On the Relationship Between Ultrasonic and Micro-Structural Properties of Imperfect Interfaces in Layered Solids

The interaction of ultrasonic waves with interfaces formed by two non-conforming, rough surfaces in contact has been the subject of numerous investigations [1–10]. The motivations behind these studies have been various: from the assessment of the real area of contact between two rough surfaces [1], to the modeling of crack closure near the tip of a fatigue crack [4]; from the identification of the nature of interfacial imperfections in kissing and partial bonds [6], to the generation of ultrasonic waves [8]. In most of these studies, the characterization of the interfacial properties has been attempted by studying the reflection of longitudinal and shears waves at normal incidence. Only recently, the problem concerning the interaction of ultrasonic waves with realistic complex systems such as that formed by two neighboring imperfect interfaces has been addressed. Lavrentyev and Rokhlin [9, 10] used ultrasonic spectroscopy to evaluate the interfacial conditions from the spectra of longitudinal and shear waves reflected normally from the interfaces

Denture base materials - what's new?

Adhesive joining of materials has found widespread use in industry because of the simplicity and versatility of the process. However, adhesive applications in critical structural joints are still limited by the absence of reliable, rapid industrial NDE methods. Weak bonds remain hidden from conventional inspection methods capable of detecting only gross defects such as voids and open delamination. Weak bonds can exhibit substantially reduced strength without apparent defects

Role of HIF-1 in physiological adaptation of the carotid body during chronic hypoxia

Ultrasonic spectroscopy has been widely used for characterization of thin layered structures. Most previous studies [1]–[12] have dealt mainly with analysis of the ultrasonic reflection or transmission spectra and the effect of bonding interfaces. More recently the inverse problem for interphase layer property determination from ultrasonic measurements has been addressed. Kinra and co-authors [6],[9] use normally incident ultrasonic waves for determination of the longitudinal properties of the layer. In this case the elastic modulus, thickness and density are coupled and cannot be simultaneously recovered. The method for simultaneous determination of layer thickness, density, longitudinal and shear moduli and wave attenuations has been described in [13]. A thin layer between two thick substrates(Fig. la) was considered. Experimental data at two angles (normal and one oblique) was used for reconstruction

Phase Correction for Ultrasonic Bulk Wave Measurements of Elastic Constants in Anisotropic Materials

When an ultrasonic wave is incident on a water/solid interface generally three waves are excited in the solid: one longitudinal and two shear. The complex amplitudes of the transmitted waves depend on the material properties and the angle of incidence. At incident angles higher than the first critical angle an evanescent longitudinal wave is excited near the surface. To satisfy the boundary conditions the imaginary parts of the shear wave amplitudes become non-zero. This implies that the shear waves experience a phase shift at the water/solid interface at incident angles higher than the first critical

Bidirectional transport of cholesterol between gallbladder epithelial cells and model bile

Lipids in hepatic bile may be modified by the gallbladder epithelium. The purpose of this study was to demonstrate a bidirectional exchange of cholesterol between biliary lipid carriers and gallbladder epithelial cells and to determine the factors regulating this cholesterol transfer. (Gallbladder epithelial cells were cultured to confluent monolayers, their membranes were labeled with endogenously synthesized [14C]cholesterol, and the cells were incubated with model bile introduced into the apical membrane compartment. Similarly, model bile with different lipid composition containing [3H]cholesterol was incubated with the unlabeled monolayers. We found that cholesterol in the apical membrane bilayer of the epithelial cells exchanged readily with that in bile, but only in the presence of bile salts. The rate of exchange is dependent on the concentration and species of bile salts. The net gain of cholesterol (absorption) or net loss of cholesterol (cytotoxicity) exhibited by the epithelial cells was regulated by the thermodynamic stability of cholesterol and the detergent effect of mixed micelles in bile. It is also possible that the physicochemical composition of lipids in bile may modify the cellular function of the gallbladder epithelium.link_to_subscribed_fulltex