bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure of Hydromagnetic Ionizing Shock Waves
Authors: Molander Roger C. , Berger Stanley A.
Published: March 2004

A physical model is formulated to describe the changes taking place within a strong ionizing shock wave in the presence of electromagnetic fields. The model assumed is composed of a strong adiabatic shock to translational equilibrium followed by initiation of ionization and interaction between the flow and the electromagnetic fields. Eventually, recombination causes the flow to relax to a downstream state of thermodynamic equilibrium and zero current flow. Mathematical equations are derived to describe the changes in flow parameters and electromagnetic fields within the nonequilibrium current-carrying region for an arbitrary gas and arbitrary upstream magnetic field configuration. The analysis removes the indeterminacy in the solution of the shock jump conditions arising from the inability to fix the upstream electric field for ionizing shock waves. The particular case of switch-on shock waves in argon is then considered in detail. Solutions were only found when the downstream transverse magnetic field component was much less than the axial component.
Resistive Force-Free Magnetic Fields
Authors: Jette A. David , Sreenivasan S. Ranga
Published: March 2004

The properties of the function α characterizing force-free fields through the relation ≇ × B = αB are studied, and it is shown that it has to be either a function of space and time or a constant independent of both. An initial integrability condition for α and B is found. Using this condition, it is demonstrated for cylindrically symmetric magnetic fields that α must be a constant.
Electrical Conductivity of a Collisionless Magnetoplasma in a Weakly Turbulent Magnetic Field
Authors: Newman C. E. , Sturrock P. A.
Published: March 2004

The behavior of test particles in the presence of uniform, parallel, and steady electric and magnetic fields in addition to a weakly turbulent magnetic field is studied. The quasilinear approach is used to find a diffusion equation for the distribution function describing the test particles; the diffusion equation describes the pitch-angle scattering experienced by the test particles due to the random fluctuations of the magnetic field. In the weak-electric-field limit the equation is analyzed in detail and an expression for the electrical conductivity in terms of the correlation tensor of the fluctuating field is found. Finally, for the case of a particular model of the turbulence and a Maxwellian distribution of test particles, an explicit formula for the conductivity is given.
High-Frequency Conductivity of a Plasma with Fluctuations
Authors: Nishikawa Kyoji , Ichikawa Yoshi-Hiko
Published: March 2004

The induced current density of a fully ionized, stationary, and uniform plasma linear in the externally applied, high-frequency electric field is calculated. In the calculation two approximations are made: neglect of the spatial dependence of the external field and neglect of the mode-coupling terms which do not significantly contribute to damping of the waves. For large ion-to-electron mass ratios, the Ohmic current can be expressed as a simple function of the density fluctuations of the electrons and those of the ions. Results previously obtained for a quiescent plasma can easily be recovered by using the expressions for these fluctuations one obtains from the velocity distribution functions in the random phase approximation. Each of the three different types of enhanced fluctuations, corresponding to the ion-acoustic, the ion plasma, and the electron plasma waves, respectively, is found to have a different effect on the resistivity. The range of frequencies of the external field in which the effect of fluctuations is important, the sign of the additional resistivity due to fluctuations, and a quantitative estimate of this resistivity in some special cases are discussed.
Finite Larmor Radius Effects in the Magnetosonic Pulse
Authors: Kinsinger R. E. , Auer P. L.
Published: March 2004

A consistent second-order adiabatic closure for the fluid description of a magnetosonic disturbance was developed earlier. Here, that closure is adapted for the description of a steady, nonlinear, dissipation-free pulse. The Adlam-Allen solitary wave is recovered in the limit where the electron inertial dispersion dominates. When the dispersive effects of finite ion Larmor radius dominate, the pulse remains compressive but scales with the ion Larmor radius. The laminarity of this solution fails due to cavitation of the ion fluid. For small ion beta, this pulse break occurs for weakly nonlinear, yet not truly adiabatic, disturbances.
Laser-Induced Anomalous Heating of a Plasma
Authors: Kaw P. K. , Dawson J. M.
Published: March 2004

It is shown that a sufficiently intense laser beam can drive low-frequency instabilities in a fully ionized plasma; these instabilities may cause considerable enhancement of the high-frequency resistivity of the plasma around certain frequencies and thus lead to an anomalous heating effect.
Ion Resonance Instability in Grossly Nonneutral Plasmas
Authors: Levy R. H. , Daugherty J. D. , Buneman O.
Published: March 2004

The addition of a certain fraction of ions to an otherwise stable cloud of electrons can, in certain circumstances, result in an instability. The case of a low-density (q = ωp2/ωc2 ≪ 1) electron cloud in which the electron motions can be described by E + ve×B = 0 is considered in detail. The condition for onset of the instability is that the unperturbed ion orbits (which characteristically traverse the entire electron cloud) should involve frequencies close to that of the diocotron wave that can propagate on the electron cloud. This condition is equivalent to having the ratio Zme/miq of the order of unity and is independent of the ion density. When instability is present, the growth rate is of the order of the ion plasma frequency.
Quasilinear Theory of the Positive Column Spiral Instability
Authors: Simon Albert , Shiau J. N.
Published: March 2004

