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Researchers fabricate all-perovskite tandem solar cells with improved efficiency

October 11, 2019 (updated October 11, 2019) Published by Kshitij Kumar

A kind of solar cell having an important perovskite structured element known as Perovskite tandem solar cells (PSCs) has been fabricated by a group of scientists from Nanjing University, China and the University of Toronto, Canada. Hairen Tan, the lead researcher told that instead of making single-junction perovskite solar cells, the primary idea was to make more efficient all-perovskite tandem solar cells. The findings are reported in Nature Energy journal.

Perovskites are a group of minerals having the same crystal structure as perovskite which is yellow, black or brown mineral comprising mostly of calcium titanate. Many researchers over the past few years have been attempting to build solar cells using this material, either wide-bandgap (~1.8 eV) or narrow-bandgap (~1.2 eV) perovskites.

Merging wide and narrow bandgap perovskites together could enhance power conversion efficiency (PCEs) than that achieved by single-junction cells without any increase in fabrication costs. Scientists need to find a method to strengthen the efficiency of individual subcells, while also integrating the wide and narrow-bandgap cells synergistically for building this type of cell.

Tan said that low efficiencies (PCE~18-20 percent) and low short-circuit current densities (Jsc~28-30 mA/cm2) have been demonstrated by the mixed Pb-Sn narrow-bandgap perovskite solar cells which fall under their capacity, and under the performance of the best Pb-based single-junction perovskite cells. One of their vital components, Sn2+, readily oxidizes into Sn4+ is responsible for the weak performance in narrow-bandgap perovskite solar cells. Tan and his team wanted to determine solutions that could overcome the high trap densities and short carrier diffusion lengths exhibited by the resultant cells.

He also added that their main purpose is to extend the diffusion of narrow-bandgap perovskite solar cells thus to achieve better-performed tandem solar cells. Also, they took a perspective to stop the oxidation of Sn2+ to Sn4+ in the precursor solution to enhance charge carrier diffusion length and whose inclusion in the mixed Pb-Sn perovskites causes Sn vacancies. A new chemical method was used by Tan’s team that is based on a comproportionation reaction and leads to significant improvements in the charge carrier diffusion lengths of mixed Pb-Sn narrow-bandgap perovskites. This could eventually increase the performance of PSCs.

The team obtained an extraordinary 3 μm diffusion length that allows performance-record-breaking Pb-Sn cells and all-perovskite tandem cells unlike the earlier intended method characterized by sub-micrometer diffusion lengths, that can reduce the efficiency of the cell. He also explained that a tin-reduced precursor solution was developed to obtain this by restoring the Sn4+ (an oxidization product of Sn2+) back to Sn2+ through comproportionation reaction in the precursor solution.

The major challenge for the advancement of solar cells with a perovskite element is the oxidation of tin-containing perovskites as it adversely affects their efficiency and hampers their utilities. A substitute path for fabricating tandem solar cells using tin-containing narrow-bandgap perovskite is given by the new chemical method introduced by Tan and his co-workers making cells more stable and efficient.

Tan added that the electronic quality of tin-containing perovskites is comparable to that of lead halide perovskites that have shown efficiency similar to crystalline silicon cells. This approach will eventually provide them a way to very inexpensive and highly efficient solar devices.

The performance of monolithic all-perovskite tandem cells was tested using the chemical approach after fabrication. Remarkable independently approved PCEs of 24.8 percent for small-area devices (0.049 cm2) and 22.1 percent for large-area devices (1.05 cm2) was obtained by their cells. Additionally, after functioning for over 400 hours at their highest power point under full one sun illumination, the cells retained 90 percent of their performance. The method introduced by this team of scientists could lead to the development of more efficient and cost-effective solar-powered devices in the future.

Tan said that they are now planning to further enhance the power conversion efficiency of all-perovskite tandem solar cells above 28 percent. Minimizing the photovoltage loss in the wide-bandgap perovskite solar cell will be the primary feasible method to attain this while minimizing the optical losses in the tunneling recombination junction is another possibility.

Journal Reference: Nature Energy

NASA detects organic compounds suitable for life in an ocean on Enceladus

October 5, 2019 (updated October 6, 2019) Published by Sai Teja

Scientists have detected the basic ingredients for life from an ocean on Enceladus, one of Saturn’s moons. Analysis of NASA data shows the presence of organic compounds in plumes of liquid water shooting into space from the ocean. The findings appear in Monthly Notices of the Royal Astronomical Society journal.

These compounds contain nitrogen, oxygen and play a major role in creating amino acids, the building blocks of protein. Researchers previously detected organic molecules from the moon but this is the first time molecules were found to be dissolved in water. This indicates that compounds could take part in chemical reactions under the sea leading to amino acids.

