Search Results (1,385)

This paper presents a co-optimization framework for sparse concentric ring arrays based on an improved Dueling Deep Q-Network (DDQN) with a two-tier adaptive step-size strategy. The method aims at joint sidelobe suppression and structural optimization under non-ideal conditions. A tri-domain stochastic error model is introduced to characterize position, phase, and amplitude perturbations, and atmospheric-effect-aware evaluation is incorporated for high-frequency propagation scenarios. For a six-ring sparse array, radius-only optimization achieves a PSLL of $-24.4810$ dB, corresponding to an average improvement of $5.809$ dB over the initial array and an additional reduction compared with the baseline DDQN method. Extending the design to joint optimization of ring radii and element counts further reduces the PSLL to $-30.629$ dB, demonstrating the effectiveness of combined geometric and sparsity control. Monte Carlo simulations show that the optimized array maintains stable sidelobe performance under tri-domain stochastic perturbations, with an average PSLL of $-26.758$ dB. Further analysis using real meteorological data indicates that atmospheric effects introduce moderate variations in the normalized beam pattern, while the overall performance remains primarily influenced by stochastic perturbations under the considered modeling conditions. The proposed framework provides an effective and robust optimization approach for sparse concentric ring arrays in practical high-frequency scenarios. Full article

In this paper, we provide another proof of Levitzki’s theorem for prime rings with $k!$-torsion-free using the Vandermonde determinant, which states that a prime ring contains no nonzero nilpotent left or right ideal. As an application of this theorem, we prove that the k-skew commuting element in torsion-free prime *-rings with nonsymmetric element must be zero without using any deep structural results from ring theory. Full article

This review synthesizes findings from more than 100 journal articles, reports, and design standards on the design, simulation, and testing of steel beam-to-column connections, with emphasis on semi-rigid bolted extended end-plate (EEP) joints. The core objective of this study is to highlight the critical importance of accurately capturing this semi-rigid behavior, given the significant implications of improper modeling for the global response, safety, and design reliability of steel frames. While connections are often idealized as fully rigid or pinned, EEP connections typically exhibit a semi-rigid response governed by nonlinear moment–rotation (M–θ) behavior. The reviewed literature is organized around: (i) mechanical response and key failure mechanisms (end-plate yielding, bolt fracture, and prying action); (ii) analytical and numerical prediction methods, including component-based models and finite-element approaches capable of representing contact, bolt pretension, and cyclic degradation; and (iii) system-level implications for steel frames. Approaches used in major standards (AISC and Eurocode 3) for classifying connection stiffness and strength are compared, and experimental programs are summarized to identify the dominant parameters controlling resistance, ductility, and failure mode. Translating these component-level findings to the structural-system level, the review highlights how appropriately detailed semi-rigid EEP connections can enable moment redistribution, reduce member demands, and support stable inelastic deformation under seismic actions. Key research gaps include three-dimensional and multiaxial loading, impact and other high-rate actions, and the performance of alternative materials such as stainless steel. Full article

Small unmanned aerial vehicles are difficult short-range radar targets because their millimeter-wave radar cross-sections often fall between −10 and −25 dBsm. This paper presents a modular analytical and simulation-based benchmark of a cascaded 77 GHz TDM-MIMO FMCW radar with 12 transmitters and 16 receivers, yielding a 192-element virtual ULA over a 40 m instrumented range. The framework is organized around the main counter-UAV sensing functions: range–Doppler processing first evaluates target observability and provides range–Doppler gates; Doppler-dependent TDM phase compensation is then required before virtual-array snapshots are formed for DoA estimation; and a separate long-dwell single-transmitter branch evaluates micro-Doppler separability using handcrafted features and a nearest-centroid Mahalanobis classifier. Four benchmarks are considered: detection under Swerling fluctuation models, residual TDM phase error caused by Doppler quantization, DoA estimation under an idealized far-field snapshot model, and micro-Doppler separability among UAV and bird classes. Under Swerling I, targets with a mean RCS of $-10$ dBsm or larger maintain detection probability above 0.9 throughout the 40 m window, whereas the $-20$ and $-25$ dBsm classes fall below that level at about 28 m and 21 m. In the far-field DoA benchmark, TLS-ESPRIT gives the lowest conditional RMSE and remains about 13–14 dB above the subarray CRLB at moderate SNR; however, these angular results are reference ceilings because the short-range operating region violates the full-aperture far-field condition and because residual TDM phase error can be severe without accurate compensation. In the micro-Doppler benchmark, birds exceed 95% per-class accuracy at 20 dB total SNR, but overall four-class accuracy saturates near 72–75% and UAV-only three-class accuracy near 63%, with most confusion between the micro-quadrotor and fixed-wing classes. This study therefore identifies architecture-specific performance margins and limitations before measured-data field validation, rather than claiming complete deployment-level performance. Full article

