bluuebunny/crossref_metadata_2025 huggingface dataset:
Black Theatre: Present Condition
Authors: King Woodie
Published: April 2006

A black who works in the theatre, who cannot survive without it, can easily go out of his mind trying to write about it. It is even more difficult if he is a black writer writing in a white publication for a white majority. The white majority— who have unlimited access to the mass media—always expects a black writer to prove something about the black state of mind, something most blacks know exist, and that whites know exist—after four major riots. Yet these same1 whites are trying to deny that knowledge by pretending integration is just around the corner.
The Icon and the Absurd
Authors: Kott Jan
Published: April 2006

In the casinos of Las Vegas the black-jack tables and roulette wheels stand silent from five to seven A.M. Slotmachines alone remain for the stragglers unconquered by night and fatigue. These slotmachines do not give their players even the illusion of control, for the game consists only of throwing in money and moving the metal arms. Fate is blind and completely encased in the mechanism. The player merely sets fate in motion, and fate in turn brings either a loss of the stake or its manifold increase. The slotmachines are closed structures: the player and the mechanism—no one and nothing beyond that. “Others” in this structure do not exist. No one stands between the player and fate. “God,” who arranges the mechanism, repairs it, takes out the money, is invisible. He doesn't exist, at least not for the player.
Predation, Competition, and the Composition of Larval Anuran Guilds
Authors: Morin Peter J.
Published: April 2006

Experimental manipulations of densities of the predatory salamanders Notophthalmus viridescens dorsalis and Ambystoma tigrinum significantly altered relative abundances of six species of larval anurans in 22 artificial—pond communities. One competitively inferior anuran, Hyla crucifer, was virtually excluded from predator—free control communities but survived best and occurred at greater relative abundances in communities containing high densities of Notophthalmus. A second competitively inferior species, Hyla gratiosa, survived best at intermediate intensities of predation. Each of four competitively superior species (Scaphiopus holbrooki, Rana sphenocephala, Bufo terrestris, and Hyla chrysocelis) exhibited inverse relationships between relative abundance and Notophthalmus density. Ambystoma eliminated the entire anuran guild from tank communities and had a much greater per capita impact on anuran guild composition than did Notophthalmus. In most anuran species, maximum and mean mass at metamorphosis were positively correlated with predator density, suggesting an inverse relationship between intensities of predation and competition among tadpoles. Low growth rates of most anuran species in the absence of predators were correlated with high abundances of superior competitors. These results indicate that predators mediated interspecific competition among larval anurans. Intermediate values of Notophthalmus density maximized the total production of anuran metamorph biomass. Biomass of metamorphs of each species varied in a species—specific manner with predation. The propensity of Rana sphenocephala for overwintering as tadpoles following a season of growth was also related to predator density. Laboratory feeding experiments demonstrated that at least two competitively superior anurans, Scaphiopus holbrooki and Bufo terrestris, were especially vulnerable to predation by salamanders. This suggested that Notophthalmus may preferentially remove competitively superior anurans from pond communities, allowing competitively inferior anurans to persist and to complete development successfully at moderate to high predator densities.
Equilibrium and Nonequilibrium Concepts in Ecological Models
Authors: DeAngelis D. L. , Waterhouse J. C.
Published: April 2006

Mathematical models and empirical studies have revealed two potentially disruptive influences on ecosystems; (1) instabilities caused by nonlinear feedbacks and time—lags in the interactions of biological species, and (2) stochastic forcings by a fluctuating environment. Because both of these phenomena can severely affect system survival, ecologists are confronted with the question of why complex ecosystems do, in fact, exist. Our study analyzes the basic themes of this research and identifies five general hypotheses that, in recent years, theoretical ecologists have built into models to increase their stability against disruptive feedback and stochasticity. To counter feedback instabilities, theoreticians have considered (1) functional interactions between species that act as stabilizers, (2) disturbance patterns that interrupt adverse feedback effects, and (3) the stabilizing effect of integrating small—spatial—scale systems into large landscapes. To decrease the influence of stochasticity, modelers have hypothesized (4) compensatory mechanisms operating at low population densities, and (5) the moderating effect of spatial extent and heterogeneity. We show that modeling based on these ideas can be organized in a systematic way. We also show that the stable equilibrium state should not be viewed as a fundamental property of ecological systems, but as a property that can emerge asymptotically from extrapolation to sufficiently large spatial scales.
Binding diversity of the two binding sites of ricin B lectin
Authors: Ganguly Debabani , Mukhopadhyay Chaitali
Published: April 2006

Ricin B is a galactose‐binding protein, which contains two binding sites. We have compared the binding properties of the two binding sites of ricin B chain toward different mono‐ and disaccharide ligands. The free energies of binding are calculated using the free energy perturbation simulation (thermodynamic integration method) and linear interaction energy approach using CHARMM force field. The second binding site of the protein was found to be weaker compared to the first. The details of the hydrogen‐bonding scheme suggested the origin of the epimeric specificity of the protein. The reason for the weaker binding capacity of the second binding site has been addressed. © 2006 Wiley Periodicals, Inc. Biopolymers 83: 83–94, 2006

