ALTHOUGH the birth of the universe is inaccessible to human experimental investigation, aspects of cosmological theories can nonetheless be explored in the laboratory. Tiny inhomogeneities in the mix of particles and radiation produced in the Big Bang grew into the clusters of galaxies that we see today, but how those inhomogeneities arose and grew is still unclear. Cos

A new experiment has been performed to study the formation of topological defects (quantized vortices) during rapid quenches of liquid 4 He through the superfluid transition, with particular care taken to minimize vortex creation via conventional hydrodynamic flow processes. It is found that the generated vortices, if any, are being produced at densities at least 2 orders of magnitude less than might be expected on the basis of the Kibble-Zurek mechanism. [S0031-9007(98)

Osteoporosis affects both the organic and mineral phases of bone resulting in a decrease in resistance to fracture. Dual x-ray absorptiometry (DEXA) scans are used for diagnosing osteoporosis, which is conventionally characterised by a decrease in mineral density. Unfortunately, some patients who suffer osteoporotic fractures have normal bone density, because both the organic and the mineral phase are affected. However, there are currently no methods of evaluating the health of the organic phase. Patients undergoing treatment for osteoporosis have reported hardening of their fingernails. As the properties of nail and bone may be linked in a comparable, measurable way, this work used both mechanical (nano-indentation) and chemical (Raman spectroscopy) methods to evaluate differences between fingernails sourced from osteoporotic and non-osteoporotic patients. The difference in mean modulus between the nails sourced from the groups was 1.1 GPa. The disulphide bond content of fingernail samples from each group was measured by Raman spectroscopy and disulphide bond content of fingernail was found to be significantly lower in the osteoporotic group. It can be concluded that a relationship between the mechanical and chemical properties of nail and bone may exist in a measurable way. This work has suggested that changes in the organic phase of bone are reflected in similar proteins, such as keratin, from which fingernails are composed. Collagen and keratin are two distinct structural proteins, but they share the need for protein sulphation and disulphide bond formation, via cysteine, for their structural integrity. A disorder of either process should lead to disordered collagen and keratin synthesis.

Bone collagen and nail keratin are two distinct structural proteins, and both require protein sulfation and disulfide bond formation, via cysteine, for structural integrity. A disorder of either process may lead to disordered collagen and keratin synthesis. This is reflected in the structural abnormalities seen in clinical syndromes in which there is either protein deficiency, disorders of sulfur metabolism, or cystathione beta-synthase deficiency. The relationship between nail and bone may exist in a measurable way. This pilot study should lead to further work to explore this relationship. Could nail prove to be a valuable adjunct to diagnosis or provide a means of more rapid follow-up after commencement of therapy?

Experimental evidence is presented showing that the creation of vortices in He II involves macroscopic quantum tunneling through, or thermal activation over, a potential-energy barrier e. The investigations, based on measurements of the rate at which negative ions create vortex rings in the isotopically pure superfluid within the temperature range 50 < T < 500 mK, have yielded a barrier height of e/kn^lA ± 0.1 K, in excellent agreement with the theoretical value predicted by Muirhead, Vinen, and Donnelly.