bluuebunny/crossref_metadata_2025 huggingface dataset:
Parametrically excited, standing cross-waves
Authors: Miles John
Published: April 2006

Luke's (1967) variational formulation for surface waves is extended to incorporate the motion of a wavemaker and applied to the cross-wave problem. Whitham's average-Lagrangian method then is invoked to obtain the evolution equations for the slowly varying complex amplitude of the parametrically excited cross-wave that is associated with symmetric excitation of standing waves in a rectangular tank of width π/k, lengthland depthdfor whichkl=O(1) andkd[Gt ] 1. These evolution equations are Hamiltonian and isomorphic to those for parametric excitation of surface waves in a cylinder that is subjected to a vertical oscillation, for which phase-plane trajectories, stability criteria and the effects of damping are known (Miles 1984a). The formulation and results differ from those of Garrett (1970) in consequence of his linearization of the boundary condition at the wavemaker and his neglect of self-interaction of the cross-waves in the free-surface conditions (although Garrett does incorporate self-interaction in his calculation of the equilibrium amplitude of the cross-waves). These differences have only a small effect on the criterion for the stability of plane waves, but the self-interaction is crucial for the determination of the stability of the cross-waves.
Simulation of particle dispersion in an axisymmetric jet
Authors: Chung J. N. , Troutt T. R.
Published: April 2006

Particle dispersion in an axisymmetric jet is analysed numerically by following particle trajectories in a jet flow simulated by discrete vortex rings. Important global and local flow quantities reported in experimental measurements are successfully simulated by this method.

The particle dispersion results demonstrate that the extent of particle dispersion depends strongly on γτ, the ratio of particle aerodynamic response time to the characteristic time of the jet flow. Particles with relatively small γτ values are dispersed at approximately the fluid dispersion rate. Particles with large γτ values are dispersed less than the fluid. Particles at intermediate values of γτ may be dispersed faster than the fluid and actually be flung outside the fluid mixing region of the jet. This result is in agreement with some previous experimental observations. As a consequence of this analysis, it is suggested that there exists a specific range of intermediate γτ at which optimal dispersion of particles in the turbulent mixing layer of a free jet may be achieved.
Lagrangian moments and mass transport in Stokes waves Part 2. Water of finite depth
Authors: Longuet-Higgins M. S.
Published: April 2006

Some simple relations between the Lagrangian moments and cumulants in a steady finite-amplitude gravity wave on deep water are here generalized to water of finite depth. The first three Lagrangian moments are shown to be given in term of the mass-transport velocity U at the free surface, the potential and kinetic energy densities V and T, and the mean-square particle velocity $\overline{u^2_B}$ on the bottom.

A simple method of calculation is described, which exploits certain quadratic relations between the Fourier coefficients in Stokes's series. The ratio U/c and the associated Lagrangian skewness is calculated for periodic waves, as a function of the wave steepness and the mean water depth.

For limiting waves, i.e. those with sharp crests, it is found that the most symmetric orbits, in the Lagrangian sense, occur not in very deep or very shallow water, but at one intermediate value of the ratio of depth to wavelength. When the depth parameter kd equals 1.93 the vertical displacement of a marked particle at the free surface is closely sinusoidal in the time t.
Gravity waves on a rough bottom: experimental evidence of one-dimensional localization
Authors: Belzons Max , Guazzelli Elisabeth , Parodi Olivier
Published: April 2006

We present experimental evidence of the localization of linear gravity waves on a rough (i.e. random) bottom in a one-dimensional channel. The localization phenomenon is observed through very precise measurements in a wave tank. Viscous dissipation and rough-bed finite-size effects are examined. The experimental estimation of the localization lengths are compared with the theoretical predictions of Devillard, Dunlop & Souillard (1988). Finally, the resonant modes due to the disorder are directly observed for the first time.
Two-dimensional bifurcation phenomena in thermal convection in horizontal, concentric annuli containing saturated porous media
Authors: Himasekhar K. , Bau Haim H.
Published: April 2006

A saturated porous medium confined between two horizontal cylinders is considered. As a result of a temperature difference between the cylinders, thermal convection is induced in the medium. The flow structure is investigated in a parameter space (R, Ra) whereRis the radii ratio andRais the Darcy-Rayleigh number. In particular, the cases ofR= 2, 2½, 21/4and 2½are considered. The fluid motion is described by the two-dimensional Darcy-Oberbeck-Boussinesq's (DOB) equations, which we solve using regular perturbation expansion. Terms up toO(Ra60) are calculated to obtain a series presentation for the Nusselt number Nu in the form\[ Nu(Ra^2) = \sum_{s=0}^{30} N_sRa^{2s}. \]This series has a limited range of utility due to singularities of the functionNu(Ra). The singularities lie both on and off the real axis in the complexRaplane. ForR= 2, the nearest singularity lies off the real axis, has no physical significance, and unnecessarily limits the range of utility of the aforementioned series. ForR= 2½, 2¼and 21/8, the singularity nearest to the origin is real and indicates that the functionNu(Ra) is no longer unique beyond the singular point.

