ANID

Permanent URI for this collection

https://repositorio.uc.cl/handle/11534/74801

Browse

Now showing 1 - 20 of 25

A longitudinal approach for understanding algorithm use
(WILEY, 2022) Chacón Hiriart, Álvaro Marcelo; Kausel, Edgar E.; Reyes Torres Tomas Hernan
Research suggests that algorithms-based on artificial intelligence or linear regression models-make better predictions than humans in a wide range of domains. Several studies have examined the degree to which people use algorithms. However, these studies have been mostly cross-sectional and thus have failed to address the dynamic nature of algorithm use. In the present paper, we examined algorithm use with a novel longitudinal approach outside the lab. Specifically, we conducted two ecological momentary assessment studies in which 401 participants made financial predictions for 18 days in two tasks. Relying on the judge-advisor system framework, we examined how time interacted with advice source (human vs. algorithm) and advisor accuracy to predict advice taking. Our results showed that when the advice was inaccurate, people tended to use algorithm advice less than human advice across the period studied. Inaccurate algorithms were penalized logarithmically; the effect was initially strong but tended to fade over time. This suggests that first impressions are crucial and produce significant changes in advice taking at the beginning of the interaction, which later tends to stabilize as days go by. Therefore, inaccurate algorithms are more likely to accrue a negative reputation than inaccurate humans, even when having the same level of performance.
A robust DPG method for large domains
(2021) Führer, Thomas; Heuer, Norbert
We observe a dramatic lack of robustness of the DPG method when solving problems on large domains and where stability is based on a Poincare-type inequality. We show how robustness can be re-established by using appropriately scaled test norms. As model cases we study the Poisson problem and the Kirchhoff-Love plate bending model, and also include fully discrete variants where optimal test functions are approximated. Numerical experiments for both model problems, including an-isotropic domains and mixed boundary conditions, confirm our findings.
Analysis of Backward Euler Primal DPG Methods
(2021) Führer, Thomas; Heuer, Norbert; Karkulik, Michael
We analyze backward Euler time stepping schemes for a primal DPG formulation of a class of parabolic problems. Optimal error estimates are shown in a natural norm and in the L-2 norm of the field variable. For the heat equation the solution of our primal DPG formulation equals the solution of a standard Galerkin scheme and, thus, optimal error bounds are found in the literature. In the presence of advection and reaction terms, however, the latter identity is not valid anymore and the analysis of optimal error bounds requires to resort to elliptic projection operators. It is essential that these operators be projections with respect to the spatial part of the PDE, as in standard Galerkin schemes, and not with respect to the full PDE at a time step, as done previously.
Biomechanical analysis of expert anesthesiologists and novice residents performing a simulated central venous access procedure
(2021) Villagrán Gutiérrez, Ignacio Andrés; Moenne Vargas, Cristóbal Matías; Aguilera Siviragol, Victoria Ignacia; Garcia, Vicente; Reyes, Jose Tomas; Rodriguez, Sebastian; Miranda Mendoza, Constanza; Altermatt, Fernando; Fuentes López, Eduardo; Delgado Bravo, Mauricio Antonio; Neyem, Andrés
Background Central venous access (CVA) is a frequent procedure taught in medical residencies. However, since CVA is a high-risk procedure requiring a detailed teaching and learning process to ensure trainee proficiency, it is necessary to determine objective differences between the expert’s and the novice’s performance to guide novice practitioners during their training process. This study compares experts’ and novices’ biomechanical variables during a simulated CVA performance. Methods Seven experts and seven novices were part of this study. The participants’ motion data during a CVA simulation procedure was collected using the Vicon Motion System. The procedure was divided into four stages for analysis, and each hand’s speed, acceleration, and jerk were obtained. Also, the procedural time was analyzed. Descriptive analysis and multilevel linear models with random intercept and interaction were used to analyze group, hand, and stage differences. Results There were statistically significant differences between experts and novices regarding time, speed, acceleration, and jerk during a simulated CVA performance. These differences vary significantly by the procedure stage for right-hand acceleration and left-hand jerk. Conclusions Experts take less time to perform the CVA procedure, which is reflected in higher speed, acceleration, and jerk values. This difference varies according to the procedure’s stage, depending on the hand and variable studied, demonstrating that these variables could play an essential role in differentiating between experts and novices, and could be used when designing training strategies.
Chinese Nominal Groups: The Metaphorical Realization of Figures
(Routledge Journals, Taylor & Francis LTD, 2022) Hao, Jing; Wang, Pin
