We investigate the impact of pricing policies (i.e., flat pricing versus peak pricing) on the investment levels of a utility firm in two competing energy sources (renewable and conventional), with a ...focus on the renewable investment level. We consider generation patterns and intermittency of solar and wind energy in relation to the electricity demand throughout a day. Industry experts generally promote peak pricing policy as it smoothens the demand and reduces inefficiencies in the supply system. We find that the same pricing policy may lead to distinct outcomes for different renewable energy sources due to their generation patterns. Specifically, flat pricing leads to a higher investment level for solar energy, and it can lead to still more investments in wind energy if a considerable amount of wind energy is generated throughout the day. We validate these results by using electricity generation and demand data of the state of Texas. We also show that flat pricing can lead to substantially lower carbon emissions and a higher consumer surplus. Finally, we explore the effect of direct (e.g., tax credit) and indirect (e.g., carbon tax) subsidies on investment levels and carbon emissions. We show that both types of subsidies generally lead to a lower emission level but that indirect subsidies may result in lower renewable energy investments. Our study suggests that reducing carbon emissions through increasing renewable energy investments requires careful attention to the pricing policy and the market characteristics of each region.
This paper was accepted by Serguei Netessine, operations management
.
The Future of Retail Operations Caro, Felipe; Kök, A. Gürhan; Martínez-de-Albéniz, Victor
Manufacturing & service operations management,
01/2020, Letnik:
22, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Retailing consists of all the activities associated with the selling of goods to the final consumer. In this article, we review the research on retail operations published in
Manufacturing & Service ...Operations Research
(
M&SOM
) since 1999. We then discuss the current retail landscape and the new research directions it offers, in which
M&SOM
can play a prominent role.
Problem definition
:
There is an ongoing debate on how providing a subsidy for one energy source affects the investment level of other sources.
Academic/practical relevance
:
To investigate this ...issue, we study a capacity investment problem for a utility firm that invests in renewable and conventional energy, with a consideration of two critical factors. First, conventional sources have different levels of operational flexibility—inflexible (e.g., nuclear and coal) and flexible (e.g., natural gas). Second, random renewable energy supply and electricity demand are correlated and nonstationary.
Methodology
:
We model this problem as a two-stage stochastic program in which a utility firm first determines the capacity investment levels followed by the dispatch quantities of energy sources to minimize the sum of investment and generation-related costs.
Results
:
We derive the optimal capacity portfolio to characterize the interactions between renewable and conventional sources.
Policy implications
:
We find that renewable and inflexible sources are substitutes, suggesting that a subsidy for nuclear or coal-fired power plants leads to a lower investment level in wind or solar energy. However, wind energy and flexible sources are complements. Thus, a subsidy for flexible natural gas-fired power plants leads to a higher investment in wind energy. This result holds for solar energy if the subsidy for the flexible source is sufficiently high. We validate these insights by using real electricity generation and demand data from the state of Texas.
Competing events are often ignored in epidemiological studies. Conventional methods for the analysis of survival data assume independent or noninformative censoring, which is violated when subjects ...that experience a competing event are censored. Because many survival studies do not apply competing risk analysis, we explain and illustrate in a nonmathematical way how to analyze and interpret survival data in the presence of competing events.
Using data from the Longitudinal Aging Study Amsterdam, both marginal analyses (Kaplan–Meier method and Cox proportional-hazards regression) and competing risk analyses (cumulative incidence function CIF, cause-specific and subdistribution hazard regression) were performed. We analyzed the association between sex and depressive symptoms, in which death before the onset of depression was a competing event.
The Kaplan–Meier method overestimated the cumulative incidence of depressive symptoms. Instead, the CIF should be used. As the subdistribution hazard model has a one-to-one relation with the CIF, it is recommended for prediction research, whereas the cause-specific hazard model is recommended for etiologic research.
When competing risks are present, the type of research question guides the choice of the analytical model to be used. In any case, results should be presented for all event types.
Daily traffic congestion forms a major problem for businesses such as logistic service providers and distribution firms. It causes late arrivals at customers and additional costs for hiring the truck ...drivers. Such costs caused by traffic congestion can be reduced by taking into account and avoiding predictable traffic congestion within vehicle route plans. In the literature, various strategies are proposed to avoid traffic congestion, such as selecting alternative routes, changing the customer visit sequences, and changing the vehicle-customer assignments. We investigate the impact of these and other strategies in off-line vehicle routing on the performance of vehicle route plans in reality. For this purpose, we develop a set of vehicle routing problem instances on real road networks, and a speed model that reflects the key elements of peak hour traffic congestion. The instances are solved for different levels of congestion avoidance using a modified Dijkstra algorithm and a restricted dynamic programming heuristic. Computational experiments show that 99% of late arrivals at customers can be eliminated if traffic congestion is accounted for off-line. On top of that, about 87% of the extra duty time caused by traffic congestion can be eliminated by clever congestion avoidance strategies.
