Search Results (171)

A new fractional dynamic sliding mode control (FD-SMC) framework is introduced to reduce chattering in the control of fractional-order chaotic systems. In this method, chattering is eliminated by placing a fractional integrator before the system control input. As a result, the augmented system has a higher dimension than the original system, meaning that additional states are introduced. Effective control therefore requires identifying or estimating these new states or the corresponding plant model. To address this issue, a robust optimal fractional loop-transfer-recovery observer (ROF-LTRO) is developed. Furthermore, the key advantage of sliding mode control (SMC)—its invariance to matched uncertainties—is often lost in many plants such as chaotic systems, because many of them contain mismatched uncertainties. To restore and extend the invariance property, multiple sliding surfaces combined with a virtual control input are employed. In addition, the proposed FD-SMC and ROF-LTRO do not rely on prior knowledge of uncertainty bounds, which is beneficial for practical implementation. Then, a two-stage design procedure based on two-surface definition is presented, and simulation results are provided for the extended fractional Duffing–Holmes chaotic system (EF-DHCS) under both matched and mismatched uncertainties. Full article

Historic masonry towers are iconic components of the world’s architectural heritage, yet their seismic vulnerability remains to be investigated, particularly regarding the influence of vertical ground motion. This study investigates the seismic response of the Roncole bell tower, a 35 m high slender masonry structure located in Emilia-Romagna, Italy, that experienced severe damage during the 2012 Emilia earthquake sequence, presumably related to the second shock of 29 May, the epicenter of which was within approximately 5 km of the tower. In the absence of direct site recordings, a simplified seismic scenario was reconstructed using accelerograms from two nearby stations and interpolation procedures based on logarithmic attenuation relationships. Nonlinear finite element analyses were performed in Abaqus using a detailed three-dimensional model comprising approximately 263,000 tetrahedral elements and a Concrete Damage Plasticity constitutive law for masonry. Four elastic moduli of the material and multiple seismic input scenarios were considered, with and without inclusion of the vertical seismic component. Modal analysis showed that the tower response is governed by the first two dominant horizontal bending modes and one significant vertical mode involving a high percentage of participating mass. Results indicate that while horizontal excitation controls global sway behavior, the vertical component strongly amplifies axial force fluctuations and vertical displacements located close the tower base and rules the bending capacity of the tower. Nonlinear time-history analyses also revealed residual drifts close to collapse thresholds drifts under most of the scenarios considered. Simulated crack patterns closely matched the actual earthquake damage, at the base of the tower, window openings, and the façade in the tilting side. The study demonstrates that three-component seismic analyses are essential for reliable assessment of historic slender masonry towers subjected to near-source earthquakes. Full article

Remaining useful life (RUL) prediction is a critical procedure to avoid catastrophic failure of shielding sleeves and prevent nuclear safety risks. Affected by the structural characteristics and service conditions of shielding sleeves, it is difficult to obtain sufficient full-life-cycle actual degradation data, which greatly restricts the training and application of data-driven prediction models. This paper proposes a remaining useful life prediction method for shielding sleeves based on data augmentation and a hybrid model. Firstly, starting from the physical failure mechanisms of two typical failure modes of shielding sleeves, namely bulging and wear. Secondly, based on the analytical models of typical failures of shielding sleeves, a degradation data augmentation method using Monte Carlo simulation is proposed to address the problem of missing full-life-cycle degradation data. Finally, a hybrid RUL prediction model for shielding sleeves based on Stacking ensemble learning is presented, which integrates the advantages of physical degradation models and deep learning methods. Experimental verification is carried out through multiple sets of degradation datasets with different failure modes. The root-mean-square error (RMSE) of the proposed prediction method can reach a minimum of 0.0058, and the mean absolute error (MAE) can reach a minimum of 0.0044. The prediction accuracy is superior to that of single models, which verifies the prediction performance and engineering applicability of the proposed method. Full article

