bluuebunny/crossref_metadata_2025 huggingface dataset:
Codep: Maximizing co‐evolutionary interdependencies to discover interacting proteins
Authors: Tillier Elisabeth R. M. , Biro Laurence , Li Ginny , Tillo Desiree
Published: April 2006

Approaches for the determination of interacting partners from different protein families (such as ligands and their receptors) have made use of the property that interacting proteins follow similar patterns and relative rates of evolution. Interacting protein partners can then be predicted from the similarity of their phylogenetic trees or evolutionary distances matrices. We present a novel method called Codep, for the determination of interacting protein partners by maximizing co‐evolutionary signals. The order of sequences in the multiple sequence alignments from two protein families is determined in such a manner as to maximize the similarity of substitution patterns at amino acid sites in the two alignments and, thus, phylogenetic congruency. This is achieved by maximizing the total number of interdependencies of amino acids sites between the alignments. Once ordered, the corresponding sequences in the two alignments indicate the predicted interacting partners. We demonstrate the efficacy of this approach with computer simulations and in analyses of several protein families. A program implementing our method, Codep, is freely available to academic users from our website: http://www.uhnresearch.ca/labs/tillier/. Proteins 2006. © 2006 Wiley‐Liss, Inc.
Understanding the earth systems of Malawi: Ecological sustainability, culture, and place‐based education
Authors: Glasson George E. , Frykholm Jeffrey A. , Mhango Ndalapa A. , Phiri Absalom D.
Published: April 2006

The purpose of this 2‐year study was to investigate Malawian teacher educators' perspectives and dispositions toward teaching about ecological sustainability issues in Malawi, a developing country in sub‐Sahara Africa. This study was embedded in a larger theoretical framework of investigating earth systems science through the understanding of nature–knowledge–culture systems from local, place‐based perspectives. Specifically, we were interested in learning more about eco‐justice issues that are related to environmental degradation in Malawi and the potential role of inquiry‐oriented pedagogies in addressing these issues. In a science methods course, the African educators' views on deforestation and teaching about ecological sustainability were explored within the context of the local environment and culture. Teachers participated in inquiry pedagogies designed to promote the sharing of perspectives related to the connections between culture and ecological degradation. Strategies encouraging dialogue and reflection included role‐playing, class discussions, curriculum development activities, teaching experiences with children, and field trips to a nature preserve. Data were analyzed from postcolonial and critical pedagogy of place theoretical perspectives to better understand the hybridization of viewpoints influenced by both Western and indigenous science and the political hegemonies that impact sustainable living in Malawi. Findings suggested that the colonial legacy of Malawi continues to impact the ecological sustainability issue of deforestation. Inquiry‐oriented pedagogies and connections to indigenous science were embraced by the Malawian educators as a means to involve children in investigation, decision making, and ownership of critical environmental issues. © 2006 Wiley Periodicals, Inc. Sci Ed 90:660–680, 2006
A comparative evaluation of implementation methods for controlling the execution speed of a program by regulating I/O performance
Authors: Taniguchi Hideo
Published: April 2006

As the performance capacity of computer hardware increases, the processing time taken by software becomes shorter and it is now possible to have programs execute complex procedures. However, processing speed is highly dependent on the actual performance of the hardware. Therefore, it is necessary to establish control mechanisms in order to execute a given set of processing instructions at a speed within the limits of the hardware capacity that matches the demands of the user as well as the nature of the service provided by the software. In addition, there are various methods for implementing such control mechanisms: in the kernel of the operating system (OS) or as a library that is external to the OS. Each method has its own advantages and disadvantages. In this paper we describe and compare different methods for implementing program execution speed regulation procedures by controlling the input–output (I/O) performance. Specifically, we describe and compare implementations of a basic method for adjusting the number of times I/O is performed and a fundamental method for adjusting the time spent on I/O. In addition, we compare an implementation of a method for regulating I/O timing implemented as a library with an implementation in the OS kernel and highlight the advantages of each approach. © 2006 Wiley Periodicals, Inc. Syst Comp Jpn, 37(7): 72–82, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10185
Autonomous distributed secret sharing storage system
Authors: Miyamoto Toshiyuki , Doi Shinji , Nogawa Hiroki , Kumagai Sadatoshi
Published: April 2006

A safe and durable storage system is essential for mission critical and safe critical operations. In this paper, the authors propose a distributed storage system that uses the (k, n) threshold scheme. Using the (k, n) threshold scheme enables robustness to network problems or data loss due to disk failures to be increased and data secrecy to be improved at the same time. Since the authors have already developed agents for implementing the basic functions for realizing the distributed storage system, they introduce them here. © 2006 Wiley Periodicals, Inc. Syst Comp Jpn, 37(6): 55–63, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20388
HTML text segmentation for Web page summarization by a key sentence extraction method
Authors: Sunayama Wataru , Iyama Akihiro , Yachida Masahiko
Published: April 2006

