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.
LIST OF SCIENTIFIC HIGHLIGHTS
Molecular mechanism underlying neurodegeneration in adrenoleukodystrophy.
(2013)
Molecular mechanism underlying neurodegeneration in adrenoleukodystrophy.
We propose a model that sheds light on the mechanisms of mitochondrial dysfunction in adrenoleukodystrophy (X-ALD), a rare neurodegenerative disease caused by loss of function of the peroxisomal transporter ABCD1.As hexacosanoic acid (C26:0) cannot enter peroxisomes for degradation, it accumulates intracellularly (1). This excess of C26:0 may affect the inner mitochondrial membrane permeability by unknown mechanisms. As a consequence, this alteration may decrease mitochondrial membrane potential (2) and generate a certain extent of electron leakage promoting radical oxygen species (ROS) formation (3). These free radicals attack and oxidize mitochondrial proteins of TCA cycle and oxidative phosphorylation system (OXPHOS), leading to impaired bioenergetics and cellular respiration. Moreover, the ROS oxidize mitochondrial DNA (mtDNA), contributing to a vicious cycle of mitochondrial dysfunction and ultimately, cell demise.
Using a head-mounted display and body tracking suit, entering into a virtual reality, you can experience yourself as a child of about 4 years old. You look into a mirror, or directly down towards your own body, but you see the child body instead. The brain appears to be remarkably flexible in quickly accepting the proposition that your body is different - especially when you move your body and the virtual body is seen to be moving synchronously. The virtual body has substituted your real body. Alternatively you can be embodied in a virtual body of the same size as the child, except that this is a scaled down adult body. In both conditions people tend to have a strong illusion that the virtual body is their body. The question we set out to answer in this experiment is whether embodiment in the two different types of bodies would lead to differences in perception and attitudes. Many objects used to look enormous when you were a child, but now do not seem that way. Is it just a question of your size, or is something more at work? Our results showed that there was overestimation of object sizes in both conditions (child and scaled adult). However, the child condition led to a much greater size overestimation. It must therefore be not just the size but the type of the body that is responsible for this effect. We also gave people an implicit association test. This requires people to quickly categorise themselves according to child or adult attributes. Those in the child condition were found to identify themselves more with child like attributes than those in the adult condition. A critical aspect of the findings was that the differences between the child and adult embodiment were due to their degree of illusory 'ownership' over the virtual body. We ran another experimental condition where everything in the setup was the same, except that the virtual body moved asynchronously with respect to the person's real body movements. In this condition the illusion of body ownership was very much reduced compared to the original. In this asynchronous condition the differences between the child and adult results vanished. Both groups still overestimated sizes, but there was no difference between them, and the overestimation was about the same as that in the synchronous adult condition. The work suggests that the body type itself carries meaning for the brain. Perhaps embodying people in such a child-like body automatically leads the brain
All laser devices—from the now ubiquitous "red dot" handheld pointers to sophisticated experimental set-ups that occupy entire laboratories—function in basically the same way: electronic level transitions inside a material (the lasing medium) are excited via externally applied light, heat or electricity, and then relax to emit photons in the form of a highly coherent, unidirectional beam of light at one specific wavelength (the emission wavelength). Photonic crystals—crystals that enable strict control over the movement of photons, analogously to the way that semiconductors enable control over the movement of electrons—have become a hot topic in research on lasing media.Out strategy was to combine the light control offered by photonic crystals with the practical advantages offered by dye-doped polymers by fabricating photonic crystals of dye-doped polymers by nanoimprint lithography and obtaining lasing via optical-pumping. Dye-doped polymers have garnered attention as a lasing medium, owing to the ease with which dyes can be incorporated into polymers; the broad range of tuneable emission frequencies enabled by the ample variety of available dyes; and the fact that polymers can be patterned over large areas at relatively low-cost, using established micro- and nanofabrication methods.The lasing frequency was as predicted by our simulations, at the phononic bad gap edge, depending on the simulations and geometry of the photonic crystal. The lasing threshold was as low as 3 μJ/mm-2. Our 2D photonic crystal laser offered better performance than standard 1D lasers, as measured by its (2.5 times) lower lasing threshold and (50 times) smaller laser surface.The realization of photonic crystals has been hampered by expensive fabrication top-down technologies involving electron beam lithography and reactive ion etching. In this work we have demonstrated the feasibility and precision of nanoimprint lithography for rapid, cost-efficient, one-step fabrication of polymer photonic crystals of diverse compositions, which should provide access to numerous practical laser applications in areas like medical analysis (lab-on-a-chip) and sensing. It is known that dyes have too short lifetime, however, the lifetime can be increased to device-like performance by replacing the dyes by optically active semiconductor quantum dots, without compromising the nanoimprinting-based fabrication. The possibility to up-scale to volume production using roll
Flexoelectricity via coordinate transformations
(2013)
