Researchers using ESO's Very Large Telescope (VLT) have observed an extreme planet where they suspect it rains iron. The ultra-hot giant exoplanet has a day side where temperatures climb above 2400 degrees Celsius, high enough to vaporise metals. Strong winds carry iron vapour to the cooler night side where it condenses into iron droplets.
"One could say that this planet gets rainy in the evening, except it rains iron," says David Ehrenreich, a professor at the University of Geneva in Switzerland. He led a study, published today in the journal Nature, of this exotic exoplanet. Known as WASP-76b, it is located some 640 light-years away in the constellation of Pisces.
This strange phenomenon happens because the 'iron rain' planet only ever shows one face, its day side, to its parent star, its cooler night side remaining in perpetual darkness. Like the Moon on its orbit around the Earth, WASP-76b is 'tidally locked': it takes as long to rotate around its axis as it does to go around the star.
On its day side, it receives thousands of times more radiation from its parent star than the Earth does from the Sun. It's so hot that molecules separate into atoms, and metals like iron evaporate into the atmosphere. The extreme temperature difference between the day and night sides results in vigorous winds that bring the iron vapour from the ultra-hot day side to the cooler night side, where temperatures decrease to around 1500 degrees Celsius.
Not only does WASP-76b have different day-night temperatures, it also has distinct day-night chemistry, according to the new study. Using the new ESPRESSO instrument on ESO's VLT in the Chilean Atacama Desert, the astronomers identified for the first time chemical variations on an ultra-hot gas giant planet. They detected a strong signature of iron vapour at the evening border that separates the planet's day side from its night side. "Surprisingly, however, we do not see the iron vapour in the morning," says Ehrenreich. The reason, he says, is that "it is raining iron on the night side of this extreme exoplanet."
"The observations show that iron vapour is abundant in the atmosphere of the hot day side of WASP-76b," adds María Rosa Zapatero Osorio, an astrophysicist at the Centre for Astrobiology in Madrid, Spain, and the chair of the ESPRESSO science team. "A fraction of this iron is injected into the night side owing to the planet's rotation and atmospheric winds. There, the iron encounters much cooler environments, condenses and rains down."
This result was obtained from the very first science observations done with ESPRESSO, in September 2018, by the scientific consortium who built the instrument: a team from Portugal, Italy, Switzerland, Spain and ESO.
ESPRESSO -- the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations -- was originally designed to hunt for Earth-like planets around Sun-like stars. However, it has proven to be much more versatile. "We soon realised that the remarkable collecting power of the VLT and the extreme stability of ESPRESSO made it a prime machine to study exoplanet atmospheres," says Pedro Figueira, ESPRESSO instrument scientist at ESO in Chile.
Read more at Science Daily
Mar 11, 2020
Community factors influence how long you'll live, study shows
While lifestyle choices and genetics go a long way toward predicting longevity, a new study shows that certain community characteristics also play important roles. American communities with more fast food restaurants, a larger share of extraction industry-based jobs, or higher population density have shorter life expectancies, according to researchers from Penn State, West Virginia, and Michigan State Universities. Their findings can help communities identify and implement changes that may promote longer lifespans among their residents.
"American life expectancy recently declined for the first time in decades, and we wanted to explore the factors contributing to this decline. Because of regional variation in life expectancy, we knew community-level factors must matter," said Elizabeth Dobis, a postdoctoral scholar at the Penn State-based Northeast Regional Center for Rural Development (NERCRD), and lead author of the study. "By analyzing place-based factors alongside personal factors, we were able to draw several conclusions about which community characteristics contribute most strongly to this variation in life expectancy."
Life expectancy refers to the length of time a person born in a given year can expect to live. Dobis and her colleagues analyzed on a county-by-county basis how life expectancy in 2014 has changed from a 1980 baseline, using data from more than 3,000 U.S. counties.
They developed a statistical model to determine the relationship between a dozen community variables and each county's 2014 life expectancy, while controlling for personal variables that are known to be important, such as sex, race, education, single-parent status, obesity, and alcohol use.
The community variables they examined included health care access, population growth and density, fast food restaurants, healthy food access, employment by sector, urbanization, and social capital, which measures the networks and bonds providing social cohesion among residents. They looked at each variable in isolation while holding others constant, allowing them to determine which variables independently exert the strongest effect on life expectancy.
The researchers found that a county's 1980 life expectancy value strongly predicted variations in the 2014 value, but it didn't account for all of the variation.
"When we controlled for historical life expectancy, we found three additional community factors that each exert a significant negative effect -- a greater number of fast food restaurants, higher population density, and a greater share of jobs in mining, quarrying, and oil and gas extraction," Dobis said. "For example, for every one percentage point increase in the number of fast food restaurants in a county, life expectancy declined by .004 years for men and .006 years for women."
This represents a 15-20 days shorter life span for every man, woman and child in a community, for each 10 percentage point increase in fast food restaurants in a community -- or a 150-200 day shorter life span if the number of fast food restaurants were to double.
Similarly, a one percent increase in a county's share of jobs in the mining, quarrying, oil and gas sectors was found to decrease average life expectancy by .04 years for men (or 15 days) and .06 years (22 days) for women.
The research, which was published recently in Social Science and Medicine, also revealed several community factors that are positively related to life expectancy, including a growing population, good access to physicians, and a greater level of social cohesion.
"We were surprised by the strong positive contribution of social capital to life expectancy within communities," said NERCRD Director Stephan Goetz, professor of agricultural economics and regional economics at Penn State and a co-author on the study. "Places with residents who stick together more on a community or social level also appear to do a better of job of helping people in general live longer."
"Another interesting finding was that lower population density, or living in more rural areas, is associated with higher life expectancy," Goetz said. "This suggests that living in large, densely-settled metropolitan areas, with all of their amenities and other advantages, comes at the expense of lower life expectancy, at least in a statistical sense."
In addition to being the first life-expectancy study to include community variables in a county-level analysis, this also was the first study to statistically analyze the extent to which disparities in life expectancy are geographically clustered. This analysis revealed some striking patterns.
"We found exceptionally low life expectancies in the areas of the Pine Ridge and Rosebud Reservations in South Dakota," Dobis said. "We found similar 'cold spots' of low life expectancy in the arctic and interior portions of Alaska, the Deep South surrounding the Mississippi River, and in the Appalachian regions of Kentucky and West Virginia."
The research also revealed four "hot spots" of high life expectancy: a section of the Northeast spanning from Philadelphia to New England, southern Minnesota and the eastern Dakotas into Nebraska, an area in Colorado, and an area spanning central Idaho into the upper Rocky Mountains.
The team's findings have important policy implications, as they suggest that certain aspects of the built environment can be changed to enhance life expectancy. For example, public places that promote social interaction could increase a community's social capital levels, which in turn promote longer lifespans.
Read more at Science Daily
"American life expectancy recently declined for the first time in decades, and we wanted to explore the factors contributing to this decline. Because of regional variation in life expectancy, we knew community-level factors must matter," said Elizabeth Dobis, a postdoctoral scholar at the Penn State-based Northeast Regional Center for Rural Development (NERCRD), and lead author of the study. "By analyzing place-based factors alongside personal factors, we were able to draw several conclusions about which community characteristics contribute most strongly to this variation in life expectancy."
Life expectancy refers to the length of time a person born in a given year can expect to live. Dobis and her colleagues analyzed on a county-by-county basis how life expectancy in 2014 has changed from a 1980 baseline, using data from more than 3,000 U.S. counties.
They developed a statistical model to determine the relationship between a dozen community variables and each county's 2014 life expectancy, while controlling for personal variables that are known to be important, such as sex, race, education, single-parent status, obesity, and alcohol use.
The community variables they examined included health care access, population growth and density, fast food restaurants, healthy food access, employment by sector, urbanization, and social capital, which measures the networks and bonds providing social cohesion among residents. They looked at each variable in isolation while holding others constant, allowing them to determine which variables independently exert the strongest effect on life expectancy.
