Highlights

Every year, a committee of experts sits down with a tough job to do: from among all ICREA publications, they must find a handful that stand out from all the others. This is indeed a challenge. The debates are sometimes heated and always difficult but, in the end, a shortlist of 24 publications is produced. No prize is awarded, and the only additional acknowledge is the honour of being chosen and highlighted by ICREA. Each piece has something unique about it, whether it be a particularly elegant solution, the huge impact it has in the media or the sheer fascination it generates as a truly new idea. For whatever the reason, these are the best of the best and, as such, we are proud to share them here.

LIST OF SCIENTIFIC HIGHLIGHTS

Format: 2017
  • Entanglement between spin and pseudospin in graphene: An unprecedented effect yielding spin relaxation and spin manipulation possibility (2014)

    Roche, Stephan (ICN2)
    Valenzuela, Sergio O. (ICN2)

    view details
    CLOSE

    The prospect of transporting spin information over long distances in graphene, possible because of its small intrinsic spin–orbit coupling and vanishing hyperfine interaction, has stimulated intense research exploring spintronics applications. However, measured spin relaxation times are orders of magnitude smaller than initially predicted, while the main physical process for spin dephasing and its charge-density and disorder dependences remain unconvincingly described by conventional mechanisms.

    Our team has unraveled an unprecedented spin relaxation mechanism for non-magnetic samples that follows from an entanglement between spin and pseudospin driven by random spin-orbit coupling, unique to graphene.

    The mixing between spin and pseudospin-related Berry's phases results in fast spin dephasing even when approaching the ballistic limit, with increasing relaxation times away from the Dirac point, as observed experimentally. The origin of spin-orbit coupling can stem from adatoms, ripples or even the substrate, suggesting novel spin manipulation strategies based on the pseudospin degree of freedom.

    Such possibilities suggest unprecedented approaches for the emergence of non-charge-based information processing and computing, resulting in a new generation of active (CMOS compatible) spintronic devices together with non-volatile low-energy MRAM memories. This phenomenon not only revisits years of experimental and theoretical controversies, but also opens a new window into the formidable challenge of manipulating spin degree of freedom in future information-processing technologies.

  • Catalase-peroxidase reaction mechanism deciphered (2014)

    Rovira Virgili, Carme (UB)

    view details
    CLOSE

    When it comes to enzymes and hydrogen peroxide, there are catalases and peroxidases. The former degrade hydrogen peroxide; the latter use it to oxidize other molecules. The heme-containing catalase-peroxidases (KatGs) perform both activities, but as the enzymes’ active sites tend to resemble peroxidases (which have poor catalase activity), it has never been clear how they work. Now Ignacio Fita, Carme Rovira  and colleagues describe a reaction mechanism that resolves this mystery.Traditional catalases degrade hydrogen peroxide via a mechanism involving a heme group and proton transfer from a key histidine residue. KatGs lack that amino acid, but they do have a methionine-tryptophan-tyrosine (MWY) “covalent adduct” near the heme ring, as well as a critical arginine residue that alternates between “in” and “out” orientations. Using quantum mechanical/molecular mechanics calculations and x-ray crystallography of the active site, the authors propose an eight-step mechanism in which the MWY complex and mobile arginine act as an “electronic switch” that drives conversion of hydrogen peroxide to water and oxygen.

  • 60-year old theory from Alan Turing explains finger formation (2014)

    Sharpe, James (CRG)

    view details
    CLOSE

    Alan Turing, the British mathematician (1912-1954), is famous for a number of breakthroughs: the foundations of computer science, cracking the Enigma code, and helping to found the field of artificial intelligence. His contribution to mathematical biology is much less famous, but was no less profound. He published just one paper (1952), but it triggered a whole new field of mathematical enquiry into pattern formation. He discovered that a system with just 2 reacting and diffusing molecules could spontaneously self-organise into repetitive spatial patterns of concentrations, such as spots or stripes. His theory has come to be accepted as an explanation of simple patterns such as zebra stripes and leopard spots, but in embryology it has been resisted for decades as an explanation of how structures such as fingers are formed. The group of ICREA Research Prof. James Sharpe at the CRG in Barcelona, has now provided data supporting the idea that fingers and toes are indeed patterned by a Turing mechanism. They had previously provided evidence that Hox genes and FGF signaling modulated a hypothetical Turing system (Science 338:1476, 2012), but the identity of the Turing molecules themselves was still a mystery. The new study completes the picture, by revealing which signaling molecules act as the Turing system. It was achieved by a systems biology approach – combining experimental work with computational modelling. In this way, the two equal-first authors of the paper were able to iterate between the empirical and the theoretical: the lab-work of Jelena Raspopovic providing experimental data for the model, and the computer simulations of Luciano Marcon making predictions to be tested back in the lab. By screening for the expression of many different genes, they found that two signalling pathways stood out as having the required activity patterns: BMPs and WNTs. They gradually constructed the minimal possible mathematical model compatible with all the data, and were able to make computational predictions about how inhibiting these 2 pathways should alter the pattern of fingers. Strikingly, when the same experiments were done on small pieces of limb bud tissue cultured in a petri dish the same alterations in embryonic finger pattern were observed, strongly supporting the hypothesized model. Their result goes beyond the question of finger development. It challenges the dominance of an important theory for embryology called positional information, which states that cel

  • Was it me who was speaking? Virtual body ownership can cause illusory agency (2014)

