Search Results (87)

Background and Objectives: Three-dimensional printing is increasingly used to fabricate dental restorations; however, limited evidence is available on the mechanical performance and fracture behavior of printable resin materials used for endocrown restorations. Fracture load alone may not fully describe material performance, particularly when brittle or defect-sensitive failure occurs. This in vitro study aimed to compare the fracture resistance, Weibull parameters, experimental Mode I fracture toughness parameter, and failure patterns of three 3D-printed resin materials used for endocrown restorations. Materials and Methods: Thirty anatomically identical molar replicas were produced from a single prepared tooth model and restored with endocrowns fabricated from NextDent C&B MFH (NextDent B.V., Soesterberg, The Netherlands), SprintRay Crown (SprintRay Inc., Los Angeles, CA, USA), and BEGO VarseoSmile Crown Plus (BEGO GmbH & Co. KG, Bremen, Germany) (n = 10/group). The restorations were cemented and subjected to compressive loading until fracture. Maximum fracture force values were analyzed using Welch’s ANOVA and Weibull statistics. In parallel, single-edge-notched bend (SENB) specimens were fabricated from the same materials and tested using an ASTM D5045-based configuration to calculate an experimental Mode I fracture toughness parameter. Representative fractured crowns and standardized specimens were examined using stereomicroscopy to assess visible failure morphology. Results: No statistically significant difference in maximum fracture force was found among the three materials (Welch’s ANOVA, p = 0.217). The mean fracture force values were 862.37 N for NextDent C&B MFH, 804.37 N for SprintRay Crown, and 699.43 N for BEGO VarseoSmile Crown Plus. In the complementary analyses, BEGO VarseoSmile Crown Plus showed the highest Weibull modulus (m = 9.36), indicating a narrower distribution of fracture values, and the highest mean experimental Mode I fracture toughness parameter (5.250 MPa·m^0.5) under the present experimental conditions. Qualitative stereomicroscopic analysis revealed material-dependent visible failure patterns: SprintRay Crown exhibited more extensive fragmentation, whereas BEGO VarseoSmile Crown Plus showed a more defined visible fracture pattern with less secondary fragmentation. Conclusions: Fracture load alone was insufficient to characterize the mechanical behavior of the tested materials fully. Weibull parameters, the experimental fracture toughness parameter, and failure morphology provided complementary information and should be considered when evaluating 3D-printed resin materials for endocrown restorations. Full article

To reduce the modeling effort and computational cost of assembled composite shear walls with C-shaped steel frames in global structural analysis, this study proposes an engineering-oriented simplified mechanical analysis method. Three representative specimens—a C-shaped steel-frame composite shear wall (CSCSW), a rectangular steel-frame composite shear wall (RSCSW), and a T-shaped, C-shaped steel-frame composite shear wall with a vertical connection (VTCSWC)—are decomposed into functional modules according to their load-transfer mechanisms. Simplified models comprising axial springs, diagonal braces, and a modified three-vertical-line-element model are established. Degrading bilinear Clough and trilinear Takeda models are adopted as the restoring-force relationships, and the governing parameters are determined through mechanical equilibrium analyses. The three simplified wall models are implemented in OpenSees to obtain hysteresis curves, skeleton curves, and stiffness-degradation responses. Comparisons with quasi-static test results show that the errors in peak load and secant stiffness are both within 10%, while the models reproduce the stiffness degradation and pinching characteristics of the specimens. Relative to refined three-dimensional solid finite element models, the proposed approach substantially reduces computational cost without compromising engineering accuracy, providing an efficient tool for structural design and seismic performance assessment of assembled C-shaped steel-framed composite shear-wall systems. Full article

Mechanical properties are considered key determinants of the long-term success of implant-supported zirconia restorations. However, limited data are available regarding the parameters that influence the fracture strength of implant-supported zirconia restorations. Generative design is well suited for the optimization in implant prosthodontics, as it allows the definition of a constrained design space and the application of optimization algorithms to evaluate numerous design iterations based on predefined biomechanical objectives. Prior to the implementation of generative design, it is essential to identify and define the parameters that influence the optimization of structures such as hybrid implant abutments. The parameters identified in this review will be incorporated into the parametric model and subsequently applied within the generative design workflow to facilitate the customization of hybrid implant abutments. A comprehensive literature search was conducted in the PubMed and Scopus databases to identify relevant studies published between 1 December 2025 and 1 May 2026. In vitro studies investigating fracture strength of implant-supported zirconia restorations were considered eligible for inclusion. A total of 12 studies met the eligibility criteria. Their findings indicated that implant-supported zirconia restorations generally withstood fracture loads exceeding the maximum masticatory forces reported in the oral environment, although the recorded values varied according to restoration design, abutment type, surface modifications, material thickness, retention type, material selection, luting agents, and interface characteristics. Full article

