Researchers find orange manganesedoped quantum dots made up of many colors

first_imgA solution containing millions of manganese-doped quantum dots in a plastic container glows orange. Credit: APS (Phys.org) —A team of researchers working at the Indian Institute of Science in Bangalore has found that manganese-doped quantum dots that appear orange are actually a mixture of many dots of different colors. In their paper published in the journal Physical Review Letters, the team describes how upon microscopic examination of a sample of seemingly orange quantum dots, they discovered a mix of dots of different colors that gave the sample its overall orange hue. Prior research has found that quantum dots can be created that emit different colors depending on how large they are. Such dots absorb short wavelength photons and emit long wavelength photons. The color of the emitted photon stream depends on the size of the dot because it determines its quantum and energy state. Scientists are studying colored quantum dots because it’s thought they might be used to create lighting or display devices. One major drawback to their use, however, is the material used to create them: cadmium-selenide. It’s highly toxic. For that reason, researchers have been looking to other materials as a replacement. In this new effort, the researchers created light emitting quantum dots using a zinc-cadmium-sulfur alloy that had been doped with manganese. Prior research with similar materials has resulted in samples that result in emitting just one color—orange.To learn more about why the dot samples emitted just one color, the researchers spread a single layer of the dots over a polymer film, allowing for a closer look using a microscope. To their surprise, they discovered a rainbow of colors being emitted by the dots. The orange was simply the color that was produced when they were blended. Because quantum dots created via manganese doping are not color dependent on size, the researchers theorized that the different colors they witnessed were the result of where their ions were located on the dots—some were on or near the surface, others were near the center.To test their theory, the team coated some of the dots with a layer of material that hadn’t been doped, preventing ions from residing on the dot surface. In so doing, they discovered the light emitted was bluer than similar dots without the coating. Thus, they showed that their theory was correct while also demonstrating a way to customize the color of the dots they created.The researchers believe the colored dots have more wide ranging uses than simply in lighting or display devices, suggesting they might wind up in solar cells as well. Explore further Journal information: Physical Review Letters Citation: Researchers find orange manganese-doped quantum dots made up of many colors (2013, July 1) retrieved 18 August 2019 from https://phys.org/news/2013-07-orange-manganese-doped-quantum-dots.htmlcenter_img More information: Ultranarrow and Widely Tunable Mn2+-Induced Photoluminescence from Single Mn-Doped Nanocrystals of ZnS-CdS Alloys, Phys. Rev. Lett. 110, 267401 (2013). prl.aps.org/abstract/PRL/v110/i26/e267401AbstractExtensively studied Mn-doped semiconductor nanocrystals have invariably exhibited photoluminescence over a narrow energy window of width ?150??meV in the orange-red region and a surprisingly large spectral width (?180??meV), contrary to its presumed atomic-like origin. Carrying out emission measurements on individual single nanocrystals and supported by ab initio calculations, we show that Mn PL emission, in fact, can (i) vary over a much wider range (?370??meV) covering the deep green—deep red region and (ii) exhibit widths substantially lower (?60–75??meV) than reported so far, opening newer application possibilities and requiring a fundamental shift in our perception of the emission from Mn-doped semiconductor nanocrystals.via Physics Focus © 2013 Phys.org Perfectly doped quantum dots yield colors to dye for 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.last_img read more

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University team has AR SeeThrough System for safe driving w Video

