Monitorización de estructuras aeronáuticas mediante técnicas de inteligencia artificial

Una de las barreras para la aplicación de las técnicas de monitorización de la integridad estructural (SHM) basadas en ondas elásticas guiadas (GLW) en aeronaves es la influencia perniciosa de las condiciones ambientales y de operación (EOC). En esta tesis se ha estudiado dicha influencia y la compensación de la misma, particularizando en variaciones del estado de carga y temperatura. La compensación de dichos efectos se fundamenta en Redes Neuronales Artificiales (ANN) empleando datos experimentales procesados con la Transformada Chirplet. Los cambios en la geometría y en las propiedades del material respecto al estado inicial de la estructura (lo daños) provocan cambios en la forma de onda de las GLW (lo que denominamos característica sensible al daño o DSF). Mediante técnicas de tratamiento de señal se puede buscar una relación entre dichas variaciones y los daños, esto se conoce como SHM. Sin embargo, las variaciones en las EOC producen también cambios en los datos adquiridos relativos a las GLW (DSF) que provocan errores en los algoritmos de diagnóstico de daño (SHM). Esto sucede porque las firmas de daño y de las EOC en la DSF son del mismo orden. Por lo tanto, es necesario cuantificar y compensar el efecto de las EOC sobre la GLW. Si bien existen diversas metodologías para compensar los efectos de las EOC como por ejemplo “Optimal Baseline Selection” (OBS) o “Baseline Signal Stretching” (BSS), estas, se emplean exclusivamente en la compensación de los efectos térmicos. El método propuesto en esta tesis mezcla análisis de datos experimentales, como en el método OBS, y modelos basados en Redes Neuronales Artificiales (ANN) que reemplazan el modelado físico requerido por el método BSS. El análisis de datos experimentales consiste en aplicar la Transformada Chirplet (CT) para extraer la firma de las EOC sobre la DSF. Con esta información, obtenida bajo diversas EOC, se entrena una ANN. A continuación, la ANN actuará como un interpolador de referencias de la estructura sin daño, generando información de referencia para cualquier EOC. La comparación de las mediciones reales de la DSF con los valores simulados por la ANN, dará como resultado la firma daño en la DSF, lo que permite el diagnóstico de daño. Este esquema se ha aplicado y verificado, en diversas EOC, para una estructura unidimensional con un único camino de daño, y para una estructura representativa de un fuselaje de una aeronave, con curvatura y múltiples elementos rigidizadores, sometida a un estado de cargas complejo, con múltiples caminos de daños. Los efectos de las EOC se han estudiado en detalle en la estructura unidimensional y se han generalizado para el fuselaje, demostrando la independencia del método respecto a la configuración de la estructura y el tipo de sensores utilizados para la adquisición de datos GLW. Por otra parte, esta metodología se puede utilizar para la compensación simultánea de una variedad medible de EOC, que afecten a la adquisición de datos de la onda elástica guiada. El principal resultado entre otros, de esta tesis, es la metodología CT-ANN para la compensación de EOC en técnicas SHM basadas en ondas elásticas guiadas para el diagnóstico de daño. ABSTRACT One of the open problems to implement Structural Health Monitoring techniques based on elastic guided waves in real aircraft structures at operation is the influence of the environmental and operational conditions (EOC) on the damage diagnosis problem. This thesis deals with the compensation of these environmental and operational effects, specifically, the temperature and the external loading, by the use of the Chirplet Transform working with Artificial Neural Networks. It is well known that the guided elastic wave form is affected by the damage appearance (what is known as the damage sensitive feature or DSF). The DSF is modified by the temperature and by the load applied to the structure. The EOC promotes variations in the acquired data (DSF) and cause mistakes in damage diagnosis algorithms. This effect promotes changes on the waveform due to the EOC variations of the same order than the damage occurrence. It is difficult to separate both effects in order to avoid damage diagnosis mistakes. Therefore it is necessary to quantify and compensate the effect of EOC over the GLW forms. There are several approaches to compensate the EOC effects such as Optimal Baseline Selection (OBS) or Baseline Signal Stretching (BSS). Usually, they are used for temperature compensation. The new method proposed here mixes experimental data analysis, as in the OBS method, and Artificial Neural Network (ANN) models to replace the physical modelling which involves the BSS method. The experimental data analysis studied is based on apply the Chirplet Transform (CT) to extract the EOC signature on the DSF. The information obtained varying EOC is employed to train an ANN. Then, the ANN will act as a baselines interpolator of the undamaged structure. The ANN generates reference information at any EOC. By comparing real measurements of the DSF against the ANN simulated values, the damage signature appears clearly in the DSF, enabling an accurate damage diagnosis. This schema has been applied in a range of EOC for a one-dimensional structure containing single damage path and two dimensional real fuselage structure with stiffener elements and multiple damage paths. The EOC effects tested in the one-dimensional structure have been generalized to the fuselage showing its independence from structural arrangement and the type of sensors used for GLW data acquisition. Moreover, it can be used for the simultaneous compensation of a variety of measurable EOC, which affects the guided wave data acquisition. The main result, among others, of this thesis is the CT-ANN methodology for the compensation of EOC in GLW based SHM technique for damage diagnosis.

