bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlates of placental infection with cytomegalovirus, parvovirus B19 or human herpes virus 7
Authors: Chow S.S.W. , Craig M.E. , Jacques C.F.H. , Hall B. , Catteau J. , Munro S.C. , Scott G.M. , Camaris C. , McIver C.J. , Rawlinson W.D.
Published: April 2006

Vertical transmission of viruses is an important cause of morbidity in the fetus and neonate. Placental viral infection indicates risk of vertical transmission, but not always transmission to, or disease of the fetus. Specimens from mothers and babies from three groups—two prospective and one retrospective cohort—were tested for pathogens of teratogenic potential using multiplex PCR. Placental infection was present in 13% of the 105 samples collected. Assessment of the prospective cohorts showed cytomegalovirus (CMV) detected in 4% of placentae from unselected women, parvovirus B19 in 1% and Ureaplasma parvum in 1% of placentae. In a retrospective cohort of women at high risk of transmitting congenital infection due to seroconversion during pregnancy, miscarriage or stillbirth, CMV was detected in 64% and human herpes virus type 7 in 9% of placentae. Of 14 PCR‐positive placentae, two were associated with the birth of a living symptomatic infant, two with stillbirth, one with miscarriage, and two with elective terminations of pregnancy. Directed laboratory assessment of women at high risk of transmitting congenital infection, on the basis of clinical or laboratory markers, is important for accurate diagnosis of adverse outcomes of pregnancy. However, routine screening for viruses in the placentae from women with a low‐risk serological profile for transmitting congenital infection is unlikely to result in significant numbers of additional diagnoses and is confounded by inadequacy of current diagnostic methods. The major pathogen detected in all cases of placental infection associated with fetal death was human CMV. J. Med. Virol. 78:747–756, 2006. © 2006 Wiley‐Liss, Inc.
High‐risk human papillomavirus infection of the genital tract of women with a previous history or current high‐grade vulvar intraepithelial neoplasia
Authors: Goffin Frederic , Mayrand Marie‐Hélène , Gauthier Philippe , Alobaid A. , Lussier Christian , Provencher Diane , Drouin Pierre , Franco Eduardo L. , Coutlée François
Published: April 2006

Human papillomavirus (HPV) infection is associated with high‐grade vulvar intraepithelial neoplasia (VIN‐3). The prevalence of anogenital HPV infection in women with previously treated VIN‐3 has not been documented yet. This cross‐sectional study compared high‐risk HPV DNA detection rates in women with past (n = 30) and current (n = 22) VIN‐3 to those without current or past VIN (n = 86). HPV DNA was detected in vulvar and cervical samples with Hybrid Capture 2 (HC‐2). Smoking was associated in multivariate analysis with current VIN‐3 (odds ratio (OR) 8.3, 95% confidence interval (CI) 2.0–8.2) and any VIN‐3 history (OR 6.5, 95% CI 2.5–16.5). High‐risk HPV DNA was found on the vulva of 64%, 33%, and 20% of women with current VIN‐3, past VIN‐3, and without previous or current VIN, respectively. After controlling for age and smoking, high‐risk HPV vulvar infection was associated with cervical high‐risk HPV infection (OR 8.6, 95% CI 2.8–26.5; P = 0.001). After controlling for age, HPV infection was more often multifocal in women with current VIN‐3 compared to women with previous but no current VIN‐3 lesion (OR 17.6, 95% CI 1.4–227.2). Multifocal vulvar HPV infection was detected in women with previous or active VIN‐3. Longitudinal studies are required to determine if the multifocality of HPV infection on the vulva could explain the high recurrence rate of VIN‐3. J. Med. Virol. 78:814–819, 2006. © 2006 Wiley‐Liss, Inc.
Kainate induces rapid redistribution of the actin cytoskeleton in ameboid microglia
Authors: Christensen Randolph N. , Ha Byeong Keun , Sun Fang , Bresnahan Jacqueline C. , Beattie Michael S.
Published: April 2006

Microglia are key mediators of the immune response in the central nervous system (CNS). They are closely related to macrophages and undergo dramatic morphological and functional changes after CNS trauma or excitotoxic lesions. Microglia can be directly stimulated by excitatory neurotransmitters and are known to express many neurotransmitter receptors. The role of these receptors, however, is not clear. This study describes the microglial response to the glutamate receptor agonist kainate (KA) and shows via immunochemistry that the α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionate (AMPA)‐type glutamate receptor subunit GluR1 is present on cultured microglia. In the presence of 100 μM or 1 mM KA, cultured microglia underwent dramatic morphological and cytoskeletal changes as observed by time‐lapse photography and quantitative confocal analysis of phalloidin labeling. KA‐stimulated microglia showed condensation of cytoplasmic actin filaments, rapid de‐ and repolymerization, and cytoplasmic redistribution of condensed actin bundles. Rearrangement of actin filaments—thought to be involved in locomotion and phagocytosis and to indicate an increased level of activation (for reviews see Greenberg [ 1995] Trends Cell Biol. 5:93–99; Imai and Kohsaka [ 2002] Glia 40:164–174)—was significantly increased in treated vs. control cultures. Morphological plasticity and membrane ruffling were also seen. These findings suggest direct microglial excitation via glutamate receptor pathways. Thus, neurotransmitter release after brain or spinal cord injury might directly modulate the inflammatory response. © 2006 Wiley‐Liss, Inc.
Phrenic nerve neurotization of the musculocutaneous nerve with end‐to‐side neurorrhaphy: A short report in a rabbit model
Authors: Stamatoukou Anna , Papadogeorgou Ellada , Zhang Zijie , Pavlakis Kitty , Zoubos Aristides B. , Soucacos Panayotis N.
Published: April 2006

