Effect of expanded perlite on the mechanical properties and thermal conductivity of lightweight concrete

The main objective of this study is to provide more data on the effects of expanded perlite on the mechanical properties and thermal conductivity of lightweight concrete. In the experimental program, mixtures were prepared by partially replacing natural aggregate by expanded perlite and as a result, unit weights of lightweight concretes in fresh state varied between 700 and 2000 kg/m³. Water to cement ratio was kept constant in all mixtures. Compressive strength, modulus of elasticity, water absorption and capillarity coefficient of the mixtures were determined. Thermal conductivity of the specimens was also obtained. Test results show that the compressive strength and modulus of elasticity decreases with increasing in perlite content. Water absorption and sorptivity coefficient, however, increase with the higher perlite contents. The test results indicate that the thermal conductivity is substantially improved with the use of perlite and a strong relationship between thermal conductivity and unit weight is obtained.     

Synthesis and Characterization of High Catalytic Activity Magnetic Fe3O4 Supported Pd Nanocatalyst

This study reports the fabrication and characterization of magnetically recyclable catalysts of Fe₃O₄–Pd nanocomposite as highly effective catalysts for reduction reactions in liquid phase. The characterization of Fe₃O₄–Pd MRCs were done by X-ray powder diffraction, ?nfrared spectroscopy, thermal analyzer, transmission electron spectroscopy, ?nductively coupled plasma, UV-Vis spectroscopy, vibrating sample magnetometer, respectively. The reduction of Pd²⁺ was accomplished with polyethylene glycol 400 (PEG-400) and Fe₃O₄ nanoparticles were prepared by co-precipitation of FeCI₃?6H₂O and FeCl₂?4H₂O. Thus formed Fe₃O₄–Pd MRCs showed a very high activity in reduction reactions of 4-nitro-aniline and 1,3-di-nitrobenzene in liquid phase. Magnetic character of this system allowed recovery and multiple use without significant loss of its catalytic activity.     

DIRECT CONTACT HEAT TRANSFER BETWEEN TWO IMMISCIBLE LIQUIDS

Direct-contact heat transfer between two immiscible liquids in turbulent pipe flow is studied under non-boiling conditions. The salt water and BP-Transcal 65 heat transfer oil are used as immiscible liquids. The diameter and the length of the pipe are 1.33 cm. and 304 cm., respectively. The effects of oil volume fraction, inlet salt water concentration, average liquid velocity, inlet oil temperature and pipe length on the over-all volumetric heat transfer coefficient are investigated.     

Computer-aided retinal vessel segmentation in retinal images: convolutional neural networks

In medicine, diagnosis is as important as treatment. Retinal blood vessels are the most easily visible vessels in the whole body, and therefore, play a key role in the diagnosis of numerous diseases and eye disorders. Systematic and eye diseases cause morphologic variations, such as the growing, narrowing or branching of retinal blood vessels. Imaging-based screening of retinal blood vessels plays an important role in the identification and follow-up of eye diseases. Therefore, automatic retinal vessel segmentation can be used to diagnose and monitor those diseases. Computer-aided algorithms are required for the analysis of progression of eye diseases. This study proposes a hybrid method that provides a combination of pre-processing and data augmentation methods with a deep learning model. Pre-processing was used to solve the irregular clarification problems and to form a contrast between the background and retinal blood vessels. After pre-processing step, a convolutional neural network (CNN) was designed and then trained for the extraction of retinal blood vessels. In the training phase, data augmentation was performed to improve training performance. The CNN was trained and tested in the DRIVE database, which is commonly used in retinal blood vessel segmentation and publicly available for studies in this area. Results showed that the proposed system extracted vessels with a sensitivity of 77.78%, specificity of 97,84%, precision of 84.17% and accuracy of 95.27%.

This study also compared the results to those of previous studies. The comparison showed that the proposed method is an efficient and successful method for extracting retinal blood vessels. Moreover, the pre-processing phases improved the system performance. We believe that the proposed method and results will make contribution to the literature.

     

The effects of different cement dosages, slumps, and pumice aggregate ratios on the thermal conductivity and density of concrete

Thermal conductivity coefficients of concretes made up of mixtures of pumice aggregate (PA) and normal aggregate were measured. To determine the effect of PA ratio, different cement dosage, and slumps on the thermal conductivity of concrete, 25%, 50%, 75%, and 100% pumice ratios were used in place of normal aggregate by volume, 200-, 250-, 350-, 400-, and 500-kg/m³ cement dosages, and 3±1-, 5±1-, and 7±1-cm slumps were used in this study. The analysis of the test results leads to the conclusion that PA decreased the density and thermal conductivity of concretes up to 40% and 46%, respectively. Increasing the cement dosage in the mixtures caused both density and thermal conductivity of the concrete to increase. The effect of slump on the density and thermal conductivity fluctuated.     

The oxidation of NaBH4 on electrochemicaly treated silver electrodes

This study is related to the development of suitable anode material for the direct borohyride fuel cells (DBFCs). The effect of electroactive Ag oxides upon the oxidation of NaBH₄ was investigated. The treatment of Ag surface with H₂O₂ gave a granulated compact layer which was observed to give a very high current density and good reversibility at lower concentration compared with the electrode treated with NaOH which resulted a fibrous layer with a lower electrocatalytic effect. The mode of surface oxidation was found to have a profound effect upon the behavior of the electrode. It was also observed that there is an optimum NaBH₄ concentration to obtain the maximum current density.     

Mass transfer enhancement factor for chemical absorption of carbon dioxide into sodium metaborate solution

Hydrogen is getting increasing attention as a medium for energy storage, and sodium borohydride is accepted as a suitable carrier for hydrogen. The main product of the process by means of which hydrogen is produced from sodium borohydride is sodium metaborate. Our aim was to find an alternative use for sodium metaborate and specifically investigating the feasibility to use it for carbon dioxide capture from flue gases. The products of this chemical absorption are sodium carbonate, sodium bicarbonate and boric acid, all of which are industrially important chemicals. A bubble column was used in the experiments. Oxygen desorption technique was employed to determine the liquid side physical mass transfer coefficient. Chemical mass transfer coefficient was determined by absorption of carbon dioxide from its mixture with nitrogen into sodium metaborate solution. Enhancement factor was then calculated and a correlation was developed for it.