bluuebunny/crossref_metadata_2025_split huggingface dataset:
Instability and transitions of flow in a curved square duct: the development of two pairs of Dean vortices
Authors: Mees Philip A. J. , Nandakumar K. , Masliyah J. H. 
Published: April 2006

Steady developing flow of an incompressible Newtonian fluid in a curved duct of square cross-section (the Dean problem) is investigated both experimentally and numerically. This study is a continuation of the work by Bara, Nandakumar & Masliyah (1992) and is focused on flow rates between Dn = 200 and Dn = 600 (Dn = Re/(R/a)1/2, where Re is the Reynolds number, R is the radius of curvature of the duct and a is the duct dimension; the curvature ratio, R/a, is 15.1).Numerical simulations based on the steady three-dimensional Navier – Stokes equations predict the development of a 6-cell secondary flow pattern above a Dean number of 350. The 6-cell state consists of two large Ekman vortices and two pairs of small Dean vortices near the outer wall that result from the primary instability that is of centrifugal nature. The 6-cell flow state develops near θ = 80° and breaks down symmetrically into a 2-cell flow pattern.The apparatus used to verify the simulations had a duct dimension of 1.27 cm and a streamwise length of 270°. At a Dean number of 453, different velocity profiles of the 6-cell flow state at θ = 90° and spanwise profiles of the streamwise velocity at every 20° were measured using a laser-Doppler anemometer. All measured velocity profiles, as well as flow visualization of secondary flow patterns, are in very good agreement with the simulations, indicating that the parabolized Navier – Stokes equations give an accurate description of the flow.Based on the similarity with boundary layer flow over a concave wall (the Görtler problem), it is suggested that the transition to the 6-cell flow state is the result of a decreasing spanwise wavelength of the Dean vortices with increasing flow rate. A numerical stability analysis shows that the 6-cell flow state is unconditionally unstable. This is the first time that detailed experiments and simulations of the development of a 6-cell flow state are reported.
Dynamics of a vortex ring in a rotating fluid
Authors: Verzicco R. , Orlandi P. , Eisenga A. H. M. , Heijst G. J. F. Van , Carnevale G. F. 
Published: April 2006

The formation and the evolution of axisymmetric vortex rings in a uniformly rotating fluid, with the rotation axis orthogonal to the ring vorticity, have been investigated by numerical and laboratory experiments. The flow dynamics turned out to be strongly affected by the presence of the rotation. In particular, as the background rotation increases, the translation velocity of the ring decreases, a structure with opposite circulation forms ahead of the ring and an intense axial vortex is generated on the axis of symmetry in the tail of the ring. The occurrence of these structures has been explained by the presence of a self-induced swirl flow and by inspection of the extra terms in the Navier–Stokes equations due to rotation. Although in the present case the swirl was generated by the vortex ring itself, these results are in agreement with those of Virk et al. (1994) for polarized vortex rings, in which the swirl flow was initially assigned as a ‘degree of polarization’.If the rotation rate is further increased beyond a certain value, the flow starts to be dominated by Coriolis forces. In this flow regime, the impulse imparted to the fluid no longer generates a vortex ring, but rather it excites inertial waves allowing the flow to radiate energy. Evidence of this phenomenon is shown.Finally, some three-dimensional numerical results are discussed in order to justify some asymmetries observed in flow visualizations.
Computer simulations of polymer chain relaxation via Brownian motion
Authors: Grassia P. , Hinch E. J. 
Published: April 2006

