bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental investigation of coherent structures in turbulent boundary layers
Authors: Wark C. E. , Nagib H. M.
Published: April 2006

The events which are responsible for strong Reynolds-stress production in the near-wall region of a bounded turbulent shear flow have been investigated in a turbulent boundary layer at a Reynolds number based on momentum thickness of Reθ = 4650. The coherent structures associated with the production process have been studied using the quadrant detection technique. All three velocity components were measured in a three-dimensional sampling volume about the point of detection. The conditional ensemble-averaged velocity field associated with the detection of a sweep or an ejection is presented and compared with non-conditioned space–time correlations. Conditional space–time probability density distributions were calculated at all measurement locations based on the occurrence of a Reynolds-stress-producing event at the detection point. The resulting three-dimensional representation of the conditional probability demonstrates that a significant fraction of the events are relatively large in scale, that a hierarchy of sizes exists and that there is a link between the outer flow and the ’bursting’ process. However, many investigators have shown that the ’bursting’ frequency scales with wall variables. Therefore all indications suggest that the scales are generated by a wall-layer mechanism but grow to sizes and convect with velocities scaling with the outer layer.
On the refraction of shock waves at a slow–fast gas interface
Authors: Henderson L. F. , Colella P. , Puckett E. G.
Published: April 2006

We present the results of numerical computations of the refraction of a plane shock wave at a CO2/CH4 gas interface. The numerical method was an operator split version of a second-order Godunov method, with adaptive grid refinement. We solved the unsteady, two-dimensional, compressible, Euler equations numerically, assuming perfect gas equations of state, and compared our results with the experiments of Abd-El-Fattah & Henderson. Good agreement was usually obtained, especially when the contamination of the CH4 by the CO2 was taken into account. Remaining discrepancies were ascribed to the uncertainties in measuring certain wave angles, due to sharp curvature, poor definition, or short length of the waves at large angles of incidence. All the main features of the regular and irregular refractions were resolved numerically for shock strengths that were weak, intermediate, or strong. These include free precursor shock waves in the intermediate and strong cases, evanescent (smeared out) compressions in the weak case, and the appearance of an extra expansion wave in the bound precursor refraction (BPR). The structure of a BPR was elucidated for the first time.
The effect of jet injection geometry on two-dimensional momentumless wakes
Authors: Park W. J. , Cimbala J. M.
Published: April 2006

It is shown experimentally that a two-dimensional momentumless wake is strongly dependent on the jet injection configuration of the model. Namely, the decay rate of mean velocity overshoot ranged fromx−0.92tox−2.0for three different configurations, while the spreading rate ranged fromx0.3tox0.46for those same configurations. The magnitude of axial turbulence intensity was also found to depend on model configuration. On the other hand, the rate of decay of axial turbulence intensity was the same (x−0.81) for all three models. In all cases the mean shear and Reynolds stress decayed rapidly, leaving nearly isotropic turbulence beyond 30 or 40 model diameters.

Appropriate length- and velocity scales are identified which normalize the mean velocity profiles into self-similar form. The shape of the normalized profile, however, was different for each configuration, indicating again that the initial conditions are felt very far downstream.
The response of microscopic bubbles to sudden changes in the ambient pressure
Authors: Ran Bing , Katz Joseph
Published: April 2006

This paper focuses on the résponse of bubbles to sudden changes in the ambient pressure. Trains of bubbles with radii varying between 45 and 200 μm were exposed to various pressure steps, and their response was monitored by pulsed laser holography. The experiments were performed in a specially constructed chamber, allowing generation of pressure steps ranging from 0.1 to 20 times the initial value. Air, CO2, helium and hydrogen bubbles were selected, providing a range of mass, thermal diffusivities, solubilities in water and isentropic constants. The changes in the bubbles’ diameters were determined by reconstructing the holograms, magnifying the images and measuring the sizes of individual bubbles. Most of the experiments were performed with pressure changes at the rate of 20 KPa/ms, and most data were recorded in less than 20 ms. The results confirm that, within the present range of test conditions, the bubbles can respond instantaneously to changes in the ambient pressure. The experiments also demonstrate that the response of the bubbles at the present timescales can be assumed to be isothermal (polytropic constant of 1.0), irrespective of the bubble content or size. Repeated measurements with different pressure waveforms, but with the same final pressure resulted in identical results, demonstrating that bubbles can be used as pressure sensors. Variations in timescales up to a few hundred milliseconds still resulted in the same response, confirming the isothermal assumption. The dissolved gas content had a noticeable effect on the behaviour of the CO2 bubbles, the most soluble of the gases tested, and had no detectable effect on the behaviour of air bubbles. The paper also includes a detailed error evaluation of the present experiments and an estimate of the expected error when the bubbles are utilized as pressure sensors.
Screening in sedimenting suspensions
Authors: Koch Donald L. , Shaqfeh E. S. G.
Published: April 2006

