On the use of modification functions when Fourier transforming total scattering data

When Fourier transforming radiation total scattering data to the pair distribution function it is common to use a `modification' function to help reduce the termination ripples that would otherwise occur as a result of the finite range and counting statistics of the scattering data. One of the most common functions employed was proposed by Lorch [J. Phys. C Solid State Phys.(1969),2, 229–237]. In a recent article [Soper & Barney (2011).J. Appl. Cryst.44, 714–726] a revised version of this function was proposed. Here the effectiveness of these two functions at removing spurious structure from Fourier transformed data is compared. It is found that the two functions produce equivalent results, unless the broadening is allowed to increase withr, in which case the revised Lorch function is better at suppressing spurious oscillations. The presence of counting statistics produces a marked increase in the amplitude of the truncation oscillations.

Design of viscometers corresponding to a universal molecular simulation method

We present conceptual designs of viscometers corresponding to our new exact molecular simulation method (Dayal & James, J. Mech. Phys. Solids, vol. 58 (2), 2010, pp. 145–163). The molecular simulation method is a generalization of the method of Lees & Edwards (J. Phys. C: Solid State Phys., vol. 5, 1972, p. 1921), and includes a three-parameter family of incompressible flows, as well as compressible flows and unsteady flows exhibiting vortex stretching. All fluids are allowed. The method gives a way to simulate these flows using relatively few molecules, in the absence of a constitutive relation describing the fluid. This paper presents conceptual designs for viscometers that produce large families of these flows. The basic theme of this paper is that the flows discussed here are a better way to characterize the properties of complex fluids than the currently available methods, such as those based on viscometric flows.