Month: August 2019

Precise Alignment to Quantum Dots

first_img Explore further Localised excitons in 2-D materials for integrated quantum optics “Precise lithographic alignment to site-controlled quantum dots is of major importance for numerous nano-photonic, nano-electronic and nano-spintronic devices,” Sven Höfling tells PhysOrg.com. Höfling continues: “So far, most of the devices based on single quantum dots use a layer of self-organized quantum dots, where the dots are at random positions and a post-fabrication screening is employed to select devices with proper spectral and spatial alignment, for example, with respect to a cavity mode. After all, whether or not you can find a proper quantum dot is largely a matter of chance“ Höfling and his colleagues at Julius Maximilians University in Würzburg, Germany believe that they have come up with a scheme that would make it much easier to produce single dot-based devices to be used in the fabrication process of nano devices. The results from the team in Würzburg are reported in Applied Physics Letters: “Lithographic alignment to site-controlled quantum dots for device integration.” “Previously used approaches were sufficient for the realization of single, research type devices, whose main purpose is the study of basic physics,” Höfling concedes, “but it does not allow for large scale device fabrication needed for widespread applications.” Right now, he points out, in many cases the yield of these nano devices is close to zero.In order to usher in an era of widespread applications for nano devices, the Würzburg team combined two processes to produce single dot device with higher yield: a site-controlled quantum dot growth by pre-patterning and an accurate alignment technique. “People have pioneered this pre-patterned quantum dot growth before,” says Höfling. “Others have made accurate alignment. By combining them together, we are investigating a serious scheme that is scalable. This will significantly increase the yield of single quantum dot based devices.” By using the accurate alignment, it is possible to know where the quantum dots are, allowing fabricators to pinpoint them and “use, for instance, a pulsed laser to excite them so that they emit single photons on demand,” Höfling says. “Before, it was guesswork. A random distribution of quantum dots would have to be used, shining light on it and hoping to find a proper located quantum dot in the device. Now, it’s much easier”.Höfling does point out that the work needs to carry on further. “Right now, this work addresses spatial aspects only. We know in advance where the quantum dots are, but they can still have different properties. We also need to control better their properties, namely we need additionally a spectrally deterministic technology. That is what we are working on now, but site-control can here also be very useful to manipulate the properties of the quantum dots.”Even without the spectral aspect, though, Höfling thinks that the work done by him and his peers has the potential to be very useful in the future. He says that single photon sources, single quantum dot lasers, electron memory devices, entangled photon pair emitters and the semiconductor building blocks for quantum information processing could all advance with help from this technology.“Everything is decreasing in size,” Höfling points out, “and we need smaller and smaller devices. At some point, we are going to need to be able to produce single quantum dot based devices.” “We have, in the meantime, succeeded to couple a single quantum dot spatially in a spatially deterministic way with a single photonic crystal mode,” he continues, “yielding a device which is capable of efficiently emitting single photons on demand.”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.center_img Citation: Precise Alignment to Quantum Dots (2008, May 12) retrieved 18 August 2019 from https://phys.org/news/2008-05-precise-alignment-quantum-dots.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

