Month: August 2019

Researchers design more reliable invisibility cloakResearchers design more reliable invisibility cloak

first_img More information: Elena Semouchkina, et al. “An infrared invisibility cloak composed of glass.” Applied Physics Letters 96, 233503 (2010). DOI:10.1063/1.3447794 Citation: Researchers design more reliable invisibility cloak (2010, June 24) retrieved 18 August 2019 from In the study, Elena Semouchkina from Michigan Technological University and Pennsylvania State University and her coauthors designed an invisibility cloak made of glass for the infrared range. Currently, most metamaterial cloak designs require that the metamaterial response be homogeneous. However, the new design relies on simulations of a true multi-element cloak structure and takes into account the inhomogeneity of a real metamaterial response.“This is one of the first designs of an optical cloak, in particular, of a cylindrical shell,” Semouchkina told “This is a non-metallic low-loss all-dielectric cloak. … In contrast to the previous designs, the design of our cloak has been developed at a careful control of interactions between resonators, since a true multi-resonator structure has been simulated. It makes the design essentially more reliable.”The structure of the proposed cloak consists of identical nanosized chalcogenide glass resonators arranged in a concentric pattern. In simulations, the researchers found that glass resonators in the shape of a cylinder with a diameter of 300 nm and a height of 150 nm provided the best results for the light wavelength of 1 micron. “The design employs identical resonators in all layers of the cloak, which, from the point of view of fabrication tolerance, presents a tremendous advantage versus fabricating nano-sized elements of different prescribed dimensions,” Semouchkina said. The spoke-like configuration of the resonators forms radial magnetic moments despite different incidence angles of incoming light. As Semouchkina explained, the magnetic resonance response creates the desired effective parameters of the medium.“Our cloak is based on the magnetic resonance in dielectric resonators,” Semouchkina said. “This resonance is used to obtain the desired values of the effective permeability of the medium. The simulations of real 3D resonators, and not of effective medium layers, allowed us to find optimal resonator shapes and their arrangement to assure the magnetic moment formation in resonators illuminated under different incidence angles.”The researchers simulated cloaked cylindrical objects of infinite lengths and of diameters ranging from 5 to 15 wavelengths. Simulations also showed that objects could be cloaked over a wide range of infrared frequencies at the manipulation of inter-resonator distances.Overall, the new design is one more example of the progress made in invisibility cloaks since they were first designed in 2006. Since then, researchers have been working on different design approaches in an attempt to expand the cloaking spectrum, simplify fabrication, and make other improvements.“We are currently performing detailed investigations of the interactions between the resonators in metamaterials and their role in controlling the wave propagation, as well as working on the experimental demonstration of an all-dielectric cloak operation at microwaves,” Semouchkina said. The design of the invisibility cloak consists of a spoke-like configuration of glass resonators, which form a magnetic resonance that is used to obtain the desired parameters of the medium. The illustration shows the glass cloak designed to hide a metal cylinder of 15 micrometers in diameter. Image credit: Semouchkina, et al. 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. ( — Researchers have proposed a new design for an invisibility cloak – a device that could make objects invisible by guiding light around anything placed inside the cloak. Explore further New invisibility cloak allows object to ‘see’ out through the cloak Copyright 2010 All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of read more

The emergence of complex behaviors through causal entropic forcesThe emergence of complex behaviors through causal entropic forces

