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Nanoscale fuel cells may be closer than we think thanks to an

first_imgWe live in a world of hand-held devices: iPods, cell phones, PDAs, pagers… the list of essential personal technology keeps expanding, and the natural response is consolidation. It’s rare these days to see a new cell phone that isn’t also a digital camera, and MP3 players can be integrated into just about anything. We’re just a short step away from universal, hand-held devices that combine communication, media, and entertainment into one slim package. What’s stopping us? In a word, power. Scanning electron microscope image of two individual electrodes. Copyright Kenneth Lux. Used with permission. Lux and Rodriguez found their fuel channels ready-made in a commonly available, porous alumina filter costing only about $1. The filter is riddled with neat, cylindrical holes only 200 nanometers in diameter, and was already being used at their lab as a template for the growth of nanowires. Lux hit on the idea of creating nanowires in a platinum-copper alloy, then dissolving the copper by soaking the filter in nitric acid. In place of a solid nanowire, each hole was left with a porous platinum electrode. The partially dissolved wires are structurally complex, as befits their random nature, and have an enormous surface area for their size. To build a fuel cell, they fill the pores with acid. A sheet of electrolyte-loaded filter paper (or polymer-electrolyte) is placed between two of the nano-electrode arrays to carry off the hydrogen ions. Electrodes can then be placed anywhere on the outer surface of the sandwich, allowing the electrical connections to be easily configured. Stacks of these fuel cell arrays can be connected in series or parallel, to provide higher voltage or current respectively.Of course, the result is hardly perfect. Lux estimates that only a third of the electrodes are active, and admits that there is a lot of room for improvement. Even this proof-of-concept prototype, however, has an energy capacity an order of magnitude higher than its two-dimensional lithographic counterparts! The price can’t be beat, either, with a total materials cost of only $200. “It’s a really simple method.” says Lux, “My power source [for making the nanowires] was a AA battery.”If fuel-cell technology can be perfected, we might be looking at a future of cheap, disposable battery packs for our favorite electronic gadgets. When your universal media manager runs out of energy, you’ll just run to the store and buy it a methanol sandwich! Citation: Template Synthesis of Arrays of Nano Fuel Cells, Kenneth W. Lux and Karien Rodriguez, Nano Letters 6, 2006by Ben Mathiesen, Copyright 2006 PhysOrg.com Fuel cell prototype. Copyright Kenneth Lux. Used with permission. Fiat Lux!Researchers Kenneth Lux and Karien Rodriguez, at the University of Wisconson, came up with an exciting new approach to the problem. Their method not only improves the performance of nano-scale fuel cells, but completely sidesteps the need for industrial-strength technology. “Even the best electrocatalysts, on a flat surface, give only hundreds of microamps per square centimeter. What you really want is … to increase the surface area by orders of magnitude.” Lux explains to PhysOrg.com, “To do this you need a three-dimensional structure.” Toyota to test solar panels for electric carscenter_img Cell phones last a few days on a single battery; laptop computers, two to three hours. If you could have a pocket-sized personal computer with a cell-phone sized battery, how long do you think it would last? Just long enough to check your e-mail, or play a game of solitaire? It’s a sad but unavoidable fact that the more complicated an electronic device gets, the less efficient it is. Enter fuel cells, with an energy capacity at least ten times greater than that of conventional batteries. Where a lithium-ion battery can provide 300 Watt-hours per liter, the methanol in a fuel cell has a theoretical capacity of up to 4800 Watt-hours per liter! Imagine your laptop running for a full day without needing to recharge, and you can see why industry leaders such as Toshiba, IBM, and NEC have been pouring funds into fuel cell research.A polymer-electrolyte membrane (PEM) fuel cell generates current by stripping hydrogen atoms from a chemical source, breaking them apart on a catalyst (such as platinum), and harvesting the electrons. The hydrogen ions (protons) left over from this process are separated from the fuel by an electrolyte, and when brought into contact with the atmosphere they bind to oxygen molecules and produce water. The more fuel you can bring into contact with the catalyst, the more current can be drawn from the cell. A high catalytic surface area is the key to efficiency.To compress more power into smaller volumes, researchers have begun to build fuel cells on the fuzzy frontier of nanotechnology. Silicon etching, evaporation, and other processes borrowed from chip manufacturers have been used to create tightly packed channel arrays to guide the flow of fuel through the cell. The point is to pack a large catalytic surface area into a wafer-thin volume. This approach is not only expensive, but inherently limited by its two-dimensional nature. Citation: Nano-scale fuel cells may be closer than we think, thanks to an inexpensive new manufacturing method (2006, March 12) retrieved 18 August 2019 from https://phys.org/news/2006-03-nano-scale-fuel-cells-closer-inexpensive.html 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. 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The future cometh Science technology and humanity at Singularity Summit 2011 Part

