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An accurate photovoltaic (PV) generation forecasting is important for grid scheduling and dispatching. However, ultra-short-term PV generation forecasting is rather challenging because weather conditions may change significantly in a short time period largely due to the dynamics and movement of clouds above a solar PV farm. For monitoring clouds above the solar PV farm, ground-based whole-sky cameras (Sky-Imagers) have been installed. This paper develops a novel cloud image-based ultra-short-term forecasting framework. Within the framework, an integration of the Vision Transformer (ViT) model and the Gated Recurrent Unit (GRU) encoder is designed for the high-dimensional latent feature analysis. A Multi-Layer Perception (MLP) is employed to generate the one-step-ahead PV generation forecasting. Numeric experiments are conducted using real-world solar PV datasets. The results show that the proposed framework and algorithms can achieve higher accuracy compared to several baseline methods for ultra-short-term PV generation forecasting.

Electric-field control of spin dynamics is significant for spintronic device applications. Thus far, effectively electric-field control of magnetic order, magnetic damping factor and spin-orbit torque (SOT) has been studied in magnetic materials, but the electric field control of spin relaxation still remains unexplored. Here, we use ionic liquid gating to control spin-related property in the ultra-thin (4 nm) heavy metal (HM) platinum (Pt) and ferromagnetic insulator (FMI) yttrium iron garnet (Y3Fe5O12, YIG) heterostructure. It is found that the anomalous Hall effect (AHE), spin relaxation time and spin diffusion length can be effectively controlled by the electric field. The anomalous Hall resistance is almost twice as large as at 0 voltage after applying a small voltage of 5.5 V. The spin relaxation time can vary by more than 50 percent with the electric field, from 41.6 to 64.5 fs. In addition, spin relaxation time at different gate voltage follows the reciprocal law of the electron momentum scattering time, which indicates that the D'yakonov-Perel' mechanism is dominant in the Pt/YIG system. Furthermore, the spin diffusion length can be effectively controlled by an ionic gate, which can be well explained by voltage-modulated interfacial spin scattering. These results help us to improve the interface spin transport properties in magnetic materials, with great contributions to the exploration of new physical mechanisms and spintronics device.

The Dzyaloshinskii-Moriya interaction (DMI) is an antisymmetric exchange interaction that stabilizes spin chirality. One scientific and technological challenge is understanding and controlling the interaction between spin chirality and electric field. In this study, we investigate an unconventional electric field effect on interfacial DMI, skyrmion helicity, and skyrmion dynamics in a system with broken inversion symmetry. We design heterostructures with a 3d-5d atomic orbital interface to demonstrate the gate bias control of the DMI energy and thus transform the DMI between opposite chiralities. Furthermore, we use this voltage-controlled DMI (VCDMI) to manipulate the skyrmion spin texture. As a result, a type of intermediate skyrmion with a unique helicity is created, and its motion can be controlled and made to go straight. Our work shows the effective control of spin chirality, skyrmion helicity, and skyrmion dynamics by VCDMI. It promotes the emerging field of voltage-controlled chiral interactions and voltage-controlled skyrmionics.

In the present study, large eddy simulation is used to investigate combustion recession for the Engine Combustion Network Spray A flame at two ambient temperatures (850 K and 800 K) and two injection pressures (100 MPa and 50 MPa). The present numerical results are able to capture different combustion recession phenomena after the end-of-injection (AEOI). With an injection pressure of 100 MPa, the model predicts a ‘‘separated’’ combustion recession at the ambient temperature of 850 K and no combustion recession at the ambient temperature of 800 K, in which both predictions correspond to the measurements. The combustion recession is mainly controlled by the auto-ignition process at the ambient temperature of 850 K. At the ambient temperature of 800 K, the local temperature within the fuel-rich region is not high enough to promote the hightemperature ignition process. As time progresses, the mixture within the fuel-rich region rapidly transitions to become an overly fuel-lean mixture, which further hinders high-temperature ignition to occur. Nonetheless, it is shown that lowering the injection pressure to 50 MPa causes the combustion recession to occur at the ambient temperature of 800 K. This is likely attributed to the low injection case having a lower air entrainment rate AEOI, which causes the mixtures upstream of the lift-off position to transition slower from fuel-rich to fuel-lean mixtures.

The optical transitions and random walking dynamics of the three types of excitons, namely, free, donor-bound, and acceptor-like surface-defect-bound excitons, in both the graphene−GaN hybrid structure and bare GaN are comparatively examined using variable-temperature steady-state photoluminescence and time-resolved photoluminescence. The results reveal that the effective suppression of surface defects may be realized by a graphene capping monolayer, evidenced by the strong reduction of the luminescence signal of the surface-defect-bound excitons and the simultaneous enhancement of the free exciton luminescence. More interestingly, the coupling strengths between all the three kinds of excitons and the longitudinal optical phonons tend to weaken, especially for the surface-defect-bound excitons, which exhibit a reduction of ≈40%. These findings indicate that capping GaN by graphene could be an effective way to passivate harmful surface defects and address the heating problem in GaN-based devices. © 2021 Wiley-VCH GmbH.

The optical transitions and random walking dynamics of the three types of excitons, namely, free, donor-bound, and acceptor-like surface-defect-bound excitons, in both the graphene−GaN hybrid structure and bare GaN are comparatively examined using variable-temperature steady-state photoluminescence and time-resolved photoluminescence. The results reveal that the effective suppression of surface defects may be realized by a graphene capping monolayer, evidenced by the strong reduction of the luminescence signal of the surface-defect-bound excitons and the simultaneous enhancement of the free exciton luminescence. More interestingly, the coupling strengths between all the three kinds of excitons and the longitudinal optical phonons tend to weaken, especially for the surface-defect-bound excitons, which exhibit a reduction of ≈40%. These findings indicate that capping GaN by graphene could be an effective way to passivate harmful surface defects and address the heating problem in GaN-based devices. © 2021 Wiley-VCH GmbH.

The optical transitions and random walking dynamics of the three types of excitons, namely, free, donor-bound, and acceptor-like surface-defect-bound excitons, in both the graphene−GaN hybrid structure and bare GaN are comparatively examined using variable-temperature steady-state photoluminescence and time-resolved photoluminescence. The results reveal that the effective suppression of surface defects may be realized by a graphene capping monolayer, evidenced by the strong reduction of the luminescence signal of the surface-defect-bound excitons and the simultaneous enhancement of the free exciton luminescence. More interestingly, the coupling strengths between all the three kinds of excitons and the longitudinal optical phonons tend to weaken, especially for the surface-defect-bound excitons, which exhibit a reduction of ≈40%. These findings indicate that capping GaN by graphene could be an effective way to passivate harmful surface defects and address the heating problem in GaN-based devices. © 2021 Wiley-VCH GmbH.

