Tuesday, 25 February 2014

Bullying black holes force galaxies to stay red and dead

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Astronomers have discovered massive elliptical galaxies in the nearby Universe containing plenty of cold gas, even though the galaxies fail to produce new stars. Comparison with other data suggests that, while hot gas cools down in these galaxies, stars do not form because jets from the central supermassive black hole heat or stir up the gas and prevent it from turning into stars. Giant elliptical galaxies are the most puzzling type of galaxy in the Universe.

via Science Daily

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Water detected in a planet outside our solar system

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Water has been detected in the atmosphere of a planet outside our solar system with a new technique that could help researchers to learn how many planets with water, like Earth, exist throughout the universe. The team of scientists that made the discovery detected the water in the atmosphere of a planet as massive as Jupiter that is orbiting the nearby star tau Bo├Âtis.

via Science Daily

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Rare form of nitrogen detected in comet ISON

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Astronomers observed the Comet ISON during its bright outburst in the middle of November 2013. Subaru Telescope's High Dispersion Spectrograph has detected two rare forms of nitrogen in the comet ISON. Their results support the hypothesis that there were two distinct reservoirs of nitrogen the massive, dense cloud ("solar nebula") from which our Solar System may have formed and evolved.

via Science Daily

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How to create selective holes in graphene

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Researchers have devised a way of making tiny holes of controllable size in sheets of graphene, a development that could lead to ultrathin filters for improved desalination or water purification.



The team of researchers at MIT, Oak Ridge National Laboratory, and in Saudi Arabia succeeded in creating subnanoscale pores in a sheet of the one-atom-thick material, which is one of the strongest materials known. Their findings are published in the journal Nano Letters.



The concept of using graphene, perforated by nanoscale pores, as a filter in desalination has been proposed and analyzed by other MIT researchers. The new work, led by graduate student Sean O’Hern and associate professor of mechanical engineering Rohit Karnik, is the first step toward actual production of such a graphene filter.



Making these minuscule holes in graphene — a hexagonal array of carbon atoms, like atomic-scale chicken wire — occurs in a two-stage process. First, the graphene is bombarded with gallium ions, which disrupt the carbon bonds. Then, the graphene is etched with an oxidizing solution that reacts strongly with the disrupted bonds — producing a hole at each spot where the gallium ions struck. By controlling how long the graphene sheet is left in the oxidizing solution, the MIT researchers can control the average size of the pores.



A big limitation in existing nanofiltration and reverse-osmosis desalination plants, which use filters to separate salt from seawater, is their low permeability: Water flows very slowly through them. The graphene filters, being much thinner, yet very strong, can sustain a much higher flow. “We’ve developed the first membrane that consists of a high density of subnanometer-scale pores in an atomically thin, single sheet of graphene,” O’Hern says.



For efficient desalination, a membrane must demonstrate “a high rejection rate of salt, yet a high flow rate of water,” he adds. One way of doing that is decreasing the membrane’s thickness, but this quickly renders conventional polymer-based membranes too weak to sustain the water pressure, or too ineffective at rejecting salt, he explains.



With graphene membranes, it becomes simply a matter of controlling the size of the pores, making them “larger than water molecules, but smaller than everything else,” O’Hern says — whether salt, impurities, or particular kinds of biochemical molecules.



The permeability of such graphene filters, according to computer simulations, could be 50 times greater than that of conventional membranes, as demonstrated earlier by a team of MIT researchers led by graduate student David Cohen-Tanugi of the Department of Materials Science and Engineering. But producing such filters with controlled pore sizes has remained a challenge. The new work, O’Hern says, demonstrates a method for actually producing such material with dense concentrations of nanometer-scale holes over large areas.



“We bombard the graphene with gallium ions at high energy,” O’Hern says. “That creates defects in the graphene structure, and these defects are more chemically reactive.” When the material is bathed in a reactive oxidant solution, the oxidant “preferentially attacks the defects,” and etches away many holes of roughly similar size. O’Hern and his co-authors were able to produce a membrane with 5 trillion pores per square centimeter, well suited to use for filtration. “To better understand how small and dense these graphene pores are, if our graphene membrane were to be magnified about a million times, the pores would be less than 1 millimeter in size, spaced about 4 millimeters apart, and span over 38 square miles, an area roughly half the size of Boston,” O’Hern says.