The information displayed as the search result by search engines is important for quickly finding the desired information. In particular, the summary of each Web page in the search results is important for determining the Web page content, as well as for determining how the input search term is used in each Web page, namely, the relation between the search term and the Web page. However, the summaries of the search results in conventional search engines have problems such as extracting only the opening text and not containing the search term, or containing the search term but having the sentence truncated in the middle so that the context of the term or the content of the Web page cannot be determined. Therefore, a summary in sentence units is desirable, but since HTML text includes many nonsentence items that do not contain punctuation, if they are unprocessed, it is difficult for a key sentence extraction system that treats sentences as units to provide a summary. Thus, in this paper, we propose an HTML text segmentation system that divides the source text of each Web page into meaningfully connected groups of text corresponding to sentences. We also verify experimentally that the text generated by this system can be used effectively in a Web page summarization. © 2006 Wiley Periodicals, Inc. Syst Comp Jpn, 37(7): 26–36, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20416
Temporal posture estimation of nonrigid objects lacking sufficient features based on the automatically generated stick and ellipse model
Authors: Ukita Norimichi , Kitajima Toshihiro , Kidode Masatsugu
Published: April 2006

We propose a method for tracking nonrigid objects using an object model automatically generated from a set of sample images. Our model consists of multiple sticks and ellipses that represent the skeleton and the areas of an object, respectively. In previous methods, it is difficult to estimate the entire area and posture of a nonrigid object, which lacks sufficient characteristic features (e.g., texture patterns and shapes), because the previous methods have not dealt with the extraction of appearance features for any object from a 2D image of the object. With the proposed model, on the other hand, our method is effective because (1) each component of the model can fit each rigid part of a nonrigid object and (2) the reliability of each component is evaluated. In order to confirm the effectiveness of the proposed method, we conducted several experiments with goldfish and human subjects. The tracking system automatically generated a model of the target; it could then track multiple targets even when they were partially occluded. © 2006 Wiley Periodicals, Inc. Syst Comp Jpn, 37(6): 21–31, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20493
Vortex shedding and lock-on of a circular cylinder in oscillatory flow
Authors: Barbi C. , Favier D. P. , Maresca C. A. , Telionis D. P.
Published: April 2006

An experimental study has been made of a circular cylinder in steady and oscillatory flow with non-zero mean velocity up to a Reynolds number of 40000. The results for the stationary cylinder are in close agreement with previously published data. Skin-friction measurements revealed the amplitude of fluctuation of the boundary layer for different angular locations. It has been universally accepted that bluff bodies shed vortices at their natural frequency of shedding (Strouhal frequency), or, when synchronized with an external unsteadiness, at the frequency of the disturbance or half of it, depending of the direction of the unsteadiness. Our findings, instead, indicate that the shedding frequency may vary smoothly with the driving frequency before locking on its subharmonic. Moreover, the present results indicate that, at the lowest frequency limit of lock-on, vortices are shed simultaneously on both sides of the model. A more traditional alternate pattern of vortex shedding is then recovered at higher driving frequencies.
Viscous fingering in Hele-Shaw cells
Authors: Saffman P. G.
Published: April 2006

The phenomenon of interfacial motion between two immiscible viscous fluids in the narrow gap between two parallel plates (Hele-Shaw cell) is considered. This flow is currently of interest because of its relation to pattern selection mechanisms and the formation of fractal, structures in a number of physical applications. Attention is concentrated on the fingers that result from the instability when a less-viscous fluid drives a more-viscous one. The status of the problem is reviewed and progress with the thirty-year-old problem of explaining the shape and stability of the fingers is described. The paradoxes and controversies are both mathematical and physical. Theoretical results on the structure and stability of steady shapes are presented for a particular formulation of the boundary conditions at the interface and compared with the experimental phenomenon. Alternative boundary conditions and future approaches are discussed.
Bubble formation, motion and interaction in a Hele-Shaw cell
Authors: Maxworthy T.
Published: April 2006

We consider the motion of the flattened bubbles which form when air is injected into a viscous fluid contained in the narrow gap between two flat, parallel plates which make up a conventional Hele-Shaw cell, inclined at an angle x to the horizontal. We present a number of qualitative observations on the formation and interaction of the streams of bubbles that appear when air is injected continuously into the cell. The majority of this paper is then concerned with the shape and velocity of rise of single, isolated bubbles over a wide range of bubble size and cell inclination. We compare these results to theories by Taylor & Saffman (1959), and Tanveer (1986). It appears that the bubble characteristics found by an ad hoc speculation in Taylor & Saffman (1959) and by Tanveer (1986) only agree with the experimental results in the limit α → 0, and for large bubble widths (D). For finite values of α, it is necessary to use the measured bubble shape in order to calculate the rise velocity using the more general Taylor & Saffman (1959) formulation. Deviations from these theories for small D can be explained by considering the effects of the detailed flow close to the bubble surface.
Viscous starting jets
Authors: Cantwell Brian J.
Published: April 2006

