Researchers created a mathematical model that helps transplant centers make decisions about when to move forward with a matching donor and when to wait. This work can potentially help decision making in other industries. Photo via Getty Images

To wait, or not to wait? That is the question — or at least it might be, if you need a kidney transplant.

Nearly 89,000 Americans with chronic kidney disease are on a waitlist for a new organ, and an estimated 13 people die each day while awaiting a transplant. But there are real costs to matching patients with the first donor that becomes available, just as there are equally real costs to having them wait in hopes of finding a better one.

Recently, Rice Business professor Süleyman Kerimov and colleagues at Stanford University and Northwestern University developed a mathematical model that helps clarify when it's best to match patients to donors as quickly as possible and when it's best to wait.

Their findings, which appear in two papers published in Management Science and Operations Research, respectively, could help optimize all manner of matching markets in which participants seek to connect with potential partners based on mutual compatibility — a sprawling category that encompasses everything from e-commerce platforms to labor markets that match employees with employers.

Kerimov and his colleagues focused on programs that match live kidney donors with people who need transplants. Live donors typically volunteer to give one of their kidneys to a loved one. But biological differences between a donor and their intended recipient can render the pair incompatible.

Kidney exchange programs solve this problem by swapping donors amongst different patient-donor pairs, choreographing a kind of kidney-transplant square dance aimed at finding a compatible partner for every willing donor.

In countries such as Canada and the Netherlands, kidney-matching programs perform a batch of matches every few months (called periodic policies). American programs, meanwhile, tend to perform daily matches (called greedy policies). Both models seek to produce the greatest number of high-quality transplants possible, but they each have advantages and disadvantages.

Less frequent matches in a periodic policy allow more patient-donor pairs to accumulate in the kidney exchange network, creating potential for better matches over time. But this approach risks making some patients sicker as they wait for a better match that might never appear.

Arranging feasible matches as soon as they become available in a greedy policy avoids that predicament. But it means passing up the opportunity to make a potentially better match that could represent the possibility of a longer, healthier life.

Balancing these trade-offs is tricky. There is no way of predicting precisely when a patient-donor pair with a particular set of characteristics will show up at the kidney-exchange network. And in the world of organ transplants, there are no do-overs.

Kerimov and his colleagues have constructed a mathematical model that represents a simplified version of a kidney exchange network.

Within the model, the researchers could dictate which patient-donor pairs could be matched with one another. They can also assign different values to individual matches based on the number of life years they provide. And they can establish the probability that various kinds of patient-donor pairs with particular characteristics might arrive at the network and queue up for a transplant at any given time.

Having set those parameters, the researchers applied different matching policies and compared the results. As it turns out, the answer to whether one should wait or not is: It depends.

To determine which policies generated the best outcomes — i.e., performing matches either daily or periodically — the researchers calculated the difference between the total value in life years that could possibly be generated within the network and the amount generated by a specific policy at a particular point in time. The goal was to keep that number, evocatively dubbed "all-time regret," as small as possible over both the short and long term.

In their first paper, Kerimov and his team explored a complex network in which donor kidneys could be swapped amongst three or more patient-donor pairs. When such multiway matches were possible, the cost of applying a daily-match policy turned out to be onerous. Using all available matches as quickly as possible eliminated the chance of later performing potentially higher-value matches.

Instead, the researchers found they could minimize regret by applying a periodic policy that required waiting for a certain number of patient-donor pairs to arrive before attempting to match them. The model even allowed the team to calculate precisely how long to wait between matchmaking sessions to get the best possible results.

In their second paper, however, the team looked at a simpler network in which kidneys could only be swapped between two donor-patient pairs. Here, their findings contradicted the first: Applying a daily-match policy minimized regret; a periodic matching process yielded no benefit whatsoever.

To their surprise, the researchers discovered they could design a foolproof algorithm for making two-way matches in simple networks. The algorithm employed a ranked list of possible match types; and the researchers found that no matter how many patient-donor pairs of various kinds randomly arrived at the network, the best choice was always simply to perform the highest-ranked match on the list.

In future research, Kerimov hopes to refine the model by feeding it data on real patient-donor pairs that have participated in actual kidney exchange programs. This would allow him to create a more realistic network, more accurately calculate the likelihood that particular kinds of patient-donor pairs will show up, and assign values to matches based not only on life years but also on rarity and difficulty. (Certain blood types and antibody profiles, for example, are rarer or more difficult to match than others.)

But Kerimov already suspects that in a real-world situation, the wisest course of action will be to alternate between periodic and greedy policies as circumstances dictate. In a simple region within a kidney exchange network that only allows for two-way matches, pursuing a greedy policy that involves taking the first match that appears on a fixed menu of options would be the best choice. In a more complex region that allows three-way matches, however, pursuing a periodic matching policy that involves waiting to make rarer and more difficult matches would ultimately offer more patients more years of healthy life.

The benefits of choosing flexibly between greedy and periodic policies should hold for any kind of matching market that can be represented by a network with simpler and more complex regions, such as a logistics system that matches online orders to delivery trucks or a carpooling system that matches passengers with drivers across different parts of a city.

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This article originally ran on Rice Business Wisdom and was based on research from Süleyman Kerimov, an assistant professor of management – operations management in the Jones Graduate School of Business at Rice University.

