Search Results (2,807)

This article examines the behavior of gyroscopic orientation systems, which, unlike inertial navigation systems and gyrocompasses (with internal and external correction), are described solely by Euler’s equations. It is shown that, contrary to established views, obtaining the position of the meridian line using a balanced directional gyroscope corrected by information on the transport angular velocity (or a two-axis inertial platform controlled by integrating gyroscopes) is non-asymptotically stable over a wide range of initial conditions, disturbance torques, and parameters of the object’s motion on the Earth’s surface—more than sufficient for practical use. A comparison of a directional gyroscope and a gyrocompass provides a new interpretation of the role of pendulosity in the design of gyroscopic orientation systems. The fundamental theoretical propositions of the present work are accompanied, to the required extent, by the results of numerical solutions of the equations of motion. Full article

This paper presents a systematic reward engineering methodology for training a Proximal Policy Optimization (PPO) quadrotor navigation policy in the Webots simulator, using a hierarchical architecture in which a PID controller handles low-level stabilization and a PPO policy issues velocity commands. We document the complete evolution of a composite ten-term reward function across seven versions (v5 through v11) and retrain the key versions with multiple independent training seeds. The multi-seed study revises the single-seed history: penalty-dominated configurations (v8, v10) fail across all seeds, while the strongest historical version proves seed-sensitive (v11: 32.2 +/− 15.8%). An ablation removing the continuous distance-shaping term from v11 yields 0% success across seven seeds, identifying that term as necessary for convergence. We further isolate a previously hidden co-factor: with the library-default exploration-noise initialization (sigma_0 = 1.0), sampled actions saturate the bounded action space, the exploration variance receives no learning gradient, and curriculum progression deadlocks regardless of reward design; initializing sigma_0 = 0.37 restores gradient flow. With this correction and a deterministic evaluation-gated curriculum, the final configuration is evaluated across the full curriculum rather than at a single operating point: across five independent training seeds under a deterministic protocol, it attains 95.0% ± 6.2% navigation success at Stage 0 conditions (2 m targets, no obstacles), 89.6% ± 6.9% at Stage 1 conditions (4 m, one obstacle), and 48.4% ± 10.8% at Stage 2 conditions (7 m, three obstacles). Reporting this difficulty curve, rather than a single headline value, exposes a substantial generalization gap whose dominant failure mode is obstacle collision (45–52% of episodes at Stage 2). Matched retraining of Soft Actor-Critic and TD3 baselines under identical reward and curriculum conditions yields one completed seed each both baselines show non-monotonic difficulty curves, and at Stage 2 conditions, TD3 (64.0%) exceeds PPO (48.4% ± 10.8%) while SAC (43.0%) falls just below it, whereas at Stage 0, PPO (95.0%) leads both, so the ranking is operating point-dependent on the current single-seed evidence. We conclude that a continuous shaping gradient and the exploration-noise initialization, interacting with the curriculum advancement criterion, determine convergence in continuous control deep reinforcement learning, and that reward polarity by itself does not. Full article

To address the issues of low mechanical rock-breaking efficiency and severe tool wear in hard rock, this study investigates the mechanical deterioration and abrasivity response of granite subjected to rapid flame-jet heating followed by liquid nitrogen cooling, with rock pre-treatment in thermal-assisted rock breaking as the background. Fine-grained granite specimens were heated by flame jet to temperatures ranging between 200 and 600 °C and then subjected to natural cooling or sudden liquid nitrogen cooling. Physical parameter measurements, uniaxial compression tests, Brazilian splitting tests, and CERCHAR abrasivity tests were conducted using national standards to investigate the evolution of thermal damage and the effect of cooling path. The results show that the damage degree of granite continuously increases with increasing heating temperature, and the damage induced by liquid nitrogen cooling is greater than that induced by natural cooling. Visible cracks begin to appear on the specimen surface after 300 °C, while crack propagation and structural deterioration become more pronounced at 500–600 °C. Among the measured physical parameters, P-wave velocity is the most sensitive to damage, with a maximum attenuation rate of 60.6%. The deterioration of the physical structure further reduces the load-bearing capacity and deformation performance of granite. After liquid nitrogen cooling at 600 °C, the uniaxial compressive strength, tensile strength, and elastic modulus decrease to 92.6 MPa, 1.42 MPa, and 17.4 GPa, respectively, corresponding to reductions of 56.0%, 87.7%, and 69.3% compared with the untreated specimens. The tensile strength is the most sensitive mechanical parameter to liquid nitrogen cooling. The CERCHAR abrasivity index decreases from 3.81 to 2.12. Liquid nitrogen cooling advances the transition of granite abrasivity from high to medium from 400–500 °C to 300–400 °C. The integrated analysis indicates that the non-uniform temperature field generated by rapid flame-jet heating and the differences in thermal deformation among minerals promote the initiation of initial cracks. The additional shrinkage stress induced by liquid nitrogen cooling further drives crack propagation and coalescence, eventually leading to the coupled reduction in the strength, stiffness, and abrasivity of granite. The results provide laboratory-scale evidence for evaluating granite pre-treatment under rapid flame-jet heating and liquid nitrogen cooling and offer a reference for thermal-assisted mechanical rock breaking and standardized abrasivity reduction. However, the relationship between CAI and actual tool wear still requires further verification. Full article

