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Ni–Fe alloy coatings with Nb contents of 0, 4.2 at.%, 7.0 at.% and 9.0 at.% were electrodeposited on ferritic stainless steels for intermediate-temperature solid oxide fuel cell (SOFC) interconnect application. The oxidation behavior, scale-growth mechanisms and electrical performances of the Ni–Fe- and NiFe–Nb-coated steels were then investigated in air at 800 °C corresponding to the cathode environment of SOFC. It was found that the scales formed are mainly composed of an external NiFe2O4 layer and an inner Cr2O3-rich layer after oxidation, with some Nb-rich oxides also observed for the Nb-containing coatings. Doping 4.2 at.%Nb into the coating decreased the growth rate of Cr2O3 and suppressed the formation of voids at the scale/alloy interface, whereas excess Nb impaired the oxidation resistance of the steel. The Nb addition affects the oxide growth direction by suppressing the cation transport. All the coatings decreased the area-specific resistance (ASR) of the steel, with the NiFe–4.2 at.%Nb-coated sample exhibiting the lowest ASR value. The effects of Nb on the oxidation mechanism and electrical properties of the Ni–Fe-coated steels are discussed.

Dual layer coatings CrNx and Ni-Fe alloy have been developed for metallic interconnects application by a combined approach. The CrNx layer was deposited on ferritic stainless steel using multi-arc ion plating, and the Ni-Fe alloy coating was electroplated on the CrNx coated steel subsequently. After oxidation at 800 °C in air for 5 h, a multi-layer scale composed of NiFe2O4, Cr2O3, Ni-Fe-Cr alloy and CrNx from outside to inside was formed on the CrNx/substrate with a 1.6 μm thick Ni-32 at%Fe alloy coating. Further oxidation led to the decomposition of the CrNx layer, but no pores could be observed near the scale/substrate interface even after an oxidation of 1000 h. The CrNx layer acted as an effective barrier against the mutual diffusion of elements between the coating and the substrate either before or after decomposition. The employment of the Ni-Fe/CrNx dual layer coating decreased the growth rate of the Cr2O3 scale and thus a lower scale area specific resistance (ASR). The oxidation behavior of the Ni-Fe/CrNx coated substrate and the influence mechanism of the CrNx barrier layer were discussed. Keywords: Solid oxide fuel cell, Interconnect, NiFe2O4, CrNx, Oxidation resistance, Area specific resistance

Numerical pattern synthesis (NPS) algorithm based on adaptive array theory is an effective spatial power pattern synthesis method for antenna arrays. In this letter, instead of using the artificial interferences weighted on the total power pattern in the conventional NPS algorithm, a generalized two-dimensional (2-D) NPS algorithm is proposed in which two weighting functions are assigned to control the copolarization and cross-polarization patterns, respectively. The weighting functions are iteratively updated until both the sidelobe and cross-polarization levels reach their prescribed ones. Two numerical examples for synthesizing the patterns of a linearly polarized planar array and a circularly polarized cylindrical array are provided to validate effectiveness and advantages of the proposed generalized 2-D NPS algorithm.

© 2002-2011 IEEE. A novel method called alternating convex optimization is presented to synthesize unequally spaced linear arrays with minimum element spacing constraint. In this method, the problem of synthesizing an unequally spaced array is formulated as a sequence of alternating convex optimization problems, and the excitation vector and auxiliary weighting vector are alternately chosen as the optimization variables. The minimum spacing constraint for considering the physical element antenna size can be easily imposed in this alternating optimization process. Two examples for synthesizing unequally spaced linear arrays with focused and shaped patterns are provided to validate the effectiveness and advantages of the proposed method.

Optimizing the Map process is important for the improvement of the MapReduce performance. Many efforts have been devoted into the problem to design more efficient scheduling strategies. However, there exists a kind of MapReduce applications, named imprecise applications, where the imprecise results based on part of map tasks can satisfy the requirements of imprecise applications and thus the job processes can be completed when enough map tasks are processed. According to the feature of imprecise applications, the authors propose an improved MapReduce model, named MapCheckReduce, which can terminate the map process when the requirements of an imprecise application is satisfied. Compared to MapReduce, a Check mechanism and a set of extended programming interfaces are added to MapCheckReduce. The Check mechanism receives and analyzes messages submitted by completed map tasks and then determines whether to terminate the map phase according to the analysis results. The programming interfaces are used by the programmers to define the termination conditions of the map process. A data-prefetching mechanism is designed and implemented in MapCheckReduce which can improve the performance of MapCheckReduce effectively. The MapCheckReduce prototype has been implemented and experiment results verify the feasibility and effectiveness of MapCheckReduce.

