Pole-Zero Modeling and Classification of Phonocardiograms

Phonocardiography, the analysis of heart sounds, is a noninvasive diagnostic method useful in studying heart valve function. Phonocardiograms (PCG's) of porcine prosthetic heart valves in the aortic position were analyzed by a parametric signal modeling method in order to derive frequency domain features suitable for the classification of the valve state.     

Time-frequency and time-scale techniques for the classification ofnative and bioprosthetic heart valve sounds

The determination of diagnostic features in recorded heart sounds was investigated with Carpentier-Edwards (CE) bioprosthetic valves. Morphological features, extracted using the Choi-Williams distribution, achieved between 96 and 61% correct classification. The time-scale wavelet-transform feature set achieved 100% correct classification with native valve populations, and 87% with the CE replacements     

Control of an air pressure actuated disposable bioreactor for cultivating heart valves

A disposable injection molded bioreactor for growing tissue-engineered heart valves is controlled to mimic the physiological heart cycle. Tissue-engineered heart valves, cultured from human stem cells, are a possible alternative for replacing failing aortic heart valves, where nowadays biological and mechanical heart valves are used. Growing and conditioning is done by mechanically stimulating the tissue in a bioreactor. The disposable injection molded bioreactor uses flexible membranes and steering valves to mimic a physiological heart cycle. In this work, an air pressure actuation control system for this bioreactor is designed. One membrane is position controlled to achieve a desired flow through the heart valve, while another membrane controls the aortic pressure. A third actuator controls a steering valve used to impose a resistance on the flow back to the first membrane, in order to control the heart valve closing pressure. Due to the repetitive character of the setpoints, repetitive controllers are designed and implemented. A high position tracking performance is achieved and pressure setpoints are mimicked successfully, while preventing large pressure oscillations and suppressing disturbances that could be damaging for the tissue heart valve. The control system allows full adjustability of operating conditions needed for the growing, conditioning and testing phases of tissue engineered heart valves.     

Spectral composition of heart sounds before and after mechanicalheart valve implantation using a modified forward-backward Prony'smethod

This paper investigates the impact of the lung-thorax and heart-valve system on the overall spectral composition of the externally recorded heart sounds. The study concentrates on the case of the first and the second heart sounds for normal patients and patients before and after implantation of a mechanical valve in the mitral or aortic position. The analysis is performed using a modified forward-backward overdetermined Prony's method (MFBPM) which uses a forward-backward mean filter and a modified procedure for estimating the position of the signal poles. In terms of the normalized cross-correlation coefficient, this method has an average modeling accuracy of 99.62% for representing the first and second heart sounds and an average least square time-domain error of 0.43%. Results obtained from 40 subjects show that the condition of the native mitral or aortic valve affects mostly the distribution of the amplitudes of the spectral components, whereas the number of the spectral components or their respective relative energy remains more or less unchanged. It has been found that the amplitudes of frequency components in the range 120-250 Hz are more affected by abnormalities of native mitral valves. Furthermore, in the case of the second heart sound the region 250-400 Hz has been found to be more affected by abnormalities in the aortic valve. It has also been found that the mechanical prosthetic heart valve affects mostly the spectrum beyond 400 Hz. A clear difference has been observed in the frequency spectrum above 400 Hz between both normally and abnormally functioning native valves and normally functioning mechanical valves. Preliminary results in some malfunctioning cases of mechanical prosthesis suggest that spectral components beyond 400 Hz can be used to monitor the condition of these prostheses     

An advanced engine thermal management system: nonlinear control and test

Internal combustion engine thermal management system functionality can be enhanced through the introduction of smart thermostat valves and variable speed electric pumps and fans. The traditional automotive cooling system components include a wax based thermostat valve and crankshaft driven water pump. However, servo-motor driven valves, pumps, and fans can better regulate the engine's coolant fluid flow to realize fuel economy gains and tailpipe emission reductions. To study these cooling system actuators, with accompanying nonlinear control strategy, a scale experimental system has been fabricated which features a smart valve, electric coolant pump, radiator with electric fan, and immersion heater. In this paper, mathematical models will be presented to describe the system's behavior. A nonlinear controller will then be designed for transient temperature tracking. Representative experimental results are presented and discussed to demonstrate the smart valve's operation in maintaining the temperature within a neighborhood of the target value for various scenarios including highway mode, full power with load disturbance, and quick heat.     