Xiaotao Jiang,1,2 Fan Liu,2,3 Peng Liu,1,2 Yanhua Yan,1,2 Shaoyang Lan,1 Kunhai Zhuang,1,4 Yufeng Liu,5 Kailin Jiang,1,2 Yuancheng Huang,1,2 Kechao Nie,1,2 Zhihua Zheng,1,2 Jinglin Pan,6 Junhui Zheng,1,2 Fengbin Liu,1,4 Shijie Xu,5 Peiwu Li,1 Yi Wen1 1Department of Gastroenterology, The First Affiliated Hospital of Guangzhou University of Chinese Medicine, Guangzhou, Guangdong, People’s Republic of China; 2First Clinical Medical College, Guangzhou University of Chinese Medicine, Guangzhou, Guangdong, People’s Republic of China; 3Zhaoqing Hospital of Chinese Medicine Affiliated to Southern Medical University, Zhaoqing, Guangdong, People’s Republic of China; 4Baiyun Hospital of the First Affiliated Hospital of Guangzhou University of Chinese Medicine, Guangzhou, Guangdong, People’s Republic of China; 5Guangzhou University of Chinese Medicine, Guangzhou, Guangdong, People’s Republic of China; 6Department of Gastroenterology, Hainan Provincial Hospital of Traditional Chinese Medicine, Haikou, Hainan, People’s Republic of ChinaCorrespondence: Peiwu Li; Yi Wen Email doctorlipw2@163.com; 421491922@qq.comObjective: We aimed to build a ferroptosis-based classifier to characterize the molecular features of gastric cancers (GC) and investigate the relationship between different ferroptosis patterns and GC tumor microenvironment (TME).Methods: Based on the genomic and clinical information from TCGA portal and GEO database, non-negative matrix factorization (NMF) was used to identify ferroptosis subtypes in GC patients. In order to estimate the ferroptosis levels, we established ferroptosis subtype score (FSS) to quantify ferroptosis patterns and ferroptosis potential index (FPI) by principal component analysis (PCA). The correlations of different ferroptosis patterns with TME cell-infiltrating characteristics (including immune cell infiltration, immune checkpoints expression levels, tumor mutational burden (TMB) and immunotherapy response) were systematically analyz

The present thesis aims at studying n-heptane/methanol dual-fuel combustion under internal combustion engine conditions and strives to improve the understanding of its ignition, combustion, and pollutant emission mechanisms. Large-eddy simulation (LES) coupled with Eulerian stochastic fields (ESF) approach is employed to simulate single/dual-fuel combustion in a constant-volume vessel to mimic the single/dual-fuel combustion in conventional/dual-fuel premixed engines. The experimental configuration from Engine Combustion Network (ECN) is considered as the baseline case in the simulations. The main works are summarized in two parts: model development and studies of the fundamental physics involved in dual-fuel combustion.First, the ESF approach with a novel modified method is proposed, implemented, and evaluated. Results show that the modified ESF method removes the numerical error in the element mass conservation and shows capability in predicting both premixed and non-premixed flames relevant to dual-fuel combustion. Second, LES of n-heptane single-fuel and n-heptane/methanol dual-fuel combustion is carried out and validated against ECN Spray-H experiments. A good agreement is obtained in terms of flow, combustion, and emissions characteristics. Finally, a parameter study is performed to investigate the effects of the dual-fuel strategies, including the primary fuel concentration, the ambient temperature, and the pilot fuel injection timing. It is concluded that: 1) The ambient methanol is found to have an effect of suppressing the two-stage ignition and heat release of n-heptane, this is more significant under high ambient methanol concentration conditions. 2) The effects of methanol on the n-heptane ignition and NOx formation are strongly dependent on the ambient temperatures. The retardation of the n-heptane high temperature ignition is more remarkable under low ambient temperatures. The NOx and soot in the dual-fuel case is lower than that of the single-fuel ca

In this paper, we develop a novel weighted Laplacian method, which is partially inspired by the theory of graph Laplacian, to study recent popular graph problems, such as multilevel graph partitioning and balanced minimum cut problem, in a more convenient manner. Since the weighted Laplacian strategy inherits the virtues of spectral methods, graph algorithms designed using weighted Laplacian will necessarily possess more robust theoretical guarantees for algorithmic performances, comparing with those existing algorithms that are heuristically proposed. In order to illustrate its powerful utility both in theory and in practice, we also present two effective applications of our weighted Laplacian method to multilevel graph partitioning and balanced minimum cut problem, respectively. By means of variational methods and theory of partial differential equations (PDEs), we have established the equivalence relations among the weighted cut problem, balanced minimum cut problem and the initial clustering problem that arises in the middle stage of graph partitioning algorithms under a multilevel structure. These equivalence relations can indeed provide solid theoretical support for algorithms based on our proposed weighted Laplacian strategy. Moreover, from the perspective of the application to the balanced minimum cut problem, weighted Laplacian can make it possible for research of numerical solutions of PDEs to be a powerful tool for the algorithmic study of graph problems. Experimental results also indicate that the algorithm embedded with our strategy indeed outperforms other existing graph algorithms, especially in terms of accuracy, thus verifying the efficacy of the proposed weighted Laplacian.