IBM demonstrates nonoscale 3D patterning technique w Video

first_img PausePlay% buffered00:0000:00UnmuteMuteDisable captionsEnable captionsSettingsCaptionsDisabledQuality0SpeedNormalCaptionsGo back to previous menuQualityGo back to previous menuSpeedGo back to previous menu0.5×0.75×Normal1.25×1.5×1.75×2×Exit fullscreenEnter fullscreen Explore further IBM scientists have created the smallest 3D map of the earth – so small that 1,000 maps could fit on a grain of salt. © 2010 PhysOrg.com Play The movie depicts the process of carving the ‘Matterhorn’ out of the molecular glass resist layer in a series of topographical images. The initial surface was imaged and the following frames were taken with always 12 patterning steps in between the frames. A total of 10 frames was recorded. Credit: IBM/Science. At that scale IBM’s technique could replace EBL, which costs 80 to 90% more and is slower. According Michel Despont, an IBM physicist and co-author of the research paper, the technique needs fewer processes than EBL, and the fact that it can be used to create structures in 3D means it could be used for applications no one has yet considered. In their paper, published in the Science journal, the IBM researchers say they plan to use the technique to create meta-materials, optical components, for prototyping CMOS nanoelectronics components, and for making templates for nanorod or nanotube self-assembly. Despont said the system would not be commercially available for around five years, but they hope to make it available for universities and research laboratories before then. EBL (also called e-beam lithography) uses a focused beam of electrons to etch micro- or nano-scale patterns into a substrate covered by a film (the resist) that is sensitive to the electrons. It was initially developed for fabricating integrated circuits.The 25-nanometer (nm) high model of the mountain was sculpted in around three minutes from a glassy organic material using a 500-nm long and 5-nm thick silicon scanning probe heated to above 330°C for a few microseconds — long enough to break hydrogen bonds within the material without breaking other bonds. The probe was fixed to a flexible cantilever that can scan the substrate to an accuracy of 1 nm. The probe acts like a microscopic milling machine removing layers of the substrate by heat and force.The demonstration also sculpted a relief map of the world that measured 22 by 11 micrometers. According to the IBM press release the scale of the map is so small 1,000 of them could be drawn on a single grain of salt. IBM says the current technology can go as small as 15 nanometers, but in the future could go even smaller. Image credit: IBM/Science. Citation: IBM demonstrates nonoscale 3D patterning technique (w/ Video) (2010, April 23) retrieved 18 August 2019 from https://phys.org/news/2010-04-ibm-nonoscale-3d-patterning-technique.html 3D rendered image showing a heated nanoscale silicon tip, borrowed from atomic force microscopy, that is chiselling away material from a substrate to create a nanoscale replica of the Matterhorn. As reported in the scientific journal Science, IBM Researchers used this new nanopatterning technique to create a 25 nanometer high 3D replica of the Matterhorn, a famous Swiss mountain that soars 4,478 m (14,692 ft) high, in molecular glass, representing a scale of 1:5 billion (1 nanometer of the replica corresponds to 57 altitude meters). Image courtesy of IBM Research – Zurich More information: Nanoscale Three-Dimensional Patterning of Molecular Resists by Scanning Probes, David Pires et al., Published Online April 22, 2010Science DOI:10.1126/science.1187851 (PhysOrg.com) — IBM Research in Zurich has demonstrated a new nanoscale patterning technique that could replace electron beam lithography (EBL). The demonstration carved a 1:5 billion scale three-dimensional model of the Matterhorn, a 4,478 meter high mountain lying on the border between Italy and Switzerland, to show how their technique could be used for a number of applications, such as creating nanoscale lenses on silicon chips for carrying optical circuits at a scale so small that electronic circuits are inefficient. IBM Scientists Effectively Eliminate Wear at the Nanoscale 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

Research duo report first observation of cross species mimicry to ward off

first_img Citation: Research duo report first observation of cross species mimicry to ward off reproductive efforts (2013, August 26) retrieved 18 August 2019 from https://phys.org/news/2013-08-duo-species-mimicry-ward-reproductive.html (Phys.org) —Biology researchers Nikolai Tatarnic and Gerasimos Cassis of the University of New South Wales and Macquarie University in Sydney, report in a paper they’ve had published in the journal The American Naturalist, the first known incidence of cross species mimicry to ward off the reproductive efforts of the males of another species. Journal information: American Naturalist In Tahiti, there are two kinds of crawling bugs (Coridromius tahitiensis and Coridromius taravao) that mate in a rare way, called traumatic insemination—the male stabs the female in the abdomen with a sharp appendage, piercing her side, causing injury and sometimes infections. The male C. tahitiensis are particulary ardent, willing to attempt to mate with other males of its species, as well as both male and female C. taravao. That has led to the females of both species developing markings on their body that resemble the male C. tahitiensis, which are apparently less likely to be targeted by males. The researchers report that this is the first observed instance of the females of one species developing markings on their body to specifically ward off the amorous advances of the males of another species.The researchers discovered these tendencies in the two species by collecting large groups of both and studying their behavior in the lab. Interestingly, the females of both species do have female genitals on their right sides, which is what the males are apparently supposed to be aiming for. In watching the insects, the researchers found the males rather clumsy, piercing the female abdomen just as often as finding the actual genitalia. The males of both species have a distinctive (and hairy) color pattern on their sides, which coincidently or not, lies near the same area on their abdomen that serves as targets on the females. It was this pattern that the females of both species had evolved to mimic being male, and therefore less likely to be targeted. The researchers also noted that female C. tahitiensis have what appear to be sexual organs on the left side of the abdomens as well but suspect they are not real and only serve as a decoy. Reversal of the black widow myth More information: Surviving in Sympatry: Paragenital Divergence and Sexual Mimicry between a Pair of Traumatically Inseminating Plant Bugs, The American Naturalist, www.jstor.org/stable/10.1086/671931AbstractReproductive interactions between species can carry significant costs (e.g., wasted time, energy, and gametes). In traumatically inseminating insects, heterospecific mating costs may be intensified, with indiscriminate mating and damaging genitalia leading to damage or death. When closely related traumatically inseminating species are sympatric, we predict selection should favor the rapid evolution of reproductive isolation. Here we report on a cryptic species of traumatically inseminating plant bug, Coridromius taravao, living sympatrically with its sister species, Coridromius tahitiensis, in French Polynesia. Despite their sister-species relationship, they exhibit striking differences in reproductive morphology, with females of each species stabbed and inseminated through different parts of their abdomens. Furthermore, C. tahitiensis is sexually dimorphic in coloration and vestiture, while both sexes of C. taravao share the C. tahitiensis male expression of these traits. These findings support a role for (1) reproductive character divergence and (2) interspecies sexual mimicry in limiting interspecific mating brought about by indiscriminate male mating behavior.center_img Explore further Coridromius tahitiensis mating The two kinds of bugs are distinctive species, though they look very much alike. It’s not known if cross breeding attempts ever result in offspring, but the researchers intend to go back to Tahiti to find out. © 2013 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.last_img read more

