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- Aberg, Jan, et al.
(författare)
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Multialphabet coding with separate alphabet description
- 1997
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Ingår i: Proceedings. Compression and Complexity of SEQUENCES 1997. - 0818681322 ; , s. 56-65
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Konferensbidrag (refereegranskat)abstract
- For lossless universal source coding of memoryless sequences with an a priori unknown alphabet size (multialphabet coding), the alphabet of the sequence must be described as well as the sequence itself. Usually an efficient description of the alphabet can be made only by taking into account some additional information. We show that these descriptions can be separated in such a way that the encoding of the actual sequence can be performed independently of the alphabet description, and present sequential coding methods for such sequences. Such methods have applications in coding methods where the alphabet description is made available sequentially, such as PPM.
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- Aberg, J., et al.
(författare)
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Non-uniform PPM and context tree models
- 1998
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Ingår i: Proceedings DCC '98 Data Compression Conference. - 0818684062 ; , s. 279-288
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Konferensbidrag (refereegranskat)abstract
- The problem of optimizing PPM with the help of different choices of estimators and their parameters for different subsets of nodes in the context tree is considered. Methods of such optimization for Markov chain and context tree models for individual files and over given sets of files are presented, and it is demonstrated that the extension from Markov chain models to context tree models is necessary to receive significant improvements of the compression ratio.
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- Aberg, J., et al.
(författare)
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Towards understanding and improving escape probabilities in PPM
- 1997
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Ingår i: Proceedings DCC '97. Data Compression Conference. - 0818677619 ; , s. 22-31
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Konferensbidrag (refereegranskat)abstract
- The choice of expressions for the coding probabilities in general, and the escape probability in particular, is of great importance in the family of PPM algorithms. We present a parameterized version of the escape probability estimator which, together with a 'compactness' criterion, provides guidelines for the estimator design given a 'representative' set of files. This parameterization also makes it possible to adapt the expression of the escape probability during one-pass coding. Finally, we present results for one such compression scheme that illustrates the usefulness of our approach.
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| 7. |
- Abkar, Ali
(författare)
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Invariant Subspaces in Spaces of Analytic Functions
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Let D be a finitely connected bounded domain with smooth boundary in the complex plane. We first study Banach spaces of analytic functions on D . The main result is a theorem which converts the study of hyperinvariant subspaces on multiply connected domains into the study of hyperinvariant subspaces on domains with fewer holes. The Banach spaces are defined by a natural set of axioms fulfilled by the familiar Hardy, Dirichlet, and Bergman spaces. Let D_1 be a bounded domain obtained from D by adding some of the connectivity components of the complement of D ; hence D_1 has fewer holes. Let B and B_1 be the Banach spaces of analytic functions on the domains D and D_1 , respectively. Assume that I is a hyperinvariant subspace of B_1 , and consider the smallest hyperinvariant subspace of B containing I ; this is Lambda (I) , the closure in B of the span of I cdot M(B) , where M(B) denotes the space of multipliers of B . Under reasonable assumptions, we prove that I mapsto Lambda (I) gives a one-to-one correspondence between a class of hyperinvariant subspaces of B_1 , and a class of hyperinvariant subspaces of B . The inverse mapping is given by J mapsto J cap B_1 . We then generalize the above result to the setting of the quasi-Banach spaces of analytic functions on D . In Chapter IV, we shall establish a Riesz-type representation formula for super-biharmonic functions satisfying certain growth conditions on the unit disk. This representation formula can be regarded as an analogue of the Poisson-Jensen representation formula for subharmonic functions. In Chapter V, this representation formula will be used to prove an approximation theorem in certain weighted Bergman spaces. More precisely, we consider those weighted Bergman spaces whose (non-radial) weights are super-biharmonic and fulfill a certain growth condition. We shall prove that the polynomials are dense in such weighted Bergman spaces.
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- Abrahamson, Magnus, et al.
