5,913 research outputs found
InAs/InP single quantum wire formation and emission at 1.5 microns
Isolated InAs/InP self-assembled quantum wires have been grown using in situ
accumulated stress measurements to adjust the optimal InAs thickness. Atomic
force microscopy imaging shows highly asymmetric nanostructures with average
length exceeding more than ten times their width. High resolution optical
investigation of as-grown samples reveals strong photoluminescence from
individual quantum wires at 1.5 microns. Additional sharp features are related
to monolayer fluctuations of the two dimensional InAs layer present during the
early stages of the quantum wire self-assembling process.Comment: 4 pages and 3 figures submitted to Applied Physics Letter
Excitons in coupled InAs/InP self-assembled quantum wires
Optical transitions in coupled InAs/InP self-assembled quantum wires are
studied within the single-band effective mass approximation including effects
due to strain. Both vertically and horizontally coupled quantum wires are
investigated and the ground state, excited states and the photoluminescence
peak energies are calculated. Where possible we compare with available
photo-luminescence data from which it was possible to determine the height of
the quantum wires. An anti-crossing of the energy of excited states is found
for vertically coupled wires signaling a change of symmetry of the exciton
wavefunction. This crossing is the signature of two different coupling regimes.Comment: 8 pages, 8 figures. To appear in Physical Review
A momentum-conserving, consistent, Volume-of-Fluid method for incompressible flow on staggered grids
The computation of flows with large density contrasts is notoriously
difficult. To alleviate the difficulty we consider a consistent mass and
momentum-conserving discretization of the Navier-Stokes equation.
Incompressible flow with capillary forces is modelled and the discretization is
performed on a staggered grid of Marker and Cell type. The Volume-of-Fluid
method is used to track the interface and a Height-Function method is used to
compute surface tension. The advection of the volume fraction is performed
using either the Lagrangian-Explicit / CIAM (Calcul d'Interface Affine par
Morceaux) method or the Weymouth and Yue (WY) Eulerian-Implicit method. The WY
method conserves fluid mass to machine accuracy provided incompressiblity is
satisfied which leads to a method that is both momentum and mass-conserving. To
improve the stability of these methods momentum fluxes are advected in a manner
"consistent" with the volume-fraction fluxes, that is a discontinuity of the
momentum is advected at the same speed as a discontinuity of the density. To
find the density on the staggered cells on which the velocity is centered, an
auxiliary reconstruction of the density is performed. The method is tested for
a droplet without surface tension in uniform flow, for a droplet suddenly
accelerated in a carrying gas at rest at very large density ratio without
viscosity or surface tension, for the Kelvin-Helmholtz instability, for a
falling raindrop and for an atomizing flow in air-water conditions
Exciton Gas Compression and Metallic Condensation in a Single Semiconductor Quantum Wire
We study the metal-insulator transition in individual self-assembled quantum
wires and report optical evidences of metallic liquid condensation at low
temperatures. Firstly, we observe that the temperature and power dependence of
the single nanowire photoluminescence follow the evolution expected for an
electron-hole liquid in one dimension. Secondly, we find novel spectral
features that suggest that in this situation the expanding liquid condensate
compresses the exciton gas in real space. Finally, we estimate the critical
density and critical temperature of the phase transition diagram at
cm and K, respectively.Comment: 4 pages, 5 figure
Charge control in laterally coupled double quantum dots
We investigate the electronic and optical properties of InAs double quantum
dots grown on GaAs (001) and laterally aligned along the [110] crystal
direction. The emission spectrum has been investigated as a function of a
lateral electric field applied along the quantum dot pair mutual axis. The
number of confined electrons can be controlled with the external bias leading
to sharp energy shifts which we use to identify the emission from neutral and
charged exciton complexes. Quantum tunnelling of these electrons is proposed to
explain the reversed ordering of the trion emission lines as compared to that
of excitons in our system.Comment: 4 pages, 4 figures submitted to PRB Rapid Com
Staphylococcus Aureus Infective Endocarditis: JACC Patient Pathways.
A 19-year-old female patient presented with Staphylococcus aureus infective endocarditis, with suspected subdural brain hemorrhage, disseminated intravascular coagulopathy, and septic renal as well as spleen infarcts. The patient had extensive vegetations on the mitral and tricuspid valves and underwent urgent mitral and tricuspid repair. This paper discusses the clinical case and current evidence regarding the management and treatment of Staphylococcus aureus endocarditis.S
Food groups and risk of coronary heart disease, stroke and heart failure : a systematic review and dose-response meta-analysis of prospective studies
Background: Despite growing evidence for food-based dietary patterns' potential to reduce cardiovascular disease risk, knowledge about the amounts of food associated with the greatest change in risk of specific cardiovascular outcomes and about the quality of meta-evidence is limited. Therefore, the aim of this meta-analysis was to synthesize the knowledge about the relation between intake of 12 major food groups (whole grains, refined grains, vegetables, fruits, nuts, legumes, eggs, dairy, fish, red meat, processed meat, and sugar-sweetened beverages [SSB]) and the risk of coronary heart disease (CHD), stroke and heart failure (HF).
Methods: We conducted a systematic search in PubMed and Embase up to March 2017 for prospective studies. Summary risk ratios (RRs) and 95% confidence intervals (95% CI) were estimated using a random effects model for highest versus lowest intake categories, as well as for linear and non-linear relationships.
Results: Overall, 123 reports were included in the meta-analyses. An inverse association was present for whole grains (RRCHD: 0.95 (95% CI: 0.92-0.98), RRHF: 0.96 (0.95-0.97)), vegetables and fruits (RRCHD: 0.97 (0.96-0.99), and 0.94 (0.90-0.97); RRstroke: 0.92 (0.86-0.98), and 0.90 (0.84-0.97)), nuts (RRCHD: 0.67 (0.43-1.05)), and fish consumption (RRCHD: 0.88 (0.79-0.99), RRstroke: 0.86 (0.75-0.99), and RRHF: 0.80 (0.67-0.95)), while a positive association was present for egg (RRHF: 1.16 (1.03-1.31)), red meat (RRCHD: 1.15 (1.08-1.23), RRstroke: 1.12 (1.06-1.17), RRHF: 1.08 (1.02-1.14)), processed meat (RRCHD: 1.27 (1.09-1.49), RRstroke: 1.17 (1.02-1.34), RRHF: 1.12 (1.05-1.19)), and SSB consumption (RRCHD: 1.17 (1.11-1.23), RRstroke: 1.07 (1.02-1.12), RRHF: 1.08 (1.05-1.12)) in the linear dose-response meta-analysis. There were clear indications for non-linear dose-response relationships between whole grains, fruits, nuts, dairy, and red meat and CHD.
Conclusion: An optimal intake of whole grains, vegetables, fruits, nuts, legumes, dairy, fish, red and processed meat, eggs and SSB showed an important lower risk of CHD, stroke, and HF
Self-assembling processes involved in the molecular beam epitaxy growth of stacked InAs/InP quantum wires
The growth mechanism of stacked InAs/InP(001) quantum wires (QWRs) is studied by combining an atomic-scale cross-sectional scanning tunnelling microscopy analysis with in situ and in real-time stress measurements along the [110] direction (sensitive to stress relaxation during QWR formation). QWRs in stacked layers grow by a non-Stranski–Krastanov (SK) process which involves the production of extra InAs by strain-enhanced As/P exchange and a strong strain driven mass transport. Despite the different growth mechanism of the QWR between the first and following layers of the stack, the QWRs maintain on average the same shape and composition in all the layers of the stack, revealing the high stability of this QWR configuration
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