31Aug/19

Large mammal species live harder die out faster

center_img Citation: Large mammal species live harder, die out faster (2008, May 7) retrieved 18 August 2019 from https://phys.org/news/2008-05-large-mammal-species-harder-die.html Throughout Earth’s history, species have come and gone, being replaced by new ones that are better able to cope with life’s challenges. But some species last longer than others, while others may die out sooner or evolve more quickly. 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

31Aug/19

Study Shows How We Evolved Different Personalities

first_img Explore further This observation has led researchers to ask how evolution may have selected for personality variation within a species. A team from the UK has recently suggested a novel yet simple answer: that variation begets variation. They explain how there is no single ideal personality (as there is an ideal hand or eye, which we all share), but nature instead promotes different personalities.In their recent study, John McNamara, Philip Stephens, and Alasdair Houston from the University of Bristol, and Sasha Dall of the University of Exeter, Cornwall Campus, explain how natural selection can prevent individuals in a species from evolving toward a single optimum personality, using a game theory scenario. In their study, the researchers focus on the evolution of trust and trustworthiness. The game scenario they use is a variant of the Prisoner’s Dilemma. First, Player 1 chooses to trust or not trust Player 2. Not trusting gives Player 1 a small payoff, and Player 2 gets nothing. If Player 1 trusts Player 2, and Player 2 is trustworthy, then both players receive the same medium-size payoff. But if Player 1 trusts Player 2, and Player 2 isn’t trustworthy, Player 1 receives nothing, and Player 2 receives the maximum pay-off. In other words, Player 1 takes a risk if choosing to trust Player 2.At this point, it seems that Player 2 should always choose to be untrustworthy, so that he always receives the maximum payoff. However, as in real life, the game is iterative. And – this is the important factor – Player 1 can do some background research on Player 2, and find out how often Player 2 has been trustworthy in the past. If Player 2 has a record of being untrustworthy, then Player 1 probably won’t trust him. This “social awareness” comes at a cost for Player 1, so Player 1 must decide if the cost is worth the information. If a population of Player 2’s has variation in its records of trustworthiness, then Player 1 could learn useful information by learning a Player 2’s history. (Realistic methods of acquiring information include, for example, talking to third parties or observing facial expression.) But if a Player 2 population generally has the same records, then the cost of social awareness wouldn’t be worthwhile for Player 1. Who you gonna trust? How power affects our faith in others In simulations with multiple players, individual patterns of trust and trustworthiness were allowed to evolve freely. By watching simulations of the game, the researchers found that the Player 2 population evolved variability in trustworthiness in response to sampling by the Player 1 population. For the Player 2 population, variation was the best strategy for gaining the trust of Player 1, and then exploiting that trust to maximize their pay-off on occasion. This variation, in turn, meant that Player 1 could gain helpful information by paying the cost of being socially aware – which, once again, provoked more variation in the Player 2 population. The researchers noted several interesting results of the game. If the Player 1 population was too trusting, the Player 2 population exploited that, and became less trustworthy. Dall said the team was pleasantly surprised by two results: that the model predicted behavioral variation in both player types, and also predicted two distinct variation patterns for Player 2’s behavior. “Not only were we able to explain why variation should be maintained as social interactions become more extensive, we were able to explain how discrete behavioral types might evolve in otherwise continuous behavioral traits,” Dall said to PhysOrg.com.As he elaborated, the presence of a few socially aware Player 1’s will not only keep the Player 2’s in check, but also allow for more variation among Player 1’s. “You only need a certain number of samplers to enforce trustworthy Player 2 behavior, and so there will be a limit to the numbers of samplers that will be maintained by selection. Once samplers are common enough, everyone else should adopt unconditional, cost-free Player 1 behavior.” In other words, some Player 1’s will always trust, while other Player 1’s will never trust one another.As the researchers concluded, even though this study focuses on a specific model, the general finding that variation begets variation in social contexts has broad implications for understanding evolution and game theory. Past results in game theory have discovered individual differences in trust and trustworthiness, and now studies like this one help to explain this variation. This study and others also show that evolutionary game theorists cannot ignore the importance of individual variation in their models. Meanwhile, the researchers will continue to investigate exactly why we have different personalities.“More generally, the question of ‘why personality variation evolves’ requires a more complex answer, which we’re only just starting to unravel as evolutionary biologists,” Dall said. “The chances are that there isn’t just one reason, and which particular reason is relevant depends on the context. So far, our social awareness reason is one of the few that has been proposed to explain variation in a cooperative context. Social awareness also appears to work in an aggressive context: individuals adopt consistent levels of aggression to avoid getting in real fights, since if someone can predict you’re going to be aggressive, they will avoid provoking you; individual differences arise via frequency dependence again, as the more aggression there is around you, the less you should bother fighting – this is the famous Hawk-Dove game outcome.”More information: McNamara, John M.; Stephens, Philip A.; Dall, Sasha R. X.; Houston, Alasdair I. “Evolution of trust and trustworthiness: social awareness favours personality differences.” Proceedings of the Royal Society, doi:10.1098/rspb.2008.1182.Copyright 2008 PhysOrg.com. All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com. (PhysOrg.com) — Although members of the same species share more than 99 percent of their genetic makeup, individuals often have small differences, such as in their appearance, susceptibility to disease, and life expectancy. Another difference, one that has gone overlooked from the evolutionary perspective, is personality variation. Even identical twins can have personality types at opposite ends of the spectrum.center_img The researchers performed simulations of the above game to understand how behavior variation evolves in a population. Player 1 (P1) chooses to trust or not trust Player 2 (P2). If trusted, P2 chooses to take advantage of P1 to gain a higher pay-off, or be trustworthy. The pay-off relation is 0 < s < r < 1. P1’s cost of sampling P2 is c, where 0 < c < s. Image credit: J. M. McNamara et al. ©2008 The Royal Society. Citation: Study Shows How We Evolved Different Personalities (2008, November 13) retrieved 18 August 2019 from https://phys.org/news/2008-11-evolved-personalities.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

