Bosonic effective action for interacting fermions

We compare different versions of a bosonic description for systems of interacting fermions, with particular emphasis on the free energy functional. The bosonic effective action makes the issue of symmetries particularly transparent and we present for the Hubbard model an exact mapping between repulsive and attractive interactions. A systematic expansion for the bosonic effective action starts with a solution to the lowest order Schwinger-Dyson or gap equation. We propose a two particle irreducible formulation of an exact functional renormalization group equation for computations beyond leading order. On this basis we suggest a renormalized gap equation. This approach is compared with functional renormalization in a partially bosonized setting.Comment: new sections on exact mapping between attractive and repulsive Hubbard model and relation between two-particle-irreducible formalism, 32 pages,1 figure,LaTe

Moduli spaces of toric manifolds

We construct a distance on the moduli space of symplectic toric manifolds of dimension four. Then we study some basic topological properties of this space, in particular, path-connectedness, compactness, and completeness. The construction of the distance is related to the Duistermaat-Heckman measure and the Hausdorff metric. While the moduli space, its topology and metric, may be constructed in any dimension, the tools we use in the proofs are four-dimensional, and hence so is our main result.Comment: To appear in Geometriae Dedicata, minor changes to previous version, 19 pages, 6 figure

The Dynamics of Nestedness Predicts the Evolution of Industrial Ecosystems

In economic systems, the mix of products that countries make or export has been shown to be a strong leading indicator of economic growth. Hence, methods to characterize and predict the structure of the network connecting countries to the products that they export are relevant for understanding the dynamics of economic development. Here we study the presence and absence of industries at the global and national levels and show that these networks are significantly nested. This means that the less filled rows and columns of these networks' adjacency matrices tend to be subsets of the fuller rows and columns. Moreover, we show that nestedness remains relatively stable as the matrices become more filled over time and that this occurs because of a bias for industries that deviate from the networks' nestedness to disappear, and a bias for the missing industries that reduce nestedness to appear. This makes the appearance and disappearance of individual industries in each location predictable. We interpret the high level of nestedness observed in these networks in the context of the neutral model of development introduced by Hidalgo and Hausmann (2009). We show that, for the observed fills, the model can reproduce the high level of nestedness observed in these networks only when we assume a high level of heterogeneity in the distribution of capabilities available in countries and required by products. In the context of the neutral model, this implies that the high level of nestedness observed in these economic networks emerges as a combination of both, the complementarity of inputs and heterogeneity in the number of capabilities available in countries and required by products. The stability of nestedness in industrial ecosystems, and the predictability implied by it, demonstrates the importance of the study of network properties in the evolution of economic networks.Comment: 26 page

High-resolution 3D phenotyping of the grapevine root system using X-ray Computed Tomography

Plant roots are essential for water and nutrient uptake and contribute to the plants' response to environmental stress factors. As the hidden half of a plant, investigation of root systems is highly challenging, most of available methods are destructive and very labour-intensive. In this proof-of-concept study, a non-invasive X-ray micro computed tomography (X-ray µCT) method was applied to investigate the phenotypic variation of the complex three-dimensional (3D) architecture of grapevine roots as a function of genotype and soil. Woody cuttings of 'Calardis Musqué', 'Villard Blanc' and V3125 ('Schiava Grossa' x 'Riesling') were cultivated in polypropylene columns filled with two different soil types, clay loam and sandy loam, for 6 weeks. Afterwards, the columns were scanned once using the technique of X-ray µCT. The received raw data were analysed for the reconstruction of 3D root system models (3D model), which display a non-destructive visualization of whole, intact root systems with a spatial resolution of 42 µm. The 3D models of all investigated plants (in total 18) were applied to quantify root system characteristics precisely by measuring adventitious root length, lateral root length, total root length, root system surface area, root system volume and root growth angles from the woody cutting relative to a horizontal axis. The results showed that: (i) early root formation and root growth differed between genotypes, especially between 'Calardis Musqué' and 'Villard Blanc'; and (ii) the soil type does influence adventitious root formation of V3125, but had minor effects on 'Calardis Musqué' and 'Villard Blanc'. In conclusion, this innovative, high-resolution method of X-ray µCT is suitable for high resolution phenotyping of root formation, architecture, and rooting characteristics of grapevine woody cuttings in a non-destructive manner, e.g. to investigate root response to drought stress and would provide new insights into phylloxera root infection

