22 research outputs found
Wind Power Integration into Power Systems: Stability and Control Aspects
Power network operators are rapidly incorporating wind power generation into their power grids to meet the widely accepted carbon neutrality targets and facilitate the transition from conventional fossil-fuel energy sources to clean and low-carbon renewable energy sources. Complex stability issues, such as frequency, voltage, and oscillatory instability, are frequently reported in the power grids of many countries and regions (e.g., Germany, Denmark, Ireland, and South Australia) due to the substantially increased wind power generation. Control techniques, such as virtual/emulated inertia and damping controls, could be developed to address these stability issues, and additional devices, such as energy storage systems, can also be deployed to mitigate the adverse impact of high wind power generation on various system stability problems. Moreover, other wind power integration aspects, such as capacity planning and the short- and long-term forecasting of wind power generation, also require careful attention to ensure grid security and reliability. This book includes fourteen novel research articles published in this Energies Special Issue on Wind Power Integration into Power Systems: Stability and Control Aspects, with topics ranging from stability and control to system capacity planning and forecasting
Untangling hotel industry’s inefficiency: An SFA approach applied to a renowned Portuguese hotel chain
The present paper explores the technical efficiency of four hotels from Teixeira Duarte Group - a renowned Portuguese hotel chain. An efficiency ranking is established from these four hotel units located in Portugal using Stochastic Frontier Analysis. This methodology allows to discriminate between measurement error and systematic inefficiencies in the estimation process enabling to investigate the main inefficiency causes. Several suggestions concerning efficiency improvement are undertaken for each hotel studied.info:eu-repo/semantics/publishedVersio
Estimating Dependences and Risk between Gold Prices and S&P500: New Evidences from ARCH,GARCH, Copula and ES-VaR models
This thesis examines the correlations and linkages between the stock and commodity in order to quantify the risk present for investors in financial market (stock and commodity) using the
Value at Risk measure. The risk assessed in this thesis is losses on investments in stock (S&P500) and commodity (gold prices). The structure of this thesis is based on three empirical chapters. We emphasise the focus by acknowledging the risk factor which is the non-stop fluctuation in the prices of commodity and stock prices. The thesis starts by measuring volatility, then dependence which is the correlation and lastly measure the expected shortfalls and Value at risk (VaR). The research focuses on mitigating the risk using VaR measures and assessing the use of the volatility measures such as ARCH and GARCH and basic VaR calculations, we also measured the correlation using the Copula method. Since, the measures of volatility methods have limitations that they can measure single security at a time, the second empirical chapter measures the interdependence of stock and commodity (S&P500 and Gold Price Index) by investigating the risk transmission involved in investing in any of them and whether the ups and downs in the prices of one effect the prices of the other using the Time Varying copula method. Lastly, the third empirical chapter which is the last chapter, investigates the expected shortfalls and Value at Risk (VaR) between the S&P500 and Gold prices Index using the ES-VaR method proposed by Patton, Ziegel and Chen (2018). Volatility is considered to be the most popular and traditional measure of risk. For which we have used ARCH and GARCH model in our first empirical chapter. However, the problem with volatility is that it does not take into account the direction of an investments’ movement: volatility of stocks is that they suddenly jump higher and investors are not distressed with gains. When we talk about investors for them the risk is about the odds of losing money, after my research and findings VaR is based on the common-sense fact. Hence, investors care about the odds of big losses, VaR answers the question, what is my worst-case scenario? Or simply how much I could lose in a really bad month? The results of the thesis demonstrated that measuring volatility (ARCH GARCH) alone was not sufficient in measuring the risk involved in an investment therefore
methodologies such as correlation and VAR demonstrates better results. In terms of measuring the interdependence, the Time Varying Copula is used since the dynamic structure of the de-
pendence between the data can be modelled by allowing either the copula function or the dependence parameter to be time varying. Lastly, hybrid model further demonstrates the average return on a risky asset for which Expected Shortfall (ES) along with some quantile dependence and VaR (Value at risk) is utilised. Basel III Accord which is applied in coming years till 2019 focuses more on ES unlike VaR, hence there is little existing work on modelling ES. The thesis focused on the results from the model of Patton, Ziegel and Chen (2018) which is based on the statistical decision theory. Patton, Ziegel and Chen (2018), overcame the problem of elicitability for ES by using ES and VaR jointly and propose the new dynamic model of risk measure. This research adds to the contribution of knowledge that measuring risk by using volatility is not enough for measuring risk, interdependence helps in measuring the dependency of one variable over the other and estimations and inference methods proposed by Patton, Ziegel and Chen (2018) using simulations proposed in ES-VaR model further concludes that ARCH and GARCH or other rolling window models are not enough for determining the risk forecasts. The results suggest, in first empirical chapter we see volatility between Gold prices and S&P500. The second empirical chapter results suggest conditional dependence of the two indexes is strongly time varying. The correlation between the stock is high before 2008. The results further displayed slight stronger bivariate upper tail, which signifies that the conditional dependence of the indexes is influence by positive shocks. The last empirical chapter findings
