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The role of immune-relevant genes involved in disease biology as well as innate and adaptive immunity is at the centre stage while exploring the genetic basis of disease occurrence. The macrophage expressed lysozyme gene product contributes to innate immunity by cleaving the ß- 1,4 linkage of bacterial peptidoglycan in phagocytosis. Higher specific activity observed in bubaline milk/ serum lysozymes over their bovine counterparts is expected to contribute higher resistances to diseases in general and mastitis in particular. To explore the reasons for higher activity in terms of sequence variations, macrophage expressed lysozyme cDNA was synthesized, cloned and sequenced. The 593 bp mRNA sequence revealed a 444 bp (27nt to 470nt) ORF bearing usual start codon ATG and end codon TAA with GC content of 46 % coding for precursor polypeptide of 147 amino acids. The comparative sequence analysis of cattle and buffalo revealed the difference at 10 places leading to 3 non-synonymous (5th, 116th and 142th) substitutions which did not affect the predicted 3D structure. The mLYS polypeptide had signal sequence (1st to 18th residue) and the mature peptide had two lysozyme catalytic sites, three Ca++ binding sites as well as eleven catalytic clefts prominent among the conserved domains. Secondly, bubaline mLYS was phylogenetically closer to the abomasum type than mammary gland type. The high similarity in the coding sequences and predicted structure suggested that bubaline lysozyme gene if hyper-expressed either in native or recombinant form in bovine udder may result in better udder health. [ABSTRACT FROM AUTHOR]

The article discusses the effects of various weaning methods on the behaviour and blood profile of kids. The kids were grouped in three, group 1 traditional weaning at three months, group 2 partial weaning from 30th day during daytime with visual contact with dam and group 3 early weaning at two months. The study showed no abnormal behaviour in any of the weaning methods while blood cortisol levels decreased in G1 and G3 and marginally increased in G2 after weaning.

Abstract: Gypsum is an authigenic precipitate that forms under periods of accentuated aridity and occurs widely in arid zones. However its use in quantitative paleoclimatology has been limited due to the absence of a method to determine the timing of its formation. We present here the results of a feasibility study that demonstrates that the timing of the formation event of gypsum can be estimated using Electron Spin Resonance (ESR) analysis. We used well documented samples from White Sands in New Mexico, USA, the Thar Desert, India and lakes in the Simpson Desert and Mallee Region, Australia and found that ESR ages could be obtained using radiation sensitive SO4 −, SO3 − radicals and a photobleachable signal O3 −. ESR signals were consistent with control ages based on contextual information. These suggest that the dating signals (SO4 −, SO3 −) are stable over time scales >100 ka. We propose that this stability of the SO4 − signals over geological time scales arises due to hydrogen bonding between the water proton and the SO4 − radical and that the suitability of these radiation-induced radicals comes from their being a part of the host matrix. Further, ESR along with Fourier Transform Infrared (FT-IR) Spectroscopy methods additionally inform on the geochemical pathways for gypsum formation and help elucidate complex formation processes even in samples that appeared unambiguous gypsum precipitates. Thus, the presence of Hannebachite (CaSO3.½H2O) and Mn2+ in Thar and Australian samples suggested a reducing environment such that low valence sulfur reacted with CaCO3 to form hannebachite and eventually gypsum. The presence of sulfur, partially as sulfite in Thar gypsum samples suggested that redox cycles were mediated by microbial activity. Absence of these features in White Sands samples suggested oxic conditions during gypsum precipitation. [Copyright &y& Elsevier]

