Near-infrared photoluminescence enhancement in Ge/CdS and Ge/ZnS core/shell nanocrystals: Utilizing IV/II-VI semiconductor epitaxy

Ge nanocrystals have a large Bohr radius and a small, size-tunable band gap that may engender direct character via strain or doping. Colloidal Ge nanocrystals are particularly interesting in the development of near-infrared materials for applications in bioimaging, telecommunications and energy conversion. Epitaxial growth of a passivating shell is a common strategy employed in the synthesis of highly luminescent II-VI, III-V and IV-VI semiconductor quantum dots. Here, we use relatively unexplored IV/II-VI epitaxy as a way to enhance the photoluminescence and improve the optical stability of colloidal Ge nanocrystals. Selected on the basis of their relatively small lattice mismatch compared with crystalline Ge, we explore the growth of epitaxial CdS and ZnS shells using the successive ion layer adsorption and reaction method. Powder X-ray diffraction and electron microscopy techniques, including energy dispersive X-ray spectroscopy and selected area electron diffraction, clearly show the controllable growth of as many as 20 epitaxial monolayers of CdS atop Ge cores. In contrast, Ge etching and/or replacement by ZnS result in relatively small Ge/ZnS nanocrystals. The presence of an epitaxial II-VI shell greatly enhances the near-infrared photoluminescence and improves the photoluminescence stability of Ge. Ge/II-VI nanocrystals are reproducibly 1-3 orders of magnitude brighter than the brightest Ge cores. Ge/4.9CdS core/shells show the highest photoluminescence quantum yield and longest radiative recombination lifetime. Thiol ligand exchange easily results in near-infrared active, water-soluble Ge/II-VI nanocrystals. We expect this synthetic IV/II-VI epitaxial approach will lead to further studies into the optoelectronic behavior and practical applications of Si and Ge-based nanomaterials

The relationship between team ability and home advantage in the English football league system

The existence of home advantage (HA) has been found in a variety of team sports including football. There is a paucity of research on the relationship between team ability and HA in domestic football leagues and the findings of previous studies are inconclusive. Using longitudinal data from the top four football divisions in England, this study investigates the influence of team ability on the HA of teams. The data collected for this study spans 24 seasons from 1995/96 to 2018/19 and includes 48,864 matches from the English Premier League (n=9,120), the Championship (n=13,248), League One (n=13,248) and League Two (n=13,248). Team ability was interpreted in two ways: (1) the division in which teams play; and, (2) their league table position within each division. For both the divisional and positional analysis, HA was calculated as the ratio of home points to total points achieved by teams in each season under review. Evidence of a statistically significant HA was found in all four divisions and for teams of all abilities within each division. Small but statistically significant differences in HA were observed between divisions and between high, moderate and low ability teams within divisions

Factors affecting home advantage in football world cup qualification

An analysis is made of home advantage in the group stages of qualification for the 2006, 2010 and 2014 football World Cup finals, the first such study of national teams worldwide in a competitive setting. Home advantage was greatest in Africa and South America where the home team won just over 69% of all points earned; it was lowest in Europe (56%). Bolivia was the country with the greatest home advantage. Using each of the 2040 games as the observational units, a general linear model produced a significant fit to the data (R2 = 0.326), home points being the dependent variable, with a set of factors believed to influence home advantage as predictor variables. After controlling for team strength and allowing for the effects of other variables in the model, home points were significantly related to altitude of the home stadium, crowd size and number of time zones crossed by the visiting team (all p < 0.05). There was no significant effect for distance travelled by the away team, the existence of a running track or crowd density. Referees, especially in Africa, issued red cards and awarded penalties against the away team significantly more often than against the home team. © 2017 Cardiff Metropolitan University

Combined effects of tactical, technical and contextual factors on shooting effectiveness in European professional soccer

The aim of this paper was to investigate the combined effects of tactical, technical and contextual dimensions on shooting effectiveness in European professional soccer. The sample included 1608 team possessions that led to a shot from 80 random matches (English Premier League = 20; Spanish La Liga = 20; Italian Serie A = 20; German Bundesliga = 20), which were evaluated by multidimensional observation. Multilevel logistic regression models were constructed to determine the effects of nine technical-tactical dimensions and four contextual variables on the shooting effectiveness. Multivariate analyses showed that shooting from the ultra-offensive zone was more effective than shooting from the offensive and advanced zones (OR = 0.385: CI: 0.263–0.564; P > 0.001–OR = 0.101; CI: 0.054–0.188; P.0.001). Also, shooting against opponent defensive pressure decreased the probabilities of scoring goal, in comparison with shooting without defensive pressure (OR = 1.542; CI: 1.032–2.304; P.0.05). Additionally, high-ranked teams had higher odds of scoring goal than low-ranked teams (OR = 2.028; CI: 1.281–3.211; P > 0.01) when shooting at goal, regardless of the effect of the defensive pressure. This study concludes that not only offensive but also defensive and contextual dimensions play a relevant impact on determining the shooting effectiveness in European professional soccer. © 2020, © 2020 Cardiff Metropolitan University