Mechanical Properties of the Respiratory System Derived From Morphologic Insight

This paper aims to provide the mechanical parameters of the respiratory airways (resistance, inertance, and compliance) from morphological insight, in order to facilitate the correlations of fractional-order models with pathologic changes. The approach consists of taking into account wall thickness, inner radius, tube length, and tissue structure for each airway level to combine them into a set of equations for modeling the pressure drop, flow, wall elasticity, and air velocity (axial and radial). Effects of pulmonary disease affecting the inner radius and elastic modulus of bronchial tree are discussed. A brief comparison with the circulatory system, which poses similarities with the respiratory system, is also given. The derived mechanical parameters can serve as elements in a transmission line equivalent, whose structure preserves the geometry of the human respiratory tree. The mechanical parameters derived in this paper offer the possibility to evaluate input impedance by altering the morphological parameters in relation to the pulmonary disease. In this way, we obtain a simple, yet accurate, model to simulate and understand specific effects in respiratory diseases; e.g., airway remodeling. The final scope of the research is to relate the variations in airway structure with disease to the values of fractional-order model parameters.      

Fractal based ultra-wideband antenna development for wireless personal area communication applications

This paper presents a bandwidth enhanced, compact planar ultra-wideband antenna design for wireless personal area communication (WPAN) applications. The proposed antenna has fractal based geometry and is constructed using several iterations of a pentagon slot inside a circular metallic structure. The partial ground plane of the basic radiator is tapered, defected and a U slit is etched out from the microstrip feed to improve the −10 dB |S11| bandwidth. The proposed fractal based antenna has an impedance bandwidth from 2.9 GHz to 15 GHz with low profile configuration and is fabricated on FR4 substrate with dimensions of 32 mm × 32 mm × 1.6 mm. To authenticate the designed prototype, the antenna is fabricated and tested for impedance and radiation characteristics. The designed antenna has stable radiation characteristics in the operating band. Furthermore, the antenna is validated for its applicability in WPAN, by calculating fidelity factor through time domain analysis along with the transmission coefficient and group delay measurements.     

Study of electromagnetic waves diffraction by bi-dimensional fractal structures using the renormalization method

The analysis of fractal structures by conventional methods gets harder and harder when the number of length scales rises. In this study, we try to combine the renormalization method and the surface impedance model to help rigorous studying of electromagnetic diffraction of fractal structures at their final (infinitum) iteration. As an application, we applied the method to a couple of fractal structures: Cantor Iris 1D and 2D.     

Measurement of fractional order model parameters of respiratory mechanical impedance in total liquid ventilation

This study presents a methodology for applying the forced-oscillation technique in total liquid ventilation. It mainly consists of applying sinusoidal volumetric excitation to the respiratory system, and determining the transfer function between the delivered flow rate and resulting airway pressure. The investigated frequency range was f ∈ [0.05, 4] Hz at a constant flow amplitude of 7.5 mL/s. The five parameters of a fractional order lung model, the existing "5-parameter constant-phase model," were identified based on measured impedance spectra. The identification method was validated in silico on computer-generated datasets and the overall process was validated in vitro on a simplified single-compartment mechanical lung model. In vivo data on ten newborn lambs suggested the appropriateness of a fractional-order compliance term to the mechanical impedance to describe the low-frequency behavior of the lung, but did not demonstrate the relevance of a fractional-order inertance term. Typical respiratory system frequency response is presented together with statistical data of the measured in vivo impedance model parameters. This information will be useful for both the design of a robust pressure controller for total liquid ventilators and the monitoring of the patient's respiratory parameters during total liquid ventilation treatment.     

Input impedance and reflection coefficient in fractal-like modelsof asymmetrically branching compliant tubes

A mathematical model is described, based on linear transmission line theory, for the computation of hydraulic input impedance spectra in complex, dichotomously branching networks similar to mammalian arterial systems. Conceptually, the networks are constructed from a discretized set of self-similar compliant tubes whose dimensions are described by an integer power law. The model allows specification of the branching geometry, i.e., the daughter-parent branch area ratio and the daughter-daughter area asymmetry ratio, as functions of vessel size. Characteristic impedances of individual vessels are described by linear theory for a fully constrained thick-walled elastic tube. Besides termination impedances and fluid density and viscosity, other model parameters included relative vessel length and phase velocity, each as a function of vessel size (elastic nonuniformity). The primary goal of the study was to examine systematically the effect of fractal branching asymmetry, both degree and location within the network, on the complex input impedance spectrum and reflection coefficient. With progressive branching asymmetry, fractal model spectra exhibit some of the features inherent in natural arterial systems such as the loss of prominent, regularly-occurring maxima and minima; the effect is most apparent at higher frequencies. Marked reduction of the reflection coefficient occurs, due to disparities in wave path length, when branching is asymmetric. Because of path length differences, branching asymmetry near the system input has a far greater effect on minimizing spectrum oscillations and reflections than downstream asymmetry. Fractal-like constructs suggest a means by which arterial trees of realistic complexity might be described, both structurally and functionally     