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Frequent gene dosage alterations in stromal cells of epithelial ovarian carcinomas
Authors: Tuhkanen Hanna , Anttila Maarit , Kosma Veli‐Matti , Heinonen Seppo , Juhola Matti , Helisalmi Seppo , Kataja Vesa , Mannermaa Arto
Published: April 2006

Stromal cells are an active and integral part of epithelial neoplasms. We have previously observed allelic imbalance on chromosome 3p21 in both stromal and epithelial cells of ovarian tumors. This study was designed to explore gene dosage alterations throughout human chromosomes from stromal and epithelial cells of epithelial ovarian carcinomas. Thirteen stromal and 24 epithelial samples, microdissected from epithelial ovarian carcinomas, were analyzed using multiplex ligation‐dependent probe amplification technique. Analysis covered 110 cancer related genes. Frequent genetic alterations were detected both in the stroma and epithelium of ovarian carcinomas. The mean number of altered genes per tumor was 10.8 in stroma and 23.6 in epithelium. In the stroma, the mean number of gains was 6.6 and of losses 4.2 and in the epithelium 13.7 and 9.9. The high number of changes associated with advanced tumor stage (p = 0.035) and death due to ovarian cancer (p = 0.032). The most frequent alteration was the deletion of the deleted in colorectal carcinoma (DCC) on chromosome 18q21.3 in 62% of samples. Loss of DCC was related to endometrioid subtype (p = 0.033). Large chromosomal aberrations were detected on the basis of alterations in adjacent genes. Most importantly, 38 genes showed similar genetic alterations (gain–gain or loss–loss) in stromal and epithelial compartments of 11 tumor pairs. Thus, frequent genetic alterations in stromal cells of epithelial ovarian carcinomas resembled those of malignant epithelial cells and may indicate a common precursor cell type. Epithelial–mesenchymal transition may generate transformed cancer cells and modify the tumor microenvironment with distinct properties. © 2006 Wiley‐Liss, Inc.
Radon, secondhand smoke, glutathione‐S‐transferase M1 and lung cancer among women
Authors: Bonner Matthew R. , Bennett William P. , Xiong Wenying , Lan Qing , Brownson Ross C. , Harris Curtis C. , Field R. William , Lubin Jay H. , Alavanja Michael C.R.
Published: April 2006

Tobacco smoke and ionizing radiation induce oxidative stress by transmitting or generating reactive oxygen species (ROS). We hypothesized that glutathione‐S‐transferase M1 (GSTM1) null homozygotes would have decreased ability to neutralize ROS that might increase their susceptibility to lung cancer. A case‐only design was used with lung cancer cases pooled from 3 previously completed case‐control studies using archival tissue samples from 270 lung cancer cases to genotype GSTM1. Radon concentrations were measured with long‐term α‐track radon detectors. Secondhand smoke (SHS) was measured with questionnaires and interviews. Unconditional logistic regression was used to calculate the interaction odds ratios (OR) and 95% confidence intervals (95% CI). Radon concentrations >121 Bq m−3 were associated with a >3‐fold interaction OR (OR = 3.41; 95% CI = 1.10, 10.61) for GSTM1 null homozygotes compared to GSTM1 carriers; the linear trend was significant (p trend = 0.03). The SHS and GSTM1 interaction OR was also elevated (OR = 2.28; 95% CI = 1.15–4.51) among never‐smokers. This may be the first study to provide evidence of a GSTM1 and radon interaction in risk of lung cancer. Additionally, these findings support the hypothesis that radon and SHS promote neoplasia through shared elements of a common pathway. © 2006 Wiley‐Liss, Inc.
Die Werkstoffermüdung bei Wälzbeanspruchung – Eine Hypothese zum Mechanismus
Authors: Schlicht H.
Published: April 2006

Die Erforschung der Wälzermüdung liefert eine Fülle experimenteller Ergebnisse und theoretischer Erkenntnisse. Aus einer Zusammenschau dieser bekannten Einzel‐Informationen wird eine Hypothese zum Mechanismus der Wälzermüdung entwickelt und im Folgenden vorgestellt.

Nach dieser Hypothese läuft der Ermüdungsprozess in drei Phasen ab. In den Phasen 1 und 2 wird der Werkstoff mikroplastisch verformt. Das Gefüge verliert an Festigkeit. Es entstehen Druckeigenspannungen, die sich den Lastspannungen überlagern und die Belastung stetig verändern. Die Verformungen kommen in der Phase 2 annähernd zum Stillstand. Bei einem kritischen Werkstoff‐ und Eigenspannungszustand, dem Übergang der Phase 2 in die Phase 3, geht die mikroplastische Verformung in einen makroplastischen Vorgang über. Das Gefüge „fließt”︁ in Teilbereichen – entsprechend der dann vorliegenden Richtung der „relativen”︁ Zugspannungen – zunehmend in Richtung Oberfläche. Dort entstehen zu beiden Seiten der Laufbahnfläche Aufwölbungen. Auch in der Laufbahn selbst entstehen Aufwölbungen; sie werden aber durch die Überrollungen wieder eingeebnet. Hierdurch bilden sich Zugeigenspannungen senkrecht zur Oberfläche. Die Eigenspannungen nehmen zu und lösen schließlich während der Entlastung, die der Überrollung folgt, die Bildung von „subsurface cracks”︁ aus.