Future lunar missions, like the International Lunar Research Station (ILRS), demand single-launch multi-point operations, urgently requiring reusable energy-absorbing structures. Integrating shape memory alloy (SMA) into honeycombs offers a promising solution; however, deformation exceeding the SMA’s recoverable limit induces structural residual deformation, altering the configuration and degrading subsequent energy absorption. To address this, we propose a semi-analytical, data-calibrated hybrid model predicting SMA honeycomb residual deformation. A four-stage linear constitutive model is established capturing superelasticity and martensitic yielding. Cell walls are idealized as equivalent beams. Using layered fiber integration and numerical interpolation, a nonlinear moment–curvature relationship is constructed, enabling rapid structural residual deflection evaluation from material residual strains. Finite element results confirm that initial residual deformation stabilizes the honeycomb into a reusable configuration, governing subsequent plateau stresses. Calibrated by uniaxial test data, the proposed model accurately predicts residual deformation ratios and reusable plateau stresses with errors within 8%. By bridging material-level strain with structural-level deformation, this approach circumvents computationally expensive full-scale simulations and costly experimental trials, providing a highly efficient tool for designing reusable SMA absorbers. Full article

Based on the Infinite State Representation (ISR) of the Riemann–Liouville integral, the energy stored in a fractional-order integrator is revisited, together with the energy dissipated through Joule losses. Using an idealized ultracapacitor model based on the Constant Phase Element (CPE), i.e., a fractional-order capacitor, theoretical expressions for the stored and dissipated energies during current charging of the CPE are derived. Numerical simulation of the fractional integrator over a frequency interval {ω_min, ω_max} validates a realistic CPE model, in which low-frequency modes correspond to energy storage, while high-frequency modes account for self-discharge and the origin of dissipated energy. This theoretical study leads to the definition of a new ultracapacitor model composed of an internal resistor and the previous realistic CPE, whose frequency-distributed representation enables prediction of the internal state variables and, consequently, the State of Charge. Full article

Introduction: The Cananéia–Iguape Lagoon Complex, part of the Lagamar Mosaic of Conservation Units, comprises interconnected ecosystems that facilitate the dispersal and exchange of larvae, juveniles, and adults across habitats. This connectivity is a vital ecological process, driving the demographic linkage of local populations. Due to its commercial importance and abundance, the fat snook (Centropomus parallelus) serves as an ideal model for connectivity studies in this region. This study evaluated the otolith fingerprints of fat snook nursery areas within an estuarine complex using elemental chemical signatures. Methodology: Otoliths from 24 juveniles (n = 6 per site) were sampled across four nurseries: Ariri (AR), Itapanhapima (IT), Subauma (SU), and Iguape (IG). Multi-elemental signatures (Na, Mg, P, K, Ca, Mn, Sr, Ba, and Pb) at the otolith edge were measured via Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Results: Multivariate analysis (PERMANOVA, p < 0.05) revealed significant chemical differences between nurseries, corroborated by pairwise tests. Canonical Analysis of Principal Coordinates (CAP) with leave-one-out cross-validation successfully assigned individuals to their collection sites with accuracies of 55% (AR), 72% (IT), 94% (SU), and 88% (IG), achieving a 78% global reclassification rate. CAP results distinguished two primary groups: the southern nurseries (AR/IT) and northern nurseries (SU/IG). This spatial separation was primarily driven by Sr:Ca and Ba:Ca ratios, reflecting the higher marine influence in the south versus freshwater input from the Ribeira de Iguape River in the north. Conclusions: These findings provide critical data to support public policies for the conservation of coastal ecosystems and the management of associated fish stocks. Full article

