bluuebunny/crossref_metadata_2025 huggingface dataset:
Ring Transformation Reactions of 3‐[3/4‐Acetylphenyl] Sydnones; Synthesis of Oxime, Hydrazone and Dibromo Derivatives of 3‐[3/4‐Acetylphenyl] sydnones and 3‐[3/4‐Acetylphenyl]‐5‐methyl‐[1,3,4]oxadiazolin‐2‐ones.
Authors: Latthe Prashant R. , Kamble Ravindra R. , Badami Bharati V.
Published: April 2006

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Synthesis and Biological Evaluation of Functionalized Coumarins as Acetylcholinesterase Inhibitors.
Authors: Shen Qiong , Peng Quan , Shao Jialiang , Liu Xufeng , Huang Zhishu , Pu Xianzhang , Ma Lin , Li Yue‐Ming , Chan Albert S. C. , Gu Lianquan
Published: April 2006

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Tandem Directed Lithiations of N‐Boc‐1,2‐dihydropyridines Toward Highly Functionalized 2,3‐Dihydro‐4‐pyridones.
Authors: Young Damian W. , Comins Daniel L.
Published: April 2006

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Synthesis of Some New Thioquinazolinone Derivatives of Biological Activity.
Authors: Sharma Bimal Prasad , Lakhan Ram , Singh B. N.
Published: April 2006

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Optically Pure N‐Hydroxy‐O‐triisopropylsilyl‐α‐L‐amino Acid Methyl Esters from AlCl3‐Assisted Ring Opening of Chiral Oxaziridines by Nitrogen Containing Nucleophiles.
Authors: Di Gioia Maria Luisa , Leggio Antonella , Le Pera Adolfo , Liguori Angelo , Siciliano Carlo
Published: April 2006

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Stereoselective Synthesis of Oligo‐α(2,8)‐3‐deoxy‐D‐manno‐2‐octulosonic Acid Derivatives.
Authors: Tanaka Hiroshi , Takahashi Daisuke , Takahashi Takashi
Published: April 2006

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Studies Directed Toward the Synthesis of the Guanidine Alkaloid, Spiroleucettadine: Some Observations at the Level of Structure.
Authors: Li Chaomin , Danishefsky Samuel J.
Published: April 2006

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Termolecular One‐Pot Synthesis of Symmetrical Azines of 4‐Acetyl‐3‐arylsydnones. Hydrazone and Azine Derivatives of 4‐Acetyl‐3‐arylsydnones, Their Spectral Characterization and Biological Properties.
Authors: Shinge Prashant S. , Mallur Shanta G. , Badami Bharati V.
Published: April 2006

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Synthesis and Activity of Four (N,N‐Dimethylamino)benzamide Non‐steroidal Antiinflammatory Drugs Based on Thiazole and Thiazoline.
Authors: Lynch Daniel E. , Hayer Ravinder , Beddows Samantha , Howdle Joy , Thake C. Douglas
Published: April 2006

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Expanding Structural Diversity of Terpene Trilactones from Ginkgo biloba Extract: Studies Towards Core‐Modified Ginkgolides
Authors: Dzyuba Sergei V. , Bolshakov Sergei , Li Jean , Nakanishi Koji
Published: April 2006

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
Assessing the relationships between e-tail success and product and Web site factors
Authors: Weathers Danny , Makienko Igor
Published: April 2006

The probability of e-tail success may be related to the products sold and the service that online shoppers receive. We investigate these possibilities using data collected on 755 e-tailers from BizRate.com in 2000 and 2004. The results indicate that the likelihood of success is negatively related to the e-tailer's reliance on selling experience goods and positively related to the number of ordering methods and e-tailer prominence, while the relationship between e-tail success and the number of product categories sold is moderated by the presence of features that allowshoppers to search for products. Further, we find that while successful e-tailers typically added service-related features between 2000 and 2004, these e-tailers reduced shoppers’ contact ability over these years. This research has implications for marketing strategy pertaining to the products e-tailers should sell and the site features and services that e-tailers should provide.
Nanoporous Noninvasive Cellular Electrical Activity-Based Analysis Devices
Authors: Prasad Shalini , Quijano Jorge
Published: April 2006

In recent years, rapid advancements have been made in the biomedical applications of microtechnology and nanotechnology. While the focus of such technologies have been primarily on in vitro analytical and diagnostic tools, more recently in vivo therapeutic and sensing applications have gained attention. The long-term integration of cells with inorganic materials provides the basis for novel sensing platforms. The work presented here focuses on the ability to maintain cells long-term in nanoporous silicon-based microenvironments. This paper describes the creation of nanoporous, biocompatible, alumina membranes as a platform for incorporation into a cell-based device targeted for in situ recording of cellular electrical activity variations due to the changes associated with the surrounding microenvironments. Studies described herein focus on the interaction of nanoporous alumina substrates embedded in silicon patterned with cells of interest. The fidelity of such a system is demonstrated in terms of viability, proliferation, and functionality. The capability of such microfabricated nanoporous membranes, as in vitro for cell-based assays for sensing and drug delivery applications, is also demonstrated. It has potential in vivo application for therapeutic immunoisolation.
Two-Staged Reconstruction of the Flexor Pollicis Longus Tendon
Authors: UNGLAUB F. , BULTMANN C. , REITER A. , HAHN P.
Published: April 2006