Skeletal tests suggest sacrificial victims during Shang Dynasty were held for a

first_img © 2017 Phys.org Prior research has shown that there were a large number of human sacrifices during the Shang Dynasty, which ran from the 16th to 11th century BC in what is now modern China. Also, some research has suggested that many of the victims were captives from wars. In this new effort, the researchers have found evidence showing that the bones of the victims were from elsewhere, but lived locally for several years before they were killed.Sacrificial victims were buried in various places, one of which was the royal cemetery in Yinxu. The researchers note that prior research showed that victims fell into two classes, “rensheng” and “renxun”—the former were generally mutilated and buried in mass graves while the latter were most often buried in more elaborate individualized ceremonies. The skeletal remains the group studied all represented the rensheng group, except in one case. As the team notes, normal testing of ancient peoples to learn more about their diet and geographic origin involved testing the teeth. In this case, that was not possible, because the victims were all decapitated. Instead, the team studied isotopes in their bones. That allowed them to infer the diet of the victim over the course of a lifetime.In looking at the victims, the researchers found that they were not from the same areas as the locals—their large bones showed evidence of a different diet for most of their life. But smaller bones such as ribs indicated that they had lived in Yinxu for several years before they were killed. This, the researchers suggest, offers evidence that the victims were likely captured in wars and then were used as slaves before they were killed. It also suggests that the victims were kept as a store of sorts, allowing the king to call for sacrificial rituals even during times of peace. The researchers also noted that the diet of the victims was substandard during incarceration, offering further proof that they were used as slaves. Citation: Skeletal tests suggest sacrificial victims during Shang Dynasty were held for a time (2017, June 19) retrieved 18 August 2019 from https://phys.org/news/2017-06-skeletal-sacrificial-victims-shang-dynasty.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. More information: Christina Cheung et al. Diets, social roles, and geographical origins of sacrificial victims at the royal cemetery at Yinxu, Shang China: New evidence from stable carbon, nitrogen, and sulfur isotope analysis, Journal of Anthropological Archaeology (2017). DOI: 10.1016/j.jaa.2017.05.006AbstractThe practice of ritual killing, using both human and animal subjects, was prevalent in early Bronze Age China. This study addresses one key archaeological question that concerns the social roles and geographical origins of these human victims. Although oracle bone inscriptions from the site of Yinxu mentioned that many of these victims were war captives, little archaeological evidence could support or confirm this assertion. Using stable carbon, nitrogen, and sulfur isotope analysis, we reconstructed and compared the dietary practices of 68 sacrificial victims with those of 39 local residents from Yinxu. In addition, for 30 of the sacrificial victims, δ13C, δ15N, and δ34S values from two different bone elements per individual were compared to look for evidence of migration. Our results suggest that these sacrificial victims were likely not local, but moved to Yinxu and adopted the local diet for at least a few years before being killed. This discovery has significant implications for understanding the various tactics used by the Shang kings to consolidate power over their subjects, including the display of violence through mass sacrificial rituals. Photograph of Yinxu. Credit: Wikipedia London fire may have destroyed DNA needed to ID victims (Phys.org)—A team of researchers from Canada and China has found skeletal evidence of sacrificial victims during the Shang Dynasty being held for a period of time before being killed. In their paper published in Journal of Anthropological Archaeology, the group describes their chemical analysis of bones from 68 sacrificial victims from Yinxu—the Shang capital. Explore furtherlast_img read more