first_img More information: Research paper: www.it.pt/papconf_pdf_p.asp?ID … onference=10281&id=3ismar.vgtc.org/www.newscientist.com/article/m … cars-seethrough.htmlwww.dcc.fc.up.pt/~michel/ 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. Michel Ferreira and his colleagues at the University of Porto in Portugal developed the See-Through System. Ferreira is also founder of a technology-based company specialized in the “optimization of vehicular mobility,” called Geolink. Ferreira has stated that he is not only interested in “Intelligent Transportation Systems” (ITS) but in what he terms “Cooperative ITS,” where inter-vehicle communication plays an important role. In a scenario involving the See Through System, large vehicles drive with a forward-facing webcam on their windshield. Cars have a transparent LCD screen built into their windshield. The driver is able to see what the road in front of the blocking vehicle looks like, in the position that the vehicle occupies on the road. The system has been tested in a driving simulator, and on the road. Their work was presented at The International Symposium on Mixed and Augmented Reality in Australia earlier this month. Actually, this is an initiative that has been ongoing for several years. In 2010, the paper, “The See-Through System: A VANET-Enabled Assistant for Overtaking Maneuvers ” was presented at an IEEE symposium. The authors said that thus far the “results are promising, since the use of the 802.11p standard wireless communication protocol allows a vehicle-to-vehicle connection without significant delay and the totality of the participants regarded the information provided by the STS as useful.” Honda demonstrates new technology to prevent cars hitting pedestrians (w/ Video) Citation: University team has AR See-Through System for safe driving (w/ Video) (2013, October 19) retrieved 18 August 2019 from https://phys.org/news/2013-10-university-team-ar-see-through-safe.html © 2013 Phys.org Explore further (Phys.org) —University of Porto in Portugal researchers have come up with a See-Through System (STS) designed to see through vehicles, making view-blocking vehicles transparent. A lightweight heads-up display is used to look through a truck, for example, ahead. The idea is to support a driver who is stuck behind a large, slow-moving vehicle on the highway and has no way to check if it is safe or not to pass. According to a New Scientist report on the system, the image has a delay of 200 milliseconds, and it shows an oncoming car to be ten meters further away than it actually is, if both it and the driver’s car are moving at 90 kilometers per hour. The term VANET stands for Vehicular Ad Hoc Networks, a key focal point in Ferreir’a research.”Vehicular Networks are a particular case of networks where the geographical awareness of nodes is crucial in the design of protocols and applications,” he said. “A major goal in my research is the efficient design of large-scale distributed systems that use infrastructureless communication to self-organize, based on spatial reasoning.”In that 2010 paper, the authors noted that the STS system is based on the following assumptions: Equipped vehicles have windshield-installed cameras, connected to an on-board computer that can compress video, recognize traffic signs and support inter-vehicle communication protocols; equipped vehicles have GPS, and DSRC radios; equipped vision-obstructing/long vehicles display a rear sign mentioning “STS Enabled” (a VANET enhancement over the typical “Long Vehicle” sign); and equipped overtaking vehicles have a screen on the dashboard where the video streaming can be visualized.last_img read more

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Soda can array revisited It may not beat the diffraction limit after