31Aug/19

Scientists Create LightBending Nanoparticles

first_img Smart drug delivery system — Gold nanocage covered with polymer (w/ Video) Citation: Scientists Create Light-Bending Nanoparticles (2009, March 3) retrieved 18 August 2019 from https://phys.org/news/2009-03-scientists-light-bending-nanoparticles.html (PhysOrg.com) — Metallic nanoparticles and other structures can manipulate light in ways that are not possible with conventional optical materials. In a recent example of this, Rice University researchers discovered that cup-shaped gold nanostructures can bend light in a controllable way. The cups act like three-dimensional nano-antennas. Directional scattering of an incoming electromagnetic wave by oriented nanocups. Image courtesy Nikolay Mirin, Rice University. The research is described in the February 19, 2008, online edition of Nano Letters.When light interacts with nanoparticles and other tiny structures, many interesting and even dramatic physical effects can occur. For example, man-made “metamaterials” have very fine structures with features smaller than the wavelength of light, some just tens of atoms across, imparting them with unique and often intriguing optical behaviors. Metamaterials are of interest to scientists because they may be able to interact with light in ways that naturally occurring materials cannot.The gold nanocups created in this research interact with light in two main ways: axially, the up-down direction, or transverse, the left-right direction. The transverse mode is by far the stronger of the two.”When we illuminated the nanocups, the transverse interaction exhibited a strong scattering resonance,” said Rice University researcher Naomi Halas, the study’s corresponding scientist, to PhysOrg.com. She conducted the study with colleague Nikolay Mirin. “We learned that the direction of the transverse resonant light scattering depends on the orientation of the cups, a property that has not been observed in studies of similar structures.”Specifically, the cups behave like a “split-ring resonator,” a type of metamaterial with a negative refractive index—the ability to refract (not reflect) light partially or fully backward. Split-ring resonators look like two concentric, non-touching rings that have each been split in half. When placed in a microwave or infrared field, an alternating current of that same frequency is induced in each ring. Each current in turn induces its own magnetic field at that same microwave or infrared frequency, which can either oppose or enhance the original field.Split-ring resonators can support resonant wavelengths that are much larger than their size. But since split-ring resonators are flat, their light-scattering abilities are restricted to a plane.Halas and Mirin’s nanocups are much like three dimensional versions of split-ring resonators. When light with the proper frequency is applied, a resonant electron current is induced in the cups. This current produces an electric field that is parallel to the cup opening (not parallel to the cup axis). The scattered light is emitted perpendicular to that field; in other words, in whatever direction the cup’s axis is pointing.This unique light-redirecting property should prove to be very useful in the development of new optical materials and devices, from solar cells to light attenuators to chip-to-chip optical interconnects in futuristic circuitry.”In this line of research, many other types of nanoparticles and nanostructures can be designed to have this type of light-redirecting property,” said Halas.Halas and Mirin created the nanocups by depositing latex or polystyrene nanoparticles, each about 80 nanometers in diameter, onto a sheet of glass. They coated the particles and the glass with a 20-nanometer-thick layer of gold, applying the gold from different angles to make sure both the sides and tops of each particle were covered, yet leaving an uncoated circular or elliptical “shadow” next to each particle, exposing the surface below.Finally, they poured an elastic polymer was poured over the array and, when the polymer had cured, peeled it off to reveal a transparent film embedded with gold nanocups.More information: Nano Lett., Article ASAP • DOI: 10.1021/nl900208zCopyright 2009 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 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

