Discrete-time modeling and control of a boost converter by means of a variational integrator and sliding modes     

Jorge Rivera  Florentino Chavira  Alexander Loukianov  Susana Ortega  Juan J. Raygoza 《Journal of The Franklin Institute》2014

This work deals with the discrete-time modeling of a boost DC-to-DC power converter by means of a discrete Lagrangian formulation based on the midpoint rule integration method. Then in the basis of this model, a discrete-time sliding mode regulator is designed in order to force the boost circuit to track a DC-biased sinusoidal signal. Simulations and experimental tests are carried on where the great performance of the proposed methodology is verified.  相似文献   

A Lakatosian Framework to Analyze Situations of Cognitive Conflict and Controversy in Students' Understanding of Heat Energy and Temperature     

Laburú  Carlos Eduardo  Niaz  Mansoor 《Journal of Science Education and Technology》2002,11(3):211-219

The objective of this study is to analyze secondary school students' interactions (conflicts, controversies, and arguments) as they participate in an intact classroom activity designed to facilitate their understanding of heat energy and temperature. The study is based on 32 ninth-grade students in a public school in Londrina, Brazil. Results obtained show that the differentiation between heat energy and temperature constitutes considerable difficulties for the students, and can be considered as part of the hard-core of their understanding (Lakatos, 1970, Criticism and the Growth of Knowledge, Cambridge University Press, Cambridge, UK, pp. 91–196). Student interactions (video taped) were classified into an Alternative Model, Transitional Model, and Scientific Model, depending on the degree to which they reflected a progressive transition in their hard-core. Students generally resisted a change in their conceptual understanding. Some students were able to question the hard-core of their beliefs and construct a Transitory Model. Some students experienced a further progressive transition by constructing a Scientific Model, based on the understanding that Temperature only measures the energy of agitation. Methodology used also provided a glimpse of how a particular student grappled with the conflicts in order to facilitate progressive transition in understanding. It is concluded that given the opportunity to discuss, reflect, consider alternative/conflicting situations, students can construct models that increase progressively in their heuristic/explanatory power.  相似文献   

Teacher counter stories to a citizenship education mega policy narrative. Preparing for citizenship in Chile     

Eduardo Cavieres-Fernández 《课程研究杂志》2017,49(4):414-436

The present article focuses on the counter stories of two Chilean social studies high school teachers. Counter stories describe how teachers use their professional experience to confront those mega narratives composed of dominant educational policies that impinge upon their pedagogical practices. The mega narrative described in this study as a citizenship education mega policy narrative is composed by citizenship educational guidelines that have become influenced by other market-driven educational policies, and is not only present in Chile but has also been influenced by policies coming from countries such as England and the US. Therefore, the discussions that emerge from these counter stories on the nature of this mega narrative and the ways through which teachers can confront it through their teaching, and the implications that all this has for the field of citizenship education, do not only fill a gap in Chilean research but also contribute to discussions on counter and mega narratives in the field of citizenship education within a wider international scope.  相似文献   

Ethnic Identity Development and Acculturation Preferences Among Minority and Majority Youth: Norms and Contact          下载免费PDF全文

Roberto González  Brian Lickel  Manisha Gupta  Linda R. Tropp  Bernadette P. Luengo Kanacri  Eduardo Mora  Pablo De Tezanos‐Pinto  Christian Berger  Daniel Valdenegro  Oscar Cayul  Daniel Miranda  Patricio Saavedra  Michelle Bernardino 《Child development》2017,88(3):743-760

This article tests a longitudinal model of the antecedents and consequences of changes in identification with indigenous (Mapuche) among indigenous and nonindigenous youth in Chilean school contexts over a 6‐month period (633 nonindigenous and 270 Mapuche students, M_ages = 12.47 and 12.80 years, respectively). Results revealed that in‐group norms supporting contact and quality of intergroup contact at Time 1 predicted student's changes in Mapuche identification at Time 2, which in turn predicted changes in support for adoption of Chilean culture and maintenance of Mapuche culture at Time 2; some of the relationships between these variables were found to be moderated by age and ethnicity. Conceptual and policy implications are addressed in the Discussion .  相似文献   

Signal constellations in the hyperbolic plane: A proposal for new communication systems     

Eduardo Brandani da Silva  Marcelo Firer 《Journal of The Franklin Institute》2006,343(1):69-82

Signal constellations in the hyperbolic plane are provided as an alternative to traditional signal constellations in the Euclidean plane, since channels may actually exist for which the latter signal constellations are not as suitable as the former. A hyperbolic gaussian probability density function, based solely on geometrical considerations, is derived to determine the performance of the hyperbolic signal constellations. Benefits result from an approach conceived in terms of reduced signal-to-noise ratio, needed to achieve a prescribed error rate and equivalent optimum receiver complexity.  相似文献   

Cross-over, thresholds, and interactions between science and technology: lessons for less-developed countries     