Quasi-brittle structures modeled with softening constitutive laws may lose the uniqueness of equilibrium, producing bifurcation and multiple admissible crack evolutions even under symmetric loading. This paper develops a stability test and a constructive multiplicity procedure for finite element cracking analyses formulated as a Parametric Linear Complementarity Problem (PLCP) solved in tableau form. The approach exploits the pivot sequence of a complementary tableau to monitor stability by tracking the positive definiteness of the reduced active-mode Hessian $\widehat{\mathbf{A}}$ through a complement condition, without eigenvalue computations. A direct relationship between loss of positive definiteness and the sign of the incremental load factor $\Delta \dot{\mathsf{\alpha }}$ is established, providing an intrinsic indicator of transition to descending response. When degeneracy occurs, a “void pivot” mechanism is introduced to generate an alternative admissible tableau, enabling a systematic construction of multiple isolated solutions associated with competing crack patterns. The method is demonstrated on a two-notched direct tension specimen with cohesive softening, where symmetric and antisymmetric paths emerge at a critical step. The implementation is compatible with parallelized matrix operations and remains effective in the presence of non-holonomic constraints. Full article

This study presents the dynamic characterization of a gas turbine blade manufactured from two different nickel-based superalloys: on the first hand, a superalloy called René 80 and, on the second hand, a directionally solidified (DS) nickel-based anisotropic superalloy, investigated during the validation phase of the development process. Starting from the original CAD geometry, precise and very detailed finite-element models were developed, progressively refined and modified, and consequently validated to ensure mesh-independent modal predictions. The study examines multiple possible sources of discrepancy between experimentally measured and numerically predicted natural frequencies, including geometric deviations, grouping of different interesting points, broach-block test configuration, material anisotropy, and the influence of internal rib turbulators. Statistical analyses of dimensional variations revealed no significant correlation with the observed frequency scatter, redirecting the investigation toward material behavior and modeling fidelity. The inclusion of turbulators in the finite-element model proved essential, reducing prediction errors for the first two modes by approximately 2–3%. For the DS superalloy, the effect of grain orientation was evaluated over permissible angular deviations (extremes were considered); however, no systematic and clear improvement in frequency prediction was observed. Finally, several tuning strategies were assessed, leading to an optimization procedure that simultaneously adjusted the elastic moduli $E_x$ and $E_z$, reducing modal frequency deviations to below 1% for the first two modes. The proposed methodology provides a robust and solid framework for the validation of turbine blade dynamic behavior across different materials and manufacturing conditions. Full article

Lateral buckling is the governing failure mode affecting the strength of cold-formed steel purlins. In industrial roofing systems, these purlins are frequently restrained by two or three anti-sag bars within their spans. Previous research by the authors indicated that under wind suction, the buckling behaviour of purlins with multiple anti-sag bars differs significantly from those with fewer restraints, primarily due to the semi-rigid nature of the bracing. This paper investigates the lateral buckling of C-section purlins with two or three anti-sag bars, explicitly accounting for lateral restraints provided by both the roof sheeting and the bars. Simplified analytical solutions are derived to facilitate practical design. Notably, a novel parameter is introduced to identify the controlling buckling mode, which significantly simplifies the calculation procedure. The proposed solutions show excellent agreement with results obtained from both commercial and custom-developed finite element codes. Full article

Adulteration of milk powder (MP) is performed, especially in underdeveloped countries, by adding corn starch (CS) or wheat flour (WF) without mentioning it. Multiple techniques have been established to reduce these deceptive methods. Most of these techniques require samples to be sent to the laboratory for results through a time-consuming, expert-requiring, and destructive procedure. Raman spectroscopy (RS) has seen application due to the availability of portable modalities and its non-destructive, water-insensitive nature. Using principal component analysis (PCA), the differences and similarities between MP and the adulterants (CS and WF) have been evaluated. To quantify the percentages of CS and WF binary mixtures independently with MP, partial least squares regression (PLSR) has been employed. A total of 70 MP samples independently adulterated with CS and WF were prepared. Thirteen chemometric modes were developed by combining the first and second derivatives with Standard Normal Variate (SNV) and Multiplicative Scatter Correction (MSC) to quantify adulteration. The results obtained for CS and WF mixtures show errors of 0.76 and 0.77 %w/w, respectively, with the optimized math pretreatment. These results demonstrate that the portable RS modality can be used as an effective technique for detecting adulterants in milk powder. Full article

