Experimental Verification And Theoretical Analysis Of The Relationships Between Hardness, Elastic Modulus, And The Work Of Indentation

The relationship between hardness (H), reduced modulus (E-r), unloading work (W-u), and total work (W-t) of indentation is examined in detail experimentally and theoretically. Experimental study verifies the approximate linear relationship. Theoretical analysis confirms it. Furthermore, the solutions to the conical indentation in elastic-perfectly plastic solid, including elastic work (W-e), H, W-t, and W-u are obtained using Johnson's expanding cavity model and Lame solution. Consequently, it is found that the W-e should be distinguished from W-u, rather than their equivalence as suggested in ISO14577, and (H/E-r)/(W-u/W-t) depends mainly on the conical angle, which are also verified with numerical simulations. (C) 2008 American Institute of Physics.

Barium-Functionalized Multiwalled Carbon Nanotube Yarns As Low-Work-Function Thermionic Cathodes

Barium-functionalized multiwalled carbon nanotube yarns were fabricated by drawing and twisting multiwalled carbon nanotube forests through a solution containing barium nitrate. After heat activation under vacuum, the functionalized yarns were enriched in barium oxide due to the high surface-to-volume ratio of the nanotubes. The cathodes exhibited good thermionic properties, with a work function as low as 1.73-2.06 eV and thermionic current density that exceeded 185 mA/cm(2) in a field of 850 V/5 mm at 1317 K. The barium-functionalized yarns had high tensile strength of up to 420 MPa and retained strength of similar to 250 MPa after a 2 h activation process. (C) 2008 American Institute of Physics.

Paulo Orosio : una interpretación de la historiografía providencialista cristiana ante la caída de Roma en el 410

Resumen: En el entramado histórico del mundo Romano, la vida política y religiosa se han visto imbricadas de modo particular. El mito político ha sido fundamental para hilvanar el devenir de los hechos históricos centrales en el modo de vida de los romanos. La caída de Roma o el fin de la Pars Occidentalis del Imperio Romano han servido de arquetipo histórico o de referente político para el resto de los Imperios del Mundo Occidental. En ese contexto se insertará este trabajo, que pretenderá echar luz a una temática rodeada por líneas historiográficas y analíticas no solo diferentes sino antagónicas. El centro de la discordia historiográfica de hoy se pondrá en sincronía con la discordia histórica de ayer, puesto que tanto los paganos como los cristianos forjaron durante la Tardo-antigüedad un mito de fin de ciclo, que le agrega una fascinación particular a esta temática. En este trabajo me abocaré a interpretar la postura del historiador romano - cristiano Paulo Orosio, quien describió su propia visión sobre los hechos que antecedieron y provocaron, la caída de Roma.