Why Not Consider Closed Universes?

We consider structure formation and CMB anisotropies in a closed universe, both with and without a cosmological constant. The CMB angular power spectrum and the matter transfer function are presented, along with a discussion of their relative normalization. This represents the first full numerical evolution of density perturbations and anisotropies in a spherical geometry. We extend the likelihood function vs. Omega from the COBE 2-year data to Omega>=1. For large Omega the presence of a very steep rise in the spectrum towards low ell allows us to put an upper limit of Omega<=1.5 (95%CL) for primordial spectra with n<=1. This compares favorably with existing limits on Omega. We show that there are a range of closed models which are consistent with observational constraints while being even older than the currently popular flat models with a cosmological constant. Future constraints from degree scale CMB data may soon probe this region of parameter space. A derivation of the perturbed Einstein, fluid and Boltzmann equations for open and closed geometries is presented in an appendix.Comment: 24 pages, including 13 figures in a uuencoded self-unpacking shell script. Submitted to Ap

Lessons From a Health Information Technology Demonstration in New York Nursing Homes

Outlines the New York State Nursing Home Health Information Technology Demonstration Project; variations in organizational aims in adopting HIT, perceived or real effects, and resulting quality improvement efforts; and considerations for replication

A Characteristic Scale on the Cosmic Microwave Sky

The current suite of results from Cosmic Microwave Background anisotropy experiments is fulfilling the promise of providing extraordinary levels of discrimination between cosmological models. We calculate a binned anisotropy power spectrum, which we tabulate, along with error bars and bin-to-bin correlations, so that it can be easily used for constraining models. The resulting power spectrum is flat at large angles, with a gradual rise to a prominent peak at around 0.5 degrees and a decrease thereafter. This is precisely the shape predicted by inflationary-inspired adiabatic models. Within that class of cosmologies, this characteristic scale imprinted on the CMB sky can be used to infer that the geometry of the Universe is very close to flat. The next wave of CMB results should add fuel to the debate about whether or not the Universe once inflated, as well as beginning in earnest the task of measuring cosmological parameters.Comment: 6 pages, 1 figure. A less technical article based on the same work has appeared in Science Perspectives under the title "How Flat is the Universe?" (Science, Mar 24, 2000, 2171-2172

Nonlinear Filtering for Stochastic Volatility Models with Heavy Tails and Leverage

This paper develops a computationally efficient filtering based procedure for the estimation of the heavy tailed SV model with leverage. While there are many accepted techniques for the estimation of standard SV models, incorporating these effects into an SV framework is difficult. Simulation evidence provided in this paper indicates that the proposed procedure outperforms competing approaches in terms of the accuracy of parameter estimation. In an empirical setting, it is shown how the individual effects of heavy tails and leverage can be isolated using standard likelihood ratio tests.

Cure kinetics of ring-opening metathesis polymerization of dicyclopentadiene

The cure kinetics of polydicyclopentadiene (pDCPD) prepared by ring-opening metathesis polymerization with three different concentrations of Grubbs' catalyst was examined using differential scanning calirimetry (DSC). The experimental data were used to test several different phenomenological kinetic models. The data are best modeled with a "model-free" isoconversional method. This analysis reveals that the activation energy increases significantly for degree of cure greater than 60%. Catalyst concentration is shown to have a large effect on the cure kinetics.published or submitted for publicationis peer reviewe

Solar tracking system

A solar tracker for a solar collector is described in detail. The collector is angularly oriented by a motor wherein the outputs of two side-by-side photodetectors are discriminated as to three ranges: a first corresponding to a low light or darkness condition; a second corresponding to light intensity lying in an intermediate range; and a third corresponding to light above an intermediate range, direct sunlight. The first output drives the motor to a selected maximum easterly angular position; the second enables the motor to be driven westerly at the Earth rotational rate; and the third output, the separate outputs of the two photodetectors, differentially controls the direction of rotation of the motor to effect actual tracking of the Sun

"Sample Variance" in Small-Scale CMB Anisotropy Experiments

We discuss the effects of finite sky coverage and the uncertainty in extracting information about the power spectrum from experiments on small angular scales. In general the cosmic variance is enhanced by a factor of $4\pi/A$, where $A$ is the solid angle sampled by the experiment. As a rough guide, an experiment with sensitivity peaking at the $\ell$th multipole has to cover \simgt\ell independent patches to have a lower ``sample variance'' than for a whole-sky measurement of the quadrupole. Our approach gives a relatively simple way of attaching an error bar to the theoretical prediction for a particular experiment, and thereby comparing theories with experimental results, without the need for computationally-intensive Maximum Likelihood or Monte Carlo calculations.Comment: 6 pages in Plain TeX with 1 postscript figure appende

A generative model for feedback networks

We investigate a simple generative model for network formation. The model is designed to describe the growth of networks of kinship, trading, corporate alliances, or autocatalytic chemical reactions, where feedback is an essential element of network growth. The underlying graphs in these situations grow via a competition between cycle formation and node addition. After choosing a given node, a search is made for another node at a suitable distance. If such a node is found, a link is added connecting this to the original node, and increasing the number of cycles in the graph; if such a node cannot be found, a new node is added, which is linked to the original node. We simulate this algorithm and find that we cannot reject the hypothesis that the empirical degree distribution is a q-exponential function, which has been used to model long-range processes in nonequilibrium statistical mechanics.Comment: 11 pages, 6 figure