Lightemitting transistor uses light to transfer an electrical signal

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. At left, the drawing of the LET describes the scientists’ observation, shown in the electroluminescence intensity map at right. The infrared light emitted from the LET reaches the detector, meaning that an electrical signal can be transferred to the detector by light. Credit: Shin-ichi Saito, et al. In one of the early discoveries of the current “silicon electrophotonics era,” scientists from Hitachi, Ltd. in Tokyo have built a light-emitting transistor (LET) that transfers, detects and controls an electrical signal all on a single nanometer-sized chip. Using a silicon-on-insulator (SOI) substrate, the group could optically connect the LET to a detector, resulting in a tiny chip that may integrate a wide range of microelectronics and photonics nano devices. Citation: Light-emitting transistor uses light to transfer an electrical signal (2006, November 1) retrieved 18 August 2019 from https://phys.org/news/2006-11-light-emitting-transistor-electrical.html “With LETs, we could develop an optical interconnection beyond the present copper interconnection,” Shin-Ichi Saito, co-author of the study in Applied Physics Letters, told PhysOrg.com. “If LETs are really integrated on silicon chips, we might reduce power dissipation (since light does not have electrical resistance), as well as RC [Resistive Capacitive] delay: in electrical circuits, the interlayer coupling capacitance reduces the speed of electrical signals, while such a delay might be reduced in optical interconnections.”Similar to a standard field-effect transistor, Saito et al.’s LET takes advantage of some interesting properties of 2D electron and electron hole systems, called “quantum confinement effects.” By reducing the thickness of the crystal silicon down to the nanometer scale, the scientists fabricated an ultra-thin single crystal silicon film, directly connected to the thick silicon electrodes. In such a design, n-type (electrons) and p-type (holes) semiconductors lie next to each other separated by a narrow junction. As the electrons and holes efficiently eliminate each other in a process called “recombination,” photons are emitted; thus electrical signals can be converted to optical signals. This close-up drawing of the LET shows the ultrathin silicon junction acting as a quantum well. After recombination, the electric carriers are confined into a standing wave, greatly increasing the electroluminescence efficiency. Credit: Shin-ichi Saito, et al.center_img Explore further “The key idea is that the 2D conduction band electrons behave just like electrons in direct band-gap semiconductors,” said Saito. “In bulk Si, the conduction band electrons move very fast with a large momentum. However, in the ultra-thin Si, the electrons cannot move perpendicular to the substrate with such a large momentum, simply because that direction is restricted. Many people also consider that this quantum mechanical confinement plays some role for the enhanced luminescence in nano-scale silicon.”To optically interconnect this electrical signal from the LET to a detector–which were electrically isolated but on the same silicon chip–the group applied a forward voltage bias to the LET. The scientists observed the light from the LET to reach the photodetector, and measured the “photocurrent” in the detector to increase with a voltage increase, and decrease when the voltage was turned off (detector limitations caused some current to continue flowing).Although the Hitachi group points out limitations to the present experimental set-up that need to be fixed before applying the principle to marketable technology, they suggest solutions for these problems: for example, reducing the response time of the detector and using waveguides to contain the light on the chip. However, the achievement shows how, using curious phenomena of quantum mechanics, photons, just like electrons, can be manipulated on a silicon chip. Quite possibly, future integrated circuits may use lights instead of currents to enhance performance while reducing power dissipation.“We have just confirmed the basic operation principle for this LET,” said Saito. “The hope is that this is just the beginning of more research; we have lots to do.”Citation: Saito, Shin-ichi, Hisamoto, Digh, Shimizu, Haruka, Hamamura, Hirotaka, Tsuchiya, Ryuta, Matsui, Yuichi, Mine, Toshiyuki, Arai, Tadashi, Sugii, Nobuyuki, Torii, Kazuyoshi, Kimura, Shin’ichiro, and Onai, Takahiro. “Silicon light-emitting transistor for on-chip optical interconnection.” Applied Physics Letters 89, 163504 (2006).By Lisa Zyga, Copyright 2006 PhysOrg.com “With the lateral carrier injections that we used, we can efficiently inject both electrons and holes directly in the quantum confined silicon,” said Saito. “Usually, nano-scale silicon structures are passivated by SiO2, which has huge potential barriers for carriers. Such a limitation does not exist in our device.”In this set-up, the p-n junction consists of a light-emitting diode (LED) made of ultrathin silicon. At a 9nm thickness, the silicon acts as a quantum well, confining the electric carriers to two dimensions, which forms a standing wave consisting of an electron. This confinement serves an especially useful purpose for integrating optical components into silicon circuits, as it enhances the electroluminescence efficiency of the junction. While other LETs–from carbon nanotubes and organic models to semiconductor and nanocrystal devices–have been demonstrated, Saito et al.’s is the first in which recombination occurs along the silicon junction and takes advantage of quantum confinement’s electroluminescence. Decline of entrepreneurship blamed for Japan woeslast_img read more

