1,709 research outputs found
Crop Yields: Stripper Header Technology vs. Conventional Header Technology
The purpose of this paper is to compare crop yields on acres where stripper header technology was used to those where conventional header technology was used in a dryland cropping system. The results are based on experimental data collected at the USDA-ARS Central Great Plains Research Station, and include information on Northeastern Colorado wheat, millet, and sorghum yields. This analysis is important to demonstrate the benefits of using stripper header technology in a dryland cropping system. In the next section, the approaches and major findings of the previous literature are reviewed
Electrostatic control of quantum dot entanglement induced by coupling to external reservoirs
We propose a quantum transport experiment to prepare and measure
charge-entanglement between two electrostatically defined quantum dots.
Coherent population trapping, as realized in cavity quantum electrodynamics,
can be carried out by using a third quantum dot to play the role of the optical
cavity. In our proposal, a pumping which is quantum mechanically
indistinguishable for the quantum dots drives the system into a state with a
high degree of entanglement. The whole effect can be switched on and off by
means of a gate potential allowing both state preparation and entanglement
detection by simply measuring the total current.Comment: 5 pages, 4 figures, Latex2e with EPL macros, to appear in Europhysics
Letter
Stub model for dephasing in a quantum dot
As an alternative to Buttiker's dephasing lead model, we examine a dephasing
stub. Both models are phenomenological ways to introduce decoherence in chaotic
scattering by a quantum dot. The difference is that the dephasing lead opens up
the quantum dot by connecting it to an electron reservoir, while the dephasing
stub is closed at one end. Voltage fluctuations in the stub take over the
dephasing role from the reservoir. Because the quantum dot with dephasing lead
is an open system, only expectation values of the current can be forced to
vanish at low frequencies, while the outcome of an individual measurement is
not so constrained. The quantum dot with dephasing stub, in contrast, remains a
closed system with a vanishing low-frequency current at each and every
measurement. This difference is a crucial one in the context of quantum
algorithms, which are based on the outcome of individual measurements rather
than on expectation values. We demonstrate that the dephasing stub model has a
parameter range in which the voltage fluctuations are sufficiently strong to
suppress quantum interference effects, while still being sufficiently weak that
classical current fluctuations can be neglected relative to the nonequilibrium
shot noise.Comment: 8 pages with 1 figure; contribution for the special issue of J.Phys.A
on "Trends in Quantum Chaotic Scattering
Michaelis-Menten Relations for Complex Enzymatic Networks
All biological processes are controlled by complex systems of enzymatic
chemical reactions. Although the majority of enzymatic networks have very
elaborate structures, there are many experimental observations indicating that
some turnover rates still follow a simple Michaelis-Menten relation with a
hyperbolic dependence on a substrate concentration. The original
Michaelis-Menten mechanism has been derived as a steady-state approximation for
a single-pathway enzymatic chain. The validity of this mechanism for many
complex enzymatic systems is surprising. To determine general conditions when
this relation might be observed in experiments, enzymatic networks consisting
of coupled parallel pathways are investigated theoretically. It is found that
the Michaelis-Menten equation is satisfied for specific relations between
chemical rates, and it also corresponds to the situation with no fluxes between
parallel pathways. Our results are illustrated for simple models. The
importance of the Michaelis-Menten relationship and derived criteria for
single-molecule experimental studies of enzymatic processes are discussed.Comment: 10 pages, 4 figure
Theory of electronic transport through a triple quantum dot in the presence of magnetic field
Theory of electronic transport through a triangular triple quantum dot
subject to a perpendicular magnetic field is developed using a tight binding
model. We show that magnetic field allows to engineer degeneracies in the
triple quantum dot energy spectrum. The degeneracies lead to zero electronic
transmission and sharp dips in the current whenever a pair of degenerate states
lies between the chemical potential of the two leads. These dips can occur with
a periodicity of one flux quantum if only two levels contribute to the current
or with half flux quantum if the three levels of the triple dot contribute. The
effect of strong bias voltage and different lead-to-dot connections on
Aharonov-Bohm oscillations in the conductance is also discussed
A robust, scanning quantum system for nanoscale sensing and imaging
Controllable atomic-scale quantum systems hold great potential as sensitive
tools for nanoscale imaging and metrology. Possible applications range from
nanoscale electric and magnetic field sensing to single photon microscopy,
quantum information processing, and bioimaging. At the heart of such schemes is
the ability to scan and accurately position a robust sensor within a few
nanometers of a sample of interest, while preserving the sensor's quantum
coherence and readout fidelity. These combined requirements remain a challenge
for all existing approaches that rely on direct grafting of individual solid
state quantum systems or single molecules onto scanning-probe tips. Here, we
demonstrate the fabrication and room temperature operation of a robust and
isolated atomic-scale quantum sensor for scanning probe microscopy.
Specifically, we employ a high-purity, single-crystalline diamond nanopillar
probe containing a single Nitrogen-Vacancy (NV) color center. We illustrate the
versatility and performance of our scanning NV sensor by conducting
quantitative nanoscale magnetic field imaging and near-field single-photon
fluorescence quenching microscopy. In both cases, we obtain imaging resolution
in the range of 20 nm and sensitivity unprecedented in scanning quantum probe
microscopy
The Uncertainty in Newton's Constant and Precision Predictions of the Primordial Helium Abundance
The current uncertainty in Newton's constant, G_N, is of the order of 0.15%.
For values of the baryon to photon ratio consistent with both cosmic microwave
background observations and the primordial deuterium abundance, this
uncertainty in G_N corresponds to an uncertainty in the primordial 4He mass
fraction, Y_P, of +-1.3 x 10^{-4}. This uncertainty in Y_P is comparable to the
effect from the current uncertainty in the neutron lifetime, which is often
treated as the dominant uncertainty in calculations of Y_P. Recent measurements
of G_N seem to be converging within a smaller range; a reduction in the
estimated error on G_N by a factor of 10 would essentially eliminate it as a
source of uncertainty in the calculation of the primordial 4He abundance.Comment: 3 pages, no figures, fixed typos, to appear in Phys. Rev.
An outline of an asymmetric two-component theory of aspect
The paper presents the bases of an asymmetric two-component model of aspect. The main theoretical conclusion of the study is that (grammatical) viewpoint aspect and situation aspect are not independent aspectual levels, since the former often modifies the input situation aspect of the phrase/sentence. As it is shown, besides the arguments and adjuncts of the predicate, viewpoint aspect is also an important factor in compositionally marking situation aspect. The aspectual framework put forward in the paper is verified and illustrated on the basis of the aspectual system of Hungarian and some examples taken from English linguistic data
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