bluuebunny/crossref_metadata_2025 huggingface dataset:
Combining protein identification and quantification: C‐terminal isotope‐coded tagging using sulfanilic acid
Authors: Panchaud Alexandre , Guillaume Elisabeth , Affolter Michael , Robert Fabien , Moreillon Philippe , Kussmann Martin
Published: April 2006

Two methods of differential isotopic coding of carboxylic groups have been developed to date. The first approach uses d0‐ or d3‐methanol to convert carboxyl groups into the corresponding methyl esters. The second relies on the incorporation of two 18O atoms into the C‐terminal carboxylic group during tryptic digestion of proteins in H218O. However, both methods have limitations such as chromatographic separation of 1H and 2H derivatives or overlap of isotopic distributions of light and heavy forms due to small mass shifts. Here we present a new tagging approach based on the specific incorporation of sulfanilic acid into carboxylic groups. The reagent was synthesized in a heavy form (13C phenyl ring), showing no chromatographic shift and an optimal isotopic separation with a 6 Da mass shift. Moreover, sulfanilic acid allows for simplified fragmentation in matrix‐assisted laser desorption/ionization (MALDI) due the charge fixation of the sulfonate group at the C‐terminus of the peptide. The derivatization is simple, specific and minimizes the number of sample treatment steps that can strongly alter the sample composition. The quantification is reproducible within an order of magnitude and can be analyzed either by electrospray ionization (ESI) or MALDI. Finally, the method is able to specifically identify the C‐terminal peptide of a protein by using GluC as the proteolytic enzyme. Copyright © 2006 John Wiley & Sons, Ltd.
Simultaneous analysis of prostanoids using liquid chromatography/high‐field asymmetric waveform ion mobility spectrometry/tandem mass spectrometry
Authors: Kapron James , Wu Jin , Mauriala Timo , Clark Patsy , Purves Randy W. , Bateman Kevin P.
Published: April 2006

A liquid chromatography/high‐field asymmetric waveform ion mobility spectrometry/tandem mass spectrometry (LC‐FAIMS‐MS/MS) semi‐quantitative method was developed for the simultaneous determination of prostaglandin (PG) E2, PGD2, PGF2α, 6‐keto‐PGF1α, and thromboxane (TX) B2. Diluted samples containing these prostanoids and their tetra‐deuterium‐substituted internal standards were analyzed by LC followed by either selected reaction monitoring (LC‐SRM) or FAIMS and selected reaction monitoring (LC‐FRM). FAIMS reduced background noise, separated the isobaric ions PGE2 and PGD2, and separated dynamically interchanging TXB2 anomers. This is the first report of the separation of interconverting anomers by FAIMS. Generally, the LC‐FRM chromatograms were more selective than the LC‐SRM chromatograms. Its potential was demonstrated by analysis of prostanoids in guinea pig lumbar spinal cord homogenate. Copyright © 2006 John Wiley & Sons, Ltd.
Nonsingular path following control of a unicycle in the presence of parametric modelling uncertainties
Authors: Lapierre L. , Soetanto D. , Pascoal A.
Published: April 2006

A new type of control law is derived to steer the dynamic model of a wheeled robot of unicycle type along a desired path. The methodology adopted for path following control deals explicitly with vehicle dynamics and plant parameter uncertainty. Furthermore, it overcomes stringent initial condition constraints that are present in a number of path following control strategies described in the literature. This is done by controlling explicitly the rate of progression of a ‘virtual target’ to be tracked along the path, thus bypassing the problems that arise when the position of the virtual target is simply defined by the projection of the actual vehicle on that path. In the paper, a nonlinear adaptive control law is derived that yields convergence of the (closed‐loop system) path following error trajectories to zero. Controller design relies on Lyapunov theory and backstepping techniques. Simulation results illustrate the performance of the control system proposed. Copyright © 2006 John Wiley & Sons, Ltd.
Tipping point failure and robustness in single development projects
Authors: Taylor Tim , Ford David N.
Published: April 2006

Tipping point feedback structures can push a series of product development projects into fire‐fighting mode in which rework overwhelms progress. Similar dynamics also threaten the performance of individual development projects. The current work extends previous tipping point dynamics research to single projects and demonstrates how a simple, common feedback structure can cause complex tipping point dynamics, trap projects in deteriorating modes of behavior, and cause projects to fail. Basic tipping point dynamics in single projects are described, demonstrated, and analyzed with a model. The concept of applying robustness to project design is preliminarily tested and system robustness to tipping point‐induced failure is quantified for a simple project and analyzed with sensitivity analysis. Impacts of tipping points on project performance and future research opportunities concerning tipping point and robustness in project management are discussed. Copyright © 2006 John Wiley & Sons, Ltd.
Ultrasound‐guided radiofrequency‐driven umbilical cord occlusion: an in‐vitro study
Authors: Morel O. , Tran N. , Marchal F. , Hennequin V. , Foliguet B. , Villemot J. P. , Thiebaugeorges O.
Published: April 2006

Objectives

To assess the ability and safety of radiofrequency (RF) to induce cord thermal lesions using in‐vitro perfused umbilical cords.

