The Case for Habitable Exoplanet Moons

first_img The direct detection of terrestrial planets around stars like our Sun may have to wait until the launch of dedicated satellites such as COROT and Kepler (scheduled for 2006 and 2008, respectively). In the meantime, some researchers have begun to wonder whether these extrasolar gas giants could harbor habitable moons.Our own solar system has four gas giants, and each has been blessed with an abundance of satellites. All these moons are far smaller than the Earth, but six could qualify as planets in their own right if they orbited the Sun: Jupiter’s four Galilean satellites Europa, Callisto, Ganymede, and Io; Saturn’s Titan; and Neptune’s Triton. Europa is known to have large amounts of water ice, and Titan has a thick atmosphere. If our solar system is not atypical, many of the known exoplanets probably have rich moon systems as well.Caleb Scharf, Columbia University’s Director of Astrobiology, has been exploring the conditions necessary for such moons to be habitable. His recent work investigates the conditions necessary for a moon to contain enough water to sustain biological life, at temperatures capable of supporting biological activity. Under zero-pressure conditions, water ice will sublimate (transform from solid to vapor directly) at temperatures higher than about 170 K (-103 °C). This means that water-rich protoplanets must form relatively far from the star — well outside the traditional “habitable zone” where stellar radiation raises temperatures high enough to support liquid water. Gas giants are also likely to form in these icy reaches — so the known exoplanets are highly likely to have acquired one or more icy moons early on. Icy moons may be carried into warmer regions later, as the host planet migrates inward.What happens to the water then? The answer depends mainly on the size of the moon. A moon or planet with about 10% the Earth’s mass has enough gravity to retain water vapor and other gases in a temperate atmosphere. (As a counterexample, Venus has enough gravity but is much too hot to retain water — the speed of water molecules in the atmosphere exceeds the escape velocity of the planet.) Mars-sized or larger moons may therefore be able to sustain both an atmosphere and liquid water, if their host planet is not too far from the star. More Heat Kneaded!Scharf is able to show that such moons may be habitable at greater distances than a similar planet would be, thanks to the process of tidal heating. Since gravity weakens with distance, the pull from the host planet will be slightly different on the near and far sides of a moon. If the moon’s orbit is circular this gravity differential will be constant, and the moon can adjust to it by changing its shape slightly. When a moon travels in an eccentric orbit around its planet, however, it approaches and recedes at regular intervals. The gravity differential therefore changes slightly as it orbits, resulting in a rhythmic compression of the moon’s core. In other words, the host planet will slowly knead the moon like a lump of dough. The activity can generates a lot of heat, even if the moon’s core is not molten. “You’re basically draining the spin energy of the parent planet.” Scharf explains. In the case of Jupiter, that spin energy is enormous—more than enough to sustain moderate levels of tidal heating indefinitely. To sustain the eccentricity of its moons’ orbits, the ideal exoplanet will have multiple moons in proximity (such as Jupiter’s Galilean satellites). To illustrate the potency of this process, Scharf offers the following example. “If you took Mars and put it where Europa is now, Mars would get heated by several tens of degrees [from tidal heating] at its surface. This would also probably start up its volcanic activity again.” Tidal heating can give an extra boost of energy to moons which receive too little light from the system’s star to thaw. Scharf finds that an Earth-sized moon could reach habitable temperatures about twice as far from the Sun as the Earth itself, under favorable assumptions.Most moons in the Solar system, however, are not large enough to hold an atmosphere; Ganymede is the largest, at about 0.025 (1/40) Earth masses. Scharf therefore postulates that habitable moons such as Europa are much more likely. The surface temperature of such moons must be cold enough to preserve ice even in the absence of an atmosphere, but the process of tidal heating could potentially warm the planet enough to create a warm, liquid ocean under the ice layer. Evidence of liquid water has not only been found on Europa, but also recently on Saturn’s moon Enceladus by the Cassini mission(http://www.solarviews.com/eng/enceladuswater.htm). Again, tidal heating is thought to be the culprit.In his most recent paper Scharf analyzes the properties of 74 exoplanets, those far enough from their star for satellite orbits to be stable over several billion years. He finds that between 28 and 51% of the planets in this sample are capable of harboring Europa-like moons with icy mantles and liquid water, depending on the size of the satellites and the eccentricity of their orbits. When one considers the total population of known exoplanets, the fraction falls to 15 to 27%, which is still quite favorable. Even if the planetary systems discovered so far lack Earth-like worlds, Scharf’s work makes a strong case that the moon systems of gas giants could also sustain life.Reference: Caleb A. Scharf, “The potential for tidally heated icy and temperate moons around exoplanets” 2006, to appear in Astrophysical Journal. http://xxx.lanl.gov/astro-ph/0604413By Ben Mathiesen, Copyright 2006 PhysOrg.comBen Mathiesen is an astrophysicist at the Service d’Astrophysique in Saclay, France, and owner of the agency Physical Science Editing, which helps researchers around the world meet native English writing standards in their academic publications. India prepares to land rover on moon in global space race Citation: The Case for Habitable Exoplanet Moons (2006, April 27) retrieved 18 August 2019 from https://phys.org/news/2006-04-case-habitable-exoplanet-moons.html Artist’s impression of an exoplanet. Credit: European Southern Observatory.center_img Explore further As scientists refine their methods, exoplanets are becoming easier and easier to detect. The current count is 163 planets orbiting 97 main-sequence stars, of which only one is even remotely Earth-like. All the others are massive bodies, ranging from “tiny” Uranus-like worlds (at about 15 Earth masses) to super-Jupiters (at thousands of Earth masses). 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