This paper is concerned with the transient motion produced when a viscous incompressible fluid is forced from an initial state of rest. The applied force is time dependent in the form of an impulse, step and ramp function applied at a point and along a line. These cases have been chosen because they form a logical progression for investigating the connection between the flow Reynolds number and the sequence of events leading to the creation of a starting vortex. Much of the structure of the starting process can be revealed through a study of boundary conditions, integrals of the motion and the invariance properties of the governing equations prior to the consideration of a particular solution. The method used to bring out the flow structure is applicable to flows that can be treated as self-similar over some interval in time. The equations for unsteady particle paths are written in terms of similarity variables and then analysed as a quasi-autonomous system with the, usually time-dependent, Reynolds number treated as a parameter. The structure of the flow is examined by finding and classifying critical points in the phase portrait of this system. Bifurcations in the phase portrait are found to occur at specific values of the Reynolds number of the flow in question. When exact solutions of the Stokes equations for the low-Reynolds-number limit are examined they are found to contain two critical Reynolds numbers and three distinct states of motion which culminate in the onset of a vortex roll-up. An interesting feature of the Stokes solutions for planar unsteady jets is that they are uniformly valid over 0 < r < ∞.
A series-expansion study of the Navier–Stokes equations with applications to three-dimensional separation patterns
Authors: Perry A. E. , Chong M. S.
Published: April 2006

An algorithm has been developed which enables local Taylor-series-expansion solutions of the Navier-Stokes and continuity equations to be generated to arbitrary order. Much of the necessary algebra for generating these solutions can be done on a computer. Various properties of the algorithm are investigated and checked by making comparisons with known solutions of the equations of motion. A method of synthesizing nonlinear viscous-flow patterns with certain required properties is developed and applied to the construction of a number of two- and three-dimensional flow-separation patterns. These patterns are asymptotically exact solutions of the equations of motion close to the origin of the expansion. The region where the truncated series solution satisfies the full equations of motion to within a specified accuracy can be found.
The fractal facets of turbulence
Authors: Sreenivasan K. R. , Meneveau C.
Published: April 2006

Speculations abound that several facets of fully developed turbulent flows are fractals. Although the earlier leading work of Mandelbrot (1974, 1975) suggests that these speculations, initiated largely by himself, are plausible, no effort has yet been made to put them on firmer ground by, resorting to actual measurements in turbulent shear flows. This work is an attempt at filling this gap. In particular, we examine the following questions: (a) Is the turbulent/non-turbulent interface a self-similar fractal, and (if so) what is its fractal dimension ? Does this quantity differ from one class of flows to another? (b) Are constant-property surfaces (such as the iso-velocity and iso-concentration surfaces) in fully developed flows fractals? What are their fractal dimensions? (c) Do dissipative structures in fully developed turbulence form a fractal set? What is the fractal dimension of this set? Answers to these questions (and others to be less fully discussed here) are interesting because they bring the theory of fractals closer to application to turbulence and shed new light on some classical problems in turbulence - for example, the growth of material lines in a turbulent environment. The other feature of this work is that it tries to quantify the seemingly complicated geometric aspects of turbulent flows, a feature that has not received its proper share of attention. The overwhelming conclusion of this work is that several aspects of turbulence can be described roughly by fractals, and that their fractal dimensions can be measured. However, it is not clear how (or whether), given the dimensions for several of its facets, one can solve (up to a useful accuracy) the inverse problem of reconstructing the original set (that is, the turbulent flow itself).
Turbulent entrainment: the development of the entrainment assumption, and its application to geophysical flows
Authors: Turner J. S.
Published: April 2006

The entrainment assumption, relating the inflow velocity to the local mean velocity of a turbulent flow, has been used successfully to describe natural phenomena over a wide range of scales. Its first application was to plumes rising in stably stratified surroundings, and it has been extended to inclined plumes (gravity currents) and related problems by adding the effect of buoyancy forces, which inhibit mixing across a density interface. More recently, the influence of viscosity differences between a turbulent flow and its surroundings has been studied. This paper surveys the background theory and the laboratory experiments that have been used to understand and quantify each of these phenomena, and discusses their applications in the atmosphere, the ocean and various geological contexts.
Fundamentals concerning wave loading on offshore structures
Authors: Lighthill James
Published: April 2006

This article is aimed at relating a certain substantial body of established material concerning wave loading on offshore structures to fundamental principles of mechanics of solids and of fluids and to important results by G. I. Taylor (1928a,b). The object is to make some key parts within a rather specialised field accessible to the general fluid-mechanics reader.

