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Ni-catalyzed cross-electrophile alkyl-alkyl coupling reactions

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Science China Chemistry 2025年

作者： Li-Xu you Lan Tian chun-Ling Guo Shun-Xi Li yu-Cheng Liu yu-Long Li Wei Shu College of Chemistry and Environmental Engineering Key Laboratory of Green Catalysis of Higher Education Institutes of Sichuan Sichuan University of Science and Engineering Guangming Advanced Research Institute Shenzhen Grubbs Institute Department of Chemistry and Guangdong Provincial Key Laboratory of Catalysis Southern University of Science and Technology

Introducing saturated carbon-carbon bonds into organic molecules significantly increases the three-dimensional configuration,thus altering the physical and chemical properties as well as the functions of molecules. Transition-metal-catalyzed carboncarbon cross-couplings represent one of the most straightforward, efficient and modular alternatives to build saturation in a single step. However, the efficient construction of alkyl-alkyl bonds remains a formidable challenge due to the precise manipulation of multiple alkyl metallic intermediates as well as associated competitive side reactions and selectivity control. Over the past years, Ni-catalyzed cross-coupling under reductive conditions has gained more and more attention for alkyl-alkyl crosscoupling partially attributing to the low-valent state of metal centers under reducing conditions, which suppresses the competitive β-hydride elimination process, thus facilitating the formation of alkyl-alkyl bonds. In this review, the initiative and progress of Ni-catalyzed cross-electrophile alkyl-alkyl cross-coupling, including the efforts in racemic and enantioselective formation of alkyl-alkyl bonds, have been summarized and discussed. Moreover, the challenges and further opportunities in this area have also been discussed.

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An advanced integrated framework for moving object tracking

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Journal of Zhejiang University-Science C(Computers and Electronics) 2014年第10期15卷 861-877页

作者： Gwang-Min CHOE Tian-jiang WANG Fang LIU chun-Hwa CHOE Hyo-Son SO Chol-ung PAK School of Computer Science and Technology Huazhong University of Science and Technology School of Computer Science and Technology Kim Il Sung University School of Wireless Engineering Huichon Institute of Technology

This paper first introduces the concept of a geogram that captures richer features to represent the objects. The spatiogram contains some moments upon the coordinates of the pixels corresponding to each bin, while the geogram contains information about the perimeter of grouped regions in addition to features in the *** we consider that a convergence process of mean shift is divided into obvious dynamic and steady states,and introduce a hybrid technique of feature description, to control the convergence process. Also, we propose a spline resampling to control the balance between computational cost and accuracy of particle filtering. Finally, we propose a boosting-refining approach, which is boosting the particles positioned in the ill-posed condition instead of eliminating the ill-posed particles, to refine the particles. It enables the estimation of the object state to obtain high accuracy. Experimental results show that our approach has promising discriminative capability in comparison with the state-of-the-art approaches.

关键词： Geogram Mean shift Hybrid gradient descent algorithm Particle filter Spline resampling Matrix condition number

Numerical study on the ozone formation inside street canyons using a chemistry box model

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Journal of Environmental Sciences 2008年第7期20卷 832-837页

作者： chun-Ho Liu Dennis y.C.Leung Department of Mechanical Engineering The University of Hong KongHong Kong.

Tropospheric ozone is a secondary air pollutant produced in the presence of nitrogen oxides (NO_x),volatile organic compounds (VOCs),and solar *** an urban environment,ground-level vehicular exhaust is the major anthropogenic source of ozone *** the cases of street canyons,pollutant dilution is weakened by the surrounding buildings that creates localized high concentration of NO_x and VOCs,and thus leads to high potential of ozone *** considering the major physical and chemical p...

