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Hydrogen isotopic composition of plant leaf wax in response to soil moisture in an arid ecosystem of the northeast Qinghai-Tibetan Plateau, China

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Journal of Arid Land 2014年第5期6卷 592-600页

作者： Yuan YAO WeiGuo liu School of Human Settlements and Civil Engineering Xi'an Jiaotong University State Key Laboratory of Loess and Quaternary Geology Institute of Earth Environment Chinese Academy of Sciences

The hydrogen isotopic composition of plant leaf wax（δDwax） is used as an important tool for paleohydrologic reconstruction. However, the understanding of the relative importance of environmental and biological factors in determining δDwax values still remains incomplete. To identify the effects of soil moisture and plant physiology on δDwax values in an arid ecosystem, and to explore the implication of these values for paleoclimatic reconstruction, we measured δD values of soil water（δDwater） and δDwax values in surface soils along two distance transects extending from the lakeshore to wetland to dryland around Lake Qinghai and Lake Gahai on the northeast Qinghai-Tibetan Plateau. The results showed that the δDwater values were negatively correlated with soil water content（SWC）（R^2=0.9166）, and ranged from –67‰ to –46‰ with changes in SWC from 6.2% to 42.1% in the arid areas of the Gangcha（GCh） and Gahai（GH） transects. This indicated that evaporative D-enrichment in soil water was sensitive to soil moisture in an arid ecosystem. Although the shift from grasses to shrubs with increasing aridity occurred in the arid area of the GH transect, the δDwax values in surface soils from the arid areas of the two transects still showed a negative correlation with SWC（R^2=0.6835）, which may be due to the controls of primary evaporative D-enrichment in the soil water and additional transpirational D-enrichment in the leaf water on the δDwaxvalues. Our preliminary research suggested that δDwax values can potentially be applied as a paleo-humidity indicator on the northeast Qinghai-Tibetan Plateau.

关键词： hydrogen isotope D-enrichment soil water content northeast Qinghai-Tibetan Plateau

Strain-Modulated Photoelectric Responses from a Flexibleα-In_(2)Se_(3)/3R MoS_(2)Heterojunction

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Nano-Micro Letters 2021年第7期13卷 1-11页

作者： Weifan Cai Jingyuan Wang Yongmin He Sheng liu Qihua Xiong Zheng liu Qing Zhang Center for Micro-and Nano-Electronics School of Electrical and Electronic EngineeringNanyang Technological UniversitySingapore 639798Singapore School of Materials Science and Engineering Nanyang Technological UniversitySingapore 639798Singapore Division of Physics and Applied Physics School of Physical and Mathematical SciencesNanyang Technological UniversitySingapore 639798Singapore

Semiconducting piezoelectricα-In_(2)Se_(3) and 3R MoS_(2) have attracted tremendous attention due to their unique electronic *** van der Waals(vdWs)hetero-structures constructed withα-In_(2)Se_(3)and 3R MoS_(2)flakes have shown promising applications in optoelectronics and ***,we present the first flexibleα-In_(2)Se_(3)/3R MoS_(2)vdWs p-n heterojunction devices for photodetection from the visible to near infrared *** heterojunction devices exhibit an ultrahigh photoresponsivity of 2.9×10^(3)A W^(−1) and a substantial specific detectivity of 6.2×10^(10) Jones under a compressive strain of−0.26%.The photocurrent can be increased by 64%under a tensile strain of+0.35%,due to the heterojunction energy band modulation by piezoelectric polarization charges at the hetero-junction *** work demonstrates a feasible approach to enhancement of α-In_(2)Se_(3)/3R MoS_(2) photoelectric response through an appropriate mechanical stimulus.

