Month: August 2019
Cao is a scientist at Yale University, and she explains that the biggest issue with creating nanoscale photonic devices to replace electronic devices, as in optical interconnects, is that the light won’t stay confined on the nanoscale. “The photons leak out quickly, so there has to be a way to keep them in place so that there is enough time for them to perform functions. It is also necessary to make small light sources, such as nanolasers on chips,” she says.In an effort to move nanophotonic devices a step closer to realization, Cao and Q.H. Song, also at Yale, worked out a way that it might be possible to confine light in nanostructures. Their work is described in Physical Review Letters: “Improving Optical Confinement in Nanostructures via External Mode Coupling.””Consider two modes, both of which are pretty leaky,” Cao explains. “There is an A mode and a B mode. These two modes can be couple so that mode A gives part of its leakiness to mode B. Mode A becomes less leaking, while mode B becomes more leaky. As a result, you have efficiently increased the lifetime of mode A.” The increase in the lifetime of one of the modes in this coupling provides just what is needed to create a situation in which the light is confined. “It is no longer leaking out as much for light in mode A, and there is more time for functions to be performed,” Cao says. She also points out that this type of external coupling has been successful in other fields. “It’s somewhat fundamental, and once you have the ability to keep light in a nanostructure, it becomes possible to contemplate smaller photonic devices with speed capabilities beyond our current electronic devices.”So far, Cao and Song have only presented their ideas in the form of numerical simulations. “We don’t have experimental results yet, but our extensive numerical calculations indicate that this should be possible, and a similar concept has been used in other fields, such as resonance trapping in atomic and molecular physics. However, this approach has not been used in nanophotonics yet.”Cao thinks that the main obstacles to experiments with this idea include fine control over nanostructures, as well as access to the proper facilities. “There is a challenge in fine control of nanostructures, but the technology does exist to overcome this,” Cao says. “Mainly we are looking for access to the kinds of facilities that can fabricate the type of structure we propose. I think this kind of structure can be made using nanofabrication technology, with the right set up.”As long as an experiment can be performed to back up the numerical simulations performed by Cao and Song, there is a chance that this technique could help advance the use of nanophotonic devices. “It’s kind of novel, the way we use fundamental physics to solve this problem,” Cao says. “It’s also realistic, and something that could be used practically in the advance of nanotechnology.” “There is a strong drive to make smaller and smaller devices,” Hui Cao tells PhysOrg.com. “However, there are limitations to what we can do. We want faster devices than what we can get from electronics, so we are looking to photonics. Unfortunately, photonics, while having the potential to be much faster, are larger in size. Devices using electrons are smaller, on the nanoscale, while photonic devices are still on the microscale-defined by the wavelength of light.” 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 Chromium revision log indicates that Chrome for Android will become a mobile browser that integrates much of desktop browser’s feature set, which will help Google to patch bugs and security issues much faster than before. The Android browser could also see more updates in the future and evolve at a much faster pace,” said ConceivablyTech.Numerous other sites have since commented on the probability, not possibility, of Chrome made available as a browser for Android some time soon. Google watchers think that the Chrome-Android union might be part of the upcoming Samsung and Google joint event next week. An announcement is expected about an Ice Cream Sandwich (the next major Android update and the first version of Android to unify the phone and tablet parts of the OS) Android phone. Chrome for Android is expected to include features seen on the desktop version. Based on latest reports about Chrome in general, the browser is fast taking hold. Google’s Chrome browser could surpass Mozilla Firefox before the year end or by the middle of next year, predict browser stat-watching groups. While the popularity of Chrome for the desktop has grown as a browser that gets you where you want to go fast, the Android browser has underwhelmed Android users. Chrome for Android raises hopes that the result will be better unity and synchronization between Google’s desktop and