The purpose of this study was to evaluate the results of two-stage reconstruction of the flexor pollicis longus (FPL) tendon. Sixteen patients who underwent reconstructive surgery of the FPL tendon were assessed retrospectively. Eight weeks after implantation of a silastic spacer, a tendon graft was used for reconstruction (thirteen palmaris longus tendons, two plantaris tendons, one half of the flexor carpi radialis tendon). Power grip, active range of motion, passive range of motion, the Buck-Gramcko assessment, the ASSH assessment and the DASH score were used to evaluate the results. Adequate function in 75% of the cases and a median of 11 on the DASH score was achieved. The results showed that two-stage reconstruction of the FPL tendon can produce satisfactory results, even if primary repair is the ideal.
Sequence Similarity and Functional Relationship Among Eukaryotic ZIP and CDF Transporters
Authors: Kambe Taiho , Suzuki Tomoyuki , Nagao Masaya , Yamaguchi-Iwai Yuko
Published: April 2006

ZIP (ZRT/IRT-like Protein) and CDF (Cation Diffusion Facilitator) are two large metal transporter families mainly transporting zinc into and out of the cytosol. Several ZIP and CDF transporters have been characterized in mammals and various model organisms, such as yeast, nematode, fruit fly, and zebrafish, and many candidate genes have been identified by genome projects. Unexpected functions of ZIP and CDF transporters have been recently reported in some model organisms, leading to major advances in our understanding of the functions of mammalian counterparts. Here, we review the recent information on the sequence similarity and functional relationship among eukaryotic ZIP and CDF transporters obtained from the representative model organisms.
High-Throughput Three-Dimensional Gel Electrophoresis for Versatile Utilities: A Stacked Slice-Gel System for Separation and Reactions (4SR)
Authors: Salimullah Md. , Mori Masaki , Nishigaki Koichi
Published: April 2006

A novel high-throughput system, called the stacked slice-gel system for separation and reactions (4SR), was developed for the analysis of DNA/RNA and protein/peptide. The system provides a novel three-dimensional gel electrophoresis approach that exploits the property of stacked slice gels. It allows multiple samples simultaneously to react as well as to be separated, offering a two-dimensional (m × n) sample loading system. For this purpose, high-throughput multi-micro vessels (MMVs) containing variable numbers of wells (100 wells in this paper) have been used, which are made of 25 mm square-size polyacrylamide gels. Furthermore, after electrophoretic separation, a slice gel containing a desired sample can be easily removed and proceeded to the next step. Different biological reactions as well as successive separation of products were effectively carried out dealing with DNA/RNA and protein/peptide. It shows that this system has a diversity of potentials to be developed.
Don DeLillo's Transatlantic Dialogue with Sergei Eisenstein
Authors: MORLEY CATHERINE
Published: April 2006

There are only connections. Everything is connected. All human knowledge gathered and hyperlinked, this site leading to that, this fact referenced to that, a key-stroke, a mouse-click, a password – world without end amen … Everything is connected in the end.
The large-scale structure of unsteady self-similar rolled-up vortex sheets
Authors: Pullin D. I.
Published: April 2006

Two problems involving the unsteady motion of two-dimensional vortex sheets are considered. The first is the roll-up of an initially plane semi-infinite vortex sheet while the second is the power-law starting flow past an infinite wedge with separation at the wedge apex modelled by a growing vortex sheet. In both cases well-known similarity solutions are used to transform the time-dependent problem for the sheet motion into an integro-differential equation. Finite-difference numerical solutions to these equations are obtained which give details of the large-scale structure of the rolled-up portion of the sheet. For the semi-infinite sheet good agreement with Kaden's asymptotic spiral solution is obtained. However, for the starting-flow problem distortions in the sheet shape and strength not predicted by the leading-order asymptotic solutions were found to be significant.
The turbulent concentration field of a methane jet
Authors: Birch A. D. , Brown D. R. , Dodson M. G. , Thomas J. R.
Published: April 2006

Detailed measurements of turbulent concentration parameters in a round free methane jet up to 70 diameters downstream from the jet source are described. The concentration changes were obtained using a Raman spectrometer designed for the measurement of a methane vibrational transition function, and processed using a photon correlator. Mean and fluctuating concentration levels are given, together with the concentration probability density distribution.