Caflisch & Luke (1985) showed that, owing to the long range of the hydrodynamie interactions, the variance of the sedimentation velocity in a random suspension with uniform probability for the positions of the particles is divergent in the sense that it grows without bound as the macroscopic linear dimension of the settling vessel is increased. It is shown here, however, that a Debye-like screening of a particle's velocity disturbance, leading to a finite variance, will occur if the pair probability reflects a net deficit of one particle in the vicinity of each particle. The three-particle interactions, which determine the structure of a dilute, monodisperse suspension of spheres, lead to a deficit of neighbouring particles. The magnitude and range of this deficit are shown to be sufficient to lead to a Debye-like screening of the velocity disturbance at a radial distance of order aϕ−1, where a is the particle radius and ϕ their volume fraction. A self-consistent approximation to the screened conditional average velocity field and pair distribution is presented. The screening leads to a variance of the particle velocity and a particle tracer diffusion coefficient that are finite and of order Us2 and Usaϕ−1, respectively, where Vs is the Stokes settling velocity of the particles in unbounded fluid.
Natural convection in a mushy layer
Authors: Worster M. Grae
Published: April 2006

Governing equations for a mushy layer are analysed in the asymptotic regime Rm [Gt ] 1, where Rm is an appropriately defined Rayleigh number. A model is proposed in which there is downward flow everywhere in the mushy layer except in and near localized chimneys, which are characterized by having zero solid fraction. Upward, convective flow within the chimneys is driven by compositional buoyancy. The radius of each chimney is determined locally by thermal balances within a boundary layer that surrounds it. Simple solutions are derived to determine the structure of the mushy layer away from the immediate vicinity of chimneys in order to demonstrate the gross effects of convection upon the solidification within the layer.
Evolution and dynamics of shear-layer structures in near-wall turbulence
Authors: Johansson Arne V. , Alfredsson P. Henrik , Kim John
Published: April 2006

Near-wall flow structures in turbulent shear flows are analysed, with particular emphasis on the study of their space–time evolution and connection to turbulence production. The results are obtained from investigation of a database generated from direct numerical simulation of turbulent channel flow at a Reynolds number of 180 based on half-channel width and friction velocity. New light is shed on problems associated with conditional sampling techniques, together with methods to improve these techniques, for use both in physical and numerical experiments. The results clearly indicate that earlier conceptual models of the processes associated with near-wall turbulence production, based on flow visualization and probe measurements need to be modified. For instance, the development of asymmetry in the spanwise direction seems to be an important element in the evolution of near-wall structures in general, and for shear layers in particular. The inhibition of spanwise motion of the near-wall streaky pattern may be the primary reason for the ability of small longitudinal riblets to reduce turbulent skin friction below the value for a flat surface.
Hydrodynamic forces on a submerged cylinder advancing in water waves of finite depth
Authors: Wu G. X.
Published: April 2006

The hydrodynamic problem of a submerged horizontal cylinder advancing in regular water waves of finite depth at constant forward speed is analysed by the linearized velocity potential theory. The Green function is first derived. Far-field equations for calculating damping coefficients and exciting forces are obtained. The numerical method used combines a finite-element approximation of the potential in a region surrounding the cylinder with a boundary-integral-equation representation of the outer region. Numerical results for the hydrodynamic forces on submerged circular cylinders and elliptical cylinders are provided.
The spatial structure and statistical properties of homogeneous turbulence
Authors: Vincent A. , Meneguzzi M.
Published: April 2006

A direct numerical simulation at resolution 2403is used to obtain a statistically stationary three-dimensional homogeneous and isotropic turbulent field at a Reynolds number around 1000 (Rλ≈ 150). The energy spectrum displays an inertial subrange. The velocity derivative distribution, known to be strongly non-Gaussian, is found to be close to, but not, exponential. Thenth-order moments of this distribution, as well as the velocity structure functions, do not scale withnas predicted by intermittency models. Visualization of the flow confirms the previous finding that the strongest vorticity is organized in very elongated thin tubes. The width of these tubes is of the order of a few dissipation scales, while their length can reach the integral scale of the flow.
Double-diffusive instabilities at a sloping boundary
Authors: Kerr O. S.
Published: April 2006

When a body of fluid with a vertical salinity and temperature gradient is bounded by a sloping boundary, convective instabilities are often observed. These can occur if the fluid is subjected to heating or the addition of solute at the boundary, or if the boundary is an insulator. These instabilities often take the form of long thin convection cells that are almost horizontal. We present a linear stability analysis of the background states associated with these different boundary conditions and derive criteria for their stability in terms of one non-dimensional parameter, Q. This parameter is related to the Rayleigh number and is a generalization of the similar parameter found by Kerr (1989) in his study of heating a salinity gradient from a vertical boundary. This analysis uses a quasi-static assumption that is valid when the vertical lengthscales of the instabilities are less than the horizontal lengthscales.
Fluctuations in wall-shear stress and pressure at low streamwise wavenumbers in turbulent boundary-layer flow
Authors: Chase D. M.
Published: April 2006

