203 research outputs found
Impacts of land use, population, and climate change on global food security
No full textElke Stehfest and Jonathan Doelman are acknowledged for provision of land use data and we thank the two anonymous reviewers for their constructive and helpful suggestions which have strengthened this manuscript.Peer reviewe
Sequential convex relaxation for convex optimization with bilinear matrix equalities
No full textWe consider the use of the nuclear norm operator, and its tendency to produce low rank results, to provide a convex relaxation of Bilinear Matrix Inequalities (BMIs). The BMI is first written as a Linear Matrix Inequality (LMI) subject to a bi-affine equality constraint and subsequently rewritten into an LMI subject to a rank constraint on a matrix affine in the decision variables. The convex nuclear norm operator is used to relax this rank constraint. We provide an algorithm that iteratively improves on the sum of the objective function and the norm of the equality constraint violation. The algorithm is demonstrated on a controller synthesis example.Accepted Author ManuscriptTeam Raf Van de Pla
Verslag fabrieksschema: Adipinezuur
No full textDocument(en) uit de collectie Chemische ProcestechnologieDelftChemTechApplied Science
De verwijdering van zwavel en stikstof uit minerale oliën door katalytisch hydrogeneren
No full textApplied Science
Rank-based optimization techniques for estimation problems in optics
No full textAberrations in optical systems, such as telescopes and microscopes, degrade the quality of the images that can be produced by these systems. For example, an object that is positioned out of focus produces a blurred image on a camera sensor and the turbulent air in the earth’s atmosphere reduces the imaging performance of telescopes. In this thesis we only consider wavefront aberrations. AO can be used to compensate for these wavefront aberrations. The working principle of AO is to quantify by measuring or estimation the wavefront aberration and to dynamically adjust wavefront modulating devices, such as Deformable Mirrors (DMs), to counteract the aberration and thereby improving the optical performance. The estimation of the wavefront aberration based on images of a point source is called phase retrieval, which is a highly nonlinear estimation problem. The success of the estimation usually depends on the (type of) algorithm, the available information on the aberration that is incorporated in the estimate, and the degree to which the model of the optical system corresponds to reality. In this thesis we propose a convex optimization-based method for phase retrieval. The method allows for easy inclusion of many types of prior information on the aberration. Furthermore, we develop an efficient implementation of the optimization. The robustness of the approach against measurement noise is investigated and compared with several other state of the art algorithms. Experimental validation shows the algorithmis well able to estimate aberrations in real-life circumstances. A new type of prior information is introduced to estimate dynamic wavefront aberrations. In literature and in practice, the optical path is split between either a wavefront sensor and a camera, or between multiple cameras in order to reliable estimate an aberration. The inherent problem is that between the sensor and cameras the aberration can differ (Non-Common Path (NCP) errors), and a wrong estimate is used in the compensation by the AO system. We propose a method to estimate the aberration from measurements by a single camera, by assuming that the aberration evolves according to (non-specific) model, i.e. the dynamics are contained in a model-set. At the same time that we estimate the aberration, we also identify the dynamics according to which the aberration evolves over time. The estimation of the wavefront aberration based on images of an unknown object is called blind deconvolution if both the aberration and object are estimated. Like phase retrieval, this too is a highly nonlinear estimation problem. We propose the first convexoptimization based estimation method for blind deconvolution problems that estimate aberration and object when the images are acquired using coherent illumination. The method allows for the inclusion of many existing types of prior information on the object and/or aberration. Finally, we analyze controllers for segmented mirrors in large ground-based telescopes. These mirrors consist of many interconnected hexagonal segments. This distributed nature of the system warrants the investigation into whether the controller that keeps the segments aligned can be designed in such a way that it can be distributed over the segments as well, essentially resulting in a distributed controller where local controllers communicate with each other. What complicates the analysis is that the dynamics across segments are not necessarily decoupled: the wind load can be correlated and the flexibility in the supporting structure of the segments can cause dynamic coupling. We investigate the design of a distributed controller that incorporates these global dynamics. Furthermore, we investigate the performance of the distributed controller and howit relates to the communication and interconnection pattern of the local controllers.Team Raf Van de Pla
History Database of the Global Environment 3.2
No full textThis database presents an update and expansion of the History Database of the Global Environment (HYDE, v 3.2.1).
