bluuebunny/crossref_metadata_2025 huggingface dataset:
Linear stability of a cylindrical falling film
Authors: Solorio Francisco J. , Sen Mihir
Published: April 2006

The problem of a cylindrical falling film, descending vertically outside an infinitely long cylinder is considered. The linear stability of the fully developed flow is studied, first with a perturbation technique for small wavenumbers, and then by direct numerical computation. The numerical results are in agreement with other published values for the cylindrical jet and flat plate limits. The study shows that the cylindrical falling film is unstable for all Reynolds numbers, Weber numbers and radius ratios. Stability and amplification curves are calculated for different values of the parameters. With increasing curvature of the film the range of unstable wavenumbers and the wavenumber of the most amplified wave increase. For low curvature the wavenumber of the most amplified wave decreases with Reynolds number or Weber number, while for high curvatures it increases.
On the resonant nature of the breakdown of a laminar boundary layer
Authors: Kachanov Yu. S.
Published: April 2006

The first part of this paper (§2) briefly reviews the history of the idea of the resonant nature of laminar-boundary-layer breakdown. In the second part a new wave-resonance concept of the breakdown mechanism is proposed. The existing experimental data on the laminar boundary layer (and plane channel flow) breakdown are analysed from the viewpoint of this concept and are compared with the well-known local high-frequency secondary-instability concept. The results testify to the correctness of the proposed wave-resonant concept for the initial stages of breakdown, in particular for the K-regime of transition up to the spike formation and its doubling.

Within the framework of the wave-resonance concept, before constructing the corresponding theory, many important features of the disturbance development can be qualitatively explained and understood. Concerning the understanding of the spike appearance, the wave-resonance concept complements the local high-frequency secondary-instability one and represents by itself a new fruitful viewpoint on this phenomenon. The development of the wave-resonance concept and its application to the analysis of numerical and physical experiments, together with the construction on this basis of the corresponding theory, can give an essential impetus towards the better understanding of the breakdown nature.
Influence of viscosity on the capillary instability of a stretching jet
Authors: Frankel I. , Weihs D.
Published: April 2006

The hydrodynamic stability of a rapidly elongating, viscous liquid jet such as obtained in shaped charges is presented. The flow field depends on three characteristic timescales associated with the growth of perturbations (due essentially to the effect of the surface tension), the elongation of the jet, and the inward diffusion of vorticity from the free surface, respectively. The latter process introduces a time lag resulting in the current values of the free-surface perturbation and its time derivative being a function of their past history. Solutions of the integro-differential equation for the evolution of disturbances exhibit a novel dual role played by the viscosity: besides the traditional damping effect it is associated with a destabilizing mechanism in the elongating jet. The wavelength of maximum instability is also a function of time elapsed since the jet formation, longer wavelengths becoming dominant at later stages. Understanding of these instability processes can help in both promoting and delaying instability as required by specific applications.
Mean drift forces on arrays of bodies due to incident long waves
Authors: McIver P.
Published: April 2006

The scattering of long water waves by an array of bodies is investigated using the method of matched asymptotic expansions. Two particular geometries are considered: a group of vertical cylinders extending throughout the depth and a group of floating hemispheres. From these solutions, the low-frequency limit of the ratio of the mean drift force on a group of N bodies to that on a single body is calculated. For a wide range of circumstances this drift-force ratio is N2, which is in agreement with previous numerical work. Further drift-force enhancement is possible for certain configurations of vertical cylinders.
The runup of solitary waves
Authors: Synolakis Costas Emmanuel
Published: April 2006

This is a study of the runup of solitary waves on plane beaches. An approximate theory is presented for non-breaking waves and an asymptotic result is derived for the maximum runup of solitary waves. A series of laboratory experiments is described to support the theory. It is shown that the linear theory predicts the maximum runup satisfactorily, and that the nonlinear theory describes the climb of solitary waves equally well. Different runup regimes are found to exist for the runup of breaking and non-breaking waves. A breaking criterion is derived for determining whether a solitary wave will break as it climbs up a sloping beach, and a different criterion is shown to apply for determining whether a wave will break during rundown. These results are used to explain some of the existing empirical runup relationships.
Compressible laminar boundary-layer flows of a dusty gas over a semi-infinite flat plate
Authors: Wang B. Y. , Glass I. I.
Published: April 2006

The compressible laminar boundary-layer flows of a dilute gas-particle mixture over a semi-infinite flat plate are investigated analytically. The governing equations are presented in a general form where more reasonable relations for the two-phase interaction and the gas viscosity are included. The detailed flow structures of the gas and particle phases are given in three distinct regions: the large-slip region near the leading edge, the moderate-slip region and the small-slip region far downstream. The asymptotic solutions for the two limiting regions are obtained by using a series-expansion method. The finite-difference solutions along the whole length of the plate are obtained by using implicit four-point and six-point schemes. The results from these two methods are compared and very good agreement is achieved. The characteristic quantities of the boundary layer are calculated and the effects on the flow produced by the particles are discussed. It is found that in the case of laminar boundary-layer flows, the skin friction and wall heat-transfer are higher and the displacement thickness is lower than in the pure-gas case alone. The results indicate that the Stokes-interaction relation is reasonable qualitatively but not correct quantitatively and a relevant non-Stokes relation of the interaction between the two phases should be specified when the particle Reynolds number is higher than unity.
Current effects on resonant reflection of surface water waves by sand bars
Authors: Kirby James T.
Published: April 2006

