Showing papers by "Roma Tre University published in 2008"

Interaction ruling animal collective behavior depends on topological rather than metric distance: Evidence from a field study

Abstract: Numerical models indicate that collective animal behavior may emerge from simple local rules of interaction among the individuals. However, very little is known about the nature of such interaction, so that models and theories mostly rely on aprioristic assumptions. By reconstructing the three-dimensional positions of individual birds in airborne flocks of a few thousand members, we show that the interaction does not depend on the metric distance, as most current models and theories assume, but rather on the topological distance. In fact, we discovered that each bird interacts on average with a fixed number of neighbors (six to seven), rather than with all neighbors within a fixed metric distance. We argue that a topological interaction is indispensable to maintain a flock's cohesion against the large density changes caused by external perturbations, typically predation. We support this hypothesis by numerical simulations, showing that a topological interaction grants significantly higher cohesion of the aggregation compared with a standard metric one.

A test of the nature of cosmic acceleration using galaxy redshift distortions

Abstract: Observations of distant supernovae indicate that the Universe is now in a phase of accelerated expansion the physical cause of which is a mystery. Formally, this requires the inclusion of a term acting as a negative pressure in the equations of cosmic expansion, accounting for about 75 per cent of the total energy density in the Universe. The simplest option for this "dark energy" corresponds to a cosmological constant, perhaps related to the quantum vacuum energy. Physically viable alternatives invoke either the presence of a scalar field with an evolving equation of state, or extensions of general relativity involving higher-order curvature terms or extra dimensions. Although they produce similar expansion rates, different models predict measurable differences in the growth rate of large-scale structure with cosmic time. A fingerprint of this growth is provided by coherent galaxy motions, which introduce a radial anisotropy in the clustering pattern reconstructed by galaxy redshift surveys. Here we report a measurement of this effect at a redshift of 0.8. Using a new survey of more than 10,000 faint galaxies, we measure the anisotropy parameter b = 0.70 +/- 0.26, which corresponds to a growth rate of structure at that time of f = 0.91 +/- 0.36. This is consistent with the standard cosmological-constant model with low matter density and flat geometry, although the error bars are still too large to distinguish among alternative origins for the accelerated expansion. This could be achieved with a further factor-of-ten increase in the sampled volume at similar redshift.

Research and development, spillovers, innovation systems, and the genesis of regional growth in Europe

Abstract: Rodriguez-Pose A. and Crescenzi R. Research and development, spillovers, innovation systems, and the genesis of regional growth in Europe. Regional Studies. Research on the impact of innovation on regional economic performance in Europe has fundamentally followed three approaches: (1) the analysis of the link between investment in research and development (RD (2) the study of the existence and efficiency of regional innovation systems; and (3) the examination of the geographical diffusion of regional knowledge spillovers. These complementary approaches have, however, rarely been combined. Important operational and methodological barriers have thwarted any potential cross-fertilization. This paper tries to fill this gap in the literature by combining in one model R&D, spillovers, and innovation systems approaches. A multiple regression analysis is conducted for all regions of the group of 25 European Union countries (EU-25), including measures of R&D investment, proxies for...

Research and development, spillovers, innovation systems, and the genesis of regional growth in Europe

Abstract: Research on the impact of innovation on regional economic performance in Europe has fundamentally followed three approaches: (1) the analysis of the link between investment in research and development (RD (2) the study of the existence and efficiency of regional innovation systems; and (3) the examination of the geographical diffusion of regional knowledge spillovers. These complementary approaches have, however, rarely been combined. Important operational and methodological barriers have thwarted any potential cross-fertilization. This paper tries to fill this gap in the literature by combining in one model R&D, spillovers, and innovation systems approaches. A multiple regression analysis is conducted for all regions of the group of 25 European Union countries (EU-25), including measures of R&D investment, proxies for regional innovation systems, and knowledge and socio-economic spillovers. This approach allows the discrimination between the influence of internal factors and external knowledge and institutional flows on regional economic growth. The empirical results highlight how the complex interaction between local and external research, on the one hand, with local and external socio-economic and institutional conditions, on the other, shapes the innovation capacity of every region. They also indicate the importance of proximity for the transmission of economically productive knowledge, as spillovers are affected by strong distance decay effects.

