3,265 research outputs found
Econometric Analysis of the Effects of Subsidies on Farm Production in Case of Endogenous Input Quantities
The effect of subsidies on farm production has been a major topic in agricultural economics for several decades. We present a new approach for analyzing the effects of different types of coupled and decoupled subsidies on farm production with econometric methods. In contrast to most previous studies, our approach is entirely based on a theoretical microeconomic model, explicitly allows subsidies to have an impact on input use, and takes linkages between the farm and the farm household into account.Agricultural and Food Policy, Productivity Analysis,
Econometric Analysis of the Effects of Subsidies on Farm Production in Case of Endogenous Input Quantities
Replaced with revised version of paper 07/29/09.panel data, subsidies, household model, endogeneity, Norwegian grain farming, Agricultural and Food Policy, Consumer/Household Economics, Production Economics,
Quantum Spin Tomography in Ferromagnet-Normal Conductors
We present a theory for a complete reconstruction of non-local spin
correlations in ferromagnet-normal conductors. This quantum spin tomography is
based on cross correlation measurements of electric currents into ferromagnetic
terminals with controllable magnetization directions. For normal injectors,
non-local spin correlations are universal and strong. The correlations are
suppressed by spin-flip scattering and, for ferromagnetic injectors, by
increasing injector polarization.Comment: 4+ page
Dynamics of a cold trapped ion in a Bose-Einstein condensate
We investigate the interaction of a laser-cooled trapped ion (Ba or
Rb) with an optically confined Rb Bose-Einstein condensate (BEC).
The system features interesting dynamics of the ion and the atom cloud as
determined by their collisions and their motion in their respective traps.
Elastic as well as inelastic processes are observed and their respective cross
sections are determined. We demonstrate that a single ion can be used to probe
the density profile of an ultracold atom cloud.Comment: 4 pages, 5 figure
Optical Visualization of Radiative Recombination at Partial Dislocations in GaAs
Individual dislocations in an ultra-pure GaAs epilayer are investigated with
spatially and spectrally resolved photoluminescence imaging at 5~K. We find
that some dislocations act as strong non-radiative recombination centers, while
others are efficient radiative recombination centers. We characterize
luminescence bands in GaAs due to dislocations, stacking faults, and pairs of
stacking faults. These results indicate that low-temperature,
spatially-resolved photoluminescence imaging can be a powerful tool for
identifying luminescence bands of extended defects. This mapping could then be
used to identify extended defects in other GaAs samples solely based on
low-temperature photoluminescence spectra.Comment: 4 pages, 4 figure
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
Nuclear Dynamics During Landau-Zener Singlet-Triplet Transitions in Double Quantum Dots
We consider nuclear spin dynamics in a two-electron double dot system near
the intersection of the electron spin singlet and the lower energy
component of the spin triplet. The electron spin interacts with nuclear
spins and is influenced by the spin-orbit coupling. Our approach is based on a
quantum description of the electron spin in combination with the coherent
semiclassical dynamics of nuclear spins. We consider single and double
Landau-Zener passages across the - anticrossings. For linear sweeps,
the electron dynamics is expressed in terms of parabolic cylinder functions.
The dynamical nuclear polarization is described by two complex conjugate
functions related to the integrals of the products of the
singlet and triplet amplitudes
along the sweep. The real part of is related to the
- spin-transition probability, accumulates in the vicinity of the
anticrossing, and for long linear passages coincides with the Landau-Zener
probability , where is the Landau-Zener
parameter. The imaginary part of is specific for the nuclear
spin dynamics, accumulates during the whole sweep, and for
is typically an order of magnitude larger than . has a profound effect
on the nuclear spin dynamics, by (i) causing intensive shake-up processes among
the nuclear spins and (ii) producing a high nuclear spin generation rate when
the hyperfine and spin-orbit interactions are comparable in magnitude. We find
analytical expressions for the back-action of the nuclear reservoir represented
via the change in the Overhauser fields the electron subsystem experiences.Comment: 19 pages, 5 figure
Effects of demographic stochasticity on biological community assembly on evolutionary time scales
We study the effects of demographic stochasticity on the long-term dynamics
of biological coevolution models of community assembly. The noise is induced in
order to check the validity of deterministic population dynamics. While
mutualistic communities show little dependence on the stochastic population
fluctuations, predator-prey models show strong dependence on the stochasticity,
indicating the relevance of the finiteness of the populations. For a
predator-prey model, the noise causes drastic decreases in diversity and total
population size. The communities that emerge under influence of the noise
consist of species strongly coupled with each other and have stronger linear
stability around the fixed-point populations than the corresponding noiseless
model. The dynamics on evolutionary time scales for the predator-prey model are
also altered by the noise. Approximate fluctuations are observed with
noise, while fluctuations are found for the model without demographic
noise
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