Tags: , , , , , , , , , , ,

Thinnest eggs belonged to largest Moas

first_imgGiant Haast’s eagle attacking New Zealand moa. Artwork: John Megahan. Copyright: PLoS Biology. Via Wikipedia. (PhysOrg.com) — In a detailed online study published by the Proceedings of the National Academy of Sciences on August 30th, scientists investigate questions surrounding New Zealand’s moa eggs and the results are mystifying. (c) 2010 PhysOrg.com Citation: Thinnest eggs belonged to largest Moas (2010, August 31) retrieved 18 August 2019 from https://phys.org/news/2010-08-thinnest-eggs-largest-moas.html More information: Ancient DNA reveals extreme egg morphology and nesting behavior in New Zealand’s extinct moa, Proceedings of the National Academy of Sciences, Published online before print August 30, 2010, doi:10.1073/pnas.0914096107 The 10 known species of moas, extinct relative of the ostrich and emus, were believed to be widely diverse in size varying from a small turkey-size to eight feet tall and beyond. For over a century, scientists and esteemed colleagues have studied 36 delicate, thin-shelled eggs, discovering a few of which belonged to two of the largest, heaviest flightless bird species. Scientists scrutinized DNA from various moas found throughout New Zealand and compared each to eggshells. Their findings concluded the two thinnest eggshells belonged to the largest, heaviest female moas, Dinornis robustus and Dinornis novaezealandiae.This begs the question, how did these giant creatures incubate such delicate eggs — without breaking them?With shells ranging from only 1.41-1.06 millimeters thick, it seems implausible for an adult female moa, weighing more than 550 pounds, to safely and effectively incubate such fragile eggs. One theory based on trace DNA evidence is that male moas, weighing in at around 165 pounds, might have been responsible for incubation and caring for the young, much like the ostrich and emu. Though, it’s been said the process would have been very difficult and hasn’t yet been proven. Out of the 3,434 bird species studied both living and extinct, moa eggs are the most vulnerable to breakage, thus adding to the possibility that they had very unusual nesting habits. Researcher David Lambert, an evolutionary biologist at Griffith University in Australia who was part of the investigation, told Live Science that moa nests weren’t uncommon in the way they were built. With nothing but a mere scrape in the ground surrounded by a thin layer of twigs and leaves, this is something else the moas might have had in common with ostrich and emu relatives. Lambert also added it’s been thought the moas may have curled around the eggs to warm them, instead of sitting directly on top of them to keep from obliterating their unborn offspring.Moas were killed off into extinction once the Maori colonized in New Zealand in the late 13th century, but their size mixed with curious incubation and nesting habits are a mystery scientists hope to someday solve for good. Extinct moa rewrites New Zealand’s history Explore further This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.last_img read more

