Die Instandsetzung der Old White Nile Bridge in Khartoum/Sudan

Die Old White Nile und die Old Blue Nile Bridge waren die ersten beiden Brücken überhaupt, die in Khartoum, der Hauptstadt des Sudan über den Nil führten. Sie wurden von der Britischen Baufirma Dorman Long Ltd. in den Jahren 1908 und 1928 gebaut und erfüllen bis heute in nahezu unveränderter Form ihren Dienst. Sie stellen damit funktionstüchtige, ingenieurtechnische Denkmale dar und zeugen von der außergewöhnlichen Ingenieurleistung, die hier unter schwierigen klimatischen und technologischen Bedingung erbracht wurde. Der folgende Beitrag befasst sich mit der Instandsetzung der Old White Nile Bridge, welche im Zeitraum von 2004 bis 2007 durchgeführt wurde. Die Schüßler‐Plan Ingenieurgesellschaft wurde von der Brückenbauverwaltung der Stadt Khartoum mit verschiedenen Untersuchungen im Zusammenhang mit dem Sanierungskonzept betraut. Der Aufsatz befasst sich neben einem historischen Rückblick mit der Entscheidung, ob ein Auswechseln der 80 Jahre alten, in ihrer Funktion stark eingeschränkten Brückenlager aus statischer Sicht notwendig ist oder diese am Bauwerk belassen werden können. Auch für die Old Blue Nile Bridge ist in den kommenden Jahren eine grundlegende Instandsetzung vorgesehen. Da die Konstruktion vergleichbar ist, können die bei der Old White Nile Bridge gewonnenen Erkenntnisse hierbei einen wertvollen Beitrag leisten. Rehabilitation of old steel bridges over the Nile in Khartoum/Sudan. The Old White Nile Bridge and the Old Blue Nile Bridge were the first bridges ever to cross the Nile at Khartoum – Capital of the Sudan. They were build In 1928 and 1908 by the British Company Dorman Long Ltd. and till today service the traffic in Khartoum in their since then unchanged form. They represent as such a functional technical monument and an attest of the unusual engineering achievement, which was realised under the most extreme climatic and technological conditions. The following report is about the rehabilitation of the Old White Nile Bridge, which was carried out from 2004 till 2007. The Schüßler‐Plan Ingenieurgesellschaft was contracted by the Bridge Department of the State of Khartoum with several analysis related with the rehabilitation concept. The report starts with an historic review of the bridge and continuous with the decision weather it is statically necessary to exchange the nearly 80 year old bearings that are strongly hindered in their function, or weather they could be left unchanged. For the Blue Nile Bridge also, a complete rehabilitation is planned in the near future. Since the two bridge structures are comparable, the knowledge collected at the Old White Nile Bridge could be of great advantage for the Blue Nile rehabilitation.     

Experimental investigation of the rising behavior of CO2 droplets in seawater under hydrate-forming conditions

In a laboratory-based test series, seven experiments along a simulated Pacific hydrotherm at 152 degrees W, 40 degrees N were carried out to measure the rise velocities of liquefied CO2 droplets under (clathrate) hydrate forming conditions. The impact of a hydrate skin on the rising behavior was investigated by comparing the results with those from outside the field of hydrate stability at matching buoyancy. A thermostatted high-pressure tank was used to establish conditions along the natural oceanic hydrotherm. Under P-/T-conditions allowing hydrate formation, the majority of the droplets quickly developed a skin of CO2 hydrate upon contact with seawater. Rise rates of these droplets support the parametrization by Chen et al. (Tellus 2003, 55B, 723-730), which is based on empirical equations developed to match momentum of hydrate covered, deformed droplets. Our data do not support other parametrizations recently suggested in the literature. In the experiments from 5.7 MPa, 4.8 oC to 11.9 MPa, 2.8 degrees C positive and negative deviations from predicted rise rates occurred, which we propose were caused by lacking hydrate formation and reflect intact droplet surface mobility and droplet shape oscillations, respectively. This interpretation is supported by rise rates measured at P-/T-conditions outside the hydrate stability field atthe same liquid CO2-seawater density difference (delta rho) matching the rise rates of the deviating data within the stability field. The results also show that droplets without a hydrate skin ascend up to 50% faster than equally buoyant droplets with a hydrate skin. This feature has a significant impact on the vertical pattern of dissolution of liquid CO2 released into the ocean. The experiments and data presented considerably reduce the uncertainty of the parametrization of CO2 droplet rise velocity, which in the past emerged partly from their scarcity and contradictions in constraints of earlier experiments.     