(författare)
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Modification of cystatin C activity by bacterial proteinases and neutrophil elastase in periodontitis
- 1997
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Ingår i: Molecular Pathology. - 1366-8714. ; 50:6, s. 291-297
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Tidskriftsartikel (refereegranskat)abstract
- AIM: To study the interaction between the human cysteine proteinase inhibitor, cystatin C, and proteinases of periodontitis associated bacteria. METHODS: Gingival crevicular fluid samples were collected from discrete periodontitis sites and their cystatin C content was estimated by enzyme linked immunosorbent assay (ELISA). The interaction between cystatin C and proteolytic enzymes from cultured strains of the gingival bacteria Porphyromonas gingivalis, Prevotella intermedia, and Actinobacillus actinomycetemcomitans was studied by measuring inhibition of enzyme activity against peptidyl substrates, by detection of break down patterns of solid phase coupled and soluble cystatin C, and by N-terminal sequence analysis of cystatin C products resulting from the interactions. RESULTS: Gingival crevicular fluid contained cystatin C at a concentration of approximately 15 nM. Cystatin C did not inhibit the principal thiol stimulated proteinase activity of P gingivalis. Instead, strains of P gingivalis and P intermedia, but not A actinomycetemcomitans, released cystatin C modifying proteinases. Extracts of five P gingivalis and five P intermedia strains all hydrolysed bonds in the N-terminal region of cystatin C at physiological pH values. The modified cystatin C resulting from incubation with one P gingivalis strain was isolated and found to lack the eight most N-terminal residues. The affinity of the modified inhibitor for cathepsin B was 20-fold lower (Ki 5 nM) than that of full length cystatin C. A 50 kDa thiol stimulated proteinase, gingipain R, was isolated from P gingivalis and shown to be responsible for the Arg8-bond hydrolysis in cystatin C. The cathepsin B inhibitory activity of cystatin C incubated with gingival crevicular fluid was rapidly abolished after Val10-bond cleavage by elastase from exudate neutrophils, but cleavage at the gingipain specific Arg8-bond was also demonstrated. CONCLUSIONS: The physiological control of cathepsin B activity is impeded in periodontitis, owing to the release of proteinases from infecting P gingivalis and neutrophils, with a contribution to the tissue destruction seen in periodontitis as a probable consequence.
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- Abrahamsson, K, et al.
(författare)
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Application of heat pump systems for energy conservation in paper drying
- 1997
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Ingår i: International Journal of Energy Research. - 0363-907X. ; 21:7, s. 631-642
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Tidskriftsartikel (refereegranskat)abstract
- Drying is one of the most energy intensive and common operations in the chemical and process industries. Scope for energy recovery is substantial, particularly from the latent heat of the exhaust moist air. Using real operating data from a major Swedish mill, optimal energy conservation strategies were investigated using different heat pump systems in paper drying. Simulation results are compared for compressor-driven and absorption heat pump systems. An absorption heat transformer was also investigated. A CH3OH-LiBr double-lift cycle would have a low COP value due to the low temperature of the moist air stream and the restricted temperature of the cooling water available. A total of 30 MW thermal equivalent is currently needed in the mill at a temperature of 75 degrees C for mixing-pits, district heating and a log store. Exhaust humid air at a temperature of 54 degrees C from only three of the paper machines was used in this study. SHPUMP simulations revealed that installing a mechanical heat pump unit using HFC 134a would result in a recovery of 22 MW due to the temperature level of this application. On the other hand, 12 MW can be recovered with an absorption heat pump. To optimize the operating conditions, H2O-NaOH was selected as the best of three based on exergy index criteria. Assuming a steam cost of 22 $/MW h and an electricity cost of 32 $/MW h, the pay-off periods would be 3.3 and 2.9 years for compressor-driven and absorption heat pump alternatives, respectively. (C) 1997 by John Wiley & Sons, Ltd.
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| 10. |
- Abrahamsson, Mats, et al.
(författare)
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Distribution Channel Reengineering - Organisational Separation of Distribution and Sales Functions in the European Market
- 1998
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Ingår i: Transport Logistics. ; 1:4, s. 237-249
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Tidskriftsartikel (refereegranskat)abstract
- In this article, the concept of distribution channel re-engineering stands for a restructuring of distribution activities where the physical distribution and sales functions are organizationally separated from each other. The objective of the re-engineering process is primarily to reach dramatic improvements in operational efficiency. Our study indicates improvements in the distribution process in terms of: (1) economies of scale; (2) specialization and increased expertise; and (3) coordination and control. Altogether, the competitive outcomes of distribution channel re-engineering can be dramatic improvements both in cost efficiency and customer services. Modern information technology is the necessary vehicle both for a successful organizational separation of functions, including an efficient coordination between functions, and at the same time a closer integration within each function. Distribution channel re-engineering is probably the most important key to a successful restructuring of distribution channels of standardized products on the European market. In a case study of a multinational tool manufacturer, the improvements in terms of decreased costs and increased customer services have been remarkable. Traditional distribution structures, building chains of warehouses from factories through central warehouses to national warehouses at the sales company level, have been replaced with distribution structures of centralized warehousing to one single distribution centre and also of centralized administration from sales companies to one single administrative centre covering the European market.
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