first_img Citation: The emergence of complex behaviors through causal entropic forces (2013, April 22) retrieved 18 August 2019 from ( —An ambitious new paper published in Physical Review Letters seeks to describe intelligence as a fundamentally thermodynamic process. The authors made an appeal to entropy to inspire a new formalism that has shown remarkable predictive power. To illustrate their principles they developed software called Entropica, which when applied to a broad class of rudimentary examples, efficiently leads to unexpectedly complex behaviors. By extending traditional definitions of entropic force, they demonstrate its influence on simulated examples of tool use, cooperation, and even stabilizing an upright pendulum. The familiar concept of entropy which states that systems are biased to evolve towards greater disorder, gives little indication about exactly how they evolve. Recently, physicists have begun to explore the idea that proceeding in a direction of maximum instantaneous entropy production is only one among many ways to go. More generally, the authors now suggest that systems which show intelligence, uniformly maximize the total entropy produced over their entire path through configuration space between the present time and some future time. In accordance with Fermat’s original principle, for the simple case where light travels in a constant medium, the path which minimizes time is a straight line. If however, the second point under consideration is within a different medium, the shortest path partitions the time spent in either according their refractive indexes. By analogy to Fermat, this new and more general view of thermodynamic systems, looks at the total path, rather than just the current state of the system.The first author on the paper, Alex Wissner-Gross, describes intelligent behavior as a way to maximize the capture of possible future histories of a particular system. Starting from a formalism known as the ‘canonical ensemble’ (which is basically a probability distribution of states) the authors ultimately derive a measure they call causal entropic forcing. When following a causal path, entropy is based not on the internal arrangements accessible to a system at any particular time, but rather on the number of arrangements it could pass through on the way to possible future states. Prediction or cause? Information theory may hold the key Many of these kinds of behaviors might also be compared to activities we now know exist in the normal biochemical operations of cells. For example, enzymes use complex changes in conformation, and various small cofactors, to manipulate proteins and other molecules. The nucleus extrudes mRNAs through pores against entropic forces which tend to hold the polymer coiled up in the the interior. The speed and efficiency at which machines like ribosomes and polymeraces operate, suggests that effects other than just pure Brownian motion are responsible for delivery of their substrates and subsequently binding them with the selectivity that is observed. The biggest imaginative leap of the paper involved simulating a rigid, inverted pendulum stabilized by a translating cart. The authors suggest that when operating under a causal forcing function, this systems bears rudimentary resemblance to achieving upright walking. While this example may appear more relevant to finding new ways to program walking robots, as opposed to understanding the transition to walking in hominids, the overall diversity of behaviors modeled with this formalism does not fail to impress.The spontaneous emergence of complex behaviors now has a new tool which can be used to probe its possible origins. New methods of solving traditional challenges in artificial intelligence may also be investigated. Programming machines to play games like GO, where humans still appear to have the edge might also be make use of these methods. The Entropica simulation software is available in demo form from the authors website, as are other materials related to their new paper. 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: Physical Review Letterscenter_img A modified version of thermodynamics causes a pendulum (green) swinging from a sliding pivot (red) to stabilize in an inverted, and normally unstable, configuration, from which it has a greater variety of options for its future motion. Credit: Physics Focus / A. Wissner-Gross/Harvard Univ. & MIT More information: Causal Entropic Forces, Phys. Rev. Lett. 110, 168702 (2013) advances in fields ranging from cosmology to computer science have hinted at a possible deep connection between intelligence and entropy maximization, but no formal physical relationship between them has yet been established. Here, we explicitly propose a first step toward such a relationship in the form of a causal generalization of entropic forces that we find can cause two defining behaviors of the human “cognitive niche”—tool use and social cooperation—to spontaneously emerge in simple physical systems. Our results suggest a potentially general thermodynamic model of adaptive behavior as a nonequilibrium process in open systems. Does Cosmology Hint At How To Build Artificial Minds? In a practical simulation of a particle in a box, for example, the effect of causal entropic forcing is to keep the particle in a relatively central location. This effect can be understood as the system maximizing the diversity of causal paths that would be accessible by Brownian motion within the box. The authors also simulated different sized disks diffusing in a 2D geometry. With application of the causal forcing function, the system rapidly produced behaviors were larger disks “used” smaller disks to release other disks from trapped locations. In different scenarios of this general paradigm, disks cooperated together to achieve seemingly improbable results. © 2013 Explore furtherlast_img read more

Researchers use new method to calculate interstellar cloud core ageResearchers use new method to calculate interstellar cloud core age

