efectele unghiului de tragere și deplasarea preliminară;Până în prezent, o mână de adezivi asemănători gecko-ului inspirat de firele de atașare în formă de spatula au fost sugerate pe baza geometriei pană și a clapetei elementelor de contact
Armata slovacă intenționează să-și modernizeze echipamentul în următorul deceniu, inclusiv vehicule noi de luptă cu patru roți
Oamenii de stiinta de la Laboratorul Ames al Departamentului de Energie din SUA au descoperit un nou proces de imbracare a metalelor sub un singur strat de grafit care pot conduce la proprietati noi si mai bine controlate pentru aceste tipuri de materiale
| Posted: Dec 18, 2017 | |
Getting under graphite’s skin(Nanowerk News) Scientists at the U.S. Department of Energy’s Ames Laboratory have discovered a new process to sheathe metal under a single layer of graphite which may lead to new and better-controlled properties for these types of materials (Carbon, „Defect-mediated, thermally-activated encapsulation of metals at the surface of graphite”). |
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| A „mesa” of dysprosium, draped with a single layer of graphene. Research from Ames Laboratory suggests that this method will work with a wide variety of metal and graphite combinations, opening up the possibility of diverse applications including quantum computing, solar cells, catalysis, and sensing. (Image: Ames Laboratory) | |
| Graphene—two-dimensional graphite—was first produced in 2004, and because electrons move rapidly along its surface, holds great promise as a useful material in applications as diverse as quantum computing, solar cells, catalysis, and sensing. In order for graphene to live up to that potential, fundamental discovery science at Ames Laboratory is working to master its assembly in combination with other materials—a tricky, delicate process performed in ultra-high vacuum lab environments at the atomic scale. | |
| The researchers encapsulated dysprosium, a magnetic rare-earth metal, by bombarding the top layer of bulk graphite with ions to create defects on its surface, followed by high-temperature deposition of the metal. It resulted in “mesas” or islands of dysprosium underneath a single layer of graphene. The formations are significantly different than anything the Laboratory’s two-dimensional materials experts have ever seen. | |
| “It’s well-known that certain metals can be embedded between bulk graphite layers,” said Research Assistant Ann Lii-Rosales. “But these mesas form at the top graphite surface only, and they are pure metal composed of multilayers, which is a first. The combined properties of the metal plus graphene may be very different than other, previously produced materials. That’s something we’re exploring now.” | |
| The researchers were also able to achieve the same mesa-like formations with two transition metals, ruthenium and copper. | |
| “That suggests we have a very adaptable recipe for producing this kind of surface material, which makes its discovery very exciting in terms of potential applications,” said Pat Thiel, an Ames Laboratory scientist and Distinguished Professor of Chemistry and Materials Science and Engineering at Iowa State University. “If we can control the process so that we can deliberately pattern the formation of these little metal slabs, perhaps we can harness and control their magnetic and electronic properties.” |
| Source: Ames Laboratory |
Caracteristicile cheie ale echipamentelor de luptă individuale de înaltă tehnologie pentru infanteriștii ruși care au fost expuse recent.
MOF sunt materiale compuse care sunt fabricate din ioni și liganzi pentru a face structuri tridimensionale. MOF-urile sunt în mod obișnuit folosite pentru a stoca gaze și pentru a separa și purifica substanțele chimice, dar oamenii de știință speră că noua lor descoperire ar putea duce la folosirea MOF pentru a face materiale fotoactive, cum ar fi celulele solare.
Profesorul Ravi Silva, directorul Institutului de Tehnologie Advance, a declarat: „Cadrele organice din metal au câștigat un interes extraordinar de târziu pentru potențialul lor de a fi utilizate pentru stocarea gazului, pentru detectarea și cataliza – dar este clar că acestea ar putea fi utilizate pentru mult mai mult.