The article is concerned primarily to develop the ideas which validate a separation of hydrodynamic loadings into vortex-flow forces and potential-flow forces; and to clarify, as Taylor (1928b) first did, the major role played by components of the potential-flow forces which are of the second order in the amplitude of ambient velocity fluctuations. Recent methods for calculating these forces have proved increasingly important for modes of motion of structures (such as tension-leg platforms) of very low natural frequency.
Wake interference of a row of normal flat plates arranged side by side in a uniform flow
Authors: Hayashi Masanori , Sakurai Akira , Ohya Yuji
Published: April 2006

The wake characteristic of groups of normal flat plates, consisting of two, three, or four plates placed side by side with slits in between, have been investigated experimentally. When the ratio of the slit width to the plate width (slit ratio) was small, the gap flows were observed to be biased either upward or downward in a stable way, leading to multiple, stable flow patterns for a single slit-ratio value. Some regularities were recognized in the gap-flow directions and the appearance of the flow patterns. The plates on the biased side showed high drag and regular vortex shedding, while those on the unbiased side showed the opposite. The origin of the biased flow has also been investigated with water-tank experiments, numerical calculations and wind-tunnel experiments. The-results showed that the origin of biasing is strongly related to the vortex shedding of each plate of a row.
Flow regimes in a circular Couette system with independently rotating cylinders
Authors: Andereck C. David , Liu S. S. , Swinney Harry L.
Published: April 2006

Our flow-visualization and spectral studies of flow between concentric independently rotating cylinders have revealed a surprisingly large variety of different flow states. (The system studied has radius ratio 0.883, aspect ratios ranging from 20 to 48, and the end boundaries were attached to the outer cylinder.) Different states were distinguished by their symmetry under rotation and reflection, by their azimuthal and axial wavenumbers, and by the rotation frequencies of the azimuthal travelling waves. Transitions between states were determined as functions of the inner- and outer-cylinder Reynolds numbers, Ri and Ro, respectively. The transitions were located by fixing Ro and slowly increasing Ri. Observed states include Taylor vortices, wavy vortices, modulated wavy vortices, vortices with wavy outflow boundaries, vortices with wavy inflow boundaries, vortices with flat boundaries and internal waves (twists), laminar spirals, interpenetrating spirals, waves on interpenetrating spirals, spiral turbulence, a flow with intermittent turbulent spots, turbulent Taylor vortices, a turbulent flow with no large-scale features, and various combinations of these flows. Some of these flow states have not been previously described, and even for those states that were previously described the present work provides the first coherent characterization of the states and the transitions between them. These flow states are all stable to small perturbations, and the transition boundaries between the states are reproducible. These observations can serve as a challenge and test for future analytic and numerical studies, and the map of the transitions provides several possible codimension-2 bifurcations that warrant further study.
Solute dispersion and weak second-order recombination at large times in parallel flow
Authors: Barton N. G.
Published: April 2006

This work is concerned with the parallel-flow shear dispersion of a solute which undergoes a second-order recombination reaction. The primary goal of the work is to provide background theory for the determination of the coefficient of diffusion of reactive-gas-phase species. Approximations are sought for large time and weak combination. At first, dispersion dominates recombination, and a modification of the Chatwin (1970) asymptotic expansion gives the concentration distribution as a regular perturbation expansion in e and t−½, where e is a dimensionless parameter characterizing recombination and t is dimensionless time. The regular expansion breaks down for dimensionless times t of O(ε−2) when dispersion and recombination are of the same importance. At these times, the governing equation is nonlinear and this regime is analysed by a numerical method. Finally, a similarity solution is derived for the concentration of solute when ε2t is large. Overall, the major effect of second-order recombination on dispersion is to flatten the peak of the dominant Gaussian concentration distribution. The speed of the centre of mass of the solute cloud is not affected at leading order by recombination.
Experimental study on the coherent structure of turbulent open-channel flow using visualization and picture processing
Authors: Utami Tadashi , Ueno Tetsuo
Published: April 2006

Coherent structures of turbulent open-channel flow in the wall region of a channel bed were examined quantitatively using experimental data obtained by flow visualization. Successive pictures of flow patterns in two horizontal cross-sections at different levels near the channel bed were taken, and then were digitized and analysed by a computer.

This method of flow visualization and picture processing enabled us to calculate the distributions of the three components of the velocity vectors. The distributions of velocities, streamlines, two-dimensional divergence and three components of vorticity could be calculated and are displayed as graphical output. In our numerical analyses, the idea of a two-dimensional correlation coefficient is introduced, through which the degree of similarity of turbulence structures can be better estimated than with the usual one-dimensional coefficient. Use of the data was based on the premise that the essential element in a turbulence structure is vortex motion.

