Coherent optical phase transfer over a 32-km fiber with 1-s instability at 10−1710^{-17}

The phase coherence of an ultrastable optical frequency reference is fully maintained over actively stabilized fiber networks of lengths exceeding 30 km. For a 7-km link installed in an urban environment, the transfer instability is $6 \times 10^{-18}$ at 1-s. The excess phase noise of 0.15 rad, integrated from 8 mHz to 25 MHz, yields a total timing jitter of 0.085 fs. A 32-km link achieves similar performance. Using frequency combs at each end of the coherent-transfer fiber link, a heterodyne beat between two independent ultrastable lasers, separated by 3.5 km and 163 THz, achieves a 1-Hz linewidth.Comment: 4 pages, 4 figure

Progress and challenges in coupled hydrodynamic-ecological estuarine modeling

© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Estuaries and Coasts 39 (2016): 311-332, doi:10.1007/s12237-015-0011-y.Numerical modeling has emerged over the last several decades as a widely accepted tool for investigations in environmental sciences. In estuarine research, hydrodynamic and ecological models have moved along parallel tracks with regard to complexity, refinement, computational power, and incorporation of uncertainty. Coupled hydrodynamic-ecological models have been used to assess ecosystem processes and interactions, simulate future scenarios, and evaluate remedial actions in response to eutrophication, habitat loss, and freshwater diversion. The need to couple hydrodynamic and ecological models to address research and management questions is clear because dynamic feedbacks between biotic and physical processes are critical interactions within ecosystems. In this review, we present historical and modern perspectives on estuarine hydrodynamic and ecological modeling, consider model limitations, and address aspects of model linkage, skill assessment, and complexity. We discuss the balance between spatial and temporal resolution and present examples using different spatiotemporal scales. Finally, we recommend future lines of inquiry, approaches to balance complexity and uncertainty, and model transparency and utility. It is idealistic to think we can pursue a “theory of everything” for estuarine models, but recent advances suggest that models for both scientific investigations and management applications will continue to improve in terms of realism, precision, and accuracy.NKG, ALA, and RPS acknowledge support from the USGS Coastal and Marine Geology Program. DKR gratefully acknowledges support from NSF (OCE-1314642) and NIEHS (1P50-ES021923-01). MJB and JMPV gratefully acknowledge support from NOAA NOS NCCOS (NA05NOS4781201 and NA11NOS4780043). MJB and SJL gratefully acknowledge support from the Strategic Environmental Research and Development Program—Defense Coastal/Estuarine Research Program (RC-1413 and RC-2245)

Magnetic Propulsion for a Hypervelocity Launcher

The concept of using electromagnetic forces to launch projectiles to high-velocity has been pursued since the laws of electro-motion were first derived by Oersted and Ampere in the early 1800's. During the l 960's, there were a number of attempts to develop practical hypervelocity accelerators using electro-magnetic forces. These investigations did not meet with notable success [1,2]. There has been greatly increased interest in electromagnetic propulsion in recent years for a variety of applications including hypervelocity weapons, meteoroid simulation at impact velocities above 10 km/s, high pressure shock physics, and space propulsion. This paper describes an electromagnetic launcher which was developed at the Australian National University (ANU) in the early 1970's, [3] and was successfully used to accelerate projectiles to hypervelocities [4].Center for Electromechanic

Using Long-Term Chemical and Biological Indicators to Assess Stream Health in the Upper Oconee River Watershed

Proceedings of the 2007 Georgia Water Resources Conference, March 27-29, 2007, Athens, Georgia.Macroinvertebrates are commonly used as biological indicators of stream habitat and water quality. Chemical variables, such as dissolved oxygen (DO), specific conductance (SC), and turbidity are used to measure stream water quality. Many aquatic macroinvertebrates are sensitive to changes in water chemistry, and streams with degraded water quality are often characterized by low macroinvertebrate diversity. Chemical (DO, SC, turbidity) and biological (macroinvertebrates) data from multiple tributaries of the North and Middle Oconee Rivers in Clarke County, Georgia, USA were collected seasonally from 2000 – 2006. Macroinvertebrates were identified, and communities were scored using the Georgia Adopt-AStream biotic index. Significant differences in biotic index scores were identified across sites and time using a two-way ANOVA. A general linear model relating chemical variables to biological score was more parsimonious than a model without chemical variables. These relationships varied by sample site, but they were consistent across seasons and years. Macroinvertebrate communities became degraded with increasing specific conductance, but associations with the other chemical variables were unclear. Results suggest the importance of using long-term chemical and biological indices in assessing stream health.Sponsored and Organized by: U.S. Geological Survey, Georgia Department of Natural Resources, Natural Resources Conservation Service, The University of Georgia, Georgia State University, Georgia Institute of TechnologyThis book was published by the Institute of Ecology, The University of Georgia, Athens, Georgia 30602-2202. The views and statements advanced in this publication are solely those of the authors and do not represent official views or policies of The University of Georgia, the U.S. Geological Survey, the Georgia Water Research Institute as authorized by the Water Resources Research Act of 1990 (P.L. 101-397) or the other conference sponsors