Showing papers by "Roma Tre University published in 2005"

Achieving transparency with plasmonic and metamaterial coatings

Abstract: The possibility of using plasmonic and metamaterial covers to drastically reduce the total scattering cross section of spherical and cylindrical objects is discussed. While it is intuitively expected that increasing the physical size of an object may lead to an increase in its overall scattering cross section, here we see how a proper design of these lossless metamaterial covers near their plasma resonance may induce a dramatic drop in the scattering cross section, making these objects nearly "invisible" or "transparent" to an outside observer--a phenomenon with obvious applications for low-observability and noninvasive probe design. Physical insights into this phenomenon and some numerical results are provided.

Circuit Elements at Optical Frequencies: Nanoinductors, Nanocapacitors, and Nanoresistors

Abstract: We present the concept of circuit nanoelements in the optical domain using plasmonic and nonplasmonic nanoparticles. Three basic circuit elements, i.e., nanoinductors, nanocapacitors, and nanoresistors, are discussed in terms of small nanostructures with different material properties. Coupled nanoscale circuits and parallel and series combinations are also envisioned, which may provide road maps for the synthesis of more complex circuits in the IR and visible bands. Ideas for the optical implementation of right-handed and left-handed nanotransmission lines are also forecasted.

The HELLAS2XMM Survey. VII. The Hard X-Ray Luminosity Function of AGNs up to z = 4: More Absorbed AGNs at Low Luminosities and High Redshifts

Abstract: We have determined the cosmological evolution of the density of active galactic nuclei (AGNs) and of their NH distribution as a function of the unabsorbed 2–10 keV luminosity up to redshift 4. We used the HELLAS2XMM sample combined with other published catalogs, yielding a total of 508 AGNs. Our best fit is obtained with a luminosity-dependent density evolution (LDDE) model where low-luminosity (LX � 10 43 ergs s � 1 ) AGNs peak at z � 0:7, while high-luminosity AGNs (LX > 10 45 ergs s � 1 )p eak atz � 2:0. A pure luminosity evolution model (PLE) can instead be rejected. There is evidence that the fraction of absorbed (NH > 10 22 cm � 2 ) AGNs decreases with the intrinsic X-ray luminosity and increases with the redshift. Our best-fit solution provides a good fit to the observed counts, the cosmic X-ray background, and to the observed fraction of absorbed AGNs as a function of the flux in the 10 � 15 ergs cm � 2 s � 1 10 44 ergs s � 1 ) AGNs have a density of 267 deg � 2 at fluxesS2� 10 > 10 � 15 ergs cm � 2 s � 1 . Using these results, "# (

The evolution of the timing properties of the black-hole transient GX 339-4 during its 2002/2003 outburst

Abstract: We present the results of the timing and color analysis of more than two hundred RXTE/PCA observations of the bright black-hole transient GX 339-4 obtained during its 2002/2003 outburst. The color-intensity evolution of the system, coupled to the properties of its fast time variability, allow the identification of four separate states. Depending on the state, strong noise is detected, together with a variety of quasi-periodic oscillations at frequencies from 0.2 to 8 Hz. We present a characterization of the timing parameters of these states and compare them to what has been observed in other systems. These results, together with those obtained from energy spectra, point towards a common evolution of black-hole transients through their outbursts.

