Nanoparticles for clean drinking water

One way of removing harmful nitrate from drinking water is to catalyse its conversion to nitrogen. This process suffers from the drawback that it often produces ammonia. By using palladium nanoparticles as a catalyst, and by carefully controlling their size, this drawback can be partially eliminated. It was research conducted by Yingnan Zhao of the University of Twente's MESA+ Institute for Nanotechnology that led to this discovery.

Due to the excessive use of fertilizers, our groundwater is contaminated with nitrates, which pose a problem if they enter the mains water supply. Levels have fallen significantly in recent years, as a result of various European directives. In addition, the Integrated Approach to Nitrogen programme was launched in various Dutch nature reserves at the start of January. Tackling the problem at source is one thing, but it will still be necessary to treat the mains water supply. While this can be achieved through biological conversion (using bacteria to convert the nitrate to nitrogen gas), this is a slow process. Using palladium to catalyse the conversion of nitrate to nitrogen speeds up the process enormously. However, this reaction suffers from the drawback that it produces a harmful by-product -- ammonia.
Exposed surface
The amount of ammonia produced appears to depend on the method used to prepare the palladium and on the catalyst's physical structure. Yingnan Zhao decided to use nanometre-sized colloidal palladium particles, as their dimensions can be easily controlled. These particles are fixed to a surface, so they do not end up in the mains water supply. However, it is important to stop them clumping together, so stabilizers such as polyvinyl alcohol are added. Unfortunately, these stabilizers tend to shield the surface of the palladium particles, which reduces their effectiveness as a catalyst. By introducing additional treatments, Yingnan Zhao has managed to fully expose the catalytic surface once again or to manipulate it in a controlled manner. This has resulted in palladium nanoparticles that can catalyse the conversion to nitrogen, while producing very little ammonia. This has brought the further development of catalytic water treatment (in compact devices for home use, for example) one step closer.
Yingnan Zhao, who is from Heze, Shandong, China, conducted his research in Prof. Leon Lefferts' Catalytic Processes and Materials group. He defended his thesis, which is entitled "Colloidal Nanoparticles as Catalysts and Catalyst Precursors for Nitrite Hydrogenation" on Thursday 15 January.

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Record-breaking black hole outburst detected

An image of a simulation of the gas cloud's encounter with Sgr A*. The blue lines mark the orbits of the so-called "S" stars that are in close orbits around the supermassive black hole

Last September, after years of watching, a team of scientists led by Amherst College astronomy professor Daryl Haggard observed and recorded the largest-ever flare in X-rays from a supermassive black hole at the center of the Milky Way. The astronomical event, which was detected by NASA's Chandra X-ray Observatory, puts the scientific community one step closer to understanding the nature and behavior of supermassive black holes.

Haggard and her colleagues discussed the flare today during this year's meeting of the American Astronomical Society in Seattle.
Supermassive black holes are the largest of black holes, and all large galaxies have one. The one at the center of our galaxy, the Milky Way, is called Sagittarius A* (or, Sgr A*, as it is called), and scientists estimate that it contains about four and a half million times the mass of our Sun.
Scientists working with Chandra have observed Sgr A* repeatedly since the telescope was launched into space in 1999. Haggard and fellow astronomers were originally using Chandra to see if Sgr A* would consume parts of a cloud of gas, known as G2.
"Unfortunately, the G2 gas cloud didn't produce the fireworks we were hoping for when it got close to Sgr A*," she said. "However, nature often surprises us and we saw something else that was really exciting."
Haggard and her team detected an X-ray outburst last September that was 400 times brighter than the usual X-ray output from Sgr A*. This "megaflare" was nearly three times brighter than the previous record holder that was seen in early 2012. A second enormous X-ray flare, 200 times brighter than Sgr A* in its quiet state, was observed with Chandra on October 20, 2014.
Haggard and her team have two main ideas about what could be causing Sgr A* to erupt in this extreme way. One hypothesis is that the gravity of the supermassive black hole has torn apart a couple of asteroids that wandered too close. The debris from such a "tidal disruption" would become very hot and produce X-rays before disappearing forever across the black hole's point of no return (called the "event horizon").
"If an asteroid was torn apart, it would go around the black hole for a couple of hours -- like water circling an open drain -- before falling in," said colleague and co-principal investigator Fred Baganoff of the Massachusetts Institute of Technology in Cambridge, MA. "That's just how long we saw the brightest X-ray flare last, so that is an intriguing clue for us to consider."
If that theory holds up, it means astronomers have found evidence for the largest asteroid ever to be torn apart by the Milky Way's black hole.
Another, different idea is that the magnetic field lines within the material flowing towards Sgr A* are packed incredibly tightly. If this were the case, these field lines would occasionally interconnect and reconfigure themselves. When this happens, their magnetic energy is converted into the energy of motion, heat and the acceleration of particles -- which could produce a bright X-ray flare. Such magnetic flares are seen on the Sun, and the Sgr A* flares have a similar pattern of brightness levels to the solar events.
"At the moment, we can't distinguish between these two very different ideas," said Haggard. "It's exciting to identify tensions between models and to have a chance to resolve them with present and future observations."
In addition to the giant flares, Haggard and her team also collected more data on a magnetar -- a neutron star with a strong magnetic field -- located close to Sgr A*. This magnetar is undergoing a long X-ray outburst, and the Chandra data are allowing astronomers to better understand this unusual object.
As for the G2: Astronomers estimate that the gas cloud made its closest approach -- still about 15 billion miles away from the edge of the black hole -- in the spring of 2014. The researchers estimate the record breaking X-ray flares were produced about a hundred times closer to the black hole, making it very unlikely that the Chandra flares were associated with G2.

