Polyhedral vesicles

Polyhedral vesicles with a large bending modulus of the membrane such as the gel phase lipid membrane were studied using a Brownian dynamics simulation. The vesicles exhibit various polyhedral morphologies such as tetrahedron and cube shapes. We clarified two types of line defects on the edges of the polyhedrons: cracks of both monolayers at the spontaneous curvature of monolayer $C_{\text {0}}<0$, and a crack of the inner monolayer at $C_{\text {0}}\ge0$. Around the latter defect, the inner monolayer curves positively. Our results suggested that the polyhedral morphology is controlled by $C_{\text {0}}$.Comment: 4 pages, 5 figure

Some critical considerations on the serum diagnosis of syphilis

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Dynamics of Fluid Vesicles in Shear Flow: Effect of Membrane Viscosity and Thermal Fluctuations

The dynamical behavior of vesicles is investigated in simple shear flow. A simulation technique is presented that combines a three-dimensional particle-based mesoscopic model (multiparticle collision dynamics) for the solvent with a dynamically triangulated surface model for the membrane. In this model, thermal fluctuations of the solvent and of the membrane are consistently taken into account. The membrane viscosity can be varied by changing the bond-flip rate of the dynamically triangulated surface. Vesicles are found to transit from steady tank-treading to unsteady tumbling motion with increasing membrane viscosity. At small reduced volumes, the shear induces a transformation from a discocyte to a prolate shape at low membrane viscosity. On the other hand, at high membrane viscosity, the shear induces a transformation from prolate to discocyte, or tumbling motion accompanied by shape oscillations between these two states. Thermal fluctuations induce intermittent tumbling and smooth out the transitions. This effect can be understood from a simplified stochastic model

Microscopic Theory of Current-Spin Interaction in Ferromagnets

Interplay between magnetization dynamics and electric current in a conducting ferromagnet is theoretically studied based on a microscopic model calculation. First, the effects of the current on magnetization dynamics (spin torques) are studied with special attention to the "dissipative" torques arising from spin-relaxation processes of conduction electrons. Next, an analysis is given of the "spin motive force", namely, a spin-dependent 'voltage' generation due to magnetization dynamics, which is the reaction to spin torques. Finally, an attempt is presented of a unified description of these effects.Comment: Written in December 2008, published in July 200

Feasibility of Application of Modern Methods of Construction in Iran

Various plans and policies have been adopted by the Iranian Government to address the housing shortages in Iran. Some of these policies have been successful and some have failed dramatically deteriorating the housing conditions. Technology transfer from other countries, such as the UK, may facilitate industrialisation which has been recognised as an effective way to address housing deficiencies in Iran. The Iranian and UK construction industries, however, differ in various respects which may increase the risk of failure if transferred technologies are not adapted to Iranian needs and conditions. This paper compares the current conditions of the Iranian and UK construction industries to identify the risks and opportunities if Modern Methods of Construction (MMC) were to be transferred from the UK to Iran. Several issues such as demand and supply, regulations and standards, practicality, costs, design, sustainability, and governmental policies have been studied in detail. The results reveal that MMC could potentially improve the housing conditions in Iran by addressing major issues such as skilled labour shortages, energy and materials wastes, building quality and speed of construction. The major risks are also identified as volatile economy and housing market, transportation and industry capacity. The chance of successful adoption is considerably higher for those MMC that are suitable for small projects, do not require highly skilled labour and heavy machinery, and are compatible with prevailing methods of construction in Iran

Reversibility of Red blood Cell deformation

The ability of cells to undergo reversible shape changes is often crucial to their survival. For Red Blood Cells (RBCs), irreversible alteration of the cell shape and flexibility often causes anemia. Here we show theoretically that RBCs may react irreversibly to mechanical perturbations because of tensile stress in their cytoskeleton. The transient polymerization of protein fibers inside the cell seen in sickle cell anemia or a transient external force can trigger the formation of a cytoskeleton-free membrane protrusion of micrometer dimensions. The complex relaxation kinetics of the cell shape is shown to be responsible for selecting the final state once the perturbation is removed, thereby controlling the reversibility of the deformation. In some case, tubular protrusion are expected to relax via a peculiar "pearling instability".Comment: 4 pages, 3 figure

Ordering and arrangement of deformed red blood cells in flow through microcapillaries

The shapes and alignment of elastic vesicles similar to red blood cells (RBCs) in cylindrical capillary flow are investigated by mesoscopic hydrodynamic simulations. We study the collective flow behavior of many RBCs, where the capillary diameter is comparable to the diameter of the RBCs. Two essential control parameters are the RBC volume fraction (the tube hematocrit, H-T), and the suspension flow velocity. Depending on H-T, flow velocity and capillary radius, the RBC suspension exhibits a disordered phase and two distinct ordered phases, consisting of a single file of parachute-shaped cells and a zigzag arrangement of slipper-shaped cells, respectively. We argue that thermal fluctuations, included in the simulation method, coupled to hydrodynamic flows are important contributors to the RBC morphology. We examine the changes to the phase structures when the capillary diameter and the material properties (bending rigidity kappa and stretching modulus mu) of the model RBCs are varied, constructing phase diagrams for each case. We focus on capillary diameters, which range from about 1.0 to about 1.4 times the RBC long diameter. For the smallest capillary diameter, the single-file arrangement dominates; for the largest diameter, the ordered zigzag arrangement begins to loose its stability and alternates with an asymmetric structure with two lanes of differently oriented cells. In simulations with long capillaries, the coexistence of different phases can be observed