bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of antiretroviral immunotherapy trials with potentially non‐normal and incomplete longitudinal data
Authors: Mogg Robin , Mehrotra Devan V.
Published: April 2006

For many HIV‐infected patients, use of antiretroviral therapy (ART) results in a sustained suppression of plasma viral load to undetectable levels. However, due to lack of antigenic stimulation, this may also result in a gradual loss of cell‐mediated immune (CMI) responses that help control HIV infection. In concept, augmenting ART with periodic administrations of an HIV vaccine that boosts CMI responses could enhance control of viral replication. Researchers are designing ‘antiretroviral immunotherapy’ (ARI) trials to test this hypothesis. In a typical ARI trial, HIV‐infected patients with sustained viral suppression will receive inoculations of an experimental HIV vaccine or a placebo, and subsequently stop taking their antiretroviral drugs. The goal is to assess whether plasma viral loads during the ART interruption phase are generally lower in the vaccine group. Assessment of a vaccine effect will be challenging if some subjects resume ART or drop out before the end of the treatment interruption phase. To tackle this ‘missing’ data problem and potential non‐normality of the viral loads in ARI trials, we propose a two‐step approach: multiple imputation of the missing values followed by use of the Wei–Lachin method with Wilcoxon scores. We use a numerical example and extensive simulations to illustrate the robustness and power advantages of our proposed method compared with other methods for incomplete longitudinal data, including REML, weighted GEE, last observation carried forward, and ‘worst‐rank’ methods. Our proposed method is general enough for the robust analysis of longitudinal data in other therapeutic areas as well. Copyright © 2006 John Wiley & Sons, Ltd.
Endoscopic Lateral Approach Thyroid Lobectomy: Safe Evolution from Endoscopic Parathyroidectomy
Authors: Sebag F. , Palazzo F.F. , Harding J. , Sierra M. , Ippolito G. , Henry J.F.
Published: April 2006

Introduction

Endoscopic thyroid surgery has been shown to be feasible. Most minimal access procedures have been performed via a midline approach. Based on our experience of more than 500 endoscopic parathyroidectomies via a lateral approach we have used the same method for thyroid lobectomy.

Methods

We present our experience of endoscopic thyroid lobectomy via a lateral approach (ETLA) and review of the results over a 1‐year period (2004). Inclusion criteria for ETLA were (1) solitary nodule with atypical/suspicious fine–needle biopsy (FNB) or solitary toxic nodule; (2) lesions with a diameter of <3 cm. Patients with a history of previous neck surgery or radiation exposure were excluded. All patients underwent postoperative vocal cord checks and plasma calcium evaluation.

Results

A total of 742 thyroid procedures were performed during 2004. Among them, 38 patients (5.1%) underwent ETLA. Indications for surgery were suspicious FNB results (36 patients) and a toxic nodule (2 patients). Mean nodule size was 19.2 mm. Mean ± SD operating time was 102 ± 27 minutes. All recurrent laryngeal nerves were identified (including one that was nonrecurrent). Of the 38 patients, the superior parathyroid gland was identified in 36 and the inferior parathyroid gland in 33. There were two conversions due to difficulty with the dissection. Two operations were converted because malignancy was diagnosed on frozen section examination. Two patients underwent a delayed completion thyroidectomy when definitive histology necessitated it. There were no permanent operative complications, and all patients were discharged on the first postoperative day.

Conclusions

ETLA offers excellent intraoperative visualization of the vital structures and is a safe alternative to conventional thyroid lobectomy in selected cases.
Efficient Sample Logistics: From the Chemist to the Assay Plate and beyond
Authors: Moore Kevin W. , Chandler Glenda , Whalley Pat , Gannon David , Simpson Peter B.
Published: April 2006

A seamless workflow from the medicinal chemist to the screening collections and then to project team assays for new chemical entities has been achieved, by using 1.4-ml 2D bar-coded tubes, an automated tube store system, and a database built in-house. A process of sample collecting, logging, shipping, and sample reformatting has been established with a ComPOUND/ ComMOTION automated tube store system at the heart of the process.
Integrating a Raman Microscope into the Workflow of a High-Throughput Crystallization Laboratory
Authors: Lowry Steve , Dalrymple Dave , Song Anne , Rosso Victor , Pommier Carolyn , Venit John
Published: April 2006

Optimizing the choice of polymorphs of an active pharmaceutical ingredient (API) has become a significant step in the drug development process. High-throughput combinatorial techniques have been developed to reduce the time required to identify and select the best form of an API. A very important part of the high-throughput crystallization (HTC) workflow is reliable integration of information produced by various analytical instruments and easy access to the information by multiple scientists. Raman spectroscopy has become one of the key analytic techniques used to differentiate between the polymorphs and salts of the API. A Raman microscope has been integrated into an HTC workflow analyzing samples in a 96-well microtiter plate. The control software on the Raman instrument has been modified to open a text file prepared by the HTC software suite to initiate semiautomated analysis of the samples in a specified well plate. All of the data acquisition and spectral analysis is performed by the Raman instrument including various chemometric techniques for classifying and clustering the samples based on their Raman spectra. The final analytical results and spectra are then formatted and saved for easy entry into the central database (SQL LIMS). An HTC software suite has been developed in-house for the HTC laboratory, which includes routines for display and manipulation of the combined information.
The Free Fibular Flap: A Useful Flap for Reconstruction Following Composite Hand Injuries
Authors: MOMENI A. , STARK G. B.
Published: April 2006