In this paper, we examine how nominal groups in Mandarin Chinese are involved in the realization of experiential grammatical metaphors, drawing on data from a history textbook chapter that recounts historical activities in the Opium War. We approach nominal group realizations of historical activities from a 'top-down' perspective along the hierarchy of stratification. While the discourse semantic figures construing activities can be realized congruently through a clause, the academic discourse of history favors nominal realizations. Previous descriptions of nominal groups in Mandarin Chinese have focused predominantly on the realization of entities. The nominal realizations of figures, however, have yet to be given sufficient consideration. We will show that some elements involved in such nominal groups do not share the functional characteristics of congruent ones. In addition to recognizable functions including Thing, Epithet, Measurer, Deictic and Qualifier, two distinctive functions, named here as Target and Orientation, are also identified. Our study aims to illustrate a descriptive method that considers multiple strata and provide a description of nominal groups involved in metaphorical realizations. The study suggests that grammatical descriptions need to reason from above, as well as round about and below - taking into account both discourse semantics and register variation.
Domestic military missions in Latin America: Civil-military relations and the perpetuation of democratic deficits
(2022) Jenne, Nicole; Martínez, Rafael
Latin American militaries are today in many regards inoperative and obsolete as an instrument of defence. Yet, they seek to maintain their organisational power and privileges. Governments, on the other hand, lack the adequate means to fight criminality, persisting poverty and social inequality. In an apparent win-win situation, Latin American governments have used the military as a wildcard to step in where civilian state capacity falls short, including for urban and border patrols, literacy campaigns and to collect garbage, among many other tasks. The military's manifold internal use has been defended mainly based on pragmatic reasons. We argue instead that the ostensive pareto optimality between militaries and governments has had negative effects for civil-military relations from a democratic governance point of view that takes into consideration the efficiency and effectiveness of how the state delivers basic services across different policy areas.
Eucryphia cordifolia extracts: Phytochemical screening, antibacterial and antioxidant activities
(2021) Viteri, Rafael; Giordano, Ady; Montenegro, Gloria; Zacconi, Flavia C. M.
Eucryphia cordifolia is a native and dominant species from the Temperate Forest in the southern region of Chile. It is a crucial melliferous species producing unifloral honey with outstanding antibacterial properties with great commercial value at international markets. A phytochemical screening was developed by colorimetric and gravimetric methods. Antioxidant activities were assessed by using 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS), and ferric ion reducing antioxidant power (FRAP) method. The minimum bactericidal concentration (MBC) was the method used to determine the antibacterial activity. The results revealed the highest antioxidant activity for the methanolic extracts of branches (IC50 35.7 mu g/mL for DPPH, IC50 11.0 mu g/mL for ABTS, and 4.6 mM FeSO4 center dot 7H(2)O/g in FRAP), attributed to its high content of total phenols (332.8 mg GAE/g). The quantification of the MBC led to values in the range of 0.78-12.5 mg/mL for S. aureus and S. pyogenes, and 6.25-50 mg/mL for E. coli and P. aeruginosa, respectively. The presented work provides valuable first in vitro evidence regarding the potential application of E. cordifolia extracts as antioxidants and antibacterial agents in the nutraceutical and phytopharmaceutical industry.
Full-scale shaking table test and numerical modeling of a 3000-liter legged storage tank isolated with a vertical rocking isolation system
(WILEY, 2022) Reyes, Sergio, I; Almazán Campillay, José Luis; Vassiliou, Michalis F.; Tapia Flores, Nicolás Felipe; Colombo, Jose, I; Llera Martin, Juan Carlos de la
This paper presents the numerical and experimental evaluation of a vertical-rocking isolation (VRI). This evaluation is done by 1-D shaking table tests performed on a full-scale legged storage tank of 3000-liters capacity and its representation through a simple yet representative rigid lumped-mass model approach. The isolation system setup consisted of four ISO3D-2G devices, each one placed on each leg of the tank, which uses high-damping natural rubber to generate the restoring and dissipative forces. The ISO3D-2G device is vertically flexible and laterally rigid, enabling the isolation mechanism of the rocking motion of the tank. The experiments were carried out using three white noise for the system identification and 17 ground motions inputs for the system validation. The measured variables included the lateral acceleration and displacement of the tank, and the vertical and rotational behavior of the isolation interface. The identification results showed a vertical-rotational coupled fundamental mode that is highly dependent on the amplitude of deformation, with a period varying from 0.5 to more than 1 s, depending on the intensity of the motion. The maximum displacement of the tank at the top remained below 13 cm with total accelerations of nearly 0.3 g, both for motions with Peak Ground Acceleration (PGA) values ranging from 0.3 to 0.8 g. The mean maximum values were predicted with the simplified model with errors of less than 10% and 21% for displacements and accelerations, respectively. Finally, the results show that the behavior of vertical-rocking isolated structures can be predicted by simplified models with reasonable errors and that the development of simple design guidelines and equations for VRI systems is possible.
