bluuebunny/crossref_metadata_2025 huggingface dataset:
The linear stability of the flow in a narrow spherical annulus
Authors: Walton I. C.
Published: April 2006

The flow of a fluid in a narrow spherical annulus is considered. When the outer sphere remains fixed and the angular velocity of the inner one is increased beyond a critical value an instability resembling Taylor vortices appears. This instability is investigated by expanding the solution in powers of the small parameter ε, the ratio of the gap thickness to the radius, and assuming that two length scales, O(1) and O(ε), are important in the latitudinal direction.

The perturbation then takes the form of cells which are of roughly square cross-section, at least near the equator, but whose amplitude decays rapidly with latitude; it is also subject to a slow spatial modulation. The critical value of the Taylor number at which the instability first appears is shown to be that for infinite concentric cylinders plus a correction O(ε) due to secondary motions and a correction not greater than O(ε) due to the domain being bounded.
On Itoh's finite amplitude stability theory for pipe flow
Authors: Davey A.
Published: April 2006

In two recent papers Itoh has developed a finite amplitude stability theory which indicates that nonlinearity increases the damping rate of a small but finite amplitude disturbance to flow in a circular pipe when the disturbance is concentrated near the axis of the pipe. For such a centre mode, which is the only mode considered by Itoh, Davey & Nguyen found, in an earlier paper, the opposite result that nonlinearity decreases the damping rate. We examine the reasons for this discrepancy and we explain the subtle difference between Itoh's method and the method of Reynolds & Potter, which was used by Davey & Nguyen.

We suggest that for the centre mode of pipe flow neither Itoh's result nor Davey & Nguyen's result is a reliable guide to the true situation. However, for the wall mode of pipe flow, and especially for plane Couette flow, both methods give very similar results and we suggest that this similarity indicates that in these cases the damping rate is decreased by nonlinearity. For a particular problem we believe that it is only when the results of the two methods are very similar that either method is likely to be useful.
Fluid transport by cilia between parallel plates
Authors: Liron N.
Published: April 2006

The problem of fluid transport by cilia is investigated using the Green's function for a Stokeslet between two parallel plates. The discrete-cilia approach is used in building the model, and a readily usable expression for the velocities is obtained. Dependence on the direction of the metachronal wave and on time is not averaged out. Velocity fields, pressure fields and fluxes due to a single Stokeslet and to an infinite line of Stokeslets are discussed. It is found that the flux associated with Stokeslets in between two parallel plates is always zero, in contrast to a Stokeslet parallel to, and above, one plate. In the model one also has to add a plane Poiseuille flow, which incorporates non-zero flux. The flow due to the Stokeslet solution imposes a positive pressure gradient downstream, and the Poiseuille flow a negative pressure gradient. Calculated velocity profiles, in the pumping range, are seen to be time-independent in the centre of the channel and vary between a negative parabolic profile and a plug flow. The reason for these profiles and some possible biological applications are discussed.
Stokes flow due to a Stokeslet in a pipe
Authors: Liron N. , Shahar R.
Published: April 2006

Velocity and pressure fields for Stokes flow due to a force singularity (Stokeslet) of arbitrary orientation and at arbitrary location inside an infinite circular pipe are obtained. Two alternative expressions for the solution, one in terms of a Fourier-Bessel type expansion, and the other as a doubly infinite series, are given. The latter is especially suitable for computational purposes as it is shown to be an exponentially decaying series. From the series it is found that all velocity components decay exponentially to zero up- or downstream away from the Stokeslet. This is also true for pressure fields of Stokeslets perpendicular to the axis of the pipe. A Stokeslet parallel to the axis of the pipe raises the pressure difference between − ∞ to + ∞ by a finite non-zero amount. Some numerical results for a Stokeslet parallel to the axis are given. Comparison of the results with flow in a two-dimensional channel is also discussed.
Calculation of axisymmetric jets and wakes with a three-equation model of turbulence
Authors: Biringen Sedat
Published: April 2006

The concept of diffusion by bulk convection formulated by Bradshaw is applied to the transport equations for the turbulent kinetic energy, turbulent shear stress and an integral length scale. The resulting set of hyperbolic partial differential equations is solved by an explicit finite-difference scheme for the cases of incompressible axisymmetric wakes and jets in a coflowing air stream. It is found that the profiles of mean velocity and shear stress are almost insensitive to the empirical input whereas the profiles of kinetic energy are very sensitive.
A depth-averaged mathematical model for the near field of side discharges into open-channel flow
Authors: Mcguirk J. J. , Rodi W.
Published: April 2006

A two-dimensional mathematical model is described for the calculation of the depth-averaged velocity and temperature or concentration distribution in open-channel flows, an essential feature of the model being its ability to handle recirculation zones. The model employs the depth-averaged continuity, momentum and temperature/concentration equations, which are solved by an efficient finite-difference procedure. The ‘rigid lid’ approximation is used to treat the free surface. The turbulent stresses and heat or concentration fluxes are determined from a depth-averaged version of the so-calledk, ε turbulence model which characterizes the local state of turbulence by the turbulence kinetic energykand the rate of its dissipation ε. Differential transport equations are solved forkand ε to determine these two quantities. The bottom shear stress and turbulence production are accounted for by source/sink terms in the relevant equations. The model is applied to the problem of a side discharge into open-channel flow, where a recirculation zone develops downstream of the discharge. Predicted size of the recirculation zone, jet trajectories, dilution, and isotherms are compared with experiments for a wide range of discharge to channel velocity ratios; the agreement is generally good. An assessment of the numerical accuracy shows that the predictions are not influenced significantly by numerical diffusion.
Oblique instability of periodic waves in shallow water
Authors: Bryant P. J.
Published: April 2006