关键词： volatile organic compounds VOCs-to-NO_x ratio air quality vehicular emission chemistry box model

The ratio of measured to total sediment discharge

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International Journal of Sediment Research 2019年第3期34卷 262-269页

作者： chun-yao yangn Pierre y.Julien Department of Civil and Environmental Engineering Colorado State University

It is important to examine the ratio of measured to total sediment discharge to determine the error in measured sediment transport rates from depth-integrated samplers. The ratio of measured to total sediment discharge as well as the ratio of suspended to total sediment discharge are examined based on the Modified Einstein Procedure. Both ratios reduce to a function of the ratio of shear velocity, u?, to the fall velocity, ω, of suspended material, u?=ω, and the ratio, h=ds, of flow depth, h, to the median grain size of bed material, d50. In rivers transporting fine material(such as silt or clay), the ratio of suspended to total load is a function of the ratio, h=d50. In this study, it is found that the ratio of measured to total load becomes a simple function of flow depth. For fine sediment transport, with a Rouse number(Ro) o 0:3,at least 80% of sediment load is in suspension when h=d50415, and at least 90% of sediment load is measured from depth integrating samples when h 4 1 m. Detailed measurements from 35 river stations in South Korea demonstrate that sand sizes and finer fractions predominantly are transported in suspension. Also, at least 90% of sand and finer fractions are transported in suspension in gravel and sand bed rivers when the discharge is larger than the mean annual discharge.

关键词： Modied Einstein Procedure Total sediment load South Korea

Effects of Magnetic Field on Charge—Ordering Transitions in La2CuO4.08 and Pr0.5Sr0.5Mno3

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Chinese Physics Letters 2003年第5期20卷 738-741页

作者： LIJian-Qi CHENLing yUHong-chun y.Matsui ZHAOZhong-Xian InstituteofPhysicsandCondensedMatterPhysics ChineseAcademyofSciencesBeijing100080 NationalInstituteforResearchinInorganicMaterials 1-1NamikiTsukubaIbaraki305Japan

The applied magnetic field can result in evident changes on the charge-ordering transitions in both Cu-based high Tc superconductors and Mn-based colossal magnetioresistance materials. Alternations of charge modulation and melting of well-defined charge stripes can be commonly observed when the magnetic field is over 2 T. We herein present the experimental data obtained in LaCuO4.08 and Pr0.5Sr0.5MnO3 materials, illustrating this kind of interesting phenomena at low temperatures. In particular, some essential structural features alternating along with charge-ordering transition have been discussed.

关键词： Manganese compounds

Saliency-guided meta-hallucinator for few-shot learning

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Science China(Information Sciences) 2024年第10期67卷 189-210页

作者： Hongguang ZHANG chun LIU Jiandong WANG Linru MA Piotr KONIUSZ philip H.S.TORR Lin yANG Systems Engineering Institute Academy of Military Sciences Data61 Commonwealth Scientific and Industrial Research Organisation Australian National University Oxford University

Learning novel object concepts from limited samples remains a considerable challenge in deep learning. The main directions for improving the few-shot learning models include(i) designing a stronger backbone,(ii) designing a powerful(dynamic) meta-classifier, and(iii) using a larger pre-training set obtained by generating or hallucinating additional samples from the small scale dataset. In this paper, we focus on item(iii) and present a novel meta-hallucination strategy. Presently, most image generators are based on a generative network(i.e., GAN) that generates new samples from the captured distribution of images. However, such networks require numerous annotated samples for training. In contrast, we propose a novel saliency-based end-to-end meta-hallucinator, where a saliency detector produces foregrounds and backgrounds of support images. Such images are fed into a two-stream network to hallucinate feature samples directly in the feature space by mixing foreground and background feature samples. Then, we propose several novel mixing strategies that improve the quality and diversity of hallucinated feature ***, as not all saliency maps are meaningful or high quality, we further introduce a meta-hallucination controller that decides which foreground feature samples should participate in mixing with backgrounds. To our knowledge, we are the first to leverage saliency detection for few-shot learning. Our proposed network achieves state-of-the-art results on publicly available few-shot image classification and anomaly detection benchmarks, and outperforms competing sample mixing strategies such as the so-called Manifold Mixup.

