Kingston, Ontario’s Grafoid Inc. has signed a Memorandum of Understanding (MOU) for the establishment of a strategic joint venture partnership with China’s largest producer and exporter of tungsten products, Xiamen Tungsten Co. Ltd., which will see Xiamen take up to a 20% equity stake in privately held Grafoid, pending the completion of due diligence which is set to conclude on May 22, 2016.
Xiamen’s equity position in Grafoid was negotiated through its parent company, Ottawa’s Focus Graphite Inc. (TSX VENTURE:FMS) (OTCQX:FCSMF) (FRANKFURT:FKC), through the purchase of up to 7 million Grafoid common shares currently held by Focus Graphite.
“In addition to providing Grafoid with a strategic partner, Grafoid’s MOU with Xiamen, has benefits for Focus Graphite. When finalized, it will provide additional funding to allow us to advance our overall mine and transformation plant financing, and potentially open the China market to Focus Graphite for additional offtake partners and the sale of value added graphite products,” said Focus Graphite CEO and Director Gary Economo.
“Specifically, this injection of funding could enable Focus Graphite to advance our Lac Knife detailed engineering and finalize the environmental permitting process” said Economo. “And, it enables us to move to the next stage in assembling our mine CAPEX financing.”
Last September, Grafoid and Focus Graphite finalized two offtake agreements for obtaining graphite concentrate from a mining project at Lac Knife in Quebec for the next 10 years, one of the priorities of the Quebec government’s Plan Nord initiative.
Focus Graphite, with 7.9 million shares, is currently Grafoid’s largest stakeholder.
The MOU will also see the establishment of Xiamen’s business office at the Grafoid Global Technology Center in Kingston, providing Xiamen with a North American base for future business expansion, as well as the establishment of a Grafoid business office in China.
Grafoid’s path to commercialization lies in its patented product, a high-quality graphene trading under the name Mesograf.
Other terms of the MOU include the desire of Xiamen to introduce a clean energy technology platform and associated technologies to the Chinese market, and the opportunity for Grafoid to bring its suite of Mesograf and Amphioxide graphene based products to China.
With the Lac Knife project moving forward, Grafoid is well positioned to supply global markets with with high purity, value-added, cost-competitive graphite products while supporting the next generation battery development platform of Grafoid, Focus Graphite, Stria Lithium Inc., and Braille Battery Inc.
With annual revenue surpassing 10.143B CNY ($1.55B US), Xiamen, a publicly traded company listed on the Shanghai Exchange (SHA:600549), is a major player in that country’s smelting, processing and exporting of tungsten and other non-ferrous metal products, the operation of rare earth business interests, and the supply of battery materials.
Grafoid currently has 17 joint partnership ventures with industrial and academic partners, including Japan’s Mitsui & Co., Hydro Quebec, Rutgers University, the University of Waterloo, and Phos Solar Systems in Greece.
Last February, Grafoid received an $8.1 million investment from the SD Tech Fund of Sustainable Development Technology Canada (SDTC) to help automate the production of Mesograf and end-product development.
Earlier this month, Professor Aiping Yu of the University of Waterloo’s Chemical Engineering department received a $450,000 Strategic Partnership Grant through the Natural Sciences and Engineering Research Council of Canada (NSERC) to help Grafoid develop an advanced graphene fiber based wearable supercapacitor
11 Mar 2016
A new type of graphene-based filter could be the key to managing the global water crisis, a study has revealed. The new graphene filter, which has been developed by Monash University and the University of Kentucky, allows water and other liquids to be filtered nine times faster than the current leading commercial filter.
According to the World Economic Forum’s Global Risks Report, lack of access to safe, clean water is the biggest risk to society over the coming decade. Yet some of these risks could be mitigated by the development of this filter, which is so strong and stable that it can be used for extended periods in the harshest corrosive environments, and with less maintenance than other filters on the market.
The research team was led by Associate Professor Mainak Majumder from Monash University. Associate Professor Majumder said the key to making their filter was developing a viscous form of graphene oxide that could be spread very thinly with a blade.
“This technique creates a uniform arrangement in the graphene, and that evenness gives our filter special properties,” Associate Prof Majumder said.
