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‘Dolomite Problem’: 200-year-old geology mystery resolved

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‘Dolomite Problem’: 200-year-old geology mystery resolved


For 200 years, scientists have failed to grow a common mineral in the laboratory under the conditions believed to have formed it naturally. Now, a team of researchers from the University of Michigan and Hokkaido University in Sapporo, Japan have finally pulled it off, thanks to a new theory developed from atomic simulations.

Their success resolves a long-standing geology mystery called the “Dolomite Problem.” Dolomite — a key mineral in the Dolomite mountains in Italy, Niagara Falls, the White Cliffs of Dover and Utah’s Hoodoos — is very abundant in rocks older than 100 million years, but nearly absent in younger formations.

“If we understand how dolomite grows in nature, we might learn new strategies to promote the crystal growth of modern technological materials,” said Wenhao Sun, the Dow Early Career Professor of Materials Science and Engineering at U-M and the corresponding author of the paper published today in Science.

The secret to finally growing dolomite in the lab was removing defects in the mineral structure as it grows. When minerals form in water, atoms usually deposit neatly onto an edge of the growing crystal surface. However, the growth edge of dolomite consists of alternating rows of calcium and magnesium. In water, calcium and magnesium will randomly attach to the growing dolomite crystal, often lodging into the wrong spot and creating defects that prevent additional layers of dolomite from forming. This disorder slows dolomite growth to a crawl, meaning it would take 10 million years to make just one layer of ordered dolomite.

Luckily, these defects aren’t locked in place. Because the disordered atoms are less stable than atoms in the correct position, they are the first to dissolve when the mineral is washed with water. Repeatedly rinsing away these defects — for example, with rain or tidal cycles — allows a dolomite layer to form in only a matter of years. Over geologic time, mountains of dolomite can accumulate.

To simulate dolomite growth accurately, the researchers needed to calculate how strongly or loosely atoms will attach to an existing dolomite surface. The most accurate simulations require the energy of every single interaction between electrons and atoms in the growing crystal. Such exhaustive calculations usually require huge amounts of computing power, but software developed at U-M’s Predictive Structure Materials Science (PRISMS) Center offered a shortcut.

“Our software calculates the energy for some atomic arrangements, then extrapolates to predict the energies for other arrangements based on the symmetry of the crystal structure,” said Brian Puchala, one of the software’s lead developers and an associate research scientist in U-M’s Department of Materials Science and Engineering.

That shortcut made it feasible to simulate dolomite growth over geologic timescales.

“Each atomic step would normally take over 5,000 CPU hours on a supercomputer. Now, we can do the same calculation in 2 milliseconds on a desktop,” said Joonsoo Kim, a doctoral student of materials science and engineering and the study’s first author.

The few areas where dolomite forms today intermittently flood and later dry out, which aligns well with Sun and Kim’s theory. But such evidence alone wasn’t enough to be fully convincing. Enter Yuki Kimura, a professor of materials science from Hokkaido University, and Tomoya Yamazaki, a postdoctoral researcher in Kimura’s lab. They tested the new theory with a quirk of transmission electron microscopes.

“Electron microscopes usually use electron beams just to image samples,” Kimura said. “However, the beam can also split water, which makes acid that can cause crystals to dissolve. Usually this is bad for imaging, but in this case, dissolution is exactly what we wanted.”

After placing a tiny dolomite crystal in a solution of calcium and magnesium, Kimura and Yamazaki gently pulsed the electron beam 4,000 times over two hours, dissolving away the defects. After the pulses, dolomite was seen to grow approximately 100 nanometers — around 250,000 times smaller than an inch. Although this was only 300 layers of dolomite, never had more than five layers of dolomite been grown in the lab before.

The lessons learned from the Dolomite Problem can help engineers manufacture higher-quality materials for semiconductors, solar panels, batteries and other tech.

“In the past, crystal growers who wanted to make materials without defects would try to grow them really slowly,” Sun said. “Our theory shows that you can grow defect-free materials quickly, if you periodically dissolve the defects away during growth.”

The research was funded by the American Chemical Society PRF New Doctoral Investigator grant, the U.S. Department of Energy and the Japanese Society for the Promotion of Science.



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New snake discovery rewrites history, points to North America’s role in snake evolution

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‘Dolomite Problem’: 200-year-old geology mystery resolved


A new species of fossil snake unearthed in Wyoming is rewriting our understanding of snake evolution. The discovery, based on four remarkably well-preserved specimens found curled together in a burrow, reveals a new species named Hibernophis breithaupti. This snake lived in North America 34 million years ago and sheds light on the origin and diversification of boas and pythons.