The researchers found that a county's 1980 life expectancy value strongly predicted variations in the 2014 value, but it didn't account for all of the variation.
"When we controlled for historical life expectancy, we found three additional community factors that each exert a significant negative effect -- a greater number of fast food restaurants, higher population density, and a greater share of jobs in mining, quarrying, and oil and gas extraction," Dobis said. "For example, for every one percentage point increase in the number of fast food restaurants in a county, life expectancy declined by .004 years for men and .006 years for women."
This represents a 15-20 days shorter life span for every man, woman and child in a community, for each 10 percentage point increase in fast food restaurants in a community -- or a 150-200 day shorter life span if the number of fast food restaurants were to double.
Similarly, a one percent increase in a county's share of jobs in the mining, quarrying, oil and gas sectors was found to decrease average life expectancy by .04 years for men (or 15 days) and .06 years (22 days) for women.
The research, which was published recently in Social Science and Medicine, also revealed several community factors that are positively related to life expectancy, including a growing population, good access to physicians, and a greater level of social cohesion.
"We were surprised by the strong positive contribution of social capital to life expectancy within communities," said NERCRD Director Stephan Goetz, professor of agricultural economics and regional economics at Penn State and a co-author on the study. "Places with residents who stick together more on a community or social level also appear to do a better of job of helping people in general live longer."
"Another interesting finding was that lower population density, or living in more rural areas, is associated with higher life expectancy," Goetz said. "This suggests that living in large, densely-settled metropolitan areas, with all of their amenities and other advantages, comes at the expense of lower life expectancy, at least in a statistical sense."
In addition to being the first life-expectancy study to include community variables in a county-level analysis, this also was the first study to statistically analyze the extent to which disparities in life expectancy are geographically clustered. This analysis revealed some striking patterns.
"We found exceptionally low life expectancies in the areas of the Pine Ridge and Rosebud Reservations in South Dakota," Dobis said. "We found similar 'cold spots' of low life expectancy in the arctic and interior portions of Alaska, the Deep South surrounding the Mississippi River, and in the Appalachian regions of Kentucky and West Virginia."
The research also revealed four "hot spots" of high life expectancy: a section of the Northeast spanning from Philadelphia to New England, southern Minnesota and the eastern Dakotas into Nebraska, an area in Colorado, and an area spanning central Idaho into the upper Rocky Mountains.
The team's findings have important policy implications, as they suggest that certain aspects of the built environment can be changed to enhance life expectancy. For example, public places that promote social interaction could increase a community's social capital levels, which in turn promote longer lifespans.
Read more at Science Daily
Mar 10, 2020
How plants protect themselves from sun damage
For plants, sunlight can be a double-edged sword. They need it to drive photosynthesis, the process that allows them to store solar energy as sugar molecules, but too much sun can dehydrate and damage their leaves.
A primary strategy that plants use to protect themselves from this kind of photodamage is to dissipate the extra light as heat. However, there has been much debate over the past several decades over how plants actually achieve this.
"During photosynthesis, light-harvesting complexes play two seemingly contradictory roles. They absorb energy to drive water-splitting and photosynthesis, but at the same time, when there's too much energy, they have to also be able to get rid of it," says Gabriela Schlau-Cohen, the Thomas D. and Virginia W. Cabot Career Development Assistant Professor of Chemistry at MIT.
In a new study, Schlau-Cohen and colleagues at MIT, the University of Pavia, and the University of Verona directly observed, for the first time, one of the possible mechanisms that have been proposed for how plants dissipate energy. The researchers used a highly sensitive type of spectroscopy to determine that excess energy is transferred from chlorophyll, the pigment that gives leaves their green color, to other pigments called carotenoids, which can then release the energy as heat.
"This is the first direct observation of chlorophyll-to-carotenoid energy transfer in the light-harvesting complex of green plants," says Schlau-Cohen, who is the senior author of the study. "That's the simplest proposal, but no one's been able to find this photophysical pathway until now."
MIT graduate student Minjung Son is the lead author of the study, which appears today in Nature Communications. Other authors are Samuel Gordon '18, Alberta Pinnola of the University of Pavia, in Italy, and Roberto Bassi of the University of Verona.
Excess energy
When sunlight strikes a plant, specialized proteins known as light-harvesting complexes absorb light energy in the form of photons, with the help of pigments such as chlorophyll. These photons drive the production of sugar molecules, which store the energy for later use.
Much previous research has shown that plants are able to quickly adapt to changes in sunlight intensity. In very sunny conditions, they convert only about 30 percent of the available sunlight into sugar, while the rest is released as heat. If this excess energy is allowed to remain in the plant cells, it creates harmful molecules called free radicals that can damage proteins and other important cellular molecules.
"Plants can respond to fast changes in solar intensity by getting rid of extra energy, but what that photophysical pathway is has been debated for decades," Schlau-Cohen says.
The simplest hypothesis for how plants get rid of these extra photons is that once the light-harvesting complex absorbs them, chlorophylls pass them to nearby molecules called carotenoids. Carotenoids, which include lycopene and beta-carotene, are very good at getting rid of excess energy through rapid vibration. They are also skillful scavengers of free radicals, which helps to prevent damage to cells.
A similar type of energy transfer has been observed in bacterial proteins that are related to chlorophyll, but until now, it had not been seen in plants. One reason why it has been hard to observe this phenomenon is that it occurs on a very fast time scale (femtoseconds, or quadrillionths of a second). Another obstacle is that the energy transfer spans a broad range of energy levels. Until recently, existing methods for observing this process could only measure a small swath of the spectrum of visible light.
In 2017, Schlau-Cohen's lab developed a modification to a femtosecond spectroscopic technique that allows them to look at a broader range of energy levels, spanning red to blue light. This meant that they could monitor energy transfer between chlorophylls, which absorb red light, and carotenoids, which absorb blue and green light.
In this study, the researchers used this technique to show that photons move from an excited state, which is spread over multiple chlorophyll molecules within a light-harvesting complex, to nearby carotenoid molecules within the complex.
"By broadening the spectral bandwidth, we could look at the connection between the blue and the red ranges, allowing us to map out the changes in energy level. You can see energy moving from one excited state to another," Schlau-Cohen says.
Once the carotenoids accept the excess energy, they release most of it as heat, preventing light-induced damage to the cells.
Boosting crop yields
The researchers performed their experiments in two different environments -- one in which the proteins were in a detergent solution, and one in which they were embedded in a special type of self-assembling membrane called a nanodisc. They found that the energy transfer occurred more rapidly in the nanodisc, suggesting that environmental conditions affect the rate of energy dissipation.
It remains a mystery exactly how excess sunlight triggers this mechanism within plant cells. Schlau-Cohen's lab is now exploring whether the organization of chlorophylls and carotenoids within the chloroplast membrane play a role in activating the photoprotection system.
A better understanding of plants' natural photoprotection system could help scientists develop new ways to improve crop yields, Schlau-Cohen says. A 2016 paper from University of Illinois researchers showed that by overproducing all of the proteins involved in photoprotection, crop yields could be boosted by 15 to 20 percent. That paper also suggested that production could be further increased to a theoretical maximum of about 30 percent.
Read more at Science Daily
A primary strategy that plants use to protect themselves from this kind of photodamage is to dissipate the extra light as heat. However, there has been much debate over the past several decades over how plants actually achieve this.
"During photosynthesis, light-harvesting complexes play two seemingly contradictory roles. They absorb energy to drive water-splitting and photosynthesis, but at the same time, when there's too much energy, they have to also be able to get rid of it," says Gabriela Schlau-Cohen, the Thomas D. and Virginia W. Cabot Career Development Assistant Professor of Chemistry at MIT.
In a new study, Schlau-Cohen and colleagues at MIT, the University of Pavia, and the University of Verona directly observed, for the first time, one of the possible mechanisms that have been proposed for how plants dissipate energy. The researchers used a highly sensitive type of spectroscopy to determine that excess energy is transferred from chlorophyll, the pigment that gives leaves their green color, to other pigments called carotenoids, which can then release the energy as heat.
