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first_img Physicists add amplifier to quantum communication toolbox Practically speaking, single photon detection has not been something pursued very heavily at the wavelengths used for telecommunication signals. Part of the problem is that performance of single photon detectors are rather constrained at such long wavelengths. But, says Robert Thew, a scientist at the University of Geneva, the time is coming when single photon detectors may be needed in telecommunications. Citation: Single photon detectors for telecommunications wavelengths (2008, August 29) retrieved 18 August 2019 from https://phys.org/news/2008-08-photon-detectors-telecommunications-wavelengths.html Explore furthercenter_img 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. “Up until now,” Thew tells PhysOrg.com, “classical communication has not done too badly with the detectors available now. But now they are getting pushed to the limit as optical communications explodes. Single photon detectors are becoming more important.”In order to improve the ability of a single photon detector to work with signals with telecommunications wavelengths (about 1550 nanometers), Thew and his colleagues at the University of Geneva, Zbinden and Gisin, suggest a scheme that involves upconverting these signals using a tunable pump source to a silicon detector. Their work is published in Applied Physics Letters: “Tunable upconversion photon detector.”“Photon detection in general is a key enabling field of research,” Thew explains. “And it is improving all the time. Photon detection is used for quantum cryptography and computing as well as for metrology and telecommunications. Our experiment is one that shows how telecom wavelength photons can be converted into the regime of silicon detectors.”These Silicon detectors, Thew explains, are useful because they offer a high temporal resolution. While experiments have been done showing upconversion of silicon detectors, this Geneva group has added another element: tunability.Usually, upconversion experiments do not feature a simple and practical method of controlling wavelengths. “These systems are dedicated at well-defined wavelengths,” Thew says. “This works well for some things, but sometimes you want to be able to change the wavelength. That is what we are working on.” Of those that do seek for tunability, they can rely on temperature control to change the wavelength or use the nonlinear phase matching scheme with different poling periods. Thew and his peers decided to make a tunable photon detector using laser tuning.“All upconversion schemes rely on mixing two lasers to generate a third with the desired wavelength by a nonlinear process,” Thew explains. “Our practicality comes from the choice of components. The precision comes from the choice of silicon detector. The tunability comes from being able to tune one of these lasers that are initially mixed.” Not only is this detector tunable, but it is also compact and more cost efficient than similar photon detectors. And, as telecommunications continues to advance, this could be a good way to continue the improvements seen in the last few years. “[F]aster communication systems necessarily have to work with lower intensities (fewer photons) and it is here that the single photon detection technologies will be needed,” Thew explains. “This offers practicality and low cost. The idea is that we keep simplicity, but gain the advantage of tuning wavelengths.”“Things are improving all the time in this area of study,” Thew continues. “Having tunable photon detectors would be helpful for many experiments and applications. We are taking advantage of being able to do this with a silicon detector. What we have done offers a huge advantage for this type of approach.”Copyright 2007 PhysOrg.com. All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.last_img read more

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first_img Jarillo-Herrero is a scientist at MIT. He worked with Thiti Taychatanapat, at Harvard, to investigate some of the properties of bilayer graphene, and to determine how electronic transport works under certain conditions. Their findings are described in Physical Review Letters: “Electronic Transport in Dual-Gated Bilayer Graphene at Large Displacement Fields.”One of the reasons that semiconductors work so well in digital electronics is that they have what is known a band gap. This band gap allows semiconductors to be switched on and off. In order for graphene to work as a viable replacement for these semiconductors, some sort of gap would need to be opened up in the electronic structure. “It has already been shown that it is possible to open a band gap in bilayer graphene,” Jarillo-Herrero says. “However, the effective electronic transport gap is about 100 times smaller than the theoretical