University of Los Andes

About: University of Los Andes is a education organization based out in Bogotá, Colombia. It is known for research contribution in the topics: Population & Large Hadron Collider. The organization has 17616 authors who have published 25555 publications receiving 413463 citations.

Structural and vibrational study of Bi 2 Se 3 under high pressure

Abstract: The structural and vibrational properties of bismuth selenide (Bi${}_{2}$Se${}_{3}$) have been studied by means of x-ray diffraction and Raman scattering measurements up to 20 and 30 GPa, respectively. The measurements have been complemented with ab initio total-energy and lattice dynamics calculations. Our experimental results evidence a phase transition from the low-pressure rhombohedral ($R$-3$m$) phase (\ensuremath{\alpha}-Bi${}_{2}$Se${}_{3}$) with sixfold coordination for Bi to a monoclinic $C$2/$m$ structure (\ensuremath{\beta}-Bi${}_{2}$Se${}_{3}$) with sevenfold coordination for Bi above 10 GPa. The equation of state and the pressure dependence of the lattice parameters and volume of \ensuremath{\alpha} and \ensuremath{\beta} phases of Bi${}_{2}$Se${}_{3}$ are reported. Furthermore, the presence of a pressure-induced electronic topological phase transition in \ensuremath{\alpha}-Bi${}_{2}$Se${}_{3}$ is discussed. Raman measurements evidence that Bi${}_{2}$Se${}_{3}$ undergoes two additional phase transitions around 20 and 28 GPa, likely toward a monoclinic $C$2/$c$ and a disordered body-centered cubic structure with 8-fold and 9- or 10-fold coordination, respectively. These two high-pressure structures are the same as those recently found at high pressures in Bi${}_{2}$Te${}_{3}$ and Sb${}_{2}$Te${}_{3}$. On pressure release, Bi${}_{2}$Se${}_{3}$ reverts to the original rhombohedral phase after considerable hysteresis. Symmetries, frequencies, and pressure coefficients of the Raman and infrared modes in the different phases are reported and discussed.

ISLES 2016 and 2017-Benchmarking Ischemic Stroke Lesion Outcome Prediction Based on Multispectral MRI.

Abstract: Performance of models highly depend not only on the used algorithm but also the data set it was applied to This makes the comparison of newly developed tools to previously published approaches difficult Either researchers need to implement others' algorithms first, to establish an adequate benchmark on their data, or a direct comparison of new and old techniques is infeasible The Ischemic Stroke Lesion Segmentation (ISLES) challenge, which has ran now consecutively for 3 years, aims to address this problem of comparability ISLES 2016 and 2017 focused on lesion outcome prediction after ischemic stroke: By providing a uniformly pre-processed data set, researchers from all over the world could apply their algorithm directly A total of nine teams participated in ISLES 2015, and 15 teams participated in ISLES 2016 Their performance was evaluated in a fair and transparent way to identify the state-of-the-art among all submissions Top ranked teams almost always employed deep learning tools, which were predominately convolutional neural networks (CNNs) Despite the great efforts, lesion outcome prediction persists challenging The annotated data set remains publicly available and new approaches can be compared directly via the online evaluation system, serving as a continuing benchmark (wwwisles-challengeorg)

Combination of CDF and D0 W-Boson mass measurements

Abstract: We summarize and combine direct measurements of the mass of the $W$ boson in $\sqrt{s} = 1.96 \text{TeV}$ proton-antiproton collision data collected by CDF and D0 experiments at the Fermilab Tevatron Collider. Earlier measurements from CDF and D0 are combined with the two latest, more precise measurements: a CDF measurement in the electron and muon channels using data corresponding to $2.2 \mathrm{fb}^{-1}$ of integrated luminosity, and a D0 measurement in the electron channel using data corresponding to $4.3 \mathrm{fb}^{-1}$ of integrated luminosity. The resulting Tevatron average for the mass of the $W$ boson is $\MW = 80\,387 \pm 16 \text{MeV}$. Including measurements obtained in electron-positron collisions at LEP yields the most precise value of $\MW = 80\,385 \pm 15 \text{MeV}$.

How Context Shapes Entrepreneurial Self-Efficacy as a Driver of Entrepreneurial Intentions: A Multilevel Approach:

Abstract: We study how the proximate and distal sociocultural environments affect the well-established relationship between entrepreneurial self-efficacy and entrepreneurial intentions. We focus on the insti...

How to Attain an Ultralow Interfacial Tension and a Three-Phase Behavior with a Surfactant Formulation for Enhanced Oil Recovery: A Review. Part 2. Performance Improvement Trends from Winsor’s Premise to Currently Proposed Inter- and Intra-Molecular Mixtures

Abstract: The minimum interfacial tension occurrence along a formulation scan at the so-called optimum formulation is discussed to be related to the interfacial curvature. The attained minimum tension is inversely proportional to the domain size of the bicontinuous microemulsion and to the interfacial layer rigidity, but no accurate prediction is available. The data from a very simple ternary system made of pure products accurately follows the correlation for optimum formulation, and exhibit a linear relationship between the performance index as the logarithm of the minimum tension at optimum, and the formulation variables. This relation is probably too simple when the number of variables is increased as in practical cases. The review of published data for more realistic systems proposed for enhanced oil recovery over the past 30 years indicates a general guidelines following Winsor’s basic studies concerning the surfactant–oil–water interfacial interactions. It is well known that the major performance benefits are achieved by blending amphiphilic species at the interface as intermolecular or intramolecular mixtures, sometimes in extremely complex formulations. The complexity is such that a good knowledge of the possible trends and an experienced practical know-how to avoid trial and error are important for the practitioner in enhanced oil recovery.