Tailorable thermal expansion hybrid structures

A design concept is presented for a macro or microstructure that combines materials with differing thermal expansion to achieve an overall effective expansion that differs substantially from either of the constituents. Near-zero-CTE and isotropic negative expansion designs are achieved by creating compliant structures where overall expansion is compensated by internal bending deformation. Such structures have application where dimensional stability is required when subject to large thermal gradients, e.g. space mirrors. In this paper, we present closed form analytic expressions for prediction of the effective expansion, and consequent internal stressing, of the structure, as well as several finite element simulations that demonstrate the design performance under non-uniform thermal load.     

6,7‐Dihydrodibenzo[e,g]azulen‐8(5H)‐one and 12,13‐dihydrobenzo[e]­napth­[2,1‐g]­azulen‐14(11H)‐one

In the structures of the title compounds, 6,7‐di­hydro­dibenzo[e,g]­azulen‐8(5H)‐one, C₁₈H₁₄O, (I), and 12,13‐di­hydro­benzo[e]­napth­[2,1‐g]­azulen‐14(11H)‐one, C₂₂H₁₆O, (II), the azulene group is in a boat‐envelope conformation. The structures are stabilized by weak C—H?O interactions.     

On Gribov ambiguity in finite temperature Abelian gauge theory

It is shown that there is Gribov ambiguity in finite temperature Abelian gauge theory if the gauge theory is defined on the full gauge orbit space. This is demonstrated geometrically and by an explicit construction of solutions to the Gribov equation. Its effects on the evaluation of the temperature-dependent partition function are noted using the Faddeev-Popov procedure.     

On stochastic games

In this paper, we consider the stochastic games of Shapley, when the state and action spaces are all infinite. We prove that, under certain conditions, the stochastic game has a value and that both players have optimal strategies.Part of this research was supported by NSF grant. The authors are indebted to L. S. Shapley for the useful discussions on this and related topics. The authors thank the referee for pointing out an ambiguity in the formulation of Lemma 2.4 in an earlier draft of this article.     

Percolating through networks of random thresholds: finite temperature electron tunneling in metal nanocrystal arrays

We investigate how temperature affects transport through large networks of nonlinear conductances with distributed thresholds. In monolayers of weakly coupled gold nanocrystals, quenched charge disorder produces a range of local thresholds for the onset of electron tunneling. Our measurements delineate two regimes separated by a crossover temperature T*. Up to T* the nonlinear zero-temperature shape of the current-voltage curves survives, but with a threshold voltage for conduction that decreases linearly with temperature. Above T* the threshold vanishes and the low-bias conductance increases rapidly with temperature. We develop a model that accounts for these findings and predicts T*.     

Tea CO2 laser-induced deuterium exchange in the ammonia—fluoroform-d system

Vibrational excitation of CDF₃ and NH₃ at 970 cm^?1 by a TEA CO₂ laser results in deuterium—hydrogen exchange suppressing the IR-laser-induced multiphoton chemistry of CDF₃.