mobile browsers. The advantages are summed up by Mobile.Blorge:”As a Chrome user on my own desktop PC, I can certainly see the appeal of using the same browser on mobile devices, partly because I trust it not to lead to crashes and freezes (even more important on a low-memory device), and partly because the synced bookmarks and user ID details would be incredibly convenient.”Emphasis in talk about Chrome coming to Android is on Chrome as a “first version,” which is expected to be simple and focused on speed. Chrome unseats Safari as third most popular Internet browser 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. (PhysOrg.com) — The first version of Chrome for Android should be just around the corner, according to ConceivablyTech. “Google is heading toward the finish line for the first release of Chrome for Android,” said the report. The information points to a developer posting on the Chromium site, where a build target was set for the browser. Chromium is the open source project on which the Google Chrome browser is based. © 2011 PhysOrg.com Citation: Bringing Chrome to Android more than wishful thinking (2011, October 5) retrieved 18 August 2019 from https://phys.org/news/2011-10-chrome-android.html Explore further
More information: www.raspberrypi.org/ Foundation readies $25 computer to seed tech talents 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. © 2011 PhysOrg.com Explore further (PhysOrg.com) — No long lines winding down Madison Avenue; no marching bands in Barcelona; no glossy ads in mainstream magazines. Just news of a product available for pre-order is all it took to trigger a crush of responders and to sell out the long awaited, credit-card sized computer with a $35 pricetag. The Raspberry Pi computer sold out in hours on Wednesday, after sites distributing the product witnessed unprecedented traffic. Citation: Distributors reel from Mad Wednesday rush for $35 Pi (2012, March 1) retrieved 18 August 2019 from https://phys.org/news/2012-03-distributors-reel-mad-wednesday-pi.html According to the Financial Times, one of the two device distributors, Premier Farnell, reported half a million hits in 15 minutes, The other distributor, RS Components, said they had never before witnessed that level of demand for any one product at one go.What’s the big deal? Those following the rise of the Raspberry Pi say the answer is not only price but principle. Developed by the Raspberry Pi Foundation in the UK, the miniature PC is intended to eventually become an affordable mainstay for schools to use, to expose children and youths to programming and command lines rather than just touchscreens and in-store apps.Wednesday’s opening offer for pre-orders is actually for a developer release. The Foundation aims to build a community of developers who can write software for the device before they issue the school-targeted product, priced even lower, at $25, which will be available at a later date.In the UK, the Foundation efforts are widely applauded and not only for aiming to educate youth. Some observers think the mad rush for the devices reflect a backlash trend toward old-school hobbyist programming among those tired of showroom computer bling.The Raspberry Pi, based on the ARM chip, does not come with monitor or keyboard; it is a bareboned PC on a naked circuit board with connectors. The Raspberry Pi is designed so that it can plug into a TV and a keyboard. The computer supports Python, a suitable programming language even for novices. The device runs Linux. (Its first proof of concept is based on Debian but a Fedora ARM secondary architecture project has a Fedora Linux distribution for ARM-based devices. The Fedora version is the work of faculty and students at Seneca College, Canada, where they configured and optimized it to work with the Raspberry Pi.)The chips and connectors allow users to connect cameras and other gadgets via USB, and can deal with high-definition video and sound. More specifically, the device has a 700MHz processor, 256MB of RAM, SD card support, two USB ports, an Ethernet hookup and HDMI and RCA outputs.“Although we are still waiting for units to arrive from China, you can start buying the Raspberry Pi today,” announced the foundation site.They entered into licensed manufacture partnerships with the two British companies, Premier Farnell and RS Components, and the two will be manufacturing and distributing the devices on behalf of the foundation. Each Raspberry Pi sold will generate a small profit for the foundation, which it will put back into the charity.The foundation’s web site also sought to explain on Wednesday that both distributor websites were experiencing heavy load and that international customers may find that Raspberry Pi was not yet available in their areas. The foundation asked for patience and to check back.