Die Hypothese vermittelt ein Ermüdungsmodell, das die Phänomene, die bislang bei der experimentellen Erforschung des Ermüdungsvorgangs festgestellt wurden, weitgehend erklärt.

Sie eröffnet Möglichkeiten, Wälzsysteme auch weiterhin in ihrer Leistungsfähigkeit zu optimieren.
Semi-preserving development of a slightly heated free swirling jet
Authors: Elsner J. W. , Kurzak L.
Published: April 2006

The paper formulates the concept of a semi-preserving developing of a free nonisothermal swirling jet. On the basis of experimental data it may be estimated that the semi-preserving conditions are established at the distance x − x0 ≈ (15−20) D. Also, it has been pointed out that self-preservation, which requires the turbulence structure to be similar during decay, may be considered as an asymptotic state of the semi-preserving development achieved in practice at a distance where $\overline{u_r u_{\phi}/ \overline(u_x u_r) \ll 1\cdot 0$.
Effects of heat release on the large-scale structure in turbulent mixing layers
Authors: Mcmurtry P. A. , Riley J. J. , Metcalfe R. W.
Published: April 2006

The effects of chemical heat release on the large-scale structure in a chemically reacting, turbulent mixing layer are investigated using direct numerical simulations. Three-dimensional, time-dependent simulations are performed for a binary, single-step chemical reaction occurring across a temporally developing turbulent mixing layer. It is found that moderate heat release slows the development of the large-scale structures and shifts their wavelengths to larger scales. The resulting entrainment of reactants is reduced, decreasing the overall chemical product formation rate. The simulation results are interpreted in terms of turbulence energetics, vorticity dynamics, and stability theory. The baroclinic torque and thermal expansion in the mixing layer produce changes in the flame vortex structure that result in more diffuse vortices than in the constant-density case, resulting in lower rotation rates of the large-scale structures. Previously unexplained anomalies observed in the mean velocity profiles of reacting jets and mixing layers are shown to result from vorticity generation by baroclinic torques.
Transient flow in a side-heated cavity at high Rayleigh number: a numerical study
Authors: Schladow S. G. , Patterson J. C. , Street R. L.
Published: April 2006

A series of two- and three-dimensional numerical simulations of transient flow in a side-heated cavity has been conducted. The motivation for the work has been to resolve discrepancies between a flow description based on scaling arguments and one based on laboratory experiments, and to provide a more detailed description of the approach to steady state. All simulations were for a Rayleigh number of 2 × 109, and a water-filled cavity of aspect ratio 1. The simulations (beginning with an isothermal fluid at rest) generally agree with the results of the scaling arguments. In addition, the experimental observations are entirely accounted for by the position of the measurement instruments and the presence of an extremely weak, stabilizing temperature gradient in the vertical.
The secondary flow and its stability for natural convection in a tall vertical enclosure
Authors: Chait Arnon , Korpela Seppo A.
Published: April 2006

The multicellular flow between two vertical parallel plates is numerically simulated using a time-splitting pseudospectral method. The steady flow of air, and the time-periodic flow of oil (Prandtl numbers of 0.71 and 1000, respectively) are investigated and descriptions of these flows using both physical and spectral approaches are presented. The details of the time dependency of the flow and temperature fields of oil are shown, and the dynamics of the process is discussed. The spectral transfer of energy among the axial modes comprising the flow is explored. The spectra of kinetic energy and thermal variance for air are found to be smooth and viscously dominated. Similar spectra for oil are bumpier, and the dynamics of the time-dependent flow are determined to be confined to the lower end of the spectrum alone.

The three-dimensional linear stability of the multicellular flow of air is parametrically studied. The domain of stable two-dimensional cellular motion was found to be constrained by the Eckhaus instability and by two types of monotone instability. The two-dimensional multicellular flow is unstable above a Grashof number of about 8550 (with the critical Grashof number for the base flow being 8037). Therefore the flow of air in a sufficiently tall vertical enclosure should be considered to be three-dimensional for most practical applications.
The viscosity-volume fraction relation for suspensions of rod-like particles by falling-ball rheometry
Authors: Milliken William J. , Gottlieb Moshe , Graham Alan L. , Mondy Lisa A. , Powell Robert L.
Published: April 2006

