11,084 research outputs found
A Comparison of Risk and Return Characteristics of Efficient Crop Portfolios for the Brown Soil Zones Saskatchewan and Mecklenburg, Germany
Two efficient farms are constructed for the brown soils of Saskatchewan, Canada and for Mecklenburg, Germany based on producer panels. Both farms feature highly integrated cropping systems which take advantage of cropping synergies. However, farm risk is inherently different between the two because differences in 1) climate that gives rise to very different yield risk and cost structure, and 2) EU programs which offer fixed cash payments and stable sugar beet prices. As expected, risk is much higher for the Saskatchewan case farm - it has a chance of a negative cash flow of approximately one year in five. In sharp contrast, the Mecklenburg has very little chance of generating a negative cash flow. Hence, it is easy to understand why crop insurance and other risk reducing types of programs have long been popular in Saskatchewan grain and oilseed price and yield risk make for a very real possibility of cash shortfalls on even the most efficient farm with moderate debt. On the other hand, there is little need for such risk reducing programs by efficient German farms because risk remains relatively low unless he/she is financially imprudent. Moving to higher farmland rents associated with an equilibrated land market or removing government payments increases risk considerably, but still at levels well below those of the Saskatchewan case farm.risk and return, EV model, Saskatchewan and German grain farms, Crop Production/Industries,
Magnon-mediated interactions between fermions depend strongly on the lattice structure
We propose two new methods to calculate exactly the spectrum of two
spin- charge carriers moving in a ferromagnetic background, at zero
temperature. We find that if the spins are located on a different sublattice
than that on which the fermions move, magnon-mediated effective interactions
are very strong and can bind the fermions into low-energy bipolarons with
triplet character. This never happens in models where spins and charge carriers
share the same lattice, whether they are in the same band or in different
bands. This proves that effective one-lattice models do not describe correctly
the low-energy part of the two-carrier spectrum of a two-sublattice model, even
though they may describe the low-energy single-carrier spectrum appropriately
Energy Momentum Tensor and Marginal Deformations in Open String Field Theory
Marginal boundary deformations in a two dimensional conformal field theory
correspond to a family of classical solutions of the equations of motion of
open string field theory. In this paper we develop a systematic method for
relating the parameter labelling the marginal boundary deformation in the
conformal field theory to the parameter labelling the classical solution in
open string field theory. This is done by first constructing the
energy-momentum tensor associated with the classical solution in open string
field theory using Noether method, and then comparing this to the answer
obtained in the conformal field theory by analysing the boundary state. We also
use this method to demonstrate that in open string field theory the tachyon
lump solution on a circle of radius larger than one has vanishing pressure
along the circle direction, as is expected for a codimension one D-brane.Comment: LaTeX file, 25 pages; v2: minor addition
Testing Closed String Field Theory with Marginal Fields
We study the feasibility of level expansion and test the quartic vertex of
closed string field theory by checking the flatness of the potential in
marginal directions. The tests, which work out correctly, require the
cancellation of two contributions: one from an infinite-level computation with
the cubic vertex and the other from a finite-level computation with the quartic
vertex. The numerical results suggest that the quartic vertex contributions are
comparable or smaller than those of level four fields.Comment: 14 pages, LaTeX. v2: New references to work of Beccaria and Rampino,
and Taylor. Improved numerical analysis at the end of section
Domestic Relations: Custody: Refusal to Award Custody of Retarded Child to State Where Parents Would Not Permit Heart Surgery. (In re Phillip B.).
Tachyon condensation in open-closed p-adic string theory
We study a simple model of p-adic closed and open strings. It sheds some
light on the dynamics of tachyon condensation for both types of strings. We
calculate the effect of static and decaying D-brane configurations on the
closed string background. For closed string tachyons we find lumps analogous to
D-branes. By studying their fluctuation spectrum and the D-branes they admit,
we argue that closed string lumps should be interpreted as spacetimes of lower
dimensionality described by some noncritical p-adic string theory.Comment: 21 pages, 3 figures; v2: discussion of the fluctuations of the double
lump substantially improve
Tachyon cosmology with non-vanishing minimum potential: a unified model
We investigate the tachyon condensation process in the effective theory with
non-vanishing minimum potential and its implications to cosmology. It is shown
that the tachyon condensation on an unstable three-brane described by this
modified tachyon field theory leads to lower-dimensional branes (defects)
forming within a stable three-brane. Thus, in the cosmological background, we
can get well-behaved tachyon matter after tachyon inflation, (partially)
avoiding difficulties encountered in the original tachyon cosmological models.
This feature also implies that the tachyon inflated and reheated universe is
followed by a Chaplygin gas dark matter and dark energy universe. Hence, such
an unstable three-brane behaves quite like our universe, reproducing the key
features of the whole evolutionary history of the universe and providing a
unified description of inflaton, dark matter and dark energy in a very simple
single-scalar field model.Comment: 18 p
Thrust Stand for Vertically Oriented Electric Propulsion Performance Evaluation
A variation of a hanging pendulum thrust stand capable of measuring the performance of an electric thruster operating in the vertical orientation is presented. The vertical orientation of the thruster dictates that the thruster must be horizontally offset from the pendulum pivot arm, necessitating the use of a counterweight system to provide a neutrally-stable system. Motion of the pendulum arm is transferred through a balance mechanism to a secondary arm on which deflection is measured. A non-contact light-based transducer is used to measure displacement of the secondary beam. The members experience very little friction, rotating on twisting torsional pivots with oscillatory motion attenuated by a passive, eddy current damper. Displacement is calibrated using an in situ thrust calibration system. Thermal management and self-leveling systems are incorporated to mitigate thermal and mechanical drifts. Gravitational restoring force and torsional spring constants associated with flexure pivots provide restoring moments. An analysis of the design indicates that the thrust measurement range spans roughly four decades, with the stand capable of measuring thrust up to 12 N for a 200 kg thruster and up to approximately 800 mN for a 10 kg thruster. Data obtained from calibration tests performed using a 26.8 lbm simulated thruster indicated a resolution of 1 mN on 100 mN-level thrusts, while those tests conducted on 200 lbm thruster yielded a resolution of roughly 2.5 micro at thrust levels of 0.5 N and greater
TRIP13 is a protein-remodeling AAA+ ATPase that catalyzes MAD2 conformation switching.
The AAA+ family ATPase TRIP13 is a key regulator of meiotic recombination and the spindle assembly checkpoint, acting on signaling proteins of the conserved HORMA domain family. Here we present the structure of the Caenorhabditis elegans TRIP13 ortholog PCH-2, revealing a new family of AAA+ ATPase protein remodelers. PCH-2 possesses a substrate-recognition domain related to those of the protein remodelers NSF and p97, while its overall hexameric architecture and likely structural mechanism bear close similarities to the bacterial protein unfoldase ClpX. We find that TRIP13, aided by the adapter protein p31(comet), converts the HORMA-family spindle checkpoint protein MAD2 from a signaling-active 'closed' conformer to an inactive 'open' conformer. We propose that TRIP13 and p31(comet) collaborate to inactivate the spindle assembly checkpoint through MAD2 conformational conversion and disassembly of mitotic checkpoint complexes. A parallel HORMA protein disassembly activity likely underlies TRIP13's critical regulatory functions in meiotic chromosome structure and recombination
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