Showing papers by "Roma Tre University published in 2004"
TL;DR: In this article, the authors show that the median probability model is often the optimal predictive model, which is defined as the model consisting of those variables which have overall posterior probability greater than or equal to 1/2 of being in a model.
Abstract: Often the goal of model selection is to choose a model for future prediction, and it is natural to measure the accuracy of a future prediction by squared error loss. Under the Bayesian approach, it is commonly perceived that the optimal predictive model is the model with highest posterior probability, but this is not necessarily the case. In this paper we show that, for selection among normal linear models, the optimal predictive model is often the median probability model, which is defined as the model consisting of those variables which have overall posterior probability greater than or equal to 1/2 of being in a model. The median probability model often differs from the highest probability model.
881 citations
TL;DR: This paper considers the scheduling problems arising when two agents, each with a set of nonpreemptive jobs, compete to perform their respective jobs on a common processing resource, and addresses the complexity of various problems.
Abstract: We consider the scheduling problems arising when two agents, each with a set of nonpreemptive jobs, compete to perform their respective jobs on a common processing resource. Each agent wants to minimize a certain objective function, which depends on the completion times of its jobs only. The objective functions we consider in this paper are maximum of regular functions (associated with each job), number of late jobs, and total weighted completion times. We obtain different scenarios, depending on the objective function of each agent, and on the structure of the processing system (single machine or shop). For each scenario, we address the complexity of various problems, namely, finding the optimal solution for one agent with a constraint on the other agent's cost function, finding single nondominated schedules (i.e., such that a better schedule for one of the two agents necessarily results in a worse schedule for the other agent), and generating all nondominated schedules.
401 citations
TL;DR: In this article, the electroweak corrections due to light fermions to the production cross section σ(gg! H) and to the partial decay widths (H! γ γ) and ( H! g g) were computed in terms of generalized harmonic polylogarithms.
396 citations
TL;DR: In this article, the role of palmitoylation and the impact of E2 stimulation on ERα membrane localization was investigated in cancer cell lines expressing transfected or endogenous human ERα (HeLa and HepG2, respectively).
Abstract: A fraction of the nuclear estrogen receptor α (ERα) is localized to the plasma membrane region of 17β-estradiol (E2) target cells. We previously reported that ERα is a palmitoylated protein. To gain insight into the molecular mechanism of ERα residence at the plasma membrane, we tested both the role of palmitoylation and the impact of E2 stimulation on ERα membrane localization. The cancer cell lines expressing transfected or endogenous human ERα (HeLa and HepG2, respectively) or the ERα nonpalmitoylable Cys447Ala mutant transfected in HeLa cells were used as experimental models. We found that palmitoylation of ERα enacts ERα association with the plasma membrane, interaction with the membrane protein caveolin-1, and nongenomic activities, including activation of signaling pathways and cell proliferation (i.e., ERK and AKT activation, cyclin D1 promoter activity, DNA synthesis). Moreover, E2 reduces both ERα palmitoylation and its interaction with caveolin-1, in a time- and dose-dependent manner. These data point to the physiological role of ERα palmitoylation in the receptor localization to the cell membrane and in the regulation of the E2-induced cell proliferation.
388 citations
TL;DR: In this article, an extensive timing analysis of the 1999 outburst of the soft X-ray transient and black hole candidate XTE J1859+226 as observed with the Rossi X-Ray Timing Explorer is presented.
Abstract: We present the results of an extensive timing analysis of the 1999 outburst of the soft X-ray transient and black hole candidate XTE J1859+226 as observed with the Rossi X-Ray Timing Explorer . Three main different types of low frequency (1-9 Hz) quasi-periodic oscillations (QPOs) were observed and classified, strengthening the general picture that is emerging for the variability properties of black hole X-ray binaires. Rapid transitions between different power spectral shapes were observed and their link with the count rate was studied. Furthermore, we show that a frequency of ~6 Hz seems to hold a particular place: one of the three QPO types we found was very stable when at this frequency, as it happens in Z sources as well. The coherence of its subharmonic peak was higher when the fundamental was close to 6 Hz, thus suggesting the presence of some resonance at this frequency.
