X-ray pulsar-based navigation (XNAV) using one X-ray detector is investigated as an augmentation to the capability of an ultraviolet (UV) sensor-based satellite autonomous navigation system. The satellite state dynamics are analyzed to establish the dynamical equations of the satellite autonomous navigation system. A time transformation equation that accounts for relativistic effects is presented and the measurement model of the XNAV system is derived using pulse phase information from only one pulsar. The measurement model of the UV sensor-based satellite navigation system is presented using the Earth image information from the UV sensor. In order to integrate the measurements from the X-ray sensor and the UV sensor, a federated filter is developed to provide the optimal simultaneous estimation of position and velocity of the satellite. The concept is demonstrated on a GPS orbit and a geosynchronous orbit and it is found that the performance of the integrated satellite navigation system is improved with respect to that of the UV sensor-based satellite navigation system. 相似文献
The organic magnetoconductance (MC) effects in poly(3-hexylthiophene): [6,6]-phenyl-C61-butyricacid methylester based bulk heterojunction solar cells were studied in dark and under illumination. The correlations between the MC and current character were revealed in this study. Results show that the dark current always exhibits a negative MC whereas a sign change in MC under illumination occurs at the bias around the open circuit voltage Voc. We suggest that the positive MC in photocurrent is due to the field dependent conversion of singlet electron–hole pairs to triplet states and the negative MC is associated with space charge limited current with traps. Other possible mechanisms about the magnetoconductance effects are also discussed. 相似文献
Authentication schemes are widely used mechanisms to thwart unauthorized access of resources over insecure networks. Several smart card based password authentication schemes have been proposed in the literature. In this paper, we demonstrate the security limitations of a recently proposed password based authentication scheme, and show that their scheme is still vulnerable to forgery and offline password guessing attacks and it is also unable to provide user anonymity, forward secrecy and mutual authentication. With the intention of fixing the weaknesses of that scheme, we present a secure authentication scheme. We show that the proposed scheme is invulnerable to various attacks together with attacks observed in the analyzed scheme through both rigorous formal and informal security analysis. Furthermore, the security analysis using the widely-accepted Real-Or-Random (ROR) model ensures that the proposed scheme provides the session key (SK) security. Finally, we carry out the performance evaluation of the proposed scheme and other related schemes, and the result favors that the proposed scheme provides better trade-off among security and performance as compared to other existing related schemes.
Dry etching of C-plane sapphire wafer has been studied using Ga+ focused ion beam milling (FIBM). Due to a much lower milling rate of sapphire compared to GaN, it has been proven that gas-assisted FIBM (GAFIBM) is a necessity. Furthermore, it needs to be determined whether XeF2- or I2-GAFIBM can improve the technique. We found that XeF2-GAFIBM gave the highest milling rate. The obtained enhancement factor of the XeF2-GAFIBM milling rate compared to FIBM rate varied from 2.3 to 1.2 for the ion beam current in the range 20 pA-1 nA. A favorable milling rate selectivity of sapphire to nickel film of about 1.5 was obtained by XeF2-GAFIBM at 350 pA. We have successfully fabricated a variety of 2D sapphire-based submicron pillar or hole arrays in regular crystals, quasicrystals and aperiodic symmetries. The nearest neighbor distance was down to 230 nm. The depth achieved was deeper than 400 nm. The air filling factor ranged from 12% to 60%. These sapphire-based 2D microstructures were applied on flip-chip GaN-based light emitting diodes (LEDs) and more than 40% improvement in light extraction was obtained. 相似文献
A low complexity punctured belief propagation ( BP) detection utilizing channel puncturing for multi-user
multiple-input multiple-output (MU-MIMO) systems is proposed in this paper. This paper constructs a cycle-freefator graph by puncturing certain non-zero entries in a transformed channel matrix, and proposes an adjusted BPalgorithm with a more exact a posteriori message updating equation. The proposed algorithm converges rapidly inseveral iterations due to the cycle-free structure in the factor graph. Nevertheless, puncturing brings distorted noiseand thus leads to performance degradation. To tackle this issue, this article further designs a layered detection withthe help of maximum likelihood detector ( MLD). Simulations demonstrate that the proposed detection algorithmachieves the identical performance to MLD with much lower complexity. 相似文献
A facile one‐step hydrothermal method is developed for large‐scale production of well‐designed flexible and free‐standing Co3O4/reduced graphene oxide (rGO)/carbon nanotubes (CNTs) hybrid paper as an electrode for electrochemical capacitors. Densely packed unique Co3O4 monolayer microsphere arrays uniformly cover the surface of the rGO/CNTs film. The alkaline hydrothermal treatment leads to not only the deposition of Co3O4 microspheres array, but also the reduction of the GO sheets at the same time. The unique hybrid paper is evaluated as an electrode for electrochemical capacitors without any ancillary materials. It is found that the obtained hybrid flexible paper, composed of Co3O4 microsphere array anchored to the underling conductive rGO/CNTs substrate with robust adhesion, is able to deliver high specific capacitance with excellent electrochemical stability even at high current densities, suggesting its promising application as an efficient electrode material for electrochemical capacitors. 相似文献