bluuebunny/crossref_metadata_2025 huggingface dataset:
Time‐resolved photoacoustic calorimetry as a tool to determine rate constants of hydrogen‐abstraction reactions
Authors: Nunes Paulo M. , Correia Catarina F. , Borges Dos Santos Rui M. , Martinho Simões José A.
Published: April 2006

The hydrogen‐abstraction reaction from phenol by tert‐butoxyl radical was used to test time‐resolved photoacoustic calorimetry (TR‐PAC) as a method to obtain kinetic data. Absolute rate constants for this reaction were determined in benzene and in the 298–312 K temperature range, using a temperature‐controlled photoacoustic calorimeter, yielding an average value of 3.5 × 108 M−1 s−1. This is in good agreement with the literature results obtained by laser flash photolysis (LFP). Kinetic solvent effects (KSE) in the same reaction were also studied using acetonitrile, carbon tetrachloride, and ethyl acetate as solvents. The results obtained by TR‐PAC are close to those derived by LFP (using the cumyloxyl radical as the abstracting species) and follow the expected trend based on the KSE. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 357–363, 2006
Radial point interpolation based finite difference method for mechanics problems
Authors: Liu G. R. , Zhang Jian , Li Hua , Lam K. Y. , Kee Bernard B. T.
Published: April 2006

A radial point interpolation based finite difference method (RFDM) is proposed in this paper. In this novel method, radial point interpolation using local irregular nodes is used together with the conventional finite difference procedure to achieve both the adaptivity to irregular domain and the stability in the solution that is often encountered in the collocation methods. A least‐square technique is adopted, which leads to a system matrix with good properties such as symmetry and positive definiteness. Several numerical examples are presented to demonstrate the accuracy and stability of the RFDM for problems with complex shapes and regular and extremely irregular nodes. The results are examined in detail in comparison with other numerical approaches such as the radial point collocation method that uses local nodes, conventional finite difference and finite element methods. Copyright © 2006 John Wiley & Sons, Ltd.
Long‐term remission of children with relapsed and secondary anaplastic large cell non‐Hodgkin lymphoma (ALCL) following treatment with pulsed dexamethasone and low dose etoposide
Authors: Stockklausner Clemens , Behnisch Wolfgang , Mechtersheimer Gunhild , Möller Peter , Kulozik Andreas E.
Published: April 2006

Anaplastic large cell lymphoma (ALCL) accounts for approximately 15% of childhood NHL. Relapsed ALCL represents a formidable challenge because outcome is poor despite the use of high‐dose chemotherapy regimens. We report two patients with relapsed T‐type and 0‐type ALCL who achieved long‐term 3rd and 4th remissions with 4‐weekly oral dexamethasone (DEX) and etoposide pulses for 2 years. This regimen also induced and maintained remission in a third patient with Nijmegen breakage syndrome (NBS) with secondary T‐type ALCL. These patients demonstrate that low‐intensity oral chemotherapy can induce long‐term remissions and offer a curative perspective in refractory, relapsed and secondary ALCL. Pediatr Blood Cancer 2008;50:126–129. © 2006 Wiley‐Liss, Inc.
Role of chemotherapy resistance genes in outcome of neuroblastoma
Authors: de Cremoux Patricia , Jourdan‐Da‐Silva Nathalie , Couturier Jérôme , Tran‐Perennou Carine , Schleiermacher Gudrun , Fehlbaum Pascale , Doz François , Mosseri Véronique , Delattre Olivier , Klijanienko Jerzy , Vielh Philippe , Michon Jean
Published: April 2006

Background

Neuroblastoma is a heterogeneous pediatric disease. Most patients with localized disease usually have a favorable prognosis, but patients with advanced disease have a poor prognosis despite combination chemotherapy. Treatment failure may be attributable to resistance to cytotoxic drugs.

Procedure

Using quantitative RT‐PCR, we investigated the clinical significance of the level of mRNA expression of multidrug resistance genes (MDR1, MRP1, MRP5, LRP) in a series of 29 advanced neuroblastoma samples.

Results

At the end of induction chemotherapy, 48% of patients achieved a clinical complete response, 28% achieved a partial response or stable disease, and 24% presented progressive disease. MDR1 mRNA overexpression (i.e., mRNA level >2 copies of MDR1 gene) was observed in 74% of samples, and MRP1, MRP5, LRP overexpression was observed less frequently (30, 33, and 33% of samples, respectively). None of these parameters were predictive of response, relapse, or survival. However, clinical response to treatment was highly predictive of relapse‐free survival and overall survival.