关键词： few-shot learning saliency detection object recognition anomaly detection computer vision

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New solid superbases: potassium nitrate supported on porous materials

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Chinese Science Bulletin 1997年第17期42卷 1493-1494页

作者： Zhu, JH chun, y Wang, y Tu, M Chemistry Department Chemistry & Chemical Engineering College Nanjing University Nanjing China

ACCORDING to Tanabe’s definition, all materials possessing the basic strength （H-） over 26.5 are superbases. However, most of superbases known up to now, including CaO and SrO evacuated at 1173 K, K or Na metal supported on KOH/γ-Al2O3, etc. are extremely sensitive to CO2 or H2O in the atmosphere, which limits their application in industrial scale. In or-

关键词： potassium nitrate supported on porous materials New solid superbases

A New Theropod Dinosaur from the Middle Jurassic of Lufeng,yunnan,China

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Acta Geologica Sinica(English Edition) 2009年第1期83卷 9-24页

作者： WU Xiao-chun philip J. CURRIE DONG Zhiming PAN Shigang WANG Tao Canadian Museum of Nature Ottawa Canada Department of Biological Sciences University of Alberta Edmonton Canada Institute of Vertebrate Paleontology and Paleoanthropology Chinese Academy of Sciences Beijing 100044 China Lufeng Dinosaur Museum Lufeng 651200 China

A new theropod dinosaur, Shidaisaurusjinae gen. et sp. nov., has been described on the basis of an incomplete skeleton. The specimen was found near the base of the Upper Lufeng Formation （early Middle Jurassic） in yunnan, China. It is the first theropod dinosaur from the Middle Jurassic of yunnan. Shidaisaurus jinae is distinguishable from other Jurassic theropods by certain features from the braincase, axis, and pelvic girdle. The absence of any pleurocoels in the axis or in any anterior dorsal vertebrae suggests that the new Lufeng theropod is relatively primitive and more plesiomorphic than most of the Middle to Late Jurassic theropods from China. Most Chinese taxa of Jurassic theropod dinosaurs have not been well described; a further detailed study will be necessary for us to determine their phylogenetic relationships with Shidaisaurusjinae.

关键词： Shidaisaurus jinae theropod dinosaur Upper Lufeng Formation Middle Jurassic,Lufeng yunnan

Stigmatic exudate in the Annonaceae:Pollinator reward,pollen germination medium or extragynoecial compitum?

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Journal of Integrative Plant Biology 2017年第12期59卷 881-894页

作者： Jenny y.y.Lau chun-Chiu Pang Lawrence Ramsden Richard M.K.Saunders School of Biological Sciences the University of Hong KongPokfulam RoadHong KongChina

Although ＂dry-type＂ stigmas are widely re- garded as ancestral in angiosperms, the early-divergent family Annonaceae has copious stigmatic exudate. We evaluate three putative functions for this exudate： as a nutritive reward for pollinators; as a pollen germination medium; and as an extragynoecial compitum that enables pollen tube growth between carpels. Stigmatic exudate is fructose dominated （72.2%）, but with high levels of glucose and sucrose; the dominance of hexose sugars and the diversity of amino acids observed, including many that are essential for insects, support a nutritive role for pollinators. Sugar concentration in pre-receptive flowers is high （28.2%）, falling during the peak period of stigmatic receptivity （17.4%）, and then rising again toward the end of the pistillate phase （32.9%）. Pollen germination was highest in sugar concentrations 〈2%. Sugar concentrations during the peak pistillate phase therefore provide optimal osmolarity for pollen hydration and germination; subsequent changes in sugar concentration during anthesis reinforce protogyny （in which carpels mature before stamens）, enabling the retention of concentrated exudate into the staminate phase as a pollinator food reward without the possibility of pollen germination. Intercarpellary growth of pollen tubes was confirmed： the exudate therefore also functions as a suprastylar extragynoecial compitum, overcoming the limitations of apocarpy.

关键词： Stigmatic exudate in the Annonaceae pollen germination medium or extragynoecial compitum Pollinator reward