Methods

Nineteen human term umbilical cords were cannulated at both ends and perfused continuously with saline serum in a saline serum bath (37 °C). The RF electrode was then inserted into the cord close to the umbilical vein. Different RF power and temperature controls were applied to determine the optimal RF procedure in terms of cord tissue injury and safety in nine experiments. The safety of RF procedures was investigated in ten cords by measuring temperature changes at different sites close to the RF electrode insertion and the impact of RF on cord narrowing was evaluated by continuous monitoring of intraluminal pressure. Subsequent histopathological analysis was carried out in all cases.

Results

The optimal RF procedure reached a temperature of 100 °C in 10 min. RF produced a significant increase in intraluminal pressure (from 54.2 ± 16.4 mmHg at baseline to 118.3 ± 42.7 mmHg after 10 min, P < 0.05). There was no significant increase in temperature next to the site of insertion during the RF procedure. Histopathological analysis confirmed a > 30% decrease in cord and vein diameter. Cord tissue lesions were characterized by damage in the vessel walls and in the surrounding Wharton's jelly.

Conclusion

Our results suggest that RF might be a feasible and safe technique to induce occlusion of umbilical vessels. Further in‐vivo experiments are needed to assess its ability to induce a complete occlusion of the umbilical cord. Copyright © 2006 ISUOG. Published by John Wiley & Sons, Ltd.
A kinase independent function for Tec kinase ITK in regulating antigen receptor induced serum response factor activation
Authors: Hao Shengli , Qi Qian , Hu Jianfang , August Avery
Published: April 2006

The Tec family kinases are critical downstream regulators of antigen receptor signals in lymphocytes. As kinases, they act on critical substrates to regulate signals such as calcium increase leading to activation of transcription factors such as NFAT, NFκB and SRF. We now show here that ITK, a member of the Tec family of tyrosine kinases, has a kinase independent function. Mutants of ITK that lack kinase activity or a kinase domain can rescue cells lacking Tec family kinases for antigen receptor induced SRF activation, but not for NFAT, AP‐1 or NFκB activation. Furthermore, expression of these mutants in WT cells enhanced SRF activation. This kinase independent function required the SH2 domain since a mutant lacking both the kinase and SH2 domains was much less effective at rescuing SRF activation. This kinase‐deleted mutant could partially rescue ERK activation, and interact with multiple tyrosine phosphorylated proteins during antigen receptor signaling, suggesting that ITK uses a scaffolding function that regulates signals leading to specific regulation of SRF activation.
Hot-wire and hot-film anemometry and conditional measurements: A report on Euromech 132
Authors: Comte-Bellot G. , Charnay G. , Sabot J.
Published: April 2006

The European Mechanics Colloquium, Euromech 132, was held at the Ecole Centrale de Lyon from 2 to 4 July 1980. Specific areas of hot-wire or hot-film anemometry were presented and discussed, more especially the effect of the finite time constant of the wire supports, the use of yawed hot wires in supersonic flows, the possible improvement of vorticity meters, and multi-point measurements of wall-shear-stress fluctuations. Other subjects described during the meeting included a new technique for concentration measurements in flames, developments and new uses of digitization and conditional sampling, pattern recognition analysis of fluid flow from multi-point, multi-time velocity measurements, and new turbulence measurements in complex flows and in fluid-flow machinery.

An exhibition of hot-wire and hot-film anemometers and associated equipment was held during the colloquium.
The stability of a periodically heated layer of fluid
Authors: Dowden John
Published: April 2006

The stability of an infinite layer of fluid of uniform thickness at rest with two horizontal boundaries is investigated when the difference between the temperatures at the top and bottom boundaries has a component which is a fluctuating periodic function of time in addition to a constant part. When both boundaries are free small fluctuations have a stabilizing effect on the layer, while large fluctuations tend to make it less stable, consistently with the numerical results of Yih & Li (1972); the effect is attributable entirely to the variation of the temperature gradient with time. An approximate relation between the mean Rayleigh number and the amplitude of the fluctuations is found which separates stable situations from unstable ones. This is compared with the criteria deduced by Homsy (1974) using energy arguments for disturbances of any amplitude.
Turbulence structure of a reattaching mixing layer
Authors: Chandrsuda C. , Bradshaw P.
Published: April 2006

Hot-wire measurements of second- and third-order mean products of velocity fluctuations have been made in the flow behind a backward-facing step with a thin, laminar boundary layer at the top of the step. Measurements extend to a distance of about 12 step heights downstream of the step, and include parts of the recirculating-flow region: approximate limits of validity of hot-wire results are given. The Reynolds number based on step height is about 105, the mixing layer being fully turbulent (fully three-dimensional eddies) well before reattachment, and fairly close to self-preservation in contrast to the results of some previous workers. Rapid changes in turbulence quantities occur in the reattachment region: Reynolds shear stress and triple products decrease spectacularly, mainly because of the confinement of the large eddies by the solid surface. The terms in the turbulent energy and shear stress balances also change rapidly but are still far from the self-preserving boundary-layer state even at the end of the measurement region.
Stokes flow past a sphere coated with a thin fluid film
Authors: Johnson Robert Edward
Published: April 2006

The present study examines the steady, axisymmetric Stokes flow past a sphere coated with a thin, immiscible fluid layer. Inertial effects are neglected for both the outer fluid and the fluid film, and surface tension forces are assumed large compared with the viscous forces which deform the fluid film. Furthermore, the present analysis assumes that the mechanism driving the fluid circulation within the film is not too large. From force equilibrium on the film we find that a steady fluid film can only partially cover the sphere, i.e. the film must be held to the sphere by surface tension forces at the contact line. The extent of the sphere covered by the film is specified, in terms of the solid–fluid contact angle, by the condition of global force equilibrium on the fluid film.

