Tech

A new lithium-based electrolyte invented by Stanford University scientists could pave the way for the next generation of battery-powered electric vehicles.

In a study published June 22 in Nature Energy, Stanford researchers demonstrate how their novel electrolyte design boosts the performance of lithium metal batteries, a promising technology for powering electric vehicles, laptops and other devices.

"Most electric cars run on lithium-ion batteries, which are rapidly approaching their theoretical limit on energy density," said study co-author Yi Cui, professor of materials science and engineering and of photon science at the SLAC National Accelerator Laboratory. "Our study focused on lithium metal batteries, which are lighter than lithium-ion batteries and can potentially deliver more energy per unit weight and volume."

Lithium-ion batteries, used in everything from smartphones to electric cars, have two electrodes - a positively charged cathode containing lithium and a negatively charged anode usually made of graphite. An electrolyte solution allows lithium ions to shuttle back and forth between the anode and the cathode when the battery is used and when it recharges.

A lithium metal battery can hold about twice as much electricity per kilogram as today's conventional lithium-ion battery. Lithium metal batteries do this by replacing the graphite anode with lithium metal, which can store significantly more energy.

"Lithium metal batteries are very promising for electric vehicles, where weight and volume are a big concern," said study co-author Zhenan Bao, the K.K. Lee Professor in the School of Engineering. "But during operation, the lithium metal anode reacts with the liquid electrolyte. This causes the growth of lithium microstructures called dendrites on the surface of the anode, which can cause the battery to catch fire and fail."

Researchers have spent decades trying to address the dendrite problem.

"The electrolyte has been the Achilles' heel of lithium metal batteries," said co-lead author Zhiao Yu, a graduate student in chemistry. "In our study, we use organic chemistry to rationally design and create new, stable electrolytes for these batteries."

For the study, Yu and his colleagues explored whether they could address the stability issues with a common, commercially available liquid electrolyte.

"We hypothesized that adding fluorine atoms onto the electrolyte molecule would make the liquid more stable," Yu said. "Fluorine is a widely used element in electrolytes for lithium batteries. We used its ability to attract electrons to create a new molecule that allows the lithium metal anode to function well in the electrolyte."

The result was a novel synthetic compound, abbreviated FDMB, that can be readily produced in bulk.

"Electrolyte designs are getting very exotic," Bao said. "Some have shown good promise but are very expensive to produce. The FDMB molecule that Zhiao came up with is easy to make in large quantity and quite cheap."

The Stanford team tested the new electrolyte in a lithium metal battery.

The results were dramatic. The experimental battery retained 90 percent of its initial charge after 420 cycles of charging and discharging. In laboratories, typical lithium metal batteries stop working after about 30 cycles.

The researchers also measured how efficiently lithium ions are transferred between the anode and the cathode during charging and discharging, a property known as "coulombic efficiency."

"If you charge 1,000 lithium ions, how many do you get back after you discharge?" Cui said. "Ideally you want 1,000 out of 1,000 for a coulombic efficiency of 100 percent. To be commercially viable, a battery cell needs a coulombic efficiency of at least 99.9 percent. In our study we got 99.52 percent in the half cells and 99.98 percent in the full cells; an incredible performance."

For potential use in consumer electronics, the Stanford team also tested the FDMB electrolyte in anode-free lithium metal pouch cells - commercially available batteries with cathodes that supply lithium to the anode.

"The idea is to only use lithium on the cathode side to reduce weight," said co-lead author Hansen Wang, a graduate student in materials science and engineering. "The anode-free battery ran 100 cycles before its capacity dropped to 80 percent - not as good as an equivalent lithium-ion battery, which can go for 500 to 1,000 cycles, but still one of the best performing anode-free cells."

"These results show promise for a wide range of devices," Bao added. "Lightweight, anode-free batteries will be an attractive feature for drones and many other consumer electronics."

The U.S. Department of Energy (DOE) is funding a large research consortium called Battery500 to make lithium metal batteries viable, which would allow car manufacturers to build lighter electric vehicles that can drive much longer distances between charges. This study was supported in part by a grant from the consortium, which includes Stanford and SLAC.

By improving anodes, electrolytes and other components, Battery500 aims to nearly triple the amount of electricity that a lithium metal battery can deliver, from about 180 watt-hours per kilogram when the program started in 2016 to 500 watt-hours per kilogram. A higher energy-to-weight ratio, or "specific energy," is key to solving the range anxiety that potential electric car buyers often have.

"The anode-free battery in our lab achieved about 325 watt-hours per kilogram specific energy, a respectable number," Cui said. "Our next step could be to work collaboratively with other researchers in Battery500 to build cells that approach the consortium's goal of 500 watt-hours per kilogram."

In addition to longer cycle life and better stability, the FDMB electrolyte is also far less flammable than conventional electrolytes.

"Our study basically provides a design principle that people can apply to come up with better electrolytes," Bao added. "We just showed one example, but there are many other possibilities."

Porous rock containing oil and natural gas are buried so deep inside the earth that shale operators rely on complex models of the underground environment to estimate fossil fuel recovery. These simulations are notoriously complex, requiring highly-skilled operators to run them. These factors indirectly impact the cost of shale oil production and ultimately, how much consumers pay for their fuel.

Researchers at Texas A&M University have developed an analytical procedure that can be used in spreadsheets to predict the amount of oil and gas that can be recovered from newly drilled wells. By modeling the pattern of oil and gas flow from older wells in the same drilling field, the researchers said they can now accurately forecast the rate of oil and gas flow for newer wells, a framework that is quicker and easier to use than complicated reservoir simulations.

