Contact Shape Research Articles

Smart carrier from electrospun core-shell thermo-sensitive ultrafine fibers for controlled drug release

In this study, electrospun core-shell thermo-sensitive (CSTS) ultrafine fibers were prepared successfully. The optimum structural polyethersulfone (PES) porous ultrafine fibers were chosen as core fabricated by electrospinning technology. In addition, in order to improve the lower critical solution temperature (LCST) of poly (N-isopropylacrylamide) (PNIPAm), acrylamide (Am) was chosen as the comonomer with excellent hydrophilicity and structural similarity to N-isopropylacrylamide. Thus, poly(N-isopropylacrylamide-co-acrylamide) P(NIPAm-co-Am) with higher LCST (LCST = 43 °C) was synthesized on the surface of PES fibers via radical copolymerization as shell. The introduction of the P(NIPAm-co-Am) influenced the morphology and performance of the PES ultrafine fibers significantly. Meanwhile, SEM, FTIR and XPS results all showed the P(NIPAm-co-Am) covered on the surface of PES fibers after polymerization for 4 h. Both the contact angle and shape change test indicated that the CSTS ultrafine fibers exhibited different wettability and area when the temperature was below and above the LCST due to the thermo-sensitive of P(NIPAm-co-Am) gels shell. Furthermore, curcumin was selected to use as drug model loaded in CSTS ultrafine fibers and the curcumin release behavior was tested to study the thermo-sensivity of CSTS ultrafine fibers. At 20 °C and 60 °C, the max curcumin release amount is w 33.21% and w 80.15%, respectively. The result directly demonstrated that CSTS ultrafine fibers had thermo-sensity as drug carrier. Finally, the cell culture studies showed that the prepared CSTS ultrafine fibers have a potential application in the biomedical fields.

Proposal of a novel approach for 3D tooth contact analysis and calculation of the static transmission error in loaded gears

The static transmission error in gears represents the main noise and vibration source of mechanical transmissions, both for self-excitation and for the excitation of powertrain components. An accurate determination of it is very complex, since it requires experimental tests or highly detailed models. In both cases the costs and the computational time are high, therefore the possible different types of geometries to analyse are significantly reduced. In the present work, a semi-analytical methodology is proposed, with the aim of evaluating the variation of the contact area in gears during their meshing and at different levels of applied torque. This model considers the tooth compliance (tooth shear and bending, foundation and rim, gear body) and the local contact effects. The present semi-analytical methodology allows a detailed analysis of the tooth compliance and the contact area on a high number of points along the meshing cycle (typically over 100 points). It also enables the definition of the correct contact area geometry between meshing teeth, depending on the possible geometry modification (micro-geometry and/or manufacturing errors) and on the input torque. In particular, the contact is simulated through a non-Hertzian model able to evaluate every contact shape, overcoming the limits of the Hertzian theory. The goal of the proposed methodology is to determine with high precision the static transmission error between gears in a limited time with respect to the classical finite element method. Furthermore, it is useful for a reliable prediction of the transmission dynamic behaviour, considering the load exchanged between the teeth in relation to spin speed and torque, in a computational time lower than the classical techniques.

저소음 기어펌프용 연속접촉 헬리컬기어의 형상 설계에 관한 연구

The use of external gear pumps is an effective way to achieve adequate performance at low cost when composing hydraulic systems. The biggest drawback, on the other hand, is the accompanying noise. Gears of continuous contact shape are actively used for the pump recently. The continuous contact shape must be the helical type due to the nature of the gear pump that is driven only by the drive gear. In this paper the theoretical shape of continuous contact gear is analyzed using simple rack shape of straight lines and two circular arcs. Using such geometry, the theoretical equation will be developed by envelope curves according to the conjugate gear shape rules. After checking the validity of the theory by the shape of gear rules, the grinding shape was also developed. The 3D shapes using equation can be also drawn. It was also shown that contact ratio and radius of curvature are easily developed by the theoretical equations.