| Posted: Dec 15, 2017 | |
Record high photoconductivity for new metal-organic framework material(Nanowerk News) An international team of scientists, from the University of Surrey, University of São Paulo (Brazil), the University of Warwick and the University of Grenoble-Alpes (France), has created a new metal-organic framework (MOF) that has shown record-high photo-conductivity levels for a material of its type. |
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| A representation of MOF-CoNDI-py-2 crystal structure including its unit cell obtained by single-crystal XRD. Pink = cobalt, grey = carbon, white = hydrogen, blue = nitrogen and red = oxygen. The unit cell belongs to a C2/c monoclinic space group, water was modelled at 1/4 occupancy and its hydrogens are not shown for clarity. The structure shows the NDI-py molecules oriented in a layered fashion. The distances between NDI-py entities are 9.43 Å along the c-axis, 9.57 Å along the b-axis and 11.10 Å through the metal cluster. (© NPG) | |
| The team published its findings in Nature Communications („Electrical conduction modulated by light in a cobalt and naphthalene diimide metal-organic framework”) where it reported that its MOF had a responsivity rate of 2.5 x 105 amperes per watt. The team’s MOF was made by using cobalt (II) ions and naphthalene diimides and acid ligands. | |
| MOFs are compound materials that are made of ions and ligands to make 3 dimensional structures. MOFs are typically used to store gas and to separate and purify chemicals, but the scientists hope that their new discovery could lead to MOFs being used to make photoactive materials such as solar cells. | |
| Professor Ravi Silva, Director of the Advance Technology Institute, said: “Metal Organic Frameworks have been gaining a tremendous amount of interest of late for their potential to be used for gas storage, sensing and catalysis – but it is clear that they could be used for so much more. | |
| “This is a great example of how collaborating on an international scale can result in truly exciting discoveries that have the potential to change the direction of a number of industries.” |
| Source: University of Surrey |
demonstrează că este posibil ca, în principiu, să se regleze conductivitatea termică a materialelor nanostructurate cu un grad ridicat de precizie, însă materialele în curs de dezvoltare care permit controlul precis al transferului termic sunt doar începutul. au dezvaluit concepte interesante pentru construirea de materiale izolante mai eficiente din punct de vedere energetic
| Posted: Dec 15, 2017 | |
Nanostructures control heat transfer: Researchers demonstrate new concepts for heat management(Nanowerk News) For the first time, Prof. Dr. Markus Retsch and his research group at the University of Bayreuth have succeeded in precisely controlling temperature-dependent thermal conductivity with the help of polymer materials. These advanced functional materials – initially produced for laboratory experiments – have now been presented in the journal Science Advances(„Tailor-made temperature-dependent thermal conductivity via interparticle constriction”). The findings are of great relevance to the development of new concepts of thermal insulation. |
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| An electron microscope image displaying the regular nanostructure of a photonic crystal. Scale bar: 5 micrometres. (Image: Markus Retsch) | |
From butterfly wings to new functional materials |
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| The polymer materials that allow thermal conductivity to be controlled are photonic crystals. They often give butterflies, beetles, and other insects dazzling colours and have mainly been investigated due to their optical effects. Prof. Dr. Markus Retsch, Lichtenberg Junior Professor of Polymer Systems, and his doctoral student Fabian Nutz (M.Sc.) have developed four different methods to control temperature-dependent heat transfer in such photonic crystals. | |
| These methods exploit the fact that polymer nanomaterials become more heat-permeable once they lose their nanostructure by crossing a certain temperature threshold. That is when the thermal conductivity of the photonic crystals skyrockets to a level that is two or three times as high as it was before. On this basis, clearly defined effects on thermal transfer can be achieved via changes in the nanostructure of the crystals. | |
Film formation increases thermal conductivity |
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| The research of the scientists in Bayreuth has shown that the temperature at which thermal conductivity jumps to a higher level depends crucially on the composition of the nanoparticles that make up the photonic crystals. This temperature can be precisely adjusted by incorporating a plasticizer into the polymer structure. Whether thermal conductivity changes within a wide or narrow temperature range when the temperature rises can also be precisely controlled: doing so only requires nanoparticles which are similar in size but which differ with regard to plasticizer content to be equally mixed. This leads to a gradual loss of the nanostructure across a wide temperature range. Consequently, the increase in thermal conductivity also spans a larger temperature range. | |
| In addition, by using a layered structure, the researchers also managed to transform the continuous increase into a multi-level increase in conductivity. By adjusting the thickness of individual crystal layers, one can also precisely influence the conductivity level that is reached at the respective level. | |
