DSpace Community:

Expressões analíticas aproximadas em forma fechada para a probabilidade média de erro de símbolo da modulação QAM cruzada nos canais de desvanecimento η–μ e κ–μ

2026-03-26T06:22:23Z

Title: Expressões analíticas aproximadas em forma fechada para a probabilidade média de erro de símbolo da modulação QAM cruzada nos canais de desvanecimento η–μ e κ–μ Abstract: Introduction: Modern communication systems, such as 5G and 6G, require high reliability and low latency, but are heavily affected by channel fading, which compromises signal quality in multipath environments. Although traditional models, such as Rayleigh, Rician, and Nakagami-m, are widely used, they present limitations by assuming specific propagation conditions and failing to accurately represent the diversity of real-world scenarios, especially at millimeter-wave frequencies. To overcome these limitations, generalized models such as the η–μ and κ–μ have been proposed, offering greater flexibility by accounting for multiple dominant components and unbalanced scattering. However, the estimation of error probabilities associated with these models is essential for their practical implementation. Objectives: This work presents the derivation of approximate closed-form analytical expressions for the Average Symbol Error Probability (SEP) and investigates their performance for M-QAM modulation under generalized fading models. Materials and Methods: The adequacy of the derived expressions was analyzed considering standardized millimeter-wave frequency bands of 26, 28, 39, 55, 60, and 65 GHz. These analyses were based on channel modeling results obtained from an extensive measurement campaign in indoor environments under both Line-of-Sight (LoS) and non-Line-of-Sight (nLoS) conditions, as well as varying distances between transmitting and receiving antennas (Tx and Rx) with vertical and horizontal polarizations (VV and HV). Results: The expressions were validated through simulations performed using the MATLAB software, demonstrating strong agreement between the theoretical curves and the simulated results. The analyses revealed that line-of-sight scenarios exhibit significantly superior performance compared to nLoS cases. Furthermore, it was observed that increasing the frequency does not necessarily lead to worse performance, and that higher modulation orders require higher Eb/N0 values to achieve low error rates, highlighting the importance of employing robust coding techniques. The results contribute to a better understanding of the potential and challenges of M-QAM modulation in realistic 5G millimeter-wave communication scenarios.

Contribuições para o processo da atribuição de responsabilidade das variações de tensão de curta duração baseado nos fatores de desequilíbrio

2026-03-24T06:26:54Z

Title: Contribuições para o processo da atribuição de responsabilidade das variações de tensão de curta duração baseado nos fatores de desequilíbrio Abstract: Short-Duration Voltage Variation (SDVVs) represent significant deviations in the amplitude of the rms voltage value over a time interval shorter than three minutes. Despite their short duration, such phenomena exert substantial impacts on the quality, reliability, and safety of electrical power systems. Indeed, research studies indicate that the majority of complaints from generation, transmission, distribution agents, as well as end users, are predominantly associated with this type of disturbance. In response, the Brazilian Electricity Regulatory Agency (ANEEL), through the most recent revision of its Distribution Procedures (PRODIST), has introduced preliminary guidelines to regulate these disturbances and ensure adequate power quality levels. Within this context, the issue of identifying the agent responsible for such phenomena emerges as a motivating theme of this doctoral research. In this regard, although several publications addressing the determination of the responsible agent can be found in the literature, there is, to date, no methodology grounded on feasible procedures that enables straightforward field application. Aiming to fill this gap, a previous master’s dissertation developed within the UFU graduate program established the foundational elements of a related procedure. This approach was based on the mechanism of transferring voltage unbalance indicators through the boundary transformer between two agents, by comparing voltage unbalance factor measurements on both sides of the transformer during the occurrence of an SDVV. Notwithstanding the promising perspectives obtained, the methodology was investigated only at an embryonic stage, which motivated the continuation and expansion of the studies through the present doctoral research. Therefore, this work introduces methodological enhancements consisting of: the establishment of conceptual and mathematical foundations to support the proposed process; the extension of its applicability to topological configurations more representative of real-world power systems; and, finally, the experimental validation of the methodology. These advances, which constitute the focus of this research, enable the assessment of the reliability, robustness, and practical applicability of the proposed analytical method.