The relative viscosities of suspensions of randomly oriented rods in a Newtonian fluid were measured using falling-ball rheometry. The rods were monodisperse and sufficiently large to render colloidal and Brownian forces negligible. Steel and brass ball bearings were dropped along the centreline of cylindrical columns containing the suspensions. The terminal velocities of the falling balls were measured and used to determine the average viscosities of the suspensions. The suspensions behaved as Newtonian fluids in that they were characterized by a constant viscosity. They exhibited a linear relative viscosity-volume fraction relationship for volume fractions less than 0.125, and, for volume fractions between 0.125 and 0.2315, the specific viscosity increased with the cube of the volume fraction. The relative viscosity was found to be independent of falling-ball size for a ratio of falling ball to fibre length greater than 0.3. It was found to be independent of the diameter of the containing cylindrical column for a ratio of column diameter to fibre length greater than 3.2. The value determined for the intrinsic viscosity is in good agreement with theoretical predictions for suspensions of randomly oriented rods.
A theory of turbulent transport
Authors: Weinstock J.
Published: April 2006

A calculation is made of the turbulent transport terms (third moments) that occur in the Reynolds stress equation for buoyant and/or sheared fluids. This calculation is based on neglect of a two-time fourth-order cumulant – a weaker approximation than neglect of the usual single-time fourth-order cumulant. The previously used eddy-damping assumption for single point moments is avoided. This assumption is then examined critically. Comparison is afterward made between the turbulent transport terms derived here and those derived previously by the eddy-damping method, and between the respective derivations. Also the dissipation of third moments is calculated. The calculation is formally limited to mean quantities which vary but slowly in space and time, and to small anisotropy.
The onset of convective instability in a triply diffusive fluid layer
Authors: Pearlstein Arne J. , Harris Rodney M. , Terrones Guillermo
Published: April 2006

The onset of instability is investigated in a triply diffusive fluid layer in which the density depends on three stratifying agencies having different diffusivities. It is found that, in some cases, three critical values of the Rayleigh number are required to specify the linear stability criteria. As in the case of another problem requiring three Rayleigh numbers for the specification of linear stability criteria (the rotating doubly diffusive case studied by Pearlstein 1981), the cause is traceable to the existence of disconnected oscillatory neutral curves. The multivalued nature of the stability boundaries is considerably more interesting and complicated than in the previous case, however, owing to the existence of heart-shaped oscillatory neutral curves. An interesting consequence of the heart shape is the possibility of ‘quasi-periodic bifurcation’ to convection from the motionless state when the twin maxima of the heart-shaped oscillatory neutral curve lie below the minimum of the stationary neutral curve. In this case, there are two distinct disturbances, with (generally) incommensurable values of the frequency and wavenumber, that simultaneously become unstable at the same Rayleigh number. This work complements the earlier efforts of Griffiths (1979a), who found none of the interesting results obtained herein.
Pressure fluctuations on an oscillating trailing edge
Authors: Staubli Thomas , Rockwell Donald
Published: April 2006

Turbulent boundary layers separating from a blunt trailing edge give rise to organized vortical structures in the downstream wake. The perturbation of this inherent flow-instability atf0by controlled oscillations of the edge atfeproduces corresponding, organized components of unsteady surface pressure along the edge. For edge excitation near the ‘natural’ vortex shedding frequencyf0, the phase between the local pressure fluctuations and the edge displacement shows large changes for small changes in excitation frequency. Moreover, in this range of excitation, there is quenching (or attenuation) of the surface pressure component atf0and resonant peaking of the component atfe. These phenomena are related to the change in sign of the energy transfer between the fluid and the body. Integration of the instantaneous pressure distributions along the surfaces of the edge leads to the instantaneous lift atfeandf0acting upon the oscillating trailing edge. The location of the lift varies as the cotangent of the dimensionless time during an oscillation cycle. When the edge is excited near, or at, the natural vortex shedding frequency, there is a resonant peak in the amplitude of oscillation of the lift location atfe; that atf0is invariant. Moreover, the mean location of the lift atfeundergoes abrupt changes in this region of excitation. Flow visualization allows determination of the phasing of the organized vortical structures shed from the trailing edge relative to the edge displacement. Modulation of the flow structure at the frequenciesf0andfe, as well as interaction of small-scale vortices at high excitation frequencies, was observed. These aspects of the near-wake structure are related to the instantaneous pressure field.
Stationary instability of the convective flow between differentially heated vertical planes
Authors: Daniels P. G.
Published: April 2006

An asymptotic theory describes the stationary instability of convective flow between differentially heated vertical planes at large Prandtl numbers. The theory is concerned with the structure for A [Gt ] 1 where A is a Rayleigh number based on the horizontal temperature difference and the distance between the planes. As such it is relevant to the instability of flow in a vertical slot of aspect ratio h [Gt ] 1 where the convective regime corresponds to order-one values of a non-dimensional parameter γ which partly depends on the vertical temperature gradient generated in the slot and can be approximated by γ4 = A/8h. Instability is shown to set in at a critical value of γ that compares well with experimental observation. The lower branch of the neutral curve conforms to a boundary-layer type approximation while the upper branch has a critical-layer structure midway between the planes which becomes fully developed as the first reversal of the vertical velocity of the base flow is encountered near the centreline.
Flow past short circular cylinders with two free ends
Authors: Zdravkovich M. M. , Brand V. P. , Mathew G. , Weston A.
Published: April 2006

