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排序方式: 共有1866条查询结果,搜索用时 15 毫秒
91.
Francesca Palombo C. Peter Winlove Ryan S. Edginton Ellen Green Nick Stone Silvia Caponi Marco Madami Daniele Fioretto 《Journal of the Royal Society Interface》2014,11(101)
Brillouin light scattering (BLS) spectroscopy is a technique that is able to detect thermally excited phonons within a material. The speed of propagation of these phonons can be determined from the magnitude of the Brillouin frequency shift between incident and scattered light, thereby providing a measure of the mechanical properties of the material in the gigahertz range. The mechanical properties of the extracellular matrices of biological tissues and their constituent biopolymers are important for normal tissue function and disturbances in these properties are widely implicated in disease. BLS offers the prospect of measuring mechanical properties on a microscopic scale in living tissues, thereby providing insights into structure–function relationships under normal and pathological conditions. In this study, we investigated BLS in collagen and elastin—the fibrous proteins of the extracellular matrix (ECM). Measurements were made on type I collagen in rat tail tendon, type II collagen in articular cartilage and nuchal ligament elastin. The dependence of the BLS spectrum on fibre orientation was investigated in a backscattering geometry using a reflective substrate. Two peaks, a bulk mode arising from phonon propagation along a quasi-radial direction to the fibre axis and a mode parallel to the surface, depending on sample orientation relative to the fibre axis, could be distinguished. The latter peak was fitted to a model of wave propagation through a hexagonally symmetric elastic solid, and the five components of the elasticity tensor were combined to give axial and transverse Young''s, shear and bulk moduli of the fibres. These were 10.2, 8.3, 3.2 and 10.9 GPa, and 6.1, 5.3, 1.9 and 8 GPa for dehydrated type I collagen and elastin, respectively. The former values are close to those previously reported. A microfocused BLS approach was also applied providing selection of single fibres. The moduli of collagen and elastin are much higher than those measured at lower frequency using macroscopic strains, and the difference between them is much less. We therefore believe, like previous investigators, that molecular-scale viscoelastic effects are responsible for the frequency dependence of the fibre biomechanics. Combining BLS with larger-scale mechanical testing methods therefore should, in the future, provide a means of following the evolution of mechanical properties in the formation of the complex structures found in the ECM. 相似文献
92.
93.
Daniele Lettieri-BarbatoDebora Villaño Bram BeheydtFiorella Guadagni Isabel TroghMauro Serafini 《Food chemistry》2012,132(3):1305-1310
The association between in vitro antioxidant capacity of dark chocolates with different cocoa percentage and the in vivo response on antioxidant status was investigated. In a randomized crossover design, 15 healthy volunteer consumed 100 g of high antioxidants dark chocolate (HADC) or dark chocolate (DC). In vitro, HADC displayed a higher Total Antioxidant Capacity (TAC) than DC. In vivo, plasma TAC significantly peaked 2 h after ingestion of both chocolates. TAC levels went back to zero 5 h after DC ingestion whilst levels remained significantly higher for HADC. HADC induced a significantly higher urinary TAC in the 5-12 h interval time than DC. No change was detected in urinary excretion of F2-isoprostanes. Plasma thiols and triacylglycerol (TG) levels significantly increased for both chocolate with a peak at 2 h remaining significantly higher for DC after 5 h respect to HADC. Results provide evidence of a direct association between antioxidant content of chocolate and the extent of in vivo response on plasma antioxidant capacity. 相似文献
94.
Daniele Passeri Ugo Sassi Andrea Bettucci Emanuela Tamburri Francesco Toschi Silvia Orlanducci Maria Letizia Terranova Marco Rossi 《Advanced functional materials》2012,22(14):2956-2963
The thermoacoustic effect of isolated single‐wall carbon nanotubes aligned between electrodes is experimentally observed for the first time by imaging the emitted acoustic wave using an atomic force microscopy‐based technique specifically developed for the task. The capability of such a technique for single‐point thermoacoustic measurements is first verified on carbon nanotubes layers with two electrodes for injecting alternate electric current. The technique is then demonstrated to allow the acquisition, simultaneously with the topography, of images reflecting the pressure of the acoustic wave at fixed distance from the sample. Such a capability is used to collect images reflecting the amplitude of acoustic waves generated by isolated nanotubes and nanotube bundles by the thermoacoustic effect. 相似文献
95.
