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A coring structure in which δ (fcc) grains have Ga-rich cores with Ga-poor shells forms during the \(\varepsilon\) (bcc) to δ (fcc) phase transformations in Pu-Ga alloys. There are considerable differences between the diffusivities of Ga in \(\varepsilon\) and δ and a large and anisotropic stress field exists in the coring structure due to the large lattice mismatch between these two phases and strong elastic anisotropy. We developed a phase-field model for simulating the coring structure evolution in three dimensions, taking into account the inhomogeneities of both Ga diffusivity and elastic properties. It is shown that the elastic interactions among different oriented δ grains and diffusive Ga atoms affect Ga diffusion path, the coring structure, and the growth kinetics of the δ phase.

We have designed and built the first fully functional vacuum microprobe test facility specifically intended to optimize the development of microelectromechanical systems (MEMS) devices for space applications. This facility includes an ion-pumped, ultraclean vacuum system outfitted with four three-axis precision microprobe stages. The testing is monitored with a long focal length microscope through a thin sapphire window. Testing of several initial MEMS designs shows extremely promising results for using such devices in space applications. In particular, we show that significantly reduced voltages are adequate to resonantly drive some MEMS devices in vacuum owing to significantly reduced damping and the consequent much higher Q of the systems (∼1000×) in the absence of air. We also show the results of a many cycle (>1010) test of a comb-driven, force–distance multiplied sliding aperture door and demonstrate that potential show-stopper issues such as stiction and vacuum welding can be overcome in MEMS devic...

This paper describes the structure, fabrication and detailed characterization of a polycrystalline silicon passive microvalve. The microvalves were fabricated utilizing micromachining techniques, and automated measurement systems were developed for device characterization. The valves were successfully characterized to determine the effect of dimensions on fluid flow rate and valve deflection. Methanol, deionized water and nitrogen were used for fluid flow tests, and nitrogen gas was used in the deflection measurements. The ratio of reverse to forward flow rates of methanol was found to be less than 3% at a pressure of 11 kPa. The measured data are in good agreement with a first-order model for the device taking into account applied pressure, valve plate deflection and the resistance of the inlet hole. Using nitrogen gas, analysis of the device was extended to measure the valve plate deflection as a function of inlet pressure. Valve plate deflections of up to 15.3 μm were recorded at 31 kPa. The nitrogen gas flow characteristics differ significantly from the liquid flow characteristics due to the compressible nature of the fluid, but agree well with the theoretical flow for gases.

The Early Proterozoic (2449 ± 1.1 Ma) Burakovsky layered intrusion of southern Karelia, Russia, is the largest (700 km2) mafic pluton in the Fennoscandian Shield. The layered series contains two main parts: (i) an ultramafic series (85% dunite), and (ii) a mafic series (mostly gabbros). Mineral and whole-rock chemical variations in the ultramafic zone indicate little variation in chemistry over the entire sequence (e.g., in olivine, variations are from Fo89 to Fo87 over the upper 1600 m). In contrast, the Mg# in pyroxenes from the gabbronorite zone varies from 85 to 58 over an interval of 500 m. On the basis of the current data, there are no apparent reversals in chemistry in the ultramafic zone, whereas there is evidence for several in the gabbronorite zone. Furthermore, there is a distinctive reversal to more primitive compositions in mineral and whole-rock chemistry at the top of the ultramafic zone. These differences indicate that either (i) the gabbronorite zone crystallized from the residue left from formation of the ultramafic zone and the subsequent "flushing" of the more evolved portions to form the Early Proterozoic Karelian volcanic fields, or (ii) there were two separate magmas. Plagioclase crystals from the gabbronorite zone are chemically zoned, providing evidence of the local processes affecting crystallization of this sequence. Plagioclase crystals from near the base commonly display relatively Na-rich cores that are believed to result from either supersaturation at the onset of nucleation or the prior crystallization of some other, Ca-rich phase (e.g., clinopyroxene). Many plagioclase grains also contain reversely zoned rims, indicative of either (i) exchange between trapped liquid and the main magma during times of replenishment; or (ii) an increase in the CIPW-normative plagioclase–liquid partition coefficient for Ca, due to an increase in the augite component of the melt. The lack of evidence for abundant magma influxes in the ultramafic zone contrasts with the chemical reversals observed in the gabbronorite zone, suggesting that replenishment was a prevailing process only in the upper half of the intrusion.

