Influence of the beam divergence on the scintillation in a free-space laser communication link: simulations and experiments

Tesina realitzada en col.laboració amb IFC

Influence of the beam divergence on the scintillation in a free-space laser communication link: simulations and experiments

Tesina realitzada en col.laboració amb IFC

Exponentiated weibull fading channel model in free-space optical communications under atmospheric turbulence

Free-space optical (FSO) communications is drawing increasing attention as a promising technology to overcome bandwidth shortage, of an evermore crowded wireless marketplace. Currently radio-frequency (RF) technology struggles to cope with the ever increasing demand for high-bandwidth data. Moreover, as the number of users increases, the RF spectrum is getting so crowded that there is virtually no room for new wireless services, with the additional inconvenient of limited bandwidth restriction for using a RF band and the license fees that have to be paid for such bands. FSO communications offer clear advantages over other alternatives such as narrower and more secure beams, virtually limitless bandwidth and no regulatory policies for using optical frequencies and bandwidth. Moreover, in the space sector FSO technology is becoming more attractive for satellite communication systems due to the less mass and power requirements --compared to RF. The major drawback for deploying wireless links based on FSO technology is the perturbation of the optical wave as it propagates through the turbulent atmosphere. Many effects are produced, of which the most noticeable is the random fluctuations of the signal-carrying laser beam irradiance (intensity), phenomenon known as scintillation and quantified by the scintillation index (SI). The statistical analysis of the random irradiance fluctuations in FSO links is conducted through the probability density function (PDF), from which one can obtain other statistical tools to measure link performance such as the probability of fade and the bit error-rate (BER). Nowadays, the most widespread models for the irradiance data are, by far, the Lognormal (LN) and Gamma-Gamma (GG) distributions. Although both models comply with actual data in most scenarios neither of them is capable of fitting the irradiance data under all conditions of atmospheric turbulence for finite receiving aperture sizes, i.e. in the presence of aperture averaging. Furthermore, there are several cases where neither the LN or the GG model seem to accurately fit the irradiance data, specially in the left tail of the PDF. The work presented in this thesis is devoted to propose a new model for the irradiance fluctuations in FSO links under atmospheric turbulence, in the presence of aperture averaging; resulting in the exponentiated Weibull (EW) distribution. A physical justification for the appearance of the new model is provided along with numerous test scenarios in the weak-to-strong turbulence regime --including numerical simulations and experimental data-- to assess its suitability to model the irradiance data in terms of the PDF and probability of fade. Here, a semi-heuristic approach is used to find a set of equations relating the EW parameters directly to the SI. Such expressions were tested offering a fairly good fitting the actual PDF of irradiance data. Furthermore, for all the scenarios tested a best fit version of the EW PDF is obtained and always presents itself as an excellent fit to the PDF data. The new model has been compared to the LN and GG distributions proving to cope to the predictions made by those and, in some cases, even outperforming their predictions. Additionally, a new closed-form expression has been derived for estimating the BER performance under EW turbulence, for intensity-modulation/direct-detection (IM/DD) systems using on-off keying (OOK) modulation. Moreover, this expression has been extended to include pointing errors. Finally, the exponentiated Weibull PDF has been proved to be valid with fully and partially coherent beams. The results presented here suggest that the EW distribution presents the better fit for data under different scenarios, thus, the exponentiated Weibull distribution becomes an excellent alternative to model the PDF of irradiance data under all conditions of atmospheric turbulence in the presence of aperture averaging

The slippery slope : explaining the increase in extreme poverty in urban Brazil, 1976-96

Despite tremendous macroeconomic instability in Brazil, the country's distributions of urban income in 1976 and 1996 appear, at first glance, deceptively similar. Mean household income per capita was stagnant, with minute accumulated growth (4.3 percent) over the two decades. The Gini coefficient hovered just above 0.59 in both years, and the incidence of poverty (relative to a poverty line of R$60 a month in 1996 prices) remained effectively unchanged over the period, at 22 percent. Behind this apparent stability, however, a powerful combination of labor market, demographic, and educational dynamics was at work, one effect of which was to generate a substantial increase in extreme urban poverty. Using a decomposition methodology based on micro-simulation, which endogenizes labor incomes, individual occupational choices, and decisions about education, the authors show that the distribution of income was being affected by: 1) Three factors that tended to increase poverty-a decline in average returns to education and experience, a negative"growth"effect, and unfortunate changes in the structure of occupations and participation in the labor force. 2) Two factors that tended to reduce poverty-improved educational endowments across the board, and a progressive reduction in dependency ratios. The net effect was small and negative for measured inequality overall, and negligible for the incidence of poverty (relative to"high"poverty lines). But the net effect was to substantially increase extreme poverty-suggesting the creation of a group of urban households excluded from any labor market and trapped in indigence. Above the 15th percentile, urban Brazilians have"stayed put"only by climbing hard up a slippery slope. Counteracting failing returns in both self-employment and the labor market required substantially reduced fertility rates and an average of two extra years of schooling (which still left them undereducated for that income level).Economic Theory&Research,Health Economics&Finance,Environmental Economics&Policies,Public Health Promotion,Health Monitoring&Evaluation,Inequality,Health Economics&Finance,Environmental Economics&Policies,Governance Indicators,Poverty Assessment