Bridge damage identification from moving load induced deflection based on wavelet transform and Lipschitz exponent

The wavelet transform and Lipschitz exponent perform well in detecting signal singularity.With the bridge crack damage modeled as rotational springs based on fracture mechanics, the deflection time history of the beam under the moving load is determined with a numerical method. The continuous wavelet transformation (CWT) is applied to the deflection of the beam to identify the location of the damage, and the Lipschitz exponent is used to evaluate the damage degree. The influence of different damage degrees,multiple damage, different sensor locations, load velocity and load magnitude are studied.Besides, the feasibility of this method is verified by a model experiment.

Differential Epitope Tagging of Actin in Transformed Drosophila Produces Distinct Effects on Myofibril Assembly and Function of the Indirect Flight Muscle

We have tested the impact of tags on the structure and function of indirect flight muscle (IFM)-specific Act88F actin by transforming mutant Drosophila melanogaster, which do not express endogenous actin in their IFMs, with tagged Act88F constructs. Epitope tagging is often the method of choice to monitor the fate of a protein when a specific antibody is not available. Studies addressing the functional significance of the closely related actin isoforms rely almost exclusively on tagged exogenous actin, because only few antibodies exist that can discriminate between isoforms. Thereby it is widely presumed that the tag does not significantly interfere with protein function. However, in most studies the tagged actin is expressed in a background of endogenous actin and, as a rule, represents only a minor fraction of the total actin. The Act88F gene encodes the only Drosophila actin isoform exclusively expressed in the highly ordered IFM. Null mutations in this gene do not affect viability, but phenotypic effects in transformants can be directly attributed to the transgene. Transgenic flies that express Act88F with either a 6x histidine tag or an 11-residue peptide derived from vesicular stomatitis virus G protein at the C terminus were flightless. Overall, the ultrastructure of the IFM resembled that of the Act88F null mutant, and only low amounts of C-terminally tagged actins were found. In contrast, expression of N-terminally tagged Act88F at amounts comparable with that of wild-type flies yielded fairly normal-looking myofibrils and partially reconstituted flight ability in the transformants. Our findings suggest that the N terminus of actin is less sensitive to modifications than the C terminus, because it can be tagged and still polymerize into functional thin filaments.

