1,721,067 research outputs found
Thermal parameters estimation by heating and cooling and thermographic measurement
No full textThe use of a Peltier device in thermal contact with a specimen can provide heat source and sink. The utilization of this equipment is experimented, applying successive heating and cooling stages on various specimens and measuring the temperature outside of the contact area. Oscillating temperature in time and space can provide indication on the thermal diffusivity.The appealing ability of sourcing and sinking heat, with average null effect on temperature, may represent an innovative approach with respect to traditional stimulation technique.A simple analytical model is exploited for recovering the inversion equations. Numerical simulation allows to better understand the real process on the sample
Thermal diffusivity measurement in slabs using harmonic and one-dimensional propagation of thermal waves
No full textThe development of a novel approach to the well-known Angstrom ́s method for the measurement of the thermal diffusivity is reported. In this method, the diffusivity is determined from the damping and the phase shift of a periodic thermal signal during its propagation along the specimen. The propagation can be easily monitored by infrared thermography. In general, a non-contact source is used to apply the signal. In the present work, however, a direct-contact source is employed, with a temperature-oscillation signal supplied on a portion of one of the two main surfaces of the specimen, where a homogeneous contact can be yielded by using a proper contact pressure. Such practice implies that the measures of surface temperature can be used to estimate the diffusivity only beyond a certain distance from the source, where the wave-front of the temperature oscillation within the specimen becomes plane and perpendicular to the main surfaces. This distance is investigated here, to establish a general rule for the performance of the experiments. A thermoelectric device based on the Peltier effect is employed as the thermal source. The main difficulty about its use is to obtain a perfectly harmonic and well-balanced thermal signal. This is necessary to avoid a complex processing of the experimental data, and it can be achieved by supplying a current with a properly-chosen time-evolution pattern. Such an approach, which is built upon previous work, is here enhanced by improving the underlying analytical model
Modeling of thermal non-destructive evaluation techniques for composite materials
No full textThe inspection of composite structures by thermal non-destructive evaluation (TNDE) techniques based on Infrared Thermography is relatively common in the aerospace industry. However, state-of-the-art is far to be reached and there is still place for substantial improvement, in terms of development of the inspection procedures, optimization of the experimental set-up and assessment of the inversion algorithms. This requires the availability of large amounts of reference data, which can be provided in a cost-effective way by mathematically modeling the thermal behavior of the inspected structures.The numerical simulation of procedures for thermographic inspection is investigated in this work. The analysis is focused on the strategies that can be implemented to model the heat conduction processes in composite structures typical of TNDE procedures by means of commercial software packages for coupled mechanical-thermal analyses. The results of a pilot application of a commercial software packages to a real case are finally presented
Diffusivity measurement of thick samples by thermography and heating-cooling technique
No full textThe technique consisting in using a Peltier cell in contact with the material and producing successively heating and cooling conditions is presented for the measurement of diffusivity. Results on thermally thin materials with well known characteristics like stainless steel AISI 304 gives measurement values with precision around 10%. Analyzing the situation of a thermally thick marble sample, the in-depth propagation affects also the lateral ones. This is of general interest for a future use of this technique in the field where the thickness of the material may be important
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Measurement of thermal diffusivity by propagation of thermal waves: a new modification of the Ångström method
No full textA new technique for measurement of the thermal diffusivity is presented here. The technique is a modification of the well-known Ångström’s method, which relies on the steady-periodic propagation of thermal waves along a specimen to estimate the diffusivity. The novelty of the proposed modification is that harmonic thermal waves with mean value equal to the ambient temperature are induced in the specimen by means of a purposely developed source, based on the Peltier effect. This allows estimating the diffusivity by relatively simple processing of surface-temperature data, acquired by infrared thermography.The mathematical formulation of the thermal problem is described here, together with the experimental procedure and the apparatus by which the most proper thermal signal can be achieved. A cross comparison with other measurement techniques is finally reported
Thermal diffusivity measurement of stainless steel by periodic heating technique
No full textThe use of a device based on the Peltier effect can provide heat source and sink suitable for diffusivity measurements. By performing a one-side test it is possible to estimate the diffusivity value, provided that some conditions are met. In a previous work the basic idea and the experimental set up of this method were described. A crucial point is the inversion formula that allows recovering the diffusivity value from the temperature data. The proposed analytical formula works only if the experimental parameters are suitably chosen for the particular sample under test. This paper is focused on the conditions to be met in order to correctly apply that formula. To this end, tests have been performed on a material with known thermal properties
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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