Shijie Xu,1,* Fangbo Cui,2,3,* Dafu Huang,4,* Dinghu Zhang,5 Anqing Zhu,6 Xia Sun,6 Yiming Cao,7 Sheng Ding,7 Yao Wang,7 Eryun Gao,3 Fenglin Zhang3 1Center for Public Health Research, Medical School, Nanjing University, Nanjing, China; 2Department of Oncology, Wannan Medical College, Wuhu, Anhui, China; 3Department of Oncology, The People’s Hospital of Ma Anshan, Ma Anshan, Anhui, China; 4Department of Oncology, Nanjing Lishui People’s Hospital, Zhongda Hospital Lishui Branch, Southeast University, Nanjing, Jiangsu, China; 5Department of Oncology, Tongde Hospital of Zhejiang Province, Hangzhou, China; 6Department of Oncology, The Affliated Jiangyin Hospital of Southeast University Medical College, Jiangyin, Jiangsu, China; 7Department of General Surgery, The People’s Hospital of Ma Anshan, Ma Anshan, Anhui, China *These authors contributed equally to this work Background: Docetaxel (DOC) is widely used as a chemotherapy drug for various tumors, including gastric cancer (GC), but the clinical application of DOC has been limited due to the hydrophobicity of the drug. We aimed to formulate a multifunctional nanoparticle (NP) system to reduce the side effects of the chemotherapy agent, to promote synergistic therapeutic effects, and to achieve targeted delivery of the therapy. Methods: The polyethylene glycol-poly(ε-caprolactone) NPs (PEG-PCL NPs) were prepared by a ring opening copolymerization technique and were then conjugated with a programmed death-ligand 1 (PD-L1) monoclonal antibody (mAb). The effects of the surface coating on particle size, size distribution, zeta potential, drug encapsulation efficiency, loading capacity, and the drug release kinetics were investigated. By using a panel of PD-L1-expressing human GC cell lines and PD-L1-overexpressing cells, we studied cellular uptake, cytotoxic effects, and cellular apoptosis in the presence of PD-L1 mAb-conjugated NPs. Results: The characterization of the structure and

Shijie Xu,1,* Fangbo Cui,2,3,* Dafu Huang,4,* Dinghu Zhang,5 Anqing Zhu,6 Xia Sun,6 Yiming Cao,7 Sheng Ding,7 Yao Wang,7 Eryun Gao,3 Fenglin Zhang3 1Center for Public Health Research, Medical School, Nanjing University, Nanjing, China; 2Department of Oncology, Wannan Medical College, Wuhu, Anhui, China; 3Department of Oncology, The People’s Hospital of Ma Anshan, Ma Anshan, Anhui, China; 4Department of Oncology, Nanjing Lishui People’s Hospital, Zhongda Hospital Lishui Branch, Southeast University, Nanjing, Jiangsu, China; 5Department of Oncology, Tongde Hospital of Zhejiang Province, Hangzhou, China; 6Department of Oncology, The Affliated Jiangyin Hospital of Southeast University Medical College, Jiangyin, Jiangsu, China; 7Department of General Surgery, The People’s Hospital of Ma Anshan, Ma Anshan, Anhui, China *These authors contributed equally to this work Background: Docetaxel (DOC) is widely used as a chemotherapy drug for various tumors, including gastric cancer (GC), but the clinical application of DOC has been limited due to the hydrophobicity of the drug. We aimed to formulate a multifunctional nanoparticle (NP) system to reduce the side effects of the chemotherapy agent, to promote synergistic therapeutic effects, and to achieve targeted delivery of the therapy. Methods: The polyethylene glycol-poly(ε-caprolactone) NPs (PEG-PCL NPs) were prepared by a ring opening copolymerization technique and were then conjugated with a programmed death-ligand 1 (PD-L1) monoclonal antibody (mAb). The effects of the surface coating on particle size, size distribution, zeta potential, drug encapsulation efficiency, loading capacity, and the drug release kinetics were investigated. By using a panel of PD-L1-expressing human GC cell lines and PD-L1-overexpressing cells, we studied cellular uptake, cytotoxic effects, and cellular apoptosis in the presence of PD-L1 mAb-conjugated NPs. Results: The characterization of the structure and

By utilizing and designing coupled InGaN QW-QDs nanostructures as active layer, we show a demonstration of significant enhancement of green emission in the hybrid nanostructure with a 4.5 nm GaN barrier layer at high temperatures. Such enhancement is ascribed to temperature-dependent phonon-assisted tunneling of excitons from QW to QDs and suppression of nonradiative recombination of excitons localized in the QDs layer in the sample with a 4.5 nm barrier layer. This study shall be useful for optimization design of high-efficiency InGaN-based green LEDs and also could shed some light on the complicated internal luminescence mechanisms in InGaN QW-QDs hybrid nanostructures.

By utilizing and designing coupled InGaN QW-QDs nanostructures as active layer, we show a demonstration of significant enhancement of green emission in the hybrid nanostructure with a 4.5 nm GaN barrier layer at high temperatures. Such enhancement is ascribed to temperature-dependent phonon-assisted tunneling of excitons from QW to QDs and suppression of nonradiative recombination of excitons localized in the QDs layer in the sample with a 4.5 nm barrier layer. This study shall be useful for optimization design of high-efficiency InGaN-based green LEDs and also could shed some light on the complicated internal luminescence mechanisms in InGaN QW-QDs hybrid nanostructures.

Copyright © 2016 by the American Institute of Aeronautics and Astronautics, Inc. Design of the transfer from lunar orbits to the sun-Earth libration point region by direct searching in the highfidelity ephemeris model is an accurate but time-consuming practice. A computationally efficient methodology that takes advantage of the patched elliptic restricted three-body problem model, the power of graphics processing unit parallel computing, and the programming platform of MATLAB is presented. Taking the CHANG'E-2 extension mission as an instance, the proposed implementation obtains almost identical results with that in the ephemeris model and shows significant speedup. Moreover, the methodology can be carried out on inexpensive hardware platforms. Numerical results demonstrate that significant speedups can be achieved using the graphics processing unit parallel computing when compared to solving the same problem on the central processing unit., Peer Reviewed, Postprint (author's final draft)

By utilizing and designing coupled InGaN QW-QDs nanostructures as active layer, we show a demonstration of significant enhancement of green emission in the hybrid nanostructure with a 4.5 nm GaN barrier layer at high temperatures. Such enhancement is ascribed to temperature-dependent phonon-assisted tunneling of excitons from QW to QDs and suppression of nonradiative recombination of excitons localized in the QDs layer in the sample with a 4.5 nm barrier layer. This study shall be useful for optimization design of high-efficiency InGaN-based green LEDs and also could shed some light on the complicated internal luminescence mechanisms in InGaN QW-QDs hybrid nanostructures.

