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- Xie, Qiancheng
(författare)
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Field Measurements and Predictions of River Flow, Sediment Transport and Morphological Changes
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In an alluvial lowland river, sediment is transported in the form of suspended and bed loads. The fluvial process is the macroscopic view and long-term consequence of sediment movement. The river frequently adjusts its cross-section, longitudinal profile, course of flow and pattern through the natural process of sediment transport, scour and deposition. Anthropogenic factors, e.g., river damming, channelization and other wading projects, also modify the natural processes. With long-term alluvial changes, the river often exhibits patterns such as meandering, braiding and wandering. If the river course has a free connection with open sea, its flow is often bi-directional. The river is typically influenced by the interplay between the runoff and tides, which makes the behaviours of flow and sediment transport extremely complicated.By combining field measurements, numerical simulations, physical model tests and machine learning techniques, this research investigates the fluvial river dynamics and processes, paying attention to the flow patterns, bed shear stresses, steady and unsteady sediment transport and morphological changes. Measurements of flow and sediment, and mapping of bathymetry in both tidal and non-tidal river systems, are presented and discussed. Based on field data, 2D and 3D numerical simulations are performed with the open source code Delft3D, allowing a couped modelling between complex river geometry, bathymetry, and flow and sediment boundaries. A hybrid approach of physical and numerical simulations is adopted for examination of reservoir sedimentation issues, in which both suspended and bed load transport are taken into account. A machine learning method is also applied for predications of suspended load in a river. In a tidal river including a confluence and meander reach, the research elucidates the interplay between freshwater flows and tidal currents. This discloses the circulatory patterns of suspended load transport during the tidal rising and falling. From the interplay also the bed scour changes of hole at the confluence and asymmetric cross-sectional changes at the bends are illustrated. In addition, it is shown that the shifting tidal directions result in a migration of erosion and deposition in both directions, which does not exist in unidirectional runoff flows. The flood tides govern sediment transport and deposition, while the ebb tides with run-offs lead to erosion. Based on the perturbation theory, an improved sediment carrying capacity formula is also derived, suitable for calculations in a tidal environment.At a diffluence-confluence unit, the flow and sediment characteristics and the resulting bed changes are examined. The results indicate that incoming flow variations have a bearing on the diffluence flow partition. Secondary flow structures are found to be more influenced by the thalweg curvature than the flow division. The ‘inlet step’ or differential topography contributes to the unequal flow division. In the confluence, a two-cell flow structure coexists, which may diminish along with the dynamical adjustment of the two merging flows. The classical bed discordance is also observed.Based on extensive recorded hydrologic data and surveyed bathymetries, the sedimentation of the 500-km Lower Yangtze River reach is elucidated before and after the commissioning of the Three Gorges dam. The analyses demonstrate that the impoundment modulates the seasonal flow discharges and traps an appreciable amount of sediment, resulting in enhanced erosion potential and coarsening of sediment. The reach has not yet achieved a hydro-morphological equilibrium; the riverbed down-cutting is supposed to continue for some years and the noticeable sediment reduction from upstream is the extrinsic cause for the bed erosion. Some river training measures, e.g., training wall at the diffluence and guide vanes in the reservoir, are employed to modify flow patterns and sediment transport. With proper training wall layout, acceptable flow patterns are achieved in the diffluence and the branch flow efficiently is increased. With respect to the layout of the vanes, 15º‒20º is suitable under typical operating conditions. The vanes modify effectively the flow patterns and suppress the flow circulations, leading to less sedimentation and enhancing the sediment flushing efficiency. In overall, this research provides support a decision-making process when considering the integrated river management and it also provides reference for other similar situations.
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| 2. |
- You, Yang
(författare)
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Intelligent System Designs : Data-driven Sensor Calibration & Smart Meter Privacy
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nowadays, the intelligent system has gained high popularity in successful implementation of real-time tasks due to its capability of providing efficient and powerful decision making in real applications. In this thesis, we aim for exploring and exploiting different concepts or methods to handle different tasks towards the intelligent system design. In particular, we focus on the following two problems: (i) Consumer-centric privacy-cost trade-off in smart metering system; (ii) Data-driven calibration for gas sensing system.For the first target problem, an optimal privacy-preserving and cost-efficient energy management strategy is designed for each smart grid consumer that is equipped with a rechargeable energy storage. The Kullback-Leibler divergence rate is used as privacy measure and the expected cost-saving rate is used as utility measure. The corresponding energy management strategy is designed by optimizing a weighted sum of both privacy and cost measures over a finite time horizon, which is achieved by formulating our problem into a partial observed Markov decision process problem. A computationally efficient approximated Q-learning method is proposed as a extension to high-dimensional problems over an infinite time horizon. Furthermore, the privacy-preserving and cost-efficient energy management strategy is designed for multiple smart grid consumers that are equipped with renewable energy sources. Different from the previous problem, the adversary is assumed to employ a factorial hidden Markov model based inference for load disaggregation, and the corresponding joint log-likelihood of the model is utilized as privacy measure. A dynamic pricing model is studied, where the price of unit amount of energy is determined by the consumers' aggregated power request, which suits a commodity-limited market. The consumers' energy management strategy is designed under a non-cooperative game framework by optimizing a weighted sum of both privacy measure and the user's energy cost savings. The consumers' non-cooperative game is shown to admit a unique pure strategy Nash equilibrium. As an extension, a computational-efficient distributed Nash equilibrium energy management strategy seeking method is proposed, which also avoids the privacy leakage due to the sharing of payoff functions between consumers.For the second target problem, several data-driven self-calibration algorithms are developed for low-cost non-dispersive infrared sensors. The measurement errors of the sensors are mainly caused by the remaining model errors and can be fully described by the drift of the calibration parameter. This leads to our first formulation of a statistical inference problem on the true calibration parameter under the HMM framework, which is a stochastic model that jointly builds on different quantities introduced by the physical model. To better track the time-varying drift process of the sensor, a time-adaptive expectation maximization learning framework is proposed to efficiently update the HMM parameters. For the joint calibration of the gas sensing system, sensors firsttransmit their belief functions of the true gas concentration levelto the cloud. Then the cloud fusion center computes a fusedbelief function according to certain rules. This belief functionis then used as reference for calibrating the sensors. To dealwith the case where belief functions highly conflict with eachother, a Wasserstein distance based weighted average belieffunction fusion approach is first proposed as networked calibration algorithm. To achieve more long-term stable calibration results, the networked calibration problem is further formulated as a partially observed Markov decision process problem, and the calibration strategies are derived in a sequential manner. Correspondingly, the deep Q-network approach is applied as a computationally efficient method to solve the proposed Markovdecision process problem.The results in this thesis have shown that our proposed design frameworks can provide concise but precise mathematical models, proper problem formulations, and efficient solutions for the target design objectives of different intelligent systems.