This paper develops a generalized kinematic model for a lever-link-type flat pressing mechanism used in food processing applications for compacting the coagulate. The study aims to highlight the influence of the geometric parameter that defines the position of the intermediate coupling on the driving element on the mechanism’s configuration and on the main kinematic variables of the active pressing point. Under an idealized representation—assuming rigid links, perfect joints, and a vertical constraint acting on the active element—general analytical expressions for displacement, velocity, and acceleration were established using the vector-kinematic method. The results show that modifying the position of the intermediate coupling produces nonlinear variations in the length of the connecting element, its spatial orientation, and the vertical motion of the active point. Increased values of this parameter are associated with a greater effective stroke and higher vertical velocities toward the end of the motion, while the calculated accelerations remain relatively low, indicating a smooth kinematic evolution. The model establishes analytical relationships that describe the influence of geometric parameters on the kinematic behavior of the mechanism and can serve as a basis for further developments involving dynamic analysis and experimental validation. Full article

The objective of this study is to mitigate the bottom-out failure and improve the energy absorption of conventional helmet liners during high-energy impacts, thereby reducing the risk of head injuries. To this end, a locally reinforced Primitive-type triply periodic minimal surface (P-TPMS) energy-absorbing liner is proposed for the helmet forehead region, which facilitates progressive energy dissipation through layer-by-layer buckling deformation. A finite element model of a helmet–head coupling was created based on a previously verified high-fidelity head model and subsequently validated against the ECE 22.06 standard drop-test methodology. Three critical design parameters—outer protective layer thickness, triply periodic minimal surface (TPMS) unit cell size, and wall thickness—were optimized employing the Box–Behnken Design (BBD) response surface methodology, resulting in quadratic regression models for the head injury criteria (HIC) and peak linear acceleration (PLA) with good fit ($R^2$ > 0.97). Optimal parameter combinations were established using multi-objective optimization, with protective efficacy carefully assessed from both head dynamic response and biomechanical response perspectives. The ideal P-TPMS liner possesses an outer protective layer thickness of 14.95 mm, a TPMS unit cell size of 12.23 mm, and a wall thickness of 3.93 mm. Compared to the traditional expanded polystyrene (EPS) liner, the optimized P-TPMS liner significantly reduces HIC (by ∼16%) and PLA (by ∼14%) while extending the impact duration. More critically, it transitions both intracranial pressure and brain tissue strain below their respective clinical injury thresholds, substantially lowering the risks of skull fracture and mild traumatic brain injury (mTBI). The P-TPMS construction facilitates continuous energy dissipation during impacts via incremental layer-by-layer buckling deformation, hence extending impact duration and markedly improving helmet protective efficacy. These findings offer theoretical foundations and technical direction for the creation of localized heterogeneous liner designs in advanced high-performance helmets, although the results are limited to frontal flat-anvil impact conditions. Full article

