Impact of climate change and development scenarios on flow patterns in the Okavango River

This paper lays the foundation for the use of scenario modelling as a tool for integrated water resource management in the Okavango River basin. The Pitman hydrological model is used to assess the impact of various development and climate change scenarios on downstream river flow. The simulated impact on modelled river discharge of increased water use for domestic use, livestock, and informal irrigation (proportional to expected population increase) is very limited. Implementation of all likely potential formal irrigation schemes mentioned in available reports is expected to decrease the annual flow by 2% and the minimum monthly flow by 5%. The maximum possible impact of irrigation on annual average flow is estimated as 8%, with a reduction of minimum monthly flow by 17%. Deforestation of all areas within a 1 km buffer around the rivers is estimated to increase the flow by 6%. However, construction of all potential hydropower reservoirs in the basin may change the monthly mean flow distribution dramatically, although under the assumed operational rules, the impact of the dams is only substantial during wet years. The simulated impacts of climate change are considerable larger that those of the development scenarios (with exception of the high development scenario of hydropower schemes) although the results are sensitive to the choice of GCM and the IPCC SRES greenhouse gas (GHG) emission scenarios. The annual mean water flow predictions for the period 2020-2050 averaged over scenarios from all the four GCMs used in this study are close to the present situation for both the A2 and B2 GHG scenarios. For the 2050-2080 and 2070-2099 periods the all-GCM mean shows a flow decrease of 20% (14%) and 26% (17%) respectively for the A2 (B2) GHG scenarios. However, the uncertainty in the magnitude of simulated future changes remains high. The simulated effect of climate change on minimum monthly flow is proportionally higher

Optimized Sections for Major Prestressed Concrete Bridge Girders

DOT-FH-11-9598The objectives of this investigation were to evaluate the latest prestressed concrete bridge girder designs being used in the United States and to determine which represent optimum designs that could be promoted as national or regional standards. Bridges built with pretensioned I- and T-sections for spans in excess of 80 ft (24.4 m) and concrete compressive strengths up to 7000 psi (48.3 MPa) were considered. Information on current designs was collected from selected highway agencies and producers throughout the United States. In all states surveyed except California, the most economical bridges for spans of 70 to 130 ft (21.3 to 39.6 m) were constructed with pretensioned bridge girders. Precast prestressed bridge girder sections inventoried were analyzed on three efficiency scales. Bulb-T's, Colorado, and Washington girders were more structurally efficient than AASHTO-PCI girders. A computer program called "BRIDGE" was developed to perform cost analyses. Parameters included girder span, girder spacing, deck thickness and concrete compressive strength. Based on relative unit costs for in-lace materials and labor, cost charts were prepared for existing Bulb-T's, Colorado, Washington and AASHTO girders, and for their modified counterparts with 6-in. (152 mm) thick webs. All girders were compared using optimum cost curves. Bulb-T's were found most cost-effective with estimated cost savings of 17% on the in-place cost of girders and deck compared to the AASHTO girders. Next most cost-effective sections were the Washington Series girders. Modified Bulb-T's are recommended for use as national standards

A review of diagnostic and functional imaging in headache

The neuroimaging of headache patients has revolutionised our understanding of the pathophysiology of primary headaches and provided unique insights into these syndromes. Modern imaging studies point, together with the clinical picture, towards a central triggering cause. The early functional imaging work using positron emission tomography shed light on the genesis of some syndromes, and has recently been refined, implying that the observed activation in migraine (brainstem) and in several trigeminal-autonomic headaches (hypothalamic grey) is involved in the pain process in either a permissive or triggering manner rather than simply as a response to first-division nociception per se. Using the advanced method of voxel-based morphometry, it has been suggested that there is a correlation between the brain area activated specifically in acute cluster headache — the posterior hypothalamic grey matter — and an increase in grey matter in the same region. No structural changes have been found for migraine and medication overuse headache, whereas patients with chronic tension-type headache demonstrated a significant grey matter decrease in regions known to be involved in pain processing. Modern neuroimaging thus clearly suggests that most primary headache syndromes are predominantly driven from the brain, activating the trigeminovascular reflex and needing therapeutics that act on both sides: centrally and peripherally

Effects of High Temperature on the Residual Performance of Portland Cement Concretes

In this work we analyzed the "residual" performance of Portland cement concretes heat-treated at 600 °C after cooling down to room temperature. Concretes with characteristic compressive strength at 28 days of 45 MPa and of 60 MPa were studied. The heat-treatment was carried out without any imposed load. We measured the residual compressive strength and modulus of elasticity. The geometry of the structure was described by mercury intrusion porosimetry and nitrogen sorption tests. We observed a decrease of residual compressive strength and modulus of elasticity, with the raise of heat-treatment temperature, as a result of heat-induced material degradation. The results also indicated that the microstructural damage increased steadily with increasing temperature. Based on the results of this experimental work we concluded that residual mechanical properties of concrete are dependent of their original non heat-treated values