The effect of currents flowing across a bar field on resonant reflection of surface waves by the bars is investigated. Using a multiple-scale expansion, evolution equations for the amplitudes of linear waves are derived and used to investigate the reflection of periodic wave trains with steady amplitude for both normal and oblique incidence. The presence of a current is found to shift resonant frequencies by possibly significant amounts and is also found to enhance reflection of waves by bar fields due to the additional effect of the perturbed current field.
Experimental and numerical investigation of a forced circular shear layer
Authors: Chomaz J. M. , Rabaud M. , Basdevant C. , Couder Y.
Published: April 2006

In a previous article we introduced a dissipative circular geometry in which stationary states of the shear flow instability were obtained. We show here that the dynamical behaviour of this flow depends strongly on the aspect ratio of the cell. In large cells, where the number of vortices is large, transitions from a mode with m vortices to a mode with (m−1) vortices occur through localized processes. In contrast to that situation, in small cells, transition takes place after a series of bifurcations which correspond to the successive breaking of all the symmetries of the flow.

We show that, provided an adequate forcing term is introduced, a two-dimensional numerical simulation of this flow is sufficient to recover all the dynamical processes which characterize the experimental flow.
The evolution of a weakly nonlinear, weakly damped, capillary-gravity wave packet
Authors: Miles John W.
Published: April 2006

Longuet-Higgins's (1976) analysis of energy transfer within a narrow spectrum of gravity waves with approximately uncorrelated phases is generalized to accommodate capillarity and weak damping. The analysis is based on the corresponding generalization of Zakharov's (1968) evolution equation for weakly nonlinear, deep-water gravity-wave packets. The results for a symmetric normal spectrum are expressed in terms of elliptic integrals and depend, after appropriate scaling, on a single similarity parameter and on the sign of the curvature of the linear dispersion relation. Energy transfer is away from the peak of that spectrum if kl* < 0.393, where k is the wavenumber and l* is the capillary length (2.8 mm for water), but may be towards the peak if 0.343 < kl* < 0.707 (4.5 cm > 2π/k > 2.5 cm for water). The formulation is based on energy exchange through resonant quartets and is not valid in the neighbourhood of kl* = 0.707; at which the second harmonic of a capillary-gravity wave resonates with its fundamental (Wilton's ripples). The modulational instability of a weakly damped capillary-gravity wave is examined in an Appendix.
Small-amplitude perturbations of shape for a nearly spherical bubble in an inviscid straining flow (steady shapes and oscillatory motion)
Authors: Kang I. S. , Leal L. G.
Published: April 2006

The method of domain perturbations is used to study the problem of a nearly spherical bubble in an inviscid, axisymmetric straining flow. Steady-state shapes and axisymmetric oscillatory motions are considered. The steady-state solutions suggest the existence of a limit point at a critical Weber number, beyond which no solution exists on the steady-state solution branch which includes the spherical equilibrium state in the absence of flow (e.g. the critical value of 1.73 is estimated from the third-order solution). In addition, the first-order steady-state shape exhibits a maximum radius at θ = ⅙π which clearly indicates the barrel-like shape that was found earlier via numerical finite-deformation theories for higher Weber numbers. The oscillatory motion of a nearly spherical bubble is considered in two different ways. First, a small perturbation to a spherical base state is studied with the ad hoc assumption that the steady-state shape is spherical for the complete Weber-number range of interest. This analysis shows that the frequency of oscillation decreases as Weber number increases, and that a spherical bubble shape is unstable if Weber number is larger than 4.62. Secondly, the correct steady-state shape up to O(W) is included to obtain a rigorous asymptotic formula for the frequency change at small Weber number. This asymptotic analysis also shows that the frequency decreases as Weber number increases; for example, in the case of the principal mode (n = 2), ω2 = ω00(1−0.31W), where ω0 is the oscillation frequency of a bubble in a quiescent fluid.
Vertical and lateral turbulent dispersion: some experimental results
Authors: Nokes R. I. , Wood I. R.
Published: April 2006

The results of an experimental programme designed to investigate turbulent dispersion of a continuous contaminant source in a wide channel are presented. Both two-dimensional vertical dispersion and the determination of the lateral diffusion coefficient are described. The eigenfunction solution to the turbulent diffusion equation, presented in Nokes et al. (1984) and discussed in greater detail in Nokes (1985), is strongly supported by the results of vertical mixing described here. A variety of source locations are examined in this study and the location of the ideal source, predicted by theory, is verified by the experimental results. For the two smooth-bed flows investigated the depth-averaged values of εz, deduced from the rates of lateral spreading of the plume, lie at the lower end of the range of values obtained by other researchers. Considering only the results obtained in wide channels, the authors demonstrate that previously published values of the lateral diffusion coefficient, non-dimensionalized by the shear velocity u* and the flow depth d are independent of all flow parameters except the friction factor f = 8u*/ū where ū is the mean velocity in the flow. Indeed, above a value of f = 0.055 εz/u*d is also found to be independent of f, and takes a value of 0.134. A brief mathematical analysis of the three-dimensional mixing processes in the near-source region is presented, and utilized to investigate the coupling between the lateral and vertical diffusion processes in this region. Based on these mathematical arguments the experimental results imply that the vertical and lateral diffusion processes are essentially uncoupled in the near-source zone, and thus the lateral diffusivity and longitudinal velocity have similar vertical dependence.
The dynamics of towed flexible cylinders Part 2. Negatively buoyant elements
Authors: Dowling A. P.
Published: April 2006

