6 research outputs found
Influence of the materials magnetic state on the accurate determination of the magnetocaloric effect
No full textIn this paper, we report a detailed study of the magnetocaloric effect (MCE) in different first order magnetic transition (FOMT) materials with different situation of the magnetic state (magnetic order). For this purpose, R-Co2, MnAs based compounds were considered in this study. The MCE is discussed in terms of Maxwell relation (MR) and Clausius-Clapeyron (C-C) equation. The deviation observed between both methods is discussed and analyzed. On the other hand, practically all the reported data of the MCE in the literature are associated to the applied external magnetic field and have not been corrected taking into account the demagnetization effect related to the materials shape. The obtained results demonstrate that this phenomenon can alter drastically the MCE values by cancelling out a large part of the external field, resulting in spurious values of the measured MCE. The effect of the demagnetization field on the magnetocaloric performances is also the subject of this paper
Enclosed Electronic System for Force Measurements in Knee Implants
No full textTotal knee arthroplasty is a widely performed surgical technique. Soft tissue force balancing during the operation relies strongly on the experience of the surgeon in equilibrating tension in the collateral ligaments. Little information on the forces in the implanted prosthesis is available during surgery and post-operative treatment. This paper presents the design, fabrication and testing of an instrumented insert performing force measurements in a knee prosthesis. The insert contains a closed structure composed of printed circuit boards and incorporates a microfabricated polyimide thin-film piezoresistive strain sensor for each condylar compartment. The sensor is tested in a mechanical knee simulator that mimics in-vivo conditions. For characterization purposes, static and dynamic load patterns are applied to the instrumented insert. Results show that the sensors are able to measure forces up to 1.5 times body weight with a sensitivity fitting the requirements for the proposed use. Dynamic testing of the insert shows a good tracking of slow and fast changing forces in the knee prosthesis by the sensors
Separation of blood microsamples by exploiting sedimentation at the microscale
No full textAbstract Microsample analysis is highly beneficial in blood-based testing where cutting-edge bioanalytical technologies enable the analysis of volumes down to a few tens of microliters. Despite the availability of analytical methods, the difficulty in obtaining high-quality and standardized microsamples at the point of collection remains a major limitation of the process. Here, we detail and model a blood separation principle which exploits discrete viscosity differences caused by blood particle sedimentation in a laminar flow. Based on this phenomenon, we developed a portable capillary-driven microfluidic device that separates blood microsamples collected from finger-pricks and delivers 2 µL of metered serum for bench-top analysis. Flow cytometric analysis demonstrated the high purity of generated microsamples. Proteomic and metabolomic analyses of the microsamples of 283 proteins and 1351 metabolite features was consistent with samples generated via a conventional centrifugation method. These results were confirmed by a clinical study scrutinising 8 blood markers in obese patients
Polymerization Shrinkage with Light-Initiated Dental Composites
No full textThe present work addressed the determination and visualization of the direction and extent of polymerization shrinkage in the light-initiated composite. Hypotheses about the light-cured composite contraction patterns are controversial. With high resolution µCT images, the displacement vector fields are examined and calculated two-dimensionally via an elastic registration algorithm using vector-spline regularization and three-dimensionally with a local rigid registration (block matching) following images segmentation (corresponding traceable fillers in composite). It appears that the light-initiated resin composites do not always shrink toward the light source. Two major contraction patterns were observed: either shrink toward the top-surface (free surface), or toward one side of the cavity wall, in which the bonding was stronger or remained intact. With the proposed methods, it is possible to describe the contraction patterns in great detail. We could demonstrate that the bonding quality to the tooth affects the material movement more than described so far. In addition, the geometry of the cavity also acts as a factor. The continuation of the studies into the interaction of tooth-adhesive-composite indicated the shortcomings and limitations of the current FEA simulation studies. This meant that the assumption of FEA, especially in adhesive systems (i.e., bonding situations and hybridizations), is too perfect and simplificative to interpret the real condition in clinical. The qualitative and quantitative analysis of the shrinkage vector field along with the µCT datasets supply more insight into the shrinkage behavior in real teeth with all their variations of the boundary conditions than with any currently available method. This new approach has the potential to reevaluate and hopefully unify all the currently available hypotheses concerning the extent and orientation of polymerization shrinkage