first_img Koene (Artificial General Intelligence and Neuroscience at AGI 2011) For Koene, substrate independence is about successful long-term evolution rather than the actual technological mind uploading process of achieving that independence. “If you look forward billions of years toward the end perspective,” Koene told PhysOrg, “what will take up the majority of intelligent spacetime? Since there’s always going to be the competitive natural selection of universal Darwinism, the entities that survive are those that are the most able to understand, adapt to and address new challenges in their surroundings. If you’re dependent on a particular substrate, you can’t be that flexible.” To Koene, then, ultimate adaptability is substrate independence as pattern rather than genetic propagation – a concept he explicated in Pattern Survival versus Gene Survival.In the near term, Koene points out, the focus is on the whole brain emulation approach to creating substrate-independent minds because “it’s the one approach that is so conservative, we can work on it today. It’s the process of emulating processes as they operate in the brain right now rather than creating something more abstract. In this case you don’t want to do the latter because we don’t have a clear understanding of how the brain works on a cognitive level: We wouldn’t know what to capture where – that is, what’s important to keep in order to create a substrate-independent version of yourself that retains what you personally consider essential about you.” Since Koene sees the mind as emerging from the brain, his approach to whole brain emulation therefore looks to neuroanatomy and neurophysiology as the determinants of how and what we think.Alexander Wissner-Gross offered his own implementation-centric view of mind uploading, telling PhysOrg that this will be accomplished using a non-invasive technique – i.e., not a Hans Moravec-type procedure, which appears rather barbaric despite its technological sophistication: A robot surgeon is equipped with a manipulator which subdivides into ever-finer branches that terminate in billions of nanometer-scale sensitive probes equipped with electrochemical sensors that translate single-neuron activity into a functional simulation. Once so virtually replicated, a neuron is removed, with the process continuing until the brain has been, in a sense, consumed.“I’m not sure how long it will take,” adds Wissner-Gross, “but, again, I’m optimistic. A non-invasive mind uploading technology might look something like fMRI capture of brain states with a veneer of machine learning.” Wissner-Gross also waxes enthusiastic about optogenetics, a groundbreaking photonics-based technique developed by Ed Boyden in the Synthetic Neurobiology Group at MIT for reading from, and writing to, single neurons. Other recent research is also suggestive: Neuroanatomy and neurophysiology are inherently three-dimensional domains. Neuronal cell body projections – axons and dendrites – can interconnect large numbers of neurons distributed over large cortical distances. Since the brain processes sensory, somatic, conceptual, and other classes of information in this 3D structural space, the need to (1) image neural structures and (2) stimulate and record neural signals are essential to understanding the relationship between brain structure and function. While 3D imaging and 3D photostimulation using scanning or parallel excitation methods have been used, they have not previously been combined into an optical system that can successfully decouple the corresponding optical planes when using a single lens – a shortcoming that has limited investigators to small neural areas. Recently, however, scientists at Université Paris Descartes have combined digital single photon holographic stimulation with remote-focusing-based epifluorescent functional imaging to overcome these limitations.Working at the intersection of physics and biology, Francesca Anselmi and Cathie Ventalon in the Emiliani Wavefront-Engineering Microscopy Group led by Dr. Valentina Emiliani, along with Aurélien Bègue and David Ogden, have demonstrated simultaneous high-resolution single-neuron 3D neural imaging and photostimulation by integrating digital single photon holographic stimulation with scanless remote-focusing-based epifluorescent functional imaging.Asked about the role of quantum processes in consciousness – specifically, as extrapolated from Coherently wired light-harvesting in photosynthetic marine algae at ambient temperature, research conducted at University of Toronto by Elisabetta Collini and others – Wissner-Gross adds that while this and related channelrhodopsin research disproves the argument that quantum events don’t occur at room temperature, he cautions that it still is the case that capturing quantum states may not be necessary for mind uploading.Not necessarily so for Eliezer Yudkowsky, an AI theorist focused on ensuring that the Singularity gives rise to what he terms a friendly AI (as witnessed by his talk, Open Problems in Friendly Artificial Intelligence). Speaking with PhysOrg, Yudkowsky succinctly proclaimed, “It’s all quarks.” Christof Koch on “The Neurobiology and Mathematics of Consciousness” at Singularity Summit 2011 For Koch, whose research has focused on the physical basis of consciousness for well over a decade, consciousness is a fundamental property of networked entities that may well be explained by psychiatrist Giulio Tononi’s integrated information theory (IIT) – an approach hypothesizing that consciousness is measure in that it corresponds to the capacity of a system to integrate information. Koch also sees IIT as a blueprint for building sentient machines. 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. Eliezer Yudkowsky on “Open Problems in Friendly Artificial Intelligence” at Singularity Summit 2011 Intimately related to human-like AI is an ability to recognize, understand and act upon complex visual images, motion and sensory flow fields. Stealth startup Vicarious Systems co-founders Scott Brown and Dileep George – the latter previously CTO of Numenta (which pioneered the neocortical-like technology Hierarchical Temporal Memory, or HTM, a theory first described by Numenta co-founder Jeff Hawkins in On Intelligence) and before that Research Fellow at the Redwood Neuroscience Institute – gave a seductively sparse talk. From Planes to Brains: Building AI the Wright Way described their neurobiological approach to artificial vision software that at first will understand the contents of images and videos the way humans do, eventually expanding to all sensory systems by building what might be called a sensory mode-agnostic model – that is, by capturing neocortical invariants common across vision, hearing, olfaction, taste and touch – that mirrors human learning and thought. While the Vicarious system wasn’t demonstrated, details will be revealed…soon. While the Singularity is not to be confused with the astronomical description of an infinitesimal object of infinite density, it can be seen as a technological event horizon at which present models of the future may break down in the not-too-distant future when the accelerating rate of scientific discovery and technological innovation approaches a real-time asymptote. Beyond lies a future (be it utopian or dystopian) in which a key question emerges: Evolving at dramatically slower biological time scales, must Homo sapiens become Homo syntheticus in order to retain our position as the self-acclaimed crown of creation – or will that title be usurped by sentient Artificial Intelligence? The Singularity and all of its implications were recently addressed at Singularity Summit 2011 in New York City.Part 1: The future cometh: Science, technology and humanity at Singularity Summit 2011 (Part I)In an ambitious talk (and accompanied by his engaging dry wit), neuroscientist Christof Koch – Professor of Biology and Engineering at the California Institute of Technology in Pasadena and the Chief Scientific Officer of the Allen Institute for Brain Science in Seattle – discussed The Neurobiology and Mathematics of Consciousness – a thorny problem at the forefront of cognitive neuroscience. The challenge is derived from the quixotic nature of consciousness as an instance of qualia: introspectively accessible, phenomenal aspects of our mental lives we experience as real, but which nonetheless elude definition and neurobiological localization. Koch rejects a number of popular concepts of consciousness, including the views that consciousness emerges from the brain or is inherent in complexity. “It is not the nature of the stuff that the brain is made out of that matters for mind, it is rather the organization of that stuff—the way the parts of the system are hooked up, their causal interactions,” he writes in his latest book, Consciousness – Confessions of a Romantic Reductionist, scheduled to be published by MIT Press in early 2012. “A fancier way of stating this is consciousness is substrate-independent.”Speaking of substrate independence, it should be noted that some of the Singularity’s most noteworthy thinkers, researchers and futurists did not present at Singularity Summit 2011. Among them is Randal Koene, neuroscientist, neuroengineer leading the effort in advancing substrate-independent minds (ASIM) – that is, advancing the field of substrate-independent mind (SIM) research, which is focused on transferring mind functions from the biological substrate to another substrate on which those functions can be replicated. (The process of moving our mind from our biological brain to a SIM is referred to as mind uploading, while whole brain emulation is a specific SIM implementation.) In fact, Koene – Co-Founder of carboncopies, Founder of MindUploading, Director of Neural Engineering Corporation, and Director of Analysis at Halcyon Molecular – is a member of the Oxford working group that convened in 2007 to create a first roadmap toward whole brain emulation, a topic he addressed at Singularity Summit 2009. He also discussed Artificial General Intelligence and Neuroscience at AGI 2011.Randal Koene at Singularity Summit 2009 — The Time is Now: As a Species and as Individuals we Need Whole Brain Emulation The future cometh: Science, technology and humanity at Singularity Summit 2011 (Part I) (PhysOrg.com) — In its essence, technology can be seen as our perpetually evolving attempt to extend our sensorimotor cortex into physical reality: From the earliest spears and boomerangs augmenting our arms, horses and carts our legs, and fire our environment, we’re now investigating and manipulating the fabric of that reality – including the very components of life itself. Moreover, this progression has not been linear, but instead follows an iterative curve of inflection points demarcating disruptive changes in dominant societal paradigms. Suggested by mathematician Vernor Vinge in his acclaimed science fiction novel True Names (1981) and introduced explicitly in his essay The Coming Technological Singularity (1993), the term was popularized by inventor and futurist Ray Kurzweil in The Singularity is Near (2005). The two even had a Singularity Chat in 2002. Dileep George and Scott Brown on “From Planes to Brains: Building AI the Wright Way” Given the historical difficulties of instantiating human-like visual performance and comprehension in AI systems, it will be disruptive indeed if that revelation occurs far in advance of the Singularity it portends. Copyright 2011 PhysOrg.com. All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com. Explore further Citation: The future cometh: Science, technology and humanity at Singularity Summit 2011 (Part II) (2011, December 2) retrieved 18 August 2019 from https://phys.org/news/2011-12-future-cometh-science-technology-humanity_1.html More information: Part 1: The future cometh: Science, technology and humanity at Singularity Summit 2011 (Part I)last_img read more

