@article{15239, abstract = {Using images from the Hubble Space Telescope Advanced Camera for Surveys, we measure the rate of cooling of white dwarfs in the globular cluster 47 Tucanae and compare it to modelled cooling curves. We examine the effects of the outer convective envelope reaching the nearly isothermal degenerate core and the release of latent heat during core crystallization on the white dwarf cooling rates. For white dwarfs typical of 47 Tuc, the onset of these effects occur at similar times. The latent heat released during crystallization is a small heat source. In contrast, the heat reservoir of the degenerate core is substantially larger. When the convective envelope reaches the nearly isothermal interior of the white dwarf, the star becomes brighter than it would be in the absence of this effect. Our modelled cooling curves that include this convective coupling closely match the observed luminosity function of the white dwarfs in 47 Tuc.}, author = {Obertas, Alysa and Caiazzo, Ilaria and Heyl, Jeremy and Richer, Harvey and Kalirai, Jason and Tremblay, Pier-Emmanuel}, issn = {1365-2966}, journal = {Monthly Notices of the Royal Astronomical Society}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, number = {1}, pages = {677--682}, publisher = {Oxford University Press}, title = {{The onset of convective coupling and freezing in the white dwarfs of 47 Tucanae}}, doi = {10.1093/mnras/stx2759}, volume = {474}, year = {2017}, } @article{15240, abstract = {Multi-epoch observations with the Advanced Camera Survey and WFC3 on the Hubble Space Telescope provide a unique and comprehensive probe of stellar dynamics within 47 Tucanae. We confront analytic models of the globular cluster with the observed stellar proper motions that probe along the main sequence from just above 0.8–0.1M⊙ as well as white dwarfs younger than 1 Gyr. One field lies just beyond the half-light radius where dynamical models (e.g., lowered Maxwellian distributions) make robust predictions for the stellar proper motions. The observed proper motions in this outer field show evidence for anisotropy in the velocity distribution as well as skewness; the latter is evidence of rotation. The measured velocity dispersions and surface brightness distributions agree in detail with a rotating anisotropic model of the stellar distribution function with mild dependence of the proper-motion dispersion on mass. However, the best-fitting models underpredict the rotation and skewness of the stellar velocities. In the second field, centered on the core of the cluster, the mass segregation in proper motion is much stronger. Nevertheless the model developed in the outer field can be extended inward by taking this mass segregation into account in a heuristic fashion. The proper motions of the main-sequence stars yield a mass estimate of the cluster of at a distance of 4.7 kpc. By comparing the proper motions of a sample of giant and subgiant stars with the observed radial velocities we estimate the distance to the cluster kinematically to be 4.29 ± 0.47 kpc.}, author = {Heyl, J. and Caiazzo, Ilaria and Richer, H. and Anderson, J. and Kalirai, J. and Parada, J.}, issn = {1538-4357}, journal = {The Astrophysical Journal}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, number = {2}, publisher = {American Astronomical Society}, title = {{Deep HST imaging in 47 Tucanae: A global dynamical model}}, doi = {10.3847/1538-4357/aa974f}, volume = {850}, year = {2017}, } @article{15241, abstract = {We present a model to account for the observed debris discs around young white dwarfs and the presence of metal lines in their spectra. Stellar evolution models predict that the mass-loss on the AGB will be pulsed; furthermore, observations indicate that the bulk of the mass-loss occurs on the AGB. In this case, if the progenitors of the white dwarfs had remnants of planetary formation like the Sun’s Oort cloud or the Kuiper Belt and a planet lying within that cloud or nearby, we find that up to 2 per cent of the planetesimals will fall either into planet-crossing orbits or into chaotic regions after the mass-loss, depending on the location and mass of the planet (from Mars to Neptune). This yields a sufficient mass of comets that can be scattered towards the star, form a debris disc and pollute the atmosphere.}, author = {Caiazzo, Ilaria and Heyl, Jeremy S.