A correction procedure for the asymmetry of differential pressuretransducers in respiratory impedance measurements

The usual setup for measuring respiratory input impedance requires a differential pressure transducer attached to a pneumotachograph. Because no data correction procedure has been devised to account for transducer asymmetry, a highly symmetrical transducer is required to obtain reliable impedance data. Here, a general model for the measuring system is presented. Its main feature is that differential pressure transducers are modeled as two-input-one-output systems. From the theoretical model, a dynamic calibration and data correction procedure is defined. This was tested using highly asymmetrical transducers (common-mode rejection ratio between 45 and 27 dB) to measure the impedance of two respiratory analogs. Results obtained show that respiratory input impedance can be adequately measured if data are corrected for transducer asymmetry     

Impedance spectroscopy of human erythrocytes: system calibration,and nonlinear modeling

The authors present an impedance measurement method, the cell embedding technique, for human erythrocytes, and an accurate calibration procedure for a four-electrode impedance measurement system that gives reliable results over a wide frequency range-1 Hz to 10 MHz. To achieve high sensitivity, the cells are embedded in the pores of a Nuclepore filter. The calibration procedure assumes that the measurement system is linear and require measurement of three reference impedances. The reliability of the procedure is demonstrated with various RC circuits. Its application to the bio-impedance measurement system eliminates a quasi-dispersion in the high-frequency range and increases the bandwidth at both the low- and high-frequency ends of the range by about a decade. The experimental data are fitted to, an equivalent circuit model of the impedance of the embedded cells. The impedance spectra display constant-phase-angle (CPA) characteristics, which are used to describe the AC response of the interface between the cell surface, and the external electrolyte solution. Such a CPA element may be related to fractal character of the interface     

Equivalent Circuit Analysis of High-Frequency Ventilators Including a New High-Impedance Flow-Interrupting Ventilator

The small tidal volumes (VT) delivered to the lungs by highfrequency ventilators can be very sensitive to changes in the patient's respiratory mechanics. Analysis of a Thevenin equivalent circuit, consisting of a ventilator internal oscillatory pressure source in series with a ventilator internal impedance and a patient's respiratory impedance, reveals the need of a high-internal-impedance ventilator to minimize this VT sensitivity problem. We present a general methodology to estimate the internal impedance of any type of ventilator. The internal impedance, at a given frequency and flow setting, is calculated from the slope of the relationship between the generated peak-to-peak pressure and the VT delivered into a calibrated rigid tank through a varying constriction. We tested a typical high-frequency jet (HFJ) ventilator and a new high-impedance flow-interrupting (HIFI) ventilator consisting of a flow source, a rotary valve, a high-impedance expiratory tube, and a servocontrolled mean proximal airway pressure (MPAP) regulator. We found that the VT delivered by the HIFI ventilator was independent of MPAP and decreased by 12 percent after a fivefold increase in the constriction-tank system impedance. In contrast, the VT delivered by the HFJ ventilator decreased by 80 percent after a similar change in load. We therefore conclude that the VT delivered by the HIFI ventilator should be significantly less sensitive to changes in patient's respiratory impedance than the VT delivered by an HFJ ventilator.     

一种二叉树状分形偶极子天线的设计

提出了一种基于二叉树状分形结构的分形偶极子贴片天线。该天线的介质基片采用相对介电常数为4.4,介电损耗角正切为0.02的FR4介质板,由微带线经阻抗变换后进行馈电。该天线利用分形技术实现了33%的尺寸缩减;通过平行双线结构和开U型槽技术,优化了阻抗匹配,降低了天线的谐振频率。通过仿真分析与模型优化,天线的最终尺寸为35 mm×22 mm×1.6 mm,中心工作频率为2.87 GHz,工作频率为2.77~2.97 GHz,-10 dB阻抗相对带宽为6.9%,工作频带内最小回波损耗可达-49 dB,最大增益可达2.36 dB。该天线具有小型化、阻抗匹配良好的优点,在当代小型化通信系统中具有良好的应用前景。     

