Elastic Contact and Friction Between Sliders and Circumferentially Textured Disks—Part II: Meniscus Force

1998 ◽  
Vol 120 (1) ◽  
pp. 35-41 ◽  
Author(s):  
K. Tanaka
Keyword(s):  
Frictional Coefficient ◽  
Critical Factor ◽  
Liquid Bridges ◽  
Height Distribution ◽  
Asperity Height ◽  
Lubricant Thickness ◽  
Theoretical Formulation ◽  
Meniscus Force ◽  
Elliptical Contact ◽  
The Mean

This series of three papers presents an experimental and numerical analysis of friction in a thin-film rigid disk with a circumferential surface texture, under various humidities. In Part II, we develop a theoretical formulation of the meniscus force of elliptical contact at isolated liquid bridges. This model predicts that the mean real pressure due to the meniscus force apparently decreases the net real contact pressure pr and increases the frictional coefficient. This effect becomes significant when the relative surface energy of the liquid 2γ/σ is comparable to pr, where σ is the standard deviation of asperity height distribution. When the disk is covered with lubricant and the liquid bridges are connected with each other, the solid noncontacting asperities play an important role in the formation of the meniscus force, and the relative lubricant thickness t/σ is the critical factor determining the friction.

scholarly journals Different long-term trends of the oxygen red 630.0 nm line nightglow intensity as the result of lowering the ionosphere F2 layer

2008 ◽  
Vol 26 (8) ◽  
pp. 2069-2080 ◽  
Author(s):  
N. B. Gudadze ◽  
G. G. Didebulidze ◽  
L. N. Lomidze ◽  
G. Sh. Javakhishvili ◽  
M. A. Marsagishvili ◽  
...  
Keyword(s):  
Electron Density ◽  
Line Intensity ◽  
Peak Height ◽  
Height Distribution ◽  
Theoretical Simulation ◽  
Type Layer ◽  
Long Term Trends ◽  
The Mean ◽  
Long Term Trend

Abstract. Long-term observations of total nightglow intensity of the atomic oxygen red 630.0 nm line at Abastumani (41.75° N, 42.82° E) in 1957–1993 and measurements of the ionosphere F2 layer parameters from the Tbilisi ionosphere station (41.65° N, 44.75° E) in 1963–1986 have been analyzed. It is shown that a decrease in the long-term trend of the mean annual red 630.0 nm line intensity from the pre-midnight value (+0.770±1.045 R/year) to its minimum negative value (−1.080±0.670 R/year) at the midnight/after midnight is a possible result of the observed lowering of the peak height of the ionosphere F2 layer electron density hmF2 (−0.455±0.343 km/year). A theoretical simulation is carried out using a simple Chapman-type layer (damping in time) for the height distribution of the F2 layer electron density. The estimated values of the lowering in the hmF2, the increase in the red line intensity at pre-midnight and its decrease at midnight/after midnight are close to their observational ones, when a negative trend in the total neutral density of the upper atmosphere and an increase in the mean northward wind (or its possible consequence – a decrease in the southward one) are assumed.

Human Joint Performance and the Roughness of Articular Cartilage

1980 ◽  
Vol 102 (1) ◽  
pp. 50-56 ◽  
Author(s):  
T. R. Thomas ◽  
R. S. Sayles ◽  
I. Haslock
Keyword(s):  
Articular Cartilage ◽  
Heel Strike ◽  
Height Distribution ◽  
Normal Walking ◽  
Cartilage Surface ◽  
Real Area Of Contact ◽  
The Mean ◽  
Human Joints ◽  
Human Joint ◽  
Real Area

It is known that the surface of articular cartilage is rough and it has been suggested that this is likely to affect the lubrication of human joints. This paper describes the direct measurement of a cartilage surface with a stylus instrument. It is found that the height distribution is Gaussian with an inverse-square power spectrum. It is thus possible to calculate the elastic deflection of the surface under normal walking loads and it is shown that the mean separation of the cartilage surfaces in a human joint varies rather slowly with load. In one particular hip joint at heel strike the real area of contact was calculated to be about 1.3 cm2, the mean gap to be about 60 μm and the trapped volume to be about 80 percent of that when standing.

Microchemical Oxygen Flask Sulfur Determination: General Review and Collaborative Study of an Alternative Method Using Thorin-Methylene Blue Indicator

1976 ◽  
Vol 59 (5) ◽  
pp. 1135-1139
Author(s):  
Laverne H Scroggins
Keyword(s):  
Methylene Blue ◽  
Collaborative Study ◽  
Critical Factor ◽  
Potassium Sulfate ◽  
Masking Effect ◽  
Average Deviation ◽  
Collaborative Studies ◽  
Sulfur Determination ◽  
The Mean ◽  
Barium Perchlorate