Evaporation of Water on Suspended Graphene: Suppressing the Effect of Physically Heterogeneous Surfaces

Evaporation of water nanodroplets on a hydrophilically adjusted graphene sheet was studied based on a molecular dynamics approach. Suspended graphene was used as a physically heterogeneous surface, and fixed graphene was considered as an ideally flat surface. State of the triple-phase contact line (TPCL) and shape evolution were addressed at four different temperatures on both substrates. Additionally, contact angle (CA) was studied during 3 and 22.5 ns simulations in both closed and opened conditions. The observed constant contact angle regime was predictable for the fixed graphene. However, it was not expected for the suspended system and was attributed to the oscillations of the substrate atoms. The size of the nanodroplet also affects the constant-contact-angle mode in both systems, when the number of water molecules decreases to less than 500. The oscillations created a surface on which physical heterogeneities were varying through time. Examination of the evaporation and condensation processes revealed higher rates for the fixed systems. Local mass fluxes were calculated to reveal the contribution of TPCL and meridian surface (MS) of the nanodroplet to evaporation and condensation. The obtained results indicate similar values for the mass flux ratio at the TPCL, which remains twice as large as the MS for both suspended and fixed graphene. The results confirm the assumption that a surface with varying heterogeneities can overwhelm the droplet and act as an ideally flat surface.

Comparison of non-Hertzian modeling approaches for wheel–rail rolling contact mechanics in the switch panel of a railway turnout

Due to the complicated wheel–rail contact relation of railway turnouts, it is necessary to select a reasonable rolling contact model to simulate the vehicle–turnout dynamics and wheel–rail damages. This paper mainly aims to evaluate the calculation accuracy and efficiency of different non-Hertzian modeling approaches in solving normal and tangential wheel–rail contact problems of railway turnouts. Four different non-Hertzian approaches, namely CONTACT, Kik–Piotrowski, Ayasse–Chollet, and Sichani methods are compared and analyzed. The above four models are built considering the relative motion of stock/switch rails. A wheel profile called LMA contacting with stock/switch rails (head width 35 mm) of CN60-1100-1:18 turnouts is selected as the object of analysis. The normal contact problems are evaluated by the wheel–rail contact areas, shapes, and normal contact pressures. The assessment of tangential contact problems is based on the creep curves, tangential contact stresses, and distribution of the stick/slip region. In addition, a contrast analysis is performed on the calculation efficiencies of the four approaches. It is found that the normal and tangential contact results calculated based on the Sichani method coincide well with those obtained according to CONTACT, and the calculation efficiency is about 262 times that of CONTACT. The conclusions can provide some guidance to the selection of wheel–rail rolling contact approach in the simulation of vehicle–turnout dynamics and wheel–rail damages.

Impact of the Periphery Electrostatic Field on the Photovoltaic Effect in Metal–Semiconductor Contacts with a Schottky Barrier

Studies of an electrostatic system of flat metal–semiconductor contacts with a Schottky barrier reveals a nontrivial dependence of their current and voltage photosensitivity (the photovoltaic effect) on the contact shape. The specific features of using the photovoltaic effect in such contacts are determined, to a great extent, by the built-in periphery electrostatic field with an absolute value that depends on the contact perimeter and area. Thus, to increase the efficiency of light-to-electrical energy conversion by Schottky contacts, it is necessary to use optimization techniques based on the concepts of the proposed physical model of an electrostatic system of flat Schottky contacts with regard to periphery electrostatic fields. The “hot electron resonance” effect, which enhances the external quantum efficiency of photodiodes with a Schottky barrier, can be explained by enhancement of the field emission of electrons by the periphery electrostatic field.

