INANOE Repositorio (Inst- Nacional de Astrofísica, Óptica y Electrónica
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X-ray detections of submillimetre galaxies: active galactic nuclei versus starburst contribution
No full textWe present a large-scale study of the X-ray properties and near-IR-to-radio spectral energy distributions (SEDs) of submillimetre galaxies (SMGs) detected at 1.1 mm with the AzTEC instrument across a ∼1.2 square degree area of the sky. Combining deep 2–4 Ms Chandra data with Spitzer IRAC/MIPS and Very Large Array data within the Great Observatories Origins Deep Survey North (GOODS-N), GOODS-S and COSMOS fields, we find evidence for active galactic nucleus (AGN) activity in ∼14 per cent of 271 AzTEC SMGs, ∼28 per cent considering only the two GOODS fields. Through X-ray spectral modelling and multiwavelength SED fitting using Monte Carlo Markov chain techniques to Siebenmorgen et al. (AGN) and Efstathiou, Rowan-Robinson & Siebenmorgen (starburst) templates, we find that while star formation dominates the IR emission, with star formation rates (SFRs) ∼100–1000M⊙ yr⁻¹, the X-ray emission for most sources is almost exclusively from obscured AGNs, with column densities in excess of 10²³ cm⁻². Only for ∼6 per cent of our sources do we find an X-ray-derived SFR consistent with NIR-to-radio SED derived SFRs. Inclusion of the X-ray luminosities as a prior to the NIR-to-radio SED effectively sets the AGN luminosity and SFR, preventing significant contribution from the AGN template. Our SED modelling further shows that the AGN and starburst templates typically lack the required 1.1 mm emission necessary to match observations, arguing for an extended, cool dust component. The cross-correlation function between the full samples of X-ray sources and SMGs in these fields does not indicate a strong correlation between the two populations at large scales, suggesting that SMGs and AGNs do not necessarily trace the same underlying large-scale structure. Combined with the remaining X-ray-dim SMGs, this suggests that sub-mm-bright sources may evolve along multiple tracks, with X-ray-detected SMGs representing transitionary objects between periods of high star formation and AGN activity, while X-ray-faint SMGs represent a brief starburst phase of more normal galaxies
Discovery of x-ray emission from young suns in the small magellanic cloud
Get PDFWe report the discovery of extended X-ray emission within the young star cluster NGC602a in the Wing of the Small Magellanic Cloud (SMC) based on observations obtained with the Chandra X-ray Observatory. X-ray emission is detected from the cluster core area with the highest stellar density and from a dusty ridge surrounding the HII region. We use a census of massive stars in the cluster to demonstrate that a cluster wind or wind-blown bubble is unlikely to provide a significant contribution to the X-ray emission detected from the central area of the cluster. We therefore suggest that X-ray emission at the cluster core originates from an ensemble of low- and solar-mass pre-main-sequence (PMS) stars, each of which would be too weak in X-rays to be detected individually. We attribute the X-ray emission from the dusty ridge to the embedded tight cluster of the new-born stars known in this area from infrared studies. Assuming that the levels of X-ray activity in young stars in the low-metallicity environment of NGC 602a are comparable to their Galactic counterparts, then the detected spatial distribution, spectral properties, and level of X-ray emission are largely consistent with those expected from low- and solar-mass PMS stars and young stellar objects (YSOs). This is the first discovery of X-ray emission attributable to PMS stars and YSOs in the SMC, which suggests that the accretion and dynamo processes in young, low-mass objects in the SMC resemble those in the Galaxy
Dusty supernovae running the thermodynamics of the matter reinserted within young and massive super stellar clusters
Get PDFFollowing the observational and theoretical evidence that points at core collapse supernovae as major producers of dust, here we calculate the hydrodynamics of the matter reinserted within young and massive super stellar clusters under the assumption of gas and dust radiative cooling. The large supernova rate expected in massive clusters allows for a continuous replenishment of dust immersed in the high temperature thermalized reinserted matter and warrants a stationary presence of dust within the cluster volume during the type II supernova era. We first show that such a balance determines the range of dust to gas mass ratio and this the dust cooling law. We then search for the critical line that separates stationary cluster winds from the bimodal cases in the cluster mechanical luminosity (or cluster mass) vs cluster size parameter space. In the latter, strong radiative cooling reduces considerably the cluster wind mechanical energy output and affects particularly the cluster central regions, leading to frequent thermal instabilities that diminish the pressure and inhibit the exit of the reinserted matter. Instead matter accumulates there and is expected to eventually lead to gravitational instabilities and to further stellar formation with the matter reinserted by former massive stars. The main outcome of the calculations is that the critical line is almost two orders of magnitude or more, depending on the assumed value of VA∞, lower than when only gas radiative cooling is applied. And thus, many massive clusters are predicted to enter the bimodal regime