"This is the first direct observation of chlorophyll-to-carotenoid energy transfer in the light-harvesting complex of green plants," says Schlau-Cohen, who is the senior author of the study. "That's the simplest proposal, but no one's been able to find this photophysical pathway until now."
MIT graduate student Minjung Son is the lead author of the study, which appears today in Nature Communications. Other authors are Samuel Gordon '18, Alberta Pinnola of the University of Pavia, in Italy, and Roberto Bassi of the University of Verona.
Excess energy
When sunlight strikes a plant, specialized proteins known as light-harvesting complexes absorb light energy in the form of photons, with the help of pigments such as chlorophyll. These photons drive the production of sugar molecules, which store the energy for later use.
Much previous research has shown that plants are able to quickly adapt to changes in sunlight intensity. In very sunny conditions, they convert only about 30 percent of the available sunlight into sugar, while the rest is released as heat. If this excess energy is allowed to remain in the plant cells, it creates harmful molecules called free radicals that can damage proteins and other important cellular molecules.
"Plants can respond to fast changes in solar intensity by getting rid of extra energy, but what that photophysical pathway is has been debated for decades," Schlau-Cohen says.
The simplest hypothesis for how plants get rid of these extra photons is that once the light-harvesting complex absorbs them, chlorophylls pass them to nearby molecules called carotenoids. Carotenoids, which include lycopene and beta-carotene, are very good at getting rid of excess energy through rapid vibration. They are also skillful scavengers of free radicals, which helps to prevent damage to cells.
A similar type of energy transfer has been observed in bacterial proteins that are related to chlorophyll, but until now, it had not been seen in plants. One reason why it has been hard to observe this phenomenon is that it occurs on a very fast time scale (femtoseconds, or quadrillionths of a second). Another obstacle is that the energy transfer spans a broad range of energy levels. Until recently, existing methods for observing this process could only measure a small swath of the spectrum of visible light.
In 2017, Schlau-Cohen's lab developed a modification to a femtosecond spectroscopic technique that allows them to look at a broader range of energy levels, spanning red to blue light. This meant that they could monitor energy transfer between chlorophylls, which absorb red light, and carotenoids, which absorb blue and green light.
In this study, the researchers used this technique to show that photons move from an excited state, which is spread over multiple chlorophyll molecules within a light-harvesting complex, to nearby carotenoid molecules within the complex.
"By broadening the spectral bandwidth, we could look at the connection between the blue and the red ranges, allowing us to map out the changes in energy level. You can see energy moving from one excited state to another," Schlau-Cohen says.
Once the carotenoids accept the excess energy, they release most of it as heat, preventing light-induced damage to the cells.
Boosting crop yields
The researchers performed their experiments in two different environments -- one in which the proteins were in a detergent solution, and one in which they were embedded in a special type of self-assembling membrane called a nanodisc. They found that the energy transfer occurred more rapidly in the nanodisc, suggesting that environmental conditions affect the rate of energy dissipation.
It remains a mystery exactly how excess sunlight triggers this mechanism within plant cells. Schlau-Cohen's lab is now exploring whether the organization of chlorophylls and carotenoids within the chloroplast membrane play a role in activating the photoprotection system.
A better understanding of plants' natural photoprotection system could help scientists develop new ways to improve crop yields, Schlau-Cohen says. A 2016 paper from University of Illinois researchers showed that by overproducing all of the proteins involved in photoprotection, crop yields could be boosted by 15 to 20 percent. That paper also suggested that production could be further increased to a theoretical maximum of about 30 percent.
Read more at Science Daily
Our brains are powerful -- but secretive -- forecasters of video virality
When Stanford University neuroscientist Brian Knutson tracked his smartphone usage, he was shocked to learn that he spent twice as much time on his phone as he had anticipated.
"In many of our lives, every day, there is often a gap between what we actually do and what we intend to do," said Knutson, who is a professor of psychology in the School of Humanities and Sciences, reflecting on his smartphone habits. "We want to understand how and why people's choices lead to unintended consequences -- like wasting money or even time -- and also whether processes that generate individual choice can tell us something about choices made by large groups of people."
Toward that end, Knutson and colleagues are investigating an approach he calls "neuroforecasting" -- in which they use brain data from individuals who are in the process of making decisions to forecast how larger groups of unrelated people will respond to the same choices. His lab's latest neuroforecasting work in collaboration with researchers at Stanford's Graduate School of Business, published Mar. 9 in the journal Proceedings of the National Academy of Sciences, focused on how people spend time watching videos online.
By scanning people's brains as they selected and watched videos, the researchers discovered that both neural and behavioral responses to a video could forecast how long other people will watch that same video on the internet. When forecasting video popularity on the internet, however, brain responses were the only measure that mattered.
"Here, we have a case where there is information contained in subjects' brain activity that allows us to forecast the behavior of other, unrelated, people -- but it's not necessarily reflected in their self-reports or behavior," explained Lester Tong, a graduate student in the Knutson lab. "One of the key takeaways here is that brain activity matters, and can even reveal hidden information."
Cerebral secrets
The researchers analyzed data from 36 participants, who watched videos while being scanned with a brain imaging technique known as fMRI. The researchers also monitored participants' behavior -- like whether they chose to skip a video -- and asked them questions about each video, like how it made them feel and whether they thought it would be popular. Then, they examined how those same videos performed on the internet in terms of daily views and average duration of viewings.
Because videos are complex and change over time, the researchers specifically examined brain responses to the start and end of videos, as well as average responses to each video. They focused on activity in brain regions previously shown to predict peoples' willingness to spend money.
The researchers found that longer video views were associated with activity in reward-sensitive regions of the brain, while shorter video views were associated with activity in regions sensitive to arousal or punishment. The subjects' answers to questions about the videos also predicted their own behavior.
When it came to forecasting the behavior of others online, however, the data told a different story. Both the group's behavior and brain activity forecasted how long people would watch the videos online. However, only group brain activity forecasted the popularity (or views per day) of each video online. During just the first four seconds of watching each video, more activity in the brain region associated with anticipating reward forecasted a video's popularity online, whereas heightened activity in the region associated with anticipating punishment forecasted decreased popularity.
"If we examine our subjects' choices to watch the video or even their reported responses to the videos, they don't tell us about the general response online. Only brain activity seems to forecast a video's popularity on the internet," explained Knutson, who co-leads the NeuroChoice Initiative of the Stanford Wu Tsai Neurosciences Institute.
This and related research indicate that some steps of the choice process may prove more useful for broad neuroforecasting than others. By teasing out the specifics of which steps matter, the researchers think neuroforecasting might even apply across groups of different ages, genders, races or cultures when they show similar early neural responses.
Valuable choices
These findings suggest similarities between neuroforecasting how people spend time and how they spend money online, which the team has previously studied in non-traditional markets, including online markets for micro-loans and crowdfunding.
Knutson and his NeuroChoice colleagues have also been investigating neural mechanisms of choice in the context of drug addiction. In the future, they aim to continue exploring when brain data can complement behavioral data, and in which situations.
Read more at Science Daily
"In many of our lives, every day, there is often a gap between what we actually do and what we intend to do," said Knutson, who is a professor of psychology in the School of Humanities and Sciences, reflecting on his smartphone habits. "We want to understand how and why people's choices lead to unintended consequences -- like wasting money or even time -- and also whether processes that generate individual choice can tell us something about choices made by large groups of people."
Toward that end, Knutson and colleagues are investigating an approach he calls "neuroforecasting" -- in which they use brain data from individuals who are in the process of making decisions to forecast how larger groups of unrelated people will respond to the same choices. His lab's latest neuroforecasting work in collaboration with researchers at Stanford's Graduate School of Business, published Mar. 9 in the journal Proceedings of the National Academy of Sciences, focused on how people spend time watching videos online.
By scanning people's brains as they selected and watched videos, the researchers discovered that both neural and behavioral responses to a video could forecast how long other people will watch that same video on the internet. When forecasting video popularity on the internet, however, brain responses were the only measure that mattered.