Using a perturbation scheme based on the thinness of the fluid layer the solution to the flow field is obtained analytically, except for the fluid-film profile (i.e. the fluid–fluid interface) which requires numerical calculations. One of the principal results is an expression for the drag force on the fluid-coated particle. In particular, we find that the drag on a sphere is reduced by the presence of a fluid coating when the ratio of the film fluid viscosity to the surrounding fluid viscosity is less than ¼. Detailed numerical computations are conducted for a few typical cases. The calculations show that a film of prescribed areal extent, i.e. specified contact angle, is only possible when the magnitude of the driving force on the film is below some maximum value. A simple experiment was also performed, and photographs, which qualitatively illustrate the fundamental fluid-film configurations predicted by the theory, are presented.
The amplitude equation near the convective threshold: application to time-dependent heating experiments
Authors: Ahlers Guenter , Cross M. C. , Hohenberg P. C. , Safran S.
Published: April 2006

High-resolution measurements have been performed of the convective heat current as a function of time when a Rayleigh-Bénard cell is swept through its threshold with a specified time-dependent heat input. The results are interpreted in terms of the amplitude equation which exactly describes the slow variations in space and time of hydrodynamic quantities near the threshold. A phenomenological forcing field is added to this equation, and its form and magnitude are fitted to the onset time of the convective heat current. A deterministic model in which the field is an adjustable constant yields a good fit to the data for both a step and a linear ramp in the heat input. An alternative stochastic model, in which the field is a Gaussian variable with zero mean and a white-noise spectrum, is adequate for the ramp experiments, but cannot fit the step data for any value of the mean-square field. The systematics of the field and onset time versus ramp rate are studied in both the deterministic and stochastic models, and attempts are made to interpret the field in terms of physical mechanisms. When the data for long times are analysed in terms of the amplitude equation, it is found that the state first excited at onset is not the roll pattern which is stable in steady state. Instead, the system goes first to an intermediate state, which we tentatively identify as a hexagonal configuration. The decay of this state is governed by a further adjustable field in the amplitude equation.
Linear growth rates for the Rayleigh-Bénard instability in cylindrical geometry
Authors: Shaumeyer J. N. , Behringer R. P. , Baierlein Ralph
Published: April 2006

We report theoretical growth rates for the Rayleigh–Bénard instability when the fluid layer is contained by non-slip walls in a cylindrical geometry with diameter D and height L. Our results are for the growth rates of the first two axisymmetric modes as functions of the Prandtl number P and the aspect ratio γ≡D/2L. We have considered the two extreme cases of ideally insulating and ideally conducting side walls, and found that the growth rate is relatively insensitive to the choice of the thermal boundary conditions on the side walls. Our results are useful in understanding recent experimental measurements of the convective time-scale.
A numerical study of the deformation and burst of a viscous drop in general shear flows
Authors: Rallison J. M.
Published: April 2006

The time-dependent deformation and burst of a viscous drop in an arbitrary shear flow at zero Reynolds number is studied. The viscosities of the drop and the suspending fluid are assumed to be equal. A numerical scheme to track the (non-axisymmetric) drop shape in time is presented, and used to investigate the deformation induced by two-dimensional shear and orthogonal rheometer flows. Steady deformations, critical flow rates and burst modes are determined, and compared with asymptotic (small and large) deformation theories, and with experiment.
Stability of modulated finite-gap cylindrical Couette flow: linear theory
Authors: Carmi S. , Tustaniwskyj J. I.
Published: April 2006

The linear stability of an extensively modulated cylindrical Couette flow is investigated in the finite-gap range. A closed form analytic solution is obtained for the basic unsteady flow after modulation is introduced through the boundary conditions. The general linear perturbation equations for three-dimensional disturbances are then derived and subsequently solved using the Galerkin method with the stability analysed by the Floquet theory. Modulation is found to destabilize the flow in most cases and results compare very favourably with the ones obtained experimentally. Stabilization is possible only for some cases of outer cylinder modulation.
The propagation of capillary-gravity waves on a clean water surface
Authors: Scott John C.
Published: April 2006

Measurements are reported on the wavelength of small-amplitude water waves in a parallel-sided channel, covering the frequency range 2 to 10 Hz. Clean-surface techniques were employed in the experiments, and the results show good agreement with the predictions of linearized hydrodynamic theory.
Correlated unsteady and steady laminar trailing-edge flows
Authors: Brown S. N. , Cheng H. K.
Published: April 2006