Continuous rigid-frame bridges with standardized spans are increasingly favored in high-speed railway networks owing to their stable structural mechanics and economical lifecycle maintenance. Despite their widespread adoption, comprehensive quantitative analyses detailing wind–vehicle–bridge coupled dynamic interactions remain notably sparse, particularly under the combined excitations of high-speed transit and overall track geometry deviations, which incorporate both stochastic irregularities and deterministic long-term deck creep. To bridge this knowledge gap, the present study investigates the dynamic stability and operational safety of a 4 × 40 m continuous rigid-frame bridge featuring a specialized parallel double-box cross-section. Initially, the tri-component aerodynamic force coefficients for this coupled system are extracted utilizing computational fluid dynamics (CFD) simulations. Subsequently, a three-dimensional wind–vehicle–bridge interaction model is formulated. This governing dynamic framework integrates turbulent wind pressures and track geometry deviations as external excitations. The mathematical derivation of this model is fundamentally based on d’Alembert’s principle. Utilizing this advanced model, the transient dynamic responses of traversing CRH6 trainsets are systematically evaluated across a comprehensive matrix of environmental lateral wind velocities, ranging from 0 to 30 m/s, and operational speeds varying between 120 and 200 km/h. The computational outcomes demonstrate that both the vehicular accelerations, in lateral and vertical directions, and the structural deflections strictly satisfy stringent statutory safety limits across all simulated environmental scenarios. This ensures satisfactory ride comfort and running stability for the high-speed trains. Ultimately, this research substantiates that the investigated bridge topology maintains an adequate dynamic safety margin even under severe crosswinds. It does not constitute a kinematic bottleneck for the maximum operational speed of the railway corridor under the modeled conditions. These insights establish a solid theoretical foundation for the aerodynamic design and safety evaluation of analogous high-capacity rail infrastructure. Full article

Focusing on the complex aerodynamic interference and attitude response during multibody separation in the low-pressure and low-density environment of near space, a numerical investigation of the effects of different initial separation conditions on submunition motion is conducted. A three-dimensional unsteady flow model is established by coupling the six-degree-of-freedom rigid-body equations with the overset mesh technique. The effects of the free stream Mach number, initial angle of attack, initial separation velocity, and separation altitude on the motion characteristics of the submunition are systematically analyzed. The results show that, compared with conventional low-altitude conditions, aerodynamic forces have a weaker corrective effect on the separation motion and attitude in near space, making the initial separation parameters more influential. Increasing the free stream Mach number and initial angle of attack enhances the radial separation capability but intensifies the attitude response. As the separation altitude increases, the aerodynamic forces weaken, and the displacement and attitude variations in the submunition decrease accordingly. The initial axial separation velocity V_x0 has relatively little influence on the radial separation distance and pitching response. Increasing the initial radial separation velocity V_y0 increases the radial separation distance and reduces pitch oscillations, whereas increasing the magnitude of the initial lateral separation velocity $\left|V_{z0}\right|$ significantly amplifies the roll and yaw responses. The results provide a reference for the design of initial parameters for multi-body separation systems operating in near space. Full article

