bluuebunny/crossref_metadata_2025_split huggingface dataset:
Assessing the properties of internal standards for quantitative matrix‐assisted laser desorption/ionization mass spectrometry of small molecules
Authors: Sleno Lekha , Volmer Dietrich A. 
Published: April 2006

AbstractGrowing interest in the ability to conduct quantitative assays for small molecules by matrix‐assisted laser desorption/ionization (MALDI) has been the driving force for several recent studies. This present work includes the investigation of internal standards for these analyses using a high‐repetition rate MALDI triple quadrupole instrument. Certain physicochemical properties are assessed for predicting possible matches for internal standards for different small molecules. The importance of similar molecular weight of an internal standard to its analyte is seen through experiments with a series of acylcarnitines, having a fixed charge site and growing alkyl chain length. Both acetyl‐ and hexanoyl‐carnitine were systematically assessed with several other acylcarnitine compounds as internal standards. The results clearly demonstrate that closely matched molecular weights between analyte and internal standard are essential for acceptable quantitation results. Using α‐cyano‐4‐hydroxycinnamic acid as the organic matrix, the similarities between analyte and internal standard remain the most important parameter and not necessarily their even distribution within the solid sample spot. Several 4‐quinolone antibiotics as well as a diverse group of pharmaceutical drugs were tested as internal standards for the 4‐quinolone, ciprofloxacin. Quantitative results were shown using the solution‐phase properties, log D and pKa, of these molecules. Their distribution coefficients, log D, are demonstrated as a fundamental parameter for similar crystallization patterns of analyte and internal standard. In the end, it was also possible to quantify ciprofloxacin using a drug from a different compound class, namely quinidine, having a similar log D value as the analyte. Copyright © 2006 John Wiley & Sons, Ltd.
Global output feedback stabilization of upper‐triangular nonlinear systems using a homogeneous domination approach
Authors: Qian Chunjiang , Li Ji 
Published: April 2006

AbstractThis paper addresses the problem of global output feedback stabilization for a class of upper‐triangular systems with perturbing nonlinearities that are higher‐order in the unmeasurable states. A new design method based on the homogeneous domination approach and finite‐time stabilization technique is developed, which leads to global output feedback stabilizers for the upper‐triangular nonlinear systems under a homogeneous growth condition. A new perspective shown in this paper is that the finite‐time stabilization, in addition to its faster convergence rate, can also be utilized to handle control problems that were previously unresolved under asymptotic stabilization. Copyright © 2006 John Wiley & Sons, Ltd.
The impact of macroeconomic uncertainty on non‐financial firms' demand for liquidity
Authors: Baum Christopher F. , Caglayan Mustafa , Ozkan Neslihan , Talavera Oleksandr 
Published: April 2006

AbstractThis paper empirically investigates whether changes in macroeconomic volatility affect the efficient allocation of non‐financial firms' liquid assets. We argue that higher uncertainty will hamper managers' ability to accurately predict firm‐specific information and induce them to implement similar cash management policies. Contrarily, when the macroeconomic environment becomes more tranquil, each manager will have the latitude to behave more idiosyncratically as she can adjust liquid assets based on the specific requirements of the firm, bringing about a more efficient allocation of liquid assets. Our empirical analysis provides support for these predictions.
Sound diffraction at a trailing edge
Authors: Rienstra S. W. 
Published: April 2006

The diffraction of externally generated sound in a uniformly moving flow at the trailing edge of a semi-infinite flat plate is studied. In particular, the coupling of the sound field to the hydrodynamic field by way of vortex shedding from the edge is considered in detail, both in inviscid and in viscous flow.In the inviscid model the (two-dimensional) diffracted fields of a cylindrical pulse wave, a plane harmonic wave and a plane pulse wave are calculated. The viscous proess of vortex shedding is represented by an appropriate trailing-edge condition. Two specific cases are compared, in one of which the full Kutta condition is applied, and in the other no vortex shedding is permitted. The results show good agreement with Heavens’ (1978) observations from his schlieren photographs, and confirm his conclusions. It is further demonstrated, by an explicit expression, that the sound power absorbed by the wake may be positive or negative, depending on Mach number and source position. So the process of vortex shedding does not necessarily imply an attenuation of the sound.In the viscous model a high-Reynolds-number approximation is constructed, based on a triple-deck boundary-layer structure, matching the harmonic plane wave outer solution to a known incompressible inner solution near the edge, to obtain the viscous correction to the Kutta condition.
A Fourier approximation method for steady water waves
Authors: Rienecker M. M. , Fenton J. D. 
Published: April 2006