Numerical simulations are employed to study the Brownian motion of a bead-rod polymer chain dissolved in a solvent. An investigation is conducted of the relaxation of the stress for an initially straight chain as it begins to coil.For a numerical time step δt in the simulations, conventional formulae for the stress involve averaging large ±O(1/(δt)1/2) contributions over many realizations, in order to yield an O(1) average. An alternative formula for the stress is derived which only contains O(1) contributions, thereby improving the quality of the statistics.For a chain consisting of n rods in a solvent at temperature T, the component of the bulk stress along the initial chain direction arising from tensions in the rods at the initial instant is $k\hat{T}\times n(\frac{1}{3}n^2 + n +\frac{2}{3})$. Thus the bead-rod model yields results very different from other polymer models, such as the entropic spring of Flory (1969), which would assign an infinite stress to a fully aligned chain. For rods of length l and beads of friction factor $\hat{\zeta}$ the stress decays at first on $O(\hat{\zeta}\hat{l}^2/k\hat{T}\times 1/n^2)$ time scales. On longer time scales, this behaviour gives way to a more gradual stress decay, characterized by an $O(k\hat{T}\times n)$ stress following a simple exponential decay with an $O(k\hat{T}/\hat{\zeta}\hat{l}^2\times 1/n^2)$ rate. Matching these two limiting regimes, a power law decay in time t is found with stress $O(k\hat{T}\times n^2\times (k\hat{T}\hat{t}/\hat{\zeta}\hat{l}^2)^{-1/2})$. The dominant physical processes occurring in these separate short, long and intermediate time regimes are identified.
The initial response of a stratified lake to a surface shear stress
Authors: Stevens Craig , Imberger Jörg 
Published: April 2006

Laboratory experiments are used to study the initial response of a stratified fluid to the action of a wind stress. The experiments are described in the context of a parameterization scheme that quantifies the strength of the applied stress relative to the bulk stability of the fluid and also the duration of the wind stress relative to the periods of the waves generated by the stress. This study concentrates on the first fundamental internal wave period in experiments where the fluid is considered to have upwelled, i.e. the stratified region of the fluid reaches the surface at the upwind endwall. The majority of the experiments use three-layer initial density profiles as an approximation to a continuously stratified water column.A linear model using normal modes proved successful prior to the commencement of upwelling and this enabled an estimate to be made of the time at which upwelling occurred. At this point the wave development ceased and the flows developed via entrainment mechanisms. Consideration of the energy budget showed that little of the input energy was stored in the system. The initial mixing efficiency, defined as the ratio of the mean potential energy gained to the energy imparted by the belt, never exceeded 30%. Peak efficiency occurred when the surface stress was just sufficient to bring the interfacial region to the surface.
Non-continuum lubrication flows between particles colliding in a gas
Authors: Sundararajakumar R. R. , Koch Donald L. 
Published: April 2006

Solid-body collisions between smooth particles in a gas would not occur if the lubrication force for a continuum incompressible fluid were to hold at all particle separations. When the gap between the particles is of the order of the mean free path λ0 of the gas, the discrete molecular nature of the gas becomes important. For particles of radii a smaller than about 50 μm colliding in air at a relative velocity comparable to their terminal velocity, the effects of compressibility of the gas in the gap are not important.The nature of the flow in the gap depends on the relative magnitudes of the minimum gap thickness h0 ≡ aε, the mean-free path λ0, and the distance aε1/2 over which the effects of curvature become important. The slip-flow regime, a[Gt ]λ0, was analysed by Hocking (1973) using the Maxwell slip boundary condition at the particle surface. To find the lubrication force in the transition regime (aε ∼ O(λ0)), we use the results of Cercignani & Daneri (1963) for the flux as a function of the pressure gradient in a Poiseuille channel flow. When aε[Lt ]λ0[Lt ]aε1/2, one might expect the local flow in the gap to be governed by Knudsen diffusion. However, an attempt to calculate the Knudsen diffusivity between parallel plates leads to a logarithmic divergence, which is cut off by intermolecular collisions, and the flux is therefore proportional to h0c log(λ0/h0), where c is the mean molecular speed. The non-continuum lubrication force is shown to have a weak, log - log divergence as the particle separation goes to zero. As a result, the energy dissipated in the collision is finite. In the limit of large particle inertia, the energy dissipated is 6πμU0a2(log h0/λ0 – 1.28), where 2U0 is the relative velocity of the particles.When λ0[Gt ]aε1/2, we have a free molecular flow in the gap. In this case, owing to the curvature of the particles, the flux versus pressure gradient relation is non-local. We analyse the free molecular flow between two cylinders and obtain scalings for the lubrication force.
Active sonic boom control
Authors: Crow Steven C. , Bergmeier Gene G. 
Published: April 2006

