•Flexibility in CLSCN design to cover demands and returns based on market conditions.•A novel hybrid robust-stochastic programming approach.•Scenario generation using Latin Hypercube Sampling with ...backward reduction.•Accelerated Benders decomposition with valid inequalities and Pareto-optimal cuts.
Environmental, social and economic concerns motivate the operation of closed-loop supply chain networks (CLSCN) in many industries. We propose a novel profit maximization model for CLSCN design as a mixed-integer linear program in which there is flexibility in covering the proportions of demand satisfied and returns collected based on the firm's policies. Our major contribution is to develop a novel hybrid robust-stochastic programming (HRSP) approach to simultaneously model two different types of uncertainties by including stochastic scenarios for transportation costs and polyhedral uncertainty sets for demands and returns. Transportation cost scenarios are generated using a Latin Hypercube Sampling method and scenario reduction is applied to consolidate them. An accelerated stochastic Benders decomposition algorithm is proposed for solving this model. To speed up the convergence of this algorithm, valid inequalities are introduced to improve the lower bound quality, and also a Pareto-optimal cut generation scheme is used to strengthen the Benders optimality cuts. Numerical studies are performed to verify our mathematical formulation and also demonstrate the benefits of the HRSP approach. The performance improvements achieved by the valid inequalities and Pareto-optimal cuts are demonstrated in randomly generated instances.
We optimize the design of a closed-loop supply chain network that encompasses flows in both forward and reverse directions and is subject to uncertainty in demands for both new and returned products. ...The model also accommodates a carbon tax with tax rate uncertainty. The proposed model is a three-stage hybrid robust/stochastic program that combines probabilistic scenarios for the demands and return quantities with uncertainty sets for the carbon tax rates. The first stage decisions are facility investments, the second stage concerns the plan for distributing new and collecting returned products after realization of demands and returns, and the numbers of transportation units of various modes are the third stage decisions. The second- and third-stage decisions may adjust to the realization of the carbon tax rate. For computational tractability, we restrict them to be affine functions of the carbon tax rate. Benders cuts are generated using recent duality developments for robust linear programs. Computational results show that adjusting product flows to the tax rate provides negligible benefit, but the ability to adjust transportation mode capacities can substitute for building additional facilities as a way to respond to carbon tax uncertainty.
This paper proposes a novel method to co-optimize the distribution system operation and repair crew routing for outage restoration after extreme weather events. A two-stage stochastic mixed integer ...linear program is developed. The first stage is to dispatch the repair crews to the damaged components. The second stage is distribution system restoration using distributed generators, and reconfiguration. We consider demand uncertainty in terms of a truncated normal forecast error distribution, and model the uncertainty of the repair time using a lognormal distribution. A new decomposition approach, combined with the progressive hedging algorithm, is developed for solving large-scale outage management problems in an effective and timely manner. The proposed method is validated on modified IEEE 34- and 8500-bus distribution test systems.
Reaction discovery using
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-heterocyclic carbene organocatalysis has been dominated by the chemistry of acyl anion equivalents. Recent studies demonstrate that NHCs are far more diverse catalysts, ...with a variety of reactions discovered that proceed without acyl anion equivalent formation. In this tutorial review selected examples of acyl anion free NHC catalysis using carbonyl compounds are presented.
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-Heterocyclic carbenes are powerful nucleophilic catalysts that catalyse a range of reactions that occur
without
acyl anion equivalent formation.
We develop a tri-level model of transmission and generation expansion planning in a deregulated power market environment. Due to long planning/construction lead times and concerns for network ...reliability, transmission expansion is considered in the top level as a centralized decision. In the second level, multiple decentralized GENCOs make their own capacity expansion decisions while anticipating a wholesale electricity market equilibrium in the third level. The collection of bi-level games in the lower two levels forms an equilibrium problem with equilibrium constraints (EPEC) that can be approached by either the diagonalization method (DM) or a complementarity problem (CP) reformulation. We propose a hybrid iterative solution algorithm that combines a CP reformulation of the tri-level problem and DM solutions of the EPEC sub-problem.
A challenging aspect of applying stochastic programming in a dynamic setting is to construct a set of discrete scenarios that well represents multivariate stochastic processes for uncertain ...parameters. Often this is done by generating a scenario tree using a statistical procedure and then reducing its size while maintaining its statistical properties. In this paper, we test a new scenario reduction heuristic in the context of long-term power generation expansion planning. We generate two different sets of scenarios for future electricity demands and fuel prices by statistical extrapolation of long-term historical trends. The cardinality of the first set is controlled by employing increasing length time periods in a tree structure while that of the second set is limited by its lattice structure with periods of equal length. Nevertheless, some method of scenario thinning is necessary to achieve manageable solution times. To mitigate the computational complexity of the widely-used forward selection heuristic for scenario reduction, we customize a new heuristic scenario reduction method named forward selection in wait-and-see clusters (FSWC) for this application. In this method, we first cluster the scenarios based on their wait-and-see solutions and then apply fast forward selection within clusters. Numerical results for a twenty year generation expansion planning case study indicate substantial computational savings to achieve similar solutions as those obtained by forward selection alone.
