201 research outputs found
Does OO sync with the way we think?
No full textGiven that corrective-maintenance costs already dominate the software life cycle and look set to increase significantly, reliability in the form of reducing such costs should be the most important software improvement goal. Yet the results are not promising when we review recent corrective-maintenance data for big systems in general and for OO in particular-possibly because of mismatches between the OO paradigm and how we think
Photochemical oxidation of dimethylsulphide to dimethylsulphoxide in estuarine and coastal waters
No full textDimethylsulphide (DMS) photo-oxidation and dimethylsulphoxide (DMSO) photoproduction were estimated in 26 laboratory irradiations of coastal samples from NE England (Tyne estuary) and W Scotland (Loch Linnhe and River Nant at Taynuilt). Pseudo-first order rate constants of DMS photo-oxidation (0.038 h−1 to 0.345 h−1) and DMSO photo-production (0.017 h−1 to 0.283 h−1) varied by one order of magnitude and were lowest in the coastal North Sea. Estuarine samples (salinity S 30) to be most reactive with respect to DMS photo-oxidation. Estimates of water column averaged DMS photo-oxidation rate constants, obtained by scaling to mean daily irradiance (July, NE England) and mid-UV underwater irradiance, were 0.012 d−1, 0.019 d−1, and 0.017 d−1 for upper estuary (S 30), at the lower end of previous observations. Comparing our water column averaged DMS photo-oxidation rate constants with estimated DMS losses via air-sea gas exchange and previously reported biological consumption implies that DMS photochemical removal is of only minor importance in our study area
Influence of photochemistry on the marine biogeochemical cycle of dimethylsulphide in the northern North Sea
No full textShipboard experiments were conducted in the northern North Sea to assess the rate of removal of dimethylsulphide (DMS) and the rate of production of DMSO due to both UVB and UVA/visible light. Experiments were conducted using 0.2-μm filtered seawater and natural light conditions. The DMS photolysis rate constant was determined to be between 0.03 and 0.07 h−1, and initial photolysis rates were between 1.3 and 2.5 nmol dm−3 d−1. Using these rates, the in situ profiles for downward irradiance, and the DMS concentration in the water column, a photochemical turnover rate constant of between 0.1 and 0.37 d−1 was determined for the upper 20 m of the water column, with a photochemical turnover time of between 2.5 and 9.5 days. DMSO photoproduction rates were up to 1.20 nmol dm−3 d−1. Furthermore, results indicate that under UVA/visible light most of the DMS is photo-oxidised to form DMSO, whereas under UVB radiation DMS may be removed via a second photolysis pathway
Ecosystem service impacts of urban water supply and demand management
No full textUtilities face the challenge of enhancing long-term water security while minimising undesirable economic, social and environmental impacts of supply and demand management options. This paper provides an example of how the ecosystem services concept can be used to enumerate and organise broad impacts of water supply options. A case study of Adelaide, South Australia, is used to examine costs and benefits associated with different sources of water and source-water mix scenarios. Ecosystem service impacts are estimated using estimates from the literature. Seven water supply and demand management options are considered for Adelaide: 1) the River Murray, 2) Mt. Lofty Ranges catchments, 3) wastewater reuse, 4) desalination, 5) stormwater harvesting, 6) groundwater and 7) water conservation. The largest costs are associated with sourcing water from conservation measures such as water restrictions on outdoor watering estimated at 1.54/kL. Salinity damage costs of wastewater reuse were estimated at 1.03/kL. Results show that there is a trade-off between financial costs and ecosystem services impacts with source-water mix scenarios with the highest ecosystem services cost having the lowest financial O&M cost and vice versa. This highlights the importance of taking ecosystem services into account when evaluating water supply options.John M. Kandulu, Darla Hatton MacDonald, Graeme Dandy, Angela March
Coralline algae as a globally significant pool of marine dimethylated sulfur
No full textThis research was conducted while H.B. was in receipt of Natural Environment Research Council funding (NE/H525303/1) and a Marine Alliance for Science and Technology for Scotland (MASTS) Research Fellowship (funding provided by the Scottish Funding Council (grant reference HR09011) and contributing institutions), and while N.K. was in receipt of Royal Society of Edinburgh / Scottish Government funding (RES 48704/1). Additional support for sampling collections at the 10 study sites was provided by the European Community via ASSEMBLE (grant 227799), a University of Glasgow Mobility Scholarship, and the Joseph Burr Tyrrell Fund from The Geological Society of London and the British Antarctic Survey.Marine algae are key sources of the biogenic sulfur compound dimethylsulphoniopropionate (DMSP), a vital component of the marine sulfur cycle. Autotrophic ecosystem engineers such as red coralline algae support highly diverse and biogeochemically active ecosystems and are known to be high DMSP producers, but their importance in the global marine sulfur cycle has not yet been appreciated. Using a global sampling approach, we show that red coralline algae are a globally significant pool of DMSP in the oceans, estimated to be ~110 × 1012 moles worldwide during the summer months. Latitude was a major driver of observed regional-scale variations, with peaks in polar and tropical climate regimes, reflecting the varied cellular functions for DMSP (e.g., as a cryoprotectant and antioxidant). A temperate coralline algal bed was investigated in more detail to also identify local-scale temporal variations. Here, water column DMSP was driven by water temperature, and to a lesser extent, cloud cover; two factors which are also vital in controlling coralline algal growth. This study demonstrates that coralline algae harbor a large pool of dimethylated sulfur, thereby playing a significant role in both the sulfur and carbon marine biogeochemical cycles. However, coralline algal habitats are severely threatened by projected climate change; a loss of this habitat may thus detrimentally impact oceanic sulfur and carbon biogeochemical cycling.Peer reviewe
