Screening of heterogeneous surfaces: charge renormalization of Janus particles

Nonlinear ionic screening theory for heterogeneously charged spheres is developed in terms of a mode-decomposition of the surface charge. A far-field analysis of the resulting electrostatic potential leads to a natural generalization of charge renormalization from purely monopolar to dipolar, quadropolar, etc., including mode-couplings. Our novel scheme is generally applicable to large classes of surface heterogeneities, and is explicitly applied here to Janus spheres with differently charged upper and lower hemispheres, revealing strong renormalization effects for all multipoles.Comment: 2 figure

Phase diagram and magnetic properties of La1−x_{1-x}Cax_xMnO3_3 compound for 0≤x≤0.230\leq x \leq 0.23

In this article a detailed study of La$_{1-x}$Ca$_x$MnO$_3$ ($0\leq x \leq 0.23$) phase diagram using powder x-ray diffraction and magnetization measurements is presented. Unfortunately, in the related literature no properly characterized samples have been used, with consequence the smearing of the real physics in this complicated system. As the present results reveal, there are two families of samples. The first family concerns samples prepared in atmosphere ($P({\rm O}_2)=0.2$ Atm) which are all ferromagnetic with Curie temperature rising with $x$. The second family concerns samples, where a post annealing in nearly zero oxygen partial pressure is applied. These samples show a canted antiferromagnetic structure for $0\leq x \leq 0.1$ below $T_N$, while for $0.125\leq x <0.23$ an unconventional ferromagnetic insulated phase is present below $T_c$. The most important difference between nonstoichiometric and stoichiometric samples concerning the magnetic behavior, is the anisotropy in the exchange interactions, in the stoichiometric samples putting forward the idea that a new orbital ordered phase is responsible for the ferromagnetic insulating regime in the La$_{1-x}$Ca$_x$MnO$_3$ compound

El SIE, letra muerta en la instituci?n educativa

139 p. Recurso Electr?nicoEn Colombia, la evaluaci?n de los aprendizajes de los estudiantes, se rige por el Decreto 1290 del a?o 2009, el cual brinda autonom?a a las instituciones educativas para crear su propio Sistema Institucional de Evaluaci?n. El objetivo de la presente investigaci?n es describir el papel del SIE en el desarrollo de las pr?cticas evaluativas de los docentes de la Instituci?n Educativa T?cnica Pedro Pab?n Parga, en su proceso de ense?anza aprendizaje, para hacer de la evaluaci?n un elemento motivador y generador de aprendizaje, debido a que en la realidad, los prop?sitos que este documento contempla, no se reflejan de manera planeada y contundente en las pr?cticas evaluativas desarrolladas por los profesores en las aulas de clase. Para el desarrollo de este estudio, se emple? una investigaci?n de enfoque cualitativo, con dise?o descriptivo y se emple? una muestra representativa, compuesta por 16 docentes integrantes del consejo acad?mico y 38 alumnos del consejo estudiantil. En el dise?o metodol?gico se elabor? una tabla de cotejo que permiti? realizar una revisi?n documental del SIE, de acuerdo con los criterios establecidos en el art?culo 4? del Decreto 1290 de 2009; Igualmente, se administraron encuestas a docentes y estudiantes, adem?s se dise?? un grupo focal, con el fin de determinar el conocimiento y apropiaci?n del SIE, develar la definici?n de evaluaci?n que el SIE proclama como documento institucional y la que le asignan los docentes, las t?cnicas e instrumentos utilizados y el uso que le dan a los resultados de la evaluaci?n. Con los resultados obtenidos, se realiz? un an?lisis que permiti? sugerir estrategias para darle funcionalidad al Sistema de Evaluaci?n de la Instituci?n Educativa T?cnica Pedro Pab?n Parga, dentro del proceso educativo y de esta manera fortalecer las pr?cticas evaluativas, en beneficio de toda la comunidad educativa. Palabras claves: Evaluaci?n educativa, Sistema Institucional de Evaluaci?n de Estudiantes (SIE), pr?cticas evaluativas y Decreto 1290 del 16 de abril de 2009.In Colombia, the evaluation of students learning is oriented by Decree 1290 of 2009, which gives educational institutions the autonomy to create their own Institutional Evaluation System. The objective of this research is to describe the role of the SIE in the development of the evaluation practices of the teachers of the Pedro Pab?n Parga Technical Educational Institution, in their process of teaching and learning, in order to make the evaluation an element that motivates and generates learning, due to the fact that in reality, the purposes that this document contemplates are not reflected in a planned and forceful way in the evaluation practices developed by the teachers in the classrooms. For the development of this study, qualitative approach was used, with a descriptive design, and are presentative sample of 16 faculty members from the academic council and 38 students from the student council was used. In the methodological design, a checklist was prepared that allowed for a documentary review of the SIE in accordance with the criteria established in article 4 of Decree 1290 of 2009; Likewise, surveys were administered to teachers and students, in addition to a focal group, to determine the knowledge and appropriation of the SIE, to reveal the definition of evaluation that the SIE proclaims as an institutional document and that which the teachers assign to it, the techniques and instruments used and the use they make of the results of the evaluation. With the results obtained, an analysis was made that allowed to suggest strategies to give functionality to the Evaluation System of the Pedro Pab?n Parga Technical Educational Institution, within the educational process and in this way strengthen the evaluation practices, for the benefit of the entire educational community. Keywords: Educational evaluation, Institutional Evaluation System (SIE), evaluation practices, Decree 1290 of April 16 of 2009