A ship, towing a heavier-than-water cable with a neutrally buoyant slender cylinder attached to the downstream end of the cable, is considered. The neutrally buoyant element contains a sonar array. Linear changes in the ship's velocity cause perturbations of both the cable and cylinder. The form of transverse vibrations of the neutrally buoyant cylinder was determined in Part 1. The propagation of disturbances along the cable is investigated in this paper. In particular, the effectiveness of the cable at isolating the sonar array from forcing due to unsteady ship motion is examined.

The cable and cylinder are found to be stable under constant towing conditions. It is therefore appropriate to investigate their response to forcing. Meanderings in the ship's track produce transverse displacements of both the cable and the cylinder. These transverse oscillations entirely decouple from any in-plane motion. The propagation of disturbances of frequency ω along the cable depends strongly on the value of the non-dimensional frequency ωlC/U, where lC is the cable length and U is the towing speed, and only weakly on the other cable parameters. The cable acts as an effective low-pass filter to transverse oscillations, the amplitude of disturbances with non-dimensional frequency greater than 10 being reduced by at least 90% as they propagate along the cable.

Unsteadiness in the ship's speed can result in in-plane deflections of the cable, and vertical oscillations of the cylinder containing the sonar array. In contrast to the transverse oscillations a significant proportion of the in-plane disturbances at the ship travels to the sonar array at all values of the frequency. Low- and high-frequency analytical forms are derived to explain why this occurs. Perturbations in the ship's position are most effectively transformed into vertical oscillations of the array at a frequency of 2.8U/lC. The effect of cable properties on transmission along the cable is investigated. The transmission again depends on the value of the non-dimensional frequency ωlC/U. Parameter changes, which increase the cable critical angle, increase the proportion of the disturbance at the towing point that is transformed into vertical array motion, for a fixed value of ωlC/U. This is explained by reference to the low- and high-frequency analytical solutions.
Scattering of long waves by cylindrical obstacles and gratings using matched asymptotic expansions
Authors: Martin P. A. , Dalrymple Robert A.
Published: April 2006

The method of matched asymptotic expansions is applied to several long-wave problems including the scattering of acoustic waves by a grating of cylinders and the scattering of water waves incident on horizontal cylinders. It is shown that a naïve application of the method can lead to incorrect results. A modified expansion procedure is developed and applied to a number of problems.
Three-dimensional shear layers via vortex dynamics
Authors: Ashurst W. T. , Meiburg Eckart
Published: April 2006

The evolution of the two- and three-dimensional structures in a temporally growing plane shear layer is numerically simulated with the discrete vortex dynamics method. We include two signs of vorticity and thus account for the effect of the weaker boundary layer leaving the splitter plate which is used to create a spatially developing mixing layer. The interaction between the two layers changes the symmetry properties seen in a single vorticity-layer calculation and results in closer agreement with experimental observations of the interface between the two streams. Our calculations show the formation of concentrated streamwise vortices in the braid region between the spanwise rollers, whereas the spanwise core instability is observed to grow only initially. Comparison with flow visualization experiments is given, and we find that the processes dominating the early stages of the mixing-layer development can be understood in terms of essentially inviscid vortex dynamics.
Guided surface waves near cutoff
Authors: Miles John
Published: April 2006

The joint effects of weak nonlinearity and weak linear damping on the dominant, antisymmetric gravity wave (excited by torsional oscillations of a plane wavemaker about a vertical axis) near its cutoff frequency in a rectangular channel are investigated, following Barnard, Mahony & Pritchard (1977). The evolution equations for the envelope of this mode are derived from the variational formulation previously developed for the parametrically excited cross-wave problem (Miles & Becker 1988). They are equivalent to those of Barnard et al., after correcting their damping and self-interaction terms, and, after appropriate normalization, differ from the cross-wave evolution equations only in the boundary condition at the wavemaker. Analytical approximations and the results of numerical integration for stationary envelopes (as observed in the experiments of Barnard et al.) are presented. The present results are somewhat closer to the observations of Barnard et al. than are their calculations, but the differences between the two calculations are not qualitatively significant.
Differential mixing in a stratified fluid
Authors: Maxworthy T. , Monismith S. G.
Published: April 2006

