1,576 research outputs found
Improved efficiency of nutrient and water use for high quality field vegetable production using fertigation
Drip-based fertigation may improve the application efficiency of water and nutrients while maintaining or improving marketable yield and quality at harvest and post-harvest. Two plantings of lettuce (Lactuca sativa) were grown in the UK, with six N treatments and two methods of irrigation and N application. The conventional overhead irrigated treatments had all N applied in the base dressing with irrigation scheduled from SMD calculations. The closed loop treatments had nitrogen and irrigation delivered via drip automatically controlled by a sensor and logger system. The work established that water content in the root zone can be monitored in real time using horizontally oriented soil moisture sensors linked to data logging and telemetry, and that these data can be used to automatically trigger drip irrigation for commercially grown field vegetables. When the closed loop irrigation control was combined with fertigation treatments, lettuce crops were grown with savings of up to 60% and 75% of water and nitrogen respectively, compared to standard UK production systems. However, excess supply of N through fertigation rather than solid fertiliser was more detrimental to marketable yield and post harvest quality highlighting that care is needed when selecting N rates for fertigation
Strong spin fluctuations in -FeSe observed by neutron spectroscopy
We have performed powder inelastic neutron scattering measurements on the
unconventional superconductor -FeSe ().
The spectra reveal highly dispersive paramagnetic fluctuations emerging from
the square-lattice wave vector extending beyond 80 meV in energy.
Measurements as a function of temperature at an energy of did not show any variation from to
. The results show that FeSe is close to an instability
towards antiferromagnetism characteristic of the parent phases of the
high- iron arsenide superconductors, and that the iron paramagnetic
moment is neither affected by the orthorhombic-to-tetragonal structural
transition at nor does it undergo a change in
spin state over the temperature range studied.Comment: Revised version, includes Supplementary Materia
Paramagnon dispersion in -FeSe observed by Fe -edge resonant inelastic x-ray scattering
We report an Fe -edge resonant inelastic x-ray scattering (RIXS) study of
the unusual superconductor -FeSe. The high energy resolution of this
RIXS experiment (55meV FWHM) made it possible to resolve
low-energy excitations of the Fe manifold. These include a broad peak
which shows dispersive trends between 100-200meV along the and
directions of the one-Fe square reciprocal lattice, and which can
be attributed to paramagnon excitations. The multi-band valence state of FeSe
is among the most metallic in which such excitations have been discerned by
soft x-ray RIXS
Spin resonance in the superconducting state of LiFeODFeSe observed by neutron spectroscopy
We have performed inelastic neutron scattering measurements on a powder
sample of the superconductor lithium iron selenide hydroxide
LiFeODFeSe (, \,K). The spectrum shows an enhanced intensity below over an
energy range , where is the
superconducting gap, with maxima at the wave vectors \,\AA and \,\AA. The behavior of this
feature is consistent with the spin resonance mode found in other
unconventional superconductors, and strongly resembles the spin resonance
observed in the spectrum of the molecular-intercalated iron selenide,
Li(ND)(ND)FeSe. The signal can
be described with a characteristic two-dimensional wave vector
in the Brillouin zone of the iron square lattice, consistent with the nesting
vector between electron Fermi sheets
Topological aspects of multi-k antiferromagnetism in cubic rare-earth compounds
We advertise rare-earth intermetallics with high-symmetry crystal structures and competing interactions as a possible materials platform hosting spin structures with non-trivial topological properties. Focusing on the series of cubic RCu compounds, where R = Ho, Er, Tm, the bulk properties of these systems display exceptionally rich magnetic phase diagrams hosting an abundance of different phase pockets characteristic of antiferromagnetic order in the presence of delicately balanced interactions. The electrical transport properties exhibit large anomalous contributions suggestive of topologically non-trivial winding in the electronic and magnetic structures. Neutron diffraction identifies spontaneous long-range magnetic order in terms of commensurate and incommensurate variations of ππ0 antiferromagnetism with the possibility for various multi-k configurations. Motivated by general trends in these materials, we discuss the possible existence of topologically non-trivial winding in real and reciprocal space in the class of RCu compounds including antiferromagnetic skyrmion lattices. Putatively bringing together different limits of non-trivial topological winding in the same material, the combination of properties in RCu systems promises access to advanced functionalities
Exact Performance of Concatenated Quantum Codes
When a logical qubit is protected using a quantum error-correcting code, the
net effect of coding, decoherence (a physical channel acting on qubits in the
codeword) and recovery can be represented exactly by an effective channel
acting directly on the logical qubit. In this paper we describe a procedure for
deriving the map between physical and effective channels that results from a
given coding and recovery procedure. We show that the map for a concatenation
of codes is given by the composition of the maps for the constituent codes.
This perspective leads to an efficient means for calculating the exact
performance of quantum codes with arbitrary levels of concatenation. We present
explicit results for single-bit Pauli channels. For certain codes under the
symmetric depolarizing channel, we use the coding maps to compute exact
threshold error probabilities for achievability of perfect fidelity in the
infinite concatenation limit.Comment: An expanded presentation of the analytic methods and results from
quant-ph/0111003; 13 pages, 6 figure
Versatile module for experiments with focussing neutron guides
We report the development of a versatile module that permits fast and
reliable use of focussing neutron guides under varying scattering angles. A
simple procedure for setting up the module and neutron guides is illustrated by
typical intensity patterns to highlight operational aspects as well as typical
parasitic artefacts. Combining a high-precision alignment table with separate
housings for the neutron guides on kinematic mounts, the change-over between
neutron guides with different focussing characteristics requires no
readjustments of the experimental set-up. Exploiting substantial gain factors,
we demonstrate the performance of this versatile neutron scattering module in a
study of the effects of uniaxial stress on the domain populations in the
transverse spin density wave phase of single crystal Cr
EU-Rotate_N – a decision support system – to predict environmental and economic consequences of the management of nitrogen fertiliser in crop rotations
A model has been developed which assesses the economic and environmental performance of crop rotations, in both conventional and organic cropping, for over 70 arable and horticultural crops, and a wide range of growing conditions in Europe. The model, though originally based on the N_ABLE model, has been completely rewritten and contains new routines to simulate root development, the mineralisation and release of nitrogen (N) from soil organic matter and crop residues, and water dynamics in soil. New routines have been added to estimate the effects of sub-optimal rates of N and spacing on the marketable outputs and gross margins. The model provides a mechanism for generating scenarios to represent a range of differing crop and fertiliser management strategies which can be used to evaluate their effects on yield, gross margin and losses of nitrogen through leaching. Such testing has revealed that nitrogen management can be improved and that there is potential to increase gross margins whilst reducing nitrogen losses
Nuclear Magnetic Resonance and Impedance Spectroscopy Studies on Lithium Ion Diffusion in γ-LiAlO2
In this work we show conductivity spectra of γ-LiAlO2 single crystals purchased from
CrysTec and microcrystalline powder prepared by solid state synthesis
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