A theory for interpreting the statistical aspects of the signal is presented and results are compared with other data from the literature on jets of uniform and non-uniform density. It is shown that the intensity of concentration fluctuations has an asymptotic value of 28·5% in the far field region of the jet. One interesting feature of the data is the deviation from Gaussian statistics along the jet centre-line.
Hydrodynamic propulsion by large amplitude oscillation of an airfoil with chordwise flexibility
Authors: Katz J. , Weihs D.
Published: April 2006

The hydrodynamic forces due to the motion of a flexible foil in a large amplitude curved path in an inviscid incompressible flow are analysed. A parametric study of large amplitude oscillatory propulsion, with special emphasis on the effect of chordwise flexibility of the fin, is presented. This flexibility was found to increase the propulsive efficiency by up to 2% while causing small decreases in the overall thrust, compared with similar motion with rigid foils.
Large-scale motion in a turbulent boundary layer: a study using temperature contamination
Authors: Chen Chyan-Hai P. , Blackwelder Ron F.
Published: April 2006

A fully developed turbulent boundary layer with a zero pressure gradient was explored by using temperature as a passive contaminant in order to study the large-scale structure. The temperature tracer was introduced into the flow field by heating the entire wall to approximately 12°C above the free-stream temperature. The most interesting observation was the existence of a sharp internal temperature front, characterized by a rapid decrease in temperature, that extended throughout the entire boundary layer. In the outer, intermittent region, the internal temperature front was always associated with the upstream side of the turbulent bulges, i.e. the ‘backs’. It extended across the entire logarithmic region and was related to the sharp acceleration associated with the bursting phenomenon near the wall. Conditional averages of the velocities measured with the temperature front revealed that it was associated with an internal shear layer. The results suggest that this shear layer provides a dynamical relationship between the large structures in the outer, intermittent region and the bursting phenomenon near the wall.
Analysis of a cylindrical imploding shock wave
Authors: Mishkin E. A. , Fujimoto Y.
Published: April 2006

The self-similar solution of the gasdynamic equations of a strong cylindrical shock wave moving through an ideal gas, with γ = cp/cv, is considered. These equations are greatly simplified following the transformation of the reduced velocity
\[
U_1(\xi)\rightarrow U_1 = {\textstyle\frac{1}{2}}(\gamma + 1)(U+\xi).
\]
The requirement of a single maximum pressure, dζP = 0, leads to an analytical determination of the self-similarity exponent α(γ). For gases with γ < 2 + 3½ the slight maximum pressure occurs behind the shock front, nearing it as γ increases. For γ < 2 + 3½, this maximum ensues right at the shock front and the pressure distribution then decreases monotonically. The postulate of analyticity by Gelfand and Butler is shown to concur with the requirement dζP = 0. The saturated density of the gas left in the wake of the shock is computed and − U is shown to be the reduced velocity of sound at P = Pm.
The effect of a transverse magnetic field on shear turbulence
Authors: Reed Claude B. , Lykoudis Paul S.
Published: April 2006

Turbulence measurements under the influence of a transverse magnetic field have been made at Purdue University's Magneto-Fluid-Mechanic Laboratory in a high aspect ratio channel. The Reynolds number range covered was 25000 ≤Re282000; the geometry and experimental conditions were such that the experiment approximated turbulent Hartmann flow. The aspect ratio of the channel was 5·8:1, its walls were electrically insulated and the working fluid was mercury. Measurements in the presence of a magnetic field were made of the skin friction coefficient, the mean velocity profiles, the turbulence intensity profiles (bothu’ andv’) and the Reynolds stress profiles.

A sudden change in the damping of the Reynolds stresses was manifested by a ‘hump’ in the curves ofCfversusM/Retaken with the Reynolds number held constant. This ‘hump’ occurs as a gentle rise and sudden drop to the Hartmann laminar line of theCfdata. Close examination of the$\overline{u^{\prime}v^{\prime}}$data near the wall confirms this behaviour, indicating that the turbulent contribution to the shear stress is the controlling factor in this behaviour ofCf. The Reynolds stresses were completely suppressed to zero at high values of the magnetic field, though the turbulence intensities ofu’ andv’ were not. The Reynolds stress data are fundamental in revealing the mechanisms which are at work during the suppression of turbulence by a magnetic field.

It was also found that at high magnetic fields, when most of the turbulence was damped, the skin friction coefficient fell below the values predicted by Hartmann's (1937) laminar solution for high values ofM/Re. This result was linked to the presence of ‘M-shaped’ velocity profiles in the direction perpendicular to both the magnetic field and the mean velocity vector. The presence of ‘M-shaped’ profiles has not previously been linked to a reduction inCf.
Stochastic properties of scalar quantities advected by a non-buoyant plume
Authors: O'Brien Edward E.
Published: April 2006