X-ray obscuration and obscured AGN in the local universe

Abstract: We discuss the X-ray properties of 49 local ($z Chandra and XMM-Newton observations, which yield 25 (22) new X-ray detections in the 0.5–2 keV (2–10 keV) energy band. Our sample covers a range in the 2–10 keV observed flux, F 2-10 , from $3 \times 10^{-11}$ to $6 \times 10^{-15}$ erg cm -2 s -1 . The percentage of objects that are likely obscured by Compton-thick matter (column density, $N_{\rm H} \ge \sigma_t^{-1} \simeq 1.6 \times 10^{24}$ cm -2 ) is $\simeq$50%, and reaches $\simeq$80% for $\log\, (F_{2-10}) α fluorescent iron lines with large Equivalent Width (${\it EW} > 0.6$ keV) are common in our sample (6 new detections at a confidence level ≥ 2 σ ). They are explained as due to reflection off the illuminated side of optically thick material. We confirm a correlation between the presence of a ~100-pc scale nuclear dust in the WFC2 images and Compton-thin obscuration. We interpret this correlation as due to the large covering fraction of gas associated with the dust lanes. The X-ray spectra of highly obscured AGN invariably present a prominent soft excess emission above the extrapolation of the hard X-ray component. This soft component can account for a very large fraction of the overall X-ray energy budget. As this component is generally unobscured – and therefore likely produced in extended gas structures – it may lead to a severe underestimation of the nuclear obscuration in $z \sim 1$ absorbed AGN, if standard X-ray colors are used to classify them. As a by-product of our study, we report the discovery of a soft X-ray, luminous ($\simeq$7$\,\times\, 10^{40}$ erg s -1 ) halo embedding the interacting galaxy pair Mkn 266.

On the existence of blowing-up solutions for a mean field equation ✩

Abstract: In this paper we construct single and multiple blowing-up solutions to the mean field equation: {−Δu=λV(x)eu∫ΩV(x)euin Ω,u=0on ∂Ω, where Ω is a smooth bounded domain in R2, V is a smooth function positive somewhere in Ω and λ is a positive parameter.

Properties of Lyα emitters around the radio galaxy MRC 0316 257

Abstract: Observations of the radio galaxy MRC 0316–257 at $z = 3.13$ and the surrounding field are presented. Using narrow- and broad-band imaging obtained with the VLT, 77 candidate Ly α emitters with a rest-frame equivalent width of >15 A were selected in a ∼ 7´$\,\times\,7$´ field around the radio galaxy. Spectroscopy of 40 candidate emitters resulted in the discovery of 33 emission line galaxies of which 31 are Ly α emitters with redshifts similar to that of the radio galaxy, while the remaining two galaxies turned out to be [$\ion{O}{ii}$] emitters. The Ly α profiles have widths ( FWHM ) in the range of 120–800 km s -1 , with a median of 260 km s -1 . Where the signal-to-noise was large enough, the Ly α profiles were found to be asymmetric, with apparent absorption troughs blueward of the profile peaks, indicative of absorption along the line of sight of an $\ion{H}{i}$ mass of at least $2 \times 10^2 {-} 5 \times 10^4$ M $_{\odot}$. Besides that of the radio galaxy and one of the emitters that is a QSO, the continuum of the emitters is faint, with luminosities ranging from 1.3 L * to L * . The colors of the confirmed emitters are, on average, very blue. The median UV continuum slope is $\beta = -1.76$, bluer than the average slope of LBGs with Ly α emission ($\beta \sim -1.09$). A large fraction of the confirmed emitters ( ∼ 2/3) have colors consistent with that of dust-free starburst galaxies. Observations with the Advanced Camera for Surveys on the Hubble Space Telescope show that the emitters that were detected in the ACS image have a range of different morphologies. Four Ly α emitters ( ∼ 25%) were unresolved with upper limits on their half light radii of $r_{\rm h} ∼ 19%) show multiple clumps of emission, as does the radio galaxy, and the rest ( ∼ 56%) are single, resolved objects with $r_{\rm h} α emitters are on average smaller than LBGs. The average star formation rate of the Ly α emitters is 2.6 M $_{\odot}\;{\rm yr}^{-1}$ as measured by the Ly α emission line or M $_{\odot}\;{\rm yr}^{-1}$ as measured by the UV continuum. The properties of the Ly α galaxies (faint, blue and small) are consistent with young star forming galaxies which are still nearly dust free. The volume density of Ly α emitting galaxies in the field around MRC 0316–257 is a factor of $3.3^{+0.5}_{-0.4}$ larger compared with the density of field Ly α emitters at that redshift. The velocity distribution of the spectroscopically confirmed emitters has a dispersion of 640 km s -1 , corresponding to a FWHM of 1510 km s -1 , which is substantially smaller than the width of the narrow-band filter (${\it FWHM} \sim 3500$ km s -1 ). The peak of the velocity distribution is located within 200 km s -1 of the redshift of the radio galaxy. We conclude that the confirmed Ly α emitters are members of a protocluster of galaxies at $z \sim 3.13$. The size of the protocluster is unconstrained and is larger than $3.3 \times 3.3$ Mpc 2 . The mass of this structure is estimated to be >$3{-}6 \times 10^{14}$ M $_{\odot}$ and could be the progenitor of a cluster of galaxies similar to e.g. the Virgo cluster.

