Graphene quantum dot LEDs Citation: Scientists demonstrate first color-tunable and first graphene-based LED (2015, July 28) retrieved 18 August 2019 from https://phys.org/news/2015-07-scientists-color-tunable-graphene-based.html Journal information: Nature Communications Instead of having a bandgap somewhere in between GO and rGO, the partially reduced interfacial GO actually has many different intermediate bandgaps as a result of how the blending occurs—not as a smooth transition, but in the form of rGO nanoclusters embedded within the GO layer. Because these rGO nanoclusters are reduced to varying degrees at the interface, they exhibit variations in their energy levels and, consequently, in the color of emitted light. These energy levels can be easily modulated by changing the applied voltage or by chemical doping, which selectively stimulates a single color of luminescence and enables tuning of the LED’s color.”We found that a combination of GO and rGO can create a conductive and wide bandgap material,” Ren told Phys.org. “It is commonly known that graphene does not have a bandgap. Therefore we were all surprised that our GO/rGO interface (a graphene-based system) can actually be luminescent.” Commercial expectationsThe fact that this is the first observation of luminescence in a graphene-based system paves the way toward using graphene as a light source in future graphene-based photonic devices. A color-tunable LED has also been highly desired for high-quality LED displays and light fixtures. Because the color changes in response to certain chemicals, the devices could also have sensing applications. “Graphene-based, color-tunable LEDs can enable the realization of flexible display technologies that can cover the entire visible spectrum,” Ren said. “Conventional LEDs only emit a fixed wavelength of light and thus display technologies require a mixture of red, green, and blue LEDs. If a graphene-based, color-tunable LED is used, a full-color and flexible display can be realized in a simple way. A wide range of consumer and medical electronics can benefit from such a technology.”In their work, the researchers designed, fabricated, and tested 20 graphene-based LEDs. Overall, the devices demonstrated good brightness but low efficiency, which they plan to improve. Another drawback of the current prototype is a very short emission lifetime of less than a minute or so in ambient conditions and about 2 hours in vacuum. The researchers attribute the short lifetime to oxidation in the air and predict that protective coatings may improve this area.Despite the room for improvement, the researchers expect the graphene-based LEDs to have encouraging commercial prospects due to several advantages, including their precise color tunability, compact structure, and straightforward fabrication.”The efficiency of the graphene LED could be improved further,” Ren said. “One way to achieve this would be by using n-type [semiconductor] materials combined with graphene. The short lifetime could also be improved by vacuum sealing. Commercialization may be expected in a few years since our method is simple and low-cost. As with any other technological development coming out of a lab, challenges exist; however, we believe these challenges can be overcome in the near future. We believe that graphene-based, color-tunable LEDs are a promising technology for flexible displays.” So it’s quite remarkable that in a new study, scientists have demonstrated an LED that not only can be tuned to emit different colors of light, but can do so across nearly the entire visible spectrum: from blue (450-nm wavelength) to red (750-nm wavelength)—basically all colors but the darkest blues and violets.The key to achieving the color-tunable LED is making it out of graphene—the same material that has led to groundbreaking research in a number of areas, from batteries to solar cells to semiconductors. Despite graphene’s success in these areas, graphene-based LEDs have never been realized before now, making the new device the first-ever graphene-based LED in addition to being the first color-tunable LED. Applications of the new LED include high-quality, color-tunable LED displays for TVs and mobile devices, color-tunable LED light fixtures, and the potential for a variety of future graphene-based photonic devices. Blending two forms of grapheneThe researchers, led by Professor Tian-Ling Ren at Tsinghua University in Beijing, made the light-emitting material from the interface of two different forms of graphene. These forms are graphene oxide (GO), which is produced from inexpensive graphite, and reduced graphene oxide (rGO), which is a more pristine form of GO. (Top) The light-emitting layer lies at the interface between graphene oxide (GO) and reduced graphene oxide (rGO). (Bottom) Typical electroluminescent spectra of a single graphene-based LED. Credit: Wang, et al. ©2015 Nature © 2015 Phys.org Lying at the interface of the GO and rGO is a special type of partially reduced GO that has optical, physical, and chemical properties that lie somewhere in between those of GO and rGO. The most important “blended” property of the interfacial layer is that it has a series of discrete energy levels, which ultimately allows for the emission of light at many different energies, or colors. The occurrence of this property is especially interesting because, on their own, neither GO nor rGO (or any other known form of graphene, for that matter) can emit any light at all. This is because neither material has the right size “bandgap,” which is the gap between two energy bands that electrons must jump across to conduct electricity or emit light. While GO has an extremely large bandgap, rGO has a zero bandgap. 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 graphene-based LED’s color depends on the applied voltage. The red and blue diagrams show electrons excited to different energy levels, corresponding to different photon energies and therefore different colors of light emission. Credit: Wang, et al. ©2015 Nature Explore further More information: Xiaomu Wang, et al. “A spectrally tunable all-graphene-based flexible field-effect light-emitting device.” Nature Communications. DOI: 10.1038/ncomms8767 (Phys.org)—Currently, all light-emitting diodes (LEDs) emit light of only one color, which is predefined during fabrication. So far, tuning the color of light produced by a single LED has never been realized, despite numerous attempts.