HYDE is and internally consistent combination of updated historical population estimates and land use. Categories include cropland,
with a new distinction into irrigated and rain fed crops (other than rice) and irrigated and rain fed rice. Also grazing lands are provided, divided into more intensively used pasture, converted rangeland and non-converted natural (less intensively used) rangeland. Population is represented by maps of total, urban, rural population and population density as well as built-up area. The period covered is 10 000 BCE to 2015 CE. Spatial resolution is 5 arc minutes (approx. 85 km2 at the equator), the files are in ESRI ASCII grid format. Contact person: Kees Klein Goldewijk - [email protected]
GLM2 Code (Global Land-use Model 2) for generating LUH2 datasets (Land-Use Harmonization 2)
No full textThis repository houses the Global Land-use Model 2 (GLM2) code used to produce the LUH2 v2h, LUH2 v2f, and LUH2 v2e datasets (Land Use Harmonization 2 datasets) used for CMIP6 simulations.
The repository contains all code files used when running GLM2, along with a document providing sources and links to all inputs used as drivers of the code.
More information about the GLM2 code and LUH2 datasets can be found in the following locations:
The LUH2 website: https://luh.umd.edu
The CMIP6 dataset archive:
https://doi.org/10.22033/ESGF/input4MIPs.10454
Hurtt, George; Chini, Louise; Sahajpal, Ritvik; Frolking, Steve; Bodirsky, Benjamin Leon; Calvin, Kate; Doelman, Jonathan; Fisk, Justin; Fujimori, Shinichiro; Goldewijk, Kees Klein; Hasegawa, Tomoko; Havlik, Petr; Heinimann, Andreas; Humpenöder, Florian; Jungclaus, Johann; Kaplan, Jed; Krisztin, Tamás; Lawrence, David; Lawrence, Peter; Mertz, Ole; Pongratz, Julia; Popp, Alexander; Riahi, Keywan; Shevliakova, Elena; Stehfest, Elke; Thornton, Peter; van Vuuren, Detlef; Zhang, Xin (2019). Harmonization of Global Land Use Change and Management for the Period 850-2015. Version YYYYMMDD. Earth System Grid Federation.
https://doi.org/10.22033/ESGF/input4MIPs.10468
Hurtt, George; Chini, Louise; Sahajpal, Ritvik; Frolking, Steve; Bodirsky, Benjamin Leon; Calvin, Kate; Doelman, Jonathan; Fisk, Justin; Fujimori, Shinichiro; Goldewijk, Kees Klein; Hasegawa, Tomoko; Havlik, Petr; Heinimann, Andreas; Humpenöder, Florian; Jungclaus, Johann; Kaplan, Jed; Krisztin, Tamás; Lawrence, David; Lawrence, Peter; Mertz, Ole; Pongratz, Julia; Popp, Alexander; Riahi, Keywan; Shevliakova, Elena; Stehfest, Elke; Thornton, Peter; van Vuuren, Detlef; Zhang, Xin (2019). Harmonization of Global Land Use Change and Management for the Period 2015-2300. Version YYYYMMDD. Earth System Grid Federation.