"Here, we have a case where there is information contained in subjects' brain activity that allows us to forecast the behavior of other, unrelated, people -- but it's not necessarily reflected in their self-reports or behavior," explained Lester Tong, a graduate student in the Knutson lab. "One of the key takeaways here is that brain activity matters, and can even reveal hidden information."
Cerebral secrets
The researchers analyzed data from 36 participants, who watched videos while being scanned with a brain imaging technique known as fMRI. The researchers also monitored participants' behavior -- like whether they chose to skip a video -- and asked them questions about each video, like how it made them feel and whether they thought it would be popular. Then, they examined how those same videos performed on the internet in terms of daily views and average duration of viewings.
Because videos are complex and change over time, the researchers specifically examined brain responses to the start and end of videos, as well as average responses to each video. They focused on activity in brain regions previously shown to predict peoples' willingness to spend money.
The researchers found that longer video views were associated with activity in reward-sensitive regions of the brain, while shorter video views were associated with activity in regions sensitive to arousal or punishment. The subjects' answers to questions about the videos also predicted their own behavior.
When it came to forecasting the behavior of others online, however, the data told a different story. Both the group's behavior and brain activity forecasted how long people would watch the videos online. However, only group brain activity forecasted the popularity (or views per day) of each video online. During just the first four seconds of watching each video, more activity in the brain region associated with anticipating reward forecasted a video's popularity online, whereas heightened activity in the region associated with anticipating punishment forecasted decreased popularity.
"If we examine our subjects' choices to watch the video or even their reported responses to the videos, they don't tell us about the general response online. Only brain activity seems to forecast a video's popularity on the internet," explained Knutson, who co-leads the NeuroChoice Initiative of the Stanford Wu Tsai Neurosciences Institute.
This and related research indicate that some steps of the choice process may prove more useful for broad neuroforecasting than others. By teasing out the specifics of which steps matter, the researchers think neuroforecasting might even apply across groups of different ages, genders, races or cultures when they show similar early neural responses.
Valuable choices
These findings suggest similarities between neuroforecasting how people spend time and how they spend money online, which the team has previously studied in non-traditional markets, including online markets for micro-loans and crowdfunding.
Knutson and his NeuroChoice colleagues have also been investigating neural mechanisms of choice in the context of drug addiction. In the future, they aim to continue exploring when brain data can complement behavioral data, and in which situations.
Read more at Science Daily
How a virus forms its symmetric shells
Viruses -- small disease-causing parasites that can infect all types of life forms -- have been well studied, but many mysteries linger. One such mystery is how a spherical virus circumvents energy barriers to form symmetric shells.
A research team led by physicist Roya Zandi at the University of California, Riverside, has made progress is solving this mystery. The team reports in a paper published in ACS Nano that an interplay of energies at the molecular level makes the formation of a shell possible.
Understanding the factors that contribute to viral assembly could enable biomedical attempts to block viral replication and infection. A better understanding of how viral shells -- nature's nano-containers -- form is of vital importance to material scientists and a crucial step in the design of engineered nano-shells that could serve as vehicles for delivering drugs to specific targets in the body.
Zandi's team explored the role of protein concentration and elastic energy in the self-organization of proteins on the curved shell surface to understand how a virus circumvents many energy barriers.
"Understanding the combined effect of elastic energy, genome-protein interaction, and protein concentration in the viral assembly constitutes the breakthrough of our work," said Zandi, a professor in the Department of Physics and Astronomy. "Our study shows that if a messy shell forms because of the high protein concentration or strong attractive interaction, then, as the shell grows larger, the cost of elastic energy becomes so high that several bonds can get broken, resulting in the disassembly and subsequent reassembly of a symmetric shell."
What is a virus?
The simplest physical object in biology, a virus consists of a protein shell called the capsid, which protects its nucleic acid genome -- RNA or DNA. Viruses can be thought of as mobile containers of RNA or DNA that insert their genetic material into living cells. They then take over the cells' reproductive machinery to reproduce their own genome and capsid.
Capsid formation is one of the most crucial steps in the process of viral infection. The capsid can be cylindrical or conical in shape, but more commonly it assumes an icosahedral structure, like a soccer ball.
An icosahedron is a geometrical structure with 12 vertices, 20 faces, and 30 sides. An official soccer ball is a kind of icosahedron called a truncated icosahedron; it has 32 panels cut into the shape of 20 hexagons and 12 pentagons, with the pentagons separated from each other by hexagons.
Viral assembly is not well understood because viruses are very small, measuring in nanometers, a nanometer being one-billionth of a meter. The assembly also happens very quickly, typically in milliseconds, a millisecond being one-thousandth of a second. Theoretical work and simulations are necessary to understand how a virus grows.
"A viral shell is highly symmetric," Zandi said. "If one pentagonal defect forms in the wrong location, it breaks down the symmetry. Despite this sensitivity, viral shells are often assembled into well-defined symmetric structures."
Nano vehicles
Zandi explained that due to a lack of experimental data, the virus assembly process is not well understood. The new work found the elastic properties of capsid proteins and the attractive interaction between them go hand in hand to form highly symmetric configurations that are energetically very stable.
"By fine-tuning these parameters, we can control the final structure and stability of viral capsids," she said. "These viral capsids can be used as nano-containers for transporting drugs as cargo to specific targets. What makes them highly promising for drug delivery and gene delivery purposes is that they are stable, have a high uptake efficiency, and have low toxicity."
Already, some experimental groups are working with pharmaceutical companies to design drugs that interfere or block viral assembly. Her lab is working with international collaborators to design simulations to better understand virus assembly.
Read more at Science Daily
A research team led by physicist Roya Zandi at the University of California, Riverside, has made progress is solving this mystery. The team reports in a paper published in ACS Nano that an interplay of energies at the molecular level makes the formation of a shell possible.
Understanding the factors that contribute to viral assembly could enable biomedical attempts to block viral replication and infection. A better understanding of how viral shells -- nature's nano-containers -- form is of vital importance to material scientists and a crucial step in the design of engineered nano-shells that could serve as vehicles for delivering drugs to specific targets in the body.
Zandi's team explored the role of protein concentration and elastic energy in the self-organization of proteins on the curved shell surface to understand how a virus circumvents many energy barriers.
"Understanding the combined effect of elastic energy, genome-protein interaction, and protein concentration in the viral assembly constitutes the breakthrough of our work," said Zandi, a professor in the Department of Physics and Astronomy. "Our study shows that if a messy shell forms because of the high protein concentration or strong attractive interaction, then, as the shell grows larger, the cost of elastic energy becomes so high that several bonds can get broken, resulting in the disassembly and subsequent reassembly of a symmetric shell."
What is a virus?
The simplest physical object in biology, a virus consists of a protein shell called the capsid, which protects its nucleic acid genome -- RNA or DNA. Viruses can be thought of as mobile containers of RNA or DNA that insert their genetic material into living cells. They then take over the cells' reproductive machinery to reproduce their own genome and capsid.
Capsid formation is one of the most crucial steps in the process of viral infection. The capsid can be cylindrical or conical in shape, but more commonly it assumes an icosahedral structure, like a soccer ball.
An icosahedron is a geometrical structure with 12 vertices, 20 faces, and 30 sides. An official soccer ball is a kind of icosahedron called a truncated icosahedron; it has 32 panels cut into the shape of 20 hexagons and 12 pentagons, with the pentagons separated from each other by hexagons.
Viral assembly is not well understood because viruses are very small, measuring in nanometers, a nanometer being one-billionth of a meter. The assembly also happens very quickly, typically in milliseconds, a millisecond being one-thousandth of a second. Theoretical work and simulations are necessary to understand how a virus grows.
"A viral shell is highly symmetric," Zandi said. "If one pentagonal defect forms in the wrong location, it breaks down the symmetry. Despite this sensitivity, viral shells are often assembled into well-defined symmetric structures."
