bluuebunny/crossref_metadata_2025 huggingface dataset:
Revisiting a Classic Approach to the Aspidosperma Alkaloids: An Intramolecular Schmidt Reaction Mediated Synthesis of (+)‐Aspidospermidine.
Authors: Iyengar Rajesh , Schildknegt Klaas , Morton Martha , Aube Jeffrey
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.
Stavudine.
Authors: Mirmehrabi Mahmoud , Rohani Sohrab , Jennings Michael C.
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.
Bimetallic Oxidation Catalysts: Hydrogen Peroxide Generation and Its Use in Hydrocarbon Oxidation
Authors: Remias Joseph E. , Sen Ayusman
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.
Heat Capacity in Proteins
Authors: Prabhu Ninad V. , Sharp Kim A.
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.
High‐Zirconium‐Content Nano‐Sized Bimodal Mesoporous Silicas
Authors: Ortiz de Zárate David , Gómez‐Moratalla Andrés , Guillem Carmen , Beltrán Aurelio , Latorre Julio , Beltrán Daniel , Amorós Pedro
Published: April 2006

Silica‐based nanoparticulated bimodal mesoporous materials with high Zr content (43 ≥ Si/Zr ≥ 4) have been synthesized by a one‐pot surfactant‐assisted procedure from a hydroalcoholic medium using a cationic surfactant (CTMABr = cetyltrimethylammonium bromide) as structure‐directing agent, and starting from molecular atrane complexes of Zr and Si as hydrolytic inorganic precursors. This preparative technique allows optimization of the dispersion of the Zr guest species in the silica walls. The bimodal mesoporous nature of the final high surface area nano‐sized materials is confirmed by XRD, TEM, and N2 adsorption–desorption isotherms. The small intraparticle mesopore system (with pore sizes around 2–3 nm) is due to the supramolecular templating effect of the surfactant, while the large mesopores (around 12–24 nm) have their origin in the packing voids generated by aggregation of the primary nanometric mesoporous particles. The basicity of the reaction medium seems to be a key parameter in the definition of this last pore system. The effects induced by the progressive incorporation of Zr atoms on the mesostructure have been examined, and the local environment of the Zr sites in the framework has been investigated by UV/Vis spectroscopy. Observations based on the consequences of post‐treatments of the as‐synthesized materials with HCl/ethanol mixtures corroborate that the atrane method leads to Zr‐rich materials showing enhanced site accessibility and high chemical homogeneity throughout the pore walls. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Thyroid MALT lymphoma in patients with a compressive goiter
Authors: Earnest Lisa M. , Cooper David S. , Sciubba James J. , Tufano Ralph P.
Published: April 2006

Background.

Mucosa‐associated lymphoid tissue (MALT) lymphomas account for less than 1% of all primary thyroid malignancies. They typically arise as neoplastic transformations within areas of autoimmune thyroiditis. Although they tend to have an indolent course, these lymphomas present a diagnostic challenge requiring a high level of suspicion in patients at increased risk of development.

Methods.

We retrospectively reviewed 3 cases of primary MALT thyroid lymphoma discovered in patients with a compressive goiter. This represents the experience at a single institution from 1996 to 2005. Hospital and clinic records were reviewed to identify the workup, treatment, and outcome.

Results.

One of 3 patients underwent preoperative fine‐needle aspiration (FNA). All patients underwent total thyroidectomy to relieve compressive symptoms, and the final pathology revealed MALT lymphoma. Two patients subsequently underwent radiation therapy. All patients are alive without evidence of disease recurrence.

Conclusions.

These cases are notable for the unexpected presentation of MALT lymphoma within a compressive goiter. © 2006 Wiley Periodicals, Inc. Head Neck, 2006
Pharmacodynamics of PEG-IFN α differentiate HIV/HCV coinfected sustained virological responders from nonresponders
Authors: Talal Andrew H. , Ribeiro Ruy M. , Powers Kimberly A. , Grace Michael , Cullen Constance , Hussain Musaddeq , Markatou Marianthi , Perelson Alan S.
Published: April 2006

Pegylated interferon (PEG-IFN) has become standard therapy for hepatitis C virus (HCV) infection. We evaluated whether PEG-IFN pharmacodynamics and pharmacokinetics account for differences in treatment outcome and whether these parameters might be predictors of therapeutic outcome. Twenty-four IFN-naïve, HCV/human immunodeficiency virus–coinfected patients received PEG-IFN α-2b (1.5 μg/kg) once weekly plus daily ribavirin (1,000 or 1,200 mg) for up to 48 weeks. HCV RNA and PEG-IFN α concentrations were obtained from samples collected frequently after the first 3 PEG-IFN doses. We modeled HCV kinetics incorporating pharmacokinetic and pharmacodynamic parameters. Although PEG-IFN concentrations and pharmacokinetic parameters were similar in sustained virological responders (SVRs) and nonresponders (NRs), the PEG-IFN α-2b concentration that decreases HCV production by 50% (EC50) was lower in SVRs compared with NRs (0.04 vs. 0.45 μg/L [

P

= .014]). Additionally, the median therapeutic quotient (

i.e.