31Aug/19

The Mighty Mississippi Basin and Gulf Suffocating Inertia Not An Option

first_imgThe final report and study recommends a long terms solution to the hypoxic conditions present in the Mississippi River Basin and the Northern Gulf of Mexico. The proposed plan to reduce nutrient discharges across the river basin and ecological water will take up to a decade to realize a difference in water quality downstream in the gulf. Nine states; Arkansas, Illinois, Indiana, Iowa, Kentucky, Mississippi, Missouri, Ohio and Tennessee contribute three-fourths of the phosphorous and nitrogen discharged into the Gulf of Mexico, according to the American Chemical Society study by Anderson et. al. 2008. WTSB recommends a targeted approach to curb nutrient discharges by prioritizing intervention at the highest nutrient loading areas by directing conservation in watershed areas located in the river basin area. As a corollary objective the EPA and Department of Agriculture should identify specific areas within watersheds where the expenditure of funds and resources will have the highest probability of achieving a positive result. WTSB suggests EPA and the Department of Agriculture establish a Nutrient Control Implementation Initiative, (NCII) and a new Mississippi River Basin Water Quality Center. The WTSB further recommends certain goals for evaluating, demonstrating and creating an institutional model for local, state and federal counterparts to share research and their efforts to control nutrient discharges. WTSB recommends that Municipal and industrial point dischargers should be required as a condition to their permit under the National Pollutant Discharge Elimination System to monitor phosphorous and nitrogen levels. Further,WTSB recommends a cost analysis of community and governmental efforts of various nutrient control actions. Lastly, conduct a pilot project and compile and disseminate a best practices guidelines.According to the report, the most significant task for improving water quality everywhere, but in particular the Mississippi River Basin comes from nonpoint source pollutants derived from runoff flowing across agricultural land, forests, urban lawns, streets and other paved areas. The primary culprit for this region is the use of nitrogen and phosphorous based fertilizers used in agriculture. A relatively recent change in land use including subsurface drainage, increase demand for commodities and use of fertilizers with added boosts of phosphorous and nitrogen has made the most significant impact in nutrient pollution in the region. Row crops like soybeans and corn contribute 25-percent phosphorous and 52-percent nitrogen of all nutrients in the Gulf of Mexico. Pasture and range land is the next highest source of nutrient discharge with a combined discharge of 42-percent, ‘other crops’ discharge approximately 32-percent of all nutrients with ‘urban and population’ contributing 21-percent. The least nutrient discharger is ‘natural land’ and atmospheric conditions contribute only nitrogen at a rate of about 16-percent.The report states that unequivocal and decisive action is necessary for the implementation of its recommendations. For years the region has languished in a state of inertia due to a variety of reasons. Some reasons simply lack awareness of the current scientific knowledge gathered by the USGS SPARROW modeling team identifying sources and related work developing an adaptive management paradigm. More importantly, the expansive, complex, ecosystem combined with an ever fluctuating human factor will never have a perfect approach. The quest for perfection has in effect resulted in no action whatsoever to ameliorate the deteriorating conditions. Other objections by some include a lack of knowledge of the level of reduction of nutrient discharges it would take to improve water quality. The report finds that whether the recommended Mississippi River Basin Water Quality Center uses the EPA’s 45-percent reduction of nutrient discharges or 20 to 30-percent reduction in nutrient discharges is not the pivotal question. A dramatic reduction in phosphorous and nitrogen is necessary now. Other objections include state and federal conflicts, leadership and other bureaucratic turf wars for funding.The report concludes that the Clean Water Act has broad authority and overlapping authority with the states concerning nutrient use and discharge into the region. Governmental agencies and non-profit association do have access to resources including conservation and remediation funding. The recommended Mississippi River Water Quality Center would serve as the vehicle to incorporate federal, state, private sector, NGOs and interested citizens in the creation of an overall plan of action. The report indicates that the current state of inertia is not an option.Source:Nutrient Control Actions for Improving Water Quality in the Mississippi River Basin and Northern Gulf of Mexico (2009),Water Science and Technology Board (WSTB)© 2009 PhysOrg.com Explore further Stronger EPA leadership needed to improve water quality in Mississippi River Phosphorous Delivered to Gulf of Mexico. Courtesy of USGS 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 Hypoxia is caused by an excess discharge of nutrients, in particular phosphorous and nitrogen into a waterway. A chain of naturally occurring events take place which include widespread algae blooms and ends with the decomposition of the dead algae blooms which in turn depletes dissolved oxygen from the water column causing hypoxia in the Northern Gulf of Mexico and Mississippi River Basin. The hypoxic conditions and related nutrient pollutants in the basin region literally chokes the oxygen from the waterway causing fish kills and potential toxic effects to humans and fish alike. The problem has increased dramatically over the past decades for varying reasons including changing land use,urbanization and the introduction of new varieties of agricultural products.According to the study, “Nutrient Control Actions for Improving Water Quality in the Mississippi River Basin and Northern Gulf of Mexico, 2009” data compiled since 1985 of the region is complicated by the fact that the source of phosphorous and nitrogen discharges are attributable to numerous watersheds and tributaries involving a huge land mass spanning 31 states, covering approximately 41-percent of the conterminous land in the United States with multiple governmental authorities responsible for managing the Mississippi River Basin leading to the Gulf of Mexico. Cooperative efforts between state, federal and cross-discipline regulatory schemes (ie. water quality and nutrient control) was key in the assessment of downstream effects and analysis of decades of data in order to create the WTSB recommendations. The plan for implementation was produced by the National Research Council, WTSB at the behest of the U.S. Environmental Protection Agency and Department of Agriculture with the objective of implementing the Clean Water Act. The specific charge of the request was to advise the EPA in the following areas: 1) initiate nutrient pollutant control programs; 2) identifying alternatives for allocating nutrient load reductions across the river basin and 3) documenting the effectiveness of pollutant loading reduction strategies on the gulf hypoxic zone and state designated uses. Special committees were formed and met during the last half of 2008 under the auspices of the WTSB. Citation: The Mighty Mississippi Basin and Gulf Suffocating: Inertia Not An Option (2009, July 27) retrieved 18 August 2019 from https://phys.org/news/2009-07-mighty-mississippi-basin-gulf-suffocating.html The Water Science and Technology Board, (WTSB), Division on Earth and Life Sciences of the National Research Council has released for publication its study for improving water quality in the Mississippi River Basin and Northern Gulf of Mexico. The purpose of the study was to create an action plan for reducing nutrient load in the effected areas causing low levels of oxygen and creating a condition called hypoxia. last_img read more

