Citation: New catalyst for hydrogen fuel cells resists CO contamination (2010, July 19) retrieved 18 August 2019 from https://phys.org/news/2010-07-catalyst-hydrogen-fuel-cells-resists.html More information: Highly Stable and CO-Tolerant Pt/Ti0.7W0.3O2 Electrocatalyst for Proton-Exchange Membrane Fuel Cells, J. Am. Chem. Soc., Article ASAP, Publication Date (Web): July 12, 2010. pubs.acs.org/doi/abs/10.1021/ja102931d Image credit: Journal of the American Chemical Society Explore further Nano World: Methanol fuel cell thru nano Hydrogen fuel cells use platinum electrocatalysts to combine hydrogen and oxygen to produce water and generate electricity. The problem is that the hydrogen is produced from sources such as gasoline, natural gas, or ethanol, and the process often introduces carbon monoxide into the gas. Even miniscule amounts of carbon monoxide in the hydrogen are sufficient to bind to the platinum catalysts and prevent them working. Scientists at Brookhaven National Lab in New York have recently found a platinum/ruthenium catalyst that blocks CO poisoning, but since this catalyst is extremely expensive, researchers have been seeing an alternative.The new catalyst was developed by Professor Héctor Abruña and colleagues from Cornell University, the National Institute for Materials Science in Ibaraki, Japan, and the University of Pennsylvania. They began with the knowledge that tungsten alloys resist CO poisoning. Tungsten is not used in fuel cell electrodes because it is a poor electrical conductor, so Abruña and the team added tungsten to nanoparticles of titanium dioxide, which is a good electrical conductor. The result was titanium tungsten oxide nanoparticles, which they coated with platinum to make an electrode.The researchers tested their nanoparticles catalysts with hydrogen contaminated with two percent carbon monoxide, and found performance was reduced by only five percent compared to 30 percent for ordinary catalysts.Abruña said he is not sure how the new catalyst works, and much more testing is required, but he thinks a likely mechanism is that hydroxide (OH-) groups bind during the reaction to the titanium tungsten oxide near to the platinum, where they are close enough to the CO molecules to react and form CO2.If the tests prove successful and the new catalyst can be made economically, it could spark renewed interest in using liquid fuels such as gasoline in cars to make the hydrogen required to power fuel cells. This in turn could enable fuel cells cars to have a longer range than those using gaseous hydrogen and those using gasoline conventionally.The research paper was published in the Journal of the American Chemical Society. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. © 2010 PhysOrg.com (PhysOrg.com) — Hydrogen fuel cell vehicles promise faster refueling and the ability to travel longer distances before refueling than battery-powered cars, but they are susceptible to poisoning by carbon monoxide (CO). Now, scientists in the US and Japan have created new nanoparticles catalysts that enable hydrogen fuel cells to resist CO poisoning.
(PhysOrg.com) — A new study has discovered that animal cells communicate electrically with each other via tunneling nanotubes (TNTs). The membrane tubes contain a protein called F-actin and connect cells over long distances to enable the exchange of molecules and organelles between the cells. Nanotube Coating Meshes with Living Cells This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. The formation of TNT between NRK cells. Image credit: PNAS, doi:10.1073/pnas.1006785107. More information: Xiang Wang, et al. Animal cells connected by nanotubes can be electrically coupled through interposed gap-junction channels, Proceedings of the National Academy of Sciences, Published online before print September 20, 2010, doi:10.1073/pnas.1006785107 Researchers based at the Department of Biomedicine of the University of Bergen in Norway demonstrated a two-way exchange of electrical signals between cells connected by nanotubes 10 to 70 μm long in a normal rat kidney. They also demonstrated electrical coupling in other types of cells, which suggests electrical coupling via TNTs may be a much more common phenomenon in animal cells than previously thought.The study found the strength of electrical coupling depended on the length and number of TNT connections, and the coupling was voltage-sensitive. Electrical coupling was inhibited by the presence of a known gap-junction blocker, meclofenamic acid, and was not present in cell types that lacked gap junctions. Gap junctions are proteins that form a porous junction between adjacent cells, and the study clearly demonstrated that a current flows down the nanotube and causes ion channels to open in the connecting cell’s membrane, as long as a gap junction is present. The ions entering the cell can have a variety of effects, such as modulating cell movements, and this may help to explain phenomena like the coordinated cell migrations seen in developing embryos as cells congregate to form structures such as the neural tube.Co-author of the paper, published in the Proceedings of the National Academy of Sciences (PNAS), Hans-Hermann Gerdes, said the discovery was akin to ultra-thin telephone cables between cells, allowing them to talk to one another.Gerdes and his colleagues first discovered protein nanotubes (also called membrane nanotubes) in the