Modeling of the lung impedance using a fractional order ladder network with constant phase elements

The self similar branching arrangement of the airways makes the respiratory system an ideal candidate for the application of fractional calculus theory. The fractal geometry is typically characterized by a recurrent structure. This study investigates the identification of a model for the respiratory tree by means of its electrical equivalent based on intrinsic morphology. Measurements were obtained from seven volunteers, in terms of their respiratory impedance by means of its complex representation for frequencies below 5 Hz. A parametric modeling is then applied to the complex valued data points. Since at low-frequency range the inertance is negligible, each airway branch is modeled by using gamma cell resistance and capacitance, the latter having a fractional-order constant phase element (CPE), which is identified from measurements. In addition, the complex impedance is also approximated by means of a model consisting of a lumped series resistance and a lumped fractional-order capacitance. The results reveal that both models characterize the data well, whereas the averaged CPE values are supraunitary and subunitary for the ladder network and the lumped model, respectively.

Probing disorder and transport properties in polypyrrole thin-film devices by impedance and Raman spectroscopy

In the present study, impedance and Raman spectroscopy are adopted to probe the nature and extent of disorder to correlate with transport properties in doped polypyrrole (PPy) thin-film devices, synthesized electrochemically at different temperatures. A comparative study of the impedance spectroscopy is performed on PPy devices by both experimental and simulation approach with varying extent of disorder. The impedance measurements of PPy devices are well described by introducing a constant phase element (CPE) (Q) in modified RQ circuit, which accounts for frequency dependence of dielectric response. However, for the PPy grown at lower temperature, an equivalent circuit consisting of two such RQ elements in series is used for successful modelling of the impedance results, which accounts for the depletion region near the electrode. Raman spectroscopy and the de-convoluted spectra are successfully studied to probe the variation in C=C bond stretching and distribution of conjugation length, which relates to disorder in PPy films and the interpretation is well correlated to the impedance results.

Comportamento tribocorrosivo do aço inoxidável e de ligas de titânio em meio salino

No presente trabalho, foram realizados ensaios de tribocorrosão no aço inoxidável AISI 304L, no titânio comercialmente puro (CPTi) e na liga de titânio Ti6Al4V em solução aquosa de 0,90% m/v NaCl. Amostras de ligas de titânio com tratamento térmico superficial de refusão a laser também foram utilizadas. Um tribômetro do tipo pino-no-disco com contracorpo de alumina foi usado. Técnicas eletroquímicas in situ de monitoramento em circuito aberto, espectroscopia de impedância eletroquímica, curvas de polarização e amperimetria de resistência nula foram empregadas. Os resultados obtidos indicam que o desgaste tribocorrosivo das ligas de titânio é mais intenso do que o observado no aço inoxidável, apresentando perfis de superfície mais irregulares. A análise da impedância eletroquímica mostrou que todos os materiais utilizados apresentam uma rápida recuperação da camada passiva, exibindo módulos e fases um pouco menores do que os medidos antes do desgaste. Sob atrito, os diagramas de impedância apresentam uma forte redução do módulo. Sob desgaste, o expoente α do elemento de fase constante (CPE) atinge seu valor mais baixo, enquanto o parâmetro γ é máximo. As curvas de polarização exibem potenciais menores e densidades de corrente de corrosão maiores durante o desgaste. O tratamento de refusão a laser, embora mude a microestrutura e a dureza superficial das amostras, não indica uma mudança aparente nos parâmetros eletroquímicos sob tribocorrosão, bem como do coeficiente de atrito. Nos ensaios de amperimetria de resistência nula, foi possível estimar a corrente mensurada no ARN por meio do emprego de um circuito elétrico equivalente. A densidade espectral de potência dos sinais de potencial e de corrente exibe a frequência de rotação (1,25 Hz) e seus harmônicos. Para baixas frequências (abaixo de 10 mHz), o decaimento obedece à relação 1 ⁄ e 1⁄ para os sinais de potencial e corrente, respectivamente.