}, issn = {1365-2966}, journal = {Monthly Notices of the Royal Astronomical Society}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, number = {3}, pages = {2750--2759}, publisher = {Oxford University Press}, title = {{Polluting white dwarfs with perturbed exo-comets}}, doi = {10.1093/mnras/stx1036}, volume = {469}, year = {2017}, } @article{15243, abstract = {High-energy (>250 keV) emission has been detected persisting for several tens of seconds after the initial spike of magnetar giant flares (GFs). It has been conjectured that this emission might arise via inverse Compton scattering in a highly extended corona generated by super-Eddington outflows high up in the magnetosphere. In this paper, we undertake a detailed examination of this model. We investigate the properties of the required scatterers, and whether the mechanism is consistent with the degree of pulsed emission observed in the tail of the GF. We conclude that the mechanism is consistent with current data, although the origin of the scattering population remains an open question. We propose an alternative picture in which the emission is closer to that star and is dominated by synchrotron radiation. The Reuven Ramaty High Energy Solar Spectroscopic Imager observations of the 2004 December flare modestly favour this latter picture. We assess the prospects for the Fermi Gamma-ray Space Telescope to detect and characterize a similar high-energy component in a future GF. Such a detection should help to resolve some of the outstanding issues.}, author = {Elenbaas, C. and Huppenkothen, D. and Omand, C. and Watts, A. L. and Bissaldi, E. and Caiazzo, Ilaria and Heyl, J.}, issn = {1365-2966}, journal = {Monthly Notices of the Royal Astronomical Society}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, number = {2}, pages = {1856--1872}, publisher = {Oxford University Press}, title = {{Magnetar giant flare high-energy emission}}, doi = {10.1093/mnras/stx1727}, volume = {471}, year = {2017}, } @article{1528, abstract = {We consider N×N Hermitian random matrices H consisting of blocks of size M≥N6/7. The matrix elements are i.i.d. within the blocks, close to a Gaussian in the four moment matching sense, but their distribution varies from block to block to form a block-band structure, with an essential band width M. We show that the entries of the Green’s function G(z)=(H−z)−1 satisfy the local semicircle law with spectral parameter z=E+iη down to the real axis for any η≫N−1, using a combination of the supersymmetry method inspired by Shcherbina (J Stat Phys 155(3): 466–499, 2014) and the Green’s function comparison strategy. Previous estimates were valid only for η≫M−1. The new estimate also implies that the eigenvectors in the middle of the spectrum are fully delocalized.}, author = {Bao, Zhigang and Erdös, László}, issn = {01788051}, journal = {Probability Theory and Related Fields}, number = {3-4}, pages = {673 -- 776}, publisher = {Springer}, title = {{Delocalization for a class of random block band matrices}}, doi = {10.1007/s00440-015-0692-y}, volume = {167}, year = {2017}, } @article{1061, abstract = {Background: Metabolic engineering and synthetic biology of cyanobacteria offer a promising sustainable alternative approach for fossil-based ethylene production, by using sunlight via oxygenic photosynthesis, to convert carbon dioxide directly into ethylene. Towards this, both well-studied cyanobacteria, i.e., Synechocystis sp PCC 6803 and Synechococcus elongatus PCC 7942, have been engineered to produce ethylene by introducing the ethylene-forming enzyme (Efe) from Pseudomonas syringae pv. phaseolicola PK2 (the Kudzu strain), which catalyzes the conversion of the ubiquitous tricarboxylic acid cycle intermediate 2-oxoglutarate into ethylene. Results: This study focuses on Synechocystis sp PCC 6803 and shows stable ethylene production through the integration of a codon-optimized version of the efe gene under control of the Ptrc promoter and the core Shine-Dalgarno sequence (5\'-AGGAGG-3\') as the ribosome-binding site (RBS), at the slr0168 neutral site. We have increased ethylene production twofold by RBS screening and further investigated improving ethylene production from a single gene copy of efe, using multiple tandem promoters and by putting our best construct on an RSF1010-based broad-host-self-replicating plasmid, which has a higher copy number than the genome. Moreover, to raise the intracellular amounts of the key Efe substrate, 2-oxoglutarate, from which ethylene is formed, we constructed a glycogen-synthesis knockout mutant (glgC) and introduced the ethylene biosynthetic pathway in it. Under nitrogen limiting conditions, the glycogen knockout strain has increased intracellular 2-oxoglutarate levels; however, surprisingly, ethylene production was lower in this strain than in the wild-type background. Conclusion: Making use of different RBS sequences, production of ethylene ranging over a 20-fold difference has been achieved. However, a further increase of production through multiple tandem promoters and a broad-host plasmid was not achieved speculating that the transcription strength and the gene copy number are not the limiting factors in our system.