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151.
Glassy ribbons of Pd–Si alloys were prepared by a combination of melt spinning and flux treatment. The crystallization behaviour of a Pd81Si19 glassy alloy was studied through isothermal annealing at temperatures ranging lower than the glass-transition temperature T g to around the onset of crystallization. The evolution of microstructures arising from isothermal annealing was investigated by X-ray diffraction (XRD) and (high-resolution) transmission electron microscopy ((HR)TEM). XRD spectra showed that, after the sample was annealed at a sub-T g temperature, its first diffraction peak was split into two overlapping broad peaks. TEM analysis revealed the formation of a spherical, particle-like glassy phase embedded in the glassy matrix together with a finely connected network morphology within both. Combining these observations with compositional analysis suggested that phase separation had taken place during sub-T g annealing. When the glassy alloy was annealed at temperatures higher than T g, nanocrystalline structures, composed of Pd3Si and Pd phases plus a Pd9Si2 phase with a lamellar structure, was formed. 相似文献
152.
The pressure dependence of the electrical resistivity of three different samples of cassiterite, namely natural cassiterite SnO2, synthetic nanocrystalline SnO2 (with crystallite size 46?nm) and nanocrystalline Co-doped SnO2 (with crystallite size 32?nm), has been measured up to 7?GPa at room temperature. The resistivity of natural cassiterite SnO2 decreases from 2.5?×?104?Ωm at normal pressure and temperature to 1.7?×?104?Ωm at 7.0?GPa. The nanocrystalline SnO2 has a high resistivity 6.0?×?105?Ωm at normal pressure and temperature and decreases with pressure reaching a value of 2.98?×?105?Ωm at 7?GPa. The activation energy of the electrical conduction of the studied samples were found to be 0.32?eV for the natural SnO2, 0.40?eV for the nanocrystalline SnO2 sample and 0.28?eV for the nanocrystalline Co-doped SnO2. Measurements of the pressure dependence of the electrical resistivity of the Co-doped SnO2 showed a decrease from 3.60?×?105 to 5.4?×?104?Ωm at 7.0?GPa. We did not observe any pressure-induced phase transition in SnO2 up to 7?GPa. This study of the high-pressure phase stability of cassiterite corroborates the experimental findings of SnO2 nanoinclusions in diamonds. 相似文献
153.
The monoclinic phase in the Al–Ta system has been identified by means of X-ray single-crystal structure analysis as Al19+ x Ta24? x (x?=?1.6), Pearson symbol mP86. Al20.58Ta22.42 crystallizes in the space group P21/n, with a?=?987.86?pm, b?=?990.12?pm, c?=?1489.45?pm and β?=?99.958°. Twinned crystals of the title compound can be obtained by iodine-promoted reactions of the elements. In the experiments described here, the reactions took place in sealed tantalum ampoules at 1400°C. Single-phase samples were obtained by a metallurgical powder method, which minimizes aluminium loss by incongruent vapourization. The composition was found to span the range 0.51?≤?x Ta?≤?0.53. Al19+ x Ta24? x decomposes in the solid state at 1450°C into Al69Ta39 and σ-AlTa2. The crystal structure is analyzed in relation to tetrahedral close-packed structures. The kinship with Cr3Si-type and H-type structures is accentuated. 相似文献
154.
Seung Zeon Han Satoshi Semboshi Jee Hyuk Ahn Eun-Ae Choi Minah Cho Yusuke Kadoi 《Philosophical Magazine Letters》2013,93(8):275-283
ABSTRACTDeformation bands, especially shear bands were intentionally formed in supersaturated Cu-4 at.% Ti alloy by groove-rolling with 75% area reduction. Cold deformation prior to the ageing process changed the precipitation behaviour of the alloy. The deformed structure with shear bands was maintained, without showing recovery and recrystallisation, even after prolonged ageing at 450°C for more than one day. The thermally stable shear bands act as nucleation initiation sites and prevent the expansion of discontinuous cellular precipitates. The hardness reached a value of 305?Hv and an electrical conductivity of 15% IACS (IACS?=?International Annealed Copper Standard. 100% IACS is defined as the conductivity corresponding to a volume resistivity at 20°C of 17.241?nΩ), compared to 283?Hv and 13% IACS for conventional solid-solutioned and peak-hardened alloy. In addition, the ageing time to reach the highest hardness was shortened from 720 to 180?min at 450°C. 相似文献
155.
Jean-Philippe Couzinié Sylvie Lartigue-Korinek Jany Thibault-Pénisson Brigitte Décamps Louisette Priester 《Philosophical Magazine Letters》2013,93(12):757-767
The atomic structure of an asymmetrical near Σ = 27 {525} tilt grain boundary (GB) in copper is determined by coupling high-resolution transmission electron microscopy and molecular dynamics simulation. The average GB plane is parallel to {414} in crystal (1) and {343} in crystal (2). The detailed GB structure shows that it is composed of facets always parallel to {101} and {111} in crystals (1) and (2), respectively. The atomic structure of one facet is described using the structural units model. Each facet is displaced with respect to its neighbours by a pure step, giving rise to the asymmetry of the GB plane orientation. The energy of this asymmetrical GB is significantly lower than that of both the {525} symmetrical and the {11,1,11}/{111} asymmetrical Σ = 27 GBs. One GB region displays another atomic structure with a dislocation that accounts for the misfit between interatomic distances in the {414} and {343} GB planes. 相似文献
156.