Frank Postberg, one of the study’s authors said that this work reveals the building blocks that are abundant in the ocean of Enceladus. This is a positive indication to carry out research for the habitability of the moon. Jets of ocean water and ice shoot out into space regularly through the cracks in the crust of the moon.

The compounds were dissolved in the ocean water which then evaporated with surface water finally getting condensed and frozen into the crust of the moon. They were carried into space by the plumes and detected by Cassini spacecraft of NASA. This is an indication that Enceladus might have its own method of generation of life.

In the oceans of Earth, seawater combines with magma which comes out through the cracks in the ocean floor. This results in the production of hydrothermal vents whose temperature can rise till 370 degrees Celsius. The water from these vents is rich in hydrogen, catalyzing chemical reactions of organic compounds into amino acids. These then combine to form proteins, one of the main components of life. This method works without sunlight and this is significant in the case of Enceladus where the sunlight is reflected back to space in its entirety. So life has to develop in the dark.

Nozair Khawaja, the research team leader said that the molecules might follow the same pathway in oceans of Enceladus as that of Earth. The discovery of molecules forming amino acids is quite significant. The compounds discovered by the team last were not soluble in water hence researchers were not sure if the organic molecules on Enceladus were capable of life formation.

Cassini was launched in 1997 and it spent 13 years in the exploration of Saturn and its moons. Scientists purposefully crashed the spacecraft into Saturn thereby ending its mission as they did not want to contaminate Enceladus or Titan in any manner.

Cassini found a global ocean containing liquid saltwater below the surface of Enceladus and captured images of water jets shooting to space. The data about their composition was collected in 2008. Scientists will continue studying the data collected by Cassini as NASA also plans of sending a probe to Titan, another moon of Saturn which also contains organic compounds. Dragonfly, a nuclear-powered helicopter will start for Titan in 2026 and arrive in 2034.

Reference: Monthly Notices of the Royal Astronomical Society journal.

Virtual Reality for Scientists

October 5, 2019 Published by California Institute of Technology

When you think of virtual reality, or VR, you might conjure up images of action-packed video games or immersive tours of deep ocean waters and other exotic locale. But, in recent years, scientists have started to don VR goggles too—not for entertainment, but for analyzing and comprehending their data.

At Caltech, efforts to design VR tools for the future are underway, with prototypes in development for studying everything from worms to ocean waters to biomolecules and more.

“We are thinking about what doing science will look like 10 to 15 years from now,” says Santiago Lombeyda, a computational scientist at the Center for Data-Driven Discovery (CD3), the group behind the virtual reality research, as well as other data science projects. CD3 is a joint partnership between Caltech and JPL, which is managed by Caltech for NASA. “In the future, a scientist might be working on their desktop, and then they could just grab a pair of virtual reality glasses, or they may even be already wearing regular glasses that enable VR, and then start manipulating their data in the same shared visual context of their actual work area.”

“Billions of dollars have been poured into VR in the gaming industry. We can leverage their software and ask what it can do for science and scholarship,” says George Djorgovski, director of CD3 and a professor of astronomy at Caltech. Djorgovski has been working on developing VR tools for data analylsis for more than a decade and, in 2015, developed a related startup company called Virtualitics, which combines VR with machine learning.

The CD3 group’s latest project, in collaboration with the National Cancer Institute, is to develop better tools for finding tumors in diagnostic imaging scans. To that end, they have developed a virtual reality environment, using a Vive VR headset, where a user can visualize computed tomography (CT) scans from patients and identify possible tumors. According to the Caltech and JPL researchers, the 3-D virtual environment allows radiologists to better visualize and identify potential tumors than with the standard 2-D imaging methods available now.

“The 3-D environment can really have an impact in understanding three-dimensional structures,” says Lombeyda. “And that’s why it applies so well to looking for tumors. By walking around the data and seeing it from all sides, you might find things you wouldn’t otherwise see by just looking at 2-D slices of tissues.”

The group has begun working with several radiologists to identify possible tumors in patients. The idea is to then take this VR training data and feed it into machine-learning, or artificial intelligence (AI), programs, an effort being managed by Caltech’s Ashish Mahabal, lead computational and data scientist for CD3. Once those programs have learned how to better identify tumors, they could be used in the future to help medical professionals find candidate tumors for follow-up. “The better the training data, the better the machine-learning program,” says Djorgovski.

“There is a synergy with machine learning and virtual reality,” says Dan Crichton, director of the Center for Data Science and Technology at JPL, a partner organization to CD3. “We are training AI to see things, such as tumors, that otherwise might have gone missing. This can be a useful aid to medical practitioners.”