We consider a retailer with limited inventory of identically priced, substitutable products. The retailer faces a market with multiple segments of customers that are heterogeneous with respect to ...their product preferences. Customers arrive sequentially, and the firm decides which subset of products to offer to each arriving customer depending on the customer’s preferences, the inventory levels, and the remaining time in the season. We show that it is optimal to limit the choice set of some customers (even when the products are in stock), reserving products with low inventory levels for future customers who may have a stronger preference for those products. In certain settings, we prove that it is optimal to follow a threshold policy under which a product is offered to a customer segment if its inventory level is higher than a threshold value. The thresholds are decreasing in time and increasing in the inventory levels of other products. We introduce two heuristics derived by approximating the future marginal expected revenue by the marginal value of a newsvendor function that captures the substitution dynamics between products. We test the impact of assortment customization using data from a fashion retailer. We find that the potential revenue impact of assortment customization can be significant, especially when customer heterogeneity is high and when the products’ inventory-to-demand ratios are asymmetric. Our findings suggest that assortment customization can be used as another lever for revenue maximization in addition to pricing.
Enzymes that depend on sophisticated electron transfer via ferredoxins (Fds) exhibit outstanding catalytic capabilities, but despite decades of research, many of them are still not well understood or ...exploited for synthetic applications. This review aims to provide a general overview of the most important Fd‐dependent enzymes and the electron transfer processes involved. While several examples are discussed, we focus in particular on the family of Rieske non‐heme iron‐dependent oxygenases (ROs). In addition to illustrating their electron transfer principles and catalytic potential, the current state of knowledge on structure–function relationships and the mode of interaction between the redox partner proteins is reviewed. Moreover, we highlight several key catalyzed transformations, but also take a deeper dive into their engineerability for biocatalytic applications. The overall findings from these case studies highlight the catalytic capabilities of these biocatalysts and could stimulate future interest in developing additional Fd‐dependent enzyme classes for synthetic applications.
In the spotlight! Ferredoxin‐dependent enzymes often rely on a complicated electron‐transfer chain to enable the catalysis of challenging chemical reactions. In this review, we showcase several Fd‐dependent enzymes and their potential biocatalytic applications, while particularly focusing on Rieske oxygenases as a class of enzymes with huge application potential in synthetic organic chemistry that are nonetheless still not very well understood.
Due to the growing concern over environmental issues, regardless of whether companies are going to voluntarily incorporate green policies in practice, or will be forced to do so in the context of new ...legislation, change is foreseen in the future of transportation management. Assigning and scheduling vehicles to service a pre‐determined set of clients is a common distribution problem. Accounting for time‐dependent travel times between customers, we present a model that considers travel time, fuel, and CO2 emissions costs. Specifically, we propose a framework for modeling CO2 emissions in a time‐dependent vehicle routing context. The model is solved via a tabu search procedure. As the amount of CO2 emissions is correlated with vehicle speed, our model considers limiting vehicle speed as part of the optimization. The emissions per kilometer as a function of speed are minimized at a unique speed. However, we show that in a time‐dependent environment this speed is sub‐optimal in terms of total emissions. This occurs if vehicles are able to avoid running into congestion periods where they incur high emissions. Clearly, considering this trade‐off in the vehicle routing problem has great practical potential. In the same line, we construct bounds on the total amount of emissions to be saved by making use of the standard VRP solutions. As fuel consumption is correlated with CO2 emissions, we show that reducing emissions leads to reducing costs. For a number of experimental settings, we show that limiting vehicle speeds is desired from a total cost perspective. This namely stems from the trade‐off between fuel and travel time costs.
Does the payment scheme have an effect on inventory decisions in the newsvendor problem? Keeping the net profit structure constant, we examine three payment schemes that can be interpreted as the ...newsvendor's order being financed by the newsvendor herself (scheme O), by the supplier through delayed order payment (scheme S), and by the customer through advanced revenue (scheme C). In a laboratory study, we find that inventory quantities exhibit a consistent decreasing pattern in the order of schemes O, S, and C, with the order quantities of scheme S being close to the expected-profit-maximizing solution. These observations are inconsistent with the expected-profit-maximizing model, contradict what a regular or hyperbolic time-discounting model would predict, and cannot be explained by the loss aversion model. Instead, they are consistent with a model that underweights the order-time payments, which can be explained by the "prospective accounting" theory in the mental accounting literature. A second study shows that the results hold even if all physical payments are conducted at the same time, suggesting that the framing of the payment scheme is sufficient to induce the prospective accounting behavior. We further validate the robustness of our model under different profit conditions. Our findings contribute to the understanding of the psychological processes involved in newsvendor decisions and have implications for supply chain financing and contract design.
This paper was accepted by Christian Terwiesch, operations management.
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