An analysis of the nonlinear behavior of the spiral instability of the positive column is presented. The finite amplitude and frequency shift of the single mode which results from raising the magnetic field slightly above the critical value are determined. The slope of the E-H curve is also obtained. The method is based on a general theory of nonlinear behavior in weakly ionized plasma. The quasilinear results are in excellent agreement with experiment.
Feedback Stabilization of Drift Waves by Modulated Electron Sources
Authors: Furth H. P. , Rutherford P. H.
Published: March 2004

A theory is presented for feedback stabilization of collisional and collisionless drift waves by modulated electron sources within the plasma, such as may be provided by probes responding to the measured electron density perturbation.
Spectroscopic Investigation of Enhanced Plasma Oscillations in a High-Voltage Theta Pinch
Authors: Kunze H.-J. , Griem H. R. , DeSilva A. W. , Goldenbaum G. C. , Spalding I. J.
Published: March 2004

Intensity and frequency of fluctuating electric fields are obtained from a “plasma satellite” on the 21P - 41D line of helium observed in the piston field of a collisionless shock. In contrast to second-order perturbation theory only one satellite is seen. The perturbation theory is developed, therefore, to higher orders. Agreement between this theory and experiment is achieved. From the observed level of electric field fluctuations an effective collision frequency of about one-fourth of the ion plasma frequency can be deduced.
Experiments on the Injection and Containment of Electron Clouds in a Toroidal Apparatus
Authors: Daugherty J. D. , Eninger J. E. , Janes G. S.
Published: March 2004

Injection and containment of unneutralized clouds of electrons has been accomplished with an azimuthally symmetric, toroidal, magnetic field. The confining magnetic field is produced within a conducting toroidal chamber. The induction of this magnetic field has been used to inject the electron cloud (inductive charging). Average electron densities of 4 × 109 cm−3 and peak electrostatic well depths of ≈ 400 kV have been achieved. Semiempirical correlations are given which show the inductive charging scheme to be governed by an electron energy restriction and finally limited by the occurrence of anomalous crossed field beam noise. Stable equilibria, without the necessity of a rotational transform have been observed for times in excess of 60 μsec. Correlation of the containment time observations with the predictions of a theoretical model for an ion-diocotron wave instability shows that the containment time is governed by the rate of ionization of the residual neutral gas (p > 10−7 Torr) in the apparatus. The correlation of theory and experiment appear to confirm the theoretical prediction that a significant degree of charge neutralization (in the range of 10-20%) can be stably contained. Interpretation of these results suggests that significant improvement in both electron cloud density and containment time should be possible.
Shielding of Slow Test Particles in a Plasma
Authors: Cooper Gilbert
Published: March 2004

The effective field of a test particle moving slower than the electron thermal velocity is calculated. Within a few Debye lengths, the field exhibits the usual exponential shielding. At further distances, the velocity induced r−3 field is seen.
Numerical Study of the Flow of a Viscous Fluid in a Curved Channel
Authors: Kawaguti Mitutosi
Published: March 2004

Steady flow of a viscous fluid in a channel with a corner was studied numerically. Three types of corners were investigated: (a) Both inner and outer corners are rectangular, (b) inner corner is rectangular but outer corner is circular, (c) both corners are circular. Main results obtained are as follows: (i) For the flow in a channel with a corner, conventional method of integration of Navier-Stokes equation is effective for Reynolds number less than about 50. (ii) With Greenspan's method, convergent results are obtained for Reynolds number as large as 256. (iii) A standing vortex appears near the inner wall just downstream of the corner with Reynolds number about 30 for cases (a) and (b), but its appearance is postponed until the Reynolds number is increased to 128 for case (c). (iv) Pressure loss due to the existence of a corner is nearly proportional to Reynolds number.
Structure of Steady Closed Streamline Flows within a Boundary Layer
Authors: Leal L. G. , Acrivos Andreas
Published: March 2004

Numerical solutions to the full Navier-Stokes equations have been obtained for flow past a flat plate of length L in which a finite slip velocity U0 opposite in direction to that of the free stream is imposed. These solutions, which covered the range 0 ≤|U0/U∞| ≤ 0.4 and 0.1 ≤ Re ≤ 80 with U∞ being the freestream velocity and Re the Reynolds number U∞L/ν, strongly suggest that, as Re → ∞, the region of closed streamline flow adjacent to the plate decreases in width as Re−1/2 and thus remains imbedded within the viscous layer for all Re. In turn, this implies that, as Re → ∞, the flow field near the plate, including even the recirculating region, is described by the parabolic boundary-layer equations.
Numerical Solutions of Two-Dimensional Stall in Fluid Diffusers
Authors: Fromm J. E.
Published: March 2004