Abstract: Objective: To evaluate the effect of sodium fluoride (NaF) on cytochemical distribution of proteins, DNA, and RNA in the gastrocnemius muscle of rat in experimental fluorosis. Methods: Young Sprague Dawley albino rats were administered with NaF at 30, 45, and 75 mg/kg bw/day subcutaneously for 15 and 30 days, respectively. The control animals were given the vehicle (1cc deionized double distilled water/kg bw/day). Results: In the first phase of 15 days experimentation, the gastrocnemius muscle of rats intoxicated with NaF at 30, 45, and 75 mg/kg bw/day showed decline in proteins including α amino acids as compared to control. In the second phase of 30 days experimentation, the muscle fibers of rat showed elevation in sarcolemmal and sarcoplasmic proteins in 30 mg NaF dose group, and angulated fibers exhibited increase in sarcolemmal proteins in 45 mg NaF group. The marginal regions of angular and rim fibers showed deeply stained rings of sarcoplasmic proteins whereas the split fibers were faintly stained in rats treated with NaF at 75 mg/kg bw/day for 30 days. In rats treated with NaF at 30 mg/kg bw/day for 15 days, the hypertrophied peripheral muscle fibers contained more DNA, however the atrophied fibers had more RNA. In 45 mg NaF group, RNA was located in sarcolemmal regions, while DNA content decreased as compared to control. In 75 mg NaF group, the muscle fibers had dark and light staining regions of DNA and RNA. In the 30 days of experimentation, the DNA level decreased whereas RNA content increased in the gastrocnemius muscle fibers of the rat treated with NaF at 30 mg/kg bw/day. In treatment group with NaF at 45 mg/kg bw/day, the RNA content slightly declined in comparison to control, in all treatments for 15 days as well as in treatment group with NaF at 30 mg/kg bw/day for 30 days whereas the amount of DNA slightly increased as compared to treatment group with NaF at 75 mg/kg bw/day for 15 days. The highest dose group revealed elevated amount of RNA whereas DNA content remained stable. Conclusions: The findings of present study demonstrate that certain concentrations of fluoride can induce muscle lesions and damage DNA, RNA, and protein in muscle cells and excessive intake and accumulation of fluoride is therefore a serious risk factor for muscular abnormalities in fluorosis. [Copyright &y& Elsevier]

The article discusses findings of a study on genetic polymorphism mLYS gene and its effect on activity of serum lysozyme, citing use of different buffalo breeds in the study, and mentions that that the polymorphism can be used to selection of animals against mastitis.

The ever increasing demand for greater storage capacity is prompting the development of thinner data storage tapes. As tapes are made thinner than ever, it brings magnetic and physical durability into question. Today's tapes are approximately 9.0 μm thick with next generation tapes being 7.0 μm thick and thinner tapes are in development. These thinner tapes damage more easily, especially near the edges, creating problems as debris from damaged areas finds its way into the head to tape interface. The objective of the current study is to determine the effects a thinner substrate has on a tape's magnetic and tribological performance. Root-mean-square head output and dropouts were monitored to provide a metric of magnetic performance, whereas lateral tape motion was monitored using a dual edge probe methodology to monitor the tracking quality. Coefficient of friction was monitored to gauge the tribological performance. Changes in tape edge quality were quantified using optical microscopy as a measure of physical durability. Thinner tapes have less lateral tape motion, a higher coefficient of friction, and a greater tendency to produce debris. Although thinner tapes are not better in every way, the transition to thinner tape presents no formidable challenges. [ABSTRACT FROM AUTHOR]

Improving the performance of computer tape drives is an ongoing process. The magnetic and tribological performance of metal particle (MP) tape during head stepping was evaluated in a commercial linear tape drive. Head output and head-tape interface friction were monitored during short-pass (10 m) shuttling tests with stepping of the head. The test without stepping showed no signs of failure. To evaluate the effect of stepping on the head-tape interface, three different kinds of stepping test, namely normal stepping, reverse stepping and normal stepping with inverted drive, were performed. All these tests with head stepping failed far sooner than the test without stepping. Nonparallelism between the head and tape surfaces caused a reduction in hydrodynamic air bearing pressure. Less spacing between the lower tape edge and the head resulted in high wear of the lower edge of the tape and outer outrigger surfaces of the head. Additional sliding in a direction orthogonal to the tape motion from head stepping aggravated the friction and wear of the lower tape edge. The inability of the drive to overcome this high friction ultimately resulted in failure. On the head surface, different kinds of debris were found, and unsymmetrical debris distribution was observed. Some manufacturing improvements are presented to prolong drive durability. [ABSTRACT FROM AUTHOR]

The effect of the operating environment on the failure mechanism of a head-tape interface in a linear tape drive with a belt-driven cartridge was studied. A modified commercial drive with magnetoresistive head and metal particle tape were used. Durability tests for the full tape length were performed at ambient and extreme environmental conditions. Head output, coefficient of friction and number of dropouts per minute were measured during the test. Optical and atomic force microscopy and Auger electron spectroscopy were used to evaluate changes at the head-tape interface at the end of the tests. Magnetic and tribological performance of head-tape interface is the best at low temperatures and low relative humidities. Increases in both temperature and relative humidity result in performance degradation, with the worst performance at the highest temperature. At ambient conditions, sporadic variations in the coefficient of friction and the number of dropouts per minute are observed, associated with a cycle of stain formation and removal. Possible mechanisms responsible for the observed tribological behaviour of the interface at various environmental conditions are discussed. [ABSTRACT FROM AUTHOR]