Modelling interdependent infrastructures using interacting dynamical models

Abstract: We investigate the consequence of failures, occurring on the electrical grid, on a telecommunication network We have focused on the Italian electrical transmission network and the backbone of the internet network for research (GARR) Electrical network has been simulated using the DC power flow method; data traffic on GARR by a model of the TCP/IP basic features The status of GARR nodes has been related to the power level of the (geographically) neighbouring electrical nodes (if the power level of a node is lower than a threshold, all communication nodes depending on it are switched off) The electrical network has been perturbed by lines removal: the consequent re-dispatching reduces the power level in all nodes This reduces the number of active GARR nodes and, thus, its Quality of Service (QoS) Averaging over many configurations of perturbed electrical network, we have correlated the degradation of the electrical network with that of the communication network Results point to a sizeable amplification of the effects of faults on the electrical network on the communication network, also in the case of a moderate coupling between the two networks

Global Value Chains and Technological Capabilities: A Framework to Study Industrial Innovation in Developing Countries

Abstract: This paper presents a critical review of the global value chain (GVC) literature in light of the “technological capabilities” approach to innovation in less-developed countries (LDCs). Participation in GVC is beneficial for firms in LDCs, which are bound to source technology internationally. However, the issues of learning and technological efforts at the firm level remain largely hidden in the GVC literature. We propose a shift in the empirical and theoretical agenda, arguing that research should integrate the analysis of the endogenous process of technological capability development, including specific firm-level efforts, and of the mechanisms allowing knowledge to flow within and between different global value chains into the GVC literature.

Quality Assessment of Stereoscopic Images

Abstract: Several metrics have been proposed in literature to assess the perceptual quality of two-dimensional images. However, no similar effort has been devoted to quality assessment of stereoscopic images. Therefore, in this paper, we review the different issues related to 3D visualization, and we propose a quality metric for the assessment of stereopairs using the fusion of 2D quality metrics and of the depth information. The proposed metric is evaluated using the SAMVIQ methodology for subjective assessment. Specifically, distortions deriving from coding are taken into account and the quality degradation of the stereopair is estimated by means of subjective tests.

Mars North Polar Deposits: Stratigraphy, Age, and Geodynamical Response

Abstract: The Shallow Radar (SHARAD) on the Mars Reconnaissance Orbiter has imaged the internal stratigraphy of the north polar layered deposits of Mars. Radar reflections within the deposits reveal a laterally continuous deposition of layers, which typically consist of four packets of finely spaced reflectors separated by homogeneous interpacket regions of nearly pure ice. The packet/interpacket structure can be explained by approximately million-year periodicities in Mars' obliquity or orbital eccentricity. The observed ∼100-meter maximum deflection of the underlying substrate in response to the ice load implies that the present-day thickness of an equilibrium elastic lithosphere is greater than 300 kilometers. Alternatively, the response to the load may be in a transient state controlled by mantle viscosity. Both scenarios probably require that Mars has a subchondritic abundance of heat-producing elements.

