bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spondylolysis, spondylolisthesis, and lumbo‐sacral morphology in a medieval English skeletal population
Authors: Mays S. 
Published: April 2006

AbstractThe prevalence of spondylolysis and spondylolisthesis was studied in an adult skeletal series from a rural English medieval archaeological site. Attempts were made to evaluate the association of three aspects of lumbo‐sacral skeletal morphology (pelvic incidence (a measure of the anterior inclination of the sacral table), lumbar transverse process width, and the presence of lumbo‐sacral spina bifida occulta) with spondylolysis and spondylolisthesis. Results indicated a high prevalence of spondylolysis compared with a modern reference population, but few cases of spondylolisthesis were identified. Analysis of prevalence with respect to age suggests that in the study population, pars interarticularis defects generally formed late in the growth period or early in adult life. The study group showed a high mean pelvic incidence compared with modern Western Europeans, indicating a more steeply inclined sacral table, which may have elevated the risk of developing pars interarticularis defects. However, no statistically valid association could be demonstrated between the presence/absence of spondylolysis and pelvic incidence in the study material. There was no evidence for a link between lumbar transverse process index or lumbo‐sacral spina bifida occulta and spondylolysis/spondylolisthesis. It is concluded that the potential role of lumbo‐sacral morphology, as well as of activity regimes, should be considered when interpreting spondylolysis in paleopathological studies. If the frequency of spondylolysis is to some extent an indicator of past activity regimes, it may reflect lifestyle in younger individuals rather than in mature adults. Further work investigating the link between spondylolysis and lumbo‐sacral morphological variables in premodern populations would be of value. Am J Phys Anthropol, 2006. © 2006 Wiley‐Liss, Inc.
The Oxa‐Pictet—Spengler Cyclization: Synthesis of Isochromans and Related Pyran‐Type Heterocycles
Authors: Larghi Enrique L. , Kaufman Teodoro S. 
Published: April 2006

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Asymptotic stability of the relativistic Maxwellian
Authors: Hsiao Ling , Yu Hongjun 
Published: April 2006

AbstractGlobal classical solutions near the relativistic Maxwellian are constructed for the relativistic Boltzmann equation in both a periodic box and the whole space. For both cases, we are able to get the non‐negativity of the global solution under less restriction than in (Publ. Res. Inst. Math. Sci. 1993; 29:301–347) on the scattering kernel. Copyright © 2006 John Wiley & Sons, Ltd.
Non‐linear stability for convection with quadratic temperature dependent viscosity
Authors: Vaidya Ashwin , Wulandana Rachmadian 
Published: April 2006

AbstractIn this paper, we study the non‐linear stability of convection for a Newtonian fluid heated from below, where the viscosity of the fluid depends upon temperature. We are able to show that for Rayleigh numbers below a certain critical value, Rac, the rest state of the fluid and the steady temperature distribution remains non‐linearly stable, using the calculations of Diaz and Straughan (Continuum Mech. Thermodyn. 2004; 16:347–352). The central contribution of this paper lies in a simpler proof of non‐linear stability, than the ones in the current literature, by use of a suitable maximum principle argument. Copyright © 2006 John Wiley & Sons, Ltd.
Tracking pedestrians using multiple single‐row laser range scanners and its reliability evaluation
Authors: Nakamura Katsuyuki , Zhao Hujing , Shibasaki Ryosuke , Sakamoto Kiyoshi , Ohga Tomowo , Suzukawa Naoki 
Published: April 2006

