TY - JOUR AB - The International Young Physicists' Tournament (IYPT) continued in 2018 in Beijing, China and 2019 in Warsaw, Poland with its 31st and 32nd editions. The IYPT is a modern scientific competition for teams of high school students, also known as the Physics World Cup. It involves long-term theoretical and experimental work focused on solving 17 publicly announced open-ended problems in teams of five. On top of that, teams have to present their solutions in front of other teams and a scientific jury, and get opposed and reviewed by their peers. Here we present a brief information about the competition with a specific focus on one of the IYPT 2018 tasks, the 'Ring Oiler'. This seemingly simple mechanical problem appeared to be of such a complexity that even the dozens of participating teams and jurying scientists were not able to solve all of its subtleties. AU - Plesch, Martin AU - Plesník, Samuel AU - Ruzickova, Natalia ID - 7622 IS - 3 JF - European Journal of Physics SN - 01430807 TI - The IYPT and the 'Ring Oiler' problem VL - 41 ER - TY - JOUR AB - Assemblies of colloidal semiconductor nanocrystals (NCs) in the form of thin solid films leverage the size-dependent quantum confinement properties and the wet chemical methods vital for the development of the emerging solution-processable electronics, photonics, and optoelectronics technologies. The ability to control the charge carrier transport in the colloidal NC assemblies is fundamental for altering their electronic and optical properties for the desired applications. Here we demonstrate a strategy to render the solids of narrow-bandgap NC assemblies exclusively electron-transporting by creating a type-II heterojunction via shelling. Electronic transport of molecularly cross-linked PbTe@PbS core@shell NC assemblies is measured using both a conventional solid gate transistor and an electric-double-layer transistor, as well as compared with those of core-only PbTe NCs. In contrast to the ambipolar characteristics demonstrated by many narrow-bandgap NCs, the core@shell NCs exhibit exclusive n-type transport, i.e., drastically suppressed contribution of holes to the overall transport. The PbS shell that forms a type-II heterojunction assists the selective carrier transport by heavy doping of electrons into the PbTe-core conduction level and simultaneously strongly localizes the holes within the NC core valence level. This strongly enhanced n-type transport makes these core@shell NCs suitable for applications where ambipolar characteristics should be actively suppressed, in particular, for thermoelectric and electron-transporting layers in photovoltaic devices. AU - Miranti, Retno AU - Shin, Daiki AU - Septianto, Ricky Dwi AU - Ibáñez, Maria AU - Kovalenko, Maksym V. AU - Matsushita, Nobuhiro AU - Iwasa, Yoshihiro AU - Bisri, Satria Zulkarnaen ID - 7634 IS - 3 JF - ACS Nano TI - Exclusive electron transport in Core@Shell PbTe@PbS colloidal semiconductor nanocrystal assemblies VL - 14 ER - TY - JOUR AB - A two-dimensional mathematical model for cells migrating without adhesion capabilities is presented and analyzed. Cells are represented by their cortex, which is modeled as an elastic curve, subject to an internal pressure force. Net polymerization or depolymerization in the cortex is modeled via local addition or removal of material, driving a cortical flow. The model takes the form of a fully nonlinear degenerate parabolic system. An existence analysis is carried out by adapting ideas from the theory of gradient flows. Numerical simulations show that these simple rules can account for the behavior observed in experiments, suggesting a possible mechanical mechanism for adhesion-independent motility. AU - Jankowiak, Gaspard AU - Peurichard, Diane AU - Reversat, Anne AU - Schmeiser, Christian AU - Sixt, Michael K ID - 7623 IS - 3 JF - Mathematical Models and Methods in Applied Sciences SN - 02182025 TI - Modeling adhesion-independent cell migration VL - 30 ER - TY - JOUR AB - In plant cells, environmental stressors promote changes in connectivity between the cortical ER and the PM. Although this process is tightly regulated in space and time, the molecular signals and structural components mediating these changes in inter-organelle communication are only starting