Scientists solve solar secret

The further we move away from a heat source, the cooler the air gets. Bizarrely, the same can't be said for the Sun, but University of Otago scientists may have just explained a key part of why.

Study lead Dr Jonathan Squire, of the Department of Physics, says the surface of the Sun starts at 6000 degree C, but over a short distance of only a few hundred kilometers, it suddenly heats up to more than a million degrees, becoming its atmosphere, or corona.

"This is so hot that the gas escapes the Sun's gravity as 'solar wind', and flies into space, smashing into Earth and other planets.

"We know from measurements and theory that the sudden temperature jump is related to magnetic fields which thread out of the Sun's surface. But, exactly how these work to heat the gas is not well understood -- this is known as the Coronal Heating Problem.

"Astrophysicists have several different ideas about how the magnetic-field energy could be converted into heat to explain the heating, but most have difficulty explaining some aspect of observations," he says.

Dr Squire and co-author Dr Romain Meyrand have been working with scientists at Princeton University and the University of Oxford and found two previous theories can be merged into one to solve a key piece of the 'problem'. The group's findings have just been published in Nature Astronomy.

The popular theories are based on heating caused by turbulence, and heating caused by a type of magnetic wave called ion cyclotron waves.

"Both, however, have some problem -- turbulence struggles to explain why Hydrogen, Helium and Oxygen in the gas become as hot as they do, while electrons remain surprisingly cold; while the magnetic waves theory could explain this feature, there doesn't seem to be enough of the waves coming off the Sun's surface to heat up the gas," Dr Meyrand says.

The group used six-dimensional supercomputer simulations of the coronal gas to show how these two theories are actually part of the same process, linked together by a bizarre effect called the 'helicity barrier'.

This intriguing occurrence was discovered in an earlier Otago study, led by Dr Meyrand.

"If we imagine plasma heating as occurring a bit like water flowing down a hill, with electrons heated right at the bottom, then the helicity barrier acts like a dam, stopping the flow and diverting its energy into ion cyclotron waves. In this way, the helicity barrier links the two theories and resolves each of their individual problems," he explains.

For this latest study, the group stirred the magnetic field lines in simulations and found the turbulence created the waves, which then caused the heating.

"As this happens, the structures and eddies that form end up looking extremely similar to cutting-edge measurements from NASA's Parker Solar Probe spacecraft, which has recently become the first human-made object to actually fly into the corona.

"This gives us confidence that we are accurately capturing key physics in the corona, which -- coupled with the theoretical findings about the heating mechanisms -- is a promising path to understanding the coronal heating problem," Dr Meyrand says.

Understanding more about the Sun's atmosphere and the subsequent solar wind is important because of the profound impacts they have on Earth, Dr Squire explains.

Effects which result from solar wind's interaction with the Earth's magnetic field is called 'space weather', which causes everything from Aurora to satellite-destroying radiation and geomagnetic currents which damage the power grid.

"All of this is sourced, fundamentally, by the corona and its heating by magnetic fields, so as well as being interesting for our general understanding of the solar system, the solar-corona's dynamics can have profound impacts on Earth.

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A solar illusion: Coronal loops may not be what they seem

Many coronal loops -- ropey strands of plasma that scientists have long thought existed in the Sun's atmosphere -- may actually be optical illusions, according to a new paper that challenges prevailing assumptions of what we know, and don't know, about the Sun.

The research, led by the National Center for Atmospheric Research (NCAR) and published in The Astrophysical Journal, relied on a cutting-edge, realistic 3D simulation of the solar corona. The simulation, carried out at NCAR several years ago, allowed the scientists to slice the corona in distinct sections in an effort to isolate individual coronal loops.

What they found is that many of the loops weren't loops at all.

While the research team was able to pinpoint some of the coronal loops they were looking for, they also found that in many cases what appear to be loops in images taken of the Sun may actually be wrinkles of bright plasma in the solar atmosphere. As sheets of bright plasma fold over themselves, the folds look like bright thin lines, mimicking the look of distinct and self-contained strands of plasma.

The findings, which the research team is calling the "coronal veil" hypothesis, have significant implications for our understanding of the Sun, since the presumed coronal loops have been used for decades as a way to infer information about density, temperature, and other physical characteristics of the solar atmosphere.