Mingjuan Liu,1 Ming Yao,1,2 Hanqi Wang,1 Longsheng Xu,1 Ying Zheng,1 Bing Huang,1 Huadong Ni,1 Shijie Xu,1 Xuyan Zhou,1 Qingquan Lian2 1Department of Anesthesiology and Pain Medicine, The First Hospital of Jiaxing, The First Affiliated Hospital of Jiaxing University, Jiaxing, 2Department of Anesthesiology, The Second Affiliated Hospital of Wenzhou Medical University, Wenzhou, People’s Republic of China Background: Cancer-induced bone pain (CIBP) is one of the most challenging clinical problems due to a lack of understanding the mechanisms. Recent evidence has demonstrated that activation of microglial G-protein-coupled P2Y12 receptor (P2Y12R) and proinflammatory cytokine production play an important role in neuropathic pain generation and maintenance. However, whether P2Y12R is involved in CIBP remains unknown.Methods: The purpose of this study was to investigate the role of P2Y12R in CIBP and its molecular mechanisms. Using the bone cancer model inoculated with Walker 256 tumor cells into the left tibia of Sprague Dawley rat, we blocked spinal P2Y12R through intrathecal administration of its selective antagonist MRS2395 (400 pmol/µL, 15 µL).Results: We found that not only the ionized calcium-binding adapter molecule 1 (Iba-1)-positive microglia in the ipsilateral spinal cord but also mechanical allodynia was significantly inhibited. Furthermore, it decreased the phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK) and the production of proinflammatory cytokines interleukin-1β (IL-1β) and interleukin-6 (IL-6), whereas it increased tumor necrosis factor-α (TNF-α).Conclusion: Taken together, our present results suggest that microglial P2Y12R in the spinal cord may contribute to CIBP by the activation of spinal microglia and p38MAPK pathway, thus identifying a potential therapeutic target for the treatment of CIBP. Keywords: P2Y12 receptor, cancer-induced bone pain, p38MAPK pathway, cytok

Large-area graphene grown on Cu foil with chemical vapor deposition was transferred onto intentionally undoped GaN epilayer to form a graphene/GaN Schottky junction. Optical spectroscopic techniques including steady-state and time-resolved photoluminescence (PL) were employed to investigate the electron transfer between graphene and n-type GaN at different temperatures. By comparing the near-band-edge excitonic emissions before and after the graphene covering, some structures in the excitonic PL spectra are found to show interesting changes. In particular, a distinct

Large-area graphene grown on Cu foil with chemical vapor deposition was transferred onto intentionally undoped GaN epilayer to form a graphene/GaN Schottky junction. Optical spectroscopic techniques including steady-state and time-resolved photoluminescence (PL) were employed to investigate the electron transfer between graphene and n-type GaN at different temperatures. By comparing the near-band-edge excitonic emissions before and after the graphene covering, some structures in the excitonic PL spectra are found to show interesting changes. In particular, a distinct

Room-temperature Raman scattering studies of new InP1−xBix alloys grown by molecular beam epitaxy are reported. Two new Bi-induced vibrations observed at 149 and 171 cm−1 are assigned to InBi-like TO and LO phonon modes, respectively, and exhibit an unusually strong intensity for the dilute regime. Two additional modes at 311 and 337 cm−1 are resolved as well with unknown origins. The Raman intensities of the InBi-like TO and LO bands, as well as the new mode at 337 cm−1, exhibit strong and linear dependence on the Bi concentration for the composition range studied, 0.003 ≤ x ≤ 0.023. This correlation may serve as a fast and convenient means of characterizing bismuth composition not only in the ternary alloy InP1−xBix but also in the quaternaries such as In1−yGayP1−xBix and In1−yAlyP1−xBix.

Room-temperature Raman scattering studies of new InP1−xBix alloys grown by molecular beam epitaxy are reported. Two new Bi-induced vibrations observed at 149 and 171 cm−1 are assigned to InBi-like TO and LO phonon modes, respectively, and exhibit an unusually strong intensity for the dilute regime. Two additional modes at 311 and 337 cm−1 are resolved as well with unknown origins. The Raman intensities of the InBi-like TO and LO bands, as well as the new mode at 337 cm−1, exhibit strong and linear dependence on the Bi concentration for the composition range studied, 0.003 ≤ x ≤ 0.023. This correlation may serve as a fast and convenient means of characterizing bismuth composition not only in the ternary alloy InP1−xBix but also in the quaternaries such as In1−yGayP1−xBix and In1−yAlyP1−xBix.

Large-area graphene grown on Cu foil with chemical vapor deposition was transferred onto intentionally undoped GaN epilayer to form a graphene/GaN Schottky junction. Optical spectroscopic techniques including steady-state and time-resolved photoluminescence (PL) were employed to investigate the electron transfer between graphene and n-type GaN at different temperatures. By comparing the near-band-edge excitonic emissions before and after the graphene covering, some structures in the excitonic PL spectra are found to show interesting changes. In particular, a distinct

The motion of a point mass in the J2 problem is generalized to that of a rigid body in a J2 gravity field. Different with the original J2 problem, the gravitational orbit-rotation coupling of the rigid body is considered in this generalized problem. The linear stability of the classical type of relative equilibria of the rigid body, which have been obtained in our previous paper, is studied in the framework of geometric mechanics with the second-order gravitational potential. Non-canonical Hamiltonian structure of the problem, i.e., Poisson tensor, Casimir functions and equations of motion, are obtained through a Poisson reduction process by means of the symmetry of the problem. The linear system matrix at the relative equilibria is given through the multiplication of the Poisson tensor and Hessian matrix of the variational Lagrangian. Based on the characteristic equation of the linear system matrix, the conditions of linear stability of the relative equilibria are obtained. With the stability conditions obtained, the linear stability of the relative equilibria is investigated in details in a wide range of the parameters of the gravity field and the rigid body. We find that both the zonal harmonic J2 and the characteristic dimension of the rigid body have significant effects on the linear stability. Similar to the attitude stability in a central gravity field, the linear stability region is also consisted of two regions that are analogues of the Lagrange region and the DeBra-Delp region. Our results are very useful for the studies on the motion of natural satellites in our solar system., Comment: The 2013 AAS/AIAA Astrodynamics Specialist Conference, AAS 13-760, Hilton Head, South Carolina, August 11-15, 2013

