Showing papers by "Lei Wang published in 2011"

Necessary and sufficient asymptotic stability criterion for 2-D positive systems with time-varying state delays described by Roesser model

Abstract: This study addresses the stability problem of two-dimensional (2-D) positive systems described by Roesser model and involving delays in the states. The delays are time varying and bounded. A necessary and sufficient stability condition is established for such systems. It is shown that a 2-D positive system with time-varying delays is asymptotically stable for any bounded delays if and only if the corresponding constantly delayed system is asymptotically stable, or equivalently, if and only if the sum of the system matrices is a Schur matrix. An example illustrates the theoretical result.

Grain Orientation Evolution and Deformation Behaviors in Pb-Free Solder Interconnects Under Mechanical Stresses

Abstract: In this study, the effect of mechanical stresses on the recrystallization behavior of Sn-3.0Ag-0.5Cu Pb-free solder interconnects was studied by four-point cyclic bending, shear tests, and tensile tests. Scanning electronic microscopy with electron backscattered diffraction was used to characterize the microstructure and crystallographic orientation of the solder interconnects. The results show that recrystallization occurs under the different mechanical stresses in these tests at room temperature, and that recrystallized grains evolve from subgrains by rotation. Microhardness measurements after shear tests show that the hardness of the recrystallized microstructure was decreased by 15% and 41%, respectively, compared with that of the nonrecrystallized and as-solidified microstructures. Furthermore, the fine-grained microstructure produced after recrystallization facilitated grain boundary sliding. Therefore, the deformation and cracking behaviors were localized in the degraded recrystallized microstructures once recrystallization occurred, accelerating failure of the solder interconnects.

Male cone morphogenesis, pollen development and pollen dispersal mechanism in Ginkgo biloba L.

Abstract: Lu, Y., Wang, L., Wang, D., Wang, Y., Zhang, M., Jin, B. and Chen, P. 2011. Male cone morphogenesis, pollen development and pollen dispersal mechanism inGinkgo bilobaL. Can. J. Plant Sci. 91: 971-981. Ginkgo biloba L. is one of the oldest gymnosperms. Male cone morphogenesis, pollen development and dispersal are important for successful pollination and reproduction. In this study, we investigated the development of male cone, pollen and the sporangial wall in detail. The results indicate that: (1) The primordia of male cones and leaves begin to differentiate in early June and remain open until the following March. The male cones then mature and release pollen in mid-April. The male cones are drooped and approximately perpendicular to the leaves during pollination. (2) The microsporocytes develop from the sporogenous cell and form a tetrahedral tetrad after two simultaneous asymmetrically meioses, then produce a matured four-cell pollen after three polar mitotic divisions. The matured pollen is hemispheric in shape with a large aperture area and three pollen wall layers; once released from the microsporangia, the pollen becomes boat-like in shape. (3) The sporangial walls are eusporangiate and consist of epidermis, endothecium and tapetum. The differentiation of the tapetum occurs separately from that of the epidermis and endothecium, and originates from the outermost layer of sporogenous cells. The sporangial walls exhibit shrinkage of the epidermis, fibrous thickening of the endothecium, and enzymic dissolution of the tapetum during pollen dispersal, which contributes to microsporangia opening. Based on these results, we conclude that there many unique and primitive characteristics of the development of the male cones, pollen and sporangial wall of G. biloba. In addition, we also found that the male cones, pollen and sporangial walls have evolved efficient structural and morphological adaptations to anemophily.

The effect of carbon source on the properties of chemical doped MgB2 tapes

Abstract: The doping effect of different carbon source on the properties of MgB 2 tapes was compared using three typical dopants, nano-C, C 60 , and C 9 H 11 NO. It is found that C 60 doped samples showed the highest carbon substitution ratio and resistivity, with the lowest T c . For the nano-C doped samples, T c did not drop so significant, which is only 2 K lower than that of the pure ones. Compared to C 60 and C 9 H 11 NO doped samples, the nano-C doped samples show a lower J c value at 5 K. On the other hand, the C 9 H 11 NO doped samples show a high J c value at both 5 K and 20 K. This is a representative demonstration to the complex affecting factors on the J c – H property of MgB 2 tapes. Detailed mechanism for the property difference in MgB 2 induced by different chemical doping is discussed based on the systematically examined results.

Cross-industry dimensionality of the commitment to change scale in China.

Abstract: Summary Commitment to organizational change can explain a range of employees' attitudes and behaviors during organizational change, and its measurement is central to explaining such organizational linkages. The purpose of this study is to re-examine the dimensionality of Herscovitch and Meyer's Commitment to Change Scale across two different industrial samples in a non-Western cultural context (China). The two samples were 198 civil servants (60.0% men; M age = 29.3 yr., M organizational tenure = 62.7 mo.) and 442 high-tech company employees (58.2% men; M age = 30.5 yr., M organizational tenure = 66.5 mo.) who had respectively undergone major changes in compensation and performance appraisal systems in their organizations at the time of the research. Results of exploratory and confirmatory factor analyses showed that a four-factor model with 14 items fit the data best in both samples. The generality of the scale's structure as well as its implications for change-management practices are discussed.

A hybrid tabu search for steelmaking-continuous casting production scheduling problem

Abstract: In this paper, we study the steelmaking-continuous casting (SCC) production scheduling problem. Considering the constraints of the practical technological requirements and the objective of minimizing the total waiting time of jobs, we formulate a mathematical programming model. Due to the complexity of the model, we solve it by a decomposition strategy, i.e. jobs are allocated and sequenced on machines first, and the time table of all jobs is then established. We propose a tabu search algorithm to deal with the allocation and sequencing decisions and use a linear programming model to establish the time table of jobs. For tabu search algorithm, we design three different neighborhood structures, including the insertion neighborhood, the restricted neighborhood whose size is changeable, and a kick strategy based on swap move. We test the proposed algorithm on a set of real problems, and the computational results demonstrate the effectiveness of the proposed algorithm.

Recyclable Catalysts for Suzuki-MiyauraCross-Coupling Reactions at Ambient Temperature Basedon a Simple Merrifield Resin Supported Phenanthroline-Palladium(II)Complex

Abstract: A novel Merrifield resin immobilized phenanthroline-palladium(II)complex has been developed and was found to be an efficient catalystfor Suzuki-Miyaura cross-coupling reaction between arylboronicacids and a range of aryl halides under mild reaction conditions.The catalyst exhibited both high catalytic activity and stabilityfor Suzuki-Miyaura reaction. Furthermore, the catalyst couldbe recycled at least 10 times without a significant loss of catalyticactivity.