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Mostrando 25-36 de 66 artigos, teses e dissertações.
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25. An ordered sequence of events is required before BALB/c-3T3 cells become committed to DNA synthesis
An ordered sequence of events must be completed before cells become committed to synthesize DNA. A platelet-derived growth factor (PDGF), present in heated (100°) extracts of human platelets, induces density-inhibited BALB/c-3T3 cells to become competent to proliferate. Platelet-poor plasma induces these competent cells to leave the competence point, progre
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26. Selection bias in gene extraction on the basis of microarray gene-expression data
In the context of cancer diagnosis and treatment, we consider the problem of constructing an accurate prediction rule on the basis of a relatively small number of tumor tissue samples of known type containing the expression data on very many (possibly thousands) genes. Recently, results have been presented in the literature suggesting that it is possible to
The National Academy of Sciences.
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27. Influenza surveillance: experiences from establishing a sentinel surveillance system in Germany.
OBJECTIVES--Before and during peak influenza periods there is increased morbidity from other respiratory tract disorders. Sentinel networks of primary care physicians can be very effective in the early detection of influenza epidemics and the German network, the Arbeitsgemeinschaft Influenza (AGI), began its work in this area in 1992. METHODS--Data are trans
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28. Cell clusters on rat ventral roots: postnatal development.
The cell clusters found on the most proximal parts of rat ventral spinal nerve rootlets during prenatal development, persist into the postnatal period. Clusters become smaller as cells leave them to invest axon segments. By 2 weeks after birth, clusters have largely disappeared. Fine processes stemming from clusters interweave at first to envelop axons in a
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29. Cell and tumor classification using gene expression data: Construction of forests
The advent of gene chips has led to a promising technology for cell, tumor, and cancer classification. We exploit and expand the methodology of recursive partitioning trees for tumor and cell classification from microarray gene expression data. To improve classification and prediction accuracy, we introduce a deterministic procedure to form forests of classi
The National Academy of Sciences.
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30. Efficient transfer of large DNA fragments from agarose gels to diazobenzyloxymethyl-paper and rapid hybridization by using dextran sulfate.
We describe a technique for transferring electrophoretically separated bands of double-stranded DNA from agarose gels to diazobenzyloxymethyl-paper. Controlled cleavage of the DNA in situ by sequential treatment with dilute acid, which causes partial depurination, and dilute alkali, which causes cleavage and separation of the strands, allows the DNA to leave
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31. Mode of cell proliferation in the developing mouse neocortex.
There are two proliferative populations in the developing cerebral wall: the pseudostratified ventricular epithelium (PVE) and the secondary proliferative population (SPP). The present experiments provide on embryonic day 14 (E14) in the mouse direct measures of the values for the proportions of daughter cells that continue to proliferate (proliferative, P f
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32. Do Cells Cycle?
We propose that a cell's life is divided into two fundamentally different parts. Some time after mitosis all cells enter a state (A) in which their activity is not directed towards replication. A cell may remain in the A-state for any lenght of time, throughout which its probability of leaving A-state remains constant. On leaving A-state, cells enter B-phase
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33. Comparative superoxide-generating system of granulocytes from blood and peritoneal exudates.
Blood polymorphonuclear leukocytes (PMN), upon interaction with specific chemotactic stimuli, leave the blood stream and migrate to tissues. At such a location, and upon contact with invading microorganisms, they generate superoxide (O2-) as a part of the respiratory burst of phagocytosis. We have compared the O2(-)-generating system of guinea pig peritoneal
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34. Urinary metabolites of 14C-labeled thyroxine in man
Studies were carried out to determine the chemical structures of thyroxine metabolites after total deiodination. Normal subjects were given thyroxine labeled with 14C on the nonphenolic ring and the alanine side chain, 8-11 μg/day for 10 days. By paper chromatography of fresh urine, six or more 14C-labeled compounds were separated. The 14C-labeled metabolit
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35. Comparison of transformation mechanisms of Haemophilus parainfluenzae and Haemophilus influenzae.
Transformation pathways in two closely related bacterial species, Haemophilus parainfluenzae and Haemophilus influenzae, were studied. Both organisms rapidly take up transforming DNA within minutes into specialized membranous structures on the cell surface (transformasomes). DNA within transformasomes is in a protected state, inaccessible to external DNase o
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36. Degradation of linear DNA by a strand-specific exonuclease activity in Xenopus laevis oocytes.
Linear DNA injected into Xenopus laevis oocyte nuclei recombines with high efficiency if homologous sequences are present at overlapping molecular ends. We found that injected linear DNA was degraded by a 5'----3' strand-specific exonuclease activity during incubation in the oocyte nucleus to leave a heterogeneous population of 3'-tailed molecules. Decreasin