The classical problem of attitude stability in a central gravity field is generalized to that on a stationary orbit around a uniformly-rotating asteroid. This generalized problem is studied in the framework of geometric mechanics. Based on the natural symplectic structure, the non-canonical Hamiltonian structure of the problem is derived. The Poisson tensor, Casimir functions and equations of motion are obtained in a differential geometric method. The equilibrium of the equations of motion, i.e. the equilibrium attitude of the spacecraft, is determined from a global point of view. Nonlinear stability conditions of the equilibrium attitude are obtained with the energy-Casimir method. The nonlinear attitude stability is then investigated versus three parameters of the asteroid, including the ratio of the mean radius to the stationary orbital radius, the harmonic coefficients C20 and C22. It is found that when the spacecraft is located on the intermediate-moment principal axis of the asteroid, the nonlinear stability domain can be totally different from the classical Lagrange region on a circular orbit in a central gravity field., Comment: The 23rd AAS/AIAA Space Flight Mechanics Meeting, AAS 13-219, Kauai, Hawaii, February 10-14, 2013

Orbit-attitude hovering of a spacecraft at the natural relative equilibria in the body-fixed frame of a uniformly rotating asteroid is discussed in the framework of the full spacecraft dynamics, in which the spacecraft is modeled as a rigid body with the gravitational orbit-attitude coupling. In this hovering model, both the position and attitude of the spacecraft are kept to be stationary in the asteroid body-fixed frame. A Hamiltonian structure-based feedback control law is proposed to stabilize the relative equilibria of the full dynamics to achieve the orbit-attitude hovering. The control law is consisted of two parts: potential shaping and energy dissipation. The potential shaping is to make the relative equilibrium a minimum of the modified Hamiltonian on the invariant manifold by modifying the potential artificially. With the energy-Casimir method, it is shown that the unstable relative equilibrium can always be stabilized in the Lyapunov sense by the potential shaping with sufficiently large feedback gains. Then the energy dissipation leads the motion to converge asymptotically to the minimum of the modified Hamiltonian on the invariant manifold, i.e., the relative equilibrium. The feasibility of the proposed stabilization control law is validated through numerical simulations in the case of a spacecraft orbiting around a small asteroid. The main advantage of the proposed hovering control law is that it is very simple and is easy to implement autonomously by the spacecraft with little computation. This advantage is attributed to the utilization of dynamical behaviors of the system in the control design., Comment: The 24th AAS/AIAA Space Flight Mechanics Meeting, AAS 14-352, Santa Fe, New Mexico, January 26-30, 2014

The dynamical behavior of spacecraft around asteroids is a key element in design of such missions. An asteroid's irregular shape, non-spherical mass distribution and its rotational sate make the dynamics of spacecraft quite complex. This paper focuses on the gravity gradient torque of spacecraft around non-spherical asteroids. The gravity field of the asteroid is approximated as a 2nd degree and order-gravity field with harmonic coefficients C20 and C22. By introducing the spacecraft's higher-order inertia integrals, a full fourth-order gravity gradient torque model of the spacecraft is established through the gravitational potential derivatives. Our full fourth-order model is more precise than previous fourth-order model due to the consideration of higher-order inertia integrals of the spacecraft. Some interesting conclusions about the gravity gradient torque model are reached. Then a numerical simulation is carried out to verify our model. In the numerical simulation, a special spacecraft consisted of 36 point masses connected by rigid massless rods is considered. We assume that the asteroid is in a uniform rotation around its maximum-moment principal axis, and the spacecraft is on the stationary orbit in the equatorial plane. Simulation results show that the motion of previous fourth-order model is quite different from the exact motion, while our full fourth-order model fits the exact motion very well. And our model is precise enough for practical applications., Comment: The 22nd AAS/AIAA Space Flight Mechanics Meeting, AAS 12-133, Charleston, South Carolina, January 29-February 2, 2012. arXiv admin note: substantial text overlap with arXiv:1311.4127

There exist cislunar and trans-lunar libration points near the Moon, which are referred as the LL1 and LL2 points respectively and can generate the different types of low-energy trajectories transferring from Earth to Moon. The time-dependent analytic model including the gravitational forces from the Sun, Earth and Moon is employed to investigate the energy-minimal and practical transfer trajectories. However, different from the circular restricted three-body problem, the equivalent gravitational equilibria are defined according to the geometry of instantaneous Hill's boundary due to the gravitational perturbation from the Sun. The relationship between the altitudes of periapsis and eccentricities is achieved from the Poincar\'e mapping for all the lunar captured trajectories, which presents the statistical feature of the fuel cost and captured orbital elements rather than generating a specified Moon-captured segment. The minimum energy required by the captured trajectory on a lunar circular orbit is deduced in the spatial bi-circular model. It is presented that the asymptotical behaviors of invariant manifolds approaching to/from the libration points or halo orbits are destroyed by the solar perturbation. In fact, the energy-minimal cislunar transfer trajectory is acquired by transiting LL1 point, while the energy-minimal trans-lunar transfer trajectory is obtained by transiting LL2 point. Finally, the transfer opportunities for the practical trajectories escaped from the Earth and captured by the Moon are yielded by transiting halo orbits near LL1 and LL2 points, which can be used to generate the whole trajectories., Comment: 45 pages, 28 figures

The dynamical behavior of spacecraft around asteroids is a key element in design of such missions. An asteroid's irregular shape, non-spherical mass distribution and its rotational sate make the dynamics of spacecraft quite complex. This paper focuses on the gravity gradient torque of spacecraft around non-spherical asteroids. The gravity field of the asteroid is approximated as a 2nd degree and order-gravity field with harmonic coefficients C20 and C22. By introducing the spacecraft's higher-order inertia integrals, a full fourth-order gravity gradient torque model of the spacecraft is established through the gravitational potential derivatives. Our full fourth-order model is more precise than previous fourth-order model due to the consideration of higher-order inertia integrals of the spacecraft. Some interesting conclusions about the gravity gradient torque model are reached. Then a numerical simulation is carried out to verify our model. In the numerical simulation, a special spacecraft consisted of 36 point masses connected by rigid massless rods is considered. We assume that the asteroid is in a uniform rotation around its maximum-moment principal axis, and the spacecraft is on the stationary orbit in the equatorial plane. Simulation results show that the motion of previous fourth-order model is quite different from the exact motion, while our full fourth-order model fits the exact motion very well. And our model is precise enough for practical applications., Comment: The 22nd AAS/AIAA Space Flight Mechanics Meeting, AAS 12-133, Charleston, South Carolina, January 29-February 2, 2012. arXiv admin note: substantial text overlap with arXiv:1311.4127

