Tying Two Forces

Labor tying

We study labor-tying in a competitive agricultural economy. The co-existence of seasonal fluctuations in income and imperfect credit markets suggests that tied contracts should dominate casual labor markets. However, empirical observation from India suggests that this is far from being the case, and indeed, that there is a declining trend in labor tying. We consider a model that permits deviati...

Simulated Knot Tying

Applications such as suturing in medical simulations require the modeling of knot tying in physically realistic rope. The paper describes the design and implementation of such a system. Our model uses a spline of linear springs, adaptive subdivision and a dynamics simulation. Collisions are discrete event simulated and follow the impulse model. Although some care must be taken to maintain stabl...

Tying rings for sex.

The primary component of the sex pilus encoded by IncP (RP4) and Ti plasmids has been identified as a circular pilin protein with a peptide bond between the amino and carboxyl terminus. Here, we review the key experiments that led to this discovery, and the present mechanistic model for pilin-precursor processing and the cyclization reaction. In addition, we discuss the implications for horizon...

Tying It All Together

Two oldies join forces to guard homeostasis.

THE COMPLEMENT SYSTEM APPEARS early during the evolution of multicellular organisms (10). It is well-known that complement constitutes one of the first, innate, lines of defense against microbial invaders. But complement functions are not limited to immune processes. The complement system is involved in angiogenesis, inflammation, tissue repair, hematopoietic stem cell mobilization, lipid metab...