Interwell relaxation times in p-Si/SiGe asymmetric quantum well structures: the role of interface roughness

We report the direct determination of nonradiative lifetimes in Si∕SiGe asymmetric quantum well structures designed to access spatially indirect (diagonal) interwell transitions between heavy-hole ground states, at photon energies below the optical phonon energy. We show both experimentally and theoretically, using a six-band k∙p model and a time-domain rate equation scheme, that, for the interface quality currently achievable experimentally (with an average step height ⩾1 Å), interface roughness will dominate all other scattering processes up to about 200 K. By comparing our results obtained for two different structures we deduce that in this regime both barrier and well widths play an important role in the determination of the carrier lifetime. Comparison with recently published experimental and theoretical data obtained for mid-infrared GaAs∕AlxGa1−xAs multiple quantum well systems leads us to the conclusion that the dominant role of interface roughness scattering at low temperature is a general feature of a wide range of semiconductor heterostructures not limited to IV-IV material

Seventy years of sex education in Health Education Journal: a critical review

This paper examines key debates and perspectives on sex education in Health Education Journal (HEJ), from the date of the journal’s first publication in March 1943 to the present day. Matters relating to sexuality and sexual health are revealed to be integral to HEJ’s history. First published as Health and Empire (1921 – 1942), a key purpose of the journal since its inception has been to share information on venereal disease and its prevention within the UK and across the former British Empire. From 1943 to the present day, discussions on sex education in the newly-christened HEJ both reflect and respond to evolving socio-cultural attitudes towards sexuality in the UK. Changing definitions of sex education across the decades are examined, from the prevention of venereal disease and moral decline in war-time Britain in the 1940s, to a range of responses to sexual liberation in the 1960s and 1970s; from a focus on preventing sexually-transmitted infections, teenage pregnancy and HIV in the 1980s, to the provision of sexual health services alongside sex education in the 2000s. Over the past 70 years, a shift from prevention of pre-marital sexual activity to the management of its outcomes is apparent; however, while these changes over time are notable, perhaps the most striking findings of this review are the continuities in arguments for and against the discussion of sexual issues. After more than 70 years of debate, it would seem that there is little consensus concerning motivations for and the content of sex education

Global impacts of energy demand on the freshwater resources of nations

The growing geographic disconnect between consumption of goods, the extraction and processing of resources, and the environmental impacts associated with production activities makes it crucial to factor global trade into sustainability assessments. Using an empirically validated environmentally extended global trade model, we examine the relationship between two key resources underpinning economies and human well-being—energy and freshwater. A comparison of three energy sectors (petroleum, gas, and electricity) reveals that freshwater consumption associated with gas and electricity production is largely confined within the territorial boundaries where demand originates. This finding contrasts with petroleum, which exhibits a varying ratio of territorial to international freshwater consumption, depending on the origin of demand. For example, although the United States and China have similar demand associated with the petroleum sector, international freshwater consumption is three times higher for the former than the latter. Based on mapping patterns of freshwater consumption associated with energy sectors at subnational scales, our analysis also reveals concordance between pressure on freshwater resources associated with energy production and freshwater scarcity in a number of river basins globally. These energy-driven pressures on freshwater resources in areas distant from the origin of energy demand complicate the design of policy to ensure security of fresh water and energy supply. Although much of the debate around energy is focused on greenhouse gas emissions, our findings highlight the need to consider the full range of consequences of energy production when designing policy

Enhancing faba bean (Vicia faba L.) genome resources

Grain legume improvement is currently impeded by a lack of genomic resources. The paucity of genome information for faba bean can be attributed to the intrinsic difficulties of assembling/annotating its giant (~13Gb) genome. In order to address this challenge, RNA-seq analysis was performed on faba bean (cv Wizard) leaves. Read alignment to the faba bean reference transcriptome identified 16,300 high quality unigenes. In addition, Illumina paired-end sequencing was used to establish a baseline for genomic information assembly. Genomic reads were assembled de novo into contigs with a size range of 50-5000 bp. Over 85% of sequences did not align to known genes, of which ~10 % could be aligned to known repetitive genetic elements. Over 26,000 of the reference transcriptome unigenes could be aligned to DNA-seq reads with high confidence. Moreover, this comparison identified 56,668 potential splice points in all identified unigenes. Sequence length data was extended at 461 putative loci through alignment of DNA-seq contigs to full length, publically available linkage marker sequences. Reads also yielded coverages of 3466x and 650x for the chloroplast and mitochondrial genomes respectively. Inter- and intra-species organelle genome comparisons established core legume organelle gene sets, and revealed polymorphic regions of faba bean organelle genomes