Design of Miniaturized Metamaterial Patch Antennas With $\mu$ -Negative Loading

Abstract: Recent theoretical studies have shown that circular patch antennas loaded by an inhomogeneous substrate partially filled with a mu-negative (MNG) metamaterial may in principle support a resonant radiating mode, even if the total size of the radiator is significantly smaller than the wavelength of operation. In those theoretical analyses, MNG metamaterials have been assumed as continuous, isotropic and readily available materials, characterized by a proper dispersion in frequency and by inherent ohmic losses. The fabrication of such compact antennas, however, would require the major effort of designing proper subwavelength inclusions that realize the MNG behavior of the substrate, and consequently a careful design of their geometry, location and orientation. The fabrication of a fully isotropic MNG sample to reside underneath the sub-wavelength patch, moreover, may be challenging with the current technological limitations. In this paper, we first show that the proposed sub-wavelength radiator may operate even when the fabricated MNG sample is not isotropic, due to the specific polarization of the magnetic field in the MNG region. Then, we propose a complete design of the magnetic inclusions, presenting full-wave numerical simulations of the structure, which effectively supports the expected resonant mode, despite the small size of the antenna. The comparisons among analytical results of the patch loaded by: (a) the ideal MNG sample applying a simple cavity model; (b) full-wave numerical simulations of the same antenna considering the presence of the feed; and (c) full-wave numerical simulations of the antenna loaded by the proposed magnetic inclusions, show how our design effectively simulate the presence of an MNG sample, allowing the realistic design of a sub-wavelength metamaterial patch antenna with satisfactory matching and radiating features. This may open up new venues in the realization of efficient metamaterial radiating components for practical purposes.

Reordering and Local Rerouting Strategies to Manage Train Traffic in Real Time

Abstract: Traffic controllers regulate railway traffic by sequencing train movements and setting routes with the aim of ensuring smooth train behaviour and limiting, as much as possible, train delays. In this paper, we describe the implementation of a real-time traffic management system, called ROMA (Railway traffic Optimization by Means of Alternative graphs), to support controllers in the everyday task of managing disturbances. We make use of a branch-and-bound algorithm for sequencing train movements, while a local search algorithm is developed for rerouting optimization purposes. The compound problem of routing and sequencing trains is approached iteratively, computing an optimal train sequencing for given train routes and then improving this solution by locally rerouting some trains. An extensive computational study is carried out, based on a dispatching area of the Dutch railway network. We study practical size instances, and include in the model important operational constraints, including rolling stock and passenger connections. Different types of disturbances are analysed, including train delays and blocked tracks. Comparison with common dispatching practice shows the high potential of the system as an effective support tool to improve punctuality.

Chandra unveils a binary Active Galactic Nucleus in Mrk 463

Abstract: We analyse Chandra, XMM‐Newton and Hubble Space Telescope (HST) data of the doublenucleus Ultraluminous Infrared Galaxy (ULIRG), Mrk 463. The Chandra detection of two luminous (L2‐10 keV = 1.5 × 10 43 and 3.8 × 10 42 erg cm −2 s −1 ), unresolved nuclei in Mrk 463 indicates that this galaxy hosts a binary active galactic nucleus (AGN), with a projected separation of � 3.8 kpc (3.83 ± 0.01 arcsec). While the East nucleus was already known to be a type 2 Seyfert (and this is further confirmed by our Chandra detection of a neutral iron line), this is the first unambiguous evidence in favour of the AGN nature of the West nucleus. Mrk 463 is therefore the clearest case so far for a binary AGN, after NGC 6240.

A Review and Evaluation of Multiobjective Algorithms for the Flowshop Scheduling Problem

Abstract: This paper contains a complete and updated review of the literature for multiobjective flowshop problems, which are among the most studied environments in the scheduling research area. No previous comprehensive reviews exist in the literature. Papers about lexicographical, goal programming, objective weighting, and Pareto approaches have been reviewed. Exact, heuristic, and metaheuristic methods have been surveyed. Furthermore, a complete computational evaluation is also carried out. A total of 23 different algorithms including both flowshop-specific methods as well as general multiobjective optimization approaches have been tested under three different two-criteria combinations with a comprehensive benchmark. All methods have been studied under recent state-of-the-art quality measures. Parametric and nonparametric statistical testing is profusely employed to support the observed performance of the compared methods. As a result, we have identified the best-performing methods from the literature, which along with the review, constitutes a reference work for further research.

