Heavens

Femtosecond hard X-ray pulses are an important tool for unraveling structure changes of condensed matter on atomic length and time scales. A novel laser-driven X-ray source provides femtosecond copper Kα pulses at a 1 kHz repetition rate with an unprecedented flux of some 10^12 X-ray photons per second.

Elementary processes in physics, chemistry, and biology are connected with changes of the atomic or molecular structure on a femtosecond time scale (1 femtosecond (fs) = 10^-15 seconds). Ultrafast X-ray methods hold strong potential for following structure changes in space and time and generate 'movies' of the motions of electrons, atoms and molecules. This perspective has resulted in a strong demand for femtosecond hard X-ray pulses to be applied in X-ray scattering and spectroscopy.

There are two main approaches to generate ultrashort hard X-ray pulses. The first are sources based on large-scale electron accelerators and undulators in which femtosecond electron bunches radiate bright X-ray pulses. The second are small-frame laboratory sources driven by intense femtosecond optical lasers. Here, electron acceleration occurs in the strong electric field of an optical pulse and X-ray pulses are generated by collisional interaction of such electrons with atoms of a metal target, similar to a conventional X-ray tube.

Researchers at the Max Born Institute (MBI) in Berlin have now accomplished a breakthrough in table-top generation of femtosecond X-ray pulses by demonstrating a stable pulse train at kilohertz repetition rate with a total flux of some 10^12 X-ray photons per second. As they report in Optics Letters, the combination of a novel optical driver providing femtosecond mid-infrared pulses around a 5 μm (5000 nm) wavelength with a metallic tape target in a transmission geometry allows for generating hard X-ray pulses at a wavelength of 0.154 nm with very high efficiency.

The optical driver is based on optical parametric chirped pulse amplification (OPCPA) and provides 80-fs pulses at a central wavelength of 5 μm with an energy of 3 mJ and a repetition rate of 1 kHz. To generate X-ray pulses, the mid-infrared pulses are tightly focused onto a thin copper target (Fig 1). In an optical cycle of the optical field, electrons are extracted from the copper tape, accelerated in vacuum and steered back to the target. Electrons with a kinetic energy of up to 100 keV reenter the target and generate bright copper Kα pulses at a wavelength of 0.154 nm, accompanied by spectrally broad bremsstrahlung. The longer optical cycle of the mid-infrared pulses compared to pulses at shorter optical wavelengths results in longer acceleration times of the electrons, higher kinetic energies, and eventually higher efficiency in X-ray generation (Fig. 2).

The new table-top X-ray source reaches an average number of Cu-Kα photons up to 1.5x10^9 photons per pulse in the full solid angle or 1.5x10^12 photons per second (blue dots in Fig 2c). This photon flux is 30 times higher than from commonly used table-top X-ray sources driven by Ti:sapphire lasers at the central wavelength of 0.8 μm (black dots in Fig 2c). Such source parameters open exciting perspectives for investigating ultrafast structure changes in condensed matter by time-resolved X-ray scattering.

Researchers at Paderborn University have developed a new method of distance measurement for systems such as GPS, which achieves more precise results than ever before. Using quantum physics, the team led by Leibniz Prize winner Professor Christine Silberhorn has successfully overcome the so-called resolution limit, which causes the "noise" we may see in photos, for example. Their findings have just been published in the academic journal "Physical Review X Quantum" (PRX Quantum). In "Physics", the publisher's online magazine, the paper has also been highlighted with an expert Viewpoint - an honour which is given to only certain selected publications.

Physicist Dr Benjamin Brecht explains the problem of the resolution limit: "In laser distance measurements a detector registers two light pulses of different intensities with a time difference. The more precise the time measurement is, the more accurately the distance can be determined. Providing the time separation between the pulses is greater than the length of the pulses, this works well." Problems arise, however, as Brecht explains, if the pulses overlap: "Then you can no longer measure the time difference using conventional methods. This is known as the "resolution limit" and is a well-known effect in photos. Very small structures or textures can no longer be resolved. That's the same problem - just with position rather than time."

A further challenge, according to Brecht, is to determine the different intensities of two light pulses, simultaneously with their time difference and the arrival time. But this is exactly what the researchers have managed to do - "with quantum-limited precision", adds Brecht. Working with partners from the Czech Republic and Spain, the Paderborn physicists were even able to measure these values when the pulses overlapped by 90 per cent. Brecht says: "This is far beyond the resolution limit. The precision of the measurement is 10,000 times better. Using methods from quantum information theory, we can find new forms of measurement which overcome the limitations of established methods."

These findings could allow significant improvements in the future to the precision of applications such as LIDAR, a method of optical distance and speed measurement, and GPS. It will take some time, however, before this is ready for the market, points out Brecht.

Diamond is the hardest material in nature. But out of many expectations, it also has great potential as an excellent electronic material. A joint research team led by City University of Hong Kong (CityU) has demonstrated for the first time the large, uniform tensile elastic straining of microfabricated diamond arrays through the nanomechanical approach. Their findings have shown the potential of strained diamonds as prime candidates for advanced functional devices in microelectronics, photonics, and quantum information technologies.

The research was co-led by Dr Lu Yang, Associate Professor in the Department of Mechanical Engineering (MNE) at CityU and researchers from Massachusetts Institute of Technology (MIT) and Harbin Institute of Technology (HIT). Their findings have been recently published in the prestigious scientific journal Science, titled "Achieving large uniform tensile elasticity in microfabricated diamond".

"This is the first time showing the extremely large, uniform elasticity of diamond by tensile experiments. Our findings demonstrate the possibility of developing electronic devices through 'deep elastic strain engineering' of microfabricated diamond structures," said Dr Lu.

Diamond: "Mount Everest" of electronic materials

Well known for its hardness, industrial applications of diamonds are usually cutting, drilling, or grinding. But diamond is also considered as a high-performance electronic and photonic material due to its ultra-high thermal conductivity, exceptional electric charge carrier mobility, high breakdown strength and ultra-wide bandgap. Bandgap is a key property in semi-conductor, and wide bandgap allows operation of high-power or high-frequency devices. "That's why diamond can be considered as 'Mount Everest' of electronic materials, possessing all these excellent properties," Dr Lu said.