Crichton says that components of the software they are using for their VR programs were developed originally for astronomy and planetary imaging. “Anytime you look at data in three or more dimensions, it’s challenging,” he says. “When we study planetary surfaces, for example, we want to see more than just a one-dimensional slice. We want to see the depth and how other variables change. The principles we’ve learned from this kind of imaging apply to our VR programs.”

According to the scientists, the virtual reality environment offers scientists a more instinctive way to understand their data, whether it signifies an object such as a tumor or a molecule, or is represented in the form of a graph, with many variables plotted out.

“In a 3-D virtual environment, scientists have a more intuitive and longer-lasting grasp of the spatial relations of objects. In today’s world, more and more multidimensional data are becoming available, and these tools are improving the ability of humans to comprehend them,” says Djorgovski. “In the same way that we went from black-and-white photography to color photography, or from phone calls to Skype chats, people will not want to go back from virtual reality.”

In another application of the VR program developed by the CD3 group, in collaboration with Paul Sternberg, Bren Professor of Biology, a user has the ability to manipulate a model of a tiny transparent worm called Caenorhabditis elegans (C. elegans) using a tool that seemingly grasps the worm like a pair of tongs. When the program turns on, the worm first appears on a desk surface in a virtual office environment, at a fairly small scale. The user can then enlarge the worm by throwing it on the floor. And if the user wants to see a huge model of the worm, they can toss it out of a virtual window, where it blows up to a scale bigger than a human.

“We want researchers to come to us with data that we can then quickly prep for viewing in a VR space,” says Lombeyda. “Whatever they are studying can be seen at desktop scale, or they can drop it on the floor and walk around it.”

One of the challenges of developing VR tools that scientists will actually use lies in making the experience smooth, without jerky motions. VR programs can leave people feeling dizzy, and avoiding this is something that the CD3 group continues to work on. Lombeyda says that their overall goal is to make the experience as natural and seamless as possible for a scientist working at an office desk, so that they might be checking email and then could pop on a pair of VR glasses to quickly examine new data.

“Most of the time, scientists work at desks, so we want to optimize that experience,” says Lombeyda, adding that augmented reality, or AR, glasses, in which a viewer is only partially immersed in a virtual environment, may also become a common tool for scientists. But, he says, they are focusing on VR now in this early phase of development.

The group is also working on building VR classrooms, and last year they taught a course in a virtual space. VR classrooms can bring together students in different locations, and even across the globe, to understand and manipulate data in 3-D. According to Djorgovski, this kind of setup could also be used to improve teaching skills. For example, students in a VR classroom could anonymously hit a button if they were not comprehending a certain topic. “If the teacher were to get a few alerts, they would know at that point the students were confused and they needed to backtrack.This is something that can be done more easily and more quickly in VR versus traditional classrooms.”

Recently, the scientists presented their VR tumor program at a computer graphics conference, called SIGGRAPH, to favorable reviews. “Some of the comments we kept hearing were how people were excited to see VR for something other than gaming, and also how natural the experience was in our VR setup,” says Lombeyda.

Though the technology may still be in its early phases, the researchers are excited to press on. The future of VR, they say, is not just for fun and games but for collectively making sense of our world. “All sciences are undergoing the same transformations of having to deal with larger and larger data sets, and traditional tools won’t work,” says Djorgovski. “Instead of reinventing the wheel everywhere, scientific groups are developing new methodologies for big and complex data sets. Everybody faces the same problems so we have a great opportunity for sharing solutions and ideas.”

Materials provided by California Institute of Technology

Hacker claims access to 218 million accounts of one of the most popular games

October 5, 2019 (updated October 5, 2019) Published by Kalpit Veerwal

A hacker going by the name Gnosticplayers has claimed to obtain access records of 218 million players of Words with Friends which includes names, email and login IDs, hashed passwords, Facebook IDs and phone numbers. If a user has signed up for Words with Friends as recent as last month, then it is best to change the password as soon as possible since there lies a possibility of the data being stolen and misused.

Cracking a hashed password can be very simple if it is a commonly used term or a simple word or if the original encryption is weak. Thus it is considered a best practice to change the passwords on remaining social accounts where the same email address and password are used. More damage can be caused in these sites than just attacking a simple game like Words with Friends. Security experts thus advice to use different passwords and login details for various social media applications and websites. Any breach of data on one application does not affect any of the remaining ones.

Zynga, the developer of Words with Friends said that they discovered some player account information to be accessed by external hackers. They initiated immediate investigation along with the assistance of leading forensic firms and the support of law enforcement.