Depending on the radii ratio, the loss of uniqueness may occur as a result of either (perfect) bifurcations or the appearance of isolated solutions (imperfect bifurcations). The structure of the multiple solutions is investigated by solving the DOB equations numerically. The nonlinear partial differential equations are converted into a truncated set of ordinary differential equations via projection. The steady-state problem is solved using Newton's technique. At each step the determinant of the Jacobian is evaluated. Bifurcation points are identified with singularities of the Jacobian. Linear stability analysis is used to determine the stability of various solution branches. The results we obtained from solving the DOB equations using perturbation expansion are compared with those we obtained from solving the nonlinear partial differential equations numerically and are found to agree well.
Experimental investigation of double-diffusive groundwater fingers
Authors: Imhoff Paul T. , Green Theodore
Published: April 2006

Using a sand-tank model and the salt-sugar system, double-diffusive fingers formed in a saturated porous medium. In contrast to the quasi-steady fingering typically observed in a viscous fluid, the fingering here was quite unsteady. The fingers’ structure was observed, and measurements of the sugar flux indicate that double-diffusive groundwater fingers can transport solutes at rates as much as two orders of magnitude larger than those associated with molecular diffusion in motionless groundwater. The buoyancy-flux ratio, r = αFT/βFS, increased from r = 0.65 ± 0.02 (at Rρ = 1.02) to r = 0.81 ± 0.06 (at Rρ = 1.50), where Rρ is the density-anomaly ratio. (Using the salt-sugar system in a viscous fluid, r was previously shown to decrease with increasing Rρ.) The buoyancy flux due to sugar varied approximately as R−5.6ρ, which is almost identical with the variation found for salt-sugar fingers in a viscous fluid. The model of Green (1984) was applied to the experiments and predicted buoyancy-flux ratios and finger widths that were in fairly good agreement with the measured values, although the predicted buoyancy fluxes due to sugar were significantly larger than the measured fluxes.
Development of the turbulent near wake of a tapered thick flat plate
Authors: Haji-Haidari A. , Smith C. R.
Published: April 2006

The velocity field and turbulence structure in the near wake of a thick flat plate with a tapered trailing-edge geometry are examined using both hydrogen-bubble flow visualization and hot-film anemometry measurements. Tests were conducted for Re1 = 8.5 × 105 in the region 0 < x+ < 6400 behind the trailing edge. The probe and visualization results indicate a similarity between both (i) velocity and turbulence structure variations wih x+ in the near wake, and (ii) the corresponding changes in similar flow characteristics with y+ within a turbulent boundary layer. In particular, visualization data in the vicinity of the wake centreline reveal the existence of strong streamwise flow structures in the region close (x+ < 270) to the trailing edge. The streamwise orientation of the observed structures diminishes as x+ increases. From hot-film measurements, two separate regions along the wake centreline can be distinguished: (i) a linear growth region which extends over 0 < x+ < 100, wherein the centreline velocity varies linearly with x+; and (ii) a logarithmic growth region for x+ > 270, wherein the centreline velocity varies as log x+. The similarity in behaviour between these regions and the comparable wall region of a turbulent boundary layer suggests the existence of a common functionality. This similarity is demonstrated by a simple linear relationship of the form y+ = Kx+, which is shown to approximately collapse the velocity behaviour both across a turbulent boundary layer and along the wake centreline to a unified set of empirical relationships.
The structure of turbulent shear-induced countercurrent flow
Authors: Tsanis Ioannis K. , Leutheusser Hans J.
Published: April 2006

Countercurrent flow is a generalized plane Couette flow in which a shear-induced drift current is opposed by a pressure-driven return flow such that the resulting mass flux is zero. This type of flow is encountered in both environmental fluid mechanics and tribology. Measurements are described that were undertaken in steady turbulent countercurrent flow, generated in a novel type of apparatus between smooth walls, at Reynolds numbers, expressed in terms of surface velocity and depth of the flow, from 200 to 20000; the critical Reynolds number of laminar to turbulent transition as determined herein is approximately 1750. The laboratory facility is explained, and experimental data are presented on mean velocities, pressure gradient, turbulence intensities, Reynolds stresses, and energy spectra. It is found that the velocity distributions follow the universal law of the wall in the drift current, but that the flow is undeveloped in the return portion of the flow. The non-dimensional longitudinal pressure gradient increases with Reynolds number, and a semi-empirical law of resistance is proposed and experimentally verified. Turbulence intensities in the drift current increase toward the shearing surface but are essentially constant in the opposing pressure-driven flow. The distribution of the Reynolds stress is found to be consistent with previous measurements obtained in this type of flow using different apparatus, but only approximately follows the theoretically linear distribution. Energy spectra in the shear-induced portion of the flow involve higher frequencies closer to the shearing surface than in the return current. There, the spectral energy is essentially the same throughout the flow, reflecting the constancy of turbulent intensity in this region.
The growth of a turbulent patch in a stratified fluid
Authors: Fernando Harindra J. S.
Published: April 2006