ANSOM Microscope Achieves Sub 10nm Resolution

first_imgThe idea behind near-field microscopy is to offer a technique by which extremely small structures (at the nanometer level) can be measured and manipulated. However, 20 nanometers has been the best resolution accomplished. Until now. “We were able to resolve molecules when they were only 15 nanometers apart,” Stephen Quake tells PhysOrg.com. Quake and his group at the California Institute of Technology in Pasadena have created a fluorescence near-field microscope that can distinguish single molecules. The results are published in an article titled “Fluorescence Near-Field Microscopy of DNA at Sub-10 nm Resolution” in Physical Review Letters.“Conventional light microscopes use lenses, and so their imaging properties are limited by the properties of these lenses,” Quake explains. “The main limitation is the wavelength of light. But for the last 20 years, near-field microscopy has provided ways to look at objects without being limited by the wavelength of light. For the most part, that has meant two to four times better than the diffraction limit.”Along with Ziyang Ma, Jordan Gerton and Lawrence Wade, Quake designed and built a microscope that worked with fluorescence near-field microscopy (ANSOM — apertureless near-field scanning optical microscope). In their Letter, the authors describe how fluorescence fluctuations and the limited number of photons available before the molecule is destroyed has created problems in imaging fluorescent molecules. However, thanks to a new phase filtering method, Quake’s group demonstrates how this new kind of microscope can be useful for any number of applications, but especially for biomolecules like DNA.In fact, Quake and his collaborators used DNA to test their microscope. “One of the most stringent tests for a microscope is to put two items together and see how close you can get them and still tell them apart.” He points out that in near-field microscopy this test is not often done. “But we wanted rigorous evidence that the resolution is as high as we claim.” Quake feels that this new kind of microscope could be valuable if commercially produced. “If a commercial manufacturer picked these up and got them into labs, it could greatly advance the frontiers of both biology and nanoscience. They could be used as tools to learn more about the function of macromolecules.”According to the Letter, the microscope’s phase filtering method can also be applied to such things a nanoantennas and supersharp carbon nanotube probes. The resolution of both of these instruments could be improved with the group’s process. Additionally, the microscope could be altered to work on a level that approaches the resolution of an electron microscope.Quake predicts that there will be more to this new fluorescence near-field microscope. “So far, we only have results from molecules in air,” he says. “The next step is to make it work in water, and we have been modifying the instrument for that purpose.” The advantages to having such a microscope are obvious. Right now, with an electron microscope (which has sharper resolution), biomolecules cannot be observed directly in their natural conditions. But this new microscope, if properly adapted, could change that. “We could image live cells, for example. Look at things in motion. Observe proteins that are on the cell surface membranes. This microscope offers a powerful new tool for imaging single molecules and nanostructures.”By Miranda Marquit, Copyright 2006 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. Citation: ANSOM Microscope Achieves Sub 10nm Resolution (2007, January 18) retrieved 18 August 2019 from https://phys.org/news/2007-01-ansom-microscope-10nm-resolution.htmlcenter_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.last_img read more

