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Search Results: 1 - 10 of 1872 matches for " Ll. Abad "
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Magnetic dead layers in La2/3Ca1/3MnO3 thin films probed by X-ray magnetic circular dichroism in reflection
S. Valencia,A. Gaupp,W. Gudat,Ll. Abad,Ll. Balcells,B. Martinez
Physics , 2007,
Abstract: Surface magnetic properties of perovskite manganites have been a recurrent topic during last years since they play a major role in the implementation of magnetoelectronic devices. Magneto-optical techniques, such as X-ray magnetic circular dichroism, turn out to be a very efficient tool to study surface magnetism due to their sensitivity to magnetic and chemical variations across the sample depth. Nevertheless, the application of the sum rules for the determination of the spin magnetic moment might lead to uncertainties as large as 40% in case of Mn ions. To overcome this problem we present an alternative approach consisting of using X-ray magnetic circular dichroism in reflection geometry. Fit of the data by using a computer code based in a 4X4 matrix formalism leads to realistic results. In particular, we show that surface and interface roughness are of major relevance for a proper description of the experimental data and a correct interpretation of the results. By using such an approach we demonstrate the presence of a narrow surface region with strongly depressed magnetic properties in La2/3Ca1/3MnO3 thin films.
Mn valence instability in La2/3Ca1/3MnO3 thin films
S. Valencia,A. Gaupp,W. Gudat,Ll. Abad,Ll. Balcells,A. Cavallaro,B. Martinez,F. J. Palomares
Physics , 2009, DOI: 10.1103/PhysRevB.73.104402
Abstract: A Mn valence instability on La2/3Ca1/3MnO3 thin films, grown on LaAlO3 (001)substrates is observed by x-ray absorption spectroscopy at the Mn L-edge and O K-edge. As-grown samples, in situ annealed at 800 C in oxygen, exhibit a Curie temperature well below that of the bulk material. Upon air exposure a reduction of the saturation magnetization, MS, of the films is detected. Simultaneously a Mn2+ spectral signature develops, in addition to the expected Mn3+ and Mn4+ contributions, which increases with time. The similarity of the spectral results obtained by total electron yield and fluorescence yield spectroscopy indicates that the location of the Mn valence anomalies is not confined to a narrow surface region of the film, but can extend throughout the whole thickness of the sample. High temperature annealing at 1000 C in air, immediately after growth, improves the magnetic and transport properties of such films towards the bulk values and the Mn2+ signature in the spectra does not appear. The Mn valence is then stable even to prolonged air exposure. We propose a mechanism for the Mn2+ ions formation and discuss the importance of these observations with respect to previous findings and production of thin films devices.
Formation of Mn2+ in La2/3Ca1/3MnO3 Thin Films due to Air Exposure
S. Valencia,A. Gaupp,Ll. Abad,Ll. Balcells,F. J. Palomares,A. Cavallaro,B. Martinez,W. Gudat
Physics , 2005,
Abstract: We report on the chemical stability of La2/3Ca1/3MnO3 thin films. X-ray absorption spectroscopy at the Mn L-edge and O K-edge makes evident deviations from the nominally expected (2/3-1/3) Mn3+/Mn4+ ratio after the growth of thin films on LaAlO3 substrates. As-grown thin films, exhibiting Curie temperature, TC, well below that of the LCMO bulk material, develop an unexpected Mn2+ contribution after a few days of air exposure which increases with time. Moreover, a reduction of the saturation magnetization, MS, is also detected. The similarity of the results obtained by electron yield and fluorescence yield demonstrates that the location of the Mn valence anomalies are not confined to a narrow surface region of the film but can extend throughout the film thickness in case of granular films. High temperature annealing not only improves the magnetic and transport properties of such as-grown films but also recovers the expected 2/3-1/3 Mn3+/Mn4+ ratio, which thereafter is stable to air exposure. Similar results on La2/3Ca1/3MnO3 films grown on SrTiO3 and NdGaO3 substrates demonstrate that there is no direct relation between the observed Mn valence instability and the strain state of the films due to their lattice mismatch with the substrate. A mechanism for the formation of Mn2+ ions formation is discussed.
