| 1. |
- Li, Jun
(författare)
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Effects of Environment on Charge Recombination in Organo-Metal-Halide Perovskite Observed by Photoluminescence Microscopy and Spectroscopy
- 2021. - Media-Tryck
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Organo-metal-halide (OMH) perovskites form a new class of materials withperovskite crystal structure ABX3 where A is an organic molecule, B is lead (Pb)and X is a halide atom (I or Br). OMH perovskite semiconductors have been widely used in photovoltaics due to their very strong absorption of sun light, very suitable electrical properties, and the ease of preparation. Today the power conversion efficiency of record devices based on OMH is as large as 25.5%.There are still many challenges for commercial application of OMH perovskitebased solar cells and other devices. One of the problems we can formulate assensitivity of the properties of OMP semiconductors and devices based on them on factors like electric field, atmosphere, light, temperature and so on. Despite large efforts spent in the scientific community on investigation of the environmental effects on OMH perovskites and stability of devices many issues are still not wellunderstood.In this thesis, I present results of several research projects where photoluminescence (PL) properties of OMH perovskites were studied by optical luminescence microscopy and spectroscopy under different environmental conditions such as humidity, electric field, local pressure and low temperature. We observed that water molecules can play an important role in the transformation of OMH perovskite from its intermediate phase containing solvent molecules to the perovskite crystal structure. We found that both electric field and local pressure and mechanical damage at nano-scale can create temporal PL quenching in OMH perovskites microand nanocrystals. We propose that PL quenching is induced by deep defects states created by electric field, pressure or mechanical manipulation. However, the destructive influence of all these factors on PL disappears several minutes after the influence was stopped due to self-healing properties of OHP. By comparing PL spectra and PL intensity and cryogenic temperatures and at room temperature we found that the concentration of shallow defect states and deep defect states are proportional to each other.
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| 2. |
- Li, Jun
(författare)
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Learning reactive behaviors with constructive neural networks in mobile robotics
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates a learning system for acquiring robot behaviors by mapping sensor information directly to motor actions. It addresses the integration of three learning paradigms, namely unsupervised learning (UL), supervised learning (SL), and reinforcement learning (RL). The approach is characterized by the use of constructive artificial neural networks (ANNs). The sensor-motor mappings acquired by the learning system form part of a tight "sense-learn-act" cycle, as opposed to "sense-plan-act", thus allowing the robot to learn concepts within its own sensorimotor experience while avoiding anthropomorphic bias.Novel techniques for robot learning using constructive radial basis function (RBF) networks are introduced. This leads to a self-organizing, incremental and local construction of the sensorimotor space for learning different behaviors with the same basic architecture, thus a great simplification of the engineering design process of the ANN's structure. Integration of the different learning paradigms takes place in a two-layer learning architecture.The lower layer with the UL and SL paradigms is used to quickly construct a controller for the required behavior. The upper layer with the RL paradigm is used for tuning and refining of the controller resulting from the lower layer (or a controller obtained from other prior knowledge) to further improve the robustness and performance of the behavior. Both layers apply constructive RBF networks, taking into account the different requirements of the respective learning paradigms.The learning system is verified by a number of experiments on a real robot. We begin our experiments with the lower layer together with a teaching-by-demonstration approach for acquiring different behaviors. The experimental results show that the lower layer can learn a wide range of robot behaviors, thus demonstrating the task non-specific nature of the architecture. We then demonstrate the necessity of the layered learning architecture for more complex behaviors by a docking behavior requiring precise positioning at a goal location. The results obtained show that learning with only the lower layer can not obtain robust performance and optimal trajectories, while learning with only the upper layer is impractical and even infeasible on the real robot due to the slow learning process of the RL paradigm. With layered learning, however, the upper layer is speeded up by bootstrapping from the learnedcontroller in the lower layer, and a robust and time-optimal controller can be obtained.