Kind and Gentle Molecular Machine Could Operate at NearEquilibrium

first_img But R. Dean Astumian, a Physics Professor at the University of Maine, has recently proposed a concept in which molecular machines can operate arbitrarily close to chemical equilibrium at every instant of the cycle, and still perform work at the rate of several micrometers per second against piconewton loads. The study, “Adiabatic operation of a molecular machine,” is published in a recent issue of the Proceedings of the National Academy of Sciences.“The main significance is conceptual – it changes the way we think about molecular motors,” Astumian told PhysOrg.com. “Much emphasis has been put on the ‘non-equilibrium’ aspects of the system, but in fact this is not really important. The motion of the rings here arises due to a combination of topology that break spatial symmetry, and the slow external modulation that breaks time symmetry. It is also important to recognize that, in the molecular world, we can truly have motors that operate with nearly 100% efficiency.”Astumian’s example of such a molecular machine is a three-ring “catenane” structure that serves as a rotating motor. The catenane, about 3 nanometers in diameter, consists of one large ring with two smaller rings linked to the large ring, like rings on a keychain. Three binding stations on the large ring provide locations where the two small rings can bind, depending on the interaction energy between ring and station. Astumian gets the small rings to move clockwise from station to station around the large ring, a movement that results in mechanical cycling. Further, he achieves this movement without any heat gain or heat loss and without a change of entropy, but simply by thermal noise due to Brownian motion. This type of “adiabatic” system is arbitrarily close to equilibrium at every point of the cycle.The key to making the small rings move from station to station is by periodically modulating the interaction energy. The rings will bind to the station that requires the lowest interaction energy. This modulation must be done slowly enough not to generate heat, but at a sufficient rate to produce significant work. Slowly modulating the energy of a single molecule is challenging, and Astumian explains that it is nearly impossible to do with chemical systems. However, the net interaction energy for many molecules can be slowly modulated by very slow titrations of pH and redox potential. For example, a condition that is strongly acidic and strongly reducing corresponds with high interaction energy at station 2. Therefore, the two rings will bind at stations 1 and 3. Explore further Molecular machines – tiny machines made of molecules that do mechanical work – are usually thought to operate in a state of non-equilibrium. This makes sense, considering that macro-sized machines operate at non-equilibrium, requiring an additional force to move. On the other hand, equilibrium implies that forces cancel each other out, resulting in an unchanging system, often at rest. Then, by titrating with oxidant to reach a strongly oxidizing and strongly basic condition, the energy at station 1 is highest. So the rings now occupy stations 2 and 3. Astumian explains that the rings could switch to this state by either the ring at station 1 moving clockwise to bind at station 2, or the ring at station 3 moving counter-clockwise to bind at station 2. However, after more modulations, the majority (about 75%) of the movements will be clockwise due to the changing energy levels at different stations. By figuring this probability, Astumian concludes that, every time the small rings move around the large ring, the system will complete one-half of a mechanical rotation.He also mentions that there might be more creative architectures where counter-clockwise motions don’t undo the clockwise motions. He likens this mechanism to a ratcheting screwdriver used to drive a screw. When the ratchet turns counter-clockwise to reset itself, it releases so that it doesn’t undo the forward turn of the screw. Although a molecular machine would use thermal noise instead of external torque, the concept is similar. In the molecular machine, one of the small rings could be fixed to prevent counterclockwise motion.“I would say that the biggest challenge is to arrange the molecules on a surface so that the movement can be used to do work on the outside world,” Astumian said. He added that the chemical structures have already been synthesized by David Leigh at the University of Edinburgh, as the next step in the development of the machines.Astumian also explains that operating this system requires a fine balance between modulating slowly enough so that the system is in chemical and mechanical equilibrium at every instant, but rapidly enough to perform substantial work. While biomolecular motors are often described in “violent” terms, he hopes that this “kindler, gentler” description may be more appropriate for designing more efficient molecular machines.“I plan to extend the theory to explain the mechanism of biological motors,” Astumian said. “While they doubtless do not operate exactly by the mechanism described for the three-ring catenane, I think the flavor of how they operate is much better characterized by this near-equilibrium description than by various biological models involving cars, judo throws, and steam engines.”More information: Astumian, R. Dean. “Adiabatic operation of a molecular machine.” PNAS, December 11, 2007, vol. 104, no. 50, 19715-19718.Copyright 2007 PhysOrg.com. All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com. Illustration of the possible transitions for a catenane structure that consists of one large ring with three stations for two small rings. The two small rings move around the large ring to bind at a station. Each binding state is favored by a different energetic condition, as indicated. ©2007 PNAS. Image credit: R. Dean Astumian.center_img Citation: ‘Kind and Gentle’ Molecular Machine Could Operate at Near-Equilibrium (2007, December 20) retrieved 18 August 2019 from https://phys.org/news/2007-12-kind-gentle-molecular-machine-near-equilibrium.html SLAC makes ‘electron camera,’ a world-class tool for ultrafast science, available to scientists worldwide 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