Periodic permanent waves in shallow water are stable to periodic disturbances in the same direction, but are unstable to certain oblique periodic disturbances. A computer-assisted stability analysis is made of such waves for oblique disturbances with wavelengths comparable to and long compared with the fundamental wavelength. Regions of instability are calculated, and an explanation is given for the occurrence of instability. It is shown that disturbances in the same direction with a small margin of stability may cause a greater modification to the permanent wave in practice than do oblique unstable disturbances.
The effects of eccentricity on torque and load in Taylor-vortex flow
Authors: Eagles P.M. , Stuart J. T. , Diprima R. C.
Published: April 2006

This paper extends two earlier papers in which DiPrima & Stuart calculated first (1972b) the critical Taylor number to order ε2, where the eccentricity ε is proportional to the displacement of the axes of the circular cylinders, and second (1975) the torque and load to order ε associated with nonlinear effects of Taylor vortices. In the latter paper, it was shown that to order ε the torque arising from the Taylor vortices is identical with that for the concentric problem, which was first calculated, by a perturbation method, by Davey (1962). This deficiency is remedied in the present paper, where the calculation is taken to order ε2. It is found that, as ε rises, the torque associated with the Taylor vortices falls slightly when we keep constant the percentage elevation of the Taylor number above the ε-dependent critical value. This result is in accordance with experimental observations by Vohr (1967, 1968). In addition, results of calculations of the pressure field developed by the Taylor-vortex flow in association with the eccentric geometry are presented; this is larger than in the concentric case owing to a Reynolds lubrication effect. Also given are the associated components of the load on the inner cylinder, but only for Taylor numbers close to the critical value.

One additional observation by Vohr, for cylinders with a mean ratio of the gap to the inner radius of 0·099, was that the maximum Taylor-vortex strength with ε = 0·475 occurred some 50° downstream of the maximum gap for a 20% elevation of the Taylor number above the critical value. Calculations in the two earlier papers (1972b, 1975) gave 90 and 76°, respectively, for that angle. Note that in the 1975 paper a geometrical correction of order ε was included. Here, with an additional modification of order ε due to the flow, this result is improved to 49° by the extended analysis presented, although the ‘small’ parameters are somewhat outside the range for which perturbation theory is expected to be valid.
On the stability of flow in an elliptic pipe which is nearly circular
Authors: Davey A.
Published: April 2006

The linear stability of Poiseuille flow in an elliptic pipe which is nearly circular is examined by regarding the flow as a perturbation of Poiseuille flow in a circular pipe. We show that the temporal damping rates of non-axisymmetric infinitesimal disturbances which are concentrated near the wall of the pipe are decreased by the ellipticity. In particular we estimate that if the length of the minor axis of the cross-section of the pipe is less than about 96 ½% of that of the major axis then the flow will be unstable and a critical Reynolds number will exist. Also we calculate estimates of the ellipticities which will produce critical Reynolds numbers ranging from 1000 upwards.
Magnetic flux ropes and convection
Authors: Galloway D. J. , Proctor M. R. E. , Weiss N. O.
Published: April 2006

Three-dimensional cellular convection concentrates magnetic flux into ropes when the magnetic Reynolds number is large. Amplification of the magnetic field is limited by the Lorentz force and the maximum field in a flux rope can be estimated. Boundary-layer analysis yields a completely self-consistent solution for a model of convection driven by imposed horizontal temperature gradients, and the transition from a kinematic to a dynamic regime can be followed in detail. The maximum value of the amplified field is proportional to the square root of the ratio of the viscous to the magnetic diffusivity.
The film drainage problem in droplet coalescence
Authors: Jones A. F. , Wilson S. D. R.
Published: April 2006

A small drop of liquid 1 falls through a less dense liquid 2 and approaches the horizontal interface between liquid 2 and an underlying layer of liquid 1. After a short time the drop will be brought to rest (or nearly) in a hollow in the interface. Before the drop can coalesce with its bulk phase, the thin film of liquid 2 trapped between them must be squeezed out, and become sufficiently thin that rupture can occur. This is the film drainage problem. Early calculations, based on simple lubrication theory, fail to take proper account of two effects which are investigated here and shown to be decisive. They are the circulation induced in the drop and in the lower bulk fluid, which tends to speed up drainage, and the constriction in the film thickness at its periphery, which tends to slow it down. This constriction has been observed and some existing theories have attempted to model it in an ad hoc manner. We give here a physical explanation and calculate the minimum thickness explicitly. The effect of circulation in the adjacent fluids is also calculated.
Stability of thin, radially moving liquid sheets
Authors: Weihs Daniel
Published: April 2006

An analysis of the stability of thin viscous liquid sheets, such as those emitted from industrial spraying nozzles, is presented. These sheets are in the form of a circular sector whose thickness reduces as the distance from the nozzle increases.