Conclusions

High expression of these multidrug resistance genes in advanced neuroblastoma is not the main parameter of response to cytotoxic drugs; clinical response to treatment remains the most important parameter in predicting the prognosis of patients with advanced neuroblastoma, until other relevant laboratory parameters have been identified. Pediatr Blood Cancer 2007;48:311–317. © 2006 Wiley‐Liss, Inc.
Individual and simultaneous swelling of amphiphilic conetworks in water and n‐heptane
Authors: He Chunju , Erdodi G. , Kennedy J. P.
Published: April 2006

A series of amphiphilic conetworks of different compositions comprising poly(ethylene glycol) and poly(dimethylsiloxane) nanodomains were made, and their cocontinuity was characterized via separate swelling in water and n‐heptane and simultaneous swelling in water/n‐heptane mixtures. The extent and rate of swelling were determined and analyzed. The swelling of the cocontinuous hydrophilic poly(ethylene glycol) and hydrophobic poly(dimethylsiloxane) domains progressed independently of each other, and morphological changes, which occurred during swelling, influenced the rate of swelling. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1474–1481, 2006
Black holes and rings of minimal 5‐dim. supergravity
Authors: Behrndt K.
Published: April 2006

In this talk, I will summarize recent developments in 5‐dimensional supergravity. This includes a discussion about black ring solutions, we will see how one can construct regular (bubbling) solutions with the same charges as black holes and finally will explore the close relationship between 4‐ and 5‐dimensional supersymmetric stationary solutions.
New results for AdS/CFT and beyond
Authors: Bertolini M. , Bigazzi F. , Cotrone A.L.
Published: April 2006

We report on some recent results within the string/gauge theory correspondence, both in the conformal and in the non conformal cases, for a recently found class of 𝒩 = 1 dual pairs. These results provide the first cross check of AdS/CFT and field theory techniques like a‐maximization. Moreover, they furnish new examples of cascading gauge theories and the first instance of 4d dynamical supersymmetry breaking embedded in the correspondence.
Instantons on D7 brane probes and AdS/CFT with flavour
Authors: Apreda R. , Erdmenger J. , Evans N. , Große J. , Guralnik Z.
Published: April 2006

Recent work on adding flavour to the generalized AdS/CFT correspondence is reviewed. In particular, we consider instanton configurations on two coincident D7 brane probes. These are matched to the Higgs branch of the dual field theory. In AdS5 × S5, the instanton generates a flow of the meson spectrum. For non‐supersymmetric gravity backgrounds, the Higgs branch is lifted by a potential with non‐trivial physical implications. Based on talk given by J. Erdmenger.
Standard model statistics of a type II orientifold
Authors: Gmeiner F.
Published: April 2006

We analyse four‐dimensional, supersymmetric intersecting D‐brane models in a toroidal orientifold background from a statistical perspective. The distribution and correlation of observables, like gauge groups and couplings, are discussed. We focus on models with a Standard Model‐like gauge sector, derive frequency distributions for their occurence and analyse the properties of the hidden sector.
Partition function of dyonic black holes in N = 4 string theory
Authors: Käppeli J.
Published: April 2006

The dominant contribution to the semicanonical partition function of dyonic black holes of N = 4 string theory is computed for generic charges, generalizing recent results of Shih and Yin. The result is compared to the black hole free energy obtained from the conjectured relation to topological strings. If certain perturbative corrections are included agreement is found to subleading order. These corrections modify the conjectured relation and implement covariance with respect to electric‐magnetic duality transformations.
Continuous families of conformal field theories from string theory
Authors: Mateos T.
Published: April 2006

We discuss the interplay between field theories and string theory in the quest for new fixed points of the renormalization group. First, we use the recent ideas of Lunin and Maldacena (LM) to make new predictions about the so‐called γ‐deformation of 𝒩 = 4 by taking a Penrose limit which leads to a solvable string theory background. We then extend the LM construction to deal with three dimensional field theories, we study the supersymmetry preservation of the γ‐deformed backgrounds, and we obtain the lagrangian deformations of the corresponding dual field theories.
Renormalization‐group flows and charge transmutation in string theory
Authors: Orlando D. , Petropoulos P.M. , Sfetsos K.
Published: April 2006

We analyze the behaviour of heterotic squashed‐Wess–Zumino–Witten backgrounds under renormalization‐group flow. The flows we consider are driven by perturbation creating extra gauge fluxes. We show how the conformal point acts as an attractor from both the target‐space and world‐sheet points of view. We also address the question of instabilities created by the presence of closed time‐like curves in string backgrounds.
Non‐critical string duals of four‐dimensional CFTs with fundamental matter
Authors: Bigazzi F. , Casero R. , Cotrone A.L. , Paredes A.
Published: April 2006

The two‐derivative approximation to non‐critical strings is used as a qualitative tool to find solutions dual to four dimensional CFTs with matter in the fundamental. Two solutions are discussed: an $AdS_5 \times \tilde{S}^3$, which is dual to an 𝒩 = 1 SCFT only for a ratio of ${{N_f}\over{N_c}}$ and an AdS5 which is proposed to be dual to 𝒩 = 0 QCD in the conformal window. All solutions have curvatures of the order of the string scale. This contribution is based on [1].
Marginal deformations of tree‐level 𝒩 = 4 SYM from twistor string theory
Authors: Kulaxizi M. , Zoubos K.
Published: April 2006

The topological B–model with target the supertwistor space ℂP3|4 is known to describe perturbative amplitudes of 𝒩 = 4 Super Yang–Mills theory. We review the extension of this correspondence to the superconformal gauge theories that arise as marginal deformations of 𝒩 = 4 by considering the effects of turning on a certain closed string background, which results in non–anticommutativity in the fermionic directions of ℂP3|4. We generalise the twistor string prescription for amplitudes to this case and illustrate it with some simple examples.
Fibrous long spacing type collagen fibrils have a hierarchical internal structure
Authors: Wen Chuck K. , Goh M. Cynthia
Published: April 2006