}, author = {Veetil, Vinod and Angermayr, Andreas and Hellingwerf, Klaas}, issn = {14752859}, journal = {Microbial Cell Factories}, number = {1}, publisher = {BioMed Central}, title = {{Ethylene production with engineered Synechocystis sp PCC 6803 strains}}, doi = {10.1186/s12934-017-0645-5}, volume = {16}, year = {2017}, } @article{1062, abstract = {Mouse chromaffin cells (MCCs) generate action potential (AP) firing that regulates the Ca2+‐dependent release of catecholamines (CAs). Recent findings indicate that MCCs possess a variety of spontaneous firing modes that span from the common ‘tonic‐irregular’ to the less frequent ‘burst’ firing. This latter is evident in a small fraction of MCCs but occurs regularly when Nav1.3/1.7 channels are made less available or when the Slo1β2‐subunit responsible for BK channel inactivation is deleted. Burst firing causes large increases of Ca2+‐entry and potentiates CA release by ∼3.5‐fold and thus may be a key mechanism for regulating MCC function. With the aim to uncover a physiological role for burst‐firing we investigated the effects of acidosis on MCC activity. Lowering the extracellular pH (pHo) from 7.4 to 7.0 and 6.6 induces cell depolarizations of 10–15 mV that generate repeated bursts. Bursts at pHo 6.6 lasted ∼330 ms, occurred at 1–2 Hz and caused an ∼7‐fold increase of CA cumulative release. Burst firing originates from the inhibition of the pH‐sensitive TASK‐1/TASK‐3 channels and from a 40% BK channel conductance reduction at pHo 7.0. The same pHo had little or no effect on Nav, Cav, Kv and SK channels that support AP firing in MCCs. Burst firing of pHo 6.6 could be mimicked by mixtures of the TASK‐1 blocker A1899 (300 nm) and BK blocker paxilline (300 nm) and could be prevented by blocking L‐type channels by adding 3 μm nifedipine. Mixtures of the two blockers raised cumulative CA‐secretion even more than low pHo (∼12‐fold), showing that the action of protons on vesicle release is mainly a result of the ionic conductance changes that increase Ca2+‐entry during bursts. Our data provide direct evidence suggesting that MCCs respond to low pHo with sustained depolarization, burst firing and enhanced CA‐secretion, thus mimicking the physiological response of CCs to acute acidosis and hyperkalaemia generated during heavy exercise and muscle fatigue.}, author = {Guarina, Laura and Vandael, David H and Carabelli, Valentina and Carbone, Emilio}, journal = {Journal of Physiology}, number = {8}, pages = {2587 -- 2609 }, publisher = {Wiley-Blackwell}, title = {{Low pH inf o boosts burst firing and catecholamine release by blocking TASK-1 and BK channels while preserving Cav1 channels in mouse chromaffin cells}}, doi = {10.1113/JP273735}, volume = {595}, year = {2017}, } @article{1063, abstract = {Severe environmental change can drive a population extinct unless the population adapts in time to the new conditions (“evolutionary rescue”). How does biparental sexual reproduction influence the chances of population persistence compared to clonal reproduction or selfing? In this article, we set up a one‐locus two‐allele model for adaptation in diploid species, where rescue is contingent on the establishment of the mutant homozygote. Reproduction can occur by random mating, selfing, or clonally. Random mating generates and destroys the rescue mutant; selfing is efficient at generating it but at the same time depletes the heterozygote, which can lead to a low mutant frequency in the standing genetic variation. Due to these (and other) antagonistic effects, we find a nontrivial dependence of population survival on the rate of sex/selfing, which is strongly influenced by the dominance coefficient of the mutation before and after the environmental change. Importantly, since mating with the wild‐type breaks the mutant homozygote up, a slow decay of the wild‐type population size can impede rescue in randomly mating populations.}, author = {Uecker, Hildegard}, issn = {0014-3820}, journal = {Evolution}, number = {4}, pages = {845 -- 858}, publisher = {Wiley-Blackwell}, title = {{Evolutionary rescue in randomly mating, selfing, and clonal populations}}, doi = {10.1111/evo.13191}, volume = {71}, year = {2017}, } @article{1065, abstract = {We consider the problem of reachability in pushdown graphs. We study the problem for pushdown graphs with constant treewidth. Even for pushdown graphs with treewidth 1, for the reachability problem we establish the following: (i) the problem is PTIME-complete, and (ii) any subcubic algorithm for the problem would contradict the k-clique conjecture and imply faster combinatorial algorithms for cliques in graphs.