Radius Research Articles

Achieving Low Voltage Plasma Discharge in Aqueous Solution Using Lithographically Defined Electrodes and Metal/Dielectric Nanoparticles.

Because of the high dielectric strength of water, it is extremely difficult to discharge plasma in a controllable way in the aqueous phase. By using lithographically defined electrodes and metal/dielectric nanoparticles, we create electric field enhancement that enables plasma discharge in liquid electrolytes at significantly reduced applied voltages. Here, we use high voltage (10-30 kV) nanosecond pulse (20 ns) discharges to generate a transient plasma in the aqueous phase. An electrode geometry with a radius of curvature of approximately 10 μm, a gap distance of 300 μm, and an estimated field strength of 5 × 106 V/cm resulted in a reduction in the plasma discharge threshold from 28 to 23 kV. A second structure had a radius of curvature of around 5 μm and a gap distance of 100 μm had an estimated field strength of 9 × 106 V/cm but did not perform as well as the larger gap electrodes. Adding gold nanoparticles (20 nm diameter) in solution further reduced the threshold for plasma discharge to 17 kV due to the electric field enhancement at the water/gold interface, with an estimated E-field enhancement of 4×. Adding alumina nanoparticles decorated with Pt reduced the plasma discharge threshold to 14 kV. In this scenario, the emergence of a triple point at the juncture of alumina, Pt, and water results in the coexistence of three distinct dielectric constants at a singular location. This leads to a notable concentration of electric field, effectively aiding in the initiation of plasma discharge at a reduced voltage. To gain a more comprehensive and detailed understanding of the electric field enhancement mechanism, we performed rigorous numerical simulations. These simulations provide valuable insights into the intricate interplay between the lithographically defined electrodes, the nanoparticles, and the resulting electric field distribution, enabling us to extract crucial information and optimize the design parameters for enhanced performance.

Unloading Model of Elastic-Plastic Half-Space Contacted by an Elastic Spherical Indenter.

A new unloading contact model of an elastic-perfectly plastic half-space indented by an elastic spherical indenter is presented analytically. The recovered deformation of the elastic indenter and the indented half-space has been found to be dependent on the elastic modulus ratio after fully unloading. The recovered deformation of the indented half-space can be calculated based on the deformation of the purely elastic indenter. The unloading process is assumed to be entirely elastic, and then the relationship of contact force and indentation can be determined based on the solved recovered deformation and conforms to Hertzian-type. The model can accurately predict the residual indentation and residual curvature radius after fully unloading. Numerical simulations are performed to demonstrate the assumptions and the unloading model. The proposed unloading model can cover a wide range of indentations and material properties and is compared with existing unloading models. The cyclic behavior including loading and unloading can be predicted by combining the proposed unloading law with the existing contact loading model. The combined model can be employed for low-velocity impact and nanoindentation tests and the comparison results are in good agreement.

Kinetics of voids evolution during diffusion bonding of dissimilar metals on consideration of the realistic surface morphology: Modeling and experiments

A comprehensive model for analyzing the kinetics of void evolution and shrinkage during dissimilar diffusion bonding is proposed based on the sinusoidal profile. The model incorporates atom accumulation at void tip to determine the curvature radius of void neck, and integrates the local effect of surface diffusion to quantify the contribution of surface diffusion, thus avoiding the unrealistic void evolution observed in previous models. Furthermore, the model utilizes a combined diffusion coefficient for multicomponent alloys under the effect of stress and concentration gradients, to determine the interfacial diffusion coefficient for dissimilar joints. In contrast to previous models, the current model demonstrates significant improvements in predicted accuracy, efficiently depicting the realistic void evolution and interpreting the formation of various interfacial voids, which can be applied in various bonding cases, including for the dissimilar base metals with different surface conditions. Simulation results from bonding between austenitic steel and ferritic steel with different surface roughness reveal that interfacial voids predominantly form on the side of the base metal with the rougher bonding surface. Additionally, as surface roughness decreases, the prevailing surface source diffusion and interface source diffusion mechanisms promote void evolution and shrinkage, resulting in a significant reduction of the final bonding time. To achieve a high-quality bonding joint, it's suggested to place the smoother bonding surface on the higher creep-resistant base metal, which can accelerate the void closure process.

