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A high-order target phase approach for the station-keeping of periodic orbits

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Astrodynamics 2024年第1期8卷 61-75页

作者： Xiaoyu Fu Nicola Baresi Roberto Armellin Surrey space Centre University of SurreyGuildfordGU27XHUK te pūnahaĀtea-Auckland space institute University of AucklandAuckland1010New Zealand

A novel high-order target phase approach(TphA)for the station-keeping of periodic orbits is proposed in this *** key elements of the TphA method,the phase-angle poincare map and high-order maneuver map,are constructed using differential algebra(DA)techniques to determine station-keeping epochs and calculate correction maneuvers.A stochastic optimization framework tailored for the TphA-based station-keeping process is leveraged to search for fuel-optimal and error-robust TphA ***-satellite orbits(QSOs)around phobos are investigated to demonstrate the efficacy of TphA in mutli-fidelity dynamical *** Carlo simulations demonstrated that the baseline QSO of JAXA’s Martian Moons eXploration(MMX)mission could be maintained with a monthly maneuver budget of approximately 1 m/s.

关键词： target phase approach(TphA) station-keeping poincarémap differential algebra(DA) quasi-satellite orbit(QSO)

perturbed initial orbit determination

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Astrodynamics 2024年第3期8卷 401-416页

作者： Alberto Fossà Matteo Losacco Roberto Armellin Institut Supérieur de l’Aéronautique et de l’Espace Toulouse31400France te pūnahaĀtea-space institute The University of AucklandAuckland1010New Zealand

An algorithm for robust initial orbit determination (IOD) under perturbed orbital dynamics is presented. By leveraging map inversion techniques defined in the algebra of Taylor polynomials, this tool returns a highly accurate solution to the IOD problem and estimates a range centered on the aforementioned solution in which the true orbit should lie. To meet the specified accuracy requirements, automatic domain splitting is used to wrap the IOD routines and ensure that the local truncation error, introduced by a polynomial representation of the state estimate, remains below a predefined threshold. The algorithm is presented for three types of ground-based sensors, namely range radars, Doppler-only radars, and optical telescopes, by considering their different constraints in terms of available measurements and sensor noise. Finally, the improvement in performance with respect to a Keplerian-based IOD solution is demonstrated using large-scale numerical simulations over a subset of tracked objects in low Earth orbit.

关键词： initial orbit determination(IOD) range radar Doppler radar optical telescope differential algebra(DA)

Safe-event pruning in spacecraft conjunction management

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Astrodynamics 2023年第4期7卷 401-413页

作者： Sébastien Henry Roberto Armellin Thibault Gateau Guggenheim School of Aerospace Engineering Georgia Institute of TechnologyAtlantaGA 30332USA te punaha atea-space institute The University of AucklandAuckland 1010New Zealand Department of Aerospace Vehicles Design and Control Institut Superieur de I'Aeronautique et de I'EspaceToulouse 31055France

spacecraft conjunction management plays a crucial role in the mitigation of space *** a conjunction event occurs,resources and time are spent analyzing,planning,and potentially maneuvering the *** work contributes to a subpart of the problem:Confidently identifying events that will not lead to a high collision probability,and therefore do not require further *** method reduces the dimensionality of the data via principal component analysis(pCA)on a subset of ***-risk regions are then determined by clustering the projected data,and events that do not belong to a high-risk cluster are pruned.A genetic algorithm(GA)is developed to optimize the number of clusters and feature selection of the ***,an ensemble learning framework is proposed to combine the suboptimal models for better *** results show that the first set of parameters pruned approximately 50%of the events in the testing set with no false negatives,whereas the second set of parameters pruned 70%of the events and maintained a near-perfect *** results could benefit the optimization of operational resources and allow operators to focus better on the events of interest.

关键词： space situational awareness collision avoidance genetic algorithm(GA) ensemble learning

Effect of Wall Thicknesses on Broadband Design of Ka-Band te_(21)-Mode Coupler

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Journal of Electronic Science and technology 2021年第4期19卷 350-356页

作者： Wei Zheng Chao Wang Wen-Li Yang Chun-Bang Wu with the institute of space Antenna China Academy of Space TechnologyXi’an 710100

Commonly,the classical formulas are suitable for designing the te21-mode coupler for the operating frequency under Ka-band by ignoring the wall ***,in practice,for the one operated in the Ka-band,such classical formulas are not valid and the effect of wall thicknesses should be ***,we propose a design method for the Ka-band te21-mode coupler via computer simulations,taking into account the wall *** experimental results show that using the linear twice-weighted algorithm to optimize the coupling hole size can improve the coupler *** the bandwidth of such coupler increases by 10%with lower coupling loss(40 dB).