31Aug/19

Researchers discover way to allow 80 percent of sound to pass through

first_img In this new effort, the researchers sought to extend prior research done by Thomas Ebbesen and colleagues in 1998 where it was discovered that holes, made in a metal sheet that were smaller than the wavelength of light shone on it, allowed more light to pass through than expected—a property that has come to be known as extraordinary optical transmission. Subsequent research found the principle did not apply to sound waves due to rigid parts of the barrier reflecting back most of the applied sound. The researchers on this new team suspected that altering certain aspects of the barrier might allow for the property to hold for sound after all.They began by drilling several holes (10 millimeters in diameter) in a 5-millimeter -thick piece of metal. Next, they placed a speaker on one side of the “wall” and a microphone on the other. With just the holes, they found the wall blocked sound almost as effectively as if there were no holes drilled in it. Next, they covered one side of the wall with a thin tensioned membrane (plastic wrap). After playing the sound again, the researchers discovered that the addition of the membrane allowed much more sound to pass through the wall—on average 80 percent more—almost as if the wall weren’t there at all.The membrane, the team explains, allows for “zero resistance” as the sound encounters the holes. At the resonance frequency of the membrane (1200 hertz), air moved in the holes as if it had no mass at all. That in turn allowed sound waves to move through very quickly. The sound in the holes was actually concentrated as it passed through, suggesting that the technique might be used as a way to magnify small signals. One application of this discovery could be walls that serve as security barriers. More information: Giant Acoustic Concentration by Extraordinary Transmission in Zero-Mass Metamaterials, Phys. Rev. Lett. 110, 244302 (2013) prl.aps.org/abstract/PRL/v110/i24/e244302AbstractWe demonstrate 97%, 89%, and 76% transmission of sound amplitude in air through walls perforated with subwavelength holes of areal coverage fractions 0.10, 0.03, and 0.01, respectively, producing 94-, 950-, and 5700-fold intensity enhancements therein. This remarkable level of extraordinary acoustic transmission is achieved with thin tensioned circular membranes, making the mass of the air in the holes effectively vanish. Imaging the pressure field confirms incident-angle independent transmission, thus realizing a bona fide invisible wall. Applications include high-resolution acoustic sensing. New experiment helps explain extraordinary optical transmission Journal information: Physical Review Letters Citation: Researchers discover way to allow 80 percent of sound to pass through walls (2013, June 21) retrieved 18 August 2019 from https://phys.org/news/2013-06-percent-walls.html © 2013 Phys.orgcenter_img Explore further (Phys.org) —A team of researchers in Korea has discovered a way to allow sound to pass through walls almost as if they were not there at all. As the group describes in their paper published in the journal Physical Review Letters, the technique involves drilling very small holes in a wall and then tightly covering them with a thin sheet of plastic. Credit: Oula Lehtinen/Wikipedia 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

