Henri Leinonen and colleagues found how people with retinal degenerative disease can maintain their night vision for a relatively long period of time. Their study in mice suggested that second-order neurons in the retina, which relay visual signals to the retinal ganglion cells that project into the brain, maintain their activity in response to photoreceptor degeneration to resist visual decline—a process known as homeostatic plasticity. Rod photoreceptors are the cells responsible for the most sensitive aspects of our vision, allowing us to see at night, but can be lost during retinal degenerative disease. The new findings pave the way for further research to understand how our eyes and other sensory systems respond and adapt to potentially compromising changes throughout life.
Leinonen and colleagues studied a mouse model of retinitis pigmentosa. This is the name given to a group of related genetic disorders caused by the P23H mutation in rhodopsin, a protein that enables us to see in low-light conditions. Retinitis pigmentosa causes the breakdown and loss of rod-shaped photoreceptor cells in the retina, leading to difficulties seeing at night.
The team combined whole-retinal RNA-sequencing, electrophysiology and behavioral experiments in both healthy mice and those with retinitis pigmentosa as the disease progressed. Their experiments showed that the degeneration of rod photoreceptors triggers genomic changes that involve robust compensatory molecular changes in the retina and increases in electrical signaling between rod photoreceptors and rod bipolar cells. These changes were associated with well-maintained behavioral night vision despite the loss of over half of the rod photoreceptor cells in mice with retinitis pigmentosa.
This mechanism may explain why patients with inherited retinal diseases can maintain their normal vision until the disease reaches a relatively advanced state. It could also inspire novel treatment strategies for diseases that lead to blindness.
References: Henri Leinonen et al, Homeostatic plasticity in the retina is associated with maintenance of night vision during retinal degenerative disease, eLife (2020). DOI: 10.7554/eLife.59422 link: https://elifesciences.org/articles/59422
Interstellar medium consists not only of gas, but also of dust. At some point in time, stars and planets originated in such an environment, because the dust particles can clump together and merge into celestial bodies. Important chemical processes also take place on these particles, from which complex organic—possibly even prebiotic—molecules emerge.
However, for these processes to be possible, there has to be water. In particularly cold cosmic environments, water occurs in the form of ice. Until now, however, the connection between ice and dust in these regions of space was unclear. Now, Alexey Potapov and colleagues has now proven that the dust particles and the ice are mixed.
Whether ice in cold cosmic environments is physically separated from the silicate dust or mixed with individual silicate moieties is not known. However, different grain models give very different compositions and temperatures of grains. In the study the researchers compared the mid-infrared spectra of laboratory silicate grain/water ice mixtures with astronomical observations to evaluate the presence of dust/ice mixtures in interstellar and circumstellar environments. The laboratory data can explain the observations, assuming reasonable mass-averaged temperatures for the protostellar envelopes and protoplanetary disks, demonstrating that a substantial fraction of water ice may be mixed with silicate grains. This result would enable researchers to better estimate the amount of material and to make more accurate statements about the temperatures in different regions of the interstellar and circumstellar media.
Through experiments and comparisons, scientists at the University of Jena also observed what happens with water when the temperatures increase and the ice leaves the solid body to which it is bound and passes into the gas phase at about 180 Kelvin (-93 degrees Celsius).
Some water molecules are so strongly bound to the silicate that they remain on the surface or inside dust particles. They suspected that such ‘trapped water’ also exists on or in dust particles in space. At least that is what is suggested by the comparison between the spectra obtained from the laboratory experiments and those in what is called the diffuse interstellar medium. They found clear indications that trapped water molecules exist there.
The existence of such solid-state water suggests that complex molecules may also be present on the dust particles in the diffuse interstellar medium. If water is present on such particles, it is not a very long way to complex organic molecules, for example. This is because the dust particles usually consist of carbon, among other things, which, in combination with water and under the influence of ultraviolet radiation such as that found in the environment, promotes the formation of methanol, for example. Organic compounds have already been observed in these regions of the interstellar medium, but until now it has not been known where they originated.
The presence of solid-state water can also answer questions about another element: although we know the amount of oxygen in the interstellar medium, we previously had no information about where exactly around a third of it is located. The new research results suggest that the solid-state water in silicates is a hidden reservoir of oxygen.
