SEARCH · PubMed Health

Results for “LUBRICATION”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 487 records · Page 27Linked to original sources

PubMed2004

Hybrid atomistic-coarse-grained treatment of thin-film lubrication. II.

A new hybrid atomistic-coarse-grained (HACG) treatment of reversible processes in multiple-scale systems involving fluid-solid interfaces was tested through isothermal-isobaric Monte Carlo simulations of the quasistatic shearing of a model two-dimensional lubricated contact comprising two planar Lennard-Jones solid substrates that sandwich a softer Lennard-Jones film. Shear-stress profiles (plots of shear stress T(yx) versus lateral displacement of the substrates) obtained by the HACG technique, which combines an atomistic description of the interfacial region with a continuum description of regions well removed from the interface, are compared with "exact" profiles (obtained by treating the whole system at the atomic scale) for a selection of thermodynamic states that correspond to systematic variations of temperature, load (normal stress), film-substrate coupling strength, and film thickness. The HACG profiles are in excellent agreement overall with the exact ones. The HACG scheme provides a reliable description of quasistatic shearing under a wide range of conditions. It is demonstrated that the elastic response of the remote regions of the substrates can have a significant impact on the static friction profile (plot of maximum magnitude of T(yx) versus load).

Journal Article↗

PubMed2006

Water as a lubricant for graphite: a computer simulation study.

The phase state and shear behavior of water confined between parallel graphite sheets are studied using the grand canonical Monte Carlo technique and TIP4P model for water. In describing the water-graphite interaction, two orientation-dependent potentials are tried. Both potentials are fitted to many-body polarizable model predictions for the binding energy and the equilibrium conformation of the water-graphite complex [K. Karapetian and K. D. Jordan in Water in Confining Geometries, edited by V. Buch and J. P. Devlin (Springer, Berlin, 2003), pp. 139-150]. Based on the simulation results, the property of water to serve as a lubricant between the rubbing surfaces of graphitic particles is associated, first, with the capillary condensation of water occurring in graphitic pores of monolayer width and, second, with the fact that the water monolayer compressed between graphite particles retains a liquidlike structure and offers only slight resistance to shear.

Journal Article↗

PubMed2004

Insect aquaplaning: Nepenthes pitcher plants capture prey with the peristome, a fully wettable water-lubricated anisotropic surface.

Pitcher plants of the genus Nepenthes have highly specialized leaves adapted to attract, capture, retain, and digest arthropod prey. Several mechanisms have been proposed for the capture of insects, ranging from slippery epicuticular wax crystals to downward-pointing lunate cells and alkaloid secretions that anesthetize insects. Here we report that perhaps the most important capture mechanism has thus far remained overlooked. It is based on special surface properties of the pitcher rim (peristome) and insect "aquaplaning." The peristome is characterized by a regular microstructure with radial ridges of smooth overlapping epidermal cells, which form a series of steps toward the pitcher inside. This surface is completely wettable by nectar secreted at the inner margin of the peristome and by rain water, so that homogenous liquid films cover the surface under humid weather conditions. Only when wet, the peristome surface is slippery for insects, so that most ant visitors become trapped. By measuring friction forces of weaver ants (Oecophylla smaragdina) on the peristome surface of Nepenthes bicalcarata, we demonstrate that the two factors preventing insect attachment to the peristome, i.e., water lubrication and anisotropic surface topography, are effective against different attachment structures of the insect tarsus. Peristome water films disrupt attachment only for the soft adhesive pads but not for the claws, whereas surface topography leads to anisotropic friction only for the claws but not for the adhesive pads. Experiments on Nepenthes alata show that the trapping mechanism of the peristome is also essential in Nepenthes species with waxy inner pitcher walls.

Animals↗

PubMedDate not supplied

Food contamination by hydrocarbons from lubricating oils and release agents: determination by coupled LC-GC.

We have found that many foods are contaminated with mineral oil products used as lubricating oils/greases or as release agents. The mineral oil base of such products usually consists of branched alkanes ranging between C17 and C35. It forms a broad 'hump' of unresolved compounds in the gas chromatogram. Examples of such products are described; contamination is shown for a sample of bread, bonbon, and chocolate, respectively. The results suggest that contamination of foodstuffs with mineral oils does not always receive the required attention. However, there is also a lack of guidelines.

