On some measurements of the propagation properties of thermal waves in the Nb-H and Ta-H systems

Summary By means of an experimental technique based on a nonsteady-state method,i.e. on the propagation of thermal waves, we have measured at room temperature for oscillation frequencies between 6 and 30 mHz the thermal diffusivity, the lateral thermal-loss coefficient and the ?fractional heat loss? in Nb and Ta wires as a function of hydrogen doping. The appearance of hydride formation and precipitation notably changes the behaviour of these quantities. From these measurements it was also possible to calculate the propagation velocity and attenuation coefficient of thermal waves. It was found that the increase of the hydrogen concentration in the solid solution produces a gradual decrease in the velocity and increase in the attenuation coefficient until the solubility limit is reached. For larger hydrogen concentrations, the velocity showed a tendency to increase towards the value of the pure metal, while the attenuation coefficient decreased below the value of the pure metal. These results as a whole appear quite promising for studying the properties of hydrogenated systems. This work was supported by the Gruppo Nazionale di Struttura della Materia of the Consiglio Nazionale delle Ricerche and by the Centro Interuniversitario di Struttura della Materia of the M.P.I., Roma (Italia).     

Synthesis of polyethylene‐octene elastomer/SiO2‐TiO2 nanocomposites via in situ polymerization: Properties and characterization of the hybrid

In this study, a silicic acid and tetra isopropyl ortho titanate ceramic precursor and a metallocene polyethylene‐octene elastomer (POE) or acrylic acid grafted metallocene polyethylene‐octene elastomer (POE‐g‐AA) were used in the preparation of hybrids (POE/SiO₂? TiO₂ and POE‐g‐AA/SiO₂? TiO₂) using an in situ sol‐gel process, with a view to identifying a hybrid with improved thermal and mechanical properties. Hybrids were characterized using Fourier transform infrared spectroscopy, ²⁹Si solid‐state nuclear magnetic resonance (NMR), X‐ray diffraction, differential scanning calorimetry, thermogravimetry analysis, dynamic mechanical thermal analysis, and Instron mechanical testing. Properties of the POE‐g‐AA/SiO₂? TiO₂ hybrid were superior to those of the POE/SiO₂? TiO₂ hybrid. This was because the carboxylic acid groups of acrylic acid acted as coordination sites for the silica‐titania phase to allow the formation of stronger chemical bonds. ²⁹Si solid‐state NMR showed that Si atoms coordinated around SiO₄ units were predominantly Q₃ and Q₄. The 10 wt % SiO₂? TiO₂ hybrids gave the maximum values of tensile strength and glass transition temperature in both POE/SiO₂? TiO₂ and POE‐g‐AA/SiO₂? TiO₂. It is proposed that above this wt %, excess SiO₂? TiO₂ particles caused separation between the organic and inorganic phases. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1690–1701, 2005     

Determination of phosphorus in steel by the combined technique of laser induced breakdown spectrometry with laser induced fluorescence spectrometry

Laser induced breakdown spectrometry (LIBS) combined with laser induced fluorescence spectrometry (LIFS) has been applied for detection of trace-level phosphorus in steel. The plasma induced by irradiation of Nd:YAG laser pulse for ablation was illuminated by the 3rd harmonic of Ti:Sapphire laser tuned to one of the resonant lines for phosphorus in the wavelength region of 253–256 nm. An excitation line for phosphorus was selected to give the highest signal-to-noise ratio. Fluorescence signals, P213.62 and P214.91 nm, were observed with high selectivity at the contents as low as several tens µg g^− 1. Fluorescence intensities were in a good linear correlation with the contents. Fluorescence intensity ratio of a collisionally assisted line (213.62 nm) to a direct transition line (214.91 nm) was discussed in terms of the analytical conditions and experimental results were compared with a calculation based on rate equations. Since the fluorescence signal light in the wavelength range longer than 200 nm can be transmitted relatively easily, even through fiber optics of moderate length, LIBS/LIFS would be a versatile technique in on-site applications for the monitoring of phosphorus contents in steel.     

Microdeformation behavior in nanotemplated epoxy thermosets: A study with in situ tensile deformation technique in transmission electron microscopy

Microdeformation behavior in nanostructured block copolymer‐toughened epoxy resins, or templated epoxy thermosets, was studied using an in situ tensile deformation technique performed directly in a transmission electron microscope. The observed microdeformation modes were found to correlate well with the macroscopic mechanical properties of the materials. In the order of decreasing macroscopic fracture toughness, the microdeformation modes were observed to change from large uniform plastic deformation over an extensive area, to localized plastic deformation bands, to little plastic deformation observed in the most brittle material. A similar trend was also observed when samples of the same material were tested at different temperatures, reflecting changes in the deformation mechanism as a function of temperature. Structural defects were observed in nanotoughening phases when plastic deformation was observed. The implication of the observed microdeformation modes to the macroscopic toughening mechanisms is discussed in the context of the micromorphology of the nanometer sized toughening phases and parameters of the epoxy matrix chemistry such as bromination, molecular weight, and interfacial miscibility. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 393–406, 2009     

Consistency,stability and convergence of the finite-difference equations for flow about a rotating sphere in an axial stream

The finite-difference equations which have previously been developed to solve the problem of laminar boundary layer flow about a rotating sphere in an axial stream are analysed according to the available numerical stability theories. This analysis is necessary to determine the restrictions on velocities and mesh sizes required to obtain a convergent numerical solution. Convergence can be achieved if both consistency and stability of the finite-difference equations are fulfilled. The analysis reported in the present paper shows that the developed finite-difference equations are consistent with their original partial differential equations. Also, the analysis proves that the developed finite-difference procedure is numerically stable for all mesh sizes as long as the downstream meridional velocity is non-negative, i.e.as long as no flow reversals occur within the domain of solution.     

Determination of glibenclamide in human serum by HPLC

The antidiabetic drug glibenclamide can be reliably quantitated in human serum with high performance liquid chromatography. The serum is buffered and extracted with toluene. The organic solvent is evaporated, the residue dissolved in the mobile phase and an aliquot sampled automatically and chromatographed. UV-detection at 229 m allows a lower limit of quantitation of 5 ng/ml. Precise handling of exact volumes facilitates external calibration. Statistical data for imprecision and inaccuracy are given and illustrate reliable quantification. Application of the method to experimental and clinical pharmacokinetic studies with specific problems is illustrated.     

An improved theory of microwave open resonators

The analytic theory of microwave open resonators is improved here by means of solving the complex Airy equation, that the Q-value as well as the argument of field profile may be given accurately. The resonance conditions for open cavities with high and moderate Q-values are derived analytically. Theoreticl Q-values are well agreed with the measured ones from experiments.     

On natural homomorphisms of Witt rings

We prove that the kernel of the ring homomorphism between the Witt ring of any order of a global field and the Witt ring of the field is a nilideal.