Reaction mechanism for the formation of intermetallic compounds from layered Sm/Fe powder obtained by mechanical milling

Solid-state reactions in layered Sm/Fe powder particles with an overall composition of Sm₁₂Fe₈₈, obtained by ball milling, have been investigated by X-ray diffraction. During annealing at 500C, one reaction, Sm+2FeSmFe₂ was observed in the time-range studied. However, during annealing at 800C, five reactions were observed: Sm+2FeSmFe₂, Sm +3FeSmFe₃, 2Sm+17FeSm₂Fe₁₇, 2SmFe₂+13FeSm₂Fe₁₇, and 2SmFe₃ +11FeSm₂Fe₁₇. It is proposed that such reactions occur by a nucleation and growth process. Reactions of samarium with iron can be governed by nucleation; Sm/Fe interfaces possessing a higher free energy per unit area can play an important role in the nucleation. The observed results are discussed.     

Electronic Raman scattering of superconducting YBa2Cu3Oy single crystals

TheA _1g andB _1g low-energy Raman continua of YBa₂Cu₃O _y (Y123) single crystals, withy=7.0, 6.99, and 6.93, have been investigated. It is found that the peak frequency of theA _1g continuum is equal to 310±10 cm^–1 and independent of oxygen concentration fory in the above range. The central frequency of the broad peak in theB _1g continuum, however, shifts from about 470 cm^–1 fory7.0 to 550 cm^–1 fory6.93. Thus, a relatively small change in oxygen concentration results in a significant redistribution of the states contributing to theB _1g continuum. Assuming the low-energy portions of the continua are electronic in origin, the Raman spectra have been calculated and the results compared to the experimental spectra. It is suggested that the Raman continua arise, at least in part, from scattering across a spin fluctuation-induced pseudogap.     

Mammalian class IV alcohol dehydrogenase (stomach alcohol dehydrogenase): structure, origin, and correlation with enzymology

The structure of a mammalian class IV alcohol dehydrogenase has been determined by peptide analysis of the protein isolated from rat stomach. The structure indicates that the enzyme constitutes a separate alcohol dehydrogenase class, in agreement with the distinct enzymatic properties; the class IV enzyme is somewhat closer to class I (the "classical" liver alcohol dehydrogenase; approximately 68% residue identities) than to the other classes (II, III, and V; approximately 60% residue identities), suggesting that class IV might have originated through duplication of an early vertebrate class I gene. The activity of the class IV protein toward ethanol is even higher than that of the classical liver enzyme. Both Km and kcat values are high, the latter being the highest of any class characterized so far. Structurally, these properties are correlated with replacements at the active site, affecting both substrate and coenzyme binding. In particular, Ala-294 (instead of valine) results in increased space in the middle section of the substrate cleft, Gly-47 (instead of a basic residue) results in decreased charge interactions with the coenzyme pyrophosphate, and Tyr-363 (instead of a basic residue) may also affect coenzyme binding. In combination, these exchanges are compatible with a promotion of the off dissociation and an increased turnover rate. In contrast, residues at the inner part of the substrate cleft are bulky, accounting for low activity toward secondary alcohols and cyclohexanol. Exchanges at positions 259-261 involve minor shifts in glycine residues at a reverse turn in the coenzyme-binding fold. Clearly, class IV is distinct in structure, ethanol turnover, stomach expression, and possible emergence from class I.     

Full-wave analysis of radiation effect of microstrip transmission lines

A full-wave analysis of radiation effects produced by discontinuities in microstrip and buried microstrip transmission lines is presented. Beginning with the dyadic Green's function for a dielectric slab, with an embedded source, an integral equation is formulated. This equation is then solved by the method of moments to obtain the current distributions along the transmission line, in particular, near the discontinuities. Employing these results, the near- and far-zone fields, as well as radiation patterns are computed. The results from our method showed good agreement with those of previous publications in complex reflection and transmission coefficients, and equivalent capacitance values. It is found that under resonance conditions the radiation efficiency of a simple structure can exceed 41%, which may cause a potential problem in electromagnetic compatibility. Our analytic result also shows that the maximum radiation occurs when the source is located at the height of from the bottom ground plane, which should be prevented.     

Effect of the modulation transfer function of a digital image-acquisition device on phase-measuring profilometry

Systematic errors in phase-measuring profilometry that are introduced by the modulation transfer function of a digital image-acquisition device are analyzed. New phase expressions and phase-deviation formulas are given. The results for simulations and experiments demonstrate that the algorithm of phase-measuring profilometry cannot be regarded as a point-to-point operation. To obtain precise results, an optimum scheme for setting the measurement system is also proposed.     

Two-dimensional optical wavelet transform in space domain and its performance analysis

A new architecture of an optical wavelet transform system with a lenslet array is proposed, and its optical performance and optical limits are analyzed.     

Wafer fault measurement by coherent optical processor

A microscope coherent optical processor based on the VanderLugt optical correlator is applied to the measurement of registration error in multilayer integrated-circuit wafers. A treatment of the effects of wafer faults on the correlation signal is given. Threshold criteria and fault-induced peak splitting of the correlation signal from reject production samples are exploited to demonstrate the easy and rapid detection of faults in partially processed integrated-circuit wafers.     

Fabry-Perot resonator composed of a photoinduced birefringent fiber grating

The periodic mode coupling between the x- and y-polarization modes that is induced by a photoinduced birefringent fiber grating is analyzed through the use of the coupled-mode theory. A novel Fabry-Perot resonator composed of a photoinduced birefringent fiber grating is proposed and theoretically investigated. In the ideal case, the x- and y-polarization resonances of the resonator coincide with each other because of the polarization power exchange by the photoinduced birefringent grating, which results in the total resonator output's being polarization independent. However, if there are some external perturbations (e.g., temperature change or strain), the phase matching is detuned, which could destroy the coincidence between the two polarization resonances, which can further result in the total output resonance's having two peaks. The separation between these two resonant peaks depends on perturbations of the environment (temperature changes or strain).     

Planar waveguide refractive index distribution functions determined precisely from mode indices

The inverse WKB (IWKB) approximation has been extended to derive the index distribution functions from the measured mode indices of a planar waveguide. Through the use of this technique, the forms of the index distribution functions are obtained by IWKB approximation and a criterion is used to derive the functions accurately. The results are compared to the exponential and Fermi distributions. It is shown that the index profile, surface index, and waveguide depth can be obtained more accurately than with the original IWKB approximation. Finally, the index distribution function of a c-cut proton-exchanged LiTaO(3) waveguide is given by this technique, the mode indices calculated with this function agree with the experimental results in the range of 10(-4).     

Temperature and frequency effects on fatigue crack growth of uPVC

Temperature and frequency effects on fatigue crack growth rate have been modelled. The stress intensity factor- biased Arrhenius equation and a result from the two-stage zone model have been incorporated into the present model. Subsequently, temperature and frequency effects on fatigue crack growth in unplasticized polyvinyl chloride (uPVC) were studied over a temperature range 15–55 °C and a frequency range 0.01–10 Hz. Data for PVC taken from the literature were also included for analysis. It was found that the predicted values from the proposed model are in good agreement with experimental results.