The decomposition mechanisms of the perfluoropolyether (PFPE) lubricants have been studied through calculation of chemical reaction kinetics and several experimental approaches. Four degradation mechanisms were considered: thermal and catalytic decomposition, triboelectrical decomposition and mechanical scission. The results show that the effect of catalytic reaction on the degradation of the PFPE lubricants is negligible in sliding conditions because of the short contact time, small contact area and low interface temperature. Illumination with ultraviolet light is found to accelerate the decomposition of the lubricant, reducing the head-disk interface durability and causing more gaseous fragments because low-energy electrons created by the illumination interact with the lubricant molecules, activating and breaking up the molecules. A decomposition mechanism of the lubricant from the effect of low-energy electrons is proposed. Mechanical shear is also found to have an important effect on the decomposition of the lubricant. The partial pressures of the gaseous fragments of the lubricant increase rapidly with increase in the sliding velocity. The temperature from ambient up to 70 °C has no obvious effect on the decomposition of the PFPE lubricant, although higher temperatures are expected to be detrimental. Dominant degradation mechanisms in the sliding conditions are triboelectrical reaction and mechanical scission. [ABSTRACT FROM AUTHOR]

Improving the performance of computer tape drives is an ongoing process that has recently involved the utilization of metal-evaporated (ME) tapes. The magnetic and tribological performance of the current metal particle (MP) tape and a new dual-magnetic-layer ME tape were evaluated in a Quantum DLT 4000 linear tape drive. Head output, drop-outs and head-tape interface friction were monitored during high-tension (1.7 N) high-speed (4 m/s) short-pass (10 m) shuttling tests without stepping the head. The severe MP test never showed signs of failure, but wear of the head's outriggers is believed to impact the stability of the head output signal. MP tape significantly outperformed ME tape; ME even performed poorly at nominal tension (0.8 N) and speed (2.5 m/s) conditions. ME tape lubricant was stripped away by corners on the DLT head, resulting in increased friction, wear and exposure of the relatively brittle diamond-like carbon layer. A high-tension high-speed MP test with head stepping was also performed to evaluate the effect of stepping; it failed far sooner than the non-step MP test. The nominal ME test and severe MP head step test are both believed to have failed because of the drive's inability to overcome high (wear-induced) static friction experienced during changes in tape direction. Modifications to the existing head or a new head design could improve the performance of ME tape in the DLT 4000 linear tape drive. [ABSTRACT FROM AUTHOR]

Silicon-based microelectromechanical system (MEMS) devices are made from single-crystal silicon, polycrystalline silicon (polysilicon) films obtained by low-pressure chemical vapour deposition and certain ceramic films. For high-temperature applications, SiC films are being developed to replace polysilicon films. Tribology in the MEMS devices requiring relative motion is of importance. Atomic force microscopy/friction force microscopy (AFM/FFM) and nanoindentation techniques have been used for tribological studies on a microscale to nanoscale on materials of interest. These techniques have been used to study surface roughness, friction, scratching and wear, indentation and boundary lubrication of bulk and treated silicon, polysilicon films and SiC films. Macroscale friction and wear tests have also been conducted using the ball-on-flat tribometer. Measurements of microscale and macroscale frictional forces show that friction values on both scales of all the silicon samples are about the same for different silicon materials and higher than that of SiC. The microscale values are lower than the macroscale values as there is less ploughing contribution in the microscale measurements. Surface roughness has an effect on friction. In microscale and macroscale tests, C[sup +]-implanted, oxidized and plasma-enhanced chemically vapour-deposited oxide-coated single-crystal silicon samples exhibit much larger scratching and wear resistance than untreated samples. Polysilicon films and undoped single-crystal silicon show similar friction and wear characteristics. The doping of polysilicon film does not significantly affect its tribological properties. Microscratching, microwear and nanoindentation, and macroscale friction and wear studies indicate that SiC films are superior to the other materials currently used in MEMS devices. Higher hardness and fracture toughness of the SiC film is believed to be responsible for its superior mechanical integrity and lower friction. Chemically grafted self-assembled monolayers and chemically bonded liquid lubricants show promising performance for boundary lubrication in MEMS devices. [ABSTRACT FROM AUTHOR]