Green by Design: Convergent Synthesis, Computational Analyses, and Activity Evaluation of New FXa Inhibitors Bearing Peptide Triazole Linking Units
(2022) Rodriguez, Diego F.; Duran Osorio, Francisca; Duarte, Yorley; Olivares, Pedro; Moglie, Yanina; Dua, Kamal; Zacconi, Flavia C. M.
Green chemistry implementation has led to promising results in waste reduction in the pharmaceutical industry. However, the early sustainable development of pharmaceutically active compounds and ingredients remains a considerable challenge. Herein, we wish to report a green synthesis of new pharmaceutically active peptide triazoles as potent factor Xa inhibitors, an important drug target associated with the treatment of diverse cardiovascular diseases. The new inhibitors were synthesized in three steps, featuring cycloaddition reactions (high atom economy), microwave-assisted organic synthesis (energy efficiency), and copper nanoparticle catalysis, thus featuring Earth-abundant metals. The molecules obtained showed FXa inhibition, with IC50-values as low as 17.2 mu M and no associated cytotoxicity in HEK293 and HeLa cells. These results showcase the environmental potential and chemical implications of the applied methodologies for the development of new molecules with pharmacological potential.
Inclusion of latent variables in Mixed Logit models: Modelling and forecasting
(2010) Yáñez Castillo, María Francisca; Raveau Feliú, Sebastián; Ortúzar Salas, Juan de Dios
Travel demand models typically use mainly objective modal attributes as explanatory variables. Nevertheless, it has been well known for many years that attitudes and perceptions also influence users' behaviour. The use of hybrid discrete choice models constitutes a good alternative to incorporate the effect of subjective factors. We estimated hybrid models in a short-survey panel context for data among many alternatives. The paper analyses the results of applying these models to a real urban case study, and also proposes an approach to forecasting using these models. Our results show that hybrid models are clearly superior to even highly flexible traditional models that ignore the effect of subjective attitudes and perceptions.
Incremental construction: a strategy to facilitate access to housing
(International Institute for Environment and Development (IIED), 2008) Greene, Margarita; Rojas, Eduardo
The "enabling" approach to housing markets promotes financing systems based on family savings, public subsidies and mortgage loans to unleash the potential of individuals and communities to produce and improve dwellings. However, the approach failed to benefit lower-income households, as they have less ability to generate savings or make mortgage payments. These households are forced to use informal mechanisms to access housing, such as purchasing land in illegal sub-divisions or squatting on public land and incrementally building their dwellings. The present work argues that supporting the incremental housing construction undertaken by poor households through an enabling approach can make a significant contribution to solving the housing problem in Latin America. The paper discusses the challenges and opportunities in executing this new type of programme, which requires coordinating the resources and capabilities of the beneficiaries with those of the different levels of government and the civil society. While this paper draws on experiences in Latin America and the Caribbean, the proposed approach is also relevant in other settings.
Internet Addiction of Older Women and Its Relationship With Social Influence and Social Networks Use as a Mediator
(2022) Rosell Cisternas, Javiera; Leeson, George W.; Verges, Alvaro
The aim is to analyse the relationship between social influence for Internet use and Internet addiction (IA) in older women, considering the use of Internet-based social networks as a mediator. The participants were 480 older women Internet users. Social influence, frequency of use of social networks and IA (including loss of control and emotional dysregulation) were evaluated. Structural Equation Modeling (SEM) was conducted to analyse the proposed model. The use of social networks was a significant mediator in the relationship between social influence for Internet use and the dimension of loss of control of IA. On the contrary, social network use was not a significant mediator. Older women with more social influence reported more frequency of social networking and, in turn, more loss of control in Internet use. Public policy and clinicians should address addictive behaviours about Internet use in older women, preventing the negative consequences.
Lipschitz stability for backward heat equation with application to fluorescence microscopy
(SIAM PUBLICATIONS, 2021) Arratia, Pablo; Courdurier Bettancourt, Matías Alejandro; Cueva, Evelyn; Osses, Axel; Palacios Farias, Benjamin Pablo