We propose a conceptual model of turbulence structure in which the elementary unit of coherent structure in the buffer layer is presumed to be a horseshoe vortex and in which the characteristics of the multiple structure of turbulence are shown with respect to the scale, arrangement and generating process of horseshoe vortices and longitudinal vortices. Our model clearly explains the generating mechanism and mutual relations of low-speed regions, high-speed regions, ejections, sweeps and localized free-shear layers.
An experimental study of the Saffman-Taylor instability
Authors: Tabeling P. , Zocchi G. , Libchaber A.
Published: April 2006

An experiment on the Saffman-Taylor instability with wetting fluids is presented that explores a greater range of capillary numbers than did the original experiment of Saffman and Taylor. It turns out that no clear one-half plateau for the finger size is observed, and that the ensemble of experiments cannot be analysed in terms of a single control parameter. The effect of the film of oil left behind the finger is important, and we measure its thickness. A qualitative discussion of the instabilities of the fingers for large capillary numbers is presented, the first instability leading to asymmetrical fingers. Tip splitting appears for larger values of 1/B. The 1/B value for the onset of instabilities is shown to be noise dependent.
Energy separation in a vortex street
Authors: Kurosaka M. , Gertz J. B. , Graham J. E. , Goodman J. R. , Sundaram P. , Riner W. C. , Kuroda H. , Hankey W. L.
Published: April 2006

When a bluff body is placed in a crossflow, the total temperature in its wake can become substantially less than the incoming one, as manifested by the fact that the recovery factorRon its rearmost surface takes negative values at high subsonic flow: this is the phenomenon referred to here as the Eckert-Weise effect. Although a vortex street has been a suspected cause, the issue of whether this is so, and what the mechanism is, has remained unsettled. In this experimental and theoretical investigation, we first examine the cause of the Eckert-Weise effect by enhancing the vortex shedding through acoustic synchronization: resonance between the vortex shedding and transversely standing acoustic waves in a wind tunnel. At the lowest synchronization, where a ringing sound emanates from the wind tunnel,Rat the rearmost section of the cylinder is found to become negative even at a Mach number of 0.2; the base pressure (Cpb) takes dips correspondingly, indicative of the intensification of the vortex street. At this lowest acoustic resonance, the decrease ofRandCpb, uniform along the span, agrees with the expectation based on the spanwise uniformity of the lowest standing wave. At the next acoustic resonance where the standing wave now varies along the span, the corresponding dips inRandCpb, non-uniform along the span, reveals an interesting ‘strip-theory’-like behaviour of the vortex intensities in the vortex street. These results correlating the change inRwithCpbconfirm that the Eckert-Weise effect is indeed caused by the vortex shedding, the mechanism of which is examined theoretically in the latter half of the paper.

A simple theoretical argument, bolstered by a full numerical simulation, shows that the time-varying static pressure field due to the vortex movement separates the instantaneous total temperature into hot and cold spots located around vortices; once time-averaged, however, the total temperature distribution conceals the presence of hot spots and takes the guise of a colder wake, the Eckert-Weise effect. Therefore the correct explanation of the Eckert-Weise effect, a time-averaged phenomenon, emerges only out of, and only as a superposition of, instantaneous total temperature separation around vortices. Such a separation is not confined to the outside of vortex cores; every vortex in its entirety becomes thermally separated. Nor is it limited to the far downstream equilibrium configuration of the Kármán vortex street but applies to the important near-wake vortices, and to any three-dimensional vortical structure as well. For low subsonic flows in particular, this dynamical explanation also leads to a similar separation of total pressure; these features may thus be potentially exploited as a general marker to identify and quantify vortices.
Microscopic flow near the surface of two-dimensional porous media. Part 2. Transverse flow
Authors: Larson R. E. , Higdon J. J. L.
Published: April 2006

A model problem is analysed to study the microscopic flow near the surface of porous media. In the idealized system, we consider two-dimensional media consisting of infinite and semi-infinite periodic lattices of cylindrical inclusions. In Part 1, results for axial flow were presented. In this work results for transverse flow are presented and discussed in the context of macroscopic approaches such as slip coefficients and Brinkman's equation.
Bragg scattering of surface waves by periodic bars: theory and experiment
Authors: Hara Tetsu , Mei Chiang C.
Published: April 2006

We extend a recent linearized theory on Bragg scattering of surface waves by periodic sandbars to include second-order effects of the free surface and of the bars. New experiments are performed to verify the existence of the cutoff detuning frequency, the dispersive nature of the first-order wave envelope, and the radiation of second-order long waves. Measured transient and quasi-steady responses to incident wave packets and uniform wavetrains are compared with corresponding theoretical results. For quasi-steady incident waves of relatively small steepness it is found necessary to improve the theory to the second order in bar slope, in order that the calculated short-wave envelopes agree with those measured over the bars.
Waves on a static water surface beneath a layer of moving air
Authors: Grundy I. H. , Tuck E. O.
Published: April 2006