We present an experimental and theoretical study of the effects of localized mixing on a stratified fluid contained in a reservoir. In the experiments, mixing is accomplished by means of a vertically oscillating, horizontal grid located near the water surface at one end of the reservoir. Once the grid is set in motion, a mixed layer forms immediately beneath it. As this layer deepens, a horizontal pressure gradient builds up which drives an outflow of mixed fluid into the unmixed interior of the reservoir. This outflow slows, and eventually brings to a halt, mixed-layer deepening under the grid. At this equilibrium depth, the vertical velocity of the entrainment interface induced by the outflow exactly equals the velocity at which the entrainment interface would move downwards because of mixing. This equilibrium state persists until the outflow intrusion is blocked by the far wall of the reservoir, at which time deepening resumes under the grid. Asymptotically, the fluid reaches a state in which mixed-layer deepening is independent of position.
Experimental and numerical investigation of the three-dimensional transition in plane wakes
Authors: Meiburg E. , Lasheras J. C.
Published: April 2006

The three-dimensional structure of a moderate-Reynolds-number (≈ 100) plane wake behind a flat plate subjected to periodic spanwise perturbations has been studied both experimentally and numerically. Comparisons between experimental interface visualizations and numerical calculations demonstrate that important features of the development of the three-dimensional evolution can be reproduced by numerical inviscid vortex dynamics.

It is shown that the redistribution, reorientation and stretching of vorticity leads to the formation of counter-rotating pairs of streamwise vortices which superimpose onto the spanwise Kármán-like vortices. These streamwise vortices exhibit lambdashaped structures and are located in the braids connecting consecutive Kármán vortices of opposite sign.

The interaction of the evolving streamwise structure with the spanwise Kármán vortices results in the formation of closed vortex loops. Depending on the orientation of the initial perturbation, the three-dimensional vorticity field of the wake acquires either a symmetric or a non-symmetric configuration. Under the effect of a periodic vertical perturbation, the wake develops a non-symmetric vorticity mode exhibiting a staggered array of closed vortex loops of alternating sign. In contrast, under the effect of a periodic horizontal perturbation, the wake acquires a symmetric vorticity mode with the closed vortex loops of alternating sign aligned in the flow direction.
Flow in a channel with a moving indentation
Authors: Ralph M. E. , Pedley T. J.
Published: April 2006

The unsteady flow of a viscous, incompressible fluid in a channel with a moving indentation in one wall has been studied by numerical solution of the Navier-Stokes equations. The solution was obtained in stream-function-vorticity form using finite differences. Leapfrog time-differencing and the Dufort-Frankel substitution were used in the vorticity transport equation, and the Poisson equation for the stream function was solved by multigrid methods. In order to resolve the boundary-condition difficulties arising from the presence of the moving wall, a time-dependent transformation was applied, complicating the equations but ensuring that the computational domain remained a fixed rectangle.

Downstream of the moving indentation, the flow in the centre of the channel becomes wavy, and eddies are formed between the wave crests/troughs and the walls. Subsequently, certain of these eddies ‘double’, that is a second vortex centre appears upstream of the first. These observations are qualitatively similar to previous experimental findings (Stephanoff et al. 1983, and Pedley & Stephanoff 1985), and quantitative comparisons are also shown to be favourable. Plots of vorticity contours confirm that the wave generation process is essentially inviscid and reveal the vorticity dynamics of eddy doubling, in which viscous diffusion and advection are important at different stages. The maximum magnitude of wall vorticity is found to be much larger than in quasi-steady flow, with possibly important biomedical implications.
Models for very wide-angle water waves and wave diffraction
Authors: Dalrymple Robert A. , Kirby James T.
Published: April 2006

For a bathymetry consisting of parallel bottom contours, wide-angle parabolic models are developed to describe the diffraction of linear water waves. The first model, developed by operator correspondence, extends the validity of conventional forms of the parabolic model for wave angles up to 70° from the assumed wave direction. Through the use of Fourier decomposition, wave models valid to 90° are developed for three different lateral boundary conditions. By application, it is shown that the diffraction of waves through gaps or around structures is governed by the initial wave condition at the structure, which can be expanded into progressive and evanescent wave modes. Away from the structure, the wave field consists of only the progressive wave modes, which disperse according to their direction of propagation, the water depth and Snell's Law. Examples are shown for oblique waves through a gap, directional seas past a breakwater, a plane wave with varying crest amplitude, and finally for the diffraction of waves into a channel.
Modifications to the wake of a wire across Poiseuille flow due to a unipolar space charge
Authors: Mccluskey F. M. J. , Atten P.
Published: April 2006

A wake behind a wire in a developed Poiseuille flow is examined with and without ionic injection into the liquid by the wire. Mean electric fields of up to 50 kV/cm between the wire and two plate electrodes on either side were used to bring about this injection. The resulting Coulomb force can modify the wake flow in two ways. When this force is weak, the injected ions are transported downstream in a thin charged wake, the only effect being that the deficit velocity is compensated over shorter distances. Once the Coulomb force is strong, there are two charged and turbulent plume-like structures going from the wire to the plates. These are perpendicular to the plates for zero forced flow and are pushed downstream to smaller angles as the forced flow is increased. The wake in this case is not present. Different experimental laws are given to characterize the different regimes and the transition between them.
Turbulence reduction by screens
Authors: Groth Johan , Johansson Arne V.
Published: April 2006