The behaviour of a turbulent region generated within a linearly-stratified fluid by an external energy source has been studied experimentally. A monoplanar grid that generated small-amplitude oscillations was used as the energy source. The results show that the mixed layer initially grows rapidly, as in an unstratified fluid, but when its physical vertical size becomes rf ∼ (K1/N)½, at a time tf ≈ 4.0 N−1, where N is the buoyancy frequency and K1 is the ‘action’ of the grid, the buoyancy forces become dominant and drastically reduce further vertical growth of the patch. While the patch size remains at rf, a well-defined density interfacial layer is formed at the entrainment interface. An important feature of the interfacial layer is the presence of internal waves, excited by the mixed-layer turbulence. If the grid oscillations are continuously maintained, the interfacial waves break and cause turbulent mixing, thereby increasing the size of the patch beyond rf at a very slow rate. Theoretical estimates are made for the growth characteristics and are compared with the experimental results.
Laminar flow through slots
Authors: Tulapurkara E. G. , Gowda B. H. Lakshmana , Balachandran N.
Published: April 2006

Laminar flow through slots is investigated using a flow-visualization technique and the numerical solution of the Navier-Stokes equations for steady flow. In the flow situation studied here, the fluid enters an upper channel blocked at the rear end and leaves through a lower channel blocked at the front end. The two channels are interconnected by one, two and three slots. The flow-visualization technique effectively brings out the various features of the flow through slot(s). The ratio of the slot width to the channel height w/h is varied between 0.5 to 4.0 and the Reynolds number Re, based on the velocity at the entry to the channel and the height of the channel, is varied between 300 and 2000. Both w/h and Re influence the flow in general and the extent of the regions of recirculating flow in particular. The Reynolds number at which the vortex shedding begins depends on w/h. Computations are carried out using the computer code 2/E/FIX of Pun & Spalding (1977). The computed flow patterns closely resemble the observed patterns at various Reynolds numbers investigated except around the Reynolds number where the vortex shedding begins.
The axisymmetric rise of a spherical bubble at the exit of an orifice in the presence of a stagnant cap of insoluble surfactants
Authors: Dagan Zeev , Yan Zong-Yi , Shen Huixian
Published: April 2006

The motion of a spherical droplet in unbounded exterior phase in the presence of a stagnant cap of adsorbed insoluble surfactants has been recently presented by Sadhal & Johnson (1983). The present study considers the axisymmetric motion of a gas bubble at the exit of a circular orifice in the presence of a similar stagnant cap.

The solution procedure utilizes the boundary integral representation in order to obtain the drag correction factor for a bubble translating away from the orifice in otherwise quiescent fluid, and for a fixed bubble exposed to Sampson's flow towards the orifice. It is demonstrated that the presence of the confining orifice boundaries substantially increases the drag acting on the bubble, and the solution approaches the exact result of Sadhal and Johnson as the distance between the bubble and the orifice is increased. Furthermore, it is shown that for a fixed amount of surfactants on the bubble surface the cap angle increases with distance from the orifice due to the diminishing hydrodynamic interaction. Hence, the quasi-steady terminal velocity of a bubble rising from an orifice is reduced by the viscous boundary interaction, and by the growing immobile cap size.
Bragg scattering of water waves by a doubly periodic seabed
Authors: Naciri Mamoun , Mei Chiang C.
Published: April 2006

We extend the recent work on Bragg scattering of water waves by one-dimensional parallel bars of sinusoidal profile to two-dimensional, doubly sinusoidal bed waves. The resonance condition governing the phase matching between the incident, scattered and bed waves is now more complicated and a much richer variety of resonant reflection can occur. In particular, for one normally incident wave there can be two reflected waves forming a standing wave in the transverse direction. Solutions for a wide strip of bed waves are discussed for incident water waves satisfying approximately the Bragg resonance condition. Modifications for a two-dimensional array of hemispheroids are also given. Possible application to the design of submerged breakwaters is suggested.
On the changes in phase speed of one train of water waves in the presence of another
Authors: Hogan S. J. , Gruman Idith , Stiassnie M.
Published: April 2006

We present calculations of the change in phase speed of one train of water waves in the presence of another. We use a general method, based on Zakharov's (1968) integral equation. It is shown that the change in phase speed of each wavetrain is directly proportional to the square of the amplitude of the other. This generalizes the work of Longuet-Higgins & Phillips (1962) who considered gravity waves only.

In the important case of gravity-capillary waves, we present the correct form of the Zakharov kernel. This is used to find the expressions for the changes in phase speed. These results are then checked using a perturbation method based on that of Longuet-Higgins & Phillips (1962). Agreement to 6 significant digits has been obtained between the calculations based on these two distinct methods. Full numerical results in the form of polar diagrams over a wide range of wavelengths, away from conditions of triad resonance, are provided.
Bedload transport of fine gravel observed by motion-picture photography
Authors: Drake Thomas G. , Shreve Ronald L. , Dietrich William E. , Whiting Peter J. , Leopold Luna B.
Published: April 2006