31Aug/19

Macrophages create the elusive spermatogonial stem cell niche

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. Journal information: Cell Reports Explore further (Phys.org)—Every organ strikes its own balance between self-renewal and differentiation. At one extreme is the brain, where only a few isolated outposts are known to contribute to a largely quiescent population. At another extreme are the testes, where at least in males, prolific germline turnover is maintained amidst a protracted and deliberate multi-month creation cycle. Perhaps surprisingly, both organs are uniquely immunoprivileged against various vascular indiscretions and yet rely on various myeloid-derived cells like macrophages or microglia to instruct important structural maturations. The so-called stem cell ‘niche’ is the microenvironment of the stem cell: all those physical and molecular intangibles that nourish, shield and inform its major life decisions. In creatures like worms and flies a well-defined stem cell niche is distally localized within a polarized gonad. By contrast, each testes of the mammal can contain up to 40,000 potential stem cell niches more-or-less randomly dispersed among its seminiferous tubules. A recent paper published in Cell Reports has removed some of the mystery in the mammalian reproductive system by showing that a unique class of testicular macrophages define its putative stem cell niche.Perhaps even more importantly, they also show that these macrophages control spermatogonial differentiation through the expression of critical factors including CSF1 (colony-stimulating factor) and retinoic acid synthesis enzymes. When the researchers ablated the macrophages by making them selectively and transiently susceptible to the diphtheria toxin, they found a drastic reduction in the number of spermatogonia. This new found responsibility of macrophages complements their previous known testicular functions in promoting steroidogenesis in Leydig cells. They are also known to be intimately involved in vascular development in several places, including the brain. We should mention that the immune barrier in the brain is due mainly to the endfeet of astroglial cells while in the testes it is created by tight junctions in the Sertoli cells that nurse the developing spermatogonia.The single spermatogonium is the most undifferentiated cell within the prevailing model of the spermatogonial stem cell hierarchy. In the fullness of time each one progresses through an incomplete cytokinesis, giving rise to syncytial cysts of spermatogonia progeny that are held together in formation by cytoplasmic bridges. In this way those cells in the syncytium that lack and X chromosome can still get copies for things like glucose 6 phosphate dehydrogenase. Similarly those cells that find themselves without a Y still have access to essentials like the RBM gene, which is critical later in spermatogenesis. Testes. Credit: smithlhhsb122.wikispaces.com More information: The New Director of “the Spermatogonial Niche”: Introducing the Peritubular Macrophage, Cell Reports, Volume 12, Issue 7, p1069–1070, 18 August 2015. dx.doi.org/10.1016/j.celrep.2015.07.057Macrophages Contribute to the Spermatogonial Niche in the Adult Testis, Cell Reports, Volume 12, Issue 7, p1107–1119, 18 August 2015. dx.doi.org/10.1016/j.celrep.2015.07.015 Mechanisms for continually producing sperm © 2015 Phys.org For most men, the only time they ever hear the word macrophage in reference to their testicles is when it comes time for the vasectomy. Upon being told during that actual sperm production is totally unaffected by a vasectomy, any reasonable man might be expected to wonder, perhaps aloud, ‘what happens to all the sperm’? Typically there is some mumbling about macrophages taking care of all that, although the actual details are a bit shoddy. This new evidence regarding the intimate relationship between macrophages, spermatogenesis, and perhaps even spermicide, points to the indebtedness we have to these dynamic cells.Since we have already broached the subject we might take the opportunity to share a few more illuminative details that may benefit anyone undergoing significant alterations to their reproductive plumbing. While a general attitude of ‘the less you know, the better’ may often prevail in such matters, there are some things a patient should probably know. In up to half of patients something known in the business simply as ‘epididymal blowout’ will occur. This is something every bit as horrid to imagine as it sounds. Typically, pressure in the vas deferens (which usually is tied off or electrocauterized) builds up over the course of several weeks post-op to the point that it ruptures, frequently accompanied by some pain and possible formation of epidydimal cysts. Fortunately, through a cooperative macrophage effort, this situation largely resolves on its own.However for some men something even more sinister lurks within. Another word that can bring even the strongest to their knees is ‘re-canalization’. This situation is also precisely as it sounds—complete regrowth and functional connection of a severed vas deferens. It is not yet known exactly how or when this can occur other than to say that ‘where there’s a will there’s a way’. For men lucky enough to avoid any of these potential pitfalls there is probably only one remaining concern: what happens to levels of testosterone?Studies have apparently shown that testosterone levels remain the same on average. What such a devilish statement hides is that depending on your particular constitution and sequalae, you might your own individual expect levels to change, either for the better or for worse. In other words, with evidence in literature for both increases and decreases, it is fair to say we need more research on how such things are ultimately controlled in the gonads. Citation: Macrophages create the elusive spermatogonial stem cell niche (2015, September 3) retrieved 18 August 2019 from https://phys.org/news/2015-09-macrophages-elusive-spermatogonial-stem-cell.htmllast_img read more

31Aug/19

Research pair suggest crowd sourcing could improve social science experiment results

first_img The two social scientists have experience in this area, together they published the results of a study they conducted a couple of years ago where they found that German people with royal sounding last names, tended to become business managers. A colleague asked for their data and after conducting an analysis of his own, subsequently refuted the claims made by the pair. This led the pair and some of their colleagues to look for a way to improve social science experiment results—they came up with crowd sourcing.To test their idea, the researchers picked a topic—do soccer refs give red cards to dark skinned people more often than light skinned people? To find out, they consulted with a sports data gathering company that pulled statistics from actual matches—the data was then given to 29 teams of researchers who volunteered to give their time to the project. Each team was asked to use the same data given to them to make a determination, with no other constraints. Each team sent back their results along with the methods they used to obtain them. Each of the research team was then sent a document outlining all the methodologies used by all the teams, but without the results and were asked to rate them and to provide feedback. Each research team received all feedback and ratings and a chance to change their initial findings. Then, finally, all of the teams were invited to participate in an e-mail exchange to discus methodologies and results. Teams were then given another chance to modify their own results and then a final document was drawn up that gave a group consensus on the original question.The result was that 20 of the research teams found that darker skin color did indeed lead to more red cards, but the researchers varied widely on how prevalent it was—the group consensus was that it was 1.3 times more likely. And while that number is significant all by itself, what is really important Silberzahn and Uhlmann write, is that the experiment revealed that using crowd sourcing resulted in a more hesitant response from researchers, which they believe led to a reduced incentive for publishing flashy results. Journal information: Nature Explore further © 2015 Phys.org Credit: George Hodan/Public Domain (Phys.org)—Social science experiments do not have the best track records—oftentimes, studies are conducted, followed by wild claims which are then either contested or outright refuted by colleagues. There might be a better way Raphael Silberzahn and Eric Uhlmann suggest in an essay piece published in the journal Nature—crowdsourcing.last_img read more

