bluuebunny/crossref_metadata_2025 huggingface dataset:
Tapered CPW‐fed printed monopole antenna
Authors: Liang Xian‐Ling , Zhong Shun‐Shi , Wang Wei
Published: April 2006

A compact coplanar rectangular monopole antenna fed by a tapered coplanar waveguide (CPW) feeder in the middle of a trapeziform ground plane is introduced. By using the tapered CPW feeder, the impedance bandwidth of the antenna is enhanced by a factor of about 1.7 times compared with a 50Ω CPW feeder. The measured ratio impedance bandwidth reaches about 10.7:1, covering frequencies from 0.76 to 8.15 GHz. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1242–1244, 2006; Published online in Wiley Inter‐Science (www.interscience.wiley.com). DOI 10.1002/mop.21666
Synthesis and realization of ultra‐wideband bandpass filters using the Z‐transform technique
Authors: Cai Peng , Ma Zhewang , Guan Xuehui , Anada Tetsuo , Hagiwara Gen
Published: April 2006

A modified synthesis theory using the Z‐transform technique is presented to design and realize ultra‐wideband (UWB) bandpass filters. Instead of using a system function based on lumped‐element prototypes, a transfer function based on distributed transmission lines is employed to synthesize the filter. In order to get sharp attenuations of the filter, shunt two‐section open‐circuited stubs are employed to produce transmission zeros. A 3° UWB filter is designed and implemented in the form of microstrip lines, and the measured characteristics show good agreement with the theoretical results. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1398–1401, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21677
1H HR‐MAS NMR of carotenoids in aqueous samples and raw vegetables
Authors: Miglietta M. L. , Lamanna R.
Published: April 2006

Carotenoids are linear C40 tetraterpenoid hydrocarbons and represent a wide category of natural pigments. They are components of the pigment system of chloroplasts and are involved in the primary light absorption and the photon canalization of photosynthesis. Moreover, they also behave as quenchers of singlet oxygen, protecting cells and organisms against lipid peroxidation.

Carotenoids have a strong lipophilic character and are usually analyzed in organic solvents. However, because of their biological activity, the characterization of these compounds in an aqueous environment or in the natural matrix is very important.

One of the most important dietary carotenoids is β‐carotene, which has been extensively studied both in vivo and in model systems, but because of the low concentration and strong interaction with the biological matrix, β‐carotene has never been observed by NMR in solid aqueous samples.

In the present work, a model system has been developed for the detection and identification of β‐carotene in solid aqueous samples by 1H HR‐MAS NMR. The efficiency of the model has led to the identification of β‐carotene in a raw vegetable matrix. Copyright © 2006 John Wiley & Sons, Ltd.
Smeared crack approach: back to the original track
Authors: Cervera M. , Chiumenti M.
Published: April 2006

This paper briefly reviews the formulations used over the last 40 years for the solution of problems involving tensile cracking, with both the discrete and the smeared crack approaches. The paper focuses on the smeared approach, identifying as its main drawbacks the observed mesh‐size and mesh‐bias spurious dependence when the method is applied ‘straightly’. A simple isotropic local damage constitutive model is considered, and the (exponential) softening modulus is regularized according to the material fracture energy and the element size. The continuum and discrete mechanical problems corresponding to both the weak discontinuity (smeared cracks) and the strong discontinuity (discrete cracks) approaches are analysed and the question of propagation of the strain localization band (crack) is identified as the main difficulty to be overcome in the numerical procedure. A tracking technique is used to ensure stability of the solution, attaining the necessary convergence properties of the corresponding discrete finite element formulation. Numerical examples show that the formulation derived is stable and remarkably robust. As a consequence, the results obtained do not suffer from spurious mesh‐size or mesh‐bias dependence, comparing very favourably with those obtained with other fracture and continuum mechanics approaches. Copyright © 2006 John Wiley & Sons, Ltd.
Optimized damage detection of steel plates from noisy impact test
Authors: Rus G. , Lee S. Y. , Chang S. Y. , Wooh S. C.
Published: April 2006

Model‐based non‐destructive evaluation proceeds measuring the response after an excitation on an accessible area of the structure. The basis for processing this information has been established in recent years as an iterative scheme that minimizes the discrepancy between this experimental measurement and sequence of measurement trials predicted by a numerical model. The unknown damage that minimizes this discrepancy by means of a cost functional is to be found. The damage location and size is quantified and sought by means of a well‐conditioned parametrization. The design of the magnitude to measure, its filtering for reducing noise effects and calibration, as well as the design of the cost functional and parametrization, determines the robustness of the search to combat noise and other uncertainty factors. These are key open issues to improve the sensitivity and identifiability during the information processing. Among them, a filter for the cost functional is proposed in this study for maximal sensitivity to the damage detection of steel plate under the impact loading. This filter is designed by means of a wavelet decomposition together with a selection of the measuring points, and the optimization criterion is built on an estimate of the probability of detection, using genetic algorithms. Numerical examples show that the use of the optimal filter allows to find damage of a magnitude several times smaller. Copyright © 2006 John Wiley & Sons, Ltd.
Adaptive computational methods for variational inequalities based on mixed formulations
Authors: Suttmeier F. T.
Published: April 2006