Communication is defined as the process of transferring data and exchanging information between interconnected systems. Due to the increasing reliance on digital infrastructures by the military, financial, and healthcare sectors, it is important to ensure the confidential, authentication, and tamper-proof nature of communications. In addition, the increasing need for secure communications in the fields of network security and cryptography have led to the development of numerous systems. The basic requirement of these systems is that under the same key, identical plaintexts do not result in identical ciphertexts. The most significant contribution to this requirement has came from block cipher modes. There are many traditional modes of operation such as the Electronic Code Book (ECB) compromises between simplicity and security. Probabilistic Modes such as the Cipher Block Chaining Mode (CBC) provide a method to randomize data so that the potential for pattern analysis is eliminated, while Deterministic Modes such as ECB enable potential access to the patterns within the plaintexts. Conversely, since the randomization is in the Probabilistic Mode, there is no access to the patterns; however, the sequentiality of the blocks creates dependence and increases the computing overhead. To address these issues, a novel block cipher mode that provides the highest level of security and the most effective method for performing encryption and decryption will be proposed in this paper. It is anticipated that the improved security features and efficient encryption and decryption procedures will significantly improve confidentiality. The methods proposed will utilize compact key structures, parallel processing, a header generation based on multiple random values, and a Key-derived S Box. The experimental results show that SEBCM is more effective than CBC with respect to speed in both encryption and decryption. Full article

Planar multi-loop fractionated kinematic chains (FKCs)—kinematic chains that can be decomposed into two or more coupled subchains by separating joints or links—are widely used in heavy-duty manipulators, yet their large design space makes automatic synthesis and application-oriented screening challenging. The novelty of this paper is a general automated synthesis-and-screening framework for planar fractionated kinematic chains, regardless of whether multiple joints are present; multiple-joint chains are handled via an equivalent transformation to single-joint models, enabling the construction of a deduplicated topological graph atlas. In the mine scaler manipulator case study, an 18-link, 5-DOF (N18_M5) FKC with two multiple joints is taken as the target and converted into a single-joint equivalent N20_M7 model consisting of three subchains (KC1–KC3). Atlases of the required non-fractionated kinematic chains (NFKCs) for KC1 and KC3 are generated according to their link counts and DOFs. The subchains are then combined as building blocks under joint-fractionation (A-mode) and link-fractionation (B-mode) to enumerate fractionated candidates, and a WL-hash-based procedure is employed for isomorphism discrimination to obtain a non-isomorphic N20_M7 atlas. Finally, a connectivity-calculation-based screening is performed under task-driven structural and functional constraints, yielding 249 feasible configurations for the overall manipulator arm. The proposed pipeline provides standardized representations and reproducible outputs, offering a practical and transferable route from large-scale enumeration to engineering-feasible configuration sets for planar multi-loop FKCs, including those with multiple joints. Full article