Bread↗

PubMed1979

Effect of oil mists on the irritancy of sulfur dioxide. I. Mineral oils and light lubricating oil.

The increase in pulmonary flow resistance in unanesthetized guinea pigs was used to assess the effect of sub-micrometer oil aerosols on the response to sulfur dioxide. At a concentration of about 10 mg/m3 neither a medicinal grade mineral oil nor a light lubricating oil altered the response when given simultaneously with 1 or 10 ppm sulfur dioxide. The naphthenic medicinal oil at 100 mg/m3 failed to protect against 50 ppm sulfur dioxide when administerd simultaneously. A 30-minute pre-exposure, however, conferred complete protection. A paraffinic laboratory grade mineral oil conferred protection when given simultaneously but was less effective when the pre-exposure protocol was used.

Aerosols↗

PubMed2005

Effects of various lubricants on corneal surface regularity in rabbits.

The aim of this study was to establish a method for analysis of tear film stability and thereby to investigate the effects of lubricants on corneal surface regularity and corneal epithelial damage in anesthetized rabbits with the eye held open. Saline-instilled and noninstilled eyes manifested a time-dependent increase in the corneal surface regularity index (SRI). In contrast, 0.1% hyaluronic acid (HA) prevented the increase in the SRI for up to 20 min after instillation. Methylene blue uptake into the damaged cornea was significantly greater in eyes that received saline than in those treated with HA. Whereas eyes instilled with 0.5% methylcellulose (MC) or 0.35% sodium carboxymethylcellulose (CMC) manifested an increase in the SRI similar to that apparent in those that received saline, 1.0% chondroitin sulfate (CS) prevented the increase in the SRI for up to 10 min after instillation. In conclusion, we have established a method for analysis of tear film stability in rabbits. Our results suggest that tear film stability is closely related to corneal surface damage and that topical instillation of 0.1% HA or 1.0% chondroitin sulfate warrants further investigation as a potential treatment for patients with dry eye.

Animals↗

PubMed2004

Rejuvenation of visual functions in older adult drivers and drivers with cataract during a short-term administration of N-acetylcarnosine lubricant eye drops.

The purpose of this study was to examine using the original halometer glare test of the type of visual impairment mediated by the increased glare sensitivity (halos) and associated with poorer visual function in both the better and worse eyes of older adult drivers and older drivers with cataract. The clinically validated (by Innovative Vision Products Inc.) formula of 1% N-acetylcarnosine (NAC) lubricant eye drops were applied topically to the eyes of older drivers to reduce glare disability and improve distance acuities for driving. This was a randomized, double-blind, placebo-controlled study. The examined subjects consisted of 65 older adults with cataract in one or both eyes, and 72 adult drivers who did not have cataract in either eye. In the control group, comparison with baseline values showed some variability of data in gradual worsening of glare sensitivity at red and green targets and minimal VA changes over 4 months. In the NAC-treated group, 4-month follow-up generally showed an improvement in VA and a significant improvement in glare sensitivity at red and green targets was documented in worse and better eyes using a critical cut point halometer score for driving. The NAC-treated eyes had statistically significant difference in VA, glare sensitivity compared with the control group ( p < 0.001) at 4-month timepoint of treatment, as supported by the overall t-test results of the ratio of the follow-up data to the baseline values. Tolerability of NAC eyedrops was good in almost all patients, with no reports of ocular or systemic adverse effects. It would be advisable for traffic safety if a Halometer glare sensitivity test was implemented for vehicles and/or was regularly added to the requirements for a driver's licence. The results of this study provide a substantial basis for further evaluation of NAC in the treatment and prevention of vision impairment in the older population of drivers for legal driving. The developed ophthalmic drug NAC formula showed potential for the non-surgical treatment of age-related cataracts.

Aged↗

PubMed2000

An unfermented gel component of psyllium seed husk promotes laxation as a lubricant in humans.

