Search results for "layer"
showing 10 items of 2667 documents
Singular behavior of a vortex layer in the zero thickness limit
2017
The aim of this paper is to study the Euler dynamics of a 2D periodic layer of non uniform vorticity. We consider the zero thickness limit and we compare the Euler solution with the vortex sheet evolution predicted by the Birkhoff-Rott equation. The well known process of singularity formation in shape of the vortex sheet correlates with the appearance of several complex singularities in the Euler solution with the vortex layer datum. These singularities approach the real axis and are responsible for the roll-up process in the layer motion.
Surface effects on spinodal decomposition in binary mixtures: The case with long-ranged surface fields
1997
We present detailed numerical results for phase-separation kinetics of critical binary mixtures in the vicinity of a surface that exerts a long-ranged attractive force on one of the components of the mixture. We consider surface potentials of the form $V(Z)\ensuremath{\sim}{Z}^{\ensuremath{-}n}$, where $Z$ is the distance from the surface and $n=1,2,3$. In particular, we investigate the interplay of the surface wetting layer with the dynamics of domain growth. We find that the wetting layer at the surface exhibits power-law growth with an exponent that depends on $n$, in contrast to the case with a short-ranged surface potential, where the growth is presumably logarithmic. From correlation …
Self‐similar problems for modeling the surface chemical reactions with the gravitation
1998
The mathematical model of a chemical reaction which takes place on the surface of the uniformly moving vertically imbedded glass fibre material is considered. The effect of gravitation is taken into account. Boussinesq's and boundary layer fittings allow to derive boundary value problems for self‐similar systems of ordinary differential equations. First Published Online: 14 Oct 2010
THEORETISGHE UNTERSUCHUNGEN UBER DEN EINFLUSS DER VERWITTERUNGSSCHICHT AUF DAS SPEKTRUM ELASTISCHER WELLEN IN DER REFLEXIONSSEISMIK
1957
The following assumptions are made in the mathematical treatment of the problem. Below a plane earth's surface there is a three-layered elastic medium the interfaces of which are parallel to the earth's surface. The uppermost layer represents the weathered layer in which the velocity of propagation of seismic waves increases linearly with depth. The two lower layers, the so-called intermediate layer and the substratum each have a constant velocity. The surface of the earth is acted on simultaneously by a normal pressure N in the form of a Heaviside pulse. The seismic wave thus generated is propagated through the elastic media. The aim of the investigation is to study the shape of the wave 1…
Advanced models for nonlocal magneto-electro-elastic multilayered plates based on Reissner mixed variational theorem
2019
In the present work, nonlocal layer-wise models for the analysis of magneto-electro-elastic multilayered plates are formulated. An Eringen non-local continuum behaviour is assumed for the layers material; in particular, as usual in plate theories, partial in-plane nonlocality is assumed whereas local constitutive behaviour is considered in the thickness direction. The proposed plate theories are obtained via the Reissner Mixed Variational Theorem, assuming the generalized displacements and generalized out-of-plane stresses as primary variables, and expressing them as through-the-thickness expansions of suitably selected functions, considering the expansion order as a free parameter. In the …
X-ray spectroscopy and dosimetry with a portable CdTe device.
2007
Abstract X-ray spectra and dosimetry information are very important for quality assurance (QA) and quality control (QC) in medical diagnostic X-ray systems. An accurate knowledge of the diagnostic X-ray spectra would improve the patient dose optimization, without compromising image information. In this work, we performed direct diagnostic X-ray spectra measurements with a portable device, based on a CdTe solid-state detector. The portable device is able to directly measure X-ray spectra at high photon fluence rates, as typical of clinical radiography. We investigated on the spectral performances of the system in the mammographic energy range (up to ∼40 keV). Good system response to monoener…
Sodium vapor cell laser guide star experiments for continuous wave model validation
2016
Recent numerical simulations and experiments on sodium Laser Guide Star (LGS) have shown that a continuous wave (CW) laser with circular polarization and re-pumping should maximize the fluorescent photon return flux to the wavefront sensor for adaptive optics applications. The orientation and strength of the geomagnetic field in the sodium layer also play an important role affecting the LGS return ux. Field measurements of the LGS return flux show agreement with the CW LGS model, however, fluctuations in the sodium column abundance and geomagnetic field intensity, as well as atmospheric turbulence, induce experimental uncertainties. We describe a laboratory experiment to measure the photon …
High-rate x-ray spectroscopy in mammography with a CdTe detector: A digital pulse processing approach
2010
Purpose:Direct measurement of mammographic x-ray spectra under clinical conditions is a difficult task due to the high fluence rate of the x-ray beams as well as the limits in the development of high resolution detection systems in a high counting rate environment. In this work we present a detection system, based on a CdTe detector and an innovative digital pulse processing (DPP) system, for high-rate x-ray spectroscopy in mammography. Methods: The DPP system performs a digital pile-up inspection and a digital pulse height analysis of the detector signals, digitized through a 14-bit, 100 MHz digitizer, for x-ray spectroscopy even at high photon counting rates. We investigated on the respon…
A lumped model for a seismic source
1993
A lumped mechanical model is proposed and solved. This model is dynamically equivalent, in the mean field approximation, to a faulted lithosphere. The transition from the continuous system (modelled according to W. H. Prescott and A. Nur) to the lumped one, has been made by preserving all the relevant features exhibited by the continuous system. In particular the coupling between different components of the stress and strain tensors is suitably taken into account. The dynamics of the lumped system depends on six control parameters fixed by the physical properties of the continuous system. Three of the control parameters are dimensionless and describe: the seismic wave quality factor of the…
Heat Conduction Problem for Double-Layered Ball
2014
Heat conduction models for double layered spherical sample are developed. Parabolic (classic, based on Fourier’s Law) and hyperbolic (based on Modified Fourier’s Law) heat conduction equations are used to describe processes in the sample during Intensive Quenching. Solution and numerical results are obtained for 1D model using Conservative Averaging method and transforming the original problem for a sphere to a new problem for a slab, with non classic boundary condition. Models include boundary conditions of third kind and non-linear BC case. Numerical results are presented for several relaxation time and initial heat flux values.