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  • richardmitnick 5:35 pm on November 30, 2019 Permalink | Reply
    Tags: , EPFL-École Polytechnique Fédérale de Lausanne, Excitons, , ,   

    From École Polytechnique Fédérale de Lausanne: “Controlling the optical properties of solids with acoustic waves” 


    From École Polytechnique Fédérale de Lausanne

    29.11.19
    Majed Chergui
    Nik Papageorgiou

    1
    Physicists from Switzerland, Germany, and France have found that large-amplitude acoustic waves, launched by ultrashort laser pulses, can dynamically manipulate the optical response of semiconductors.

    One of the main challenges in materials science research is to achieve high tunability of the optical properties of semiconductors at room temperature. These properties are governed by “excitons”, which are bound pairs of negative electrons and positive holes in a semiconductor.

    Excitons have become increasingly important in optoelectronics and the last years have witnessed a surge in the search for control parameters – temperature, pressure, electric and magnetic fields – that can tune excitonic properties. However, moderately large changes have only been achieved under equilibrium conditions and at low temperatures. Significant changes at ambient temperatures, which are important for applications, have so far been lacking.

    This has now just been achieved in the lab of Majed Chergui at EPFL within the Lausanne Centre for Ultrafast Science, in collaboration with the theory groups of Angel Rubio (Max-Planck Institute, Hamburg) and Pascal Ruello (Université de Le Mans). Publishing in Science Advances, the international team shows, for the first time, control of excitonic properties using acoustic waves. To do this, the researchers launched a high-frequency (hundreds of gigahertz), large-amplitude acoustic wave in a material using ultrashort laser pulses. This strategy further allows for the dynamical manipulation of the exciton properties at high speed.

    This remarkable result was reached on titanium dioxide at room temperature, a cheap and abundant semiconductor that is used in a wide variety of light-energy conversion technologies such as photovoltaics, photocatalysis, and transparent conductive substrates.

    “Our findings and the complete description we offer open very exciting perspectives for applications such as cheap acousto-optic devices or in sensor technology for external mechanical strain,” says Majed Chergui. “The use of high-frequency acoustic waves, as those generated by ultrashort laser pulses, as control schemes of excitons pave a new era for acousto-excitonics and active-excitonics, analogous to active plasmonics, which exploits the plasmon excitations of metals.”

    “These results are just the beginning of what can be explored by launching high-frequency acoustic waves in materials,” adds Edoardo Baldini, the lead author of the article who is currently at MIT. “We expect to use them in the future to control the fundamental interactions governing magnetism or trigger novel phase transitions in complex solids”.

    Other contributors

    University of the Basque Country
    Max Planck Institute for the Structure and Dynamics of Matter
    Simons Foundation (Flatiron Institute)
    CNRS Joint Research Units

    Funding

    Swiss National Science Foundation (NCCR:MUST and R’EQUIP), European Research Council (Advanced Grant DYNAMOX), Horizon 2020

    See the full article here .

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    EPFL campus

    EPFL is Europe’s most cosmopolitan technical university. It receives students, professors and staff from over 120 nationalities. With both a Swiss and international calling, it is therefore guided by a constant wish to open up; its missions of teaching, research and partnership impact various circles: universities and engineering schools, developing and emerging countries, secondary schools and gymnasiums, industry and economy, political circles and the general public.

     
  • richardmitnick 10:13 am on October 29, 2019 Permalink | Reply
    Tags: , EPFL-École Polytechnique Fédérale de Lausanne, , Ophthalmology, SPOT-RVC which is short for Safe Puncture Optimized Tool for Retinal Vein Cannulation., We wanted to develop a surgical method for treating retinal vein occlusion which occurs when the main vein carrying blood away from the eye is blocked., When the retinal vein is blocked by a blood clot this reduces the amount of oxygen carried to the retina and can trigger sudden vision loss.   

    From École Polytechnique Fédérale de Lausanne: “A high-precision instrument for ophthalmologists” 

    From École Polytechnique Fédérale de Lausanne

    29.10.19
    Nathalie Jollien

    1
    The high-precision miniaturized medical device, SPOT-RVC © Instant-Lab

    EPFL scientists have helped develop a microscopic glass device that doctors could use to inject medicine into retinal veins with unprecedented accuracy. Their instrument meets an important need in eye surgery, delivering exceptional stability and precision.

    A team of researchers presented a breakthrough device for eye surgery at EPFL Neuchâtel’s Research Day on 11 September. The device – called SPOT-RVC, which is short for Safe Puncture Optimized Tool for Retinal Vein Cannulation – was developed through an Innosuisse sponsored R&D project involving two EPFL Neuchâtel labs (Instant-Lab and Galatea), the Jules-Gonin Hospital of Ophthalmology in Lausanne and Ticino-based FEMTOprint as implementation partner. The team’s findings has been the subject of several publications, including one recently in the Journal of Medical Devices.

    SPOT-RVC is a high-precision, miniaturized medical device made entirely of glass. It’s just 6 cm long and 1 mm thick, and it contains a tiny fluidic channel no wider than a strand of hair as well as a sophisticated mechanism of flexible blades. Doctors can use the device to inject medicine directly into a patient’s retinal veins – something that has never before been possible.

