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Cimini G.,CNR Institute for Complex Systems | Gabrielli A.,CNR Institute for Complex Systems | Gabrielli A.,IMT Institute for Advanced Studies | Labini F.S.,Centro Studi e Ricerche Enrico Fermi | Labini F.S.,CNR Institute for Complex Systems
PLoS ONE | Year: 2014

We use citation data of scientific articles produced by individual nations in different scientific domains to determine the structure and efficiency of national research systems. We characterize the scientific fitness of each nation-that is, the competitiveness of its research system-and the complexity of each scientific domain by means of a non-linear iterative algorithm able to assess quantitatively the advantage of scientific diversification. We find that technological leading nations, beyond having the largest production of scientific papers and the largest number of citations, do not specialize in a few scientific domains. Rather, they diversify as much as possible their research system. On the other side, less developed nations are competitive only in scientific domains where also many other nations are present. Diversification thus represents the key element that correlates with scientific and technological competitiveness. A remarkable implication of this structure of the scientific competition is that the scientific domains playing the role of "markers" of national scientific competitiveness are those not necessarily of high technological requirements, but rather addressing the most "sophisticated" needs of the society. © 2014 Cimini et al.

Beraudo A.,CERN | Beraudo A.,Centro Studi e Ricerche Enrico Fermi | Milhano J.G.,CERN | Milhano J.G.,University of Lisbon | Wiedemann U.A.,CERN
Physical Review C - Nuclear Physics | Year: 2012

Medium-induced parton energy loss, resulting from gluon exchanges between the QCD matter and partonic projectiles, is expected to underlie the strong suppression of jets and high-p T hadron spectra observed in ultrarelativistic heavy-ion collisions. Here, we present the first color-differential calculation of parton energy loss. We find that color exchange between medium and projectile decoheres the color of radiated gluons from that of the most energetic fragments and enhances parametrically the invariant mass of energetic color singlet clusters in the parton shower. These effects are seen in more than half of the medium-modified parton branchings. As shown for a cluster hadronization model and as argued for a Lund string fragmentation model, this leads to additional softening of hadronic spectra. Compared to standard parton energy loss calculations, a lower density of the QCD matter is then needed to account for the nuclear modification factor at the Large Hadron Collider. © 2012 American Physical Society.

Farnesi D.,Centro Studi e Ricerche Enrico Fermi | Farnesi D.,CNR Institute of Applied Physics Nello Carrara | Chiavaioli F.,CNR Institute of Applied Physics Nello Carrara | Righini G.C.,Centro Studi e Ricerche Enrico Fermi | And 5 more authors.
Optics Letters | Year: 2014

We present a new method for coupling light to high-Q silica whispering gallery mode resonators (WGMs) that is based on long period fiber gratings (LPGs) written in silica fibers. An LPG allows selective excitation of high-order azimuthally symmetric cladding modes in a fiber. Coupling of these cladding modes to WGMs in silica resonators is possible when partial tapering of the fiber is also implemented in order to reduce the optical field size and increase its external evanescent portion. Importantly, the taper size is about one order of magnitude larger than that of a standard fiber taper coupler. The suggested approach is therefore much more robust and useful especially for practical applications. We demonstrate coupling to high-Q silica microspheres and microbubbles detecting the transmission dip at the fiber output when crossing a resonance. An additional feature of this approach is that by cascading LPGs with different periods, a wavelength selective addressing of different resonators along the same fiber is also possible. © 2014 Optical Society of America.

