Investigation of heat transfer by means of pool film boiling on vertical cylinders in gravity

In this study, the heat transfer by means of pool film boiling on immersed vertical cylindrical rods was investigated. For this purpose, the rods with various dimensions, which have been heated up to 600°C, were immersed in a pure water pool in the different temperatures. The centre temperature and water temperature versus operation time were measured by K type thermocouples at the atmospheric pressure. After experimental studies, the surface temperatures of rods and heat transfer coefficients were calculated by means of Lumped method from the measured temperatures. Consequently, an empirical equation was developed between the Nusselt, Grashof, Prandtl and Jakob numbers. The experimental results showed that the specimens having the same characteristic lengths exhibited the same heat transfers performance although the specimen’s diameters and lengths differed considerably.     

An in-service primary teacher’s implementation of mathematical tasks: the case of length measurement and perimeter instruction

The purpose of this paper is to examine the cognitive demand levels of tasks used by an in-service primary teacher during length measurement and perimeter instruction and to examine a possible link between these tasks and the teacher’s mathematical knowledge in teaching. For this purpose, a case study approach was used and the data was drawn from classroom observations, semi-structured interviews, and field notes. Specific tasks from length measurement and perimeter instruction were presented and analyzed according to the Mathematical Tasks Framework. Then, how these tasks gave information about the teacher’s mathematical knowledge in teaching in the length measurement and perimeter topics was examined according to the Knowledge Quartet model. According to the findings of the study, the tasks used during length measurement and perimeter instruction were mostly categorized as low-level tasks. In addition, teacher’s mathematical knowledge in teaching affected the implementation of the tasks.     

Determination of the local inhomogeneity of a crystal lattice using a two-frequency nuclear quadrupole resonance method

Nonuniform line broadening in quadrupole spin systems is analyzed. It is shown theoretically that this broadening is of the tensor type. This forms the basis of the method for analyzing the distribution of local inhomogeneities in the crystal lattice, which is verified experimentally on a sodium nitride sample.     

Effect of reactive and nonreactive surface modifications and compatibilizer use on mechanical and flame-retardant properties of linear low-density polyethylene filled with huntite and hydromagnesite mineral

Journal of Thermal Analysis and Calorimetry - In the current study, huntite and hydromagnesite (HH) was used as flame-retardant additive in linear low-density polyethylene (LLDPE). The effect of HH...     

Nonlinear Response of Cylindrical Shells to Random Excitation

An analytical study of nonlinear flexural vibrations of cylindrical shells to random excitation is presented. Donnell's thin-shell theory is used to develop the governing equations of motion. Thermal effects for a uniform temperature rise through the shell thickness are included in the formulation. A Monte Carlo simulation technique of stationary random processes, multi-mode Galerkin-like approach and numerical integration procedures are used to develop nonlinear response solutions of simply-supported cylindrical shells. Numerical results include time domain response histories, root-mean-square values and histograms of probability density. Comparison of Monte Carlo results is made to those obtained by statistical linearization and the Fokker–Planck equation.     

Biomimetic mineralization of hydroxyapatite crystals on the copolymers of vinylphosphonic acid and 4-vinilyimidazole

In the present work, copolymers of vinylphosphonic acid and 4-vinilyimidazole (poly(4-VIm-co-VPA)) were found to be substrates favoring the precipitation of nanohydroxyapatite (HAP) crystals from stable supersaturated solutions at pH 7.4 and 37 degrees C. Deposition kinetics were studied by the constant composition technique. The rates of crystallization both on HAP seed crystals as reference and on the copolymer in powder form were investigated at constant supersaturation conditions. The rates of HAP crystal growth on the polymeric substrate were found to depend on the amount of seed material and on the phosphate content of the copolymer.     

Efficient synthesis of ferrocenylenones by Friedel-Crafts acylation with EtAlCl2-Me3Al

Efficient synthesis of ferrocenylenones using a Friedel-Crafts acylation reaction is described. Acryloyl, methacryloyl, crotonoyl, cinnamoyl, and β-methylcrotonoyl chlorides react with ferrocene in the presence of a Lewis acid (EtAlCl₂ or EtAlCl₂-Me₃Al) to give the corresponding ferrocenylenones (acryloyl, methacryloyl, crotonoyl, cinnamoyl, and methylcrotonoylferrocenes) in good isolated yields. Besides ferrocenylenones, chloroactylferrocene is also synthesised by this method.     

An investigation of influencing of Sb and Bi contents on surface tensions associated with Pb-free Sn-Zn-Sb-Bi quaternary and sub-quaternary solder alloys

The surface tensions of ternary and quaternary systems of Sn-based Pb-free solder alloys have been calculated using geometric models, such as Muggianu, Kohler, Chou’s general solution model (GSM), Toop, Guggenheim, ideal Butler and Butler models. It is observed from the calculation carried out in the present work that Sb and Bi contents decrease the surface tension of the solder alloys Sn-Zn-Sb-Bi. It is inferred from the statistical analysis that the best agreement between the experimental results and the corresponding calculated values of the surface tensions is generally observed in GSM and Muggianu models among the geometric models. Whereas Muggianu model is the most appropriate. Relatively good agreements have been observed between models considered in this study and experimental data.