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A simple path to ambient temperature ionic H^(-)superconductors

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Science China Chemistry 2024年第1期67卷 321-322页

作者： Bingru liu Shiyuan liu Jianglan Shui School of Materials Science and Engineering Beihang UniversityBeijing 100191China

Hydride ion(H^(-))has high polarizability(α_(H^(-))=10.17A^(3))and high redox potential(H^(-)/H_(2):-2.3 V),and therefore is an attractive energy carrier[1,2].The H^(-)superconductors play a crucial role in the devel... 详细信息

关键词： attractive ambient superconductors

Power Flow Analytical Solutions and Multi-dimensional Voltage Stability Boundaries Based on Multivariate Quotient-difference Method

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CSEE Journal of Power and Energy Systems 2024年第3期10卷 1168-1178页

作者： Chengxi liu Qiupin Lai School of Electrical Engineering and Automation Wuhan UniversityWuhan 430072China Hubei Engineering and Technology Research Center for AC/DC Intelligent Distribution Network Wuhan 430072China IEEE

This paper proposes a novel Multivariate Quotient-Difference(MQD)method to obtain the approximate analytical solution for AC power flow ***,in the online environment,the power flow solutions covering different operating conditions can be directly obtained by plugging values into multiple symbolic variables,such that the power injections and consumptions of selected buses or areas can be independently *** method first derives a power flow solution through a Multivariate Power Series(MPS).Next,the MQD method is applied to transform the obtained MPS to a Multivariate Pad´e Approximants(MPA)to expand the Radius of Convergence(ROC),so that the accuracy of the derived analytical solution can be significantly *** addition,the hypersurface of the voltage stability boundary can be identified by an analytical formula obtained from the coefficients of *** direct method for power flow solutions and voltage stability boundaries is fast for many online applications,since such analytical solutions can be derived offline and evaluated online by only plugging values into the symbolic variables according to the actual operating *** proposed method is validated in detail on New England 39-bus and IEEE 118-bus systems with independent load variations in multi-regions.

关键词： Analytical power flow solution multivariate power series multivariate Padéapproximants multivariate quotient-difference multi-dimensional voltage stability boundary

Using vitamin C to improve both performance and stability of n-type organic semiconductors

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Science China Materials 2024年第11期67卷 3755-3756页

作者： Sizhe liu Xingxin Shao Jun liu Key Laboratory of Polymer Physics and Chemistry Changchun Institute of Applied ChemistryChinese Academy of Sciences School of Applied Chemistry and Engineering University of Science and Technology of China

Organic semiconductors(OSCs) have the great advantages of flexibility, light weight, low-cost and large-area processing [1].After intensively studied for several decades, OSCs are now considered to be the most promising candidate materials for next-generation electronic circuits. N-type OSCs are the vital component for the basic electronic element, such as p-n junctions, light-emitting diodes and complementary circuits [2].

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Cooperative Covert Communication in Multi-Antenna Broadcast Channels

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China Communications 2024年第6期21卷 246-260页

作者： Qiao Sen liu Guangjie Ji Xiaopeng liu Weiwei School of Electrical and Information Engineering Nanjing University of Information Science and TechnologyNanjing 210044China School of Automation Nanjing University of Science and TechnologyNanjing 210094China

With the gradual popularization of 5G communications,the application of multi-antenna broadcasting technology has become ***,this study aims to investigate the wireless covert communication in the two-user cooperative multi-antenna broadcast *** focus on the issue that the deteriorated reliability and undetectability are mainly affected by the transmission *** tackle this issue,we design a scheme based on beamforming to increase the reliability and undetectability of wireless covert communication in the multi-antenna broadcast *** first modeled and analyzed the cooperative multi-antenna broadcasting system,and put forward the target *** we use the SCA(successive convex approximation)algorithm to transform the target problem into a series of convex *** the convex problems are solved and the covert channel capacity is *** order to verify the effectiveness of the scheme,we conducted simulation *** simulation results show that the proposed beamforming scheme can effectively improve the reliability and undetectability of covert communication in multi-antenna broadcast channels.