A description and results are given for finite difference computation of incompressible flow in a flared channel. Stall geometry simulations are discussed for Reynolds numbers up to R =  4000. A fourth-order convective approximation is used and its implementation in conservative form is described. Empirical downstream boundary conditions are established which limit the calculation region and permit long running times. Provisions for modifying channel flare angle are discussed.
Treatment of the Prager Problem of Potential Theory by the Integral Equation Method
Authors: Kress R.
Published: March 2004

The Prager problem deals with the derivation of source-free vector fields from vector potentials of vortices. Necessary and sufficient conditions are given for the requested volume and surface vortex distribution in multiply connected three-dimensional regions. Further examinations are made for the vectorial Fredholm integral equation of the second kind holding for the surface vortex density. For the numerical treatment of this integral equation in arbitrary doubly connected three-dimensional regions an iteration method is developed, which requires the knowledge of a qualified approximate solution of the adjoint homogeneous equation. Integrating by the trapezoidal rule, the numerical calculation is executed for a torus and a special stellarator.
Numerical Investigation of an Axisymmetric Flow around Long Bodies
Authors: Rusanov V. V.
Published: March 2004

A finite-difference method for calculation of a supersonic flow has been used for investigating the flow field around bodies of revolution at large distances from the nose. Consideration is given to flow around cylinders and cones with blunt noses as well as hyperboloids and bodies with the equation of the generatrix r = zn (0 < n < 1). The flow field near these bodies has been obtained up to distances of 10 000 bluntness radii with Mach numbers from 2 to infinity. Studies have been made of the asymptotics of shock waves and parameters of the gas in the region between the surface of the body and the shock wave.
Numerical Solution of Free Boundary Problems by the Method of Steepest Descent
Authors: Bloch Eugene
Published: March 2004

A finite difference method is described which solves steady free boundary problems arising in classical hydrodynamics. The vena contracta model for both plane and axially symmetric geometries are considered. The approach is to establish a fixed rectangle R in a parameter domain and seek the stream function and the physical plane in terms of the parameter variables. The physical plane is determined as a conformal map of R. Well-known variational principles connected with conformal mapping and free boundary problems are used, combined with the method of steepest descent, to produce an iterative scheme which yields the desired parametric form of the solution.
Importance of Boundary Conditions in the Numerical Treatment of Hyperbolic Equations
Authors: Moretti Gino
Published: March 2004

Many of the existing computations of initial- and boundary-value problems in fluid mechanics suffer from unrealistic treatment of boundary points. Three categories of boundaries are discussed briefly: rigid walls, arbitrary boundaries of a computational region in a subsonic flow, and shock waves. An attempt is made to show in what sense the numerical treatment of such boundaries may be physically wrong and what can be done instead. Examples from the blunt body problem, the transonic flow in a nozzle, the incompressible inviscid flow past a circle, and the quasi-one-dimensional flow in a Laval nozzle, are shown.
Examination of the Stability of Disturbed Boundary-Layer Flow by a Numerical Method
Authors: Loer Stefan
Published: March 2004

A simplified form of the equations of Navier-Stokes, lying between the boundary-layer equations of Prandtl and the complete Navier-Stokes equations, can describe the instability of a boundary-layer flow along a flat plate. Results of the computation of such a flow will be discussed. The difference between a numerical instability and an instability of the system of differential equations will be demonstrated by the unsteady boundary-layer equations of Prandtl for the flow on the backside of a circular cylinder.
Results of Parallel-Flow Stability Calculations Obtained by Time-Sharing Computations
Authors: Landahl M.
Published: March 2004

A series of programs for calculation of eigenvalues and eigenfunctions for parallel incompressible flow have been developed for use on the Massachusetts Institute of Technology time-sharing computer system. The programs were designed building-block fashion allowing a great variety of combinations of velocity profiles and boundary conditions (flexible walls, etc.) to be treated. Also, running instructions are built into the programs themselves and communicated to the user dialog-fashion during the run making their use very simple for anyone with a minimum of prior instructions thus greatly facilitating numerical experimentation. The program system serves, in effect, as an extensive and rather complete set of tables of solutions for the problem area considered. Several examples are shown and discussed such as channel and boundary-layer flows with and without inflection points, boundary layers over compliant surfaces, comparisons between viscous and inviscid calculations, and wave propagation constants for a turbulent boundary layer. The efficiency of the particular method employed for supressing numerical instability is also discussed.
Three-Dimensional Study of Flow between Concentric Rotating Cylinders
Authors: Meyer Kenneth A.
Published: March 2004