A model probability density equation is obtained by approximating the convective and diffusive terms in a single-point density formulation of homogeneous turbulent scalar transport, with first-order reaction, in a plume. The equation, which includes the intermittency factor of the scalar field explicitly, is then shown to support similarity solutions under some constraining assumptions. Comparison of the similarity solutions with field measurements of conditioned concentrations shows that they can reproduce the general features of the data for both low intermittency and high intermittency measurement regimes. On the basis of these asymptotic results a speculative modelling of the terms representing entrainment at the plume interface is proposed and a class of similarity solutions for the intermittency factor is obtained by numerical integration.
Stability of Couette flow in nematic liquid crystals
Authors: Dubois-Violette E. , Manneville P.
Published: April 2006

We study the stability of the cylindrical Couette flow in nematics when the director is parallel to the rotation axis. The contribution of the inertial coupling of velocity fluctuations (responsible for the Taylor instability in isotropic liquids) is shown to be destabilizing when the inner cylinder rotates faster than the outer one. However, the instability remains driven by the mechanisms first discovered by Pieranski & Guyon for the plane shear case and quite specific to nematics. This mechanism couples the different orientation fluctuations via viscous torques and the corresponding threshold is given by
\[
s\tau_0\sim 1,
\]
where τ0 is the time constant for the diffusion of orientation fluctuations. The contribution of inertia terms is measured by 2ωm τv, where τv is the time constant for the diffusion of velocity fluctuations. In usual nematics one has τv/τ0 ∼ 10−5 so that corrections due to rotation are small in general. At different stages of the discussion differences between the case of nematics and that of isotropic liquids are pointed out. We also study the possibility of an oscillatory instability when α3 is positive and large, where no stationary instability can occur.
Small amplitude gasdynamic disturbances in an exploding atmosphere
Authors: Clarke J. F.
Published: April 2006

The propagation of disturbances through an atmosphere that is, in its undisturbed condition, undergoing a spatially uniform chemical explosion is analysed on the assumption that the disturbances are of small amplitude. When the latter are arbitrarily small, and therefore classifiable as acoustic, the progress of the ambient explosion is undisturbed to first order and a rather complete history of the acoustic waves (including weak shock waves) can be constructed. The generally amplifying effect of the explosion on the disturbances, which has previously been identified at wave heads, is found to occur throughout the disturbed domains.

When the disturbance amplitude becomes comparable to the ratio of the thermal energy of the gas to the combustion-reaction activation energy, the ambient explosion becomes involved in the disturbance to first order. For large activation energies a small disturbance theory can be constructed to account for the disturbance behaviour; at present it is limited to time intervals from initiation that are shorter than the ‘no-depletion’ homogeneous ignition time.
Large-scale structure in the mixing layer of a round jet
Authors: Yule A. J.
Published: April 2006

Late transitional and turbulent flows in the mixing-layer region of a round jet are investigated for a range of Reynolds numbers by using flow-visualization and hotwire techniques. Attention is focused on the vortices in the transition region and the large eddies in the turbulent region. The interaction and coalescence of vortex rings in the transition region are described. The transition region is characterized by a growth of three-dimensional flow due to a wave instability of the cores of the vortex rings. The merging of these distorted vortices produces large eddies which can remain coherent up to the end of the potential-core region of the jet. A conditional sampling technique is used to measure eddies moving near the jet centre-line. These eddies differ significantly from the ring vortices as they are three-dimensional and contain irregular small-scale turbulence. However, when averaged, their structure is similar in cross-section to that of a vortex ring. These sampled eddies contribute greatly to local velocity fluctuations and statistical correlations. The experiments indicate a need for careful consideration of the meanings of terms such as ‘vortex’, ‘eddy’ and ‘turbulent flow’. In particular care must be taken to discriminate between the orderly, easily visualized, vortices in the transition regions of free shear flows and the less clearly visualized, but strong, large eddies in the fully developed turbulent regions.
Triple-deck solutions for viscous supersonic and hypersonic flow past corners
Authors: Rizzetta D. P. , Burggraf O. R. , Jenson Richard
Published: April 2006

A viscous-inviscid interaction is produced when a compressible laminar boundary layer encounters a corner. The correct mathematical structure for such interactions at large Reynolds number is given by the asymptotic triple-deck theory. In the present work the triple-deck equations for supersonic and hypersonic flows are solved for both compression and expansion corners. Results are presented for a range of corner angles, including separated cases, and are compared with experimental data and with finite Reynolds number calculations based on an interacting boundary-layer model.
The turbulent mixing layer with an asymmetrical distribution of temperature
Authors: Béguier Claude , Fulachier Louis , Keffer James F.
Published: April 2006

An experimental programme has been carried out to examine the spread of heat as a passive scalar contaminant in a turbulent shear flow. The situation involves a slightly heated two-dimensional jet expanding into a quiescent medium on one side and a uniform stream with velocity equal to that of the warm jet on the other. Thus the developed flow is a typical mixing layer with an asymmetric mean temperature profile superimposed on it. Measurements of the mean and fluctuating velocity and temperature fields show the existence of a region where the production of temperature fluctuations is negative. Spectral analysis in this zone indicates a separation of large and small wavenumber components of the cospectrum into two regimes. The sign of the high-frequency portion is consistent with gradient-transport concepts while the low-frequency component is of opposite sign. From this it is inferred that the large eddies are mainly responsible for the negative production. A mathematical model has been developed to describe the transport within this region.
An exact theory of nonlinear waves on a Lagrangian-mean flow
Authors: Andrews D. G. , Mcintyre M. E.
Published: April 2006

