Energy levels of few electron quantum dots imaged and characterized by atomic force microscopy

Strong confinement of charges in few electron systems such as in atoms, molecules and quantum dots leads to a spectrum of discrete energy levels that are often shared by several degenerate quantum states. Since the electronic structure is key to understanding their chemical properties, methods that probe these energy levels in situ are important. We show how electrostatic force detection using atomic force microscopy reveals the electronic structure of individual and coupled self-assembled quantum dots. An electron addition spectrum in the Coulomb blockade regime, resulting from a change in cantilever resonance frequency and dissipation during tunneling events, shows one by one electron charging of a dot. The spectra show clear level degeneracies in isolated quantum dots, supported by the first observation of predicted temperature-dependent shifts of Coulomb blockade peaks. Further, by scanning the surface we observe that several quantum dots may reside on what topologically appears to be just one. These images of grouped weakly and strongly coupled dots allow us to estimate their relative coupling strengths.Comment: 11 pages, 6 figure

Depression and mortality: Artifact of measurement and analysis?

Background Previous research demonstrates various associations between depression, cardiovascular disease (CVD) incidence and mortality, possibly as a result of the different methodologies used to measure depression and analyse relationships. This analysis investigated the association between depression, CVD incidence (CVDI) and mortality from CVD (MCVD), smoking related conditions (MSRC), and all causes (MALL), in a sample data set, where depression was measured using items from a validated questionnaire and using items derived from the factor analysis of a larger questionnaire, and analyses were conducted based on continuous data and grouped data. Methods Data from the PRIME Study (N=9798 men) on depression and 10-year CVD incidence and mortality were analysed using Cox proportional hazards models. Results Using continuous data, both measures of depression resulted in the emergence of positive associations between depression and mortality (MCVD, MSRC, MALL). Using grouped data, however, associations between a validated measure of depression and MCVD, and between a measure of depression derived from factor analysis and all measures of mortality were lost. Limitations Low levels of depression, low numbers of individuals with high depression and low numbers of outcome events may limit these analyses, but levels are usual for the population studied. Conclusions These data demonstrate a possible association between depression and mortality but detecting this association is dependent on the measurement used and method of analysis. Different findings based on methodology present clear problems for the elucidation and determination of relationships. The differences here argue for the use of validated scales where possible and suggest against over-reduction via factor analysis and grouping. CrownCopyright © 2013PublishedbyElsevierB.V.Allrightsreserved

Exploring perceived support of postgraduate medical science research students

There is still much to learn about the support required by postgraduate research students, across academic disciplines, to facilitate successful completion of a research degree. The primary aim of this study was to explore postgraduate medical science research students’ perceptions of academic and mentoring support at different stages during their degree programme. A second aim was to explore the feasibility and acceptability of peer mentoring as a strategy to enhance student support in this population. A mixed method study design was used. Students first completed an online questionnaire, which was then supplemented with focus group discussion to explore emergent findings in greater depth. The main results indicated that the nature and quality of academic supervision support have a significant influence on research student training and development. ‘Functional’ and ‘relationship development’ concepts of supervisory styles were highlighted as important aspects to perceived support in this research population. The main facilitators to enhance academic support were effective communication, project planning and timely feedback. There was a high degree of acceptability for a peer mentoring programme as a complementary approach to enhance student support. Peer mentoring psychosocial functions such as friendship, counselling and career guidance were considered potentially beneficial to enhancing student support. Students also discussed peer coaching as central to their learning and research skill development. This work is a useful starting point to explore perceptions of research student support in the target population. Further work is required to develop strategies to enhance student support in academic practice

Imaging Inter-Edge State Scattering Centers in the Quantum Hall Regime

We use an atomic force microscope tip as a local gate to study the scattering between edge channels in a 2D electron gas in the quantum Hall regime. The scattering is dominated by individual, microscopic scattering centers, which we directly image here for the first time. The tip voltage dependence of the scattering indicates that tunneling occurs through weak links and localized states.Comment: 4 pages, 5 figure

Is dieting behaviour decreasing in young adolescents?

Abstract Objective: To report trends in underweight, overweight and obesity in 12–15-year-oldadolescents and examine changes in dieting behaviour, which have been less well documented.Design: Comparison of two independent representative cross-sectional surveys. Setting: Northern Ireland.Subjects: Weight and height were objectively measured in 1324 boys and 1160girls in 1996 and 1274 boys and 1374 girls in 2007. Participants reported whether they were following any particular diet including a self-proposed or prescribed weight-reduction diet.Results:Overweight and obesity increased in girls from 15% to 23% and 2% to6%, respectively. Increases were more modest in boys with overweight increasing from 13% to 18% and obesity from 3% to 6%. The proportion of underweight adolescents decreased from 9% to 6% in girls and 8% to 5% in boys. Evidence of social disparity was observed in girls from a manual socio-economic background, with overweight/obesity prevalence rates increasing from 21% to 36% compared with 15% to 26% in girls from a non-manual background. Despite these trends fewer adolescents, in particular girls, reported following weight-reduction diets(14% of overweight/obese girls in 2007 v. 21% in 1996; 8% of boys in 2007 v.13% in 1996). Of these girls, the proportion from a manual background following weight-reduction diets decreased from 25% to 11%.Conclusions: Overweight and obesity are continuing to increase in adolescents despite government and media awareness strategies. There also appears to be reduced dieting behaviour, despite increasing body weight, particularly in girls from manual socio-economic backgrounds.<br/