first_img More information: A. A. Maznev, et al. “Extraordinary focusing of sound above a soda can array without time reversal.” New Journal of Physics. DOI: 10.1088/1367-2630/17/4/042001 Experimental arrangement of the soda can array inside the anechoic room. The green line shows the scan line of the microphone that measures the acoustic intensity of the array. Credit: A. A. Maznev, et al. CC-BY-3.0 Explore further Although it was thought that the time reversal technique was essential for achieving the extreme focusing, the technique used in the new study is more straightforward: six speakers surrounding the array produce sound at a single frequency that continually increases. When the frequency approaches the cans’ resonant frequency of 420 Hz, the focal spot at the center of the array becomes progressively smaller, as measured by a microphone hanging overhead.The researchers’ analysis reveals that the principal reason for the sharp focusing is the same in both studies: the wavelength of the acoustic wave propagating above the array gets progressively shorter as its frequency approaches the Helmholtz resonance of the cans. In other words, the focusing effect is a result of the resonant nature of the metamaterial, and not a result of time reversal. The researchers explained that conventional materials don’t have acoustic resonances because atoms or molecules do not resonate at acoustic frequencies. However, using artificial building blocks such as soda cans, it’s possible to build locally resonant metamaterials with tailored properties that don’t have analogues in nature.Although time reversal may not be essential for achieving the sharp focusing, the technique still has undisputed advantages. For instance, time reversal allows the researchers to control the acoustic waves to focus on any chosen can, and it does not require the can array to have a specific shape. In contrast, the array that does not use time reversal must be shaped as a lens—in the current study the researchers used a hexagonal array approximating a circle.Although the researchers don’t see any direct practical applications of the soda can array for now, they note that there’s a certain educational value because the soda cans make a nice model system of a metamaterial: a metamaterial built of soda cans is just like a natural material built of atoms, but in this case the metamaterial can exhibit some remarkable acoustic properties. Despite this strong focusing, the scientists argue that neither study truly beats the diffraction limit. The problem lies in the fact that the above comparisons (1/25 and 1/40 the size of the wavelength) refer to the wavelength in air. The scientists explain that the comparison should instead be made with the wavelength of the acoustic wave in the soda can metamaterial, which becomes progressively smaller as the acoustic frequency approaches the resonant frequency of the cans from below. Furthermore, they found that the technique used in the previous study, called time reversal, which was thought to be crucial for the sharp focusing, is not a fundamental requirement. In both set-ups, the array of cans is surrounded by several speakers. However, in the array that used time reversal, a microphone placed above a can was used to emit a short sound pulse. Each speaker recorded a signal originating from this pulse, and then each speaker played back its own signal in reverse. When receiving the playback, the only can that resonated was the one from which the sound was originally captured. Everywhere else, the waves cancelled out. (Phys.org)—In 2011, scientists from the Institute Langevin in Paris built an array of 49 empty coke cans that resonate when exposed to an acoustic wave, causing the cans to produce sound similar to the way blowing across the top of an empty bottle produces sound. The researchers wanted to test the sound-focusing abilities of this array, which can be considered a metamaterial built of soda cans, whose properties depend on the structure of the array. © 2015 Phys.org 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. Coke cans focus sound waves beyond the diffraction limit Journal information: New Journal of Physics Coauthor Gen Gu of Nanjing University with the soda can array in the anechoic (non-echoing) room. Although the array achieves extraordinary acoustic focusing due to its metamaterial properties, the scientists found that it does not truly beat the diffraction limit. Credit: A. A. Maznev, et al. Citation: Soda can array revisited: It may not beat the diffraction limit after all (2015, April 28) retrieved 18 August 2019 from https://phys.org/news/2015-04-soda-array-revisited-diffraction-limit.html For any wave-focusing device—whether it be a microscope lens or a sound lens—the resolution is generally limited by the diffracting (bending) of the optical or acoustic waves. The resulting diffraction limit restricts the resolution to about half a wavelength. However, the researchers demonstrated that the soda can array can focus a 0.8-meter-long acoustic wave to a spot size of just a few centimeters, or about 1/25th the size of the acoustic wavelength—significantly beating the diffraction limit. But now, four years later, scientists have found that the soda can array may not truly beat the diffraction limit, and further, it may not even work in the way that was originally thought.In a paper published in the New Journal of Physics, A. A. Maznev, et al., from Nanjing University and MIT, have constructed an array of 37 empty coke cans and demonstrated that it can focus an acoustic wave to a spot size as small as 1/40 of the acoustic wavelength, making its focusing ability even stronger than in the previous work. last_img read more

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Delicately opening a band gap in graphene enables highperformance transistors