, the ratio between average PEG-IFN concentration and EC50[C̄/EC50]), and the PEG-IFN concentration at day 7 divided by EC50 (C(7)/EC50) were significantly increased in SVRs compared with NRs after the first (10.1 vs. 1.0 [

P

= .012], 2.8 vs. 0.3 [

P

= .007], respectively) and second (14.0 vs. 1.1 [

P

= .016], 5.4 vs. 0.4 [

P

= .02], respectively) PEG-IFN doses. All 3 parameters may be used to identify NRs.

In conclusion

, PEG-IFN concentrations and pharmacokinetic parameters do not differ between SVRs and NRs. In contrast, pharmacodynamic measurements—namely EC50, the therapeutic quotient, and C(7)/EC50—are different in coinfected SVRs and NRs. These parameters might be useful predictors of treatment outcome during the first month of therapy. (Hepatology 2006;43:943–953.)
Mechanisms underlying the inability to induce area CA1 LTP in the mouse after traumatic brain injury
Authors: Schwarzbach E. , Bonislawski D.P. , Xiong G. , Cohen A.S.
Published: April 2006

Traumatic brain injury (TBI) is a significant health issue that often causes enduring cognitive deficits, in particular memory dysfunction. The hippocampus, a structure crucial in learning and memory, is frequently damaged during TBI. Since long‐term potentiation (LTP) is the leading cellular model underlying learning and memory, this study was undertaken to examine how injury affects area CA1 LTP in mice using lateral fluid percussion injury (FPI). Brain slices derived from FPI animals demonstrated an inability to induce LTP in area CA1 7 days postinjury. However, area CA1 long‐term depression could be induced in neurons 7 days postinjury, demonstrating that some forms of synaptic plasticity can still be elicited. Using a multidisciplined approach, potential mechanisms underlying the inability to induce and maintain area CA1 LTP were investigated. This study demonstrates that injury leads to significantly smaller N‐methyl‐D‐aspartate potentials and glutamate‐induced excitatory currents, increased dendritic spine size, and decreased expression of α‐calcium calmodulin kinase II. These findings may underlie the injury‐induced lack of LTP and thus, contribute to cognitive impairments often associated with TBI. Furthermore, these results provide attractive sites for potential therapeutic intervention directed toward alleviating the devastating consequences of human TBI. © 2006 Wiley‐Liss, Inc.
Rat Schwann cells express M1–M4 muscarinic receptor subtypes
Authors: Loreti Simona , Vilaró M. Teresa , Visentin S. , Rees H. , Levey Allan I. , Tata Ada Maria
Published: April 2006

The expression of different muscarinic receptor subtypes was analyzed in immature Schwann cells obtained from sciatic nerve of 2‐day neonatal rats. By using RT‐PCR analysis, we demonstrated the presence of M1, M2, M3, and M4 receptor subtypes in cultured Schwann cells, with M2 displaying the highest expression levels. Muscarinic subtypes were also quantified by immunoprecipitation and [3H]QNB binding. With this approach, we found the levels of receptor expression to be M2 > M3 > M1. M4 is expressed at very low levels, and M5 receptor was not detectable. Moreover, we also demonstrated that stimulation of the receptors by muscarinic agonists activates previously described signal transduction pathways, leading to a decrease of cAMP and an increase of IP3 levels not associated with an efficient intracellular Ca2+ release. The presence and activity of particular muscarinic receptors in immature Schwann cells suggest that ACh may play an important role in Schwann cell development. © 2006 Wiley‐Liss, Inc.
Walker detection in outdoor scenes using spatial‐temporal feature analysis of variation regions
Authors: Haga Tetsuji , Sumi Kazuhiko , Yagi Yasushi
Published: April 2006

We propose an image processing algorithm to detect walkers in outdoor images containing movement in the background such as swaying trees or irregular reflections from water. Previously proposed methods to detect walkers focus on the fact that locally distributed movement is reinforced along a spatial and temporal path marked out by an object such as a human that moves at approximately a constant speed and in a straight line while other background movement tends to cancel itself out. However, false alarms can occur with methods that are based on the time‐averaged strength of movement due to mistaken associations between moving objects and the fact that temporary movement in high‐contrast areas can significantly raise the average value. In our method we use features based on a spatially averaged strength of movement and the uniformity of movement over time in addition to the time‐averaged strength of movement, attempting to distinguish walkers from background movement within a feature space made up of these three features. In experiments with real images we have confirmed that the proposed method can reduce the rate of both false positives and false negatives compared to a method that focuses only on the time‐averaged strength of movement. In addition, we have constructed an on‐line system to implement the proposed method and the results of evaluation experiments conducted in a real‐life environment over a period of two weeks show that we were able to obtain a level of performances in which the failure rate was less than 1 percent and false alarms occurred less than three times per day. © 2006 Wiley Periodicals, Inc. Syst Comp Jpn, 37(7): 37–46, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20295
Measurement of neuromagnetic fields accompanying movements by patient with acute stroke
Authors: Kotani Kentaro , Esaka Shigeaki , Yamada Makoto , Deguchi Jun , Horii Ken , Tonoike Mitsuo , Noguchi Taro
Published: April 2006

