabricated in package, and the curvature calibration verification experiments are performed on the sensor. Finally, the experimental results show that the deviation index of the FBG curvature sensor is between −1.89 % and 1.62 %, which indicates a better repeatability consistency. Based on the computation, the maximum sensitivity of the FBG curvature sensor is 13.32 µε/m−1 when the spacing between the fiber and the substrate layer is 2.50 mm, and its error is 0.30 % comparing with the simulation of the same condition, which supports the accuracy of the theoretical analysis and simulation of the multilayer strain transfer of the encapsulated FBG sensor conducted in this paper, meanwhile, the optimal encapsulation process of the FBG curvature sensor is obtained.

Efficient degradation of tetracycline by cobalt ferrite modified alkaline solution nanofibrous Ti3C2Tx MXene activated peroxymonosulfate system: Mechanism analysis and pathway

Magnetic CoFe2O4 nanoparticles have received considerable attention as an activator for peroxymonosulfate (PMS) in the degradation of tetracycline. However, it is still challenging to construct CoFe2O4 composites with good dispersion and highly exposed reactive sites. Herein, the KOH fiber-functionalized MXene matrix decorated by cobalt ferrite nanoparticles (denoted as CoFe2O4@Alk-MXene) was developed by electrostatic self-assembly method. The layered fibrotic structure effectively disperses and fixes cobalt ferrite nanoparticles, increasing the exposure of reactive sites. The as-prepared CoFe2O4@Alk-MXene material exhibited rapid removal of 100% tetracycline hydrochloride (TC-HCl) within 10 minutes by activating PMS, leveraging the excellent conductivity of alkalized MXene and the efficient activation of transition metal atoms. The experimental and theoretical analysis revealed that the electron transfer process of Ti2+/Ti4+, Co2+/Co3+ and Fe3+/Fe2+, as well as the free radical and non-free radical attack behaviors produced by the adsorption of PMS by the composite, are the primary mechanisms for achieving rapid removal of pollutants. A comprehensive degradation mechanism and potential pathways were proposed based on these findings. Overall, CoFe2O4@Alk-MXene/PMS emerges as a promising catalytic system for TC removal.

Electrochemical Nitrate Reduction to Ammonia on AuCu Single-atom Alloy Aerogels under Wide Potential Window.

Electrocatalytic nitrate reduction to ammonia (NO3RR) is very attractive for nitrate removal and ammonia production in industrial processes. However, the nitrate reduction reaction is characterized by intense hydrogen competition at strong reduction potentials, which greatly limits the Faraday efficiency at strong reduction potentials. Herein, we reported an AuxCu single-atom alloy aerogels (AuxCu SAAs) with three-dimensional network structure with significant nitrate reduction performance of Faraday efficiency (FE) higher than 90% over a wide potential range (0 ~ -1 VRHE). The FE of the catalyst was close to 100% at a high reduction potential of -0.8 VRHE, accompanying with NH3 yield reaching 6.21 mmol h-1 cm-2. More importantly, the catalyst maintained a long-term operation over 400 h at 400 mA cm-2 for the NO3RR using a continuous flow system in a H-cell. Experimental and theoretical analysis demonstrate that the catalyst can lower the energy barrier for the hydrogenation reaction of *NO2, leading to a rapid consumption of the generated *H, facilitate the hydrogenation process of NO3RR, and inhibit the competitive HER at high overpotentials, which efficiently promotes the nitrate reduction reaction, especially in industrial applications.

The effect of interpersonal relationships on epidemic spreading in weighted multilayer networks

During the epidemic outbreak, people's reactions to social contacts of varying degrees of intimacy exhibited significant differences. Historical data further reveal that interactions between groups play a crucial role in the epidemic's transmission chain. In light of this, it is essential for epidemiological models to account for more complex interaction mechanisms. Based on this understanding, we have developed a weighted dual-layer network model. One layer simulates the spread of information through 2-simplexes, while the other simulates the actual transmission paths of the disease based on physical contact. The weight between two nodes represents individual differences in information acceptance and self-protection among neighbors with different relationships. We conducted a theoretical analysis using the Micro-Markov Chain Approach to examine transmission behaviors, and we also implemented numerical simulations using the Monte Carlo Method. The simulation results aligned with the theoretical analysis, indicating that stronger interpersonal relationships can enhance information dissemination, prompting more individuals to adopt protective measures, which in turn helps curb the spread of the disease.

