| 1. |
- Lu, Lu, 1986-
(författare)
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Wireless Broadcasting with Network Coding
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wireless digital broadcasting applications such as digital audio broadcast (DAB) and digital video broadcast (DVB) are becoming increasingly popular since the digital format allows for quality improvements as compared to traditional analogue broadcast. The broadcasting is commonly based on packet transmission. In this thesis, we consider broadcasting over packet erasure channels. To achieve reliable transmission, error-control schemes are needed. By carefully designing the error-control schemes, transmission efficiency can be improved compared to traditiona lautomatic repeat-request (ARQ) schemes and rateless codes. Here, we first study the application of a novel binary deterministic rateless (BDR) code. Then, we focus on the design of network coding for the wireless broadcasting system, which can significantly improve the system performance compared to traditional ARQ. Both the one-hop broadcasting system and a relay-aided broadcasting system areconsidered. In the one-hop broadcasting system, we investigate the application of systematic BDR (SBDR) codes and instantaneously decodable network coding (IDNC). For the SBDR codes, we determine the number of encoded redundancy packets that guarantees high broadcast transmission efficiencies and simultaneous lowcomplexity. Moreover, with limited feedback the efficiency performance can be further improved. Then, we propose an improved network coding scheme that can asymptotically achieve the theoretical lower bound on transmission overhead for a sufficiently large number of information packets. In the relay-aided system, we consider a scenario where the relay node operates in half duplex mode, and transmissions from the BS and the relay, respectively, are over orthogonal channels. Based on random network coding, a scheduling problem for the transmissions of redundancy packets from the BS and the relay is formulated. Two scenarios; namely instantaneous feedback after each redundancy packet, and feedback after multiple redundancy packets are investigated. We further extend the algorithms to multi-cell networks. Besides random network coding, IDNC based schemes are proposed as well. We show that significant improvements in transmission efficiency are obtained as compared to previously proposed ARQ and network-coding-based schemes.
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| 2. |
- Farcas, Florentina Angela
(författare)
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Evaluation of Asphalt Field Cores with Simple Performance Tester and X-ray Computed Tomography
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The importance of aggregate structure and air voids distribution for asphalt mixture rutting and cracking performance has been well established on the basis of experience and is well documented in the literature. Past and current investigations are limited to assessment of performance based on macroscopic behavior due to the difficulty associated with the quantitative measurement and analysis of the internal structure of asphalt mixtures. Lately, technical advances in X-ray Computed Tomography (CT) and image processing and analysis has made possible to bring the attention also to the internal structure of asphalt mixtures. SPT results from asphalt field cores, including dynamic modulus (before and after loading) and microstrain accumulation (flow number), exhibited significant variability; most likely, induced by irregularities in the core shape. The analysis of aggregate structure and air voids distribution performed trough X-ray CT, clearly identified segregation in the asphalt mixture as a key factor that induced variability in SPT results.
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| 3. |
- Halim, Joseph, 1985-
(författare)
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Synthesis and Characterization of 2D Nanocrystals and Thin Films of Transition Metal Carbides (MXenes)
