Effects of environmental factors on the adhesion and durability characteristics of epoxy-bonded concrete prisms

This work is concerned with the effects of environmental factors on the adhesion and durability characteristics of epoxy-bonded concrete prisms. The results indicate that the presence of liquid water at the interfacial zone during the epoxy injection process disrupts the initial bond configurations. The freezing and thawing up to about 40 cycles do not have a significant effect on the bond stability. An adequate degree of chemical stability is maintained in the bond line by the epoxy adhesives after 120 days of exposure to corrosive environments such as MgSO₄ and MgCl₂. However, there is a pronounced effect of these chemical substances on the concrete strength. The load-bearing capacity of epoxy-bonded concrete prisms decreases with increasing temperature. Despite this fact, the EP3-bonded concrete prisms give relatively high joint strengths at temperatures up to 100 °C.     

Magnetic Properties of Zn1?x Ni x O (0.25≤x≤ 0.50) Prepared by Solid-State Reactions

In this study the origin of ferromagnetism in ZnO-based bulk systems has been investigated using Ni-doped ZnO samples, Zn_1−x Ni _x O with 0.25≤x≤0.50, prepared by solid-state reactions. The structural characterizations indicated that the Ni²⁺ ions almost uniformly distributed in all the samples, and the samples have hexagonal wurtzite structure; however, when x is increased toward 0.50, a new NiO phase is formed. A ferromagnetism (FM) has been observed for all the samples at and below the room temperature. In other words, the room temperature results of (M–H) curves show that the FM observed is intrinsic for all the Ni-doped ZnO samples. However, the saturated magnetizations decrease gradually with increasing Ni concentration. This indicates that, in addition to FM, the excessive doping of Ni in ZnO also causes an antiferromagnetic (AFM) contribution which increases with increasing Ni amount. This result is also supported by the magnetization against temperature measurements. Furthermore, the trend of the ac-susceptibility (χ) versus temperature curves, measured under an ac-magnetic field of 100 Oe, also support our conclusion about the antiferromagnetic contribution to ferromagnetism in our samples.     

Investigation of the effects of geometrical parameters on heat transfer from buried finned pipes

Heat transfer from finned pipes buried in the soil has been investigated using experimental, analytical and numerical techniques. The experimental setup consists of a ground source heat pump system and two separate ground heat exchangers. Constant surface temperature approach based on Carslaw and Jaeger’s theory study was used for calculating the heat transfer from the pipes analytically. The problem was modeled and solved using a CFD program numerically. Effects of the fin number, fin length and simulation time on the heat transfer rate have been investigated and compared with bare tube. A modified analytical formula was also proposed for finned pipes in this study.     

Modification of cyclohexanone-formaldehyde-resin

The reactions of cyclohexanone-formaldehyde-resin via its hydroxy and carbonyl functional groups with a number of different reagents such as acetic anhydride, benzoyl chloride, hydroxylamine, semicarbazide, and phenyl hydrazine were studied. Melting points, IR spectrums, and solubilities in various solvents of the products were determined.     

Digital Image Analysis in Geotechnical Engineering Education

Existing research has shown that visual input significantly contributes to learning, therefore, it is paramount to use visual tools to help demonstrate engineering concepts. One of these tools, digital image analysis, can help effectively communicate complex concepts to students in a simple and understandable format as a supplement to traditional lecturing, while simultaneously enabling students to have hands-on experience. This note describes a series of activities to incorporate digital image analysis into engineering education. The undergraduate students worked in research projects that involved image-based analysis of geomaterials. Based on these activities and the students’ response to a questionnaire, it was recognized that digital image analysis can enhance the understanding of engineering phenomena for undergraduate students. The hands-on experience and visual demonstration improved the students’ grasp of fundamental concepts in research projects. The research experience allowed the students to build a connection between the classroom and the solution of state-of-the-art engineering scientific problems. It also taught them about cooperation and teamwork, as well as academic independence.     

Genetic Algorithm for the Multiple-Query Optimization Problem

Producing answers to a set of queries with common tasks efficiently is known as the multiple-query optimization (MQO) problem. Each query can have several alternative evaluation plans, each with a different set of tasks. Therefore, the goal of MQO is to choose the right set of plans for queries which minimizes the total execution time by performing common tasks only once. Since MQO is an NP-hard problem, several, mostly heuristics based, solutions have been proposed for solving it. To the best of our knowledge, this correspondence is the first attempt to solve MQO using an evolutionary technique, genetic algorithms     

Solver and Shell Element Performances for Curved Bridge Analysis

A study has been undertaken to investigate different solver and shell element performances for curved bridge finite-element analysis. Three sparse solvers were implemented into a bridge finite-element analysis code, and the solution times and memory requirements for typical bridges were compared. In addition, the use of four-node and nine-node shell elements in modeling was investigated for different mesh densities. Based on the comparative studies performed, modeling guidelines for practicing engineers have been developed and are presented herein.     

Solubility Enhancement of Fe in ZnO Nanoparticles Prepared by Co-Precipitation Method

Journal of Superconductivity and Novel Magnetism - Crystalline ZnO offers an excellent host matrix to create a dilute magnetic semiconductor (DMS) owing to its facile Zn-atom substitution with the...     

Synthesis and thermal properties of poly(styrene-co-ally alcohol)-graft-stearic acid copolymers as novel solid–solid PCMs for thermal energy storage

A series of poly(styrene-co-allyalcohol)-graft-stearic acid copolymers were synthesized as novel polymeric solid–solid phase change materials (SSPCMs). The graft copolymerization reactions between poly(styrene-co-allyalcohol) and stearoyl chloride were verified by Fourier transform infrared (FT-IR) and Proton Nuclear Magnetic Resonance (¹H NMR) spectroscopy techniques. The crystal morphology of the SSPCMs was investigated using polarized optical microscopy (POM) technique. Thermal energy storage properties of the synthesized SSPCMs were measured using differential scanning calorimetry (DSC) analysis. The POM results showed that the crystalline phase of the copolymers transformed to amorphous phase above their phase transition temperatures. Thermal energy storage properties of the synthesized SSPCMs were investigated by differential scanning calorimetry (DSC) and found that they had typical solid–solid phase transition temperatures in the range of 27–30 °C and high latent heat enthalpy between 34 and 74 J/g. Especially, the copolymer with the mole ratio of 1/1 (poly(styrene-co-allyalcohol)/stearoyl chloride) is the most attractive one due to the highest latent heat storage capacity among them. The results of DSC and FT-IR analysis indicated that the synthesized SSPCMs had good thermal reliability and chemical stability after 5000 thermal cycles. Thermogravimetric (TG) analysis results suggested that the synthesized SSPCMs had high thermal resistance. In addition, thermal conductivity measurements signified that the synthesized PCMs had higher thermal conductivity compared to that of poly(styrene-co-allyalcohol). The synthesized copolymers as novel SSPCMs have considerable potential for thermal energy storage applications such as solar space heating and cooling in buildings and greenhouses.