461 research outputs found
Sign-symmetry of temperature structure functions
New scalar structure functions with different sign-symmetry properties are
defined. These structure functions possess different scaling exponents even
when their order is the same. Their scaling properties are investigated for
second and third orders, using data from high-Reynolds-number atmospheric
boundary layer. It is only when structure functions with disparate
sign-symmetry properties are compared can the extended self-similarity detect
two different scaling ranges that may exist, as in the example of convective
turbulence.Comment: 18 pages, 5 figures, accepted for publication in Physical Review
Resection and resolution of bone marrow lesions associated with an improvement of pain after total knee replacement: a novel case study using a 3-Tesla metal artefact reduction MRI sequence
We present our case report using a novel metal artefact reduction magnetic resonance imaging (MRI) sequence to observe resolution of subchondral bone marrow lesions (BMLs), which are strongly associated with pain, in a patient after total knee replacement surgery. Large BMLs were seen preoperatively on the 3-Tesla MRI scans in a patient with severe end stage OA awaiting total knee replacement surgery. Twelve months after surgery, using a novel metal artefact reduction MRI sequence, we were able to visualize the bone-prosthesis interface and found complete resection and resolution of these BMLs. This is the first reported study in the UK to use this metal artefact reduction MRI sequence at 3-Tesla showing that resection and resolution of BMLs in this patient were associated with an improvement of pain and function after total knee replacement surgery. In this case it was associated with a clinically significant improvement of pain and function after surgery. Failure to eradicate these lesions may be a cause of persistent postoperative pain that is seen in up to 20% of patients following TKR surgery
Dynamical equations for high-order structure functions, and a comparison of a mean field theory with experiments in three-dimensional turbulence
Two recent publications [V. Yakhot, Phys. Rev. E {\bf 63}, 026307, (2001) and
R.J. Hill, J. Fluid Mech. {\bf 434}, 379, (2001)] derive, through two different
approaches that have the Navier-Stokes equations as the common starting point,
a set of steady-state dynamic equations for structure functions of arbitrary
order in hydrodynamic turbulence. These equations are not closed. Yakhot
proposed a "mean field theory" to close the equations for locally isotropic
turbulence, and obtained scaling exponents of structure functions and an
expression for the tails of the probability density function of transverse
velocity increments. At high Reynolds numbers, we present some relevant
experimental data on pressure and dissipation terms that are needed to provide
closure, as well as on aspects predicted by the theory. Comparison between the
theory and the data shows varying levels of agreement, and reveals gaps
inherent to the implementation of the theory.Comment: 16 pages, 23 figure
Closure of two dimensional turbulence: the role of pressure gradients
Inverse energy cascade regime of two dimensional turbulence is investigated
by means of high resolution numerical simulations. Numerical computations of
conditional averages of transverse pressure gradient increments are found to be
compatible with a recently proposed self-consistent Gaussian model. An
analogous low order closure model for the longitudinal pressure gradient is
proposed and its validity is numerically examined. In this case numerical
evidence for the presence of higher order terms in the closure is found. The
fundamental role of conditional statistics between longitudinal and transverse
components is highlighted.Comment: 4 pages, 2 figures, in press on PR
The Scaling Structure of the Velocity Statistics in Atmospheric Boundary Layer
The statistical objects characterizing turbulence in real turbulent flows
differ from those of the ideal homogeneous isotropic model.They
containcontributions from various 2d and 3d aspects, and from the superposition
ofinhomogeneous and anisotropic contributions. We employ the recently
introduceddecomposition of statistical tensor objects into irreducible
representations of theSO(3) symmetry group (characterized by and
indices), to disentangle someof these contributions, separating the universal
and the asymptotic from the specific aspects of the flow. The different
contributions transform differently under rotations and so form a complete
basis in which to represent the tensor objects under study. The experimental
data arerecorded with hot-wire probes placed at various heights in the
atmospheric surfacelayer. Time series data from single probes and from pairs of
probes are analyzed to compute the amplitudes and exponents of different
contributions to the second order statistical objects characterized by ,
and . The analysis shows the need to make a careful distinction
between long-lived quasi 2d turbulent motions (close to the ground) and
relatively short-lived 3d motions. We demonstrate that the leading scaling
exponents in the three leading sectors () appear to be different
butuniversal, independent of the positions of the probe, and the large
scaleproperties. The measured values of the exponent are , and .
We present theoretical arguments for the values of these exponents usingthe
Clebsch representation of the Euler equations; neglecting anomalous
corrections, the values obtained are 2/3, 1 and 4/3 respectively.Comment: PRE, submitted. RevTex, 38 pages, 8 figures included . Online (HTML)
version of this paper is avaliable at http://lvov.weizmann.ac.il
Anomalous and dimensional scaling in anisotropic turbulence
We present a numerical study of anisotropic statistical fluctuations in
homogeneous turbulent flows. We give an argument to predict the dimensional
scaling exponents, (p+j)/3, for the projections of p-th order structure
function in the j-th sector of the rotational group. We show that measured
exponents are anomalous, showing a clear deviation from the dimensional
prediction. Dimensional scaling is subleading and it is recovered only after a
random reshuffling of all velocity phases, in the stationary ensemble. This
supports the idea that anomalous scaling is the result of a genuine inertial
evolution, independent of large-scale behavior.Comment: 4 pages, 3 figure
Optical pathology of oral tissue: a Raman spectroscopy diagnostic method
Raman and fluorescence spectroscopy methods are being considered as techniques which could be complementary or even alternative to biopsy, and pathology and clinical assays in many medical applications. The present paper discusses the results of Raman spectral studies on oral tissues for optical pathology. It is shown that Raman spectra of oral tissues can be classified into spectra of normal and malignant sets and a model based on such a classification can be used to analyse oral tissue for detection of oral malignancy. Sensitivity and specificity calculated from 90 test spectra are better than 85 and 90 per cent respectively
Inhomogeneous Anisotropic Passive Scalars
We investigate the behaviour of the two-point correlation function in the
context of passive scalars for non homogeneous, non isotropic forcing
ensembles. Exact analytical computations can be carried out in the framework of
the Kraichnan model for each anisotropic sector. It is shown how the
homogeneous solution is recovered at separations smaller than an intrinsic
typical lengthscale induced by inhomogeneities, and how the different Fourier
modes in the centre-of-mass variable recombine themselves to give a ``beating''
(superposition of power laws) described by Bessel functions. The pure power-law
behaviour is restored even if the inhomogeneous excitation takes place at very
small scales.Comment: 14 pages, 5 figure
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