Imbibition in Disordered Media

The physics of liquids in porous media gives rise to many interesting phenomena, including imbibition where a viscous fluid displaces a less viscous one. Here we discuss the theoretical and experimental progress made in recent years in this field. The emphasis is on an interfacial description, akin to the focus of a statistical physics approach. Coarse-grained equations of motion have been recently presented in the literature. These contain terms that take into account the pertinent features of imbibition: non-locality and the quenched noise that arises from the random environment, fluctuations of the fluid flow and capillary forces. The theoretical progress has highlighted the presence of intrinsic length-scales that invalidate scale invariance often assumed to be present in kinetic roughening processes such as that of a two-phase boundary in liquid penetration. Another important fact is that the macroscopic fluid flow, the kinetic roughening properties, and the effective noise in the problem are all coupled. Many possible deviations from simple scaling behaviour exist, and we outline the experimental evidence. Finally, prospects for further work, both theoretical and experimental, are discussed.Comment: Review article, to appear in Advances in Physics, 53 pages LaTe

Study protocol: The Intensive Care Outcome Network ('ICON') study

<p>Abstract</p> <p>Background</p> <p>Extended follow-up of survivors of ICU treatment has shown many patients suffer long-term physical and psychological consequences that affect their health-related quality of life. The current lack of rigorous longitudinal studies means that the true prevalence of these physical and psychological problems remains undetermined.</p> <p>Methods/Design</p> <p>The ICON (Intensive Care Outcome Network) study is a multi-centre, longitudinal study of survivors of critical illness. Patients will be recruited prior to hospital discharge from 20–30 ICUs in the UK and will be assessed at 3, 6, and 12 months following ICU discharge for health-related quality of life as measured by the Short Form-36 (SF-36) and the EuroQoL (EQ-5D); anxiety and depression as measured by the Hospital Anxiety and Depression Scale (HADS); and post traumatic stress disorder (PTSD) symptoms as measured by the PTSD Civilian Checklist (PCL-C). Postal questionnaires will be used.</p> <p>Discussion</p> <p>The ICON study will create a valuable UK database detailing the prevalence of physical and psychological morbidity experienced by patients as they recover from critical illness. Knowledge of the prevalence of physical and psychological morbidity in ICU survivors is important because research to generate models of causality, prognosis and treatment effects is dependent on accurate determination of prevalence. The results will also inform economic modelling of the long-term burden of critical illness.</p> <p>Trial Registration</p> <p>ISRCTN69112866</p

Fracture in mesoscopic disordered systems

A simple mechanical model of planar fibrous materials with mesoscopic disorder is introduced and analyzed. In this scalar model a shear modulus controls the stress transfer in the transverse direction. The system is studied using the effective medium approximation and computer simulations; the comparison between them is quite favorable. In the disorder-controlled regime the stress-strain relation, the number of broken cells at the onset of crack propagation, and the length of the final crack scale with the system size as L2, L1.7, and L, respectively. The mechanical properties are controlled by the interplay between disorder and shear modulus, which is studied in detail

Simulation of network shrinkage

We report numerical simulations oil shrinkage in a fiber network when the fibers shrink more in their transverse to length direction than the axial direction. The effect of network density and anisotropic fiber properties on sheet shrinkage, elastic modulus and segment strain distributions is explored. The macroscopic free shrinkage follows a simple mathematical expression that is consistent with the hygroexpansivity theory of Uesaka. The shrinkage of fiber segments agrees qualitatively with the microscopic measurements of Nanko and Wu. In addition, we found that in free drying the mean length changes of free and bonded fiber segments are almost independent of network density