Time filter

Source Type

Rome, Italy

Labini F.S.,Centro Enrico Fermi | Labini F.S.,CNR Institute for Complex Systems
Classical and Quantum Gravity | Year: 2011

Standard models of galaxy formation predict that matter distribution is statistically homogeneous and isotropic and characterized by (i) spatial homogeneity for r < 10 Mpc h-1, (ii) small-amplitude structures of relatively limited size (i.e. r < 100) Mpc h-1 and (iii) anti-correlations for r > rc ≈ 150 Mpc h-1 (i.e. no structures of size larger than rc). Whether or not the observed galaxy distribution is interpreted to be compatible with these predictions depends on the a priori assumptions encoded in the statistical methods employed to characterize the data and on the a posteriori hypotheses made to interpret the results. We present strategies to test the most common assumptions and we find evidence that, in the available samples, galaxy distribution is spatially inhomogeneous for r < 100 Mpc h-1 but statistically homogeneous and isotropic. We conclude that the observed inhomogeneities pose a fundamental challenge to the standard picture of cosmology but they also represent an important opportunity which may open new directions for many cosmological puzzles. © 2011 IOP Publishing Ltd.

de Divitiis G.M.,University of Rome Tor Vergata | Petronzio R.,University of Rome Tor Vergata | Tantalo N.,University of Rome Tor Vergata | Tantalo N.,Centro Enrico Fermi
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2010

We propose a preconditioning of the Dirac operator based on the factorisation of a predefined function related to the decay of the propagator with the distance. We show that it can improve the accuracy of correlators involving heavy quarks at large distances and accelerate the computation of light quark propagators. © 2010 Elsevier B.V.

Goffredo S.,University of Bologna | Prada F.,University of Bologna | Caroselli E.,University of Bologna | Capaccioni B.,University of Bologna | And 10 more authors.
Nature Climate Change | Year: 2014

Anthropogenic CO2 is a major driver of present environmental change in most ecosystems1, and the related ocean acidification is threatening marine biota2. With increasing pCO2, calcification rates of several species decrease3, although cases of upregulation are observed4. Here, we show that biological control over mineralization relates to species abundance along a natural pH gradient. As pCO2 increased, the mineralogy of a scleractinian coral (Balanophyllia europaea) and a mollusc (Vermetus triqueter) did not change. In contrast, two calcifying algae (Padina pavonica and Acetabularia acetabulum) reduced and changed mineralization with increasing pCO2, from aragonite to the less soluble calcium sulphates and whewellite, respectively. As pCO2 increased, the coral and mollusc abundance was severely reduced, with both species disappearing at pH < 7.8. Conversely, the two calcifying and a non-calcifying algae (Lobophora variegata) showed less severe or no reductions with increasing pCO2, and were all found at the lowest pH site. The mineralization response to decreasing pH suggests a link with the degree of control over the biomineralization process by the organism, as only species with lower control managed to thrive in the lowest pH. © 2014 Macmillan Publishers Limited. All rights reserved.

Fritzsch P.,University of Southampton | Fritzsch P.,University of Munster | Heitger J.,University of Munster | Tantalo N.,University of Rome Tor Vergata | Tantalo N.,Centro Enrico Fermi
Journal of High Energy Physics | Year: 2010

We non-perturbatively determine the renormalization constant and the improvement coefficients relating the renormalized current and subtracted quark mass of (quenched) valence quarks propagating in a sea of O(a) improved two massless quarks. We employ the Schrödinger functional scheme and fix the physical extent of the box by working at a constant value of the renormalized coupling. Our calculation yields results which cover two regions of bare parameter space. One is the weak-coupling region suitable for volumes of about half a fermi. By making simulations in this region, quarks as heavy as the bottom can be propagated with the full relativistic QCD action and renormalization problems in HQET can be solved non-perturbatively by a matching to QCD infinite volume. The other region refers to the common parameter range in large-volume simulations of two-flavour lattice QCD, where our results have particular relevance for charm physics applications. © 2010 SISSA, Trieste, Italy.

Murtas G.,Centro Enrico Fermi
Systems and Synthetic Biology | Year: 2010

One of the major properties of the semi-synthetic minimal cell, as a model for early living cells, is the ability to self-reproduce itself, and the reproduction of the boundary layer or vesicle compartment is part of this process. A minimal bio-molecular mechanism based on the activity of one single enzyme, the FAS-B (Fatty Acid Synthase) Type I enzyme from Brevibacterium ammoniagenes, is encapsulated in 1-palmitoyl-2oleoyl-sn-glycero-3-phosphatidylcholine (POPC) liposomes to control lipid synthesis. Consequently molecules of palmitic acid released from the FAS catalysis, within the internal lumen, move toward the membrane compartment and become incorporated into the phospholipid bilayer. As a result the vesicle membranes change in lipid composition and liposome growth can be monitored. Here we report the first experiments showing vesicles growth by catalysis of one enzyme only that produces cell boundary from within. This is the prototype of the simplest autopoietic minimal cell. © 2009 The Author(s).

Discover hidden collaborations