"I have spent my entire career studying coronal loops," said NCAR scientist Anna Malanushenko, who led the study. "I was excited that this simulation would give me the opportunity to study them in more detail. I never expected this. When I saw the results, my mind exploded. This is an entirely new paradigm of understanding the Sun's atmosphere."

The research was funded by NASA and included collaborators from NCAR's High Altitude Observatory, Lockheed Martin Solar and Astrophysics Laboratory, the Southwest Research Institute, and NASA Goddard. NCAR is sponsored by the National Science Foundation.

Challenging intuition

What appears to be coronal loops can be seen in images taken of the Sun in extreme ultraviolet light. The assumption that they exist is a natural one for scientists because it fits our most basic understanding of magnetism.

Most schoolchildren have at some point seen what happens when iron filings are sprinkled near a bar magnet. The filings orient themselves along magnetic field lines that loop from one pole of the bar magnet to the other. These curving lines spread out, becoming weaker and less dense, the further they are from the magnet.

The apparent coronal loops in images of the Sun look strikingly similar, and since there is a significant magnetic field in the Sun, the existence of magnetic field lines that could trap a rope of plasma between them and create loops seems like an obvious explanation. And in fact, the new study confirms that such loops likely exist.

However, the coronal loops seen on the Sun have never behaved exactly as they should, based on our understanding of magnets. For example, scientists would expect the magnetic field lines on the Sun to spread apart, just as in the iron filings experiment, as you move higher in the corona. If this happened, the plasma trapped between the field lines would also spread out between the boundaries, creating thicker, less bright loops. But images of the Sun do not show this phenomenon. Instead, the loops further out still appear thin and bright.

The possibility that these loops are instead wrinkles in a coronal veil helps explain this and other discrepancies with our expectations of the loops -- but it also asks new questions. For example, what determines the shape and thickness of the folds? And how many of the apparent loops in images of the Sun are actually real strands, and how many are optical illusions?

"This study reminds us as scientists that we must always question our assumptions and that sometimes our intuition can work against us," Malanushenko said.

Innovative model offers new view of the Sun

The discovery that coronal loops may be illusions was made possible thanks to an extremely detailed simulation of the solar corona produced by MURaM, a radiative magnetohydrodynamic model that was extended to model the solar corona in an effort led by NCAR.

The simulation was groundbreaking when it was first produced because it was able to simultaneously model what was happening in multiple regions of the Sun, from the upper part of the convective zone -- about 10,000 kilometers below the Sun's surface -- through the solar surface and beyond, up to nearly 40,000 kilometers into the solar corona. These varied regions of the Sun cover a vast range of physical conditions, including differences in density and pressure, and so scientists had not previously figured out a way to mathematically represent these regions in a unified simulation.

Among other results, the new simulation was able to capture the entire life cycle of a solar flare for the first time, from the build up of energy below the solar surface to the emergence of flare at the surface, and finally to the explosive release of energy.

The model also produced 3-dimensional data sets that contain the structure of the magnetic field and plasma, which can be used to generate "synthetic" observations. Because the solar corona is optically thin -- meaning it's relatively easy to see through it -- structures in the corona overlap one another in images of the Sun. This makes it difficult to tell whether a "loop" that is overlapping other loops is in front or behind. It's also difficult to tell whether the loop itself has a compact cross section, like a garden hose, or resembles a long ribbon viewed edge on. It's also possible that what appears to be a thin strand may be an optical artifact caused by a fold in a sheet of bright plasma.

The cubes of data produced by MURaM provide scientists the opportunity to dissect the solar atmosphere and study the overlapping structures separately, something that is not possible with the observatories and instruments we currently have.

While the MURaM simulation is one of the most realistic ever created of the solar corona, it's still just a model. Understanding how many coronal loops are actually optical illusions will require carefully designed observational methods that probe the corona and new data analysis techniques.

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A spacecraft has 'touched' the sun for the first time

NASA's Parker Solar Probe reached the sun's extended solar atmosphere, known as the corona, and spent five hours there. The spacecraft is the first to enter the outer boundaries of our sun.