"In the oil and gas industry, professionals use sophisticated reservoir simulators to get a sense of how much hydrocarbons can be recovered from the layers below the Earth's surface. These simulations are very useful but extremely time-consuming and computationally intense," said Dr. Ruud Weijermars, professor in the Harold Vance Department of Petroleum Engineering. "We can now do the same kind of predictions as these simulations in a spreadsheet environment, which is much faster, saving a lot of time and cost for shale operators, without loss of accuracy."

The researchers described their findings in the March issue of the journal Energies.

Shale rocks containing oil and gas are crammed within layers that are between 3,000 and 14,000 feet underground. To access these fossil fuels, holes are first drilled vertically into the ground with the help of high-powered drills to reach the shale rock layers. The drill bit then moves in horizontally, parallel to the shale deposits. When the rocks surrounding the horizontal borehole are forced to crack by hydraulic fracturing, they begin to release valuable oil and natural gas molecules, which then rush into the borehole and rise up to storage tanks at the surface.

Before the drilling operation begins, a 3D model of the reservoir is generally created to predict the amount of oil that can be recovered from the wells. These models consider the permeability of rocks, underground geography and seismic features, among other parameters. With these inputs in place, the model virtually tiles the reservoir into small blocks, or cells, and then simulates the flow of oil through these individual blocks based on the difference in pressure on the different faces of the block.

"These simulations can run from hours to days to weeks, depending upon the number of blocks within a grid," said Weijermars. "So, if the reservoir model has a billion cells, you would have to compute how these billion cells behave and interact to know what the resulting oil flow will be."

To circumvent these complicated mathematical computations, Weijermars and his team focused their attention on the flow of oil within a single cell in an existing well. First, they calculated the flow of oil from the fracture site into the single cell using physics-based equations. By assuming that all the flow cells within a well are identical, they were able to scale up and obtain the oil flow rate for a period of several months' time¬ using an analytical procedure called decline curve analysis.

The researchers then compared the predictions made by their method against those of the simulations and found that the two matched very well. However, unlike complex simulations, the researchers said their spreadsheet-based analysis was much quicker.

Once the researchers modeled the flow rate from an existing well, they could predict and improve the behavior of new wells by tweaking some aspect of the flow cells, such as the height, length or spacing of hydraulic fractures and between wells. Furthermore, they noted that this type of analysis could be done before drilling the new wells so that oil and gas recovery from the lease region can be maximized.

The researchers also said that unlike reservoir simulations that require highly trained professionals to run them, their spreadsheets can be used by technicians with very little training.

"Shale operators need to cut costs tremendously because of low global prices of crude oil. However, they also need to forecast and improve the performance of the new wells that they plan to drill," said Weijermars. "We have tested our spreadsheet-based flow-cell analysis against sophisticated reservoir simulators in a series of studies, and the flow-cell model does a great job. This is good news for shale operators -- our technique helps them cut costs and is also much faster."

Laser light traveling through ornately microfabricated glass has been shown to interact with itself to form self-sustaining wave patterns called solitons. The intricate design fabricated in the glass is a type of "photonic topological insulator," a device that could potentially be used to make photonic technologies like lasers and medical imaging more efficient.

Topological materials, which were awarded the Nobel Prize in 2016, have the ability to "protect" the flow of waves through them against unwanted disorder and defects. Until now, our understanding of topological protection of light has been mostly limited to particles of light acting independently, but in a new paper that appears May 22, 2020 in the journal Science, researchers at Penn State report that they have used the glass to mediate interaction between photons, directly observing the fundamental wave patterns of these intricate devices.

"People are perhaps more familiar with electronics, but there is a whole parallel world of 'photonics,' where we are concerned with the properties of light instead of electrons," said Mikael Rechtsman, Downsbrough Early Career Development Professor of Physics at Penn State, and senior author of the paper. "There are myriad applications of photonics, including in solar energy, fiber optics for telecommunication, manufacturing using laser cutting, and lidar, which is used, for example, to help control autonomous vehicles. Topological protection offers the promise to make photonic devices more energy efficient, lighter, and more compact."

The concept of topological protection can be applied in electronic, photonic, atomic, and mechanical systems. In electronics, for example, topological protection can improve efficiency by getting electrons to flow reliably through a material without scattering. For electrons this protection requires extremely cold temperatures, nearing absolute zero, and very often a strong external magnetic field, but with photons all of the experiments can be performed at room temperature, and because photons do not have a charge, without a magnetic field.

To perform their experiments, the researchers shine a laser through a piece of glass that has a series of extremely precise tunnels carved through it, each with a diameter of about one-tenth that of a human hair. The tunnels, called "waveguides," act like wires, concentrating the flow of light through them. The waveguides in the piece of glass are arranged in a grid, forming an array, but the path of each waveguide through the glass is not straight--it is perhaps better described as serpentine, with twists and turns designed by the researchers with a geometry that leads to the topological protection of light.

"We had to build the fabrication facility in our lab to precisely carve the three-dimensional waveguides through the glass, a process called femtosecond laser writing," said Sebabrata Mukherjee, a postdoctoral researcher at Penn State and first author of the paper. "The ability to write three-dimensional waveguides is crucial to making the device topological, a property that is confirmed experimentally by observing the 'protected' one-way flow of light along the edge of the device."