一种新型的超宽带树形天线

提出了一种新型的双分枝树形超宽带天线,该天线是在矩形树形天线基础上由阶梯形缺口构成,采用了部分接地面技术和分形概念,测量结果表明天线的输入阻抗带宽达71.4%(2.7～5.7 GHz),同时数值仿真表明阶梯形缺口有利于天线阻抗匹配的改善,该天线为全向辐射,方向图与偶极子天线类似,天线增益为2.16～4.49 dB(3～5 GHz),与矩形树形天线相比,双分枝树形辐射单元面积减少28.5%。     

Fractal antennas: a novel antenna miniaturization technique, andapplications

Fractal geometry involves a recursive generating methodology that results in contours with infinitely intricate fine structures. This geometry, which has been used to model complex objects found in nature such as clouds and coastlines, has space-filling properties that can be utilized to miniaturize antennas. These contours are able to add more electrical length in less volume. In this article, we look at miniaturizing wire and patch antennas using fractals. Fractals are profoundly intricate shapes that are easy to define. It is seen that even though the mathematical foundations call for an infinitely complex structure, the complexity that is not discernible for the particular application can be truncated. For antennas, this means that we can reap the rewards of miniaturizing an antenna using fractals without paying the price of having to manufacture an infinitely complex radiator. In fact, it is shown that the required number of generating iterations, each of which adds a layer of intricacy, is only a few. A primer on the mathematical bases of fractal geometry is also given, focusing especially on the mathematical properties that apply to the analysis of antennas. Also presented is an application of these miniaturized antennas to phased arrays. It is shown how these fractal antennas can be used in tightly packed linear arrays, resulting in phased arrays that can scan to wider angles while avoiding grating lobes     

Series impedance of GaAs planar Schottky diodes operated to 500 GHz

The author discusses the impact of ohmic contacts on the series impedance of a GaAs cylindrical planar Schottky diode. The expression for the high-frequency impedance of an annular ohmic contact is developed using a novel transmission line model. This formulation is used to ascertain the contribution of the ohmic contact impedance to the overall device series impedance at both DC and 500 GHz. Diode impedance characterization indicates that the ohmic contact impedance makes a small contribution to the series impedance in comparison to that of the other components, both at DC and submillimeter wavelengths. Hence, the dimensions of the contact pads can be scaled down significantly without any appreciable increase in series impedance but with a decrease in the parasitic pad-to-pad capacitance. Finally, this modeling establishes theoretical guidelines regarding the allowable limits for specific contact resistance in small geometry diodes, so that the device I -V characteristics are not significantly altered as a result of the ohmic contact impedance     

平板显示系统的最优扫描结构及分形模型

本文首次将分形原理应用于平板显示系统灰度图像的扫描映射,提出了平板显示系统灰度图像的最优扫描结构及分形模型,以解决平板显示系统扫描形成灰度图像过程中的时间冗余问题.将显示系统的数字显示存贮空间分切成若干个具有不同时间维数的空间划分,在此基础上导出"空间划分"和"时间灰度分形"拓扑结构的分形扫描模型及FPD离散空间的分形维数,然后根据分形模型对每一维空间划分实施自相似时间灰度分形扫描.文中从理论上证明了该模型的最优性,推导了超高显示灰度与帧频的关系,并用实验结果证明该方法可在不改变扫描频率的前提下可提高平板显示系统扫描效率及成像质量.     

Fractal modeling and segmentation for the enhancement of microcalcifications in digital mammograms

The objective of this research is to model the mammographic parenchymal and ductal patterns and enhance the microcalcifications using a deterministic fractal approach. According to the theory of deterministic fractal geometry, images can be modeled by deterministic fractal objects which are attractors of sets of two-dimensional (2-D) affine transformations. The iterated functions systems and the collage theorem are the mathematical foundations of fractal image modeling. Here, a methodology based on fractal image modeling is developed to analyze and model breast background structures. The authors show that general mammographic parenchymal and ductal patterns can be well modeled by a set of parameters of affine transformations. Therefore, microcalcifications can be enhanced by taking the difference between the original image and the modeled image. The authors' results are compared with those of the partial wavelet reconstruction and morphological operation approaches. The results demonstrate that the fractal modeling method is an effective way to enhance microcalcifications. It may also be able to improve the detection and classification of microcalcifications in a computer-aided diagnosis system.     