kidney six years ago using light microscopy. Apart from forming a means of electrical coupling, the nanotubes have also been shown to be able to transport molecules, viruses and prions from cell to cell, at least in a Petri dish. It is not yet known how cells produce nanotubes or how they open the membrane of another cell several cell-widths away. Some scientists doubted the initial discovery of nanotubes, since there seemed to be no strong evidence that nanotubes are needed physiologically. One critic was Yale microbiologist Walther Mothes, who said he was impressed by the new finding that nanotubes use gap junctions for electrical communication, which he said makes a lot of sense, and should lead to further study of TNTs. © 2010 PhysOrg.com Citation: Animal cells communicate electrically over long distances via nanotubes (2010, September 21) retrieved 18 August 2019 from https://phys.org/news/2010-09-animal-cells-electrically-distances-nanotubes.html Explore further
© 2010 PhysOrg.com This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Explore further Citation: Acer announces the Iconia Tab A500 with Android 3.0 Honeycomb (2011, February 14) retrieved 18 August 2019 from https://phys.org/news/2011-02-acer-iconia-tab-a500-android.html AT&T, Sprint, T-Mobile, Verizon to sell Samsung’s iPad rival (PhysOrg.com) — Acer is making a new move into the world of tablets. They showed off their new Iconia Tab A500. The device features the Google’s Android 3.0 Honeycomb software and an interesting set of hardware specs. The Iconia Tab A500 has a 10.1-inch display, with a a wide viewing angle and a screen that allows for a high degree of color contrast. This, of course, put the new tablet on par with the Motorola Xoom and Samsung Galaxy Tab 10.1, at least for screen size. The screen also supports HD video formats, with a built-in HDMI port that will allow users to stream video from the tablet in 1080p HD. Which is good news if you love movies, but is not of much use to you if videophile is not on your social resume.The case is laser-engraved and made out of aluminum. The whole device is set to be 13.3mm thick. The Iconia Tab A500 also has a decent processor, it features a dual-core Nvidia Tegra 2 processor and an Nvidia GeForce GPU in order to handle next-generation graphics. The Iconia Tab A500 will come with choice of Wi-Fi or 3G for the Internet connection, which is a fairly standard set of choices in the tablet world. It also features a dual set of cameras. The one in the rear is a 5-megapixel and the front camera is what an high definition front cam for video calls, thought you may not always want to see your chat partners in HD. The camera also has the ability to be used as a barcode reader.The tablet does not have a release date announced or a cost listed currently.
More information: software.intel.com/en-us/vcsou … eptual-computing-sdk A voice-recognition tool by Nuance called Dragon Assistant will start appearing in Dell ultrabooks later this year. A demo at the IDF featured a Dell XPS 13 Ultrabook running Nuance’s Dragon Assistant Beta.With next month’s release of Windows 8 from Microsoft, 40 upcoming Ultrabooks based on Windows 8 will be touch-enabled.Talk of the upcoming Ultrabooks at the IDF was laced with the key technology driver behind future innovation-loaded Ultrabooks, and that is Haswell, Intel’s upcoming processor architecture. Intel fashioned Haswell with beefed-up Ultrabooks in mind. Haswell can allow for the Ultrabook’s upcoming innovations, with a design that enables lower power requirements, power boosts, and more efficient energy management. Haswell’s capabilities translate into Ultrabook capabilities. The Haswell design carries the same 22-nm process as Ivy Bridge, but will deliver better power management and battery life. Haswell processors will support Intel customers building a new crop of tablet-morphing form factors, where a flip or swivel or fold-back changes the laptop into a tablet. There are about 70 ultrabooks on the market at the moment. Next year, Intel is banking on doubling that number. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Explore further Citation: Intel: Ultrabooks will be thin and light but heavy in innovation (2012, September 12) retrieved 18 August 2019 from https://phys.org/news/2012-09-intel-ultrabooks-thin-heavy.html To prep developers, Intel announced this week that it will release an introductory software developer package, the Intel Perceptual Computing SDK 2013 Beta, in October. Developers will be able to add perceptual computing usage for immersive software applications that incorporate close-range tracking, speech recognition, facial analysis and 2-D/3-D object tracking on second and third generation core processor-powered Ultrabooks and PCs. This SDK supports the CREATIVE Interactive Gesture Camera Developer Kit, a USB-powered depth sensor camera tuned for short-range interactivity. This is for Intel-powered Ultrabooks, laptops or PCs used within a range of six inches to three feet. The camera developer kit, said Intel, will be available in Q4 of this year. Intel has also announced a Perceptual Computing Challenge with up to $1 million in awards and promotions for application developers. Intel will highlight next-gen Haswell processors at next week’s IDF (Phys.org)—Intel’s new breed of Ultrabooks will be lighter, thinner but loaded with new features and functions that end users will either see as bloat or muscle, and Intel is counting on the latter. The look and functions of Intel’s next-generation Intel Ultrabooks were revealed by Intel executives at the Intel Developer Forum. The new computers will bring in voice recognition, touch, finger tracking, augmented reality, and gesture-based interfaces. The technologies that generally are expected out of smartphones and tablets will be applied toward the thin and light computers. Ultrabook manufacturers will start to integrate sensors gyroscopes, accelerometers, GPS, NFC, and 3G and 4G-LTE connectivity. © 2012 Phys.org