The Kelvin-Helmholtz type of instability usually observed causes the breakup and atomization of the sheet, as required in most industrial spraying processes. Waviness, like that of a flapping flag, is produced and increasing amplitudes finally cause breakup.

An analytical solution in the form of hypergeometric functions for the shape of the sheet and the waves is obtained. This solution includes, as special cases, analyses existing in the literature, in addition to establishing the possibility of a new type of instability dependent on the distance from the nozzle. Also, the classical type of instability, in which the waves increase with time, is examined and relations for unstable waves as a function of parameters such as the fluid viscosity, surface tension and sheet velocity are obtained. It is shown that there is no single wave that has a maximum growth rate, but that the wavenumber for maximum instability increases with the distance from the nozzle orifice.
A note on nonlinear acoustic resonances in rectangular cavities
Authors: Keller Jakob J.
Published: April 2006

The problem of the resonant response of a gas contained in a two-dimensional rectangular cavity to periodic (sinusoidal) velocity excitations at the walls of the cavity is investigated. It is found that in some neighbourhood of each resonant frequency there are discontinuous pressure disturbances (shock waves). The present theory is an extension of Chester's theory on resonances in closed tubes.
Two-dimensional turbulence on the surface of a sphere
Authors: Tang Cha-Mei , Orszag Steven A.
Published: April 2006

Large-scale atmospheric flow shares certain attributes with two-dimensional turbulence. In this paper, we study the effect of spherical geometry on two-dimensional turbulence.

Energy transfer is multi-component in spherical geometry in contrast to energy transfer among triads of wave vectors in Cartesian geometry. It follows that energy transfer is more local in spherical than in Cartesian geometry. Enstrophy transfer to higher wavenumbers in spherical geometry is less than enstrophy transfer to higher wavenumbers in Cartesian geometry. Since both energy and enstrophy are inviscid constants of motion, the back transfer of energy is also less in spherical than in Cartesian geometry. Therefore, with a finite viscosity, enstrophy decays more slowly in spherical geometry than in Cartesian geometry. Here these conjectures are tested numerically by spectral methods. The numerical results agree well with the conjectures.
Stability of plane Poiseuille flow of a dilute suspension of slender fibres
Authors: Bark Fritz H. , Tinoco Hernán
Published: April 2006

The linear hydrodynamic stability problem for plane Poiseuille flow of a dilute suspension of rigid fibres is solved numerically. The constitutive equation given by Batchelor (1970a, b, 1971) is used to model the rheological properties of the suspension. The resulting eigenvalue problem is shown to be singular. The appropriate contour in the complex plane is determined by considering an initial-value problem. It is shown that, for a fixed, but not too large, inclination of the wave front to the mean flow, the fibres cause the critical Reynolds number to increase monotonically with the product of the volume fraction of the fibres and the square of their aspect ratio. The stabilizing influence of the fibres seems to vanish for large wave inclination angles.
Hydrodynamic pressures on sloping dams during earthquakes. Part 1. Momentum method
Authors: Chwang Allen T. , Housner George W.
Published: April 2006

Von Kármán's momentum-balance method is adopted to investigate the earthquake forces on a rigid dam with an inclined upstream face of constant slope. The distribution of the hydrodynamic pressure along the upstream face is determined. It is found that the maximum hydrodynamic pressure occurs at the base of the dam for any inclination angle between 0 and 90°. Explicit analytical formulae for evaluating the total horizontal, vertical and normal loads are presented and a useful approximate rule for practical engineers is given.
Hydrodynamic pressures on sloping dams during earthquakes. Part 2. Exact theory
Authors: Chwang Allen T.
Published: April 2006

The equations for the earthquake forces on a rigid dam with an inclined upstream face of constant slope are solved exactly by two-dimensional potential-flow theory. The distribution of the hydrodynamic pressure along the upstream face and the total horizontal, vertical and normal loads on the dam are computed from the integral solutions. The results obtained from the exact theory are compared with those derived from the momentum-balance method and there is reasonable agreement.
The free shear layer tone phenomenon and probe interference
Authors: Hussain A. K. M. F. , Zaman K. B. M. Q.
Published: April 2006

Free shear layer stability measurements with a hot wire revealed that the probe itself can trigger and sustain upstream instability modes like the slit jet-wedge edge tones. The flow fields associated with the free shear layer tones induced in axisym-metric and plane air shear layers by a hot-wire probe and by a plane wedge were then explored experimentally, and found to be different in many ways from the widely investigated jet edge tone phenomenon.

As many as four frequency stages have been identified, there being a fifth stage associated with the subharmonic attributed to vortex pairing in the free shear layer. No evidence of hysteresis could be found in the shear layer tone. In the interstage jump (i.e. bimodal) regions, the tone occurred in only one mode at a time while intermittently switching from one to the other. Frequency variations in each stage are shown to collapse on a single curve when non-dimensionalized with the initial momentum thickness θeor with the lip-wedge distanceh, and plotted as a function ofh/θe.

