At some time after the formation of Von Kármán crater, the crater floor was covered by eruptions of basaltic lava, similar to the eruptions in Hawaii last summer. Chang’e 4 will collect compositional measurements of these farside basaltic rocks, and lunar scientists are anxiously awaiting these results. Do volcanic rocks on the farside differ from the basalts collected from the nearside? We will have to wait and see!

A striking aspect of the floor of Von Kármán crater is the number and variety of impact craters. There is a high density of craters because the surface is more than 3 billion years old! During those 3 billion years, so many small craters (<200 meters (660 feet) in diameter) formed that when a new one forms, the total number of craters does not increase. This seemingly counterintuitive situation occurs because each new crater erases, on average, one older crater of comparable size, a state known as “equilibrium” to crater counting geologists. For surfaces this old (in equilibrium), only larger craters (>1000 meters (3280 feet) diameter), which are not in equilibrium, continue to increase in density and can be used to estimate the age of the surface.

Note also all of the small craters that have formed on top of larger ones. Smaller impacts wear down and degrade larger craters over time. You can easily see a wide variety of crater degradation states, ranging from sharp and crisp (new) to highly degraded (old). As result of all of these impacts (small and large), the surface of the Moon consists of a very fine powder known as regolith, in which the Apollo astronauts made their distinct boot prints.

LROC is a system of three cameras mounted on LRO that capture high resolution photos of the lunar surface.

Story Source:

Materials provided by NASA/Goddard Space Flight Center. Note: Content may be edited for style and length.

The research makes it possible to exploit this edge conduction feature to build more energy-efficient electronic devices.

In a typical conductor, electrical current flows everywhere. Insulators, on the other hand, do not readily conduct electricity. In topological insulators, a special type of material, the interior works as an insulator, but the boundaries of such materials are guaranteed to be conductive due to its topological property, resulting in a feature called “topological edge conduction.”

Topology is the mathematical study of the properties of a geometric figure or solid that is unchanged by stretching or bending. Applying this concept to electronic materials leads to discoveries of many interesting phenomena, including topological edge conduction. Working like highways for electrons, channels of topological edge conduction allow electrons to travel with little resistance. Further, because edge channels can be potentially very narrow, electronic devices can be further miniaturized.

Study results appear today in Science Advances.

“Several materials have been shown to be 3-D topological insulators,” said Yongtao Cui, an assistant professor of physics and astronomy at UCR, who led the research. “But 2-D topological insulators are rare. Several recent experiments established that monolayer WTe₂ is the first atomically thin 2-D topological insulator.”

Cui explained that for a 3-D topological insulator, conduction appears at its surfaces; for a 2-D sheet-like material, such conducting features are simply at the edges of the sheet.

Cui’s lab used a novel experimental technique called Microwave Impedance Microscopy, or MIM, to directly image the conduction at the edges of monolayer WTe₂.

“Our results unambiguously confirm edge conduction in this promising material,” Cui said.

Although WTe₂ has been known to exist for decades, interest in this material got a boost in only the last few years due to its exotic physical and electronic properties discovered using topological physics. WTe₂ layers are stacked together via van der Waals interactions and can be easily exfoliated into thin, 2-D, graphene-like sheets.

“In addition to conduction at the edges in monolayer WTe₂, we also found that the conductive channels can extend to the interior of the material, due to imperfections — such as cracks,” Cui said. “Our observations point to new ways to control and engineer such conduction channels via mechanical or chemical means.”

Cui’s collaborators at the University of Washington prepared the monolayer WTe₂ samples. At UCR, his lab performed the MIM measurement, which involved sending a microwave electrical signal to a sharp metal tip, and positioning the tip near the surface of monolayer WTe₂. By resolving the microwave signal bounced back by the sample, the researchers could determine whether the sample region directly below the tip was conductive or not.

“We scanned the tip across the entire sample and directly mapped the local conductivity,” Cui said. “We performed all the measurements at cryogenic temperatures, needed for monolayer WTe₂ to exhibit the topological property. The topological properties of monolayer WTe₂ can potentially serve as a platform to realize essential operations in quantum computing.”

Cui’s lab is already exploring new ways to manipulate the edge conduction channels and topological physics in monolayer WTe₂.

“We are looking into whether stacking monolayer WTe₂ with other 2-D materials can alter its topological property,” he said. “We are also using mechanical and chemical methods to create networks of conduction channels. The MIM technique we used offers a powerful means to characterize the conduction channels in topological materials such as monolayer WTe₂.”