关键词： beamforming covert communication multi-antenna broadcast channels OFDM

High Energy Efficiency Dynamic Connected Hybrid Precoding for mm Wave Massive MIMO Systems

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China Communications 2024年第5期21卷 36-44页

作者： Du Ruiyan liu Huajing Li Tiangui liu Fulai Lab of Key Technology of Millimeter-wave Large-scale MIMO System Northeastern University at QinhuangdaoQinhuangdao066004China School of Computer Science and Engineering Northeastern UniversityShenyang 110819China

This paper considers a high energy efficiency dynamic connected(HEDC)structure,which promotes the practicability and reduces the power consumption of hybrid precoding system by lowresolution phase shifters(PSs).Based on the proposed structure,a new hybrid precoding algorithm is presented to optimize the energy efficiency,namely,HP-HEDC ***,via a new defined effective optimal precoding matrix,the problem of optimizing the analog switch precoding matrix is formulated as a sparse representation ***,the optimal analog switch precoding matrix can be readily obtained by the branch-and-bound ***,the digital precoding matrix optimization problem is modeled as a dictionary update problem and solved by the method of optimal direction(MOD).Finally,the diagonal entries of the analog PS precoding matrix are optimized by exhaustive search independently since PS and antenna is *** results show that the HEDC structure enjoys low power consumption and satisfactory spectral *** proposed algorithm presents at least 50%energy efficiency improvement compared with other algorithms when the PS resolution is set as 3-bit.

关键词： energy efficiency hybrid precoding mmWave optimized resolution phase shifter

Tropical cyclone genesis over the western north Pacific in La Ni?a decay summers: Comparison between 2018 and 2021

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Science China Earth Sciences 2024年第10期67卷 3098-3109页

作者： Yunyun liu Zhensong GONG China Meteorological Administration Key Laboratory for Climate Prediction Studies National Climate CentreBeijing 100081China Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters Nanjing University of Information Science&TechnologyNanjing 210044China

As the primary interannual signal of variability in the tropical ocean-atmosphere interaction, the El Ni?o-Southern Oscillation has a considerable impact on tropical cyclone(TC) activity over the western North Pacific(WNP). Both 2018 and2021 were La Ni?a decay years, but TC activity over the WNP during the two summers(June–August) showed notable differences. In 2018, summer TC activity was unusually high with a total of 18 TCs, and the region of TC genesis was mainly in the central and eastern WNP. In contrast, only 9 TCs were generated in summer 2021, and the region of TC genesis was primarily in the western WNP. By comparing the characteristics of the large-scale environmental conditions over the regions of TC genesis, the thermal factors of the tropical oceans, and the activity of the Madden-Julian Oscillation(MJO), this study revealed the possible causes for the marked differences in TC genesis over the WNP during the two summers, which both had a similar background of La Ni?a decay. The Indian Ocean Basin Mode(IOBM) transitioned of a cold anomaly in the winter of 2017/2018and persisted until summer 2018. At the same time, the Pacific Meridional Mode(PMM) maintained a positive phase, leading to eastward and northward displacement of the Western Pacific Subtropical High in summer, and eastward extension of the tropical monsoon trough, which presented conditions conducive to TC genesis over the Northwest Pacific. Moreover, the days when the MJO stagnated in phases 5 and 6 in the summer of 2018 increased by approximately 150% relative to climatological state,providing dynamic conditions favorable for TC formation. In 2021, the IOBM quickly turned to a warm anomaly in March and persisted until summer, whereas the PMM became a negative phase in January and remained so until summer. At the same time,the MJO stagnated in phases 2 and 3 for up to 47 days, with the center of convection located over the western Maritime Continent, producing conditions unconducive to TC ge

关键词： Tropical cyclone La Nina events Indian Ocean Basin Mode Pacific Meridional Mode Madden-Julian Oscillation Western Pacific Subtropical High Monsoon trough

Self-Aligning Multi-Modal Transformer for Oropharyngeal Swab Point Localization

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Tsinghua Science and Technology 2024年第4期29卷 1082-1091页