Turbulence suppression by use of screens was studied in a small wind tunnel especially designed and built for the purpose. Wide ranges of mesh sizes and wire-diameter Reynolds numbers were covered in the present investigation, enabling the study of sub- and super-critical screens under the same, well-controlled, flow conditions. For the latter type small-scale fluctuations, produced by the screen itself, interact with the incoming turbulence. In the immediate vicinity of the screen the turbulence was found to be highly anisotropic and the intensities were higher than on the upstream side. Downstream of a short initial decay region, where the intensities decrease rapidly, the return to isotropy was found to be much slower than for the unmanipulated turbulence. The latter was generated by a square rod grid, and was shown to become practically isotropic beyond a distance of roughly 20 mesh widths from the grid. The role of the turbulence scales for the overall reduction effectiveness, and for the optimization of screen combinations for application in low-turbulence wind tunnels was studied.
Gravity–capillary rings generated by water drops
Authors: Le Méhauté Bernard
Published: April 2006

A theory for water waves created by the impact of small objects such as raindrops on an initially quiescent body of water is established. Capillary and dissipative viscous effects are taken into account in addition to gravity. It is shown that the prevailing waves are in a mixed capillary–gravity regime around a wavenumber km which corresponds to the minimum value of the group velocity. The waves are described as function of time and distance by the linear superposition of two transient wave components, a ‘sub-km’ (k < km) component and a ‘super-km’ (k > km) component. The super-km components prevail at a short distance from the drop, whereas only the sub-km ones remain at a larger distance. The relative time history of the wavetrain is independent of the size of the drop, and its amplitude is proportional to the drop momentum when it hits the free surface. The wave pattern is composed of a multiplicity of rings of amplitude increasing towards the drop location and is terminated by a trailing wave with an exponential decay. The number of rings increases with time and distance.
Steady Marangoni flow traveling with chemical fronts
Authors: Rongy L. , De Wit A.
Published: April 2006

When autocatalytic chemical fronts propagate in thin layers of solution in contact with air, they can induce capillary flows due to surface tension gradients across the front (Marangoni flows). We investigate here such an interplay between autocatalytic reactions, diffusion, and Marangoni effects with a theoretical model coupling the incompressible Navier-Stokes equations to a conservation equation for the autocatalytic product concentration in the absence of gravity and for isothermal conditions. The boundary condition at the open liquid/air interface takes the surface activity of this product into account and introduces the solutal Marangoni number M representing the intensity of the coupling between hydrodynamics and reaction-diffusion processes. Positive and negative Marangoni numbers correspond, respectively, to the cases where the product decreases or increases surface tension behind the front. We show that, in both cases, such coupled systems reach an asymptotic dynamics characterized by a steady fluid vortex traveling at a constant speed with the front and deforming it, with, however, an asymmetry between the results for positive and negative M. A parametric study shows that increased propagation speed, front deformation, and possible transient oscillating dynamics occur when the absolute value of M is increased.
Using massively parallel simulation and Markovian models to study protein folding: Examining the dynamics of the villin headpiece
Authors: Jayachandran Guha , Vishal V. , Pande Vijay S.
Published: April 2006

We report on the use of large-scale distributed computing simulation and novel analysis techniques for examining the dynamics of a small protein. Matters addressed include folding rate, very long time scale kinetics, ensemble properties, and interaction with water. The target system for the study, the villin headpiece, has been of great interest to experimentalists and theorists both. Sampling totaled nearly 500μs—the most extensive published to date for a system of villin’s size in explicit solvent with all atom detail—and was in the form of tens of thousands of independent molecular dynamics trajectories, each several tens of nanoseconds in length. We report on kinetics sensitivity analyses that, using a set of short simulations, probed the role of water in villin’s folding and sensitivity to the simulation’s electrostatics treatment. By constructing Markovian state models (MSMs) from the collected data, we were able to propagate dynamics to times far beyond those directly simulated and to rapidly compute mean first passage times, long time kinetics (tens of microseconds), and evolution of ensemble property distributions over long times, otherwise currently impossible. We also tested our MSM by using it to predict the structure of villin de novo.
Effects of symmetry of GaN-based two-dimensional photonic crystal with quasicrystal lattices on enhancement of surface light extraction
Authors: Zhang Z. S. , Zhang B. , Xu J. , Xu K. , Yang Z. J. , Qin Z. X. , Yu T. J. , Yu D. P.
Published: April 2006

We demonstrate enhancement of surface light extraction from two-dimensional photonic crystals (2D-PCs) on the electrical injected GaN-based light emitters. The effects of symmetry of PCs on light extraction were studied. 2.5 times enhancement of surface emission was obtained from the PCs with an octagonal symmetric quasicrystal lattice (8PQC) compared to that from a nonpatterned region. Additionally the surface emission from PCs with dodecagonal symmetric quasicrystal lattice (12PQC) exhibited about 1.7 and 1.4 times higher emission than regular PCs with triangular lattice and 8PQC, respectively. Consequently, the 12PQC provides a favorable consideration of 2D-PC in light extraction from light emitting diode.
Low-voltage pentacene field-effect transistors with ultrathin polymer gate dielectrics
Authors: Yang Sang Yoon , Kim Se Hyun , Shin Kwonwoo , Jeon Hayoung , Park Chan Eon
Published: April 2006