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| 3. |
- Li, Jun
(författare)
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Ultra-low latency communication for 5G transport networks
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The fifth generation (5G) mobile communication system is envisioned to serve various mission-critical Internet of Thing (IoT) applications such as industrial automation, cloud robotics and safety-critical vehicular communications. The requirement of the end-to-end latency for these services is typically within the range between 0.1 ms and 20 ms, which is extremely challenging for the conventional cellular network with centralized processing. As an integral part of the cellular network, the transport network, referred to as the segment in charge of the backhaul of radio base stations or/and the fronthaul of remote radio unit, plays an especially important role to meet such a stringent requirement on latency.This thesis investigates how to support the ultra-low latency communications for 5G transport networks, especially for backhaul networks. First, a novel passive optical network (PON) based mobile backhaul is proposed and tailored communication protocols are designed to enhance the connectivity among adjacent base stations (BSs). Simulation results show that an extremely low latency (less than 1 ms packet delay) for communications among the BSs can be achieved, which thereby can be used to support fast handover for users with high mobility (e.g., vehicles).Furthermore, the thesis presents a fog computing enabled cellular networks (FeCN), in which computing, storage, and network functions are provisioned closer to end users, thus the latency on transport networks can be reduced significantly. In the context of FeCN, the high mobility feature of users brings critical challenges to maintain the service continuity with stringent service requirements. In the meanwhile, transmitting the associated services from the current fog server to the target one to fulfill the service continuity, referred to as service migration, has been regarded as a promising solution for mobility management. However, service migration cannot be completed immediately, and may lead to a situation where users experience loss of access to the service. To solve such issues, a quality-of-service (QoS) aware service migration strategy is proposed. The method is based on the existing handover procedures with newly introduced distributed fog computing resource management scheme to minimize the potential negative effects induced by service migration. The performance of the proposed schemes is evaluated by a case study, where realistic vehicle mobility pattern in the metropolitan network scenario of Luxembourg is used to reflect the real world environment. Results show that low end-to-end latency (e.g., 10 ms) for vehicular communication can be achieved with typical vehicle mobility. During service migration, both the traffic generated by migration and other traffic (e.g., control information, video) are transmitted via mobile backhaul networks. To balance the performance of the two kinds of traffic, a delay-aware bandwidth slicing scheme is proposed in PON-based mobile backhaul networks. Simulation results show that, with the proposed method, migration data can be transmitted successfully within a required time threshold, while the latency and jitter for non-migration traffic with different priorities can be reduced significantly.
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| 4. |
- Li, Jun
(författare)
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Volumetric combustion of torrefied biomass for large percentage biomass co-firing up to 100% fuel switch
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The co-firing of biomass and coal plays an important role in increasing the biomass power capacity and reducing greenhouse gas (GHG) emissions. The challenges of the large percentage biomass co-firing (over 20% on energy basis) in existing pulverized coal boilers are keeping the same steam parameters and having a high boiler efficiency and a stable operating.The primary goal of this thesis is to develop a combustion concept for coal-fired boilers to enablea large percentage of biomass co-firing with up to a 100% fuel switch; these changes should increase the combustion efficiency, reduce CO2 and NOx emissions, improve the process efficiency, while maintaining the same steam parameters after switching fuels. To achieve these goals, a typical biomass pretreatment technology called torrefaction has been employed to upgrade the biofuel quality in terms of both energy density and chemical properties. Consequently, a torrefaction based co-firing system has been proposed. In addition, a novel biomass combustion method called volumetric combustion has been designed; this process involves intense mixing and flue gas internal recirculation inside the combustion chamber, increasing the residence time of the biomass particles and making the temperature and gas species more uniform.In this thesis, a series of studies based on experiments, CFD modelling, and process simulations have been performed. First, the raw material was palm kernel shells (PKS) that were torrefied over same residence time but at different temperatures in a laboratory-scale torrefaction reactor, producing three torrefied biomasses with different degrees of torrefaction. The devolatilization kinetics and char oxidation kinetics were determined based a series of high-temperature high-heating-rate tests in an isothermal plug flow reactor (IPFR), the obtained kinetic parameters were adopted for CFD modeling. Continually, the numerical investigations on the flame properties of the torrefied biomass and a 220 MWe coal-fired boiler performance were conducted, to