Inverse attenuation filtering

Inverse-[Formula: see text] filtering is an important seismic-processing operation often used to correct for attenuation and dispersion effects and increase the resolution of reflection records. However, it is important to realize that the [Formula: see text] is an apparent (phenomenological) attribute of the propagating wavefield and not guaranteed to be a material property. By recognizing the apparent character of the [Formula: see text], the attenuation-correction procedure can be significantly extended and generalized. Our approach consists of forward modeling the propagating source waveform by using multiple physical laws followed by multiple types of inverse filtering. The modeling and inverse-filtering algorithms are selectable according to the geology of the study area, data, and goals of processing, which may include reduction of attenuation effects or more general enhancements of reflectivity images. Apparent [Formula: see text] models are inherently smooth in space, which facilitates efficient use of time-variant deconvolution implemented by using overlapping tapered time windows. When using conventional [Formula: see text] models and frequency-domain deconvolution, this procedure contains all existing types of inverse-[Formula: see text] filtering. However, many more realistic forward modeling approaches can (and should) be used depending on the specific subsurface environments, such as wavefront focusing and defocusing, scattering, solid viscosity, or internal friction caused by pore-fluid flows. In general, velocity-dispersion relations cannot be inferred from the frequency-dependent [Formula: see text] and need to be considered separately. It is more precise to view frequency-dependent velocity dispersion and [Formula: see text] as concomitant and arising from a common physical mechanism of wave propagation. Time-domain deconvolution, such as an iterative method well-known in earthquake seismology, offers significant improvements in attenuation-corrected images. The approaches are illustrated on a real reflection data set by using several attenuation laws and types of deconvolution.

Dynamics of Wave Propagation Across Solid–Fluid Movable Interface in Fluid–Structure Interaction

A theoretical model for wave propagation across solid–fluid interfaces with fluid–structure interaction (FSI) was explored by conducting experiments. Although many studies have been conducted on solid–solid and fluid–fluid interfaces, the mechanism of wave propagation across solid–fluid interfaces has not been well examined. Consequently, our aim is to clarify the mechanism of wave propagation across a solid–fluid interface with the movement of the interface and develop a theoretical model to explain this phenomenon. In the experiments conducted, a free-falling steel projectile was used to impact a solid buffer placed immediately above the surface of water within a polycarbonate (PC) tube. Two different buffers (aluminum and polycarbonate) were used to examine the relation between wave propagation across the interface of the buffer and water and the interface movement. With the experimental results, we confirmed that the peak value of the interface pressure can be predicted via acoustic theory based on the assumption that projectile and buffer behave as an elastic body with local deformation by wave propagation. On the other hand, it was revealed that the average profile of the interface pressure can be predicted with the momentum conservation between the projectile and the buffer assumed to be rigid and momentum increase of fluid. The momentum transmitted to the fluid gradually increases as the wave propagates and causes a gradual decrease in the interface pressure. The amount of momentum was estimated via the wave speed in the fluid-filled tube by taking into account the coupling of the fluid and the tube.

Wave Propagation Across Solid-Fluid Interface With Fluid-Structure Interaction

This paper reports on investigations conducted with a view towards developing a theoretical model for wave propagation across solid-fluid interfaces with fluid-structure interaction. Although many studies have been conducted, the mechanism of wave propagation close to the solid-fluid interface remains unclear. Consequently, our aim is to clarify the mechanism of wave propagation across the solid-fluid interface with fluid-structure interaction and develop a theoretical model to explain this phenomenon. In experiments conducted to develop the theory, a free-falling steel projectile is used to impact the top of a solid buffer placed immediately above the surface of water within a polycarbonate tube. The stress waves created as a result of the impact of the projectile propagated through the buffer and reached the interface of the buffer and water (fluid) in the tube. Two different buffers (polycarbonate and aluminum) were used to examine the interaction effects. The results of the experiments indicated that the amplitude of the interface pressure increased in accordance with the characteristic impedance of the solid medium. This cannot be explained by the classical theory of wave reflection and transmission. Thus, it is clear that on the solid-fluid interface with fluid-structure interaction, classical theories alone cannot precisely predict the generated pressure.

Speeding Up Fluid-Structure Interaction Simulation of the Blood Flow in a Flexible Artery Using Sub-Cycling: Stability and Accuracy

In the cardiovascular system, the distensibility of the blood vessels is the driving mechanism of wave propagation. As the blood flow interacts mechanically with the flexible vessel walls, this phenomenon gives rise to complex fluid-structure interaction (FSI) problems. Several studies comparing rigid wall with FSI simulations in settings with large deformations demonstrate the importance of including the flexible wall modeling, in particular with respect to the simulation of wall shear stress. As both the equations governing the flow and the arterial deformation (and their interaction) need to be solved, FSI simulations are characterized by a high computational cost. To make them applicable to a broader range of cardiovascular problems, efforts to reduce the calculation time (such as the use of so-called ‘sub-cycling’) should be made.

Spatial characteristics to calcium signalling; the calcium wave as a basic unit in plant cell calcium signalling

Many signals that modify plant cell growth and development initiate changes in cytoplasmic Ca 2+ . The subsequent movement of Ca 2+ in the cytoplasm is thought to take place via waves of free Ca 2+ . These waves may be initiated at defined regions of the cell and movement requires release from a reticulated endoplasmic reticulum and the vacuole. The mechanism of wave propagation is outlined and the possible basis of repetitive reticulum wave formation, Ca 2+ oscillations and capacitative Ca 2+ signalling is discussed. Evidence for the presence of Ca 2+ waves in plant cells is outlined, and from studies on raphides it is suggested that the capabilities for capacitative Ca 2+ signalling are also present. The paper finishes with an outline of the possible interrelation between Ca 2+ waves and organelles and describes the intercellular movement of Ca 2+ waves and the relevance of such information communication to plant development.