"This marks the achievement of the primary objective of the Parker mission and a new era for understanding the physics of the corona," said Justin C. Kasper, the first author, Deputy Chief Technology Officer at BWX Technologies, and a professor at the University of Michigan. The mission is led by the Johns Hopkins University Applied Physics Laboratory (JHU/APL).

The probe made the first direct observations of what lies within the sun's atmosphere, measuring phenomena previously only estimated.

The sun's outer edge begins at the Alfvén critical surface: the point below which the sun and its gravitational and magnetic forces directly control the solar wind. Many scientists think that sudden reverses in the sun's magnetic field, called switchbacks, emerge from this area.

"The concept of sending spacecraft into the magnetized atmosphere of the sun -- sufficiently close that the magnetic energy is greater than both ion and electron kinetic and thermal energy -- predated NASA itself," said Kasper.

In 2018, NASA launched Parker Solar Probe with the goal of finally reaching the sun's corona and making humanity's first visit to a star.

This past April, the probe spent five hours below the Alfvén critical surface in direct contact with the sun's plasma. Below that surface, the pressure and energy of the sun's magnetic field was stronger than the pressure and energy of the particles. The spacecraft passed above and below the surface three separate times during its encounter. This is the first time a spacecraft has entered the solar corona and touched the atmosphere of the sun.

Surprisingly, the researchers discovered that the Alfvén critical surface is wrinkled. The data suggest that the largest and most distant wrinkle of the surface was produced by a pseudostreamer -- a large magnetic structure more than 40 degrees across, found back on the innermost visible face of the sun. It is not currently known why a pseudostreamer would push the Alfvén critical surface away from the sun.

Researchers noticed far fewer switchbacks below the Alfvén critical surface than above it. The finding could mean that switchbacks do not form within the corona. Alternatively, low rates of magnetic reconnection on the sun's surface could have pumped less mass into the observed wind stream, resulting in fewer switchbacks.

The probe also recorded some evidence of a potential power boost just inside the corona, which may point to unknown physics affecting heating and dissipation.

"We have been observing the sun and its corona for decades, and we know there is interesting physics going on there to heat and accelerate the solar wind plasma. Still, we cannot tell precisely what that physics is," said Nour E. Raouafi, the Parker Solar Probe Project Scientist at JHU/APL. "With Parker Solar Probe now flying into the magnetically-dominated corona, we will get the long-awaited insights into the inner workings of this mysterious region."

The observations took place during Parker Solar Probe's eighth encounter with the sun. All data is publicly available in the NASA PSP archive. Several previous studies predicted the probe would first pass within the sun's boundaries in 2021.

The fastest known object built by humans, Parker Solar Probe has made many new discoveries since its launch, including on explosions that create space weather and the dangers of super-speedy dust.

The new findings suggest that direct observations by spacecraft have much to illuminate about the physics of coronal heating and solar wind formation. Having achieved its goal of touching the sun, Parker Solar Probe will now descend even deeper into the sun's atmosphere and linger for longer periods of time.

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When breezy, wear masks outdoors to prevent coronavirus exposure

As the highly infectious delta variant of the coronavirus continues to spread across the United States, guidelines from the Centers for Disease Control and Prevention recommend even the vaccinated wear masks indoors to prevent exposure and transmission.

However, it is less clear what people should do when outside.

In Physics of Fluids, by AIP Publishing, researchers from the Indian Institute of Technology Bombay found when a person coughs outdoors, wind flowing in the same direction can propagate the virus faster over longer distances than in calm conditions.

"The study is significant in that it points to the increased infection risk that coughing in the same direction as the wind could bring about," co-author Amit Agrawal said. "Based on the results, we recommend wearing masks outdoors, particularly in breezy conditions."

Other guidelines, such as coughing in an elbow or turning the face away while coughing, should be followed to reduce transmission when socializing outdoors.

Most studies model cough flow using puffs of air or a simple pulsating profile. But a real cough is more complicated, exhibiting turbulent flow with prominent vortical structures swirling like mini whirlpools.

To investigate these vortices, the researchers used a large eddy simulation, a numerical model in computational fluid dynamics that simulatesturbulence. They modeled cough jets in breezy conditions and in calm conditions representing a typical indoor environment.

