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61.
Recursive partitioning methods are among the most popular techniques in machine learning. The purpose of this paper is to investigate how to adapt this methodology to the bipartite ranking problem. Following in the footsteps of the TreeRank approach developed in Clémençon and Vayatis (Proceedings of the 2008 Conference on Algorithmic Learning Theory, 2008 and IEEE Trans. Inf. Theory 55(9):4316–4336, 2009), we present tree-structured algorithms designed for learning to rank instances based on classification data. The main contributions of the present work are the following: the practical implementation of the TreeRank algorithm, well-founded solutions to the crucial issues related to the splitting rule and the choice of the “right” size for the ranking tree. From the angle embraced in this paper, splitting is viewed as a cost-sensitive classification task with data-dependent cost. Hence, up to straightforward modifications, any classification algorithm may serve as a splitting rule. Also, we propose to implement a cost-complexity pruning method after the growing stage in order to produce a “right-sized” ranking sub-tree with large AUC. In particular, performance bounds are established for pruning schemes inspired by recent work on nonparametric model selection. Eventually, we propose indicators for variable importance and variable dependence, plus various simulation studies illustrating the potential of our method. 相似文献
62.
检波器组内高差对高频信息压制的理论分析 总被引:1,自引:0,他引:1
在地震勘探野外采集中,目前普遍采用地表低速带的速度〖WTBX〗V0〖WTBZ〗乘以目的层反射波主频的1/4视周期来计算检波器组内高差允许值,即使在沙漠及山地的地震资料采集中也是如此。本文通过理论计算与模型试验证明:在主频不是很高而次生干扰波非常发育的一些工区,采用降速带的速度〖WTBX〗V1〖WTBZ〗乘以最浅目的层反射波主频的1/2视周期计算组内高差,就可以得到信噪比较高的用于构造解释的低频剖面;相反,如果在这类地区拘泥于原先关于组内高差的规定,就会因为强烈的次生干扰波没有得到有效压制而导致地震剖面的信噪比大大降低,进而使得企图通过减小组内高差、保护高频信息、提高分辨率的初衷也无法实现。 相似文献
63.
初至波层析影响因素分析 总被引:2,自引:0,他引:2
在山地地震勘探中,目前广泛采用初至波走时层析方法反演起伏地表速度结构,但其最终反演结果受许多因素影响。本文通过大量数值试验对影响表层模型层析反演精度的方程解法、先验信息利用、观测系统、初始模型及平滑因子等主要因素进行了详细的分析对比,总结出了最佳参数的选择原则和范围,并建立了内部约束方程。将本文方法应用于实际资料处理,取得了较好的成像效果。 相似文献
64.
65.
Marine C. R. Rauch Yann Gallou Léna Delorme Dr. Caroline E. Paul Prof. Dr. Isabel W. C. E. Arends Prof. Dr. Frank Hollmann 《Chembiochem : a European journal of chemical biology》2020,21(8):1112-1115
Elemental metals are shown to be suitable sacrificial electron donors to drive the stereoselective reduction of conjugated C=C double bonds using Old Yellow Enzymes as catalysts. Both direct electron transfer from the metal to the enzyme as well as mediated electron transfer is feasible, although the latter excels by higher reaction rates. The general applicability of this new chemoenzymatic reduction method is demonstrated, and current limitations are outlined. 相似文献
66.
Huang Yu-Sen Niisato Emi Su Mao-Yuan Marine Benkert Thomas Hsu Hsao-Hsun Shih Jin-Yuan Chen Jin-Shing Chang Yeun-Chung 《Magma (New York, N.Y.)》2021,34(3):399-409
Magnetic Resonance Materials in Physics, Biology and Medicine - This study investigated ultrashort echo time (UTE) sequences in 1.5 T magnetic resonance imaging (MRI) for small lung nodule... 相似文献
67.