In this work we study a Lipschitz stability result in the reconstruction of a compactly supported initial temperature for the heat equation in R-n, from measurements along a positive time interval and over an open set containing its support. We employ a nonconstructive method which ensures the existence of the stability constant, but it is not explicit in terms of the parameters of the problem. The main ingredients in our method are the compactness of support of the initial condition and the explicit dependency of solutions to the heat equation with respect to it. By means of Carleman estimates we obtain an analogous result for the case when the observation is made along an exterior region omega x (t, T), such that the unobserved part R-n\omega is bounded. In the latter setting, the method of Carleman estimates gives a general conditional logarithmic stability result when initial temperatures belong to a certain admissible set, without the assumption of compactness of support and allowing an explicit stability constant. Furthermore, we apply these results to deduce similar stability inequalities for the heat equation in R and with measurements available on a curve contained in Rx[0,infinity), leading to the derivation of stability estimates for an inverse problem arising in 2D fluorescence microscopy. In order to further understand this Lipschitz stability, in particular, the magnitude of its stability constant with respect to the parameters of the problem, a numerical reconstruction is presented based on the construction of a linear system for the inverse problem in fluorescence microscopy. We investigate the stability constant by analyzing the condition number of the corresponding matrix.
MINRES for Second-Order PDEs with Singular Data
(2022) Führer Thomas; Heuer, Norbert; Karkulik, Michael
Minimum residual methods such as the least-squares finite element method (FEM) or the discontinuous Petrov-Galerkin (DPG) method with optimal test functions usually exclude singular data, e.g., non-square-integrable loads. We consider a DPG method and a least-squares FEM for the Poisson problem. For both methods we analyze regularization approaches that allow the use of H-1 loads and also study the case of point loads. For all cases we prove appropriate convergence orders. We present various numerical experiments that confirm our theoretical results. Our approach extends to general well-posed second-order problems.
Nature Is for Trees, Culture Is for Humans: A Critical Reading of the IPCC Report
(2021) Matus Cánovas, Claudia; Bussenius Méndez, Pascale; Herraz Mardones, Pablo Cristián; Riberi Manzur, Valentina Constanza; Prieto, Manuel
In this article, we problematize conventional views regarding culture presented in the assessment report entitled Climate Change 2014: Impacts, Adaptation, and Vulnerability. This report is a contribution to the Fifth Assessment Report produced by the Intergovernmental Panel on Climate Change (IPCC). We posit that when culture is seen as a stable category and imagined as a space composed of humans-and, more precisely, only certain humans-an epistemological, ontological, and ethical order is reproduced in which (a) nature is framed as a passive and apolitical "out there ", (b) knowledge based on this division is misleading and partial (e.g., social scientists study culture and natural scientists study nature), and (c) dominant humanist assumptions become common-sense explanations for inequalities. We conduct a critical discourse analysis of the IPCC report to better understand which assumptions produce the conceptualization of culture as a stable category. In our conclusion, we offer an example of a semiotic-meaning intervention of a section of the report to demonstrate the vitality of the concepts presented in this document. Subsequently, we discuss the consequences of omitting the vital traffic between the biological, social, and cultural realms from discussions on climate change to reexamine the production and reproduction of inequalities.
Obstacles, facilitators, and needs in doctoral writing: A systematic review
(2022) Calle Arango, Lina; Ávila Reyes, Natalia
Writing is one of the main challenges doctoral students face in their process of becoming researchers. Nonetheless, institutional initiatives to support writing processes are relatively recent and not necessarily research-grounded. This systematic literature review aims to address this gap by answering the questions: What obstacles and facilitators in the writing process do doctoral students encounter in the areas of SS&H? And what clues do these offer about students' needs for institutional support? To do so, we focus on empirical student-centred research. Systematizing the evidence may strengthen pedagogical decisions and programmatic orientations focused on the students' experiences and writing processes. We analysed a total of 38 studies on these topics collected from mainstream databases and identified patterns of recurring results that illustrate obstacles and facilitators from which the needs arise. Negative self-perceptions and low self-regulation are among the main obstacles of the writing process, while shared writing experiences foster affective dimensions self-regulation, and improve familiarisation with the discursive community. Lastly, institutional spaces specifically dedicated to writing as well as sustained positive and constructive feedback emerged as needs.
Operational experiences, military role conceptions, and their influence on civil-military relations