Motion pictures taken at Duck Creek, a clear stream 6.5 m wide and 35 cm deep near Pinedale, Wyoming, provide detailed, quantitative information on both the modes of motion of individual bedload particles and the collective motions of large numbers of them. Bed shear stress was approximately 6 Pa (60 dynes cm−2), which was about twice the threshold for movement of the 4 mm median diameter fine gravel bed material; and transport was almost entirely as bedload. The displacements of individual particles occurred mainly by rolling of the majority of the particles and saltation of the smallest ones, and rarely by brief sliding of large, angular ones. Entrainment was principally by rollover of the larger particles and liftoff of the smaller ones, and infrequently by ejection caused by impacts, whereas distrainment was primarily by diminution of fluid forces in the case of rolling particles and by collisions with larger bed particles in the case of saltating ones. The displacement times averaged about 0.2−0.4 s and generally were much shorter than the intervening repose times. The collective motions of the particles were characterized by frequent, brief, localized, random sweep-transport events of very high rates of entrainment and transport, which in the aggregate transported approximately 70% of the total load moved. These events occurred 9% of the time at any particular point of the bed, lasted 1–2 s, affected areas typically 20–50 cm long by 10–20 cm wide, and involved bedload concentrations approximately 10 times greater than background. The distances travelled during displacements averaged about 15 times the particle diameter. Despite the differences in their dominant modes of movement, the 8–16 mm particles typically travelled only about 30% slower during displacement than the 2–4 mm ones, whose speeds averaged 21 cm s−1. Particles starting from the same point not only moved intermittently downstream but also dispersed both longitudinally and transversely, with diffusivities of 4.6 and 0.26 cm2 s−1, respectively. The bedload transport rates measured from the films were consistent with those determined conventionally with a bedload sampler. The 2–4 mm particles were entrained 6 times faster on finer areas of the bed, where 8–16 mm particles covered 6% of the surface area, than on coarser ones, where they covered 12%, even though 2–4 and 4–8 mm particles covered practically the same percentage areas in both cases. The 4–8 and 8–16 mm particles, in contrast, were entrained at the same rates in both cases. To within the statistical uncertainty, the rates of distrainment balanced the rates of entrainment for all three sizes, and were approximately proportional to the corresponding concentrations of bedload.
Dissipative effects on the resonant flow of a stratified fluid over topography
Authors: Smyth N. F.
Published: April 2006

The effect of dissipation on the flow of a stratified fluid over topography is considered in the weakly nonlinear, long-wave limit for the case when the flow is near resonance, i.e. the basic flow speed is close to a linear long-wave speed for one of the long-wave modes. The two types of dissipation considered are the dissipation due to viscosity acting in boundary layers and/or interfaces and the dissipation due to viscosity acting in the fluid as a whole. The effect of changing bottom topography on the flow produced by a force moving at a resonant velocity is also considered. In this case, the resonant condition is that the force velocity is close to a linear long-wave velocity for one of the long-wave modes. It is found that in most cases, these extra effects result in the formation of a steady state, in contrast to the flow without these effects, which remains unsteady for all time. The flow resulting under the action of boundary-layer dissipation is compared with recent experimental results.
Minimum-dissipation transport enhancement by flow destabilization: Reynolds’ analogy revisited
Authors: Karniadakis George E. , Mikic Bora B. , Patera Anthony T.
Published: April 2006

A classical transport enhancement problem is concerned with increasing the heat transfer in a system while minimizing penalties associated with shear stress, pressure drop, and viscous dissipation. It is shown by Reynolds' analogy that viscous dissipation in a wide class of flows scales linearly with the Nusselt number and quadratically with the Reynolds number. It thus follows that transport enhancement optimization is equivalent to a problem in hydrodynamic stability theory; a more unstable flow will achieve the same Nusselt number at a lower Reynolds number, and therefore at a fraction of the dissipative cost. This transport-stability theory is illustrated in a numerical study of supercritical (unsteady) two-dimensional flow in an eddy-promoter channel comprising a plane channel with an infinite periodic array of cylindrical obstructions.

It is shown that the addition of small cylinders to a plane channel results in stability modes that are little changed in form or frequency from plane-channel Tollmien-Schlichting waves. However, eddy-promoter flows are dramatically less stable than their plane-channel counterparts owing to cylinder-induced shear-layer instability (with critical Reynolds numbers on the order of hundreds rather than thousands), and thus these flows yield heat transfer rates commensurate with those of a plane-channel turbulent flow but at much lower Reynolds number. Small-cylinder supercritical eddy-promoter flows are shown to roughly preserve the convective-diffusive Reynolds analogy, and it thus follows from the transport-stability theory that eddy-promoter flows achieve the same heat transfer rates as plane-channel turbulent flows while incurring significantly less dissipation.
Resonant sound caused by flow past two plates in tandem in a duct
Authors: Stoneman S. A. T. , Hourigan K. , Stokes A. N. , Welsh M. C.
Published: April 2006