In addition, the ‘trapped water’ can help in understanding how the dust accumulates, as it could promote the sticking together of smaller particles to form larger particles. This effect may even work in planet formation.
New study led by Pieter T. Visscher ane colleagues found that much of life on planet Earth today relies on oxygen to exist, but before oxygen was present on our blue planet, lifeforms likely used arsenic instead.
A key component of the oxygen cycle is where plants and some types of bacteria essentially take sunlight, water, and CO2, and convert them to carbohydrates and oxygen, which are then cycled and used by other organisms that breathe oxygen. This oxygen serves as a vehicle for electrons, gaining and donating electrons as it powers through the metabolic processes. However, for half of the time life has existed on Earth, there was no oxygen present, and for the first 1.5 billion years, we really don’t how these systems worked, says lead author of the study and UConn Professor of Marine Sciences and Geosciences Pieter Visscher.
Light-driven, photosynthetic organisms appear in the fossil record as layered carbonate rocks called stromatolites dating to around 3.7 billion years ago, says Visscher. Stromatolite mats are deposited over the eons by microbial ecosystems, with each layer holding clues about life at that time. There are contemporary examples of microbes that photosynthesize in the absence of oxygen using a variety of elements to complete the process, however it’s unclear how this happened in the earliest life forms.
Theories as to how life’s processes functioned in the absence of oxygen have mostly relied on hydrogen, sulfur, or iron as the elements that ferried electrons around to fulfill the metabolic needs of organisms.
As Visscher explains, these theories are contested; for example, photosynthesis is possible with iron, but researchers do not find evidence of that in the fossil record before oxygen appeared some 2.4 billion years ago. Hydrogen is mentioned, yet the energetics and competition for hydrogen between different microbes shows it is highly unfeasible.
Arsenic is another theoretical possibility, and evidence for that was found in 2008. Visscher says the link with arsenic was strengthened in 2014 when he and colleagues found evidence of arsenic-based photosynthesis in deep time. To further support their theory, the researchers needed to find a modern analog to study the biogeochemistry and element cycling.
Finding an analog to the conditions on early Earth is a challenge for a number of reasons, besides the fact that oxygen is now abundant. For instance, the evidence shows early microbes captured atmospheric carbon and produced organic matter at a time when volcanic eruptions were frequent, UV light was intense in the absence of the ozone layer, and oceans were essentially a toxic soup.
Another challenging aspect of working within the fossil record, especially those as ancient as some stromatolites, is that there are few left due to the cycling of rock as continents move. However, a breakthrough happened when the team discovered an active microbial mat, currently existing in the harsh conditions in Laguna La Brava in the Atacama Desert in Chile.
The mats have not been studied previously but present an otherworldly set of conditions, like those of early Earth. The mats are in a unique environment which leaves them in a permanent oxygen-free state at high altitude where they are exposed to wild, daily temperature swings, and high UV conditions. The mats serve as powerful and informative tools for truly understanding life in the conditions of early Earth.
The team also showed that the mats were making carbonate deposits and creating a new generation of stromatolites. The carbonate materials also showed evidence for arsenic cycling—that arsenic is serving as a vehicle for electrons—proving that the microbes are actively metabolizing arsenic, much like oxygen in modern systems. Visscher says these findings, along with the fossil evidence, gives a strong sense of the early conditions of Earth.
References: Pieter T. Visscher et al. Modern arsenotrophic microbial mats provide an analog for life in the anoxic Archean, Communications Earth & Environment (2020). DOI: 10.1038/s43247-020-00025-2
Insight-HXMT, China’s first space X-ray astronomical satellite, has discovered a low-frequency quasi-periodic oscillation (QPO) above 200 kiloelectron volts (keV) in a black hole binary, making it the highest energy low-frequency QPO ever found. The scientists also found that the QPO originated from the precession of a relativistic jet (high-speed outward-moving plasma stream) near the event horizon of the black hole. These discoveries have important implications for resolving the long-running debate about the physical origin of low-frequency QPOs.