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Wild brown bear observed using a tool

first_img © 2011 PhysOrg.com (PhysOrg.com) — Because brown bears are so reclusive, not to mention dangerous to be around, not a lot is really known about their brain power. This is actually rather odd because bears have the largest brains for their body size of all carnivores and are thought to be rather clever, though mostly through anecdotal evidence. Now comes news of British researcher Volker Deecke of the University of Cumbria, who while on vacation in Alaska, came across a brown bear using a rock covered with barnacles to help alleviate the itch associated with molting. Deecke photographed the use of the tool by the bear and has published his findings in Animal Cognition. Image (c) Volker Deecke Bears of many varieties have very often been seen rubbing themselves against trees and rocks to help ease the itching that results when they replace their winter fur with a lighter summer coat. But never before has a bear of any kind been spotted picking up rocks to use as tools to help them better get at those places that itch. In fact, this discovery is only the fourth observed use of tools by any non-primate animal. Elephants commonly use branches to ward off flies and dolphins have been caught using sponges to hide their rostrum and some whales use bubbles to help in catching fish. Using a rock specifically chosen to perform a certain task, however, is clearly a demonstration of higher intelligence.Deecke, who normally studies whales, was watching a couple of brown bears feed on a whale carcass on the shores of Glacier Bay, when one of them began searching the bottom of the sea for something. A moment later, the bear reached down and grabbed a rock, which Deecke could clearly see was covered with barnacles, and began rubbing it against its face and neck. Thus it appeared that not just any rock would do, it had to be covered with barnacles which would do a better job in scratching. It wasn’t just a fluke either. After a while, the bear dropped the rock, moseyed around, and after some time searched for and retrieved another rock. In all the bear repeated the whole exercise three times, retrieving three different rocks, all covered with barnacles, which he used for scratching at his itchy hide. Deecke also noted that the bear manipulated the rock in his paw before scratching, moving it into the optimal position for the best possible scratch, a type of activity previously only seen with humans and other primates.Deecke suggests that more research ought to be focused on bears because clearly they are capable of far more than has been realized. Bears may be back in the Swiss Alps More information: Tool-use in the brown bear (Ursus arctos), Animal Cognition, DOI: 10.1007/s10071-012-0475-0AbstractThis is the first report of tool-using behaviour in a wild brown bear (Ursus arctos). Whereas the use of tools is comparatively common among primates and has also been documented in several species of birds, fishes and invertebrates, tool-using behaviours have so far been observed in only four species of non-primate mammal. The observation was made and photographed while studying the behaviour of a subadult brown bear in south-eastern Alaska. The animal repeatedly picked up barnacle-encrusted rocks in shallow water, manipulated and re-oriented them in its forepaws, and used them to rub its neck and muzzle. The behaviour probably served to relieve irritated skin or to remove food-remains from the fur. Bears habitually rub against stationary objects and overturn rocks and boulders during foraging and such rubbing behaviour could have been transferred to a freely movable object to classify as tool-use. The bear exhibited considerable motor skills when manipulating the rocks, which clearly shows that these animals possess the advanced motor learning necessary for tool-use. Advanced spatial cognition and motor skills for object manipulation during feeding and tool-use provide a possible explanation for why bears have the largest brains relative to body size of all carnivores. Systematic research into the cognitive abilities of bears, both in captivity and in the wild, is clearly warranted to fully understand their motor-learning skills and physical intelligence related to tool-use and other object manipulation tasks. Explore further Citation: Wild brown bear observed using a tool (2012, March 7) retrieved 18 August 2019 from https://phys.org/news/2012-03-wild-brown-tool.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.last_img read more

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Water water everywhere How UV irradiation reversibly switches graphene between hydrophobic and

