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: 2018
  • A new era in astronomy: the electromagnetic counterpart of the gravitational wave signal from a merger of two neutron stars (2017)

    Miquel Pascual, Ramon (IFAE)

    view details
    CLOSE

    In early 2016, the LIGO and Virgo Collaborations announced the first detection of gravitational waves, coming from a merger of two black holes, a discovery that led to the award of the 2017 Nobel Prize in Physics to three leading LIGO scientists. In 2017, LIGO and Virgo reported the first observation (GW170817) of gravitational waves coming from the merger of two neutron stars. The relevance lies in the fact that, contrary to a merger of two black holes, a merger of two neutron stars gives rise to electromagnetic waves, which can be detected on Earth. The combined observation of gravitational and electromagnetic waves from the same event enables a wide spectrum of astrophysical and cosmological studies, ranging from tests of quantum gravity models to a brand new method to determine the expansion rate of the Universe, and has been chosen as 2017 Breakthrough of the Year by the Science journal.

     

    The DECam camera of the Dark Energy Survey (DES) was one of the first optical instruments that reported the detection of an electromagnetic counterpart of GW170817, a few hours after the detection of the gravitational waves. The IFAE group led by Ramon Miquel was responsible for the design and production of most of the read-out electronics for the 74 CCDs in DECam. The electromagnetic signal observed by DECam and others pinpoint the host galaxy (NGC 4993) where the merger took place, together with its redshift and, hence, its recession velocity. On the other hand, the analysis of the detected gravitational wave signal provides the distance to the merger. Putting both things together, one can infer the current rate of expansion of the Universe, or Hubble constant, a parameter whose precise value has recently generated considerable controversy, to be H0 = (70 +12-8) km s-1 Mpc-1. While the precision achieved with this one event is rather limited, this kind of multi-messenger astronomy opens the possibility of an accurate and independent measurement of H0 in the near future.

  • Simultaneous tracking of spin angle and amplitude beyond classical limits (2017)

    Mitchell, Morgan W. (ICFO)

    view details
    CLOSE

    Measurement of spin precession is central to extreme sensing in physics, geophysics, chemistry, nanotechnology and neuroscience, and underlies the powerful spectroscopic technique of magnetic resonance. Because there is no spin-angle operator, any measurement of spin precession is necessarily indirect:  it can, for example, be inferred from projections of the spin at different times. Because the operators describing spin projections do not commute, quantum measurement back-action — the random change in one observable when a non-commuting observable is measured — necessarily enters the spin measurement record, introducing errors and limiting sensitivity. In [Colangelo et al. Nature 2017] we showed that this disturbance can be reduced by orders of magnitude, by directing the quantum measurement back-action almost entirely into an unmeasured spin component. This generates a planar squeezed state that enables simultaneous and precise knowledge of both spin angle and spin amplitude, i.e., all the variables of interest in spin precession. To prove the method in the lab, we used high-dynamic-range optical quantum non-demolition measurements applied to a precessing magnetic spin ensemble consisting of about 2 million laser-cooled atoms.  We observed spin tracking with steady-state angular sensitivity 2.9 decibels better than the "classical limit," defined as the best possible performance with independent particles, and amplitude sensitivity 7.0 decibels below the corresponding limit for spin amplitude. In sum, we identified a method to almost completely evade quantum uncertainty effects in the highest-performing technique for many important applications.

  • Nanostructuring graphene at the atomic scale (2017)

    Mugarza Ezpeleta, Aitor (ICN2)

    view details
    CLOSE

    The most important drawback of graphene, this "best-for-all" material,  for application in electronics and optoelectronics is the abscence of an electronic gap. This can be induced by scaling down the material to dimensions where electrons can be quantized. Indeed, nanometer size graphene structures exhibit quantization gaps that are comparable to that of the inherent gap of semiconductors used in actual electronic devices. this is also crucial for the optical response of the material, since it shifts optical and plasmonic resonances from the infrared towards the visible regime demanded by telecomunication. The presence of edges might also result in the emergence of novel phenomena, such as the existence of dissipationless one dimensional magnetic states. 

    All the above properties depend on the size and morphology of the nanostructure, but at this scale they are also particularly sensitive to the atomic structure, both of thet bulk and of the edges. Magnetic edge states will exist at zig zag edges, but not at armchair edges. On the other hand, the latter are more efficient on inducing quantization band gaps. It is fundamental, hence, to control the synthesis of graphene nanostructures at the atomic scale. 

    Our group has developed a bottom-up method based on chemical vapour deposition that allows to synthesize graphene nanostructures with control on the overall morphology, and crystal structure of both the bulk and the edges. By tuning the growth parameters, we are able to control the topological defects of the bulk, induce edge reconstructions, and shape ill-defined clusters into shape-selected triangular and hexagonal nanostructures. 

  • Identified a protein of our immune system that helps cancer cells to grow and inhibits their ageing. (2017)

    Postigo, Antonio (IDIBAPS)

    view details
    CLOSE

    The growth of a tumor depends not only on its cancer cells but also on their interaction with normal cells that form the "tumor microenvironment." Researchers in the Regulation of Gene Expression Group at IDIBAPS, have identified a protein, ZEB1, that causes the body's own immune cells to collaborate with cancer cells. The study used a mouse model of ovarian cancer, a Zeb1-deficient mouse, and databases of 400 patients with ovarian cancer. ZEB1 expression in both tumor cells and macrophages at the tumor microenvironment promoted tumor growth. ZEB1 activated cancer cells to produce CCL2—a chemokine that attracts macrophages to the tumor environment—and induced macrophages to release MMP9 that promotes cancer cells to acquire a more aggressive phenotype. A reduction of ZEB1 in macrophages not only inhibited their pro-tumor effect but also improved tumor cell response to chemotherapy.

