bluuebunny/crossref_metadata_2025 huggingface dataset:
Intraspecific Variation in Sapling Mortality and Growth Predicts Geographic Variation in Forest Composition
Authors: Kobe Richard K.
Published: April 2006

With a view toward understanding variation in species composition among different forest communities, I examined species—specific growth and mortality of juvenile trees (2.3—78 mm diameter at 10 cm above the ground) at three contrasting sites. Two sites differing in soil mineralogy and elevation (schist/gneiss uplands vs. calcareous bedrock valley) were situated in northwestern Connecticut, USA. To examine variation over a more extensive geographic scale, I located the third site in central—western Michigan, USA. Among the three sites, the deciduous species (American beech, white ash, and sugar maple) showed little intraspecific variation in models of relative radial growth rate as a function of light availability. Strikingly, a substantial component of the variation in radial growth at the Michigan site could be explained by sapling growth models originally calibrated for the Connecticut sites. In contrast to the deciduous species, the evergreen species (white pine and eastern hemlock) exhibited significant intraspecific differences in growth models between the two Connecticut sites. Intraspecific variation in growth models among sites was characterized by significantly different estimates of growth at low light. This result suggests that light and other resources can be simultaneously limiting, and challenges the application of Liebig's law of the minimum to tree sapling growth. For the deciduous species, mortality processes exhibited more variation among the sites than did growth. I found significant site differences in mortality as a function of recent growth for both sugar maple and white ash on the calcareous soils in comparison to the schist/gneiss soils in Connecticut. In general, the mortality functions at the Michigan and the upland Connecticut site were similar, and both differed from the Connecticut calcareous site. Community dynamics at each of the three sites were simulated with a model of forest dynamics called SORTIE, which incorporated observed differences in sapling mortality and growth functions among the sites. Using SORTIE, among—site differences in only juvenile survivorship and growth were sufficient to predict dominant species in the adult canopy, demonstrating the critical importance of sapling stages to community dynamics. If a species performs differently at a particular site, its interactions with other species at the site will also change, potentially contributing to further differences in community species composition. Changes in species' performance in response to different site conditions and the species' subsequent interactions are critical to understanding differences among the dynamics and compositions of these forest communities.
Effects of Fire Regime and Habitat on Tree Dynamics in North Florida Longleaf Pine Savannas
Authors: Glitzenstein Jeff S. , Platt William J. , Streng Donna R.
Published: April 2006

Frequent, low intensity fire was an important component of the natural disturbance regime of presettlement savannas and woodlands in the southeastern USA dominated by longleaf pine (Pinus palustris), and prescribed burning is now a critical part of the management of these endangered habitats. Fire season, fire frequency, and fire intensity are three potentially important, though still little understood, components of both natural and managed fire regimes. In this long—term (8—yr) study, we experimentally (through the use of prescribed burning) tested for effects of fire season (eight different times throughout the year) and fire frequency (annual vs. biennial burning), on population dynamics (recruitment, growth, mortality, change in density, and change in basal area [the total basal area of all stems in a plot]) and species composition of trees in two quite different types of longleaf—pine—dominated habitats (north Florida sandhills and flatwoods). Limited fire temperature and intensity data were also collected during one year to examine the relationship between fire behavior (temperature and intensity) and tree mortality. Contrary to prior hypotheses, our results showed few systematic or predictable effects of season or frequency of burning on dynamics of longleaf pine. Instead, variability in the population dynamics of this species appeared to be related largely to variation in fire behavior, regardless of the season of burning. Consistent with prior hypotheses, we found that deciduous oak species (Quercus laevis, Q. margaretta, and Q. incana) were least vulnerable to dormant—season burning and most vulnerable to burning early in the growing season. This was shown particularly by seasonal trends in the effect of burning on oak mortality (both topkill and complete kill) and, to a lesser extent, on oak recruitment. Oak densities and basal areas also declined in the spring—burned plots, resulting in a shift away from oaks and towards increased dominance by longleaf pine. Detrimental effects of spring burning on oaks were partly explained by fire behavior, but there appeared also to be an important residual effect of burning season, particularly on complete kill. Though longleaf pine population dynamics did not differ markedly as a result of burning season and frequency, we did find important differences in pine dynamics between the two habitats (i.e., sandhills and flatwoods). In general, populations of longleaf pines in the sandhills appeared to be density regulated, while flatwoods pine populations were declining regardless of the level of intraspecific competition. This suggests that long—term persistence of longleaf pine, and perhaps other fire—adapted species in frequently burned longleaf—pine—dominated communities, may be determined by complex interactions between habitat factors and fire regimes.
A compound heterozygote harboring novel and recurrent DTDST mutations with intermediate phenotype between atelosteogenesis type II and diastrophic dysplasia
Authors: Maeda Koichi , Miyamoto Yoshinari , Sawai Hideaki , Karniski Lawrence P. , Nakashima Eiji , Nishimura Gen , Ikegawa Shiro
Published: April 2006

