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Science China(Information Sciences) 2024年第2期67卷 267-278页

作者： Guofang YU Renrong LIANG Haiming ZHAO Lei XIAO Jie CUI Yue ZHAO Wenpu CUI Jing WANG Jun XU Jun FU Tianling REN School of Integrated Circuits Tsinghua University Beijing National Research Center for Information Science Technology Tsinghua University

Surface acoustic wave(SAW) resonators with an ultrahigh Q-factor are designed and fabricated on silicon-based gallium nitride(GaN/Si). The temperature-dependent performance is characterized over a wide range, from 10 to 500 K. Finite element analysis is employed to guide the design of the SAW resonator from indications of the Rayleigh mode and weak propagation direction dependence of SAW in the c-plane of GaN/Si. The SAW resonator with 100 pairs of interdigital transducers(IDT), 100 pairs of grating reflectors(GR) for each side, aperture size of 80 μm, metallization ratio of 0.5, and electrode width of 500 nm resonates at 1.9133 GHz accordingly with an ultrahigh Q-factor of 7622 at room temperature, which contributes the fr× Qr, up to 14.583×1012Hz. A resonator operating over 10 to 500 K indicates an approximately linear decreasing temperature dependence above 280 K while being approximately constant below 40 K. The fitting to resonator characteristics using the modified Butterworth Van Dyke(m BVD) model reveals a reduction in both the electrode and mechanical losses while worsening the dielectric loss with cooling down.

关键词： GaN/Si SAW resonator ultrahigh Q-factor temperature-dependent performance mBVD losses

Investigation of the Vortex Dynamic Mechanism of the Flow losses on a Transonic Compressor Stator

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Journal of Thermal Science 2019年第1期28卷 51-60页

作者： KAN Xiaoxu WANG Songtao LUO Lei SU Jiexian School of Energy Science and Engineering Harbin Institute of Technology

For a transonic axial-flow compressor, the numerical simulations, verified against experimental data, were used to study the inherent correlation between the evolutionary process of the vortex structures and the flow loss in a compressor stator passage during the throttling process. The flow loss was divided accurately and quantitatively, based on the evolutionary process of the vortex structures. According to the position of the singular points of the vortex structures, the influence of the evolution of the vortex structures on the generation and development of the flow loss was analyzed on a microscale scale. Thereafter, this paper provided the vortex dynamic mechanism of the flow loss, which was important to enrich the theoretical system of the flow field in the compressor. The results show that: the flow loss at the top of the stator tip is caused by the low-energy fluid clusters, which are transported and accumulated by the vortices from the endwall; the transport effect of the pressure separation vortex at the upper half-height only migrates the position of the flow losses, but there is new flow loss generated by its shear action to the endwall. The dominant flow loss during the throttling process concentrates upon the closed separation bubble around the middle of the suction side of the stator.

关键词： transonic compressor stator throttling process vortex structure flow losses topological analysis

Understanding Business Disruption and Economic losses Due to Electricity Failures and Flooding

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International Journal of Disaster Risk Science 2019年第4期10卷 421-438页

作者： Elco Koks Raghav Pant Scott Thacker Jim W.Hall Environmental Change Institute University of OxfordSouth Parks RoadOxford OX13QYUK Institute for Environmental Studies Vrije Universiteit AmsterdamDe Boelelaan 10851081 HV AmsterdamThe Netherlands United Nations Office for Project Services(UNOPS) Marmorvej 512100 CopenhagenDenmark

Failure of critical national infrastructures can cause disruptions with widespread economic impacts.To analyze these economic impacts,we present an integrated modeling framework that combines:(1)geospatial information on infrastructure assets/networks and the natural hazards to which they are exposed;(2)geospatial modeling of the reliance of businesses upon infrastructure services,in order to quantify disruption to businesses locations and economic activities in the event of infrastructure failures;and(3)multiregional supply-use economic modeling to analyze wider economic impacts of disruptions to businesses.The methodology is exemplified through a case study for the United Kingdom.The study uses geospatial information on the location of electricity infrastructure assets and local industrial areas,and employs a multiregional supply-use model of the UK economy that traces the impacts of floods of different return intervals across37 subnational regions of the UK.The results show up to a300%increase in total economic losses when power outages are included in the risk assessment,compared to analysis that just includes the economic impacts of business interruption due to flooded business premises.This increase indicates that risk studies that do not include failure of critical infrastructures may be underestimating the total losses.