With this technique, the researchers were able to control the filtration properties of a single, centimeter-sized sheet of graphene: Without etching, no salt flowed through the defects formed by gallium ions. With just a little etching, the membranes started allowing positive salt ions to flow through. With further etching, the membranes allowed both positive and negative salt ions to flow through, but blocked the flow of larger organic molecules. With even more etching, the pores were large enough to allow everything to go through.



Scaling up the process to produce useful sheets of the permeable graphene, while maintaining control over the pore sizes, will require further research, O’Hern says.



Karnik says that such membranes, depending on their pore size, could find various applications. Desalination and nanofiltration may be the most demanding, since the membranes required for these plants would be very large. But for other purposes, such as selective filtration of molecules — for example, removal of unreacted reagents from DNA — even the very small filters produced so far might be useful.



“For biofiltration, size or cost are not as critical,” Karnik says. “For those applications, the current scale is suitable.”



Bruce Hinds, a professor of materials engineering at the University of Kentucky who was not involved in this work, says, “Previous groups had tried just ion bombardment or plasma radical formation.” The idea of combining these methods “is nice and has the potential to be fine-tuned.” While more work needs to be done to refine the technique, he says, this approach is “promising” and could ultimately help to lead to applications in “water purification, energy storage, energy production, [and] pharmaceutical production.”



The work also included Jing Kong, the ITT Career Development Associate Professor of Electrical Engineering; MIT graduate students Michael Boutilier and Yi Song; researcher Juan-Carlos Idrobo of the Oak Ridge National Laboratory; and professors Tahar Laoui and Muataz Atieh of the King Fahd University of Petroleum and Minerals (KFUPM). The project received support from the Center for Clean Water and Clean Energy at MIT and KFUPM and the U.S. Department of Energy.



via MIT News

Crab Nebula Astronomy and Science Poster

Here's a great poster featuring a beautiful image from deep space

after scouring the Zazzle market place for a while, I settled on this as my choice for today. By walgenn, another talented creative from the Zazzle community!


tagged with: astronomy, astronomer, scientist, science, space, gift, space gift, astronomy gift, science gift, nebula, star, universe, hubble, hubble space telescope, nasa, astrophysicist, astrophysics, super nova, space exploration, big bang, birthday gift, graduation gift, unique gift idea, poster, print, astronomy poster, space poster, hubble poster, nebula poster, crab nebula, supernova

Crab Nebula a supernova explosion remnant - this striking image by the Hubble Space Telescope, is a unique gift idea for the space science, astronmer and astrophysics enthusiast on you Holiday gift list or a special gift for any occasion.

»visit the walgenn store for more designs and products like this
Click to customize with size, paper type etc.
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The Pleiades Deep and Dusty

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The well known Pleiades star cluster is slowly destroying part of a passing cloud of gas and dust. The Pleiades is the brightest open cluster of stars on Earth's sky and can be seen from almost any northerly location with the unaided eye. The passing young dust cloud is thought to be part of Gould's belt, an unusual ring of young star formation surrounding the Sun in the local Milky Way Galaxy. Over the past 100,000 years, part Gould's belt is by chance moving right through the older Pleiades and is causing a strong reaction between stars and dust. Pressure from the star's light significantly repels the dust in the surrounding blue reflection nebula, with smaller dust particles being repelled more strongly. A short-term result is that parts of the dust cloud have become filamentary and stratified, as seen in the above deep-exposure image.
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CVD graphene suitable for transistors and surface chemistry studies

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With exceptional carrier mobilities, mechanical strength, and optical transparency, graphene is a leading material for next-generation electronic devices. However, for most applications, graphene will need to be integrated with other materials, which motivates efforts to understand and tune its surface chemistry. In recent work, published in the scientific journal Small, scientists from the University of Groningen in the Netherlands studied surface chemistry and self assembly of organic molecular wires on Graphenea's CVD graphene.


Since all atoms in graphene are surface atoms, a natural approach to tune graphene’s electronic properties is to use surface interactions. In particular, the modification of graphene via functionalization with organic molecules holds promise for tuning the electronic properties of graphene, controlling interfaces with other materials, and tailoring surface chemical reactivity.