Evidence suggests Neanderthals took to boats before modern humans

first_img Citation: Evidence suggests Neanderthals took to boats before modern humans (2012, March 1) retrieved 18 August 2019 from https://phys.org/news/2012-03-evidence-neanderthals-boats-modern-humans.html © 2011 PhysOrg.com Russian site may show late Neanderthal refuge The Reconstruction of the Funeral of Homo neanderthalensis. Captured in the Hannover Zoo. (Via Wikipedia) Explore further The stone “mousterian” tools are unique to Neanderthals and have been found on the islands of Zakynthos, Lefkada and Kefalonia, which range from five to twelve kilometers from mainland Greece. Some, such as Paul Pettitt from the University of Sheffield, suggest they could have swum that far. But that doesn’t explain how similar tools found on the island of Crete got there. That would have meant swimming forty kilometers, which seems extremely unlikely, especially since such swimmers wouldn’t have known beforehand that Crete was there to find.Ferentinos et al suggest the evidence shows that Neanderthals not only figured out how to build boats and sail but did so quite extensively well before modern humans ever got the idea. They say because the tools found on the islands are believed to date back 100,000 years (and the islands have been shown to have been islands back then as well) Neanderthal people were sailing around that long ago. Thus far, evidence for modern humans sailing dates back to just 50,000 years when they made their way to Australia. If true, that would mean Neanderthal people were sailing around in the Mediterranean for fifty thousand years before modern people built their first boat.Others have suggested that hominids have been sailing for as long as a million years; stone tools found on the Indonesian island of Flores date back that far. It could be that both modern humans and Neanderthals were boating around for hundreds of thousands of years and we just don’t have any evidence of it because the boats back then would have been made of wood and evidence of their existence would have decayed to nothing long ago.center_img Journal information: Journal of Archaeological Science (PhysOrg.com) — Neanderthals, considered either a sub-species of modern humans or a separate species altogether, lived from approximately 300,000 years ago to somewhere near 24,000 years ago, when they inexplicably disappeared, leaving behind traces of their DNA in some Middle Eastern people and artifacts strewn all across the southern part of Europe and extending into western Asia. Some of those artifacts, stone tools that are uniquely associated with them, have been found on islands in the Mediterranean Sea, suggesting, according to a paper published in the Journal of Archaeological Science, by George Ferentinos and colleagues, that Neanderthals had figured out how to travel by boat. And if they did, it appears they did so before modern humans. More information: Early seafaring activity in the southern Ionian Islands, Mediterranean Sea, Journal of Archaeological Science, In Press, Corrected Proof. dx.doi.org/10.1016/j.jas.2012.01.032AbstractThis paper summarises the current development in the southern Ionian Islands (Kefallinia and Zakynthos) prehistory and places it within the context of seafaring. Archaeological data from the southern Ionian Islands show human habitation since Middle Palaeolithic going back to 110 ka BP yet bathymetry, sea-level changes and the Late Quaternary geology, show that Kefallinia and Zakynthos were insular at that time. Hence, human presence in these islands indicates inter island-mainland seafaring. Seafaring most likely started some time between 110 and 35 ka BP and the seafarers were the Neanderthals. Seafaring was encouraged by the coastal configuration, which offered the right conditions for developing seafaring skills according to the “voyaging nurseries” and “autocatalysis” concepts. 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