Nanodissection of single fibrous long spacing (FLS) type collagen fibrils by atomic force microscopy (AFM) reveals hierarchical internal structure: Fibrillar subcomponents with diameters of ∼ 10 to 20 nm were observed to be running parallel to the long axis of the fibril in which they are found. The fibrillar subcomponent displayed protrusions with characteristic ∼ 270 nm periodicity, such that protrusions on neighboring subfibrils were aligned in register. Hence, the banding pattern of mature FLS‐type collagen fibrils arises from the in‐register alignment of these fibrillar subcomponents. This hierarchical organization observed in FLS‐type collagen fibrils is different from that previously reported for native‐type collagen fibrils, displaying no supercoiling at the level of organization observed. Proteins 2006. © 2006 Wiley‐Liss, Inc.
Diffusion‐collision of foldons elucidates the kinetic effects of point mutations and suggests control strategies of the folding process of helical proteins
Authors: Capriotti Emidio , Compiani Mario
Published: April 2006

In this article we use mutation studies as a benchmark for a minimal model of the folding process of helical proteins. The model ascribes a pivotal role to the collisional dynamics of a few crucial residues (foldons) and predicts the folding rates by exploiting information drawn from the protein sequence. We show that our model rationalizes the effects of point mutations on the kinetics of folding. The folding times of two proteins and their mutants are predicted. Stability and location of foldons have a critical role as the determinants of protein folding. This allows us to elucidate two main mechanisms for the kinetic effects of mutations. First, it turns out that the mutations eliciting the most notable effects alter protein stability through stabilization or destabilization of the foldons. Secondly, the folding rate is affected via a modification of the foldon topology by those mutations that lead to the birth or death of foldons. The few mispredicted folding rates of some mutants hint at the limits of the current version of the folding model proposed in the present article. The performance of our folding model declines in case the mutated residues are subject to strong long‐range forces. That foldons are the critical targets of mutation studies has notable implications for design strategies and is of particular interest to address the issue of the kinetic regulation of single proteins in the general context of the overall dynamics of the interactome. Proteins 2006. © 2006 Wiley‐Liss, Inc.
Determination of bank erodibility for natural and anthropogenic bank materials using a model of lateral migration and observed erosion along the Willamette River, Oregon, USA
Authors: Wallick Jennifer Rose , Lancaster Stephen T. , Bolte John P.
Published: April 2006

Many large rivers flow through a variety of geologic materials. Within the span of several kilometres, bends may alternately flow against recently reworked sediments, older, more indurated sediments or highly resistant materials. As sediment size, cementation, and other properties strongly influence the erodibility of river banks, erosion rates and channel planform are likely to vary significantly along the length of large rivers. In order to assess the role of bank materials on bank erosion rates, we develop a method for detecting relative differences in erodibility between bank materials along large floodplains. By coupling historic patterns of channel change with a simple model of bank erodibility we are able to track relative changes in bank erodibility among time intervals and bank materials. We apply our analysis to the upper Willamette River, in northwestern Oregon for three time periods: 1850–1895, 1895–1932 and 1972–1995 and compute relative differences in bank erodibility for Holocene alluvium, partially cemented Pleistocene gravels, and revetments constructed in the 20th century. Although the Willamette is fundamentally an anastomosing river, we apply the model to single‐thread portions of the channel that evolved through lateral migration. Our simple model of bank erodibility reveals that for all three‐time periods, banks composed of Holocene alluvium are at least 2–5 times more erodible than banks composed of Pleistocene gravels. Revetment installed in the 20th century is highly resistant to erosion and is at least 10 times less erodible than Pleistocene gravels. Copyright © 2006 John Wiley & Sons, Ltd.
Stream-Based Specification of Mobile Systems
Authors: Grosu Radu , Stølen Ketil
Published: April 2006

This paper presents a formal specification technique for mobile systems based on input/output relations on streams. We consider networks of components communicating asynchronously via unbounded directed channels. Mobility is achieved by allowing the components to communicate channel ports. We distinguish between many-to-many and two variants of point-to-point communication. The communication paradigms are semantically underpinned by denotational models. The models are formulated in the context of timed non-deterministic data ow networks and presented in a stepwise fashion. The emphasis is on capturing the special kind of dynamic hiding characterising mobile systems. We demonstrate the proposed approach in a number of small examples.
Comparison of efficacy of Adeli suit and neurodevelopmental treatments in children with cerebral palsy
Authors: Bar‐Haim Simona , Harries Netta , Belokopytov Mark , Frank Alexander , Copeliovitch Leonel , Kaplanski Jacob , Lahat Eli
Published: April 2006

