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PubMed2005

Tuning diffusion and friction in microscopic contacts by mechanical excitations.

We demonstrate that lateral vibrations of a substrate can dramatically increase surface diffusivity and mobility and reduce friction at the nanoscale. Dilatancy is shown to play an essential role in the dynamics of a nanometer-size tip which interacts with a vibrating surface. We find an abrupt dilatancy transition from the state with a small tip-surface separation to the state with a large separation as the vibration frequency increases. Atomic force microscopy experiments are suggested which can test the predicted effects.

Journal Article↗
PubMed2006

Friction and diffusion of matter-wave bright solitons.

We consider the motion of a matter-wave bright soliton under the influence of a cloud of thermal particles. In the ideal one-dimensional system, the scattering process of the quasiparticles with the soliton is reflectionless; however, the quasiparticles acquire a phase shift. In the realistic system of a Bose-Einstein condensate confined in a tight waveguide trap, the transverse degrees of freedom generate an extra nonlinearity in the system which gives rise to finite reflection and leads to dissipative motion of the soliton. We calculate the velocity and temperature-dependent frictional force and diffusion coefficient of a matter-wave bright soliton immersed in a thermal cloud.

Journal Article↗
PubMed2006

Turbulent friction in rough pipes and the energy spectrum of the phenomenological theory.

The classical experiments on turbulent friction in rough pipes were performed by Nikuradse in the 1930s. Seventy years later, they continue to defy theory. Here we model Nikuradse's experiments using the phenomenological theory of Kolmogórov, a theory that is widely thought to be applicable only to highly idealized flows. Our results include both the empirical scalings of Blasius and Strickler and are otherwise in minute qualitative agreement with the experiments; they suggest that the phenomenological theory may be relevant to other flows of practical interest; and they unveil the existence of close ties between two milestones of experimental and theoretical turbulence.

Journal Article↗
PubMed2006

Contact area measurements reveal loading-history dependence of static friction.

We perform quantitative measurements of the actual area of contact, A, formed by two rough solids that are subjected to different normal loading protocols. We show that microscopic motion, induced by Poisson contraction or expansion, produces a strong memory dependence of on the loading history with a large corresponding influence on the system's frictional strength. These effects, together with accompanying transient dynamics, are independent of humidity, loading rates, and material contrast across the interface.

Journal Article↗
PubMed2006

Interlayer forces and ultralow sliding friction in multiwalled carbon nanotubes.

We describe interlayer force measurements during prolonged, cyclic telescoping motion of a multiwalled carbon nanotube. The force acting between the core and the outer casing is modulated by the presence of stable defects and generally exhibits ultralow friction, below the measurement limit of 1.4 x 10(-15) N/atom and total dissipation per cycle lower than 0.4 meV/atom. Defects intentionally introduced in the form of dangling bonds lead to temporary mechanical dissipation, but the innate ability of nanotubes to self heal rapidly optimizes the atomic structure and restores smooth motion.

Journal Article↗
PubMed2006

Predictions and observations of multiple slip modes in atomic-scale friction.

Using the quasistatic Tomlinson model as a simple representation of an atomic force microscope, conditions for transitions in atomic-scale friction behavior from smooth sliding to single slips and then multiple slip regimes are derived based on energy minimization. The calculations predict and give a general explanation for transitions between different stick-slip regimes in the limit of low damping. The predictions are consistent with experimental observations of these transitions.

Journal Article↗
PubMed2006

Stick-slip motion in spite of a slippery contact: do we get what we see in atomic friction?

Atomic force microscopy provides direct atomic-scale access to friction. In this paper, unexpected and potentially dramatic consequences of the tip elasticity are discussed. Under certain natural conditions an essentially new, nontrivial regime can be entered. Although the tip appears to perform typical stick-slip motion, the tip-surface contact is fully "lubricated" by fast thermal motion of the tip apex. The interpretation of the observations needs to be changed completely in this case.