The free fibular flap has been used extensively in facial and extremity long bone reconstruction but has not been presented as a tool for reconstruction following composite hand injuries, in particular for reconstruction of the ulnar border of the hand. We present a case of the use of this flap for reconstruction of such a complex composite hand injury.
PROPORTIONALITY AND VARIABLE INTENSITY OF REVIEW
Authors: Rivers Julian
Published: April 2006

ARTICLES 29 and 30 of the Universal Declaration of Human Rights contain a series of limitations to human rights. Article 29(2) states:

In the exercise of his rights and freedoms, everyone shall be subject only to such limitations as are determined by law solely for the purpose of securing due recognition and respect for the rights and freedoms of others and of meeting the just requirements of morality, public order and the general welfare in a democratic society.
Spirited Away: The Death of Little Eva and the Farewell Performances of “Katie King”
Authors: BENNETT BRIDGET
Published: April 2006

Depictions of deathbed scenes are commonplace within mid-nineteenth-century United States literary culture, particularly sentimental fiction. They serve a variety of ideological and aesthetic functions and have rightly received a good deal of critical attention. One aspect of their significance and broad impact that has not yet been included within revisionist assessments of the aesthetic and political strategies of sentimentalism provides the primary focus here. The stylized representational modes that characterize the dying of many characters in literary texts, magazine illustrations, paintings and other cultural productions were appropriated by nineteenth-century spiritualists to perform farewells between spirits and the living within the many seances that proliferated on both sides of the Atlantic from the late 1840s onward. The conventional structure of such partings, predicated on the imminent death of at least one of the participants, focused on an exemplary death in which tearful goodbyes and final words were significant features. Yet when spiritualists appropriated the formulae of such scenes it was within a set of practices that explicitly denied the fact of death at all. Since for spiritualists death was a chimera, the adoption of the symbolism of the deathbed scene as a model for how to facilitate different kinds of departure – not always those that took place between the soon to be dead and those they leave behind – took the rhetoric and practices of dying and transformed them into a new form of performance.
Flow in a channel with pulsating walls
Authors: Secomb T. W.
Published: April 2006

In this paper calculations are made of the two-dimensional flow field of an incompressible viscous fluid in a long parallel-sided channel whose walls pulsate in a prescribed way. The study covers all values of the unsteadiness parameter α and the steady-streaming Reynolds number. The wall motion is, in general, assumed to be of small amplitude and sinusoidal. Particular attention is given to the steady component of the flow at second order in the amplitude parameter ε. The results for the corresponding problem in axisymmetric geometry are given in an appendix.

Next the following problem is considered: the calculation of the wall motion which will result, in response to prescribed unsteady pressures imposed at the ends of the channel and outside its walls, if the walls are assumed to respond elastically to variations in transmural pressure. It is found that the system has a natural frequency of oscillation, and that resonance will occur if this frequency is close to a multiple of the frequency of the external pressure fluctuations. Finally the preceding work is applied in a discussion of blood flow in the coronary arteries of large mammals.
Time-dependent scaling relations and a cascade model of turbulence
Authors: Bell Thomas L. , Nelkin Mark
Published: April 2006

We study the time-dependent solutions of a nonlinear cascade model for homogeneous isotropic turbulence first introduced by Novikov & Desnyansky. The dynamical variables of the model are the turbulent kinetic energies in discrete wave-number shells of thickness one octave. The model equations contain a parameter C whose size governs the amount of energy cascaded to small wavenumbers relative to the amount cascaded to large wavenumbers. We show that the equations permit scale-similar evolution of the energy spectrum. For 0 ≤ C ≤ 1 and no external force, the freely evolving energy spectrum displays the Kolmogorov k power law, and the total energy decreases in time as a power t−w, where the exponent w depends on the value of C. Grid-turbulence experiments seem to favour a value of C in the range 0·3-0·6. In the presence of an external stirring force acting near a wavenumber k0, the model predicts, in addition to the Kolmogorov k spectrum for k > k0, a scale-similar flow of energy to wavenumbers k < k0. This backward energy flow falls off as a power law in time, and establishes a stationary energy spectrum for k < k0 which is a power law in k less steep than k. We discuss the similarity of the behaviour of the model for C > 1 to the behaviour of turbulent fluid for a spatial dimensionality near 2. The model is shown to approach the Kovasznay and the Leith diffusion approximation equations in the limit in which the thickness of the wavenumber shells approaches zero. However, the cascade model with finite shell thicknesses appears to behave in a more physically reasonable way than the limiting differential equations.
The force on a small sphere in slow viscous flow
Authors: Drew Donald A.
Published: April 2006