The physical properties of the first In analog of the PuMGa(5) (M = Co, Rh) family of superconductors, PuCoIn(5), are reported. With its unit cell volume being 28% larger than that of PuCoGa(5), the characteristic spin-fluctuation energy scale of PuCoIn(5) is three to four times smaller than that of PuCoGa(5), which suggests that the Pu 5f electrons are in a more localized state relative to PuCoGa(5). This raises the possibility that the high superconducting transition temperature T(c) = 18.5 K of PuCoGa(5) stems from the proximity to a valence instability, while the superconductivity at T(c) = 2.5 K of PuCoIn(5) is mediated by antiferromagnetic spin fluctuations associated with a quantum critical point.

The physical properties including magnetic susceptibility, specific heat, and electrical resistivity of two new plutonium compounds Pu2M3Si5 (M = Co, Ni) are reported. Pu2Ni3Si5 crystallizes in the orthorhombic U2Co3Si5 structure type, which can be considered a variant of the BaAl4 tetragonal structure, while Pu2Co3Si5 adopts the closely related monoclinic Lu2Co3Si5 type. Magnetic order is observed in both compounds, with Pu2Ni3Si5 ordering ferromagnetically at T(C) = 65 K then undergoing a transition into an antiferromagnetic state below T(N) = 35 K. Two successive magnetic transitions are also observed at T(mag1) = 38 K and T(mag2) = 5 K in Pu2Co3Si5. Specific heat measurements reveal that these two materials have a moderately enhanced Sommerfeld coefficient γ ∼ 100 mJ/mol Pu K(2) in the magnetic state with comparable RKKY and Kondo energy scales.

We report results of ⁵⁹Co nuclear magnetic resonance measurements on a single crystal of superconducting PuCoGa₅ in its normal state. The nuclear spin-lattice relaxation rates and the Knight shifts as a function of temperature reveal an anisotropy of spin fluctuations with finite wave vector q. By comparison with the isostructural members, we conclude that antiferromagnetic XY-type anisotropy of spin fluctuations plays an important role in mediating superconductivity in these heavy fermion materials.

We have examined the relaxation of photoinduced quasiparticles in the heavy-fermion superconductor PuCoGa5. The deduced electron-phonon coupling constant is incompatible with the measured superconducting transition temperature Tc=18.5 K, which speaks against phonon-mediated superconductivity. Upon lowering the temperature, we observe an order-of-magnitude increase of the quasiparticle relaxation time in agreement with the phonon bottleneck scenario--evidence for a hybridization gap in the electronic density of states. The modification of photoinduced reflectance in the superconducting state is consistent with the heavy character of the quasiparticles that participate in Cooper pairing.

Gender constancy judgments in children referred for problems in their gender identity development (N = 206) and controls (N = 95) were compared. On Slaby and Frey's (1975) gender constancy interview, the gender-referred children performed more poorly than the controls at three stage levels: gender identity, gender stability, and gender consistency. On the Boy-Girl Identity Task, a second measure of gender constancy (Emmerich et al., 1977), the gender-referred children also performed more poorly. Gender-referred children who had not attained gender consistency engaged in significantly less same-sex-typed play on a free-play task than the gender-referred children who had, but there were no gender consistency effects for the controls. Two other measures of sex-typed behavior were unrelated to gender consistency. In the gender-referred group alone, children who "failed" the gender identity or gender stability stages were more likely to draw an opposite-sex person first on the Draw-a-Person test and to evince more affective gender confusion on the Gender Identity Interview (Zucker et al., 1993) than children who had "passed." It is concluded that children referred for problems in their gender identity development have a developmental lag in gender constancy acquisition. Possible reasons for the lag are discussed.