Cognitive flexibility is an executive functioning skill that develops in childhood, and when impaired, has transdiagnostic implications for psychiatric disorders. To identify how intrinsic neural ...architecture at rest is linked to cognitive flexibility performance, we used the data-driven method of Independent Components Analysis (ICA) to investigate resting state networks (RSNs) and their whole-brain connectivity associated with levels of cognitive flexibility performance in children. We hypothesized differences by cognitive flexibility performance in RSN connectivity strength in cortico-striatal circuitry, which would manifest via the executive control network, right and left frontoparietal networks (FPN), salience network, default mode network (DMN), and basal ganglia network. We selected participants from the Adolescent Brain Cognitive Development (ABCD) Study who scored at the 25th, (“CF-Low”), 50th (“CF-Average”), or 75th percentiles (“CF-High”) on a cognitive flexibility task, were early to middle puberty, and did not exhibit significant psychopathology (n = 967, 47.9% female; ages 9–10). We conducted whole-brain ICA, identifying 14 well-characterized RSNs. Groups differed in connectivity strength in the right FPN, anterior DMN, and posterior DMN. Planned comparisons indicated CF-High had stronger connectivity between right FPN and supplementary motor/anterior cingulate than CF-Low. CF-High had more anti-correlated connectivity between anterior DMN and precuneus than CF-Average. CF-Low had stronger connectivity between posterior DMN and supplementary motor/anterior cingulate than CF-Average. Post-hoc correlations with reaction time by trial type demonstrated significant associations with connectivity. In sum, our results suggest childhood cognitive flexibility performance is associated with DMN and FPN connectivity strength at rest, and that there may be optimal levels of connectivity associated with task performance that vary by network.
•We investigated resting state networks associated with cognitive flexibility.•Using Independent Components Analysis, 14 resting state networks identified.•Cognitive flexibility performance is associated with DMN, FPN connectivity strength.•Connectivity strength with networks differed in regions linked to shifting tasks.•Future studies can determine how these circuits may give rise to psychopathology.
Sequencing decisions in mixed-model assembly lines are complicated by various uncertainty factors. This paper addresses a real-life uncertainty factor identified in a manufacturer of large vehicles, ...by modelling unreliable part delivery and quality. Stochastic optimisation is applied to find sequencing policies that improve the on-time performance of its mixed-model assembly lines. As schedulers have different levels of risk aversion, a risk-averse programme is further presented to protect against the decision maker's chosen fraction of worst scenarios. Computational studies with Progressive Hedging as the solution method, and its lower bounding approach, demonstrate the high quality of resulting sequencing decisions and the time efficiency of the solution method.
•Deterministic day-ahead scheduling of a gas-power system with reserves (DR model).•Comparison of a stochastic program and the DR model for various uncertainty levels.•Experiments with various ...numbers of piecewise linear segments for approximation.•The stochastic program results in less cost and risk under high wind uncertainty.
We compare approaches for addressing uncertainty in the joint scheduling of a combined power and gas system, with the goal of minimizing the total cost of meeting demands for gas and electricity, while satisfying operational and equilibrium constraints. A stochastic programming model and a deterministic model with reserves are formulated to investigate the hourly unit commitment and economic dispatch in the power system as well as the hourly working schedule of the natural gas system. The deterministic model uses reserves proportional to the wind energy forecast to mitigate the effect of the uncertainty in wind energy, whereas the stochastic programming model makes the day-ahead decisions while explicitly considering the wind energy uncertainty. Nonlinear constraints on the gas flows in pipelines are linearized with binary variables where, based on numerical experimentation, the number of piecewise linear segments is chosen to balance accuracy and computational efficiency. A six-bus power system with a seven-node gas system and the IEEE 24-bus power system with adjusted Belgian 20-node gas system are analyzed. The simulation results indicate that, when the total wind capacity exceeds 15% of the conventional generation capacity, the stochastic programming model produces schedules with comparable or lower cost and energy shortages than the deterministic model with reserves.
Abstract Objectives This mixed-methods systematic review aimed to identify and synthesize knowledge of the characteristics, content, and preferred format of information to support people with ...inflammatory arthritis (IA) to take MTX. Methods A literature search using MEDLINE, The Cochrane Library, EMBASE, CINAHL, PsychInfo, GreyEU, Web of Science and Open Dissertation was conducted to identify all studies published from 2000 to December 2022. Included studies detailed factors related to MTX information needs of people aged ≥18 years with IA published in English. The Joanna Briggs Institute Guidelines (JBI) for convergent integrated mixed-methods systematic reviews were followed using validated tools for data extraction and quality. The data was analysed using reflexive thematic analysis. Results Thirteen studies (seven quantitative, two mixed-methods and four qualitative) were included, involving 3425 adults, mainly female n = 2434 (71%), age 20–84 years. An overarching theme of a requirement for person-centred care was developed, with three interlinking themes: (1) accepting the need for treatment with MTX, (2) concerns about taking MTX, and (3) a need for tailored information and support. Limitations of the evidence included the use of heterogeneous outcome measures and instruments for measuring information needs. Conclusion People with IA have individual, multifaceted information and support needs about MTX that are often unresolved when a one-size-fits-all approach is used. The findings of this review can inform rheumatology training to support a person-centred approach to identifying and addressing the specific needs and concerns and development of consistent easy-to-understand accessible MTX information.
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