Two plates placed in tandem in a duct flow shed vortices, which can excite and sustain an acoustic resonance associated with the duct. The sound can in turn ‘feed back’ and ‘lock’ the vortex shedding rate to the sound frequency. The experimental conditions under which loud resonant sound is sustained are described in this paper. The acoustic sources are predicted by combining a vortex model of the flow field with a finite-element solution of the sound field, and then using Howe's theory of aerodynamic sound to calculate the energy exchange between the flow and the sound field. Only in certain regions near the plates is substantial net energy exchange possible; the direction of energy transfer depends on the spacing of the plates. The region around the trailing edge of the upstream plate is found to be always a net acoustic source during resonance, while the region around the downstream plate is a net source or sink depending on the phase of the acoustic cycle at which vortices arrive there, which in turn depends on plate spacing and flow velocity. The net source region around the downstream plate is suppressed over a wide range of plate spacings by splitting this plate at midspan and rejoining it so that one half is offset in the flow direction by the distance a vortex travels in half a sound cycle.
An experimental study of the wake of gas slugs rising in liquids
Authors: Campos J. B. L. M. , Carvalho J. R. F. Guedes De
Published: April 2006

A photographic study of the wakes of slugs rising in tubes of 19 mm and 52 mm internal diameter is presented. The dependence of the flow pattern in the wake upon the Reynolds number of the rising slug, R, is established for different slug lengths. Values of R covered in this study are in the range 25 to 1.3 × 104. For low values of R the flow pattern in the wake is laminar and axisymmetric and values of wake length and wake volume could be determined from the photographs: these values were correlated with the other variables in the system by means of dimensional analysis.
The energetics of the interaction between short small-amplitude internal waves and inertial waves
Authors: Broutman D. , Grimshaw R.
Published: April 2006

The interaction between a wave packet of small-amplitude short internal waves, and a finite-amplitude inertial wave field is described to second order in the short-wave amplitude. The discussion is based on the principle of wave action conservation and the equations for the wave-induced Lagrangian mean flow. It is demonstrated that as the short internal waves propagate through the inertial wave field they generate a wave-induced train of trailing inertial waves. The contribution of this wave-induced mean flow to the total energy balance is described. The results obtained here complement the finding of Broutman & Young (1986) that the short internal waves undergo a net change in energy after their encounter with the inertial wave field.
Spreading of the interface at the top of a slightly polydisperse sedimenting suspension
Authors: Davis Robert H. , Hassen Mark A.
Published: April 2006

The interface at the top of a dilute sedimenting suspension of small particles which are not identical does not remain sharp but instead becomes increasingly diffuse as the sedimentation proceeds. For more concentrated suspensions, the self-sharpening effect of hindered settling leads to a considerable reduction in the observed spreading of the sedimenting interface. In order to quantify this spreading, a light extinction technique was used to measure the concentration profile in the interface of a suspension of particles with a small spread of sizes as it fell past a thin sheet of light. A particle volume-fraction range of 0.002 ≤ Φ0 ≤ 0.15 was examined, and each fluid-particle system had a particle Reynolds number less than 10−3 and a Péclet number greater than 107 so that inertia and colloidal effects were negligible. Calculations of the spreading arising from the small degree of polydispersity in particle sizes and the self-sharpening effect are presented. Surprisingly, the measured vertical thickness of the interface was found to be several times that predicted from this theory.

It is proposed that the observed spreading may be attributed to hydrodynamic interactions between particles that lead to fluctuations in particle settling velocities about the mean. An analysis of the data shows that the measured interface thickness, after subtracting off that predicted from polydispersity and self-sharpening, increases approximately with the square root of the settling distance and may therefore be described as a diffusion process, termed ‘self-induced hydrodynamic diffusion’. By sealing the hydrodynamic diffusivity as $D = au_{\frac{1}{2}}\hat{D}(\Phi_0)$, where u½ is the median hindered settling velocity, a is the median particle radius, and Φ0 is the volume fraction of particles well below the interface, an approximate analysis of the data was used to infer that the dimensionless scaled diffusion coefficient, $\hat{D}$, is between 1 and 2 for the smaller particle volume fractions examined, increases very rapidly with increasing concentration to a value between 10 and 15 for particle concentrations of a few percent by volume, and then levels off or declines slightly as the particle concentration is increased further.
The turbulent near wake at a sharp trailing edge
Authors: Bogucz E. A. , Walker J. D. A.
Published: April 2006

The problem of a turbulent boundary layer that evolves into a wake flow at the sharp trailing edge of a thin flat plate is considered; the formal structure of the near-wake flow is investigated using matched expansions in the limit of infinite Reynolds number. The symmetric turbulent near wake is shown to develop a two-layer structure which is independent of turbulence model. The general asymptotic analysis shows that a thin layer at the wake centreline grows linearly with distance from the trailing edge while the centreline velocity varies logarithmically in a manner that is supported strongly by experimental measurements. The relatively thick outer layer of the near-wake flow is undisturbed by the evolution of the inner layer to leading order. An additional region near the trailing edge is required to resolve a non-uniformity in transverse velocity. The general asymptotic results are used to guide the development of a zonal turbulence model for the near wake in the form of a simple eddy viscosity formula. Analytic profiles for velocity and Reynolds stress are obtained for the near-wake region; these profiles are shown to provide accurate representations of available near-wake experimental data.
Bifurcation phenomena in Taylor–Couette flow with buoyancy effects
Authors: Ball K. S. , Farouk B.
Published: April 2006

