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A. Gyenes, A. Simon, P. Lanszki and Z. Gácsi

Abstract

This paper investigates the effects of small amount nickel addition (0, 200, 400, 800, 1800 ppm) on the microstructure and the mechanical properties of Sn-0.7Cu lead-free solder alloys. It is known that even ppm level Ni additions have significant effects on the microstructure of Sn-Cu solder alloys. Ni suppresses the growth of β-Sn dendrites in favour of eutectic formation. As the nickel content increases, the microstructure undergoes a morphological evolution from hypoeutectic through fully eutectic to hypereutectic. Along with these transformations, the mechanical properties of the alloy also significantly change. Based on the experimental results presented in this paper, the Sn-0.7Cu solder achieves maximum strength at the addition level of 800 ppm Ni, when the microstructure becomes fully eutectic.

Open access

A. Lekatou, N. Gkikas, A.E. Karantzalis, G. Kaptay, Z. Gacsi, P. Baumli and A. Simon

Abstract

Aluminum matrix composites were prepared by adding submicron sized WC particles into a melt of Al 1050 under mechanical stirring, with the scope to determine: (a) the most appropriate salt flux amongst KBF4, K2TiF6, K3AlF6 and Na3AlF6 for optimum particle wetting and distribution and (b) the maximum carbide volume fraction (CVF) for optimum response to sliding wear. The nature of the wetting agent notably affected particle incorporation, with K2TiF6 providing the greatest particle insertion. A uniform aluminide (in-situ) and WC (ex-situ) particle distribution was attained. Two different sliding wear mechanisms were identified for low CVFs (≤1.5%), and high CVFs (2.0%), depending on the extent of particle agglomeration.

Open access

Saïd A. El-Hassan, Simon R. Gowen and Barbara Pembroke

Abstract

Trichoderma hamatum (Bonord.) Bainier was evaluated for its antagonistic potential against Fusarium oxysporum Schlecht. emend. Snyder and Hansen sp. lentis, the causal agent of vascular wilt disease of lentil (Lens culinaris Medikus). Hyphal interactions on Petri plates resulted in an increase in the number of conidial spores and an increase in the vegetative growth of T. hamatum, and a decrease in the hyphal formation and sporulation of F. oxysporum f. sp. lentis. Electron and light microscopical observations suggested that hyphae of T. hamatum established aggressive contact and attachment with the hyphae of the pathogen. Growing in parallel, coiled densely and tightly, T. hamatum may penetrate those of the pathogen hyphae causing collapse due to the loss of turgor pressure. The cellulolytic enzymes produced by T. hamatum presented sufficient characteristics for its antifungal activity in the hyphae hydrolysis and competition process. In growth room and glasshouse experiments, the addition of the conidial suspension of T. hamatum or its culture filtrate to soil, significantly (p ≤ 0.05) reduced development and spore germination of F. oxysporum. In the rhizosphere, T. hamatum occupied the same ecological niches (rhizosphere, roots, and stems) parasitizing F. oxysporum f. sp. lentis. Treatments using T. hamatum delayed the time of infection by F. oxysporum, promoted the growth, and increased the dry weight of a susceptible variety of lentil (cv. Precoz). The percent of mortality was reduced to 33 and 40% when using T. hamatum and its filtrate, respectively, compared to 93% in the control treatment during the 65 days of growing in loam/sand (2:1 vol/vol) under glasshouse conditions. Plant colonization results indicate that T. hamatum and its filtrate significantly (p ≤ 0.05) reduced development of the pathogen in the vascular tissue of lentil to < 30 and < 40% stem colonization, respectively, compared to 100% in the plant pathogen control. Our results suggest that potential biocontrol mechanisms of T. hamatum towards F. oxysporum f. sp. lentis were antibiosis by production of antifungal enzymes, complex mechanisms of mycoparasitism, competition for key nutrients and/or ecological niches, growth promotion, and a combination of these effects. This study results hold important suggestions for further development of effective strategies of the biological control of Fusarium vascular wilt of lentil.

Open access

M. Armenteros, Anto J. Benítez, R. Flores, M. Sillero-Quintana, M. Sánchez Cid and J.A. Simón

Abstract

The main objective of this article was to analyse whether the Interactive Video Test (IVT) is a useful tool for the practical off-field training of soccer assistant referees, and if its use could reduce erroneous on-field decisions when applying Law 11 of the Laws of the Game. Assistant referees were taken from the Spanish 2nd “B” and 3rd Divisions, and were divided into two groups, the Experimental Group (EG) and the Control Group (CG). The referees in the EG were trained with the Interactive Video Test by analysing 720 off-side decisions. Subsequently, both groups were assessed in on-field tests involving the simulation of 326 possible off-side situations. When the results of both groups were compared, there was a continuous improvement over time in the EG associated to the use of the IVT, significantly better than the improvement of the CG. Moreover, the IVT proved to be a good diagnostic tool to assess the skills of assistant referees in perceiving and evaluating off-side situations.

Open access

Michael A. Henning, Simon Jäger and Dieter Rautenbach

Abstract

We characterize a large subclass of the class of those graphs G for which the exponential domination number of H equals the domination number of H for every induced subgraph H of G.

Open access

A. Simon, D. Lipusz, P. Baumli, P. Balint, G. Kaptay, G. Gergely, A. Sfikas, A. Lekatou, A. Karantzalis and Z. Gacsi

Abstract

The scope of the research work is the production and characterization of Al matrix composites reinforced with WC ceramic nanoparticles. The synthesis process was powder metallurgy. The produced composites were examined as far as their microstructure and mechanical properties (resistance to wear, micro/macrohardness). Intermetallic phases (Al12W and Al2Cu) were identified in the microstrucutre. Al4C3 was not detected in the composites. Adding more than 5 wt% WC to the aluminum, microhardness and wear resistance exceed the values of Al alloy. Composites having weak interface bond performed the highest wear rate.