Recently, a number of studies on self-assembly of organic molecules on graphene have been reported, albeit with few reports combining both the surface organization and its effect on the electrical performance of graphene devices. The scarcity of combined studies is likely to be due to the specific limitations presented by each source of graphene used. For example, mechanically exfoliated flakes of graphene on an insulating substrate, such as the commonly used silicon dioxide, allow fabrication of electronic devices, but are very challenging to approach with the tip of a scanning tunneling microscope (STM) due to their small dimensions. On the other hand, large-area graphene grown epitaxially from silicon carbide or grown by chemical vapor deposition (CVD) on a metal is suitable for studying self-assembly, but is not readily used in field-effect transistors due to the lack of a back gate electrode in the substrate.


In contrast, graphene grown by CVD and subsequently transferred to silicon/silicon dioxide wafers combines the accessibility of large-area graphene with the utility of a back gate present in the substrate. Furthermore, waferscale CVD graphene transferred to silicon/silicon dioxide has become widely available. In the work detailed in the Small publication, the team led by Prof. Ben L. Feringa used our commercially available CVD graphene on silicon/silicon dioxide. High quality CVD graphene on this substrate is available from Graphenea on wafer sizes ranging from 10mm x 10mm to a full 4'' diameter wafer, or on any other custom-sized wafer or substrate material.



Figure: Molecular wires grown on a graphene layer, imaged by scanning tunneling microscopy (from Small, a Wiley publication)


The research team discovered several surprising features of molecular wire self-assembly on graphene. Notably, it is found that the wires grow in patches oriented at 60 degrees to each other (see figure, part b), indicating the the atomic structure of graphene (a honeycomb lattice with 60 degree symmetry) plays a role in the self-assembly process, reflecting on the macroscopic topology of the wires. A second surprising finding is that the performance (doping level and mobility) of graphene transistors becomes better when they are covered by the layer of organic molecular wires. The performance increase is attributed mostly to cleaning of the graphene by the solvents used in the chemistry process.


In conclusion, this top-ranking publication confirms the importance of surface properties of graphene, studying the important interaction of the graphene surface with organic molecules. Importantly, the results show that CVD graphene is compatible with graphene transistor technology, touting a quality high enough to investigate surface chemistry effects. Combined with the ability to grow wafer-scale layers, CVD graphene is so far the most serious contender for fast graphene electronics and precise sensors.




via Graphenea

How to create selective holes in graphene

more »

Researchers have devised a way of making tiny holes of controllable size in sheets of graphene, a development that could lead to ultrathin filters for improved desalination or water purification.



The team of researchers at MIT, Oak Ridge National Laboratory, and in Saudi Arabia succeeded in creating subnanoscale pores in a sheet of the one-atom-thick material, which is one of the strongest materials known. Their findings are published in the journal Nano Letters.



The concept of using graphene, perforated by nanoscale pores, as a filter in desalination has been proposed and analyzed by other MIT researchers. The new work, led by graduate student Sean O’Hern and associate professor of mechanical engineering Rohit Karnik, is the first step toward actual production of such a graphene filter.



Making these minuscule holes in graphene — a hexagonal array of carbon atoms, like atomic-scale chicken wire — occurs in a two-stage process. First, the graphene is bombarded with gallium ions, which disrupt the carbon bonds. Then, the graphene is etched with an oxidizing solution that reacts strongly with the disrupted bonds — producing a hole at each spot where the gallium ions struck. By controlling how long the graphene sheet is left in the oxidizing solution, the MIT researchers can control the average size of the pores.



A big limitation in existing nanofiltration and reverse-osmosis desalination plants, which use filters to separate salt from seawater, is their low permeability: Water flows very slowly through them. The graphene filters, being much thinner, yet very strong, can sustain a much higher flow. “We’ve developed the first membrane that consists of a high density of subnanometer-scale pores in an atomically thin, single sheet of graphene,” O’Hern says.



For efficient desalination, a membrane must demonstrate “a high rejection rate of salt, yet a high flow rate of water,” he adds. One way of doing that is decreasing the membrane’s thickness, but this quickly renders conventional polymer-based membranes too weak to sustain the water pressure, or too ineffective at rejecting salt, he explains.



With graphene membranes, it becomes simply a matter of controlling the size of the pores, making them “larger than water molecules, but smaller than everything else,” O’Hern says — whether salt, impurities, or particular kinds of biochemical molecules.