proposed that measuring forecasts using ES-Var model proposed by Patton, Ziegel and Chen (2018) does outer perform forecasts based on univariate GARCH model. Investors want to 10
protect themselves from high losses and ES-VaR model discussed in last chapter would certainly help them to manage their funds properly
CLADAG 2021 BOOK OF ABSTRACTS AND SHORT PAPERS
The book collects the short papers presented at the 13th Scientific Meeting of the Classification and Data Analysis Group (CLADAG) of the Italian Statistical Society (SIS). The meeting has been organized by the Department of Statistics, Computer Science and Applications of the University of Florence, under the auspices of the Italian Statistical Society and the International Federation of Classification Societies (IFCS). CLADAG is a member of the IFCS, a federation of national, regional, and linguistically-based classification societies. It is a non-profit, non-political scientific organization, whose aims are to further classification research
ADVANCES IN SYSTEM RELIABILITY-BASED DESIGN AND PROGNOSTICS AND HEALTH MANAGEMENT (PHM) FOR SYSTEM RESILIENCE ANALYSIS AND DESIGN
Failures of engineered systems can lead to significant economic and societal losses. Despite tremendous efforts (e.g., $200 billion annually) denoted to reliability and maintenance, unexpected catastrophic failures still occurs. To minimize the losses, reliability of engineered systems must be ensured throughout their life-cycle amidst uncertain operational condition and manufacturing variability. In most engineered systems, the required system reliability level under adverse events is achieved by adding system redundancies and/or conducting system reliability-based design optimization (RBDO). However, a high level of system redundancy increases a system's life-cycle cost (LCC) and system RBDO cannot ensure the system reliability when unexpected loading/environmental conditions are applied and unexpected system failures are developed. In contrast, a new design paradigm, referred to as resilience-driven system design, can ensure highly reliable system designs under any loading/environmental conditions and system failures while considerably reducing systems' LCC.
In order to facilitate the development of formal methodologies for this design paradigm, this research aims at advancing two essential and co-related research areas: Research Thrust 1 - system RBDO and Research Thrust 2 - system prognostics and health management (PHM). In Research Thrust 1, reliability analyses under uncertainty will be carried out in both component and system levels against critical failure mechanisms. In Research Thrust 2, highly accurate and robust PHM systems will be designed for engineered systems with a single or multiple time-scale(s). To demonstrate the effectiveness of the proposed system RBDO and PHM techniques, multiple engineering case studies will be presented and discussed. Following the development of Research Thrusts 1 and 2, Research Thrust 3 - resilience-driven system design will establish a theoretical basis and design framework of engineering resilience in a mathematical and statistical context, where engineering resilience will be formulated in terms of system reliability and restoration and the proposed design framework will be demonstrated with a simplified aircraft control actuator design problem
Development of Machine Learning Techniques for Diabetic Retinopathy Risk Estimation
La retinopatia diabètica (DR) és una malaltia crònica. És una de les principals complicacions de
diabetis i una causa essencial de pèrdua de visió entre les persones que pateixen diabetis.
Els pacients diabètics han de ser analitzats periòdicament per tal de detectar signes de
desenvolupament de la retinopatia en una fase inicial. El cribratge precoç i freqüent disminueix
el risc de pèrdua de visió i minimitza la cà rrega als centres assistencials. El nombre
dels pacients diabètics està en augment i creixements rà pids, de manera que el fa difÃcil
que consumeix recursos per realitzar un cribatge anual a tots ells.
L’objectiu principal d’aquest doctorat. la tesi consisteix en construir un sistema de suport de decisions clÃniques
(CDSS) basat en dades de registre de salut electrònic (EHR). S'utilitzarà aquest CDSS per estimar el risc de desenvolupar RD.
En aquesta tesi doctoral s'estudien mètodes d'aprenentatge automà tic per constuir un CDSS basat en regles lingüÃstiques difuses. El coneixement expressat en aquest tipus de regles facilita que el metge sà piga quines combindacions de les condicions són les poden provocar el risc de desenvolupar RD.
En aquest treball, proposo un mètode per reduir la incertesa en la classificació dels
pacients que utilitzen arbres de decisió difusos (FDT). A continuació es combinen diferents arbres, usant la tècnica de
Fuzzy Random Forest per millorar la qualitat de la predicció.
A continuació es proposen diverses tècniques d'agregació que millorin la fusió dels resultats que ens dóna
cadascun dels arbres FDT. Per millorar la decisió final dels nostres models, proposo tres mesures difuses que
s'utilitzen amb integrals de Choquet i Sugeno. La definició d’aquestes mesures difuses es basa en els valors de confiança de les regles. En particular, una d'elles és una mesura difusa que es troba en la qual
l'estructura jerà rquica de la FDT és explotada per trobar els valors de la mesura difusa.
El resultat final de la recerca feta ha donat lloc a un programari que es pot instal·lar en centres d’assistència primà ria i hospitals, i pot ser usat pels metges de capçalera per fer l'avaluació preventiva i el cribatge de la Retinopatia Diabètica.La retinopatÃa diabética (RD) es una enfermedad crónica. Es una de las principales complicaciones de
diabetes y una causa esencial de pérdida de visión entre las personas que padecen diabetes.