An exact and very general Lagrangian-mean description of the back effect of oscillatory disturbances upon the mean state is given. The basic formalism applies to any problem whose governing equations are given in the usual Eulerian form, and irrespective of whether spatial, temporal, ensemble, or ‘two-timing’ averages are appropriate. The generalized Lagrangian-mean velocity cannot be defined exactly as the ‘mean following a single fluid particle’, but in cases where spatial averages are taken can easily be visualized, for instance, as the motion of the centre of mass of a tube of fluid particles which lay along the direction of averaging in a hypothetical initial state of no disturbance.

The equations for the Lagrangian-mean flow are more useful than their Eulerian-mean counterparts in significant respects, for instance in explicitly representing the effect upon mean-flow evolution of wave dissipation or forcing. Applications to irrotational acoustic or water waves, and to astrogeophysical problems of waves on axisymmetric mean flows are discussed. In the latter context the equations embody generalizations of the Eliassen-Palm and Charney-Drazin theorems showing the effects on the mean flow of departures from steady, conservative waves, for arbitrary, finite-amplitude disturbances to a stratified, rotating fluid, with allowance for self-gravitation as well as for an external gravitational field.

The equations show generally how the pseudomomentum (or wave ‘momentum’) enters problems of mean-flow evolution. They also indicate the extent to which the net effect of the waves on the mean flow can be described by a ‘radiation stress’, and provide a general framework for explaining the asymmetry of radiation-stress tensors along the lines proposed by Jones (1973).
Laser speckle measurements of transient Bénard convection
Authors: Simpkins P. G. , Dudderar T. D.
Published: April 2006

Quantitative velocity measurements of unsteady convection in a Bénard cell suddenly cooled from above to a supercritical Rayleigh number are reported. The results are obtained by a novel application of laser speckle photography adapted for the study of fluid dynamics. This technique allows two-dimensional full-field velocity information to be obtained solely from a selected plane within the volume of moving liquid at any given instant in time. The convective rolls are found to be regular and oriented parallel to the short side of the cell. The number of rolls within the cell is approximately twice as great as the number reported for steady conditions. The maximum vertical velocity distribution is observed to be a sinusoidal function of the horizontal distance with a detectable third-harmonic component.
The spectral broadening of sound by turbulent shear layers. Part 1. The transmission of sound through turbulent shear layers
Authors: Campos L. M. B. C.
Published: April 2006

The transmission of sound through a turbulent shear layer is reviewed both with respect to the mathematical theory of the distortion of signals during propagation and also as the basis of the analysis in part 2 of the spectral broadening evinced by experimental results relevant to the study of aircraft noise. The reflexion and transmission coefficients, which involve both amplitude and phase changes, are obtained for scattering by an irregular and unsteady interface convected between two media; diffraction of high frequency sound by small-scale turbulence in a shear layer is accounted for by means of a phase shift and conservation laws for energy, wavenumber and amplitude. These results may be used to construct the sound field transmitted through a turbulent shear layer from a source in the interior of a jet; multiple internal reflexions are accounted for in the case of transmission through two parallel shear layers, i.e. a jet of finite width shielding a noise source. A statistical description is given of the process of attenuation of the transmitted wave as energy is diffracted by the turbulence, and of the partial compensation by interference between correlated components of the refracted wave; the reference case is a monochromatic point source, which, when placed behind a system of shear layers, has its energy redistributed directionally and spread over a range of frequencies. The expressions obtained for the energy flux include as particular cases the results of Howe for the plane (1975) and impedance (1976) layers, the effects of turbulence being shown to be consistent with the experiments of Schmidt & Tilmann (1970) and Ho & Kovasznay (1976a, b).
‘Explosive’ resonant wave interactions in a three-layer fluid flow
Authors: Craik A. D. D. , Adam J. A.
Published: April 2006

Cairns (1979) has recently shown how the concept of negative wave energy used in plasma physics can be exploited to obtain insights into the linear and nonlinear instability of certain parallel flows. We here analyse the linear stability and nonlinear three-wave resonance in a three-layer flow with step-wise velocity and density profiles. The results are in complete agreement with Cairns’ qualitative predictions. In particular, the existence is confirmed of an ‘explosive’ instability in which all three waves of a resonant triad grow simultaneously while total wave energy is conserved. Such nonlinear instabilities, previously undetected in fluid flows, may well be important in the ocean and atmosphere.
A statistical model of turbulence in two-dimensional mixing layers
Authors: Tam Christopher K. W. , Chen K. C.
Published: April 2006

