CONDUCTIVITY

Author: LLANCAQUEO HERNIQUEZ ALFONSO.
Year: 2005.
University: BURGOS [www.ubu.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: This thesis describes memory of the inquiry to learn the process of learning the concept of field in Physics in college students. This process is studied in the light of the conceptual theory of fields, considering the relevance of this conceptual framework for the study of learning scientific concepts. Previous studies indicate that students show low levels of learning of this concept. This result reflects the need to know on the one hand, the concept of conceptual field, and secondly, the cognitive structure of the students, so that the teaching establishment of a mediation between the two. Thus, the main purposes of the thesis was to design and implement a methodology to investigate the relationship between cognitive structure of the students, and the structure of the concept of field built by the Physical and describing the progressivity of the process of coneptualización in the field conceptually. The results obtained in the five studies that comprise the empirical part of this work, confirm that these relations are manifested in the use of symbolic representations and explicitness partial meanings; they shape representations -esquemas- used by students in their shares of situations and problems that require scientific conceptualization acceptable. The characteristics dela initial conceptualization, show that students are approaching situations from diagrams of concepts of vector algebra and function, without achieving match the patterns that represent the concept of field. Learning moves towards greater explicitness of scientific meanings, and is manifested in a tendency to balance performance in action on situations. At the end of the course, most students delos, has a repertoire still small schemes, with appropriate scientific meanings, but they are insufficient to cope with a broad spectrum of the concept of field situations, in line with the objectives of the curriculum. Predominantly two levels of conceptualization: a level of transition-between knowledge and significance part of campo- with the concept of applying concepts to situations and problems, and another layer of knowledge and partial explanation of the concept of meaning without application to problems. Work performed under the conceptual theory of fields, helped describe the pattern of progression in conceptualizing the concept of field and provide practical knowledge that can be used in teaching physics.

Author: LARIO GARCIA JAVIER.
Year: 2006.
University: POLITÉCNICA DE CATALUÑA [www.upc.edu].
Place of defense: Sala 001 - EPSC.
Place of preparation: C4 Jordi Girona, 1-3, campus nord 08034.

Summary: The measures electrical impedance is the foundation for multiple applications in sensors, the study of biological parameters, measures electrolyte conductivity and corrosion studies, among others. This explains the wide variety of measurement methods proposed, because the demands peden be very different depending on the scope. Much of the methods of measuring electrical impedance currently used are based on sinusoidal signals, and some signposts square and spectral analysis. The methods that allow for a lot of information about the impedance measurement, ie for determining various elements describing their behavior as often, are relatively complex, and therefore are inadequate for measuring instruments portable or small. This argument raises an alternative method of measuring electrical impedance, also valid when it is constructed with a grid formed by the interconnection of several simple elements. The main features of the new method are: 1) the generation of signals is muys simple, which minimizes the complexity of the hardware; 2) the method for measuring impedances modeled with multiple elements (has been demonstrated for three elements, including a phase constant), and 3) requires a minimum computing power, which implies that the necessary software is also minimal. The excitation signals are digital proposals, because they are easy to generate because they have a finite set of amplitude levels. These signals contain multiple harmonics, which is why they pued extract information from multiple components of the impedance. The proposed method is based on applying a digital signal voltage and measure the impedance to the flow in so many different moments of time, as unknowns (P) is the model of the impedance. To determine the P elemtnos modeling an impedance from the P measures the flow, you need to know the analytical equation of the flow through the impedance, and for that you need to know in advance the model of the impedance and its response the digital signal. Therefore, the proposed method is completely analytical, and not necestia any adjustment curavas to experimental results. To verify the feasibility of the method has been calculated response of an impedance modeled with three components ideals (a resistor in series with a capacitor in parallel with another resistor) to a square voltage signal. It also has studied the effect of sampling time is not zero in the measure, and this effect was considered in the analysis of signal resputa to reduce the error of that time on the measure. From that first method has been proposed two other methods of measurement impedances electrical signals based on square, which explains the pros and incovenientes. Many electrical impedance model can not be used exclusively concentrated elements ideals, and required elements such as the phase constant. As implementation of the proposed method to measure impedances with elements not ideal, it has shaped the whole electrodos-electrolito a conductivity probe immersed in a salt solution, has developed the formulation, and that has been measured impedance Here , and to simplify the calculations, the excitation signal was running instead of tension. The result has been satisfactory, as the mistake of measures conductivity is reduced by an order of magnitude connection to the case modeling electrodes with a capacitor parallel with a resistor. The new method of measurement impedances with digital signals it is appropriate for isntrumentos measuring impedances and Conductivity and industrial portable low cost.