Journal Article↗
PubMed2006

Giant wave-drag enhancement of friction in sliding carbon nanotubes.

Molecular dynamics simulations of coaxial carbon nanotubes in relative sliding motion reveal a striking enhancement of friction when phonons whose group velocity is close to the sliding velocity of the nanotubes are strongly excited. The effect is analogous to the dramatic increase in air drag experienced by aircraft flying close to the speed of sound but differs in that it can occur in multiple velocity ranges with varying magnitude, depending on the atomic level structures of the nanotubes. The phenomenon is a general one that may occur in other nanoscale mechanical systems.

Journal Article↗
PubMed2006

Frictional dissipation and interfacial glass transition of polymeric solids.

We present single contact friction experiments between a glassy polymer and smooth silica substrates grafted with alkylsilane layers of different coverage densities and morphologies. This allows us to adjust the polymer-substrate interaction strength. We find that, when going from weak to strong interaction, the response of the interfacial junction where shear localizes evolves from that of a highly viscous threshold fluid to that of a plastically deformed glassy solid. This we analyze as resulting from an interaction-induced "interfacial glass transition" helped by pressure.

Journal Article↗
PubMed1991

Biphasic amyloidosis arising from friction melanosis.

A 40-year-old woman who had used nylon towels in the bath for about 10 years noticed hyperpigmentation on the prominent regions over the bones of the trunk and extremities. She also developed lichenoid papules with itching on her back. Histologically, both the pigmented and the papular lesions had amyloid deposits beneath the epidermis. In this case it is presumed that the papular lesions with amyloid (lichen amyloidosus) developed initially from friction melanosis which became macular pigmented lesion (macular amyloidosis). The etiologic factor of these sequential pathologic changes is considered to be repeated scrubbing with nylon towels.

Adult↗
PubMed2002

Frictional hair loss in Iraqi patients.

A total of 50 Iraqi male patients with frictional hair loss were studied. Their ages ranged from 27-55 years with a mean +/- SD of 40.60 +/- 7.82 years. The age of onset ranged from 26-50 years with a mean +/- SD of 38 +/- 7.3 years. The duration of disease was 1-5 years, mean +/- SD 2.2 +/- 1.3. Middle age was the most common age group affected. Patterns of hair loss were as follows; bilateral thighs & legs 13 (26%), bilateral thighs alone in 9 patients (18%), bilateral shins & calves (legs) in 4 patients (8%), abdomen alone in 8 patients (16%), thigh and abdomen 4 (8%) patients, legs & abdomen 4 (8%) patients, and all sites in 12 patients (24%). The pattern of patchy hair loss showed some etiological preference. It was found to be due to continuous pressure from socks, trousers and bed. Skin biopsies from five patients showed apparently normal histology. Twenty-six (52%) of the cases were healthy. There were no important medical or dermatological associations, such as alopecia areata or peripheral neuropathy in any patient although unrelated medical conditions were seen in 24 (48%). To the best of our knowledge, this type of patchy hair loss has attracted very little attention in the past, and the literature appeared to be deficient in references to this problem.

Adult↗
PubMed1989

Hyperpigmentation of the clavicular zone: a variant of friction melanosis.

This paper reports on clinical, laboratory, and pathologic findings of 10 cases of an idiopathic form of hyperpigmentation of the clavicular zone, a peculiar entity of circumscribed, glistening, pigmented lesions affecting young Latin women. Pathologic findings consisted of focal to extensive necrosis of the epidermis, focal areas of junctional cleavage, and melanin deposition within the epidermis, dermis, and melanophages, which places this lesion within the group of brown hypermelanoses. The authors feel that friction with clothing or with scrub pads made of sedge (a very common practice amongst mexicans in the bath room) against clavicular protuberances is fundamental in its pathogenesis.

Adolescent↗
PubMed1994

Long-term results of intermittent low-friction self-catheterization in patients with recurrent urethral strictures.