Nano vehicles
Zandi explained that due to a lack of experimental data, the virus assembly process is not well understood. The new work found the elastic properties of capsid proteins and the attractive interaction between them go hand in hand to form highly symmetric configurations that are energetically very stable.
"By fine-tuning these parameters, we can control the final structure and stability of viral capsids," she said. "These viral capsids can be used as nano-containers for transporting drugs as cargo to specific targets. What makes them highly promising for drug delivery and gene delivery purposes is that they are stable, have a high uptake efficiency, and have low toxicity."
Already, some experimental groups are working with pharmaceutical companies to design drugs that interfere or block viral assembly. Her lab is working with international collaborators to design simulations to better understand virus assembly.
Read more at Science Daily
Knowing more about a virus threat may not satisfy you
People who rate themselves as highly knowledgeable about a new infectious disease threat could also be more likely to believe they don't know enough, a new study suggests.
In the case of this study, the infectious disease threat was the Zika virus. But the authors of the new study, published recently in the journal Risk Analysis, say the results could apply to the recent novel coronavirus (COVID-19) outbreak.
"The Zika virus and the coronavirus have important things in common," said Shelly Hovick, co-author of the study and assistant professor of communication at The Ohio State University.
"In both cases, they are shrouded in uncertainty and have received a lot of media attention. Our research looks at how people seek and process information when there is so much uncertainty."
One of the key findings of the new study: With limited information about Zika available, more knowledge was not that comforting.
"We found that the more people thought they knew, the more they realized they didn't know enough," said Austin Hubner, lead author of the study and a doctoral student in communication at Ohio State.
"With the Zika virus, even the experts themselves didn't know much at the time. That's the same thing we're seeing with the coronavirus, and that's scary for people who believe they are at risk."
For the study, the researchers conducted an online survey of 494 people of childbearing age living in Florida in December 2016.
Florida residents were recruited for the study because it had the highest number of locally transmitted cases of Zika in the United States at the time.
Although most people infected with Zika don't have symptoms, pregnant women with the virus have a higher likelihood of their child being born with a specific birth defect.
Zika is primarily spread by mosquitoes, but it can also be transmitted from men and women to their sexual partners and through blood transfusions.
In the survey, respondents were asked a variety of questions about their knowledge and attitudes toward seeking information, how they processed what they learned about the Zika virus, and their plans for seeking more information.
As expected, participants who were pregnant or wanted to get pregnant (and men whose wives were in those situations) felt more at risk from Zika and were more likely to say they felt scared of Zika. But they weren't the only ones who felt worried about Zika.
"Novel risks like Zika or coronavirus may make some people react differently than well-known risks like cancer or the flu," Hovick said.
"Even if the data suggest someone is at low risk, the lack of information may make some people feel they are at high risk."
The findings showed that people who felt they didn't know enough about Zika didn't intend to spend more time than others seeking information. That was probably because they realized that there wasn't more information available, Hovick said.
But they did spend more time processing the information they uncovered and were more likely to agree with statements like "After I encounter information about Zika, I am likely to stop and think about it."
These findings suggest it is important for public health agencies to continuously update the public, Hovick said. Those who are worried or concerned about risks such as Zika are likely to process the information they encounter deeply, but they may not seek information on their own.
Participants were also more likely to intend to seek information about Zika if they believed other people expected them to do so. They were more likely to want to search for information if they agreed with statements like "People in my life whose opinions I value seek information about Zika."
"We should aim not just to provide information, but also shape messages that encourage people to stay on top of the situation, particularly in high-uncertainty environments," Hovick said.
"You have to make it clear that seeking more knowledge is something that their friends and family expect of them."
Hovick said they have considered trying to replicate the study with the current coronavirus outbreak, but that Zika virus was slower developing.
Read more at Science Daily
In the case of this study, the infectious disease threat was the Zika virus. But the authors of the new study, published recently in the journal Risk Analysis, say the results could apply to the recent novel coronavirus (COVID-19) outbreak.
"The Zika virus and the coronavirus have important things in common," said Shelly Hovick, co-author of the study and assistant professor of communication at The Ohio State University.
"In both cases, they are shrouded in uncertainty and have received a lot of media attention. Our research looks at how people seek and process information when there is so much uncertainty."
One of the key findings of the new study: With limited information about Zika available, more knowledge was not that comforting.
"We found that the more people thought they knew, the more they realized they didn't know enough," said Austin Hubner, lead author of the study and a doctoral student in communication at Ohio State.
"With the Zika virus, even the experts themselves didn't know much at the time. That's the same thing we're seeing with the coronavirus, and that's scary for people who believe they are at risk."
For the study, the researchers conducted an online survey of 494 people of childbearing age living in Florida in December 2016.
Florida residents were recruited for the study because it had the highest number of locally transmitted cases of Zika in the United States at the time.
Although most people infected with Zika don't have symptoms, pregnant women with the virus have a higher likelihood of their child being born with a specific birth defect.
Zika is primarily spread by mosquitoes, but it can also be transmitted from men and women to their sexual partners and through blood transfusions.
In the survey, respondents were asked a variety of questions about their knowledge and attitudes toward seeking information, how they processed what they learned about the Zika virus, and their plans for seeking more information.
As expected, participants who were pregnant or wanted to get pregnant (and men whose wives were in those situations) felt more at risk from Zika and were more likely to say they felt scared of Zika. But they weren't the only ones who felt worried about Zika.
"Novel risks like Zika or coronavirus may make some people react differently than well-known risks like cancer or the flu," Hovick said.
"Even if the data suggest someone is at low risk, the lack of information may make some people feel they are at high risk."
The findings showed that people who felt they didn't know enough about Zika didn't intend to spend more time than others seeking information. That was probably because they realized that there wasn't more information available, Hovick said.
But they did spend more time processing the information they uncovered and were more likely to agree with statements like "After I encounter information about Zika, I am likely to stop and think about it."
These findings suggest it is important for public health agencies to continuously update the public, Hovick said. Those who are worried or concerned about risks such as Zika are likely to process the information they encounter deeply, but they may not seek information on their own.
Participants were also more likely to intend to seek information about Zika if they believed other people expected them to do so. They were more likely to want to search for information if they agreed with statements like "People in my life whose opinions I value seek information about Zika."
"We should aim not just to provide information, but also shape messages that encourage people to stay on top of the situation, particularly in high-uncertainty environments," Hovick said.
"You have to make it clear that seeking more knowledge is something that their friends and family expect of them."
Hovick said they have considered trying to replicate the study with the current coronavirus outbreak, but that Zika virus was slower developing.
Read more at Science Daily
Mar 9, 2020
Cosmic impact caused destruction of one of world's earliest human settlements
Before the Taqba Dam impounded the Euphrates River in northern Syria in the 1970s, an archaeological site named Abu Hureyra bore witness to the moment ancient nomadic people first settled down and started cultivating crops. A large mound marks the settlement, which now lies under Lake Assad.
But before the lake formed, archaeologists were able to carefully extract and describe much material, including parts of houses, food and tools -- an abundance of evidence that allowed them to identify the transition to agriculture nearly 12,800 years ago. It was one of the most significant events in our Earth's cultural and environmental history.
Abu Hureyra, it turns out, has another story to tell. Found among the cereals and grains and splashed on early building material and animal bones was meltglass, some features of which suggest it was formed at extremely high temperatures -- far higher than what humans could achieve at the time -- or that could be attributed to fire, lighting or volcanism.
"To help with perspective, such high temperatures would completely melt an automobile in less than a minute," said James Kennett, a UC Santa Barbara emeritus professor of geology. Such intensity, he added, could only have resulted from an extremely violent, high-energy, high-velocity phenomenon, something on the order of a cosmic impact.
Based on materials collected before the site was flooded, Kennett and his colleagues contend Abu Hureyra is the first site to document the direct effects of a fragmented comet on a human settlement. These fragments are all part of the same comet that likely slammed into Earth and exploded in the atmosphere at the end of the Pleistocene epoch, according to Kennett. This impact contributed to the extinction of most large animals, including mammoths, and American horses and camels; the disappearance of the North American Clovis culture; and to the abrupt onset of the end-glacial Younger Dryas cooling episode.
