arXiv subjects

Iván Sánchez

Publications and source records attributed to Iván Sánchez.

6 recordsLinked to original sources

arXiv2024

Transitivity of some uniformities on fuzzy sets

Given a uniform space $(X, \mathcal{U})$, we denote by $\mathcal{F}(X)$ to the family of all normal upper semicontinuous fuzzy sets $u \colon X \to [0,1]$ with compact support. In this paper, we study transitivity on some uniformities on $\mathcal{F}(X)$: the level-wise uniformity $\mathcal{U}_{\infty}$, the Skorokhod uniformity $\mathcal{U}_{0}$, and the sendograph uniformity $\mathcal{U}_S$. If $f \colon (X, \mathcal{U}) \to (X, \mathcal{U})$ is a continuous function, we mainly characterize when the induced dynamical systems $\widehat{f} \colon (\mathcal{F}(X), \mathcal{U}_{\infty}) \to (\mathcal{F}(X), \mathcal{U}_{\infty})$, $\widehat{f} \colon (\mathcal{F}(X), \mathcal{U}_{0}) \to (\mathcal{F}(X), \mathcal{U}_{0})$ and $\widehat{f} \colon (\mathcal{F}(X), \mathcal{U}_{S}) \to (\mathcal{F}(X), \mathcal{U}_{S})$ are transitive, where $\widehat{f}$ is the Zadeh's extension of $f$.

math.GN↗

arXiv2022

Long-term collaboration with strong friendship ties improves academic performance in remote and hybrid teaching modalities in high school physics

Collaboration among students is fundamental for knowledge building and competency development. Yet, the effectiveness of student collaboration depends on the extent that these interactions occur under conditions that favor commitment, trust, and decision-making among those who interact. The sanitary situation and the transition to emergency remote teaching have added new challenges for collaboration, mainly because now, Information and Communication Technologies mediate students' interactions. This study first explores the effectiveness of different collaborative relationships on physics from a sample of secondary students from two schools located in rural and urban areas in southern Chile. We used Social Network Analysis to map students' academic prestige, collaboration, and friendship ties. We define a strong association if two students are declared mutually as friends. Using multiple linear regression models, we found positive effects of collaboration on grades, particularly among students working with friends (strong ties). Then, the second study corresponds to a quasi-experiment on four classes at the analyzed urban school during the following academic year. Here, students attended hybrid sessions to test whether the effects of collaboration found on the first study were stable throughout two semesters. Following the same procedures as in the exploratory phase, we found that the initial effects of collaboration on grades are negative for all collaborative variables, while strong working ties afford academic gains later into the year. These results contribute to the literature of collaboration in physics education and its effectiveness, taking into account social relationships and the needed time for developing beneficial collective processes among students in the classroom.

physics.ed-ph↗

arXiv2021

Student networks on online teaching due to COVID-19: Academic effects of strong friendship ties and perceived academic prestige in physics and mathematics courses

Collaboration among students is fundamental for knowledge building and competency development. Nonetheless, the effectiveness of student collaboration depends on the extent that these interactions take place under conditions that favor commitment, trust, and decision-making among those who interact. The sanitary situation and the transition to remote teaching has added new challenges for collaboration given that students' interactions are mediated by Information and Communication Technologies (ICTs). In this study we explore the effectiveness of different collaborative relationships on physics and mathematics, from a sample of secondary students from two schools located in rural and urban areas in southern Chile. We used Social Network Analysis (SNA) to map students' friendships relations, academic prestige, and collaboration on both courses. Later we combined the collaboration network with friendship and academic prestige on the course, to separate strong from weak friendship working ties, and those among students who enjoy or not academic prestige. Multiple linear regression models showed, on average, positive effects of collaboration on grades. Yet, when isolating the effects of the types of collaboration, the positive effects are observed only between those who display more strong friendship ties. Also, we found differences on the social networks and their effects over grades between both courses, presumably due to their pedagogical nature. With these results we contribute to the literature of collaboration and its effectiveness based on the nature of students' relationships, and advocate for the importance of instructional design in fostering appropriate motivations and guidelines for constructive collaboration in the classroom.

physics.ed-ph↗

arXiv2017

Contact angle entropy and macroscopic friction in non-cohesive two dimensional granular packings

We study the relationship between the granular contact angle distribution and local particle friction on the macroscopic friction and bulk modulus in non-cohesive disk packings. Molecular dynamics in two dimensions are used to simulate uniaxial loading-unloading cycles imposed on the granular packings. While macroscopic Mohr-friction depends on the granular pack geometric details, it reaches a stationary limit after a finite number of loading-unloading cycles that render well-defined values for bulk modulus, grain coordination, porosity, and friction. For random packings and for all polydispersities analyzed, we found that as inter-particle friction increases, the bulk modulus for the limit cycle decreases linearly, while the mean coordination number is reduced and the porosity increased, also as approximately linear functions. On the other hand, the macroscopic Mohr-friction increases in a monotonous trend with inter-particle friction. The latter result is compared to a theoretical model which assumes the existence of sliding planes corresponding to definite Mohr-friction values. The simulation results for macroscopic friction are well described by the theoretical model that incorporates the local neighbour angle distribution that can be quantified through the contact angle entropy. As local friction is increased, the limit entropy of the neighbour angle distribution is reduced, thus introducing the geometric component to granular friction. Surprisingly, once the limit cycle is reached, the Mohr-friction seem to be insensitive to polydispersity as has been recently reported.

cond-mat.soft↗

arXiv2014

Characterization of invariant patterns in a slowly rotated granular tumbler

We report experimental results of the pattern developed by a mixture of two types of grains in a triangular rotating tumbler operating in the avalanche regime. At the centroid of the triangular tumbler an invariant zone appears where the grains do not move relative to the tumbler. We characterize this invariant zone by its normalized area, $A_i$, and its circularity index as a function of the normalized filling area $A$. We find a critical filling area so that only for $A>A_c$ invariant zones are obtained. These zones scale as $A_i\sim (A-A_c)^2$ near $A_c$. We have obtained a maximum in the circularity index for $A\approx 0.8$, for which the shape of the invariant zone is closer to a circular one. The experimental results are reproduced by a simple model which, based on the surface position, accounts for all the possible straight lines within the triangle that satisfy the condition of constant $A$. We have obtained an analytic expression for the contour of the invariant zone.

cond-mat.soft↗

arXiv2010

Towards a relevant set of state variables to describe static granular packings

We analyze, experimentally and numerically, the steady states, obtained by tapping, of a 2D granular layer. Contrary to the usual assumption, we show that the reversible (steady state branch) of the density--acceleration curve is nonmonotonous. Accordingly, steady states with the same mean volume can be reached by tapping the system with very different intensities. Simulations of dissipative frictional disks show that equal volume steady states have different values of the force moment tensor. Additionally, we find that steady states of equal stress can be obtained by changing the duration of the taps; however, these states present distinct mean volumes. These results confirm previous speculations that the volume and the force moment tensor are both needed to describe univocally equilibrium states in static granular assemblies.

cond-mat.stat-mech↗