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排序方式: 共有764条查询结果,搜索用时 15 毫秒
1.
排名聚合将多个排名列表聚合成一个综合排名列表,可应用于推荐系统、链路预测、元搜索、提案评选等.当前已有工作从不同角度对不同排名聚合算法进行了综述、比较,但存在算法种类较少、数据统计特性不清晰、评价指标不够合理等局限性.不同排名聚合算法在提出时均声称优于已有算法,但是用于比较的方法不同,测试的数据不同,应用的场景不同,因此何种算法最能适应某一任务在很多情况下仍不甚清楚.本文基于Mallows模型,提出一套生成统计特性可控的不同类型的排名列表的算法,使用一个可应用于不同类型排名列表的通用评价指标,介绍9种排名聚合算法以及它们在聚合少量长列表时的表现.结果发现启发式方法虽然简单,但是在排名列表相似度较高、列表相对简单的情况下,能够接近甚至超过一些优化类方法的结果;列表中平局数量的增长会降低聚合排名的一致性并增加波动;列表数量的增加对聚合效果的影响呈现非单调性.整体而言,基于距离优化的分支定界方法 (FAST)优于其他各类算法,在不同类型的排名列表中表现非常稳定,能够很好地完成少量长列表的排名聚合. 相似文献
2.
CV Tomy D Pal SS Banerjee S Ramakrishnan AK Grover S Bhattacharya MJ Higgins G Balakrishnan McK Paul 《Pramana》2002,58(5-6):925-935
The weakly pinned single crystals of the hexagonal 2H-NbSe2 compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder
transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of
the peak effect phenomenon in three crystals of 2H-NbSe2, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of
a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability
effects and pinning. 相似文献
3.
The peak effect (PE) in the critical current density in both low and high temperature superconductors has been the subject
of a large amount of experimental and theoretical work in the last few/several years. In the case of YBCO, crucial discussions
describing a dynamic or a static picture are not settled. In that region of field and temperature the mobility of the vortex
lattice (VL) is found to be dependent on the dynamical history. Recently we reported evidence that the VL reorganizes and
accesses to robust VL configurations (VLCs) with different effective pinning potential wells arising in response to different
system histories. One of the keys to understand the nature of the PE is to investigate the VL behavior in the vicinity of
the various VLCs in the region of the PE. The stability of these VLCs was investigated and it was found that they have distinct
characteristic relaxation times, which may be related to elastic or plastic creep processes. In this paper we review some
of these results and propose a scenario to describe the PE in YBCO crystals. 相似文献
4.
在 1,10 -邻菲罗啉显色体系中 ,引入二阶导数光谱 -峰面积积分技术 ,建立了同时测定痕量铁 ( )和钴 ( )的新方法。该法可有效消除共存离子的干扰 ,提高了准确度和灵敏度。对铁和钴的表观摩尔吸光系数分别为 εFe5 .4 5× 10 6 L·mol-1·cm-1,εCo 1.1× 10 4 L· mol-1· cm-1;铁含量在 0 .0— 8.5 μg·m L-1,钴含量在 0 .0— 7.3μg· m L-1范围内遵守比耳定律。可用于芦荟中铁和钴的同时测定 ,结果令人满意 相似文献
5.
We examine to what extent finite-dimensional spaces defined on locally compact subsets of the line and possessing various weak Chebyshev properties (involving sign changes, zeros, alternation of best approximations, and peak points) can be uniformly approximated by a sequence of spaces having related properties. 相似文献
6.
7.
基于Prony算法的Delsuc谱预测是目前NMR LPSVD(Linear Prediction SingularValue Decomposition)法中比较实用的方法。但在高噪声的条件下,时有失峰和假峰出现且要事先知道谱的峰数。本文通过跟踪迭代过程发现Delsuc法的判别因子r_(mis) 很难选定。如果它太小会失峰,而过大又会出现假峰。同时,由于噪声的影响,弱信号的采样点之间的相关性比强信号小,从而在迭代过程中会增加数值不稳定性。文中引入峰面积判据来改善Delsuc法,经模拟与实验均证明结果有效。 相似文献
8.
Luiza Amália Moraes Luis Romero Grados 《Journal of Mathematical Analysis and Applications》2003,281(2):575-586
Let Au(BG) be the Banach algebra of all complex valued functions defined on the closed unit ball BG of a complex Banach space G which are uniformly continuous on BG and holomorphic in the interior of BG, endowed with the sup norm. A characterization of the boundaries for Au(BG) is given in case G belongs to a class of Banach spaces that includes the pre-dual of a Lorentz sequence space studied by Gowers in Israel J. Math. 69 (1990) 129-151. The non-existence of the Shilov boundary for Au(BG) is also proved. 相似文献
9.
The copper(II) complex [Cu(sat)], where Hsat is salicylidene-2-aminothiazole (bidentate Schiff - base), was studied in variety of solvents. In the solid state, the complex is black. It has been characterized by elemental analysis, solubility in common solvents, molar conductivity, and ultraviolet (UV) and visible (Vis) spectroscopy. The complex is easily soluble in common solvents such as chloroform, dimethylformamide, dimethyl sulfoxide, and 1,4-dioxane. The known crystal structure of similar compounds shows planar coordination geometry for the copper center. Combined multitechnique experiments have been applied to confirm the structure of the complex in solutions. The molar conductivities indicate their nonelectrolyte properties in all these solvents. The spectroscopic measurements were used to study the coordination properties of donoratoms and their bonding abilities. 相似文献
10.
H. Wätzig 《Chromatographia》1992,33(5-6):218-224
Summary It is still difficult to determine peaks and peak boundaries properly, though peak recognition is very important for the precision of quantitative data. A new computer program overcomes these problems using a method which is adapted from human judgements. The algorithm was developed for HPLC but can also be used in other fields of analytical chemistry. 相似文献