first_img On the edge of graphene (Phys.org) —Scientists have long observed that the wettability of graphene – an essentially two-dimensional crystalline allotrope of carbon that it interacts oddly with light and with other materials – can be reversed between hydrophobic and hydrophilic states by applying ultraviolet (UV) irradiation. However, an explanation for this behavior has remained elusive. Recently, researchers at The University of New South Wales and University of Technology, Sydney investigating this phenomenon both experimentally and by calculations using density functional theory (DFT) – a computational quantum mechanical modeling method – finding that UV irradiation enables this reversible and controllable transition in graphene films having induced defects by water splitting adsorption on the graphene surface of H2O molecules in air. (Water splitting is the chemically dissociative reaction in which water is separated into hydroxyl and hydrogen; hydroxyl is a chemical functional group containing an oxygen atom connected by a covalent bond to a hydrogen atom; and adsorption is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface.) The direct application for this approach is water splitting – a very important step in, for example, hydrogen generation: Using the technique in this work, H2O molecules could be easily split into OH- and H+ groups and adsorbed on defect-induced graphene under UV irradiation. After irradiation, the two groups can be easily desorbed from the graphene and produce hydrogen, allowing the graphene to be used continually as a catalyst for water splitting. Ao points out that when fabricating devices based on graphene – for example, solar cells – layer-by-layer materials fabrication is required. “Hydrophilic graphene is more easily modified and combined with other materials than is hydrophobic graphene. For example, in the case of biomaterials, hydrophilic graphene would be desirable for the biomolecule contact.”It turns out that achieving graphene reversible wettability can be accomplished using other techniques, including external electric fields, plasma treatment, magnetic fields, and neutron diffraction. “Actually, the work with achieving graphene reversible wettability using external electric fields was also reported2 by my group based on first-principle calculations. Compared with using external electric fields, UV irradiation is easily realized in experiment, while a very high electric field is required to realize the wettability transition,” noting that an experiment under a strong electric field is underway. “Plasma has even greater energy, and may induce more defects in graphene. However, the plasma treatment process is more complicated and has greater requirements.” The reaction pathways for the dissociative adsorption of an H2O and an O2 molecule on graphene. Pristine graphene (a) and (b); graphene with mono-atom vacancy (c) and (d); divacancy (e) and (f); edge (g) and (h); grain boundary (i) and (j). Credit: Xu, Z. et al. Reversible Hydrophobic to Hydrophilic Transition in Graphene via Water Splitting Induced by UV Irradiation. Sci. Rep. 4, 6450. Explore further Calculated Raman spectra of graphene. (a) With water, and (b) with oxygen dissociatively adsorbed. Credit: Xu, Z. et al. Reversible Hydrophobic to Hydrophilic Transition in Graphene via Water Splitting Induced by UV Irradiation. Sci. Rep. 4, 6450. The key technique the researchers used to address these challenges was to combine experiment and first-principles calculations. “In our experiment, we demonstrated that the wettability of graphene could be reversibly tuned through UV irradiation in air and vacuum storage,” Ao says. “In addition, computational calculations enable us to understand the exact effect of each individual factor.” After comparing their experimental and calculation results, the scientists found that Raman spectra from the experiment were similar to that of H2O dissociative adsorption on graphene. (In graphene research, Raman spectroscopy is used to determine the number and orientation of layers, the quality and types of edge, and the effects of perturbations, such as electric and magnetic fields, strain, and doping.) Moreover, they also considered irradiations at different conditions, such as in O2 and H2O rich environments, and found that H2O concentration clearly affected the wettability change of graphene after irradiation. “Therefore,” Ao adds, “we concluded that H2O dissociative adsorption on graphene induces the reversible wettability transition.” More information: Reversible Hydrophobic to Hydrophilic Transition in Graphene via Water Splitting Induced by UV Irradiation, Scientific Reports (Published online September 23 2014), 4:6450, doi:10.1038/srep06450Related:1First principles study on the hydrophilic and conductive graphene doped with Al atoms, Physical Chemistry Chemical Physics, 2013, 15, 10859-10865, doi:10.1039/C3CP00128H2Reversible Transition of Graphene from Hydrophobic to Hydrophilic in the Presence of an Electric Field, Journal of Physical Chemistry C, 2012, 116 (36), doi:10.1021/jp3050466 The scientists conclude that their discovery may provide new insights into the fundamental principles of water splitting with graphene-based materials, and could thereby lead to other applications – including electrocatalysis, nanomaterials; nanoelectromechanical systems, biomaterials, microfluidic devices, hybrid organic systems, and other advanced multifunctional systems.Dr. Zhimin Ao discussed the paper that he, Doctoral Student Zhemi Xu and their co-authors published in Scientific Reports and the main challenges the researchers faced. “The main challenge – and the motivation for the conducting the study – was to reveal the real mechanism of the reversible wettability transition under UV irradiation and isolate it from various possible reasons, such as the contamination of chemicals on samples or induced by molecules in air,” Ao tells Phys.org. “We also had to identify H2O rather than other possible molecules in air, which contributes the wettability transition under UV irradiation.” After determining the contribution of H2O, he adds, another challenge was to understand the adsorption type of H2O for the wettability transition – that is, chemical or physical adsorption.”Secondly,” Ao continues, “to eliminate drawbacks from chemical doping and induced defects – such as organic molecules on the graphene sample – that may be an important factor in graphene’s wettability transition under UV, the samples were stored for two hours in a vacuum to remove contaminants on the graphene surface.” As a result, most of the remaining graphene defects, such as vacancies, edges and grain boundary, would be there due to the synthesis process. “According to our calculations, on defects of vacancies, edge and grain boundary, water splitting can be easier to achieve. However, other defects can also affect the wettability of graphene, such as aluminum doping, which has been reported by another paper1 of my group.” Looking ahead, Ao notes that they need to further clarify the mechanism for graphene’s hydrophobic to hydrophilic transition under UV irradiation because the latter itself can induce graphene defects. “Although UV irradiation was believed to induce defects in graphene, the problem is that these defects aren’t obvious because this energy source is not strong enough. To further clarify the reversible wettability mechanism, we may use different energy sources to investigate the transition, such as X-ray and neutron diffraction.” They also plan to investigate conductivity change and transport properties under UV irradiation.”High electrical conductivity graphene film with high hydrophilicity is always desirable,” Ao tells Phys.org. “However, these two properties are normally resisting each other. When working with graphene-based devices, exploring the electric conductivity variation of graphene in such processes can help to control and balance these two properties.”Other areas that might benefit from their study, Ao concludes, include sensors and hydrogen generation and storage. Citation: Water, water everywhere: How UV irradiation reversibly switches graphene between hydrophobic and hydrophilic states (2014, October 27) retrieved 18 August 2019 from https://phys.org/news/2014-10-uv-irradiation-reversibly-graphene-hydrophobic.html Journal information: Scientific Reports , Physical Chemistry Chemical Physics © 2014 Phys.org , Journal of Physical Chemistry C Atomic structures of a H2O or an O2 molecule adsorbed on graphene with different types of defects. Credit: Xu, Z. et al. Reversible Hydrophobic to Hydrophilic Transition in Graphene via Water Splitting Induced by UV Irradiation. Sci. Rep. 4, 6450. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.last_img read more

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Tiniest spin devices becoming more stable

first_img This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. © 2016 Phys.org The problem is that the atoms don’t want to stay in their designated positions for very long. Even the tiniest amount of heat can overcome the weak magnetic coupling between an atom and substrate that helps keep the atom in place. As a result, the spin-based logic device only works at temperatures below 0.3 K, barely above absolute zero.Now in a new paper published in Nano Letters, Wiesendanger’s team has demonstrated spin-based logic devices that are made of molecules instead of atoms. The molecules are held in place by superexchange magnetic coupling, which is much stronger than weak magnetic coupling. The stronger interactions translate to an order of magnitude higher operation temperature, up to 6 K. The molecular spin devices, which are almost as small as the atomic version, have much higher stability and they still offer the same potential advantages of high-speed operation and low-power consumption that make spintronics devices so attractive.”We now have all the building pieces on the surface to create devices out of molecular building blocks,” lead author Maciej Bazarnik, a physicist at the University of Hamburg and at the Poznan University of Technology in Poland, told Phys.org.In general, spin-based devices work by controlling the spins of electrons, just as conventional electronics devices control electron charge. Similar to how charge is considered to be either negative or positive, spin is regarded as being either up or down. By applying a magnetic field, researchers can generate an excess of spin up or spin down electrons, creating a net spin polarization and producing a magnetic spin current.To build an all-spin logic device, the challenge is that the atoms and molecules must be arranged so that they act as wires, junctions, and other building blocks for transmitting the easily disturbed spin information from one place to another. In the new study, the researchers built these components out of coordination compounds, which are magnetic molecules that consist of a central metal atom (here, cobalt) linked to surrounding groups of atoms. These groups are carefully chosen to achieve strong magnetic interactions between the spin-carrying metal atoms of adjacent compounds, allowing the spin information to be transferred. The researchers also engineered the chemical structure to alleviate another problem facing atomic-scale spin devices: by transporting the spin information more directly between junctions, they could greatly reduce unwanted interference with neighboring devices. With their greater stability, the molecular spin logic devices represent a step toward making very small spin devices at higher temperatures, which is necessary for realizing future applications. “We are exploring different magnetic centers in our molecules to achieve stronger magnetic couplings and raise the operating temperature even higher,” Bazarnik said. “Since all-spin devices are ultimately small, using them in future nanoelectronics would be beneficial. They operate on a spin degree of freedom and therefore no flow of [electric] current is necessary for the information to be transmitted. Hence there is no heating and very low power consumption.” Citation: Tiniest spin devices becoming more stable (2016, February 3) retrieved 18 August 2019 from https://phys.org/news/2016-02-tiniest-devices-stable.html A new magnetoresistance effect occurring in materials with strong spin-orbit coupling (Phys.org)—In 2011, the research group of Roland Wiesendanger, Physics Professor at the University of Hamburg in Germany, fabricated a spin-based logic device using the spins of single atoms, a feat that represents the ultimate limits of miniaturization. In these tiny devices, all of the atoms must be precisely positioned so that their spin information can be transmitted from one atom to the next.center_img Explore further A spin-based logic device made of molecules (shown here) is more stable than one made of atoms. Credit: Bazarnik, et al. ©2015 American Chemical Society Journal information: Nano Letters More information: Maciej Bazarnik, et al. “Toward Tailored All-Spin Molecular Devices.” Nano Letters. DOI: 10.1021/acs.nanolett.5b04266last_img read more

