10,391 research outputs found
ADJUSTMENTS OF MIDWEST GRAIN FARM BUSINESSES IN RESPONSE TO INCREASES IN PETROLEUM ENERGY PRICES
Crop Production/Industries, Resource /Energy Economics and Policy,
MARKET STRUCTURE AND SPATIAL PRICE DYNAMICS
A method was developed with time series models to test hypotheses about the relationship between market structure and spatial price dynamics. Long-run dynamic multipliers measuring the magnitude of lagged adjustments for spatial milled rice prices were calculated from the time series model and used as the dependent variable in a regression model that included a number of factors expected to influence price determination. Results show that price adjustments were slower as regional submarket concentration increased and were faster in the regions with a higher market share. Arkansas, the state with the largest market share, was consistently a price leaderDemand and Price Analysis, Industrial Organization,
Advanced Coordinated Beamforming for the Downlink of Future LTE Cellular Networks
Modern cellular networks in traditional frequency bands are notoriously
interference-limited especially in urban areas, where base stations are
deployed in close proximity to one another. The latest releases of Long Term
Evolution (LTE) incorporate features for coordinating downlink transmissions as
an efficient means of managing interference. Recent field trial results and
theoretical studies of the performance of joint transmission (JT) coordinated
multi-point (CoMP) schemes revealed, however, that their gains are not as high
as initially expected, despite the large coordination overhead. These schemes
are known to be very sensitive to defects in synchronization or information
exchange between coordinating bases stations as well as uncoordinated
interference. In this article, we review recent advanced coordinated
beamforming (CB) schemes as alternatives, requiring less overhead than JT CoMP
while achieving good performance in realistic conditions. By stipulating that,
in certain LTE scenarios of increasing interest, uncoordinated interference
constitutes a major factor in the performance of CoMP techniques at large, we
hereby assess the resilience of the state-of-the-art CB to uncoordinated
interference. We also describe how these techniques can leverage the latest
specifications of current cellular networks, and how they may perform when we
consider standardized feedback and coordination. This allows us to identify
some key roadblocks and research directions to address as LTE evolves towards
the future of mobile communications.Comment: 16 pages, 6 figures, accepted to IEEE Communications Magazin
The Mr 28,000 gap junction proteins from rat heart and liver are different but related
The sequence of the amino-terminal 32 residues of the rat heart Mr 28,000 gap junction protein presented here allows, for the first time, a sequence comparison of gap junctional proteins from different tissues (heart and liver). Comparison of the rat heart gap junction protein sequence and that available from rat liver reveals 43% sequence identity and conservative changes at an additional 25% of the positions. Both proteins exhibit a hydrophobic domain which could represent a transmembrane span of the junction. This result unequivocally demonstrates the existence of at least two forms of the gap junction protein. As yet, no homology is evident between the gap junctional proteins of either heart or liver and main intrinsic protein from rat eye lens
Phase transitions in the Shastry-Sutherland lattice
Two recently developed theoretical approaches are applied to the
Shastry-Sutherland lattice, varying the ratio between the couplings on
the square lattice and on the oblique bonds. A self-consistent perturbation,
starting from either Ising or plaquette bond singlets, supports the existence
of an intermediate phase between the dimer phase and the Ising phase. This
existence is confirmed by the results of a renormalized excitonic method. This
method, which satisfactorily reproduces the singlet triplet gap in the dimer
phase, confirms the existence of a gapped phase in the interval
Comment: Submited for publication in Phys. Rev.
Three-dimensional dynamic rupture simulation with a high-order discontinuous Galerkin method on unstructured tetrahedral meshes
Accurate and efficient numerical methods to simulate dynamic earthquake rupture and wave propagation in complex media and complex fault geometries are needed to address fundamental questions in earthquake dynamics, to integrate seismic and geodetic data into emerging approaches for dynamic source inversion, and to generate realistic physics-based earthquake scenarios for hazard assessment. Modeling of spontaneous earthquake rupture and seismic wave propagation by a high-order discontinuous Galerkin (DG) method combined with an arbitrarily high-order derivatives (ADER) time integration method was introduced in two dimensions by de la Puente et al. (2009). The ADER-DG method enables high accuracy in space and time and discretization by unstructured meshes. Here we extend this method to three-dimensional dynamic rupture problems. The high geometrical flexibility provided by the usage of tetrahedral elements and the lack of spurious mesh reflections in the ADER-DG method allows the refinement of the mesh close to the fault to model the rupture dynamics adequately while concentrating computational resources only where needed. Moreover, ADER-DG does not generate spurious high-frequency perturbations on the fault and hence does not require artificial Kelvin-Voigt damping. We verify our three-dimensional implementation by comparing results of the SCEC TPV3 test problem with two well-established numerical methods, finite differences, and spectral boundary integral. Furthermore, a convergence study is presented to demonstrate the systematic consistency of the method. To illustrate the capabilities of the high-order accurate ADER-DG scheme on unstructured meshes, we simulate an earthquake scenario, inspired by the 1992 Landers earthquake, that includes curved faults, fault branches, and surface topography
Quasiparticles and phonon satellites in spectral functions of semiconductors and insulators: Cumulants applied to full first principles theory and Fr\"ohlich polaron
The electron-phonon interaction causes thermal and zero-point motion shifts
of electron quasiparticle (QP) energies . Other consequences of
interactions, visible in angle-resolved photoemission spectroscopy (ARPES)
experiments, are broadening of QP peaks and appearance of sidebands, contained
in the electron spectral function
, where is the retarded Green's
function. Electronic structure codes (e.g. using density-functional theory) are
now available that compute the shifts and start to address broadening and
sidebands. Here we consider MgO and LiF, and determine their nonadiabatic
Migdal self energy. The spectral function obtained from the Dyson equation
makes errors in the weight and energy of the QP peak and the position and
weight of the phonon-induced sidebands. Only one phonon satellite appears, with
an unphysically large energy difference (larger than the highest phonon energy)
with respect to the QP peak. By contrast, the spectral function from a cumulant
treatment of the same self energy is physically better, giving a quite accurate
QP energy and several satellites approximately spaced by the LO phonon energy.
In particular, the positions of the QP peak and first satellite agree closely
with those found for the Fr\"ohlich Hamiltonian by Mishchenko
(2000) using diagrammatic Monte Carlo. We provide a detailed comparison between
the first-principles MgO and LiF results and those of the Fr\"ohlich
Hamiltonian. Such an analysis applies widely to materials with infra-red active
phonons. We also compare the retarded and time-ordered cumulant treatments:
they are equivalent for the Fr\"ohlich Hamiltonian, and only slightly differ in
first-principles electron-phonon results for wide-band gap materials.Comment: 21 pages, 19 figure
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