关键词： Economic impacts Flood hazard Indirect economic losses Infrastructure failure United Kingdom

Simulation study of the losses and influences of geminate and bimolecular recombination on the performances of bulk heterojunction organic solar cells

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Chinese Physics B 2015年第10期24卷 584-590页

作者：朱键卓祁令辉杜会静柴莺春 College of Science Yanshan University

We use the method of device simulation to study the losses and influences of geminate and bimolecular recombinations on the performances and properties of the bulk heterojunction organic solar cells. We find that a fraction of electrons（holes）in the device are collected by anode（cathode）. The direction of the corresponding current is opposite to the direction of photocurrent. And the current density increases with the bias increasing but decreases as bimolecular recombination（BR）or geminate recombination（GR） intensity increases. The maximum power, short circuit current, and fill factor display a stronger dependence on GR than on BR. While the influences of GR and BR on open circuit voltage are about the same.Our studies shed a new light on the loss mechanism and may provide a new way of improving the efficiency of bulk heterojunction organic solar cells.

关键词： bulk heterojunction organic solar cells losses device simulation geminate recombination bi- molecular recombination

Event-Triggered Sampled-Data Consensus of Nonlinear Multi-Agent Systems with Control Input losses

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Journal of Systems Science & Complexity 2018年第6期31卷 1469-1497页

作者： XING Mali DENG Feiqi Department of Automation Science and Engineering South China University of Technology

This paper investigates the leader-following consensus problem for multi-agent systems with event-triggered mechanism and control packet losses.Based on the local synchronization error, event-triggered mechanisms are proposed in order to reduce the number of controller update.The control packet may lose due to unreliability of communication channel.With the assumption that once the packet loss happens the controller will be set to zero,sufficient consensus criteria for multi-agent system with event-triggered mechanism and control packet losses is obtained.It is also shown that the interplay among the allowable packet loss rate,event-triggered mechanism and sampling period.An illustrative example is given to demonstrate the effectiveness of the theoretical results.

关键词： Consensus control packet losses event-triggered mechanism multi-agent systems

Experimental study of an insert and its influence on churning losses in a high-speed electro-hydrostatic actuator pump of an aircraft

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Chinese Journal of Aeronautics 2019年第8期32卷 2028-2036页

作者： Junhui ZHANG Ying LI Bing XU Min PAN Qun CHAO The State Key Laboratory of Fluid Power and Mechatronic Systems Zhejiang UniversityHangzhou 310027China Department of Mechanical Engineering University of BathBath BA2 7AYUnited Kingdom

The speed of an Electro-Hydrostatic Actuator(EHA) pump can recently reach 20000 r/min, and its churning losses increase obviously with an increasing speed, which results in low efficiency and thus increasing heat in aircraft EHA systems. In order to reduce churning losses at high speeds, more attention should be given to the design of an insert. In this paper, the effect of an insert with different design parameters on churning losses is investigated through Computational Fluid Dynamics(CFD) simulation and experiments by calculating the difference between churning losses torques of the test pump with and without the insert based on a high-speed churning losses test rig.Analytical results show that the gap between the insert and the cylinder is critical for churning losses reduction. It is found that the churning losses of the test pump can be reduced with a decreasing gap between the cylinder block and the insert at high speeds. This is because the insert can decrease the turbulence occurrence at high speeds. The results can be used for flow field analysis and optimization of the high-speed EHA pump and provide a new method for improving efficiency of high-speed EHA pumps.

关键词： Churning losses Efficiency Electro-hydrostatic actuator pump High speed Insert

Efficiency of wheat straw mulching in reducing soil and water losses from three typical soils of the Loess Plateau, China

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International Soil and Water Conservation Research 2019年第4期7卷 335-345页

作者： Abbas ERahma David NWarrington Tingwu Lei College of Agricultural Studies Department of Agricultural EngineeringSudan University of Science and TechnologyShambatKhartoumSudan College of Water Conservancy and Civil Engineering Shandong Agricultural UniversityTaianShandong Province 271018PR China State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau Institute of Soil and Water ConservationChinese Academy of Science and Ministry of Water ResourcesYanglingShaanxi Province 712100PR China College of Water Resources and Civil Engineering China Agricultural UniversityBeijing 100083PR China

