Low friction rolling element bearings

In this paper some unusual designs of rolling element bearings are discussed, with a view to reducing the friction to a minimum by optimizing their shape. Such bearings may have use in certain applications where low friction is important, some applications envisaged being radar antennae and gyroscope gimbals.     

Preparation and characterization of hybrid pH-sensitive hydrogels of chitosan-co-acrylic acid for controlled release of verapamil

In the present work crosslinked hydrogels based on chitosan (CS) and acrylic acid (AA) were prepared by free radical polymerization with various feed compositions using N,N methylenebisacrylamide (MBA) as crosslinking agent. Benzoyl peroxide was used as catalyst. Fourier transform infrared spectra (FTIR) confirmed the formation of the crosslinked hydrogels. This hydrogel is formed due to electrostatic interaction between cationic groups in CS and anionic groups in AA. Prepared hydrogels were used for dynamic and equilibrium swelling studies. For swelling behavior, effect of pH, polymeric and monomeric compositions and degree of crosslinking were investigated. Swelling studies were performed in USP phosphate buffer solutions of varying pH 1.2, 5.5, 6.5 and 7.5. Results showed that swelling increased by increasing AA contents in structure of hydrogels in solutions of higher pH values. This is due to the presence of more carboxylic groups available for ionization. On the other hand by increasing the chitosan content swelling increased in a solution of acidic pH, but this swelling was not significant and it is due to ionization of amine groups present in the structure of hydrogel. Swelling decreased with increase in crosslinking ratio owing to tighter hydrogel structure. Porosity and sol-gel fraction were also measured. With increase in CS and AA contents porosity and gel fraction increased, whereas by increasing MBA content porosity decreased and gel fraction increased. Furthermore, diffusion coefficient (D) and the network parameters i.e., the average molecular weight between crosslinks (M_c), polymer volume fraction in swollen state (V_2s), number of repeating units between crosslinks (M_r) and crosslinking density (q) were calculated using Flory-Rehner theory. Selected samples were loaded with a model drug verapamil. Release of verapamil depends on the ratios of CS/AA, degree of crosslinking and pH of the medium. The release mechanisms were studied by fitting experimental data to model equations and calculating the corresponding parameters. The result showed that the kinetics of drug release from the hydrogels in both pH 1.2 and 7.5 buffer solutions was mainly non-Fickian diffusion.     

A socio-technical perspective on e-government issues in developing countries: a scientometrics approach

Many researchers have analyzed e-government literature as a whole or a specific area to focus on statistical methodologies, lessons learnt, or problem related to the area. However, no investigation from socio-technical perspective on e-government issues, in developing countries (DCs), has been carried out. Utilizing scientometrics approach, we analyzed and synthesized e-government (EG) literature that deals with the issues/topics in developing countries from the lens of socio-technical theory (STT). 145 articles from 7 core e-government journals published during the last decade were selected and reviewed for analyzing e-government literature related to developing countries. The growth pattern of e-government literature showed that e-government studies pertaining developing countries issues/topics have rapidly increased during the last decade; covering a range of topics/issues studied from socio-technical aspects. We found that e-government literature in developing countries has somewhat adopted a balanced approach and is moving away from a merely theoretical or conceptual bases toward an empirical foundation; however, the literature lacked depth and balance in terms of issues/topics discussed and methodologies applied. In the light of the findings, strengths, limitations, and future directions for e-government research in developing countries are discussed.     

Roller bearings under radial and eccentric loads

The influence of the roller axial profile on the contact pressure distributions is discussed for the cases of aligned and misaligned rollers. The results of numerical solutions show that careful profiling using radial arcs can result in a more even distribution of pressure. A design method employed by Harris for predicting pressures on misaligned rollers can underestimate the maximum value. However, its use in a shaft and roller bearing system enables the maximum misalignment angle to be predicted for the worst loaded roller with fair accuracy. Numerical methods are then used to find the detailed pressure distribution, thus allowing bearing selection to be made, based upon the maximum pressure present     

Deflexion of a roller compressed between platens

The model of a roller compressed between platens is used to compare the various theories giving roller bearing deflexion. By experiment, it is shown that the formula quoted by Palmgren, $\text{2}\text{x}\text{= 7.62}\text{w}{}^{\mathrm{(0.9)}}$, is the most appropriate for normal roller application.     

Surface damage resistance and yielding of chemically strengthened silicate glasses: From normal indentation to scratch loading

We report on surface elasticity, plastic deformation and crack initiation of chemically strengthened soda-lime silicate and sodium aluminosilicate glasses during lateral indentation and scratch testing. Instrumented indentation using a normal indenter set-up corroborated previous findings on the effects of chemical strengthening on surface Young's modulus, hardness, and indentation cracking. Using lateral indentation in the elastic-plastic regime, we find a pronounced increase in the scratch hardness as a result of chemical strengthening, manifest in higher work of deformation required for creating the scratch groove. Thereby, the glass composition is found to play a stronger role than the absolute magnitude of surface compressive stress. Using a blunt conical stylus for instrumented scratch testing reveals three distinct modes of scratch-induced surface fracture, which occur during scratching or after unloading. Occasional micro-cracking caused by pre-existing surface flaws at low scratching load can be completely suppressed through chemical strengthening. The intrinsic defect resistance to microcracking is reduced as a result of ion stuffing, depending on the initial glass composition, whereas the resistance to abrasive yielding is enhanced by several hundred MPa.     

Performance evaluation of modified fabricated cotton membrane for oil/water separation and heavy metal ions removal

Preparation of effective membrane with special surface treatment for oil/water separation having promising future and low manufacturing cost. The suggested membrane was fabricated by a simple treatment via increasing the hydrophilicity of the cotton fabric surface. The cotton fabric was impregnated in poly(acrylic acid-co-N-methylol acrylamide), poly(AA-co-NMA), where NMA acts as bonding agent. Sodium hypophosphite (SHP) was added to the modification solution to enhance the bonding between the cotton fabric and the PAA. The modified fabric was thermally dried and cured at different temperatures. It was found that, the presence of 3.5% NMA and addition of 5% SHP to the modification solution then curing at 190°C gave the highest amount of bonded PAA to the cotton fabric. The success of the modification process was confirmed by scanning electron microscope, Fourier transformer infrared and the increase in the contact angle of the cotton fabric after modification. Furthermore, the prepared membrane was evaluated for oil (n-hexane, toluene, and petroleum ether)/water separation and also for heavy metal ions removal (Cd²⁺ and Co²⁺). Neutralization of the produced membrane with ammonium hydroxide resulting in a higher contact angle and consequently higher separation efficiency for oil/water mixtures and higher performance for heavy metal ions removal compared to the unneutralized one.     

Elastohydrodynamic lubrication of line contacts

Elastohydrodynamic film thickness measurements for rolling line contact under fully flooded and starved conditions have been made using optical interferometry. From the results it was found that the film shape at the end of the roller becomes more parallel as lubricant starvation increases.

Two main regions of starvation have been studied, namely progressive and catastrophic regions of lubricant starvation. Furthermore, it was found that the severity of conditions within the hertzian contact increases rapidly as m decreases and dry contact conditions are approached. It has been possible to express the dimensionless inlet distance for catastrophic and progressive lubricant starvation conditions respectively as

It has been concluded that the experimental dimensionless central and minimum film thicknesses under starvation conditions can be written respectively as