OBJECTIVE: To ascertain the duration of intermittent low-friction self-catheterization (ILSC) required to cause stricture stabilization. PATIENTS AND METHODS: Over a 4 year period, 101 patients with a median age of 62 years (range 16-85) with recurrent urethral strictures were recruited to the trial. All the strictures were treated by internal urethrotomy and the patients were then randomized to perform ILSC twice weekly for either 6 months (group 1) or 36 months (group 2). Out-patient follow-up with urinary flow rate was initially at 1 month and then at 3 monthly intervals. Stricture recurrence rates were compared between the two groups. RESULTS: Of 101 patients, seven failed to attend after the first out-patient appointment. A further 21 died of unrelated disease whilst on ILSC (although 13 had been followed up for at least 24 months and so were included in the analysis). The median follow-up was 67 months (range 24-78). Ten patients in group 2, who had suffered from recurrent strictures, refused to stop catheterizing at the appointed time and all remain stricture-free on permanent ILSC. Of the remaining 76 patients, 48 catheterized for 6 months and 28 patients performed ILSC for 12 to 36 months (nine stopped earlier than intended). Forty per cent of patients who stopped at 6 months developed a recurrence compared with 14% who catheterized for more than 12 months (P < 0.05) (chi-square test with Yates' correction). CONCLUSIONS: Our results indicate that ILSC is safe and effective in preventing stricture recurrence in the long term. The recurrence rate of urethral strictures was significantly lower when ILSC was continued for more than 12 months compared with ILSC that was stopped at 6 months. We conclude that catheterization for at least 1 year is required to achieve adequate urethral stabilization.

Adolescent↗
PubMed1989

An in vitro comparison of the single cone and lateral condensation techniques using 'friction-fitted' and 'solvent dip-fitted' primary gutta-percha cones.

Extracted teeth, root-filled by single cone and lateral condensation techniques, using friction fitted and solvent (chloroform and eucalyptol) dip-fitted primary gutta-percha cones, were compared with respect to apical sealing as measured by length of dye penetration and frequency of no dye penetration. Overall, the single cone techniques were significantly more effective than lateral condensation techniques regarding length of dye penetration. The single cone techniques were not significantly different from the lateral condensation technique which employed chloroform dip-fitted primary gutta-percha cones regarding length of dye penetration. The single cone and lateral condensation techniques which utilized chloroform dip-fitted cones ranked first and second with respect to frequency of no dye penetration.

Chloroform↗
PubMed2004

Local corticosteroid injection in iliotibial band friction syndrome in runners: a randomised controlled trial.

OBJECTIVE: To establish whether a local injection of methylprednisolone acetate (40 mg) is effective in decreasing pain during running in runners with recent onset (less than two weeks) iliotibial band friction syndrome (ITBFS). METHODS: Eighteen runners with at least grade 2 ITBFS underwent baseline investigations including a treadmill running test during which pain was recorded on a visual analogue scale every minute. The runners were then randomly assigned to either the experimental (EXP; nine) or a placebo control (CON; nine) group. The EXP group was infiltrated in the area where the iliotibial band crosses the lateral femoral condyle with 40 mg methylprednisolone acetate mixed with a short acting local anaesthetic, and the CON group with short acting local anaesthetic only. The same laboratory based running test was repeated after seven and 14 days. The main measure of outcome was total pain during running (calculated as the area under the pain versus time graph for each running test). RESULTS: There was a tendency (p = 0.07) for a greater decrease in total pain (mean (SEM)) during the treadmill running in the EXP group than the CON group tests from day 0 (EXP = 222 (71), CON = 197 (31)) to day 7 (EXP = 140 (87), CON = 178 (76)), but there was a significant decrease in total pain during running (p = 0.01) from day 7 (EXP = 140 (87), CON = 178 (76)) to day 14 (EXP = 103 (89), CON = 157 (109)) in the EXP group compared with the CON group. CONCLUSION: Local corticosteroid infiltration effectively decreases pain during running in the first two weeks of treatment in patients with recent onset ITBFS.