}, author = {Chatterjee, Krishnendu and Osang, Georg F}, issn = {0020-0190}, journal = {Information Processing Letters}, pages = {25 -- 29}, publisher = {Elsevier}, title = {{Pushdown reachability with constant treewidth}}, doi = {10.1016/j.ipl.2017.02.003}, volume = {122}, year = {2017}, } @article{1066, abstract = {Simulation is an attractive alternative to language inclusion for automata as it is an under-approximation of language inclusion, but usually has much lower complexity. Simulation has also been extended in two orthogonal directions, namely, (1) fair simulation, for simulation over specified set of infinite runs; and (2) quantitative simulation, for simulation between weighted automata. While fair trace inclusion is PSPACE-complete, fair simulation can be computed in polynomial time. For weighted automata, the (quantitative) language inclusion problem is undecidable in general, whereas the (quantitative) simulation reduces to quantitative games, which admit pseudo-polynomial time algorithms. In this work, we study (quantitative) simulation for weighted automata with Büchi acceptance conditions, i.e., we generalize fair simulation from non-weighted automata to weighted automata. We show that imposing Büchi acceptance conditions on weighted automata changes many fundamental properties of the simulation games, yet they still admit pseudo-polynomial time algorithms.}, author = {Chatterjee, Krishnendu and Henzinger, Thomas A and Otop, Jan and Velner, Yaron}, journal = {Information and Computation}, number = {2}, pages = {143 -- 166}, publisher = {Elsevier}, title = {{Quantitative fair simulation games}}, doi = {10.1016/j.ic.2016.10.006}, volume = {254}, year = {2017}, } @phdthesis{10663, abstract = {The superconducting state of matter enables one to observe quantum effects on the macroscopic scale and hosts many fascinating phenomena. Topological defects of the superconducting order parameter, such as vortices and fluxoid states in multiply connected structures, are often the key ingredients of these phenomena. This dissertation describes a new mode of magnetic force microscopy (Φ0-MFM) for investigating vortex and fluxoid sates in mesoscopic superconducting (SC) structures. The technique relies on the magneto-mechanical coupling of a MFM cantilever to the motion of fluxons. The novelty of the technique is that a magnetic particle attached to the cantilever is used not only to sense the state of a SC structure, but also as a primary source of the inhomogeneous magnetic field which induces that state. Φ0-MFM enables us to map the transitions between tip-induced states during a scan: at the positions of the tip, where the two lowest energy states become degenerate, small oscillations of the tip drive the transitions between these states, which causes a significant shift in the resonant frequency and dissipation of the cantilever. For narrow-wall aluminum rings, the mapped fluxoid transitions form concentric contours on a scan. We show that the changes in the cantilever resonant frequency and dissipation are well-described by a stochastic resonance (SR) of cantilever-driven thermally activated phase slips (TAPS). The SR model allows us to experimentally determine the rate of TAPS and compare it to the Langer-Ambegaokar-McCumber-Halperin (LAMH) theory for TAPS in 1D superconducting structures. Further, we use the SR model to qualitatively study the effects of a locally applied magnetic field on the phase slip rate in rings containing constrictions. The states with multiple vortices or winding numbers could be useful for the development of novel superconducting devices, or the study of vortex interactions and interference effects. Using Φ0-MFM allows us to induce, probe and control fluxoid states in thin wall structures comprised of multiple loops. We show that Φ0-MFM images of the fluxoid transitions allow us to identify the underlying states and to investigate their energetics and dynamics even in complicated structures.}, author = {Polshyn, Hryhoriy}, keywords = {physics, superconductivity, magnetic force microscopy, phase slips}, pages = {103}, publisher = {University of Illinois at Urbana-Champaign}, title = {{Magnetic force microscopy studies of mesoscopic superconducting structures}}, year = {2017}, } @article{1067, abstract = {Embryo morphogenesis relies on highly coordinated movements of different tissues. However, remarkably little is known about how tissues coordinate their movements to shape the embryo. In zebrafish embryogenesis, coordinated tissue movements first become apparent during “doming,” when the blastoderm begins to spread over the yolk sac, a process involving coordinated epithelial surface cell layer expansion and mesenchymal deep cell intercalations. Here, we find that active surface cell expansion represents the key process coordinating tissue movements during doming. By using a combination of theory and experiments, we show that epithelial surface cells not only trigger blastoderm expansion by reducing tissue surface tension, but also drive blastoderm thinning by inducing tissue contraction through radial deep cell intercalations. Thus, coordinated tissue expansion and thinning during doming relies on surface cells simultaneously controlling tissue surface tension and radial tissue contraction.