Articular cartilage possesses a limited intrinsic repair capacity, and current treatment strategies frequently result in fibrocartilaginous repair tissue with inferior structural and mechanical properties compared with native hyaline cartilage. Increasing evidence indicates that successful restoration of joint function requires regeneration of the entire osteochondral unit and adequate integration between cartilage and subchondral bone. Cartilage tissue engineering has emerged as an effective approach for repairing damaged cartilage. The present study evaluated the long-term performance of electrospun PLA/PCL (70/30) scaffolds coated with iodine-doped polypyrrole (PPy-I), with and without aggrecan incorporation, in a rabbit osteochondral defect model after 12 months of implantation. Two scaffold formulations were evaluated: M1 (PLA-PCL-PPy-I) and M2 (PLA-PCL-PPy-I-AG), each implanted either without cells or after in vitro pre-culture with autologous chondrocytes prior to implantation. Histological analyses were performed to assess tissue organization and osteochondral integration, while indentation testing was used to characterize the mechanical behavior of the regenerated tissues. Experimental force–displacement data were further analyzed using a generalized nonlinear Maxwell viscoelastic model. Histological evaluation revealed that scaffold composition and cellularization influenced the characteristics of the regenerated tissue. The M2 scaffold pre-cultured with autologous chondrocytes exhibited the structural organization most closely resembling native hyaline cartilage, including a tri-zonal architecture and a continuous tidemark indicative of improved osteochondral integration. Mechanical testing demonstrated nonlinear viscoelastic behavior and hysteresis in both regenerated and native tissues. The proposed generalized nonlinear Maxwell viscoelastic model provides a practical framework for the mechanical characterization of regenerated osteochondral tissues using only two effective parameters representing the elastic and viscous response, and may support future studies aimed at estimating their intrinsic mechanical properties. Full article

Conventional linear isolators struggle to combine high static load-bearing capacity with effective low-frequency vibration isolation. To address this limitation, this study proposes an inclined rhombic crab-inspired quasi-zero-stiffness (I-QZS) isolator. A generalized static model is established based on the segmented linkage of crab walking legs. A physics-constrained NSGA-II algorithm is used to optimize the key geometric parameters while preventing bistable snap-through by imposing a positive-stiffness constraint over the full stroke. A stiffness-compensation strategy bridges the gap between the ideal rigid-body model and the actual 3D-printed compliant structure. The dynamic response is represented by a cubic polynomial restoring-force model, and the resulting equations are solved using the incremental harmonic balance method with SVD (singular value decomposition)-based null-space continuation. Large-amplitude excitation experiments show that the I-QZS shifts the resonance peak to 0.77 Hz, reducing the peak frequency by 64.19% and the peak transmissibility by 67.06% relative to a linear isolator, while substantially broadening the isolation bandwidth. Bifurcation analysis further identifies stability boundaries for engineering design. These results provide an integrated theoretical and experimental framework for ultra-low-frequency passive vibration isolation. Full article

To address the cleaning requirements for marine growth on offshore platform jackets, an underwater cleaning robot featuring a combined “chassis + thruster-assisted adhesion + magnetic adhesion” mode is designed. The robot is equipped with four thrusters and a magnetic-adhesion wheeled chassis, enabling stable attachment and movement on varying-diameter pipes. Kinematic models in both inertial and body-fixed coordinate systems are established, and six-degree-of-freedom (6-DOF) dynamic equations are derived. These equations systematically incorporate key factors including added-mass forces, damping forces, hydrostatic restoring forces, ocean current disturbances, and thruster torques. Based on CFD simulations employing overset grids, moving reference frames, and simple harmonic motion techniques, the damping, added-mass, and thruster thrust and torque coefficients for each degree of freedom are identified. The obtained parameters demonstrate reasonable consistency with the CFD internal validation and preliminary external verification, providing a complete theoretical model and simulation data to support the motion control and operational stability analysis of the underwater cleaning robot. The established dynamic model addresses the free-navigation condition of the robot without cleaning operation. The additional hydrodynamic effects during cleaning operations will be considered in future work. Full article