first_img(a) A band gap was opened in bilayer graphene by chemical doping with an electron-donating dopant (BV) on the bottom and an electron-accepting dopant (atmospheric molecules) on the top, which creates a vertical electric current. (b) A field-effect transistor fabricated from the dual-side doped bilayer graphene shown in (a). (c) Optical image of the fabricated transistor with a bilayer graphene channel, source, and drain on the BV layer. Credit: Lee, et al. ©2015 American Chemical Society Their method is based on applying a vertical electric field through the bilayer graphene, which has been shown to break the symmetry between the two graphene layers. This modification creates atomic sites with different electric potentials, which produces a band gap. Previous studies have also used this strategy, in which the electric field is generated by “dual-side doping” of opposite sides of the bilayer with different chemicals. However, the previous results have been limited due to ineffective types and levels of dopants, which have generated relatively small electric fields and have also damaged the highly ordered graphene structure.In the new study, the researchers demonstrate that one key to improving these areas is the choice of benzyl viologen (BV) as an electron-donating (n-type) dopant at the bottom of the bilayer graphene. The top side is then doped simply with oxygen and moisture from the atmosphere, which act as electron-withdrawing (p-type) dopants. As the BV molecules donate electrons to the bottom graphene layer, the atmospheric dopants withdraw the electrons from the top graphene layer, generating a vertical electric field. Since a stronger electric field induces a larger band gap, the researchers could control the band gap by using higher concentrations of dopants. All of the dopants used here are absorbed on the surface of the bilayer graphene without damaging the graphene structure, which helps to maintain graphene’s high electron mobility and corresponding high “on” current.To demonstrate the usefulness of the band-gap-opened graphene, the researchers fabricated a transistor with memory behavior. The device is programmed and erased by applying a positive and negative voltage, respectively. The transistor’s high program/erase current ratio corresponds to a longer retention time. However, the researchers note that the device still has room for improvement. For example, its speed can be increased. Also, using atmospheric molecules as dopants is not ideal for industrial-scale manufacturing due to low stability, so a more durable p-doping method will be needed. “It is necessary to develop more stable and effective dopants for higher device performances,” Si Young Lee said. “Furthermore, our device can be realized on flexible and transparent substrates for future electronics.” (Phys.org)—Electrons can move through graphene with almost no resistance, a property that gives graphene great potential for replacing silicon in next-generation, highly efficient electronic devices. But currently it’s very difficult to control the electrons moving through graphene because graphene has no band gap, which means the electrons don’t need to cross any energy barrier in order to conduct electricity. As a result, the electrons are always conducting, all the time, which means that this form of graphene can’t be used to build transistors because it has no “off” state. In order to control the electron movement in graphene and enable “off” states in future graphene transistors, graphene needs a non-zero band gap—an energy barrier that can prevent electrons from conducting electricity when desired, making graphene a semiconductor instead of a full conductor. Citation: Delicately opening a band gap in graphene enables high-performance transistors (2015, September 21) retrieved 18 August 2019 from https://phys.org/news/2015-09-delicately-band-gap-graphene-enables.html Journal information: ACS Nano Phagraphene, a relative of graphene, discovered Explore further More information: Si Young Lee, et al. “Chemically Modulated Band gap in Bilayer Graphene Memory Transistors with High On/Off Ratio.” ACS Nano. DOI: 10.1021/acsnano.5b03130 In a new study, scientists have opened a band gap in graphene by carefully doping both sides of bilayer graphene in a way that avoids creating disorder in the graphene structure. Delicately opening up a band gap in graphene in this way enabled the researchers to fabricate a graphene-based memory transistor with the highest initial program/erase current ratio reported to date for a graphene transistor (34.5 compared to 4), along with the highest on/off ratio for a device of its kind (76.1 compared to 26), while maintaining graphene’s naturally high electron mobility (3100 cm2/V·s). The researchers, led by Professor Young Hee Lee at Sungkyunkwan University and the Institute for Basic Science in Suwon, South Korea, have published their paper on the new method for opening up a band gap in graphene in a recent issue of ACS Nano. “We successfully demonstrated a graphene transistor with a high on/off ratio and mobility by chemical methods and showed its feasibility as a memory application with a significantly improved program/erase current ratio,” first author Si Young Lee, at the Institute for Basic Science and Harvard University, told Phys.org. © 2015 Phys.org Examples of the band structure (with calculated band gap energies indicated) for different samples of bilayer graphene: (a) doped on one side with BV only, (b) doped on one side with oxygen only, (c) doped on both sides with BV and oxygen, and (d) doped on both sides with BV and twice as much oxygen as in (c). Above each graph is an illustration of the charge distribution induced by doping. Credit: Lee, et al. ©2015 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.last_img read more