However, the large bandgap and tight crystal structure of diamond make it difficult to "dope", a common way to modulate the semi-conductors' electronic properties during production, hence hampering the diamond's industrial application in electronic and optoelectronic devices. A potential alternative is by "strain engineering", that is to apply very large lattice strain, to change the electronic band structure and associated functional properties. But it was considered as "impossible" for diamond due to its extremely high hardness.

Then in 2018, Dr Lu and his collaborators discovered that, surprisingly, nanoscale diamond can be elastically bent with unexpected large local strain. This discovery suggests the change of physical properties in diamond through elastic strain engineering can be possible. Based on this, the latest study showed how this phenomenon can be utilized for developing functional diamond devices.

Uniform tensile straining across the sample

The team firstly microfabricated single-crystalline diamond samples from a solid diamond single crystals. The samples were in bridge-like shape - about one micrometre long and 300 nanometres wide, with both ends wider for gripping (See image: Tensile straining of diamond bridges). The diamond bridges were then uniaxially stretched in a well-controlled manner within an electron microscope. Under cycles of continuous and controllable loading-unloading of quantitative tensile tests, the diamond bridges demonstrated a highly uniform, large elastic deformation of about 7.5% strain across the whole gauge section of the specimen, rather than deforming at a localized area in bending. And they recovered their original shape after unloading.

By further optimizing the sample geometry using the American Society for Testing and Materials (ASTM) standard, they achieved a maximum uniform tensile strain of up to 9.7%, which even surpassed the maximum local value in the 2018 study, and was close to the theoretical elastic limit of diamond. More importantly, to demonstrate the strained diamond device concept, the team also realized elastic straining of microfabricated diamond arrays.

Tuning the bandgap by elastic strains

The team then performed density functional theory (DFT) calculations to estimate the impact of elastic straining from 0 to 12% on the diamond's electronic properties. The simulation results indicated that the bandgap of diamond generally decreased as the tensile strain increased, with the largest bandgap reduction rate down from about 5 eV to 3 eV at around 9% strain along a specific crystalline orientation. The team performed an electron energy-loss spectroscopy analysis on a pre-strained diamond sample and verified this bandgap decreasing trend.

Their calculation results also showed that, interestingly, the bandgap could change from indirect to direct with the tensile strains larger than 9% along another crystalline orientation. Direct bandgap in semi-conductor means an electron can directly emit a photon, allowing many optoelectronic applications with higher efficiency.

These findings are an early step in achieving deep elastic strain engineering of microfabricated diamonds. By nanomechanical approach, the team demonstrated that the diamond's band structure can be changed, and more importantly, these changes can be continuous and reversible, allowing different applications, from micro/nanoelectromechanical systems (MEMS/NEMS), strain-engineered transistors, to novel optoelectronic and quantum technologies. "I believe a new era for diamond is ahead of us," said Dr Lu.

It took fifteen years of imaging and nearly three years of stitching the pieces together to create the largest image ever made, the 8-trillion-pixel mosaic of Mars' surface. Now, the first study to utilize the image in its entirety provides unprecedented insight into the ancient river systems that once covered the expansive plains in the planet's southern hemisphere. These three billion-year-old sedimentary rocks, like those in Earth's geologic record, could prove valuable targets for future exploration of past climates and tectonics on Mars.

The work, published this month in Geology, complements existing research into Mars' hydrologic history by mapping ancient fluvial (river) ridges, which are essentially the inverse of a riverbed. "If you have a river channel, that's the erosion part of a river. So, by definition, there aren't any deposits there for you to study," Jay Dickson, lead author on the paper, explains. "You have rivers eroding rocks, so where did those rocks go? These ridges are the other half of the puzzle." Using the mosaic, as opposed to more localized imagery, let the researchers solve that puzzle on a global scale.

Mars used to be a wet world, as evidenced by rock records of lakes, rivers, and glaciers. The river ridges were formed between 4 and 3 billion years ago, when large, flat-lying rivers deposited sediments in their channels (rather than only having the water cut away at the surface). Similar systems today can be found in places like southern Utah and Death Valley in the U.S., and the Atacama Desert in Chile. Over time, sediment built up in the channels; once the water dried up, those ridges were all that was left of some rivers.

The ridges are present only in the southern hemisphere, where some of Mars' oldest and most rugged terrain is, but this pattern is likely a preservation artifact. "These ridges probably used to be all over the entire planet, but subsequent processes have buried them or eroded them away," Dickson says. "The northern hemisphere is very smooth because it's been resurfaced, primarily by lava flows." Additionally, the southern highlands are "some of the flattest surfaces in the solar system," says Woodward Fischer, who was involved in this work. That exceptional flatness made for good sedimentary deposition, allowing the creation of the records being studied today.

Whether or not a region has fluvial ridges is a basic observation that wasn't possible until this high-resolution image of the planet's surface was assembled. Each of the 8 trillion pixels represents 5 to 6 square meters, and coverage is nearly 100 percent, thanks to the "spectacular engineering" of NASA's context camera that has allowed it to operate continuously for well over a decade. An earlier attempt to map these ridges was published in 2007 by Rebecca Williams, a co-author on the new study, but that work was limited by imagery coverage and quality.

"The first inventory of fluvial ridges using meter-scale images was conducted on data acquired between 1997 and 2006," Williams says. "These image strips sampled the planet and provided tantalizing snapshots of the surface, but there was lingering uncertainty about missing fluvial ridges in the data gaps."

The resolution and coverage of Mars' surface in the mosaic has eliminated much of the team's uncertainty, filling in gaps and providing context for the features. The mosaic allows researchers to explore questions at global scales, rather than being limited to patchier, localized studies and extrapolating results to the whole hemisphere. Much previous research on Mars hydrology has been limited to craters or single systems, where both the sediment source and destination are known. That's useful, but more context is better in order to really understand a planet's environmental history and to be more certain in how an individual feature formed.

