Artículos de revistas

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https://repositorio.uc.cl/handle/11534/1156

Esta colección incluye artículos de revistas de profesores de la Pontificia Universidad Católica de Chile, publicados en revistas nacionales y extranjeras.

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Now showing 1 - 20 of 47

A method for unique phase retrieval of ultrafast optical fields
(2009) Seifert, Birger
A new true triaxial apparatus with pore fluid system for rock deformation under representative crustal stress conditions
(2025) Stanton-Yonge, Ashley; Mitchell, Thomas M.; Meredith, Philip G.; Hughes, Neil; Boon, Steve; Browning, John; Healy, David; Bowles, John
We have developed a new true triaxial apparatus for rock deformation, featuring six servo-controlled loading rams capable of applying maximum stresses of 220 MPa along the two horizontal axes and 400 MPa along the vertical axis to cubic rock samples of 50 mm side. Samples are introduced into a steel vessel, allowing rock specimens to be subjected to confining pressures of up to 60 MPa. Pore fluid lines connected to two pump intensifiers enable high-precision permeability measurements along all three principal stress directions. Experiments are conducted at room temperature. We present a suite of finite element method models implemented to determine the conditions and loading configuration that minimize the loading boundary effects during true triaxial loading. These observations are generic, and we expect they will contribute to the development of true triaxial loading systems generally. Finally, we validate our experimental configuration by presenting results on permeability measurements along the three axes on cubic samples of three types of well-studied rocks: Darley Dale sandstone, Crab Orchard sandstone, and Etna basalt.
A penalized estimation of the variogram and effective sample size
(2025) Acosta Salazar, Jonathan Daniel; Ronny Vallejos; García Soidán, Pilar
The variogram function plays a key role in modeling intrinsically stationary random fields, especially in spatial prediction using kriging equations. However, determining whether a computed variogram accurately fits the underlying dependence structure can be challenging. Current nonparametric estimators often fail to guarantee a conditionally negative definite function. In this paper, we propose a new valid variogram estimator, constructed as a linear combination of functions from a predefined class, ensuring it meets essential mathematical properties. A penalty coefficient is introduced to prevent overfitting, reducing spurious fluctuations in the estimated variogram. We also extend the concept of effective sample size (ESS), an important metric in spatial regression, to a nonparametric framework. Our ESS estimator is based on the reciprocal of the average correlation and is calculated using a plug-in approach, with the consistency of the estimator being demonstrated. The performance of these estimates is investigated through Monte Carlo simulations across various scenarios. Finally, we apply the methodology to rasterized forest images, illustrating both the strengths and limitations of the proposed approach.
Análisis descriptivo de las concepciones sobre historia de las ciencias en profesores en formación inicial
(2019) Cabrera Castillo, Henry Giovany; Durán Piamba, Stefania; Quintanilla Gatica, Mario R.
Este artículo tuvo como objetivo identificar las concepciones sobre historia de la ciencia que tie-nen los profesores en formación inicial. Se utilizó una metodología cualitativo-descriptiva. Los datos fueron obtenidos a partir de un cuestionario inicial, estructurado por preguntas abiertas y la cons-trucción de un documento escrito final aplicado a veinticinco participantes de un programa de licen-ciatura en la Universidad del Valle. Los resultados de la propuesta se obtuvieron a partir de un análisis descrito de tres categorías (visión de la historia de las ciencias, función de la historia de las ciencias en la enseñanza y producción de la ciencia) que permitió determinar que las concepciones sobre historia de las ciencias que los profesores en formación inicial han elaborado corresponden a las visiones anacrónica y diacrónica, funciones como actividad social, recurso y disciplinar, y producción de conocimiento. Como conclusión, podemos establecer que es necesario implementar propuestas didácticas direccionadas hacia el uso de la historia de las ciencias con el propósito de favorecer en ellos el reconocimiento, la reflexión y el uso de componentes históricos en sus prácticas educativas.