Phase average measurements locked onto the tone fundamental show that the phase velocity and wavelength of the tone-induced velocity fluctuation are essentially independent of the stage of tone generation; in each stage, both phase velocity and wavelength decrease with increasing frequency but undergo jumps at starts of new stages. The measured amplitude and phase profiles, as well as the variations of the shear tone wavenumber and phase velocity with the Strouhal number, show reasonable agreement with the predictions of the spatial stability theory. The wavelength λ bears a unique relation toh, thish, δ relation being different from the Brown-Curle equation for the jet edge tone.

Shear layer tones would be typically induced in near-field shear layer measurements involving invasive probes, and can produce misleading results. A method for determining the true free shear layer natural instability frequency is recommended.
On the existence of three-dimensional convection in a rectangular box containing fluid-saturated porous material
Authors: Straus Joe M. , Schubert Gerald
Published: April 2006

On the basis of a stability analysis of finite amplitude, two-dimensional convection, we have determined the dimensions of boxes containing fluid-saturated porous material in which convection is necessarily unsteady or steady and three-dimensional. For certain box sizes, convective rolls are unstable at Rayleigh numbers Ra lower than 380, the value below which rolls are stable forms of convection between infinite parallel planes. For Ra = 100 and 200, it appears unlikely that there are any box dimensions for which there is not a stable (possibly multicellular) two-dimensional steady motion. At Ra = 340 and 400, boxes in which rolls are unstable have heights which range from one to five times their horizontal dimensions.
The steady flow of closely fitting incompressible elastic spheres in a tube
Authors: Tözeren Hüsnü , Skalak Richard
Published: April 2006

The steady flow of a suspension of closely fitting, neutrally buoyant, incompressible and elastic spheres through a circular cylindrical tube is investigated under the assumption that lubrication theory is valid in the fluid region. A series solution giving the displacement field of an elastic incompressible sphere under axisymmetrically distributed surface tractions is developed. It is found that, for closely fitting particles, flow properties of the suspension are strongly dependent on the shear modulus of the elastic material and the velocity of the particle.
Interpretation of three-soliton interactions in terms of resonant triads
Authors: Anker D. , Freeman N. C.
Published: April 2006

The three-soliton solution of the two-dimensional Korteweg-de Vries equation is analysed to show that the structure of the interaction can be represented in terms of the motion of two-soliton resonant interactions (resonant triads) as described by Miles (1977). The schematic development of the interaction with time is obtained and shown to approximate closely to computer calculations of the analytic solution. Similar results follow for interactions of more solitons and other equations.
The continuous spectrum of the Orr-Sommerfeld equation. Part 1. The spectrum and the eigenfunctions
Authors: Grosch Chester E. , Salwen Harold
Published: April 2006

It is shown that the Orr-Sommerfeld equation, which governs the stability of any mean shear flow in an unbounded domain which approaches a constant velocity in the far field, has a continuous spectrum. This result applies to both the temporal and the spatial stability problem. Formulae for the location of this continuum in the complex wave-speed plane are given. The temporal continuum eigenfunctions are calculated for two sample problems: the Blasius boundary layer and the two-dimensional laminar jet. The nature of the eigenfunctions, which are very different from the Tollmien-Schlichting waves, is discussed. Three mechanisms are proposed by which these continuum modes could cause transition in a shear flow while bypassing the usual linear Tollmien-Schlichting stage.
A note on the conservation of the axial momentum of a turbulent jet
Authors: Kotsovinos Nikolas E.
Published: April 2006

The conservation law for the flux of axial momentum in a turbulent jet is examined. The examination discloses that for a plane jet out of a wall the momentum flux is reduced appreciably because the induced flow towards the jet has a component in the direction opposite to the main jet flow and because of the pressure field generated in the ambient fluid. Existing experimental results confirm this conclusion.
On the stability of thermally driven shear flow heated from below
Authors: Weber J. E.
Published: April 2006

The onset of convection in shear flow driven by lateral heating and also uniformly heated from below is investigated numerically by Galerkin's method. Stress-free as well as rigid, perfectly conducting boundaries are considered. The analysis is valid for small and moderate Prandtl numbers. The magnitude of the lateral basic temperature gradient may be expressed by a dimensionless Grashof number G, while the uniform heating from below is represented by a Rayleigh number Ra. Depending on the values of G, Ra and the Prandtl number Pr, a variety of interesting situations arise. In particular it is demonstrated that the form of the most unstable mode, i.e. whether it is a roll with axis aligned along the basic flow (a longitudinal roll) or one with axis normal to the basic flow (a transverse roll), depends on the value of the Prandtl number. For small values of G, the marginally stable disturbances are found to be steady, while for larger values of G, oscillatory instability occurs. For all values of G considered here (G [lsim ] 3000), computations of the energy balance for the marginally stable disturbances show that the main instability mechanism is of thermal origin, while the effect of shear may be important in selecting the preferred mode of disturbance.
Drag on a sphere in unsteady motion in a liquid at rest
Authors: Karanfilian S. K. , Kotas T. J.
Published: April 2006