Diastrophic dysplasia sulfate transporter (DTDST) is a sulfate transporter required for the synthesis of sulfated proteoglycans in the cartilage. Over 30 mutations have been described in the DTDST gene, which result in a continuous clinical spectrum of recessively inherited chondrodysplasias, including, in order of increasing severity, a recessive form of multiple epiphyseal dysplasia (rMED), diastrophic dysplasia (DTD), atelosteogenesis type II (AO‐II) and achondrogenesis 1B (ACG‐1B). Correlation between disease severity and residual sulfate transport activity has been reported. Here we report a patient with DTDST mutations, whose manifestations fell in a range between AO‐II and DTD. The patient was a compound heterozygote for the recurrent c.835C>T (p.R279W) and novel c.1987G>A (p.G663R) mutations. Immunocytochemical analysis in HEK293 cells showed that the p.G663R mutation was localized within the cytoplasm, and not to the cell membrane, suggesting p.G663R is a loss‐of‐function mutation. Our case supports the previously described correlation between the severity of the phenotype and the putative level of residual transport function. © 2006 Wiley‐Liss, Inc.
Enantioselective Rhodium‐Catalyzed Hydrogenation of Enamides in the Presence of Chiral Monodentate Phosphanes
Authors: Enthaler Stephan , Hagemann Bernhard , Junge Kathrin , Erre Giulia , Beller Matthias
Published: April 2006

The rhodium‐catalyzed asymmetric hydrogenation of different acyclic and cyclic N‐acyl enamides to give N‐acyl‐protected optically active amines has been examined for the first time in detail in the presence of chiral monodentate 4,5‐dihydro‐3H‐dinaphthophosphepines 5a–i. The enantioselectivity is largely dependent on the nature of the substituent at the phosphorus atom and the enamide substrate. Applying optimized conditions up to 95 % ee and catalyst activity up to 2000 h–1 (TOF) have been achieved.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Hereditary cancer predisposition in children: Genetic basis and clinical implications
Authors: Strahm Brigitte , Malkin David
Published: April 2006

Although cancer predisposition syndromes are rare and malignancies arising in this context account for only 1–10% of childhood tumors, studies performed in affected patients and their families have been of unique value for the understanding of cancer development. Three classes of genes (tumor suppressor genes, oncogenes and stability genes) have been identified and shown to be involved in the pathogenesis of familial, as well as sporadic tumors. Cancer has long been recognized as a genetic disease of somatic cells. Despite improved understanding of the molecular basis of predisposition to cancer and better diagnostic tools, the care of these patients and their families remains a major challenge for the clinician. Medical, psychological, ethical and legal issues have to be considered. This review focuses on examples of each class of inherited cancer predisposition syndromes with special implications for patients in the pediatric age group, including retinoblastoma predisposition, Li‐Fraumeni syndrome, multiple endocrine neoplasia disorders and Fanconi anemia. The genetic basis of cancer predisposition is discussed as well as the major concepts and controversies in the clinical management of these patients and their families. © 2006 Wiley‐Liss, Inc.
Development of a membrane array‐based multimarker assay for detection of circulating cancer cells in patients with non‐small cell lung cancer
Authors: Sheu Chau‐Chyun , Yu Ya‐Ping , Tsai Jong‐Rung , Chang Mei‐Yin , Lin Shiu‐Ru , Hwang Jhi‐Jhu , Chong Inn‐Wen
Published: April 2006

Combination of multiple mRNA markers has been largely investigated for detection of circulating cancer cells. However, current PCR‐based methods are relatively expensive and time consuming. The aim of this study was to develop a membrane array‐based multimarker assay for detection of circulating cancer cells in nonsmall cell lung cancer (NSCLC) patients. At first, we selected 22 candidate genes by means of suppression subtractive hybridization and Northern blot analysis. The diagnostic value of each candidate gene was then preliminarily evaluated in 50 pairs of blood samples by membrane array method. Accordingly, 17 genes with area under the ROC curve (AUC) ≥ 0.8 were selected as target genes to reconstruct the diagnostic membrane array, which was then used to test peripheral blood samples from 100 NSCLC patients and 147 control subjects. ROC curve analysis demonstrated that the optimal threshold number of overexpressed markers on membrane array for discrimination between NSCLC patients and control subjects was 12. As a result, the diagnostic membrane array could detect circulating cancer cells in 90 (90%) of 100 NSCLC patients and in 14 (9.5%) of 147 control subjects (including 6 of 100 normal persons, 3 of 20 breast cancer patients, 3 of 15 colorectal cancer patients and 2 of 12 gastric cancer patients). Moreover, the detection rate was significantly correlated with NSCLC patients' metastatic status and overall stage (p = 0.028 and 0.014, respectively). These results suggested that our blood‐based membrane array assay for molecular detection of circulating lung cancer cells has great potential for clinical applications. © 2006 Wiley‐Liss, Inc.
Silencing of the UCHL1 gene in human colorectal and ovarian cancers
Authors: Okochi‐Takada Eriko , Nakazawa Kazuyuki , Wakabayashi Mika , Mori Akiko , Ichimura Shizue , Yasugi Toshiharu , Ushijima Toshikazu
Published: April 2006

