Tensorial hydrodynamic slip

We describe a tensorial generalization of the Navier slip boundary condition and illustrate its use in solving for flows around anisotropic textured surfaces. Tensorial slip can be derived from molecular or microstructural theories or simply postulated as an constitutive relation, subject to certain general constraints on the interfacial mobility. The power of the tensor formalism is to capture complicated effects of surface anisotropy, while preserving a simple fluid domain. This is demonstrated by exact solutions for laminar shear flow and pressure-driven flow between parallel plates of arbitrary and different textures. From such solutions, the effects of rotating a texture follow from simple matrix algebra. Our results may be useful to extracting local slip tensors from global measurements, such as the permeability of a textured channel or the force required to move a patterned surface, in experiments or simulations.Comment: 10 page

Coral relocation in Chabahar Bay, the North-east of Oman Sea

Corals are marine benthic animals typically living in compact colonies of many identical individual polyps (Barnes, 1987; Gateno et al., 1996; Sumich, 1996). Coral reefs are important for many reasons including: a) Most importantly, they provide protection and shelter for many different species of fish. b) They turn surplus carbon dioxide in the water into a limestone shell. Without coral, the amount of carbon dioxide in the water would increase dramatically and that would affect all living things on Earth. c) Similar to a barrier, the coral reefs protect coasts from strong currents and waves by slowing down the water before it gets to the shore. d) Coral reef ecosystems support a variety of human needs such as fisheries and tourism (James and Spurgeon, 1992; Moberg and Folke, 1999; Cesar, 2000). Therefore, the conservation of coral colonies is very vital for marine organisms and human. In Chabahar Bay, the coral reefs are in danger of destruction due to the development program of Shahid Beheshti Port. Since the corals are very sensitive to turbidity and suspended sediments from land reclamation and dredging projects, therefore appropriate measures should be conducted for conservation and recovery of them. At present, the coral relocation is suggested as a good method for recovery of coral reefs after a disturbance in condition of their native habitats. In our project, over 28,000 hard corals were transported to coast of Hotel Lipar (Fig. 1), an area at a distance of 3.5 km far from Shahid Beheshti Port. Also, the new techniques were used for coral reattachment and transportation

Nonlinear electrokinetics at large voltages

The classical theory of electrokinetic phenomena assumes a dilute solution of point-like ions in chemical equilibrium with a surface whose double-layer voltage is of order the thermal voltage, kBT/e=25 mV. In nonlinear 'induced-charge' electrokinetic phenomena, such as ac electro-osmosis, several volts ≈100kBT/e are applied to the double layer, and the theory breaks down and cannot explain many observed features. We argue that, under such a large voltage, counterions 'condense' near the surface, even for dilute bulk solutions. Based on simple models, we predict that the double-layer capacitance decreases and the electro-osmotic mobility saturates at large voltages, due to steric repulsion and increased viscosity of the condensed layer, respectively. The former suffices to explain observed high-frequency flow reversal in ac electro-osmosis; the latter leads to a salt concentration dependence of induced-charge flows comparable to experiments, although a complete theory is still lacking.National Science Foundation (U.S.) (Grant No. DMS-0707641)United States. Army Research Office. Institute for Soldier Nanotechnologies (Contract No. DAAD- 19-02-0002

Molecular Motor of Double-Walled Carbon Nanotube Driven by Temperature Variation

An elegant formula for coordinates of carbon atoms in a unit cell of a single-walled nanotube (SWNT) is presented and a new molecular motor of double-walled carbon nanotube whose inner tube is a long (8,4) SWNT and outer tube a short (14,8) SWNT is constructed. The interaction between inner an outer tubes is analytically derived by summing the Lennard-Jones potentials between atoms in inner and outer tubes. It is proved that the molecular motor in a thermal bath exhibits a directional motion with the temperature variation of the bath.Comment: 9 pages, 4 figures, revtex

Molecular Motor Constructed from a Double-Walled Carbon Nanotube Driven by Axially Varying Voltage

A new molecular motor is conceptually constructed from a double-walled carbon nanotube (DWNT) consisting of a long inner single-walled carbon nanotube (SWNT) and a short outer SWNT with different chirality. The interaction between inner and outer tubes is the sum of the Lennard-Jones potentials between carbon atoms in inner tube and those in outer one. Within the framework of Smoluchowski-Feynman ratchet, it is theoretically shown that this system in an isothermal bath will exhibit a unidirectional rotation in the presence of a varying axial electrical voltage.Comment: 11 pages + 3 figure

Effective Area-Elasticity and Tension of Micro-manipulated Membranes

We evaluate the effective Hamiltonian governing, at the optically resolved scale, the elastic properties of micro-manipulated membranes. We identify floppy, entropic-tense and stretched-tense regimes, representing different behaviors of the effective area-elasticity of the membrane. The corresponding effective tension depends on the microscopic parameters (total area, bending rigidity) and on the optically visible area, which is controlled by the imposed external constraints. We successfully compare our predictions with recent data on micropipette experiments.Comment: To be published in Phys. Rev. Let