968 resultados para Maxima


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This paper analyzes the role of Computer Algebra Systems (CAS) in a model of learning based on competences. The proposal is an e-learning model Linear Algebra course for Engineering, which includes the use of a CAS (Maxima) and focuses on problem solving. A reference model has been taken from the Spanish Open University. The proper use of CAS is defined as an indicator of the generic ompetence: Use of Technology. Additionally, we show that using CAS could help to enhance the following generic competences: Self Learning, Planning and Organization, Communication and Writing, Mathematical and Technical Writing, Information Management and Critical Thinking.

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Inclui notas explicativas e bibliograficas

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In angiosperms, the functional enucleate sieve tube system of the phloem appears to be maintained by the surrounding companion cells. In this study, we tested the hypothesis that polypeptides present within the phloem sap traffic cell to cell from the companion cells, where they are synthesized, into the sieve tube via plasmodesmata. Coinjection of fluorescently labeled dextrans along with size-fractionated Cucurbita maxima phloem proteins, ranging in size from 10 to 200 kDa, as well as injection of individual fluorescently labeled phloem proteins, provided unambiguous evidence that these proteins have the capacity to interact with mesophyll plasmodesmata in cucurbit cotyledons to induce an increase in size exclusion limit and traffic cell to cell. Plasmodesmal size exclusion limit increased to greater than 20 kDa, but less than 40 kDa, irrespective of the size of the injected protein, indicating that partial protein unfolding may be a requirement for transport. A threshold concentration in the 20–100 nM range was required for cell-to-cell transport indicating that phloem proteins have a high affinity for the mesophyll plasmodesmal binding site(s). Parallel experiments with glutaredoxin and cystatin, phloem sap proteins from Ricinus communis, established that these proteins can also traffic through cucurbit mesophyll plasmodesmata. These results are discussed in terms of the requirements for regulated protein trafficking between companion cells and the sieve tube system. As the threshold value for plasmodesmal transport of phloem sap proteins falls within the same range as many plant hormones, the possibility is discussed that some of these proteins may act as long-distance signaling molecules.

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Contiene: Collectio nova piscium amboinemsium partim ibi ad vivum delineatorum partim ex museo Henrici Ruysch, 40 p., XX h. de grab. ; Historia naturalis piscium / cura H. Ruysch ; praefatio Joh. Jonstoni, [6], 160 p., XLVIII h. de grab. ; Theatri universalis animalium : pars secunda sive Historiae naturalis de avibus ..., [12], 160 [i.e. 168] p., 62 h. de grab., la última con port. propia

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Contiene: Historiae naturalis de quadrupedibus, 163, [1] p., LXXX h. de grab. ; Theatro universalis animalium pars quarta sive Historiae naturalis de exanguibus ..., [4], 3-58, [2] p., XX h. de grab. ; Theatri universalis animalium pars quinta sive Historiae naturalis de insectis ..., [6], 147, [1] p., XXVIII h. de grab. ; Theatri universalis animalium pars sexta sive Historiae naturalis de serpentibus, [4], 3-37 [i.e. 39], [1] p., XII h. de grab., las tres últimas con port. propia

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Mode of access: Internet.