scholarly journals The effect of surface roughness on the adhesion of elastic solids

1975 ◽  
Vol 345 (1642) ◽  
pp. 327-342 ◽  
Keyword(s):  
Flat Surface ◽  
The Other ◽  
Contact Theory ◽  
Elastic Displacement ◽  
Radius Of Curvature ◽  
Statistical Average ◽  
Elastic Solids ◽  
Maximum Value ◽  
Effect Of Surface ◽  
Adhesive Forces

This paper describes a study of the adhesion between elastic solids and the effect of roughness in reducing the adhesion. The experiments were carried out between optically smooth rubber spheres and a hard smooth flat surface of Perspex which could be roughened to various degrees. The radius of the rubber spheres was varied by a factor of 8, their elastic modulus by a factor of 10, while the centre line average (c.l.a.)of the roughened Perspex surface was varied from 0.12 to 1.5 μm. The results show that c.l.a. roughnesses which are small compared with the overall deformation occurring at the region of the rubber-Perspex contact can produce an extremely large reduction in adhesion. The effect is more marked for rubbers of higher modulus. On the other hand the curvature of the sphere (over the range examined) has little influence. For this reason and because the analytical problem of a sphere on a rough flat is extremely complicated a theoretical analysis has been developed for the simpler case of a smooth flat in contact with a rough flat surface. As in Greenwood & Williamson (1966) the rough surface is modelled by asperities all of the same radius of curvature and with heights following a Gaussian distribution of standard deviation σ. The overall contact force is obtained by applying the contact theory of Johnson, Kendall & Roberts (1971) to each individual asperity. The theory predicts that the adhesion expressed as a fraction of the maximum value depends upon a single parameter, 1/Δ e ,which is the ratio between a and the elastic displacement δ C that the tip of an asperity can sustain before it pulls off from the other surface. The analysis shows that the adhesion parameter may also be regarded as representing the statistical average of a competition between the compressive forces exerted by the higher asperities trying to prize the surfaces apart and the adhesive forces between the lower asperities trying to hold the surfaces together. Although the theory is derived for two nominally plane surfaces it is found to fit the experimental results for a sphere on a flat reasonably well.

scholarly journals Effect of surface treatments on push-out bond strength of calcium silicate-based cements to fiber posts

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Amr M. Elnaghy ◽  
Ayman Mandorah ◽  
Ali H. Hassan ◽  
Alaa Elshazli ◽  
Shaymaa Elsaka
Keyword(s):  
Bond Strength ◽  
Surface Treatment ◽  
Glass Fiber ◽  
Calcium Silicate ◽  
Surface Treatments ◽  
The Other ◽  
Fiber Posts ◽  
Glass Fiber Posts ◽  
Push Out ◽  
Effect Of Surface

Abstract Background To evaluate the effect of surface treatments on the push-out bond strength of Biodentine (BD) and white mineral trioxide aggregate (WMTA) to fiber posts. Methods Two brands of fiber posts were used: Reblida post; RP and RelyX post; RX. Each type of post (n = 80/group) was divided into four groups (n = 20/group) and exposed to surface treatment as follows: Control (no treatment), sandblasting (SB), hydrofluoric acid (HF), and TiF4 4 wt/v%. Each group was further subdivided into two subgroups (n = 10/subgroup) based on the type of CSCs used as follows: Subgroup A: BD and Subgroup B: WMTA. Push-out bond strength of BD and WMTA to glass fiber posts was assessed. Data were statistically analyzed using three-way ANOVA and Tukey’s test. A Weibull analysis was performed on the push-out bond strength data. Results BD showed higher bond strength than WMTA (P < 0.001). The push-out bond strength for posts treated with TiF4 4 wt/v% showed greater bond strength than the other surface treatments (P < 0.05). The BD/RP-TiF4 4 wt/v% showed the greater characteristic bond strength (σ0) (15.93) compared with the other groups. Surface treatments modified the surface topography of glass fiber posts. Conclusions The BD/RP-TiF4 4 wt/v% showed greater bond strength compared with the other groups. The TiF4 4 wt/v% surface treatment enhanced the bond strength of BD and WMTA to glass fiber posts than the other treatments. Surface treatment of fiber post with TiF4 4 wt/v% could be used to improve the bond strength with calcium silicate-based cements.