Organic field-effect transistors (OFETs) for low-voltage operation have been realized with conventional polymer gate dielectrics such as polyimides and cross-linked poly-4-vinyl phenols (PVPs) by fabricating ultrathin films. These ultrathin polymers (thickness ∼10nm) have shown good insulating properties, including high breakdown fields (>2.5MV∕cm). With ultrathin dielectrics, high capacitances (>250nF∕cm2) have been achieved, allowing operation of OFETs within −3V. Pentacene OFETs with ultrathin PVP dielectrics exhibit a mobility of 0.5cm2∕Vs, an on-off ratio of 105, and a small subthreshold swing of 174mV∕decade when devices are operated at −3V.
The primary function of RNA binding by the influenza A virus NS1 protein in infected cells: Inhibiting the 2′-5′ oligo (A) synthetase/RNase L pathway
Authors: Min Ji-Young , Krug Robert M.
Published: April 2006

The NS1 protein of influenza A virus (NS1A protein) is a multifunctional protein that counters cellular antiviral activities and is a virulence factor. Its N-terminal RNA-binding domain binds dsRNA. The only amino acid absolutely required for dsRNA binding is the R at position 38. To identify the role of this dsRNA-binding activity during influenza A virus infection, we generated a recombinant influenza A/Udorn/72 virus expressing an NS1A protein containing an RNA-binding domain in which R38 is mutated to A. This R38A mutant virus is highly attenuated, and the mutant NS1A protein, like the WT protein, is localized in the nucleus. Using the R38A mutant virus, we establish that dsRNA binding by the NS1A protein does not inhibit production of IFN-β mRNA. Rather, we demonstrate that the primary role of this dsRNA-binding activity is to protect the virus against the antiviral state induced by IFN-β. Pretreatment of A549 cells with IFN-β for 6 h did not inhibit replication of WT Udorn virus, whereas replication of R38A mutant virus was inhibited 1,000-fold. Using both RNA interference in A549 cells and mouse knockout cells, we show that this enhanced sensitivity to IFN-β-induced antiviral activity is due predominantly to the activation of RNase L. Because activation of RNase L is totally dependent on dsRNA activation of 2′-5′ oligo (A) synthetase (OAS), it is likely that the primary role of dsRNA binding by the NS1A protein in virus-infected cells is to sequester dsRNA away from 2′-5′ OAS.
Coping Responses and the Experience of Discrimination1
Authors: Sanders Thompson Vetta L.
Published: April 2006

This study examines the coping responses of individuals reporting experiences of racial/ethnic discrimination (N=156). Racial/ethnic differences in contextual appraisals and coping strategies were reported in response to discrimination. African and Asian American participants reporting experiences of discrimination were more likely to perceive the situation as a challenge. African Americans reporting experiences of discrimination were more likely to report seeking support and guidance when compared to Asian and European Americans. Contextual appraisals did not predict the use of coping strategies in response to experiences of discrimination. Emotional discharge and past experiences of discrimination were positively associated with re‐experiencing symptoms. Cognitive avoidance coping strategies were associated with avoidance symptoms. Clinical implications of the findings are explored.
Role of hematopoietic lineage cells as accessory components in blood vessel formation
Authors: Takakura Nobuyuki
Published: April 2006

In adults, the vasculature is normally quiescent, due to the dominant influence of endogenous angiogenesis inhibitors over angiogenic stimuli. However, blood vessels in adults retain the capacity for brisk initiation of angiogenesis, the growth of new vessels from pre‐existing vessels, during tissue repair and in numerous diseases, including inflammation and cancer. Because of the role of angiogenesis in tumor growth, many new cancer therapies are being conducted against tumor angiogenesis. It is thought that these anti‐angiogenic therapies destroy the tumor vessels, thereby depriving the tumor of oxygen and nutrients. Therefore, a better understanding of the molecular mechanisms in the process of sprouting angiogenesis may lead to more effective therapies not only for cancer but also for diseases involving abnormal vasculature. It is widely believed that after birth, endothelial cells (EC) in new blood vessels are derived from resident EC of pre‐existing vessels. However, evidence is now emerging that cells derived from the bone marrow may also contribute to postnatal angiogenesis. Most studies have focused initially on the contribution of endothelial progenitor cells in this process. However, we have proposed a concept in which cells of the hematopoietic lineage are mobilized and then entrapped in peripheral tissues, where they function as accessory cells that promote the sprouting of resident EC by releasing angiogenic signals. Most recently we found that hematopoietic cells play major roles in tumor angiogenesis by initiating sprouting angiogenesis and also in maturation of blood vessels in the fibrous cap of tumors. Therefore, manipulating these entrapment signals may offer therapeutic opportunities to stimulate or inhibit angiogenesis. (Cancer Sci 2006; 97: 568–574)
Increased risk of myocardial infarction as first manifestation of ischaemic heart disease and nonselective nonsteroidal anti‐inflammatory drugs
Authors: Hawkey C. J. , Hawkey G. M. , Everitt S. , Skelly M. M. , Stack W. A. , Gray D.
Published: April 2006

Aims

Selective cyclooxygenase (COX)‐2 inhibitors have recently been implicated as enhancing risk of myocardial infarction (MI). Nonselective nonsteroidal anti‐inflammatory drugs (NSAIDs) are also effective COX‐2 inhibitors, so we investigated the hypothesis that they too increase risk of MI.