Los pacientes diabéticos deben ser examinados periódicamente para detectar signos de diabetes.
desarrollo de retinopatÃa en una etapa temprana. La detección temprana y frecuente disminuye
el riesgo de pérdida de visión y minimiza la carga en los centros de salud. El número
de pacientes diabéticos es enorme y está aumentando rápidamente, lo que lo hace difÃcil y
Consume recursos para realizar una evaluación anual para todos ellos.
El objetivo principal de esta tesis es construir un sistema de apoyo a la decisión clÃnica
(CDSS) basado en datos de registros de salud electrónicos (EHR). Este CDSS será utilizado
para estimar el riesgo de desarrollar RD.
En este tesis doctoral se estudian métodos de aprendizaje automático para construir un CDSS basado
en reglas lingüÃsticas difusas. El conocimiento expresado en este tipo de reglas facilita que el médico
pueda saber que combinaciones de las condiciones son las que pueden provocar el riesgo de desarrollar RD.
En este trabajo propongo un método para reducir la incertidumbre en la clasificación de los
pacientes que usan árboles de decisión difusos (FDT). A continuación se combinan diferentes árboles usando
la técnica de Fuzzy Random Forest para mejorar la calidad de la predicción.
Se proponen también varias polÃticas para fusionar los resultados de que nos da cada uno de los árboles (FDT).
Para mejorar la decisión final propongo tres medidas difusas que se usan con las integrales Choquet y Sugeno.
La definición de estas medidas difusas se basa en los valores de confianza de
las reglas. En particular, uno de ellos es una medida difusa descomponible en la que se usa
la estructura jerárquica del FDT para encontrar los valores de la medida difusa.
Como resultado final de la investigación se ha construido un software que puede instalarse en centros de atención médica y hospitales, i que puede ser usado por los médicos de cabecera para hacer la evaluación preventiva y
el cribado de la RetinopatÃa Diabética.Diabetic retinopathy (DR) is a chronic illness. It is one of the main complications of
diabetes, and an essential cause of vision loss among people suffering from diabetes.
Diabetic patients must be periodically screened in order to detect signs of diabetic
retinopathy development in an early stage. Early and frequent screening decreases
the risk of vision loss and minimizes the load on the health care centres. The number
of the diabetic patients is huge and rapidly increasing so that makes it hard and
resource-consuming to perform a yearly screening to all of them.
The main goal of this Ph.D. thesis is to build a clinical decision support system
(CDSS) based on electronic health record (EHR) data. This CDSS will be utilised
to estimate the risk of developing RD.
In this Ph.D. thesis, I focus on developing novel interpretable machine learning
systems. Fuzzy based systems with linguistic terms are going to be proposed. The
output of such systems makes the physician know what combinations of the features
that can cause the risk of developing DR.
In this work, I propose a method to reduce the uncertainty in classifying diabetic
patients using fuzzy decision trees. A Fuzzy Random forest (FRF) approach is
proposed as well to estimate the risk for developing DR.
Several policies are going to be proposed to merge the classification results
achieved by different Fuzzy Decision Trees (FDT) models to improve the quality of
the final decision of our models, I propose three fuzzy measures that are used with Choquet and Sugeno integrals.
The definition of these fuzzy measures is based on the confidence values of
the rules. In particular, one of them is a decomposable fuzzy measure in which the
hierarchical structure of the FDT is exploited to find the values of the fuzzy measure.
Out of this Ph.D. work, we have built a CDSS software that may be installed in the health care centres and hospitals
in order to evaluate and detect Diabetic Retinopathy at early stages
Forecasting: theory and practice
Forecasting has always been in the forefront of decision making and planning.
The uncertainty that surrounds the future is both exciting and challenging,
with individuals and organisations seeking to minimise risks and maximise
utilities. The lack of a free-lunch theorem implies the need for a diverse set
of forecasting methods to tackle an array of applications. This unique article
provides a non-systematic review of the theory and the practice of forecasting.
We offer a wide range of theoretical, state-of-the-art models, methods,
principles, and approaches to prepare, produce, organise, and evaluate
forecasts. We then demonstrate how such theoretical concepts are applied in a
variety of real-life contexts, including operations, economics, finance,
energy, environment, and social good. We do not claim that this review is an
exhaustive list of methods and applications. The list was compiled based on the
expertise and interests of the authors. However, we wish that our encyclopedic
presentation will offer a point of reference for the rich work that has been
undertaken over the last decades, with some key insights for the future of the
forecasting theory and practice
Soft Computing
Soft computing is used where a complex problem is not adequately specified for the use of conventional math and computer techniques. Soft computing has numerous real-world applications in domestic, commercial and industrial situations. This book elaborates on the most recent applications in various fields of engineering
Soft Computing
Soft computing is used where a complex problem is not adequately specified for the use of conventional math and computer techniques. Soft computing has numerous real-world applications in domestic, commercial and industrial situations. This book elaborates on the most recent applications in various fields of engineering