Preliminary tests have been carried out on short circular cylinders with both ends free. Drag force is measured across the range 6 × 104 < Re < 2.6 × 105 for cylinders of length to diameter ratio L/D between 1 and 10. The effect of hemispherical ends is also investigated. A kind of periodic vortex shedding is found in the range 2 < L/D < 8. The oil-film surface flow visualization shows that the ‘eyes’ near the free ends (regions of low pressure) gradually disappear as L/D is reduced to 3. An asymmetric flow pattern is established for very short cylinders (L/D < 3). The detailed measurements of pressure distribution along and across models shows asymmetries of minimum and base pressures along the span. The asymmetric flow produces yawing and rolling moments which are also measured.
Influence of density variations on the structure of low-speed turbulent flows: a report on Euromech 237
Authors: Fulachier L. , Borghi R. , Anselmet F. , Paranthoen P.
Published: April 2006

The European Mechanics Colloquium number 237 was held at the Institut de Mécanique Statistique de la Turbulence (Université d'Aix-Marseille II) from 18 to 21 July 1988. This was the first meeting to consider the influence of density variations on turbulent flows for both non-reacting and reacting flows in a variety of configurations. Several new experiments, computational models and theoretical analyses were presented for non-reacting flows. All these approaches showed the marked effects of density variations on coherent structures in turbulent shear flows. It was found that the approximate models used for turbulent Reynolds stresses in homogeneous flows do not need to be changed for the mean flow field but predictions for variances and correlations are still rather uncertain: in fact experimental results providing such information in variable-density flows are rare. The special problem of measuring turbulence in flows with density variations was discussed. In the discussions it was agreed that there are in fact strong similarities in the effects of density gradients on the dynamics of non-reacting flows and reacting flows despite the differences in the distributions of density gradients. Participants at the meeting from industry emphasized the importance of these flows to many different kinds of industrial and environmental problems.
On the foundations of generalized Taylor dispersion theory
Authors: Frankel I. , Brenner H.
Published: April 2006

Generalized Taylor dispersion theory extends the basic long-time, asymptotic scheme of Taylor and Aris greatly beyond the class of rectilinear duct and channel flow dispersion problems originally addressed by them. This feature has rendered it indispensable for studying flow and dispersion phenomena in porous media, chromatographic separation processes, heat transfer in cellular media, sedimentation of non-spherical Brownian particles, and transport of flexible clusters of interacting Brownian particles, to mention just a few examples of the broad class of non-unidirectional transport phenomena encompassed by this scheme. Moreover, generalized Taylor dispersion theory enjoys the attractive feature of conferring a unified paradigmatic structure upon the analysis of such apparently disparate physical problems. For each of the problems thus treated it provides an asymptotic, macroscale description of the original microscale transport process, being based upon a convective-diffusive ‘model’ problem characterized by a set of constant (position- and time-independent) phenomenological coefficients.

The present contribution formally substantiates the scheme. This is accomplished by demonstrating that the coarse-grained (macroscale) transport ‘model’ equation leads to a solution which accords asymptotically with the leading-order behaviour of the comparable solution of the exact (microscale) convective–diffusive problem underlying the transport process. It is also shown, contrary to current belief, that no systematic improvement in the asymptotic order of approximation is possible through the incorporation of higher-order gradient terms into the model constitutive equation for the coarse-grained flux. Moreover, the inherent difference between the present rigorous asymptotic scheme and the dispersion models resulting from Gill–Subramanian moment-gradient expansions is illuminated, thereby conclusively resolving a long-standing puzzle in longitudinal dispersion theory.
Solitary waves in magma dynamics
Authors: Barcilon Victor , Lovera Oscar M.
Published: April 2006

We investigate the stability of the one-dimensional solitary waves solutions of the equations proposed by McKenzie to model the ascent of melts in the Earth interior. We show that for small porosity and two-dimensional horizontal disturbances with long wavelength, these solitary waves are unstable. We also exhibit two- and three-dimensional solitary-wave solutions of the McKenzie equations.
A variational method for water wave radiation and diffraction problems
Authors: Aranha J. A. P. , Pesce C. P.
Published: April 2006

It is shown that the linear and nonlinear exciting force coefficients, the added mass and radiation damping matrices, and the far-field wave amplitude (reflection and transmission coefficients in the two-dimensional case) can all be written as stationary values of well-defined functionals. As a consequence these quantities can be accurately determined with relatively crude approximations for the diffraction and radiation potentials. Numerical experiments confirm this feature: by inverting a 4 × 4 real symmetric matrix the results obtained by Vugts (1968), who computed the added mass and radiation damping matrices for several different geometries, were recovered over the whole range of frequencies.
Modal exchange mechanisms in Lapwood convection
Authors: Riley D. S. , Winters K. H.
Published: April 2006

Techniques of bifurcation theory are used to study the porous-medium analogue of the classical Rayleigh-Bénard problem: Lapwood convection in a two-dimensional saturated porous cavity heated from below. Two particular aspects of the problem are focused upon: (i) the existence of multiple steady solutions and (ii) the influence of aspect ratio.