Ants follow Fermats principle of least time

first_img“We found that a general rule applies to a dynamic system that relies solely on communication (pheromones) and social cooperation,” Oettler told Phys.org. “This system depends on two features. One is routing information that decays over time and needs to be refreshed, thus making the system flexible. And second on behavioral flexibility by the worker ants that carry this information. A path can only be adjusted by worker ants that do not follow this path, but rather take alternative routes (that they advertise), which may be faster (or slower) than the already established path.”Oettler added that the speed with which information decays is crucial to this system, so the results here may be adapted to information routing problems.The researchers noted that Wasmannia worker ants also resemble humans in this way, since humans have also been found to follow Fermat’s principle when forced to cross surfaces with different qualities. One clear example is when a lifeguard has to find the fastest way to traverse both beach and water in order to reach a drowning swimmer. The researchers also noted that several other factors likely influence why ants choose the paths they do. For instance, the results here suggest that ants prefer to move along edges of borders (in real life, for example, ants are often seen walking along the edges of a sidewalk). Landmarks facilitate orientation, and for ants this could mean that lower amounts of pheromone are needed to mark trails when combined with the physical cues. This is one area that the researchers hope to study more in the future.”We have only shown the outcome of this process,” Oettler said. “In the future we want to study the dynamics of the trail pheromones, their active compounds and evaporation rates. We want to perform behavioral tests with synthetic compounds and detect perception thresholds of individual ants. We also want to study the early dynamics of trail formation over time.” Explore further A ‘refracted’ trail of Wasmannia auropunctata workers at the medium border between smooth (white) and rough (green) felt. The position of the food is on the rough felt. The density of workers on the rough felt is higher than on the smooth felt because travel speed is lower. In addition, it appears, although not very obvious, as if the ants on the rough felt ‘float’ on top of the felt hairs, indicating the difficulty of walking on this substrate. Credit: Simon Tragust. 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. (Phys.org) —Ants have long been known to choose the shortest of several routes to a food source, but what happens when the shortest route is not the fastest? This situation can occur, for example, when ants are forced to travel on two different surfaces, where they can walk faster on one surface than on the other. In a new study, scientists have found that ants behave the same way as light does when traveling through different media: both paths obey Fermat’s principle of least time, taking the fastest route rather than the most direct one. Besides revealing insight into ant communities, the findings could offer inspiration to researchers working on solving complex problems in robotics, logistics, and information technology. More information: Jan Oettler, et al. “Fermat’s Principle of Least Time Predicts Refraction of Ant Trails at Substrate Borders.” PLOS ONE. DOI:10.1371/journal.pone.0059739.g001 http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0059739 The researchers, Jan Oettler, et al., from institutions in Germany, France, and China, have published their paper on using Fermat’s principle of least time to predict ant trails in a recent issue of PLOS ONE. The scientists experimentally studied the behavior of the little fire ant, Wasmannia auropunctata, one of the world’s 100 most invasive species. They collected three colonies, each containing several thousand workers and multiple queens, from different sites in Israel. They put the ants in plastic boxes without food, and then connected each box to its own foraging arena where cockroaches were provided as food in the corner opposite from the entrance. The surface of each foraging arena was split in half, and each half was covered by a different material. The researchers experimented with combinations of three materials that differentially affected the ants’ average walking speed: rough polyester felt (1.73 mm/s), smooth polyester felt (2.97 mm/s), and polyethylene glass (4.89 mm/s). When ants forage, they deposit pheromones to build a trail, and favorable trails become reinforced with increased usage.Given the ants’ average walking speeds on different materials, along with information on the distances across the foraging arena and the angle defining the shortest path (the straight line) between the entrance and the food, the researchers predicted the angle at which the ants would cross from one surface to the other if they chose the fastest path. In accordance with Fermat’s principle of least time, this angle can be thought of as the angle of refraction, similar to how light refracts at a certain angle at the boundary of two media in which it travels at different speeds. Robot ants successfully mimic real colony behavior The researchers calculated the fastest path as predicted by Fermat’s principle of least time (dotted yellow line), which is not the direct path. In this example, the ants can walk faster on Surface 1 than on Surface 2. Credit: Jan Oettler, et al. Journal information: PLoS ONE Copyright 2013 Phys.org All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of Phys.org. The researchers found that the ants’ paths closely matched those predicted by Fermat’s principle of least time and did not follow the most direct route. In other words, the ants accounted for the different walking speeds on the different surfaces and traveled a longer distance on the surface where they could walk faster. Citation: Ants follow Fermat’s principle of least time (2013, April 1) retrieved 18 August 2019 from https://phys.org/news/2013-04-ants-fermat-principle.htmllast_img read more

Hybrid nanostructure with extreme light absorption looks promising for photovoltaics