A theory and simulation code are developed to study non-steady sources as means to control sonic booms of supersonic aircraft. A key result is that the source of sonic boom pressure is not confined to the length of the aircraft but occupies an extensive segment of the flight path. An aircraft in non-steady flight functions as a synthetic aperture antenna, generating complex acoustic waves with no simple relation to instantaneous volume or lift distributions.The theory applies linear acoustics to slender non-steady sources but requires no far-field approximation. The solution for pressure contains a term not seen in Whitham's theory for sonic booms of distant supersonic aircraft. The term describes a pressure field that decays algebraically behind the Mach cone and, in the case of steady flight, integrates to a ground load equal to the weight of the aircraft. The algebraic term is separate from those that describe the sonic boom.Two non-steady source phenomena are evaluated: periodic velocity changes (surge), and periodic longitudinal lift redistribution (slosh). Surge can attenuate a sonic boom and covert it into prolonged weak reverberation, but accelerations needed to produce the phenomenon seem too large for practical use. Slosh may be practical and can alter sonic booms but does not, on average, result in boom attenuation. The conclusion is that active sonic boom abatement is possible in theory but maybe not practical.
Stability of stationary endwall boundary layers during spin-down
Authors: Lopez J. M. , Weidman P. D. 
Published: April 2006

Since Bödewadt's (1940) seminal work on the boundary layer flow produced by a fluid in solid-body rotation over a stationary disk of infinite radius there has been much interest in determining the stability of such flows. To date, it appears that there is no theoretical study of the stability of Bödewadt's self-similar solution to perturbations that are not self-similar. Experimental studies have been compromised due to the difficulty in establishing these steady flows in the laboratory. Savaç (1983, 1987) has studied the endwall boundary layers of flow in a circular cylinder following impulsive spin-down. During the first few radians of rotation, the endwall boundary layers have a structure very similar to Bödewadt layers. For certain conditions, SavaÇ has observed a series of axisymmetric waves travelling radially inwards in the endwall boundary layers. The conjecture is that these waves represent a mode of instability of the Bödewadt layer. Within a few radians of rotation however, the centrifugal instability of the sidewall layer dominates the spin-down process and the endwall waves are difficult to examine further.Here, the impulsive spin-down problem is examined numerically for Savaç’ (1983, 1987) conditions and good agreement with his experiments is achieved. New experimental results are also presented, which include quantitative space-time information regarding the axisymmetric waves. These agree well with both the numerics and the earlier experimental work. Further, a related problem is considered numerically. This flow is also initially in solid-body rotation, but only the endwalls are impulsively stopped, keeping the sidewall rotating. This results in a flow virtually identical to the usual spin-down flow for the first few radians of rotation, except in the immediate vicinity of the sidewall. The sidewall layer is no longer centrifugally unstable and the circular waves on the endwalls are observed without the influence of the sidewall instability.
Wave pattern formation in a fluid annulus with a radially vibrating inner cylinder
Authors: Krasnopolskaya T. S. , Heijst G. J. F. Van 
Published: April 2006

The phenomenon of pattern formation of free-surface waves of a fluid confined in an annulus the inner wall of which vibrates radially, is investigated both theoretically and experimentally. Although the waves are excited by harmonic axisymmetric deformations of the inner shell, depending on the vibration frequency both axisymmetric and non-symmetric wave patterns may arise.Experimental observations have revealed that waves are excited in two different resonance regimes. The first type corresponds to forced resonance, in which axisymmetric patterns are realized with eigenfrequencies equal to the frequency of excitation. The second kind is parametric resonance, in which case the waves are ‘transverse’, with their crests and troughs aligned perpendicular to the vibrating wall. These so-called cross-waves have frequencies equal to half of that of the wavemaker.Both kinds of resonance were investigated theoretically using Lamé's method of superposition. It was shown experimentally that the pure forced resonant standing waves are not realized when the amplitude of excitation is beyond the threshold of parametric resonance for non-symmetric waves. The experimental observations agree very well with the theoretical results.
Gi-coupled receptors mediate phosphorylation of CPI-17 and MLC20 via preferential activation of the PI3K/ILK pathway
Authors: Huang Jiean , Mahavadi Sunila , Sriwai Wimolpak , Hu Wenhui , Murthy Karnam S. 
Published: April 2006

