23 research outputs found
Swaziland's relations with Britain and South Africa since 1968
No full textThis work looks into Swaziland's political, economic, social and cultural relations with Britain (its former colonial master) and South Africa (its big and rich neighbour) in the period since Swaziland's Independence in 1968. The focus is on how Swaziland's relations with Britain and South Africa influence its socio-economic and political developments, and its internal and external security. As a micro-state, with a population of less than 0.7 million people, the assumption is made that Swaziland's progress and security can be reasonably assessed by examining its relations with the two powerful states with whom it has close links. This assumption arises from the fact that (i) Swaziland inherited political institutions from Britain, (ii) there were strong economic links (investments, trade, aid) between it and Britain at Independence and these ties continue today, (iii) there were, and still are, economic links in almost every aspect between Swaziland and South Africa at Independence and (iv) South Africa dominates the Southern Africa region - militarily and economically. The main arguments in the Thesis are (a) that the economic links between Swaziland and the two states provide economic growth for the former, thus helping to maintain stability, although South African domination threatens to undermine Swaziland's independence (b) that Swaziland has pursued a "tightrope policy" in Southern Africa, and that this regional strategy has, on the whole, succeeded in helping the country's survival; and (c) that the political system of Swaziland has an in-built tension in that the traditional institutions exist alongside modern ones and this is a threat to political stability
Hydrazine-hydraat fabriek
No full textDocument(en) uit de collectie Chemische ProcestechnologieDelftChemTechApplied Science
Development and Validation of a Dynamic Model for Flotation Predictive Control Incorporating Froth Physics
No full textData Availability Statement:
The data that support the findings of this study are available from the corresponding author, P.Q, upon reasonable request.Paulina Quintanilla would like to acknowledge the National Agency for Research and Development (ANID) for funding this research with a scholarship from “Becas Chile”. The Society of Chemical Industry is also greatly acknowledged for the support granted by the SCI Messel Scholarship 2020
Spatial compression in ultrasound imaging
No full textHigh quality three dimensional ultrasound imaging is typically attained by increasing the amount of sensors, resulting in complex hardware. Compressing measurements before sensing addresses this problem, and could enable new clinical applications. We have developed an analogue compression technique, by positioning a plastic coding mask in front of the aperture, which distorts the ultrasound field by inducing varying local echo delays. This results in a compression of the spatial ultrasound field across the sensor surface, while retaining sufficient information for 3D imaging. Using only a single sensor, complementary measurements can be obtained by rotation of the sensor and the mask to increase the conditioning of the reconstruction problem. In this work, we study a method to optimize the shape of the coding mask. To this end, we define an approximate signal model that captures the ultrasound response of the mask, and use it to pose mask shape optimization as a sensor selection problem. We solve it by relaxing it to a convex problem, as well as by using a greedy selection method. Our simulation results show that these approaches are able to outperform the random design strategy, in particular when mask rotations are included in the problem.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Signal Processing SystemsImPhys/Acoustical Wavefield Imagin
Ultrasound imaging through aberrating layers
No full textWhereas aberrating layers are typically viewed as an impediment to medical ultrasound imaging, they can, surprisingly, also be used to our benefit. As long as we can model the effect of an aberrating layer, we can utilize ‘model-based imaging’, the imaging technique explored throughout this thesis, to reconstruct ultrasound images where traditional beamforming methods would fail, employing the ever increasing computational power available to us nowadays. Not only does this allow us to image through layers, but it also leads to interesting applications, such as 3D ultrasound imaging with spatially undersampled data, using an aberrating ‘coding mask’. The formulation of a measurementmodel, a fundamental part ofmodel-based imaging, also gives insight into the imaging problem mathematically, and allows us to investigate methods for estimating the effect of an aberrating layer ‘blindly’, i.e., without explicitly measuring it. In this thesis, we thus investigate (a), imaging through a layer when the layer’s aberration effect is known, and how it can be applied to imaging with spatially undersampled data, and (b), methods and algorithms for estimating the effect of the aberrating layer without knowing it a priori. In the first part of this thesis, we illustrate how using model-based imaging can be utilized for 3D ultrasound imaging using a single ultrasound transducer, and equipping it with a plastic coding mask. The plastic mask acts as an analog coder, that scrambles the transmitted and received waves in a manner that is location dependent. As a result, the temporal shape of an ultrasound echo can be used instead of the traditional method of using phase differences between sensors in a sensor array. Imaging is instead accomplished using model-based imaging. By measuring the pulse-echo response of each pixel, we can form an image by solving a regularized linear least squares problem, which takes into account the measured pixel-specific pulse-echo signals. The proposed device and imaging method is then