Flexoelectricity describes the electric polarization that is linearly induced by a strain gradient, and is being intensely investigated as a tantalizing new route to converting mechanical stimulation into electrical signals and vice versa.Contrary to its close cousin, piezoelectricity (the polarization response to a uniform strain), flexoelectricity is a universalproperty of all insulators regardless of crystal symmetry, and therefore appears highly attractive as a cost-effective andenvironment-friendly (piezoelectrics are typically based on lead, a toxic element) alternative to the former. Strain gradientscan be easily generated by bending a sample or by applying pressure by means of a local probe, and naturally arise when certain topological defects, such as dislocations or ferroelastic domain walls, are present in the bulk material. Particularly at the nanoscale, it is becoming increasingly clear that understanding the fundamentals of strain-gradient effects is crucially important, either for avoiding their sometimes deleterious impact (e.g. in ferroelectric memories, or in foldable electronic devices), or for harnessing the exciting new functionalities that they provide.While several breakthough experiments have been reported in the past few years, progress on the theoretical front has been comparatively slow, especially in the context of first-principles electronic-structure theory. The main difficulty with calculating the flexoelectric response of a material is the inherent breakdown of translational periodicity that a strain gradient entails, which at first sight questions the very applicability of traditional plane-wave pseudopotential methods.Here I show how these obstacles can be overcome by combining density-functional perturbation theory with generalized coordinate transformations of space. In particular, by writing the equations of electrostatics in a fully covariant form, I derive the full microscopic response (in terms of electronic charge density, polarization and atomic displacements) of a crystal or nanostructure to an arbitrary deformation field. This methodological advance sets the stage for attacking an essentially endless variety of curvature-related phenomena with full ab initio power; here I address, in full generality, the surface contributions to the flexoelectric response of a finite sample. Inspiration for solving this important materials science problem has come from the apparently unrelated field of transformation
Swings between rotation and accretion power in a binary millisecond pulsar [astro-ph/1305.3884]
(2013)
Swings between rotation and accretion power in a binary millisecond pulsar [astro-ph/1305.3884]
Pulsars are the highly magnetised, spinning remnants of massive stars and are primarily observed as pulsating sources of radio waves. The radio emission is powered by the rotating magnetic field and focused in two beams stemming from the magnetic poles. As the pulsar rotates, the effect is similar to that of a rotating lighthouse beacon, resulting in distant observers seeing regular pulses of radio waves.The emission mechanism of pulsars transforms kinetic rotational energy into radiation, and as this energy is radiated over time, the rotation is slowed down. Whilst pulsars spin rapidly at birth, they tend to rotate more slowly – with periods of up to a few seconds – as they age. For this reason, astronomers in the 1980s were puzzled by the discovery of millisecond pulsars – old but extremely quickly rotating pulsars with periods of a few thousandths of a second. For the first time, astronomers have caught a pulsar in a crucial transitional phase that explains the origin of the mysterious millisecond pulsars. This ends a quest that has been going on the last 30 years.These pulsars spin much faster than expected for their old age, and astronomers believe their rotation receives a boost as they accrete matter in a binary system. This year, astronomer have found the first pulsar swinging back and forth between accretion-powered X-ray emission and rotation-driven radio emission, bringing conclusive evidence for their 'rejuvenation'. The discovery was made possible by the coordinated efforts of ESA's two missions that scan the high-energy sky: INTEGRAL and XMM-Newton, working together with Chandra X-ray Observatory, Green Bank Telescope, the Parkes radio telescope, and the Westerbork Synthesis Radio Telescope.(Adapted from the European Space Agency Press Release.)
Plants, bacteria and algae collect sunlight to store its energy and synthesize high energy molecular species to power life. This photosynthetic process involves light harvesting complexes, sophisticated molecular constructs which act as antennas to capture light. Surprisingly almost every visible photon is captured and transferred to makes its energy to work. What hidden mechanism does nature use to transfer energy so efficiently?
Nature has arranged the photosynthetic systems rather cleverly: the reaction center is surrounded by many antenna complexes, which all capture photons, funnelling the energy from one site to the next, to finally reach the reaction centre. Such dense network of antennas explains the high capture efficiency. Yet what guarantees that the diffusing photon energy does actually reach its target? In recent experimental and theoretical studies it was found that the photon-hopping picture is a good model, however it is not the full story. To surprise of many researchers, coherences were observed in the energy transfer, which could only be explained by concepts of Quantum Mechanics!
Quantum Mechanics, normally associated to physics at low temperatures, would not quite be expected in warm and wet soft living entities. Yet even at room temperature quantum phenomena do occur at the ultrafast femtosecond timescale and can even persist when protected against environmental disorder. Exactly such persistent coherence is observed in photosynthesis. The new field is coined “Quantum Biology” and could be a revolution in Science, if the bit of Quantum would actually have a biological role.
To address such important question it is essential to track the femtosecond energy hops amidst the complex network, best at the level of single sites. This is exactly what we have done. We developed a unique experimental technique, pushing ultrafast spectroscopy to the single-molecule limit: with dedicated femtosecond light flashes we capture a high-speed series of ‘pictures’ of the states of individual antenna complexes after light absorption. We indeed found persistent coherence, a genuine quantum effect of superposition of states. A surprising discovery was that transport pathways within a single antenna complex can vary over time, while maintaining coherence at each path.
Fascinating questions remain. Did quantum transport outcompete other mechanisms during evolution to achieve such extraordinary efficiencies in photosynthesis? Are there other biological processes