first_img( —A team of space researchers with members from Germany, Finland and the U.K. has calculated the age of an interstellar cloud core using a new chemical analysis method. In their paper published in the journal Nature, the team describes their new technique and explains how measuring chemical changes as cloud contraction occurs can lead to revealing the core’s age. More information: H2D+ observations give an age of at least one million years for a cloud core forming Sun-like stars, Nature (2014) DOI: 10.1038/nature13924AbstractThe age of dense interstellar cloud cores, where stars and planets form, is a crucial parameter in star formation and difficult to measure. Some models predict rapid collapse, whereas others predict timescales of more than one million years. One possible approach to determining the age is through chemical changes as cloud contraction occurs, in particular through indirect measurements of the ratio of the two spin isomers (ortho/para) of molecular hydrogen, H2, which decreases monotonically with age. This has been done for the dense cloud core L183, for which the deuterium fractionation of diazenylium (N2H+) was used as a chemical clock to infer7 that the core has contracted rapidly (on a timescale of less than 700,000 years). Among astronomically observable molecules, the spin isomers of the deuterated trihydrogen cation, ortho-H2D+ and para-H2D+, have the most direct chemical connections to H2 and their abundance ratio provides a chemical clock that is sensitive to greater cloud core ages. So far this ratio has not been determined because para-H2D+ is very difficult to observe. The detection of its rotational ground-state line has only now become possible thanks to accurate measurements of its transition frequency in the laboratory, and recent progress in instrumentation technolog. Here we report observations of ortho- and para-H2D+ emission and absorption, respectively, from the dense cloud core hosting IRAS 16293-2422 A/B, a group of nascent solar-type stars (with ages of less than 100,000 years). Using the ortho/para ratio in conjunction with chemical models, we find that the dense core has been chemically processed for at least one million years. The apparent discrepancy with the earlier N2H+ work arises because that chemical clock turns off sooner than the H2D+ clock, but both results imply that star-forming dense cores have ages of about one million years, rather than 100,000 years. Explore further Researchers find evidence of speedy core formation in solar system planetesimals This image, taken by NASA’s Hubble Space Telescope, shows the colorful “last hurrah” of a star like our Sun. The star is ending its life by casting off its outer layers of gas, which formed a cocoon around the star’s remaining core. Credit: NASA/ESA Scientists believe that stars, like our own sun, form in clouds made up of gases and dust—a nursery of sorts that sets the stage for both birth and development. Stars form inside them as material initially coalesces and then when compaction occurs, giving birth first to a proto-star. But determining how this process actually works and how long it takes has been elusive—it’s believed the process is driven by gravity, but exactly how remains a mystery.Determining interstellar cloud core age has been notoriously difficult, the researchers point out and because of that, estimates of their ages has ranged from tens of thousands of years, to millions of years. In this new effort the researchers used data obtained from the aircraft observatory SOFIA and the APEX telescope in Chile, to gather chemical composition data of the core at the center of a star system known as IRAS 16293-2422 in the constellation Ophiuchus, approximately 400 light years from us. Specifically, they looked at two types of molecular ions that are made from two hydrogen atoms and one heavy hydrogen (deuterium) atom (ortho- and para-H2D+). The relative amounts of the two change over time, the team notes, as the cloud ages, offering researchers a type of “chemical clock.” Using this method, the team calculated that the stars in the system are not older than 100,000 years, but the core itself is approximately a million years old, which means the core apparently sat brewing for approximately 900,000 years before giving birth to the stars.Figuring out how old cloud cores are is important in cosmological study, because if offers a way of dating our own system and the stars that make up the Milky Way Galaxy. The research team claims that their new method of dating cloud cores is the most accurate every used.center_img Journal information: Nature 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. © 2014 Citation: Researchers use new method to calculate interstellar cloud core age (2014, November 18) retrieved 18 August 2019 from read more

Remotely operated vehicle finds heterotrophs abundant in deepest part of the oceanRemotely operated vehicle finds heterotrophs abundant in deepest part of the ocean

first_img More information: PNAS DOI: 10.1073/pnas.1421816112 The Challenger Deep is the deepest canyon in the oceans. The red circle shows the sampling location. Credit: JAMSTEC New species and surprising findings in the Mariana Trench This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. A team of researchers with ties to several institutions in Japan has found an abundance of microscopic bacteria known as heterotrophs living on or near the ocean floor in the deepest part of the Mariana Trench. In their paper published in Proceedings of the National Academy of Sciences, the team describes their expedition work and what they found using a remotely operated vehicle (ROV). The Mariana Trench is located in the western Pacific Ocean, some distance east of Taiwan. One part of it known as Challenger Deep, is the deepest, and holds the record for the deepest part of the ocean. Scientists are eager to learn more about what sort of life forms can live there, approximately 36,000 feet below the surface, both for curiosity’s sake and because what they learn may help with the search for life on other planets. In this new effort, the researchers took a closer look than those before them, sifting the waters below looking for creatures too small to be spotted with cameras. They sent their ROV down with an ability to not just note microscopic sized life forms, but to count how many were seen.Near the surface, where sunlight can penetrate, the team found an abundance of plantlike phytoplankton. Below that is known as the abyssal zone, because of the lack of nutrients available—there is very little life, it is mostly made up of tiny chemolithotrophs which can convert compounds such as ammonia or sulfur into food. Much farther down there is little in the way of observable life, but a closer look revealed that the abundance of tiny organisms increased again as food was more plentiful near the bottom. Heterotrophs cannot fix carbon and thus must use organic carbon to survive in the extremely cold and dark environment. It appears, the team reports, that they live on fecal matter or other dust particles that fall down from above. They also note that infrequent landslides in the area can release food that has been trapped, providing food for years at a time. For comparison purposes, the researchers pointed out that the number of microbes in the water was comparable to untreated well water. The researchers also measured salinity, temperature and chemistry at various depths. They were able to differentiate between different microbes using genetic testing.via LiveSciencecenter_img © 2015 Citation: Remotely operated vehicle finds heterotrophs abundant in deepest part of the ocean (2015, February 26) retrieved 18 August 2019 from Explore further Journal information: Proceedings of the National Academy of Scienceslast_img read more