Aberrant DNA methylation is associated with many types of human cancers. To identify genes silenced in human colorectal cancers, we performed a microarray analysis for genes whose expression was induced by treatment of HCT116 human colon cancer cells with a demethylating agent, 5‐aza‐2′‐deoxycitidine (5‐aza‐dC). Seven known genes were identified as being upregulated (≥8‐fold) and expressed at more than twice as high as the average level. Among these was the UCHL1 gene (also known as PGP9.5), which is involved in regulation of cellular ubiquitin levels. A dense CpG island in its promoter region was completely methylated in HCT116 cells, and no mRNA was detected. 5‐Aza‐dC treatment of HCT116 cells induced dose‐dependent demethylation of the CpG island, and restored UCHL1 mRNA and protein expression. UCHL1 silencing was observed in 11 of 12 human colorectal cancer cell lines, and its methylation was detected in 8 of 17 primary colorectal cancers. Further, UCHL1 silencing was observed in 6 of 13 ovarian cancer cell lines, and its methylation was detected in 1 of 17 primary ovarian cancers. These results showed that UCHL1 is inactivated in human colorectal and ovarian cancers by its promoter methylation, and suggest that disturbance of cellular ubiquitin levels is present. © 2006 Wiley‐Liss, Inc.
Storage studies of tomato and bell pepper using eco‐friendly films
Authors: Srinivasa Ponnachanna C , Harish Prashanth Keelara V , Susheelamma Nuggenahalli S , Ravi Ramasamy , Tharanathan Rudrapatnam N
Published: April 2006

Tomato (Lycopersicon esculentum) and bell pepper (Capsicum annuum), packaged in cartons (approximately 0.35 kg per box) covered with either eco‐friendly chitosan film or synthetic petroleum‐based low‐density polyethylene (LDPE) film, were stored at room temperature (27 ± 1 °C) and 65 ± 3% relative humidity (RH). Fruits were withdrawn periodically and changes in physico‐chemical, instrumental and sensory characteristics were analysed. During storage, oxygen levels showed only marginal changes, while CO2 levels showed a gradual increase, especially so in LDPE film‐covered cartons. The fresh weight loss, colour, firmness, formation of defective spots and shrivelling showed greater changes for unpackaged fruits as well as for those in LDPE film‐covered cartons, in comparison with fruits stored in chitosan film‐covered cartons, which retained many of the desirable attributes. Principle component analysis of data from sensory or instrumental sensory analyses indicated segregation of samples stored under different conditions with respect to both desirable and undesirable attributes. The fruits showed greater deterioration, including the loss of characteristic bell pepper odour, when packaged in cartons covered with LDPE films, while those packaged in chitosan film retained more of the desirable quality attributes for a longer period. Copyright © 2006 Society of Chemical Industry
Light‐induced neutralization of hydrogen shallow donors in zinc oxide
Authors: Nickel N. H.
Published: April 2006

Infrared absorption measurements of the O–H shallow donor complex in zinc oxide show that its vibrational mode is very sensitive to sub band‐gap illumination. Upon illumination the intensity of the O–H vibrational line exhibits a pronounced decrease. This effect is completely reversible. Annealing the specimens at temperatures above 30 K restores the O–H vibrational line. The decrease and increase of the O–H absorption line is caused by a change of the infrared effective charge due to neutralization and ionization, respectively, of H shallow donors. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of an excited jet diffusion flame at elevated pressure
Authors: Strawa Anthony W. , Cantwell Brian J.
Published: April 2006

Experiments have been carried out with the objective of studying the relationship between flow structure, flow excitation and the reaction process in the near field of a low-speed coflowing jet diffusion flame. The effect of axial forcing and increasing pressure on the structure and controllability of the flame has been studied in an attempt to elucidate some of the underlying mechanisms of control. The experiments were conducted in a variable-pressure flow facility which permits the study of reacting flows at pressures ranging from 10 to 1000 kPa (0.1 to 10 atm.). The flame was excited by adding a small-amplitude, periodic fluctuation to the central fuel jet exit velocity. The flow was visualized using an optical scheme which superimposes the luminous image of the flame on its schlieren image, giving a useful picture of the relationship between the luminous soot-laden core flow and the edge of the surrounding hot-gas envelope. Phase-conditioned velocity measurements were made with a one-component laser Doppler anemometer. The excitation frequency was varied, and it was found that a narrow band of frequencies exists in which several of the instabilities of the flow seem to be in coincidence, causing the flame to break up periodically into a series of distinct eddies. Hereafter this will be called the strongly coupled state. Maps of the one-dimensional velocity vector field, viewed in a frame of reference convecting with the large eddies, are used to study the topology of the flow. When the excitation frequency lies above the strongly coupled range, the flow pattern is found to contain stagnation points which straddle the axis of the jet. When the excitation frequency is reduced to a point where strong coupling occurs the stagnation points move onto the axis promoting breakup of the flame. As the pressure is increased, the relative role of diffusion is decreased and the flame becomes highly three-dimensional. In the strongly coupled state, the flow continues to be very periodic, even to the extent that much of the three-dimensional structure is repeatable from cycle to cycle.
Numerical experiments in forced stably stratified turbulence
Authors: Herring Jackson R. , Métais Olivier
Published: April 2006

