3,584 research outputs found
Deformation of vortex patches by boundaries
The deformation of two-dimensional vortex patches in the vicinity of fluid
boundaries is investigated. The presence of a boundary causes an initially
circular patch of uniform vorticity to deform. Sufficiently far away from the
boundary, the deformed shape is well approximated by an ellipse. This leading
order elliptical deformation is investigated via the elliptic moment model of
Melander, Zabusky & Styczek [M. V. Melander, N. J. Zabusky & A. S. Styczek, J.
Fluid. Mech., 167, 95 (1986)]. When the boundary is straight, the centre of the
elliptic patch remains at a constant distance from the boundary, and the motion
is integrable. Furthermore, since the straining flow acting on the patch is
constant in time, the problem is that of an elliptic vortex patch in constant
strain, which was analysed by Kida [S. Kida, J. Phys. Soc. Japan, 50, 3517
(1981)]. For more complicated boundary shapes, such as a square corner, the
motion is no longer integrable. Instead, there is an adiabatic invariant for
the motion. This adiabatic invariant arises due to the separation in times
scales between the relatively rapid time scale associated with the rotation of
the patch and the slower time scale associated with the self-advection of the
patch along the boundary. The interaction of a vortex patch with a circular
island is also considered. Without a background flow, conservation of angular
impulse implies that the motion is again integrable. The addition of an
irrotational flow past the island can drive the patch towards the boundary,
leading to the possibility of large deformations and breakup.Comment: 19 pages, 16 figure
Seed Size and Its Relationship with Crop Establishment, Productivity and Nutritive Value in Genotypes of Maize for Silage
For a high dry matter (DM) yield of forage maize an adequate population of plants is required, which is related to germination, vigour, and seed size (Ellis, 1992). The objective of the present study was to investigate seed size and its relationship to establishment, productive and nutritional potential of silage maize, which has not before been reported in the literature
Novel ulcerative leg lesions in yearling lambs: Clinical features, microbiology and histopathology
Here we report an outbreak of an atypical, ulcerative dermatitis in North Country mule lambs, located in South Gloucestershire, UK. The lesions, which appeared to be contagious, occured between the coronary band and the carpal joint as a focal, well demarcated, circular, ulcerative dermatitis. Histopathological examination of the lesion biopsies revealed areas of ulceration, epidermal hyperplasia, suppurative dermatitis and granulation tissue. Clumped keratohyalin granules and intracellular keratinocyte oedema (ballooning degeneration) were evident within lesion biopsies, consistent with an underlying viral aetiology. A PCR-based microbiological investigation failed to detect bovine digital dermatitis-associated treponeme phylogroups, Dichelobacter nodosus, Staphylococcus aureus, Dermatophilus congolensis or Chordopoxvirinae virus DNA. However, 3 of the 10 (30 %) and 6 of 10 (60 %) lesion samples were positive for Fusobacterium necrophorum and Streptococcus dysgalactiae DNA, respectively. Contralateral limb swabs were negative by all standard PCR assays. To better define the involvement of F. necrophorum in the aetiology of these lesions, a qPCR targeting the rpoB gene was employed and confirmed the presence of F. necrophorum DNA in both the control and lesions swab samples, although the mean F. necrophorum genome copy number detected in the lesion swab samples was ∼19-fold higher than detected in the contralateral control swab samples (245 versus 4752 genome copies/μl, respectively; P < 0.001). Although we have not been able to conclusively define an aetiological agent, the presence of both F. necrophorum and S. dysgalactiae in the majority of lesions assayed supports their role in the aetiopathogenesis of these lesions
Noise storm continua: power estimates for electron acceleration
We use a generic stochastic acceleration formalism to examine the power
() input to nonthermal electrons that cause
noise storm continuum emission. The analytical approach includes the derivation
of the Green's function for a general second-order Fermi process, and its
application to obtain the particular solution for the nonthermal electron
distribution resulting from the acceleration of a Maxwellian source in the
corona. We compare with the power observed in noise
storm radiation. Using typical values for the various parameters, we find that
, yielding an efficiency
estimate in the range 10^{-10} \lsim \eta
\lsim 10^{-6} for this nonthermal acceleration/radiation process. These
results reflect the efficiency of the overall process, starting from electron
acceleration and culminating in the observed noise storm emission.Comment: Accepted for publication in Solar Physic
RHESSI Microflare Statistics II. X-ray Imaging, Spectroscopy & Energy Distributions
We present X-ray imaging and spectral analysis of all microflares the Reuven
Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observed between March
2002 and March 2007, a total of 25,705 events. These microflares are small
flares, from low GOES C Class to below A Class (background subtracted) and are
associated with active regions. They were found by searching the 6-12 keV
energy range during periods when the full sensitivity of RHESSI's detectors was
available (see paper I). Each microflare is automatically analyzed at the peak
time of the 6-12 keV emission: the thermal source size is found by
forward-fitting the complex visibilities for 4-8 keV, and the spectral
parameters (temperature, emission measure, power-law index) are found by
forward fitting a thermal plus non-thermal model. The combination of these
parameters allows us to present the first statistical analysis of the thermal
and non-thermal energy at the peak times of microflares.Comment: 17 pages, 21 figs, Ap
Adapting SAM for CDF
The CDF and D0 experiments probe the high-energy frontier and as they do so
have accumulated hundreds of Terabytes of data on the way to petabytes of data
over the next two years. The experiments have made a commitment to use the
developing Grid based on the SAM system to handle these data. The D0 SAM has
been extended for use in CDF as common patterns of design emerged to meet the
similar requirements of these experiments. The process by which the merger was
achieved is explained with particular emphasis on lessons learned concerning
the database design patterns plus realization of the use cases.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics
(CHEP03), La Jolla, Ca, USA, March 2003, 4 pages, pdf format, TUAT00
Distributed Ledger for Provenance Tracking of Artificial Intelligence Assets
High availability of data is responsible for the current trends in Artificial
Intelligence (AI) and Machine Learning (ML). However, high-grade datasets are
reluctantly shared between actors because of lacking trust and fear of losing
control. Provenance tracing systems are a possible measure to build trust by
improving transparency. Especially the tracing of AI assets along complete AI
value chains bears various challenges such as trust, privacy, confidentiality,
traceability, and fair remuneration. In this paper we design a graph-based
provenance model for AI assets and their relations within an AI value chain.
Moreover, we propose a protocol to exchange AI assets securely to selected
parties. The provenance model and exchange protocol are then combined and
implemented as a smart contract on a permission-less blockchain. We show how
the smart contract enables the tracing of AI assets in an existing industry use
case while solving all challenges. Consequently, our smart contract helps to
increase traceability and transparency, encourages trust between actors and
thus fosters collaboration between them
Long-range interactions of metastable helium atoms
Polarizabilities, dispersion coefficients, and long-range atom-surface
interaction potentials are calculated for the n=2 triplet and singlet states of
helium using highly accurate, variationally determined, wave functions.Comment: RevTeX, epsf, 4 fig
How unique is the Asymptotic Normalisation Coefficient (ANC) method?
The asymptotic normalisation coefficients (ANC) for the vertex B
Be + p is deduced from a set of different proton transfer reactions at
different energies. This set should ensure the peripheral character of the
reaction and availability of data for the elastic channels. The problems
associated with the characteristics of the data and the analysis are discussed.
For a subgroup of the set of available data, the uniqueness property of the
extracted ANC is fulfilled. However, more measurements are needed before a
definite conclusion can be drawn.Comment: 19 pages, 11 figures, to be published in Phys Rev
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