Low-frequency QPOs, discovered in the 1980s, are a common observational timing feature in transient black hole binaries. They are quasi-periodic, but not precisely periodic, modulations in light curves. For more than 30 years, the origin of low-frequency QPOs was not understood. The two most popular models explaining their origin are: 1) the oscillations are caused by the instability of the accretion disk when matter rotates around and finally falls into the black hole; and 2) the quasi-periodic X-ray modulations are produced by the oscillation or precession of the coronal X-ray emitting region close to the black hole.
Before the era of Insight-HXMT, X-ray satellites could only detect and study low-frequency QPOs below 30 keV; thus, it was difficult to test these models. Insight-HXMT, in contrast, has a wide effective energy range of 1-250 keV and has the largest effective area above 30 keV. Therefore, after Insight-HXMT was launched, scientists expected it would detect rich low-frequency QPOs above 30 keV, and thus be able to fully test previous models.
The new black hole X-ray binary MAXI J1820+070, consisting of a black hole of several solar masses and a companion star, started to undergo an outburst on March 11, 2018. It has been one of the brightest X-ray sources in the sky for a long time. Insight-HXMT quickly responded and performed high-cadence pointing observations on this source for several months, accumulating a huge amount of observational data.
Based on these data, the scientists found that the low-frequency QPO of MAXI J1820+070 appeared in a wide energy range and its maximum detection energy exceeded 200 keV, which is almost an order of magnitude higher than previous QPOs observed by other telescopes, indicating that the QPO could not come from the thermal radiation region of the accretion disk. Further studies revealed that the frequency and variability amplitude of the QPO are energy independent and the high-energy QPO precedes the low-energy one.
These results unambiguously conflicted with most currently existing models. Therefore, the scientists proposed that the low-frequency QPO was produced by the precession of a jet near the black hole’s event horizon; the precession was probably caused by the frame-dragging effect of general relativity, generated by the rotation of the black hole.
Jets are high-speed matter streams moving at close to the speed of light. Plenty of jets have been observed in black hole binaries and distant quasars hosting supermassive black holes (i.e., those of millions to tens of billions of solar masses) in the radio, optical and X-ray bands. Jets are an important observational characteristic of black hole systems, and are the main means by which black holes influence the surrounding environment via feedback when swallowing nearby matter.
However, these jets are far from black holes. They are usually located at a distance of more than a million times the black hole’s event horizon. At such a long distance, the black hole’s gravitational force actually has no effect. Therefore, it is unclear where these jets are generated, how far they are from the black holes, how they can escape from the strong gravitational field of the black holes and how they are accelerated to a speed close to the speed of light.
Insight-HXMT’s discovery is particularly important because it’s the first time a jet has been found only hundreds of kilometers away from a black hole (i.e., several times the black hole’s event horizon). As the closest relativistic jet observed in a black hole so far, the finding is of great significance for studying the relativistic effects, dynamical processes and radiation mechanisms.
Colloidal quantum dots are tiny semiconductor particles capable of absorbing light over a broad range of wavelengths. Because these dots are easy to mix into liquid solvents, researchers have used them as ‘solar inks’ that can be printed onto bendable plastic sheets. However, early prototypes revealed that exposure to air and ultraviolet radiation degraded the cell’s ability to transform sunlight into electricity.
The latest quantum dot solar cells sandwich the tiny particles between two films referred to as either electron- or hole-transporting layers. These coatings are designed to quickly extract negative or positive charges generated by photoexcited dots to an external circuit. In addition, the layers provide much-needed protection against external elements.
Kirmani and his colleagues realized that reducing the size of the electron-transporting layer could boost quantum dot solar cell performance. These films often comprise ultraviolet-sensitive materials, such as zinc oxide, and typically need to be more than 100-nanometers thick to prevent formation of defects that may short out the device. In contrast, thinner films are more desirable because they can extract photogenerated electrons at higher speeds.
The KAUST team developed a two-step technique to produce ultrathin films that are smooth enough for efficient electron collection. First, they deposited an indium oxide coating onto a transparent electrode to promote highly ordered film growth. A second deposition of zinc oxide, only 20-nanometers high, sealed up any porous defects and generated an extremely uniform interface.