    2
    The high-precision miniaturized medical device, SPOT-RVC © Instant-Lab

    “We wanted to develop a surgical method for treating retinal vein occlusion, which occurs when the main vein carrying blood away from the eye is blocked. There is currently no way to treat this condition – we can only treat the resulting complications,” says Professor Thomas J. Wolfensberger, the chief physician at Jules-Gonin Hospital. And those complications can be severe. When the retinal vein is blocked by a blood clot, this reduces the amount of oxygen carried to the retina and can trigger sudden vision loss. Over 16 million people around the world suffer from this condition, which mostly afflicts the elderly.

    Combining microengineering and microfluid mechanics

    Thanks to SPOT-RVC, doctors will be able to inject blood-clot-dissolving compounds directly into patients’ retinal veins safely, without damaging the surrounding tissue. “One of the biggest problems we faced is that because veins are so small and their walls so thin, it’s hard to get the needle into the vein without overpuncturing. It’s like if you want to drill a hole into a plank of wood but don’t want the hole to go all the way through,” says Dr. Charles Baur, a senior scientist at Instant-Lab who imagined this novel concept of surgical instruments.

    The researchers therefore drew on Instant-Lab’s expertise in flexible microstructures and multistable systems to engineer a microscopic device (< 1 mm in diameter) that can transition from one stable state to another very quickly – in around a millisecond – and in a controlled manner. “With this dynamic perforation mechanism that controls both the penetration force and direction of the needle, retinal veins don’t have time to deform. In addition, the penetration force is independent of the force exerted by the surgeon’s hand, which limits the risk of overpuncturing,” says Dr. Baur.

    Another innovative feature of SPOT-RVC is its microscopic, flexible channel that extends all the way down to the needle tip, enabling doctors to inject the medicine. The channel was developed using an innovative process developed by scientists at Galatea, that allows for fabricating, arbitrarily long and shaped, sealed cavities.

    And finally, the device is made of a single piece of fused silica (SiO2), thanks to the unique expertise of FEMTOprint for integrating multiple functions in a same substrate. “Since it’s monolithic, there’s no assembly required – a step that would be nearly impossible and would make it very difficult to sterilize the instrument,” says Dr. Baur. To achieve this complex monolithic integration with the required levels of precision, FEMTOprint uses ultrafast lasers 3D printing and proprietary post-processing techniques. In this context, the Galatea lab provides expertise in the understanding of ultrafast laser-matter interactions and its use for making complex micro-devices, such as optofluidics and optomechanical devices.

    Winner of the Swiss high-precision industry award

    FEMTOprint presented SPOT-RVC at the Swiss high-precision industry convention (EPHJ), which was held this past June in Geneva. The device won the 2019 Exhibitors’ Grand Prix – an encouraging start.

    For now the device is still in the prototyping stage. “We got good results from our in vitro and in vivo tests,” says Dr. Baur. “Now it is necessary to conduct preclinical trials and obtain the necessary certifications. Then we’ll move on to the production stage, which will require a fairly large investment from the industrial partner. We genuinely hope that one day the device will become a useful tool for eye surgeons.”

    Discover the mechanism in video on https://youtu.be/1ZNGuvkzNsE.

    See the full article here .

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    EPFL bloc

    EPFL campus

    EPFL is Europe’s most cosmopolitan technical university. It receives students, professors and staff from over 120 nationalities. With both a Swiss and international calling, it is therefore guided by a constant wish to open up; its missions of teaching, research and partnership impact various circles: universities and engineering schools, developing and emerging countries, secondary schools and gymnasiums, industry and economy, political circles and the general public.

     
  • richardmitnick 8:43 am on October 21, 2019 Permalink | Reply
    Tags: , EPFL-École Polytechnique Fédérale de Lausanne, The Giotto project   

    From École Polytechnique Fédérale de Lausanne: “With Giotto, artificial intelligence gets a third dimension” 

    EPFL bloc

    From École Polytechnique Fédérale de Lausanne

    21.10.19
    Sarah Aubort

    1
    The Giotto project, launched by EPFL startup Learn to Forecast, intends to revolutionize the way we use artificial intelligence. Drawing on the science of shapes, Giotto pushes AI forward by making it more reliable and intuitive in areas such as materials science, neuroscience and biology. Giotto is open-source and available free of charge on GitHub, and it’s already being used by some EPFL scientists.

    Researchers use artificial intelligence to solve complex problems, but it’s not a transparent science: AI’s computational capabilities often exceed our understanding and raise issues of reliability and trust among users. “Algorithms are becoming increasingly complex,” says Matteo Caorsi, the lead scientist at Learn to Forecast (L2F). “It’s very hard to understand how they work and thus to trust the solutions they provide or predict when they might get things wrong.”

    Shapes hidden within data

    To address this problem, L2F followed an intuitive approach based on the science of shapes. The result is Giotto, a free and open-source library that aims to revolutionize the way we use machine learning. “Humans understand shapes and colors better than numbers and equations,” says Aldo Podestà, the CEO of L2F, “which is why we think that we can use topology – the science of shapes – to build a new language between AI and users.”