first_img © 2013 Phys.org. All rights reserved. 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: Sander A. Mann and Erik C. Garnett. “Extreme Light Absorption in Thin Semiconductor Films Wrapped around Metal Nanowires.” Nano Letters. DOI: 10.1021/nl401179h The core-shell hybrid nanowire consists of a metal core wrapped with semiconductor thin films. Three different resonances excited at different wavelengths are shown. (b) The fraction of absorbed above-band gap photons in the silicon shell for a wide variety of configurations. Credit: Mann and Garnett. ©2013 American Chemical Society Now, somewhat counterintuitively, scientists have theoretically found that thin semiconductor films wrapped around metal nanowires have substantially better light absorption properties than solid semiconducting nanowires, despite the fact that they use less semiconducting material. At the same time, the metal core acts as a contact to efficiently extract charge carriers. By confronting the semiconductor thickness trade-off and offering exceptional performance, the nanostructures might become ideal building blocks for inexpensive photovoltaic and solar fuel applications.A paper on the new devices by Sander A. Mann and Erik C. Garnett at the Center for Nanophotonics at FOM Institute AMOLF in Amsterdam, The Netherlands, will be published in a future issue of Nano Letters.”The greatest significance to our work is that we provide a design for nanowire building blocks that incorporates both excellent light trapping properties and a local metal electrode contact (for current extraction),” Garnett told Phys.org. “Silver nanowire networks have already been used as high performance transparent electrodes and we expect that by coating them with thin semiconducting shells we will be able to make high-efficiency solar cells using cheap materials. It has now been observed in a number of papers that nanostructuring a material can increase light absorption even while using less semiconductor material. However, this paper takes the next step and starts thinking about how to design such structures with integrated electrical contacts.” One of the biggest advantages of the design is that it uses very thin semiconducting films while at the same time providing very good light absorption. As mentioned, thick semiconductor layers are needed for good light absorption, but high-quality semiconductor is very costly. This new core-shell geometry opens up a pathway to using cheap, abundant, and environmentally friendly semiconductors that previously were of too low quality for good charge extraction.In semiconductor objects smaller than the wavelength of light, as is the case with most nanowires for photovoltaic purposes, the optical properties are determined primarily by resonances. These resonances enhance absorption the most when they are critically coupled: the loss rates due to absorption in the semiconductor and due to radiative leakage (light escaping the nanowire before being absorbed) are equal. This is often the case near the band gap of the material, where absorption is weak, which leads to the highly counterintuitive result that absorption in the nanowire actually increases when the absorption coefficient decreases.As the scientists explain, in the core-shell geometry, extreme light absorption arises from increasing the number and strength of these resonances. Whereas in horizontal nanowires resonances are always spectrally separated (at different wavelengths), in the core-shell geometry they can overlap. Furthermore, horizontal solid seminconductor nanowires are very polarization-sensitive, but this is undesirable as light from the sun is unpolarized. The core-shell geometry gets rid of this polarization dependence by aligning resonances in both polarizations simultaneously.Overall, by demonstrating that excellent light absorption can be achieved in very thin semiconductor layers, this hybrid nanostructure offers an exciting new path toward realizing inexpensive solar technologies based on abundant and environmentally friendly semiconductors. The researchers plan to fabricate prototypes of the devices soon.”Our immediate plans are to make both single-nanowire and array solar cells based on these core-shell building blocks to verify our calculations experimentally,” Garnett said. Explore furthercenter_img Nanowire solar cells raise efficiency limit (Phys.org) —In photovoltaics, there is generally a trade-off in terms of semiconductor thickness, with thicker semiconductors offering better photon absorption and thinner ones offering higher charge carrier extraction efficiency. In recent years, scientists have begun investigating semiconductor nanowire solar cells, which tackle this tradeoff through morphology-dependent resonances that significantly enhance the absorption compared to a planar film. Journal information: Nano Letters Citation: Hybrid nanostructure with extreme light absorption looks promising for photovoltaics (2013, July 1) retrieved 18 August 2019 from https://phys.org/news/2013-07-hybrid-nanostructure-extreme-absorption-photovoltaics.htmllast_img read more

