Resistive switching effects on the spatial distribution of phases in metal-complex oxide interfaces

In order to determine the key parameters that control the resistive switching mechanism in metal-complex oxides interfaces, we have studied the electrical properties of metal / YBa2Cu3O7-d (YBCO) interfaces using metals with different oxidation energy and work function (Au, Pt, Ag) deposited by sputtering on the surface of a YBCO ceramic sample. By analyzing the IV characteristics of the contact interfaces and the temperature dependence of their resistance, we inferred that ion migration may generate or cancel conducting filaments, which modify the resistance near the interface, in accordance with the predictions of a recent model.Comment: 3 pages, 5 figures, to be published in Physica B. Corresponding author: C. Acha ([email protected]

Technology Frames: The Art of Perspective and Interpretation in Strategy

In this paper, I bring together the literatures of the economics of innovation, corporate strategy and managerial and organizational cognition to explore how and why companies come to different conclusions and strategies for technology when presented with essentially very similar situations and information. Building on the work of Orlikowski and Gash (1994) on technological frames, I seek to explore the role of the technology frame of key senior managers in defining corporate strategy with respect to technology. To provide an empirical basis for the study, I take the case of the 6 leading US vertically integrated oil companies involved in the exploration and production of petroleum during the period 1984 to 1997. The analysis considers two key salients for the technology frame which are operationalised for the six companies based on their R&D expenditures, patents, publications and contrasted with their operational performance measures. These salients reflect respectively adaptational mapping (whereby signals in the environment prompt adaptation) and formational mapping (whereby experience and path-dependency influence interpretation) within the technology frame. The findings indicate support for the proposed approach to proxying technology frames on the two key points of salience for the upstream petroleum industry, and the paper concludes with a short discussion of future lines of research.technology frames, upstream petroleum, technology strategy, adaptational mapping, formational mapping

Cyclic electric field stress on bipolar resistive switching devices

We have studied the effects of accumulating cyclic electrical pulses of increasing amplitude on the non-volatile resistance state of interfaces made by sputtering a metal (Au, Pt) on top of the surface of a cuprate superconductor YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO). We have analyzed the influence of the number of applied pulses $N$ on the relative amplitude of the remnant resistance change between the high ($R_H$) and the low ($R_L$) state [$\alpha=(R_{H}-R_{L})/R_{L}$] at different temperatures ($T$). We show that the critical voltage ($V_c$) needed to produce a resistive switching (RS, i.e. $\alpha >0$) decreases with increasing $N$ or $T$. We also find a power law relation between the voltage of the pulses and the number of pulses $N_{\alpha_0}$ required to produce a RS of $\alpha=\alpha_0$. This relation remains very similar to the Basquin equation used to describe the stress-fatigue lifetime curves in mechanical tests. This points out to the similarity between the physics of the RS, associated with the diffusion of oxygen vacancies induced by electrical pulses, and the propagation of defects in materials subjected to repeated mechanical stress.Comment: 5 pages, 5 figures. To be published in JAP. Corresponding author: [email protected]

Impacts of plug-in hybrid vehicles and combined heat and power technologies on electric and gas distribution network losses

Distribution network operators (DNOs) require strategies that can offset the tradeoffs new embedded technologies have on their assets. This paper employs modelling to show that through control device manipulation, gas and electric (G&E) network operators can influence savings in energy losses under the presence of plug-in hybrid vehicles (PHEVs) and combined heat and power technologies (CHPs). An integrated gas and electric optimal power flow (OPF) tool is introduced to undertake various case studies. The OPF tool evaluates the technical impacts experienced in the networks when DNOs apply a "plug and forget" operation strategy and then compares the results against a "loss minimisation" strategy. Results show the benefits in applying different strategies are more considerable in electric networks than in gas networks. The study corroborates that an integrated G&E analysis offers a fresh perspective for stakeholders in evaluating energy service networks performance under different operation strategies

Poole-Frenkel effect and Variable-Range Hopping conduction in metal / YBCO resistive switching devices

Current-voltage (IV) characteristics and the temperature dependence of the contact resistance [$R(T)$] of Au / YBa$_2$Cu$_3$O$_{7-\delta}$ (optimally doped YBCO) interfaces have been studied at different resistance states. This states were produced by resistive switching after accumulating cyclic electrical pulses of increasing number and voltage amplitude. The IV characteristics and the $R(T)$ dependence of the different states are consistent with a Poole-Frenkel (P-F) emission mechanism with trapping-energy levels $E_t$ in the 0.06-0.11 eV range. $E_t$ remains constant up to a number-of-pulses-dependent critical voltage and increases linearly with further increasing the voltage amplitude of the pulses. The observation of a P-F mechanism reveals the existence of an oxygen-depleted layer of YBCO near the interface. A simple electrical transport scenario is discussed, where the degree of disorder, the trap energy level and the temperature range determine an electrical conduction dominated by non-linear effects, or by a P-F emission or by a Variable-Range Hopping regime.Comment: 16 pages, 5 figure