A method for the numerical solution of steadily progressing periodic waves on irrotational flow over a horizontal bed is presented. No analytical approximations are made. A finite Fourier series, similar to Dean's stream function series, is used to give a set of nonlinear equations which can be solved using Newton's method. Application to laboratory and field situations is emphasized throughout. When compared with known results for wave speed, results from the method agree closely. Results for fluid velocities are compared with experiment and agreement found to be good, unlike results from analytical theories for high waves.The problem of shoaling waves can conveniently be studied using the present method because of its validity for all wavelengths except the solitary wave limit, using the conventional first-order approximation that on a sloping bottom the waves at any depth act as if the bed were horizontal. Wave period, energy flux and mass flux are conserved. Comparisons with experimental results show good agreement.
The absorption of wave energy by a three-dimensional submerged duct
Authors: Thomas J. R. 
Published: April 2006

It has been shown (Evans 1976) that the power absorbed by a general, axisymmetric body depends solely upon the added-mass and damping coefficients. These coefficients are fundamental properties of the body, representing the component of the force on the body proportional to the acceleration and velocity of the body respectively in the radiation problem, where the body is forced to oscillate in the absence of incoming waves.In the present paper these coefficients are determined by solution of the radiation problem, for a mouth-upward cylindrical duct situated on the sea bed and fitted with a piston undergoing forced oscillations. The added-mass and damping coefficients are then used to study the power absorption properties of the duct when the power take-off is modelled by a linear-spring–dashpot system attached to the piston. Curves of the added mass, damping coefficients and absorption length (a measure of the power absorbed) as functions of wavenumber are presented, for different duct diameters and different depths of submergence.
Fully developed MHD turbulence near critical magnetic Reynolds number
Authors: Léorat J. , Pouquet A. , Frisch U. 
Published: April 2006

Liquid-sodium-cooled breeder reactors may soon be operating at magnetic Reynolds numbers RM where magnetic fields can be self-excited by a dynamo mechanism (as first suggested by Bevir 1973). Such flows have kinetic Reynolds numbers RV of the order of 107 and are therefore highly turbulent.This leads us to investigate the behaviour of MHD turbulence with high RV and low magnetic Prandtl numbers. We use the eddy-damped quasi-normal Markovian closure applied to the MHD equations. For simplicity we restrict ourselves to homogeneous and isotropic turbulence, but we do include helicity.We obtain a critical magnetic Reynolds number RMc of the order of a few tens (non-helical case) above which magnetic energy is present. RMc is practically independent of RV (in the range 40 to 106). RMc can be considerably decreased by the presence of helicity: when the overall size of the flow L is much larger than the integral scale l0, RMc can drop below unity as suggested by an α-effect argument. When L ≈ l0 the drop can still be substantial (factor of 6) when helicity is a maximum. We examine how the turbulence is modified when RM crosses RMc: presence of magnetic energy, decreased kinetic energy, steepening of kinetic-energy spectrum, etc.We make no attempt to obtain quantitative estimates for a breeder reactor, but discuss some of the possible consequences of exceeding RMc, such as decreased turbulent heat transport. More precise information may be obtained from numerical simulations and experiments (including some in the subcritical regime).
Quasilinear approximation for the spectrum of wind-generated water waves
Authors: Janssen Peter A. E. M. 
Published: April 2006

According to Miles’ theory of wind-wave generation, water waves grow if the curvature of the wind profile at the critical height is negative. As a result, the wind profile changes in time owing to the transfer of energy to the waves. In the quasilinear approximation (where the interaction of the waves with one another is neglected) equations for the coupled air–water system are obtained by means of a multiple-time-scale analysis. In this way the validity of Miles’ calculations is extended, thereby allowing a study of the large-time behaviour.While the water waves grow owing to the energy transfer from the air flow, the waves in turn modify the flow in such a way that for large times the curvature of the velocity profile vanishes. The amplitude of the waves is then limited because the energy transfer is quenched.In the high-frequency range the asymptotic wave spectrum is given by a ‘–4’ law in the frequency domain rather than the ‘classical’ ‘–5’ law.
Turbulent Couette flow between concentric cylinders at large Taylor numbers
Authors: Smith G. P. , Townsend A. A. 
Published: April 2006