As the world goes more and more digital, the threat of such attacks increases and the users are often left vulnerable since it is their data which is being tampered with. Millions of user credentials are being leaked out every year even with big giants such as Facebook.

However, there are certain tips to prevent these damages. One of them includes using unique and long passwords for every account. Using password managers can also help so that you need not remember every password. It is also advised to use the advantage of two-factor authentication wherever provided. Most major accounts including Google, Facebook, Apple support this. Besides the password, this method requires entering the unique code sent to the user’s mobile number in every login attempt.

Users should also delete their old accounts which they decide not to use anymore. People often uninstall the application and forget but it does not end there. The user should delete their entire account information from the application or contact the developer if such an option is not provided. If all of these practices are followed, then it is highly unlikely for a user to have his/her information compromised. We should learn to protect our data and keep ourselves safe.

Time reversibility might be the reason why gamma-rays seem to travel backward

October 2, 2019 (updated October 2, 2019) Published by Sai Teja

It is known that time can move in only one direction. However, last year scientists detected some events in which the gamma-ray bursts seemed to repeat as if they were moving backward in time.

New research suggests the potential answer to the cause of this time reversibility effect. If the waves in the relativistic jets producing gamma-ray bursts propagate faster than light at what is known as “superluminal speeds”, then one of its possible effects could be time reversibility. The work appears in The Astrophysical Journal.

When light travels through a medium, the phase velocity is lesser than the light’s speed in a vacuum, which is the ultimate speed barrier in the Universe. Hence a wave could move through gamma-ray burst jet at superluminal speeds without violating relativity. The most energetic explosions in the Universe are gamma-ray bursts. While they can last a time span ranging milliseconds to hours, they are very bright and till now no concrete reason for their cause is found.

From 2017 observations of colliding neutron stars, it is known that gamma-ray bursts can be created from these collisions. When a huge, violently spinning star collapses to black hole resulting in the ejection of material in a colossal hypernova then these bursts can be produced. Then the black hole is surrounded by the accretion material around the equator. With quick rotation, the exploded material falls back resulting in relativistic jets from the polar regions. It blasts through the outer envelope of the star resulting in gamma-ray bursts.

Particles can move faster than light when traveling through a medium. This causes Cherenkov radiation which is viewed as a blue glow, also known as a luminal boom. When particles such as electrons travel faster than the phase velocity of light in the medium then the glow is produced.

Scientists Jon Hakkila, College of Charleston and Robert Nemiroff, Michigan Technological University think that the same effect is responsible for gamma-ray burst jets. They have created mathematical modeling to demonstrate it. They mention in their model that an impactor wave in a gamma-ray burst either propagates from subluminal to superluminal velocities or decelerates vice-versa. This impactor wave interacts with the medium resulting in Cherenkov radiation when moving faster than light’s speed in the medium or creates a synchrotron shock radiation when moving slower than the light’s speed.

A time-forward and time-reversed set of light curve features are created by the transitions by relativistic image doubling. When a charged particle enters the water near to light’s speed, it moves faster than Cherenkov radiation resulting in the illusion of appearing at two places simultaneously, one seems to travel ahead in time and one backward.

This has not yet been observed experimentally. If verified it might be responsible for the time-reversibility in gamma-ray burst light curves.

Researchers made an assumption that impactor creating gamma-ray burst would be a wave of a large scale produced by changes of the magnetic field. More analysis is needed in this direction. Since the model includes time-reversibility it explains gamma-ray bursts much better than those which don’t.

Reference: The Astrophysical Journal.

Discovery in gallium nitride a key enabler of energy efficient electronics

October 2, 2019 Published by Cornell University

Gallium nitride, a semiconductor that revolutionized energy-efficient LED lighting, could also transform electronics and wireless communication, thanks to a discovery made by Cornell researchers.

Jimy Encomendero/Provided From left, Ph.D. student Samuel J. Bader; Debdeep Jena, professor of electrical and computer engineering and materials science and engineering; Huili Grace Xing, professor of electrical and computer engineering and materials science and engineering; David Muller, professor of applied and engineering physics; Ph.D. student Reet Chaudhuri; and postdoctoral associate Zhen Chen have discovered fast-moving positive charges in gallium nitride that could transform electronics and wireless communication.

Their paper, “A Polarization-Induced 2D Hole Gas in Undoped Gallium Nitride Quantum Wells,” was published Sept. 26 in Science.

Silicon has long been the king of semiconductors, but it has had a little help. The pure material is often augmented, or “doped,” with impurities like phosphorus or boron to enhance current flow by providing negative charges (electrons) or positive charges (“holes,” the absence of electrons) as needed.