The wavy vortex mode of flow between concentric rotating cylinders is studied using a combination of Fourier analysis and finite differencing. Series expansions of the form u(r, z, θ, t) = u0(r, z, t) + u1(r, z, t) sin nθ + u¯1(r, z, t) cos nθ + . . . are introduced into the full Navier-Stokes equations. The resulting time-dependent partial differential equations for u0, u1, u¯1, etc., obtained by separating the various harmonics are solved by finite differencing in the r, z plane. Numerical results were obtained at Reynolds numbers of 750, 1000, and 2000 at a radius ratio (of outer to inner cylinder) of 1.2. The growth rates of small three-dimensional disturbances are obtained for a laminar base flow and a Taylor cell base flow. Azimuthal wave velocities for small disturbance cases and the fully established wavy mode case are obtained and agree with linear stability calculations and experiment. The effect of the three-dimensional motion (at constant axial wavenumber) on the torque is examined and appears to be small. The effect, on torque, of varying axial wavenumber is reconsidered, and it is suggested that this is the predominant mechanism for affecting the torque in the wavy mode regime.
Numerical Study of Heat Transport by Internal Gravity Waves above a Growing Unstable Layer
Authors: Deardorff James W.
Published: March 2004

A stable layer of fluid which is suddenly heated at the bottom is studied numerically in two dimensions. Internal waves are soon set in motion by penetrative convection elements, and are found to transport heat downward, on the average, even at heights well above the interface separating the stable and convective layers. This heat transport is found to be associated primarily with a finite-amplitude effect, to a lesser extent with the increase of internal wave amplitudes with time, and only slightly associated with processes of molecular diffusion.
Numerical Experiments with Thermohaline Convection
Authors: Elder J. W.
Published: March 2004

Numerical experiments in 0, 1, 2 space dimensions are used to simulate the temporal and spatial structure of features of the finite amplitude oscillatory multilayered structures found in thermohaline convection.
Natural Convection between Concentric Vertical Cylinders
Authors: Davis G. de Vahl , Thomas R. W.
Published: March 2004

The motion of a fluid in the closed annular cavity formed by two concentric vertical cylinders and two horizontal planes has been analyzed by a numerical solution of the equations of motion and energy using a high-speed digital computer. The motion is generated by a radial density gradient caused by the thermal boundary conditions which are, typically: inner cylinder at a (dimensionless) temperature of unity; outer cylinder at a temperature of zero; horizontal boundaries adiabatic. The fluid is assumed to have constant thermodynamic and transport properties except for the density, which is temperature-dependent in the buoyancy term of the equation of vertical motion (the Boussinesq approximation); the flow is assumed to be axisymmetric. The equations of time-dependent motion have been solved, so that both transient and steady-state solutions are obtained. The parameters of the problem, and the respective ranges of values which have been considered, are: Rayleigh number (based on gap width) up to 2 × 105; Prandtl number 0.5 to 5; radius ratio 1 to 4; aspect ratio (cavity height/gap) 1 to 20. At moderate Rayleigh numbers the motion consists of a single cell (i.e., torus), while at higher Rayleigh numbers the onset of a multicellular motion is observed. The local and average Nusselt numbers, of interest in determining the insulating value of an annular cavity, have been obtained.
Numerical Study of Natural Convection in a Vertical Rectangular Enclosure
Authors: Rubel Arthur , Landis Fred
Published: March 2004

The steady-state natural convection of a fluid in a vertical rectangular cavity with isothermal side walls and adiabatic top and bottom walls is considered for 6 × 104 ≤ Ra ≤ 3.6 × 105 with Pr = 1, 6, 2000, and at an aspect ratio of 5.0. The governing nonlinear fourth-order equation in the stream function and the coupled second-order energy equation are solved numerically by a stable and rapidly converging iteration scheme. The computed flow distributions, including the appearance of multicellular flows, the temperature profiles, and the heat transfer predictions compare favorably with experimental results and with other numerical studies.
Numerical Experiments with a Difference Model for the Navier-Stokes Equations (Turbulence Model)
Authors: Schönauer W.
Published: March 2004

The time-dependent Navier-Stokes equations are solved numerically with a difference method. Theory and numerical experiments show that the space mesh size must be inversely proportional to the Reynolds number. A coarse net produces a “numerical turbulence,” which tends to the physical turbulence when the mesh size tends to zero. The existing computers, however, are not fast enough to solve the Navier-Stokes equations for values of the Reynolds number in the turbulent regime.
Numerical Simulation of Two-Dimensional Turbulence
Authors: Lilly Douglas K.
Published: March 2004

The two-dimensional incompressible Navier-Stokes equations are numerically integrated in order to test the validity of Kraichnan's predictions on the structure of two-dimensional turbulence. The numerically simulated turbulence is produced by an artificial forcing function, constructed from a randomly varying set of Fourier modes lying within a narrow spectral band near scalar wavenumber ke. For the case of turbulence maintained by a constant rate of energy injection, Kraichnan predicts the development of two power-law energy spectra, a k−5/3 range for frequencies less than ke, and a k−3 range for those greater than ke. The numerical results are consistent with these predictions, although truncation and aliasing errors restrict the useful spectral range of the calculations to less than that desirable for a fully satisfactory test. The predictions and results are apparently relevant to several areas of geophysical fluid dynamics and to the correct interpretation of other numerical simulation experiments.
Correlation Measurements in Turbulence using Digital Fourier Analysis
Authors: Van Atta C. W. , Chen W. Y.
Published: March 2004

