After the discovery of the Higgs boson in 2012, the next mission of the LHC, in addition to carry out a detailed study of the new particle, is to put light on the nature of the dark matter in the cosmos, and to determine whether super-symmetry and/or new extra spatial dimensions are realized in nature. Monojet final states (see Figure 1) have been traditionally studied in these contexts.Astronomical observations of galaxies and galaxy clusters have established the existence of an important non-baryonic dark matter (non-luminous) component in the universe. According to the current understanding of cosmology, the dark matter would contribute about 23% of the total mass-energy budget of the universe. The nature of the dark matter remains unknown. It is now commonly accepted that the dark matter should be made of weakly interacting massive particles (WIMPs) acting through gravitational or weak interactions. At the LHC, WIMPs could be produced in pairs leaving the experimental devices undetected. Such events could be identified by the presence of an energetic jet from initial-state radiation, leading again to a monojet signature. The LHC experiments have a unique sensitivity for dark matter candidates with masses below 4 GeV and are complementary to other dark matter searches. Models with large extra spatial dimensions aim to provide a solution to the mass hierarchy problem (related to the large difference between the electroweak unification scale ~102 GeV and the Planck scale ~1019 GeV) by postulating the presence of n extra dimensions such that the Planck scale in 4+n dimensions becomes naturally close to the electroweak scale. In these models, gravitons (the hypothesized particle acting as mediator of the gravitational interaction) are produced in association with a jet of hadrons leading to a monojet signature in the final state.The ATLAS collaboration have searched for new phenomena in monojet final states in the 2011 and 2012 data at 7 TeV and 8 TeV, respectively [1,2]. The data are in good agreement with the SM predictions (see Figure 2). The results have been translated into updated exclusion limits on the presence of large extra spatial dimensions and the production of WIMPs, and new limits on gravitino production (the supersymmetric partner of the graviton) resulting in the best lower bound to date on the gravitino mass.
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
The search for the dark side of the Universe (2013)
Martínez Pérez, Mario (IFAE)view details
Nanoscale metal-organic frameworks and related hollow superstructures built with fast-spray-drying (2013)
Maspoch Comamala, Daniel (ICN2)view details
Metal-organic frameworks (MOFs) are among the most attractive porous materials today. Their miniaturization to the nanoscale, to yield nanoMOFs, is expected to expand their scope to myriad applications, from drug-delivery to membranes, open up novel avenues to more traditional storage and catalysis applications, and enable creation of sophisticated superstructures. However, methods for reliable nanoscale MOF synthesis, in which the precise patterning of the structure is intimately linked to its functional capacity, have been limited. We have reported and patented the use of spray drying as a versatile, general methodology to confine the crystallization of nanoMOFs and their assembly into hollow MOF superstructures smaller than 5 μm-in-diameter. This strategy conceptually mimics emulsions used by chemists to confine the synthesis of materials, but does not require secondary immiscible solvents or surfactants. We have demonstrated that this process enables shaping of MOFs into hollow superstructures that can subsequently be processed into stable colloids comprising discrete, homogeneous nanoMOFs. We have also showed that our spray-drying strategy can be applied to entrap guest species within the superstructures, thereby providing new routes to capsules, reactors and composite materials.
CPEB1 coordinates alternative 3'UTR formation with translational regulation (2013)
Méndez de la Iglesia, Raúl (IRB Barcelona)view details
Valcárcel Juárez, Juan (CRG)
More than half of mammalian genes generate multiple mRNA isoforms that differ in their 3’ untranslated regions (3’UTRs) and therefore in regulatory sequences; however, the mechanisms coordinating alternative 3’UTR processing for specific mRNA populations remain poorly defined. Here we report that the Cytoplasmic Polyadenylation Element Binding protein 1 (CPEB1), an RNA-binding protein that regulates mRNA translation, also controls alternative 3’UTR processing. CPEB1 shuttles to the nucleus, where it co-localizes with splicing factors and mediates 3’UTR shortening of hundreds of mRNAs, thereby modulating their translation efficiency in the cytoplasm. CPEB1-mediated 3’UTR shortening correlates with cell proliferation and tumorigenesis. CPEB1 binding to pre-mRNAs not only directs the use of alternative polyadenylation sites, but also changes alternative splicing by preventing U2AF65 recruitment. Our results reveal a novel function of CPEB1 in mediating alternative 3' UTR processing, coupled to regulation of mRNA translation.
Molecular mechanism underlying neurodegeneration in adrenoleukodystrophy. (2013)
Pujol Onofre, Aurora (IDIBELL)view details
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.
Perceiving with the Body of a Child (2013)
Slater, Mel (UB)view details
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
PRINTED PHOTONIC CRYSTAL LASERS (2013)
Sotomayor Torres, Clivia Marfa (ICN2)view details
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