Spherical Contact Research Articles

THEORETICAL-EXPERIMENTAL POSSIBILLITIES OF MICROSTRUCTURE QUANTIFICATION OF DISPERSION STRENGTHENED MATERIALS

The present paper is devoted to the possibilities to classify the spatial arrangement of the elements (features) of a stochastic process with geometrical objects. The fundamental quantities describing point processes were introduced. Experimental possibilities of structural objects determination, possibilities of evaluation of the size distribution of the secondary phases, testing of planar point structures (estimation of the process intensity, square method and characteristics of the second order) were estimated. Interparticle distances, namely mean interparticle distance, mean minimum distance, mean visibility and mean path of spherical contact were defined. Selected processes were described and demonstrated from simulated realizations on Al-Al4C3 dispersion strengthened material, prepared by a powder metallurgy method of reaction milling. Interparticle distances of Al4C3 particles were evaluated. Polygonal methods and quadrant counts method were used for characterization of the particle arrangement.

Exotic symplectomorphisms and contact circle actions

Using Floer-theoretic methods, we prove that the non-existence of an exotic symplectomorphism on the standard symplectic ball, [Formula: see text] implies a rather strict topological condition on the free contact circle actions on the standard contact sphere, [Formula: see text] We also prove an analogue for a Liouville domain and contact circle actions on its boundary. Applications include results concerning the symplectic mapping class group and the fundamental group of the group of contactomorphisms.

Greater higher order aberrations induced by toric orthokeratology versus soft toric multifocal contact lens wear.

Spherical orthokeratology and soft multifocal contact lenses are commonly used for myopia control and correction, but have been shown to increase spherical aberration, coma and total higher order root mean square (HORMS) aberrations. There are limited myopia control contact lens options for patients with moderate to high astigmatism. The purpose of this study was to quantify changes in higher order aberrations (HOA) in myopic astigmatic eyes fitted with toric orthokeratology (TOK) and soft toric multifocal (STM) contact lenses. Ocular wavefront aberrations were measured in both eyes of 30 adult subjects and are reported through the 6th radial order over a 5mm, dilated pupil. All eyes met refractive criteria of myopia (-5.00 D to plano) and cylinder (-3.50 to -1.25 D). Three measurements were taken at baseline and after 10±2days of lens wear (TOK, STM). Sixteen subjects achieved logMAR high contrast visual acuity of 0.30 or better in both eyes and were included in this analysis. Repeated measures analysis of variance and post-hoc paired t-tests were used, as appropriate, with Benjamini-Hochberg correction. Higher order root mean square, spherical aberration (C12), and coma RMS (C7, C8) increased with TOK (0.641 [0.222], 0.409 [0.157], 0.426 [0.187] µm, respectively) and STM (0.481 [0.107], 0.223 [0.139], 0.320 [0.130] µm, respectively) from baseline (all p<0.001). TOK was elevated compared to STM for HORMS (p=0.03), spherical aberration (p=0.001) and coma RMS (p=0.04). Toric orthokeratology induced more HORMS, spherical aberration and coma RMS than STM in myopic astigmats; however, both lens types showed an increase in HOA compared to baseline, which placed patients outside the age and pupil size matched normative ranges. While the optical changes that accompany these modalities are helpful for myopia management, the induction of HOAs may have unintended consequences on visual performance.

Microscratch of copper by a Rockwell C diamond indenter under a constant load

The scratch test is used for quality control mostly in phenomenological ways, and whether fracture toughness can be obtained from this test is still a matter of debate requiring further elucidation. In this paper, values of the fracture toughness of copper obtained by different scratch-based approaches are compared in order to examine the applicability of scratch-based methodologies to characterize the fracture toughness of soft metals. The scratch response of copper to a Rockwell C diamond indenter is studied under a constant normal load condition. The variations of penetration depth, residual depth, and residual scratch width with applied normal load are quantified from spherical to sphero-conical contact regimes by piecewise functions. A newly proposed size effect law is found to be the most suitable for scratch-based approaches to characterizing the fracture toughness of soft metallic materials with significant plasticity. A simple expression relating the nominal stress to the penetration depth is proposed for the spherical contact regime and gives almost the same value of fracture toughness. The residual scratch width provides useful information on pile-up of material and on the spherical tip radius of the indenter. It is found that the values of the fracture toughness obtained from the microscratch test are influenced by the data range for analysis.