Citation: Humpback whales found to compose new communal song every few years (2018, November 21) retrieved 18 August 2019 from https://phys.org/news/2018-11-humpback-whales-song-years.html A team of researchers from the University of Queensland and the University of St. Andrews has found that humpback whales abandon community songs every few years and pick up new ones. In their paper published in Proceedings of the Royal Society B, the group describes their multiyear study of humpback whale songs and what they found. 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 More information: Jenny A. Allen et al. Cultural revolutions reduce complexity in the songs of humpback whales, Proceedings of the Royal Society B: Biological Sciences (2018). DOI: 10.1098/rspb.2018.2088 Credit: CC0 Public Domain Some species of whales sing—humpback whales, in particular, are known for their songs. Interestingly, all male humpback whales sing the same song—though some do make some minor modifications to it. In this new effort, the researchers have discovered that every few years, humpback whales choose to abandon the song they all know, and learn to sing a new one. The research team made this finding by conducting a study of whale songs over the course of 13 years—listening in on humpback whales singing off the eastern coast of Australia and in the South Pacific.The researchers noticed that a new song would start out as a simple tune that would grow in size and complexity over time, eventually reaching a point at which it became ungainly. Some new group of whales would eventually abandon the song and come up with a new one, which they carried with them as they migrated to other parts of the ocean. Along the way, other whales would hear the song and abandon the old one, as well. Eventually, all the humpback males would be singing the same new tune.The researchers still cannot say for sure why the whales sing, though it is tied to the breeding season, or why they change their song every few years. They suspect it is because the song grows too complex, suggesting a cap on a learning curve—though it is possible the whales simply grow bored with it. The researchers note that social singing by the whales is an example of animal culture. And learning about animal culture could perhaps lead to a better understanding of how complex human culture evolved. They also note that the kind of cultural transmission seen in the whale songs has only ever been observed in humans. © 2018 Science X Network Journal information: Proceedings of the Royal Society B Male humpback whales change their songs when human noise is present
As I write this, India celebrates its 43rd Navy Day. For the uninitiated, every year December 4 is celebrated as Navy Day to commemorate the start of Operation Trident during the Indo-Pakistan war of 1971. Not something many of us, at least from our smartphone generation, are aware of, are we? I mean, why do we even need to know? Not like it’s a festival that brings new clothes and parties with it, or a public holiday so we can catch up on our sleep, or a dry day that we need to stock up on liquor! Also Read – Find your own happinessWe belong to a generation that laughs at Indian war films, considers the Armed Forces a ‘bad’ career choice, and has little, or no, respect for the men and women in uniform who tirelessly watch over us, guard us, keep us safe so we can live freely and sleep peacefully. Clearly, ’99, 26/11, have had no effect on us. Let others die for the nation. Why us? We belong to a generation with parents who aspire to have money-minting engineer/banker/lawyer children. None of my friends are in the Forces. And, none of my friends’ friends are either. Which is what amazes me. Didn’t our parents live through ’65, 71? Don’t they have enough to thank our Forces for? Evidently not. Instead of taking pride and showing them our gratitude, we’ve taken them for granted. Also Read – Into the wildJust the other day somebody remarked during the course of a discussion, “Why is it such a big deal if a soldier dies? Why must we weep over every war casualty? They were just doing their job. They signed up for it!” I was too stunned to utter even a word. We were in a room full of people, most of whom seemed to agree with her. Dear girl, you know who you are. And, I also know you’re reading this. There are a few things you need to know. It IS a big deal if a soldier dies. Hell, it’s a big deal if anybody dies, and more so when it’s somebody who has lost his life trying to protect you! We WILL cry over every war casualty. If we don’t, then we aren’t humane enough. And, finally, it isn’t a soldier’s ‘job’ to die. His job is to protect, and yes, if that means at the cost of life, then that too. We should be indebted to these selfless, brave souls, and instead, we have the gall to belittle their tremendous sacrifice? Today isn’t about the various scandals that have rocked our Armed Forces over the years. Today isn’t about the Government’s seemingly step-motherly treatment, or the controversial AFSPA and its repercussions either. Today is about a young man who spends his childhood dreaming of being a soldier, undergoes backbreaking, rigorous training for years to become one, sacrifices relationships, friendships for his first love-his nation, plays with fire to keep his countrymen safe, and if necessary, doesn’t