Measurements have been made of the Couette flow in the annular space between concentric cylinders with a radius ratio of 1.5, the outer cylinder being held stationary and the inner one rotated at speeds to give Taylor numbers in the range 1.0 × 104−2.3 × l06 times the critical value for first instability of the steady viscous flow. Mean velocities have been measured both with Pitot tubes and with linearized hot-wire anemometers, and turbulent intensities and stresses, frequency spectra and space-time correlations have been obtained using single hot-wire anemometers of X-form and linear arrays of eight single-wire anemometers. For Taylor-number ratios to the critical number less than 3 × l05, the most prominent feature of the flow is a system of toroidal eddies, encircling the inner cylinder and uniformly spaced in the axial direction with nearly the separation of the Taylor vortices of the viscous instability. They are superimposed on a background of irregular motion and, except within the thin wall layers, the toroidal eddies contribute more to the total intensity. With increase of rotation speed, the toroidal eddies lose their regularity, and they cannot be clearly distinguished at Taylor-number ratios beyond 5 × l05.The change of flow type from quasi-regular toroidal to fully irregular turbulent takes place over an extensive range of Taylor-number ratio centred near 3 × l05, and it may be linked with changes in the thin wall layers that separate the flow boundaries from the central region of nearly constant circulation. For ratios over 5 × l05, an appreciable part of the wall layers is comparatively unaffected by flow curvature and has a logarithmic distribution of mean velocity similar to that found in channel flows. It is suggested that the motion in the wall layers changes from a set of Gortler vortices characteristic of curved-wall flow to the more irregular motion found on plane walls, causing the toroidal eddies to break into sections of length ranging from a considerable fraction of the flow perimeter to nearly the separation of the cylinders. Changes in the frequency spectra of the radial and azimuthal velocit'y fluctuations are consistent with such a change.
Stokes flow past bubbles and drops partially coated with thin films. Part 1. Stagnant cap of surfactant film – exact solution
Authors: Sadhal S. S. , Johnson Robert E. 
Published: April 2006

In this investigation the creeping flow due to the motion of a liquid drop or a bubble in another immiscible fluid is examined when the interface is partially covered by a stagnant layer of surfactant. The associated boundary-value problem involves mixed boundary conditions at the interface, which lead to a set of dual series equations. An inversion of these equations yields the exact solution to the stagnant cap problem.Several useful results are obtained in closed form. Among these are the expressions for the drag force, the difference between the maximum and the minimum interfacial tensions, and the amount of adsorbed surfactant. A shifting of the centre of the internal vortex is observed.
Oscillating-grid turbulence including effects of rotation
Authors: Dickinson Stuart C. , Long Robert R. 
Published: April 2006

Experiments were performed to investigate some aspects of turbulence in rotating and non-rotating fluid systems where the turbulence was induced by a horizontal grid oscillating vertically. An earlier theory by the second author made use of a planar source of energy, which appeared to be similar to the energy source of the grid, in determining the characteristics of the turbulence at points some distance away. The simplicity of the theory was in the parameterization of the grid ‘action’ by a single quantity K, with dimensions and characteristics of eddy viscosity.The experimental results provide additional confirmation of the theory in the non-rotating case, and indicate the usefulness of the idealized energy source in the rotating case. In the latter, we measured the propagation of the front separating disturbed and undisturbed fluid, moving along the axis of rotation. The thickness d(t) of the disturbed region increases at first as (Kt)½, as in a non-rotating fluid, until the Rossby number K/Ωd2k becomes of order unity.Beyond this the disturbances are wavelike and rotationally dominated, and the thickness now increases linearly with time, yielding a speed of propagation for the front proportional to the wave speed (KΩ)½. Finally, the disturbances reach the bottom and the vessel is in statistical steady state. Then a region of thickness dk independent of time is found, and it contains motion that resembles ordinary, three-dimensional turbulence. dk ∼ (K/Ω)½ is analogous to the depth of the turbulent Ekman layer H ∼ (K/Ω)½, where K is taken as an eddy viscosity.McEwan constructed a similar rotating experiment, although with a different energy source, and observed vortices parallel to the axis of rotation, provided that the Rossby number was less than a critical value. Our observations and theory indicate that the disappearance of the vortices corresponds to h < dk, where h is the total depth of the fluid. At that point, the whole tank is filled with three-dimensional turbulence.
Numerical analysis of the flow through a corrugated tube with application to arterial prostheses
Authors: Savvides C. N. , Gerrard J. H. 
Published: April 2006

