Measures of spectral slope using an excised larynx model

Spectral measures of the glottal source were investigated using an excised canine larynx (CL) model for various aerodynamic and phonatory conditions. These measures included spectral harmonic difference H1-H2 and spectral slope that are highly correlated with voice quality but not reported in a systematic manner using an excised larynx model. It was hypothesized that the acoustic spectra of the glottal source were significantly influenced by the subglottal pressure, glottal adduction, and vocal fold elongation, as well as the resulting vibration pattern. CLs were prepared, mounted on the bench with and without false vocal folds, and made to oscillate with a flow of heated and humidified air. Major control parameters were subglottal pressure, adduction, and elongation. Electroglottograph, subglottal pressure, flow rate, and audio signals were analyzed using custom software. Results suggest that an increase in subglottal pressure and glottal adduction may change the energy balance between harmonics by increasing the spectral energy of the first few harmonics in an unpredictable manner. It is suggested that changes in the dynamics of vocal fold motion may be responsible for different spectral patterns. The finding that the spectral harmonics do not conform to previous findings was demonstrated through various cases. Results of this study may shed light on phonatory spectral control when the larynx is part of a complete vocal tract system.     

Suppression of the primary resonance vibrations of a forced nonlinear system using a dynamic vibration absorber

In a single degree-of-freedom weakly nonlinear oscillator subjected to periodic external excitation, a small-amplitude excitation may produce a relatively large-amplitude response under primary resonance conditions. Jump and hysteresis phenomena that result from saddle-node bifurcations may occur in the steady-state response of the forced nonlinear oscillator. A simple mass-spring-damper vibration absorber is thus employed to suppress the nonlinear vibrations of the forced nonlinear oscillator for the primary resonance conditions. The values of the spring stiffness and mass of the vibration absorber are significantly lower than their counterpart of the forced nonlinear oscillator. Vibrational energy of the forced nonlinear oscillator is transferred to the attached light mass through linked spring and damper. As a result, the nonlinear vibrations of the forced oscillator are greatly reduced and the vibrations of the absorber are significant. The method of multiple scales is used to obtain the averaged equations that determine the amplitude and phases of the first-order approximate solutions to primary resonance vibrations of the forced nonlinear oscillator. Illustrative examples are given to show the effectiveness of the dynamic vibration absorber for suppressing primary resonance vibrations. The effects of the linked spring and damper and the attached mass on the reduction of nonlinear vibrations are studied with the help of frequency response curves, the attenuation ratio of response amplitude and the desensitisation ratio of the critical amplitude of excitation.     

Improving spatiotemporal resolution of USPIO-enhanced dynamic imaging of rat kidneys

This paper addresses the problem of enhancing spatiotemporal resolution of ultra-small superparamagnetic iron oxide (USPIO)-enhanced dynamic MRI of rat kidneys. To alleviate the limited resolution problem of conventional full-scan Fourier imaging methods, we use a generalized series-based imaging scheme to reduce coverage of kappa-space. Experimental results demonstrate that the generalized series imaging method with basis functions constructed using two references (pre- and post-contrast) can reduce the number of phase encodings measured during the dynamic contrast wash-in process by a factor of 4 with a negligible or minimal loss of image quality. The method is expected to make 3D studies possible using USPIO-enhanced dynamic imaging of rat kidneys, and prove valuable for early detection of renal rejection after kidney transplantation.     

Bifurcations and chaos in register transitions of excised larynx experiments

Experimental data from an excised larynx are analyzed in the light of nonlinear dynamics. The excised larynx provides an experimental framework that enables artificial control and direct observation of the vocal fold vibrations. Of particular interest in this experiment is the coexistence of two distinct vibration patterns, which closely resemble chest and falsetto registers of the human voice. Abrupt transitions between the two registers are typically accompanied by irregular vibrations. Two approaches are presented for the modeling of the excised larynx experiment; one is the nonlinear predictive modeling of the experimental time series and the other is the biomechanical modeling (three-mass model) that takes into account basic mechanisms of the vocal fold vibrations. The two approaches show that the chest and falsetto vibrations correspond to two coexisting limit cycles, which jump to each other with a change in the bifurcation parameter. Irregular vibrations observed at the register jumps are due to chaos that exists near the two limit cycles. This provides an alternative mechanism to generate chaotic vibrations in excised larynx experiment, which is different from the conventionally known mechanisms such as strong asymmetry between the left and right vocal folds or excessively high subglottal pressure.     