Sustained smooth-muscle contraction or its experimental counterpart, Ca2+ sensitization, by Gq/13-coupled receptor agonists is mediated via RhoA-dependent inhibition of MLC (myosin light chain) phosphatase and MLC20 (20 kDa regulatory light chain of myosin II) phosphorylation by a Ca2+-independent MLCK (MLC kinase). The present study identified the corresponding pathways initiated by Gi-coupled receptors. Somatostatin acting via Gi1-coupled sstr3 receptor, DPDPE ([D-Pen2,D-Pen5]enkephalin; where Pen is penicillamine) acting via Gi2-coupled δ-opioid receptors, and cyclopentyl adenosine acting via Gi3-coupled adenosine A1 receptors preferentially activated PI3K (phosphoinositide 3-kinase) and ILK (integrin-linked kinase), whereas ACh (acetylcholine) acting via Gi3-coupled M2 receptors preferentially activated PI3K, Cdc42 (cell division cycle 42)/Rac1, PAK1 (p21-activated kinase 1) and p38 MAPK (mitogen-activated protein kinase). Only agonists that activated ILK induced sustained CPI-17 (protein kinase C potentiated inhibitor 17 kDa protein) phosphorylation at Thr38, MLC20 phosphorylation at Ser19, and contraction, consistent with recent evidence that ILK can act as a Ca2+-independent MLCK capable of phosphorylating the MLC phosphatase inhibitor, CPI-17, at Thr38. ILK activity, and CPI-17 and MLC20 phosphorylation were inhibited by LY294002 and in muscle cells expressing ILK(R211A) or treated with siRNA (small interfering RNA) for ILK. ACh acting via M2 receptors activated ILK, and induced CPI-17 and MLC20 phosphorylation and muscle contraction, but only after inhibition of p38 MAPK; all these responses were inhibited in cells expressing ILK(R211A). Conversely, ACh activated PAK1, a step upstream of p38 MAPK, whereas the three other agonists did so only in cells transfected with ILK(R211A) or siRNA for ILK. The results demonstrate reciprocal inhibition between two pathways downstream of PI3K, with ILK inhibiting PAK1, and p38 MAPK inhibiting ILK. Sustained contraction via Gi-coupled receptors is dependent on CPI-17 and MLC20 phosphorylation by ILK.
Expression of bovine interferon-γ inEscherichia coliandPichia pastorisand comparison of their antiviral activities
Authors: Xi-Ju Shi , Can Zhang , Chun-Lai Han , Chun Xia , Ming Wang 
Published: April 2006

AbstractThe bovine interferon-γ gene cloned from total RNA of peripheral blood lymphocytes stimulated with concanavalin A (ConA), using the reverse transcriptase-polymerase chain reaction (RT-PCR), was cloned into pGEM T-easy vector and sequenced. The mature peptide without signal peptide was then subcloned and constructed into the expression plasmids pET28a/BoIFN-γand pPICZα/BoIFN-γ, respectively. The former was highly expressed, induced by isopropyl β-d-thiogalactoside (IPTG), inEscherichia coliBL21, with 30% of bacterial proteins in inclusion bodies. The latter was expressed inPichia pastorisGS115 with methanol induction. The expressed products were secreted directly into cultural supernatant at concentrations of 1.0 g/l. The same recombinant proteins had antiviral activities 10 times higher in an MDBK (Madan-Darby bovine kidney)/VSV (Vesicular stomatitis virus) cell line than in a CEF (chicken embryo fibroblast)/VSV) cell line, and the antiviral activities expressed inP. pastoriswere higher than those expressed inE. coliin the same cell line.
Should your lips be zipped? How therapist self‐disclosure and non‐disclosure affects clients
Authors: Hanson Jean 
Published: April 2006