The recovery mechanism of stroke patients with motion disorder is becoming clear through observation of changes in the activated area in the brain cortex, using brain function imaging. At the present stage, however, consistent results have not been obtained. Consequently, this study attempts an analysis of the neuromagnetic fields by combining the conventional equivalent current dipole method and the MCE method, which can reveal changes in multiple activity sources accompanying the recovery of brain function by stroke patients and those observable in healthy subjects. In the experiment, button‐pressing by the thumb is performed by a patient group and a normal group, and the neuromagnetic field response and the force of the motion are simultaneously measured. Thus, the task consists of simple button‐pressing motion and the generation of a force of specified magnitude. In the normal group, activation is observed in the motor area on the other side of the moving limb. In stroke patients, on the other hand, activation is observed on the same side as the moving limb, which agrees with the results of preceding studies. Neural activity is sometimes observed near the damaged lesion, suggesting that the brain on the ipsilateral hemisphere of the moving limb, or neural activity near the damaged lesion, is enhanced in the recovery of motor function after an acute stroke. It is concluded that a temporal course of changes in the activated area in the brain of patients with acute stroke, which exhibits patterns different from the neuromagnetic field of normal subjects, can be observed. © 2006 Wiley Periodicals, Inc. Syst Comp Jpn, 37(7): 12–25, 2006; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/scj.20448
Neural regression model, resampling and diagnosis
Authors: Tsujitani Masaaki , Aoki Masahiko
Published: April 2006

In this article logistic regression model is highlighted using a feedforward neural network model. Suggested here is a simple more precise prognostic technique by incorporating follow‐up data in the development of the model when the data consist of grouped binary response and a set of predictor variables, which is closely related to classical logistic regression model. Statistical techniques are formulated in terms of the principle of the likelihood when a resampling process such as bootstrapping and cross‐validation is applied. We then attempt to determine the number of units in the hidden layer, to verify the asymptotic χ2behavior of the deviance for the goodness‐of‐fit test of the model, to detect inappropriate influential observations and outliers, and to improve the goodness‐of‐fit test of the neural network model. © 2006 Wiley Periodicals, Inc. Syst Comp Jpn, 37(6): 13–20, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20497
Hypocalcaemia and Parathyroid Hormone Assay Following Total Thyroidectomy: Predicting the Future
Authors: Wong C. , Price S. , Scott‐Coombes D.
Published: April 2006

Background

Ambulatory surgery (23:59‐hour hospital stay) is gaining popularity in endocrine surgery. Hypocalcaemia is common following total thyroidectomy. Identifying patients with low risk of hypocalcaemia may facilitate early discharge (24‐hour stay).

Methods

We conducted a prospective study including all patients undergoing total thyroidectomy. Blood samples were taken immediately following skin closure and the following morning for parathyroid hormone (PTH) and calcium measurement. Calcium supplements were routinely given when serum calcium was below 2.0 mmol/l.

Results

Thirty patients (27 females, 3 males) underwent total thyroidectomy (including 4 nodal dissection) for multinodular goitre (14), Graves’ disease (11), papillary (4) and follicular (1) thyroid carcinoma. Twelve patients developed symptomatic transient hypocalcaemia. Based on morning calcium of <2.0 mmol/l as trigger for calcium supplementation, 8 patients received calcium supplement with 4 false negatives, resulting in a specificity of 94.4%, sensitivity of 66.7%, positive predictive value (PPV) of 88.9% and negative predictive value (NPV) of 81%. Based on PTH levels (<1.5 pmol/l) immediately following skin closure, 11 patients would receive calcium supplement, with 1 false negative resulting in a specificity of 83.3%, sensitivity of 91.7%, PPV of 78.6% and NPV of 93.8%. If supplementation is based on PTH levels (<1.5 pmol/l) immediately following skin closure and morning calcium level (<2.0 mmol/l), all 12 symptomatic patients will be correctly treated, with 4 false positives resulting in a combined specificity of 77.8%, sensitivity of 100%, PPV of 75% and NPV of 100%.

Conclusions

Combining the immediate postoperation PTH levels (<1.5 pmol/l) and morning serum calcium (<2.0 mmol/l) can accurately identify patients at risk of hypocalcaemia following total thyroidectomy, allowing safe, early discharge.
The hydrodynamic stability of flow over Kramer-type compliant surfaces. Part 2. Flow-induced surface instabilities
Authors: Carpenter P. W. , Garrad A. D.
Published: April 2006

The flow-induced surface instabilities of Kramer-type compliant surfaces are investigated by a variety of theoretical approaches. This class of instability includes all those modes of instability for which the mechanism of generation involves essentially inviscid processes. The results should be applicable to all compliant surfaces that could be modelled theoretically by a thin elastic plate, with or without applied longitudinal tension, supported on a springy elastic foundation. with or without a viscous fluid substrate; material damping is also taken into account through the viscoelastic properties of the solid constituents of the coatings.