The force on a small sphere translating relative to a slow viscous flow is found to O(Re½) for two different fluid flows far from the sphere, namely pure rotation and pure shear. For pure rotation, the O(Re½) correction to the Stokes drag consists of an increase in the drag. For pure shear, the O(Re½) force contains a component perpendicular to the Stokes drag force.
Acoustic emulsification. Part 1. The instability of the oil-water interface to form the initial droplets
Authors: Li M. K. , Fogler H. S.
Published: April 2006

A technique has been developed to study the phenomenon of ultrasonic emulsification in which oil is dispersed as a fine suspension into water at 20 kHz. It was found that the emulsification takes place in two stages. In the first stage, oil droplets of the order of 70 μm are formed from the instability of interfacial waves. In the second stage these large droplets are successively broken into small droplets by cavitation until a stable droplet size is reached. In this paper, the criterion for the instability of the interfacial waves is developed from a linearized stability analysis of the planar oil-water interface exposed to acoustic excitation. The characteristic droplet diameter produced by the instability is related to the induced capillary wavelength at the interface.

The amplitude of the ultrasonic transducer and the theoretical amplitude of vibration necessary for the instability of the interfacial waves were found to be in agreement. In addition, the sizes of the large droplets present in the suspension systems at short irradiation times agree closely with the predicted droplet diameters.
Acoustic emulsification. Part 2. Breakup of the large primary oil droplets in a water medium
Authors: Li M. K. , Fogler H. S.
Published: April 2006

A theoretical model is presented for the liquid-liquid emulsification phenomenon based on the deformation and breakup of an oil droplet exposed to a cavitation shock wave generated by an acoustic field. The model predicts a relationship between the Ohnesorge number and the critical Weber number ratio for long acoustic irradiation times. At short irradiation times, the mean particle size and variance decrease with increasing time of acoustic irradiation. The results show remarkable agreement when compared with results obtained from the studies on liquid droplets exposed to shock impact from a gas stream. The mechanism for acoustic emulsification is that large oil droplets originally formed from the instability oil-water interface are disintegrated into smaller ones by the cavitation until a critical size, characteristic of the particular oil-water system, is reached.
An experimental study of the decay of temperature fluctuations in grid-generated turbulence
Authors: Warhaft Z. , Lumley J. L.
Published: April 2006

Previous measurements of the decay rate of the fluctuation intensity of passive scalars in grid-generated turbulence show large variation. New results presented here show that the decay rate of passive temperature fluctuations produced by heating the grid is a function of the initial temperature fluctuation intensity. Although a full reason for this is wanting, spectra of the temperature fluctuations show that, by varying the heat applied to the grid, the wavenumber of the maximum in the temperature spectrum changes, indicating that the geometry of the thermal fluctuations is being altered in some way. In these experiments the one-dimensional temperature spectrum shows an anomalous $-\frac{5}{3}$ slope. In order to eliminate the dependence of the decay rate of the temperature fluctuations on their intensity, we describe a new way of generating temperature fluctuations by means of placing a heated parallel array of fine wires (a mandoline) downstream from the unheated grid. Results of this experiment show that the decay rate of passive thermal fluctuations is uniquely determined by the wave-number of the initial temperature fluctuations. In this type of flow there appears to be no equilibrium value for the thermal fluctuation decay rate and hence for the mechanical/thermal time-scale ratio since the thermal fluctuation decay rate does not change within the tunnel length, which is the equivalent of nearly one turbulence decay time.
Natural convection in an infinite porous medium with a concentrated heat source
Authors: Bejan Adrian
Published: April 2006

The phenomenon of buoyancy-induced convection in an infinite porous medium with a concentrated heat source is studied analytically. The transient and steady-state temperature distribution and flow pattern around the source are determined using a perturbation analysis in the Rayleigh number based on the heat generation rate at the source. The first-order transient solution derived in the paper is valid for Rayleigh numbers less than 10. The transient flow pattern consists of an expanding vortex ring situated in the horizontal plane containing the source. The steady-state solution, valid for Rayleigh numbers of the order of 20 or less, reveals an upward flow pattern which becomes very intense near the source. The upward flow extends throughout the medium. Both solutions show that as the Rayleigh number increases the region situated above the source is effectively heated by natural convection in addition to direct heat conduction from the source.
Self-formed straight rivers with equilibrium banks and mobile bed. Part 1. The sand-silt river
Authors: Parker Gary
Published: April 2006

Rivers and canals with perimeters composed of non-cohesive sand and silt have self-formed active beds and banks. They thus provide a most interesting fluid flow problem, for which one must determine the container as well as the flow. If bed load alone occurs across the perimeter of a wide channel, gravity will pull particles down the lateral slope of the banks; bank erosion is accomplished and the channel widens. In order to maintain equilibrium, this export of material from the banks must be countered by an import of sediment from the channel centre.