Turbulent boundary-layer fluctuations in the incompressive domain are expressed in terms of fluctuating velocity-product 'sources’ in order to elucidate relative characteristics of fluctuating wall-shear stress and pressure in the subconvective range of streamwise wavenumbers. Appropriate viscous wall conditions are applied, and results are obtained to lowest order in this Strouhal-scaled wavenumber which serves as the expansion parameter. The spectral amplitudes of pressure and of the shear stress component directed along the wavevector both contain additive terms proportional to source integrals with exponential wall-distance weighting characteristic respectively of the irrotational and the rotational fields. At low wavenumbers, barring unexpected relative smallness of the pertinent boundary-layer source term, the rotational terms become dominant. There the wall pressure and shear-stress component have spectra that approach the same non-vanishing, wavevector-white but generally viscous-scale-dependent level and are totally coherent with phase difference ½π. The other, irrotational contributions to the shear-stress and pressure amplitudes likewise bear a simple and previously known, generally wavevector– and frequency-dependent, ratio to one another. In an inviscid limit this contribution to the pressure amplitude reduces to the one obtained previously from inviscid treatments. A representative class of models is introduced for the source spectrum, and the resulting rotational contribution to the spectral density of wall pressure andK-aligned shear stress at low (but incompressive) wavenumbers is estimated. It is suggested that this contribution may predominate and account for measured low-wavenumber levels of wall pressure.
Viscous flow in a channel with periodic cross-bridging fibres: exact solutions and Brinkman approximation
Authors: Tsay Ruey-Yug , Weinbaum Sheldon
Published: April 2006

A general solution of the three-dimensional Stokes equations is developed for the viscous flow past a square array of circular cylindrical fibres confined between two parallel walls. This doubly periodic solution, which is an extension of the theory developed by Lee & Fung (1969) for flow around a single fibre, successfully describes the transition in behaviour from the Hele-Shaw potential flow limit (aspect ratioB[Lt ] 1) to the viscous two-dimensional limiting case (B[Gt ] 1, Sangani & Acrivos 1982) for the hydrodynamic interaction between the fibres. These results are also compared with the solution of the Brinkman equation for the flow through a porous medium in a channel. This comparison shows that the Brinkman approximation is very good whenB> 5, but breaks down whenB[les ]O(1). A new interpolation formula is proposed for this last regime. Numerical results for the detailed velocity profiles, the drag coefficientf, and the Darcy permeabilityKpare presented. It is shown that the velocity component perpendicular to the parallel walls is only significant within the viscous layers surrounding the fibres, whose thickness is of the order of half the channel heightB′. One finds that when the aspect ratioB> 5, the neglect of the vertical velocity componentvzcan lead to large errors in the satisfaction of the no-slip boundary conditions on the surfaces of the fibres and large deviations from the approximate solution in Lee (1969), in whichvzand the normal pressure field are neglected. The numerical results show that the drag coefficient of the fibrous bed increases dramatically when the open gap between adjacent fibres Δ′ becomes smaller thanB′. The predictions of the new theory are used to examine the possibility that a cross-bridging slender fibre matrix can exist in the intercellular cleft of capillary endothelium as proposed by Curry & Michel (1980).
On the temporal instability of a two-dimensional viscous liquid sheet
Authors: Li Xianguo , Tankin R. S.
Published: April 2006

This paper reports a temporal instability analysis of a moving thin viscous liquid sheet in an inviscid gas medium. The results show that surface tension always opposes, while surrounding gas and relative velocity between the sheet and gas favour, the onset and development of instability. It is found that there exist two modes of instability for viscous liquid sheets – aerodynamic and viscosity-enhanced instability – in contrast to inviscid liquid sheets for which the only mode of instability is aerodynamic. It is also found that axisymmetrical disturbances control the instability process for small Weber numbers, while antisymmetrical disturbances dominate for large Weber numbers. For antisymmetrical disturbances, liquid viscosity, through the Ohnesorge number, enhances instability at small Weber numbers, while liquid viscosity reduces the growth rate and the dominant wavenumber at large Weber numbers. At the intermediate Weber-number range, Liquid viscosity has complicated effects due to the interaction of viscosity-enhanced and aerodynamic instabilities. In this range, the growth rate curve exhibits two local maxima, one corresponding to aerodynamic instability, for which liquid viscosity has a negligible effect, and the other due to viscosity-enhanced instability, which is influenced by the presence and variation of liquid viscosity. For axisymmetrical disturbances, liquid viscosity always reduces the growth rate and the dominant wavenumber, aerodynamic instability always prevails, and although the regime of viscosity-enhanced instability is always present, its growth rate curve does not possess a local maximum.
Mach reflection of a ring shock wave from the axis of symmetry
Authors: Barkhudarov E. M. , Mdivnishvili M. O. , Sokolov I. V. , Taktakishvili M. I. , Terekhin V. E.
Published: April 2006

The paper is devoted to the theoretical and experimental investigation of the ring (toroidal) shock wave near the axis of symmetry. The theoretical approach is based upon the Chester–Chisnell–Whitman method. The experimental toroidal shock wave is generated by a novel inducer and visualized by the shadow technique. Attention is paid to the manner of reflection of the shock wave from the axis of symmetry. This reflection appears to be irregular even at small distances from the centre of the ring. This phenomenon is due to the cumulative acceleration of the converging axisymmetric shock front near the axis. The acceleration results in an increase in the incidence angle up to that characteristic of Mach (irregular) reflection.
Experiments on transitional boundary layers with wake-induced unsteadiness
Authors: Liu X. , Rodi W.
Published: April 2006