The simple case of a potential main flow is studied first. The eigenmodes for this case are subjected to an energy analysis following the methods of Landahl (1962). Instabilities that grow both in space and time are then considered, and absolute and convective instabilities identified and analysed.

The effects of irreversible processes on the flow-induced surface instabilities are investigated. The shear flow in the boundary layer gives rise to a fluctuating pressure component which is out of phase with the surface motion. This leads to an irreversible transfer of energy from the main stream to the compliant surface. This mechanism is studied in detail and is shown to be responsible for travelling-wave flutter. Simple results are obtained for the critical velocity, wavenumber and stability boundaries. These last are shown to be in good agreement with the results obtained by the numerical integration of the Orr–Sommerfeld equation. An analysis of the effects of a viscous fluid substrate and of material damping is then carried out. The simpler inviscid theory is shown to predict values of the maximum growth rate which are, again, in good agreement with the results obtained by the numerical integration of the Orr–Sommerfeld equation provided that the instability is fairly weak.

Compliant surfaces of finite length are analysed in the limit as wave-length tends to zero. In this way the static-divergence instability is predicted. Simple formulae for critical velocity and wavenumber are derived. These are in exact agreement with the results of the simpler infinite-length theory. But, whereas a substantial level of damping is required for the instability on a surface of infinite length, static divergence grows fastest in the absence of damping on a surface of finite length.
Effective equations for flow in random porous media with a large number of scales
Authors: Rubinstein Jacob
Published: April 2006

We rederive Brinkman's equations for the flow of slow viscous fluid past a random distribution of identical obstacles using the Foldy's approximation. It is shown explicitly that such a derivation is valid for extremely dilute systems. We argue that Brinkman's equation can be used even in systems with lower porosity by proposing a model of porous media that has a very large number of scales.
One-dimensional models for topographic Rossby waves in elongated basins on thef-plane
Authors: Stocker Thomas , Hutter Kolumban
Published: April 2006

Topographic Rossby waves in elongated basins on thef-plane are studied by transforming the linear boundary-value problem for the mass transport stream function into a class of two-point boundary-value problems of which the independent spatial variable is the (curved) basin axis. The procedure for deriving the substitute problems is theMethod of Weighted Residuals. What emerges is a vector differential equation and associated boundary conditions, its dimension indicating the order of the approximate model. It is shown that each substitute problem in the class entails the qualitative features typical of topographic waves, and increasing the order of the model corresponds to higher-order approximations. Equations are explicitly presented for cross-sectional distributions of the lake topography which has a power-law representation and permits the analysis of weak and strong topographies.

Straight channels in which the depth profile does not change with position along the axis are studied in detail. The dispersion relation is discussed and dispersion curves are shown for the three lowest-order models. Convergence properties are thereby uncovered and phase speed and group velocity properties are found as they depend on wavenumber and topography. Further, for the lowest two modes, cross-channel stream-function distributions are presented. Apart from further convergence properties these distributions show that forU-shaped channels wave activity is nearer to the shore than forV-shaped channels, important information in the design of mooring systems.

An analysis of topographic Rossby wave reflection follows, which emphasizes the importance of the depth profile in the reflecting zone. Based on these results some lake solutions are presented.
On the formation of vortex streets behind stationary cylinders
Authors: Triantafyllou George S. , Triantafyllou Michael S. , Chryssostomidis C.
Published: April 2006

The formation of vortex streets behind stationary cylinders is found to be caused by an absolute instability in the wake immediately behind the cylinder. The inviscid Orr–Sommerfeld equation is used together with measured profiles at Reynolds numbers of (a) Re = 56 when the absolute instability provides a Strouhal number of 0.13; and (b) Re = 140000 providing a Strouhal number of 0.21, both in agreement with experimental values. At the subcritical Re = 34 the instability is of the convective type; i.e. the disturbance decays, being convected away once the external disturbance is removed, in agreement with experimental observations. Finally, the instability of the mode which causes a symmetric array of vortices is shown to be always of the convective type.
Transient cavities near boundaries. Part 1. Rigid boundary
Authors: Blake J. R. , Taib B. B. , Doherty G.
Published: April 2006

The growth and collapse of transient vapour cavities near a rigid boundary in the presence of buoyancy forces and an incident stagnation-point flow are modelled via a boundary-integral method. Bubble shapes, particle pathlines and pressure contours are used to illustrate the results of the numerical solutions. Migration of the collapsing bubble, and subsequent jet formation, may be directed either towards or away from the rigid boundary, depending on the relative magnitude of the physical parameters. For appropriate parameter ranges in stagnation-point flow, unusual ‘hour-glass’ shaped bubbles are formed towards the end of the collapse of the bubble. It is postulated that the final collapsed state of the bubble may be two toroidal bubbles/ring vortices of opposite circulation. For buoyant vapour cavities the Kelvin impulse is used to obtain criteria which determine the direction of migration and subsequent jet formation in the collapsing bubble.
Acoustic monitoring of ocean gyres
Authors: Munk Walter
Published: April 2006

There has been an increased interest in ocean phenomena with horizontal scales comparable to the radius of the Earth, and timescales of years and beyond. These phenomena occur in the presence of intense processes of higher spatial and temporal frequency. An observational programme for the large-scale phenomena has an inherent advantage if it can rely on measurements that are, by their very nature, integrated moments over the prerequisite scale.