Analysis of Drivers’ Workload States on Highways in High Elevation Regions

The low-pressure (and low-oxygen) environment in plateau regions affects drivers’ psychophysiological states and, thus, driving behavior and road safety. Six scenarios of expressway exit ramps were constructed based on the UC/win-road simulator to quantitatively analyze the effect of the plateau environment on workload state. A total of 50 participants in Nanjing (altitude 50 m) and 50 participants in Lhasa (altitude 3,650 m) were recruited for the simulation experiments. Based on the principal component analysis, a sample entropy index (SEI) was constructed to reflect the drivers’ psychophysiological levels by combining the sample entropy of electroencephalogram (EEG) signals β%, β/(α+θ), β/α, and heart rate (HR). Meanwhile, the pupil area change rate and the percentage of fixation time and duration within the region of interest were analyzed to characterize the drivers’ visual workload. Based on the psychophysiological and visual load, the differences in workload states among plain and plateau drivers were analyzed using a regression model and a one-way analysis of variance (ANOVA) test. At the same time, the changing trends of the drivers’ workload states in the curved section of the exit ramp under different scenarios were analyzed. The plateau drivers experienced a higher level of mental stress and greater psychological load. Furthermore, the higher radius of horizontal curves reduced the visual load level for drivers when traveling on the highway exit ramp sections. These findings should serve as a valuable reference for refining the design of plateau expressway exit ramps and providing a theoretical basis for improving driving safety in plateau areas.

Causes and analysis of position offset of curvilinear continuous beam bridge

This study investigates the problem of beam deflection in curved continuous beam bridges. Taking the D0–D6 spans of the Gongbin Road viaduct as a basis, the main factors influencing the deflection of curved beam bridges are analyzed. The Midas/Civil finite element simulation software is used to calculate and analyze the causes of transverse and longitudinal deflection in curved beam bridges. The results show that the main influencing factor for beam deflection during operation is the system temperature, which causes a displacement greater than the combined displacement caused by self-weight, construction stage, gradient load, vehicle load, and bearing settlement. Damages to expansion joints during operation change the boundary conditions of the beam, preventing longitudinal free expansion under temperature load, and increasing the transverse displacement to 2–3 times the normal working state of the expansion joint, resulting in beam deflection. In the design phase, the selection of curvature radius and fixed support displacement is also a major factor affecting deflection. The smaller the curvature radius, the greater the influence on transverse and longitudinal deflection of the beam. However, when the curvature radius R is greater than 400 m, the impact on beam deflection can be neglected. The closer the fixed support position is to the ends of the bridge, the higher the possibility of bearing detachment, ultimately leading to beam deflection.

Multi-Objective Optimization of Bogie Stability for Minimum Radius Curve of Battery Track Engineering Vehicle

A battery track engineering vehicle faces challenges such as derailment and other safety concerns when navigating an R20m minimum radius curve, primarily owing to its low vertical and horizontal stabilities. To address these issues, a methodology integrating genetic optimization algorithms with a rigid and flexible coupled multi-body dynamics simulation is proposed to optimize the primary suspensions of the bogie of the vehicle. Initially, a multi-objective optimization model combining rigid and flexible coupled multi-body dynamics of battery track engineering vehicles with a genetic optimization algorithm was formulated. Subsequently, the optimal Latin hypercube design was applied to analyze the sensitivity of vertical and horizontal stability to various suspension parameters. Finally, a non-dominated sorting genetic algorithm (NSGA-II) and an archive-based micro genetic algorithm (AMGA) were applied to optimize the primary suspensions to enhance stability. Consequently, a set of optimal suspension parameter combinations was obtained. A notable enhancement was observed in the lateral stability of the optimized battery track engineering vehicles by 23.33% and in the vertical stability by 3.5% when traversing the R20m minimum radius curve, thereby establishing a theoretical foundation for further improving the running safety of railway vehicles and resolving the shortcomings of less research on the smallest radius curve.