A performance comparison of CMOS voltage-controlled ring oscillators for its application to generation and distribution clock networks
Get PDFIn this work, a performance comparison of expanded CMOS voltage-controlled ring oscillators for non-resonant local clock generation and distribution networks is presented. Several differential and single-ended ring oscillators are designed and fabricated using long interconnection lines to achieve wide coverage chip. A test chip containing the several oscillators was fabricated using an Austria Microsystems (AMS) 0.35 μm CMOS technology. Experimental results show that it is possible to generate and distribute high frequency signals (GHz range) on a relativity large area (coverage) and low phase noise using non-resonant ring oscillators. This represents an attractive alternative for the design and implementation of local Clock Generation and Distribution Networks for systems on chip
Fine-tuning of the interface in high-quality epitaxial silicon films deposited by plasma-enhanced chemical vapor deposition at 200 °C
Get PDFHigh-quality epitaxial silicon thin films have been deposited by plasma-enhanced chemical vapor deposition (PECVD) at 200 °C in a standard radiofrequency (RF) PECVD reactor. We optimized a silicon tetrafluoride (SiF₄) plasma to clean the surface of crystalline silicon wafers and without breaking vacuum, an epitaxial silicon film was grown from SiF₄, hydrogen (H₂), and argon (Ar) gas mixtures. We demonstrate that the H₂/SiF₄ flow rate ratio is a key parameter to grow high-quality epitaxial silicon films. Moreover, by changing this ratio, we can fine-tune the composition of the interface between the crystalline silicon (c-Si) wafer and the epitaxial film. In this way, at low values of the H₂/SiF₄ flow rate ratio, an abrupt interface is achieved. On the contrary, by increasing this ratio we can obtain a porous and fragile interface layer, composed of hydrogen-rich microcavities, which allows the transfer of the epitaxial film to foreign substrates
FPGA-Based Broken Bars Detection on Induction Motors Under Different Load Using Motor Current Signature Analysis and Mathematical Morphology
Get PDFBroken bars detection on induction motors has been a topic of interest in recent years. Its detection is important due to the fact that the failure is silent and the consequences it produces as power consumption increasing, vibration, introduction of spurious frequencies in the electric line, among others, can be catastrophic. In this paper, the use of motor current signature analysis and mathematical morphology to detect broken bars on induction motors under different mechanical load condition is analyzed. The proposed algorithm first identifies the motor load and then the motor condition. The statistical analysis of several tests under different motor loads (100%, 75%, 50%, and 25%) and motor condition (healthy, one broken bar, and two broken bars) is presented. The proposed method has been implemented in a field programmable gate array, to be used in real-time online applications. The algorithm obtained in average a 95% accuracy of failure detection
Discovering human immunodeficiency virus mutational pathways using temporal Bayesian networks
No full textObjective: The human immunodeficiency virus (HIV) is one of the fastest evolving organisms in the planet. Its remarkable variation capability makes HIV able to escape from multiple evolutionary forces naturally or artificially acting on it, through the development and selection of adaptive mutations. Although most drug resistance mutations have been well identified, the dynamics and temporal patterns of appearance of these mutations can still be further explored. The use of models to predict mutational pathways as well as temporal patterns of appearance of adaptive mutations could greatly benefit clinical management of individuals under antiretroviral therapy. Methods and material: We apply a temporal nodes Bayesian network (TNBN) model to data extracted from the Stanford HIV drug resistance database in order to explore the probabilistic relationships between drug resistance mutations and antiretroviral drugs unveiling possible mutational pathways and establishing their probabilistic-temporal sequence of appearance. Results: In a first experiment, we compared the TNBN approach with other models such as static Bayesian networks, dynamic Bayesian networks and association rules. TNBN achieved a 64.2% sparser structure over the static network. In a second experiment, the TNBN model was applied to a dataset associating antiretroviral drugs with mutations developed under different antiretroviral regimes. The learned models captured previously described mutational pathways and associations between antiretroviral drugs and drug resistance mutations. Predictive accuracy reached 90.5%. Conclusion: Our results suggest possible applications of TNBN for studying drug-mutation and mutation–mutation networks in the context of antiretroviral therapy, with direct impact on the clinical management of patients under antiretroviral therapy. This opens new horizons for predicting HIV muta- tional pathways in immune selection with relevance for antiretroviral drug development and therapy plan