Hibernophis breithaupti has unique anatomical features, in part because the specimens are articulated — meaning they were found all in one piece with the bones still arranged in the proper order — which is unusual for fossil snakes. Researchers believe it may be an early member of Booidea, a group that includes modern boas and pythons. Modern boas are widespread in the Americas, but their early evolution is not well understood.These new and very complete fossils add important new information, in particular, on the evolution of small, burrowing boas known as rubber boas.

Traditionally, there has been much debate on the evolution of small burrowing boas. Hibernophis breithaupti shows that northern and more central parts of North America might have been a key hub for their development. The discovery of these snakes curled together also hints at the oldest potential evidence for a behavior familiar to us today — hibernation in groups.

“Modern garter snakes are famous for gathering by the thousands to hibernate together in dens and burrows,” says Michael Caldwell, a U of A paleontologist who co-led the research along with his former graduate student Jasmine Croghan, and collaborators from Australia and Brazil. “They do this to conserve heat through the effect created by the ball of hibernating animals. It’s fascinating to see possible evidence of such social behavior or hibernation dating back 34 million years.”



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Good timing: Study unravels how our brains track time

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‘Dolomite Problem’: 200-year-old geology mystery resolved


Ever hear the old adage that time flies when you’re having fun? A new study by a team of UNLV researchers suggests that there’s a lot of truth to the trope.

Many people think of their brains as being intrinsically synced to the human-made clocks on their electronic devices, counting time in very specific, minute-by-minute increments. But the study, published this month in the latest issue of the peer-reviewed Cell Press journal Current Biology, showed that our brains don’t work that way.

By analyzing changes in brain activity patterns, the research team found that we perceive the passage of time based on the number of experiences we have — not some kind of internal clock. What’s more, increasing speed or output during an activity appears to affect how our brains perceive time.

“We tell time in our own experience by things we do, things that happen to us,” said James Hyman, a UNLV associate professor of psychology and the study’s senior author. “When we’re still and we’re bored, time goes very slowly because we’re not doing anything or nothing is happening. On the contrary, when a lot of events happen, each one of those activities is advancing our brains forward. And if this is how our brains objectively tell time, then the more that we do and the more that happens to us, the faster time goes.”

Methodology and Findings

The findings are based on analysis of activity in the anterior cingulate cortex (ACC), a portion of the brain important for monitoring activity and tracking experiences. To do this, rodents were tasked with using their noses to respond to a prompt 200 times.

Scientists already knew that brain patterns are similar, but slightly different, each time you do a repetitive motion, so they set out to answer: Is it possible to detect whether these slight differences in brain pattern changes correspond with doing the first versus 200th motion in series? And does the amount of time it takes to complete a series of motions impact brain wave activity?

By comparing pattern changes throughout the course of the task, researchers observed that there are indeed detectable changes in brain activity that occur as one moves from the beginning to middle to end of carrying out a task. And regardless of how slowly or quickly the animals moved, the brain patterns followed the same path. The patterns were consistent when researchers applied a machine learning-based mathematical model to predict the flow of brain activity, bolstering evidence that it’s experiences — not time, or a prescribed number of minutes, as you would measure it on a clock — that produce changes in our neurons’ activity patterns.

Hyman drove home the crux of the findings by sharing an anecdote of two factory workers tasked with making 100 widgets during their shift, with one worker completing the task in 30 minutes and the other in 90 minutes.

“The length of time it took to complete the task didn’t impact the brain patterns. The brain is not a clock; it acts like a counter,” Hyman explained. “Our brains register a vibe, a feeling about time. …And what that means for our workers making widgets is that you can tell the difference between making widget No. 85 and widget No. 60, but not necessarily between No. 85 and No. 88.”

But exactly “how” does the brain count? Researchers discovered that as the brain progresses through a task involving a series of motions, various small groups of firing cells begin to collaborate — essentially passing off the task to a different group of neurons every few repetitions, similar to runners passing the baton in a relay race.

“So, the cells are working together and over time randomly align to get the job done: one cell will take a few tasks and then another takes a few tasks,” Hyman said. “The cells are tracking motions and, thus, chunks of activities and time over the course of the task.”

And the study’s findings about our brains’ perception of time applies to activities-based actions other than physical motions too.

“This is the part of the brain we use for tracking something like a conversation through dinner,” Hyman said. “Think of the flow of conversation and you can recall things earlier and later in the dinner. But to pick apart one sentence from the next in your memory, it’s impossible. But you know you talked about one topic at the start, another topic during dessert, and another at the end.”