This study compared the efficacy of Adeli suit treatment (AST) with neurodevelopmental treatment (NDT) in children with cerebral palsy (CP). Twenty‐four children with CP, Levels II to IV according to the Gross Motor Function Classification System (GMFCS), were matched by age and functional status and randomly assigned to the AST or NDT treatment groups. In the AST group (n=12; eight males, four females; mean age 8.3y [SD 2.0]), six children had spastic/ataxic diplegia, one triplegia and five spastic/mixed quadriplegia. In the NDT group (n=12; nine males, three females; mean age 8.1y [SD 2.2]), five children had spastic diplegia and seven had spastic/mixed quadriplegia. Both groups were treated for 4 weeks (2 hours daily, 5 days per week, 20 sessions). To compare treatments, the Gross Motor Function Measure (GMFM‐66) and the mechanical efficiency index (EIHB) during stair‐climbing were measured at baseline, immediately after 1 month of treatment, and 10 months after baseline. The small but significant time effects for GMFM‐66 and EIHB that were noted after 1 month of both intensive physiotherapy courses were greater than expected from natural maturation of children with CP at this age. Improvements in motor skills and their retention 9 months after treatment were not significantly different between the two treatment modes. Post hoc analysis indicated a greater increase in EIHB after 1 month (p=0.16) and 10 months (p=0.004) in AST than that in NDT, predominantly in the children with higher motor function (GMFCS Levels II and III). The results suggest that AST might improve mechanical efficiency without a corresponding gain in gross motor skills, especially in children with higher levels of motor function.
Patterns of participation in recreational and leisure activities among children with complex physical disabilities
Authors: Law Mary , King Gillian , King Susanne , Kertoy Marilyn , Hurley Patricia , Rosenbaum Peter , Young Nancy , Hanna Steven
Published: April 2006

Children with physical disabilities are at increased risk of limitations to participation in everyday activities. This study describes research examining the participation of children in day‐to‐day formal and informal activities (excluding mandated academic schooling). Using the Children's Assessment of Participation and Enjoyment (CAPE) measure, data on participation patterns were collected from 427 children (229 males, 198 females; mean age 10y [SD 2y 4mo]; range 6–14y) with physical limitations and from their families. The primary types of physical disability in the sample included cerebral palsy, spina bifida, acquired brain injury, and musculoskeletal limitations. Findings indicate a broad range of diversity and intensity of participation, with proportionately greater involvement in informal rather than formal activities. Significant differences in participation and enjoyment were found between males and females, and for children more than 12 years of age. Children's participation was less diverse in families reporting lower income, single‐parent status, and lower respondent parent education. These findings provide a foundation for an improved understanding of the participation of children with physical disabilities, which can assist families and service providers in planning activities that fit with their child's preferences and ensure active participation.
Longitudinal use of the Child Health Questionnaire in childhood cerebral palsy
Authors: Vargus‐Adams Jilda
Published: April 2006

This study sought to describe change and stability in health‐related quality of life (HRQL) over time in a cross‐section of children with cerebral palsy (CP) using the Child Health Questionnaire (CHQ) through repeated surveys of the children's parents/caregivers. A total of 177 children with CP (98 males, 79 females); age range 3 to 18 years (mean age 8y 6mo, [SD 4y 2mo]; Gross Motor Function Classification System: Level I 40%, Level II 14%, Level III 14%, Level IV 16%, and Level V 17%) were enrolled as a convenience sample from the outpatient clinics at a tertiary‐care children's hospital. The main outcome measure was HRQL as determined by the CHQ — Parent Form 50. Parents reported reduced HRQL for their children with CP relative to norms for the CHQ. Although Role — Physical functioning (reflecting how physical impairment interferes with daily activity) declined with time, all other subscales of the CHQ were stable over the course of 1 year. CHQ scores were not measurably affected by common medical interventions. Children with CP have lower CHQ scores than other children that are, on average, stable over the course of 1 year.
Interobserver reliability of visual interpretation of electroencephalograms in children with newly diagnosed seizures
Authors: Stroink Hans , Schimsheimer Robbert‐Jan , de Weerd Al W , Geerts Ada T , Arts Willem F , MC Erasmus , Peeters Els A , Brouwer Oebele F , Peters A Boudewijn , van Donselaar Cees A
Published: April 2006

The reliability of visual interpretation of electroencephalograms (EEG) is of great importance in assessing the value of this diagnostic tool. We prospectively obtained 50 standard EEGs and 61 EEGs after partial sleep deprivation from 93 children (56 males, 37 females) with a mean age of 6 years 10 months (SE 5mo; range 4mo–15y 7mo) with one or more newly diagnosed, unprovoked seizures. Two clinical neurophysiologists independently classified the background pattern and the presence of epileptiform discharges or focal non‐epileptiform abnormalities of each EEG. The agreement was substantial for the interpretation of the EEG as normal or abnormal (kappa 0.66), almost perfect for the presence of epileptiform discharges (kappa 0.83), substantial for the occurrence of an abnormal background pattern (kappa 0.73), and moderate for the presence of focal non‐epileptiform discharges (kappa 0.54). In conclusion, the reliability of the visual interpretation of EEGs in children is almost perfect as regards the presence of epileptiform abnormalities, and moderate to substantial for the presence of other abnormalities.
Atypical clinical course in juvenile metachromatic leukodystrophy involving novel arylsulfatase A gene mutations
Authors: Anlar Banu , Waye John S , Eng Barry , Karli Kader
Published: April 2006