Magnetocrystalline Anisotropy and Twinning Stress of 10M and 2M Martensites in Ni-Mn-Ga System

2006 ◽  
Vol 512 ◽  
pp. 195-200 ◽  
Author(s):  
Nariaki Okamoto ◽  
Takashi Fukuda ◽  
Tomoyuki Kakeshita ◽  
Tetsuya Takeuchi
Keyword(s):  
Magnetic Field ◽  
Shear Stress ◽  
Magnetocrystalline Anisotropy ◽  
Anisotropy Constant ◽  
The Other ◽  
Magnetic Shear ◽  
Maximum Value ◽  
Twinning Plane ◽  
Twinning Shear ◽  
The Difference

Ni2MnGa alloy with 10M martensite exhibits rearrangement of martensite variants (RMV) by magnetic field, but Ni2.14Mn0.92Ga0.94 with 2M martensite does not. In order to explain the difference, we measured uniaxial magnetocrystalline anisotropy constant Ku and the stress required for twinning plane movement τreq in these alloys. Concerning the former alloy, the maximum value of magnetic shear stress acting across twinning plane τmag, which is evaluated as |Ku| divided by twinning shear, becomes larger than τr eq. On the other hand, concerning the latter alloy, the maximum of τmag is only one-tenth of τreq at any temperature examined. Obviously, the relation, τmag> τr eq, is satisfied when RMV occurs by magnetic field and vice versa. In this martensite, the large twinning shear of 2M martensite is responsible for small τmag and large τreq.

Effect of Surface Roughness on the Total Hemispherical and Specular Reflectance of Metallic Surfaces

1964 ◽  
Vol 86 (2) ◽  
pp. 193-199 ◽  
Author(s):  
R. C. Birkebak ◽  
E. M. Sparrow ◽  
E. R. G. Eckert ◽  
J. W. Ramsey
Keyword(s):  
Surface Roughness ◽  
Black Body ◽  
Black Body Radiation ◽  
The Other ◽  
Angle Of Incidence ◽  
Metallic Surfaces ◽  
Specular Reflectance ◽  
Other Hand ◽  
Hemispherical Reflectance ◽  
Effect Of Surface

Measurements have been made of the hemispherical and specular reflectance of metallic surfaces of controlled roughness. The surfaces, which were ground nickel rectangles, were irradiated at various angles of incidence by a beam of black-body radiation, the temperature of which was also varied. The instrumentation which was devised to perform the experiments is described. The measurements show that beyond a certain surface roughness, the hemispherical reflectance is virtually independent of further increases in roughness. On the other hand, the specular reflectance decreases steadily with increasing roughness. Additionally, the hemispherical reflectance is found to be quite insensitive to the angle of incidence, while the specular reflectance increases with angle of incidence for the rougher surfaces.

scholarly journals Morphological Aspects of Ciliary Motility

1967 ◽  
Vol 50 (6) ◽  
pp. 241-258 ◽  
Author(s):  
Peter Satir
Keyword(s):  
The Other ◽  
Radius Of Curvature ◽  
Arc Length ◽  
Apparent Displacement ◽  
Shaft Length ◽  
Ciliary Motility ◽  
Morphological Aspects ◽  
Circular Arcs ◽  
The Relationship

In Elliptio complanatus lateral cilia, two distinct patterns of filament termination can be discerned. In one case, all nine filaments are present and all are single; in the second, at least one filament is missing but doublets are still present. These probably represent different configurations within one cilium in different stroke positions; to get from one to the other, some peripheral filaments must move with respect to others. The data are consistent with the hypothesis that the filaments themselves do not change length, but rather slide past one another to accommodate increasing curvature. The bent regions of the cilium are in the form of circular arcs. In a few cases, apparent displacement of filaments at the tip (Δl) can be shown to be accounted for if we assume that all differences are generated within these arcs. The displacement per degree of bend is 35 A. Regions of bent arc are initially confined to the base of the cilium but move up the shaft as straight regions appear below them. From the relationship between arc length and radius of curvature, a shaft length that is the unit that initially bends and slides may be defined. Quantal displacements of the length of one 14S dynein may perhaps occur at sites between filaments at opposite sides of such a unit as sliding occurs.

