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.     

Cloud point extraction procedure for flame atomic absorption spectrometric determination of lead(II) in sediment and water samples

The conditions for cloud point extraction of lead(II) from aqueous solutions were investigated and optimized. The procedure is based on the separation of Pb(II) – brillant cresyl blue (BCB) complexes into the micellar media by adding the surfactant Triton X-114. After phase separation, the surfactant-rich phase was dissolved with 1 mol L⁻¹ HNO₃ in ethanol and diluted with 1 mol L⁻¹ HNO₃ solution before lead was determined by flame atomic absorption spectrometry. Optimization of the pH, ligand and surfactant quantities, incubation time, temperature, viscosity, sample volume, and interfering ions was performed. The effects of the matrix ions were also examined. The detection limits for three times the standard deviations of the blank for lead were 7.5 μg L⁻¹ for water samples and 0.33 μg g⁻¹ for sediment samples. The validity of cloud point extraction was checked by employing certified reference samples of Lake Sediment IAEA-SL-1 and Sewage Sludge BCR-CRM 144R. The procedure was applied to natural waters and sediment samples with satisfactory results (recoveries >95%, relative standard deviations <6.4%).     

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.     

Phase diagram for stripes in YBa2Cu3O6+x superconductors

Neutron scattering has been used to measure the charge and spin structure in the YBa₂Cu₃O_6+x superconductors. Incommensurate static charge ordering is found at low doping levels while only charge fluctuations are found at higher doping. The spin structure is complex with both a commensurate resonance and incommensurate structure observed at low temperatures. The scattering results are used to construct a phase diagram for stripes in the YBa₂Cu₃O_6+x system.     

Cyclosiloxane‐based networks: Synthesis,thermal characterization,and microstructure

This article mainly concerns the synthesis of novel PD₅/PDMS conetworks by the copolymerization of cyclic D₅H and linear HO? PDMS? OH units, and the characterization of the product by DMTA, DSC, and TGA. The ultimate properties of the conetworks may be controlled by varying the relative composition of D₅H and PDMS components. DMTA and DSC thermograms indicate compatibility between the PD₅ and PDMS domains. Understanding of the polymer chemical transformations involved in conetwork formation combined with an analysis of DMTA and DSC thermograms led to a proposition of the microarchitecture of PD₅/PDMS conetworks. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 630–637, 2005     

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.     

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.