Effect of mechanical properties on frictional behaviour of metals

The coefficient of friction was experimentally determined for some common metals and is correlated with their mechanical properties. Strong metals are shown to give a lower coefficient of friction and are characterised by high hardness, low shear to hardness ratio and low surface energy to hardness ratio     

Design of annular recess hydrostatic thrust bearing under dynamic loading

Design charts are presented of a dynamically loaded thrust bearing with as annular recess. The effect of non-parallelism between the bearing and the runner surfaces is also considered, since this is a common problem in hydrostatic thrust bearings. Based on pre-assigned dynamic excitations the pressure equation is solved numerically by finite difference methods to render the bearing performance characteristics namely: load capacity; bearing stiffness; damping coefficient; and lubricant flow rate. Results concluded that the bearing performance chareacteristics are dependent on the bearing radii ratios, the squeeze number, the bearing number and the tilt parameter.     

Chemical Composition and Sensory Quality of Tunisian ‘Sayali’ Virgin Olive Oils as Affected by Fruit Ripening: Toward an Appropriate Harvesting Time

Herein, the influence of the ripeness of Tunisian Sayali olives on the chemical composition and sensory quality of virgin olive oils have been investigated, with a particular focus on minor metabolites. Towards this end, five samples (S1–S5) were produced from fruits at increasing stages of maturity and then analyzed. Quality indices (free acidity, peroxide value, specific extinction in UV, sensory characteristics) and composition in major (fatty acids) and minor compounds (squalene, pigments, tocopherols, phenolic compounds, volatile compounds), as well as oxidative stability, were evaluated. Significant variations for the most analytical parameters of Sayali samples were demonstrated, highlighting the impact of stage of ripening. In particular, at later stages of ripening a decreased tendency was seen in minor compounds that are able to inhibit lipid oxidation (tocopherols, carotenoids, squalene and polar phenolic compounds) and, as a consequence, in the oxidative stability value. Moreover, a higher intensity of positive sensory notes (fruity, bitter and pungent) characteristic of extra virgin olive oil were found for samples produced with less ripe olives. Finally, a deeper knowledge of the influence of this factor would be helpful to correctly manage the optimal fruit harvesting time for producers for this variety and to improve the marketing of extra virgin olive oils by using a promising secondary variety (with a high oxidative stability and an interesting fatty acid composition).     

Towards Data and Computation Offloading in Mobile Cloud Computing: Taxonomy,Overview, and Future Directions

Wireless Personal Communications - The rapid developments in the mobile application context illuminate the demand for more resources and processing power at Smart Mobile Devices (SMDs). Mobile...     

Storm Water Harvesting in Saudi Arabia: a Multipurpose Water Management Alternative

This work evaluates the potential for rainwater harvesting at the household level in the dry climate of Saudi Arabia. The amounts of rainwater that can be harvested in several cities in Saudi Arabia were estimated and it was found that a significant volume, exceeding 7.5 m³/100 m² per year, can be harvested. The per cubic meter cost of harvesting rainwater was compared to that of producing desalinated water. It was found that harvested rainwater is cheaper to capture than desalinated water produced from renewable energy-driven desalination plants, but that is not the case for fossil fuel-powered desalination. The study also considered the effects of rainwater harvesting on mitigating floods and reducing greenhouse gas emissions. A cost-benefit analysis of installing rooftop rainwater harvesting systems in Saudi Arabia was performed. It revealed that it is economically feasible to harvest rain in cities including Hail, Jeddah, Taif, and Riyadh, while it is not recommended in the holy cities of Makkah, Medina, and Buraidah.     

A new impedance and robust adaptive inverse control approach for a teleoperation system with varying time delay

This paper presents a new robust adaptive inverse control approach for a force-reflecting teleoperation system with varying time delay. First, an impedance control is designed for the master robot. Second, an adaptive inverse control is proposed for the slave robot. Finally, the slave side controller is modified such that the robust stability and performance are achieved. In addition, robust stability analysis has been performed and optimal behavior is ensured by using standard characteristic polynomials. It is shown that despite of presence of randomly-varying time delay, the proposed control algorithm compensates the position drifts efficiently. Demonstrable simulation studies confirm the effectiveness of the proposed control system and its advantages over the existing sliding mode control strategies.     

Removal of mercury from natural gas by a new activated adsorbent from olive stones

This study was devoted to the valorization of a plant waste (olive stones): that is widely available in Mediterranean countries in order to remove mercury from natural gas. The raw material from olive stones was prepared by pyrolysis, chemical activation with phosphoric acid, and physical activation under steam. Two olive stone‐based granular activated carbons were prepared: one with the virgin stones, while the other was impregnated with sulphur. After treatment, the adsorbents obtained were characterized by determining the iodine number, the methylene blue index, and by estimating the porous properties by N₂ adsorption at 77 K. Thermogravimetric analysis and infrared spectroscopy analysis were carried out to determine the functional groups before and after mercury adsorption. An experimental study of vapour‐phase mercury adsorption by the activated carbons (virgin and sulphur‐impregnated) and a comparison with a commercial material (HGR) were performed. The comparison, made by analyzing the adsorption in a continuous mode, showed that the proportion of sulphur and the porosity were important for the removal of mercury. In the conditions used, the mercury adsorption on the ACs studied follows a physisorption mechanism. The results showed that granular activated carbon‐based olive stones (sulphur‐impregnated) are very efficient to remove mercury (with 2864 μg/g) and also less expensive than commercial activated carbon due to their local availability.     

Correlation between the frictional behaviour and the physical properties of metals

The surface topography of mating surfaces is characterized by plastically deformed asperities which form real areas of contact. As sliding leads to the shearing of junctions, it is feasible that physical properties will affect adhesion and shear strength and influence frictional behaviour.The sliding friction of similar metals and of metals sliding against a steel specimen was investigated for most commonly used metals in terms of their fundamental physical properties including atomic volume, surface energy and thermal properties.     

Electrodeposition and characterization of ZnO thin films using sodium thiosulfate as an additive for photovoltaic solar cells

Zinc oxide thin films have been grown by electrodeposition technique onto Cu and ITO-coated glass substrates from an aqueous zinc nitrate solution with addition of sodium thiosulfate at 90℃.The effects of sodium thiosulfate on the electrochemical deposition of ZnO were investigated by cyclic voltammetry and chronoamperometry techniques.Deposited films were obtained at -0:60 V vs.SCE and characterized by XRD,SEM,FTIR, optical,photoelectrochemical and electrical measurements.Thickness of the deposited film was measured to be 357 nm.X-ray diffraction results indicated that the synthesized ZnO has a pure hexagonal wurtzite structure with a marked preferential orientation along (002) plane.FTIR results confirmed the presence of ZnO films at peak 558 cm^-1.SEM images showed uniform,compact morphology without any cracks and films composed of large flower-like ZnO agglomerates with star-shape.Optical properties of ZnO reveal a high optical transmission (>80%) and high absorption coefficient (α>105 cm^-1)in visible region.The optical energy band gap was found to be 3.28 eV.Photoelectrochemical measurements indicated that the ZnO films had n-type semiconductor conduction.Electrical properties of ZnO films showed a low electrical resistivity of 6.54 Ω·cm,carrier concentration of -1.3×10¹⁷cm^-3 and mobility of 7.35 cm²V^-1s^-1.