Analysis of stirred mill performance using DEM simulation: Part 1 - Media motion, energy consumption and collisional environment

Stirred mills are becoming increasingly used for fine and ultra-fine grinding. This technology is still poorly understood when used in the mineral processing context. This makes process optimisation of such devices problematic. 3D DEM simulations of the flow of grinding media in pilot scale tower mills and pin mills are carried out in order to investigate the relative performance of these stirred mills. Media flow patterns and energy absorption rates and distributions are analysed here. In the second part of this paper, coherent flow structures, equipment wear and mixing and transport efficiency are analysed. (C) 2006 Published by Elsevier Ltd.

Anodizing treatments for magnesium alloys and their effecton corrosion resistance in various environments

This paper reviews various aspects of anodizing of magnesium alloys, such as the basics, processes, properties and applications. It systematically summarises the existing fundamental studies and technical developments of anodizing of magnesium alloys, and concludes that new anodizing processes based on electrolytic plasma anodizing that convert the surface of a magnesium alloy into a hard ceramic coating in an electrolytic bath using high energy electric discharges can offer improved wear and corrosion resistance. These new anodized coatings are often claimed to perform better than the traditional ones obtained through older anodizing processes, such as DOW17 or HAE. The new anodizing techniques are chromate free and hence environment friendly. It is expected that more cost-effective, environment-friendly and non-toxic anodizing techniques will be developed and applied to magnesium alloy components in the future.

Objective clinical performance of ‘comfort-enhanced' daily disposable soft contact lenses

Purpose: To examine the objective clinical performance of ‘comfort-enhanced’ daily disposable contact lenses over a 16-h day. Methods: Four contact lenses (Hilafilcon B, Etafilcon A Plus, Nelfilcon A and Nelfilcon A Plus) were evaluated in an investigator masked, open label trial at the end of a week’s bilateral wear. Pre-lens noninvasive tear break-up time (PL-NITBUT), tear prism height, bulbar hyperaemia and ocular surface temperature (OST) were measured with the lens in situ at 8, 12 and 16 h of wear. Results: There was no difference between how many hours the lenses types were worn each day (F = 0.90, p = 0.44). The PL-NITBUT decreased with the duration of daily lens wear (F = 32.0, p < 0.001) and was more stable with Nelfilcon A Plus (F = 6.00, p = 0.002) than with the other lenses evaluated. Bulbar blood vessels increased in coverage (F = 11.5, p < 0.001) but not overall redness (F = 0.0, p = 0.99) with the duration of daily lens wear, but there was no difference between the lenses (p > 0.05). The tear prism height decreased with the duration of daily wear (F = 27.0, p < 0.001) and differed between lenses (F = 2.9, p = 0.04). The OST decreased with the duration of lens wear (F = 119.7, p < 0.001) and was reduced by daily disposable lens wear (F = 7.88, p < 0.001), but did not differ between lenses (F = 0.88, p = 0.45). Conclusions: Objective measures of tear film indicated a difference between the lenses evaluated for PLNITBUT and tear prism height, but not for wearing time or bulbar conjunctival hyperaemia. Therefore clinical benefits of daily disposable ‘comfort enhancing’ contact lenses can be measured, but challenges remain in producing contact lenses that do not compromise anterior eye physiology over the whole day. 2010 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.

Modelling tribology of slider and disk in a computer hard drive system

Issues of wear and tribology are increasingly important in computer hard drives as slider flying heights are becoming lower and disk protective coatings thinner to minimise spacing loss and allow higher areal density. Friction, stiction and wear between the slider and disk in a hard drive were studied using Accelerated Friction Test (AFT) apparatus. Contact Start Stop (CSS) and constant speed drag tests were performed using commercial rigid disks and two different air bearing slider types. Friction and stiction were captured during testing by a set of strain gauges. System parameters were varied to investigate their effect on tribology at the head/disk interface. Chosen parameters were disk spinning velocity, slider fly height, temperature, humidity and intercycle pause. The effect of different disk texturing methods was also studied. Models were proposed to explain the influence of these parameters on tribology. Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) were used to study head and disk topography at various test stages and to provide physical parameters to verify the models. X-ray Photoelectron Spectroscopy (XPS) was employed to identify surface composition and determine if any chemical changes had occurred as a result of testing. The parameters most likely to influence the interface were identified for both CSS and drag testing. Neural Network modelling was used to substantiate results. Topographical AFM scans of disk and slider were exported numerically to file and explored extensively. Techniques were developed which improved line and area analysis. A method for detecting surface contacts was also deduced, results supported and explained observed AFT behaviour. Finally surfaces were computer generated to simulate real disk scans, this allowed contact analysis of many types of surface to be performed. Conclusions were drawn about what disk characteristics most affected contacts and hence friction, stiction and wear.