A statistical model based on the proposition that the turbulence of a fully developed two-dimensional incompressible mixing layer is in a state of quasi-equilibrium is developed. In this model the large structures observed by Brown & Roshko (1974) which will be assumed to persist into the fully developed turbulent region are represented by a superposition of the normal wave modes of the flow with arbitrary random amplitudes. The turbulence at a point in the flow is assumed to be dominated by the fluctuations associated with these large structures. These structures grow and amalgamate as they are convected in the flow direction. Because of the lack of intrinsic length and time scales the turbulence in question can, therefore, be regarded as created or initiated at an upstream point, the virtual origin of the mixing layer, by turbulence with a white noise spectrum and are subsequently convected downstream. The model is used to predict the second-order turbulence statistics of the flow including single point turbulent Reynolds stress distribution, intensity of turbulent velocity components, root-mean-square turbulent pressure fluctuations, power spectra and two-point space-time correlation functions. Numerical results based on the proposed model compare favourably with available experimental measurements. Predictions of physical quantities not yet measured by experiments, e.g. the root-mean-square pressure distribution across the mixing layer, are also made. This permits the present model to be further tested experimentally.
The spectral energy transfer from surface waves to internal waves
Authors: Olbers Dirk J. , Herterich Klaus
Published: April 2006

The generation of internal waves by resonantly interacting surface waves is examined in the framework of spectral scattering theory in the random-phase approximation. Coupling coefficients are derived from Euler's equation of motion for arbitrary stratification. The spectral energy transfer is discussed for deep-water surface waves and a simple three-layer model of the stability frequency. Analytical and numerical evaluation of the transfer integral leads to a parametrization in terms of the basic model parameters. These are the depth, thickness and stability frequency of the thermocline and the scale parameters and bandwidth of the surface wave spectrum. Strong dependence on some of these parameters, in particular the surface wave energy and the ratio of surface and internal wave frequencies, indicates a large spatial and temporal variability of the transfer rate. The transfer to the internal wave field in the oceanic main thermocline is found to be negligible compared with the effect of other processes. High frequency waves in the seasonal thermocline may be generated very efficiently.
Convective instabilities in a closed vertical cylinder heated from below. Part 1. Monocomponent gases
Authors: Olson J. M. , Rosenberger F.
Published: April 2006

Kr, Xe and SiCI4have been investigated for convective instabilities in closed vertical cylinders with conductive walls heated from below. Critical Rayleigh numbersNiRafor the onset of various convective modes (including the onset of marginally stable and periodic flow) have been determined with a high resolution differential temperature sensing method. Flow patterns were deduced from a multiple sensor arrangement. For the three lowest modes (i= 1, 2, 3) good quantitative agreement with linear stability theory is found. Stable oscillatory modes (periodic fluctuations of the mean flow) with a period of approximately 5 s are found for a relatively narrow range ofNRa. The critical Rayleigh numberNoscRafor the onset of oscillatory temperature fluctuations is 1348 ± 50 for an aspect ratio (height/radius) of 6.
The round laminar jet in a spherical envelope
Authors: Pickering W. M. , Sozou C.
Published: April 2006

A nonlinear solution is constructed representing the steady flow field generated in viscous incompressible fluid in a spherical envelope by a constant point force F0 acting at the centre O of the envelope. Our analysis shows that when F0 = O(3ν2ρ), where v is the coefficient of kinematic viscosity and ρ the density of the fluid, the linear solution, which is symmetric about a plane through O perpendicular to the force, represents a reasonable approximation to the velocity field. As F0 increases the velocity field develops an asymmetry and the centre of the eddy, that exists in a meridian section, is displaced towards the direction of the force and is closer to the boundary. Also as F0 increases, on the axis of symmetry, the fluid speed per unit force decreases behind the force and increases ahead of it and percentage-wise the increase is larger further from O.
Sink flow in a rotating basin
Authors: Kranenburg C.
Published: April 2006

The flow of a homogeneous viscous liquid towards a sink in the interior of a rotating basin with a free surface, a horizontal bottom and a vertical side wall is considered. The conditions assumed are such that an Ekman layer occurs at the bottom beyond a small distance from the sink. A first-order correction to the Ekman model accounting for the influence of the inertial terms in the equations of motion is given for a special case. It is shown theoretically and experimentally that eccentric withdrawal from a circular basin causes a vortex at the sink and a counter-rotating gyre attached to the far wall.
Is the Weis-Fogh principle exploitable in turbomachinery?
Authors: Furber S. B. , Williams J. E. Ffowcs
Published: April 2006

Weis-Fogh discovered a remarkable new principle of aerodynamic lift. Hovering wasps exploit the principle and fly with an aerodynamic performance superior in some respects to anything previously known. In this paper we address the question of whether the Weis-Fogh effect can be exploited in turbomachinery. We think the answer is yes.