A numerical study has been conducted to determine the various modes of Taylor–Couette flow that exist between concentric vertical cylinders, as the aspect ratio Γ (height to gap width, H/d) and the Reynolds number Re (based on the inner cylinder speed) are varied. Furthermore, the effects of the introduction of buoyancy on the development of the flow are examined. This is accomplished by considering both cylinders to be isothermal, with the rotating inner cylinder at a higher temperature than the stationary outer cylinder. Results are presented for a wide range of the Grashof number Gr (based on the temperature difference ΔT across the annular gap). The structure of the Taylor vortices is observed to be distorted considerably with the buoyant flows, and the nature of the onset and subsequent development of the vortices is altered. The hysteresis between the different modes of cellular flow, characteristic of the bifurcation phenomena, is also substantially modified.
The reflection of a solitary wave by a vertical wall
Authors: Byatt-Smith J. G. B.
Published: April 2006

In this paper we consider the head-on collision of two equal solitary waves this being equivalent, in the absence of viscosity to the reflection of one solitary wave by a vertical wall. The perturbation expansion of the Euler equations, which lead to the Boussinesq equation at lowest order, is recast to obtain two weakly coupled KdV equations. We show analytically that the amplitude of the solitary wave after reflection is reduced. This change in amplitude is shown to be fifth order in ε, the amplitude of the wave. It is also shown that the experimentally observed transient loss of amplitude can be explained by the presence of the third-order dispersive tail.
A reassessment of the efficacy of Anglo-Saxon medicine
Authors: Brennessel Barbara , Drout Michael D.C. , Gravel Robyn
Published: April 2006

Laboratory in vitro testing of various remedies from the Old English
Leechbooks and Lacnunga does not support previous assertions that
Anglo-Saxon medical remedies would have been efficacious. For
example, the remedy for a stye in the eye takes ingredients that
individually have anti-bacterial properties and compounds them into a
mixture with no effect on common bacteria. We conclude that
Anglo-Saxon remedies were not likely to have cured the ailments for
which they were prescribed and that researchers, rather than
asserting the probable prowess of the Anglo-Saxon læce, should
instead focus on what people in the time period believed would have
helped them.
Metal-carbon clusters: The origin of the delayed atomic ion
Authors: Davis K. M. , Peppernick S. J. , Castleman A. W.
Published: April 2006

Studies of the emission of electrons from excited metal-carbon cluster systems that include the Met-Car (M8C12, where M is Ti, Zr, and V) also have revealed the evolution of a delayed atomic ion. The source of the delayed atomic ion, which involves the emission of ionized atoms on the microsecond time scale, is the focus of this investigation. By studying the delayed ionization of mixed zirconium and titanium carbon complexes produced in a laser vaporization source coupled to a time-of-flight mass spectrometer, for the first time both the zirconium and titanium delayed atomic ions were observed to be emitted in the same experiment. These studies allowed a determination that the source of the delayed atomic ion is an excited metal dicarbide. A plausible mechanism involving the excitation of a high Rydberg state of the metal dicarbide prior to an excited ion pair separation is proposed.
Anomalous temperature-isotope dependence in proton-coupled electron transfer
Authors: Pressé Steve , Silbey Robert
Published: April 2006

Motivated by the experiments of Hodgkiss et al. [J. Phys. Chem. (submitted)] on electron transfer (ET) through a H-bonding interface, we present a new theoretical model for proton-coupled electron transfer (PCET) in the condensed phase, that does not involve real proton transfer. These experiments, which directly probe the joint T-isotope effects in coupled charge transfer reactions, show anomalous T dependence in kH∕kD, where kH and kD are the ET rates through the H-bonding interface with H-bonded protons and deuterons, respectively. We address the anomalous T dependence of the kH∕kD in our model by attributing the modulation of the electron tunneling dynamics to bath-induced fluctuations in the proton coordinate, so that the mechanism for coupled charge transfer might be better termed vibrationally assisted ET rather than PCET. We argue that such a mechanism may be relevant to understanding traditional PCET processes, i.e., those in which protons undergo a transfer from donor to acceptor during the course of ET, provided there is an appropriate time scale separating both coupled charge transfers. Likewise, it may also be useful in understanding long-range ET in proteins, where tunneling pathways between redox cofactors often pass through H-bonded amino acid residues, or other systems with sufficiently decoupled proton and electron donating functionalities.
Coupling a versatile aerosol apparatus to a synchrotron: Vacuum ultraviolet light scattering, photoelectron imaging, and fragment free mass spectrometry
Authors: Shu Jinian , Wilson Kevin R. , Ahmed Musahid , Leone Stephen R.
Published: April 2006