Integrative analysis of gene expression profile and DNA methylation profile of long-term cultivated porcine bone marrow mesenchymal stem cells

To integrate the result of whole genome expression data and whole genome promoter CpG island methylation data, to screen the epigenetic modulated differentially expressed genes from transformed porcine bone marrow mesenchymal stem cells (BMSCs) after long-term cultivation. Bone marrow from 6 landrace pigs, 3-month-old about 50 kg weight, was aspirated from the medullary cavity of the proximal tibia. The BMSCs were isolated, and purified by Ficoll density gradient centrifugation combined with adherent culture method. The transfor mation of BMSCs was tested by several methods including cell morphology observation, karyotype analysis, clone forming in soft agarose, serum requirement assay, and tumor forming in mice. The Agilent Pig 4x44k Gene Expression Microarray was used to investigate the differentially expressed mRNA. The methylated genes expression profile was performed using customized pig methylation chip. The gene expression and DNA methylation profiles were integrated to find out the epigenetic modulated differentially expressed genes, and to complete the bioinformatic analysis. BMSCs showed a change in appearance, from the initial spindle shape to a more flatted morphology then to small contact shape. After additional passages, BMSCs gradually acquired recovery of proliferating capacity and transformation properties such as anchorage-independent growth, chromosomal abnormality, and tumor formation in nude mice. The gene chip analysis demonstrated that 257 genes were upregulated and 315 genes were downregulated during long-term cultures as well as multiple signal pathways transduction involved, such as cell cycle, ECM-receptor interaction, focal adhesion, regulation of actin cytoskeleton, pathways in cancer, and P53. The analysis from methylation chip of coding genes suggested epigenetic regulation was involved in BMSCs spontaneous transformation and play a important role on it; 962 genes were hypermethylated and 1219 genes were hypomethylated, which were involved in the biological process of cellular metabolic, structure, and tumor generation. The combined analysis of genes regulated by methylation in the transformation process of BMSCs found that the methylation changes of the 35 genes were contrary to the direction of expression change (correlation coefficient r=-0.686, P=0.000); in which the methylation level of 21 genes promoter regions were increased while the gene expression decreased, and the methylation level of the 14 genes promoter regions decreased and the gene expression increased. At the same time, KEGG enrichment analysis revealed multiple genes regulated by methylation, involved in stem cell differentiation and multiple cell signaling pathways. Among the 14 down-regulated genes, many of them have the role of regulating the interaction of tumor and immunization, and the change of the methylation status of the CDKN3 promoter region may be closely related to the cell oncology. The results deepen our understanding of the crucial role of coding genes methylation modification in BMSCs transformation, and may provide new approach to establish safe criteria for BMSCs clinical applications and transformation prevention.

Friction of Poroelastic Contacts with Thin Hydrogel Films.

We report on the frictional behavior of thin poly(dimethylacrylamide) hydrogel films grafted on glass substrates in sliding contact with a glass spherical probe. Friction experiments are carried out at various velocities and normal loads applied with the contact fully immersed in water. In addition to friction force measurements, a novel optical setup is designed to image the shape of the contact under steady-state sliding. The velocity dependence of both friction force Ft and contact shape is found to be controlled by a Péclet number, Pe, defined as the ratio of the time τ needed to drain the water out of the contact region to a contact time a/ v, where v is the sliding velocity and a is the contact radius. When Pe < 1, the equilibrium circular contact achieved under static normal indentation remains unchanged during sliding. Conversely, for Pe > 1, a decrease in the contact area is observed together with the development of a contact asymmetry when the sliding velocity is increased. A maximum in Ft is also observed at Pe ≈1. These experimental observations are discussed in the light of a poroelastic contact model based on a thin-film approximation. This model indicates that the observed changes in contact geometry are due to the development of a pore pressure imbalance when Pe > 1. An order-of-magnitude estimate of the friction force and its dependence on normal load and velocity are also provided under the assumption that most of the frictional energy is dissipated by poroelastic flow at the leading and trailing edges of the sliding contact.

