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News Article | April 13, 2016
Site: www.cemag.us

Researchers involved in an international study, in which the UPV/EHU-University of the Basque Country has participated, have stabilized chains of more than 6,400 carbon atoms using double-walled nanotubes In a study, in which researchers in the UPV/EHU's Nano-Bio Spectroscopy Group led by Professor Ángel Rubio have participated, a new route has been developed to produce carbyne (infinitely long carbon chains whose mechanical properties surpass those of diamond and graphene) by using double-walled carbon nanotubes to protect the carbon chain due to its extreme instability in ambient conditions. The results of the study have been published in the journal Nature Materials. Elemental carbon appears in many different forms, some of which are very well-known and have been thoroughly studied: diamond, graphite, graphene, fullerenes, nanotubes and carbyne. Within this "carbon family," carbyne (a truly one-dimensional carbon structure) is the only one that has not been synthesized until now, despite having been studied for more than 50 years. Organic chemists across the world had been trying to synthesize increasingly longer carbyne chains by using stabilizing agents; the longest chain obtained so far (achieved in 2010) was 44 carbon atoms. A research group at the University of Vienna, led by Professor Thomas Pichler, has presented a new, simple means for stabilizing carbon chains with a record-breaking length of over 6,400 carbon atoms. They have thus broken the previous record by more than two orders of magnitude. To do this, they used the confined space inside a double-walled carbon nanotube as a nano-reactor to make the ultra-long carbon chains grow and also to provide the chains with great stability. This stability is tremendously important for future applications. The work carried out in collaboration with various highly prominent research groups worldwide, including the UPV/EHU's Nano-Bio Spectroscopy research Group led by Rubio, has unambiguously confirmed the existence of these chains by means of structural and optical probes. The researchers have presented their study in the latest edition of the prestigious Nature Materials journal. According to the researchers, the direct experimental proof of the confined, ultra-long carbon chains, which are two orders of magnitude longer than the previously proven ones, can be seen as a promising step towards the final objective to obtain perfectly linear carbon chains. Theoretical studies have shown that after having made these linear chains grow inside the carbon nanotube, the hybrid system could have a metallic nature due to the load transfer from the carbon nanotubes towards the chain, although both the nanotube and the chain are vacuum semiconductors. So it is possible to control the electronic properties of this hybrid system. Therefore, this new system is not only interesting from the chemical point of view, it could also be very important in the field of nano devices. According to theoretical models, carbyne has mechanical properties that are unmatched by any known material, as it even outperforms the mechanical resistance and flexibility properties of graphene and diamond. Furthermore, its electronic properties are pointing towards new nano-electronic applications, such as in the development of new magnetic semiconductors, high power density batteries, or in quantum spin transport electronics (spintronics). However, the researchers point out that to do this it would be necessary to extract these ultra-long, linear carbon chains from the double-walled nanotube containing them and stabilize them in some liquid environment. Source: University of the Basque Country

The thesis, titled "Computational intelligent methods for trusting in social networks," produced by the computer engineer David Núñez in the Computational Intelligence Group at the UPV/EHU's Faculty of Computing, falls within the framework of the European research project Social and Smart (SandS). A part of the project focuses its attention on user interaction with smart domestic appliances linked to a smart module. These are household appliances (systems) to which the user describes in ordinary language the problem that he/she wants to solve (such as "making bread," "removing a stain from a pair of trousers," etc. depending on the type of household appliance). The system analyses the problem that needs to be solved and searches the database to see whether there is a solution (recipe) for the problem described by the user. If one exists, it is provided, and if not, the system forwards the description of the problem to an intelligent module so that a new solution can be produced and then passed on to the user. The user can execute the proposed solution or else readjust its parameters. Once the execution of the problem has been completed, the user will express his/her satisfaction with the result obtained. The users can communicate with each other over the system's social network and propose recipes that can be evaluated by other users. The thesis by Núñez has provided new intelligent techniques in the area of social networks. Specifically, he has covered three lines of research in this area: trust, the recommendation systems and the maximising of influence. The first line of research seeks to predict the trust that a user will place in another person belonging to her social environment on the basis of the opinions that other contacts have expressed about the target user. The researcher has developed some tools for predicting trust that are more straightforward than the ones found in the literature, and are more algebra-based. The second line of research focuses on the systems of recommendation, and two experiments have been carried out. The first is linked to the generating of recipes for making bread in a smart bread maker. An attempt has been made to simulate the prediction of the bread recipe (solution of the problem) on the basis of the satisfaction expressed (description of the problem), and even to predict satisfaction (solution of the problem) on the basis of a recipe provided (description of the problem). The second task in this second line of research has endeavoured to make recommendations about products. The recommendation is based on the previous evaluations of the users. What is being proposed are techniques based on the Web of Trust of the target user to whom one wishes to make a recommendation and also on similarities between users and their means of evaluation. The third line of research is related to maximising influence. The aim of this line is to detect what would be the minimum set of users of a social network that is capable of influencing the maximum possible number of users of the network. "We have come up with a new algorithm that improves the algorithm that exists in the literature in terms of time—the classical Greedy method," explained David Núñez. "Our method has succeeded in getting closer to the optimum like the Greedy one, but does so more rapidly." Explore further: Who goes there? Verifying identity online More information: J. David Nuñez-Gonzalez et al, A new heuristic for influence maximization in social networks, Logic Journal of IGPL (2016). DOI: 10.1093/jigpal/jzw048