Multiple gammaray emission regions detected in the blazar 3C 279

first_imgAn example composite image of 3C 279 convolved with a beam size of 0.1 mas (circle in the bottom left corner). The contours represent the total intensity while the color scale is for polarized intensity image of 3C 279. The line segments (length of the segments is proportional to fractional polarization) marks the EVPA direction. Credit: Rani et al., 2018. Citation: Multiple gamma-ray emission regions detected in the blazar 3C 279 (2018, May 23) retrieved 18 August 2019 from https://phys.org/news/2018-05-multiple-gamma-ray-emission-regions-blazar.html Explore further © 2018 Phys.org Researchers discover a blazar-like narrow-line Seyfert 1 galaxy Using very long baseline interferometry (VLBI), astronomers have investigated the magnetic field topology of the blazar 3C 279, uncovering the presence of multiple gamma-ray emission regions in this source. The discovery was presented May 11 in a paper published on arXiv.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. More information: — High-resolution polarization imaging of the Fermi blazar 3C 279, arXiv:1805.04588 [astro-ph.HE] arxiv.org/abs/1805.04588AbstractEver since the discovery by the Fermi mission that active galactic nuclei (AGN) produce copious amounts of high-energy emission, its origin has remained elusive. Using high-frequency radio interferometry (VLBI) polarization imaging, we could probe the magnetic field topology of the compact high-energy emission regions in blazars. A case study for the blazar 3C 279 reveals the presence of multiple gamma-ray emission regions. Pass 8 Fermi-Large Area Telescope (LAT) data are used to investigate the flux variations in the GeV regime; six gamma-ray flares were observed in the source during November 2013 to August 2014. We use the 43 GHz VLBI data to study the morphological changes in the jet. Ejection of a new component (NC2) during the first three gamma-ray flares suggests the VLBI core as the possible site of the high-energy emission. A delay between the last three flares and the ejection of a new component (NC3) indicates that high-energy emission in this case is located upstream of the 43 GHz core (closer to the black hole).— B. Rani et al. Exploring the Connection between Parsec-scale Jet Activity and Broadband Outbursts in 3C 279, The Astrophysical Journal (2018). DOI: 10.3847/1538-4357/aab785 , iopscience.iop.org/article/10. … 1538-4357/aab785/pdf Blazars, classified as members of a larger group of active galaxies that host active galactic nuclei (AGN), are the most numerous extragalactic gamma-ray sources. Their characteristic features are relativistic jets pointed almost exactly toward the Earth. In general, blazars are perceived by astronomers as high-energy engines serving as natural laboratories to study particle acceleration, relativistic plasma processes, magnetic field dynamics and black hole physics.NASA’s Fermi Gamma-ray Space Telescope is an essential instrument for blazar studies. The spacecraft is equipped with in the Large Area Telescope (LAT), which allows it to detect photons with energy from about 20 million to about 300 billion electronvolts. So far, Fermi has discovered more than 1,600 blazars.A team of astronomers led by Bindu Rani of NASA’s Goddard Space Flight Center has analyzed the data provided by LAT and by the U.S.-based Very Long Baseline Array (VLBA) to investigate the blazar 3C 279. The studied object, located in the constellation Virgo. It is one of the brightest and most variable sources in the gamma-ray sky monitored by Fermi. The data allowed Rani’s team to uncover more insight into the nature of gamma-ray emission from this blazar.”Using high-frequency radio interferometry (VLBI) polarization imaging, we could probe the magnetic field topology of the compact high-energy emission regions in blazars. A case study for the blazar 3C 279 reveals the presence of multiple gamma-ray emission regions,” the researchers wrote in the paper.Six gamma-ray flares were observed in 3C 279 between November 2013 and August 2014. The researchers also investigated the morphological changes in the blazar’s jet.The team found that ejection of a new component (designated NC2) during the first three gamma-ray flares suggests the VLBI core as the possible site of the high-energy emission. Furthermore, a delay between the last three flares and the ejection of a new component (NC3) indicates that high-energy emission in this case is located upstream of the 43 GHz core (closer to the blazar’s black hole).The astronomers concluded that their results are indicative of multiple sites of high-energy dissipation in 3C 279. Moreover, according to the authors of the paper, their study proves that VLBI is the most promising technique to probe the high-energy dissipation regions. However, they added that still more observations are needed to fully understand these features and mechanisms behind them.”The Fermi mission will continue observing the GeV sky at least for next couple of years. The TeV missions are on their way to probe the most energetic part of the electromagnetic spectrum. High-energy polarization observations (AMEGO, IXPE, etc.) will be of extreme importance in understanding the high-energy dissipation mechanisms,” the researchers concluded.last_img read more