to be characterized. In this report, we confirm the presence of a putative tethering complex containing the synaptotagmins 1 and 5 (SYT1 and SYT5) and the Ca2+ and lipid binding protein 1 (CLB1/SYT7). This complex is enriched at ER-PM contact sites (EPCS), have slow responses to changes in extracellular Ca2+, and display severe cytoskeleton-dependent rearrangements in response to the trivalent lanthanum (La3+) and gadolinium (Gd3+) rare earth elements (REEs). Although REEs are generally used as non-selective cation channel blockers at the PM, here we show that the slow internalization of REEs into the cytosol underlies the activation of the Ca2+/Calmodulin intracellular signaling, the accumulation of phosphatidylinositol-4-phosphate (PI4P) at the PM, and the cytoskeleton-dependent rearrangement of the SYT1/SYT5 EPCS complexes. We propose that the observed EPCS rearrangements act as a slow adaptive response to sustained stress conditions, and that this process involves the accumulation of stress-specific phosphoinositides species at the PM. AU - Lee, E AU - Vila Nova Santana, B AU - Samuels, E AU - Benitez-Fuente, F AU - Corsi, E AU - Botella, MA AU - Perez-Sancho, J AU - Vanneste, S AU - Friml, Jiří AU - Macho, A AU - Alves Azevedo, A AU - Rosado, A ID - 7646 IS - 14 JF - Journal of Experimental Botany SN - 0022-0957 TI - Rare earth elements induce cytoskeleton-dependent and PI4P-associated rearrangement of SYT1/SYT5 ER-PM contact site complexes in Arabidopsis VL - 71 ER - TY - JOUR AB - We propose that correlations among neurons are generically strong enough to organize neural activity patterns into a discrete set of clusters, which can each be viewed as a population codeword. Our reasoning starts with the analysis of retinal ganglion cell data using maximum entropy models, showing that the population is robustly in a frustrated, marginally sub-critical, or glassy, state. This leads to an argument that neural populations in many other brain areas might share this structure. Next, we use latent variable models to show that this glassy state possesses well-defined clusters of neural activity. Clusters have three appealing properties: (i) clusters exhibit error correction, i.e., they are reproducibly elicited by the same stimulus despite variability at the level of constituent neurons; (ii) clusters encode qualitatively different visual features than their constituent neurons; and (iii) clusters can be learned by downstream neural circuits in an unsupervised fashion. We hypothesize that these properties give rise to a “learnable” neural code which the cortical hierarchy uses to extract increasingly complex features without supervision or reinforcement. AU - Berry, Michael J. AU - Tkačik, Gašper ID - 7656 JF - Frontiers in Computational Neuroscience TI - Clustering of neural activity: A design principle for population codes VL - 14 ER - TY - JOUR AB - Following on from our recent work, we investigate a stochastic approach to non-equilibrium quantum spin systems. We show how the method can be applied to a variety of physical observables and for different initial conditions. We provide exact formulae of broad applicability for the time-dependence of expectation values and correlation functions following a quantum quench in terms of averages over classical stochastic processes. We further explore the behavior of the classical stochastic variables in the presence of dynamical quantum phase transitions, including results for their distributions and correlation functions. We provide details on the numerical solution of the associated stochastic differential equations, and examine the growth of fluctuations in the classical description. We discuss the strengths and limitations of the current implementation of the stochastic approach and the potential for further development. AU - De Nicola, Stefano AU - Doyon, B. AU - Bhaseen, M. J. ID - 7638 IS - 1 JF - Journal of Statistical Mechanics: Theory and Experiment TI - Non-equilibrium quantum spin dynamics from classical stochastic processes VL - 2020 ER - TY - JOUR AB - The evolution of finitely many particles obeying Langevin dynamics is described by Dean–Kawasaki equations, a class of stochastic equations featuring a non-Lipschitz multiplicative noise in divergence form. We