113 research outputs found
EFFECTS OF BALANCING HAMSTRING AND QUADRICEPS MUSCLE TORQUE ON RUNNING TECHNIQUE
It has been suggested that balancing the isokinetic strength of quadriceps (Q) and hamstring (H) muscles can reduce hamstring injuries during running (Croisier et al 2008). The efficacy of this type of intervention has been previously explored. To further the knowledge of the H: Q relationship we have examined the intervention’s affect on running technique as presented here
Multigluon tree amplitudes with a pair of massive fermions
We consider the calculation of n-point multigluon tree amplitudes with a pair
of massive fermions in QCD. We give the explicit transformation rules of this
kind of massive fermion-pair amplitudes with respect to different reference
momenta and check the correctness of them by SUSY Ward identities. Using these
rules and onshell BCFW recursion relation, we calculate the analytic results of
several n-point multigluon amplitudes.Comment: 15page
Solution to the Ward Identities for Superamplitudes
Supersymmetry and R-symmetry Ward identities relate on-shell amplitudes in a
supersymmetric field theory. We solve these Ward identities for (Next-to)^K MHV
amplitudes of the maximally supersymmetric N=4 and N=8 theories. The resulting
superamplitude is written in a new, manifestly supersymmetric and R-invariant
form: it is expressed as a sum of very simple SUSY and SU(N)_R-invariant
Grassmann polynomials, each multiplied by a "basis amplitude". For (Next-to)^K
MHV n-point superamplitudes the number of basis amplitudes is equal to the
dimension of the irreducible representation of SU(n-4) corresponding to the
rectangular Young diagram with N columns and K rows. The linearly independent
amplitudes in this algebraic basis may still be functionally related by
permutation of momenta. We show how cyclic and reflection symmetries can be
used to obtain a smaller functional basis of color-ordered single-trace
amplitudes in N=4 gauge theory. We also analyze the more significant reduction
that occurs in N=8 supergravity because gravity amplitudes are not ordered. All
results are valid at both tree and loop level.Comment: 29 pages, published versio
MHV Rules for Higgs Plus Multi-Gluon Amplitudes
We use tree-level perturbation theory to show how non-supersymmetric one-loop
scattering amplitudes for a Higgs boson plus an arbitrary number of partons can
be constructed, in the limit of a heavy top quark, from a generalization of the
scalar graph approach of Cachazo, Svrcek and Witten. The Higgs boson couples to
gluons through a top quark loop which generates, for large top mass, a
dimension-5 operator H tr G^2. This effective interaction leads to amplitudes
which cannot be described by the standard MHV rules; for example, amplitudes
where all of the gluons have positive helicity. We split the effective
interaction into the sum of two terms, one holomorphic (selfdual) and one
anti-holomorphic (anti-selfdual). The holomorphic interactions give a new set
of MHV vertices -- identical in form to those of pure gauge theory, except for
momentum conservation -- that can be combined with pure gauge theory MHV
vertices to produce a tower of amplitudes with more than two negative
helicities. Similarly, the anti-holomorphic interactions give anti-MHV vertices
that can be combined with pure gauge theory anti-MHV vertices to produce a
tower of amplitudes with more than two positive helicities. A Higgs boson
amplitude is the sum of one MHV-tower amplitude and one anti-MHV-tower
amplitude. We present all MHV-tower amplitudes with up to four
negative-helicity gluons and any number of positive-helicity gluons (NNMHV).