Pole tip recession in linear tape systems

The tribology of linear tape storage system including Linear Tape Open (LTO) and Travan5 was investigated by combining X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES), Optical Microscopy and Atomic Force Microscopy (AFM) technologies. The purpose of this study was to understand the tribology mechanism of linear tape systems then projected recording densities may be achieved in future systems. Water vapour pressure or Normalized Water Content (NWC) rather than the Relative Humidity (RH) values (as are used almost universally in this field) determined the extent of PTR and stain (if produced) in linear heads. Approximately linear dependencies were found for saturated PTR increasing with normalized water content increasing over the range studied using the same tape. Fe Stain (if produced) preferentially formed on the head surfaces at the lower water contents. The stain formation mechanism had been identified. Adhesive bond formation is a chemical process that is governed by temperature. Thus the higher the contact pressure, the higher the contact temperature in the interface of head and tape, was produced higher the probability of adhesive bond formation and the greater the amount of transferred material (stain). Water molecules at the interface saturate the surface bonds and makes adhesive junctions less likely. Tape polymeric binder formulation also has a significant role in stain formation, with the latest generation binders producing less transfer of material. This is almost certainly due to higher cohesive bonds within the body of the magnetic layer. TiC in the two-phase ceramic tape-bearing surface (AlTiC) was found to oxidise to form TiO2.The oxidation rate of TiC increased with water content increasing. The oxide was less dense than the underlying carbide; hence the interface between TiO2 oxide and TiC was stressed. Removals of the oxide phase results in the formation of three-body abrasive particles that were swept across the tape head, and gave rise to three-body abrasive wear, particularly in the pole regions. Hence, PTR and subsequent which signal loss and error growth. The lower contact pressure of the LTO system comparing with the Travan5 system ensures that fewer and smaller three-body abrasive particles were swept across the poles and insulator regions. Hence, lower contact pressure, as well as reducing stain in the same time significantly reduces PTR in the LTO system.

Effect of a liposomal spray on the pre-ocular tear film

Purpose: With the potential to address evaporative dry eye, a novel spray has been developed in which phospholipid liposomes are delivered to the tear film via the surface of the closed eyelid. This study evaluated the short-term effects of liposomal spray application on the lipid and stability characteristics of the pre-ocular tear film in normal eyes. Methods: Twenty-two subjects (12M, 10F) aged 35.1 ± 7.1 years participated in this prospective, randomised, double-masked investigation in which the liposomal spray was applied to one eye, and an equal volume of saline spray (control) applied to the contralateral eye. Lipid layer grade (LLG), non-invasive tear film stability (NIBUT) and tear meniscus height (TMH) were evaluated at baseline, and at 30, 60, 90 and 135 minutes post-application. Subjective reports of comfort were also compared. Results: Treated and control eyes were not significantly different at baseline (p>0.05). Post-application, LLG increased significantly, at 30 and 60 minutes, only in the treated eyes (p=0.005). NIBUT also increased significantly in the treated eyes only (p<0.001), at 30, 60 and 90 minutes. TMH did not alter significantly (p>0.05). Comfort improved relative to baseline in 46% of treated and 18% of control eyes, respectively, at 30 minutes post-application. Of those expressing a preference in comfort between the eyes, 68% preferred the liposomal spray. Conclusions: Consistent with subjective reports of improved comfort, statistically and clinically significant improvements in lipid layer thickness and tear film stability are observed in normal eyes for at least an hour after a single application of a phospholipid liposomal spray.

The effects of metallurgical variables on the mechanical properties of high-chromium cast irons

