2,489 research outputs found
VALUE OF SOIL TEST INFORMATION FOR CROP PRODUCTION
This study was conducted to determine the value of independent and joint nitrogen and phosphorus soil tests. Generalized stochastic dominance was used to estimate the value of information. Combined information from both the nitrogen and phosphorus tests was substantially more valuable than the knowledge of only one of the tests.Crop Production/Industries, Land Economics/Use,
Quantum limited measurements of atomic scattering properties
We propose a method to perform precision measurements of the interaction
parameters in systems of N ultra-cold spin 1/2 atoms. The spectroscopy is
realized by first creating a coherent spin superposition of the two relevant
internal states of each atom and then letting the atoms evolve under a
squeezing Hamiltonian. The non-linear nature of the Hamiltonian decreases the
fundamental limit imposed by the Heisenberg uncertainty principle to N^(-2), a
factor of N smaller than the fundamental limit achievable with non-interacting
atoms. We study the effect of decoherence and show that even with decoherence,
entangled states can outperform the signal to noise limit of non-entangled
states. We present two possible experimental implementations of the method
using Bose-Einstein spinor condensates and fermionic atoms loaded in optical
lattices and discuss their advantages and disadvantages.Comment: 7 pages, 5 figures. References adde
Dynamical Crystallization in the Dipole Blockade of Ultracold Atoms
We describe a method for controlling many-body states in extended ensembles
of Rydberg atoms, forming crystalline structures during laser excitation of a
frozen atomic gas. Specifically, we predict the existence of an excitation
number staircase in laser excitation of atomic ensembles into Rydberg states.
Each step corresponds to a crystalline state with a well-defined of regularly
spaced Rydberg atoms. We show that such states can be selectively excited by
chirped laser pulses. Finally, we demonstarte that, sing quantum state transfer
from atoms to light, such crystals can be used to create crystalline photonic
states and can be probed via photon correlation measurements
Electron spin decoherence of single Nitrogen-Vacancy defects in diamond
We present a theoretical analysis of the electron spin decoherence in single
Nitrogen-Vacancy defects in ultra-pure diamond. The electron spin decoherence
is due to the interactions with Carbon-13 nuclear spins in the diamond lattice.
Our approach takes advantage of the low concentration (1.1%) of Carbon-13 and
their random distribution in the diamond lattice by an algorithmic aggregation
of spins into small, strongly interacting groups. By making use of this
\emph{disjoint cluster} approach, we demonstrate a possibility of non-trival
dynamics of the electron spin that can not be described by a single time
constant. This dependance is caused by a strong coupling between the electron
and few nuclei and results, in particular, in a substantial echo signal even at
microsecond time scales. Our results are in good agreement with recent
experimental observations
On Flux Rope Stability and Atmospheric Stratification in Models of Coronal Mass Ejections Triggered by Flux Emergence
Flux emergence is widely recognized to play an important role in the
initiation of coronal mass ejections. The Chen-Shibata (2000) model, which
addresses the connection between emerging flux and flux rope eruptions, can be
implemented numerically to study how emerging flux through the photosphere can
impact the eruption of a pre-existing coronal flux rope. The model's
sensitivity to the initial conditions and reconnection micro-physics is
investigated with a parameter study. In particular, we aim to understand the
stability of the coronal flux rope in the context of X-point collapse and the
effects of boundary driving in both unstratified and stratified atmospheres. In
the absence of driving, we assess the behavior of waves in the vicinity of the
X-point. With boundary driving applied, we study the effects of reconnection
micro-physics and atmospheric stratification on the eruption. We find that the
Chen-Shibata equilibrium can be unstable to an X-point collapse even in the
absence of driving due to wave accumulation at the X-point. However, the
equilibrium can be stabilized by reducing the compressibility of the plasma,
which allows small-amplitude waves to pass through the X-point without
accumulation. Simulations with the photospheric boundary driving evaluate the
impact of reconnection micro-physics and atmospheric stratification on the
resulting dynamics: we show the evolution of the system to be determined
primarily by the structure of the global magnetic fields with little
sensitivity to the micro-physics of magnetic reconnection; and in a stratified
atmosphere, we identify a novel mechanism for producing quasi-periodic behavior
at the reconnection site behind a rising flux rope as a possible explanation of
similar phenomena observed in solar and stellar flares.Comment: Submitted Feb 28, 2014 to, accepted Aug 14, 2014 by Astronomy &
Astrophysics. 13 pages, 10 figures, 2 table
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