Graphene’s love affair with water: Water filters allow precise and fast sieving of salts and organic molecules

Graphene has proven itself as a wonder material with a vast range of unique properties. Among the least-known marvels of graphene is its strange love affair with water.Graphene is hydrophobic — it repels water — but narrow capillaries made from graphene vigorously suck in water allowing its rapid permeation, if the water layer is only one atom thick — that is, as thin as graphene itself.This bizarre property has attracted intense academic and industrial interest with intent to develop new water filtration and desalination technologies.One-atom-wide graphene capillaries can now be made easily and cheaply by piling layers of graphene oxide — a derivative of graphene — on top of each other. The resulting multilayer stacks (laminates) have a structure similar to nacre (mother of pearl), which makes them also mechanically strong.Two years ago, University of Manchester researchers discovered that thin membranes made from such laminates were impermeable to all gases and vapours, except for water. This means that even helium, the hardest gas to block off, cannot pass through the membranes whereas water vapour went through with no resistance.Now the same team led by Dr Rahul Nair and Prof Andre Geim has tested how good the graphene membranes are as filters for liquid water. The results appear in the latest issue (Feb 14, 2014) of Science.The researchers report that, if immersed in water, the laminates become slightly swollen but still allow ultrafast flow of not one but two monolayers of water.Small salts with a size of less than nine Angstroms can flow along but larger ions or molecules are blocked. Ten Angstroms is equivalent to a billionth of a metre.The graphene filters have an astonishingly accurate mesh that allows them to distinguish between atomic species that are only a few percent different in size.On top of this ultraprecise separation, it is also ultrafast. Those ions that can go through do so with such a speed as if the graphene membranes were an ordinary coffee filter.The latter effect is due to a property that the Manchester scientists call “ion sponging.” Their graphene capillaries suck up small ions as powerful hoovers leading to internal concentrations that can be hundreds of times higher than in external salty solutions.Dr Nair said: “The water filtration is as fast and as precise as one could possibly hope for such narrow capillaries. Now we want to control the graphene mesh size and reduce it below nine Angstroms to filter out even the smallest salts like in seawater. Our work shows that it is possible.”Dr Irina Grigorieva, a co-author of the study, added: “Our ultimate goal is to make a filter device that allows a glass of drinkable water made from seawater after a few minutes of hand pumping. We are not there yet but this is no longer science fiction.”Story Source:The above story is based on materials provided by University of Manchester. …

Read more

Hubble bubble may explain different measurements of expansion rate of the universe

Sep. 9, 2013 — The existence of the “Hubble Bubble” may explain, at least in part, the differing measurements for the expansion and therefore the age of the universe. That is the assumption of a team of physicists headed by Prof. Dr. Luca Amendola from the Institute for Theoretical Physics at Heidelberg University. In collaboration with colleagues from the Netherlands, the Heidelberg physicists developed a theoretical model that places the Milky Way inside of this type of cosmic bubble. The researchers believe the bubble can explain some of the deviations between previous measurements and the latest ones from the Planck satellite of the European Space Agency (ESA).The results of their research were published in the journal Physical Review Letters.The observable universe has been expanding since the Big Bang. It still is, causing galaxies in our Milky Way to recede. The actual speed of this expansion is known as the Hubble constant. Due to its importance in calculating basic properties of the universe, such as its age, modern cosmology is tasked with determining the value of the constant. …

Read more

Temperature in the quantum world

Sep. 9, 2013 — How does a classical temperature form in the quantum world? An experiment at the Vienna University of Technology has directly observed the emergence and the spreading of a temperature in a quantum system. Remarkably, the quantum properties are lost, even though the quantum system is completely isolated and not connected to the outside world. The experimental results are being published in this week’s issue of Nature Physics.Quantum and Classical Physics: From the Microscopic to the Macroscopic WorldThe connection between the microscopic world of quantum physics and our everyday experience, which is concerned with much larger objects, still remains puzzling. When a quantum system is measured, it is inevitably disturbed and some of its quantum properties are lost.A cloud of atoms, for example, can be prepared in such away that each atom is simultaneously located at two different places, forming a perfect quantum superposition. As soon as the location of the atoms is measured, however, this superposition is destroyed. All that is left are atoms sitting at some well-defined places. They behave just as classical objects would.In this case, the transition from quantum behavior to classical behavior is initiated by the measurement — a contact with the outside world. But what happens, if a quantum system is not influenced from the outside at all? …

