| 1. |
- Bolivar, Juan M, et al.
(författare)
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Coating of soluble and immobilized enzymes with ionic polymers : full stabilization of the quaternary structure of multimeric enzymes
- 2009
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 10:4, s. 742-747
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Tidskriftsartikel (refereegranskat)abstract
- This paper shows a simple and effective way to avoid the dissociation of multimeric enzymes by coating their surface with a large cationic polymer (e.g., polyethylenimine (PEI)) by ionic exchange. As model enzymes, glutamate dehydrogenase (GDH) from Thermus thermophilus and formate dehydrogenase (FDH) from Pseudomonas sp. were used. Both enzymes are very unstable at acidic pH values due to the rapid dissociation of their subunits (half-life of diluted preparations is few minutes at pH 4 and 25 degrees C). GDH and FDH were incubated in the presence of PEI yielding an enzyme-PEI composite with full activity. To stabilize the enzyme-polymer composite, a treatment with glutaraldehyde was required. These enzyme-PEI composites can be crosslinked with glutaraldehyde by immobilizing previously the composite onto a weak cationic exchanger. The soluble GDH-PEI composite was much more stable than unmodified GDH at pH 4 and 30 degrees C (retaining over 90% activity after 24 h incubation) with no effect of the GDH concentration in the inactivation course. The composite could be very strongly, but reversibly, adsorbed on cationic exchangers. Similarly, FDH could be treated with PEI and glutaraldehyde after adsorption on cationic exchangers, This permitted a stabilized FDH preparation. In this way, the coating of the enzymes surfaces with PEI is used as a simple and efficient strategy to prevent enzyme dissociation of multimeric enzymes. These composites can be used as a soluble catalyst or reversibly immobilized onto a cationic exchanger (e.g., CM-agarose).
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| 2. |
- Bolivar, Juan M, et al.
(författare)
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Immobilization-stabilization of a new recombinant glutamate dehydrogenase from Thermus thermophilus
- 2008
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Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 0175-7598 .- 1432-0614. ; 80:1, s. 49-58
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Tidskriftsartikel (refereegranskat)abstract
- The genome of Thermus thermophilus contains two genes encoding putative glutamate dehydrogenases. One of these genes (TTC1211) was cloned and overexpressed in Escherichia coli. The purified enzyme was a trimer that catalyzed the oxidation of glutamate to alpha-ketoglutarate and ammonia with either NAD+ or NADP+ as cofactors. The enzyme was also able to catalyze the inverse reductive reaction. The thermostability of the enzyme at neutral pH was very high even at 70 degrees C, but at acidic pH values, the dissociation of enzyme subunits produced the rapid enzyme inactivation even at 25 degrees C. The immobilization of the enzyme on glyoxyl agarose permitted to greatly increase the enzyme stability under all conditions studied. It was found that the multimeric structure of the enzyme was stabilized by the immobilization (enzyme subunits could be not desorbed from the support by boiling it in the presence of sodium dodecyl sulfate). This makes the enzyme very stable at pH 4 (e.g., the enzyme activity did not decrease after 12 h at 45 degrees C) and even improved the enzyme stability at neutral pH values. This immobilized enzyme can be of great interest as a biosensor or as a biocatalyst to regenerate both reduced and oxidized cofactors.
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| 3. |
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| 4. |
- Galindo, Cipriano, et al.
(författare)
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Life-long optimization of the symbolic model of indoor environments for a mobile robot
- 2007
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Ingår i: IEEE transactions on systems, man and cybernetics. Part B. Cybernetics. - 1083-4419 .- 1941-0492. ; 37:5, s. 1290-1304
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Tidskriftsartikel (refereegranskat)abstract
- The use of a symbolic model of the spatial environment becomes crucial for a mobile robot. that is intended to operate optimally and intelligently in indoor scenarios. Constructing such a model involves important problems that are not solved completely at present. One is called anchoring, which implies to maintain a correct dynamic correspondence between the real world and the symbols in the model. The other problem is adaptation: among the numerous possible models that could be constructed for representing a given environment, optimization involves the selection of one that improves as much as possible the operations of the robot. To cope with both problems, in this paper, we propose a framework that allows an indoor mobile robot to learn automatically a symbolic model of its environment and to optimize it over time with respect to changes in both the environment and the robot operational needs through an evolutionary algorithm. For coping efficiently with the large amounts of information that the real world provides, we use abstraction, which also helps in improving task planning. Our experiments demonstrate that the proposed framework is suitable for providing an indoor mobile robot with a good symbolic model and adaptation capabilities.
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| 5. |
- Galindo, Cipriano, et al.
(författare)
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Robot Task Planning Using Semantic Maps
- 2008
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Ingår i: Robotics and Autonomous Systems. - Amsterdam : Elsevier. - 0921-8890 .- 1872-793X. ; 56:11, s. 955-966
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Tidskriftsartikel (refereegranskat)abstract
- Task planning for mobile robots usually relies solely on spatial information and on shallow domain knowledge, like labels attached to objects and places. Although spatial information is necessary for performing basic robot operations (navigation and localization), the use of deeper domain knowledge is pivotal to endow a robot with higher degrees of autonomy and intelligence. In this paper, we focus on semantic knowledge, and show how this type of knowledge can be profitably used for robot task planning. We start by defining a specific type of semantic maps, which integrate hierarchical spatial information and semantic knowledge. We then proceed to describe how these semantic maps can improve task planning in two ways: extending the capabilities of the planner by reasoning about semantic information, and improving the planning efficiency in large domains. We show several experiments that demonstrate the effectiveness of our solutions in a domain involving robot navigation in a domestic environment.