band gap or optical band gap. This difference presents problems. We want to understand the properties of bilayer graphene that make this happen, and how it can be changed.”Jarillo-Herrero and Taychatanapat offer a systemic look at how the band gap works in bilayer graphene. They found that the band gap is smaller by measuring at low temperatures of less than four degrees Kelvin. “Our studies show that the band gap is still large enough to switch the transistors on and off, but the on/off ratio is only high enough – of order a million – at low temperatures, and we report this for the first time in bilayer graphene,” Jarillo-Herrero says.However, the main problem is that in order for bilayer graphene to work as a viable semiconductor replacement, it needs to be operable at room temperature. Jarillo-Herrero is hopeful, though. “This is a very important first step that helps us scientifically understand what is happening at low temperatures, and understanding the mechanism that does not permit the electronic transport to work as well at higher temperatures.” One of the issues, Jarillo-Herrero believes, is that the graphene is usually put on silicon oxide, which introduces electronic disorder. “On silicon oxide, the electrons don’t see their full band gap,” Jarillo-Herrero explains. “So we try to characterize the disorder and get rid of it. One way to do this is to try putting the graphene on different substrates. When this is done, enormous progress is made. Boron nitride is especially promising, but a number of groups are also trying bilayer graphene on different substrates.”In the end, Jarillo-Herrero hopes that the information learned from this demonstration will help lead to the use of bilayer graphene in digital electronics. “Our work offers a beginning for learning how bilayer graphene transistors operate, and learning about the mobility of electrons in graphene. Hopefully, as we understand the properties of graphene better, we can work toward future integration with electronics and other applications,” he says.“This sort of basic science research is very important,” Jarillo-Herrero continues. “Things always have to start at the basic level before we move on, and our work could lead to the use of graphene in electronics.” 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. Citation: Toward a better understanding of bilayer graphene (2010, October 26) retrieved 18 August 2019 from https://phys.org/news/2010-10-bilayer-graphene.html More information: Thiti Taychatanapat and Pablo Jarillo-Herrero, “Electronic Transport in Dual-Gated Bilayer Graphene at Large Displacement Fields,” Physical Review Letters (2010). Available online: link.aps.org/doi/10.1103/PhysRevLett.105.166601 Explore furthercenter_img (PhysOrg.com) — “Graphene is a very exciting material with a number of interesting possibilities, including for use in electronic devices,” Pablo Jarillo-Herrero tells PhysOrg.com. “However, all graphene systems are electronically different from each other. Single layer graphene has different properties from bilayer graphene, and these have different properties from graphene with more layers. What we want to do is to understand the specific properties of bilayer graphene so that we can learn how to use it for different applications.” Copyright 2010 PhysOrg.com. All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com. Can graphene nanoribbons replace silicon?last_img read more

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first_img Led by Michael R. Vanner in Prof. Markus Aspelmeyer’s Aspelmeyer Group for Quantum Foundation and Quantum Information at the Nano- and Microscale, the team – which also included I. Pikovski, G. D. Cole, M. S. Kim, Č. Brukner, K. Hammerer, and G. J. Milburn – faced a number of challenges in devising their optomechanical scheme to fully reconstruct quantum states of mechanical motion. One of the most fundamental is the attempt to observe quantum mechanical behavior of a macroscopic mechanical object, since any potential quantum features would exhibit themselves only on truly miniscule scales. “For the mechanical structures that we consider,” Vanner explains, “one needs to resolve position displacements of about a femtometer,” or one-trillionth of a millimeter. “This is a mind‐bogglingly small distance that is, in fact, smaller than even the diameter of a hydrogen nucleus.”This then leads to additional challenges: In the attempt to measure an object’s position, the object moves and causes positional smearing by injecting uncertainty into the resulting position information, which is referred to as the Standard Quantum Limit (SQL). “The first challenge that we had to overcome was to find a method which circumvents the SQL,” Vanner continues. “The second was that making measurements of the position alone is insufficient to reconstruct a quantum state. This is because