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| 3. |
- Yu, Yang, 1970-
(författare)
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Molecular Mechanisms Underlying Abnormal Placentation in the Mouse
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Placental development can be disturbed by various factors, such as mutation of specific genes or maternal diabetes. Our previous work on interspecies hybrid placental dysplasia (IHPD) and two additional models of placental hyperplasia, cloned mice and Esx1 mutants, showed that many genes are deregulated in placental dysplasia. Two of these candidate placentation genes, Cpe and Lhx3, were further studied. We performed in situ hybridization to determine their spatio-temporal expression in the placentas and placental phenotypes were analyzed in mutant mice. Our results showed that the placental phenotype in Cpe mutant mice mimics some IHPD phenotypes. Deregulated expression of Cpe and Cpd, a functionally equivalent gene, prior to the manifestation of the IHPD phenotype, indicated that Cpe and Cpd are potentially causative genes in IHPD. Lhx3 mutants lacked any placental phenotype. Deletion of Lhx3 and Lhx4 together caused an inconsistent placental phenotype which did not affect placental lipid transport function or expression of Lhx3/Lhx4 target genes. Down regulation of Lhx3/Lhx4 did not rescue the placental phenotype of AT24 mice and hence could be excluded as causative genes in IHPD. Analysis of placental development in diabetic mice showed that severe maternal diabetes resulted in fetal intrauterine growth restriction (IUGR) without any change in placental weight and lipid transport function. The diabetic placentas however exhibited abnormal morphology. Gene expression profiling identified some genes that might contribute to diabetic pathology. In another study, it was found that the heterochromatin protein CBX1 is required for normal placentation, as deletion of the gene caused consistent spongiotrophoblast and labyrinthine phenotypes. Gene expression profiling and spatio-temporal expression analysis showed that several genes with known function in placental development were deregulated in the Cbx1 null placenta.
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| 4. |
- Zhang, Xiaolei, 1986-
(författare)
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Micro-reaction Mechanism Study of the Biomass Thermal Conversion Process using Density Functional Theory
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biomass, or bio-energy, is one of the most important alternative energies because of environmental concerns and the future shortage of fossil fuels. Multi-scaled bioenergy studies have been performed in the division of Energy and Furnace Technology, which included studies of macroscopic systems such as systems and reactors, modeling of computational fluid dynamics (CFD), and atomic/molecular level studies. The present thesis focus on the atomic/molecular level that based on quantum chemistry methods.The microscopic structure study of biomass is the first and an important step for the investigation of the biomass thermal conversion mechanism. Cellulose, hemicellulose, and lignin are the three most important components for biomass. The atomic interactions among these three main components were studied, including the hydrogen bond linkages between cellulose and hemicellulose, and the covalent bond linkages between hemicellulose and lignin.The decomposition of biomass is complicated and includes cellulose decomposition, hemicellulose decomposition, and lignin decomposition. As the main component of biomass, the mechanism of cellulose pyrolysis mechanism was focused on in this thesis. The study of this mechanism included an investigation of the pathways from cellulose to levoglucosan then to lower-molecular-weight species. Three different pathways were studied for the formation of levoglucosan from cellulose, and three different pathways were studied for the levoglucosan decomposition. The thermal properties for every reactant, intermediate, and product were obtained. The kinetics parameters (rate constant, pre-exponential factor, and activation energy) for every elementary step and pathway were calculated. For the formation of levoglucosan, the levoglucosan chain-end mechanism is the favored pathway due to the lower energy barrier; for the subsequent levoglucosan decomposition process, dehydration is a preferred first step and C-C bond scission is the most difficult pathway due to the strength of the C-C bonds.The biomass gasification process includes pyrolysis, char gasification, and a gas-phase reaction; Char gasification is considered to be the rate-controlling step because of its slower reaction rate. Char steam gasification can be described as the adsorption of steam on the char surface to form a surface complex, which may transfer to another surface complex, which then desorbs to give the gaseous products (CO and H2) and the solid product of the remaining char. The influences of several radicals (O, H, and OH) and molecules (H2 and O2) on steam adsorption were investigated. It was concluded that the reactivity order for these particles adsorbed onto both zigzag and armchair surfaces is O > H2 > H > OH > O2. For water adsorbs on both zigzag and armchair carbon surfaces, O and OH radicals accelerate water adsorption, but H, O2, and H2 have no significant influence on water adsorption.It was also shown that quantum chemistry (also known as molecular modeling) can be used to investigate the reaction mechanism of a macroscopic system. Detailed atomic/molecular descriptions can provide further understanding of the reaction process and possible products.
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