Home > Press > Quantum effects affect the best superconductor: Quantum effects explain why hydrogen sulphide is a superconductor at record-breaking temperatures Abstract: The theoretical results of a piece of international research published in Nature, whose first author is Ion Errea, a researcher at the UPV/EHU and DIPC, suggest that the quantum nature of hydrogen (in other words, the possibility of it behaving like a particle or a wave) considerably affects the structural properties of hydrogen-rich compounds (potential room-temperature superconducting substances). This is in fact the case of the superconductor hydrogen sulphide: a stinking compound that smells of rotten eggs, which when subjected to pressures a million times higher than atmospheric pressure, behaves like a superconductor at the highest temperature ever identified. This new advance in understanding the physics of high-temperature superconductivity could help to drive forward progress in the search for room-temperature superconductors, which could be used in levitating trains or next-generation supercomputers, for example. Superconductors are materials that carry electrical current with zero electrical resistance. Conventional or low-temperature ones behave that way only when the substance is cooled down to temperatures close to absolute zero (-273 °C o 0 degrees Kelvin). Last year, however, German researchers identified the high-temperature superconducting properties of hydrogen sulphide which makes it the superconductor at the highest temperature ever discovered: -70 °C or 203 K. The structure of the chemical bonds between atoms changes In classical or Newtonian physics it is possible to measure the position and momentum of a moving object to determine where it is going and how long it will take to reach its destination. These two properties are inherently linked. However, in the strange world of quantum physics, it is impossible, according to Heisenberg's uncertainty principle, for specific pairs of observable complementary physical magnitudes of a particle to be known at the same time. Hydrogen is the lightest element in the periodic table, so it is an atom that is very strongly affected by quantum behaviour. Its quantum nature affects the structural and physical properties of various hydrogen compounds. An example is high-pressure ice where quantum fluctuations of the proton lead to a change in the way the molecules are held together, due to the fact that the chemical bonds between atoms end up being symmetrical. The researchers in this study believe that a similar quantum hydrogen-bond symmetrisation occurs in the hydrogen sulphide superconductor. The researchers have formulated the calculations by considering the hydrogen atoms as quantum particles behaving like waves, and they have concluded that they form symmetrical bonds at a pressure similar to that used experimentally by the German researchers. So they have succeeded in explaining the phenomenon of superconductivity at record-breaking temperatures because in previous calculations hydrogen atoms were treated as classical particles, which made impossible to explain the experiment. All this highlights the fact that quantum physics and symmetrical hydrogen bonds lie behind high-temperature conductivity in hydrogen sulphide. The researchers are delighted that the good results obtained in this research show that quantitative predictions and computation can be used with complete confidence to speed up the discovery of high-temperature superconductors. According to the calculations made, the quantum symmetrisation of the hydrogen bonds has a great impact on the vibrational and superconducting properties of hydrogen sulphide. "In order to theoretically reproduce the observed pressure dependence of the superconducting critical temperature, the quantum symmetrisation needs to be taken into account," explained Ion Errea, the lead researcher in the study. This theoretical study shows that in hydrogen-rich compounds, the quantum motion of hydrogen can strongly affect the structural properties (even modifying the chemical bonding), as well as the electron-phonon interaction that drives the superconducting transition. In the view of the researchers, theory and computation have played a key role in the search for superconducting hydrides subjected to extreme compression. And they also pointed out that in the future an attempt will be made to increase the temperature until room-temperature superconductivity is achieved while dramatically reducing the pressures required. ### Additional information This international research was carried out with the collaboration of researchers from the UPV/EHU-University of the Basque Country and Donostia International Physics Center (DIPC), the UPMC Université Paris 06 (Sorbonne), the University of Cambridge (Cavendish Laboratory), the Jiangsu Normal University, the Carnegie Institution of Washington, Jilin University, and the University of Rome 'La Sapienza'. The lead researcher in the study was Ion Errea (Donostia-San Sebastian, 1984); he is a PhD holder in Physics and is currently a researcher at DIPC and a lecturer in the UPV/EHU's Department of Applied Physics. For more information, please click If you have a comment, please us. 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News Article | October 23, 2015
Site: phys.org

An international research collaborative has published a paper in the prestigious journal Nature Communications titled "Digital quantum simulation of fermionic models with a superconducting circuit." The paper reports on the performance of the most advanced quantum algorithm known and which achieves the implementation of a quantum simulation of electronic models of materials in superconducting circuits. This algorithm has been developed at the superconducting circuit laboratories of Google/UCSB on the basis of original ideas proposed by the UPV/EHU QUTIS group.

