J. R. D. Copley

National user facilities such as the NIST Center for Neutron Research (NCNR) require a significant base of software to treat the data produced by their specialized measurement instruments. There is no universally accepted and used data treatment package for the reduction, visualization, and analysis of inelastic neutron scattering data. However, we believe that the software development approach adopted at the NCNR has some key characteristics that have resulted in a successful software package called DAVE (the Data Analysis and Visualization Environment). It is developed using a high level scientific programming language, and it has been widely adopted in the United States and abroad. In this paper we describe the development approach, elements of the DAVE software suite, its usage and impact, and future directions and opportunities for development.

Herein, we report the synthesis of multiscale nanostructured p-type (Bi,Sb)(2)Te(3) bulk materials by melt-spinning single elements of Bi, Sb, and Te followed by a spark plasma sintering process. The samples that were most optimized with the resulting composition (Bi(0.48)Sb(1.52)Te(3)) and specific nanostructures showed an increase of approximately 50% or more in the figure of merit, ZT, over that of the commercial bulk material between 280 and 475 K, making it suitable for commercial applications related to both power generation and refrigeration. The results of high-resolution electron microscopy and small angle and inelastic neutron scattering along with corresponding thermoelectric property measurements corroborate that the 10-20 nm nanocrystalline domains with coherent boundaries are the key constituent that accounts for the resulting exceptionally low lattice thermal conductivity and significant improvement of ZT.

The computer simulation and inelastic neutron scattering studies of simple, monatomic liquids are reviewed, together with the theory appropriate for their interpretation. Computer simulation (molecular dynamics) studies influenced development of non-equilibrium statistical mechanics techniques for the calculation of correlation functions that enter the various measured susceptibilities. Studies of systems interacting via continuous potentials have developed to a high level of sophistication. Neutron scattering experiments are difficult to perform with high accuracy, yet offer a unique means of investigating the dynamics of simple liquids in the domain of wavevectors and frequencies larger than about 0.05 AA-1 and 5*1011 s-1 respectively. The problems faced in analysing neutron data to the level required are reviewed in detail. Theory has developed through the rigorous generalization of the Markovian theory of fluctuations set out by Landau and Lifshitz (1959). The development has taken the form of a generalized Langevin equation, which provides a framework within which neutron and molecular dynamics data may be interpreted.

The short-wavelength collective excitations in liquid rubidium at 320 K have been studied by coherent neutron scattering. For values of $\ensuremath{\kappa}=\frac{2\ensuremath{\pi}}{\ensuremath{\lambda}}$ up to 1.0 ${\mathrm{\AA{}}}^{\ensuremath{-}1}$, clear evidence of propagating modes was found from the shape of the scattering function $S(\ensuremath{\kappa}, \ensuremath{\omega})$ at constant values of $\ensuremath{\kappa}$. This result shows that the existence of such modes does not depend upon either quantum effects or low thermal population of the modes.