AbstractIs therapist self‐disclosure a therapeutic technique or a therapeutic mistake? Is it useful? Is it ethical? This study attempts to address this controversy among therapeutic modalities by asking clients about their perceptions of self‐disclosure and non‐disclosure. Eighteen people (16 women, two men), currently in therapy in two Canadian cities, generated 157 incidents of both disclosure and non‐disclosure. The incidents were first coded as helpful or unhelpful. Cross‐tabulation of the results showed that disclosures were more than twice as likely to be experienced as helpful; non‐disclosures were twice as likely to be unhelpful (χ2 (3, N=157) = 14.439, p≤0.002). One‐quarter of these incidents was coded by two independent raters; inter‐rater reliability was high (Pearson corr. ranged from 0.755 to 1.0, p≤0.01). The data was then sorted, using the Constant Comparison method, into themes, starting with, but not limited to, the themes suggested by the literature. The greatest single effect was on the therapeutic alliance, both positive and negative. Clients’ perceptions of helpful disclosures and non‐disclosures generally supported therapists’ rationales. There was also some evidence that when clients found disclosures unhelpful, the reasons also supported theoretical rationales against disclosing. Rather than simply supporting either position in the controversy, this study suggests that skill, or lack of it, was the intervening variable that affected the perceptions of both techniques. Further research on the effects of skill on both disclosure and non‐disclosure are warranted. This study has implications for both researchers and practitioners.
Baroreflex Failure: A Rare Complication of Carotid Paraganglioma Surgery
Authors: Maturo Stephen , Brennan Joseph 
Published: April 2006

AbstractMultiple head and neck paragangliomas are a rare occurrence. We report a patient with removal of bilateral carotid paragangliomas who subsequently developed baroreflex failure 1 month after surgery. The pathology and physiology of this presentation is extremely interesting because it exhibits the complex homeostatic mechanisms involved in the maintenance of steady‐state blood pressure. Although rare, it is important to be aware of baroreflex failure and its variable course. Most postsurgical cases occur within days of surgery but, as this report demonstrates, hypertensive urgency can occur weeks to months after surgery; and if not recognized early, it can lead to disastrous postoperative complications such as stroke and myocardial infarction.
Intratympanic Dexamethasone Injection for Refractory Sudden Sensorineural Hearing Loss
Authors: Choung Yun‐Hoon , Park Keehyun , Shin You Ree , Cho Min Jung 
Published: April 2006

AbstractObjective: This case‐control study aimed to analyze the effect of intratympanic dexamethasone injection (ITDI) as a treatment option for patients with sudden sensorineural hearing loss (SSNHL) who were refractory to classic oral steroid treatment.Methods: Sixty‐six patients with SSNHL, who were refractory to a course of oral steroid therapy, were included in this study. We prospectively treated consecutive 33 patients (34 ears) with ITDI from August 2002 to January 2004. We then retrospectively collected data from age‐ and sex‐matched previous patients who did not take any more treatments after the initial regimen between March 2000 and July 2002. ITDI was performed in the supine position on four separate occasions over the course of 2 weeks. Hearing was assessed immediately before every injection and at 1 week after therapy. Hearing improvement was defined as more than 10 dB in pure‐tone average (PTA).Results: Hearing improvement was observed in 13 (39.4%) of 33 patients who underwent ITDI and in two (6.1%) of 33 patients in the control group. Five of 13 represented hearing improvement over than 20 dB in PTA, and 11 of 20 patients, who showed no improvement in PTA by ITDI, showed improvement over 10 dB in some frequencies. There were no definite prognostic factors between the patients who responded to ITDI and those who did not.Conclusion: ITDI may be a simple and effective therapy for patients with refractory SSNHL.
A Rare Differential Diagnosis in Dysphagia: Wound Botulism
Authors: Preuss Simon Florian , Veelken Florian , Galldiks Norbert , Klussmann Jens Peter , Neugebauer Peter , Nolden‐Hoverath Silke , Huttenbrink Karl‐Bernd 
Published: April 2006

AbstractThe incidence of wound botulism is increasing dramatically among intravenous drug users. Efficient intensive care and early treatment with antitoxin is essential to avoid lethal courses. The clinical picture of botulism is of descending, symmetric, flaccid paralysis. Early symptoms include cranial nerve palsies resulting in blurred vision and diplopia, difficulty in focusing, ptosis, facial weakness, dysphagia, dysphonia, and dysarthria. Because patients presenting with dysarthria and dysphagia will often be seen by an ear, nose and throat specialist initially, this rare but upcoming neurologic disease must be considered in the differential diagnoses.