Understanding why green wave breakdown occurs may improve the green wave synchronization strategy and improve traffic flow in urban areas. Citation: Physics of ‘green waves’ could make city traffic flow more smoothly (2013, May 22) retrieved 18 August 2019 from https://phys.org/news/2013-05-physics-green-city-traffic-smoothly.html Kerner’s paper, “The physics of green-wave breakdown in a city,” is published in a recent issue of EPL.Many large cities around the world, especially in Europe and the US, synchronize traffic lights on the busiest streets to create green waves. When a green wave works as intended, all vehicles within the wave can drive through a sequence of green traffic lights at a certain speed without having to stop at the signals. The timing of the lights can be controlled either by sensors or timers, and can be set up for traffic in one direction or both directions. Green waves have several benefits, such as allowing for higher traffic loads, reducing traffic jams, controlling traffic speed, reducing fuel consumption and emissions, and facilitating bicycle and pedestrian traffic.The biggest disadvantage of green waves is that, when the wave is disturbed, the disturbance can cause traffic problems that can be exacerbated by the synchronization. In such cases, the queue of vehicles in a green wave grows in size until it becomes too large and some of the vehicles cannot reach the green lights in time and must stop. This is called over-saturation. As more and more vehicles stop, the traffic can cause a gridlock where vehicles can’t move forward even when the light turns green because vehicles are backed up at the light ahead, which may still be red or turning green at the same time.The physics of this green wave breakdown has not been thoroughly studied until now. In his paper, Kerner used two kinds of models to investigate the underlying mechanisms. He identified several general features of green wave breakdown that are independent of the traffic flow model used, and also discovered that the physical characteristics of green wave breakdown depend crucially on which model is used. In one model, called a three-phase model, green wave breakdown occurs due to an initial speed disturbance (for example, a car turning onto the main road from a side street) that causes a moving synchronized flow pattern (MSP). In an MSP, vehicles move slower than in the initial free flow of green wave, causing delays that destroy the green wave synchronization with the traffic lights. The result is oversaturated traffic at the traffic signals.In the other model, called a two-phase model, an initial speed disturbance does not cause an MSP and the delays associated with MSPs. However, if the initial speed disturbance is large enough, and there is a large number of vehicles in the wave, then oversaturation and green wave breakdown can still occur. In both models, Kerner found that one or more phase transitions are involved in the breakdown process. Also, breakdown occurs with a certain probability of less than 1; in simulations runs with the same parameters, breakdown occurs at some times but not at others.While the models offer a theoretical explanation of how green wave breakdown may occur, experimental tests are needed to gather data and determine which model best fits the data. Kerner hopes that an empirical test will be performed in which the vehicle speed and flow rate are measured both upstream and downstream of a synchronized traffic signal. By studying speed disturbances and the possible emergence of MSPs, researchers could then determine the initial disturbances and how they lead to green wave breakdown.”This would be a very interesting test for an EU project,” Kerner told Phys.org. “However, as far as I know, there are no EU programs for such empirical studies of signal control. The problem is that my theory contradicts all classical theories of urban traffic, which, as is well known, do not work in the real world.” What causes traffic gridlock? More information: Boris S. Kerner. “The physics of green-wave breakdown in a city.” EPL, 102 (2013) 28010. DOI: 10.1209/0295-5075/102/28010 Explore further © 2013 Phys.org. All rights reserved. Journal information: Europhysics Letters (EPL) (Phys.org) —If you’ve been lucky enough to catch all the green lights as you drive down a busy street, you may have been benefiting from intentional synchronization called a “green wave.” The green wave concept has been around in the US since the 1920s, but it doesn’t always work as it should. When traffic gets backed up for some reason, “green wave breakdown” occurs. In a new paper, physicist Boris Kerner at the University of Duisburg-Essen in Essen, Germany, has modeled and analyzed the causes of green wave breakdown, and the results may lead to better coordinated green waves and more efficient traffic flow. 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.
