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Results for “LUBRICATION”

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At least 379 records · Page 21Linked to original sources

PubMed2003

Solid-liquid transition of ultrathin lubricant film.

We represent a melting of ultrathin lubricant film by friction between atomically flat surfaces as a result of action of spontaneously appearing elastic field of stress shear component caused by the external supercritical heating. The kinetics of this solid-liquid transition is described by the Maxwell-type and Voigt-Kelvin equations for viscoelastic matter as well as by the relaxation equation for temperature. We show that these equations coincide formally with the synergetic Lorenz system, where the stress acts as the order parameter, the conjugate field is reduced to the elastic shear strain, and the temperature is the control parameter. Using the adiabatic approximation we find the steady-state values of these quantities. Taking into account the deformational defect of the shear modulus, we show that lubricant melting is realized according to mechanism of the first-order transition. The critical temperature of the friction surfaces increases with growth of the characteristic value of shear viscosity and decreases with growth of the shear modulus value linearly.

Journal Article↗

PubMed2005

Theory of lubrication due to collective pinning.

In collective pinning theory, the problem of two three-dimensional solids in contact is at its critical dimension. This implies that when the disordered forces acting between the two solids at the interface are relatively strong, the force of static friction should be large, but at smaller values of these forces, the system switches over to a regime of weak static friction. It is argued that this provides a mechanism for the reduction of friction in boundary lubrication. Lubricant molecules reduce static friction by smoothing the roughness of the surface, thus allowing the force pushing the surfaces together to be supported by more points of contact, which can switch the interface from the strong- to weak-static-friction regime.

Journal Article↗

PubMed2006

Molecular simulations of lubrication and solvation forces.

We report on molecular-dynamics simulations of the drag force experienced by a smooth sphere as it approaches a smooth planar surface to test the predictions of classical hydrodynamic theory. We use a simple repulsive Lennard-Jones-like model to represent the fluid interactions, and calculate the total force on the sphere as a function of its radius, velocity, and distance from the surface. We find that the presence of static solvation forces complicates the testing of hydrodynamic theory which predicts a divergent repulsive lubrication force as the gap vanishes. The solvation force contribution is most prominent at small gaps and small velocities. For a smooth wall its presence can lead to a total force that is oscillating between positive and negative, quite different from the hydrodynamic prediction. To enable an improved test of the lubrication predictions, we propose a different approach that measures the total force for approaching as well as receding spheres. We suggest a simple general analysis that decouples the dynamic and static force contributions on the sphere. The new decoupling method is applicable to simulations and laboratory experiments alike. We illustrate its power by applying it to the molecular-dynamics data.

Journal Article↗

PubMed2002

Can vacancies lubricate dislocation motion in aluminum?

The interaction of vacancy with dislocations in Al is studied using the semidiscrete variational Peierls-Nabarro model with ab initio determined gamma surface. For the first time, we confirm theoretically the so-called vacancy lubrication effect on dislocation motion in Al, a discovery that can settle a long-standing controversy in dislocation theory for fcc metals. We provide insights into the lubrication effect by exploring the connection between dislocation mobility and its core width. We predict an increased dislocation splitting in the presence of vacancy. We find that on average there is a weak repulsion between vacancies and dislocations which is independent of dislocation character.

Journal Article↗

PubMed2004

Peeling, healing, and bursting in a lubricated elastic sheet.

We consider the dynamics of an elastic sheet lubricated by the flow of a thin layer of fluid that separates it from a rigid wall. By considering long wavelength deformations of the sheet, we derive an evolution equation for its motion, accounting for the effects of elastic bending, viscous lubrication, and body forces. We then analyze various steady and unsteady problems for the sheet, such as peeling, healing, levitating, and bursting, using a combination of numerical simulation and dimensional analysis. On the macroscale, we corroborate our theory with a simple experiment, and, on the microscale, we analyze an oscillatory valve that can transform a continuous stream of fluid into a series of discrete pulses.

Journal Article↗

PubMed2006

Natural and experimental evidence of melt lubrication of faults during earthquakes.

Melt produced by friction during earthquakes may act either as a coseismic fault lubricant or as a viscous brake. Here we estimate the dynamic shear resistance (tau(f)) in the presence of friction-induced melts from both exhumed faults and high-velocity (1.28 meters per second) frictional experiments. Exhumed faults within granitoids (tonalites) indicate low tau(f) at 10 kilometers in depth. Friction experiments on tonalite samples show that tau(f) depends weakly on normal stress. Extrapolation of experimental data yields tau(f) values consistent with the field estimates and well below the Byerlee strength. We conclude that friction-induced melts can lubricate faults at intermediate crustal depths.