In recent years, a newer, sturdier family of lab-grown compound semiconductor materials has emerged: group III-nitrides. Gallium nitride (GaN) and aluminum nitride (AlN) and their alloys have a wider bandgap, allowing them to withstand greater voltages and higher frequencies for faster, more efficient energy transmission.

“Silicon is very good at switching off and on and controlling electrical energy flow, but when you take it to high voltages it doesn’t operate very well because silicon has a weak electric strength, whereas GaN can sustain much higher electric fields,” said co-senior author Debdeep Jena, the David E. Burr Professorin Electrical and Computer Engineering and in Materials Science and Engineering. “If you’re doing very large amounts of energy conversion, then wide-bandgap semiconductors such as GaN and silicon carbide are the solutions.”

Since the 1990s, researchers have doped GaN by adding magnesium impurities to create holes, but the process is highly inefficient. For every hundred magnesium atoms introduced into the crystal, only three or four holes might appear at room temperature, and even fewer at low temperatures.

Rather than using impurities, Ph.D. student Reet Chaudhuri stacked a thin GaN crystal layer – called a quantum well – atop an AlN crystal, and the difference in their crystal structures was found to generate a high density of mobile holes. Compared with magnesium-doping, the researchers discovered that the resulting 2D hole gas makes the GaN structures almost 10 times more conductive.

“In 1992, researchers discovered that when aluminum nitride is deposited on top of gallium nitride, you get free electrons at the interface. Having electrons conduct inside GaN makes what we call n-type electronic devices,” said Chaudhuri, the paper’s lead author. “The polarization theory that explains why we get mobile electrons in this structure, which in fact was conceptualized and validated by Cornell researchers in late ’90s, also predicts that we should expect holes when the structure is flipped. But to date, there had not been any report of holes in an undoped III-nitride semiconductor structure. And that’s what we have found in this work.”

Xiang Li/Provided Ph.D. student Reet Chaudhuri takes measurements on the 2D hole gas.

Using the new material structure created by Reet, co-author and Ph.D. student Samuel James Bader recently demonstrated some of the most efficient p-type GaN transistors in a collaborative project with Intel. Now that the team has the capability to make hole-channel transistors – which are called p-type – they plan to pair them with n-type transistors to form more complex circuits, opening up new possibilities in high-power switching, 5G cellular technology and energy efficient electronics, including phone and laptop chargers.

“It’s very difficult to simultaneously achieve n-type and p-type in a wide bandgap semiconductor. Right now, silicon carbide is the only other one that has both besides GaN. But the mobile electrons in silicon carbide are more sluggish than those in GaN,” said co-senior author Huili Grace Xing, the William L. Quackenbush Professor in electrical and computer engineering and in materials science and engineering. “Using these complementary operations enabled by both n-type and p-type devices, much more energy efficient architecture can be built.”

Another advantage of the 2D hole gas is that its conductivity improves as the temperature is lowered, meaning that researchers will now be able to study fundamental GaN properties in ways that haven’t been previously possible. Equally important is its ability to retain energy that would otherwise be lost in less efficient power systems.

“Gallium nitride caused a revolution in the lighting industry,” Jena said. “It enabled the white lighting that is in our cellphones, laptops, and LED bulbs that are replacing the incandescent bulbs in our homes. With a regular 100W incandescent light bulb, which is about 4% energy efficient, you might get 4 watts of light and the rest is heat. You know this very well if you touch the bulb when it is on. LEDs on the other hand can be almost 80% efficient, and only 20% is heat. A similar change in energy-efficiency of electronics has not yet happened. And maybe this finding is a step in that direction.”

A patent application has been filed through the Center for Technology Licensing for the discovery. Other contributors included David Muller, the Samuel B. Eckert Professor in Applied and Engineering physics; and Zhen Chen, a postdoctoral researcher in Muller’s lab.

The research was supported in part by Intel, the Air Force Office of Scientific Research, the National Science Foundation and the Cornell Center for Materials Research.

Materials provided by Cornell University

Researchers come up with battery models powering more than a million miles

October 2, 2019 (updated October 2, 2019) Published by Kshitij Kumar

Jeffrey Dahn and his research group from Dalhousie University, Nova Scotia has filed for a new patent on lithium battery technology which can power more than a million miles. Dahn holds an exclusive agreement with Tesla and his team has published the testing results on new batteries which according to them can be used as benchmarks for other scientists dealing with similar technologies. The report can be found in the Journal of the Electrochemical Society.