204 citations
TL;DR: In this article, the authors analyzed the peculiar velocity field traced by 56 clusters within 120 h − 1 Mpc in the Streaming Motions of Abell Clusters (SMAC) sample.
Abstract: We analyse in detail the peculiar velocity field traced by 56 clusters within 120 h −1 Mpc in the ‘Streaming Motions of Abell Clusters’ (SMAC) sample. The bulk flow of the SMAC sample is 687 ± 203 km s −1 , toward l = 260 ◦ ± 13 ◦ , b = 0 ◦ ± 11 ◦ . We discuss possible systematic errors and show that no systematic effect is larger than half of the random error. The flow does not drop off significantly with depth, which suggests that it is generated by structures on large scales. In particular, a Great Attractor as originally proposed by Lynden-Bell et al. cannot be responsible for the SMAC bulk flow. The SMAC data suggest infall into an attractor at the location of the Shapley Concentration, but the detection is marginal (at the 90 per cent confidence level). We find that distant attractors in addition to the Shapley Concentration are required to explain the SMAC bulk flow. A comparison with peculiar velocities predicted from the IRAS Point Source Catalogue redshift (PSCz) survey shows good agreement with a best-fitting value of β I = � 0.6 m /bI = 0.39 ± 0.17. However, the PSCz density field is not sufficient to account for all of the SMAC bulk motion. We also detect, at the 98 per cent confidence level, a residual bulk flow of 372 ± 127 km s −1 toward l = 273 ◦ , b = 6 ◦ which must be generated by sources not included in the PSCz catalogue, that is, either beyond 200 h −1 Mpc, in the zone of avoidance or in superclusters undersampled by IRAS. Finally, we compare the SMAC bulk flow with other recent measurements. We argue that, at depths ranging from 60 to 120 h −1 Mpc, flows of order 600 km s −1 are excluded by multiple data sets. However, convergence to the cosmic microwave background frame by a depth of 60 h −1 Mpc is also excluded by multiple data sets. We suggest that a bulk flow of 225 km s −1 toward l = 300 ◦ , b = 10 ◦ at depths greater than 60 h −1 Mpc is consistent with all peculiar velocity surveys, when allowance is made for sparse
168 citations
TL;DR: In this article, the authors proposed that radio-quiet quasars and Seyfert galaxies have central black holes powering outflows and jets which propagate only for a short distance, because the velocity of the ejected material is smaller than the escape velocity.
Abstract: We propose that radio-quiet quasars and Seyfert galaxies have central black holes powering outflows and jets which propagate only for a short distance, because the velocity of the ejected material is smaller than the escape velocity. We call them "aborted" jets. If the central engine works intermittently, blobs of material may be produced, which can reach a maximum radial distance and then fall back, colliding with the blobs produced later and still moving outwards. These collisions dissipate the bulk kinetic energy of the blobs by heating the plasma, and can be responsible (entirely or at least in part) for the generation of the high energy emission in radio-quiet objects. This is alternative to the more conventional scenario in which the X-ray spectrum of radio-quiet sources originates in a hot (and possibly patchy) corona above the accretion disk. In the latter case the ultimate source of energy of the emission of both the disk and the corona is accretion. Here we instead propose that the high energy emission is powered also by the extraction of the rotational energy of the black hole (and possibly of the disk). By means of Montecarlo simulations we calculate the time dependent spectra and light curves, and discuss their relevance to the X-ray spectra in radio-quiet AGNs and galactic black hole sources. In particular, we show that time variability and spectra are similar to those observed in Narrow Line Seyfert 1 galaxies.
