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.


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  • Higher-order multipolar interactions in insulating crystals (2020)

    Stengel, Massimiliano (CSIC - ICMAB)

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    Higher-order multipolar interactions in insulating crystals

    The theoretical foundation of lattice dynamics in crystalline insulators rests on the separation between short-range and long-range interatomic force constants (IFCs). The latter stem from the macroscopic electric fields that are associated with long-wavelength phonons. These, in turn, result in a nonanalytic behavior of the dynamical matrix near the Brillouin zone center, which manifests itself as a polynomial (rather than exponential) decay of the IFCs in real space.

    The leading long-range contribution, which has the form of a dipole-dipole interaction and decays as the inverse cube of the interatomic distance, has been known since the fifties. The work of Cochran and Cowley, and later Pick, Cohen and Martin, established the correct formula in the generic case of an anisotropic crystal, paving the way for modern first-principles implementations. The main physical consequence of the dipole-dipole interaction resides in the frequency splitting between longitudinal (LO) and transverse (TO) optical phonons near the Brillouin zone center. 

    The Cochran-Cowley formula is, however, only the leading term in a multipolar expansion of the charge response to atomic motion. Here we provide an exact generalization to higher multipolar orders, involving e.g. dipole-quadrupole interactions. We demonstrate that such generalization can be crucial in piezoelectric crystals, where the sound velocity is influenced by electrostatics. Neglect of dynamical quadrupoles often results in an erroneous description of the acoustic branches near the zone center, as we demonstrate with our calculations of rhombohedral BaTiO3. [1]

    The importance of quadrupoles is not limited to lattice dynamics. The long-range potentials produced by atomic motion are crucial for a correct description of electron-phonon couplings as well, which govern a wide range of physical properties (e.g., electron mobility). The counterpart of the Cochran-Cowley formula in this context consists in the Fröhlich model, which we have also generalized to the quadrupolar level. [2] This allows for a substantial improvement in the accuracy and efficiency of the calculations.

  • Mutations in cancer genomes: foggy with a chance of thunderstorms (2020)

    Supek, Fran (IRB Barcelona)

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    Mutations in cancer genomes: foggy with a chance of thunderstorms

    Local hypermutation is an unusual occurence of a cluster of nearby mutations that arose in a single event, which can severely damage genetic material. The best known type of local hypermutation, called a mutation shower or thunderstorm, can contain tens of closely spaced mutations. However, these spectacular mutational events occur only rarely. Nonetheless their existence suggests that other types of local hypermutation may be more widespread in genomes than previously appreciated.

    We have developed a sensitive statistical framework, HyperClust, to detect mutation clustering in cancer genomes. The application of HyperClust to thousands of cancer genome sequences revealed a new type of localized hypermutation pattern that we named mutation fog. This can generate hundreds of mutations per cell and can occur in different human somatic tissues. Such mutations are unevenly distributed across the human chromosomes: they preferentially accumulate in the most important, euchromatic regions of the genome, where gene density is higher.

    Surprisingly, this new hypermutation type is facilitated by a normal DNA repair process. When cells sense a mismatch in their DNA, they undergo a DNA repair reaction, in order to preserve genetic information. Remarkably, this reaction can become coupled with the APOBEC3A enzyme, which is normally used by human cells to defend against retrotransposons and viruses by damaging their nucleic acids. In some cases, when both the APOBEC enzyme and the DNA repair process are active at the same time, APOBEC is able to hijack the DNA repair process, generating the mutation fog.

    Such APOBEC mutagenesis has a high propensity to generate impactful mutations in oncogenes and tumor suppressor genes, which can exceed that of other common carcinogens such as tobacco smoke and ultraviolet radiation. Because human cells direct their DNA repair capacity towards more important genomic regions, carcinogens that subvert DNA repair can be remarkably potent.

  • Shedding light on the control of microtubule nucleation (2020)

    Surrey, Thomas (CRG)

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    Shedding light on the control of microtubule nucleation

    Microtubules are tube-like protein polymers that are essential for correct intracellular organization and for cell division. The number of microtubules needs to be precisely controlled and this is done by a protein complex that is thought to serve as a template for microtubule growth. We have developed a fluorescence microscopy-based assay allowing us to observe new microtubule formation from single templates. We found that the isolated templating complex is surprisingly inefficient in starting microtubule growth. Cryo-electron microsopy allowed then to obtain the structure of the complex at high resolution which revealed a mismatch between template and microtubule. This suggest that a shape change of the template is required to activate it and that in living cells template-binding proteins may induce this chance controlling the formation of new microtubules.

  • 3D Printing the Next Generation of Energy Devices (2020)

    Tarancón Rubio, Albert (IREC)

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    3D Printing the Next Generation of Energy Devices

    Three dimensional printing technologies represent a manufacturing revolution because of their unique capabilities for increasing shape complexity while reducing waste material, capital cost and design for manufacturing. However, the application of 3D printing technologies for the fabrication of devices remains an almost unexplored field due to their elevated complexity from the materials and functional points of view. The use of 3D printing technologies in energy and environmental applications is of special interest since the related devices usually involve expensive advanced materials such as ceramics or composites, which present strong limitations in shape and functionality when processed with classical manufacturing methods.

    Among other technologies, Solid Oxide Fuel and Electrolysis Cells (SOFC/SOECs) are one of the candidates to strongly benefit from 3D printing. SOFC/SOECs are ceramic-based multilayer complex devices able to efficiently generate electricity from clean fuels like hydrogen (fuel cell mode) as well as store renewable electricity in the form of transportable gases (electrolysis mode). In the last years, we have been developing an innovative 3D printing technology able to fabricate free-form complete SOCs with up to 60% of improved performance even using state-of-the-art materials.This work was reported this year in Journal of Materials Chemistry A (selected as HOT paper and cover image) and was recognized with the internationally reputed "Solar Impulse Efficient Solution" label. 

  • How does the replication of SARS-CoV-2 work (2020)

    Tartaglia, Gian Gaetano (CRG)

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    How does the replication of SARS-CoV-2 work

    The main question is which type of host proteins are exploited by the virus to spread.

    We produced an atlas of human proteins interacting with SARS-CoV-2. Our results were shared with the community since the very beginning of the pandemic.  The most important concept is that there are proteins binding to specific regions (3’ and 5’ ends of RNA genome) that regulate viral replication in a tight way. One of these interactions, if blocked, could be key to stop the infection.

    SARS-CoV-2 interactions tend to form blobs (phase separated assemblies in more technical terms) where specific components end up. These interactions help viral replication. Some of them are elements of the cell that are trapped to avoid the self-defence of the cell. How cool is that? Knowing these interactions is important to develop an anti-viral strategy, which would complement the current approach based on vaccination.

  • Sharp Remez inequality (2020)

    Tikhonov, Sergey (CRM)

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    Sharp Remez inequality

    Take your favorite function f(x) on an interval [a,b]. Let us slightly modify it as follows. On a smaller interval (or a couple of intervals), redefine it to be zero. Is it possible that the maxima of the original function f(x) and the modified one g(x) are comparable in some sense? In general, the answer is NO since the original function might be huge exactly on the smaller interval. However, this is true for some special classes of functions, in particular, for polynomials. A proof of this fact as well as the precise meaning of comparability are obtained in this work.

    More formally, we find a sharp constant C in the so-called Remez inequality max1 |f(x)| < C max2 |f(x)| in the case when f(x) is a trigonometric polynomial of a certain degree. Here the maximum max is taken over all x [a,b] and the maximum max is taken over all x [a,b]\B for a measurable set B. This problem was open for a long time even though a similar result for algebraic polynomials was obtained already in 1936.