Time correlations of longitudinal and lateral velocity fluctuations in grid-generated turbulence have been measured using linearized hot-wire anemometry, digital sampling, and a high-speed digital computer. A novel feature of the present measurements is the adoption of digital Fourier analysis, using the recently developed fast-Fourier transform method. The assumptions of isotropy are approximately satisfied by all of the present measured odd-order correlation functions, cross correlations, and moments, in contrast with previous measurements by other investigators. The even moments and certain types of even-order correlations and cross correlations are in excellent quantitative agreement with previous results. The remaining even-order quantities are considerably different, but generally are closer to the values for an isotropic and Gaussian fluctuating field. Differences in the low-frequency response of hot-wire amplifiers and associated instruments may account for the differences between the present data for certain odd-order correlations and that of earlier investigators.
Hybrid Computer Techniques in the Laboratory and Classroom
Authors: Elder J. W.
Published: March 2004

Present and future uses of hybrid computer techniques in a university department are described. There are two main uses: (1) in the laboratory; (2) in the classroom. (1) When a phenomenon or process is being studied by means of a laboratory model or analog, connected to an electronic computer which performs the real time functions of control, measurement, analysis, and display in such a way that the model, the computer, and the experimenter interact, we see the laboratory as a computer. (2) The real-time feature of a machine of this type is of great value in the lecture theatre. For example, solutions of systems of algebraic and ordinary and partial differential equations can be presented in visual form directly to the class in the course of a lecture. Supplementing this use, the machine can be run on a workshop basis as in an experimental physics laboratory class.
First Differential Approximation Method and Approximate Viscosity of Difference Schemes
Authors: Yanenko N. N. , Shokin Yu. I.
Published: March 2004

When hyperbolic systems are integrated, effects of so-called approximation viscosity appear. To investigate the latter, there is a very effective method which allows the reduction of the problem of the stability of a difference scheme to the stability (correctness) of a system of differential equations (the so-called first differential approximation). Such a reduction is possible in the classes of simple and majorant schemes. In a sense, the approximation viscosity of the scheme and its dissipative properties are determined by a first differential approximation. The stated method can be used in the investigation of difference schemes for the problems of compressible and viscous fluid.
Accuracy of Difference Formulation of Navier-Stokes Equations
Authors: Cheng Sin-I
Published: March 2004

An error analysis is formulated under the assumption that Lax's equivalence theorem is valid for quasilinear equations. Analysis is carried out for a class of difference approximations of the Burgers' equation. Explicit estimates of the errors due to various sources are obtained and verified by numerical integration. The boundary errors do not decay rapidly away from the boundary and often dominate the truncation errors. The boundary errors led to significant differences between apparently smooth and physically reasonable results of carefully executed computations of the same problem. The results based on difference formulations that are more nearly consistent with the differential formulation are likely to be more accurate. A conservative difference formulation is proposed to meet this consistency requirement as far as is practically possible. Calculations of multidimensional flow examples guided by these inferences are given. The results tend to support such inferences.
Numerical Investigation of the Formation of Discontinuities in Nonisentropic Inviscid Flows
Authors: Gordon Paul , Scala Sinclaire M.
Published: March 2004

The occurrence of discontinuities in inviscid flows has led to the development of artificial viscosity techniques. In this paper, an investigation of the following two questions has been initiated. Is it possible to utilize a numerical scheme for the inviscid equations, such that the stability of the method does not depend on an artifical viscosity effect? Is it possible to have continuous nonisentropic, inviscid flows in which there are subsonic and supersonic regions? The results of two numerical studies presented here indicate that the finite difference representation that has been utilized to solve the Euler equations is stable, even in the presence of mathematical discontinuities, and that this stability is not due to what is commonly referred to as an artificial viscosity. Also, in the physical problem containing a region of constant entropy and a region of varying entropy it was found that the discontinuity formed only after the pressure wave had reached a region of constant entropy.
Numerical Solution of Unsteady Viscous Incompressible Fluid Flow past a Circular Cylinder
Authors: Jain P. C. , Rao K. Sankara
Published: March 2004