understand the predicted results of the coal-fired boiler performance at varying biomass co-firing ratios. Afterward, analyses of the impacts of the degree of torrefaction and the biomass co-firing ratio on process operation, performance and electricity efficiency of a torrefaction based co-firing power plant were performed. Finally, the properties of the pollutants emitted from biomass volumetric combustions under various combustion modes and co-firing ratios were studied using Aspen Plus.According to the results, the following conclusions can be reached: 1) a high heating rate enhances the yields of the volatiles for biomass devolatilization processes with the same final temperature; 2) the enhanced drag force on the biomass particles causes a late release of volatile matter and delays the ignition of the fuel-air mixture. Furthermore, oxidizers with lower oxygen concentrations normally generate larger flame volumes, lower peak flame temperatures and lower NO emission; 3) the co-firing simulation reveals that a boiler load reduction of less than 10% is observed when firing 100% torrefied biomass; 4) deep torrefaction is not recommended because the energy saved during biomass grinding is lower than that consumed by the additional torrefaction process; the electrical efficiency of power plant is reduced when increasing either the degree of torrefaction or the biomass substitution ratio; 5) the amount of flue gas that needs to be recycled for NOx reduction decreased when the percentage of co-fired biomass increased.Overall, from the perspective of combustion, both the torrefaction process and volumetric combustion are promising steps toward realizing large percentage biomass co-firing in coal-fired boilers with high efficiency and reduced emissions.
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| 5. |
- Li, Ke-Jun
(författare)
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Semliki forest virus-derived packaging system for production of retroviral vectors
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Gene therapy is a treatment of disease by transfer of genetic material into somatic cells of an individual. Successful gene therapy depends on a delivery system which can efficiently transfer the gene into target cells and lead to high level expression of the gene. Because retroviruses can integrate their genome into the chromosomes of infected cells, they have been used as vectors for stable expression of heterologous genes. Usually, the retroviral vectors are produced by transfection of vector DNA into a packaging cell line that synthesizes all retroviral proteins. One major drawback of this vector system is that it is limited to transduce the cDNA forms of processed mRNAs. These minigenes lack important control elements for gene expression and, therefore, often support low level of expression. For example, it is difficult to use the vector system for transduction of genes containing introns because any intron present in an engineered provirus will be removed from the transcribed RNA by the nuclear splicing machinery. In this thesis, I describe the development of a Semliki Forest virus (SFV)-derived packaging system for efficient production of retroviral vectors that can carry a foreign gene with an intron. We first inserted the gag-pol, ecotropic env and amphotropic env genes into individual SFV1 expression plasmids and transcribed the corresponding replication-competent SFV vector RNAs in vitro. The latter were introduced into the cytoplasm of BHK-21 cells by electroporation. We showed that the transfected cells synthesized a retroviral proteins, that is Gag proteins, Env proteins and viral enzymes, and that these were used for the assembly of mature virus like particles. To test if this system could produce infectious retroviral vectors, a recombinant Moloney murine leukemia virus genome containing the neomycin phosphotransferase gene (LTR-[psi]+-neoR-LTR) was inserted into SFV1 plasmid and the in vitro made RNA was cotransfected into BHK-21 cells together with the SFV1/gagpol RNA and SFV1/env RNA. We found that infectious retroviral vectors were produced from the transfected cells at titers up to 4 x 106 colony-forming units (cfu)/mil during a 5-hour incubation period. In this SFV-based system, the RNAs are synthesized in the cytoplasm of the cell, not in the nucleus. We reasoned that intron-containing genes can be packaged into retroviral vectors with the system. This was tested with a recombinant Molony murine leukemia virus genome containing the chloramphenicol. acetyltransferase (CAT) gene in association with an intron. When this RNA was cotransfected into BHK-21 cells together with the SFV1/gag-pol RNA and SFV1/env RNA, 1.3 X 106 cfu/ml were produced during a 5-hour incubation period. These vectors faithfully transduced the intron-containing gene into NIH 3T3 cells and HeLa cells, where the intron-CAT RNA was subjected to efficient splicing and used for high level expression. I conclude that we have developed a retroviral vector packaging system that is based on RNA replication in cell cytoplasm and can be used for transduction of intron-containing genes into mammalian cells. The fact that no helper virus could be detected in the virus stocks makes the system very interesting for gene therapy. In this thesis, I also present a study of human bone marrow stromal cells as target cells for retroviral-mediated gene transfer. Ninety one percent of the cells in a stromal cell culture were transduced by four rounds of retroviral vector infection without cytokine stimulation. The transduced stromal cells could settle in the bone marrow of SCID mice and survive for at least two months. This suggests that human bone marrow stromal cells might be used as target cells for certain types of clinical gene therapy.
