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Study reveals how to break symmetry in colloidal crystals – EurekAlert

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image: This triple-double gyroid is a new colloidal crystal structure that has never been found in nature or synthesized before. The translucent red/green/blue balls show the positions of programmable atom equivalents (PAEs), while the dark grey balls and sticks show locations of electron equivalents (EEs).
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Credit: Sangmin Lee

Nature keeps a few secrets. While plenty of structures with low symmetry are found in nature, scientists have been confined to high-symmetry designs when synthesizing colloidal crystals, a valuable type of nanomaterial used for chemical and biological sensing and optoelectronic devices.

Now, research from Northwestern University and the University of Michigan has drawn back the curtain, showing for the first time how low-symmetry colloidal crystals can be made – including one phase for which there is no known natural equivalent.

“We’ve discovered something fundamental about the system for making new materials,” said Northwestern’s Chad A. Mirkin. “This strategy for breaking symmetry rewrites the rules for material design and synthesis.”

The research was published today (Jan. 13) in the journal Nature Materials.

Mirkin is the George B. Rathmann Professor of Chemistry in the Weinberg College of Arts and Sciences; a professor of chemical and biological engineering, biomedical engineering, and materials science and engineering at the McCormick School of Engineering; and a professor of medicine at the Feinberg School of Medicine. He also is the founding director of the International Institute for Nanotechnology.

The research was directed by Mirkin and Sharon C. Glotzer, the Anthony C. Lembke Department Chair of Chemical Engineering at the University of Michigan.

Nanoparticles can be programmed and assembled into ordered arrays known as colloidal crystals, which can be engineered for applications from light sensors and lasers to communications and computing.

“Using large and small nanoparticles, where the smaller ones move around like electrons in a crystal of metal atoms, is a whole new approach to building complex colloidal crystal structures,” said Glotzer.

In this research, metal nanoparticles whose surfaces were coated with designer DNA were used to create the crystals. The DNA acted as an encodable bonding material, transforming them into what are called programmable atom equivalents (PAEs). This approach offers exceptional control over the shape and parameters of the crystal lattices, as the nanoparticles can be ‘programmed’ to arrange themselves in specified ways, following a set of rules previously developed by Mirkin and his colleagues.

However, to this point, scientists have not had a way to prepare lattices with certain crystal symmetries. Because many PAEs are isotropic – meaning that their structures are uniform in all directions – they tend to arrange into highly symmetric assemblies, and it is difficult to create low-symmetry lattices. This has limited the kinds of structures that can be synthesized, and therefore the optical properties that can be realized with them.

The breakthrough came through a new approach to controlling valency. In chemistry, valency is related to the arrangement of electrons around an atom. It determines the number of bonds the atom can form and the geometry it assumes. Building on a recent discovery that small PAEs can behave as electron equivalents, roaming through and stabilizing lattices of larger PAEs, the Northwestern and Michigan researchers altered the valency of their electron equivalents by adjusting the density of the strands of DNA grafted to their surfaces.

Next, they used advanced electron microscopy to observe how changing the valency of the electron equivalents affected their spatial distribution among the PAEs and therefore the resulting lattices. They also examined the effects of changing temperatures and altering the ratio of PAEs to electron equivalents.

“We explored more complex structures where control over the number of neighbors around each particle produced further symmetry breaking,” said Glotzer. “Our computer simulations helped to decipher the complicated patterns and reveal the mechanisms that enabled the nanoparticles to create them.” 

This approach set the stage for three new, never-before synthesized crystalline phases. One, a triple double-gyroid structure, has no known natural equivalent.

These low-symmetry colloidal crystals have optical properties that can’t be achieved with other crystal structures and may find use in a wide range of technologies. Their catalytic properties are different as well. But the new structures unveiled here are only the beginning of the possibilities now that the conditions for breaking symmetry are understood.

“We’re in the midst of an unprecedented era of materials synthesis and discovery,” said Mirkin. “This is another step forward in bringing new, unexplored materials out of the sketchbook and into applications that can take advantage of their rare and unusual properties.”