Through a process called the "Kerr effect," the properties of the glass are changed due to the presence of the intense laser light. This change in the glass mediates an interaction between the many photons, which usually do not interact, propagating through the array. As the power was increased, the light collapsed into a beam that didn't spread out (i.e., diffract), but rather rotated in spirals. The spiral rotation of the solitons is a signature of the specific shape of the waveguides designed by the researchers and an indicator that the device is, indeed, topological.

"Under normal circumstances, photons are oblivious to one another," said Rechtsman. "You can cross two laser beams and neither will be changed by the other. In our system, we were able to get photons to interact and form solitons because the intensity of the laser altered the properties of the glass. The photons became 'aware' of each other through the change in their environment."

Solitons are known to be the most fundamental waveforms in many systems where interaction is mediated by the surrounding environment.

"Theoretically understanding and experimentally probing solitons in topological systems like our waveguide arrays will be a key ingredient in applying topological protection for practical use in photonic devices, especially those that require high optical power," said Rechtsman.

Just as a meter stick with hundreds of tick marks can be used to measure distances with great precision, a device known as a laser frequency comb, with its hundreds of evenly spaced, sharply defined frequencies, can be used to measure the colors of light waves with great precision.

Small enough to fit on a chip, miniature versions of these combs -- so named because their set of uniformly spaced frequencies resembles the teeth of a comb -- are making possible a new generation of atomic clocks, a great increase in the number of signals traveling through optical fibers, and the ability to discern tiny frequency shifts in starlight that hint at the presence of unseen planets. The newest version of these chip-based "microcombs," created by researchers at the National Institute of Standards and Technology (NIST) and the University of California at Santa Barbara (UCSB), is poised to further advance time and frequency measurements by improving and extending the capabilities of these tiny devices.

At the heart of these frequency microcombs lies an optical microresonator, a ring-shaped device about the width of a human hair in which light from an external laser races around thousands of times until it builds up high intensity. Microcombs, often made of glass or silicon nitride, typically require an amplifier for the external laser light, which can make the comb complex, cumbersome and costly to produce.

The NIST scientists and their UCSB collaborators have demonstrated that microcombs created from the semiconductor aluminum gallium arsenide have two essential properties that make them especially promising. The new combs operate at such low power that they do not need an amplifier, and they can be manipulated to produce an extraordinarily steady set of frequencies -- exactly what is needed to use the microchip comb as a sensitive tool for measuring frequencies with extraordinary precision. (The research is part of the NIST on a Chip program.)

The newly developed microcomb technology can help enable engineers and scientists to make precision optical frequency measurements outside the laboratory, said NIST scientist Gregory Moille. In addition, the microcomb can be mass-produced through nanofabrication techniques similar to the ones already used to manufacture microelectronics.

The researchers at UCSB led earlier efforts in examining microresonators composed of aluminum gallium arsenide. The frequency combs made from these microresonators require only one-hundredth the power of devices fabricated from other materials. However, the scientists had been unable to demonstrate a key property -- that a discrete set of unwavering, or highly stable, frequencies could be generated from a microresonator made of this semiconductor.

The NIST team tackled the problem by placing the microresonator within a customized cryogenic apparatus that allowed the researchers to probe the device at temperatures as low as 4 degrees above absolute zero. The low-temperature experiment revealed that the interaction between the heat generated by the laser light and the light circulating in the microresonator was the one and only obstacle preventing the device from generating the highly stable frequencies needed for successful operation.

At low temperatures, the team demonstrated that it could reach the so-called soliton regime -- where individual pulses of light that never change their shape, frequency or speed circulate within the microresonator. The researchers describe their work in the June issue of Laser and Photonics Reviews.

With such solitons, all teeth of the frequency comb are in phase with each other, so that they can be used as a ruler to measure the frequencies employed in optical clocks, frequency synthesis, or laser-based distance measurements.

Although some recently developed cryogenic systems are small enough that they could be used with the new microcomb outside the laboratory, the ultimate goal is to operate the device at room temperature. The new findings show that scientists will either have to quench or entirely avoid excess heating to achieve room-temperature operation.

HOUSTON -- (June 22, 2020) -- Rice University engineers have created a light-powered catalyst that can break the strong chemical bonds in fluorocarbons, a group of synthetic materials that includes persistent environmental pollutants.

In a study published this month in Nature Catalysis, Rice nanophotonics pioneer Naomi Halas and collaborators at the University of California, Santa Barbara (UCSB) and Princeton University showed that tiny spheres of aluminum dotted with specks of palladium could break carbon-fluorine (C-F) bonds via a catalytic process known as hydrodefluorination in which a fluorine atom is replaced by an atom of hydrogen.

The strength and stability of C-F bonds are behind some of the 20th century's most recognizable chemical brands, including Teflon, Freon and Scotchgard. But the strength of those bonds can be problematic when fluorocarbons get into the air, soil and water. Chlorofluorocarbons, or CFCs, for example, were banned by international treaty in the 1980s after they were found to be destroying Earth's protective ozone layer, and other fluorocarbons were on the list of "forever chemicals" targeted by a 2001 treaty.

"The hardest part about remediating any of the fluorine-containing compounds is breaking the C-F bond; it requires a lot of energy," said Halas, an engineer and chemist whose Laboratory for Nanophotonics (LANP) specializes in creating and studying nanoparticles that interact with light.

Over the past five years, Halas and colleagues have pioneered methods for making "antenna-reactor" catalysts that spur or speed up chemical reactions. While catalysts are widely used in industry, they are typically used in energy-intensive processes that require high temperature, high pressure or both. For example, a mesh of catalytic material is inserted into a high-pressure vessel at a chemical plant, and natural gas or another fossil fuel is burned to heat the gas or liquid that's flowed through the mesh. LANP's antenna-reactors dramatically improve energy efficiency by capturing light energy and inserting it directly at the point of the catalytic reaction.