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| 6. |
- Luo, Jun, 1979-
(författare)
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Integration of metallic source/drain contacts in MOSFET technology
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The continuous and aggressive downscaling of conventional CMOS devices has been driving the vast growth of ICs over the last few decades. As the CMOS downscaling approaches the fundamental limits, novel device architectures such as metallic source/drain Schottky barrier MOSFET (SB-MOSFET) and SB-FinFET are probably needed to further push the ultimate downscaling. The ultimate goal of this thesis is to integrate metallic Ni1-xPtx silicide (x=0~1) source/drain into SB-MOSFET and SB-FinFET, with an emphasis on both material and processing issues related to the integration of Ni1-xPtx silicides towards competitive devices. First, the effects of both carbon (C) and nitrogen (N) on the formation and on the Schottky barrier height (SBH) of NiSi are studied. The presence of both C and N is found to improve the poor thermal stability of NiSi significantly. The present work also explores dopant segregation (DS) using B and As for the NiSi/Si contact system. The effects of C and N implantation into the Si substrate prior to the NiSi formation are examined, and it is found that the presence of C yields positive effects in helping reduce the effective SBH to 0.1-0.2 eV for both conduction polarities. In order to unveil the mechanism of SBH tuning by DS, the variation of specific contact resistivity between silicide and Si substrates by DS is monitored. The formation of a thin interfacial dipole layer at silicide/Si interface is confirmed to be the reason of SBH modification. Second, a systematic experimental study is performed for Ni1-xPtx silicide (x=0~1) films aiming at the integration into SB-MOSFET. A distinct behavior is found for the formation of Ni silicide films. Epitaxially aligned NiSi2-y films readily grow and exhibit extraordinary morphological stability up to 800 oC when the thickness of deposited Ni (tNi) <4 nm. Polycrystalline NiSi films form and tend to agglomerate at lower temperatures for thinner films for tNi≥4 nm. Such a distinct annealing behavior is absent for the formation of Pt silicide films with all thicknesses of deposited Pt. The addition of Pt into Ni supports the above observations. Surface energy is discussed as the cause responsible for the distinct behavior in phase formation and morphological stability. Finally, three different Ni-SALICIDE schemes towards a controllable NiSi-based metallic source/drain process without severe lateral encroachment of NiSi are carried out. All of them are found to be effective in controlling the lateral encroachment. Combined with DS technology, both n- and p-types of NiSi source/drain SB-MOSFETs with excellent performance are fabricated successfully. By using the reproducible sidewall transfer lithography (STL) technology developed at KTH, PtSi source/drain SB-FinFET is also realized in this thesis. With As DS, the characteristics of PtSi source/drain SB-FinFET are transformed from p-type to n-type. This thesis work places Ni1-xPtx (x=0~1) silicides SB-MOSFETs as a competitive candidate for future CMOS technology.
