2,846 research outputs found
Efficiency of Nitrogen Use with Corn on a Tiled and Untiled Soil
Excessive water is one of the largest contributors to the inefficient use of nitrogen in Kentucky. Because of this, nitrogen is often lost by both leaching and,denitrification. The amount, of these losses can be great depending on soil type and weather. Well-drained soils in Kentucky have been shown to lose less nitrogen than poorly drained soils. The nitrogen lost from well drained soils is usually due, to leaching. The nitrogen in the soil, even soon after applying non-nitrate forms of fertilizer N, is mostly in the water soluble nitrate form. When more water falls onto a well-drained soil than the soil can hold, then both water and nitrogen move through the soil below the root zone and are lost for plant use. On poorly-drained soils, the mostly likely method of nitrogen loss is due to denitrification. Nitrogen loss by this mechanism is due to the soil becoming saturated with water (waterlogged) and forcing the air out of the soil. In an effort to survive, some of the microorganisms in the soil take oxygen from nitrate. This process (denitrification) turns the nitrogen into a gas that will diffuse out of the saturated soil and be lost ,into the air. It usually occurs when the soil temperature is above 50°F and the soil is saturated for more than a two day period. If nitrogen fertilizer has been added to the soil prior to the existence of the above conditions, then fairly large amounts of nitrogen can be lost. These conditions are most prevalent in Kentucky on poorly drained soil in April and May. In the past, most farmers have tried to manage this problem by adding excess fertilizer nitrogen to still obtain maximum yields after the loss has been sustained. This management practice may not be economically feasible in the future if nitrogen prices continue to escalate. An alternative management practice used by many farmers is to reduce the amount of nitrogen lost by simply delaying the application of nitrogen until the conditions for denitrification have little chance of occurring. This usually means that the nitrogen is applied in late May or June after the corn has been planted and the risk of waterlogged soil conditions is greatly reduced. To determine the magnitude of such factors, we began an experiment on a poorly drained bottom soil in 1970 to determine 1) the proper rates of preplant nitrogen 2) effectiveness of sidedressing nitrogen and 3) effect of soil tiling on the above two factors
Robustness of adiabatic quantum computation
We study the fault tolerance of quantum computation by adiabatic evolution, a
quantum algorithm for solving various combinatorial search problems. We
describe an inherent robustness of adiabatic computation against two kinds of
errors, unitary control errors and decoherence, and we study this robustness
using numerical simulations of the algorithm.Comment: 11 pages, 5 figures, REVTe
Sim-to-Real Model-Based and Model-Free Deep Reinforcement Learning for Tactile Pushing
Object pushing presents a key non-prehensile manipulation problem that is
illustrative of more complex robotic manipulation tasks. While deep
reinforcement learning (RL) methods have demonstrated impressive learning
capabilities using visual input, a lack of tactile sensing limits their
capability for fine and reliable control during manipulation. Here we propose a
deep RL approach to object pushing using tactile sensing without visual input,
namely tactile pushing. We present a goal-conditioned formulation that allows
both model-free and model-based RL to obtain accurate policies for pushing an
object to a goal. To achieve real-world performance, we adopt a sim-to-real
approach. Our results demonstrate that it is possible to train on a single
object and a limited sample of goals to produce precise and reliable policies
that can generalize to a variety of unseen objects and pushing scenarios
without domain randomization. We experiment with the trained agents in harsh
pushing conditions, and show that with significantly more training samples, a
model-free policy can outperform a model-based planner, generating shorter and
more reliable pushing trajectories despite large disturbances. The simplicity
of our training environment and effective real-world performance highlights the
value of rich tactile information for fine manipulation. Code and videos are
available at https://sites.google.com/view/tactile-rl-pushing/.Comment: Accepted by IEEE Robotics and Automation Letters (RA-L
Extrasolar planet science with the Antarctic planet interferometer
The primary limitation to ground based astronomy is the Earth's atmosphere. The atmosphere above the Antarctic plateau is different in many regards compared to the atmosphere at temperate sites. The extreme altitude, cold and low humidity offer a uniquely transparent atmosphere at many wavelengths. Studies at the South Pole have shown additionally that the turbulence properties of the night time polar atmosphere are fundamentally different to mid latitudes. Despite relatively strong ground layer turbulence, the lack of high altitude turbulence combined with low wind speeds presents favorable conditions for interferometry. The unique properties of the polar atmosphere can be exploited for Extrasolar Planet studies with differential astrometry, differential phase and nulling intereferometers. This paper combines the available data on the properties of the atmosphere at the South Pole and other Antarctic plateau sites for Extrasolar Planet science with interferometry
