Fundamental measure density functional theory for hard spherocylinders in static and time-dependent aligning fields.

The recently developed fundamental measure density functional theory (Hansen-Goos and Mecke 2009 Phys. Rev. Lett. 102 018302) for an inhomogeneous anisotropic hard body fluid is used as a basic ingredient in treating the Brownian dynamics of hard spherocylinders. After discussing the relevance of a free parameter in the fundamental measure density functional for the isotropic-nematic transition in equilibrium, we discuss the equilibrium phase behaviour of hard spherocylinders in a static external potential which couples only to the orientations. For external potentials favouring rod orientations along the poles of the unit sphere, there is a well-known paranematic-nematic transition which ceases to exist above a threshold of the strength V(0) of the external potential. However, when orientations along the equator are more favoured, in the plane of the potential energy V(0) and density, there is a phase transition from paranematic to nematic for any strength, which becomes second order above a critical threshold of V(0). The full equilibrium phase diagram in the V(0)-density plane is computed for a fixed rod aspect ratio of 5. For the equatorial cases, strength V(0) is then oscillating in time and dynamical density functional theory is used to compute the evolution of the orientational distribution. A subtle resonance for increasing oscillation frequencies is detected if the oscillating V(0) crosses the paranematic-nematic phase transition.

Bringing physics to bear on the phenomenon of life: the divergent positions of Bohr, Delbrück, and Schrödinger.

The received view on the contributions of the physics community to the birth of molecular biology tends to present the physics community as sharing a basic level consensus on how physics should be brought to bear on biology. I argue, however, that a close examination of the views of three leading physicists involved in the birth of molecular biology, Bohr, Delbrück, and Schrödinger, suggests that there existed fundamental disagreements on how physics should be employed to solve problems in biology even within the physics community. In particular, I focus on how these three figures differed sharply in their assessment of the relevance of complementarity, the potential of chemical methods, and the relative importance of classical physics. In addition, I assess and develop Roll-Hansen's attempt to conceptualize this history in terms of models of scientific change advanced by Kuhn and Lakatos. Though neither model is fully successful in explaining the divergence of views among these three physicists, I argue that the extent and quality of difference in their views help elucidate and extend some themes that are left opaque in Kuhn's model.

Use of the Semmes-Weinstein 5.07/10 gram monofilament: the long and the short of it.

The Semmes-Weinstein monofilament has been developed for the detection of patients at risk of neuropathic ulceration. In this study we evaluated how the physical characteristics of the monofilaments can impact on their performance. Commercially purchased monofilaments from the Hansen's Disease Center (HDC) and a batch produced 'in-house' (RPAH) were calibrated using a Mettler Balance. To assess the effects of varying lengths on buckling force, the monofilaments were tested repeatedly while the length of the filament was reduced stepwise from 4.1 to 3.1 cm. The correct length of the monofilament to generate a buckling force of 10 g was also determined theoretically by applying the Euler's Buckling Equation. Results showed neither batch of monofilaments buckled at a strength of 10 g (HDC 6.8 g, CI 5.7-7.9, and RPAH 7.2 g, CI 7.1-7.3). In addition HDC showed a wide interfilament variation range, 4.1-10.3 g with CV 29% versus corresponding figures of range 7.1-7.9 g, CV 4.9% for the RPAH monofilaments. As predicted by Euler's Buckling Theory, buckling force can be increased by reducing the length of the filament. These results demonstrate that the physical characteristics of the monofilament are important determinants of buckling force and are not necessarily uniform in commercial filaments. The clinical relevance of variance in buckling force remains to be determined.