Methods

We conducted a case–control study with direct structured interview of cases and controls. Cases were all subjects (N = 205) with a first nonfatal MI who had no previously recognized cardiovascular disease. Community controls (N = 258) were randomly selected from the same practice as the index case. Hospital controls (N = 205) were those admitted at the same time as index cases for nonmyocardial conditions not influenced by NSAID use. The effects of aspirin, NSAIDs and previously recognized influences on MI were investigated by unconditional logistic regression analysis.

Results

NSAID use was associated with an increase risk of MI with an odds ratio of 1.77 (1.03, 3.03) vs. community controls and 2.61 (1.38, 4.95) vs. hospital controls. These values were 5.00 (1.18, 21.28) and 7.66 (0.87, 67.48), respectively, in aspirin users. Results were similar when naproxen was grouped with aspirin. Odds ratios for smoking and for use of antidiabetic medication were 3.91 (2.52, 6.04) and 3.92 (1.25, 12,33), respectively, vs. community controls.

Conclusions

Like nonselective NSAIDs, selective COX‐2 inhibitors are associated with an increased risk of MI. The extent to which this reflects interference with aspirin warrants further investigation.
Transfer of escitalopram and its metabolite demethylescitalopram into breastmilk
Authors: Rampono Jonathan , Hackett L. Peter , Kristensen Judith H. , Kohan Rolland , Page‐Sharp Madhu , Ilett Kenneth F.
Published: April 2006

Aims

To investigate the transfer of escitalopram and its demethyl metabolite into milk, the absolute and relative infant doses via milk and to assess any unwanted effects in the breastfed infant.

Methods

Multiple samples of blood and milk were obtained over a dose interval at steady state from eight women who were taking escitalopram for postnatal depression. Drug concentrations in plasma and milk were measured by high‐performance liquid chromatography and milk/plasma ratio (M/PAUC), absolute infant dose and relative infant dose were estimated by standard methods. Their breastfed infants were also examined clinically and in five infants a blood sample was taken for drug analysis.

Results

The median dose taken by the women was 10 mg day−1. The mean (95% confidence interval) M/PAUC was 2.2 (2.0, 2.4) for escitalopram and 2.2 (1.9, 2.5) for demethylescitalopram. Absolute infant doses were 7.6 µg kg−1 day−1 (5.2, 10.0) for escitalopram and 3.0 µg kg−1 day−1 (2.4, 3.6) for demethylescitalopram. The total relative infant dose for escitalopram plus its demethyl metabolite was 5.3% (4.2, 6.4) as escitalopram equivalents. All of the infants had met normal developmental milestones and no adverse effects were seen. Compared with average maternal plasma concentrations (24 µg l−1), the concentrations of the parent drug and its metabolite in plasma from five infants were most commonly below the limit of detection (≤3 µg l−1).

Conclusion

The study shows that escitalopram is safe for use during breastfeeding. Because its absolute infant dose is lower than that for an equivalent antidepressant dose of rac‐citalopram, it may be preferred over rac‐citalopram in treating depression in lactating women. Nevertheless, each decision to breastfeed should always be made on the basis of an individual risk:benefit analysis.
Activated γδ T cells express the natural cytotoxicity receptor natural killer p44 and show cytotoxic activity against myeloma cells
Authors: Von Lilienfeld-Toal M , Nattermann J , Feldmann G , Sievers E , Frank S , Strehl J , Schmidt-Wolf I G H
Published: April 2006

γδ T cells account for up to 10% of T lymphocytes in the peripheral blood of healthy donors. They can be activated by cytokines such as interleukin (IL)-2, IL-12 and IL-15, express natural killer (NK) cell markers such as NKG2D and show cytotoxic activity against several tumour cells, including multiple myeloma. Here, we present activated polyclonal γδ T cells from healthy donors with an NK T cell-like phenotype expressing the natural cytotoxicity receptor NKp44. Natural cytotoxicity receptors NKp30, NKp44 and NKp46 have been regarded as specific NK receptors; only two γδ T cell clones described so far expressed NKp44. Isolated polyclonal γδ T cells cultured for 7 days according to the cytokine-induced killer cell (CIK) protocol with additional IL-15 revealed a surface expression of NKp44 of 8 ± 7% (n = 22). This could be confirmed by detection of NKp44 mRNA by reverse transcription–polymerase chain reaction (RT–PCR). γδ T cells exhibited a marked cytotoxic activity against myeloma cells, which could be reduced by inhibition of NKp44. To our knowledge, this is the first description of the expression of NKp44 on polyclonal γδ T cells.
The PPAR‐gamma activator rosiglitazone fails to lower plasma ACTH levels in patients with Nelson's syndrome
Authors: Mullan Karen R. , Leslie Hilary , McCance David R. , Sheridan Brian , Atkinson A. Brew
Published: April 2006

Backround  Peroxisomal proliferator‐activated receptors (PPAR)‐ γ are expressed abundantly in ACTH‐secreting pituitary tumours. The PPAR‐gamma activator rosiglitazone has been shown to suppress ACTH secretion in human adrenocorticotroph tumour cells in vitro, and prevent and reduce adrenocorticotroph tumour development in mouse models in vivo.