derive a regularised Dean–Kawasaki model based on second order Langevin dynamics by analysing a system of particles interacting via a pairwise potential. Key tools of our analysis are the propagation of chaos and Simon's compactness criterion. The model we obtain is a small-noise stochastic perturbation of the undamped McKean–Vlasov equation. We also provide a high-probability result for existence and uniqueness for our model. AU - Cornalba, Federico AU - Shardlow, Tony AU - Zimmer, Johannes ID - 7637 IS - 2 JF - Nonlinearity SN - 09517715 TI - From weakly interacting particles to a regularised Dean-Kawasaki model VL - 33 ER - TY - JOUR AB - Metabotropic γ-aminobutyric acid (GABAB) receptors contribute to the control of network activity and information processing in hippocampal circuits by regulating neuronal excitability and synaptic transmission. The dysfunction in the dentate gyrus (DG) has been implicated in Alzheimer´s disease (AD). Given the involvement of GABAB receptors in AD, to determine their subcellular localisation and possible alteration in granule cells of the DG in a mouse model of AD at 12 months of age, we used high-resolution immunoelectron microscopic analysis. Immunohistochemistry at the light microscopic level showed that the regional and cellular expression pattern of GABAB1 was similar in an AD model mouse expressing mutated human amyloid precursor protein and presenilin1 (APP/PS1) and in age-matched wild type mice. High-resolution immunoelectron microscopy revealed a distance-dependent gradient of immunolabelling for GABAB receptors, increasing from proximal to distal dendrites in both wild type and APP/PS1 mice. However, the overall density of GABAB receptors at the neuronal surface of these postsynaptic compartments of granule cells was significantly reduced in APP/PS1 mice. Parallel to this reduction in surface receptors, we found a significant increase in GABAB1 at cytoplasmic sites. GABAB receptors were also detected at presynaptic sites in the molecular layer of the DG. We also found a decrease in plasma membrane GABAB receptors in axon terminals contacting dendritic spines of granule cells, which was more pronounced in the outer than in the inner molecular layer. Altogether, our data showing post- and presynaptic reduction in surface GABAB receptors in the DG suggest the alteration of the GABAB-mediated modulation of excitability and synaptic transmission in granule cells, which may contribute to the cognitive dysfunctions in the APP/PS1 model of AD AU - Martín-Belmonte, Alejandro AU - Aguado, Carolina AU - Alfaro-Ruíz, Rocío AU - Moreno-Martínez, Ana Esther AU - De La Ossa, Luis AU - Martínez-Hernández, José AU - Buisson, Alain AU - Shigemoto, Ryuichi AU - Fukazawa, Yugo AU - Luján, Rafael ID - 7664 IS - 7 JF - International journal of molecular sciences TI - Density of GABAB receptors is reduced in granule cells of the hippocampus in a mouse model of Alzheimer's disease VL - 21 ER - TY - JOUR AB - Acute brain slice preparation is a powerful experimental model for investigating the characteristics of synaptic function in the brain. Although brain tissue is usually cut at ice-cold temperature (CT) to facilitate slicing and avoid neuronal damage, exposure to CT causes molecular and architectural changes of synapses. To address these issues, we investigated ultrastructural and electrophysiological features of synapses in mouse acute cerebellar slices prepared at ice-cold and physiological temperature (PT). In the slices prepared at CT, we found significant spine loss and reconstruction, synaptic vesicle rearrangement and decrease in synaptic proteins, all of which were not detected in slices prepared at PT. Consistent with these structural findings, slices prepared at PT showed higher release probability. Furthermore, preparation at PT allows electrophysiological recording immediately after slicing resulting in higher detectability of long-term depression (LTD) after motor learning compared with that at CT. These results indicate substantial advantages of the slice preparation at PT for investigating synaptic functions in different physiological conditions. AU - Eguchi, Kohgaku AU - Velicky, Philipp AU - Hollergschwandtner, Elena AU - Itakura, Makoto AU - Fukazawa, Yugo AU - Danzl, Johann G