A study of fly stiction caused after a head slider flew over a disk surface was conducted to understand the mechanisms responsible for high stiction. In this paper, laser-textured disks and three types of nanosliders (50 per cent of the standard size) were used. Friction/stiction was measured and the r.m.s. acoustic emission was recorded in both a short sweep test where the slider swept for periods of 1 h and a long-sweep test where the slider swept for periods of 6 days. The surface of the head slider after tests was analysed using optical microscopy, atomic force microscopy/frictional force microscopy and Raman spectroscopy. Results showed that, in the short sweep test, stiction was sensitive to environmental humidity. Stiction was low at low humidities and increased with increase in the humidity. In the long-sweep test, liquid droplets accumulated during flying were observed on the head slider surface. The vortex around the head slider was found to be responsible for the accumulation of liquid droplets. The droplets then migrated to the rail surface and led to fly stiction during the following start-up. Stiction was sensitive to these liquid droplets in addition to the humidity. Both negative- and positive-pressure sliders could cause fly stiction. A lower flying height was found to be more susceptible to fly stiction. A disk with a fully bonded lubricant film lowered the stiction. Increasing the disk speed could increase the stiction of a negative-pressure slider whereas it lowered the stiction of a positive-pressure slider because of the effects of flying heights, lubricant spin-off and intensity of the vortex. [ABSTRACT FROM AUTHOR]

The durability and failure mechanism of digital metal-evaporated (ME) and digital metal particulate (MP) tapes were investigated. Shuttle and pause mode tests were performed at ambient and different environmental conditions using a modified digital camcorder as a wear tester. Physical and chemical analyses of worn surfaces were conducted to study failure mechanisms. Digital ME tape exhibited higher overall durability than digital MP tape and Hi-8 ME tape without a diamond-like carbon (DLC) overcoat in the study. The performance of digital ME tape was sensitive to temperature and relative humidity. In the pause test, digital ME tape demonstrated highest durability under hot and moderate humidity conditions and lowest durability under cold and dry conditions. The reasons for high durability for digital ME tape compared with digital MP tape and Hi-8 ME tape without a DLC overcoat lie in lubricant selection, controlled surface topography and DLC coating. With the correct combinations of these three parameters, the durability of ME tape is vastly improved. [ABSTRACT FROM AUTHOR]

Decomposition and tribological performance of Z-Dol and X-1P lubricants on the magnetic recording thin-film disks are studied during sliding in a high-vacuum environment. Gaseous products generated from the head--disk interfaces and frictional force are detected and monitored as functions of the sliding distance by using a quadrupole mass spectrometer and friction measurements. The thin-film disks with mechanical and laser texture were used and different thermal treatments were applied to the lubricant films. The effects of the disk texture, lubricant thermal treatment and lubricant additive on the degradation and durability of head--disk interface, are studied in detail. Experimental results show that, firstly, fluorocarbon fragments are generated from lubricants during a period of sliding with a low and stable coefficient of friction, followed by a sharp rise in the frictional force and generation of gaseous products of diamond-like carbon overcoat material. The disk texture has effects on the decomposition of the lubricant and durability of the head--disk interface; the laser-textured disk surface caused Z-Dol lubricant to decompose at lower sliding distances and with more gaseous species compared with the mechanically textured disk. Thermal treatment of the lubricant films and the application of X-1P as an additive to the Z-Dol lubricant improved the durability of the head--disk interfaces. [ABSTRACT FROM AUTHOR]

The decomposition mechanisms of the perfluoropolyether (PFPE) lubricants were studied in this paper using several experimental approaches. The PFPE lubricant film can be bonded to disk surface by illuminating the lubricant film with ultraviolet (UV) light; then the durability of the head--disk interface can be improved. However, during the sliding process, the illumination with UV light can accelerate the decomposition of the lubricant, reducing the head--disk interface durability and causing more gaseous fragments because low-energy electrons created by the illumination interact with the lubricant molecules, activating and breaking up the molecules. A decomposition mechanism of the lubricant with the effect of low-energy electrons was proposed. Mechanical shear is also found to have an important effect on the decomposition of the lubricant. The partial pressures of the gaseous fragments of the lubricant increase rapidly with increase in the sliding velocity. No obvious effect of ambient temperature up to 70 °C on the decomposition of the PFPE lubricant was observed, although higher temperatures are expected to be detrimental. [ABSTRACT FROM AUTHOR]

