705 research outputs found
Lithostratigraphy, sedimentation and evolution of the Volta Basin in Ghana
We present a revised lithostratigraphy for the Voltaian Supergroup of Ghana, based on a review of existing literature, interpretations of remotely sensed data and reconnaissance field survey of the Volta Basin. These strata thicken eastwards, to a maximum of between 5 and 6 km adjacent to the Pan-African Dahomeyide orogen. They began to accumulate some time after about 1000 Ma, along the margin of an epicontinental sea. Initial sedimentation, comprising the age-equivalent Kwahu and Bombouaka Groups, shows a cyclical mode of deposition controlled by eustatic changes in sea-level that produced a range of nearshore marine, littoral and terrestrial environments.
A major erosional interval was followed by deposition of the 3–4 km thick Oti-Pendjari Group. Basal tillites and associated sandy diamictons are correlated with the Marinoan (end-Cryogenian) glaciation, indicating a maximum depositional age of about 635 Ma. The overlying cap carbonates and tuffs were deposited within a shallow epeiric sea bordered by a volcanically active rift system. The main part of the group records the transition from a rifted passive margin to a fully developed foreland basin receiving marine flysch in the form of argillaceous strata interbedded with highly immature wacke-type sandstones and conglomerates. Maximum accommodation space was developed within a foredeep adjacent to the Dahomeyide belt. Towards the end of the orogenic phase, the foredeep succession became partially inverted and then was buried under coarse terrestrial, red-bed molasse of the Obosum Group
LOCOMOOR : a LOw-COst MOORing for the measurement of internal solitary waves
Presented at the ONR/MTS Buoy Workshop, May 9-11, 2000, Clark Laboratory, Woods Hole Oceanographic Institution, Woods Hole, MAIn order to supplement the ASIAEX field effort to measure the temporal and spatial
structure of the internal solitary wave field in relationship to acoustic propagation and scattering
studies, an array of low-cost temperature moorings (LOCOMOOR) has been developed. The
basic concept is to provide spatial coverage as opposed to dense vertical resolution in
temperature. Three temperature sensors on each mooring will adequately measure the time of
passage of the internal solitary waves. A horizontal array of 20 of these moorings deployed for
about three weeks will allow the internal solitary wave front geometry (curvature) and velocity to
be measured as they propagate through the experiment region. The arrival time of each pulse
within the packet of internal waves will be easily resolved, but the wave amplitude less exactly
estimated. However, the amplitude will be very well measured by the velocity and density
observations on the more heavily instrumented environmental moorings associated with the
acoustic experiment
Deployment operation procedures for the WHOI Ice-Tethered Profiler
Deployed and fixed to a suitable multi-year ice floe, the Ice-Tethered Profiler (ITP) can
sustain near-real time measurements of upper ocean temperature and salinity for up to three years.
Incorporating a specifically designed winch system and deployment apparatus that is both light
weight and easily assembled or disassembled on a ship or at a deployment site, the ITP can be
deployed in less than four hours by either transporting the gear and field personnel to the
deployment site via aircraft, or by lowering the gear over the side of a ship and hauling on the ice.
Using daily satellite imagery (if available), visual reconnaissance flights, and ice surveying, the
choice of an appropriate ice floe is a necessity to select a site that will sustain the system for a
prolonged period of time (depending upon the instrument sampling rate). If available, the
helicopter is the preferable method for surveying different sites and for deployment operations.
Working from a ship typically limits the distance and selection of ice floes. Pre-deployment
procedures include powering and configuring the ITP instruments and preparing the apparatus
for transport to the deployment site. Specific deployment methods include the assembly and
disassembly of the ITP winch, proper placement of the total ITP deployment apparatus, ‘Yale
Grip’ braiding and slipping techniques, and testing the Iridium and Inductive communication
links. The operations described here provide a safe and efficient manner to easily deploy the
WHOI ITP.Funding was provided by the National Science Foundation under Grant No. OCE-0324233 and by the Office of Polar Programs under award numbers ARC-0519899 and ARC-0631951
New Horizons in Hepatitis B and C in the Older Adult
Hepatitis C (HCV) and hepatitis B (HBV), are blood-borne viruses that can cause acute hepatitis; but are clinically relevant because chronic infection is associated with development of cirrhosis and hepatocellular carcinoma. Both these viruses are becoming more common in the older population, due to the ageing of generations exposed to the risk factors associated with infection; intravenous drug use, multiple sexual partners and men who have sex with men. This review will cover the natural history and epidemiology of these infections as well as the revolution in drug therapy that now allows cure of HCV infection and complete control of HBV infection.</p
Beaufort Gyre Freshwater Experiment : deployment operations and technology 2003
The Beaufort Gyre Freshwater Experiment (BGFE) observational program was designed to
measure the freshwater content of the upper ocean and sea ice in the Beaufort Gyre of the Arctic
Ocean using bottom-tethered moorings, drifting buoys, and hydrographic stations. The mooring
program required the development of a safe and efficient deployment method by which the
subsurface system could be deployed in waters surrounded by sea ice. This report documents the
mooring procedure used to deploy the three BGFE moorings from the CCGS Louis S. St-
Laurent, during the Joint Western Arctic Climate Study – 2003 (August 6 – September 7). The
technical details of the instrumentation attached to each mooring and the specific deployment
parameters are described. Specifics pertaining to the deployment of four surface-tethered drifters
in the ice are also documented.Funding was provided by the National Science Foundation under Grant Number OPP-0230184
The Beaufort Gyre Observing System 2004 : mooring recovery and deployment operations in pack ice
Situated beneath the Arctic perennial ice pack, the principal components of the
Beaufort Gyre Observing System are three deep-ocean bottom-tethered moorings with
CTD and velocity profilers, upward looking sonars for ice draft measurements, and
bottom pressure recorders. A major goal of this project is to investigate basin-scale
mechanisms regulating freshwater and heat content in the Arctic Ocean and particularly
in the Beaufort Gyre throughout several complete annual cycles. The methods of
recovering and re-deploying the 3800 m long instrumented moorings from the Canadian
Coast Guard Icebreaker Louis S. St. Laurent in August 2004 are described.