The 1973 M_S7.6 Luhuo earthquake is the most representative strike-slip event in the Xianshuihe fault zone, yet published source models differ markedly, and the mechanism that arrested its rupture near Renda remains poorly understood. Using spectral-element dynamic rupture simulations with a nonplanar fault geometry, three-dimensional velocity model, and depth-dependent initial stress field, we test whether fault geometry or inherited stress heterogeneity controlled the termination. Our results show that N75° W is the optimal maximum principal stress orientation, yielding surface offsets, a bilateral rupture mode, and an intensity pattern consistent with observations. Fault geometry alone cannot explain the termination: continuous and dipping faults rupture completely, and a 1 km stepover at Renda blocks the rupture jump yet leaves minor slip on the secondary fault. Introducing the 1923 Daofu earthquake stress change as a low-stress barrier instead terminates rupture near Renda, and simulated magnitude, offsets, and intensity then agree with observations. A compliant damage zone raises coseismic slip and lowers the moment magnitude while contracting the meizoseismal zone, whereas topography barely alters the rupture but appreciably modulates ground motion. These findings demonstrate that inherited stress heterogeneity, rather than fault geometry, can be the primary control on rupture arrest and can inform seismic hazard assessment for the Sichuan-Yunnan fault system. Full article

Trans-medium vehicles, including supercavitating torpedoes, submarine-launched projectiles, and high-speed hydroballistic bodies, demonstrate increasingly diverse applications in crossing the air–water interface. For such vehicles, the truncated-cone (flat-headed) configuration represents a geometry of significant engineering relevance, as it is widely adopted in the nose sections of supercavitating projectiles and certain underwater ballistic penetrators where the flat head promotes rapid vaporization and cavity generation during high-speed water entry. The air-to-water transition process typically generates extreme hydrodynamic impact loads due to complex multiphase flow and fluid–structure coupling interactions, with water compressibility playing a significant role under hydroballistic conditions. This study focuses on the water-entry regime at velocities ranging from 300 to 1100 m/s, corresponding to hydroballistic speeds relevant to supercavitating vehicles (e.g., the Shkval torpedo operates at approximately 370 m/s) and the initial impact phase of high-speed trans-medium projectiles. Parametric studies are conducted with varying entry velocities (Mach 0.20~0.73 in water), impact angles, and structural dimensions to systematically investigate their effects on the peak slamming overload, using a dynamic mesh technique coupled with a VOF multiphase model with compressibility effects for both air and water phases. The results demonstrate that compressibility effects induce a pronounced air cushion effect during water impact, wherein compression waves generated during high-speed entry dominate the load formation process. Velocity is identified as the most sensitive factor affecting peak overload, followed by structural size parameters. The findings provide valuable guidance for the protective design of high-speed water-entry structures operating in the hydroballistic regime. Full article

To promote the high-value utilization of construction and industrial solid wastes, this study prepared an all-solid-waste-based flowable solidified soil (FSS) using soft clay and recycled fine aggregate (RFA) as the main constituents. The binder system comprised ground-granulated blast-furnace slag (GGBS), carbide slag (CS), and desulfurization gypsum (DG), while fly ash (FA) was incorporated to improve workability. The primary objective was to identify an appropriate RFA content for this FSS system through a combined evaluation of workability, mechanical performance, durability, and microstructural characteristics. The results showed that increasing the RFA content increased flowability and shortened the setting time. Unconfined compressive strength (UCS) and ultrasonic pulse velocity (UPV) both increased initially and then decreased as the RFA content increased, and relatively favorable mechanical performance was observed at RFA contents of 40–60%. In the durability tests, the mixture containing 40% RFA exhibited the lowest mass loss and UCS loss after both wetting–drying and freeze–thaw cycles within the investigated range. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses suggested that a moderate RFA content was associated with the development of C-(A)-S-H-gel-related phases and ettringite (AFt), together with a denser and more continuous microstructure. The improved strength and durability at moderate RFA contents were therefore interpreted as the combined results of hydration-product development and the physical skeleton effect provided by RFA. By contrast, the performance decline at excessive RFA contents appeared to be related to a less favorable internal structure, as indicated by SEM observations. Overall, when workability, mechanical performance, durability, and microstructural observations are considered together, 40% RFA is recommended as the most suitable content for the material system and test conditions investigated in this study. These findings demonstrate the potential of RFA to regulate the performance of all-solid-waste-based FSS and to improve the resource efficiency of multiple solid-waste streams. Full article