    Giotto offers a toolkit that uses algorithms inspired by topology to address some of the shortcomings of machine learning. Users don’t need to be fluent in advanced mathematics, since Giotto is a turnkey method of revealing structures previously hidden within a dataset. “This new form of AI is based on graphs and their multidimensional versions, in other words, geometrical objects that can reveal essential structures within the data,” says Thomas Boys, a co-founder at L2F.

    Until now, machine learning algorithms sought performance, even if that meant depriving users of a fuller understanding of the nature of the results. “Giotto helps identify the framework underlying all relationships among the data, and this allows users to understand the data better and extract meaning from them with greater accuracy,” adds Boys. The project is named for Giotto di Bondone, the 13th-century artist who first introduced perspective into painting. L2F hopes to usher in a similar paradigm change in data science by combining machine learning with topology.

    New horizons

    To develop Giotto, its creators worked with EPFL researchers who use topology every day. This includes Professor Kathryn Hess Bellwald, the head of the Laboratory for Topology and Neuroscience. “One of Giotto’s main advantages is that, because of its user friendliness, it will be possible for scientists from all kinds of fields to use these tools as a regular part of their data science toolkit,” says Prof. Hess Bellwald. “This should lead to new insights in many different areas that one could not attain without Giotto.”

    Learn to Forecast (L2F) was founded at EPFL in 2017. Its aim is to use artificial intelligence to address a wide variety of issues. The company raised three million francs via 4FO Ventures to develop the Giotto library, and it now has 25 employees.

    For more information : https://www.giotto.ai
    Git Hub : https://github.com/giotto-learn/giotto-learn

    See the full article here .

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    Please help promote STEM in your local schools.

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    EPFL campus

    EPFL is Europe’s most cosmopolitan technical university. It receives students, professors and staff from over 120 nationalities. With both a Swiss and international calling, it is therefore guided by a constant wish to open up; its missions of teaching, research and partnership impact various circles: universities and engineering schools, developing and emerging countries, secondary schools and gymnasiums, industry and economy, political circles and the general public.

     
  • richardmitnick 12:32 pm on October 11, 2019 Permalink | Reply
    Tags: EPFL-École Polytechnique Fédérale de Lausanne, Heavy fermion materials, , The challenge is to find new materials in which the superconducting state can be easily manipulated in a device.   

    From École Polytechnique Fédérale de Lausanne: “Controlling superconducting regions within an exotic metal” 

    EPFL bloc

    From École Polytechnique Fédérale de Lausanne

    11.10.19
    Laure-Anne Pessina

    1
    Researchers at EPFL have created a metallic microdevice in which they can define and tune patterns of superconductivity. Their discovery, which holds great promise for quantum technologies of the future, has just been published in Science.

    Superconductivity has fascinated scientists for many years since it offers the potential to revolutionize current technologies. Materials only become superconductors – meaning that electrons can travel in them with no resistance – at very low temperatures. These days, this unique zero resistance superconductivity is commonly found in a number of technologies, such as magnetic resonance imaging (MRI). Future technologies, however, will harness the total synchrony of electronic behavior in superconductors – a property called the phase. There is currently a race to build the world’s first quantum computer, which will use these phases to perform calculations. Conventional superconductors are very robust and hard to influence, and the challenge is to find new materials in which the superconducting state can be easily manipulated in a device.

    EPFL’s Laboratory of Quantum Materials (QMAT), headed by Philip Moll, professor at the School of Engineering, has been working on a specific group of unconventional superconductors known as heavy fermion materials. The QMAT scientists, as part of a broad international collaboration between EPFL, the Max Planck Institute for Chemical Physics of Solids, the Los Alamos National Laboratory and Cornell University, made a surprising discovery about one of these materials, CeIrIn5.

    CeIrIn5 is a metal that superconducts at a very low temperature, only 0.4°C above absolute zero (around -273°C). The QMAT scientists, together with Katja C. Nowack from Cornell University, have now shown that this material could be produced with superconducting regions coexisting alongside regions in a normal metallic state. Better still, they produced a model that allows researchers to design complex conducting patterns and, by varying the temperature, to distribute them within the material in a highly controlled way. Their research has just been published in Science.

    To achieve this feat, the scientists sliced very thin layers of CeIrIn5 – only around a thousandth of a millimeter thick – that they joined to a sapphire substrate. When cooled, the material contracts significantly whereas the sapphire contracts very little. The resulting interaction puts stress on the material, as if it were being pulled in all directions, thus slightly distorting the atomic bonds in the slice. As the superconductivity in CeIrIn5 is unusually sensitive to the material’s exact atomic configuration, engineering a distortion pattern is all it takes to achieve a complex pattern of superconductivity. This new approach allows researchers to “draw” superconducting circuitry on a single crystal bar, a step that paves the way for new quantum technologies.

    3
    2
    The image illustrates the temperature evolution of the spatially modulated superconducting state.