Kawaguti and Jain have reported a systematic numerical investigation of unsteady viscous incompressible fluid flow past a circular cylinder for obtaining limiting steady-state solutions at Reynolds numbers up to 50. After removing the symmetry conditions the flow pattern has been studied to investigate the existence of the limiting steady state or the Kármán vortex street numerically at Reynolds number R = 40, 60, 100, and 200. At R = 40 and 60, steady-state solutions have been obtained and found to be in agreement with the other results. Results at R = 100 and 200 are also reported. Figures have been drawn to show the dependence of the flow pattern, the vorticity distribution, the pressure distribution, and the drag on the Reynolds number and the time.
Numerical Solution of the Incompressible Time-Dependent Viscous Flow past a Thin Oblate Spheroid
Authors: Rimon Yermiyahu
Published: March 2004

Numerical solutions of the transient axisymmetric flow around a thin disk normal to the flow are obtained. The fluid is incompressible, homogeneous, and its flow is governed by the complete Navier-Stokes equations. The Reynolds-number range studied is 10-600. The study investigates the effects that a very large curvature of the body has on the numerical procedure for the solution of the flow field, and the fundamental fluid-dynamical phenomena of separation, of a recirculatory wake, and of vorticity shedding. A time-dependent stream function-vorticity formulation is adopted. The solutions are obtained on an oblate spheroidal grid system. The high curvature has profound adverse effects on the numerical stability and accuracy. This is due to the extreme gradients of vorticity that appear near the edge of the disk. The results show that no vorticity shedding occurs for axisymmetric flow in the Reynolds-number range studied. In addition, some new interesting fluid-dynamical features are revealed. These include a different behavior of the pressure distribution at low and high Reynolds numbers and a local maximum of vorticity inside the wake at the higher Reynolds numbers studied.
Time-Dependent Viscous Flow over a Circular Cylinder
Authors: Thoman David C. , Szewczyk Albin A.
Published: March 2004

A finite difference method is extended to high Reynolds number flow about circular cylinders with particular emphasis given to the quantitative description of fine flow features. The method is of the explicit type and includes a directional difference scheme for the nonlinear terms which enhances calculational stability at high Reynolds numbers. A cell structure is chosen which provides local cell dimensions consistent with the structure of solutions expected. Solutions are presented for a range of Reynolds numbers from 1 to 3 × 105 in which the flow is started impulsively from rest, and the development is studied up to the approach of the steady-state or the limit cycle condition, whichever is appropriate to the particular Reynolds number.
Place as a Practical Concern of Mobile Workers
Authors: Brown Barry , O'Hara Kenton
Published: March 2004

In this paper we examine the spatial practices of mobile workers—how mobile workers manage their use of technology and place. Data from interviews with highly mobile workers and ‘hot-deskers’ are used to explore the reciprocal relationship between practice and place: how places change work, but also how work changes places. Mobile workers often need to configure their activities to take account of the different places in which they find themselves. This can involve considerable ‘juggling’ of their plans, humble office equipment, and their coworkers. In turn mobile workers change places, as they appropriate different sites for their work. Specifically, technology allows for the limited reappropriation of travel and leisure sites as places for work (such as trains and cafés). Time is also an important practical concern for mobile workers. Although mobile work may be seen as relatively flexible, fixed temporal structures allow mobile workers to ‘accomplish synchronicity’ with others. Although this paper focuses on the specific practices of mobile workers, it also explores how ‘grand social theory’ can help us understand the practical details of mobile work, yet how practice cannot be simply reduced to theory.
The Effect of Long-Distance Family Migration and Motherhood on Partnered Women's Labour-Market Activity Rates in Great Britain and the USA
Authors: Boyle Paul , Cooke Thomas , Halfacree Keith , Smith Darren
Published: March 2004

Many studies of long-distance family migration demonstrate that female partners are often disenfranchised in the labour market. One factor that has not been fully considered is the role of children. Heterosexual couples may be more likely to migrate in favour of the male ‘breadwinner's’ career if the couple have children, or are planning to commence childrearing in the foreseeable future. However, little work seems to have examined this empirically. The authors focus on the influence of ‘motherhood’ in different national contexts, using comparable census microdata for Great Britain and the United States. They test whether apparent ‘tied migration’ effects may in fact be influenced by family decisions related to childbearing/childrearing, and two sets of modelling results are provided. First, they examine whether the effects of long-distance family migration on women's labour-market status is influenced by the presence or absence of children of different ages. Second, they conduct the same analysis for women who have a high-status occupation. The results demonstrate that women in families with young children are most likely to be out of employment after family migration. A smaller, but similar, tied-migration effect exists for families with older children and families with no children. The same pattern exists for women in high-status occupations. Tied migration appears to influence women's labour-market status equally in Great Britain and the United States, regardless of the presence or absence of children.
Urban Water and the Politics of Citizenship: The Case of the Mexico City Metropolitan Area during the 1980s and 1990s
Authors: Castro José Esteban
Published: March 2004