Chemically induced solidification : a new way to produce thin solid-near- net shapes

In-situ observation of the solidification of high carbon steel (4 wt% C) through decarburization has been carried out as a feasibility study into reducing high power usage and high CO2 production involved in steel making. Decarburization has been carried out under both air and pure N2 atmospheres at temperature of 1573K (1300 °C) and 1673K (1400 °C). A solidified shell of around 500μm was formed with carbon concentrations reduced down to 1% in as short as 18s

Energetics and atomic mechanisms of dislocation nucleation in strained epitaxial layers

We study numerically the energetics and atomic mechanisms of misfit dislocation nucleation and stress relaxation in a two-dimensional atomistic model of strained epitaxial layers on a substrate with lattice misfit. Relaxation processes from coherent to incoherent states for different transition paths are studied using interatomic potentials of Lennard-Jones type and a systematic saddle point and transition path search method. The method is based on a combination of repulsive potential minimization and the Nudged Elastic Band method. For a final state with a single misfit dislocation, the minimum energy path and the corresponding activation barrier are obtained for different misfits and interatomic potentials. We find that the energy barrier decreases strongly with misfit. In contrast to continuous elastic theory, a strong tensile-compressive asymmetry is observed. This asymmetry can be understood as manifestation of asymmetry between repulsive and attractive branches of pair potential and it is found to depend sensitively on the form of the potential.Comment: 11 pages, 9 figures, to appear in Phys. Rev.

Marine reserves can mitigate and promote adaptation to climate change

Strong decreases in greenhouse gas emissions are required to meet the reduction trajectory resolved within the 2015 Paris Agreement. However, even these decreases will not avert serious stress and damage to life on Earth, and additional steps are needed to boost the resilience of ecosystems, safeguard their wildlife, and protect their capacity to supply vital goods and services. We discuss how well-managed marine reserves may help marine ecosystems and people adapt to five prominent impacts of climate change: acidification, sea-level rise, intensification of storms, shifts in species distribution, and decreased productivity and oxygen availability, as well as their cumulative effects. We explore the role of managed ecosystems in mitigating climate change by promoting carbon sequestration and storage and by buffering against uncertainty in management, environmental fluctuations, directional change, and extreme events. We highlight both strengths and limitations and conclude that marine reserves are a viable low-tech, cost-effective adaptation strategy that would yield multiple cobenefits from local to global scales, improving the outlook for the environment and people into the future

Landscapes of progress: the place of physical geography in Scottish Enlightenment accounts of stadial theory

The aim of this thesis is to explore the place of physical geography in Scottish Enlightenment accounts of stadial theory. It does this through examining the historical works of the following authors: Adam Ferguson, Henry Home, (Lord Kames), John Millar and Adam Smith. Stimulated by the 1748 publication of Montesquieu’s Spirit of the Laws each of these individuals presented distinctive explanations for historical progress. Conventional interpretations of Scottish Enlightenment accounts of stadial theory have tended to stress how these were informed by debates over moral conduct and political practice in line with the rise of commercial society. However, these approaches have neglected to consider the place of physical geography within Scottish Enlightenment accounts of historical progress. Consequently, this thesis aims to amend this picture and demonstrate how physical geography provided further insight into the arguments deployed by stadial theorists. This thesis will therefore be structured in the following way. In the introductory chapter, the focus will be on Montesquieu’s understanding of physical geography within the Spirit of the Laws, in demonstrating that his account provided key insights into the differences between European and Asiatic societies which Scottish Enlightenment authors would draw from in order to develop their individual arguments. The second chapter will focus on the work of Adam Ferguson and his An Essay on the History of Civil Society. In the process, it will demonstrate how he used physical geography to illustrate the way social stability was rooted in civic virtue. In the third chapter, Henry Home’s (Lord Kames) Sketches of the History of Man will be examined. It will be argued that physical geography allowed Kames to demonstrate a sceptical interpretation of societal progress which culminated in an ambiguous view of humanity. The final chapter considers the place of physical geography in Adam Smith’s Lectures on Jurisprudence and the Wealth of Nations. In addition to this, this chapter will consider the work of John Millar as an example of the legacy of Smith’s argument and how it informed accounts of physical geography in stadial theory written after the Lectures. Doing so it demonstrates Smith’s understanding of physical geography to be concerned with the way historical progress was conditioned by local influences. This thesis will therefore argue that physical geography provides a way of viewing Scottish Enlightenment accounts of stadial theory which use the premise that societal development was intrinsically linked to a range of physical factors including location, climate, topography and fertility