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  the most outstanding publications of the year 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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  • Most brilliant and broad laser light source (2021)

    Biegert, Jens (ICFO)

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    Most brilliant and broad laser light source

    In a recent study published in Nature Photonics, the team of ICREA Prof. Biegert at ICFO reports on a compact high-brightness mid-IR-driven source combining a gas-filled anti-resonant-ring photonic crystal fiber with a novel nonlinear-crystal. The table top source provides a seven-octave coherent spectrum from 340 nm to 40,000 nm with spectral brightness 2-5 orders of magnitude higher than one of the brightest Synchrotron facilities.

  • Strain brings electrons together (2021)

    Bromley, Stefan T. (UB)

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    Strain brings electrons together

    Published in Nature Communications, a collaborative theoretical study led by Prof. Stefan Bromley shows how to reversibly switch between closed-shell and open-shell states in radical-based 2D organic materials. The work was featured as an Editor’s Highlight (www.nature.com/collections/eecgdgijhh).

    Since the discovery of graphene, a number of inorganic 2D materials with a range of physical and chemical properties have been synthesized by top-down approaches. Such materials possess very high in-plane tensile strengths, which only allow for moderate strains generating modest electronic changes. In parallel, chemists have developed bottom-up synthesis approaches to produce 2D covalent organic frameworks (2D-COFs) based on linking arrays of molecular building blocks. Here the authors show that a particular family of 2D-COFs may provide an ideal basis for highly sensitive strain-control of electronic properties. Using persistent radicals as building blocks for new two-dimensional covalent organic radical frameworks (2D-CORFs) promises to provide a platform for new flexible materials in which optical, magnetic and electrical properties can be reversibly controlled by modest structural strain.

    In this work, the effect of uniaxial in-plane strain on a series of 2D covalent organic radical frameworks (2D-CORFs) is studied by means of density functional theory (DFT) based calculations. The results demonstrate that uniaxial in-plane tensile strains may be used to efficiently switch between antiferromagnetic multi-radical (i.e. open-shell) and diamagnetic quinoidal (i.e. closed-shell) states in a reversible manner. In addition, the authors demonstrate that the strain-induced electronic switching is robust at finite temperatures, which is a prerequisite for experimental viability, and thus technological applicability. Overall, their work shows that integrating bi-radical moieties into covalent 2D materials is a promising route to achieve macroscopic control over molecular-scale electronic states.

    For furher info check out a “Behind the paper” post by Stefan Bromley at the Nature Portfolio Chemistry Community: Strain-induced radical change: a 2D perspective.

  • The interactions among species are crucial for structuring lake fish communities (2021)

    Brucet, Sandra (UVIC)

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    The interactions among species are crucial for structuring lake fish communities

    The contribution of species interactions such as predation, competition and facilitation to forming local communities is an intensely discussed topic in ecological research. A major methodological challenge is to disentangle the effects of geographical and abiotic predictors from those caused by species interactions.

    In this study we applied a model-based approach on fish community composition in 772 European lakes, to find empirical evidence for contributions of species interactions to fish community composition. Our study reveals that positive and negative interactions between species are contributing substantially to the structuring of fish communities in European lakes, in addition to environmental filters and dispersal limitation.

  • Why is optical refractive index so small? (2021)

    Chang, Darrick (ICFO)

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    Why is optical refractive index so small?

    The refractive index of a material directly determines the minimum size that we can construct optical devices and the smallest length scales that light can resolve. Despite the game-changing implications that an ultrahigh index material would have, it is interesting to observe that all optical materials that we know of have an index that is of order unity. Surprisingly, a deep understanding of the mechanisms that lead to this universal behavior seems to be lacking. Moreover, this observation is difficult to reconcile with the fact that a single isolated atom is known to have a giant optical response, as characterized by a resonant scattering cross section that far exceeds its physical size. We have developed a theory of the maximum index of a disordered atomic ensemble. Interestingly, despite the giant response of an isolated atom, we find that the maximum index does not indefinitely grow with increasing density but rather reaches a limiting value of n ≈ 1.7. This limit arises from the highly non-perturbative nature of multiple light scattering and near-field optical interactions in such a system. Our work is a promising first step to understand the limits of refractive index from a bottom-up, atomic physics perspective. Furthermore, identifying the limiting mechanisms should also pave the way to developing circumventing strategies, in order to realize an ultrahigh index material and open up vast new technological possibilities with light.

