44,856 research outputs found
Interplay between disorder and local field effects in photonic crystal waveguides
We introduce a theory to describe disorder-induced scattering in photonic
crystal waveguides, specifically addressing the influence of local field
effects and scattering within high-index-contrast perturbations. Local field
effects are shown to increase the predicted disorder-induced scattering loss
and result in significant resonance shifts of the waveguide mode. We
demonstrate that two types of frequency shifts can be expected, a mean
frequency shift and a RMS frequency shift, both acting in concert to blueshift
and broaden the nominal band structure. For a representative waveguide, we
predict substantial meV frequency shifts and band structure broadening for a
telecommunications operating frequency, even for state of the art fabrication.
The disorder-induced broadening is found to increase as the propagation
frequency approaches the slow light regime (mode edge) due to restructuring of
the electric field distribution. These findings have a dramatic impact on
high-index-contrast nanoscale waveguides, and, for photonic crystal waveguides,
suggest that the nominal slow-light mode edge may not even exist. Furthermore,
our results shed new light on why it has hitherto been impossible to observe
the very slow light regime for photonic crystal waveguides.Comment: 4 page lette
Theory of disorder-induced multiple coherent scattering in photonic crystal waveguides
We introduce a theoretical formalism to describe disorder-induced extrinsic
scattering in slow-light photonic crystal waveguides. This work details and
extends the optical scattering theory used in a recent \emph{Physical Review
Letter} [M. Patterson \emph{et al.}, \emph{Phys. Rev. Lett.} \textbf{102},
103901 (2009)] to describe coherent scattering phenomena and successfully
explain complex experimental measurements. Our presented theory, that combines
Green function and coupled mode methods, allows one to self-consistently
account for arbitrary multiple scattering for the propagating electric field
and recover experimental features such as resonances near the band edge. The
technique is fully three-dimensional and can calculate the effects of disorder
on the propagating field over thousands of unit cells. As an application of
this theory, we explore various sample lengths and disordered instances, and
demonstrate the profound effect of multiple scattering in the waveguide
transmission. The spectra yield rich features associated with disorder-induced
localization and multiple scattering, which are shown to be exasperated in the
slow light propagation regime
Orbital evolution of a test particle around a black hole: higher-order corrections
We study the orbital evolution of a radiation-damped binary in the extreme
mass ratio limit, and the resulting waveforms, to one order beyond what can be
obtained using the conservation laws approach. The equations of motion are
solved perturbatively in the mass ratio (or the corresponding parameter in the
scalar field toy model), using the self force, for quasi-circular orbits around
a Schwarzschild black hole. This approach is applied for the scalar model.
Higher-order corrections yield a phase shift which, if included, may make
gravitational-wave astronomy potentially highly accurate.Comment: 4 pages, 3 Encapsulated PostScript figure
The effect of movement variability on putting proficiency during the golf putting stroke
Movement variability has been considered important to execute an effective golf swing yet is comparatively unexplored regarding the golf putt. Movement variability could potentially be important considering the small margins of error between a successful and a missed putt. The aim of this study was to assess whether variability of body segment rotations influence putting performance (ball kinematic measures). Eight golfers (handicap range 0–10) performed a 3.2 m level putt wearing retro-reflective markers which were tracked using a three-dimensional motion analysis system sampling at 120 Hz. Ball roll kinematics were recorded using Quintic Ball Roll launch monitor. Movement (segment) variability was calculated based on a scalene ellipsoid volume concept and correlated with the coefficient of variation of ball kinematics. Statistical analysis showed no significant relationships between segment variability and putting proficiency. One significant relationship was identified between left forearm variability and horizontal launch angle, but this did not result in deficits in putting success. Results show that performance variability in the backswing and downswing is not related to putting proficiency or the majority of ball roll measures. Differing strategies may exist where certain golfers may have more fluid movement patterns thereby effectively utilising variability of movement. Therefore, golf instructors should consider movement variability when coaching the golf putt
Reliability of an experimental method to analyse the impact point on a golf ball during putting
This study aimed to examine the reliability of an experimental method identifying the location of the impact point on a golf ball during putting. Forty trials were completed using a mechanical putting robot set to reproduce a putt of 3.2 m, with four different putter-ball combinations. After locating the centre of the dimple pattern (centroid) the following variables were tested; distance of the impact point from the centroid, angle of the impact point from the centroid and distance of the impact point from the centroid derived from the X, Y coordinates. Good to excellent reliability was demonstrated in all impact variables reflected in very strong relative (ICC = 0.98–1.00) and absolute reliability (SEM% = 0.9–4.3%). The highest SEM% observed was 7% for the angle of the impact point from the centroid. In conclusion, the experimental method was shown to be reliable at locating the centroid location of a golf ball, therefore allowing for the identification of the point of impact with the putter head and is suitable for use in subsequent studies
Raising the Dead: Clues to Type Ia Supernova Physics from the Remnant 0509-67.5
We present Chandra X-ray observations of the young supernova remnant (SNR)
0509-67.5 in the Large Magellanic Cloud (LMC), believed to be the product of a
Type Ia supernova (SN Ia). The remnant is very round in shape, with a distinct
clumpy shell-like structure. Our Chandra data reveal the remnant to be rich in
silicon, sulfur, and iron. The yields of our fits to the global spectrum
confirm that 0509-67.5 is the remnant of an SN Ia and show a clear preference
for delayed detonation explosion models for SNe Ia. We study the spectrum of
the single brightest isolated knot in the remnant and find that it is enhanced
in iron by a factor of roughly two relative to the global remnant abundances.
This feature, along with similar knots seen in Tycho's SNR, argues for the
presence of modest small-scale composition inhomogeneities in SNe Ia. The
presence of both Si and Fe, with abundance ratios that vary from knot to knot,
indicates that these came from the transition region between the Si- and
Fe-rich zones in the exploded star, possibly as a result of energy input to the
ejecta at late times due to the radioactive decay of 56Ni and 56Co. Two cases
for the continuum emission from the global spectrum were modeled: one where the
continuum is dominated by hydrogen thermal bremsstrahlung radiation; another
where the continuum arises from non-thermal synchrotron radiation. The former
case requires a relatively large value for the ambient density (~1 cm^-3).
Another estimate of the ambient density comes from using the shell structure of
the remnant in the context of dynamical models. This requires a much lower
value for the density (<0.05 cm^-3) which is more consistent with other
evidence known about 0509-67.5. We therefore conclude that the bulk of the
continuum emission from 0509-67.5 has a non-thermal origin.Comment: 34 pages, 9 figures (1 color), accepted to ApJ (10 June 2004 issue);
correction made to calculation of magnetic field, small sentence change
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