Characterization of Optical Frequency Transfer Over 154 km of Aerial Fiber

We present measurements of the frequency transfer stability and analysis of the noise characteristics of an optical signal propagating over aerial suspended fiber links up to 153.6 km in length. The measured frequency transfer stability over these links is on the order of 10^-11 at an integration time of one second dropping to 10^-12 for integration times longer than 100 s. We show that wind-loading of the cable spans is the dominant source of short-timescale noise on the fiber links. We also report an attempt to stabilize the optical frequency transfer over these aerial links.Comment: 4 pages, submitted to Optics Letter

Astronomical verification of a stabilized frequency reference transfer system for the Square Kilometre Array

In order to meet its cutting-edge scientific objectives, the Square Kilometre Array (SKA) telescope requires high-precision frequency references to be distributed to each of its antennas. The frequency references are distributed via fiber-optic links and must be actively stabilized to compensate for phase-noise imposed on the signals by environmental perturbations on the links. SKA engineering requirements demand that any proposed frequency reference distribution system be proved in "astronomical verification" tests. We present results of the astronomical verification of a stabilized frequency reference transfer system proposed for SKA-mid. The dual-receiver architecture of the Australia Telescope Compact Array was exploited to subtract the phase-noise of the sky signal from the data, allowing the phase-noise of observations performed using a standard frequency reference, as well as the stabilized frequency reference transfer system transmitting over 77 km of fiber-optic cable, to be directly compared. Results are presented for the fractional frequency stability and phase-drift of the stabilized frequency reference transfer system for celestial calibrator observations at 5 GHz and 25 GHz. These observations plus additional laboratory results for the transferred signal stability over a 166 km metropolitan fiber-optic link are used to show that the stabilized transfer system under test exceeds all SKA phase-stability requirements under a broad range of observing conditions. Furthermore, we have shown that alternative reference dissemination systems that use multiple synthesizers to supply reference signals to sub-sections of an array may limit the imaging capability of the telescope.Comment: 12 pages, accepted to The Astronomical Journa

Development of a risk assessment tool to assess the significance of septic tanks around freshwater SSSIs. Phase 1 – Understanding better the retention of phosphorus in the drainage fields

The findings contained within this report have allowed Natural England to refine and implement a risk assessment methodology for septic tanks, which was developed through a previous project with CEH (NECR170)

High-frequency water quality monitoring in an urban catchment: hydrochemical dynamics, primary production and implications for the Water Framework Directive

This paper describes the hydrochemistry of a lowland, urbanised river-system, The Cut in England, using in situ sub-daily sampling. The Cut receives effluent discharges from four major sewage treatment works serving around 190,000 people. These discharges consist largely of treated water, originally abstracted from the River Thames and returned via the water supply network, substantially increasing the natural flow. The hourly water quality data were supplemented by weekly manual sampling with laboratory analysis to check the hourly data and measure further determinands. Mean phosphorus and nitrate concentrations were very high, breaching standards set by EU legislation. Though 56% of the catchment area is agricultural, the hydrochemical dynamics were significantly impacted by effluent discharges which accounted for approximately 50% of the annual P catchment input loads and, on average, 59% of river flow at the monitoring point. Diurnal dissolved oxygen data demonstrated high in-stream productivity. From a comparison of high frequency and conventional monitoring data, it is inferred that much of the primary production was dominated by benthic algae, largely diatoms. Despite the high productivity and nutrient concentrations, the river water did not become anoxic and major phytoplankton blooms were not observed. The strong diurnal and annual variation observed showed that assessments of water quality made under the Water Framework Directive (WFD) are sensitive to the time and season of sampling. It is recommended that specific sampling time windows be specified for each determinand, and that WFD targets should be applied in combination to help identify periods of greatest ecological risk. This article is protected by copyright. All rights reserved

High-precision optical-frequency dissemination on branching optical-fiber networks

We present a technique for the simultaneous dissemination of high-precision optical-frequency signals to multiple independent remote sites on a branching optical-fiber network. The technique corrects optical-fiber length fluctuations at the output of the link, rather than at the input as is conventional. As the transmitted optical signal remains unaltered until it reaches the remote site, it can be transmitted simultaneously to multiple remote sites on an arbitrarily complex branching network. This technique maintains the same servo-loop bandwidth limit as in conventional techniques and is compatible with active telecommunication links.Sascha W. Schediwy, David Gozzard, Kenneth G. H. Baldwin, Brian J. Orr, R. Bruce Warrington, Guido Aben and Andre N. Luite

James Gozzard Interview

Transcript of oral history interview with James Gozzard by John Hanrahan on his experiences during the Vietnam War on February 29, 1984

Union of an intra-articular distal radius fracture after successive failures of three locking plates: a case report

We report a case of a 30-year old male, who presented with a right distal radius intra-articular fracture complicated by compartment syndrome. He was treated with fasciotomies and fracture fixation with a 3.5 mm LCP (Synthes™), followed 7 days later by skin graft. Repeat radiographs 8 weeks later showed a break across the plate at the level of an unfilled screw hole over the fracture. He underwent exchange plating with a 2.4 mm LCP Distal Radius Plate (Synthes™). This revision was complicated by an infected wound dehiscence 2 weeks later requiring multiple procedures. Radiographs at 20 weeks showed broken distal screws. A second revision was performed. At 12 months, the fracture had healed clinically and radiologically, but the three distal screws had broken. We discuss the multifactorial failures of the these three attempts at osteosynthesis, and which factors helped achieve osseous union. We also discuss the literature on volar locking plate breakage and conclude with the recommendations to avoid this rare complication