Study charts changes in island biodiversity as oceans rose over past 20000Study charts changes in island biodiversity as oceans rose over past 20000

first_img Many of the unique species that formed on islands over hundreds of thousands of years are threatened by extinction today. Only few individuals of Lotus maculatus remain in its natural habitat on Tenerife. Credit: Manuel Steinbauer (—A team of researchers affiliated with several institutions in Germany has conducted a study of island biodiversity over the past 20,000 years, a timeframe where sea levels have risen approximately 100 meters due to warmer temperatures and melting ice. In their paper published in the journal Nature, the team describes how they went about their study, their findings and their hopes that their efforts will help predict changes to come as the planet continues to heat up. José María Fernández-Palacios with Universidad de La Laguna in the Canary Islands, has provided a News & Views piece on the efforts by done by the team in the same journal issue and also gives an overview of current research regarding island biodiversity. In Hawai’i, the islands of the so-called Maui-Nui complex were merged during the last ice age (beige areas were above sea-level during the last ice age and are below sea-level today). Credit: Patrick Weigelt For many years, the main themes regarding island biodiversity fell into two categories, degree of isolation and island size—it was believed that both contributed significantly to the degree of diversity for any given island as well as to the numbers of endemic species. In this new effort, the researchers have found another factor that appears to be just as important—how big an island was before the seas began to rise. Changes in overall island size when sea levels rise depends, of course, on how much slope there is—thus volcanic-type islands lose land area very slowly, whereas islands that became islands only because some past event caused them to be cleaved from a continent, tend to “shrink” much faster.To learn more about how sea level rise related to diversity, the researchers looked at 184 oceanic islands across the globe over the course of the past 21,000 years—which covered the time from the last glacial maximum, till the present day—focusing most specifically on data regarding land area, degree of isolation, elevation, the number of islands in any given chain, and of course temperature and precipitation levels. Their study also looked at the diversity of flowering plants including those that are believed to be endemic to an island or chain. In looking at patterns that emerged, the researchers found that the degree of endemic species is higher today for islands that had a lot more land mass back then. Interestingly, they also found that changes in temperature and precipitation didn’t appear to have much of an impact on changes in diversity, nor did the degree of isolation. This last point, they note, was not a surprise—a rise in sea levels does not tend to cause an island to become more remote. How have changing sea-levels influenced evolution on the Galapagos Islands? Explore further More information: Patrick Weigelt et al. Late Quaternary climate change shapes island biodiversity, Nature (2016). DOI: 10.1038/nature17443AbstractIsland biogeographical models consider islands either as geologically static with biodiversity resulting from ecologically neutral immigration–extinction dynamics, or as geologically dynamic with biodiversity resulting from immigration–speciation–extinction dynamics influenced by changes in island characteristics over millions of years. Present climate and spatial arrangement of islands, however, are rather exceptional compared to most of the Late Quaternary, which is characterized by recurrent cooler and drier glacial periods. These climatic oscillations over short geological timescales strongly affected sea levels and caused massive changes in island area, isolation and connectivity, orders of magnitude faster than the geological processes of island formation, subsidence and erosion considered in island theory. Consequences of these oscillations for present biodiversity remain unassessed. Here we analyse the effects of present and Last Glacial Maximum (LGM) island area, isolation, elevation and climate on key components of angiosperm diversity on islands worldwide. We find that post-LGM changes in island characteristics, especially in area, have left a strong imprint on present diversity of endemic species. Specifically, the number and proportion of endemic species today is significantly higher on islands that were larger during the LGM. Native species richness, in turn, is mostly determined by present island characteristics. We conclude that an appreciation of Late Quaternary environmental change is essential to understand patterns of island endemism and its underlying evolutionary dynamics. Journal information: Nature © 2016 This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Citation: Study charts changes in island biodiversity as oceans rose over past 20,000 years (2016, March 31) retrieved 18 August 2019 from read more

Liquid marbles can be caused to move with laser light w VideoLiquid marbles can be caused to move with laser light w Video