They found that this bilayer ETL results in solar cells with significantly improved overall stability without compromising performance, with an 11.1% power conversion efficiency hero device. While, comparisons with a control device demonstrated that the ultrathin electron-transporting layer worked just as efficiently as a thicker zinc oxide film. Surprisingly, the mix of zinc and indium oxides in the new solar cell prolonged its shelf life, operational stability and tolerance to ultraviolet rays—advantages that the team attributes in part to enhanced optical transmittance through the device.
References: Ahmad R. Kirmani et al. Colloidal Quantum Dot Photovoltaics Using Ultrathin, Solution-Processed Bilayer In2O3/ZnO Electron Transport Layers with Improved Stability, ACS Applied Energy Materials, 3(6), (2020). DOI: 10.1021/acsaem.0c00831 link: https://pubs.acs.org/doi/10.1021/acsaem.0c00831
Until now, the history of superconducting materials has been a tale of two types: s-wave and d-wave. Now, Cornell researchers—led by Brad Ramshaw, the Dick & Dale Reis Johnson Assistant Professor in the College of Arts and Sciences—have discovered a possible third type: g-wave.
Electrons in superconductors move together in what are known as Cooper pairs. This “pairing” endows superconductors with their most famous property—no electrical resistance—because, in order to generate resistance, the Cooper pairs have to be broken apart, and this takes energy.
In s-wave superconductors—generally conventional materials, such as lead, tin and mercury—the Cooper pairs are made of one electron pointing up and one pointing down, both moving head-on toward each other, with no net angular momentum. In recent decades, a new class of exotic materials has exhibited what’s called d-wave superconductivity, whereby the Cooper pairs have two quanta of angular momentum.
Physicists have theorized the existence of a third type of superconductor between these two so-called “singlet” states: a p-wave superconductor, with one quanta of angular momentum and the electrons pairing with parallel rather than antiparallel spins. This spin-triplet superconductor would be a major breakthrough for quantum computing because it can be used to create Majorana fermions, a unique particle which is its own antiparticle.
For more than 20 years, one of the leading candidates for a p-wave superconductor has been strontium ruthenate (Sr2RuO4), although recent research has started to poke holes in the idea.
Ramshaw and his team set out to determine once and for all whether strontium ruthenate is a highly desired p-wave superconductor. Using high-resolution resonant ultrasound spectroscopy, they discovered that the material is potentially an entirely new kind of superconductor altogether: g-wave.
“This experiment really shows the possibility of this new type of superconductor that we had never thought about before,” Ramshaw said. “It really opens up the space of possibilities for what a superconductor can be and how it can manifest itself. If we’re ever going to get a handle on controlling superconductors and using them in technology with the kind of fine-tuned control we have with semiconductors, we really want to know how they work and what varieties and flavors they come in.”
As with previous projects, Ramshaw and Ghosh used resonant ultrasound spectroscopy to study the symmetry properties of the superconductivity in a crystal of strontium ruthenate that was grown and precision-cut by collaborators at the Max Planck Institute for Chemical Physics of Solids in Germany.
However, unlike previous attempts, Ramshaw and Ghosh encountered a significant problem when trying to conduct the experiment.
“Cooling down resonant ultrasound to 1 kelvin (minus 457.87 degrees Fahrenheit) is difficult, and we had to build a completely new apparatus to achieve this,” Ghosh said.
With their new setup, the Cornell team measured the response of the crystal’s elastic constants – essentially the speed of sound in the material – to a variety of sound waves as the material cooled through its superconducting transition at 1.4 kelvin (minus 457 degrees Fahrenheit).
“This is by far the highest-precision resonant ultrasound spectroscopy data ever taken at these low temperatures,” Ramshaw said.
Based on the data, they determined that strontium ruthenate is what’s called a two-component superconductor, meaning the way electrons bind together is so complex, it can’t be described by a single number; it needs a direction as well.
Previous studies had used nuclear magnetic resonance (NMR) spectroscopy to narrow the possibilities of what kind of wave material strontium ruthenate might be, effectively eliminating p-wave as an option.
By determining that the material was two-component, Ramshaw’s team not only confirmed those findings, but also showed strontium ruthenate wasn’t a conventional s- or d-wave superconductor, either.
