Browsing by Author "Garcia, Cristian"

Now showing 1 - 8 of 8
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    An Overview of Microgrids Challenges in the Mining Industry
    (2020) Gómez, Juan S.; Rodriguez, Jose; Garcia, Cristian; Tarisciotti, Luca; Flores-Bahamonde, Freddy; Pereda Torres, Javier Eduardo; Nuñez Retamal, Felipe Eduardo; Cipriano, Aldo; Salas, Juan Carlos
    The transition from fossil fuels to renewable energies as power sources in the heavy industries is one of the main climate change mitigation strategies. The carbon footprint in mining is related to its inherent extraction process, its high demand of electric power and water, and the use of diesel. However, considering its particular power requirements, the integration of microgrids throughout the whole control hierarchy of mining industry is an emergent topic. This paper provides an overview of the opportunities and challenges derived from the synergy between microgrids and the mining industry. Bidirectional and optimal power flow, as well as the integration of power quality have been identified as microgrid features that could potentially enhance mining processes. Recommendations pertaining to the technological transition and the improvement of energy issues in mining environments are also highlighted in this work.
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    Early Obesity: Risk Factor for Fatty Liver Disease
    (LIPPINCOTT WILLIAMS & WILKINS, 2020) Cuzmar, Valeriau; Alberti, Gigliola; Uauy, Ricardo; Pereira, Ana; Garcia, Cristian; De Barbieri, Florencia; Corvalan, Camila; Santos, Jose L.; Mericq, Veronica; Villarroel, Luis; Gana, Juan Cristobal
    Nonalcoholic fatty liver disease (NAFLD), defined as fat accumulation greater than 5% in hepatocytes, may progress to fibrosis or cirrhosis later in life. NAFLD prevalence in adolescents has increased significantly in direct relation with obesity prevalence. Fatty liver has become the most frequent indication for liver transplantation in adults. Objective: The aim of the study was to identify anthropometric variables during the first 10 years of life associated to the risk of developing NAFLD in adolescence. Methods: Longitudinal cohort study 'Growth and Obesity Chilean Cohort Study' (GOCS) consisting of 513 children born in 2002 to 2003, with yearly anthropometric data collected over a 10-year period. The presence of intrahepatic fat in the livers of subjects 14 to 16 years of age was determined using abdominal ultrasound. In addition, elastography was performed on all participants with ultrasound evidence of NAFLD. Results: 9.7% of the participants presented findings compatible with NAFLD. After 2 years of age, obesity significantly and progressively increased the probability of NAFLD occurrence in adolescence. Obesity at 5 years of age was associated with the highest OR for NAFLD, reaching values of 8.91 (95% CI 3.03-16.11). Among participants with NAFLD, those with altered liver elasticity (>= 7 kPa) had greater weight, BMIz-score, waist and hip circumference, and altered liver enzymes (P < 0.05). Conclusion: The risk of developing NAFLD in adolescence increases progressively with early obesity starting at age 2 years.
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    Infantile/Capillary Hemangioma of the Uterine Corpus: A Rare Cause of Abnormal Genital Bleeding
    (2022) Ralph, Constanza; Cuello, Mauricio A.; Merino, Paulina M.; De Barbieri, Florencia M.; Astudillo, Katya; Huete, Alvaro; Garcia, Cristian; Pomes, Cristian
    Background: Infantile hemangiomas are vascular anomalies. However, they rarely cause genital bleeding. Here, we present the case of a young female with an endocavitary hemangioma who presented with abnormal uterine bleeding (AUB).Case: The patient was an 8-year-old female with genital bleeding. Transabdominal pelvic ultrasound showed a 20-mm highly vascularized focal intrauterine endocavitary lesion. Vascular computerized tomography excluded vascular anomalies. Magnetic resonance imaging sug-gested a hemangioma. Minimally invasive open surgery was performed to remove the lesion. Subsequent pathology analyses confirmed an infantile/capillary hemangioma. Conclusions: Infantile hemangiomas are vascular anomalies that should be considered potential causes of AUB in early puberty. The study of these cases should include pelvic ultrasound and vascular magnetic resonance imaging. Experienced surgeons can successfully accomplish fertility-sparing surgical procedures. Summary: We describe an unusual case of peripubertal AUB caused by an endocavitary capillary hemangioma. Management included fertility-sparing surgery and the complete resolution of symptoms.