AU - Shigemoto, Ryuichi ID - 7665 JF - Frontiers in Cellular Neuroscience SN - 16625102 TI - Advantages of acute brain slices prepared at physiological temperature in the characterization of synaptic functions VL - 14 ER - TY - JOUR AB - Wood, as the most abundant carbon dioxide storing bioresource, is currently driven beyond its traditional use through creative innovations and nanotechnology. For many properties the micro- and nanostructure plays a crucial role and one key challenge is control and detection of chemical and physical processes in the confined microstructure and nanopores of the wooden cell wall. In this study, correlative Raman and atomic force microscopy show high potential for tracking in situ molecular rearrangement of wood polymers during compression. More water molecules (interpreted as wider cellulose microfibril distances) and disentangling of hemicellulose chains are detected in the opened cell wall regions, whereas an increase of lignin is revealed in the compressed areas. These results support a new more “loose” cell wall model based on flexible lignin nanodomains and advance our knowledge of the molecular reorganization during deformation of wood for optimized processing and utilization. AU - Felhofer, Martin AU - Bock, Peter AU - Singh, Adya AU - Prats Mateu, Batirtze AU - Zirbs, Ronald AU - Gierlinger, Notburga ID - 7663 IS - 4 JF - Nano Letters TI - Wood deformation leads to rearrangement of molecules at the nanoscale VL - 20 ER - TY - JOUR AB - Generalizing the decomposition of a connected planar graph into a tree and a dual tree, we prove a combinatorial analog of the classic Helmholtz–Hodge decomposition of a smooth vector field. Specifically, we show that for every polyhedral complex, K, and every dimension, p, there is a partition of the set of p-cells into a maximal p-tree, a maximal p-cotree, and a collection of p-cells whose cardinality is the p-th reduced Betti number of K. Given an ordering of the p-cells, this tri-partition is unique, and it can be computed by a matrix reduction algorithm that also constructs canonical bases of cycle and boundary groups. AU - Edelsbrunner, Herbert AU - Ölsböck, Katharina ID - 7666 JF - Discrete and Computational Geometry SN - 01795376 TI - Tri-partitions and bases of an ordered complex VL - 64 ER - TY - JOUR AB - For any free oriented Borel–Moore homology theory A, we construct an associative product on the A-theory of the stack of Higgs torsion sheaves over a projective curve C. We show that the resulting algebra AHa0C admits a natural shuffle presentation, and prove it is faithful when A is replaced with usual Borel–Moore homology groups. We also introduce moduli spaces of stable triples, heavily inspired by Nakajima quiver varieties, whose A-theory admits an AHa0C-action. These triples can be interpreted as certain sheaves on PC(ωC⊕OC). In particular, we obtain an action of AHa0C on the cohomology of Hilbert schemes of points on T∗C. AU - Minets, Sasha ID - 7683 IS - 2 JF - Selecta Mathematica, New Series SN - 10221824 TI - Cohomological Hall algebras for Higgs torsion sheaves, moduli of triples and sheaves on surfaces VL - 26 ER - TY - JOUR AB - Large overpotentials upon discharge and charge of Li-O2 cells have motivated extensive research into heterogeneous solid electrocatalysts or non-carbon electrodes with the aim to improve rate capability, round-trip efficiency and cycle life. These features are equally governed by parasitic reactions, which are now recognized to be caused by the highly reactive singlet oxygen (1O2). However, the link between the presence of electrocatalysts and 1O2 formation in metal-O2 cells is unknown. Here, we show that, compared to pristine carbon black electrodes, a representative selection of electrocatalysts or non-carbon electrodes (noble metal, transition metal compounds) may both slightly reduce or severely increase the 1O2 formation. The individual reaction steps, where the surfaces impact the 1O2 yield are deciphered, showing that 1O2 yield from superoxide disproportionation as well as the decomposition of trace H2O2 are sensitive to catalysts. Transition metal compounds in general are prone to increase 1O2. AU - Samojlov, Aleksej AU - Schuster, David AU - Kahr, Jürgen AU - Freunberger, Stefan Alexander