A sphere was subjected to a simple harmonic motion in an otherwise undisturbed liquid. Records of the resistance of the liquid to the motion for various amplitudes and frequencies were obtained. The resistance was first represented by an equation consisting of three terms with empirical coefficients: the steady-motion drag, a term due to the ‘added mass’ and a term due to the history of the motion. It was found that the data could be correlated only with a large degree of scatter by this type of equation. Subsequently an attempt was made to represent the resistance by means of a single term, with an empirical coefficient C. It was found that C correlated well with the acceleration number Vd/V2 and the Reynolds number Vd/v, where V, V and d are the acceleration, velocity and diameter of the sphere respectively and v is the kinematic viscosity of the liquid. C increased with Vd/V2 and decreased in the limit to the steady-motion drag coefficient Cd when Vd/V2 became very small. The range of the Reynolds number in the experiments was 102 < Vd/v < 104 and the range of the acceleration number was 0 ≤ Vd/V2 ≤ 10·5.
Flow in the entrance of the aorta
Authors: Singh M. P. , Sinha P. C. , Aggarwal Meena
Published: April 2006

This paper supplements an earlier study (Singh 1974) of the steady case of ‘Entry flow in a curved pipe’. Here we consider an entrance profile of the form
\[
w = Q(t)/(1+\delta r\cos\alpha),
\]
which is physiologically more relevant for blood being pumped from the left ventricle into the ascending aorta. A boundary-layer analysis is applied to determine the effects of curvature and an adverse pressure gradient (associated with the primary flow) on the wall shear. The study shows how the negative wall shear and backflow near the wall develop during the decelerating phase of the cycle as the boundary layer grows. The analysis shows how the increasing effect of the secondary flow due to curvature draws off slower moving fluid azimuthally from the outer bend to the inner bend; this induces a cross-flow of faster moving fluid from the inner bend to the outer bend which results in a thinning of the boundary layer at the outer bend and a thickening at the inner bend. This implies an increased wall shear at the outer bend compared with that at the inner bend as the flow develops further downstream; this is in contrast with the initial stages of the motion near the entrance where the higher wall shear occurs at the inner bend owing to the external flow and to geometric factors. The analysis shows that the displacement effect of the boundary layer on the core is not significant because the boundary layer remains thin, about one-tenth of the tube diameter.
A turbulent boundary layer disturbed by a cylinder
Authors: Marumo Eisuke , Suzuki Kenjiro , Sato Takashi
Published: April 2006

This paper deals with a two-dimensional turbulent boundary layer disturbed by a circular cylinder. The cylinder was placed inside or outside the boundary layer with its axis parallel to the wall and normal to the flow direction. The mean velocity, wall shear stress, longitudinal turbulent intensity, autocorrelations and turbulent length scale were measured and here the relaxation features of the disturbed boundary layer are discussed. The measurements were made for a ratio of the cylinder diameter d to the undisturbed boundary-layer thickness δ0 equal to 0·30 and for three values of the ratio of the height h of the cylinder axis to δ0 equal to 0·222, 0·556 and 1·24.

The results show that the near-wall region of the disturbed boundary layer recovers much more quickly than the outer region and that in the case h/δ0 = 0·222 the recovery is faster than in other cases, as reported by Clauser (1956). Moreover, it is found that the fluctuating velocity field recovers more slowly than the mean velocity field, and that the characteristics of the turbulence in the outer region are still close to those in the wake of an isolated cylinder at the last measurement station, although the mean velocity profile has almost completely returned to its natural shape.
A harbour theory for wind-generated waves based on ray methods
Authors: Larsen Jesper
Published: April 2006

In the paper we consider harbour oscillations excited by wind-generated gravity waves. The analysis is based on the fact that waves propagate along rays (wave orthogonals). In this way the elliptic boundary-value problem is turned into an initial-value problem along each ray. When a ray strikes the boundary (the harbour walls), reflected rays are produced in accordance with the law of reflexion. When a ray strikes an edge point of the boundary (e.g. the tip of a breakwater) diffracted rays are produced and emitted in all directions into the harbour. Algorithms for the tracing of incident, multiply reflected and singly diffracted rays as well as the computation of the field on each ray are presented. Attenuation mechanisms (e.g. partial reflexion), which limit the number of rays needed to compute the field, are included. Numerical examples for a rectangular and an actual harbour are given. A comparison between the results obtained by ray methods and finite difference methods is included.
The unsteady motion of a two-dimensional aerofoil in incompressible inviscid flow
Authors: Basu B. C. , Hancock G. J.
Published: April 2006

A numerical method has been developed for the calculation of the pressure distribution, forces and moments on a two-dimensional aerofoil undergoing an arbitrary unsteady motion in an inviscid incompressible flow. In a discussion of the appropriate Kutta condition(s) it is argued that two Kutta conditions are required to obtain a satisfactory solution. The method is applied to (i) a sudden change in aerofoil incidence, (ii) an aerofoil oscillating at high frequency and (iii) an aerofoil passing through a sharp-edged gust.
Flow over a containment dyke
Authors: Greenspan H. P. , Young R. E.
Published: April 2006

The wall of a large tank or reservoir breaks, sending fluid against a secondary containment dyke. The impact of the surging fluid against the safety barrier is studied. The results of theoretical analysis and numerical simulation (for vertical dykes) are in good agreement with experimental data concerning overflow and total spillage as well as the fluid motion after collision, including the development and formation of a strong shock. The dependence of spillage on the inclination of the dyke is also determined by experiment.
On the response of a poro-elastic bed to water waves
Authors: Yamamoto Tokuo , Koning H. L. , Sellmeijer Hans , Hijum Ep Van
Published: April 2006