Analysen der beiden cis-regulierenden Sequenzelemente translational control element (TCE) und cytoplasmic polyadenylation element (CPE) in der Drosophila-Spermatogenese

Ein essentieller Bestandteil in dem Mechanismus der Translationskontrolle sind RNA-Pro­tein-Wechselwirkungen. Solche Interaktionen konnten in Translationssystemen an zwei unabhängigen cis-regulierenden Elementen durch in vitro-Bindungsanalysen mit individu­ellen rekombinanten Proteinen dokumentiert werden. Im Fall des translational control elements (TCE), welches ein konserviertes Sequenz-Ele­ment in der Mst(3)CGP-Genfamilie darstellt, wird eine negative Translationskontrolle durch die Bindung der Proteine CG3213, CG12470, CG1898, dFMR1, Exuperantia und Orb2 an diese Sequenz vermittelt (Stinski, 2011). Neben den in Bindungsstudien positiv getesteten Kandidaten dFMR1 und Orb2 (Stinski, 2011) wurde in der vorliegenden Dis­sertation CG3213 als weiterer direkter Bindungspartner an das TCE dokumentiert. Ein Abgleich der genomweiten Zusammenstellung von Proteininteraktionen in der Datenbank InterologFinder lieferte zwei weitere potentielle Kandidaten: CG34404 und CG3727. Al­lerdings schließen Northern-Analysen und das Proteinexpressionsmuster eine zentrale Rolle in der Drosophila-Spermatogenese für diese nahezu aus. In Kolokalisationsstudien einiger TCE-Komplex-Kandidaten mit CG3213 als Referenz konnten eindeutige Überein­stimmungen der Fluoreszenzmuster mit CG12470 in der postmeiotischen Phase be­schrieben werden, wohingegen mit Orb2 (postmeiotisch) und CG1898 (prämeiotisch) nur eine geringe Kolokalisation erkannt wurde. Punktstrukturen in den Verteilungsmustern sowohl von CG3213 als auch von CG12470 ließen sich nicht mit ER- und mitochondrien­spezifischen Markern korrelieren. Im Anschluss der Meiose konnte eine deutliche Intensitätserhöhung des CG3213-Proteins beobachtet werden, was eventuell durch eine veränderte Translationseffizienz zustande kommen könnte. Exuperantia (Exu) stellt einen bekannten Regulator für eine Reihe von translationskontrollierten mRNAs dar (Wang und Hazelrigg, 1994). Die Quantifizierungen der CG3213-mRNA in exu-mutantem Hintergrund bestätigen, dass auch die Transkript­menge der CG3213-mRNA durch Exu reguliert wird, was die obige Interpretation stützen würde. Für das zweite cis-regulierende Element, das cytoplasmic polyadenylation element (CPE), konnte eine direkte Bindung mit dem CPEB-Homolog in Drosophila (Orb2) gezeigt wer­den, welches auch eine Komponente des mst87F-RNP-Komplexes ist. Ein vermuteter Interaktionspartner dieses CPEBs ist Tob, weshalb die Verteilung beider Proteine in einem Kombinationsstamm verglichen wurde. In dem teilweise übereinstimmenden Fluoreszenz­muster ist Tob an den distalen Spermatidenenden auffallend konzentriert. Das gesamte Tob-Muster jedoch legt eine Verteilung in den Mitochondrien nahe, wie die MitoTracker®-Färbung belegt. Somit wurde erstmals ein Mitglied der Tob/BTG-Genfamilie in der Droso­phila-Spermatogenese mit Mitochondrien in Verbindung gebracht. Die Lokalisierung die­ser Proteine ist bislang unklar, jedoch konnte eine Kernlokalisation trotz der N-terminalen NLS-Sequenz mit Hilfe einer Kernfärbung ausgeschlossen werden.

Glassy dielectric response in Tb2NiMnO6 double perovskite with similarities to a Griffiths phase

Results of frequency-dependent and temperature-dependent dielectric measurements performed on the double-perovskite Tb2NiMnO6 are presented. The real (epsilon(1)(f,T)) and imaginary (epsilon(2)(f,T)) parts of dielectric permittivity show three plateaus suggesting dielectric relaxation originating from the bulk, grain boundaries and the sample-electrode interfaces, respectively. The epsilon(1)(f,T) and epsilon(2)(f,T) are successfully simulated by a RC circuit model. The complex plane of impedance, Z'-Z `', is simulated using a series network with a resistor R and a constant phase element. Through the analysis of epsilon(f,T) using the modified Debye model, two different relaxation time regimes separated by a characteristic temperature, T*, are identified. The temperature variation of R and C corresponding to the bulk and the parameter alpha from modified Debye fit lend support to this hypothesis. Interestingly, the T* compares with the Griffiths temperature for this compound observed in magnetic measurements. Though these results cannot be interpreted as magnetoelectric coupling, the relationship between lattice and magnetism is markedly clear. We assume that the observed features have their origin in the polar nanoregions which originate from the inherent cationic defect structure of double perovskites. Copyright (C) EPLA, 2013

