Measuring Gaussian rigidity using curved substrates

The Gaussian (saddle splay) rigidity of fluid membranes controls their equilibrium topology but is notoriously difficult to measure. In lipid mixtures, typical of living cells, linear interfaces separate liquid ordered (LO) from liquid disordered (LD) bilayer phases at subcritical temperatures. Here we consider such membranes supported by curved supports that thereby control the membrane curvatures. We show how spectral analysis of the fluctuations of the LO-LD interface provides a novel way of measuring the difference in Gaussian rigidity between the two phases. We provide a number of conditions for such interface fluctuations to be both experimentally measurable and sufficiently sensitive to the value of the Gaussian rigidity, whilst remaining in the perturbative regime of our analysis.Comment: 5 pages, 3 figures. v2: version accepted for publicatio

Climate Change and the Law: Cushioning the Effects of Climate Change- In Niger Delta

Climate change has been defined as any natural or induced change in climate either globally or in a particular area However the United Nations Framework Convention on Climate Change gives its own definition as a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods This definition is holistic as it includes the causative elements of climate change There is consensus that climate change is a critical issue for Africa and indeed its greatest challenge in the 21st century along with poverty There is a speculation that climate change in no specified measure is likely to affect the continent s development trajectory as most African countries are characterized by undiversified economic structures poor infrastructure fragile structures and institutions poor human development and most importantly the heavy reliance on agriculture for the majority of the population The reason for climate change is that Mother Earth our only home is under pressur

Hydro-osmotic instabilities in active membrane tubes

We study a membrane tube with unidirectional ion pumps driving an osmotic pressure difference. A pressure driven peristaltic instability is identified, qualitatively distinct from similar tension-driven Rayleigh type instabilities on membrane tubes. We discuss how this instability could be related to the function and biogenesis of membrane bound organelles, in particular the contractile vacuole complex. The unusually long natural wavelength of this instability is in agreement with that observed in cells

Dynamics of passive and active membrane tubes

Utilising Onsager's variational formulation, we derive dynamical equations for the relaxation of a fluid membrane tube in the limit of small deformation, allowing for a contrast of solvent viscosity across the membrane and variations in surface tension due to membrane incompressibility. We compute the relaxation rates, recovering known results in the case of purely axis-symmetric perturbations and making new predictions for higher order (azimuthal) $m$-modes. We analyse the long and short wavelength limits of these modes by making use of various asymptotic arguments. We incorporate stochastic terms to our dynamical equations suitable to describe both passive thermal forces and non-equilibrium active forces. We derive expressions for the fluctuation amplitudes, an effective temperature associated with active fluctuations, and the power spectral density for both the thermal and active fluctuations. We discuss an experimental assay that might enable measurement of these fluctuations to infer the properties of the active noise. Finally we discuss our results in the context of active membranes more generally and give an overview of some open questions in the field.Comment: 14 pages, 9 figure

Dynamics of lipid membrane tubes

Membrane tubes are structures ubiquitous in cells, and understanding their dynamics and morphology is of vital importance for cellular biophysics. This thesis will discuss several aspects of the dynamics of membrane tubes in situations where they are driven out of equilibrium by various biologically inspired processes. We analyse the inflation of membrane tubes and their subsequent instability due to ion pumps driving an osmotic pressure difference. This is inspired by the structure of an organelle called the contractile vacuole complex, and leads to a new instability with a much longer natural wavelength than a typical pearling instability. The stability of membrane tubes with a shear in the membrane ow is analysed and a novel helical instability which acts to amplify the fluctuations is found. We discuss the relevance of this instability in the process of dynamin-mediated tube scission. Finally we consider the dynamics and fluctuations of a membrane tube with active forces acting on it

Non-alcoholic fatty liver disease in women – current knowledge and emerging concepts

Non-alcoholic fatty liver disease (NAFLD) is a major cause of liver disease worldwide, affecting up to 30% of adults. Progression to non-alcoholic steatohepatitis (NASH) is a key risk factor for cirrhosis, hepatocellular carcinoma and cardiovascular events. Alterations in reproductive hormones are linked to the development and/or progression of NAFLD/NASH in women. Women with Polycystic Ovary Syndrome (PCOS) and those with estrogen deficiency are at increased risk of NAFLD/NASH, with higher mortality rates in older women compared to men of similar ages. NAFLD/NASH is currently the leading indication for liver transplantation in women without hepatocellular carcinoma. Therefore, a better understanding of NAFLD in women is needed to improve outcomes. In this review, we discuss the hormonal and non-hormonal factors contributing to NAFLD development and progression in women. Furthermore, we highlight areas of focus for clinical practice and for future research