This work describes concepts for a posteriori error estimation and adaptive mesh design for finite element models where the solution is subjected to inequality constraints. These methods are developed here for several model problems. Based on these examples, unified frameworks are proposed, which provide a systematic way of adaptive error control for problems stated in form of variational inequalities. Copyright © 2006 John Wiley & Sons, Ltd.
Hyperostosis Frontalis Interna and sex identification of two skeletons from the Early Middle Ages necropolis of Vicenne‐Campochiaro (Molise, Italy)
Authors: Belcastro M. G. , Facchini F. , Rastelli E.
Published: April 2006

Lesions attributable to Hyperostosis Frontalis Interna (HFI) were examined in two skulls (from graves 100 and 113) from the Early Middle Ages necropolis of Vicenne‐Campochiaro (Molise, Italy). Both skeletons were of older individuals and it was difficult to sex them using standard anthropological methods. We discuss the sex identification of the skeletons in relation to the presence of HFI, as well as the usefulness of this pathological condition as a sex marker, underlining the importance of the relationship between palaeopathological and clinical‐forensic studies. Our study is a further contribution to the case history of HFI in osteoarchaeological material. Copyright © 2006 John Wiley & Sons, Ltd.
Proteomic analysis of a meningococcal outer membrane vesicle vaccine prepared from the group B strain NZ98/254
Authors: Vipond Caroline , Suker Janet , Jones Christopher , Tang Christoph , Feavers Ian M. , Wheeler Jun X.
Published: April 2006

In the absence of a suitable carbohydrate‐based vaccine, outer membrane vesicle (OMV) vaccines have been used to disrupt outbreaks of serogroup B meningococcal disease for more than 20 years. Proteomic technology provides physical methods with the potential to assess the composition and consistency of these complex vaccines. 2‐DE, combined with MS, were used to generate a proteome map of an OMV vaccine, developed to disrupt a long‐running outbreak of group B disease in New Zealand. Seventy four spots from the protein map were identified including the outer membrane protein (OMP) antigens: PorA, PorB, RmpM and OpcA. Protein identification indicates that, in addition to OMPs, OMV vaccines contain periplasmic, membrane‐associated and cytoplasmic proteins. 2‐D‐DIGE technology highlighted differences between preclinical development batches of vaccines from two different manufacturers.
Depletion efficiency and recovery of trace markers from a multiparameter immunodepletion column
Authors: Brand Joachim , Haslberger Tobias , Zolg Werner , Pestlin Gabriele , Palme Stefan
Published: April 2006

The selective removal of high‐abundance proteins is considered to be an important prerequisite for a sensitive proteome analysis in plasma. In this study, we examined the “multiaffinity removal system”, an immunoaffinity depletion column targeted against six plasma proteins. As determined by sandwich ELISA, the depletion rate for each target protein is >99% over 200 cycles of regeneration. Our data give evidence that two column antibodies are slowly inactivated during the repeated use of the column; however, the individual depletion rate meets the specification of the manufacturer. To estimate a potential loss of analytes after the immunodepletion, we performed spiking/recovery experiments with a selection of tumor markers at concentrations in the lower to medium ng/mL range. The average recovery of 9 out of 11 markers is 78%. A significant proportion of two other markers binds to the column. Based on the average marker recovery and a depletion of ˜;85% of the total protein we estimate a five‐fold enrichment of a potential biomarker by the use of this depletion column. We conclude that the selective depletion of plasma proteins by immunoaffinity chromatography is a valid strategy for the enrichment of potential biomarkers sought by proteomics methodologies.
Protein–protein interactions in actin–myosin binding and structural effects of R405Q mutation: A molecular dynamics study
Authors: Liu Yuemin , Scolari Megan , Im Wonpil , Woo Hyung‐June
Published: April 2006

Detailed residue‐wise interactions involved in the binding of myosin to actin in the rigor conformation without nucleotides have been examined using molecular dynamics simulations of the chicken skeletal myosin head complexed with two actin monomers, based on the cryo‐microscopic model of Holmes et al. (Nature 2003;425:423–427). The overall interaction is largely electrostatic in nature, because of the charged residues in the four loops surrounding the central primary binding site. The 50k/20k loop, disordered in crystal structures and in simulations of free myosin in solution, was found to be in a conformation stabilized with 1∼2 internal salt bridges. The cardiomyopathy loop forms 2∼3 interprotein salt bridges with actin monomers upon binding, whereas its Arg405 residue, the mutation site associated with the hypertrophic cardiomyopathy, forms a strong salt bridge with Glu605 in the neighboring helix away from actin in the actin‐bound myosin. The myopathy loop of the R405Q mutant maintains a high degree of two‐strand β‐sheet character when bound to actin with the corresponding salt bridges broken. Proteins 2006. © 2006 Wiley‐Liss, Inc.
Surface effects on magnetic properties of superparamagnetic magnetite nanoparticles
Authors: Köseoğlu Y. , Kavas H. , Aktaş and B.
Published: April 2006