Hot-wire measurements were carried out in boundary layers developing along a flat plate over which wakes passed periodically. The wakes were generated by cylinders moving on a squirrel cage in front of the plate leading edge. The flow situation studied is an idealization of that occurring on turbomachinery blades where unsteady wakes are generated by the preceding row of blades. The influence of wake-passing frequency on the boundary-layer development and in particular on the transition processes was examined. The hot-wire signals were processed to yield ensemble-average values and the fluctuations could be separated into periodic and stochastic turbulent components. Hot-wire traces are reported as well as time variations of periodic and ensemble-averaged turbulent fluctuations and of the boundary-layer integral parameters, yielding a detailed picture of the flow development. The Reynolds number was relatively low so that in the limiting case of a boundary layer undisturbed by wakes this remained laminar over the full length of the test plate. When wakes passed over the plate, the boundary layer was found to be turbulent quite early underneath the free-stream disturbances due to the wakes, while it remained initially laminar underneath the undisturbed free-stream regions in between. The turbulent boundary-layer stripes underneath the disturbed free stream travel downstream and grow together so that the embedded laminar regions disappear and the boundary layer becomes fully turbulent. The streamwise location where this happens moves upstream with increasing wake-passing frequency, and a clear correlation could be determined in the experiments. The results are also reported in a mean Lagrangian frame by following fluid parcels underneath the disturbed and undisturbed free stream, respectively, as they travel downstream.
Internal wave generation in uniformly stratified fluids. Part 1. Green's function and point sources
Authors: Voisin Bruno
Published: April 2006

In both Boussinesq and non-Boussinesq cases the Green's function of internal gravity waves is calculated, exactly for monochromatic waves and asymptotically for impulsive waves. From its differentiation the pressure and velocity fields generated by a point source are deduced. by the same method the Boussinesq monochromatic and impulsive waves radiated by a pulsating sphere are investigated.

Boussinesq monochromatic waves of frequency ω < N are confined between characteristic cones θ = arccos(ω/N) tangent to the source region (N being the buoyancy frequency and θ the observation angle from the vertical). In that zone the point source model is inadequate. For the sphere an explicit form is given for the waves, which describes their conical 1/r½ radial decay and their transverse phase variations.

Impulsive waves comprise gravity and buoyancy waves, whose separation process is non-Boussinesq and follows the arrival of an Airy wave. As time t elapses, inside the torus of vertical axis and horizontal radius 2Nt/β for gravity waves and inside the circumscribing cylinder for buoyancy waves, both components become Boussinesq and have wavelengths negligible compared with the scale height 2/β of the stratification. Then, gravity waves are plane propagating waves of frequency N cos θ, and buoyancy waves are radial oscillations of the fluid at frequency N; for the latter, initially propagating waves comparable with gravity waves, the horizontal phase variations have vanished and the amplitude has become insignificant as the Boussinesq zone has been entered. In this zone, outside the torus of vertical axis and horizontal radius Nta, a sphere of radius a [Lt ] 2/β is compact compared with the wavelength of the dominant gravity waves. Inside the torus gravity waves vanish by destructive interference. For the remaining buoyancy oscillations the sphere is compact outside the vertical cylinder circumscribing it, whereas the fluid is quiescent inside this cylinder.
A parametric acoustic instability in premixed flames
Authors: Searby G. , Rochwerger D.
Published: April 2006

We present an experimental and theoretical investigation of some aspects of the coupling between a premixed laminar quasi-planar flame front and acoustic standing waves in tubes. A multidimensional instability of the front arises from its interaction with the oscillating field of acceleration. This instability can be described by the Clavin–Williams laminar wrinkled flame theory in which the periodic acceleration created by the acoustic field is added to the acceleration due to gravity. As first suggested by Markstein, the resulting equation can be reduced to the Mathieu equation for a parametric oscillator. A cellular instability appears with a finite excitation threshold. This instability is responsible for the spontaneous generation of intense acoustic oscillations observed elsewhere. The value of the acoustic field at the threshold of instability and the wavelength of the cellular structures are measured experimentally for propane flames and are found to be in good agreement with the calculated values. It is also seen, both experimentally and theoretically, that for certain amplitudes of pumping, the parametric mechanism can also stabilize an initially unstable system.
Nonlinear instability of viscous plane Couette flow Part 1. Analytical approach to a necessary condition
Authors: Dubrulle Bérengére , Zahn Jean-Paul
Published: April 2006

We perform a two-dimensional analytical stability analysis of a viscous, unbounded plane Couette flow perturbed by a finite-amplitude defect and generalize the results obtained in the inviscid limit by Lerner and Knobloch. The dispersion relation is derived and is used to establish the condition of marginal stability, as well as the growth rates at different Reynolds numbers. We confirm that instability occurs at wavenumbers of the order of ε, the non-dimensional amplitude of the defect. For large enough εR (R being the Reynolds number based on the width of the defect), the maximum growth rate is about ½ε, at approximately half the critical wavenumber. We formulate the instability conditions in the case where the flow has a finite extension in the downstream direction. Instability appears when ε is greater than RL1/3, where RL is the Reynolds number based on the downstream scale, and when the ratio of the defect width to the downstream scale lies in the interval [(εRL}−½, ε].
The economic importance of freshwater crayfish harvesting in Madagascar and the potential of community-based conservation to improve management
Authors: Jones Julia P.G. , Andriahajaina Fortunat B. , Ranambinintsoa Emma H. , Hockley Neal J. , Ravoahangimalala Olga
Published: April 2006