Daniele Bortoluzzi Claudio CinquemaniElisa Torresani Sara Spilimbergo 《The Journal of Supercritical Fluids》2011,56(1):6-13
The main aim of this work is to investigate the effect of CO2 and N2O under pressure in aqueous solution - both on-line and in real-time. In particular, the paper presents the kinetics of pH behaviour of either slightly buffered minimal medium (MM) or non-buffered solution (Ringer solution) during high-pressure treatment at 5, 30 and 60 bar at 25 °C.An innovative spectrophotometric approach has been developed: an optical fiber conducted the inlet signal of a light source into the high-pressure reactor, while another fiber conducted the outlet signal to a spectrometer, thus, obtaining measurements on-line and real-time.CO2 treatment resulted in a pH decrease down to 3.0 in Ringer solution with the equilibrium being reached after 800 s, while the slightly buffered MM allows only for a decrease down to 4.5 with equilibrium being reached after slightly more than 40 s at 60 bar.N2O treatment, as expected, did not lead to any acidification of the treated medium at any conditions tested.Furthermore, a mathematical model describing both the solubilization kinetics of CO2 and in aqueous solution and the decrease of extracellular pH has been implemented. This model may easily be applied to different reactor configurations. The theoretical results and the goodness of the fit has been verified using the experimental results showing a good accuracy of the complex phenomena with a simplification that is of vital relevance for technical processes. 相似文献
96.
John Colombo 《Lipids》2001,36(9):919-926
The assessment of cognitive function in early life has recently become an issue for consideration in long-chain polyunsaturated
fatty acid (LC-PUFA) supplementation studies. This article reviews the various means by which such assessment has been done
in past LC-PUFA supplementation studies and provides some background on recent advances in the measurement of infant cognition
that may need to be considered when planning or designing future supplementation studies. These include (i) consideration
of the specificity of LC-PUFA effects on cognition, (ii) inclusion of multiple tasks or levels of measurement as outcome measures,
and (iii) a stronger emphasis on developmental processes in the design of such studies. 相似文献
97.
Studies of spatial representation generally focus on flat environments and visual input. However, the world is not flat, and slopes are part of most natural environments. In a series of 4 experiments, we examined whether humans can use a slope as a source of allocentric, directional information for reorientation. A target was hidden in a corner of a square, featureless enclosure tilted at a 5° angle. Finding it required using the vestibular, kinesthetic, and visual cues associated with the slope gradient. In Experiment 1, the overall sample performed above chance, showing that slope is sufficient for reorientation in a real environment. However, a sex difference emerged; men outperformed women by 1.4 SDs because they were more likely to use a slope-based strategy. In Experiment 2, attention was drawn to the slope, and participants were prompted to rely on it to solve the task; however, men still outperformed women, indicating a greater ability to use slope. In Experiment 3, we excluded the possibility that women's disadvantage was due to wearing heeled footwear. In Experiment 4, women required more time than men to identify the uphill direction of the slope gradient; this suggests that, in a bottom-up fashion, a perceptual or attentional difficulty underlies women's disadvantage in the ability to use slope and their decreased reliance on this cue. Overall, a bi-coordinate representation was used to find the goal: The target was encoded primarily with respect to the vertical axis and secondarily with respect to the orthogonal axis of the slope. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
98.
99.
Mauro Marangoni Lukas Arnout Lieven Machiels Lieven Pandelaers Enrico Bernardo Paolo Colombo Yiannis Pontikes 《Journal of the American Ceramic Society》2016,99(6):1985-1991
The present paper deals with the synthesis of porous, sintered glass‐ceramics obtained at temperatures below 1150°C, originating from inorganic polymers based on fayalite slag. Firing led to the evaporation of water, dehydroxylation, and oxidation of Fe2+ above 345°C. For heating >700°C, the Si–O stretching band shifted from the 1160 and 750 cm?1 to the 1255 and 830 cm?1 region, due to a structural reorganization of the amorphous phase, whereas Fe–O bands appeared at 550 cm?1. The final microstructure consisted predominantly of an amorphous phase, hematite, and franklinite. The open porosity and compressive strength decreased and increased, respectively, as the firing temperature increased. The final values suggest properties comparable to that of structural lightweight concrete, still, the materials synthesized herein, are lighter, and made primarily from secondary resources. 相似文献
100.
Direct Ink Writing of a Preceramic Polymer and Fillers to Produce Hardystonite (Ca2ZnSi2O7) Bioceramic Scaffolds 下载免费PDF全文
Andrea Zocca Giorgia Franchin Hamada Elsayed Emilia Gioffredi Enrico Bernardo Paolo Colombo 《Journal of the American Ceramic Society》2016,99(6):1960-1967
The direct ink writing of an ink composed of a preceramic polymer and fillers was used to produce hardystonite (Ca2ZnSi2O7) bioceramic scaffolds. Suitable formulations were developed for the extrusion of fine filaments (350 μm diameter) through a nozzle. The preceramic polymer was employed with the double purpose of contributing to the rheology of the ink by increasing its viscosity and of forming the hardystonite phase upon heat treatment by reacting with the fillers. A control of the rheology is essential when spanning features have to be produced, and therefore the main rheological characteristics of the inks were measured (flow curves, dynamic oscillation tests, viscosity recovery tests) and compared to models reported in the literature. Highly porous scaffolds (up to 80% total porosity) were produced and heat treated in air or in nitrogen atmosphere. The influence of the heat‐treatment atmosphere on the morphology, crystalline phase assemblage, and compressive strength of the scaffolds was investigated. 相似文献