In addition to identifying 18 new fluvial ridges, using the mosaic image allowed the team to re-examine features that had previously been identified as fluvial ridges. Upon closer inspection, some weren't formed by rivers after all, but rather lava flows or glaciers. "If you only see a small part of [a ridge], you might have an idea of how it formed," Dickson says. "But then you see it in a larger context--like, oh, it's the flank of a volcano, it's a lava flow. So now we can more confidently determine which are fluvial ridges, versus ridges formed by other processes."

Now that we have a global understanding of the distribution of ancient rivers on Mars, future explorations--whether by rover or by astronauts--could use these rock records to investigate what past climates and tectonics were like. "One of the biggest breakthroughs in the last twenty years is the recognition that Mars has a sedimentary record, which means we're not limited to studying the planet today," Fischer says. "We can ask questions about its history." And in doing so, he says, we learn not only about a single planet's past, but also find "truths about how planets evolved... and why the Earth is habitable."

As this study is only the first to use the full mosaic, Dickson looks forward to seeing how it gets put to use next. "We expect to see more and more studies, similar in scale to what we're doing here, by other researchers around the world," he says. "We hope that this 'maiden voyage' scientific study sets an example for the scale of science that can be done with a product this big."

Catalysts are indispensable for many technologies. To further improve heterogeneous catalysts, it is required to analyze the complex processes on their surfaces, where the active sites are located. Scientists of Karlsruhe Institute of Technology (KIT), together with colleagues from Spain and Argentina, have now reached decisive progress: As reported in Physical Review Letters, they use calculation methods with so-called hybrid functionals for the reliable interpretation of experimental data. (DOI: 10.1103/PhysRevLett.125.256101).

Many important technologies, such as processes for energy conversion, emission reduction, or the production of chemicals, work with suitable catalysts only. For this reason, highly efficient materials for heterogeneous catalysis are gaining importance. In heterogeneous catalysis, the material acting as a catalyst and the reacting substances exist in different phases as a solid or gas, for instance. Material compositions can be determined reliably by various methods. Processes taking place on the catalyst surface, however, can be detected by hardly any analysis method. "But it is these highly complex chemical processes on the outermost surface of the catalyst that are of decisive importance," says Professor Christof Wöll, Head of KIT's Institute of Functional Interfaces (IFG). "There, the active sites are located, where the catalyzed reaction takes place."

Precise Examination of the Surface of Powder Catalysts

Among the most important heterogeneous catalysts are cerium oxides, i.e. compounds of the rare-earth metal cerium with oxygen. They exist in powder form and consist of nanoparticles of controlled structure. The shape of the nanoparticles considerably influences the reactivity of the catalyst. To study the processes on the surface of such powder catalysts, researchers recently started to use probe molecules, such as carbon monoxide molecules, that bind to the nanoparticles. These probes are then measured by infrared reflection absorption spectroscopy (IRRAS). Infrared radiation causes molecules to vibrate. From the vibration frequencies of the probe molecules, detailed information can be obtained on the type and composition of the catalytic sites. So far, however, interpretation of the experimental IRRAS data has been very difficult, because technologically relevant powder catalysts have many vibration bands, whose exact allocation is challenging. Theoretical calculations were of no help, because the deviation from the experiment, also in the case of model systems, was so large that experimentally observed vibration bands could not be allocated precisely.

Long Calculation Time - High Accuracy

Researchers of KIT's Institute of Functional Interfaces (IFG) and Institute of Catalysis Research and Technology (IKFT), in cooperation with colleagues from Spain and Argentina coordinated by Dr. M. Verónica Ganduglia-Pirovano from Consejo Superior de Investigaciones Científicas (CSIC) in Madrid, have now identified and solved a major problem of theoretical analysis. As reported in Physical Review Letters, systematic theoretical studies and validation of the results using model systems revealed that theoretical methods used so far have some fundamental weaknesses. In general, such weaknesses can be observed in calculations using the density functional theory (DFT), a method with which the quantum mechanics basic state of a multi-electron system can be determined based on the density of the electrons. The researchers found that the weaknesses can be overcome with so-called hybrid functionals that combine DFT with the Hartree-Fock method, an approximation method in quantum chemistry. This makes the calculations very complex, but also highly precise. "The calculation times required by these new methods are longer by a factor of 100 than for conventional methods," says Christof Wöll. "But this drawback is more than compensated by the excellent agreement with the experimental systems." Using nanoscaled cerium oxide catalysts, the researchers demonstrated this progress that may contribute to making heterogeneous catalysts more effective and durable.

The results of the work also represent an important contribution to the new Collaborative Research Center (CRC) "TrackAct - Tracking the Active Site in Heterogeneous Catalysis for Emission Control" at KIT. Professor Christof Wöll and Dr. Yuemin Wang from IFG as well as Professor Felix Studt and Dr. Philipp Pleßow from IKFT are among the principal investigators of this interdisciplinary CRC that is aimed at holistically understanding catalytic processes. For more information on the CRC TrackAct, clickhttps://www.kit.edu/kit/english/pi_2020_106_how-to-make-catalysts-more-efficient.php.

Astronomers using NASA's Hubble Space Telescope watched a mysterious dark vortex on Neptune abruptly steer away from a likely death on the giant blue planet.

The storm, which is wider than the Atlantic Ocean, was born in the planet's northern hemisphere and discovered by Hubble in 2018. Observations a year later showed that it began drifting southward toward the equator, where such storms are expected to vanish from sight. To the surprise of observers, Hubble spotted the vortex change direction by August 2020, doubling back to the north. Though Hubble has tracked similar dark spots over the past 30 years, this unpredictable atmospheric behavior is something new to see.

Equally as puzzling, the storm was not alone. Hubble spotted another, smaller dark spot in January this year that temporarily appeared near its larger cousin. It might possibly have been a piece of the giant vortex that broke off, drifted away, and then disappeared in subsequent observations.