BACKGROUND: In addition to increasing stool weight, supplements of psyllium seed husk produce stools that are slick and gelatinous. OBJECTIVE: Our purpose was to test the hypothesis that a gel-forming fraction of psyllium escapes microbial fermentation and is responsible for the characteristics that enhance laxation. DESIGN: Fifteen healthy adults consumed controlled diets for two 7-d periods, one of which included 8.8 g dietary fiber provided by 15 g/d of a psyllium seed husk preparation. All stools were collected and evaluated and diet was monitored throughout. RESULTS: Psyllium significantly increased the apparent viscosity of an aqueous stool extract, stool moisture, and wet and dry stool weights. A very viscous fraction, not present in low-fiber stool and containing predominantly 2 sugars that are also found in abundance in psyllium husk, was isolated from psyllium stool. CONCLUSIONS: In contrast with other viscous fibers that are fermented completely in the colon, a component of psyllium is not fermented. This gel provided lubrication that facilitated propulsion of colon contents and produced a stool that was bulkier and more moist than were stools resulting with use of comparable amounts of other bowel-regulating fiber sources.

Adolescent↗

PubMed1989

32P-postlabelling analysis of DNA adducts in the skin of mice treated with petrol and diesel engine lubricating oils and exhaust condensates.

Samples of unused or used petrol and diesel engine lubricating oils were applied to the shaved dorsal skin of 4- to 6-week-old male Parkes mice, either as a single treatment (50 microliters/mouse) or as four consecutive daily treatments (50 microliters/application). DNA isolated from the skin 24 h after the final treatment was digested to 3'-mononucleotides and analysed by 32P-postlabelling for the presence of aromatic adducts. Enhancement of sensitivity using butanol extraction or nuclease P1 digestion of the DNA hydrolysates led to the detection of up to eight adduct spots on polyethyleneimine-cellulose thin-layer chromatograms with samples of DNA from skin treated with used engine oils, at levels of 40-150 amol total adducts/micrograms DNA. Multiple treatments with the used oils gave rise to similar patterns of adducts in lung DNA. A single treatment of mouse skin with petrol engine exhaust condensate (50 microliters), or diesel engine exhaust condensate (50 microliters), containing 20 and 46 micrograms benzo[a]pyrene (BaP)/g respectively, gave rise to approximately 75 amol total adducts/micrograms DNA in skin. A significant proportion, 31 and 48% respectively, of the adducts formed by the petrol and diesel engine exhaust condensates co-chromatographed with the major BaP-DNA adduct, but with the used engine oils, only petrol engine oil, and not diesel engine oil, produced significant amounts of an adduct (22% of total) that corresponded to the BaP-DNA adduct.

Adenosine Triphosphate↗

PubMed2000

Friction and noise-induced coherent structures in boundary lubrication

We examine the effect of stick-slip boundary conditions on the friction generated by a molecularly thin layer of a liquid lubricant separating two plates. For one-dimensional compressible flows, noise-induced coherent dissipative structures on a micron scale are generated due to cooperation between the external drive and the thermal noise. As a function of the thermal noise these structures show a peak in their amplitudes similar to stochastic resonance. At low velocities a reduction in friction with increasing thermal noise is observed.

Journal Article↗

PubMed2001

Friction in a solid lubricant film.

Molecular-dynamics study of a thin (one to five layers) lubricant film between two substrates in moving contact are performed using Langevin equations with an external damping coefficient depending on distance and velocity of atoms relative the substrates, motivated by microscopic configurations. They show that the minimal friction coefficient is obtained for the solid-sliding regime. A detailed analysis of the results, the comparison with other microscopic modeling approaches of friction, and the evaluation of quantities that can be compared to experiments, such as the velocity of the transition from stick slip to smooth sliding, are used to discuss the relevance of the microscopic simulations of friction.

Journal Article↗

PubMed2001

Transverse electrokinetic and microfluidic effects in micropatterned channels: lubrication analysis for slab geometries.

Off-diagonal (transverse) effects in micropatterned geometries are predicted and analyzed within the general frame of linear-response theory, relating applied pressure gradient and electric field to flow and electric current. These effects could contribute to the design of pumps, mixers, or flow detectors. Shape and charge-density modulations are proposed as a means to obtain sizeable transverse effects, as demonstrated by focusing on simple geometries and using the lubrication approximation.

Journal Article↗

PubMed2002

Lubrication corrections for lattice-Boltzmann simulations of particle suspensions.