    This discovery represents a major step forward in controlling superconductivity in heavy fermion materials. But that’s not the end of the story. Following on from this project, a post-doc researcher has just begun exploring possible technological applications.

    “We could, for example, change the regions of superconductivity by modifying the material’s distortion using a microactuator,” says Moll. “The ability to isolate and connect superconducting regions on a chip could also create a kind of switch for future quantum technologies, a little like the transistors used in today’s computing.”

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    EPFL campus

    EPFL is Europe’s most cosmopolitan technical university. It receives students, professors and staff from over 120 nationalities. With both a Swiss and international calling, it is therefore guided by a constant wish to open up; its missions of teaching, research and partnership impact various circles: universities and engineering schools, developing and emerging countries, secondary schools and gymnasiums, industry and economy, political circles and the general public.

     
  • richardmitnick 9:15 am on May 28, 2019 Permalink | Reply
    Tags: "EPFL researchers crack an enduring physics enigma", , EPFL-École Polytechnique Fédérale de Lausanne, ,   

    From École Polytechnique Fédérale de Lausanne: “EPFL researchers crack an enduring physics enigma” 

    EPFL bloc

    From École Polytechnique Fédérale de Lausanne

    28.05.19
    Laure-Anne Pessina

    1
    Researchers from EPFL have found the mechanism that lies behind a mysterious physics phenomenon in fluid mechanics: the fact that turbulence in fluids spontaneously self-organizes into parallel patterns of oblique turbulent bands – an example of order emerging spontaneously from chaos. In so doing, they solved a problem that had stumped generations of physicists.

    For decades, physicists, engineers and mathematicians failed to explain a remarkable phenomenon in fluid mechanics: the natural tendency of turbulence in fluids to move from disordered chaos to perfectly parallel patterns of oblique turbulent bands. This transition from a state of chaotic turbulence to a highly structured pattern was observed by many scientists, but never understood.

    At EPFL’s Emerging Complexity in Physical Systems Laboratory, Tobias Schneider and his team have identified the mechanism that explains this phenomenon. Their findings have been published in Nature Communications.

    From chaos to order

    The equations used to describe the large variety of phenomena occurring in fluid flows are well known. These equations capture the fundamental laws of physics that govern fluid dynamics, a subject taught to all physics and engineering students from undergraduate level onwards.

    But when turbulence comes into play, the solutions to the equations become non-linear, complex and chaotic. This makes it impossible, for example, to predict weather over an extended time horizon. Yet turbulence has a surprising tendency to move from chaos to a highly structured pattern of turbulent and laminar bands. This is a remarkable phenomenon, yet the underlying mechanism remained hidden in the equations until now.

    Here’s what happens: when a fluid is placed between two parallel plates, each moving in an opposite direction, turbulence is created. At first, the turbulence is chaotic, then it self-organizes to form regular oblique bands, separated by zones of calm (or laminar flows). No obvious mechanism selects the oblique orientation of the bands or determines the wavelength of the periodic pattern.

    Concealed in simple equations

    Schneider and his team solved the mystery. “As the physicist Richard Feynman predicted, the solution was not to be found in new equations, but rather within the equation that was already available to us,” explains Schneider. “Until now, researchers didn’t have powerful enough mathematical tools to verify this.”

    The researchers combined one such tool, known as dynamical systems theory, with existing theories on pattern formation in fluids and advanced numerical simulations. They calculated specific equilibrium solutions for each step of the process, enabling them to explain the transition from the chaotic to the structured state.

    “We can now describe the initial instability mechanism that creates the oblique pattern,” explains Florian Reetz, the study’s lead author. “We have thus solved one of the most fundamental problems in our field. The methods we developed will help clarify the chaotic dynamics of turbulent-laminar patterns in many flow problems. They may one day allow us to better control flows.”

    An important phenomenon
    In fluid mechanics, stripe pattern formation is important because it shows how turbulent and laminar flows are in constant competition with each other to determine the final state of the fluid, i.e., turbulent or laminar. This competition arises whenever turbulence forms, such as when air flows over a car. The turbulence starts in a small area on the car’s roof, but then it spreads – because turbulence is stronger than laminar flow in this particular case. The final state is therefore turbulent.
    When the stripe pattern forms, it means that the laminar and turbulent flows are equal in strength. However, this is very difficult to observe in nature, outside of the controlled conditions of a laboratory. This fact points to the significance of the EPFL researchers’ success in explaining a fundamental property of turbulence. Not only do their findings account for a phenomenon that can be observed in a laboratory, but they could help to better understand and control flow-related phenomena occurring in nature as well.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    EPFL campus

    EPFL is Europe’s most cosmopolitan technical university. It receives students, professors and staff from over 120 nationalities. With both a Swiss and international calling, it is therefore guided by a constant wish to open up; its missions of teaching, research and partnership impact various circles: universities and engineering schools, developing and emerging countries, secondary schools and gymnasiums, industry and economy, political circles and the general public.