"We are excited about these observations because this smaller dark fragment is potentially part of the dark spot's disruption process," said Michael H. Wong of the University of California at Berkeley. "This is a process that's never been observed. We have seen some other dark spots fading away, and they're gone, but we've never seen anything disrupt, even though it's predicted in computer simulations."

The large storm, which is 4,600 miles across, is the fourth dark spot Hubble has observed on Neptune since 1993. Two other dark storms were discovered by the Voyager 2 spacecraft in 1989 as it flew by the distant planet, but they had disappeared before Hubble could observe them. Since then, only Hubble has had the sharpness and sensitivity in visible light to track these elusive features, which have sequentially appeared and then faded away over a duration of about two years each. Hubble uncovered this latest storm in September 2018.

Wicked Weather

Neptune's dark vortices are high-pressure systems that can form at mid-latitudes and may then migrate toward the equator. They start out remaining stable due to Coriolis forces, which cause northern hemisphere storms to rotate clockwise, due to the planet's rotation. (These storms are unlike hurricanes on Earth, which rotate counterclockwise because they are low-pressure systems.) However, as a storm drifts toward the equator, the Coriolis effect weakens and the storm disintegrates. In computer simulations by several different teams, these storms follow a more-or-less straight path to the equator, until there is no Coriolis effect to hold them together. Unlike the simulations, the latest giant storm didn't migrate into the equatorial "kill zone."

"It was really exciting to see this one act like it's supposed to act and then all of a sudden it just stops and swings back," Wong said. "That was surprising."

Dark Spot Jr.

The Hubble observations also revealed that the dark vortex's puzzling path reversal occurred at the same time that a new spot, informally deemed "dark spot jr.," appeared. The newest spot was slightly smaller than its cousin, measuring about 3,900 miles across. It was near the side of the main dark spot that faces the equator -- the location that some simulations show a disruption would occur.

However, the timing of the smaller spot's emergence was unusual. "When I first saw the small spot, I thought the bigger one was being disrupted," Wong said. "I didn't think another vortex was forming because the small one is farther towards the equator. So it's within this unstable region. But we can't prove the two are related. It remains a complete mystery.

"It was also in January that the dark vortex stopped its motion and started moving northward again," Wong added. "Maybe by shedding that fragment, that was enough to stop it from moving towards the equator."

The researchers are continuing to analyze more data to determine whether remnants of dark spot jr. persisted through the rest of 2020.

Dark Storms Still Puzzling

It's still a mystery how these storms form, but this latest giant dark vortex is the best studied so far. The storm's dark appearance may be due to an elevated dark cloud layer, and it could be telling astronomers about the storm's vertical structure.

Another unusual feature of the dark spot is the absence of bright companion clouds around it, which were present in Hubble images taken when the vortex was discovered in 2018. Apparently, the clouds disappeared when the vortex halted its southward journey. The bright clouds form when the flow of air is perturbed and diverted upward over the vortex, causing gases to likely freeze into methane ice crystals. The lack of clouds could be revealing information on how spots evolve, say researchers.

Weather Eye on the Outer Planets

Hubble snapped many of the images of the dark spots as part of the Outer Planet Atmospheres Legacy (OPAL) program, a long-term Hubble project, led by Amy Simon of NASA's Goddard Space Flight Center in Greenbelt, Maryland, that annually captures global maps of our solar system's outer planets when they are closest to Earth in their orbits.

OPAL's key goals are to study long-term seasonal changes, as well as capture comparatively transitory events, such as the appearance of dark spots on Neptune or potentially Uranus. These dark storms may be so fleeting that in the past some of them may have appeared and faded during multi-year gaps in Hubble's observations of Neptune. The OPAL program ensures that astronomers won't miss another one.

"We wouldn't know anything about these latest dark spots if it wasn't for Hubble," Simon said. "We can now follow the large storm for years and watch its complete life cycle. If we didn't have Hubble, then we might think the Great Dark Spot seen by Voyager in 1989 is still there on Neptune, just like Jupiter's Great Red Spot. And, we wouldn't have known about the four other spots Hubble discovered." Wong will present the team's findings Dec. 15 at the fall meeting of the American Geophysical Union.

The bedrock beneath our feet has a reputation as an inhospitable place. In contrast, soil is known to be teeming with life - from microbes to plant roots to bugs.

This perspective has set soil up as the most important source of carbon dioxide produced by forests, the CO2 being a natural byproduct of the life within it. But according to a study led by The University of Texas at Austin, the prevailing view is just scratching the surface.

The study found that CO2 can also be produced deeper underground in bedrock fractures, and that this source could account for up to 29% of the daily average CO2 emitted by the land, depending on the season.

This finding does not mean that landscapes are emitting more CO2 into the atmosphere, but it does challenge the conventional wisdom about where CO2 is being produced. It can also help improve climate change models because understanding how and where CO2 is produced is an essential part of creating accurate forecasts.

The study linked CO2 production in the rock to the seasonal uptake of water by deep tree roots many meters below the surface, a finding that suggests that tree roots and the microbial communities around them are the source of the CO2 - and that bedrock fractures are a place for life to thrive.

"This is paradigm shifting in terms of where the action is," said Daniella Rempe, an assistant professor at the UT Jackson School of Geosciences who coauthored the study. "Soils may not be the only key player in forests."

The study was published on Dec.6 in the JGR Biogeosciences.

Alison Tune, a graduate student at the Jackson School, led the research. Other coauthors include Jackson School Professor Philip Bennett, Jia Wang, a graduate student at the University of Illinois Urbana-Champaign, and Jennifer Druhan, an assistant professor at the University of Illinois Urbana-Champaign who played a key role in designing and executing the research.

Soil does not sit on top of solid bedrock. Rather, a transition zone of fractured and weathered bedrock sits between these two extremes. This altered rock is notoriously difficult to sample. The research relied on a specialized sampling tool buried in a hill slope in northern California, that extended from the top of the fractured bedrock to the bottom, about 44 feet.