Superparamagnetic nanoparticles of magnetite (Fe3O4) 2 nm in size were produced by a co‐precipitation method. Superparamagnetic resonance (SPR) spectra at room temperature show a broad line with a Landé g ‐factor, g eff ≈ 2. It was observed that, as the temperature decreased to 24 K, the apparent resonance field decreases while the line width considerably increases. We used a theoretical formalism based on a distribution of diameters or volumes of the nanoparticles. The nanoparticles behave as single magnetic domains with random orientations of magnetic moments which are subject to thermal fluctuations. A Landau–Lifshitz line shape function presents adequate results which are in good agreement with the experimental ones. A single set of parameters provides good fits to the spectra recorded at different temperatures. At high T the SPR line shape is governed by the core anisotropy and the thermal fluctuations. By decreasing the temperature, the magnetic susceptibility of shell spins increases. As a result of this, the surface spins produce an effective field on the core leading to a decrease of resonance field, B r. Also, the effective anisotropy increases as the shell spins begin to order. So, the results are interpreted by a simple model, in which each single‐domain nanoparticle is considered as a core–shell system, with magnetocrystalline anisotropy on the core and surface anisotropy on the shell. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural properties of quaternary InAlGaN MQW grown by plasma‐assisted MBE
Authors: Dimitrakopulos G. P. , Kioseoglou J. , Dimakis E. , Georgakilas A. , Nouet G. , Komninou Ph.
Published: April 2006

Quaternary In0.085Al0.285Ga0.63N/GaN multiple quantum wells (MQW) grown by plasma‐assisted molecular beam epitaxy are characterized by high resolution transmission electron microscopy (HRTEM), geometric phase analysis, and energy dispersive X‐ray (EDX) nano‐analysis. The MQW exhibit sharp well‐defined InAlGaN/GaN interfaces while the GaN/InAlGaN interfaces are more smeared. The InAlGaN quantum wells and the GaN barriers are lattice‐matched. Chemical distribution profiles are extracted from EDX line scans, obtained with a nanoprobe, which are compared to convoluted theoretical profiles, and are in good agreement with the HRTEM observations. Indium clustering occurs after prolonged observation under the electron beam. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of partial dislocations in wurtzite GaN using gradient elasticity
Authors: Kioseoglou J. , Dimitrakopulos G. P. , Komninou Ph. , Karakostas Th. , Konstantopoulos I. , Avlonitis M. , Aifantis E. C.
Published: April 2006

A non‐singular gradient elasticity solution for the dislocation self‐energy is employed and compared to previous results for 1/6〈20$ \bar 2 $3〉 partial dislocations fault in wurtzite GaN obtained by empirical potential calculations. Twenty‐four previously obtained stable dislocation cores, twelve for each GaN polarity, are considered. It is shown that the gradient elasticity solution can be fitted to the atomistic simulations with good agreement and can be employed to trace the energetically favourable cores without the requirement of defining a core radius. As a byproduct of this continuum approach, a dislocation self‐energy quantity is derived as a constant material property in terms of a gradient coefficient. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hydro‐, Halo‐ and Seleno‐Carbamoylation of Cyclic Enol Ethers and Dihydropyridines: New Mechanistic Pathways for Passerini‐ and Ugi‐type Multicomponent Reactions
Authors: Masdeu Carme , Gómez Elena , Williams Nana Aba , Lavilla Rodolfo
Published: April 2006

The interaction of electrophilic reagents (sulphonic acids, halogens and phenylselenyl chloride) with dihydropyridines and cyclic enol ethers generates reactive cationic intermediates which interact with isocyanides to afford α‐carbamoylated (β‐substituted) heterocycles after aqueous quenching, in Ugi‐ and Passerini‐type reactions. Some post‐condensation transformations (elimination and nucleophilic substitution reactions) on these compounds further expand the synthetic scope of these processes.
Meldrum's Acid in Multicomponent Reactions: Applications to Combinatorial and Diversity‐Oriented Synthesis
Authors: Gerencsér János , Dormán György , Darvas Ferenc
Published: April 2006

In a multicomponent reaction (MCR), one can create multiple new bonds in a single reaction from readily available starting materials; thus, MCRs are resource‐ and time‐effective and therefore economically favorable processes in diversity generation. In contrast, there are MCRs where a multifunctional building block is introduced instead of an additional diversity‐holding component, and these can be derivatized using very diverse reactions post‐synthetically leading to novel chemotypes. The synthetic applications of Meldrum's acid are focusing primarily on reactions where it is applied as an alternative for acyclic malonic esters. However, its highly acidic character broadened its applications and made it a very useful reagent for MCRs or more precisely in tandem or domino reactions. There are numerous examples reported for the use of the alkylidene conjugates of Meldrum's acid as dienophiles in hetero‐Diels–Alder reactions, as well as Michael acceptors. In most cases spontaneous or concomitant post‐synthetic derivatization increased its synthetic utility. This minireview gives a non‐exhaustive insight into MCRs involving Meldrum's acid, describing various applications in combinatorial and diversity‐oriented synthesis.
Navigating Social Class Roles in Community Research
Authors: Shpungin Elaine , Lyubansky Mikhail
Published: April 2006

