bluuebunny/crossref_metadata_2025_split huggingface dataset:
1,2,5‐Oxadiazole (Furazan) Derivatives from Benzoylnitromethane and Dipolarophiles in the Presence of DABCO: Structure and Intermediates
Authors: Cecchi Luca , De Sarlo Francesco , Faggi Cristina , Machetti Fabrizio 
Published: April 2006

AbstractFurazan (1,2,5‐oxadiazole) derivatives are obtained along with isoxazolines from the reaction of benzoylnitromethane with dipolarophiles in the presence of DABCO. Furazans are shown to derive from the intermediate dibenzoylfuroxan (3,4‐dibenzoyl‐1,2,5‐oxadiazole‐5‐oxide) and dipolarophiles under hydrolytic conditions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Genetic aberrations in prostate cancer by microarray analysis
Authors: Saramäki Outi R. , Porkka Kati P. , Vessella Robert L. , Visakorpi Tapio 
Published: April 2006

AbstractThe aim of this study was to screen genetic as well as expression alterations in prostate cancer. Array comparative genomic hybridization (aCGH) to a 16K cDNA microarray was performed to analyze DNA sequence copy number alterations in 5 prostate cancer cell lines and 13 xenografts. The aCGH confirmed the previously implicated common gains and losses, such as gains at 1q, 7, 8q, 16p and 17q and losses at 2q, 4p/q, 6q, 8p, 13q, 16q, 17p and 18q, which have previously been identified by chromosomal CGH (cCGH). Because of the higher resolution of aCGH, the minimal commonly altered regions were significantly narrowed‐down. For example, the gain of 8q was mapped to three independent regions, 8q13.3‐q21.11, 8q22.2 and 8q24.13‐q24.3. In addition, a novel recurrent gain at 9p13‐q21 was identified. The concomitant expression analysis indicated that genome‐wide DNA sequence copy number (gene dosage) was significantly associated with the expression level (p < 0.0001). The analyses indicated several individual genes whose expression was associated with the gene copy number. For example, gains of PTK2 and FZD6, were associated with the increased expression, whereas losses of TNFRSF10B (alias DR5) and ITGA4 with decreased expression. In conclusion, the aCGH mapping data will aid in the identification of genes altered in prostate cancer. The combined expression and copy number analysis suggested that even a low‐level copy number change may have significant effect on gene expression, and thus on the development of prostate cancer. © 2006 Wiley‐Liss, Inc.
Deviation from the mobile proton model in amino‐modified peptides: implications for multiple reaction monitoring analysis of peptides
Authors: Locke Steven J. , Leslie Andrew D. , Melanson Jeremy E. , Pinto Devanand M. 
Published: April 2006

AbstractThe study of peptide fragmentation is important to the understanding of chemical processes occurring in the gas phase and the more practical concern of peptide identification for proteomic analysis. Using the mobile proton model as a framework, we explore the effect of amino‐group modifications on peptide fragmentation. Three aldehydes are used to transform the peptides' primary amino groups into either a dimethylamino or a heterocyclic structure (five‐ or six‐membered). The observed fragmentation patterns deviate strongly from those observed for the analogous underivatised peptides. In particular, the a1 ion is the base peak in most tandem mass spectra of the derivatised peptides. The a1 ion intensity depends strongly on the N‐terminal amino acid, with tyrosine and phenylalanine having the strongest enhancement. Despite the change in fragmentation patterns of the derivatised peptides, they still provide high‐quality tandem mass spectra that, in many cases, are more amenable to database searching than the spectra of underivatised peptides. In addition, the reliable presence of the a1 ion facilitates rapid quantitative measurements using the multiple reaction monitoring approach. Copyright © 2006 John Wiley & Sons, Ltd.
Frequency selection and asymptotic states in laminar wakes
Authors: Karniadakis George Em , Triantafyllou George S. 
Published: April 2006

A better understanding of the transition process in open flows can be obtained through identification of the possible asymptotic response states in the flow. In the present work, the asymptotic states in laminar wakes behind circular cylinders at low supercritical Reynolds numbers are investigated. Direct numerical simulation of the flow is performed, using spectral-element techniques. Naturally produced wakes, and periodically forced wakes are considered separately.It is shown that, in the absence of external forcing, a periodic state is obtained, the frequency of which is selected by the absolute instability of the time-average flow. The non-dimensional frequency of the vortex street (Strouhal number) is a continuous function of the Reynolds number. In periodically forced wakes, however, non-periodic states are also possible, resulting from the bifurcation of the natural periodic state. The response of forced wakes can be characterized as: (i) lock-in, if the dominant frequency in the wake equals the excitation frequency, or (ii) non-lock-in, when the dominant frequency in the wake equals the Strouhal frequency. Both types of response can be periodic or quasi-periodic, depending on the combination of the amplitude and frequency of the forcing. At the boundary separating the two types of response transitional states develop, which are found to exhibit a low-order chaotic behaviour. Finally, all states resulting from the bifurcation of the natural state can be represented in a two-parameter space inside ‘resonant horn’ type of regions.
Nonlinear stability of a weakly supercritical mixing layer in a rotating fluid
Authors: Shukhman I. G. 
Published: April 2006