Diabetes mellitus (DM) is a chronic metabolic disease characterized by hyperglycemia, and the diaphragm—the primary respiratory muscle—is adversely affected by this diabetic process. The aim of this study is to investigate the effects of zinc sulfate (ZnSO₄) treatment on diaphragm muscle contractile dynamics, calcium homeostasis, apoptosis, and fibrosis in an 18-month-old female Type 2 diabetic rat model. Thirty-two 18-month-old female Wistar rats were randomly divided into four groups: Control (CON), CON + ZnSO₄, Diabetes Mellitus (DM), and DM + ZnSO₄. The DM model was induced by a high-fat diet and administration of 30 mg/kg streptozotocin (STZ); after the disease was confirmed, ZnSO₄ was administered intraperitoneally at a daily dose of 10 mg/kg to the treatment groups. The mechanical functions of the diaphragm muscle were evaluated using a post-rest potentiation protocol in an isolated organ bath; qPCR analyses (Caspase-3, TGF-β1, SERCA2a) were performed to investigate cellular apoptosis, fibrosis, and calcium regulation. Compared with the CON group, the DM group exhibited a severe ~90% reduction in diaphragmatic contraction force (CF) and a ~97% decline in maximal contraction/relaxation velocities (±dF/dt_max) (p < 0.0001), which strongly correlated with a 30% suppression of SERCA2a gene expression (p < 0.01). Concomitantly, apoptotic Caspase-3 (~2.6-fold) and profibrotic TGF-β1 (~3.1-fold) mRNA levels were significantly elevated (p < 0.0001). In the DM + ZnSO₄ group, daily zinc treatment (10 mg/kg/day, i.p. for 6 weeks, initiated 4 weeks after diabetes confirmation) did not reverse the elevated Caspase-3 and TGF-β1 expressions (p > 0.05). However, SERCA2a expression was fully preserved back to control levels (p < 0.05 vs. DM), leading to a substantial ~3-fold improvement in CF and velocities (p < 0.05 to p < 0.0001 vs. DM). On the other hand, the healthy CON + ZnSO₄ group exhibited a physiological slowing of contractility (~53% decrease in CF), without histological damage, likely due to a competitive antagonism between excess divalent zinc (Zn²⁺) and calcium (Ca²⁺) on myofilaments. Although zinc cannot reverse the structural apoptotic and fibrotic remodeling in the aged diabetic diaphragm, it successfully rescues functional contractility by preserving SERCA2a transcriptional expression. Full article

The tunnel portal section is one of the most seismically vulnerable parts of a tunnel, where strong earthquakes may trigger slope instability and induce plastic damage in the tunnel lining. Based on viscous-spring artificial boundary theory, a seismic oblique-incidence method applicable to tunnel portal sections is developed by incorporating the effects of slope topography. A three-dimensional finite element model is then established to investigate the seismic response and damage mechanisms of the tunnel portal section subjected to obliquely incident SV waves. The numerical calculation results in this study indicate that fully connected plastic deformation zones eventually develop in both the original slope site and the slope site with a tunnel structure, leading to slope instability characterized by downward sliding of the rock mass along a slip surface. However, in the presence of a tunnel structure, plastic deformation initiates simultaneously at the slope toe and near the tunnel portal. The maximum plastic strain is concentrated near the tunnel portal. Both topographic amplification and the accumulation of sliding debris markedly aggravate lining damage. The seismic-wave incidence angle, ground conditions and seismic-wave spectral characteristics all have pronounced effects on plastic deformation in both the slope site and tunnel lining at the tunnel portal section. In addition, tensile damage is more pronounced and extends over a wider area than compressive damage. At shear-wave velocities of 450–550 m/s in the upper soft-rock site, the damage zone is approximately two to three times the horizontal projection length of the slope, which is identified as the primary damage zone and should be regarded as a key seismic fortification area in tunnel design. Full article