Large-amplitude waves can exist on an air-water interface where the air is in steady non-uniform flow and the water is stationary. Computations of such waves are provided here, both for periodic nonlinear Stokes-like waves, and for a specific wave-making configuration in which the periodic solution appears as the downstream far field. The wavemaker geometry chosen here is relevant to the edge region of a hovercraft, and the large-amplitude free-surface disturbance caused by the escaping air is computed as a function of the Froude number based on air-jet velocity and thickness.
Dynamically consistent magnetic fields produced by differential rotation
Authors: Fearn D. R. , Proctor M. R. E.
Published: April 2006

We investigate the dynamical consequences of an axisymmetric velocity field with a poloidal magnetic field driven by a prescribed e.m.f. E. The problem is motivated by previous investigations of dynamically driven dynamos in the magnetostrophic range. A geostrophic zonal flow field is added to a previously described velocity, and determined by the requirement that Taylor's constraint (Taylor 1963) (guaranteeing dynamical self-consistency of the fields) be satisfied. Several solutions are exhibited, and it is suggested that self-consistent solutions can always be found to this ‘forced’ problem, whereas the usual α-effect dynamo formalism in which E is a linear function of the magnetic field leads to a difficult transcendentally nonlinear characteristic value problem that may not always possess solutions.
Self-sustained oscillation of a jet impinging upon a Helmholtz resonator
Authors: Jungowski W. M. , Grabitz G.
Published: April 2006

A planar, sonic, underexpanded air jet induced strong and self-sustained flow oscillation. The jet was bounded by two parallel walls extending between the nozzle and the Helmholtz resonator opposite. This oscillation was characterized by large pressure amplitudes in the resonator and periodic displacement of a detached shock wave. The observed phenomena were in some measure similar to those occurring with Hartmann-Sprenger tubes. Based on the experimental results, including Mach-Zehnder interferograms and fluctuating pressure and velocity measurements, the properties of the oscillation have been described and a model for theoretical analysis has been established. Experimental and numerical investigations have made possible a description of the oscillation mechanism, which is of the relaxation type.
Secondary bifurcation and change of type for three-dimensional standing waves in finite depth
Authors: Bridges Thomas J.
Published: April 2006

The nonlinear periodic free oscillations of irrotational surface waves in a three-dimensional basin with a rectangular cross-section and finite depth are considered. A previous work by Verma & Keller (1962) has analysed the case when the linear natural frequencies are non-commensurate. For particular values of the parameters, however, strong internal resonance occurs (two natural frequencies are equal). Instead of the usual loss of stability and exchange of energy, it is found that the double eigenvalue generates a higher multiplicity of periodic solutions. Eight solution branches are found to be emitted by the double eigenvalues. It is also shown that perturbing the double eigenvalue results in a secondary bifurcation of periodic solutions. The direction of the branches for the multiple and secondary bifurcation changes with the depth. Finally it is shown that the formal solutions obtained are not uniformly valid and an additional expansion in the Boussinesq regime shows that the wave field changes type. One of the solutions in this regime is a field of three-dimensional cnoidal standing waves.
On a series expansion for the solitary wave
Authors: Pennell Stephen A.
Published: April 2006

The first 27 terms in a series expansion for the profile of a solitary wave are computed. From this, series expansions for the wave amplitude, mass and potential energy are obtained. A previous study indicated that the partial sums of these series converged for small- to medium-amplitude waves and that the diagonal Padé approximants converged for waves of all amplitudes. The data derived here show that this is not the case and that apparent convergence of Padé approximants can be misleading.
The far field of an oscillating airfoil in supersonic flow
Authors: Messiter A. F. , Woodruff S. L.
Published: April 2006

An approach utilizing multiple scales and matched asymptotic expansions is developed for the description of small perturbations at large distances from a thin airfoil oscillating harmonically in a uniform supersonic flow. The problem of determining the unsteady perturbation potential is formulated in general, and an analytical solution is derived for an airfoil with parabolic or flat surfaces. The results describe the flow ahead of the region influenced by the trailing edge. The variation in the pressure jump across an attached leading-edge shock wave is also obtained.
Non-equilibrium vapour condensation on a shock-tube endwall behind a reflected shock wave
Authors: Fujikawa Shigeo , Okuda Masahiko , Akamatsu Teruaki , Goto Tomonobu
Published: April 2006

This paper deals theoretically with a filmwise condensation of a vapour on the endwall of a shock tube behind a reflected shock wave. The gas dynamics, accompanied by heat and mass transfer at the vapour-liquid interface, is treated by the method of matched asymptotic expansions. The first and second approximate solutions are obtained and evaluated numerically. It is clarified that there exists a transition process on the growth of a liquid film, that is, the liquid film grows approximately in proportion to the time t in the early stages after the reflection of the shock wave, and after some time, it grows in proportion to the square root of the time. This transition process from the t-dependent growth to the t½-dependent one is mainly controlled by the intensity of condensation. In the t-dependent growth region, the growth rate of the liquid film is proportional to the condensation parameter, depending both upon an initial condition and upon thermal properties of the vapour and the liquid film, while in the t½-dependent growth region it becomes independent of the condensation parameter and is controlled only by thermal properties of the vapour, liquid film and shock-tube endwall. This result suggests that the measurement of the condensation parameter by shock tubes should be made in the t-dependent growth region immediately after the reflection of the shock wave.
Rossby waves and two-dimensional turbulence in a large-scale zonal jet
Authors: Shepherd Theodore G.
Published: April 2006

The theory of homogeneous barotropic beta-plane turbulence is here extended to include effects arising from spatial inhomogeneity in the form of a zonal shear flow. Attention is restricted to the geophysically important case of zonal flows that are barotropically stable and are of larger scale than the resulting transient eddy field.