Attention is Turing complete
(2021) Pérez, Jorge; Barceló Baeza, Pablo; Marinkovic, Javier
Alternatives to recurrent neural networks, in particular, architectures based on self-attention, are gaining momentum for processing input sequences. In spite of their relevance, the computational properties of such networks have not yet been fully explored. We study the computational power of the Transformer, one of the most paradigmatic architectures exemplifying self-attention. We show that the Transformer with hard-attention is Turing complete exclusively based on their capacity to compute and access internal dense representations of the data. Our study also reveals some minimal sets of elements needed to obtain this completeness result.
Bayesian variable selection and survival modeling : assessing the most important comorbidities that impact lung and colorectal cancer survival in Spain
(2022) Rubio, Francisco J.; Silva, Danilo Alvares da; Redondo-Sanchez, Daniel; Marcos-Gragera, Rafael; Sánchez, María-José; Luque-Fernandez, Miguel A.
Cancer survival represents one of the main indicators of interest in cancer epidemiology. However, the survival of cancer patients can be affected by several factors, such as comorbidities, that may interact with the cancer biology. Moreover, it is interesting to understand how different cancer sites and tumour stages are affected by different comorbidities. Identifying the comorbidities that affect cancer survival is thus of interest as it can be used to identify factors driving the survival of cancer patients. This information can also be used to identify vulnerable groups of patients with comorbidities that may lead to worst prognosis of cancer. We address these questions and propose a principled selection and evaluation of the effect of comorbidities on the overall survival of cancer patients. In the first step, we apply a Bayesian variable selection method that can be used to identify the comorbidities that predict overall survival. In the second step, we build a general Bayesian survival model that accounts for time-varying effects. In the third step, we derive several posterior predictive measures to quantify the effect of individual comorbidities on the population overall survival. We present applications to data on lung and colorectal cancers from two Spanish population-based cancer registries. The proposed methodology is implemented with a combination of the R-packages mombf and rstan. We provide the code for reproducibility at https://github.com/migariane/BayesVarImpComorbiCancer .
Beyond the GUM: variance-based sensitivity analysis in metrology
(2016) Lira, I.
Biofilm formation on collagen substrates modulates Streptococcus mutans bacterial extracellular nanovesicle production and cargo
(2025) Leiva Sabadini, Camila Andrea; Berríos Segovia, Pablo Germán; Saavedra Godoy, Paula Andrea; Carrasco Rojas, Javiera; González Aramundiz, José Vicente; Vera Véliz, Mario Andrés; Tarifeño Saldivia, Estefanía; Schuh, Christina M. A. P.; Aguayo Paul, Sebastián
Streptococcus mutans is the major microbial etiological agent of dental caries and can adhere to surfaces such as type-I collagen, which is present in dentin and periodontal tissues. Recent studies have characterized planktonic S. mutans bacterial extracellular vesicles (bEVs) at the nanoscale range and demonstrated environmental-induced changes due to sugar presence or pH alterations. However, to date, no studies have explored whether surface-derived changes can modulate bEV production in the context of oral biofilm formation in the elderly. Therefore, this work aimed to determine the role of biofilm formation and collagen glycation on the nanoscale morphology and proteomic composition of S. mutans bEVs. For this, bEVs from S. mutans biofilms on native and glycated collagen surfaces were isolated, characterized, and compared to bEVs from planktonic cells. Nanoparticle tracking analysis (NTA), atomic force microscopy (AFM), and electron microscopy confirmed bEV production and showed that bEVs from biofilms are smaller in size and less abundant than those from planktonic cells. Furthermore, proteome analysis revealed that S. mutans biofilm formation on native and glycated collagen led to the enrichment of several key virulence proteins. Also, a shift towards proteins involved in metabolic processes was found in bEVs following biofilm formation on collagen surfaces, whereas glucan metabolism proteins were overexpressed in vesicles from the planktonic state. These results demonstrate that biofilm formation, as well as the glycation of collagen associated with aging and hyperglycaemia, can modulate bEV characteristics and cargo and could play a central role in S. mutans virulence and the development of diseases such as dental caries and periodontal disease.