Separation of blood microsamples by exploiting sedimentation at the microscale
No full textMicrosample analysis is highly beneficial in blood-based testing where cutting-edge bioanalytical technologies enable the analysis of volumes down to a few tens of microliters. Despite the availability of analytical methods, the difficulty in obtaining high-quality and standardized microsamples at the point of collection remains a major limitation of the process. Here, we detail and model a blood separation principle which exploits discrete viscosity differences caused by blood particle sedimentation in a laminar flow. Based on this phenomenon, we developed a portable capillary-driven microfluidic device that separates blood microsamples collected from finger-pricks and delivers 2 µL of metered serum for bench-top analysis. Flow cytometric analysis demonstrated the high purity of generated microsamples. Proteomic and metabolomic analyses of the microsamples of 283 proteins and 1351 metabolite features was consistent with samples generated via a conventional centrifugation method. These results were confirmed by a clinical study scrutinising 8 blood markers in obese patients
Synthesis and evaluation of the morphology, structure and electrochemical parameters of a magnetocaloric material (MMC) manufactured by auto-combustion
No full textThe magnetocaloric effect (EMC) is defined as the heating or cooling of magnetic material when the applied magnetic field changes. Various types and families of magnetocaloric materials (MMC) have been developed around the theme of EMC, within which are ceramic magnetocaloric materials (MMCC), and within these, lanthanum manganites. The last one has become a focus of research interest, due to the good properties that have been obtained for technological applications in the area of solid state refrigeration. In studies on magnetic refrigeration, a point that must be taken into account; but that is poorly evaluated, is the interaction of the working fluid with the magnetocaloric material, that is, the chemical stability and degradation of the material when exposed to the corrosive/erosive action of the working fluid. The manganites synthesized in this work, have the general formula La0.7Ca0.3Mn1-xNixO3 (x = 0; 0,02; 0,07; 0,1), which were made by solution combustion method. Morphological and structural characterization was performed by Field Emission Scanning Electron Microscopy (FE-SEM) and X-ray diffraction, respectively. Electrochemical behavior was evaluated by Electrochemical Impedance Spectroscopy and Potentiodynamic Polarization curves in a 3.5% NaCl solution. The electrochemical results indicated that the Ecorr values were 2; 87; 79 and 88 mV and for the icorr were 0,78; 0,55; 0,48 and 0,39 µA/cm2 for x = 0; 0.02; 0.07 and 0.1, indicating that doping with nickel could improve the electrochemical resistance of the material. On the other hand, the possible mechanism of degradation of the MMC is the dissolution, evidenced in the overpotential curves, the SEM micrographs and in the color change observed in the electrolyte at the end of the polarization tests.El efecto magnetocalórico (EMC) consiste en el cambio de temperatura que experimenta un material magnético cuando éste es expuesto a un campo magnético externo variable. Alrededor de la temática del EMC se han desarrollado varios tipos y familias de materiales magnetocalóricos (MMC), dentro de los cuales se encuentran los materiales magnetocalóricos cerámicos (MMCC), y dentro de éstos, las manganitas de lantano. Estas últimas se han convertido en foco de interés investigativo, debido a las buenas propiedades que se han obtenido para aplicaciones tecnológicas en el área de la refrigeración en estado sólido. En estudios sobre refrigeración magnética, un punto que debe tenerse en cuenta; pero que ha sido poco evaluado, es la interacción entre el MMC y el fluido en el que estará inmerso, es decir, la estabilidad química y la degradación del material cuando se expone a la acción oxidante/corrosiva/erosiva del fluido de trabajo. Las manganitas sintetizadas en el presente trabajo, tienen la fórmula general La0.7Ca0.3Mn1-xNixO3 (x = 0; 0,02; 0,07; 0,1), las cuales fueron fabricadas por autocombustión. Al MMC obtenido se le realizó una caracterización morfológica y estructural mediante microscopía electrónica de barrido de emisión de campo y difracción de rayos X, respectivamente. El comportamiento electroquímico del material en estudio se evaluó mediante espectroscopía de impedancia electroquímica y curvas de polarización potenciodinámicas en una solución de NaCl al 3,5%. Los resultados electroquímicos mostraron que los valores de Ecorr fueron de 2; 87; 79 y 88 mV y los de icorr de 0,78; 0,55; 0,48 y 0,39 µA/cm2 para x = 0; 0,02; 0,07 y 0,1, respectivamente, indicando que el dopaje con níquel podría mejorar la resistencia electroquímica del material. Por otro lado, el posible mecanismo de degradación identificado del MMC es la disolución, evidenciado en las curvas de sobrepotencial, las micrografías SEM y en el cambio de coloración observado en el electrolito al finalizar los ensayos de polarización. (texto tomado de la fuente)MaestríaMagíster en Ingeniería – Materiales y Proceso