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Liposomes modified with temperatureresponsive polymers are tuned for cellular uptake

first_img Explore further © 2017 Phys.org Credit: Jian Wang More information: Jian Wang et al. Tunable Surface Properties of Temperature-Responsive Polymer-Modified Liposomes Induce Faster Cellular Uptake, ACS Omega (2017). DOI: 10.1021/acsomega.6b00342AbstractDrug delivery by nanoparticle carriers has been limited by inefficient intracellular drug delivery. Temperature-responsive poly(N-isopropylacrylamide) (PNIPAAm)-modified liposomes can release their content following heating. In this study, we synthesized the temperature-responsive polymer poly(N-isopropylacrylamide)-co-N,N′-dimethylaminopropylacrylamide (P(NIPAAm-co-DMAPAAm)) and investigated the properties of liposomes modified with P(NIPAAm-co-DMAPAAm) for intracellular drug carriers. The copolymer displayed a thermosensitive transition at a lower critical solution temperature (LCST) that is higher than body temperature. Above the LCST, the temperature-responsive liposomes started to aggregate and release. The liposomes showed a fixed aqueous layer thickness (FALT) at the surface below the LCST, and the FALT decreased with increasing temperature. Above 37 °C, cytosolic release from the temperature-responsive liposomes was higher than that from the PEGylated liposomes, indicating intracellular uptake. Here, we showed that the tunable surface properties of the temperature-responsive polymer-modified liposomes possibly enabled their dehydration by heating, which likely induced a faster cellular uptake and release. Therefore, the liposomes could be highly applicable for improving intracellular drug-delivery carriers. Heating targeted cancer drugs increases uptake in tumour cells 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 Citation: Liposomes modified with temperature-responsive polymers are tuned for cellular uptake (2017, February 10) retrieved 18 August 2019 from https://phys.org/news/2017-02-liposomes-temperature-responsive-polymers-tuned-cellular.html Studies with carboxyfluorescein (CF) encased in the liposome showed that CF was released once aggregates started to form. Specifically, above 37oC 15% of CF was released in thirty minutes. Then, near the LCST, more CF was released and at 42oC 80% of CF had been released.Wang et al. then studied changes in the fixed aqueous layer thickness (FALT) on the surface of the polymer-modified liposome and compared it to PEGylated liposomes. These results showed that as the temperature increased, the aqueous layer decreased in size only in the temperature-responsive polymer-modified liposomes, but not in the PEGylated liposomes. Importantly, the aqueous layer’s thickness decreased at the LCST.The next step was to see if the temperature-responsive polymer-modified liposomes displayed good cellular uptake. Wang et al. noted that cellular uptake of the polymer-modified liposomes was much more temperature dependent than the PEGylated liposome controls. Fluorescence microscopy showed that CF-entrapped liposomes (rhodamine labeled) in RAW264.7 and HeLa cells released CF in the cells, while cells treated with free CF and liposomes without CF did exhibit the same level of fluorescence within the temperature range. At 40oC, CF fluorescence appeared throughout the cytosol verifying that the polymer-modified liposomes are temperature dependent in terms of cellular uptake and delivery.The actual mechanism of cellular uptake was analyzed using HeLa cells. The cells were incubated for one hour at 37oC with or without several types of endocytic inhibitors. The cells were then treated with temperature-responsive polymer modified liposomes at either 4oC or 40oC for 30 minutes. Cellular uptake did not occur at 4oC indicating that uptake is an energy-dependent process. Additionally, based on the results from the inhibitors, cellular uptake occurred via microtubule-dependent transport and clathrin-mediated endocytosis, although additional studies will need to be done to gain further insight into the uptake mechanism.This research makes headway in the area of drug delivery via liposomes modified with stimuli-responsive polymers. The polymers reported here respond to temperatures that are higher than body temperature but still within physiological range. They likely dehydrate at LCST, leading to good cellular uptake and controlled drug release. (Phys.org)—Drug delivery is tricky because the therapeutic compound needs to be non-toxic and deliver the correct dosage at the correct time. Some therapeutics are chemically unstable and others do not have the correct solubility profile for cellular uptake. One way that researchers have overcome some of these drawbacks is using stimuli-responsive polymers. In a research paper in ACS Omega, Jian Wang, Eri Ayano, Yoshie Maitani, and Hideko Kanazawa of Keio University in Japan report the synthesis of the temperature-responsive polymer poly(N-isopropylacrylamide)-co-N,N’-dimethylaminopropylacrylamide (P(NIPAAm-co-DMAPAAm)) and analyzed liposomes modified with this polymer. They found that their polymer undergoes dehydration at around 40oC and that temperature-responsive polymer-modified liposomes had faster cellular uptake and release compared to nonmodified liposomes.Researchers have been interested in finding ways to modify liposomes, hollow spheres comprised of phospholipid bilayers, so that they can be a more effective drug delivery system. One way is to modify the surface of liposomes with polymers that respond to certain environmental stimuli, such as temperature.A key factor in liposomes modified with temperature-dependent polymers is the temperature at which its solubility profile changes, known as the lower critical solution temperature (LCST). Below this temperature, the polymers are soluble in an aqueous solution, while above this temperature they become hydrophobic. This causes the polymer to become dehydrated and to aggregate. This behavior guides the release of a drug within a polymer-modified liposome.In this study Wang et al. synthesized the temperature-responsive polymer poly(N-isopropylacrylamide)-co-N,N-dimethylaminopropylacrylamide (P(NIPAAm-co-DMAPAAm)). NIPAAm is temperature responsive and DMAPAAm is hydrophilic. They then evaluated the LCST of this polymer by looking at the transition of PNIPAAm from a coil configuration to a globular shape after it is dehydrated using differential scanning calorimetry and transmittance curves. They found that the copolymer’s LCST was about 40oC.They then tested this polymer as a modification to the surface of a liposome, DOTAP/DOPE, and compared this to PEGylated liposomes. After optimizing for stability, they studied colloidal stability by looking at particle size in a suspension. They found that as temperature increased, the particle size remained constant until about 39oC. Above 40oC, the particle size increased started forming aggregates.last_img read more