first_img Journal information: Advanced Functional Materials Smart materials: Fused liquid marbles show their strength Explore further PausePlay% buffered00:0000:00UnmuteMuteDisable captionsEnable captionsSettingsCaptionsDisabledQuality0SpeedNormalCaptionsGo back to previous menuQualityGo back to previous menuSpeedGo back to previous menu0.5×0.75×Normal1.25×1.5×1.75×2×Exit fullscreenEnter fullscreen Play Credit: Advanced Functional Materials (2016). DOI: 10.1002/adfm.201600034 PausePlay% buffered00:0000:00UnmuteMuteDisable captionsEnable captionsSettingsCaptionsDisabledQuality0SpeedNormalCaptionsGo back to previous menuQualityGo back to previous menuSpeedGo back to previous menu0.5×0.75×Normal1.25×1.5×1.75×2×Exit fullscreenEnter fullscreen Scheme illustrating the light-driven delivery of material using liquid marbles (LMs). Credit: © WILEY‐VCH (2016) Play Credit: Advanced Functional Materials (2016). DOI: 10.1002/adfm.201600034 center_img (—A team of researchers with Osaka Institute of Technology in Japan, has developed liquid balls that propel themselves when exposed to laser light. In their paper published in the journal Advanced Functional Materials, the team describes how the liquid balls are made, how they can be used and some possible applications for them. More information: Maxime Paven et al. Light-Driven Delivery and Release of Materials Using Liquid Marbles, Advanced Functional Materials (2016). DOI: 10.1002/adfm.201600034AbstractRemote control of the locomotion of small objects is a challenge in itself and may also allow for the stimuli control of entire systems. Here, it is described how encapsulated liquids, referred to as liquid marbles, can be moved on a water surface with a simple near-infrared laser or sunlight. Using light rather than pH or temperature as an external stimulus allows for the control of the position, area, timing, direction, and velocity of delivery. This approach makes it possible to not only transport the materials encapsulated within the liquid marble but also to release them at a specific place and time, as controlled by external stimuli. Furthermore, it is shown that liquid marbles can work as light-driven towing engines to push or pull objects. Being able to remotely transport and push/pull the small objects by light and control the release of active substances on demand should open up a wide field of conceivable applications. © 2016 The idea for the liquid balls came, the team reports, from noting how Stenus beetles propel themselves across the surface of the water—when alarmed, they emit a droplet of stenusin from their anal gland, which causes a change in surface tension behind them, pushing them forward. In this new effort, the researchers used a nanometer-scale powder of polypyrrole (a type of plastic) to accomplish much the same thing—when exposed to light, it heats up and expands.To make the balls, or liquid marbles, as the team calls them, the researches coated very small drops of water with the plastic. Like the Stenus beetle they float on the surface of the water and also like the beetle, they can be propelled by a change in surface tension behind them—in this case, that comes about by laser light—as the light strikes, the plastic heats up and expands, causing a change in the surface tension on the water behind the marble, which causes it to move forward. The team found that the marble had strength as well—they rigged up a floating apparatus that hooked onto one of their marbles, then shone the light, and in so doing, discovered that the marbles could pull floating structures that weighed up to 150 times more than they did. It is worth noting, the team points out, that the laser does not push the marble, instead it causes a chemical reaction that results in the marble moving.And that was not all, they also found that if they blasted the marble long enough with the laser, they could cause it to burst on demand. That means, the team explains, that the marbles could be used as both a transport and delivery mechanism—a service that could find applications in pollution detection, delivery of drugs inside the body, microfluids and even micromachinery. Citation: Liquid marbles can be caused to move with laser light (w/ Video) (2016, April 14) retrieved 18 August 2019 from 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 accreting millisecond Xray pulsar discoveredNew accreting millisecond Xray pulsar discovered

first_img Explore further X-ray pulsars exhibit strict periodic variations in X-ray intensity, which can be as short as a fraction of a second. Accreting millisecond X-ray pulsars (AMXPs) are a peculiar type of X-ray pulsars in which short spin periods are caused by long-lasting mass transfer from a low-mass companion star through an accretion disc onto a slow-rotating neutron star. Astronomers perceive AMXPs as astrophysical laboratories that could be crucial in advancing our knowledge about thermonuclear burst processes.To date, only 21 AMXPs have been discovered, with spin periods ranging from 1.7 to 9.5 milliseconds. In order to expand the list of this peculiar objects, the scientific community is still actively searching for such sources using space observatories like NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) telescope.Recently, a group of researchers led by Andrea Sanna of the University of Cagliari, Italy, has used NuSTAR to identify a new AMXP. The source, named IGR J17591−2342, was initially classified as an X-ray transient by European Space Agency’s INTernational Gamma-Ray Astrophysics Laboratory (INTEGRAL) during galactic center scanning on August 10, 2018. The team observed this source with NuSTAR, which revealed evidence about the nature of this object. Additional observations of the pulsar were conducted using the Neutron Star Interior Composition Explorer (NICER) onboard the International Space Station (ISS).”In this letter, we describe a coherent timing analysis of the NuSTAR and NICER observations that provided the pulsar spin period and binary ephemeris,” the researchers wrote in the paper.The team detected coherent X-ray pulsations around 527.4 Hz (1.9 milliseconds) in the NuSTAR and NICER observations performed almost 25 days from the beginning of the outburst, with a pulse fraction of 15 percent.According to the paper, IGR J17591−2342 has an orbital period of about 8.8 hours. The mass of the neutron star was calculated to be approximately 1.4 solar masses, while the minimum mass of the companion is most likely 0.42 solar masses.Furthermore, the astronomers noted that IGR J17591−2342 is located near the center of our Milky Way galaxy, some 28,000 light years away from the Earth. The estimated accretion rate was found to be about 0.52 billionth of one solar mass per year. IGR J17591−2342 is so far the 22nd known AMXP. The authors of the paper underlined that their discovery enriches the census of these objects that are essential for the understanding of the late stages of stellar evolution. © 2018 New accreting millisecond X-ray pulsar discovered IGR J17591−2342 pulse profiles (black points) from epochfolding the NuSTAR (top-panel) and the NICER (bottom-panel) observations after correcting for the orbital parameters. The best-fitting model (red line) is the superposition of three sinus functions with harmonically related periods. For clarity, we show two cycles of the pulse profile. Credit: Sanna et al., 2018. Citation: New accreting millisecond X-ray pulsar discovered (2018, September 12) retrieved 18 August 2019 from Using NuSTAR spacecraft and NICER instrument, an international team of astronomers has found a new accreting millisecond X-ray pulsar. The newly discovered object, designated IGR J17591−2342, is the newest addition to a still short list of known accreting millisecond X-ray pulsars. The finding is reported in a paper published August 30 on the arXiv pre-print server. More information: NuSTAR and NICER reveal IGR J17591-2342 as a new accreting millisecond X-ray pulsar, arXiv:1808.10195 [astro-ph.HE] report on the discovery by the Nuclear Spectroscopic Telescope Array (NuSTAR) and the Neutron Star Interior Composition Explorer (NICER) of the accreting millisecond X-ray pulsar IGR J17591-2342, detecting coherent X-ray pulsations around 527.4 Hz (1.9 ms) with a clear Doppler modulation. This implies an orbital period of ~8.8 hours and a projected semi-major axis of ~1.23 lt-s. From the binary mass function, we estimate a minimum companion mass of 0.42 solar masses, obtained assuming a neutron star mass of 1.4 solar masses and an inclination angle lower than 60 degrees, as suggested by the absence of eclipses or dips in the light-curve of the source. The broad-band energy spectrum is dominated by Comptonisation of soft thermal seed photons with a temperature of ~0.7 keV by electrons heated to 21 keV. We also detect black-body-like thermal direct emission compatible with an emission region of a few kilometers and temperature compatible with the seed source of Comptonisation. A weak Gaussian line centered on the iron K-alpha; complex can be interpreted as a signature of disc reflection. A similar spectrum characterises the NICER spectra, measured during the outburst fading. 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