The team's findings are highlighted in a paper published in the Nature journal Scientific Reports.
"Our new discoveries represent much more powerful evidence for very high temperatures that could only be associated with a cosmic impact," said Kennett, who with his colleagues first reported evidence of such an event in the region in 2012.
Abu Hureyra lies at the easternmost sector of what is known as the Younger Dryas Boundary (YDB) strewnfield, which encompasses about 30 other sites in the Americas, Europe and parts of the Middle East. These sites hold evidence of massive burning, including a widespread carbon-rich "black mat" layer that contains millions of nanodiamonds, high concentrations of platinum and tiny metallic spherules formed at very high temperatures. The YDB impact hypothesis has gained more traction in recent years because of many new discoveries, including a very young impact crater beneath the Hiawatha Glacier of the Greenland ice sheet, and high-temperature meltglass and other similar evidence at an archaeological site in Pilauco, located in southern Chile.
"The Abu Hureyra village would have been abruptly destroyed," Kennett said. Unlike the evidence from Pilauco, which was limited to human butchering of large animals up to but not younger than the YDB impact burn layer, Abu Hureyra shows direct evidence of the disaster on this early human settlement. An impact or an airburst must have occurred sufficiently close to send massive heat and molten glass over the entire early village, Kennett noted.
The glass was analyzed for geochemical composition, shape, structure, formation temperature, magnetic characteristics and water content. Results from the analysis showed that it formed at very high temperatures and included minerals rich in chromium, iron, nickel, sulfides, titanium and even platinum- and iridium-rich melted iron -- all of which formed in temperatures higher than 2200 degrees Celsius.
"The critical materials are extremely rare under normal temperatures, but are commonly found during impact events," Kennett said. According to the study, the meltglass was formed "from the nearly instantaneous melting and vaporization of regional biomass, soils and floodplain deposits, followed by instantaneous cooling." Additionally, because the materials found are consistent with those found in the YDB layers at the other sites across the world, it's likely that they resulted from a fragmented comet, as opposed to impacts caused by individual comets or asteroids.
Read more at Science Daily
But before the lake formed, archaeologists were able to carefully extract and describe much material, including parts of houses, food and tools -- an abundance of evidence that allowed them to identify the transition to agriculture nearly 12,800 years ago. It was one of the most significant events in our Earth's cultural and environmental history.
Abu Hureyra, it turns out, has another story to tell. Found among the cereals and grains and splashed on early building material and animal bones was meltglass, some features of which suggest it was formed at extremely high temperatures -- far higher than what humans could achieve at the time -- or that could be attributed to fire, lighting or volcanism.
"To help with perspective, such high temperatures would completely melt an automobile in less than a minute," said James Kennett, a UC Santa Barbara emeritus professor of geology. Such intensity, he added, could only have resulted from an extremely violent, high-energy, high-velocity phenomenon, something on the order of a cosmic impact.
Based on materials collected before the site was flooded, Kennett and his colleagues contend Abu Hureyra is the first site to document the direct effects of a fragmented comet on a human settlement. These fragments are all part of the same comet that likely slammed into Earth and exploded in the atmosphere at the end of the Pleistocene epoch, according to Kennett. This impact contributed to the extinction of most large animals, including mammoths, and American horses and camels; the disappearance of the North American Clovis culture; and to the abrupt onset of the end-glacial Younger Dryas cooling episode.
The team's findings are highlighted in a paper published in the Nature journal Scientific Reports.
"Our new discoveries represent much more powerful evidence for very high temperatures that could only be associated with a cosmic impact," said Kennett, who with his colleagues first reported evidence of such an event in the region in 2012.
Abu Hureyra lies at the easternmost sector of what is known as the Younger Dryas Boundary (YDB) strewnfield, which encompasses about 30 other sites in the Americas, Europe and parts of the Middle East. These sites hold evidence of massive burning, including a widespread carbon-rich "black mat" layer that contains millions of nanodiamonds, high concentrations of platinum and tiny metallic spherules formed at very high temperatures. The YDB impact hypothesis has gained more traction in recent years because of many new discoveries, including a very young impact crater beneath the Hiawatha Glacier of the Greenland ice sheet, and high-temperature meltglass and other similar evidence at an archaeological site in Pilauco, located in southern Chile.
"The Abu Hureyra village would have been abruptly destroyed," Kennett said. Unlike the evidence from Pilauco, which was limited to human butchering of large animals up to but not younger than the YDB impact burn layer, Abu Hureyra shows direct evidence of the disaster on this early human settlement. An impact or an airburst must have occurred sufficiently close to send massive heat and molten glass over the entire early village, Kennett noted.
The glass was analyzed for geochemical composition, shape, structure, formation temperature, magnetic characteristics and water content. Results from the analysis showed that it formed at very high temperatures and included minerals rich in chromium, iron, nickel, sulfides, titanium and even platinum- and iridium-rich melted iron -- all of which formed in temperatures higher than 2200 degrees Celsius.
"The critical materials are extremely rare under normal temperatures, but are commonly found during impact events," Kennett said. According to the study, the meltglass was formed "from the nearly instantaneous melting and vaporization of regional biomass, soils and floodplain deposits, followed by instantaneous cooling." Additionally, because the materials found are consistent with those found in the YDB layers at the other sites across the world, it's likely that they resulted from a fragmented comet, as opposed to impacts caused by individual comets or asteroids.
Read more at Science Daily
Safety zone saves giant moons from fatal plunge
Numerical simulations showed that the temperature gradient in the disk of gas around a young gas giant planet could play a critical role in the development of a satellite system dominated by a single large moon, similar to Titan around Saturn. Researchers found that dust in the circumplanetary disk can create a "safety zone," which keeps the moon from falling into the planet as the system evolves.
Astronomers believe that many of the moons we see in the Solar System, especially large moons, formed along with the parent planet. In this scenario, moons form from the gas and dust spinning around the still forming planet. But previous simulations have resulted in either all large moons falling into the planet and being swallowed-up or in multiple large moons remaining. The situation we observe around Saturn, with many small moons but only one large moon, does not fit in either of these models.
Yuri Fujii, a Designated Assistant Professor at Nagoya University, and Masahiro Ogihara, a Project Assistant Professor at the National Astronomical Observatory of Japan (NAOJ), created a new model of circumplanetary disks with a more realistic temperature distribution by considering multiple sources of opacities including dust and ice. Then, they simulated the orbital migration of moons considering pressure from disk gas and the gravity of other satellites.
Their simulations show that there is a "safety zone" where a moon is pushed away from the planet. In this area, warmer gas inside the orbit pushes the satellite outward and prevents it from falling into the planet.
"We demonstrated for the first time that a system with only one large moon around a giant planet can form," says Fujii. "This is an important milestone to understand the origin of Titan."
But Ogihara cautions, "It would be difficult to examine whether Titan actually experienced this process. Our scenario could be verified through research of satellites around extrasolar planets. If many single-exomoon systems are found, the formation mechanisms of such systems will become a red-hot issue."
From Science Daily
Astronomers believe that many of the moons we see in the Solar System, especially large moons, formed along with the parent planet. In this scenario, moons form from the gas and dust spinning around the still forming planet. But previous simulations have resulted in either all large moons falling into the planet and being swallowed-up or in multiple large moons remaining. The situation we observe around Saturn, with many small moons but only one large moon, does not fit in either of these models.
Yuri Fujii, a Designated Assistant Professor at Nagoya University, and Masahiro Ogihara, a Project Assistant Professor at the National Astronomical Observatory of Japan (NAOJ), created a new model of circumplanetary disks with a more realistic temperature distribution by considering multiple sources of opacities including dust and ice. Then, they simulated the orbital migration of moons considering pressure from disk gas and the gravity of other satellites.
