Boundary Effects Research Articles

Propeller scour phenomenon in the presence of a quay-wall and currents

Investigating the interaction between flow intensity and a ship propeller jet scouring process is paramount to predict scour dimensions in mooring sites in navigation channels, for instance. While the condition of still water is typical in protected mooring sites, in other real-world conditions, like docking in waterways, the presence of an additional flow approaching a rotating propeller can induce changes in the propeller jet hydrodynamics and in turn in the scouring process. Note that, although ship-hull and rudders influence the jet propagation and the flow field, the present research project aimed at studying the propeller-inducing effects only. Literature studies that have relied on this assumption are rarely found, with only a few examining the impact of the intensity of the flow on the propeller jet scour. This study presents an experimental campaign aimed at assessing the effects of flow intensity on propeller jets in confined conditions. Specifically, three different flow intensities and three propeller distances from a vertical quay-wall were tested. The findings are presented through profiles of the scoured bed, and bathymetries at the equilibrium condition and empirical formulas for calculating the principal dimensions of the scour holes are given.To explore the intricate hydrodynamics and understand how the intensity of the flow affects the scour hole development, and to investigate boundary effects on the flow field, we performed Reynolds-Averaged Navier–Stokes (RANS) simulations. These simulations were applied to the three-dimensional scoured bathymetry in a state of equilibrium. The satisfactory match between numerical results and sampled velocities at the equilibrium stage ensures the reliability of the simulations. To the authors’ knowledge, these configurations had not been previously simulated, owing to the complexities involved in computing a moving mesh in presence of a bathymetry and a confining vertical wall. The results offer the first numerical demonstration of boundary effects on the characteristics of propeller jets both in the presence and in the absence of an additional channel flow.

Inhibitory effect of low-angle grain boundaries on the creep behavior of gradient nano-grained Cu: A molecular dynamics study

Inhibitory effect of low-angle grain boundaries on the creep behavior of gradient nano-grained Cu: A molecular dynamics study

Edge dislocations, alloy composition, and grain boundaries effects on the mechanical properties in NiCo binary alloy.

In this research, we investigated the mechanical properties of NiCo binary alloy both with and without grain boundaries, across various alloy compositions. We investigated the effects of edge dislocation, alloy compositions, and grain boundaries on the mechanical properties of FCC using molecular dynamics (MD) simulations. By analyzing the influence of the grain boundaries with different alloy compositions on several mechanical properties, we were able to gain a deeper understanding of how these characteristics were modified. The elastic moduli increased with increasing grain boundaries for a specific chemical composition, indicating that becomes more rigid. The anisotropy factor analysis showed that have a natural tendency toward anisotropy, which is further influenced by the presence of grain boundaries. Grain boundaries have a significant effect on strength and ductility across a wide range of alloy compositions. These results indicate that a deeper comprehension of these implications can aid in designing improved binary alloy with superior mechanical characteristics.

Local linear estimators for reflected diffusions

In this paper, we investigate the nonparametric local linear estimator for the drift function of reflected stochastic differential equations based on the discretely observed process. Under certain regularity conditions, we prove the strong consistency and establish the asymptotic normality for our proposed estimator. We also propose the optimal bandwidth selector for the estimator and show that the estimator does not have a boundary effect. Simulation results demonstrate that our method is superior to the method proposed by Cholaquidis et al. [Stat. Sin. 2021, 31: 29–51]. We apply the EUR/USD currency exchange rate data to illustrate our theoretical results.

In situ phase engineering during additive manufacturing enables high-performance soft-magnetic medium-entropy alloys.