the quantum state contains all that is, at least in principle, knowable about the object. And so, one needs to also measure all the complementary properties of the state, such as its momentum, and to do so also in an equally precise manner.”Since no existing microscopy technology is capable of resolving quantum-scale features, the team addressed these challenges with optical interferometry. “Perhaps where we benefited most,” Vanner reflects, “was from the work of V. B. Braginsky, who made several seminal contributions to the field of quantum measurement1. In particular he introduced a scheme using short pulses of light that can overcome the SQL.” A short pulsed interaction can achieve this because the mechanical object has very little time to move during the interaction, and thus smearing can be dramatically reduced. “Braginsky developed this technique to make sensitive force detectors with the goal of detecting gravitational waves,” notes Vanner. “We’ve utilized this technique to allow for very sensitive position measurements. What we introduce in our proposal is a protocol using these pulsed measurements to perform quantum state reconstruction, which was our primary interest, and also a protocol to prepare low entropy squeezed states.” Proposed design and fabrication procedure for high-finesse optomechanical microcavities: Using microcavities provides optomechanical coupling rates many orders of magnitude larger than current millimeter or centimeter length scale implementations of optomechanical Fabry-Pérot cavities and can provide sufficient radiation-pressure interaction to resolve the small scale quantum properties of the mechanical resonator. Cross-sectional view with a quarter of the device removed. Uppermost (colored green) is the mechanical resonator supported by auxiliary beams. The optical field is injected into the device from below through a transparent handle (colored blue) and the curved rigid input mirror (colored pink) and then resonates in the vacuum-gap between this and the mechanical device before being retroreflected. Image: Copyright © PNAS, doi:10.1073/pnas.1105098108 Quantum behavior with a flash The state reconstruction scheme works in much the same way as many modern medical imaging techniques – that is, by taking images from many angles, as in X‐ray computed tomography, it is possible to determine the three-dimensional internal structure within the body. “Applying this analogy to our case,” Vanner continues, “the internal structure is the quantum state and the angles are its various properties: position, momentum, and their combinations. Our state reconstruction protocol uses appropriately timed pulses of light to access all these properties, thus providing a means to determine all the information in the quantum state.” An important point is that the team has analyzed the experimental feasibility and demonstrated that the scheme is realizable with current state‐of‐the‐art technology.Vanner is optimistic about the development of additional innovations and extensions in pulse sequences and measurements based on their pulsed design. “As an example,” Vanner notes, “we’re currently trying to compliment our work reported in PNAS by developing pulsed approaches to quantum state preparation. Combining such results with our state reconstruction results provides a complete experimental framework.”In terms of how their findings might enhance the future exploration of quantum mechanical phenomena on a macroscopic scale, Vanner points out that one important quantum mechanical phenomenon that is little explored in the laboratory is decoherence – the term given to the processes by which the environment surrounding a quantum object gains information about its state, often leading to the undesirable consequence of loss of quantum coherence between superposition components. “Decoherence is often regarded as one of the primary hindrances in efforts to construct a quantum computer. The quantum state tomography scheme that we have introduced can be used to observe and characterize decoherence, thus providing vital experimental data for the development of quantum mechanics based technology.” Moreover, adds Vanner, “It is a fascinating prospect that quantum information can be encoded into the motion of a mechanical object. This may lead to a number of interesting possibilities, such as transduction between flying qubits – i.e., photons – and qubits in a solid state device or superconductor. A pulsed approach may indeed be a feasible route to achieving this goal.”In addition to decoherence as discussed above, adds Vanner, “An attractive feature of the quantum state reconstruction scheme is that it can reconstruct and analyze any quantum state of motion. Thus, a large number of state‐dependent quantum effects can be studied. For example, one could utilize the fragility of a quantum superposition state as an extremely sensitive detector.”For Vanner, one of the key prospects is to see their design actually realized. “We’re currently building an experiment to implement our quantum state reconstruction protocol,” he concludes. “I’m finding it very exciting to be able to physically implement our ideas and begin to experimentally see behavior that is predicted in our theoretical model.” Citation: The quantum world writ large: Using short optical pulses to study macroscopic quantum behavior (2011, September 27) retrieved 18 August 2019 from https://phys.org/news/2011-09-quantum-world-writ-large-short.