Since the pioneering work of Brockhouse on inelastic neutron scattering the triple-axis spectrometer has been the instrument of choice for studies of dynamics, both magnetic and structural, in single crystals. In the years since the late fifties improvements in source brightness, beam optics, and detector technology have resulted in increased sensitivity and capabilities of the basic triple-axis design. Work has begun at Risø National Laboratory on a new spectrometer design, RITA, the reinvented triple axis, which attempts to incorporate more recent innovations such as multilayer supermirrors and microstrip proportional counters into a rethinking of the triple-axis spectrometer. By optimizing the beam optics using supermirrors and extending the analyser to map regions of (Q, ω) space using an array of independently controllable pyrolytic graphite crystals focussed on an area detector, we hope to increase the efficiency of single-crystal inelastic experiments by about a factor of 20.

Recent experiments on the thermal transport in systems with partial fractal geometry, silica aerogels, are reviewed. The individual contributions from phonons, fractons and particle modes, respectively, have been identified and can be described by quantitative models consistent with heat capacity data. The interpretation in the particle mode regime sheds light on the mechanisms for thermal conductivity in normal vitreous silica.

Specific heat and thermal conductivity data for a homologous series of base‐catalyzed silica aerogels in the temperature range 0.1–20 K are analyzed in a three regime model. The three regimes, dominated by phonons, fractions and particle modes, respectively, reflect three structural regions as found by SANS measurements. The thermal properties of aerogels are compared to those of dense amorphous quartz and important differences are found.

The authors report inelastic polarized neutron scattering measurements of the excitations in the S=1, quasi-one-dimensional antiferromagnet CsNiCl3 with applied magnetic field. A field up to 5.9 T was applied perpendicular to the chain direction and the field dependence of spin excitation modes at wave vectors corresponding to the one-dimensional zone centre (i.e. ( xi , xi ,1)) was studied. Near the antiferromagnetic ordering point Q=(1/3,1/3,1) two types of field dependence are observed. The behaviour of the higher energy mode suggests that it is the novel longitudinal mode recently proposed by Affleck (1989). The application of the field also reveals a near-degeneracy of the excitations observed at Q=(0,0,1) in zero field. This degeneracy is incompatible with the result of the classical spin wave theory based on the Heisenberg Hamiltonian with a single-site anisotropy.