Mountains in a flat world: why proximity still matters for the location of economic activity

Abstract: Thomas Friedman (2005, The World Is Flat: A Brief History of the Twenty-First Century. New York: Farrar, Straus, and Giroux) argues that the expansion of trade, the internationalization of firms, the galloping process of outsourcing and the possibility of networking are creating a ‘flat world’: a level playing field where individuals are empowered and better off. This paper challenges this view of the world by arguing that not all territories have the same capacity to maximize the benefits and opportunities and minimize the risks linked to globalization. Numerous forces are coalescing in order to provoke the emergence of urban ‘mountains’ where wealth, economic activity and innovative capacity agglomerate. The interactions of these forces in the close geographical proximity of large urban areas give shape to a much more complex geography of the world economy.

Scalable and Efficient Provable Data Possession.

Abstract: Storage outsourcing is a rising trend which prompts a number of interesting security issues, many of which have been extensively investigated in the past. However, Provable Data Possession (PDP) is a topic that has only recently appeared in the research literature. The main issue is how to frequently, efficiently and securely verify that a storage server is faithfully storing its client’s (potentially very large) outsourced data. The storage server is assumed to be untrusted in terms of both security and reliability. (In other words, it might maliciously or accidentally erase hosted data; it might also relegate it to slow or off-line storage.) The problem is exacerbated by the client being a small computing device with limited resources. Prior work has addressed this problem using either public key cryptography or requiring the client to outsource its data in encrypted form. In this paper, we construct a highly efficient and provably secure PDP technique based entirely on symmetric key cryptography, while not requiring any bulk encryption. Also, in contrast with its predecessors, our PDP technique allows outsourcing of dynamic data, i.e, it efficiently supports operations, such as block modification, deletion and append.

Dark matter annihilation in substructures revised

Abstract: Upcoming $\gamma$-ray satellites will search for Dark Matter annihilations in Milky Way substructures (or 'clumps'). The prospects for detecting these objects strongly depend on the assumptions made on the distribution of Dark Matter in substructures, and on the distribution of substructures in the Milky Way halo. By adopting simplified, yet rather extreme, prescriptions for these quantities, we compute the number of sources that can be detected with upcoming experiments such as GLAST, and show that, for the most optimistic particle physics setup ($m_\chi=40$ GeV and annihilation cross section $\sigma v = 3 \times 10^{-26}$ cm$^3$ s$^{-1}$), the result ranges from zero to $\sim$ hundred sources, all with mass above $10^{5}M\odot$. However, for a fiducial DM candidate with mass $m_\chi=100$ GeV and $\sigma v = 10^{-26}$ cm$^3$ s$^{-1}$, at most a handful of large mass substructures can be detected at $5 \sigma$, with a 1-year exposure time, by a GLAST-like experiment. Scenarios where micro-clumps (i.e. clumps with mass as small as $10^{-6}M\odot$) can be detected are severely constrained by the diffuse $\gamma$-ray background detected by EGRET.

Optical properties of V 1 − x Cr x O 2 compounds under high pressure

Abstract: Raman and infrared transmission and reflectivity measurements were carried out at room temperature and high pressure (0--15 GPa) on ${\text{V}}_{1\ensuremath{-}x}{\text{Cr}}_{x}{\text{O}}_{2}$ compounds. Raman spectra were collected at ambient conditions on the $x=0.007$ and 0.025 materials, which are characterized by different insulating monoclinic phases ($M3$ and $M2$, respectively), while infrared spectra were collected on the $x=0.025$ sample only. The present data were compared with companion results on undoped ${\text{VO}}_{2}$ [E. Arcangeletti et al., Phys. Rev. Lett. 98, 196406 (2007)], which is found at ambient conditions in a different, third insulating monoclinic phase, named $M1$. This comparison allowed us to investigate the effects of different extents of structural distortions (Peierls distortion) on the lattice dynamics and the electronic properties of this family of compounds. The pressure dependence of the Raman spectrum of ${\text{VO}}_{2}$ and Cr-doped samples shows that all the systems retain the monoclinic structure up to the highest explored pressure, regardless the specific monoclinic structure ($M1$, $M2$, and $M3$) at ambient condition. Moreover, the Raman spectra of the two Cr-doped samples, which exhibit an anomalous behavior over the low-pressure range $(Pl8\text{ }\text{GPa})$, merge into that of ${\text{VO}}_{2}$ in the high-pressure regime and are all found into a common monoclinic phase (a possible fourth kind phase). Combining Raman and infrared results on both the ${\text{VO}}_{2}$ and the present data, we found that a common metallic monoclinic phase appears accessible in the high-pressure regime at room temperature for both undoped and Cr-doped samples independently of the different extents of Peierls distortion at ambient conditions. This finding differs from the behavior observed at ambient pressure, where the metallic phase is found only in conjunction with the rutile structure. The whole of these results suggests a major role of the electron correlations, rather than of the Peierls distortion, in driving the metal-insulator transition in vanadium dioxide systems, thus opening to new experimental and theoretical queries.

