Electronic interactions in the expanded metal compound Li-NH3

Inelastic x-ray scattering was used to measure the plasmon as a function of electron density in liquid lithium ammonia as well as the low temperature solid phase. As the electronic density is lowered, electronic correlation effects cause the random-phase approximation (RPA) to break down, requiring more advanced theoretical treatments. The deviation from RPA becomes greatest at the lowest electronic densities. We also see evidence for decreased electronic screening as shown by an increase in the strength of the pseudopotential at lower concentrations. Plasmon behavior in the solid is similar to that of the heavier alkali metals, but surprisingly different than in the liquid.     

The role of the hydration configuration in electronic processes involving ions in aqueous solution

The nature of small ions in electrolytic (e.g., aqueous) solutions is discussed in terms of the configuration of the adjoining polarized medium, and the role of this configuration in electronic transitions involving one or a pair of ions is treated in a general way. Light absorption by a single ion is shown to depend critically on this configuration; a theory developed previously by the authors is reviewed, and future possibilities of exploring the nature of the configuration by investigation of such spectra are explained. Electronic transitions, such as an “electron transfer” process, during binary collisions of ions are treated, and a general method is developed, based uponDebye's “diffusion” theory for ion collision rates and a nonadiabatic type of potential curve. Rates of chemical processes are found to depend decisively on the interaction of two ions at separations where the simple coulomb law is not valid.     

An O(N log N) planar travelling salesman heuristic based on spacefilling curves

N points in a square of area A may be sorted according to their images under a spacefilling mapping to give a tour of length at most 2√NA. If the points are statistically independent under a smooth distribution, with N large, then the tour will be roughly 25% longer than optimum (and a simple enhancement reduces this to 15%). The algorithm is easily coded: a complete BASIC program is included in the appendix. Since the algorithm consists essentially of sorting, points are easily added or removed. Our method may also be used with simple dynamic programming to solve TSP path problems.     

Artificial Cytoskeleton Assembly for Synthetic Cell Motility

Imitation of cellular processes in cell-like compartments is a current research focus in synthetic biology. Here, a method is introduced for assembling an artificial cytoskeleton in a synthetic cell model system based on a poly(N-isopropyl acrylamide) (PNIPAM) composite material. Toward this end, a PNIPAM-based composite material inside water-in-oil droplets that are stabilized with PNIPAM-functionalized and commercial fluorosurfactants is introduced. The temperature-mediated contraction/release behavior of the PNIPAM-based cytoskeleton is investigated. The reversibility of the PNIPAM transition is further examined in bulk and in droplets and it could be shown that hydrogel induced deformation could be used to controllably manipulate droplet-based synthetic cell motility upon temperature changes. It is envisioned that a combination of the presented artificial cytoskeleton with naturally occurring components might expand the bandwidth of the bottom-up synthetic biology.