Team tests feasibility of EmDrive and Mach Effect Thrusters

first_img © 2018 Phys.org A team of German physicists with TU Dresden has independently tested the feasibility of the EmDrive and Mach Effect Thrusters. They have presented their findings at this year’s Aeronautics and Astronautics Association of France’s Space Propulsion conference. Here’s why scientists haven’t invented an impossible space engine – despite what you may have read EMDrive Thruster: Cavity (Left), Antenna (Middle) and On Balance (Right). Credit: Martin Tajmar, et al. More information: The SpaceDrive Project – First Results on EMDrive and Mach-Effect Thrusters, Conference: Space Propulsion Conference, At Seville, Spain , www.researchgate.net/publicati … ach-Effect_Thrusters AbstractPropellantless propulsion is believed to be the best option for interstellar travel. However, photon rockets or solar sails have thrusts so low that maybe only nano-scaled spacecraft may reach the next star within our lifetime using very high-power laser beams. Following into the footsteps of earlier breakthrough propulsion programs, we are investigating different concepts based on non-classical/revolutionary propulsion ideas that claim to be at least an order of magnitude more efficient in producing thrust compared to photon rockets. Our intention is to develop an excellent research infrastructure to test new ideas and measure thrusts and/or artefacts with high confidence to determine if a concept works and if it does how to scale it up. At present, we are focusing on two possible revolutionary concepts: The EMDrive and the Mach-Effect Thruster. The first concept uses microwaves in a truncated cone-shaped cavity that is claimed to produce thrust. Although it is not clear on which theoretical basis this can work, several experimental tests have been reported in the literature, which warrants a closer examination. The second concept is believed to generate mass fluctuations in a piezo-crystal stack that creates non-zero time-averaged thrusts. Here we are reporting first results of our improved thrust balance as well as EMDrive and Mach-Effect thruster models. Special attention is given to the investigation and identification of error sources that cause false thrust signals. Our results show that the magnetic interaction from not sufficiently shielded cables or thrusters are a major factor that needs to be taken into account for proper µN thrust measurements for these type of devices. Citation: Team tests feasibility of EmDrive and Mach Effect Thrusters (2018, May 23) retrieved 18 August 2019 from https://phys.org/news/2018-05-team-feasibility-emdrive-mach-effect.html Explore further The EmDrive is an experimental space engine design that came to light several years ago. It gained some prominence two years ago after NASA reported a team had been testing the engine to find out if it had merit. That team has not presented its findings, which led the team in Germany to test the idea for themselves.The idea behind the EmDrive is simple—it is a hollow cone made of copper or other material and placed in a frame. Natural microwaves bouncing around inside the cone are supposed to provide thrust. If feasible, such an engine could push a rocket through space without the need to carry fuel. But as many physicists have pointed out, such an engine would defy the laws of physics as we know them. To test this concept anyway, the team in Germany built an EmDrive similar to the one NASA had looked at (a leaked paper offered some details), set it inside a highly shielded vacuum chamber and fired microwaves at it. They report that while the EmDrive did experience thrust, the thrust did not appear to come from the engine itself—there was thrust no matter which direction the engine was pointing, suggesting it originated from a secondary source, possibly magnetism from the Earth.Mach Effect Thrusters have a stronger basis in known science, but are still considered to be an unlikely proposition. They are based on the idea that fluctuations generated in a piezo-crystal stack will create non-zero time-averaged thrust. The researchers in Germany built some for testing in their vacuum chamber, as well. They report that the results were more promising than for the EmDrive, but there is still not enough evidence to show such an idea might work. They found that the thrusters did provide thrust and they did it in the right direction. They also noted that thrust ceased when the thrusters were turned off. But they also found that the thrust produced was approximately 100 times more than was predicted by theory. Also, throwing the thrusters into reverse did not work, either. The researchers suggest there was likely an outside factor impacting the generated thrust. 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

