Reconstruction of Microscopic Thermal Fields from Oversampled Infrared Images in Laser-Based Powder Bed Fusion

This article elucidates the need to consider the inherent spatial transfer function (blur), of any thermographic instrument used to measure thermal fields. Infrared thermographic data were acquired from a modified, commercial, laser-based powder bed fusion printer. A validated methodology was used to correct for spatial transfer function errors in the measured thermal fields. The methodology was found to make a difference of 40% to the measured signal levels and a 174 °C difference to the calculated effective temperature. The spatial gradients in the processed thermal fields were found to increase significantly. These corrections make a significant difference to the accuracy of validation data for process and microstructure modeling. We demonstrate the need for consideration of image blur when quantifying the thermal fields in laser-based powder bed fusion in this work.

Elementary linear filtering tasks using CNNs with minimum-size templates

In this paper we investigate the linear filtering capabilities of the standard cellular neural network in the general case of non-symmetric templates. We approached here systematically the CNNs with minimum-size templates (1x3), analyzing in detail their filtering capabilities in the one-dimensional case. Starting from a general form of the spatial transfer function, we emphasize some useful filtering functions that can be obtained. For each filter type, we derive the relations which give the template parameter values, in order to design a given CNN filter with specified characteristics-like central frequency, bandwidth, selectivity etc. Filters with symmetric templates are treated as a particular case. For each type of filtering the characteristics are shown and simulation results are presented as well. Some of these results are then extended to 2-D CNNs and several simulations of useful filtering tasks are presented on real images.

The receptive field of the primate P retinal ganglion cell, I: Linear dynamics

The ganglion cells of the primate retina include two major anatomical and functional classes: P cells which project to the four parvocellular layers of the lateral geniculate nucleus (LGN), and M cells which project to the two magnocellular layers. The characteristics of the P-cell receptive field are central to understanding early form and color vision processing (Kaplan et al., 1990; Schiller & Logothetis, 1990). In this and in the following paper, P-cell dynamics are systematically analyzed in terms of linear and nonlinear response properties. Stimuli that favor either the center or the surround of the receptive field were produced on a CRT and modulated with a broadband signal composed of multiple m-sequences (Benardete et al., 1992b; Benardete & Victor, 1994). The first-order responses were calculated and analyzed in this paper (part I). The findings are: (1) The first-order responses of the center and surround depend linearly on contrast. (2) The dynamics of the center and surround are well described by a bandpass filter model. The most significant difference between center and surround dynamics is a delay of approximately 8 ms in the surround response. (3) In the LGN, these responses are attenuated and delayed by an additional 1–5 ms. (4) The spatial transfer function of the P cell in response to drifting sine gratings at three temporal frequencies was measured. This independent method confirmed the delay between the (first-order) responses of the center and surround. This delay accounts for the dependence of the spatial transfer function on the frequency of stimulation.

Spatial and temporal properties of luminosity horizontal cells in the turtle retina.

Luminosity horizontal cells in the turtle retina respond approximately linearly to visual stimuli with contrast levels spanning a large part of the physiological range. We characterized the response properties of these cells under conditions of low photopic background illumination by measuring their spatial and temporal frequency transfer functions. Our experimental results indicate in two ways that, under these conditions, feedback from luminosity horizontal cells to cones does not play a major role in the mechanisms underlying the spatial and temporal tuning of horizontal cell responses. First, the shape of the spatial transfer function depended only weakly on the temporal frequency with which it was measured. Second, the shape of the temporal transfer function depended only weakly on the spatial frequency with which it was measured.

Spatial Response of Arbitrarily Electroded Piezoelectric Plates by Plane-Wave Decomposition

The spatial response of resonant piezoelectric plates used in various acoustic imaging systems is of significant practical interest and is closely related to the resolving ability of these systems. In a certain class of applications, in order to achieve the desired transducing action, the faces of the plate are only partially electroded. There, it is advantageous to be able to predict and control the spatial distribution of the acoustic output from the knowledge of the spatial distribution of the electrodes. A new technique is presented for determining the spatial distribution of the acoustic output of an arbitrarily electroded piezoelectric plate. This technique regards the transducer as a linear spatial system, with the electrode pattern considered as the input and the resulting acoustic particle displacement pattern immediately in front of the transducer in the propagation medium as the output. Once the spatial transfer function or the spatial impulse response of the system is known, the output for any electrode configuration can be found using Fourier techniques. Experimental measurements of the output of several piezoelectric plates due to different electrode patterns compare closely with calculations based on the above theory.