Tags: , , , , , , , , , ,

Ancient avian bones found in China may be oldest example of chicken

first_img Journal information: Proceedings of the National Academy of Sciences (Phys.org) —A team of researchers in China studying ancient avian bones found in the northern part of that country, suspect the remains may be that of the oldest known example of chicken domestication. In their paper published in Proceedings of the National Academy of Sciences, the researchers describe their analysis and report on their findings. More information: “Early Holocene chicken domestication in northern China.” PNAS 2014 ; published ahead of print November 24, 2014, DOI: 10.1073/pnas.1411882111AbstractChickens represent by far the most important poultry species, yet the number, locations, and timings of their domestication have remained controversial for more than a century. Here we report ancient mitochondrial DNA sequences from the earliest archaeological chicken bones from China, dating back to ∼10,000 B.P. The results clearly show that all investigated bones, including the oldest from the Nanzhuangtou site, are derived from the genus Gallus, rather than any other related genus, such as Phasianus. Our analyses also suggest that northern China represents one region of the earliest chicken domestication, possibly dating as early as 10,000 y B.P. Similar to the evidence from pig domestication, our results suggest that these early domesticated chickens contributed to the gene pool of modern chicken populations. Moreover, our results support the idea that multiple members of the genus Gallus, specifically Gallus gallus and Gallus sonneratii contributed to the gene pool of the modern domestic chicken. Our results provide further support for the growing evidence of an early mixed agricultural complex in northern China.Press release Beijing Fatty Chicken, a local Chinese breed. Credit: Huagui Liu. Researchers track global dispersion of chickens throughout history using DNA Citation: Ancient avian bones found in China may be oldest example of chicken domestication (2014, November 25) retrieved 18 August 2019 from https://phys.org/news/2014-11-ancient-avian-bones-china-oldest.htmlcenter_img Explore further © 2014 Phys.org Identifying the first culture to domesticate chickens has been hotly debated for over a century, without any clear winner, and it may remain that way as evidence is piling up suggesting that chickens were likely domesticated in a variety of places across the globe and have since undergone comingling, creating a mish-mash of genetic evidence. In this new effort, the researchers sought to find out if ancient bone samples found in four different archeological sites in northern China were chicken ancestors and if so, if they were domesticated. The bones were found alongside charcoal and other animal remains, such as dogs and pigs, both of which are believed to have been domesticated by that time in history, suggesting that the bird bones were from a species that had been domesticated as well. The excavation sites have also given up other findings which suggest the people who’d been barbecuing the animals were farmers, not hunters, which also adds credence to the idea that the birds they were eating were domesticated. The bones in question (39 in all) had been previously carbon dated to various ages, ranging from 2,300 to 10,500 years ago. The new research focused on gathering genetic evidence and using mitochondrial DNA sequencing to determine if the birds were chicken ancestors, or not. The team compared the DNA of the ancient birds with modern birds of the Galliformes order, which include rock partridges, pheasants and of course chickens and also to samples of ancient bones found in other places, such as Spain, Hawaii, Easter Island and Chile. Their analyses revealed that the birds were members of the genus Gallus, which includes modern chickens. But it’s still not enough to prove that they were actually the first example of domesticated chickens because there is still no conclusive proof that the birds were actually domesticated. 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

Tags: , , , , , , , , , , ,

Chemists deduce the correct structure of the A and B baulamycins

first_img Citation: Chemists deduce the correct structure of the A and B baulamycins (2017, July 27) retrieved 18 August 2019 from https://phys.org/news/2017-07-chemists-deduce-baulamycins.html Journal information: Nature Despite their seemingly simple nature, molecules do not always display their true structure—they actually show a number of unique conformations. This makes it difficult for chemists attempting to understand or recreate them. Especially difficult is getting a handle on the true structure of flexible compounds. In this new effort, the researchers describe their discovery that the structure of A and B baulamycins had been incorrectly described by previous researchers and their efforts to find its correct structure, which led them to develop a new procedure to deduce the structure of a wide variety of natural compounds.A and B baulamycins are polyketide antibiotics with long, flexible carbon chains. Because of their benefits, researchers have tried to create synthetic versions of them, but until now, have failed. The reason appears to be earlier incorrect descriptions of their structure. After making that discovery, the researchers set about determining the true structure.The new method developed by the team involves using both computational methods and nuclear magnetic resonance spectra of the original material to figure out which configurations the compounds naturally take. They then made mixtures of possible isomers of baulamycin A with unequal ratios to identify which of the compounds matched the compound in its natural state. Once they had the correct structure, the team synthesized the compound, which can be used as an antibiotic. The team suggests the same process could be used by other researchers to deduce the correct structure of other natural complex molecules. Previously proposed and actual molecular structures of the baulamycins. Credit: Nature (2017). doi:10.1038/nature23265 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. © 2017 Phys.orgcenter_img Explore further (Phys.org)—A team of chemists at the University of Bristol has correctly deduced the correct structure of the A and B baulamycins. In their paper published in the journal Nature, the team describes how they discovered that the baulamycins had been incorrectly structured and how they developed the new method for deducing the structure of flexible compounds in general. Severin Thompson and Thomas Hoye with the University of Minnesota offer a News & Views piece on the work done by the group in the same issue and explain how the new method could be used to help medical scientists identify natural compounds that might offer medical benefits. Chemists discover structure of cancer drug candidate More information: Synergy of synthesis, computation and NMR reveals correct baulamycin structures, Nature (2017). nature.com/articles/doi:10.1038/nature23265AbstractSmall-molecule, biologically active natural products continue to be our most rewarding source of, and inspiration for, new medicines. Sometimes we happen upon such molecules in minute quantities in unique, difficult-to-reach, and often fleeting environments, perhaps never to be discovered again. In these cases, determining the structure of a molecule—including assigning its relative and absolute configurations—is paramount, enabling one to understand its biological activity. Molecules that comprise stereochemically complex acyclic and conformationally flexible carbon chains make such a task extremely challenging . The baulamycins (A and B) serve as a contemporary example. Isolated in small quantities and shown to have promising antimicrobial activity, the structure of the conformationally flexible molecules was determined largely through J-based configurational analysis, but has been found to be incorrect. Our subsequent campaign to identify the true structures of the baulamycins has revealed a powerful method for the rapid structural elucidation of such molecules. Specifically, the prediction of nuclear magnetic resonance (NMR) parameters through density functional theory—combined with an efficient sequence of boron-based synthetic transformations, which allowed an encoded (labelled) mixture of natural-product diastereomers to be prepared—enabled us rapidly to pinpoint and synthesize the correct structures.last_img read more

