| 1. |
- Al-Askary, Omar
(författare)
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Iterative decoding of product codes
- 2003
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Iterative decoding of block codes is a rather old subjectthat regained much interest recently. The main idea behinditerative decoding is to break up the decoding problem into asequence of stages, iterations, such that each stage utilizesthe output from the previous stages to formulate its ownresult. In order for the iterative decoding algorithms to bepractically feasible, the complexity in each stage, in terms ofnumber of operations and hardware complexity, should be muchless than that for the original non-iterative decoding problem.At the same time, the performance should approach the optimum,maximum likelihood decoding performance in terms of bit errorrate.In this thesis, we study the problem of iterative decodingof product codes. We propose an iterative decoding algorithmthat best suits product codes but can be applied to other blockcodes of similar construction. The algorithm approaches maximumlikelihood performance. We also present another algorithm whichis suboptimal and can be viewed as a practical implementationof the rst algorithm on product codes. The performance of thesuboptimal algorithm is investigated both analytically and bycomputer simulations. The complexity is also investigated andcompared to the complexity of GMD and Viterbi decoding ofproduct codes.
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| 2. |
- Al-Askary, Omar
(författare)
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Papr reduction of coded OFDM signals based on iterative codeword construction
- 2004
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Ingår i: ISCCSP. - NEW YORK : IEEE. - 0780383796 ; , s. 763-766
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Konferensbidrag (refereegranskat)abstract
- Orthogonal Frequency Division Multiplexing (OFDM) allows transmission of data with high data rates over broad-band radio channels without the need for powerful equalization. However, OFDM is sensitive to non-linearities in the system due to the high Peak to Average Power Ratio (PAPR) in the transmitted signal. In this paper, we propose a simple method for reducing the PAPR in the OFDM signals using the well known BCH codes. The method relies on an iterative procedure to select a codeword that has a low PAPR from a translation of the code to another partition in a larger BCH code. The information about the chosen partition is loaded in the redundancy of the sent codeword and, therefore, no subcarriers are reserved for transmitting this information. The cost payed for this PAPR reduction is reduced error correction capability. Using this method, a reduction of the PAPR of up to 6 dB can be achieved with moderate complexity.
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| 3. |
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| 4. |
- Farah, Idle Omar
(författare)
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Immunopathogenesis of schistosomiasis mansoni : Immunity and pathology in a primary and a secondary infection following chemotherapy in the mouse and the baboo models
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes a series of experiments aimed at elucidating the mechanisms ofimmunity and pathology elicited by both a primary infection and a reinfection exposure toSchistosoma mansoni following chemotherapy. The effects of a single large cercarial doseand a cumulatively equivalent dose, administered as multiple small doses are compared. Inaddition, the suitability of two animal models, a murine (BALB/c mice) and a non-humanprimate (Olive baboons, Papio cynocephalus anubis) for this purpose is evaluated. Duringthe primary infection, single-dose infected (SI) baboons developed more severe clinicaldisease than the multiple-dose infected (MI) group. Hepatic granulomata developed morerapidly and modulated more slowly in the SI group than in the MI group. Intestinal lesions inthe infected baboons included smooth muscle hypertrophy, villous atrophy and goblet cellhyperplasia, which were all less severe in baboons previously immunised with irradiatedcercariae. High tissue eosinophilia and recruitment of giant cells was observed in modulatingbaboon granulomata. By contrast, fibroblasts and collagen around the schistosome eggs werethe features of modulating mouse granulomata. In both animal models, reinfection followingchemotherapy resulted in reduced morbidity compared to a primary infection and a primaryMI dose elicited a T helper (Th) 2 cell associated immune response on reinfection. A primarySI dose in mice, however, led to a dominant Th1 response. Baboons exposed to multipleinfections, both prior to and following chemotherapy, developed peri-portal fibrosis. Insummary, i) variation in cercarial exposure contributes to the heterogeneity of the immuneresponse and morbidity ii) although the consequences of reinfection exposures are milder, they may be associated with increased risk for the development of hepatic fibrosis and iii)regarding the pathogenesis of natural schistosome infections, particularly repeated infections,the baboon is a better model than the mouse.
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| 5. |
- Gutierrez Arenas, Omar, 1975-, et al.
(författare)
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A Theoretical Approach to Some Analytical Properties of Heterogeneous Enzymatic Assays
- 2004
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 76:9, s. 2664-2668
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Tidskriftsartikel (refereegranskat)abstract
- Heterogeneous enzymatic assays (HEA), where an enzyme in solution acts upon an immobilized substrate, are been increasingly used. Given their high throughput and versatility they hold great potential for developing massive enzyme inhibitor screening. However, current HEA lack, in general, rigorous quantitative use. This is in part due to technical problems as a multiplicity of suboptimal substrate populations achieved with traditional immobilization techniques but, more importantly, is due to a poor understanding of the particular kinetic behavior of these systems. This paper addresses the kinetic features of HEA that arise from the very low amount of solid-phase substrate and the resulting inalterability of the free enzyme concentration during the assay, which classify HEA as enzyme quasi-saturable systems (EQSS). We assessed the optimal enzyme concentration working range and time of reaction. We also considered certain attributes of HEA for evaluating isosteric inhibitors. These studies were done on the basis of a simplified model for the kinetics of EQSS and a formal splitting of the functional factor of the analytical sensitivity of an enzymatic assay into [E-0]/K-m-dependent and temporal components.
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| 9. |
- Salas, Emir, et al.
(författare)
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A heterogeneous enzymatic assay for quantification of Plasmepsin II activity and the evaluation of its inhibitors
- 2004
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Ingår i: Journal of Pharmaceutical and Biomedical Analysis. - 0731-7085 .- 1873-264X. ; 34:4, s. 833-840
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Tidskriftsartikel (refereegranskat)abstract
- The emergence and worldwide spreading of Plasmodium falciparum strains that shown to be resistant to traditional drugs is considered a very serious health problem, given the high mortality and morbidity rate of Malaria. In the search for new drugs against this parasite, Hb hydrolyzing enzymes, such as Plasmepsin II (Plm II), have been classified as very promising targets for therapeutic attacks. In this work, it is developed a cheap and high-throughput heterogeneous enzymatic assay for measuring Plasmepsin II activity in order to use it as a tool in the discovery of new inhibitors of this enzyme. In this assay, Plasmepsin II acts upon a solid-phase bound synthetic peptide (DU2) whose sequence comprises the cleavage site F(33)-L(34) present in Hb alpha-chain. The peptide surface density is quantified by means of a classical ELISA-based procedure. In order to estimate the kinetic constants of the system and to quantify both, enzymatic and inhibitory activity, it was used a model for the kinetics of enzyme quasi-saturable systems previously developed by our group, that fitted very well to the experimental data. It was used Pepstatin as a model inhibitor of Plasmepsin II and the resulting dose-response relation agreed with the expected behavior for the Pepstatin-Plasmepsin II pair under the employed experimental conditions.
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