This technique allows the filters to be produced much faster and in larger sizes, which is critical for developing commercial applications. The graphene-based filter could be used to filter chemicals, viruses, or bacteria from a range of liquids. It could be used to purify water, dairy products or wine, or in the production of pharmaceuticals.
This is the first time that a graphene filter has been able to be produced on an industrial scale – a problem that has plagued the scientific community for years.
Research team member and PhD candidate, Abozar Akbari, said scientists had known for years that graphene filters had impressive qualities, but in the past they had been difficult and expensive to produce.
“It’s been a race to see who could develop this technology first, because until now graphene-based filters could only be used on a small scale in the lab,” Mr Akbari said.
Graphene is a lattice of carbon atoms so thin it’s considered to be two-dimensional. It has been hailed as a “wonder-material” because of its incredible performance characteristics and range of potential applications.
The team’s new filter can filter out anything bigger than one nanometre, which is about 100,000 times smaller than the width of a human hair.
The research has gathered interest from a number of companies in the United States and the Asia Pacific, the largest and fastest-growing markets for nano-filtration technologies.
The team’s research was supported by industry partner Ionic Industries, as well as a number of Australian Research Council grants.
Ionic Industries’ CEO, Mark Muzzin, said the next step was to get the patented graphene-based filter on the market.
“We are currently developing ways to test how the filter fares against particular contaminants that are of interest to our customers” Mr Muzzin said.
Co-author of the research and Director of the Center for Membrane Science, Professor Dibakar Bhattacharyya, from the University of Kentucky, said: “The ability to control the thickness of the filter and attain a sharper cut-off in separation, and the use of only water as the casting solvent, is a commercial breakthrough.”
Explore further: Graphene’s love affair with water
More information: Abozar Akbari et al. Large-area graphene-based nanofiltration membranes by shear alignment of discotic nematic liquid crystals of graphene oxide, Nature Communications (2016). DOI: 10.1038/ncomms10891
23 Feb 2016
Yat Li (left) and Tianyu Liu worked with researchers at Lawrence Livermore National Laboratory to develop supercapacitors using 3D-printed graphene aerogel electrodes. Credit: T. Stephens
Scientists at UC Santa Cruz and Lawrence Livermore National Laboratory (LLNL) have reported the first example of ultrafast 3D-printed graphene supercapacitor electrodes that outperform comparable electrodes made via traditional methods. Their results open the door to novel, unconstrained designs of highly efficient energy storage systems for smartphones, wearables, implantable devices, electric cars and wireless sensors.
Using a 3D-printing process called direct-ink writing and a graphene-oxide composite ink, the team was able to print micro-architected electrodes and build supercapacitors with excellent performance characteristics. The results were published online January 20 in the journal Nano Letters and will be featured on the cover of the March issue of the journal.
“Supercapacitor devices using our 3D-printed graphene electrodes with thicknesses on the order of millimeters exhibit outstanding capacitance retention and power densities,” said corresponding author Yat Li, associate professor of chemistry at UC Santa Cruz. “This performance greatly exceeds the performance of conventional devices with thick electrodes, and it equals or exceeds the performance of reported devices made with electrodes 10 to 100 times thinner.”
LLNL engineer Cheng Zhu and UCSC graduate student Tianyu Liu are lead authors of the paper. “This breaks through the limitations of what 2D manufacturing can do,” Zhu said. “We can fabricate a large range of 3D architectures. In a phone, for instance, you would only need to leave a small area for energy storage. The geometry can be very complex.”
Supercapacitors also can charge incredibly fast, Zhu said, in theory requiring just a few minutes or seconds to reach full capacity. In the future, the researchers believe newly designed 3D-printed supercapacitors will be used to create unique electronics that are currently difficult or even impossible to make using other synthetic methods, including fully customized smartphones and paper-based or foldable devices, while at the same time achieving unprecedented levels of performance.
According to Li, several key breakthroughs made these novel devices possible, starting with the development of a printable graphene-based ink. Modification of the 3D printing scheme to be compatible with aerogel processing made it possible to maintain the important mechanical and electrical properties of single graphene sheets in the 3D-printed structures. Finally, the use of 3D printing to intelligently engineer periodic macropores into the graphene electrode significantly enhances mass transport, allowing the device to support much faster charge/discharge rates without degrading its capacity.
“This work provides an example of how 3D-printed materials such as graphene aerogels can significantly expand the design space for fabricating high-performance and fully integrable energy storage devices optimized for a broad range of applications,” Li said.