Américo Tristão Bernardes  Eduardo da Motta e Albuquerque 《Research Policy》2003,32(5):865-885

Presently, science is an important precondition for the economic development of less-developed countries. This paper discusses the specific roles that science has at initial stages of development, pointing to its contributions for the countries’ absorptive capability. Furthermore, this paper specifies the role of science for initiating a positive interaction with technological development, since initial stages of development and during catching up processes. For less-developed countries, neither the linear model of technology nor an “inverted linear model” would take place: a more interactive approach is necessary for development. Using statistics of patents (USPTO) and scientific papers (ISI) for 120 countries (1974, 1982, 1990, and 1998), this paper analyses some evidences on thresholds levels of scientific production to originate an interactive relationship between science and technology. These data also document that the value of this threshold seems to double from one period to another. Although this paper presents tentative results, some policy implications are discussed: scientific institutional building must be seen as a component of modern industrial policies.  相似文献   

Multiple audience rating form strategies for student evaluation of college teaching   总被引：1，自引：0，他引：1  

Ken Peterson  G. Manny Gunne  Paul Miller  Orlando Rivera 《Research in higher education》1984,20(3):309-321

Michael Scriven has suggested that student rating forms, for the purpose of evaluating college teaching, be designed for multiple audiences (instructor, administrator, student), and with a single global item for summative functions (determination of merit, retention, or promotion). This study reviewed approaches to rating form construction, e.g., factor analytic strategies of Marsh, and recommended the multiple audience design of Scriven. An empirical test of the representativeness of the single global item was reported from an analysis of 1,378 forms collected in a university department of education. The global item correlated most satisfactorily with other items, a computed total of items, items that represented underlying factors, and various triplets of items selected to represent all possible combinations of items. It was concluded that a multiple audience rating form showed distinct advantages in design and that the single global item most fairly and highly represented the overall teaching performance, as judged by students, for decisions about retention, promotion, and merit made by administrators.  相似文献   

Skills‐Based Training and Counseling Self‐Efficacy     

Steve Urbani  Michael Robert Smith  Cleborne D. Maddux  Marlowe H. Smaby  Edil Torres‐Rivera  Judith Crews 《Counselor Education & Supervision》2002,42(2):92-106

The authors studied the effectiveness of the skilled counselor training model (SCTM). Counseling students who completed the SCTM demonstrated greater gains in skills acquisition and counseling self‐efficacy than counseling students who did not receive the training. At pretest, the counseling students in both groups, doing self‐appraisals, rated their performance of counseling skills significantly higher than trained raters assessed the students' performance of counseling skills. At posttest, members of the control group continued to overestimate their skills levels when compared with the ratings given by the trained raters, whereas, in comparison, students who received SCTM training underestimated their performance.  相似文献   

Reflections on urban science teacher-student self-efficacy dynamics     

Sumi Hagiwara  Maria S. Rivera Maulucci  S. Lizette Ramos 《Cultural Studies of Science Education》2011,6(4):999-1018

This forum article consists of commentaries—authored by Sumi Hagiwara, Maria S. Rivera Maulucci and Lizette Ramos—on the feature article by Virginia Jennings Bolshakova, Carla C. Johnson, and Charlene M. Czerniak. We reflect on a series of questions that take retrospective, introspective, and prospective views of self-efficacy in science education. We review selected studies that explore some of the historical developments and methodological approaches in the literature and examine a teacher-student self-efficacy system model that shows the ways in which teachers’ and students’ self-efficacy judgments are based upon multiple individual and shared components, such as identity and social interaction within the classroom and school. We close with a call for the design of measures of teacher-student self-efficacy systems, so that we can begin to tailor professional development experiences to the goals and motivations of individual and collective groups of teachers and students in ways that accommodate the unique cultural features of their classrooms and foster student self-efficacy.  相似文献   

George Glasson and George Bogg��s prospects on the environmental friendly relationship and ecojustice     

Eduardo Dopico 《Cultural Studies of Science Education》2011,6(2):347-350

This rejoinder to George Glasson and George Bogg’s papers provides additional conversation for considering the idea that we try to develop: leaving the classroom to continue teaching. Converting the teaching–learning process into research experiences brings our students not only scientific knowledge, but also an understanding of the research procedures. To be involved in field work, students can connect more personally the local action with global issues. On the ground in which we operate, environmental science, teaching of knowledge is insufficient if not accompanied by ecological experiences where students can see and share the needs of environmental protection and the idea of sustainability. Both response authors tell us about their own experiences in research in this regard. In their essays we can appreciate the desire to investigate human activities on ecosystems. Reading it makes us look with passion and awareness at the different consequences for our ecological environments: if we develop environmentally consequential behavior or harmful lifestyles for the planet. Furthermore, they warn us of the need to follow the development of students learning and reflect on the ways in which it produces time-causal relationship between persons and the environment.  相似文献