Anode sputtering in high-voltage mercury arc valves

A method is described whereby the anode sputtering rate during recovery of a mercury arc valve can be estimated from its transient inverse current and voltage waveforms. Inverse currents have been measured in an experimental valve, from which corresponding anode sputtering rates are deduced for a variety of cathode coolant temperatures and commutation conditions. These measurements substantiate proposed methods of reducing anode sputtering in valves. The accuracy of the method has been confirmed by examining sputtered deposits found in an experimental valve after several hundred hours of rectifier operation. Major applications of this method are in the development and testing of valves for high-voltage direct current (hvdc) transmission. These include rapid assessment of the effect of design modifications on anode sputtering, and increasing the anode sputtering rate by a known factor through manipulation of the test conditions (e.g., cathode coolant temperature and dI/dt), thereby considerably shortening the time required for sputtering life tests. The latter application is particularly valuable in the case of single-gap valves where the effects of anode sputtering during recovery are likely to be the ultimate limitation on serviceable life. The saving in testing time is especially important because of the high operating cost of test plant at relevant levels, in our case 50 kV, 1000-ampere dc bridge rating.     

Comparison of pattern recognition methods for computer-assistedclassification of spectra of heart sounds in patients with a porcinebioprosthetic valve implanted in the mitral position

The diagnostic performance of two pattern recognition methods (or classifiers) to detect valvular degeneration was evaluated in 48 patients with a porcine bioprosthetic heart valve inserted in the mitral position. Twenty patients had a normal porcine bioprosthetic valve and 28 patients had a degenerated bioprosthetic valve. One method was based on the Gaussian-Bayes model and the second on the "nearest neighbor" algorithm using three distance measurements. Eighteen diagnostic features were extracted from the sound spectrum of each patient and, for each method, a two-class supervised learning approach was used to determine the most discriminant diagnostic patterns composed of 6 features or less. The probability of error of the classifiers was estimated with the leave-one-out approach. The performance of each method to discriminate between normal and degenerated bioprosthetic valves was verified by clinical evaluation of the valves. The best performance in evaluation of the sound spectrum (98% correct classifications) was obtained with the Bayes classifier and two patterns of six features each. The percentage of false positive classifications of valve degeneration was 0% and the percentage of false negative classifications was 4%. Sensitivity for the detection of valve degeneration was 96%, specificity was 100%, positive predictive value was 100%, and negative predictive value was 95%. The best performance of the nearest neighbor method (94% correct classifications) was obtained by using the Mahalanobis distance and five patterns composed of three, four, five, or six diagnostic features. Using a pattern composed of only three features, the percentage of false positive classifications for degeneration was 10% and the percentage of false negative classifications was 4%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Maximum likelihood approach to image texture and acoustic signalclassification

The authors describe a method of classifying natural textures based on the maximum likelihood parameter estimation technique. The novelty of the technique lies in the use of textural features that are derived from the subbands of a wavelet transformed image via the co-occurrence matrices. A maximum likelihood classifier is designed using a set of training texture samples. Ten different Brodotz (1965) textures have been classified using this procedure with an average classification accuracy of 99.7%. The main emphasis is to apply this technique to the classification of underwater acoustic signals. A time-frequency plot is obtained for each segment of the acoustic signal and then converted to an intensity pattern. The textural classification scheme is then applied to the intensity patterns of the acoustic signals. Eight different underwater acoustic signals have been classified by this procedure with an average accuracy of 99.99%     

衬底温度对机械瓣膜上沉积的类金刚石薄膜的影响

为掌握机械瓣膜衬底温度对类金刚石薄膜的影响规律,在实验中保持其它实验参数不变,机械瓣膜衬底温度分别取室温和150℃时,用脉冲激光沉积法在机械瓣膜上制备类金刚石薄膜。用Raman光谱仪对薄膜的微观结构进行检测;用原子力显微镜对薄膜的表面形貌和粗糙度进行检测。结果表明：当其它实验参数不变时,机械瓣膜衬底温度从室温升高到150℃时,薄膜的微观结构没有发生明显改变;薄膜表面的粗糙度减小。类金刚石薄膜和机械瓣膜衬底之间具有很好的黏附性。     