The study, “The emergence of valency in colloidal crystals through electron equivalents”, was supported primarily by the Center for Bio-Inspired Energy Science, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences (award DE-SC0000989) and also by the Air Force Office of Scientific Research (award FA9550-17-1-0348) and the Sherman Fairchild Foundation.

Glotzer is also the John Werner Cahn Distinguished University Professor of Engineering, the Stuart W. Churchill Collegiate Professor of Chemical Engineering, and a professor of material science & engineering, macromolecular science and engineering, and physics at the University of Michigan. Byeongdu Lee from Argonne National Laboratory is a corresponding author with Mirkin and Glotzer.


Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.

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Scientists study travels of meteorite that landed in B.C. in October – Vancouver Sun

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The small meteorite broke through a woman’s ceiling in Golden, B.C., in October, landing on her pillow, next to where she had been sleeping moments earlier.

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Scientists studying a meteorite that landed next to a B.C. woman’s head last year say it was diverted to that path about 470 million years ago.

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The small meteorite broke through a woman’s ceiling in Golden in October, landing on her pillow, next to where she had been sleeping moments earlier.

Philip McCausland, a lead researcher mapping the meteorite’s journey, said Monday they know the 4.5-billion-year-old rock collided with something about 470 million years ago, breaking into fragments and changing the trajectory of some of the pieces.

McCausland, who’s an adjunct professor at Western University in London, Ont., said the meteorite is of scientific significance because it will allow scientists to study how material from the asteroid belt arrives on Earth.

“There’s 50,000 to 60,000 identified meteorites now in the world, but most have no context. We don’t know really where they came from,” he said.

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“In cases where we have known orbits, where they were observed coming in well enough that we can reconstruct what the orbit was before it hit the Earth’s atmosphere, we can actually (determine) where they came from in the asteroid belt. Golden is one of those,” he said, referring to the location of where the meteorite landed.

Researchers determined the meteorite is an L chondrite, one of the most commonly found types of meteorites to fall to Earth. Despite this, he said only about five L chondrites have known orbits.

He said the Canadian team is now working with scientists in Switzerland, the U.K., U.S. and Italy to learn more about the meteorite and its path to Golden.

“We know we’re still going to get something interesting out of this,” McCausland said. “We actually do want to get a good handle on how things get delivered from the asteroid belt, and this is a useful part of putting that together.”

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Most of the meteorite has been returned to Ruth Hamilton, the woman who had the close call, and McCausland said it’s up to her to decide what to do with it.

Whether she decides to keep, sell or donate the rock, he said there is cultural significance of the rock to Canada. If she sells it to an international buyer, she would be required to go through the exportation process, he said.

Hamilton said she hasn’t yet made up her mind on what to do with the meteor. It’s currently sitting in a safety deposit box.

“I don’t have any plans for it right now, but once they’re done analyzing it, I’ll get all the documentation that proves it’s a meteorite,” she said. “It’s going to be officially named the Golden Meteorite.”

Before her roof is permanently repaired this spring, Hamilton said she intends to remove the section where the meteorite crashed through to keep it preserved alongside the rock.

McCausland said the research will likely conclude in May, and the scientists will then publish their work in an academic journal.

“Whenever something like this happens, I like to tell people it could happen to any of us; anyone can find a meteorite. It’s unlikely one will crash through your roof, but it can happen,” McCausland said. “It’s nature and, if anything, it’s a reminder that we’re part of something bigger.”

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Researchers at UBCO determine 'smart windows' can disinfect surfaces – Kelowna News – Castanet.net

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A new study at the University of British Columbia Okanagan shines a light on how sunlight can be used to disinfect surfaces in your home or workplace.

The COVID-19 pandemic has magnified concerns over how buildings might influence the health of the people who live and work in them. There has been some attention paid to ventilation, cleaning and filtration, however, the importance of daylight has been ignored, until now.

The UBCO research shows daylight passing through smart windows results in almost complete disinfection of surfaces within 24 hours while still blocking harmful ultraviolet light.