In the Nature Catalysis study, the energy-capturing antenna is an aluminum particle smaller than a living cell, and the reactors are islands of palladium scattered across the aluminum surface. The energy-saving feature of antenna-reactor catalysts is perhaps best illustrated by another of Halas' previous successes: solar steam. In 2012, her team showed its energy-harvesting particles could instantly vaporize water molecules near their surface, meaning Halas and colleagues could make steam without boiling water. To drive home the point, they showed they could make steam from ice-cold water.

The antenna-reactor catalyst design allows Halas' team to mix and match metals that are best suited for capturing light and catalyzing reactions in a particular context. The work is part of the green chemistry movement toward cleaner, more efficient chemical processes, and LANP has previously demonstrated catalysts for producing ethylene and syngas and for splitting ammonia to produce hydrogen fuel.

Study lead author Hossein Robatjazi, a Beckman Postdoctoral Fellow at UCSB who earned his Ph.D. from Rice in 2019, conducted the bulk of the research during his graduate studies in Halas' lab. He said the project also shows the importance of interdisciplinary collaboration.

"I finished the experiments last year, but our experimental results had some interesting features, changes to the reaction kinetics under illumination, that raised an important but interesting question: What role does light play to promote the C-F breaking chemistry?" he said.

The answers came after Robatjazi arrived for his postdoctoral experience at UCSB. He was tasked with developing a microkinetics model, and a combination of insights from the model and from theoretical calculations performed by collaborators at Princeton helped explain the puzzling results.

"With this model, we used the perspective from surface science in traditional catalysis to uniquely link the experimental results to changes to the reaction pathway and reactivity under the light," he said.

The demonstration experiments on fluoromethane could be just the beginning for the C-F breaking catalyst.

"This general reaction may be useful for remediating many other types of fluorinated molecules," Halas said.

Electronic properties of condensed matter are often determined by an intricate competition between kinetic energy that aims to overlap and delocalize electronic wave functions across the crystal lattice, and localizing electron-electron interactions. In contrast, the gaseous phase is characterized by valence electrons tightly localized around the ionic atom cores in discrete quantum states with well-defined energies. As an exotic hybrid of both situations, one may wonder which state of matter is created when a gas of isolated atoms is suddenly excited to a state where electronic wave functions spatially overlap like in a solid? Such an exotic phase of matter, however, has so far been impossible to be created in principle. Here, Professor Kenji Ohmori, Institute for Molecular Science, National Institutes of Natural Sciences in Japan, and his coworkers have realized such an exotic hybrid with overlapping high-lying electronic (Rydberg1)) wave-functions created coherently within only 10 picoseconds (pico = one trillionth) by ultrafast laser excitation in an artificial micro-crystal of ultracold atoms (see Fig. 1). The degree of spatial overlap is actively tuned with nearly 50 nanometer precision and accuracy (nano = one billionth). This exotic metal-like quantum gas under exquisite control and long-lived, decaying in nanoseconds, opens up a completely new regime of many-body physics for simulating ultrafast many-body electron dynamics dominated by Coulomb interactions (see Fig. 2 and its VIDEO version).

The experiment was performed with an ensemble of 30,000 rubidium atoms in the gas phase. It was cooled to a temperature below one 10-millionth of 1 Kelvin above an absolute zero temperature2) by laser/evaporative cooling3). Those ultracold atoms in the energetically lowest quantum state, referred to as a Bose-Einstein condensate4), are loaded into a cubic lattice of optical traps formed with counter-propagating laser beams, resulting in an artificial micro-crystal consisting of 30,000 atoms, whose nearest neighbor distance is 0.5 micron. This micro-crystal with a size of a few tens of micrometers was irradiated with an ultrashort laser pulse whose pulse width was 10 pico-seconds (pico = one trillionth). It was then observed that an electron confined in each of the neighboring atoms was excited to its giant electronic orbital (Rydberg orbital1)), so that they spatially overlapped with each other (see Fig. 1). The degree of the overlap was exquisitely controlled with nearly 50 nanometer precision and accuracy (nano = one billionth) by changing the laser frequency which selects the orbital.

When the orbitals of these loosely bound electrons overlap each other and the atoms start to share their orbitals, they enter into a new metal-like quantum-gas regime. Prof. Ohmori and his coworkers have thus created a metal-like quantum gas for the first time. This exotic matter phase is expected as a pathbreaking platform for quantum simulation5) of ultrafast many-body electron dynamics dominated by Coulomb interactions (see Fig. 2 and its VIDEO version) that would enhance our understanding of physical properties of matter including superconductivity and magnetism, and could contribute to disruptive innovation in the development of new functional materials.

A team of Korean researchers has developed a processing technology for maximizing energy densities of high-capacity batteries. The joint research team, which consists of Dr. Lee, Minah of the Center for Energy Storage Research and Dr. Hong, Jihyun of the Center for Energy Materials Research, both of the Clean Energy Institute, Korea Institute of Science and Technology (KIST), announced the development of a technology that provides a simple solution to a persistent issue associated with silicon-based anode (-) materials.