164 citations
TL;DR: In this paper, the authors present 3D laboratory experiments constructed to investigate the pattern of mantle flow around a subducting slab under different boundary conditions and highlight the importance of suitable simulations of lateral viscosity variations to obtain a realistic simulation of the history of subduction.
Abstract: SUMMARY We present 3-D laboratory experiments constructed to investigate the pattern of mantle flow around a subducting slab under different boundary conditions. In particular we present a set of experiments, characterized by different conditions imposed at the trailing edge of the subducting plate (that is, plate fixed in the far field, plate detached in the far field, imposed plate motion). Experiments have been performed using a silicone slab floating inside a honey tank to simulate a thin viscous lithosphere subducting in a viscous mantle. For each set, we show differences between models that do or do not include the possibility of out-of-plane lateral flow in the mantle by varying the lateral boundary conditions. Our results illustrate how a subducting slab vertically confined over a 660-km equivalent depth can be influenced in its geometry and in its kinematics by the presence or absence of possible lateral pathways. On the basis of these results we show implications for natural subduction systems and we highlight the importance of suitable simulations of lateral viscosity variations to obtain a realistic simulation of the history of subduction.
138 citations
TL;DR: Alpha-bisabolol may be considered a novel compound able to inhibit glioma cell growth and survival and triggered by cytotoxicity resulted from apoptosis induction.
134 citations
Imperial College London1, Spanish National Research Council2, University of Cambridge3, Roma Tre University4, University of Padua5, University of Sussex6, Kapteyn Astronomical Institute7, University of Kent8, Cyprus College9, European Southern Observatory10, University of Helsinki11, University of Edinburgh12, Max Planck Society13, European Space Research and Technology Centre14, University of Cantabria15, International School for Advanced Studies16, University of Arizona17, National and Kapodistrian University of Athens18, University of Turku19, Niels Bohr Institute20, Danish Space Research Institute21, Space Telescope Science Institute22, University of Paris23, University of Oxford24, Institut d'Astrophysique de Paris25, University of Hertfordshire26, Herzberg Institute of Astrophysics27
TL;DR: In this article, the authors present the final band-merged European Large Area ISO Survey (ELAIS) Catalogue at 6.7, 15, 90 and 175 mum, and the associated data at U, g, r', r', i', Z, Z, J, H, K and 20 cm.
Abstract: We present the final band-merged European Large-Area ISO Survey (ELAIS) Catalogue at 6.7, 15, 90 and 175 mum, and the associated data at U, g', r', i', Z, J, H, K and 20 cm. The origin of the survey, infrared and radio observations, data-reduction and optical identifications are briefly reviewed, and a summary of the area covered and the completeness limit for each infrared band is given. A detailed discussion of the band-merging and optical association strategy is given. The total Catalogue consists of 3762 sources. 23 per cent of the 15-mum sources and 75 per cent of the 6.7-mum sources are stars. For extragalactic sources observed in three or more infrared bands, colour-colour diagrams are presented and discussed in terms of the contributing infrared populations. Spectral energy distributions (SEDs) are shown for selected sources and compared with cirrus, M82 and Arp220 starburst, and active galactic nuclei (AGN) dust torus models. Spectroscopic redshifts are tabulated, where available. For the N1 and N2 areas, the Isaac Newton Telescope ugriz Wide Field Survey permits photometric redshifts to be estimated for galaxies and quasars. These agree well with the spectroscopic redshifts, within the uncertainty of the photometric method [similar to10 per cent in (1 + z) for galaxies]. The redshift distribution is given for selected ELAIS bands and colour-redshift diagrams are discussed. There is a high proportion of ultraluminous infrared galaxies (log(10) of 1-1000 mum luminosity L-ir > 12.22) in the ELAIS Catalogue (14 per cent of 15-mum galaxies with known z), many with Arp220-like SEDs. 10 per cent of the 15-mum sources are genuine optically blank fields to r' = 24: these must have very high infrared-to-optical ratios and probably have z > 0.6, so are high-luminosity dusty starbursts or Type 2 AGN. Nine hyperluminous infrared galaxies (L-ir > 13.22) and nine extremely red objects (EROs) (r - K > 6) are found in the survey. The latter are interpreted as ultraluminous dusty infrared galaxies at z similar to 1. The large numbers of ultraluminous galaxies imply very strong evolution in the star formation rate between z = 0 and 1. There is also a surprisingly large population of luminous (L-ir > 11.5), cool (cirrus-type SEDs) galaxies, with L-ir L-opt > 0, implying A(V) > 1.