It is shown in this paper that the problem of reducing the number of elements for multiple- pattern arrays can be solved by a sequence of reweighted � 1 optimizations under multiple linear constraints. To do so, conjugate symmetric excitations are assumed so that the upper and lower bounds for each pattern can be formulated as linear inequality constraints. In addition, we introduce an auxiliary variable for each element to define the common upper bound of both the real and imaginary parts of multiple excitations for different patterns, so that only linear inequality constraints are required. The objective function minimizes the reweighted � 1-norm of these auxiliary variables for all elements. Thus, the proposed method can be efficiently implemented by the iterative linear programming. For multiple desired patterns, the proposed method can select the common elements with multiple set of optimized amplitudes and phases, consequently reducing the number of elements. The radiation characteristics for each pattern, such as the mainlobe shape, response ripple, sidelobe level and nulling region, can be accurately controlled. Several synthesis examples for linear array, rectangular/triangular-grid and randomly spaced planar arrays are presented to validate the effectiveness of the proposed method in the reduction of the number of elements.

Distributed storage systems, built on peer-to-peer networks, can provide large-scale data storage and high data reliability by redundancy. Data backup is the process to store data into a set of redundant storage nodes. Rapid completion of such a process is very critical to maintain system performance. In traditional data backup in distributed systems based on erasure codes, star-structured scheme is used, in which each redundant block is just sent to each target storage node from the source node directly, so the storage throughput and delay are limited by the bottleneck bandwidth, due to bandwidth heterogeneity. The recent “in-network” redundancy generation scheme uses locally repairable property of self-repairing codes to speed up data backup. However, such kind of code does not own maximum distance separable property, thus does not achieve optimal storage efficiency. We still lack a fast backup scheme in distributed systems based on general erasure coding. To this end, we proposed that instead of only focusing on bandwidths between the source node and target nodes, the bandwidths between target storage nodes should be fully taken into account. In our scheme, each redundant data block is divided into some parts according to different proportions and each part of the block is sent to the target storage node via other different storage nodes. The benefit is that spare bandwidths between target storage nodes are used to reduce backup time. We further show how this process can be modeled and derive a formula about the final backup time. We can achieve minimum backup time by solution for classical quadratic programming problem. We conduct both numerical analysis and experimental study. Our experiments shows, the delay reduces 59 %, compared with common star-structured scheme. Meanwhile, the throughput is increased significantly in backup process.

In this paper, numerical pattern synthesis (NPS) algorithm integrated with seeded region growing (SRG) method is proposed to synthesize the array in the presence of mutual coupling. In order to obtain the mutual coupling between the array elements, active pattern technique is used to find active element patterns. A 4 × 8 microstrip antenna array is employed to validate the effectiveness of the proposed algorithm including mutual coupling.

© The Institution of Engineering and Technology. Antenna arrays with shaped patterns have drawn significant attention for their wide applications in radar, sonar and communication systems. The combination of genetic algorithm (GA) and fast Fourier transform (FFT) has been used to synthesise shaped pattern of antenna array's factor without considering coupling effects. In this work, the GA-FFT method is generalised by integrating with a new virtual active element pattern (AEP) expansion method which approximates each AEP as the radiation pattern by exciting several equally spaced virtual elements surrounding the real element position. The generalised GA-FFT can be applied for the shaped pattern synthesis of unequally spaced linear arrays including mutual coupling and platform effect. Several synthesis examples with different pattern shapes and different antenna structures are given to demonstrate the effectiveness, accuracy and robustness of the proposed method.

© 2002-2011 IEEE. A novel method incorporating the least-squares active element pattern expansion (LS-AEPE) into the iterative Fourier transform (IFT) procedure is presented to efficiently synthesize linear arrays including mutual coupling and platform effects. The proposed method has better pattern synthesis accuracy than the original IFT, and is much faster than the combination of LS-AEPE and the genetic algorithm. Numerical examples are given for synthesizing the patterns of two microstrip antenna arrays mounted on inhomogeneous platforms. Synthesis results show the effectiveness and advantages of the proposed method.

A shaped power pattern synthesis with reduction of dynamic range ratio (DRR) is presented in this paper. Controlling the DRR of the excitations for the shaped power pattern synthesis is very useful since it can reduce the output power loss and also simplifies the complexity of the feeding network design. The synthesis of shaped pattern is typically a nonconvex optimization problem. To solve this problem efficiently, we formulate the synthesis as Semi-definite relaxation (SDR) form which allows to relax some non-convex constraints so as to formulate the problem into a convex form. Then it can be efficiently solved using readily available toolbox. Finally, numerical example is presented to show the effectiveness and advantages of the proposed method.

The least-square active element pattern expansion (LS-AEPE) has been introduced for linear array synthesis including mutual coupling and platform effect. A new method based on combination of LS-AEPE and iterative Fourier transform (IFT) is proposed to optimize the excitation phases for sidelobe reduction and null control. Simulation results illustrate the new method outperforms the GA-FFT method base on LS-AEPE in terms of computational efficiency.