Recently, silicon anode materials capable of storing four times more lithium ions than graphite anode materials in lithium-ion batteries have gained growing attention due to their potential to improve the mileage of electric vehicles. But when charged in the initial cycle, a battery with a silicon-based anode loses more than 20% of the lithium ions it uses for electricity storage, which results in an issue of reduced battery capacity. To resolve this issue, a method of "lithium pre-loading," or "pre-lithiation," which is adding extra lithium before battery assembly to compensate the lithium loss during battery cycling, has been studied. Methods applied so far such as using lithium powder have the drawbacks regarding a safety hazard and high cost.

Dr. Lee and Dr. Hong of KIST have developed a technology that enables the pre-loading of lithium ions using a lithium-containing solution rather than the lithium powder, to prevent lithium loss in a silicon-based anode. Submerging an electrode in the tailored solution just for five minutes is enough to achieve a successful lithium pre-loading, by which electrons and lithium ions are inserted in the silicon-based anode through a spontaneous chemical reaction. What made this simple process possible was that unlike the conventional method of adding lithium powder to an electrode leading heterogeneous lithium distribution, the tailored prelithiation solution rapidly seeps into an electrode ensuring homogeneous delivery of lithium into silicon oxide.

The prelithiated silicon-based anode developed by the research team loses less than 1% of active lithium in the first charge, yielding a high initial battery efficiency of 99% or higher. A battery manufactured with the prelithated anode exhibited an energy density 25% higher than that of a comparable battery using a graphite anode available on the market (406 Wh/kg ? 504 Wh/kg).

Dr. Lee, who headed the research, commented "By incorporating a *computational materials science technique into the design of an optimal molecular structure, we were able to improve the efficiency of a high-capacity silicon-based anode by leaps and bounds with the simple method of just controlling the solution temperature and reaction time. As this technology is readily applicable to the **roll-to-roll process used in existing battery manufacturing facilities, our method has potential to achieve a breakthrough in the implementation of silicon-based anodes for practical batteries." Co-lead researcher Dr. Hong said, "This collaborative work could be realized because KIST encourages joint research between members from different research teams." He went on to add, "this prelithation technology can increase the mileage of electric vehicles by a minimum of 100 km on average."

Traveling restraints and shelter-in-place orders that grounded planes and emptied streets during the first wave of the COVID-19 pandemic brought greenhouse gas emissions down and air quality up. In a commentary published June 19 in the journal Joule, environmental economists argue COVID-19 may seem like a "silver lining" for climate change in the short run, but in the long run it is more likely to harm the climate due to its potential to delay clean energy investments and innovation.

"If you are going to slow down this transition to cleaner technologies, it will have real ramifications," says first author Kenneth Gillingham, an associate professor of economics at Yale University. "Some of these ramifications could actually outweigh the short-run improvements in air quality and the short-run reductions in emission that we've been seeing around the world."

Gillingham and colleagues show that after the shutdown in the United States, the energy consumption for jet fuel and gasoline dropped by 50 percent and 30 percent, respectively, while natural gas use decreased by almost 20 percent. These declines led to a 15 percent CO2 emission decrease. If the trend continues, the country will experience the largest annual CO2 emission decline in history, roughly meeting the 2025 emission reduction goals set under the Paris Agreement.

However, the impact of COVID-19 runs deeper and longer. The authors write that massive investments in clean energy innovation have played a part in bringing down the cost of new technologies that are essential to decarbonizing in recent years. But "if you're struggling as a company just to stay alive, you're not going to be spending large sums to invest in the next generation of technologies, you're just trying to make it to tomorrow," Gillingham says.

The researchers' simulation shows that should the energy consumption pattern remain as before the pandemic, the delays in clean energy technology investments can lead to an additional 2,500 million tons of CO2 from 2020 to 2035. The extra local air pollutants can also result in 7,500 deaths in the same period. However, this crisis can be an opportunity depending on how the government leads and its energy policy response.

"Something that we've been seeing around the world is that many countries are considering adding a green component or a clean technology component as a crucial part of their stimulus packages in their response to the virus," says Gillingham. "It also has the short-run benefit as helping stimulate the country's economy."

At the local level, states and cities can ensure that the clean energy transition is on track by investing in renewables and expediting permits under environmental guidelines. Although local governments may face some budget challenges, state green banks can help with financing.

While people may argue that the budget is tight and the country should focus on getting by, Gillingham says it's also important to think long term. "We want to make sure that we pay attention to the well-being in our country today and in the next 10 years, the next 20 years, and for future generations."

During the COVID-19 pandemic, one unexpected outcome in cities around the world has been a reduction in air pollution, as people stay home to avoid contracting the coronavirus. Based on data collected in Delhi, India, researchers report that this cleaner air has led to more sunlight reaching solar panels, resulting in the production of more clean energy. The work appears June 19 in the journal Joule.

"Delhi is one of the most polluted cities on the planet," says first author Ian Marius Peters of Helmholtz-Institut Erlangen-Nürnberg for Renewable Energies in Germany. "Moreover, India enacted a drastic and sudden lockdown at the start of the pandemic. That means that reductions in air pollution happened very suddenly, making them easier to detect."

Peters and his colleagues had previously done research in different cities, including Delhi, looking at how haze and air pollution impact how much sunlight reaches the ground and the effect of air pollution on the output of solar panels. The photovoltaic (PV) system installation in Delhi used for the earlier work was still in place, and data on the amount of solar radiation reaching the PV installation (called the level of insolation) was available for the time before and during the shutdown.

Insolation is measured with a pyranometer, an instrument that determines the solar radiation flux density from the hemisphere within a given range of wavelengths. Using data from some of their previous studies, the researchers calculated the changes in insolation.