Electrical transport properties of manganite powders under pressure

We have measured the electrical resistance of micrometric to nanometric powders of the La$_{5/8-y}$Pr$_y$Ca$_{3/8}$MnO$_3$ (LPCMO with y=0.3) manganite for hydrostatic pressures up to 4 kbar. By applying different final thermal treatments to samples synthesized by a microwave assisted denitration process, we obtained two particular grain characteristic dimensions (40 nm and 1000 nm) which allowed us to analyze the grain size sensitivity of the electrical conduction properties of both the metal electrode interface with manganite (Pt / LPCMO) as well as the intrinsic intergranular interfaces formed by the LPCMO powder, conglomerate under the only effect of external pressure. We also analyzed the effects of pressure on the phase diagram of these powders. Our results indicate that different magnetic phases coexist at low temperatures and that the electrical transport properties are related to the intrinsic interfaces, as we observe evidences of a granular behavior and an electronic transport dominated by the Space Charge limited Current mechanism.Comment: 4 pages, 7 figures, to be published in Physica B Corresponding author: C. Acha ([email protected]

Interest Rates in Nigeria: An Analytical Perspective

This paper set out to examine the implications of interest rate for savings and investment in Nigeria. It used data obtained from the Central Bank of Nigeria (CBN). Data were analyzed using Pearson's Correlation Coefficient and regression. Evidence showed interest rate as a poor determinant of savings and investment indicating that bank loans are mostly not used for productive purposes. Therefore, bank loans should be channeled to productive investments if interest is to play its catalytic role in the Nigerian economy

Francisco Valsecchi and the Adventures of a Catholic Economic Axiology in 20th Century Argentina

El recorrido intelectual de Francisco Valsecchi (1907-1992) en la historia de las ideas económicas católicas muestra las inflexiones teóricas de una axiología derivada de la Doctrina Social de la Iglesia. Sin embargo, las condiciones históricas del desarrollo de una economía católica en la Argentina y las transformaciones sociales, económicas y políticas del periodo 1930-1970 incidieron sobre las tendencias conceptuales de esa axiología en apariencia perenne. Para explicar los cambios operados se sigue la trayectoria de Valsecchi. Se muestran las fases principales de sus posiciones, destacando tres momentos fundamentales coincidentes con los tres momentos de la economía católica en la Argentina. Al mismo tiempo se muestra la curva teórica de los economistas católicos, que los aleja de una propuesta propiamente católica de una economía política para concentrar su punto de vista en la dimensión ética de las prácticas empresariales. El recorrido intelectual de Valsecchi revela el pasaje de una visión crítica de la economía predominante en 1930 a una funcionalidad con la propuesta en clave antipopulista por las clases propietarias en 1970.The intellectual trajectory of Francisco Valsecchi (1907-1992) in the history of Catholic economic ideas shows the theoretical turns of an axiology derived from the Social Doctrine of the Church. Both the historical circumstances of a Catholic economic thought in Argentina and the social, economic, and political changes of the 1930-1970 period had an impact on the conceptual trends of this apparently perennial axiology. To explain the changes in the economic perspectives the main stages of his theoretical positions are studied, emphasizing the three key moments of Catholic economy. At the same time the article shows the theoretical path followed by Catholic economists from their original proposal of a political economy towards a view orientated to the construction of an axiology of business practices. Valsecchi’s intellectual trajectory reveals the passage from a critical perspective of economy prevailing in the 1930’s to an antipopulist point of view strongly related to the proprietor class in the 1970’s.Fil: Acha, Omar. Universidad de Buenos Aire

PROGRESSING STUDENTS’ MOTIVATION IN LEARNING ENGLISH BY USING HYPNOSIS (HYPNOLEARNING) AT STUDENTS OF STAN 2 JILC PERINTIS MAKASSAR

ABSTRACT, This article provides a description of the students’ motivation in learning English by using hypnosis (hypnolearning) at the students of STAN 2 of JILC Perintis, Makassar 2010/2011. The population of the research consisted of the students of STAN 2 of JILC Perintis, Makassar in academic year of 2010/2011. It consisted of one class. The number of the students was 20 and the sample of this research was total sampling. It means that all students of STAN 2 of JILC Perintis, Makassar were taken as samples namely 20 students. In this research, the data was collected by using questionnaire. The questionnaire was used to obtain data on students’ motivation by using hypnosis (hypnolearning). It consisted of 20 items. Based on the data obtained, this article discovered that students were motivated in learning English by using hypnosis (hypnolearning). The data showed that the students always choose “agree” in every item of the questionnaire which was given. It indicated that the level of the students’ motivation by the students of STAN 2 of JILC Perintis, Makassar in learning English by using hypnosis (hypnolearning) was “agree”. Keywords: Students’ Motivation, Hyposis, English Learning Styl