Dr. Sepideh Pakpour, an assistant professor at UBCO’s School of Engineering tested four strains of hazardous bacteria—methicillin-resistance Staphylococcus aureus, Klebsiella pneumoniae, E. coli and Pseudomonas aeruginosa—using a mini-living lab set-up. The lab used smart windows, which tint based on outdoor light conditions, and traditional windows with blinds. Dr. Pakpour found that, compared to windows with blinds, the smart windows significantly reduce bacterial growth rate. In fact the smart windows blocked more than 99.9 per cent of UV light, but still let in short-wavelength, high-energy daylight which acts as a disinfectant. This shorter wavelength light effectively eliminated contamination on glass, plastic and fabric surfaces.

Traditional window blinds block daylight, therefore, preventing surfaces from being disinfected. Dr. Pakpour noted previous research shows 92 per cent of hospital curtains can get contaminated within a week of being cleaned.

“We know that daylight kills bacteria and fungi,” she says. “But the question is, are there ways to harness that benefit in buildings, while still protecting us from glare and UV radiation? Our findings demonstrate the benefits of smart windows for disinfection, and have implications for infectious disease transmission in laboratories, health-care facilities and the buildings in which we live and work.”

A study from the Harvard Business Review points to natural light and views being among the most sought after by potential employees. Combine that with a push for “healthy buildings” as part of the COVID-19 return to work and employers could benefit from installing smart windows.

“Our buildings need to go beyond sustainable and smart to become healthy and safe environments first and foremost,” says Dr. Rao Mulpuri, Chairman and CEO at View, the company partnering with UBC for this research. “Companies are grappling with how to bring their people back to the office in a safe way. This research provides yet another reason why increased access to natural light needs to be part of the equation.”

Studies have shown that pathogenic bacteria and fungi can survive on inanimate surfaces for prolonged periods, which can lead to disease transmission.

“With the rise of antimicrobial resistance, antibiotics are no longer a silver bullet in treating health-care-associated infections, which cause tens of thousands of deaths in the US each year,” says Dr. Tex Kissoon, Vice Chair of the Global Sepsis Alliance, UBC Children’s Hospital Endowed Chair in Acute and Critical Care for Global Child Health. “The potential for daylight to sterilize surfaces and avoid these infections altogether is promising and should be factored into health-care facility design.”

Dr. Pakpour presented her findings Wednesday at the international Healthy Buildings Conference in Amsterdam.

“Our findings demonstrate the benefits of smart windows for disinfection, and have implications for infectious disease transmission in laboratories, health care facilities and the buildings in which we live and work.”

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Asteroid Bigger Than the Tallest Building on Earth Just Flew by Safely: Here's How People Are Reacting to… – Gadgets 360

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An asteroid bigger than the tallest building on Earth safely flew by on January 19. The giant rock, named 7482 (1994 PC1), zipped past our planet, nearly 1.93 million kilometres away. That’s more than five times the distance between Earth and Moon. It has been classified as “potentially hazardous” because of its size and its regular close visits to our planet, and not because it poses any threat to us. The asteroid came closest to Earth at 3:21am IST.

Astronomers say this will remain the closest approach of the asteroid for at least the next 200 years. They added that regular close visits by this asteroid should not lead to fear among people as its trajectory has a margin of error of only 133km.

The rock was travelling at a speed of 19.56kmph, relative to Earth, when it flew by us. The considerable speed with which it was travelling should have enabled amateur astronomers to spot it. It should have appeared as a point of light in the night sky. Earth Sky has shared a video of the asteroid moving rapidly in the sky. It said the video was recorded in Puerto Rico and the asteroid was visible despite a Full Moon on January 18 (local time) since the Moon was at a good distance from the asteroid’s path. See the video below (published by kevinizooropa):

Many people shared their excitement on Twitter at being able to see the asteroid or even after simply knowing that something like this had happened.

“While we were busy surviving another day, another year, another job, an asteroid bigger than Burj Khalifa just passed by…Notice the shooting star, which steals the show. Money and jobs are the biggest distraction to our real growth and finding answers to our existence,” said a user.

Some users have also shared images of the asteroid.

Many just found an opportunity to have a little fun, now that the celestial event passed safely. Check out their reactions below:

The asteroid was discovered by Australian astronomer Robert McNaught in 1994.


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