稀疏集

It is proved that if'sparse NP complete sets under polynomial-time Turing reductions exist'then 'SAT is polynomial-time non-adaptively search reducible to decision', and that if 'P is not equal to NP'then either'SAT is not polynomial-time non-adaptively search reducible to decision'or'SAT is not polynomial-time truth-table reducible to bounded approximable sets', and that if'P is not equal to NP'then'sparse complete sets for NP under polynomial-time disjunctive reductions do not exist'.

因为用现有的证明技术不可能绝对地解决这个假设，本文研究了这个假设与其他关于SAT结构性质的假设之间的关系，证明了如果'NP有多项式时间图灵归约下的稀疏完全集'则'SAT是多项式时间并行地搜索归约为判定'，以及如果假设'P不等于NP'，则要么'SAT不是多项式时间并行地搜索归约为判定'，要么'SAT不能用多项式时间真值表归约归约为有界可近似集'。

This approach not only inherits the advantages of absolute density based algorithms which can discover arbitrary shape clusters and are insensitive to noises , but also efficiently solves the following common problems: clustering results are very sensitive to the user-deflned parameters, reasonable parameters are hard to be determined, and high density clusters are contained fully in coterminous low density clusters. With this approach, incremental clustering can also be supported effectively by defining the affected sets and seed sets of the updating objects in this approach.

聚类算法的有效性问题主要表现在三个方面：其一，聚类算法大多要求用户输入一定的参数，例如希望产生的簇的数目，而这些参数通常难以确定，特别是针对高维空间中稀疏分布的实际应用数据集，用户几乎无法给出合适的算法参数，因此非专业用户需要与数据分析专家密切配合才能保证获得理想的聚类结果，导致算法的使用极为不便；其二，聚类结果对于输入的参数值过于敏感J，往往参数值的一些轻微变化却产生聚类结果的很大差异；其三，对于高维的实际应用数据集，其数据分布往往是稀疏的、杂乱的，很难为算法选择全局的参数进行准确的聚类分析，使得聚类的质量难以保证。

1 Day after injury ruptured capillary could be seen in ganglion cell layer, 4 weeks after injury cells in each layer arranged sparsely and disorderedly, in some RGCs chromatin became dense, 8 weeks after injury the cells in each layer became fewer and large amount of RGCs without nucleus could be seen.

3光镜下伤后1 d视网膜神经节细胞层出血，伤后4周视网膜各层细胞稀疏、排列欠整齐，GCL散在核染色质浓集、边聚的节细胞，伤后8周视网膜各层细胞明显减少，GCL内大量空化节细胞。

A new algorithm Eclat~+ was brought out, which is an improvement of Eclat and show good performance with a lot of datasets. We compare the two vertical formats, Tidset and Diffset.

本文系统地比较了Tidset垂直数据表示和Diffset垂直数据表示，对稀疏数据集，采用Tidset表示的数据库的规模远远小于Diffset表示。

The method includes the following steps: firstly, a spherical neighborhood of present sample points is established by using the geometric spherical-modelling theory and all the sample points contained in the spherical neighborhood are adopted as candidate neighbor points, thus not only preserving the effectivity of the dimension reduction capability when data sets are sparse but also getting the advantages of low-sensitivity to isolated points and good stability of the preserved topological structure; then a data relevance matrix more matching semantics can be obtained by relevance measurement based on route clusters to update the candidate neighbor points in the spherical neighborhood and optimize the regular neighborhood space of the present sample points, thus improving the phenomenon that the dimension reduction of sample sets provided with folded curved faces is apt to suffer the integrated-structure distortion in case of heterogeneous data distribution.

首先利用几何开球原理建立当前样本点的球状邻域，将包含在球状邻域内的所有样本点作为候选近邻点，不但能够保持在数据集稀疏情况下的降维性能的有效性，而且具有对孤立点敏感性不高、保留拓扑结构稳定性好的优点。然后利用基于路径聚类的相关性度量得到更符合语义的数据相关性矩阵，用来对球状邻域内的候选近邻点进行更新，优化当前样本点的规则邻域空间，改善了当数据不均匀分布时在带有折叠弯曲面的样本集上降维容易出现整体结构扭曲的现象。

Sparsity of source data sets is one major reason causing the poor quality.

数据集的极端稀疏是造成推荐质量低的主要原因之一。

In a graph-theoretic version for a graph G,it is to find a set F of added edges such that the graph G+F is chordal and |F| is minimized.Here the minimum value |F| is called the finll-in number of G,denoted as f.

起源于稀疏矩阵计算和其它应用领域的图G的最小填充问题是在图G中寻求一个内含边数最小的边集F使得G+F是弦图。

The fill-in minimization problem comes from the elimination process of sparse matrix computation. In a graph-theoretic version for a graph G, it is to find a set F of added edges such that the graph G+F is chordal and |F| is minimized.

起源于稀疏矩阵计算和其它应用领域的图G的最小填充问题是在图G中寻求一个内含边数最小的边集F使得G+F是弦图。

Hours after infusion, the radioactivity accumulation appeared in lung, and it revealed that the infused cells distributed mainly in lung, and some appeared in liver, spleen, kidney and bladder. 6 hours after infusion, the radioactivity in lung diminished compared with that at 3 hours after infusion, and bilateral kidneys imagine appeared intensively. 9 hours after infusion, the radioactivity in lung appeared reduced significantly than that at 3 hours after infusion, and liver imagined increasedly, intestine tract imagine appeared in several rats.

本研究中，静脉移植MSCs后3h，肺脏放射性浓集，移植细胞主要分布在双侧肺部，肝脏、脾脏、肾脏和膀胱分布较少；移植6h后，肺脏放射性较移植3h时减弱，双侧肾脏显像明显增强；移植9h后，肺脏放射性较移植3h时明显减弱，肝脏显像增强，个别大鼠肠道出现显像；移植18h后，此时肺脏显像明显稀疏，肝脏和脾脏显像显著加强。

In this paper, the generator model of constant transient voltage and the invariableness impedance model was used, and the saliency of generator is included; through the analysis of the characteristic of the network equation calculation in the transient stability analysis, a new node ordering algorithm is proposed. Better initial value can accelerate the convergence rate of the networking equations, reduce the number of iterations, thus to cut down the amount of calculating time.

本文首先建立了适合于暂态稳定分析的简单模型，其中发电机采用E_q恒定模型，考虑了发电机的暂态凸极效应，负荷采用恒定阻抗模型；研究了电力系统的暂态稳定分析方法，指出目前数值积分暂态稳定计算方法中存在的不足，主要是网络方程的求解速度过慢；分析了暂态稳定计算中网络方程的特点，将稀疏技术应用于网络方程的求解，提出了一种新的节点编号方法——最小度最小有源节点道路集算法，减少了网络方程的计算量；在进行交替迭代求解时，将预测算法应用于每一积分步网络方程功角和电压的初值估计当中，应用自回归算法和广义延拓算法，期望给出一个更有效的电压和功角初值方案，来加快方程的收敛过程，减少方程迭代的次数，以提高计算速度。

The split between the two groups can hardly be papered over.

这两个团体间的分歧难以掩饰。

This approach not only encourages a greater number of responses, but minimizes the likelihood of stale groupthink.

这种做法不仅鼓励了更多的反应，而且减少跟风的可能性。