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131.
简单介绍朗讯系统cdma 1x基站分组管(PP)宽度的配置,并对朗讯cdma 1x基站分组管宽度不合理的配置及信道板扩容后的PP宽度配置进行了案例分析。 相似文献
132.
Guobao Zhang Jianming Zhang Shenguo Wang Deyan Shen 《Journal of Polymer Science.Polymer Physics》2003,41(1):23-30
Blends of amorphous poly(DL‐lactide) (DL‐PLA) and crystalline poly(L‐lactide) (PLLA) with poly(methyl methacrylate) (PMMA) were prepared by both solution/precipitation and solution‐casting film methods. The miscibility, crystallization behavior, and component interaction of these blends were examined by differential scanning calorimetry. Only one glass‐transition temperature (Tg) was found in the DL‐PLA/PMMA solution/precipitation blends, indicating miscibility in this system. Two isolated Tg's appeared in the DL‐PLA/PMMA solution‐casting film blends, suggesting two segregated phases in the blend system, but evidence showed that two components were partially miscible. In the PLLA/PMMA blend, the crystallization of PLLA was greatly restricted by amorphous PMMA. Once the thermal history of the blend was destroyed, PLLA and PMMA were miscible. The Tg composition relationship for both DL‐PLA/PMMA and PLLA/PMMA miscible systems obeyed the Gordon–Taylor equation. Experiment results indicated that there is no more favorable trend of DL‐PLA to form miscible blends with PMMA than PLLA when PLLA is in the amorphous state. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 23–30, 2003 相似文献
133.
This Note addresses the derivation of an improved On-Surface Radiation Condition for the numerical solution of the exterior Helmholtz equation at high-frequencies. This condition is built as an approximation of the Neumann-to-Dirichlet map by using a local regularization of its principal classical symbol in the gliding zone for modelling the creeping waves. The numerical simulation of this pseudodifferential operator is efficiently realized with a linear cost according to the dimension of the boundary element approximation space using suitable complex Padé approximants. A numerical example is provided. To cite this article: X. Antoine et al., C. R. Acad. Sci. Paris, Ser. I 340 (2005). 相似文献
134.
A locally convex space is said to be a Gateaux differentiability space (GDS)provided every continuous convex function defined on a nonempty convex open subset D of the space is densely Gateaux differentiable in D.This paper shows that the product of a GDS and a family of separable Frechet spaces is a GDS,and that the product of a GDS and an arbitrary locally convex space endowed with the weak topology is a GDS. 相似文献
135.
双金属催化剂是一类重要的多相催化剂。其中d电子在催化活性方面起着重要的作用.本文在Co_3[Fe(CN)_6]_2的工作基础上,进一步研究了该配合物在硅胶、氧化铝、以及氧化镁上的热性质,同时考察了CN~-在Co-Fe体系双端基配位的活化加氢,探讨了载体的影响. 相似文献
136.
We show that determining the minimum number of resolve filters that need to be added to a set of two-dimensional (2-D) prefix filters so that the filter set can implement a given policy using the first-matching-rule-in-table tie breaker is NP-hard. Additionally, we develop a fast O(nlogn+s) time, where n is the number of filters and s is the number of conflicts, plane-sweep algorithm to detect and report all pairs of conflicting 2-D prefix filters. The space complexity of our algorithm is O(n). On our test set of 15 2-D filter sets, our algorithm runs between 4 and 17 times as fast as the 2-D trie algorithm of A. Hari et al. (2000) and uses between 1/4th and 1/8th the memory used by the algorithm of Hari et al. On the same test set, our algorithm is between 4 and 27 times as fast as the bit-vector algorithm of Baboescu and Varghese (2002) and uses between 1/205 and 1/6 as much memory. We introduce the notion of an essential resolve filter and develop an efficient algorithm to determine the essential resolve filters of a prefix filter set. 相似文献
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139.
MRI fuzzy segmentation of brain tissue using neighborhood attraction with neural-network optimization. 总被引:11,自引:0,他引:11
Shan Shen William Sandham Malcolm Granat Annette Sterr 《IEEE transactions on information technology in biomedicine》2005,9(3):459-467
Image segmentation is an indispensable process in the visualization of human tissues, particularly during clinical analysis of magnetic resonance (MR) images. Unfortunately, MR images always contain a significant amount of noise caused by operator performance, equipment, and the environment, which can lead to serious inaccuracies with segmentation. A robust segmentation technique based on an extension to the traditional fuzzy c-means (FCM) clustering algorithm is proposed in this paper. A neighborhood attraction, which is dependent on the relative location and features of neighboring pixels, is shown to improve the segmentation performance dramatically. The degree of attraction is optimized by a neural-network model. Simulated and real brain MR images with different noise levels are segmented to demonstrate the superiority of the proposed technique compared to other FCM-based methods. This segmentation method is a key component of an MR image-based classification system for brain tumors, currently being developed. Index Terms-Improved fuzzy c-means clustering (IFCM), magnetic resonance imaging (MRI), neighborhood attraction, segmentation. 相似文献
140.
Pyroelectricity and Spontaneous Polarization in [111] Oriented 0.955 Pb(Zn1/3Nb2/3)O3-0.045PbTiO3 Single Crystals
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We report that the measurements of the pyroelectric current of the pre-poled [111]-oriented 0.955 Pb(Zn1/3Nb2/3) O3-0.045 PbTiO3 (PZN-4.5%PT) single crystals can shed some light on the phase transition and spontaneous polarization characters of this material in a similar way to measures of remanent polarization and dielectric properties. The pyroelectric current is measured and the corresponding spontaneous polarization is calculated as a function of temperature with various poling fields added during cooling the sample from 200℃ to room temperature. Critical electric field of 0.061 k V/cm is found to be essential to induce the intermediate ferroelectric orthorhombic phase between the ferroelectric rhombohedral and tetragonal phases. Below the critical field, the polarization increases almost linearly with the increase of poling field. At the critical field, the polarization at 30OC increases abruptly from 14μC/cm^2 for a poling field of O.06kV/cm to 29.5μC/cm^2 for a poling field of 0.061 kV/cm, and afterwards, increases slowly and saturates to 31 μC/cm^2 for poling fields beyond 0.55 kV/cm. 相似文献