关键词： Coupling loss isolation te21-mode coupler useless hole

Are the well-fed less thirsty?Effects of drought and salinity on New Zealand mangroves

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Journal of plant Ecology 2022年第1期15卷 85-99页

作者： Sridevi Ravi Martin K-FBader Tim Young Mark Duxbury Michael Clearwater Cate Macinnis-Ng Sebastian Leuzinger School of Science Auckland University of TechnologyAucklandNew Zealand Department of Forestry and Wood technology Linnaeus UniversityVäxjöSweden Centre for Biomedical and Chemical Sciences School of ScienceAuckland University of TechnologyAucklandNew Zealand School of Science and Environmental Research institute University of WaikatoPrivate Bag 3105HamiltonNew Zealand School of Biological Sciences and te pūnaha Matatini University of AucklandAucklandNew Zealand

Despite a large number of studies examining the effects of abiotic stress factors on plants,the mechanistic explanations of drought-induced tree mortality remain inconclusive and even less is known about how multiple stressors *** role of non-structural carbohydrates(NSCs)in preventing or postponing drought mortality is gaining ***,we tested the role of NSCs in mitigating the effects of drought and salinity in New Zealand mangroves,Avicennia marina *** experimentally manipulated plant NSC levels,prior to subjecting them to combinations of drought and *** growth and survival rates were 2-and 3-fold higher in the high-NSC(H-NSC)group than in the low-NSC(L-NSC)group under high salinity and drought conditions,*** 12 weeks under high salinity-high drought conditions,the H-NSC group showed higher stem hydraulic conductivity(281±50 mmol cm^(−1)s^(−1)Mpa^(−1))compared with the L-NSC group(134±40 mmol cm^(−1)s^(−1)Mpa^(−1)).Although starch levels remained relatively constant,we found a 20%increase in soluble sugars in the stems of H-NSC group under high drought and high salinity in week 8 compared with week *** results suggest(i)an important role of NSCs in mitigating the effects of low soil water potential caused by drought and salinity,and(ii)sink-limited growth under conditions of combined salinity and drought.

关键词： non-structural carbohydrates Avicennia marina subsp.australasica drought and salt tolerance carbon limitation temperate mangroves

te doped ultrabroad band tunnel junction

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Journal of Semiconductors 2014年第10期35卷 23-25页

作者：陆宏波沈静曼李欣益张玮周大勇孙利杰陈开建 Research Center for photovoltaics Shanghai Institute of Space Power-Source

A Galnp/AlGaAs broadband tunnel junction （TJ） with a peak current density of 65.3 A/cm2 and an AlGalnp/AlGaAs ultrabroad band TJ with a peak current density of 6.1 A/cm2 were studied and fabricated. Di- ethyltellurium （DEte） was chosen as an n-type dopant in the TJ. The growth temperature, valve switching and flow variation parameters of DEte were studied for better performance. Measurements, including predoping of DEte before growth and heating up reactor temperature after growth, were taken to deal with the effect of turn-on and off of tellurium. The strain balance method was used to the manage lattice mismatch that was introduced by the tellurium. Various flows of DEte were studied to get the appropriate value needed to fabricate a high peak current density tunnel junction.

关键词： tunnel junction solar cell broadband

Magnetopause properties at the dusk magnetospheric flank from global magnetohydrodynamic simulations,the kinetic Vlasov equilibrium,and in situ observations--potential implications for SMILE

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Earth and planetary physics 2024年第1期8卷 222-233页

作者： Marius Echim Costel Munteanu Gabriel Voitcu Eliza teodorescu institute of space Science Măgurele 077125Romania Royal Belgian institute for space Aeronomy 1180 BrusselsBelgium Solar-terrestrial Centre of Excellence(STCE) 1180 BrusselsBelgium