Cui was joined in the study by Yanmeng Shi, Ben Niu, and Brian A. Francisco of UCR; Joshua Kahn, Zaiyao Fei, Bosong Sun, Xinghan Cai, Xiaodong Xu, and David H. Cobden of the University of Washington; Di Wu of Nanjing University, China; and Zhi-Xun Shen of Stanford University; Shi, Kahn, and Niu are co-first authors of the research paper.

The work done at UCR was supported by Cui’s startup funds.

Rice synthetic organic chemist László Kürti said the method, reported in the Journal of the American Chemical Society, is a major step forward as it quickens and boosts the yield of valuable molecules known as alpha-aminoketones.

Ketones are carbon-based compounds found in nature and important feedstocks for the chemical industry. The primary amino group (NH2) is a functional group present in many important chemical products. It contains one nitrogen atom and two hydrogen atoms. When a ketone is functionalized with a primary amino group at the alpha carbon, it forms a compound called a primary alpha-aminoketone.

“It’s a good precursor, because there’s no extra functionalization, like an acyl group, on the NH2 and it can then be converted to whatever you want,” said Kürti, an associate professor of chemistry. “Previously, this was the issue: People would put nitrogen in there with extra functionality, but the further processing necessary to get to a free NH2 was complicated.”

Postdoctoral researcher Zhe Zhou discovered the reaction when he mixed a silyl enol ether and a nitrogen source in a common solvent, hexafluoroisopropanol, at room temperature and found that it mimicked Rubottom oxidation, an established technique to oxidize enol ethers.

“Oxygen is routinely put into the alpha position,” Kürti said. “But nitrogen, no. We are the first to show this is possible in a large number of substrates, and it’s simple. It turns out that the solvent itself catalyzes the reaction.”

Zhou and co-author and postdoctoral researcher Qing-Qing Cheng refined the method and subsequently tested it by making 19 aminoketones, including three synthetic amino acid precursors. “These unnatural amino acids are significant for drug design,” Kürti said. “The enzymatic processes in living organisms are not going to attack them, because they don’t fit in the enzymes’ pockets.”

“Before we had this process, it wasn’t impossible to make these kinds of structures,” Zhou said. “It was just very complicated and took many steps. The goal, generally, is to get them by the most direct method possible.”

Earlier synthetic processes by the Kürti lab eliminated the need for transition metal-based catalysts in the manufacture of amines in order to simplify the usual and often inefficient trial-and-error approach involved in making new chemical compounds like drugs. Metal-based catalysts that speed up amination — the introduction of amine groups to an organic molecule — can also contaminate the product, so the new process avoids them as well.

“Our amination method promises to replace a common three-step process to make alpha-aminoketones, and the yield, comparably, is very good,” Zhou said. “In the standard process, each step cuts the yield, so one-step process is still superior even if the yields are identical, because it takes less time and there’s less risk of something going wrong.

“The last thing you want is to get eight steps from the beginning and then ruin it on the ninth because the conditions are not selective enough,” he said. “Cutting steps is always beneficial in organic synthesis.”

Kürti was delighted to see his social media accounts light up with congratulations from peers and industrial acquaintances upon publication of the paper.

“There’s a new trend toward late-stage functionalization, where companies with an existing library of compounds can take 100 of them and perform an additional step to make 100 new compounds,” he said. “So from an intellectual property perspective, our discovery is a great gift to industry. This really is a gem of a find.”

The National Institutes of Health, the National Science Foundation, the Robert A. Welch Foundation and Rice University supported the research.

“It’s amazing that we can pinpoint the production area of materials from an 800-year-old shipwreck,” says Wenpeng Xu, the study’s lead author, a graduate student at the University of Illinois at Chicago, which has a joint graduate program in Anthropology with the Field Museum. “It helps us learn the details of trade relationships — knowing how people interacted in the past is very important for us to understand the present.”

The Field Museum is home to an estimated 7,500 pieces of cargo recovered from the wreck, including the 60 ceramic pieces from the shipwreck analyzed in this study: bowls and boxes made of porcelain covered in a bluish-white glaze called qingbai. Based on the style of the ceramics, scientists knew that it came from southeastern China, but style alone isn’t enough to pinpoint a piece’s origin because many kilns produced similar-looking pieces. By comparing the chemical makeups of ceramics from the wreck and from different kiln sites in China, the researchers were able to more precisely determine where the ceramics were made.