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.center_img Explore further More information: Pulsed quantum optomechanics, PNAS, Published online before print September 7, 2011, doi: 10.1073/pnas.11050981081Related: Quantum nondemolition measurements: the route from toys to tools, V. B. Braginsky and F. Ya. Khalili, Reviews of Modern Physics 68, 1–11 (1996), doi: 10.1103/RevModPhys.68.1 Copyright 2011 PhysOrg.com. All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com. (PhysOrg.com) — Einstein infamously dismissed quantum entanglement as spooky action at a distance and quantum uncertainty with his quip that God does not play dice with the universe. Aside from revealing his conceptual prejudices, Einstein’s rejection of these now-established hallmarks of quantum mechanics point to the field’s elusive nature: Coherent quantum mechanical phenomena, such as entanglement and superposition, are not apparent at macroscopic levels of scale. In fact, a common view is that on these scales quantum behavior is masked by decoherence, or even that quantum mechanics itself needs revision. Encouragingly, however, researchers at the Vienna Center for Quantum Science and Technology (VCQ), University of Vienna, have recently proposed an experimental design that would use a macroscopic mechanical resonator, short optical pulses and optical microcavities to realize quantum state tomography, squeezing, and state purification that could shed light on this elusive boundary between the quantum and classical worlds.last_img read more

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first_img © 2014 Phys.org. All rights reserved. (Phys.org) —With the rise of social media, it is possible to organize public demonstrations on larger scales and in less time than ever before. In response, some governments are trying to decide how to regulate and impede the organization of these demonstrations, in order to maintain safety, order, or for other reasons. But very little is known about exactly how repressive legislation affects social media networks and their users. New research now suggests that social networks may be surprisingly resistant to such legislation. “Our work shows that social media are very powerful tools to spread information,” Marcoux told Phys.org. “The reason for this is because of the scale-free and hierarchical structure of social media networks, in which some highly connected individuals act as hubs to transfer information. In such a network, it only takes a few steps for information to travel between two individuals at extreme locations on the network. Also, the overall structure of the network of interactions on Twitter did not change after the passage of the Bill. Thus, information could still travel quickly after the passage of the Bill. It demonstrates nicely the resilience of big scale-free and hierarchical networks to perturbations.”Because the network structure was not significantly affected by the legislation, information about the protests continued to flow through the network like before. Individuals were still able to organize mass protests, despite some changes in user behavior. Overall, the researchers concluded that this natural experiment shows the power of social media to connect and mobilize a large number of individuals, as well as the resilience of social networks to changes in individual behavior. As the researchers note, a better understanding of networks is already helping policymakers in other areas.”Policymakers can use network knowledge to influence social changes,” Marcoux said. “For example, in a vaccination campaign, a better understanding of the social structure of a community might help to identify key individuals (highly connected hubs) that could speed up the spread of positive information about vaccination.”Currently, the researchers are working on other projects, although they explain that more work could be done in this area.”This project was a side to my other research projects, but I would love if someone took over to look at the content of messages that were sent before and after the legislation,” Marcoux. On the other hand, the network structure was relatively the same before and after the legislation. The structure was hierarchical and followed a scale-free distribution, in