18,026 research outputs found
The most important factor in producing clubhead speed in golf
Substantial experiential research into x-factor, and to a lesser extent crunch-factor has been undertaken with the aim of increasing clubhead speed. However, a direct comparison of the golf swing kinematics associated with each ‘factor’ has not, and possible differences when using a driver compared to an iron. Fifteen low handicap male golfers who displayed a modern swing had their golf swing kinematic data measured when hitting their own driver and five-iron, using a 10-camera motion analysis system operating at 250 Hz. Clubhead speed was collected using a validated launch monitor. No between-club differences in x-factor and crunch-factor existed. Correlation analyses revealed within-club segment (trunk and lower trunk) interaction was different for the driver, compared to the five-iron, and that a greater number of kinematic variables associated with x-factor, compared to crunch-factor were shown to be correlated with faster clubhead speeds. This was further explained in the five-iron regression model, where a significant amount of variance in clubhead speed was associated with increased lower trunk x-factor stretch, and reduced trunk lateral bending. Given that greens in regulation was shown to be the strongest correlated variable with PGA Tour earnings (1990-2004), the findings suggests a link to player performance for approach shots. These findings support other empiric research into the importance of x-factor as well as anecdotal evidence on how crunch-factor can negatively affect clubhead speed
Phase diagrams of SU(N) gauge theories with fermions in various representations
We minimize the one-loop effective potential for SU(N) gauge theories
including fermions with finite mass in the fundamental (F), adjoint (Adj),
symmetric (S), and antisymmetric (AS) representations. We calculate the phase
diagram on S^1 x R^3 as a function of the length of the compact dimension,
beta, and the fermion mass, m. We consider the effect of periodic boundary
conditions [PBC(+)] on fermions as well as antiperiodic boundary conditions
[ABC(-)]. The use of PBC(+) produces a rich phase structure. These phases are
distinguished by the eigenvalues of the Polyakov loop P. Minimization of the
effective potential for QCD(AS/S,+) results in a phase where | Im Tr P | is
maximized, resulting in charge conjugation (C) symmetry breaking for all N and
all values of (m beta), however, the partition function is the same up to
O(1/N) corrections as when ABC are applied. Therefore, regarding orientifold
planar equivalence, we argue that in the one-loop approximation C-breaking in
QCD(AS/S,+) resulting from the application of PBC to fermions does not
invalidate the large N equivalence with QCD(Adj,-). Similarly, with respect to
orbifold planar equivalence, breaking of Z(2) interchange symmetry resulting
from application of PBC to bifundamental (BF) representation fermions does not
invalidate equivalence with QCD(Adj,-) in the one-loop perturbative limit
because the partition functions of QCD(BF,-) and QCD(BF,+) are the same. Of
particular interest as well is the case of adjoint fermions where for Nf > 1
Majorana flavour confinement is obtained for sufficiently small (m beta), and
deconfinement for sufficiently large (m beta). For N >= 3 these two phases are
separated by one or more additional phases, some of which can be characterized
as partially-confining phases.Comment: 39 pages, 26 figures, JHEP3; references added, small corrections mad
Risk Prediction of a Multiple Sclerosis Diagnosis
Multiple sclerosis (MS) is a chronic autoimmune disease that affects the
central nervous system. The progression and severity of MS varies by
individual, but it is generally a disabling disease. Although medications have
been developed to slow the disease progression and help manage symptoms, MS
research has yet to result in a cure. Early diagnosis and treatment of the
disease have been shown to be effective at slowing the development of
disabilities. However, early MS diagnosis is difficult because symptoms are
intermittent and shared with other diseases. Thus most previous works have
focused on uncovering the risk factors associated with MS and predicting the
progression of disease after a diagnosis rather than disease prediction. This
paper investigates the use of data available in electronic medical records
(EMRs) to create a risk prediction model; thereby helping clinicians perform
the difficult task of diagnosing an MS patient. Our results demonstrate that
even given a limited time window of patient data, one can achieve reasonable
classification with an area under the receiver operating characteristic curve
of 0.724. By restricting our features to common EMR components, the developed
models also generalize to other healthcare systems
The QCD sign problem as a total derivative
We consider the distribution of the complex phase of the fermion determinant
in QCD at nonzero chemical potential and examine the physical conditions under
which the distribution takes a Gaussian form. We then calculate the baryon
number as a function of the complex phase of the fermion determinant and show
1) that the exponential cancellations produced by the sign problem take the
form of total derivatives 2) that the full baryon number is orthogonal to this
noise. These insights allow us to define a self-consistency requirement for
measurements of the baryon number in lattice simulations.Comment: 5 pages, reference added, version to appear in PRD rapid
communication
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