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31.
Cynn H Yoo CS Baer B Iota-Herbei V McMahan AK Nicol M Carlson S 《Physical review letters》2001,86(20):4552-4555
Angle-resolved x-ray diffraction patterns of Xe to 127 GPa indicate that the fcc-to-hcp transition occurs martensitically between 3 and 70 GPa in diamond-anvil cells without an intermediate phase. These data also reveal that the transition occurs by the introduction of stacking disorder in the fcc lattice at low pressure, which grows into hcp domains with increasing pressure. The small energy difference between the hcp and the fcc structures may allow the two phases to coexist over a wide pressure range. Evidence of similar stacking disorder and incipient growth of an hcp phase are also observed in solid Kr. 相似文献
32.
33.
Luis Esquivias Víctor Morales-Flórez María J. Mosquera Nicolás de la Rosa-Fox 《Journal of Sol-Gel Science and Technology》2008,47(2):194-202
Monolithic gels, prepared from different mixtures of colloidal silica in a sol solution containing tetraethoxysilane under
powerful ultrasonic agitation (sonosols), were compacted at an isostatic pressure of 390 MPa. Then N2 adsorption-desorption data were used to construct structural models of the gels using Monte-Carlo calculations on the basis
of random close-packing (RCP) premises. Structural information on these composites obtained before compaction indicates that
the characteristic uniform structure of silica colloid gel undergoes profound modification when it is mixed with silica sonogel.
From a structural point of view, the behaviour under compaction of the sonogel phase, which exhibits a significant degree
of microporosity, depends on the relative concentration of the colloidal phase. Two hierarchic levels of micropores were discerned.
After compression, the size of the elementary particles—and their aggregates—of the sonogel phase increases from 1.6 to 2.1 nm
radius when the colloidal phase content is increased from 30 to 82% by weight. For an intermediate content, 50% of the volume
reduction is caused by compression of the sonogel phase at the micropore level. 相似文献
34.
Nicolò Spampinato 《Annali di Matematica Pura ed Applicata》1935,14(1):305-325
Sunto Si studiano le superficie e le trasformazioni caratteristiche dell'S
4 complesso, immagini dei legami e delle trasformazioni su due variabili bicomplesse, ottenute con funzioni totalmente derivabili. 相似文献
35.
Cristian Rodrigo Muzzio Nicolás Gabriel Dini Adrián César Razzitte 《Physics and Chemistry of Liquids》2017,55(4):506-521
Highly concentrated electrolyte solutions were studied through a Monte Carlo-based simulator, developed to consider the water molecules not a homogeneous dielectric as usual, but as dipoles that can move and rotate within a 3D lattice. This approach allowed fast calculations of detailed interactions between the particles, which were described from mechanistic potentials including dipole–dipole, ion–dipole, ion–ion, and hydrogen bonding (HB) interactions. A good agreement was found between experimental data and simulated results. The study also provides new insights about the balance of the different interactions in systems with or without electrolytes, and the effects of the electrolytes addition on the original water structure. The proposed model was also compared with previous explicit models. 相似文献
36.
Neuman NI Perec M González PJ Passeggi MC Rizzi AC Brondino CD 《The journal of physical chemistry. A》2010,114(50):13069-13075
We report powder and single crystal EPR measurements of [Cu(tda)(phen)](2)·H(2)tda (tda = thiodiacetate, phen = phenanthroline) at 9.7 GHz. This compound consists of centrosymmetric copper(II) ion dimers, weakly ferromagnetically exchange-coupled (J = +3.2 cm(-1)), in which the dimeric units are linked by hydrophobic chemical paths involving the phen molecules. EPR revealed that the triplet spectra are collapsed by interdimeric exchange interactions mediated by that chemical path. Analysis and simulation of the single crystal EPR spectra were performed using Anderson's exchange narrowing model, together with statistical arguments. This approach allowed us to interpret the spectra modulated by the interdimeric interactions in situations of weak, intermediate, and strong exchange. We evaluated an interdimeric exchange constant J' = 0.0070(3) cm(-1), indicating that hydrophobic paths can transmit weak exchange interactions between centers at relatively long distances of the order of ~10 ?. 相似文献
37.