This paper describes the first author's attempt to collect data in a homeless shelter without attending to her role in the social class hierarchy of the organization. The author's egalitarian approach towards the homeless clients, and her lack of involvement in “staff‐only” activities, transgress the social class norms within the organizational structure. While the author is successful in gaining the trust of the homeless clients, her approach alienates shelter staff, especially those in the higher echelons of the social hierarchy. The concepts of classism, world views, and Social Identity Theory, are utilized to discuss the dilemma faced by researchers who want to challenge, or work outside, a setting's status quo.
Geostatistical analysis of regional differences in stem taper form of Pinus densiflora in central Korea
Authors: Lee Woo‐Kyun , Biging Greg S. , Son Yowhan , Byun Woo‐Hyuk , Lee Kyeong‐Hak , Son Yeong‐Mo , Seo Jeong‐Ho
Published: April 2006

This study verified regional differences in the stem form of Pinus densiflora Sieb. et Zucc. (red pine) and identified the relationship between stem form and climatic factors in the central region of the Korean peninsula. Regional differences in stem form index at tree base (butt) and top stem section were found. Compared to the stem form in the eastern uplands, the stem form in the western lowlands could be characterized by a more conical butt section and more cylindrical middle and upper section. Through geostatistical analysis of kriging and spatial regression, several climatic factors proved to exert a meaningful influence on stem taper form. On the stem form at the butt section, the precipitation during the late growing season exerts statistically significant effects. High precipitation during the growing season in the western lowland and coastal region causes the stem form at the butt section to be more tapered. On the stem form at the middle and upper section, temperature and precipitation during the growing season, and wind during the late growing season have statistically meaningful influences. High temperature, precipitation, and wind during the growing season in the western lowland and coastal region jointly influence the stem form at the middle and upper sections which result in more cylindrical profiles. This study can be considered an initial investigation into the factors controlling stem form variability in the central region of the Korean peninsula. The results can be used to develop more accurate regional stem taper models needed for reasonable management of red pine stands in different regions.
Instability of bounded flows with elliptical streamlines
Authors: Gledzer E. B. , Ponomarev V. M.
Published: April 2006

In connection with the recent investigations of the instability of unbounded elliptical flows, some methods are discussed for the study of the instability of bounded flows. The stability of a ‘basic flow’ which is two-dimensional and rotating, with elliptical streamlines similar to the elliptical section of an experimentally studied cavity, is investigated in the framework of linear theory (for circular rotation, the flow discussed is stable). The regions of instability for three-dimensional disturbances are found in the plane of the parameters defining the geometry of the system (the height of the ellipsoidal cavity and the degree of ellipticity). It is shown that two types of instability exist, characterized by either monotone or oscillatory growth of the amplitudes of small disturbances.

The influence of the Coriolis force field on this instability mechanism is also studied. Rotation of the system as a whole changes the regions of instability in parameter space characterizing the geometry of the cavity and the wavenumbers of unstable disturbances. As a result, the Coriolis force may stabilize or destabilize the basic flow for a given geometry.

The instability of rotating density-stratified flow with elliptical streamlines is also considered.
A new modelling of cavitating flows: a numerical study of unsteady cavitation on a hydrofoil section
Authors: Kubota Akihiro , Kato Hiroharu , Yamaguchi Hajime
Published: April 2006

A new cavity model that can explain the interaction between viscous effects including vortices and cavitation bubbles is presented in this study. This model, which is named a bubble two-phase flow (BTF) model, treats the inside and outside of a cavity as one continuum by regarding the cavity as a compressible viscous fluid whose density changes greatly. Navier–Stokes equations including cavitation bubble clusters are solved in finite-difference form by a time-marching scheme, where the growth and collapse of a bubble cluster is given by a modified Rayleigh's equation. Computation was made on a two-dimensional flow field around a hydrofoil NACA0015 at angles of attack of 8° and 20°. The Reynolds number was 3 × 105. The experiments were also performed at the same Reynolds number for comparison. The computed results by the BTF cavity model can express the feature of cloud-type cavitation shed from the trailing edge of the attached cavities when the angle of attack is 8°. It shows the mechanism of cavitation cloud generation and large-scale vortices. The boundary layer separates at the cavity leading edge. Then it rolls up and produces the cavitation cloud. In other words, the instability of the shear layer may produce the cavitation cloud. When the angle of attack is 20°, the flow was fully separated from the leading edge of the hydrofoil and vortex cavitation occurs in the separated region. The BTF cavity model can also express the generation of such vortex cavitation and the effect of cavitation nuclei in the uniform flow.
Lubricated pipelining: stability of core—annular flow. Part 5. Experiments and comparison with theory
Authors: Bai Runyuan , Chen Kangping , Joseph D. D.
Published: April 2006

