Search

This paper studies the problem of simultaneously locating trauma centers and helicopters. The standard approach to locating helicopters involves the use of helicopter busy fractions to model the random availability of helicopters. However, busy fractions cannot be estimated a priori in our problem because the demand for each helicopter cannot be determined until the trauma center locations are selected. To overcome this challenge, we endogenize the computation of busy fractions within an optimization problem. The resulting formulation has nonconvex bilinear terms in the objective, for which we develop an integrated method that iteratively solves a sequence of problem relaxations and restrictions. Specifically, we devise a specialized algorithm, called the shifting quadratic envelopes algorithm, that (1) generates tighter outer approximations than linear McCormick envelopes and (2) outperforms a Benders-like cut generation scheme. We apply our integrated method to the design of a nationwide trauma care system in Korea. By running a trace-based simulation on a full year of patient data, we find that the solutions generated by our model outperform several benchmark heuristics by up to 20%, as measured by an industry-standard metric: the proportion of patients successfully transported to a care facility within one hour. Our results have helped the Korean government to plan its nationwide trauma care system. More generally, our method can be applied to a class of optimization problems that aim to find the locations of both fixed and mobile servers when service needs to be carried out within a certain time threshold.

Abstract. Problem definition: We investigate multinational firms' inspection and pricing strategies to address the challenges of combating child labor in global supply chains. We also examine how several factors (such [...]

A large US retailer that procures transportation services from third-party carriers experienced an unexpected jump in fuel surcharges as the price of diesel fuel skyrocketed in the summer of 2008. As a result, it sought to limit its future exposure to diesel price risk. We collaborated with this retailer to create a lane assignment optimizer (LAO) that incorporates diesel price risk when selecting carriers for its transportation lanes. The LAO tool has significantly improved the retailer's capability to evaluate the trade-off between the two crucial components of a lane's per-shipment cost: base price and risk-adjusted fuel surcharge. The retailer can now take diesel price risk into account when selecting cost-effective carriers for its lanes, negotiating fuel surcharge limits to share diesel price risk with its carriers, and better aligning the fuel surcharges it pays with the true cost of diesel. We estimate that the more favorable contract terms the retailer negotiated for 2009-2011 translate to nearly $5 million in potential savings during years with unexpected diesel price hikes, such as 2008. © 2012 INFORMS.

Problem definition: Generating recommendations of compatible dating partners is a challenging task for online dating platforms because uncovering users' idiosyncratic preferences is difficult. Thus, platforms tend to recommend popular users to others more frequently than unpopular users. This paper studies such popularity bias in an online dating platform's recommendations and its consequences for users' likelihood of finding dating partners. Methodology/results: Motivated by the empirical evidence that a user's chance of being recommended by the platform's algorithm increases significantly with the user's popularity, we study an online dating platform's incentive that generates popularity bias by modeling the platform's recommendations and users' subsequent interactions in a three-stage matching game. Our analysis shows that the recommendations that maximize the platform's revenue and those that maximize the number of successful matches between users are not necessarily at odds, even though the former leads to a higher bias against unpopular users. Unbiased recommendations result in significantly lower revenue for the platform and fewer matches when users' implicit cost of evaluating incoming messages is low. Popular users help the platform generate more revenue and a higher number of successful matches as long as these popular users do not become "out of reach." We validate our theoretical results by running simulations of the platform based on a machine learning–based predictive model that estimates users' behavior. Managerial implications: Our result indicates that an online dating platform can increase revenue and users' chances of finding dating partners simultaneously with a certain degree of bias against unpopular users. Online dating platforms can use our theoretical results to understand user behavior and our predictive model to improve their recommendation systems (e.g., by selecting a set of users leading to the highest probabilities of matching or other revenue-generating interactions). Supplemental Material: The online appendices are available at https://doi.org/10.1287/msom.2022.0132. [ABSTRACT FROM AUTHOR]

The hot corrosion behaviors of Inconel alloys with different Cr contents (Inconel 600, 601, and 690), which are used widely in nuclear plants, were investigated in molten LiCl–Li2O salts. The hot corrosion behaviors were studied by measuring the mass and attack depth changes, surface and cross-sectional morphologies and elemental distributions, and compositional changes at the subscale and substrate scale as well as the spalled oxide scale. At 288 h, the weight losses of Inconel 601 and Inconel 690 were approximately four and twelve times higher, respectively, than that of Inconel 600. The corrosion products of all tested alloys were Cr2O3, NiO, and FeCr2O4. Inconel 600, which exhibited a dense and continuous external corrosion layer and an internal corrosion layer with localized corrosion behavior, exhibited superior corrosion resistance compared with those of Inconel 601 and 690, which showed a spalled external corrosion layer and an internal corrosion layer with uniform corrosion behavior. Thus, the corrosion resistance of the Inconel alloys tested in the hot lithium molten salts in an oxidizing atmosphere is closely related to the contents of the primary alloying elements in the alloys. Of the various alloys analyzed in this study, Inconel 600 exhibited the highest corrosion resistance. Thus, a Cr content of 16.30 wt% or less, Ni content of at least 73.66 wt%, and Fe content considerably lower than 8.15 wt% can result in excellent corrosion resistance. [ABSTRACT FROM AUTHOR]

Although influenza vaccine shortage is often attributed to low supply, it has been observed that even with abundant supply, a major shortage can still occur because of late delivery. In [...]

Counterfeit goods are becoming more sophisticated, from shoes to infant milk powder to aircraft parts, creating problems for consumers, firms, and governments. By comparing two types of counterfeiters--deceptive, so infiltrating [...]

We examine three selling strategies of a manufacturer who produces and sells a seasonal product to a retailer under uncertain supply and demand: (1) advance selling--presells the product before observing [...]