2,593 research outputs found
Recent astronomical results from the infrared spatial interferometer and their implications for LOUISA
A new heterodyne interferometer for the atmospheric window from 9 to 12 microns was developed during the past five years. This instrument, called the Infrared Spatial Interferometer (ISI), was designed to use earth rotation aperture synthesis techniques developed in radio interferometry. It was moved to Mt. Wilson, California, in January 1988 and first fringes were obtained in June of that year. Systematic observations of some of the brighter late-type stars began shortly after the first fringes were obtained. We describe the basic principles and design of the ISI and give an overview of some of the initial results obtained from these observations. The implications of our work to the proposed Lunar Optical/UV/IR Synthesis Array (LOUISA) are discussed. We also analyze the conditions for the maximum signal-to-noise ratio of such an interferometer as a function of wavelength. The optimum wavelength is found to depend on the assumed scaling relation between telescope area and wavelength
Electronic phase diagrams of carriers in self-assembled InAs/GaAs quantum dots: violation of Hund's rule and the Aufbau principle for holes
We study the orbital and spin configurations of up to six electrons or holes
charged into self-assembled InAs/GaAs quantum dots via single-particle
pseudopotential and many-particle configuration interaction method. We find
that while the charging of {\it electrons} follows both Hund's rule and the
Aufbau principle, the charging of {\it holes} follows a non-trivial charging
pattern which violates both the Aufbau principle and Hund's rule, and is robust
against the details of the quantum dot size. The predicted hole charging
sequence offers a new interpretation of recent charging experiments
Singlet-triplet splitting, correlation and entanglement of two electrons in quantum dot molecules
Starting with an accurate pseudopotential description of the single-particle
states, and following by configuration-interaction treatment of correlated
electrons in vertically coupled, self-assembled InAs/GaAs quantum
dot-molecules, we show how simpler, popularly-practiced approximations, depict
the basic physical characteristics including the singlet-triplet splitting,
degree of entanglement (DOE) and correlation. The mean-field-like
single-configuration approaches such as Hartree-Fock and local spin density,
lacking correlation, incorrectly identify the ground state symmetry and give
inaccurate values for the singlet-triplet splitting and the DOE. The Hubbard
model gives qualitatively correct results for the ground state symmetry and
singlet-triplet splitting, but produces significant errors in the DOE because
it ignores the fact that the strain is asymmetric even if the dots within a
molecule are identical. Finally, the Heisenberg model gives qualitatively
correct ground state symmetry and singlet-triplet splitting only for rather
large inter-dot separations, but it greatly overestimates the DOE as a
consequence of ignoring the electron double occupancy effect.Comment: 13 pages, 9 figures. To appear in Phys. Rev.
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
Impact of Plant-Based Meat Alternatives on the Gut Microbiota of Consumers: A Real-World Study
Eating less meat is increasingly seen as a healthier, more ethical option. This is leading to growing numbers of flexitarian consumers looking for plant-based meat alternatives (PBMAs) to replace at least some of the animal meat they consume. Popular PBMA products amongst flexitarians, including plant-based mince, burgers, sausages and meatballs, are often perceived as low-quality, ultra-processed foods. However, we argue that the mere industrial processing of ingredients of plant origin does not make a PBMA product ultra-processed by default. To test our hypothesis, we conducted a randomised controlled trial to assess the changes to the gut microbiota of a group of 20 participants who replaced several meat-containing meals per week with meals cooked with PBMA products and compared these changes to those experienced by a size-matched control. Stool samples were subjected to 16S rRNA sequencing. The resulting raw data was analysed in a compositionality-aware manner, using a range of innovative bioinformatic methods. Noteworthy changes included an increase in butyrate metabolising potential—chiefly in the 4-aminobutyrate/succinate and glutarate pathways—and in the joint abundance of butyrate-producing taxa in the intervention group compared to control. We also observed a decrease in the Tenericutes phylum in the intervention group and an increase in the control group. Based on our findings, we concluded that the occasional replacement of animal meat with PBMA products seen in flexitarian dietary patterns can promote positive changes in the gut microbiome of consumers
Paediatric burns anaesthesia: the things that make a difference
Anaesthesia and pain management for paediatric burns continues to challenge and frustrate healthcare professionals in this field of medicine. This review aims to provide some practical management strategies to enable the improved care of burned children. The pathophysiology of burns, toxic shock syndrome, inhalational injuries and perioperative care of paediatric burns is addressed.Keywords: paediatric, burns, pathophysiology, anaesthesia, analgesia, inhalational injurie
Interatomic potentials for the vibrational properties of III-V semiconductor nanostructures
We derive interatomic potentials for zinc blende InAs, InP, GaAs and GaP
semiconductors with possible applications in the realm of nanostructures. The
potentials include bond stretching interaction between the nearest and
next-nearest neighbors, a three body term and a long-range Coulomb interaction.
The optimized potential parameters are obtained by (i) fitting to bulk phonon
dispersions and elastic properties and (ii) constraining the parameter space to
deliver well behaved potentials for the structural relaxation and vibrational
properties of nanostructure clusters. The targets are thereby calculated by
density functional theory for clusters of up to 633 atoms. We illustrate the
new capability by the calculation Kleinman and Gr\"uneisen parameters and of
the vibrational properties of nanostructures with 3 to 5.5 nm diameter.Comment: 22 pages, 5 figures; Phys. Rev. B 201
- …