This experimental study was performed to evaluate the efficacy of end‐to‐side coaptation between the musculocutaneous nerve and the phrenic nerve for brachial plexus injuries with nerve‐root avulsions. In an experimental rabbit model, neurotization of the musculocutaneous nerve with the phrenic nerve was compared using end‐to‐end and end‐to‐side neurorrhaphy. Preliminary results from electrophysiologic and histologic examinations indicate that end‐to‐side neurotization of the musculocutaneous nerve with the phrenic nerve is an effective means for musculocutaneous nerve repair. The effectiveness of the phrenic nerve is attributed to its large number of motor axons. © 2006 Wiley‐Liss, Inc. Microsurgery, 2006
1H and 13C NMR study of 5‐substituted‐4‐ (arylidene)amino‐2,4‐dihydro‐3H‐1,2,4‐triazole‐3‐thiones and 6‐aryl‐3‐(D‐gluco‐ pentitol‐1‐yl)‐7H‐1,2,4‐triazolo[3,4‐b] [1,3,4]thiadiazines
Authors: Zhang Anjiang , Zhang Lixue , Lei Xinxiang
Published: April 2006

Five 5‐substituted‐4‐(arylidene)amino‐2,4‐dihydro‐3H‐1, 2,4‐triazole‐3‐thiones (2a–2e) and seven 6‐aryl‐3‐(D‐gluco‐pentitol‐1‐yl)‐7H‐1,2,4‐triazolo[3,4‐b][1,3,4]thiadiazines (3a–3g) were synthesized. The complete 1H and 13C NMR chemical shift assignments were analyzed on one‐ and two‐dimensional NMR techniques, including DEPT, NOE‐DIF, COSY, gHMBC, and gHSQC. Copyright © 2006 John Wiley & Sons, Ltd.
Electronic structures of double perovskites Ba2MnMO6 (M = W and Re) from first‐principles studies
Authors: Cheng J. , Yang Z. Q.
Published: April 2006

The cover picture of the current issue refers to the work of J. Cheng and Z. Q. Yang which is featured as Editor's Choice [1]. Double perovskites, A2B′B″O6 (A is an alkaline earth; B′B″ sites are occupied alternately by transition metals) have recently attracted considerable attention due to the discovery of large low‐field room‐temperature magnetoresistance in this kind of materials. The authors study from first principles the electronic structure of two double perovskites, Ba2MnWO6 and Ba2MnReO6, using Density Functional Theory. The ground magnetic phases for the two compounds are found to be antiferromagnetic and ferrimagnetic, respectively, in agreement with experimental results. Ba2MnWO6 was predicted to have semiconductor band structure. For Ba2MnReO6, a finite energy gap can appear only when spin–orbital coupling together with on‐site Coulomb interactions on Re ions are taken into account. The results explain the curve of resistivity versus temperature for Ba2MnReO6.

The first author J. Cheng works in the field of theoretical condensed matter physics from first‐principles calculations at the Surface Physics Laboratory, Fudan University, Shanghai, China.
Inhibition of nifedipine‐induced proliferation of cultured human gingival fibroblasts by Saiko, a Chinese herbal medicine
Authors: Hattori Toshimi , Matsunaga Shozo , Nakazono Youdai , Wang Pao‐Li
Published: April 2006

Saiko is predominantly contained in Saireito, a Chinese herbal medicine. The present study was conducted to determine whether or not Saiko is involved in the inhibition by Saireito of nifedipine‐induced proliferation and collagen synthesis in gingival fibroblasts. Nifedipine (10 µm) significantly enhanced the proliferation starting on day 5 of the culture period. When added together with nifedipine, Saiko at concentrations of 0.05%–0.2% (w/v) dose‐dependently inhibited the nifedipine‐induced proliferation, and at the highest concentration tested (0.2%), Saiko inhibited the nifedipine‐induced proliferation by about 40%. Moreover, Saiko (0.2%) also inhibited the normal proliferation at days 11 and 14. Sole application of nifedipine (10 µm) augmented the release of bFGF, and Saiko concentration‐dependently reduced the level of bFGF in the nifedipine‐containing culture medium. Nifedipine (10 µm) increased the production of type I collagen to almost twice that of the control (normal medium), and Saiko at concentrations above 0.1% significantly reduced the nifedipineinduced production of collagen. In conclusion, the present findings demonstrate that Saiko inhibited the nifedipine‐induced proliferation of gingival fibroblasts by reducing the release of bFGF and that Saiko is involved in the Saireito‐induced inhibition of nifedipine‐stimulated proliferation and collagen synthesis in gingival fibroblasts. Copyright © 2006 John Wiley & Sons, Ltd.
Constrained simulated annealing for stability margin computation in a time‐delay system
Authors: Kim Kyungsup , Bae Jinho
Published: April 2006