ID - 7672 IS - 12 JF - Electrochimica Acta TI - Surface and catalyst driven singlet oxygen formation in Li-O2 cells VL - 362 ER - TY - JOUR AU - Gridchyn, Igor AU - Schönenberger, Philipp AU - O'Neill, Joseph AU - Csicsvari, Jozsef L ID - 7684 IS - 2 JF - Neuron SN - 08966273 TI - Assembly-specific disruption of hippocampal replay leads to selective memory deficit VL - 106 ER - TY - JOUR AB - The agricultural green revolution spectacularly enhanced crop yield and lodging resistance with modified DELLA-mediated gibberellin signaling. However, this was achieved at the expense of reduced nitrogen-use efficiency (NUE). Recently, Wu et al. revealed novel gibberellin signaling that provides a blueprint for improving tillering and NUE in Green Revolution varieties (GRVs). AU - Xue, Huidan AU - Zhang, Yuzhou AU - Xiao, Guanghui ID - 7686 IS - 6 JF - Trends in Plant Science SN - 1360-1385 TI - Neo-gibberellin signaling: Guiding the next generation of the green revolution VL - 25 ER - TY - JOUR AB - Mutations in NDUFS4, which encodes an accessory subunit of mitochondrial oxidative phosphorylation (OXPHOS) complex I (CI), induce Leigh syndrome (LS). LS is a poorly understood pediatric disorder featuring brain-specific anomalies and early death. To study the LS pathomechanism, we here compared OXPHOS proteomes between various Ndufs4−/− mouse tissues. Ndufs4−/− animals displayed significantly lower CI subunit levels in brain/diaphragm relative to other tissues (liver/heart/kidney/skeletal muscle), whereas other OXPHOS subunit levels were not reduced. Absence of NDUFS4 induced near complete absence of the NDUFA12 accessory subunit, a 50% reduction in other CI subunit levels, and an increase in specific CI assembly factors. Among the latter, NDUFAF2 was most highly increased. Regarding NDUFS4, NDUFA12 and NDUFAF2, identical results were obtained in Ndufs4−/− mouse embryonic fibroblasts (MEFs) and NDUFS4-mutated LS patient cells. Ndufs4−/− MEFs contained active CI in situ but blue-native-PAGE highlighted that NDUFAF2 attached to an inactive CI subcomplex (CI-830) and inactive assemblies of higher MW. In NDUFA12-mutated LS patient cells, NDUFA12 absence did not reduce NDUFS4 levels but triggered NDUFAF2 association to active CI. BN-PAGE revealed no such association in LS patient fibroblasts with mutations in other CI subunit-encoding genes where NDUFAF2 was attached to CI-830 (NDUFS1, NDUFV1 mutation) or not detected (NDUFS7 mutation). Supported by enzymological and CI in silico structural analysis, we conclude that absence of NDUFS4 induces near complete absence of NDUFA12 but not vice versa, and that NDUFAF2 stabilizes active CI in Ndufs4−/− mice and LS patient cells, perhaps in concert with mitochondrial inner membrane lipids. AU - Adjobo-Hermans, Merel J.W. AU - De Haas, Ria AU - Willems, Peter H.G.M. AU - Wojtala, Aleksandra AU - Van Emst-De Vries, Sjenet E. AU - Wagenaars, Jori A. AU - Van Den Brand, Mariel AU - Rodenburg, Richard J. AU - Smeitink, Jan A.M. AU - Nijtmans, Leo G. AU - Sazanov, Leonid A AU - Wieckowski, Mariusz R. AU - Koopman, Werner J.H. ID - 7788 IS - 8 JF - Biochimica et Biophysica Acta - Bioenergetics SN - 00052728 TI - NDUFS4 deletion triggers loss of NDUFA12 in Ndufs4−/− mice and Leigh syndrome patients: A stabilizing role for NDUFAF2 VL - 1861 ER - TY - JOUR AB - During embryonic and postnatal development, organs and tissues grow steadily to achieve their final size at the end of puberty. However, little is known about the cellular dynamics that mediate postnatal growth. By combining in vivo clonal lineage tracing, proliferation kinetics, single-cell transcriptomics, andin vitro micro-pattern experiments, we resolved the cellular dynamics taking place during postnatal skin epidermis expansion. Our data revealed that harmonious growth is engineered by a single population of developmental progenitors presenting a fixed fate imbalance of self-renewing divisions with an ever-decreasing proliferation rate. Single-cell RNA sequencing revealed that epidermal developmental progenitors form a more uniform population compared with adult stem and progenitor cells. Finally, we found that the spatial pattern of cell division orientation is dictated locally by the underlying collagen fiber orientation. Our results uncover