Search Results (579)

The cantilever pick-and-place arm of the high-speed placement machine is susceptible to micro-vibration and elastic deformation under high-acceleration motion, thereby degrading chip placement accuracy. To address this issue, this paper presents an analytical study on the natural frequency characteristics and structural optimization of slender variable-cross-section rods. First, based on the thin-walled shell theory, a displacement field model of the thin-walled cantilever rod is established. Second, combining the energy method and Hamilton’s principle, the undamped free vibration equation is derived. Using the Rayleigh–Ritz method with Chebyshev polynomials as the basis functions, an analytical calculation model for the natural frequency of the variable-section thin-walled rod is constructed. The model is validated against finite element simulations, and the relative errors of the low-order natural frequencies are controlled within 5%, confirming its favorable accuracy and robustness. Furthermore, the four-factor three-level orthogonal experiment is designed with the objective of maximizing natural frequency to conduct parameters sensitivity analysis. Accordingly, the optimal structural parameter combination ϕ₃ = 8 mm, L₁ = 10 mm, L₂ = 50 mm, and L₃ = 5 mm) is determined. Finally, the maximum dynamic deformation under high-acceleration motion decreases from 0.066 mm to 0.021 mm, a reduction of 68.2%, which effectively suppresses residual vibration and end displacement deviation. The analytical method proposed in this study provides a theoretical basis for the rapid dynamic performance evaluation of flexible components in high-speed precision equipment, and the optimization strategy can offer engineering references for the high-stiffness design of key components in chip placement machines. Full article

This study scientifically assessed the safety of the Ming Dynasty official-style timber structure of Taiyuan Chongshan Temple’s Great Mercy Hall, a nationally protected cultural relic. An integrated framework was adopted, including form restoration via 3D laser scanning and manual surveying, damage detection using impedance meters, stress wave tomography and one-dimensional stress wave testing, mechanical analysis with a differentiated material finite element model, and short-term on-site monitoring at risk points. Results showed that the 303.3 mm construction ruler length was restored, with the column grid tilting northwestward; the main structure was hardwood pine, and critical columns had severe localized damage (24% internal damage rate, 13% cross-sectional damage ratio) with 42% residual strength in some members; and the structure remained elastically safe, with material degradation causing 6.3–13.3% linear displacement amplification. Two weak links (eave purlin deflection: 33–37 mm; double-eave golden column axial force concentration: 86.9–88.5 kN) and dougong’s outward inclination due to eccentric compression were identified. Short-term monitoring indicated temperature-driven elastic responses and an 8 mm cumulative residual displacement in the northern single-step beam, and a three-level early warning threshold system was proposed. This study clarified the hall’s state as “overall stable with localized weaknesses”, providing a methodological reference for the preventive protection of similar ancient timber structures. Full article

Single point incremental forming (SPIF) represents a flexible manufacturing process capable of producing complex sheet metal parts without the need for dedicated forming dies. However, achieving high dimensional accuracy remains a major challenge due to phenomena such as elastic springback and localized deformation. In this context, the present study investigates the influence of tool-axis orientation on the dimensional accuracy of parts manufactured through robot-based single point incremental sheet forming (RB-SPIF). The experimental analysis considered two toolpath strategies (contour and spiral), two vertical step sizes (0.5 mm and 1 mm), and two tool-axis configurations (fixed tool-axis and wall-normal tool-axis orientation), resulting in eight experimental cases. The dimensional accuracy of the manufactured parts was evaluated using optical 3D scanning and cross-sectional profile analysis. The results show that the vertical step size has a significant influence on the resulting geometry, with smaller step sizes generating profiles closer to the nominal geometry. The toolpath strategy also affects the geometry, with spiral trajectories generally producing slightly improved profiles compared to contour strategies; however, this effect was not found to be statistically significant under the investigated conditions. Furthermore, the use of a wall-normal tool-axis configuration improves the agreement between the measured and nominal profiles by enhancing the contact conditions between the tool and the metal sheet surface. These findings indicate that adaptive tool-axis orientation represents a promising strategy for improving the dimensional accuracy of parts produced by robot-based incremental sheet forming systems. Full article