The stability margin of a time‐delay system is formulated via factorization. This paper provides a numerical method for computing the stability margin of time‐delay linear time‐invariant systems with delay dependence by using a constrained simulated annealing algorithm. The constrained simulated annealing is used to solve a nonlinear continuous constrained optimization problem, which is derived from computing the stability margin of a delay system. Illustrative examples show that the established method can verify the stability for a class of time‐delay systems. Copyright © 2006 John Wiley & Sons, Ltd.
Detecting and monitoring change in models
Authors: Schaffernicht Martin
Published: April 2006

System dynamics is often brought into connection with a double‐loop learning process. Learning has been the object of an increasing number of studies. However, inquiry has focused on using models rather than modeling, and there are huge differences in assessment approaches. If learning changes models then it can be inferred from comparing models. Here it is argued that monitoring learning from modeling is feasible and desirable. One possibility is to conceive of a model as a series of versions and compare their structure. One possible method for comparing model versions is presented. Copyright © 2006 John Wiley & Sons, Ltd.
Structural elements to convert Escherichia coli α‐xylosidase (YicI) into α‐glucosidase
Authors: Okuyama Masayuki , Kaneko Akira , Mori Haruhide , Chiba Seiya , Kimura Atsuo
Published: April 2006

Escherichia coli YicI, a member of glycoside hydrolase family (GH) 31, is an α‐xylosidase, although its amino‐acid sequence displays approximately 30% identity with α‐glucosidases. By comparing the amino‐acid sequence of GH 31 enzymes and through structural comparison of the (β/α)8 barrels of GH 27 and GH 31 enzymes, the amino acids Phe277, Cys307, Phe308, Trp345, Lys414, and β → α loop 1 of (β/α)8 barrel of YicI have been identified as elements that might be important for YicI substrate specificity. In attempt to convert YicI into an α‐glucosidase these elements have been targeted by site‐directed mutagenesis. Two mutated YicI, short loop1‐enzyme and C307I/F308D, showed higher α‐glucosidase activity than wild‐type YicI. C307I/F308D, which lost α‐xylosidase activity, was converted into α‐glucosidase.
Numerical simulation of relative dispersion in two-dimensional, homogeneous, decaying turbulence
Authors: Kowalski A. D. , Peskin R. L.
Published: April 2006

Lagrangian statistical results are presented from numerical simulations of an ensemble of fluid particles which were generated from a two-dimensional pseudospectral code. The single-particle results are in qualitative agreement with previous simulations on a lower-resolution grid. The two-particle, relative velocity correlations were found to fall off more rapidly than the single-particle correlations for short to intermediate times due to large-scale eddy advection in the single-particle case. The temporal behaviour of the mean square relative separation, 〈rl2〉, is analysed for short to intermediate times and is found to be consistent with scaling arguments based on Kraichnan's expression for the non-local strain acting in the high-wavenumber enstrophy cascade spectral range. For longer times, 〈rl2〉 exhibitstnbehaviour. The power-law region is associated with the locally determined strain rates which characterize a backward energy-cascade spectrum.
Non-Boussinesq and penetrative convection in a cylindrical cell
Authors: Walden R. W. , Ahlers Guenter
Published: April 2006

Measurements of Rayleigh numbers R and Nusselt numbers N have been made for a cylindrical cell having a radius to height ratio of 4·72 and containing liquid helium I. The upper surface of the cell was maintained at a constant temperature T2 near T0 = 2·178 K where the fluid density has a maximum. The heat input to the cell bottom was varied quasi-statically while the lower surface temperature T1 was recorded. The penetration parameter [Pscr ]≡(T1−T2)/(T1−T0) ranged between 0·1 and 3 for our experiments.

For [Pscr ] < 1, the initial slope of N(R) for R near the critical Rayleigh number Rc was independent of [Pscr ]. For ${\cal P}\;{\mathop {\raise-2pt\hbox{$>$}}\limits^{\raise-8pt\hbox{$\sim$}}}\;1$, two hysteresis loops of N(R) were observed. One of them occurred very near Rc and is interpreted in terms of the inverted bifurcation associated with the onset of cellular convection of non-Boussinesq systems. The other, for R > Rc, is believed to correspond to the transition from cellular to two-dimensional flow. Near Rc and with [Pscr ] > 2 we also observed multistability, with the states believed to correspond to different numbers of convective cells.

For large [Pscr ] the onset of time-dependent flow occurred much closer to Rc than is the case for Boussinesq systems.
The influence of mean shear on unsteady aperture flow, with application to acoustical diffraction and self-sustained cavity oscillations
Authors: Howe M. S.
Published: April 2006

This paper discusses the linearized theory of unsteady flow through a two-dimensional aperture in a thin plate in the presence of a grazing mean flow on one side of the plate. The mean shear layer is modelled by a vortex sheet, and it is predicted that at low mean-flow Mach numbers there is a transfer of energy from the mean flow to the disturbed motion of the vortex sheet provided (i) the Kutta condition is imposed at the leading edge of the aperture, resulting in the unsteady shedding of vorticity from the edge, and (ii) the width of the aperture 2s satisfies ½ < 2s/λ < 1.1, where λ is the hydrodynamic wavelength of the disturbance on the vortex sheet within the aperture. The theory is used to examine the effect of mean shear on the diffraction of sound by a perforated screen, and to predict the spontaneous excitation and suppression of self-sustained oscillations in a wall-cavity beneath a nominally steady mean flow. In the latter case support for the proposed theory is provided by a favourable comparison of theoretical results with experimental data available in the literature.
Resonant over-reflection of internal gravity waves from a thin shear layer
Authors: Grimshaw R. H. J.
Published: April 2006