The sampling hut in Tiksi. Credit: Oleg Dudarev While most of the press regarding global warming centers on the release of carbon dioxide into the atmosphere, very little is heard about other man-made activities that are also heating the planet. One such activity is the emission of soot. It comes from factory chimneys, particularly those that burn coal, burning gasoline in car engines, burning fields as part of agricultural efforts, and from other activities that involve burning some type of material. Because of inefficiencies, some bits of carbon, in the form of soot, make their way into the atmosphere. They do not stay there nearly as long as carbon dioxide does—the problem occurs when they come back down. When it lands on ice in the Arctic, it turns the ice from white to black. Blackened ice absorbs heat, white ice reflects it. Thus, the carbon-covered ice tends to have more surface melting than normal, and there is much less reflection of heat back into the atmosphere. Both contribute to the rapidity of global warming happening in the Arctic compared to other parts of the world. In recent years, several research efforts have explored the impact of black carbon in the Arctic and sought to ascertain its sources. The researchers with this new effort claim most prior studies have produced unreliable results due to what they describe as “a lack of observational restraints” and less-than-clear emission inventories. To address such problems, the team undertook a five-year study of black carbon in the Arctic, which involved collecting samples from multiple sites and subjecting each to chemical analysis to determine which kind of source it came from. Explore further The team reports that the majority of black carbon in the Arctic (approximately 70 percent) comes from burning fossil fuels, not croplands (or wildfires) as some have suggested. But they also found that the ratios vary by season—during the winter, much more fossil fuel is burned to keep buildings warm. In contrast, most of the crop burning and other types of fires occur in the warmer months. More information: P. Winiger et al. Source apportionment of circum-Arctic atmospheric black carbon from isotopes and modeling, Science Advances (2019). DOI: 10.1126/sciadv.aau8052 The Dr. Neil Trivett Global Atmosphere Watch (GAW) Observatory is the most northerly site in the global network, located at Alert, Nunavut, Canada (approximately 800km south of the geographic North Pole). Environment and Climate Change Canada operates the observatory, which hosts research campaigns and facilitates long-term measurements of a number of atmospheric constituents including greenhouse gases, aerosols including black carbon, stratospheric ozone, Persistent Organic Pollutants, mercury, etc. Credit: Janice Lange © 2019 Science X Network Equipment being packed up for transport back to Stockholm. Credit: Patrik Winiger Journal information: Science Advances An international team of researchers has conducted the most thorough study yet of the sources of black carbon in the Arctic. In their paper published in the journal Science Advances, the group describes their findings and explain why what they found relates to global warming. The Arctic is especially sensitive to black carbon emissions from within the region Citation: Long term study shows sources of black carbon in the Arctic (2019, February 14) retrieved 18 August 2019 from https://phys.org/news/2019-02-term-sources-black-carbon-arctic.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Quantum-critical scattering rate of the Dirac fluid. (A) Real and (B) imaginary parts of the change in optical conductivity at charge neutrality upon optically heating the electron system to a temperature Te above the equilibrium temperature T0 = 77 K. Each curve corresponds to a different delay between the optical pump pulse (fluence 21 nJ cm–2) and terahertz probe pulse. Solid curves are fits to a difference between Drude functions at Te and T0, using Te and the scattering rate τ–1(Te) as free fit parameters for each pair of curves of the complex conductivity. (C) Blue markers indicate the scattering rates and electron temperatures extracted from the fits shown in (A) and (B); error bars indicate standard error in the fits. The experimental scattering rate follows τ–1 = τee–1 + τd –1 (dashed curve), where τee–1 = 0.20kBTe/ħ (green line) is the scattering rate due to charge-carrier interactions, and τd –1 ∝ nimpTe –1 (dotted curve) is the scattering rate due to unscreened, singly charged impurities with density nimp = 2.1 × 109 cm–2. (D) Real and imaginary parts (open and filled circles, respectively) of σ at different Te (i.e., different optical pump delay), replotted as a function of ħω/kBTe. The data for Te = 100 K (21.3 ps delay) do not collapse and are omitted. Credit: Science, doi: 