Mulching the soil surface with a layer of plant residue is considered an effective method of conserving water and soil because it increases water infiltration into the soil,reduces surface runoff and the soil erosion,and reduces flow velocity and the sediment carrying capacity of overland flow.However,application of plant residues increases operational costs and so optimal levels of mulch in order to prevent soil and/or water losses should be used according to the soil type and rainfall and slope conditions.In this study,the effect of wheat straw mulch rate on the total runoff and total soil losses from 60-mm simulated rainstorms was assessed for two intensive rainfalls (90 and 180mmh^-1) on three slope gradients typical conditions on the Loess Plateau of China and elsewhere.For short slopes (1 m),the optimal mulch rate to save water for a silt loam and a loam soil was 0.4 kg m^-2.However,for a clay loam soil the mulch rate of 0.4 kg m^-2 would be optimal only under the 90 mm h^-1 rainfall;0.8 kg m^-2 was required for the 180 mm h^-1.In order to save soil,a mulch rate of 0.2 kg m^-2 on the silt loam slopes prevented 60%-80% of the soil losses.For the loam soil,mulch at the rate of 0.4 kg m^-2 was essential in most cases in order to reduce soil losses substantially.For the clay loam,0.4 kg m^-2 may be optimal under the 90 mm h^-1 rain,but 0.8 kg m^-2 may be required for the 180 mm h^-1 rainstorm.These optimal values would also need to be considered alongside other factors since the mulch may have value if used elsewhere.Hence doubling the optimal mulch rate for the silt loam soil from 0.2 kg m^-2 or the clay loam soil under 90 mm h^-1 rainfall from 0.4 kg m^-2 in order to achieve a further 10% reduction in soil loss needs to be assessed in that context.Therefore,Optimal mulch rate can be an effective approach to virtually reduce costs or to maximize the area that can be treated.Meantime,soil conservationist should be aware that levels of mulch for short slopes might not be suitable for long slopes.

关键词： Straw mulch Soil losses Runoff Rain simulator

Numerical simulation and analysis of losses in air-core plastic photonic bandgap fibers

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Chinese Optics Letters 2005年第6期3卷 313-315页

作者：关铁山陈明阳张志龙于荣金 School of Information Science and Engineering Yanshan University Qinhuangdao 066004 School of Information Science and Engineering Yanshan University Qinhuangdao 066004

The loss properties of air-core plastic photonic bandgap fibers are analyzed by multipole method. Despite the relatively large absorption loss of plastics (PMMA), the contribution of material absorption loss can be reduced significantly through appropriate selection of operating wavelength, number of cladding air-hole rings, radius of air-core, and position of photonic band gap. The transmission loss in this type of fiber can be decreased by an order of magnitude in comparison with that of conventional plastic optical fiber.

关键词： Computer simulation Energy gap Fiber optic networks losses Polymethyl methacrylates

Experimental Study of Churning losses in Swash Plate Axial Piston Pump

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Journal of Beijing Institute of Technology 2019年第3期28卷 529-535页

作者： Chongbo Jing Junjie Zhou Jichen Zhou School of Mechanical Engineering Beijing Institute of Technology

The problem of the churning loss in swash plate axial piston machines is investigated through experimental measurement and theoretical analysis. Several works surrounding churning loss in hydraulic components have been proposed in the past, but few have conducted experimental studies and accounted for both dry and wet housing conditions. In this study,a specialized experimental setup is established, which includes a transparent test pump diligently designed for performing various functions of tests. The test pump can work as a real pump without losing any actual features of pump operation. The torque loss in both the dry housing pump and wet housing pump is measured in terms of the shaft speed and its predictive model is also developed analytically. The comparisons between measured and calculated torque loss are presented, showing how speed influences torque loss in both conditions. The advantage/disadvantages of the two cases are summarized. The significance of the test setup is highlighted by verifying the proposed model, which can advance the understanding of energy losses of high speed pumps in future.

关键词： axial piston pump churning losses experimental analysis theoretical model

Development and testing of a weather-based model to determine potential yield losses caused by potato late blight and optimize fungicide application

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Frontiers of Agricultural Science and Engineering 2018年第4期5卷 462-468页

作者： Alexey FILIPPOV Maria KUZNETSOVA AlexANDer ROGOZHIN Olga IAKUSHEVA Valentina DEMIDOVA Natalia STATSYUK Laboratory of Potato & Vegetable Diseases All-Russian Research Institute of Phytopathology

Late blight is one of the most important potato diseases. To minimize yield losses, various protective measures are used including fungicide application. Active use of fungicides results in a contamination of the environment. Therefore, crop protection strategies optimizing the number of treatments are of great interest.Using information about late blight development in an experimental potato field recorded over 30 seasons, a simulator to forecast yield losses caused by the disease was developed based on the number of 5-d periods favorable for reinfection of plants during a vegetation season. The simulator was successfully verified using independent data on the disease development from nine unprotected potato fields in the Netherlands and Germany. The average difference between the calculated and real yield losses did not exceed 5%. Using the simulator and weather data for a period of 2007–2017, yield losses were calculated for several areas of the Bryansk, Tambov, and Orenburg Regions of Russia. The results revealed differences in disease development between these regions and may be used to develop recommendations for a frequency of fungicide applications according to the regional risk of epidemics, leading to a significant reduction in fungicide use.

关键词： potato late blight Phytophthora infestans yield losses retrospective analysis mathematical model