We present fully relativistic calculations of integral cross sections and swarm transport properties for positron–radon scattering over a wide energy range (0–1000 eV) and reduced electric field range (0.01–1000 Td). Elastic (total, momentum-transfer and viscosity-transfer), discrete excitation, direct annihilation, positronium formation and positron-impact ionization cross sections are obtained using a complex relativistic optical potential method. Owing to the large atomic number of radon and the absence of experimental scattering data, a consistent relativistic treatment is essential. The present work provides the first fully relativistic, internally consistent cross-section dataset for positron swarms in radon gas. Using a multi-term solution of Boltzmann’s equation, steady-state transport coefficients are calculated and found to be strongly influenced by energy-dependent reactive loss, particularly positronium formation. Significant divergence between bulk and flux transport coefficients is observed, including non-monotonic bulk drift velocities and pronounced suppression of longitudinal bulk diffusion at intermediate fields (0.3–1000 Td). Time-dependent field-free calculations further quantify thermalization and annihilation dynamics through the evolution of the mean energy and $⟨Z_{\mathrm{eff}}⟩\left(t\right)$. These results provide a robust theoretical foundation for modelling positron transport and annihilation in radon and other heavy noble gases where relativistic and reactive effects are crucial. Full article

This paper examines whether broad enterprise AI adoption in Europe is best understood as an isolated technology decision or as the outcome of a wider bundle of digital capabilities. Using harmonized Eurostat data for European enterprises, the analysis builds a repeated cross-section at the country–size-class–year level and models high AI adoption with a combination of random forest and elastic-net estimation. The dependent variable captures enterprises using at least one AI technology, while the explanatory set focuses on cloud adoption, cloud CRM, cloud ERP, cloud database hosting, cloud security, cloud software use, e-sales intensity, and enterprise size. The findings reveal a stable predictive structure and consistent classification performance across specifications. Across models, cloud CRM and e-sales emerge as the strongest predictors of high AI adoption, followed by general cloud use and selected data-related cloud capabilities. This ordering remains largely stable in threshold-sensitivity checks based on alternative definitions of high adoption. The pattern also remains visible when country controls are removed, which suggests that the result is not merely a reflection of national heterogeneity. The paper contributes by shifting attention from broad claims about “digital readiness” to a narrower and more operational notion of capability complementarity: AI uptake tends to cluster where firms already possess customer-facing, cloud-based, and commercially digital infrastructures. In that sense, the paper offers a transparent, reproducible, and policy-relevant account of the digital foundations of enterprise AI adoption in Europe. Full article

The condition assessment of alkali-silica reaction (ASR)-damaged concrete structures necessitates accurate reproduction of ASR expansion progression and its induced load effects across time and spatial dimensions. To address this challenge, a time-dependent free ASR expansion model was developed based on experimental measurements. A user subroutine incorporating stress-dependent behavior for restrained ASR expansion evolution was implemented on the ABAQUS platform and validated through simulation of ASR expansion in specimens under external loading and internal reinforcement restraint. Finite element analyses of the reinforced concrete specimens revealed distinct variations in ASR expansion between the surface and interior zones of concrete members. The assumption that surface ASR expansion strain equals steel rebar strain leads to significant overestimation of actual rebar stress and strain conditions. Additionally, based on the validated finite element model, the influence of elastic modulus, creep, stress-dependent function, steel plate thickness, and reinforcement ratio on the ASR expansion was investigated. For the reinforced concrete specimens, the stress variation over the cross-section is considerably reduced when creep is considered, while the concrete strain at the surface is only slightly influenced by creep. Full article