Journal Article↗

PubMed1983

Distribution of surfactants in the canine gastrointestinal tract and their ability to lubricate.

Surface-active phospholipids, chemically similar to pulmonary surfactants, have been identified by thin-layer chromatography in gastric juice and on the mucosal lining of five tissues along the canine gastrointestinal tract. These included esophagus, oxyntic tissue, midduodenum, midjenunum, and midcolon. The mucosal phospholipid composition did not change appreciably along the length of the gastrointestinal tract, with the most prominent species being phosphatidylcholine (PC) (34-45%) and phosphatidylethanolamine (PE) (18-32%). The gastrointestinal mucosal surface also contained lesser amounts (5-10% each) of sphingomyelin (Sp), lysophosphatidylcholine, phosphatidylinositol (PI), and phosphatidylserine (PS) and small but detectable quantities of phosphatidylglycerol (PG) and phosphatidic acid. Both the lipid extracts of all six gastrointestinal sources as well as commercially available phospholipids identified in these samples (PC, Sp, PE, PI, PS, and PG) proved to be good boundary lubricants. Each reduced the coefficient of friction by greater than 75% between glass and carboxylated yarn when tested by a standard method for evaluating textile "sizes." The results are discussed in relation to the possible role of the surface-active molecules in imparting properties conducive to lubrication and acid protection onto the gastrointestinal epithelium.

Animals↗

PubMed2004

Determination of refractory elements in used lubricating oil by ICPOES employing emulsified sample introduction and calibration with inorganic standards.

The quantification of trace elements in used lubricating oil is useful for evaluating the wearing of specific components of engines. In the present work, inductively coupled plasma optical emission spectrometry (ICPOES) was used for determining five refractory elements (Ni, Mo, Cr, V and Ti) in lubricating-oil samples. The methodology was developed while aiming at the introduction of such organic samples into the ICP as emulsions. Several nebulization systems were tested with clear advantage for Meinhard K3 coupled with a cyclonic spray chamber. The carbon deposition on the injector tip as well as the plasma background was minimized through careful optimization of the Ar and O2 gas mixture flows into the plasma. The optimization of instrumental and experimental parameters allowed quantification using calibration curves prepared with analyte inorganic standards. An internal standard (Sc) was used to correct the matrix effects and signal fluctuations. The limits of detection (3Sb/m), in the ng g(-1) range were obtained for all five elements. The methodology was validated through an analysis of standard reference materials (SRM 1084a, 1085a and 1085b). Good analyte recoveries (from 92.6 to 104.7%) were achieved. Comparison studies against established ICPOES methodologies (sample acid decomposition or sample direct dilution in an organic solvent) have shown that the proposed methodology present clear advantages in terms of simplicity of sample preparation, overall analysis time, and the use of inorganic standards for calibration instead of expensive metallorganic standards.

Journal Article↗

PubMed1990

Enhanced response of psoriasis to UVB therapy after pretreatment with a lubricating base. A single-blind controlled study.

Forty-three out-patients with stable plaque-type psoriasis involving 10-30% of the skin participated in a single-blind controlled study. The psoriasis lesions on one half of the body were treated with a lubricating base of the oil-in-water type before UVB exposure, while those on the other side of the body received UVB only. The rates of improvement of scaling, infiltration and erythema were compared in 127 symmetrical pairs of psoriasis plaques. The scores for the three variables were then summed to yield a total score for the effect of treatment. After only 2 weeks of treatment and throughout the treatment period the rate of improvement in the total score was significantly (p less than 0.001) accelerated on the body half treated with the emollient compared with the control side. Pretreatment with a suitable lubricating base can thus result in shorter treatment periods, which means that the surrounding skin will be exposed to smaller doses of UVB, with a diminished risk of actinic damage.

Adult↗

PubMed2003

Lubricated squeezing flow: a useful method for measuring the viscoelastic properties of soft tissues.

Conducting experiments on very soft biological tissues can be difficult. Traditionally, unconfined compression and shear have been used. Here, an improved method of compression testing, lubricated squeezing flow is described. This gives a uniform compression along the squeezing axis and almost uniform equi-biaxial elongation at right angles to the squeezing axis, with minimal shear deformation due to the constant lubrication of the sample surfaces during testing. Sample results for porcine liver obtained using this method are described here.

Animals↗

PubMed1992

[Data on the standardization of a lubricant F-11 in the air of the work area].