分形图像压缩方法

分形几何方法是一种新的图像压缩编码方法。本文介绍了分形几何和分形图像压缩的一些基本概念，以及以分形为基础的几种图像压缩编码方法。     

On the relationship between fractal dimension and the performance of multi-resonant dipole antennas using Koch curves

This paper relates for the first time, multiple resonant frequencies of fractal element antennas using Koch curves to their fractal dimension. Dipole and monopole antennas based fractal Koch curves studied so far have generally been limited to certain standard configurations of the geometry. It is possible to generalize the geometry by changing its indentation angle, to vary its fractal similarity dimension. This variation results in self-similar geometry which can be generated by a recursive algorithm. Such a variation is found to have a direct influence on the input characteristics of dipole antennas. The primary resonant frequency, the input resistance at this resonance, and the ratio of first two resonant frequencies, have all been directly related to the fractal dimension. Curve-fit expressions can also be obtained for the performance of antennas at their primary resonance, in terms of fractal iteration and fractal dimension. The antenna characteristics have been studied using extensive numerical simulations and are experimentally verified. These findings underscore the significance of fractal dimension as an important mathematical property of fractals that can be used as a design parameter for antennas. The use of these ideas would not only reduce the computational intensity of optimization approaches for design of fractal shaped antennas, but also help antenna designers approach the problem systematically. Design formulation for antennas based on other fractal geometries can be similarly obtained after identifying suitable parameters of variation. This would therefore help analytical design of multiband and multifunctional antennas using fractal geometries.     

An efficient recursive procedure for evaluating the impedance matrix of linear and planar fractal arrays

The self-similar geometrical properties of fractal arrays are exploited in this paper to develop fast recursive algorithms for efficient evaluation of the associated impedance matrices as well as driving point impedances. The methodology is demonstrated by considering two types of uniformly excited fractal arrays consisting of side-by-side half-wave dipole antenna elements. These examples include a triadic Cantor linear fractal array and a Sierpinski carpet planar fractal array. This class of self-similar antenna arrays become significantly large at higher order stages of growth and utilization of fractal analysis allows the impedance matrix, and hence the driving point impedances, to be obtained much more efficiently than would be possible using conventional analysis techniques.     

Mathematical analysis and computer simulation of the respiratorysystem in the newborn infant

A mathematical model of neonatal respiratory control which can be used to simulate the system under different physiological conditions is proposed. The model consists of a continuous plant and a discrete controller. Included in the plant are lungs, body tissue, brain tissue, a cerebrospinal fluid compartment, and central and peripheral receptors. The effect of shunt in the lungs is included in the model, and the lung volume and the dead space are time varying. The controller utilizes outputs from peripheral and central receptors to adjust the depth and rate of breathing, and the effects of prematurity of peripheral receptors are included in the system. Hering-Breuer-type reflexes are embodied in the controller to accomplish respiratory synchronization. The model is examined and its simulation results under test conditions in hypoxia and hypercapnia are presented     

Impedance matrix of an antenna array in a quasi-optical resonator

The power from numerous millimeter-wave solid-state sources can be efficiently combined using quasi-optical techniques. One technique is to place an array of active radiating sources within a quasi-optical resonator. The driving point impedance of each antenna is strongly affected by the presence of all other active antennas as well as by the mode structure and Q of the resonator. The impedance matrix for an array of antennas radiating into a plano-concave open resonator is determined here through use of the Lorentz integral. The resulting expressions include the effect of diffraction loss and are valid for arbitrary reflector spacing, source frequency, array location and geometry. The result can be used for impedance matching of each active source to its antenna, facilitating design of an efficient power combining system. Simulations using the impedance matrix in conjunction with an antenna impedance model are compared with two-port measurements     

Importance of low-frequency impedance data for reliably quantifying parallel inhomogeneities of respiratory mechanics

The ability to reliably measure total respiratory input impedance Z/sup rs/ from 0.25 to 4 Hz has only recently been reported and only in healthy subjects. The real part of Z/sup rs/ decreased substantially with frequency. One explanation is provided by the Otis model, which contains parallel resistance-compliance time-constant inhomogeneities. Several investigators have suggested the use of this model at the level of estimating its parameters by fitting the model to data. Such an approach would permit quantification of the functional inhomogeneity of an individual's respiratory system and may be useful diagnostically. In this study, experimental data and a sensitivity analysis are combined to specify the requirements and limitations associated with estimating the parameters. The data acquisition technique was improved to acquire Z/sup rs/ as low as 0.125 Hz in seven healthy subjects. The Otis model provided an excellent fit to the data with reasonably low intra- and intersubject variability.<>