Assessment of crack suppression in glass/epoxy curved laminates by incorporating micro and nanofillers

AbstractThe design of structures with a large radius of curvature is challenging because fiber‐reinforced composite materials have low resistance to delamination in the direction perpendicular to their thickness. These structures are commonly found in a wide variety of structural components that are used in the wind turbine and aviation industries. The objective of this study is to conduct an experimental investigation into the efficacy of incorporating milled glass fiber, cellulose nanoparticles, and carbon nanoparticles as fillers into an epoxy matrix to improve the resistance to delamination of glass/epoxy curved laminates and thereby inhibit crack growth. In contrast to the baseline samples, curved samples containing 3% cellulose nanoparticles demonstrated enhanced curved beam strength and interlaminar tensile strength by 4.95% and 3.82%, respectively. Additionally, filler‐loaded samples exhibited reduced delamination and fracture propagation damage compared with baseline samples. The adhesion between the epoxy matrix and infill was investigated by means of Fourier transform infrared analysis. In addition, live photographic images and fractured micrographs were correlated with mechanical findings in order to assess delamination suppression and damage processes in both the arm and arc directions.

An in-silico study on the mechanical behavior of colorectal cancer cell lines in the micropipette aspiration process

Cancer alters the structural integrity and morphology of cells. Consequently, the cell function is overshadowed. In this study, the micropipette aspiration process is computationally modeled to predict the mechanical behavior of the colorectal cancer cells. The intended cancer cells are modeled as an incompressible Neo-Hookean visco-hyperelastic material. Also, the micropipette is assumed to be rigid with no deformation. The proposed model is validated with an in-vitro study. To capture the equilibrium and time-dependent behaviors of cells, ramp, and creep tests are respectively performed using the finite element method. Through the simulations, the effects of the micropipette geometry and the aspiration pressure on the colorectal cancer cell lines are investigated. Our findings indicate that, as the inner radius of the micropipette increases, despite the increase in deformation rate and aspirated length, the time to reach the equilibrium state increases. Nevertheless, it is obvious that increasing the tip curvature radius has a small effect on the change of the aspirated length. But, due to the decrease in the stress concentration, it drastically reduces the equilibrium time and increases the deformation rate significantly. Interestingly, our results demonstrate that increasing the aspiration pressure somehow causes the cell stiffening, thereby reducing the upward trend of deformation rate, equilibrium time, and aspirated length. Our findings provide valuable insights for researchers in cell therapy and cancer treatment and can aid in developing more precise microfluidic.

ОБОСНОВАНИЕ КОНСТРУКЦИИ КРЫТОГО ГРУЗОВОГО ВАГОНА С УВЕЛИЧЕННЫМ ОБЪЕМОМ ГРУЗОВОГО ПОМЕЩЕНИЯ

The market of covered freight cars, as well as existing designs of this car type of domestic and foreign production is analyzed. Promising trends of making innovative designs of freight cars for the transportation of piece and container goods are found out. The original design of a covered freight car with an increased body space due to the use of the space between trucks is proposed. To reduce the complexity of loading and unloading operations, sliding sections of the side walls and roof are provided in the car design. To confirm the compliance of the proposed design with the requirements of regulatory and technical documents, the car was entered into the dimension, checking for automatic coupling at the junction of a straight line and a curve, passage in the coupling of an s-shaped curve and coupling of a straight line and a curve, and a single car along a circular curve of a small radius, as well as passing without self-decoupling of the hump of the sorting slide, the ramp exit of the train ferry. A safety assessment is carried out with regard to rolling the wheel onto the rail and overturning the car in curves. The car dynamic characteristics are found out by mathematical modeling methods. The assessment of the strength of the body load-bearing structure, lifting mechanisms of the floor sections, sliding sections of the roof and side walls is performed using the finite element method implemented in the environment of a specialized software package. The results obtained as a result of calculations and computer modeling confirmed the operability and safety of the proposed design of a covered freight car with an increased loading space.

