Comparison of Artificial Neural Network and Polynomial Approximation Models for Reflectance Spectra Reconstruction.

Knowledge of surface reflection of an object is essential in many technological fields, including graphics and cultural heritage. Compared to direct multi- or hyper-spectral capturing approaches, commercial RGB cameras allow for a high resolution and fast acquisition, so the idea of mapping this information into a reflectance spectrum (RS) is promising. This study compared two modelling approaches based on a training set of RGB-reflectance pairs, one implementing artificial neural networks (ANN) and the other one using multivariate polynomial approximation (PA). The effect of various parameters was investigated: the ANN learning algorithm-standard backpropagation (BP) or Levenberg-Marquardt (LM), the number of hidden layers (HLs) and neurons, the degree of multivariate polynomials in PA, the number of inputs, and the training set size on both models. In the two-layer ANN with significantly fewer inputs than outputs, a better MSE performance was found where the number of neurons in the first HL was smaller than in the second one. For ANNs with one and two HLs with the same number of neurons in the first layer, the RS reconstruction performance depends on the choice of BP or LM learning algorithm. RS reconstruction methods based on ANN and PA are comparable, but the ANN models' better fine-tuning capabilities enable, under realistic constraints, finding ANNs that outperform PA models. A profiling approach was proposed to determine the initial number of neurons in HLs-the search centre of ANN models for different training set sizes.

Optical Assessment of Porosity Parameters in Transparent Woven Fabrics.

This paper deals with the possibility of a fast and accurate assessment of the number, size, and distribution of pores in transparent woven fabrics based on light penetration. The procedure of analyzing the pore structure in the fabrics based on a digital image is presented in detail. Fabric pores are treated as image particles and analyzed with the Java-based image processing software ImageJ. The obtained data relate to the constructional parameters of the fabric that allow for further analysis, provide the possibility to compare structurally similar or different samples as well as double check the results generated by optical or other means. This paper describes work on plain and similar to plain weaves. The conducted analysis revealed several expected and some unexpected results. Among the former, we can list the range of pore sizes in the examined woven fabrics, the distribution of pores in regard to their similarity, and the effect of dents. Examples of the latter are the magnitude of the cumulative percentage of pores in regard to the weave and the degree to which they participate in the inter-yarn and inter-fiber pores.

Slovenian Validation of the Children's Perceived Use of Self-Regulated Learning Inventory.

The importance of self-regulated learning (SRL) has increased during the COVID-19 pandemic and measures for assessing students' self-regulation skills and knowledge are greatly needed. We present the results of the first thorough adaptation of the Children's Perceived use of Self-Regulated Learning Inventory (CP-SRLI). The inventory, consisting of 15 scales measuring nine components of SRL, was administered to a sample of 541 Slovenian ninth graders. Confirmatory factor analyses supported internal structure validity of most components, but two components required some structural modifications. Internal consistency coefficients were acceptable for the majority of scale scores and were highly comparable to the original ones. While metric invariance across gender was confirmed, the scalar invariance of some scales needs further examination. Meaningful correlations with relevant externally assessed and self-reported self-regulation and school performance variables indicated good criterion validity of the inventory. The Slovenian version of the CP-SRLI thus proved to be a sufficiently valid and reliable instrument for assessing pupils' learning self-regulation.

Relation between colour- and phase changes of a leuco dye-based thermochromic composite.

Reversible colour change of leuco dye-based composites is in general closely related to their phase change, thus the two phenomena should occur at around the same temperature and should be influenced similarly. However, spatial confinement of the analysed sample affects the change in colour differently compared to its phase transition and the most pronounced effects can be observed during cooling. The bulk composite is coloured while still liquid and the colour hysteresis does not exhibit a loop. In an open-porous medium the colouration coincides well with the crystallization and the colour hysteresis widens to about 4 °C. Microencapsulated composite exhibits two crystallization processes, one of them taking place at the bulk crystallization temperature and the other one at about 20 °C lower. Under such conditions the composite is coloured just before the onset of the second crystallization, i.e. about 15 °C below crystallization in the bulk, and the corresponding colour hysteresis widens to 18 °C. The two crystallization forms are thermally independent and have the same crystalline structure. These effects should be taken into account when designing future applications where the phase-changing materials are implemented.

Characterisation and functional properties of antimicrobial bio-barriers formed by natural fibres.

Antimicrobial bio-barriers formed on cotton (CO), silk (SE), and woollen (WO) fabrics were prepared by the application of 3-(trimethoxysilyl)-propyldimethyloctadecyl ammonium chloride (Si-QAC) at 11 concentrations ranging from 0.5% to 20% using an exhaustion method. The presence of the Si-QAC coating on the treated fabric samples was detected by X-ray photoelectron spectroscopy. The bromophenol blue reagent was used to determine the concentration of quaternary ammonium groups in the coating. The antimicrobial activity of the coated fibres against Gram-negative and Gram-positive bacteria (Escherichia coli and Staphylococcus aureus), fungi (Aspergillus niger and Chaetomium globosum), and soil microflora was assessed using standard microbiological methods. The antimicrobial protection of the fibres increased with increases in the applied concentration of Si-QAC. The fibre type strongly influenced the antimicrobial activity of Si-QAC. Si-QAC was most effective for CO fibres, less effective for WO fibres, and least effective for SE fibres, suggesting that Si-QAC is less accessible for interactions with microorganisms when applied to protein fibres than to cellulose. Although Si-QAC reduced the microbial growth, it did not significantly hinder the biodegradability or sustainability of the coated fibres when exposed to soil microflora. The extent of rotting was more influenced by the morphological and chemical properties of the fibres than by the presence of Si-QAC.

Determination of point-spread function of paper substrate based on light-scattering simulation.

The objective of this work was to establish the relationship between the calculated subsurface scattered-photon distribution and the mathematical quantity known as point-spread function (PSF). Photon distribution of subsurface scattered light was calculated using the Monte Carlo method developed for describing reflectance and opacity of paper and of images printed on paper. The obtained normalized photon distribution made it possible to separate optical and mechanical components of dot gain for the paper-ink system. In the presented method of obtaining the reflectance profile of a screen element, the PSF convolves with a modelled reflectance profile of that element. It was found that the PSF can be better approximated by means of the Lorentzian function when compared to the Gaussian profile that was used in the past research on this topic.