非线性耦合完全网络的时空混沌同步

利用N个Fitzhugh-Nagumo模型作为网络节点,通过非线性耦合构成完全网络,研究了这种网络的时空混沌同步问题.首先给出了复杂网络中连接节点之间的非线性耦合函数的一般性选取原则.进一步基于Lyapunov稳定性定理,理论分析了实现网络同步的条件以及控制增益的取值范围.最后,通过仿真模拟检验了以Fitzhugh-Nagumo模型作为网络节点所构成的完全网络的时空混沌同步效果.仿真结果表明,这种完全网络不但同步快速有效,而且网络规模的大小对网络同步稳定性的影响不敏感. 关键词： 同步 复杂网络 时空混沌 非线性耦合     

B模式实时成像定量监控超声空化时空行为的研究

提出一种采用B超图像实现高强聚焦超声(HIFU)治疗时声空化的时空量化监控的方法。首先,采用B模式实时成像系统对不同声辐照能量下的HIFU在凝胶仿体中引发的超声空化进行实验监测;接着,利用二维数字图像处理算法消除高强聚焦超声(HIFU)在B超图像中产生的干涉条纹,并在此基础上,对B超成像中观察到的高亮区域的面积变化情况进行量化分析;最后,进一步讨论了驱动声压或脉冲宽度对超声空化产生的高亮区域的生成速度和面积大小的影响。结果显示该方法可以有效去除B超图像中的干涉条纹,并对HIFU引发的空化现象进行实时监测。实验结果还表明辐照声能量的提高将引发更强烈的声空化行为,并且显著缩短HIFU引发的空化泡群的初始生成时间。研究结果对进一步优化HIFU治疗有重要意义。     

B模式实时成像定量监控超声空化时空行为的研究

提出一种采用B超图像实现高强聚焦超声(HIFU)治疗时声空化的时空量化监控的方法。首先,采用B模式实时成像系统对不同声辐照能量下的HIFU在凝胶仿体中引发的超声空化进行实验监测;接着,利用二维数字图像处理算法消除高强聚焦超声(HIFU)在B超图像中产生的干涉条纹,并在此基础上,对B超成像中观察到的高亮区域的面积变化情况进行量化分析;最后,进一步讨论了驱动声压或脉冲宽度对超声空化产生的高亮区域的生成速度和面积大小的影响。结果显示该方法可以有效去除B超图像中的干涉条纹,并对HIFU引发的空化现象进行实时监测。实验结果还表明辐照声能量的提高将引发更强烈的声空化行为,并且显著缩短HIFU引发的空化泡群的初始生成时间。研究结果对进一步优化HIFU治疗有重要意义。     

Passive structural health monitoring of a high-speed naval ship from ambient vibrations

Previous studies have used the cross-correlation of ambient vibrations (CAV) technique to estimate the impulse response (or Green's function) between passive sensors for passive imaging purposes in various engineering applications. The technique (CAV) relies on extracting deterministic coherent time signatures from the noise cross-correlation function computed between passive sensors, without the use of controlled active sources. Provided that the ambient structure-borne noise field remains stable, these resulting coherent waveforms obtained from CAV can then be used for structural monitoring even if they differ from the actual impulse response between the passive sensors. This article presents experimental CAV results using low-frequency random vibration data (<50 Hz) collected on an all-aluminum naval vessel (the HSV-2 Swift) operating at high speed (up to 40 knots) during high sea states. The primary excitation sources were strong wave impact loadings and rotating machinery vibrations. The consistency of the CAV results is established by extracting similar coherent arrivals from ambient vibrations between the pairs of strain gages, symmetrically located across the ship's centerline. The influence of the ship's operating conditions on the stability of the peak coherent arrival time, during the 7 days trial, is also discussed.     

Controlling and synchronizing spatiotemporal chaos of the coupled Bragg acousto-optical bistable map system using nonlinear feedback

In this paper we present the control and synchronization of a coupled Bragg acousto-optic bistable map system using nonlinear feedback technology. This nonlinear feedback technology is useful to control a temporally chaotic system as well as a spatiotemporally chaotic system. It can be extended to synchronize the spatiotemporal chaos. It can work in a wide range of the controlled and synchronized signals, so it can decrease the sensitivity down to a noise level. The synchronization can be obtained by the analysis of the largest conditional Lyapunov exponent spectrum, and easily implemented in practical systems just by adjusting the coupled strength without any pre-knowledge of the dynamic system required.     