Daily Variation in Plasma Zinc Concentrations in Women Fed Meals at Six-Hour Intervals
(1994) King, Janet C.; Hambidge, K. Michael; Westcott, Jamie L.; Kern, Deborah L.; Marshall Rivera, Guillermo
Ten pre-menopausal women participated in two studies to measure the daily variations in plasma zinc when meals were fed at 6-h intervals and to determine if the response was related to shifts in serum insulin, glucose, calcium, or phosphorus concentrations. In Study 1, identical meals were fed at 6-h intervals for 2 d, and blood was sampled 8 times between each meal. In Study 2, the women fasted from 1800 h on d 1 to noon the next day, and blood was sampled hourly from 0700–1200 on d 2. The postprandial plasma zinc response was similar following all four meals and accounted for 50% of the total within subject variation in plasma zinc. A small (2–6%) increase occurred within the first 60 min; then plasma zinc declined to a low point at 4 h after the meal. This characteristic pattern was not observed during the fasting study. Serum phosphorus varied consistently after each meal with a net efflux from circulation that preceded an efflux of zinc by 2 h. The postprandial response of serum glucose and insulin were related to the postprandial plasma zinc response measured 6 h earlier; the variables were not correlated at concurrent time points. The data show that food intake is a determinant of the daily variations in plasma zinc. The net efflux of zinc from circulation following meals may reflect hepatic zinc uptake in association with an increase in postprandial liver metabolism.
Developing and implementing an effective public outreach program
(2009) Harrison, J.; Dassow, Peter von
Developing Core/Shell Capsules Based on Hydroxypropyl Methylcellulose and Gelatin through Electrodynamic Atomization for Betalain Encapsulation
(2023) López de Dicastillo, Carol; Velásquez, Eliezer; Rojas, Adrián; Garrido, Luan; Moreno Constenla, María Carolina; Guarda, Abel; Galotto, María José
Betalains are bioactive compounds with remarkable functional and nutritional activities for health and food preservation and attractiveness. Nevertheless, they are highly sensitive to external factors, such as oxygen presence, light, and high temperatures. Therefore, the search for new structures, polymeric matrices, and efficient methods of encapsulation of these compounds is of great interest to increase their addition to food products. In this work, betalains were extracted from red beetroot. Betacyanin and betaxanthin contents were quantified. Subsequently, these compounds were successfully encapsulated into the core of coaxial electrosprayed capsules composed of hydroxypropyl methylcellulose (HPMC) and gelatin (G). The effect of incorporating the carbohydrate and the protein both in the core or shell structures was studied to elucidate the best composition for betalain protection. Morphological, optical, and structural properties were analyzed to understand the effect of the incorporation of the bioactive compounds in the morphology, color, and chemical interactions between components of resulting electrosprayed capsules. The results of the thermogravimetric and encapsulation efficiency analysis coincided that the incorporation of beetroot extract in G in the core and HPMC in the shell resulted in the structure with greater betalain protection. The effectiveness of the core/shell structure was confirmed for future food applications.
La difusión de la ciencia en Chile.
(1985) Illanes, Juan Pablo
Dual thinking for scientists
(2015) Scheffer, M.; Marquet, P. A. (Pablo A.)
Editorial: Open Access
(2013) Zacconi, Flavia C. M.; Arias, Hugo R.
¿ES EL OBJETO DE LA ’EΠIΣTHMH ARISTOTÉLICA SÓLO LO NECESARIO? REFLEXIONES SOBRE EL VALOR DE LO ‘ΩΣ ’EΠI TO ΠOΛϒ EN EL MODELO ARISTOTÉLICO DE CIENCIA
(2007) Boeri, Marcelo D.