When an exciton (blue spot) moving along a nanotube collides with a zero-dimensional state (red spot), the exciton decays radiatively by emitting a photon. Here, the scientists generated local zero-dimensional states by doping the nanotubes with oxygen atoms. Credit: Yuhei Miyauchi, et al. ©2013 Macmillan Publishers Limited More information: Yuhei Miyauchi, et al. “Brightening of excitons in carbon nanotubes on dimensionality modification.” Nature Photonics. DOI: 10.1038/NPHOTON.2013.179 The researchers, Yuhei Miyauchi, et al., have published their paper on modifying the dimensionality of carbon nanotubes in a recent issue of Nature Photonics.Under an applied electric current or light irradiation, excited electrons and holes (positively charged locations where electrons are missing) are created, and carbon nanotubes emit near-infrared light. In this process, excited electrons and holes form bound states called excitons, and a photon is emitted due to the recombination of an electron and a hole during this process. As the researchers explain, a nanotube’s brightness, or luminescence quantum yield, is determined by the balance between the radiative and non-radiative decay rates of its excitons. In nanotubes, non-radiative decay dominates, resulting in low luminescence. Previous research has shown that this non-radiative decay is mainly due to the rapid collision between excitons and nanotube defects, which quench, or suppress, the excitons. Efforts have been made to reduce the defect quenching of the excitons, with varying success.However, not all defects quench excitons. As the scientists explain, defects with certain electronic structures can capture excitons and convert them into photons with a very high radiative decay rate, possibly even higher than the excitons’ intrinsic rate. These beneficial defects function as zero-dimensional states, and the scientists saw them as an opportunity to improve nanotube luminescence.In experiments, the researchers sparsely doped the carbon nanotubes with oxygen atoms, which act as zero-dimension-like states embedded in the one-dimensional nanotubes. They found that, at room temperature, excitons in the zero-dimension-like states can achieve a luminescence quantum yield of 18%, an order of magnitude larger than the 1% value of those in one-dimensional nanotubes. The researchers attribute this improvement to mechanisms that reduce the non-radiative decay rate and enhance the radiative decay rate, and predict that the luminescence could be further improved. Journal information: Nature Photonics Explore further Citation: Light-emitting nanotubes get brighter with zero-dimensional states (2013, July 23) retrieved 18 August 2019 from https://phys.org/news/2013-07-light-emitting-nanotubes-brighter-zero-dimensional-states.html Advances in the understanding of how carbon nanotubes move charges created by light © 2013 Phys.org. All rights reserved. “We think that the luminescence can be further increased if we can find a better local atomic structure of an artificial zero-dimensional state,” Miyauchi, a researcher at Kyoto University and the Japan Science and Technology Agency, told Phys.org. “At this point, our zero-dimensional state has a lower lying dark state just below the bright state, which results in about 50% reduction of the quantum yield at room temperature. If one can find a better local structure, we expect that it may be possible to remove this dark state below the bright state. Then, we expect further increase of the luminescence yield of excitons in the local state.”In the future, the researchers hope that the results will stimulate further investigation of zero-dimensional—one-dimensional hybrid systems, regarding applications as well as the fundamental physics behind the systems.”We plan to develop a more sophisticated technique to generate only one zero-dimensional state in a single suspended carbon nanotube connected to electrodes, which is necessary to develop a real near-infrared single-photon emitter operable at room temperature using carbon nanotubes,” Miyauchi said. “We also plan to try to achieve lasing using this material. Although it has been considered to be very difficult to achieve lasing using carbon nanotubes as gain media because of the very rapid non-radiative decay due to rapid collisions between excitons under a strong excitation regime, we believe that it would be possible using zero-dimensional states in carbon nanotubes, because excitons in zero-dimensional states would avoid collision with other excitons.”Our findings could also lead to the fabrication of all-carbon near-infrared LEDs or lasers. Near-infrared light sources are very important for telecommunications using optical fibers. One usually needs minor metals such as In, Ga, and As, to fabricate light emitters for this wavelength range. If one can make efficient light sources using only abundant carbon and without any minor metals, it would be very nice from the viewpoint of the resource problem.”We are also very interested in the fundamental physics in these nice hybrid low-dimensional nanostructures, and we will explore another more interesting physics in them that possibly emerges from the interactions between the states with different dimensions in the same nanostructures.” Carbon nanotubes have the potential to function as light-emitting devices, which could lead to a variety of nanophotonics applications. However, nanotubes currently have a low luminescence quantum yield, typically around 1%, which is restricted by their one-dimensional nature. In a new study, scientists have demonstrated that artificially modifying the dimensionality of carbon nanotubes by doping them with zero-dimensional states can increase their luminosity to 18%. The findings could lead to the development of nanophotonics devices such as a near-infrared single-photon emitter that operates at room temperature. 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.