This study explores the impact of renewable energy consumption on environmental quality in ten OECD economies over the period 1990–2024, aiming to assess its contribution as a structural driver of decarbonization in advanced economies. Given the presence of strong cross-sectional dependence and heterogeneous country dynamics, the analysis employs second-generation panel econometric techniques. Stationarity is assessed using the CIPS unit root test. Long-run relationships are examined using the Westerlund error-correction-based cointegration approach. Long-run elasticities are estimated using the Common Correlated Effects Mean Group (CCE-MG) and Augmented Mean Group (AMG) estimators. Short-run dynamics are analyzed within a panel error-correction framework. The results confirm the existence of a stable long-run equilibrium relationship among the variables. Renewable energy consumption is associated with a negative effect on CO₂ emissions, with the CCE-MG estimate indicating that a 1% increase in renewable energy reduces emissions by approximately 0.067%, although the long-run statistical significance remains marginal. In the short run, renewable energy is also associated with lower emissions, indicating both structural and immediate mitigation dynamics. By contrast, energy consumption and financial development increase emissions, while economic growth does not exhibit a robust long-run effect, providing no support for the Environmental Kuznets Curve hypothesis. The error-correction term confirms rapid convergence toward long-run equilibrium. Robustness analysis using carbon intensity as an alternative environmental indicator yields consistent findings. In sum, the results suggest that renewable energy expansion should be complemented by energy efficiency policies and the reorientation of financial systems toward green investments to achieve effective decarbonization. From a policy perspective, coordinated strategies integrating renewable deployment, efficiency improvements, and sustainable finance are essential for achieving long-term environmental sustainability in OECD economies. Full article

Background/Objectives: Autoimmune thyroiditis affects physical and cognitive development in children. Therefore, early detection can prevent symptoms that could lead to lifelong changes. Autoimmune thyroiditis can frequently accompany type 1 diabetes (T1DM) and celiac disease (CD). The goal in this study is to evaluate its usability as a screening method by assessing thyroid elasticity in children with negative thyroid autoantibodies and T1DM or CD. Methods: This cross-sectional, case–control, single-center study was conducted with children who had applied to the Pediatrics outpatient clinic of Kayseri City Education and Research Hospital (Turkey). The study included three groups of cases (T1DM, CD and control). The value of the shear wave elastography (SWE) color map was recorded in kPa. Comparisons between two independent groups were conducted using either Student’s t-test or the Mann–Whitney U-test, while categorical variables were analyzed with the Chi-square test. A correlation analysis was conducted to evaluate the relationship between the variables. Results: The study cohort comprised 185 children, of whom 71 had T1DM, 54 had CD, and 60 constituted the healthy control group. The participants ranged in age from 4 to 17.9 years, with a mean age of 11.4 ± 3.8 years. The gender distribution did not differ significantly between the groups. Anti-thyroid peroxidase (TPOAb) levels did not differ significantly between the groups (p = 0.894). Thyroid volume or standard deviation score did not differ significantly between the groups. Corresponding SWE values in the T1DM, CD and control groups were 7.7 (6.0–9.3), 5.9 (5.2–7.9) versus 7.1 (6.0–9.6), respectively (p = 0.002). Correlations were significantly associated between SWE scores and anti-thyroglobulin (TgAb), thyroid volume, mean hemoglobin A1c (HbA1c), and time elapsed from a diagnosis of CD. Conclusions: The SWE scores were observed to be higher in children with T1DM compared to those with CD. Full article

Weight reduction and dynamic performance optimization are critical for airborne direct-drive VICTS satellite communication antennas, which require lightweight, high-speed, and high-precision rotation. Traditional vibration suppression methods, such as uniform support layout and added damping, rely heavily on empirical trial and error, lack targeted modal control, and cannot balance lightweight design with dynamic stiffness. To address these issues, this paper proposes a wave-theory-based dynamic modeling and rapid optimization method for multi-layer rotating components in direct-drive VICTS antennas. The kinematic model of the rotating ring and ball revolution excitation are derived using the annular wave equation and bearing kinematics. A Modal Blocking Mechanism is established: placing support balls at positions satisfying the half-wavelength constraint suppresses target mode shapes via wave interference, achieving vibration attenuation at the source. A homogenization equivalent method based on RVE is developed for irregular cross-section rings, yielding analytical expressions for in-plane equivalent elastic modulus and out-of-plane equivalent shear modulus. These parameters are integrated into the wave equation to analytically solve vibration modes, avoiding iterative finite element computations. A rapid multi-objective optimization framework is then constructed, minimizing the structural weight and maximizing the modal separation interval under dynamic stiffness and excitation frequency constraints. Numerical simulations, FE analysis, and prototype tests validate the method: the maximum analytical error is only 3.1%. Compared with uniform support designs, the optimized structure achieves a 40% weight reduction, a 40% increase in minimum modal separation, and a 65% reduction in the RMS tracking error. This work provides an efficient, deterministic dynamic design method for large-diameter ring structures, transforming vibration control from empirical adjustment into a precise, physics-informed optimization. Full article

