Analysis of the Dynamic Behavior of Magnetorheological Elastomer Composite: Elaboration and Identification of Rheological Properties

Silicon - The present work is devoted to experimental analysis of the magnetorheological elastomer composite behavior under dynamic loading. The elastomer is charged to 40% of ferromagnetic...     

Forced transverse vibration of composite sandwich beam with magnetorheological elastomer core

We studied, experimentally and numerically, the vibrational response of a magnetorheological elastomer sandwich beam, clampedfree, delimited by two skins aluminum 7075T6, first subjected to a variable magnetic field perpendicular to the skin of the beam, and second to a harmonic excitation by magnetic force applied at the free end. Our main objective was to predict the effect of the intensity of the current flowing through a coil on several dynamic factors. The maximum amplitude of resonance and the variation of the loss factor as a function of structural stiffness are adjusted simultaneously by the application of different magnetic fields. The results of both methods are compared.     

Biodegradable wound-closing devices for gastrointestinal interventions: Degradation performance of the magnesium tip

The aim of this study was to investigate the degradation performance of the magnesium tip of a biodegradable rivet intended for tissue joining and fixing via endoscopic surgery. The in vitro degradation performance was assessed by immersion tests in simulated gastric fluid. The influence of the chemical composition of the alloy, salt concentration, temperature and pH value was investigated. Among the parameters varied, the pH value exhibits the most significant influence on the degradation performance. It represents a potentially useful tool for controlling the tip degradation, allowing the greatest amount of flexibility during the surgical intervention. The biodegradable Mg alloy WZ21 is shown to be a suitable material for the short-term component (the tip) of the rivet. It allows precise tip fabrication with adequate sharpness and degrades homogeneously and sufficiently fast in simulated gastric fluid at low pH values. Due to a suitable surface-to-volume ratio and its rotationally symmetrical geometry, the Trocar tip design is considered the most promising tip shape among the various designs investigated. The results of this study confirm the feasibility of this new concept of completely degradable wound-closing devices and provide a solid basis for further product development.     

Experimental validation of a tissue-joining implant providing flexible adaptation to the thickness of the stomach wall

Endoscopy is gradually replacing open surgery in the gastrointestinal tract. Therefore, novel medical devices and instrumentation are required, such as flexible miniaturized mechanisms for tissue joining and manipulation. In this paper, an absorbable implant for the purpose of long-term tissue fixation is presented. An experimental validation of the implant design and functionality is introduced. The implant achieves tissue penetration and provides flexible adaptation according to the thickness of two stomach walls. This mechanism is easy as it is based on push-pull principle using unidirectional forces. The shape optimization of each implant part occurs by varying design-influencing factors. The load transmission on postmortem porcine tissue was measured in the frame of the experimental setup. The feasibility of the implant was tested, and the forces needed for the intended application quantified. The implant successfully achieves tissue penetration, load transmission, adjustment, and fixation. It is a new alternative to conventional tissue-joining mechanisms.     

Assessing Groundwater Geospatial Variation Using Microgravity Investigation in the Arid Riyadh Metropolitan Area,Saudi Arabia: a Case Study

A combination of relative microgravity measurements at ground surface, and depth to water and water table measurements from adjacent wells were used to estimate geospatial variation of groundwater. A highly accurate portable Grav-Map gravimeter was used for gravimetric measurements at locations nearby a 42 well water table monitoring program. To efficiently correlate the two data sets, wells were clustered into five groups by geological unit and water saturation. Microgravity data was processed, interpreted, and correlated with both the depths to groundwater and the water table levels. Regression analyses revealed a strong negative correlation for microgravity and depth to groundwater in all five clusters; correlation coefficients varied between 0.70 and 0.97, and measured 0.78 over the entire study area. Microgravity values increased as groundwater depth decreased, likely because rising groundwater fills voids and fractures within soil and rocks, increasing rock density and therefore relative gravity. To validate the correlation, we superimposed a map of depths to water on the first derivative of microgravity measurements. The shallowest groundwater depths were positively related to the zero first derivatives, having intersection areas within a 75 % significance interval. Negative first derivatives covered the rest of the study area, with relative gravity decreasing with increasing groundwater depth. This technique can precisely and efficiently determine changes in subsurface geology and geospatial changes in depths to the groundwater table. Distances between microgravity stations should be small, to better detect small changes in gravity values, reflecting density contrasts underground.