}, author = {Morita, Hitoshi and Grigolon, Silvia and Bock, Martin and Krens, Gabriel and Salbreux, Guillaume and Heisenberg, Carl-Philipp J}, issn = {1534-5807}, journal = {Developmental Cell}, number = {4}, pages = {354 -- 366}, publisher = {Cell Press}, title = {{The physical basis of coordinated tissue spreading in zebrafish gastrulation}}, doi = {10.1016/j.devcel.2017.01.010}, volume = {40}, year = {2017}, } @article{1072, abstract = {Given a finite set of points in Rn and a radius parameter, we study the Čech, Delaunay–Čech, Delaunay (or alpha), and Wrap complexes in the light of generalized discrete Morse theory. Establishing the Čech and Delaunay complexes as sublevel sets of generalized discrete Morse functions, we prove that the four complexes are simple-homotopy equivalent by a sequence of simplicial collapses, which are explicitly described by a single discrete gradient field.}, author = {Bauer, Ulrich and Edelsbrunner, Herbert}, journal = {Transactions of the American Mathematical Society}, number = {5}, pages = {3741 -- 3762}, publisher = {American Mathematical Society}, title = {{The Morse theory of Čech and delaunay complexes}}, doi = {10.1090/tran/6991}, volume = {369}, year = {2017}, } @article{1073, abstract = {Let X and Y be finite simplicial sets (e.g. finite simplicial complexes), both equipped with a free simplicial action of a finite group G. Assuming that Y is d-connected and dimX≤2d, for some d≥1, we provide an algorithm that computes the set of all equivariant homotopy classes of equivariant continuous maps |X|→|Y|; the existence of such a map can be decided even for dimX≤2d+1. This yields the first algorithm for deciding topological embeddability of a k-dimensional finite simplicial complex into Rn under the condition k≤23n−1. More generally, we present an algorithm that, given a lifting-extension problem satisfying an appropriate stability assumption, computes the set of all homotopy classes of solutions. This result is new even in the non-equivariant situation.}, author = {Čadek, Martin and Krcál, Marek and Vokřínek, Lukáš}, issn = {01795376}, journal = {Discrete & Computational Geometry}, number = {4}, pages = {915 -- 965}, publisher = {Springer}, title = {{Algorithmic solvability of the lifting extension problem}}, doi = {10.1007/s00454-016-9855-6}, volume = {54}, year = {2017}, } @inproceedings{10745, abstract = {New ways to investigate and manipulate fluxoid and vortex states of mesoscopic superconducting structures are of great interest. The states with multiple vortices or winding numbers could be useful for the study of vortex interactions and interference effects, the braiding of Majorana bound states by winding vortices, and the development of novel superconducting devices. We demonstrate a methodology based on magnetic force microscopy that allows us to induce, probe and control fluxoid states in thin wall structures comprised of multiple loops. By using micro-magnet as a source of inhomogeneous magnetic field, we can efficiently explore the configuration space of fluxoid states. Scanning over the structure reveals the energy crossing points of the lowest laying fluxoid states. This is due the strong interaction of cantilever with thermally activated fluxoid transitions at points of degeneracy. We show that measured patterns of fluxoid transitions allow to identify the states, investigate their energetics, and manipulate them. Further, we show that the dynamics of driven fluxoid transitions can be described by stochastic resonance model, which provides a unique way of measuring fluxoid transition rate and related energy barrier for chosen transitions even in complicated structures}, author = {Polshyn, Hryhoriy and Naibert, Tyler and Budakian, Raffi}, booktitle = {APS March Meeting 2017}, issn = {0003-0503}, location = {New Orleans, LA, United States}, number = {4}, publisher = {American Physical Society}, title = {{ Probing and controlling fluxoid states in multiply-connected mesoscopic superconducting structures}}, volume = {62}, year = {2017}, } @inbook{1075, author = {Wenzl, Bernhard}, booktitle = {Austria and America: 20th-Century Cross-Cultural Encounters}, editor = {Parker, Joshua and Poole, Ralph}, isbn = {978-3643908124}, pages = {73 -- 80}, publisher = {LIT Verlag Berlin-Münster-Wien-Zürich-London}, title = {{An American in Allied-occupied Austria: John Dos Passos Reports on "The Vienna Frontier"}}, volume = {15}, year = {2017}, } @article{1076, abstract = {Signatures of the Coulomb corrections in the photoelectron momentum distribution during laser-induced ionization of atoms or ions in tunneling and multiphoton regimes are investigated analytically in the case of a one-dimensional problem. A high-order Coulomb-corrected strong-field approximation is applied, where the exact continuum state in the S matrix is approximated by the eikonal Coulomb-Volkov state including the second-order corrections to the eikonal. Although without high-order corrections our theory coincides with the known analytical R-matrix (ARM) theory, we propose a simplified procedure for the matrix element derivation. Rather than matching the eikonal Coulomb-Volkov wave function with the bound state as in the ARM theory to remove the Coulomb singularity, we calculate the matrix element via the saddle-point integration method by time as well as by coordinate, and in this way avoiding the Coulomb singularity. The momentum shift in the photoelectron momentum distribution with respect to the ARM theory due to high-order corrections is analyzed for tunneling and multiphoton regimes. The relation of the quantum corrections to the tunneling delay time is discussed.