10.1126/science.aat8687 In all measurements, the scientists heavily doped the graphene beneath the waveguide traces to minimize its impedance. The extracted scattering rates at 77 K were below 0.5 and 1 THz, indicating infrequent scattering by disorder and phonons, consistent with previous transport studies of similar doping; thus confirming the anticipated Fermi liquid behavior of graphene. The scientists probed the transport at charge neutrality by observing the change in terahertz transmission. For this, they optically heated the system and calculated the corresponding change in conductivity and the current carried in charge-neutral graphene under experimental conditions. The observed linear evolution in the experiments was a key signature of charge-carrier interactions in the quantum-critical Dirac fluid. More information: Patrick Gallagher et al. Quantum-critical conductivity of the Dirac fluid in graphene, Science (2019). DOI: 10.1126/science.aat8687 K. S. Novoselov et al. Two-dimensional gas of massless Dirac fermions in graphene, Nature (2005). DOI: 10.1038/nature04233 Experimental setup. Left: Large-area photograph of the waveguide device. Right: Cross-sectional view of the heterostructure beneath the waveguide electrodes. Credit: Science, doi: 10.1126/science.aat8687 Experimentally, time-domain terahertz spectroscopy is an ideal probe across a broad frequency range to observe quantum-critical conductivity, but use of the device is limited to lower-quality large-area films, within which Dirac fluid physics is obscured. In the present work, therefore, Gallagher et al. leveraged the subwavelength confinement of a coplanar waveguide to measure the terahertz optical conductivity of graphene, at ten-micron scale thickness ,encapsulated within hexagonal boron nitride (HBN). They used the experimental setup to measure the material’s conductivity at electron temperatures (Te) ranging between 77 and 300 K to confirm the quantum-critical scattering rate near charge neutrality. The scientists also demonstrated the co-existence of zero- and finite-momentum modes at non-zero doping. Frequency-dependent optical conductivity of graphene in the Fermi liquid regime. (A) Real and (B) imaginary parts of extracted optical conductivity for several Fermi energies between 46 and 119 meV (electron doping) at 77 K. Solid curves are Drude fits using only the scattering rate τ–1 as a free fitting parameter for each curve. Inset in (A) shows an example of the time-domain current data used to extract conductivity in the frequency domain; the purple trace shows the transmitted waveform at 119 meV, and the black trace shows the transmitted waveform at charge neutrality, which is used as a reference. Inset in (B) shows the extracted τ–1 at lattice temperatures 77 K and 300 K. Credit: Science, doi: 10.1126/science.aat8687 In this way, Gallagher et al. elegantly demonstrated the quantitative agreement between the experimental results and relativistic hydrodynamic theory of the Dirac fluid graphene. The scientists implied that graphene should host relativistic phenomena that are not observed in typical electron systems (to which relativistic hydrodynamics do not apply). For instance, in conventional metals, electronic sound waves either morph into plasmons or are destroyed by momentum relaxation. However, the new results indicate that such waves can exist in charge-neutral graphene as a result of low disorder and zero-coupling to plasmon modes. The experimental work by Gallagher et al. thus provided access to the subtle and rich physics of relativistic hydrodynamics of graphene in a bench top experiment. Further experiments can investigate the cyclotron resonance of graphene at high temperatures in the future. The work revealed the quantum criticality of the material in which each site is in a quantum superposition of order and disorder (similar to Schrödinger’s hypothetical cat in a quantum superposition of ‘dead’ and ‘alive’) and the unusual dynamic excitation in graphene near charge neutrality. Physicists consider quantum relativistic effects in the experimental systems influencing condensed matter to be too minute for accurate description by the non-relativistic Schrödinger’s equation. As a result, previous studies have reported on experimental condensed matter systems such as graphene (a single atomic layer of carbon) in which electron transport was governed by Dirac’s (relativistic) equation. Landau’s theory of the Fermi liquid defines electron interactions of a typical metal as an ideal gas of non-interacting quasiparticles. In monolayer graphene, this description does not apply due to its structure of linearly dispersing bands and minimally screened Coulomb interactions. Near charge neutrality, graphene is thus expected to host a “Dirac fluid,” which is a quantum-critical plasma of electrons and holes that are governed by relativistic hydrodynamics. In lightly doped graphene, a surprising consequence of relativistic hydrodynamics is that current can be carried by two distinct modes; with zero and non-zero total momenta, also referred to as “energy waves” and “plasmons” in some studies. Coexistence of zero- and finite-momentum modes at low doping. (A) Calculated Drude weights DZ and DF of the zero- and finite-momentum modes (27) in lightly electron-doped (εF = 33 meV) and undoped graphene. (B) Real and (C) imaginary parts of the measured change in optical conductivity