13,505 research outputs found
A preliminary investigation of trunk and wrist kinematics when using drivers with different shaft properties
It is unknown whether skilled golfers will modify their kinematics when using drivers of different shaft properties. This study aimed to firstly, determine if golf swing kinematics and swing parameters and related launch conditions differed when using modified drivers, then secondly, determine which kinematics were associated with clubhead speed. Twenty high level amateur male golfers (Mean ± SD: handicap = 1.9 ± 1.9 score) had their three-dimensional trunk and wrist kinematics collected for two driver trials. Swing parameters and related launch conditions were collected using a launch monitor. A one-way repeated measures ANOVA revealed significant (p ≤ 0.003) between-driver differences; specifically, faster trunk axial rotation velocity and an early wrist release for the low kick point driver. Launch angle was shown to be 2° lower for the high kick point driver. Regression models for both drivers explained a significant amount of variance (60 – 67%) in clubhead speed. Wrist kinematics were most associated with clubhead speed, indicating the importance of the wrists in producing clubhead speed regardless of driver shaft properties
Quasi-stationary states and the range of pair interactions
"Quasi-stationary" states are approximately time-independent out of
equilibrium states which have been observed in a variety of systems of
particles interacting by long-range interactions. We investigate here the
conditions of their occurrence for a generic pair interaction V(r \rightarrow
\infty) \sim 1/r^a with a > 0, in d>1 dimensions. We generalize analytic
calculations known for gravity in d=3 to determine the scaling parametric
dependences of their relaxation rates due to two body collisions, and report
extensive numerical simulations testing their validity. Our results lead to the
conclusion that, for a < d-1, the existence of quasi-stationary states is
ensured by the large distance behavior of the interaction alone, while for a >
d-1 it is conditioned on the short distance properties of the interaction,
requiring the presence of a sufficiently large soft-core in the interaction
potential.Comment: 5 pages, 3 figures; final version to appear in Phys. Rev. Let
The influence of atmosphere on the performance of pure-phase WZ and ZB InAs nanowire transistors
We compare the characteristics of phase-pure MOCVD grown ZB and WZ InAs
nanowire transistors in several atmospheres: air, dry pure N and O, and
N bubbled through liquid HO and alcohols to identify whether
phase-related structural/surface differences affect their response. Both WZ and
ZB give poor gate characteristics in dry state. Adsorption of polar species
reduces off-current by 2-3 orders of magnitude, increases on-off ratio and
significantly reduces sub-threshold slope. The key difference is the greater
sensitivity of WZ to low adsorbate level. We attribute this to facet structure
and its influence on the separation between conduction electrons and surface
adsorption sites. We highlight the important role adsorbed species play in
nanowire device characterisation. WZ is commonly thought superior to ZB in InAs
nanowire transistors. We show this is an artefact of the moderate humidity
found in ambient laboratory conditions: WZ and ZB perform equally poorly in the
dry gas limit yet equally well in the wet gas limit. We also highlight the
vital role density-lowering disorder has in improving gate characteristics, be
it stacking faults in mixed-phase WZ or surface adsorbates in pure-phase
nanowires.Comment: Accepted for publication in Nanotechnolog
Possible origin of 60-K plateau in the YBa2Cu3O(6+y) phase diagram
We study a model of YBa2Cu3O(6+y) to investigate the influence of oxygen
ordering and doping imbalance on the critical temperature Tc(y) and to
elucidate a possible origin of well-known feature of YBCO phase diagram: the
60-K plateau. Focusing on "phase only" description of the high-temperature
superconducting system in terms of collective variables we utilize a
three-dimensional semi microscopic XY model with two-component vectors that
involve phase variables and adjustable parameters representing microscopic
phase stiffnesses. The model captures characteristic energy scales present in
YBCO and allows for strong anisotropy within basal planes to simulate oxygen
ordering. Applying spherical closure relation we have solved the phase XY model
with the help of transfer matrix method and calculated Tc for chosen system
parameters. Furthermore, we investigate the influence of oxygen ordering and
doping imbalance on the shape of YBCO phase diagram. We find it unlikely that
oxygen ordering alone can be responsible for the existence of 60-K plateau.
Relying on experimental data unveiling that oxygen doping of YBCO may introduce
significant charge imbalance between CuO2 planes and other sites, we show that
simultaneously the former are underdoped, while the latter -- strongly
overdoped almost in the whole region of oxygen doping in which YBCO is
superconducting. As a result, while oxygen content is increased, this provides
two counter acting factors, which possibly lead to rise of 60K plateau.
Additionally, our result can provide an important contribution to understanding
of experimental data supporting existence of multicomponent superconductivity
in YBCO.Comment: 9 pages, 8 figures, submitted to PRB, see http://prb.aps.or
Spanning tree generating functions and Mahler measures
We define the notion of a spanning tree generating function (STGF) , which gives the spanning tree constant when evaluated at and gives
the lattice Green function (LGF) when differentiated. By making use of known
results for logarithmic Mahler measures of certain Laurent polynomials, and
proving new results, we express the STGFs as hypergeometric functions for all
regular two and three dimensional lattices (and one higher-dimensional
lattice). This gives closed form expressions for the spanning tree constants
for all such lattices, which were previously largely unknown in all but one
three-dimensional case. We show for all lattices that these can also be
represented as Dirichlet -series. Making the connection between spanning
tree generating functions and lattice Green functions produces integral
identities and hypergeometric connections, some of which appear to be new.Comment: 26 pages. Dedicated to F Y Wu on the occasion of his 80th birthday.
This version has additional references, additional calculations, and minor
correction
Maturity, physical ability, technical skill and coaches\u27 perception of semi-elite adolescent Australian footballers
Purpose: To confirm the effect of maturational differences on anthropometric and physical testing and explore the effect of maturation on technical skill and coaches’ perceptions of skill in adolescent Australian footballers.
Methods: Athletes were recruited from a semi-elite under 16 competition (n = 94, age 15.7 ± 0.3 years) and completed anthropometric, physical, and technical skill tests. Coaches from each team provided subjective ratings of athletes’ technical skills. Maturation groups were derived from years from peak height velocity estimates, with classifications either later, average or earlier maturing.
Results: Effect size comparisons revealed very large to moderate effects between groups for anthropometric measures and performance in sprint and jump tasks. Small to moderate effects were reported between groups for coaches’ perceptions of skill, with the earlier maturing group perceived to have better overall technical skills, marking and ball winning abilities. Small to trivial effects were reported for performance in the technical skill tests. Conclusions: Despite no differences in skill tests, earlier maturing athletes may be afforded significant selection and competition advantages due to advanced physical capacities and coaches’ perceptions of skill
A combinatorial approach to knot recognition
This is a report on our ongoing research on a combinatorial approach to knot
recognition, using coloring of knots by certain algebraic objects called
quandles. The aim of the paper is to summarize the mathematical theory of knot
coloring in a compact, accessible manner, and to show how to use it for
computational purposes. In particular, we address how to determine colorability
of a knot, and propose to use SAT solving to search for colorings. The
computational complexity of the problem, both in theory and in our
implementation, is discussed. In the last part, we explain how coloring can be
utilized in knot recognition
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