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.

Enterotoxigenic Escherichia coli infection of pigs: expression, extraction, purification and the adhesive properties of the K88 fimbrial adhesin

The ability of Escherichia coli to express the K88 fimbrial adhesin was satisfactorily indicated by the combined techniques of ELISA, haemagglutination and latex agglutination. Detection of expression by electron microscopy and the ability to metabolize raffinose were unsuitable. Quantitative expression of the K88 adhesin was determined by ELISA. Expression was found to vary according to the E.coli strain examined, media type and form. In general it was found that the total amount was greater, while the amount/cfu was less on agar than in broth cultures. Expression of the K88 adhesin during unshaken batch culture was related to the growth rate and was maximal during late logarithmic to early stationary phase. A combination of heat extraction, ammonium sulphate and isoelectric precipitation was found suitable for both large and small scale preparation of purified K88ab adhesin. Extraction of the K88 adhesin was sensitive to pH and it was postulated that this may affect the site of colonisation of by ETEC in vivo. Results of haemagglutination experiments were consistent with the hypothesis that the K88 receptor present on erythrocytes is composed of two elements, one responsible for the binding of K88ab and K88ac and a second responsible for the binding of the K88ad adhesin. Comparison of the haemagglutinating properties of cell-free and cell-bound K88 adhesin revealed some differences probably indicating a minor conformational change in the K88 adhesin on its isolation. The K88ab adhesin was found to bind to erythrocytes over a wide pH range (PH 4-9) and was inhibited by αK88ab and αK88b antisera. Inhibition of haemagglutination was noted with crude heparin, mannan and porcine gastric mucin, chondrosine and several hexosamines, glucosamine in particular. The most potent inhibitor of haemagglutination was n-dodecyl-β-D-glucopyranoside, one of a series of glucosides found to have inhibitory properties. Correlation between hydrophobicity of glucosides tested and degree of inhibition observed suggested hydrophobic forces were important in the interaction of the K88 adhesin with its receptor. The results of Scatchard and Hill plots indicated that binding of the K88ab adhesin to porcine enterocytes in the majority of cases is a two-step, three component system. The first K88 receptor (or site) had a K2. of 1.59x1014M-1 and a minimum of 4.3x104 sites/enterocyte. The second receptor (or site) had a K2 of 4.2x1012M-1 with a calculated 1.75x105 sites/enterocyte. Attempts to inhibit binding of cell-free K88 adhesin to porcine enterocytes by lectins were unsuccessful. However, several carbohydrates including trehalose, lactulose, galactose 1→4 mannopyranoside, chondrosine, galactosamine, stachyose and mannan were inhibitory. The most potent inhibitor was found to be porcine gastric mucin. Inhibition observed with n-octyl-α-D-glucopyranose was difficult to interpret in isolation because of interference with the assay, however, it agreed with the results of haemagglutination inhibition experiments.

Adhesive bonding of aluminium

Adhesive bonding of aluminium is widely used in the aerospace industry. High initial bood strengths can be obtained, but bond failure occurs atter prolonged exposure to humid enviroments. The thesis contains details ot a test procedure which has been designed and developed for the assessment of different alloys, pretreatments, and adhesives, which will give adhesively bonded aluminium joints of high strength coupled with long term durability. The test involves assembly of lap shear specimens in a precision jig using 250 ballotini spacers in the adhesive to control the bond line thickness. The test is modified by drilling three accurately located holes through the bonded area after assembly of the joint and curing of the adhesive. Further important features at the test, such as fillet control, are detailed. The test was assessed, modified and developed to give a reliable and reproducible method which would discriminate amongst different bonding systems after exposure to humid test environments. This is the first test to have achieved the discrimination necessary for short term assessment of bond systems where long term durability is required. Even better discrimination has been obtained by applying stress in a stress humidity test. Having established accurate, reliable and discriminating test methods they were used to study the durability of structural epoxy adhesive bonds to aluminium as a function of alloy, pretreatment, adhesive and environment. It was established that the long term durability or adhesively bonded aluminium was directly related to the infulence of water migrating within the adhesive. Pretreatments differed in their ability to prevent hydration of the aluminium oxide by the water absorbed within the adhesive.

Skin adhesive hydrogels for the topical delivery of active agents

This thesis illustrates the development of tailor-made, partially hydrated skin adhesive hydrogels as a vehicle for the topical delivery of moisturising agents. Maintaining an optimum hydration level of the stratum corneum ensures that the barrier properties of the skin are preserved. An unsaturated ionic monomer 2-acrylamido-2-methylpropanesulfonic acid sodium salt, glycerol, water, a photoinitiator Irgacure 184 and crosslinker Ebacryl II facilitated the production of monophasic sheet skin adhesives using photopolymerisation. The exploration and modification of the hydrogel components coupled with their influence on the adhesive and dynamic mechanical behaviour led to the development of novel monophasic and biphasic hydrogels. Biphasic pregels comprising of a hydrophobic monomer (epoxidised soybean oil acrylate, lauryl acrylate or stearyl acrylate) micellised with a non ionic surfactant Tween 60 allowed a homogeneous distribution throughout a predominantly hydrophilic phase (2-acrylamido-2-methylpropanesulfonic acid sodium salt, 4-acryloylmorpholine, glycerol and water). Further development of biphasic hydrogel technology led to the incorporation of preformed commercial O/W emulsions (Acronal, Flexbond 150, DM137 or Texicryl 13056WB) allowing the hydrophobic component to be added without prior stabilisation. The topical release of moisturising agents 2-pyrrolidone-5-carboxylic acid, lactobionic acid and d-calcium pantothenate results in the deposition onto the skin by an initial burst mechanism. The hydration level of the stratum corneum was measured using a Comeometer CM 825, Skin Reader MY810 or FT-ATR. The use of hydrophilic actives in conjunction with lipophilic agents for example Vitamin E or Jojoba oil provided an occlusive barrier, which reduced the rate of transepidermal water loss. The partition coefficients of the release agents provided invaluable information which enabled the appropriate gel technology to be selected. In summary the synthetic studies led to the understanding and generation of transferable technology. This enabled the synthesis of novel vehicles allowing an array of actives with a range of solubilities to be incorporated.