which a few Twitter users had very high rates of tweet exchanges while most users had low rates of exchanges. The few individuals with high connectivity were positioned between cliques, while users with low connectivity tended to be part of highly connected cliques. The number of tweets per day related to the 2012 Quebec student strike changes before and after the passage of Bill 78. Despite this change in user behavior, however, the scale-free hierarchical network structure remained the same. Credit: Marcoux, et al. ©2013 EPLA Study examines best methods for gaining Twitter followers Journal information: Europhysics Letters (EPL) The largest connected cluster in the network of tweet exchanges related to the 2012 Quebec student strike (a) before and (b) after the passage of Bill 78. Importantly, the network’s structure does not significantly change. Credit: Marcoux, et al. ©2013 EPLA Explore further In a new paper published in EPL, Marianne Marcoux and David Lusseau at the University of Aberdeen in Aberdeen, UK, have analyzed millions of tweets from Twitter users in Quebec, Canada, who were protesting an increase in college tuition in 2012. That winter, 300,000 students—about 75% of all college and university students in Quebec—went on strike for several weeks. The strike and related protests were organized primarily with Twitter.On May 18, after 14 weeks of the strike, the Quebec government passed special emergency legislation called Bill 78 in an attempt to block the organization of the protests. Bill 78 requires that any organizer of a demonstration involving more than 50 people must provide the local police with an itinerary of the demonstration at least 8 hours before the event, and also ensure that the demonstration follows the itinerary. Individuals and organizations that did not follow Bill 78 were severely fined, and the government also considered fining any individual who transferred information about illegal demonstrations.To determine what effect Bill 78 had on Twitter users, the researchers compared the behavior of Twitter users who were involved in the protests, as well as the structure of their interaction network, before and after the passage of the bill. They analyzed nearly 200,000 tweets sent from February 12 to June 4, 2012, that contained relevant hashtags, using Twitter data that was made freely available by O. H. Beauchesne at olihb.com. The researchers’ main result was that the legislation changed the behavior of Twitter users, but not the overall structure of the network in which they interacted. In terms of behavior, although the number of tweets posted per day was higher on average after Bill 78 was implemented than before, the rate of increase dropped. Twitter users also showed an increase in “cliquishness” by limiting the tweets they sent to users within tight clusters to which they belonged. The researchers suspect that this change in behavior may indicate that the students became more cautious regarding who they sent tweets to. More information: Marianne Marcoux and David Lusseau. “The influence of repressive legislation on the structure of a social media network.” EPL, 104 (2013) 58004. DOI: 10.1209/0295-5075/104/58004 Citation: Anti-protest law changes Twitter users’ behavior, but not network structure, physicists show (2014, January 20) retrieved 18 August 2019 from https://phys.org/news/2014-01-anti-protest-law-twitter-users-behavior.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.last_img read more

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first_img Human eye inspires clog-free ink jet printer invention Explore further Citation: High-resolution patterns of quantum dots with e-jet printing (2015, January 28) retrieved 18 August 2019 from https://phys.org/news/2015-01-high-resolution-patterns-quantum-dots-e-jet.html Their work on high-resolution patterns of quantum dots is of interest as it shows that advanced techniques in “e-jet printing” offer powerful capabilities in patterning quantum dot materials from solution inks, over large areas. (E-jet printing refers to a technique called electrohydrodynamic jet, described as a micro/nano-manufacturing process that uses an electric field to induce fluid jet printing through micro/nano-scale nozzles.)Katherine Bourzac in Chemical & Engineering News wrote about this technique and the research interests of John Rogers, co-author of the paper and a materials scientist at the University of Illinois, Urbana-Champaign. The resolution of conventional ink-jet printers is limited. For the past seven years, she said, Rogers has been developing the electrohydrodynamic jet printing method. “This kind of printer works by pulling ink droplets out of the nozzle rather than pushing them, allowing for smaller droplets. An electric field at the nozzle opening causes ions to form on the meniscus of the ink droplet. The