Mostrando recursos 1 - 20 de 193

  1. Piezoelectric micro-machined ultrasonic transducers for medical imaging

    Smyth, Katherine Marie
    Next generation medical imaging technology hinges on the development of cost effective and array compatible transducers making piezoelectric micro-machined ultrasonic transducers (pMUTs) an attractive alternative to the current bulk piezoelectric technology. This thesis aims to realize pMUT potential starting with the development of an effective single cell model that is further scaled to optimize multi-cell elements in a 1D array. In the first half of this work, a transverse mode, lead zirconate titanate (PZT) pMUT plate cell is fabricated using common micro-fabrication techniques and a PZT sol-gel deposition process. Through derivation using a novel Greens function solution technique, an equivalent...

  2. Sistema de comunicação ótica inter-satélites para aplicações em Defesa - I

    Trindade, João Miguel Madeira
    Atualmente, os sistemas de comunicação via satélite são cada vez mais utilizados pela sociedade, em diversas aplicações, sendo a sua evolução uma grande prioridade para a comunidade científica. A necessidade de larguras de banda cada vez maiores, para satisfazer os utilizadores, torna as comunicações óticas em espaço livre (FSO) inter-satélites preferidas em comparação com as tradicionais comunicações por radiofrequência. A comunicação inter-satélites com ritmos binários elevados e de baixa potência é um fator determinante no desempenho destes sistemas. Como este tipo de comunicações são efetuadas a longas distâncias e em órbitas de elevada altitude, as fontes óticas laser tornam-se essenciais, uma...

  3. Acoustic impact of the glottal chink on the production of fricatives: A numerical study

    Elie, Benjamin; Laprie, Yves
    The paper presents a numerical study about the acoustic impact of the glottal chink opening on the production of fricatives. Sustained fricatives are simulated by using classic lumped circuit element methods to compute the propagation of the acoustic wave along the vocal tract. A recent glottis model is connected to the wave solver to simulate a partial abduction of the vocal folds during their self-oscillating cycles. Area functions of fricatives at the three places of articulation of French (palato-alveolar, alveolar, and labiodental) have been extracted from static MRI acquisitions. Simulations highlight the existence of three distinct regimes, named A, B,...

  4. Optical Frequency Mixing Through Nanoantenna Enhanced Difference Frequency Generation: Metatronic Mixer

    Chettiar, Uday K; Engheta, Nader
    A design for a subwavelength all-optical frequency mixer is proposed. The method relies on enhanced difference-frequency generation, which is achieved in two steps with the help of plasmonic nanoantennas. The interaction of the two input signals with the nonlinear material is increased through the use of input nanoantennas, which focus the incident energy of two different frequencies onto the nanoparticle formed by a nonlinear material. Next, the difference-frequency emission is enhanced through the Purcell effect by the use of a separate output nanoantenna that is resonant at the difference frequency. The application of this twofold approach allows for a significant...

  5. Evaluation of arithmetic operators for the MPPA-256 manycore architecture

    Rocha, Leandro Mateus Giacomini
    1.1 Introdução Este capítulo apresenta um resumo estendido em português sobre o Trabalho de Final de Estudos, escrito em inglês, realizado na França durante a participação do Programa de Intercâmbio Brafitec com a obtenção do duplo diploma. A motivação do trabalho assim como as etapas de desenvolvimento do mesmo são apresentadas brevemente para que se tenha uma compreensão geral texto. 1.1.1 Contexto do trabalho Este trabalho de conclusão de curso em microeletrônica, decorrente da co-tutela firmada entre as universidades Institut Polytechnique de Grenoble – École Nationale de Physique, Électronique et Matériaux (Phelma) e Universidade Federal do Rio Grande do Sul,...

  6. Generation and tuning of learned sensorimotor behavior by multiple neural circuit architectures

    Lynn, Michael (Michael Benjamin)
    Organisms have a remarkable ability to respond to complex sensory inputs with intricate, tuned motor patterns. How does the brain organize and tune these motor responses, and are certain circuit architectures, or connectivity patterns, optimally suited for certain sensorimotor applications? This thesis presents progress towards this particular problem in three subprojects. The first section re-analyzes a large data set of single-unit recordings in zebra finch area HVC during singing. While HVC is known to be essential for proper expression of adult vocalization, its circuit architecture is contentious. Evidence is presented against the recently postulated gesture-trajectory extrema hypothesis for the organization...

  7. A Superconducting-Nanowire 3-Terminal Electronic Device

    McCaughan, Adam N.; Berggren, Karl K.
    Superconducting electronics based on Josephson junctions are used to sense and process electronic signals with minimal loss; however, they are ultrasensitive to magnetic fields, limited in their amplification capabilities, and difficult to manufacture. We have developed a 3-terminal, nanowire-based superconducting electrothermal device which has no Josephson junctions. This device, which we call the nanocryotron, can be patterned from a single thin film of superconducting material with conventional electron-beam lithography. The nanocryotron has a demonstrated gain of >20, can drive impedances of 100 kΩ, and operates in typical ambient magnetic fields. We have additionally applied it both as a digital logic...