They found that in late March, the amount of sunlight reaching the solar panels in Delhi increased about 8%, compared with data from the same dates from 2017 to 2019. The insolation at noon increased from about 880 W/sqm to about 950 W/sqm. Information on air quality and particulate matter suggested that reduced pollution levels were a major cause for the rise.

"The increase that we saw is equivalent to the difference between what a PV installation in Houston would produce compared with one in Toronto," Peters says. "I expected to see some difference, but I was surprised by how clearly the effect was visible."

The researchers say the new data from Delhi, combined with their earlier findings, provide a solid foundation to further study the impact of air pollution on solar resources. They expect to also find increased output of power from solar panels in other areas where air was cleaner due to lockdown measures.

"The pandemic has been a dramatic event in so many ways, and the world will emerge different than how it was before," Peters says. "We've gotten a glimpse of what a world with better air looks like and see that there may be an opportunity to 'flatten the climate curve.' I believe solar panels can play an important role, and that going forward having more PV installations could help drive a positive feedback loop that will result in clearer and cleaner skies."

Researchers have created a Bose-Einstein condensate with record speed, creating the fascinating phase of matter in about 100 femtoseconds. To get an idea of how quick that is, hundred femtoseconds compared to one second is proportionally the same as a day compared to the age of the universe. The project was the result of a collaboration between Aalto University the and University of Eastern Finland.

Bose-Einstein condensation is a quantum phenomenon where a large number of particles starts to behave as if they were one. Albert Einstein and Satyendra Nath Bose predicted this fascinating behavior in the beginning of last century. Many different systems, like gases of alkali atoms or semiconductors coupled with light, have been used for observing these condensates. None of them comes into being, however, as fast as the Finnish researchers' Bose-Einstein condensate.

Bose-Einstein condensates composed of light are similar to lasers and particularly promising for information and quantum technologies. The information transfer of the internet today relies on the high speed of light. In principle, light can also be used to provide ultrafast computing with low energy consumption, but achieving this requires pushing the limits of what we know about the interaction of light with matter.

In our everyday world, water molecules of humid air condense on the surface of a cold beer can. Similarly, in the quantum world, particles have to find a way to lose their energy in order to condense to the lowest possible energy state. This process typically takes time from thousands of a second to trillionths of a second. How was it possible to form a condensate even faster?

'After carefully analyzing our measurement data, we realized that the energy relaxation in our system is a highly stimulated process. This means that the effective interaction of photons, which leads into condensation, accelerates when the number of photons increases. Such a phenomenon is the key for the speed-up,' explains Aaro Väkeväinen who completed his PhD degree with these results. Another challenge was to prove that condensation indeed happens with record speed, since even advanced lab cameras fall short of such time resolution. 'When we pumped energy into the molecules in 50 femtoseconds, the condensate was observed. But with 300 femtosecond pump pulse we did not see it, which indicated that the condensation must be triggered even faster,' says doctoral student Antti Moilanen.

'This condensate produces a coherent light beam that is 100 000 times brighter than the first surface plasmon polariton condensate we observed in a metal nanorod array two years ago,' comments Academy Professor Päivi Törmä. The large number of photons in the beam allows clear observation of the distribution of photons at different energies that was predicted by Bose and Einstein, as shown in the figure. 'The brightness of the beam makes it easier to explore new areas of fundamental research and applications with these condensates,' she continues. An invention that emerged from the condensate research of the group has just been granted a patent and will be developed further.

Tsukuba, Japan - Lurking inside pipes and on the surfaces of indwelling medical devices, slimy layers of bacteria, called biofilms, cause problems ranging from largescale product contamination to potentially fatal chronic infections. Biofilms are notoriously difficult to eliminate--not surprising given that one of their main functions is to protect encased bacteria from threats such as predation, antibiotics, and chemical cleaning agents.

Bleach, harsh oxidizing cleaning products, and petrochemical-derived detergents called surfactants combined with scrubbing are the most effective methods of removing biofilms. However, bleach and harsh chemicals are obviously unsuitable for use in biological settings, and while surfactants are used in products such as hand soap and cosmetics, many are toxic to the environment and can damage the surfaces that they are used on.

But in a study published this month in peer-reviewed journal Langmuir, researchers from the University of Tsukuba have found a new way of tackling biofilms, using cleaning agents derived from microbes themselves.

"Certain Candida yeasts can naturally produce biosurfactants called sophorolipids during the fermentation of oils," explains co-lead author Professor Andrew Utada. "Previous studies have shown that sophorolipids have some degree of antimicrobial activity, but there is conflicting information on the effects of these compounds on biofilms composed of the Gram-negative pathogen Pseudomonas aeruginosa."

Gram-negative bacteria such as P. aeruginosa and Escherichia coli are a major cause of hospital-acquired infections, killing thousands of people every year. Using microfluidic channels, the researchers showed that sophorolipids do a better job of disrupting established P. aeruginosa biofilms than commonly used chemical surfactants.

Surprisingly though, there was no evidence that sophorolipids actually killed the bacteria. A mutant P. aeruginosa strain that produces excessive amounts of biofilm matrix was therefore used to examine the underlying mechanism of biofilm dispersal, revealing that sophorolipids appear to weaken the interaction between the biofilm and the underlying surface and break the internal cohesiveness of the biofilm itself, leading to disruption.

Although biosurfactants are biodegradable and far less harmful to the environment than their chemical counterparts, they are costly to produce. To address this issue, the researchers tested the effects of sophorolipids in combination with the widely used chemical surfactant sodium dodecyl sulfate, with encouraging results.