The lattice-Boltzmann method has been refined to take account of near-contact interactions between spherical particles. First, we describe a comprehensive solution to the technical problems that arise when two discretized surfaces come into contact. Second, we describe how to incorporate lubrication forces and torques into lattice-Boltzmann simulations, and test our method by calculating the forces and torques between a spherical particle and a plane wall. Third, we describe an efficient update of the particle velocities, taking into account the possibility that some of the differential equations are stiff.

Journal Article↗

PubMed2004

Boundary lubrication with a glassy interface.

Recently introduced constitutive equations for the rheology of dense, disordered materials are investigated in the context of stick-slip experiments in boundary lubrication. The model is based on a generalization of the shear transformation zone (STZ) theory, in which plastic deformation is represented by a population of mesoscopic regions which may undergo nonaffine deformations in response to stress. The generalization we study phenomenologically incorporates the effects of aging and glassy relaxation. Under experimental conditions associated with typical transitions from stick-slip to steady sliding and stop-start tests, these effects can be dominant, although the full STZ description is necessary to account for more complex, chaotic transitions.

Journal Article↗

PubMed2005

Cavitation in a lubrication flow between a moving sphere and a boundary.

A heavy sphere is free to move inside a rotating horizontal cylinder filled with viscous liquid. The steady motion is essentially Stokesian, and the sphere rotates at a fixed location with a lubrication layer between the ball and the wall. The symmetry of the flow field suggests there will be no force to balance the normal component of the ball's weight. However, we show that a normal force can arise when a cavitation bubble is present. The bubble size was measured as a function of the cylinder rotation rate and agrees well with a model which uses the force and torque balances on the sphere.

Journal Article↗

PubMed2006

Viscosity and lubricity of aqueous NaCl solution confined between mica surfaces studied by shear resonance measurement.

We report the viscoelasticity of the thin film of aqueous NaCl solution confined between mica surfaces measured by shear resonance apparatus. The observed shear resonance curves at separations less than ca. 2 nm indicated that the solution exhibits the high lubrication effects under some loads. The effective viscosity (0.1-10 Pa s) obtained for the separations less than 1 nm from a mechanical model was 2-4 orders of magnitude larger than the bulk value. Our study employing a novel shear measurement provided a comprehensive picture for the dynamics of confined water thinner than a few nanometers.

Journal Article↗

PubMed2006

Crystal bridge formation marks the transition to rigidity in a thin lubrication film.

We report that the rheological transition in a thin lubrication film of dodecane from bulk to high viscosity states as the thickness is decreased is the result of a novel structural transition. Using nonequilibrium molecular dynamics simulations we find that the initial increase in viscosity as the film thins is due to the formation of isolated crystalline bridges between the surfaces. As the thickness decreases further, these bridges increase in number and organize themselves into a tetratic order in the plane of the surface. We show that this ordered state melts at a temperature of 350 K.

Journal Article↗

PubMed2003

A power transducer system for the ultrasonic lubrication of the continuous steel casting.

A critical point in the continuous steel casting process exists in the meniscus zone of the cooled mould, i.e., the region in which the steel stream flowing out of the tundish nozzle starts to solidify. This is a critical point because of the sticking that occurs between the solid shell of steel and the mould. In this work, a new system for the ultrasonic lubrication of the continuous steel casting is proposed and experimentally tested. The basic idea is to excite one of the mould's natural vibration modes by means of a distributed ultrasonic source. This source is composed of an array of power emitters, with each of them placed upon an antinode of the mould. An experimental characterization of the vibrational behavior of a square mould was first carried out. The most active resonance modes of the mould were detected with an experimental technique based on a simple impedance measurement. The modal shape of the selected mode, and hence the position of antinodes, was obtained by means of interferometer measurements. Additional experimental investigations were performed by exciting mould vibrations with up to four piezoceramic disks placed on different sets of antinodes. Some positioning criteria to maximize the superposition effect were derived. Measurements were obtained through excitation of the mould with up to four Langevin-type power emitters, designed and manufactured to work at the mould's selected resonance frequency. These measurements have shown that, by increasing the number of emitters, the ultrasonic power transmitted to the mould and, consequently, the maximum available displacement, increases. Other practical advantages of the proposed system are highlighted and discussed.

Journal Article↗