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• Autores: Karl Dahlke, Robertson D. Davenport, Clay Shields
• Localización: Scientific American, ISSN 0036-8733, Vol. 290, Nº. 3, 2004, págs. 111-111
• Idioma: inglés
• Texto completo no disponible (Saber más ...)
• Resumen

  • This article presents questions from readers on science. "Why are blood transfusions not rejected, as can happen with organs?" Rejection of blood is relatively rare. Organ transplants, in contrast, usually evoke cellular immune responses, which lead to the creation of cell-killing agents called cytotoxic lymphocytes. The key antigens in blood transfusions are in the ABO system. Blood types can be A (having A but not B antigens on red cells), B (having B but not A), AB (both A and B), or O (neither). How can deleted computer files be retrieved at a later date? "Deleted" files can be restored because they aren't really gone--at least not right away. This is because it is faster and more efficient for computers to overwrite data only when necessary, when no other space is available to write new data.