Acute myocardial ischemia, caused by a sudden reduction in coronary blood flow, initiates metabolic disturbances that lead to severe pathophysiological consequences. These include electrophysiological alterations, such as changes in action potential morphology and impaired electrotonic coupling between cardiomyocytes, and mechanical dysfunction, characterized by reduced contractile force and subsequent mechanical discoordination across the ventricular wall. This study employs multi-scale mathematical modeling to investigate the effects of acute ischemia on the electromechanical activity of a single human cardiomyocyte and a one-dimensional myocardial tissue. We identify the conditions for conduction block initiation and the parameters governing conduction restoration in ischemic tissue, and analyze the underlying mechanisms. Our simulations demonstrate that conduction slowing in the one-dimensional strand under ischemia directly results from the hyperkalemia-induced reduction in the fast sodium current (i_Na). This i_Na reduction is enhanced by direct electromechanical coupling and mechano-electric/mechano-calcium feedback in the mechanically and electrically interacting cardiomyocytes of the one-dimensional tissue. Under 15 min ischemia conditions, i_Na decreases to a level insufficient to sustain excitation propagation, causing conduction block. Under the conditions of this simulation, where gap junction conductance was held unchanged, the block occurred via the i_Na reduction which is itself amplified by mechano-calcium feedback. Furthermore, our model suggests a potential compensatory mechanism against conduction block in ischemic myocardium. Experimental evidence indicates that ischemia can disrupt gap junctions. A moderate reduction in the electrodiffusion coefficient along the strand, simulating reduced gap junction conductance, can convert persistent conduction block into a transient form and even eliminate it completely, facilitating the maintenance of excitation wave propagation. Full article

Precast concrete (PC) structures are increasingly adopted in building construction for their sustainable construction advantages. However, theoretical models for seismic design of precast concrete walls with concrete-filled steel tubular (CFST) elements remain limited. The lack of such models hinders the performance-based seismic design and resilience assessment of these hybrid structures. This study investigates the seismic mechanism and develops a restoring force model for precast concrete superposed shear walls with CFST end columns (PCSSWEC). A refined three-dimensional finite element model was established using ABAQUS and validated against quasi-static cyclic test results of three full-scale specimens. The four-stage loading mechanism—elastic, wall cracking, elastoplastic yielding, and ultimate failure—was revealed, with the precast–postcast concrete interface identified as the primary weak link governing post-peak strength degradation. Comprehensive parametric studies examined the influence of shear span ratio (λ = 0.75–3.25), axial compression ratio (n_a = 0.1–0.6), steel tube width-to-thickness ratio (B/t = 20–80), and concrete strength (C30–C60) on seismic performance. Results indicate that intermediate walls (λ = 1.75–2.25) exhibit optimal ductility, and a steel tube with B/t = 40–60 provides a balanced combination of strength and deformation capacity. A tri-linear backbone curve model with explicit formulae for equivalent stiffness and load capacity was developed, along with modified Clough-based hysteretic rules incorporating stiffness degradation through a common yield-point approach. Validation against experimental and numerical results demonstrates reliable model performance for primary structural parameters: lateral load bearing capacity and ultimate drift ratio are predicted within ±10%, while yield load and ductility predictions show larger scatter due to inherent challenges in cyclic behavior characterization. The proposed restoring force model provides a practical tool for performance-based seismic design and resilience assessment of precast concrete buildings. Full article