Contact lens procurement and usage habits among adults in Sudan.

The study aimed to assess contact lens (CL) wear and care habits among adults in Sudan. An observational, non-interventional, multi-center, cross-sectional study was conducted in the CL departments of all the eye hospitals and centers, and optical centers in the Khartoum State, Sudan. Established CL wearers residing in Khartoum State, Sudan. CL wear profile, CL usage habits, hand and CL hygiene habits were assessed using an interviewer-administered questionnaire. The average age of the 442 participants was 24.57 (± 4.87) years. Women comprised 92% of the sample. Smoking was reported by 15.8% of the sample. 81.9% wore soft spherical CL, with 43.4% of the participants were prescribed CL on a yearly replacement schedule. Only 68.3% were prescribed CL by an eye care practitioner. Multipurpose solutions were used by 78.8% of the sample to clean CL, and by 52% to clean the lens case. Compliance rate for CL wear and care among participants was 81.1%. None of the participants reported sharing CL or CL case and rinsing the case with tap water. High compliance level was observed for overnight wear; swimming and showering with CL; handwashing before CL insertion; and cleaning of CL. Moderate compliance rates were recorded for cleaning and replacing lens case, and topping up or sharing solution. Low compliance was noted for attending after care visits. CL wearers in Sudan exhibit high to moderate levels of compliance to most contact lens wear and care aspects, except for attending aftercare visits. CL practitioners in Sudan are encouraged to prescribe CL appropriate to the lifestyle and economic situation of patients and actively recommend care products. In addition, practitioners need to follow up with patients to attend aftercare appointments, where hygienic wear and care habits should be emphasized.

Tunable adhesion of an elastic pillar by pressurizing inner cavity

This work studies the effect of a cavity with inner pressure on the adhesion of circular pillars with a flat tip in contact with a rigid smooth surface. The inner cavity of pillars is pressurized positively before the contact. The effect of the cavity on the adhesion is examined for different cavity diameters and different membrane thicknesses over the cavity. The shape of the tip of the pillars is changed in accordance with the cavity dimension and the positive cavity pressure, which allows the change of an adhesive contact type from a flat-punch adhesive contact to a spherical adhesive contact that results in tunable adhesion strength of circular pillars. The results demonstrate that having an inner cavity reduces the adhesion, where the cavity diameter is more effective than the membrane thickness over the cavity on the reduction of the adhesive force. Applying pressure to the inner cavity of the pillars changes the sphericity, which alters the adhesive force accordingly. The sphericity [Formula: see text]0.1 almost has no effect on the tunable adhesion strength, where the higher sphericity results in the reduction of the adhesive force from high adhesive force to low adhesive force linearly with a tunable efficiency between 95% and 98%.

A Fractal Model of Elastic–Plastic Contact Between Rough Surfaces for a Low-Velocity Impact Process

Under the low-velocity impact conditions, in order to study the contact load variation law of the ellipsoid elastic bodies, an elastic–plastic contact analysis model of rough ellipsoid surfaces is provided based on elastic–plastic fractal theory. A spherical elastic–plastic fractal model considering friction factors is established, and the spherical diameter density distribution function and elastic contact mechanics are used as the solution methods. The two contact surfaces are taken as the research object, and the influence of relevant variables on the contact intensity is analyzed. The analysis results show that the fractal dimension and roughness have a greater effect on contact performance, the contact load is positively related to the surface roughness, and the lower friction coefficient has a weaker effect on the contact load, and the correctness of the present model is verified by comparing finite element simulation results and other studies. The modified spherical contact load function provides a theoretical basis for the friction and wear of the microscopic surface, it can be applied for solving the sliding contact problems with different impact velocities and the surface bearing capacity of the impact parts can be improved.

Crystal structure of potassium tri-ethyl-hydridoborate ('superhydride').

