bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rossby waves and two-dimensional turbulence in a large-scale zonal jet
Authors: Shepherd Theodore G. 
Published: April 2006

The theory of homogeneous barotropic beta-plane turbulence is here extended to include effects arising from spatial inhomogeneity in the form of a zonal shear flow. Attention is restricted to the geophysically important case of zonal flows that are barotropically stable and are of larger scale than the resulting transient eddy field.Because of the presumed scale separation, the disturbance enstrophy is approximately conserved in a fully nonlinear sense, and the (nonlinear) wave-mean-flow interaction may be characterized as a shear-induced spectral transfer of disturbance enstrophy along lines of constant zonal wavenumber k. In this transfer the disturbance energy is generally not conserved. The nonlinear interactions between different disturbance components are turbulent for scales smaller than the inverse of Rhines's cascade-arrest scale κβ≡ (β0/2urms)½ and in this regime their leading-order effect may be characterized as a tendency to spread the enstrophy (and energy) along contours of constant total wavenumber κ ≡ (k2 + l2)½. Insofar as this process of turbulent isotropization involves spectral transfer of disturbance enstrophy across lines of constant zonal wavenumber k, it can be readily distinguished from the shear-induced transfer which proceeds along them. However, an analysis in terms of total wavenumber K alone, which would be justified if the flow were homogeneous, would tend to mask the differences.The foregoing theoretical ideas are tested by performing direct numerical simulation experiments. It is found that the picture of classical beta-plane turbulence is altered, through the effect of the large-scale zonal flow, in the following ways: (i) while the turbulence is still confined to KKβ, the disturbance field penetrates to the largest scales of motion; (ii) the larger disturbance scales K < Kβ exhibit a tendency to meridional rather than zonal anisotropy, namely towards v2 > u2 rather than vice versa; (iii) the initial spectral transfer rate away from an isotropic intermediate-scale source is significantly enhanced by the shear-induced transfer associated with straining by the zonal flow. This last effect occurs even when the large-scale shear appears weak to the energy-containing eddies, in the sense that dU/dy [Lt ] κ for typical eddy length and velocity scales.
Reflection of water waves in a channel with corrugated bed
Authors: Benjamin T. Brooke , Boczar-Karakiewicz B. , Pritchard W. G. 
Published: April 2006

Intended as a contribution towards understanding the multiple processes entailed in the development of coastal sand bars due to wave action, this theoretical and experimental study deals with the Bragg reflection of long-crested surface waves in a water channel whose bed is corrugated sinusoidally. The present findings complement and in a few respects improve upon those in previous investigations, particularly Davies & Heathershaw (1984).In §2 a linearized theory is presented, being directed to the elucidation of experimental situations where monochromatic waves propagate into a channel with a limited stretch of corrugations on its bed and an imperfectly absorbing beach at its far end. Allowance is made fully for dispersive effects (§2.2) and approximately for small frictional effects (§2.3). Points of interpretation (§2.4) include accounts of degenerate but non-trivial solutions that apply at frequencies terminating the stopping band, wherein the spatial wavefield has an exponential envelope. The experimental results presented in §4 derive from measurements of the wavefield over a stretch of 24 corrugations, at various frequencies both inside and outside the stopping band. Quantitative comparisons (§4.2 and 4.3) demonstrate close agreements with the theory.
Wave splitting in a fluid of large heat capacity
Authors: Thompson Philip A. , Craves Humberto , Meier G. E. A. , Kim Yoon-Gon , Speckmann H.-D. 
Published: April 2006

