12,429 research outputs found
The C*-algebra of an affine map on the 3-torus
We study the C*-algebra of an affine map on a compact abelian group and give
necessary and sufficient conditions for strong transitivity when the group is a
torus. The structure of the C*-algebra is completely determined for all
strongly transitive affine maps on a torus of dimension one, two or three
Radiation effects in MOS integrated circuits
High energy electron irradiation effects on field effect transistors in integrated circuit device
Bioethanol from Germinated Grains.
The most well-known way to produce bioethanol is by the enzymatic hydrolysis and fermentation of starch. In a new project “BioConcens” (2007) sponsored by DARCOF (DAnish Research Center for Organic Food and farming) one aim is to develop a combined ethanol and biogas production for use in organic farming using starch containing biomass. Natural enzymes from cereals will be used for hydrolysis of starch to glucose in accordance with technology in brewing technology. Commercial enzymes are often produced from gene-modified organisms and will therefore not be used in the suggested organic context or process.
A preliminary study was performed in which grains of wheat, rye, and barley were germinated using traditional methods applied in malting for beer production. During malting the amylase enzymes present in the grain are activated (autoamylolytic effect). Three steps were applied in the malting process; steeping, germination, and drying of the grains. After malting the grains were milled and mixed with water to 13% DM, cooked at 57.5C for 2 hours (to activate the enzymes), and cooled to 30C before adding Bakers Yeast.
The results of this study indicate that efficient hydrolysis of starch can be achieved by activation of autoamylolytic enzymes in cereal grains after a malting process. The ethanol yields obtained in the autoamylolytic hydrolysis was comparable (or slightly higher) to that of reference experiments using commercial enzymes (amylases). The highest ethanol yield was obtained with wheat (0.34 g/g DM grain), followed by barley (0.31 g/g DM grain), and rye (0.29 g/g DM grain)
Exciton resonances quench the photoluminescence of zigzag carbon nanotubes
We show that the photoluminescence intensity of single-walled carbon
nanotubes is much stronger in tubes with large chiral angles - armchair tubes -
because exciton resonances make the luminescence of zigzag tubes intrinsically
weak. This exciton-exciton resonance depends on the electronic structure of the
tubes and is found more often in nanotubes of the +1 family. Armchair tubes do
not necessarily grow preferentially with present growth techniques; they just
have stronger luminescence. Our analysis allows to normalize photoluminescence
intensities and find the abundance of nanotube chiralities in macroscopic
samples.Comment: 4 pages and 2 supplementary pages; 6 figure
Dirac model of electronic transport in graphene antidot barriers
In order to use graphene for semiconductor applications, such as transistors
with high on/off ratios, a band gap must be introduced into this otherwise
semimetallic material. A promising method of achieving a band gap is by
introducing nanoscale perforations (antidots) in a periodic pattern, known as a
graphene antidot lattice (GAL). A graphene antidot barrier (GAB) can be made by
introducing a 1D GAL strip in an otherwise pristine sheet of graphene. In this
paper, we will use the Dirac equation (DE) with a spatially varying mass term
to calculate the electronic transport through such structures. Our approach is
much more general than previous attempts to use the Dirac equation to calculate
scattering of Dirac electrons on antidots. The advantage of using the DE is
that the computational time is scale invariant and our method may therefore be
used to calculate properties of arbitrarily large structures. We show that the
results of our Dirac model are in quantitative agreement with tight-binding for
hexagonal antidots with armchair edges. Furthermore, for a wide range of
structures, we verify that a relatively narrow GAB, with only a few antidots in
the unit cell, is sufficient to give rise to a transport gap
Electronic and optical properties of graphene antidot lattices: Comparison of Dirac and tight-binding models
The electronic properties of graphene may be changed from semimetallic to
semiconducting by introducing perforations (antidots) in a periodic pattern.
The properties of such graphene antidot lattices (GALs) have previously been
studied using atomistic models, which are very time consuming for large
structures. We present a continuum model that uses the Dirac equation (DE) to
describe the electronic and optical properties of GALs. The advantages of the
Dirac model are that the calculation time does not depend on the size of the
structures and that the results are scalable. In addition, an approximation of
the band gap using the DE is presented. The Dirac model is compared with
nearest-neighbour tight-binding (TB) in order to assess its accuracy. Extended
zigzag regions give rise to localized edge states, whereas armchair edges do
not. We find that the Dirac model is in quantitative agreement with TB for GALs
without edge states, but deviates for antidots with large zigzag regions.Comment: 15 pages, 7 figures. Accepted by Journal of Physics: Condensed matte
Chirality distribution and transition energies of carbon nanotubes
From resonant Raman scattering on isolated nanotubes we obtained the optical
transition energies, the radial breathing mode frequency and Raman intensity of
both metallic and semiconducting tubes. We unambiguously assigned the chiral
index (n_1,n_2) of approximately 50 nanotubes based solely on a third-neighbor
tight-binding Kataura plot and find omega_RBM=214.4cm^-1nm/d+18.7cm^-1. In
contrast to luminescence experiments we observe all chiralities including
zig-zag tubes. The Raman intensities have a systematic chiral-angle dependence
confirming recent ab-initio calculations.Comment: 4 pages, to be published in Phys. Rev. Let
Integrating Field Methods, Remote Sensing and Modeling to Monitor Climate-Adapted Tidal Marsh Restoration
Sea level rise threatens coastal wetlands worldwide. In response, wetland restoration projects are implementing strategies that decrease vulnerability to this threat. Vegetation monitoring at sites employing new restoration strategies, including determination of appropriate and efficient monitoring techniques, is critical to improve understanding of factors leading to restoration success and maximize benefits of future projects. In Central California, sediment addition raised a degraded marsh plain to a high elevation expected to be resilient to sea level rise over the next century. We conducted area searches of plant survival and modeled effects of nine predictors on new vegetation cover using two monitoring strategies: 1) transect surveys, and 2) unmanned aircraft systems (UAS) imagery. We conducted targeted sediment sampling to examine additional chemical or physical sediment properties contributing to vegetation patterns. Limited vegetation survived sediment addition, likely due to the thickness and placement method. Cover reached 8-14% in the initially-bare area after one year. Elevation and inundation frequency were particularly critical to understanding restoration success, with greatest cover in high-elevation areas tidally-inundated \u3c 0.85% of the time. Sediment analysis suggested greater salinity stress and ammonia levels in poorly-vegetated compared to well-vegetated areas at the same elevation, which may be driven by variation in physical sediment properties. Similar modeling results indicate both transect and UAS methods were suitable for monitoring this site. Field transects may provide the best approach for tracking vegetation colonization if resources are limited, but UAS can complement this to provide landscape perspective
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