Silver salt used to break C–C bonds in unstrained cyclic amines

first_img In the world of chemists, the goal is quite often to instigate the creation of bonds to hold molecules together in useful ways. Such bonds form the basis of new materials such as drugs for treating human ailments. But as has been often noted, before creating new bonds, old ones must often be broken. One of the most notorious bonds that need to be broken are carbon-carbon bonds. Double C–C bonds are typically easy to functionalize; it is the inert C–C single bonds that give chemists so much trouble. But that might be changing, as the researchers with this new effort claim they have developed a simple and straightforward technique to do the job. They even suggest it is ready for pharmaceutical or other biological applications.The technique involves breaking C–C bonds in nitrogen-containing rings. An amount of silver salt along with a dose of a fluorinating reagent (an electrophilic fluorine) is introduced. The researchers explain that the resulting reactions starts with the silver first oxidizing the α carbon that lies just next to the nitrogen. That is followed by a radical mechanism involving the β carbon ring-opening fluorination. Afterward, a chain results with a fluorine atom at one end of a chain. The researchers note that in some instances, the technique can also be used to cause a formyl group to wind up on the other end of the chain. The researchers report that they tested their technique by using it to open several four-membered rings—attempts to do so with five-membered rings resulted in oxygenated rings. They also found it could be used for ring-opening with fluorination of peptides. The group reports that they have plans to continue their research with the technique and hope to find a way to achieve the same results while lowering the metal content involved. More information: Deconstructive fluorination of cyclic amines by carbon-carbon cleavage, Science  13 Jul 2018: Vol. 361, Issue 6398, pp. 171-174, DOI: 10.1126/science.aat6365 , http://science.sciencemag.org/content/361/6398/171AbstractDeconstructive functionalizations involving scission of carbon-carbon double bonds are well established. In contrast, unstrained C(sp3)–C(sp3) bond cleavage and functionalization have less precedent. Here we report the use of deconstructive fluorination to access mono- and difluorinated amine derivatives by C(sp3)–C(sp3) bond cleavage in saturated nitrogen heterocycles such as piperidines and pyrrolidines. Silver-mediated ring-opening fluorination using Selectfluor highlights a strategy for cyclic amine functionalization and late-stage skeletal diversification, establishing cyclic amines as synthons for amino alkyl radicals and providing synthetic routes to valuable building blocks. Development of a deconstructive fluorination of cyclic amines. (A) Well-established deconstructive functionalization. (B) An elusive deconstructive functionalization. (C) A blueprint for deconstructive fluorination of cyclic amines. (D) Optimization of silver-mediated deconstructive fluorination of N-Bz piperidine 1a. R, any functional group; Me, methyl; Ph, phenyl; equiv, equivalents; h, hour. Credit: (c) Science  13 Jul 2018: Vol. 361, Issue 6398, pp. 171-174, DOI: 10.1126/science.aat6365 Journal information: Science Citation: Silver salt used to break C–C bonds in unstrained cyclic amines (2018, July 16) retrieved 18 August 2019 from https://phys.org/news/2018-07-silver-salt-cc-bonds-unstrained.html Explore furthercenter_img Chemists build new chemical structures on unreactive bonds A team of researchers at the University of California has found a way to break C–C bonds in unstrained cyclic amines using silver salt. In their paper published in the journal Science, the group describes the technique they developed and how well it worked. © 2018 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.last_img read more