The problem of the response of a porous elastic bed to water waves is treated analytically on the basis of the three-dimensional consolidation theory of Biot (1941). Exact solutions for the pore-water pressure and the displacements of the porous medium are obtained in closed form for the case of waves propagating over the poro-elastic bed. The theoretical results indicate that the bed response to waves is strongly dependent on the permeabilitykand the stiffness ratioG/K’, whereGis the shear modulus of the porous medium andK’is the apparent bulk modulus of elasticity of the pore fluid. The earlier solutions for pore-water pressure by various authors are given as the limiting cases of the present solution. For the limitsG/K′→ 0 ork→ ∞, the present solution for pressure approaches the solution of the Laplace equation by Putnam (1949). For the limitG/K′→ ∞, the present solution approaches the solution of the heat conduction equation by Nakamuraet al.(1973) and Moshagen & Tørum (1975).

The theoretical results are compared with wave tank experimental data on pore-water pressure in coarse and fine sand beds which contain small amounts of air. Good agreement between theory and experiment is obtained.
On the value of a language
Authors: LEHMANN CHRISTIAN
Published: April 2006

We live in an age where the extinction of languages has become a topic of discussion in many different circles. Opinions on whether the process should be stopped or considered profitable differ widely even in the field of linguistics, let alone in the public domain. A rational attitude presupposes the recognition that a language may constitute a value for some and that value judgements are controlled by more or less outspoken and divergent interests. In the case of a language, interest is taken in its maintenance (or suppression) at all the levels from the individual via the speech community and the scientific community up to mankind. These interests have to be made explicit before the value of a language can be assessed. Ultimately, such an evaluation must even be confronted with the costs that arise in the maintenance of a minority language or in the revitalization of a dying language.
The 1755 Lisbon disaster, the earthquake that shook Europe
Authors: POIRIER JEAN-PAUL
Published: April 2006

The Lisbon earthquake is famous for its central role in the 18th century ‘quarrel of Optimism’. The accounts of the disaster by some witnesses are presented and the contributions that the earthquake inspired to many European authors, less well-known than Voltaire, in the domains of science, literature, religion and philosophy, are summarily reviewed. The paper emphasizes the repercussions the earthquake had in Germany, quite remote from the disaster area, but intellectually much alive, at the time of Frederic II.
The great Lisbon earthquake and tsunami of 1755: lessons from the recent Sumatra earthquakes and possible link to Plato's Atlantis
Authors: GUTSCHER M.-A.
Published: April 2006

Great earthquakes and tsunami can have a tremendous societal impact. The Lisbon earthquake and tsunami of 1755 caused tens of thousands of deaths in Portugal, Spain and NW Morocco. Felt as far as Hamburg and the Azores islands, its magnitude is estimated to be 8.5–9. However, because of the complex tectonics in Southern Iberia, the fault that produced the earthquake has not yet been clearly identified. Recently acquired data from the Gulf of Cadiz area (tomography, seismic profiles, high-resolution bathymetry, sampled active mud volcanoes) provide strong evidence for an active east dipping subduction zone beneath Gibraltar. Eleven out of 12 of the strongest earthquakes (M>8.5) of the past 100 years occurred along subduction zone megathrusts (including the December 2004 and March 2005 Sumatra earthquakes). Thus, it appears likely that the 1755 earthquake and tsunami were generated in a similar fashion, along the shallow east-dipping subduction fault plane. This implies that the Cadiz subduction zone is locked (like the Cascadia and Nankai/Japan subduction zones), with great earthquakes occurring over long return periods. Indeed, the regional paleoseismic record (contained in deep-water turbidites and shallow lagoon deposits) suggests great earthquakes off South West Iberia every 1500–2000 years. Tsunami deposits indicate an earlier great earthquake struck SW Iberia around 200 BC, as noted by Roman records from Cadiz. A written record of even older events may also exist. According to Plato's dialogues The Critias and The Timaeus, Atlantis was destroyed by ‘strong earthquakes and floods … in a single day and night’ at a date given as 11,600 BP. A 1 m thick turbidite deposit, containing coarse grained sediments from underwater avalanches, has been dated at 12,000 BP and may correspond to the destructive earthquake and tsunami described by Plato. The effects on a paleo-island (Spartel) in the straits of Gibraltar would have been devastating, if inhabited, and may have formed the basis for the Atlantis legend.
The 1755 Lisbon earthquake and the beginning of closure of the Atlantic
Authors: RIBEIRO A. , MENDES-VICTOR L. , CABRAL J. , MATIAS L. , TERRINHA P.
Published: April 2006

The 1755 Lisbon earthquake and tsunami had one of the highest magnitudes in the history of Europe. The source mechanism requires generation at a subduction zone. Intensity distribution and tsunami modelling excludes the Gorringe Bank as a source area and suggests generation by the incipient convergence of the Atlantic with the Southwest Iberia and Morocco margin rather than at the less active Gulf of Cadiz Accretionary Prism. The comparison with the 2004 Sumatra earthquake and tsunami supports this interpretation. A tsunami warning alert system is urgent for the Atlantic.
The great earthquakes of Lisbon 1755 and Aceh 2004 shook the world. Seismologists' societal responsibility
Authors: FUCHS KARL
Published: April 2006