Because of the presumed scale separation, the disturbance enstrophy is approximately conserved in a fully nonlinear sense, and the (nonlinear) wave-mean-flow interaction may be characterized as a shear-induced spectral transfer of disturbance enstrophy along lines of constant zonal wavenumber k. In this transfer the disturbance energy is generally not conserved. The nonlinear interactions between different disturbance components are turbulent for scales smaller than the inverse of Rhines's cascade-arrest scale κβ≡ (β0/2urms)½ and in this regime their leading-order effect may be characterized as a tendency to spread the enstrophy (and energy) along contours of constant total wavenumber κ ≡ (k2 + l2)½. Insofar as this process of turbulent isotropization involves spectral transfer of disturbance enstrophy across lines of constant zonal wavenumber k, it can be readily distinguished from the shear-induced transfer which proceeds along them. However, an analysis in terms of total wavenumber K alone, which would be justified if the flow were homogeneous, would tend to mask the differences.

The foregoing theoretical ideas are tested by performing direct numerical simulation experiments. It is found that the picture of classical beta-plane turbulence is altered, through the effect of the large-scale zonal flow, in the following ways: (i) while the turbulence is still confined to KKβ, the disturbance field penetrates to the largest scales of motion; (ii) the larger disturbance scales K < Kβ exhibit a tendency to meridional rather than zonal anisotropy, namely towards v2 > u2 rather than vice versa; (iii) the initial spectral transfer rate away from an isotropic intermediate-scale source is significantly enhanced by the shear-induced transfer associated with straining by the zonal flow. This last effect occurs even when the large-scale shear appears weak to the energy-containing eddies, in the sense that dU/dy [Lt ] κ for typical eddy length and velocity scales.
A high-order spectral method for the study of nonlinear gravity waves
Authors: Dommermuth Douglas G. , Yue Dick K. P.
Published: April 2006

We develop a robust numerical method for modelling nonlinear gravity waves which is based on the Zakharov equation/mode-coupling idea but is generalized to include interactions up to an arbitrary order M in wave steepness. A large number (N = O(1000)) of free wave modes are typically used whose amplitude evolutions are determined through a pseudospectral treatment of the nonlinear free-surface conditions. The computational effort is directly proportional to N and M, and the convergence with N and M is exponentially fast for waves up to approximately 80% of Stokes limiting steepness (ka ∼ 0.35). The efficiency and accuracy of the method is demonstrated by comparisons to fully nonlinear semi-Lagrangian computations (Vinje & Brevig 1981); calculations of long-time evolution of wavetrains using the modified (fourth-order) Zakharov equations (Stiassnie & Shemer 1987); and experimental measurements of a travelling wave packet (Su 1982). As a final example of the usefulness of the method, we consider the nonlinear interactions between two colliding wave envelopes of different carrier frequencies.
Topographic waves in rectangular basins
Authors: Stocker Thomas , Hutter Kolumban
Published: April 2006

The channel model of Stocker & Hutter (1986, 1987) is used to construct topographic wave solutions in a rectangular basin on the f-plane with variable but symmetric bathymetry. We show that in a narrow period band three types of eigenmodes can be discerned which exhibit local, midscale and global structure, respectively. Wave motion can be trapped either at the long sides of the elongated basin (channel mode) or at the ends of it (bay mode) or alternatively, a basinwide phase rotation is observed (Ball mode). The new bay modes are explained as resonances of topographic wave reflection in a semi-infinite channel. The influence of the variation of the aspect ratio of the rectangle and the topography parameter on the wave periods is also investigated.
The compressible vortex pair
Authors: Moore D. W. , Pullin D. I.
Published: April 2006