关键词： α-In_(2)Se_(3)/3R MoS_(2)heterojunction Flexible Self-powered photodetector Strain modulation Piezoelectric charge

Improved smoothed L0 reconstruction algorithm for ISI sparse channel estimation

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The Journal of China Universities of Posts and Telecommunications 2014年第2期21卷 40-47页

作者： liu Ting ZHOU Jie Department of Communications Nanjing University of Information Science and Technology Department of Electronic and Electrical Engineering Niigata University

In this paper, the problem of inter symbol interference （ISI） sparse channel estimation in wireless communication with the application of compressed sensing is investigated. However, smoothed L0 norm algorithm （SL0） has ＇notched effect＇ due to the negative iterative gradient direction. Moreover, the property of continuous function in SL0 is not steep enough, which results in inaccurate estimations and low convergence. Afterwards, we propose the Lagrange multipliers as well as Newton method to optimize SL0 algorithm in order to obtain a more rapid and efficient signal reconstruction algorithm, improved smoothed L0 （ISL0）. ISI channel estimation will have a direct effect on the performance of ISI equalizer at the receiver. So, we design a pre-filter model which with no considerable loss of optimality and do analyses of the equalization methods of the sparse multi-path channel. Real-time simulation results clearly show that the ISL0 algorithm can estimate the ISI sparse channel much better in both signal noise ratio （SNR） and compression levels. In the same channel conditions, ISL0 algorithm has been greatly improved when compared with the SL0 algorithm and other compressed-sensing algorithms.

关键词： compressed-sensing channel model ISI improved SLO algorithm sparse channel estimation MIMO system

PLDMLT:Multi-Task Learning of Diabetic Retinopathy Using the Pixel-Level Labeled Fundus Images

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Computers, Materials & Continua 2023年第8期76卷 1745-1761页

作者： Hengyang liu Chuncheng Huang Department of Computer Science and Engineering Chongqing University of TechnologyChongqing400054China

In the field of medical images,pixel-level labels are time-consuming and expensive to acquire,while image-level labels are relatively easier to ***,it makes sense to learn more information(knowledge)from a small number of hard-to-get pixel-level annotated images to apply to different tasks to maximize their usefulness and save time and training *** this paper,using Pixel-Level Labeled Images forMulti-Task Learning(PLDMLT),we focus on grading the severity of fundus images for Diabetic Retinopathy(DR).This is because,for the segmentation task,there is a finely labeled mask,while the severity grading task is without classification *** this end,we propose a two-stage multi-label learning weakly supervised algorithm,which generates initial classification pseudo labels in the first stage and visualizes heat maps at all levels of severity using Grad-Cam to further provide medical interpretability for the classification task.A multitask model framework with U-net as the baseline is proposed in the second stage.A label update network is designed to alleviate the gradient balance between the classification and segmentation *** experimental results show that our PLDMLTmethod significantly outperforms other stateof-the-art methods in DR segmentation on two public datasets,achieving up to 98.897%segmentation *** addition,our method achieves comparable competitiveness with single-task fully supervised learning in the DR severity grading task.

关键词： DR lesion segmentation pseudo labels grading task class activation heat map update label network

Continuum description for the characteristic resistance sensed by a cylinder colliding against granular medium

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Science China(Physics,Mechanics & Astronomy) 2013年第8期56卷 1428-1436页

作者： PANG Yong liu CaiShan State Key Laboratory for Turbulence and Complex Systems College of EngineeringPeking University

In this paper, we experimentally and theoretically study the resistance force that develops when a cylinder with a flat face colliding against dry quartzite sand. Observations from experimental data clearly show that the acceleration curves are characterized by a double-peak structure. The first agitated peak can be attributed to a shock process where sand responds elastically, and the valley bottom in the double-peak structure is related to a limited plastic load when a fully plastic region is formed in the sand, while the second agitated peak corresponds to a the occurrence of the maximum of viscous force in a homogeneous developed bulk flow. We use slip line theory (SL) developed in plastic mechanics to capture the value at the valley bottom, adopt the double shearing theory (DS), together with a Local Rheological Constitutive Law (LRCL) suggested in this paper, to capture the drag force generated in a homogeneous bulk flow. Good agreements in the comparisons between numerical and experimental results support the characteristic resistance by the cylinder to predict granular states.