The motion of a point mass in the J2 problem is generalized to that of a rigid body in a J2 gravity field. Different with the original J2 problem, the gravitational orbit-rotation coupling of the rigid body is considered in this generalized problem. The linear stability of the classical type of relative equilibria of the rigid body, which have been obtained in our previous paper, is studied in the framework of geometric mechanics with the second-order gravitational potential. Non-canonical Hamiltonian structure of the problem, i.e., Poisson tensor, Casimir functions and equations of motion, are obtained through a Poisson reduction process by means of the symmetry of the problem. The linear system matrix at the relative equilibria is given through the multiplication of the Poisson tensor and Hessian matrix of the variational Lagrangian. Based on the characteristic equation of the linear system matrix, the conditions of linear stability of the relative equilibria are obtained. With the stability conditions obtained, the linear stability of the relative equilibria is investigated in details in a wide range of the parameters of the gravity field and the rigid body. We find that both the zonal harmonic J2 and the characteristic dimension of the rigid body have significant effects on the linear stability. Similar to the attitude stability in a central gravity field, the linear stability region is also consisted of two regions that are analogues of the Lagrange region and the DeBra-Delp region. Our results are very useful for the studies on the motion of natural satellites in our solar system., Comment: The 2013 AAS/AIAA Astrodynamics Specialist Conference, AAS 13-760, Hilton Head, South Carolina, August 11-15, 2013

Orbit-attitude hovering of a spacecraft at the natural relative equilibria in the body-fixed frame of a uniformly rotating asteroid is discussed in the framework of the full spacecraft dynamics, in which the spacecraft is modeled as a rigid body with the gravitational orbit-attitude coupling. In this hovering model, both the position and attitude of the spacecraft are kept to be stationary in the asteroid body-fixed frame. A Hamiltonian structure-based feedback control law is proposed to stabilize the relative equilibria of the full dynamics to achieve the orbit-attitude hovering. The control law is consisted of two parts: potential shaping and energy dissipation. The potential shaping is to make the relative equilibrium a minimum of the modified Hamiltonian on the invariant manifold by modifying the potential artificially. With the energy-Casimir method, it is shown that the unstable relative equilibrium can always be stabilized in the Lyapunov sense by the potential shaping with sufficiently large feedback gains. Then the energy dissipation leads the motion to converge asymptotically to the minimum of the modified Hamiltonian on the invariant manifold, i.e., the relative equilibrium. The feasibility of the proposed stabilization control law is validated through numerical simulations in the case of a spacecraft orbiting around a small asteroid. The main advantage of the proposed hovering control law is that it is very simple and is easy to implement autonomously by the spacecraft with little computation. This advantage is attributed to the utilization of dynamical behaviors of the system in the control design., Comment: The 24th AAS/AIAA Space Flight Mechanics Meeting, AAS 14-352, Santa Fe, New Mexico, January 26-30, 2014

The classical problem of attitude stability in a central gravity field is generalized to that on a stationary orbit around a uniformly-rotating asteroid. This generalized problem is studied in the framework of geometric mechanics. Based on the natural symplectic structure, the non-canonical Hamiltonian structure of the problem is derived. The Poisson tensor, Casimir functions and equations of motion are obtained in a differential geometric method. The equilibrium of the equations of motion, i.e. the equilibrium attitude of the spacecraft, is determined from a global point of view. Nonlinear stability conditions of the equilibrium attitude are obtained with the energy-Casimir method. The nonlinear attitude stability is then investigated versus three parameters of the asteroid, including the ratio of the mean radius to the stationary orbital radius, the harmonic coefficients C20 and C22. It is found that when the spacecraft is located on the intermediate-moment principal axis of the asteroid, the nonlinear stability domain can be totally different from the classical Lagrange region on a circular orbit in a central gravity field., Comment: The 23rd AAS/AIAA Space Flight Mechanics Meeting, AAS 13-219, Kauai, Hawaii, February 10-14, 2013

There exist cislunar and trans-lunar libration points near the Moon, which are referred as the LL1 and LL2 points respectively and can generate the different types of low-energy trajectories transferring from Earth to Moon. The time-dependent analytic model including the gravitational forces from the Sun, Earth and Moon is employed to investigate the energy-minimal and practical transfer trajectories. However, different from the circular restricted three-body problem, the equivalent gravitational equilibria are defined according to the geometry of instantaneous Hill's boundary due to the gravitational perturbation from the Sun. The relationship between the altitudes of periapsis and eccentricities is achieved from the Poincar\'e mapping for all the lunar captured trajectories, which presents the statistical feature of the fuel cost and captured orbital elements rather than generating a specified Moon-captured segment. The minimum energy required by the captured trajectory on a lunar circular orbit is deduced in the spatial bi-circular model. It is presented that the asymptotical behaviors of invariant manifolds approaching to/from the libration points or halo orbits are destroyed by the solar perturbation. In fact, the energy-minimal cislunar transfer trajectory is acquired by transiting LL1 point, while the energy-minimal trans-lunar transfer trajectory is obtained by transiting LL2 point. Finally, the transfer opportunities for the practical trajectories escaped from the Earth and captured by the Moon are yielded by transiting halo orbits near LL1 and LL2 points, which can be used to generate the whole trajectories., Comment: 45 pages, 28 figures

Purpose: This paper presents a full fourth-order model of the gravity gradient torque of spacecraft around asteroids by taking into consideration of the inertia integrals of the spacecraft up to the fourth order, which is an improvement of the previous fourth-order model of the gravity gradient torque. Design, methodology and approach: The fourth-order gravitational potential of the spacecraft is derived based on Taylor expansion. Then the expression of the gravity gradient torque in terms of gravitational potential derivatives is derived. By using the formulation of the gravitational potential, explicit formulations of the full fourth-order gravity gradient torque are obtained. Then a numerical simulation is carried out to verify our model. Findings: We find that our model is more sound and precise than the previous fourth-order model due to the consideration of higher-order inertia integrals of the spacecraft. Numerical simulation results show that the motion of the previous fourth-order model is quite different from the exact motion, while our full fourth-order model fits the exact motion very well. Our full fourth-order model is precise enough for high-precision attitude dynamics and control around asteroids. Practical implications: This high-precision model is of importance for the future asteroids missions for scientific explorations and near-Earth objects mitigation. Originality and value: In comparison with the previous model, a gravity gradient torque model around asteroids that is more sound and precise is established. This model is valuable for high-precision attitude dynamics and control around asteroids.