     
  • richardmitnick 3:09 pm on May 7, 2019 Permalink | Reply
    Tags: "Twisting whirlpools of electrons", EPFL-École Polytechnique Fédérale de Lausanne   

    From École Polytechnique Fédérale de Lausanne: “Twisting whirlpools of electrons” 

    EPFL bloc

    From École Polytechnique Fédérale de Lausanne

    5.7.19
    Nik Papageorgiou

    1
    Using a novel approach, EPFL physicists have been able to create ultrafast electron vortex beams, with significant implications for fundamental physics, quantum computing, future data-storage, and even certain medical treatments.

    In Jules Verne’s famous classic Twenty Thousand Leagues Under the Sea, the iconic submarine Nautilus disappears into the Moskenstraumen, a massive whirlpool off the coast of Norway. In space, stars spiral around black holes; on Earth, swirling cyclones, tornadoes, and dust-devils rip across the land.

    All these phenomena have a particular shape in common: the vortex. From galaxies to stirring milk into coffee, vortices appear everywhere in nature – even in the subatomic world, when a stream of elementary particles or energy can spiral around a fixed axis like the tip of a cork-screw.

    When particles move like this, they form what we call “vortex beams”. These beams are very interesting because they imply that the particle has a well-defined orbital angular momentum, which describes the rotation of a particle around a fixed point.

    What this means is that vortex beams can give us new ways of interacting with matter, e.g. enhanced sensitivity to magnetic fields in sensors, or generate new absorption channels for the interaction between radiation and tissue in medical treatments (e.g. radiotherapy). But vortex beams also enable new channels in basic interactions among elementary particles, promising new insights into the inner structure of particles such as neutrons, protons or ions.

    The strange thing about matter is that, along with its particle nature, it also has a wave-nature. This means that we can make massive particles form vortex beams by simply modulating their wave function. This can be done with a device called a “passive phase mask”, which can be thought of as a standing obstacle in the sea. When waves at sea crash into it, their “wave-ness” shifts and they form whirlpools. So far, physicists have been using the passive phase mask method to make vortex beams of electrons and neutrons.

    But now, scientists from the lab of Fabrizio Carbone at EPFL are challenging this idea. Demonstrating for the first time that it is possible to use light to dynamically twist an individual electron’s wave function, the researchers were able to generate an ultrashort vortex electron beam and actively switching its vorticity on the attosecond (10-18 seconds) timescale.

    To do this, the team exploited one of the fundamental rules governing the interaction of particles on the nanoscale level: energy and momentum conservation. What this means is that the sum of the energies, masses and velocities of two particles before and after their collision must be the same. Such a constraint is responsible for an electron to gain orbital angular momentum during its interaction with an ad hoc prepared light field, i.e. a chiral plasmon.

    In experimental terms, the scientists fired circularly polarized, ultrashort laser pulses through a nano-hole fabricated onto a metallic film. This induced a strong, localized electromagnetic field (the chiral plasmon), and individual electrons were made to interact with it.

    The scientists used an ultrafast transmission electron microscope to monitor the resulting phase profiles of the electrons. What they discovered was that, during the interaction of the electrons with the field, the wave function of the electrons took on a “chiral modulation”; a right- or left-handed movement whose “handiness” can be actively controlled by adjusting the polarization of the laser pulses.

    2
    A schematic representation of the OAM transfer to electrons: the interaction between a pulsed electron plane wave synchronized with a chiral plasmonic field creates an OAM-carrying vortex electron wavepacket. Credit: F. Carbone, EPFL

    “There are many practical applications from these experiments,” says Fabrizio Carbone. “Ultrafast vortex electron beams can be used to encode and manipulate quantum information; the electrons’ orbital angular momentum can be transferred to the spins of magnetic materials to control the topological charge in new devices for data storage. But even more intriguingly, using light to dynamically ‘twist’ matter waves offers a new perspective in shaping protons or ion beams such as those used in medical therapy, possibly enabling new radiation-matter interaction mechanisms that can be very useful for selective tissue ablation techniques.”

    Other contributors

    Politecnico di Milano
    University of Glasgow
    Technion – Israel Institute of Technology
    Ripon College (US)
    University of Ottawa
    CNR Istituto Nanoscienze
    The Barcelona Institute of Science and Technology
    ICREA-Institució Catalana de Recerca i Estudis Avançats

    Science paper:
    Ultrafast generation and control of an electron vortex beam via chiral plasmonic near fields
    Nature Materials

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    EPFL campus

    EPFL is Europe’s most cosmopolitan technical university. It receives students, professors and staff from over 120 nationalities. With both a Swiss and international calling, it is therefore guided by a constant wish to open up; its missions of teaching, research and partnership impact various circles: universities and engineering schools, developing and emerging countries, secondary schools and gymnasiums, industry and economy, political circles and the general public.

     
  • richardmitnick 10:53 am on April 29, 2019 Permalink | Reply
    Tags: "Record solar hydrogen production with concentrated sunlight", , , , , EPFL-École Polytechnique Fédérale de Lausanne, LRESE-EPFL’s Laboratory of Renewable Energy Science and Engineering, The research team installed a 7-meter diameter parabolic mirror that concentrates solar irradiation by a factor of 1000 and drives the device. The first tests are under way.   