Additive manufacturing (AM) shows promise as a method for producing soft-magnetic multicomponent alloys for use in electric motors and sustainable electromobility applications. However, the simultaneous achievement of a high saturation magnetic flux density (Bs) and a low coercivity (Hc) in AM soft-magnetic materials remains challenging. Herein, we present an approach that integrates an elemental powder mixture of Fe45Co30Ni25 with Fe2O3 nano-oxides, which is then subjected to laser powder bed fusion (LPBF) followed by high-temperature annealing to achieve an FCC-structured Fe45Co30Ni25 MEA/FeO composite. The FeO nanoparticles, a byproduct of the reaction between Fe powders and Fe2O3 nano-oxides, serve as nucleation sites for the formation of a single FCC phase in the MEA matrix. The resulting LPBF MEA/FeO composite has a Bs of 2.05 T and an exceedingly low Hc of 115 A m-1, compared to those of the BCC/FCC dual phase MEA and other state-of-the-art additively manufactured soft-magnetic alloys. In situ Lorentz transmission electron microscope (TEM) revealed that the low Hc of the FCC-structured MEA/FeO composite originates from the reduced pinning effect of grain boundaries in the FCC phase on domain wall movement compared with those in the FCC/BCC dual phase.

Influence of nano‐silica particles on fracture features of recycled aggregate concrete using boundary effect method: Experiments and prediction models

AbstractThe aim of this investigation is to assess the impact of using nano‐silica (Na) at varying weight percentages of 0%, 1.5%, 3%, 4.5%, and 6% as partial cement substitute on fracture parameters of recycled aggregate concrete (RAC). A servo‐controlled testing system was employed to carry out three‐point flexure tests on 90 notched beams. Boundary effect method was used in order to interpret the fracture features. The results illustrate that adding Na increases the size‐independent fracture energy, fracture toughness and initial fracture energy of RAC by 29%, 32%, and 24% compared to that without Na, respectively. The maximum values of these parameters occur at 4.5% Na. The reference crack length () decreases from 6% to 22% by adding 1.5% to 6% Na. This shows that the RAC gets more brittle by the addition of Na. Moreover, the RAC behavior moves towards linear elastic fracture mechanics criteria by adding Na. Finally, according to the mechanical properties and test variables, multivariable models were suggested for prediction of the fracture parameters of the RAC containing Na. The models predictions were compared with experimental findings of the previous research.

Micro-fracture mechanism of microwave induced fracturing of basalt based on a novel Electromagnetic–Thermal–Mechanical coupling model

Microwave-assisted rock fracturing is recognized for its efficiency, energy savings, and environmental benefits. Investigating microscopic mechanisms of microwave-induced rock fracturing is essential for predicting the weakening effect on rock. A coupled Electromagnetic–Thermal–Mechanical model based on FEM–DEM was established to describe the response of rock under microwave irradiation. This model employs interpolation algorithms and mineral lattices randomization algorithms to establish a 2D cross-sectional representation of rock. A discrete element calculation method is proposed to synchronize computational time with the experimental time. The model can simulate the multi-physical field response of different rocks under various conditions, making it an effective tool for studying microwave-induced rock fracturing. The effectiveness of the numerical model was validated through open-end microwave-induced fracturing experiments on basalt. Additionally, the study elucidates the micro-fracture mechanism of basalt under microwave irradiation. The results indicate that the direction of crack propagation is influenced by microwave power and boundary effects. The patterns of fracture development between minerals are summarized as follows: Initial fractures primarily result from the rapid heating of microwave-absorbing minerals like enstatite,creating a significant temperature gradient. With increased heating time, heat transfers to highly expansive minerals such as olivine, causing fractures due to localized thermal expansion.

Research on damage identification of simply supported bridge based on effect size method for vehicle-bridge coupled vibration