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| 6. |
- Galindo, Cipriano, et al.
(författare)
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Using semantic information for improving efficiency of robot task planning
- 2007
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Konferensbidrag (refereegranskat)abstract
- The use of semantic information in robotics is an emergent field of research. As a supplement to other types of information, like geometrical or topological, semantics can improve mobile robot reasoning or knowledge inference, and can also facilitate human-robot communication. These abilities are particularly relevant for robots intended to operate in everyday environments populated by people, which typically involve a great number of objects, places, and possible actions. In this paper, we explore a novel usage of semantic information: as an improvement for task planning in complex scenarios like the mentioned ones, where other planners easily find intractable situations. More specifically, we propose to first construct a "semantic" plan composed of categories of objects, places, etc. that solves a "generalized" version of the requested task, and then to use that plan for discarding irrelevant information in the definitive planning carried out on the symbolic instances of those elements (that correspond to physical elements of the world with which the robot can operate). Our results using this approach are promising, and have been compared to other existing approaches.
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| 7. |
- Gil, David, et al.
(författare)
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Application of artificial neural networks in the diagnosis of urological dysfunctions
- 2009
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Ingår i: Expert Systems with Applications. - : Elsevier BV. - 0957-4174. ; 36:3, s. 5754-5760
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Forskningsöversikt (refereegranskat)abstract
- In this article, we evaluate the work out of some artificial neural network models as tools for support in the medical diagnosis of urological dysfunctions. We develop two types of unsupervised and one supervised neural network. This scheme is meant to help the urologists in obtaining a diagnosis for complex multi-variable diseases and to reduce painful and costly medical treatments since neurological dysfunctions are difficult to diagnose. The clinical study has been carried out using medical registers of patients with urological dysfunctions. The proposal is able to distinguish and classify between ill and healthy patients. (C) 2008 Elsevier Ltd. All rights reserved.
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| 8. |
- Rønnow-Rasmussen, Toni, et al.
(författare)
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L.W. Sumner’s account of Welfare
- 2001
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Ingår i: Actas del III Congreso de la Sociedad Española de Filosofía Analítica, Granada.
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 9. |
- Westin, Carl-Fredrik, et al.
(författare)
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Tensor Field Regularization Using Normalized Convolution and Markov Random Fields in a Bayesian Framework
- 2006
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Ingår i: Visualization and Image Processing of Tensor Fields. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 3540250328 - 9783540312727 ; , s. 381-398
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Bokkapitel (refereegranskat)abstract
- This chapter presents two techniques for regularization of tensor fields. We first present a nonlinear filtering technique based on normalized convolution, a general method for filtering missing and uncertain data. We describe how the signal certainty function can be constructed to depend on locally derived certainty information and further combined with a spatially dependent certainty field. This results in reduced mixing between regions of different signal characteristics, and increased robustness to outliers, compared to the standard approach of normalized convolution using only a spatial certainty field. We contrast this deterministic approach with a stochastic technique based on a multivariate Gaussian signal model in a Bayesian framework. This method uses a Markov random field approach with a 3D neighborhood system for modeling spatial interactions between the tensors locally. Experiments both on synthetic and real data are presented. The driving tensor application for this work throughout the chapter is the filtering of diffusion tensor MRI data.
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| 10. |
- Åberg, Anna, et al.
(författare)
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Similar and divergent effects of ppGpp and DksA deficiencies on transcription in Escherichia coli
- 2009
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Ingår i: Journal of Bacteriology. - : American Society for Microbiology. - 0021-9193 .- 1098-5530. ; 191:10, s. 3226-3236
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Tidskriftsartikel (refereegranskat)abstract
- The concerted action of ppGpp and DksA in transcription has been widely documented. In disparity with this model, phenotypic studies showed that ppGpp and DksA might also have independent and opposing roles in gene expression in Escherichia coli. In this study we used a transcriptomic approach to compare the global transcriptional patterns of gene expression in strains deficient in ppGpp (ppGpp(0)) and/or DksA (DeltadksA). Approximately 6 and 7% of all genes were significantly affected by more than twofold in ppGpp- and DksA-deficient strains, respectively, increasing to 13% of all genes in the ppGpp(0) DeltadksA strain. Although the data indicate that most of the affected genes were copositively or conegatively regulated by ppGpp and DksA, some genes that were independently and/or differentially regulated by the two factors were found. The large functional group of chemotaxis and flagellum synthesis genes were notably differentially affected, with all genes being upregulated in the DksA-deficient strain but 60% of them being downregulated in the ppGpp-deficient strain. Revealingly, mutations in the antipausing Gre factors suppress the upregulation observed in the DksA-deficient strain, emphasizing the importance of the secondary channel of the RNA polymerase for regulation and fine-tuning of gene expression in E. coli.
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