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Flexible methane production from electricity and bio-mass

The DemoSNG plant was installed into a standard shipping container (12 m x 2.4 m x 2.4 m) and is mobile

Interlinkage of the power and gas grids is planned to make electricity supply sustainable and robust in the future. Fluctuating amounts of wind and solar power, for instance, might be stored in the form of the chemical energy carrier methane. Researchers of the KIT and DVGW have now proved that this element of the Energiewende is technically feasible. The DemoSNG pilot plant constructed by the KIT will be used in Sweden for the reliable and efficient production of methane from biomass-based carbon dioxide and variable amounts of hydrogen from green power.

"The variable operation modes were the biggest challenge during development," says Project Head Siegfried Bajohr of the Engler-Bunte Institute (EBI) of KIT. From the products of a biomass gasification plant, i.e. hydrogen, carbon dioxide, and carbon monoxide, the DemoSNG pilot plant directly produces methane and water by means of a nickel catalyst (SNG operation). If green power is available, it is used for electrolysis and the production of additional hydrogen. Then, the volume flow in the plant can be doubled, utilization of carbon from biomass will increase to nearly 100%, and a large amount of usable waste heat will be produced by the catalyst (PtG operation).
"As conventional methanation processes reach their limits at this point, we have developed a new reactor concept," Bajohr says. The initial feedstock flows meet in a honeycomb catalyst carrier that can be designed for the efficient operation of both modes and mixing states."The DemoSNG plant shows that our concept also works in a large-scale pilot plant." Metallic honeycombs are already used as catalytic convertors of exhaust gas in cars. They are characterized by a high thermal conductivity and mechanical robustness with a low pressure loss during alternating operation modes.
The DemoSNG plant was installed into a standard shipping container (12 m x 2.4 m x 2.4 m) and is mobile. The first tests of operation at KIT have now been completed. The plant will be moved to Köping in Sweden. There, it will be integrated into the gas flows of a biomass gasification plant utilizing wooden residues. The honeycomb catalyst can be implemented easily in various plant sizes. In the future, it might be possible to efficiently operate even smaller decentralized units, e.g. at rural biogas facilities.
"DemoSNG shows the way to storing green power and transporting it in our gas grids in the form of methane," Thomas Kolb, Head of the Engler-Bunte Institute of KIT, emphasizes. Frank Graf, Section Head of the test laboratory of the German Technical and Scientific Association of Gas and Water (DVGW) at KIT, adds: "So far, admixture of hydrogen in the natural gas grid has been limited to a few percent, as storage, distribution, and use require the solution of various technical problems." Methanation has the advantage that the infrastructure existing for the distribution and storage of natural gas and the standard appliances can be used further without any modifications or readjustments being required. Via an effective methanation, wind and solar power can be fed into the natural gas grid without any limitations.
"DemoSNG demonstrates how sustainable European innovations are," Karl-Friedrich Ziegahn, Head of the Natural and Built Environment Division of KIT and Chairman of the Supervisory Board of the European KIC InnoEnergy, says. With plants, such as DemoSNG, excessive green electricity can be used much better. For example, it might be converted decentrally with the carbon dioxide produced by the about 800,000 biogas facilities and stored in the form of methane. Thanks to the newly developed honeycomb catalyst, also smaller and medium-sized plants can be operated efficiently.