Madagascar's endemic freshwater crayfish (Parastacidae: Astacoides) are harvested by local people for both subsistence use and small-scale trade. There has been concern that populations, and even species, are threatened by overexploitation but little is known about the harvest or its economic importance. We studied crayfish exploitation in eastern Madagascar over 3 years. The existence of local taboos (fady) preventing commercial crayfish harvesting, as well as access to markets and forest, influenced involvement in the harvest. All four crayfish species found in the region were harvested, but A. granulimanus provided the majority of the catch. In one harvesting village more than 50% of the 47 households were directly involved in the harvest, which contributed USD 2,382 to the village economy in 2003/2004, an important sum in the context of local incomes. Subsistence use was widespread, particularly by children to whom it may provide an important protein source. Community-based conservation (through transfer of harvesting rights and responsibilities for forest management to local communities) is central to a new conservation paradigm in Madagascar. This recognizes communities' long term interest in their natural resources and offers an ideal opportunity for those concerned with the sustainability of the harvest to implement management tools (such as avoiding reproductive females, size limits and no-take zones). We discuss each tool with respect to biological implications and practical constraints. We note that community-based approaches may not be sufficient to conserve rarer species, which make up a small proportion of the value of the harvest.
Introduction: Themed Section: Partnerships, Governance and Citizenship
Authors: Rummery Kirstein
Published: April 2006

The issue of ‘joined up’ governance and partnership working (between statutory partners, between the state and the voluntary sector and between the state and the private sector) is one which currently occupies the attention of policy makers and academics across mixed-liberal welfare states such as the European Union, Nordic, Commonwealth and North American welfare regimes (Geddes and Benington, 2001; Considine and Lewis, 2003; Bradford, 2003; Ovretveit, 2003). Many of these states, the UK included, are attempting to tackle the issues of growing demands for services, the perceived ineffectiveness and inefficiency of governments in responding to welfare need and the ‘hollowing out’ of the state that is a feature of modern mixed-liberal welfare states, particularly those which are attempting to find a ‘Third Way’ between socialist bureaucracies and market-driven liberalism (Giddens, 1998). The policy response, both in the UK and internationally, has been to encourage ‘partnership’ working between the various arms of the state, and between the state and the private and voluntary sector, as well as emphasizing ‘partnership’ working between the state and local users and communities.
Komorbidität der Aufmerksamkeitsdefizit-/Hyperaktivitätsstörung (ADHS) im Erwachsenenalter
Authors: Schmidt Sören , Brücher Klaus , Petermann Franz
Published: April 2006

Zusammenfassung: Der Verlauf der Aufmerksamkeitsdefizit-/Hyperaktivitätsstörung ist bereits in der Kindheit durch ein hohes Maß an komorbid auftretenden Störungen gekennzeichnet, was schon zu diesem Zeitpunkt hohe Anforderungen an den diagnostischen Prozess stellt. Betrachtet man die Symptomausprägung der ADHS im Erwachsenenalter, so sind hier einerseits vielfältige psychische Begleiterkrankungen zu verzeichnen, andererseits besteht eine hohe Symptomüberschneidung mit anderen Störungsbildern, wodurch eine eindeutige Diagnose häufig erschwert wird. Für die Diagnostik der ADHS im Erwachsenenalter ergibt sich demnach folgende Konsequenz: Außer den neuropsychologischen Beeinträchtigungen müssen Probleme auf der sozialen und Verhaltensebene erfasst werden, um eine möglichst valide Aussage über die individuelle Symptomausprägung und die differenzialdiagnostische Abgrenzung zu ermöglichen. Es wird ein Ausblick auf das neu entwickelte “Bremer ADHS-Screening für Erwachsene” (BAS-E) gegeben, mit dem die genannten Bereiche erfasst sowie retrospektiv ADHS-Symptome in der Kindheit abgefragt werden. Eine Zusatzskala ermöglicht die quantitative und qualitative (Selbstmedikation) Erfassung des Alkohol-, Drogen- und Medikamentenkonsums, was sowohl für den weiteren diagnostischen Prozess als auch für die Therapieplanung von Bedeutung ist.
Efflux of Drugs and Solutes from Brain: The Interactive Roles of Diffusional Transcapillary Transport, Bulk Flow and Capillary Transporters
Authors: Groothuis Dennis R , Vavra Michael W , Schlageter Kurt E , Kang Eric W-Y , Itskovich Andrea C , Hertzler Shannon , Allen Cathleen V , Lipton Howard L
Published: April 2006