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Two dimensional (2D) materials have received growing interest because of their unique properties compared to their bulk counterparts. Graphene is the archetype 2D solid, but other materials beyond graphene, such as MoS2 and BN have become potential candidates for several applications. Recently, a new family of 2D materials of early transition metal carbides and carbonitrides (Ti2CTx, Ti3C2Tx, Ti3CNTx, Ta4C3Tx, and more), labelled MXenes, has been discovered, where T stands for the surface-terminating groups.Before the present work, MXenes had only been synthesized in the form of exfoliated and delaminated powders, which is not suitable for electronic applications. In this thesis, I demonstrate the synthesis of MXenes as epitaxial thin films, a more suitable form for electronic and photonic applications. Results show that 2D epitaxial Ti3C2Tx films - produced by HF and NH4HF2 etching of magnetron sputter-grown Ti3AlC2 - exhibit metallic conductive behaviour down to 100 K and are 90% transparent to light in the visible-infrared range. The results from this work may open the door for MXenes as potential candidates for transparent conductive electrodes as well as in electronic, photonic and sensing applications.MXenes have been shown to intercalate cations and molecules between their layers that in turn can alter the surface termination groups. There is therefore a need to study the surface chemistries of synthetized MXenes to be able to study the effect of intercalation as well as altering the surface termination groups on the electronic structure and chemical states of the elements present in MXene layers. X-ray Photoelectron Spectroscopy (XPS) in-depth characterization was used to investigate surface chemistries of Ti3C2Tx and Ti2CTx. This thesis includes the discussion of the effect of Ar+ sputtering and the number of layers on the surface chemistry of MXenes. This study serves as a baseline for chemical modification and tailoring of the surface chemistry groups to potential uses and applications.New MXene phases, Nb2CTx and V2CTx, are shown in this thesis to be produced from HF chemical etching of Nb2AlC and V2AlC powders. Characterization of the produced MXenes was carried out using Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Transmission Electron Microscope (TEM) and XPS. Nb2CTx and V2CTx showed promising performance as electrodes for Li-ion batteries.In this thesis, electrochemical etching was used in an attempt to produce 2D metal carbides (MXene) from their ternary metal carbides, Ti3SiC2, Ti3AlC2 and Ti2AlC MAX phases. MAX phases in the form of highly dense bulk produced by Hot Isostatic Press. Several etching solutions were used such as HF, NaCl and HCl. Unlike the HF chemical etching of MAX phases, which results in MXenes, the electrochemical etching resulted in Carbide Derived Carbon (CDC). Here, I show the characterization of the produced CDC using several techniques such as XRD, TEM, Raman spectroscopy, and XPS. Electrochemical characterization was performed in the form of cyclic voltammetry, which sheds light on the etching mechanism.
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| 4. |
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| 5. |
- Liu, Ming, 1982-
(författare)
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A High-end Reconfigurable Computation Platform for Particle Physics Experiments
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Modern nuclear and particle physics experiments run at a very high reaction rate and are able to deliver a data rate of up to hundred GBytes/s. This data rate is far beyond the storage and on-line analysis capability. Fortunately physicists have only interest in a very small proportion among the huge amounts of data. Therefore in order to select the interesting data and reject the background by sophisticated pattern recognition processing, it is essential to realize an efficient data acquisition and trigger system which results in a reduced data rate by several orders of magnitude. Motivated by the requirements from multiple experiment applications, we are developing a high-end reconfigurable computation platform for data acquisition and triggering. The system consists of a scalable number of compute nodes, which are fully interconnected by high-speed communication channels. Each compute node features 5 Xilinx Virtex-4 FX60 FPGAs and up to 10 GBytesDDR2 memory. A hardware/software co-design approach is proposed to develop custom applications on the platform, partitioning performance-critical calculation to the FPGA hardware fabric while leaving flexible and slow controls to the embedded CPU plus the operating system. The system is expected to be high-performance and general-purpose for various applications especially in the physics experiment domain. As a case study, the particle track reconstruction algorithm for HADES has been developed and implemented on the computation platform in the format of processing engines. The Tracking Processing Unit (TPU) recognizes peak bins on the projection plane and reconstructs particle tracks in realtime. Implementation results demonstrate its acceptable resource utilization and the feasibility to implement the module together with the sys-tem design on the FPGA. Experimental results show that the online track reconstruction computation achieves 10.8 - 24.3 times performance acceleration per TPU module when compared to the software solution on a Xeon2.4 GHz commodity server.
