Conjunctival epithelial flaps with 18 months of silicone hydrogel contact lens wear

Purpose. To report differences in the incidence of conjunctival epithelial flaps (CEFs) found in a group of neophyte contact wearers using two different silicone hydrogel contact lenses on a daily- and continuous-wear basis during an 18-month period. Methods. Sixty-one subjects were initially examined, and 53 were eligible to participate in the study. Eligible subjects were randomly assigned to wear one of two silicone hydrogel materials, lotrafilcon A or balafilcon A, on a daily- or continuous-wear basis. After an initial screening, subjects were monitored weekly for the first month and then after 3, 6, 12, and IS months. The incidence of CEFs in each of the four contact lens groups was recorded. Results. Five of the 53 subjects enrolled in the study showed bilateral CEFs. A higher incidence of CEFs was found in subjects wearing lotrafilcon A lenses (n = 4) compared to balafilcon A lenses (it = 1) (chi(2) = 4.37, P=0.04). Differences in the incidence of CEFs between subjects wearing lenses on a daily-wear basis (n = 1) versus a continuous-wear basis (it = 4) showed a weak statistical significance (chi(2) = 3.03, P=0.08). Conclusions. Lotrafilcon A lenses were associated with a higher incidence of CEFs than balafilcon A lenses were, and this difference may be attributed to differences in the edge design, material, or modulus of rigidity between the two lens types. Subjects wearing lenses on a daily-wear basis showed fewer adverse events than did subjects wearing lenses on a continuous-wear basis. The longer wearing times of subjects wearing lenses on a continuous-wear basis are likely to exacerbate the incidence of CEFs.

Mild wear in dry and lubricated sliding systems

A vertical pin on horizontal disc machine has been used to conduct a series of experiments in air under dry and lubricating sliding conditions. For dry sliding low load and speed combinations were chosen to correspond to the mild wear region below the Welsh T1 transition. Lubricated tests were conducted under flooded conditions using Esso Technical White Oil alone and with a 0.1% stearic acid additive, for load and speed ranges that produced substantial amounts of asperity contact and thus a boundary lubricated regime of wear. The test material in all cases was AISI 52100 steel, for unlubricated sliding subjected to loads from 5 to 50 N and a range of speeds from 10-3 to 1.0 ms-1, and for lubricated sliding loads of 50 to 123 N and for speeds of 10-2 to 1.0 ms-1. Unlubricated wear debris was found to be a mixture of -Fe_2O_3 and -Fe. Unlubricated wear was found to occur via a thin film logarithmic oxide growth followed by agglomeration into thicker oxide plateaux 2 to 10 m in thickness. Lubricated wear occurred via thick film diffusion controlled oxide growth producing homogeneous oxide plateaux 0.1 to 0.2 m in thickness. X-ray photoelectron spectroscopy identified the presence of a surface film on pins worn in White Oil with stearic acid, which is thought to be iron stearate. A model has been developed for unlubricated wear based upon the postulated growth of thin film oxides by a logarithmic rate law. The importance of sliding geometry and environment to the dominant wear mechanism has been illustrated.

The role of oxidation in the protection of sliding metal surfaces

This study is concerned with the mechanisms of growth and wear of protective oxide films formed under various tribological conditions. In the study three different tribological systems are examined in each of which oxidational wear is the dominant equilibrium mode. These are an unlubricated steel on steel system sliding at low and elevated temperatures, a boundary lubricated aluminium bronze on steel system and an unlubricated reciprocating sliding 9% Cr steel system operated at elevated temperature, in an atmosphere of carbon dioxide. The results of mechanical measurements of wear and friction are presented for a range of conditions of load, speed and temper.ature for the systems, together with the results of extensive examinations of the surfaces and sub­ surfaces by various physical methods of analysis. The major part of the thesis, however, is devoted to the development and application of surface models and theoretical quantative expressions in order to explain the observed oxidational wear phenomena. In this work, the mechanisms of formation of load bearing ox ide plateaux are described and are found to be dependent on system geometry and environment. The relative importance of ''in contact" and "out of contact" oxidation is identified together with growth rate constants appropriate to the two situations. Hypotheses are presented to explain the mechanisms of removal of plateaux to form wear debris. The latter hypotheses include the effects of cyclic stressing and dislocation accumulation, together with effects associated with the kinetics of growth and physical properties of the various oxides. The proposed surf ace mode1s have led to the develop­ ment of quantitative expressions for contact temperature, unlubricated wear rates, boundary lubricated wear rates and the wear of rna ter ial during the transition from severe to mild wear. In general theoretical predictions from these expressions are in very good agreement with experimental values.

Investigation of noise and vibration within an oil flooded sliding vane rotary air compressor

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Non-periodic quasi-stable nonlinear optical carrier pulses with sliding chirp-free points for transmission at 40 Gbit/s rate

In this paper, we demonstrate the possibility of reaching a quasi-stable nonlinear transmission regime with carrier pulses of 12.5 ps width in multi-channel 40 Gbit/s systems. The quasi-stable pulses that are presented in this work for the first time are not dispersion-managed solitons, and are indeed supported by a large normal span average dispersion and misbalanced optical amplification, and representing a new type of nonlinear carrier.

Conjunctival UV autofluorescence - prevalence and risk factors

Purpose: Autofluorescence of ultraviolet (UV) light has been shown to occur in localised areas of the bulbar conjunctiva, which map to active cellular changes due to UV and environmental exposure. This study examined the presence of conjunctival UV autofluorescence in eye care practitioners (ECPs) across Europe and the Middle East and its associated risk factors. Method: Images were captured of 307 ECPs right eyes in the Czech Republic, Germany, Greece, Kuwait, Netherlands, Sweden, Switzerland, United Arab Emirates and the United Kingdom using a Nikon D100 camera and dual flash units through UV filters. UV autofluorescence was outlined using ImageJ software and the nasal and temporal area quantified. Subjects were required to complete a questionnaire on their demographics and lifestyle including general exposure to UV and refractive correction. Results: Average age of the subjects was 38.5±12.2 years (range 19-68) and 39.7% were male. Sixty-two percent of eyes had some conjunctival damage as indicated by UV autofluorescence. The average area of damage was higher (p=0.005) nasally (2.95±4.52mm2) than temporally (2.19±4.17mm2). The area of UV damage was not related to age (r=0.03, p=0.674), gender (p=0.194), self-reported sun exposure lifestyle (p>0.05), geographical location (p=0174), sunglasses use (p>0.05) or UV-blocking contact lens use (p>0.05), although it was higher in those wearing contact lenses with minimal UV-blocking and no spectacles (p=0.015). The area of UV damage was also less nasally in those who wore contact lenses and spectacles compared to those with no refractive correction use (p=0.011 nasal; p=0.958 temporal). Conclusion: UV conjunctival damage is common even in Europe, Kuwait and UAE, and among ECPs. The area of damage appears to be linked with the use of refractive correction, with greater damage nasally than temporally which may be explained by the peripheral light focusing effect.