We examined the roles of diffusion, convection and capillary transporters in solute removal from extracellular space (ECS) of the brain. Radiolabeled solutes (eight with passive distribution and four with capillary or cell transporters) were injected into the brains of rats ( n = 497) and multiple-time point experiments measured the amount remaining in brain as a function of time. For passively distributed compounds, there was a relationship between lipid:water solubility and total brain efflux:diffusional efflux, which dominated when kp, the transcapillary efflux rate constant, was >100h−1; when 10−1< kp< 10−2h−1both diffusion and convection contributed, and when kp< 10−3h−1, convective efflux dominated. Para-aminohippuric acid (PAH) experiments ( n = 112) showed that PAH entered the brain passively, but had efflux transporters. The total efflux rate constant, keff, was the sum of a passive component (kp= 0.0018 h−1), a convective component ( kcsf= 0.2 h−1), and a variable, concentration-dependent component ( kx= 0 to 0.45 h−1). Compounds with cell membrane transporters had longer clearance half times as did an oligonucleotide, which interacted with cell surface receptors. Manipulation of physiologic state ( n = 35) did not affect efflux, but sucrose efflux half time was longer with pentobarbital anesthesia (24 h) than with no anesthesia or ketamine-xylazine anesthesia (2 to 3 h). These results show that solute clearance from normal brain ECS may involve multiple physiologic pathways, may be affected by anesthesia, and suggests that convection-mediated efflux may be manipulated to increase or decrease drug clearance from brain.
Simultaneous investigation of sedimentation and diffusion of a single colloidal particle near an interface
Authors: Oetama Ratna J. , Walz John Y.
Published: April 2006

We describe here a new procedure for the simultaneous investigation of sedimentation and diffusion of a colloidal particle in close proximity to a solid, planar wall. The measurements were made using the optical technique of total internal reflection microscopy, coupled with optical radiation pressure, for dimensionless separation distances (gap width/radius of particle) ranging from 0.01 to 0.05. In this region, the hydrodynamic mobility and diffusion coefficient are substantially reduced below bulk values. The procedure involved measuring the mean and the variance of vertical displacements of a Brownian particle settling under gravity toward the plate. The spatially varying diffusion coefficient was calculated from the displacements at small times (where diffusive motion was dominant). The mobility relationship for motion normal to a flat plate was tested by measuring the average distance of travel versus time as the particle settled under the constant force of gravity. For the simple Newtonian fluid used here (aqueous salt solution), the magnitude of the diffusion coefficient and mobility, plus their dependence on separation distance, showed excellent agreement with predictions. This new technique could be of great value in measuring the mobility and diffusion coefficient for near-contact motion in more complex fluids for which the hydrodynamic correction factors are not known a priori, such as shear-thinning fluids.
Primary and secondary relaxations in supercooled eugenol and isoeugenol at ambient and elevated pressures: Dependence on chemical microstructure
Authors: Kaminska E. , Kaminski K. , Paluch M. , Ngai K. L.
Published: April 2006

Dielectric loss spectra of two glass-forming isomers, eugenol and isoeugenol, measured at ambient and elevated pressures in the normal liquid, supercooled, and glassy states are presented. The isomeric chemical compounds studied differ only by the location of the double bond in the alkyl chain. Above the glass transition temperature Tg, the dielectric loss spectra of both isomers exhibit an excess wing on the high frequency flank of the loss peak of the α relaxation and an additional faster γ process at the megahertz frequency range. By decreasing temperature below Tg at ambient pressure or by elevating pressure above Pg, the glass transition pressure, at constant temperature, the excess wing of isoeugenol shifts to lower frequencies and is transformed into a secondary β-loss peak, while in eugenol it becomes a shoulder. These spectral features enable the β-relaxation time τβ to be determined in the glassy state. These changes indicate that the excess wings in isoeugenol and eugenol are similar and both are secondary β relaxations that are not resolved in the liquid state. While in both isoeugenol and eugenol the loss peak of the β relaxation in the glassy state and the corresponding excess wing in the liquid state shifts to lower frequencies on elevating pressure, the locations of their γ relaxation show little change with increasing pressure. The different pressure sensitivities of the excess wing and γ relaxation are further demonstrated by the nearly perfect superposition of the α-loss peak together with excess wing from the data taken at ambient pressure and at elevated pressure (and higher temperature so as to have the same α-peak frequency), but not the γ-loss peak in both isoeugenol and eugenol. On physical aging isoeugenol, the β-loss peak shifts to lower frequencies, but not the γ relaxation. Basing on these experimental facts, the faster γ relaxation is a local intramolecular process involving a side group and the slower β relaxation mimics the structural α relaxation in behavior, involves the entire molecule and satisfies the criteria for being the Johari-Goldstein β relaxation. Analysis and interpretation of the spectra utilizing the coupling model further demonstrate that the excess wings seen in the equilibrium liquid states of these two isomers are their genuine Johari-Goldstein β relaxation.
A fluid approach to linear beam plasma electromagnetic instabilities
Authors: Bret A. , Deutsch C.
Published: April 2006

Electromagnetic instabilities found for an arbitrary oriented wave vector are typically difficult to investigate analytically within the framework of kinetic theory. The case of a small density relativistic electron beam interacting with a plasma is considered, and a two-fluid theory of the system including a kinetic pressure tensor is developed. The model obtained agrees very well with temperature effects found on oblique instabilities from a kinetic model, and the respective roles of parallel and transverse beam temperatures are correctly reproduced. An analysis of the phase velocities of the unstable waves allows for an explanation of this similarity. Such a formalism could be used to study oblique instabilities in settings where kinetic theory becomes problematic to implement.
Size dependence of Zn 2p 3∕2 binding energy in nanocrystalline ZnO
Authors: Tay Y. Y. , Li S. , Sun C. Q. , Chen P.
Published: April 2006