The most innovative section of the battery used by Dahn’s team is the cathode. Different batteries use different types of lithium compounds for achieving good characteristics. Dahn’s team has been investigating on NMC – lithium nickel manganese cobalt oxide. This material has been used by several other electric vehicle makers in the past such as Nissan and Chevrolet but not Tesla. Dahn uses synthetic graphite for anode with the electrode being a blend of lithium salts and several other ionic compounds. These components do not differ much in compositions used by other makers however Dahn’s team used a different technique for the NMC cathode’s structure. The team used large single crystals replacing smaller ones which would develop lesser cracks as the battery goes through charged and discharged states.

Battery research has been mostly focused on increasing the range that can be powered in a single charge. Dahn, on the other hand, has focused on improving the battery’s overall lifetime making it suitable for self-driving taxis and electric trucks that are expected to go through several charges and discharge cycles. The current Tesla battery pack lasts for 300,000 to 500,000 miles which is not enough. On the other hand, batteries in this paper are expected to last 4000 charges – four times more than the present commercial batteries.

Since the paper has been categorized for “benchmarking”, it implies that the batteries mentioned in the paper would not be used by Tesla in its vehicles. Dahn mentioned that these batteries are capable of powering an electric vehicle for more than a million miles while lasting two decades in grid energy storage.

Tesla and Dahn were awarded the patent for a single crystal NMC battery with an additive named ODTO, similar to the description in the paper, which has been described by Dahn’s team in another paper last year. There is still room for improvement in the batteries described in the current paper as the specific energy density of mentioned batteries is lesser than the maximum ability of advanced Li-ion batteries. There is a possibility of Li-ion batteries powering more than 500kms in a single charge.

Reference: Journal of the Electrochemical Society.

Astronomers detect three supermassive black holes at the center of three colliding galaxies

October 1, 2019 (updated October 1, 2019) Published by Kalpit Veerwal

Three supermassive black holes (SMBHs) glowing in x-ray emissions have been identified by astronomers at the center of three colliding galaxies a billion light-years away from Earth. All three black holes are active galactic nuclei(AGN), consuming material. This finding may clarify a long-standing issue in astrophysics and black hole mergers known as “final parsec problem”. The study appears in The Astrophysical Journal.

Researchers detected the three SMBHs with the data from several telescopes, Sloan Digital Sky Survey (SDSS,) the Chandra X-ray Observatory, and the Wide-field Infrared Survey Explorer (WISE)A nearly unbelievably astronomical event, the fusion of three galaxies may play a crucial role in how the most massive black holes expand over time.

Ryan Pfeifle from George Mason University in Fairfax, Virginia, the paper’s first author said that they found this incredible system through their selection technique while they were only looking for black hole pairs. He also added that this is the most powerful evidence found for such a triple system of active supermassive black holes. It is very challenging to locate triple black hole systems since they are wrapped in gas and dust. It took several telescopes functioning in different parts of the electromagnetic spectrum and also the work with researchers to detect these black holes.

Co-author Shobita Satyapal, also belonging to George Mason said that dual and triple black holes are extremely rare but such systems are actually a natural outcome of galaxy mergers, through which galaxies grow. This triple-merger was first spotted in visible light by the SDSS and only through a citizen science project named Galaxy Zoo the system of colliding galaxies was detected. The system was in a state of galaxy merger glowing in the infrared as seen by the WISE when more than one black holes were expected to be feeding.

Researchers shifted to the Chandra Observatory and the Large Binocular Telescope (LBT) for confirmation as Sloan and WISE data were fascinating clues. Chandra observations revealed bright x-ray sources in the galactic centers where SMBHs are expected to detect. Chandra and Nuclear Spectroscopic Telescope Array (NuSTAR) satellite of NASA discovered more shreds of evidence showing the presence of SMBHs and the existence of large amounts of gas and dust near one of them. It was expected in merging of black holes. Spectral evidence received by optical light data from SDSS and LBT shows that these are characteristics of the feeding SMBHs.

Christina Manzano-King, co-author from the University of California, Riverside said that optical spectra include plenty of information about a galaxy which is frequently used to detect active accreting supermassive black holes and can tell about their influence on the inhabitant galaxies. Pfeifle said that they have found a new method of identifying triple supermassive black holes using these major observatories as each telescope gives them a distinct idea about these systems. They expect to extend their work to find more triples using the same method.

The final parsec problem is a theoretical problem that is fundamental to our understanding of binary black hole mergers that states that the enormous orbital energy of two approaching black holes stops them from merging. They can get separated by a few light-years, then the merging process stables.

The hyperbolic trajectories of two initially approaching black hole carry them right past each other. The two holes catapult the stars as they interact with them in their proximity transferring a fraction of their orbital energy to a star every time. The energy of the black holes gets reduced by the emission of gravitational waves. The two black holes finally slow down and approach each other more closely shedding enough orbital energy finally getting within just a few parsecs of each other. More matter is discharged via sling-shotting as they come closer. As a result, for the black holes, no more matter is left to interact with and shed more orbital energy. The merging process halts.