The mechanism postulated for this import is lateral diffusion of suspended sediment, which overloads the flow near the banks and causes deposition. The model is formulated analytically with the aid of a series of approximate but reasonable assumptions. Singular perturbation techniques are used to define the channel geometry and obtain rational regime relations for straight channels. A comparison with data lends credence to the model.

It is hoped that a first step has been made towards a more general treatment, which would include various complicating factors that are important features of natural rivers but are not essential to the maintenance of channel width. Among these factors are meandering, sediment sorting and seepage.
Excitation of instability waves in a two-dimensional shear layer by sound
Authors: Tam Christopher K. W.
Published: April 2006

The excitation of instability waves in a plane compressible shear layer by sound waves is studied. The problem is formulated mathematically as an inhomogeneous boundary-value problem. A general solution for arbitrary incident sound wave is found by first constructing the Green's function of the problem. Numerical values of the coupling constants between incident sound waves and excited instability waves for a range of flow Mach numbers are calculated. The effect of the angle of incidence in the case of a beam of acoustic waves is analysed. It is found that for moderate subsonic Mach numbers a narrow beam aiming at an angle between 50 to 80° to the flow direction is most effective in exciting instability waves.
On the tones and pressure oscillations induced by flow over rectangular cavities
Authors: Tam Christopher K. W. , Block Patricia J. W.
Published: April 2006

Experimental measurements of the frequencies of discrete tones induced by flow over rectangular cavities were carried out over a range of low subsonic Mach numbers to provide a reliable data base for (aircraft wheel well) cavity noise consideration. A mathematical model of the cavity tones and pressure oscillation phenomenon based on the coupling between shear layer instabilities and acoustic feedback is developed to help in understanding the tone generation mechanism. Good agreement is found between discrete tone frequencies predicted by the model and experimental measurements over a wide range of Mach numbers. Evidence of tones generated by the cavity normal mode resonance mechanism at very low subsonic Mach numbers is also presented.
A note on the stability of steady inviscid helical gas flows
Authors: Eckhoff Knut S. , Storesletten Leiv
Published: April 2006

A necessary condition for linear stability of steady inviscid helical gas flows is found by the generalized progressing-wave expansion method. The criterion obtained is compared with the known Richardson number criteria giving sufficient conditions for stability.
Unsteady vortical and entropic distortions of potential flows round arbitrary obstacles
Authors: Goldstein M. E.
Published: April 2006

This paper is concerned with small amplitude vortical and entropic unsteady motions imposed on steady potential flows. Its main purpose is to show that, even in this unsteady compressible and vortical flow, the perturbations in pressure p’ and velocity u can be written as p’ = ρ0D0ϕ/Dt and u = ϕ + u(I) respectively, where D0/Dt is the convective derivative relative to the mean potential flow, u(I) is a known function of the imposed upstream disturbance and ϕ is a solution to the linear inhomogeneous wave equation
\[
\frac{D_0}{Dt}\bigg(\frac{1}{c^2_0}\frac{D_0\phi}{Dt}\bigg)-\frac{1}{\rho_0}\nabla\cdot(\rho_0\nabla\phi)=\frac{1}{\rho_0}\nabla\cdot\rho_0{\bf u}^{(I)}
\]
with a dipole source term ρ0−1 [xdtri ]ρ0u(I) whose strength ρ0u(I) is a known function of the imposed upstream distortion field. (Here c0 and ρ0 denote the speed of sound and density of the background potential flow.) This equation is used to extend Hunt's (1973) generalization of the ‘rapid-distortion’ theory of turbulence developed by Batchelor & Proudman (1954) and Ribner & Tucker (1953). These theories predict changes occurring in weakly turbulent flows that are distorted (by solid obstacles and other external influences) in a time short relative to the Lagrangian integral scale.

The theory is applied to the unsteady supersonic flow around a corner and a closed-form analytical solution is obtained. Detailed calculations are carried out to show how the expansion at the corner affects a turbulent incident stream.
Turbulence memory in self-preserving wakes
Authors: Bevilaqua Paul M. , Lykoudis Paul S.
Published: April 2006

The persistence of the large vortices formed at the origin of wakes and mixing layers constitutes a kind of memory of initial conditions by the turbulence. In order to study the fading of this turbulence memory, and its effect on the rate of approach to the fully developed state, two wakes with different initial conditions have been examined experimentally. The wake of a sphere was compared with the wake of a porous disk which had the same drag, but did not exhibit vortex shedding. Measurements were made of the mean and fluctuating velocities, the anisotropy of the turbulence, and the intermittency. It was found that the wake of the sphere developed self-preserving behaviour more rapidly than the wake of the disk, and that even after both wakes became self-preserving there were differences between them in the structure of the turbulence and the scale of the mean flow. From this it is concluded that the behaviour of self-preserving wakes does not depend on the drag alone, but also on the structure of the dominant eddies. Generalizing these results, it is suggested that reported differences in the value of the entrainment constant of jets, wakes, and mixing layers are due to differences in the structure of the dominant eddies, rather than differences in the type of flow.
Thermoelectric magnetohydrodynamics
Authors: Shercliff J. A.
Published: April 2006