In the title compound, formally K+·C6H16B-, the contact sphere of potassium consists of eleven hydrogen atoms from three different anions, assuming an arbitrary cut-off of 3 Å. The shortest inter-action, 2.53 (2) Å, involves the hydridic hydrogen H01, which fulfils a bridging function in the formation of chains of KHBEt3 units parallel to the a axis [K1-H01i 2.71 (2) Å, K1-H01-K1ii 126.7 (9)°, operators x∓1/2, -y+, -z+1].

Analysis of Dynamic Characteristics of 6-PSS Parallel Mechanism Considering Spherical Hinge Clearance

This paper is based on a new type of 6-PSS parallel mechanism. Firstly, considering the clearance between the kinematic pair connecting the upper platform and the link, establish a kinematic model considering the spherical hinge clearance. Then, based on the Lankarani-Nikravesh(L-N) contact model and the modified Coulomb friction model calculate the contact force when the spherical elements contact, which is equivalent to the center of the corresponding member as the generalized external force. Apply for Newton Euler method with Lagrange Multiplier to establish the dynamics model of the parallel mechanism with clearance. Finally, the R-K method is used to solve the dynamic equation and analyze the influence of different spherical hinge gap sizes on the dynamic characteristics of the mechanism.

Induced Refractive Error Changes the Optical Coherence Tomography Angiography Transverse Magnification and Vascular Indices

To assess the effect of changing anterior eye refractive power with contact lenses on the transverse magnification of en face images and associated vascular indices from optical coherence tomographic angiography (OCT-A). Prospective crossover study. Spherical soft contact lenses (-6 diopter [D] to +6 D in 2 D steps) were used to induce anterior eye refractive power changes in 11 healthy young adults and 3×3-mm macular scans were captured using OCT-A (Zeiss AngioPlex, software version 11.0; Cirrus HD-OCT 5000, Carl Zeiss Meditec Inc). Image transverse magnification was predicted based on refraction and biometry measurements and compared with empirical changes in the en face images measured with image analysis. Linear regression analysis was performed to assess the relationship between induced refractive ametropia and foveal avascular zone (FAZ) area, perimeter, circularity, and vessel density and perfusion density. The predicted transverse magnification was linearly related to induced refractive ametropia and to the empirical transverse magnification changes (average slope: 1.02, 95% CI: 0.90-1.34). All the OCT-A indices showed linear relationships with induced refractive ametropia (P < .05) with the 12 D tested range altering the indices by 7% to 12%. After correcting for transverse magnification, all OCT-A indices except FAZ area were linearly related to induced refractive ametropia (P < .05) and were reduced to 1% to 9%. This study is the first to show that induced refractive ametropia can affect OCT-A image magnification and indices. These changes are clinically important and need to be considered along with biometry effects when interpreting OCT-A indices. Transverse magnification changes can affect the ability of OCT-A to precisely measure linear dimensions of blood vessels.

The study and comparison of elastic modulus of pineapple fruit in macroscopic and microscopic modes.

According to bibliography, elastic modulus studies of agricultural produce at the macro-scale using a resistance measuring (as Magness-Taylor penetration test or compression test) by an Instron Universal Mechanical Testing Machine is often used to express this characteristic. However, the determination of the elastic properties of agricultural produce at the macro-scale result widely varying values for a particular agricultural produce. So in this study, to decrease the variability which now exists in the elastic modulus results of agricultural produce measured at the macro-scale, measuring and comparison of the elastic modulus of agricultural produce, pineapple fruit as case study, in macroscopic (by Hook's theory on the cylindrical specimen and Hertz theory in the mode of spherical indenter contact on the whole specimen) and microscopic (by atomic force microscopy) modes was investigate. There is concluded that with changing the type of theory, the behavior of the elastic modulus changes significantly at a 1% level. In microscopic mode studies, the lowest elastic modulus (0.135 MPa) was obtained by using Hertz theory in the mode of spherical indenter contact on the whole specimen while the highest elastic modulus value (0.779 MPa) was seen by using Hook's theory on the cylindrical specimen. In microscopic mode studies, the Sneddon model had the lowest elastic modulus while Hertzian model showed the highest elastic modulus value. Consequently, due to some reasons such as complex shape of most agricultural produce, assumptions required for three elastic theories of contacting bodies in macroscopic mode, complex structure and viscoelastic behavior of agricultural produce, it is found that the variability of the information can be reduced at micro-scale, or, to a lesser extent.