The experimental results in size dependence of electronic structure and optical band gap show that the nanocrystalline ZnO has two binding states which energies are lower than that of the bulk ZnO. This size dependence of binding states is associated with the number of broken bonds of the individual Zn ion, which could be modified by size reduction in nanoscale. Varying the number of broken bonds on the surface and the underneath layer might result in possible complications in the electronic structure of the nanocrystalline ZnO, thus giving rise to different optical properties rather than those relating to quantum size effects.
Enhanced critical currents through field compensation with magnetic strips
Authors: Morelle M. , Moshchalkov V. V.
Published: April 2006

We have studied a system consisting of a superconducting Al strip placed close to a perpendicularly magnetized Co∕Pd rectangle. The stray fields of the rectangle produce a nonhomogeneous magnetic field in the superconductor. These stray fields can efficiently compensate the self-field inside the current-carrying superconductor. We have observed a current-polarity dependence of the critical current. The compensation effects are strongly dependent on the current in the superconductor and also on the temperature. The studied configuration is easily tunable for a large range of applied currents.
Spectroscopic study of debris mitigation with minimum-mass Sn laser plasma for extreme ultraviolet lithography
Authors: Namba S. , Fujioka S. , Nishimura H. , Yasuda Y. , Nagai K. , Miyanaga N. , Izawa Y. , Mima K. , Takiyama K.
Published: April 2006

An experimental study was made of a target consisting of the minimum mass of pure tin (Sn) necessary for the highest conversion to extreme ultraviolet (EUV) light while minimizing the generation of plasma debris. The minimum-mass target comprised a thin Sn layer coated on a plastic shell and was irradiated with a Nd:YAG laser pulse. The expansion behavior of neutral atoms and singly charged ions emanating from the Sn plasma were investigated by spatially resolved visible spectroscopy. A remarkable reduction of debris emission in the backward direction with respect to the incident laser beam was demonstrated with a decrease in the thickness of the Sn layer. The optimal thickness of the Sn layer for a laser pulse of 9ns at 7×1010W∕cm2 was found to be 40nm, at which low-debris emission in the backward direction and a high conversion to 13.5nm EUV radiation were simultaneously attained.
Geographic Regional Differences in Rocuronium Bromide Dose–Response Relation and Time Course of Action
Authors: Dahaba Ashraf A. , Perelman Seth I. , Moskowitz David M. , Bennett Henry L. , Shander Aryeh , Xiao Zhaoyang , Huang Lin , An Gang , Bornemann Helmar , Wilfinger Georg , Hager Barbara , Rehak Peter H. , List Werner F. , Metzler Helfried
Published: April 2006

Background

Geographic location is not acknowledged as a stratifying factor that can directly affect drug potency, because drugs are still licensed with the same recommended dose for different geographic regions. The aim of the current study was to compare the potency and duration of action of rocuronium bromide in 54 patients in three countries with different life habits, diet, and ambient conditions, namely white Austrians, white North Americans, and Han Chinese in China.

Methods

Neuromuscular block of six consecutive 50-microg/kg rocuronium incremental doses followed by 300 microg/kg was evaluated using the Relaxometer mechanomyograph (Groningen University, Groningen, Holland). Dose-response curves were created using log-dose-probit transformation. The authors compared rocuronium bromide ED50, ED90, and ED95 (effective doses required for 50%, 90%, and 95% first twitch depression, respectively) as well as Dur25 and Dur0.8 (times from last incremental dose administration until 25% first twitch and 0.8 train-of-four ratio recovery, respectively) in patients of the three countries.

Results

Rocuronium ED50, ED90, and ED95 were significantly higher in Austrian patients (258 +/- 68, 530 +/- 159, and 598 +/- 189 microg/kg) and Chinese patients (201 +/- 59, 413 +/- 107, and 475 +/- 155 microg/kg) compared with American patients (148 +/- 48, 316 +/- 116, and 362 +/- 149 microg/kg, respectively). Dur25 and Dur0.8 were significantly shorter in Austrian patients (22.3 +/- 5.5 and 36.9 +/- 12.8 min) and Chinese patients (30.4 +/- 7.5 and 45.7 +/- 15.9 min) compared with American patients (36.7 +/- 8.5 and 56.2 +/- 16.7 min, respectively).

Conclusions

The authors demonstrated a significant difference in rocuronium potency and duration of action among patients in the three countries. Larger studies are required for determining dosage recommendations for different geographic regions.
Propofol Decreases Myofilament Ca2+Sensitivity via a Protein Kinase C–, Nitric Oxide Synthase–dependent Pathway in Diabetic Cardiomyocytes
Authors: Wickley Peter J. , Shiga Toshiya , Murray Paul A. , Damron Derek S.
Published: April 2006

Background

The authors' objective was to assess the role of protein kinase C (PKC) and nitric oxide synthase (NOS) in mediating the effects of propofol on diabetic cardiomyocyte contractility, intracellular free Ca2+ concentration ([Ca2+]i), and myofilament Ca2+ sensitivity.

Methods

Freshly isolated ventricular myocytes were obtained from normal and diabetic rat hearts. [Ca2+]i and cell shortening were simultaneously measured in electrically stimulated, ventricular myocytes using fura-2 and video-edge detection, respectively. Actomyosin adenosine triphosphatase activity and troponin I (TnI) phosphorylation were assessed in [32P]orthophosphate-labeled myofibrils. Western blot analysis was used to assess expression of PKC and NOS.