Grounding connectors critically influence the safety and long-term reliability of earthing systems through coupled electro-thermal, mechanical, and corrosion behaviors, yet no standardized quantitative framework exists for jointly evaluating these performance dimensions across diverse deployment scenarios. This study introduces a unified multi-criteria evaluation framework applied to six grounding connector configurations spanning four alloy families and three joining technologies. Electro-thermal response was characterized by coupled finite element simulations (0–100 A), mechanical reliability by quasi-static tensile testing (n = 10 per configuration), and corrosion durability by accelerated salt-spray exposure with image-based corroded area fraction quantification. Performance metrics were normalized and aggregated using equal-weight, Analytic Hierarchy Process, and Shannon entropy weighting schemes, with the Technique for Order of Preference by Similarity to Ideal Solution applied for multi-scenario ranking. One-way analysis of variance confirmed statistically significant effects of connector type on tensile performance (F(5, 54) = 3154.90, p < 0.001). The exothermic welded joint achieved the highest mean ultimate tensile load (61.5 ± 1.5 kN), while copper mechanical connectors exhibited the lowest steady-state temperature rise (~2 K above ambient at 100 A). Compression-crimped connectors ranked first under both equal and Analytic Hierarchy Process weighting (closeness coefficients 0.737 and 0.807, respectively), while stainless steel connectors ranked first under corrosion-critical deployment scenarios. Scenario-weighted analyses demonstrate that the optimal material–process combination shifts with environmental severity, current duty, and mechanical demand, providing a reproducible, evidence-based basis for context-dependent connector specification. Full article

Soil vulnerability is commonly assessed using environmental indicators; however, the lack of systematic and continuous monitoring often leads to incomplete and fragmented data, particularly in surface coal mining areas affected by potentially toxic element (PTE) contamination. Existing studies mainly focus on impact assessment, with limited emphasis on structured decision-support frameworks for selecting optimal soil protection strategies. This study addresses this gap by proposing an integrated hybrid decision-making framework that combines the Analytic Hierarchy Process (AHP), Sustainability Balanced Scorecard (SBSC), and the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS). The main contribution lies in integrating strategic sustainability perspectives (SBSC) with quantitative multi-criteria methods (AHP and TOPSIS), enabling a transparent and consistent evaluation of soil protection strategies across environmental, economic, technical, and social dimensions. The framework was applied to the Kostolac mining and energy complex in Serbia as a representative case study, using data from the State of the Environment Report as the basis for expert evaluation. The results identify risk reduction and environmental effectiveness as the dominant criteria, while the Progressive Strategy (SBSC) achieved the highest ranking. Sensitivity analysis confirmed the robustness of the model. From a policy perspective, the findings support prioritizing sustainability-oriented and risk-reduction strategies in mining regulations and investment planning. Full article

Water is a key factor affecting the mechanical properties and stability of rock masses in underground engineering. In practical engineering settings, water distribution is commonly spatially heterogeneous, and the relative orientation between water distribution and the stress direction may further complicate the mechanical response and failure behavior of rocks. To investigate this issue under controlled laboratory conditions, Linyi red sandstone was selected, and four groups of specimens with distinct water-bearing states (oven-dried, fully saturated, axially semi-saturated, and radially semi-saturated) were prepared using tailored immersion protocols. Laboratory uniaxial compression tests and simplified discrete element simulations were combined to examine the macroscopic mechanical response, failure localization, and mesoscopic damage evolution of sandstone under directional heterogeneous water distribution. The results indicate that the water-bearing state strongly affects the uniaxial compressive strength and apparent deformation modulus of sandstone; compared with oven-dried specimens, fully saturated specimens show an approximately 40–60% reduction in these parameters, whereas semi-saturated specimens exhibit intermediate values. The relative orientation between the water distribution and loading direction further influences the failure pattern of semi-saturated specimens. Failure in semi-saturated specimens tends to initiate or localize in water-affected regions, while the multi-stage post-peak response of radially semi-saturated specimens can be interpreted as a sequential load-transfer process between saturated and dry regions. Heterogeneous water distribution also affects microcrack development and force-chain redistribution, with the idealized dry–wet transition region acting as a sensitive zone for crack initiation and stress redistribution. This study clarifies the first-order influence of directional heterogeneous water distribution on the mechanical behavior of sandstone and provides support for stability assessment and disaster mitigation in underground rock engineering under complex water-bearing conditions. Full article

