INANOE Repositorio (Inst- Nacional de Astrofísica, Óptica y Electrónica
Not a member yet
2571 research outputs found
Sort by
BL Lacertae identifications in a ROSAT-selected sample of Fermi unidentified objects⋆,⋆⋆
Get PDFThe optical spectroscopic followup of 27 sources belonging to a sample of 30 high-energy objects selected by positionally cross correlating the first Fermi/LAT Catalog and the ROSAT All-Sky Survey Bright Source Catalog is presented here. It has been found or confirmed that 25 of them are BL Lacertae objects (BL Lacs), while the remaining two are Galactic cataclysmic variables (CVs). This strongly suggests that the sources in the first group are responsible for the GeV emission detected with Fermi, while the two CVs most likely represent spurious associations. We thus find an 80% a posteriori probability that the sources selected by matching GeV and X-ray catalogs belong to the BL Lac class. We also show suggestions that the BL Lacs selected with this approach are probably high-synchrotron-peaked sources and in turn good candidates for the detection of ultra-high-energy (TeV) photons from them
On the nature of the brightest globular cluster in M81
Get PDFWe analyse the photometric, chemical, star formation history and structural properties of the brightest globular cluster (GC) in M81, referred as GC1 in this work, with the intention of establishing its nature and origin. We find that it is a metal-rich ([Fe/H]=−0.60 ± 0.10), alpha-enhanced ([α/Fe] ~ 0.20 ± 0.05), core-collapsed (core radius rc = 1.2 pc, tidal radius rt = 76rc), old (> 13 Gyr) cluster. It has an ultraviolet excess equivalent of ~ 2500 blue horizontal branch stars. It is detected in X-rays indicative of the presence of low-mass binaries. With a mass of 1.0 × 10⁷ Mʘ, the cluster is comparable in mass to M31-G1 and is four times more massive than ω Cen. The values of rc, absolute magnitude and mean surface brightness of GC1 suggest that it could be, like massive GCs in other giant galaxies, the left-over nucleus of a dissolved dwarf galaxy
Disk Mass-to-Light ratio distribution from stellar population synthesis: Application to rotation curve decomposition of NGC 5278 (KPG 390 A).
Get PDFIn this work we extend the study on the mass distribution of the spiral galaxy NGC 5278, performing 1D and 2D (GALFIT) bulge-disk decomposition to determine which components constitute the baryonic mass in this galaxy. Our analysis does not detect any bulge, instead we find a bright source, probably related with the central AGN, and an exponential disk. We fix the stellar disk contribution to the rotation curve (RC) with broad band photometric observations and population synthesis models, to obtain the 2D mass distribution of the stellar disk. In particular, for NGC 5278, we find that the typical assumption of considering the mass-to-luminosity ratio (M/L) of the disk as constant along the galactocentric radius is not valid. We also extract a baryonic RC from the mass profile, to determine the inability of this baryonic RC (also taking into account ± 30% errors in the disk mass), to fit the entire RC. We perform the RC decomposition of NGC 5278 considering the determined baryonic RC and four types of dark matter (DM) halo: Hernquist, Burkert, Navarro, Frenk, & White and Einasto. Our results determine that Hernquist DM halo better models our observed RC in the case of disk mass Md = 5.6 × 10¹⁰ Mʘ and also with less 30% disk mass. In the case of more 30% disk mass the cored Einasto (n < 4) DM halo is the best fitting model
Complex-valued Thiran allpole filters
Get PDFThis paper describes the generalization of the real-valued Thiran allpole filter to the complex case. The design specifications for the complex case are the phase value φα, the group delay τ, and the degree of flatness K at ω = 0. The complex filter coefficients are obtained by solving a set of closed form linear equations derived from the design specification. Depending on the parity of the degree of flatness K, we proposed three classes of complex-valued allpole filters. We also establish the stability conditions, which depend on τ and φα. Finally, the application of the proposed filters for the design of a casual complex-valued cardinal orthogonal scaling function is described
Chemical and Morphological Characteristics of ALD Al₂O₃ Thin-Film Surfaces after Immersion in pH Buffer Solutions
No full textThe chemical and morphological properties of thin aluminum oxide film surfaces (Al₂O₃ having 10 nm in thickness) in the asdeposited (dry) and after immersion (in pH buffer solutions) conditions were studied. Careful measurement conditions have been followed in order to determine any possible physical and/or chemical change on the surface of these films (after immersion in pH), so that proper correlation to their high and stable sensitivity to pH is possible. After deposition of thin Al₂O₃ films (by Atomic Layer Deposition, ALD) on chemically oxidized p-type silicon wafers, the resulting Al₂O₃/SiOₓ/Si stacked structures were characterized by Fourier-Transform Infrared Spectroscopy (FTIR) and Atomic Force Microscopy (AFM) before and after immersion in pH buffer solutions. Also, the Capacitance-Voltage (C-V) and Current-Voltage (I-V) characteristics were obtained after fabrication of Metal-Insulator-Semiconductor (MIS) devices in order to correlate the good chemical and morphological characteristics of thin Al₂O₃ to its electrical properties. Based on the characterization results, low surface oxidation/dissolution mechanisms are found in ALD aluminum oxide films when immersed in pH buffer solutions during short immersion times (immersion time ≤ 10 minutes); therefore, leading to the characteristic slow degradation of the sensitivity to pH for this dielectric material. © 2013 The Electrochemical Society. [DOI: 10.1149/2.060310jes] All rights reserved
Modeling and Parameter Extraction of Test Fixtures for MOSFET On-Wafer Measurements up to 60 GHz
Get PDFWe present a circuit model and parameter determination methodology for test fixtures used for on-wafer S-parameter measurements on CMOS devices. The model incorporates the frequency dependence of the series resistances and inductances due to the skin effect occurring in the metal pads. Physically based representations for this effect allow for excellent theory-experiment correlations for different dummy structures, as well as when de-embedding transistor measurements up to 60 GHz. VC 2012 Wiley Periodicals, Inc. IntJ RF and Microwave CAE 23:655–661, 2013
