Malthus revisited

Although mineral resources are non-renewable and unevenly distributed, global supply has so far kept up with demand. However, mankind is now moving into an era of unprecedented population growth and environmental change. As demand continues to rise and the need to mitigate and adapt to environmental change becomes more pressing can the abundant mineral supply we have enjoyed be sustained

Sub-Bandgap Photon-Assisted Electron Trapping and Detrapping in AlGaN/GaN Heterostructure Field-Effect Transistors

We have investigated photon-assisted trapping and detrapping of electrons injected from the gate under negative bias in a heterostructure field-effect transistor (HFET). The electron injection rate from the gate was found to be dramatically affected by sub-bandgap laser illumination. The trapped electrons reduced the two-dimensional electron gas (2DEG) density at the AlGaN/GaN heterointerface but could also be emitted from their trap states by sub-bandgap photons, leading to a recovery of 2DEG density. The trapping and detrapping dynamics were found to be strongly dependent on the wavelength and focal position of the laser, as well as the gate bias stress time prior to illumination of the HFET. Applying this phenomenon of trapping and detrapping assisted by sub-bandgap photons, red, green, and purple lasers were used to demonstrate photo-assisted dynamic switching operations by manipulation of trapped carriers at the surface of an AlGaN/GaN HFET. A physical model based on band diagrams, explaining the trapping and detrapping behavior of electrons, has been presented

Assessing the potential of the European Universities Initiative

The European Universities Initiative is a new framework for collaboration between universities in the European Union. Andrew Gunn reflects on the first few years of the initiative and assesses how it might help shape the future of European higher education

Late-successional and old-growth forests in the northeastern United States: Structure, dynamics, and prospects for restoration.

Abstract Restoration of old-growth forest structure is an emerging silvicultural goal, especially in those regions where old-growth abundance falls below the historic range of variability. However, longitudinal studies of old-growth dynamics that can inform silvicultural and policy options are few. We analyzed the change in structure, including stand density, diameter distribution, and the abundance of large live, standing dead, and downed dead trees on 58 late-successional and old-growth plots in Maine, USA, and compared these to regional data from the U.S. Forest Inventory and Analysis program. Structural dynamics on the late-successional plots reflected orderly change associated with density-dependent growth and mortality, but dynamics on the old-growth plots were more variable. Some plots experienced heavy mortality associated with beech bark disease. Diameter distributions conformed poorly to a classic exponential distribution, and did not converge toward such a distribution at the plot scale. Although large live trees showed a broad trend of increasing density in regional forests, recent harvesting patterns offset a considerable fraction of those gains, while mean diameter was static and the number of large dead trees was weakly declining. Even though forests of the northeast are aging, changes in silviculture and forest policy are necessary to accelerate restoration of old-growth structure

Combining social and nutritional perspectives: from adolescence to adulthood (the ASH30 study)

Purpose The purpose of this paper is to focus specifically on the benefits of using mixed methods to investigate dietary change from adolescence to adulthood exemplified using the findings from the ASH30 longitudinal study. The ASH30 study is a longitudinal dietary survey which provided quantitative evidence of dietary change and investigated factors influencing dietary change from adolescence to adulthood. Design/methodology/approach Two three-day food diaries were collected both in 1980 (aged 11-12 years) and 2000 (aged 31-32 years) from the same 198 respondents in North East England. In 2,000 questionnaires were used to collect perceptions of, and attributions for, dietary change and open-ended responses were analysed using content analysis. Findings The use of mixed methods brings added breadth and depth to the research which cannot be achieved by a single discipline or method. Determining what has influenced change in dietary behaviour from adolescence to adulthood is a complex and multifaceted task. Eating habits are influenced by multiple factors throughout the life course. Change in food intake between adolescence and adulthood related to life-course events and trajectories. The qualitative findings highlighted relevant contextual information such as themes of moral panics, the concept of “convenience” and “fresh” foods. Practical implications Adopting mixed method approaches to exploring dietary change should offer a rich perspective from which to base realistic interventions. Originality/value Longitudinal dietary surveys present an opportunity to understand the complex process of dietary change throughout the life course in terms both of how diets have changed but also of why they have changed

Fluoride toothpastes and fluoride mouthrinses for home use

Objective. To provide a brief commentary review of fluoride-containing toothpastes and mouthrinses with emphasis on their use at home. Toothpastes and mouthrinses are just two of many ways of providing fluoride for the prevention of dental caries. The first investigations into incorporating fluoride into toothpastes and mouthrinses were reported in the middle 1940s. Unlike water fluoridation (which is ‘automatic fluoridation’), fluoride-containing toothpastes and fluoride-containing mouthrinses are, primarily, for home use and need to be purchased by the individual. By the 1960s, research indicated that fluoride could be successfully incorporated into toothpastes and clinical trials demonstrated their effectiveness. By the end of the 1970s, almost all toothpastes contained fluoride. The widespread use of fluoride-containing toothpastes is thought to be the main reason for much improved oral health in many countries. Of the many fluoride compounds investigated, sodium fluoride, with a compatible abrasive, is the most popular, although amine fluorides are used widely in Europe. The situation is similar for mouthrinses. Concentrations of fluoride (F), commonly found, are 1500 ppm (1500 μg F/g) for toothpastes and 225 ppm (225 μg F/ml) for mouthrinse. Several systematic reviews have concluded that fluoride-containing toothpastes and mouthrinses are effective, and that there is added benefit from their use with other fluoride delivery methods such as water fluoridation. Guidelines for the appropriate use of fluoride toothpastes and mouthrinses are available in many countries.Conclusion. Fluoride toothpastes and mouthrinses have been developed and extensive testing has demonstrated that they are effective and their use should be encouraged