scholarly journals A.C conductivity and dielectric properties of (PVA/ PEO) blends doped with MWCNTs

2019 ◽  
Vol 14 (30) ◽  
pp. 64-72
Author(s):  
Ahmad A. Hasan
Keyword(s):  
Electrical Conductivity ◽  
Dielectric Properties ◽  
The Other ◽  
Poly Vinyl Alcohol ◽  
Conductivity Measurements ◽  
Frequency Range ◽  
Maximum Value ◽  
Multi Walled Carbon Nanotube ◽  
Poly Ethylene Oxide ◽  
Poly Ethylene

A.C electrical conductivity and dielectric properties for poly(vinyl alcohol) (PVA) /poly (ethylene oxide) (PEO) blends undopedand doped with multi-walled carbon nanotube (MWCNTs) withdifferent concentrations (1, and 3 wt %) in the frequency range(25x103 - 5x106 Hz) were investigated. Samples of (PVA/PEO)blends undoped and doped with MWCNTs were prepared usingcasting technique. The electrical conductivity measurements showedthat σA.C is frequency dependent and obey the relation σA.C =Aωs forundoped and doped blends with 1% MWCNTs, while it is frequencyindependent with increases of MWCNTs content to 3%. Theexponent s showed proceeding increase with the increase of PEOratio (≥50%) for undoped blends samples, while s value for dopedblends exhibits to change in different manner, i.e. s increases andreach maximum value at 50/50 PVA/PEO, then decreases forresidual doped blends samples with 1% MWCNTs on the other handthe exponent s decrease and reach minimum value at 50/50PVA/PEO for samples doped with 3% MWCNTs, then return toincrease. The results explained in different terms.

Coordinated righting behaviour in locusts

2001 ◽  
Vol 204 (4) ◽  
pp. 637-648 ◽  
Author(s):  
A.A. Faisal ◽  
T. Matheson
Keyword(s):  
Driving Force ◽  
Flat Surface ◽  
Longitudinal Axis ◽  
Upright Position ◽  
The Body ◽  
The Other ◽  
Legged Robots ◽  
Naturally Occurring ◽  
Key Features ◽  
Low Levels

A locust placed upside down on a flat surface uses a predictable sequence of leg movements to right itself. To analyse this behaviour, we made use of a naturally occurring state of quiescence (thanatosis) to position locusts in a standardised upside-down position from which they spontaneously right themselves. Locusts grasped around the pronotum enter a state of thanatosis during which the limbs can be manipulated into particular postures, where they remain, and the animal can be placed upside down on the ground. When released, thanatosis lasts 4–456 s (mean 73 s) before the animal suddenly becomes active again and rights itself within a further 600 ms. Thanatosis is characterised by very low levels of leg motor activity. During righting, one hind leg provides most of the downward force against the ground that rolls the body around a longitudinal axis towards the other side. The driving force is produced by femoral levation (relative to the body) at the trochanter and by tibial extension. As the animal rolls over, the hind leg on the other side is also levated at the trochanter, so that it does not obstruct the movement. The forelegs and middle legs are not required for successful righting but they can help initially to tip the locust to one side, and at the end of the movement they help stop the roll as the animal turns upright. Individual locusts have a preferred righting direction but can, nevertheless, roll to either side. Locusts falling upside down through the air use both passive and active mechanisms to right themselves before they land. Without active movements, falling locusts tend to rotate into an upright position, but most locusts extend their hind leg tibiae and/or spread their wings, which increases the success of mid-air righting from 28 to 49 % when falling from 30 cm. The rapid and reliable righting behaviour of locusts reduces the time spent in a vulnerable upside-down position. Their narrow body geometry, large hind legs, which can generate substantial dorsally directed force, and the particular patterns of coordinated movements of the legs on both sides of the body are the key features that permit locusts to right themselves effectively. The reliability of autonomous multi-legged robots may be enhanced by incorporating these features into their design.