Generalized nonlinear Schrödinger equation for dispersive susceptibility and permeability: application to negative index materials.

Abstract: A new generalized nonlinear Schr\"odinger equation describing the propagation of ultrashort pulses in bulk media exhibiting frequency dependent dielectric susceptibility and magnetic permeability is derived and used to characterize wave propagation in a negative index material. The equation has new features that are distinct from ordinary materials ($\ensuremath{\mu}=1$): the linear and nonlinear coefficients can be tailored through the linear properties of the medium to attain any combination of signs unachievable in ordinary matter, with significant potential to realize a wide class of solitary waves.

Photon events with missing energy in e(+)e(-) collisions at root s=130 to 209 GeV

Abstract: The production of single- and multi-photon events has been studied in the reaction e+e- -> gamma (gamma) + invisible particles. The data collected with the DELPHI detector during the years 1999 and 2000 at centre-of-mass energies between 191 GeV and 209 GeV was combined with earlier data to search for phenomena beyond the Standard Model. The measured number of light neutrino families was consistent with three and the absence of an excess of events beyond that predicted by the Standard Model processes was used to set limits on new physics. Both model-independent searches and searches for new processes predicted by supersymmetric and extra-dimensional models have been made. Limits on new non-standard model interactions between neutrinos and electrons were also determined.

Dynamics of subduction and plate motion in laboratory experiments: Insights into the “plate tectonics” behavior of the Earth

Abstract: [1] Three-dimensional laboratory experiments have been designed to investigate the way slab-bearing plates move during subduction inside the mantle. In our experiments a viscous plate of silicone (lithosphere) subducts under its negative buoyancy in a viscous layer of pure honey (mantle). Varying thickness, width, viscosity, and density of the plate and mantle, three characteristic modes of subduction are observed: a retreating trench mode (mode I), a retreating trench mode following a transient period of advancing trench (mode II), and an advancing trench mode (mode III). These modes are characterized by different partitioning of the amount of subduction into plate and trench motion. Our experiments show that the velocity of subduction can be modeled by the dynamic interaction between acting and resisting forces, where lithospheric bending represents 75–95% of the total resisting forces. However, our experimental results also show the impossibility to predict a priori the plate velocity only from the velocity of subduction without considering trench migrations. We find experimentally that the lithospheric radius of curvature, which depends upon plate characteristics (stiffness and thickness) and the mantle thickness, exerts a primary control on the trench behavior. Our results suggest that the complexity of the style of subduction could be controlled by geometrical rules of a plate bending inside a stratified mantle. The Earth system is in the crucial range for the interplay between the rigidity of the plate and the mantle stratification: this setting may be the responsible for the complexity of the past and present tectonic styles.

Innovation and Regional Growth in the Enlarged Europe: The Role of Local Innovative Capabilities, Peripherality, and Education

Abstract: In this paper, a formal model for the relationship between innovation and growth in European Union regions is developed drawing upon the theoretical contribution of the systems of innovation approach. The model combines the analytical approach of the regional growth models with the insights of the systemic approach. The cross-sectional analysis, covering all the Enlarged Europe (EU-25) regions (for which data are available), shows that regional innovative activities (for which a specific measure is developed) play a significant role in determining differential regional growth patterns. Furthermore, the model sheds light on how geographical accessibility and human capital accumulation, by shaping the regional system of innovation, interact (in a statistically significant way) with local innovative activities, thus allowing them to be more (or less) effectively translated into economic growth. The paper shows that an increase in innovative effort is not necessarily likely to produce the same effect in all EU-25 regions. Indeed, the empirical analysis suggests that in order to allow innovative efforts in peripheral regions to be as productive as in core areas, they need to be complemented by huge investments in human capital.