"Combination testing revealed a synergy between sophorolipids and chemical surfactants, with the two agents together demonstrating stronger antibiofilm effects at concentrations about 100-fold lower than when either one was used in isolation," says Ph.D. candidate Bac Nguyen.

Although reducing the costs associated with the production of biosurfactants is the long-term goal, this synergistic approach to biofilm elimination may open new doors for the treatment of persistent bacterial biofilm-mediated infections.

Direct reprogramming or Transdifferentiation is a way of inducing changes in the cell type from one lineage into another lineage, bypassing pluripotency. This approach is an innovative choice to replace the lost cardiomyocytes after an end-stage myocardial infraction because transplantation is the only feasible remedial option at present. According to the World Health Organization (WHO) estimates, a staggering 17.9 million casualties are reported worldwide each year due to myocardial infarction. It is also the leading cause of death, with an estimated 31% of all deaths globally, which clearly outlines the inadequacies in the current cardiac therapy.

Today, only a handful of cell therapy-based strategies that include induced pluripotent stem cells, embryonic stem cells, bone marrow, liposuction, heart biopsies are known to restore the function of cardiomyocytes after myocardial infarction. Yet, the risks associated with the cell therapy-based strategies necessitate an alternative strategy that satisfies all standards necessary for safe and efficacious reprogramming. To overcome the perils of iPSC cell-based therapies, transdifferentiation of cardiac fibroblasts using microRNAs (miRNAs, miRs) hold a promising role in repair and regeneration. Extensive research in this regard has made it possible to identify an ideal reprogramming cocktail for high yield of reprogrammed cells. However, there is no ideal strategy available with an optimal delivery method for genetic reprogramming.

Researchers from Bio-Nano Electronics Research Centre (BNERC), Toyo University, Japan, present a review that provides an overview and understanding of the direct reprogramming strategies focusing on the merits and the limitations of the strategies. The review also discusses various miRNA delivery strategies for safe, effective, and sustained delivery to achieve better tissue repair with a primary focus on biomaterials like electrospun scaffolds and nanoparticles as potential non-viral vectors. The reviewers emphasize that customized biomaterial-based scaffolds with miRNA not only co-exist with the tissue by providing an intramyocardial cellular environment but also provides precision control of miRNA release that may be crucial for direct cardiac reprogramming. The review has been published in Current Pharmaceutical Design.

Small-scale water bodies with areas less than 0.1 km2, such as natural ponds, constitute the quantitative bulk of global inland water bodies, and are very susceptible to human disturbances and environmental change. In agricultural regions of China, water quality in ponds has deteriorated by high loads of nitrogen and phosphorous from agricultural sources. Many natural water bodies and farmlands in rural China have recently been converted into fish farming ponds as part of an economic development strategy. Researchers today still have a limited understanding of how clusters of microorganism (or microbial communities), along with nitrogen and phosphorous fractions in the environment change when a natural pond is converted into a fish farming reserve.

A team of researchers from Huaiyin Normal University and the Institute of Agricultural Resources and Regional Planning in China has conducted a whole-ecology field experiment in a typically subtropical agricultural watershed in China to examine the microbial diversity of the surrounding area. The data from the study might give how fish farming affects microbial communities and nitrogen and phosphorous fractions in pond ecosystems. The team collected RNA samples from water samples in the pond ecosystem under study over a period of one year. Datasets of 16S rRNA amplicon sequencing experiments were collected and compared with the concentrations of nitrogen and phosphorous fractions from the corresponding water samples. Bioinformatics analysis was used to analyze the diversity and structure of the microbial communities. The team's experimental results have indicated that the diversity and structure of the microbial communities has significantly changed after the conversion of a selected natural pond ecosystem into an aquacultural site. Dr. Jiangen Zhou, who led the study notes, "Fish farming also had a significant effect on nitrogen levels. Generally, when compared with nitrogen levels in the natural phase, the nitrate contents decreased substantially by 92.8% in the fish farming phase."

The findings have some implications for the environmental health as well as measures required to clean the water in such areas. "Our findings suggest that fish farming may be considered as an effective and ecological way to reduce nitrate pollution in ponds, especially with high nitrate levels," says D. Zhou. However, we should still be alert to the potential risk of environmental pollution of animal parasites or human pathogens caused by fish farming," he adds. Further research on how to cost-effectively and efficiently reduce nitrogen and phosphorous pollution through fish farming will be conducted in pond ecosystems in the future to improve existing knowledge on this area. The research has been published in Current Bioinformatics.

Washington, DC - June 20, 2020 - Two types of tests are used to track SARS-CoV-2. Reverse transcriptase PCR (rt-PCR) tests for current infection. Antibody tests reveal that an infection has taken place, even long after the fact.

Each of 2 papers published in the Journal of Clinical Microbiology (JCM) addresses one of these testing modalities. One paper, on antibody testing, by Elitza S. Theel, Ph.D., and colleagues, of the Department of Clinical Microbiology the Mayo Clinic, Rochester Minnesota found that 2 tests for SARS-CoV-2 antibodies are highly accurate. The other paper, on using rt-PCR to test for current infection, by Daniel A. Green, M.D., of Columbia University Irving Medical Center, New York, NY, and colleagues, found that when patients test negative for the presence of COVID-19 RNA, despite either a "high clinical suspicion" of infection or a likelihood that the patient has been exposed, a repeat test is indicated. JCM is published by the American Society for Microbiology.