This study investigates the mechanical behavior of molybdenum tailings (MT) concrete circular specimens under combined chloride salt dry–wet cycling and high-temperature exposure, simulating post-fire conditions in corrosive environments. A total of 50 circular cross-sectional specimens were fabricated with varying concrete strength grades (C30 and C40), MT replacement ratios (0–100%), and exposure conditions (NaCl solutions: 20,000 and 50,000 mg/L; temperature: ambient/400 °C). Axial compression experiments were conducted to evaluate their performance. Analysis of mass change rates and post-cycling phenomena indicated that MT content significantly influenced mass variation, with the 100% MT group having a 2.3 times higher mass increase than the 0% MT group. Especially, under coupled conditions, compared with the 0% MT control group, the 25% MT group showed a 28.6% increase in peak stress, 8.3% reduction in peak strain, 12.1% rise in Elastic modulus, and 13.3% decrease in Poisson’s ratio, confirming that MT incorporation mitigates coupled strength degradation. Two failure modes were identified: end-cone failure and overall splitting failure. Chloride salt corrosion markedly reduced the load-bearing capacity of the specimens, decreasing both their peak displacement and peak strain. Furthermore, peak strain decreased as the molybdenum tailings replacement ratio increased. Scanning electron microscopy (SEM) revealed that dry–wet cycling prior to high-temperature exposure promoted hydration product densification, indicating a partial enhancement of hydration reactions and consequent strength improvement. Although high-temperature exposure degraded the strength of MT concrete, the incorporation of MT mitigated this weakening effect. The relationship between the peak stress of concrete and its axial compressive strength under the coupled effects of MT replacement ratio and NaCl solution concentration has been established via fitting. This study reveals the coupled damage mechanism, verifying the mitigating effect of MT on coupled chloride-thermal damage, and establishing a validated bearing capacity prediction model, which provides a valuable reference for assessing the behavior of MT concrete circular specimens subjected to salt corrosion and elevated temperatures. Full article

This study presents an analytical formulation for predicting the additional elastic deflection of tapered steel beams with variable-diameter circular web openings, a configuration that is not addressed by existing analytical models or current design codes. The proposed formulation accounts for the coupled effects of cross-section tapering, progressive variation in opening diameter along the span, and shear–bending interaction within perforated regions. To the best of the authors’ knowledge, this is the first analytical model addressing such complex non-prismatic cellular beam configurations. The formulation is implemented in MATLAB R2019a, enabling fast and automated deflection calculations over a wide parametric range, including various loading cases, tapering ratios, beam spans, web-post widths, and opening dimensions. For prismatic configurations, the analytical predictions are benchmarked against Eurocode 3 and the SCI P355 design guide, both originally developed for beams with constant cross-sections and regular openings. The results demonstrate the improved accuracy and broader applicability of the proposed approach. For tapered configurations with variable-diameter openings, the formulation is assessed against finite element simulations performed in Abaqus/CAE 2017, with the numerical model previously validated against experimental results available in the literature. The proposed method provides a reliable and practical analytical tool for the serviceability assessment of tapered perforated steel beams in structural engineering applications. Full article

Present and future rare isotope accelerator facilities provide new opportunities to explore the structure of unstable nuclei. We report the measurements of the elastic scattering angular distributions of ²¹Na and ²²Na on the doubly magic ⁴⁰Ca above the Coulomb barrier energies, using high-purity post-accelerated ISOL beams from Beijing Radioactive Ion Beam Facility (BRIF). Angular distributions were measured with a silicon detector telescope array, and relative cross sections were determined with a CaF₂ target on Au backing. The data were well reproduced by optical model calculations with Woods–Saxon and USNP potentials, the latter giving better agreement. These results confirm the stable operation and performance of the BRIF ISOL production and post-acceleration system, demonstrate its capability to provide radioactive beams of useful intensity and purity for future investigations of reaction dynamics and astrophysically relevant processes involving proton-rich nuclei, and simultaneously extend proton-rich elastic scattering studies to heavier systems. Full article