The author focuses on the interrelations between access to urban water services and citizenship rights, taking the case of Mexico City Metropolitan Area as the empirical reference. Recent research has shown that social struggles over the access to and improvement of water services have been an important component of Mexican public life during at least the last twenty years. The author argues that mainstream explanations of the water crises tend to reduce the problem to its economic, technological, and physical – natural dimensions. Although the relevance of these factors affecting the provision of efficient and universal water and sanitation service is recognized the emphasis is placed on the socioeconomic and political inequalities that determine the exclusion of large sectors of the population from full access to essential living conditions, including water services.
Modelling Tourist Destination Choice Using a Decision Table Induction Algorithm
Authors: van Middelkoop Manon , Borgers Aloys W J , Timmermans H J P
Published: March 2004

The authors report on the development and test of a rule-based model of tourist destination choice, using decision tables to represent the rules that specify the conditions under which particular destination choices are made. Rules are extracted from empirical data on tourist destination choice, collected in the Netherlands in 1998. The specification of the model and its performance are discussed.
Behind the Cube Rule: Implications of, and Evidence against a Fractal Electoral Geography
Authors: Maloney John , Pearson Bernard , Pickering Andrew
Published: March 2004

In 1909 Parker Smith showed that the ratio of seats won by the two major parties in Britain was close to the cube of the ratio of their votes. Taagepera and Shugart argue, wrongly, that a fractal electoral map implies this. In fact, their premises imply that the seats' ratio will be the votes' ratio to the power of √3, not 3. However, in the six countries we examine, the figure is between 2 and 3. This implies that the electoral map is nonfractal, political allegiances becoming less ‘clustered’ as you move from a macro to a micro scale. Taking the United Kingdom, we ask if this is a result of the geographical pattern of income distribution, and find that this is even further away from fractality than is voting. This fits the well-known ‘neighbourhood effect’ whereby poor (rich) people in rich (poor) constituencies vote as if richer (poorer) than they really are.
Job Access and Employment among Low-Skilled Autoless Workers in US Metropolitan Areas
Authors: Kawabata Mizuki
Published: March 2004

Focusing on low-skilled workers, I present an empirical analysis of the relationship between transit-based job accessibility and employment outcomes for workers without automobiles. The metropolitan areas examined are Boston, San Francisco, and Los Angeles. Two essential components of the analysis are the calculation of refined job-access measures that take into account travel modes as well as the supply and demand of the labor market, and the incorporation of job-access measures into multinomial logit models. The results indicate that improved transit-based job accessibility significantly augments both the probability of being employed and the probability of working 30 hours or more per week for autoless workers in San Francisco and Los Angeles. Further, in these two areas, job accessibility has a greater effect for autoless workers than for auto-owning workers. Job accessibility plays a more significant role in employment outcomes for autoless workers in San Francisco and Los Angeles, highly auto-dependent areas, than it does in Boston, a more compact area with relatively well-developed transit systems. The empirical findings hold important implications for the theory and policy debate surrounding spatial mismatch.
Technologies Making Space Visible
Authors: Ueno Naoki , Kawatoko Yasuko
Published: March 2004

Studies of information technologies in workplaces are of growing significance to people in a broad range of professions and organizations, particularly those involved in the development of new technologies. The authors examine two kinds of information technologies for the support of service technicians, which have been developed in a copier customer service and support company. One is a mobile self-dispatch system with which service technicians monitor a list of customers' requests to repair machines in their service area. The other is a knowledge system. Particular attention is paid to investigating how these systems are embedded in a specific sociotechnological organization and work in service technicians' daily activities. Through the analysis of service technicians' activities, and interviews, the authors show that service technicians organize and make their workspace and activities visible with these technologies.
Transportation Impact Statement (TIS)—A New Tool for Transportation and Land-Use Planning
Authors: Ben-Elia Eran , Shefer Daniel , Shiftan Yoram
Published: March 2004

The authors advance a new approach to transportation and land-use planning: the transportation impact statement (TIS). Current planning practice suffers from a lack of understanding of and adequate tools to evaluate the complex relationships that exist between land use and transportation. Consequently, land-use development frequently overloads the transportation system. A TIS exposes the complex interdependencies with a multimodal and regional assessment of the impact of land-use development on the transportation system. The authors offer a theoretical background for this new approach and an empirical illustration of its potential use through a case study based on the city of Haifa in Israel. The objective of the study is to investigate the local and regional transport-related impacts of proposed land developments, thus improving the planning decisionmaking process. The impact of the proposed land developments on the transportation system was studied utilizing several transportation scenarios, including travel-demand management (TDM) strategies, using the metropolitan database and travel-demand modeling systems. The results show that the total number of trips generated by the proposed land developments is by far inconsistent with the capacity of the transportation network to accommodate all the forecasted demands under all transport scenarios. These results have a number of implications. First, TIS clearly improves our understanding of the impact of land development on the transportation system, and thus it should be utilized in decisionmaking regarding land-development strategy. Second, TIS stresses the importance of transit and TDM strategies as mitigation measures in the planning process. Third, TIS illustrates the need for a wider (that is, not site-related) planning perspective—including setting overall metropolitan goals and objectives.
Pension Security in the Global Economy: Markets and National Institutions in the 21st Century
Authors: Clark Gordon L
Published: March 2004