A male and female with juvenile metachromatic leukodystrophy (MLD) with unusual manifestations are presented, each involving a novel arylsulfatase A gene mutation. One patient demonstrated acute intermittent encephalopathic episodes for 1 year after having received the diagnosis of MLD at the age of 6 years. The other patient presented at the age of 5 years with acute hemiparesis, which was diagnosed as acute disseminated encephalomyelitis and resolved in 3 weeks. After 2 years of remission he started to show progressive neurological deterioration. The episodic manifestations in both patients were associated with acute, resolving cerebral lesions on magnetic resonance imaging accompanying or preceding the classical demyelinating lesions of MLD. The diagnosis of MLD was based on arylsulfatase A enzyme activity levels and genetic analysis, and after the exclusion of neurological conditions such as encephalitis, vasculopathy, or mitochondrial disorders. The pathogenesis of this previously undescribed finding in MLD is unknown but might be related to a susceptibility of myelin to acute damage.
Prolonged coexistence of transient and permanent circuitry elements in the developing cerebral cortex of fetuses and preterm infants
Authors: Kostović Ivica , Judaš Miloš
Published: April 2006

The aim of this paper is to evaluate correlative magnetic resonance imaging (MRI) and histological parameters of development of cortical afferents during pathfinding and target selection in transient fetal cerebral laminas in human fetuses and preterm infants. The transient fetal subplate zone, situated between the fetal white matter (i.e. intermediate zone) and the cortical plate, is the crucial laminar compartment for development of thalamocortical and corticocortical afferents. The prolonged coexistence of transient (endogenously active) and permanent (sensorydriven) circuitry within the transient fetal zones is a salient feature of the fetal and preterm cortex; this transient circuitry is the substrate of cerebral functions in preterm infants. Another transient aspect of organization of developing fibre pathways is the abundance of extracellular matrix and guidance molecules in periventricular crossroads of projection and corticocortical pathways. Both the subplate zone and periventricular crossroads are visible on MRI in vivo and in vitro. Hypoxic‐ischaemic lesions of periventricular crossroads are the substrate for motor, sensory, and cognitive deficits after focal periventricular leukomalacia (PVL). Lesions of distal portions of the white matter and the subplate zone are the substrate for diffuse PVL. The neuronal elements in transient fetal zones form a developmental potential for plasticity after perinatal cerebral lesions.
On the structure of hypersonic turbulent boundary layers
Authors: Owen F. K. , Horstman C. C.
Published: April 2006

Extensive hot-wire auto- and cross-correlation measurements obtained in a fully developed compressible turbulent boundary layer are presented. A tentative mechanism of turbulence production and growth in hypersonic flow suggested by these measurements is developed. This flow model is consistent with previous observations in incompressible flows. Detailed measurements of the mean properties of the hypersonic turbulent boundary layer are also presented and compared with results from various transformation and finite-difference prediction methods. It is shown that none of the theories predict all the properties of the hypersonic turbulent boundary layer and that additional measurements are needed to provide more adequate physics of turbulent processes for use in the various theories.
Axisymmetric rotating flow past a circular disk
Authors: Miles John W.
Published: April 2006

The steady, inviscid, axisymmetric, rotating flow past a circular disk in an unbounded liquid is determined on the hypothesis that all streamlines originate in a uniform flow far upstream of the body. The characteristic parameter for the flow is k = 2ωa/U, where ω and U are the angular and axial velocities of the basic flow and α is the radius of the disk. Forward separation is found to occur for k > k = 1.9, in agreement with observation (Orloff & Bossel 1971). The length of the upstream separation bubble is determined on the hypothesis that the previous solution remains valid for k > k, despite the existence of closed streamlines within the upstream separation bubble (which may, but do not necessarily, inva,lidate the solution). This length increases rapidly for k > 3, in qualitative agreement with observation. The hypothesis of unseparated flow implies a singularity at the rim of the disk, just as in potential flow. The strength of this singularity departs only slightly from its potential-flow value for 0 ≤ k ≤ 2, but increases rapidly with k for k > 3, which suggests that (quite apart from the difficulties implied by the existence of closed streamlines) the solution cannot remain valid for sufficiently large k.
The response of a turbulent boundary layer to a step change in surface roughness. Part 2. Rough-to-smooth
Authors: Antonia R. A. , Luxton R. E.
Published: April 2006

An experimental study of the structure of the internal layer which grows down-stream from a rough-to-smooth surface change shows it to be essentially different from that studied by Antonia & Luxton (1971 b) for the case of a smooth-to-rough perturbation. The rate of growth of the internal layer is less than that for the smooth-to-rough step and it appears that the more intense initial rough-wall flow dictates the rate of diffusion of the disturbance for a considerable distance. Inside the internal layer the mixing lengthIis increased relative to the equilibrium distributionI=KY.A turbulent energy budget shows that the advection is comparable with the production or dissipation, whilst there seems to be some diffusion of energy into the internal-layer region close to the wall. The boundary layer, as a whole, recovers much more slowly following a rough-to-smooth change than following a smooth-to-rough change, and at the last measuring station (16 boundary-layer thicknesses from the start of the smooth surface) the distributions of mean velocity and Reynolds shear stress are far from self-preserving.
Effects of the lower boundary on the head of a gravity current
Authors: Simpson John E.
Published: April 2006

