A Growth model for DNA evolution

A simple growth model for DNA evolution is introduced which is analytically solvable and reproduces the observed statistical behavior of real sequences.Comment: To be published in Europhysics Letter

Dangling-bond spin relaxation and magnetic 1/f noise from the amorphous-semiconductor/oxide interface: Theory

We propose a model for magnetic noise based on spin-flips (not electron-trapping) of paramagnetic dangling-bonds at the amorphous-semiconductor/oxide interface. A wide distribution of spin-flip times is derived from the single-phonon cross-relaxation mechanism for a dangling-bond interacting with the tunneling two-level systems of the amorphous interface. The temperature and frequency dependence is sensitive to three energy scales: The dangling-bond spin Zeeman energy delta, as well as the minimum (E_min) and maximum (E_max) values for the energy splittings of the tunneling two-level systems. We compare and fit our model parameters to a recent experiment probing spin coherence of antimony donors implanted in nuclear-spin-free silicon [T. Schenkel {\it et al.}, Appl. Phys. Lett. 88, 112101 (2006)], and conclude that a dangling-bond area density of the order of 10^{14}cm^{-2} is consistent with the data. This enables the prediction of single spin qubit coherence times as a function of the distance from the interface and the dangling-bond area density in a real device structure. We apply our theory to calculations of magnetic flux noise affecting SQUID devices due to their Si/SiO_2 substrate. Our explicit estimates of flux noise in SQUIDs lead to a noise spectral density of the order of 10^{-12}Phi_{0}^{2} {Hz}^{-1} at f=1Hz. This value might explain the origin of flux noise in some SQUID devices. Finally, we consider the suppression of these effects using surface passivation with hydrogen, and the residual nuclear-spin noise resulting from a perfect silicon-hydride surface.Comment: Final published versio

Problem-based learning to potentiate the learning achievements and motivation of the higher education students

Educators are using new pedagogical methodologies to engage students in the learning process, and numerous studies have shown evidence of increased interest to learn when real-life problems are incorporated into the learning environment. This paper presents research on the impact on academic achievement and motivation of learning through the application of Problem-Based Learning (PBL) methodology in higher education. Specifically, the study was designed to analyses the benefits in terms of learning outcomes using methodologies that are showed to be more effective approaches to student learning processes than traditional classrooms. The main research questions are: Rq1: What are the impacts of PBL in the academic achievement of the students? Rq2: What are the impacts of PBL in the student's motivation for the learning process? The methodological approach is an experimental design that specifies an experimental group and a control group. The independent variable was administered to the experimental group and not to the control group, and both groups were measured on the same dependent variable. The sample composed of 62 undergraduate students from management courses. Of the participants 31 students in the control group and 31 in the experimental group. The materials were multiple-choice digital assessments applied to the experimental groups and the same multiple-choice assessments in paper form for the control group. The motivation measure was a 5-point Likert Scale questionnaire used as a pre and post-assessment. This questionnaire assessed students' motivation and attitudes before any intervention and again after the intervention. Specifically, the survey measured students' motivation to learn using PBL. The constructs designed for the motivation survey are perceptions of student learning, interest in PBL, and academic motivation. The questionnaire contained twenty items with five choices: strongly agree, agree, neutral, disagree, and strongly disagree and included also positively and negatively worded items to ensure reliability. The control group answered the same multiple-choice questions as the experimental group, but without using PBL methodology. The experimental group used the online learning platform and answered the same multiple-choice questions by selecting the answer that was correct. The statistical analyses were based on ANCOVA to measure students' achievement and motivation for learning using PBL methodology. For the analysis, the dependent variable was either the post-survey or post-achievement measure, and the covariate was either the pre-survey or pre-achievement measure, and the condition was the group status. The findings reveal that the students who used the PBL methodology showed a significant increase in their learning outcomes. This finding suggests that the students of the experimental group felt a positive change in their learning processes. Regarding academic achievement, experimental groups did not have significant growth as compared to the control groups, but their perception of learning was much higher. Finally, students in the experimental groups felt like they had increased academic motivation in learning when using PBL methodologies. Based on the results it is possible to state that are benefits for the learning process and classroom lessons will improve the academic outcomes if delivered more frequently using PBL methodologies.info:eu-repo/semantics/acceptedVersio

Chaos and Synchronized Chaos in an Earthquake Model

We show that chaos is present in the symmetric two-block Burridge-Knopoff model for earthquakes. This is in contrast with previous numerical studies, but in agreement with experimental results. In this system, we have found a rich dynamical behavior with an unusual route to chaos. In the three-block system, we see the appearance of synchronized chaos, showing that this concept can have potential applications in the field of seismology.Comment: To appear in Physical Review Letters (13 pages, 6 figures

Self-Similarity of Friction Laws

The change of the friction law from a mesoscopic level to a macroscopic level is studied in the spring-block models introduced by Burridge-Knopoff. We find that the Coulomb law is always scale invariant. Other proposed scaling laws are only invariant under certain conditions.}Comment: Plain TEX. Figures not include

Of the significance of business relationships

The Industrial Network Theory aims to describe and explain the business relationships and networks in which the focal firm is deeply embedded. One of its major propositions is that business relationships somehow influence, to different extents and over time, the focal firm’s survival. This pertains to the diverse and time-varying significance of business relationships for the focal firm. It has often been implicitly sustained that such significance is strongly related to the role played by business relationships and consequently the relationship outcomes accruing to the focal firm. The logic underlying the relationship significance proposition is outwardly oriented, somewhat overlooking the focal firm’s inside and in particular the conspicuous influence of business relationships on what the focal firm does competently both within and across its vertical boundaries. Arguably, the (predominantly ‘functional’) network-based arguments currently advanced represent a necessary but not sufficient condition for relationship significance. This conceptual paper tentatively suggests that there may be missing a supplementary (essentially internal) explanation supported by Competence-based Theories of the Firm.Industrial Network Theory; relationship significance proposition