The advantages of graphene-based inks include their ultrahigh surface area, lightweight properties, elasticity, and superior electrical conductivity. The graphene composite aerogel supercapacitors are also extremely stable, the researchers reported, capable of nearly fully retaining their energy capacity after 10,000 consecutive charging and discharging cycles.
“Graphene is a really incredible material because it is essentially a single atomic layer that can be created from graphite. Because of its structure and crystalline arrangement, it has really phenomenal capabilities,” said LLNL materials engineer Eric Duoss.
Over the next year, the researchers intend to expand the technology by developing new 3D designs, using different inks, and improving the performance of existing materials.
Explore further: Energy storage of the future
More information: Cheng Zhu et al. Supercapacitors Based on Three-Dimensional Hierarchical Graphene Aerogels with Periodic Macropores, Nano Letters (2016). DOI: 10.1021/acs.nanolett.5b04965
Graphene is a single-atomic carbon sheet with a hexagonal honeycomb network. Electrons in graphene take a special electronic state called Dirac-cone where they behave as if they have no mass. This allows them to flow at very high speed, giving graphene a very high level of electrical conductivity.
This is significant because electrons with no mass flowing with no resistance in graphene could lead to the realization of an ultimately high-speed nano electronic device.
The collaborative team of Tohoku University and the University of Tokyo has developed a method to grow high-quality graphene on a silicon carbide (SiC) crystal by controlling the number of graphene sheets. The team fabricated bilayer graphene with this method and then inserted calcium (Ca) atoms between the two graphene layers like a sandwich.
They measured the electrical conductivity with the micro four-point probe method and found that the electrical resistivity rapidly drops at around 4 K (-269 °C), indicative of an emergence of superconductivity.
The team also found that neither genuine bilayer graphene nor lithium-intercalated bilayer graphene shows superconductivity, indicating that the superconductivity is driven by the electron transfer from Ca atoms to graphene sheets.
The success in fabricating superconducting graphene is expected to greatly impact both the basic and applied researches of graphene.
It is currently not clear what phenomenon takes place when the Dirac electrons with no mass become superconductive with no resistance. But based on the latest study results, further experimental and theoretical investigations would help to unravel the properties of superconducting graphene.
The superconducting transition temperature (Tc) observed in this study on Ca-intercalated bilayer graphene is still low (4 K). This prompts further studies into ways to increase Tc, for example, by replacing Ca with other metals and alloys, or changing the number of graphene sheets.
From the application point of view, the latest results pave the way for the further development of ultrahigh-speed superconducting nano devices such as a quantum computing device, which utilizes superconducting graphene in its integrated circuit.
- Satoru Ichinokura, Katsuaki Sugawara, Akari Takayama, Takashi Takahashi, Shuji Hasegawa. Superconducting Calcium-Intercalated Bilayer Graphene. ACS Nano, 2016; DOI: 10.1021/acsnano.5b07848
Graphene is a two-dimensional form of carbon, and successful demonstrations have been carried out by researchers to prove the possibility of interfacing graphene with nerve cells, or neurons, without affecting their integrity.
The demonstrations could help to develop graphene-based electrodes, which could be safely implanted into the brain. This study shows potential in restoring the sensory functions for individuals with Parkinson’s disease, epilepsy, amputees or paralyzed patients.
The Cambridge Graphene Centre and the University of Trieste in Italy together worked on this research, which was published in ACS Nano.
Other research teams have earlier demonstrated the possibility of using treated graphene to work with neurons. However very low signal to noise ratio was obtained from this interface. In this work, techniques were developed that allow the use of untreated graphene, and as a result they were able to retain the electrical conductivity of the material. This enables the graphene to function as a better electrode.
For the first time we interfaced graphene to neurons directly. We then tested the ability of neurons to generate electrical signals known to represent brain activities, and found that the neurons retained their neuronal signaling properties unaltered. This is the first functional study of neuronal synaptic activity using uncoated graphene based materials.
Professor Laura Ballerini, University of Trieste
It is possible to control some of the functions of the brain, by directly interfacing between the brain and the outside environment. For instance, it is possible to retrieve the sensory organs by evaluating the electrical impulses of the brain. This could help to control an amputee patient’s robotic arms or basic processes for paralyzed individuals, such as helping them with their speech and movement of objects surrounding them. It is also possible to control motor disorders like Parkinson’s disease or epilepsy when these electrical impulses are interfered with.