Abstract Recent collaborative studies of microchemical oxygen flask sulfur determinations are summarized and compared statistically, and the 1975 collaborative study is presented. This volumetric technique, using a peroxide solution as absorbent, barium perchlorate as titrant, and a combination of thorin and methylene blue as indicator, was tested by 8 collaborators. Data from 72 determinations were reported. The samples studied were sulfanilamide, benzylisothiourea hydrochloride, cystine, potassium sulfate, and potassium sulfate with a phosphate additive. Overall statistical results for the 3 pure organic compounds gave satisfactory values: average standard deviation 0.10, overall average deviation of the mean from the theoretical value 0.13, and average bias −0.04. The overall average deviation of the mean from the theoretical value for the potassium sulfate compound was high (1.94) in this study, and that of the phosphated potassium sulfate compound was even higher (6.46). Thorin-methylene blue does not require a titration assembly (required by tetrahydroxyquinone) and has greater stability than dimethylsulfonazo III whose indicator lag-time causes troublesome pseudo end points. However, a critical factor, when using thorin-methylene blue, is the masking effect of foreign ions. All reagents must be as pure as possible, since concentrations of chloride, fluoride, nitrate, phosphate, potassium, and sodium interfere. The thorin-methylene blue method for sulfur determination has been adopted as official first action as an alternative oxygen flask microchemical method of analysis.

scholarly journals Similarities and differences in polar mesosphere summer echoes observed in the Arctic and Antarctica

2008 ◽  
Vol 26 (9) ◽  
pp. 2795-2806 ◽  
Author(s):  
R. Latteck ◽  
W. Singer ◽  
R. J. Morris ◽  
W. K. Hocking ◽  
D. J. Murphy ◽  
...  
Keyword(s):  
Noise Source ◽  
Late Summer ◽  
The Arctic ◽  
Occurrence Rate ◽  
Height Distribution ◽  
Summer Echoes ◽  
Polar Mesosphere Summer Echoes ◽  
The Mean ◽  
Resolute Bay ◽  
Highly Correlated

Abstract. Polar Mesosphere Summer Echoes (PMSE) have been observed in the high latitudes of the Northern and Southern Hemisphere for several years using VHF radars located at Andenes/Norway (69° N, 16° E), Resolute Bay/Canada (75° N, 95° W), and Davis/Antarctica (69° S, 78° E). The VHF radars at the three sites were calibrated using the same methods (noise source and delayed transmitting signal) and identical equipment. Volume reflectivity was derived from the calibrated echo power and the characteristics of the seasonal variation of PMSE were estimated at the sites for the years 2004 to 2007. The largest peak volume reflectivity of about 2×10−9 m−1 was observed at Andenes compared with their counterparts at Davis (~4×10−11 m−1) and Resolute Bay (~6×10−12 m−1). The peak of the PMSE height distribution is 85.6 km at Davis which is about 1 km higher than at Andenes. At Resolute Bay the height distribution peaks at about 85 km but only a few layers were found below 84 km. The mean PMSE occurrence rate is 83% at Andenes, 38% at Davis with larger variability and only 18% at Resolute Bay (in late summer). The duration of the PMSE season varies at Andenes from 104 to 113 days and at Davis from 88 to 93 days. In general the PMSE seasons starts about 5 days later at Davis and ends about 10 days earlier compared to Andenes. In all three seasons the PMSE occurrence suddenly drops to a much lower level at Davis about 32 days after solstice whereas the PMSE season decays smoothly at Andenes. The duration of the PMSE season at Andenes and Davis is highly correlated with the presence of equatorward directed winds, the observed differences in PMSE occurrence are related to the mesospheric temperatures at both sites.

Analysis of contact and bending stiffness for Curvic couplings considering contact angle and surface roughness

2019 ◽  
Vol 233 (6) ◽  
pp. 1257-1267 ◽  
Author(s):  
Younghun Yu ◽  
Bora Lee ◽  
Yongjoo Cho
Keyword(s):  
Surface Roughness ◽  
Contact Angle ◽  
Standard Deviation ◽  
Bending Stiffness ◽  
Height Distribution ◽  
Average Radius ◽  
Asperity Height ◽  
Surface Parameter ◽  
Tangential Stiffness ◽  
Nominal Contact Area

This paper develops a method for calculating the contact and bending stiffness of a Curvic coupling, and investigates stiffness changes according to the coupling shape and surface roughness characteristics. The surface of the on-site Curvic coupling is chosen as reference for a most accurate simulation. The three parameters representing the surface roughness characteristics—the standard deviation of the asperity height distribution, the average radius of asperities, and the density of asperity on the nominal contact area—are calculated with a profile of the coupling surface through a random process: the contact problem between rough surfaces is tackled using the Greenwood-Williamson model, the Curvic coupling is modeled assuming that it has as many teeth as possible within the machining limits depending on the contact angle, and the tangential stiffness resulting from the contact angle is calculated by dividing into the stick and slip regions, and is taken into account in terms of total stiffness. With this, results showed that using Curvic couplings reduces stiffness than using flat disc couplings because of the contact angle, and that the standard deviation of rough surface height is the most crucial surface parameter affecting stiffness.

