980 resultados para VIS SPECTROSCOPY


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We report on a high peak power femtosecond modelocked VECSEL and its application as a drive laser for an all semiconductor terahertz time domain spectrometer. The VECSEL produced near-transform-limited 335 fs sech2 pulses at a fundamental repetition rate of 1 GHz, a centre wavelength of 999 nm and an average output power of 120 mW. We report on the effect that this high peak power and short pulse duration has on our generated THz signal.

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Internal friction of nanocrystalline nickel is investigated by mechanical spectroscopy from 360 K to 120 K. Two relaxation peaks are found when nanocrystalline nickel is bent up to 10% strain at room temperature and fast cooling. However, these two peaks disappear when the sample is annealed at room temperature in vacuum for ten days. The occurrence and disappearance of the two relaxation peaks can be explained by the interactions of partial dislocations and point defects in nanocrystalline materials.

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Various Plasma Electrolytic Oxidation (PEO) ceramic coatings were prepared on LY12 aluminum alloy by adjusting the concentration of sodium silicate solution. Optical microscope (OM), XRD and EIS were used to study their morphology, composition and anti corrosion behavior in NaCl solution. Increasing concentration of sodium silicate leads to the increase of the total coating thickness while too high and too low concentration lead to the decrease of inner dense layer. The main composition of PEO coatings prepared in 20, 40 and above 60g/L concentration solution are correspondingly alumina, alumina with mullite, and amorphous phase. The corrosion resistance is determined by the inner dense layer. Increasing the thickness of inner dense layer can improve the anti-corrosion performance. PEO coating's corrosion resistance in acidic, alkaline and neutral NaCl solution is proved and the corrosion mechanism involved is also discussed.

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Resumen: De acuerdo a la mente de Santo Tomás de Aquino, la potencia de conocimiento sensible que se denomina «cogitativa » es susceptible de una doble consideración. Por un lado, es la estimativa animal y, como tal, aprehende su mismo objeto formal quod, esto es, las intenciones de beneficio o perjuicio a nivel sensible. Pero a causa de su particular modo de operar, esas intenciones no son conocidas por ella solamente en orden a la conservación del individuo humano o de la especie a la que él pertenece. El reconocimiento de una doble dimensión de la cogitativa está en Santo Tomás justificado por la particular relación que existe entre ella y la razón universal. Por un lado, la cogitativa no es una facultad distinta de la estimativa natural. Por esto, ella aprehende las intenciones necesarias para la perfección de la vida sensitiva humana. Por otro lado, la razón ejerce sobre la cogitativa un influjo particular que la hace operar a su modo, esto es, de manera discursiva. Este carácter móvil en la aprehensión de la cogitativa permite la conformación de una experiencia a nivel sensible, en virtud de la cual su objeto formal se ve ampliado. Esto resulta aún más razonable si se tiene en cuenta que el conocimiento sensorial del hombre prepara el intelectual. De esta manera, la cogitativa no aprehende simplemente al individuo como beneficioso o perjudicial para la subsistencia del cognoscente, sino como sujeto de una cierta naturaleza.

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Mechanical spectroscopy measurement is performed to study the internal friction of nanocrystalline ( NC) nickel with an average grain size of 23 nm from room temperature to 610 K. An internal friction peak is observed at about 550 K, which corresponds to the Curie transition process of the NC nickel according to the result of magnetization test. Moreover, the fact that the Curie temperature of NC nickel is lower than that of coarse-grained nickel is explained by an analytical model based on the weakening of cohesive energy.