Normal turbomachinery design is based on the analysis of isolated cascades of blades with steady entry and exit flows. The interactions between adjacent cascades and nonuniformities of the flow are usually regarded as problems which have to be minimized. Unsteadiness gives rise to noise. In this paper we take the opposite view and examine a novel type of turbomachinery stage that depends on the interaction between rotor and stator for its normal operation. The stage exploits the Weis-Fogh principle and has the unusual property that when started from rest it generates a pressure rise without shedding any vorticity into the fluid. We argue that there may be a performance advantage for stages of this new type.

Experiments were done to check the validity of the theoretical model and these are described. The results seem to show that under certain circumstances a strong rotor-stator interaction can result in an improved stage performance, and we suggest that this improvement may be due to the Weis-Fogh effect.
Further experiments on transition to Mach reflexion
Authors: Henderson L. F. , Lozzi A.
Published: April 2006

Our 1975 paper reported the results of experiments on shock reflexion in a wind tunnel and a shock tube; further results are presented here. For strong shocks it is shown that transition to Mach reflexion takes place continuously at the shock wave incidence angle ω0 corresponding to the normal shock point ω0 = ωN, unless the downstream boundaries form a throat. In this event transition can be promoted anywhere within the range ω0 [les ] ωN, and it is even possible to suppress regular reflexion altogether! However when ω0 < ωN the transition is discontinuous and accompanied by hysteresis. Again for strong shocks evidence is presented which suggests that the famous persistence of regular reflexion beyond the ωN point ω0 > ωN is spurious. For weak shocks the transition condition is not known but it is found that even for regular reflexion a marked discrepancy between theory and experiment develops as the shocks become progressively weaker. Also when weak shocks diffract over single concave corners there is a somewhat surprising discontinuity in the regular reflexion range. It seems that none of these phenomena can be adequately explained by real gas effects such as viscosity and variation of specific heats.
Experimental investigation of the origin of residual disturbances in turbulent MHD flows after laminarization
Authors: Branover H. , Gershon P.
Published: April 2006

The problem of the strong velocity disturbances remaining after the laminarization of an electroconductive fluid flow in a transverse magnetic field was investigated experimentally. The turbulence intensities, two-point correlations, and energy spectra of the velocity pulsations were measured using two-electrode probes and hot-film sensors. The two hypotheses with regard to a physical explanation of the persistence of the disturbances were examined, and it was concluded that these disturbances are generated mainly at the entry of the flow into the magnetic-field region. An almost undisturbed laminarized flow was obtained by eliminating the entry effects.
Experimental investigation of flow and heating in a resonance tube
Authors: Sarohia Virendra , Back Lloyd H.
Published: April 2006

Experiments have been performed to determine the basic mechanism of heating in resonance tubes of square section with constant area excited by underexpanded jet flows. The jet flow between the nozzle exit and the tube inlet plays a key role in the performance of a resonance tube. A detailed and systematic investigation of the unsteady complex shock structure in this part of the flow region has led to a better understanding of the fundamental mechanisms associated with the gas heating in such tubes. A study of the effects of tube location in relation to free-jet shock location (without the presence of the resonance tube) has shed further light on the underlying mechanism of sustained oscillations of the flow in a resonance tube.
Numerical solution of the exact equations for capillary–gravity waves
Authors: Schwartz Leonard W. , Vanden-Broeck Jean-Marc
Published: April 2006

A numerical method is presented for the computation of two-dimensional periodic progressive surface waves propagating under the combined influence of gravity and surface tension. The dynamic boundary equation is used in its exact nonlinear form. The procedure involves a boundary-integral formulation coupled with a Newtonian iteration. Solutions of high accuracy can be achieved over much of the range of wavelengths and heights including limiting waves. A number of different continuous families of solutions have been produced, all of which ultimately exhibit closed bubbles at their troughs. The so-called critical wavelengths are less important than have been previously assumed; the number of possible wave forms does increase with increasing wavelength, however.
Surface pressures and their corrections for the flow past a finite-length plate in supersonic low density flow
Authors: Gai S. L.
Published: April 2006

An experimental study of the flow past a thin finite length plate in a supersonic low density stream is reported. The paper discusses the corrections that are necessary for surface pressures measured under rarefied conditions. It is shown that the recent method of ‘orifice’ corrections due to Harbour & Bienkowski is versatile and reliable to use for both cold wall and insulated wall measurements. For the conditions of the experiment, the flow over the plate was found to be dominated by both leading-edge and trailing-edge interactions.
Lifting three-dimensional wings in transonic flow
Authors: Cramer M. S.
Published: April 2006

The far field of a lifting three-dimensional wing in transonic flow is analysed. The boundary-value problem governing the flow far from the wing is derived by the method of matched asymptotic expansions. The main result is to show that corrections which are second order in the near field make a first-order contribution to the far field. The present study corrects and simplifies the work of Cheng & Hafez (1975) and Barnwell (1975).
Mass transfer from a particle suspended in fluid with a steady linear ambient velocity distribution
Authors: Batchelor G. K.
Published: April 2006

This paper is concerned with the rate of transfer of heat or mass from a force-free couple-free particle immersed in fluid whose velocity far from the particle is steady and varies linearly with position. Asymptotic results for both small and large Péclet numbers are considered. There is at least a four-parameter family of different linear ambient velocity distributions, but nevertheless a comprehensive set of results for the transfer rate may be compiled by combining previously published work with some new developments. Some of these are exact results for particular linear ambient flow fields and some are approximate results for classes of linear flow fields.