In a previous paper (Grimshaw 1979) the resonant over-reflection of internal gravity waves from a vortex sheet was considered in the weakly nonlinear regime. It was shown there that the time evolution of the amplitude of the vortex sheet displacement was balanced by a cubic nonlinearity. For one vortex sheet mode, symmetrical with respect to the interface, it was shown that a steady finite-amplitude wave was possible. For the other, asymmetric modes, a singularity develops in a finite time. In the present paper, that analysis is extended by replacing the vortex sheet with a thin shear layer of thickness α2, where α is the amplitude of the shear layer displacement. The effect of this extension is to introduce a linear growth rate term in the amplitude equation, which is otherwise unaltered. The linear growth rate can be computed from a formula due to Drazin & Howard (1966, p. 67). The effect on the modes is that the symmetric mode is linearly damped and requires sustained forcing to be observed, while the asymmetric modes are slightly destabilized by the linear term and, as in the vortex-sheet model, develop a singularity in finite time.
Steady, supercritical flow in collapsible tubes. Part 2. Theoretical studies
Authors: Mcclurken Michael E. , Kececioglu Ifiyenia , Kamm Roger D. , Shapiro Ascher H.
Published: April 2006

Theories are developed to explain the experimental observations of steady, supercritical flow in compliant, partially collapsed tubes, presented in the companion paper (part 1).

It is shown that the measured curves of area vs. distance are governed by a combination of (i) friction and gravity, which produce mean gradients of area, and (ii) longitudinal bending and tension forces, which produce standing waves of area superposed upon the mean gradients. The experiments confirm the one-dimensional theory for the mean gradients: (i) in the absence of gravity, friction causes a pressure rise and a positive mean gradient of area; (ii) a downward slope can cancel gravity and lead asymptotically to a uniform state having zero gradients of pressure and area.

The inviscid dispersion relationship for area waves due to longitudinal bending and tension is developed, based on a simple, approximate model for the mechanics of the tube. The phase velocity increases as the wavelength decreases, hence the group velocity exceeds the phase velocity. Consequently, in steady flows that are supercritical with respect to the infinite-wavelength phase velocity, energy can propagate upstream and standing waves of area may appear.

In the experiments of part 1, longitudinal tension predominated over longitudinal bending. The measured wavelengths of standing waves were found to be in general agreement with the dispersion relationship for tension-induced area waves. The observed streamwise growth of standing area waves is interpreted physically as the attenuation of waves radiating upstream from a source of disturbance such as a shock-like rapid increase of area. The rate of wave attenuation indicates that the skin-friction coefficient has a large out-of-phase oscillatory component. The observed steepness of shock transitions agrees with an approximate theory based on treating the forward portion of the shock as the rearward part of the standing wave train that the shock drives upstream.
The importance of discharge siting upon contaminant dispersion in narrow rivers and estuaries
Authors: Smith Ronald
Published: April 2006

Far downstream of a sudden contaminant release in a narrow channel the concentration depends on the cloud size. This is largely determined by the longitudinal shear dispersion and the time of travel of the cloud. Near the source the efficiency of the shear dispersion and the velocity of the cloud are strongly dependent upon the source location across the flow. The shear dispersion is greatest when there is both strong shear and strong turbulent mixing (i.e. away from either the centre-line or the banks), while the velocity is least and the time-lag maximized for a source on the banks. The quantitative influence far downstream can be characterized in terms of a deficit variance and a centroid displacement. In this paper exact results are derived for these quantities. It is shown that, except when the banks are extremely steep, the time-lag has the strongest effect and the concentration far downstream of a point discharge is minimized when the discharge is sited at the bank.
Linear stability of rotating Hagen-Poiseuille flow
Authors: Cotton Fredrick W. , Salwen Harold
Published: April 2006

Linear stability of rotating Hagen-Poiseuille flow has been investigated by an orthonormal expansion technique, confirming results by Pedley and Mackrodt and extending those results to higher values of the wavenumber |α|, the Reynolds number R, and the azimuthal index n. For |α| [gsim ] 2, the unstable region is pushed to considerably higher values of R and the angular velocity, Ω. In this region, the neutral stability curves obey a simple scaling, consistent with the unstable modes being centre modes. For n = 1, individual neutral stability curves have been calculated for several of the low-lying eigenmodes, revealing a complicated coupling between modes which manifests itself in kinks, cusps and loops in the neutral stability curves; points of degeneracy in the R, Ω plane; and branching behaviour on curves which circle a point of degeneracy.
An asymptotic model of two-dimensional convection in the limit of low Prandtl number
Authors: Busse F. H. , Clever R. M.
Published: April 2006

An approximate solution of two-dimensional convection in the limit of low Prandtl number is presented in which the buoyancy force is balanced by the inertial terms. The results indicate that inertial convection becomes possible when the Rayleigh number exceeds a critical value of about 7 × 103. Beyond this value the velocity and temperature fields become independent of the Prandtl number except in thin boundary layers. The convective heat transport approaches the law Nu = 0·175 R¼ for the Nusselt number Nu. These results are in reasonably close agreement with the numerical results described in the preceding paper by Clever & Busse (1980).
Experiments in nearly homogenous turbulent shear flow with a uniform mean temperature gradient. Part 1
Authors: Tavoularis Stavros , Corrsin Stanley
Published: April 2006