Generalized flows, intrinsic stochasticity, and turbulent transport

The study of passive scalar transport in a turbulent velocity field leads naturally to the notion of generalized flows, which are families of probability distributions on the space of solutions to the associated ordinary differential equations which no longer satisfy the uniqueness theorem for ordinary differential equations. Two most natural regularizations of this problem, namely the regularization via adding small molecular diffusion and the regularization via smoothing out the velocity field, are considered. White-in-time random velocity fields are used as an example to examine the variety of phenomena that take place when the velocity field is not spatially regular. Three different regimes, characterized by their degrees of compressibility, are isolated in the parameter space. In the regime of intermediate compressibility, the two different regularizations give rise to two different scaling behaviors for the structure functions of the passive scalar. Physically, this means that the scaling depends on Prandtl number. In the other two regimes, the two different regularizations give rise to the same generalized flows even though the sense of convergence can be very different. The “one force, one solution” principle is established for the scalar field in the weakly compressible regime, and for the difference of the scalar in the strongly compressible regime, which is the regime of inverse cascade. Existence and uniqueness of an invariant measure are also proved in these regimes when the transport equation is suitably forced. Finally incomplete self similarity in the sense of Barenblatt and Chorin is established.

Computational method to reduce the search space for directed protein evolution

We introduce a computational method to optimize the in vitro evolution of proteins. Simulating evolution with a simple model that statistically describes the fitness landscape, we find that beneficial mutations tend to occur at amino acid positions that are tolerant to substitutions, in the limit of small libraries and low mutation rates. We transform this observation into a design strategy by applying mean-field theory to a structure-based computational model to calculate each residue's structural tolerance. Thermostabilizing and activity-increasing mutations accumulated during the experimental directed evolution of subtilisin E and T4 lysozyme are strongly directed to sites identified by using this computational approach. This method can be used to predict positions where mutations are likely to lead to improvement of specific protein properties.

Differential display of intestinal mRNAs regulated by dietary zinc.

Regulation of gene expression by zinc is well established, especially through the metal response elements of the metallothionein genes; however, most other aspects of the functions of zinc in gene expression remain unknown. We have looked for intestinal mRNAs that are regulated by dietary zinc status. Using the reverse transcriptase-PCR method of mRNA differential display, we compared intestinal mRNA from rats that were maintained for 18 days in one of three dietary groups: zinc-deficient, zinc-adequate, and pair-fed zinc-adequate. At the end of this period, total RNA was prepared from the intestine and analyzed by mRNA differential display. Under these conditions, only differentially displayed cDNA bands that varied in the zinc-deficient group, relative to the zinc-adequate groups, were selected. Utilizing two anchored oligo-dT3' PCR primers and a total of 27 arbitrary decamers as 5' PCR primers, our results yielded 47 differentially displayed cDNA bands from intestinal RNA. Thirty were increased in zinc deficiency, and 17 were decreased. Nineteen bands were subcloned and sequenced. Eleven of these were detectable on Northern blots, of which four were confirmed as regulated. Three of these have homology to known genes: cholecystokinin, uroguanylin, and ubiquinone oxidoreductase. The fourth is a novel sequence as it has no significant homology in GenBank. The remainder of those cloned included novel sequences, as well as matches to reported expressed sequence tags, and functionally identified genes. Further characterization of the regulated sequences identified here will show whether they are primary or secondary effects of zinc deficiency.

A fast marching level set method for monotonically advancing fronts.

A fast marching level set method is presented for monotonically advancing fronts, which leads to an extremely fast scheme for solving the Eikonal equation. Level set methods are numerical techniques for computing the position of propagating fronts. They rely on an initial value partial differential equation for a propagating level set function and use techniques borrowed from hyperbolic conservation laws. Topological changes, corner and cusp development, and accurate determination of geometric properties such as curvature and normal direction are naturally obtained in this setting. This paper describes a particular case of such methods for interfaces whose speed depends only on local position. The technique works by coupling work on entropy conditions for interface motion, the theory of viscosity solutions for Hamilton-Jacobi equations, and fast adaptive narrow band level set methods. The technique is applicable to a variety of problems, including shape-from-shading problems, lithographic development calculations in microchip manufacturing, and arrival time problems in control theory.

