Magnetism driven dislocation dissociation, cross-slip and mobility in NiAl

We have examined the interplay between magnetism and dislocation core properties in NiAl alloys using quantum mechanics/molecular mechanics simulations. We observe the magnetism-driven site preference of Fe and Co impurities at the dislocation core. When occupying the Ni sublattice, Fe and Co impurities are found to induce spontaneous dislocation cross slip. When occupying the Al sublattice, the impurities render the originally undissociated dislocation to split into two partials. Finally we observe the magnetism-driven dislocation mobility when Fe impurity occupies the Al sublattice, which has also been discovered experimentally. The magnetic interaction between the impurities and the host atoms is responsible for the significant changes in the dislocation core structure and mobilityPhysical Review B 82(6), 060404R. (2010)2469-995

Error analysis and applications of a general QM/MM approach

Combing computational efficiency and accuracy, quantum mechanic/molecular mechanic (QM/MM) methods are promising for understanding and predicting materials properties at atomic scales. We present a general QM/MM method that can be implemented in a variety of QM and MM combinations; we focus on a tight-binding and a plane-wave pseudopotential methods for the QM part and the Stillinger-Weber and EAM potentials for the MM part. The QM/MM coupling errors are analyzed. It is found that a sufficient size of the coupling region and the buffer zone is crucial in minimizing the coupling errors. On the other hand, the size of the weighting zone turns out to be less important. The QM/MM method is applied to model the dynamical propagation of Si cracks with different orientations and under different mode I loadings. The QM/MM method is found to correctly reproduce the brittle fracture of Si, whereas the SW potential fails to do the same. The QM/MM method is also used to study the ductile fracture in Au and compared to the EAM potential. Finally, the QM/MM method is applied study the vacancy diffusion in a Cu grain boundary. The QM/MM results compare very well to the previous EAM results.Computational Materials Science 50(2), 714-719. (2010)0927-025

Quantum Computing for MIMO Beam Selection Problem: Model and Optical Experimental Solution

Massive multiple-input multiple-output (MIMO) has gained widespread popularity in recent years due to its ability to increase data rates, improve signal quality, and provide better coverage in challenging environments. In this paper, we investigate the MIMO beam selection (MBS) problem, which is proven to be NP-hard and computationally intractable. To deal with this problem, quantum computing that can provide faster and more efficient solutions to large-scale combinatorial optimization is considered. MBS is formulated in a quadratic unbounded binary optimization form and solved with Coherent Ising Machine (CIM) physical machine. We compare the performance of our solution with two classic heuristics, simulated annealing and Tabu search. The results demonstrate an average performance improvement by a factor of 261.23 and 20.6, respectively, which shows that CIM-based solution performs significantly better in terms of selecting the optimal subset of beams. This work shows great promise for practical 5G operation and promotes the application of quantum computing in solving computationally hard problems in communication.Comment: Accepted by IEEE Globecom 202

Click Behavior in Search Engine Marketing

This dissertation consists of two essays, both seeking to advance our understanding of consumer click behavior on search engine results pages. The first essay aims at resolving a critical controversy about the interaction between paid and organic search results, which our empirical results show depends on the nature of the underlining search query. Specifically, a firm’s paid search ad increases the searcher’s tendency to click on the firm’s link in the organic section for unbranded searches (the ‘spillover effect’); while a firm’s paid search ad decreases the searcher’s tendency to click on the firm’s link in the organic section for branded searches (the ‘substitution effect’). The second essay examines how consumer click behavior on paid search ads differs across devices by examining their tendency to click on the top ad and sensitivity to ad position. We find that, as compared to desktop users, a) tablet users are more likely to click on the top ad for both branded and unbranded searches; b) smartphone users are more likely to click on the top ad for unbranded searches but not for branded searches; and c) both smartphone and tablet users are more sensitive to ad position for unbranded searches.Marketing and Entrepreneurship, Department o

Service Quality and Share-of-Wallet as Predictors of Loyalty: Examining the Intermediating Impact of Satisfaction, Trust, and Commitment in the Retail Industry

By segmenting the customer of different retail stores into low and high relational groups, this study investigates the effects of overall satisfaction, trust and commitment on both purchase intentions and willingness to pay a higher price for both low and high relational consumers. The results indicate that the impact of retail service quality on loyalty when mediated by satisfaction is significantly stronger for low share customers compared to high share customers; whereas the impact of retail service quality on loyalty when mediated by trust and commitment is significantly stronger for high share customers compared to low share customers