A reasonably uniform mean temperature gradient has been superimposed upon a nearly homogeneous turbulent shear flow in a wind tunnel. The overheat is small enough to have negligible effect on the turbulence. Away from the wind-tunnel entrance, the transverse statistical homogeneity is good and the temperature fluctuations and their integral scales grow monotonically like the corresponding velocity fluctuations (Harris, Graham & Corrsin 1977). Measurements of several moments, one- and two-point correlation functions, spectra, integral scales, microscales, probability densities, and joint probability densities of the turbulent velocities, temperature fluctuations, and temperature-velocity products are reported. The heat-transport characteristics are much like those of momentum transport, with the turbulent Prandtl number nearly 1. The temperature fluctuation is better correlated with the streamwise than the transverse velocity component, and the cross-componentD12of the turbulent diffusivity tensor has sign opposite to and about twice the magnitude of the diagonal componentD22. Some resemblance of directional properties (relative magnitudes of correlation functions, integral scales, microscales) of the temperature with those of the streamwise velocity is also observed. Comparisons of the present data with measurements in the inner part of a heated boundary layer and a fully turbulent pipe flow (x2/d= 0·25) show comparable magnitudes of temperature-velocity correlation coefficients, turbulent Prandtl numbers and ratios of turbulent diffusivities, and show similar shapes of two-point correlation functions.
Transition in the axisymmetric jet
Authors: Cantwell Brian J.
Published: April 2006

The unsteady laminar flow from a point source of momentum is considered. Dimensional considerations lead to a formulation of the problem which is self-similar in time. Three limiting cases are examined. In the limit t → ∞ the solution corresponds to the classic steady solution first discovered by Landau (1944). The limit t → 0 was examined recently by Sozou & Pickering (1977) and was shown to correspond to the flow from an unsteady dipole of linearly increasing strength. More recently Sozou (1979) determined an analytic solution for the creeping flow limit Re → 0. In the present work, unsteady particle trajectories for each of these cases are examined by reducing the particle path equations to an autonomous system with the Reynolds number as a parameter. Transition of the jet is examined as a bifurcation of this system. In the case of the creeping-flow solution, the particle-path pattern exhibits a structure which is not easily discerned in any of the other variables which govern the flow. For sufficiently small Reynolds number the particle paths converge to a single stable node which lies on the axis of the jet. At a Reynolds number of 6·7806 the pattern bifurcates to a saddle lying on the axis of the jet plus two stable nodes lying symmetrically to either side of the axis. At a Reynolds number of 10·09089 the pattern bifurcates a second time to form a saddle and two stable foci.
Shock–like structure of phase-change flow in porous media
Authors: Romero L. A. , Nilson R. H.
Published: April 2006

Shock-like features of phase-change flows in porous media are explained, based on the generalized Darcy model. The flow field consists of two-phase zones of parabolic/hyperbolic type as well as adjacent or imbedded single-phase zones of either parabolic (superheated, compressible vapour) or elliptic (subcooled, incompressible liquid) type. Within the two-phase zones or at the two-phase/single-phase interfaces, there may be steep gradients in saturation and temperature approaching shock-like behaviour when the dissipative effects of capillarity and heat-conduction are negligible. Illustrative of these shocked, multizone flow-structures are the transient condensing flows in porous media, for which a self-similar, shock-preserving (Rankine–Hugoniot) analysis is presented.
Head-sea diffraction by a slender raft with application to wave-power absorption
Authors: Haren Pierre , Mei Chiang C.
Published: April 2006

The parabolic approximation which has recently been found to be useful in other physical contexts, is extended to head-sea diffraction of short waves by a slender raft on deep water. In particular, it is a much more direct way of getting the inner approximation of the outer solution in a scheme of matched asymptotics than the original method of Faltinsen (1971). The present results are compared with a more involved integral equation method and are found to be remarkably accurate even when the raft length is comparable to the wavelength. Finally, the asymptotic method is modified for a compliant raft which absorbs wave power by suitably controlled impedance. Optimum efficiency and other performance characteristics are predicted.
Information decay and the predictability of turbulent flows
Authors: Carnevale George F. , Holloway Greg
Published: April 2006

A measure of predictability that has many superior features compared to currently used measures is introduced. Through statistical theory it is demonstrated that in inviscid truncated flow this new predictability measure increases monotonically in time while all initial information about the system decays. Under the influence of forcing and viscosity the behaviour of this measure is shown always to satisfy intuitive expectations.
Equilibrium shape and stability of a liquid cylinder in cross flow at low Weber numbers
Authors: Weihs D. , Frankel I.
Published: April 2006

The cross-section shape and stability of a liquid cylinder moving perpendicularly to its axis in a gaseous medium is studied. Such liquid cylinders are formed during the break-up process of thin, rapidly moving liquid sheets, appearing in spray and atomization processes. The equilibrium shape is affected mainly by two factors: the dynamic-pressure distribution in the gas flow and the surface tension on the liquid boundary. The former tends to distort the liquid cross-section into an oval shape while the latter tends to restore the circular cross-section.