The incompressible laminar flow in the neighbourhood of the trailing edge of an aerofoil undergoing sinusoidal oscillations of small amplitude in a uniform stream is described in the limit as the Reynolds number R tends to infinity. It is shown that if the frequency parameter is of any order less than R¼ the viscous correction to the Kutta condition and hence to the lift and moment may be determined from the results for the steady case. Justification of this correlation requires discussion of the flow in an additional region not encountered in previous studies.
Convection in an imposed magnetic field. Part 2. The dynamical regime
Authors: Weiss N. O.
Published: April 2006

Nonlinear, two-dimensional magnetoconvection has been investigated numerically for a fixed Rayleigh number of 104, with the ratio ζ of the magnetic to the thermal diffusivity in the range 0·4 ≥ ζ ≥ 0·05. As the Chandrasekhar number Q is decreased, convection first sets in as overstable oscillations, which are succeeded by steady convection with dynamically active flux sheets and, eventually, with kinematically concentrated fields. In the dynamical regime spatially asymmetrical convection, with most of the flux on one side of the cell, is preferred. As Q increases, these asymmetrical solutions become time-dependent, with oscillations about the steady state which develop into large-scale oscillations with reversals of the flow. Although linear theory predicts that narrow cells should be most unstable, the nonlinear results show that steady convection occurs most easily in cells that are roughly twice as wide as they are deep.
Enhanced sedimentation in narrow tilted channels
Authors: Herbolzheimer Eric , Acrivos Andreas
Published: April 2006

The analysis of Acrivos & Herbolzheimer (1979) is extended to describe the sedimentation of dilute suspensions in tilted two-dimensional channels in which the spacing between the plates is small compared with their length. The theory assumes that the flow is laminar and that the suspension consists of monodisperse spherical beads having small particle Reynolds number. Expressions for the flow fields in the clearfluid region and in the suspension, as well as for the location of the interface separating these two regions, are obtained asymptotically in the limit of Λ [Gt ] 1 with $R\Lambda^{-\frac{1}{3}}\ll 1$, where R and A are as defined in the previous work. The present analysis differs from that given earlier in that the aspect ratio, i.e. the ratio of the height of the suspension to the channel width, is now taken to be O(A1/3) rather than O(1) as was the case before. Under these conditions, the solution of the time-dependent equations leads to the surprising prediction that the clear-fluid layer which forms beneath the downward-facing plate attains a steady shape only along the lower portion of the channel while, in contrast, its thickness increases with time for locations along the channel that are above some critical point. Because of this transient behaviour, the well-known Ponder-Nakamura-Kuroda (PNK) formula overestimates the rate at which the top of the suspension region falls with time; however, the PNK results for the volumetric settling rate still hold under the conditions considered in this paper. It is shown that this discontinuity in the interface shape can be suppressed in continuous settling systems but only if the feed and withdrawal locations are chosen properly.

Batch sedimentation experiments were conducted in a channel with parallel flat walls under the following sets of conditions: H0/b ≈ 90, 5° ≤ θ ≤ 45°, 0·01 ≤ c0 ≤ 0·025, 1·7 × 107 < Λ < 3·5 × 107, and 1·8 < R < 2·1, where θ is the angle of inclination of the vessel from the vertical, and c0 is the initial volume fraction of solids in the suspension. The experimental observations were found to be in excellent agreement with the theoretical predictions.
Spatial stability of the non-parallel Bickley jet
Authors: Garg Vijay K.
Published: April 2006

The spatial stability of the plane, two-dimensional jet flow to infinitesimal disturbances is investigated by taking into account the effects of transverse velocity component and the streamwise variations of the basic flow and of the disturbance amplitude, wave-number and spatial growth rate. This renders the growth rate dependent on the flow variable as well as on the transverse and streamwise co-ordinates. Growth rates for the energy density of the disturbance and the associated neutral curves are provided as a function of the streamwise co-ordinate. Variation of growth rate of the disturbance stream function and streamwise component of velocity with the transverse co-ordinate is also given for different disturbance frequencies and streamwise locations. Results are compared with those for the parallel-flow stability analysis, and also with those for an analysis that accounts for only some of the non-parallel effects. It is found that the critical Reynolds number based on the growth of energy density of the disturbance depends on the streamwise co-ordinate and lies within the range (around 20) found experimentally, while the parallel-flow theory yields a rather low value of 4·0.
Boundary-layer solutions of single-mode convection equations
Authors: Riahi N.
Published: April 2006

Nonlinear thermal convection between two stress-free horizontal boundaries is studied using the modal equations for cellular convection. Assuming a large Rayleigh number R the boundary-layer method is used for different ranges of the Prandtl number σ. The heat flux F is determined for the values of the horizontal wavenumber a which maximizes F. For a large Prandtl number, σ [Gt ] R⅙(log R)−1, inertial terms are insignificant, a is either of order one (for $\sigma \geqslant R^{\frac{2}{3}}$) or proportional to $R^{\frac{1}{3}}\sigma^{-\frac{1}{2}}$ (for $\sigma \ll R^{\frac{2}{3}}$) and F is proportional to $R^{\frac{1}{3}}$. For a moderate Prandtl number,
\[
(R^{-1}\log R)^{\frac{1}{9}} \ll \sigma \ll R^{\frac{1}{6}}(\log R)^{-1},
\]
inertial terms first become significant in an inertial layer adjacent to the viscous buoyancy-dominated interior, and a and F are proportional to R¼ and
\[
R^{\frac{3}{10}}\sigma^{\frac{1}{5}} (\log\sigma R^{\frac{1}{4}})^{\frac{1}{10}},
\]
respectively. For a small Prandtl number, $R^{-1} \ll \sigma \ll (R^{-1} \log R)^{\frac{1}{9}}$, inertial terms are significant both in the interior and the boundary layers, and a and F are proportional to ($R \sigma)^{\frac{9}{32}} (\log R\sigma)^{-\frac{1}{32}}$ and ($R \sigma)^{\frac{5}{16}} (\log R \sigma)^{\frac{3}{16}}$, respectively.
The structure of organized vortices in a free shear layer
Authors: Pierrehumbert R. T. , Widnall S. E.
Published: April 2006