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New Photon Detectors – A Crucial Step Toward Quantum Chips

One of the researchers’ new photon detectors, deposited athwart a light channel — or “waveguide” (horizontal black band) — on a silicon optical chip

A team of researchers has built an array of light detectors sensitive enough to register the arrival of individual light particles, or photons, and mounted them on a silicon optical chip. Such arrays are crucial components of devices that use photons to perform quantum computations.
Single-photon detectors are notoriously temperamental: Of 100 deposited on a chip using standard manufacturing techniques, only a handful will generally work. In a paper appearing in Nature Communications, the researchers at MIT and elsewhere describe a procedure for fabricating and testing the detectors separately and then transferring those that work to an optical chip built using standard manufacturing processes.
In addition to yielding much denser and larger arrays, the approach also increases the detectors’ sensitivity. In experiments, the researchers found that their detectors were up to 100 times more likely to accurately register the arrival of a single photon than those found in earlier arrays.
“You make both parts — the detectors and the photonic chip — through their best fabrication process, which is dedicated, and then bring them together,” explains Faraz Najafi, a graduate student in electrical engineering and computer science at MIT and first author on the new paper.
Thinking small
According to quantum mechanics, tiny physical particles are, counterintuitively, able to inhabit mutually exclusive states at the same time. A computational element made from such a particle — known as a quantum bit, or qubit — could thus represent zero and one simultaneously. If multiple qubits are “entangled,” meaning that their quantum states depend on each other, then a single quantum computation is, in some sense, like performing many computations in parallel.
With most particles, entanglement is difficult to maintain, but it’s relatively easy with photons. For that reason, optical systems are a promising approach to quantum computation. But any quantum computer — say, one whose qubits are laser-trapped ions or nitrogen atoms embedded in diamond — would still benefit from using entangled photons to move quantum information around.
“Because ultimately one will want to make such optical processors with maybe tens or hundreds of photonic qubits, it becomes unwieldy to do this using traditional optical components,” says Dirk Englund, the Jamieson Career Development Assistant Professor in Electrical Engineering and Computer Science at MIT and corresponding author on the new paper. “It’s not only unwieldy but probably impossible, because if you tried to build it on a large optical table, simply the random motion of the table would cause noise on these optical states. So there’s been an effort to miniaturize these optical circuits onto photonic integrated circuits.”
The project was a collaboration between Englund’s group and the Quantum Nanostructures and Nanofabrication Group, which is led by Karl Berggren, an associate professor of electrical engineering and computer science, and of which Najafi is a member. The MIT researchers were also joined by colleagues at IBM and NASA’s Jet Propulsion Laboratory.
Relocation
The researchers’ process begins with a silicon optical chip made using conventional manufacturing techniques. On a separate silicon chip, they grow a thin, flexible film of silicon nitride, upon which they deposit the superconductor niobium nitride in a pattern useful for photon detection. At both ends of the resulting detector, they deposit gold electrodes.
Then, to one end of the silicon nitride film, they attach a small droplet of polydimethylsiloxane, a type of silicone. They then press a tungsten probe, typically used to measure voltages in experimental chips, against the silicone.
“It’s almost like Silly Putty,” Englund says. “You put it down, it spreads out and makes high surface-contact area, and when you pick it up quickly, it will maintain that large surface area. And then it relaxes back so that it comes back to one point. It’s like if you try to pick up a coin with your finger. You press on it and pick it up quickly, and shortly after, it will fall off.”
With the tungsten probe, the researchers peel the film off its substrate and attach it to the optical chip.
In previous arrays, the detectors registered only 0.2 percent of the single photons directed at them. Even on-chip detectors deposited individually have historically topped out at about 2 percent. But the detectors on the researchers’ new chip got as high as 20 percent. That’s still a long way from the 90 percent or more required for a practical quantum circuit, but it’s a big step in the right direction.
“This work is a technical tour de force,” says Robert Hadfield, a professor of photonics at the University of Glasgow who was not involved in the research. “There is potential for scale-up to large circuits requiring hundreds of detectors using commercial pick-and-place technology.”
Publication: Faraz Najafi,et al., “On-chip detection of non-classical light by scalable integration of single-photon detectors,” Nature Communications 6, Article number: 5873; doi:10.1038/ncomms6873
Source: Larry Hardesty, MIT News