F-11 lubricant is used in synthetic fibers industry for the polyamide fibers processing. LD50 in intragastric administration is over 11,000 mg/kg. Acute action threshold (limac) is 180 mg/m3 (as evidenced by changes of the investigatory reflex). Chronic action threshold (limch) is 100 mg/m3. MAC in the air is 5 mg/m3, hazard class III. F-11 lubricant is a moderately hazardous chemical compound.

Air Pollutants, Occupational↗

PubMed1999

[Detection of low temperature rheologic behavior of lubricating oil by FTIR].

The composition and structure of lubricating oil expressed by FTIR were used for its characterization. Artificial nervous network was used as a mathematical model. CCS-15C viscosity of base oil was forecasted and good result was obtained. The result has shown that the artificial nervous network is an effective mathematical model for studying the relation between the composition and structure of lubricating oil and its performance.

English Abstract↗

PubMed1992

[The effect of two lubricants (magnesium stearate and pruv) in the formation of tablets of four anti-ulcer agents/ by means of direct compression].

In this research we study the influence of two lubricants-Magnesium Stearate and Pruv--on the tablets elaboration of Cimetidine, Ranitidine, Famotidine and Pirenzepine by direct compression. The presence of 0.5% of lubricants improved the flow of all the formulations, but especially the Famotidine's formulation. The formulations with Magnesium Stearate had the worst results in tests of friability and tensile strength. All tablets with drugs and Pruv had high data in indentation hardness. The tablets of Cimetidine, Famotidine and Pirenzepine with Magnesium Stearate had less time of disintegration.

Anti-Ulcer Agents↗

PubMedDate not supplied

Criteria for determining steam sterilization cycles for lubricated and nonlubricated mechanical equipment.

Requirements and procedures for determining steam sterilization cycles for lubricated and nonlubricated, complex, mechanical equipment are established. Factors affecting exposure times are discussed, as are procedures and data needed to determine the penetrability of steam into mechanical equipment, and the effect of lubricating oil in impeding steam penetration to the spore. The total effects of these factors in sterilizing times are presented. Sterilizers with a prevacuum cycle, which can remove air from the equipment efficiently and replace it with saturated steam, are recommended for complex mechanical equipment.

Equipment and Supplies, Hospital↗

PubMed1984

Changes in thyroid function and serum iodine levels after prepartum use of a povidone-iodine vaginal lubricant.

To determine if application of iodide to vaginal mucosa of pregnant women results in significant iodide absorption or changes in thyroid function, we studied 18 intrapartum women for whose examinations during labor povidone-iodine gel was used as a lubricant and 16 for whose examinations an iodine-free lubricant was used. Both serum inorganic iodine and total serum iodine increased significantly (p less than 0.001) after iodide exposure and fell (p = 0.003) to near baseline within two days. In both groups, serum thyroxine and triiodothyronine fell during labor and delivery; differences between groups were not significant. In the iodine-treated group, however, there was a significant increase in thyroid-stimulating hormone at two days postpartum (p less than 0.001). Iodide applied to vaginal mucosa of pregnant women is absorbed and affects the maternal pituitary-thyroid axis.

Administration, Topical↗

PubMed1995

Viscosity comparisons of polydimethylsiloxane lubricants in latex condom brands via Fourier self-deconvolution of their FT-IR spectra.

Many brands of latex condoms use a polydimethylsiloxane lubricant. The lubricant viscosity in ten different brands was compared by determining the average chain length through the ratio of the dimethyl to trimethyl peak area obtained after applying the resolution enhancement technique of Fourier self-deconvolution to their diffuse reflectance FT-IR spectra in the area around 800 cm-1.

Condoms↗

PubMed1994

[Peritoneal reactions caused by starch used regularly for lubricating surgical gloves. Review of the literature].

The contamination of the operating field by a number of substances including the starch used to lubricate surgical gloves is one of the causes of foreign body granuloma formation. The role of starch is particularly clearly documented in the peritoneal cavity where it may provide the basis of a well defined nosological phenomenon, "starch peritonitis", but it has also been reported in most other anatomical districts. The most logical solution to this problem is to use starch-free surgical gloves prepared using another type of lubricant without the aforesaid drawbacks. This paper analyses international clinical and experimental literature focusing on the damaging effects resulting from the introduction of starch into the peritoneal cavity.

Gloves, Surgical↗

PubMed1994

The effect of a surgical lubricant on in vivo sperm penetration of cervical mucus.

The implications of these data is that coital lubricants may impair fertility of some couples. Unfortunately, conception was not an end point on this study, and our conclusions must be considered inferential. Nevertheless, the results from this study lead us to recommend avoidance of surgical lubricants by couples attempting pregnancy.

Adult↗