Thermoelectric currents in the presence of magnetic fields can cause pumping or stirring of liquid-metal coolants in nuclear reactors or stirring of molten metal in industrial metallurgy. The interaction between the thermal and magnetohydrodynamic fields is a mutual one owing to alterations in the thermal convection and to the Peltier and Thomson effects (although these are usually small). This paper sets up the equations of magnetohydrodynamics and thermal convection when coupled by thermoelectricity and solves some illustrative problems in which the thermal field is known ab initio. Examples where the effects are due to either continuous or discontinuous variation of material composition are included. Practical magnitudes are discussed for the case of a fusion-reactor blanket, where the effects are potentially important owing to the unusual thermoelectric power of lithium.
On the structure of inertial waves produced by an obstacle in a deep, rotating container
Authors: Stewartson K. , Cheng H. K.
Published: April 2006

The inviscid flow above an obstacle in slow transverse motion inside a rotating vessel is analysed to study the influence of the container depth on the basic steady flow structure. An asymptotic theory is presented for an arbitrarily small Rossby number Ro = U0/2Ωl under a fixed H = hRo/l (where Ω is the angular velocity of the container, U0 the obstacle velocity relative to the vessel, h the depth of the container, and l a body length measured transversely to the rotation axis). The equations when linearized for a thin obstacle or shallow topography take on the form of the inertial-wave equation; their solutions for non-vanishing H are obtained for obstacles of three-dimensional as well as ridge-like two-dimensional shapes. In all cases analysed, the solution possesses a bimodal structure, of which one part is column-like with a vorticity proportional to the body elevation (or ground topography). The other part is confined mainly to a region enclosing the body, extending a distance O(H½) upstream of the obstacle and behind a wedge-shaped caustic front at large distances; its contribution consists of lee waves similar to that discussed by Cheng (1977) for an infinite depth. The field associated with the lee waves is then biased on the downstream side, but there is little indication of any tendency to tilting in the sense of Hide, Ibbetson & Lighthill (1968).
A vortex theory of animal flight. Part 2. The forward flight of birds
Authors: Rayner J. M. V.
Published: April 2006

The vortex wake of a bird in steady forward flight is modelled by a chain of elliptical vortex rings, each generated by a single downstroke. The shape and inclination of each ring are determined by the downstroke geometry, and the size of each ring by the wing circulation; the momentum of the ring must overcome parasitic and profile drags and the bird's weight for the duration of a stroke period. From the equation of motion it is possible to determine exactly the kinematics of the wing-stroke for any flight velocity. This approach agrees more readily with the nature of the wing-stroke than the classical actuator disk and momentum-jet theory; it also dispenses with lift and induced drag coefficients and is not bound by the constraints of steady-state aerodynamics. The induced power is calculated as the mean rate of increase of wake kinetic energy. The remaining components of the flight power (parasite and profile) are calculated by traditional methods; there is some consideration of different representations of body parasite drag. The lift coefficient required for flight is also calculated; for virtually all birds the lift coefficient in slow flight and hovering is too large to be consistent with steady-state aerodynamics.

A bird is concerned largely to reduce its power consumption on all but the shortest flights. The model suggests that there are a number of ways in which power reduction can be achieved. These various strategies are in good agreement with observation.
The role of negative energy waves in some instabilities of parallel flows
Authors: Cairns R. A.
Published: April 2006

Parallel flows with step function velocity and density profiles can support waves which have negative energy, in the sense that exciting them lowers the total energy of the system. A number of instabilities can occur because of the coexistence of positive and negative energy waves, or because of the damping of negative energy waves; some particular examples are discussed to show how appreciation of this role of negative energy waves allows one to predict the existence of instability before doing any detailed analysis, and to gain insight into the instability mechanism.
The motion of a deformable drop in a second-order fluid
Authors: Chan P. C.-H. , Leal L. G.
Published: April 2006

The cross-stream migration of a deformable drop in a unidirectional shear flow of a second-order fluid is considered. Expressions for the particle velocity due to the separate effects of deformation and viscoelastic rheology are obtained. The direction and magnitude of migration are calculated for the particular cases of Poiseuille flow and simple shear flow and compared with experimental data.
Laminar flow of an incompressible fluid past a bluff body: the separation, reattachment, eddy properties and drag
Authors: Smith F. T.
Published: April 2006