The.use of high-chromium cast irons for abrasive wear resistance is restricted due to their poor fracture toughness properties. An.attempt was made to improve the fracture characteristics by altering the distribution, size and.shape of the eutectic carbide phase without sacrificing their excellent wear resistance. This was achieved by additions of molybdenum or tungsten followed by high temperature heat treatments. The absence of these alloying elements or replacement of them with vanadium or manganese did not show any significant effect and the continuous eutectic carbide morphology remained the same after application of high temperature heat treatments. The fracture characteristics of the alloys with these metallurgical variables were evaluated for both sharp-cracks and blunt notches. The results were used in conjunction with metallographic and fractographic observations to establish possible failure mechanisms. The fracture mechanism of the austenitic alloys was found to be controlled not only by the volume percent but was also greatly influenced by the size and distribution of the eutectic carbides. On the other hand, the fracture mechanism of martensitic alloys was independent of the eutectic carbide morphology. The uniformity of the secondary carbide precipitation during hardening heat treatments was shown to be a reason for consistant fracture toughness results being obtained with this series of alloys although their eutectic carbide morphologies were different. The collected data were applied to a model which incorporated the microstructural parameters and correlated them with the experimentally obtained valid stress intensity factors. The stress intensity coefficients of different short-bar fracture toughness test specimens were evaluated from analytical and experimental compliance studies. The.validity and applicability of this non-standard testing technique for determination of the fracture toughness of high-chromium cast irons were investigated. The results obtained correlated well with the valid results obtained from standard fracture toughness tests.

Do ‘passive’ medical titanium surfaces deteriorate in service in the absence of wear?

Globally, more than 1000 tonnes of titanium (Ti) is implanted into patients in the form of biomedical devices on an annual basis. Ti is perceived to be ‘biocompatible’ owing to the presence of a robust passive oxide film (approx. 4 nm thick) at the metal surface. However, surface deterioration can lead to the release of Ti ions, and particles can arise as the result of wear and/or corrosion processes. This surface deterioration can result in peri-implant inflammation, leading to the premature loss of the implanted device or the requirement for surgical revision. Soft tissues surrounding commercially pure cranial anchorage devices (bone-anchored hearing aid) were investigated using synchrotron X-ray micro-fluorescence spectroscopy and X-ray absorption near edge structure. Here, we present the first experimental evidence that minimal load-bearing Ti implants, which are not subjected to macroscopic wear processes, can release Ti debris into the surrounding soft tissue. As such debris has been shown to be pro-inflammatory, we propose that such distributions of Ti are likely to effect to the service life of the device.

Predicting success with silicone-hydrogel contact lenses in new wearers

Purpose: to evaluate changes in tear metrics and ocular signs induced by six months of silicone-hydrogel contact lens wear and the difference in baseline characteristics between those who successfully continued in contact lens wear compared to those that did not. Methods: Non-invasive Keratograph, Tearscope and fluorescein tear break-up times (TBUTs), tear meniscus height, bulbar and limbal hyperaemia, lid-parallel conjunctival folds (LIPCOF), phenol red thread, fluorescein and lissamine-green staining, and lid wiper epitheliopathy were measured on 60 new contact lens wearers fitted with monthly silicone-hydrogels (average age 36 ± 14 years, 40 females). Symptoms were evaluated by the Ocular Surface Disease Index (OSDI). After six months full time contact lens wear the above metrics were re-measured on those patients still in contact lens wear (n= 33). The initial measurements were also compared between the group still wearing lenses after six months and those who had ceased lens wear (n= 27). Results: There were significant changes in tear meniscus height (p= 0.031), bulbar hyperaemia (p= 0.011), fluorescein TBUT (p= 0.027), corneal (p= 0.007) and conjunctival (p= 0.009) staining, LIPCOF (p= 0.011) and lid wiper epitheliopathy (p= 0.002) after six months of silicone-hydrogel wear. Successful wearers had a higher non-invasive (17.0 ± 8.2. s vs 12.0 ± 5.6. s; p= 0.001) and fluorescein (10.7 ± 6.4. s vs 7.5 ± 4.7. s; p= 0.001) TBUT than drop-outs, although OSDI (cut-off 4.2) was also a strong predictor of success. Conclusion: Silicone-hydrogel lenses induced significant changes in the tear film and ocular surface as well as lid margin staining. Wettability of the ocular surface is the main factor affecting contact lens drop-out. © 2013 British Contact Lens Association.

Clinical performance of daily disposable soft contact lenses using sustained release technology