Convection begins only when the applied temperature difference (say) exceeds a critical value defined by linear stability theory. The resulting convective flow pattern depends both on the magnitude of the temperature difference and on the aspect ratio of the cavity. A weakly nonlinear analysis reveals the roles played by so-called secondary bifurcations in determining the formation of further, anomalous patterns at fixed aspect ratio. In addition to giving rise to alternative stable flows for identical operating conditions, the secondary bifurcations are required for the modal exchanges which take place as the aspect ratio varies, a process which causes an abrupt change in preferred flow pattern at certain critical values of the aspect ratio.

As a complement to and an extension of the weakly nonlinear analysis, numerical methods are used to determine the bifurcation processes and to elucidate the modal exchange mechanisms in both weakly and strongly convective flows. The effect of container size is studied by continuation methods to predict the variation of the critical Rayleigh number of the bifurcation points for aspect ratios in the range 0.5 to 2.0. In this way a stability map is obtained which shows the alternative patterns expected for particular operating conditions. The Nusselt number is computed and it is found that the alternative stable modes transfer significantly different amounts of heat through the medium.

The study has provided new information on the existence and characteristics of, and interactions between, alternative steady modes of two-dimensional Lapwood convection. The results have important ramifications for the modelling and design of physical systems in which convective flow in a saturated porous medium is stimulated by an imposed unstable temperature gradient.
A note on complete sets of material conservation laws
Authors: Egger Joseph
Published: April 2006

An attempt is made to derive complete sets of conservation laws for various flows. It is shown that the equations of three-dimensional adiabatic flow cannot be transformed into a complete set of conservation laws. It is demonstrated that potential vorticity is the only material invariant of shallow-water flow. A complete set can be derived for three-dimensional homogeneous flow, if Lagrangian tracers are added.
Loss of frequency response along sampling tubes for the measurements of gaseous composition at high temperature and pressures
Authors: Smith Ronald
Published: April 2006

Measurements of the rapidly changing gaseous composition in engines at low speed can be made via narrow tubes which convey the gases to monitoring equipment in a less hostile environment. This paper quantifies the extent to which the tube smooths out any changes in concentration. Exact (and approximate) formulae are derived for the temporal variance as weighted double (and single) integrals of the steady flow properties along the tube. Such is the non-uniformity that typically the region near the engine contributes 100 times as much to the spreading as does the region near the monitoring equipment. The advantages of keeping the sampling tubes short and heated are made explicit.
Planetary semi-geostrophic equations derived from Hamilton's principle
Authors: Shutts G. J.
Published: April 2006

A new set of balanced equations (to be called planetary semi-geostrophic equations) for planetary-scale flow is derived from Hamilton's principle and constitutes a natural generalization of the semi-geostrophic equations of motion. Analogues of the global conservation of energy and the Lagrangian conservation of potential vorticity follow automatically by introducing approximations directly into the Hamiltonian in such a way that time and particle label symmetries are preserved. Two approximations are required: first, the kinetic energy associated with the component of velocity parallel to the axis of rotation is neglected; and secondly, the Lagrangian rate of change of the wind and pressure gradient directions (when projected onto the equatorial plane) must be small compared with twice the angular rotation rate of the system. Although the first of these approximations entails some loss of accuracy for application to the terrestrial atmosphere it is not nearly as severe as that for the Phillips type II geostrophic equations in which all of the kinetic energy is omitted from the Hamiltonian. The resulting equations take exactly the same form as the f-plane semi-geostrophic equations apart from a modification to the pseudo-density appearing in the continuity equation. They are also amenable to the geostrophic momentum coordinate transformation – a device which has had considerable impact on the theory of atmospheric fronts. In order to assess the accuracy of the equations, three different linearized eigenvalue problems on the sphere are solved and compared with the equivalent primitive equation problems. Eigenmodes are least accurate for high-zonal-wavenumber disturbances with grave meridional structure. Stationary, baroclinic planetary waves with zonal wavenumber less than ≈ 7 are shown to be accurately treated. The equations also support equatorially trapped Kelvin and Rossby modes which are accurate in the long-wave limit for meteorologically relevant equivalent depths.
On the prediction of equilibrium states in homogeneous turbulence
Authors: Speziale Charles G. , Mhuiris Nessan Mac Giolla
Published: April 2006

A comparison of several commonly used turbulence models (including the K–ε model and three second-order closures) is made for the test problem of homogeneous turbulent shear flow in a rotating frame. The time evolution of the turbulent kinetic energy and dissipation rate is calculated for these models and comparisons are made with previously published experiments and numerical simulations. Particular emphasis is placed on examining the ability of each model to predict equilibrium states accurately for a range of the parameter Ω/S (the ratio of the rotation rate to the shear rate). It is found that none of the commonly used second-order closure models yield substantially improved predictions for the time evolution of the turbulent kinetic energy and dissipation rate over the somewhat defective results obtained from the simpler K–ε model for the unstable flow regime. There is also a problem with the equilibrium states predicted by the various models. For example, the K–ε model erroneously yields equilibrium states that are independent of Ω/S while the Launder, Reece & Rodi model and the Shih-Lumley model predict a flow relaminarization when Ω/S > 0.39 - a result that is contrary to numerical simulations and linear spectral analyses, which indicate flow instability for at least the range 0 [les ] Ω/S [les ] 0.5. The physical implications of the results obtained from the various turbulence models considered herein are discussed in detail along with proposals to remedy the deficiencies based on a dynamical systems approach.
Linear-eddy modelling of turbulent transport. Part 3. Mixing and differential molecular diffusion in round jets
Authors: Kerstein Alan R.
Published: April 2006

