958 resultados para Simpson, Robert
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Contains correspondence, printed material, and photographs relating to Jews in the medical profession, used as a basis for Kagan's several works on Jews in medicine, including the correspondence of members of the American Physicians Fellowship Committee of the Israel Medical Association; includes also correspondence relating to the Near East and the internationalization of Jerusalem, 1945-1954; and personal correspondence. Among the correspondents are Bernard M. Baruch and Christian A. Herter.
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Gas fermentation using acetogenic bacteria offers a promising route for the sustainable production of low carbon fuels and commodity chemicals from abundant, inexpensive C1 feedstocks including industrial waste gases, syngas, reformed methane or methanol. Clostridium autoethanogenum is a model gas fermenting acetogen that produces fuel ethanol and 2,3-butanediol, a precursor for nylon and rubber. Acetogens have already been used in large scale industrial fermentations, they are ubiquitous and known to play a prominent role in the global carbon cycle. Still, they are considered to live on the thermodynamic edge of life and potential energy constraints when growing on C1 gases pose a major challange for the commercial production of fuels and chemicals. We have developed a systematic platform to investigate acetogenic energy metabolism, exemplified here by experiments contrasting heterotrophic and autotrophic metabolism. The platform is built from complete omics technologies, augmented with genetic tools and complemented by a manually curated genome-scale mathematical model. Together the tools enable the design and development of new, energy efficient pathways and strains for the production of chemicals and advanced fuels via C1 gas fermentation. As a proof-of-platform, we investigated heterotrophic growth on fructose versus autotrophic growth on gas that demonstrate the role of the Rnf complex and Nfn complex in maintaining growth using the Wood–Ljungdahl pathway. Pyruvate carboxykinase was found to control the rate-limiting step of gluconeogenesis and a new specialized glyceraldehyde-3-phosphate dehydrogenase was identified that potentially enhances anabolic capacity by reducing the amount of ATP consumed by gluconeogenesis. The results have been confirmed by the construction of mutant strains.
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Although the importance of clathrin- and caveolin-independent endocytic pathways has recently emerged, key aspects of these routes remain unknown. Using quantitative ultrastructural approaches, we show that clathrin-independent carriers (CLICs) account for approximately three times the volume internalized by the clathrin-mediated endocytic pathway, forming the major pathway involved in uptake of fluid and bulk membrane in fibroblasts. Electron tomographic analysis of the 3D morphology of the earliest carriers shows that they are multidomain organelles that form a complex sorting station as they mature. Proteomic analysis provides direct links between CLICs, cellular adhesion turnover, and migration. Consistent with this, CLIC-mediated endocytosis of key cargo proteins, CD44 and Thy-1, is polarized at the leading edge of migrating fibroblasts, while transient ablation of CLICs impairs their ability to migrate. These studies provide the first quantitative ultrastructural analysis and molecular characterization of the major endocytic pathway in fibroblasts, a pathway that provides rapid membrane turnover at the leading edge of migrating cells.
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We present two online algorithms for maintaining a topological order of a directed acyclic graph as arcs are added, and detecting a cycle when one is created. Our first algorithm takes O(m 1/2) amortized time per arc and our second algorithm takes O(n 2.5/m) amortized time per arc, where n is the number of vertices and m is the total number of arcs. For sparse graphs, our O(m 1/2) bound improves the best previous bound by a factor of logn and is tight to within a constant factor for a natural class of algorithms that includes all the existing ones. Our main insight is that the two-way search method of previous algorithms does not require an ordered search, but can be more general, allowing us to avoid the use of heaps (priority queues). Instead, the deterministic version of our algorithm uses (approximate) median-finding; the randomized version of our algorithm uses uniform random sampling. For dense graphs, our O(n 2.5/m) bound improves the best previously published bound by a factor of n 1/4 and a recent bound obtained independently of our work by a factor of logn. Our main insight is that graph search is wasteful when the graph is dense and can be avoided by searching the topological order space instead. Our algorithms extend to the maintenance of strong components, in the same asymptotic time bounds.
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Resumen: En ocasión de la autobiografía de Robert Spaemann aparecida en 2012, este trabajo examina la lectura que Spaemann hace de la teleología en la doctrina de Santo Tomás de Aquino, especialmente en su obra Natürliche Ziele (2005) que prosigue la versión de 1981. En la primera parte, se estudia la historia de la teleología en el pensamiento filosófico y científico expuesta en «Fines naturales». La finalidad intrínseca en la naturaleza de los seres es conocida con profundidad creciente gracias a Platón, Aristóteles, al estoicismo y a la tradición cristiana. Estos aportes se integran en una estructura teleológica unitaria en el Aquinate. Después acontece una «inversión» de la teleología centrada en la conservación del propio ser y una consideración de los fines como algo externo a la realidad. Con la teoría evolucionista surge la teleonomía que se limita a las reglas del dinamismo, suprimiendo el fin. Con todo, los científicos no logran eliminar los términos «con el fin de» o «para» en su lenguaje. Eso permite proceder a un redescubrimiento de los fines naturales. En la segunda parte, se ve cómo Tomás de Aquino lleva el conocimiento de la finalidad más allá de Aristóteles, porque ella remite a una inteligencia creadora. La teleología implica una teología, aunque no queda del todo claro si es la teología filosófica o la cristiana. Spaemann tiene un planteo ontológico de tipo persuasivo, pero en algunos momentos siente dificultad para superar en el plano teorético a quien se limita a una teleonomía.
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1 carta (manuscrita) ; 202x145mm.