Análise Multicritério de Viabilidade de uma Fonte Emergencial Híbrida para Suprimento de Sistema de Serviços Auxiliares em Subestações de Transmissão

2026-03-13T06:20:39Z

Title: Análise Multicritério de Viabilidade de uma Fonte Emergencial Híbrida para Suprimento de Sistema de Serviços Auxiliares em Subestações de Transmissão Abstract: This thesis proposes, evaluates, and implements a solution for the emergency power supply of the auxiliary services alternating current system of high-voltage substations, aiming to enhance operational reliability and reduce regulatory impacts associated with unavailability, particularly in remote substations without internal power sources. The study is grounded in a systematic literature review, which reveals the predominance of arrangements based on diesel generator sets and the lack of integrated approaches that reconcile economic performance, reliability, and environmental criteria. Based on this assessment, a replicable techno-economic and multicriteria evaluation methodology is developed to compare four supply alternatives: a hybrid system combining battery energy storage and photovoltaic generation, an owned diesel generator set, a rented diesel generator set, and an external feeder. The economic analysis employs discounted cash flow methods (NPV, IRR, and Payback), incorporating variable penalties derived from the Annual Allowed Revenue, while the multicriteria assessment applies the TOPSIS method, integrating economic, technical, and environmental criteria. The methodology is validated through a real-world case study conducted at a Brazilian power system substation. The results indicate that the proposed hybrid solution is technically feasible and economically attractive in the medium and long term, standing out for its operational robustness, reduced dependence on fossil fuels, and superior environmental performance, without loss of economic competitiveness, while also presenting potential for scalability and replication. This thesis consolidates an original contribution by demonstrating the technical, economic, and regulatory feasibility of an implementable solution and by structuring a decision-support methodology aligned with the requirements of the Brazilian power sector.

Avaliação dos protocolos de morte encefálica

2026-03-06T06:22:17Z

Title: Avaliação dos protocolos de morte encefálica Abstract: The inherent complexity and urgency of diagnosing Brain Death (BD) constitute a persistent challenge in Intensive Care Units (ICU), representing a critical factor for the success of the National Transplant Policy (PNT). BD, defined as the irreversible cessation of all brain functions, is the legal premise of death authorizing organ removal, in accordance with Law No. 9,434/97 and CFM Resolution No. 2,173/17. The ethical and logistical imperative demands absolute celerity and safety, given that delay compromises organ viability. Furthermore, initiating the BD diagnostic protocol entails a fatal prognosis, culminating either in BD confirmation or Cardiac Arrest (PCR). With the objective of optimizing the diagnosis and the rational use of ancillary tests, such as the Electroencephalogram (EEG), this thesis sought to establish a robust predictive score capable of differentiating progression to BD from Death by Cardiac Arrest (PCR) in neurocritical patients. The study was conducted as a retrospective cohort analysis, approved by the Ethics Committee (CEP) of the Universidade Federal de Uberlândia (UFU), utilizing an Analytical Sample of N=66 patients and applying Binary Logistic Regression to identify independent predictive factors. The statistical model confirmed that the outcome is primarily determined by the initial neurovascular severity. Two clinical factors were identified as the most robust predictors for the outcome of Brain Death: the initial Glasgow Coma Scale (GCS) score and the Use of Vasoactive Drugs (DVA). The initial GCS score proved to be the strongest independent predictor (OR = 1.70; p=0.002), indicating that the BD outcome is intrinsically linked to catastrophic initial neurological injury. Complementarily, the use of DVA was a strong predictor of BD (OR = 0.04; p=0.031), as the need for pressure support (observed in approximately 95% of BD cases) is a robust marker of neurogenic shock and brainstem failure, reducing the chance of death by PCR by 96%. Univariate analyses corroborated that Traumatic Brain Injury (TBI) etiology was significantly more prevalent in the BD Group (approximately 44% vs. 0% in the PCR Group; p=0.022), reinforcing the epidemiological profile of high-impact acute lesions. Furthermore, the extremely low rate of Cardiac Arrest in the BD Group (approximately 1.7%; p<0.001) attested to the high quality of intensive clinical management, maintaining organ viability until the legal declaration of death. Regarding ancillary testing, Quantitative EEG (QEEG) analysis in selected cases demonstrated that progression to BD is marked by a profound electrophysiological disorganization, featuring an inversion in power patterns and extreme, dysregulated variability of electrical activity. This reinforces the potential of EEG, due to its non-invasive and cost-effective nature, as an ideal tool within the reality of the public health system (SUS). The main practical contribution of this thesis resides in the proposition of the Predictive Triage Model (GCS + DVA). This model allows for the quicker and more focused activation of the BD protocol and complementary examinations, particularly concentrating on EEG use. This optimization directly contributes to maintaining organ viability. In summary, the work demonstrates that the integration of methodological rigor from data science with clinical physiology establishes powerful tools to refine the diagnosis of Brain Death, ensuring the excellence and efficiency demanded by the ethical and legal imperative