An augmented EM algorithm for monotonic Bayesian networks using parameterized conditional probability tables

Bayesian networks offer an attractive framework for describing the relationship between latent proficiency variables and observable outcomes. In educational applications, it is useful to restrict the conditional probability tables of the Bayesian network to be monotonic—increasing skill implies a high chance of a good performance. This paper describes the DiBello family of models for Bayesian networks, which enforce monotonicity, and introduces an augmented EM algorithm for estimating the parameters of these models. In a calibration experiment using simulated data, the algorithm did a good job recovering the model parameters and the conditional probability tables with sample sizes as low as 400.

     

Preparation and thermal properties of polyethylene terephthalate/huntite–hydromagnesite composites

In this report, it was aimed to the improve thermal stability of polyethylene terephthalate (PET) by adding huntite/hydromagnesite minerale. PET/huntite/hydromagnesite composites were prepared by adding various proportions of huntite/hydromagnesite to PET. The chemical structures of the composites were characterized by Fourier transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD) analysis. Thermal properties of the composites were determined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Glass‐transition temperatures and char yields increased with the increase of the huntite/hydromagnesite content in the composites. The surface morphologies of the composites were investigated by a scanning electron microscopy. The obtained results proved that the composite system is more thermally stable than the pure PET itself. POLYM. COMPOS., 37:3275–3279, 2016. © 2015 Society of Plastics Engineers     

Preparation,characterization and electrical properties of polyacrylonitrile/huntite composites

We focused on polyacrylonitrile (PAN)/huntite composites to reinforce the polymer prepared by adding different percentages (wt%) of huntite to PAN. The composites were characterized using thermogravimetric analysis, differential scanning calorimetry, fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy techniques. It was clearly seen that the composites of PAN/huntite have better thermal stability than pure PAN. The effect of the huntite adding to Polyacrylonitrile (PAN) on dc conductivity and dielectric constant was also investigated. Dc conductivity values were increased with increasing temperature. Activation energy values were calculated depending on huntite contents in PAN. Relative dielectric constant values varied in the range of 16.5–21.2 at room temperature at 100 kHz frequency depending on huntite concentrations. All the electrical measurements were performed in dark and vacuum ambient between the temperatures of 295 and 523 K. Dielectric measurements were performed in the frequency range of 40 Hz–100 kHz.     

Digital Image Analysis to Determine Pore Opening Size Distribution of Nonwoven Geotextiles

The filtration performance of a geotextile is controlled by its pore opening size distribution (PSD). Current methods for determining PSD are mostly indirect and contain inherent disadvantages. Recent technological advancements in image analysis offer great potential for a more accurate and direct way of determining the PSD of nonwoven geotextiles. A new and accurate method of image analysis for PSD determination of nonwoven geotextiles is presented in this paper. The image analysis method was developed using various mathematical morphology algorithms to provide a complete PSD curve for each geotextile. The two characteristic pore opening sizes, O95 and O50, were determined from image analysis and were compared to the results from laboratory tests, analytical equations, as well as manufacturer’s reported apparent opening sizes (AOS). The image-based O95 pore opening size of various geotextiles was comparable to the manufacturer’s reported AOS as well as to those determined from the laboratory dry sieving test. However, the measured O50 pore opening size was lower than the one determined using the analytical equations developed by two previous researchers. Overall, the image analysis method presented provides a unique and accurate method that can measure fiber thickness and pore opening sizes in a cross-sectional image of a woven geotextile.     

Efficiency enhancement for bulk-heterojunction hybrid solar cells based on acid treated CdSe quantum dots and low bandgap polymer PCPDTBT

We report on the efficiency enhancement for bulk-heterojunction hybrid solar cells based on hexanoic acid treated trioctylphosphine/oleic acid-capped CdSe quantum dots (QDs) and low bandgap polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) compared to devices based on poly(3-hexylthiophene) (P3HT). Photovoltaic devices with optimized polymer:QD weight ratio, photoactive film thickness, thermal annealing treatment, and cathode materials exhibited a power conversion efficiency of 2.7% after spectral mismatch correction, which is the highest reported value for spherical CdSe QD based photovoltaic devices. The efficiency enhancement is attributed to the surface treatment of the QDs together with the use of the low bandgap polymer PCPDTBT leading to an increased short-circuit current density due to additional light absorption between 650 and 850 nm. Our results suggest that the hexanoic acid treatment is generally applicable to various ligand-capped CdSe and confirm that low bandgap polymers with adequate HOMO and LUMO levels are promising to be incorporated into hybrid solar cells for further device performance improvement.     

Thermal and Morphological Properties of Organo Modified Nanoclay/Polyethylene Terephthalate Composites

The purpose of this study is polyethylene terephthalate (PET) and modified organo-nanoclay with different masses and to contribute to the different areas of use and literature by examining these nanocomposites physical, chemical and thermal features. In this study, nanocomposite films, which work in PET that is a type of polymeric material, and work into modified organo-nanoclays with different percentages, obtained with the method called as in situ polymerization. The chemical structures of nanocomposites prepared were investigated by fourier transform infrared spectroscopy. The surface morphologies of this nanocomposites were examined by scanning electron microscope. Their thermal properties were analyzed by differential scanning calorimetry and thermogravimetric analysis. According to the results obtained, the thermal stabilities of modified nanoclay composites got better than PET. Besides, while the percent of clay in the doped PET was rising, its fragility increased. At the same time, high mass of clay formed when the percent of contribution developed. Thus, the surface interaction of polymer–clay decreased, because the composed aggregations prevented the polymer matrix from going into the layer of clay.     

Preparation and characterization of polyaniline/Turkish Huntite‐hydromagnesite composites

The aim of this study was to improve thermal stability of polyaniline (PANI) by adding Turkish Huntite. PANI was synthesized and PANI/Turkish Huntite composites were prepared by adding various proportions of huntite to aniline. The chemical structures of the samples were investigated by Fourier transform infrared spectroscopy. Thermal properties of the composites were determined by thermogravimetric analysis and differential scanning calorimetry. The surface morphologies of the samples were investigated by a scanning electron microscopy. The obtained results proved that the composite system is more thermally stable than the pure PANI. POLYM. COMPOS., 35:456–460, 2014. © 2013 Society of Plastics Engineers