Constraints on mantle circulation around the deforming Calabrian slab

Abstract: [1] Combining tectonics, with seismological and geochemical data, we reconstruct the deformation history of the presently narrow Calabrian slab and the path of mantle circulation during the last 10 Ma. We show that during the slab deformation the mantle laterally flowed inside the back arc region permitting its retrograde motion and giving a seismological and volcanological record after 1–2 myr.

Validation of a Driving Simulator for Work Zone Design

Abstract: The research project aimed at calibrating and validating the driving simulator of the European Interuniversity Research Center for Road Safety to enable its use for design and verification of the effectiveness of temporary traffic signs on highways. The research was developed through the following steps: (a) a survey of speed measurements on highways next to a work zone of medium duration, (b) reconstruction in virtual reality of the real situation by using the driving simulator and subsequent running of a series of driving tests, and (c) statistical analysis of the field speeds and of the speeds from driving simulations for validation of the simulator. The surveyed work zone was located on Highway A1 from Milan to Naples, Italy. Speed measurements were conducted with a laser speed meter in the transition area, the activity area, and the termination area, and in the advance warning area speeds were shot with a camera from an overpass. Speed data from the field and the simulator were analyzed by using the bilateral Z-test for nonmatched samples to determine whether drivers responded differently in the simulator compared with their response during the real driving experience. The activity carried out revealed that differences between the speeds observed in the real situation and those measured with the simulator were not statistically significant.

Space weather conditions and spacecraft anomalies in different orbits

Abstract: [1] A large database of anomalies, registered by 220 satellites in different orbits over the period 1971–1994, has been compiled. For the first time, data of 49 Russian Kosmos satellites have been included in a statistical analysis. The database also contains a large set of daily and hourly space weather parameters. A series of statistical analyses made it possible to quantify, for different satellite orbits, space weather conditions in the days characterized by anomaly occurrences. In particular, very intense fluxes (>1000 particles cm−2 s−1 sr−1 (pfu) at energy >10 MeV) of solar protons are linked to anomalies registered by satellites in high-altitude (>15,000 km) near-polar (inclination >55°) orbits typical for navigation satellites such as those used in the GPS network, NAVSTAR, etc. (the rate of anomalies increases by a factor of ∼20) and to a much smaller extent to anomalies in geostationary orbits (the rate increases by a factor of ∼4). The efficiency in producing anomalies is found to be negligible for proton fluences 10 MeV. Elevated fluxes of energetic (>2 MeV) electrons >108 cm−2 d−1 sr−1 are observed by GOES on days with satellite anomalies occurring at geostationary (GOES, SCATHA, METEOSAT, MARECS A, etc.) and low-altitude ( 55°) orbits (Kosmos, SAMPEX, etc.). These elevated fluxes are not observed on days of anomalies registered in high-altitude near-polar orbits. Direct and indirect connections between anomaly occurrence and geomagnetic perturbations are also discussed.

Ions in water: the microscopic structure of concentrated hydroxide solutions.

Abstract: Neutron-diffraction data on aqueous solutions of hydroxides, at solute concentrations ranging from 1 solute per 12 water molecules to 1 solute per 3 water molecules, are analyzed by means of a Monte Carlo simulation (empirical potential structure refinement), in order to determine the hydration shell of the OH- in the presence of the smaller alkali metal ions. It is demonstrated that the symmetry argument between H+ and OH- cannot be used, at least in the liquid phase at such high concentrations, for determining the hydroxide hydration shell. Water molecules in the hydration shell of K+ orient their dipole moment at about 45 degrees from the K+-water oxygen director, instead of radially as in the case of the Li+ and Na+ hydration shells. The K+-water oxygen radial distribution function shows a shallower first minimum compared to the other cation-water oxygen functions. The influence of the solutes on the water-water radial distribution functions is shown to have an effect on the water structure equivalent to an increase in the pressure of the water, depending on both ion concentration and ionic radius. The changes of the water structure in the presence of charged solutes and the differences among the hydration shells of the different cations are used to present a qualitative explanation of the observed cation mobility.