131 citations
TL;DR: In this article, the authors studied the effect of the anomalous magnetic and electric dipole moments of the tau lepton in the DELPHI experiment at LEP2 during the years 1997 - 2000.
Abstract: Tau-pair production in the process e(+)e(-) --> e(+)e(-) tau(+)tau(-) was studied using data collected by the DELPHI experiment at LEP2 during the years 1997 - 2000. The corresponding integrated luminosity is 650 pb(-1). The values of the cross-section obtained are found to be in agreement with QED predictions. Limits on the anomalous magnetic and electric dipole moments of the tau lepton are deduced.
TL;DR: In this paper, the authors used the HELLAS2XMM 1df (1 degree field) survey data to evaluate the fraction of X-ray absorbed (log NH > 22) Active Galactic Nuclei (AGN) in the 2−10 keV flux range 0.8−20 × 10 −14 erg cm −2 s −1.
Abstract: The spectroscopic analysis of 117 serendipitous sources in the HELLAS2XMM 1df (1 degree field) survey is de- scribed. Of these, 106 sources, of which 86% have a spectroscopic redshift, are used to evaluate the fraction of X-ray absorbed (log NH > 22) Active Galactic Nuclei (AGN) in the 2−10 keV flux range 0.8−20 × 10 −14 erg cm −2 s −1 . This fraction turns out lower than what is predicted by two well known Cosmic X-Ray Background synthesis models, and the discrepancy is signifi- cant at the 99.999% level. This result consolidates the findings recently obtained by other authors. In the flux interval explored, the data are consistent with an intrinsic distribution of the absorbing columns (flat per decade above log NH > 21) independent of luminosity and redshift, together with an AGN luminosity function evolving purely in luminosity. It is shown that, on the other hand, extrapolation to lower fluxes fails to reproduce the results inferred from the Chandra Deep Field North survey. It is found that about 40% of the high luminosity sources in our sample have best fit log NH > 22, and the surface density of these X-ray obscured QSOs can then be estimated at about 48 per square degree, at the flux limit of ∼10 −14 erg cm −2 s −1 of the HELLAS2XMM 1df survey. As a side issue, 5 or 6 out of 60 sources, that is about 10%, identified with broad line AGN, turn out to be affected by log NH > 22 absorption.
TL;DR: In this article, the authors reconstruct the nappe-structured belt of Calabria through a multidisciplinary approach which integrates structural investigations with metamorphic thermobarometry and 40Ar/39Ar geochronology.
Abstract: [1] The nappe-structured belt of Calabria constitutes the eastward termination of the southern branch of the Alpine Mediterranean belt that delimits the northern edge of the Africa plate Contrasting hypotheses for the origin and tectonic significance of the north Calabrian nappe edifice have been proposed, and kinematic data from north Calabria have been used to support different interpretations of the Alps-Apennines linkage and the polarity of the Tethyan subduction in the Apennine region We reconstruct the architecture of the north Calabria nappe edifice through a multidisciplinary approach which integrates structural investigations with metamorphic thermobarometry and 40Ar/39Ar geochronology Results from this study indicate that north Calabria consists of a Tertiary nappe stack, resulting from superimposed top-to-the-west extensional shearing (late Oligocene to middle Miocene in age) onto a previously structured top-to-the-east compressional belt (Eocene to Oligocene in age) This study also documents that the top-to-the-west extensional tectonics was achieved by means of regionally sized extensional detachment fault systems, stretching apart and translating as allochthonous fragments the previously accreted units Thinning operated by top-to-the-west extensional detachment tectonics also resulted in the direct juxtaposition of non-Alpine or slightly Alpine metamorphosed units (upper plate complex) onto the previously exhumed deep-seated portions of the orogenic wedge, metamorphosed under blueschist facies metamorphic conditions (lower plate complex) These findings support a new tectonic scenario for the orogenic history of north Calabria, which may be adequately framed within the Tertiary Apennine-Tyrrhenian system evolution
TL;DR: This work investigates the discrete propagation of near-infrared light in a voltage-controlled array of channel waveguides in undoped nematic liquid crystals under planar anchoring conditions and develops a scalar model that encompasses the voltage-dependent reorientational response of the material.