This tool quickly revealed that this region was an active site of CO2 production.

"There is a large CO2 source below the soil," Tune said. "When we first measured the [CO2] concentration profiles in the field we were pretty excited by what we found."

By analyzing thousands of samples collected from 2017-2019, the researchers discovered that the CO2 didn't stay put. During the dry season, the CO2 primarily travelled up into the soil where it was released into the atmosphere. During the wet season, when groundwater rose up to fill the fractures, nearly 50% of the CO2 dissolved into the water, which eventually flows to streams and rivers.

The researchers found that this dissolved CO2 ramps up rock weathering, with as much as 80% of the dissolved carbon in groundwater exiting the study area coming from the fractured bedrock. This finding is significant, Rempe said, because it is the first time scientists have been able to pinpoint where ongoing rock weathering is happening within the hillslope.

This study builds on a growing body of knowledge showing fractured bedrock as an ecologically important region. For example, in a 2018 study, Rempe and collaborators found evidence for rock moisture in fractured rock sustaining trees during droughts.

Mark Torres, an assistant professor at Rice University who studies how carbon cycles through environments, said that the research is significant because it sheds light on a part of the landscape that is considered a "black box" between the soil and the groundwater.

"In the work I do, I usually scoop up river water and I have to infer what's going on underneath a hill," he said. "What's really impressive about the work is how they observed things that are incredibly difficult to see."

The researchers are planning on investigating fractured bedrock in other places, including a local research site at the Jackson School's White Family Outdoor Learning Center, a 266-acre site in Dripping Springs, Texas.

"Fractured bedrock is really common in Texas, where the soil is really thin and there's lots of deep rooting," Tune said. "It could be an important part of the carbon cycle in these ecosystems and it could be important to understand that as we go forward and as the climate changes over time."

FAYETTEVILLE, Ark. - Water on Mars, in the form of brines, may not be as widespread as previously thought, according to a new study by researchers at the Arkansas Center for Space and Planetary Sciences.

Researchers combined data on brine evaporation rates, collected through experiments at the center's Mars simulation chamber, with a global weather circulation model of the planet to create planetwide maps of where brines are most likely to be found.

Brines are mixtures of water and salts that are more resistant to boiling, freezing and evaporation than pure water. Finding them has implications for where scientists will look for past or present life on Mars and where humans who eventually travel to the planet could look for water.

The scientists took all major phase changes of liquids into account -- freezing, boiling and evaporation - instead of just a single phase, as has commonly been the approach in the past, said Vincent Chevrier, associate professor and first author of a study published in The Planetary Science Journal. Former U of A doctoral students Edgard G. Rivera-Valentín and Travis S. Altheide were coauthors of the paper.

"It is looking at all the properties at the same time, instead of one at a time," said Chevrier. "Then we build maps taking into account all those processes simultaneously."

Doing so indicates that previous studies may have overestimated how long brines remain on the surface in the cold, thin and arid Martian atmosphere, Chevrier said. "The most important conclusion is that if you do not take all these processes together, you always overestimate the stability of brines. That is the reality of the situation."

Favorable conditions for stable brines on the planet's surface are most likely to be present in mid- to high-northern latitudes, and in large impact craters in the southern hemisphere, he said. In the shallow subsurface, brines might be present near the equator.

In the best-case scenario, brines could be present for up to 12 hours per day. "Nowhere is any brine stable for an entire day on Mars," he said.

A pioneering study carried out among patients in remission from Rheumatoid Arthritis has determined that they display significantly higher temperatures than healthy individuals.

The work, published in PLOSONE and undertaken by University of Malta and Staffordshire University, compares thermographic patterns of patients with Rheumatoid Arthritis (RA) in remission with healthy individuals.

More than 31 RA patients in remission were recruited from the clinics in Malta and thermal images of their feet were taken. Temperatures in the different regions of the foot - medial, lateral, forefoot and heel regions - were analysed and compared to a cohort of more than 52 healthy adults.

Dr Alfred Gatt, from the University of Malta and a Visiting Fellow at the Centre for Biomechanics and Rehabilitation Technologies, Staffordshire University, led the study. He said: "Our previous study which looked at the joints of the hands highlighted that thermal imaging has the potential to become an important method to assess Rheumatoid Arthritis.

"These tests demonstrated a significant difference in temperatures in all the regions of the forefoot between RA patients in remission and healthy patients. This provides the basis of future studies to assess whether thermographic patterns change with disease activity."

Dr Cynthia Formosa, Head of Podiatry at the University of Malta and Visiting Fellow at Staffordshire University added: "This paper has set out a baseline that demonstrates that even when there is no inflammation detected by conventional methods, the heat emitted over each foot joint is higher than that of healthy adults.

"This is important because it implies that some underlying disease process and that thermography is sensitive enough to detect these changes."

Professor Nachi Chockalingam, co-author of the paper and the Director of the Centre for Biomechanics and Rehabilitation Technologies, Staffordshire University, said; "This has implications for both the continued management and self-care of patients in remission from RA.

"In future it may be possible to use small thermal imaging cameras as a screening tool that can be used by both clinician or patient themselves to detect early changes and prevent further damage to the joints, which can result in significant deformity and disability."

"Remission is a state whereby the RA, which is an autoimmune disease, is in a controlled state and there is no active inflammation going on in the joints. It does not mean that RA is not present and that it cannot flare up again What we are now saying is that these patients need continuous monitoring."

The discovery of the first known fossil iguana nesting burrow, on an outer island of the Bahamas, fills in a gap of scientific knowledge for a prehistoric behavior of an iconic lizard. PLOS ONE published the finding by scientists from Emory University, which also uncovers new clues to the geologic and natural history of the Bahamas.

The fossilized burrow dates back to the Late Pleistocene Epoch, about 115,000 years ago, and is located on the island of San Salvador -- best known as the likely spot where Christopher Columbus made his first landfall in his 1492 voyage.