We derived the properties of the terrestrial magnetopause(Mp)from two modeling approaches,one global–fluid,the other local–kinetic,and compared the results with data collected in situ by the Magnetospheric Multiscale 2(MMS2)*** used global magnetohydrodynamic(MHD)simulations of the Earth’s magnetosphere(publicly available from the NASA-CCMC[National Aeronautics and space Administration–Community Coordinated Modeling Center])and local Vlasov equilibrium models(based on kinetic models for tangential discontinuities)to extract spatial profiles of the plasma and field variables at the Earth’s *** global MHD simulations used initial solar wind conditions extracted from the OMNI database at the time epoch when the MMS2 observes the *** kinetic Vlasov model used asymptotic boundary conditions derived from the same in situ MMS measurements upstream or downstream of the *** global MHD simulations provide a three-dimensional image of the magnetosphere at the time when the MMS2 crosses the *** Vlasov model provides a one-dimensional local view of the Mp derived from first principles of kinetic *** MMS2 experimental data also serve as a reference for comparing and validating the numerical simulations and *** found that the Mp transition layer formed in global MHD simulations was generally localized closer to the Earth(roughly by one Earth radius)from the position of the real Mp observed by the *** also found that the global MHD simulations overestimated the thickness of the Mp transition by one order of magnitude for three analyzed variables:magnetic field,density,and tangential *** Mp thickness derived from the local Vlasov equilibrium was consistent with observations for all three of these *** overestimation of density in the Vlasov equilibrium was reduced compared with the global MHD *** discuss our results in the context of future SMILE(Solar wind Magnetosphere Ionosphere Link Explorer)campaigns for observing

关键词： magnetopause magnetohydrodynamic numerical simulations Vlasov equilibrium Magnetospheric Multiscale observations

2D Materials Based Optoelectronic Memory: Convergence of Electronic Memory and Optical Sensor

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Research 2019年第1期2019卷 624-640页

作者： Feichi Zhou Jiewei Chen Xiaoming Tao Xinran Wang Yang Chai Department of Applied physics Te Hong Kong Polytechnic UniversityHong Kong institute of textiles and Clothing Te Hong Kong Polytechnic UniversityHong Kong School of Electronic Science and Engineering Nanjing UniversityNanjingChina

te continuous development of electron devices towards the trend of“More than Moore”requires functional diversifcation that can collect data(sensors)and store(memories)and process(computing units)*** the large occupation proportion of image data in both data center and edge devices,a device integration with optical sensing and data storage and processing is highly demanded for future energy-efcient and miniaturized electronic ***-dimensional(2D)materials and their heterostructures have exhibited broadband photoresponse and high photoresponsivity in the confguration of optical sensors and showed fast switching speed,multi-bit data storage,and large ON/OFF ratio in memory *** addition,its ultrathin body thickness and transfer process at low temperature allow 2D materials to be heterogeneously integrated with other existing materials *** this paper,we overview the state-of-the-art optoelectronic random-access memories(ORAMs)based on 2D materials,as well as ORAM synaptic devices and their applications in neural network and image *** ORAM devices potentially enable direct storage/processing of sensory data from external *** also provide perspectives on possible directions of other neuromorphic sensor design(e.g.,auditory and olfactory)based on 2D materials towards the future smart electronic systems for artifcial intelligence.

关键词： system. neural image

Influences of Yttrium on Microstructure and Mechanical properties of NiAl-28Cr-5.5Mo-0.5Hf Alloy

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Journal of Rare Earths 2002年第4期20卷 295-298页

作者：任维丽郭建亭周继扬 Department of aterials Engineering Dalian University of Te chnology Dalian 116024 China institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China Department of aterials Engineering Dalian University of Te chnology Dalian 116024 China

The influences of yttrium on the microstructure and mechanical properties of NiAl-28Cr-5.5Mo-0.5Hf alloy were investigated by using SEM, XRD and compressive tests, respectively. The study indicates that the compressive strength and ductility of 0.05% Y(mass fraction)-containing alloy are superior to those of other alloys at the strain rate of 1.94×10 -3 s -1 over a range from room temperature to high temperature. It is also found that the microstructure of alloys is refined gradually with increasing Y content. This is reflected by more grain cells, finer spacing between Cr(Mo) fibers and smaller Cr(Mo) rods at the grain boundary. When 0.1% Y(mass fraction) and above are added to the matrix, the yttrious compounds of Y 2Ni 17 and Al 3Y form at the interfaces between NiAl and Cr(Mo) phases, which leads to the decrease of strength and ductility. Therefore, the proper addition of Y can improve the compressive strength and ductility of the alloy.

关键词： rare earths NiAl alloy microstructure mechanical properties