To make this possible, scientists have created electrodes that can be inserted deep into the human brain. These electrodes come into direct contact with the neurons and then send out electrical signals from the body to decode their meaning.
The issue that exists in the interface between neurons and electrodes is that the electrodes are not only expected to be extremely sensitive to electrical impulses, but they are also expected to be firm in the body without making changes in the tissue that is measured.
Often modern electrodes used for the tungsten-based or silicon-based interface suffer from complete or partial loss of signal over time. This occurs when scar tissues are created when the electrode is inserted, stopping the movement of the electrode with the natural movements of the brain due to its firm nature.
These issues can be solved using graphene due to its efficient stability, flexibility, conductivity, and biocompatibility within the body.
The researchers carried out experiments in the brain cell cultures of rats and concluded that interfacing with neurons was efficient in the case of untreated graphene electrodes. Based on the studies conducted on the neurons with electron microscopy and immunofluorescence, the researchers highlighted that the neurons continued to be healthy and transmitted normal electric impulses. Negative reactions that cause damage to the scar tissue were also not seen.
The research team considered this to be the first step in using pristine graphene-based materials instead of electrodes for a neuro-interface. The team plan to examine how different types of graphene, ranging from multiple layers to monolayers, are capable of affecting neurons. The researchers also plan to analyze whether changes made to the material properties of graphene can alter the neuronal excitability and synapses in unique ways.
Hopefully this will pave the way for better deep brain implants to both harness and control the brain, with higher sensitivity and fewer unwanted side effects.
Professor Laura Ballerini, University of Trieste
“We are currently involved in frontline research in graphene technology towards biomedical applications,” said Professor Maurizio Prato from the University of Trieste. “In this scenario, the development and translation in neurology of graphene-based high-performance biodevices requires the exploration of the interactions between graphene nano- and micro-sheets with the sophisticated signaling machinery of nerve cells. Our work is only a first step in that direction.”
These initial results show how we are just scratching the tip of an iceberg when it comes to the potential of graphene and related materials in bio-applications and medicine. The expertise developed at the Cambridge Graphene Centre allows us to produce large quantities of pristine material in solution, and this study proves the compatibility of our process with neuro-interfaces.
Professor Andrea Ferrari, Director of the Cambridge Graphene Centre
The research was financially supported by the European initiative, Graphene Flagship.
25 Jan 2016
Rice University scientists embedded graphene nanoribbon-infused epoxy in a section of helicopter blade to test its ability to remove ice through Joule heating. Credit: Tour Group/Rice University
A thin coating of graphene nanoribbons in epoxy developed at Rice University has proven effective at melting ice on a helicopter blade.
The coating by the Rice lab of chemist James Tour may be an effective real-time de-icer for aircraft, wind turbines, transmission lines and other surfaces exposed to winter weather, according to a new paper in the American Chemical Society journal ACS Applied Materials and Interfaces.
In tests, the lab melted centimeter-thick ice from a static helicopter rotor blade in a minus-4-degree Fahrenheit environment. When a small voltage was applied, the coating delivered electrothermal heat – called Joule heating – to the surface, which melted the ice.
The nanoribbons produced commercially by unzipping nanotubes, a process also invented at Rice, are highly conductive. Rather than trying to produce large sheets of expensive graphene, the lab determined years ago that nanoribbons in composites would interconnect and conduct electricity across the material with much lower loadings than traditionally needed.
Previous experiments showed how the nanoribbons in films could be used to de-ice radar domes and even glass, since the films can be transparent to the eye.
“Applying this composite to wings could save time and money at airports where the glycol-based chemicals now used to de-ice aircraft are also an environmental concern,” Tour said.
In Rice’s lab tests, nanoribbons were no more than 5 percent of the composite. The researchers led by Rice graduate student Abdul-Rahman Raji spread a thin coat of the composite on a segment of rotor blade supplied by a helicopter manufacturer; they then replaced the thermally conductive nickel abrasion sleeve used as a leading edge on rotor blades. They were able to heat the composite to more than 200 degrees Fahrenheit.