Experimental measurements of the advancing head of a gravity current are described. The head, of depthdin mean cross-section and advancing at mean speedU, has an elevated nose whose mean heighthsatisfiesh/d= 0·61Re-0·23±0·01through the range 300 <Re< 10000 (Re=Ud/ν). Ashifting pattern of lobes and clefts ranges across the head, in which the mean lobe width$\overline{b}$is found experimentally to satisfy$\overline{b}/d = 7.4\,Re^{-0.39\pm 0.02}$. By moving the floor in the direction of the current, or by introducing a thin dense layer beneath it, the lobes and clefts can be suppressed and a purely two-dimensional flow obtained. It is concluded that the lower boundary plays an essential role in determining the substructure of the head and that this originates in convective instability as the head rides over less dense fluid.
Damping of weakly nonlinear shallow-water waves
Authors: Miles John W.
Published: April 2006

Boundary-layer damping of one-dimensional gravity waves of slowly varying amplitude a(t), characteristic wavenumber k, and characteristic frequency ω in water of depth d and kinematic viscosity v is calculated for a [Lt ] d, d [Lt ] 1/k and (2ν/ω)½ [Lt ] d. General results are given for the temporal evolution of the power spectral density determined by either a Fourier-integral (spatially aperiodic) or Fourier-series (spatially periodic) representation of the wave. Solitary and cnoidal waves are considered as examples. Keulegan's (1948) inverse-fourth-power decay for the solitary wave is recovered, and the numerical parameter therein is evaluated by reduction to a Riemann zeta function. A universal decay curve is obtained for the Stokes-scaled amplitude S = a/k2d3 of the cnoidal wave as a function of the boundary-layer-scaled time (νω)½t/d; the result is both more flexible and more compact than that obtained by Isaacson (1976). The decay is within 5% of that for a solitary wave (inverse fourth power) for S > 2 or that for an infinitesimal wave (exponential) for S < 2. An analytical approximation with a maximum error of less than 1% is obtained by joining an asymptotic approximation for S > 1 to the exponential approximation for S < 1.
Internal wave reflexion from a sinusoidally corrugated surface
Authors: Mied R. P. , Dugan J. P.
Published: April 2006

The reflexion of an internal gravity wave with stream function
\[
\psi = \exp\{i(kx + lz - \omega t)\}
\]
from a corrugated surface of the form z = a cos px is investigated using an extension of Rayleigh's method for an inviscid non-diffusive fluid. It is found that the method converges for many wall slopes ap and incoming-wave phase propagation incidence angles θ = tan−1l/k but that the appropriate series solution is only asymptotic in other cases. The accuracy of the calculations is assured by requiring that the solution satisfy the boundary condition at the wall using a least-squares error minimization technique. The accuracy is then verified through the conservation of energy flux. It is found that, as the surface slope is increased for constant θ, less energy appears in specular reflexions and more is either back-scattered or redistributed into other forward-scattered modes. As the horizontal internal wavelength is decreased to become comparable to the corrugation wavelength of the wall, substantially less energy appears in specular reflexion, but of the order of 95% of the incoming energy is specularly reflected for 30° < θ < 60° when the two wavelengths are equal. In contrast to this, it is found that the general level of the ratio of back-scattered to forward-scattered energy is reduced by O(10−3) to O(10−2) as the incident horizontal internal wavelength becomes smaller than the corrugation wavelength. The results are compared with the linear theory of Baines (1971); agreement is good for forward-scattered energy and excellent for the back-scattered flux when p ≥ k.
Couette flow for a gas with a discrete velocity distribution
Authors: Cabannes Henri
Published: April 2006

We consider a kinetic theory model of a gas, whose molecular velocities are restricted to a set of fourteen given vectors. For this model we study the Couette flow problem, the boundary conditions on the walls being the conditions of pure diffuse reflexion. The kinetic equations can be integrated by quadrature under the assumption that the walls have opposite velocities and equal temperatures. The presence on the walls of tangential velocities leads to the consequence that the velocity slip coefficient does not in general vanish when the Knudsen number goes to zero.

Considering the same problem again after the suppression of tangential velocities, we obtain formulae for the velocity and temperature slip coefficients which generalize results of Broadwell (1964b), and which agree qualitatively with experiments.
On the stability of the Stewartson layer
Authors: Hashimoto Kiyoshi
Published: April 2006

The stability of the Stewartson layer in a rotating incompressible fluid is investigated within the framework of a linear theory. The boundary-layer structure of the shear layer is correctly taken into account and the effect of viscous dissipation on the disturbance is included in the governing equations. The growth rate ωi of the disturbance is given as a function of the unified parameter mRo/(γ½), where m, an integer, is the azimuthal component of the wavenumber vector, γ the radius of the layer, Ro the Rossby number and E the Ekman number. Instability occurs when m Ro/(γ½) > 9·5. The time evolution of a growing disturbance is given schematically. Comparison of our results with the experiments by Hide & Titman shows good agreement.
The impingement of underexpanded axisymmetric jets on wedges
Authors: Lamont P. J. , Hunt B. L.
Published: April 2006

This paper reports an experimental investigation into the impingement of underexpanded axisymmetric jets on each of three wedges arranged symmetrically in the jets. Three jets were used; two were produced by a convergent-divergent nozzle of exit Mach number 2.2 which was operated at underexpansion ratios of 1·2 and 2, while the third jet was produced by a convergent nozzle operated at an underexpansion ratio of 4. The base widths of the wedges equalled the exit diameter of the convergent-divergent nozzle, their apex angles were 90°, 60° and 45° and they were situated within or just downstream of the first cell of each jet.