The permeability of such graphene filters, according to computer simulations, could be 50 times greater than that of conventional membranes, as demonstrated earlier by a team of MIT researchers led by graduate student David Cohen-Tanugi of the Department of Materials Science and Engineering. But producing such filters with controlled pore sizes has remained a challenge. The new work, O’Hern says, demonstrates a method for actually producing such material with dense concentrations of nanometer-scale holes over large areas.



“We bombard the graphene with gallium ions at high energy,” O’Hern says. “That creates defects in the graphene structure, and these defects are more chemically reactive.” When the material is bathed in a reactive oxidant solution, the oxidant “preferentially attacks the defects,” and etches away many holes of roughly similar size. O’Hern and his co-authors were able to produce a membrane with 5 trillion pores per square centimeter, well suited to use for filtration. “To better understand how small and dense these graphene pores are, if our graphene membrane were to be magnified about a million times, the pores would be less than 1 millimeter in size, spaced about 4 millimeters apart, and span over 38 square miles, an area roughly half the size of Boston,” O’Hern says.



With this technique, the researchers were able to control the filtration properties of a single, centimeter-sized sheet of graphene: Without etching, no salt flowed through the defects formed by gallium ions. With just a little etching, the membranes started allowing positive salt ions to flow through. With further etching, the membranes allowed both positive and negative salt ions to flow through, but blocked the flow of larger organic molecules. With even more etching, the pores were large enough to allow everything to go through.



Scaling up the process to produce useful sheets of the permeable graphene, while maintaining control over the pore sizes, will require further research, O’Hern says.



Karnik says that such membranes, depending on their pore size, could find various applications. Desalination and nanofiltration may be the most demanding, since the membranes required for these plants would be very large. But for other purposes, such as selective filtration of molecules — for example, removal of unreacted reagents from DNA — even the very small filters produced so far might be useful.



“For biofiltration, size or cost are not as critical,” Karnik says. “For those applications, the current scale is suitable.”



Bruce Hinds, a professor of materials engineering at the University of Kentucky who was not involved in this work, says, “Previous groups had tried just ion bombardment or plasma radical formation.” The idea of combining these methods “is nice and has the potential to be fine-tuned.” While more work needs to be done to refine the technique, he says, this approach is “promising” and could ultimately help to lead to applications in “water purification, energy storage, energy production, [and] pharmaceutical production.”



The work also included Jing Kong, the ITT Career Development Associate Professor of Electrical Engineering; MIT graduate students Michael Boutilier and Yi Song; researcher Juan-Carlos Idrobo of the Oak Ridge National Laboratory; and professors Tahar Laoui and Muataz Atieh of the King Fahd University of Petroleum and Minerals (KFUPM). The project received support from the Center for Clean Water and Clean Energy at MIT and KFUPM and the U.S. Department of Energy.



via MIT News

Astronomers spot record-breaking lunar impact

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A meteorite with the mass of a small car crashed into the Moon last September, according to Spanish astronomers. The impact, the biggest seen to date, produced a bright flash and would have been easy to spot from Earth.

via Science Daily

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Hubble's Ultra Deep Field Image Poster

Here's a great poster featuring a beautiful image from deep space

so many products with fantastic designs on Zazzle... which to choose today? How about this one from HubbleView, another talented creative from the Zazzle community!


tagged with: hubble, ultra deep field, ultra, deep, field, astronomical, astronomy, distant, galaxies, ancient, red shift, space images

This view of nearly 10,000 galaxies is called the Hubble Ultra Deep Field. The snapshot includes galaxies of various ages, sizes, shapes, and colors. The smallest, reddest galaxies may be among the most distant known, existing when the universe was just about 800 million years old. The nearest galaxies - the larger, brighter, well-defined spirals and ellipticals - thrived about 1 billion years ago, when the cosmos was 13 billion years old. The image required 800 exposures taken over the course of 400 Hubble orbits around Earth. The total amount of exposure time was 11.3 days, taken between Sept. 24, 2003 and Jan. 16, 2004. Credit: NASA, ESA, and S. Beckwith (STScI) and the HUDF Team For more information, visit http://hubblesite.org/newscenter/archive/releases/2006/12/image/b/

»visit the HubbleView store for more designs and products like this
Click to customize with size, paper type etc.
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