Trees under tension

Random RNA under tension

The Lässig-Wiese (LW) field theory for the freezing transition of random RNA secondary structures is generalized to the situation of an external force. We find a second-order phase transition at a critical applied force f = fc. For f < fc forces are irrelevant. For f > fc, the extension L as a function of pulling force f scales as L(f) ∼ (f − fc) 1/γ−1. The exponent γ is calculated in an ǫ-expa...

Semiflexible chains under tension

A functional integral formalism is used to derive the extension of a stiff chain subject to an external force. The force versus extension curves are calculated using a mean-field approach in which the hard constraint u(s)51 is replaced by a global constraint ^u(s)&51 where u(s) is the tangent vector describing the chain and s is the arclength. The theory quantitatively reproduces the experiment...

Neutrophils under tension.

An article by Houk et al. (2012) in Cell provides insight into the mechanisms confining membrane protrusions to the front of migrating neutrophils. The authors rule out a role for diffusion of inhibitory signals and show that membrane tension is necessary and sufficient to restrict signals that lead to protrusions.

Strength Under Tension

Russell Bainer 1,2 and Valerie Weaver 1,2, 3, 4, 5, 6 Mechanical tension on a cell from its environment alters the expression of a protein that changes the physical properties of the nucleus. and accreted onto the black hole ( 6). Summing over the total wind loss from the surrounding stars, this gives an accretion rate of 10 solar masses per year ( 7). The mysterious thing is, this accretion ra...

Fusion under Tension