The splitting of a single pressure discontinuity into a propagating two-wave system is studied for the case of saturated-liquid expansion (liquid-evaporation wave splitting) and vapour compression (vapour-condensation wave splitting). Experimental results from the Max-Planck-Institut für Strömungsforschung and from Rensselaer Polytechnic Institute show that splitting occurs in test fluids of large molar heat capacity, such as iso-octane (Cv0/R≈ 37). Each of the two forms of splitting results in a single-phase forerunner wave carrying a pressure discontinuity followed by a phase-change wave, also with a pressure discontinuity. The thermodynamic state between the forerunner wave and the phase-change wave is metastable (supersaturated liquid or vapour). The waves are quantitatively described by systems of adiabats, e.g. shock adiabats. It appears that nucleation processes are predominantly homogeneous.In vapour-compression shock-wave splitting, a combined wave (liquefaction shock) splits into discrete forerunner and condensation waves at a triple point, the intersection of a liquefaction shockfront, forerunner shock and condensation discontinuity: such a point occurs just at critical supersaturation (i.e. the Wilson-line state), where condensation is spontaneous and immediate. For shock waves that produce a metastable state of subcritical supersaturation, condensation is delayed, that is, the condensation discontinuity propagates more slowly; for a split-shock system, the condensation discontinuity propagates subsonically. The pressure amplitude of a real split-shock system is much larger than that predicted by an equilibrium model.In liquid-evaporation wave splitting, the forerunner wave is an acoustic expansion wave and the second wave an evaporation wave with a propagation velocity approximately determined by the Chapman-Jouguet condition for deflagration. Such evaporation wavefronts are increasingly distinct as the temperature approaches the critical-point value. The evaporation rates across the wavefront are comparable to those found in vapour explosions.
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.
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.
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.
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.
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.
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.
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

AimsOur 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.MethodsTwenty 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.ResultsTwo 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.ConclusionsIn 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.
Development of a dosage strategy in patients receiving enoxaparin by continuous intravenous infusion using modelling and simulation
Authors: Feng Yan , Green Bruce , Duffull Stephen B. , Kane‐Gill Sandra L. , Bobek Mary B. , Bies Robert R. 
Published: April 2006

AimTo develop an appropriate dosing strategy for continuous intravenous infusions (CII) of enoxaparin by minimizing the percentage of steady‐state anti‐Xa concentration (Css) outside the therapeutic range of 0.5–1.2 IU ml−1.MethodsA nonlinear mixed effects model was developed with NONMEM® for 48 adult patients who received CII of enoxaparin with infusion durations that ranged from 8 to 894 h at rates between 100 and 1600 IU h−1. Three hundred and sixty‐three anti‐Xa concentration measurements were available from patients who received CII. These were combined with 309 anti‐Xa concentrations from 35 patients who received subcutaneous enoxaparin. The effects of age, body size, height, sex, creatinine clearance (CrCL) and patient location [intensive care unit (ICU) or general medical unit] on pharmacokinetic (PK) parameters were evaluated. Monte Carlo simulations were used to (i) evaluate covariate effects on Css and (ii) compare the impact of different infusion rates on predicted Css. The best dose was selected based on the highest probability that the Css achieved would lie within the therapeutic range.ResultsA two‐compartment linear model with additive and proportional residual error for general medical unit patients and only a proportional error for patients in ICU provided the best description of the data. Both CrCL and weight were found to affect significantly clearance and volume of distribution of the central compartment, respectively. Simulations suggested that the best doses for patients in the ICU setting were 50 IU kg−1 per 12 h (4.2 IU kg−1 h−1) if CrCL < 30 ml min−1; 60 IU kg−1 per 12 h (5.0 IU kg−1 h−1) if CrCL was 30–50 ml min−1; and 70 IU kg−1 per 12 h (5.8 IU kg−1 h−1) if CrCL > 50 ml min−1. The best doses for patients in the general medical unit were 60 IU kg−1 per 12 h (5.0 IU kg−1 h−1) if CrCL < 30 ml min−1; 70 IU kg−1 per 12 h (5.8 IU kg−1 h−1) if CrCL was 30–50 ml min−1; and 100 IU kg−1 per 12 h (8.3 IU kg−1 h−1) if CrCL > 50 ml min−1. These best doses were selected based on providing the lowest equal probability of either being above or below the therapeutic range and the highest probability that the Css achieved would lie within the therapeutic range.ConclusionsThe dose of enoxaparin should be individualized to the patients’ renal function and weight. There is some evidence to support slightly lower doses of CII enoxaparin in patients in the ICU setting.