Abstract: We investigate, for the first time to our knowledge, the discrete propagation of near-infrared light in a voltage-controlled array of channel waveguides in undoped nematic liquid crystals under planar anchoring conditions. This novel geometry enables us to drive the system from one-dimensional bulk diffraction to discrete propagation and, for larger excitations, to discrete spatial solitons, or nematicons. The observed phenomena are adequately described by a scalar model that encompasses the voltage-dependent reorientational response of the material.
TL;DR: In this paper, the role of extensional structures on collapse and resurgence of calderas was studied using an analogue model, where dry sand simulated the brittle crust; silicone, located at the base of the sand-pack, simulated magma.
TL;DR: In this paper, the authors presented the results of narrow-band and broad-band imaging with the Very Large Telescope* of the field surrounding the radio galaxy TN J0924-2201 at z = 5.2.
Abstract: We present the results of narrow-band and broad-band imaging with the Very Large Telescope* of the field surrounding the radio galaxy TN J0924-2201 at z = 5.2. Fourteen candidate Lya emitters with a rest-frame equivalent width of >20 A were detected. Spectroscopy of 8 of these objects showed that 6 have redshifts similar to that of the radio galaxy. The density of emitters at the redshift of the radio galaxy is estimated to be a factor 1.5-6.2 higher than in the field, and comparable to the density of Lya emitters in radio galaxy protoclusters at z = 4.1, 3.1 and 2.2. The Lya emitters near TN J0924-2201 could therefore be part of a structure that will evolve into a massive cluster. These observations confirm that substantial clustering of Lyα emitters occurs at z > 5 and support the idea that radio galaxies pinpoint high density regions in the early Universe.
TL;DR: Evidence is provided for the limiting amount of freely available polyamines in the extracellular space in tobacco plants under physiological conditions, which was further confirmed for untransformed maize and pea plants.
Abstract: To test the feasibility of altering polyamine levels by influencing their catabolic pathway, we obtained transgenic tobacco (Nicotiana tabacum) plants constitutively expressing either maize (Zea mays) polyamine oxidase (MPAO) or pea (Pisum sativum) copper amine oxidase (PCuAO), two extracellular and H2O2-producing enzymes. Despite the high expression levels of the transgenes in the extracellular space, the amount of free polyamines in the homozygous transgenic plants was similar to that in the wild-type ones, suggesting either a tight regulation of polyamine levels or a different compartmentalization of the two recombinant proteins and the bulk amount of endogenous polyamines. Furthermore, no change in lignification levels and plant morphology was observed in the transgenic plants compared to untransformed plants, while a small but significant change in reactive oxygen species-scavenging capacity was verified. Both the MPAO and the PCuAO tobacco transgenic plants produced high amounts of H2O2 only in the presence of exogenously added enzyme substrates. These observations provided evidence for the limiting amount of freely available polyamines in the extracellular space in tobacco plants under physiological conditions, which was further confirmed for untransformed maize and pea plants. The amount of H2O2 produced by exogenously added polyamines in cell suspensions from the MPAO transgenic plants was sufficient to induce programmed cell death, which was sensitive to catalase treatment and required gene expression and caspase-like activity. The MPAO and PCuAO transgenic plants represent excellent tools to study polyamine secretion and conjugation in the extracellular space, as well as to determine when and how polyamine catabolism actually intervenes both in cell wall development and in response to stress.
