[…]

In 2022 at least 506m tonnes of plastics were produced worldwide, but only 9% gets recycled globally. The rest is burned, landfilled or dumped where it can leach into the environment. Microplastics are now everywhere, from the top of Mount Everest to the Mariana Trench, the deepest point on earth.

The new study of plastic pollution examined the mounting evidence of the effects of plastics on the environment, health and human wellbeing. The authors are urging delegates at the UN talks to stop viewing plastic pollution as merely a waste problem, and instead to tackle material flows through the whole life pathway of plastic, from raw material extraction, production and use, to its environmental release and its fate, and the Earth system effects.

“It’s necessary to consider the full life cycle of plastics, starting from the extraction of fossil fuel and the primary plastic polymer production” said the article’s lead author, Patricia Villarrubia-Gómez, at Stockholm Resilience Centre.

The research team showed that plastics pollution was changing the processes of the entire Earth system, and affected all pressing global environmental problems, including climate change, biodiversity loss, ocean acidification, and the use of freshwater and land.

“Plastics are seen as those inert products that protect our favourite products, or that make our lives easier that can be “easily cleaned-up” once they become waste,” Villarrubia-Gómez said. “But this is far from reality. Plastics are made out of the combination of thousands of chemicals. Many of them, such as endocrine disruptors and forever chemicals, pose toxicity and harm to ecosystems and human health. We should see plastics as the combination of these chemicals with which we interact on a daily basis.”

[…]

“We now find plastics in the most remote regions of the planet and in the most intimate, within human bodies. And we know that plastics are complex materials, released to the environment throughout the plastics life cycle, resulting in harm in many systems.

“The solutions we strive to develop must be considered with this complexity in mind, addressing the full spectra of safety and sustainability to protect people and the planet.”

Source: Plastic pollution is changing entire Earth system, scientists find | Plastics | The Guardian

Consider an example from climate science. Experts studying large atmospheric circulation patterns and their impacts on global weather would like to know how these systems might change with warming climates. Here, many variables come into play: ocean and air temperatures and pressures, ocean currents and depths, and even details of the earth’s rotation over time. But which variables cause which measured effects?

That is where information theory comes in as the framework to formulate causality. Adrián Lozano-Durán, an associate professor of aerospace at Caltech, and members of his group both at Caltech and MIT have developed a method that can be used to determine causality even in such complex systems.

The new mathematical tool can tease out the contributions that each variable in a system makes to a measured effect — both separately and, more importantly, in combination. The team describes its new method, called synergistic-unique-redundant decomposition of causality (SURD), in a paper published today, November 1, in the journal Nature Communications.

The new model can be used in any situation in which scientists are trying to determine the true cause or causes of a measured effect. That could be anything from what triggered the downturn of the stock market in 2008, to the contribution of various risk factors in heart failure, to which oceanic variables affect the population of certain fish species, to what mechanical properties are responsible for the failure of a material.

“Causal inference is very multidisciplinary and has the potential to drive progress across many fields,” says Álvaro Martínez-Sánchez, a graduate student at MIT in Lozano-Durán’s group, who is lead author of the new paper.

For Lozano-Durán’s group, SURD will be most useful in designing aerospace systems. For instance, by identifying which variable is increasing an aircraft’s drag, the method could help engineers optimize the vehicle’s design.

“Previous methods will only tell you how much causality comes from one variable or another,” explains Lozano-Durán. “What is unique about our method is its ability to capture the full picture of everything that is causing an effect.”

The new method also avoids the incorrect identification of causalities. This is largely because it goes beyond merely quantifying the effect produced by each variable independently. In addition to what the authors refer to as “unique causality,” the method incorporates two new categories of causality, namely redundant and synergistic causality.

Redundant causality occurs when more than one variable produces a measured effect, but not all the variables are needed to arrive at the same outcome. For example, a student can get a good grade in class because she is very smart or because she is a hard worker. Both could result in the good grade, but only one is necessary. The two variables are redundant.

Synergistic causality, on the other hand, involves multiple variables that must work together to produce an effect. Each variable on its own will not yield the same outcome. For instance, a patient takes medication A, but he does not recuperate from his illness. Similarly, when he takes medication B, he sees no improvement. But when he takes both medications, he fully recovers. Medications A and B are synergistic.