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Large ancient flightless birds from Australia Europe and North America found to

first_imgAn artist’s rendition of a Haast’s eagle attacking moa. Credit: John Megahan – Ancient DNA Tells Story of Giant Eagle Evolution. PLoS Biol 3(1): e20. doi:10.1371/journal.pbio.0030020.g001 (Phys.org)—A small team of researchers from Flinders University, Centro de Investigaciones en Ciencias de la Tierra and the South Australian Museum has found evidence that suggests large flightless birds that once lived in Australia, Europe and North America were related to one another. In their paper published in Royal Society Open Science, the group describes using a variety of techniques to study the ancient birds and offers a theory on how birds that were unable to fly were related to other birds that could not fly such a great distance. Explore further Dromornithidae were a type of very large flightless bird (much bigger than today’s ostriches) that lived in what is now Australia approximately 50,000 years ago. Gastornithidae were similar to birds that once lived in parts of North America and Europe. The researchers with this new effort have found that the two bird types were related and that both were also related to modern fowl, rather than ratite, which include ostriches, emu and the extinct moa. The birds and their modern cousins all belong to the group known as galloanseres, which includes ducks, geese and chickens. Fossil remains of Dromornithidae suggest they did not resemble modern fowl—they could not fly, stood taller than modern humans and weighed on average 650 kilograms.Prior research has shown that ancestors of Dromornithidae first appeared approximately 50 million years ago. The researchers with this new effort used both heuristic guides and tip-dated Bayesian approaches in their analysis of the birds and their possible relatives to link them together. They noted also that both bird types evolved to gigantism while existing on a purely vegetarian diet, as do modern fowl. They suggest that they evolved from a common bird that was able to fly, which explains how they could have evolved so far apart. This theory is similar to that proposed for ratites to explain their distant evolutionary history.The researchers also concluded that vegavis, an extinct bird that once lived in what is now Antarctica was not related to modern fowl and neither was Brontornis, an extinct flightless bird that lived in what is now South America. 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: Trevor H. Worthy et al. The evolution of giant flightless birds and novel phylogenetic relationships for extinct fowl (Aves, Galloanseres), Royal Society Open Science (2017). DOI: 10.1098/rsos.170975AbstractThe extinct dromornithids, gastornithids and phorusrhacids are among the most spectacular birds to have ever lived, with some giants exceeding 500 kg. The affinities and evolution of these and other related extinct birds remain contentious, with previous phylogenetic analyses being affected by widespread convergence and limited taxon sampling. We address these problems using both parsimony and tip-dated Bayesian approaches on an expansive taxon set that includes all key extinct flightless and flighted (e.g. Vegavis and lithornithids) forms, an extensive array of extant fowl (Galloanseres), representative Neoaves and palaeognaths. The Paleogene volant Lithornithidae are recovered as stem palaeognaths in the Bayesian analyses. The Galloanseres comprise four clades inferred to have diverged in the Late Cretaceous on Gondwana. In addition to Anseriformes and Galliformes, we recognize a robust new clade (Gastornithiformes) for the giant flightless Dromornithidae (Australia) and Gastornithidae (Eurasia, North America). This clade exhibits parallels to ratite palaeognaths in that flight presumably was lost and giant size attained multiple times. A fourth clade is represented by the Cretaceous Vegavis (Antarctica), which was strongly excluded from Anseriformes; thus, a crucial molecular calibration point needs to be reconsidered. The presbyornithids Wilaru (Australia) and Presbyornis (Northern Hemisphere) are robustly found to be the sister group to Anatoidea (Anseranatidae + Anatidae), a relatively more basal position than hitherto recognized. South America’s largest bird, Brontornis, is not a galloansere, but a member of Neoaves related to Cariamiformes; therefore, giant Galloanseres remain unknown from this continent. Trait analyses showed that while gigantism and flightlessness evolved repeatedly in groups, diet is constrained by phylogeny: all giant Galloanseres and palaeognaths are herbivores or mainly herbivorous, and giant neoavians are zoophagous or omnivorous.center_img Journal information: Royal Society Open Science Citation: Large ancient flightless birds from Australia, Europe and North America found to be related (2017, October 11) retrieved 18 August 2019 from https://phys.org/news/2017-10-large-ancient-flightless-birds-australia.html © 2017 Phys.org Fossils from ancient extinct giant flightless goose suggests it was a fighterlast_img read more

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Optical forceinduced selfguiding light in human red blood cell suspensions