More information: Generalist-specialist trade-off during thermal acclimation, Royal Society Open Science, rsos.royalsocietypublishing.or … /10.1098/rsos.140251 As it appears we humans are not likely to alter the course of global warming, at least any time soon, scientists continue to study other animals to try to ascertain how they might fare in an increasingly uncertain climatic future. In this new effort, the researchers chose to focus on mosquitofish because they have a reputation of being able to acclimate to changes in their environment. The fish were introduced into Australia in 1925, in hopes that they would help reduce the mosquito population. Since then they have come to inhabit waters all across the country, due to their uncanny ability to acclimate to water temperature differences and are now considered a pest.To learn more about the acclimation abilities of the fish, the team captured specimens from a well studied site with known temperature variations, and placed them in tanks of water of varying degrees, from 20 to 30 degrees centigrade and tested their ability to acclimate by creating an artificial stream, also of varying degrees and noting how well they swam against it. Analysis of the data revealed that some specimens were much better at acclimating to warmer temperatures than others, offering a clue as to how the fish species was able to spread so successfully. But the data also showed that despite their hardy reputation, the fish that were able to acclimate to colder water were not able to do so for warmer water, which suggests that such fish will likely fare poorly as average temperatures in their environment increase over the next century—because of the difficulty in acclimating to more extreme fluctuations in temperature.The team says their findings likely apply to other species as well, and theorize that as the world grows warmer, animals that live in colder climates are likely to experience more difficulty acclimating than will those that live in warmer places, particularly cold blooded species. Polar Bear (Ursus maritimus) near Kaktovik, Barter Island, Alaska. Credit: Alan Wilson/Wikipedia. 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. Shape up quickly—applies to fish, too (Phys.org)—A study conducted by a quartet of researchers from the University of Sydney, Université de Lausanne and the University of Glasgow has led to findings that suggest cold climate animals are more likely to suffer adverse impacts due to global warming than are animals that naturally live in warmer parts of the world. In their paper published in the journal Royal Society Open Science, the team describes how exposing mosquitofish to various temperature changes showed its ability to acclimate to changes in its environment and why the team believes such findings likely apply to other species as well. Journal information: Royal Society Open Science © 2015 Phys.org Citation: Study shows cold climate animals may suffer as global temperatures rise (2015, January 21) retrieved 18 August 2019 from https://phys.org/news/2015-01-cold-climate-animals-global-temperatures.html Explore further
Credit: M. Malischewski Newly created ‘sandwich rings’ could lead to better computers © 2016 Phys.org Explore further 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. More information: M. Malischewski et al. Isolation and structural and electronic characterization of salts of the decamethylferrocene dication, Science (2016). DOI: 10.1126/science.aaf6362AbstractFerrocene and its decamethyl derivative [Cp*2Fe] are the most common standards for nonaqueous electrochemical investigations because of their well-defined and only mildly solvent-dependent reversible Fe(II)/Fe(III) redox couple. Higher oxidation states have only rarely been studied. We report the isolation and crystallographic and spectroscopic characterization of surprisingly stable Fe(IV) salts of the [Cp*2Fe]2+ dication, produced by oxidation of [Cp*2Fe] with AsF5, SbF5, or ReF6 in