The oceans provide an excellent medium for transmitting sound waves of low frequency, as demonstrated in the closing days of World War II, and subsequently confirmed by a 20000 km acoustic transmission between Perth, Australia and Bermuda. For the last six years we have been developing a method (Ocean Acoustic Tomography) to take advantage of the favourable ocean acoustic properties. We measure travel time Δ+ from mooring m to mooring n (positive x), and Δ− from n to m. The sum Δ+ + Δ− then gives information about the sound speed C (e.g. temperature) averaged along the acoustic ray path; the difference Δ+ – Δ− gives information about the x-component u of current velocity. The recorded acoustic signal can be decomposed into 10-20 distinct ray arrivals Δi, each with a distinct ray path and associated depth-weighting of the ocean column; the ray travel times can be inverted to yield information about the depth profiles C(z) and u(z). The product 〈C〉 〈u〉 of these range-averaged quantities is related to the climatological large-scale heat flux; the space-time average $\overline{\langle \delta C\,\delta u\rangle}$ is related to the eddy heat flux, and can be estimated by measuring the difference variance (Δ+) – variance (Δ−).
Experimental and numerical study of vortex couples in two-dimensional flows
Authors: Couder Y. , Basdevant C.
Published: April 2006

Two-dimensional turbulence is investigated experimentally in thin liquid films. This study shows the spontaneous formation of couples of opposite-sign vortices in von Kármán wakes. The structure of these couples, their behaviour and their role in turbulent flows is then studied using both a numerical simulation and laboratory results.
Convective flows with multiple spatial periodicities
Authors: Lowe Mary , Albert B. Steven , Gollub J. P.
Published: April 2006

The response of a convective flow to spatially periodic forcing at a period different from the critical wavelength is investigated experimentally. For reasons of experimental convenience, we utilize an electrohydrodynamic instability in a thin layer of nematic liquid. With this system, a sample containing several hundred rolls is easily obtained, and periodic forcing is imposed electrically using a specially designed interdigitated electrode. Several novel flows with multiple periodicities are found. They may be broadly classified as commensurate (phase-locked) or incommensurate (quasi-periodic) flows, depending on whether the dominant periodicity of the perturbed flow and the periodicity of the forcing are in the ratio of small integers. Near the instability threshold and for weak forcing, an approximation of slow spatial variations is satisfied. In that case, the flows can be described quantitatively by an amplitude equation. We note a close connection between these hydrodynamic phenomena and a problem of competing periodicities that occurs in statistical mechanics. This relationship leads us to suggest the use of a discontinuous function for describing certain incommensurate flows in which non-repeating short and long groups of rolls are observed to occur in an irregular sequence. We also note, as predicted by Pal & Kelly, that two-dimensional forcing can lead to a three-dimensional flow.
An experiment on boundary mixing: mean circulation and transport rates
Authors: Phillips O. M. , Shyu Jinn-Hwa , Salmun Haydee
Published: April 2006

An experiment is described in which a turbulent boundary layer was generated along a sloping wall of a laboratory tank containing salt-stratified fluid. Initially, the pycnocline separating the upper fresh-water layer from the lower saline layer was relatively thin; it thickened in response to the mixing as the experiment proceeded. Two types of mean circulation developed as a result of the boundary mixing. In the boundary layer, counterflowing mean streams were observed that augmented the diffusion of salt up- and downslope. This augmented dispersion in turn tended to spread the salt beyond the depth range of the pycnocline in the ambient fluid, producing a mean convergence in the boundary layer and intrusions from the layer into the ambient fluid.

The evolving density structure in the ambient fluid was measured by conductivity-probe traverses, from which the net buoyancy flux (or salt flux) and volume flux in the boundary layer were determined. The level of zero volume flux was found to coincide closely with the level of maximum stability frequency N, so that the buoyancy transport across this level was entirely the result of turbulent dispersion in the boundary layer. At other levels, the convective transports up and down contribute significantly. A simple theory provides scaling in terms of the laboratory parameters; in terms of the inferred overall turbulent viscosity νe, the buoyancy transport resulting from boundary-layer dispersion was found to be
\[
F_{\rm B} = 0.60 \left\{\frac{\nu_{\rm e}N(z)}{\sin\theta}\right\}^{\frac{3}{2}}\cos^2\theta,
\]
and the intrusion velocity into the ambient fluid is
\[
v_1 = 0.42\frac{\nu_{\rm e}^{\frac{3}{2}}}{N^{\frac{1}{2}}h^2}\frac{\cos^2\theta}{(\sin\theta)^{\frac{3}{2}}},
\]
where θ is the angle of the sloping bed. These expressions must become invalid when θ becomes vanishingly small; their application to estuarine and continental slope flows is discussed briefly.
The hydraulics of two flowing layers with different densities
Authors: Armi Laurence
Published: April 2006