Analysis of differential gene expression by display of 3' end restriction fragments of cDNAs.

We have developed an approach to study changes in gene expression by selective PCR amplification and display of 3' end restriction fragments of double-stranded cDNAs. This method produces highly consistent and reproducible patterns, can detect almost all mRNAs in a sample, and can resolve hidden differences such as bands that differ in their sequence but comigrate on a gel. Bands corresponding to known cDNAs move to predictable positions on the gel, making this a powerful approach to correlate gel patterns with cDNA data bases. Applying this method, we have examined differences in gene expression patterns during T-cell activation. Of a total of 700 bands that were evaluated in this study, as many as 3-4% represented mRNAs that are upregulated, while approximately 2% were down-regulated within 4 hr of activation of Jurkat T cells. These and other results suggest that this approach is suitable for the systematic, expeditious, and nearly exhaustive elucidation of subtle changes in the patterns of gene expression in cells with altered physiologic states.

Restriction fragment length polymorphism-coupled domain-directed differential display: a highly efficient technique for expression analysis of multigene families.

In this paper, a reverse-transcriptase PCR-based protocol suitable for efficient expression analysis of multigene families is presented. The method combines restriction fragment length polymorphism (RFLP) technology with a gene family-specific version of mRNA differential display and hence is called "RFLP-coupled domain-directed differential display. "With this method, expression of all members of a multigene family at many different developmental stages, in diverse tissues and even in different organisms, can be displayed on one gel. Moreover, bands of interest, representing gene family members, are directly accessible to sequence analysis, without the need for subcloning. The method thus enables a detailed, high-resolution expression analysis of known gene family members as well as the identification and characterization of new ones. Here the technique was used to analyze differential expression of MADS-box genes in male and female inflorescences of maize (Zea mays ssp. mays). Six different MADS-box genes could be identified, being either specifically expressed in the female sex or preferentially expressed in male or female inflorescences, respectively. Other possible applications of the method are discussed.

Obtenção de gel mucoadesivo de nistatina para o tratamento da candidíase oral. Desenvolvimento e caracterização de dispersões sólidas de nistatina