A model has been constructed for a mixing layer of a rotating fluid with a large Reynolds number which is an analogue of a mixing-layer model for a plane flow widely used in the literature. The angular velocity profile in such a model has the form:\[ \Omega(r) = {\textstyle\frac{1}{2}}(\Omega_1 + \Omega_2)-{\textstyle\frac{1}{2}}(\Omega_1 - \Omega_2)\tan h\left(\frac{1}{D}\ln\frac{r}{R}\right), \]whereris the distance from the rotation axis; andR, Ω1,2, andDare the model's parameters. The model permits a relatively simple analytical study of the stability for two-dimensional disturbances. It is shown that the stability is defined by the ‘shear-width’ parameterD, namely the model is unstable whenD<Dcrit= ½. In a weakly supercritical flow (|D−Dcrit| [Lt ] 1), one mode with azimuthal numberm= 2 develops. In this case two vortices are produced in the vicinity of a critical layer (CL), i.e. a radius where the wave's azimuthal velocity Ωpcoincides with the rotation velocity Ω(r). A study is made of their nonlinear evolution corresponding to different CL regimes: viscous, nonlinear, and unsteady. It is found that the instability saturates at a low enough level and the equilibrium amplitude depends on the degree of supercriticality ΔD= |D−Dcrit|, but the character of this dependence is different in different regions of the supercriticality parameter ΔD.It is shown that, despite the specific form of the velocity profile in the model under consideration, results concerning the critical-layer dynamics have a high degree of universality. In particular, it becomes possible to formulate the criterion that the instability will be saturated at a low level for an arbitrary weakly supercritical flow.
The motion of a rigid body in viscous fluid bounded by a plane wall
Authors: Hsu Richard , Ganatos Peter 
Published: April 2006

The boundary-integral method is used to calculate the hydrodynamic force and torque on an arbitrary body of revolution whose axis of symmetry is oriented at an arbitrary angle relative to a planar wall in the zero-Reynolds-number limit. The singular solution of the Stokes equations in the presence of a planar wall is used to formulate the integral equations, which are then reduced to a system of linear algebraic equations by satisfying the no-slip boundary conditions on the body surface using the boundary collocation method or weighted residual technique.Numerical tests for the special case of a sphere moving parallel or perpendicular to a planar wall show that the present theory is accurate to at least three significant figures when compared with the exact solutions for gap widths as small as only one-tenth of the particle radius. Higher accuracy can be achieved and solutions can be obtained for smaller gap widths at the expense of more computation time and larger storage requirements.The hydrodynamic force and torque on a spheroid with varying aspect ratio and orientation angle relative to the planar wall are obtained. The theory is also applied to study the motion of a toroidal particle or biconcave shaped disc adjacent to a planar wall. The coincidence of the drag and torque of a biconcave-shaped body and a torus having an aspect ratio b/a = 2 with the same surface area shows that in this case the hole of a torus has little influence on the flow field. On the other hand, for an aspect ratio b/a = 10, the effect of the hole is significant. It is also shown that when the body is not very close to the wall, an oblate spheroid can be used as a good approximation of a biconcave-shaped disc.
Extremal energy properties and construction of stable solutions of the Euler equations
Authors: Vallis G. K. , Carnevale G. F. , Young W. R. 
Published: April 2006

Certain modifications of the Euler equations of fluid motion lead to systems in which the energy decays or grows monotonically, yet which preserve other dynamically important characteristics of the field. In particular, all topological invariants associated with the vorticity field are preserved. In cases where isolated energy extrema exist, a stable steady flow can be found. In two dimensions, highly constrained by vorticity invariants, it is shown that the modified dynamics will lead to at least one non-trivial stationary, generally stable, solution of the equations of motion from any initial conditions. Numerical implementation of the altered dynamics is straightforward, and thus provides a practical method for finding stable flows. The method is sufficiently general to be of use in other dynamical systems.Insofar as three-dimensional turbulence is characterized by a cascade of energy, but not topological invariants, from large to small scales, the procedure has direct physical significance. It may be useful as a parameterization of the effects of small unresolved scales on those explicitly resolved in a calculation of turbulent flow.
Lagrangian statistics from direct numerical simulations of isotropic turbulence
Authors: Yeung P. K. , Pope S. B. 
Published: April 2006

