24,027 research outputs found
An example of active circulation control of the unsteady separated flow past a semi-infinite plate
Active circulation control of the two-dimensional unsteady separated flow past a semiinfinite plate with transverse motion is considered. The rolling-up of the separated shear layer is modelled by a point vortex whose time-dependent circulation is predicted by an unsteady Kutta condition. A suitable vortex shedding mechanism introduced. A control strategy able to maintain constant circulation when a vortex is present is derived. An exact solution for the nonlinear controller is then obtained. Dynamical systems analysis is used to explore the performance of the controlled system. The control strategy is applied to a class of flows and the results are discussed. A procedure to determine the position and the circulation of the vortex, knowing the velocity signature on the plate, is derived. Finally, a physical explanation of the control mechanism is presented
Small and medium agility dogs alter their kinematics when the distance between hurdles differs
There is currently a lack of research examining the health and welfare implications for competitive agility dogs. The aim of this study was to examine if jump kinematics and apparent joint angles in medium (351 mm - 430 mm to the withers) and small (< 350 mm to the withers) agility dogs altered when distances between consecutive upright hurdles differ. Dogs ran a course of nine hurdles; three set at 3.6 m apart; three at 4 m apart and three at 5 m apart. Both medium (P=0.044) and small (P=0.006) dogs landed closer to the hurdle when consecutive hurdles were set at 3.6 m apart, with small dogs jumping slower at this distance (P=0.006). Results indicate that jump kinematics, but not apparent joint angles, alter when the spacing between hurdles differs. These findings may have implications for the health and welfare of agility dogs and should be used to inform future changes to rules and regulations
A framework for assessing crop production from rotations
This report was presented at the UK Organic Research 2002 Conference of the Colloquium of Organic Researchers (COR).
Organic farming systems rely on the management of biological cycles for the provision of nutrients, which are crucial to maximising the production from the system. Rotations based on the use of grass-legume leys are central to the concept of organic farming systems, because they have the potential to support both animal production, and a subsequent, exploitative, arable cropping phase. A major challenge in organic farming is managing the supply of nitrogen, since it has a key role in governing both productivity and environmental impact. Hence, within a rotational system, there is a need to understand the complex interactions that are occurring between crop species and management, livestock production system and the impact of soil and climate on these processes. To understand these interactions, a framework is being developed for rotational farming systems that describes the soil nitrogen, crop growth and livestock production. The framework must address questions that are relevant to researchers and extensions workers. Typical questions relate to the management of nutrients in the short and long-term. Additionally, there are concerns over the impact of weeds, pests and diseases on productivity, as well as the impact of adopting new strategies or crops on the farming system
Prevention of osteoporotic refractures in regional Australia
Objective: Clinical guidelines recommend that patients who sustain a minimal trauma fracture (MTF) should receive a bone mineral density (BMD) scan and bisphosphonate (or equivalent) therapy if diagnosed with osteoporosis. A pilot fracture liaison service (FLS) was implemented in regional NSW to improve adherence to the guidelines.
Design: Prospective cohort study with an historical control.
Setting: Primary care.
Participants: Control (n = 47) and cohort (n = 93) groups comprised patients consenting to interview who presented with a MTF to the major referral hospital 4 months before and 12 months after FLS implementation respectively.
Main outcome measures: Primary outcome measures were the rates of BMD scans and anti-osteoporotic medication initiation/review after MTF. Hospital admission data were also examined to determine death and refracture rates for all patients presenting during the study period with a primary diagnosis of MTF within 3 years of their initial fracture.
Results: Although there was no improvement in BMD scanning rates, the reported rate of medication initiation/review after fracture was significantly higher (P \u3c 0.05) in the FLS cohort. However, once adjusted for age, this association was not significant (P = 0.086). There was a lower refracture rate during the cohort period (P = 0.013), however, there were significantly more deaths (P = 0.035) within 3 years of initial fracture. When deaths were taken into account via competing risk regression, patients in the cohort period were significantly less likely to refracture than those in the control period (Hazard ratio = 0.576, P = 0.032).
Conclusions: A rurally based nurse-led FLS was associated with modest improvement after MTF. Consideration should be given to ways to strengthen the model of care to improve outcomes
Chromospheric Inversions of a Micro-flaring Region
We use spectropolarimetric observations of the Ca II 8542~\AA\ line, taken
from the Swedish 1-m Solar Telescope (SST), in an attempt to recover dynamic
activity in a micro-flaring region near a sunspot via inversions. These
inversions show localized mean temperature enhancements of 1000~K in the
chromosphere and upper photosphere, along with co-spatial bi-directional
Doppler shifting of 5 - 10 km s. This heating also extends along a
nearby chromospheric fibril, co-spatial to 10 - 15 km s down-flows.