Air supply subsystem efficiency optimization for fuel cell power system with layered control method

Efficient and stable operation is critical for the large-scale commercialization of the proton exchange membrane fuel cell power system. The effective control and optimization of the operating conditions, such as oxygen excess ratio and cathode pressure of the air supply system, is a solution to improve the overall system efficiency. This work proposes a novel layered control method to achieve rapid and stable control of the operating conditions. The control structure in this paper consists of the optimization and control layers. A two-dimensional objective optimization function for the optimization layer is established to characterize the system efficiency based on theoretical analysis and experimental testing on the fuel cell power generation process and air supply system power consumption pattern. Then, a modified salp swarm algorithm with adaptive inertia weight is proposed to quickly and accurately obtain the optimal operating conditions for the maximum efficiency under different load current densities. Meanwhile, the local optimal solutions are avoided by introducing mutation operations. For the control layer, a third-order state space equation is developed to accurately describe the operating characteristics of the air supply system according to its operating principles. A feedback linearization-based sliding mode controller is designed to achieve rapid and stable control of the optimal working conditions outputted from the optimization layer. Finally, the fuel cell system was tested in the lab and verified on the fuel cell city buses. The results show that the system's operating efficiency is improved by 0.6 %–2.6 % at different current densities, and the hydrogen consumption of all three city buses is reduced by more than 5 %. The optimization effect was enhanced significantly. Therefore, the layered control method is effective in solving the optimization and control problems of the fuel cell power system.

Single-atom Cu sites on covalent organic frameworks with Kagome lattices for visible-light-driven CO2 reduction to propylene

CO2 to multicarbon fuels via photocatalytic conversion, especially propylene, is a viable pathway, but propylene remains unreported due to the two C-C coupling with the eighteen-electron reduction process. Herein, [1,1′-biphenyl]-3,3′,5,5′-tetracarbaldehyde, and [2,2-bipyridine]-5,5-diamine units were condensed and synthesized in combination with a post-modification strategy, named BTA-COF-M (M = H, Cu, Fe, Co, Ni or Zn). BTA-COF-Cu has distinct kagome lattices and abundant exposed-atom Cu sites, which can induce CO2 to undergo two C-C couplings into C3H6 products under visible light illumination. According to experimental and theoretical analyses, the outstanding performance of BTA-COF-Cu can be attributed to the ideal synergistic contribution of the Kagome lattices and the atomic Cu active sites, which promote CO2 adsorption/activation, facilitate photoexcited charge carrier dynamics, and induce secondary coupling of key intermediates. This research provides an innovative perspective for the construction of Kagome lattice COF with monatomic metal sites for CO2 reduction to high value-added propylene.

Research on a frequency-increasing piezoelectric wave energy harvester based on gear mechanism and magnetic rotor

Abstract Wave energy is a widespread clean energy source, but harvesting low-frequency wave energy efficiently remains a challenge. In this paper, a frequency-increasing piezoelectric wave energy harvester (FPWEH) based on gear mechanism and magnetic rotor is proposed. The gear mechanism transforms the vertical motion of the wave into the higher-frequency rotational motion of the magnetic rotor. The magnetic rotor is equipped with several rotating magnets and one revolution of the magnetic rotor enables multiple excitations of the piezoelectric cantilevers. Therefore, the wave excitation frequency is increased, so that the FPWEH can obtain better output performance. The major factors influencing output performance are determined through theoretical and simulation analysis, and a test system to simulate the wave environment is established. According to experimental findings, the FPWEH can generate an output voltage of 69.82 V and a maximum power of 28.33 mW when the external resistance is 20 kΩ. It can also successfully power thermohygrometer and light-emitting diodes (LEDs). These results validate the feasibility of the FPWEH for providing electricity to electronics with low power requirements. This research also offers a novel approach to harvesting low-frequency wave energy.

Land reclamation in the field of subsoil use in Ukraine: theoretical and legal analysis

Land reclamation in the field of subsoil use in Ukraine: theoretical and legal analysis

Numerical simulation and theoretical analysis of pattern dynamics for the fractional-in-space Schnakenberg model

Numerical simulation and theoretical analysis of pattern dynamics for the fractional-in-space Schnakenberg model