first_imgAnimation of red blood cells (RBCs) moving inward and forward due to the action of optical forces, forming an effective waveguide of light. Credit: Light: Science & Applications, doi: 10.1038/s41377-019-0142-1 New photonic tools for medical imaging can be used to understand the nonlinear behavior of laser light in human blood for theranostic applications. When light enters biological fluids it is quickly scattered, however, some cell suspensions can induce nonlinear responses in laser beams to self-focus and enhance the penetration of light for biomedical applications as a quantifiable marker of disease. In a recent study now published in Light: Science and Applications, Rekha Gautam and her colleagues at the San Francisco State University and an international team of co-workers showed that a laser beam shining through red blood cell suspensions could become “self-trapped.” The process reduced light scattering to retain the power of the beam of laser light within the biological samples. The observed nonlinearity depended on osmotic conditions and the age of the samples. The scientists propose using the technique to diagnose sickle cell anemia or malaria; diseases which impact the size and shape of blood cells. Osmotic conditions play an important role in the properties of human red blood cells (RBCs) crucial during disease analysis. Numerous efforts in the past decade have focused on the study of the biomechanical properties of RBCs suspended in varying osmotic solutions. In the present work, Gautam et al. determined the self-trapping and scattering-resistant nonlinear propagation of a laser beam through three different osmotic solutions/conditions. The results showed that the strength of the optical nonlinearity increased with osmotic pressure on the cells. Interestingly, in aged blood samples with lysed cells the nonlinear behavior was notably different due to the presence of free hemoglobin. To explain the experimental observations, Gautam et al. used a theoretical model with an optical force-mediated nonlocal nonlinearity. The present work on light self-guiding through scattered soft biological matter can introduce new photonic tools for noninvasive biomedical imaging and medical diagnosis. The scientists obtained blood samples from anonymous donors for the experiments. In the first set of experiments, they used a linearly polarized continuous wave (CW) laser beam with a wavelength of 532 nm. They focused the light into a 3 cm long glass cuvette filled with RBC suspensions in diverse osmotic conditions, as previously described. They monitored the linear and nonlinear outputs from the sample using a CCD camera and power detector, and measured the beam diameters using the Beamview program. The beam first diffracted normally at a low power of 10 mW and experienced strong scattering thereafter due to random distribution of non-spherically shaped RBCs. Gautam et al. then measured normalized laser transmission (output/input power) as a function of the input beam power. In hypotonic solutions, they noted the RBCs were in a “swollen” state where the effective refractive index of the cells decreased as the water-to-Hb ratio increased. In contrast, in the hypertonic solution, the scientists observed that RBCs shrunk, and their effective index increased due to reduced water-to-Hb ratio. In a third isotonic solution, the cells exhibited a “normal” state, in which the RBCs showed intermediate behavior. When the experiments were performed using the same blood samples two weeks later, the scientists observed notably different outcomes in which the nonlinear focus dramatically enhanced for the hypertonic solution. New shapes of laser beam ‘sneak’ through opaque media More information: Rekha Gautam et al. Optical force-induced nonlinearity and self-guiding of light in human red blood cell suspensions, Light: Science & Applications (2019). DOI: 10.1038/s41377-019-0142-1 I. M. Vellekoop et al. Exploiting disorder for perfect focusing, Nature Photonics (2010). DOI: 10.1038/nphoton.2010.3 Roarke Horstmeyer et al. Guidestar-assisted wavefront-shaping methods for focusing light into biological tissue, Nature Photonics (2015). DOI: 10.1038/nphoton.2015.140Roadmap on structured light. Journal of Optics. iopscience.iop.org/article/10. … 978/19/1/013001/meta UPPER PANEL: Normalized transmission and output beam size as a function of input power. a Measurement of the normalized transmission and b output beam size change in fresh RBC suspensions of different buffer solutions. The cyan (triangle) curve depicts the results obtained from the PBS background solution without RBCs as a reference, which indicates no appreciable self-action of the beam in the buffer solution itself. The blue (circle), red (square), and green (diamond) curves show the data obtained from RBC suspensions in hypertonic, isotonic, and hypotonic solutions, respectively, where the error ranges in (b) are indicated by the shaded regions. c Corresponding results from the same blood sample but after the RBCs have been stored in a refrigerator for two weeks, where the nonlinear focusing is dramatically enhanced in the hypotonic solutions. LOWER: Optical gradient forces on RBCs under different osmotic conditions examined by optical tweezers. a–c Snapshots of RBC movement towards a 960-nm laser beam (position marked by a dashed green circle) in isotonic, hypotonic, and hypertonic solutions, respectively, as observed under a microscope. The red arrows illustrate the directional cell movement. d–f Power spectrum analyses showing the trap stiffness κx of a single RBC from the three suspensions in accordance with (a–c), where the vertical dashed lines mark the corner frequency fc. The inset in (f) illustrates a single RBC that moves into the trap under the action of the gradient force. Credit: Light: Science & Applications, doi: 10.1038/s41377-019-0142-1. Explore further Self-trapping light through human RBC suspensions under different osmotic conditions. a–c Illustrations of the beam dynamics in (a) isotonic, (b) hypotonic, and (c) hypertonic suspensions. d Side-view image of a self-trapped beam. e–g Observed output intensity patterns at a low power, which show the linear diffraction and strong scattering of the laser beam. i–k Corresponding patterns at a high power, which show the beam localization due to nonlinear self-trapping. h, l 3D plots of the intensity patterns corresponding to (g, k), respectively. Credit: Light: Science & Applications, doi: 10.1038/s41377-019-0142-1. , Light: Science & Applications Nonlinear optical response of lysed RBCs (free hemoglobin) in water. a Output beam size as a function of input power through the Hb solutions for four different concentrations. The RBC concentrations for the four curves (Hb1-Hb4) are 2.4, 5.1, 8.6, and 15.0 million cells per mL. Nonlinear self-focusing of the beam occurs at ~100 mW for high concentrations of Hb, but it subsequently expands into thermal defocusing rings at high powers. b–e Typical output transverse intensity patterns taken for the self-trapped beam (b, d) and thermally expanded beam (c, e) for low (d, e) and high (b, c) concentrations. Credit: Light: Science & Applications, doi: 10.1038/s41377-019-0142-1center_img In this way, Gautam et al. studied nonlinear beam propagation in human RBCs suspended in three diverse buffer solutions. They found that RBCs exhibited a strong self-focusing nonlinearity that could be chemically controlled based on the buffer solution. They therefore propose tuning the optical nonlinearity via osmosis and increased osmotic pressure, outside the cells in fresh blood samples. When the samples aged, free hemoglobin from the lysed RBCs played an active role in the observed optical nonlinearity and enhanced the nonlinear response in hypotonic conditions. Using direct video microscopy and optical tweezer measurements, the scientists showed that the beam trapping force was greatest for RBCs in the hypertonic conditions and weakest for hypotonic solutions. The scientists introduced a theoretical model to validate the observed experimental effects. The work will introduce a new perspective in the development of diagnostic tools as the results are very promising towards the development of laser treatment therapies for blood-related diseases. In a second set of experiments, the scientists used a home-built optical tweezer system to measure the optical gradient force on RBCs. Gautam et al. collected the forward-scattering light from the trapped cells with a condenser lens and subsequently focused onto a position sensitive detector (PSD). They calculated the stiffness and gradient force in the three separate solutions. To simplify the measurements, Gautam et al. treated hypotonic and hypertonic RBCs as disk shaped objects. They used a CCD camera to record cell movements from the three different solutions along with a microscope with two objectives, where the setup was driven using a 960 nm laser beam. The results illustrated the movement of cells against Brownian motion under the action of optical forces based on the conditions of the cell (shape, size) and their beam trapping capacity. Gautam et al. estimated the trapping force using the Langevin equation and informed that the force followed a trend of hypertonic > isotonic > hypotonic conditions.The scientists then developed a model to simulate nonlinear beam propagation in biological soft matter in order to understand the physics of optical force-mediated nonlinearity. They modelled time evolution of the particle concentration distribution using a diffusion-advection equation and considered the presence of a forward-scattering force to push the particles along the direction of beam propagation, alongside the optical gradient force. Gautam et al. calculated the change in beam size for the different gradient and scattering force parameters to simulate the nonlinear self-focusing effects under different buffer conditions. They recorded the changing size, volume and refractive indices of RBCs under diverse osmotic conditions that were accountable for the varying magnitude of optical forces that modified the optical nonlinearity. The simulated results were qualitatively consistent with the experimental observations. Pathophysiological conditions such as sickle cell anemia, malaria and sepsis are often closely related to the physical properties of RBCs, their shape and size. The fundamental features of varying refractive indices and cell shapes allow RBCs to react to changes in different osmotic environments making them ideal candidates to study scattering light. In the present work, Gautam et al. showed nonlinear self-trapping of light across a centimeter distance of propagation by scattering RBC suspensions. When they increased the power of the laser beam, they showed the beam dramatically self-focus within all three osmotic conditions – much like optical spatial solitons (nonlinear self-trapped wave packets). The optical forces that change with cell density and morphology can provide noninvasive tools to sort diverse cells, according to a specific stage of a given disease. © 2019 Science X Network Journal information: Nature Photonics Human RBCs are disc-shaped malleable cells that possess a spatially uniform refractive index as they lack nuclei unlike most organelles, and show distinctive deformability for passage through veins and microcapillaries. The shape change can be prompted by modifying the osmolarity of the surrounding liquid buffer to use RBCs as tunable optofluidic microlenses. The optical properties of RBCs are important for in vitro and in vivo disease diagnostics in which the refractive index of the RBC is determined by hemoglobin (Hb)—the largest part of the erythrocyte dry content by weight. As a result, if the cell volume decreased due to varying osmotic conditions, the refractive index increased. Simulations of the optical force-induced nonlinear beam dynamics in RBC-like suspensions. a–c Beam size (FWHM) change as a function of the gradient and scattering forces obtained via numerical simulations using a 350-mW input power and neglecting random scattering effects, where one observes the change in beam size when either the gradient or the scattering force is “turned off”. d, f Side-view of the beam propagation and e, g corresponding output transverse intensity patterns after propagating through an RBC-like random scattering medium at low (d, e) and high (f, g) beam power. The beam side-views and output intensity patterns are normalized with respect to their respective maximal input powers. Credit: Light: Science & Applications, doi: 10.1038/s41377-019-0142-1. Citation: Optical force-induced self-guiding light in human red blood cell suspensions (2019, March 21) retrieved 18 August 2019 from https://phys.org/news/2019-03-optical-force-induced-self-guiding-human-red.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.last_img read more