    From École Polytechnique Fédérale de Lausanne: “Record solar hydrogen production with concentrated sunlight” 

    EPFL bloc

    From École Polytechnique Fédérale de Lausanne

    4.29.19
    Laure-Anne Pessina

    1
    Saurabh Tembhurne, Sophia Haussener and Fredy Nandjou© Marc Delachaux / 2019 EPFL

    EPFL researchers have created a smart device capable of producing large amounts of clean hydrogen. By concentrating sunlight, their device uses a smaller amount of the rare, costly materials that are required to produce hydrogen, yet it still maintains a high solar-to-fuel efficiency. Their research has been taken to the next scale with a pilot facility installed on the EPFL campus.

    Hydrogen will play a key role in reducing our dependence on fossil fuels. It can be sustainably produced by using solar energy to split water molecules. The resulting clean energy can be stored, used to fuel cars or converted into electricity on demand. But making it reliably on a large scale and at an affordable cost is a challenge for researchers. Efficient solar hydrogen production requires rare and expensive materials – for both the solar cells and the catalyst – in order to collect energy and then convert it.

    Scientists at EPFL’s Laboratory of Renewable Energy Science and Engineering (LRESE) came up with the idea of concentrating solar irradiation to produce a larger amount of hydrogen over a given area at a lower cost. They developed an enhanced photo-electrochemical system that, when used in conjunction with concentrated solar irradiation and smart thermal management, can turn solar power into hydrogen with a 17% conversion rate and unprecedented power and current density. What’s more, their technology is stable and can handle the stochastic dynamics of daily solar irradiation.

    The results of their research have just been published in Nature Energy. “In our device, a thin layer of water runs over a solar cell to cool it. The system temperature remains relatively low, allowing the solar cell to deliver better performance,” says Saurabh Tembhurne, a co-author of the study. “At the same time, the heat extracted by the water is transferred to catalysts, thereby improving the chemical reaction and increasing the hydrogen production rate,” adds Fredy Nandjou, a researcher at the LRESE. Hydrogen production is therefore optimized at each step of the conversion process.

    The scientists used the LRESE’s unique solar simulator to demonstrate the stable performance of their device. The results from the lab-scale demonstrations were so promising that the device has been upscaled and is now being tested outdoors, on EPFL’s Lausanne campus. The research team installed a 7-meter diameter parabolic mirror that concentrates solar irradiation by a factor of 1,000 and drives the device. The first tests are under way.

    Hydrogen stations

    The scientists estimate that their system can run for over 30,000 hours – or nearly four years – without any part replacements, and up to 20 years if some parts are replaced every four years. Their solar concentrator turns and follows the sun across the sky in order to maximize its yield. Sophia Haussener, the head of the LRESE and the project lead, explains: “In sunny weather, our system can generate up to 1 kilogram of hydrogen per day, which is enough fuel for a hydrogen-powered car to travel 100 to 150 kilometers.”

    For distributed, large-scale hydrogen generation, several concentrator systems could be used together to produce hydrogen at chemical plants or for hydrogen stations. Tembhurne and Haussener are planning to take their technology from the lab to industry with a spin-off company called SoHHytec.

    Open source software

    Thanks to an open interface, it will be possible to monitor the instantaneous performance of the system.
    As part of their research, the scientists also performed a technological and economic feasibility study and developed an open-source software program called SPECDO (Solar PhotoElectroChemical Device Optimization, http://specdo.epfl.ch). This program can help engineers design components for low-cost photoelectrochemical systems for producing solar hydrogen. Additionally, they provided a dynamic benchmarking tool called SPECDC (Solar PhotoElectroChemical Device Comparison), for the comparison and assessment of all photoelectrochemical system demonstrations.
    Funding

    This research is being funded by the NanoTera project SHINE and the SNFS Starting Grant SCOUTS; the scale-up is being funded by SNSF-Bridge, the Swiss Federal Office of Energy and EPFL.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    EPFL campus

    EPFL is Europe’s most cosmopolitan technical university. It receives students, professors and staff from over 120 nationalities. With both a Swiss and international calling, it is therefore guided by a constant wish to open up; its missions of teaching, research and partnership impact various circles: universities and engineering schools, developing and emerging countries, secondary schools and gymnasiums, industry and economy, political circles and the general public.

     
  • richardmitnick 9:43 am on March 25, 2019 Permalink | Reply
    Tags: "In a new quantum simulator light behaves like a magnet", , EPFL-École Polytechnique Fédérale de Lausanne, , ,   

    From École Polytechnique Fédérale de Lausanne: “In a new quantum simulator, light behaves like a magnet” 

    EPFL bloc

    From École Polytechnique Fédérale de Lausanne

    3.25.19
    Nik Papageorgiou

    1
    Physicists at EPFL propose a new “quantum simulator”: a laser-based device that can be used to study a wide range of quantum systems. Studying it, the researchers have found that photons can behave like magnetic dipoles at temperatures close to absolute zero, following the laws of quantum mechanics. The simple simulator can be used to better understand the properties of complex materials under such extreme conditions.

