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991.
We report five experiments in which we investigated the effects of "feedback signals" on the pattern of hypoalgesia produced by inescapable shocks. A 5-s lights-out stimulus coincident with shock termination had no effect on the naltrexone-insensitive (nonopioid) hypoalgesia, which occurred after 10 inescapable shocks, but completely blocked the naltrexone-sensitive (opioid) hypoalgesia, which followed 100 inescapable shocks. The stimulus prevented the development of the opioid hypoalgesia rather than merely masking its measurement. This effect did not depend on the use of lights-out as the stimulus but did depend on the temporal relation between the stimulus and shock. Stimuli immediately preceding or simultaneous with shock had no effect. Surprisingly, stimuli randomly related to shock also blocked the opioid hypoalgesia. Simultaneous measurement of both hypoalgesia and fear conditioned to contextual cues revealed that the level of fear did not predict the blockade of hypoalgesia. Different backward groups received different temporal gaps between shock termination and the signal. An interval between 2.5 s and 7.5 s eliminated the effect of the signal on fear, but 12.5–27.5 s were required to eliminate the effect of the signal on hypoalgesia. The opioid hypoalgesia blocking power of the random stimulus was entirely attributable to those stimuli occurring within 15 s of the termination of the preceding shock. The implications of these results for the explanation of stimulus feedback effects and for stress-induced analgesia are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
992.
993.
Francesco Calise Massimo Dentice d’Accadia Giulio Restuccia 《International Journal of Hydrogen Energy》2007
This paper presents a very detailed finite volume axial-symmetric model of a tubular internal reforming solid oxide fuel cells (SOFCs), in which the effects of heat/mass transfer and chemical/electrochemical reactions are included. The model allows one to predict the performance of a single SOFC tube once a series of design and operative parameters are fixed, but also to investigate the source and localization of inefficiency. To this scope, an exergy analysis was implemented. 相似文献
994.
Three-dimensional (3D) X-ray imaging methods have advanced tremendously during recent years. Traditional tomography uses absorption as the contrast mechanism, but for many purposes its sensitivity is limited. The introduction of diffraction, small-angle scattering, refraction, and phase contrasts has increased the sensitivity, especially in materials composed of light elements (for example, carbon and oxygen). X-ray spectroscopy, in principle, offers information on element composition and chemical environment. However, its application in 3D imaging over macroscopic length scales has not been possible for light elements. Here we introduce a new hard-X-ray spectroscopic tomography with a unique sensitivity to light elements. In this method, dark-field section images are obtained directly without any reconstruction algorithms. We apply the method to acquire the 3D structure and map the chemical bonding in selected samples relevant to materials science. The novel aspects make this technique a powerful new imaging tool, with an inherent access to the molecular-level chemical environment. 相似文献
995.
996.
Anne-Kathrin Maier Laura Dezmirean Julia Will Peter Greil 《Journal of Materials Science》2011,46(9):2947-2954
Three-dimensional indirect printing of flash-setting calcium aluminate cement (CAC) was investigated. Upon water injection
into a biphasic mixture of tricalcium aluminate (3CaO·Al2O3) and dodecacalcium heptaaluminate (12CaO·7Al2O3) (phase ratio 0.56/0.44) initially a gel formed acting as a bonding phase which stabilizes the printed object geometry. Post-exposure
in water finally resulted in the formation of 2CaO·Al2O3·8H2O and 4CaO·Al2O3·19H2O reaction phases as confirmed by SEM, X-ray diffraction, and FTIR analyses. Reduction of porosity by volume expansion upon
hydrolysis reaction from 50% after printing to 20% after post-treatment gave rise for an increase of compressive strength
from 5 to 20 MPa, respectively. A bone regenerating scaffold for a micro-vascular loop model was fabricated by 3D printing
and hydraulic reaction bonding to demonstrate the potential of using flash-setting calcium aluminate cement powder for biomedical
ceramic applications. 相似文献
997.