Tags: , , , , , , , , , , ,

Genetic study shows explosion of diversity in fish after endCretaceous mass extinction

first_img Reef fish arrived in two waves Journal information: Nature Ecology & Evolution A team of researchers from several institutions across the U.S. has found evidence suggesting that there was an explosion of diversity in fish after the end-Cretaceous mass extinction. In their paper published in the journal Nature Ecology and Evolution, the team describes their genetic study involving more than 1800 species of fish and what they found. Credit: CC0 Public Domain After the end-Cretaceous mass extinction—the one that killed off the dinosaurs—mammals became much more diverse and dominant. Without the dinosaurs to feast on them, they were free to prosper. Much less is known about what went on in the oceans. In this new effort, the researchers have added some new pieces to that puzzle.Prior research has suggested that the asteroid or comet that smashed into the Earth approximately 65 million years ago killed off more than the dinosaurs—approximately 50 percent of all species worldwide disappeared. These include many sharks and other reptiles, leaving a void of sorts in the world’s oceans that allowed fish to flourish. And flourish they did, according to the researchers with this new effort.To learn more about what happened with sea creatures after the end-Cretaceous mass extinction, the researchers collected tissue samples from 118 acanthomorph species, looking specifically at 1,000 DNA sequences that were similar across the genomes of their samples—as part of that effort, they searched for variations in genetic sequences that offered clues regarding how closely related the fish were to one another.The researchers found that six large groups of fish originated over the course of 10 million years after the mass extinction. Of those groups, five were acanthomorphs (spiny-rayed fish). Today, there are approximately 18,000 members of the acanthomorphs species and they represent approximately one in three vertebrate species alive today. That so many of them originated in the time after the dinosaurs disappeared shows that they, like mammals, found the world a much friendlier place—one where they were allowed to prosper. Such an explosion suggests that sharks and other reptile populations and their diversity must have plunged, leaving a vast void for the acanthomorphs to fill. Still unclear is why acanthomorphs, rather than other fish species, became so dominant. 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: Michael E. Alfaro et al. Explosive diversification of marine fishes at the Cretaceous–Palaeogene boundary, Nature Ecology & Evolution (2018). DOI: 10.1038/s41559-018-0494-6AbstractThe Cretaceous–Palaeogene (K–Pg) mass extinction is linked to the rapid emergence of ecologically divergent higher taxa (for example, families and orders) across terrestrial vertebrates, but its impact on the diversification of marine vertebrates is less clear. Spiny-rayed fishes (Acanthomorpha) provide an ideal system for exploring the effects of the K–Pg on fish diversification, yet despite decades of morphological and molecular phylogenetic efforts, resolution of both early diverging lineages and enormously diverse subclades remains problematic. Recent multilocus studies have provided the first resolved phylogenetic backbone for acanthomorphs and suggested novel relationships among major lineages. However, these new relationships and associated timescales have not been interrogated using phylogenomic approaches. Here, we use targeted enrichment of >1,000 ultraconserved elements in conjunction with a divergence time analysis to resolve relationships among 120 major acanthomorph lineages and provide a new timescale for acanthomorph radiation. Our results include a well-supported topology that strongly resolves relationships along the acanthomorph backbone and the recovery of several new relationships within six major percomorph subclades. Divergence time analyses also reveal that crown ages for five of these subclades, and for the bulk of the species diversity in the sixth, coincide with the K–Pg boundary, with divergences between anatomically and ecologically distinctive suprafamilial clades concentrated in the first 10 million years of the Cenozoic. © 2018 Phys.org Citation: Genetic study shows explosion of diversity in fish after end-Cretaceous mass extinction (2018, March 13) retrieved 18 August 2019 from https://phys.org/news/2018-03-genetic-explosion-diversity-fish-end-cretaceous.htmllast_img read more