Prediction of silicon dry etching using a piecewise linear algorithm
Get PDFA piecewise linear algorithm for predicting silicon etch rates in fluorine-based plasmas is shown. Discrete experimental data of pressure and RF power in reactive ion etching are used to construct a set of local two-dimensional etching functions that serve as a basis for computing numerical solutions (pressure and power values for a specific predicted silicon etch rate). It must be pointed out that, although the algorithm scans the entire data domain, a testing procedure is applied to ensure that the computing task will be invoked only when a solution exists, and otherwise it will be discarded (this avoids brute force methods). In the last step of the algorithm, all solutions are collected and interpolated to construct a solution path. In order to verify the match between the experimental etching results and numerical predictions, the algorithm has been coded and tested using Maple® Release 13.0, showing a successful validation with a difference between experimental data and computed numerical solutions as low as 1% for SF₆, and 4% for SF₆/O₂ in the best case and a root-mean squared error of 0.03
Indoor propagation modeling for radiating cable systems in the frequency range of 900-2500 MHz
Get PDFThe aim of this paper is to propose and evaluate a semi-empirical propagation modeling for radiating cable used in indoor environments. This propagation modeling takes into consideration propagation mechanisms such as reflections, penetration loss and cable termination that result from a particular environment, as well as specific cable paths that actual propagation models for radiating cable systems have not considered. The proposed modeling is carried out using three different propagation models and has been experimentally validated by sets of measurements performed in a university building in the frequency range from 900 MHz to 2.5 GHz. A careful selection of the data sets validates the robustness of the proposed model. The results show a mean of the error less than 1 dB while the standard deviation is between 2.2 dB and 4.6 dB in all cases. To the best of our knowledge, this is the first time such a robust modeling for radiating cable operating between 900 MHz to 2.5 GHz has been presented
Estructuras Eficientes para Conversión de Tasa de Muestreo en Radio Definido por Software
Get PDFEsta tesis presenta las aportaciones realizadas al diseño e implementación de filtros de decimación utilizados en sistemas de radio definido por software. Inicialmente se tratan las bases del procesamiento multirazón, donde se explican las operaciones principales en la conversión de frecuencia de muestreo, decimación e interpolación. Así mismo, se describen las etapas y bloques de cada una de estas operaciones. En seguida, se estudian las características de los filtro comb y se muestran las estructuras utilizadas para su implementación. Más adelante, se revisan algunos métodos transcendentes en el diseño de filtros de decimación incluyendo algunas técnicas para disminuir el consumo de potencia. Se presentan las ventajas y desventajas para cada estructura y método. Por último se describen las contribuciones mencionadas anteriormente. La propuesta de una estructura de decimación basada en lo que más adelante se presentará como estructura especial no recursiva del filtro comb, cuya mejora en la característica de magnitud se lleva a cabo aplicando la técnica Sharpening mejorada. A través de ejemplos y comparaciones, se demuestra la efectividad del método. Por otra parte, se analiza la implementación en FPGA de un filtro de decimación basado en comb que utiliza la técnica de rotación de ceros para aumentar la atenuación en la banda de rechazo y un compensador para mejorar la caída en la banda de paso. El correcto funcionamiento del filtro y la cantidad de recursos utilizados, se analizan mediante simulaciones.This thesis presents the contributions made on the design and implementation of decimation filters used in of software defined radio systems. Initially we treat multi-rate processing bases, where the major operations in the sampling rate conversion are explained, decimation and interpolation. It also describes the steps and blocks of each of these operations. Next, we study the characteristics of the comb filter and show the structures used for its implementation. Later, we review some transcendental methods in the design of decimation filters including some techniques to reduce power consumption. We present the advantages and disadvantages for each structure and method. Finally, we describe the contributions mentioned above. The proposed decimation structure based on what later will be presented as the special non-recursive comb filter structure, which improvement in the characteristic magnitude is performed using improved Sharpening technique. Through examples and comparisons demonstrate the effectiveness of the method. Moreover, we analyze the FPGA implementation of a decimation filter comb based that uses rotation of zeros technique to increase the attenuation in the rejection band and a compensator for improving the drop in passband. The correct operation of the filter and the amount of resources used are analyzed by simulations