A nistatina (NYS) é o fármaco de primeira escolha no tratamento da candidíase oral, que frequentemente acomete mais os indivíduos imunocomprometidos e pacientes com outras desordens (diabetes não tratada, neoplasias, imunodeficiências). No mercado brasileiro, a NYS é encontrada na forma de suspensão oral aquosa, onde o procedimento para sua administração consiste em bochechar o medicamento. Apesar de haver a indicação de que se mantenha o contato direto entre fármaco e a mucosa oral, na qual se encontra a Candida spp., o que aumentaria expressivamente o sucesso terapêutico, a suspensão não apresenta tal propriedade. Assim, a NYS que é fármaco com ação efetiva contra a candidíase oral, é considerada pertencente à Classe IV do Sistema de Classificação Biofarmacêutica, ou seja, apresenta baixa solubilidade e baixa permeabilidade. A baixa solubilidade pode comprometer sua disponibilidade na cavidade oral, e consequentemente, sua ação farmacológica. Diante desse quadro, o objetivo do presente trabalho foi o desenvolvimento de dispersões sólidas de NYS para o tratamento da candidíase oral, e sua posterior incorporação em gel mucoadesivo oral, favorecendo a formulação no local de ação. As dispersões sólidas são sistemas farmacêuticos, onde um fármaco pouco solúvel em água encontra-se dispersado em um carreador, no estado sólido. Os carreadores normalmente são hidrofílicos, o que permite que esses sistemas sejam empregados para aumentar a solubilidade aquosa do fármaco. Assim, foram desenvolvidas as dispersões sólidas de NYS, pelo método de eliminação do solvente, empregando como carreadores, lactose, HPMC, poloxamer 407 e poloxamer 188. Essas foram submetidas à caracterização por análise térmica, usando os ensaios de calorimetria exploratória diferencial (DSC) e termogravimetria/termogravimetria derivada (TG/DTG). Dentre essas dispersões sólidas, aquelas que se mostraram com comportamento térmico sugerindo a formação de um novo \"sistema\", foram analisadas por meio de ensaio de solubilidade. Dessa forma, a formulação NYS DS G2 (49) se destacou, pois apresentou maior solubilidade em água (4,484 mg/mL); em pH 5,5 (4,249 mg/mL) e em pH 7,0 (4,293 mg/mL), ou seja, houve um aumento de 1,426 vezes em água; 4,227 vezes em pH 5,5; e 2,743 vezes em pH 7,0. Essa formulação foi, por fim avaliada por difração de raio-X e espectroscopia de infravermelho com transformada de Fourier, técnicas que corroboraram com a análise térmica quanto à indicação de formação da dispersão sólida. Por sua vez, essa dispersão sólida foi incorporada em 4 bases de géis mucoadesivos de carbopol ® 934 PNF, alterando apenas a concentração do polímero (0,5; 1,0; 1,5; 2,0 %p/p). Foi observado que a liberação de NYS DS G2 (49) foi superior, quando comparada à liberação de NYS MP a partir do gel, e através do ensaio de mucoadesão, percebeu-se que os géis desenvolvidos apresentaram propriedades mucoadesivas compatíveis com relatos na literatura, independentemente da quantidade de carbopol ® empregada. As características reológicas foram distintas, e foi observado que as formulações Gel A e Gel B, que possuem menor quantidade de polímero, tiverem um indicativo de comportamento de fluido newtoniano, diferente dos demais, o que pode não ser desejado para esse tipo de forma farmacêutica tópica e semi-sólida. Ao final desse trabalho, pode-se concluir que foi possível desenvolver um sistema farmacêutico na forma de dispersão sólida com maior solubilidade que a NYS pura, e sua incorporação em uma forma farmacêutica mucoadesiva, e que a liberação da NYS na forma DS foi muito superior que o fármaco na forma \"convencional\", o que permite que a NYS esteja mais disponível na cavidade oral, e também junto à mucosa bucal, o que levaria a efeito farmacológico mais efetivo do antifúngico.

Magnetic activity and differential rotation in the young Sun-like stars KIC 7985370 and KIC 7765135

Aims. We present a detailed study of the two Sun-like stars KIC 7985370 and KIC 7765135, to determine their activity level, spot distribution, and differential rotation. Both stars were previously discovered by us to be young stars and were observed by the NASA Kepler mission. Methods. The fundamental stellar parameters (vsini, spectral type, T_eff, log g, and [Fe/H]) were derived from optical spectroscopy by comparison with both standard-star and synthetic spectra. The spectra of the targets allowed us to study the chromospheric activity based on the emission in the core of hydrogen Hα and Ca ii infrared triplet (IRT) lines, which was revealed by the subtraction of inactive templates. The high-precision Kepler photometric data spanning over 229 days were then fitted with a robust spot model. Model selection and parameter estimation were performed in a Bayesian manner, using a Markov chain Monte Carlo method. Results. We find that both stars are Sun-like (of G1.5 V spectral type) and have an age of about 100–200 Myr, based on their lithium content and kinematics. Their youth is confirmed by their high level of chromospheric activity, which is comparable to that displayed by the early G-type stars in the Pleiades cluster. The Balmer decrement and flux ratio of their Ca ii-IRT lines suggest that the formation of the core of these lines occurs mainly in optically thick regions that are analogous to solar plages. The spot model applied to the Kepler photometry requires at least seven persistent spots in the case of KIC 7985370 and nine spots in the case of KIC 7765135 to provide a satisfactory fit to the data. The assumption of the longevity of the star spots, whose area is allowed to evolve with time, is at the heart of our spot-modelling approach. On both stars, the surface differential rotation is Sun-like, with the high-latitude spots rotating slower than the low-latitude ones. We found, for both stars, a rather high value of the equator-to-pole differential rotation (dΩ ≈ 0.18 rad d^-1), which disagrees with the predictions of some mean-field models of differential rotation for rapidly rotating stars. Our results agree instead with previous works on solar-type stars and other models that predict a higher latitudinal shear, increasing with equatorial angular velocity, that can vary during the magnetic cycle.