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Astronomers take a closer look at a nearby dwarf active galactic nucleus

first_imgAn international team of astronomers has conducted optical and spectroscopic observations of the dwarf galaxy NGC 4395 that contains an active galactic nucleus (AGN). The observations, described in a paper published March 19 on arXiv.org, allowed the researchers to take a closer look at this dwarf AGN, what could provide essential insights into the nature of this object. Left panel: large-scale image of NGC 4395 at R-band (Cook et al 2014). Right panels: optical (top) and K-band (bottom) continuum images obtained from the GMOS and NIFS data cubes, respectively. Credit: Brum et al., 2019. Astronomers study star formation and gas flows in the galaxy NGC 1365 Explore further AGNs are compact regions at the center of galaxies, more luminous than surrounding galaxy light. They are very energetic due either to the presence of a black hole or star formation activity at the core of the galaxy.AGNs in local dwarf galaxies offer an excellent opportunity to study relatively small supermassive black holes (SMBHs). By conducting detailed analysis of the gas kinematics ionization structure and gas morphology in such dwarfs, astronomers could gather crucial information about evolution of small SMBHs.Located some 14.3 million light years away, NGC 4395 is an example of a nearby dwarf galaxy known to harbor an AGN. It is perceived as a great candidate to investigate the nature of a dwarf AGN, as its proximity allows telescopes to take a close look at its nucleus.That is why a group of astronomers led by Carine Brum of Federal University of Santa Maria in Brazil decided to perform optical and near-infrared integral field spectroscopic observations of the inner region of NGC 4395. For this purpose, they employed the Gemini Multi-Object Spectrograph (GMOS) and the Gemini Near-infrared Integral Field Spectrograph (NIFS), both mounted on the Gemini North Telescope in Hawaii.The observational campaign allowed the researchers to estimate the properties of ionized and molecular gas in NGC 4395. In particular, optical and near-infrared emission-line flux distributions uncovered an elongated structure at about 78 light years west of the nucleus.”The line emission peaks at the nucleus but is also extended in a blob at 1.’2 (24 pc) west of the nucleus,” the astronomers wrote in the paper. Gas in this blob is blueshifted by approximately 30 km/s compared to the surrounding material. This, according to the researchers, suggests that the gas flowing toward the nucleus at a rate of about 0.00032 solar masses per year. However, the origin of the inflowing material is uncertain. The scientists assume that it may be an ongoing minor merger of a gas-rich small galaxy, or the accretion of a low-metallicity cosmic cloud.Furthermore, the authors of the paper estimated that the bolometric luminosity of the AGN in NGC 4395 is about 99 duodecillion erg/s, and the mass of the central black hole is approximately 250,000 solar masses. They also calculated that the mass within the radius of about 32.6 light years from the nucleus is around 770,000 solar masses, most likely due to the presence of a young nuclear stellar cluster in this region.All in all, the results of the study allowed the researchers to find out that NGC 4395 differs from typical Seyfert galaxies due to the lower mass inflow rate and due to the fact that gas inflow in the studied galaxy seems to be undergoing a minor merger or accretion event. Citation: Astronomers take a closer look at a nearby dwarf active galactic nucleus (2019, April 1) retrieved 18 August 2019 from https://phys.org/news/2019-04-astronomers-closer-nearby-dwarf-galactic.html More information: Carine Brum et al. A close look at the dwarf AGN of NGC 4395: optical and near-IR integral field spectroscopy. arXiv:1903.08083 [astro-ph.GA]. arxiv.org/abs/1903.08083 © 2019 Science X Network This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.last_img read more

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An eye on the neighbour

first_imgWhen neighbours turn friends and display their artworks, it is a sight to watch out for. Jagath Weerasinghe, Anura Krishantha and Pala Pothupitiye are three artists from Sri Lanka who unveiled through their work narratives of a community redefined by transgressions and traumas. Together, the three artists depict diverse narratives of resistance developed in a society and a country that has for last 30 years witnessed multiple crises, the most visible of them being a highly destructive civil war that ended in 2009. Also Read – ‘Playing Jojo was emotionally exhausting’Notions of nationhood, citizenry and humanity are problematised in these narratives, painted, drawn and constructed to be read without compromising either the meanings or the aesthetics.Among the three artists, Jagath Weerasinghe is the seniormost who successfully dislodged the milieu from its excessive affinity with an Oriental sensibility. In his present works, Weerasinghe presents a series of works titled ‘Who Are You Soldier’, a re-formulated theme from his 1996 series with the same title. Also Read – Leslie doing new comedy special with NetflixPala Pothupitiye represents the second generation of artists that continue the legacy of the 90s art. Pothupitiye’s current works executed on maps cast a profound gaze upon the land and its people as victims of geopolitical agendas of states and dissenting groups. His attention on the politics of cartography and the emotions that overwhelm communities, nations and individuals on the basis of mythical and historical claims for ownership over land that fuel wars, domination and victimisation has produced a significant array of layered artworks in the form of maps. Anura Krishantha represents the most recent generation of artists whose art-making playfully absorbs the youthful preoccupations of urbanity and its globalised visuals and consumerist aspects of life, it discontents are presented as a fantasy imbued with power, illusion and danger. Krishantha, who has been working with the visual motif of chairs for over five years, predominantly bases his aesthetics on a mixture of pop and kitsch.Autobiographical in many senses and cathartic in other, the Sri Lankan artistes traces the transformations through a process of placing themselves in the center of the work. They are part of the anguished society.last_img read more

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