Astronomers know that strong gravitational waves are responsible for black hole mergers.LIGO (Laser Interferometry Gravitational-Wave Observatory) discovers a black hole merger almost every week. The final parsec problem is about how they merge with each other finally. Researchers think that a third black hole like seen in this system could give the push needed for the black holes to get merged. Nearly 16% of supermassive black hole pairs in colliding galaxies are expected to interact with a third supermassive black hole before they merge.

The challenge is that gravitational waves produced during merging would be too low-frequency for LIGO or the VIRGO observatory to detect. Researchers may have to depend on future observatories like LISA, ESA/NASA’s Laser Interferometer Space Antenna to detect those waves. LISA is better-equipped than LIGO or VIRGO to detect merging of giant and massive black holes as it can detect lower frequency gravitational waves.

Reference: The Astrophysical Journal.

This flat structure morphs into shape of a human face when temperature changes

October 1, 2019 (updated October 1, 2019) Published by Massachusetts Institute of Technology

Researchers at MIT and elsewhere have designed 3-D printed mesh-like structures that morph from flat layers into predetermined shapes, in response to changes in ambient temperature. The new structures can transform into configurations that are more complex than what other shape-shifting materials and structures can achieve.

As a demonstration, the researchers printed a flat mesh that, when exposed to a certain temperature difference, deforms into the shape of a human face. They also designed a mesh embedded with conductive liquid metal, that curves into a dome to form an active antenna, the resonance frequency of which changes as it deforms.

The team’s new design method can be used to determine the specific pattern of flat mesh structures to print, given the material’s properties, in order to make the structure transform into a desired shape.

The researchers say that down the road, their technique may be used to design deployable structures, such as tents or coverings that automatically unfurl and inflate in response to changes in temperature or other ambient conditions.

Such complex, shape-shifting structures could also be of use as stents or scaffolds for artificial tissue, or as deformable lenses in telescopes. Wim van Rees, assistant professor of mechanical engineering at MIT, also sees applications in soft robotics.

“I’d like to see this incorporated in, for example, a robotic jellyfish that changes shape to swim as we put it in water,” says van Rees. “If you could use this as an actuator, like an artificial muscle, the actuator could be any arbitrary shape that transforms into another arbitrary shape. Then you’re entering an entirely new design space in soft robotics.”

Van Rees and his colleagues are publishing their results this week in the Proceedings of the National Academy of Sciences. His co-authors are J. William Boley of Boston University; Ryan Truby, Arda Kotikian, Jennifer Lewis, and L. Mahadevan of Harvard University; Charles Lissandrello of Draper Laboratory; and Mark Horenstein of Boston University.

Gift wrap’s limit

Two years ago, van Rees came up with a theoretical design for how to transform a thin flat sheet into a complex shape such as a human face. Until then, researchers in the field of 4-D materials — materials designed to deform over time — had developed ways for certain materials to change, or morph, but only into relatively simple structures.

“My goal was to start with a complex 3-D shape that we want to achieve, like a human face, and then ask, ‘How do we program a material so it gets there?’” van Rees says. “That’s a problem of inverse design.”

He came up with a formula to compute the expansion and contraction that regions of a bilayer material sheet would have to achieve in order to reach a desired shape, and developed a code to simulate this in a theoretical material. He then put the formula to work, and visualized how the method could transform a flat, continuous disc into a complex human face.

But he and his collaborators quickly found that the method wouldn’t apply to most physical materials, at least if they were trying to work with continuous sheets. While van Rees used a continuous sheet for his simulations, it was of an idealized material, with no physical constraints on the amount of expansion and contraction it could achieve. Most materials, in contrast, have very limited growth capabilities. This limitation has profound consequences on a property known as double curvature, meaning a surface that can curve simultaneously in two perpendicular directions — an effect that is described in an almost 200-year-old theorem by Carl Friedrich Gauss called the Theorema Egregium, Latin for “Remarkable Theorem.”

If you’ve ever tried to gift wrap a soccer ball, you’ve experienced this concept in practice: To transform paper, which has no curvature at all, to the shape of a ball, which has positive double curvature, you have to crease and crumple the paper at the sides and bottom to completely wrap the ball. In other words, for the paper sheet to adapt to a shape with double curvature, it would have to stretch or contract, or both, in the necessary places to wrap a ball uniformly.

