Asymmetry in self-assembled quantum dot-molecules made of identical InAs/GaAs quantum dots

We show that a diatomic dot molecule made of two identical, vertically stacked, strained InAs/GaAs self-assembled dots exhibits an asymmetry in its single-particle and may-particle wavefunctions. The single-particle wave function is asymmetric due to the inhomogeneous strain, while the asymmetry of the many-particle wavefunctions is caused by the correlation induced localization: the lowest singlet $^1\Sigma_g$ and triplet $^3\Sigma$ states show that the two electrons are each localized on different dots within the molecule, for the next singlet states $^1\Sigma_u$ both electrons are localized on the same (bottom) dot for interdot separation $d>$ 8 nm. The singlet-triplet splitting is found to be $\sim 0.1$ meV at inter-dot separation $d$=9 nm and as large as 100 meV for $d$=4 nm, orders of magnitude larger than the few meV found in the large (50 - 100 nm) electrostatically confined dots

Atomic Effective Pseudopotentials for Semiconductors

We derive an analytic connection between the screened self-consistent effective potential from density functional theory (DFT) and atomic effective pseudopotentials (AEPs). The motivation to derive AEPs is to address structures with thousands to hundred thousand atoms, as given in most nanostructures. The use of AEPs allows to bypass a self-consistent procedure and to address eigenstates around a certain region of the spectrum (e.g., around the band gap). The bulk AEP construction requires two simple DFT calculations of slightly deformed elongated cells. The ensuing AEPs are given on a fine reciprocal space grid, including the small reciprocal vector components, are free of parameters, and involve no fitting procedure. We further show how to connect the AEPs of different bulk materials, which is necessary to obtain accurate band offsets. We derive a total of 20 AEPs for III-V, II-VI and group IV semiconductors and demonstrate their accuracy and transferability by comparison to DFT calculations of strained bulk structures, quantum wells with varying thickness, and semiconductor alloys.Comment: 10 pages, 5 figures, submitted to PR

Project-based learning: Panacea for change or old wine in new bottles?

One of the key characteristics of vocational higher education is the incorporation of work-integrated learning (WIL) where students draw on theoretical principles to deal with workplace dynamics and solve problems within workplace contexts. While workplace-based learning (WPBL) was the default modality for diploma qualifications at this institution, a curriculum revision process revealed a shift from workplace-based learning to project-based learning (PJBL). This study explored the reasons for the shift to PJBL as the preferred WIL modality in four diploma qualifications. Curriculum Officers were interviewed to establish the rationale for shifting to PJBL as well as how PJBL would be structured as pedagogy for learning in and outside the workplace. The interview data were subjected to content analysis to extract themes based on the core questions of the interview protocol. Curriculum documents were analysed to determine whether interview data were validated with documented evidence. The second generation of activity theory components provided a theoretical lens for data analysis and discussion.  The findings showed that the prevailing view was that PJBL would provide an improved and more effective learning experience, but attention to detail as to how PJBL would be operationalized were scant. Although PJBL holds the promise of positive change, the absence of project details might scupper any envisaged successes. Since this shift towards PJBL is groundbreaking given the legacy of WPBL in diploma qualifications at universities of technology, this study will provide insights into the merits of current and future WIL practices for diploma qualifications

Electric field control and optical signature of entanglement in quantum dot molecules

The degree of entanglement of an electron with a hole in a vertically coupled self-assembled dot molecule is shown to be tunable by an external electric field. Using atomistic pseudopotential calculations followed by a configuration interaction many-body treatment of correlations, we calculate the electronic states, degree of entanglement and optical absorption. We offer a novel way to spectroscopically detect the magnitude of electric field needed to maximize the entanglement.Comment: 4 pages, 6 figure

Ethical demand and first year civil engineering study : applying virtue ethics

Abstract: Incidents within the civil engineering profession (structural collapses, collusion, and the like) draw attention to the need for ethical conduct on the part of civil engineering practitioners. This paper explores ethical action in first-year civil engineering study. This is done to discuss the role of universities in the development of civil engineering graduates with a critical awareness of the need for ethical action. The paperusesaparticularapproachtovirtueethicstotheorizefirst-yearstudentactionsduringapracticalexerciseinconcretemixproportioning. Three aspects of ethical action emerged from observation of the students’ completion of this practicum: corner-cutting, erroneous reporting, and misrepresentation of knowledge and ability. The paper argues that ethical behavior should be nurtured and discussed throughout the undergraduate degree, so that students are more likely to practice ethical behavior after graduation. There is thus opportunity to better integrateconsiderationofethicalresponsibilityintotheundergraduatecurriculum, and to shift the focus of higher education away from external goods to the good of the profession and the communities it serves

Experimental imaging and atomistic modeling of electron and hole quasiparticle wave functions in InAs/GaAs quantum dots

We present experimental magnetotunneling results and atomistic pseudopotential calculations of quasiparticle electron and hole wave functions of self-assembled InAs/GaAs quantum dots. The combination of a predictive theory along with the experimental results allows us to gain direct insight into the quantum states. We monitor the effects of (i) correlations, (ii) atomistic symmetry and (iii) piezoelectricity on the confined carriers and (iv) observe a peculiar charging sequence of holes that violates the Aufbau principle.Comment: Submitted to Physical Review B. A version of this paper with figures can be found at http://www.sst.nrel.gov/nano_pub/mts_preprint.pd

Characterisation of different GLRaV-3 variant infections by determining virus concentration ratios and miRNA expression profiles

Grapevine leafroll disease (GLD) is present in all grape-growing regions of the world and is considered the most significant grapevine viral disease. Grapevine leafroll-associated virus 3 (GLRaV-3) is considered the primary cause of GLD and in South African vineyards five genetic variant groups (I, II, III, VI and VII) have been confirmed. Biological distinctions between GLRaV-3 variants have not been fully validated. By characterising virus concentration and stress-responsive microRNA expression in GLRaV-3 infected plants, this study aimed to glean a better understanding of the possible biological distinctions between GLRaV-3 variants. Quantitative reverse transcription PCR was utilised for virus concentration ratio (VCR) determination and miRNA quantitation in GLRaV-3 positive and negative grapevines grown under greenhouse and field conditions. This study found statistically significant differences in VCRs in plants singly infected with different GLRaV-3 variants. Interestingly, no difference in mean VCRs were observed between data sets, despite notable differences in plant age, duration of GLRaV-3 infection, scion/rootstock combination and growing conditions. Several miRNAs showed statistically significant expression modulation between infected and healthy samples. miRNA expression between data sets varied substantially and a greater overall miRNA response was observed in plants with more established GLRaV-3 infections. The lack of significant differences in mean VCRs between data sets, coupled with the consistent modulation of certain miRNAs in plants that have likely been infected for longer is a promising result. This finding could indicate that successful inhibition of further virus replication by plant defence mechanisms occurred, and that these miRNAs are implicated in this response

Biochemical reference values in elderly black subjects

Biochemical reference values for the black age group of ≥ 65 years were determined from the black urban population of the Orange Free State. Biochemical investigations performed were those included in the Sequential Multiple Analyser Computer profile because it includes the 20 most requested clinical chemistry investigations. Most of the reference values corresponded to values for the same age groups in the Western world. There was no age-related rise in the alkaline phosphatase values, which suggested absence of occult Paget's disease. Reference values for serum total protein and globulin were found to be higher than values derived from elderly white groups