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Dancing Jewel of Kathak

first_imgThe Kathak  performance was presented in a dance drama format, portraying  the entire story of Goddess Durga and the myths associated with her.  The  show was conceptialised and choreographed by Pawar, who played the role of  Durga.Hailed as the ‘Dancing Jewel of India’, Pawar has inherited a love for this art form from her father, Pratap Pawar, who is regarded as one of the leading exponents of the Lucknow gharana of Kathak and has won international acclaim for his work and. Pawar  started dancing from the age of 8 as a part of her father’s dance troupe in London. Also Read – ‘Playing Jojo was emotionally exhausting’After continuing her practice under the guidance of her father, she matured into a dancer of immense potential and promise. She returned to India and spent three years of rigorous training under Pandit Vijay Shankar and perfected the art of Kathak dance form, assimilating its Abhinaya and Layakari aspects. She also took training in classical singing under Girija Devi.Endowed with an inherent grace, Pawar’s recitals have been suffused with a rare kind of lyricism. Her scintillating performances with communicative facial expressions, sustained spins and vibrant footwork have established an instant rapport with the spectators. She has a vast, limitless repertoire of emotions and  casts a mesmeric impact on her audiences.This program was organised   by Gurupranami, honouring  Pandit Vijai Shankar .The organisation is supported by Ministry of Culture, Government of India, ICCR (Indian Council for Cultural Relations) and SAIL.last_img read more

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A flight of fantasy

first_imgRecently artist and illustrator Sumedha Sah successfully showcased a selection of her artworks, The Umbrella Bar at Cafe Turtle. Udaan by Nandini Thirani Mehta is the latest in line to be showcased at the cafe, and is a reflection of the artist’s experiences while travelling to different parts of the world – Cambodia, Italy, Spain, Jordan and South India. ‘On my journeys I found that art, like music, brought the most diverse sets of people together. My work and perspective as an artist allowed me to build common ground and strike up conversations with people from all walks of life,’ says Nandini Thirani Mehta.  ‘The bright colours and textures in the paintings represent parts of me that I have left with the people I met along the way,’ she says. Also Read – ‘Playing Jojo was emotionally exhausting’The artist’s interest in art has been profoundly shaped by her early experiences studying under the late Padma Shree artist Badri Narayan. She had him as her art teacher in the second and third grade. She tells how amazing his teaching style was, ‘he would tell us fascinating stories drawn from mythology and ask us to draw what we imagined when we were listening to them. At that early stage, I knew that I was happiest when I was drawing and painting.’Her photography is hugely inspired by Raghu Rai. His work introduced her to the magical world of black and white photography. Chirodeep Chaudhari’s amazing ability to capture the essence of street life is another big inspiration. So head on and fly! When: 5 – 11 July Where: Cafe Turtle, N block GK 1last_img read more

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Cout stays defamation cases against TN editor Nakkheeran

first_imgIn a relief to Tamil Nadu-based editor and publisher, Nakkheeran Gopal, the Supreme Court on Friday stayed proceedings against him in 15 criminal defamation cases lodged in Chennai local courts. A bench of Justices Dipak Misra and P C Pant also issued notices to Union Law Ministry and the Tamil Nadu government on Gopal’s petition which has also challenged the constitutional validity of penal laws on defamation law and a CrPC provision.last_img

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Good sleep improves work satisfaction

first_imgAdequate sleep every night may improve working life by reducing perceived job stress and minimising negative attitude toward work, says a study. Disturbed sleep increases stress response and emotional reactivity, the results showed.“The effect of sleep problems on stress emphasises the importance of good sleep for functioning in everyday life,” said lead author Torbjorn Akerstedt, professor at Karolinska Institute in Stockholm, Sweden. The researchers analysed data from the 2008 and 2010 surveys of a study comprising 4,827 participants with a mean age of 48 years, including 2,655 females and 2,171 males. Results showed that higher work demands predicted subsequent sleep disturbances at the two-year follow-up. Also Read – ‘Playing Jojo was emotionally exhausting’Similarly, sleep disturbances predicted a higher perception of stress, higher work demands, a lower degree of control, and less social support at work two years later.The results suggest that there may be a reciprocal, causal pathway between job strain and disturbed sleep, implying that interventions to treat sleep problems may improve work satisfaction.The study was published in the journal Sleep.last_img read more