AbstractIn this paper the authors propose a method for pedestrian tracking using multiple laser range scanners and describe verification experiments in a railway station. The proposed method involves synchronizing multiple laser scanners using a network and tracking pedestrians based on range data for foot cross‐sections. The tracking algorithm consists of the following functions: detection of foot candidates using range data clustering; detection of pedestrian candidates using grouping of foot candidates; detection of movement vectors for pedestrian candidates; extended processing of existing tracings using an extended Kalman filter based on a walking model. The results of using the proposed method in a station concourse in Tokyo Station found that at a maximum 150 people could be tracked at the same time. The tracking precision exceeded 80% during commuter rush hour. Applications to high‐precision crowd observations in wide areas can be expected. © 2006 Wiley Periodicals, Inc. Syst Comp Jpn, 37(7): 1–11, 2006; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/scj.20578
Larval distribution and growth of the rockfish, Sebastes capensis (Sebastidae, Pisces), in the fjords of southern Chile
Authors: Landaeta Mauricio F. , Castro Leonardo R. 
Published: April 2006

Abstract
The distribution and the growth of larval rockfish Sebastes capensis were studied during two oceanographic cruises carried out in a sector of the Chilean fjords (43°30′S–46°S) during spring 2002 (November) and winter 2003 (August). Abundance (up to 600 per 10 m2) of pre- and post-flexion larvae was higher during the austral spring than in winter (20 per 10 m2). Larvae were smaller principally above the halocline in the first 50 m of the water column throughout the channels and fjords; in contrast, post-flexion larvae were more abundant seawards and were totally absent in the freshest waters. Analysis of the otoliths indicated that larvae between 3.3 and 12.2-mm standard length collected during November grew 0.15 mm d−1. Additionally, it showed that older larvae from the outer part of the channels and over the shelf laid down wider otolith increments than larvae found in the interior waters, coinciding with the area of greatest abundance of larger calanoid copepods. Ontogenetic differences in distributions suggest that different habitats are utilized during the early life stages of S. capensis, and that they seem to be shared with several other Sebastes species. However, the mechanisms for transport in different areas vary widely, making the question of the evolutionary forces driving these ontogenetic changes in distribution even more intriguing.
The role of wave-induced pressure fluctuations in the transfer processes across an air–water interface
Authors: Papadimitrakis Yiannis Alex , Hsu En Yun , Street Robert L. 
Published: April 2006

The structure of the pressure and velocity fields in the air above mechanically generated water waves was investigated in order to evaluate their contribution to the transfer of momentum and energy from wind to water waves. The measurements were taken in a transformed Eulerian wave-following frame of reference, in a wind-wave research facility at Stanford University.The organized component of the fluctuating static pressure at the channel roof was found to contain contributions from both the sound field and the reflected water wave. The acoustic contributions were accounted for by appropriately correcting the pressure amplitude and phase (relative to the wave) and its contribution to the momentum and energy exchange. The wave-induced pressure coefficient at the fundamental mode shows in general an exponential decay behaviour with height, but the rate of decay is different from that predicted by potential-flow theory. The wave-induced pressure phase relative to the wave remains fairly constant throughout the boundary layer, except when the ratio of the wave speed to the freestream velocity, c/Uδ0 = 0.78 and 0.68. This phase difference was found to be about 130° during active wave generation, with the pressure lagging the wave. The momentum and energy transfer rates supported by the waves were found to be dominated by the wave-induced pressure, but the transfer of the corresponding total quantities to both waves and currents may or may not be so dominated, depending on the ratio c/Uδ0. The direct contribution of the wave-induced Reynolds stresses to the transfer processes is negligible.
Large-scale flow in turbulent convection: a mathematical model
Authors: Howard L. N. , Krishnamurti R. 
Published: April 2006

A mathematical model of convection, obtained by truncation from the two-dimensional Boussinesq equations, is shown to exhibit a bifurcation from symmetrical cells to tilted non-symmetrical ones. A subsequent bifurcation leads to time-dependent flow with similarly tilted transient plumes and a large-scale Lagrangian mean flow. This change of symmetry is similar to that occurring with the advent of a large-scale flow and transient tilted plumes seen in laboratory experiments on turbulent convection at high Rayleigh number. Though not intended as a description of turbulent convection, the model does bring out in a theoretically tractable context the possibility of the spontaneous change of symmetry suggested by the experiments.Further bifurcations of the model lead to stable chaotic phenomena as well. These are numerically found to occur in association with heteroclinic orbits. Some mathematical results clarifying this association are also presented.
On the existence of localized rotational disturbances which propagate without change of structure in an inviscid fluid
Authors: Moffatt H. K. 
Published: April 2006