Study of stalagmites in caves in China reveals 640000 years of Asian

first_imgSanbao cave (red star) is on the northern slope of Mt. Shennongjia, Hubei, central China Credit: Hai Cheng © 2016 Phys.org The annual monsoon season in Asia is a major event, bringing rains that are used to grow crops for an enormous number of people. Because of its importance, scientists would like to know more about it, such as what might happen as the planet heats up. To learn more, the researchers looked for a way to look back at what has happened in the past, and to do that, they ventured to the mountains in central China and descended into Sanbao Cave—there stalagmites have been growing up from the cave floor for hundreds of thousands of years, carrying with them, a history of the factors that led to their growth.The stalagmites grow at different rates depending on how much rain falls and leaks through the mountain above and down into the cave—during heavy rains, such as occur during monsoon seasons, layers of calcium carbonate build up, holding information about the air and rainwater at a particular point in time, which scientists can analyze to gain a good measurement of climate conditions. They can also look for dissolved uranium, which can be used to date the layers of stalagmite buildup. Together, the two sources of information can be used to create a climate timetable for past monsoon seasons, going back as far as 640,000 years—the most detailed and accurate monsoon record to date. In so doing, the researchers were also able to show that changes in solar radiation over the Northern Hemisphere were due to the planet’s precession cycle (a shift that occurs periodically in the planet’s axis of rotation)—which wound up bringing an end to the past seven ice ages. Speleothems inside of Sanbao cave (about 1500 meters from cave entrance). Credit: Hai Cheng Journal information: Nature Explore further (Phys.org)—A team of researchers with members from China, the U.S., Austria and Singapore has used their analysis of stalagmites in a cave deep in central China to map over 640,000 years of monsoons in Asia. In their paper published in the journal Nature, the team describes their analysis of the cave formations, what they found and how they were able to use what they learned to better understand other world events over the same time period. Nele Meckler with University of Bergen in Norway provides a more in-depth description of the work done by the team in a News & Views article in the same journal issue. Menacing monsoons More information: Hai Cheng et al. The Asian monsoon over the past 640,000 years and ice age terminations, Nature (2016). DOI: 10.1038/nature18591AbstractOxygen isotope records from Chinese caves characterize changes in both the Asian monsoon and global climate. Here, using our new speleothem data, we extend the Chinese record to cover the full uranium/thorium dating range, that is, the past 640,000 years. The record’s length and temporal precision allow us to test the idea that insolation changes caused by the Earth’s precession drove the terminations of each of the last seven ice ages as well as the millennia-long intervals of reduced monsoon rainfall associated with each of the terminations. On the basis of our record’s timing, the terminations are separated by four or five precession cycles, supporting the idea that the ‘100,000-year’ ice age cycle is an average of discrete numbers of precession cycles. Furthermore, the suborbital component of monsoon rainfall variability exhibits power in both the precession and obliquity bands, and is nearly in anti-phase with summer boreal insolation. These observations indicate that insolation, in part, sets the pace of the occurrence of millennial-scale events, including those associated with terminations and ‘unfinished terminations’. Citation: Study of stalagmites in caves in China reveals 640,000 years of Asian monsoon history (2016, June 30) retrieved 18 August 2019 from https://phys.org/news/2016-06-stalagmites-caves-china-reveals-years.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

Researchers design and partially assemble a synthetic Escherichia coli genome

first_imgAn international team of researchers working in a lab at Harvard University has taken a bold step towards the development of a bacteria with a completely rewritten genome. They describe their work in a paper published in the journal Science and the reasons they believe the ultimate results will be safe for use in the real world. Science correspondent John Bohannon offers an In Depth piece on the work done by the team in the same issue and further discusses safety concerns tied to the new technology. More information: N. Ostrov et al. Design, synthesis, and testing toward a 57-codon genome, Science (2016). DOI: 10.1126/science.aaf3639 Citation: Researchers design and partially assemble a synthetic Escherichia coli genome (2016, August 19) retrieved 18 August 2019 from https://phys.org/news/2016-08-partially-synthetic-escherichia-coli-genome.html © 2016 Phys.org Journal information: Science Scientists would like to be able to modify the genomes of creatures because they believe such creatures could offer benefits to us humans that are not available naturally. One example would be changing the genome of a certain type of bacteria to make it immune to viral attacks—this would be important because we humans use bacteria in a variety of applications and viruses tend to cause problems in many of them.In this new effort, the researchers took a step into the future by eliminating redundant codons—triplets that represent four-letter DNA alphabet clusters—from the DNA of an E. coli bacterium, opening the door to the possibility of inserting new coding that would allow for the creation of new types of amino acids. To achieve this feat, they used machines to synthesize stretches of the genome (in its recoded form) and then inserted the chunks they had created into the genome of a living E. coli bacterium. The team managed to eliminate seven of the bacterium’s 64 natural codons in the chunks they inserted and were able to test approximately 63 percent of them. They report that doing so resulted in very few interruptions to natural functions, which suggests the technique may prove a viable means for creating an entirely new genome for a given creature. Perhaps more impressive is the possibility of creating new types of codons to replace the redundancies that were removed, which could, for example, endow bacteria or other creatures with new capabilities, such as producing amino acids that could fight off new types of viruses.The good news must be tempered with the bad of course as such research is likely to stir fear in people who wonder what havoc might ensue should such bacteria make their way into the real world. The team has added a fail-safe, of course, and others will no doubt be developed, but because we humans are prone to error, no such fail-safe could ever be deemed 100 percent safe.center_img Explore further Using CRISPR as a recording device Escherichia coli. Credit: Rocky Mountain Laboratories, NIAID, NIH 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