neat sulfur dioxide as well as [XeF](Sb2F11) in neat hydrogen fluoride. The Sb2F11– salt exhibits a metallocene with the expected mutually parallel arrangements of the Cp* rings, whereas the As2F11–, AsF6–, SbF6–, and ReF6– salts manifest tilt angles ranging from 4° to 17°. Both 57Fe Mössbauer spectroscopy and superconducting quantum interference device magnetization studies reveal identical d-orbital splitting with an S = 1, 3E ground state based on the 3d electronic configuration e2g3a1g1 of all [Cp*2Fe]2+ salts. Journal information: Science Due to its instability, very little research has been done to characterize Fe(IV) compounds. Researchers from Free University Berlin and Fredrich-Alexander-University Erlangen-Nürnberg have demonstrated that pentamethylcyclopentadienide (C5Me5- or Cp*) acts as a strong π-donating ligand that creates a stable Fe(IV)-containing compound. This ligand may serve as a model for investigating higher oxidation states for other metals. This work is published the recent issue of Science.In most cases in which researchers have isolated a compound with an Fe(IV) oxidation state, the metal was coordinated to ligands that offer strong π-donor properties such as terminal nitrido and oxido ligands. These compounds are typically unstable and difficult to analyze. Malischewski, et al. were able to isolate the [Cp*2Fe]2+ dication as a salt with several different anions, allowing them to conduct crystal studies as well as electronic studies using SQUID and Mössbauer spectroscopy.To make the Fe(IV) organometallic salts, [Cp*2Fe] was combined with strong oxidizers (AsF5, SbF5, ReF6, [XeF](Sb2F11)) in either sulfur dioxide or hydrogen fluoride. The resulting salts were isolable and analyzed.The crystal structures of each of the salts showed slight differences in the way the Cp* ring was tilted, which the authors attribute to the identity of the counterion. The rings displayed no tilt with Sb2F11- and tilts ranging from 4.17o for As2F11- to 16.56o for SbF6-. The large anions with eleven fluorides seem to promote little ring tilt while the smaller anions with six fluorides promoted a more pronounced tilt. This may be due the stronger interactions of the polarized cation with the smaller anions, which possess higher charge densities. All of the structures showed hydrogen bonding between methyl and fluorine and a large distance between fluorine and iron. The hydrogen bonding between the methyl and fluorine is more pronounced in the smaller anions and may be another contributing factor to the observed ring tilting. Notably, the Fe-C bond lengths were much longer than the Fe-C bonds in its lower oxidation states. SQUID studies showed that the compounds possess effective magnetic moments of slightly over 3 µB, indicative of two unpaired electrons. The temperature dependencies of the magnetic moments further suggest the presence of considerable spin-orbit interactions. Additionally, Mössbauer spectroscopy studies correlate with the obtained structural parameters and indicate an oxidation state of +4. Both techniques suggest a d-orbital ordering similar to that of ferrocene. This means that the ordering changes two times in a stepwise fashion going from Fe(II) to Fe(IV).This research provides interesting insights into a stable Fe(IV) metallocene. Further research may include possible applications of [Cp*2Fe]2+ salts as well as studying other metals with multiple oxidation states. Citation: Isolation of Fe(IV) decamethylferrocene salts (2016, August 29) retrieved 18 August 2019 from https://phys.org/news/2016-08-isolation-feiv-decamethylferrocene-salts.html (Phys.org)—Ferrocene is the model compound that students often learn when they are introduced to organometallic chemistry. It has an iron center that is coordinated to the π electrons in two cyclopentadienyl rings. (C5H5- or Cp). Ferrocene is often used as a standard in electrochemical experiments because of its characteristic reversible oxidation of Fe(II) to Fe(III).