These simulations show even a light breeze of about 5 mph extends effective social distancing by around 20%, from 3-6 feet to 3.6-7.2 feet, depending on cough strength. At 9-11 mph, spreading of the virus increases in distance and duration.

The researchers found the vortices enable bigger droplets to persist in the air longer than has been typically assumed, increasing the time it takes to adequately dilute the viral load in fresh air. As the cough jet evolves and spreads, it interacts with the wind flowing in the same direction, and the bigger infected droplets become trapped in the jet's vortices instead of falling relatively quickly to the ground under gravity.

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New vaccine blocks COVID-19 and variants, plus other coronaviruses

A potential new vaccine developed by members of the Duke Human Vaccine Institute has proven effective in protecting monkeys and mice from a variety of coronavirus infections -- including SARS-CoV-2 as well as the original SARS-CoV-1 and related bat coronaviruses that could potentially cause the next pandemic.

The new vaccine, called a pan-coronavirus vaccine, triggers neutralizing antibodies via a nanoparticle. The nanoparticle is composed of the coronavirus part that allows it to bind to the body's cell receptors and is formulated with a chemical booster called an adjuvant. Success in primates is highly relevant to humans.

The findings appear Monday, May 10, in the journal Nature.

"We began this work last spring with the understanding that, like all viruses, mutations would occur in the SARS-CoV-2 virus, which causes COVID-19," said senior author Barton F. Haynes, M.D., director of the Duke Human Vaccine Institute (DHVI). "The mRNA vaccines were already under development, so we were looking for ways to sustain their efficacy once those variants appeared.

"This approach not only provided protection against SARS-CoV-2, but the antibodies induced by the vaccine also neutralized variants of concern that originated in the United Kingdom, South Africa and Brazil," Haynes said. "And the induced antibodies reacted with quite a large panel of coronaviruses."

Haynes and colleagues, including lead author Kevin Saunders, Ph.D., director of research at DHVI, built on earlier studies involving SARS, the respiratory illness caused by a coronavirus called SARS-CoV-1. They found a person who had been infected with SARS developed antibodies capable of neutralizing multiple coronaviruses, suggesting that a pan-coronavirus might be possible.

The Achilles heel for the coronaviruses is their receptor-binding domain, located on the spike that links the viruses to receptors in human cells. While this binding site enables it to enter the body and cause infection, it can also be targeted by antibodies.

The research team identified one particular receptor-binding domain site that is present on SARS-CoV-2, its circulating variants and SARS-related bat viruses that makes them highly vulnerable to cross-neutralizing antibodies.

The team then designed a nanoparticle displaying this vulnerable spot. The nanoparticle is combined with a small molecule adjuvant -- specifically, the toll-like receptor 7 and 8 agonist called 3M-052, formulated with Alum, which was developed by 3M and the Infectious Disease Research Institute. The adjuvant boosts the body's immune response.

In tests of its effect on monkeys, the nanoparticle vaccine blocked COVID-19 infection by 100%. The new vaccine also elicited significantly higher neutralizing levels in the animals than current vaccine platforms or natural infection in humans.

"Basically what we've done is take multiple copies of a small part of the coronavirus to make the body's immune system respond to it in a heightened way," Saunders said. "We found that not only did that increase the body's ability to inhibit the virus from causing infection, but it also targets this cross-reactive site of vulnerability on the spike protein more frequently. We think that's why this vaccine is effective against SARS-CoV-1, SARS-CoV-2 and at least four of its common variants, plus additional animal coronaviruses."

"There have been three coronavirus epidemics in the past 20 years, so there is a need to develop effective vaccines that can target these pathogens prior to the next pandemic," Haynes said. "This work represents a platform that could prevent, rapidly temper, or extinguish a pandemic."

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Coronavirus does not infect the brain but still inflicts damage, study finds

SARS-CoV-2, the virus that causes COVID-19, likely does not directly infect the brain but can still inflict significant neurological damage, according to a new study from neuropathologists, neurologists, and neuroradiologists at Columbia University Vagelos College of Physicians and Surgeons.