For wings or blades in motion, the thin layer of water that forms first between the heated composite and the surface should be enough to loosen ice and allow it to fall off without having to melt completely, Tour said.
The lab reported that the composite remained robust in temperatures up to nearly 600 degrees Fahrenheit.
As a bonus, Tour said, the coating may also help protect aircraft from lightning strikes and provide an extra layer of electromagnetic shielding.
Explore further: Researchers create sub-10-nanometer graphene nanoribbon patterns
More information: Abdul-Rahman O. Raji et al. Composites of Graphene Nanoribbon Stacks and Epoxy for Joule Heating and Deicing of Surfaces, ACS Applied Materials & Interfaces (2016). DOI: 10.1021/acsami.5b11131
15 Jan 2016
Rice University researchers who pioneered the development of laser-induced graphene have configured their discovery into flexible, solid-state microsupercapacitors that rival the best available for energy storage and delivery.
The devices developed in the lab of Rice chemist James Tour are geared toward electronics and apparel. They are the subject of a new paper in the journal Advanced Materials.
Microsupercapacitors are not batteries, but inch closer to them as the technology improves. Traditional capacitors store energy and release it quickly (as in a camera flash), unlike common lithium-ion batteries that take a long time to charge and release their energy as needed.
14 Jan 2016
EDMONTON, ALBERTA – SUNVAULT ENERGY INC. (“Sunvault”) announced today that in conjunction with the Edison Power Company, have completed a Smartphone Battery Case that is built initially for the IPhone. Smartphone case designs for major brands such as LG and Samsung and other Smartphone manufactured devices will follow shortly. The Company will be submitting this prototype for certification and verification in order to start to fulfill the demand that exists for this product line.
The Battery Case will provide approximately 5000 mAh (milliamp hours) of energy to the first prototype IPhone model. The Battery Case prototype will be the best performing battery case on the market because of one of its most compelling features.
That feature being that the case will charge in roughly 3 minutes and will provide approximately 200% of additional power for most smartphones that are in the average 2400 mAh battery range. As displays on Smartphones become larger and usage becomes more and more prevalent, increasing energy to these devices will be widely accepted by the pent up demand for better energy solutions by the 2 Billion Smartphone users worldwide.
In addition to the fast charging, the case will not experience or generate any significant heat, and will have the unique attributes of both a battery and Supercapacitor. Additional attributes will include superior cycles that will go far beyond the Lithium Ion spec of 500 cycles of charge / discharge before battery requires replacement. It will be considerably lighter than current products on the market and will form the perfect marriage between Smartphone requirements of protection and esthetics of a case, combined with energy release and quick recharge that is necessary for today’s enjoyment of these devices. The Company will start by focusing on the top Smartphone lines, which include: Samsung, Apple IPhone, Lenovo, LG, Huawei, Xiaomi and Sony.
Edison Power Company will be launching a KICKSTARTER campaign for all Smartphone users in the near future. Smartphone users will want to stay tuned for details of the campaign that will be further described just prior to launch. This will be a unique opportunity for Smartphone users to be first in line to receive the 5000 mAh battery case.
Supercapacitors can be charged and discharged tens of thousands of times, but their relatively low energy density compared to conventional batteries limits their application for energy storage. Now, A*STAR researchers have developed an ‘asymmetric’ supercapacitor based on metal nitrides and graphene that could be a viable energy storage solution (“All Metal Nitrides Solid-State Asymmetric Supercapacitors”).