By observing the rodents who worked quickly, scientists also concluded that keeping up a good pace helps influence time perception: “The more we do, the faster time moves. They say that time flies when you’re having fun. As opposed to having fun, maybe it should be ‘time flies when you’re doing a lot’.”

Takeaways

While there’s already a wealth of information on brain processes over very short time scales of less than a second, Hyman said that the UNLV study is groundbreaking in its examination of brain patterns and perception of time over a span of just a few minutes to hours — “which is how we live much of our life: one hour at a time. ”

“This is among the first studies looking at behavioral time scales in this particular part of the brain called the ACC, which we know is so important for our behavior and our emotions,” Hyman said.

The ACC is implicated in most psychiatric and neurodegenerative disorders, and is a concentration area for mood disorders, PTSD, addiction, and anxiety. ACC function is also central to various dementias including Alzheimer’s disease, which is characterized by distortions in time. The ACC has long been linked to helping humans with sequencing events or tasks such as following recipes, and the research team speculates that their findings about time perception might fall within this realm.

While the findings are a breakthrough, more research is needed. Still, Hyman said, the preliminary findings posit some potentially helpful tidbits about time perception and its likely connection to memory processes for everyday citizens’ daily lives. For example, researchers speculate that it could lend insights for navigating things like school assignments or even breakups.

“If we want to remember something, we may want to slow down by studying in short bouts and take time before engaging in the next activity. Give yourself quiet times to not move,” Hyman said. “Conversely, if you want to move on from something quickly, get involved in an activity right away.”

Hyman said there’s also a huge relationship between the ACC, emotion, and cognition. Thinking of the brain as a physical entity that one can take ownership over might help us control our subjective experiences.

“When things move faster, we tend to think it’s more fun — or sometimes overwhelming. But we don’t need to think of it as being a purely psychological experience, as fun or overwhelming; rather, if you view it as a physical process, it can be helpful,” he said. “If it’s overwhelming, slow down or if you’re bored, add activities. People already do this, but it’s empowering to know it’s a way to work your own mental health, since our brains are working like this already.”



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Another intermediate-mass black hole discovered at the center of our galaxy

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‘Dolomite Problem’: 200-year-old geology mystery resolved


While researching a cluster of stars in the immediate vicinity of the supermassive black hole SgrA* (Sagittarius A*) at the centre of our galaxy, an international team of researchers led by PD Dr Florian Peißker has found signs of another, intermediate-mass black hole. Despite enormous research efforts, only about ten of these intermediate-mass black holes have been found in our entire universe so far. Scientists believe that they formed shortly after the Big Bang. By merging, they act as ‘seeds’ for supermassive black holes. The study ‘The Evaporating Massive Embedded Stellar Cluster IRS 13 Close to Sgr A*. II. Kinematic structure’ was published in The Astrophysical Journal.

The analysed star cluster IRS 13 is located 0.1 light years from the centre of our galaxy. This is very close in astronomical terms, but would still require travelling from one end of our solar system to the other twenty times to cover the distance. The researchers noticed that the stars in IRS 13 move in an unexpectedly orderly pattern. They had actually expected the stars to be arranged randomly. Two conclusions can be drawn from this regular pattern: On the one hand, IRS 13 appears to interact with SgrA*, which leads to the orderly motion of the stars. On the other hand, there must be something inside the cluster for it to be able to maintain its observed compact shape.

Multi-wavelength observations with the Very Large Telescope as well as the ALMA and Chandra telescopes now suggest that the reason for the compact shape of IRS 13 could be an intermediate-mass black hole located at the centre of the star cluster. This would be supported by the fact that the researchers were able to observe characteristic X-rays and ionized gas rotating at a speed of several 100 km/s in a ring around the suspected location of the intermediate-mass black hole.

Another indication of the presence of an intermediate-mass black hole is the unusually high density of the star cluster, which is higher than that of any other known density of a star cluster in our Milky Way. “IRS 13 appears to be an essential building block for the growth of our central black hole SgrA*,” said Florian Peißker, first author of the study. “This fascinating star cluster has continued to surprise the scientific community ever since it was discovered around twenty years ago. At first it was thought to be an unusually heavy star. With the high-resolution data, however, we can now confirm the building-block composition with an intermediate-mass black hole at the centre.” Planned observations with the James Webb Space Telescope and the Extremely Large Telescope, which is currently under construction, will provide further insights into the processes within the star cluster.



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