An aerosol apparatus has been coupled to the Chemical Dynamics Beamline of the Advanced Light Source at Lawrence Berkeley National Laboratory. This apparatus has multiple capabilities for aerosol studies, including vacuum ultraviolet (VUV) light scattering, photoelectron imaging, and mass spectroscopy of aerosols. By utilizing an inlet system consisting of a 200μm orifice nozzle and aerodynamic lenses, aerosol particles of ∼50nm–∼1μm in diameter can be sampled directly from atmospheric pressure. The machine is versatile and can probe carbonaceous aerosols generated by a laboratory flame, nebulized solutions of biological molecules, hydrocarbon aerosol reaction products, and synthesized inorganic nanoparticles. The sensitivity of this apparatus is demonstrated by the detection of nanoparticles with VUV light scattering, photoelectron imaging, and charged particle detection. In addition to the detection of nanoparticles, the thermal vaporization of aerosols on a heater tip leads to the generation of intact gas phase molecules. This phenomenon coupled to threshold single photon ionization, accessible with tunable VUV light, allows for fragment-free mass spectrometry of complex molecules. The initial experiments with light scattering, photoelectron imaging, and aerosol mass spectrometry reported here serve as a demonstration of the design philosophy and multiple capabilities of the apparatus.
Investigations of HfO2∕AlGaN∕GaN metal-oxide-semiconductor high electron mobility transistors
Authors: Liu Chang , Chor Eng Fong , Tan Leng Seow
Published: April 2006

We report the studies of AlGaN∕GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) using reactive-sputtered HfO2 as the gate dielectric and the surface passivation layer. X-ray photoemission method reveals a conduction-band offset of 1.71eV for the HfO2∕GaN heterostructure. The dielectric constant of HfO2 is estimated to be 21 by capacitance-voltage measurements. MOS-HEMTs with a 1.5-μm-long gate exhibit a maximum drain current of 830mA∕mm and a peak transconductance of 115mS∕mm, while the gate leakage current is at least five orders of magnitude lower than that of the reference HEMTs. Good surface passivation effects of HfO2 have also been confirmed by pulsed gate measurements, with MOS-HEMTs showing a significant drain current recovery from current collapse observed in HEMTs.
Direct phosphorylation and regulation of poly(ADP-ribose) polymerase-1 by extracellular signal-regulated kinases 1/2
Authors: Kauppinen Tiina M. , Chan Wai Y. , Suh Sang Won , Wiggins Amanda K. , Huang Eric J. , Swanson Raymond A.
Published: April 2006

Sustained activation of poly(ADP-ribose) polymerase-1 (PARP-1) and extracellular signal-regulated kinases 1/2 (ERK1/2) both promote neuronal death. Here we identify a direct link between these two cell death pathways. In a rat model of hypoglycemic brain injury, neuronal PARP-1 activation and subsequent neuronal death were blocked by the ERK1/2 inhibitor 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one (PD98059). In neuron cultures, PARP-1-mediated neuronal death induced by
N
-methyl-
d
-aspartate, peroxynitrite, or DNA alkylation was similarly blocked by ERK1/2 pathway inhibitors. These inhibitors also blocked PARP-1 activation and PARP-1-mediated death in astrocytes. siRNA down-regulation of ERK2 expression in astrocytes also blocked PARP-1 activation and cell death. Direct effects of ERK1/2 on PARP-1 were evaluated by using isolated recombinant enzymes. The activity of recombinant human PARP-1 was reduced by incubation with alkaline phosphatase and restored by incubation with active ERK1 or ERK2. Putative ERK1/2 phosphorylation sites on PARP-1 were identified by mass spectrometry. Using site-directed mutagenesis, these sites were replaced with alanine (S372A and T373A) to block phosphorylation, or with glutamate (S372E and T373E) to mimic constitutive phosphorylation. Transfection of PARP-1 deficient mouse embryonic fibroblasts with the mutant PARP-1 species showed that the S372A and T373A mutations impaired PARP-1 activation, whereas the S372E and T373E mutations increased PARP-1 activity and eliminated the effect of ERK1/2 inhibitors on PARP-1 activation. These results suggest that PARP1 phosphorylation by ERK1/2 is required for maximal PARP-1 activation after DNA damage.
Dysregulation of signaling pathways in CD45-deficient NK cells leads to differentially regulated cytotoxicity and cytokine production
Authors: Hesslein David G. T. , Takaki Rayna , Hermiston Michelle L. , Weiss Arthur , Lanier Lewis L.
Published: April 2006

CD45, a protein tyrosine phosphatase that regulates Src family kinases, is important for regulating T cell and B cell receptor signaling; however, little is known about how CD45 regulates immunoreceptor tyrosine-based activation motif (ITAM)-dependent natural killer (NK) cell receptor signaling and the resulting effector functions. NK cells from CD45-deficient mice are relatively competent for ITAM receptor-induced cell-mediated cytotoxicity, yet completely deficient for cytokine secretion after stimulation with ligands to or antibodies against NK1.1, CD16, Ly49H, Ly49D, and NKG2D. This deficiency in cytokine/chemokine production occurs at the level of mRNA expression. After receptor engagement, extracellular signal-regulated kinase and c-Jun N-terminal kinase activation was markedly perturbed, whereas p38 activation was not substantially affected. The pattern and amounts of basal tyrosine phosphorylation were altered in freshly isolated NK cells and were surprisingly and markedly increased in IL-2-expanded NK cells fromCD45−/− mice. These findings indicate that CD45-dependent regulation of ITAM-dependent signaling pathways is essential for NK cell-mediated cytokine production but not cytolytic activity.
TSC1/TSC2 and Rheb have different effects on TORC1 and TORC2 activity
Authors: Yang Qian , Inoki Ken , Kim Eunjung , Guan Kun-Liang
Published: April 2006