MORPHOMETRIC CHARACTERISTICS OF THE MEANDERS OF THE DNIESTER ON THE PODILIA

The purpose of the work is to determine the exact number of formed meanders on the Podilia part of the Dniester, to provide them with the most complete morphometric characteristics, to separate them into separate groups according to the available morphometric data and territorial proximity. Morphometric characteristics of meanders is an important initial stage of their research. With the help of the Google Earth application, cartographic and generally descriptive methods, 30 separate meanders on the Dniester have been identified. To provide a complete morphometric characteristic of each meander, the following parameters were used in the work - the length of the meander in the circuit, the length of the meandering direction, the length and width of the meandering belt of adjacent meanders, the width of the meander deflection, the radius of curvature of the meander, the curvature of the meander bed and the shape of the meander. Each meander is given a separate name in order to distinguish it from other meanders and to use this name in subsequent works. The names of the meanders coincide with the corresponding name of the locality, which is located closest to the top of the meander. Each name of the meander is the author's and does not always coincide with the names given to them by previous researchers. In the work, detailed attention is paid to the presence or absence of tributaries of the Dniester near the windings. After all, this may indicate active neotectonic movements in this area and help determine the genesis of meanders. Separate large groups of meanders have been identified on the basis of available data - detailed morphometric characteristics and the presence of adjacent meanders in separate territories. It is also worth noting that in the last century such well-known scientists as Oleksandr Marynych and Kalenyk Gerenchuk [6] already carried out the zoning of the Dniester meanders. Everyone used their own methods, so the number of groups of meanders of the Dniester was different for everyone. The work also presents drawings depicting the largest meanders on the Dniester. Using the determined morphometric data, the largest and smallest meanders, the largest belts of meanders, compared different meanders with each other, determined the degree of meandering of the river in these areas, and also expressed the most probable reasons that influenced the development of this kind of meanders. Key words: meanders of the Dniester, morphometry, Podillia, morphometric characteristics of meanders.

Coherent point drift with Skewed Distribution for accurate point cloud registration

Point cloud registration methods based on Gaussian Mixture Models (GMMs) exhibit high robustness. However, GMM cannot precisely depict point clouds, because the Gaussian distribution is spatially symmetric and local surfaces of point clouds are typically non-symmetric. In this paper, we propose a novel method for rigid point cloud registration, termed coherent point drift with Skewed Distribution (Skewed CPD). Our method employs an asymmetric distribution constructed from the local surface normals and curvature radii. Compared to the Gaussian distribution, this skewed distribution provides a more accurate spatial description of points on local surfaces. Additionally, we integrate an adaptive multiplier to the covariance, which reallocates the weight of the covariance for different components in the probabilistic mixture model. We employ the EM algorithm to address this maximum likelihood estimation (MLE) issue and leverage GPU acceleration. In the M-step, we adopt an unconstrained optimization technique rooted in a Lie group and Lie algebra to attain the optimal transformation. Experimental results indicate that our method outperforms state-of-the-art methods in both accuracy and robustness. Remarkably, even without loop closure detection, the cumulative error of our approach remains minimal.

Experimental investigations on the effect of upstream-edge rounding on the BARC configuration

We experimentally investigate the influence of upstream-edge roundness on the flow around a 5:1 rectangular cylinder. We examine various values of edge curvature radius, ranging from nearly sharp edges to r/D=0.1104 at Reynolds number Re=40000, based on the freestream velocity and the crossflow dimension of the cylinder. Additionally, we explore the combined effects of edge roundness and (i) Reynolds number (Re=20000−80000) and (ii) angle of attack (|α|≤2deg). For all examined Re and α, limited sensitivity to upstream-edge rounding is observed up to r/D=0.0360, with results close to those obtained for nominally sharp edges. For r/D≥0.0781, and fixed Re and α=0deg, a noticeable decrease in the size of the mean recirculation region alongside the rectangular cylinder, lr, is observed with increasing r/D. For r/D≥0.0781, the flow features are also sensitive to Re, with a reduction in the length of the mean recirculation with increasing Re. The reduction of lr with increasing r/D and Re is due to the detached shear layer becoming more tilted towards the cylinder. Finally, for r/D≥0.0781, the effect of α, that is the increase of lr on the leeward side surface and the opposite on the windward side, is more important than for small r/D values.