A new family of solutions to the steady Euler equations corresponding to spatially periodic states of a free shear layer is reported. This family bifurcates from a parallel shear layer of finite thickness and uniform vorticity, and extends continuously to a shear layer consisting of a row of concentrated pointlike vortices. The energetic properties of the family are considered, and it is concluded that a vortex in a row of uniform vortices produced by periodic roll-up of a vortex sheet must have a major axis of length approximately 50% or more of the distance between vortex centres; it is also concluded that vortex amalgamation events tend to reduce vortex size relative to spacing. The geometric and energetic properties of the solutions confirm the mathematical basis of the tearing mechanism of shear-layer growth first proposed in an approximate theory of Moore & Saffman (1975).
The use of dual heat injection to infer scalar covariance decay in grid turbulence
Authors: Warhaft Z.
Published: April 2006

Thermal fluctuations introduced into decaying grid turbulence at two different downstream locations are shown to be initially correlated and this correlation decays with distance from the grid. The fluctuations are introduced by placing twomandolines(Warhaft & Lumley 1978) at different distances downstream from the grid. The sum of the thermal variances produced by eachmandolineoperating separately,$\overline{\theta^2_1}+\overline{\theta^2_2}$, is significantly less than the total variance produced by bothmandolinesoperating simultaneously,$\overline{(\theta_1+\theta_2)^2} = \overline{\theta^2_1} + \overline{\theta^2_2} + \overline{2\theta_1\theta_2} $, i.e. the deficit is due to the covariance term$\overline{2\overline{\theta_1\theta_2}}$. This covariance is responsible for a cross-correlation,$\rho = \overline{\theta_1\theta_2}/(\overline{\theta_1^2}\overline{\theta^2_2})^{\frac{1}{2}}$, as great as 0·6. The decay of$\overline{\theta_1\theta_2} $and ρ is studied for various initial input thermal scale sizes and for various input locations. It is shown that the covariance follows a power-law decay, the exponent varying from - 5·5 if the thermal fluctuations are introduced close to the grid where the turbulence dissipation rate is large and the flow is inhomogeneous to - 4 if they are introduced further downstream (x/M≥ 10, wherexis the distance from the grid andMis the grid mesh length) in the region where the approximately isotropic turbulence is beginning to develop. The decay rate of$\overline{\theta_1\theta_2} $and ρ was insensitive to the intensity of the thermal fluctuations. In all these experiments the cross-correlation between velocity and temperature fluctuations was very small (∼ − 0·05) and temperature was a passive additive. The results, which appear to be the first quantitative measurements of the rate of destruction of scalar covariance and hence of the mixing rate between two scalars, are shown to provide good confirmation of recent predictions of the decay of ρ by the second-order closure techniques of Lumley (1978a, b).
Experiments in nearly homogeneous turbulent shear flow with a uniform mean temperature gradient. Part 2. The fine structure
Authors: Tavoularis Stavros , Corrsin Stanley
Published: April 2006

Previous measurements in nearly homogeneous sheared turbulence with a uniform mean temperature gradient are here supplemented with data on the fine structure of the velocity and temperature fluctuation fields. The statistics of signal derivatives and of band-passed signals show that neither field is locally isotropic in the spectral range covered, possibly because of the insufficiently large turbulent Reynolds and Péclet numbers. Observed skewnesses of both velocity and temperature derivatives are explained qualitatively with the use of a kind of ‘mixing-length’ model. The flatness factors of the derivatives and of band-passed, high-frequency signals indicate appreciable departures from normality, consistent with the spatially ‘spotty’ fine structure. The temperature flatnesses are a bit larger than those of the streamwise velocity. The homogeneous shear flow data are compatible with measurements in turbulent boundary layers at comparable RΛ and PΛθ.
The continuous spectrum of the Orr-Sommerfeld equation. Part 2. Eigenfunction expansions
Authors: Salwen Harold , Grosch Chester E.
Published: April 2006

The expansion of an arbitrary two-dimensional solution of the linearized stream-function equation in terms of the discrete and continuum eigenfunctions of the Orr-Sommerfeld equation is discussed for flows in the half-space, y ε [0, ∞). A recent result of Salwen is used to derive a biorthogonality relation between the solution of the linearized equation for the stream function and the solutions of the adjoint problem.