TL;DR: An optimization procedure for planning the production of steel ingots in a steelmaking-continuous casting plant by using a beam search procedure and comparing the results with a lower bound of the optimal solutions and with the actual performance obtained in the plant.
University of Naples Federico II1, University of Bologna2, University of Pisa3, California Institute of Technology4, University of Bari5, University of Salento6, Indiana University7, National Research Council8, Roma Tre University9, University of Trieste10, University of Minnesota11, Boston University12, University of Michigan13, Sapienza University of Rome14, Massachusetts Institute of Technology15, University of Calabria16, Drexel University17, Pakistan Institute of Nuclear Science and Technology18, University of Turin19, University of L'Aquila20, University of Basilicata21, University of Eastern Piedmont22, Texas A&M University23
TL;DR: The final analysis of atmospheric neutrino events collected with the MACRO detector is presented in this article, where three different classes of events, generated by neutrinos in different energy ranges, are studied.
Abstract: The final analysis of atmospheric neutrino events collected with the MACRO detector is presented. Three different classes of events, generated by neutrinos in different energy ranges, are studied l ...
TL;DR: In this article, a sample of eight bright unobscured (at least at the iron line energy) Seyfert Galaxies observed simul- taneously by XMM-Newton and BeppoSAX was selected, taking advantage of the complementary characteristics of the two missions.
Abstract: We selected a sample of eight bright unobscured (at least at the iron line energy) Seyfert Galaxies observed simul- taneously by XMM-Newton and BeppoSAX, taking advantage of the complementary characteristics of the two missions. The main results of our analysis can be summarized as follows: narrow neutral iron lines are confirmed to be an ubiquitous comp o- nent in Seyfert spectra; none of the analyzed sources shows unambiguously a broad relativistic iron line; all the source s of our sample (with a single exception) show the presence of a Compton reflection component; emission lines from ionized iron ar e observed in some sources; peculiar weak features around 5-6 keV (possibly arising from rotating spots on the accretion disk) are detected in two sources. The scenario emerging from these results strongly requires some corrections for the classi cal model of reprocessing from the accretion disk. As for materials farther away from the Black Hole, our results represent a positive test for the Unification Model, suggesting the presence of the tor us in (almost) all sources, even if unobscured.
TL;DR: It is shown that, for selection among normal linear models, the optimal predictive model is often the median probability model, which is defined as the model consisting of those variables which have overall posterior probability greater than or equal to 1/2 of being in a model.
Abstract: Often the goal of model selection is to choose a model for future prediction, and it is natural to measure the accuracy of a future prediction by squared error loss. Under the Bayesian approach, it is commonly perceived that the optimal predictive model is the model with highest posterior probability, but this is not necessarily the case. In this paper we show that, for selection among normal linear models, the optimal predictive model is often the median probability model, which is defined as the model consisting of those variables which have overall posterior probability greater than or equal to 1/2 of being in a model. The median probability model often differs from the highest probability model.
TL;DR: In this paper, searches for neutral Higgs bosons produced at LEP in association with Z bosons, in pairs and in the Yukawa process are presented, and results are presented in the form of mass-dependent upper bounds on coupling factors (in units of model independent reference cross-sections) for all processes, allowing interpretation of the data in a large class of models.
Abstract: Searches for neutral Higgs bosons produced at LEP in association with Z bosons, in pairs and in the Yukawa process are presented in this paper. Higgs boson decays into b quarks, tau leptons, or other Higgs bosons are considered, giving rise to four-b, four-b+jets, six-b and four-tau final states, as well as mixed modes with b quarks and tau leptons. The whole mass domain kinematically accessible at LEP in these topologies is searched. The analysed data set covers both the LEP1 and LEP2 energy ranges and exploits most of the luminosity recorded by the DELPHI experiment. No convincing evidence for a signal is found, and results are presented in the form of mass-dependent upper bounds on coupling factors (in units of model-independent reference cross-sections) for all processes, allowing interpretation of the data in a large class of models.