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| 7. |
- Wang, Jianfeng, 1984-
(författare)
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Enhanced block sparse signal recovery and bayesian hierarchical models with applications
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is carried out within two projects ‘Statistical modelling and intelligentdata sampling in Magnetic resonance imaging (MRI) and positron-emission tomography(PET) measurements for cancer therapy assessment’ and ‘WindCoE -Nordic Wind Energy Center’ during my PhD study. It mainly focuses on applicationsof Bayesian hierarchical models (BHMs) and theoretical developments ofcompressive sensing (CS). Under the first project, Paper I improves the quantityestimation of MRI parametric imaging by utilizing inherent dependent structure inthe image through BHMs; Paper III constructs a theoretically unbiased and asymptoticallynormal estimator of sparsity of a sparsified MR image by using a BHM;Paper IV extends block sparsity estimation from real-valued signal recovery tocomplex-valued signal recovery. It also demonstrates the importance of accuratelyestimating the block sparsity through a sensitivity analysis; Paper V proposes anew measure, i.e. q-ratio block constrained minimal singular value, of measurementmatrix for block sparse signal recovery. An algorithm for computing thisnew measure is also presented. In the second project, Paper II estimates the uncertaintyof Weather Research and Forecasting (WRF) model’s daily-mean 2-metertemperature in a cold region by using a BHM. It is a computationally cheaper andfaster alternative to traditional ensemble approach. In summary, this thesis makessignificant contributions in improving and optimizing the estimation proceduresof parameters of interest in MRI and WRF in practice, and developing the novelestimators and measure under the framework of CS in theory.
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| 8. |
- Zhang, Jun, Dr. 1987-
(författare)
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Synthesis and characterization of fluorescent stilbene-based probes targeting amyloid fibrils
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Alzheimer’s disease (AD) is characterized by two main protein aggregate hallmarks in the brain: extracellular deposition of the amyloid-β (Aβ) in senile plaques and intracellular neurofibrillary tangles (NFTs) consisting of hyperphosphorylated tau protein. The past decade has seen great progress in the development of imaging probes for the non-invasive detection of Aβ and tau aggregates. Here positron emission tomography (PET), single-photon emission computed tomography (SPECT) and magnetic resonance imaging (MRI), are highly promising technologies for clinical diagnostics. However, as a research tool, optical imaging is superior because it is real-time, sensitive, inexpensive, not radioactive and that it in particular affords high-resolution studies both in vitro and in vivo. Fluorescent probes are especially useful for designing novel binding scaffolds for structure investigations of protein aggregates. This thesis describes design, synthesis and evaluation of a series of fluorescent probes for detection of amyloid fibrils, especially Aβ or tau aggregates in vitro.Firstly, trans-stilbenoid vinylbenzene-1,2-diol with benzene, naphthalene, anthracene, and pyrene are investigated with respect to their photophysical properties free in solution and when bound to amyloid fibrils, including time-resolved fluorescence measurements. It is noted that the extended conjugated systems retained the amyloid targeting properties of the probes and both the anthracene and pyrene moieties extensively enhanced the fluorescence intensity and prolonged lifetimes.Secondly, the synthesis of two molecules, Py1SA and Py2SA, based on pyrene linked to salicylic acid via a trans-stilbene C = C bond is presented. The compounds show strikingly different emission spectra when bound to preformed Aβ1-42 fibrils as well as to fibrils from four other distinct proteins. Additionally, excited state intramolecular proton transfer (ESIPT) coupled-charge transfer (ICT) is observed for the anionic form of the probes in polar solvents. This is likely the reason for the spectral differences of the probes when bound to amyloid fibrils.Moreover, the synthesis of a further development of the Congo red analogue X-34 [2,5-bis(4’-hydroxy-3’-carboxy-styryl) benzene] by rational design and synthesis is described. Full photophysical characterization was performed, including recording absorbance and fluorescence spectra, Stokes shift, quantum yield and fluorescence lifetimes. All ligands displayed high affinity towards recombinant amyloid fibrils of Aβ1-42 and tau as well as selectivity towards the corresponding disease-associated protein aggregates in human post mortem AD tissue.Lastly, the synthesis of a set of 2,1,3-benzothiadiazole (BTD)-based ligands with different conjugated spacers and variable patterns of OH substitutions of bis-styryl-BTD prototypes were developed. Aβ binding affinities (Aβ1-42 and Aβ1-40 fibrils) and the specificity towards Aβ plaques of all ligands were determined. These findings extend the structure to activity relationships of BTD-based ligands for Aβ fibril binding.Throughout the studies in this dissertation, new interesting properties of small molecule fluorescence probes have been discovered and analyzed. This knowledge should facilitate the development of noninvasive probes for early detection of Alzheimer's disease and to distinguish different Aβ fibril polymorphs.
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