For the case of temporal stability, the orthogonality relation obtained is equivalent to that of Schensted for bounded flows. This relationship is used to carry out the formal solution of the initial-value problem for temporal stability. It is found that the vorticity of the disturbance at t = 0 is the proper initial condition for the temporal stability problem. Finally, it is shown that the set consisting of the discrete eigen-modes and continuum eigenfunctions is complete.

For the spatial stability problem, it is shown that the continuous spectrum of the Orr-Sommerfeld equation contains four branches. The biorthogonality relation is used to derive the formal solution to the boundary-value problem of spatial stability. It is shown that the boundary-value problem of spatial stability requires the stream function and its first three partial derivatives with respect to x to be specified at x = 0 for all t. To be applicable to practical problems, this solution will require modification to eliminate disturbances originating at x = ∞ and travelling upstream to x = 0.

For the special case of a constant base flow, the method is used to calculate the evolution in time of a particular initial disturbance.
Quadrupoles in potential flow: two model problems
Authors: Blackburn H. W.
Published: April 2006

The Ffowcs Williams-Hawkings formulation of the sources of the acoustic analogy is examined by reference to two compressible inviscid flows whose density and velocity fields are known exactly. The purpose of this exercise is to generate some feel for the importance of the various source terms in determining the sound of moving surfaces with shocks, and to help quantify the errors involved in approximating those sources. Practical applications of the theory involve flows that cannot be known exactly and the errors of approximation cannot be checked directly. Progress must start with simple cases, and these model problems represent a first move. The flows considered are the one-dimensional flow caused by a plane boundary impulsively accelerated into a fluid, and the two-dimensional flow due to a wedge moving supersonically and supporting a plane attached shock.

For each of these flows, a system of analogous acoustic sources is developed, the fields of which, when superposed, produce a density field (an acoustic field) identical with that of the original flow. The acoustic fields generated by the component source terms are calculated and compared. This suggests that the volume quadrupoles of potential flow play only a minor role as sound generators. When properly viewed the field is generated entirely on the bounding surfaces of the flow. A general argument shows that volume quadrupoles in steady rectilinear motion only influence the sound field through propagation effects.
Boundary conditions at a liquid/air interface in lubrication flows
Authors: Ruschak K. J.
Published: April 2006

A difficulty in applying the lubrication approximation to flows where a liquid/air interface forms lies in supplying boundary conditions at the point of formation of the interface that are consistent with the lubrication approximation. The method of matched asymptotic expansions is applied to the flow between partially submerged, counter-rotating rollers, a representative problem from this class, and the lubrication approximation is found to generate the first term of an outer expansion of the problem solution. The first term of an inner expansion describes the two-dimensional flow in the vicinity of the interface, and approximate results are found by the finite-element method. Matching between the inner and outer solutions determines boundary conditions on the pressure and the pressure gradient at the point of formation of the interface which allow the solution to the outer, lubrication flow to be completed.
Measurement of the Reynolds stresses and the mean-flow field in a three-dimensional pressure-driven boundary layer
Authors: Müller Udo R.
Published: April 2006

An experimental study of a steady, incompressible, three-dimensional turbulent boundary layer approaching separation is reported. The flow field external to the boundary layer was deflected laterally by turning vanes so that streamwise flow deceleration occurred simultaneous with cross-flow acceleration. At 21 stations profiles of the mean-velocity components and of the six Reynolds stresses were measured with single- and X-hot-wire probes, which were rotatable around their longitudinal axes. The calibration of the hot wires with respect to magnitude and direction of the velocity vector as well as the method of evaluating the Reynolds stresses from the measured data are described in a separate paper (Müller 1982, hereinafter referred to as II). At each measuring station the wall shear stress was inferred from a Preston-tube measurement as well as from a Clauser chart. With the measured profiles of the mean velocities and of the Reynolds stresses several assumptions used for turbulence modelling were checked for their validity in this flow. For example, eddy viscosities for both tangential directions and the corresponding mixing lengths as well as the ratio of resultant turbulent shear stress to turbulent kinetic energy were derived from the data.
Creeping flow in two-dimensional networks
Authors: Koplik Joel
Published: April 2006

We discuss creeping incompressible fluid flow in two-dimensional networks consisting of regular lattice arrays of variable-sized channels and junctions. The intended application is to low-Reynolds-number flow in models of porous media. The flow problem is reduced to an analogue linear-network problem and is solved by numerical matrix inversion. It is found that ‘effective-medium theory’ provides an excellent approximation to flow in such networks. Various qualitative features of such flows are discussed, and an elegant general form for the absolute permeability is derived. The latter, and the effective-medium approximation, are equally applicable to three-dimensional networks.
Concentration fluctuations and fluxes in plumes from point sources in a turbulent boundary layer
Authors: Fackrell J. E. , Robins A. G.
Published: April 2006