Study Identifies Which Fossil Fuels Must Remain in the Ground to Limit Global Warming

New research led by the University College London shows that a third of oil reserves, half of gas reserves and over 80% of current coal reserves globally should remain in the ground and not be used before 2050 if global warming is to stay below the 2°C target agreed by policy makers

The study funded by the UK Energy Research Center and published in Nature today, also identifies the geographic location of existing reserves that should remain unused and so sets out the regions that stand to lose most from achieving the 2°C goal.
The authors show that the overwhelming majority of the huge coal reserves in China, Russia and the United States should remain unused along with over 260 thousand million barrels oil reserves in the Middle East, equivalent to all of the oil reserves held by Saudi Arabia. The Middle East should also leave over 60% of its gas reserves in the ground.
The development of resources in the Arctic and any increase in unconventional oil – oil of a poor quality which is hard to extract – are also found to be inconsistent with efforts to limit climate change.
For the study, the scientists first developed an innovative method for estimating the quantities, locations and nature of the world’s oil, gas and coal reserves and resources. They then used an integrated assessment model to explore which of these, along with low-carbon energy sources, should be used up to 2050 to meet the world’s energy needs. The model, which uses an internationally-recognized modelling framework, has multiple improvements on previous models, allowing it to provide a world-leading representation of the long-term production dynamics and resource potential of fossil fuels.
Lead author Dr Christophe McGlade, Research Associate at the UCL Institute for Sustainable Resources said: “We’ve now got tangible figures of the quantities and locations of fossil fuels that should remain unused in trying to keep within the 2°C temperature limit.
“Policy makers must realize that their instincts to completely use the fossil fuels within their countries are wholly incompatible with their commitments to the 2°C goal. If they go ahead with developing their own resources, they must be asked which reserves elsewhere should remain unburnt in order for the carbon budget not to be exceeded.”
Co-author Professor Paul Ekins, Professor of Resources and Environmental Policy at and Director of the UCL Institute for Sustainable Resources, who received an OBE for services to environmental policy in the 2015 New Year’s Honors list, said: “Companies spent over $670 billion (£430 billion) last year searching for and developing new fossil fuel resources. They will need to rethink such substantial budgets if policies are implemented to support the 2°C limit, especially as new discoveries cannot lead to increased aggregate production.
“Investors in these companies should also question spending such budgets. The greater global attention to climate policy also means that fossil fuel companies are becoming increasingly risky for investors in terms of the delivery of long-term returns. I would expect prudent investors in energy to shift increasingly towards low-carbon energy sources.”
The scientists’ analysis shows that their results are consistent with a wide variety of alternative modelling approaches from groups across the world with differing assumptions. Building on this analysis, their future work aims to investigate further the shifts in cumulative fossil fuel production between scenarios that lead to different long-term average global temperature rises
Publication: Christophe McGlade & Paul Ekins, “The geographical distribution of fossil fuels unused when limiting global warming to 2 °C,” Nature 517, 187–190 (08 January 2015); doi:10.1038/nature14016
Source: University College London

Study Details Why Super-Earths Have Long-Lasting Oceans

This artist’s depiction shows a gas giant planet rising over the horizon of an alien waterworld.