The linear-eddy model of turbulent mixing represents a spatially developing flow by simulating the time development along a comoving transverse line. Along this line, scalar quantities evolve by molecular diffusion and by randomly occurring spatial rearrangements, representing turbulent convection. The modelling approach, previously applied to homogeneous turbulence and to planar shear layers, is generalized to axisymmetric flows. This formulation captures many features of jet mixing, including differential molecular diffusion effects. A novel experiment involving two unmixed species in the nozzle fluid is proposed and analysed.
The turbulent near wake of a flat plate at low Reynolds number
Authors: Nakayama A. , Liu B.
Published: April 2006

Mean-velocity and turbulence measurements have been made in the turbulent near wake of a flat plate at various Reynolds numbers in order to investigate the low-Reynolds-number effects in this region. The results indicate that the low-Reynolds-number effects are significant enough to partially explain the discrepancies in the existing mean-velocity data. It has been found that, while the Reynolds-number-independent, inner-law similarity of the boundary layers continues to exist, the width of the inner wake that develops within the inner-law region scales with the outer variable. Therefore, the mean velocity near the wake centreline depends on the Reynolds number. It is conjectured that this is due to the influence of the large eddies of the outer layer on the spreading of the inner wake.

Measured turbulence quantities indicate that sudden changes occurring just downstream of the trailing edge are independent of the Reynolds number, but the subsequent development of the turbulent stress profiles depends on the Reynolds number. The Reynolds shear stress and the mean-velocity profiles within the inner wake show approximate similarity.
Mixing at large Schmidt number in the self-similar far field of turbulent jets
Authors: Dahm Werner J. A. , Dimotakis Paul E.
Published: April 2006

We present results from an experimental investigation of turbulent transport and molecular mixing of a Sc [Gt ] 1 conserved scalar in the fully developed self-similar far field of a steady, axisymmetric, momentum-driven, free turbulent jet issuing into a quiescent medium. Our experiments cover the axial range from the jet exit to 350 diameters downstream, and span the range of Reynolds numbers from 1500 to 20000. Flow visualizations of the scalar concentration field directly verify the presence of an underlying characteristic large-scale organization in the jet far field essentially consistent with a simplified conceptual picture proposed in an earlier study (Dahm & Dimotakis 1987). High-resolution imaging measurements of successive instantaneous scalar concentration profiles in the jet support the presence of such a large-scale organization and provide details of its implications for mixing. These results also establish the proper similarity scaling for the mean concentration in the jet far field and give the scaling constant on the jet centreline as 5.4. We also present conserved scalar concentration p.d.f.s throughout the jet far field, and introduce a chemical reaction method for measuring the p.d.f.s with potentially molecular resolution. The amount of unmixed ambient fluid that reaches the jet centreline is found to decrease with increasing Reynolds number over the range investigated. The distribution of mixed fluid compositions in the concentration p.d.f. also appears to change over this range of Reynolds numbers, indicating that some aspects of large Schmidt number mixing in the jet far field have not yet become Reynolds number independent.
Breakup of concentric double emulsion droplets in linear flows
Authors: Stone H. A. , Leal L. G.
Published: April 2006

The behaviour of concentric double emulsion droplets in linear flows is examined analytically, for the case when both fluid–fluid interfaces remain nearly spherical, and numerically, for the effect of finite interface deformation. The theoretical analysis is used to calculate the velocity fields interior and exterior to the particle, the first effects of flow-induced deformation, and the effective viscosity of a dilute emulsion of compound droplets. The numerical simulations allow for a complete investigation of the finite deformation of both the outer drop and the encapsulated particle. For concentric multiphase particles, there appear to be two distinct mechanisms of globule breakup: (i) continuous extension of the globule corresponding to non-existence of a steady particle shape or (ii) contact of the two interfaces at the globule centre, owing to incompatibility of the steady inner and outer interface shapes, even though the globule is only modestly deformed. Finally, the effect of different flow-types, i.e. uniaxial or biaxial extensional flows, is shown, in one example, to suggest breakup of the inner droplet even though the outer droplet maintains a steady shape.
Nonlinear flow phenomena in a symmetric sudden expansion
Authors: Fearn R. M. , Mullin T. , Cliffe K. A.
Published: April 2006

The origin of steady asymmetric flows in a symmetric sudden expansion is studied using experimental and numerical techniques. We show that the asymmetry arises at a symmetry-breaking bifurcation and good agreement between the experiments and numerical calculations is obtained. At higher Reynolds numbers the flow becomes time-dependent and there is experimental evidence that this is associated with three-dimensional effects.
Evolution of weakly nonlinear waves in a cylinder with a movable piston
Authors: Wang Meng , Kassoy D. R.
Published: April 2006