Accurately simulating convective initiation (CI) in capped High Plains dryline environments remains a significant challenge for convection-permitting numerical weather prediction. As a follow-up work to Lu and White, this study utilizes the Model for Prediction Across Scales (MPAS) at a 3 km grid resolution to evaluate the sensitivity of dryline morphology and CI to two planetary boundary layer (PBL) parameterization schemes: the non-local Yonsei University (YSU) and the local Mellor-Yamada-Nakanishi-Niino (MYNN) frameworks. Radar observations and simulated maximum reflectivity show that while the YSU scheme successfully replicates the timing and spatial development of convective cores triggered along the elevated terrain slope at 21:30 UTC, the MYNN scheme completely suppresses deep convection throughout the study period. Vertical thermodynamic profiles indicate that YSU establishes a deeply mixed boundary layer that weakens the regional capping inversion, enabling surface parcels to break the stable lid and reach their level of free convection (LFC). Conversely, the MYNN scheme confines moisture to a thin layer near the surface beneath an unyielding temperature inversion, preventing parcels from achieving free buoyancy. For the 3 km “grey zone” of turbulence resolution, both PBL schemes successfully resolve horizontal convective rolls (HCRs) near the primary dryline boundary. YSU’s non-local mixing permits these HCR perturbations to couple vertically into deep, cap-breaching updraft plumes, while MYNN’s local turbulent kinetic energy (TKE) closure traps them as shallow horizontal waves. It was shown that the MYNN failure is driven by an intrusive synoptic wind bias, generating anomaly wind velocities of 24–28 m/s throughout the column. These winds act as a mechanical sweeper across the terrain slope which shears, flattens, and dilutes the moisture pool below 2000 m Mean Sea Level (MSL) and physically reduces fuel from the western initiation zone. In contrast, the YSU scheme maintains a well-regulated, moderate wind profile (8–12 m/s aloft), preserving a state of mesoscale equilibrium that allows moisture to ascend the terrain slope and continuously feed developing convective cells. Our findings demonstrate that the choice of PBL parameterization plays significant role in not only local vertical mixing but also the structural translation of macroscale synoptic forcing versus localized thermodynamic regulation in complex terrain. Full article

Background and Objectives: Although modern oncologic therapies have substantially improved cancer survival and overall prognosis, they have also led to an increasing burden of cardiovascular toxicity. Preventing severe complications such as heart failure and death remains a major priority, while maintaining the need for effective and potentially curative cancer therapy. Careful patient monitoring and early detection of cardiovascular complications may allow the timely implementation of cardioprotective strategies and treatments that could delay or prevent myocardial toxicity. Materials and Methods: A total of 92 women with breast cancer were enrolled in a prospective observational cohort study. All patients received an anthracycline-based chemotherapy regimen, cyclophosphamide, docetaxel and trastuzumab. Biomarker assessment, including NT-proBNP, high-sensitivity cardiac troponin I (hs-cTnI), Gal-3, and GDF-15, was performed at baseline and at the initiation of trastuzumab-based therapy. A comprehensive diastolic function assessment was performed, including transmitral Doppler flow parameters and tissue velocities. Patients were followed for 12 months, and all cardiovascular events occurring during the follow-up period were recorded. Results: Biological and ecocardiographic parameters were analyzed and multiple models of prediction were made. To identify predictors of estimated left ventricular filling pressure (eLVFP), stepwise multiple linear regression analyses were performed, and four significant predictors of left ventricular end-diastolic filling pressure were identified: one echocardiographic parameter (baseline LV filling pressure) and three biological variables (changes in Gal-3, GDF-15, and hs-cTnI levels after treatment). The overall regression model was highly significant (p < 0.001) and explained 77.07% of the variance in the dependent variable. Gal-3 was the strongest predictor of left ventricular filling pressure (p < 0.001). Conclusions: The regression analyses suggest that this phenotype is multifactorial, with echocardiographic indices capturing the functional component and circulating biomarkers reflecting complementary aspects of the underlying biological response. This multimodal approach may therefore help identify patients with early treatment-related cardiac changes and potentially those at increased risk of subsequent CTRCD, particularly during a period when conventional LVEF-based surveillance may still appear reassuring. Full article