Large Eddy Simulation of Laminar and Turbulent Shock/Boundary Layer Interactions in a Transonic Passage

Abstract Shock/boundary layer interactions (SBLI) are a fundamental fluid mechanics problem relevant in a wide range of applications including transonic rotors in turbomachinery. This paper uses wall-resolved large eddy simulation (LES) to examine the interaction of normal shocks with laminar and turbulent inflow boundary layers in transonic flow. The calculations were performed using GENESIS, a high-order, unstructured LES solver. The geometry created for this study is a transonic passage with a convergent-divergent nozzle that expands the flow to the desired Mach number upstream of the shock and then introduces constant radius curvature to simulate local airfoil camber. The Mach numbers in the divergent section of the transonic passage simulate single stage commercial fan blades. The results predicted with the LES calculations show significant differences between laminar and turbulent SBLI in terms of shock structure, boundary layer separation and transition, and aerodynamic losses. For laminar flow into the shock, significant flow separation and low-frequency unsteadiness occur, while for turbulent flow into the shock, both the boundary layer loss and the low-frequency unsteadiness are reduced. The time period of the unsteadiness was hypothesized to align with the time it takes for turbulent structures to convect from the shock to the trailing edge and acoustic disturbances to travel back from the trailing edge to the shock, and this is supported by the LES results.

Curvature of the Focal Conic in the Isotropic Plane

It is shown in \cite{beba} that every focal conic $\mathcal{C}$ in the isotropic plane can be represented by the equation $y^2=\epsilon x^2+x$, $\epsilon \in \{-1,0,1\}$ and a parametrization. This paper gives the equation of the circle of curvature at the point $T$ of the focal conic $\mathcal{C}$. The radius of curvature $\rho$ at the point $T$ of the focal conic $\mathcal{C}$ is given as well as its relation to the span $\delta $ from the center of $\mathcal{C}$ to the tangent $\lijepot$ at the point $T$ and to the length of the half diameter of $\mathcal{C}$ on the diameter parallel to the $\textup{tangent}$. 2000 Mathematics Subject Classification. 51N25

Investigation of bending behavior of two and three-dimensional honeycomb and auxetic sandwich beams

The bending behavior of two (2D) and three-dimensional (3D) sandwich beams that have a negative Poisson’s ratio (auxetic) and conventional honeycomb was investigated for different geometries, sheet thicknesses, and cell thicknesses. The re-entrant and solid specimens were produced with a stereolithographic (SLA) 3D printer and subjected to a three-point bending test under the conditions specified in the ASTM C393 standard. The data obtained from the tests were used to verify finite element analysis (FEA) results. The radius of curvatures was calculated for each specimen depending on the load step. In addition, Poisson’s ratio was calculated for each auxetic sample. As a result, the 3D arrowhead beam, with a cell thickness of 1 mm and a sheet thickness of 2 mm, exhibits peak force values that are 497.340% and 461.500% higher than re-entrant and missing rib beams, respectively. Besides, the maximum strain energy values of same 3D arrowhead specimens (596.120 mJ) are higher than re-entrant (101.032 mJ) and missing rib (108.201 mJ) specimens. It was determined that the arrowhead is the most durable structure compared to other auxetic structure geometries. Therefore, when arrowhead and honeycomb 3D beams are compared, it was observed that the maximum strain energy of arrowhead specimens was higher in both horizontal (84.310%) and perpendicular (131.910%) positioned specimens. Comparing the arrowhead and honeycomb 2D beams with the highest maximum strain energy, it can be concluded that the arrowhead beam absorbs 20.000% more energy.

Fast evaluation of the temperature dependence of residual stress in ceramic coatings via an image relative method

AbstractAlthough the residual stress in one‐side coating (type‐I coating) on a beam specimen can be determined by comparing the bending deformation before and after coating, the stress of a coated component without bending deformation (type‐II coating) is difficult to obtain via conventional methods, especially at high temperature. An image relative method is presented to determine variations in the curvature radius with temperatures for stress analysis at high temperature. A relationship between the residual stresses in type‐I and type‐II coatings was established so that the residual stress of type‐II coating was determined from the measured stress in type‐I coating. Thus, the core issue is to measure the temperature dependence of the bending deformation of the sample with one‐side coating. The temperature dependence of the residual stress in thermal barrier coatings on metal substrate was obtained by continuously photographing deflections of the beam specimen at temperatures ranging from 20°C to 1000°C, and the residual stress in components with symmetrical coatings in the temperature range was then determined.