A series expansion for the shape of the cylinder cross-section was determined by assuming incompressible potential flow, neglecting the effects of body forces and internal circulation in the liquid.

The stability analysis shows that in the range of low Weber numbers the cylinder break-up is due to the divergence of varicose perturbations. The wavenumber of the most rapidly growing perturbation, its rate of growth and the maximal wavenumber for which varicose instability occurs, are all found to decrease as the Weber number grows, owing to a pressure distribution caused by the varicose distortion, which tends to reduce these perturbations.
An experimental study of the interaction between a glancing shock wave and a turbulent boundary layer
Authors: Kubota Hayao , Stollery John L.
Published: April 2006

The glancing interaction between an oblique shock wave and a turbulent boundary layer has been studied experimentally using a variable-incidence wedge mounted from the side wall of a supersonic wind tunnel. The Mach number was 2·3 and the Reynolds number 5 × 104, based on the 99·5 % thickness of the boundary layer just upstream of the interaction region. The study includes oil flow pictures, vapour and smoke-screen photographs, wall-pressure distributions and local heat-transfer measurements. The results suggest that the complicated interaction region involves two viscous layers: an induced layer formed from fluid initially in the boundary layer growing along the wedge surface near the root, and the thick turbulent layer on the tunnel side wall. The mutual interference between these layers is described, separation is defined and a discussion of incipient separation is included.
Statistics of fine-scale velocity in turbulent plane and circular jets
Authors: Antonia R. A. , Satyaprakash B. R. , Hussain A. K. M. F.
Published: April 2006

Higher-order statistics of the streamwise velocity derivative have been measured on the centre-line of turbulent plane and circular jets. The instrumentation and sources of error are discussed to establish the accuracy of the data and convergence of statistics. The optimum setting for the low-pass filter cut-off was found to be 1·75 times the Kolmogorov frequencyfK, in contrast with the majority of previous investigations where it was set equal tofK. The magnitude of the constant μ in Kolmogorov's revised hypothesis is obtained using statistics derived from the instantaneous velocity derivative or its squared value. The correlation and spectrum of fluctuations of the squared velocity derivative and the Reynolds-number variation of the skewness and flatness factors of the velocity derivative are consistent with μ ≃ 0·2, while the most popular value used is 0·5. Second-order moments of the locally averaged dissipation, assumed proportional to the squared streamwise velocity derivative, and breakdown coefficients also suggest a value of μ of about 0·2. Higher-order correlations and spectra of the dissipation are in closer agreement with the Novikov-Stewart or β-model than with Kolmogorov's lognormal model. Higher-order moments of locally averaged values of the dissipation rate are more closely represented by the lognormal than the β-model.
Computer analysis of a high-speed film of the plane turbulent mixing layer
Authors: Hernan Miguel A. , Jimenez Javier
Published: April 2006

To evaluate the usefulness of digital image analysis in extracting quantitative information from flow pictures we have studied a 16 mm ciné film of a turbulent mixing layer. A sequence of 373 frames is digitized and analysed to isolate and measure the concentration eddies that constitute the large structure and to follow their individual evolution in time. As a result, statistics are given on the life history of the eddies, the structure of the amalgamation process and the amount of entrainment, as measured by area change, due to amalgamation as compared to the total. It is found that most of the entrainment occurs during the normal life of eddies and not during pairing. Mixing intermittency is computed from the observed shape of the eddies and seen to compare well with previous measurements. The significance of these results in modelling the mixing layer is discussed briefly and some comments are given on the general usefulness of the techniques presented.
Transport in the near aerodynamic wakes of flat plates
Authors: Maclennan A. S. M. , Vincent J. H.
Published: April 2006

An experimental investigation has been carried out into the nature of the transport of airborne material in the near aerodynamic wakes of bluff bodies with simple shapes. The main attention was focused on the essential differences existing between axi- symmetric flows (as about disks) and two-dimensional flows (as about rectangular long thin flat plates). Measurements were made for such bodies of the near-wake residence time of injected small particles, along with other and more familiar near- wake properties such as the vortex-shedding frequency and base pressure. It was concluded for disks that the transport of material into and out of the near-wake region is dominated by turbulent diffusion, and is strongly influenced by free-stream turbulence, especially for free-stream turbulence whose length scale is substantially smaller than the disk diameter. For rectangular flat plates, transport is dominated by the periodic shedding of vortices, and to only a secondary extent by turbulent motions, and is not strongly influenced by free-stream turbulence.
The effects of obstacle shape and viscosity in deep rotating flow over finite-height topography
Authors: Johnson E. R.
Published: April 2006

The limiting process introduced by Stewartson & Cheng (1979) is used to obtain solutions in the limit of vanishing Rossby number for deep rotating flows at arbitrary Reynolds number over cross-stream ridges of finite slope. Examination of inviscid solutions for infinite-depth flow shows strong dependence on obstacle shape of not only the magnitudes but also the positions of disturbances in the far field. In finite-depth flow there is present the Stewartson & Cheng inertial wave wake, which may be expressed as a sum of vertical modes whose amplitudes depend on the obstacle shape but are independent of distance downstream; the smoother the topography and the shallower the flow, the fewer the number of modes required to describe the motion. For abrupt topography the strength of the wake does not, however, decrease monoton- ically with decreasing container depth (or Rossby number). In very deep flows viscosity causes the wake to decay on a length scale of order the Reynolds number times the ridge width. In shallower flows, where only a few modes are present, the decay of the wake is more rapid. For Reynolds numbers and depths of the order of those in the experiments of Hide, Ibbetson & Lighthill (1968)) viscosity causes the disturbance to take on the appearance of a leaning column.
The separation vortex in the Weis-Fogh circulation-generation mechanism
Authors: Edwards R. H. , Cheng H. K.
Published: April 2006