Electronically programmable photonic moleculeElectronically programmable photonic molecule

first_img Team develops optically controlled, non-reciprocal multifunctional photonic devices The results are now published on Nature Photonics, where Zhang et al. overcame the existing performance trade-off, to realize a programmable photonic two-level system that can be controlled dynamically via gigahertz microwave signals. To accomplish this, the scientists created a microwave addressable photonic molecule using a pair of integrated lithium niobate micro-ring resonators patterned close to each other (radius 80 μm). The combined effects of low optical loss, efficient co-integration of optical waveguides and microwave electrodes allowed the simultaneous realization of a large electrical bandwidth (> 30 GHz), strong modulation efficiency and long photon lifetime (~2 ns). A photonic analogue of a two-level system can typically facilitate the investigation of complex physical phenomena in materials, electronics and optics. Such systems convey important functions, including unique on-demand photon storage and retrieval, coherent optical frequency shift and optical quantum information processing at room temperature. For dynamic control of photonic two-level systems, electro-optic methods are ideally suited due to their fast response, programmability and possibility for large-scale integration. In their work, Zhang et al. showed that optical transmission of the photonic molecule measured using a telecom-wavelength laser, supported a pair of well-defined optical energy levels. The evanescent coupling of light from one resonator to another was enabled through a 500 nm gap between the micro-ring resonators to form the two well-resolved optical energy levels. The scientists explored the analogy between an atomic and photonic two-level system to demonstrate control of the photonic molecule. Physical systems with discrete energy levels are ubiquitous in nature and form fundamental building blocks of quantum technology. Artificial atom-like and molecule-like systems were previously demonstrated to regulate light for coherent and dynamic control of the frequency, amplitude and the phase of photons. In a recent study, Mian Zhang and colleagues engineered a photonic molecule with two distinct energy levels, using coupled lithium niobate micro-ring resonators that could be controlled via external microwave excitation. The frequency and phase of light could be precisely operated by programmed microwave signals using canonical two-level systems to include Autler-Townes splitting, Stark shift, Rabi oscillation and Ramsey interference phenomena in the study. Through such coherent control, the scientists showed on-demand optical storage and retrieval by reconfiguring the photonic molecule into a bright-dark mode pair. The dynamic control of light in a programmable and scalable electro-optic system will open doors for applications in microwave-signal processing, quantum photonic gates in the frequency domain and to explore concepts in optical computing as well as in topological physics. In the experiments, light from the tunable telecom wavelength laser was launched into the lithium niobate waveguides and collected from them via a pair of lensed optical fibres. The scientists used an arbitrary waveform generator to operate microwave control signals before sending them to electrical amplifiers. The efficient overlap between microwaves and optical fields observed in the system enabled higher tuning/modulation efficiency than those previously observed with bulk electro-optic systems. Such coherent microwave-to-optical conversion can link electronic quantum processes and memories via low-loss optical telecommunication, for applications in future quantum information networks.Zhang et al. next used a continuous-wave coherent microwave field to control a photonic two-level system. In this system, the number of photons that could populate each of the two levels was not limited to one. The splitting frequency of the system was precisely controlled up to several gigahertz by controlling the amplitude of the microwave signals. The effect was used to control the effective coupling strength between the energy levels of the photonic molecule. Coherent spectral dynamics in the photonic molecule were investigated for a variety of microwave strengths applied to the photonic two-level system. The scientists also described the controlled amplitude and phase of the system using Rabi oscillation and Ramsey interference, while using Bloch spheres/geometric representations of the photonic two-level energy system to represent the phenomena. Microwave dressed photonic waveguides. a) When the applied microwave frequency is tuned to match the mode separation, dissipative coupling leads the two photonic levels to split into four levels. This effect is analogous to Autler–Townes splitting. When the microwave is detuned far from the photonic mode splitting, the photonic energy levels experience a dispersive effect, leading to a shift in the photonic levels. This effect is analogous to a.c. Stark shifts. b) Measured Autler–Townes splitting in the photonic molecule, where the splitting can be accurately controlled by the amplitude of the applied microwave signal. c) Measured photonic a.c. Stark shifts for a microwave signal at 4.5 GHz. Credit: Nature Photonics, doi: © 2018 Science X Network For electro-optic control of a two-level system, the photon lifetime of each energy state must be longer than the time required for the system to be driven from one state to the other. Conventional integrated photonic platforms have not met the requirements of a simultaneously long photon life-time and fast modulation so far. Electrically active photonic platforms (based on silicon, graphene and other polymers), allow fast electro-optic modulation at gigahertz frequencies but suffer from shorter photon lifetimes. However, pure electrical tuning is still highly