Subduction, convergence and the mode of backarc extension in the Mediterranean region

Abstract: 30-35 Ma ago a major change occurred in the Mediterranean region, from a regionally compressional subduction coeval with the formation of Alpine mountain belts, to extensional subduction and backarc rifting. Backarc extension was accompanied by gravitational spreading of the mountain belts formed before this Oligocene revolution. Syn-rift basins formed during this process above detachments and low-angle normal faults. Parameters that control the formation and the kinematics of such flat-lying detachments are still poorly understood. From the Aegean Sea to the Tyrrhenian Sea and the Alboran Sea, we have analysed onshore the deformation and P-T-t evolution of the ductile crust exhumed by extension, and the transition from ductile to brittle conditions as well as the relations between deep deformation and basin formation. We show that the sense of shear along crustal-scale detachments is toward the trench when subduction proceeds with little or no convergence (northern Tyrrhenian and Alboran after 20 Ma) and away from the trench in the case of true convergence (Aegean). We tentatively propose a scheme explaining how interactions between the subducting slab and the mantle control the basal shear below the upper plate and the geometry and distribution of detachments and associated sedimentary basins. We propose that ablative subduction below the Aegean is responsible for the observed kinematics on detachments (i.e. away from the trench). The example of the Betic Cordillera and the Rif orogen, where the directions of stretching were different in the lower and the upper crust and changed through time, is also discussed following this hypothesis.

Observational constraints on the linear fluctuation growth rate

Abstract: Many experiments in the near future will test dark energy through its effects on the linear growth of matter perturbations. It is therefore important to find simple and at the same time general parametrizations of the linear growth rate. We show that a simple fitting formula that generalizes previous expressions reproduces the growth function in models that allow for a growth faster than standard, as for instance in interacting or scalar-tensor models. We use data from galaxy and Lyman-$\ensuremath{\alpha}$ power spectra to constrain the linear growth rate. We find $\ensuremath{\gamma}={0.6}_{\ensuremath{-}0.3}^{+0.4}$ for the growth rate index and $\ensuremath{\eta}={0.0}_{\ensuremath{-}0.2}^{+0.3}$ for the additional growth parameter we introduce.

Adaptive course generation through learning styles representation

Abstract: This paper presents an approach to automatic course generation and student modeling. The method has been developed during the European funded projects Diogene and Intraserv, focused on the construction of an adaptive e-learning platform. The aim of the platform is the automatic generation and personalization of courses, taking into account pedagogical knowledge on the didactic domain as well as statistic information on both the student’s knowledge degree and learning preferences. Pedagogical information is described by means of an innovative methodology suitable for effective and efficient course generation and personalization. Moreover, statistic information can be collected and exploited by the system in order to better describe the student’s preferences and learning performances. Learning material is chosen by the system matching the student’s learning preferences with the learning material type, following a pedagogical approach suggested by Felder and Silverman. The paper discusses how automatic learning material personalization makes it possible to facilitate distance learning access to both able-bodied and disabled people. Results from the Diogene and Intraserv evaluation are reported and discussed.