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101.
102.
The acquisition of new skills over a life span is a remarkable human ability. This ability, however, is constrained by age of acquisition (AoA); that is, the age at which learning occurs significantly affects the outcome. This is most clearly reflected in domains such as language, music, and athletics. This article provides a perspective on the neural and computational mechanisms underlying AoA in language acquisition. The authors show how AoA modulates both monolingual lexical processing and bilingual language acquisition. They consider the conditions under which syntactic processing and semantic processing may be differentially sensitive to AoA effects in second-language acquisition. The authors conclude that AoA effects are pervasive and that the neural and computational mechanisms underlying learning and sensorimotor integration provide a general account of these effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
103.
Previous work by Li et al. in the area of axial vibrations of bellows dealt with fixed end conditions. However, it is seen on several occasions that bellow ends are welded to a small pipe spool that has a lumped mass such as a valve or an instrument. Hence, the present paper aims at finding out the effect of elastically restrained ends on the axial natural frequencies. The analysis considers finite stiffness axial restraints on the bellows, i.e. solving the set of equations with non-homogeneous boundary conditions. Two bellow specimens are considered for comparison having the same dimensions as taken by Li in his analysis. The transcendental frequency equation deduced is accurate as the first, second and third mode frequencies computed are in close agreement to the ones obtained by Li. 相似文献
104.
Ternary Ti-Al-Nb elemental powder blends with minor addition of SiC were synthesized in a high energy ball mill in order to understand the structural evolution during mechanical alloying (MA) and subsequent thermal treatment. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) techniques were employed to study the structural development during MA. Ti-48%Al-4%Nb-3%SiC and Ti-48%Al-8%Nb-3%SiC blends milled to 20 h were subjected to thermal treatment at 750 °C for 1 h in vacuum. Repeated cold welding and fracturing events of MA resulted in nanocrystalline structure with supersaturated solid solution and amorphous phase. The powder particles were also refined to submicron size due to high energy collision. The nanocrystalline supersaturated solid solution evolved by MA was sustained for prolonged milling time. There was no evidence of intermetallics formation even after early solid solubility extension and formation of nanocrystalline structure. However, nanostructured TiAl and Ti3Al intermetallic compounds were observed after giving thermal treatment to MA powder blend. Since their surface area and energy were enhanced to a great extent, the dispersed ceramic particles reacted with titanium and formed nanosilicide particles. 相似文献
105.
106.
应用功率控制、波束赋形和多用户检测可以有效地消除和减少CDMA系统中的干扰。本文结合波束赋形和多用户检测的特性,提出一种应用波束赋形增益和多用户相关矩阵的解相关算法。基于算法的复杂性,提出一种区分聚集用户进行多用户检测的的算法。由于波束赋形能够消减主瓣波束之外的多用户干扰,对聚集移动台采用解相关检测达到减少运算量和消除多用户干扰的目的。对算法进行了仿真分析,证明了本算法的优越性。 相似文献
107.
The development of the semi-theoretical correlation in Hadzisdmajlovic et al. (1983) for predicting the maximum spoutable height in a spout-fluid bed, is observed to involve certain discrepancies. Based on their experimental data, a new correlation is proposed. 相似文献
108.
109.
以工业偏钛酸、硫酸锌、氨水为主要原料,用直接沉淀法并进行热处理得到钛酸锌粉体,并用XRD对产物成分进行了检测。结果表明,不同的锌钛比对钛酸锌(ZnO-TiO2)体系的成分有较大影响。 相似文献
110.
In this paper, we examine methods of characterizing somatosensory evoked potentials (SEP's) in both the time and frequency domains. We have found that the truncated impulse response (TIR) method produced an accurate time domain model of the SEP signals at model orders greatly reduced from the original state space matrix. The TIR method was valuable for smoothing signals that were slightly corrupted by noise. In this case, the simulated data sequence was close to the original data sequence in the mean squared error sense. For signals that were greatly corrupted by noise, the TIR method was not able to perform as well. Therefore, the TIR method was not a feature extraction method but was valuable for data simulation. In the frequency domain, we have used the autoregressive moving average model (ARMA) to parameterize the SEP signal. An overdetermined set of Yule-Walker equations was created to determine the autoregressive (AR) parameters of the original data with the model order established by the singular value decomposition. From these AR parameters, a residual time series was generated which was used to find the moving average parameters. The resulting ARMA model was used to produce a simulated data sequence. The frequency domain characteristics of the simulated sequence and the corresponding power spectral density of the ARMA filter were very close to the periodogram of the original data sequence. Accurate parameterization was achieved for the SEP waveforms at low filter lengths. 相似文献