Karatsuba-Ofman Multiplier with Integrated Modular Reduction for (2m )
Get PDFIn this paper a novel GF(2m) multiplier based on Karatsuba-Ofman Algorithm is presented. A binary field multiplication in polynomial basis is typically viewed as a two steps process, a polynomial multiplication followed by a modular reduction step. This research proposes a modification to the original Karatsuba-Ofman Algorithm in order to integrate the modular reduction inside the polynomial multiplication step. Modular reduction is achieved by using parallel linear feedback registers. The new algorithm is described in detail and results from a hardware implementation on FPGA technology are discussed. The hardware architecture is described in VHDL and synthesized for a Virtex-6 device. Although the proposed field multiplier can be implemented for arbitrary finite fields, the targeted finite fields are recommended for Elliptic Curve Cryptography. Comparing other KOA multipliers, our proposed multiplier uses 36% less area resources and improves the maximum delay in 10%
Near-optimal continuous patrolling with teams of mobile information gathering agents
Get PDFAutonomous unmanned vehicles equipped with sensors are rapidly becoming the de facto means of achieving situational awareness — the ability to make sense of, and predict what is happening in an environment. Particularly in environments that are subject to continuous change, the use of such teams to maintain accurate and up-to-date situational awareness is a challenging problem. To perform well, the vehicles need to patrol their environment continuously and in a coordinated manner. To address this challenge, we develop a near-optimal multi-agent algorithm for conti- nuously patrolling such environments. We first define a general class of multi-agent information gathering problems in which vehicles are represented by information gathering agents — autonomous entities that direct their activity towards collecting information with the aim of providing accurate and up-to-date situational awareness. These agents move on a graph, while taking measurements with the aim of maximising the cumulative discounted observation value over time. Here, observation value is an abstract measure of reward, which encodes the properties of the agents’ sensors, and the spatial and temporal properties of the measured phenomena. Concrete instantiations of this class of problems include monitoring environmental phenomena (temperature, pressure, etc.), disaster response, and patrolling environments to prevent intrusions from (non-strategic) attackers.In more detail, we derive a single-agent divide and conquer algorithm to compute a continuous patrol (an infinitely long path in the graph) that yields a near-optimal amount of observation value. This algorithm recursively decomposes the graph, until high-quality paths in the resulting components can be computed outright by a greedy algorithm. It then constructs a patrol by concatenating these paths using dynamic programming. For multiple agents, the algorithm sequentially computes patrols for each agent in a greedy fashion, in order to maximise its marginal contribution to the team. Moreover, to achieve robustness, we develop algorithms for repairing patrols when one or more agents fail or the graph changes. For both the single- and the multi-agent case, we give theoretical guarantees (lower bounds on the solution quality and an upper bound on the computational complexity in the size of the graph and the number agents) on the performance of the algorithms. We benchmark the single- and multi-agent algorithm against the state of the art and demonstrate that it typically performs 35% and 33% better in terms of average and minimum solution quality respectively
Perfect transfer of path-entangled photons in Jx photonic lattices
Get PDFWe demonstrate that perfect transfer of path-entangled photons as well as of single-photon states is possible in a certain class of spin inspired optical systems—the so-called Jx photonic lattices. In these fully integrable optical arrangements, perfect cyclic transitions from correlated states to totally anticorrelated states can naturally occur. Moreover we show that the bunching and antibunching response of path-entangled photons can be preengineered at will in such coupled optical arrangements. We elucidate these effects via pertinent examples
Reverberation and photoionization estimates of the Broad Line Region Radius in Low-z Quasars
No full textBlack Hole Mass estimation in quasars, especially at high redshift, involves use of single epoch spectra with s/n and resolution that permit accurate measurement of the width of a broad line assumed to be a reliable virial estimator. Coupled with an estimate of the radius of the broad line region this yields MMB· The radius of the broad line region (BLR) may be inferred from an extrapolation of the correlation between source luminosity and reverberation derived rBLR measures (the so-called Kaspi relation involving about 60 low z sources). We are exploring a different method for estimating rBLR directly from inferred physical conditions in the BLR of each source. We report here on a comparison of rBLR estimates that come from our method and from reverberation mapping. Our “photoionization” method employs diagnostic line intensity ratios in the rest-frame range 1400-2000 Å (AlIIIλ1860/ SiIII]λ1892, Civλ1549/AlIIIλ1860) that enable derivation of the product of density and ionization parameter with the BLR distance derived from the definition of the ionization parameter. We find good agreement between our estimates of the density, ionization parameter and rBLR and those from reverberation mapping. We suggest empirical corrections to improve the agreement between individual photoionization-derived rBLR values and those obtained from reverberation mapping. The results in this paper can be exploited to estimate black hole masses MBH for large samples of high-z quasars using an appropriate virial broadening estimator. We show that the width of the UV intermediate emission lines are consistent with the width of Hβ, therefore providing a reliable virial broadening estimator that can be measured in large samples of high-z quasars