To impart double curvature to a shape-shifting sheet, the researchers switched the basis of the structure from a continuous sheet to a lattice, or mesh. The idea was twofold: first, a temperature-induced bending of the lattice’s ribs would result in much larger expansions and contractions of the mesh nodes, than could be achieved in a continuous sheet. Second, the voids in the lattice can easily accommodate large changes in surface area when the ribs are designed to grow at different rates across the sheet.

The researchers also designed each individual rib of the lattice to bend by a predetermined degree in order to create the shape of, say, a nose rather than an eye-socket.

For each rib, they incorporated four skinnier ribs, arranging two to line up atop the other two. All four miniribs were made from carefully selected variations of the same base material, to calibrate the required different responses to temperature.

When the four miniribs were bonded together in the printing process to form one larger rib, the rib as a whole could curve due to the difference in temperature response between the materials of the smaller ribs: If one material is more responsive to temperature, it may prefer to elongate. But because it is bonded to a less responsive rib, which resists the elongation, the whole rib will curve instead.

The researchers can play with the arrangement of the four ribs to “preprogram” whether the rib as a whole curves up to form part of a nose, or dips down as part of an eye socket.

Shapes unlocked

To fabricate a lattice that changes into the shape of a human face, the researchers started with a 3-D image of a face — to be specific, the face of Gauss, whose principles of geometry underly much of the team’s approach. From this image, they created a map of the distances a flat surface would require to rise up or dip down to conform to the shape of the face. Van Rees then devised an algorithm to translate these distances into a lattice with a specific pattern of ribs, and ratios of miniribs within each rib.

The team printed the lattice from PDMS, a common rubbery material which naturally expands when exposed to an increase in temperature. They adjusted the material’s temperature responsiveness by infusing one solution of it with glass fibers, making it physically stiffer and more resistant to a change in temperature. After printing lattice patterns of the material, they cured the lattice in a 250-degree-Celsius oven, then took it out and placed it in a saltwater bath, where it cooled to room temperature and morphed into the shape of a human face.

Courtesy of the researchers

The team also printed a latticed disc made from ribs embedded with a liquid metal ink — an antenna of sorts, that changed its resonant frequency as the lattice transformed into a dome.

Van Rees and his colleagues are currently investigating ways to apply the design of complex shape-shifting to stiffer materials, for sturdier applications, such as temperature-responsive tents and self-propelling fins and wings.

This research was supported, in part, by the National Science Foundation, and Draper Laboratory.

Materials provided by Massachusetts Institute of Technology

The Gap between quantum and classical computing is bridged by this new chip

September 30, 2019 (updated September 30, 2019) Published by Shruti

Quantum computers existing today are limited versions of the futuristic quantum computers that we hope to achieve in the future. However, scientists have created the hardware for the “probabilistic computer” – a device to bridge the gap between the standard PCs of today and the genuine quantum computers. The study appears in the Nature journal.

This probabilistic computer can solve quantum problems using a special trick. It uses a p-bit which is described by the research team as “poor man’s qubit”. In classical computing, a bit can either take the value 1 or 0, while qubits can take both of these values at the same time as per the laws of quantum computing. Meanwhile, the p-bit can take only 1 or 0 at a time, but the switch between two states occurs very quickly. Using the fluctuations properly, researchers can tackle the problems that are considered quantum computing problems without using a real quantum computer.

In addition to this, the p-bit can operate at room temperature whereas the qubits need super-cold conditions for their operation. P-bits can be easily adapted to the existing computers. Supriyo Datta, an electrical engineer at Purdue University, in Indiana, said that there are a group of problems solved with the help of qubits that can also be solved by the p-bits. Hence getting the name “poor man’s qubit”.

The result of the research has been a modified magnetoresistive random access memory(MRAM) device for storing information in the computers of the present day. Magnetic orientations are used to represent 0s or 1s using states of resistance. Eight custom-made MRAM p-bit units were put with a controller chip to create a probabilistic computer – where units are used to take a specific value.

Scientists were able to solve the integer factorization problems, which are usually considered quantum problems. It can also be solved by classical computers however with lesser efficiency. The probabilistic computer along with p-bits represents a middle ground between two ends. Scientists feel that the fully developed p-bit computers would solve integer factorization problems with lesser energy and time than the computers of the present day.

Ahmed Zeeshan Pervaiz, Purdue University said that the circuit occupies the same area as that of a transistor but performs the function which would take several thousand transistors to perform. The calculation speed could also be increased by parallel operation of a huge number of p-bits.

For the practical use of these machines, there is a need for more refining which would not take much time. After that, these can handle certain problems until the final leap in quantum computing occurs. Connecting qubits for practical use is a tough challenge until then p-bits can be used for machine learning and optimization problems.

Journal Reference: Nature

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