verified experimentally. In the following chapter, a coding mask design method is proposed for the aforementioned imaging device. A measurement model is formulatedwhere themask geometry is an explicit parameter to be optimized. After forming this model, a numerical optimization method is proposed and numerically tested. Our numerical experiments show that optimized mask geometries exhibit an energy focusing effect on the region-of-interest, whilst simultaneously decorrelating echo signals between pixels. In the second part of this thesis, in contrast, we consider methods for calibrating propagation models when the pulse-echo response per pixel is not known. The most important calibration challenge we consider is that of imaging through an aberrating layer in front of an ultrasound array. This could be subcutaneous fat or the human skull, for example. In this thesiswe formulate ameasurement model consisting of a partwhere wave propagation is known (i.e., the assumed homogeneous region behind the aberrating layer, where the contrast image of interest is located), and an unknown propagation part, consisting of the Green’s functions from an array sensor to any point on the the interface of the aberrating layer and the imaging medium. We then investigate methods for finding this set of Green’s functions without explicitly measuring them (so called ‘blind’ calibration). The first proposed method exploits the singular value decomposition of the measurement data in combination with the assumed Toeplitz structure of the matrices representing the aberrating layer’s Green’s functions. However, the method is lacking in practicality since an additional set ofmeasurements is required with a phase screen mounted on the interface of the aberration layer and the imaging medium. The second method resolves these practical issues by utilizing a covariance matching technique. A sufficiently large set of measurements is obtained where each measurement is different due to e.g. moving particles such as blood flow or micro-bubbles. Using the covariance of the data, algorithms are then defined that can estimate the transfer functions of the aberrating layer from the measurement covariance data. Finally,we propose amethod for estimating the electro-mechanical impulse response of an ultrasound sensor, by simply measuring its pulse-echo response from a flat plate reflector in front of the sensor. Estimating the one-way (electro-mechanical) impulse response then becomes a de-autoconvolution problem, for which we propose a method by solving a semi-definite relaxation of the de-autoconvolution problem. <br/
Calibration techniques for single-sensor ultrasound imaging with a coding mask
No full textWe consider a model-based ultrasound imaging scenario using a single transducer with a coding mask, and assume that the pulse-echo model is erroneously estimated, resulting in decreased imaging performance. Although the pulse-echo Green's function to each pixel has to be measured to obtain a good model, typically only forward-field measurements are obtained for better SNR, from which the pulse-echo Green's functions are estimated. However, if the transducer's receive transfer function is different from the transmit transfer function, the forward-field measurements do not incorporate the receive transfer function, resulting in an incorrect pulse-echo model. We propose two calibration techniques that start with this erroneous model, and update it using pulse-echo measurements. In the first technique we assume the calibration phantom is known a priori, whereas in the second technique we use multiple random calibration phantoms of which only the second-order statistics are assumed to be known beforehand. Both methods are able to significantly improve the pulse-echo model, strongly improving imaging performance. Our simulation results show that the first technique works best, since there is no uncertainty about the calibration image, whereas the blind calibration technique requires no exact knowledge of the calibration phantom, making it robust to positioning or manufacturing errors.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Signal Processing System
Coding Mask Design for Single Sensor Ultrasound Imaging
No full textWe study the design of a coding mask for pulse-echo ultrasound imaging. We are interested in the scenario of a single receiving transducer with an aberrating layer, or ‘mask,’ in front of the transducer's receive surface, with a separate co-located transmit transducer. The mask encodes spatial measurements into a single output signal, containing more information about a reflector's position than a transducer without a mask. The amount of information in such measurements is dependent on the mask geometry, which we propose to optimize using an image reconstruction mean square error (MSE) criterion. We approximate the physics involved to define a linear measurement model, which we use to find an expression for the image error covariance matrix. By discretizing the mask surface and defining a discrete number of mask thickness levels per point on its surface, we show how finding the best mask can be posed as a variation of a sensor selection problem. We propose a convex relaxation in combination with randomized rounding, as well as a greedy optimization algorithm to solve this problem. We show empirically that both algorithms come close to the global optimum. Our simulations further show that the optimized masks have better a MSE than nearly all randomly shaped masks. We observe that an optimized mask amplifies echoes coming from within the region of interest (ROI), and strongly reduces the correlation between echoes of pixels within the ROI.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Signal Processing System
After Enron: Remembering Loyalty Discourse in Corporate Law