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| 6. |
- Lü, Bo
(författare)
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Dynamics of the Early Stages in Metal-on-Insulator Thin Film Deposition
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thin films consist of nanoscale layers of material that are used in many technological applications to either functionalize a surface or serve as parts in miniaturized devices. The properties of a film are closely related to its microstructure, which in turn can be tuned during film preparation. Thin film growth involves a multitude of atomic-scale processes that cannot always be easily studied experimentally. Therefore, different types of computer simulations have been developed in order to test theoretical models of thin film growth in a highly controlled way. To be able to compare simulation and experimental results, the simulations must be able to model events on experimental time-scales, i.e. several seconds or minutes. This is achievable with the kinetic Monte Carlo method.In this work, kinetic Monte Carlo simulations are used to model the initial growth stages of metal films on insulating, amorphous substrates. This includes the processes of island nucleation, three-dimensional island growth and island coalescence. Both continuous and pulsed vapor fluxes are investigated as deposition sources, and relations between deposition parameters and film morphology are formulated. Specifically, the film thickness at what is known as the “elongation transition” is studied as a function of the temporal profile of the vapor flux, adatom diffusivity and the coalescence rate. Since the elongation transition occurs due to hindrance of coalescence completion, two separate scaling behaviors of the elongation transition film thickness are found: one where coalescence occurs frequently and one where coalescence occurs infrequently. In the latter case, known nucleation behaviors can be used favorably to control the morphology of thin films, as these behaviors are not erased by island coalescence. Experimental results of Ag growth on amorphous SiO2 that confirm the existence of these two “growth regimes” are also presented for both pulsed and continuous deposition by magnetron sputtering. Knowledge of how to avoid coalescence for different deposition conditions allows nucleation for metal-on-insulator material systems to be studied and relevant physical quantities to be determined in a way not previously possible. This work also aids understanding of the growth evolution of polycrystalline films, which in conjunction with advanced deposition techniques allows thin films to be tailored to specific applications.
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| 7. |
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| 8. |
- Lu, Hai
(författare)
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Energy Quality Management for New Building Clusters and Districts
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The level of concern regarding the total energy consumption in new building clusters and urban districts (BCDs) has increased recently. Rising living standards have led to a significant increase in building energy consumption over the past few decades. A great potential for energy savings exists through energy quality management (EQM) for new BCDs. Quality of energy measures the useful work potential of certain energy. EQM in this thesis is defined as reducing energy demand, applying distributed renewable energy sources, and utilizing energy technology in sustainable way. According to this definition, tasks of EQM include energy supply system optimization and energy demand prediction.Based on EQM, the optimization of BCDs’ energy supply systems aims to search for the most appropriate scenario, which is a trade-off between various aspects, such as energy performance and environmental impacts as well as system reliability. A novel multi-objective optimization approach for new BCDs is established in this thesis. Optimization algorithm is known as Genetic Algorithm (GA), which is used to address non-linear optimization problems. Two case studies are included in this thesis: the U.K. eco-town residential BCDs case and the Norway office BCDs case.The U.K. case examines the application possibility of the approach in practical design. Optimization objectives involved in this case are the life-cycle global warming potential of the system and the system exergy efficiency. The total life-cycle global warming potential is minimized while the exergy efficiency is maximized. Different types of energy supply system scenarios are recommended with different optimization objective combinations (equal-importance, slightly exergy efficiency-oriented and slightly environment-oriented). The results show that the proposed approach can feasibly be an optimal design tool in practical use.To provide deeper insights into the problem, the Norway case checks the expansibility of inserting additional objectives into the approach. Loss of Power Supply Probability (LPSP), which is one of the system reliability indicators, is additionally included in the optimization objectives. For this case, the approach guarantees the optimal scenarios that cannot exceed the desired LPSP with minimum life-cycle global warming potential and maximum exergy efficiency. Optimal scenarios with different desired LPSP values (0, 1%, and 5%) are compared. Comparison results demonstrate that optimal scenarios change significantly along with variations of the desired LPSP values. Therefore, system reliability is proven as one of the most important objectives for renewable energy system optimization. In the future, this approach can be applied to complex problems with more objectives.Besides energy supply system optimization, an effective and precise BCDs energy demand model is needed. This model should be capable of providing reliable inputs (energy demand and load profiles) for energy supply system optimization and reducing unnecessary energy consumption. In principle, energy demand in BCDs is a complex task because numerous design criteria influence energy performance, which is hard to plan and pre-calculate. Establishing such a model would require a thorough decision base that prioritizes these design criteria and generally distinguishes the more important criteria from the less important ones. The study uses general survey aims to collect and identify the design criteria that affect the BCDs energy demand model and to evaluate the priorities of each criterion using the fuzzy Analytical Hierarchy Process (AHP) method. Four main criteria – location, building characteristics, government, and outdoor surrounding characteristics – are established, along with 13 secondary criteria. The results show that the use of the AHP method can accurately guide the energy demand model and automatically rank significant criteria. The method can provide the weighting value for each criterion as well as the relative ranking for the energy demand model.This thesis aims to provide a systematic and holistic EQM method for BCDs energy system design at the beginning of the decision-making stage.
