Formation of offshore tidal sandbanks triggered by a gasmined bed subsidence

Offshore gasmining is an example of a human intervention with a morphological impact. On land, it is usually attended with a dish-like bed depression. We show that, if located at sea, such a bed depression can become morphodynamically active by triggering mechanisms related to tidal sand bank formation. To that end, a simple morphological model is considered which describes an erodible bed subject to a tidal wave in a shallow sea. The continuous subsidence is modelled by a sink term in the sediment balance. Then, a linear approximation is carried out to describe the bed evolution after the onset of subsidence. The results, presented in physical space, show that the subsidence triggers the formation of a sand bank pattern that gradually spreads around the centre of subsidence, at a rate that may go up to 160 m year¿1, depending on the tidal transport rate and the tidal eccentricity. The dimension of the depression does not affect the spreading rate nor the orientation of the sand banks, but it does influence their spacing. The main conclusion is that the horizontal extent of the area influenced by the bed depression by far exceeds that of the direct subsidence, thus showing that bed depressions on land and at sea indeed behave in fundamentally different ways. The results suggest that nonlinear effects are worthwhile to be investigated in order to describe finite amplitude development of sand banks as well as the interaction between subsidence and bed forms

On the crest of sandwave modelling:Achievements from the past, directions for the future.

Tidal sandwaves form a prominent bed pattern in shallow sandy shelf seas. Here the class of idealised process-based models, aimed at obtaining generic insight in sandwave dynamics, is reviewed. Since many model studies focus on the instability underlying sandwave formation, first an outline of linear stability analysis is given. Then, an overview of model results is presented, highlighting two ongoing research projects (SMARTSEA and SANDBOX) and followed by suggestions for future research

Seabed pattern dynamics and offshore sand extraction

This thesis aims at understanding the long-term morphodynamic e®ects of large-scale o®shore sand extraction, including the potential interaction with sandbank and sandwave dynamics. To that end, we follow an idealized processbased morphodynamic modelling approach, focusing on a tidally dominated o®shore environment where such patterns may exist. Regarding tidal sandbanks, we distinguish between a °at bed and one with sandbanks in morphodynamic equilibrium. On a smaller spatial scale, we investigate the potential interaction of sand extraction and sandwave formation

A simple morphodynamic model for sand banks and large-scale sand pits subject to asymetrical tides

We extend existing knowledge on theoretical growth characteristics of tidal sand banks by including asymmetrical tides with an M0, M2 and M4-constituent, thus allowing for migration. Furthermore, in the context of the continuously increasing demand on the Dutch sand market, we show that creating a large-scale offshore sand pit has long-term morphological implications, both for the pit itself and the surrounding area. The pit deepens, while around it a sand bank pattern emerges, spreading at a constant rate of the order of tens to hundred metres per year

Formulating an IT governance framework

Modern organisations make substantial investments in Information Technology (IT). Corporate governance practices can no longer ignore the importance of effectively governing IT. Consequently, the third King Report on Corporate Governance (King III) makes specific provision for IT governance, which is implemented through the establishment of an IT governance framework. The purpose of this research is to develop a generic IT governance framework, suitable to any large South African organisation in the public or private sector. The literature considered for this research confirmed the extent of standards and practices available in support of IT governance, together with the roles and structures required to implement them. These included well-known publications such as COBIT, Prince2, ITIL and ISO/IEC27000. Based on the literature review, a theoretical Processes, Enablers and Structures (PES) IT Governance Framework was formulated. The framework was further explored by means of a survey of and structured interview with ten Chief Information Officers (CIOs) of South African organisations with a turnover in excess of R1bn per annum. The final PES IT Governance Framework comprises three dimensions, each of which contains a set of constituent components: • Processes: Strategic Alignment, Value Delivery, Resource Management, Risk Management and Performance Measurement. • Enablers: IT Sub Processes, Supporting Documentation, IT Control Framework, Technology Architecture, Desirable Practice, IT Portfolio Management and Regulation. • Structures: The Board, Office of the CIO, IT Steering Committee, Technology Architecture Forum, IT Programme Management Office and Information Security Organisation. As the number of regulatory requirements and associated compliance pressures grow, the importance of an effective IT governance framework also becomes more prominent. The PES IT Governance Framework offers a uniquely practical approach to addressing IT governance principles that are often regarded as abstract. The final PES IT Governance Framework provides clear guidance on how organisations could implement an IT governance framework, which addresses the strategic alignment of IT to business, value delivery by IT investments, IT risk management, IT resource management and IT performance measurement

Two sphere immunoassay on a microfluidic device

Clinical measurements of biologically important proteins and peptides are routinely carried out in the laboratory setting using immunoassays. However, the most recent trend in medicine is the advance of personalized medicine. The goal is to tailor the diagnosis, care and the drugs to the individual. To make this a reality, fast and inexpensive, analytical tools need to be developed that are capable of measuring multiple biological markers at one time in small volumes. When an assay can use very small volumes less invasive methods for obtaining samples such as blood can be used (finger prick). The measurement of more than one biomarker from the same sample using the traditional ELISA method requires a separate immunoassay for each analyte. This is expensive, requires large amount of sample and is time consuming. A faster and more economical way is by developing a multiplexing assay where not one but several analytes are measured at one time. The immunoassay we developed uses microspheres (capture spheres) conjugated with monoclonal antibodies specific to the targeted analyte. These microspheres capture the antigen and form a microsphere-antibody-antigen complex, which are then bound by a secondary monoclonal antibody, recognizing a different exposed epitope on the antigen. This secondary antibody is conjugated to a second microsphere (detection sphere). The capture and detection spheres are loaded with fluorescent dyes, each with a different wavelength, allowing for easy differentiation. Detection of the capture sphere-antigen-detection sphere complexes can accomplished by three different formats, 96 well plate, Flow cytometer and Microfluidic devices. In this Thesis we will discuss the development of this fast and sensitive aminoassay using these three formats. We will show that the assay can be performed in less then 15 minutes with sensitivity comparable to, or better than that obtained with the gold standard ELISA assay. Also we will calculate the theoretical limits of this assay and compare them to a commercial single bead assa

Process-based modelling of bank-breaking mechanisms of tidal sandbanks

Tidal sandbanks are large-scale dynamic bed forms observed in shallow shelf seas. Their plan view evolution may display a single bank breaking into two or more banks, for which two mechanisms have been proposed in the literature. However, as both were based on interpretation of observations, generic support from a process-based modelling perspective is lacking so far. Here we present a new idealised process-based model study into the transient evolution of tidal sandbanks. Key elements are the inclusion of nonlinear dynamics for topographies that vary in both horizontal directions, and the focus on long-term evolution (centuries and longer). As a further novelty, the hydrodynamic solution, satisfying the nonlinear shallow water equations including bottom friction and the Coriolis effect, is obtained from a truncated expansion in the ratio of maximum bank elevation (w.r.t. mean depth) and mean water depth. Bed evolution follows from the tidally averaged bed load sediment transport, enhanced by depth-dependent wind-wave stirring. From our model results, we identify two paths of evolution, leading to either bank-breaking or an S-shape. Which of these paths occurs depends on initial topography, with bank orientation and bank length as major control parameters. The breaking and S-shape obtained in our model results show resemblance with banks observed in the North Sea