Ceramics from different sites have different chemical compositions because of variations in the elements present in that region’s clay or in the recipes that potters used to mix their clay. If a piece of pottery from the shipwreck matches the pottery found at an archaeological site, it’s a pretty safe bet that the pottery originated there. “Each kiln site uses its own materials and ingredients for clay — that’s what makes each sample’s fingerprint unique,” explains Xu. “If the fingerprint of the sample matches the fingerprint of the kiln site, then it’s highly possible that that’s where the sample came from.” This is where the X-ray gun comes in.

“We used a portable X-ray fluorescence detector — it looks a lot like a ray gun,” says Lisa Niziolek, Field Museum Boone Research Scientist and co-author of the study. The science behind the compositional analysis is complex, but Niziolek breaks it down: “You’re shooting X-rays into a material you’re interested in. It excites the material’s atoms. Energy goes flying out, and this measures that energy. Different elements have different signatures of energy that comes back out.”

Knowing the precise origins of cargo on the ship reveals the size and complexity of trade networks at the time. The ceramics in the study were created over 2,000 miles from where the ship sank — about the distance between New York and Las Vegas.

“A key that’s emerging is that the shipwreck tells us that there were huge trade networks in the 12th and 13th centuries,” says Field Museum MacArthur Curator of Anthropology and study co-author Gary Feinman. “We’re taught to associate vast trade networks with Europeans like Magellan and Marco Polo, but Europeans weren’t a big part of this network that went from Asia to Africa. Globalization isn’t just a recent phenomenon — it’s not just Eurocentric, not just tied to modern capitalism. The ancient world was more interconnected than a lot of people thought.”

“People often refer to shipwrecks as time capsules, but the Java Sea Wreck is more than just that,” says Niziolek. “A time capsule represents a moment frozen in time, but that ignores the way these results reveal these vast and changing socioeconomic networks.”

Feinman agrees: “It’s almost the opposite of a nice, bounded time capsule, it’s more like a window that opens up to a wide horizon and tells us how this material came onto this ship before it sank.”

Story Source:

Materials provided by Field Museum. Note: Content may be edited for style and length.

Information about texture is transmitted from sensors in the skin and through the nerves to the somatosensory cortex, the part of the brain responsible for interpreting the sense of touch. New research by neuroscientists at the University of Chicago shows that as neurons in this part of the brain process this information, they each respond differently to various features of a surface, creating a high-dimensional representation of texture in the brain.

“Objects can have textures that we can describe in simple terms like rough or soft or hard. But they can also be velvety or cottony or furry,” said Sliman Bensmaia, PhD, associate professor of organismal biology and anatomy at UChicago and senior author of the study. “The variety of different adjectives you can use to describe texture just highlights that it’s a rich sensory space. So, it makes sense that you need to have a rich neural space in the brain to interpret that too.”

The study was published this week in the Proceedings of the National Academy of Sciences (PNAS). Bensmaia is a leading expert on how the brain and nervous system interpret the sense of touch, including texture. In a 2013 study from PNAS, his lab showed how different kinds of nerve fibers respond to different aspects of texture. Some nerves respond mainly to spatial elements of coarse textures, like the raised bumps of a Braille letter that create a pattern when pressed against the skin. Others respond to vibrations created when the skin rubs across fine textures, like fabrics, which account for the vast majority of textures we encounter in the real world.

In that study, Bensmaia and his colleagues used a rotating drum covered with strips of various coarse and fine textures, such as sandpaper, fabrics and plastics. The drum then ran the textures across the fingertips of Rhesus macaque monkeys, whose somatosensory system is similar to humans, while the researchers recorded the responses in the nerve.

For the new study, led by postdoctoral scholar Justin Lieber, PhD, the researchers recorded the corresponding responses to the same textures directly from the brain, using electrodes implanted into the somatosensory cortex of the monkeys.

The new data shows that the neurons respond in a highly idiosyncratic way to different aspects of texture. Some neurons respond to coarse features of a texture. Others respond to fine features, certain patterns of indentation in the skin, or any number of combinations in between. Bensmaia and Lieber identified at least 20 different patterns of response.

“Some of them map onto things we understand, like roughness or the spatial pattern of a texture,” Bensmaia said. “But then it becomes combinations of skin vibration coupled with patterns of skin deformation, things that are abstract and a little harder to describe.”

But these more abstract features of texture are what can make the difference in being able to distinguish between bedsheets with different thread counts. The researchers recorded responses to 55 different textures, and Bensmaia says he can tell which one was used just by looking at the pattern of activity it generated in the brain.

“Velvet is going to excite one subpopulation of neurons more than another, and sandpaper is going to excite another overlapping population,” he said. “So, it’s this variety in the response that allows for the richness of the sensation.”