31Aug/19

Multichannel vectorial holographic display and encryption

first_imgThe birefringent dielectric metasurfaces were designed using silicon nanofins on top of a glass substrate. To achieve the desired phase shifts, 2-D parameter optimization was conducted using a rigorous coupled wave analysis (RCWA) method. The RCWA semi-analytical method is typically applied in computational electromagnetics to solve scattering from periodic dielectric structures. The length L and width W of the nanofin were in the range of 80 to 280 nm, height at 600 nm and period size P at 400 nm. The values were carefully selected to ensure the phase of the output light eliminated any undesired orders of diffraction. For the simulation, the nanofin was placed on a glass substrate and subjected to a fixed wavelength of incident light at 800 nm. Simulation results indicated the amplitude of transmission for most nanofins with diverse cross-sections were beyond 90 percent efficiency. The scientists determined orientation angles of the nanofins using equations derived in the study to experimentally demonstrate multichannel polarization multiplexing. Holography is a powerful tool that can reconstruct wavefronts of light and combine the fundamental wave properties of amplitude, phase, polarization, wave vector and frequency. Smart multiplexing techniques (multiple signal integration) together with metasurface designs are currently in high demand to explore the capacity to engineer information storage systems and enhance optical encryption security using such metasurface holograms. The scientists first derived a multiplexing algorithm to support the dynamic vectorial holographic display and encryption process. By using the correct polarization keys, the receiver could obtain the exact information delivered. By increasing the complexity of such images, even higher flexibility was obtained alongside detailed analysis of the reconstructed vectorial image properties. Since the device containing metasurfaces is compact in size, in practice, it can be easily transported with encoded information. , Nature Communications To pattern the design of interest, Zhao et al. engineered several dielectric silicon metasurfaces on top of a glass substrate using plasma etching, followed by electron beam lithography. The metasurfaces were composed of 1000 x 1000 nanofins, i.e. nanostructures with the ability to augment heat transfer via surface area enhancement and liquid-solid-interactions. The researchers studied two schemes of multiple polarization channels; with or without rotation using the birefringent dielectric metasurfaces—to realize the holograms. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. a) Schematic illustration of an amorphous silicon nanofin positioned on a glass substrate. The metasurface will be composed of a periodic arrangement of such unit-cells. b–e) Simulation results for the amplitude and phase of the transmission coefficients txx and tyy shown for a 2D parameter optimization by using a rigorous coupled wave analysis method. The length and width of the nanofin are both swept in the range of 80–280 nm at an incident wavelength of 800 nm. Credit: Light: Science & Applications, doi: 10.1038/s41377-018-0091-0. Experimental setup and scanning electron microscopy images of the fabricated metasurface samples. a) The experimental setup for the observation of the holographic images. The two linear polarizers (LP1, LP2) and two quarter-wave plates (QWP1, QWP2) are used to set the precise polarization combination for the incident/transmitted light. The lens images the back focal plane of the microscope objective lens (×40/0.6) to a CCD camera. b–e) Scanning electron microscopy images of two typical fabricated silicon metasurface samples shown with a top and side view. The metasurface holograms are composed of 1000 × 1000 nanofins with different cross-sections and orientation angles. Credit: Light: Science & Applications, doi: 10.1038/s41377-018-0091-0. The two-channel polarization and angle-multiplexed hologram represents a cartoon tiger, cartoon snowman, teapot and teacup. Credit: Light: Science & Applications, doi: 10.1038/s41377-018-0091-0. , Nature Nanotechnology Multichannel polarization-multiplexed holograms (“Dice”). Credit: Light: Science & Applications, doi: 10.1038/s41377-018-0091-0. More information: Ruizhe Zhao et al. Multichannel vectorial holographic display and encryption, Light: Science & Applications (2018). DOI: 10.1038/s41377-018-0091-0 Guoxing Zheng et al. Metasurface holograms reaching 80% efficiency, Nature Nanotechnology (2015). DOI: 10.1038/nnano.2015.2 Lingling Huang et al. Three-dimensional optical holography using a plasmonic metasurface, Nature Communications (2013). DOI: 10.1038/ncomms3808 Journal information: Light: Science & Applications Holography based on metasurfaces is a promising candidate for applications in optical displays/storage with enormous information bearing capacity alongside a large field of view compared to traditional methods. To practically realize metasurface holograms, holographic profiles should be encoded on ultrathin nanostructures that possess strong light-matter interactions (plasmonic interactions) in an ultrashort distance. Metasurfaces can control light and acoustic waves in a manner not seen in nature to provide a flexible and compact platform and realize a variety of vectorial holograms, with high dimensional information that surpass the limits of liquid crystals or optical photoresists. Among the existing techniques employed to achieve highly desired optical properties, polarization multiplexing (multiple signal integration) is an attractive method. The strong cross-talk associated with such platforms can, however, be prevented with birefringent metasurfaces (two-dimensional surfaces with two different refractive indices) composed of a single meta-atom per unit-cell for