作者： Tianyu liu Fuchun Sun Department of Computer Science and Technology Tsinghua UniversityBeijing 100083China

The oropharyngeal swabbing is a pre-diagnostic procedure used to test various respiratory diseases, including COVID and Influenza A (H1N1). To improve the testing efficiency of testing, a real-time, accurate, and robust sampling point localization algorithm is needed for robots. However, current solutions rely heavily on visual input, which is not reliable enough for large-scale deployment. The transformer has significantly improved the performance of image-related tasks and challenged the dominance of traditional convolutional neural networks (CNNs) in the image field. Inspired by its success, we propose a novel self-aligning multi-modal transformer (SAMMT) to dynamically attend to different parts of unaligned feature maps, preventing information loss caused by perspective disparity and simplifying overall implementation. Unlike preexisting multi-modal transformers, our attention mechanism works in image space instead of embedding space, rendering the need for the sensor registration process obsolete. To facilitate the multi-modal task, we collected and annotate an oropharynx localization/segmentation dataset by trained medical personnel. This dataset is open-sourced and can be used for future multi-modal research. Our experiments show that our model improves the performance of the localization task by 4.2% compared to the pure visual model, and reduces the pixel-wise error rate of the segmentation task by 16.7% compared to the CNN baseline.

关键词： segmentation localization transformer multi-modal perception robotic perception

Design of efficient thermoelectric generators

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Science China Materials 2024年第1期67卷 377-378页

作者： Min liu Yanzhong Pei Interdisciplinary Materials Research Center School of Materials Science and EngineeringTongji UniversityShanghai 201804China

Thermoelectricity,which enables direct conversion between heat and electricity,undergoes impressive developments in recent decades,and is particularly promising for recovering low-grade heat of<600 K[1,2].Currently,only Bi2Te3-based thermoelectric devices are commercialized[3].However,the scarcity of tellurium(Te)(Fig.1a)is the main *** leads to numerous recent efforts on the development of efficient nonBi2Te3 thermoelectrics as potential alternatives,and successful examples(Fig.1b)include Mg3Sb2-alloys[2,3]and MgAgSb[1,2].

关键词： enable efficient electricity

In situ probing of electron transfer at the dynamic MoS_(2)/graphene–water interface for modulating boundary slip

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Nano Research 2024年第8期17卷 7513-7521页

作者： Yishu Han Dameng liu State Key Laboratory of Tribology in Advanced Equipment Tsinghua UniversityBeijing 100084China

The boundary slip condition is pivotal for nanoscale fluid *** research has primarily focused on simulating the interaction mechanism between the electronic structure of two-dimensional materials and slip of water at the nanoscale,raising the possibility for ultralow friction flow of water at the ***,experimentally elucidating electronic interactions at the dynamic solid–liquid interface to control boundary slip poses a significant *** this study,the crucial role of electron structures at the dynamic solid–liquid interface in regulating slip length was ***,the slip length of water on the molybdenum disulfide/graphene(MoS_(2)/G)heterostructure(100.9±3.6 nm)significantly exceeded that of either graphene(27.7±2.2 nm)or MoS_(2)(5.7±3.1 nm)*** was also analyzed how electron transfer significantly affected interface *** electrons played a crucial role in determining the type and proportion of excitons at both MoS_(2)–water and MoS_(2)/G–water ***,by applying voltage,distinct photoluminescence(PL)responses at static and dynamic interfaces were discovered,achieving a 5-fold modulation in PL intensity and a 2-fold modulation in the trion to exciton intensity *** electrons transfer from the top graphene to the bottom MoS_(2)at the MoS_(2)/G–water interface,reducing surface charge ***,the reduction of electrostatic interactions between the solid and water leads to an increased slip length of water on the MoS_(2)/G *** process aids in comprehending the origin of frictional resistance at the subatomic *** work establishes a foundation for actively controlling and designing of fluid transport at the nanoscale.

关键词： two-dimensional materials solid-liquid interface photoluminescence excitons electron transfer slip length