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    Model Predictive Control in Multilevel Inverters Part I: Basic Strategy and Performance Improvement
    (2024) Garcia, Cristian; Mora, Andres; Norambuena, Margarita; Rodriguez, Jose; Aly, Mokhtar; Carnielutti, Fernanda; Pereda, Javier; Acuna, Pablo; Aguilera, Ricardo; Tarisciotti, Luca
    Multilevel inverters (MLIs) have lately become important due to their extended application to electrical transmission and distribution systems. At the same time, the control and modulation of MLIs are especially challenging due to the high number of switching states, many of them redundant in terms of output voltage generation, and their nonlinear characteristics. In order to ease their implementation in real environment, model predictive control (MPC) is often considered, where the main control targets are: 1) to generate a the desired output current and 2) to keep the internal converter capacitor voltages at their reference value. However, a major issue with the implementation of MPC in MLIs is that the number of calculations to be done online increases dramatically with the number of levels, making it almost impossible to apply MPC in some practical cases. For these reasons, one of the main research trend in MPC for MLIs is to provide an algorithm which can reduce the computational burden necessary to operate the control. The article proposes a review of such control techniques. Starting from the basic MPC implementation and using a flying capacitor converter as an example the article review the basic strategies to avoid calculating the weighting factor in the cost function, simplifying the implementation. Also, methods to reduce the number of calculations necessary to implement MPC are shown and applied to cascaded H-bridge converters. These techniques allow to keep an high load current quality while reducing more than 95% in the number of calculations necessary to implement the control. Finally, other operation improvements of MPC are also included, such as fixed switching frequency operation and multistep MPC, reaching an important performance improvement compared to the basic MPC strategy.
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    Model Predictive Control in Multilevel Inverters Part II: Renewable Energies and Grid Applications
    (2024) Norambuena, Margarita; Mora, Andres; Garcia, Cristian; Rodriguez, Jose; Aly, Mokhtar; Carnielutti, Fernanda; Pereda, Javier; Castillo, Cristian; Zhang, Zhenbin; Yaramasu, Venkata; Tarisciotti, Luca; Yin, Yafei
    This article presents the use of model predictive control (MPC) in multilevel inverters for some applications, such as, first, wind generation and, second, photovoltaics, showing that the particular restrictions of each of them can be very easily included in the control algorithm, which is an important advantage of this technique. Another application is in modular multilevel cascaded converters, where it is demonstrated that MPC can operate with very few calculations and fixed switching frequency. The second part of this article is dedicated to comparing MPC with linear control and pulsewidth modulation for multilevel inverters. The main comparison criteria are the switching losses, the distortion in the load current, and the number of commutations. The main conclusion is that MPC is a competitive alternative to linear control for application in multilevel inverters.
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    Osteoporosis in children with severe congenital neutropenia: Bone mineral density and treatment with bisphosphonates
    (LIPPINCOTT WILLIAMS & WILKINS, 2006) Borzutzky, Arturo; Reyes, Maria Loreto; Figueroa, Valeria; Garcia, Cristian; Cavieres, Mirta
    A high incidence of decreased bone mineral density (BMD) has been described in patients with severe congenital neutropenia (SCN). The objectives of the study are to describe changes in BMD in children with SCN treated with granulocyte colony-stimulating factor and evaluate the response to treatment with bisphosphonates in those two had osteoporosis. A prospective open-label study was performed evaluating BMD and metabolism in 9 Chilean patients with SCN, administrating bisphosphonates in those with osteoporosis. Follow-up ranged between 7 months and 3.5 years. Six out of 9 patients had reduced BMD on initial assessment: 3 had osteoporosis (z score < - 2) and 3, had osteopenia (z score < - 1). Four children presented vertebral fractures. Two presented osteopenia on follow-up without Clinical Symptoms. Five patients were treated with biphosphonates, increasing their BMD z Score (mean increase 1.2. range 0.27 to 2.62). z Score of hydroxyproline/ creatinine ratios, which was elevated in 4 patients with osteoperosis, decreases during treatment (mean decrease 2.18, range 1.56 to 2.53). Four patients remodeled and reexpanded fractured vertebrae during treatment. No side effects of bisphosphonate were seen on follow-up. Osteoporosis is an important comorbidity in SCN patients probably due to an increased bone resorption. Bisphosphonates seem to be an effective treatment for osteoporosis in these patients.