(2022) Harig, Christoph; Jenne, Nicole; Ruffa, Chiara
A considerable amount of research within security studies has explored the military's increasingly diverse and multifaceted tasks. However, this debate has been disconnected from the literature on civil-military relations to the effect that we still lack knowledge about how and why these operational tasks have consequences for the relations between the armed forces, civilian authorities, and society at large. In order to provide for a better understanding of these effects, this introduction to the Special Issue debates the concept of operational experiences to capture how the military's routine activities affect the equilibria, logics, and mechanisms of civil-military relations. The article then provides an overview of the Special Issue's six contributions, whose diverse and global perspectives shed light on different aspects of the relationship between military missions and the military's roles in society and politics. Among other factors, they highlight role conceptions - the military's shared views on the purpose of the institution - as crucial in shaping the dynamic relation between what the military does and what place it occupies within the state and society. The article concludes by describing potentially fruitful areas of future research.
Optimal Quasi-diagonal Preconditioners for Pseudodifferential Operators of Order Minus Two
(2019) Führer, Thomas; Heuer, Norbert
We present quasi-diagonal preconditioners for piecewise polynomial discretizations of pseudodifferential operators of order minus two in any space dimension. Here, quasi-diagonal means diagonal up to a sparse transformation. Considering shape regular simplicial meshes and arbitrary fixed polynomial degrees, we prove, for dimensions larger than one, that our preconditioners are asymptotically optimal. Numerical experiments in two, three and four dimensions confirm our results. For each dimension, we report on condition numbers for piecewise constant and piecewise linear polynomials.
Rupture parameter sensitivity of low frequency ground motion response spectra using synthetic scenarios in North Chile
(SPRINGER, 2021) Fortuño Jara, Catalina Pía; Llera Martin, Juan Carlos de la; Gonzalez, Gabriel; Gonzalez, Juan; Aguirre Aparicio, Paula
This research performs a sensitivity analysis of response spectrum values for various physical earthquake parameters, which are used to generate synthetic seismograms consistent with the expected seismicity in north Chile. Sensitivity analyses are based on the earthquake scenario and slip distribution model of the 2014, M-w 8.1 Pisagua earthquake, and seven other physically plausible interplate events for north Chile. A finite-fault rupture model, and slip distribution of the Pisagua earthquake, were obtained using inversion of InSAR and GPS data. Three other rupture models based on previous studies of interplate locking for north Chile and capable of generating M-w 8.3-8.6 earthquakes with an estimated maximum slip of 9.2 m, were incorporated in the analyses. Also, four additional scenarios with moment magnitudes in the range M-w 8.6-8.9 were generated by concatenating these physical scenarios into larger rupture areas within the north segment. Using these scenarios, synthetic ground motions were built at four observation sites: Pisagua, Iquique, Tocopilla, and Calama. Response sensitivity was studied for three key rupture parameters: mean rupture velocity, slip rise-time, and rupture directivity. Responses selected were peak ground displacement (PGD), spectral pseudo-velocities, S-v, and spectral displacements, S-d. First and second order variations of PGD, S-v, and S-d relative to the source parameters were computed and used together with a Taylor series expansion to propagate uncertainty into the responses as a function of v(r) and rise-time t(r). To study the effect of rupture directivity, three different foci locations were considered for each scenario: north, south, and at the centroid of the slip model. Response PGD values show no clear trends with rupture velocity, v(r); however, the variability increases as the system period increases. The effect of the slip rise-time is significant, and as t(r) increases, the spectral responses tend to decrease, suggesting that shorter slip rise-times lead to higher seismic demands in long period structures. The results obtained for the directivity analysis suggest that two factors control the expected waveforms and spectral responses: first, the direction of the rupture relative to the location of each site, and the hypocentral distance.
Space-time least-squares finite elements for parabolic equations
(2021) Führer, Thomas; Karkulik, Michael
We present a space-time least-squares finite element method for the heat equation. It is based on residual minimization in L-2 norms in space-time of an equivalent first order system. This implies that (i) the resulting bilinear form is symmetric and coercive and hence any conforming discretization is uniformly stable, (ii) stiffness matrices are symmetric, positive definite, and sparse, (iii) we have a local a-posteriori error estimator for free. In particular, our approach features full space-time adaptivity. We also present a-priori error analysis on simplicial space-time meshes which are highly structured. Numerical results conclude this work.

Browse

Browsing ANID by browse.metadata.fuente "WOS"

Results Per Page

Sort Options