Abstract This paper presents a novel bridge damage identification method employing Cohen's d as an effect size indicator, predicated on the detection of bridge damage through the coupled vibration between a vehicle and the bridge. By analyzing the dynamic response of the bridge as a vehicle passes over, this method effectively extracts the modal parameters of the bridge and facilitates the identification of bridge damage. Numerical models of the bridge under various damage conditions, including no damage, mid-span damage, and damage at the 1/4 and 3/4 span locations, have been constructed to substantiate the efficacy and precision of the effect size as a damage indicator. Furthermore, to address the challenge of accurately identifying damage at boundaries, which is often confounded by boundary effects, a boundary subdivision method has been defined for the detection of boundary damage. Through the implementation of a real-bridge test based on indirect measurement technology, the self-vibration frequency of the bridge was successfully extracted. This empirical data was then compared and analyzed against results from ANSYS numerical simulations, thereby validating the practicality and accuracy of the proposed method. In the final analysis, the influence of random traffic flow on the bridge damage identification results was examined. The findings indicate that the vibrations in simply supported beam bridges are intensified due to the impact of random traffic flow, which aids in enhancing the accuracy of damage identification. The introduction of this method provides a new quantitative tool for bridge health monitoring, enabling the rapid and accurate identification of bridge damage without interrupting traffic. It holds significant value for engineering applications in bridge maintenance and safety assessment.

Pattern phase transition of spin particle lattice system

To better understand the pattern phase transition of both physical and biological systems, we investigate a two-dimensional spin particle lattice system using statistical mechanics methods together with XY model governed by Hamiltonian equations of motion. By tweaking the coupling strength and the intensity of the generalization field, we observe phase transitions among four patterns of spin particles, i.e., vortex, ferromagnet, worm and anti-ferromagnet. In addition, we analyze the effect of space boundaries on the formations of vortex and worm. Considering the inherent dynamics of individual particles, we revealed the forming mechanism of such phase transitions, which provides a new perspective for understanding the emergence of phase transition of spin particles systems.

Covariant formulation of spinodal decomposition in rapidly expanding quark gluon plasma

Quantum chromodynamics (QCD) is expected to have a first order phase transition between the confined hadron gas and the deconfined quark gluon plasma at high baryon densities. This will result in phase boundary effects in the metastable and unstable regions. It is important to include these effects in phenomenological models of heavy ion collisions to identify experimental signatures of a phase transition. This requires building intuition on phase separation in rapidly expanding fluids. In this work we present the covariant equations of relativistic hydrodynamics with a phase boundary, provide prescriptions to extend the equation of state to metastable and unstable regions, and show the effects of spinodal separation in a Bjorken flow. Published by the American Physical Society 2024

Development of a Cone Penetration Testing Apparatus with a Textured Shaft

The anisotropy of shear resistance depending on friction direction can be selectively utilized in geotechnical structures. For instance, deep foundations and soil nailing, which are subject to axial loads, benefit from increased load transfer due to greater shear resistance. In contrast, minimal shear resistance is desirable in applications such as pile driving and soil sampling. Previous studies explored the shear resistance by interface between soil and surface asperities of a plate inspired by the geometry of snake scales. In this study, the interface friction anisotropy based on the load direction of cones with surface asperities is evaluated. First, a laboratory model chamber and a small-scale cone system are developed to quantitatively assess shear resistance under two load directions (penetration ⟶ pull-out). A preliminary test is conducted to analyze the boundary effects for the size of the model chamber and the distance between cones by confirming similar penetration resistance values at four cone penetration points. The interface shear behavior between the cone surface and the surrounding sand is quantitatively analyzed using cones with various asperity geometries under constant vertical stress. The results show that penetration resistance and pull-out resistance are increased with a higher height, shorter length of asperity and shearing direction with a decreasing height of surface asperity.

Fracture Toughness of Ordinary Plain Concrete Under Three-Point Bending Based on Double-K and Boundary Effect Fracture Models.

