Amorphous metals for hard-tissue prosthesis

Owing to a unique atomic structure lacking microstructural defects, glassy metals demonstrate certain universal properties that are attractive for load-bearing biomedical-implant applications. These include a superb strength, which gives rise to very high hardness and a potential for minimizing wear and associated adverse biological reactions, and a relatively low modulus, which enables high elasticity and holds a promise for mitigating stress shielding. There are, however, other non-universal properties specific to particular amorphous metal alloys that are inferior to presently used biometals and may be below acceptable limits for hard-tissue prosthesis. In this article, features of the performance of amorphous metals relevant to hard-tissue prosthesis are surveyed and contrasted to those of the current state of the art, and guidelines for development of new biocompatible amorphous metal alloys suitable for hard-tissue prosthesis are proposed.     

Mass transfer coefficient and concentration boundary layer thickness for a dissolving NAPL pool in porous media

Analytical expressions for the time invariant, average mass transfer coefficient and the concentration boundary layer thickness applicable to dissolving single-component nonaqueous phase liquid (NAPL) pools in two-dimensional, saturated, homogeneous and isotropic porous formations are derived. Good agreement between predicted and experimentally determined time invariant average mass transfer coefficients is observed.     

Dithiopheneindenofluorene (TIF) Semiconducting Polymers with Very High Mobility in Field‐Effect Transistors

The charge‐carrier mobility of organic semiconducting polymers is known to be enhanced when the energetic disorder of the polymer is minimized. Fused, planar aromatic ring structures contribute to reducing the polymer conformational disorder, as demonstrated by polymers containing the indacenodithiophene ( IDT ) repeat unit, which have both a low Urbach energy and a high mobility in thin‐film‐transistor (TFT) devices. Expanding on this design motif, copolymers containing the dithiopheneindenofluorene repeat unit are synthesized, which extends the fused aromatic structure with two additional phenyl rings, further rigidifying the polymer backbone. A range of copolymers are prepared and their electrical properties and thin‐film morphology evaluated, with the co ‐benzothiadiazole polymer having a twofold increase in hole mobility when compared to the IDT analog, reaching values of almost 3 cm² V^?1 s^?1 in bottom‐gate top‐contact organic field‐effect transistors.     

The structure and complexity of Nash equilibria for a selfish routing game

In this work, we study the combinatorial structure and the computational complexity of Nash equilibria for a certain game that models selfish routing over a network consisting of m$m$ parallel links. We assume a collection of n$n$ users, each employing a mixed strategy, which is a probability distribution over links, to control the routing of her own traffic. In a Nash equilibrium, each user selfishly routes her traffic on those links that minimize her expected latency cost, given the network congestion caused by the other users. The social cost of a Nash equilibrium is the expectation, over all random choices of the users, of the maximum, over all links, latency through a link.     

The impact of randomization in smoothing networks

We revisit randomized smoothing networks (Herlihy and Tirthapura in J Parallel Distrib Comput 66(5):626–632, 2006), which are made up of balancers and wires. We assume that balancers are oriented independently and uniformly at random. Tokens arrive arbitrarily on w input wires and propagate asynchronously through the network; each token is served on the output wire it arrives at. The smoothness is the maximum discrepancy among the numbers of tokens arriving at the w output wires. We present a collection of lower and upper bounds on smoothness, which are to some extent surprising: (1) The smoothness of a single block network is lg lg w+Θ(1) (with high probability), where the additive constant is between ?2 and 3. This tight bound improves vastly over the upper bound of ${\mathcal{O}(\sqrt{lg\, w})}$ from Herlihy and Tirthapura (2006), and it essentially settles our understanding of the smoothing properties of the block network. Further, this lg lg w+Θ(1) bound cannot be extended to universal smoothing a property stronger than smoothing that we introduce. (2) Most significantly, the smoothness of the cascade of two block networks is no more than 17 (with high probability); this is the first known randomized network with so small depth (2 lg w) and so good (constant) smoothness. The proof introduces some combinatorial and probabilistic structures and techniques which may be further applicable; the result demonstrates the full power of randomization in smoothing networks. (3) There is no randomized 1-smoothing network of width w and depth d that achieves 1-smoothness with probability better than ${\frac{\mathsf{d}} {w-1} }$ . In view of the deterministic, Θ(lg w)-depth, 1-smoothing network in Klugerman and Plaxton (Proceedings of the 24th Annual ACM Symposium on Theory of Computing, 1992), this result implies the first separation between deterministic and randomized smoothing networks. These results demonstrate an unexpected limitation on the power of randomization for smoothing networks: although it yields constant smoothness using small depth, going down to smoothness of 1 requires linear depth.     

Book Review

Abstract

COMPUTER ABUSE, by Donn B. Parker, Susan Nycum, and S. Stephen Oura; National Science Foundation, 1973, 131 pages, $4.75. (Obtain from National Technical Information Service, U.S. Department of Commerce, Springfield, VA, 22151. Order No. PB-231–320.)