"There's been considerable debate about whether this virus infects the brain, but we were unable to find any signs of virus inside brain cells of more than 40 COVID-19 patients," says James E. Goldman, MD, PhD, professor of pathology & cell biology (in psychiatry), who led the study with Peter D. Canoll, MD, PhD, professor of pathology & cell biology, and Kiran T. Thakur, MD, the Winifred Mercer Pitkin Assistant Professor of Neurology.

"At the same time, we observed many pathological changes in these brains, which could explain why severely ill patients experience confusion and delirium and other serious neurological effects -- and why those with mild cases may experience 'brain fog' for weeks and months."

The study, published in the journal Brain, is the largest and most detailed COVID-19 brain autopsy report published to date, suggests that the neurological changes often seen in these patients may result from inflammation triggered by the virus in other parts of the body or in the brain's blood vessels.

No Virus in Brain Cells

The study examined the brains of 41 patients with COVID-19 who succumbed to the disease during their hospitalization. The patients ranged in age from 38 to 97; about half had been intubated and all had lung damage caused by the virus. Many of the patients were of Hispanic ethnicity. There was a wide range of hospital length with some patients dying soon after arrival to the emergency room while others remained in the hospital for months. All of the patients had extensive clinical and laboratory investigations, and some had brain MRI and CT scans.

To detect any virus in the neurons and glia cells of the brain, the researchers used multiple methods including RNA in situ hybridization, which can detect viral RNA within intact cells; antibodies that can detect viral proteins within cells; and RT-PCR, a sensitive technique for detecting viral RNA.

Despite their intensive search, the researchers found no evidence of the virus in the patients' brain cells. Though they did detect very low levels of viral RNA by RT-PCR, this was likely due to virus in blood vessels or leptomeninges covering the brain.

"We've looked at more brains than other studies, and we've used more techniques to search for the virus. The bottom line is that we find no evidence of viral RNA or protein in brain cells," Goldman says. "Though there are some papers that claim to have found virus in neurons or glia, we think that those result from contamination, and any virus in the brain is contained within the brain's blood vessels." "If there's any virus present in the brain tissue, it has to be in very small amounts and does not correlate with the distribution or abundance of neuropathological findings," Canoll says.

The tests were conducted on more than two dozen brain regions, including the olfactory bulb, which was searched because some reports have speculated that the coronavirus can travel from the nasal cavity into the brain via the olfactory nerve. "Even there, we didn't find any viral protein or RNA," Goldman says, "though we found viral RNA and protein in the patients' nasal mucosa and in the olfactory mucosa high in the nasal cavity." (The latter finding appears in an unpublished study, currently on BioRxiv, led by Jonathan Overdevest, MD, PhD, assistant professor of otolaryngology, and Stavros Lomvardas, PhD, professor of biochemistry & molecular biophysics and neuroscience.)

Hypoxic Damage and Signs of Neuronal Death

Despite the absence of virus in the brain, in every patient the researchers found significant brain pathology, which mostly fell into two categories.

"The first thing we noticed was a lot of areas with damage from a lack of oxygen," Goldman says. "They all had severe lung disease, so it's not surprising that there's hypoxic damage in the brain."

Some of these were large areas caused by strokes, but most were very small and only detectable with a microscope. Based on other features, the researchers believe these small areas of hypoxic damage were caused by blood clots, common in patients with severe COVID-19, that temporarily stopped the supply of oxygen to that area.

A more surprising finding, Goldman says, was the large number of activated microglia they found in the brains of most patients. Microglia are immune cells that reside in the brain and can be activated by pathogens.

"We found clusters of microglia attacking neurons, a process called 'neuronophagia,'" says Canoll. Since no virus was found in the brain, it's possible the microglia may have been activated by inflammatory cytokines, such as Interleukin-6, associated with SARS-CoV-2 infection.

"At the same time, hypoxia can induce the expression of 'eat me' signals on the surface of neurons, making hypoxic neurons more vulnerable to activated microglia," Canoll says, "so even without directly infecting brain cells, COVID-19 can cause damage to the brain."

The group found this pattern of pathology in one of their first autopsies, described by Osama Al-Dalahmah, MD, PhD, instructor in pathology & cell biology, in a case report published last March in Acta Neuropathologica Communications. Over the next few months, as the neuropathologists did many more COVID brain autopsies, they saw similar findings over and over again and realized that this is a prominent and common neuropathological finding in patients who die of COVID.