Benenti G Casati G 《Philosophical transactions. Series A, Mathematical, physical, and engineering sciences》2011,369(1935):466-481
Dynamical nonlinear systems provide a new approach to the old problem of increasing the efficiency of thermoelectric machines. In this review, we discuss stylized models of classical dynamics, including non-interacting complex molecules in an ergodic billiard, a disordered hard-point gas and an abstract thermoelectric machine. The main focus will be on the physical mechanisms, unveiled by these dynamical models, which lead to high thermoelectric efficiency approaching the Carnot limit. 相似文献
998.
Barbani N Rosellini E Cristallini C Guerra GD Krajewski A Mazzocchi M 《Journal of materials science. Materials in medicine》2011,22(3):637-646
The interactions of Type I acid soluble collagen (Col) with both carbonate-free hydroxyapatite (HA1100) and carbonate-rich one (CHA) were investigated. The aim was to ascertain whether the increase of bone CO3
2− with ageing could relate to the disease known as osteoporosis. HA1100-Col and CHA-Col composites with various ratios were prepared and examined. Scanning electron microscopy and differential
scanning calorimetry showed a stronger adhesion of the Col matrix to the granules of HA1100 than to those of CHA. FT-IR spectroscopy showed that with HA1100 both multiple hydrogen bonds of Col peptide –NH groups with HA PO4
3−, and electrochemical interactions between Col peptide –C=O groups and HA Ca2+ were present. In the presence of CO3
2−, the interactions between –NH and phosphate were diminished, and Ca2+ interacted more strongly with CO3
2− than with peptide –C=O, so causing a separation between the two components of the bone extra-cellular matrix. The results
obtained strengthen the hypothesis that the substitution of PO4
3− ions by CO3
2− ions in the HA lattice might be a significant component of osteoporosis, although further investigation is needed. 相似文献
999.
G. PurcekG.G. Yapici I. Karaman H.J. Maier 《Materials Science and Engineering: A》2011,528(6):2303-2308
Two grades of commercial purity (CP) titanium (grades 2 and 4) were processed using equal-channel angular extrusion (ECAE) at 300 °C and 450 °C, respectively. The processing temperatures were the minimum temperatures at which eight pass ECAE could be performed without any shear-localization. The coarse-grained (CG) microstructures of as-received grade-2 and grade-4 CP-Ti, with average grain sizes of 110 μm and 70 μm, respectively, were refined down to sub-micron levels with a mean grain size of about 300 nm for both grades after 8 ECAE passes. The ultrafine-grained (UFG) microstructures led to substantial enhancement in strength for both grades. The grade-2 sample showed a more than two fold increase in yield strength (σy), from 307 MPa for the as-received one to about 620 MPa for the processed samples. The grade-4 CP-Ti exhibited a relatively smaller increase in strength due to the higher processing temperature, and it showed about 50% increase in σy after eight pass ECAE, from 531 to 758 MPa. These strength levels were obtained with high ductility levels of 21% and 25% for UFG grade-2 and grade-4 Ti, respectively. These improvements in mechanical properties are attributed to the substantially refined grain size and increased dislocation density. Grade-4 Ti is stronger than grade-2 because of the higher oxygen content. The higher ductility and significantly higher strain hardening capability of UFG grade-4 Ti, in spite of the similar grain size and microstructure with UFG grade-2 Ti, is also due to the higher impurity content, probably resulting in a higher dislocation storage capability during room temperature deformation, and thus, higher strain hardening capacity. Such properties make UFG grade-4 Ti comparable to the commercial Ti-6Al-4V alloy for biomedical applications without negative effects of the alloying elements on biocompatibility. 相似文献
1000.
Hervé Saint-Jalmes Pierre-Antoine Eliat Johanne Bezy-Wendling Alejandro Bordelois Giulio Gambarota 《Magma (New York, N.Y.)》2014,27(5):419-424