A new class of codes defined as Separable Code has been considered to be successfully applied to a new error-control scheme called Type- Hyprid ARQ, which is based on the concept that some of the parity-check digits of the codes are sent to the receiver only when they are requested for error correction. Sevaral separable codes suitable to random error channels have been constructed and analyzed. In this paper, a new class of separable codes suitable to the burst error channels is constructed by modifying the Fire codes. Performance analysis of the codes based on the generalized Gilbert channel is given, showing that the proposed codes are superior to the Fire codes. Also, a new method of constructing a class of separable codes suitable to random error channels by puncturing linear block codes is given. It is shown that these codes are easier to implement than the known separable code.

Due to its simplicity and efficiency, differential evolution (DE) has gained the interest of researchers from various fields for solving global optimization problems. However, it is prone to premature convergence at local minima. To overcome this drawback, a novel hybrid dragonfly algorithm with differential evolution (Hybrid DA-DE) for solving global optimization problems is proposed. Firstly, a novel mutation operator is introduced based on the dragonfly algorithm (DA). Secondly, the scaling factor (F) is adjusted in a self-adaptive and individual-dependent way without extra parameters. The proposed algorithm combines the exploitation capability of DE and exploration capability of DA to achieve optimal global solutions. The effectiveness of this algorithm is evaluated using 30 classical benchmark functions with sixteen state-of-the-art meta-heuristic algorithms. A series of experimental results show that Hybrid DA-DE outperforms other algorithms significantly. Meanwhile, Hybrid DA-DE has the best adaptability to high-dimensional problems.

Magnetic tunnel junctions (MTJ), i.e., structures consisting of two ferromagnetic layers (FM1 and FM2), separated by a very thin insulator barrier (I), have recently attracted attention for their large tunneling magnetoresistance (TMR) which appears when the magnetization of the ferromagnets of FM1 and FM2 changes their relative orientation from parallel to antiparallel in an applied magnetic field. Using an ultrahigh vacuum magnetron sputtering system, a variety of MTJ structures have been explored. Double Hc magnetic tunnel junction, NiFe/Al2O3/Co and FeCo/Al2O3/Co, were fabricated directly using placement of successive contact mask. The tunnel barrier was prepared by in situ plasma oxidation of thin Al layers sputter deposited. For NiFe/Al2O3/Co junctions, the maximum TMR value reaches 5.0% at room temperature, the switching field can be less than 10 Oe and the relative step width is about 30 Oe. The junction resistance changes from hundreds of ohms to hundreds of kilo-ohms and TMR values decrease monotonously with the increase of applied junction voltage bias. For FeCo/Al2O3/Co junctions, TMR values exceeding 7% were obtained at room temperature. It is surprising that an inverse TMR of 4% was observed in FeCo/Al2O3/Co. The physics governing the spin polarization of tunneling electrons remains unclear. Structures, NiFe/FeMn/NiFe/Al2O3/NiFe, in which one of the FM layers is exchange biased with an antiferromagnetic FeMn layer, were also prepared by patterning using optical lithography techniques. Thus, the junctions exhibit two well-defined magnetic states in which the FM layers are either parallel or antiparallel to one another. TMR values of 16% at room temperature were obtained. The switching field is less than 10 Oe and step width is larger than 30 Oe.

Trellis coded modulation (TCM) is a new and attractive communication technique which yields significant coding gain with no degradation of the bandwidth efficiency. So far, researches concerning the TCM have concentrated upon minimizing the error-event probability (EEP). However, for the various bitwise data transmission systems, decreasing the post-decoding information-bit error rate (IBER) is more important than only minimizing the EEP. This paper is concerned with a simple but important problem that how to improve the IBER in TCM systems. The IBER of a TCM system depends not only on the EEP but also on the mapping of a binary m-tuple to a 2m-ary channel signal. A signal mapping called Set Partitioning mapping has been well adopted in the previously known TCM systems. In this paper, another well known signal mapping, the Gray-code mapping, is investigated as a promising signal mapping in TCM, and compared with the Set Partitioning mapping. Through a computer search, a number of optimun trellis codes with Gray-code mapping are found. It is shown that these codes have the minimum Euclidean distances as large as those of the Ungerboeck codes and yet yield smaller EEP and IBER.

The literature on codes for write-once memories (WOM) has been growing steadily in recent years. In this paper, a new method for constructing womcodes is presented. On the basis of the numerical analysis and the computer simulations related to the performance of the proposed womcodes, we show that the codes have the rates higher than any other known womcodes. The upper bounds on the rates of the codes are obtained as well. We also show that, by combining the proposed womcodes with other womcodes known previously, we can significantly improve the utilization efficiency of WOM.