Magnetic reliability of a linear tape drive is intimately related to the tribology at the head--tape interface because an increase in the spacing between the read element of the head and the magnetic particles in the tape reduces the strength of the magnetic signal read from the tape. In this study, Co--γ-Fe[sub 2]O[sub 3] tape was worn against magnetoresistive (MR) heads in a modified commercial tape drive. Friction, the head output and the number of drop-outs were used to determine the wear mechanisms at the head--tape interface. Additionally, atomic force microscope (AFM) measurements, Auger material composition analysis and stain thickness measurement using a nanoindentation scratch test were used to support the friction and magnetic data. Using these methods, it was found that three different wear mechanisms occur at the head--tape interface, which first involves adhesion building a stain on the head surface, followed by the cyclic wearing and accumulation of the stain. Finally, the tape binder is sufficiently worn away, causing the stain to be permanently removed by abrasion of the hard magnetic particles. The life of the head--tape interface can be improved by cleaning the stain from the head with an abrasive tape before the stain becomes too thick. Therefore, if only one tape was used in the lifetime of the head, the head would need to be cleaned only once because the tape has a finite amount of stain-producing material available. However, if the stain thickness is reduced too much, the head--tape interface will not function without an increase in stain material because the presence of the stain provides lubrication without which the friction at the head--tape interface exceeds the motor force, causing the drive to stop. [ABSTRACT FROM AUTHOR]

Most contact analyses assume that the surface heights and peak (summit) height distributions follow a single modal distribution, Gaussian or non-Gaussian. However, height distributions of many surfaces follow multi-modal distributions. In this study, for the first time, algorithms are developed to generate various bimodal surfaces on the computer. Statistical analyses and contact analyses of these surfaces have been carried out. The present algorithms are applied to particulate tapes and head-finishing processes to illustrate the effect of the bimodal distribution on the contact performance. From these analyses, an optimum bimodal roughness distribution is predicted for minimum friction and wear. [ABSTRACT FROM AUTHOR]

Friction/stiction behaviour of ultrahigh-density magnetic disk drives can be controlled by controlling the size and shape of the laser bumps. Tribological behaviour of laser-textured disk surfaces depends on the size and shape of the laser bumps, bump density and operating conditions. In this study, theoretical and experimental analyses have been carried out on nine different laser-textured disk surfaces. Stiction and friction experiments have been carried out on sombrero, V-type and W-type laser-textured disks and these results are compared with theoretical results. A good correlation is obtained between experimental and theoretical results. The effect of laser bump uniformity on critical number of bumps required to prevent plastic deformation and stiction has also been studied. [ABSTRACT FROM AUTHOR]

Particulate contamination studies were carried out with laser-textured and mechanically textured magnetic rigid disks and nanosliders. The effects of particle concentration and its size, particle material, duration of exposure to contamination, interface speed and disk textures were studied. The head--disk interface (HDI) durability increased as particle concentration decreased. The effect of different hard-particle materials was attributed to how easily it can form agglomerates. Data indicate that limited-time exposure to a class 10 000 environment will not deter tribological performance of the HDI. In a contaminated environment, head flying in the data zone exhibited higher durability than that in the laser-textured zone. However, the mechanically textured disk and the data zone of laser-textured disks showed comparable durability in the presence of contamination. The HDI damage mechanism and pattern changed as the disk speed changed. A failure mechanism to show how the airborne particles interact with the interface is presented. The effects of the HDI geometry, flying height, pitch angle which controls the air flow pattern govern the failure mechanism in the flying mode. [ABSTRACT FROM AUTHOR]

The failure mechanism for a head--disc interface has been studied using in situ multi-instrumentation. Combined with ex situ atomic force microscopy observations, the sequence of events for the failure of a head--disc interface is proposed as depletion of the lubricant on laser bumps, uniform wear of the carbon coating on laser bumps, failure of the carbon coating on laser bumps and abrasive wear of the underlying substrate. [ABSTRACT FROM AUTHOR]

The presence of tape debris at the head--tape interface can cause an increase in spacing and consequently an increase in signal loss. In this study, the generation of tape debris in linear tape drives is analysed. Functional drive tests are conducted using thin-film Al[sub 2]O[sub 3]--TiC and Ni--Zn ferrite heads run against commercial metal particle (MP) tape. Three types of tape debris are found: magnetic particle rich, polymer rich and adherent (stain). Each type is found at a distinct location on the head surface. Optical microscopy and computerized image analysis are used both to quantify the tape debris and to find its distribution on the head. Atomic force microscopy is used to measure the thickness of adherent debris. The Al[sub 2]O[sub 3]--TiC sample generates more of all three types than does the Ni--Zn ferrite sample. This is probably a result of the higher hardness of Al[sub 2]O[sub 3]--TiC. The differential wear of Al[sub 2]O[sub 3] and TiC probably accounts for the presence of adherent debris on the Al[sub 2]O[sub 3]--TiC head. No adherent debris can be found on the Ni--Zn ferrite head. Since the adherent debris collects near the pole tip and is difficult to remove, it potentially poses the greatest head--tape spacing problem, even though its thickness is only of the order of a few nanometres. A relationship is found between the generation of loose debris and the tape speed, tape tension and head wrap. Loose debris generation increases as the tape speed decreases and as the tape tension and head wrap increase. Its generation is found to be approximately proportional to the frictional force. Loose debris, especially the magnetic-particle-rich type, continues to be generated in abundant amounts beyond the burnishing phase for MP tape. The use of an abrasive tape leader is found to reduce the amount of debris at the interface. [ABSTRACT FROM AUTHOR]