We study a class of evolutionary variational inequalities in a Hilbert space that models the long-run balanced-growth equilibrium of a competitive economy with transaction costs, time-dependent production and infrastructure constraints, and exogenous price dynamics. The paper makes four contributions. First, we introduce a parametrized monotonicity functional ${\mu }_{\alpha }(t;F;u,v;p)$ and prove an exact equivalence theorem: the inequality ${\mu }_{\alpha }\ge \beta {∥u-v∥}^2$ holds if and only if the operator F is strongly monotone with the explicitly computed constant $m=\beta -\alpha (1+{∥p∥}_{\infty })$. This turns the growth parameter $\alpha$ and the price level into explicit terms of a single admissibility threshold and, for $\beta <\alpha (1+{∥p∥}_{\infty })$, produces a scale of conditions that covers operators which are not monotone, i.e., economies with a bounded degree of increasing returns. Second, we prove well-posedness: for every admissible initial state there is exactly one Lipschitz equilibrium trajectory $u^{*}(·)$, obtained through Moreau’s catching-up algorithm for the associated perturbed sweeping process, together with the explicit velocity bound $∥{\dot{u}}^{*}∥\le L_K+2C_F$. Third, we derive one comparison estimate from which global exponential stability, the convergence rate $∥u\left(t\right)-u^{*}\left(t\right)∥\le r e^{-mt}+L_p{m}^{-1}\sup ∥\Delta p∥+\epsilon m^{-1}$, and robustness with respect to perturbations of prices and of the operator all follow; we also show that, when the constraint sets stabilize, the trajectory converges to the stationary equilibrium of the limit problem. Fourth, we prove that strong monotonicity implies the c-covering property with $c=m$, so that the shock-absorbing capacity of the economy is governed by the same constant as the speed of convergence. Two examples—a two-resource system and an n-market network with nonlinear transaction costs—are worked out with a complete verification of every hypothesis and with explicit numerical constants. Full article

Bearing-grade PEEK composites are intended to improve sliding performance, but filler addition does not necessarily reduce friction. This study compared the dry sliding tribological behaviour of neat PEEK and hybrid PEEK containing PTFE, graphite, and carbon fibre against 42CrMo4+QT steel. Ring-on-block tests were performed at nominal PV values of 0.3–3.2 MPa·m/s, contact pressures of 0.87–5.82 MPa, and sliding velocities of 0.26–0.55 m/s. Each material–condition combination was tested using three independent specimens. Coefficient of friction was calculated from simultaneously measured tangential and normal forces, and subsurface temperature was recorded continuously. Initial and post-test surfaces were examined using optical and extended depth-of-field microscopy. Group mean COF values ranged from 0.052 to 0.123. Hybrid PEEK exhibited a higher numerical mean COF than neat PEEK in all six operating conditions, with relative differences of approximately 1.53–8.36%. Two-factor ANOVA estimated an overall hybrid-minus-neat difference of +0.003388 COF units (95% CI 0.001279–0.005496; p = 0.0029), whereas none of the six condition-specific neat–hybrid comparisons was significant after Holm correction. Initial temperature, maximum temperature, and baseline-normalised temperature rise were reported for every specimen and treated descriptively. Both materials reached stable sliding states without seizure or uncontrolled thermal escalation. Post-test EDF observations showed a denser pattern of fine grooves on neat PEEK, whereas hybrid PEEK exhibited comparatively smoother intervening regions interrupted by fewer but locally deeper features. Mass changes remained close to the capability of the applied balance and did not permit quantitative wear-rate comparison. The results show that the investigated hybrid formulation did not provide a dry-friction reduction advantage over neat PEEK under the tested conditions. Full article

This paper studies predefined-time trajectory tracking for Euler–Lagrange systems with composite uncertainties encompassing partially known dynamics, parametric variations, and bounded disturbances. A two-step backstepping architecture is developed. In Step 1, a predefined-time virtual control law is constructed for the position subsystem. In Step 2, an energy-based torque controller is designed for the velocity subsystem using nominal model compensation, adaptive parameter estimation, actor neural network approximation of residual dynamics, a critic network for performance-oriented learning, and a continuous robust term. A rigorous Lyapunov analysis shows that all closed-loop signals are uniformly ultimately bounded and that the tracking errors converge to a computable residual set within a predefined time for all initial conditions contained in the selected compact set. Comparative simulations on a 2-DOF planar manipulator demonstrate that the proposed method provides faster convergence and improved steady-state tracking accuracy than both a PID baseline and a classical Slotine–Li adaptive baseline, while respecting the predefined-time bound. Full article