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Chevron enters the lithium market with major Texas land acquisition

to market

Chevron U.S.A., a subsidiary of Houston-based energy company Chevron, has taken its first big step toward establishing a commercial-scale lithium business.

Chevron acquired leaseholds totaling about 125,000 acres in Northeast Texas and southwest Arkansas from TerraVolta Resources and East Texas Natural Resources. The acreage contains a high amount of lithium, which Chevron plans to extract from brines produced from the subsurface.

Lithium-ion batteries are used in an array of technologies, such as smartwatches, e-bikes, pacemakers, and batteries for electric vehicles, according to Chevron. The International Energy Agency estimates lithium demand could grow more than 400 percent by 2040.

“This acquisition represents a strategic investment to support energy manufacturing and expand U.S.-based critical mineral supplies,” Jeff Gustavson, president of Chevron New Energies, said in a news release. “Establishing domestic and resilient lithium supply chains is essential not only to maintaining U.S. energy leadership but also to meeting the growing demand from customers.”

Rania Yacoub, corporate business development manager at Chevron New Energies, said that amid heightening demand, lithium is “one of the world’s most sought-after natural resources.”

“Chevron is looking to help meet that demand and drive U.S. energy competitiveness by sourcing lithium domestically,” Yacoub said.

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This article originally appeared on EnergyCapital.

International Space Station welcomes astronauts from successful Axiom Mission 4

Out In Space

The first astronauts in more than 40 years from India, Poland and Hungary arrived at the International Space Station on Thursday, ferried there by SpaceX on a private flight.

The crew of four will spend two weeks at the orbiting lab, performing dozens of experiments. They launched Wednesday from NASA’s Kennedy Space Center.

America’s most experienced astronaut, Peggy Whitson, is the commander of the visiting crew. She works for Axiom Space, the Houston company that arranged the chartered flight.

Besides Whitson, the crew includes India’s Shubhanshu Shukla, a pilot in the Indian Air Force; Hungary’s Tibor Kapu, a mechanical engineer; and Poland’s Slawosz Uznanski-Wisniewski, a radiation expert and one of the European Space Agency’s project astronauts on temporary flight duty.

No one has ever visited the International Space Station from those countries before. The time anyone rocketed into orbit from those countries was in the late 1970s and 1980s, traveling with the Soviets.

“It’s an honor to have you join our outpost of international cooperation and exploration," NASA's Mission Control radioed from Houston minutes after the linkup high above the North Atlantic.

The new arrivals shared hugs and handshakes with the space station's seven full-time residents, celebrating with drink pouches sipped through straws. Six nations were represented: four from the U.S., three from Russia and one each from Japan, India, Poland and Hungary.

"It’s so great to be here finally. It was a long quarantine," Whitson said, referring to the crew's extra-long isolation before liftoff to stay healthy.

They went into quarantine on May 25, stuck in it as their launch kept getting delayed. The latest postponement was for space station leak monitoring, NASA wanted to make sure everything was safe following repairs to a longtime leak on the Russian side of the outpost.

It's the fourth Axiom-sponsored flight to the space station since 2022. The company is one of several that are developing their own space stations due to launch in the coming years. NASA plans to abandon the International Space Station in 2030 after more than three decades of operation, and is encouraging private ventures to replace it.

Screen-free hiking app developed in Houston earns 'Best of the Best' award

Peak Prize

An AI-powered, screen-free hiking system developed by Varshini Chouthri, a recent industrial design graduate from the University of Houston, has received Red Dot’s “Best of the Best” award, which recognizes the top innovative designs around the world.

Known as NOMAD, the system aims to help users stay in the moment while still utilizing technology. It will go on to compete for the Red Dot Luminary Award, the highest recognition given at the international event.

“NOMAD was truly a passion project, inspired by years of hiking growing up, where the outdoors became a place of peace, challenge, and reflection,” Chouthri said in a news release.

“I wanted to design something supporting those kinds of experiences by helping hikers feel more grounded and confident while staying present in nature. It was a way to give back to the moments that made me fall in love with the outdoors in the first place.”

The app “reimagines” outdoor exploration by removing the dependence on screens by using adaptive AI, contextual sensing, and an optional, wearable companion device. It employs a circular learning model that enables hikers to receive real-time guidance, safety alerts, personalized trip planning, hands-free navigation and more through a natural interface, according to UH.

NOMAD was developed at the Hines College of Architecture and Design’s PXD LAB. In 2023, Lunet, developed by David Edquilang at Hines College, received the “Best of the Best” recognition and went on to win the Red Dot Luminary Award.

The PXD LAB offers a platform to expand concepts into system-level designs that address real-world challenges, according to UH.

“Varshini’s work on NOMAD exemplifies the future-focused, systems-driven thinking we promote in the Advanced UX Design curriculum,” Min Kang, director of PXD LAB, added in the release. “NOMAD goes beyond being just a product; it reimagines how technology can enhance outdoor exploration without disrupting the experience.”

In addition to the Red Dot honors, NOMAD has already earned distinction from the FIT Sport Design Awards and was a finalist for the International Design Excellence Awards (IDEA) presented by the Industrial Designers Society of America.