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391.
田大钢 《数学的实践与认识》2009,39(23)
给出一种通过适当地选择输入层与隐层间的连接权,来减少单隐层前馈型神经网络隐层节点的个数的方法.应用此方法,分析了具有两个隐层节点的标准单隐层网络的学习能力,并对二元和三元XOR问题中的权值的选择问题进行了详细的讨论. 相似文献
392.
本文在低压弱浮力环境中模拟了微重力过载电流时导线绝缘层的着火先期过程,研究了压力对绝缘层着火先期特性的影响。结果表明,2 A时,绝缘层的温升率和最终平衡温度随压力降低而不断增大,模拟出了微重力下绝缘层的温升特性;10 A时,随着压力降低,绝缘层存在三种破坏机制;在不同区域压力对着火延迟时间的影响不同。最后,提高环境氧气浓度修正了低压对化学反应速率的抑制。结果表明,当压力在一定范围内降低时,随着氧气浓度的提高,绝缘层的着火极限范围拓宽,着火延迟时间缩短,可以初步模拟微重力下绝缘层的着火先期过程。 相似文献
393.
Measurement of cardiac T2 has emerged as an important tool to noninvasively quantify cardiac iron concentration in order to detect preclinical evidence of toxic levels and titrate chelation therapy. However, there exists variation among practitioners in cardiac T2 measurement methods. This study examines the impact of different imaging parameters and data analysis techniques on the calculated cardiac R2 (1/T2) in patients at risk for cardiac siderosis. The study group consisted of 36 patients with thalassemia syndromes who had undergone clinical magnetic resonance imaging assessment of cardiac siderosis using a standardized protocol and who were selected to yield a broad range of cardiac R2 values. Cardiac R2 measurements were performed on a 1.5-T scanner using an electrocardiogram-gated, segmented, multiecho gradient echo sequence obtained in a single breath-hold. R2 was calculated from the signal intensity versus echo time data in the ventricular septum on a single midventricular short-axis slice. There was good agreement between R2 measured with a blood suppression prepulse (black blood technique) and without (mean difference 6.0 ± 10.7 Hz). The black blood technique had superior within-study reproducibility (R2 mean difference 1.6 ± 8.6 Hz versus 2.7 ± 14.6 Hz) and better interobserver agreement (R2 mean difference 3.4 ± 8.2 Hz versus 8.3 ± 16.5 Hz). With the same minimum echo time, the use of small (1.0 ms) versus large (2.2 ms) echo spacing had minimal impact on cardiac R2 (mean difference 0.3 ± 8.7 Hz). The application of a region-of-interest-based versus a pixel-based data analysis also had little effect on cardiac R2 calculation (mean difference 8.4 ± 6.9 Hz). With black blood images, fitting the signal curve to a monoexponential decay or to a monoexponential decay with a constant offset yielded similar R2 values (mean difference 3.4 ± 8.1 Hz). In conclusion, the addition of a blood suppression prepulse for cardiac R2 measurement yields similar R2 values and improves reproducibility and interobserver agreement. The findings regarding other variations may be helpful in establishing a broadly accepted imaging and analysis technique for cardiac R2 calculation. 相似文献
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The possibility of improving the discrimination capability (DC) in color pattern recognition is analyzed. In each channel, red, green and blue (R, G, B), a region of support is designed to improve the behavior of the Phase Only Filter matched to the corresponding component of the target. The procedure of optimization is based on the analytical expressions which give the DC in R, G, B channels, for real valued input scenes. Computer simulation results are presented and discussed. 相似文献