when charge neutral graphene in equilibrium (T0 = 77 K) is simultaneously heated to an electron temperature Te (optical pump delay 3 ps, fluence 21 nJ cm–2) and doped to εF = 33 meV. (D) Real and (E) imaginary parts of the measured change in optical conductivity when charge neutral graphene at an electron temperature Te (optical pump delay 4 ps, fluence 20 nJ cm–2) is doped to various εF. Data at each doping are well fit by a single Drude function (solid curves) describing the conductivity of the finite-momentum mode with free fit parameters Te = 267 ± 3 K and τd –1(εF) ~ 1 THz. Inset in (D) shows the scattering rate for the finite momentum mode τd –1 versus Te extracted from fits at varying Te. Colors indicate εF as in (D), (E). Credit: Science, doi: 10.1126/science.aat8687 Graphene is expected to behave like a quantum-critical, relativistic plasma known as “Dirac fluid” near charge neutrality in which massless electrons and holes rapidly collide. In a recent study now published in Science, Patrick Gallagher and co-workers at the departments of physics and materials science in the U.S., Taiwan, China and Japan used on-chip terahertz spectroscopy and measured the frequency-dependent optical conductivity of graphene between 77 K and 300 K electron temperatures for the first time. Additionally, the scientists observed the quantum-critical scattering rate characteristic of the Dirac fluid. At higher doping, Gallagher et al. uncovered two distinct current-carrying modes with zero and nonzero total momenta as a manifestation of relativistic hydrodynamics. © 2019 Science X Network Citation: Quantum-critical conductivity of the Dirac fluid in graphene (2019, March 13) retrieved 18 August 2019 from https://phys.org/news/2019-03-quantum-critical-dirac-fluid-graphene.html Explore further In the experimental setup, Gallagher et al. used photoconductive switches made of semiconducting materials with approximately one picosecond (ps) carrier lifetime to accomplish emission and detection of terahertz pulses. The emitter switch contacting the lower waveguide trace was biased with a dc voltage. When triggered by a laser pulse, the biased emitter became highly conductive for 1 ps. The process injected a current pulse into the coplanar waveguide to interact with graphene prior to reaching a detector switch spanning both traces. In practice, the scientists obtained lower noise by controlling the length of the optical path and detecting the current, to measure the time-domain profile of the transmitted voltage pulse (dV/dt). After optimizing experimental conditions, the scientists first investigated the optical conductivity of the Fermi liquid at 77 K (T0). The transmitted waveforms contained sharp, sub-picosecond features that evolved with gate voltage to result in maximum transmission at charge neutrality. To extract the optical conductivity from the time-domain data and justify the finite-element simulations, the scientists modeled the device as an infinite, lossless transmission line. Gallagher et al. then probed transport at charge neutrality by observing the change in terahertz transmission (∆V) by optically heating the electron system from T0 = 77 K to varying electron temperatures (Te). To vary temperature in the experimental setup, they adjusted the delay between the optical pump and terahertz probe pulse. Journal information: Science Hall effect becomes viscous in graphene Probing the electrodynamics of graphene using on-chip terahertz spectroscopy. (A) Current carrying modes of a graphene sheet. The zero-momentum mode corresponds to a plasma of counterpropagating electrons and holes and can be relaxed by electron-hole interactions. The finite-momentum mode corresponds to a fluid of co-propagating electrons or holes with nonzero net charge and cannot be relaxed by charge-carrier interactions. The vector J denotes the net current flow. (B) Cartoon of the sample. Photoconductive switches (“emitter” and “detector”) triggered by a pulsed laser emit and detect terahertz pulses within the waveguide. The transmitted pulse is reconstructed by measuring the current collected by the preamplifier (“A”) as a function of delay between laser pulse trains illuminating the emitter and detector. The graphene is optionally excited by a separate pulsed beam (“pump”) to heat the electron system. (C) Photograph of the heterostructure embedded in the waveguide. Few-layer graphene (FLG) electrodes make contact to the monolayer graphene sheet under study and the WS2 gate electrode. Scale bar: 15 micron. Credit: Science, doi:10.1126/science.aat8687 , Nature As doping increased, the weight of the zero-momentum mode was expected to decrease, while that of the finite-momentum mode increased to cross over smoothly from Dirac fluid to Fermi liquid behavior. Previous experiments on clean, monolayer graphene have demonstrated many-body physics in graphene, with examples including studies on low-frequency transport phenomena consistent with hydrodynamic descriptions. Additional experiments indicated violation of the Wiedemann-Franz law – as a signature of the Dirac fluid and as direct evidence of collective motion in a quantum electronic fluid, and the viscous flow of electrons. Even though electron-hole collisions have shown to limit conductivity in charge-neutral bilayer graphene, the direct observation of quantum-critical conductivity of the Dirac fluid has remained elusive.