Seabird guano is an efficient conveyer of persistent organic pollutants (POPs) to Arctic lake ecosystems

Migratory seabirds have been linked to localized "hotspots" of contamination in remote Arctic lakes. One of these lakes is Lake Ellasj?en on Bj?rn?ya in the Barents Sea. Here we provide quantitative evidence demonstrating that even relatively small populations of certain seabird species can lead to major impacts for ecosystems. In the present example, seabird guano accounts for approximately 14% of the contaminant inventory of the Lake Ellasj?en catchment area, approximately 80% of the contaminant inventory of the lake itself, and is approximately thirty times more efficient as a contaminant transport pathway compared to atmospheric long-range transport. We have further shown that this biological transport mechanism is an important contaminant exposure route for ecosystems, responsible for POPs levels in freshwater fish that are an order of magnitude higher than those in Arctic top predators. Given the worldwide presence of seabird colonies in coastal marine areas where resources are also harvested by humans, this biological transport pathway may be a greater source of dietary contamination than is currently recognized with consequent risks for human health.     

Dynamic Boundary Conditions and Boundary Control for the One-Dimensional Heat Equation

In this note we show how the theory of one-sided coupled operator matrices developed by K.-J. Engel [6-8] can be applied to boundary control problems. We illustrate the abstract results by considering the one-dimensional heat equation with dynamic boundary conditions and boundary control.     

Feedforward-feedback control of a solid oxide fuel cell power system

One of the main challenges for wide-spread utilization of the solid oxide fuel cell (SOFC) power systems is how to achieve high electrical efficiency without increasing the degradation rate of the fuel cells. To run the SOFC power system at high efficiency over a long period of time, properly designed controllers are indispensable.Although a number of various approaches to control SOFC have been proposed so far, it seems that the design of control system, along with simple tuning procedure, has not been treated in a consistent manner. This issue is addressed in the present paper resulting in a feedforward-feedback control structure. The feedforward part is based on the stoichiometry of electro-oxidation, reforming and combustion reactions, which allow immediate response to variable current demand. The feedback part performs additional fine adjustment of fuel and air supply in order to minimize the undesired system temperatures variations. The selection of pairings of manipulated and controlled variables for control is based on physical knowledge of the system. Input/output pairing for single-loop feedback control is assessed by the relative gain analysis. An efficient procedure for tuning the parameters of the feedback controllers is suggested, relying on simple open-loop step responses of the system.The proposed low-level control is assessed on a detailed physical model of a 2.5 kW SOFC power system by simulating two nonstationary load regimes. Simulations show that the control provides a robust operation under large load variations while meeting the operating constraints. Due to its simplicity, the control is feasible for implementation on a real SOFC system.     

Senile macular changes in the black African

One thousand black African and 380 white Caucasian patients over the age of 50 were examined for evidence of age-related macular changes, namely, drusen, pigment epithelial atrophy, and disciform macular degeneration. Drusen and pigment epithelial changes were found to occur twice as commonly in Caucasians as in Africans; there was a much greater difference in the prevalence of disciform macular degeneration between the 2 groups. The cause of the differences remains unexplained.     

Evaluating winds and vertical wind shear from Weather Research and Forecasting model forecasts using seven planetary boundary layer schemes

The existence of vertical wind shear in the atmosphere close to the ground requires that wind resource assessment and prediction with numerical weather prediction (NWP) models use wind forecasts at levels within the full rotor span of modern large wind turbines. The performance of NWP models regarding wind energy at these levels partly depends on the formulation and implementation of planetary boundary layer (PBL) parameterizations in these models. This study evaluates wind speeds and vertical wind shears simulated by the Weather Research and Forecasting model using seven sets of simulations with different PBL parameterizations at one coastal site over western Denmark. The evaluation focuses on determining which PBL parameterization performs best for wind energy forecasting, and presenting a validation methodology that takes into account wind speed at different heights. Winds speeds at heights ranging from 10 to 160 m, wind shears, temperatures and surface turbulent fluxes from seven sets of hindcasts are evaluated against observations at Høvsøre, Denmark. The ability of these hindcast sets to simulate mean wind speeds, wind shear, and their time variability strongly depends on atmospheric static stability. Wind speed hindcasts using the Yonsei University PBL scheme compared best with observations during unstable atmospheric conditions, whereas the Asymmetric Convective Model version 2 PBL scheme did so during near‐stable and neutral conditions, and the Mellor–Yamada–Janjic PBL scheme prevailed during stable and very stable conditions. The evaluation of the simulated wind speed errors and how these vary with height clearly indicates that for wind power forecasting and wind resource assessment, validation against 10 m wind speeds alone is not sufficient. Copyright © 2012 John Wiley & Sons, Ltd.     

The kernel Kalman rule

Machine Learning - Enabling robots to act in unstructured and unknown environments requires versatile state estimation techniques. While traditional state estimation methods require known models...