Mitigating ground effect on mini quadcopters with model reference adaptive control

Mitigating ground effect becomes a big challenge for autonomous aerial vehicles when they are flying in close proximity to the ground. This paper aims to develop a precise model of ground effect on mini quadcopters, provide an advanced control algorithm to counter the model uncertainty and, as a result, improves the command tracking performance when the vehicle is in the ground effect region. The mathematical model of ground effect has been established through a series of experiments and validated by a flight test. The experiments show that the total thrust generated by rotors increases linearly as the vehicle gets closer to the ground, which is different from the commonly-used ground effect model for a single rotor vehicle. In addition, the model switches from a piecewise linear to a quadratic function when the rotor to rotor distance is increased. A control architecture that utilizes the model reference adaptive controller (MRAC) has also been designed, where MRAC is added to the altitude loop. The performance of the proposed control algorithm has been evaluated through a set of flight tests on a mini quadcopter platform and compared with a traditional proportional–integral–derivative (PID) controller. The results demonstrate that MRAC dramatically improves the tracking performance of altitude command and can reduce the rise time by 80 % under the ground effect

Effect of carrot puree edible films on quality preservation of fresh-cut carrots

peer-reviewedFinancial support from the high level talent fund of Henan University of Technology Science and Technology (No. 2012BS024) is gratefully acknowledged.The effect of edible films based on carrot puree, chitosan, corn starch, gelatin, glycerol and cinnamaldehyde on fresh-cut carrots was studied during storage. Several parameters, such as firmness, colour, weight loss, total carotenoids, total phenols, polyphenol oxidase (PPO) activity and peroxidase (POD) activity in coated carrots were determined at regular intervals and then compared with the uncoated carrots throughout the storage period. Significant and expected changes were observed in all carrot samples that were compared. The coating treatment significantly (P < 0.05) delayed the senescence, reduced the deterioration of exterior quality and retained total carotenoids well compared with control (P < 0.05). In addition, significant inhibition of PPO activity (P < 0.05) and POD activity (P < 0.05) as well as reduced accumulation of polyphenols (P < 0.05) were observed for all coated samples. All of these favourable responses induced by coating treatment on minimally processed fresh-cut carrots showed beneficial physiological effects, which would give some useful references to the fresh-cut fruit and vegetable processing industry and satisfy people’s requirements allowing for extending product shelf life without negatively affecting the sensory quality or acceptability.Henan University of Technology Science and Technolog

Validation of multiprocessor systems

Experiments that can be used to validate fault free performance of multiprocessor systems in aerospace systems integrating flight controls and avionics are discussed. Engineering prototypes for two fault tolerant multiprocessors are tested

Induced Growth of Asymmetric Nanocantilever Arrays on Polar Surfaces

©2003 The American Physical Society. The electronic version of this article is the complete one and can be found online at: http://link.aps.org/doi/10.1103/PhysRevLett.91.185502DOI: 10.1103/PhysRevLett.91.185502We report that the Zn-terminated ZnO (0001) polar surface is chemically active and the oxygenterminated (0001) polar surface is inert in the growth of nanocantilever arrays. Longer and wider "comblike" nanocantilever arrays are grown from the (0001)-Zn surface, which is suggested to be a self-catalyzed process due to the enrichment of Zn at the growth front. The chemically inactive (0001)-O surface typically does not initiate any growth, but controlling experimental conditions could lead to the growth of shorter and narrower nanocantilevers from the intersections between (0001)-O with (0110) surfaces

Efficient wireless packet scheduling in a non-cooperative environment: Game theoretic analysis and algorithms

In many practical scenarios, wireless devices are autonomous and thus, may exhibit non-cooperative behaviors due to self-interests. For instance, a wireless cellular device may be programmed to report bogus channel information to gain resource allocation advantages. Such non-cooperative behaviors are highly probable as the device's software can be modified by the user. In this paper, we first analyze the impact of these rationally selfish behaviors on the performance of packet scheduling algorithms in time-slotted wireless networks. Using a mixed strategy game model, we show that the traditional maximum rate packet scheduling algorithm can cause non-cooperative devices to converge to highly inefficient Nash equilibria, in which the wireless channel resources are significantly wasted. By using a repeated game to enforce cooperation, we further propose a novel game theoretic algorithm that can lead to an efficient equilibrium. © 2010 Elsevier Inc. All rights reserved.postprin

VCG-based time-slot auctioning in IEEE 802.16 OFDM/TDMA wireless mesh networks

In this paper, we study the problem of bandwidth resource allocation in a non-cooperative IEEE 802.16 OFDM/TDMA based wireless mesh network, and propose an auction based framework in which the gateway, equipped with the precious high speed Internet connection, serves as the auctioneer while the first-level mesh routers (MRs) (i.e., those with direct wireless connections to the gateway) act as bidders competing resources among each other. We then present Vickrey-Clarke-Groves (VCG) based auction approaches to allocate time-slots among MRs. Through simulations, we find that the proposed VCG algorithms can achieve much better throughput and connection blocking probability performance than traditional resource allocation approaches in a non-cooperative environment. ©2009 IEEE.published_or_final_versionThe 5th International Conference on Wireless Communications, Networking and Mobile Computing (WiCOM 2009), Beijing, China, 24-26 September 2009. In Proceedings of the International Conference on Wireless Communications, Networking and Mobile Computing, 2009, p. 1-

Relay auction algorithms for downlink bandwidth allocation in IEEE 802.16-based OFDM/TDMA wireless mesh networks

In this paper, we study the problem of downlink bandwidth allocation in a non-cooperative IEEE 802.16 OFDM/TDMA based wireless mesh network, and propose an auction based framework in which the gateway, equipped with the precious high speed Internet connection, serves as the auctioneer while the first-level mesh routers (MRs) (i.e., those with direct wireless connections to the gateway) act as bidders competing resources among each other. We then present two novel relay auction (RA) approaches to allocate time-slots among MRs and analyze the bidding strategy using the solution concept of Nash equilibrium. Through simulations, we find that the proposed RA algorithms can achieve competitive performance in terms of resource allocation efficiency compared with Vickrey-Clarke-Groves (VCG) approaches, while having the capability to strike a proper balance between efficiency and fairness by adjusting the payment function. Specifically, with a smaller payment parameter value, the RA algorithms can also achieve much better connection blocking probability performance than VCG algorithms.published_or_final_versionThe 4th International Conference on Communications and Networking in China (ChinaCOM 2009), Xian, China, 26-28 August 2009. In Proceedings of ChinaCOM, 2009, p. 1-