    When subject to the laws of quantum mechanics, systems made of many interacting particles can display behaviour so complex that its quantitative description defies the capabilities of the most powerful computers in the world. In 1981, the visionary physicist Richard Feynman argued we can simulate such complex behavior using an artificial apparatus governed by the very same quantum laws – what has come to be known as a “quantum simulator”.

    One example of a complex quantum system is that of magnets placed at really low temperatures. Close to absolute zero (-273.15°C), magnetic materials may undergo what is known as a “quantum phase transition”. Like a conventional phase transition (e.g. ice melting into water, or water evaporating into steam), the system still switches between two states, except that close to the transition point the system manifests quantum entanglement – the most profound feature predicted by quantum mechanics. Studying this phenomenon in real materials is an astoundingly challenging task for experimental physicists.

    But physicists led by Vincenzo Savona at EPFL have now come up with a quantum simulator that promises to solve the problem. “The simulator is a simple photonic device that can easily be built and run with current experimental techniques,” says Riccardo Rota, the postdoc at Savona’s lab who led the study. “But more importantly, it can simulate the complex behavior of real, interacting magnets at very low temperatures.”

    The simulator may be built using superconducting circuits – the same technological platform used in modern quantum computers. The circuits are coupled to laser fields in such a way that it causes an effective interaction among light particles (photons). “When we studied the simulator, we found that the photons behaved in the same way as magnetic dipoles across the quantum phase transition in real materials,” says Rota. In short, we can now use photons to run a virtual experiment on quantum magnets instead of having to set up the experiment itself.

    “We are theorists,” says Savona. “We came up with the idea for this particular quantum simulator and modelled its behavior using traditional computer simulations, which can be done when the quantum simulator addresses a small enough system. Our findings prove that the quantum simulator we propose is viable, and we are now in talks with experimental groups who would like to actually build and use it.”

    Understandably, Rota is excited: “Our simulator can be applied to a broad class of quantum systems, allowing physicists to study several complex quantum phenomena. It is a truly remarkable advance in the development of quantum technologies.”

    Science paper:
    Riccardo Rota, Fabrizio Minganti, Cristiano Ciuti, Vincenzo Savona.
    “Quantum Critical Regime in a Quadratically Driven Nonlinear Photonic Lattice”
    Physical Review Letters

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    EPFL campus

    EPFL is Europe’s most cosmopolitan technical university. It receives students, professors and staff from over 120 nationalities. With both a Swiss and international calling, it is therefore guided by a constant wish to open up; its missions of teaching, research and partnership impact various circles: universities and engineering schools, developing and emerging countries, secondary schools and gymnasiums, industry and economy, political circles and the general public.

     
  • richardmitnick 10:28 am on March 4, 2019 Permalink | Reply
    Tags: , , , Directed evolution, Engineer synthetic nanoparticles as optical biosensors, EPFL-École Polytechnique Fédérale de Lausanne, ,   

    From École Polytechnique Fédérale de Lausanne: “Directed evolution builds nanoparticles” 

    EPFL bloc

    From École Polytechnique Fédérale de Lausanne

    3.3.19
    Nik Papageorgiou

    1
    Directed evolution is a powerful technique for engineering proteins. EPFL scientists now show that it can also be used to engineer synthetic nanoparticles as optical biosensors, which are used widely in biology, drug development, and even medical diagnostics such as real-time monitoring of glucose.

    The 2018 Nobel Prize in Chemistry went to three scientists who developed the method that forever changed protein engineering: directed evolution. Mimicking natural evolution, directed evolution guides the synthesis of proteins with improved or new functions.

    First, the original protein is mutated to create a collection of mutant protein variants. The protein variants that show improved or more desirable functions are selected. These selected proteins are then once more mutated to create another collection of protein variants for another round of selection. This cycle is repeated until a final, mutated protein is evolved with optimized performance compared to the original protein.

    Now, scientists from the lab of Ardemis Boghossian at EPFL, have been able to use directed evolution to build not proteins, but synthetic nanoparticles. These nanoparticles are used as optical biosensors – tiny devices that use light to detect biological molecules in air, water, or blood. Optical biosensors are widely used in biological research, drug development, and medical diagnostics, such as real-time monitoring of insulin and glucose in diabetics.

    “The beauty of directed evolution is that we can engineer a protein without even knowing how its structure is related to its function,” says Boghossian. “And we don’t even have this information for the vast, vast majority of proteins.”

    Her group used directed evolution to modify the optoelectronic properties of DNA-wrapped single-walled carbon nanotubes (or, DNA-SWCNTs, as they are abbreviated), which are nano-sized tubes of carbon atoms that resemble rolled up sheets of graphene covered by DNA. When they detect their target, the DNA-SWCNTs emit an optical signal that can penetrate through complex biological fluids, like blood or urine.

