Chain conformation in polymer nanocomposites with uniformly dispersed nanoparticles.

The effect of nanoparticles (NP) on chain dimensions in polymer melts has been the source of considerable theoretical and experimental controversy. We exploit our ability to ensure a spatially uniform dispersion of 13 nm silica NPs miscible in polystyrene melts, together with neutron scattering, x-ray scattering, and transmission electron microscopy, to show that there is no measurable change in the polymer size in miscible mixtures, regardless of the relative sizes of the chains and the nanoparticles, and for NP loadings as high as 32.7 vol%. Our results provide a firm basis from which to understand the properties of polymer nanocomposites.

Introduction to the DAPPLE Air Pollution Project.

The Dispersion of Air Pollution and its Penetration into the Local Environment (DAPPLE) project brings together a multidisciplinary research group that is undertaking field measurements, wind tunnel modelling and computer simulations in order to provide better understanding of the physical processes affecting street and neighbourhood-scale flow of air, traffic and people, and their corresponding interactions with the dispersion of pollutants at street canyon intersections. The street canyon intersection is of interest as it provides the basic case study to demonstrate most of the factors that will apply in a wide range of urban situations. The aims of this paper are to introduce the background of the DAPPLE project, the study design and methodology for data collection, some preliminary results from the first field campaign in central London (28 April-24 May 2003) and the future for this work. Updated information and contact details are available on the web site at http://www.dapple.org.uk.

Similarity solution of temperature structure functions in decaying homogeneous isotropic turbulence.

An equilibrium similarity analysis is applied to the transport equation for <(deltatheta)(2)>, the second-order temperature structure function, for decaying homogeneous isotropic turbulence. A possible solution is that the temperature variance decays as x(n), and that the characteristic length scale, identifiable with the Taylor microscale lambda, or equivalently the Corrsin microscale lambda(theta), varies as x(1/2). The turbulent Reynolds and Péclet numbers decay as x((m+1)/2) when m<-1, where m is the exponent which characterizes the decay of the turbulent energy , viz., approximately x(m). Measurements downstream of a grid-heated mandoline combination show that, like <(deltaq)(2)>, <(deltatheta)(2)> satisfies similarity approximately over a significant range of scales r, when lambda, lambda(theta), , and are used as the normalizing scales. This approximate similarity is exploited to calculate the third-order structure functions. Satisfactory agreement is found between measured and calculated distributions of and , where deltau is the longitudinal velocity increment.

Anomalous scaling of velocity and temperature structure functions.

Scaling-range power-law exponents of velocity and temperature structure functions are examined through the dimensional analysis framework of the refined similarity hypotheses using measurements in a variety of turbulent flows and Reynolds numbers. The resulting magnitude of the scaling exponent associated with the locally averaged energy dissipation rate epsilon(r) is always larger than 2/3, whereas the exponent for the locally averaged temperature dissipation rate chi(r) is always smaller than 2/3. While the epsilon(r) exponent may be reconciled with the exponent of the velocity structure function, the distributions of the chi(r) and temperature structure function exponents are inherently different.