Climate change models mimics and predators A complicated relationship

first_img Explore further The common carder bee, Bombus pascuorum. Credit: Arnstein Staverløkk (Norwegian Institute for Nature Research, Trondheim, Norway). © 2018 Science X Network Poor mimics can succeed as long as they mimic the right trait For the next study in their experiment, Hassall and colleagues looked at the comparative phenology of models and mimics—that is, the relationship between Syrphidae mimics and Hymenoptera models in priority of emergence or overlap of emergence when compared with phenological advance in terms of increase in mean annual temperature in the study area (central England). To evaluate this statistically, they used rank biserial correlation (RBC). The researchers found no significant evidence that models and mimics were “advancing their phenology at the same rate.” To examine “the fitness consequences of phenological mismatch,” the third part of the study again relied on human participants, this time to fulfil the role of predators in a video game scenario whereby they were presented with three pairs of model-mimic prey stimuli. The participants were asked to make decisions regarding the profitability of each pair of stimuli from the perspective of a predator. Participants were presented with these three pairs in one of three scenarios, each involving 25 models and 25 mimics. The three phenologic scenarios represent 1) mimics on average emerging first 2) models on average appearing first, or 3) random presentation, with an equal mean order of each model and mimic. Game participants scored five points for clicking a mimic, were penalized 10 points for clicking a model, and were neither penalized nor rewarded for passing on a decision.From this gamification of the Batesian model-mimic-predator relationship with regard to phenological scenarios, the authors found statistically significant rates of prediction with all three members in the complex. Random presentation was associated with the greatest fitness in mimics here, while the model-first scenario worked in the best interest of models; these results were generally congruent with classic Batesisan theory. Random presentation, on the other hand, worked to the detriment of predators, who benefit most from a clear educational signal regarding their prey.In the final section of their experiment, the authors applied the results of the previous section to an historical dataset spanning the years 1960 to 2005 with reference to each of the 237 previously identified high-fidelity pairs. From this, they were able to pair RBC score thresholds with “model-first,” “mimic-first,” or “random” categories, which in turn allowed them to infer fitness consequences with regard to real-world temporal sequences in the context of contemporary climate change. They found a significant increase over this time span in the “model-first” pattern, a significant decrease in “mimic-first” occurrences, and a less-significant decline in which species pairs emerged randomly. From all this, they were able to infer a fitness trend showing models benefiting most from emerging first, a mixed trend for mimics due to a decrease in random pairs, but positive benefits also for predators, who benefit most when models emerge first.So what does all this mean in the context of a changing climate? Well, it’s complicated. Past studies, as the researchers note, have shown phenological decoupling to be definitely harmful in many ecosystems. They cite as one example the plight of the snowshoe hare that molts after early snow melt and how this increases mortality in this case. But where other studies demonstrate the negatives associated with phenological shifts, data from this research “suggest that climate change will result in phenologically optimal emergence patterns that benefit (at least in part) all three actors within the mimicry system.” More than this though, the authors conclude, their study also illustrates “the benefits of integrating mechanistic and organizational data to study large-scale eco-evolutionary processes within a phenologically antagonistic Batesian mimicry complex.” Journal information: Proceedings of the National Academy of Sciences More information: Christopher Hassall et al. Climate-induced phenological shifts in a Batesian mimicry complex, Proceedings of the National Academy of Sciences (2018). DOI: 10.1073/pnas.1813367115 The hairy-footed flower bee, Anthophora plumipes. Credit: Steven Falk (photographer). Citation: Climate change, models, mimics and predators: A complicated relationship (2018, December 11) retrieved 18 August 2019 from https://phys.org/news/2018-12-climate-mimics-predators-complicated-relationship.html Climate change as a disruptive force has been studied in terms of its effects on direct interactions in ecological relationships, such as those between predator and prey, for example. Until now however, little has been known about how the effect of a changing climate on the annual emergence cycles of species—phenological synchrony—may be affecting more complicated evolutionary relationships such as those within a Batesian mimicry complex. In a Batesian complex, one species mimics the behavior of another (model) species that has evolved defensive measures against a third predator species. 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. In a recent paper published in PNAS, Christopher Hassall, Jac Billington and Thomas N. Sherratt detail how they modelled a Batesian mimicry complex by leveraging the power of citizen science and online video gaming, which they then applied to a large historical observational dataset in an attempt to better understand the complicated relationship among models, mimics and predators in a changing climate. Their results are ultimately understood in reference to each member of the relationship’s evolutionary fitness costs and benefits as they relate to each other partner within the complex.In this study, Hassall and colleagues examined the relationship between Hymenoptera models (stinging wasp and bee species), their Diptera: Syrphidae mimic species (hoverflies), and the predators that attempt to feed on both: naive bird hatchlings. Some previous research on Batesian complexes indicates phenologic order of appearance is important, and that mimics benefit by emerging prior to their model species. Other research counters that model and mimic species appear synchronously and independently of avian fledgling emergence dates. Regardless, no previous studies using adequately large datasets exist to elaborate on questions of phenological synchrony with respect to this Batesian complex and the fitness costs or benefits of its members. The relationship is further confounded by the role of climate change in this ecological milieu.The first part of their experiment details the selection of 42 species of Syrphidae mimics and 56 species of bee and wasp models—2,353 pairs. Selection was based mainly on abundance from biological records in an area of central England in which both model and mimic species were known to coexist, but also on their taxonomic and morphologic distinctness. The researchers then asked users to rate randomly paired representative images from Syrphidae and Hymenoptera based on their visual similarity. From these, 237 high-fidelity pairwise combinations were selected. When compared with similar experiments using pigeons, these combinations correlated significantly, thus legitimating the researchers’ method of pairing based on human vision.last_img read more