A newly published study from the Harvard-Smithsonian Center for Astrophysics reveals why oceans on super-Earths, once established, can last for billions of years.
Cambridge, Massachusetts – For life as we know it to develop on other planets, those planets would need liquid water, or oceans. Geologic evidence suggests that Earth’s oceans have existed for nearly the entire history of our world. But would that be true of other planets, particularly super-Earths? New research suggests the answer is yes and that oceans on super-Earths, once established, can last for billions of years.
“When people consider whether a planet is in the habitable zone, they think about its distance from the star and its temperature. However, they should also think about oceans, and look at super-Earths to find a good sailing or surfing destination,” says lead author Laura Schaefer of the Harvard-Smithsonian Center for Astrophysics (CfA).
Schaefer presented her findings today in a press conference at a meeting of the American Astronomical Society.
Even though water covers 70 percent of Earth’s surface, it makes up a very small fraction of the planet’s overall bulk. Earth is mostly rock and iron; only about a tenth of a percent is water.
“Earth’s oceans are a very thin film, like fog on a bathroom mirror,” explains study co-author Dimitar Sasselov (CfA).
However, Earth’s water isn’t just on the surface. Studies have shown that Earth’s mantle holds several oceans’ worth of water that was dragged underground by plate tectonics and subduction of the ocean seafloor. Earth’s oceans would disappear due to this process, if it weren’t for water returning to the surface via volcanism (mainly at mid-ocean ridges). Earth maintains its oceans through this planet-wide recycling.
Schaefer used computer simulations to see if this recycling process would take place on super-Earths, which are planets up to five times the mass, or 1.5 times the size, of Earth. She also examined the question of how long it would take oceans to form after the planet cooled enough for its crust to solidify.
She found that planets two to four times the mass of Earth are even better at establishing and maintaining oceans than our Earth. The oceans of super-Earths would persist for at least 10 billion years (unless boiled away by an evolving red giant star).
Interestingly, the largest planet that was studied, five times the mass of Earth, took a while to get going. Its oceans didn’t develop for about a billion years, due to a thicker crust and lithosphere that delayed the start of volcanic outgassing.
“This suggests that if you want to look for life, you should look at older super-Earths,” Schaefer says.
Sasselov agrees. “It takes time to develop the chemical processes for life on a global scale, and time for life to change a planet’s atmosphere. So, it takes time for life to become detectable.”
This also suggests that, assuming evolution takes place at a similar rate to Earth’s, you want to search for complex life on planets that are about five and a half billion years old, a billion years older than Earth.
Headquartered in Cambridge, Massachusetts, the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.
Publication: Accepted for publication at the Astrophysical Journal
PDF Copy of the Study: The persistence of oceans on Earth-like planets: insights from the deep-water cycle
Source: Harvard-Smithsonian Center for Astrophysics

Atoms queue up for quantum computer networks

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In order to develop future quantum computer networks, it is necessary to hold a known number of atoms and read them without them disappearing. To do this, researchers from the Niels Bohr Institute have developed a method with a trap that captures the atoms along an ultra thin glass fiber, where the atoms can be controlled. The results are published in the scientific journal, Physical Review Letters.

The research is carried out in the quantum optics laboratory in the basement of the Niels Bohr Institute in Copenhagen. The underground laboratory is set back from the road so there are no vibrations from traffic. Here, the researchers have designed experiments in which they can perform ultrasensitive trials with quantum optics.
"We have an ultra-thin glass fiber with a diameter of half a micrometer (a hundred times smaller than a strand of hair). Along this glass fiber we capture cesium atoms. They are cooled down to 100 micro Kelvin using a laser -- this is almost absolute zero, which is equivalent to minus 273 degrees Celsius. This system acts like a trap that holds the atoms on the side of the glass fiber," explains Jürgen Appel, Associate Professor in the research group Quantop at the Niels Bohr Institute, University of Copenhagen.
Atoms and light linked together
When light is transmitted through the glass fiber thread, the light will also move along the surface because the fiber is thinner than wavelength of the light. This creates strong interaction between the light and the atoms sitting securely above the surface of the fiber.
"We have developed a method where we can measure the number of atoms. We send two laser beams with different frequencies through the glass fiber. If there were no atoms on the fiber, the speed of light would be the same for both light beams. However, the atoms affect the two frequencies differently and by measuring the difference in the speed of light for the two light beams on each side of the atoms' absorption lines, you can measure the number of atoms along the fiber. We have shown that we can hold 2,500 atoms with an uncertainty of just eight atoms," says Jürgen Appel.
These are fantastic results. Without this method, you would have to use resonant light (light that the atoms absorb) and then you would scatter photons, which would kick the atoms out of the trap, says Jürgen Appel and explains that with this new method they can measure and control the atoms so that only 14 percent are kicked out of the trap and are lost.
"Our resolution is only limited by the natural quantum noise (the laser light's own minimal fluctuations) so our method could be used for so-called entangled states of atoms along the fiber. Such an entangled system with strongly interacting atoms and light is of great interest for future quantum computer networks," notes Jürgen Appel.

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Journal Reference:

1. J.-B. Béguin, E. M. Bookjans, S. L. Christensen, H. L. Sørensen, J. H. Müller, E. S. Polzik, J. Appel. Generation and Detection of a Sub-Poissonian Atom Number Distribution in a One-Dimensional Optical Lattice. Physical Review Letters, 2014; 113 (26) DOI: 10.1103/PhysRevLett.113.263603

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