    In a parallel study, the same group has found that ZEB1 inhibits their own senescence, a type of cell ageing. For cancer cells to proliferate, they need to first overcome and inhibit their own mechanisms of tumor suppression being senescence one of them. Analysis of more than 1,000 colorectal carcinomas (CRC) revealed that ZEB1 expression in cancer cells is inversely correlated with a senescence signature and associates with poorer prognosis. Using a Zeb1-deficient mouse and a transgenic mouse model of CRC, the study found that ZEB1 triggers a newly identified pathway (DKK1-mut p53-Mdm2-CtBP-macroH2AY) to inhibit senescence in cancer cells and promote tumor growth. A reduction of ZEB1 in CRC cancer cells to just half of their basal levels was enough to trigger senescence and block the progression of premalignant adenomas into invasive carcinomas.

    New cancer therapies seek not only to eliminate tumor cells but also to regulate the immune response against cancer. Likewise, the development of drugs that induce tumor cell senescence is one of the most active areas in anti-cancer therapy and these two studies open the door to the design of new therapeutic strategies towards those goals.

  • On the road towards spin manipulation in large scale graphene (2017)

    Roche, Stephan (ICN2)

    view details
    CLOSE

    Spin relaxation is the process whereby the spins in a spin current lose their orientation, reverting to a natural disoriented state. This causes spin signal to be lost, since spins are only useful for transporting information when they are oriented in a certain direction.

    Graphene is a two-dimensional material exhibiting a series of remarkable properties that makes it uniquely suited for maintaining spin orientation over long lifetimes. However, its low spin-orbit coupling (SOC) makes it ineffective for spin manipulation.

    The solution we have proposed to advance in the development of graphene spintronics is to create layered heterostructures, harnessing the the presence of a high SOC material (such as a transition-metal dichalcogenide-TMDC) which imprints new spin features in the graphene layer. Our theoretical work reveals that the rate at which spins relax in graphene/TMDC systems depends strongly on whether they are pointing in or out of the graphene plane, with out-of-plane spins lasting tens or hundreds of times longer than in-plane spins. Such a high ratio has not previously been observed in graphene or any other 2D material, and stands as a primer in controlling the spin degree of freedom using weak proximity effects

    This behaviour is mediated by the so-called spin-valley locking induced in graphene by the TMDC, which ties the lifetime of in-plane spin to the intervalley scattering time (induced by disorder). This causes in-plane spin to relax much faster than out-of-plane spin. Furthermore, the numerical simulations suggest that this mechanism should come into play in any substrate with strong spin-valley locking, including the TMDCs themselves.

    Effectively inducing a spin filter effect –the ability to sort or tweak spin orientations–, these findings evidences that it is possible, through proximity effects to manipulate spin information in graphene. This theoretical prediction has been just confirmed experimentally at ICN2. These results open new avenue for exploring innovative spin logics protocols and quantum computing paradigms based on this large class of two-dimensional materials.

  • Designing an enzyme to synthetize carbohydrates via an unusual chemical reaction (2017)

    Rovira Virgili, Carme (UB)

    view details
    CLOSE

    Sugar or carbohydrate synthesis is important for the development of diagnostic tests, vaccines and new drugs. Conventional chemical synthesis in the laboratory is usually expensive and cumbersome; therefore lots of efforts have been made over the last years to do so with enzymes, which are natural catalysts. However, the enzymes that synthetize sugars (called glycosyltransferases) are hard to express and usually use expensive substrates (nucleotide sugars). Now the teams of the University of Barcelona (C. Rovira) and Oxford (Benjamin G. Davis) have found the way to modify a robust glycosidase enzyme, which normally degrades carbohydrates (by catalyzing the hydrolysis of glycosidic bonds) so that it acts reversely and synthetizes carbohydrates. The modification consisted on a single mutation of one of the catalytic residues. Using properly activated carbohydrate substrates, synthesis instead of hydrolysis was exclusively observed. Moreover, such synthesis takes place with a chemical reaction that had not been observed in glycosidases yet, the so called front-face or SNi-like reaction, which the team of Rovira uncovered in 2011 (see previous Highlight) for glycosyltransferases.

    To prove that the reaction follows a front-face mechanism, Rovira’s team modeled the binding of two carbohydrate molecules in the active site of the engineered enzyme using free energy enhanced sampling methods and modern supercomputers (MareNostrum at BSC-CNS). Afterwards, they obtained the chemical reaction mechanism using quantum mechanics/molecular mechanics (QM/MM) approaches. The computed free energy landscape of the reaction confirmed that the engineered enzyme had changed its catalytic mechanism from SN2 to a SNi type of reaction.

    The advantage of this reaction in glycosidases is that it makes the synthesis in a clean way, without hydrolysis residues and using economically viable substrates (activated sugars). In the study, the synthesis was carried out with a specific enzyme, the Sulfolobus solfataricus β-glycosidase (SSβG), but it can be applied to other enzymes using a similar engineering method, opening new possibilities for carbohydrate biosynthesis.

Pages