Electron correlations, spontaneous magnetization and momentum density in quantum dots

The magnetization of quantum dots is discussed in terms of a relatively simple but exactly solvable model Hamiltonian. The model predicts oscillations in spin polarization as a function of dot radius for a fixed electron density. These oscillations in magnetization are shown to yield distinct signature in the momentum density of the electron gas, suggesting the usefulness of momentum resolved spectroscopies for investigating the magnetization of dot systems. We also present variational quantum Monte Carlo calculations on a square dot containing 12 electrons in order to gain insight into correlation effects on the interactions between like and unlike spins in a quantum dot.Comment: 6 pages, 4 figure

Target Geometry Dependence of Electron Energy Loss Spectra in Scanning Transmission Electron Microscopy (STEM)

In the frame of the Self-Energy formalism, we study the interaction between STEM electrons and small particles in the range of the valence electron excitations. We first calculate the energy loss probability for an isolated sphere and study the loss spectrum dependence on the size of the particle and on the relative impact parameter. Then we analyze the loss spectra in more realistic situations: (a) the effect of the coupling between the particle and supporting surface is studied in a simple geometrical model; and (b) we analyze the dependence of the losses on the geometrical shape of the target by considering hemispherical particle. Our results are in a good qualitative (and in simple cases, quantitative too) agreement with several experimental results which show anomalous excitations. We restate the suitability of the dielectric theory to study the surface excitations of these systems

Precolonial institutions and deforestation in Africa

We find that local institutions inherited from the precolonial era continue to play an important role in natural resource governance in Africa. Using satellite image data, we find a significant and robust relationship between deforestation and precolonial succession rules of local leaders (local chiefs). In particular, we find that those precolonial areas where local leaders were appointed by ‘social standing’ have higher rates of deforestation compared to the base case of hereditary rule and where local leaders were appointed from above (by paramount chiefs). While the transmission mechanisms behind these results are complex, we suggest that areas where local leaders were appointed by social standing are more likely to have poorer institutions governing local leadership and forest management.This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.landusepol.2015.10.03

Magnetism in Atomic-Sized Palladium Contacts and Nanowires

We have investigated Pd nanowires theoretically, and found that, unlike either metallic or free atomic Pd, they exhibit Hund's rule magnetism. In long, monoatomic wires, we find a spin moment of 0.7 Bohr magnetons per atom, whereas for short, monoatomic wires between bulk leads, the predicted moment is about 0.3 Bohr magnetons per wire atom. In contrast, a coaxial (6,1) wire was found to be nonmagnetic. The origin of the wire magnetism is analyzed.Comment: 6 pages, including 4 figure

Revisión de la literatura sobre estudios de juventud rural en América Latina y el Caribe durante 2001-2019

This literature review includes 45 research studies focused on Latin American rural youth. The studies were published in peer-reviewed research journals between 2001-2019. The analysis is divided into study approaches, methods, participants, and findings. Four research approaches were identified: 1) rural youth migration, 2) education and/or communication, 3) expectations or future perspectives of the rural youth, and 4) rural youth characterization. Although traditional definitions of youth use an age range of 14-25 years, a broad criterion for selecting participants was observed. Regarding methods, the studies used quantitative, qualitative, and mixed-method analyses; however, in some cases, elements such as the qualitative research approach, the statistical representativeness (for quantitative studies), and the triangulation strategy in the mixed-method analysis were not mentioned or followed. The findings of the four research approaches coincided with the fact that the rural contexts in Latin America create socioeconomic barriers for rural youth development; therefore, rural youth aspirations are more focused on urban activities. In addition, some authors highlighted the importance of education or extension programs developed by local governments to empower rural youth in Latin America.Esta revisión de la literatura se basó en 45 estudios de investigación que se enfocaron en la juventud rural latinoamericana. Dichos estudios fueron publicados en revistas arbitradas entre 2001 y 2019. El análisis de los documentos se dividió en enfoques de investigación, métodos utilizados, participantes y principales hallazgos. Se identificaron cuatro enfoques de investigación: 1) migración rural juvenil, 2) educación y/o comunicación para juventud rural, 3) expectativas y perspectivas de la juventud rural y 4) caracterizaciones de la juventud rural. Aunque las definiciones tradicionales de juventud utilizan rangos de edad entre 14 y 25 años, se observó un concepto ampliado dentro de los estudios analizados. Con respecto a los métodos, los estudios utilizaron estrategias cuantitativas, cualitativas y de métodos mixtos. Sin embargo, en algunos casos, no se desarrollaron o se mencionaron elementos como el enfoque de investigación cualitativa, la representatividad estadística (para estudios cuantitativos) o la triangulación en el análisis mixto. Por último, se observó que los cuatro enfoques de investigación coinciden en que el contexto rural latinoamericano impone barreras para la juventud; por tanto, sus aspiraciones están más orientadas hacia las actividades urbanas. Además, algunos autores subrayaron la importancia de la educación y la extensión para el empoderamiento de la juventud rural en América Latina

Comment on “Phase contribution of image potential on empty quantum well states in Pb islands on the Cu(111) surface”

1 página, 1 figura.-- PACS numbers: 68.37.Ef, 68.65.Fg, 73.21.FgThis work was partially funded by MCINN(FIS2010- 19609-C02-01) and G.V-UPV/EHU(IT-366-07).Peer reviewe

The minimum shear stress range criterion and its application to crack orientation prediction in incomplete contact fretting problems

[EN] A proper prediction of crack paths is required when assessing accurately the fatigue crack propagation life. Recently, some authors have pointed out that the criterion of minimum shear stress range leads to inconsistent results when predicting fretting crack paths under incomplete contacts. In this paper, different fretting experiments with cylinder-to-flat contact found in the literature are reviewed, and the corresponding crack path prediction using the extended finite element method and the minimum shear stress range crack orientation criterion is performed. Results show the applicability of the criterion to predict the crack orientation during stage II in incomplete contact fretting problems.The authors gratefully acknowledge the financial support given by the Spanish Ministry of Economy and Competitiveness and the FEDER program through the project DPI2017-89197-C2-1-R, DPI2017-89197-C2-2-R and DPI2014-56137-C2-2-R and the FPI subprogram associated to the project with the reference BES-2015-072070. The support of the Generalitat Valenciana, Programme PROMETEO 2016/007, is also acknowledged. The financial support given by the Eusko Jaurlaritza under "Programa de apoyo a la investigacion colaborativa en areas estrategicas" (Project MEDECA: Ref. KK-2017/00053, and MEDECA2: Ref. KK-2018/00013) programs is also acknowledged.Infante, D.; Llavori, I.; Zabala, A.; Giner Maravilla, E. (2019). The minimum shear stress range criterion and its application to crack orientation prediction in incomplete contact fretting problems. International Journal of Fatigue. 129:1-9. https://doi.org/10.1016/j.ijfatigue.2019.105223S1912

Spontaneous Magnetization and Electron Momentum Density in 3D Quantum Dots

We discuss an exactly solvable model Hamiltonian for describing the interacting electron gas in a quantum dot. Results for a spherical square well confining potential are presented. The ground state is found to exhibit striking oscillations in spin polarization with dot radius at a fixed electron density. These oscillations are shown to induce characteristic signatures in the momentum density of the electron gas, providing a novel route for direct experimental observation of the dot magnetization via spectroscopies sensitive to the electron momentum density.Comment: 5 pages (Revtex4), 4 (eps) figure