WANG Feng-li GAO Hong-tao ZHAO De-you School of Ship Engineering Dalian University of Technology Dalian ChinaCollege of Marine Engineering Dalian Maritime University Dalian China 《国际设备工程与管理》2010,(1)
Aiming at the mode mixture in local wave decomposition(LWD) caused by a noise signal, the original data is preprocessed using the lifting wavelet transformation to suppress abnormal interference of noise and improve the quality of decomposition. It is employed to analyze the vibration signal of rotor rub-impact for extracting the weak impulsive feature. The signal is decomposed into intrinsic mode functions by LWD, then the high-frequency components are analyzed by Hilbert envelop demodulation. The period o... 相似文献
68.
琼东南盆地多边形断层在流体运移和天然气水合物成藏中的作用 总被引:2,自引:0,他引:2
多边形断层是由未固结沉积物脱水使得体积收缩而在平面上呈现多边形形状,且具有微小断距、分布密集的张性断层。在琼东南盆地深水区的中新世—上新世地层中,利用三维地震相干切片可以发现小规模流体运移通道——多边形断层。同样在二维高分辨率地震剖面上也能发现多边形断层、底辟和同相轴下拉的管状构造,距海底双程走时250ms和300ms位置存在强的似海底反射层(Bottom Simulating Reflector,简称BSR)。利用约束稀疏脉冲反演和地震属性分析表明,多边形断层上部地层的管状构造和模糊反射区为低声波阻抗异常和低频率异常,BSR上为高声波阻抗和高频率异常。多边形断层、管状和底辟构造破坏了琼东南盆地裂后热沉降阶段巨厚的泥岩地层的封闭性,使大量流体垂直和近似垂直向上运移,为天然气水合物形成提供了充足气源。 相似文献
69.
利用短小芽孢杆菌(Bacillus pumilus)的ω-1-羟基脂肪酸高产突变菌株M-F641、M-F81、M-F8272及B.pumilus20075的总DNA为模板,通过Primer Premier5.0软件设计引物,对决定长链脂肪酸无效降解途径中的关键酶基因fadD-like基因进行克隆,得到4条长约1 720 bp的fadD-like基因全序列;利用MEGA3.1、DNAStar等软件进行序列分析结合脂酰辅酶A合成酶系统进化分析,结果表明其与fadD基因具有较高的相似性,克隆得到的核苷酸为编码脂酰辅酶A合成酶的fadD基因序列;研究结果为长链脂肪酸高效转化生产ω-1-羟基脂肪酸提供基础。 相似文献
70.
Cotte M Susini J Metrich N Moscato A Gratziu C Bertagnini A Pagano M 《Analytical chemistry》2006,78(21):7484-7492
Red Pompeian paintings, very famous for their deep intensity, are currently suffering from darkening. The origins of this darkening degradation are not clearly identified yet and remain a major issue for curators. In the specific case of cinnabar (HgS)-based red pigment, a photoinduced conversion into black metacinnabar is usually suspected. This work is focused on the blackening of red cinnabar paintings coated on a sparry calcite mortar. Different samples exhibiting different levels of degradation were selected upon visual observations and analyzed by synchrotron-based microanalytical techniques. Atomic and molecular compositions of the different debased regions revealed two possible degradation mechanisms. On one hand, micro X-ray fluorescence elemental maps show peculiar distributions of chlorine and sulfur. On the other hand, X-ray absorption spectroscopy performed at both Cl and S K-edges confirms the presence of characteristic degradation products: (i) Hg-Cl compounds (e.g., corderoite, calomel, and terlinguaite), which may result from the reaction with exogenous NaCl, in gray areas; (ii) gypsum, produced by the calcite sulfation, in black coatings. Metacinnabar is never detected. Finally, a cross section was analyzed to map the in-depth alteration gradient. Reduced and oxidized sulfur distributions reveal that the sulfated black coating consists of a approximately 5-mum-thick layer covering intact cinnabar. 相似文献