Adult↗
PubMed1983

Mortality of workers manufacturing friction materials using asbestos.

A mortality (1942-80) study was carried out on 13460 workers of a factory producing friction materials. The only type of asbestos used was chrysotile, except during two well-defined periods before 1945 when crocidolite was used, and over 99% of the population was traced. Compared with national death rates there were no detectable excesses of deaths due to lung cancer, gastrointestinal cancer, or other cancers; 11 deaths were due to pleural mesothelioma. A case-control study was carried out on deaths due to mesothelioma; this showed that eight workers had been exposed to crocidolite and another was possibly exposed intermittently to crocidolite. The other two had been employed for most of their working lives outside the factory, and their mesotheliomas could not be definitely attributed to exposure to chrysotile. Limiting the study to cases and controls who had exposure to 5 fibres/ml of chrysotile asbestos it was found that five of the six cases compared with two of the 10 controls had also been exposed to crocidolite. The probability (1:36) of this occurring were there no association with crocidolite is most unlikely. A case-control study was also carried out on deaths due to lung cancer and gastrointestinal cancer to investigate the dose-response relationships between these tumours and exposure to chrysotile. Measured and estimated fibre concentrations were available for the different jobs over the period of the study. No dose-response relationships were observed, but the exposures were low with only 5% of men accumulating 100 fibre-years/ml. The experience at this factory over a 40-year period showed that chrysotile asbestos was processed with no detectable excess mortality.

Adult↗
PubMed1983

Environmental history of a factory producing friction material.

The fibre concentrations generated during the production of friction materials, incorporating asbestos, over the past 60 years have been studied to provide cumulative dust exposure data for a mortality study of the work-force. Chrysotile has been used almost exclusively during this period. The measurements made routinely by the factory staff provided information from 1950 onwards; concentrations for earlier years were derived from simulation studies using original materials, machines, and methods. These have shown that while high concentrations prevailed in the earliest years dust suppression measures initiated in 1931, and other factors, reduced the time-weighted average concentrations to moderate levels. There were two four-year periods when the production of brake blocks incorporating crocidolite occupied a well-defined area of the factory. The simulation of this production was not permissible, but the employees concerned could be identified.

Air Pollutants↗
PubMed1984

Dust exposure and mortality in an American chrysotile asbestos friction products plant.

Cohort studies in three American asbestos factories were undertaken to investigate the effect of fibre type and manufacturing process on lung cancer, mesothelioma, and asbestosis. Reports have been published on a chrysotile textile plant in South Carolina and a mainly textile plant in Pennsylvania, which also used amphiboles. In the third plant in Connecticut friction products and packings were made from chrysotile only. In a cohort of 3641 men employed for one month or more, 1938-58, 3513 (96.5%) were traced, 1267 (36%) had died, and death certificates were obtained for 1228 (96.9%). Individual exposures were estimated (in mcpf . years) from impinger measurements. Life table analyses using Connecticut mortality rates gave an SMR for all causes of 108.5 (USA 107.9). The SMR (all causes) for men who had worked for less than a year was 129.9 and for those who had worked for a year or more, 101.2. The equivalent SMRs for respiratory cancer were 167.4 and 136.7 respectively. Excluding men who had worked for less than a year, there was possible evidence of some increase in risk of lung cancer with increasing exposure, supported also by a "log-rank" (case-control) analysis, of the same order as that observed in chrysotile mining and milling. These findings may be compared with chrysotile textile manufacture where the risk of lung cancer was some 50-fold greater. It is suggested that the differences in risk are perhaps related to the higher proportion of submicroscopic fibres in textile manufacture that may result from the traumatic carding , spinning, and weaving processes. No case of mesothelioma was found, consistent with a much lower risk of this tumour with chrysotile than with amphiboles. Twelve deaths (nine in men with very short and low asbestos exposure) were given ICD code 523 (pneumoconiosis); all but two were ascribed to anthracosilicosis or silicosis and none to asbestosis.

Adult↗