Results are given for experiments on water-lubricated pipelining of 6.01 P cylinder oil in a vertical apparatus in up- and downflow in regimes of modest flow rates, less than 3 ft/s. Measured values of the flow rates, holdup ratios, pressure gradients and flow types are presented and compared with theoretical predictions based on ideal laminar flow and on the predictions of the linear theory of stability. New flow types, not achieved in horizontal flows, are observed: bamboo waves in upflow and corkscrew waves in downflow. Nearly perfect core–annular flows are observed in downflows and these are nearly optimally efficient with values close to the ideal. The holdup ratio in upflow and fast downflow is a constant independent of the value and the ratio of values of the flow rates of oil and water. A vanishing holdup ratio can be achieved by fluidizing a long lubricated column of oil in the downflow of water. The results of experiments are compared with computations from ideal theory for perfect core–annular flow and from the linear theory of stability. Satisfactory agreements are achieved for the celerity and diagnosis of flow type. The wave is shown to be nearly stationary, convected with the oil core in this oil and all oils of relatively high viscosity. These results are robust with respect to moderate changes in the values of viscosity and surface tension. The computed wavelengths are somewhat smaller than the average length of the bamboo waves which are observed. This is explained by stretching effects of buoyancy and lubrication forces induced by the wave. Other points of agreement and disagreement are reviewed.
Interaction of electrostatic and fluid dynamic fields in wire—plate electrostatic precipitators
Authors: Kallio G. A. , Stock D. E.
Published: April 2006

Gas flow through wire–plate electrostatic precipitators is influenced by a secondary flow of electrical origin known as electric wind. This phenomenon arises when significant momentum is transferred from corona-generated ions to the gas. Electric wind can produce turbulence and recirculation. This complex flow field was characterized in a simple, three-wire precipitator by flow visualization, electrostatic and fluid dynamic numerical modelling, and laser-Doppler anemometry (LDA).

Velocity of seeded smoke was measured by two-component LDA. Coulomb effects were regionally eliminated by performing measurements along symmetry axes where the electric field and streamwise velocity component were mutually perpendicular. Coulomb drift velocities were also estimated from field charging theory to allow interpretation of measured transverse velocities. For a low inlet velocity (0.5 m/s), mean flow recirculation was evident and turbulence intensities as high as 50 % were measured. Higher inlet velocities (1.0, 2.0 m/s) yielded no flow recirculation and lower turbulence levels that were polarity-dependent. Measured profiles of streamwise velocity showed that flow acceleration zones occurred upstream of each wire and also between wires near the collecting plate. The induced turbulence displayed significant inhomogeneity and anisotropy.

A combined finite-element, finite-difference electrostatic model was developed to yield ion density and electric field distributions within the precipitator. These predictions were used to incorporate an electric body force into a two-dimensional, turbulent fluid dynamic model based upon the k–ε formulation. The model predicted recirculating mean flow and turbulent diffusivities that were consistent with the smoke flow visualizations and LDA measurements.
Zero-Prandtl-number convection
Authors: Thual Olivier
Published: April 2006

The zero-Prandtl-number limit of the Oberbeck—Boussinesq equations is compared to small-Prandtl-number Rayleigh—Bénard convection through numerical simulations. Both no-slip and free-slip boundary conditions, imposed at the top and bottom of a small-aspect-ratio, horizontally periodic box are considered. A rich variety of regimes is observed as the Rayleigh number is increased: supercritical oscillatory instabilities for various values of the aspect ratios, competition between two-dimensional rolls, squares and hexagonal patterns, competition between travelling and standing waves, transition to chaos, and scalings laws for the first Rayleigh-number decade. This multiplicity of regimes can be attributed to the close interaction between the stationary and oscillatory instabilities at zero Prandtl number.
Insoluble surfactant spreading on a thin viscous film: shock evolution and film rupture
Authors: Jensen O. E. , Grotberg J. B.
Published: April 2006

Lubrication theory and similarity methods are used to determine the spreading rate of a localized monolayer of insoluble surfactant on the surface of a thin viscous film, in the limit of weak capillarity and weak surface diffusion. If the total mass of surfactant increases as tα, then at early times, when spreading is driven predominantly by Marangoni forces, a planar (axisymmetric) region of surfactant is shown to spread as t(1 + α)/3 (t(1 + α)/4). A shock exists at the leading edge of the monolayer; asymptotic methods are used to show that a wavetrain due to capillary forces exists ahead of the shock at small times, but that after a finite time it is swamped by diffusive effects. For α < ½ (α < 1), the diffusive lengthscale at the shock grows faster than the length of the monolayer, ultimately destroying the shock; subsequently, spreading is driven by diffusion, and proceeds as t½. The asymptotic results are shown to be good approximations of numerical solutions of the governing partial differential equations in the appropriate limits. Additional forces are also considered: weak vertical gravity can also destroy the shock in finite time, while effects usually neglected from lubrication theory are important only early in spreading. Experiments have shown that the severe thinning of the film behind the shock can cause it to rupture: the dryout process is modelled by introducing van der Waals forces.
Linear-eddy modelling of turbulent transport. Part 7. Finite-rate chemistry and multi-stream mixing
Authors: Kerstein Alan R.
Published: April 2006