optimized polarization multiplexing.Nevertheless, the full capacity of all polarization channels remains to be explored for improved information storage capacity within metasurface holograms and in holographic optical devices. In a recent study, Ruizhe Zhao and co-workers demonstrated a new method to realize multichannel vectorial holography for dynamic display and high-security applications. In the study, birefringent metasurfaces were explored to control polarization channels and process very different information through rotation. The reconstructed vectorial images could be switched from one form to another with negligible cross-talk by selecting a combination of input/output polarization states. The results are now published in Light: Science & Applications. The scientists were able to design and construct more complex multiplexing functionalities with 12 channels using the same principles of design thereafter. The vectorial images were viewed as holographic reconstructions with the input/output polarization combinations developed as proposed. The technique could also be used to encrypt different images at the same spatial location. In encryption, such superposition can convey a different meaning on reconstruction. As an example, the scientists chose the image of a die with six representative surfaces, and by using different combinations of input/output polarization states, encoded up to six images for viewing.The multiplexing algorithm derived in the study aided the dynamic vectorial holographic display and the encryption of images encoded on birefringent dielectric metasurfaces. By using the correct polarization keys, a receiver could obtain the exact information delivered. Higher flexibility could be obtained by increasing the complexity of the image and changing the medium of encryption to titanium dioxide (TiO2) or silicon nitride (SiN). The correct polarization combination secured the information for enhanced complexity during decryption.The multichannel hologram maintained a relatively large working bandwidth since the reconstructed images could be observed away from the designed wavelength of 800 nm. The study established a design and engineering technique that combined birefringent properties of simple nanofins used as the building blocks, with extra-design freedom of rotation matrix and smart multiplexing algorithms. The results enabled high-dimensional multichannel polarization multiplexed holograms, with up to 12 polarization channels. In this way, efficient light-based encryption and integrated multichannel holographic display techniques can pave the way for advanced communication in high security applications. Principle of the metasurface holography design and statistical results of the number of each nanofin (different cross-sections and orientation angles) contained in the designed metasurface holograms. Schematic illustrations of polarization multiplexed holograms based on dielectric metasurfaces. The red and blue arrows indicate the polarization of the incident light and the transmission axis of the polarizer placed behind the metasurface sample. The red, blue, and green color of the reconstructed images (the words “holography”, “meta”, and “surface”) represent components of the output light, respectively. a) Two channel polarization and an angle multiplexed hologram based on metasurfaces composed of nanofins with different cross-sections but fixed orientation angles, which can be used to reconstruct two sets of off-axis images. b) Multichannel polarization multiplexed hologram based on metasurfaces composed of nanofins with different cross-sections and orientation angles, which can be used to reconstruct three independent images and all combinations of these images (12 channels in total). c) Two-channel polarization- and angle-multiplexed hologram (enables appearance of “cartoon tiger”, “cartoon snowman”, “teapot”, “cup”), b) Multichannel polarization-multiplexed hologram (appearance of the word “holography”, “meta”, “surface”) c) Multichannel polarization-multiplexed hologram (appearance of “dice”) d Multichannel polarization-multiplexed hologram (appearance of a “cartoon person”). Credit: Light: Science & Applications, doi: 10.1038/s41377-018-0091-0. © 2018 Science X Network For optical characterization of the metasurface holograms, Zhao et al. used an experimental setup. The magnifying ratio and numerical aperture of the objective lens were carefully chosen to collect all the diffraction light from the sample and reconstruct holographic images in the Fourier plane. The scientists used a second objective/lens to capture the Fourier plane on a CCD camera. They also separately observed two scanning electron microscopy images of the samples with or without rotation to characterize the engineered surface.As a proof-of-principle, using the metasurfaces, Zhao et al. constructed holographic images of a cartoon tiger and a snowman that appeared with high fidelity and high resolution when illuminated by x-polarized light. When the incident light was switched to y-polarization, the reconstructed images changed to a teapot and a teacup. In this experiment, only two polarization channels were available in the setup, with both pairs of the holographic images reconstructed and made to disappear simultaneously by rotating the polarizer behind the sample. The experimental results were in agreement with the simulation to confirm the study’s fundamental design principle. The net diffraction efficiency of the hologram was defined as the ratio of intensity of the single reconstructed image to the power of incident light. Explore further Citation: Multichannel vectorial holographic display and encryption (2018, December 7) retrieved 18 August 2019 from https://phys.org/news/2018-12-multichannel-vectorial-holographic-encryption.html Technique makes more efficient, independent hologramslast_img read more

