Protein gradients in single cells induced by their coupling to "morphogen"-like diffusion

One of the many ways cells transmit information within their volume is through steady spatial gradients of different proteins. However, the mechanism through which proteins without any sources or sinks form such single-cell gradients is not yet fully understood. One of the models for such gradient formation, based on differential diffusion, is limited to proteins with large ratios of their diffusion constants or to specific protein-large molecule interactions. We introduce a novel mechanism for gradient formation via the coupling of the proteins within a single cell with a molecule, that we call a "pronogen", whose action is similar to that of morphogens in multi-cell assemblies, the pronogen is produced with a fixed flux at one side of the cell. This coupling results in an effectively non-linear diffusion degradation model for the pronogen dynamics within the cell, which leads to a steady-state gradient of the protein concentration. We use a stability analysis to show that these gradients are linearly stable with respect to perturbations.Comment: To appear in J. Chem. Phy

Study of high viscous multiphase phase flow in a horizontal pipe

Heavy oil accounts for a major portion of the world’s total oil reserves. Its production and transportation through pipelines is beset with great challenges due to its highly viscous nature. This paper studies the effects of high viscosity on heavy oil two-phase flow characteristics such as pressure gradient, liquid holdup, slug liquid holdup, slug frequency and slug liquid holdup using an advanced instrumentation (i.e. Electrical Capacitance Tomography). Experiments were conducted in a horizontal flow loop with a pipe internal diameter (ID) of 0.0762 m; larger than most reported in the open literature for heavy oil flow. Mineral oil of 1.0–5.0 Pa.s viscosity range and compressed air were used as the liquid and gas phases respectively. Pressure gradient (measured by means differential pressure transducers) and mean liquid holdup was observed to increase as viscosity of oil is increased. Obtained results also revealed that increase in liquid viscosity has significant effects on flow pattern and slug flow features.</p

Gap Opening of Graphene by Dual FeCl3-Acceptor and K-Donor Doping

The band gap opening of graphene is the most desired property in the device industry because it is vital to the application of graphene as a logical device of semiconductors. Here, we show how to make a reasonably wide band gap in graphene. This is accomplished with bilayer graphene (BLG) dual-doped with FeCl3-acceptor and K-donor. To elucidate this phenomenon, we employed the first-principles method taking into account van der Waals interaction. For the FeCl3 adsorbed BLG, the optimal distance between the adjacent graphene and FeCl3 layers is 4.6-4.8 angstrom, consistent with experiments. Due to the high electronegativity of FeCl3, these graphene layers are hole-doped. The dual-doped BLG gives a band gap of 0.27 eV due to broken symmetry, with a Dirac point shift by -0.09 eV. This increased band gap and proper Dirac point shift could make the dual-doped BLG useful for applications toward future field effect transistor devices.close272