Results

Propofol (10 microM) decreased peak shortening by 47 +/- 6% with little effect on peak [Ca2+]i (92 +/- 5% of control) in diabetic myocytes. Maximal actomyosin adenosine triphosphatase activity was reduced by 43 +/- 7% and TnI phosphorylation was greater (32 +/- 6%) in diabetic myofibrils compared with normal. Propofol reduced actomyosin adenosine triphosphatase activity by 17 +/- 7% and increased TnI phosphorylation in diabetic myofibrils. PKC inhibition prevented the propofol-induced increase in TnI phosphorylation and decrease in shortening. Expression of PKC-alpha, PKC-delta, PKC-epsilon, and constitutive NOS were up-regulated and inducible NOS was expressed in diabetic cardiomyocytes. NOS inhibition attenuated the propofol-induced decrease in shortening.

Conclusion

Myofilament Ca2+ sensitivity and, to a lesser extent, peak [Ca2+]i are decreased in diabetic cardiomyocytes. Increases in PKC and NOS expression in combination with TnI phosphorylation seem to contribute to the decrease in [Ca2+]i and myofilament Ca2+ sensitivity. Propofol decreases [Ca2+]i and shortening via a PKC-, NOS-dependent pathway.
Long‐Term Clinical Outcome in Patients With Congenital Chloride Diarrhea
Authors: Hihnala Satu , Höglund Pia , Lammi Laura , Kokkonen Jorma , Örmälä Timo , Holmberg Christer
Published: April 2006

Objectives:

Congenital chloride diarrhea (CLD) is a rare, autosomal recessive disorder of intestinal Cl−/HCO3− exchange caused by mutations in the SLC26A3 gene and characterized by persistent Cl− rich diarrhea from birth. Treatment is symptomatic and replacement therapy with NaCl and KCl has been shown to be effective in children, but the long‐term prognosis remains unclear. We studied the largest known cohort of patients to evaluate the long‐term outcome of CLD and to search for extraintestinal manifestations.

Methods:

This is a cross‐sectional clinical evaluation and retrospective analysis of medical history of 36 Finnish patients with CLD, born in the 1960s (n = 8), 1970s (n = 7) and 1980s (n = 21).

Results:

Early diagnosis and aggressive salt replacement therapy were associated with normal growth and development, in addition to significantly reduced mortality rates among the groups of patients born in the different decades, respectively (P = 0.001). No deaths due to CLD were observed after 1972. Enuresis, slight soiling and hospitalizations for gastroenteritis were common, especially in childhood, but 92% of the patients found their health excellent or good. Complications documented were end‐stage renal disease (n = 1) and hyperuricemia (n = 4), novel findings possibly associated with CLD being male subfertility (n = 3), spermatoceles (n = 3), intestinal inflammation (n = 2), inguinal hernias (n = 4) and increased concentrations of sweat Cl− in 12% of the patients.

Conclusions:

When early diagnosed and adequately treated, the long‐term prognosis of CLD is favorable. A putative role of a primary anion exchange defect of SLC26A3 in male subfertility and the decline of renal function due to chronic dehydration deserve further characterization.
Systemic Vasculitis
Authors: Brogan P. A. , Malik M. , Shah N. , Kilday J. P. , Ramsay A. , Shah V. , Murch S. H. , Thomson M. A. , Walker‐Smith J. A. , Lindley K. J. , Milla P J. , Dillon M. J.
Published: April 2006

Objectives:

Indeterminate intestinal inflammation may result from a variety of inflammatory conditions in addition to ulcerative colitis and Crohn disease. The primary systemic vasculitides may present with intestinal inflammation and an indeterminate colitis. We set out to describe a series of children with primary systemic vasculitis who initially presented with clinical features suggestive of inflammatory bowel disease (IBD) to establish criteria that might help discriminate between IBD and primary systemic vasculitis.

Methods:

Ten children (6 boys, median age at presentation 8.9 years, range 0.9‐14.5 years) satisfied inclusion criteria.

Results:

All had abdominal pain, weight loss, diarrhea (6 of 10 bloody) and laboratory evidence of a severe acute phase response. Extraintestinal clinical features included vasculitic rash, renal impairment, myalgia, testicular pain and polyarthritis. Endoscopy showed vascular changes or other macroscopic findings suggestive of vasculitis in 5 of 10 patients. Gut histology revealed indeterminate chronic inflammatory mucosal changes and one patient with small artery fibrinoid necrosis in the submucosal vessels. Extraintestinal biopsy was performed in 6 patients and had a higher yield for the demonstration of vasculitis than intestinal biopsy. The results of selective visceral angiography was suggestive of vasculitis in all patients, but was normal in 7 cases of treatment‐unresponsive classic IBD. Treatment comprised corticosteroid and azathioprine in all patients. Cyclophosphamide was given to 7 of 10 patients.

Conclusions:

Extraintestinal manifestations and inflammatory responses that may be disproportionate to the degree of intestinal inflammation provide clues to the presence of an underlying primary systemic vasculitis, and these data suggest that selective visceral angiography plays a key role in the diagnosis of vasculitis in this context. It is important to identify and treat any vasculitic component because failure to do so may result in consequential morbidity or mortality.