A wide class of solutions of the steady Euler equations, representing localized rotational disturbances imbedded in a uniform stream U0 is inferred by considering the process of magnetic relaxation to analogous magnetostatic equilibria. These solutions, which may be regarded as generalizations of vortex rings, are characterized by their streamline topology, distinct topologies giving rise to distinct solutions.Particular attention is paid to the class of axisymmetric solutions described by Stokes stream function ψ(s, z). It is argued that the appropriate topological ‘invariant’ characterizing the flow is the function Vψ representing the volume inside toroidal surfaces ψ = const, in the region of closed streamlines where ψ > 0. This function is described as the ‘signature’ of the flow, and it is shown that in a certain sense, flows with different signatures are topologically distinct. The approach yields a method by which flows of arbitrary signature V(ψ) may in principle be found, and the corresponding vorticity ωφ = sFψ calculated.
The propagation of short surface waves on longer gravity waves
Authors: Longuet-Higgins M. S. 
Published: April 2006

To understand the imaging of the sea surface by radar, it is useful to know the theoretical variations in the wavelength and steepness of short gravity waves propagated over the surface of a train of longer gravity waves of finite amplitude. Such variations may be calculated once the orbital accelerations and surface velocities in the longer waves have been accurately determined – a non-trivial computational task.The results show that the linearized theory used previously for the longer waves is generally inadequate. The fully nonlinear theory used here indicates that for longer waves having a steepness parameter AK = 0.4, for example, the short-wave steepness can be increased at the crests of the longer waves by a factor of order 8, compared with its value at the mean level. (Linear theory gives a factor less than 2.)The calculations so far reported are for free, irrotational gravity waves travelling in the same or directly opposite sense to the longer waves. However, the method of calculation could be extended without essential difficulty so as to include effects of surface tension, energy dissipation due to short-wave breaking, surface wind-drift currents, and to arbitrary angles of wave propagation.
On the reflection of a train of finite-amplitude internal waves from a uniform slope
Authors: Thorpe S. A. , Thorpe S. A. , Haines A. P. 
Published: April 2006

The reflection of a train of two-dimensional finite-amplitude internal waves propagating at an angle β to the horizontal in an inviscid fluid of constant buoyancy frequency and incident on a uniform slope of inclination α is examined, specifically when β > α. Expressions for the stream function and density perturbation are derived to third order by a standard iterative process. Exact solutions of the equations of motion are chosen for the incident and reflected first-order waves. Whilst these individually generate no harmonics, their interaction does force additional components. In addition to the singularity at α = β when the reflected wave propagates in a direction parallel to the slope, singularities occur for values of α and β at which the incident-wave and reflected-wave components are in resonance; strong nonlinearity is found at adjacent values of α and β. When the waves are travelling in a vertical plane normal to the slope, resonance is possible at second order only for α < 8.4° and β < 30°. At third order the incident wave is itself modified by interaction with reflected components. Third-order resonances are only possible for α < 11.8° and, at a given α, the width of the β-domain in which nonlinearities connected to these resonances is important is much less than at second order. The effect of nonlinearity is to reduce the steepness of the incident wave at which the vertical density gradient in the wave field first becomes zero, and to promote local regions of low static stability remote from the slope. The importance of nonlinearity in the boundary reflection of oceanic internal waves is discussed.In an Appendix some results of an experimental study of internal waves are described. The boundary layer on the slope is found to have a three-dimensional structure.
Observations of dispersion of entrained fluid in the self-preserving region of a turbulent jet
Authors: Shlien D. Joseph 
Published: April 2006