Pole tip recession (PTR) in linear tape heads causes an increase in spacing and consequently an increase in signal loss. In this study, PTR in linear tape drives is analysed. Functional drive tests are conducted using thin-film Al[sub 2]O[sub 3]--TiC and Ni--Zn ferrite heads sliding against metal particle tape. Atomic force microscopy is used to measure PTR and the recession of the overcoat material used in the construction of the head. In measuring PTR, care must be taken in correctly orienting the stand-alone atomic force microscope tip with respect to the head sample. Care must also be taken in post-processing the raw stand-alone atomic force microscopy data. Based on PTR data with Al[sub 2]O[sub 3]--TiC and Ni--Zn ferrite heads, no significant differences exist in the PTR of Al[sub 2]O[sub 3]--TiC heads compared with Ni--Zn ferrite heads. In the case of the Ni--Zn ferrite head, the softer Ni--Zn ferrite substrate has mechanical properties close to those of the poles, suggesting that PTR growth should be low. However, additional third-body wear particles from the ferrite substrate result in additional pole tip wear. No significant difference is seen in the wear of Co--Zr--Ta poles and Ni--Fe poles, as they have comparable mechanical properties. No strong conclusion may be drawn about the effect of tape speed on PTR. An increase in tape tension leads to an increase in PTR. This is a result of an increase in the normal force, which causes an increase in the abrasive wear. An increase in interface contamination also leads to an increase in PTR. [ABSTRACT FROM AUTHOR]

Presents information on the importance of static friction to tribological studies while focusing on the increase of static friction in the time of stationary contact (rest static friction or rest stiction). Observation of the effect in computer disk drives especially at high humidities; Proposal of a kinetic meniscus model; Reasons for the proposed model; Detailed information on the results.

Atomic force microscopy/friction force microscopy (AFM/FFM) techniques are increasingly used for tribological studies of engineering surfaces at scales ranging from atomic and molecular to microscales. These techniques have been used to study surface roughness, adhesion, friction, scratching/wear, indentation, detection of material transfer and boundary lubrication and for nanofabrication/nanomachining purposes. Micro/nanotribological studies of materials of scientific and engineering interest have been conducted. Commonly measured roughness parameters are found to be scale dependent, requiring the need of scale-independent fractal parameters to characterize surface roughness. Measurement of atomic-scale friction of a freshly cleaved highly orientated pyrolytic graphite exhibited the same periodicity as that of corresponding topography. However, the peaks in friction and those in corresponding topography were displaced relative to each other. Variations in atomic-scale friction and the observed displacement have been explained by the variations in interatomic forces in the normal and lateral directions. Local variation in microscale friction is found to correspond to the local slope, suggesting that a ratchet mechanism is responsible for this variation. Directionality in the friction is ob served on both micro- and macroscales which results from the surface preparat ion and anisotropy in surface roughness. Microscale friction is generally found to be smaller than macroscale friction as there is less ploughing contribution in microscale measurements. Microscale friction is load dependent and friction values increase with an increase in the normal load, approaching the macrofriction at contact stresses higher than the hardness of the softer material. The wear rate for single-crystal silicon is negligible below 20 μ N and is much higher and remains approximately constant at higher loads. Elastic deformation at low loads is responsible for neg ligible wear. The mechanism of material removal on a microscale is studied. At the loads used in the study, material is removed by the ploughing mode in a brittle manner without much plastic deformation. Most of the wear debris is loose. Evolution of the wear has also been studied using AFM. Wear is found to be initiated at nanoscratches. AFM has been modified to obtain load--displacement curves and for measurement of nanoindentation hardness and Young's modulus of elasticity, with the depth of indentation as low as 1 nm. Hardness of ceramics on the nanoscale is found to be higher than that on the microscale. Ceramics exhibit signifi cant plasticity and creep on the nanoscale. Scratching and indentation on nanoscales are powerful ways to screen for adhesion and resistance to deformation of ultra-thin films. Detection of material transfer on the nanoscale is possible with AFM. Boundary lubrication studies and measurement of lubricant-film thickness with a lateral resolution on a nanoscale have been conducted using AFM. Self-assembled monolayers and chemically bonded lubricant films with a mobile fraction are superior in wear resistance. Friction and wear on micro- and nanoscales at low loads have been found to be generally smaller compared to that at macroscales. Therefore, micro/nanotribological studies may help define the regimes for ultra-low friction and near-zero wear. [ABSTRACT FROM AUTHOR]