Comparative analysis of nanostructured multilayer Cr/(Cr/a-C)ml coatings on HS6-5-2 steel was carried out. The coatings were deposited at various chromium target power values using PVD technology, particularly the magnetron sputtering method. The effect of different technological regimes on the properties of the nanostructured multilayer Cr/(Cr/a-C)ml coatings was studied. Identical characterization methods were used for the three types of coatings obtained. Cross-sections of the coated samples were prepared in order to directly determine the thickness of the resulting coatings, their uniformity, and the presence of defects or imperfections, both at the substrate–coating interface and within the coatings themselves. Calotest and Daimler-Benz adhesion test were also performed to evaluate the coated layers’ thickness and evaluate their adhesion strength. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analyses were carried out to define the chemical composition of the multilayered coatings. To evaluate the hardness and modulus of elasticity of the resulting coatings, nanoindentation measurements were also conducted. The data obtained under the three different deposition regimes were analyzed and compared, which allowed us to assess the influence of the chromium target power during the deposition process on the properties of the obtained coatings. Full article

Decoupling between CO₂ emissions and economic growth is critical to reversing climate change. The OECD plays a crucial role in this regard, given its considerable share of global CO₂ emissions and GDP. This study examines the decoupling performance and the roles of renewable energy transition, as well as specific eco-innovations on climate change mitigation and environmental technology development across the OECD economies. The preliminary tests on a large panel of OECD countries identify cross-sectional dependence, structural breaks and heterogeneity. For robustness, the study proposes Fourier-CS-ARDL, Fourier-AMG, and Fourier–Dumitrescu–Hurlin methods as generalizations of their linear counterparts. After identifying cointegration and its singularity with Fourier-bootstrapping bounds and Fourier–Johansen tests, the modeling stage suggested a positive, but significantly inelastic long- and short-run elasticity of emissions to economic growth. Most of these effects are reversed by renewable energy transition in the long run and partially reversed in the short run. These CO₂ mitigation effects are also evident across different eco-innovations with varying temporal impacts. Novel Fourier causality tests identify feedback loops between CO₂ and CO₂-mitigating factors, as well as unidirectional causality from growth to all mitigating factors, confirming the indirect effect of growth on CO₂ mitigation. Overall, these results clearly suggest “relative” decoupling in OECD accompanied by CO₂e mitigation effects from eco-innovations and energy transition, and highlight the potential for green growth following the successful adaptation of energy transition and eco-innovations. Policymakers in OECD are encouraged to leverage the identified feedback mechanisms and establish international technology transfer policies to homogenously curb CO₂ emissions. Full article

In this paper, aiming at the aging problem of rubber sealing strips in key parts of hydropower units under long-term load, this study proposes a quantitative aging-feature-extraction technique centered on the ratio of the short-axis length to the original diameter (b/D) of serviced rubber strips. Through a systematic approach combining theoretical analysis, numerical simulation, and measured data calculations, the research first derives from energy principles that the elastic modulus (E) and yield stress (σ_s) are key physical parameters characterizing rubber aging, reflecting the material’s energy storage capacity and irreversible deformation threshold, respectively. Based on this, a radial compression simulation model of rubber strips is established, focusing on the cross-sectional deformation laws under 25% and 30% compression ratios in serviced conditions. It is found that the short-axis diameter ratio b/D exhibits a significant linear relationship with the dimensionless yield stress (σ_s/E), and a quadratic relationship with the dimensionless unit-length reaction force (F/ED). Using measured data, fluororubber (FKM) and nitrile rubber (NBR) specimens after 17 years of service are selected for radial compression experiments to extract the elastic modulus. The calculated results are compared with elasticity modulus estimates based on hardness empirical formulas (Gent’s and Qi’s formulas), showing consistency, particularly with Qi’s formula for NBR. This method enables rapid and accurate assessment of rubber aging, demonstrating the effectiveness and practicality of using b/D as a feature parameter. The study provides a quantitative and convenient tool for condition monitoring and life prediction of industrial equipment seals, especially suitable for the operation and maintenance of rubber components in complex environments such as hydropower units. Full article