A study on dynamic friction of different spun yarns

This article presents the results from a study of yarn-to-yarn (YY) and yarn-to-metal (YM) frictions conducted on ring, rotor, air-jet, and open-end friction (OE friction) spun yarns at different relative speeds and input tensions. The results indicate that the behavior of frictions for YY is different than that of YM. In case of YY friction, OE friction yarn shows maximum friction followed by rotor, air-jet, and ring spun yarns; however, a reverse order is noticed for YM friction. The relative speed and input tension have significant influence on the frictional behavior of spun yarns. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Analysis of performance and device parameters of CIGS PV modules deployed outdoors

Two 20 W copper indium gallium diselenide photovoltaic modules were subjected to a thorough indoor assessment procedure, followed by outdoor deployment at the Nelson Mandela Metropolitan University as part of an ongoing study. The initial indoor measurement of maximum power output (P_MAX) of one of the modules was considerably higher than the manufacturer's rating (E.E. van Dyk, C. Radue and A.R. Gxasheka, Thin Solid Films 515 (2007) 6196). The modules were deployed on a dual-axis solar tracker and current-voltage characteristics were obtained weekly. In addition to the normal PV parameters of short-circuit current, open-circuit voltage, P_MAX, fill factor and efficiency, shunt and series resistances were also monitored. The performances of the two modules are compared and analyzed and the results presented in this paper.     

Synthesis and properties of ZnS nanoparticles by solvothermal and pyrolysis routes using the Zn dithiocarbamate complex as novel single source precursor

In this work, the synthesis and characterization of ZnS nanoparticles prepared via two approaches, involving the thermal decomposition of the precursor complex in a furnace (pyrolysis) and by solvothermal process in the presence of hexadecylamine (HDA-ZnS), are reported. The precursor complex, Zinc (II) bis (N,N-diallyl dithiocarbamate), was synthesized and characterized by spectroscopic and single-crystal X-ray techniques. The spectroscopic analyses of the complex indicated a symmetrical bidentate coordination of the dithio ligand through the S-atoms. The single-crystal X-ray structure revealed a distorted square pyramidal coordinate geometry with S atoms around the Zn ion. The optical properties and the morphology of the as-prepared nanoparticles were studied by UV-Vis and photoluminescense spectroscopy, and transmission electron microscopy (TEM), respectively. HDA-ZnS are spherical and monodispersed with an average size of 4.5?nm, as estimated from the optical absorption spectrum and the TEM image. The ZnS nanoparticles obtained via pyrolysis in a furnace yielded the hexagonal wurtzite phase, whereas the HDA-ZnS nanoparticles showed a mixture of wurtzite and cubic phase with the cubic phase being dominant.     

Crack retardation mechanism due to overload in base material and laser welds of Al alloys

To determine the retardation mechanisms due to overload and to predict the subsequent evolution of crack growth rate, investigations are conducted on crack retardation caused by single tensile overloads in base material and laser-welded sheets of AA6056-T6 Al alloy. The effect of the overload ratio on the fatigue crack propagation behaviour of the C(T) 100 specimens was analysed by using experimental and Finite Element (FE) methods. The crack growth rate and fracture surface features were investigated for both base material and laser-welded sheets. The retardation due to overload is described in terms of the affected regions in front of the crack tip. The size and shape of the crack-tip plastic zone and the damage profile induced during the application of the overload in the base material are predicted by FE analysis in conjunction with a porous-metal plasticity model. The results show that the mechanisms of retardation in under-matched welds are substantially different from that of the homogenous base material. More significant crack retardation due to overload has been observed in the laser weld of AA6056-T6. Based on SEM observations of the fracture surfaces and the damage profiles predicted by the proposed FE model, the shape of the crack front formed during the overload application can be predicted. During the overload, the crack front extends into a new shape, which can be predicted by the ductile damage model; a higher load results in a more curved crack front. These outcomes are used to determine the dominant retardation mechanisms and the significance of retardation observed in each region ahead of the crack tip and finally to define the minimum crack growth rate after overload.     

Determination of the laterally homogeneous barrier height of palladium Schottky barrier diodes on n-Ge (1 1 1)

We have studied the experimental linear relationship between barrier heights and ideality factors for palladium (Pd) on bulk-grown (1 1 1) Sb-doped n-type germanium (Ge) metal-semiconductor structures with a doping density of about 2.5×10¹⁵ cm^?3. The Pd Schottky contacts were fabricated by vacuum resistive evaporation. The electrical analysis of the contacts was investigated by means of current–voltage (I–V) and capacitance–voltage (C–V) measurements at a temperature of 296 K. The effective barrier heights from I–V characteristics varied from 0.492 to 0.550 eV, the ideality factor n varied from 1.140 to 1.950, and from reverse bias capacitance–voltage (C^?2–V) characteristics the barrier height varied from 0.427 to 0.509 eV. The lateral homogenous barrier height value of 0.558 eV for the contacts was obtained from the linear relationship between experimental barrier heights and ideality factors. Furthermore the experimental barrier height distribution obtained from I–V and (C^?2?V) characteristics were fitted by Gaussian distribution function, and their mean values were found to be 0.529 and 0.463 eV, respectively.     

