| 1. |
- Li, Duan, 1987-
(författare)
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Rapid sintering of ceramics by intense thermal radiation
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sintering is an important processing step for obtaining the necessary mechanical stability and rigidity of ceramic bulk materials. Both mass and heat transfer are essential in the sintering process. The importance of radiation heat transfer is significantly enhanced at high temperatures according to the well-known Stefan-Boltzmann’s law. In this thesis, we modified the pressure-less spark plasma sintering set-up to generate intense thermal radiation, aiming at rapid consolidation of ceramic bulk materials. This approach was named as “Sintering by Intense Thermal Radiation (SITR)” as only thermal radiation contributed.Firstly, the heat and mass transfer mechanisms during the SITR process were studied by choosing zirconia ceramics as references. The results revealed that the multiple scattering and absorption of radiation by the materials contributed to the heat diffusion. The observed enhanced densification and grain growth can be explained by a multiple ordered coalescence of zirconia nanocrystals using high heating rates.Secondly, the temperature distribution during the SITR process was investigated by both numerical simulation and experimental verifications. It showed that the radiator geometry, sample geometry and radiating area were influencing factors. Besides, the change of material and geometry of the radiators resulted in an asymmetric temperature distribution that favored the formation of SiC foams. The foams had gradient structures with different open porosity levels and pore sizes and size distributions.Finally, ceramic bulk materials were successfully fabricated by the SITR method within minutes. These materials included dense and strong ZrO2 ceramics, Si3N4 foams decorated with one-dimensional nanostructures, and nasal cavity-like SiC-Si3N4 foams with hierarchical heterogeneities. Sufficient densification or formed strong necks were used for tailoring these unique microstructures. The SITR approach is well applicable for fast manufacture of ceramic bulk materials because it is clean and requires low energy consumption and properties can be controlled and tuned by selective heating, heating speed or temperature distribution.
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| 2. |
- Li, Shen
(författare)
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Advanced Optical Diagnostics in Particle Combustion for Biomass and Metal as Alternative Fuels
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The energy sector is in urgent need for carbon-free strategies considering environmental pollutions and climate change impact. Two kinds of solid fuels, biomass and metal particles have been studied in this thesis aiming at CO2 emission reduction or zero carbon emission. Biomass is a renewable and carbon-neutral energy source that provides heat and power through gasification and combustion. Biomass fuels usually contain varying amounts of potassium, which will cause severe operational problems, such as slagging and corrosion by the potassium released during thermal conversion processes. The detailed potassium chemistry in biomass thermochemical conversion processes has been investigated in our previous study and presented in Weng’s doctoral dissertation. Based on these quantitative studies, the work presented in this thesis is mainly focused on the quantitative measurement of burning a single biomass pellet and the potassium released from burning pulverized biomass char particles. The motivation for the study of biomass char particles is that over 80% of the potassium can remain in the char particles from the raw biomass. Laser-induced photofragmentation fluorescence (LIPF) imaging was adopted here to measure the potassium release process for biomass char particles, which provides spatially resolved information of the dominant species of KCl and KOH that formed during the char oxidation period. A hot laminar gas flow was used for calibration with gas-phase KOH and KCl provided by a homemade multi-jet burner, in which a homogenous temperatures distribution ranging from 1000 to 2000 K are provided. Newly developed UV-absorption spectroscopy was adopted to monitor the concentrations of KOH and KCl. Based on the calibration, the KOH/KCl distribution surrounding the burning char particles was derived, revealing the potassium release process during the char oxidation period.Metal fuels have been used as sustainable energy carriers due to their zero-carbon emission and high energy density. The iron powder has been proposed as one of the most promising recyclable metal fuels for the future low-carbon society. A comprehensive understanding of the combustion behavior of iron particles is essential for investigating fundamental mechanisms and designing efficient iron powder combustors. A versatile metal powder seeding apparatus has been designed and optimized based on electrostatic dispersion. This dispersion system is well calibrated for powder concentration that can provide a stable flow of particles seeding for nearly one minute. The work presented in this thesis mainly focuses on investigating single iron particle combustion in a well-controlled laminar premixed flame with a modified Mckenna flat-flame burner through advanced optical diagnostic techniques. One of the challenges for the study of metal combustion came from the small size (~20 to 80 µm) of the metal particles and their movement in the hot combustion environment. This work, inspired by clustering algorithms, proposed a new clustering-based particle detection (CBPD) method for digital holography (DH) for particle detection. This data-driven method features automatic recognition of particles, particle edges and background, and accurate separation of overlapping particles. Based on CBPD method, high-speed digital in-line holography (DIH), a three-dimensional (3D) imaging technique, is employed to reconstruct the 3D particle field and simultaneously quantify the size, 3D location and velocity of burning iron particles in a well-controlled CH4/N2/O2 premixed Bunsen flame with a stable metal power seeded.The ignition delay time, combustion time of single micron-sized iron particles are studied by high-speed imaging in different flame conditions. Particle temperatures are measured by an ICCD camera equipped with a stereoscopy, and the results are derived through the two-color pyrometry method. An important phenomenon of nano-sized iron-oxides particles releasing during the iron particles combustion has been identified. Micro-explosion of burning iron particles was observed during the combustion process, which is complex and can affect combustion stability and the formation of product components. The morphology of raw iron particles and the combust products (iron oxides) collected by sampling meshes have been analyzed by scanning electron microscopy (SEM).