A comprehensive study is reported of the Lagrangian statistics of velocity, acceleration, dissipation and related quantities, in isotropic turbulence. High-resolution direct numerical simulations are performed on 643and 1283grids, resulting in Taylor-scale Reynolds numbers Rλin the range 38-93. The low-wavenumber modes of the velocity field are forced so that the turbulence is statistically stationary. Using an accurate numerical scheme, of order 4000 fluid particles are tracked through the computed flow field, and hence time series of Lagrangian velocity and velocity gradients are obtained.The results reported include: velocity and acceleration autocorrelations and spectra; probability density functions (p.d.f.'s) and moments of Lagrangian velocity increments; and p.d.f.'s, correlation functions and spectra of dissipation and other velocity-gradient invariants. It is found that the acceleration variance (normalized by the Kolmogorov scales) increases as R½λ- a much stronger dependence than predicted by the refined Kolmogorov hypotheses. At small time lags, the Lagrangian velocity increments are distinctly non-Gaussian with, for example, flatness factors in excess of 10. The enstrophy (vorticity squared) is found to be more intermittent than dissipation, having a standard-deviation-to-mean ratio of about 1.5 (compared to 1.0 for dissipation). The acceleration vector rotates on a timescale about twice the Kolmogorov scale, while the timescales of acceleration magnitude, dissipation and enstrophy appear to scale with the Lagrangian velocity timescale.
Velocity-derivative skewness and two-time velocity correlations of isotropic turbulence as predicted by the LET theory
Authors: Mccomb W. D. , Shanmugasundaram V. , Hutchinson P. 
Published: April 2006

The local-energy-transfer (LET) theory was used to calculate freely decaying turbulence for arbitrary initial conditions over a range of microscale-based Reynolds numbers 0.5 [les ] Rλ(tf) [les ] 1009, where tf is the final time of computation. The predicted skewness factor S(Rλ) agreed closely with the results of numerical simulations at low-to-moderate Reynolds numbers and followed the same general trend at larger values of Rλ. It was also found that, for Rλ(tf) [les ] 5, the LET calculation was almost indistinguishable from that of the direct-interaction approximation (DIA), with the difference between the two theories tending to zero as Rλ(tf)∞ 0.Two-time correlation and propagator (or response) functions were also obtained. Tests of their scaling behaviour suggest that, contrary to general belief, the convective sweeping of the energy-containing range is much less important than the Kolmogorov timescale in determining inertial-range behaviour. This result raises questions about the accepted explanation for the failure of the direct-interaction approximation, thus motivating a discussion about the relevance of random Galilean invariance (RGI). It is argued that, for a properly constructed ensemble of transformations to inertial frames, invariance in every realization necessarily implies RGI. It is suggested that the defects of the direct-interaction approximation can be understood in terms of a failure to renormalize the stirring forces.
On the dynamics of liquid spreading on solid surfaces
Authors: Ngan C. G. , V. E. B. Dussan 
Published: April 2006

Our main objective is to identify a boundary-value problem capable of describing the dynamics of fluids having moving contact lines. A number of models have been developed over the past decade and a half for describing the dynamics of just such fluid systems. We begin by discussing the deficiencies of the methods used in some of these investigations to evaluate the parameters introduced by their models. In this study we are concerned exclusively with the formulation of a boundary-value problem which can describe the dynamics of the fluids excluding that lying instantaneously in the immediate vicinity of the moving contact line. From this perspective, many of the approaches referred to above are equivalent, that is to say they give rise to velocity fields with the same asymptotic structure near the moving contact line. Part of our objecive is to show that this asymptotic structure has only one parameter. A substantial portion of our investigation is devoted to determining whether or not the velocity field in a particular experiment has this asymptotic structure, and to measuring the value of the parameter.More specifically, we use the shape of the fluid interface in the vicinity of the moving contact line to identify the asymptotic structure of the dynamics of the fluid. Experiments are performed in which silicone oil displaces air through a gap formed between two parallel narrowly-spaced glass microscope slides sealed along two opposing sides. Since we were unable to make direct measurements of the shape of the fluid interface close to the moving contact line, an indirect procedure has been devised for determining its shape from measurements of the apex height of the meniscus. We find that the deduced fluid interface shape compares well with the asymptotic form identified in the studies referred to above; however, systematic deviations do arise. The origin of these deviations is unclear. They could be attributed to systematic experimental error, or, to the fact that our analysis (valid only for small values of the capillary number) is inadequate at the conditions of our experiments.
Viscous and inviscid flows in a channel with a moving indentation
Authors: Ralph M. E. , Pedley T. J. 
Published: April 2006