  8. Back-propagation operation for analog neural network hardware with synapse components having hysteresis characteristics.

    Michihito Ueda; Yu Nishitani; Yukihiro Kaneko; Atsushi Omote
    To realize an analog artificial neural network hardware, the circuit element for synapse function is important because the number of synapse elements is much larger than that of neuron elements. One of the candidates for this synapse element is a ferroelectric memristor. This device functions as a voltage controllable variable resistor, which can be applied to a synapse weight. However, its conductance shows hysteresis characteristics and dispersion to the input voltage. Therefore, the conductance values vary according to the history of the height and the width of the applied pulse voltage. Due to the difficulty of controlling the accurate conductance,...

  9. The archipelago ubiquitin ligase subunit acts in target tissue to restrict tracheal terminal cell branching and hypoxic-induced gene expression.

    Nathan T Mortimer; Kenneth H Moberg
    The Drosophila melanogaster gene archipelago (ago) encodes the F-box/WD-repeat protein substrate specificity factor for an SCF (Skp/Cullin/F-box)-type polyubiquitin ligase that inhibits tumor-like growth by targeting proteins for degradation by the proteasome. The Ago protein is expressed widely in the fly embryo and larva and promotes degradation of pro-proliferative proteins in mitotically active cells. However the requirement for Ago in post-mitotic developmental processes remains largely unexplored. Here we show that Ago is an antagonist of the physiologic response to low oxygen (hypoxia). Reducing Ago activity in larval muscle cells elicits enhanced branching of nearby tracheal terminal cells in normoxia. This tracheogenic...

  10. Mosaic hoxb4a neuronal pleiotropism in zebrafish caudal hindbrain.

    Leung-Hang Ma; Beena Punnamoottil; Silke Rinkwitz; Robert Baker
    To better understand how individual genes and experience influence behavior, the role of a single homeotic unit, hoxb4a, was comprehensively analyzed in vivo by clonal and retrograde fluorescent labeling of caudal hindbrain neurons in a zebrafish enhancer-trap YFP line. A quantitative spatiotemporal neuronal atlas showed hoxb4a activity to be highly variable and mosaic in rhombomere 7-8 reticular, motoneuronal and precerebellar nuclei with expression decreasing differentially in all subgroups through juvenile stages. The extensive Hox mosaicism and widespread pleiotropism demonstrate that the same transcriptional protein plays a role in the development of circuits that drive behaviors from autonomic through motor function...

  11. Design and Performance Analysis of an Intrinsically Safe Ultrasonic Ranging Sensor

    Hongjuan Zhang; Yu Wang; Xu Zhang; Dong Wang; Baoquan Jin
    In flammable or explosive environments, an ultrasonic sensor for distance measurement poses an important engineering safety challenge, because the driving circuit uses an intermediate frequency transformer as an impedance transformation element, in which the produced heat or spark is available for ignition. In this paper, an intrinsically safe ultrasonic ranging sensor is designed and implemented. The waterproof piezoelectric transducer with integrated transceiver is chosen as an energy transducing element. Then a novel transducer driving circuit is designed based on an impedance matching method considering safety spark parameters to replace an intermediate frequency transformer. Then, an energy limiting circuit is developed...

  12. Espacio deportivo urbano : parkour park en Vigo

    Lago Costas, Alfredo Alberto
    En la Península Ibérica se está viviendo un fenómeno emergente en el panorama deportivo: el auge del Parkour, deporte urbano que se sirve de la morfología de la ciudad aprovechando elementos del mobiliario, escaleras, desniveles y rampas para realizar circuitos y piruetas. Al tratarse de un deporte relativamente nuevo existe una falta de estudio de la relación del deporte con el entorno urbano. Es por ello que tampoco existen muchas construcciones a día de hoy que conjuguen las necesidades del parkour con la morfología y circuitos urbanos. La ciudad de Vigo tiene un papel destacable dentro de la comunidad gallega, debido...

  13. ABOUT TRACK CIRCUIT CALCULATION METHOD DEPENDENT ON FERROMAGNET PROPERTIES IN CONDITIONS OF TRACTION CURRENT NOISE INFLUENCE

    A. Yu. Zhuravlev
    Purpose. The work is intended to investigate the electromagnetic processes in impedance bond in order to improve noise immunity of track circuits (TC) for safe railway operation. Methodology. To achieve this purpose the methods of scientific analysis, mathematical modelling, experimental study, a large-scale simulation were used. Findings. The work examined the interference affecting the normal performance of track circuits. To a large extent, part of track circuit damages account for failures in track circuit equipment. Track circuit equipment is connected directly to the track line susceptible to traction current interference, which causes changes in its electrical characteristics and electromagnetic properties....

  14. A Novel Field-Circuit FEM Modeling and Channel Gain Estimation for Galvanic Coupling Real IBC Measurements

    Yue-Ming Gao; Zhu-Mei Wu; Sio-Hang Pun; Peng-Un Mak; Mang-I Vai; Min Du
    Existing research on human channel modeling of galvanic coupling intra-body communication (IBC) is primarily focused on the human body itself. Although galvanic coupling IBC is less disturbed by external influences during signal transmission, there are inevitable factors in real measurement scenarios such as the parasitic impedance of electrodes, impedance matching of the transceiver, etc. which might lead to deviations between the human model and the in vivo measurements. This paper proposes a field-circuit finite element method (FEM) model of galvanic coupling IBC in a real measurement environment to estimate the human channel gain. First an anisotropic concentric cylinder model of...

