Communities in DSpace

Select a community to browse its collections.

Now showing 1 - 5 of 7

Recent Submissions

  • Thumbnail Image
    Item type:Item,
    Real-time crystal growth monitoring of boric acid from sodium or lithium sulfate containing aqueous solutions by atomic force microscopy
    (2023) Alavia, Wilson; Seidel-Morgenstern, Andreas; Hermsdorf, Dana; Lorenz, Heike; Graber, Teófilo A.
    The crystal growth of boric acid from an aqueous solution in the absence and presence of sodium and lithium sulfate was studied by real-time monitoring. For this purpose, atomic force microscopy in situ has been used. The results show that the growth mechanism of boric acid from its pure and impure solutions is spiral growth driven by screw dislocation and that the velocity of advancement of steps on the crystal surface, and the relative growth rate (ratio of the growth rate in presence and absence of a salt) is reduced in the presence of salts. The reduction of the relative growth rate could be explained by the inhibition of advancement of steps of the (001) face mainly in the growth direction [100] caused by the adsorption of salts on the actives sites and the inhibition of the formation of sources of steps such as dislocations. The adsorption of the salts on the crystal surface is anisotropic and independent of the supersaturation and preferentially on the active sites of the (100) edge. Moreover, this information is of significance for the improvement of the quality of boric acid recovered from brines and minerals and the synthesis of nanostructures and microstructures of boron-based materials.
  • Thumbnail Image
    Item type:Item,
    Estimación de PDFF usando una red neuronal con múltiples decodificadores para la separación de agua-grasa con un número reducido de ecos
    (Universitat de Barcelona. Observatori de Bioètica i Dret., 2023) Meneses, Juan Pablo; Arrieta, Cristobal; Maggiora, Gabriel della; Besa, Cecilia; Urbina, Jesús; Arrese, Marco; Gana, Juan Cristóbal; Galgani, Jose E.; Tejos, Cristian; Uribe, Sergio
    Objective To accurately estimate liver PDFF from chemical shift-encoded (CSE) MRI using a deep learning (DL)-based MultiDecoder Water-Fat separation Network (MDWF-Net), that operates over complex-valued CSE-MR images with only 3 echoes. Methods The proposed MDWF-Net and a U-Net model were independently trained using the frst 3 echoes of MRI data from 134 subjects, acquired with conventional 6-echoes abdomen protocol at 1.5 T. Resulting models were then evaluated using unseen CSE-MR images obtained from 14 subjects that were acquired with a 3-echoes CSE-MR pulse sequence with a shorter duration compared to the standard protocol. Resulting PDFF maps were qualitatively assessed by two radiologists, and quantitatively assessed at two corresponding liver ROIs, using Bland Altman and regression analysis for mean values, and ANOVA testing for standard deviation (STD) (signifcance level: .05). A 6-echo graph cut was considered ground truth. Results Assessment of radiologists demonstrated that, unlike U-Net, MDWF-Net had a similar quality to the ground truth, despite it considered half of the information. Regarding PDFF mean values at ROIs, MDWF-Net showed a better agreement with ground truth (regression slope=0.94, R2=0.97) than U-Net (regression slope=0.86, R2=0.93). Moreover, ANOVA post hoc analysis of STDs showed a statistical diference between graph cuts and U-Net (p<.05), unlike MDWF-Net (p=.53). Conclusion MDWF-Net showed a liver PDFF accuracy comparable to the reference graph cut method, using only 3 echoes and thus allowing a reduction in the acquisition times. Clinical relevance statement We have prospectively validated that the use of a multi-decoder convolutional neural network to estimate liver proton density fat fraction allows a signifcant reduction in MR scan time by reducing the number of echoes required by 50%. Key Points • Novel water-fat separation neural network allows for liver PDFF estimation by using multi-echo MR images with a reduced number of echoes. • Prospective single-center validation demonstrated that echo reduction leads to a signifcant shortening of the scan time, compared to standard 6-echo acquisition. • Qualitative and quantitative performance of the proposed method showed no signifcant diferences in PDFF estimation with respect to the reference technique.
  • Thumbnail Image
    Item type:Item,
    Practicum tutorials in initial teacher training: conditions, strategies, and effects of reflective practice
    ( Universidad de los Andes. Facultad de Ciencias Sociales. Departamento de Antropología, 2020) Ruffinelli, Andrea; Hoz, Silvana de la; Álvarez, Carolina
    This paper systematizes the research findings of publications in the last 5-years related to reflective practice in practicum tutorials in initial teacher training, by means of a literature review. The objective is to contribute new knowledge about reflective practice, structuring it around its conditions, development strategies, and effects, considering metacognitive and generative factors, enriching theory about how to teach reflection. The results show there is progress in the field in terms of proposals for different devices and strategies to teach reflective practice in initial teacher training, and emerging findings regarding its effects.
  • Thumbnail Image
    Item type:Item,
    More ideational than materia l: exploring the contemporary role of student voices in Chilean universities
    (Universidad del Norte. Departamento de Historia y Ciencias Sociales, 2022) Darwin, Stephen
    A key promise of neoliberalist ideologies in higher education is the valorization of student choice as a means of (re)shaping practices and improving the responsiveness of institutions. The power of this neoliberal imaginary (Ball, 2012) was grounded in market-like policies that demanded institutional accountability to both afford competition and maximizing prospects of student satisfaction. A key consequence of this imperative has been burgeoning institutional and system-level investment in metric-based instruments designed to measure and compare student experiences, engagement or satisfaction. However, how effective of these neoliberal policies been in empowering student choice and in producing more reflexive institutions? The research reported here investigated the influence of student voices in one of the earliest adopters of this neoliberal imaginary: the Chilean higher education system. This qualitative study explored the contemporary institutional role and function of student voices using a university typology, with data developed through artefact analyses and interviews with educational leaders. The findings suggest that institutions have heterogeneous orientations ranging from pseudo-democratic to instrumental forms of engagement, reflecting the distinctive sociocultural histories of institutions. However, the outcomes suggest that student voices are not a substantial presence in quality assurance or improvement practices.
  • Thumbnail Image
    Item type:Item,
    The ethics of competition: accountability policy enactment in Chilean schools’ everyday life
    (Firenze. Biblioteca Filosofica, 2020) Falabella, Alejandra
    Public policies have a moral order, an ethical horizon. They offer a vocabulary of imagined micro-policies. Using the case of Chile, this paper examines the ways in which accountability policies are reworked within schools and how they affect actors’ subjectivities. It adds new findings to the existing body of research on school accountability policies, offering in-depth evidence based on the case of Chile, which has a high-stakes testing model and a widespread competitive voucher system. The research is based on case studies of ten public and private subsidised schools, framed by a sociological perspective of policy enactment theory. The research findings show the ways that accountability policies are recreated, expanded, and intensified at the local level, permeating an ethic of competition. The analysis focuses on three qualitative trends: school actors’ sense-making of test scores and labels; zones of safety and risk for teachers under an accountability regime; and the emergence of a sticky web of persuasion, surveillance, and coercion among school members in order to improve performance. The practices examined are not understood as ‘secondary effects’ or an ‘implementation problem’, as if they occur unconnected from the policy rationale. The outcomes are consistent with the policy itself in interaction with school life.