307 research outputs found
Estimation of quantization noise for adaptive-prediction lifting schemes
No full textThe lifting scheme represents an easy way of implementing the wavelet transform and of constructing new content-adapted transforms. However, the adaptive version of lifting schemes can result in strongly non-isometric transforms. This can be a major limitation, since all most successful coding techniques rely on the distortion estimation in the transform domain. In this paper we focus on the problem of evaluating the reconstruction distortion (due to quantization noise) in the wavelet domain when a non-isometric adaptive-prediction lifting scheme is used. The problem arises since these transforms are nonlinear, and so common techniques for distortion evaluation cannot be used in this case. We circumvent the difficulty by computing an equivalent time-varying linear filter, for which it is possible to generalize the distortion computation technique. In addition to the theoretical formulation of the distortion estimation, in this paper we provide experimental results proving the reliability of this estimation, and the consequent improvement of RD performance, thanks to a more effective resource allocation which can be performed in the transform domain. © 2009 IEEE
Influence of growth temperature on lipid and phosphate contents of superficial polysaccharides from Antarctic Pseudoalteromonas haloplanktis TAC 125 bacterium.
No full textThe chemical structural variations induced by different growth temperatures in the lipooligosaccharide and exopolysaccharide components extracted from the Antarctic bacterium Pseudoalteromonas haloplanktis TAC 125 are described. The increase in phosphorylation with the increase in growth temperature seems to be general, because it happens not only for the lipooligosaccharide but also for the exopolysaccharide. Structural variations in the lipid components of lipid A also occur. In addition, free lipid A is found at both 25 and 4 degrees C but not at 15 degrees C, which is the optimal growth temperature, suggesting a incomplete biosynthesis of the lipooligosaccharide component under the first two temperature conditions
Distortion evaluation in transform domain for adaptive lifting schemes
No full textIn this paper we study the problem of evaluating the reconstruction distortion in the wavelet domain when adaptive lifting schemes (ALS) are used for the direct and inverse transform. The distortion evaluation is necessary in order to perform efficient resource allocation over the transform coefficients. ALS is a non-linear transformation, which prevents using common techniques for distortion evaluation. However we show the equivalence of this non-linear scheme with a time-varying linear filter, and we generalize the distortion computation technique to it. Experiments show that the proposed method allows a reliable estimation of the distortion in the transform domain. This results in improved coding performance. © 2008 IEEE
Structure elucidation of the O-chain from the major lipopolysaccharide of the Xanthomonas campestris strain 642
No full textCosts and Advantages of Object-Based Image Coding with Shape-Adaptive Wavelet Transform
No full text Object-based image coding is drawing a great attention for the many opportunities it offers to high-level applications. In terms of rate-distortion performance, however, its value is still uncertain, because the gains provided by an accurate image segmentation are balanced by the inefficiency of coding objects of arbitrary shape, with losses that depend on both the coding scheme and the object geometry. This work aims at measuring rate-distortion costs and gains for a wavelet-based shape-adaptive encoder similar to the shape-adaptive texture coder adopted in MPEG-4. The analysis of the rate-distortion curves obtained in several experiments provides insight about what performance gains and losses can be expected in various operative conditions and shows the potential of such an approach for image coding.</p
Disulfides by reduction of thiosulfonic s-esters
No full textDisulfides are smoothly prepared from thiosulfonic S-esters by chlorotrimethylsilane and sodium iodide. In addition thiosulfonic S-esters have been shown to be probable intermediates in other already known reactions leading to disulfides
Synthesis of phosphonates and organofluorine compounds for bio-organic studies
No full textThis thesis focuses on two main areas: the synthesis of novel anti-metabolites of 1-deoxy- D-xyulose-5-phosphate (DXP) and the stereoelectronics which influence the conformation of fluoromethyl groups in organic compounds. DXP, a sugar phosphate, has recently been established as a key biosynthetic intermediate to a number of plant and bacterial co-enzymes and vitamins. Chapter 1 describes the role of DXP in three biosynthetic pathways; in the formation of the isoprenoid building block isopentenyl pyrophosphate, and the vitamins B(_1) and B(_6). A new strategy to novel antibiotics and / or herbicides is proposed by the inhibition of DXP metabolism. A description of phosphonates as hydrolytically stable phosphate mimics is presented, including fluorine phosphonates that enable fine tuning of these mimics. Synthetic targets are designed as inhibitors of the DXP reductoisomerase catalysed reaction from DXP to 2-C-methyl-D-erythritol-4-phosphate (MEP). In Chapter 2 the successful synthesis of the CH(_2) phosphonate analogues of DXP and MEP is described. The DXP analogue was initially approached via the diethyl phosphonate ester, however it proved necessary in the end to prepare the dibenzyl ester followed by hydrogenation. Synthesis towards the CF2, and the a-fluorinated ketone, phosphonate analogues of DXP were incomplete due to low yields. Further syntheses is described towards the reduced form of the CH2 phosphonate analogue of DXP, and to a compound related to fosmidomycin. Chapter 3 describes fluorine's stereoelectronic influence in determining the conformations of fluoromethyl containing organic compounds through n/π-σ* conjugation and gauche effects. Solid state evidence for the influence of these effects is presented through the first X-ray crystallographic data of fluoromethylaromatics and β-fiuoroethylamides respectively. Structures of bis-2,6-(fluoromethyl)pyridine and its N-oxide displayed fluoromethyl conformations with the C-F bond co-planar to the aromatic ring whereas benzyl fluoride and 4-bromobenzyl fluoride displayed conformafions with the C-F bond orthogonal to the aromatic ring. Structures of N-(2-fluoroethyl)-3,5-dinitrobenzamide and N-(2-fluoroethyl)-4-nitrobenzamide reveal a fluorine / amide gauche effect
Costs and Advantages of Object-Based Image Coding with Shape-Adaptive Wavelet Transform
No full textObject-based image coding is drawing a great attention for the many opportunities it offers to high-level applications. In terms of rate-distortion performance, however, its value is still uncertain, because the gains provided by an accurate image segmentation are balanced by the inefficiency of coding objects of arbitrary shape, with losses that depend on both the coding scheme and the object geometry. This work aims at measuring rate-distortion costs and gains for a wavelet-based shape-adaptive encoder similar to the shape-adaptive texture coder adopted in MPEG-4. The analysis of the rate-distortion curves obtained in several experiments provides insight about what performance gains and losses can be expected in various operative conditions and shows the potential of such an approach for image coding
Region based compression of multispectral images by classified KLT
No full textA new region-based algorithm is proposed for the compression of multispectral images. The image is segmented in homogeneous regions, each of which is subject to spectral KLT, spatial shape-adaptive DWT, and SPIHT encoding. We propose to use a dedicated KLT for each region or for each class rather than a single global KLT. Experiments show that the classified KLT guarantees a significant increase in energy compaction, and hence, despite the need to transmit more side information, it provides a valuable performance gain over reference techniques
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