Positive regard for difference without identity

2018 ◽  
Author(s):  
Lucy Nicholas
Keyword(s):  
Social Psychology ◽  
Ethnic Diversity ◽  
Social Groups ◽  
The Other ◽  
Contact Theory ◽  
Contact Hypothesis ◽  
Trans People ◽  
The Social ◽  
The Usa ◽  
Cis And Trans

The contact hypothesis has been the go-to social psychology concept for promoting better relations between unequal social groups since its inception in the context of ‘racial’ de-segregation in the USA. The idea that contact between groups reduces prejudice has been applied to a range of dominant / subordinate social groups such as ethnic groups, homo/heterosexuals, cis and trans people. This chapter will question whether the aims and premises of contact theory are still useful in the context of increasingly subtle and systemic biases and inequalities, and whether and how it might be usefully extended to relations between more complex identities than simple pre-defined oppositional ‘in’ and ‘out’ groups.  To do so, it considers some examples of intergroup othering using case studies pertaining to backlashes against gender, sexual and ethnic diversity in the contemporary Australian context. This chapter proposes the fruitful combination of queer ethics, post-tolerance political theory and the social psychology concept of ‘allophilia’ (love for the other) to move towards fostering ‘positive regard’ as an alternative way to tackle prejudice. It suggests that queer ethics can lend a convincing strategy here, which I call ‘reading queerly’, that is, being able to approach an other with an openness that neither homogenises nor subordinates difference.

The Influence of the Fatigue Cycles Number on Material Hardness

2014 ◽  
Vol 658 ◽  
pp. 195-200
Author(s):  
Viorel Goanta
Keyword(s):  
Plastic Deformation ◽  
Indentation Load ◽  
The Other ◽  
Stress Cycle ◽  
Elastic Range ◽  
Maximum Value ◽  
Material Hardness ◽  
Stress Fatigue ◽  
Minimum Force ◽  
Maximum Minimum

In this paper we present the experimental results obtained after determining hardness on samples previously subjected to fatigue. Firstly, 6 identical samples have been subjected to stress fatigue in the elastic range a number of 105, 5∙105, 106, 2∙106, 3∙106 and 4∙106 cycles. For all samples we used the same form of stress cycle, respectively, sinusoidal, and the same values of maximum, minimum force and the amplitude of the cycle (50 kN, 30 kN and 10 kN). It is noted that the maximum value of the load was less than that at which samples fall within the plastic deformation. Therefore, the original loading of samples was performed in the elastic range. For each of the six samples determinations of levels of hardness were performed, with the value of indentation load of 10 kgf. Indentations were made on the samples, along the length of the calibration, at a distance of 10 mm one within the other. As it will be seen below, in the areas with the highest hardness were performed several indentations, in order to determine the highest hardness area, which, in our view, also presents the largest degree of plastic deformation.

67 Effects of phytohemagglutinin on the culture of isolated bovine blastomeres derived from the 8-cell stage invitro-produced embryos

2020 ◽  
Vol 32 (2) ◽  
pp. 159
Author(s):  
Y. Hashiyada ◽  
Y. Aikawa ◽  
H. Matsuda ◽  
T. Yamanouchi
Keyword(s):  
Tissue Culture ◽  
Culture Medium ◽  
Flat Surface ◽  
Formation Rate ◽  
Cell Number ◽  
The Other ◽  
Blastocyst Formation ◽  
Culture Dish ◽  
Cell Stage ◽  
Tissue Culture Dish