Quantifying the architectural complexity of microscopic images of histology specimens

Tumour grade (a measure of the degree of cellular differentiation of malignant neoplasm) is an important prognostic factor in many types of cancer. In general, poorly differentiated tumours are characterized by a higher degree of architectural irregularity and complexity of histological structures. Fractal dimension is a useful parameter for characterizing complex irregular structures. However, one of the difficulties of estimating the fractal dimension from microscopic images is the segmentation of pathologically relevant structures for analysis. A commonly used technique to segment structures of interest is to apply a pixel intensity threshold to convert the original image to binary and extract pixel outline structures from the binary representation. The difficulty with this approach is that the value of the threshold required to segment the histological structures is highly dependent on the staining technique chosen and imaging conditions (i.e., illumination time, intensity, and uniformity) of the microscopic system. In this work, we present a method for finding the optimal intensity threshold by maximizing the corresponding fractal dimension. This method results in the segmentation of histological structures and the estimation of their fractal dimension (independent of imaging conditions). We applied our technique to 164 prostate histology sections from 82 prostate core biopsy specimens (two serial sections from each of the 63 benign prostate tissues and 19 high grade prostate carcinoma). We stained one of the serial sections with conventional hemotoxylin and eosin (H&E) and the other with pan-keratin, and found that the difference in mean fractal dimension between the two groups was statistically significant (p < 0.0001) for both stains. However, using receiver operating characteristics (ROC) analysis, we conclude that our fractal dimension method applied to the images of pan-keratin stained sections provides greater classification performance (benign versus high grade) than with those stained with H&E when compared to the original histological diagnosis. The sensitivity and specificity achieved with the pan-keratin images were 89.5% and 90.5%, respectively.     

Application of the velocity spectrum to a spatiotemporal study of high-speed processes

The dynamical problem of reconstructing an internal structure from a set of integrals depending on time and the velocity of the signals being integrated is solved. The results can be used to study dynamic objects of various kinds. Zh. Tekh. Fiz. 67, 132–134 (September 1997)     

Comparison of biomechanical modeling of register transitions and voice instabilities with excised larynx experiments

Voice instabilities were studied using excised human larynx experiments and biomechanical modeling. With a controlled elongation of the vocal folds, the experiments showed registers with chest-like and falsetto-like vibrations. Observed instabilities included abrupt jumps between the two registers exhibiting hysteresis, aphonic episodes, subharmonics, and chaos near the register transitions. In order to model these phenomena, a three-mass model was constructed by adding a third mass on top of the simplified two-mass model. Simulation studies showed that the three-mass model can vibrate in both chest-like and falsetto-like patterns. Variation of tension parameters which mimic activities of laryngeal muscles could induce transitions between both registers. For reduced prephonatory areas and damping constants, extended coexistence of chest and falsetto registers was found, in agreement with experimental data. Subharmonics and deterministic chaos were observed close to transitions between the registers. It is concluded that the abrupt changes between chest and falsetto registers can be understood as shifts in dominance of eigenmodes of the vocal folds.     

Extending the dynamic range of an energy harvester using nonlinear damping

This paper introduces the use of nonlinear damping for extending the dynamic range of vibration energy harvesters. A cubic nonlinear damper is initially considered and the average harvested power and the throw are obtained for different sinusoidal base excitation amplitudes and frequencies, both numerically and analytically. It is demonstrated that when excited at resonance, at an amplitude below its maximum operational limit, the harvested power using a nonlinear damper can be significantly larger than that of a linear energy harvester, therefore expanding its dynamic range. A potential approach to implementing cubic nonlinearity using a shunted electromagnetic device is also presented.     

Optimization and limits of optical nonlinear measurements using imaging technique

We report on analytical calculations for a 4f coherent imaging system in presence of a phase object at the entry of the set-up. We give the results of the optimized parameters to be used in this system so as to increase the sensitivity of the measurement of the nonlinear refraction coefficient. Analytical and previously reported simulated image profiles are compared here. Our study also gives the limits of the nonlinear imaging technique with a phase object for relatively high nonlinear phase shifts.     