Potential for energy technology and thermal management |
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| „These research findings demonstrate that it is possible in principle to regulate thermal conductivity in nanostructured materials with a high degree of precision. However, developing materials that enable thermal transfer to be precisely controlled is only the beginning. Our findings to date are very encouraging and have revealed interesting concepts for constructing more energy efficient insulation materials. In the long term, these concepts could be valuable for the development of thermal transistors or diodes,” Prof. Retsch explained. | |
| He did, however, point to one obstacle that must still be overcome: the increase in thermal conductivity – as regulated in the four methods developed by the team – is irreversible. This means that the conductivity remains at the level that is reached even when the temperature sinks again. „Constructing nanosystems that enable thermal transfer to be reversibly controlled is a difficult yet exciting and central task for further research in this field,” said Prof. Retsch. |
| Source: University of Bayreuth |
Agenția de Apărare Avansată a Proiectelor de Cercetare (DARPA) Biroul de Tehnologie Tactică (TTO);DARPA este interesat atât de soluții integrate, cât și de tehnologii noi de componente capabile de maparea in-situ și de navigarea terenurilor accidentate și dinamice
Acest material trece printr-o tranziție de fază structurală la o temperatură critică de tranziție (200 Kelvin), unde structura cristalină se schimbă de la cubică la tetragonală. Întrebarea este: ce conduce această tranziție și cum ar putea fi legată de structura și interacțiunile electronice?poate fi un precursor al superconductivității topologice mult timp căutate.
| Posted: Dec 14, 2017 | |
The first three-dimensional quantum liquid crystal(Nanowerk News) Scientists discovered an entirely new class of novel electronic structures. They discovered a liquid crystal-like quantum phase of matter in a 3-D material. The onset of this phase at the transition temperature is very subtle, yet, like a rudder steering a large ship, it drives a much larger effect—a structural phase transition (Science, „A parity-breaking electronic nematic phase transition in the spin-orbit coupled metal Cd2Re2O7„). |
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| Using optical second harmonic generation spectroscopy, scientists discovered a new state of matter. The patterns show reflected laser light at twice the initial laser frequency observed when illuminating the metal Cd2Re2O7. The patterns were collected from Cd2Re2O7 crystals at temperatures that were above (left) and below (right) a structural phase transition temperature (Tc), which occurs at 200 Kelvin. Scientist have concluded that the low-temperature pattern arises from a 3-D quantum liquid crystal. (Image: David Hsieh, California Institute of Technology) | |
| This discovery represents a quantum analog of classical 3-D liquid crystals. These new structures are among those that are observed as a consequence of competing interactions in 3-D metals. The competitions lead to phenomena such as ferromagnetism, which leads to the formation of permanent magnets, and superconductivity that allows electrical current to flow with zero resistance. This new class of materials may have applications in ultrafast computers. | |
| The spatial arrangement of atoms and electrons in a material is often characterized by its symmetry, which has an important role in determining the electronic properties of the material. In materials where conduction electrons are strongly interacting, it is possible for electronic configurations to exhibit a different symmetry than the underlying crystal lattice. | |
| The material Cd2Re2O7 is a poor metal characterized by strong electron-electron interactions and coupling between the electron’s spin orientation and orbital motion in atoms. | |
| This material undergoes a structural phase transition at a critical transition temperature (200 Kelvin) where the crystal structure changes from cubic to tetragonal. The question is, what drives this transition and how might it be related to the electronic structure and interactions? | |
| Researchers obtained patterns of reflected light by illuminating a Cd2Re2O7 crystal with a laser and then collecting the reflected light that has been converted to twice the frequency of the initial laser. Changes in the pattern led scientists to conclude that the temperature-dependent phase transition is driven by an unusual electronic liquid crystalline (nematic) order that spontaneously breaks certain types of symmetry (rotational and inversion) in the crystal. | |
| Scientists also demonstrated that the structural transformation follows, or is subject to, the electronic transition rather than the more commonly observed process where a structural transformation changes the electronics. Such nematic order was theoretically predicted to appear in correlated metals with strong spin-orbit coupling and may be a precursor to long-sought topological superconductivity. |
| Source: Department of Energy, Office of Science | |
Știința și tehnologia modernă au dezvoltat noi tipuri de materie cu proprietăți nefamiliare și ocazional utile. Materialele cunoscute sub denumirea de „gheață de spin” oferă un tip complet nou de magnetism, incluzând curenți de încărcături magnetice sau „monopoluri” și, prin urmare, un echivalent magnetic de energie electrică – „magnetricitatea”.