Fracture tests are a necessary means to obtain the fracture properties of concrete, which are crucial material parameters for the fracture analysis of concrete structures. This study aims to fill the gap of insufficient test results on the fracture toughness of widely used ordinary C40~C60 concrete. A three-point bending fracture test was conducted on 28 plain concrete and 6 reinforced concrete single-edge notched beam specimens with various depths of prefabricated notches. The results are reported, including the failure pattern, crack initiation load, peak load, and complete load versus crack mouth opening displacement curves. The cracking load showed significant variation due to differences in notch prefabrication and aggregate distribution, while the peak load decreased nonlinearly with an increase in the notch-to-height ratio. The reinforced concrete beams showed a significantly higher peak load than the plain concrete beams, attributed to the restraint of steel reinforcement, but the measured cracking load was comparable. A compliance versus notch-to-height ratio curve was derived for future applications, such as estimating crack length in crack growth rate tests. Finally, fracture toughness was determined based on the double-K fracture model and the boundary effect model. The average fracture toughness value for C50 concrete from this study was 2.0 MPa·m, slightly smaller than that of lower-strength concrete, indicating the strength and ductility dependency of concrete fracture toughness. The fracture toughness calculated from the two models is consistent, and both methods employ a closed-form solution and are practical to use. The derived fracture toughness was insensitive to the discrete parameters in the boundary effect model. The insights gained from this study significantly contribute to our understanding of the fracture toughness properties of ordinary structural concrete, highlighting its potential to shape future studies and applications in the field.

Profiling Phenotypic Heterogeneity of Circulating Tumor Cells through Spatially Resolved Immunocapture on Nanoporous Micropillar Arrays.

The phenotype of circulating tumor cells (CTCs) offers valuable insights into monitoring cancer metastasis and recurrence. While microfluidics presents a promising approach for capturing these rare cells in blood, the phenotypic profiling of CTCs remains technically challenging. Herein, we developed a nanoporous micropillar array chip enabling highly efficient capture and in situ phenotypic analysis of CTCs through enhanced and tunable on-chip immunoaffinity binding. The nanoporous micropillar array addresses the fundamental limits in fluidic mass transfer, surface stagnant flow boundary effect, and interface topographic and multivalent reactions simultaneously within a single device, resulting in a synergistic enhancement of CTC immunocapture efficiency. The CTC capture efficiency increased by approximately 40% for cancer cells with low surface marker expressing. By manipulating fluidic velocity (hydrodynamic drag force) on the chip, a cell adhesion gradient was generated in the capture chamber, enabling individual CTCs with varying expression levels of epithelial cellular adhesion molecules to be immunocaptured at the corresponding spatial locations where equilibrium drag force is provided. The clinical utility of the nanoporous micropillar array was demonstrated by accurately distinguishing early and advanced stages of breast cancer and further longitudinally monitoring treatment response. We envision that the nanoporous micropillar array chip will provide an in situ capture and molecular profiling approach for CTCs and enhance the clinical application of CTC liquid biopsy.

Preliminary investigation of the effects of high-temperature thermal activation on the activity of graphite tailings and the mechanical properties of graphite tailings mortar

The disposal of graphite tailings, a byproduct of graphite mining, poses significant recycling challenges. This study explores eco-friendly cement mortar by partially replacing sand with activated graphite tailings, focusing on waste utilization. Activating the pozzolanic properties of graphite tailings at various thermal activation temperatures converts them into high-quality binder materials. Quantitative assessments of graphite tailings' activity, conducted through ion leaching tests and raw material diffraction analysis, produce an activity index Ka, evaluating their performance under different thermal activation temperatures. Variable testing of substitution rates and activation temperatures examines changes in mechanical properties, microstructure, and pore distribution of the graphite tailings mortar. Optimum results reveal a 30 % substitution rate and a 750°C activation temperature. Graphite tailings, as pozzolanic binder materials, enhance mortar strength by improving particle size distribution, reducing "micro-area bleeding" and "boundary effects". After thermal activation, reactive minerals on the tailings' surface undergo secondary hydration reactions with cementitious products, modifying chemical structures and micro-morphology at the interface. Semi-quantitative XRD analysis and FT-IR spectroscopy characterize the ensuing chemical reactions, unveiling molecular bond and functional group changes. The superior performance of thermally activated graphite tailings primarily stems from increased active SiO2 and Al2O3 post-activation. The active SiO2 and Al2O3 reacts with cementitious products to form C-(A)-S-H gels, filling micro-pores at the tailings-mortar interface, which is the key characteristic that enables graphite tailings to serve as high-quality pozzolanic binder aggregates. A predictive model for compressive strength, utilizing reference models from solid waste mortar concrete, quantifies the positive impact of chemical activation. The theoretical results obtained from this predictive model closely align with the experimental findings.