“Resonant ultrasound really lets you go in and even if you can’t identify all the microscopic details, you can make broad statements about which ones are ruled out,” Ramshaw said. “So then the only things that the experiments are consistent with are these very, very weird things that nobody has ever seen before. One of which is g-wave, which means angular momentum 4. No one has ever even thought that there would be a g-wave superconductor.”
Now the researchers can use the technique to examine other materials to find out if they are potential p-wave candidates.
However, the work on strontium ruthenate isn’t finished.
“This material is extremely well studied in a lot of different contexts, not just for its superconductivity,” Ramshaw said. “We understand what kind of metal it is, why it’s a metal, how it behaves when you change temperature, how it behaves when you change the magnetic field. So you should be able to construct a theory of why it becomes a superconductor better here than just about anywhere else.”
Using data from several instruments aboard ESA’s Rosetta mission, researchers have found evidence of far-ultraviolet aurora on comet 67P/Churyumov-Gerasimenko.
The Rosetta spacecraft escorted comet 67P/Churyumov-Gerasimenko for more than two years.
The data for the current study is on what the Rosetta scientists initially interpreted as ‘dayglow,’ a process caused by photons interacting with the coma that radiates from, and surrounds, the comet’s nucleus.
But the new analysis of the Rosetta data paints a very different picture. By linking data from numerous Rosetta instruments, researchers were able to get a better picture of what was going on.
This enabled them to unambiguously identify how 67P/Churyumov-Gerasimenko’s ultraviolet atomic emissions form. The data indicate 67P/Churyumov-Gerasimenko’s emissions are actually auroral in nature.
Electrons streaming out in the solar wind interact with the gas in the comet’s coma, breaking apart water and other molecules. The resulting atoms give off a distinctive far-ultraviolet light.
Invisible to the naked eye, far-ultraviolet has the shortest wavelengths of radiation in the ultraviolet spectrum.
Exploring the emission of 67P/Churyumov-Gerasimenko will enable the researchers to learn how the particles in the solar wind change over time, something that is crucial for understanding space weather throughout the Solar System.
By providing better information on how the Sun’s radiation affects the space environment they must travel through, such information could ultimately can help protect satellites and spacecraft, as well as astronauts traveling to the Moon and Mars.
Spectral data gathered by the Visual and Infrared Mapping Spectrometer (VIMS) onboard NASA’s Cassini spacecraft provide strong evidence that the northern hemisphere of Saturn’s moon Enceladus has been resurfaced with ice from its interior.
Between 2004 and 2017, the VIMS instrument collected infrared data during 23 Enceladus close encounters, in addition to more distant surveys.
Dr. Gabriel Tobie, a researcher in the Laboratory of Planetology and Geodynamics at the University of Nantes, and colleagues used the VIMS data, combined with detailed images captured by Cassini’s Imaging Science Subsystem (ISS), to make the new global spectral map of Enceladus.
In 2005, the scientists discovered that Enceladus, which looks like a highly reflective, bright white snowball to the naked eye, shoots out enormous plumes of ice grains and vapor from an ocean that lies under the icy crust.
The new spectral map shows that infrared signals clearly correlate with that geologic activity, which is easily seen at the south pole.
That’s where the so-called ‘tiger stripes’ blast ice and vapor from the interior ocean.
But some of the same infrared features also appear in the northern hemisphere.
That tells the researchers not only that the northern area is covered with fresh ice but that the same kind of geologic activity — a resurfacing of the landscape — has occurred in both hemispheres.
The resurfacing in the north may be due either to icy jets or to a more gradual movement of ice through fractures in the crust, from the subsurface ocean to the surface.
“The infrared shows us that the surface of the south pole is young, which is not a surprise because we knew about the jets that blast icy material there,” Dr. Tobie said.
“Now, thanks to these infrared eyes, you can go back in time and say that one large region in the northern hemisphere appears also young and was probably active not that long ago, in geologic timelines.”
References: R. Robidel et al. 2020. Photometrically-corrected global infrared mosaics of Enceladus: New implications for its spectral diversity and geological activity. Icarus 349: 113848; doi: 10.1016/j.icarus.2020.113848