  • Disciplinary, gender and geographical biases dominate the production of science about ecosystem conservation and poverty alleviation  (2021)

    Corbera Elizalde, Esteve (UAB)

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    Disciplinary, gender and geographical biases dominate the production of science about ecosystem conservation and poverty alleviation 

    Research into the relationship between ecosystem services, e.g. environmental goods and functions such as carbon sequestration, and human well-being, including poverty alleviation, has blossomed since the early 2000s. We have explored who has produced this knowledge, what collaborative patterns and institutional and funding conditions have underpinned it, and what implications these matters may have for policy and the future of science. Developing a social network analysis of the most prolific writers in this field of knowledge, we have demonstrated that 70% of these authors are men, most are trained in either the biological sciences or economics and almost none in the humanities. Eighty per cent of authors obtained their PhD from universities in the EU or the USA, and they are currently employed in these regions. The co-authorship network is strongly collaborative, without dominant authors, and with the top 30 most cited scholars being based in the USA and co-authoring frequently. These findings may not be surprising to many, of course. They reflect the same geographical and gender biases that characterize knowledge production in other fields, as well as an expertise bias towards natural sciences, economics and engineering that also characterizes the study of other environmental matters, such as energy transitions, or pollution management research, which in turn invisibilizes the potential contribution that other social sciences and the humanities can make in understanding environment-human relations. Overall, the research suggests that embracing gender diversity, promoting extensive collaboration across disciplines, and being committed to knowledge co-production with affected populations is urgent to better understand and address the environmental and human challenges of our time, particularly amidst increasing calls for the decolonisation of conservation and development science.  

  • How do malaria parasites defend themselves from febrile temperatures? (2021)

    Cortés Closas, Alfred (ISGlobal)

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    How do malaria parasites defend themselves from febrile temperatures?

    Periodic fever is the most characteristic clinical symptom of human malaria, but how malaria parasites survive febrile temperatures was not known until now. Here we identified and characterized a transcription factor that regulates the protective response to febrile temperatures in Plasmodium falciparum, the parasite that causes the most severe forms of human malaria. The response of an organism to high temperature is called the heat shock response.

    This transcription factor, which we termed PfAP2-HS, activates the expression of a very small number of genes when the parasite is exposed to febrile temperatures. These genes mainly encode chaperones, which help to maintain proteins correctly folded. A gene encoding HSF1, the conserved regulator of the eukaryotic heat shock response from yeast to humans, is absent from the genome of malaria parasites. PfAP2-HS does not have any structural or sequence similarity with HSF1, but it plays an analogous function activating the expression of chaperone-encoding genes at high temperature.

    Several malarial transcription factors had been previously characterized, but all of them were found to be involved in regulating parasite development. PfAP2-HS is the first transcription factor identified in malaria parasites that drives a rapid protective response to a condition of the environment. In addition to regulating the malarial heat shock response, PfAP2-HS also plays an important role under basal (non-stress) conditions: parasites engineered to lack the PfAP2-HS protein were not only hypersensitive to febrile temperatures, but they also grew poorly at 37ºC, the physiological temperature for P. falciparum, and had to be cultured at 35ºC. These parasites could not maintain their proteins correctly folded even under optimal growth conditions. More importantly, they showed much higher sensitivity to the frontline antimalarial drug artemisinin, indicating that PfAP2-HS is needed for artemisinin resistance.

    Our findings settle a long-standing controversy about whether malaria parasites are able to produce immediate, protective transcriptional responses when changes in their environment occur: yes, they are!