}, author = {Klaiber, Michael and Daněk, Jiří and Yakaboylu, Enderalp and Hatsagortsyan, Karen and Keitel, Christoph}, issn = {2469-9926}, journal = { Physical Review A - Atomic, Molecular, and Optical Physics}, number = {2}, publisher = {American Physical Society}, title = {{Strong-field ionization via a high-order Coulomb-corrected strong-field approximation}}, doi = {10.1103/PhysRevA.95.023403}, volume = {95}, year = {2017}, } @article{1077, abstract = {Viral capsids are structurally constrained by interactions among the amino acids (AAs) of their constituent proteins. Therefore, epistasis is expected to evolve among physically interacting sites and to influence the rates of substitution. To study the evolution of epistasis, we focused on the major structural protein of the fX174 phage family by first reconstructing the ancestral protein sequences of 18 species using a Bayesian statistical framework. The inferred ancestral reconstruction differed at eight AAs, for a total of 256 possible ancestral haplotypes. For each ancestral haplotype and the extant species, we estimated, in silico, the distribution of free energies and epistasis of the capsid structure. We found that free energy has not significantly increased but epistasis has. We decomposed epistasis up to fifth order and found that higher-order epistasis sometimes compensates pairwise interactions making the free energy seem additive. The dN/dS ratio is low, suggesting strong purifying selection, and that structure is under stabilizing selection. We synthesized phages carrying ancestral haplotypes of the coat protein gene and measured their fitness experimentally. Our findings indicate that stabilizing mutations can have higher fitness, and that fitness optima do not necessarily coincide with energy minima.}, author = {Fernandes Redondo, Rodrigo A and Vladar, Harold and Włodarski, Tomasz and Bollback, Jonathan P}, issn = {1742-5689}, journal = {Journal of the Royal Society Interface}, number = {126}, publisher = {Royal Society of London}, title = {{Evolutionary interplay between structure, energy and epistasis in the coat protein of the ϕX174 phage family}}, doi = {10.1098/rsif.2016.0139}, volume = {14}, year = {2017}, } @article{1078, abstract = {One of the key questions in understanding plant development is how single cells behave in a larger context of the tissue. Therefore, it requires the observation of the whole organ with a high spatial- as well as temporal resolution over prolonged periods of time, which may cause photo-toxic effects. This protocol shows a plant sample preparation method for light-sheet microscopy, which is characterized by mounting the plant vertically on the surface of a gel. The plant is mounted in such a way that the roots are submerged in a liquid medium while the leaves remain in the air. In order to ensure photosynthetic activity of the plant, a custom-made lighting system illuminates the leaves. To keep the roots in darkness the water surface is covered with sheets of black plastic foil. This method allows long-term imaging of plant organ development in standardized conditions. }, author = {Von Wangenheim, Daniel and Hauschild, Robert and Friml, Jirí}, journal = {Journal of visualized experiments JoVE}, number = {119}, publisher = {Journal of Visualized Experiments}, title = {{Light sheet fluorescence microscopy of plant roots growing on the surface of a gel}}, doi = {10.3791/55044}, volume = {2017}, year = {2017}, } @article{1079, abstract = {We study the ionization problem in the Thomas-Fermi-Dirac-von Weizsäcker theory for atoms and molecules. We prove the nonexistence of minimizers for the energy functional when the number of electrons is large and the total nuclear charge is small. This nonexistence result also applies to external potentials decaying faster than the Coulomb potential. In the case of arbitrary nuclear charges, we obtain the nonexistence of stable minimizers and radial minimizers.}, author = {Nam, Phan and Van Den Bosch, Hanne}, issn = {1385-0172}, journal = {Mathematical Physics, Analysis and Geometry}, number = {2}, publisher = {Springer}, title = {{Nonexistence in Thomas Fermi-Dirac-von Weizsäcker theory with small nuclear charges}}, doi = {10.1007/s11040-017-9238-0}, volume = {20}, year = {2017}, }