This is a theoretical and experimental study of the basic hydraulics of two flowing layers. Unlike single-layer flows, two-layer flows respond quite differently to bottom depth as opposed to width variations. Bottom-depth changes affect the lower layer directly and the upper layer only indirectly. Changes in width can affect both layers. In fact for flows through a contraction control two distinct flow configurations are possible; which one actually occurs depends on the requirements of matching a downstream flow. Two-layer flows can pass through internally critical conditions at other than the narrowest section. When the two layers are flowing in the same direction, the result is a strong coupling between the two layers in the neighbourhood of the control. For contractions a particularly simple flow then exists upstream in which there is no longer any significant interfacial dynamics; downstream in the divergent section the flow remains internally supercritical, causing one of the layers to be rapidly accelerated with a resulting instability at the interface. A brief discussion of internal hydraulic jumps based upon the energy equations as opposed to the more traditional momentum equations is included. Previous uniqueness problems are thereby avoided.
On the instability of a three-dimensional attachment-line boundary layer: weakly nonlinear theory and a numerical approach
Authors: Hall Philip , Malik Mujeeb R.
Published: April 2006

The instability of a three-dimensional attachment-line boundary layer is considered in the nonlinear regime. Using weakly nonlinear theory, it is found that, apart from a small interval near the (linear) critical Reynolds number, finite-amplitude solutions bifurcate subcritically from the upper branch of the neutral curve. The time-dependent Navier–Stokes equations for the attachment-line flow have been solved using a Fourier–Chebyshev spectral method and the subcritical instability is found at wavenumbers that correspond to the upper branch. Both the theory and the numerical calculations show the existence of supercritical finite-amplitude (equilibrium) states near the lower branch which explains why the observed flow exhibits a preference for the lower branch modes. The effect of blowing and suction on nonlinear stability of the attachment-line boundary layer is also investigated.
Aspects of the equilibrium puff in transitional pipe flow
Authors: Bandyopadhyay Promode R.
Published: April 2006

Flow-visualization studies in transitional pipe flow are used to reveal the mechanism responsible for the self-sustenance of a turbulent equilibrium puff. The upstream laminar fluid continuously enters the relatively-slower-moving turbulent puff around the pipe centre. The passage of this high-speed laminar plug flow past the slower fluid that resides near the wall at the upstream interface leads to the shedding of a train of three-dimensional wake-like vortices near the wall. A helical motion near the upstream interface is associated with the vortex-shedding process. The remainder of the puff is a cone of turbulence filled with these wake-like vortices that are decaying slowly; the prominent feature of the decay region is the longitudinal vortices that are apparently undergoing stretching. No toroidal vortex has been observed in the instantaneous flow field at the upstream interface of an individual puff. On the other hand, the wake-like vortices reported here have not been observed before because their three-dimensional and random nature does not allow detection by an ensemble-averaging that is not phase-referenced appropriately.
Taylor dispersion in concentrated suspensions of rotating cylinders
Authors: Nadim A. , Cox R. G. , Brenner H.
Published: April 2006

Laminar heat- or mass-transfer processes are theoretically investigated for two-dimensional spatially periodic suspensions of circular cylinders, each member of which rotates steadily about its own axis under the influence of an external couple. The novelty of the ensuing convective-diffusion phenomena derives from the absence of convective motion at the suspension lengthscale (the ‘macroscale’), despite its presence at the interstitial or particle lengthscale (the ‘microscale’). The latter fluid motion consists of a cellular vortex-like flow characterized by closed streamlines. These periodically closed streamlines give rise to a situation in which there exists no net flow at the macroscale. The resulting macroscale transport of heat or mass thus proceeds purely by conduction, the rate being characterized by a tensor diffusivity — dependent upon the angular velocity of the cylinders. Matched-asymptotic-expansion methods together with generalized Taylor dispersion theory are used to calculate this macroscale conductivity in the dual limit of large rotary Péclet numbers and small gap widths between adjacent cylinders. This prototype study illustrates the fact that the usual separation of transport processes into distinct convective and conductive contributions is not generally a scale-invariant concept; that is, microscale convec-tional contributions to the transport of heat or mass are not generally representable by corresponding macroscale convectipnal contributions to the transport. Possible applications of the analysis exist in the area of enhanced conduction rates in ferrofluids or other dipolar fluids rotating relative to a fixed external field (or conversely).
Network models for two-phase flow in porous media Part 1. Immiscible microdisplacement of non-wetting fluids
Authors: Dias Madalena M. , Payatakes Alkiviades C.
Published: April 2006