Purpose: Polyvinyl alcohol (PVA) is a successful tear film stabiliser and is widely used in comfort drops and some soft contact lens materials. A PVA-containing lens, nelfilcon A has been modified to include additional (non-functional) PVA in order to provide improved comfort. This study aims to examine the clinical performance of this nelfilcon A lens with AquaRelease™ (AquaRelease). Methods: Two contralateral, investigator masked, open label, subjective and objective evaluations were conducted. The first examined the effect of adding increased molecular weight PVA to nelfilcon A (n = 5), and the second compared this AquaRelease lens to ocufilcon B (n = 34). The principal measures were non-invasive break-up time (NIBUT) and subjective comfort, which were assessed at the beginning and end of a week of daily wear, and three times throughout 1 day at 8, 12 and 16 h. Results: All subjects successfully completed the daily wearing schedule of 16 h. On initial insertion, subjective comfort and NIBUT improved for AquaRelease than original nelfilcon A lenses (p < 0.05). Initial comfort was better for AquaRelease compared to ocufilcon B lenses (p = 0.01); however, NIBUT was not statistically different (11.7 ± 15.6 s versus 8.4 ± 6.8 s; p = 0.26). Subjective comfort decreased with time (p < 0.001), but there was no significant difference between AquaRelease and ocufilcon B lenses (p = 0.16). NIBUT was not significantly affected by time (p = 0.56) or between lenses (p = 0.33). At the end of a weeks' wear, subjective initial, end-of-day, overall comfort and vision were rated significantly better with AquaRelease than ocufilcon B (p < 0.01). Conclusions: Release of additional non-functionalised PVA from the nelfilcon A lenses appears to enhance comfortable contact lens wear. © 2006 British Contact Lens Association.

Refractive and biometric changes with silicone hydrogel contact lenses

Purpose. This study reports data from an 18-month longitudinal study of neophyte contact lens wearers and compares changes in ocular refraction and biometry induced by daily wear and continuous wear of two different silicone hydrogel (SiH) materials. Methods. Forty-five subjects were enrolled in the study and randomly assigned to wear one of the two silicone hydrogel materials: Lotrafilcon A or Balafilcon A lenses on either a daily or continuous wear basis. Measurements of objective refraction, axial length, anterior chamber depth, corneal curvature, and the rate of peripheral corneal flattening were performed before and 1, 3, 6, 12, and 18 months after initial fitting. Results. Mean spherical equivalent refractive error increased in the myopic direction in all contact lens groups across time (p < 0.001). Axial length was the main biometric contributor to the development of myopia. After 18 months of lens wear, subjects in the Lotrafilcon A group showed the greater mean increase in myopia (i.e., -0.50 D). Conclusions. The results of this study show that increases in myopia, similar if not higher than those found to occur normally in young adult noncontact lens wearers, still occur with silicone hydrogel contact lens wear. The main biometric contributor to the progression of myopia was an increase in axial length. Differences between our results and those of previous studies with silicone hydrogel contact lenses could be attributed to the differing populations used in which both age and occupation may have played a role. Copyright © 2005 American Academy of Optometry.

The effect of contact lens wear on dynamic ocular surface temperature

Aim: To determine the dynamic emitted temperature changes of the anterior eye during and immediately after wearing different materials and modalities of soft contact lenses. Method: A dynamic, non-contact infrared camera (Thermo-Tracer TH7102MX, NEC San-ei) was used to record the ocular surface temperature (OST) in 48 subjects (mean age 21.7 ± 1.9 years) wearing: lotrafilcon-A contact lenses on a daily wear (LDW; n = 8) or continuous wear (LCW; n = 8) basis; balafilcon-A contact lenses on a daily wear (BDW; n = 8) or continuous wear (BCW; n = 8) basis; etafilcon-A contact lenses on a daily disposable regimen (EDW; n = 8); and no lenses (controls; n = 8). OST was measured continuously five times, for 8 s after a blink, following a minimum of 2 h wear and immediately following lens removal. Absolute temperature, changes in temperature post-blink and the dynamics of temperature changes were calculated. Results: OST immediately following contact lens wear was significantly greater compared to non-lens wearers (37.1 ± 1.7 °C versus 35.0 ± 1.1 °C; p < 0.005), predominantly in the LCW group (38.6 ± 1.0 °C; p < 0.0001). Lens surface temperature was highly correlated (r = 0.97) to, but lower than OST (by -0.62 ± 0.3 °C). There was no difference with modality of wear (DW 37.5 ± 1.6 °C versus CW 37.8 ± 1.9 °C; p = 0.63), but significant differences were found between etafilcon A and silicone hydrogel lens materials (35.3 ± 1.1 °C versus 37.5 ± 1.5 °C; p < 0.0005). Ocular surface cooling following a blink was not significantly affected by contact lens wear with (p = 0.07) or without (p = 0.47) lenses in situ. Conclusions: Ocular surface temperature is greater with hydrogel and greater still with silicone hydrogel contact lenses in situ, regardless of modality of wear. The effect is likely to be due to the thermal transmission properties of a contact lens. © 2004 British Contact Lens Association. Published by Elsevier Ltd. All rights reserved.