Detailed front-face pressure distributions were obtained for 15 different configurations. Shadowgraph photographs were taken of these and other cases. The results show a variety of possible flow patterns. The major factors determining which flow pattern occurs are the combination of the centre-line Mach number and wedge apex angle and the jet shock strength and position. It was found that observed shock intersections can be reconstructed by means of shock polars, but that a four-shock confluence will not always occur when it is possible according to the shock polars. In one case there is evidence of the existence of a β triple-shock confluence. An interesting and unusual flow involving a stagnation bubble was obtained when the wedges were situated downstream of the free-jet Mach disk.
A moving-wall boundary layer with reverse flow
Authors: Klemp J. B. , Acrivos Andreas
Published: April 2006

The problem of uniform flow past a flat plate whose surface has a constant velocity λU opposite in direction to that of the mainstream is considered for large values of the Reynolds number R. In a previous communication (Klemp & Acrivos 1972) it was shown that, if the region of reverse flow which is established next to the plate as a consequence of its motion is O(R−1/2) in thickness, the appropriate laminar boundary-layer equations have a solution provided λ ≤ 0·3541. Here the analysis is extended to the range λ > 0·3541, which cannot be treated using a conventional boundary-layer approach. Specifically, it is found that for λ > 0·3541 the flow consists of three overlapping domains: (a) the external uniform flow; (b) a conventional boundary layer with reverse flow for xs < x < 1, where xs, refers to the point of detachment of the ψ = 0 streamline and x = 1 is the trailing edge of the plate; and (c) an inviscid collision region in the neighbourhood of xs, having dimensions O(R−1/2) in both the streamwise and the normal direction, within which the reverse moving stream collides with the uniform flow, turns around and then proceeds downstream. It is established furthermore that xs = 0 for 0 ≤ λ ≤ 1 and that xs < 0 for λ > 1.

Also, detailed streamline patterns were obtained numerically for various λ's in the range of 0 ≤ λ ≤ 2 using a novel computational scheme which was found to be more efficient than that previously reported. Interestingly enough, the drag first decreased with λ, reached a minimum at λ = 0.3541, and then increased monotonically until, at λ = 2, it was found to have attained essentially the value predicted from the asymptotic λ → ∞ similarity solution available in the literature. Thus it is felt that the present numerical results plus the two similarity solutions for λ = 0 and for λ → ∞ fully describe the high-R steady flow for all non-negative values of λ.
Nonlinear Ekman-Hartmann layers and the flow outside
Authors: Chawla S. S.
Published: April 2006

We consider in this paper the hydromagnetic flow of a viscous, incompressible, electrically conducting fluid induced by the differential rotation of an insulating boundary. A uniform magnetic field parallel to the axis of rotation is applied at a large distance from the interface. The method of matched asymptotic expansions is employed to study the hydromagnetic coupling between different regions of fluid flow and the interior of the insulating boundary.
The stability of a meniscus joining a vertical rod to a bath of liquid
Authors: Pitts E.
Published: April 2006

A circular cylinder is held vertically and withdrawn from a large bath of liquid. When the horizontal end face of the cylinder rises above the mean undisturbed liquid level, an axially symmetrical meniscus is formed, which joins the cylinder at the circumference of the end. If the cylinder is further withdrawn, at a certain height the meniscus breaks. By means of the calculus of variations the condition for stability is derived in terms of the increase in height and the increase in the angle between the tangent to the meniscus and the face of the cylinder at the point where the meniscus joins it. The meniscus is unstable as long as these changes are of the same sign.
Double boundary layers in standing interfacial waves
Authors: Dore B. D.
Published: April 2006

The double-boundary-layer theory of Stuart (1963, 1966) and Riley (1965, 1967) is employed to investigate the mass transport velocity due to two-dimensional standing waves in a system comprising two homogeneous fluids of different densities and viscosities. The most important double-boundary-layer structure occurs in the neighbourhood of the oscillating interface, and the possible existence of jet-like motions is envisaged at nodal positions, owing to the nature of the mean flows in the layers. In practice, the magnitude of the mass transport velocity can be a significant fraction of that of the primary, oscillatory velocity.
A theory for wave-power absorption by oscillating bodies
Authors: Evans D. V.
Published: April 2006

A theory is given for predicting the absorption of the power in an incident sinusoidal wave train by means of a damped, oscillating, partly or completely submerged body. General expressions for the efficiency of wave absorption when the body oscillates in one or, in some cases, two modes are given. It is shown that 100% efficiency is possible in some cases. Curves describing the variation of efficiency and amplitude of the body with wavenumber for various bodies are presented.
Higher eigenstates in boundary-layer stability theory
Authors: Corner D. , Houston D. J. R. , Ross M. A. S.
Published: April 2006

Using the Orr-Sommerfeld equation with the wavenumber as the eigenvalue, a search for higher eigenstates in the stability theory of the Blasius boundary layer has revealed the existence of a number of viscous states in addition to the long established fundamental state. The viscous states are discrete, belong to two series, and are all heavily damped in space. Within the limits of the investigation the number of viscous states existing in the layer increases as the Reynolds number and the angular frequency of the perturbation increase. It is suggested that the viscous eigenstates may be responsible for the excitation of some boundary-layer disturbances by disturbances in the free stream.
An approximate theory for incompressible viscous flow past two-dimensional bluff bodies in the intermediate Reynolds number regime O(1) < Re < O(102)
Authors: Weinbaum Sheldon , Kolansky Michael S. , Gluckman Michael J. , Pfeffer Robert
Published: April 2006