Small-amplitude wave motion in an inert gas confined between a moving piston and a fixed cylinder endwall is studied using the unsteady Euler equations. The waves, generated by either initial disturbances or piston motion, reflect back and forth in the cylinder on the acoustic timescale. The accumulated effect of these waves controls the bulk variations of velocity and thermodynamic variables on the longer piston timescale. Perturbation methods, based on the small ratio of acoustic to piston time, are employed to formulate the gasdynamic problem. The application of multiple timescaling allows the gasdynamic wave field to be separated from the bulk response of the gas. The evolution of the wave phenomena, including nonlinear wave deformation and weak shock formation during the piston passage time, is described in terms of time-dependent Fourier series solutions, whose coefficients are computed from a truncated system of coupled nonlinear ordinary differential equations. The long-time asymptotic flow field after shock formation is sawtooth-like, in which case the Fourier modes become decoupled. A remarkably simple relation between the shock amplitude and piston velocity is discovered. It is demonstrated that (i) the wave amplitude and frequency strongly depend on the piston motion; (ii) shock waves can be damped in a significant way by internal dissipation; and (iii) the mathematical approach developed in this study possesses certain advantages over the more traditional method of characteristics.
On the evaluation of barotropic-baroclinic instability parameters of zonal flows on a beta-plane
Authors: Gnevyshev Vladimir G. , Shrira Victor I.
Published: April 2006

The paper is concerned with the problem of the linear stability of an arbitrary inviscid zonal flow on a β-plane. Based on the analysis of integral relations following from the linear boundary-value problem, new evaluations, considerably more exact than the previously known ones, of the parameter region of unstable disturbances are derived. Some new relations among these bounds are established.
Radial spreading of viscous-gravity currents with solidifying crust
Authors: Fink Jonathan H. , Griffiths Ross W.
Published: April 2006

We have investigated the effect of a solidifying crust on the dynamics and surface morphology of radial viscous-gravity currents. Liquid polyethylene glycol was admitted into the base of a tank filled with cold sucrose solution maintained at a temperature below the wax freezing point. As the radial current advanced away from the inlet, its surface solidified and deformed through a combination of folding and fracturing. For the warmest experiments, during which solidification did not occur, the radius of the current increased in proportion to the square root of time, as demonstrated both experimentally and theoretically for isothermal viscous fluids by Huppert (1982). When cooling was sufficiently rapid, solid crust formed and caused the spreading rate to decrease. A cooling model combining conduction in the wax with convection in the sucrose solution predicts the distance from the source at which the solid crust first appeared

Progressively colder experiments revealed a sequence of surface morphologies which resembled features observed on cooling lava flows and lava lakes. Flows in which crust formed very slowly developed marginal levees which contained and channelled the main portion of the current. Colder flows with more rapid crust growth formed regularly spaced surface folds, multi-armed rift structures complete with shear offsets, and bulbous lobate forms similar to pillow lavas seen under the ocean. The same transitions between modes of surface deformation were also generated by keeping the ambient water temperature constant and decreasing the extrusion rate. This demonstration that surfaces can exhibit a well-defined sequence of morphologies which depend on the underlying flow conditions offers the prospect of more successful interpretation of natural lava flows.
Three-dimensional oscillation characteristics of electrostatically deformed drops
Authors: Feng James Q. , Beard Kenneth V.
Published: April 2006

A three-dimensional asymptotic analysis of the oscillations of electrically charged drops in an external electric field is carried out by means of the multiple-parameter perturbation method. The mathematical framework allows separate treatments of the quiescent deformation due to the electric field and the oscillatory motions caused by other physical factors. Without oscillations, the solution for the quiescent drop shape exhibits a prolate deformation with a slight asymmetry about the drop's equatorial plane. This axisymmetric quiescent deformation of the equilibrium drop shape is shown to modify the oscillation characteristics of axisymmetric as well as asymmetric modes. The expression of the characteristic frequency modification is derived for the oscillation modes, manifesting fine structure in the frequency spectrum so the degeneracy of Rayleigh's normal modes for charged drops is removed in the presence of an electric field. Physical reasoning indicates that the degeneracy of the oscillation modes is associated with the spherical symmetry of the system, so the removal of the degeneracy may be regarded as a consequence of the symmetry breaking caused by the electric field. In addition, the small-amplitude oscillation mode shapes are also modified as a result of the coupling between the oscillatory motions and the electric field as well as the quiescent deformation.
Blocking an inviscid shear flow
Authors: Stern Melvin E.
Published: April 2006

The upstream influence in an inviscid two-dimensional shear flow around a semicircular ‘cape’ (radius A) is computed using a piecewise uniform vorticity model of a boundary-layer current. The area of this layer upstream from the cape increases as the square root of time t when A is small, and increases as t for larger A. Complete blocking occurs when A is approximately three times the boundary-layer thickness, in which case all oncoming particles accumulate in a large upstream vortex. The numerical results obtained from the contour dynamical method also show the generation of large eddies downstream from the obstacle.