Noferini F.,Centro Studi e Ricerche Enrico Fermi | Noferini F.,National Institute of Nuclear Physics, Italy
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2016

The Extreme Energy Event (EEE) experiment is devoted to the search of high energy cosmic rays through a network of telescopes installed in about 50 high schools distributed throughout the Italian territory. This project requires a peculiar data management infrastructure to collect data registered in stations very far from each other and to allow a coordinated analysis. Such an infrastructure is realized at INFN-CNAF, which operates a Cloud facility based on the OpenStack opensource Cloud framework and provides Infrastructure as a Service (IaaS) for its users. In 2014 EEE started to use it for collecting, monitoring and reconstructing the data acquired in all the EEE stations. For the synchronization between the stations and the INFN-CNAF infrastructure we used BitTorrent Sync, a free peer-to-peer software designed to optimize data syncronization between distributed nodes. All data folders are syncronized with the central repository in real time to allow an immediate reconstruction of the data and their publication in a monitoring webpage. We present the architecture and the functionalities of this data management system that provides a flexible environment for the specific needs of the EEE project. © 2015 Elsevier B.V. All rights reserved.

Bellucci S.,National Institute of Nuclear Physics, Italy | Saharian A.A.,Yerevan State University | Yeranyan A.H.,National Institute of Nuclear Physics, Italy | Yeranyan A.H.,Yerevan State University | Yeranyan A.H.,Centro Studi e Ricerche Enrico Fermi
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

The Wightman function, the vacuum expectation values (VEVs) of the field squared, and the energy-momentum tensor are investigated for a massive scalar field with general curvature coupling in a spherically symmetric static background geometry described by two distinct metric tensors inside and outside a spherical boundary. The exterior and interior geometries can correspond to different vacuum states of the same theory. In the region outside the sphere, the contributions in the VEVs, induced by the interior geometry, are explicitly separated. For the special case of the Minkowskian exterior geometry, the asymptotics of the VEVs near the boundary and at large distances are discussed in detail. In particular, it has been shown that the divergences on the boundary are weaker than in the problem of a spherical boundary in Minkowski spacetime with Dirichlet or Neumann boundary conditions. As an application of general results, de Sitter (dS) and anti-de Sitter (AdS) spaces are considered as examples of the interior geometry. For AdS interiors there are no bound states. In the case of dS geometry and for nonminimally coupled fields, bound states appear for a radius of the separating boundary sufficiently close to the dS horizon. Starting from a critical value of the radius, the Minkowskian vacuum in the exterior region becomes unstable. For small values of the AdS curvature radius, to the leading order, the VEVs in the exterior region coincide with those for a spherical boundary in Minkowski spacetime with a Dirichlet boundary condition. The exceptions are the cases of minimal and conformal couplings: for a minimal coupling, the VEVs are reduced to the case with a Neumann boundary condition, whereas for a conformally coupled field there is no reduction to Dirichlet or Neumann results. © 2014 American Physical Society.

Revol J.-P.,Centro Studi e Ricerche Enrico Fermi
EPJ Web of Conferences | Year: 2015

To meet the tremendous world energy needs, systematic R&D has to be pursued to replace fossil fuels. Nuclear energy, which produces no green house gases and no air pollution, should be a leading candidate. How nuclear energy, based on thorium rather than uranium, could be an acceptable solution is discussed. Thorium can be used both to produce energy and to destroy nuclear waste. The thorium conference, organized by iThEC at CERN in October 2013, has shown that thorium is seriously considered by some major developing countries as a key element of their energy strategy. However, developed countries do not seem to move fast enough in that direction, while global cooperation is highly desirable in this domain. Thorium is not fissile. Various possible ways of using thorium will be reviewed. However, an elegant option is to drive an "Accelerator Driven System (ADS)" with a proton accelerator, as suggested by Nobel Prize laureate Carlo Rubbia. © Owned by the authors, published by EDP Sciences, 2015.

