1,720,997 research outputs found
Hydrostatic pressure and shear stress affect endothelin-1 and nitric oxide release by endothelial cells in bioreactors
No full textThere is plenty of experimental evidence to show that endothelial cells are sensitive to flow, but very little attention has been paid to fluid pressure or pressure gradients which are used to drive viscous flow. In fact there are two principal physical forces exerted on the blood vessel wall by the passage of intra-luminal blood: pressure and shear. In order to analyze their independent effects, these two stresses were applied to cultured cells by means of two different bioreactors: the pressure-controlled bioreactor (PCB) and the laminar flow bioreactor (LFB), in which controlled levels of pressure and shear stress can be respectively generated. Using the bioreactor systems, endothelin-1 and nitric oxide release from human umbilical vein endothelial cells (HUVEC) were measured in varying conditions of shear stress and pressure. As result, a decrease of endothelin-1 production from the cells cultured in both bioreactors, with respect to the controls, was observed, whereas nitric oxide synthesis was up-regulated only in the presence of shear stress but not modulated by hydrostatic pressure. These results show that the two hemodynamic forces acting on blood vessels affect endothelial cell function in different ways, and that both should be considered when planning in vitro experiments in the presence of flow. Understanding the individual and synergic effects of the two forces could provide important insights into physiological and pathological processes involved in vascular remodeling and adaptation
High frequency poroelastic waves in hydrogels
Full text linkIn this work a continuum model for high frequency poroelastic longitudinal waves in hydrogels is presented. A viscoelastic force describing the interaction between the polymer network and the bounded water present in such materials is introduced. The model is tested by means of ultrasound wave speed and attenuation measurements in polyvinylalcohol hydrogel samples. The theory and experiments show that ultrasound attenuation decreases linearly with the increase in the water volume fraction of the hydrogel. The introduction of the viscoelastic force between the bounded water and the polymer network leads to a bi-phasic theory, showing an ultrasonic fast wave attenuation that can vary as a function of the frequency with a non-integer exponent in agreement with the experimental data in literature. When tends to 1 100% of interstitial water due to the presence of bounded water in the hydrogel, the ultrasound phase velocity acquires higher value than that of pure water. The ultrasound speed gap at =1 is confirmed by the experimental results, showing that it increases in less cross-linked gel samples which own a higher concentration of bounded water
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Label-free detection of specific RNA sequences by a DNA-based CMOS BioMEMS
No full textIn this work we propose a resonant mass sensor based on a CMOS-compatible MEMS bulk technology, targeted at the label-free, selective detection of biomolecules. Both the MEMS fabrication phase and the bioactivation protocol were designed to ensure functionality of on-chip test electronic circuitry. Specifically, the bioactivation steps were performed with single drops of the reagents on the active part of the chip to minimize impact on the electronics and package. The CMOS compatibility of the final device is demonstrated by simultaneous operation of the MEMS resonator and the test electronics. The resonator mass sensitivity, determined by resonator loading with gold nanoparticles, compares favorably with those of QCMs and other MEMS resonant mass sensors. To validate the device operation as a biosensor, synthetic oligonucleotide sequences designed to bind to a specific human mRNA (involved in the synthesis of human methylguanine-DNA methyltransferase, a DNA repair protein) were used as probes and covalently bound to the resonator surface. The resonance frequency shift of different sensors at the same concentration of the analyte confirms the inverse dependence of the sensitivity on the mass of the resonator. © 2014 Springer International Publishing Switzerland
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Fluid dynamic simulation of a measurement chamber for electronic noses
No full textA fluid dynamic study of a sensor chamber used in a hit-commercial electronic nose is presented. In order to optimise the sensor signals in terms of stability, repeatability as well as amplitude and response time, the influence of many factors of the sampling device has to be kept under control. Concerning the characteristics of flow, the existence of a time-window where each sensor is exposed to a constant odour concentration has to be assured. This condition can be achieved by the proper dimensioning of the chamber volume and by other modifications to the inlet and outlet. The numerical analysis was performed by a CFD code which solves the Navier-Stokes equations for a dilatable fluid in 3D enclosures, discretised with finite volume elements. Two configurations were simulated: a basic case, referring to the conditions existing in the commercial device, and an optimised case. In each case, a static solution was calculated for the flow field and then the dynamic evolution of odour concentration was simulated by solving the transient transport equation of a tracer injected as a square pulse flow. Far from optimum conditions were found for the basic case; the improvement achieved through simple modifications in the geometry of the chamber for the optimised case was discussed
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