Measurements have been made of concentration fluctuations and turbulent fluxes for two passive plumes from an elevated and a ground-level source in a turbulent boundary layer. For the concentration fluctuations, results are presented for the variance, the intermittency, peak values of concentration, probability-density functions and spectra. The balance of terms in the variance transport equation is examined, as is the overall level of fluctuations along the plume. It is shown that most of the production of fluctuations occurs very near the source. Then, the level of fluctuation decays, roughly in accordance with a balance between advection and dissipation. For the turbulent fluxes of concentration, results are presented for the vertical and lateral fluxes, with the associated behaviour of the vertical and lateral eddy diffusivities. The balance of terms in the transport equations for the fluxes is examined. The essential differences between vertical diffusion from ground-level and elevated sources and between near-field and far-field behaviour are shown to be due to the relative importance of the advection and diffusion terms in these equations.
Spatial and temporal characteristics of modulated waves in the circular Couette system
Authors: Gorman M. , Swinney Harry L.
Published: April 2006

We have used flow-visualization and spectral techniques to study the spatial and temporal properties of the flow that precedes the onset of weak turbulence in a fluid contained between concentric cylinders with the inner cylinder rotating (the circular Couette system). The first three flow regimes encountered as the Reynolds number is increased from zero are well-known – Couette flow, Taylor-vortex flow, and wavyvortex flow. The present study concerns the doubly periodic regime that follows the (singly periodic) wavy-vortex-flow regime. Wavy-vortex flow is characterized by a single frequency f1, which is the frequency of travelling azimuthal waves passing a point of observation in the laboratory. The doubly periodic regime was discovered in studies of power spectra several years ago, but the fluid motion corresponding to the second frequency f2 was not identified. We have found that f2 corresponds to a modulation of the azimuthal waves; the modulation can be observed visually as a periodic flattening of the wavy-vortex outflow boundaries. Moreover, in addition to the previously observed doubly periodic flow state, we have discovered 11 more doubly periodic flow states. Each state can be labelled with two integers m and k, which are simply related to physical characteristics of the flow: m is the number of azimuthal waves, and k is related to the phase angle between the modulation of successive azimuthal waves by Δϕ = 2πk/m. This expression for the phase angle was first conjectured from the flow-visualization measurements and then tested to an accuracy of 0·01π in spectral measurements. Recently Rand (1981) has used dynamical-systems concepts and symmetry considerations to derive predictions about the space–time symmetry of doubly periodic flows in circularly symmetric systems. He predicted that only flows with certain space–time symmetries should be allowed. The observed flow states are in agreement with this theory.
Stability of a vortex street of finite vortices
Authors: Saffman P. G. , Schatzman J. C.
Published: April 2006

The stability of the finite-area Kármán ‘vortex street’ to two-dimensional disturbances is determined. It is shown that for vortices of finite size there exists a finite range of spacing ratio κ for which the array is stable to infinitesimal disturbances. As the vortex size approaches zero, the range narrows to zero width about the classical von Kármán value of 0·281.
Analysis of small-aspect-ratio lifting surfaces in ground effect
Authors: Newman J. N.
Published: April 2006

A lifting surface of small aspect ratio is analysed for motion with constant forward velocity, parallel and in close proximity to a rigid plane surface of infinite extent. The gap flow beneath the lifting surface is represented by a simple nonlinear solution in the cross-flow plane, and appropriate conditions are imposed at leading and trailing edges. The transition between these two conditions depends on the kinematics of the gap flow as well as the planform geometry. For steady-state motion of a delta wing with sufficiently large angle of attack, the transition point is upstream of the tail. For oscillatory heaving motion of a delta wing the transition point is cyclic if the heave velocity is sufficiently large. Illustrative computations of the lift force are presented.
Effects of internal heat transfer on the structure of self-similar blast waves
Authors: Ghoniem A. F. , Kamel M. M. , Berger S. A. , Oppenheim A. K.
Published: April 2006

Profiles of gasdynamic parameters in self-similar blast waves, taking into account the influence of conduction and radiation fluxes due to high temperatures attained at the centre, are determined. In the blast-wave equations these fluxes are expressed in terms of the Fourier law for heat conduction and a differential expression for radiative transport in a semi-grey gas model. Various boundary conditions are considered in order to account for different ways in which blast waves are initiated and driven. Similarity requirements are implemented in the solution by compatible functional forms of gas conductivity and absorptivity, as well as the opacity of the shock front. This formulation yields a two-point boundary-value problem, which is then transformed into an initial-value problem in order to facilitate the integration. As a particular example, a detailed solution for the constant-energy case is obtained, covering the whole range of relative heat-transfer effects expressed in terms of radiative to gasdynamic energy fluxes, from the adiabatic flow field, on one extreme, to the isothermal, on the other.
Nonlinear Marangoni convection in bounded layers. Part 1. Circular cylindrical containers
Authors: Rosenblat S. , Davis S. H. , Homsy G. M.
Published: April 2006

We consider liquid in a circular cylinder that undergoes nonlinear Marangoni insta- bility. The upper free surface of the liquid is taken to have large-enough surface tension that surface deflections are neglected. The side walls are adiabatic and impenetrable, and for mathematical simplicity the liquid is allowed to slip on the side walls. The linearized stability theory for heating from below gives the critical Marangoni number Mc as a function of cylinder dimensions, surface-cooling condition and Rayleigh number. The steady nonlinear convective states near Mc are calculated using an asymptotic theory, and the stability of these states is examined. At simple eigenvalues Mc the finite-amplitude states are determined. We find th at the Prandtl number of the liquid influences the stability of axisymmetric states, distinguishing upflow at the centre from downflow. Near those aspect ratios corresponding to double eigenvalues Me, where two convective states of linear theory are equally likely, the nonlinear theory predicts sequences of transitions from one steady convective state to another as the Marangoni number is increased. These transitions are determined and discussed in detail. Time-periodic convection is possible in certain cases.
Nonlinear Marangoni convection in bounded layers. Part 2. Rectangular cylindrical containers
Authors: Rosenblat S. , Homsy G. M. , Davis S. H.
Published: April 2006