Evolution of adhesive wear and friction in elastic-plastic spherical contact

A finite element (FE) model is presented for the evolution of fracture and friction in elastic-plastic adhesive spherical contact. The model is based on a realistic criterion of ductile fracture in a three-dimensional contact problem and the failed elements are deleted. Full stick contact condition is used at the contact interface to model a strong adhesion there. Fracture evolution is presented allowing the process of material removal in the form of a wear particle. The evolution of friction with increasing tangential loading as well as sliding inception are presented. Predicted wear coefficient and static and dynamic friction coefficients are compared with experimental results and possible reasons for discrepancies between the predicted and experimental results are discussed.

Dynamical convexity and closed orbits on symmetric spheres

Our main theme here is the dynamics of Reeb flows with symmetries on the standard contact sphere. We introduce the notion of strong dynamical convexity for contact forms invariant under a group action, supporting the standard contact structure, and prove that in dimension 2n+1 any such contact form satisfying a condition slightly weaker than strong dynamical convexity has at least n+1 simple closed Reeb orbits. For contact forms with antipodal symmetry, we prove that strong dynamical convexity is a consequence of ordinary convexity. In dimension 5 or greater, we construct examples of antipodally symmetric, dynamically convex contact forms which are not strongly dynamically convex, and thus not contactomorphic to convex ones via a contactomorphism commuting with the antipodal map. Finally, we relax this condition on the contactomorphism furnishing a condition that has nonempty C1-interior.

A JKR-Like Solution for Viscoelastic Adhesive Contacts

A closed-form solution for the adhesive contact of soft spheres of linear elastic material is available since 1971 thanks to the work of Johnson, Kendall, and Roberts (JKR). A similar solution for viscoelastic spheres is still missing, though semi-analytical and numerical models are available today. In this note, we propose a closed-form analytical solution, based on JKR theory, for the detachment of a rigid sphere from a viscoelastic substrate. The solution returns the applied load and contact penetration as functions of the contact radius and correctly captures the velocity-dependent nature of the viscoelastic pull-off. Moreover, a simple approach is provided to estimate the stick time, i.e., the delay between the time the sphere starts raising from the substrate and the time the contact radius starts reducing. A simple formula is also suggested for the viscoelastic pull-off force. Finally, a comparison with experimental and numerical data is shown.

On the Effect of Shear Loading Rate on Contact Area Shrinking in Adhesive Soft Contacts

Adhesion and, its interplay with friction, is central in several engineering applications involving soft contacts. Recently, there has been an incredible push towards a better understanding on how the apparent contact area evolves when a shear load is applied to an adhesive soft contact, both experimentally and theoretically. Although soft materials are well-known to exhibit rate-dependent properties, there is still a lack of understanding in how the loading rate could affect the contact area shrinking. Indeed, most of the experiments involving a sphere-flat contact have been conducted at a fixed loading rate, and, so far, analytical models have assumed a constant work of adhesion, independent on the peeling velocity. Here, by using linear elastic fracture mechanics, an analytical model is derived for the contact of a rigid sphere on a soft adhesive substrate, which is aimed at elucidating the effect that a rate-dependent work of adhesion has on the contact area shrinking. The model results show that contact area reduction is very sensitive to the loading rate, with slower loading rates promoting a stronger shrinking, which seems in agreement with Literature results. Furthermore it is shown that rate effects enhance the apparent interfacial toughness, i.e. more energy is needed to drive the system from full stick up to gross sliding.