"San Salvador is one of the outer-most islands in the Bahamas chain and really isolated," says Anthony Martin, a professor in Emory's Department of Environmental Sciences and senior author of the PLOS ONE paper. "It's a mystery how and when the modern-day San Salvadoran rock iguanas arrived there. Today, they are among the rarest lizards in the world, with only a few hundred of them left."

Martin's specialty is ichnology -- the study of traces of life, such as tracks, nests and burrows. He documents modern-day traces to help him identify trace fossils from the deep past to learn about prehistoric animal behaviors.

The current discovery was made during a class field trip to San Salvador as part of the course "Modern and Ancient Tropical Environments," co-taught by Martin and Melissa Hage, an assistant professor of environmental science at Emory's Oxford College and a co-author of the paper. Co-authors also include two former undergraduates from the class: Dottie Stearns (now in medical school at the University of Colorado) and Meredith Whitten (who now works in fisheries management for the state of North Carolina).

"No matter how much you read about things in a textbook, a lot of concepts in geology just don't click until you see them in real life," Hage says. "It sparks a lot of excitement in students when they experience the process of scientific discovery in the field."

"Students get to actually see the connections of the past and the present," Martin adds. "On the north point of San Salvador, for instance, the undulating landscape consists of ancient sand dunes that turned into rock. We can walk across these ancient dunes to look at the rock record and get an idea of how the island changed over time."

During a stop on the shoreline road on the south end of the island, Martin happened to notice what looked like the trace of a fossil iguana burrow on a limestone outcrop exposed by a roadcut.

The fossil record for iguanas goes back to the Late Cretaceous in South America. Today iguanas are found in tropical areas of Mexico, Central America, South America, the Caribbean and the Bahamas.

Iguanas can grow up to six feet in length, including their tails. Despite their large size, formidable claws and fierce-looking spikes arrayed on their backs, iguanas are mostly herbivores.

The now endangered San Salvador rock iguana, Cyclura riyeli riyeli, and other Cyclura species were plentiful throughout the Bahamas before 1492, when European ships began introducing rats, pigs and other invasive species that feed on the lizards' eggs.

"One of the cool things about iguanas is that they are survivors," Martin says. "And one of the main ways that they survive is through burrowing. Digging burrows has helped them survive hurricanes, droughts and other bad things that might be in their environment, like most predators. But burrows are not as helpful when it comes to rats and pigs."

After further investigation, Martin and his co-authors determined that the trace fossil he noticed on the limestone outcrop was that of a nesting iguana burrow. Ample evidence, including a nearby fossil land-crab burrow discovered by Hage, showed that the outcrop was a former inland sand dune, where iguanas prefer to lay their eggs.

The iguana trace revealed the distinctive pattern of a female creating a nest. "Iguanas have evolved a behavior where a female actually buries herself alive in sand, lays her eggs, and then 'swims' out, packing the loose sand behind her as she leaves the burrow to hide the eggs from predators," Martin says.

This backfilling technique created compaction zones that weathered out over time from the surrounding limestone because they were more durable. "It's like when you pack sand to build a sandcastle at the beach," Martin explains. "It's a similar principle but, in the case of the iguana burrow, it happens underground."

The lack of burrows from hatchlings digging their way to the surface, however, suggests that the nest failed and that the eggs never produced young.

The researchers were able to date the iguana trace to about 115,000 years ago due to tell-tale red paleosols, or fossilized soils. "The red indicates oxidized iron minerals and there are no native iron minerals in that area," Martin explains. "But whenever there is a drop in sea level, the Sahara expands in size creating big dust storms. The trade winds take this red dust across the Atlantic and deposit it in the Caribbean."

The oldest iguana skeletons found on San Salvador only date back less than 12,000 years, in the Holocene Epoch, so the discovery of the iguana trace pushes their presence on the islands back significantly.

Most of the Bahamian islands sit on a relatively shallow platform, making it easy to imagine how iguanas might have migrated there during sea-level lows. San Salvador, however, is a small, isolated island surrounded by deep ocean, setting up the mystery for how the first iguanas arrived there at least 115,000 years ago.

"We're hoping researchers who study iguana evolution will be inspired by our paper to dig deeper into this question," Martin says.

The researchers also hope that the paper draws attention to the plight of modern-day San Salvador rock iguanas. "When it comes to species preservation, many people think of panda bears and other cuddly mammals," Hage says. "Making the connection between how long iguanas have been on the island and how the modern-day San Salvador rock iguanas are endangered may help more people understand why they are worth preserving."

WASHINGTON, December 8, 2020 -- Ultrasound can be used to treat cancer when used in combination with molecules that sensitize the system to sound waves. These sonosensitizers generate toxic reactive oxygen species that attack and kill tumor cells.

In Applied Physics Reviews, by AIP Publishing, scientists from Soochow University in China report a new type of sonosensitizer based on a vanadium-doped titanium dioxide, V-TiO2, that enhances the amount of damage ultrasound inflicts on tumors. Studies in mice showed that tumor growth was markedly suppressed when compared to a control group.

Organic molecules have been used in the past as sensitizers, but these are unstable and can lead to phototoxicity, where exposure to light can produce rashes or extreme sunburn. Inorganic sensitizers based on TiO2 nanomaterials are also used, but these do not work well and can remain in the body for long periods.

TiO2 does not work well as a sensitizer, because it has a wide band gap in its electronic structure. Even when the ultrasound strips electrons away from the TiO2 nanoparticles, the electrons rapidly recombine with the nanoparticles, preventing the generation of reactive oxygen species that could attack tumor cells.

The investigators realized they could avoid this effect by doping TiO2 nanoparticles with the metal vanadium to form nano-sized spindles.

"The band gap of V-TiO2 nanospindles is reduced, increasing the efficiency of ultrasound-triggered reactive oxygen species production compared to that of pure TiO2 nanoparticles," said author Liang Cheng.

The microenvironment around the tumor is key to cancer metastasizing and invading other tissue, and important for the way chemotherapy and other treatments work. The tumor microenvironment has an acidic pH but also contains a lot of hydrogen peroxide and a substance known as glutathione.