The influence of leading-edge separation vortices on the Weis-Fogh (1973) lift- generation mechanism for insect hovering is investigated. The analysis employs a vortex-shedding model (Edwards 1954; Cheng 1954) and represents an extension of Lighthill's (1973, 1975) analysis of an inviscid model without separated vortices. Results of the study compare reasonably well with observations on a laboratory model at high Reynolds number (Maxworthy 1979), confirming that vortex separation significantly enhances the initial circulation on each of the wings. Unlike the un- separated-model solution, this circulation was found to depend on the history of the wing motion and to increase with a large opening angle.
Flow visualization of steady streaming in oscillatory flow through a bifurcating tube
Authors: Haselton F. R. , Scherer P. W.
Published: April 2006

A steady streaming displacement of fluid elements is observed to occur during oscillatory flow through a Y-shaped tube bifurcation model at Womersley and Reynolds numbers that can exist in the human bronchial tree. The cause of the displacement is the effect of the asymmetric geometry on the oscillating velocity vector field. The steady streaming displacement is greatest for fluid elements that experience the highest velocity through the bifurcation junction. The maximum displacement observed increases with Re and a up to a Re of about 100 and a of about 5, after which a levelling off and gradual decline occur. Photographs of low-Re and low-a: cxpcrimcnts show the effects of secondary components of the steady-streaming displacement field which contribute to a complex circulation.
An experimental and theoretical investigation of the onset of convection in rotating spherical shells
Authors: Carrigan C. R. , Busse F. H.
Published: April 2006

Convection in a rapidly rotating spherical layer with constant-temperature boundary conditions is studied in a laboratory experiment. The asymptotic theory of Busse (1970) is extended to permit a comparison with the observations of the onset of convection and its properties. It is found that the prediction of the power-law dependences of the critical buoyancy number and the critical wavenumber on the rotation rate are borne out, although discrepancies in the actual values of these quantities do exist. Calculations on the basis of equations proposed by Roberts (1968) show that a thermal wind that is present in the basic state of the model has a stabilizing influence on the onset of convection. Stewartson layers not taken into account in the asymptotic analysis for vanishing Ekman number E appear to be responsible for the remaining disagreement between theoretical predictions and observations at finite values of E.
Effects of slowly varying depth and current on the evolution of a Stokes wavepacket
Authors: Turpin Francois-Marc , Benmoussa Chakib , Mei Chiang C.
Published: April 2006

We consider the effects of slowly varying depth and current on the evolution of a packet of Stokes waves. The lengthscale of one-dimensional depth variation is assumed to be much greater than that of the wave envelope, and the direction of the current is perpendicular to the depth contours. By the method of multiple scales, the wave envelope is found to satisfy a cubic Schrödinger equation with slowly varying coefficients The criterion of spatial instability to small sidebands is extended. Numerical integration shows that the nonlinear evolution of a wavepacket is directly related to the instability parameter, which depends strongly on the current and depth variation. The heuristic hypothesis of Djordjevic & Redekopp on the soliton evolution over a slope in the absence of current is assessed.
Thermal instability of two-dimensional stagnation-point boundary layers
Authors: Chen K. , Chen M. M. , Sohn C. W.
Published: April 2006

A study of thermal instability for the two-dimensional stagnation flow for Prandtl numbers ranging from 0.7 to infinity is presented. The analysis represents an exact solution since neither the boundary-layer approximation nor the parallel-flow assumption was invoked. Of particular interest is that the critical Rayleigh number and the critical wavenumber, when defined on the basis of the thermal boundary-layer lengthscale, are found to be relatively insensitive to the Prandtl number for the range of Prandtl numbers studied.
Scaling of the bursting frequency in turbulent boundary layers
Authors: Blackwelder R. F. , Haritonidis J. H.
Published: April 2006

The bursting frequency in turbulent boundary layers has been measured over the Reynolds-number range 103 < U∞/ν < 104. When scaled with the variables appropriate for the wall region, the non-dimensional frequency was constant independent of Reynolds number. A strong effect of the sensor size was noted on the measured bursting frequency. Only sensors having a spatial scale less than twenty viscous lengthscales were free from spatial-averaging effects and yielded consistent results. The spatial-resolution problem was apparently the reason for erroneous results reported in the past.
Trapping of water waves above a round sill
Authors: Renardy Yuriko
Published: April 2006

The three-dimensional problem of wave trapping above a submerged round sill was first analysed by Longuet-Higgins on the basis of a linear shallow-water theory. The large responses predicted by the theory were, however, not well borne out by the experiments of Barnard, Pritchard & Provis, and this has motivated a more detailed study of the problem. A full linear theory for both inviscid and weakly viscous fluid, without any shallow-water assumptions, is presented here. It reveals important limitations on the use of shallow-water theory and the reasons for them. In particular, while the qualitative features of wave trapping are similar to those of shallow-water theory, the nearly resonant frequencies differ significantly, and, since the resonances are narrow, the observed amplitudes at a given frequency differ greatly. The geometry is strongly indicative of long waves, and the dispersion relation appears quite consistent with that, but the part of the motion at wavenumbers that are not small has, despite the small amplitude, a substantial effect on the response to excitation.
Shock diffraction in channels with 90° bends
Authors: Edwards D. H. , Fearnley P. , Nettleton M. A.
Published: April 2006

