Motion of magnetotactic bacteria swarms in an external field

Magnetotactic bacteria moving on circular orbits form hydrodynamically bound states. When close to a surface and with the tilting of the field in a direction close to the perpendicular to this surface these swarms move perpendicularly to the tilting angle. We describe quantitatively this motion by a continuum model with couple stress arising from the torques produced by the rotary motors of the amphitrichous magnetotactic bacteria. The model not only correctly describes the change of direction of swarm motion while inverting the tangential field but also predicts reasonable value of the torque produced by the rotary motors

Safety-Net Suture for Aphakic Descemet Membrane Endothelial Keratoplasty

PURPOSE: The purpose of this research was to describe a low-cost, accessible method for reducing the risk of posterior donor dislocation in Descemet membrane endothelial keratoplasty (DMEK) performed in eyes with aphakia and a large iris defect (unicameral eyes)-the "safety-net suture." METHODS: We review 3 cases of aphakic bullous keratopathy in unicameral eyes treated successfully using DMEK aided by a simple technique to create a temporary, partial barrier between the anterior and posterior chambers. The safety-net suture technique is based on a continuous 10-0 polypropylene suture placed across the anterior chamber in a cat's-cradle pattern anterior to the trabecular meshwork. At the end of surgery, after air tamponade of the DMEK donor, the 10-0 polypropylene suture is removed. RESULTS: All 3 cases were completed with no intraoperative posterior dislocation. A partial postoperative detachment in 1 case was successfully treated with repeat air tamponade. The corneas remain clear in early follow-up, 1 to 10 months after surgery. CONCLUSIONS: The safety-net suture is a simple, low-cost method of reducing the risk of intraoperative posterior dislocation for DMEK in unicameral, aphakic eyes

A fast cross-entropy method for estimating buffer overflows in queueing networks

In this paper, we propose a fast adaptive importance sampling method for the efficient simulation of buffer overflow probabilities in queueing networks. The method comprises three stages. First, we estimate the minimum cross-entropy tilting parameter for a small buffer level; next, we use this as a starting value for the estimation of the optimal tilting parameter for the actual (large) buffer level. Finally, the tilting parameter just found is used to estimate the overflow probability of interest. We study various properties of the method in more detail for the M/M/1 queue and conjecture that similar properties also hold for quite general queueing networks. Numerical results support this conjecture and demonstrate the high efficiency of the proposed algorithm