We describe our research in using environmental visual landmarks as the basis for completing simple robot construction tasks. Inspired by honeybee visual navigation behavior, a visual template mechanism is proposed in which a natural landmark serves as a visual reference or template for distance determination as well as for navigation during collective construction. To validate our proposed mechanism, a wall construction problem is investigated and a minimalist solution is given. Experimental results show that, using the mechanism of a visual template, a collective robotic system can successfully build the desired structure in a decentralized fashion using only local sensing and no direct communication. In addition, a particular variable, which defines tolerance for alignment of the structure, is found to impact the system performance. By decreasing the value of the variable, system performance is improved at the expense of a longer construction time. The visual template mechanism is appealing in that it can use a reference point or salient object in a natural environment that is new or unexplored and it could be adapted to facilitate more complicated building tasks.

Maintenance of high performance formation control is important for low Earth orbit (LEO) formation missions of small spacecraft. In this paper, a model of nonlinear relative motion dynamics is built, and then nonlinear and important perturbations affecting the formation configuration, such as J₂ and atmospheric drag, are analyzed as disturbances. Global navigation satellite system based relative positioning with nonlinear filtering is adopted to provide state information associated with the perturbations. By combining disturbance observer based control with H_∞ state feedback, a composite disturbance attenuation controller is proposed for maintenance of continuous and accurate formation. With consideration of precise control relying on micro thrusters, a composite disturbance attenuation based saturated controller is designed and its stability is proved. Finally, through numerical simulations, we demonstrate that control accuracy is improved after effectively avoiding perturbations and that stabilization can be satisfied using this method.

Since Service-Oriented Architecture (SOA) reveals the black box nature of services, heterogeneity, service dynamism, and service evolvability, managing services is known to be a challenging problem. Autonomic computing (AC) is a way of designing systems that can manage themselves without direct human intervention. Hence, applying the key disciplines of AC to service management is appealing. A key task of service management is to identify probable causes for symptoms detected and to devise actuation methods that can remedy the causes. In SOA, there are a number of target elements for service remedies, and there can be a number of causes associated with each target element. However, there is not yet a comprehensive taxonomy of causes that is widely accepted. The lack of cause taxonomy results in the limited possibility of remedying the problems in an autonomic way. In this paper, we first present a meta-model, extract all target elements for service fault management, and present a computing model for autonomously managing service faults. Then we define fault taxonomy for each target element and inter-relationships among the elements. Finally, we show prototype implementation using cause taxonomy and conduct experiments with the prototype for validating its applicability and effectiveness.

One of the issues of mobility management in a low Earth orbit (LEO) satellite network is the high-frequency location binding update initiated by mobile nodes (MNs). To solve this problem, we propose a location management scheme based on dual location area (LA) in an IP/LEO satellite network. The proposed scheme uses two kinds of LA, the fixed Earth station LA and satellite LA, to manage the location of the MNs together. MNs operate the binding update procedures only when they are moving out of both of the two LAs last registered. Geographical location information of MN is used in the binding update procedures, so that the network can page the idle MNs near their last registered location first, to enhance the probability of paging success. A detailed description of the implementation of the scheme is provided. Mathematical analysis shows that the proposed scheme reduces the location management cost and minimizes the influences of the distance between MN and its home agent. Paging cost is also reduced by introducing geographical location information in the binding update procedures.

A novel frequency-selective metamaterial with negative permittivity and permeability for improving directivity and gain of a helix antenna is presented in this paper. The proposed metamaterial is composed of two Z-shape resonators printed on opposite sides of a dielectric substrate. Two forms of multilayered cells are found to be suitable for antennas and waveguides applications. In addition, a new method of designing a metamaterial-based helix antenna is presented with high directivity and gain. A comparison on radiation properties is given between the conventional and the new metamaterial-based helix antennas. Two comparisons on radiation properties are performed: (1) the effect of proposed Z-structure on monopole, dipole, and helix antennas; (2) the effect of OE3, split-ring resonator (SRR), and proposed Z-structure unit cells on the performance of helix antennas. The results show improvement of parameters such as directivity, gain, and radiation power of the new metamaterial-based helix antenna. Therefore, the combination of Z-structure with the helix antenna shows the best performance.

In existing integrated circuit (IC) fabrication methods, the yield is typically limited by defects generated in the manufacturing process. In fact, the yield often shows a good correlation with the type and density of the defect. As a result, an accurate defect limited yield model is essential for accurate correlation analysis and yield prediction. Since real defects exhibit a great variety of shapes, to ensure the accuracy of yield prediction, it is necessary to select the most appropriate defect model and to extract the critical area based on the defect model. Considering the realistic outline of scratches introduced by the chemical mechanical polishing (CMP) process, we propose a novel scratch-concerned yield model. A linear model is introduced to model scratches. Based on the linear model, the related critical area extraction algorithm and defect density distribution are discussed. Owing to higher correspondence with the realistic outline of scratches, the linear defect model enables a more accurate yield prediction caused by scratches and results in a more accurate total product yield prediction as compared to the traditional circular model.

Quantum-dot cellular automata (QCA) technology has been widely considered as an alternative to complementary metal–oxide–semiconductor (CMOS) due to QCA’s inherent merits. Many interesting QCA-based logic circuits with smaller feature size, higher operating frequency, and lower power consumption than CMOS have been presented. However, QCA is limited in its sequential circuit design with high performance flip-flops. Based on a brief introduction of QCA and dual-edge triggered (DET) flip-flop, we propose two original QCA-based D and JK DET flip-flops, offering the same data throughput of corresponding single-edge triggered (SET) flip-flops at half the clock pulse frequency. The logic functionality of the two proposed flip-flops is verified with the QCADesigner tool. All the proposed QCA-based DET flip-flops show higher performance than their SET counterparts in terms of data throughput. Furthermore, compared with a previous DET D flip-flop, the number of cells, covered area, and time delay of the proposed DET D flip-flop are reduced by 20.5%, 23.5%, and 25%, respectively. By using a lower clock pulse frequency, the proposed DET flip-flops are promising for constructing QCA sequential circuits and systems with high performance.

We develop a numerical solution algorithm of the nonlinear potential flow equations with the nonlinear free surface boundary condition. A finite difference method with a predictor-corrector method is applied to solve the nonlinear potential flow equations in a two-dimensional (2D) tank. The irregular tank is mapped onto a fixed square domain with rectangular cells through a proper mapping function. A staggered mesh system is adopted in a 2D tank to capture the wave elevation of the transient fluid. The finite difference method with a predictor-corrector scheme is applied to discretize the nonlinear dynamic boundary condition and nonlinear kinematic boundary condition. We present the numerical results of wave elevations from small to large amplitude waves with free oscillation motion, and the numerical solutions of wave elevation with horizontal excited motion. The beating period and the nonlinear phenomenon are very clear. The numerical solutions agree well with the analytical solutions and previously published results.