desirable, as narrowband microwave signals offer much better control with minimal noise and scalability. , Optica , Nature Photonics On-demand storage and retrieval of light using a photonic dark mode. a) The photonic molecule is programmed to result in localized bright and dark modes. As a result, the bright mode can be accessed from the optical waveguide, while the dark mode cannot (forbidden by geometry). b) A microwave field applied to the system can induce an effective coupling between the bright and dark modes, indicated by the avoided crossing in the optical transmission spectrum. c) Light can be stored and retrieved using the bright–dark mode pair and microwave control. A microwave π pulse can be applied to transfer light from the bright to the dark mode. As the microwave is turned off, light is restricted from any external waveguide coupling. After a certain desired storage time, a second microwave π pulse retrieves the light from the dark to the bright mode. γ, γi and γex are the lifetimes of the bright optical mode, intrinsic damping and waveguide coupling rate, respectively. d) The retrieved light from the dark mode measured at different time delays, shown by the traces from top to bottom with a 0.5 ns delay increment. Inset: the extracted intensity of the retrieved light shows nearly twice the lifetime of the critically coupled bright mode. The error bars show the uncertainty in the optical intensity readout. MW, microwave; NT, normalized transmission; a.u., arbitrary units. Credit: Nature Photonics, doi: The design parameters of the coupled resonators provide space to investigate the dynamic control of two-level and multi-level photonic systems, leading to a new class of photonic technologies. The scientists envision that these findings will lead to advances in topological photonics, advanced photonic computation concepts and on-chip frequency-based optical quantum systems in the near future. Explore further The work allowed controlled writing and reading of light into a resonator, from an external waveguide to achieve on-demand photon storage and retrieval, a critical task for optical signal processing. To facilitate this experimentally, Zhang et al. applied a large DC bias voltage (15 V) to reconfigure the double-ring system into a pair of bright and dark modes. In the setup, the mode localized in the first ring provided access to the optical waveguides and became optically bright (bright mode). The other mode was localized in the second ring that was geometrically decoupled from the input optical waveguide to become optically dark. Accordingly, the scientists demonstrated coherent and dynamic control of a two-level photonic molecule with microwave fields and on-demand photon storage/retrieval through meticulous experiments in the study. The work opens a path to a new form of control on photons. The results are an initial step with potentially immediate applications in signal processing and quantum photonics. More information: Mian Zhang et al. Electronically programmable photonic molecule, Nature Photonics (2018). DOI: 10.1038/s41566-018-0317-y J. D. Joannopoulos et al. Photonic crystals: putting a new twist on light, Nature (2003). DOI: 10.1038/386143a0 José Capmany et al. Microwave photonics combines two worlds, Nature Photonics (2007). DOI: 10.1038/nphoton.2007.89 Mian Zhang et al. Monolithic ultra-high-Q lithium niobate microring resonator, Optica (2017). DOI: 10.1364/OPTICA.4.001536 Journal information: Nature Device and experimental setup detail. a) Scanning electron microscope (SEM) image of the gap between the coupled microring resonators. b) Cross-section of the optical mode profile in the ring resonator. c) Microring image of the full device showing the double ring and microwave electrodes. d) SEM image of the array of double ring devices fabricated on a single chip. Credit: Nature Photonics, doi: 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. Extended experimental setup. The device is optically pumped by a tunable telecom laser centered around 1630 nm. The light is sent through an external electro-optic modulator and polarization controllers (PLC) before coupling into the chip with a lensed fiber. The output optical signal, also coupled with a lensed fiber is sent to a 12 GHz photodetector. The converted electrical signal is directed to an oscilloscope. The microwave control signals are generated by an arbitrary wave generator (AWG) and amplified before being sent into the device. A bias T is used to allow DC control on the microresonators. An electrical isolator is used to capture the electrical reflection from the microresonators. The oscilloscope, device drive signals and modulator drive signals are all synchronized. Credit: Nature Photonics, doi: Citation: Electronically programmable photonic molecule (2018, December 21) retrieved 18 August 2019 from Microwave-controlled photonic molecule. a) The photonic molecule is realized by a pair of identical coupled optical microring resonators (resonant frequency ω1=ω2). The system has two distinct energy levels—a symmetric and an antisymmetric optical mode (indicated here by blue/blue shading for the symmetric and red/blue for the antisymmetric mode) that are spatially out of phase by π. The microwave field can interact coherently with the two-level system through the strong Pockels effect (χ(2)) of lithium niobate. b) False-colored scanning electron microscope image of the coupled microring resonators. c) Measured transmission spectrum of the photonic two-level system. The two optical modes are separated by 2μ= 2π× 7 GHz with linewidths of γ= 2π× 96 MHz corresponding to a loaded optical quality factor of 1.9 × 106. d) The resulting transmission spectra from an applied d.c. field show an anti-crossing curve due to the finite optical coupling between the two rings, which is analogous to the d.c. Stark effect in a canonical two-level system. NT, normalized transmission. Credit: Nature Photonics, doi: read more