    2
    General principle of the directed evolution approach applied to the nanoparticle DNA-SWCNT complexes. The starting complex is a DNA-SWCNT with a dim optical signal. This is evolved through directed evolution: (1) random mutation of the DNA sequence; (2) wrapping of the SWCNTs with the DNA and screening of the complex’s optical signal; (3) selection of the DNA-SWCNT complexes exhibiting an improved optical signal. After several cycles of evolution, we can evolve DNA-SWCNT complexes that show enhanced optical behavior. Credit: Benjamin Lambert (EPFL)

    Using a directed evolution approach, Boghossian’s team was able to engineer new DNA-SWCNTs with optical signals that are increased by up to 56% – and they did it over only two evolution cycles.

    “The majority of researchers in this field just screen large libraries of different materials in hopes of finding one with the properties they are looking for,” says Boghossian. “In optical nanosensors, we try to improve properties like selectivity, brightness, and sensitivity. By applying directed evolution, we provide researchers with a guided approach to engineering these nanosensors.”

    The study [Chemical Communications] shows that what is essentially a bioengineering technique can be used to more rationally tune the optoelectronic properties of certain nanomaterials. Boghossian explains: “Fields like materials science and physics are mostly preoccupied with defining material structure-function relationships, making materials that lack this information difficult to engineer. But this is a problem that nature solved billions of years ago – and, in recent decades, biologists have tackled it as well. I think our study shows that as materials scientists and physicists, we can still learn a few pragmatic lessons from biologists.”
    Funding

    SNSF AP Energy Grant

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    EPFL campus

    EPFL is Europe’s most cosmopolitan technical university. It receives students, professors and staff from over 120 nationalities. With both a Swiss and international calling, it is therefore guided by a constant wish to open up; its missions of teaching, research and partnership impact various circles: universities and engineering schools, developing and emerging countries, secondary schools and gymnasiums, industry and economy, political circles and the general public.

     
  • richardmitnick 12:46 pm on February 20, 2019 Permalink | Reply
    Tags: , EPFL-École Polytechnique Fédérale de Lausanne, ,   

    From École Polytechnique Fédérale de Lausanne: “The holy grail of nanowire production” 

    EPFL bloc

    From École Polytechnique Fédérale de Lausanne

    2.20.19
    Laure-Anne Pessina

    1
    EPFL researchers have found a way to control and standardize the production of nanowires on silicon surfaces. This discovery could make it possible to grow nanowires on electronic platforms, with potential applications including the integration of nanolasers into electronic chips and improved energy conversion in solar panels.

    Nanowires have the potential to revolutionize the technology around us. Measuring just 5-100 nanometers in diameter (a nanometer is a millionth of a millimeter), these tiny, needle-shaped crystalline structures can alter how electricity or light passes through them.

    They can emit, concentrate and absorb light and could therefore be used to add optical functionalities to electronic chips. They could, for example, make it possible to generate lasers directly on silicon chips and to integrate single-photon emitters for coding purposes. They could even be applied in solar panels to improve how sunlight is converted into electrical energy.

    Up until now, it was impossible to reproduce the process of growing nanowires on silicon semiconductors – there was no way to repeatedly produce homogeneous nanowires in specific positions. But researchers from EPFL’s Laboratory of Semiconductor Materials, run by Anna Fontcuberta i Morral, together with colleagues from MIT and the IOFFE Institute, have come up with a way of growing nanowire networks in a highly controlled and fully reproducible manner. The key was to understand what happens at the onset of nanowire growth, which goes against currently accepted theories. Their work has been published in Nature Communications.

    2
    Two different configurations of the droplet within the opening – hole fully filled and partially filled and bellow illustration of GaAs crystals forming a full ring or a step underneath the large and small gallium droplets.

    “We think that this discovery will make it possible to realistically integrate a series of nanowires on silicon substrates,” says Fontcuberta i Morral. “Up to now, these nanowires had to be grown individually, and the process couldn’t be reproduced.”

    Getting the right ratio

    The standard process for producing nanowires is to make tiny holes in silicon monoxide and fill them with a nanodrop of liquid gallium. This substance then solidifies when it comes into contact with arsenic. But with this process, the substance tends to harden at the corners of the nanoholes, which means that the angle at which the nanowires will grow can’t be predicted. The search was on for a way to produce homogeneous nanowires and control their position.

    Research aimed at controlling the production process has tended to focus on the diameter of the hole, but this approach has not paid off. Now EPFL researchers have shown that by altering the diameter-to-height ratio of the hole, they can perfectly control how the nanowires grow. At the right ratio, the substance will solidify in a ring around the edge of the hole, which prevents the nanowires from growing at a non-perpendicular angle. And the researchers’ process should work for all types of nanowires.

    “It’s kind of like growing a plant. They need water and sunlight, but you have to get the quantities right,” says Fontcuberta i Morral.

    This new production technique will be a boon for nanowire research, and further samples should soon be developed.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    EPFL campus

    EPFL is Europe’s most cosmopolitan technical university. It receives students, professors and staff from over 120 nationalities. With both a Swiss and international calling, it is therefore guided by a constant wish to open up; its missions of teaching, research and partnership impact various circles: universities and engineering schools, developing and emerging countries, secondary schools and gymnasiums, industry and economy, political circles and the general public.

     
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