Monozygotic twin embryos which can efficiently be produced by blastomere separation and aggregation of early cleavage stages of embryos using commercially provided well-of-the-well (WOW) culture dish. Phytohaemagglutinin (PHA) is a plant lectin that binds to and aggregates on the surface of animal cells, but also contains toxicity that causes food poisoning. The present study was conducted to evaluate the toxicity to embryos and the effect to development of isolated blastomeres on PHA-supplemented WOW culture. Embryos were produced using oocytes from ovaries collected at an abattoir by IVM, IVF, and invitro culture (IVC). The tissue culture medium 199 supplemented with 5% calf serum (CS), Brackett-Oliphant solution supplemented with 10mgmL−1 bovine serum albumin, and CR1aa medium containing 5% CS were used for each culture step. For the evaluation of PHA toxicity, 89 embryos that developed to the 5-8-cell stage were obtained at Day 2 after insemination. Each embryo was cultured in a droplet of 5 µL/embryo IVC culture medium supplemented with or without PHA. For the evaluation of PHA to development of isolated blastomeres, 111 of 8-cell stage embryos were obtained 48-54h post-insemination. Zonae pellucidae were removed by exposure to 0.25% pronase. Then, embryos were separated into single blastomeres by gentle pipetting in IVC medium. Each four blastomeres were formed in the shape of a bunch inside the thin cylinder at the tip of the Pasteur pipette by gentle pipetting. Then, each mass of blastomeres in each 60 masses was cultured individually in 5-µL droplets of IVC medium supplemented with or without PHA on the flat surface of a tissue culture dish. On the other hand, each four blastomeres were introduced into a single conical micro-well each having a diameter and depth of ~287µm and 168µm (Dai Nippon Printing). This culture of blastomeres was performed covered with a droplet of 2.5µL well−1 IVC medium supplemented with or without PHA in each 50 or 52 wells. In all of investigations, PHA was used at 50µgmL−1 (Akagi et al. 2011 J. Reprod. Dev. 57). Statistical analysis was performed using Student's t-test and analysis of variance. The blastocyst formation rate (71.1±2.3% vs. 72.7±1.7%), total cell number (120 vs. 122), and inner cell mass cell number (47 vs. 51) at Day 7 after IVF did not differ between PHA-supplemented and PHA-free group in the toxicity test, respectively. In the blastomere culture, the blastocyst formation rate was very low (10.0±5.9% vs. 5.0±2.9%) regardless of the PHA supplementation in drops on the flat surface of a tissue culture dish. On the other hand, blastocyst formation was improved using the WOW culture dish (24.0±3.6% vs. 40.4±7.6%) but there was no difference with or without PHA supplementation. Although nontoxicity of PHA and efficacy of WOW culture for isolated-aggregated blastomeres were confirmed, no improvement of PHA supplementation on development was observed in this study. Subsequently, experiments on the optimum concentration of PHA for aggregation and development of blastomeres in WOW culture are required.

Surface morphology of as grown and annealed bulk GaN crystals

1996 ◽  
Vol 1 ◽  
Author(s):  
G. Nowak ◽  
S. Krukowski ◽  
I. Grzegory ◽  
S. Porowski ◽  
Jacek M. Baranowski ◽  
...  
Keyword(s):  
Surface Morphology ◽  
Flat Surface ◽  
Hydrogen Atmosphere ◽  
The Other ◽  
Crystal Surfaces ◽  
Force Microscopy ◽  
Atomic Force ◽  
Flat Side ◽  
Bulk Gan ◽  
Atomically Flat

GaN single crystals have been grown from Ga solution. The crystals grow in the form of platelets with their basal plane perpendicular to the c-axis. The two opposite crystal surfaces are not equivalent since one is N- and the other Ga-terminated. Atomic force microscopy has been applied to study surface morphology on both surfaces. It was found that one side is atomically flat. The other side consists of pyramid-like structures about 25 nm in size.The influence of annealing in an NH3+H2 atmosphere in the temperature range from 600°C to 900°C was investigated. Depending on crystal face the results were drastically different. It was found that on the rough side, annealing yields an atomically flat surface with terraces of monolayer height. The size of the terraces depends on the temperature of the annealing. On the originally flat side the surface becomes rougher after annealing. The transformation of surface morphology begins at temperatures below 700°C. Preliminary results of annealing in a hydrogen atmosphere are also reported. These findings are crucial for the understanding and development of GaN homoepitaxy.

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