Stringent Restriction from the Growth of Large-Scale Structure on Apparent Acceleration in Inhomogeneous Cosmological Models

Probes of cosmic expansion constitute the main basis for arguments to support or refute a possible apparent acceleration due to different expansion rates in the universe as described by inhomogeneous cosmological models. We present in this Letter a separate argument based on results from an analysis of the growth rate of large-scale structure in the universe as modeled by the inhomogeneous cosmological models of Szekeres. We use the models with no assumptions of spherical or axial symmetries. We find that while the Szekeres models can fit very well the observed expansion history without a $\Lambda$, they fail to produce the observed late-time suppression in the growth unless $\Lambda$ is added to the dynamics. A simultaneous fit to the supernova and growth factor data shows that the cold dark matter model with a cosmological constant ($\Lambda$CDM) provides consistency with the data at a confidence level of 99.65% while the Szekeres model without $\Lambda$ achieves only a 60.46% level. When the data sets are considered separately, the Szekeres with no $\Lambda$ fits the supernova data as well as the $\Lambda$CDM does, but provides a very poor fit to the growth data with only 31.31% consistency level compared to 99.99% for the $\Lambda$CDM. This absence of late-time growth suppression in inhomogeneous models without a $\Lambda$ is consolidated by a physical explanation.Comment: 5 pages, 1 figure, matches version published in PR

Three atmospheric dispersion experiments involving oil fog plumes measured by lidar

The Wave Propagation Lab. participated with the U.S. Environmental Protection Agency in a series of experiments with the goal of developing and validating dispersion models that perform substantially better that models currently available. The lidar systems deployed and the data processing procedures used in these experiments are briefly described. Highlights are presented of conclusions drawn thus far from the lidar data

Quantum Cryptography in Practice

BBN, Harvard, and Boston University are building the DARPA Quantum Network, the world's first network that delivers end-to-end network security via high-speed Quantum Key Distribution, and testing that Network against sophisticated eavesdropping attacks. The first network link has been up and steadily operational in our laboratory since December 2002. It provides a Virtual Private Network between private enclaves, with user traffic protected by a weak-coherent implementation of quantum cryptography. This prototype is suitable for deployment in metro-size areas via standard telecom (dark) fiber. In this paper, we introduce quantum cryptography, discuss its relation to modern secure networks, and describe its unusual physical layer, its specialized quantum cryptographic protocol suite (quite interesting in its own right), and our extensions to IPsec to integrate it with quantum cryptography.Comment: Preprint of SIGCOMM 2003 pape

Sensory Aids Research

Contains reports on two research projects

Cognitive Information Processing

Contains reports on five research projects.Associated Press (Grant)Taylor Publishing Company (Grant)Providence Gravure, Inc. (Grant

Cognitive Information Processing

Contains reports on four research projects.Associated Press (Grant)Providence Gravure, Inc. (Grant

Computer-Integrated Design and Manufacture of Integrated Circuits

Contains an introduction, principal objectives and accomplishments, reports on two research projects and a list of publications.U.S. Navy Contract N00174-92-Q-013