2,057 research outputs found
Coating thickness and elastic modulus measurement using ultrasonic bulk wave resonance
Measurement of the resonant through thickness ultrasonic modes of a homogeneous plate using a fast Fourier transform of the temporal data can be used to calculate plate thickness very accurately. We describe an extension of this principle to two-layer systems, examining a thin coating on a substrate of known properties. The resonant behavior of these systems is predicted and we explain how this approach is used to measure coating thickness and elastic modulus. Noncontact electromagnetic acoustic transducers are used for ultrasonic measurement, as they do not significantly affect the resonant response of the system, unlike alternative contact transducers
Investigation of the nonlocal coherent-potential approximation
Recently the nonlocal coherent-potential approximation (NLCPA) has been
introduced by Jarrell and Krishnamurthy for describing the electronic structure
of substitutionally disordered systems. The NLCPA provides systematic
corrections to the widely used coherent-potential approximation (CPA) whilst
preserving the full symmetry of the underlying lattice. Here an analytical and
systematic numerical study of the NLCPA is presented for a one-dimensional
tight-binding model Hamiltonian, and comparisons with the embedded cluster
method (ECM) and molecular coherent potential approximation (MCPA) are made.Comment: 18 pages, 5 figure
The flow of equatorial Kelvin waves and the equatorial undercurrent around islands
A linear theory is presented for the flow of equatorial Kelvin waves and of the equatorial undercurrent around islands situated on or near the equator. The island is modelled as an infinitesimally thin meridional barrier. It is shown that small islands affect the flow very little, while large islands effectively block the flow...
Scaling collapse and structure functions: identifying self-affinity in finite length time series
Empirical determination of the scaling properties and exponents of time series presents a formidable challenge in testing, and developing, a theoretical understanding of turbulence and other out-of-equilibrium phenomena. We discuss the special case of self affine time series in the context of a stochastic process. We highlight two complementary approaches to the differenced variable of the data: i) attempting a scaling collapse of the Probability Density Functions which should then be well described by the solution of the corresponding Fokker-Planck equation and ii) using structure functions to determine the scaling properties of the higher order moments. We consider a method of conditioning that recovers the underlying self affine scaling in a finite length time series, and illustrate it using a Lévy flight
Transduodenal Sphincteroplasty and Transampullary Septectomy for Papillary Stenosis
Twenty patients received transduodenal sphincteroplasty and transampullary septectomy between 1987
and 1993. Seven patients had post-cholecystectomy pain which was much improved or abolished in 5 of 7
patients at a mean follow-up of 4 years and 5 months. Four of five patients with chronic pancreatitis were
improved at 3 years and 2 months. Three of five patients with recurrent acute pancreatitis were improved
at 4 years and 5 months. One of three patients with chronic abdominal pain of hepatobiliary origin was
improved at 3 years. Transduodenal sphincteroplasty and transampullary septectomy can relieve pain in
patients with post-cholecystectomy pain, recurrent acute pancreatitis, chronic pancreatitis, and chronic
abdominal pain of hepatobiliary origin, presumably by improving drainage of the obstructed ducts
Effects of short-range order on the electronic structure of disordered metallic systems
For many years the Korringa-Kohn-Rostoker coherent-potential approximation
(KKR-CPA) has been widely used to describe the electronic structure of
disordered systems based upon a first-principles description of the crystal
potential. However, as a single-site theory the KKR-CPA is unable to account
for important environmental effects such as short-range order (SRO) in alloys
and spin fluctuations in magnets, amongst others. Using the recently devised
KKR-NLCPA (where NL stands for nonlocal), we show how to remedy this by
presenting explicit calculations for the effects of SRO on the electronic
structure of the bcc Cu_{50}Zn_{50} solid solution.Comment: 8 pages, 6 figures, Revised versio
The role of inertia-gravity and planetary waves in the response of a tropical ocean to the incidence of an equatorial Kelvin wave on a meridional boundary
The problem of an equatorial Kelvin wave of step-function form incident on an eastern meridional boundary is solved on an equatorial beta-plane. The nature of the transient planetary and inertia-gravity waves is examined and the way in which they combine to produce a coastally trapped Kelvin wave evaluated...
The Somali Current response to the Southwest Monsoon: The relative importance of local and remote forcing
A simple model of the Somali current is formul ated which allows both local longshore forcing and remote east-west forcing. Asymptotic solutions for the pressure perturbation and velocity fields are obtained for both cases and the sensitivity of the boundary response to changes in the shape and position of the forcing is examined. The local forcing drives a flow whose north-south velocity increases linearly with time and the remote forcing , a flow in which the north-south velocity increases quadratically...
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