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- Zoric, Neven, et al.
(författare)
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Quantitative PCR: A promising technique investigating the early bone-implant interface
- 2007
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Ingår i: Abstract, European Association for Osseointegration (EAO), 16th Annual Scientific Meeting, Barcelona, Spain. ; 25-27 October
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Konferensbidrag (refereegranskat)abstract
- Objectives: Studies on the early tissue response to materials are difficult due to the inaccessibility of the interface zone and lack of sensitive techniques. The purpose of the present study was to apply quantitative PCR (qPCR) in combination with LM and SEM for the evaluation of early gene expression response as well as cellular reactions close to titanium implants. Experimental methods: Anodically oxidized titanium (TiUniteTM; Nobel Biocare AB) and machined titanium implants (2mm×2mm) were inserted in the rat tibia. After 1,3, and 6 days, implants were unscrewed and surrounding bone was retrieved. Both the implants and bone were analyzed with qPCR, routine histology and SEM. The amount of mRNA was normalized to 18S protein subunit. Results: After the initial inflammatory response, the tissue located inside the threads became rapidly organized. SEM analysis showed mesenchymal-like cells extending their processes into the pores of the anodically oxidized surface. qPCR demonstrated significantly higher 18S around anodically oxidized screws and in the surrounding tissues. Alkaline phosphatase (osteoblast marker), TRAP and Cathepsin K (osteoclast markers) mRNA, but not the inflammatory markers (TNF-alpha and IL-1beta) were expressed at different levels around the two surfaces. Conclusions: The results demonstrate that the experimental model and qPCR provide interesting possibilities to analyze the mechanisms of osseointegration. Furthermore, remodelling and in particular the molecular processes occur at implant surfaces in vivo already 3 days after implantation. Support: Swedish Research Council and the Institute for Biomaterials and Cell Therapy, Göteborg, Sweden
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- Al-Askary, Omar, et al.
(författare)
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Adaptive coding for OFDM based systems using generalized concatenated codes
- 2005
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Ingår i: VTC2005-SPRING: 2005 IEEE 61ST VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5, PROCEEDINGS. - 0780388879 ; , s. 649-653
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Konferensbidrag (refereegranskat)abstract
- Orthogonal Frequency Division Multiplexing (OFDM) is considered to be a promising candidate for future high-speed wireless communication systems. In this paper we present an adaptive coding scheme for OFDM based systems using generalized concatenated codes. We study the performance of HIPERLAN/2 after encoding with the proposed coding scheme and compare it to the standard convolutional coding scheme currently used. The criteria of our study is the optimization of the throughput. Through the adaptive scheme, we propose a modulation selection based on the average quality of the channel, and a code assigning method for the different sub-channels, that adapts to the channel conditions. We argue that the proposed scheme protects the information better than the ones in the conventional systems, since the latter do not take advantage of the individual sub-channel condition. Our simulations show that lower packet error rate can be accomplished for even higher throughput.
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- Al-Askary, Omar, 1965-
(författare)
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Coding and Iterative Decoding of Concentrated Multi-level Codes for the Rayleigh Fading Channel
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis we present the concept of concatenated multilevel codes. These codes are a combination of generalized concatenated codes with multilevel coding. The structure of these codes is simple and relies on the concatenation of two or more codes of shorter length. These codes can be designed to have large diversity which makes them attractive for use in fading channels. We also present an iterative decoding algorithm taylored to fit the properties of the proposed codes. The iterative decoding algorithm we present has a complexity comparable to the complexity of GMD decoding of the same codes. However, The gain obtained by using the iterative decoder as compared to GMD decdoing of these codes is quite high for Rayleigh fading channels at bit error rates of interest. Some bounds on the performance of these codes are given in this thesis. Some of the bounds are information theoretic bounds which can be used regardless of the code under study. Other bounds are on the error probability of concatenated multilevel codes. Finally we give examples on the implementation of these codes in adaptive coding of OFDM channels and MIMO channels.
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- al-Askary, Omar, et al.
(författare)
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Effect of error in CSI on the capacity of Rayleigh fading channels with QAM signalling and the design of robust signal constellations
- 2007
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Ingår i: IET Communications. - : Institution of Engineering and Technology (IET). - 1751-8628 .- 1751-8636. ; 1:6, s. 1118-1125
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Tidskriftsartikel (refereegranskat)abstract
- The effects of channel estimation errors on the channel capacity of a discrete time, discrete input, infinite output Rayleigh fading channel are investigated. The case of conventional modulation methods such as phase shift keying (PSK) and quatrature amplitude modulation (QAM) is investigated at first where it was observed that the capacity degrades rapidly with increasing channel estimation errors. The effect of error in the channel estimation is similar to the effect of higher noise in the channel that depends on the transmitted signal. A genetic algorithm is used to optimise the signal constellation in order to maximise the capacity for a given finite number of signal points. The aim of trying to maximise the capacity is to estimate the remaining gap in performance between a traditional modulation scheme such as QAM and the best possible constellation that is optimised for the channel. The constellations obtained from the genetic algorithm are, in general, not directly implementable. A method to design practical robust signal constellations that overcome the effect of channel state information (CSI) error is presented. The robust signal constellations obtained show a performance that is very close to the optimal constellations. In this work, the probability distribution of the error in CSI is assumed to be known.
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- Al-Askary, Omar, et al.
(författare)
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Rate adaptive generalized concatenated codes for wireless communication
- 2005
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Ingår i: Proceedings of the INMIC 2005. - 9780780394292 ; , s. 137-142
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Konferensbidrag (refereegranskat)abstract
- This paper presents the construction and performance of rate adaptive generalized concatenated codes (GCCs) (sic) on linear block codes over Rayleigh fading Multi Input (sic) Output (MIMO) communication channels with N transmit (sic) N receive antennas. The code design criteria is chosen (sic) that it tries to follow the Shannon capacity of the MIMO (sic). It is envisaged that such codes provide a superior performance over systems that use Maximum Ratio Combining (sic) while maintaining the encoder/decoder complexity within acceptable level of practical usage. Furthermore it is expected (sic) these codes will provide good performance without an interver/deinterleaver because of their good burst error correction (sic).
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