Experimental and Numerical Analysis of a PCM-Integrated Roof for Higher Thermal Performance of Buildings
(2024) Pierre Simon, François; Ruíz Valero, Letzai; Girard, Aymeric; Galleguillos, Héctor; CEDEUS (Chile)
Phase change materials (PCMs) designate materials able to store latent heat. PCMs change state from solid to liquid over a defined temperature range. This process is reversible and can be used for thermo-technical purposes. The present paper aims to study the thermal performance of an inorganic eutectic PCM integrated into the rooftop slab of a test room and analyze its potential for building thermal management. The experiment is conducted in two test rooms in Antofagasta (Chile) during summer, fall, and winter. The PCM is integrated into the rooftop of the first test room, while the roof panel of the second room is a sealed air cavity. The work introduces a numerical model, which is built using the finite difference method and used to simulate the rooms’ thermal behavior. Several thermal simulations of the PCM room are performed for other Chilean locations to evaluate and compare the capability of the PCM panel to store latent heat thermal energy in different climates. Results show that the indoor temperature of the PCM room in Antofagasta varies only 21.1°C±10.6°C, while the one of the air-panel room varies 28.3°C±18.5°C. Under the experiment’s conditions, the PCM room’s indoor temperature observes smoother diurnal fluctuations, with lower maximum and higher minimum indoor temperatures than that of the air-panel room. Thermal simulations in other cities show that the PCM panel has a better thermal performance during winter, as it helps to maintain or increase the room temperature by some degrees to reach comfort temperatures. This demonstrates that the implementation of such PCM in the building envelope can effectively reduce space heating and cooling needs, and improve indoor thermal comfort in different climates of Chile.
From Nature to Representation. Science in the Southern Andes
(2017) Sagredo Baeza, Rafael
Hacia una nueva estructura para el desarrollo de la ciencia, la tecnología e innovación
(2011) Lavados, H.; Santelices, Bernabé
Historia natural: La discusión. Una revisión del concepto, el conflicto y sus ecos a la educación de las Ciencias Biológicas
(2015) Elórtegui Francioli, Sergio
Improved reconstruction of highly boosted τ -lepton pairs in the τ τ → ( μ ν μ ν τ ) ( hadrons + ν τ ) decay channels with the ATLAS detector
(2025) Aad, G.; Aakvaag, E. ; Abbott, B. ; Abdelhameed, S.; Abeling, K. ; Abicht, N.J.; Abidi, S.H.; Aboelela, M.; Aboulhorma, A.; Abramowicz, H.; Abulaiti, Y.; Acharya, B.S. ; Ackermann, A.; Adam Bourdarios, C.; Adamczyk, L. ; Addepalli, S. V.; Addison, M. J. ; Díaz, Marco A.; Garay Walls, F.M.; Urrejola, P.; ATLAS Collaboration
This paper presents a new τ -lepton reconstruction and identification procedure at the ATLAS detector at the Large Hadron Collider, which leads to significantly improved performance in the case of physics processes where a highly boosted pair of τ -leptons is produced and one τ -lepton decays into a muon and two neutrinos ( τ μ ), and the other decays into hadrons and one neutrino ( τ had ). By removing the muon information from the signals used for reconstruction and identification of the τ had candidate in the boosted pair, the efficiency is raised to the level expected for an isolated τ had . The new procedure is validated by selecting a sample of highly boosted Z → τ μ τ had candidates from the data sample of 140 fb - 1 of proton–proton collisions at 13 TeV recorded with the ATLAS detector. Good agreement is found between data and simulation predictions in both the Z → τ μ τ had signal region and in a background validation region. The results presented in this paper demonstrate the effectiveness of the τ had reconstruction with muon removal in enhancing the signal sensitivity of the boosted τ μ τ had channel at the ATLAS detector.

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