A new approximate theory is proposed for treating the flow past smoothly contoured two-dimensional bluff bodies in the intermediate Reynolds number rangeO(1) <Re< 0(102), where the displacement effect of the thick viscous layer near the surface of the body is large and a steady laminar wake is present. The theory is based on a new pressure hypothesis which enables one to take account of the displacement interaction and centrifugal effects in thick viscous layers using conventional first-order boundary-layer equations. The basic question asked is how the wall pressure gradient in ordinary boundary -layer theory must be modified if the pressure gradient along the displacement surface using the Prandtl pressure hypothesis is to be equal to the pressure gradient along this surface using a higher-order approximation to the Navier-Stokes equation in which centrifugal forces are considered. The inclusion of the normal pressure field with displacement interaction is shown to be equivalent to stretching the streamwise body co-ordinate in first-order boundary-layer theory such that the streamwise pressure gradient as a function of distance along the original and displacement body surfaces are equal.

While the new theory is of a non-rigorous nature, it yields results for the location of separation and detailed surface pressure and vorticity distribution which are in remarkably good agreement with the large body of available numerical Navier-Stokes solutions. A novel feature of the new boundary-value problem is the development of a simple but accurate approximate method for determining the inviscid flow past an arbitrary two-dimensional displacement body with its wake.
The Rayleigh problem for a wavy wall
Authors: Shankar P. N. , Sinha U. N.
Published: April 2006

The problem of the flow generated in a viscous fluid by the impulsive motion of a wavy wall is treated as a perturbation about the known solution for a straight wall. It is shown that, while a unified treatment for high and low Reynolds numbers is possible in principle, the two limiting cases have to be treated separately in order to get results in closed form. It is also shown that a straightforward perturbation expansion in Reynolds number is not possible because the known solution is of exponential order in that parameter. At low Reynolds numbers the waviness of the wall quickly ceases to be of importance as the liquid is dragged along by the wall. At high Reynolds numbers on the other hand, the effects of viscosity are shown to be confined to a narrow layer close to the wall and the known potential sohtion emerges in time. The latter solution is a good illustration of the interaction between a viscous fluid field and its related inviscid field.
Spectral analogy between temperature and velocity fluctuations in a turbulent boundary layer
Authors: Fulachier L. , Dumas R.
Published: April 2006

Experiments were carried out in the turbulent boundary layer on a slightly heated plate in order to establish, mainly for the larger scales of motion, any analogy that may exist between the temperature and velocity fluctuations. With this goal in mind, the spectra and cospectra of the temperature and velocity fluctuations were measured. In particular, the cospectra were obtained by the ‘fluctuation-diagram method’. It soon became evident that the temperature spectrum, except very close to the wall, differs strongly from the spectrum of the longitudinal velocity component. At least for the lower frequency spectral range, which includes about 80% of the total variance, the experimental results support an analogy between the temperature spectrum and a new type of spectrum consisting of the sum of the spectra of the three velocity components weighted by their relative energy. This analogy was established throughout most of the boundary layer.
A note on the spreading rate and virtual origin of a plane turbulent jet
Authors: Kotsovinos Nikolas E.
Published: April 2006

The reported experimental coefficients describing the spreading rate and virtual origin of a plane turbulent jet exhibit substantial scatter. The hypothesis is made that the basic reason for these variations is that the growth of the jet is not linear on a large scale. Existing experimental results are used to support this hypothesis.
The mechanism of bubble detachment from a wall at zero and negative gravity
Authors: Malcotsis G.
Published: April 2006

An experiment has been carried out in which air bubbles were caused to grow isothermally at a vertical wall between two closely spaced horizontal plates. The experiment gives an approximate representation in two dimensions for the growth of a vapour bubble at a wall under some conditions of subcooled boiling in zero gravity. Although the effect of gravity was virtually eliminated in the experiment, it was found that a bubble could still detach itself from the wall, apparently owing to the effects of surface tension and inertia.

Also, bubbles were seen to detach from a wall despite the presence of a slight gravity force directed to oppose such detachment.
The spatial viscous instability of axisymmetric jets
Authors: Morris Philip J.
Published: April 2006

The stability of three axisymmetric jet profiles is reviewed. These profiles represent the development of an incompressible jet from a nearly top-hat profile to a fully developed jet profile. The disturbance equations for arbitrary mode number in a region of zero shear, which provide the boundary conditions for the numerical solution, are solved analytically through use of the disturbance vorticity equations. Numerical solutions for the spatial stability for the axisymmetric (n= 0) disturbance and the asymmetricn= l disturbance are presented. Previously published calculations of least stable modes are shown to be incorrectly interpreted and their actual mode types are given. The critical Reynolds number is found to increase as the profile varies from a top-hat to a fully developed jet form. Closed contours of constant amplification, which are unusual in free shear flows, are shown to exist for then= 1 disturbance in the fully developed jet region. A fluctuation energy balance is used to justify the occurrence of this destabilizing effect of decreasing Reynolds number.