Tags: , , , , , , , , , , ,

Applying deep learning to motion capture with DeepLabCut

first_img Citation: Applying deep learning to motion capture with DeepLabCut (2018, August 23) retrieved 18 August 2019 from https://phys.org/news/2018-08-deep-motion-capture-deeplabcut.html © 2018 Tech Xplore More information: Alexander Mathis et al. DeepLabCut: markerless pose estimation of user-defined body parts with deep learning, Nature Neuroscience (2018). DOI: 10.1038/s41593-018-0209-yAbstractQuantifying behavior is crucial for many applications in neuroscience. Videography provides easy methods for the observation and recording of animal behavior in diverse settings, yet extracting particular aspects of a behavior for further analysis can be highly time consuming. In motor control studies, humans or other animals are often marked with reflective markers to assist with computer-based tracking, but markers are intrusive, and the number and location of the markers must be determined a priori. Here we present an efficient method for markerless pose estimation based on transfer learning with deep neural networks that achieves excellent results with minimal training data. We demonstrate the versatility of this framework by tracking various body parts in multiple species across a broad collection of behaviors. Remarkably, even when only a small number of frames are labeled (~200), the algorithm achieves excellent tracking performance on test frames that is comparable to human accuracy. As Wei and Kording note, scientists have been trying to apply motion capture to humans and animals for well over a century—the idea is to capture the intricacies of all the tiny movements that together make up a larger, more noticeable movement, such as a single dance step. Being able to track such movements in animals offers some clues regarding their biomechanics and how their brains work. Being able to do so with humans can aid in physical therapy efforts or improvements in sports performance. The current process involves video recording the subject and carrying out a laborious process of tagging images frame by frame. In this new effort, the researchers have developed a computer automation technique to carry out the process, making it much faster and easier.To create DeepLabCut, the group trained a neural network using information from a database called Imagenet that contains a massive number of images and associated metadata. They then developed an algorithm that optimized estimations of poses. The third piece was the software that runs the algorithm, interacts with users and offers output of results. The result is a tool that can be used to perform motion capture on humans and virtually any other creature. All a user has to do is upload samples of what they are after, say, pictures of a squirrel, with its major parts labeled and some videos demonstrating how it moves in general. Then the user uploads video of a subject doing an activity of interest—say, a squirrel cracking open a nut. The software does the rest, producing motion capture of the activity. The team has made the new tool freely accessible to anyone who wishes to use it for whatever purpose they choose. Wei and Kording suggest the tool could revolutionize motion capture, making it easily available to professionals and novices alike. The hand of a mouse is automatically tracked with DeepLabCut, and the trajectories show the future (left) and past (far right) movements. Credit: Mathis et al, 2018 Explore further Making animated characters jump just got easier 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. A team of researchers affiliated with several institutions in Germany and the U.S. has developed a deep learning algorithm that can be used for motion capture of animals of any kind. In their paper published in the journal Nature Neuroscience, the group describes their tracking tool called DeepLabCut, how it works and how to use it. Kunlin Wei and Konrad Kording with the University of Peking and the University of Pennsylvania respectively offer a News & Views piece on the work done by the group in the same journal issue. Journal information: Nature Neuroscience Markerless pose estimation during behavior and across multiple species is crucial for many applications in neuroscience. Common model organisms are depicted in action, with the their past trajectories illustrated. Credit: Ella Maru Studio A fruit fly moving in a 3D chamber is automatically tracked with DeepLabCut Credit: Mathis et al, 2018last_img read more