Impedance study of (PEO)(10)LiClO4-Al2O3 composite polymer electrolyte with blocking electrodes

A composite solid polymer electrolyte (SPE) of (PEO)(10)LiClO4-Al2O3 was prepared and Pt and stainless steel(SS) blocking electrodes were used for an impedance study. It was found that the semicircle in the high frequency range and the straight line in the low frequency range depend upon different blocking electrodes and polarization potentials applied in the experiments. In the equivalent circuit. two constant phase elements (CPE) have been used instead of the pure geometrical and double layer capacitances. respectively. A theoretical line calculated from their estimated values has a good correlation with the experiment data. Moreover. the equivalent circuit also can be used to explain the impedance properties of Pt and stainless steel (SS) blocking electrodes both in the high and the low frequency ranges. (C) 2001 Elsevier Science Ltd. All rights reserved.

Dielectric Dispersion of Water in the Frequency Range from 10 mHz to 30 MHz

We investigate the dielectric dispersion of water, specially in the low-frequency range, by using the impedance spectroscopy technique. The frequency dependencies of the real R and imaginary Z parts of the impedance Could not be explained by means of the Usual description of the dielectric properties of the water as all insulating liquid containing ions. This is due to the incomplete knowledge of the parameters entering in the fundamental equations describing the evolution of the system, and oil the mechanisms regulating the exchange of charge of the cell with the external circuit. We propose a simple description of our experimental data based on the model of Debye, by invoking a dc conductivity of the cell, related to the nonblocking character of the electrodes. A discussion on the electric Circuits able to simulate the cell under investigation, based oil bulk and Surface elements, is also reported. We find that the simple circuit formed by a series of two parallels of resistance and capacitance is able to reproduce the experimental data concerning the real and imaginary part of the electrical impedance of the cell for frequency larger than 1 Hz. According to this description, one of the parallels takes into account the electrical properties of interface between the electrode and water, and the other of the bulk. For frequency lower than 1 Hz, a good agreement with the experimental data is obtained by simulating the electrical properties of the interface by means of the constant phase element.

Estudo da segregação de dopantes no contorno de grão e sua influência nas propriedades elétricas de cerâmicas à base de 'SN''O IND.2'

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Electrical conductivity, dielectric constant and phase transitions in pure and doped diammonium hydrogen phosphate

DC and AC electrical conductivity measurements in single crystals of diammonium hydrogen phosphate along the c axis show anomalous variations at 174, 246 and 416 K. The low-frequency dielectric constant also exhibits peaks exactly at these temperatures with a thermal hysteresis of 13 degrees C for the peak at 416 K. These specific features of the electrical properties are in agreement with earlier NMR second-moment data and can be identified with three distinct phase transitions that occur in the crystal. The electrical conductivity values have been found to increase linearly with impurity concentration in specimens doped with a specific amount of SO42- ions. The mechanisms of the phase transition and of the electrical conduction process are discussed in detail.

Espectroscopia de impedância em soluções iônicas e mistura de etanol/água

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

A Study of Speed of the Boundary Element Method as applied to the Realtime Computational Simulation of Biological Organs

In this work, possibility of simulating biological organs in realtime using the Boundary Element Method (BEM) is investigated. Biological organs are assumed to follow linear elastostatic material behavior, and constant boundary element is the element type used. First, a Graphics Processing Unit (GPU) is used to speed up the BEM computations to achieve the realtime performance. Next, instead of the GPU, a computer cluster is used. Results indicate that BEM is fast enough to provide for realtime graphics if biological organs are assumed to follow linear elastostatic material behavior. Although the present work does not conduct any simulation using nonlinear material models, results from using the linear elastostatic material model imply that it would be difficult to obtain realtime performance if highly nonlinear material models that properly characterize biological organs are used. Although the use of BEM for the simulation of biological organs is not new, the results presented in the present study are not found elsewhere in the literature.