Two major earthquakes ‘which shook the world’, that of Lisbon of 1755 and that of Aceh/Sumatra of 2004, are compared. Both were catastrophic earthquakes with nearly identical magnitude M≈9 and accompanying destructive tsunamis. They are paradigms for Low Probability Extreme Events (LPEEs) and for the reaction of the societies in which they occurred, although 250 years apart. Modern seismology developed from its birth as disaster management following the Lisbon quake to a mature science, which however, still remains under the obligation to improve its role in enhancing society's preparedness for such catastrophes. The catastrophe of hurricane Katrina, which was predicted, showed that the realm of societal responsibility extends beyond that of scientific technical competence.
Earthquake risk reduction – obstacles and opportunities
Authors: WENZEL FRIEDEMANN
Published: April 2006

The damage to human life, property, and infrastructure by natural disasters has been growing exponentially for the past 40 years. The driving force of this development is the increase in exposure and vulnerability of human society to the impacts of disasters. On the other hand, significant local, regional and global capacities for disaster reduction have been built since the beginning of the UN International Decade for Natural Disaster Reduction in 1990. It remains unclear how the race between mitigation efforts and expanding disaster potential will develop in the coming years. This is a report on the risk potential of megacities and the strategies to reduce such risk, drawing on the experience of 8 years work in the Earthquakes and Megacities Initiative (www.earthquakesandmegacities.org/). The crucial role of science in this process will be discussed.
How to write a history of Europe: Europe, Europes, Eurasia
Authors: BURKE PETER
Published: April 2006

This article looks at the history of European culture from three angles, those of European uniqueness, European variety and European consciousness. The first section discusses the question of whether the fundamental unit of study, for cultural as well as economic historians, is not Eurasia. The second section is concerned with cultural divisions within Europe, with Europes in the plural. It asks whether it is more illuminating to distinguish two Europes (like Leopold von Ranke), or three (like Jenő Szűcs), or even five (like Hugo Hassinger), and examine both centripetal and centrifugal forces in early modern history. The final section deals with the history of the idea of Europe, or more exactly with the rise of consciousness of being European, as it is revealed in early modern histories, geographies, journals and newspapers.
Europe's history of integration and diversity
Authors: BLOCKMANS WIM
Published: April 2006

The process of European integration, the complexity of the problems involved and even the resistance it raises, astonishes observers in other parts of the world, especially in large states that have a long history of centralized government behind them. Is there really so little unity in Europe? If so, how can this be explained? Has European diversity generated only problems or has it, in fact, created new and unique opportunities? Is there a chance that growing concerns at EU-level about the cultural dimensions of European citizenship could, in fact, consolidate a sense of community? And, finally, how can historians contribute to the creation of a common European identity, if this is so weakly developed?
Does Europe have a centre? Reflections on the history of Western and Central Europe
Authors: MOUT NICOLETTE
Published: April 2006

Any definition of Central Europe based on geographical and/or historical facts causes difficulties. The line dividing Europe during the Cold War has a very limited use because it does not take into account Central Europe as a special part of the continent. Historians such as Geoffrey Barraclough, Hugh Seton-Watson and Oskar Halecki discussed the idea of a separate identity of Central Europe during the Cold War. Especially after the fall of the Berlin Wall, this discussion was re-opened. From a historian's point of view, the most important contributions came from Piotr Wandycz and Jenő Szűcs. An imaginary centre of Europe can only be found in the continent's common history.

There is a belief, rather widespread in English-speaking countries, that the eastern half of Europe is inhabited by a number of endlessly quarrelling small nations whose conflicts keep endangering the quiet and comfort of Anglophones. (Hugh Seton-Watson)
Exceptionalism? European history in a global context
Authors: MITTERAUER MICHAEL
Published: April 2006

(Translation: Stefan Menhofer, 2004, revised by Peter Burke, 2005)

The question: ‘How to write the history of Europe?’ can only be answered in context. The reply depends on what sort of readership one wants to write for, what ideas one entertains about tasks of exploring and conveying historical studies, how one views the relation of European history to other forms of historiography. The following reflections seek to take up and connect with one another two strands of historiographical discussion which are surprisingly disconnected, namely the discussions about concepts of European history and of global history. Suggestions for a European history in a global context, such as are presented here under the heading ‘exceptionalism’, are based not only on theoretical reflections but also on several attempts to put them into practice over the past few years.
The history of Europe seen from the North
Authors: ØSTERGÅRD UFFE
Published: April 2006