Effect of blisters and rims on radial hydride precipitation in fuel elements under dry storage conditions

ABSTRACT Hydrogen enters in Zry clads during fuel element life in service; when hydrogen exceeds the terminal solid solubility, circumferential hydrides are precipitated. In the presence of thermal gradients, produced for instance by oxide spallation, localized concentration of hydrides - known as blisters - can be formed. Due to the fact that zirconium hydrides have a lower density that zirconium alloys, stresses are produced around blisters. These stresses may overcome the necessary threshold to precipitate radial hydrides. Moreover, cracks inside blisters may act as initiators of delayed hydride cracking (DHC). In the dry storage facilities developed for Atucha 1, Zry - 4 clads of spent fuel elements (SFE) must withstand environmental conditions which include maximum temperature of 200°C and internal SFE pressure of ~ 75 bar (value at end of cycle). During dry storage, if blisters are present, stresses around them are superposed to circumferential stresses generated by the internal pressure due to fission gasses helping precipitation and/or growth of radial hydrides and DHC process. In order to assess this possibility, in the present work sections of Zry-4 cladding were hydrided. Blisters have been grown by thermal gradient under different conditions of temperature and shapes of thermal contact in order to obtain different blister dimensions and fraction of radial hydrides. After blister formation, some specimens were subjected to Hydride Reorientation Test (HRT) by applying an internal pressure of 75 bar at 200°C. Finally, tubes were sectioned and metallographically analyzed looking for radial hydrides. In some samples radial hydrides were observed, which effectively grew by the internal pressure of Zry-cladding during HRT.

Intergroup Contact as an Agent of Cognitive Liberalization

Intergroup contact is widely recognized as one of the most validated methods of improving attitudes toward out-groups. Yet what is intergroup contact “good for” beyond this function? To answer this question we take a panoramic view of the literature, beginning with the recognition that contact is multifaceted in both form (e.g., face-to-face, indirect, simulated) and outcome (e.g., attitudes, cognition, behavior). Taking this highly inclusive view of what contact is and what contact does suggests that it plays a fundamental role in the shaping of human cognition. An increasingly diverse body of research demonstrates that contact exerts a generalizing reaction across target out-groups, making respondents less inward looking and more open to experiences. Contact shapes ideology regarding how the world ought to operate (i.e., ideologies about social hierarchy or regulation); over time, it can promote new ways of problem-solving, enhance cognitive flexibility, and foster creativity. For these reasons, we believe that contact is a key liberalizing agent that shapes human cognition and experience; consequently, contact theory should now share the stage with other prominent theories (e.g., cognitive dissonance) that speak to a broader understanding of human nature.

In pursuit of intimacy: disability stigma, womanhood and intimate partnerships in South Africa

Notions of womanhood inculcate naturalised ideologies of femininity, sexuality, motherhood and caregiving. The paper asks how disability stigma intersects with womanhood to characterise intimate partnerships in South Africa. In-depth interviews with 30 women with a range of disabilities were conducted in informal settlements in Cape Town. Findings suggest that disability stigma may hamper attainment of normative womanhood and sexual relationships for women with disabilities in South Africa. Limited opportunities to meet potential partners, hegemonic gender expectations and restricted sexual and physical contact shape their intimate partnerships. However, women with disabilities also challenge ableist constructs of normalcy and discredit negative images of disabled womanhood. Because of this, theoretical models of intimate partner violence should consider the influence of disability on constructions of sexuality and norms in intimate partnerships. Building on women with disabilities’ stigma-avoidance strategies will help facilitate better relationship outcomes. Social norms interventions with broader society, communities, women with disabilities and their partners, family and carers can help destabilise assumptions that women with disabilities are unable to have long-lasting and fulfilling sexual and intimate partnerships. Moreover, accessible and relevant sexuality education and information on relationships, intimate partner violence, maternal and sexual and reproductive health care can ensure healthy and safe intimate partnerships for women with disabilities.