Analysis of the zone connecting consecutive sectors in distillation columns by the Ponchon-Savarit method

McCabe-Thiele and Ponchon-Savarit methods are two classical graphical methods for the design of binary distillation columns very useful for didactical purposes and for preliminary calculations. Nevertheless, their description in the literature is not complete and not all the cases are analysed. To complete the academic literature dealing with this subject we have generalized equations for the operating lines or DP that define the change between two consecutive sectors ΔkC for any feed condition, together with the different possibilities to extract products or to add or remove heat. A consistent analysis of what may happen when changing between sectors in the column is presented.

Review and extension of the McCabe-Thiele method covering multiple feeds, products and heat transfer stages

The McCabe-Thiele method is a classical approximate graphical method for the conceptual design of binary distillation columns which is still widely used, mainly for didactical purposes, though it is also valuable for quick preliminary calculations. Nevertheless, no complete description of the method has been found and situations such as different thermal feed conditions, multiple feeds, possibilities to extract by-products or to add or remove heat, are not always considered. In the present work we provide a systematic analysis of such situations by developing the generalized equations for: a) the operating lines (OL) of each sector, and b) the changeover line that provides the connection between two consecutive trays of the corresponding sectors separated by a lateral stream of feed, product, or a heat removal or addition.

Development of a novel pyrolysis-gas chromatography/mass spectrometry method for the analysis of poly(lactic acid) thermal degradation products

Thermal degradation of PLA is a complex process since it comprises many simultaneous reactions. The use of analytical techniques, such as differential scanning calorimetry (DSC) and thermogravimetry (TGA), yields useful information but a more sensitive analytical technique would be necessary to identify and quantify the PLA degradation products. In this work the thermal degradation of PLA at high temperatures was studied by using a pyrolyzer coupled to a gas chromatograph with mass spectrometry detection (Py-GC/MS). Pyrolysis conditions (temperature and time) were optimized in order to obtain an adequate chromatographic separation of the compounds formed during heating. The best resolution of chromatographic peaks was obtained by pyrolyzing the material from room temperature to 600 °C during 0.5 s. These conditions allowed identifying and quantifying the major compounds produced during the PLA thermal degradation in inert atmosphere. The strategy followed to select these operation parameters was by using sequential pyrolysis based on the adaptation of mathematical models. By application of this strategy it was demonstrated that PLA is degraded at high temperatures by following a non-linear behaviour. The application of logistic and Boltzmann models leads to good fittings to the experimental results, despite the Boltzmann model provided the best approach to calculate the time at which 50% of PLA was degraded. In conclusion, the Boltzmann method can be applied as a tool for simulating the PLA thermal degradation.

Power line interference filtering on surface electromyography based on the stationary wavelet packet transform

Power line interference is one of the main problems in surface electromyogram signals (EMG) analysis. In this work, a new method based on the stationary wavelet packet transform is proposed to estimate and remove this kind of noise from EMG data records. The performance has been quantitatively evaluated with synthetic noisy signals, obtaining good results independently from the signal to noise ratio (SNR). For the analyzed cases, the obtained results show that the correlation coefficient is around 0.99, the energy respecting to the pure EMG signal is 98–104%, the SNR is between 16.64 and 20.40 dB and the mean absolute error (MAE) is in the range of −69.02 and −65.31 dB. It has been also applied on 18 real EMG signals, evaluating the percentage of energy respecting to the noisy signals. The proposed method adjusts the reduction level to the amplitude of each harmonic present in the analyzed noisy signals (synthetic and real), reducing the harmonics with no alteration of the desired signal.