Labini F.S.,Centro Studi e Ricerche Enrico Fermi | Labini F.S.,CNR Institute for Complex Systems
Monthly Notices of the Royal Astronomical Society | Year: 2013

We study the collapse and virialization of an isolated spherical cloud of self-gravitating particles initially at rest and characterized by a power-law density profile, with exponent 0 ≤ a <3, or by a Plummer, a Hernquist, a Navarro Frenk and White, a Gaussian profile. We find that in all cases the virialized structure formed after the collapse has a density profile decaying, at large enough radii, as ~r-4, and a radial velocity dispersion profile decaying as ~r-1. We show that these profiles originate from the physical mechanism responsible for the ejection of a fraction of cloud's mass and energy during the collapse and that this same mechanism washes out the dependence on the initial conditions.When a large enough initial velocity dispersion is given to the cloud particles, ejection does not occur anymore and consequently the virialized halo density and velocity profiles display features which reflect the initial conditions. ©2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Labini F.S.,Centro Studi e Ricerche Enrico Fermi | Labini F.S.,CNR Institute for Complex Systems | Benhaiem D.,Centro Studi e Ricerche Enrico Fermi | Benhaiem D.,CNR Institute for Complex Systems | Joyce M.,CNRS Laboratory for Nuclear and High-Energy Physics
Monthly Notices of the Royal Astronomical Society | Year: 2015

Initially cold and spherically symmetric self-gravitating systems may give rise to a virial equilibrium state which is far from spherically symmetric, and typically triaxial. We focus here on how the degree of symmetry breaking in the final state depends on the initial density profile. We note that the most asymmetric structures result when, during the collapse phase, there is a strong injection of energy preferentially into the particles which are localized initially in the outer shells. These particles are still collapsing when the others, initially located in the inner part, are already re-expanding; the motion of particles in a time varying potential allow them to gain kinetic energy - in some cases enough to be ejected from the system. We show that this mechanism of energy gain amplifies the initial small deviations from perfect spherical symmetry due to finite N fluctuations. This amplification is more efficient when the initial density profile depends on radius, because particles have a greater spread of fall times compared to a uniform density profile, for which very close to symmetric final states are obtained. These effects lead to a distinctive correlation of the orientation of the final structure with the distribution of ejected mass, and also with the initial (very small) angular fluctuations. © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Sylos Labini F.,Centro Studi e Ricerche Enrico Fermi | Sylos Labini F.,CNR Institute for Complex Systems
Monthly Notices of the Royal Astronomical Society | Year: 2012

The collapse of an isolated, uniform and spherical cloud of self-gravitating particles represents a paradigmatic example of a relaxation process leading to the formation of a quasi-stationary state in virial equilibrium. We consider several N-body simulations of such a system, with the initial velocity dispersion as a free parameter. We show that there is a clear difference between structures formed when the initial virial ratio is and b 0>b c 0. These two sets of initial conditions give rise respectively to a mild and violent relaxation occurring in about the same time-scale; however, in the latter case the system contracts by a large factor, while in the former it approximately maintains its original size. Correspondingly, the resulting quasi-equilibrium state is characterized by a density profile decaying at large enough distances as r -4 or with a sharp cut-off. The case b 0b c 0 is the ejection of particles and energy, which is not captured by such a theoretical approach: for this case we introduce a simple physical model to explain the formation of the power-law density profile. This model shows that the behaviour n(r) ∼r -4 is the typical density profile that is obtained when the initial conditions are cold enough that mass and energy ejection occurs. In addition, we clarify the origin of the critical value of the initial virial ratio b c 0. © 2012 The Author Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Vallone G.,Centro Studi e Ricerche Enrico Fermi | Vallone G.,University of Rome La Sapienza | Donati G.,University of Rome La Sapienza | Ceccarelli R.,University of Rome La Sapienza | And 2 more authors.
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2010

Six-qubit cluster states built on the simultaneous entanglement of two photons in three independent degrees of freedom, that is, polarization and a double longitudinal momentum, have been recently demonstrated. We present here the peculiar entanglement properties of the linear cluster state L C6 related to the three degrees of freedom. This state has been adopted to realize various kinds of controlled not (cnot) gates, obtaining high values of the fidelity of the expected output states for all considered cases. Our results demonstrate that these states may represent a promising approach toward scalable quantum computation in a medium-term time scale. The future perspectives of a hybrid approach to one-way quantum computing based on multiple degrees of freedom and multiphoton cluster states are also discussed in the conclusion of this article. © 2010 The American Physical Society.

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