The asymptotic theory for the laminar, incompressible, separating and reattaching flow past the bluff body is based on an extension of Kirchhoff's (1869) free-streamline solution. The flow field (only the upper half of which is discussed since we consider a symmetric body and flow) consists of two basic parts. The first is the flow on the body scalel*, which is described to leading order by the Kirchhoff solution with smooth inviscid separation, but with an$O(Re^{-\frac{1}{16}})$modification to explain fully the viscous separation (hereRe([Gt ] 1) is the Reynolds number). The influence of this$O(Re^{-\frac{1}{16}})$modification is determined for the circular cylinder. The second part is the large-scale flow, comprising mainly the eddy and the ultimate wake. The eddy has length scaleO(Rel*), widthO(Re½l*) and is of elliptical shape to keep the eddy pressure almost uniform. The ultimate wake is determined numerically and fixes the eddy length. The (asymptotically small) back pressure from the eddy acts (on the body scale) both in the free stream and in the eddy, and it has a marked effect at moderate Reynolds numbers; combined with the Kirchhoff solution, it predicts the pressure drag on a circular cylinder accurately, to within 10% whenRe= 5 and to within 4% whenRe= 50. Other predictions, for the eddy length and width, the front pressure and the eddy pressure, also show encouraging agreement with experiments and Navier-Stokes solutions at moderate Reynolds numbers (of about 30), both for the circular cylinder and the normal flat plate. Finally, an analysis in the appendix indicates that, in wind-tunnel experiments, the tunnel walls (even if widely spaced) can exert considerable influence on the eddy properties, eventually forcing an upper bound on the eddy width asReincreases instead of theO(l*Re½) growth appropriate to the unbounded flow situation.
Gravity-capillary waves with edge constraints
Authors: Benjamin T. Brooke , Scott John C.
Published: April 2006

This paper presents a theoretical and experimental investigation into a novel class of water-wave motions in narrow open channels. The distinctive condition on these motions is that the lines of contact between the free surface and the sides of the channel are fixed, which condition bears crucially on the hydrodynamic effects of surface tension. Most of the account concerns travelling waves in channels of rectangular cross-section that are exactly brimful, but the relevance of this prototype to other, more usual situations is explained with reference to the phenomenon of contact-angle hysteresis.

In § 2 a linearized theory is developed which poses an eigenvalue problem of unusual kind. Unlike the familiar and much simpler problem corresponding to mobile lines of contact at which the free surface remains horizontal, the new problem has no explicit solution and the edge conditions are not automatically compatible with the kinematic conditions at the solid boundaries. Treatment by functional analytic methods is necessary to verify that solutions exist having physically appropriate properties, but this approach gives a final bonus in securing comparatively easy estimates for some of these properties. A variational characterization of the eigenvalues is used to settle questions of existence and the ordering of possible wave modes, and finally to establish approximate formulae relating wavelength to frequency.

In § 3 experiments are reported which were performed with clean water filling three channels made of Perspex. Over continuous ranges of frequency, delimited so that only the fundamental progressive-wave mode was generated, wavelengths were measured by an electronic technique. The measurements agree well with the theoretical predictions, diverging markedly from behaviour to be expected in the absence of edge constraints.

Appendix A outlines a supplementary theoretical argument proving that the first eigenvalue of the problem treated in § 2 is always simple. Appendix B reviews three generalizations of the theory.
Autorotating flat-plate wings: the effect of the moment of inertia, geometry and Reynolds number
Authors: Iversen J. D.
Published: April 2006

Free-flight and wind-tunnel measurements by previous investigators of the flat-plate autorotation phenomenon have been analysed. The variation of the autorotation characteristics with changes in the Reynolds number and the aspect ratio, thickness ratio and moment of inertia of the flat plate have been correlated. The interpretation of the role of the Reynolds number made in a previous investigation is shown to be incorrect. The tip-speed ratio, for the ranges of the dimensionless parameters investigated, is shown to be a function of only the plate aspect ratio, thickness ratio, and also the moment of inertia if the latter is sufficiently small. The lift and drag coefficients, and therefore the free-flight glide angle, are shown to be functions of the tip-speed ratio, the aspect ratio and the Reynolds numbers based on the chord and plate thickness.
Enhanced sedimentation in settling tanks with inclined walls
Authors: Acrivos Andreas , Herbolzheimer Eric
Published: April 2006

Using the principles of continuum mechanics, a theory is developed for describing quantitatively the sedimentation of small particles in vessels having walls that are inclined to the vertical. The theory assumes that the flow is laminar and that the particle Reynolds number is small, but c0, the concentration in the suspension, and the vessel geometry are left arbitrary. The settling rate S is shown to depend upon two dimensionless groups, in addition to the vessel geometry: a sedimentation Reynolds number R, typically O(1)-O(10); and Λ, the ratio of a sedimentation Grashof number to R, which is typically very large. By means of an asymptotic analysis it is then concluded that, as Λ → ∞ and for a given geometry, S can be predicted from the well-known Ponder-Nakamura-Kuroda formula which was obtained using only kinematic arguments. The present theory also gives an expression for the thickness of the clear-fluid slit that forms underneath the downward-facing segment of the vessel walls, as well as for the velocity profile both in this slit and in the adjoining suspension.