We present results of numerical simulations of stably stratified, randomly forced turbulence. The selection of forcing and damping are designed to give insight into the question of whether cascade of energy to large scales is possible for strongly stratified three-dimensional turbulence in a manner similar to two-dimensional turbulence. We consider narrow-band wavenumber forcing, whose angular distribution ranges from two-dimensional to three-dimensional isotropic. Our principal results are as follows; for two-dimensional forcing, and for sufficiently small Froude number, the statistically steady state is characterized by a weakly inverse-cascading horizontal-velocity variance field. The vertical variability of the horizontal-velocity field is pronounced, but seems to approach a limit independent of the Brunt–Väisälä frequency N, as N → ∞. If, on the other hand, the Froude number exceeds a critical value, the vertical variability is weak, and the statistics of the scales larger than the forcing scale is near that predicted by inviscid equipartitioning. For all forcing functions considered the vertical motion and temperature field (w, T), centred at smaller scales, are more three-dimensionally isotropic, with no large-scale organization. At large N, (small Froude number) the w-field scales as 1/N, with horizontal motion field nearly independent of N. Furthermore, at large N and for horizontal forcing, the horizontal motion field is consistent with the condition that a substantial fraction of the total dissipation is attributable to an effective drag acting upon all horizontal scales of motion, which in turn flattens the slope of the energy spectrum in the inverse-cascade range, and increases it in the enstrophy-cascade range.
Rossby-Kelvin instability: a new type of ageostrophic instability caused by a resonance between Rossby waves and gravity waves
Authors: Sakai Satoshi
Published: April 2006

An ageostrophic version of Phillips’ model is studied. All instabilities found are systematically interpreted in terms of resonance of wave components. The instability occurs if there is a pair of wave components which propagate in the opposite direction to the basic flow and these wave components have almost the same Doppler-shifted frequency. A new instability, identified as a resonance between the Kelvin wave and the Rossby waves, is found at Froude number F ≈ 0.7. The Rossby waves are almost completely in geostrophic balance while the ageostrophic Kelvin wave is the same as in a one-layer system. Doppler shifting matches frequencies which would otherwise be very different. This instability is presumably the mechanism of the frontal instability observed by Griffiths & Linden (1982) in a laboratory experiment. Ageostrophic, baroclinic instability with non-zero phase speed is also observed in the numerical calculation. This instability is caused by resonance between different geostrophic modes.
Divided discharges for divided flows
Authors: Smith Ronald
Published: April 2006

An effluent outlet within thirty channel breadths upstream of a branching in a river can lead to high shoreline pollution levels along one of the branches, or near the tip of the central region. This paper identifies an optimal splitting of a steady discharge that minimizes the shoreline pollution.
Inertial migration of a sphere in Poiseuille flow
Authors: Schonberg Jeffrey A. , Hinch E. J.
Published: April 2006

The inertial migration of a small sphere in a Poiseuille flow is calculated for the case when the channel Reynolds number is of order unity. The equilibrium position is found to move towards the wall as the Reynolds number increases. The migration velocity is found to increase more slowly than quadratically. These results are compared with the experiments of Segré & Silberberg (1962 a, b).
Active stabilization of compressor surge
Authors: Williams J. E. Ffowcs , Huang X. Y.
Published: April 2006

This paper describes the stabilization of compressor surge by an active method. It is known that surge follows when small disturbances grow in an unstable compression system, and that small growth can be modelled through a linear stability analysis. An active element is here introduced to counter any tendency to instability and the control law governing the active stabilizer is determined from linear theory. We follow precisely the suggestion put forward by Epstein et al. (1986) and verify that their theory conforms to practice. The theory is verified in an experiment on a compression system whose plenum volume is controlled. Suppression of the flow instability was achieved by switching on the controller and the compressor was made to operate stably on a part of its characteristic beyond the nature stall line. Furthermore the controlled compressor is much more resilient to external disturbances than is the natural case. The controller is even effective on deep surge – a feature of great interest but hardly predictable from the Epstein et al. initiative for this kind of study.
Observations of a nonlinear solitary wave packet in the Kelvin wake of a ship
Authors: Brown Ellen D. , Buchsbaum Steven B. , Hall Robert E. , Penhune John P. , Schmitt Kurt F. , Watson Kenneth M. , Wyatt Donald C.
Published: April 2006