关键词： granular material penetrating dynamics rheological property

Mid-Cretaceous Hainan back-arc basin:record of the sustained extension of South China margin

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Journal of Palaeogeography 2022年第4期11卷 584-600页

作者： Yan Chen Jun Meng Hao liu Tao liu Ze-Ying Zhao State Key Laboratory of Biogeology and Environmental Geology School of Earth Sciences and ResourcesChina University of Geosciences(Beijing)Beijing100083China School of Ocean Sciences China University of Geosciences(Beijing)Beijing100083China

The continued subduction of the Pacific oceanic lithosphere during the Jurassic-Cretaceous time formed a large magmatic province as“Basin and Range”at the South China ***,the timing and mechanisms of such a huge rifting and magmatism belt are still *** we present new petrological,sedimentological and geochemical analyses for the Cretaceous Lumuwan Formation and coeval intruded mafic dykes under the robust age constrain in Hainan *** results show that the midCretaceous Lumuwan Formation was a typical lacustrine stratigraphic sandwich that accumulated in an intracontinental back-arc extensional *** Hainan mafic dykes(~108-93 Ma)were probably sourced from asthenospheric and lithospheric mantle which were metasomatized by subducted oceanic sediments in a backarc extension of the continental *** timing of the NW-SE-directed back-arc extension in the Hainan Basin has been constrained as 108-93 Ma and played a significant role in the formation of Basin and Range-type tectonics and landscape evolution in the South China.

关键词： Mid-cretaceous Lumuwan Formation Mafic dykes Back-arc extension South China

Moments of discounted dividend payments in a risk model with randomized dividend-decision times

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Frontiers of Mathematics in China 2017年第2期12卷 493-513页

作者： Zhimin ZHANG Chaolin liu College of Mathematics and Statistics Chongqing University Chongqing 401331 China

We consider a perturbed compound Poisson risk model with randomized dividend-decision times. Different from the classical barrier dividend strategy, the insurance company makes decision on whether or not paying off dividends at some discrete time points （called dividend-decision times）. Assume that at each dividend-decision time, if the surplus is larger than a barrier b 〉 O, the excess value will be paid off as dividends. Under such a dividend strategy, we study how to compute the moments of the total discounted dividend payments paid off before ruin.

关键词： Moments of discounted dividends compound Poisson model,integro-differential equation ruin

Experimental study on visualization of the flow field in microtube

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Science China(Technological Sciences) 2005年第5期48卷 521-529页

作者： liu Zhigang ZHAO Yaohua Institute of Engineering Thermophysics Chinese Academy of Sciences Beijing 100080 China Institute of Engineering Thermophysics Chinese Academy of Sciences Beijing 100080 China

An experimental study was conducted to visualize the flow field and confirm the transitional Reynolds number from laminar to turbulent flow, as distilled water flows through quartz glass microtubes with inner diameter 315 and 520 μm. With gentian violet as colorant, the flow field pictures in the microtube, and therefore, is shot by a CCD camera with a microscope at different Reynolds numbers. Pressure drop data were also used to characterize the friction factor for those microtubes in the Reynolds number range of 200–2300. The experimental results clearly showed that the flow in the microtube was the laminar state and the friction factors agreed well with the Poiseuille equations when the Reynolds number was low. As the Reynolds number was larger than 1200 and 1500 for the microtube with inner diameter 315 and 520 μm, respectively, the friction factor departed from the classical laminar solution due to the earlier transition from laminar to tubulent flow. The flow turned into full turbulent when the Reynolds number reached 1500–1800.

关键词： visual experiment, microtube, microscale flow, friction factor, turbulent transition.

EXACT SOLUTIONS FOR FREE IN-PLANE VIBRATIONS OF RECTANGULAR PLATES

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Acta Mechanica Solida Sinica 2011年第6期24卷 556-567页

作者： Bo liu Yufeng Xing The Solid Mechanics Research Center Beijing University of Aeronautics and Astronautics Beijing 100191 China

All possible exact solutions are successfully obtained in terms of 10 sets of distinct eigensolutions for the free in-plane vibration of isotropic rectangular plates. The plates have simply supported condition at two opposite edges and any combination of classical boundary conditions at the other two edges. The exact solutions are validated through both mathematical proof and comparisons with the solutions of differential quadrature method. Some unusual phenomena are revealed in free in-plane vibrations of rectangular plates due to one of the eigenvalues being zero. This work constitutes an improved version of very recent corresponding work by the same authors lint. J. Mech. Sci., 2009, 51： 246-255]. Both the solution forms and solving procedures in the previous work are substantially simplified. Some new results are also given, which are useful for validation purpose in future.

关键词： rectangular plate in-pane free vibration frequency mode shape exact solution