Kinetics of initial stage of sintering of UO2 and UO2 with Nd2O3 addition

The kinetics of initial stage sintering of UO₂ powder were reinvestigated, using Ar-10% H₂ atmosphere. The effect of the addition of neodynium oxide was studied. The results revealed that surface and grain boundary diffusion mechanisms act simultaneously. The values of activation energies were found to be $\text{48.48 ± 3.51 kcal/mole}$ in the temperature range 870–942°C and $\text{89.88 ± 9.87 kcal/mole}$ in the temperature range of 942–1030°C for UO₂, and $\text{115.61 ± 7.77 kcal/mole}$ in the temperature range 1030–1150°C for UO₂ + Nd₂O₃. An important decrease in the calculated diffusion coefficient occurs by the addition of Nd₂O₃.     

Subband processing for broadband microphone arrays

This paper considers array processing for wideband signals. The optimization techniques and associated performance results correspond to steerable but fixed beam microphone arrays, to be used in hearing aid applications, both in free-space and reverberant conditions. We first review the results on maximum energy (ME) broadband arrays. We subsequently formulate optimization criteria for array subband processing. The uniformly spaced subband and the non-uniformly spaced subband using quadrature mirror filter approaches are treated. Finally, various simulation results for free-space and reverberant conditions are presented to demonstrate the usefulness of this class of microphone arrays, as well as the feasibility of quadrature mirror filter-based subband processing.This work was partially supported by the House Ear Institute and the Retirement Research Foundation.     

Chemical reactions between sodium and (U,Pu)02 mixed oxides

The three phase field MO₂-Na₃MO₄-Na has been studied in detail. It was shown that Na₃MO₄ exists at least in two crystallographic forms and may be above 1200°C, a third one fcc, with a small cell $\text{a = 4.77}\text{A}\text{?}$. This latter form which is considered in the literature as the “normal” uranate cannot be stable in the given conditions of preparation. The low temperature form, simple cubic $\text{a = 9.54}\text{A}\text{?}$, is the one to which the wrong Na₁₁U₅O₁₆ formula has been attributed up to now. It transforms at ca 975°C into a face-centered cubic form with $\text{a = 9.56}\text{A}\text{?}$, stable at least up to 1200°C. Isomorphism between Na-uranate and Na-uranoplutonate has been established for Pu content up to 30%, but there is still some doubt about the nature of the plutonate which is formed by direct reaction between PuO₂ and Na.For the compositions studied (Pu ≤ 30%) the monovariant domain adjacent to the “MO₂”-Na₃MO₄-Na domain, contains the three phases Na₃MO₄, Na₆MO₆ and Na.Oxygen potentials corresponding to the Na₃MO₄-MO_2-x-Na phase field with M = U_0.8Pu_0,2 have been deduced from the measurement of x₀ in equilibrium conditions. It has been foun'd that X_₀ was dependent on T, varying from 0.007 at 550°C to 0.040 at 1200°C. Corresponding values of the oxygen potentials can be represented by the expression: $\text{}\text{?}\text{sm = ? 907, 394 + 224.9 T J/mol 0}{}_2$ A thermodynamic treatment shows that this expression is quasi-independent of Pu content (Pu≤30%) and must be very close to the one valid for the UO₂-Na₃UO₄-Na domain.In conclusion, we examine very schematically how these results can offer guidelines to appreciate the evolution of failed breeder pins in reactor conditions.     

Experimental study and analysis of corner compensation structures for CMOS compatible bulk micromachining using 25 wt% TMAH

In the present work, most common compensation structures (〈1 1 0〉 squares and 〈1 0 0〉 bars) have been used for convex corner compensation with 25 wt% TMAH-water solution at 90±1 °C temperature. Etch flow morphology and self-align properties of the compensating structures have been investigated. For 25 wt% TMAH water solution {3 1 1} plane is found to be responsible for corner undercutting, which is the fast etch plane. Etch-front-attack angle is measured to be 24°. Generalized empirical formulas are also discussed for these compensation structures for TMAH-water solution. 〈1 1 0〉 square structure protects mesa and convex corner and is the most space efficient compared to other compensation structures, but unable to produce perfect convex corner as 〈1 0 0〉 bar type structures. Both the 〈1 0 0〉 bar structures provide perfect convex corners, but 〈1 0 0〉 wide bar structure is more space efficient than the 〈1 0 0〉 thin bar structure. Implications of these compensation structures with realization of accelerometer structure have also been discussed. A modified quad beam accelerometer structure has been realized with these compensation structures using 25 wt% TMAH.     

On the mechanisms of light alkane catalytic oxidation and oxy-dehydrogenation: an FT-IR study of the n-butane conversion over MgCr2O4 and a Mg-vanadate catalyst

The interaction of n-butane, 1-butene, 1,3-butadiene and of C₄ oxygenates on the surface of oxidized Mg-chromite and Mg-vanadate catalysts has been studied by FT-IR spectroscopy. The results compare well with the catalytic behavior of these materials one of which is a combustion catalyst (MgCr₂O₄) and the other is a rather selective oxy-dehydrogenation catalyst (Mg-vanadate). A mechanism for these reactions is proposed.