electric field pulls the ions forward, deforming the droplet into a conical shape. Then a tiny droplet shears off and lands on the printing surface. A computer program controls the printer by directing the movement of the substrate and varying the voltage at the nozzle to print a given pattern.”Dot, line, square, and complex images as QD patterns are possible, the researchers said, with tunable dimensions and thickness. They wrote that “these arrays as well as those constructed with multiple different QD materials, directly patterned/stacked by e-jet printing, can be utilized as photoluminescent and electroluminescent layers.”What does their work mean for consumers? As for TV technology, nearly every TV manufacturer at CES this year, remarked Geoffrey Morrison in CNET, said quantum dots helped deliver better, more lifelike color. Writing in IEEE Spectrum on Monday, Prachi Patel similarly made note that “Quantum dots (QDs) are light-emitting semiconductor nanocrystals that, used in light-emitting diodes (LEDs), hold the promise of brighter, faster displays.”In the IEEE story headlined “High-Resolution Printing of Quantum Dots For Vibrant, Inexpensive Displays,” Patel said these researchers repurposed a printing method which they devised for other applications. Patel wrote: “When used with ‘QD ink,’ it can create lines and spots that are just 0.25 micrometers wide. They made arrays and complex patterns of QDs in multiple colors, and could even print QDs on top of others of a different color. They sandwiched these patterns between electrodes to make bright QD LEDs.” Patel also reported on the team’s future efforts. They are working on arrays of multiple nozzles. Inkjet printers usually have a few hundred nozzles, said Patel. “The difficulty with the e-jet printing method is that the electric field at one nozzle affects the fields of neighboring nozzles.” They are trying to figure out “how to isolate nozzles in order to eliminate that crosstalk.” More information: High-Resolution Patterns of Quantum Dots Formed by Electrohydrodynamic Jet Printing for Light-Emitting Diodes, Nano Lett., Article ASAP. DOI: 10.1021/nl503779eAbstractHere we demonstrate materials and operating conditions that allow for high-resolution printing of layers of quantum dots (QDs) with precise control over thickness and submicron lateral resolution and capabilities for use as active layers of QD light-emitting diodes (LEDs). The shapes and thicknesses of the QD patterns exhibit systematic dependence on the dimensions of the printing nozzle and the ink composition in ways that allow nearly arbitrary, systematic control when exploited in a fully automated printing tool. Homogeneous arrays of patterns of QDs serve as the basis for corresponding arrays of QD LEDs that exhibit excellent performance. Sequential printing of different types of QDs in a multilayer stack or in an interdigitated geometry provides strategies for continuous tuning of the effective, overall emission wavelengths of the resulting QD LEDs. This strategy is useful to efficient, additive use of QDs for wide ranging types of electronic and optoelectronic devices. Journal information: Nano Letters © 2015 Phys.org A team of 17 materials science and engineering researchers from the University of Illinois at Urbana−Champaign and Erciyes University in Turkey have authored “High-Resolution Patterns of Quantum Dots are Formed by Electrohydrodynamic Jet Printing for Light-Emitting Diodes.” Their paper was published in Nano Letters, an ACS journal. They demonstrated the materials and operating conditions that allow for high-resolution printing of layers of quantum dots with precise control over thickness and submicron lateral resolution and capabilities, for use as active layers of QD light-emitting diodes. They wrote, “Patterning QDs with precise control of their thicknesses and nanoscale lateral dimensions represent two critical capabilities for advanced applications. The thickness can be controlled through a combination of printing parameters including the size of the nozzle, the stage speed, ink composition, and voltage bias.” 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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first_img Explore further (Phys.org)—A team of researchers with affiliations to research facilities in Argentina, the U.K. and New Zealand, has confirmed that fossilized pollen grains found in Antarctica are members of the flowering plant family Asteraceae. In their paper published in Proceedings of the National Academy of Sciences, the group describes their research and conclude by suggesting that the fossils represent the family’s oldest fossils ever discovered. 