The motion of a point mass in the J2 problem has been generalized to that of a rigid body in a J2 gravity field for new high-precision applications in the celestial mechanics and astrodynamics. Unlike the original J2 problem, the gravitational orbit-rotation coupling of the rigid body is considered in the generalized problem. The existence and properties of both the classical and non-classical relative equilibria of the rigid body are investigated in more details in the present paper based on our previous results. We nondimensionalize the system by the characteristic time and length to make the study more general. Through the study, it is found that the classical relative equilibria can always exist in the real physical situation. Numerical results suggest that the non-classical relative equilibria only can exist in the case of a negative J2, i.e., the central body is elongated; they cannot exist in the case of a positive J2 when the central body is oblate. In the case of a negative J2, the effect of the orbit-rotation coupling of the rigid body on the existence of the non-classical relative equilibria can be positive or negative, which depends on the values of J2 and the angular velocity. The bifurcation from the classical relative equilibria, at which the non-classical relative equilibria appear, has been shown with different parameters of the system. Our results here have given more details of the relative equilibria than our previous paper, in which the existence conditions of the relative equilibria are derived and primarily studied. Our results have also extended the previous results on the relative equilibria of a rigid body in a central gravity field by taking into account the oblateness of the central body., Comment: Accepted for publication in Astrophysics and Space Science. arXiv admin note: text overlap with arXiv:1304.6867

The motion of a point mass in the J2 problem is generalized to that of a rigid body in a J2 gravity field. The linear and nonlinear stability of the classical type of relative equilibria of the rigid body, which have been obtained in our previous paper, are studied in the framework of geometric mechanics with the second-order gravitational potential. Non-canonical Hamiltonian structure of the problem, i.e., Poisson tensor, Casimir functions and equations of motion, are obtained through a Poisson reduction process by means of the symmetry of the problem. The linear system matrix at the relative equilibria is given through the multiplication of the Poisson tensor and Hessian matrix of the variational Lagrangian. Based on the characteristic equation of the linear system matrix, the conditions of linear stability of the relative equilibria are obtained. The conditions of nonlinear stability of the relative equilibria are derived with the energy-Casimir method through the projected Hessian matrix of the variational Lagrangian. With the stability conditions obtained, both the linear and nonlinear stability of the relative equilibria are investigated in details in a wide range of the parameters of the gravity field and the rigid body. We find that both the zonal harmonic J2 and the characteristic dimension of the rigid body have significant effects on the linear and nonlinear stability. Similar to the classical attitude stability in a central gravity field, the linear stability region is also consisted of two regions that are analogues of the Lagrange region and the DeBra-Delp region respectively. The nonlinear stability region is the subset of the linear stability region in the first quadrant that is the analogue of the Lagrange region. Our results are very useful for the studies on the motion of natural satellites in our solar system., Comment: Accepted for publication in Astrophysics and Space Science

Purpose: This paper presents a full fourth-order model of the gravity gradient torque of spacecraft around asteroids by taking into consideration of the inertia integrals of the spacecraft up to the fourth order, which is an improvement of the previous fourth-order model of the gravity gradient torque. Design, methodology and approach: The fourth-order gravitational potential of the spacecraft is derived based on Taylor expansion. Then the expression of the gravity gradient torque in terms of gravitational potential derivatives is derived. By using the formulation of the gravitational potential, explicit formulations of the full fourth-order gravity gradient torque are obtained. Then a numerical simulation is carried out to verify our model. Findings: We find that our model is more sound and precise than the previous fourth-order model due to the consideration of higher-order inertia integrals of the spacecraft. Numerical simulation results show that the motion of the previous fourth-order model is quite different from the exact motion, while our full fourth-order model fits the exact motion very well. Our full fourth-order model is precise enough for high-precision attitude dynamics and control around asteroids. Practical implications: This high-precision model is of importance for the future asteroids missions for scientific explorations and near-Earth objects mitigation. Originality and value: In comparison with the previous model, a gravity gradient torque model around asteroids that is more sound and precise is established. This model is valuable for high-precision attitude dynamics and control around asteroids.

The motion of a point mass in the J2 problem has been generalized to that of a rigid body in a J2 gravity field for new high-precision applications in the celestial mechanics and astrodynamics. Unlike the original J2 problem, the gravitational orbit-rotation coupling of the rigid body is considered in the generalized problem. The existence and properties of both the classical and non-classical relative equilibria of the rigid body are investigated in more details in the present paper based on our previous results. We nondimensionalize the system by the characteristic time and length to make the study more general. Through the study, it is found that the classical relative equilibria can always exist in the real physical situation. Numerical results suggest that the non-classical relative equilibria only can exist in the case of a negative J2, i.e., the central body is elongated; they cannot exist in the case of a positive J2 when the central body is oblate. In the case of a negative J2, the effect of the orbit-rotation coupling of the rigid body on the existence of the non-classical relative equilibria can be positive or negative, which depends on the values of J2 and the angular velocity. The bifurcation from the classical relative equilibria, at which the non-classical relative equilibria appear, has been shown with different parameters of the system. Our results here have given more details of the relative equilibria than our previous paper, in which the existence conditions of the relative equilibria are derived and primarily studied. Our results have also extended the previous results on the relative equilibria of a rigid body in a central gravity field by taking into account the oblateness of the central body., Comment: Accepted for publication in Astrophysics and Space Science. arXiv admin note: text overlap with arXiv:1304.6867

The motion of a point mass in the J2 problem is generalized to that of a rigid body in a J2 gravity field. The linear and nonlinear stability of the classical type of relative equilibria of the rigid body, which have been obtained in our previous paper, are studied in the framework of geometric mechanics with the second-order gravitational potential. Non-canonical Hamiltonian structure of the problem, i.e., Poisson tensor, Casimir functions and equations of motion, are obtained through a Poisson reduction process by means of the symmetry of the problem. The linear system matrix at the relative equilibria is given through the multiplication of the Poisson tensor and Hessian matrix of the variational Lagrangian. Based on the characteristic equation of the linear system matrix, the conditions of linear stability of the relative equilibria are obtained. The conditions of nonlinear stability of the relative equilibria are derived with the energy-Casimir method through the projected Hessian matrix of the variational Lagrangian. With the stability conditions obtained, both the linear and nonlinear stability of the relative equilibria are investigated in details in a wide range of the parameters of the gravity field and the rigid body. We find that both the zonal harmonic J2 and the characteristic dimension of the rigid body have significant effects on the linear and nonlinear stability. Similar to the classical attitude stability in a central gravity field, the linear stability region is also consisted of two regions that are analogues of the Lagrange region and the DeBra-Delp region respectively. The nonlinear stability region is the subset of the linear stability region in the first quadrant that is the analogue of the Lagrange region. Our results are very useful for the studies on the motion of natural satellites in our solar system., Comment: Accepted for publication in Astrophysics and Space Science