Simultaneous high-speed planar imaging of mixture fraction and velocity using a burst-mode laser

Simultaneous high-speed quantitative imaging of mixture fraction and velocity is demonstrated using the fourth- and second-harmonic outputs, respectively, of a burst-mode Nd:YAG laser. A tenfold increase in the record length and 16-fold increase in per-pulse energy are achieved compared with previous measurements of mixture fraction using burst-mode and continuously pulsed diode-pumped solid-state lasers, respectively. The high output energy is used for quantitative, high-speed mixture-fraction imaging with acetone planar laser-induced fluorescence, which also enables simultaneous particle-based velocimetry without interference from particle scattering. A semiquantitative model is used to determine the limitations on fourth-harmonic output energy due to the effects of transient absorption and thermal phase mismatch over a range of repetition rates. Data are presented for mixing within a turbulent jet (Reynolds number of 15,000) and are validated by comparisons with known turbulent mixing laws and previously published data.     

Sustained simultaneous high-speed imaging of scalar and velocity fields using a single laser

A high-speed technique that combines planar laser induced fluorescence (PLIF) detection of biacetyl and particle image velocimetry (PIV) for simultaneous imaging of scalar and velocity fields is demonstrated at a frame rate of 12 kHz for up to 32500 consecutive frames. A single diode-pumped, frequency-tripled Nd-YAG laser was used for excitation. Wavelength-separated recording was achieved for Mie scattering from silicone oil droplets with a CMOS camera and for the red-shifted fluorescence from biacetyl with an image-intensified CMOS camera. Interference between PIV and PLIF tracers was found to be negligible. Cross-talk between PIV and PLIF signals was low and a strategy to completely eliminate it was devised and is discussed. The signal-to-noise ratio is about 9 for single-shot scalar images. Example image sequences were recorded in an atmospheric pressure air jet at Re=2000. PACS 42.62.Fi; 33.50.Dq; 06.30.Gv; 06.60.Jn     

Experimental targeting and control of spatiotemporal chaos in nonlinear optics

We demonstrate targeting and control over spatiotemporal chaos in an optical feedback loop experiment. Different stationary target patterns are stabilized in real time by means of a two dimensional space extended perturbation field driven by an interfaced computer and applied in real space to a liquid crystal display device inserted within a control optical loop. The flexibility of the system in switching between different target patterns is also demonstrated.     

Linear and nonlinear vibrations analysis of viscoelastic sandwich beams

In this paper, numerical models are proposed for linear and nonlinear vibrations analyses of viscoelastic sandwich beams with various viscoelastic frequency dependent laws using the finite element based solution. Real and various complex eigenmodes approaches are investigated as Galerkin bases. Based on harmonic balance method, simplified and general approaches are developed for nonlinear vibration analysis. Analytical frequency-amplitude and phase-amplitude relationships are elaborated based on the numerically computed complex eigenmodes. The equivalent loss factors and frequencies as well as the forced harmonic response and phase curves are performed for sandwich beams with various boundary conditions and frequency dependent viscoelastic laws.     

Nonparametric identification of nonlinear dynamic systems using a synchronisation-based method

The present study proposes an identification method for highly nonlinear mechanical systems that does not require a priori knowledge of the underlying nonlinearities to reconstruct arbitrary restoring force surfaces between degrees of freedom. This approach is based on the master–slave synchronisation between a dynamic model of the system as the slave and the real system as the master using measurements of the latter. As the model synchronises to the measurements, it becomes an observer of the real system. The optimal observer algorithm in a least-squares sense is given by the Kalman filter. Using the well-known state augmentation technique, the Kalman filter can be turned into a dual state and parameter estimator to identify parameters of a priori characterised nonlinearities. The paper proposes an extension of this technique towards nonparametric identification. A general system model is introduced by describing the restoring forces as bilateral spring-dampers with time-variant coefficients, which are estimated as augmented states. The estimation procedure is followed by an a posteriori statistical analysis to reconstruct noise-free restoring force characteristics using the estimated states and their estimated variances. Observability is provided using only one measured mechanical quantity per degree of freedom, which makes this approach less demanding in the number of necessary measurement signals compared with truly nonparametric solutions, which typically require displacement, velocity and acceleration signals. Additionally, due to the statistical rigour of the procedure, it successfully addresses signals corrupted by significant measurement noise. In the present paper, the method is described in detail, which is followed by numerical examples of one degree of freedom (1DoF) and 2DoF mechanical systems with strong nonlinearities of vibro-impact type to demonstrate the effectiveness of the proposed technique.