Their simulations show that there is a "safety zone" where a moon is pushed away from the planet. In this area, warmer gas inside the orbit pushes the satellite outward and prevents it from falling into the planet.
"We demonstrated for the first time that a system with only one large moon around a giant planet can form," says Fujii. "This is an important milestone to understand the origin of Titan."
But Ogihara cautions, "It would be difficult to examine whether Titan actually experienced this process. Our scenario could be verified through research of satellites around extrasolar planets. If many single-exomoon systems are found, the formation mechanisms of such systems will become a red-hot issue."
From Science Daily
'Strange' glimpse into neutron stars and symmetry violation
New results from precision particle detectors at the Relativistic Heavy Ion Collider (RHIC) offer a fresh glimpse of the particle interactions that take place in the cores of neutron stars and give nuclear physicists a new way to search for violations of fundamental symmetries in the universe. The results, just published in Nature Physics, could only be obtained at a powerful ion collider such as RHIC, a U.S. Department of Energy (DOE) Office of Science user facility for nuclear physics research at DOE's Brookhaven National Laboratory.
The precision measurements reveal that the binding energy holding together the components of the simplest "strange-matter" nucleus, known as a "hypertriton," is greater than obtained by previous, less-precise experiments. The new value could have important astrophysical implications for understanding the properties of neutron stars, where the presence of particles containing so-called "strange" quarks is predicted to be common.
The second measurement was a search for a difference between the mass of the hypertriton and its antimatter counterpart, the antihypertriton (the first nucleus containing an antistrange quark, discovered at RHIC in 2010). Physicists have never found a mass difference between matter-antimatter partners so seeing one would be a big discovery. It would be evidence of "CPT" violation -- a simultaneous violation of three fundamental symmetries in nature pertaining to the reversal of charge, parity (mirror symmetry), and time.
"Physicists have seen parity violation, and violation of CP together (each earning a Nobel Prize for Brookhaven Lab[ -- ), but never CPT," said Brookhaven physicist Zhangbu Xu, co-spokesperson of RHIC's STAR experiment, where the hypertriton research was done.
But no one has looked for CPT violation in the hypertriton and antihypertriton, he said, "because no one else could yet."
The previous CPT test of the heaviest nucleus was performed by the ALICE collaboration at Europe's Large Hadron Collider (LHC), with a measurement of the mass difference between ordinary helium-3 and antihelium-3. The result, showing no significant difference, was published in Nature Physics in 2015.
Spoiler alert: The STAR results also reveal no significant mass difference between the matter-antimatter partners explored at RHIC, so there's still no evidence of CPT violation. But the fact that STAR physicists could even make the measurements is a testament to the remarkable capabilities of their detector.
Strange matter
The simplest normal-matter nuclei contain just protons and neutrons, with each of those particles made of ordinary "up" and "down" quarks. In hypertritons, one neutron is replaced by a particle called a lambda, which contains one strange quark along with the ordinary up and down varieties.
Such strange matter replacements are common in the ultra-dense conditions created in RHIC's collisions -- and are also likely in the cores of neutron stars where a single teaspoon of matter would weigh more than 1 billion tons. That's because the high density makes it less costly energy-wise to make strange quarks than the ordinary up and down varieties.
For that reason, RHIC collisions give nuclear physicists a way to peer into the subatomic interactions within distant stellar objects without ever leaving Earth. And because RHIC collisions create hypertritons and antihypertritons in nearly equal amounts, they offer a way to search for CPT violation as well.
But finding those rare particles among the thousands that stream from each RHIC particle smashup -- with collisions happening thousands of times each second -- is a daunting task. Add to the challenge the fact that these unstable particles decay almost as soon as they form -- within centimeters of the center of the four-meter-wide STAR detector.
Precision detection
Fortunately, detector components added to STAR for tracking different kinds of particles made the search a relative cinch. These components, called the "Heavy-Flavor Tracker," are located very close to the STAR detector's center. They were developed and built by a team of STAR collaborators led by scientists and engineers at DOE's Lawrence Berkeley National Laboratory (Berkeley Lab). These inner components allow scientists to match up tracks created by decay products of each hypertriton and antihypertriton with their point of origin just outside the collision zone.
"What we look for are the 'daughter' particles -- the decay products that strike detector components at the outer edges of STAR," said Berkeley Lab physicist Xin Dong. Identifying tracks of pairs or triplets of daughter particles that originate from a single point just outside the primary collision zone allows the scientists to pick these signals out from the sea of other particles streaming from each RHIC collision.
"Then we calculate the momentum of each daughter particle from one decay (based on how much they bend in STAR's magnetic field), and from that we can reconstruct their masses and the mass of the parent hypertriton or antihypertriton particle before it decayed," explained Declan Keane of Kent State University (KSU). Telling the hypertriton and antihypertriton apart is easy because they decay into different daughters, he added.
"Keane's team, including Irakli Chakeberia, has specialized in tracking these particles through the detectors to 'connect the dots,'" Xu said. "They also provided much needed visualization of the events."
As noted, compiling data from many collisions revealed no mass difference between the matter and antimatter hypernuclei, so there's no evidence of CPT violation in these results.
But when STAR physicists looked at their results for the binding energy of the hypertriton, it turned out to be larger than previous measurements from the 1970s had found.
The STAR physicists derived the binding energy by subtracting their value for the hypertriton mass from the combined known masses of its building-block particles: a deuteron (a bound state of a proton and a neutron) and one lambda.
"The hypertriton weighs less than the sum of its parts because some of that mass is converted into the energy that is binding the three nucleons together," said Fudan University STAR collaborator Jinhui Chen, whose PhD student, Peng Liu, analyzed the large datasets to arrive at these results. "This binding energy is really a measure of the strength of these interactions, so our new measurement could have important implications for understanding the 'equation of state' of neutron stars," he added.
Read more at Science Daily
The precision measurements reveal that the binding energy holding together the components of the simplest "strange-matter" nucleus, known as a "hypertriton," is greater than obtained by previous, less-precise experiments. The new value could have important astrophysical implications for understanding the properties of neutron stars, where the presence of particles containing so-called "strange" quarks is predicted to be common.
The second measurement was a search for a difference between the mass of the hypertriton and its antimatter counterpart, the antihypertriton (the first nucleus containing an antistrange quark, discovered at RHIC in 2010). Physicists have never found a mass difference between matter-antimatter partners so seeing one would be a big discovery. It would be evidence of "CPT" violation -- a simultaneous violation of three fundamental symmetries in nature pertaining to the reversal of charge, parity (mirror symmetry), and time.
"Physicists have seen parity violation, and violation of CP together (each earning a Nobel Prize for Brookhaven Lab[ -- ), but never CPT," said Brookhaven physicist Zhangbu Xu, co-spokesperson of RHIC's STAR experiment, where the hypertriton research was done.
But no one has looked for CPT violation in the hypertriton and antihypertriton, he said, "because no one else could yet."
The previous CPT test of the heaviest nucleus was performed by the ALICE collaboration at Europe's Large Hadron Collider (LHC), with a measurement of the mass difference between ordinary helium-3 and antihelium-3. The result, showing no significant difference, was published in Nature Physics in 2015.
Spoiler alert: The STAR results also reveal no significant mass difference between the matter-antimatter partners explored at RHIC, so there's still no evidence of CPT violation. But the fact that STAR physicists could even make the measurements is a testament to the remarkable capabilities of their detector.
Strange matter
The simplest normal-matter nuclei contain just protons and neutrons, with each of those particles made of ordinary "up" and "down" quarks. In hypertritons, one neutron is replaced by a particle called a lambda, which contains one strange quark along with the ordinary up and down varieties.
Such strange matter replacements are common in the ultra-dense conditions created in RHIC's collisions -- and are also likely in the cores of neutron stars where a single teaspoon of matter would weigh more than 1 billion tons. That's because the high density makes it less costly energy-wise to make strange quarks than the ordinary up and down varieties.