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Forward Bloc veteran Paresh Adhikary joins TMC

first_imgKolkata: Forward Bloc leader and former Food minister Paresh Adhikari joined Trinamool Congress on Friday. The party’s flag was handed over to Adhikari by Trinamool Congress secretary general Partha Chatterjee at Trinamool Bhavan, in presence of state Backward Classes Welfare minister Rajib Banerjee.”Adhikari had spoken with our party supremo Mamata Banerjee and had expressed his interest to join our party and be a part of the all-round development of Bengal under her leadership. She has agreed to induct Adhikari and today (Friday) he is officially becoming a member of our party,” Chatterjee said. Also Read – Rain batters Kolkata, cripples normal lifeAccording to Chatterjee, Adhikari will work alongside Udayan Guha for strengthening the party’s organisational strength in North Bengal. Guha, who was a Forward Bloc MLA from Dinhata in Cooch Behar, had joined Trinamool Congress in 2016, before the Assembly elections.”Adhikari is a well-known figure in the politics in North Bengal and will play an important role in development of the state and maintaining unity among the people,” Chatterjee maintained. Also Read – Speeding Jaguar crashes into Mercedes car in Kolkata, 2 pedestrians killed”The people of Cooch Behar have been gripped by a sense of fear over the National Register of Citizens (NRC) issue in Assam. Our Chief Minister is working against NRC. So I felt that the time is ripe to join her hands in this matter,” Adhikari said, when asked about the reason of his joining the party.Adhikari is a four time MLA from Mekhliganj in Cooch Behar and had won on Forward Bloc’s ticket in 1991, 2001, 2006 and 2011. He was the Food minister under the Left regime from 2006 to 2011. He lost to Arghya Roy Pradhan of Trinamool in the 2016 Assembly polls.last_img read more

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One held at Kol Airport for stealing gold ornaments from passengers bag

first_imgKolkata: One person was arrested on Sunday from Netaji Subhas Chandra Bose International (NSCBI) Airport in Kolkata for committing theft from a passenger’s handbag. He was detained by Central Industrial Security Force (CISF) personnel as his movement was found to be suspicious.Sources informed that on Saturday night on-duty CISF personnel noticed that a person was roaming inside the terminal. When the person identified as Sajid Hossain was questioned by CISF personnel, he replied that he is waiting for his flight Also Read – Rain batters Kolkata, cripples normal lifeto Imphal. As he reached early he was just taking a walk inside the terminal. On hearing Hossain, the CISF jawan asked him sit and then left the place. But he was keeping an eye on him. A few moments later, he was seen going to a washroom. When Hossain came out of the washroom the CISF jawan noticed that he changed his dress. Thus, his suspicion grew more. He immediately informed his superiors about Hossian’s movement. To keep a tab on Hossian’s movement, one CISF jawan started montoring him on the CCTV. Also Read – Speeding Jaguar crashes into Mercedes car in Kolkata, 2 pedestrians killedIt was seen that Hossain was repeatedly going to the washroom and kept on changing his clothes. Around 11 pm CISF personnel noticed that he was not approaching the security check enclosure despite his boarding time at around 11.30 pm. He was then asked why was he changing his clothes repeatedly. As Hossian’s answer was not convincing, he was detained and taken to CISF facility at the airport. He was interrogated for a long time and was later handed over to NSCBI Airport police station on Sunday. There he was interrogated and his bag was searched. Police found some gold ornaments which did not belong to him. Meanwhile, a lady passenger complained that her handbag was missing. Some CISF personnel were able to locate the bag and returned it to her. After getting the bag she found that some ornaments inside the bag were missing. She went to the police station and lodged a complaint. After hearing the description she was showed the ornaments that were found from Hossian’s bag. She identified and said it was her. Later, Hossian was arrested.last_img read more

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