Chemical oxidation of residual carbon from ZnAl2O4 powders prepared by combustion synthesis

The removal of carbon residue from ZnAl₂O₄ nanopowders by annealing at 500–800 °C leads to a decrease of specific surface area from 228.1 m²/g to 47.6 m²/g. At the same time, the average crystallite size increased from 5.1 nm to 14.9 nm. In order to overcome these drawbacks, a new solution for removing the carbon residue has been suggested: chemical oxidation using hydrogen peroxide. In terms of carbon removal, a H₂O₂ treatment for 8 h at 107 °C proved to be equivalent to a heat treatment of 1 h at 600 °C. The benefits of chemical oxidation over thermal oxidation were obvious. The specific surface area was much larger (188.1 m²/g) in the case of the powder treated with H₂O₂. The average crystallite size (5.8 nm) of ZnAl₂O₄ powder treated with H₂O₂ was smaller than the crystallite size (8.2 nm) of the ZnAl₂O₄ powder annealed at 600 °C.     

A typology of Southern African biofuel feedstock production projects

Biofuel expansion is happening rapidly within Southern Africa, and already tens of thousands of hectares have been planted, with millions more being contemplated. As is expected with such a new and dynamic industry, this development has taken place in a relatively ad hoc fashion with the various role-players adapting as they respond to lessons learnt from experience, a changing policy environment and other external factors such as the global recession of 2008/2009. This emerging industry is extremely diverse and it is clear that biofuel projects differ enormously in their intent, feedstock choice and management practices. Some projects aim at satisfying local fuel self sufficiency whilst others focus on national and export markets driven by mandatory blending targets. In addition the area planted by a single farmer or company can range from under 1 ha intercropped with food crops to monocropped plantations of tens of thousands of hectares. In attempting to understand the potential sustainability of the industry there is a clear need for a typology which groups projects with common sustainability issues and concerns. Comparing like with like can greatly reduce the complexity of the biofuel debate; help identify areas of most concern and assists in identifying strategies for enhancing sustainability.     

Catalytic oxidation of thioanisole using oxovanadium(IV)‐functionalized electrospun polybenzimidazole nanofibers

Polybenzimidazole fibers, with an average diameter of 262 nm, were produced by the process of electrospinning. These fibers were used as a solid support material for the immobilization of oxovanadium(IV) which was achieved via a reaction with vanadyl sulfate. The oxovanadium(IV)‐functionalized nanofibers were used as heterogeneous catalysts for the oxidation of thioanisole under both batch and pseudo‐continuous flow conditions with great success. Under batch conditions near quantitative oxidation of thioanisole was achieved in under 90 min, even after four successive catalytic reactions. Under continuous conditions, excellent conversion of thioanisole was maintained throughout the period studied at flow rates of up to 2 mLh^?1. This study, therefore, proposes that electrospun polybenzimidazole nanofibers, with their small diameters, impressive chemical and thermal stability, as well as coordinating benzimidazole group, may be a desirable support material for immobilization of homogeneous catalysts. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Residual stress influences on structural reliability

Structural integrity is affected by residual stresses in a number of ways, some of which are well known to be beneficial in terms of enhancing fatigue performance of engineering components and structures, e.g. surface peening. Knowledge of some of the other more detrimental consequences of residual stresses is more confined within the metallurgical and materials science community and their occurrence during manufacture or service can cause consternation. The purposes of this paper are thus twofold; firstly to introduce several examples of failures which demonstrate more interesting or unusual problems associated with residual stresses and, secondly, to briefly outline the origins of residual stresses and to consider powerful modern ways of measuring residual stress data in real components.     

Fault tree analysis on handwashing for hygiene management

FTA (fault tree analysis) of the handwashing process was performed to investigate the causes for faults in hygiene management. The causes were deductively identified as the events causing every possible hazard by constructing a fault tree. The fault tree was constructed in a hierarchical structure with a single top event (occurrence of faults in hand washing), seven intermediate events, and fifteen basic events connected by a Boolean operator AND gate, or an OR gate. Qualitative analysis on the fault tree yielded minimal cut sets, structural importance, and common cause vulnerability. Quantitative analysis yielded simulation of the final top event fault, cut set importance, item importance, and sensitivity. Those factors are basically a measure to represent the priority order of the basic events causing the top event. The critical basic events turned out to be human errors in hand manipulation in terms of scrubbing the palms, backs, fingers, and fingertips of the hands, as well as failure to use hygienic towels for hand drying due to not using disposable paper towels and unhygienic storage of the towels. The priority order of the basic events was consistent between the qualitative and quantitative analyses. Consequently, we found that FTA, with qualitative and quantitative analyses, was a good alternative approach to hazard analysis in HACCP system implementation.