Highly Ionized Iron Absorption Lines from Outflowing Gas in the X-Ray Spectrum of NGC 1365

Abstract: We present the discovery of four absorption lines in the X-ray spectrum of the Seyfert galaxy NGC 1365, at energies between 6.7 and 8.3 keV. The lines are detected with high statistical confidence (from >20 sigma for the strongest to -4 sigma for the weakest) in two XMM-Newton observations 60 ks long. We also detect the same lines, with a lower signal-to-noise ratio (but still >2 sigma for each line), in two previous shorter (-10 ks) XMM-Newton observations. The spectral analysis identifies these features as Fe XXV and Fe XXVI Kalpha and Kbeta lines, outflowing with velocities varying between -1000 and -5000 km/s among the observations. These are the highest quality detections of such lines so far. The high equivalent widths [EW (Kalpha) approximately 100 eV] and the Kalpha/Kbeta ratios imply that the lines are due to absorption of the AGN continuum by a highly ionized gas with column density NH-5?1023 cm(exp -2) at a distance of -(50-100)RS from the continuum source.

Interplay between nonlocality and nonlinearity in nematic liquid crystals.

Abstract: Spatial nonlocality has a crucial role in the optical response of bulk liquid crystals. With specific reference to one-dimensional modulation instability, we demonstrate the tuning of transverse nonlocality in the nonlinear response of nematics.

Dynamical effects of subducting ridges: insights from 3-D laboratory models

Abstract: SUMMARY We model using analogue experiments the subduction of buoyant ridges and plateaus to study their effect on slab dynamics. Experiments show that simple local (1-D) isostatic considerations are not appropriate to predict slab behaviour during the subduction of a buoyant ridge perpendicular to the trench, because the rigidity of the plate forces the ridge to subduct with the dense oceanic lithosphere. Oceanic ridges parallel to the trench have a stronger effect on the process of subduction because they simultaneously affect a longer trench segment. Large buoyant slab segments sink more slowly into the asthenosphere, and their subduction result in a diminution of the velocity of subduction of the plate. We observe a steeping of the slab below those buoyant anomalies, resulting in smaller radius of curvature of the slab that augments the energy dissipated in folding the plate and further diminishes the velocity of subduction. When the 3-D geometry of a buoyant plateau is modelled, the dip of the slab above the plateau decreases, as a result of the larger velocity of subduction of the dense ‘normal’ oceanic plate on both sides of the plateau. Such a perturbation of the dip of the slab maintains long time after the plateau has been entirely incorporated into the subduction zone. We compare experiments with the present-day subduction zone below South America. Experiments suggest that a modest ridge perpendicular to the trench such as the present-day Juan Fernandez ridge is not buoyant enough to modify the slab geometry. Already subducted buoyant anomalies within the oceanic plate, in contrast, may be responsible for some aspects of the present-day geometry of the Nazca slab at depth.

On the transmission‐dominated to reprocessing‐dominated spectral state transitions in Seyfert 2 galaxies

Abstract: We present Chandra and XMM-Newton observations of a small sample (11 objects) of optically selected Seyfert 2 galaxies, for which ASCA and BeppoSAX had suggested Compton-thick obscuration of the active galactic nucleus (AGN). The main goal of this study is to estimate the rate of transitions between 'transmission-dominated' and 'reprocessing-dominated' states. We discover one new transition in NGC 4939, with a possible additional candidate in NGC 5643. This indicates a typical occurrence rate of at least ∼0.02 yr -1 . These transitions could be due to large changes of the obscuring gas column density, or to a transient dimming of the AGN activity, the latter scenario being supported by detailed analysis of the best-studied events. Independently of the ultimate mechanism, comparison of the observed spectral dynamics with Monte Carlo simulations demonstrates that the obscuring gas is largely inhomogeneous, with multiple absorbing components possibly spread through the whole range of distances from the nucleus between a fraction of parsecs up to several hundred parsecs. As a by-product of this study, we report the first measurement ever of the column density covering the AGN in NGC 3393 (N H ≃ 4.4 x 10 24 cm -2 ), and the discovery of soft X-ray extended emission, apparently aligned along the host galaxy main axis in NGC 5005. The latter object most likely hosts an historically misclassified low-luminosity Compton-thin AGN.