In ice-covered regions, deployments must be conducted anchor-first, so heavier
wire rope and hardware must be incorporated into the mooring design. Backup buoyancy
at the bottom of the mooring is advised for backup recovery should intermediate lengths
of the mooring system get tangled under ice floes during recovery. An accurate acoustic
survey to determine the exact location of the mooring, adequate ice conditions, and
skilled ship maneuvering are all essential requirements for a successful mooring
recovery. Windlass (or capstan) procedures could be used for the recovery, but a traction
winch arrangement is recommended.Funding was provided by the National Science Foundation under Grant Number OPP-0230184 and
Woods Hole Oceanographic Insitution’s Ocean and Climate Change Institute
1RXS J232953.9+062814: A Dwarf Nova with a 64-minute Orbital Period and a Conspicuous Secondary Star
We present spectroscopy and time-series photometry of the newly discovered
dwarf nova 1RXS J232953.9+062814. Photometry in superoutburst reveals a
superhump with a period of 66.06(6) minutes. The low state spectrum shows
Balmer and HeI emission on a blue continuum, and in addition shows a rich
absorption spectrum of type K4 +- 2. The absorption velocity is modulated
sinusoidally at P_orb = 64.176(5) min, with semi-amplitude K = 348(4) km/s. The
low-state light curve is double-humped at this period, and phased as expected
for ellipsoidal variations. The absorption strength does not vary appreciably
around the orbit. The orbital period is shorter than any other cataclysmic
variable save for a handful of helium-star systems and V485 Centauri (59
minutes). The secondary is much hotter than main sequence stars of similar
mass, but is well-matched by helium-enriched models, indicating that the
secondary evolved from a more massive progenitor. A preliminary calculation in
which a 1.2 solar-mass star begins mass transfer near the end of H burning
matches this system's characteristics remarkably well.Comment: accepted to Astrophysical Journal Letters; 14 pages, 3 eps figures +
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Array data acquisition with wireless LAN telemetry as applied to shallow water tomography in the Barents Sea
This report describes the application of a new technique of digital radio telemetry, based on a recently available wireless Local
Area Network Ethernet adapter, to the need for realtime transmission of data from a vertical line array (VLA) of hydrophones to a
nearby ship. The report is technical in nature and discusses the design and performance of the system as used during the Barents Sea Polar Front Experiment in August 1992. A key feature of the use of LAN technology in a "telemetry" application is the availability
of Transmission Control Protocol (TCP) software for Ethernet hardware that greatly eases the task of achieving error free digital
data over a radio link prone to dropouts.Funding was provided by the Long Beach Naval Regional Contracting Center Detachment
under Contract N00123-92-C-007l and the Office of Naval Research under Contract N000l4-9l-J-1246
CLIVAR Mode Water Dynamics Experiment (CLIMODE) fall 2005, R/V Oceanus voyage 419, November 9, 2005–November 27, 2005
CLIMODE (CLIVAR Mode Water Dynamic Experiment) is a program designed to understand and quantify the processes
responsible for the formation and dissipation of North Atlantic subtropical mode water, also called Eighteen Degree Water (EDW).
Among these processes, the amount of buoyancy loss at the ocean-atmosphere interface is still uncertain and needs to be accurately
quantified. In November 2005, a cruise was made aboard R/V Oceanus in the region of the separated Gulf Stream, where intense
oceanic heat loss to the atmosphere is believed to trigger the formation of EDW. During that cruise, one surface mooring with
IMET meteorological instruments was anchored in the core of the Gulf Stream as well as two moored profilers on its southeastern
edge. Surface drifters, APEX floats and bobby RAFOS floats were also deployed along with two other moorings with sound
sources. CTD profiles and water samples were also carried out. This array of instruments will permit a characterization of EDW
with high spatial and temporal resolutions, and accurate in-situ measurements of air-sea fluxes in the formation region. The
present report documents this cruise, the instruments that were deployed and the array of measurements that was set in place.Funding was provided by the National Science Foundation under Grant No. OCE 04-24536
At Sea Test 2 recovery cruise : Cruise 206 on board R/V Knorr April 10 - 15, 2012 Woods Hole - Woods Hole, MA
The R/V Knorr, on Cruise 206, carried out the recovery of three moorings for the Coastal
and Global Scale Nodes (CGSN) Implementing Organization of the NSF Ocean
Observatories Initiative. These three moorings are prototypes of the moorings to be used
by CGSN at the Pioneer, Endurance, and Global Arrays. Knorr departed from Woods
Hole, Massachusetts on April 10, 2012 and steamed south to the location of the mooring
deployments on the shelf break. Over five days, April 10-15, Knorr surveyed the bottom
at the planned mooring sites, recovered the moorings, and carried out preliminary
investigations of mechanical and electrical functionality on the recovered moorings and
mooring hardware, including observations of biofouling and corrosion. Knorr returned to
Woods Hole on April 15, 2012.Funding was provided by the National Science Foundation contract #SA9-10 through the
Consortium for Ocean Leadershi
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