Unmanned aerial vehicle (UAV)-assisted satellite downlink transmission is a promising solution for improving coverage and throughput under challenging propagation conditions. However, the achievable performance gains are fundamentally constrained by the coupling between access transmission and the satellite–UAV backhaul, especially when decode-and-forward (DF) relaying and hybrid multiple access are employed. In this paper, we investigate the problem of end-to-end downlink sum-rate maximization in a UAV-assisted satellite network with hybrid non-orthogonal multiple access (NOMA)/orthogonal multiple access (OMA) transmission. We propose a performance-driven end-to-end optimization framework, in which UAV placement is optimized as an outer-layer control variable through an iterative procedure. For each candidate UAV position, a greedy transmission mode selection mechanism and a KKT-based satellite-to-UAV backhaul bandwidth allocation scheme are jointly executed in the inner layer to evaluate the resulting end-to-end downlink performance, whose feedback is then used to update the UAV position until convergence. Simulation results show that the proposed framework consistently outperforms benchmark schemes without requiring additional spectrum or transmit power. Under low satellite elevation angles, the proposed design improves system sum rate and spectral efficiency by approximately 25–35% compared with satellite-only NOMA transmission. In addition, the average user rate is increased by up to 37% under moderate network sizes, while maintaining stable relative gains as the number of users increases, confirming the effectiveness and scalability of the proposed approach. Full article

Background/Objectives: Preterm birth remains a major cause of neonatal morbidity and mortality, particularly in multiple pregnancies and in cases of cervical shortening. While cervical cerclage is established in singleton pregnancies, its efficacy in multiple gestations remains uncertain. This study compares pregnancy and neonatal outcomes following second-trimester cerclage in singleton and multiple pregnancies with a short cervix. Methods: In this retrospective cohort study, 96 women underwent second-trimester cerclage at a tertiary perinatal center between 2020 and 2024. All had a cervical length ≤ 25 mm or prolapsed membranes without infection or premature rupture. Primary outcomes included term delivery rate, gestational age, mode of delivery, and neonatal outcomes; secondary outcomes comprised surgical complications and rehospitalization, defined as the need for renewed inpatient care due to threatened preterm labor or procedure-related complications. Results: In total, 79 singleton and 17 multiple pregnancies were analyzed. Term delivery occurred more often in singletons (54%) than multiples (18%, p = 0.006). Mean gestational age at birth was 258 ± 25 days in singletons versus 228 ± 28 days in multiples (p < 0.001). Birth weight was significantly lower in multiples (1985 g vs. 2943 g; p < 0.001), and neonatal infections were more frequent (53% vs. 26%; p = 0.008). Caesarean delivery was more common in multiples (82% vs. 33%; p < 0.001). Apart from increased postoperative contractions in multiples (24% vs. 5%; p = 0.031), complication rates and rehospitalization (27% vs. 29%; p = 0.8) were similar. Conclusions: Second-trimester cerclage is less effective in preventing preterm birth in multiple pregnancies compared to singleton pregnancies; however, it appears to be associated with a stabilizing clinical course and may facilitate outpatient management in selected high-risk cases. These findings support individualized counseling and shared decision-making, particularly in multifetal gestations. Full article

A method combining magnetic solid-phase extraction (MSPE) with ultra-high performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) was developed for the determination of diazepam residues in aquatic products. A novel magnetic nanoparticle material, Fe₃O₄@SiO₂@DVB-NVP, was synthesized and applied as an adsorbent for sample cleanup. The sample preparation procedure involved extraction with 1% ammonia–acetonitrile, followed by purification using the MSPE technique to efficiently remove matrix interferents. Chromatographic separation was achieved on an ACQUITY UPLC BEH C₁₈ column with a gradient elution program using a mobile phase composed of 0.1% formic acid–2 mM ammonium acetate solution and methanol. Detection was performed under multiple-reaction monitoring (MRM) mode with positive electrospray ionization (ESI⁺). Quantification was carried out using the external standard method. The synthesized magnetic material was characterized using SEM, TEM, FTIR, XRD, BET, and VSM, confirming its mesoporous structure, strong adsorption capacity, and excellent magnetic responsiveness. The method demonstrated good linearity over the concentration range of 0.25–50 μg/L (r² = 0.997). The limits of detection and quantification were 0.20 μg/kg and 0.50 μg/kg, respectively. Average recoveries from spiked blank matrices at three levels (0.5, 2.5, and 5.0 μg/kg) ranged from 89.3% to 119.7%, with relative standard deviations (RSDs) between 0.8% and 10.2%. The proposed method is highly selective, exhibits minimal matrix interference, and provides reliable quantitative performance, making it suitable for the qualitative and quantitative analysis of diazepam residues in aquatic products. Full article