No full textThe demise of monetary damages as a remedy for breach of the corporate director duty of due care means that only a breach of the duty of loyalty or good faith affords the possibility of holding corporate directors personally liable for wrongdoing. The author argues that the fiduciary duty of loyalty contains both a widely appreciated, but rather minimal, non-betrayal aspect and a less appreciated, but more affirmative, devotion dimension. The affirmative. thrust of loyalty, grounded in widely-shared cultural norms and finding expression in myriad literary and religious stories, offers a doctrinal avenue for addressing a potentially broader range of director misconduct than is commonly thought. In a post-Enron world of corporate governance scandal and calls for reform, fiduciary duty law presents, as a policy matter, a possible state law-based approach for attaining greater director accountability. The wisdom of doing so will depend, in part, on whether the risk of greater financial exposure will induce enhanced discharge of director responsibilities, to the advantage of shareholders, or dissuade capable prospective director candidates from service, to the detriment of shareholders. At a more theoretical level, understanding the affirmative facet of both the social norm of loyalty and the legal duty of loyalty raises deeper questions such as whether the supposed conceptual distinction between care and loyalty is as clear as widely believed and whether corporate law fiduciary discourse should continue to be conducted in moral-sounding terms at all. This, in turn, depends on whether we sensibly conceive of directors as being moral actors and regard corporate relationships as raising moral issues, rather than just economic/financial issues for which a new (or re-loaded) discourse might be more suitable. The article closes by addressing how judges-to whom both the practical and the policy-theory issues have fallen-might explore the fuller reaches of loyalty. The article coins the notion of due loyalty to express the appropriate, context-sensitive demands of loyalty understood as devotion
Joint optimization of coding mask and scan positions for compressive single sensor imaging
No full textWe study the optimal design of an aperture coding mask, and the optimal sensing positions of a single ultrasound sensor with a scanning configuration. In previous works, we have shown that 3D ultrasound imaging is possible using a randomly shaped coding mask with randomly chosen sensing positions. Here we propose an optimization algorithm for the joint design of the coding mask and the sensing positions. We first define a linear measurement model and parameterize it with respect to the mask shape. To optimize the shape of the mask, we use a greedy descent algorithm to minimize the imaging MSE, assuming a Wiener estimate is used for image reconstruction. To optimize the sensing positions, we pre-define a set of such sensing positions by gridding the measurement plane, and regard each sensing position as a virtual sensor candidate. We then use a greedy sensor selection algorithm to find a good selection of sensing positions. To jointly optimize for both the mask and the sensing positions, we alternatingly optimize between them, keeping either the mask shape or the sensing positions fixed. Using simulations we show that the joint optimization results in better imaging performance than optimizing for the mask or the sensing positions alone, or using a completely random design.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Signal Processing System
The influence of subseismic-scale fracture interconnectivity on fluid flow in fracture corridors of the Brejões carbonate karst system, Brazil
No full textThe present study used a multitool approach to characterize fractures of several orders of magnitude in large fracture corridors, caves, and canyons to investigate their impact on fluid flow in carbonate units. The study area is the Brejões carbonate karst system that is located in the Neoproterozoic Salitre Formation in the Irecê Basin, São Francisco Craton, Brazil. The approach included satellite imagery, used for interpreting the regional structural context, Unmanned Aerial Vehicle (UAV) and ground-based Light Detection And Ranging (LiDAR) imagery, used for detailed structural interpretation. Regional interpretation revealed that fracture corridors, caves and canyons occur along a N–S-oriented anticline hinge. An advanced stage of karstification caused fracture enlargement and intrabed dissolution, and the formation of caves and canyons. A river captured by the highly fractured zone along the anticline hinge played an important role as an erosive agent. Detailed characterization of fracture corridors comprised structural analysis, topological studies, persistence estimations, power-law fitting of fracture trace length distributions, and identification of network backbones. Our results indicate that fracture corridors comprise four subvertical fracture sets: N–S and E-W and a conjugate pair, NNE-SSW and NW-SE. Fractures observed in the caves show the same dominant directions. Fracture directions are consistent with a common origin associated with the anticline folding. Fracture traces range from 1.0 m to 300 m, comprising both subseismic (<50 m) and seismic scale fractures (>50 m). Networks have dominance of node terminations Y and X (notably Y), CB values higher than 1.8, high P20 and P21 persistence values, and highly interconnected backbones. Fracture network connectivity is associated with power-law exponents greater than 2.5 for the fracture trace distributions, indicating large influence of subseismic-scale fractures on fluid flow. As the final result of folding and karstification, large volumes of secondary macroporosity were created, particularly in the zone of maximum fracture intensity around the hinge zone of the anticline. This scenario can be used to understand better oil reservoirs formed in similar structural controls in near-surface conditions.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Applied Geolog