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. Journal information: Proceedings of the National Academy of Sciences The Asteraceae family includes a lot of popular modern flowers—daisy’s, chrysanthemums, sunflowers, as well as gerberas, lettuce, artichokes and even dandelions. One of their main characteristics is inflorescence, which means they have clusters of flower heads that form the larger flower. It is believed that they played a major role in the evolutionary history of many insects and pollinating birds and also perhaps that of bees and wasps. Prior research had placed their earliest known evolutionary history to approximately 60 million years ago. This new research has revealed evidence that pushes that history back another 20 million years—to the Cretaceous, which means the flowers were growing back when dinosaurs were still around.The pollen grains were found on the eastern side of the Antarctic Peninsula, a part of what was once the super-continent Gondwana—back then the area would have been covered by lush grasslands and temperate forests. In studying the fossils, the team noted their shape, size and surface sculpture, placing them in the species Tubulifloridites lillei—other samples had been found in Australia and New Zealand but it was not until the new fossils were found in Antarctica that researchers could definitively prove that they were also members of the Asteraceae family. Further study showed that the more recently found pollen grain fossils were similar in ways to members of the Barnadesioideae subfamily of Asteraceae found today in South America, which offers a hint of what the earlier flowers might have looked like.There is still more work to be done before the new fossil finds can be officially placed in the flowering plants family tree, but once that happens, the researchers are confident that they will be placed at a time approximately 80 million years ago. © 2015 Phys.orgcenter_img Early sunflower family fossil found in South America More information: Early evolution of the angiosperm clade Asteraceae in the Cretaceous of Antarctica, Viviana D. Barreda, Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1423653112AbstractThe Asteraceae (sunflowers and daisies) are the most diverse family of flowering plants. Despite their prominent role in extant terrestrial ecosystems, the early evolutionary history of this family remains poorly understood. Here we report the discovery of a number of fossil pollen grains preserved in dinosaur-bearing deposits from the Late Cretaceous of Antarctica that drastically pushes back the timing of assumed origin of the family. Reliably dated to ∼76–66 Mya, these specimens are about 20 million years older than previously known records for the Asteraceae. Using a phylogenetic approach, we interpreted these fossil specimens as members of an extinct early diverging clade of the family, associated with subfamily Barnadesioideae. Based on a molecular phylogenetic tree calibrated using fossils, including the ones reported here, we estimated that the most recent common ancestor of the family lived at least 80 Mya in Gondwana, well before the thermal and biogeographical isolation of Antarctica. Most of the early diverging lineages of the family originated in a narrow time interval after the K/P boundary, 60–50 Mya, coinciding with a pronounced climatic warming during the Late Paleocene and Early Eocene, and the scene of a dramatic rise in flowering plant diversity. Our age estimates reduce earlier discrepancies between the age of the fossil record and previous molecular estimates for the origin of the family, bearing important implications in the evolution of flowering plants in general. Citation: Fossil pollen grains found in Antarctica push back evolutionary history of daisy family (2015, August 12) retrieved 18 August 2019 from https://phys.org/news/2015-08-fossil-pollen-grains-antarctica-evolutionary.html A typical Asteraceae flower head (here Bidens torta) showing the individual flowers. Credit: Marshman/Wikipedialast_img read more

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first_imgThose who know dance, might not know about Vilasini Natyam. Reason? Its a classical dance form lost from the cultural scene from many years. The danceform has once again revived and returned to the capital stage by Dimple Kaur who wants to take this dance form across the world through her  persistent efforts.A trained dancer for 20 years, Dimple will perform Tholiviniki which will begin with  Alaaya Sampradaayam which includes  Ganesh Vandana and  Also Read – ‘Playing Jojo was emotionally exhausting’ Salaam Daravu. It will be followed by  Kutcheri Atta Varnam and  Javali. The  performance will end with Bhagvataham, an extract from Parijatam.Vilasini Natyam is a classical Indian Dance form which originated in Andhra Pradesh. It is an independent dance form related mainly to the devdasi tradition. The devdasis used to perform Vilasini Natyam in the magnificent temples,’ explained Dimple.’It was part of the rich culture of India for many centuries until Britishers banned the dance from temples in India. This dance form was later revived by Padma Bhushan Guru Swapnasundari, under whom I have learned and honed it,’ she added.’The dance from highlights the feminine aspects which includes the hundred odd Adavus (dance-units) like the Tandava (vigorous) and Lasya (soft) aspects. Vilasini Natyam’s complex Abhinaya is widely admired,’ Dimple said.last_img read more