A study has been made of how initially planar shocks in air propagate around 90° bends in channels of nearly rectangular cross-section. In shallow bends for which the radius of curvature R is much greater than the radius r of the channel, the shock recovers from a highly curved profile at the start of the bend to regain planarity towards the end of the bend. This occurs on account of the acceleration of the triple point across the channel following its interaction with the expansion waves generated at the convex wall. In sharp bends the shock profiles retain their pronounced curvature for some distance downstream of the bend.

At the start of a shallow bend (R/r ≈ 6) the shock at the concave wall, initial Mach number M0, accelerates to Mw = 1.15M0 and remains at this value until towards the end of the bend it begins to attenuate. At the convex wall, shocks of M0 > 1.7 attenuate to Mw = 0.7M0 and propagate at this value for some distance around the bend. In the early stages of a sharper bend (R/r ≈ 3) the shock at the concave wall strengthens to Mw = 1.3M0, remaining at this value for some distance downstream of the bend. At the convex wall the shock decelerates to 0.6M0.

Whitham's (1974) ray theory is shown to predict with reasonable accuracy the Mach numbers of the wall shocks at both surfaces for both bends tested and the range of incident shock velocities used, 1.2 < M0 < 3. The agreement between the theory and experimental results is particularly close for stronger shocks propagating along the inner bend. Predictions from 3-shock theory (Courant & Friedrichs 1948) of the Mach number at the outer wall are consistently higher than those from Whitham's analysis. In turn, the latter tends to slightly overestimate the strength of the wall shock.

A model is developed, based on an extension of Whitham's analysis, and is shown to predict the length of the Mach stem produced by shocks of M0 > 2 over the initial stages of the bend.
A note on the stability of low-Prandtl-number Hadley circulations
Authors: Hart John
Published: April 2006

This paper discusses the stability of the flow of a low-Prandtl-number liquid contained in a shallow slot with differentially heated vertical endwalls. The effect of thermally insulating boundaries at the top and bottom of the container on wavelength selection is emphasized. Stability calculations indicate that, for Prandtl number Pr in the range 0.015 < Pr < 0.27, the first perturbations to grow are overstable (oscillatory) longitudinal rolls with axes perpendicular to the endwalls, and with very large cross-stream wavelengths of about 9 to 15 layer depths. Previous studies using thermally conducting boundaries predict critical wavelengths of about three layer depths. The new results are in substantial agreement with an experiment using a differentially heated layer of mercury with aspect ratio (depth/length) 0.047 in both horizontal directions. The implications of the long-wavelength instability for the interpretation of thermal oscillations observed in other smaller-aspect-ratio configurations is discussed.
Low-Reynolds-number flow past a cylindrical body
Authors: Tamada Ko , Miura Hiroyuki , Miyagi Tosio
Published: April 2006

Two-dimensional flow past a cylindrical body of arbitrary profile at small Reynolds numbers is studied theoretically. The asymptotic flow field at large distances from an immersed body is shown to depend only upon the force acting on the cylinder. This universal field is determined by solving the Navier–Stokes equation numerically. The result enables us to evaluate the force acting on the body as a function of the flow Reynolds number. A detailed calculation is made of the drag coefficients of a circular cylinder and a flat plate. Results compare favourably with existing experimental and numerical data.
Streaming of fluid under a near-bottom membrane
Authors: Allison H.
Published: April 2006

Experiments are described which show the steady streaming of fluid under a flexible membrane, located near the bottom of a wave basin in shallow water. Circulation of fluid in a closed circuit was thus obtained, and measurements were made of the pressure head and total flow. The phenomenon might be used to extract power from waves at very low efficiency, but the theoretical basis is not yet understood.
Turbulence structure in thermal convection and shear-free boundary layers
Authors: Hunt J. C. R.
Published: April 2006

This paper is a study of turbulence near rigid surfaces, in the absence of any mean shear. Different sources of turbulence are considered, including thermal convection and grid turbulence. It is shown that, if a rigid boundary is introduced into the flow, then for short times the linear theory of Hunt & Graham (1978) reveals the common structure of these flows near the boundary, if the parameters used are the rate of energy dissipation per unit mass ε and the distance z from the surface. Over longer times nonlinear effects develop, such as large eddies straining smaller eddies near the boundary. Some new estimates are suggested here and compared with the computations of Biringen & Reynolds (1981) and experiments of Thomas & Hancock (1977).

It is shown that calculations based on the linear theory agree well with many measurements of the vertical profiles of turbulence in thermal convection layers, including those of the vertical variance, the low-frequency end of the spectrum of the vertical turbulence (w), the integral scale of w, and two-point cross-correlations of w. (The latter was a prediction, subsequently tested by atmospheric measurements.) Some discussion of the reasons for this agreement are suggested. The observations of the effects of mean-velocity gradients near the surface are also shown to be consistent with the theoretical arguments proposed here.