Surfaces produced by machining processes such as grinding, shaping and turning and some magnetic disk texturing processes such as sputtering and laser processing are frequently non-Gaussian. Most of the contact models developed in the past three decades assume Gaussian distribution of surface heights in their analyses. In the present paper, contact analy sis of non-Gaussian surfaces has been conducted. A computer program was developed to generate non-Gaussian surfaces with specified standard deviation, autocorrelation length, skewness and kurtosis. Contact area, maximum contact pressure and relative meniscus force as a function of skewness and kurtosis were studied at different values of σ and β*. In these studies, it is observed that a surface with slight positive skewness and kurtosis in the range of 4--7.5 results in an optimum surface with a minimum contact area and meniscus force. Further, stiction of a surface with high kurtosis is somewhat insensitive to liquid film thickness. A surface with negative skewness and/or kurtosis of less than 3 will lead to severe friction/stiction problems and a surface with very high kurtosis and σ may lead to plastic deformation . Non-Gaussian surfaces offer promise for the design of interface roughness to provide low friction/stiction and wear. [ABSTRACT FROM AUTHOR]

An experimental set-up and a procedure to make in situ localized measurements of various wear processes on magnetic thin-film disks are developed. The coeffi cient of friction, acoustic emission and optical reflectance are monitored simultaneously. Results are analysed to determine `precursors to failure' and to compare the effects of lubricant, surface roughness, overcoat and normal load on disk wear. Disk wear is observed to follow a pattern of lubricant depletion followed by head slider--overcoat asperity contact. Wear tracks are formed after asperity contact. Lubricant extends disk wear life, as does a polished surface texture, and an SiO[sub 2] overcoat wears more slowly than a diamond-like carbon overcoat. The experimental methodology developed in this study should be of interest in studying precursors to failure of any moving interface. [ABSTRACT FROM AUTHOR]

For long durability of magnetic media and head sliders, protective overcoats of hydrogenated amorphous carbon (a-C:H) are generally used. In this study, microtribological studies of hydrogenated amorphous carbon coatings deposited on a single-crystal silicon using three different deposition techniques---sputtering, ion beam and cathodic arc---we re studied using atomic force/friction force microscopy (AFM/FFM). Roughnesses of all coatings at two scan sizes of 1 mμm × 1 μm and 10 μm × 10 μm are comparable. Surface topography of sputtered carbon coating shows some particulates on the surface. Cathodic arc carbon coating exhibits the lowest coefficient of friction value followed by ion beam and sputtered carbon coatings. Microscratch and wear resistance and nanohardness of cathodic arc carbon coating are superior to those of ion beam and sputtered carbon coatings. Cathodic arc deposited carbon coatings are potential candidates for magnetic disks and heads. [ABSTRACT FROM AUTHOR]

Degradation of perfluoropolyether lubricants (Fomblin Z-Dol and Fomblin AM 2001) on the magnetic recording thin-films disks are studied during sliding with an Al[sub 2]O[sub 3]--TiC slider under high vacuum. Gaseous products generated from the head/disk interfaces are detected and monitored as a function of sliding distance using a quadrupole mass spectrometer. Effects of overcoats and surface roughnesses of disks on degradation of lubricants and coefficient of friction were also studied. Experimental results show that the gaseous products gener ated from Z-Dol and AM 2001 lubricants during sliding are quite similar. Degradation of both lubricants is found to take place from the beginning of sliding, and the evolution rate of decomposition fragments decreases with the sliding distance. Removal of the lubricants is accompanied by a rapid rise in the coefficient of friction of the interfac es, followed by gaseous products from the tribochemical reaction of the overcoat material. Surface roughness of the disk has an effect on the sliding distance to failure, but little effect on the decomposition of lubricant. [ABSTRACT FROM AUTHOR]

Drag and CSS (contact start and stop) tests were conducted to study the effects of the degree of chemical bonding of the lubricant and environmental humidity on the friction/stiction and durability of the head--disk interface. Disks with untreated, partially bonded and fully bonded films of a polar perfluoropolyether lubricant were tested at different levels of humidity. Static friction is low for unlubricated disks and disks with a fully bonded lubricant film as compared to disks with untreated and partially bonded lubricant films. Static friction gradually increases with an increase in the relative humidity and the effect of humidity at high humidity values is more pronounced in the case of disks with untreated and partially bonded lubricant films. At high humidities, durability is low for all lubricated disks but is high for unlubricated disks, as compared to that at low humidities. At low humidities, durability in drag tests is more sensitive to the degree of bonded fraction than that in the CSS tests. In general, partially bonded lubricant films are desirable for low friction/stiction and high durability and lubricated disks perform best at low to moderate humidities. Operation at high humidities must be avoided. [ABSTRACT FROM AUTHOR]