N-version Design vs. One Good Version
No full textEvidence indicates that n-version development techniques are more reliable than producing one "good" version-and cost effective in the long run. The author concludes that diverse, independent channels used in parallel are significantly superior to even the current state of the art, especially in situations where cost of failure is high
DMSP removal and DMSO production in sedimenting particulate matter in the northern North Sea
No full textWork was conducted to establish if the downward flux of sedimenting material represents a sink for particulate dimethylsulphoniopropionate (DMSP) and to investigate the fate of this DMSP within the sedimenting material. Four sediment traps were successfully deployed for a maximum of 24 h in the northern North Sea between the 5th June and the 1st July 1999. After recovery, samples were taken immediately and analysed for levels of dimethylsulphide (DMS), dimethylsulphoxide (DMSO) and DMSP. Any remaining trap material was incubated in the dark at in situ seawater temperature for a maximum of 120 h. Results from the sediment traps showed that only 1% of the DMSP standing stock was lost daily due to sedimentation. However, results from the incubation experiment demonstrated not only that the downward flux of DMSP is underestimated due to its degradation within the trap material, with between 30% and 47% of the DMSP being lost over 48 h, but also that up to 21% of the DMSP lost may be converted to DMSO. These results clearly demonstrate that DMSO is generated within sedimenting material
Roundtable 3: Perspectives on Presidential Leadership with Past HBCU Presidents from Private HBCUs, June 14, 2012
No full textVideo interviews with a complementing monograph providing reflections of former presidents of Historically Black Colleges and Universities discussing leadership, mission, challenges, successes, and issues of race and education. Moderator: Dr. Barbara R. Hatton, President, South Carolina State University 1992-1995; President, Knoxville College 1997-2005. Panelists: Johnnetta B. Cole, Ph.D., President, Spelman College 1987-1997; President, Bennett College for Women 2002-2007. Thomas W. Cole Jr., Ph.D., President, West Virginia State College 1982-1986; President, Clark Atlanta University 1989-2002; President, Interdenominational Theological Center 2009-2010. Nathaniel R. Jackson, Ed.D., President, Mary Holmes College 2000 - 2003. Burnett Joiner, Ph.D., President, LeMoyne-Owen College 1991-1995; President, Livingstone College and Hood Theological Seminary 1996-2000. Samuel D. Jolley Jr., Ed.D., President, Morris Brown College 1993-1997 and 2004-2006. Samuel Tucker, Ph.D., President, Edward Waters College 1973-1976; President, Langston University 1978-1979
Change in drag, apparent slip and optimum air layer thickness for laminar flow over an idealised superhydrophobic surface
No full textAnalytic results are derived for the apparent slip length, the change in drag and the optimum air layer thickness of laminar channel and pipe flow over an idealised superhydrophobic surface, i.e. a gas layer of constant thickness retained on a wall. For a simple Couette flow the gas layer always has a drag reducing effect, and the apparent slip length is positive, assuming that there is a favourable viscosity contrast between liquid and gas. In pressure-driven pipe and channel flow blockage limits the drag reduction caused by the lubricating effects of the gas layer; thus an optimum gas layer thickness can be derived. The values for the change in drag and the apparent slip length are strongly affected by the assumptions made for the flow in the gas phase. The standard assumptions of a constant shear rate in the gas layer or an equal pressure gradient in the gas layer and liquid layer give considerably higher values for the drag reduction and the apparent slip length than an alternative assumption of a vanishing mass flow rate in the gas layer. Similarly, a minimum viscosity contrast of four must be exceeded to achieve drag reduction under the zero mass flow rate assumption whereas the drag can be reduced for a viscosity contrast greater than unity under the conventional assumptions. Thus, traditional formulae from lubrication theory lead to an overestimation of the optimum slip length and drag reduction when applied to superhydrophobic surfaces, where the gas is trapped
Numerical simulations of the flow and sediment transport regimes surrounding a short cylinder
No full textAuthor Posting. © IEEE, 2007. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 32 (2007): 249-259, doi:10.1109/JOE.2007.890986.The 3-D flow field and bed stress surrounding a short cylinder in response to combined wave and mean-flow forcing events is examined. Model simulations are performed with a 3-D nonhydrostatic computational fluid dynamics model, FLOW-3D. The model is forced with a range of characteristic tidal and wave velocities as observed in 12–15 m of water at the Martha's Vineyard Coastal Observatory (MVCO, Edgartown, MA). The 2.4-m-long and 0.5-m diameter cylinder is buried 10% of the diameter on a flat, fixed bed. Regions of incipient motion are identified through local estimates of the Shields parameter exceeding the critical value. Potential areas of sediment deposition are identified with local estimates of the Rouse parameter exceeding ten. The model predictions of sediment response are in general in agreement with field observations of seabed morphology obtained over a one-week period during the 2003–2004 MVCO mine burial experiment. Both observations and simulations show potential transport occurring at the ends of the mine in wave-dominated events. Mean flows greater than 10 cm/s lead to the formation of larger scour pits upstream of the cylinder. Deposition in both cases tends to occur along the sides, near the center of mass of the mine. However, the fixed-bed assumption prohibits the prediction of full perimeter scour as is observed in nature. Predicted scour and burial regimes for a range of wave and mean-flow combinations are established.This work was supported in part by the U.S. Office of Naval
Research under the mine burial project N00014-00-1-0570. The work of K. A.
Hatton was supported by the National Science Foundation Graduate Research
Fellowship
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