This work presents the realization of a compact and embedded impedance-based sensor system for the characterization of lithium-ion batteries by means of electrical impedance spectroscopy (EIS). The analog magnitude-ratio and phase-difference detection (MRPDD) method is implemented and extended through a generalized formulation that models the shunt element as a frequency-dependent impedance and compensates the parasitic contributions of the printed circuit board. This reformulation corrects magnitude and phase errors introduced by the measurement hardware without increasing the overall complexity. The prototype comprises two main functional blocks: current-mode excitation and voltage-mode measurement. The excitation stage uses an operational transconductance amplifier and a power MOSFET to generate a voltage-controlled current source, whereas the sinusoidal voltage signal is generated by means of a direct digital synthesizer. The measurement chain relies on differential acquisition using instrumentation amplifiers and analog magnitude/phase detection based on the AD8302 vector detector under microcontroller control. The proposed method has been first validated by simulations using both a linear RC equivalent model and an extended Randles-type battery-equivalent model, and then experimentally characterized using a linear RC equivalent model of the device under test. Measurements show that the generalized formulation recovers the ideal impedance response in the presence of parasitic effects, both in the shunt device and in the printed circuit board. In the experimental validation with the RC model, a magnitude error of 1.65% is obtained at 1 kHz, which is adopted as the upper frequency limit for battery characterization, even though operation up to 10 kHz is possible. Phase measurements revealed that the input capacitive coupling of the vector detector, conceived for operation in the RF range, requires an adaptation for appropriate operation in the intended frequency range. The prototype has been also applied to the characterization of a commercial lithium-ion 18650 cell, enabling the measurement of battery impedance and the analysis of its dependence on the state-of-charge and on the discharge current. Full article

Analytical solutions for contaminant transport in porous media are important for understanding subsurface processes and validating numerical models. However, conventional Laplace-transform-based approaches often face difficulties in handling realistic transient boundary conditions and typically result in challenging inverse formulations that require computationally intensive convolved integration. To address these limitations, this paper presents a Fourier-FFT analytical framework for solving the well-established one-dimensional advection–dispersion–reaction (ADR) equation in homogeneous and heterogeneous porous domains. The proposed Fourier-FFT approach enables straightforward mathematical formulation, rapid computation, and incorporation of realistic transient boundary conditions beyond idealized step or impulse inputs. Verification against a Laplace-based analytical solution for a homogeneous domain and a finite element solution for a dual-permeability domain show good agreement, confirming the accuracy of the method. Parametric analyses further demonstrate that the framework captures the expected physical behaviour of contaminant transport under varying hydrogeological and reaction conditions. Full article

The fructose 1,6-bisphosphate aldolase (FBA) gene family plays crucial roles in plant energy metabolism, growth, development, and abiotic stress responses, as it modulates antioxidant synthesis and soluble sugar accumulation to enhance plant cadmium tolerance. Seashore paspalum (Paspalum vaginatum Sw.), a halophytic perennial C₄ turfgrass renowned for its exceptional cadmium tolerance, is ideal for phytoremediation of cadmium-contaminated soil. FBA family genes have been identified in several grass species, such as maize, rice, and wheat, but systematic investigations into FBA family genes and their functions in seashore paspalum remain scarce. In this study, seven class I FBAs (named as PvFBA1–PvFBA7) and one class II FBA (named as PvFBA8) in seashore paspalum were identified. The physicochemical properties, evolutionary relationships, gene structures, conserved domains, protein structures, cis-acting regulatory elements, chromosomal localizations, and collinearity relationships of eight PvFBAs were analyzed. These analyses suggested that PvFBA genes had highly conserved domains and belonged to ultra-conserved core genes. Expression pattern analysis indicated that the PvFBA gene family was dynamically responsive to cadmium stress. PvFBA6 and PvFBA7 were highly expressed in leaves, whereas PvFBA1 and PvFBA3 showed almost no expression. The RT-qPCR results suggested that the expression levels of PvFBA5 and PvFBA6 were highly consistent with the FPKM value trends analyzed in the transcriptomic data. Collectively, this study not only provides a theoretical foundation for the understanding of the evolution of the PvFBA gene family but also offers potential candidate genes for enhancing cadmium stress tolerance in plants. Full article