Models for determining a portfolio of investment decisions in risky assets have been at the forefront of financial research for almost a century. Among the celebrated researchers are Harry Markowitz and William Ziemba...
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Models for determining a portfolio of investment decisions in risky assets have been at the forefront of financial research for almost a century. Among the celebrated researchers are Harry Markowitz and William Ziemba. These titans devoted their working years to developing quantitative models and adapting the models to changes in financial markets and investor attitudes. This paper presents a general lens through which the Markowitz mean-variance model and the Ziemba capital growth model can be viewed. This lens is risk-sensitive stochastic control. The optimal control approach places the expected utility, mean-variance, and capital growth models in a common setting to elucidate their connection. In particular, benchmarking and risk factors, two standard refinements to control risk, are seamlessly incorporated into the stochastic control model. The solution to the risk-sensitive control problem isolates the effect of benchmarks and factors to provide insights into model-based portfolios.
This paper addresses a multi-period emergency facility location-routing problem, in which the uncertainties in material demands and transportation time, as well as dynamic inventory replenishment and carryover are inc...
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This paper addresses a multi-period emergency facility location-routing problem, in which the uncertainties in material demands and transportation time, as well as dynamic inventory replenishment and carryover are incorporated in the design of multi-level emergency logistics networks. To measure the risks stemming from uncertain transportation time, mean-CVaR method is used. Then, a risk-averse stochastic programming model for the presented problem is formulated to minimize the total rescue time of the network. Moreover, a genetic algorithm is developed to solve the proposed model. Extensive numerical experiments including the randomly generated instances and a case study on the Wenchuan earthquake in China are conducted to verify the effectiveness of the presented model and algorithm. Experimental results show that the genetic algorithm significantly performs better than the Gurobi solver in terms of both solution quality and solution time.
This paper presents a bi-level approach to support retailers in making investment decisions in renewable -based systems to provide clean electricity. The proposed model captures the strategic nature of the problem and...
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This paper presents a bi-level approach to support retailers in making investment decisions in renewable -based systems to provide clean electricity. The proposed model captures the strategic nature of the problem and combines capacity sizing decisions for installed technologies with pricing decisions regarding the electricity tariffs to offer to a reference end -user, representative of a class of residential prosumers. The interaction between retailer and end -user is modeled using the Stackelberg game framework, with the former acting as a leader and the latter as follower. The reaction of the follower to the electricity tariff affects the retailer's profit, which is calculated as the difference between the revenue generated from selling electricity and the total investment, operation and management costs. To account for uncertainty in wholesale electricity prices, renewable resource availability and electricity request, the upper -level problem is formulated as a two -stage stochastic programming model. First -stage decisions refer to the sizing of installed technologies and electricity tariffs, whereas second -stage decisions refer to the operation and management of the designed system. The model also incorporates a safety measure to control the average profit that can be achieved in a given percentage of worst -case situations, thus providing a contingency against unforeseen changes. At the lower level, the follower reacts to the offered tariffs by defining the procurement plan in terms of energy to purchase from the retailer or potential competitors, with the final aim of minimizing the expected value of the electricity bill. A tailored approach that exploits the specific problem structure is designed to solve the proposed formulation and extensively tested on a realistic case study. The numerical results demonstrate the efficiency of the proposed approach and validate the significance of explicitly dealing with the uncertainty and the importance of incorporat
Optimising rainwater harvesting (RWH) systems' design involves sizing the storage and catchment areas enhance cost-effectiveness, self-sufficiency, and water quality indicators. This paper considers the design RWH...
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Optimising rainwater harvesting (RWH) systems' design involves sizing the storage and catchment areas enhance cost-effectiveness, self-sufficiency, and water quality indicators. This paper considers the design RWH systems under long-term uncertainty in precipitation and demands. In this work, we formulate and solve a multi-objective stochastic optimisation problem that allows explicit trade-offs under uncertainty, maximising system efficiency and minimising deployment cost. We use the yield after spillage (YAS) approach to incorporate the physical and operational constraints and the big-M method to reformulate the nonlinear min\max rules of this approach as a mixed-integer linear programming (MILP) problem. By posing a risk averseness measure on efficiency as a conditional value at risk (CVaR) formulation, we guarantee the designer against the highest demand and driest weather conditions. We then exploit the lexicographic method effectively solve the multi-objective stochastic problem as a sequence of equivalent single-objective problems. detailed case study of a botanical garden in Amsterdam demonstrates the framework's practical application;we show significant improvements in system efficiency of up to 15.5% and 28.9% in the driest scenarios under risk neutral and risk-averse conditions, respectively, compared to deterministic approaches. The findings highlight the importance of taking into account multiple objectives and uncertainties when designing RWH systems, allowing designers to optimise efficiency and costs based on their specific requirements without extensive parameterisation.
Uncertain factors can significantly reduce the applicability of production plans and the production stability of enterprises. Therefore, considering the uncertain factors caused by external demands and internal capabi...
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Community resilience planning is challenging as it involves several large-scale systems with interdependency, populations with diverse socio-economic characteristics, and numerous stakeholders. This study introduces a...