Numerical analysis of time-varying wear with elastic deformation in line contact

Wear is an important factor for failures of mechanical components. Current research on wear is mainly focused on experiments while the numerical simulation of wear is hardly used owing to the complexities of the wear process. Explaining the effect of friction on the wear process is important, as it will lead to a deeper understanding of the evolution of wear. This study proposed a numerical method to expound the wear process in the contact between an elastic cylinder and a half-space simulating the ring-block tester. There are two difficulties during the calculation; one is that the contact shapes vary with time, causing the pressure distribution to change simultaneously and the other is the integral equation for calculating the contact pressure under different worn shapes. In the present study, the wear rate was computed using Archard’s law and the wear process was calculated step by step until the specified total sliding distance was achieved. During each step of the calculation, the contact topography was updated. The simulation intuitively reproduced the contact state of change from line to surface contact throughout the wear process. Reasonable agreements on the changes of the wear scar, achieved from experiments and numerical simulations, were obtained.

A Generalized Differential Colorimetric Interferometry Method: Extension to the Film Thickness Measurement of Any Point Contact Geometry

ABSTRACT Whereas industrial elastohydrodynamic (EHD) contacts are generally noncircular, most experimental observations are made on sphere-on-plane conjunctions. The circular case is indeed a specific elliptical case, and it was widely investigated. The differential colorimetric interferometry (DCI) technique was often used to perform precise film thickness measurements in circular EHD contacts. From a single picture of the dynamic contact, it enables mapping the film thickness of the full conjunction, and postprocessing can be applied afterwards. Moreover, it is possible to record sequences at relatively high-frequency sampling. However, until now, the method could not be directly applied to noncircular conjunctions. In the present article, a generalized DCI method is proposed and assessed by several static and EHD validation cases for elliptical and torus-on-plane contact geometries. This new method no longer necessitates particular requirements on the contact shape while retaining the advantages of the original DCI method. It allows precise film thickness measurements in realistic industrial EHD contacts and opens the way for new experimental observations.

Comparative analysis of numerical methods for the determination of contact pattern of spiral bevel gears

PurposeThis paper aims to present a comparison of numerical methods for determining the contact pattern of Gleason-type bevel gears. The mathematical model of tooth contact analysis and the finite element method were taken into consideration. Conclusions have been drawn regarding the usefulness of the considered methods and the compatibility of results. The object of the analysis was a bevel gear characterised by an 18:43 gear ratio and arc tooth line, and manufactured according to the spiral generated modified-roll method.Design/methodology/approachThe mathematical model of tooth contact analysis consists of both the mathematical model of tooth generating and the mathematical model of operating gear set. The first model is used to generate tooth flanks of the pinion and the ring gear in the form of grids of points. Then, such tooth surfaces are used for the tooth contact analysis performed with the other model. It corresponds to the no-load gear meshing condition. The finite element method model was built on the basis of the same tooth flanks obtained with the former model. The commercial finite element method software Abaqus was used to perform two instances of the contact analysis: a very light load, corresponding to the former no-load condition, and the operating load condition. The results obtained using the two models, in the form of the contact pattern for no-load condition, were compared. The effect of heavy load on contact pattern position, shape and size was shown and discussed.FindingsThe mathematical models correctly reproduce the shape, position and size of the contact pattern; thus, they can be reliably used to assess the quality of the bevel gear at the early stage of its design.Practical implicationsDetermination of the correct geometry of the flank surfaces of the gear and pinion teeth through the observation of contact pattern is a fundamental step in designing of a new aircraft bevel gear.Originality/valueA possibility of the independent use of the mathematical analysis of the contact pattern has been shown, which, thanks to the compatibility of the results, does not have to be verified experimentally.