Strong magnetic flux cancellation is also apparent in one of the footpoints,
concentrated in the chromosphere. This event more closely resembles that of an
Ellerman Bomb (EB), though placed slightly higher in the atmosphere than is
typically observed.Comment: 9 pages, 9 figures, accepted in ApJ. Movies are stored here:
https://star.pst.qub.ac.uk/webdav/public/areid/Microflare
Reproducibilty of partial weight bearing
Objectives: To find out whether partial weight bearing can be reproduced and retained. Design: In vivo experiment in normal subjects. Intervention: Training for partial weight bearing (25% of body weight) using bathroom scales. Main outcome measurement: Reproducibility on force platform immediately after training and after 60 min. Results: Twelve subjects were asked to reproduce 25% of their body weight through either the dominant or non-dominant limb on force platform after three practice attempts on bathroom scales with concurrent visual feedback. No feedback was provided after the measurements on force plate. The process was repeated after 1 h without any practice sessions in the interim period to find out if the weight practised could be retained. The mean 0-min reading was found to be 25.9% of body weight while the mean 60-min reading was found to be 24.4%. The p-value for the difference between the two means was found to be 0.3841. Conclusions: This study indicates that partial weight bearing instructions can be quantified and graded. Simple bathroom scales are sufficient to educate the patients and this can be practised at home after an initial period of supervision
How effective is lifeline banking in assisting the 'unbanked'?
Many consumers who lack checking accounts are paying relatively high costs to access the nation's payments system. Legislation aimed at opening the system to these unbanked individuals has centered on requiring commercial banks to offer low-cost "lifeline" accounts. But will cost savings alone motivate these consumers to access the payments system through banks?Checking accounts ; Banks and banking - Service charges ; Poverty
Coronal hole boundaries at small scales: IV. SOT view Magnetic field properties of small-scale transient brightenings in coronal holes
We study the magnetic properties of small-scale transients in coronal hole.
We found all brightening events are associated with bipolar regions and caused
by magnetic flux emergence followed by cancellation with the pre-existing and
newly emerging magnetic flux. In the coronal hole, 19 of 22 events have a
single stable polarity which does not change its position in time. In eleven
cases this is the dominant polarity. The dominant flux of the coronal hole form
the largest concentration of magnetic flux in terms of size while the opposite
polarity is distributed in small concentrations. In the coronal hole the number
of magnetic elements of the dominant polarity is four times higher than the
non-dominant one. The supergranulation configuration appears to preserve its
general shape during approximately nine hours of observations although the
large concentrations in the network did evolve and were slightly displaced, and
their strength either increased or decreased. The emission fluctuations seen in
the X-ray bright points are associated with reoccurring magnetic cancellation
in the footpoints. Unique observations of an X-ray jet reveal similar magnetic
behaviour in the footpoints, i.e. cancellation of the opposite polarity
magnetic flux. We found that the magnetic flux cancellation rate during the jet
is much higher than in bright points. Not all magnetic cancellations result in
an X-ray enhancement, suggesting that there is a threshold of the amount of
magnetic flux involved in a cancellation above which brightening would occur at
X-ray temperatures. Our study demonstrates that the magnetic flux in coronal
holes is continuously recycled through magnetic reconnection which is
responsible for the formation of numerous small-scale transient events. The
open magnetic flux forming the coronal-hole phenomenon is largely involved in
these transient features.Comment: 19 pages, 18 figures, A&A in pres
Diagnosing transient ionization in dynamic events
The present study aims to provide a diagnostic line ratio that will enable
the observer to determine whether a plasma is in a state of transient
ionization. We use the Atomic Data and Analysis Structure (ADAS) to calculate
line contribution functions for two lines, Si IV 1394 A and O IV 1401 A, formed
in the solar transition region. The generalized collisional-radiative theory is
used. It includes all radiative and electron collisional processes, except for
photon-induced processes. State-resolved direct ionization and recombination to
and from the next ionization stage are also taken into account. For dynamic
bursts with a decay time of a few seconds, the Si IV 1394 A line can be
enhanced by a factor of 2-4 in the first fraction of a second with the peak in
the line contribution function occurring initially at a higher electron
temperature due to transient ionization compared to ionization equilibrium
conditions. On the other hand, the O IV 1401 A does not show such any
enhancement. Thus the ratio of these two lines, which can be observed with the
Interface Region Imaging Spectrograph, can be used as a diagnostic of transient
ionization. We show that simultaneous high-cadence observations of two lines
formed in the solar transition region may be used as a direct diagnostic of
whether the observed plasma is in transient ionization. The ratio of these two
lines can change by a factor of four in a few seconds owing to transient
ionization alone.Comment: 3 pages, in press A&
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