Adhesive wear of modern and traditional engineering coatings

DUE TO COPYRIGHT RESTRICTIONS ONLY AVAILABLE FOR CONSULTATION AT ASTON UNIVERSITY LIBRARY AND INFORMATION SERVICES WITH PRIOR ARRANGEMENT

A bio-adhesive formulation for the delivery of anti-fungal agents to the oesophagus

DUE TO COPYRIGHT RESTRICTIONS ONLY AVAILABLE FOR CONSULTATION AT ASTON UNIVERSITY LIBRARY AND INFORMATION SERVICES WITH PRIOR ARRANGEMENT

1.2-μm semiconductor disk laser frequency doubled with periodically poled lithium tantalate crystal

In this letter, we demonstrate an optically pumped semiconductor disk laser frequency doubled with a periodically poled lithium tantalate crystal. Crystals with various lengths were tested for intracavity frequency conversion. The semiconductor disk laser exploited GaInNAs-based active region with GaAsAlAs distributed Bragg mirror to produce emission at 1.2- μm wavelength. The frequency doubled power up to 760 mW at the wavelength of 610 nm was achieved with a 2-mm-long crystal. © 2010 IEEE.

Physical and biological properties of a novel siloxane adhesive for soft tissue applications

The aim of this study was to investigate the adhesive properties of an in-house amino-propyltrimethoxysilane-methylenebisacrylamide (APTMS-MBA) siloxane system and compare them with a commercially available adhesive, n-butyl cyanoacrylate (nBCA). The ability of the material to perform as a soft tissue adhesive was established by measuring the physical (bond strength, curing time) and biological (cytotoxicity) properties of the adhesives on cartilage. Complementary physical techniques, X-ray photoelectron spectroscopy, Raman and infrared imaging, enabled the mode of action of the adhesive to the cartilage surface to be determined. Adhesion strength to cartilage was measured using a simple butt joint test after storage in phosphate-buffered saline solution at 37°C for periods up to 1 month. The adhesives were also characterised using two in vitro biological techniques. A live/dead stain assay enabled a measure of the viability of chondrocytes attached to the two adhesives to be made. A water-soluble tetrazolium assay was carried out using two different cell types, human dermal fibroblasts and ovine meniscal chondrocytes, in order to measure material cytotoxicity as a function of both supernatant concentration and time. IR imaging of the surface of cartilage treated with APTMS-MBA siloxane adhesive indicated that the adhesive penetrated the tissue surface marginally compared to nBCA which showed a greater depth of penetration. The curing time and adhesion strength values for APTMS-MBA siloxane and nBCA adhesives were measured to be 60 s/0.23 MPa and 38 min/0.62 MPa, respectively. These materials were found to be significantly stronger than either commercially available fibrin (0.02 MPa) or gelatin resorcinol formaldehyde (GRF) adhesives (0.1 MPa) (P <0.01). Cell culture experiments revealed that APTMS-MBA siloxane adhesive induced 2% cell death compared to 95% for the nBCA adhesive, which extended to a depth of approximately 100-150 μm into the cartilage surface. The WST-1 assay demonstrated that APTMS-MBA siloxane was significantly less cytotoxic than nBCA adhesive as an undiluted conditioned supernatant (P <0.001). These results suggest that the APTMS-MBA siloxane may be a useful adhesive for medical applications. © VSP 2005.

High-power operation of quantum-dot semiconductor disk laser at 1180 nm

In this letter, we report on a high-power operation of an optically pumped quantum-dot semiconductor disk laser designed for emission at 1180 nm. As a consequence of the optimization of the operation conditions, a record-high continuous-wave output power exceeding 7 W is obtained for this wavelength at a heat-sink temperature of 2 °C. A wavelength tuning over a range of 37 nm is achieved using a birefringent filter inside the cavity.

Generation of 49-fs pulses directly from distributed Kerr-lens mode-locked Yb:YAG thin-disk oscillator

The concept of distributed Kerr-lens mode-locking and a thin-disk Yb:YAG oscillator based on this concept are presented. The described oscillator directly generates pulses with a duration of 49 fs and spectral width of 33 nm

Energy scaling of Kerr-lens mode-locked thin-disk oscillators

Geometric scaling of a Kerr-lens mode-locked Yb:YAG thin-disk oscillator yields femtosecond pulses with an average output power of 270 W. The scaled system delivers femtosecond (210-330 fs) pulses with a peak power of 38 MW. These values of average and peak power surpass the performance of any previously reported femtosecond laser oscillator operated in atmospheric air.