blink an eye before giving up his life for the nation and its people. Today is about us, and how as a society we continue to show absolute neglect and indifference towards our soldiers! The military life isn’t about free rations, cheap alcohol, and fancy parties like most of us believe. It’s a life full of sacrifice, extreme stress-both physical and mental, inhumanly long hours, zero recreation, and constant life risk. Very few have the heart to do it. By failing to show our gratitude to those blessed few, we fail them. If this continues, there will come a day when there will be nobody to protect us. Is that where we wish to head?The day cricketer Phil Hughes died, Naik Kulvinder Singh of the Indian Army died fighting militants in Kashmir. How many of us even knew about it? None of the national dailies mentioned it. Both 26-year-olds laid down their lives doing what they loved best: batting for their country. Yet, there was one marked difference. This was shared with me by a soldier and I quote him, “…while Phil’s passing was mourned by…the world…Naik Kulvinder Singh’s name was reduced to just a footnote, a sad statistic in this ungrateful nation’s history.”Why? Yes, we are a selfish nation, but are we so heartless that we can’t even honour someone in death?? Reams are dedicated to cricketing heroes and Bollywood superstars. But, what about the real heroes for whom there are neither second chances nor retakes? Don’t they deserve some respect, too?Let’s not continue to be a nation of ingrates. It’s time we got up and saluted the selfless souls who watch over us. Who needs guardian angels when we have soldiers? Our soldiers, our heroes- let this be our motto! Jai Hind.Malini Banerjee is a snotty single child, mountain junkie, playback singer, Austen addict, and dreams of singing alongside Buddy Guy
KOLKATA: The Regional Meteorological Centre in Alipore predicted thunderstorm in some parts of South Bengal districts in the next two days. A senior official of the weather office said storm and thundershowers accompanied by strong gusty wind may occur in some parts of South Bengal districts on Tuesday and Wednesday. A cyclonic circulation has been hovering over the Bay of Bengal which will bring thunderstorm in the city and some other districts in South Bengal. Also Read – Heavy rain hits traffic, flightsThe official said it is not possible to announce the names of the districts where thunderstorm may occur. The alert of storm will be issued a few hours prior to the incident, the weather official said. There may be some cold spell in the city as well. The city dwellers were witnessing pre-monsoon rains until Sunday evening when the temperature lowered following heavy thundershowers. People got relief from the sultry weather on Monday.The month of May has been quite fruitful for city dwellers with rains lashing the city from time to time. The month began on a rainy note for Bengal. The people in the city may, however, feel sultry and discomfort during the afternoon. Also Read – Speeding Jaguar crashes into Merc, 2 B’deshi bystanders killedWeather experts predict thunder squall with wind speed exceeding 50-60 kmph along with lightning in some parts in the next two days. Light to moderate rain is likely to affect some parts of Kolkata and adjoining districts.According to an expert, these weather activities can be attributed to a cyclonic circulation. A few days ago, an anti-cyclone was also detected over Bay of Bengal that was providing moisture over the region. Some of the South Bengal districts may witness scattered rains during the next couple of days. According to a senior weather official, the situation is favourable for a thunderstorm.
Balassi Institute organized the opening reception of Zest Art works by Naresh Kapuria, a contemporary artist and recipient of Chevalier des Arts et Lettres by French Government. Naresh Kapuria’s artwork which is on display from March 15 to 17 had a grand opening reception organised by the Balassi Institute, Hungarian Information and Cultural Centre.Eminent guests present at the event were Odissi Dancer Sharon Lowen, Aruna Vasudev, Szilveszter Bus, Ambassdor of Hungary, Francois Richier; Ambassador of France, Jagdish Chandra, Niren Sengupta among others. Also Read – ‘Playing Jojo was emotionally exhausting’The three dimensional artwork depicts the journey of life towards materialistic and spiritual attainments. Clouds in the art work symbolize the abode of materialistic or spiritual journey. The works portraying materialistic struggle are the ones with chairs where the journey is to attain power ‘The Chair’.The pieces portraying spiritual enlightenment are with ladders ‘Towards Moksha’. The birds in the paintings are the living beings. There is also use on cycle and kite in his works; the wheels of the cycle symbolise ‘Karma’ and the kite symbolises the liberalisation of the spirit. Also Read – Leslie doing new comedy special with NetflixNaresh Kapuria is one of the most creative contemporary artists with over 40 years of experience. He has been awarded with the Chevalier des Arts et Lettres by the French Government, Award of excellence from the Romanian Government; The Order of the Crown from the Government of Belgium; the Charles Wallace Trust Award UK and the Triennial of India Award. He is an artist by soul, and has designed several Festivals in India and abroad.