The LUH2 publication:
Hurtt, G. C., Chini, L., Sahajpal, R., Frolking, S., Bodirsky, B. L., Calvin, K., Doelman, J. C., Fisk, J., Fujimori, S., Goldewijk, K. K., Hasegawa, T., Havlik, P., Heinimann, A., Humpenöder, F., Jungclaus, J., Kaplan, J., Kennedy, J., Kristzin, T., Lawrence, D., Lawrence, P., Ma, L., Mertz, O., Pongratz, J., Popp, A., Poulter, B., Riahi, K., Shevliakova, E., Stehfest, E., Thornton, P., Tubiello, F. N., van Vuuren, D. P., and Zhang, X.: Harmonization of Global Land-Use Change and Management for the Period 850–2100 (LUH2) for CMIP6, Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2019-360, in review, 2020.We gratefully acknowledge the support of the U.S. Department of Energy grant DESC0012972, and NASA grants NNX13AK84A and 80NSSC17K0348
Convex optimization-based blind deconvolution for images taken with coherent illumination
No full textA rank-constrained reformulation of the blind deconvolution problem on images taken with coherent illumination is proposed. Since in the reformulation the rank constraint is imposed on a matrix that is affine in the decision variables, we propose a novel convex heuristic for the blind deconvolution problem. The proposed heuristic allows for easy incorporation of prior information on the decision variables and the use of the phase diversity concept. The convex optimization problem can be iteratively re-parameterized to obtain better estimates. The proposed methods are demonstrated on numerically illustrative examples.Team Raf Van de Pla
Design of a reversible growth-from-the-tip device following a complex trajectory: An innovative everting chains principle
No full textBackground: Accessing targets through complex trajectories with multiple curves in series, remains challenging today in many application fields, like surgery, the Fukushima disaster, maintenance of complex tube networks, mining and space operations. Current steerable devices require control of an extensive amount of segments, while moving as a whole through the environment. In contrast, growth-from-the-tip devices move only at the tip by creating a solidified support structure, allowing for active curvature creation at any point of the trajectory with limited effect on the environment. However, reversible and accurate growth remain challenging for these type of devices.Method: Competitive design requirements are setup and quantified. Subsequently, a broad concept generation is performed, based on the ACRREX (i.e. Abstracting, Categorizing, Reflecting, Reformulating and Extending ) method. After selection of one working principle, a proof-of-principle is designed, prototyped and evaluated. Based on the outcome, a second prototype is created and evaluated again. Evaluation of both prototypes comprise accuracy measurements, based on the ratio of path deviation from a kinematic model and insertion length. Moreover, load bearing capacity of the support structure, forces acting on the environment and overall performance are assessed.Results: The selected concept is based on everting chains, driven by torque at the tip and consisting of two chains with lockable sliding hinged joints. Both prototypes successfully show reversible and steerable growth-from-the-tip, by the fact that counter rotation of the tip gears resulted in a translation of the tip, while differential rotation of the gears resulted in curvature creation. Prototype I (PI) had an accuracy of 4.5% for pure translations and 6.2% to 8.1% for the formation of two sequential (90 degrees) curvatures. Prototype II (PII), which was not fully operational, had a deviation per insertion length of 2.9% for a single curvature and to 10.7% to 19.1% for a combination of translations and curvatures in series. Even though the shape-locks of Prototype I had 3 degrees play per joint and a limiting amount of locking positions, the average orthogonal load bearing capacity was high (49N) with an accompanied deformation of maximally 8 degrees. In contrast, the friction-locked drum brakes of Prototype II rotated up to 70 degrees, by both deformation (22%) and slippage (78%) at a load of 20N. A rotation of 25 degrees was reached at an average load of 7.3N. Normal forces acting on the environment during movement were only measured for Prototype I, resulting in direct distortions (78%) of <4N and indirect distortions (22%) of <0.36N. Moreover, both prototypes had comparable elongation rates (PI: 92.9mm/min, PII: 156mm/min), extension rates (PI: 2.6mm/mm, PII: 0.9mm/mm) and widths (PI: 268mm, PII: 270mm). Lastly, a minimal inner curvature of zero and a minimal outer curvature equal to the device’s width were realized, due to the presence of sliding hinged joints.Conclusion and discussion: Both prototypes performed reversible growth-from-the-tip based on the everting chains principle. Accordingly, the generated kinematic model that links gear rotations to tip rotations and translations seems to be an accurate simplification of the experimental data.In addition, the normal forces acting on the environment were much lower than the load bearing capacity of Prototype I, confirming sufficient support and limited deflection and deformation by the built structure. The everting chain principle has many advantages. First, multiple curves in series can be formed in a reversible manner. Moreover, high load bearing capacity of locked chains results in high accuracy of the system’s movement. Furthermore, the system has limited interaction with the environment and no additional system is required to create curvature. Lastly, sliding hinged joints allow for movement along sharp edges. The next generation of everting chain robots should incorporate improved power and load tuning, size reduction and chains that allow for fully selfsupporting movements in 3D space.https://www.youtube.com/watch?v=GstrTG8yVGs Visualization of prototype IIBITE GroupMechanical Engineering | BioMechanical Desig
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