A theoretical simulator of immiscible displacement of a non-wetting fluid by a wetting one in a random porous medium is developed. The porous medium is modelled as a network of randomly sized unit cells of the constricted-tube type. Under creeping-flow conditions the problem is reduced to a system of linear equations, the solution of which gives the instantaneous pressures at the nodes and the corresponding flowrates through the unit cells. The pattern and rate of the displacement are obtained by assuming quasi-static flow and taking small time increments. The porous medium adopted for the simulations is a sandpack with porosity 0.395 and grain sizes in the range from 74 to 148 μrn. The effects of the capillary number, Ca, and the viscosity ratio, κ = μo/μw, are studied. The results confirm the importance of the capillary number for displacement, but they also show that for moderate and high Ca values the role of κ is pivotal. When the viscosity ratio is favourable (κ < 1), the microdisplacement efficiency begins to increase rapidly with increasing capillary number for Ca > 10−5, and becomes excellent as Ca → 10−3. On the other hand, when the viscosity ratio is unfavourable (κ > 1), the microdisplacement efficiency begins to improve only for Ca values larger than, say, 5 × 10−4, and is substantially inferior to that achieved with κ < 1 and the same Ca value. In addition to the residual saturation of the non-wetting fluid, the simulator predicts the time required for the displacement, the pattern of the transition zone, the size distribution of the entrapped ganglia, and the acceptance fraction as functions of Ca, κ, and the porous-medium geometry.
Low-Reynolds-number flow past cylindrical bodies of arbitrary cross-sectional shape
Authors: Lee S. H. , Leal L. G.
Published: April 2006

A numerical implementation of the method of matched asymptotic expansions is proposed to analyse two-dimensional uniform streaming flow at low Reynolds number past a straight cylinder (or cylinders) of arbitrary cross-sectional shape. General solutions for both the Stokes and Oseen equations in two dimensions are expressed in terms of a boundary distribution of fundamental single- and double-layer singularities. These general solutions are then converted to integral equations for the unknown distributions of singularity strengths by application of boundary conditions at the cylinder surface, and matching conditions between the Stokes and Oseen solutions. By solving these integral equations, using collocation methods familiar from three-dimensional application of ‘boundary integral’ methods for solutions of Stokes equation, we generate a uniformly valid approximation to the solution for the whole domain.

We demonstrate the method by considering, as numerical examples, uniform flow past an elliptic cylinder, uniform flow past a cylinder of rectangular cross-section, and uniform flow past two parallel cylinders which may be either equal in radius, or of different sizes.
A plate oscillating across a liquid interface: effects of contact-angle hysteresis
Authors: Young G. W. , Davis S. H.
Published: April 2006

We consider the oscillatory motion of a solid plate into and out of a bath of liquid. Assuming that the displacement amplitude of the plate motion is small and that the capillary number is small, the problem reduces to solving an interfacial boundaryvalue problem for the response of the contact line. The characteristic contact angle versus contact-line speed relationship includes contact-angle hysteresis which is assumed small and comparable to the amplitude of the plate motion. Sinusoidal and square-wave plate motions are considered. We find that the contact line moves with the plate if the contact line is fixed, but has relative motion otherwise. It would then advance part of the time, recede part of the time, and remain stationary in the transition periods. Further, we find that both contact-angle hysteresis and steepening of the contact angle with increasing contact-line speed are dissipative effects.
The gravitational settling of aerosol particles in homogeneous turbulence and random flow fields
Authors: Maxey M. R.
Published: April 2006

The average settling velocity in homogeneous turbulence of a small rigid spherical particle, subject to a Stokes drag force, is shown to depend on the particle inertia and the free-fall terminal velocity in still fluid. With no inertia the particle settles on average at the same rate as in still fluid, assuming there is no mean flow. Particle inertia produces a bias in each trajectory towards regions of high strain rate or low vorticity, which affects the mean settling velocity. Results from a Gaussian random velocity field show that this produces an increased settling velocity.
On the spatial instability of piecewise linear free shear layers
Authors: Balsa T. F.
Published: April 2006

The main goal of this paper is to clarify the spatial instability of a piecewise linear free shear flow. We do this by obtaining numerical solutions to the Orr–Sommerfeld equation at high Reynolds numbers. The velocity profile chosen is very much like a piecewise linear one, with the exception that the corners have been rounded so that the entire profile is infinitely differentiable. We find that the (viscous) spatial instability of this modified profile is virtually identical to the inviscid spatial instability of the piecewise linear profile and agrees qualitatively with the inviscid results for the tanh profile when the shear layers are convectively unstable. The unphysical features, previously identified for the piecewise linear velocity profile, arise only when the flow is absolutely unstable. In a nutshell, we see nothing wrong with the inviscid spatial instability of piecewise linear shear flows.
Density currents or density wedges: boundary-layer influence and control methods
Authors: Jirka Gerhard H. , Arita Masamitsu
Published: April 2006