The sedimentation rate and thickness of the clear-fluid slit were also measured in a vessel consisting of two parallel plates under the following set of conditions: c0 ≤ 0·1, R ∼ O(1), O(10)5 ≤ Λ ≤ O(107) and 0° ≤ α ≤ 50°, where α is the angle of inclination. Excellent agreement was obtained with the theoretical predictions. This suggests that the deviations from the Ponder-Nakamura-Kuroda formula reported in the literature are probably due to a flow instability which causes the particles to resuspend and thereby reduces the efficiency of the process.
Rotation of small non-axisymmetric particles in a simple shear flow
Authors: Hinch E. J. , Leal L. G.
Published: April 2006

The equations for the rotation of non-axisymmetric ellipsoids in a simple shear flow at low Reynolds numbers are derived in terms of Euler angles. Numerical solutions of this third-order system of equations show a doubly periodic structure to the rotation, with a change in the general nature of the solutions when a certain planar rotation of the particle becomes unstable. Some analytic progress can be made for nearly spherical ellipsoids and for nearly axisymmetric ellipsoids. The near spheres show the same qualitative behaviour as the general ellipsoids. Quite small deviations from axial symmetry are found to produce large changes in the rotation.
A test field model study of a passive scalar in isotropic turbulence
Authors: Newman Gary R. , Herring Jackson R.
Published: April 2006

This paper applies the test field model developed by Kraichnan to the study of an isotropic, passive scalar contaminant convected by decaying isotropic turbulence. Test field model predictions of scalar and velocity dissipation spectra at large Reynolds and Péclet numbers are shown to be in excellent agreement with atmospheric data, after intrinsic scale constants in the model are adjusted to give valid inertial range coefficients. Theoretical values for the inertial range coefficients are obtained for large and small Prandtl numbers. Simulation results for velocity and scalar energy, dissipation and transfer spectra and second- and third-order velocity, scalar and velocity–scalar correlations at moderate Reynolds and Péclet numbers are shown to agree moderately well with heated grid turbulence data. Simulation results are presented for the normalized decay rates of the scalar and velocity dissipation rates and for the ratio of the velocity to scalar decay time scales; these quantities are employed in second-order modelling. In the self-similar decay mode the simulations yield unity levels of the normalized decay rates and of the ratio of decay time scales over the moderate range of Reynolds and Prandtl numbers investigated. These results are compared with data from heated grid turbulence experiments and are discussed in the light of asymptotic decay of concomitant scalar and velocity fields.
The effect of short regions of high surface curvature on turbulent boundary layers
Authors: Smits A. J. , Young S. T. B. , Bradshaw P.
Published: April 2006

Measurements, including one-point double, triple or quadruple mean products of velocity fluctuations, have been made in low-speed turbulent, boundary layers on flat surfaces downstream of concave or convex bends with turning angles of 20 or 30 degrees, the length of the curved region being at most 6 times the boundary-layer thickness at entry. These short bends approximate to ‘impulses’ of curvature, and the object of the work was to investigate the impulse response of the boundary layer, essentially the decay of structural changes downstream of the bends. The work can be regarded as a sequel, with much more detailed measurements, to the study by So & Mellor (1972, 1973, 1975) who investigated the response to step increases of curvature: turbulent boundary layers being nonlinear systems, responses to several kinds of curvature history are needed to assemble an adequate description of the flow. The most striking feature of the ‘impulse’ response is that the decay of the high turbulent intensity found at exit from the concave bends is not monotonic; the Reynolds stresses in the outer layer collapse to well below the level at entry, and are still falling slowly at the end of the test rig although in principle they must recover eventually. On the convex (stabilized) side the flow recovers, monotonically in the main, from a low level of turbulent intensity at the exit. The pronounced second-order response on the concave side can be explained qualitatively by interaction between the shear stress and the mean shear and is not peculiar to curved flows, but in the present cases the response is complicated by large changes in the dimensionless structure parameters related to double or triple mean products of velocity fluctuations. Strong spanwise variations, due presumably to longitudinal vortices, further complicate the flow in the concave bends, and decay only very slowly downstream.
The response of a turbulent boundary layer to lateral divergence
Authors: Smits A. J. , Eaton J. A. , Bradshaw P.
Published: April 2006

Measurements have been made in the flow over an axisymmetric cylinder-flare body, in which the boundary layer developed in axial flow over a circular cylinder before diverging over a conical flare. The lateral divergence, and the concave curvature in the transition section between the cylinder and the flare, both tend to destabilize the turbulence. Well downstream of the transition section, the changes in turbulence structure are still significant and can be attributed to lateral divergence alone. The results confirm that lateral divergence alters the structural parameters in much the same way as longitudinal curvature, and can be allowed for by similar empirical formulae. The interaction between curvature and divergence effects in the transition section leads to qualitative differences between the behaviour of the present flow, in which the turbulence intensity is increased everywhere, and the results of Smits, Young & Bradshaw (1979) for a two-dimensional flow with the same curvature but no divergence, in which an unexpected collapse of the turbulence occurred downstream of the curved region.
Marginal instability in Taylor–Couette flows at a very high Taylor number
Authors: Barcilon A. , Brindley J. , Lessen M. , Mobbs F. R.
Published: April 2006