  15. GATA Factor-G-Protein-Coupled Receptor Circuit Suppresses Hematopoiesis

    Xin Gao; Tongyu Wu; Kirby D. Johnson; Jamie L. Lahvic; Erik A. Ranheim; Leonard I. Zon; Emery H. Bresnick
    Hematopoietic stem cells (HSCs) originate from hemogenic endothelium within the aorta-gonad-mesonephros (AGM) region of the mammalian embryo. The relationship between genetic circuits controlling stem cell genesis and multi-potency is not understood. A Gata2 cis element (+9.5) enhances Gata2 expression in the AGM and induces the endothelial to HSC transition. We demonstrated that GATA-2 rescued hematopoiesis in +9.5−/− AGMs. As G-protein-coupled receptors (GPCRs) are the most common targets for FDA-approved drugs, we analyzed the GPCR gene ensemble to identify GATA-2-regulated GPCRs. Of the 20 GATA-2-activated GPCR genes, four were GATA-1-activated, and only Gpr65 expression resembled Gata2. Contrasting with the paradigm in which GATA-2-activated...

  16. System-Level Coupled Modeling of Piezoelectric Vibration Energy Harvesting Systems by Joint Finite Element and Circuit Analysis

    Congcong Cheng; Zhongsheng Chen; Hongwu Shi; Ziniu Liu; Yeping Xiong
    A practical piezoelectric vibration energy harvesting (PVEH) system is usually composed of two coupled parts: a harvesting structure and an interface circuit. Thus, it is much necessary to build system-level coupled models for analyzing PVEH systems, so that the whole PVEH system can be optimized to obtain a high overall efficiency. In this paper, two classes of coupled models are proposed by joint finite element and circuit analysis. The first one is to integrate the equivalent circuit model of the harvesting structure with the interface circuit and the second one is to integrate the equivalent electrical impedance of the interface...

  17. PRINCIPLES OF IMPLEMENTATION OF CURRENT PROTECTION FROM INTERPHASE SHORT-CIRCUITS ON THE POWER LINES WITH UNILATERAL FEED

    F. A. Romaniuk; M. A. Shevaldin

    The article describes the implementation of the principle of overcurrent protection from interphase  short-circuits  on  the  power  lines  with  unilateral  feed.  The  expression  of  the detection of the fault location by the relative value of the distance from the installation of pro- tection to the point of damage with the help of the results of operational control of the short- circuit current damaged phases has been suggested in the article. Also the expression for determining  the  time  delay response  for  such  protection  has been  presented,  taking  into account fault location that had been detected.

    The paper proposes and describes the...

  18. Estudio de fenómenos transitorios en circuitos eléctricos de primer orden; Study of transient phenomena in first order circuits

    Bertha María Soriano González; Frank Grau Merconchini; Llohandry Cruz Carnero

    Este trabajo expone una metodología para estudiar procesos transitorios de corriente alterna y directa, en circuitos eléctricos lineales con un solo elemento almacenador de energía, empleando un sistema de instrumentación con una computadora y una tarjeta de adquisición de datos que permitió  generar un tren de  pulsos para sustituir los dispositivos de conexión y desconexión de la fuente. Se presentan los modelos matemáticos de los procesos transitorios, en presencia del tren de pulsos y para la combinación de este en serie con una fuente de señal sinusoidal; así como el diseño, la implementación de la práctica de laboratorio y las...

  19. Sistema para cálculos en redes de distribución primaria

    Leonardo Casas Fernández; Jorge Adrián Leyva Jassa

    Tradicionalmente, los cálculos relacionados con las redes de distribución se apoyan en numerosas
    aproximaciones debido fundamentalmente a la dificultad de obtener datos confiables y a las simplificaciones
    hechas para realizarlos. En este artículo se valora la representación de cada elemento de estos circuitos
    con el fin de obtener respuestas lo más exactas posible en los estudios de los circuitos de distribución
    primaria. Basado en las ideas expuestas para reducir al mínimo las simplificaciones, se ha desarrollado
    RADIAL, un sistema de computación que garantiza alta fiabilidad, con el cual es posible alcanzar resultados
    de alta calidad vinculados con los problemas más...

  20. Design of the Sequential System Automata using Temporal Equivalence Classes

    A. Ursu; G. Gruita; S. Zaporojan
    A design method of sequential system automata using temporal logic specifications is proposed in this paper. The method is based on well-known Z.Manna and P.Wolper temporal logic satisfiability analysis procedure [1] and is extended to include past time temporal operators. A new specification method which uses temporal equivalence classes is proposed to specify the behaviour of large digital circuits. The impact of the composition and decomposition operations of the temporal equivalence classes on the final automata has been studied. A case study is carried out which deals with the design of the synchronous bus arbiter circuit element. The SMV tool...

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