For small Péclet number (P), the non-dimensional additional transfer rate due to convection is equal to αN20P½, where N0 is the Nusselt number for P = 0 and the proportionality constant α is a parameter of the concentration distribution due to a steady point source in the given linear ambient flow field. A general method of determining α is developed, and numerical values are found for some particular linear ambient flow fields. It is estimated that the value of α for any linear ambient flow field in which the vorticity does not dominate the straining motion lies within 10% of 0·34 when P is defined in terms of a particular invariant of the ambient rate-of-strain tensor E.

At large Péclet number the transfer rate N depends on the velocity distribution near the particle, and attention is restricted to the case of a sphere in low-Reynolds-number flow. For a rigid sphere $N = \beta P^{\frac{1}{3}}$ for any ambient pure straining motion, and the Levich concentration-boundary-layer method may be used to show that β = 0·90 for both axisymmetric and two-dimensional ambient pure straining, and probably for any other pure straining motion, when P is suitably defined. When the ambient vorticity ω is non-zero, the sphere rotates, and the Levich method cannot be used. However, it is shown that the part of the velocity distribution that varies sinusoidally with the azimuthal angle around the rotation axis does not affect the transfer rate and that N is asymptotically the same as for an ambient axisymmetric pure straining motion with rate of extension in the direction of the axis of symmetry equal to Eω(= ω. E. ω/ω2). In the exceptional case Eω = 0, N approaches a constant as P → ∞.

It is possible to interpolate between the asymptotic relations for small and large Péclet number with comparatively little uncertainty for any ambient pure straining motion and for any linear ambient flow field in which ω and Eω are non-zero.
Slender streams
Authors: Geer James , Keller Joseph B.
Published: April 2006

Flows of incompressible inviscid heavy fluids with free or rigid boundary surfaces are considered. For slender streams of fluid, the flow and the free boundaries are represented by a number of different asymptotic expansions in powers of the slenderness ratio. There are three kinds of outer expansions representing respectively jets, which have two free boundaries, wall flows, which have one free and one rigid boundary, and channel flows, which have two rigid boundaries. The flow at the junction of two or more outer flows is represented by an inner expansion. Previously we constructed the three outer expansions and the inner expansion at the junction of a wall flow and a jet (Keller & Geer 1973). Now we construct the inner expansions at the junctions of a channel flow and a jet, a channel flow and a wall flow, and a jet and the two wall flows into which it splits upon hitting a wall. We also match each inner expansion to the adjacent outer expansions. These seven expansions can be combined to solve many problems involving flows of slender streams.
The effects of certain low frequency phenomena on the calibration of hot wires
Authors: Perry A. E. , Smits A. J. , Chong M. S.
Published: April 2006

Temperature-sensitive constant-current wires operating at very low resistance ratios have been tested for temperature fluctuation response. A significant step in the response was found to occur with a centre-frequency of typically 1/6 Hz. The step size was observed to be as large as 30% and grew from zero to its maximum value in about a decade. Analysis shows that this phenomenon is associated with axial conduction of heat to and from the prongs. If it is recognized that prongs have finite thermal inertia then a modification of the boundary conditions to the equations of Betchov (1948) predicts this step, in agreement with the simple asymptotic analysis of Maye (1970).

Experiments indicate that a similar phenomenon occurs with velocity-sensitive wires. Axial conduction appears to be the most likely cause. Aeroelastic deflexions and non-uniform cooling caused by bowing of the wire make precise predictions impossible. Here the differences in step size between wires were observed to be as large as 10% (or 20% in mean-square energy), the centre-frequency was usually beyond 10 Hz for the wires tested and the step extended over a much broader frequency range than in the temperature-sensitive case. The effect occurred at all velocities, resistance ratios and wire geometries. An analysis based on non-uniform cooling of the wire filament predicts the correct frequency range and shows that steps of 10% in frequency response are quite plausible.
The mixing of rain with near-surface water
Authors: Green T. , Houk D. F.
Published: April 2006

The mixing of rain with otherwise calm near-surface water is investigated experimentally, using both uniform drops and crude drop-size distributions. The results are interpreted in terms of mixed-layer depths and the upward entrainment of quiescent water. Large drops, even in quite small numbers, are shown to play a very important role in the mixing process. Entrainment coefficients vary as the inverse of a suitably defined bulk Richardson number, and behave similarly in both fresh and salt receiving water.