Reduced service life of components, units, and assemblies operating under extreme conditions, characterized by high cyclically varying stresses, remains a significant issue. The present work addresses this problem by enhancing the reliability and cyclic durability of materials through electric pulse force intensification. As a result of the study, appropriate equipment for electric pulse force intensification was selected. A technology for electric pulse force intensification was developed, and process parameters such as current strength, current density, and pulse duration were optimized. Using statistical analysis of experimental data, 3D models were created, and empirical mathematical equations were derived to describe the influence of key process parameters on the cyclic durability of materials. The geometric parameters of cracks were examined during cyclic durability tests under bending with low-cycle loading, both before and after electric pulse activation. Using SEM, we studied the material structure in the crack region, revealing that pulsed electric current enhances cyclic life by “partial healing” of structural defects. Statistical modeling produced empirical equations expressing the relationships between various characteristics. The mechanism of defect partial healing in materials subjected to electric pulses was described, and the impact of electric pulse activation on samples was evaluated. This demonstrated the potential to fully restore a component’s service life after cyclic loading at 80% of its ultimate limit. Full article

The Santiago River is a highly anthropogenically impaired lotic system globally, yet the mechanisms governing its contaminant transport remain poorly understood under static monitoring paradigms. This study evaluates how hydrological forcing dictates the mobilization and bioavailability of trace metals by integrating a 15-year public hydrochemical database from 10 monitoring nodes with SAR-derived discharge estimates and thermodynamic metal modeling (PHREEQC). To validate the structural integrity of the mass load estimates against hydrometric uncertainties, a deterministic boundary-sensitivity analysis was conducted. Results empirically refute the classical dilution paradigm, introducing the “Anthropogenic Pulse” to describe the non-linear acceleration of pollutant export during high-flow events (discharge Q surging from 36.62 to 286.13 m³/s). While climate-driven parameters follow seasonal cycles, industrial stressors (COD, Pb, Cd) remain in a chronic steady state, decoupling from volumetric dilution. Based on coupled × CQ × C (discharge × concentration) estimates, this dynamic induces a synchronized flushing of toxic burdens, exporting monthly peak loads exceeding 51,000 kg of Zinc, 6500 kg of Lead, and 3100 kg of Cadmium. Thermodynamic simulations reveal that this hydrological flushing functions as a chemical activator; the seasonal dilution of natural Alkalinity and Hardness suppresses the river’s theoretical buffered pH (from 8.5 to 7.0), maintaining metals in their uncomplexed free-ion states (Me²⁺). Modeling indicates that nearly 90% of the exported Cadmium remains in this highly labile, toxic form due to a dual coupling with both river Discharge (r_s = 0.87) and pH (r_s = 0.79). The identification of stochastic arsenic peaks 100 times above regulatory limits at Paso de Guadalupe (RS-08) underscores the failure of concentration-based monitoring. Our findings suggest that restoration strategies should shift toward mass-loading-based regulatory frameworks and targeted sediment management at critical nodes to mitigate the chronic export of bioavailable industrial waste. Full article

The dynamic reliability of steam-turbine governing systems is essential for the safe operation of nuclear power units. As a key regulating and protection component, the reheat valve must complete rapid closure under abnormal operating conditions. This study addresses the closing timeout problem observed in a nuclear reheat-valve oil-motor actuator after domestic substitution, with particular attention to sluggish motion and discontinuous closing at small openings. A coupled hydraulic–mechanical model was then established by integrating the coned-disc spring assembly, hydraulic circuit, cartridge valve, gear–rack transmission, and load resistance based on the mathematical model. The model was used to identify the dominant parameters controlling the fast-closing process, and the optimization strategy was subsequently verified by experiments on an actual actuator platform. The results show that coned-disc spring degradation is a critical source of closing timeout risk. When the equivalent elastic modulus decreases to approximately 195 GPa, the fast-closing time approaches the critical limit of 0.8 s, while further degradation results in evident timeout. The C0 throttling orifice has the strongest influence on the effective closing time by governing the pressure-relief capacity of the working chamber. A coordinated correction strategy, involving coned-disc spring force compensation and throttling parameter adjustment, restores the closing margin, shortens the fast-closing time to 0.78 s, and improves closing smoothness. This work provides the practical guidance for design verification, field commissioning, and domestic improvement of nuclear reheat-valve oil-motor actuator systems. Full article

