A Particle-based Multiscale Solver for Compressible Liquid-Vapor Flow

To describe complex flow systems accurately, it is in many cases important to account for the properties of fluid flows on a microscopic scale. In this work, we focus on the description of liquid-vapor flow with a sharp interface between the phases. The local phase dynamics at the interface can be interpreted as a Riemann problem for which we develop a multiscale solver in the spirit of the heterogeneous multiscale method, using a particle-based microscale model to augment the macroscopic two-phase flow system. The application of a microscale model makes it possible to use the intrinsic properties of the fluid at the microscale, instead of formulating (ad-hoc) constitutive relations

A study of acromegaly-associated headache with somatostatin analgesia.

To characterise somatostatin analogue responsive headache in acromegaly, hitherto not systematically documented in a significant cohort. Using the UK pituitary network, we have clinically characterised a cohort of 18 patients suffering from acromegaly-related headache with a clear response to somatostatin analogues. The majority of patients had chronic migraine (78%) as defined by the International Headache Society diagnostic criteria. Headache was present at the time of acromegaly presentation and clearly associated temporally with disease activity in all cases. Short-acting somatostatin analogues uniquely resolved pain within minutes and the mean duration of analgesia was 1-6 hours. Patients on long-acting analogues required less short-acting injections (mean 3.7 vs. 10.4 injections per day, p=0.005). 94% used somatostatin analogues to control ongoing headache pain. All patients presented with macroadenoma, most had incomplete resection (94%) and headache was ipsilateral to remnant tissue (94%). Although biochemical control was achieved in 78% of patients, headache remained in 71% of them. Patients selected for this study had ongoing headache post-treatment (mean duration 16 years after diagnosis); only 4 patients reached headache remission 26 years (mean, range 14-33) after the diagnosis. Headache in acromegaly patients can be persistent, severe, unrelieved by surgery, long-lasting and uncoupled from biochemical control. We show here that long-acting analogues allow a decrease in the number of short-acting analogue injections for headache relief. Further studies are needed to understand the mechanisms, markers and tumour tissue characteristics of acromegaly-related headache. Until then, this publication serves to provide the clinical characteristics as a reference point for further study

Mechanical Metamaterials with Negative Compressibility Transitions

When tensioned, ordinary materials expand along the direction of the applied force. Here, we explore network concepts to design metamaterials exhibiting negative compressibility transitions, during which a material undergoes contraction when tensioned (or expansion when pressured). Continuous contraction of a material in the same direction of an applied tension, and in response to this tension, is inherently unstable. The conceptually similar effect we demonstrate can be achieved, however, through destabilisations of (meta)stable equilibria of the constituents. These destabilisations give rise to a stress-induced solid-solid phase transition associated with a twisted hysteresis curve for the stress-strain relationship. The strain-driven counterpart of negative compressibility transitions is a force amplification phenomenon, where an increase in deformation induces a discontinuous increase in response force. We suggest that the proposed materials could be useful for the design of actuators, force amplifiers, micro-mechanical controls, and protective devices.Comment: Supplementary information available at http://www.nature.com/nmat/journal/v11/n7/abs/nmat3331.htm

On higher order gradient continuum theories in 1-D nonlinear elasticity. Derivation from and comparison to the corresponding discrete models

Higher order gradient continuum theories have often been proposed as models for solids that exhibit localization of deformation (in the form of shear bands) at sufficiently high levels of strain. These models incorporate a length scale for the localized deformation zone and are either postulated or justified from micromechanical considerations. Of interest here is the consistent derivation of such models from a given microstructure and the subsequent comparison of the solution to a boundary value problem using both the exact microscopic model and the corresponding approximate higher order gradient macroscopic model.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42682/1/10659_2004_Article_BF00043251.pd