New particle formation found to occur in heavily polluted air

first_imgCredit: CC0 Public Domain More information: Lei Yao et al. Atmospheric new particle formation from sulfuric acid and amines in a Chinese megacity, Science (2018). DOI: 10.1126/science.aao4839AbstractAtmospheric new particle formation (NPF) is an important global phenomenon that is nevertheless sensitive to ambient conditions. According to both observation and theoretical arguments, NPF usually requires a relatively high sulfuric acid (H2SO4) concentration to promote the formation of new particles and a low preexisting aerosol loading to minimize the sink of new particles. We investigated NPF in Shanghai and were able to observe both precursor vapors (H2SO4) and initial clusters at a molecular level in a megacity. High NPF rates were observed to coincide with several familiar markers suggestive of H2SO4–dimethylamine (DMA)–water (H2O) nucleation, including sulfuric acid dimers and H2SO4-DMA clusters. In a cluster kinetics simulation, the observed concentration of sulfuric acid was high enough to explain the particle growth to ~3 nanometers under the very high condensation sink, whereas the subsequent higher growth rate beyond this size is believed to result from the added contribution of condensing organic species. These findings will help in understanding urban NPF and its air quality and climate effects, as well as in formulating policies to mitigate secondary particle formation in China. An international team of researchers has found that new particle formation (NPF) can occur in the atmosphere even in heavily polluted air. In their paper published in the journal Science, the group describes air quality testing they did in China over a period of years and what they found. 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. NPF occurs in the atmosphere when certain ingredients clump together spontaneously, causing the formation of new particles. Prior research has suggested that NPF only occurs in relatively pristine air, because particles in polluted air tend to scavenge precursors. In this new effort, the research team has found evidence indicating such conclusions are wrong—they have found evidence of NPF occurring in a heavily populated and polluted part of China.The researchers explain that understanding NPF is important because of the impact it has on global warming. They note that NPFs can lead to cloud formation of a type that traps heat. To learn more about them and air pollution in China in general, they set up air quality monitoring stations in Shanghai and studied data from them covering the years 2014 to 2017.In analyzing the chemistry of particles captured by the monitoring stations, the researchers found evidence of NPF precursor vapors and also large amounts of actual NPF clusters—this, despite the presence of large amounts of other particulates in the air. They suggest the NPF events came about due to sulfuric acid-dimethylamine-water nucleation which included sulfuric acid dimers.To better understand how such clusters might form, the researchers entered their real-world data into a model and ran simulations to mimic conditions in the air over Shanghai and other large cities in China. They found that concentrations of sulfuric acid were sufficient to explain particle formation and growth during times of high condensation. They also found evidence that suggested larger cluster growth was likely due to the presence of other condensing organic species.The researchers claim their study not only shows that NPF can occur in heavily polluted air, but that it is likely having a bigger impact on global warming than has been thought. They suggest climate change models will need to be changed to reflect what they have found.center_img Citation: New particle formation found to occur in heavily polluted air (2018, July 20) retrieved 18 August 2019 from https://phys.org/news/2018-07-particle-formation-heavily-polluted-air.html © 2018 Phys.org Journal information: Science Dimethylamine can tremendously enhance atmospheric particle formationlast_img read more

Sensex rallies 154 pts on FMs growth byte

first_imgBuying in metal, auto, consumer durable and pharma counters helped the benchmark S&P BSE sensex to rally for the second session in a row by 154 points to end at 27,395.73 amid mixed to positive global trends and renewed buying by foreign funds.A statement given by the Finance Minister Arun Jaitley that the economy is expected to grow “much better” in 2015-16 as compared with the current financial year also aided the sentiment. The Indian economy grew by 5.3 per cent in the September quarter from a year earlier, and is expected to grow 5.5  per cent in the current financial year that ends on March 31. Buying was seen across-the-board as 11 out of 12 sectoral indices closed with gains while only bankex finished with minor losses.Smart rise in Tata Motors, HDFC, RIL, ITC, TCS, SSLT, Sun Pharma, Hero MotoCorp, Hindalco, HUL, Coal India, Tata Steel, Gail India and BHEL mainly supported the sensex rise.Meanwhile, extending losses for the fourth straight session, rupee on Monday declined by 10 paise to log over 13-month closing low of 63.67 against the Greenback following sustained dollar demand from importers.last_img read more