Atomic simulation for the effect of short-range order and twin boundary on mechanical behavior of FeNiCrCoAl high-entropy alloys

Short-range order (SRO) structure has been considered a potential strengthening method to improve the mechanical properties of high-entropy alloys (HEAs). However, the reinforcement mechanism of SRO structure on the HEA is still unclear. Here, the effect of SRO degree, twin boundary (TB) and temperature on the mechanical properties of the FeNiCrCoAl HEAs with different Al contents under uniaxial tensile is investigated using molecular dynamics/Monte Carlo simulations. The results indicate that the strengthening effect caused by the SRO structure and the softening effect caused by the addition of Al atoms coexist in the HEAs, and their competition determines the mechanical properties of the HEAs. And the softening caused by Al atoms dominates the mechanical properties of the HEAs, and the mechanical properties of the HEAs decrease with the increase of Al content. The results show that Al content has a significant impact on the SRO structure of the HEAs and the degree of SRO decreases in the HEAs with the increase of Al content. It is worth noting that under the same alloy composition, the strengthening effect of the SRO structure on the alloys first increases and then decreases with increasing the degree of SRO. The results indicate that the strengthening effect of the SRO structure and TB together is greater than that of TB or SRO alone. In addition, the results also show that higher temperature is not conducive to the stability of SRO structure, and the strengthening effect of SRO on the HEAs decreases with the increase of temperature.

Experimental study on effect of elastic-rigid composite boundary on shockwave from cavitation bubble collapse

Understanding the mechanisms behind the cavitation erosion resistance of elastic materials is the basis for the development of new cavitation erosion resistance materials. This paper employs underwater low-voltage discharge to induce cavitation bubble, combined with high-speed photography, shadowgraph methods, and transient pressure measurement systems to experimentally investigate the evolution and intensity of shockwave from bubble collapse near elastic-rigid composite boundary. Under the condition of constant elastic material thickness, with the bubble–wall distance increasing, shockwave shape evolves from multi-layers to single-layer. The peak pressure of the shockwave shows a trend of decreasing, then increasing, and finally stabilizing with increase in the bubble–wall distance. Furthermore, it was found that the elastic-rigid composite boundary causes the shockwave to reflect twice. As the material thickness increases, the intensity of the first reflected shockwave from the elastic surface decreases initially, then increases, and eventually stabilizes. However, that of the second reflected shockwave decreases. The total energy of the two reflections at the elastic interface is less than 4% of the mechanical energy of the bubble at its maximum volume. Finally, after the energy dissipation by the two reflections and material deformation, the elastic layer substrate withstands over 70% of the total mechanical energy of the cavitation bubble. There is an optimal elastic material thickness to minimize the shockwave load on the elastic layer substrate under the condition that the elastic-rigid composite boundary does not affect the evolution of cavitation bubble shape. These findings are significant for understanding bubble dynamics near elastic-rigid composite boundaries and provide theoretical support for developing cavitation erosion-resistant materials in engineering.

Time after Time: Preserving Temporal Memories When Experiences Repeat.

Remembering when events occur in time is fundamental to episodic memory. Yet, many experiences repeat over time creating the potential for interference when attempting to recall temporally specific memories. Here, we argue that temporal memories are protected, in part, by reinstatement of temporal context information that is triggered by stimulus repetitions. We motivate this argument by integrating seminal findings across several distinct literatures and methodologies. Specifically, we consider key insights from foundational behavioral studies of temporal memory, recent electrophysiological and neuroimaging approaches to measuring memory reinstatement, and computational models that describe how temporal context representations shape memory processes. We also note several open questions concerning how temporal context reinstatement might influence subsequent temporal memory, including potential mediating effects of event spacing and event boundaries. These ideas and questions have the potential to guide future research and, ultimately, to advance theoretical accounts of how we preserve temporal memories.