High-pressure synthesis of rock salt LiMeO2-ZnO (Me = Fe3+, Ti3+) solid solutions

Metastable LiMeO2-ZnO (Me = Fe3+, Ti3+) solid solutions with rock salt crystal structure have been synthesized by solid state reaction of ZnO with LiMeO2 complex oxides at 7.7 GPa and 1350-1450 K. Structure, phase composition, thermal stability and thermal expansion of the recovered samples have been studied by X-ray diffraction with synchrotron radiation. At ambient pressure rock salt LiMeO2-ZnO solid solutions are kinetically stable up to 670-800 K depending on the composition.Comment: 11 pages, 3 figures, 1 tabl

Antioxidant Activity Analysis for the Selection of Rosmarinus officinalis L

Rosmarinus officinalis L. presents a high genetic variability, which is reflected in the chemical composition of the different individuals, and consequently in its biological activity, including antioxidant capacity. The aim of the present research was to correlate the chemical composition of methanolic extracts of the dried leaves of eight rosemary accessions with their antioxidant activity for the selection of plants to optimize the use of rosemary. The eight samples examined, starting from a collection of more than 160 individuals selected by BOTANE Ltd, were cultivated at Illapel, north central Chile, using the same cultivation techniques. The free radical-scavenging capacity was tested by the ability of extracts to bleach the stable 1,1-diphenyl-2-picryl-hydrazyl radical (DPPH) and to inhibit superoxide anion (O2-) and hydroxyl radical (.OH) production. The metal chelating activity was estimated by the ferrozine assay. All extracts (1–8) contained high concentrations of carnosic acid, and to a minor extent rosmarinic acid, and exhibited antioxidant activity. However, extracts 7 and 8, containing 31.7 and 26.1% of carnosic acid, respectively, have shown a higher biological effect, confirming that the antioxidant activity of R. officinalis leaves is primarily related to this phenolic diterpene and suggesting that the measure of antioxidant activity could be considered a good method in the selection of this plant for its optimization. Interestingly, our experimental evidence also suggests that air pollution negatively influences the carnosic acid content. In fact, samples 3 and 4, with a low carnosic acid content, originated from a highly polluted metropolitan area of Santiago city

Observation of a Griffiths-like phase in the paramagnetic regime of ErCo_2

A systematic x-ray magnetic circular dichroism study of the paramagnetic phase of ErCo2 has recently allowed to identify the inversion of the net magnetization of the Co net moment with respect to the applied field well above the ferrimagnetic ordering temperature, Tc. The study of small angle neutron scattering measurements has also shown the presence of short range order correlations in the same temperature region. This phenomenon, which we have denoted parimagnetism, may be related with the onset of a Griffiths-like phase in paramagnetic ErCo2. We have measured ac susceptibility on ErCo2 as a function of temperature, applied field, and excitation frequency. Several characteristics shared by systems showing a Griffiths phase are present in ErCo2, namely the formation of ferromagnetic clusters in the disordered phase, the loss of analyticity of the magnetic susceptibility and its extreme sensitivity to an applied magnetic field. The paramagnetic susceptibility allows to establish that the magnetic clusters are only formed by Co moments as well as the intrinsic nature of those Co moments

Switching of the Chiral Magnetic Domains in the Hybrid Molecular/Inorganic Multiferroic (ND4)2[FeCl5(D2O)]

(ND4)2[FeCl5(D2O)] represents a promising example of the hybrid molecular/inorganic approach to create materials with strong magneto-electric coupling. Neutron spherical polarimetry, which is directly sensitive to the absolute magnetic configuration and domain population, has been used in this work to unambiguously prove the multiferroicity of this material. We demonstrate that the application of an electric field upon cooling results in the stabilization of a single-cycloidal magnetic domain below 6.9 K, while poling in the opposite electric field direction produces the full population of the domain with opposite magnetic chirality. We prove the complete switchability of the magnetic domains at low temperature by the applied electric field, which constitutes a direct proof of the strong magnetoelectric coupling. Additionally, we refine the magnetic structure of the ordered ground state, deducing the underlying magnetic space group consistent with the direction of the ferroelectric polarization, and we provide evidence of a collinear amplitude-modulated state with magnetic moments along the a-axis in the temperature region between 6.9 and 7.2 K