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first_imgReading books is something I have been doing ever since I remember. I read all kind of books whatever I can lay my hands on, the historical ones, non-fiction, biographies or fantasy. But here is the catch, I read quite a few of them on my laptop or my e-reader.Honestly, I can’t understand the whole debate between the people who read books online (or digitally) and those who don’t. I’d rather have a discussion on what one should be munching on while reading a good book. Dessert, potato chips with garlic cheese dip or maybe a hot bowl of soup will do? Because it makes no difference, just like reading a book through whichever medium  you want! Books are to be enjoyed, to cry your heart out or to close it down with a good long sigh and a smile. As long as a book does that to you, does it really matter how you read it?    Between The Covers is a weekly column on reading up and rating downlast_img read more

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first_imgBALURGHAT: Police have arrested a youth on charges alleged rape of a class X student at Basuria village of Pransagar under Gangarampur police station in South Dinajpur district on Monday.Police arrested the youth named Abdul Kader (22).The victim was admitted to Gangarampur sub-divisional hospital after her condition deteriorated. A medical test of the victim has already been done. Police said the victim met the accused on her way back home from her uncle’s house on Monday afternoon.The accused asked her to spend some time with him. He took her to a nearby footbridge where he allegedly raped her. He left the girl who became unconscious. Locals took her to a hospital where she narrated the whole story and told the name of the accused.A large contingent of police has been sent to maintain peace. There was tension in the area after the news spread. Locals have demanded stringent action of the accused.last_img read more

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first_imgAt least 10 people have been killed in violent protests in the West African nation of Niger over the French satirical weekly Charlie Hebdo’s depiction of the Prophet Muhammad, the country’s president said.President Mahamadou Issoufou said that five deaths were reported after demonstrations in Niamey, the capital, yesterday. Another five people died on Friday in the town of Zinder following prayer services there. The victims were inside churches and bars that were set ablaze, he said. Also Read – Pro-Govt supporters rally as Hong Kong’s divisions deepenThe violence erupted after Charlie Hebdo published its first issue since the January 7 attack on its headquarters by Islamic extremists that left 12 people dead.According to mainstream Islamic tradition, any physical depiction of the Prophet Muhammad even a respectful one is considered blasphemous. Elsewhere in the Muslim world yesterday, Afghanistan’s President Ashraf Ghani condemned Charlie Hebdo, calling the newest cover image of Prophet Muhammad a blasphemous and irresponsible act. “Freedom of expression should be used in a way to boost understanding between the religions,” he said in a statement issued by the presidential palace. Also Read – Pak Army ‘fully prepared’ to face any challenge: Army spokesmanIraq’s Prime Minister Haider al-Abadi also issued a statement of condemnation, warning that, “offensive words might lead to further bloodshed.”He also reiterated his condemnation of the attacks on innocent victims in Paris, saying that terrorism, “has nothing to do with Islam in any way.”Protesters also demonstrated in front of the French Embassy in the Yemeni capital of Sanaa, as well as in the Pakistani city of Karachi.In Egypt, the Islamist Noor Party denounced the latest Charlie Hebdo cover on its French-language Facebook page. “Just as the Noor Party rejects the assault on civilians and the negative effects it has for all Muslims of Europe, it also rejects this barbaric, irresponsible act under the name of freedom of expression,” the statement declared.In Gaza City, the capital of the Gaza Strip, unknown vandals scrawled graffiti on the walls of the French Cultural Center. In addition to statements praising the Prophet Muhammad and declaring him off-limits for ridicule or satire, the vandals also wrote: “To hell, to a miserable destiny, French journalists.”last_img read more

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