| Posted: Dec 14, 2017 | |
Long-ranged patterns formed in water and magnets(Nanowerk News) Modern science and technology has developed new types of matter with unfamiliar and occasionally useful properties. The materials known as “spin ice” offer a completely new type of magnetism, including currents of magnetic charges or “monopoles” and hence a magnetic equivalent of electricity – “magnetricity”. |
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| The “spins” that form “spin ice” are like atom-sized compass-needles that may be represented as arrows. The “ice” in “spin ice” refers to a deep theoretical connection with the properties of familiar ice, or solid water, H2O. If one were to place a hydrogen atom (H) on the end of every spin arrow in ice, then one would generate a pattern of H-atoms in water ice. | |
| New research (Nature Communications, „Harmonic phase in polar liquids and spin ice”) at the London Centre for Nanotechnology and Department of Physics & Astronomy, UCL, has revealed a further deep connection between the properties of spin ice ice and those of water in its more important liquid state, so crucial to life on earth. | |
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| How a central molecule in a polar liquid such as water, or a spin in spin ice, orients the other molecules or spins around it. (Image: LCN) | |
| Water is a so-called “polar liquid” – each water molecule is an electrical dipole, with a positive charge at one end and a negative charge at the other. This is revealed, for example, when a stream of tap water is deflected by a pen that has been charged with static electricity. However, the dipoles in polar liquids like water do not point in random directions but in fact form subtle patterns over extremely long distances. | |
| The new research has shown that the same long-ranged patterns that form in polar liquids are also formed by the spins in spin ice. In both cases the patterns are described mathematically by so-called “harmonic” functions. Hence polar liquids, including water, and spin ice have been collectively referred to as “harmonic” phases. Here a “phase” is a term used to describe different portions of matter that share the same property. | |
| The author of the work, LCN Professor Steve Bramwell, comments “it’s remarkable to discover that the same long-ranged patterns form in an exotic magnet—spin ice—and in polar liquids such as water: this should help us to predict new properties of both types of material.” | |
| The patterns formed by the molecular dipoles in polar liquids and the spins in spin ice can be visualised if one imagines oneself “sitting” on a particular dipole or spin. Then the pattern looks like the familiar pattern of iron filings that forms around a bar magnet. As the central dipole or spin moves, then this pattern moves with it. |
| Source: London Centre for Nanotechnology |
prin crearea de capcane moleculare prin modificarea chimică a materialelor din cadrul metalelor-organice (MOF). Punctele de legare („cârlige” chimice) sunt adăugate la acest material foarte poros, cu suprafață mare. Locurile de legare au azot reactiv care se poate lega de iodurile organice. Capcana a avut o capacitate ridicată de iodură de metil – de peste trei ori mai mare decât adsorbantul industrial folosit în prezent în condiții identice.
