Lattice Universes in 2+1-dimensional gravity

Lattice universes are spatially closed space-times of spherical topology in the large, containing masses or black holes arranged in the symmetry of a regular polygon or polytope. Exact solutions for such spacetimes are found in 2+1 dimensions for Einstein gravity with a non-positive cosmological constant. By means of a mapping that preserves the essential nature of geodesics we establish analogies between the flat and the negative curvature cases. This map also allows treatment of point particles and black holes on a similar footing.Comment: 14 pages 7 figures, to appear in Festschrift for Vince Moncrief (CQG

Electro-Reflectance Spectra of Blue Bronze

We show that the infrared reflectance of the quasi-one dimensional charge-density-wave (CDW) conductor K0.3MoO3 (blue bronze) varies with position when a voltage greater than the CDW depinning threshold is applied. The spatial dependence and spectra associated with these changes are generally as expected from the electro-transmission [B.M. Emerling, et al, Eur. Phys. J. B 16, 295 (2000)], but there are some differences which might be associated with changes in the CDW properties on the surface. We have examined the electro-reflectance spectrum associated with CDW current investigation for light polarized parallel to the conducting chains for signs of expected current-induced intragap states, and conclude that the density of any such states is at least an order of magnitude lower than expected.Comment: 1)submitted to Eur. Phys. J B 2) revised (July 24) to a) better emphasize results and b) with new figure insets to make paper more self-containe

Some finite horizon dispatching problems

An arrival process (N(t), 0 = or t = or T) is to be dispatched one or more times in the time interval (0,T). The problem is to determine the optimal number of dispatches K given there are n available and to determine sequentially the epochs of dispatch tau sub 1, ..., tau sub K. There are two trade off costs c sub w and c sub d, which are respectively the cost per unit time of a waiting customer and the cost of dispatching a single unit. A general result is found which gives one optimal tau sub 1, ..., tau sub K for fixed K (i.e. the K-optimal policy) under certain regularity conditions. This is used to obtain suboptimal policies for multiple dispatching of a Poisson process and single dispatching of a birth-death process. Applications to problems in transportation, repair facilities and insect-control are indicated. (Author)http://archive.org/details/somefinitehorizo00bri

The isolation of gravitational instantons: Flat tori V flat R^4

The role of topology in the perturbative solution of the Euclidean Einstein equations about flat instantons is examined.Comment: 15 pages, ICN-UNAM 94-1