Evaluation of the Leggett-Garg inequality by means of the neutrino oscillations observed in reactor and accelerator experiments

We revisit the study of the violation of the Leggett-Garg inequality in neutrino oscillation data as a mean to test some of the fundamental aspects of quantum mechanics. In particular, we consider the results by the Daya Bay and RENO reactor experiments, and the MINOS and NOvA accelerator experiments. We find that DB and MINOS exhibit a strong manifestation of Leggett-Garg violation, while for RENO and NOvA data the indication is weaker. Considering the particular baselines and energy ranges explored by each experiment, our results demonstrate that the Leggett-Garg violation is more evident for smaller baseline-to-energy ratio in all the data sets considered, a relevant aspect to be considered when searching for evidences of quantum mechanical decoherence on neutrino oscillations.Comment: 20 pages, 13 (16) figures. Comments are welcom

Electrical analysis of new all-plastic electrochromic devices

New all-plastic electrochromic devices have been manufactured using commercial PEDOT foils and classical polymer electrolyte electrodeposition techniques. Several devices with different areas have been electrically characterized by using an impedance spectroscopy technique. After a brief description of the manufacturing process, we discuss electrical properties with the size of the device. Real and imaginary parts of the impedance have been plotted as a function of frequency. Some interesting conclusions have been derived from those plots, and some improvements in manufacturing process of this kind of devices are also proposed.Publicad

Structural effects of steel reinforcement corrosion on statically indeterminate reinforced concrete members

The final publication is available at Springer via http://dx.doi.org/10.1617/s11527-016-0836-2Steel corrosion in reinforced concrete structures produces loss of reinforcement area and damage in the surrounding concrete. As a consequence, increases in deflections, crack widths and stresses may take place, as well as a reduction of the bearing capacity, which depends on the structural scheme and redundancy. In this paper an experimental study of twelve statically indeterminate beams subjected to different levels of forced reinforcement corrosion is presented. Different sustained loads were applied during the corrosion phase to assess their influence on the effects of corrosion. An important increase in deflections was registered in all corroded beams, especially in those subject to higher load levels. It was also found that the rate of corrosion was affected by the load level. Internal forces redistributions due to induced damage were measured. Finally, the experimental results were compared with those predicted by a non-linear time-dependent segmental analysis model developed by the authors, obtaining in general good agreement.Peer ReviewedPostprint (author's final draft

Identification of best available thermal energy storage compounds for low-to-moderate temperature storage applications in buildings

Award-winning paper at III International Congress and V National on Sustainable Construction and Eco-Efficient Solutions (CICSE) March 2017Over the last 40 years different thermal energy storage materials have been investigated with the aim of enhancing energy efficiency in buildings, improving systems performance, and increasing the share of renewable energies. However, the main requirements for their efficient implementation are not fully met by most of them. This paper develops a comparative review of thermophysical properties of materials reported in the literature. The results show that the highest volumetric storage capacities for the best available sensible, latent and thermochemical storage materials are 250 MJ/m3, 514 MJ/m3 and 2000 MJ/m3, respectively, corresponding to water, barium hydroxide octahydrate, and magnesium chloride hexahydrate. A group of salt hydrates and inorganic eutectics have been identified as the most promising for the development of competitive thermal storage materials for cooling, heating and comfort applications in the short-term. In the long-term, thermochemical storage materials seem promising. However, additional research efforts are required.Identificación de los mejores compuestos disponibles de almacenamiento de energía térmica para aplicaciones de baja a moderada temperatura en edificación. En los últimos 40 años se han investigado diferentes materiales de almacenamiento térmico con el objetivo de mejorar la eficiencia energética en los edificios, mejorar el rendimiento de sistemas y aumentar el uso de renovables. Sin embargo, la mayoría no cumple los principales requisitos para su eficiente implementación. Este artículo desarrolla una revisión de las propiedades termofísicas de los materiales existentes en la literatura. Los resultados muestran que las mayores capacidades de almacenamiento volumétrico para los mejores materiales de almacenamiento sensible, latente y termoquímico son 250 MJ/m3, 514 MJ/m3 y 2000 MJ/m3, respectivamente, correspondientes a agua, hidróxido de bario octahidratado y cloruro de magnesio hexahidratado. Un conjunto de sales hidratadas y eutécticos han sido identificados como los más prometedores para el desarrollo de materiales competitivos para aplicaciones de enfriamiento, calefacción y confort a corto plazo. A largo plazo, el almacenamiento termoquímico parece prometedor. Sin embargo, investigación adicional es requerida.Fondo Europeo de Desarrollo Regional SOE1/P3/P0429EUMinisterio de Educación, Cultura y Deportes FPU14/06583Ministerio de Economía y Competitividad BES-2015-0703149Ministerio de Economía y Competitividad CTQ2014-52763-C2-2-RMinisterio de Economía y Competitividad CTQ2017- 83602-C2-2

Wireless optical communications through the turbulent atmosphere: a review

Peer ReviewedPostprint (published version