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    Predictive Control for Current Distortion Mitigation in Mining Power Grids
    (2023) Gomez, Juan S. S.; Navas-Fonseca, Alex; Flores-Bahamonde, Freddy; Tarisciotti, Luca; Garcia, Cristian; Nunez, Felipe; Rodriguez, Jose; Cipriano, Aldo Z. Z.
    Current distortion is a critical issue of power quality because the low frequency harmonics injected by adjustable speed drives increase heating losses in transmission lines and induce torque flickering in induction motors, which are widely used in mining facilities. Although classical active filtering techniques mitigate the oscillatory components of imaginary power, they may not be sufficient to clean the sensitive nodes of undesirable power components, some of which are related to real power. However, the usage of power electronic converters for distributed generation and energy storage, allows the integration of complementary power quality control objectives in electrical systems, by using the same facilities required for active power transferring. This paper proposes a predictive control-based scheme for mitigating the current distortion in the coupling node between utility grid and the mining facility power system. Instead of the classical approach of active filtering, this task is included as a secondary level objective control referred into the microgrid control hierarchy. Hardware-in-the-Loop simulation results showed that the proposed scheme is capable of bounding the current distortion, according to IEEE standard 1547, for both individual harmonics and the total rated current distortion, through inequality constraints of the optimization problem.
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    Two Decades of Thyroid Nodule Cytology in Children: Malignancy Risk Assessment at a Tertiary Care Center
    (2024) Pino, Consuelo; Dominguez, Jose Miguel; Solar, Antonieta; Zoroquiain, Pablo; Cruz, Francisco; Garcia, Cristian; De Barbieri, Florencia; Mosso, Lorena; Lustig, Nicole; Gonzalez, Hernan; Leon, Augusto; Goni, Ignacio; Contreras, Andy; Grob, Francisca
    Introduction: Pediatric thyroid nodules exhibit higher malignancy rates compared to adults and are associated with increased incidences of metastases and recurrences. The American Thyroid Association recommends surgery for indeterminate thyroid biopsies in children based on these higher malignancy risks, though this approach may lead to overtreatment. However, there remains a lack of comprehensive pediatric data to inform clinical decisions. This study examines the risk of malignancy (ROM) in pediatric thyroid nodules using the Bethesda System for Reporting Thyroid Cytopathology (TBSRTC) and assesses the diagnostic accuracy of fine-needle aspiration (FNA) biopsy compared to histological outcomes. Methods: A retrospective cross-sectional analysis was performed on patients under 19 years with thyroid nodules who underwent FNA and thyroidectomy at a tertiary care center. The sensitivity, specificity, positive predictive value, negative predictive value, and ROM of cytological biopsies were evaluated using TBSRTC criteria, with histology serving as the gold standard. Two analyses were conducted to assess diagnostic accuracy: (a) TBSRTC II as negative and TBSRTC VI as positive and (b) TBSRTC II as negative with TBSRTC V and VI as positive. For neoplasia detection, TBSRTC II was deemed negative, while TBSRTC IV, V, and VI were considered positive. TBSRTC categories III and I were excluded from the performance analysis and evaluated separately. Follicular neoplasm or lesions suspicious for follicular neoplasm (FN/SFN) were treated as positive outcomes, correlated with the presence of adenoma or carcinoma in the surgical specimen. Results: Of 75 nodules from 73 patients, 28 (37.3%) were benign and 47 (62.6%) malignant. No significant differences in gender or age were noted between groups. The ROM in each TBSRTC was Bethesda I 0/2, 0%; II 0/13, 0%; III 2/7, 29%: IV 6/14, 43%; V 10/10, 100%, and VI 29/29, 100%. A sensitivity of 78.38% and specificity of 100% for FNA in detecting malignancy was found, with an even higher sensitivity (100%) for detecting neoplasia in TBSRTC IV. Conclusions: This study reveals that indeterminate thyroid nodules in pediatric patients exhibit a higher rate of malignancy compared to adults, yet align with rates previously reported in the pediatric population. These findings highlight the critical need for guidelines tailored specifically to the management of thyroid nodules and thyroid cancer in children.