01 Dec 2004-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, the authors present a review of the KLOE offline environment, the architecture of the data-processing system and the programs developed for data reconstruction and Monte Carlo simulation, as well as the various procedures used for data handling and transfer between the different components of the system.
Abstract: The broad physics program of the KLOE experiment is based on the high event rate at the Frascati φ factory, and calls for an up-to-date system for data acquisition and processing. In this review of the KLOE offline environment, the architecture of the data-processing system and the programs developed for data reconstruction and Monte Carlo simulation are described, as well as the various procedures used for data handling and transfer between the different components of the system.
TL;DR: A case study in adaptive information filtering systems for the Web is presented and the results of the experiments are satisfactory and support the choice of a user model-based approach to information filtering on the Web.
Abstract: A case study in adaptive information filtering systems for the Web is presented. The described system comprises two main modules, named HUMOS and WIFS. HUMOS is a user modeling system based on stereotypes. It builds and maintains long term models of individual Internet users, representing their information needs. The user model is structured as a frame containing informative words, enhanced with semantic networks. The proposed machine learning approach for the user modeling process is based on the use of an artificial neural network for stereotype assignments. WIFS is a content-based information filtering module, capable of selecting html/text documents on computer science collected from the Web according to the interests of the user. It has been created for the very purpose of the structure of the user model utilized by HUMOS. Currently, this system acts as an adaptive interface to the Web search engine ALTA VISTATM. An empirical evaluation of the system has been made in experimental settings. The experiments focused on the evaluation, by means of a non-parametric statistics approach, of the added value in terms of system performance given by the user modeling component; it also focused on the evaluation of the usability and user acceptance of the system. The results of the experiments are satisfactory and support the choice of a user model-based approach to information filtering on the Web.
TL;DR: In this article, particle size data from 31 samples of carbonate cataclastic rocks collected across the 26 m thick fault core of the Mattinata Fault in the foreland of the Southern Apennines, Italy were determined by a sieving-and-weighting technique.
TL;DR: In this paper, the effect of boundary conditions on the mixing time of the Glauber dynamics in the Bethe approximation was studied and it was shown that the spectral gap and the log-Sobolev constant for the Ising model are bounded below by a constant independent of n at all temperatures and all external fields.
Abstract: We give the first comprehensive analysis of the effect of boundary conditions on the mixing time of the Glauber dynamics in the so-called Bethe approximation Specifically, we show that the spectral gap and the log-Sobolev constant of the Glauber dynamics for the Ising model on an n-vertex regular tree with (+)-boundary are bounded below by a constant independent of n at all temperatures and all external fields This implies that the mixing time is O(logn) (in contrast to the free boundary case, where it is not bounded by any fixed polynomial at low temperatures) In addition, our methods yield simpler proofs and stronger results for the spectral gap and log-Sobolev constant in the regime where the mixing time is insensitive to the boundary condition Our techniques also apply to a much wider class of models, including those with hard-core constraints like the antiferromagnetic Potts model at zero temperature (proper colorings) and the hard–core lattice gas (independent sets)
TL;DR: The directional sensitivity and the anisotropy of the ridgelet transform (RT) are employed in order to obtain a sparse image representation, where the most significant coefficients represent the most energetic direction of an image with straight edges.
Abstract: In this letter, we propose a multiplicative watermarking method operating in the ridgelet domain. We employ the directional sensitivity and the anisotropy of the ridgelet transform (RT) in order to obtain a sparse image representation, where the most significant coefficients represent the most energetic direction of an image with straight edges. Therefore, given a natural image, the associated edge image is obtained by means of a filter bank designed using the circular harmonic functions, then the edge image is partitioned into small blocks in order to deal with straight edges. Finally, the RT is performed for each block, the most relevant coefficients are selected, and eventually the watermark is embedded. Robustness and transparency are proven by experimental results.