An Analytical Exploration of Low Reynolds Number Cilia-Driven Flow of Johnson-Segalman Fluid with Heat Transfer Effects

This article discusses the properties of heat transfer on Johnson-Segalman fluids in a complex wavy channel made of metachronal wavy cilia. Such complex wall structures can be used in the design of biomimetic systems. The movement of fluid through a two-dimensional complex wave channel produced by the metachronal wave of cilia is characterized as laminar and incompressible. Firstly, the system of equations is transformed from a fixed frame of reference to a wavy frame of reference. Secondly, the system of equations of motion (EOM) is transformed into a non-dimensional form by using the scaling factors. Mathematical analysis has been conducted using long wavelength as well as low Reynold numbers assumptions. The Perturbation approach is used to solve the simplified governing equations for the axial velocity, temperature, stream function, pressure rise, and heat transfer coefficients. The equations representing axial velocity, pressure rise, and the streaming function are illustrated, and the reason for observed changes in different physical aspects are explained using basic theoretical principles. A solution for small values of the Weissenberg numbers is generated for the resulting nonlinear system. The current study investigates the effects of different boundaries and rheology on fluid flow.The velocity profile increases near the channel center with higher Q (time-mean flow rate) and e¯ (slip parameter), but decreases with greater Weissenberg number (We). The Brinkman number (Br), Q, and e¯ directly influence the temperature distribution, while We have the opposite effect. The size and number of trapped boluses increase with higher Q but decrease with rising We and e¯. It is noteworthy that the overall number of trapped zones rises throughout the complex wavy path.

Optimizing oxygen ion conductivity by modulating crystalline homogeneity

Keeping the stoichiometry at the optimal value required for electrical conduction throughout polycrystalline ceramics is crucial for various polycrystalline oxygen ion conductors. Using the photoluminescence spectrum of Eu3+ as a structural probe, the dependence between composition uniformity and conductivity was confirmed. We found that, for apatite La9.67×0.99Eu9.67×0.01Si6O26.505 (LSO) oxygen ion conductors synthesized by glycine nitrate combustion method, higher glycine content enhances the La/Si ratio uniformity, thereby improving the bulk conductivity. Surprisingly, thermal diffusion even at 1550°C cannot achieve uniform distribution when the precursor materials are not sufficiently homogeneous. Slight non-uniformity in the La/Si ratio is beneficial for impurities aggregation at high-density grain boundary regions, thereby alleviating the blocking effect of grain boundary on oxygen ion conduction. Both the bulk and total conductivities are higher than the best reported values in polycrystalline apatite by optimizing the La/Si ratio uniformity. The insight gained in this work is beneficial for enhancing conductivity by modulating crystalline homogeneity, and it facilitates further enhancement of ionic conductivity through cations doping for various polycrystalline oxygen ion conductors.

Effect of grain boundary engineering on corrosion behavior and mechanical properties of GH3535 alloy in LiCl-KCl molten salt

This study investigated the effect of grain boundary engineering (GBE) on the corrosion behavior and high-temperature mechanical properties of GH3535 alloy in 45LiCl-55KCl wt.% molten salt at 550°C. After corrosion for 300 h, a triple-layered product was formed on the solid solution specimen (Non-GBE), consisting of discontinuous NiCr2O4 outer-layer, Ni3Fe middle-layer, and NiCr2O4 inner-layer. For the GBE specimen, quite milder corrosion occurred on it that its surface still kept original polishing scratches. The real mass loss of the Non-GBE alloy (6.85 mg/cm2) is one order of magnitude higher than that of GBE (0.65 mg/cm2). The beneficial effect of GBE on improving alloy's corrosion resistance is owing to: surface carbide dissolution, discontinuous random high angle grain boundary and low dislocation density. High proportion of Σ3n grain boundaries and less carbide precipitation ensure stable high-temperature deformation performance of GBE sample in molten salt.