We consider the steady self-propagation with respect to the fluid at infinity of two equal symmetrically shaped vortices in a compressible fluid. Each vortex core is modelled by a region of stagnant constant-pressure fluid bounded by closed constant-pressure, constant-speed streamlines of unknown shape. The external flow is assumed to be irrotational inviscid isentropic flow of a perfect gas. The flow is therefore shock free but may be locally supersonic. The nonlinear free-boundary problem for the vortex-pair flow is formulated in the hodograph plane of compressible-flow theory, and a numerical solution method based on finite differences is described. Specific results are presented for a range of parameters which control the flow, namely the Mach number of the pair translational motion and the fluid speed on each vortex bounding streamline. Perturbation-theory predictions are developed, valid for vortices of small core radius when the pair Mach number is much less than unity. These are in good agreement with the hodograph-plane calculations. The numerical and the perturbation-theory results together confirm the recently discovered (Barsony-Nagy, Er-El & Yungster 1987) existence of continuous shock-free transonic compressible flows with embedded vortices. For the vortex-pair geometry studied, solution branches corresponding to physically acceptable flows that could be calculated using the present hodograph-plane numerical method were found to be terminated when either the flow on the streamline of symmetry separating the vortiqes tends to become superonic or when limiting lines appear in the hodograph plane giving a locally multivalued mapping to the physical plane.
Reflection of water waves in a channel with corrugated bed
Authors: Benjamin T. Brooke , Boczar-Karakiewicz B. , Pritchard W. G.
Published: April 2006

Intended as a contribution towards understanding the multiple processes entailed in the development of coastal sand bars due to wave action, this theoretical and experimental study deals with the Bragg reflection of long-crested surface waves in a water channel whose bed is corrugated sinusoidally. The present findings complement and in a few respects improve upon those in previous investigations, particularly Davies & Heathershaw (1984).

In §2 a linearized theory is presented, being directed to the elucidation of experimental situations where monochromatic waves propagate into a channel with a limited stretch of corrugations on its bed and an imperfectly absorbing beach at its far end. Allowance is made fully for dispersive effects (§2.2) and approximately for small frictional effects (§2.3). Points of interpretation (§2.4) include accounts of degenerate but non-trivial solutions that apply at frequencies terminating the stopping band, wherein the spatial wavefield has an exponential envelope. The experimental results presented in §4 derive from measurements of the wavefield over a stretch of 24 corrugations, at various frequencies both inside and outside the stopping band. Quantitative comparisons (§4.2 and 4.3) demonstrate close agreements with the theory.
Bubble dynamics in a compressible liquid. Part 2. Second-order theory
Authors: Lezzi A. , Prosperetti A.
Published: April 2006

The radial dynamics of a spherical bubble in a compressible liquid is studied by means of a rigorous singular-perturbation method to second order in the bubble-wall Mach number. The results of Part 1 (Prosperetti & Lezzi, 1986) are recovered at orders zero and one. At second order the ordinary inner and outer structure of the solution proves inadequate to correctly describe the fields and it is necessary to introduce an intermediate region the characteristic length of which is the geometric mean of the inner and outer lengthscales. The degree of indeterminacy for the radial equation of motion found at first order is significantly increased by going to second order. As in Part 1 we examine several of the possible forms of this equation by comparison with results obtained from the numerical integration of the complete partial-differential-equation formulation. Expressions and results for the pressure and velocity fields in the liquid are also reported.
Wave splitting in a fluid of large heat capacity
Authors: Thompson Philip A. , Craves Humberto , Meier G. E. A. , Kim Yoon-Gon , Speckmann H.-D.
Published: April 2006

The splitting of a single pressure discontinuity into a propagating two-wave system is studied for the case of saturated-liquid expansion (liquid-evaporation wave splitting) and vapour compression (vapour-condensation wave splitting). Experimental results from the Max-Planck-Institut für Strömungsforschung and from Rensselaer Polytechnic Institute show that splitting occurs in test fluids of large molar heat capacity, such as iso-octane (Cv0/R≈ 37). Each of the two forms of splitting results in a single-phase forerunner wave carrying a pressure discontinuity followed by a phase-change wave, also with a pressure discontinuity. The thermodynamic state between the forerunner wave and the phase-change wave is metastable (supersaturated liquid or vapour). The waves are quantitatively described by systems of adiabats, e.g. shock adiabats. It appears that nucleation processes are predominantly homogeneous.

In vapour-compression shock-wave splitting, a combined wave (liquefaction shock) splits into discrete forerunner and condensation waves at a triple point, the intersection of a liquefaction shockfront, forerunner shock and condensation discontinuity: such a point occurs just at critical supersaturation (i.e. the Wilson-line state), where condensation is spontaneous and immediate. For shock waves that produce a metastable state of subcritical supersaturation, condensation is delayed, that is, the condensation discontinuity propagates more slowly; for a split-shock system, the condensation discontinuity propagates subsonically. The pressure amplitude of a real split-shock system is much larger than that predicted by an equilibrium model.

In liquid-evaporation wave splitting, the forerunner wave is an acoustic expansion wave and the second wave an evaporation wave with a propagation velocity approximately determined by the Chapman-Jouguet condition for deflagration. Such evaporation wavefronts are increasingly distinct as the temperature approaches the critical-point value. The evaporation rates across the wavefront are comparable to those found in vapour explosions.