TL;DR: In this paper, the authors present detailed line profiles as a function of orbital phase of the spot and its radial distance from a central black hole, which can provide a powerful tool to measure the mass of supermassive black holes in active galactic nuclei.
Abstract: Narrow spectral features in the 5-6 keV range were recently discovered in the X-ray spectra of a few active galactic nuclei. We discuss the possibility that these features are due to localized spots which occur on the surface of an accretion disc following its illumination by flares. We present detailed line profiles as a function of orbital phase of the spot and its radial distance from a central black hole. Comparison of these computed profiles with observed features can help to estimate parameters of the system. In principle, this method can provide a powerful tool to measure the mass of super-massive black holes in active galactic nuclei. By comparing our simulations with the Chandra and XMM-Newton results, we show, however, that spectra from present generation X-ray satellites are not of good enough quality to exploit the method fully and determine the black hole mass with sufficient accuracy. This task has to be deferred to future missions with high throughput and high energy resolution, such as Constellation-X and Xeus.
TL;DR: In this paper, a long (100 ks) XMM-Newton observation of the bright Seyfert 1 galaxy Arakelian 120 is reported, showing a Doppler broadened iron emission line (FWHM ∼ 3 × 10 4 km s -1 ) and a smooth, continuous soft excess which appears to peak at an energy 10.5 keV.
Abstract: We report on a long (100 ks) XMM-Newton observation of the bright Seyfert 1 galaxy Arakelian 120. The source previously showed no signs of intrinsic reddening in its infrared-ultraviolet continuum and previous observations had shown no evidence for ionized absorption in either the ultraviolet or X-ray bands. The new XMM-Newton Reflection Grating Spectrometer data place tight limits on the presence of an ionized X-ray absorber and confirm that the X-ray spectrum of Ark 120 is essentially unmodified by intervening matter. Thus Ark 120 can be considered a 'bare' Seyfert 1 nucleus. This observation therefore offers a clean view of the X-ray spectrum of a 'normal' Seyfert galaxy free from absorption effects. The spectrum shows a Doppler broadened iron emission line (FWHM ∼ 3 × 10 4 km s -1 ) and a smooth, continuous soft excess which appears to peak at an energy 10.5 keV. This adds weight to the claim that genuine soft excesses (i.e. those due to a real steepening of the underlying continuum below ∼2 keV) are ubiquitous in Seyfert 1 spectra. However, the detailed shape of the excess could not be reproduced by any of the simple models tested (power laws, blackbodies, Comptonized blackbodies, accretion disc reflection). This observation therefore demonstrates both the need to understand the soft excess (as a significant contributor to the luminosity of most Seyfert 1s) and the inability of the existing, simple models to explain it.
TL;DR: In this paper, the high energy XMM-Newton spectrum of the Seyfert 2 galaxy, NGC-1068, was analyzed and several Fe and Ni emission lines, from both neutral and highly ionized material, were detected.
Abstract: We present and discuss the high energy ($E>4$ keV) XMM– Newton spectrum of the Seyfert 2 galaxy, NGC 1068. Possible evidence for flux variability in both the neutral and ionized reflectors with respect to a BeppoSAX observation taken 3.5 years before is found. Several Fe and Ni emission lines, from both neutral and highly ionized material, are detected. The intensity of the iron K α Compton shoulder implies that the neutral reflector is Compton–thick, likely the visible inner wall of the $N_{\rm H} > 10^{25}$ cm -2 absorber. From the equivalent width of the ionized iron lines a column density of a few $\times 10^{21}$ cm -2 is deduced for the hot ionized reflector. Finally, an iron (nickel) overabundance, when compared to solar values, of about 2 (4) with respect to lower Z elements, is found.