Taian M.M. Vieira Marco A. Minetto Emma F. Hodson-Tole Alberto Botter 《Human movement science》2013,32(4):753-767
Ankle movements in the frontal plane are less prominent though not less relevant than movements in the plantar or dorsal flexion direction. Walking on uneven terrains and standing on narrow stances are examples of circumstances likely imposing marked demands on the ankle medio-lateral stabilization. Following our previous evidence associating lateral bodily sways in quiet standing to activation of the medial gastrocnemius (MG) muscle, in this study we ask: how large is the MG contribution to ankle torque in the frontal plane? By arranging stimulation electrodes in a selective configuration, current pulses were applied primarily to the MG nerve branch of ten subjects. The contribution of populations of MG motor units of progressively smaller recruitment threshold to ankle torque was evaluated by increasing the stimulation amplitude by fixed amounts. From smallest intensities (12–32 mA) leading to the firstly observable MG twitches in force-plate recordings, current pulses reached intensities (56–90 mA) below which twitches in other muscles could not be observed from the skin. Key results showed a substantial MG torque contribution tending to rotate upward the foot medial aspect (ankle inversion). Nerve stimulation further revealed a linear relationship between the peak torque of ankle plantar flexion and inversion, across participants (Pearson R > .81, p < .01). Specifically, regardless of the current intensity applied, the peak torque of ankle inversion amounted to about 13% of plantar flexion peak torque. Physiologically, these results provide experimental evidence that MG activation may contribute to stabilize the body in the frontal plane, especially under situations of challenged stability. 相似文献
157.
A common assumption is that phonetic sounds initiate unique processing in the superior temporal gyri and sulci (STG/STS). The anatomical areas subserving these processes are also implicated in the processing of non-phonetic stimuli such as music instrument sounds. The differential processing of phonetic and non-phonetic sounds was investigated in this study by applying a “sound-morphing” paradigm, where the presence of phonetic features were parametrically varied, creating a step-wise transition from a non-phonetic sound into a phonetic sound. The stimuli were presented in an event-related fMRI design. The fMRI-BOLD data were analysed using parametric contrasts. The results showed a higher sensitivity for sounds containing phonetic features compared to non-phonetic sounds in the middle part of STG, and in the anterior part of the planum temporale (PT) bilaterally. Although the same areas were involved in the processing of non-phonetic sounds, a difference in activation was evident in the STG, with an increase in activation related to increment of phonetic features in the sounds. The results indicate a stimulus-driven, bottom-up process that utilizes general auditory resources in the secondary auditory cortex, depending on specific phonetic features in the sounds. 相似文献
158.
Naeser MA Martin PI Theoret H Kobayashi M Fregni F Nicholas M Tormos JM Steven MS Baker EH Pascual-Leone A 《Brain and language》2011,119(3):206-213
This study sought to discover if an optimum 1 cm2 area in the non-damaged right hemisphere (RH) was present, which could temporarily improve naming in chronic, nonfluent aphasia patients when suppressed with repetitive transcranial magnetic stimulation (rTMS). Ten minutes of slow, 1 Hz rTMS was applied to suppress different RH ROIs in eight aphasia cases. Picture naming and response time (RT) were examined before, and immediately after rTMS. In aphasia patients, suppression of right pars triangularis (PTr) led to significant increase in pictures named, and significant decrease in RT. Suppression of right pars opercularis (POp), however, led to significant increase in RT, but no change in number of pictures named. Eight normals named all pictures correctly; similar to aphasia patients, RT significantly decreased following rTMS to suppress right PTr, versus right POp. Differential effects following suppression of right PTr versus right POp suggest different functional roles for these regions. 相似文献
159.
Rothwell JC 《Human movement science》2011,30(5):906-915
Transcranial magnetic stimulation is increasingly used as a tool to explore cortical motor function in healthy subjects and in patients with neurological disease or injury. This review describes a “twin coil” TMS approach that allows investigation of time related changes in functional connectivity between primary motor cortex and other areas in preparation for a forthcoming movement. Investigations into premotor–motor interactions show that these are specific to the type of task that is performed as well as the muscles used to control the movement, allowing us to monitor information flow within motor networks with millisecond time resolution. 相似文献
160.
Since about two decades neuroscientists have systematically faced the problem of consciousness: the aim is to discover the neural activity specifically related to conscious perceptions, i.e. the biological properties of what philosophers call qualia. In this view, a neural correlate of consciousness (NCC) is a precise pattern of brain activity that specifically accompanies a particular conscious experience. Almost all studies aimed at investigating the NCC have been carried out in the visual system. One of the most promising paradigms is based on sensory stimuli which elicit bistable percepts, as they allow to decouple subjective perception from the characteristics of the physical stimulation. Such kind of perception can be produced in the visual modality by using particular images (e.g. Rubin's vase/face figure) or by presenting two dissimilar stimuli separately to the two eyes (binocular rivalry). The stimuli compete for perceptual dominance and each image is visible in turn for a few seconds, while the other is suppressed. The use of this methodology has led to important findings concerning visual consciousness, which are briefly discussed. For the investigation of auditory consciousness, a similar stimulation paradigm can be achieved by using dichotic listening, consisting in two different stimuli presented each to one ear, which compete for perception (binaural rivalry). The principal aim of the present mini-review is to discuss the few contributes facing the issue of auditory consciousness and to advance the use of dichotic listening and binaural rivalry as valid tools for its investigation. 相似文献