MIT Lecture “Quantifying Uncertainty in Complex Physical Systems:” Modeling Uncertainty

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“In search of better-burning fuels, or more accurate projections of climate change, researchers inevitably work through multiple models, sometimes at great cost.Youssef Marzouk hopes to provide energy and environmental scientists constructive and efficient new approaches to modeling complex engineered systems.

In this seminar, Marzouk describes ways of managing uncertainty, which “is where a lot of idealizations of modeling meet the reality of the complex systems we’re actually trying to study.” Specifically, he aims to “quantify confidence in computational predictions, and use these predictions in design and decision-making;” learn from “noisy, indirect experimental observations,” and refine and build models based on the most informative things observed and measured.

With formulas and graphs, Marzouk shows how he applies such methodologies as polynomial chaos expansion to “construct machinery that lets us propagate uncertainties, evaluate variances, evaluate any aspect of the probability distribution in the model output,” in order “to apply robust formulations much more effectively.” With statistical (Bayesian) inference and inverse problems, Marzouk extracts information from observational data to make models better, “backing out kinetic parameters working at microscale from macroscale data.”

One real-world problem on which Marzouk has been applying his methods: ice sheet dynamics in west Antarctica, which pose “an enormous inference problem,” due to unknowns about sliding friction, geothermal heat flux, and initial temperature of ice. Researchers “need to get a handle on this from the available data,” he says. Another example involves solid oxide fuel cells, which suggest “a lot of potential as high efficiency conversion devices for vehicles or stationary power generation.” Marzouk also hopes his modeling methods can help create better techniques for refining biomass for synthetic fuels.”

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“Multiple suicide attempters differed from participants with no suicidal ideation/no past attempts on 2 emotion dysregulation dimensions—nonacceptance of emotional responses and perceived limited access to emotion regulation strategies”

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“…the female predominance in psychological distress diminishes with increasing age. The congruence between men and women may reflect changes in identity associated with age or the effect of decreased emotional valence of some social roles.”

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“About 52 million years ago, primates — an order of animals that includes, among others, humans and great apes — might have stopped foraging alone and banded together in large, loosely formed, same-sex groups to search for food. Then around 16 million years ago, primates began forming more stable social groups, such as male-female pairs and harems dominated by one male, the researchers suggest.”

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“If we didn’t have these social groups evolving in primates, we wouldn’t have the scaffolding in place for humans to build upon,”

Teaming up this way may have been prompted by a switch from a nocturnal lifestyle to moving about in the sunshine. “Being active during the day would have allowed primates to travel across larger spaces and exploit their environment more effectively, but it would have also exposed them to a huge predation risk,” says Shultz. To make it through the day, primates would have needed a new defense strategy to deal with both a greater number of predators and also new kinds of hunters.

“What’s going to nail you at night is different than what’s going to nail you during the day,” says primatologist Anthony Di Fiore of the University of Texas at Austin, who was not involved in the study. It’s tough to hide from eagle eyes in the daytime, but by joining up and serving as lookouts for each other primates would have given themselves a better chance of spotting and evading a swooping bird or other predator.

““Brains among vertebrate animals—frogs, cats, fish, bears, and even humans—are more similar than most people realize. The neurotransmitter systems that control brain activity at the molecular level are nearly identical among all vertebrates and the layout of the brain structures is the same.”

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