Attention is confined to roll-cell development and roll-cell interaction appropriate to one horizontal dimension larger than either the other horizontal dimension or the depth. At simple eigenvalues Mc the roll-cell amplitude and transport fields can be obtained. Near those aspect ratios corresponding to double eigenvalues Mc, where two roll-cell states of linear theory areequallylikely, thenonlinear theory predicts sequences of transitions from one steady convective state to another as the Marangoni number is increased. Direct comparisons are made of the results here with those of the previous paper for Marangoni convection in circular cylinders. Time-periodic convection is possible in certain cases.
Kinematic-wave theory of sedimentation beneath inclined walls
Authors: Schneider W.
Published: April 2006

The two-phase flow in settling vessels with walls that are inclined to the vertical is investigated. By neglecting inertial effects and the viscosity of the suspension i t is shown that the particle concentration remains constant on kinematic-wave fronts. The wave fronts are horizontal and propagate in a quasi-one-dimensional manner, but are imbedded in a two-dimensional or three-dimensional basic flow which, in turn, depends on the waves via the boundary conditions. Concentration discontinuities (interfaces) are described by kinematic-shock theory. The kinematic shocks are shown to be horizontal, with the possible exception of discontinuities that separate the suspension from the sediment.

At downward-facing inclined walls conservation of mass enforces the existence of a boundary-layer flow with relatively large velocity. As G/R2→∞ and G/R4→ 0, where G and R are respectively a sedimentation Grashof number and a sedimentation Reynolds number, the entrainment of suspended particles into the boundary-layer flow of clear liquid is negligibly small. This provides an appropriate boundary condi- tion for the basic flow of the suspension. Thus, in the double limit considered, a kine- matic theory suffices to determine the convective flow of the suspension due to the presence of inclined walls.

As an example batch sedimentation in vessels with inclined plane or conical walls is investigated. The settling process is terminated after a time that can be considerably smaller than the time required in a vertical vessel under the same conditions.Depending on the initial particle concentration, there are centred kinematic waves that are linked to a continuous increase of the particle concentration in the suspension. In an appendix, the flow in the boundary layer at a downward facing, inclined wall is investigated. With G/R2→∞ and G/R4→ 0, the boundary layer consists of an inviscid particle-free main part, a viscous sublayer at the wall, and a free shear sublayer at the liquid/particle interface.
The mixing of passive helium and temperature fluctuations in grid turbulence
Authors: Sirivat A. , Warhaft Z.
Published: April 2006

By producing thermal fluctuations with a mandohe and helium fluctuations with chimneys attached to the grid bars, the mixing of temperature and helium fluctuations as well as the decay of temperature and helium variance and their flux is investigated in decaying grid-generated turbulence. The helium, temperature and velocity fluctua- tions were measured with a modified ‘Way-Libby’ interference probe (Way & Libby 1970, 1971). It is shown that, as for temperature variance, the helium-variance decay rate is a function the ratio of the helium length scale to the velocity length scale. It is also shown that the decay of the cross-correlation between temperature and helium fluctuations is slow if both scalars are introduced close to the grid, but rapid if each scalar is introduced at a different distance from the grid, and hence at different scales. The results corroborate those of the inference method of Warhaft (1981), which is extended here to examine other cases. A particularly unexpected finding is that under certain circumstances the two-scalar cross-correlation may actually increase with distance from the grid, although the scalar covariance decreases. The return to isotropy of helium flux and temperature flux is also investigated and is shown to be slow if the scalar flux is produced near the grid bars, but faster if the flux is produced further downstream. For all the measurements helium and temperature were passive additives.
Rising bubbles
Authors: Miksis Michael J. , Vanden-Broeck Jean-Marc , Keller Joseph B.
Published: April 2006

The shape of a rising bubble, or of a falling drop, in an incompressible viscous fluid is computed numerically, omitting the condition on the tangential traction at the bubble or drop surface. When the bubble is sufficiently distorted, its top is found to be spherical and its bottom is found to be rather flat. Then the radius of its upper surface is in fair agreement with the formula of Davis & Taylor (1950). This distortion occurs when the effect of gravity is large while that of surface tension is small. When the effect of surface tension is large, the bubble is nearly a sphere.

The shape is found, together with the flow of the surrounding fluid, by assuming that both are steady and axially symmetric, with the Reynolds number being large. The flow is taken to be a potential flow. The boundary condition on the normal component of normal stress, including the viscous stress, is satisfied, but not that on the tangential component. The problem is converted into an integro-differential set of equations, reduced to a set of algebraic equations by a difference method, and solved by Newton's method together with parameter variation.