Bensmaia and Nicho Hatsopoulos, PhD, professor of organismal biology and anatomy, who studies how the brain directs movement in the limbs, have also pioneered research to build brain-controlled robotic prosthetic limbs. These devices work by implanting arrays of electrodes in the somatosensory cortex and areas of the brain that control movement. The electrodes pick up activity in neurons as the patient thinks about moving their own arm to direct the robotic arm to move accordingly. The prosthetic hand is fitted with sensors to detect sensations of touch, such as pressing on individual fingertips, which in turn generates electrical signals that stimulate the appropriate areas of the brain.

Theoretically, the same techniques could recreate sensations of texture through a neuroprosthetic, but Bensmaia points out that the new study shows why this could be a challenging task. The neurons that correspond to each fingertip are located in clearly defined areas of the somatosensory cortex, so it’s easier to stimulate the appropriate spot for a given touch. But neurons throughout the somatosensory cortex respond to texture inputs, and they’re mixed together. There’s no defined region of neurons that respond to sandpaper or the plastic keyboard of a laptop, for example.

“It’s going to be pretty challenging to be able to create textural sensations through electrical stimulation, because you don’t have these monolithic groups of neurons working together,” he said. “It’s very heterogenous, which could make it difficult to implement in prosthetics. But that’s also how we get this rich sensation of texture in the first place.”

The study “High-dimensional representation of texture in the somatosensory cortex of primates,” was supported by the National Institute of Neurological Disorders and Stroke.

Honey bees live in large, congested nest cavities, often in tree hollows with narrow openings. When it gets hot inside the nest, a group of bees crawl to the entrance and use their wings as fans to draw hot air out and allow cooler air to move in. The question is, how do bees self-organize into these living ventilating units?

Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Department of Organismic and Evolutionary Biology (OEB) have developed a framework that explains how bees use environmental signals to collectively cluster and continuously ventilate the hive.

“Over millennia, social insects such as bees have evolved to harness and exploit flows and forces and collectively solve physiological problems such as mechanical stabilization, thermoregulation and ventilation on scales much larger than the individual,” said L Mahadevan, de Valpine Professor of Applied Mathematics, Physics, and Organismic and Evolutionary Biology, and senior author of the study. “A combination of measurements and computational models quantify and explain how fanning bees create an emergent large-scale flow pattern to ventilate their nests.”

“We have demonstrated that bees don’t need a sophisticated recruitment or communications scheme to keep their nests cool,” said Jacob Peters, a postdoctoral fellow in SEAS and OEB, and first author of the paper. “Instead the fanning response of individual bees to temperature variations, and the physics of fluid flow leads to their collective spatial organization, which happens to lead to an efficient cooling solution.”

The paper is published in the Journal of the Royal Society Interface.

Experiments began in the dog days of the summer of 2017. Over the course of several weeks, Peters, Mahadevan and former postdoctoral fellow at SEAS Orit Peleg monitored a group of artificial beehives in Harvard University’s Concord Field Station.

The research team measured temperature, air flow into and out of the nest, and the position and density of bees fanning at the nest entrance. They observed that rather than spreading out across the entirety of the nest entrance, the bees clustered at the hottest areas and kept those areas, which had the highest air outflow, separate from the cooler areas with the highest air inflow. Importantly, they found that different bees had different temperature thresholds above which they would begin fanning, so that collectively they were better at responding to temperature variations.

In modeling the system, the researchers found that all these behaviors linked to the environmental physics of the nest. Fanning outward allows the bees to sense the upstream nest temperature; different thresholds of temperature allows for more continuous ventilation and more stable hive temperatures; and, because of the physics of friction and flow, clustering to separate inflow from outflow allows more cool air to enter the nest because of the physics of friction and flow.

“Our study demonstrates how harnessing the dynamics of the physical environment allows for large-scale organization of a physiological process,” said Peleg, who co-authored the paper and is now an Assistant Professor at the University of Colorado Boulder.

“Although this is a physics-focused story, biological variation with roots in genetics and evolution likely plays a big role in order for this system to work,” said Peters. “Our theory suggests that not only does individual variability in temperature threshold lead to a more stable hive temperature but also this diversity is critical to the stability of the patterning of fanning behavior which is required for efficient ventilation.”

“In everything from large HVAC systems to the fans that cool our computers, bioinspired, self-organizing systems may be able to adapt and respond to specific demands better than current systems,” said Peters.

“More broadly, our study highlights, yet again, the need to consider both biological organisms and their physical environments to understand the richness of collective eco-physiology, a hallmark of life itself,” said Mahadevan.

This work was supported by the National Science Foundation.