Tags: , , , , , , , , , , ,

Threedimensional femtosecond laser nanolithography of crystals

first_img Explore further Wet etching nanopore lattices engineered by 3DLW in YAG. a) Nanopore lattice etched for 120 hours with average pore dimensions (257 ± 7 nm and 454 ± 13 nm) along x and y directions and 1 mm length along z. b) Vertically overlapping nanopores after 2 h wet etching (average dimensions of 131 ± 5 nm and 1,300 ± 35 nm along x and y, and 1 mm lengths). c) Top optical microscope view of nanopores along the z direction etched for 1 hour (129 ± 6.8 µm length). Credit: Nature Photonics, doi: https://doi.org/10.1038/s41566-018-0327-9 Etching nanopores in YAG along mm to cm scale lengths. (A) Optical microscope side view of etched pores. (B) Optical microscope top view of etched nanopores. (C) SEM side view of etched nanopores. Credit: Nature Photonics, doi: https://doi.org/10.1038/s41566-018-0327-9. Subwavelength diffraction gratings and MOW (micro optical waveguides) in YAG (yttrium aluminum garnet) crystals. a) Image of a centimeter-long, 700 nm pitch grating under visible light illumination. b) Experimental and calculated absolute diffraction efficiencies of a subwavelength grating (700 nm pitch) with 1,070 nm wavelength. Efficiency is calculated as the diffracted power divided by the power incident to the embedded grating. Error bars correspond to the experimental standard deviation of ~0.07%. Inset: scanning electron microscopy (SEM) close-up image of the fabricated grating. c) Optical waveguide with hexagonal structure, 500 nm horizontal pore-to-pore spacing, mean pore size of 166 × 386 nm^2 and 4 mm length. d) Simulated intensity mode profile at 1,550 nm with full-width at half maximums (FWHMs) of 862 nm (vertical) and 972 nm (horizontal). e) Diffraction- limited near-field image of the waveguide output mode measured at 1,550 nm, with a FWHM of ~1.5 µm. Credit: Nature Photonics, doi: https://doi.org/10.1038/s41566-018-0327-9 Within 170 hours, the scientists achieved nanopores with cross-sections of 368 x 726 nm2 and lengths of 3.1 mm; to show that nanopores with millimeter-scale length could be engineered in a single etching step. Nanophotonic devices typically require such lattice dimensions from the micrometric to the centimeter scale, without brittle fracture of the crystal due to excessive stress. In this way, the scientists implemented a scheme to homogenously etch nanostructures and microstructured optical waveguides (MOWs), on the desired scale across the whole sample.To test if the observed selectivity of nanopore etching with YAG was transferrable to other crystal types, the scientists conducted similar experimental nanostructuring with sapphire. They found a parallel nanopore etch rate of ~1 x 105 in sapphire, similar to YAG and higher than the rate previously observed with microchannels etched in sapphire. Ródenas and co-workers formed millimeter-long nanopores in sapphire with cross-sections as small as ~120 nm and tested the feasibility of the method by engineering nanopore lattices etched for 170 hours without fracturing the crystal. The results showed an etching selectivity at a value larger than 1 x 105 at the molecuar level between the modified and pristine crystalline states, hitherto not observed in a photo-irradiated material. The observed value was approximately two orders of magnitude higher than that of alumina etch masks on silicon. Ródenas et al. determined the etching rate of unmodified YAG at ~1 nm/hour. The proposed method allowed the design and fabrication of nanophotonic elements inside a crystal that could provide the desired optical responses, at the subwavelength structure. The scientists were able to control the features of pore direction, size, shape, filling fraction and length of nanopore lattices in YAG crystals by combining 3DLW and wet etching.The YAG lattice was etched for 120 hours to obtain average pore dimensions in the x and y directions. The pore shape and size were controlled by tailoring the laser power and polarization. The diameter of etched nanopores depended on the laser power and could be studied for both linear and circular laser beam polarizations. As limitations of the technique, they found that 3-D photonic structures were characteristically isolated in space, needed supporting walls, and suffered shrinkage and a low optical damage threshold. Optical properties of materials are based on their chemistry and the inherent subwavelength architecture, although the latter remains to be characterized in depth. Photonic crystals and metamaterials have proven this by providing access through surface alterations to a new level of light manipulation beyond the known natural optical properties of materials. Yet, in the past three decades of research, technical methods have been unable to reliably nanostructure hard optical crystals beyond the material surface for in-depth optical characterization and related applications. The capability to control lattice formation down to the nanometer scale will be useful in practical photonic applications. For instance, photonic bandgap lattices can be designed with stopbands in the visible to mid-infrared range in solid-state laser crystals for photonic information technology. To further expand the potential of the 3-D nanolithography technique, Ródenas et al. engineered MOW (microstructured optical waveguides) with different lattice spacings and cavity sizes. They obtained dimensions in the range of a centimeter in length, with 700 nm pitch grating observed under visible light illumination. Ródenas et al. conducted theoretical and simulation methods of the subwavelength gratings prior to their material fabrication. For the numerical simulations, they used the finite element method (FEM) in COMSOL Multiphysics 4.2 software. The scientists used the same FEM software and method to model YAG MOWs prior to fabrication.This ability to create controlled 3-D nanostructures of crystals opens up new routes to design compact, monolithic solid-state lasers. The resulting crystals can incorporate traditional cavity elements (gratings, fibres, microfluidic cooling channels) or novel microresonators inside the crystal. The prospect of engineering large, nanostructured laser crystals will provide a new basis for precision technology in metrological applications and allow for potentially new applications with