    Slater, Mel (UB)

    view details
    CLOSE

    Normally we trivially distinguish between acts that we execute ourselves from those carried out by other people, our sense of agency over our own actions. Neuroscientists have developed theories of agency based on the intention to act followed by observation of the sensory consequences of the act - if these match then this is one element of the attribution of self agency to the act. Cause should precede effect, in other words the act and its consequences should follow normal common sense rules of causality. There should be no other obvious explanation for the effect, and a strong temporal binding between execution of the act and observation of the consequences of the act itself. We carried out an experiment showing that it is possible to trick the brain into the illusion that the participants were speaking when they were not. Participants wore a head-tracked head-mounted display and a full body motion capture suit that placed them in an immersive virtual reality. When they looked down towards their own body they saw a virtual body instead, which was also reflected back to them in a virtual mirror. In one experimental condition their virtual body moved synchronously with their real body movements, as captured by the motion capture suit. In another condition the virtual body moved independently of real body movements. From previous results we expected that those in the synchronous condition would experience the illusion that the virtual body was their body. This is referred to in the literature as the illusion of body ownership. After a few minutes of moving around with synchronous or asynchronous virtual body movements, the virtual body spoke some words. We found that those in the synchronous condition had the illusion that it was they who had spoken the words (even though they had said nothing). Moreover, the voice of their virtual body had a higher fundamental frequency than the real voices of the participants. Those who had experienced the synchronous moving body also later spoke with a higher fundamental frequency after their experience compared with before. Our conclusion is that a strong illusion of ownership over a virtual body can lead to the illusory attribution of agency to acts carried out solely by that virtual body. As we become represented more and more by online characters or operate tele-present robots, we must understand agency scientifically, to avoid the profound legal and ethical problems associated with self-attribution of agency to acts that w

  • OPTOMECHANICAL CRYSTALS (2014)

    Sotomayor Torres, Clivia Marfa (ICN2)

    view details
    CLOSE

    Photon-phonon interactions occur in a plethora of physical systems and phenomena such as Brillouin scattering and Raman scattering. In systems supporting both optical and mechanical resonances, these types of interaction are called optomechanical coupling. There are optomechanical systems of sizes ranging from kilometere-long interferometers, intended for gravitational waves detection, to clouds of a few atoms. Whilst optomechanical coupling is inherently weak, it can be greatly enhanced by engineering the simultaneous confinement of light and sound in cavities with characteristic dimensions in the wavelength and sub-wavelength range. This approach, known as Cavity Optomechanics, enables efficient transfer of energy from an electromagnetic field to matter vibrations (and vice versa), thereby providing unprecedented coherent control of phonons. We have combined our expertise in photonic and phononic crystals to design, fabricate and characterise an optomechanical crystals based on a corrugated beam with holes that acts as a high-quality optical cavity for telecommunication-range light and a mechanical cavity for GHz phonons. The co-localization or spatial overlap of light and sound in the same micrometre cubic volume has enabled us to achieve a strong optomechanical coupling leading to novel findings at room temperature including the experimental verification of phonon-lasing. In fact, our contributions constitute two milestones in cavity optomechanics. Firstly, we have demonstrated for the first time optomechanically coupled phonons have been placed in a complete phonon bandgap, thus minimizing the limits otherwise experience by devices due to mechanical losses through clamping and improving the coherent lifetime of the confined phonons, both crucial for coherent manipulation of mechanical states and for the controlled generation of coherent phonons with light, also known as Optomechanically-Mediated Phonon Lasing. Moreover, we decoupled the design parameters of the optical and mechanical cavities, thus demonstrating a practical advantage that overcomes the historical limitations that kept optomechanical crystals designs limited to a few examples.  Our Nature Communications paper reporting these findings has been selected as a “Research Highlight” in Nature Photonics , Vol. 7, p. 746 (2014), DOI: 10.1038/nphoton.2014.229.

  • Monograph "Analytic Capacity, the Cauchy Transform, and Non-homogeneous Calderón-Zygmund Theory" (2014)

    Tolsa Domènech, Xavier (UAB)

    view details
    CLOSE

    The book "Analytic Capacity, the Cauchy Transform, and Non-homogeneous Calderón-Zygmund Theory", written by X. Tolsa, was published in 2014 by Birkhäuser in the series "Progress in mathematis". This text got the Ferran Sunyer i Balaguer Award in 2013.The book studies some of the groundbreaking advances in the field of geometric analysis that have been made regarding the notion of analytic capacity and its relationship to rectifiability in the decade 1995–2005. The Cauchy transform is an operator which plays a fundamental role in this area and is accordingly one of the main subjects covered. Another important topic, which may be of independent interest for many analysts, is the so-called non-homogeneous Calderón-Zygmund theory, the development of which has been largely motivated by the problems arising in connection with analytic capacity.The so called Painlevé problem was first posed around 1900 by the French mathematician and politician Paul Painlevé. This consists in finding a description of the removable singularities for bounded analytic functions in metric and geometric terms. One can think of removable singularities as invisible sets for this type of functions.Analytic capacity is a key tool in the study of the Painlevé problem. In the 1960s Anatoly Vitushkin conjectured that the removable sets which have finite length coincide with those which are purely unrectifiable. Moreover, because of the applications to the theory of uniform rational approximation, he posed the question as to whether analytic capacity is semiadditive. That is to say, is the analytic capacity of the union of two arbitrary sets in the plane smaller or equal than some universal constant times the sum of the analytic capacity of each set?This monograph presents full proofs of Vitushkin’s conjecture and of the semiadditivity of analytic capacity, both of which remained open problems until very recently. Other related questions are also discussed, such as the relationship between rectifiability and the existence of principal values for the Cauchy transforms and other singular integrals. The book is largely self-contained and should be accessible for graduate students in analysis, as well as a valuable resource for researchers.

Pages