| 1. |
- Sun, Bin, 1988-
(författare)
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Automated Traffic Time Series Prediction
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Intelligent transportation systems (ITS) are becoming more and more effective. Robust and accurate short-term traffic prediction plays a key role in modern ITS and demands continuous improvement. Benefiting from better data collection and storage strategies, a huge amount of traffic data is archived which can be used for this purpose especially by using machine learning.For the data preprocessing stage, despite the amount of data available, missing data records and their messy labels are two problems that prevent many prediction algorithms in ITS from working effectively and smoothly. For the prediction stage, though there are many prediction algorithms, higher accuracy and more automated procedures are needed.Considering both preprocessing and prediction studies, one widely used algorithm is k-nearest neighbours (kNN) which has shown high accuracy and efficiency. However, the general kNN is designed for matrix instead of time series which lacks the use of time series characteristics. Choosing the right parameter values for kNN is problematic due to dynamic traffic characteristics. This thesis analyses kNN based algorithms and improves the prediction accuracy with better parameter handling using time series characteristics.Specifically, for the data preprocessing stage, this work introduces gap-sensitive windowed kNN (GSW-kNN) imputation. Besides, a Mahalanobis distance-based algorithm is improved to support correcting and complementing label information. Later, several automated and dynamic procedures are proposed and different strategies for making use of data and parameters are also compared.Two real-world datasets are used to conduct experiments in different papers. The results show that GSW-kNN imputation is 34% on average more accurate than benchmarking methods, and it is still robust even if the missing ratio increases to 90%. The Mahalanobis distance-based models efficiently correct and complement label information which is then used to fairly compare performance of algorithms. The proposed dynamic procedure (DP) performs better than manually adjusted kNN and other benchmarking methods in terms of accuracy on average. What is better, weighted parameter tuples (WPT) gives more accurate results than any human tuned parameters which cannot be achieved manually in practice. The experiments indicate that the relations among parameters are compound and the flow-aware strategy performs better than the time-aware one. Thus, it is suggested to consider all parameter strategies simultaneously as ensemble strategies especially by including window in flow-aware strategies.In summary, this thesis improves the accuracy and automation level of short-term traffic prediction with proposed high-speed algorithms.
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| 2. |
- Wei, Cheng-Hong
(författare)
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Regulation of T cell activation and death by the affinity of TCR for peptide/MHC complexes
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this study is to investigate the role of the affinity of peptide:MHC/TCR interaction in the regulation of T cell activation, death and repertoire selection. Three aspects pertinent for our understanding of this issue have been analyzed. First, we analyzed the effect of partially agonistic peptides on the activation and survival of CTL clones specific for a highly immunogenic HLA A11-restricted peptide epitope derived from the EBV nuclear Ag 4(EBNA 4), IVTDFSVIK (designated IVT). Several analogues with substitutions of TCR contact residues were able to trigger cytotoxic activity without induction of IL-2 mRNA and protein or T cell proliferation. Triggering with these partial agonists in the absence of exogenous IL-2 resulted in down-regulation of the cytotoxic potential of the specific CTLs. One analogue selectively triggered apoptosis as efficiently as the original epitope, subdividing the partial agonists into apoptosis-inducing and non-inducing ligands. Analysis of early T cell activation events did not reveal significant differences between the two types of analogue peptides. These results demonstrate that some partial agonists can dissociate the induction of CTL death from CTL activation. Then, we characterized the apoptotic programs induced by the immunogenic peptide and its partially agonistic analogues in the IVT-specific CTL clones. Our major finding is that CTL triggering with partially agonistic peptide ligands can initiate death receptor dependent and independent apoptotic programs in the effector cells. In contrast to classical AICD, death receptors are not essential for the elimination of CTLs activated with partially agonistic peptides. In addition, death receptor independent apoptosis requires caspases other than caspase 3 and 8. Induction of anti-apoptotic BCl-2 and BCl-XL expression is associated with resistance to this form of apoptosis. Also, IL-2 enhances classical and inhibits death receptor independent AICD. We concluded that TCR triggering not accompanied by IL-2 production may result in elimination of