Above-ground biomass in agroforestry refers to the total mass of living vegetation, primarily trees and shrubs, integrated into agricultural landscapes. It plays a key role in climate change mitigation by capturing and storing carbon. Accurate estimation of above-ground biomass in agroforestry systems requires effective drone deployment and sensor management. This study presents a detailed methodology for biomass estimation using Unmanned Aircraft Systems, based on an experimental campaign conducted in the Campania region of Italy. Multispectral drone platforms were used to generate calibrated reflectance maps and derive vegetation indices for biomass estimation in agroforestry landscapes. Integrating field-measured tree attributes with remote sensing indices improved the accuracy and efficiency of biomass prediction. Following the assessment of mission parameters, flights were conducted using a commercial drone to demonstrate consistency of results across multiple altitudes. Terrain-follow mode and high image overlap were employed to evaluate ground sampling distance sensitivity, radiometric performance, and overall data quality. The outcome is a defined process that enables agronomists to effectively estimate above-ground biomass in agroforestry landscapes using drone platforms, following the procedure outlined in this paper. Predictive performance was evaluated using standard model metrics, including R², RMSE, and MAE, which are essential for replicability and comparison in future studies. Full article

This study presents a novel probabilistic framework that combines the Duration Time Method (DTM) with the ATC-58 damage assessment procedure. The method reduces computational cost by 30% compared to incremental dynamic analysis (IDA) while maintaining < 10% error in collapse prediction for low-to-mid-rise buildings. Accordingly, this study proposes a simplified framework based on the duration time method to estimate seismic responses by considering the uncertainty associated with the record as the most important uncertainty in the seismic responses of structures, and to offer an alternative to the conventional and computationally intensive incremental time history analysis. Then, using the results of the incremental time history and duration analysis in the proposed framework on a sample frame set consisting of 34 concrete frames from 1 to 20 stories, the strengths and weaknesses of the aforementioned method have been investigated. Considering the results of this step, the prediction of probable collapse threshold modes as the most challenging type of response has been identified and investigated in more depth with the help of simple methods. Finally, and in accordance with the research objective, various parameters of seismic damage in the aforementioned frames were extracted using the results of incremental time history analysis and the proposed framework based on the duration time method and using the ATC-58 guideline procedure, and by presenting the related errors, an attempt has been made to provide the audience with a measure of accuracy in estimating damages using this method. Finally, considering the strengths and weaknesses of the proposed method and estimating the volume of calculations in different stages of damage estimation, an attempt has been made to present a strategy for predicting maximum damage based on probabilities in order to examine multiple design options. Full article

Electromagnetic vortex waves have received widespread attention in many fields due to their unique physical characteristics. The information dimension provided by vortex electromagnetic waves brings possibilities for future breakthroughs in radar detection and imaging. This article proposes a multi-modal aggregated electromagnetic vortex wave generation method for the first time. Moreover, it conducts vehicle imaging experiments to verify the method’s practicality. The core element of the experiment is to simultaneously generate multiple-mode electromagnetic vortex wave signals with energy accumulation and perform fusion processing. Firstly, multiple orbital angular momentum (OAM) modes are superimposed to generate a mode group, and the initial phase of the modes in the mode group is further controlled to synthesize aggregated electromagnetic vortex waves. Based on the generation of aggregated vortex waves, imaging experiments were conducted using a vehicle-mounted setup. The experimental procedure and multi-modal fusion results were presented. It has been shown that the energy of the main lobe signal of the image target is enhanced by utilizing multi-modal vortex radar information fusion, which can improve the signal-to-noise ratio of the target imaging. Full article