|llustration of the asymmetric supercapacitor, consisting of vertically aligned graphene nanosheets coated with iron nitride and titanium nitride as the anode and cathode, respectively. (©WILEY-VCH Verlag)|
|A supercapacitor’s viability is largely determined by the materials of which its anodes and cathodes are comprised. These electrodes must have a high surface area per unit weight, high electrical conductivity and capacitance and be physically robust so they do not degrade during operation in liquid or hostile environments.|
|Unlike traditional supercapacitors, which use the same material for both electrodes, the anode and cathode in an asymmetric supercapacitor are made up of different materials. Scientists initially used metal oxides as asymmetric supercapacitor electrodes, but, as metal oxides do not have particularly high electrical conductivities and become unstable over long operating cycles, it was clear that a better alternative was needed.|
|Metal nitrides such as titanium nitride, which offer both high conductivity and capacitance, are a promising alternative, but they tend to oxidize in watery environments that limits their lifetime as an electrode. A solution to this is to combine them with more stable materials.|
|Hui Huang from A*STAR’s Singapore Institute of Manufacturing Technology and his colleagues from Nanyang Technological University and Jinan University, China, have fabricated asymmetric supercapacitors which incorporate metal nitride electrodes with stacked sheets of graphene.|
|To get the maximum benefit from the graphene surface, the team used a precise method for creating thin-films, a process known as atomic layer deposition, to grow two different materials on vertically aligned graphene nanosheets: titanium nitride for their supercapacitor’s cathode and iron nitride for the anode. The cathode and anode were then heated to 800 and 600 degrees Celsius respectively, and allowed to slowly cool. The two electrodes were then separated in the asymmetric supercapacitor by a solid-state electrolyte, which prevented the oxidization of the metal nitrides.|
|The researchers tested their supercapacitor devices and showed they could cycle 20,000 times and exhibited both high capacitance and high power density. “These improvements are due to the ultra-high surface area of the vertically aligned graphene substrate and the atomic layer deposition method that enables full use of it,” says Huang. “In future research, we want to enlarge the working-voltage of the device to increase energy density further still,” says Huang.|
17 Nov 2015
Ultrasensitive gas sensors based on the infusion of boron atoms into graphene—a tightly bound matrix of carbon atoms—may soon be possible, according to an international team of researchers from six countries.
Graphene is known for its remarkable strength and ability to transport electrons at high speed, but it is also a highly sensitive gas sensor. With the addition of boron atoms, the boron graphene sensors were able to detect noxious gas molecules at extremely low concentrations, parts per billion in the case of nitrogen oxides and parts per million for ammonia, the two gases tested to date. This translates to a 27 times greater sensitivity to nitrogen oxides and 10,000 times greater sensitivity to ammonia compared to pristine graphene. The researchers believe these results, reported today (Nov. 2) in the Proceedings of the National Academy of Sciences, will open a path to high-performance sensors that can detect trace amounts of many other molecules.
“This is a project that we have been pursuing for the past four years, ” said Mauricio Terrones, professor of physics, chemistry and materials science at Penn State. “We were previously able to dope graphene with atoms of nitrogen, but boron proved to be much more difficult. Once we were able to synthesize what we believed to be boron graphene, we collaborated with experts in the United States and around the world to confirm our research and test the properties of our material.”
Both boron and nitrogen lie next to carbon on the periodic table, making their substitution feasible. But boron compounds are very air sensitive and decompose rapidly when exposed to the atmosphere. One-centimeter-square sheets were synthesized at Penn State in a one-of-a-kind bubbler-assisted chemical vapor deposition system. The result was large-area, high-quality boron-doped graphene sheets.
Once fabricated, the researchers sent boron graphene samples to researchers at the Honda Research Institute USA Inc., Columbus, Ohio, who tested the samples against their own highly sensitive gas sensors. Konstantin Novoselov’s lab at the University of Manchester, UK, studied the transport mechanism of the sensors. Novoselov was the 2010 Nobel laureate in physics. Theory collaborators in the U.S. and Belgium matched the scanning tunneling microscopy images to experimental images, confirmed the presence of the boron atoms in the graphene lattice and their effect when interacting with ammonia or nitrogen oxide molecules. Collaborators in Japan and China also contributed to the research.
“This multidisciplinary research paves a new avenue for further exploration of ultrasensitive gas sensors,” said Avetik Harutyunyan, chief scientist and project leader at Honda Research Institute USA Inc. “Our approach combines novel nanomaterials with continuous ultraviolet light radiation in the sensor design that have been developed in our laboratory by lead researcher Dr. Gugang Chen in the last five years. We believe that further development of this technology may break the parts per quadrillion level of detection limit, which is up to six orders of magnitude better sensitivity than current state-of-the-art sensors.”
These sensors can be used for labs and industries that use ammonia, a highly corrosive health hazard, or to detect nitrogen oxides, a dangerous atmospheric pollutant emitted from automobile tailpipes. In addition to detecting toxic or flammable gases, theoretical work indicates that boron-doped graphene could lead to improved lithium-ion batteries and field-effect transistors, the authors report.
Explore further: Study opens graphene band-gap
More information: Ultrasensitive gas detection of large-area boron-doped graphene, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1505993112