Encoding a qubit in an oscillator
Quantum error-correcting codes are constructed that embed a
finite-dimensional code space in the infinite-dimensional Hilbert space of a
system described by continuous quantum variables. These codes exploit the
noncommutative geometry of phase space to protect against errors that shift the
values of the canonical variables q and p. In the setting of quantum optics,
fault-tolerant universal quantum computation can be executed on the protected
code subspace using linear optical operations, squeezing, homodyne detection,
and photon counting; however, nonlinear mode coupling is required for the
preparation of the encoded states. Finite-dimensional versions of these codes
can be constructed that protect encoded quantum information against shifts in
the amplitude or phase of a d-state system. Continuous-variable codes can be
invoked to establish lower bounds on the quantum capacity of Gaussian quantum
channels.Comment: 22 pages, 8 figures, REVTeX, title change (qudit -> qubit) requested
by Phys. Rev. A, minor correction
Discovery of a potent nanoparticle Pâselectin antagonist with antiâinflammatory effects in allergic airway disease
The severity of allergic asthma is dependent, in part, on the intensity of peribronchial inflammation. Pâselectin is known to play a role in the development of allergenâinduced peribronchial inflammation and airway hyperreactivity. Selective inhibitors of Pâselectinâ mediated leukocyte endothelialâcell interactions may therefore attenuate the inflammatory processes associated with allergic airway disease. Novel Pâselectin inhibitors were created using a polyvalent polymer nanoparticle capable of displaying multiple synthetic, low molecular weight ligands. By assembling a particle that presents an array of groups, which as monomers interact with only low affinity, we created a construct that binds extremely efficiently to Pâ selectin. The ligands acted as mimetics of the key binding elements responsible for the highâ avidity adhesion of Pâselectin to the physiologic ligand, PSGLâ1. The inhibitors were initially evaluated using an in vitro shear assay system in which interactions between circulating cells and Pâselectinâcoated capillary tubes were measured. The nanoparticles were shown to preferentially bind to selectins expressed on activated endothelial cells. We subsequently demonstrated that nanoparticles displaying Pâselectin blocking arrays were functionally active in vivo, significantly reducing allergenâinduced airway hyperreactivity and peribronchial eosinophilic inflammation in a murine model of asthma.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154265/1/fsb2fj030166fje-sup-0001.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154265/2/fsb2fj030166fje.pd
Quantum Markov Channels for Qubits
We examine stochastic maps in the context of quantum optics. Making use of
the master equation, the damping basis, and the Bloch picture we calculate a
non-unital, completely positive, trace-preserving map with unequal damping
eigenvalues. This results in what we call the squeezed vacuum channel. A
geometrical picture of the effect of stochastic noise on the set of pure state
qubit density operators is provided. Finally, we study the capacity of the
squeezed vacuum channel to transmit quantum information and to distribute EPR
states.Comment: 18 pages, 4 figure
Parametrizations of Inclusive Cross Sections for Pion Production in Proton-Proton Collisions
Accurate knowledge of cross sections for pion production in proton-proton
collisions finds wide application in particle physics, astrophysics, cosmic ray
physics and space radiation problems, especially in situations where an
incident proton is transported through some medium, and one requires knowledge
of the output particle spectrum given the input spectrum. In such cases
accurate parametrizations of the cross sections are desired. In this paper we
review much of the experimental data and compare to a wide variety of different
cross section parametrizations. In so doing, we provide parametrizations of
neutral and charged pion cross sections which provide a very accurate
description of the experimental data. Lorentz invariant differential cross
sections, spectral distributions and total cross section parametrizations are
presented.Comment: 32 pages with 15 figures. Published in Physical Review D62, 094030.
File includes 6 tex files. The main file is paper.tex which has include
statements refering to the rest. figures are in graphs.di
A solvable model of a random spin-1/2 XY chain
The paper presents exact calculations of thermodynamic quantities for the
spin-1/2 isotropic XY chain with random lorentzian intersite interaction and
transverse field that depends linearly on the surrounding intersite
interactions.Comment: 14 pages (Latex), 2 tables, 13 ps-figures included, (accepted for
publication in Phys.Rev.B
Radio Astronomy
Contains reports on five research projects.National Science Foundation (Grant AST82-14296)National Aeronautics and Space Administration (Grant NAG W-373)National Aeronautics and Space Administration (Grant NAG5-537)U.S. Navy - Office of Naval Research (Contract N00014-84-C-2082)SM Systems and Research, Inc.Defense Advanced Research Project Agency (Contract MDA903-82-K-0521
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