Video-Based Measuring of Quality Parameters for Tricuspid Xenograft Heart Valve Implants

Defective heart valves are often replaced by implants in open-heart surgery. Both mechanical and biological implants are available. Among biological implants, xenograft ones—i.e., valves grafted from animals such as pigs, are widely used. Good implants should exhibit certain typical anatomical and functional characteristics to successfully replace the native tissue. Here, we describe a video-based system for measuring quality parameters of xenograft heart valve implants, including the area of the orifice and the fluttering of the valves' leaflets, i.e., their flaps (or cusps). Our system employs automatic methods that provide a precise and reproducible way to infer the quality of an implant. The automatic analysis of both a valve's orifice and the fluttering of its leaflets offers a more comprehensive quality assessment than current, mostly manual methods. We focus on valves with three leaflets, i.e., aortic, pulmonary, and tricuspid valves.      

压电执行器及其在液压阀中的应用

以压电执行器为核心的高速开关阀及伺服阀等压电式液压阀具有频响高,微动性能好,结构紧凑等优点,是新型阀控类型之一,受到国内外研究者的持续关注。首先,该文介绍了阀用压电执行器的分类和特点,根据工作原理分为直推式和步进式2类4种形式;其次,对先导型、直动型、喷嘴挡板型和开关型4种典型压电阀的研究进展进行了梳理,分析了各自的代表性结构、性能特点。结果表明,随着未来对液压阀精密化、智能化需求的提升,压电液压阀的应用前景更广。因此,除高性能介电材料开发外,如微位移放大、迟滞补偿控制等关键压电驱动与控制技术仍有待深入研究。     

声透镜指向性换能器研究

该文利用声学透镜使声波能量聚焦,实现小尺寸换能器窄波束声辐射。利用有限元方法分别建立了单凹面声透镜及双凹面声透镜仿真模型,优化了声透镜结构参数,设计并制作了双凹面声透镜指向性换能器,并在消声水池内对换能器样机和声透镜进行了性能测试。换能器样机辐射面积直径?120 mm,设置声透镜后,提高发送电压响应级4 dB,发射指向性-3 dB波束开角由76°变为约30°(@10 kHz),与仿真计算结果相符。实验结果表明,声透镜有效减小了换能器发射波束宽度,提高了换能器主瓣发送电压响应,验证了双凹面声透镜对优化换能器指向性的效果。     

Nitric Oxide Generation and Endothelial Progenitor Cells Recruitment for Improving Hemocompatibility and Accelerating Endothelialization of Tissue Engineering Heart Valve

Tissue engineering heart valve (TEHV) offers great potential to overcome the limitations of commercial artificial valves used in clinical practice as a permanent prosthetic valve. Currently, decellularized heart valve (DHV) is the most widely used scaffold for TEHV, but showed suboptimal performance due to difficulty of endothelialization. Facilitating endothelialization of DHV is indispensable for better valve performance, and excellent hemocompatibility guarantees enough time windows for endothelialization process. Herein, a dual-functional TEHV scaffold with improving hemocompatibility and accelerating endothelialization is constructed by modifying DHV with copper ions (Cu) and growth differentiation factor 11 (GDF11). Results show the newly-constructed scaffold successfully generates endogenous nitric oxide (NO) through catalysis of Cu, and possesses improved hemocompatibility by down-regulating platelets activation and adhesion. Furthermore, GDF11 immobilization significantly accelerates scaffold endothelialization through facilitating recruitment, supporting growth, and alleviating apoptosis of endothelial progenitor cells . This TEHV scaffold shows favorable performance under in vivo hemodynamic environment with intact endothelial coverage and adaptive ECM remodeling, and without thrombus or calcification formation. This newly-constructed TEHV scaffold is expected to make up for the shortcomings of currently available prosthetic valves in clinical practice and has the potential possibility of rapid translation to the clinic as a better prosthetic valve.     

用双传声器模拟"8"字型指向性的一种方法

提出了运用两个全指向性传声器来模拟“8”字型指向性的一种测量方法。通过理论分析和实验验证。表明该方法可以准确地模拟“8”字型传声器的指向性特性，应用于室内音质参量的测试中。     

Comments on "Pole-zero modeling and classification of phonocardiograms"

Recently,1 the Steiglitz-McBride method was used to identify the two most dominant frequencies in aortic heart sounds from porcine prosthetic heart valves. A quadratic classifier was developed to evaluate valve sounds in a test set. We have corrected computational errors, recomputed their results, and interchanged the training and test sets to yield new results.     