a simple design principle of organ growth where progenitors and differentiated cells expand in harmony with their surrounding tissues. AU - Dekoninck, Sophie AU - Hannezo, Edouard B AU - Sifrim, Alejandro AU - Miroshnikova, Yekaterina A. AU - Aragona, Mariaceleste AU - Malfait, Milan AU - Gargouri, Souhir AU - De Neunheuser, Charlotte AU - Dubois, Christine AU - Voet, Thierry AU - Wickström, Sara A. AU - Simons, Benjamin D. AU - Blanpain, Cédric ID - 7789 IS - 3 JF - Cell SN - 00928674 TI - Defining the design principles of skin epidermis postnatal growth VL - 181 ER - TY - JOUR AB - Hormonal signalling in animals often involves direct transcription factor-hormone interactions that modulate gene expression. In contrast, plant hormone signalling is most commonly based on de-repression via the degradation of transcriptional repressors. Recently, we uncovered a non-canonical signalling mechanism for the plant hormone auxin whereby auxin directly affects the activity of the atypical auxin response factor (ARF), ETTIN towards target genes without the requirement for protein degradation. Here we show that ETTIN directly binds auxin, leading to dissociation from co-repressor proteins of the TOPLESS/TOPLESS-RELATED family followed by histone acetylation and induction of gene expression. This mechanism is reminiscent of animal hormone signalling as it affects the activity towards regulation of target genes and provides the first example of a DNA-bound hormone receptor in plants. Whilst auxin affects canonical ARFs indirectly by facilitating degradation of Aux/IAA repressors, direct ETTIN-auxin interactions allow switching between repressive and de-repressive chromatin states in an instantly-reversible manner. AU - Kuhn, André AU - Ramans Harborough, Sigurd AU - McLaughlin, Heather M AU - Natarajan, Bhavani AU - Verstraeten, Inge AU - Friml, Jiří AU - Kepinski, Stefan AU - Østergaard, Lars ID - 7793 JF - eLife SN - 2050-084X TI - Direct ETTIN-auxin interaction controls chromatin states in gynoecium development VL - 9 ER - TY - JOUR AB - We prove a lower bound for the free energy (per unit volume) of the two-dimensional Bose gas in the thermodynamic limit. We show that the free energy at density 𝜌 and inverse temperature 𝛽 differs from the one of the noninteracting system by the correction term 𝜋𝜌𝜌𝛽𝛽 . Here, is the scattering length of the interaction potential, and 𝛽 is the inverse Berezinskii–Kosterlitz–Thouless critical temperature for superfluidity. The result is valid in the dilute limit 𝜌 and if 𝛽𝜌 . AU - Deuchert, Andreas AU - Mayer, Simon AU - Seiringer, Robert ID - 7790 JF - Forum of Mathematics, Sigma TI - The free energy of the two-dimensional dilute Bose gas. I. Lower bound VL - 8 ER - TY - JOUR AB - Phonon polaritons—light coupled to lattice vibrations—in polar van der Waals crystals are promising candidates for controlling the flow of energy on the nanoscale due to their strong field confinement, anisotropic propagation and ultra-long lifetime in the picosecond range1,2,3,4,5. However, the lack of tunability of their narrow and material-specific spectral range—the Reststrahlen band—severely limits their technological implementation. Here, we demonstrate that intercalation of Na atoms in the van der Waals semiconductor α-V2O5 enables a broad spectral shift of Reststrahlen bands, and that the phonon polaritons excited show ultra-low losses (lifetime of 4 ± 1 ps), similar to phonon polaritons in a non-intercalated crystal (lifetime of 6 ± 1 ps). We expect our intercalation method to be applicable to other van der Waals crystals, opening the door for the use of phonon polaritons in broad spectral bands in the mid-infrared domain. AU - Taboada-Gutiérrez, Javier AU - Álvarez-Pérez, Gonzalo AU - Duan, Jiahua AU - Ma, Weiliang AU - Crowley, Kyle AU - Prieto Gonzalez, Ivan AU - Bylinkin, Andrei AU - Autore, Marta AU - Volkova, Halyna AU - Kimura, Kenta AU - Kimura, Tsuyoshi AU - Berger, M. H. AU - Li, Shaojuan AU - Bao, Qiaoliang AU - Gao, Xuan P.A. AU - Errea, Ion AU - Nikitin, Alexey Y. AU - Hillenbrand, Rainer AU - Martín-Sánchez, Javier AU - Alonso-González, Pablo ID - 7792 JF - Nature Materials SN - 14761122 TI - Broad spectral tuning of ultra-low-loss polaritons in a van der Waals crystal by intercalation VL - 19 ER -