Steady and oscillating axisymmetric laminar flows are determined by a finite-difference solution of the vorticity and continuity equations for an incompressible fluid contained in a straight concertina-shaped tube far from its ends. In steady flow the size of the wall corrugations is varied as well as the Reynolds number of the flow. In unsteady flow one tube geometry is studied, and the parameters varied are the Reynolds number, the ratio of the mean volume flow rate to its amplitude, and the frequency of oscillation. The analysis produces streamlines, particle paths and the pressure difference across a length of the tube. The resistance to the flow is determined in terms of an equivalent cylindrical tube diameter.In steady flow the onset of flow separation and the growth of the separated region of flow is determined. The equivalent diameter is found to be principally a function of the product of Reynolds number and the non-dimensional pressure difference. This product depends on the height of the wall corrugations and less strongly on Reynolds number and the length of the corrugations. Resistance increases with increasing height of the corrugations. Comparison is made with other computational and experimental values of the pressure difference.In unsteady flow the mean velocity to amplitude ratio has little effect except on the particle paths. The flow pattern is found to be governed by the Stokes number (radius × (2π/(kinematic viscosity × period))½) and the Reynolds number. There is a region of quasi-steady flow at the time of zero acceleration at maximum flow, but unsteady flow in between. The mixing produced by radial convection is restricted to the outer parts of the tube where the wall is corrugated. In oscillating flow the resistance relative to a cylindrical tube decreases as frequency and Reynolds number increase.In the medical application of the work the concern is whether sustained stagnant regions occur in the corrugations and whether there is a large change in resistance relative to a cylindrical tube. This part of the investigation was made with an arterial waveform which contained six harmonics. It is found that there are no regions of stagnant fluid in the range of parameters considered. The difference between the variation with the flow parameters of the resistance of the corrugated tube and of a cylindrical tube was found not to be large.
Velocity characteristics in the turbulent near wakes of confined axisymmetric bluff bodies
Authors: Taylor A. M. K. P. , Whitelaw J. H. 
Published: April 2006

Measurements of the velocity characteristics and wall pressure are reported for the axisymmetric turbulent flow downstream of three bluff bodies (disks of 25% and 50% area blockage and a cone of 25% blockage) confined by a long pipe. The dimensions of the recirculation regions were found from the mean-velocity components, which were determined by a laser-Doppler velocimeter: the corresponding components of Reynolds stress were also recorded. The lengths and maximum widths of the recirculation bubbles (in bluff-body diameters), recirculating mass-flow rates (normalized by the average velocity in the plane of the baffle, U0, and the baffle diameter) and maximum turbulent kinetic energy (normalized by U02) were as follows: cone 1.55, 0.55, 0.19, 0.11; disk (25% blockage) 1.75, 0.62, 0.31, 0.19; disk (50% blockage) 2.20, 0.55, 0.26, 0.16. The increase in recirculation length with blockage is opposite to the trend in unconfined, annular jets. The distribution of Reynolds stresses is strongly dependent on blockage: for the smaller blockage both the disk and the cone have the maximum value of kinetic energy near the rear stagnation point. It is proposed that this is because the generation of turbulence by normal stresses is more important in the flow consequent on the smaller blockage.The measurements include profiles of the velocity characteristics at, as well as upstream of, the trailing edges of the baffles for use as boundary conditions in numerical solutions of the equations of motion.
A unified description of two-layer flow over topography
Authors: Baines Peter G. 
Published: April 2006

Observations of the flow of a two-layer fluid resulting from the motion of a towed streamlined two-dimensional obstacle are described in some detail. The experiments were designed to further our understanding of the factors governing the nature and magnitude of upstream disturbances in the general flow of stratified fluid over two-dimensional topography, and predictions for arbitrary two-dimensional flows are made from the results of these experiments. In particular, the relationship between uniformly stratified flow and single-layer flow over topography is suggested. Most of the observed features of interest in these experiments are nonlinear in character. Relatively complete descriptions of the observed flows are presented over a wide range of parameter values, and the phenomena observed include upstream undular and turbulent bores, bores with zero energy loss, ‘rarefactions’ (in which the interface height changes monotonically over a transition region of continuously increasing length), and downstream hydraulic drops and jumps. Their properties are shown to be broadly consistent with predictions from a two-layer hydrostatic model based on continuity and momentum considerations, which employs jump criteria and rarefaction equations where appropriate. Bores occur because of nonlinear steepening when the layer containing the obstacle is thinner than the other, and rarefactions occur when this layer thickness is comparable with or greater than that of the other layer. The speed and amplitude of the upstream bores are governed by nonlinear effects, but their character is determined by a balance between nonlinear steepening, wave dispersion and interfacial friction when the bore is non-turbulent.Experimental evidence is presented for two types of hysteresis or ‘multiple equilibria’ - situations where two different flow states may exist for the same external steady conditions. In the first of these hysteresis types, the upstream flow may be supercritical or consist of an upstream bore state. It is analogous to the type anticipated for single-layer flow by Baines & Davies (1980) and described numerically by Pratt (1983), but it is only found experimentally for part of the expected parameter range, apparently because of interfacial stress effects. The second hysteresis type is new, and involves the presence or absence of a downstream hydraulic drop and following jump.
A numerical study of vortex interaction
Authors: Bromilow I. G. , Clements R. R. 
Published: April 2006

Flow visualization has shown that the interaction of line vortices is a combination of tearing, elongation and rotation, the extent of each depending upon the flow conditions. A discrete-vortex model is used to study the interaction of two and three growing line vortices of different strengths and to assess the suitability of the method for such simulation.Many of the features observed in experimental studies of shear layers are reproduced. The controlled study shows the importance and rapidity of the tearing process under certain conditions.