Ambient fluid of a submerged water jet was continuously tagged with fluorescent dye at a point outside the turbulent region (at 33 jet nozzle diameters from the jet exit). This made it possible to follow the tagged entrained fluid to 73 jet diameters downstream of the exit, a distance unattainable by other methods. The dispersion of the tagged fluid in a plane containing the jet axis and the tagging source was observed and recorded using photography and simple digital image-processing techniques. Most of the entrainment activity appeared to be the result of engulfment by the large-scale structures over an axial distance of ± 1.7B from the source where B is the half-peak velocity radius. The entrained fluid crossed the jet centreline within a downstream distance of Δx = 1.5B.Downstream of the entrainment region, the spread rate of the tagged entrained fluid was close to that of the turbulent jet fluid. However, the peak mean concentration of the tagged entrained fluid was located near the r/x = 0.1 line closest to the tagging source and shifted very slowly towards the jet centreline. A self-preserving distribution of the mean concentration appears to have been approached after a distance of 6B downstream from the tagging source but further verification is needed owing to experimental uncertainties.A small fraction of the tagged entrained fluid was found on the side of the jet remote from the tagging source. On rare occurrences, tagged entrained fluid was observed at the interface most remote from the source.
On the resonant nature of the breakdown of a laminar boundary layer
Authors: Kachanov Yu. S. 
Published: April 2006

The first part of this paper (§2) briefly reviews the history of the idea of the resonant nature of laminar-boundary-layer breakdown. In the second part a new wave-resonance concept of the breakdown mechanism is proposed. The existing experimental data on the laminar boundary layer (and plane channel flow) breakdown are analysed from the viewpoint of this concept and are compared with the well-known local high-frequency secondary-instability concept. The results testify to the correctness of the proposed wave-resonant concept for the initial stages of breakdown, in particular for the K-regime of transition up to the spike formation and its doubling.Within the framework of the wave-resonance concept, before constructing the corresponding theory, many important features of the disturbance development can be qualitatively explained and understood. Concerning the understanding of the spike appearance, the wave-resonance concept complements the local high-frequency secondary-instability one and represents by itself a new fruitful viewpoint on this phenomenon. The development of the wave-resonance concept and its application to the analysis of numerical and physical experiments, together with the construction on this basis of the corresponding theory, can give an essential impetus towards the better understanding of the breakdown nature.
Experimental and numerical investigation of a forced circular shear layer
Authors: Chomaz J. M. , Rabaud M. , Basdevant C. , Couder Y. 
Published: April 2006

In a previous article we introduced a dissipative circular geometry in which stationary states of the shear flow instability were obtained. We show here that the dynamical behaviour of this flow depends strongly on the aspect ratio of the cell. In large cells, where the number of vortices is large, transitions from a mode with m vortices to a mode with (m−1) vortices occur through localized processes. In contrast to that situation, in small cells, transition takes place after a series of bifurcations which correspond to the successive breaking of all the symmetries of the flow.We show that, provided an adequate forcing term is introduced, a two-dimensional numerical simulation of this flow is sufficient to recover all the dynamical processes which characterize the experimental flow.
The dynamics of towed flexible cylinders Part 2. Negatively buoyant elements
Authors: Dowling A. P. 
Published: April 2006