Kontrola kvalitete pri biosintezi aminoacil-tRNA

The fidelity of translation is determined at two major points: the accuracy of aminoacyl-tRNA selection by the ribosomes and synthesis of cognate amino acid/tRNA pairs by aminoacyl-tRNA synthetases (aaRSs) in the course of the aminoacylation reaction. The most important point in aminoacylation is the accurate recognition of cognate substrates coupled with discrimination of non-cognates. While this is generally accomplished by a single enzyme, we have recently found that discrimination against lysine analogues requires the existence of two unrelated lysyl-tRNA synthetases. For other amino acids, initial recognition is not sufficiently accurate with errors being corrected by an intrinsic editing activity. Recent studies indicate how editing prevents the misinterpretation of phenylalanine as tyrosine in the genetic code and have shown the importance of this process in vivo. More recent studies indicate that while these editing reactions are critical in the cytoplasm, some are absent from mitochondria suggesting that the overall fidelity of protein synthesis might be reduced in this compartment.Vjernost translacije bitno ovisi o točnosti dvaju koraka: odabiru aminoacil-tRNA na ribosomu i sintezi ispravnih aminoacil-tRNA pomoću odgovarajućih aminoacil-tRNA-sintetaza u reakciji aminoaciliranja. Najvažniji događaj u aminoaciliranju precizno je prepoznavanje pripadnih supstrata (tRNA i aminokiseline) i diskriminacija nepripadnih. Iako taj posao uglavnom obavlja po jedan enzim za svaki par tRNA : aminokiselina, nedavno smo ustanovili da su za diskriminaciju analoga lizina potrebne dvije različite lizil-tRNA-sintetaze. U nekim drugim slučajevima otkriveno je da su pogreške u odabiru tRNA i njihovih pripadnih aminokiseline i suviše velike, pa je nužan naknadni popravak pogrešnih produkata u reakciji aminoaciliranja, koji također mogu katalizirati neke aminoacil-tRNA-sintetaze. Na primjeru krivog odabira tirozina umjesto fenilalanina, te naknadnog popravka, pokazano je kako je mogućnost korekcije važna u sprečavanju pogrešne translacije genetičkog koda in vivo. Najnovija istraživanja pokazala su da su mehanizmi popravka od ključne važnosti u citoplazmi, no neki se ne zbivaju u mitohondriju, ukazujući na smanjenu ukupnu točnost biosinteze proteina u ovom staničnom odjeljku

Quality Control During Aminoacyl-tRNA Synthesis

The fidelity of translation is determined at two major points: the accuracy of aminoacyl-tRNA selection by the ribosomes and synthesis of cognate amino acid/tRNA pairs by aminoacyl-tRNA synthetases (aaRSs) in the course of the aminoacylation reaction. The most important point in aminoacylation is the accurate recognition of cognate substrates coupled with discrimination of non-cognates. While this is generally accomplished by a single enzyme, we have recently found that discrimination against lysine analogues requires the existence of two unrelated lysyl-tRNA synthetases. For other amino acids, initial recognition is not sufficiently accurate with errors being corrected by an intrinsic editing activity. Recent studies indicate how editing prevents the misinterpretation of phenylalanine as tyrosine in the genetic code and have shown the importance of this process in vivo . More recent studies indicate that while these editing reactions are critical in the cytoplasm, some are absent from mitochondria suggesting that the overall idelity of protein synthesis might be reduced in this compartment

Liquid 4He near the superfluid transition in the presence of a heat current and gravity

The effects of a heat current and gravity in liquid 4He near the superfluid transition are investigated for temperatures above and below T_lambda. We present a renormalization-group calculation based on model F for the Green's function in a self-consistent approximation which in quantum many-particle theory is known as the Hartree approximation. The approach can handle a zero average order parameter above and below T_lambda and includes effects of vortices. We calculate the thermal conductivity and the specific heat for all temperatures T and heat currents Q in the critical regime. Furthermore, we calculate the temperature profile. Below T_lambda we find a second correlation length which describes the dephasing of the order parameter field due to vortices. We find dissipation and mutual friction of the superfluid-normal fluid counterflow and calculate the Gorter-Mellink coefficient A. We compare our theoretical results with recent experiments.Comment: 26 pages, 9 figure