For that reason, RHIC collisions give nuclear physicists a way to peer into the subatomic interactions within distant stellar objects without ever leaving Earth. And because RHIC collisions create hypertritons and antihypertritons in nearly equal amounts, they offer a way to search for CPT violation as well.
But finding those rare particles among the thousands that stream from each RHIC particle smashup -- with collisions happening thousands of times each second -- is a daunting task. Add to the challenge the fact that these unstable particles decay almost as soon as they form -- within centimeters of the center of the four-meter-wide STAR detector.
Precision detection
Fortunately, detector components added to STAR for tracking different kinds of particles made the search a relative cinch. These components, called the "Heavy-Flavor Tracker," are located very close to the STAR detector's center. They were developed and built by a team of STAR collaborators led by scientists and engineers at DOE's Lawrence Berkeley National Laboratory (Berkeley Lab). These inner components allow scientists to match up tracks created by decay products of each hypertriton and antihypertriton with their point of origin just outside the collision zone.
"What we look for are the 'daughter' particles -- the decay products that strike detector components at the outer edges of STAR," said Berkeley Lab physicist Xin Dong. Identifying tracks of pairs or triplets of daughter particles that originate from a single point just outside the primary collision zone allows the scientists to pick these signals out from the sea of other particles streaming from each RHIC collision.
"Then we calculate the momentum of each daughter particle from one decay (based on how much they bend in STAR's magnetic field), and from that we can reconstruct their masses and the mass of the parent hypertriton or antihypertriton particle before it decayed," explained Declan Keane of Kent State University (KSU). Telling the hypertriton and antihypertriton apart is easy because they decay into different daughters, he added.
"Keane's team, including Irakli Chakeberia, has specialized in tracking these particles through the detectors to 'connect the dots,'" Xu said. "They also provided much needed visualization of the events."
As noted, compiling data from many collisions revealed no mass difference between the matter and antimatter hypernuclei, so there's no evidence of CPT violation in these results.
But when STAR physicists looked at their results for the binding energy of the hypertriton, it turned out to be larger than previous measurements from the 1970s had found.
The STAR physicists derived the binding energy by subtracting their value for the hypertriton mass from the combined known masses of its building-block particles: a deuteron (a bound state of a proton and a neutron) and one lambda.
"The hypertriton weighs less than the sum of its parts because some of that mass is converted into the energy that is binding the three nucleons together," said Fudan University STAR collaborator Jinhui Chen, whose PhD student, Peng Liu, analyzed the large datasets to arrive at these results. "This binding energy is really a measure of the strength of these interactions, so our new measurement could have important implications for understanding the 'equation of state' of neutron stars," he added.
Read more at Science Daily
Ancient shell shows days were half-hour shorter 70 million years ago
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| Dinosaur scene illustration |
The ancient mollusk, from an extinct and wildly diverse group known as rudist clams, grew fast, laying down daily growth rings. The new study used lasers to sample minute slices of shell and count the growth rings more accurately than human researchers with microscopes.
The growth rings allowed the researchers to determine the number of days in a year and more accurately calculate the length of a day 70 million years ago. The new measurement informs models of how the Moon formed and how close to Earth it has been over the 4.5-billion-year history of the Earth-Moon gravitational dance.
The new study also found corroborating evidence that the mollusks harbored photosynthetic symbionts that may have fueled reef-building on the scale of modern-day corals.
The high resolution obtained in the new study combined with the fast growth rate of the ancient bivalves revealed unprecedented detail about how the animal lived and the water conditions it grew in, down to a fraction of a day.
"We have about four to five datapoints per day, and this is something that you almost never get in geological history. We can basically look at a day 70 million years ago. It's pretty amazing," said Niels de Winter, an analytical geochemist at Vrije Universiteit Brussel and the lead author of the new study.
Climate reconstructions of the deep past typically describe long term changes that occur on the scale of tens of thousands of years. Studies like this one give a glimpse of change on the timescale of living things and have the potential to bridge the gap between climate and weather models.
Chemical analysis of the shell indicates ocean temperatures were warmer in the Late Cretaceous than previously appreciated, reaching 40 degrees Celsius (104 degrees Fahrenheit) in summer and exceeding 30 degrees Celsius (86 degrees Fahrenheit) in winter. The summer high temperatures likely approached the physiological limits for mollusks, de Winter said.
"The high fidelity of this data-set has allowed the authors to draw two particularly interesting inferences that help to sharpen our understanding of both Cretaceous astrochronology and rudist palaeobiology," said Peter Skelton, a retired lecturer of palaeobiology at The Open University and a rudist expert unaffiliated with the new study.
Ancient reef-builders
The new study analyzed a single individual that lived for over nine years in a shallow seabed in the tropics -- a location which is now, 70-million-years later, dry land in the mountains of Oman.
Torreites sanchezi mollusks look like tall pint glasses with lids shaped like bear claw pastries. The ancient mollusks had two shells, or valves, that met in a hinge, like asymmetrical clams, and grew in dense reefs, like modern oysters. They thrived in water several degrees warmer worldwide than modern oceans.
In the late Cretaceous, rudists like T. sanchezi dominated the reef-building niche in tropical waters around the world, filling the role held by corals today. They disappeared in the same event that killed the non-avian dinosaurs 66 million years ago.
"Rudists are quite special bivalves. There's nothing like it living today," de Winter said. "In the late Cretaceous especially, worldwide most of the reef builders are these bivalves. So they really took on the ecosystem building role that the corals have nowadays."
The new method focused a laser on small bits of shell, making holes 10 micrometers in diameter, or about as wide as a red blood cell. Trace elements in these tiny samples reveal information about the temperature and chemistry of the water at the time the shell formed. The analysis provided accurate measurements of the width and number of daily growth rings as well as seasonal patterns. The researchers used seasonal variations in the fossilized shell to identify years.
The new study found the composition of the shell changed more over the course of a day than over seasons, or with the cycles of ocean tides. The fine-scale resolution of the daily layers shows the shell grew much faster during the day than at night
"This bivalve had a very strong dependence on this daily cycle, which suggests that it had photosymbionts," de Winter said. "You have the day-night rhythm of the light being recorded in the shell."
This result suggests daylight was more important to the lifestyle of the ancient mollusk than might be expected if it fed itself primarily by filtering food from the water, like modern day clams and oysters, according to the authors. De Winter said the mollusks likely had a relationship with an indwelling symbiotic species that fed on sunlight, similar to living giant clams, which harbor symbiotic algae.
"Until now, all published arguments for photosymbiosis in rudists have been essentially speculative, based on merely suggestive morphological traits, and in some cases were demonstrably erroneous. This paper is the first to provide convincing evidence in favor of the hypothesis," Skelton said, but cautioned that the new study's conclusion was specific to Torreites and could not be generalized to other rudists.
Moon retreat
De Winter's careful count of the number of daily layers found 372 for each yearly interval. This was not a surprise, because scientists know days were shorter in the past. The result is, however, the most accurate now available for the late Cretaceous, and has a surprising application to modeling the evolution of the Earth-Moon system.
The length of a year has been constant over Earth's history, because Earth's orbit around the Sun does not change. But the number of days within a year has been shortening over time because days have been growing longer. The length of a day has been growing steadily longer as friction from ocean tides, caused by the Moon's gravity, slows Earth's rotation.
The pull of the tides accelerates the Moon a little in its orbit, so as Earth's spin slows, the Moon moves farther away. The moon is pulling away from Earth at 3.82 centimeters (1.5 inches) per year. Precise laser measurements of distance to the Moon from Earth have demonstrated this increasing distance since the Apollo program left helpful reflectors on the Moon's surface.
But scientists conclude the Moon could not have been receding at this rate throughout its history, because projecting its progress linearly back in time would put the Moon inside the Earth only 1.4 billion years ago. Scientists know from other evidence that the Moon has been with us much longer, most likely coalescing in the wake of a massive collision early in Earth's history, over 4.5 billion years ago. So the Moon's rate of retreat has changed over time, and information from the past, like a year in the life of an ancient clam, helps researchers reconstruct that history and model of the formation of the moon.
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