An electronically tunable metasurface that rotates polarization

first_imgManipulating the properties of electromagnetic waves (e.g. amplitude, phase and polarization) typically involves a combination of optical components, such as lenses, polarizers and waveplates. The new metasurface introduced by the researchers has a polarization rotator, which consists of a tunable birefringent structure sandwiched between two ±45° rotated metasurface-based quarter-wave plates. Researchers at the University of Michigan and City University of New York have recently proposed and experimentally validated a transparent, electronically tunable metasurface. This metasurface, presented in a paper published in Physical Review X, can rotate the polarization of an arbitrarily polarized incident wave without changing its axial ratio. Explore further Electrically tunable metasurfaces pave the way toward dynamic holograms Metasurfaces are artificial sheet materials textured at a sub-wavelength scale in order to produce tailored electromagnetic responses. In recent years, these materials have enabled unprecedented control over electromagnetic waves, opening up interesting possibilities in numerous areas, including wireless communications, imaging and energy harvesting. Despite their numerous advantages, most metasurface designs only offer static functionalities. The new metasurface devised by the researchers, on the other hand, has dynamically tunable properties, and could hence be applied in a broader variety of areas. “A few years ago, our research group introduced a pragmatic approach to realizing metasurfaces with tailored bianisotropic responses,” Zhanni Wu, one of the researchers who carried out the study, told Phys.org. “This approach involves cascading patterned (i.e. anisotropic) metallic surfaces across a subwavelength thickness to achieve targeted electric, magnetic and chiral/omega properties. The technique is amenable to planar micro- and nano-fabrication techniques, allowing realization of metasurfaces from RF to visible wavelengths.”Over the past few years, the same team of researchers designed and realized several metasurfaces, with various functionalities. Although these ultrathin metasurfaces achieved extreme wavefront control, their functionalities remained static and dependent on their fixed geometrical parameters. “In this work, we integrated tunable devices, varactor diodes, into a metasurface to achieve dynamic control over the metasurface’s response,” Wu explained. “We demonstrated a transparent metasurface with a tunable chiral response, which can rotate the polarization of an incident wave.” More information: Zhanni Wu et al. Tunable Metasurfaces: A Polarization Rotator Design, Physical Review X (2019). DOI: 10.1103/PhysRevX.9.011036Carl Pfeiffer et al. Bianisotropic Metasurfaces for Optimal Polarization Control: Analysis and Synthesis, Physical Review Applied (2014). DOI: 10.1103/PhysRevApplied.2.044011 Citation: An electronically tunable metasurface that rotates polarization (2019, March 12) retrieved 18 August 2019 from https://phys.org/news/2019-03-electronically-tunable-metasurface-rotates-polarization.html © 2019 Science X Network Journal information: Physical Review X “A conventional tunable polarization rotator is typically multiple wavelengths in size (tens to hundreds) and consists of two rotated quarter wave plates (linear to circular polarizers) placed on either side of a tunable birefringent medium, like a liquid crystal layer,” Anthony Grbic, another researcher who carried out the study, told Phys.org. “Here, we have replaced this bulky device with a cascade of metasurfaces, resulting in a device of subwavelength thickness and equivalent functionality.”The approach demonstrated by Wu, Grbic and their colleague Younes Ra’di enables ultra-compact designs and could be applied in microwave polarimetric systems for the characterization or detection of objects. For instance, their metasurface-based polarization rotator could be integrated with an antenna element to develop a compact antenna system for polarimetric microwave imaging.”Our work paves the way for flat/low profile, dynamically tunable antennas and optical/quasioptical systems,” Grbic said. “One can envision replacing bulky electromagnetic or optical setups requiring combinations of conventional components including lenses, tuning elements, phase shifters, spatial light modulators, waveplates, linear polarizers simply with cascaded ultra-thin, tunable metasurfaces.” The recent study carried out by Wu, Grbic and Ra’di introduced a novel platform that enables full control of the transmitted wave front. The researchers demonstrated their approach by developing a tunable polarization rotator, yet it could also be used to tailor reflected waves. In the future, their method could hence be applied to the design of a tunable metasurface that not only rotates the polarization of the reflected/transmitted wave, but also steers a beam into different directions.”Our future research plans also include the development stacked metasurface designs for tunable amplitude control, in addition to the phase/polarization control we have demonstrated to date,” Ra’di told Phys.org. “A further goal of ours is to translate such metasurface designs to optical wavelengths.” Credit: Zhanni Wu. Credit: Zhanni Wu. 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

Santa Claus is coming to town

first_imgThe spirit of Christmas was shared by in-house guests and other luminaries from various walks of life. All the guests were offered Santa hats as soon as they stepped into the lobby. The central attraction was the gigantic nine-foot tall environment friendly Christmas tree made from dried twigs, pine cones and strawberries and embellished with authentic ornaments and with gifts and presents all around. The festive atmospheres was visible with decorative wreaths, holly, poinsettias and pinecones as well as elaborate Christmas decorations like life size snowmen and huge ginger bread houses. Also Read – ‘Playing Jojo was emotionally exhausting’Guests were treated to delectable Christmas delights, such as chocolate Santa, plum cake, candies, gingerbread cookies and mulled wine as they immersed themselves in the festive spirit.The evening kicked off with welcoming the guests, by  Farhat Jamal, General Manager followed by the entry of Executive Chef Darren Conole, the host for the evening. Chef Conole welcomed the tiny tots for a treasure hunt to look for the magic switch, which would light up and illuminate the Christmas tree. The excited bunch of children ran around trying to be the first to find the switch. After the lighting of the Christmas tree by Farhat Jamal and the young winner, Santa came through his chimney and went straight into the lobby to give out goodie bags to all the excited young kids. Also Read – Leslie doing new comedy special with NetflixThe sounds of Jingle Bell Rock, Joy to the World and Santa Claus is coming to town’ by young choir from St. Ann’s choir reverberated through the lobby as everyone sang along to the popular carols.Uno2Go the patisserie, was a delight for all the children, as they shopped for little gingerbread houses, chocolate Santa’s, Christmas puddings and more.  After the ceremony, guests attended a pre Christmas celebration over Christmas delicacies and mulled wine as they enjoyed the popular tunes being belted out by the three piece live band. The Christmas tree lighting ceremony day brought alive the rich tradition, heralding and unveiling the  spirit of the festive season in all its grandeur.last_img read more