Cinematic wave in the capitalCinematic wave in the capital

first_imgFROM the alcoves of Japenese cinema comes Hara Kiri: Death of a Samurai as a part of the rehash OF the first ever Dharamshala International film festival held in November 2012.    Representing the best of independent cinema from across the globe, the screenings are being held on the last Sunday of every month from April to September at blueFrog, the live music performance destination of New Delhi. Hara Kiri will be screened for the Delhi audience on 28 July. Also Read – ‘Playing Jojo was emotionally exhausting’So take your seats in time, get those popcorns and drink cans filled up as you go on an international film experience, right next door. Directed by highly acclaimed Japanese filmmaker Takashi Miike, Hara Kiri: Death of a Samurai is 3D drama film centering on a poverty-stricken samurai who discovers the fate of his ronin son-in-law, setting in motion a tense showdown of vengeance against the house of a feudal lord. With stunning cinematography and gripping performances, it makes for a thrilling exploration of revenge, honor, and individuality in the face of oppressive power. Also Read – Leslie doing new comedy special with Netflix’Hara-Kiri is remarkably sensitive and moving. More moving than shocking, it proceeds slowly and gracefully. A credible critique of violence rather than an exploitation of its horror.’ said A.O. Scott from New York Times. Being the official selection in the competition category at 2011 Cannes Film Festival, the first 3D film to do so, Hara Kiri went on to receive overwhelming reviews from the film fraternity.With rave reviews and accolades from all spheres, this film makes for an interesting watch.last_img read more

Bank staff plan severalday strike in JanBank staff plan severalday strike in Jan

first_imgA decision to this effect was taken by the United Forum of Bank Unions (UFBU) at their meeting, said C H Venkatchalam, General Secretary of All India Bank Employees Association (AIBEA) on Saturday. “UFBU has decided to launch a strike programme from January 7,” he said.The one-day strike on January 7 will be followed by continuous work stoppage from January 21 to 24 and an indefinite stir from March 16, he said. The meeting of UFBU expressed dissatisfaction over the “casual attitude” displayed by Indian Bank Association (which represents bank managements) towards the demand for wage revision, said Venkatchalam. Also Read – I-T issues 17-point checklist to trace unaccounted DeMO cashAIBEA, which has five lakh employee-members, is a major constituent of UFBU. The UFBU is an umbrella organisation representing nine bank employees and officer unions. The wage revision has been due since November 2012. The last bank strike on the issue was on November 12 followed by a zone-wise relay stir early this month. The unions want a 23 per cent wage hike (scaled down from 25 per cent earlier), but IBA is willing to give only 11 per cent.last_img read more