| Posted: Dec 14, 2017 | |
Molecular mousetraps capture more nuclear waste(Nanowerk News) At nuclear power plants and legacy waste sites, a particularly difficult-to-capture hazard is radioactive organic iodides. These compounds are made of hydrocarbons and iodine. In this work, scientists modified cage-like molecules called metal-organic frameworks (MOF). They added small “hooks” inside the cages. The modified MOFs were more than three times more effective at capturing radioactive organic iodides than the leading materials used by the U.S. nuclear fuel industry. Also, these traps were recyclable, unlike other adsorbents (Nature Communications, „Capture of organic iodides from nuclear waste by metal-organic framework-based molecular traps”). |
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| Chemically modified metal-organic frameworks (MOF) are over three times more effective at capturing radioactive iodine compounds than current industrial methods. The schematic shows the design and function of this recyclable MOF trap. First, a porous and robust MOF (yellow rods and purple balls) is modified by attaching a functional chemical “hook” (y-shaped gray molecule) inside its porous structure. The modified MOF has a high capacity for radioactive organic iodides (green) because the iodine binds strongly with the chemical “hook.” The original MOF starting material can be recovered by acid (red) washing and reused multiple times, unlike other adsorbents. (Image: Jing Li, Rutgers University) | |
| The modified MOF has a high capture capacity, stability, recyclability, and low cost. It holds promise for effective capture of a difficult byproduct from nuclear reactors. Further, this study revealed that through chemical modification, MOFs could be tuned to capture specific molecules. Molecular tuning of MOFs has potential, broad impact in the chemical industry. | |
| Since the 1980s, research has focused on containment of radioactive iodine, associated with nuclear energy and legacy environmental sites, because it is long-lived and can be incorporated into the human body, where it is linked with cancer. Radioactive organic iodide is particularly difficult to capture and sequester and thus tends to more easily leak into the environment. | |
| Effective capture of radioactive organic iodides (such as methyl iodide) remains a significant challenge due to the drawbacks of currently used adsorbents. These drawbacks include low uptake capacity, high cost, and non-recyclability. | |
| This work demonstrates a general approach to address this challenge by creating molecular traps through chemical modification of metal-organic framework (MOF) materials. Binding sites (chemical “hooks”) are added to this highly porous, high surface area material. The binding sites have reactive nitrogen that can bind to the organic iodides. The trap exhibited a high methyl iodide capacity—over three times higher than the currently used industrial adsorbent under identical conditions. | |
| Also, these new MOFs advantageously serve as good adsorbents at lower temperatures. Furthermore, the MOF adsorbent can be recycled multiple times without loss of capacity, unlike other known industrial adsorbents. The team investigated the capture mechanism by experimental and theoretical methods. | |
| Their work verified that binding is occurring at the “hook” sites in the MOF. Due to its chemical and thermal stability, high capture efficiency, and low cost, the new MOF adsorbent demonstrates promise for industrial radioactive organic iodine capture from nuclear energy or treatment of legacy environmental clean-up sites. |
| Source: Department of Energy, Office of Science |
oamenii de știință au explorat noi straturi de acoperire care pot respinge apa. Acum, o echipă a dezvoltat o cale de a direcționa unde se duce apa când este împins.
| Posted: Dec 13, 2017 | |
Creating surfaces that repel water and control its flow(Nanowerk News) To prevent water and ice from making our shoes soggy, frosting our car windows and weighing down power lines with icicles, scientists have been exploring new coatings that can repel water. Now one team has developed a way to direct where the water goes when it’s pushed away. |
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| Their report appears in the journal ACS Applied Materials & Interfaces („Superhydrophobic, Low-Hysteresis Patterning Chemistry for Water-Drop Manipulation”). | |
| Repelling water droplets and controlling their flow depends on water maintaining its spherical shape. | |
| Water-repelling, or superhyrdophobic, materials are already commercially available. But when blown by wind or subjected to a slight tilt, the water droplets on these surfaces will glide away in a direction determined by the initial nudge. To gain better control over the flow of water on superhydrophobic materials, scientists have been etching paths into coatings for the liquid to follow. And although water will take the designated path, it can leave behind a wet trail. | |
| Previous studies suggest that on these paths, rolling droplets have a different contact angle at the front and back– they’re rounded in front but flatter in the back – and this causes the wet residue. Thomas McCarthy and colleagues wanted to address this shortcoming by aiming for more rounded droplets. | |
| The researchers started with superhydrophobic silicon wafers, in which they cut straight, circular and wavy tracks using photolithography. Then they exposed the material to an oxygen plasma cleaner and treated it with a vapor of silicone nanofilaments to make the tracks hydrophobic. This novel step was critical for keeping water droplets’ spherical shape and minimizing the difference in the front and back contact angles. | |
| Testing showed that water flowed along the designated paths without leaving a trace. Watch this Headline Science video to see how the material works. |
| Source: American Chemical Society |