Slider materials with improved static and kinetic friction and durability of the head--disk interface are required for minimum separation between the head slider and magnetic medium and miniaturization of sliders. Mn--Zn ferrite, calcium titanate, Al[sub 2]O[sub 3] TiC and SiC sliders were used in drag tests, stiction tests and contact start--stop (CSS) tests. The SiC slider exhibits the best tribological performance at all humidities as compared to other sliders. Relevant mechanisms are revealed with measurement of the contact angle of perfluoropolyether (PFPE) lubricants on slider materials, lubricant transfer tests, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infra-red (FTIR) analyses on the slider surfaces before and after tests. Best friction and wear performance of SiC is attributed to lubricant transfer from the lubricated disk to the slider surface and formation of tribochemical films. A lubricant layer on the slider surface protects the slider from wear and also increases the contact angle with the water film, resultin g in a low meniscus contribution leading to low stiction. The tribochemical reaction forms a gel-like hydroxide layer on the SiC slider surface which performs as a boundary lubricant, leading to a low coefficient of friction and low wear. [ABSTRACT FROM AUTHOR]

Metal evaporated (ME), metal particle (MP) and barium ferrite (BaFeO) magnetic tapes are leading candidates for ultra-high-density magnetic tape recording applications. Using a commercial video cassette recorder as a magnetometer and the Wallace equation, changes in the r.m.s. head output level were correlated to changes in head-to-tape spacing as tape wear occurred during play/rewind cycling tests. Interface stability and recording performance at a 0.6μm recording wavelength were measured to bit level resolution using a drop-out counter. Some pause mode testing was done for comparison with streaming mode experiments. Methodologies to measure head and tape wear were developed and applied to worn specimens. Development of the experimental apparatus with nanometer vertical and submicrosecond temporal resolutions has enabled unprecedented understanding of the interplay of friction, wear and surface topography in a sliding contact. Waviness of ME tape and high roughness of BaFeO tape led to poor high-density recording performance as compared to the excellent performance of the flat MP tape. Interface stability generally improved as the tapes were used and worn smooth by the rotary heads, and head-to-tape spacing was reduced by about 10 nm over 1000 play/rewind cycles for the tapes. ME tape showed the least durability of all of the tapes, and damage areas initiated at high points or bumps on the tape surface were connected by lateral cracks (driven by longitudinal tension) across the tape width at tape failure after about 800 play/rewind cycles. MP tape performance improved gradually through 1000 play/rewind cycles. High asperities on the virgin tapes were severed off the tapes during the record pass, and those that remained on the tape surface increased friction force and tape wear by three-body abrasion early on in play/rewind cycling tests. Lower friction and virtually no wear were observed later in cycling tests when loose wear debris were no longer on the tape surface and the wear mechanism was adhesive. The wear coefficient in the streaming mode was larger than that in the pause mode due to abrasive particles in the contact interfac e in the streaming mode. MP and BaFeO tapes caused head stains on the metal core and glass surfaces of composite metal-in-gap heads. Anisotropic high tape stiffness led to asymmetrical head wear and head contours with large radii of curvature. [ABSTRACT FROM AUTHOR]

The effect of environment on the drop-out performance of magnetic tapes in a rotary head--tape drive was stud ied. A capacitance probe, mounted on the rotating upper drum and positioned to measure tangential deflection of the head, was used to measure friction force. This technique, in conjunction with the measure ment of head signal amplitude, was used to investigate the effect of environm ent on drop-outs. Streaming mode tests were conducted with two brands of S-VHS tapes at various combinations of temperature (6-- 38°C) and relative humidity (10--80% RH). From the experiments, it was found that the propensity for intermittent drop-outs increases in a low relative humidity environment. A low relative humidity environment increases the propensi ty for debris to persist over the head gap and create a loss in the head signal. High temperature further increases the propensity for drop-outs in a low relative humidity environment. The propensity for intermittent drop-outs is reduced by increasing the relative humidity, changing magnetic tapes and to some extent by lowering the temperature of the environment. It was also determined that variability in the quality of magnetic tapes has a significa nt impact on the number of intermittent and permanent drop-outs encountered during playback. [ABSTRACT FROM AUTHOR]