The detection of kinin activity in contact lens wear

Many factors can be, and have been, attributed to the appearance of complications in lens wear, but the greatest is associated with deposition. Reduced acuity, irritation and inflammatory responses are often referred to as adverse reactions arising as a result of deposition. In this study, particular attention was paid to the potential role of adsorbed proteins in activating, mediating and/or stimulating a host immune response, i.e., the hypothesis that the adsorption of certain proteins from the tears and ocular surfaces may actively affect successful lens wear. In particular, the purpose of this study was to investigate the presence of a group of proteins previously undiscovered in the ocular environment. The intention was to target a family of proteins/glycoproteins that have become prominent recently in a variety of inflammatory responses and disorders at many other mucosal associated sites around the body, e.g. in nasal rhinitis and in joint inflammation. The protein cascade in question is the kinin family of inflammatory mediators. The aim was to investigate their presence in the ocular environment, specifically in relation to contact lens wear, and consequently assess the implications of their discovery. High molecular weight kininogen (HMWK), with its central role in kinin responses, was investigated initially as the marker of kinin activity, with subsequent members examined thereafter.

The influence on unaided vision of age, pupil diameter and spherocylindrical refractive error

Background - The aim was to derive equations for the relationship between unaided vision and age, pupil diameter, iris colour and sphero-cylindrical refractive error. Methods - Data were collected from 663 healthy right eyes of white subjects aged 20 to 70 years. Subjective sphero-cylindrical refractive errors ranged from -6.8 to +9.4 D (mean spherical equivalent), -1.5 to +1.9 D (orthogonal component, J0) and -0.8 to 1.0 D (oblique component, J45). Cylinder axis orientation was orthogonal in 46 per cent of the eyes and oblique in 18 per cent. Unaided vision (-0.3 to +1.3 logMAR), pupil diameter (2.3 to 7.5 mm) and iris colour (67 per cent light/blue irides) was recorded. The sample included mostly females (60 per cent) and many contact lens wearers (42 per cent) and so the influences of these parameters were also investigated. Results - Decision tree analysis showed that sex, iris colour, contact lens wear and cylinder axis orientation did not influence the relationship between unaided vision and refractive error. New equations for the dependence of the minimum angle of resolution on age and pupil diameter arose from step backwards multiple linear regressions carried out separately on the myopes (2.91.scalar vector +0.51.pupil diameter -3.14 ) and hyperopes (1.55.scalar vector + 0.06.age – 3.45 ). Conclusion - The new equations may be useful in simulators designed for teaching purposes as they accounted for 81 per cent (for myopes) and 53 per cent (for hyperopes) of the variance in measured data. In comparison, previously published equations accounted for not more than 76 per cent (for myopes) and 24 per cent (for hyperopes) of the variance depending on whether they included pupil size. The new equations are, as far as is known to the authors, the first to include age. The age-related decline in accommodation is reflected in the equation for hyperopes.

How should initial fit inform soft contact lens prescribing

Purpose: To investigate how initial HEMA and silicone-hydrogel (SiHy) contact lens fit on insertion, which informs prescribing decisions, reflect end of day fit. Methods: Thirty participants (aged 22.9. ±. 4.9 years) were fitted contralaterally with HEMA and SiHy contact lenses. Corneal topography and tear break-up time were assessed pre-lens wear. Centration, lag, post-blink movement during up-gaze and push-up recovery speed were recorded after 5,10,20. min and 8. h of contact lens wear by a digital slit-lamp biomicroscope camera, along with reported comfort. Lens fit metrics were analysed using bespoke software. Results: Comfort and centration were similar with the HEMA and SiHy lenses (p > 0.05), but comfort decreased with time (p <. 0.01) whereas centration remained stable (F = 0.036, p = 0.991). Movement-on-blink and lag were greater with the HEMA than the SiHy lens (p <. 0.01), but movement-on-blink decreased with time after insertion (F = 22.423, p <. 0.001) whereas lag remained stable (F = 1.967, p = 0.129). Push-up recovery speed was similar with the HEMA and the SiHy lens 5-20. min after insertion (p > 0.05), but was slower with SiHy after 8. h wear (p = 0.016). Lens movement on blink and push-up recovery speed was predictive of the movement after 8. h of wear after 10-20. min SiHy wear, but after 5 to 20. min of HEMA lens wear. Conclusions: A HEMA or SiHy contact lens with poor movement on blink/push-up after at least 10. min after insertion should be rejected.