“As it was predicted, and we showed in a previous study published in June 2018, during the closest approach of the star S2 to the black hole we observe the ‘gravitational redshift’ in the light of the star,” Habibi explained. “Gravitational redshift occurs because intense gravity on the star’s surface slows the vibration of light waves, stretching them and making the star appear redder than normal from Earth.”To test Einstein’s LPI principle, the researchers used two different types of atoms in S2’s stellar atmosphere: hydrogen and helium atoms. The LPI principle states that the gravitational redshift seen in a star that is flying in and out of a strong gravitational field only depends on the gravitational potential and does not rely on other parameters, such as the internal structure of the atom. Explore further The GRAVITY Collaboration, a team of researchers at several renowned institutes including the Max Planck Institute, LESIA Paris Observatory and the European Southern Observatory, has recently tested part of the Einstein Equivalence Principle, namely the local positon invariance (LPI), near the galactic center supermassive black hole. Their study, published on Physics Review Letters (PRL), investigated the dependency of different atomic transitions on the gravitational potential in order to give an upper limit on LPI violations. © 2019 Science X Network This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Image of the Galactic Centre. Credit: European Southern Observatory (ESO). “We measured the frequency change of light from these atoms moving through a varying potential,” Habibi said. “The vibration of light waves was measured by fitting the line-of-sight velocity of the S2’s spectrum using the Hydrogen and Helium spectral lines separately. By measuring the difference in frequency change for both atoms we were able to give an upper limit on the LPI violation during the pericenter passage. If there was an obvious violation of LPI, we should have measured very different vibration of light waves, from the helium and hydrogen lines.” The equivalence principle and general relativity at large are merely theories, thus they need to be tested in order to ascertain their validity. So far, most researchers have carried out tests on Earth and in the solar system. However, these theories should also be tested in extreme scenarios, as this can determine whether they still hold and lead to more conclusive evidence. Such tests could rule out some of the principles that shape our current understanding of gravity or identify violations from the theory of general relativity. “Testing the equivalence principle in all different regimes is important as several alternative theories of gravitation predict a violation from it under extreme conditions,” Felix Widmann, another researcher involved in the study, told Phys.org. “For me the most meaningful finding of our study is that we were able to test the equivalence principle in this most extreme case: close to a supermassive black hole that is over 20 thousand light years away. The limits we put on a violation are not very restrictive yet, but they are in a gravitational regime that was completely untested before.” Habibi, Widmann and their colleagues were among the first to test part of the equivalence principle near the Milky Way’s central supermassive black hole. Their work provides valuable insight about the validity of general relativity, particularly the LPI principle. “The past year was exceptionally successful for the GRAVITY collaboration,” Widmann said. “For the first time, we observed relativistic effects in the orbit of a star around a supermassive black hole and used this star to test the Equivalence Principle. We also observed material orbiting very close to the black hole, another observation which would have been impossible without GRAVITY. However, this is more of a start than an end for us.” With the optimal season for galactic center observation just around the corner, the researchers at GRAVITY collaboration will continue to point their telescopes to S2 and the galactic center supermassive black hole. According to Widmann, the team might soon be able to detect subtler relativistic effects in the orbit of S2, which will allow them to test the theory of general relativity once again. In their future observations, the researchers also hope that they will see more flare activity around the black hole, as this would enable further studies aimed at broadening their understanding of the Milky Way’s galactic center black hole and black holes in general. “With future telescopes like the Extremely Large Telescope, which has a mirror of 39m in diameter, we will be able to perform similar experiments and look for 1 million times smaller effects of possible violations of LPI, compared to what it is possible today,” Widmann added. “This will allow us to test the other part of Einstein’s equivalence principle, called weak equivalence principle, which states that an object in gravitational free fall is physically equivalent to an object that is accelerating with the same amount of force in the absence of gravity. The galactic center is a unique observatory and with GRAVITY and future telescopes we want to learn as much about it as possible.” First successful test of Einstein’s general relativity near supermassive black hole (Update) More information: A. Amorim et