Objective  To evaluate the effect of rosiglitazone in patients with persistently elevated plasma ACTH levels postbilateral adrenalectomy for Cushing's disease.

Patients  Seven patients were treated with rosiglitazone 8 mg orally per day for 12 weeks.

Measurements  Plasma ACTH was measured at two hourly intervals from 09:00 h to 17:00 h before and after 6 and 12 weeks of treatment.

Results  Plasma ACTH at 09:00 hours immediately before the usual morning hydrocortisone dose was 2599·0 ± 899·7 ng/l (mean ± SEM) basally and 1547·6 ± 515·7 ng/l after 12 weeks of rosiglitazone, whereas levels at 17:00 h were 1433·4 ± 506·2 ng/l (mean ± SEM) basally and 1122·3 ± 460·9 ng/l at 12 weeks (all nonsignificant).

Conclusion  This study showed no effect of rosiglitazone treatment at maximum approved doses in lowering plasma ACTH levels in patients post bilateral adrenalectomy for Cushing's disease.
Coping with breast cancer in newly diagnosed Iranian women
Authors: Taleghani Fariba , Yekta Zohreh Parsa , Nasrabadi Alireza Nikbakht
Published: April 2006

Aim.  This paper reports a study exploring how Iranian women coped with newly diagnosed breast cancer and provides a foundation for cultural‐based care.

Background.  Although research has indicated that coping strategies are associated with adaptation to breast cancer, and despite the number of women with newly diagnosed breast cancer increasing each year, there is no information on how Iranian women cope with breast cancer when compared with women of other cultures.

Method.  In this qualitative study, 19 women with newly diagnosed breast cancer were interviewed during the period May–September 2004 about coping with their disease. Interviews were analysed using a content analysis method.

Findings.  The main themes emerging from this qualitative study included coping using a religious approach (acceptance of disease as God's will; spiritual fighting), thinking about the disease (positive thinking: positive suggestion, hope, intentional forgetfulness; negative thinking: hopelessness, fear, impaired body image), accepting the fact of the disease (active acceptance; passive acceptance), social and cultural factors and finally finding support from significant others.

Conclusion.  Understanding how Iranian women cope with diagnosis of breast cancer is important to nurses involved in the process of healing. The majority of strategies used by Iranian women were positive, and religious faith played a major role in this. The findings of the study can be used to design a nursing approach to improve successful coping in Iranian women suffering from breast cancer, and can provide nurses and other healthcare professionals with deeper understanding of these women as they face this diagnosis.
Change in perceived psychosocial status following a 12‐week Tai Chi exercise programme
Authors: Taylor‐Piliae Ruth E. , Haskell William L. , Waters Catherine M. , Froelicher Erika Sivarajan
Published: April 2006

Aim.  This paper reports a study to examine change in psychosocial status following a 12‐week Tai Chi exercise intervention among ethnic Chinese people with cardiovascular disease risk factors living in the United States of America.

Background.  Regular participation in physical activity is associated with protection against cardioavascular disease, and improvements in physical and psychological health. Increasing amounts of scientific evidence suggests that mind–body exercise, such as Tai Chi, are related to improvements in mental health, emotional well‐being, and stress reduction. No prior study has examined the effect of a Tai Chi exercise intervention on psychosocial status among people with cardiovascular disease risk factors.

Methods.  This was a quasi‐experimental study. Participants attended a 60‐minute Tai Chi exercise class three times per week for 12 weeks. Data were collected at baseline, 6 and 12 weeks following the intervention. Psychosocial status was assessed using Chinese versions of Cohen's Perceived Stress Scale, Profile of Mood States, Multidimensional Scale of Perceived Social Support, and Tai Chi exercise self‐efficacy.

Results.  A total of 39 participants, on average 66‐year‐old (±8·3), married (85%), Cantonese‐speaking (97%), immigrants participated. The majority were women (69%), with ≤12 years education (87%). Statistically significant improvements in all measures of psychosocial status were found (P ≤ 0·05) following the intervention. Improvement in mood state (η2 = 0·12), and reduction in perceived stress (η2 = 0·13) were found. In addition, Tai Chi exercise statistically significantly increased self‐efficacy to overcome barriers to Tai Chi (η2 = 0·19), confidence to perform Tai Chi (η2 = 0·27), and perceived social support (η2 = 0·12).

Conclusions.  Tai Chi was a culturally appropriate mind–body exercise for these older adults, with statistically significant psychosocial benefits observed over 12‐weeks. Further research examining Tai Chi exercise using a randomized clinical trial design with an attention‐control group may reduce potential confounding effects, while exploring potential mechanisms underlying the relaxation response associated with mind–body exercise. In addition, future studies with people with other chronic illnesses in all ethnic groups are recommended to determine if similar benefits can be achieved.