The flow in a channel with an oscillating constriction has been studied by the numerical solution of the Navier-Stokes and Euler equations. A vorticity wave is found downstream of the constriction in both viscous and inviscid flow, whether the downstream flow rate is held constant and the upstream flow is pulsatile, or vice versa. Closed eddies are predicted to form between the crests/troughs of the wave and the walls, in the Euler solutions as well as the Navier-Stokes flows, although their structures are different in the two cases.The positions of wave crests and troughs, as determined numerically, are compared with the predictions of a small-amplitude inviscid theory (Pedley & Stephanoff 1985). The theory agrees reasonably with the Euler equation predictions at small amplitude (ε [lsim ] 0.2) as long as the downstream flow rate is held fixed; otherwise a sinusoidal displacement is superimposed on the computed crest positions. At larger amplitude (ε = 0.38) the wave crests move downstream more rapidly than predicted by the theory, because of the rapid growth of the first eddy (‘eddy A’) attached to the downstream end of the constriction. At such larger amplitudes the Navier-Stokes predictions also agree well with the Euler predictions, when the downstream flow rate is held fixed, because the wave generation process is essentially inviscid and the undisturbed vorticity distribution is the same in each case. It is quite different, however, when the upstream flow rate is fixed, as in the experiments of Pedley & Stephanoff, because of differences in the undisturbed vorticity distribution, in the growth rate of the vorticity waves and in the dynamics of eddy A. A further finite-amplitude effect of importance, especially in an inviscid fluid, is the interaction of an eddy with its images in the channel walls.
The effects of surfactants on drop deformation and breakup
Authors: Stone H. A. , Leal L. G. 
Published: April 2006

The effects of surface-active agents on drop deformation and breakup in extensional flows at low Reynolds numbers are described. In this free-boundary problem, determination of the interfacial velocity requires knowledge of the distribution of surfactant, which, in turn, requires knowledge of the interfacial velocity field. We account for this explicit coupling of the unknown drop shape and the evolving surfactant distribution. An analytical result valid for nearly spherical distortions is presented first. Finite drop deformation is studied numerically using the boundary-integral method in conjunction with the time-dependent convective–diffusion equation for surfactant transport. This procedure accurately follows interfacial tension variations, produced by non-uniform surfactant distribution, on the evolving interface. The numerical method allows for an arbitrary equation of state relating interfacial tension to the local concentration of surfactant, although calculations are presented only for the common linear equation of state. Also, only the case of insoluble surfactant is studied.The analytical and numerical results indicate that at low capillary numbers the presence of surfactant causes larger deformation than would occur for a drop with a constant interfacial tension equal to the initial equilibrium value. The increased deformation occurs owing to surfactant being swept to the end of the drop where it acts to locally lower the interfacial tension, which therefore requires increased deformation to satisfy the normal stress balance. However, at larger capillary numbers and finite deformations, this convective effect competes with ‘dilution’ of the surfactant due to interfacial area increases. These two different effects of surface-active material are illustrated and discussed and their influence on the critical capillary number for breakup is presented.
Turbulence modulation in homogeneous dilute particle-laden flows
Authors: Parthasarathy R. N. , Faeth G. M. 
Published: April 2006

Continuous-phase properties were studied for homogeneous dilute particle-laden flows caused by nearly monodisperse glass particles falling in a stagnant water bath. Test conditions included 0.5, 1.0 and 2.0 mm diameter particles (yielding particle Reynolds numbers based on terminal velocities of 38, 156 and 545) with particle volume fractions less than 0.01%. Measurements included mean and fluctuating velocities, as well as temporal spectra and spatial correlations of velocity fluctuations in the streamwise and cross-stream directions, using a two-point phase-discriminating laser velocimeter. Flow properties were also analysed using a stochastic method involving linear superposition of randomly-arriving particle velocity fields.For present test conditions, liquid velocity fluctuations varied solely as a function of the rate of dissipation of particle energy in the liquid. The flows were highly anisotropic with streamwise velocity fluctuations being roughly twice cross-stream velocity fluctuations. Correlation coefficients and temporal spectra were independent of both particle size and the rate of dissipation of particle energy in the liquid. The temporal spectra indicated a large range of frequencies even though particle Reynolds numbers were relatively low, since both mean and fluctuating velocities in the particle wakes contributed to the spectra because particle arrivals were random. The theory predicted many of the features of the flows reasonably well but additional information concerning the mean and turbulent structure of the wakes of freely moving particles having moderate Reynolds numbers in turbulent environments is needed to address deficiencies in predictions of integral scales and streamwise spatial correlations.