One of the biggest temptations facing a scientist is to try and reproduce natural phenomena which are so fascinating given their effectiveness and perfection. This is the aim being pursued by the UPV/EHU's Molecular Spectroscopy Group which, coinciding with the International Year of Light, has designed a set of fluorescent nanomaterials which have taken their inspiration from the antenna systems of plants. These new multifunctional materials aim to imitate the photosynthetic organisms of plants. These microorganisms consist of thousands of chlorophyll molecules embedded in a protein matrix, which provides them with a specific orientation/arrangement and intermolecular distance. One of the main characteristics of these systems is their antenna function, which enables them to harvest solar energy in a broad spectral range and transport it by means of multiple, efficient energy transfer processes to a specific reaction center, where it is finally turned into chemical energy. It is a well-known fact that solar radiation is made up of many colors (blue, green, yellow, red, etc.), as borne out by the broad range of colors present in the rainbow. The aim of artificial antenna systems is to capture the greatest light range possible so that it can then be efficiently turned into electrical energy (activating of photovoltaic cells) or the emitting of red light, so useful in photonic applications, such as those of biomedical interest. In this respect, and with the aim of coming up with artificial antenna systems, the Molecular Spectroscopy Group has been developing new dyes and photoactive nanomaterials capable of absorbing a broad interval of chromatic radiation which can then be transformed into a red-only emission. Energy donor and acceptor molecules coexist in these photoactive dyes and nanomaterials developed by the Molecular Spectroscopy Group. The former are highly photostable fluorescent molecules and are responsible for absorbing the light which they then transfer to the acceptor species, which will emit light. This strategy allows the limitations inherent in the red dyes to be reduced; these red dyes are characterized by their reduced light absorption and their low photostability and offer a great advantage in photonic and biophotonic applications as they allow the photostability of the system and detection sensitivity to be improved. Three different alternatives have been chosen to develop these antenna systems: two of them are based on the encapsulation of fluorescent dyes in either inorganic or organic hosts, and the other one in the assembly of different dyes into a single molecular structure. "We have replaced the protein matrix of the natural systems by synthetic hosts of nanometric dimensions which protect the dyes and provide a significant arrangement that will help to make the energy transfer processes viable and efficient. Furthermore, with respect to the photoactive part, which is responsible for interacting with the light, the chlorophyll molecules have been replaced by fluorescent molecules many of which have been tuned à la carte," explains Leire Gartzia, author of the thesis the most salient results of which have been included in the paper published in International Reviews in Physical Chemistry. In the first of the alternatives, the solid matrix chosen to encapsulate the fluorescent dyes is of crystalline aluminosilicate known as Zeolite L., characterized by the fact that it has unidimensional channels and a suitable pore size (7Å) in which the molecules fit like a glove. "This produces a highly ordered nanomaterial that allows the light emission to be modulated to produce a red or white light depending on the control we exert on the efficiency of the energy transfer process," added the researcher. This chameleon-like property turns them into materials capable of generating new light emitting diodes (LEDs), featuring white-light emitting diodes (WLED), which are so useful in lighting technologies such as liquid crystal displays (LCD). The other matrix chosen to host dyes consists of polymer nanoparticles capable of hosting inside them extremely high dye concentrations without it becoming aggregated. "Confining the dyes reduces the photodegradation processes, considerably increases their useful service life and encourages the transfer of energy, which has enabled us not only to obtain an antenna system but also tunable red laser radiation that is efficient and long-lasting in stable aqueous suspensions," says Gartzia. Finally, they have developed antenna systems made up solely of organic molecules in which the energy donor and acceptor species are linked by a spacer ensuring short intermolecular distances, thus achieving efficiencies in the energy transfer processes of practically 100%. This has meant a great improvement in the harvesting of light across the visible spectrum, leading to exclusively stable bright red which means they are highly recommended as active hosts for tunable lasers in the zone close to the infrared. The main interest in this wavelength is its great tissue penetration capacity, a key in photodynamic therapy with uses in ophthalmology and dermatology and in cancer treatment, for example. Release Date: January 21, 2016 Source: University of the Basque Country

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