The heterostructure conduction band offset Delta E-o in In0.08Ga0.92N/Al0.075In0.045Ga0.88N quantum wells (QWs) was characterized by capacitance-voltage (C-V) and deep-level transient spectroscopy (DLTS) measurements made on the QWs, which acted as the light-emitting active layer of GaN p-n light-emitting diodes (LEDs). The thermal emission energy of the In0.08Ga0.92N wells was found to be 0.21 +/- 0.01 eV. This corresponds to a conduction band offset of about 0.25 +/- 0.02 eV. (C) 2012 The Japan Society of Applied Physics

The heterostructure conduction band offset Delta E-o in In0.08Ga0.92N/Al0.075In0.045Ga0.88N quantum wells (QWs) was characterized by capacitance-voltage (C-V) and deep-level transient spectroscopy (DLTS) measurements made on the QWs, which acted as the light-emitting active layer of GaN p-n light-emitting diodes (LEDs). The thermal emission energy of the In0.08Ga0.92N wells was found to be 0.21 +/- 0.01 eV. This corresponds to a conduction band offset of about 0.25 +/- 0.02 eV. (C) 2012 The Japan Society of Applied Physics

Formation dynamics of free and neutral donor bound excitons (FX and D 0X) in a high quality ZnO single crystal are studied by means of time-resolved photoluminescence (TRPL) at various temperatures. At low-temperatures, FX and D 0X formation times are determined to be ∼5 and ∼10 ps, respectively, by fitting the rise process with the Boltzmann sigmoidal function. Temporal information of FX- and D 0X-longitudinal optical (LO) phonon coupling is also acquired by measuring TRPL spectra of the first-order LO phonon-assisted FX and D 0X transitions. In particular, interesting time evolution of luminescence intensity in the Fano resonance region due to the configuration interaction of exciton-impurity-phonon is explored. © 2011 American Chemical Society.

The heterostructure conduction band offset Delta E-o in In0.08Ga0.92N/Al0.075In0.045Ga0.88N quantum wells (QWs) was characterized by capacitance-voltage (C-V) and deep-level transient spectroscopy (DLTS) measurements made on the QWs, which acted as the light-emitting active layer of GaN p-n light-emitting diodes (LEDs). The thermal emission energy of the In0.08Ga0.92N wells was found to be 0.21 +/- 0.01 eV. This corresponds to a conduction band offset of about 0.25 +/- 0.02 eV. (C) 2012 The Japan Society of Applied Physics

Formation dynamics of free and neutral donor bound excitons (FX and D 0X) in a high quality ZnO single crystal are studied by means of time-resolved photoluminescence (TRPL) at various temperatures. At low-temperatures, FX and D 0X formation times are determined to be ∼5 and ∼10 ps, respectively, by fitting the rise process with the Boltzmann sigmoidal function. Temporal information of FX- and D 0X-longitudinal optical (LO) phonon coupling is also acquired by measuring TRPL spectra of the first-order LO phonon-assisted FX and D 0X transitions. In particular, interesting time evolution of luminescence intensity in the Fano resonance region due to the configuration interaction of exciton-impurity-phonon is explored. © 2011 American Chemical Society.

A series of bound exciton transitions of a bulk ZnO sample has been studied by high resolution magnetophotoluminescence spectra. Ten sharp intense bound exciton emissions are classified into three groups according to their dependences on magnetic field, angle, and circular polarization of the emission lines. The charge states of the defect centers and exciton types are identified. The effective g factors of the electrons and holes are determined.

A series of bound exciton transitions of a bulk ZnO sample has been studied by high resolution magnetophotoluminescence spectra. Ten sharp intense bound exciton emissions are classified into three groups according to their dependences on magnetic field, angle, and circular polarization of the emission lines. The charge states of the defect centers and exciton types are identified. The effective g factors of the electrons and holes are determined.

Quantum dissipation and broadening mechanisms in Si-doped InGaN quantum dots are studied via the photoluminescence technique. It is found that the dissipative thermal bath that embeds the quantum dots plays an important role in the photon emission processes. Observed spontaneous emission spectra are modeled with the multimode Brownian oscillator model achieving an excellent agreement between experiment and theory for a wide temperature range. The dimensionless Huang-Rhys factor characterizing the strength of electron-LO-phonon coupling and damping constant accounting for the LO-phonon-bath interaction strength are found to be similar to 0.2 and 200 cm(-1), respectively, for the InGaN QDs. (c) 2006 American Institute of Physics.

Quantum dissipation and broadening mechanisms in Si-doped InGaN quantum dots are studied via the photoluminescence technique. It is found that the dissipative thermal bath that embeds the quantum dots plays an important role in the photon emission processes. Observed spontaneous emission spectra are modeled with the multimode Brownian oscillator model achieving an excellent agreement between experiment and theory for a wide temperature range. The dimensionless Huang-Rhys factor characterizing the strength of electron-LO-phonon coupling and damping constant accounting for the LO-phonon-bath interaction strength are found to be similar to 0.2 and 200 cm(-1), respectively, for the InGaN QDs. (c) 2006 American Institute of Physics.

Quantum dissipation and broadening mechanisms in Si-doped InGaN quantum dots are studied via the photoluminescence technique. It is found that the dissipative thermal bath that embeds the quantum dots plays an important role in the photon emission processes. Observed spontaneous emission spectra are modeled with the multimode Brownian oscillator model achieving an excellent agreement between experiment and theory for a wide temperature range. The dimensionless Huang-Rhys factor characterizing the strength of electron-LO-phonon coupling and damping constant accounting for the LO-phonon-bath interaction strength are found to be similar to 0.2 and 200 cm(-1), respectively, for the InGaN QDs. (c) 2006 American Institute of Physics.

The paper proposes an algorithm to identify state space noise model from closed-loop system via the numerical algorithm for subspace state space system identification, N4SID. It works well on both stable and unstable systems with serious noises and can derive quite accurate plant and noise models together from closed-loop measurement signals.