Examinando por Autor "Lagos, Miguel"

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    Ítem
    Limitations of transfer learning for chilean cherry tree health monitoring: when lab results do not translate to the orchard
    (MDPI, 2025-08-13) Hidalgo, Mauricio; Yanine, Fernando; Galleguillos Silva, Renato Bruno; Lagos, Miguel; Kumar Sahoo, Sarat; Paredes, Rodrigo
    Chile, which accounts for 27% of global cherry exports (USD 2.26 billion annually), faces a critical industry challenge in crop health monitoring. While automated sensors monitor environmental variables, phytosanitary diagnosis still relies on manual visual inspection, leading to detection errors and delays. Given this reality and the growing use of AI models in agriculture, our study quantifies the theory–practice gap through comparative evaluation of three transfer learning architectures (namely, VGG16, ResNet50, and EfficientNetB0) for automated disease identification in cherry leaves under both controlled and real-world orchard conditions. Our analysis reveals that excellent laboratory performance does not guarantee operational effectiveness: while two of the three models exceeded 97% controlled validation accuracy, their field performance degraded significantly, reaching only 52% in the best-case scenario (ResNet50). These findings identify a major risk in agricultural transfer learning applications: strong laboratory performance does not ensure real-world effectiveness, creating unwarranted confidence in model performance under real conditions that may compromise crop health management.
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    Ítem
    Mathematical model for the plastic flow and ductile fracture of polycrystalline solids
    (Elsevier, 2024-01-25) Lagos, Miguel; Retamal, César; Valle, Rodrigo; Paredes, Rodrigo
    It is mathematically shown that ductile fracture after finite plastic strain is a necessary consequence of the polycrystalline nature of the materials. A closed–form equation for the plastic strain to fracture of a fine–grained polycrystal with no voids is derived. The mathematical model for the plastic deformation is grounded on the physical hypothesis that adjacent grains slide with a relative velocity proportional to the local shear stress resolved in the plane of the shared grain boundary, when exceeds a finite threshold. Hence plastic flow is governed predominantly by the in–plane shear forces making grain boundaries to slide, and the induced local forces responsible for the continuous grain reshaping are much weaker. The process is shown to produce a monotonic hydrostatic pressure variation with strain that precludes a stationary flow. The hydrostatic pressure dependence on strain has two solutions. One of them leads to superplasticity, the other one is shown to diverge logarithmically at a finite fracture strain and then represents ductile behaviour. Emphasis is done in the mathematical aspects of the deformation of the polycrystal up to the initiation of fracture. Although theoretical predictions agree well with mechanical tests of commercial alloys, technical issues like the effects of the presence and evolution of porosity and other imperfections, or how fracture evolves after initiation are left for a more specific communication.
  • Miniatura
    Ítem
    Oscillations and Waves
    (Institute of Physics (AIP) Publishing, 2024-12-01) Lagos, Miguel; Paredes, Rodrigo; Elgueta, Milton; Molina, Mario
    Oscillations and waves are prevalent in the realm of physical sciences, finding applications across a wide range of technical fields. Waves can be observed everywhere, primarily due to the fact that the lowest-energy states of most spatially extended physical systems tend to exhibit wave-like characteristics. Oscillation can be regarded as a fundamental component of wave motion. It is evident in various scenarios, such as the movement of a suspended object, subtle fluctuations in air pressure within a noisy environment, or the gentle ripples on the surface of a quiet pond. Even in more intricate systems, like the dynamics of the electromagnetic field, we consistently observe the tangible consequences of oscillations and waves. For this reason, it is highly desirable to introduce the study of physical systems governed by waves at an early stage, as it fosters a sense of comprehension regarding complex aspects of real-life phenomena. The issue at hand is that the conventional exploration of oscillations and waves requires mathematical techniques that are still unfamiliar to students at the introductory level. However, the next sections aim to provide a theoretical introduction to oscillations and waves without relying on advanced mathematics, ensuring that no physical rigor is sacrificed. The article seeks to help teachers motivate students with a special interest in science.