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| 9. |
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| 10. |
- Lu, Lei
(författare)
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Alterations in activity and specificity of intracellular proteolysis in disease pathogenesis
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The ubiquitin-proteasome pathway (UPP) plays a fundamental role in many basic cellular processes. Virtually all events in cellular physiology include control by the ubiquitin-proteasome pathway. Ubiquitinated substrates are degraded by the 26S proteasome, a large multicatalytic protease complex. Through the degradation of ubiquitinated proteins all eukaryotic cells vary the protein concentration of regulatory proteins within minutes, which is the key to the very sophisticated cellular regulations of e.g. the cell cycle and apoptosis. Low proteasomal activity can be compensated by increased activity of TPPII (Tri-peptidyl-peptidase II), another large cytosolic peptidase. Over-expression of TPPII can be sufficient to maintain cellular viability although the proteasome is inhibited. The aim of the work described in the Licentiate study is to understand the regulation of cellular physiology performed by cytosolic proteolysis in Cell- and Immuno-biology, with respect to proteasome and TPPII. In the first paper, we have examined if increased activity of TPPII in EL-4 Lymphoma cells growing with reduced proteasomal activity has any consequences for pathways controlled by the ubiquitin-proteasome proteolysis. In this study, we find that EL-4 lymphoma cells that can grow in the presence of low proteasomal activity acquire apoptosis resistance due to a failure in degradation of inhibitor of apoptosis proteins (IAPs). The rate of in vivo tumor growth of such cells was strongly increased. Rapid tumor growth, as well as a delayed degradation of IAPs, could be induced by transfection of TPPII. In addition, we observe a slower degradation of IAPs in cells derived from large in vivo tumors, as well as a reduced activity of the proteasome in combination with up-regulated TPPII activity. Our data suggest a novel mechanism for apotosis resistance in tumors. In paper II, we studied whether increased expression of TPPII was an essential response to stress, and redistribution of proteasomes. Here we found that suppression of the ubiquitin-proteasome pathway during stress, mediated at least in part by expression of TPPII, was crucial for cellular survival. Our data give further support for nuclear translocation of proteasomes in tumor cell resistance to stress, and suggest that TPPII has an essential role in this process. TPPII-mediated control of proteasome distribution may be a crucial control of the rate of ubiquitin-dependent proteolysis, which is relevant to many pathogenic processes. Furthermore, expression of TPPII was important for induction of growth arrest in response to cellular stress. Here, we established a link between redistribution of proteasome complexes and control of the rate of ubiquitin-dependent proteolysis. Several aberrant gene products involved in pathogenesis of neurodegenerative diseases interfere with function of the ubiquitin-proteasome pathway. Proteins containing extended repeats of Glutamine (Q) cause inhibition of the ubiquitin-pathway and apoptotic cell death. To study the mechanism of these effects (Paper III), we have investigated how stably expressed poly-Q proteins affects the ubiquitin-proteasome pathway in lymphoma cells in vitro by using a poly-Glutamine-extended N-end rule GFP reporter. We find a significantly reduced ability to degrade ubiquitin-conjugates in poly-Q expressing cells and an alteration of the distribution of proteasome from the cytosol into perinuclear location in the presence of stable expression of poly-Q proteins. These cells failed to resist low concentrations of proteasomal inhibitor, whereas they had delayed apoptosis during exposure to several other apoptotic stimuli. This study shows that poly-Glutamine proteins may affect distribution of proteasomes to alter the efficiency of the ubiquitine-proteasome pathway and give further support for a link between cellular protection responses and pathological mechanisms during expression of poly-Q proteins. These data suggest a novel mechanism that controls the ubiquitin-proteasome pathway during stress. These are relevant in relation to new therapies for multi-therapy-resistant clinical tumors and other human diseases.
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