Read more

Weeds threaten carbon offset programs

Aug. 12, 2013 — Researchers have identified gamba grass and other invasive weeds as a potential threat to landholder involvement in environmental offset programs such as the Carbon Farming Initiative.Strategic savanna burning is one way to reduce Australia’s carbon emissions and create new markets in northern Australia, but the increased fuel load and emissions from weed infestations could make it unfeasible.Dr Vanessa Adams says that late dry season wildfires in Australia’s tropical north generate about 3% of the country’s annual greenhouse gas emissions, so strategic burning could be an important abatement activity.”But when native savannas are invaded by weeds such as gamba grass, fuel loads are dramatically increased and fires can burn up to five times hotter than a native wildfire,” Dr Adams said.”We examined the spatial and financial extent of the threat of gamba grass and found that 75% of the area across northern Australia suitable for savanna burning is also highly suitable for gamba grass.”There’s a large disparity between the profits generated from savanna burning — $1.92 per hectare — and the costs of managing gamba grass — $40 per hectare — meaning that much more savanna needs to be enrolled for carbon farming to cover the costs of weed eradication.”The good news is that in the Northern Territory, only about 20% of properties that could run profitable savanna burning programs had gamba grass, and of these, about 16% had small infestations.”A one-off investment of $200,000 would eradicate these infestations, and for the majority of properties that are gamba free, an effective control program would safeguard them into the future.”It’s really important we look at how these types of barriers might prevent landholders from getting involved in environmental offset programs and that we strategically manage weeds so that they don’t become an intractable problem in the future.”

Read more

How fish swim: Researchers examine mechanical bases for the emergence of undulatory swimmers

June 24, 2013 — How do fish swim? It is a simple question, but there is no simple answer.Researchers at Northwestern University have revealed some of the mechanical properties that allow fish to perform their complex movements. Their findings, published on June 13 in the journal PLOS Computational Biology, could provide insights in evolutionary biology and lead to an understanding of the neural control of movement and development of bio-inspired underwater vehicles.”If we could play God and create an undulatory swimmer, how stiff should its body be? At what wave frequency should its body undulate so it moves at its top speed? How does its brain control those movements?” said Neelesh Patankar, professor of mechanical engineering at Northwestern’s McCormick School of Engineering and Applied Science. “Millennia ago, undulatory swimmers like eels that had the right mechanical properties are the ones that would have survived.”The researchers used computational methods to test assumptions about the preferred evolutionary characteristics. For example, species with low muscle activation frequency and high body stiffness are the most successful; the researchers found the optimal values for each property.”The stiffness that we predict for good swimming characteristics is, in fact, the same as the experimentally determined stiffness of undulatory swimmers with a backbone,” said Amneet Bhalla, graduate student in mechanical engineering at McCormick and one of the paper’s authors.”Thus, our results suggest that precursors of a backbone would have given rise to animals with the appropriate body stiffness,” added Patankar. “We hypothesize that this would have been mechanically beneficial to the evolutionary emergence of swimming vertebrates.”In addition, species must be resilient to small changes in physical characteristics from one generation to the next. The researchers confirmed that the ability to swim, while dependent upon mechanical parameters, is not sensitive to minor generational changes; as long as the body stiffness is above a certain value, the ability to swim quickly is insensitive to the value of the stiffness, the researchers found.Finally, making a connection to the neural control of movement, the researchers analyzed the curvature of its undulations to determine if it was the result of a single bending torque, or if precise bending torques were necessary at every point along its body. They learned that a simple movement pattern gives rise to the complicated-looking deformation.”This suggests that the animal does not need precise control of its movements,” Patankar said.To make these determinations, the researchers applied a common physics concept known as “spring mass damper” — a model, applied to everything from car suspension to Slinkies, that determines movement in systems that are losing energy — to the body of the fish.This novel approach for the first time unified the concepts of active and passive swimming — swimming in which forcing comes from within the fish (active) or from the surrounding water (passive) — by calculating the conditions necessary for the fish to swim both actively and passively.

Read more

Surgeons implant bioengineered vein: Kidney dialysis patient first in U.S. to receive lab-grown blood vessel

June 6, 2013 — In a first-of-its-kind operation in the United States, a team of doctors at Duke University Hospital helped create a bioengineered blood vessel and implanted it into the arm of a patient with end-stage kidney disease.The procedure, the first U.S. clinical trial to test the safety and effectiveness of the bioengineered blood vessel, is a milestone in the field of tissue engineering. The new vein is an off-the-shelf, human cell-based product with no biological properties that would cause organ rejection.Using technology developed at Duke and at a spin-off company it started called Humacyte, the vein is engineered by cultivating donated human cells on a tubular scaffold to form a vessel. The vessel is then cleansed of the qualities that might trigger an immune response. In pre-clinical tests, the veins have performed better than other synthetic and animal-based implants.”This is a pioneering event in medicine,” said Jeffrey H. Lawson, M.D., PhD, a vascular surgeon and vascular biologist at Duke Medicine who helped develop the technology and performed the implantation. “It’s exciting to see something you’ve worked on for so long become a reality. We talk about translational technology — developing ideas from the laboratory to clinical practice — and this only happens where there is the multi-disciplinary support and collaboration to cultivate it.”Clinical trials to test the new veins began in Poland in December with the first human implantations. The U.S. Food and Drug Administration recently approved a phase 1 trial involving 20 kidney dialysis patients in the United States, followed by a safety review. …

Read more

Utilizzando il sito, accetti l'utilizzo dei cookie da parte nostra. maggiori informazioni

The cookie settings on this website are set to "allow cookies" to give you the best browsing experience possible. If you continue to use this website without changing your cookie settings or you click "Accept" below then you are consenting to this.