Thirty data sets of wavestaff measurements of a solitary feature in the Kelvin wake of the Coast Guard cutter Point Brower are analysed. The average characteristics of the feature between 1 and 4 km aft of the ship are shown to be consistent with those of an oblique nonlinear solitary wave packet. The ship speed is 7.7 m/s (Froude number 0.49) and the waves that comprise the packet have an average frequency of 3.28 rad/s. The ship speed and the wave frequency, together with Kelvin wake kinematics, imply that the feature appears at an average wake half-angle of 10.9°. The packet does not exhibit linear dispersion beyond 1 km aft of the ship and its average width is 8.9 m (measured at e−1 of the peak variance). The average amplitude is 1.1 times the theoretical amplitude of an oblique nonlinear solitary wave packet with the observed width. There is considerable variability from run to run, and there is evidence of dispersive spreading before 1 km aft of the ship. An aerial photograph shows a sinuous fluctuation of the feature; possible explanations for the fluctuation include small variations in initial conditions or a sinuous instability. The solitary feature is a possible explanation for the long bright lines observed in SEASAT SAR images in light to moderate winds and observed in sun glitter photos taken from the space shuttle.
A new equation for calculating wave loads on offshore structures
Authors: Rainey R. C. T.
Published: April 2006

This paper derives an equation for the potential-flow wave loading on a lattice-type offshore structure moving partially immersed in waves. It is for the limiting case of small lattice-member diameter, and deals entirely in member-centreline fluid properties, so that it can be applied computationally by a simple ‘stick model’ computer program. This field is currently served by a simple two-term semiempirical formula ‘Morison's equation’: the new equation is effectively a replacement for the Morison inertial term, allowing the Morison drag term (or some refinement of it) to describe exclusively the effects of vorticity, which can in principle be calculated to greater accuracy when isolated in this way.

The new equation calculates the potential-flow wave load accurate to second order in wave height, which is a great improvement on ‘Morison's equation’: such results can currently only be sought by very much more complicated and computationally intensive methods, of currently uncertain repeatability. Moreover the third-order error is localized at the free-surface intersection, so the equation remains attractive for fully nonlinear problems involving intermittent immersion of lattice members, which are currently beyond even the most sophisticated of these computationally intensive methods. It is shown that the primary reason for this large contrast in computational efficiency is that the loads are derived from energy considerations rather than direct integration of surface pressures, which requires a lower level of flow detail for a given level of load-calculation accuracy.

These improvements must of course be seen against the current levels of uncertainty over the calculation of vorticity-induced loads, which in many applications completely dwarf inaccuracies in potential-flow load calculation. The conditions are accordingly established under which the improvements are comparable to the total wave load predicted by the Morison drag and inertia terms in combination. They are that the lattice member diameter is greater than its length/10, or the relative fluid motion/5, or the structure's motion radius/20, or the wavelength/30: if any one of these conditions is satisfied, the new equation is worthwhile even when used in combination with simple vorticity-induced load calculations from a Morison drag term.
On the distortion of the static structure factor of colloidal fluids in shear flow
Authors: Dhont J. K. G.
Published: April 2006

It is shown that the shear-induced distortion of the static structure factor (or equivalently, the pair distribution function) of colloidal fluids is a non-analytic function of the shear rate. The Smoluchowski equation shows boundary-layer behaviour at zero wave vector (large separations). The width of this boundary layer is proportional to the square-root of the shear rate. An explicit perturbation analysis of the two-particle Smoluchowski equation without hydrodynamic interactions is given. The onset of the non-Newtonian behaviour of the effective vicosity is due to the boundary-layer behaviour of the structure factor.
Vertical mixing due to the breaking of critical internal waves on sloping boundaries
Authors: Ivey G. N. , Nokes R. I.
Published: April 2006

A laboratory experiment is used to examine the vertical mixing resulting from the breaking of internal waves on a sloping boundary in a continuously stratified fluid. Attention is confined to the case of critical waves when the slope of the group velocity vector of the incident waves is equal to the bottom slope. Along the sloping boundary a turbulent bottom boundary layer forms with a thickness dependent on the incident wave amplitude. The mixing efficiency, defined as the ratio of the increase in potential energy due to mixing to the loss of kinetic energy by the incident waves, is dependent upon the stability of the flow and has an upper bound of approximately 0.20.

By examining the increase in potential energy of the fluid as a result of sustained mixing, we are able to compute the transition value of the dissipation εtr below which no mixing occures. For mixing due to the breaking of critical internal waves on sloping boundaries we find that εtr = (8±2)νN2. From comparisons with experiments with grid-generated turbulence, this suggests that while εtr/νN2 = 0(10) in the available data sets, the specific value of εtr may be mechanism dependent.
Influence of thermosolutal convection on the solidification front during upwards solidification
Authors: Thi H. Nguyen , Billia B. , Jamgotchian H.
Published: April 2006