Efficient detection of resonances in anechoic chambers using thematrix pencil method

In a previous paper we have presented a method for evaluating the performance of anechoic chambers by analyzing the S-parameters of a system comprising two antennas facing each other in an anechoic chamber using the matrix pencil method. In this work, we present an improvement of this resonance detection technique using only the transmission parameter S₂₁. The propagating components of the transmission parameter S₂₁ are derived over small frequency intervals using the matrix pencil method and then removed from S₂₁ in a two-level decomposition procedure. The resonances are clearly identified from the residual signal. Two examples of resonance detection in two different anechoic chambers illustrate the proposed method     

Ultrawide band radar signal detection, estimation and experiment

With reference to the air target detection of ultra-wide band (UWB)/impulse radar(IR), the transient signal processing techniques was discussed. In weak UWB signal detection, the wavelet transforms and high order spectrum estimation techniques were preferred. In target characteristic analysis, a time domain bispectrum estimation algorithm was used to analyze the target impulse response, which could estimate accurately local scattering distribution of complex target. A free field IR experimental system installed in an anechoic chamber was used. With this system, experiments to several target models were made. The results of these experiments verified the signal processing method efficiency.     

Evoked otoacoustic emissions: nonlinearities and responseinterpretation

Evoked otoacoustic emissions (EOAEs) are acoustic signals produced by the inner ear in response to transient acoustic stimuli, and can be recorded in the external auditory canal. Since emissions can be reduced or even abolished by hearing losses of peripheral origin due to trauma and pathology, EOAEs are presently considered as the most sensitive clinical test for assessing the integrity of peripheral hearing. Recordings of emissions evoked in response to transient stimuli are contaminated by an initial artifact which in most clinical environments can be a very serious limitation. For this reason, a nonlinear estimation method called derived nonlinear response (DNLR) is widely used, instead of classical synchronous averaging. The aims of this work are: (i) to justify theoretically the use of the DNLR technique by means of a simple model and (ii) to compare the results obtained from the classical averaging (a linear estimation technique) with those obtained from the DNLR technique. Some suggestions of practical interest are made on the basis of the analysis     

Linear Signal Processing by Acoustic Surface-Wave Transversal Filters

The impulse response of acoustic surface-wave (ASW) filters is determined by the configuration of an array of planar transducers tapping the acoustic signal propagated in the piezoelectric substrate. The transducer configuration is derived here by applying the generaI procedure used for the synthesis of linear transversal filters, which consists in time sampling the required impulse response and arranging the spacing and weights of the taps according to the time intervals and amplitudes of the impulse-response samples. The design of the tapping structure that synthesizes the impulse response of ASW transversal filters is based on a nonuniform sampling procedure, previously developed by the authors, that meets the particular requirements of ASW device operation. The features of this design procedure are presented, and several geometries of tapping transducers corresponding to impulse responses of different characteristics are discussed. The application of the procedure to the design of typical ASW filters is illustrated by the results of experimental models.     

Development of a new fully flexible hydraulic variable valve actuation system for engines using rotary spool valves

In this paper, a new hydraulic variable valve actuation (VVA) system is proposed and designed. The VVA system can significantly improve the engine performance in terms of the power density, volumetric efficiency, emission, and fuel consumption. In this system, each engine valve is actuated by a hydraulic cylinder which is charged and discharged using two rotary spool valves. The rotary spool valves are rotated by the engine crankshaft while their phases are controlled by hydraulic or electric phase shifters. Similar to camless valvetrains, the new engine valve system is capable of flexible engine valve timing and lift at any engine speed without the drawbacks of existing camless valvetrains including high control complexity, low reliability, and slow actuator response. The mathematical model of the system is derived and verified by comparing simulation and experimental results. Two feedback controllers are designed and implemented for precise valve opening and closing timing and valve lift control. Experiments are performed to validate the mathematical model and evaluate the proposed system's performance. The results show excellent system repeatability and controllability at different operating conditions.