The investigators realized the V-TiO2 spindles act like tiny enzymes that catalyze chemical processes in the microenvironment. In the presence of ultrasound waves, the spindles allow a two-pronged attack on the tumor: one involving sound waves, the other a type of chemotherapy that degrades hydrogen peroxide and consumes glutathione. Both effects kill tumor cells without harming healthy tissue.

The investigators carried out a careful study using controls on both breast cancer tumor cells and on mice infected with these cancerous cells. In addition to direct measurements about tumor growth, they employed fluorescent probes to visualize reactive oxygen species and glutathione during the process.

"It is worth noting that V-TiO2 nanospindles are rapidly excreted from the body," said Cheng. "This helps prevent any possible long-term toxicity effects."

The scientists were also able to observe V-TiO2 nanospindles in the spleen and liver of the mice and, later, in the feces and urine. No obvious signs of organ inflammation or damage were observed, showing that these sensitizers are both safe and effective.

HOUSTON - (Dec. 8, 2020) - Inspired by light-sensing bacteria that thrive near hot oceanic vents, synthetic chemists at Rice University have found a mild method to make valuable hydrocarbons known as olefins, or alkenes.

Like the bacteria, the researchers use vitamin B12, eliminating harsh chemicals typically needed to make precursor molecules essential to the manufacture of drugs and agrochemicals.

The open-access work by Julian West, an assistant professor of chemistry, and his colleagues appears in the Royal Society of Chemistry journal Chemical Science.

"Arguably, these olefins, or alkenes, are the most useful functional groups in a molecule," said West, an assistant professor of chemistry recently named one of Forbes Magazine's 30 Under 30 rising stars in science. "A functional group is like a foothold in climbing: It lets you get to where you want to go, what you want to make.

"We've had methods to make olefins for a long time, but a lot of these classic methods -- late 19th or early 20th century -- use incredibly strong bases, things that would burn you and would definitely burn your molecule if it had anything sensitive on it," he said. "The other issue is that such harsh conditions might be able to make this olefin, but you might make it in the wrong place."

A mild process that allows chemists to select the olefin's functional form has been a goal for decades. The Rice process took its inspiration from labs that discovered metal catalysts to improve the process and others that studied thermus thermophilus, light-sensitive bacteria that thrive near underwater thermal vents.

"They have a lot of unusual enzymes," West said. "One of them is called carH, a photoreceptor like a bacterial retina that developed on a parallel evolutionary path to what led to our eyes."

CarH incorporates vitamin B12 and cobalt that reacts with light and prompts the formation of an alkene, which in turn alerts the organism to light's presence. "Instead of needing heat and strong bases, it only needs light energy," he said.

West said the alkene "is just a byproduct for the bacteria. It doesn't really care. But we thought we could take this cue from nature."

The Rice team used B12 and the cobalt it contains with sodium bicarbonate (aka baking soda) as a mild base to make the olefins under blue light at room temperature.

A surprise aspect of the research was the appearance of remote elimination, by which they were able to position hydrogen atoms to facilitate further reactions. That could lead to two-step processes for specific products.

"Basically, we found we could make olefins and not just isolate them," West said. "In the same flask at the same time, we can have a second reaction and turn them into something else. This could be a plug-and-play method where we can start to sub in different molecules."

He said the team is working on variations that can be scaled up for industrial production of polypropylene and other plastics based on olefins. "B12 is a little too complicated for commodity-scale synthesis," West said. "But it's great for fine chemicals, and we can buy it from any number of suppliers."

Scientists from Japan and the USA have confirmed the presence in meteorites of a key organic molecule which may have been used to build other organic molecules, including some used by life. The discovery validates theories of the formation of organic compounds in extraterrestrial environments.

The chemistry of life runs on organic compounds, molecules containing carbon and hydrogen, which also may include oxygen, nitrogen and other elements. While commonly associated with life, organic molecules also can be created by non-biological processes and are not necessarily indicators of life. An enduring mystery regarding the origin of life is how biology could have arisen from non-biological chemical processes, called prebiotic chemistry. Organic molecules from meteorites are one of the sources of organic compounds that lead to the formation of life on Earth.

Associate Professor Yasuhiro Oba from Hokkaido University led a team of researchers who discovered the presence of a prebiotic organic molecule called hexamethylenetetramine (HMT) in three different carbon-rich meteorites. Their discovery, published in the journal Nature Communications, validates models and theories that propose HMT as a key molecule in the formation of organic compounds in interstellar environments.

By confirming the presence of HMT in meteorites for the first time, this work supports the hypothesis that the compound was present in asteroids, the parent bodies of many meteorites. Early in the solar system's history, many asteroids could have been heated by collisions or the decay of radioactive elements. If some asteroids were warm enough and had liquid water, HMT could have broken down to provide building blocks that in turn reacted to make other important biological molecules which have been found in meteorites, including amino acids. Some types of amino acids are used by life to make proteins, which are used to build structures like hair and nails, or to speed up and regulate chemical reactions.

While the diversity of organic compounds in meteorites is well-documented, many questions remain about the processes by which these compounds were formed. The most important meteorites in this area of research are carbonaceous chondrites, stony meteorites that contain high percentages of water and organic compounds. Experimental models have shown that a combination of water, ammonia and methanol, when subjected to photochemical and thermal conditions common in extraterrestrial environments, give rise to a number or organic compounds, the most common of which is HMT. Interstellar ice is rich in methanol. Hypothetically, HMT should be common in water-containing extraterrestrial materials, but, until this study, it had not been detected.

HMT is susceptible to degradation when exposed to processes commonly used in the analysis of organic compounds in meteorites. The scientists developed a method that specifically extracted HMT from meteorites with minimal degradation. This method allowed them to isolate significant quantities of HMT and HMT derivatives from the meteorites Murchison, Murray and Tagish Lake.