SURD mathematically breaks down the contributions of each variable in a system to its unique, redundant, and synergistic components of causality. The sum of all these contributions must satisfy a conservation-of-information equation that can then be used to figure out the existence of hidden causality, i.e., variables that could not be measured or that were thought not to be important. (If the hidden causality turns out to be too large, the researchers know they need to reconsider the variables they included in their analysis.)

To test the new method, Lozano-Durán’s team used SURD to analyze 16 validation cases — scenarios with known solutions that would normally pose significant challenges for researchers trying to determine causality.

“Our method will consistently give you a meaningful answer across all these cases,” says Gonzalo Arranz, a postdoctoral researcher in the Graduate Aerospace Laboratories at Caltech, who is also an author of the paper. “Other methods mix causalities that should not be mixed, and sometimes they get confused. They get a false positive identifying a causality that doesn’t exist, for example.”

In the paper, the team used SURD to study the creation of turbulence as air flows around a wall. In this case, air flows more slowly at lower altitudes, close to the wall, and more quickly at higher altitudes. Previously, some theories of what is happening in this scenario have suggested that the higher-altitude flow influences what is happening close to the wall and not the other way around. Other theories have suggested just the opposite — that the air flow near the wall affects what is happening at higher altitudes.

“We analyzed the two signals with SURD to understand in which way the interactions were happening,” says Lozano-Durán. “As it turns out, causality comes from the velocity that is far away. In addition, there is some synergy where the signals interact to create another type of causality. This decomposition, or breaking into pieces of causality, is what is unique for our method.”

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Story Source:

Materials provided by California Institute of Technology. Note: Content may be edited for style and length.

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Journal Reference:

1. Álvaro Martínez-Sánchez, Gonzalo Arranz, Adrián Lozano-Durán. Decomposing causality into its synergistic, unique, and redundant components. Nature Communications, 2024; 15 (1) DOI: 10.1038/s41467-024-53373-4

Source: Using mathematics to better understand cause and effect | ScienceDaily

The type of semiconductive nanocrystals known as quantum dots are both expanding the forefront of pure science and also hard at work in practical applications including lasers, quantum QLED televisions and displays, solar cells, medical devices, and other electronics.

A new technique for growing these microscopic crystals, published this week in Science, has not only found a new, more efficient way to build a useful type of quantum dot, but also opened up a whole group of novel chemical materials for future researchers’ exploration.

[…]

by replacing the organic solvents typically used to create nanocrystals with molten salt — literally superheated sodium chloride of the type sprinkled on baked potatoes.

“Sodium chloride is not a liquid in your mind, but assume you heat it to such a crazy temperature that it becomes a liquid. It looks like liquid. It has similar viscosity as water. It’s colorless. The only problem was that nobody ever considered these liquids as media for colloidal synthesis,”

[…]

much of the previous research on quantum dots, including the Nobel work, was around dots grown using combinations of elements from the second and sixth groups on the periodic table, Rabani said. These are called “II-VI” (two-six) materials.

More promising materials for quantum dots can be found elsewhere on the periodic table.

Materials found in the third and fifth groups of the periodic table (III-V materials) are used in the most efficient solar cells, brightest LEDs, most powerful semiconductor lasers, and fastest electronic devices. They would potentially make great quantum dots, but, with few exceptions, it was impossible to use them to grow nanocrystals in solution. The temperatures required to make these materials were too high for any known organic solvent.

Molten salt can handle the heat, making these previously inaccessible materials accessible.

[…]

One of the reasons researchers synthesizing nanocrystals overlooked molten salt was because of its strong polarity, said UChicago graduate student Zirui Zhou, second author of the new paper.

Salt’s positively charged ions and negatively charged ions have a strong pull toward each other. Small things like nanocrystals have small surface charges, so researchers assumed the charge would be too weak to push back as salt’s ions pull in. Any growing crystals would be crushed before they could form a stable material.

Or so previous researchers thought.

“It’s a surprising observation,” Zhou said. “This is very contradictory to what scientists traditionally think about these systems.”

The new technique can mean new building blocks for better, faster quantum and classical computers, but for many on the research team, the truly exciting part is opening up new materials for study.

[…]

Source: Researchers unlock a ‘new synthetic frontier’ for quantum dots | ScienceDaily