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Experimental study and modelling the evolution of viscoelastic hysteresis loop at different frequencies in myocardial tissue

Smoluk A., Smoluk L., Lisin R., Protsenko Y.

Acta of Bioengineering and Biomechanics

2017

Vol. 19, no. 3

11--17

Our work involved experimental study of the influence of actomyosin complexes and the main structural components of the myocardial tissue – connective tissue collagen framework and cardiomyocytes – on the characteristics of viscoelastic hysteresis at different frequencies. In this paper a new method was introduced for the analysis of the viscoelastic characteristics of the force hysteresis in the isolated myocardial preparation for the assessment of mechanical energy expenditure in the tension-compression cycle. We established that basic myocardial structures have an impact on the to the characteristics of the viscoelastic hysteresis in many ways. It was shown that in rat’s myocardium cardiomyocytes one main factor that define the stiffness and viscosity of the myocardium in the physiological range of deformations, while binding of calcium ions with EGTA and calcium removal of sarcoplasmic reticulum with caffeine reduces viscoelasticity by ~30% and collagen framework is responsible for about 10% of viscoelasticity. It was revealed that in the physiological range of the hysteresis frequencies (3 to 7 Hz) expenditure of mechanical energy per unit of time increases linearly with increasing frequency. We proposed the structural and functional model that adequately describes the characteristics of the viscoelastic hysteresis in myocardial preparation in the range of strains and frequencies being under study.

Fluid identification based on P-wave anisotropy dispersion gradient inversion for fractured reservoirs

Zhang J. W., Huang H. D., Zhu B. H., Liao W.

Acta Geophysica

2017

Vol. 65, no. 5

1081--1093

Fluid identification in fractured reservoirs is a challenging issue and has drawn increasing attentions. As aligned fractures in subsurface formations can induce anisotropy, we must choose parameters independent with azimuths to characterize fractures and fluid effects such as anisotropy parameters for fractured reservoirs. Anisotropy is often frequency dependent due to wave-induced fluid flow between pores and fractures. This property is conducive for identifying fluid type using azimuthal seismic data in fractured reservoirs. Through the numerical simulation based on Chapman model, we choose the P-wave anisotropy parameter dispersion gradient (PADG) as the new fluid factor. PADG is dependent both on average fracture radius and fluid type but independent on azimuths. When the aligned fractures in the reservoir are meter-scaled, gas-bearing layer could be accurately identified using PADG attribute. The reflection coefficient formula for horizontal transverse isotropy media by Rüger is reformulated and simplified according to frequency and the target function for inverting PADG based on frequency-dependent amplitude versus azimuth is derived. A spectral decomposition method combining Orthogonal Matching Pursuit and Wigner–Ville distribution is used to prepare the frequency-division data. Through application to synthetic data and real seismic data, the results suggest that the method is useful for gas identification in reservoirs with meter-scaled fractures using high-qualified seismic data.