ultra-strong deformable laser nanofibers in microelectronics and for drug delivery in medicine. © 2019 Science X Network (1). Evolution of pore size and cross-sectional aspect ratio as a function of laser power for linear and circular polarizations in YAG. (A) Power dependence of pore widths (in red) and heights (in blue) for linear (LP) and circular (CP) polarizations, measured from pores etched for 1h. (B) Dependence of cross-sectional pore aspect ratio (height divided by width) for linear and circular polarizations. (2) Etching crisscrossed nanopores. (A) The large index contrast between etched and un-etched pores is depicted in a raw bright-field transmission image. (B) 3D sketch of 90º crossing pores at different vertical offset positions. (C, D) SEM pictures of crossing pores at 90º and different crossing heights. Ag sputtered nanoparticles are also visible on the main surface. (E) Close-up view of the inner smooth surface of a pore. Credit: Nature Photonics, doi: https://doi.org/10.1038/s41566-018-0327-9 Journal information: Nature Photonics In the experiments, the scientists used a standard 3DLW with an ytterbium mode-locked ultrafast fiber laser (1030 nm wavelength and 350 fs pulse duration). A 1.4 numerical aperture (NA) oil-immersion objective was used to tightly focus the laser pulses inside the crystals. Ródenas et al. used computer-controlled XYZ linear stages for 3-D nanopositioning of the samples. After laser irradiation, they laterally polished the crystals to expose the irradiated structures followed by wet chemical etching. For this, the YAG crystals were etched in hot phosphoric acid in deionized water. A key technical limitation of the etching process was the difficulty in refreshing the exhausted acid inside the nanopores fabricated using the method detailed. , Nature Materials (1) Scheme to achieve infinitely long and homogeneously etched nanopore lattices by means of 3D-connecting etching pores. (A) 3D sketch of the vertical etching channels architecture for etching microstructured optical waveguides (MOWs). (B) SEM of a polished cut through a MOW partially revealing 3D etching pores. (C) Microscope top view of an etched array of MOWs with vertical etching channels every 80 µm. (2) Etching mm long pores in sapphire. a) Dark-field image of three arrays of 1-mm-long pores after 170 h of total etching time. Pores on each array were written at ~10 mW and at depths ranging from 4 to 30 µm. b) Example of pores written at medium power (9.4 mW) and 29 µm depth, after 30 min etching. c) Example of two pores written at 24 µm depth and at the photo-modification power threshold (~4 mW) for which no secondary pores are observed. Credit: Nature Photonics, doi: https://doi.org/10.1038/s41566-018-0327-9. 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: Three-dimensional femtosecond laser nanolithography of crystals (2019, January 15) retrieved 18 August 2019 from https://phys.org/news/2019-01-three-dimensional-femtosecond-laser-nanolithography-crystals.html More information: Airán Ródenas et al. Three-dimensional femtosecond laser nanolithography of crystals, Nature Photonics (2018). DOI: 10.1038/s41566-018-0327-9Markus Deubel et al. Direct laser writing of three-dimensional photonic-crystal templates for telecommunications, Nature Materials (2004). DOI: 10.1038/nmat1155 Amit Banerjee et al. Ultralarge elastic deformation of nanoscale diamond, Science (2018). DOI: 10.1126/science.aar4165 , Science For example, laser lithography developed by the semiconductor industry is a surface-processing technique used for efficient etching of a range of materials, including silicon, silica glass and polymers. The process can produce high-quality two-dimensional (2-D) nanophotonic devices that can be extended to 3-D, which was demonstrated two decades ago with infrared femtosecond laser direct writing. However, the photopolymerized structures are impractical as they cannot be interfaced with other photonic elements. While 3-D nanostructured optical fibres have delivered functionalities well beyond those possible with ordinary unstructured glass to revolutionize nonlinear optics and optical communications, reliable manufacture of materials in crystalline media has remained elusive.Alternative methods include direct machining 3-D nanostructures with laser-induced dielectric breakdown and micro-explosions triggered inside transparent crystals to form voids and induce sub-micrometer structures within them. But such methods occurred at the risk of extended lattice damage and crack propagation. Therefore, despite efforts, a standard method for large-scale, 3-D volume crystal nanostructuring remains to be reported.In a recent study published in Nature Photonics, Airán Ródenas and co-workers at the Institute of Photonics and Nanotechnology and the Department of Physics departed from existing methods of engineering the crystal nanoarchitecture. Instead, they proposed a method whereby the inner chemical reactivity of a crystal, given by its wet etch rate, could be locally modified at the nanoscale to form dense nanopore lattices using multiphoton 3-D laser writing (3DLW). The interdisciplinary scientists showed that centimeter-long empty pore lattices with arbitrary features at the 100 nm scale could be created inside key crystals such as yttrium aluminum garnet (YAG) and sapphire, typically used for practical applications. Ródenas et al. performed direct laser writing before etching, creating the desired pore architecture inside the solid-state laser crystal for photonic applications. New insight into nanopatterning diamond The scientists engineered the photonic structures using circular polarization to reproducibly create air pores in the nanoscale region below 200 nm. The nanophotonic structures (air pore photonic lattices) created in the crystal maintained spatial resolution equivalent to that obtained with state-of-the-art multiphoton polymerization lithography. For practical applications, nanophotonic devices require robust and efficient optical interconnections to form large, complex circuit designs with other optical elements. To achieve this, Ródenas et al. controlled the differential etch rate to maintain large pore lengths between the photomodified volumes and the surrounding crystal. They used scanning electron microscopy (SEM) to observe and prove the 3-D etching process. last_img read more