For some years now, much effort has been devoted to the study of thermosolutal convection in the liquid phase during upwards solidification of a binary alloy, which is coupled to the dynamics of the solid-liquid interface. While the theoretical analysis is well developed, there is a need for experimental evidence. Experiments in cylinders have thus been carried out on lead – 30 wt % thallium alloys in order to obtain significant information about the convective patterns in the melt adjacent to the solidification front, from a knowledge of the macroscopic shape of the phase boundary. This shape is determined as a function of the lateral confinement θ (the ratio of the crucible diameter to the unstable wavelength at the threshold for an infinite medium) from a series of contour lines for the solid in the two-phase region of the quenched samples. When θ is small, the pattern always has a central axisymmetric core and an outer annulus which is at first complex or structureless and then presents a mixture of festoons and solid sectors. For θ very close to unity, a hexagon, which is the basic element of a laterally infinite array, dominates the morphology. At higher θ, a hexagon can no longer remain naturally centred and is replaced by two main cells which contact the wall by again making a completely festooned ring. The fluid flow in the liquid just ahead of the solid-liquid interface is then inferred. Analogy with Bénard-Marangoni patterns suggests a qualitative analysis of the convective structures. The present observations are finally compared to previous ones on similar alloys grown in crucibles with a smaller diameter.
Spin-up phenomena in non-axisymmetric containers
Authors: Heijst G. J. F. Van
Published: April 2006

The spin-up from rest of a contained homogeneous free-surface fluid has been examined in the laboratory for a variety of non-axisymmetric containers. It was found that in the spin-up process three stages can be distinguished before the fluid reaches the ultimate state of rigid-body rotation. When the container starts spinning, the non-axisymmetric lateral tank boundaries induce horizontal pressure gradients, and as a result relative flows arise instantaneously after the start of the experiment. The absolute vorticity of the starting flow is zero, and a description can be given in terms of potential theory. Theoretical solutions have been derived for a number of geometries, and comparison with experimentally observed streamline patterns shows good agreement. In the next stage, flow separation sets in, in most cases leading to locally intense three-dimensional turbulent flows. The basic rotation causes a transition from three-dimensional to two-dimensional motion, and a subsequent organization of the relative flow into a number of cells is observed. During the final stage, the flow in these cells gradually decays owing to the spin-up/spin-down mechanism provided by the Ekman layer at the bottom of each cell, until eventually the fluid is in solid-body rotation.
Wave-vortex dynamics in rotating shallow water
Authors: Farge Marie , Sadourny Robert
Published: April 2006

We investigate how two-dimensional turbulence is modified when the incompressibility constraint is removed, by numerically integrating the full Saint-Venant (shallow-water) equations. In the case of small geopotential fluctuations considered here, we find no energy exchange between the inertio-gravitational and the potentio-vortical components of the flow. At small scales, the potentio-vortical component behaves as if the flow were incompressible, while we observe an intense direct energy cascade within the inertio-gravitational component. At large scales, the reverse potentio-vortical energy cascade is reduced when the level of inertio-gravitational energy is high. Looking at the effect of rotation, we find that a fast rotation rate tends to inhibit all three cascades. In particular, the inhibition of the inertio-gravitational energy cascade towards small scales implies that the geostrophic adjustment process is hindered by an increase of rotation. Concerning the structure of the coherent vortices emerging out of these decaying turbulent flows, we observe that the smallest scales are concentrated inside the vortex cores and not on their periphery.
Buoyant laminar flow of air in a long, square-section cavity aligned with the ambient temperature gradient
Authors: Lock G. S. H. , Han J.-C.
Published: April 2006

Numerical solutions have been obtained for three-dimensional buoyant flow of air under laminar conditions in a slender, square-section cavity lying parallel to the gradient vector of the temperature field in which it is embedded. Velocity and temperature profiles in the cavity are presented in support of a flow model in which primary and secondary circulation are reconciled by an advective mechanism in the central region. The effect of the temperature gradient, represented by a Rayleigh number, is explored when the cavity is horizontal. The effect of inclining the cavity above and below this horizontal position is also explored. Comparisons are made with related work on cylindrical and two-dimensional rectangular cavities.
Separation in a gas centrifuge at high feed flow rate
Authors: Cunzhen Zhang , Conlisk A. T.
Published: April 2006

The separation of a binary gas mixture for high feed flow rates such that the E¼ vertical shear layer is nonlinear is considered. Numerical solutions for the velocity field and the temperature within the centrifuge are computed using the method originally described by Bennetts & Hocking (1973). These solutions are inputs to the separation problem which is characterized by a concentration boundary layer also of width of O(E¼). Results are presented for a wide range of parameters and the effect of thermal drive strength is examined in detail. Surprisingly the numerical results indicate that the analytical solution for the separation factor given by Conlisk, Foster & Walker (1983) may be used far outside its strict asymptotic region of validity.
Critical geometry of oscillating bluff bodies
Authors: Nakamura Yasuharu , Hirata Katsuya
Published: April 2006