Naila manal Nothing matches the experience of watching a movie made on your favourite book, right? You either hate it or love it but you will definitely watch it. To be honest, most of the time, we all end up finding flaws in the movie adaptations and the most common complaint is that the movie skimmed over the details. How many of us have watched the Harry Potter films, and hated the absence of Peeves in the film? Or how they almost omitted the story of Voldemort’s family? Winky? Oh, you wanted a detailed TriWizard tournament or Yule ball, bad luck! But what we forget is that the creators of the films had to choose from a huge amount of matter to make a two-three hour film and even splitting the last book into two movies wasn’t enough! Also Read – ‘Playing Jojo was emotionally exhausting’With these thoughts, it was a happy news for me when ABC Family announced that they are going to make a TV series out of the Mortal Instruments book series by Cassandra Clare. The series will be called Shadowhunters, based on the creatures around whom the story revolves, half humans, half angels. The books aren’t amazing, but good enough (the prequel series Infernal Devices were much better, I feel) but the first attempt at making it into a movie fell flat on its face. The movie, Mortal Instruments: City of Bones was well, disappointing to say the least. The characters were half baked, Also Read – Leslie doing new comedy special with Netflixthe plot changed, and the casting wasn’t appealing.Now that it is being reincarnated into a series one can hope for better, detailed insight in the lives of Shadowhunters. A TV series is any day more appealing than a film. For something like The Hunger Games or The Divergent books, a movie series would do because of the limited content but as far as the readers are concerned, one would always go for a TV series say for instance in a book like A song of Ice and Fire which was made into the epic drama Game of Thrones. Sherlock, House of Cards are all great examples of how book to TV series adaptation is a brilliant idea! Of course, it will be a treat for sure if somehow someday decide to make a TV Series out of the Harry Potter books. But till then, I will be watching out for Shadowhunters. Between The Covers is a weekly column on reading up and rating down
The Special Cell of Delhi Police encountered a criminal on Saturday evening who was wanted by the Punjab and Delhi Police in connection with more than half a dozen cases of cheating and forgery.The Special Cell on receiving a tip off that Manoj Kumar Vashishtha, the slain criminal, was to visit a restaurant in central Delhi’s New Rajender Nagar. Subsequently the police laid a trap and surrounded the restaurant. Manoj, on realising, the presence of cops opened fire at the team. Also Read – Company director arrested for swindling Rs 345 croreOn retaliation and self defence, the police fired a shot at Manoj following which he slumped to the ground. The public in the area started running helter-skelter on hearing bullets being fired. The police took Manoj to a hospital where he was announced brought dead.There are no reports of any casualty according to the police. Sources added that post-mortem will be conducted on Sunday and the body will be handed over to his family later.
This autumnal festival, popularly known as Shardotsav, celebrates the power of Shakti, symbolised by the Goddess Durga, who slays asura to re-establish peace and sanctity on earth again. Bengalis all over the world during these days rejoice to their heart’s content, reconnecting with friends and relatives. Durga Puja is not simply about celebrations and feasting. The actual carousing of the Puja is all about enlightenment of soul and the celebrations of the goodness over evil. It is about the triumph of truth over false and right over wrong. Durga Puja is about sustaining the mass believe of
Eating vanilla yoghurts with lower fat content gives people a stronger positive emotional response, says a new study.“We were surprised to find that by measuring emotions, we could get information about products independent from whether people like them,” said lead author Jozina Mojet from Food & Biobased Research, Wageningen University in the Netherlands.The researchers used a new method called an emotive projection test to determine the effect of different yoghurts on people’s moods. Three groups of at least 24 participants were each given a pair of yoghurts to taste. The pairs of yoghurts were of the same brand and were marketed in the same way, but had different flavours or fat content. The team then tested their emotions using four methods, including the new emotive projection test. Also Read – ‘Playing Jojo was emotionally exhausting’The researchers found that vanilla yoghurt elicited a strong positive emotional response, supporting previous evidence that a subtle vanilla scent in places like hospital waiting rooms can reduce aggression and encourage relationships among patients and between patients and staff.The team also looked at the sensory effect of the yoghurts. There was no difference in the emotional responses to strawberry versus pineapple yoghurts, but low-fat versions led to more positive emotional responses. The research was published in the journal Food Research International.