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| 3. |
- Li, Shen, 1994
(författare)
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Voronoi Constellations for Coherent Fiber-Optic Communication Systems
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increasing demand for higher data rates is driving the adoption of high-spectral-efficiency (SE) transmission in communication systems. The well-known 1.53 dB gap between Shannon's capacity and the mutual information (MI) of uniform quadrature amplitude modulation (QAM) formats indicates the importance of power efficiency, particularly in high-SE transmission scenarios, such as fiber-optic communication systems and wireless backhaul links. Shaping techniques are the only way to close this gap, by adapting the uniform input distribution to the capacity-achieving distribution. The two categories of shaping are probabilistic shaping (PS) and geometric shaping (GS). Various methods have been proposed for performing PS and GS, each with distinct implementation complexity and performance characteristics. In general, the complexity of these methods grows dramatically with the SE and number of dimensions. Among different methods, multidimensional Voronoi constellations (VCs) provide a good trade-off between high shaping gains and low-complexity encoding/decoding algorithms due to their nice geometric structures. However, VCs with high shaping gains are usually very large and the huge cardinality makes system analysis and design cumbersome, which motives this thesis. In this thesis, we develop a set of methods to make VCs applicable to communication systems with a low complexity. The encoding and decoding, labeling, and coded modulation schemes of VCs are investigated. Various system performance metrics including uncoded/coded bit error rate, MI, and generalized mutual information (GMI) are studied and compared with QAM formats for both the additive white Gaussian noise channel and nonlinear fiber channels. We show that the proposed methods preserve high shaping gains of VCs, enabling significant improvements on system performance for high-SE transmission in both the additive white Gaussian noise channel and nonlinear fiber channel. In addition, we propose general algorithms for estimating the MI and GMI, and approximating the log-likelihood ratios in soft-decision forward error correction codes for very large constellations.
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| 4. |
- Shen, Meigen, 1970-
(författare)
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Concurrent chip and package design for radio and mixed-signal systems
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The advances in VLSI and packaging technologies enable us to integrate a whole system on a single chip (SoC) or on a package module. In these systems, analog/RF electronics, digital circuitries, and memories coexist. This new technology brings us new freedom for system integration as well as new challenges in system design and implementation. To fully utilize the benefits of these new hardware technologies, concurrent design of system, chip, and package is necessary. This research aims to explore the new design space and opportunities for System-on-Package (SoP), with special attention on radio and mixed-signal system applications. Global level system partitioning for SoC and SoP with cost-performance trade-off, concurrent chip and design for high-speed off-chip signaling, global clock distribution, and ultra wideband (UWB) radio module are two fields in this research.Cost-performance driven for mixed-signal system partitioning in early conceptual level design is first addressed in this thesis. We develop a modeling technique to pre-estimate the cost and performance. The performance model evaluates various noise isolation technologies, such as using guard rings, and partitioning the system into several chips. In cost analysis, new factors such as extra chip area and additional process steps due to mixed signal isolation, integration of intellectual property (IP) right module or “virtual components”, yield and technology compatibility for merging logic, memory and analog/RF circuits on a single chip are considered. An efficient computation algorithm, namely COMSI, is developed for cost estimation under various mixed-signal performance constraints.System interconnect topologies have been moving away from multi-point bus architecture and towards high-speed serial links. But low interaction between chip and package design has more and more limited system performance. We address concurrent chip and package design and co-optimization for high-speed off-chip signaling in this part. First we explore the interconnect and package constraints to the circuit and system architecture. Proper equivalent circuit models for package parasitics are set up and then a 3-dimension electromagnetic (EM) solver is used to extract the parasitic parameters of package. After that, bandwidth and noise of the signal channel are estimated. The optimal off-chip singling is designed according to these packages and interconnection constraints. We also analyzed the global clock distribution using co-design method.We developed a low cost, low power consumption, and low complexity UWB radio module using co-design method and SoP technologies. The module will be used in low data rate and long-range wireless intelligent systems such as radio frequency identification (RFID) or wireless sensors networks (WSN). Liquid-crystal-polymer (LCP) based SoP technologies were used to implement the module.
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