A ship, towing a heavier-than-water cable with a neutrally buoyant slender cylinder attached to the downstream end of the cable, is considered. The neutrally buoyant element contains a sonar array. Linear changes in the ship's velocity cause perturbations of both the cable and cylinder. The form of transverse vibrations of the neutrally buoyant cylinder was determined in Part 1. The propagation of disturbances along the cable is investigated in this paper. In particular, the effectiveness of the cable at isolating the sonar array from forcing due to unsteady ship motion is examined.The cable and cylinder are found to be stable under constant towing conditions. It is therefore appropriate to investigate their response to forcing. Meanderings in the ship's track produce transverse displacements of both the cable and the cylinder. These transverse oscillations entirely decouple from any in-plane motion. The propagation of disturbances of frequency ω along the cable depends strongly on the value of the non-dimensional frequency ωlC/U, where lC is the cable length and U is the towing speed, and only weakly on the other cable parameters. The cable acts as an effective low-pass filter to transverse oscillations, the amplitude of disturbances with non-dimensional frequency greater than 10 being reduced by at least 90% as they propagate along the cable.Unsteadiness in the ship's speed can result in in-plane deflections of the cable, and vertical oscillations of the cylinder containing the sonar array. In contrast to the transverse oscillations a significant proportion of the in-plane disturbances at the ship travels to the sonar array at all values of the frequency. Low- and high-frequency analytical forms are derived to explain why this occurs. Perturbations in the ship's position are most effectively transformed into vertical oscillations of the array at a frequency of 2.8U/lC. The effect of cable properties on transmission along the cable is investigated. The transmission again depends on the value of the non-dimensional frequency ωlC/U. Parameter changes, which increase the cable critical angle, increase the proportion of the disturbance at the towing point that is transformed into vertical array motion, for a fixed value of ωlC/U. This is explained by reference to the low- and high-frequency analytical solutions.
Experimental and numerical investigation of the three-dimensional transition in plane wakes
Authors: Meiburg E. , Lasheras J. C. 
Published: April 2006

The three-dimensional structure of a moderate-Reynolds-number (≈ 100) plane wake behind a flat plate subjected to periodic spanwise perturbations has been studied both experimentally and numerically. Comparisons between experimental interface visualizations and numerical calculations demonstrate that important features of the development of the three-dimensional evolution can be reproduced by numerical inviscid vortex dynamics.It is shown that the redistribution, reorientation and stretching of vorticity leads to the formation of counter-rotating pairs of streamwise vortices which superimpose onto the spanwise Kármán-like vortices. These streamwise vortices exhibit lambdashaped structures and are located in the braids connecting consecutive Kármán vortices of opposite sign.The interaction of the evolving streamwise structure with the spanwise Kármán vortices results in the formation of closed vortex loops. Depending on the orientation of the initial perturbation, the three-dimensional vorticity field of the wake acquires either a symmetric or a non-symmetric configuration. Under the effect of a periodic vertical perturbation, the wake develops a non-symmetric vorticity mode exhibiting a staggered array of closed vortex loops of alternating sign. In contrast, under the effect of a periodic horizontal perturbation, the wake acquires a symmetric vorticity mode with the closed vortex loops of alternating sign aligned in the flow direction.
Flow in a channel with a moving indentation
Authors: Ralph M. E. , Pedley T. J. 
Published: April 2006

The unsteady flow of a viscous, incompressible fluid in a channel with a moving indentation in one wall has been studied by numerical solution of the Navier-Stokes equations. The solution was obtained in stream-function-vorticity form using finite differences. Leapfrog time-differencing and the Dufort-Frankel substitution were used in the vorticity transport equation, and the Poisson equation for the stream function was solved by multigrid methods. In order to resolve the boundary-condition difficulties arising from the presence of the moving wall, a time-dependent transformation was applied, complicating the equations but ensuring that the computational domain remained a fixed rectangle.Downstream of the moving indentation, the flow in the centre of the channel becomes wavy, and eddies are formed between the wave crests/troughs and the walls. Subsequently, certain of these eddies ‘double’, that is a second vortex centre appears upstream of the first. These observations are qualitatively similar to previous experimental findings (Stephanoff et al. 1983, and Pedley & Stephanoff 1985), and quantitative comparisons are also shown to be favourable. Plots of vorticity contours confirm that the wave generation process is essentially inviscid and reveal the vorticity dynamics of eddy doubling, in which viscous diffusion and advection are important at different stages. The maximum magnitude of wall vorticity is found to be much larger than in quasi-steady flow, with possibly important biomedical implications.