Contact Resistance Modeling of Sealed Relay Based on 3-D Topography Reduction

Since traditional simulations do not reflect true morphological changes of the contact surface in relay contacts, the concept of difference-plane is proposed in this paper to establish the contact resistance model according to the actual shapes of the disassembled contacts, considering the hypothetical contact state of static and dynamic contacts. The difference-plane is restituted from the mechanical and electrical properties by analyzing the elements types and distributions, ignoring the influence of thermodynamics and membrane resistance. The contact resistance sliding coefficient is defined from the movement process of the sealed relay. The contact resistance model of the sealed relay is established by using the dimensionless parameter as the mediator, which provides a new idea for contact resistance modeling from the actual contact morphology point.

SOLUTION OF ADHESIVE CONTACT PROBLEM ON THE BASIS OF THE KNOWN SOLUTION FOR NON-ADHESIVE ONE

The well-known procedure of reducing an adhesive contact problem to the corresponding non-adhesive one is generalized in this short communication to contacts with an arbitrary contact shape and arbitrary material properties (e.g. non homogeneous or gradient media). The only additional assumption is that the sequence of contact configurations in an adhesive contact should be exactly the same as that of contact configurations in a non-adhesive one. This assumption restricts the applicability of the present method. Nonetheless, the method can be applied to many classes of contact problems exactly and also be used for approximate analyses.

Влияние электростатического поля периферии на вентильный фотоэффект в контактах металл-полупроводник с барьером Шоттки

AbstractStudies of an electrostatic system of flat metal–semiconductor contacts with a Schottky barrier reveals a nontrivial dependence of their current and voltage photosensitivity (the photovoltaic effect) on the contact shape. The specific features of using the photovoltaic effect in such contacts are determined, to a great extent, by the built-in periphery electrostatic field with an absolute value that depends on the contact perimeter and area. Thus, to increase the efficiency of light-to-electrical energy conversion by Schottky contacts, it is necessary to use optimization techniques based on the concepts of the proposed physical model of an electrostatic system of flat Schottky contacts with regard to periphery electrostatic fields. The “hot electron resonance” effect, which enhances the external quantum efficiency of photodiodes with a Schottky barrier, can be explained by enhancement of the field emission of electrons by the periphery electrostatic field.

On the Tensor of Tangential Stiffness in Contact Problems

In a nonsliding tangential contact, vectors of tangential force and tangential displacement are related by the tensor of tangential stiffness. Using the boundary element method, we calculate the principal values of the tensor of tangential stiffness for a number of contact shapes. Of special interest for applications is that the anisotropy of the tensor of tangential stiffness is generally relatively small, even for extremely anisotropic contact shapes.

Contact Shape Estimation of Tool Based on Active Force Sensing

Contact Shape Estimation of Tool Based on Active Force Sensing

Stiffness of frictional contact of dissimilar elastic solids

The classic Sneddon relationship between the normal contact stiffness and the contact size is valid for axisymmetric, frictionless contact, in which the two contacting solids are approximated by elastic half-spaces. Deviation from this result critically affects the accuracy of the load and displacement sensing nanoindentation techniques. This paper gives a thorough numerical and analytical investigation of corrections needed to the Sneddon solution when finite Coulomb friction exists between an elastic half-space and a flat-ended rigid punch with circular or noncircular shape. Because of linearity of the Coulomb friction, the correction factor is found to be a function of the friction coefficient, Poisson's ratio, and the contact shape, but independent of the contact size. Two issues are of primary concern in the finite element simulations – adequacy of the mesh near the contact edge and the friction implementation methodology. Although the stick or slip zone sizes are quite different from the penalty or Lagrangian methods, the calculated contact stiffnesses are almost the same and may be considerably larger than those in Sneddon's solution. For circular punch contact, the numerical solutions agree remarkably well with a previous analytical solution. For non-circular punch contact, the results can be represented using the equivalence between the contact problem and bi-material fracture mechanics. The correction factor is found to be a product of that for the circular contact and a multiplicative factor that depends only on the shape of the punch but not on the friction coefficient or Poisson's ratio.