Hemispheric specialization is a widespread feature of vertebrate nervous systems, but the minimal conditions under which bilateral systems differentiate, acquire polarity, and retain asymmetric states remain unclear. Here, we examined these issues using a minimal evolutionary model with two initially equivalent processing channels. Each channel evolved a spatial integration width while receiving the same input, and fitness rewarded the magnitude of a bilateral mismatch-separation signal rather than explicit anomaly localization. Under exact developmental symmetry, 40 lineages evolved robust left–right differences in integration width without significant directional fixation (median |Δa| = 2.511; 22 right-wider, 18 left-wider). Weak developmental gain asymmetry biased polarity selection in a graded manner, shifting outcomes toward right-wider or left-wider solutions depending on bias direction. Forced-symmetry, shared-parameter, and single-channel controls showed that high performance depended on allowing differentiated bilateral processing. After biased solutions were reseeded under restored symmetry, differentiation was retained and amplified (median |Δa| > 6.6), consistent with history-dependent persistence within the sampled fitness landscape. Structured backgrounds increased differentiation magnitude but imposed greater decision-time costs. These results distinguish differentiation, polarity bias, and persistence as separable components of minimal hemispheric specialization. Full article

In this paper, the circular Sitnikov three-body problem is studied under the combined influence of radiation pressure and albedo. The model consists of two equal-mass primaries moving in circular orbits about their center of mass and an infinitesimal body constrained to oscillate along the perpendicular axis. The radiative emission from one primary and the reflected radiation from the other are incorporated into the effective potential through radiation and reflectivity parameters. Using the Jacobi integral, we determine the energetically admissible region for vertical motion and examine how radiative effects modify the accessible phase space. The study shows that the system admits a single vertical equilibrium point at the origin, which remains linearly stable within the physically admissible parameter range. Radiation and albedo reduce the effective restoring force and increase the oscillation period, producing a measurable rescaling of the physical time without altering the geometrical structure of the phase trajectories. The phase-space dynamics are further explored by means of Poincare (first-return) maps obtained from numerical integration of the nonlinear equation of motion. The resulting invariant curves confirm that the motion remains regular and bounded, while their progressive contraction reflects the reduction in the oscillation amplitude with increasing radiative effects. Overall, the results show that albedo acts as a quantitative modifier of the vertical Sitnikov dynamics by changing the effective potential, the admissible energy domain, and the observable time scale, without generating new qualitative phase-space structures. Full article

Background: Chronic unpredictable stress triggers various pathological and metabolic alterations by modulating psychophysiological balance. Valeric acid (VA), a postbiotic material, has been reported to mitigate stress-induced behavioral changes in rodents. Objectives: To investigate the protective effect of valeric acid against chronic unpredictable stress in a rodent model by assessing neuro-physiological alterations along with changes in biochemical parameters to confirm the possible mechanism. Methods: A 14-day chronic unpredictable stress (CUS) model in albino Wistar rats was developed to check the stress-induced changes using forced swim test, tail suspension test and sexual behavior observation. Quantification of IL-6, TNF-α, IL-1β, plasma corticosterone level and oxidative stress parameters were also done. Results: Findings revealed the protective effects of valeric acid against CUS, which reversed the depression caused by a forced swim and tail suspension test in rats. Proinflammatory and oxidative stress markers were significantly (p < 0.05) restored in CUS rats treated with valeric acid as compared with the vehicle control, which was comparable to the standard drug, Panax ginseng. Conclusions: The present study concludes that valeric acid demonstrated significant (p < 0.05) anti-stress effect by modulating both behavioral responses and stress-related biochemical modifications. Full article

Packed log jams (PWJs) can form naturally in streams and engineered log jams have been strategically placed in streams in river restoration projects. Their presence impacts stream hydraulics, flood inundation, morphology and ecology. Proper representation of large woods in two-dimensional hydraulic models is important, but proper guidelines are needed for any models, considering that such models have been widely used for assisting river restoration design and fish habitat evaluation. Existing large wood representation methods are inadequate. In this study, the porous-media method, widely used in groundwater modeling, is adapted and extended to represent large wood in streams. A modified formulation is proposed, which adopts only one calibration parameter to compute the drag force due to large wood presence. Two sets of experimental data with PWJs are used to assess the performance of the method. The porous-media method is found to produce good results when compared with the measured data of backwater rise as well as water depth and velocity variations along the flow. A general usage guideline is proposed on the proper way to apply the method and verified against the PWJ experimental data. Further, a regression equation is developed to estimate the large wood calibration parameter; it can be useful when no measured data are available for calibration. The proposed method, the developed guidelines, and the regression equation are found to produce satisfactory results in comparison with the measured PWJ data. Full article