Density currents and density wedges are two observed manifestations of interactions between an ambient flow and a horizontal buoyant intrusion. In a density current the buoyant pressure force is primarily balanced by the local form drag of the current head which has a blunt shape and abrupt depth change. In a density wedge a distributed interfacial drag is the primary balancing force, leading to a stretched-out shape and long-distance intrusions. A perturbation analysis of the approach flow to the inclined front of a density current shows that slight momentum changes caused by viscous effects in the ambient flow determine which of these two flow types is established. In a uniform ambient channel flow, any momentum deficit relative to the inviscid case will lead to a local flattening of the front and ultimate breakdown into a density wedge. On the other hand, a momentum surplus will support a steady-state density current. Several exploratory experiments on control of the ambient boundary layer through local non-uniformities were performed with the objective of achieving stable density-current forms with limited intrusion lengths. These methods include a small step, a barrier and suction and are applied for intrusions at either the bottom or surface of an ambient water flow. In all cases, good agreement is found with the force balances predicted by Benjamin's (1968) theory and its extension by Britter & Simpson (1978) which accounts for entrainment in the wake zone of the head.
The interaction of an oblique shock wave with a laminar boundary layer revisited. An experimental and numerical study
Authors: Degrez G. , Boccadoro C. H. , Wendt J. F.
Published: April 2006

An investigation of an oblique shock wave/laminar boundary layer interaction is presented. The Mach number was 2.15, the Reynolds number was 105 and the overall pressure ratio was 1.55. The interation has been demonstrated to be laminar and nominally two-dimensional. Experimental results include pressure distributions on the plate and single component laser-Doppler velocimetry velocity measurements both in the attached and separated regions.

The numerical results have been obtained by solving the full compressible Navier-Stokes equations with the implicit approximate factorization algorithm by Beam & Warming (1980). Comparison with experimental data shows good agreement in terms of pressure distributions, positions of separation and reattachment and velocity profiles.
Bifurcation phenomena and cellular-pattern evolution in mixed-convection heat transfer
Authors: Fung L. , Nandakumar K. , Masliyah J. H.
Published: April 2006

This investigation is concerned with the numerical calculation of multiple solutions for a mixed-convection flow problem in horizontal rectangular ducts. The numerical results are interpreted in terms of recent observations by Benjamin (1978a) on the bifurcation phenomena for a bounded incompressible fluid. The observed mutations of cellular flows are discussed in terms of dynamic interchange processes. Each cellular flow may be represented by a solution surface in the parametric space of Grashof number Gr and aspect ratio γ, which is delimited by stability boundaries. Such a stability map has been generated for each type of cellular flow by a series of numerical experiments. Once these boundaries are crossed one cellular flow mutates into another via a certain dynamical process. Although the nature of the singular points on this map have not been determined precisely, a plausible general structure of the cellular-flow exchange process emerges from this map with several features in common with the Taylor-Couette flow. The primary modes appear to exchange roles via the formation of tilted cusp. Other salient features such as primary-mode hysteresis and quasi-critical range for cellular development appear to be present. However no anomolous modes have been observed.
Transcritical two-layer flow over topography
Authors: Melville W. K. , Helfrich Karl R.
Published: April 2006

The evolution of weakly-nonlinear two-layer flow over topography is considered. The governing equations are formulated to consider the effects of quadratic and cubic nonlinearity in the transcritical regime of the internal mode. In the absence of cubic nonlinearity an inhomogeneous Korteweg-de Vries equation describes the interfacial displacement. Numerical solutions of this equation exhibit undular bores or sequences of Boussinesq solitary waves upstream in a transcritical regime. For sufficiently large supercritical Froude numbers, a locally steady flow is attained over the topography. In that regime in which both quadratic and cubic nonlinearity are comparable, the evolution of the interface is described by an inhomogeneous extended Kortewegde Vries (EKdV) equation. This equation displays undular bores upstream in a subcritical regime, but monotonic bores in a transcritical regime. The monotonic bores are solitary wave solutions of the corresponding homogeneous EKdV equation. Again, locally steady flow is attained for sufficiently large supercritical Froude numbers. The predictions of the numerical solutions are compared with laboratory experiments which show good agreement with the solutions of the forced EKdV equation for some range of parameters. It is shown that a recent result of Miles (1986), which predicts an unsteady transcritical regime for single-layer flows, may readily be extended to two-layer flows (described by the forced KdV equation) and is in agreement with the results presented here.

Numerical experiments exploiting the symmetry of the homogeneous EKdV equation show that solitary waves of fixed amplitude but arbitrary length may be generated in systems described by the inhomogeneous EKdV equation.
Triple-deck solutions for supersonic flows past flared cylinders
Authors: Gittler Ph. , Kluwick A.
Published: April 2006

Using the method of matched asymptotic expansions, the interaction between axisymmetric laminar boundary layers and supersonic external flows is investigated in the limit of large Reynolds numbers. Numerical solutions to the interaction equations are presented for flare angles α that are moderately large. If α > 0 the boundary layer separates upstream of the corner and the formation of a plateau structure similar to the two-dimensional case is observed. In contrast to the case of planar flow, however, separation can occur also if α < 0, owing to the axisymmetric effect of overexpansion and recompression. The separation point then is located downstream of the corner and, most remarkable, a hysteresis phenomenon is observed.