Target of rapamycin (TOR) plays a central role in cell growth regulation by integrating signals from growth factors, nutrients, and cellular energy levels. TOR forms two distinct physical and functional complexes, termed TOR complex 1 (TORC1) and TOR complex 2 (TORC2). TORC1, which is sensitive to rapamycin, regulates translation and cell growth, whereas TORC2, which is insensitive to rapamycin, regulates cell morphology and cell growth. The Ras homology enriched in brain (Rheb) small GTPase is known to be a key upstream activator of TORC1, although the mechanism of Rheb in TORC1 activation remains to be determined. However, the function of Rheb in the TORC2 regulation has not been elucidated. By measuring Akt and S6K phosphorylation as a functional assay for TORC1 and -2, here, we report that dRheb has an inhibitory effect on dTORC2 activity in
Drosophila
S2 cells. This negative effect of dRheb on dTORC2 is possibly due to a feedback mechanism involving dTORC1 and dS6K. We also observed that Rheb does not activate TORC2 in human embryonic kidney 293 cells, although it potently stimulates TORC1. Furthermore, tuberous sclerosis complex 1 (TSC1) and TSC2, which are negative regulators of Rheb, have negative and positive effects on TORC1 and -2, respectively. Our observations suggest that TSC1/2 and Rheb have different effects on the activity of TORC1 and -2, further supporting the complexity of TOR regulation.
Social Facilitation: A Test of Competing Theories1
Authors: Feinberg Joshua M. , Aiello John R.
Published: April 2006

Evaluation–apprehension and distraction–conflict have typically been treated as alternative explanations for social facilitation. The present study tested both theories under a single design. The study examined (a) whether each explanation predicted social‐facilitation performance outcomes and (b) whether combining evaluation and distraction manipulations produced even greater performance outcomes. The present study also explored whether physical presence is necessary to produce social‐facilitation effects when evaluation and distraction manipulations are already present. The study found significant facilitation effects on the simple task only in the evaluation–apprehension condition. Significant performance impairment was found for both evaluation and distraction. Combining evaluation with distraction led to greater effects only on the complex task. Furthermore, physical presence does not appear necessary to produce social‐facilitation effects.
Pharmacokinetics and response to pravastatin in paediatric patients with familial hypercholesterolaemia and in paediatric cardiac transplant recipients in relation to polymorphisms of theSLCO1B1andABCB1genes
Authors: Hedman Mia , Antikainen Marjatta , Holmberg Christer , Neuvonen Mikko , Eichelbaum Michel , Kivistö Kari T. , Neuvonen Pertti J. , Niemi Mikko
Published: April 2006

Aims

Our aim was to investigate associations between the single nucleotide polymorphisms (SNPs) in theSLCO1B1(encoding OATP1B1) andABCB1(encoding P‐glycoprotein) genes with the pharmacokinetics and efficacy of pravastatin in children with heterozygous familial hypercholesterolaemia (HeFH) and in paediatric cardiac transplant recipients.

Methods

Twenty children with HeFH (aged 4.9–15.6 years) and 12 cardiac transplant recipients (aged 4.4–18.7 years and receiving triple immunosuppressive medication) who had participated in previous pharmacokinetic and pharmacodynamic studies with pravastatin were genotyped for the −11187G > A and 521T > C SNPs in theSLCO1B1gene and for the 2677G > T/A and 3435C > T SNPs in theABCB1gene.

Results

Two HeFH patients with the −11187GA genotype had a 81% lower peak plasma pravastatin concentration (Cmax) (difference in means −13.9 ng ml−1, 95% CI −21.1, −6.7;P < 0.001) and a 74% smaller area under the plasma concentration‐time curve (AUC(0, ∞)) (−25.3 ng ml−1 h, 95% CI −35.6, −15.0;P < 0.0001) and significantly greater increase in high density lipoprotein (HDL) cholesterol after 2 months treatment with pravastatin than patients with the reference genotype. No significant differences were seen in the pharmacokinetics or effects of pravastatin between HeFH patients with theSLCO1B1521TC and 521TT genotypes. The cardiac transplant recipients with theSLCO1B1521TC genotype (n = 3) had a 46% lowerCmax(−67.7 ng ml−1, 95% CI −135.7, 0.3;P = 0.055) and 62% lower AUC(0,24 h) (−228.5 ng ml−1 h, 95% CI −402.7, −54.3;P = 0.016) and a shorter half‐life (t1/2) (0.9 ± 0.1vs.1.3 ± 0.4 h,P = 0.015) of pravastatin than those with the reference genotype. Decreases in total and low‐density lipoprotein cholesterol by pravastatin were significantly smaller, and the increase in HDL‐cholesterol was greater in the transplant recipients with the 521TC genotype compared with patients with the 521TT reference genotype.

Conclusions

In children with HeFH and in paediatric cardiac transplant recipients receiving immunosuppressive medication, the −11187G > A andSLCO1B1521T > C SNPs were associated with decreased plasma concentrations of pravastatin. These differences are opposite to those seen previously in healthy adults. The mechanisms underlying these phenomena are unclear and warrant further study.