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Lou T.,Zhengzhou University of Light Industry | Zhao L.,Beijing Institute of TechnologyBeijing
Acta Astronautica

A robust integrated navigation algorithm based on a special robust desensitized extended Kalman filtering with analytical gain (ADEKF) during the Mars atmospheric entry is proposed. The robust ADEKF is realized by minimizing a new function penalized by a trace weighted norm of the state error sensitivities and giving a closed-form gain matrix. The uncertainties of the Mars atmospheric density and the lift-to-drag ratio are modeled. Sensitivity matrices are defined to character the parameter uncertainties, and corresponding perturbation matrices are introduced to describe the navigation errors with respect to the parameter uncertainties. The numerical simulation results show that the robust integrated navigation algorithm based on the robust ADEKF effectively reduces the negative effects of the two parameter uncertainties and has good consistency during the Mars entry. © 2015 IAA. Source

Fang X.-Y.,Yanshan University | Yu X.-X.,Yanshan University | Zheng H.-M.,Yanshan University | Jin H.-B.,Beijing Institute of TechnologyBeijing | And 2 more authors.
Physics Letters, Section A: General, Atomic and Solid State Physics

Abstract We established a calculation model of the conductivity of multilayer graphene based on Boltzmann transport equation and 2D electron gas theory. Numerical simulations show that the conductivities of few-layer graphene and graphene nanosheets are reduced when thickness is increased. The reduction rate decreases for micron-range thicknesses and remains constant thereafter. Moreover, the conductivity increases with the increase in temperature, in which the increase rate declines as temperature increases. Higher thickness exhibits a more obvious temperature effect on conductivity. Such effect also increases with the increase in temperature. © 2015 Elsevier B.V. Source

Wei K.,Peking University | Chen H.,Beijing Institute of TechnologyBeijing | Pei Y.,Peking University | Fang D.,Peking University | Fang D.,Beijing Institute of TechnologyBeijing
Journal of the Mechanics and Physics of Solids

The unexpected thermal distortions and failures in engineering raise the big concern about thermal expansion controlling. Thus, design of tailorable coefficient of thermal expansion (CTE) is urgently needed for the materials used in large temperature variation circumstance. Here, inspired by multi-fold rotational symmetry in crystallography, we have devised six kinds of periodic planar lattices, which incorporate tailorable CTE and high specific biaxial stiffness. Fabrication process, which overcame shortcomings of welding or adhesion connection, was developed for the dual-material planar lattices. The analytical predictions agreed well with the CTE measurements. It is shown that the planar lattices fabricated from positive CTE constituents, can give large positive, near zero and even negative CTEs. Furthermore, a generalized stationary node method was proposed for aperiodic lattices and even arbitrary structures with desirable thermal expansion. As an example, aperiodic quasicrystal lattices were designed and exhibited zero thermal expansion property. The proposed method for the lattices of lightweight, robust stiffness, strength and tailorable thermal expansion is useful in the engineering applications. © 2015 Elsevier Ltd. Source

Yu Q.,Beijing Institute of TechnologyBeijing | Cao C.,Beijing Institute of TechnologyBeijing
Nanoscience and Nanotechnology Letters

As an alternative to conventional solid-state photovoltaic, regenerative photoelectrochemical (PEC) cells based on semiconductor/liquid junctions have attracted more and more attentions and attained competitive photoconversion efficiencies. However, most of the efficiency increases were achieved by various methods that can only increase the photocurrents, but not improve the photovoltage limits. Here, we show voltage-added regenerative PEC cell by combining n-Si photoanode with p-Si photocathode. By using CH3CN as the solvent, LiClO4 as the supporting electrolyte, and decamethylferrocenium/decamethylferrocene (Me10Fc+/0 ) as the redox couple, the n-p PEC cell can achieve an open-circuit photovoltage of 0.627 V, exceeding 0.480 V and 0.213 V for comprising n-PEC and p-PEC respectively. In addition, the PEC performances of single-crystal planar Si photoelectrodes and nanowire-array Si photoelectrodes prepared by electroless etching were compared. The wire-array electrodes showed an enhancement in photocurrent, but a slight decrease in phtovoltage. The high open-circuit voltage (>0.6 V) is also the highest ever reported voltage for Si-based PEC solar cells. This is paving the way for the development of a new generation of highly efficient PEC cells with high photovoltge and photocurrent. Copyright © 2015 American Scientific Publishers. Source

Chen D.,Beijing Institute of TechnologyBeijing | Zhong Y.,Beijing Institute of TechnologyBeijing
Biophysical Journal

Abstract Normal left-right patterning in vertebrates depends on the rotational movement of nodal cilia. In order to produce this ciliary motion, the activity of axonemal dyneins must be tightly regulated in a temporal and spatial manner; the specific activation pattern of the dynein motors in the nodal cilia has not been reported. Contemporary imaging techniques cannot directly assess dynein activity in a living cilium. In this study, we establish a three-dimensional model to mimic the ciliary ultrastructure and assume that the activation of dynein proteins is related to the interdoublet distance. By employing finite-element analysis and grid deformation techniques, we simulate the mechanical function of dyneins by pairs of point loads, investigate the time-variant interdoublet distance, and simulate the dynein-triggered ciliary motion. The computational results indicate that, to produce the rotational movement of nodal cilia, the dynein activity is transferred clockwise (looking from the tip) between the nine doublet microtubules, and along each microtubule, the dynein activation should occur faster at the basal region and slower when it is close to the ciliary tip. Moreover, the time cost by all the dyneins along one microtubule to be activated can be used to deduce the dynein activation pattern; it implies that, as an alternative method, measuring this time can indirectly reveal the dynein activity. The proposed protein-structure model can simulate the ciliary motion triggered by various dynein activation patterns explicitly and may contribute to furthering the studies on axonemal dynein activity. © 2015 Biophysical Society. Source

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