975 research outputs found
Composition and luminescence of AlInGaN layers grown by plasma-assisted molecular beam epitaxy
A study of AlInGaN epilayers, grown by plasma-assisted molecular beam epitaxy, was performed using spatially resolved x-ray microanalysis and luminescence spectroscopy in order to investigate competition between the incorporation of In, Al, and Ga as a function of the growth temperature in the 565-660 °C range and the nominal AlN mole fraction. The samples studied have AlN and InN mole fractions in the ranges of 4%-30% and 0%-16%, respectively. Composition measurements show the effect of decreasing temperature to be an increase in the incorporation of InN, accompanied by a small but discernible decrease in the ratio of GaN to AlN mole fractions. The incorporation of In is also shown to be significantly increased by decreasing the Al mole fraction. Optical emission peaks, observed by cathodoluminescence mapping and by photoluminescence, provide further information on the epilayer compositions as a function of substrate temperature, and the dependencies of peak energy and linewidth are plotted
Observation of large many-body Coulomb interaction effects in a doped quantum wire
We demonstrate strong one dimensional (1-D) many-body interaction effects in
photoluminescence (PL) in a GaAs single quantum wire of unprecedented optical
quality, where 1-D electron plasma densities are controlled via electrical
gating. We observed PL of 1-D charged excitons with large binding energy of 2.3
meV relative to the neutral excitons, and its evolution to a Fermi-edge
singularity at high electron density. Furthermore, we find a strong band-gap
renormalization in the 1-D wire, or a large red-shift of PL with increased
electron plasma density. Such a large PL red-shift is not observed when we
create a high density neutral electron-hole plasma in the same wire, due
probably to cancellation of the Coulomb interaction energy in the neutral
plasma.Comment: 5 pages, 4 figures, RevTeX, to be published in Solid State
Communication
Grid tool integration within the eMinerals Project
In this article we describe the eMinerals mini grid, which is now running in production mode. Thisis an integration of both compute and data components, the former build upon Condor, PBS and thefunctionality of Globus v2, and the latter being based on the combined use of the Storage ResourceBroker and the CCLRC data portal. We describe how we have integrated the middleware components,and the different facilities provided to the users for submitting jobs within such an environment. We willalso describe additional functionality we found it necessary to provide ourselves
Fermi Edge Singularities and Backscattering in a Weakly Interacting 1D Electron Gas
The photon-absorption edge in a weakly interacting one-dimensional electron
gas is studied, treating backscattering of conduction electrons from the core
hole exactly. Close to threshold, there is a power-law singularity in the
absorption, , with where is the forward scattering
phase shift of the core hole. In contrast to previous theories, is
finite (and universal) in the limit of weak core hole potential. In the case of
weak backscattering , the exponent in the power-law dependence of
absorption on energy crosses over to a value above an energy scale , where is a dimensionless measure of the
electron-electron interactions.Comment: 8 pages + 1 postscript figure, preprint TPI-MINN-93/40-
Urban Organic Farming for Diversified Agriculture
Urban organic farming had been shown in previous projects as well as the present one to have the potential of addressing the fundamental requirements of food security by addressing issues of availability since production is just in the vicinity, which also addresses the carbon footprint of food production because food need not be transported to far distances. The use of organic methods also contributed to increased food safety. More importantly, the practice of urban agriculture empowers local residents in the stewardship, specifically of their barangay’s green spaces and more broadly the whole urban environment (see Mogk, Kwiatkowski, &Weindorf, 2010). However, to make full use of the potentials of urban agriculture, the local government should integrate these initiatives in urban planning and framing of policies and regulations (see Mougeot, 2006 and Mukherji& Morales 2010)
Effect of Finite Impurity Mass on the Anderson Orthogonality Catastrophe in One Dimension
A one-dimensional tight-binding Hamiltonian describes the evolution of a
single impurity interacting locally with electrons. The impurity spectral
function has a power-law singularity
with the same exponent
that characterizes the logarithmic decay of the quasiparticle weight
with the number of electrons , . The exponent
is computed by (1) perturbation theory in the interaction strength and
(2) numerical evaluations with exact results for small systems and variational
results for larger systems. A nonanalytical behavior of is observed in
the limit of infinite impurity mass. For large interaction strength, the
exponent depends strongly on the mass of the impurity in contrast to the
perturbative result.Comment: 26 pages, RevTeX, 7 figures included, to be published in Phys. Rev.
Urban Hydroponics for Diversified Agriculture: Part II
Achieving food security in urban communities proves to be a challenging task. The inability of cities to produce its food requirement means that food has to be imported from faraway places. Traffic congestion, rising fuel prices, and poor road infrastructure have caused problems in transporting food from farms to markets. The increase in rates of spoilage of perishable vegetables and in transportation costs is a food security issue that needs to be addressed
Exact calculation of spectral properties of a particle interacting with a one dimensional fermionic system
Using the Bethe ansatz analysis as was reformulated by Edwards, we calculate
the spectral properties of a particle interacting with a bath of fermions in
one dimension for the case of equal particle-fermion masses. These are directly
related to singularities apparent in optical experiments in one dimensional
systems. The orthogonality catastrophe for the case of an infinite particle
mass survives in the limit of equal masses. We find that the exponent
of the quasiparticle weight, is different for the two
cases, and proportional to their respective phaseshifts at the Fermi surface;
we present a simple physical argument for this difference. We also show that
these exponents describe the low energy behavior of the spectral function, for
repulsive as well as attractive interaction.Comment: 22 pages + 1 postscript figure, REVTE
Transport properties of a quantum wire in the presence of impurities and long-range Coulomb forces
One-dimensional electron systems interacting with long-range Coulomb forces
(quantum wires) show a Wigner crystal structure. We investigate in this paper
the transport properties of such a Wigner crystal in the presence of
impurities. Contrary to what happens when only short-range interactions are
included, the system is dominated by scattering on the impurities.
There are two important length scales in such a problem: one is the pinning
length above which the (quasi-)long-range order of the Wigner crystal is
destroyed by disorder. The other length is the length below which
Coulomb interactions are not important and the system is behaving as a standard
Luttinger liquid with short-range interactions. We obtain the frequency and
temperature dependence of the conductivity. We show that such a system is very
similar to a classical charge density wave pinned by impurities, but with
important differences due to quantum fluctuations and long-range Coulomb
interactions. Finally we discuss our results in comparison with experimental
systems.Comment: 25 pages, RevTex3.
- …