Exchange and collective behavior of magnetic impurities in a disordered helical metal

We study the exchange interaction and the subsequent collective behavior of magnetic impurities embedded in a disordered two-dimensional (2D) helical metal. The exchange coupling follows a statistical distribution whose moments are calculated to the lowest order in $\left(p_F\ell\right)^{-1}$, where $p_F$ is the Fermi momentum of itinerant electrons and $\ell$ is the mean free path. We find that i) the first moment of the distribution decays exponentially, and ii) the variance of the interaction is long-range, however, it becomes independent of the orientation of the localized magnetic moments due to the locking between spin and momentum of the electrons that mediate the interaction. As consequence, long-range magnetic order tends to be suppressed, and a spin glass phase emerges. The formalism is applied to the surface states of a three-dimensional (3D) topological insulator. The lack of a net magnetic moment in the glassy phase and the full randomization of spin polarization at distances larger than $\ell$ excludes a spectral gap for surface states. Hence, non-magnetic disorder may explain the dispersion in results for photoemission experiments in magnetically-doped topological insulators.Comment: 5 pages, 3 figures; final version to appear in Physical Review B as a rapid communicatio

A Survey of Digital Systems Curriculum and Pedagogy in Electrical and Computer Engineering Programs

Digital Systems is one of the basic foundational courses in Electrical and Computer Engineering. One of the challenges in designing and modifying the curriculum for the course is the fast pace of technology change in the area. TTL chips that were in vogue with students building physical circuits, have given way to new paradigms like FPGA based synthesis with hardware description languages such as VHDL. However, updating a course is not as simple as just changing the book, and changing the syllabus. A large amount of work needs to be done in terms of selecting the book that will accommodate the course, the device that should be used, the laboratory content, and even how much time needs to be dedicated for every topic. All these issues, and many more makes it hard to take the decision of updating the course. For that reason, this paper surveys the pedagogy and methodology that is used to teach the digital systems curriculum at different universities. The goal is that it will serve as a resource for faculty looking to update or revamp their digital systems curricula. Within the document they will find a comparative study by electrical and computer engineering program, a list of textbooks, and the devices most commonly used.Cockrell School of Engineerin

Alternative strategies for asynchronous migration-controlled schemes in parallel genetic algorithm

Migration of individuals allows a fruitful interaction between subpopulations in the island model, a well known distributed approach for evolutionary computing, where separate subpopulations evolve in parallel. This model is well suited for a distributed environment running a Single Program Multiple Data (SPMD) scheme. Here, the same Genetic Algorithm (GA) is replicated in many processors and attempting better convergence, through an expected improvement on genetic diversity, selected individuals are exchanged periodically. For exchanging, an individual is selected from a source subpopulation and then exported towards a target subpopulation. Usually, the imported string is accepted on arrival and then inserted into the target subpopulation. Our earlier experiments on controlled migration showed an improvement on results when contrasted against those obtained by conventional migration approaches. This paper describes extended implementations of alternative strategies to oversee migration in asynchronous schemes for an island model and enlarges a previous work on three processors with a set of softer testing functions [9]. All of them try to decrease the risk of premature convergence. A first strategy attempts to prevent unbalanced p ropagation of genotypes by applying an acceptance threshold parameter to each incoming string. A second one permits independent evolution of subpopulations and acts only when a possible stagnation is detected. In such condition an attempt to evade falling towards a local optimum is done by inserting an expected d issimilar individual to improve genetic diversity. A third alternative strategy combines both previous mentioned strategies. The results presented are those obtained on the functions that showed to be more difficult for the island model using a replication of a simple GA. A description of the corresponding system architecture supporting the PGA implementation is described and results for the parallel distributed approach among 3, 6 and 12 processors is discussed.Facultad de Informátic

Parallel genetic algorithms: a feasible distributed : Implementation

Parallel genetic algorithms, models and implementations, attempts to exploit the intrinsically parallel nature of genetic algorithms. By distributing the total population, these models ref1ects a bebaviour nearer to that of natural systems. A variety of parallel computer systems architectures can offer distinct support features for their implementation. Ibis paper shows sorne remarkable characteristics of parallel genetic algorithms, details of a feasible design and their implementation. A1so some results related to the island model are shown.Eje: Redes Neuronales. Algoritmos genéticosRed de Universidades con Carreras en Informática (RedUNCI

Challenges and Implications of Implementing Strategic Intelligence Systems in Mexico

Business intelligence (BI) allows companies to make faster and better-informed decisions. Unfortunately, implementing BI systems in companies in developing countries is minimal. Limited and costly access to the technology, coupled with the cultural background affecting how people perceive BI, has restricted such implementations. The purpose of this phenomenological study was to explore and describe the lived experiences of chief executive officers (CEOs) in northern Mexico to obtain insight into the challenges of implementing BI systems. Research questions focused on the reasons behind the lack of BI systems implementation and the challenges faced by these officers when implementing a new system. This study employed semistructured interviews of 9 CEOs of small- to medium-sized companies. Interview data were coded using open coding techniques to develop themes or patterns, which in turn were aggregated to address the research questions. The lack of implementation was largely attributed to an economic concern among CEOs regarding the final price of implementation. In addition, the lack of systems offerings of localized systems and the working culture of the personnel were significant factors for the lack of investment. These findings may contribute to positive social change by informing managers and officers of companies in Mexico and other developing countries about the challenges and implications in BI implementation. When BI systems can be successfully implemented, both companies and their customers may benefit from improved information processing such as reduced number of errors and faster response times