Single-Atom Gating of Quantum State Superpositions

The ultimate miniaturization of electronic devices will likely require local and coherent control of single electronic wavefunctions. Wavefunctions exist within both physical real space and an abstract state space with a simple geometric interpretation: this state space--or Hilbert space--is spanned by mutually orthogonal state vectors corresponding to the quantized degrees of freedom of the real-space system. Measurement of superpositions is akin to accessing the direction of a vector in Hilbert space, determining an angle of rotation equivalent to quantum phase. Here we show that an individual atom inside a designed quantum corral can control this angle, producing arbitrary coherent superpositions of spatial quantum states. Using scanning tunnelling microscopy and nanostructures assembled atom-by-atom we demonstrate how single spins and quantum mirages can be harnessed to image the superposition of two electronic states. We also present a straightforward method to determine the atom path enacting phase rotations between any desired state vectors. A single atom thus becomes a real space handle for an abstract Hilbert space, providing a simple technique for coherent quantum state manipulation at the spatial limit of condensed matter.Comment: Published online 6 April 2008 in Nature Physics; 17 page manuscript (including 4 figures) + 3 page supplement (including 2 figures); supplementary movies available at http://mota.stanford.ed

The common ‘thermolabile' variant of methylene tetrahydrofolate reductase is a major determinant of mild hyperhomocysteinaemia

Mild hyperhomocysteinaemia is a major risk factor for vascular disease and neural tube defects (NTDs), conferring an approximately three-fold relative risk for each condition. It has several possible causes: heterozygosity for rare loss of function mutations in the genes for 5,10-methylene tetrahydrofolate reductase (MTHFR) or cystathionine-β-synthase (CBS); dietary insufficiency of vitamin co-factors B6, B12 or folates; or homozygosity for a common ‘thermolabile' mutation in the MTHFR gene which has also been associated with vascular disease and NTDs. We quantified the contribution of the thermolabile mutation to the hyperhomocysteinaemic phenotype in a working male population (625 individuals). Serum folate and vitamin B12 concentrations were also measured and their relationship with homocysteine status and MTHFR genotype assessed. The homozygous thermolabile genotype occurred in 48.4, 35.5, and 23.4% of the top 5,10, and 20% of individuals (respectively) ranked by plasma homocysteine levels, compared with a frequency of 11.5% in the study population as a whole, establishing that the mutation is a major determinant of homocysteine levels at the upper end of the range. Serum folate concentrations also varied with genotype, being lowest in thermolabile homozygotes. The MTHFR thermolabile genotype should be considered when population studies are designed to determine the effective homocysteine-lowering dose of dietary folate supplements, and when prophylactic doses of folate are recommended for individual

"Oh! What a tangled web we weave": Englishness, communicative leisure, identity work and the cultural web of the English folk morris dance scene

In this paper, we consider the relationship between Englishness and the English folk morris dance scene, considering how the latter draws from and reinforces the former. Englishness is considered within the context of the cultural web; a tool more often applied to business management but linked to a sociological viewpoint here. By doing so, we draw the connections between this structured business model and the cultural identity of Englishness. Then, we use the framework of the cultural web and theories of leisure, culture and identity to understand how morris dancers see their role as dancers and ‘communicative leisure’ agents in consciously defending Englishness, English traditions and inventions, the practices and traditions of folk and morris, and the various symbolic communities they inhabit. We argue that most morris dancers in our research become and maintain their leisured identities as dancers because they are attracted to the idea of tradition – even if that tradition is invented and open to change

Introduction: The tourist gaze 4.0: uncovering non-conscious meanings and motivations in the stories tourists tell of trip and destination experiences

This special issue includes unique contributions sharing advanced concepts and tools immediately applicable to building theory that describes and increases understanding of practices in tourist travel and destination experiences. Articles in this special issue focus emic-to-etic reporting on naturalistic drama-enactments that enable tourists as storytellers to experience powerful myths in actual destination settings (also recognising that mythical qualities imbue aspects of both travel and destination sites, e.g., ‘The Orient Express [train]’ and Machu Picchu, Peru, respectively). Tourists’ stories provide intimate tourist travel insights regarding destinations as well as the enactments they engender for tourists. Such insights offer the material for guidelines for productions of ‘authentic’ tourist-destination relationship engagements. This special issue contributes to developing a comprehensive understanding of non-conscious influence-paths that impact tourist-destination behaviours and experiences