The linear-eddy turbulent mixing model, formulated to capture the distinct influences of turbulent convection and molecular transport on turbulent mixing of diffusive scalars, is applied to two mixing configurations in homogeneous flow: a scalar mixing layer and a two-line-source configuration. Finite-rate second-order chemical reactions are considered, as well as the limits of fast reaction and frozen flow. Computed results are compared to measurements in a reacting-scalar mixing layer and in a two-line-source configuration involving passive-scalar mixing. For each configuration, the adjustment of a single model parameter related to the turbulence integral scale yields computed results in good agreement with a variety of measured quantities. The results are interpreted with reference to a simpler model, based solely on large-scale flapping effects, that reproduces many qualitative trends. For three-stream mixing with finite-rate chemistry, a novel dependence of the reactant correlation coefficient on the chemical reaction rate is predicted.
Dynamics of singular vortices on a beta-plane
Authors: Reznik G. M.
Published: April 2006

A new singular-vortex theory is presented for geostrophic, beta-plane dynamics. The stream function of each vortex is proportional to the modified Bessel function Ko(pr), where p can be an arbitrary positive constant. If p−1 is equal to the Rossby deformation scale Rd, then the vortex is a point vortex; for p−1 ≠ Rd the relative vorticity of the vortex contains an additional logarithmic singularity. Owing to the β-effect, the redistribution of the background potential vorticity produced by the vortices generates a regular field in addition to the velocity field induced by the vortices themselves. Equations governing the joint evolution of singular vortices and the regular field are derived. A new invariant of the motion is found for this system. If the vortex amplitudes and coordinates are set in a particular way then the regular field is zero, and the vortices form a system moving along latitude circles at a constant speed lying outside the range of the phase velocity of linear Rossby waves. Each of the systems is a discrete two-dimensional Rossby soliton and, vice versa, any distributed Rossby soliton is a superposition of the singular vortices concentrated in the interior region of the soliton. An individual singular vortex is studied for times when Rossby wave radiation can be neglected. Such a vortex produces a complicated spiral-form regular flow which consists of two dipoles with mutually perpendicular axes. The dipoles push the vortex westward and along the meridian (cyclones move northward, and anticyclones move southward). The vortex velocity and trajectory are calculated and applications to oceanic and atmospheric eddies are given.
Numerical studies of natural transition in a decelerating boundary layer
Authors: Yang Kyung-Soo , Spalart Philippe R. , Ferziger Joel H.
Published: April 2006

Laminar—turbulent transition in the decelerating boundary layer of Gad-el-Hak et al. (1984) is studied by solving the incompressible, time-dependent, three-dimensional Navier—Stokes equations numerically. The temporal and spatial evolution of the experimental flow structures is approximated with spatial periodicity and temporal evolution while maintaining mean-velocity profiles appropriate to the spatially-developing flow. Other than the mean flow, the initial flow fields include only small-amplitude white random noise. This and the large streamwise and spanwise dimensions of the numerical domain allow unstable waves to be selected by the dynamics, instead of being imposed arbitrarily as in previous numerical studies. In that sense, the transition is natural. In the early stages of transition, two-dimensional and slightly oblique waves grow rapidly owing to inflexional instability. Their subsequent nonlinear interactions trigger the breakdown and create a pattern of Λ vortices. The patterns of Λ vortices are more irregular than those found in ribbon-induced transition. The tips of the Λ vortices are rarely aligned with the flow direction, and they appear in local patches, consistent with the experimental visualizations of Gad-el-Hak et al. A simple model based on the interference of multiple modes of instability accounts for these features, but the specific pattern of Λ vortices depends on the random content of the initial flow field. A simulation of the later stages of transition is performed with higher numerical resolution, showing that the ‘naturally-born’ Λ vortices undergo breakdown processes similar to those of their ribbon-induced counterparts.
Impingement of an axisymmetric jet on unheated and heated flat plates
Authors: Özdemir İ. Bedii , Whitelaw J. H.
Published: April 2006

The aerodynamic and thermal aspects of the wall jet flow, formed after angled impingement of an axisymmetric jet, have been studied with emphasis on the large-scale transport of the passive scalar by the spatially coherent structures. Time-averaged and instantaneous structures of the turbulent flow were examined by visualization and local measurements of a jet arrangement with an impingement angle between the jet axis and the surface normal of 20°, a nozzle-to-plate distance to nozzle exit diameter ratio of 22, and a nozzle exit Reynolds number of 1.3 × 104.

The results show that the oblique impingement introduced vertical velocities so that boundary-layer approximations were inapplicable and led to the distribution of the time-averaged properties of the velocity and temperature field with strong azimuthal dependence, which increased gradually with angle of impingement to 40° where a sudden change of the orientation of the contours of surface pressure and temperature took place. It also led to instantaneous, spatially coherent structures which were most pronounced at an angle of 20°. These structures improved the large-scale transport of the passive scalar but, owing to the extreme regularity of their path, also led to an inactive zone near the vortex centre.