These rules reproduce all of the available analytic formulae for Higgs +
n-gluon scattering (n<=5) at tree level, in some cases yielding considerably
shorter expressions.Comment: 34 pages, 8 figures; v2, references correcte
Identification of animal movement patterns using tri-axial magnetometry
BackgroundAccelerometers are powerful sensors in many bio-logging devices, and are increasingly allowing researchers to investigate the performance, behaviour, energy expenditure and even state, of free-living animals. Another sensor commonly used in animal-attached loggers is the magnetometer, which has been primarily used in dead-reckoning or inertial measurement tags, but little outside that. We examine the potential of magnetometers for helping elucidate the behaviour of animals in a manner analogous to, but very different from, accelerometers. The particular responses of magnetometers to movement means that there are instances when they can resolve behaviours that are not easily perceived using accelerometers.MethodsWe calibrated the tri-axial magnetometer to rotations in each axis of movement and constructed 3-dimensional plots to inspect these stylised movements. Using the tri-axial data of Daily Diary tags, attached to individuals of number of animal species as they perform different behaviours, we used these 3-d plots to develop a framework with which tri-axial magnetometry data can be examined and introduce metrics that should help quantify movement and behaviour.ResultsTri-axial magnetometry data reveal patterns in movement at various scales of rotation that are not always evident in acceleration data. Some of these patterns may be obscure until visualised in 3D space as tri-axial spherical plots (m-spheres). A tag-fitted animal that rotates in heading while adopting a constant body attitude produces a ring of data around the pole of the m-sphere that we define as its Normal Operational Plane (NOP). Data that do not lie on this ring are created by postural rotations of the animal as it pitches and/or rolls. Consequently, stereotyped behaviours appear as specific trajectories on the sphere (m-prints), reflecting conserved sequences of postural changes (and/or angular velocities), which result from the precise relationship between body attitude and heading. This novel approach shows promise for helping researchers to identify and quantify behaviours in terms of animal body posture, including heading.ConclusionMagnetometer-based techniques and metrics can enhance our capacity to identify and examine animal behaviour, either as a technique used alone, or one that is complementary to tri-axial accelerometry
Cytogerontology since 1881: A reappraisal of August Weismann and a review of modern progress
Cytogerontology, the science of cellular ageing, originated in 1881 with the prediction by August Weismann that the somatic cells of higher animals have limited division potential. Weismann's prediction was derived by considering the role of natural selection in regulating the duration of an organism's life. For various reasons, Weismann's ideas on ageing fell into neglect following his death in 1914, and cytogerontology has only reappeared as a major research area following the demonstration by Hayflick and Moorhead in the early 1960s that diploid human fibroblasts are restricted to a finite number of divisions in vitro.
In this review we give a detailed account of Weismann's theory, and we reveal that his ideas were both more extensive in their scope and more pertinent to current research than is generally recognised. We also appraise the progress which has been made over the past hundred years in investigating the causes of ageing, with particular emphasis being given to (i) the evolution of ageing, and (ii) ageing at the cellular level. We critically assess the current state of knowledge in these areas and recommend a series of points as primary targets for future research
Minimally helicity violating, maximally simple scalar amplitudes in N=4 SYM
In planar N=4 SYM we study a particular class of helicity preserving
amplitudes. These are scalar amplitudes whose flavor configuration is chosen in
such a way that only a limited number of diagrams is allowed, which exhibit an
iterative structure. For such amplitudes we evaluate the tree level and
one-loop contributions, providing a general formula valid for any number of
particles. The ratio between the one-loop and tree level results is a simple
combination of dual conformally invariant box functions with at most two
massive legs. Along with the MHV and NMHV series, this constitutes the third
known infinite sequence of one-loop amplitudes in N=4 SYM.Comment: 22 pages, 7 figures, published versio
Classification of behaviour in housed dairy cows using an accelerometer-based activity monitoring system
Background Advances in bio-telemetry technology have made it possible to automatically monitor and classify behavioural activities in many animals, including domesticated species such as dairy cows. Automated behavioural classification has the potential to improve health and welfare monitoring processes as part of a Precision Livestock Farming approach. Recent studies have used accelerometers and pedometers to classify behavioural activities in dairy cows, but such approaches often cannot discriminate accurately between biologically important behaviours such as feeding, lying and standing or transition events between lying and standing. In this study we develop a decision-tree algorithm that uses tri-axial accelerometer data from a neck-mounted sensor to both classify biologically important behaviour in dairy cows and to detect transition events between lying and standing.
Results Data were collected from six dairy cows that were monitored continuously for 36 h. Direct visual observations of each cow were used to validate the algorithm. Results show that the decision-tree algorithm is able to accurately classify three types of biologically relevant behaviours: lying (77.42 % sensitivity, 98.63 % precision), standing (88.00 % sensitivity, 55.00 % precision), and feeding (98.78 % sensitivity, 93.10 % precision). Transitions between standing and lying were also detected accurately with an average sensitivity of 96.45 % and an average precision of 87.50 %. The sensitivity and precision of the decision-tree algorithm matches the performance of more computationally intensive algorithms such as hidden Markov models and support vector machines.
Conclusions Biologically important behavioural activities in housed dairy cows can be classified accurately using a simple decision-tree algorithm applied to data collected from a neck-mounted tri-axial accelerometer. The algorithm could form part of a real-time behavioural monitoring system in order to automatically detect dairy cow health and welfare status
One Loop Amplitudes In ABJM
For three dimensional N=6 superconformal field theories we compute one-loop
scattering amplitudes for any number of external particles. We focus on a
particular subsector of N=2 invariant superamplitudes for which the ordinary
perturbative evaluation becomes very easy. The result we obtain is in general
non-vanishing. For six external particles our findings are sufficient for
determining the complete expression of the N=6 superamplitude at this order. We
discuss the symmetries of the result and its anomalous variation under
superconformal generators.Comment: 1+34 pages, 4 figures, references added, published versio
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