Keith M Kendrick Yang Zhan Hanno Fischer Alister U Nicol Xuejuan Zhang Jianfeng Feng 《BMC neuroscience》2011,12(1):1-23
Background
How oscillatory brain rhythms alone, or in combination, influence cortical information processing to support learning has yet to be fully established. Local field potential and multi-unit neuronal activity recordings were made from 64-electrode arrays in the inferotemporal cortex of conscious sheep during and after visual discrimination learning of face or object pairs. A neural network model has been developed to simulate and aid functional interpretation of learning-evoked changes.Results
Following learning the amplitude of theta (4-8 Hz), but not gamma (30-70 Hz) oscillations was increased, as was the ratio of theta to gamma. Over 75% of electrodes showed significant coupling between theta phase and gamma amplitude (theta-nested gamma). The strength of this coupling was also increased following learning and this was not simply a consequence of increased theta amplitude. Actual discrimination performance was significantly correlated with theta and theta-gamma coupling changes. Neuronal activity was phase-locked with theta but learning had no effect on firing rates or the magnitude or latencies of visual evoked potentials during stimuli. The neural network model developed showed that a combination of fast and slow inhibitory interneurons could generate theta-nested gamma. By increasing N-methyl-D-aspartate receptor sensitivity in the model similar changes were produced as in inferotemporal cortex after learning. The model showed that these changes could potentiate the firing of downstream neurons by a temporal desynchronization of excitatory neuron output without increasing the firing frequencies of the latter. This desynchronization effect was confirmed in IT neuronal activity following learning and its magnitude was correlated with discrimination performance.Conclusions
Face discrimination learning produces significant increases in both theta amplitude and the strength of theta-gamma coupling in the inferotemporal cortex which are correlated with behavioral performance. A network model which can reproduce these changes suggests that a key function of such learning-evoked alterations in theta and theta-nested gamma activity may be increased temporal desynchronization in neuronal firing leading to optimal timing of inputs to downstream neural networks potentiating their responses. In this way learning can produce potentiation in neural networks simply through altering the temporal pattern of their inputs. 相似文献38.
Nicolás Matte Bon 《Geometric And Functional Analysis》2014,24(5):1637-1659
We study random walk on topological full groups of subshifts, and show the existence of infinite, finitely generated, simple groups with the Liouville property. Results by Matui and Juschenko-Monod have shown that the derived subgroups of topological full groups of minimal subshifts provide the first examples of finitely generated, simple amenable groups. We show that if the (not necessarily minimal) subshift has a complexity function that grows slowly enough (e.g. linearly), then every symmetric and finitely supported probability measure on the topological full group has trivial Poisson–Furstenberg boundary. We also get explicit upper bounds for the growth of Følner sets. 相似文献
39.
Nicolás de la Rosa-Fox Manuel Piñero Rocío Litrán Luis Esquivias 《Journal of Sol-Gel Science and Technology》2003,26(1-3):947-951
CdS semiconductor nanocrystals were grown as quantum dots (QDs) inside a silica matrix obtained by the sol-gelmethod and assisted in the mother liquid by high powerultrasounds. Small-angle neutron scattering (SANS) accountsfor a 3.6 nm crystal size homogeneously distributed. Optical excitation from the third harmonic of a Nd:YAG ns laser wasfocused on the sample to study the photoluminescence (PL) atroom temperature. The PL spectrum shows radiative processfrom intrinsic transitions and a broad band corresponding tothe traps. Variable stripe length (VSL) method was used to measure the optical gain spectra by the growth of theamplified luminescence. A broad optical gain spectrumproduced by the biexciton-exciton transitions revealing thestimulated emission from the CdS QDs. It is also observed ared-shift of the PL emission crystal size-dependent. 相似文献
40.