31Aug/19

The rockpaperscissors game and coexistence

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. More information: J. Menezes, B. Moura, and T.A. Pereira. “Uneven rock-paper-scissors models: Patterns and coexistence.” EPL. DOI: 10.1209/0295-5075/126/18003 Traditionally, the rock-paper-scissors model assumes that all three species have equal strength. But what if one of the species is weaker than the other two? Such a scenario may occur in nature, for example, due to seasonal variations that reduce the ability of a certain species to compete with other species. In a new paper, associate professor Josinaldo Menezes, graduate student Tibério Pereira, and undergraduate student Bia Moura at the Federal University of the Rio Grande do Norte in Brazil have addressed this question by performing more than a million simulations of a rock-paper-scissors model in which one species attacks less than it is attacked. The model helps to explain how coexistence among different species is maintained in spite of the species’ different strengths.”The results tell us that the reason why species may coexist, even if one of them is weaker, is the special selection configuration of the rock-paper-scissors model,” Pereira told Phys.org.The model works somewhat differently than the original rock-paper-scissors model when implemented as a special case of the May-Leonard model. Individuals, which are placed on a grid, can carry out three possible interactions, no matter which of the three species they belong to. The three interactions are selection, mobility, and reproduction. Selection is like killing, in which an individual of one species can wipe out a neighboring individual of the species that it dominates. For mobility, an individual of one species can switch places with a neighboring individual of the species that it dominates, or move to a neighboring empty space. For reproduction, an individual of one species can populate an empty neighboring space with another individual of its species.In the simulation, individuals of each species are randomly distributed on a grid. An individual is randomly selected, and then one of its eight neighboring sites (occupied or empty) is randomly selected. Next one of the three interactions (selection, mobility, or reproduction) is randomly chosen. The chosen individual carries out the interaction, if possible. In some cases, the interaction is not possible: for example, the neighboring site must be occupied by an individual of the correct species (the one being dominated) in order for selection to take place, and the neighboring site must be empty in order for reproduction to take place. In 1975, R.M. May and W.J. Leonard first used the rock-paper-scissors game to model ecological scenarios in which three species cyclically dominate each other: one species dominates a second species, the second species dominates a third species, and the third species dominates the first species. The game works well, for example, for modeling different strains of cyclically dominant E. coli bacteria. To make one species weaker than the other two, the researchers gave one species a lower probability of getting the selection interaction. The results of the simulations showed that, contrary to what might be expected, the weaker species does not necessarily die out. Instead, for some weakness levels, the weaker species initially dominates almost all of the territory. This happens because, since the weaker species selects (i.e., kills) fewer individuals of the species that it dominates, this species grows and, in turn, limits the growth of the third species. As this third species dominates the weaker species, its limited growth allows the weaker species to grow.For these reasons, previous research has shown that the weaker species may always dominate, even in the long run. However, here the researchers found something different.”We were surprised because the weaker species does not necessarily win the uneven rock-paper-scissors game, as it was known in the literature,” Menezes said. “We found out that, in May-Leonard-type simulations, the winner species depends on the mobility and the strength of the weaker species.”Over time, new patterns appear showing exactly how the different species spatially coexist. In particular, spiral patterns emerge and travel like waves until they meet each other, at which point they result in all three species coexisting in small colonies. The spiral patterns—and resulting coexistence—are more likely to occur on larger grids, since this increases the mobility of all species and allows for the species to come in contact with each other. “Beautiful spiral waves emerge when the lattice is almost dominated by one single species,” said Moura. “The formation of spiral spatial patterns is entirely different from the standard rock-paper-scissors model. We expect that our results can be helpful to ecologists because they describe and quantify patterns which are crucial to understanding how such species coexist.”The results also revealed that coexistence has its limits: When the strength of the weaker species is less than approximately one-third of the strength of the other two species, the probability of coexistence greatly diminishes. In the future, the researchers plan to investigate more complex scenarios, such as adaptive biological systems, where a species can change the interaction probabilities to guarantee its survival. They also plan to explore how biological interactions can balance the uneven relationships among species, as well as the effects of diseases and other predators. “We aim to understand how a disease outbreak or a common predator mediation increases the chances of coexistence in the uneven rock-paper-scissors model,” Menezes said. (Top) The selection interactions among three species. The dashed arrow indicates that species 1 is weaker than species 2 and 3. (Bottom) Some of the spatial patterns that emerge in simulations. Individuals of species 1, 2, and 3 are represented by orange, dark blue, and light blue dots, respectively. Empty spaces are represented by white dots. Credit: Menezes et al. ©2019 EPL Explore further Citation: The rock-paper-scissors game and coexistence (2019, July 4) retrieved 18 August 2019 from https://phys.org/news/2019-07-rock-paper-scissors-game-coexistence.html High diversity on coral reefs—a very big game of rock-paper-scissors Journal information: Europhysics Letters (EPL) © 2019 Science X Networklast_img read more