Emotional Reactions to Sounds without Meaning  [PDF]
Daniel V?stfj?ll
Psychology (PSYCH) , 2012, DOI: 10.4236/psych.2012.38091
Abstract: The present research examined the relationship between emotional reactions to sounds without meaning (tone and noise complexes) and objective sound descriptors. Two experiments showed that the core affect dimensions valence and activation were related to perceived loudness (intensity) and sharpness (perceived high frequency content), respectively. These results can be used as design criteria for emotion induction with sounds, implementation of emotional sounds in products, as well as in research on environmental noise perception.
Emotional Reactions to Tonal and Noise Components of Environmental Sounds  [PDF]
Daniel V?stfj?ll
Psychology (PSYCH) , 2013, DOI: 10.4236/psych.2013.412153

In the present study, a two-dimensional model of human emotional reactions is used to predict auditory perception. The models’ discriminant validity is tested in an experiment where one group of participants use a two-dimensional emotion measure to rate their reactions to sounds systematically varied in tone and noise spectral level content. Another group of participants rated the same sounds using a standard one-dimensional annoyance measure. The results showed that both the one- and two-dimensional measures discriminated between reactions to different sounds. Regression analyses showed that the two-dimensional measure tapped aspects of human experience not covered by the annoyance measure. In addition, it was shown that only modifications of the fundamental frequency and the overall noise spectral level, but not modifications of harmonics, had a marked effect on emotional reactions. The implications of these findings for both auditory emotion research and noise control engineering are discussed.

Ultima década , 2005, DOI: 10.4067/S0718-22362005000100004
Abstract: similar to the idealistic representations of the youth condition, the predominant analysis on youth unemployment and the way in which it can be solved, considerates the phenomenon of isolation in a descriptive way, without repairing capitalistic contradictions and its influence on the institutional and political-judicial relations that govern the new forms of organizations and international divisions of work. nevertheless, it is the context of labor unemployment, with its multiple relations and contradictions, and the way as it is affected by the reconstruction of capitalism on a world-wide scale. in order to make it these questions evident and to reveal its dynamics, it is necessary to put the politics of juvenile work within the the frame of the world transtition of capitalism in latin america under the fordistic supremacy in the social organization of work, with its respective state of being, corresponding to its post-fordistic capitalism and its state form, momentarily differentiated by conditions of the accumulation of capital and specific mechanisms of the regulation of antagonism of classes.
Optimal Pricing and Lot Sizing for a Single Period Problem
P. Abad
Lecture Notes in Engineering and Computer Science , 2013,
La ASEAN tras la Cumbre de Cebú: en el camino de la integración?
Gracia Abad
UNISCI Discussion Papers , 2007,
Abstract: The article analyses the contributions made by the 12th ASEAN summit to the renewal process undertaken by the organisation. To this end, together with the different issues addressed over the leaders meeting, the text pays attention to the contents and the importance of the recommendations on the ASEAN Charter made by the Eminent Persons Group. Finally, the article points out some of the obstacles the member states will face in order to deepen their cooperation.
Posibilidades y limitaciones de la participación juvenil para el impacto en la agenda pública: el caso del Consejo Municipal de Juventud en Medellín
Miguel Abad
Ultima Década , 2002,
Politicas de juventud y empleo juvenil: el traje nuevo del rey
Miguel Abad
Ultima Década , 2005,
Abstract: De forma similar a las representaciones idealistas de la condición juvenil, los análisis predominantes sobre el desempleo juvenil y sus alternativas de paliación consideran el fenómeno de manera aislada y descriptiva, sin reparar en las contradicciones capitalistas y su influencia sobre las relaciones institucionales y político/jurídicas que rigen las nuevas formas de organización y división internacional del trabajo. Sin embargo, es el contexto del desempleo juvenil, y no el desempleo en sí mismo, el que debe ser articulado a la totalidad del mundo laboral, con sus múltiples relaciones y contradicciones, y la manera como es afectado por la reestructuración del capitalismo a escala mundial. Para hacer explícitas estas cuestiones y revelar su dinámica, es necesario situar las políticas de empleo juvenil en América Latina en el marco de la transición mundial de un capitalismo bajo la hegemonía fordista en la organización social del trabajo, con su respectiva forma-estado, a un capitalismo postfordista y su forma-estado correspondiente, momentos diferenciados por condiciones de acumulación de capital y mecanismos específicos de regulación del antagonismo de clases.
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