The inner region of the decelerating wall jet exhibited a momentum equilibrium layer extending to the point of radial velocity maximum and the intercept of the linear region of the semilogarithmic wall law varied in the local streamwise direction as for turbulent flows over rough walls with adverse pressure gradient. The thermal equilibrium layer had an invariant functional form but extended far beyond the point of maximum velocity.
Gravity-capillary solitary waves in water of infinite depth and related free-surface flows
Authors: Vanden-Broeck Jean-Marc , Dias Frédéric
Published: April 2006

Two-dimensional free-surface flows due to a pressure distribution moving at a constant velocity U at the surface of a fluid of infinite depth are considered. Both gravity g and surface tension T are included in the dynamic boundary condition. The velocity U is assumed to be smaller than (4gT/ρ)¼, so that there are no waves in the far field. Here ρ is the density of the fluid. The problem is solved numerically by a boundary integral equation technique. It is shown that for some values of U, four different flows are possible. Three of these flows are interpreted as perturbations of solitary waves in water of infinite depth. It is found that both elevation and depression solitary waves are possible in water of infinite depth. The numerical results for depression waves confirm and extend the solutions previously computed by Longuet-Higgins (1989).
Compressible magnetoconvection in oblique fields: linearized theory and simple nonlinear models
Authors: Matthews P. C. , Hurlburt N. E. , Proctor M. R. E. , Brownjohn D. P.
Published: April 2006

The linear stability of a layer of compressible fluid, permeated by an oblique magnetic field, is discussed. It is shown that regardless of the system parameters, all bifurcations generically lead to travelling waves. Wave speeds and direction of the wave propagation are investigated. Symmetry arguments are used to show that when the field is almost vertical, waves with a wave vector aligned with the tilt are preferred over those with a wave vector perpendicular to the tilt. The nonlinear development of the travelling waves is explored using simple model equations.
Second-order wave diffraction by a vertical cylinder
Authors: Chau F. P. , Taylor R. Eatock
Published: April 2006

The main difficulty in second-order diffraction analysis stems from the contribution of the second-order potential, which obeys an inhomogeneous free-surface boundary condition. In some applications it is sufficient to know the second-order hydro-dynamic force, which can be calculated without explicitly evaluating this second-order potential. This technique cannot however be used for calculating other quantities such as the hydrodynamic pressure at any point, the sectional force and bending moment in the cylinder or the free-surface elevation due to the second-order effects. This paper provides a detailed analysis of the second-order diffraction problem of a uniform vertical circular cylinder in regular waves. This furnishes results not only on the cylinder surface, but also on the free surface, and in principle in the fluid domain surrounding the body. The analysis may help to throw some light on the physical interpretation of the second-order theory and its mathematical description. Moreover, this information is intended to complement the development of general numerical methods for arbitrary bodies.
Some aspects of mixing in a stratified turbulent patch
Authors: Silva I. P. D. De , Fernando H. J. S.
Published: April 2006

Mixing in a turbulent patch, that was generated within a linearly stratified fluid of buoyancy frequency No, was studied experimentally. The turbulence within the patch was induced by sustained oscillations of a mono-planar grid. Grid oscillations produced a local turbulent region, which initially grows rapidly as in a non-stratified fluid and then assumes a quasi-stationary thickness (Lp)c when the stratification inhibits its vertical growth at a time Not ≈ 4. The growth beyond (Lp)c occurs slowly via breaking of interfacial waves at the entrainment interface. As mixing proceeds, the buoyancy frequency within the patch N decreases. The time evolution of N, the buoyancy lengthscale, the Thorpe lengthscale, the maximum Thorpe displacement, the overturning lengthscale and the available potential energy fluctuations were measured and their relationships were investigated. Various aspects of the wave radiation from the patch to the outer stratified layer, the trapping of interfacial waves at the entrainment interface, and the effects of grid parameters on the evolution of the patch were also studied.
An unsteady wake-source model for flow past an oscillating circular cylinder and its implications for Morison's equation
Authors: Chew Y. T. , Low H. T. , Wong S. C. , Tan K. T.
Published: April 2006

A potential-flow modelling of flow past an oscillating circular cylinder with separated wake is developed here based on Parkinson & Jandali's (1970) wake-source model for steady flow. The phase-averaged pressure distributions, the in-line force coefficients, as well as the drag and added-mass coefficients, for an in-line oscillating circular cylinder in a steady free-stream flow are computed using the present ‘unsteady wake-source model’. The results show that Morison's equation is in some cases a satisfactory model in the study of unsteady bluff-body aerodynamics.

The two-dimensional incompressible potential-flow model simulates the effect of flow separation in unsteady flow by placing surface sources, with time-dependent strength and angular positions on the rear wetted surface of the body, and downstream sinks to form a closed wake model in the transformed plane. The unsteady Bernoulli equation is used to obtain the time-dependent pressure distributions over the front wetted surface, from which the in-line force coefficients are obtained through integration.

The in-line force equation obtained from the present model is shown to be comprised of an uncoupled drag term and inertia terms. The corresponding hydrodynamie coefficients obtained for the case of oscillatory flow are also more realistic than those obtained in a potential-flow calculation without flow separation which gives a drag coefficient of zero and a constant inertia coefficient of 2.0. The in-line force equation is reduced to the familiar Morison's equation with some simplifications and thus provides some support to the much criticized Morison's equation in the study of unsteady separated flow.