This paper begins with the issue of pension security, referencing the desired predictability, stability, long-lived nature of benefits, and coverage of retirement incomes. Also considered is the issue of pension security in the light of global financial market performance and integration. Having discussed issues of nation-state fiscal capacity and the consequences of the technology, media, and telecommunications speculative bubble for stock market returns it is suggested that pension security is also a matter of institutional integrity. This is illustrated with reference to debate in US Congress over the proper response to the Enron debacle. It is argued that no public or private institutions (including the nation-state and large corporations) can now guarantee the final value of pension benefits. As the baby boom generation comes to retirement across the Western world, pension security in the form of guaranteed pension benefit value is a hollow ideal; a chimera on the horizon of nation-state politics that cannot be sustained, notwithstanding the commitment of many to social justice and social solidarity between the generations.
Measuring the Social Environment: Social Cohesion and Material Deprivation in English and Scottish Neighbourhoods
Authors: Stafford Mai , Bartley Mel , Sacker Amanda , Marmot Michael , Wilkinson Richard , Boreham Richard , Thomas Roger
Published: March 2004

Despite increasing interest in macrosocial determinants of health, progress has been hampered by a lack of information on contextual factors and a lack of clarity in defining aspects of the social environment which may be important. A theoretical and empirical approach to measuring social cohesion in neighbourhoods in England and Scotland is described. Some forms of social networks, such as contact with friends and participation in organised groups, promoted trust, attachment to neighbourhood, and tolerance or respect for others. Notably, neighbourhoods in which family ties were predominant tended to be less tolerant. The cognitive aspects of social cohesion (trust, attachment, practical help, and tolerance or respect) tended to be lower in more materially deprived areas. Both the material and social characteristics of places may contribute to spatial variations in health.
Changing Governance Patterns in the Trade in Fresh Vegetables between Africa and the United Kingdom
Authors: Dolan Catherine , Humphrey John
Published: March 2004

Over the past twenty years the marketing of African fresh vegetables in the United Kingdom has become dominated by large retailers that have adopted competitive strategies based on quality, year-round supply, and product differentiation. This has led to a dramatic change in marketing channels, from wholesale markets to tightly knit supply chains. Global value chain analysis is used to explain why the various stages of production and marketing have become much more closely integrated and to consider the likely outcome of a further round of restructuring occurring at the present time. Although the current trends may lead to a changing role for importers, the tendency towards the concentration of production and processing in Africa in the hands of a few large firms is likely to continue.
Financial Globalization and Cross-Border Comovements of Money and Population: Foreign Bank Offices in Los Angeles
Authors: Dymski Gary , Li Wei
Published: March 2004

Studies of migration and financial globalization focus on either the movement of money, with people staying put, or on the movement of people, with little attention to the impact of the money that moves with them. This paper uses in-depth interviews with executives at ethnic-Chinese foreign-bank offices in Los Angeles to consider the comovement of people and money. We find that understanding the causes and consequences of this comovement requires adding both ethnic and macrostructural layers to discussions of financial globalization. The forces that have led to the rise of a Chinese-American banking sector and to the opening of twenty-one Chinese foreign-bank offices in Los Angeles are intertwined: immigration from the Chinese diaspora to the USA, the growth trajectory and financial transformation of East Asia, and the financial and economic evolution of Los Angeles. Ethnic-Chinese foreign-bank offices in Los Angeles have dual roles: they function both as global outposts managing their headquarters' cross-border financial flows, and as localized institutions that are gradually becoming incorporated into Southern California's internal banking and financial markets. Foreign and domestic ethnic-Chinese banks play complementary roles in facilitating ethnic-Chinese economic development in Southern California. Framing these cross-border money–population flows and this cross-border institution building, respectively, are macrostructural constraints rooted in aggregate net financial flows and the changing strategies of global megabanks.
The Link between Local Production Systems and Public and University Research in Italy
Authors: Rodríguez-Pose Andrés , Refolo Maria Cristina
Published: March 2004

Small and medium-sized firms (SMEs) are increasingly regarded as engines of innovative activity, especially in some of the most dynamic local areas in Western Europe. However, most SMEs lack the adequate resources to conduct research and development (R&D), which is traditionally considered as the main source of innovation. This apparent contradiction has induced several researchers to try to answer the question of where SMEs get their knowledge inputs. This literature, which has tended to use patents as a proxy for public research, has found that SMEs are particularly sensitive to spillovers from university and public research. In this paper the authors readdress this question by using a bibliometric indicator of public research output, instead of patents, for 100 Italian provinces during the 1990s. The results highlight that there is a strong geographical connection between the territorial concentration of SMEs and public research and that this connection is sensitive to firm size.