Using rt-PCR for determining the presence of certain RNA sequences from the virus' genome is the gold standard for determining if a person is currently infected. Nonetheless, occasionally, residues containing relevant sequences may remain in the body after an infection has cleared, yielding a false positive.

In the study, Dr. Green and his collaborators performed 27,377 tests in 22,338 patients. They performed repeat testing for 3,432 patients, among whom 2,413 had tested negative the first time and 802 had tested positive. Among the repeats in people who had tested positive, the investigators found that conversion to a negative result was unlikely to occur before 15 to 20 days following initial testing, or before 20 to 30 days post-onset of symptoms.

Among those initially testing negative, despite either having had symptoms or having been exposed to the virus, at 20 days out, one-quarter of these patients tested positive upon repeat.

The switch from testing negative to testing positive may be accounted for by viral shedding, which increases over time and eventually crosses a detection threshold. Additionally, significant numbers of patient samples are improperly collected, yielding inaccurate results, and repeat testing increase the probability of an accurate result. Finally, some patients who initially test negative are truly negative and acquire the infection in the hospital after admission.

In patients with an initial positive result, the investigators advise waiting at least 15 days before conducting a repeat test. They caution that in the case of a positive repeat, "whether repeat positivity represents active infection or more likely detection of nonviable viral RNA is unknown [and] further studies are needed to develop predictive models of the course and outcome of COVID-19."

Antibody testing is useful for determining the virus's geographic spread, the percentage of a population that has been infected and the onset of herd immunity. It likely will also be useful for finding potential donors of convalescent plasma--antibodies that could be administered to people with severe cases of COVID-19 in order to help them fight the virus--and for determining if candidate vaccines work.

Dr. Theel and her collaborators examined the accuracy of 4 test kits in identifying both people who are infected (sensitivity) and those who are not infected (specificity). Two of the tests, from Abbott Laboratories (Anbott Park, IL) and Ortho-Clinical Diagnostics (Rochester, NY)--out of 3 that excelled in sensitivity--also proved 99% accurate for specificity. The third test, from Euroimmun (Lubeck, Germany), excelled for sensitivity, but not for specificity. "With the unprecedented influx of commercially available test kits for the detection of antibodies against SARS-CoV-2, it remains imperative that laboratories thoroughly evaluate these assays for accuracy prior to implementation," the researchers wrote.

The concept of chirality is well-established in science: when an object cannot be superimposed on its mirror image, both the object and its mirror image are called chiral. In drug industry, for instance, more than 50% of the pharmaceutically active molecules used nowadays are chiral molecules. While one of the "enantiomers" is life-saving, its counterpart with opposite handedness may be poisonous. Another concept which has found widespread interest in contemporary materials science is topology as many so-called topological materials feature exotic properties. For example, topological materials can have protected edge states where electrons flow freely without resistance, as if a superconducting path of electrons were created at the edge of a material. Such unconventional properties are a manifestation of the quantum nature of matter. The topological materials can be classified by a special quantum number, called the topological charge or the Chern number.

Chiral topological materials have particularly unique properties which may be useful in future devices for quantum computers which could speed up computations considerably. An example for such a property is the long-sought large quantized photogalvanic current. Here a fixed dc current is generated in a chiral topological material once exposed to a circularly-polarized light, which is independent of the strength of incident radiation and its direction can be manipulated by the polarization of incident light. This phenomenon relies on the fact that the material possesses a high topological charge of 4, which is the maximum possible value in any material.

Solid-state chemists and physicists from the Max Planck Institute for Chemical Physics of Solids (MPI CPfS), the Leibniz Institute for Solid State and Materials Research (IFW), the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), the Helmholtz-Zentrum Berlin fuer Materialien und Energie (HZB) and the University of Science and Technology of China, Hefei succeeded to realize this peculiar electronic state for the first time in the new chiral topological compound PtGa. Their results have been published in Nature Communications1.

In the study, the researchers have used exceptionally strong spin-orbit coupling in PtGa as the key parameter to clearly resolve and count the number of special topological surface states, called the Fermi arcs, which determine the topological charge. "PtGa is the best compound existing in nature with chiral B20 structure to observe spin-split Fermi arcs and realize the maximal Chern number 4 as it has the strongest spin-orbit coupling." says Kaustuv Manna, one of the authors of the study who works as a scientist at Max Planck Institute for Chemical Physics of Solids Dresden.

Theoretical calculations performed by Yan Sun and his colleagues suggested that the compound PtGa is a highly promising candidate to observe the high topological charge which was experimentally verified by Mengyu Yao and his colleagues who performed detailed angle-resolved photoemission spectroscopy (ARPES) studies. ARPES is a powerful tool to investigate the behavior of electrons in solids.

"The work by Yao et al. reveals that PtGa is a topological semimetal with a maximal chiral charge and has the strongest spin-orbital coupling among all chiral crystals identified up to date. This observation is significant and has great implications for its transport properties, such as magnetotransport." explains Ming Shi, a professor and senior scientist at Paul Scherrer Institute, Switzerland.

The study is an example for an excellent collaboration between research groups covering different areas of expertise. Within the excellence cluster ct.qmat, scientists are cooperating to investigate fundamentally new states of matter. "We are focusing on novel materials whose observed properties and functions are driven by quantum mechanical interactions at the atomic level, with semimetals such as PtGa being one of the most exciting examples," says Jochen Wosnitza, Director of the Dresden High Magnetic Field Laboratory (HLD) at HZDR, referring to one of the cluster's main research topics. Institutes participating in the cluster and collaborating on the current publication include the DRESDEN-concept partners MPI CPfS, IFW, and HZDR.