The Nordic or Scandinavian countries represent variations on general European patterns of state and nation-building and political culture. Denmark and Sweden rank among the oldest and most typical of nation-states together with France, Britain and Spain and should be studied with the same questions in mind. Today, however, a sort of trans-state common Nordic identity coexists with independent national identifications among the Scandinavians. Nordic unity is regarded as a viable alternative to European culture and integration by large numbers of the populations. There has never existed a ‘Scandinavian model’ worthy of the name ‘model’. Because of a series of changes in great power politics in the 18th and 19th centuries, the major conflicts in Europe were relocated away from Northern Europe. This resulted in a virtual ‘neutralization’ of the Scandinavian countries north of the Baltic Sea. Today, the much promoted ‘Nordic identity’ reveals itself only through the nation-states. The ‘Association for Nordic Unity’ (Foreningerne Norden) was set up in 1919 only after all five Nordic countries had achieved independent nationhood: Norway in 1905, Finland in 1917, and Iceland in 1918 (the latter only as home rule to be followed by independence in 1944). The very different roads to independent nationhood among the Nordic countries and the idea of a common Nordic identity can be traced back to its beginnings in the 19th century
Empfehlungen zur Tumornachsorge in der hausärztlichen Praxis
Authors: Eckert
Published: April 2006

Die Nachsorge von Patienten nach Primärbehandlung einer Tumorerkrankung wird aufgrund teilweise widersprüchlicher Empfehlungen und dem Fehlen von evidenzbasierten Daten bei vielen Erkrankungen unterschiedlich gehandhabt. Nur bei wenigen Krankheiten besteht ein kurativer Ansatz oder zumindest die Chance einer deutlichen Verbesserung der Lebenserwartung bei der Diagnose eines asymptomatischen Rezidivs. Für eine weitaus grössere Zahl von Krankheitsbildern ist eine symptomorientierte Nachsorge angezeigt, die Schwerpunkte auf Aspekte der Lebensqualität, aber auch auf Behandlungskomplikationen legen sollte. Psychologische Aspekte der ärztlichen Begleitung sind von besonderer Bedeutung. Bei Abneigung von Patienten gegen regelmässige Nachsorgetermine oder bei Fehlen von Interventionsmöglichkeiten kann sich die Tumornachsorge auf Arztkontakte bei Beschwerden oder bei Krankheitssymptomen beschränken. Der Artikel empfiehlt Vorgehensweisen bei der Nachsorge häufiger Tumorkrankheiten insbesondere auf der Grundlage der Empfehlungen der Europäischen Krebsgesellschaft ESMO.
Sonographische Diagnostik der Schilddrüse
Authors: Wiesner  , Engel  , Steinbrich  , Oertli
Published: April 2006

In Anbetracht ihrer oberflächlichen Lage bietet sich die Schilddrüse bestens für die Ultraschalluntersuchung an. Die Sonographie der Schilddrüse ist eine zuverlässige Abklärungsmethode bei verschiedenen Schilddrüsenerkrankungen und sollte immer auch mit einer Sonographie der übrigen Halsweichteile sowie der beidseitigen zervikalen Gefäss- und Nervenscheide verbunden sein. Die Sonographie erlaubt neben der exakten Volumenbestimmung der Schilddrüse auch die Beurteilung der Parenchymstruktur und das Erkennen von diffusen und fokalen Veränderungen der Schilddrüse selbst sowie allfälliger assoziierter Umgebungsveränderungen. Die vorliegende Arbeit vermittelt eine Übersicht über die sonographische Diagnostik und Differentialdiagnostik von diffusen und fokalen Schilddrüsenpathologien und gibt einige Ratschläge hinsichtlich des möglichen weiteren Abklärungsganges.
Drug-eluting Stents zur Behandlung der koronaren Herzkrankheit – Halten sie was sie versprechen?
Authors: Nordmann
Published: April 2006

Drug-eluting Stents führen im Vergleich zu konventionellen koronaren Stents zu einer signifikanten Reduktion der Restenose- und Revaskularisationsraten. Sie führen jedoch nicht zu einer Reduktion der Inzidenz von Myokardinfarkten oder zu einer Reduktion der Gesamtmortalität. Im Rahmen einer Metaanalyse sämtlicher randomisierter klinischer Studien, welche den Effekt von drug-eluting Stents mit konventionellen Stents zur Behandlung der koronaren Herzkrankheit miteinander verglich, wurde eine Assoziation zwischen dem Gebrauch von drug-eluting Stents, insbesondere von mit Sirolimus beschichteten Stents, und einer erhöhten nicht-kardial bedingten Mortalität gefunden. Ob diese Assoziation der Realität entspricht oder doch nur einen Zufallsbefund darstellt, muss mittels Langzeitbeobachtungen randomisierter klinischer und Kohortenstudien geklärt werden.
Dysurie und Sekretion aus der Harnröhre nach Auslandaufenthalt
Authors: Miedinger
Published: April 2006

Wir berichten über einen jungen bisher gesunden Patienten, der sich anlässlich einer Check-up-Untersuchung nach einem Auslandaufenthalt in Bangladesch in der Sprechstunde vorstellte. Nach genauerem Nachfragen berichtet der Patient über ein Brennen beim Urinieren, welches etwa eine Woche nach einem ungeschützten Geschlechtsverkehr mit einer Prostituierten erstmals aufgetreten sei. Differentialdiagnostische Überlegungen der Leitsymptome Dysurie und Urethralfluor werden diskutiert. Weitere Abklärungsschritte werden besprochen. Die Urin-PCR-Untersuchungen waren für Neisseria gonorrhoe sowie Chlamydia trachomatis jeweils positiv. Der Patient wurde einmalig mit Antibiotika i.m. sowie p.o. therapiert und eine Partnerbehandlung eingeleitet.