Tags: , , , , , , , , , , ,

Mamata leaves today for 3day Delhi visit to attend meet on 150th

first_imgKolkata: Chief Minister Mamata Banerjee will set out for her three-day-long visit to Delhi on Tuesday.Banerjee will be attending a meeting, where there will be discussion over the programme schedule to observe the 150th birth anniversary of Mahatma Gandhi. Prime Minister Narendra Modi will also be present in the meeting of the national level committee, comprising all chief ministers, Gandhians and eminent people from different walks of life. The Bengal government will also celebrate the 150th birth anniversary of the father of the nation and it will begin from October 2 at Gandhi Bhavan in Beliaghata. The state government has set up a 46-member committee with Chief Minister Mamata Banerjee as its chairperson and the committee has already held its first meeting. Also Read – Heavy rain hits traffic, flightsThe state government has taken all necessary measures for restoration of the Gandhi Bhavan. Besides organising essay competitions and publishing booklets, the state government has also decided to place a permanent chair in the name of Gandhiji at Calcutta University.The Chief Minister will be staying in Delhi till May 3. Though the main objective of her visit is to attend the May 2 meeting over the programme schedule to observe the 150th birth anniversary of Mahatma Gandhi, her visit has come up to be a crucial one, at a time when anti-BJP leaders from different states are in constant touch with her to form the Federal Front, to ensure a one-to-one fight in the general elections in 2019. Also Read – Speeding Jaguar crashes into Merc, 2 B’deshi bystanders killedIt may be recalled that during her last visit to Delhi in March, she had met former Congress president Sonia Gandhi. She had held meeting with eminent leaders, including National Congress Party chief Sharad Pawar. In a recent development in connection with the formation of an anti-BJP front, Telangana Chief Minister K Chandrasekhar Rao and DMK working president MK Stalin had a telephonic conversation with Banerjee on Sunday. It may be recalled that Rao had held a meeting with Banerjee in Nabanna on March 19.last_img read more

Tags: , , , , , , , , , , ,

Couple burnt to death

first_imgCanning (WB): A couple were burnt to death at their home in South 24 Parganas district early today, hours before panchayat polls were to being in West Bengal, police said. Family members of the victims, stated to be a CPI(M) worker and his wife, alleged that goons of the ruling Trinamool Congress set fire to the house at Kachharabari locality of Kakdwip at around 1 am.”An incident of fire was reported. A man and his wife were burnt to death. Forensic experts have been called,” Sundarbans Coastal police district SP Tathagata Basu said.CPI(M) district secretary Shamik Lahiri named some people claiming that those goons of the Trinamool Congress had assaulted party worker Debaprasad Das and his wife Usha and then set the house afire.Minister and local Trinamool MLA Mantu Pakhira denied the allegation and said the fire may have been caused by short circuit.last_img read more

Tags: , , , , , , , , , ,

KMC faces difficulties to carry on beautification

first_imgKolkata: The recent central rules barring civic bodies from using MPLAD funds for renovation or beautification of waterbodies have posed difficulties for the Kolkata Municipal Corporation to carry on undertaking such works.A rejuvenation work for a large pond under the Green City project at the confluence of ward 92 and 104 in the city has been stalled because of this restriction.It may be mentioned that Trinamool Congress MP Jogen Chowdhury has recently allocated Rs 60 lakh from his MPLAD funds for renovation of the pond located near Sahid Nagar Bank Plot area. Also Read – Heavy rain hits traffic, flights”We had planned to take up renovation of the pond with priority. But the central directive prevented us from doing so. These funds have been diverted to the civil department of the Roads section under the KMC for road repair and similar activities,” said Swapan Samaddar, Member Mayor-in-Council (Environment).He added that the proposal seeking funds from the state government for renovating this pond has been forwarded. “We are hopeful that as this waterbody comes under the Green City project, we will get the requisite funds soon,” Samadder said. It may be mentioned that the KMC has taken up the renovation of as many as 37 waterbodies in the city under the Jal Dharo Jal Bharo project. Also Read – Speeding Jaguar crashes into Merc, 2 B’deshi bystanders killedWork for renovation of some of these ponds have already started, while the tender for the remaining ones has already been floated. Under the Green City project, 159 waterbodies in the state will be renovated with a budget of around Rs 45 crore in 5 years. The KMC has started encouraging people, particularly the local unemployed youth to take up fish farming in the ponds that they have already renovated. “Our aim is to rope in the local unemployed youth to take up fish farming in these ponds. We hope that this will help us to bring down the tendency to fill up waterbodies for commercial purposes. It will also help in increasing fish production and supply to the local markets will also keep the price in check,” Samaddar said. It may be mentioned that Mayor Sovan Chatterjee, a few days back at a KMC programme, had expressed his concerns over integration of MPLAD funds in various projects with the Centre directing that MPLAD funds cannot be utilised through clubs or similar organisations even in welfare projects.last_img read more

Tags: , , , , , , , , , ,