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Community resilience planning is challenging as it involves several large-scale systems with interdependency, populations with diverse socio-economic characteristics, and numerous stakeholders. This study introduces a new optimization model to decrease a community's burden in developing viable alternative sets of decisions while considering costs and risks associated with uncertain hazard events. The model captures the essential features of a community, and its scope extends beyond infrastructure and buildings to include social goals. Structural engineering and social science approaches are adapted and incorporated into the model formulation to facilitate the identification of engineering decisions meeting the social goals of minimizing population dislocation and time for recovery. A risk-averse approach frames the optimization problem as a two-stage mean-risk stochastic programming model, which enables effective planning for low-probability, high-consequence hazard events. A case study simulating flood hazards in Lumberton, North Carolina, is developed, and the model is run with the generated data set to showcase the model's capability in developing risk-informed mitigation and recovery plans to achieve resilience goals. The insights drawn from the numerical experiments show the effect of changing risk preference on community resilience metrics.
We develop a Design and Analysis of the Computer Experiments (DACE) approach to the stochastic unit commitment problem for power systems with significant renewable integration. For this purpose, we use a two-stage sto...
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We develop a Design and Analysis of the Computer Experiments (DACE) approach to the stochastic unit commitment problem for power systems with significant renewable integration. For this purpose, we use a two-stage stochastic programming formulation of the stochastic unit commitment-economic dispatch problem. Typically, a sample average approximation of the true problem is solved using a cutting plane method (such as the L-shaped method) or scenario decomposition (such as Progressive Hedging) algorithms. However, when the number of scenarios increases, these solution methods become computationally prohibitive. To address this challenge, we develop a novel DACE approach that exploits the structure of the first-stage unit commitment decision space in a design of experiments, uses features based upon solar generation, and trains a multivariate adaptive regression splines model to approximate the second stage of the stochastic unit commitment-economic dispatch problem. We conduct experiments on two modified IEEE-57 and IEEE-118 test systems and assess the quality of the solutions obtained from both the DACE and the L-shaped methods in a replicated procedure. The results obtained from this approach attest to the significant improvement in the computational performance of the DACE approach over the traditional L-shaped method.
Nowadays, many countries view profitable telemedicine as a viable strategy for meeting healthcare needs, especially during the pandemic. Existing appointment models are based on patients' structured data. We study...
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Nowadays, many countries view profitable telemedicine as a viable strategy for meeting healthcare needs, especially during the pandemic. Existing appointment models are based on patients' structured data. We study the value of incorporating textual patient data into telemedicine appointment optimization. Our research contributes to the healthcare operations management literature by developing a new framework showing (1) the value of the text in the telemedicine appointment problem, (2) the value of incorporating the textual and structured data in the problem. In particular, in the first phase of the framework, a text-driven classification model is developed to classify patients into normal and prolonged service time classes. In the second phase, we integrate the classification model into two existing decision-making policies. We analyze the performance of our proposed policy in the presence of existing methods on a data set from the National Telemedicine Center of China (NTCC). We first show that our classifier can achieve 90.4% AUC in a binary task based on textual data. We next show that our method outperforms the stochastic model available in the literature. In particular, with a slight change of actual distribution from historical data to a normal distribution, we observe that our policy improves the average profit of the policy obtained from the stochastic model by 42% and obtains lower relative regret (18%) from full information than the stochastic model (148%). Furthermore, our policy provides a promising trade-off between the cancellation and postponement rates of patients, resulting in a higher profit and a better schedule strategy for the telemedicine center.
In addressing the challenges of last-mile logistics, the reliability of the supply chain network becomes paramount. These challenges are intensified due to drone performance limitations and various uncertainties in su...
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In addressing the challenges of last-mile logistics, the reliability of the supply chain network becomes paramount. These challenges are intensified due to drone performance limitations and various uncertainties in supply chain operations. While recent literature recognises the potential of drones for last-mile delivery, it falls short in effectively considering these uncertainties in drone-enabled supply chain models. Our research addresses this gap with two major contributions: first, a novel stochastic mixed-integer programming model is developed to construct a feasible delivery network, including warehouses and recharging stations, enhancing both coverage and reliability. Second, a modification in the genetic algorithm by considering each scenario independently improves computational efficiency, outperforming commercial software by an average of 40% and up to 55%. Empirical findings reveal that strategic investments in system hardening can yield substantial improvements in reliability. Despite the absence of real-world stochastic parameters as a limitation, this research pioneers the design of reliable networks under uncertainties and extends drone coverage through strategic charging stations. This work sets a significant milestone for future optimization in drone logistics, offering practical implications for supply chain managers considering drone adoption.
District heating (DH) systems are an important component in the EU strategy to reach the emission goals, since they allow an efficient supply of heat while using the advantages of sector coupling between different ene...
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District heating (DH) systems are an important component in the EU strategy to reach the emission goals, since they allow an efficient supply of heat while using the advantages of sector coupling between different energy carriers such as power, heat, gas and biomass. Most DH systems use several different types of units to produce heat for hundreds or thousands of households (e.g. natural gas-fired boilers, electric boilers, biomass-fired units, waste heat from industry, solar thermal units). Furthermore, combined heat and power units units are often included to use the synergy effects of excess heat from electricity production. To address the challenge of providing optimization tools for a vast variety of different system configurations, we propose a generic mixed-integer linear programming formulation for the operational production optimization in DH systems. The model is based on a network structure that can represent different system setups while the underlying model formulation stays the same. Therefore, the model can be used for most DH systems although they might use different combinations of technologies in different system layouts. The mathematical formulation is based on stochastic programming to account for the uncertainty of energy prices and production from non-dispatchable units such as waste heat and solar heat. Furthermore, the model is easily adaptable to different application cases in DH systems such as operational planning, bidding to electricity markets and long-term evaluation. We present results from three real cases in Denmark with different requirements.
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