Effect of penguin operators in the B0 --> J/psiK0 CP asymmetry.

Abstract: Performing a fit to the available experimental data, we quantify the effect of long-distance contributions from penguin contractions in ${B}^{0}\ensuremath{\rightarrow}J/\ensuremath{\psi}{K}^{0}$ decays. We estimate the deviation of the measured ${\mathcal{S}}_{CP}$ term of the time-dependent $CP$ asymmetry from $\mathrm{sin} 2\ensuremath{\beta}$ induced by these contributions and by the penguin operators. We find $\ensuremath{\Delta}\mathcal{S}\ensuremath{\equiv}{\mathcal{S}}_{CP}(J/\ensuremath{\psi}K)\ensuremath{-}\mathrm{sin} 2\ensuremath{\beta}=0.000\ifmmode\pm\else\textpm\fi{}0.012$ ($[\ensuremath{-}0.025,0.024]@95%$ probability), an uncertainty much larger than previous estimates and comparable to the present systematic error quoted by the experiments at the $B$ factories.

Fe xxv and Fe xxvi lines from low-velocity, photoionized gas in the X-ray spectra of active galactic nuclei

Abstract: We have calculated the equivalent widths of the absorption lines produced by Fe XXV and Fe XXVI in a Compton-thin, low-velocity photoionized material illuminated by the nuclear continuum in active galactic nuclei. The results, plotted against the ionization parameter and the column density of the gas, are a complement to those presented by Bianchi & Matt for the emission lines from the same ionic species. As an extension to the work by Bianchi & Matt, we also present a qualitative discussion on the different contributions to the He-like iron emission line complex in the regimes where recombination or resonant scattering dominates, providing a useful diagnostic tool to measure the column density of the gas. Future high-resolution missions (e.g. Astro-E2) will allow us to fully take advantage of these plasma diagnostics. In the meantime, we compare our results with an up-to-date list of Compton-thick and unobscured (at least at the iron line energy) Seyfert galaxies with emission and/or absorption lines from H- and He-like iron observed with Chandra and XMM-Newton.

Clustering web pages based on their structure

Abstract: Several techniques have been recently proposed to automatically generate Web wrappers, i.e., programs that extract data from HTML pages, and transform them into a more structured format, typically in XML. These techniques automatically induce a wrapper from a set of sample pages that share a common HTML template. An open issue, however, is how to collect suitable classes of sample pages to feed the wrapper inducer. Presently, the pages are chosen manually. In this paper, we tackle the problem of automatically discovering the main classes of pages offered by a site by exploring only a small yet representative portion of it. We propose a model to describe abstract structural features of HTML pages. Based on this model, we have developed an algorithm that accepts the URL of an entry point to a target Web site, visits a limited yet representative number of pages, and produces an accurate clustering of pages based on their structure. We have developed a prototype, which has been used to perform experiments on real-life Web sites.

The XMM-Newton view of Mrk 3 and IXO 30

Abstract: We present the analysis of the XMM-Newton EPIC pn spectrum of the Seyfert 2 galaxy, Mrk 3. We confirm that the source is dominated by a pure Compton reflection component and an iron Kα line, both produced as reflection from a Compton-thick torus, likely responsible also for the large column density (1.36 +0.03 0.04 × 10 24 cm 2 ) which is pierced by the primary powerlaw only at high energies. A low inclination angle and an iron underabundance of a factor ≃ 0.82, suggested by the amount of reflection and the depth of the iron edge, are consistent with the iron Kα line EW with respect to the Compton reflection component, being 610 +30 50 eV. Moreover, the iron line width, σ = 32 +13 14 eV, if interpreted in terms of Doppler broadening due to the Keplerian rotation of the torus, puts an estimate to the inner radius of the latter, r = 0.6 +1.3 0.3 sin 2 i pc. Finally, two different photoionised reflectors are needed to take into account a large number of soft X-ray emission lines from N, O, Ne, Mg, Si, Fe L and the Fe xxv emission line at 6.71 +0.03