Another interesting feature of the present model is that it enables the calculation of instantaneous drag and inertia coefficients which have not been successfully obtained previously. In the cases considered here, the variations of drag and inertia coefficients over a cycle are shown to be small and thus the Morison's equation using mean coefficients is shown to predict the in-line forces rather precisely.

The present model was compared with experimental measurements obtained by oscillating a 0.1 m diameter circular cylinder along the direction of free-stream flow. The pressure distributions and in-line force coefficients agree well with the experimental measurements for velocity ratio rω/U∞ up to 0.25, reduced velocity U∞T/d down to 50 and Keulegan—Carpenter number 2πr/d up to 17, where r, ω, T, U∞ and d are the amplitude of oscillation, angular frequency, period of oscillation, free-stream velocity and diameter of the cylinder respectively. The computed drag and inertia coefficients also agree well with those obtained experimentally by previous investigators.
Capillary rollers and bores
Authors: Longuet-Higgins Michael S.
Published: April 2006

At any free surface at which the tangential stress τns vanishes there must be a surface vorticity ω = −2κq, where κ is the curvature and q the tangential velocity. In a surface wave on water, this condition produces a (Stokes) boundary layer with thickness of order δ = (2ν/σ)½, where ν is the kinemetic viscosity and σ the radian frequency of the wave. To first order in the wave steepness parameter ak, the vorticity remains within the boundary layer, but at second order some escapes through the Stokes layer. The mean vorticity $\overline{\omega}$ at the outer edge of the Stokes layer is of order 2(ak)2σ, twice the mean vorticity generated at the free surface.

These results are applied to steep capillary waves, particularly the parasitic capillaries often seen on the forward face of short gravity waves. Because of the high value of σ for the capillaries, the vorticity they generate is much larger than that generated by the gravity wave itself. Hence the capillaries contribute significantly to the vortex (roller) often found at the crest of short gravity waves, when capillaries are present. It is argued that the crest roller and the capillaries form a cooperative system, a ‘capillary roller’ in which each supports the other, with the aid of surface tension and viscosity. Energy is supplied by the gravity wave.

A capillary roller is one instance of a more general phenomenon: a ‘capillary bore’, which is a noticeable feature of many disturbed water surfaces.
Tollmien—Schlichting wave/Dean vortex interactions in curved channel flow
Authors: Singer Bart A. , Zang Thomas A.
Published: April 2006

Evidence from direct numerical simulations and from a recent weakly nonlinear theory is presented which shows that the weakly nonlinear results of Daudpota, Hall & Zang (1988) make incorrect predictions for the influence of the Tollmien–Schlichting wave on the Dean vortex.
Mixing by chaotic advection in a class of spatially periodic flows
Authors: Ryrie Susan C.
Published: April 2006

The paths followed by individual fluid particles can be extremely complicated even in smooth laminar flows. Such chaotic advection causes mixing of the fluid. This phenomenon is studied analytically for a class of spatially periodic flows comprising a basic flow of two-dimensional (or axisymmetric) counter-rotating vortices in a layer of fluid, and modulated by a perturbation which is periodic in time and/or space. Examples of this type of flow include Bénard convection just above the point of instability of two-dimensional roll cells, and Taylor vortex flow between concentric rotating cylinders. The transport of chaotically advected particles is modelled as a Markov process. This predicts diffusion-like mixing, and provides an expression for the diffusion coefficient. This expression explains some features of experimental results reported by Solomon & Gollub (1988): its accuracy is investigated through a detailed comparison with numerical results from a model of wavy Taylor vortex flow. The approximations used in the analysis are equivalent to those used to obtain the quasi-linear result for diffusion in the standard map.
The thermal bar
Authors: Zilitinkevich S. S. , Kreiman K. D. , Terzhevik A. Yu.
Published: April 2006

A simple theoretical model of the thermal bar is derived on the basis of heat budget equations for the following three zones of a wedge-shaped water basin warmed from above: (i) stably stratified shallow warm-water zone; (ii) vicinity of the bar; (iii) convectively mixed deep cold zone. In contrast to the traditional approach, advective warming of the vicinity of the bar and associated facilitating of the thermal bar propagation are taken into account. Theoretical predictions are compared with the data of lacustrine and laboratory measurements taken from current literature. New laboratory experiments have been carried out to examine the laminar regime of the thermal bar.
Coupled convective and morphological instability in a simple model of the solidification of a binary alloy, including a shear flow
Authors: Forth S. A. , Wheeler A. A.
Published: April 2006

In this paper we provide a detailed description of the interaction of solutal convection and morphological instability in the presence of a model boundary-layer flow. We present a detailed investigation of the structure of the marginal surfaces in Rayleigh-number, Sekerka-number, Reynolds-number space associated with a linear stability analysis. We give mathematical arguments and physical mechanisms to explain the results and present a coherent description of this complicated situation. We identify two new modes, one convective and one morphological. We show that the oscillatory so-called ‘mixed’ modes that result from the coupling of morphological and convective modes play a central role in the unfolding of the solution structure by the shear flow. This flow has the effect of decoupling the convective and morphological modes.