al. Test of the Einstein Equivalence Principle near the Galactic Center Supermassive Black Hole, Physical Review Letters (2019). DOI: 10.1103/PhysRevLett.122.101102 Detection of the gravitational redshift in the orbit of the star S2 near the Galactic centre massive black hole, Astronomy & Astrophysics (2018). DOI: 10.1051/0004-6361/201833718 “General relativity and in general all metric theories of gravity are based on the equivalence of inertial mass and gravitational mass, formalized in the Einstein equivalence principle,” Maryam Habibi, one of the researchers who carried out the study, told Phys.org. “General relativity is the best theory of gravity that we have, however, there are still many unanswered puzzles that are closely tied to our incomplete understanding of gravity.” The equivalence principle, a crucial part of Einstein’s general relativity theory, states that the gravitational force experienced in any small region of space-time is the same as the pseudo-force experienced by an observer in an accelerated frame of reference. Testing this principle is of key importance, as it could lead to interesting observations and broaden our current understanding of gravity. “Einstein’s equivalence principle consists of three main principles,” Habibi explained. “One of them, called the local position invariance (LPI), states that non-gravitational measurements should be independent of the location in space time (characterized by gravitational potential) where they are carried out. The main part of our study focuses on testing the LPI principle.”Past observations suggest that most, if not all, massive galaxies contain a supermassive black hole, which is typically located at the center of a galaxy. The mass of the Milky Way’s galactic center supermassive black hole is 4 million times greater than that of the sun. It thus generates the strongest gravitational field in the galaxy, which makes it the ideal place to hunt for unexplored phenomena and test general relativity principles.Star S2, one of the brightest stars in the Milky Way’s innermost region, has its closest encounter with the galactic center supermassive black hole at a distance of 16.3 light hours. In other words, the star takes 16 years to make a complete orbit around the black hole, which in astronomical time scales is extremely short. S2 moves in and out of the black hole’s gravitational field, hence the GRAVITY collaboration team decided to use it to test part of Einstein’s equivalence principle. Journal information: Physical Review Letters Citation: Testing Einstein’s equivalence principle near a supermassive black hole (2019, March 29) retrieved 18 August 2019 from https://phys.org/news/2019-03-einstein-equivalence-principle-supermassive-black.html , Astronomy & Astrophysics Image shows one of the Unit Telescopes of ESO’s Very Large Telescope (VLT) array, pointing a laser beam towards the Milky Way to create an artificial star. Credit: European Southern Observatory (ESO).
Explore further © 2019 Science X Network A trio of researchers with the University of Wollongong, in Australia, has published an outline of the current state of potassium-ion battery technology. In their Review piece published in the journal Science Advances, Wenchao Zhang, Yajie Liu, and Zaiping Guo highlight the current roadblocks that are preventing widespread use of the battery technology and possible workarounds for them. Journal information: Science Advances Lithium-ion batteries have proven to be very useful, particularly in recent times as they are used to power a wide range of devices—from smartphones to electric cars. But lithium is rather rare, which means costs for it is going to go up as supplies tighten. For that reason, scientists have been searching for an alternative. One alternative that has been getting a lot of attention of late is potassium-ion—it is plentiful and cheap. But it also has five main roadblocks, the researchers note.The first roadblock is low diffusion, which means the potassium ions move slowly through a solid electrode. The researchers suggest that advances in nanomaterials and nanostructures may lead to ways to solve this problem.The second roadblock has to do with the changes in volume that potassium undergoes as it first accepts a charge and then as it releases it. Repeated cycles lead to breakdown of the material, which results in the development of dead areas and ultimately, battery failure. Possible workarounds include using nanoparticle clusters.The third problem involves the side reactions that take place that can lead to degradation. The researchers expect that additives will soon be found to prevent them.The fourth problem is the growth of dendrites that can lead to short circuits. Again, the researchers suggest that the introduction of the right solvents should be able to prevent them from occurring.And finally, the fifth problem is poor heat dissipation, which can result in very hot batteries or even thermal runaway. The researchers suggest that study of electrode materials, cell configuration and electrolytes should at some point lead to a way to solve the problem.The researchers conclude by suggesting that the problems inherent with using potassium in batteries do not appear to be insurmountable, but acknowledge that it could take as long as 20 years to figure them all out. More information: Wenchao Zhang et al. Approaching