Measurements are presented of the mean pressures around rectangular and D-section cylinders, with a flat front face normal to the flow, forced to oscillate transversely at an amplitude of 10% of the length of the front face. The ratio of depth (streamwise dimension) to height (cross-stream dimension) of the cross-section ranges from 0.2 to 1.0 for rectangular cylinders and from 0.5 to 1.5 for D-section cylinders. The range of reduced velocities investigated, 3 to 11, includes the vortex-resonance region. When increasing the depth, an oscillating bluff cylinder shows a critical depth where base suction attains a peak. The value of a critical depth is lowered with decreasing reduced velocity. In particular, an extraordinarily low critical depth with a very high base suction is obtained on cylinders oscillating at vortex resonance. For cylinders with depths beyond the critical, a reattachment-type pressure distribution is established on the afterbody due to the shear-layer/edge direct interaction. The shear-layer/edge direct interaction can also occur on oscillating cylinders with a fixed splitter plate. At low reduced velocities, the reattachment-type pressure distributions on cylinders with and without a splitter plate are similar except for the mean level. A remark is made on the critical geometry of bluff bodies under various flow conditions.
Nonlinear free-surface flow at a two-dimensional bow
Authors: Grosenbaugh Mark A. , Yeung Ronald W.
Published: April 2006

Unsteady free-surface flow at the bow of a steadily moving, two-dimensional body is solved using a modified Eulerian-Lagrangian technique. Lagrangian marker particles are distributed on both the free surface and the far-field boundary. The flow field corresponding to an inviscid, double-body solution is used for the initial condition. Solutions are obtained over a range of Froude numbers for bodies of three different shapes: a vertical step, a faired profile, and a bulbous bow. A transition Froude number exists at which the bow wave begins to overturn and break. The value of the transition Froude number depends on the bow shape. A stagnation point is observed to be present below the free surface during the initial stage of the wave formation. For flows occurring above the transition Froude number, the stagnation point remains trapped below the free surface as the wave overturns. Below the transition Froude number, the stagnation point rises to the surface as the crest of the transient bow wave moves upstream and away from the body.
Spatio-temporal regimes in Rayleigh–Bénard convection in a small rectangular cell
Authors: Rubio M. A. , Bigazzi P. , Albavetti L. , Ciliberto S.
Published: April 2006

By means of an original optical technique we have studied the spatio-temporal behaviour in a Rayleigh–Bénard convection experiment of small rectangular geometry. The experimental technique allows complete reconstruction of the temperature field integrated along the roll axis. Two main spatiotemporal regimes have been found, corresponding to localized oscillations and travelling waves respectively. Several parameters are proposed for the quantitative characterization of this complex behaviour.
Sound generation by a supersonic aerofoil cutting through a steady jet flow
Authors: Guo Y. P.
Published: April 2006

This paper examines the sound generation process when a supersonic aerofoil cuts through a steady jet flow. It is shown that the principal sound is generated by the leading edge of the aerofoil when it interacts with the streaming jet. To the leading order in terms of the jet velocity, no trailing-edge sound is generated. This is not the result of the cancellation of a trailing-edge sound by that from vortex shedding through the imposition of the Kutta condition. Instead, the null acoustic radiation from the trailing edge is entirely because, to the leading order, there is no interaction between the trailing edge and the jet. The effect of the trailing edge is to diffract sound waves generated by the leading edge. It is shown that the diffracted field (as well as the incident field) is regular at the trailing edge and the issue of satisfying the Kutta condition does not arise during the diffraction process. Thus, there is no extra vortex shedding from the trailing edge owing to its interaction with the flow, apart from those resulting from the discontinuity across the aerofoil, generated by the flow-leading edge interaction. This is in sharp contrast to the case of subsonic aerofoils where the removal of the singularity in the diffracted field at the trailing edge through the imposition of the Kutta condition results in vortex shedding from the sharp edge and energy exchange between the sound field and the vortical wake.
New phenomena in the Eckhaus instability of thermal Rossby waves
Authors: Or A. C.
Published: April 2006

An analytical study on the Eckhaus instability of moderately nonlinear thermal Rossby waves is developed. A solvability condition of the lowest order is derived. The condition not only produces results that agree reasonably well with the earlier Galerkin formulation, but also leads to some new findings that are otherwise difficult to discover by the previous method. Over a wide range of parameters, this paper reports the existence of a branch of the stability limit that corresponds to a pair of disturbances with a finite, rather than an infinitesimal wavenumber modulation. As the Prandtl number tends to a small value, the asymmetry between the two branches of the stability limit becomes very pronounced, which is manifested as a severely distorted stability region.
Hypervelocity flow of dissociating nitrogen downstream of a blunt nose
Authors: Macrossan M. N.
Published: April 2006

The nature of the non-equilibrium flow of strongly dissociating nitrogen has been investigated by a series of simulation calculations using non-equilibrium (finite rate) chemical reactions. These were made with the equilibrium flux method (EFM), and the results have been found to compare favourably with experimental results obtained with a free-piston driven shock-tube wind tunnel which was used to obtain interferograms of the flow of pure nitrogen over a blunt-nosed body, 65 mm long at three angles of incidence. No simple relation between the flow with non-equilibrium chemistry and those for frozen or equilibrium chemistry has been found. The problems of relating test flows produced in the shock tunnel to flight conditions are investigated by considering the test flows that might be produced by some ‘ideal equivalent wind tunnels’. It is shown that the degree of frozen dissociation in the test flow in a shock tunnel is not a serious matter, but that the large difference in Mach number between shock tunnel flows and flight conditions may be more important.
The concentration distribution produced by shear dispersion of solute in Poiseuille flow
Authors: Stokes A. N. , Barton N. G.
Published: April 2006