Testing of spherical mirrors with extremely large R numbers using a quasi-autocollimation method

Spherical mirrors with large R numbers have extreme advantages in optical systems with large apertures and long focus lengths for improving imaging resolution and field of view. Their manufacturing and testing accuracy directly affects the final wavefront aberration of the systems. However, due to the influence of airflow disturbance in the long optical path, testing large R number spherical mirrors with high precision is difficult for the direct testing method. In this paper, a quasi-autocollimation test (QACT) method is proposed based on the consistency and reverse compensation between sphere and paraboloid with large R numbers. In QACT, the length of the testing path is reduced to half, and the test sensitivity of the surface figure error is doubled. According to the Kolmogorov turbulence theory, the suppressed degree of QACT to airflow disturbance is quantitatively evaluated, and QACT can suppress the random error in test to 35%. A comparative experiment between direct test and QACT method is carried out on a ∅100 spherical mirror with 8-meter radius of curvature. Airflow disturbance in the testing environment is calculated by mathematical fitting and the repeated accuracy is improved from 4 nm to 1.4 nm in a single test using the QACT method, which is consistent with theoretical analysis. The research results will provide a new strategy for ultra-precision and efficiency tests of large R number spherical mirrors.

Dynamic performance analysis of ball bearings with multi-factor coupling excitation

Skidding behavior and unstable cage whirling of bearings are key factors limiting the service performance of a spindle-bearing system. This study proposes an improved dynamic model of ball bearings focusing on structure deformations and poor lubrication conditions. The ring deformations induced by the radial preload for the spindle-bearing-pedestal mechanical system are first discussed, and the asperity contact and starved lubrication conditions on the traction effect are further considered. Then, the cage flexibility induced by the centrifugal effect is determined by the lumped mass method, and cage clearance deformations are analyzed. On this basis, the dynamic equations are derived by investigating the motions and stress states among the bearing components, and the calculations are compared with experimental data to verify their accuracy and reliability. Finally, the regulatory mechanism of bearing skidding and cage motion stability from the perspective of bearing preload and structural parameters is revealed. The results show that although surface roughness and starved lubrication weaken the lubrication conditions of the ball-race, the traction effect is enhanced to reduce bearing skidding. Compared with the curvature radius of inner race, the groove diameter decreases the cage guiding effect, and ensures cage motion stability by suppressing the collision behavior of the ball-pocket. The system preload is more effective for improving the bearing service performance, which can optimize the collision force of the ball-pocket and increase the cage guiding effect.

Curved mineral platelets in bone

Bone is a composite material principally made up of a mineral phase (apatite) and collagen fibrils. The mineral component of bone occurs in the form of polycrystalline platelets 2–6 nm in thickness. These platelets are packed and probably glued together in stacks of two or more, ranging up to >30 platelets. Here we show that most of these stacks are curved flat sheets whose cylindrical axes are oriented parallel to the long axes of collagen fibrils. Consequently, the curvature of the platelets is not detectable in TEM sections cut parallel to the collagen fibril axes. The radius of curvature around these axes ranges from about 25 nm (the average radius of the collagen fibrils) to 100′s of nm. The shapes of these curved forms contribute to the compressive strength of bone. Statement of significanceBone, the material of which bones are made, is mainly composed of a protein, collagen, and the mineral apatite (calcium phosphate). The crystals have long been known to be flat plates about 5 nanometers (nm) thick. Here we show that the crystals are bound together in curved platelets with a radius of curvature between 25 and several hundred nm, which weave between fibrils of collagen. Some platelets wrap tightly around fibrils. The platelets form stacks of from two to up to 30. The crystals in the platelets are all oriented parallel to the cylindrical fibrils even though most crystals are not in contact with collagen. These curved structures provide greater strength to bone.

The Influence of the external meshing gears’ contact ratio on the contact stress in the transmission system

Abstract Using the Hertz contact theory, the calculation method of tooth contact stresses at different boundary points within the double tooth meshing zone for high contact ratio external meshing gear pair is investigated. The radius of curvature and pressure angle at each boundary point of the external meshing gear with a high contact ratio is given. The boundary point meshing coefficients are introduced to convert the comprehensive radius of curvature at the boundary point into the radius of curvature at the node, to make it in line with the form of calculation of the national standard. The analysis examines how the parameters affect the contact stress at different boundary points of the gear pair with a high contact ratio. When the contact ratio of the gears is 2, there is a sudden change in the contact stress on the tooth surface, and HCR gears have smaller contact stress than LCR gears.