high-performance potassium-ion batteries via advanced design strategies and engineering, Science Advances (2019). DOI: 10.1126/sciadv.aav7412 Citation: Researchers outline the current state of potassium-ion battery technology (2019, May 13) retrieved 18 August 2019 from https://phys.org/news/2019-05-outline-current-state-potassium-ion-battery.html Sodium- and potassium-based batteries could be key for smart grid of the future Opportunities and challenges of the PIB. (A) Comparison of LIB, SIB, and PIB in terms of energy density. (B) Abundance of lithium, sodium, and potassium metal in Earth’s crust (wt %). (C) Stokes radius of Li+, Na+, and K+ in PC. (D) Number of publications on PIBs according to Google Scholar (as of January 2019). (E) Summary of challenges and their relationships for the PIB. Credit: Science Advances (2019). DOI: 10.1126/sciadv.aav7412 This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
The pale, weary and pan-stained walls and corridors of one of Delhi’s oldest shopping destinations – Shankar Market – opposite Connaught Place’s outer circle is in the makeover mode as street artists are painting its eight blocks in varied hues and narrations depicting music, dance and drama to increase the footfalls.The New Delhi Municipal Council (NDMC) has joined hands with Delhi Street Art (DSA) to reinvent and refurbish the market, best-known to many as ‘fabric market’ for women. This is the second phase of the refurbishing project that NDMC is doing after it completed its long-delayed renovation work of the Connaught Place in December, 2013. Also Read – ‘Playing Jojo was emotionally exhausting’‘To use street art for reinventing this market has been on our mind for a long time now. When the market association approached us to do something to increase their footfall, as the market was in bad condition, we thought using colourful street art can be the best way to develop this market,’ OP Mishra, NDMC’s director (Projects) said.‘This is the second phase of the refurbishing project, and we plan to restore all other arterial markets around Connaught Place. We have hired an architecture to restore Gole market to its original glory,’ he added. Also Read – Leslie doing new comedy special with NetflixBringing out art from the closed and plush confines of art galleries to the public places is what DSA has been doing, and according to Yogesh Saini, by the end of the project, Shankar Market will offer a ‘continuous cultural feast’ to the public.‘The aim is to convert this market into “rainbow street”,’ Saini, the brain behind DSA, said.‘We had given the artists guidelines and used themes like music, culture, food and dance to attract the attention of people, especially younger audience,’ he added. As the first flour blocks of the market were painted Saturday and Sunday, Saini aims to paint another three blocks by next weekend. That will leave the group with one tall building which will require certain logistics preparations before they paint it.‘There were 5-6 artists per building and we have more than 40 artists on board with us,’ he added.According to Saini, they have also suggested the officials to add some rooftop kiosks and shops to convert it into a buzzing hang-out place.This is the second time the DSA have collaborated with NDMC. Their first project was to paint garbage bins of the Lodhi garden which they undertook eight months back. Saini feels such initiatives help in bringing street art into the public domain and help the common man to understand art.
Kolkata: Howrah police have arrested four persons on the charges of extorting money posing as CID officials.The incident took place at Howrah’s Uluberia on Sunday night. The accused were extorting money from the heavy duty trucks in Malpara area of Uluberia on the National Highway 6. Police said the accused parked a car fitted with beacon light and a sticker of ‘Income Tax’ on the car.The accused stopped loaded trucks on the National Highway 6 on Sunday night and demanded a huge amount of money. Also Read – Heavy rain hits traffic, flightsThey introduced themselves as CID officials and also threatened the drivers with dire consequences if they failed to meet their demands. After being informed, police rushed to the spot. The accused managed to flee the spot before the police could reach.A truck driver told the police that the accused took around Rs 3,000 and a mobile phone from him. Police then chased the vehicle and managed to intercept the car a few kilometers away from the spot. Police arrested the four accused on various charges. Also Read – Speeding Jaguar crashes into Merc, 2 B’deshi bystanders killedPolice said the accused flashed fake ID cards while extorting money from the truck drivers. According to preliminary investigation, police came to know that the impostors used to conduct raids at various shops.The accused have been charged with cheating and extortion posing as CID officers. “They are being interrogated and we are also investigating whether more people are involved with the gang,” a senior police officer in the district said.According to police, the accused are all residents of Taratala area in the city. The investigators are yet to confirm the identity of the accused, aged between 30 and 35. Police said the accused used to conduct fake raids at various places posing as CID officials. Police have started a detailed probe in this regard.