Substituenteneffekte auf die C–C-Bindungsstärke, 8. Standardbildungsenthalpien und Spannungsenthalpien von 1,1,2,2-Tetraethylethylenglykol-dimethylether und D,L-1,2-Dimethyl-1,2-diphenylethylenglykol-dimethylether

Effects of Substituents on the Strength of C - C Bonds, 8¹. - Heats of Formation and Strain of 1,1,2,2-Tetraethylethylene Glycol Dimethyl Ether and D,L .-1,2-Dimethyl-l,2-diphenylethylene Glycol Dimethyl Ether The heats of combustion of the title compounds 1 and 2 were measured calorimetrically with the result (kcal mol ^-1, s. d. in parentheses) ΔH°_c = − 1880.1 (± 0.6) and − 2373.3 (± 1.4). The heat of vaporisation of 1 ΔH^v = 14.3 (± 0.3) and the heat of sublimation of 2 ΔH^sub = 27.2 (± 0.5) were derived from their temperature dependance of the vapor pressure. The latter were determined between 30 and 80°C using a flow method. The resulting standard heats of formation ΔH°_t(g) = −122.4 (± 0.7) and −43.8 (±1.5) for 1 and 2 correspond to a strain enthalpy (_s) of 15.9 and 8.0 kcal mol^-1, respectively. The steric strain of the dimethoxyethanes 1 and 2 is about one fourth lower than the strain of the corresponding dimethylethanes 3 and 4 bearing the same substituents. Thus, a methoxy group causes less steric stress than a methyl group.     

Two-dimensional transient dynamic response of orthotropic layered media

In this study, two-dimensional transient dynamic response of orthotropic plane layered media is investigated. The plane multilayered media consist of N different generally orthotropic, homogeneous and linearly elastic layers with different ply angles. In the generally orthotropic layer, representing a ply reinforced by unidirectional fibers with an arbitrary orientation angle, the principal material directions do not coincide with body coordinate axes. The solution is obtained by employing a numerical technique which combines the use of Fourier transform with the method of characteristics. The numerical results are displayed in curves denoting the variations of stress and displacement components with time at different locations. These curves clearly reveal, in wave profiles, the scattering effects caused by the reflections and refractions of waves at the boundaries and at the interfaces of the layers, and also the effects of anisotropy caused by fiber orientation angle. The curves properly predict the sharp variations in the response at the neighborhood of the wave fronts, which shows the power of the numerical technique employed in the study. By suitably adjusting the elastic constants, the results for multilayered media with transversely isotropic layers, or layers with cubic symmetry, or isotropic layers can easily be obtained from the general formulation. Furthermore, solutions for some special cases, including Lamb’s problem for an elastic half-space, are obtained and compared with the available solutions in the literature and very good agreement is found. Preliminary version presented at the Second International Congress on Mechatronics (MECH2K3), Graz, Austria, July 14-17, 2003.     

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.     

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.     

Crystallographic Analysis of FCC ? BCT Martensitic Transformation in the Alloy Fe-22% Ni-0.8% C

The infinitesimal deformation (ID) approach is applied to analyse the crystallography involved in the fcc to bct martensitic transformation for the case of (101)_γ[<formula><overline>1</overline>01</formula>]_γ twinning shear as LIS (lattice invariant shear) system in the alloy Fe-22% Ni-0.8% C. Analytical solutions are derived for habit plane orientation, orientation relationships between austenite and martensite phases, and the magnitude of the total shape deformation, etc. In order to compare numerical solutions with the ID approach and phenomenological crystallographic theory, the corresponding crystallographic parameters are calculated by using the Ledbetter and Dunn (L-D) theory. The numeric values obtained are compared with the predictions of the phenomenological crystallographic theories, and with experimental results.     

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.     

Ionic and electronic conductivity of nitrogen-doped YSZ single crystals

The ionic and electronic charge transport was studied for single crystals of 9.5 mol% yttria-stabilized zirconia with additional nitrogen doping (YSZ:N) of up to 7.5 at.% (referred to the anion sublattice and formula unit Zr_0.83Y_0.17O_1.91) as a function of temperature and nitrogen content. The total conductivity being almost equivalent to the oxygen ion conductivity has been measured by AC impedance spectroscopy under vacuum conditions in order to prevent re-oxidation and loss of nitrogen. The electronic conductivity has been determined by Hebb–Wagner polarization using ion-blocking Pt microelectrodes in N₂ atmosphere. The ionic conductivity of YSZ:N decreases in the presence of nitrogen at intermediate temperatures up to 1000 °C. The mean activation energy of ionic conduction strongly increases with increasing nitrogen content, from 1.0 eV for nitrogen-free YSZ up to 1.9 eV for YSZ containing 7.3 at.% N. Compared to nitrogen-free YSZ, the electronic conductivity first decreases at nitrogen contents of 2.17 and 5.80 at.%, but then increases again for a sample with 7.53 at.%. At temperatures of 850 °C and above, the presence of the N^3? dopant fixes the electrode potential and thus the oxygen partial pressure at the Pt electrode to very low values. This corresponds to a pinning of the Fermi level at a relatively high energy in the upper half of the band gap. At 7.53 at.% N and 950 °C, the oxygen partial pressure in YSZ:N corresponds to p_O2 = 3 × 10^? 18 bar. At temperatures above 850 °C, even in the presence of a very small oxygen concentration in the surrounding gas phase, the nitrogen ion dopant becomes highly mobile and thus diffuses to the surface where it is oxidized to gaseous N₂. The results are discussed in terms of the ionic and electronic defect structures and the defect mobilities in YSZ:N.     

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.     

The effect of competition between the frequency of the field and the frequency of the spin flipping on the kinetics of Ising metamagnet

We consider the effect of a variable representing the competition between the frequency of the field and the frequency of the spin flipping (Ω) on the dynamics of the metamagnetic Ising model in a cubic lattice under the presence of a time varying (oscillating) external magnetic field. The system is modelled with a formalism of master equation at a mean-field level. The time averaged staggered magnetization (Ms) acts as the order parameter and divides temperature field plane into three regions: anti-ferromagnetic, paramagnetic and coexistence of anti-ferromagnetic and paramagnetic phases. It is observed that the topology of the dynamical phase diagram depends strongly on Ω as well as the ratio between interlayer and intralayer couplings.