Standardization of surgical procedures for identifying best practices and training.

A taxonomy was developed a) to describe surgical procedures with sufficient detail to review differences among surgeons, b) to examine the relationship between individual technique and outcomes, c) to enable surgeons to standardize technique around best practices and d) to identify clinical-evidence-based key points of teaching and assessment for surgical training. Sixty-seven microvascular anastomoses were recorded through video cameras mounted in the dissecting microscope. A hierarchical task analysis was used to decompose the observed procedures into successive levels of detail. The results were then presented to individual and small groups of microvascular surgeons to help define steps and step attributes necessary to describe a procedure so that other surgeons can perform the procedure exactly the same way. Coincidently, it was found that because the surgeons' attention is confined to a very small field of view in which they can see only the veins and arteries and the ends of their instruments, they often have difficulty communicating with others in the operating room. Analyses of selected cases using the proposed taxonomy shows how subtle details are revealed that may affect outcomes, and indicate specific training needs. By comparing different methods and outcomes, it should be possible to identify best practices for given conditions.

Phase behavior of polymer/nanoparticle blends near a substrate.

We use the recent fluids density functional theory of Tripathi and Chapman [Phys. Rev. Lett. 94, 087801 (2005); J. Chem. Phys. 122, 094506 (2005)] to investigate the phase behavior of athermal polymer/nanoparticle blends near a substrate. The blends are modeled as a mixture of hard spheres and freely jointed hard chains, near a hard wall. There is a first order phase transition present in these blends in which the nanoparticles expel the polymer from the surface to form a monolayer at a certain nanoparticle concentration. The nanoparticle transition density depends on the length of the polymer, the nanoparticle diameter, and the overall bulk density of the system. The phase transition is due to both packing entropy effects related to size asymmetry between the components and to the polymer configurational entropy, justifying the so-called "entropic push" observed in experiments. In addition, a layered state is found at higher densities which resembles that in colloidal crystals, in which the polymer and nanoparticles form alternating discrete layers. We show that this laminar state has nearly the same free energy as the homogeneously mixed fluid in the bulk and is nucleated by the surface.

Surface-induced first-order transition in athermal polymer-nanoparticle blends.

We investigate the phase behavior of athermal polymer-nanoparticle blends near a substrate. We apply a recent fluids density functional theory of Tripathi and Chapman to a simple model of the blend as a mixture of hard spheres and freely jointed hard chains, near a hard wall. We find that there is a first-order phase transition in which the nanoparticles expel the polymer from the surface to form a monolayer. The nanoparticle transition density depends on the length of the polymer and the overall bulk density of the system. The effect is due both to packing entropy effects related to size asymmetry between the components and to the polymer configurational entropy. The simplicity of the system allows us to understand the so-called "entropic-push" observed in experiments.