First yield in the Maugis‐adhesive contact of elastic spheres

AbstractWe analyze the onset of plastic yield in the Maugis‐adhesive contact of elastic spheres. Written in proper dimensionless variables, the problem solution depends on Poisson's ratio, the Tabor parameter and a non‐dimensional adhesion strength. The influences of adhesion range and strength are studied in detail. First yield can either occur inside the bodies on the axis of symmetry (for long range adhesion) or at the contact boundary (for short range adhesion). Adhesion significantly reduces the external load necessary to initiate plastic yield. A simple analytic solution for the critical load in the DMT‐limit of adhesion is being derived. Our results are quantitatively similar to previously published findings based on the double Hertz model of adhesion and can for example be applied to study an adhesive spherical microcontact in the contact of rough surfaces.

BCLA CLEAR – Contact lens optics

The most fundamental aspect of a contact lens is its optics; the manner in which the refraction of light is managed to optimise vision to the clinical benefit of the lens wearer. This report presents contemporary information on the optical structure of the eye and the optical models employed to understand the correction of refractive error. The design, measurement and clinical assessment of spherical, aspheric, toric, multifocal and myopia control contact lenses are described. The complexity and variety of multifocal lenses is recognised and detailed information is provided for alternating, simultaneous, diffractive, annular, aspheric and extended depth of field lens designs. In terms of clinical assessment, a contemporary review is provided for the measurement of: visual acuity, contrast sensitivity, through focus curves, reading performance, peripheral refraction, toric displacement realignment and patient reported outcomes. Overall, the paper aims to serve as a resource for the prescribing clinician, who can optimise contact lens corrections for patients by building on the optical rationale of these devices; and also highlights future opportunities for research innovation.

A mapping discrete element method for nonlinear dynamics of vibrating plate-particle coupling system

A mapping discrete element method is presented to study dynamic behaviors of the vibrating plate-particle coupling system. The continuum is partitioned into a mesh of mass points and simulated by the discrete element method, where the mass, stiffness and damping is mapped from the global mass, stiffness and Rayleigh damping matrix in the finite element method. The coupling between the continuum and the discrete particle material is realized by expanding the surface mass points into spheres. Therefore, the continuum's internal force and deformation can be accurately calculated whilst using the efficient spherical contact detection to couple and interact with particles. In the vibrating plate-particle system, the non-linear phenomena observed during the experiment are further studied by the proposed method. The results show that the velocity distribution of the particle system changes significantly when the jump phenomenon occurs, and the disruption of the uniform motion of the particle system by the vibrating plate is one of the key factors that creates the jump phenomenon. Furthermore, it is noticed in the simulation that the movement of particles above the plate is similar to bouncing ball causing frequency and period doubling phenomenon. Moreover, a linear region is found in the low frequency band, where the particles additional effects on the mass and stiffness of the plate are evident and the excitation amplitude has a lesser effect on power dissipation compared to other frequency bands.

Fatigue Analysis of Spherical Contact Subjected to Cyclic Elastic-Plastic Normal Loading

Abstract Surface fatigue resulting from cyclic contact loading is a main reason for the rough surface wear. Since a rough surface consists of many asperities, the fatigue in one asperity is investigated. The multiaxial Fatemi–Socie fatigue criterion is adopted to study the contact fatigue in a spherical asperity subjected to cyclic elastic-plastic normal loading. The fatigue damage in the asperity is predicted. The maximum fatigue damage occurs at the edge of the maximum contact area. Two typical patterns are found for the fatigue damage distribution. Locations and orientations of fatigue microcrack initiation are also identified. Finally, future research directions are discussed.

A ML framework to predict permeability of highly porous media based on PSD

Using machine learning (ML) method to predict permeability of porous media has shown great potential in recent years. A current problem is the lack of effective models to account for highly porous media with dilated pores. This study includes (1) generation of media (porosity = 0.8) via a Boolean process, (2) the pore size distribution (PSD) control by using different groups of homogeneous packed spherical particles (3) PSD data obtainment using the spherical contact distribution model (4) computation of the permeability via LBM simulations, (4) training of artificial neuron network (ANN) and (5) analysis of the model. It is found that the PSD could outperform the previous geometry descriptors as an input of ML framework to deal with highly porous structures with different fractions of dilated pores, however there is still room for precision enhancement.