One of G. I. Taylor's most famous papers concerns the large-time behaviour of a cloud of soluble matter which has been injected into a solvent in laminar flow in a pipe. In the past thirty years, a number of successful attempts have been made to derive differently or extend Taylor's result, which is that the cloud of solute eventually takes a Gaussian profile in the flow direction. The present paper is another examination of this well-worked problem, but this time from the viewpoint of a formal integral transform representation of the solution. This approach leads to a better understanding of the solution; it also enables efficient numerical computations, and leads to extended and new asymptotic expansions.

A Laplace transform in time and a Fourier transform in the flow direction leaves a complicated eigenvalue problem to be solved to give the cross-sectional behaviour. This eigenvalue problem is examined in detail, and the transforms are then inverted to give the concentration distribution. Both numerical and asymptotic methods are used. The numerical procedures lead to an accurate description of the concentration distribution, and the method could be generalized to compute dispersion in general parallel flows. The asymptotic procedures use two different classes of eigenvalues to give leading- and trailing-edge approximations for the solute cloud at small times. Meanwhile, at larger times, one eigenvalue branch dominates the solution and Taylor's result is recovered and extended using'the computer to generate extra terms in the approximation. Sixteen terms in the approximation are calculated, and a continued fraction expansion is deduced to enhance the accuracy.
Small-scale transition in a plane mixing layer
Authors: Huang Lein-Saing , Ho Chih-Ming
Published: April 2006

An experimental study was conducted to investigate the’ generation process of random small-scale turbulence in an originally laminar mixing layer. The evolutions of the two types of deterministic structures, the spanwise and streamwise vortices, were first clarified in order to determine their roles in the transition process. A scaling rule for the streamwise distance from the trailing edge of the splitter plate to the vortex merging position was found for various velocity ratios. After this streamwise lengthscale was determined, it became clear that the spanwise wavelength of the streamwise vortices doubled after the merging of the spanwise structures which nominally doubled streamwise wavelengths. The most interesting finding was that the random small-scale eddies were produced by the interactions between the merging spanwise structures and the streamwise vortices.
Instability waves in twin supersonic jets
Authors: Morris Philip J.
Published: April 2006

Calculations are presented for the characteristics of instability waves in the initial mixing region of twin circular supersonic jets. Two models for the basic jet flow are used. In the first, the jets are modelled as two circular vortex sheets. In the second, realistic velocity and density profiles are used. It is shown that the unsteady flow fields of the two jets interact before the time-averaged jets flows have merged. The normal modes or instability waves are classified by their symmetry properties in the twin-jet case and their asymptotic behaviour for large jet separations. Calculations of the growth rates and phase velocities are made for these modes as a function of jet separation and mixing-layer thickness. The associated pressure distributions are also presented. In the realistic jet profile calculations the effect of jet separation is found to be relatively weak. For modes that are even about the symmetry plane between the two jets the pressure levels are found to increase near this plane as the jet separation decreases.
Shear-layer pressure fluctuations and superdirective acoustic sources
Authors: Crighton D. G. , Huerre P.
Published: April 2006

We consider a sequence of boundary-value problems for the acoustic wave equation, with the pressure specified on the boundary as a function of space and time, and simulating features of the pressure field measured just outside a turbulent shear layer supporting large-scale coherent structures. The boundary pressure field has the form of a travelling subsonic plane wave, modulated by a large-scale envelope function. Three models for the envelope distribution are studied in detail, and the particular features which they exhibit are shown to be representative of large classes of amplitude functions.

We start by looking at the hydrodynamic near field of the boundary pressure fluctuations, over spatial regions throughout which the motion can be taken as incompressible. Very close to the boundary, the pressure fluctuations decay exponentially with transverse distance, while at sufficiently large distances from the whole wave packet on the boundary, the pressure fluctuations have a dipole algebraic decay. We investigate the transition from exponential to algebraic decay, and find that it is effected through quite a complicated multilayer structure which depends crucially on the detailed form of the envelope.

Acoustic fields are then determined both from exact solutions to the wave equation, and from matching arguments. In some cases, where the boundary source is compact, the distant acoustic fields have a simple compressible dipole type of behaviour. In other cases, however, when the boundary source is non-compact, the acoustic field has a superdirective character, the angular variation being described by exponentials of cosines of the angle with the streamwise direction. It is shown how the superdirective acoustic sources are completely compatible with the features of the inner incompressible field, and a criterion for the occurrence of the superdirective acoustic fields will be given. Superdirective fields of this kind have been observed in measurements by Laufer & Yen (1983) on a low-speed round jet of Mach number 0.1, and the general relation of our results to those experiments is explained.