45,808 research outputs found
The development of an integrated modelling system to support decisions on organic farms
This paper was presented at the UK Organic Research 2002 Conference of the Colloquium of Organic Researchers (COR).
An Integrated Decision Support System (IDSS) is developed which synthesises current understanding of organic farming by means of a multiple objective framework incorporating GIS, biophysical models and socio-economic models of the farming goals. The IDSS uses a multitiered concept of a farming system as a collection of micro-enterprises at the field level, with individual resource endowments, objectives and activities. Farm-level decision drivers trickle down to affect the micro-level field enterprise selection. Biophysical models describe typical forage, cereal, root and legume output and a user-friendly interfaces permits easy access and output display via a GIS. A prototype of the IDSS framework, being developed as a part of the SAC organic research programme is presented
Analysis of electromagnetic waves on a dielectric rod immersed in a plasma including a discussion of diagnostic applications
Guided electromagnetic waves propagating along lossless dielectric rod immersed in isotropic and uniaxial plasmas determined for applications to plasma diagnostic
High-Tip-Speed, Low-Loading Transonic Fan Stage. Part 1: Aerodynamic and Mechanical Design
A high-tip-speed, low-loading transonic fan stage was designed to deliver an overall pressure ratio of 1.5 with an adiabatic efficiency of 86 percent. The design flow per unit annulus area is 42.0 pounds per square foot. The fan features a hub/tip ratio of 0.46, a tip diameter of 28.74 in. and operates at a design tip speed of 1600 fps. For these design conditions, the rotor blade tip region operates with supersonic inlet and supersonic discharge relative velocities. A sophisticated quasi-three-dimensional characteristic section design procedure was used for the all-supersonic sections and the inlet of the midspan transonic sections. For regions where the relative outlet velocities are supersonic, the blade operates with weak oblique shocks only
Impulsive phase flare energy transport by large-scale Alfven waves and the electron acceleration problem
The impulsive phase of a solar flare marks the epoch of rapid conversion of
energy stored in the pre-flare coronal magnetic field. Hard X-ray observations
imply that a substantial fraction of flare energy released during the impulsive
phase is converted to the kinetic energy of mildly relativistic electrons
(10-100 keV). The liberation of the magnetic free energy can occur as the
coronal magnetic field reconfigures and relaxes following reconnection. We
investigate a scenario in which products of the reconfiguration - large-scale
Alfven wave pulses - transport the energy and magnetic-field changes rapidly
through the corona to the lower atmosphere. This offers two possibilities for
electron acceleration. Firstly, in a coronal plasma with beta < m_e/m_p, the
waves propagate as inertial Alfven waves. In the presence of strong spatial
gradients, these generate field-aligned electric fields that can accelerate
electrons to energies on the order of 10 keV and above, including by repeated
interactions between electrons and wavefronts. Secondly, when they reflect and
mode-convert in the chromosphere, a cascade to high wavenumbers may develop.
This will also accelerate electrons by turbulence, in a medium with a locally
high electron number density. This concept, which bridges MHD-based and
particle-based views of a flare, provides an interpretation of the
recently-observed rapid variations of the line-of-sight component of the
photospheric magnetic field across the flare impulsive phase, and offers
solutions to some perplexing flare problems, such as the flare "number problem"
of finding and resupplying sufficient electrons to explain the impulsive-phase
hard X-ray emission.Comment: 31 pages, 6 figure
Synthetic magnetism for photon fluids
We develop a theory of artificial gauge fields in photon fluids for the cases
of both second-order and third-order optical nonlinearities. This applies to
weak excitations in the presence of pump fields carrying orbital angular
momentum, and is thus a type of Bogoliubov theory. The resulting artificial
gauge fields experienced by the weak excitations are an interesting
generalization of previous cases and reflect the PT-symmetry properties of the
underlying non-Hermitian Hamiltonian. We illustrate the observable consequences
of the resulting synthetic magnetic fields for examples involving both
second-order and third-order nonlinearities
Full-time dynamics of modulational instability in spinor Bose-Einstein condensates
We describe the full-time dynamics of modulational instability in F=1 spinor
Bose-Einstein condensates for the case of the integrable three-component model
associated with the matrix nonlinear Schroedinger equation. We obtain an exact
homoclinic solution of this model by employing the dressing method which we
generalize to the case of the higher-rank projectors. This homoclinic solution
describes the development of modulational instability beyond the linear regime,
and we show that the modulational instability demonstrates the reversal
property when the growth of the modulation amplitude is changed by its
exponential decay.Comment: 6 pages, 2 figures, text slightly extended, a reference adde
Advancement in the zone of calcified cartilage in osteoarthritic hands of patients detected by high definition macroradiography
AbstractObjective High definition macroradiography permits the advancement in the zone of calcified cartilage (described as a ZCC step) to be detected in osteoarthritic (OA) hand joints of patients. The pattern of their incidence and distribution was determined and compared to the joint space width (JSW) measurement.Design Macroradiographs, ×5 magnification, were obtained of the OA hands of 44 patients at baseline and at 18 months. The incidence of ZCC steps, identified as an advancement in the mineralized cartilage front into articular cartilage, was assessed at each articular surface. JSW was measured and was used to determine the difference in JSW between hands and groups of joints with and without ZCC steps at both X-ray visits.Results ZCC steps were only found at the convex articular surfaces in 42 (48%) of hand joints in 28 (64%) patients. Here, ZCC steps were present in 36 joints in the non-dominant hand compared to 30 joints in the dominant hand. In the former, they were present in 22 DIP, six PIP and eight MCP joints and in 12 DIP, 8 PIP and 10 MCP joints in the dominant hand. By 18 months new ZCC steps had formed in 15 hands with and 17 hands without previous ZCC steps. At both X-ray visits no statistically significant difference in JSW was found between the hands and joint groups with and without ZCC steps.Conclusion Although ZCC steps and JSW loss were greater at the PIP joints, supporting a mechanical hypothesis for ZCC formation, their presence in joints, where JSW was larger, and their greater incidence in the non-dominant PIP joints, suggest that factors associated with vascular changes, related to subchondral bone remodeling, are responsible.{copy
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