T-lymphocytes in death receptor independent manner. Our data demonstrated that engagement of TCR by MHC-peptide complexes can trigger diverse apoptotic programs of AICD and that the choice between these programs is determined by the agonistic potency of MHC- peptide ligand. Second, the molecular basis of different outcomes of CTLs stimulation with. immunogenic and partially agoistic peptide ligands was analyzed. The role of MHC:peptide/TCR affinity in the regulation of T cell activation was characterized using tetramer technology. Our results demonstrated that the All complexes assembled with the partial agonist dissociated from the surface of IVT-specific CTLs with a faster kinetics as compared with complexes containing the immunogenic peptide. We also showed that the efficiency of CTL recognition correlates with the stability of interaction between the specific TCR and MHC:peptide complex. Tetramer binding and secretion of INFgamma were shown to be compatible with T-cell activation by partially agonistic peptides. In conclusion, our results indicate that the affinity of TCR/MHC:peptide interaction determines the strength of TCR signalling, extent of CTL activation as well as the apoptosis pathway that operates in CTLs in the course of AICD. The third aim of our study was to investigate the influence of the affinity of TCR/MHC interaction on the selection and maintenance of TCR repertoire of peptide specific CTLs. Using tetramer technology, we investigated the restriction of TCR usage among CTL responses against a subdominat EBNA 4 derived peptide referred to as AWF. In agreement with the earlier findings, ex vivo analysis of AVF-specific CTLs using AVF-containing HLA All tetramers revealed the same degree of conservation of the AVF-specific response both in healthy virus carriers and in the course of primary EBV infection. Tetramer binding and dissociation experiments performed with AVF-specific: CTLs or CTLs expressing a very diverse set of TCRs and specific to another immunodominant A 11-restricted EBV-derived peptide epitope did not support a model of affinity driven selection of restricted TCR repertoires. Characterization of individuals that fail to mount responses to the immunodominant A11-restricted CTL epitope but efficiently respond to the AVF-peptide argued against interclonal competition as the reason for the observed TCR conservation. Collectively, our data confirm the existence of naturally induced peptide-specific CTL responses with highly restricted TCR usage. Our data do not support a major role for affinity of MHC:TCR interaction in the selection of structurally conserved TCR-repertoires and suggest that such conservations may be due to structural constrains in MHC:peptide/TCR interactions or endogenous pre-selection of certain clonotypes.
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| 3. |
- Wu, Wei-Cheng, 1979
(författare)
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Design, Processing, and Characterization of High Frequency Flip Chip Interconnects
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The demands for high frequency interconnect techniques for microwave integrated circuits (ICs) are growing with increasing operating frequencies of wireless communication systems. Interconnects have significant effect and impact on the overall system performance at high frequencies. To provide good performance in high frequency packaging, flip chip interconnect is one of the most attractive candidates compared to other schemes with low reflection and low insertion loss due to the lower parasitics involved. The widely used bond-wire interconnect suffers from serious parasitics when operating frequency reaches the gigahertz range. The tolerances such as the wire length and loop are very tight to enable an acceptable transition. At high frequencies, however, it still encounters stronger parasitics no matter how well it is controlled.This thesis deals with the design, processing, and characterization of flip chip interconnects at high frequencies. The main issues of the flip chip interconnect are described before the design criteria of the conventional flip chip interconnect are reviewed. In the following, the work of the hot-via transition is presented. It is a solution to the detuning effect of the microstrip (MS) flip chip assembly. The designs of the hot-via transition for the MS-to-CPW (coplanar waveguide) are presented; the results presented are currently world record for this technique to our knowledge. Another part of work in this thesis is the coaxial transition developed for the CPW-to-CPW flip chip interconnects. The coaxial-type transition was successfully fabricated in-house and demonstrated excellent transition performance up to 60 GHz. The entire fabrication processes for all demonstrated flip chip interconnect structures have been in-house developed and are described in details. All the design rules regarding to the different architectures for the flip chip interconnects are described and verified with the measured results. The main contributions of this thesis work are the innovative designs and the developments of both the hot-via transition and coaxial transition for the flip chip interconnects.
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