The activated microglia were found predominantly in the lower brain stem, which regulates heart and breathing rhythms, as well as levels of consciousness, and in the hippocampus, which is involved in memory and mood.

"We know the microglia activity will lead to loss of neurons, and that loss is permanent," Goldman says. "Is there enough loss of neurons in the hippocampus to cause memory problems? Or in other parts of the brain that help direct our attention? It's possible, but we really don't know at this point."

Persistent Neurological Problems in Survivors

Goldman says that more research is needed to understand the reasons why some post-COVID-19 patients continue to experience symptoms.

The researchers are now examining autopsies on patients who died several months after recovering from COVID-19 to learn more.

They are also examining the brains from patients who were critically ill with acute respiratory distress syndrome (ARDS) before the COVID-19 pandemic to see how much of COVID-19 brain pathology is a result of the severe lung disease.

Read more at Science Daily

1918 pandemic second wave had fatal consequences

 In the event of a pandemic, delayed reactions and a decentralized approach by the authorities at the start of a follow-up wave can lead to longer-lasting, more severe and more fatal consequences, researchers from the universities of Zurich and Toronto have found. The interdisciplinary team compared the Spanish flu of 1918 and 1919 in the Canton of Bern with the coronavirus pandemic of 2020.

The Spanish flu was the greatest demographic catastrophe in Switzerland's recent history, causing approximately 25,000 deaths in the country during 1918 and 1919. In the wake of the current coronavirus pandemic, there has been increased public and scientific interest in the events of that time. An interdisciplinary team of researchers in evolutionary medicine, history, geography and epidemiology from the universities of Zurich and Toronto has spent several years analyzing historical data on the spread of influenza-like illnesses during 1918 and 1919 in the Canton of Bern. The canton is ideally suited as a Swiss case study, because it is large and has a diverse landscape, it was hit particularly hard by the Spanish flu, and right at the start of the pandemic in July 1918 it introduced an obligation to report cases.

Public health measures effective in the first wave

The results of the new study show that the spread of Spanish flu differed depending on the region. In the first wave in July and August 1918, the Canton of Bern intervened relatively quickly, strongly and centrally, including by restricting gatherings and closing schools. "We see from the numbers that these measures -- similar to today -- were associated with a decrease in infection numbers," says co-first author Kaspar Staub of the Institute of Evolutionary Medicine at the University of Zurich. After the first wave had subsided, the canton lifted all measures entirely in September 1918, which led to a rapid resurgence of cases and the onset of a second wave after only a short time.

Delayed action at start of second wave was fatal

At the beginning of the second wave in October 1918, the Canton of Bern reacted hesitantly, unlike in the first wave. Fearing renewed economic consequences, the cantonal authorities left responsibility for new measures up to the individual municipalities for several weeks. "This hesitant and decentralized approach was fatal and contributed to the fact that the second wave became all the stronger and lasted longer," says co-first author Peter Jueni of the University of Toronto.

In addition, shortly after the peak of the second wave in November 2018, there was a national strike with demonstrations on social and labor issues and, most importantly, larger troop deployments. These mass gatherings, as well as a subsequent relaxation of the ban on gatherings when the number of cases was still far too high, were accompanied by a significant resurgence in infections. Ultimately, about 80 percent of the reported illnesses and deaths were attributable to the second wave.

History repeats itself in 2020

By comparing the weekly case counts of the Spanish flu and coronavirus, the researchers found that the second wave started in almost the same calendar week in both 1918 and 2020, and the official delayed response was similar. "While there are still considerable differences between the two pandemics, the steadily increasing parallels between 1918 and 2020 are remarkable," Staub says. The study also shows that empirical knowledge from past pandemics -- for example, on the challenges and how to deal with follow-up waves -- is available. "Since November 2020, deaths from Covid-19 have far exceeded those caused by cancer or cardiovascular disease and for around three months it has been the most common cause of death in Switzerland. In view of the high death rate during the second wave in comparison with other countries, and with the threat of a third wave due to virus mutations from England, South Africa and Brazil, lessons from the past could help the authorities and the public to rethink their response," adds Jueni.

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