24,332 research outputs found
An evaluation of errors observed in the measurement of low wind velocities
Measurements of low wind velocities (the absolute value of V sub H is approx. equal to 6 m/s) with a VHF wind profiler can be difficult if ground clutter or other biases in the system dominate in altering the position of the perceived peak in the calculated power spectrum. A variety of methods for ground clutter suppression are used in profiler systems today (Cornish, 1983). An editing method called zero suppression takes the spectral value of selectable number of points (N) on each side of 0 velocity (one point on either side, in this study) and sets them equal to the mean value of the points exterior to the specified N points on either side of 0. Analysis done with the PSU VHF(1) radar, shows that this zero-suppression method can systematically bias horizontal wings V sub H below 6 m/s. With the zero suppression, an artificial increase in absolute wind velocities occurs when the spectral peaks fall within the plus or minus N points of the FFT (personal communication, Strauch, 1985). It was also established that the method artificially decreases the absolute wind velocities inferred from spectral peaks that are outside but near the suppressed region. Comparisons of wind profiles observed with and without zero suppression are given. The range of the biased velocities extends to about plus or minus 6 m/s. Biases have been deduced to be as much as 2 m/s, but more commonly they are on the order of 1.0 m/s
Calculation of Elastic Green's Functions for Lattices with Cavities
In this Brief Report, we present an algorithm for calculating the elastic
Lattice Greens Function of a regular lattice, in which defects are created by
removing lattice points. The method is computationally efficient, since the
required matrix operations are on matrices that scale with the size of the
defect subspace, and not with the size of the full lattice. This method allows
the treatment of force fields with multi-atom interactions.Comment: 3 pages. RevTeX, using epsfig.sty. One figur
The Photonic Lantern
Photonic lanterns are made by adiabatically merging several single-mode cores
into one multimode core. They provide low-loss interfaces between single-mode
and multimode systems where the precise optical mapping between cores and
individual modes is unimportant.Comment: 45 pages; article unchanged, accepted for publication in Advances in
Optics and Photonic
Tablet computers in assessing performance in a high stakes exam : opinion matters
The authors would like to thank Dr Craig brown, University of Aberdeen for assistance with data analysis.Peer reviewedPublisher PD
Extremely low long‐term erosion rates around the Gamburtsev Mountains in interior East Antarctica
The high elevation and rugged relief (>3 km) of the Gamburtsev Subglacial Mountains (GSM) have long been considered enigmatic. Orogenesis normally occurs near plate boundaries, not cratonic interiors, and large‐scale tectonic activity last occurred in East Antarctica during the Pan‐African (480–600 Ma). We sampled detrital apatite from Eocene sands in Prydz Bay at the terminus of the Lambert Graben, which drained a large pre‐glacial basin including the northern Gamburtsev Mountains. Apatite fission‐track and (U‐Th)/He cooling ages constrain bedrock erosion rates throughout the catchment. We double‐dated apatites to resolve individual cooling histories. Erosion was very slow, averaging 0.01–0.02 km/Myr for >250 Myr, supporting the preservation of high elevation in interior East Antarctica since at least the cessation of Permian rifting. Long‐term topographic preservation lends credence to postulated high‐elevation mountain ice caps in East Antarctica since at least the Cretaceous and to the idea that cold‐based glaciation can preserve tectonically inactive topography
Resonant Processes in a Frozen Gas
We present a theory of resonant processes in a frozen gas of atoms
interacting via dipole-dipole potentials that vary as , where is
the interatomic separation. We supply an exact result for a single atom in a
given state interacting resonantly with a random gas of atoms in a different
state. The time development of the transition process is calculated both on-
and off-resonance, and the linewidth with respect to detuning is obtained as a
function of time . We introduce a random spin Hamiltonian to model a dense
system of resonators and show how it reduces to the previous model in the limit
of a sparse system. We derive approximate equations for the average effective
spin, and we use them to model the behavior seen in the experiments of Anderson
et al. and Lowell et al. The approach to equilibrium is found to be
proportional to ), where the constant is explicitly related to the system's parameters.Comment: 30 pages, 6 figure
Intrinsic Periodicity of Time and Non-maximal Entropy of Universe
The universe is certainly not yet in total thermodynamical equilibrium,so
clearly some law telling about special initial conditions is needed. A universe
or a system imposed to behave periodically gets thereby required ``initial
conditions". Those initial conditions will \underline{not} look like having
already suffered the heat death, i.e. obtained the maximal entropy, like a
random state. The intrinsic periodicity explains successfully why entropy is
not maximal, but fails phenomenologically by leading to a
\underline{constant}entropy.Comment: 8 page
Velocity, energy and helicity of vortex knots and unknots
In this paper we determine the velocity, the energy and estimate writhe and
twist helicity contributions of vortex filaments in the shape of torus knots
and unknots (toroidal and poloidal coils) in a perfect fluid. Calculations are
performed by numerical integration of the Biot-Savart law. Vortex complexity is
parametrized by the winding number , given by the ratio of the number of
meridian wraps to that of the longitudinal wraps. We find that for vortex
knots and toroidal coils move faster and carry more energy than a reference
vortex ring of same size and circulation, whereas for knots and poloidal
coils have approximately same speed and energy of the reference vortex ring.
Helicity is dominated by the writhe contribution. Finally, we confirm the
stabilizing effect of the Biot-Savart law for all knots and unknots tested,
that are found to be structurally stable over a distance of several diameters.
Our results also apply to quantized vortices in superfluid He.Comment: 17 pages, 8 figures, 2 table
Reduced healthcare utilisation following successful HCV treatment in HIV co-infected patients with mild liver disease
New direct-acting antivirals (DAA) for hepatitis C virus (HCV) infection have achieved high cure rates in many patient groups previously considered difficult-to-treat, including those HIV/HCV co-infected. The high price of these medications is likely to limit access to treatment, at least in the short term. Early treatment priority is likely to be given to those with advanced disease, but a more detailed understanding of the potential benefits in treating those with mild disease is needed. We hypothesized that successful HCV treatment within a co-infected population with mild liver disease would lead to a reduction in the use and costs of healthcare services in the 5 years following treatment completion. We performed a retrospective cohort study of HIV/HCV-co-infected patients without evidence of fibrosis/cirrhosis who received a course of HCV therapy between 2004 and 2013. Detailed analysis of healthcare utilization up to 5 years following treatment for each patient using clinical and electronic records was used to estimate healthcare costs. Sixty-three patients were investigated, of whom 48 of 63 (76.2%) achieved sustained virological response 12 weeks following completion of therapy (SVR12). Individuals achieving SVR12 incurred lower health utilization costs (£5000 per-patient) compared to (£10 775 per-patient) non-SVR patients in the 5 years after treatment. Healthcare utilization rates and costs in the immediate 5 years following treatment were significantly higher in co-infected patients with mild disease that failed to achieve SVR12. These data suggest additional value to achieving cure beyond the prevention of complications of disease
- …