The scientists also examined the role HMT derivatives may have played in the formation of amino acids in meteorites. While they were unable to make definitive conclusions in this study, the discovery of HMT and its derivatives in these meteorites will lead to future experiments to understand the origin and chemical formation processes of amino acids and other prebiotic compounds in extraterrestrial environments.

In a new paper published in the journal Nature Communications Earth and Environment, researchers at the University of Rochester were able to use magnetism to determine, for the first time, when carbonaceous chondrite asteroids--asteroids that are rich in water and amino acids--first arrived in the inner solar system. The research provides data that helps inform scientists about the early origins of the solar system and why some planets, such as Earth, became habitable and were able to sustain conditions conducive for life, while other planets, such as Mars, did not.

The research also gives scientists data that can be applied to the discovery of new exoplanets.

"There is special interest in defining this history--in reference to the huge number of exoplanet discoveries--to deduce whether events might have been similar or different in exo-solar systems," says John Tarduno, the William R. Kenan, Jr., Professor in the Department of Earth and Environmental Sciences and dean of research for Arts, Sciences & Engineering at Rochester. "This is another component of the search for other habitable planets."

SOLVING A PARADOX USING A METEORITE IN MEXICO

Some meteorites are pieces of debris from outer space objects such as asteroids. After breaking apart from their "parent bodies," these pieces are able to survive passing through the atmosphere and eventually hit the surface of a planet or moon.

Studying the magnetization of meteorites can give researchers a better idea of when the objects formed and where they were located early in the solar system's history.

"We realized several years ago that we could use the magnetism of meteorites derived from asteroids to determine how far these meteorites were from the sun when their magnetic minerals formed," Tarduno says.

In order to learn more about the origin of meteorites and their parent bodies, Tarduno and the researchers studied magnetic data collected from the Allende meteorite, which fell to Earth and landed in Mexico in 1969. The Allende meteorite is the largest carbonaceous chondrite meteorite found on Earth and contains minerals--calcium-aluminum inclusions--that are thought to be the first solids formed in the solar system. It is one of the most studied meteorites and was considered for decades to be the classic example of a meteorite from a primitive asteroid parent body.

In order to determine when the objects formed and where they were located, the researchers first had to address a paradox about meteorites that was confounding the scientific community: how did the meteorites gain magnetization?

Recently, a controversy arose when some researchers proposed that carbonaceous chondrite meteorites like Allende had been magnetized by a core dynamo, like that of Earth. Earth is known as a differentiated body because it has a crust, mantle, and core that are separated by composition and density. Early in their history, planetary bodies can gain enough heat so that there is widespread melting and the dense material--iron--sinks to the center.

New experiments by Rochester graduate student Tim O'Brien, the first author of the paper, found that magnetic signals interpreted by prior researchers was not actually from a core. Instead, O'Brien found, the magnetism is a property of Allende's unusual magnetic minerals.

DETERMINING JUPITER'S ROLE IN ASTEROID MIGRATION

Having solved this paradox, O'Brien was able to identify meteorites with other minerals that could faithfully record early solar system magnetizations.

Tarduno's magnetics group then combined this work with theoretical work from Eric Blackman, a professor of physics and astronomy, and computer simulations led by graduate student Atma Anand and Jonathan Carroll-Nellenback, a computational scientist at Rochester's Laboratory for Laser Energetics. These simulations showed that solar winds draped around early solar system bodies and it was this solar wind that magnetized the bodies.

Using these simulations and data, the researchers determined that the parent asteroids from which carbonaceous chondrite meteorites broke off arrived in the Asteroid Belt from the outer solar system about 4,562 million years ago, within the first five million years of solar system history.

Tarduno says the analyses and modeling offers more support for the so-called grand tack theory of the motion of Jupiter. While scientists once thought planets and other planetary bodies formed from dust and gas in an orderly distance from the sun, today scientists realize that the gravitational forces associated with giant planets--such as Jupiter and Saturn--can drive the formation and migration of planetary bodies and asteroids. The grand tack theory suggests that asteroids were separated by the gravitational forces of the giant planet Jupiter, whose subsequent migration then mixed the two asteroid groups.

He adds, "This early motion of carbonaceous chondrite asteroids sets the stage for further scattering of water-rich bodies--potentially to Earth--later in the development of the solar system, and it may be a pattern common to exoplanet systems."

A new study by scientists at the University of Southampton has made a breakthrough that could help the search for treatments against age related sight loss.

With an aging society, conditions such as age-related macular degeneration (AMD) are becoming more frequent, affecting around 300 new patients every week in the UK. AMD and similar conditions currently have no effective treatments.

In this new study, published in the International Journal of Molecular Sciences, researchers used a newly developed imaging technique called serial block face scanning electron microscopy, to produce a digital reconstruction of eye tissues from the outer retina, at very high resolution. This is the first time this technology has been used to fully reconstruct cells from the retina and could provide new insights into the causes of irreversible blinding diseases.

The retinal pigment epithelium (RPE) is located between the neuroretina and the outer blood supply in the eye and plays a critical role in vision by looking after the photoreceptors. Scientists currently do not fully understand the causes of damage to RPE cells that leads to sight loss. The reconstructions produced in this study provides a clear picture of the 3D organisation of the RPE in a healthy eye, which will be a crucial reference point for scientists to look at how RPE cells change with age and in diseased eyes.

The research team, led by Dr Arjuna Ratnayaka, a Lecturer in Vision Sciences at the University of Southampton, used serial block face microscopy on the central mouse retina. The process involved a state of the art microscope capturing digital images of hundreds of serial layers of the retina. The team then began the painstaking process of drawing key regions of interest (such as the cell body and the nucleus) in each scanned layer before advanced computer software rendered the images into a full 3D reconstruction.

Dr Ratnayaka said, "We now understand the technical process required to produce such high resolution 3D reconstructions of retinal tissues which is an exciting foundation to carry out further studies into deteriorating cells in the eye. The use of artificial intelligence software will make this process faster in the future".

"Our team was made up of experts in cell biology, imaging, computer science as well as ophthalmologists and shows that advances in modern research requires bringing a broad range of skills together."