We report on a set of turbulent flow experiments of the Taylor type in which the fluid is contained between a rotating inner circular cylinder and a fixed concentric outer cylinder, focusing our attention on very large Taylor number values, i.e.
\[
10^3 \leqslant T/T_c \leqslant 10^5,
\]
where Tc is the critical value of the Taylor number T for onset of Taylor vortices. At such large values of T, the turbulent vortex flow structure is similar to the one observed when T – Tc is small and this structure is apparently insensitive to further increases in T. These flows are characterized by two widely separated length scales: the scale of the gap width which characterizes the Taylor vortex flow and a much smaller scale which is made visible by streaks in the form of a ‘herring-bone’-like pattern visible at the walls. These are conjectured to be Görtler vortices which arise as a result of centrifugal instability in the wall boundary layers. Ideas of marginal instability by which we postulate that both the Taylor and Görtler vortex structures are marginally unstable on their own scale seem to provide good quantitative agreement between predicted and observed Görtler vortex spacings.
The dynamics of the head of a gravity current advancing over a horizontal surface
Authors: Simpson J. E. , Britter R. E.
Published: April 2006

The motion behind the head of a gravity current advancing over a no-slip horizontal surface is a complex three-dimensional flow. There is intense mixing between the current and its surroundings and the foremost part of the head is raised above the surface. Experimental results are obtained from (i) an apparatus in which the head is brought to rest by using an opposing flow and a moving floor and (ii) a modified lock exchange flow. The dimensionless velocity of advance, rate of mixing between the two fluids and the depth of the mixed layer left behind the head and above the following gravity current are determined for an extended range of the dimensionless gravity current depth. The mixing between the two fluids is the result of gravitational and shear instabilities at the gravity current head. A semi-empirical analysis is presented to describe the results. The influence of Reynolds number is discussed and comparison with a documented atmospheric flow is presented.
Unsteady flow in a collapsible tube subjected to external pressure or body forces
Authors: Kamm Roger D. , Shapiro Ascher H.
Published: April 2006

Flows in thin-walled, collapsible tubes are of fundamental importance to various physiologic phenomena and clinical devices.

A one-dimensional, unsteady theory is developed for flows generated either by externally applied pressures or by body forces. Part 1 deals with small-amplitude, linearized flows, part 2 with large amplitude, nonlinear flows. Experimental results for a tube collapsing under external pressure are given in part 3, together with theoretical interpretations and comparative results of numerical simulations.

Several new and unanticipated phenomena are revealed. These are in part associated with the highly nonlinear ‘equation of state’ (transmural pressure versus area) for a partially collapsed tube, and in part with whether the flow speed is sub- or supercritical relative to the speed of area waves. For instance, a flow produced by a spatially uniform external pressure applied to a limited region becomes choked at a flow-limiting throat at which point the fluid speed reaches the local wave speed. This throat forms at the edge of the pressurized region. The critical velocity can be exceeded with the application of certain types of spatially graded external pressures.
On the parabolic equation method for water-wave propagation
Authors: Radder A. C.
Published: April 2006

A parabolic approximation to the reduced wave equation is investigated for the propagation of periodic surface waves in shoaling water. The approximation is derived from splitting the wave field into transmitted and reflected components.

In the case of an area with straight and parallel bottom contour lines, the asymptotic form of the solution for high frequencies is compared with the geometrical optics approximation.

Two numerical solution techniques are applied to the propagation of an incident plane wave over a circular shoal.
On swimming in a visco-elastic liquid
Authors: Chaudhury T. K.
Published: April 2006

The velocity induced by a transversely waving infinite flexible sheet in a viscoelastic liquid is investigated by a method of successive approximation up to second order in the amplitude of oscillation of the sheet. The incompressible second-order fluid model has been used and it is found that the elastic property of the fluid augments self-propulsion (increases the induced velocity) in some range of Reynolds number (based on the phase velocity) and hampers it (reduces the induced velocity) in some other range with higher values of Reynolds number.
The laminar horseshoe vortex
Authors: Baker C. J.
Published: April 2006

The horseshoe vortex formed around the base of a cylinder by a separating laminar boundary layer has been investigated experimentally. Smoke flow visualization shows that both steady and unsteady vortex systems exist. Pressure distributions beneath both types of vortex system have been measured and the variation of the horseshoe vortex position on the plane of symmetry upstream of the cylinder has been determined. Unsteady horseshoe vortex systems are shown to have a complex oscillatory behaviour and the nature of this oscillatory behaviour is described. Using smoke flow visualization techniques some measurements have been made of the velocity distributions within horseshoe vortex systems.
On the elimination of refractive-index variations in turbulent density-stratified liquid flows
Authors: Mcdougall Trevor J.
Published: April 2006

The variations in refractive index in stratified liquid flows have been a major impediment to the use of laser-Doppler anemometry in these situations. This paper describes a method whereby these refractive-index variations can be drastically reduced while retaining the dynamically important density differences. The method uses two solutes to produce the density differences and it is shown that double-diffusive convection (of the salt-finger type) can be avoided by using a suitable pair of solutes. A theoretical model of the lateral wander of a single laser beam propagating through a turbulent medium is developed and this explains the success of the method.