A Method for Determining the Non-Gaussian Probability Density Functions of Asperity Heights for Two Contact Surface Conditions

2007 ◽  
Author(s):  
Jeng Luen Liou ◽  
Jen Fin Lin
Keyword(s):  
Probability Density ◽  
Contact Surface ◽  
Elastic Recovery ◽  
Normal Load ◽  
Plasticity Index ◽  
Asperity Height ◽  
Engineered Surfaces ◽  
Change In The Mean ◽  
The Mean ◽  
Non Gaussian

Most statistical contact analyses assume that asperity height distributions (g(z*)) follow a Gaussian distribution. However, engineered surfaces are frequently the non-Gaussian with a character dependent upon the material and surface state being evaluated. When two rough surfaces experience contact deformations, the original topography of the surfaces varies with different loads. Two kinds of topographies are considered in the present study. The first kind of topography is obtained during the contact of two surfaces under a normal load. The second kind of topography is obtained from a rough contact surface after the end of the elastic recovery. The g(z*) profile is quite sharp and has a large value at its peak if it is obtained from the surface contacts under a normal load. The g(z*) profile defined for a contact surface after the elastic recovery is quite close to the g(z*) profile before contact deformations occur if the plasticity index is a small value. However, the g(z*) profile for the contact surface after the end of elastic recovery is closer to the g(z*) profile shown in the contacts under a normal load if a large plasticity index is assumed. Skewness (Sk) and kurtosis (Kt), which are the parameters in the probability density function, are affected by the change in the mean separation of two contact surfaces, or the initial skewness (the initial kurtosis is fixed in this study), or the plasticity index of the rough surface are also discussed on the basis of the topography models mentioned above.

Comparison of Secondary Electron Emission Due to Positron, Electron, and Positive Ion Bombardment

1974 ◽  
Vol 52 (22) ◽  
pp. 2215-2219 ◽  
Author(s):  
S. Pendyala ◽  
J. Wm. McGowan
Keyword(s):  
Energy Range ◽  
Secondary Electron ◽  
Secondary Electron Emission ◽  
Pulse Height ◽  
Lead Glass ◽  
Height Distribution ◽  
Pulse Height Distribution ◽  
Alkali Ions ◽  
The Mean ◽  
Positive Ion

The relative secondary electron yield under positron, electron, and positive ion (alkali ions: Na+ or K+) bombardment is determined for the cone of a spiraltron detector (Bendix Model 4219X). The method is based on the proportionality of yield to the mean of the pulse height distribution for the bombarding particle of a given energy. The ratio of the yields under electron and positron bombardments is found to be 1.2 to 1.0 for the semiconducting lead glass of the cone of the spiraltron through the energy range of 0.1 to 1.0 keV. Cherry found this ratio to be 3.0 ± 0.3 at 0.94 keV. The positive ion yield is ≈ 1.5 (absolute) throughout this energy range.

Elastic Contact and Friction Between Sliders and Circumferentially Textured Disks—Part I: Analytical Model

1998 ◽  
Vol 120 (1) ◽  
pp. 28-34 ◽  
Author(s):  
K. Tanaka ◽  
T. Kusumi
Keyword(s):  
Thin Film ◽  
Contact Angle ◽  
Numerical Analysis ◽  
Frictional Coefficient ◽  
Elastic Contact ◽  
Height Distribution ◽  
Head Slider ◽  
Real Contact ◽  
Dry Conditions ◽  
Weakly Dependent

This series of three papers presents an experimental and numerical analysis of the friction between a head slider and a thin-film rigid disk with circumferential surface texture, under various humidities. In Part I, we develop a model of a cylindrical contact of a slider rail with strong anisotropic asperities under dry conditions. This model predicts that the real contact pressure is primarily determined by the height distribution and geometry of asperities on the disk, whereas it is very weakly dependent on the surface curvature of the rail. The result of the latter calculation suggests that the frictional coefficient is insensitive to variation in the head contact angle due to head pitching motion.

scholarly journals Height of Male Prisoners in Santiago de Chile during the Nitrate Era: The Penalty of being Unskilled, Illiterate, Illegitimate and Mapuche

2020 ◽  
Vol 17 (17) ◽  
pp. 6261
Author(s):  
Manuel Llorca-Jaña ◽  
Javier Rivas ◽  
Damian Clarke ◽  
Diego Barría Traverso
Keyword(s):  
Adult Population ◽  
Physical Growth ◽  
Height Distribution ◽  
Santiago De Chile ◽  
Northern European ◽  
The Mean ◽  
Male Inmates ◽  
University Degree ◽  
The Impact ◽  
Male Prisoners

This article contributes to the study of inequality in the biological welfare of Chile’s adult population during the nitrate era, ca. 1880s–1930s, and in particular focuses on the impact of socioeconomic variables on height, making use of a sample of over 20,000 male inmates of the capital’s main jail. It shows that inmates with a university degree were taller than the rest; that those born legitimate were taller in adulthood; that those (Chilean born) whose surnames were Northern European were also taller than the rest, and in particular than those with Mapuche background; and that those able to read and write were also taller than illiterate inmates. Conditional regression analysis, examining both correlates at the mean and correlates across the height distribution, supports these findings. We show that there was more height inequality in the population according to socioeconomic status and human capital than previously thought, while also confirming the importance of socioeconomic influences during childhood on physical growth.

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