Temperature dependence of field-response mechanisms in 0.4Ba(Zr\u3csub\u3e0.2\u3c/sub\u3eTi\u3csub\u3e0.8\u3c/sub\u3e)O\u3csub\u3e3\u3c/sub\u3e-0.6(Ba\u3csub\u3e0.7\u3c/sub\u3eCa\u3csub\u3e0.3\u3c/sub\u3e)TiO\u3csub\u3e3\u3c/sub\u3e

Understanding the temperature dependence of how ferroelectric materials respond to electric fields is critical for determining how best to use these materials in applications. Here, temperature dependent in situ x-ray diffraction is used to study how field-response mechanism Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 evolves with temperature. Increasing the measurement temperature was found to slightly reduce the extent of domain reversal and the magnitude of the 111 lattice strain. Instead, these results indicate that temperature predominantly impacted the angular dependence of the 002/200 lattice strain. We attribute the observed differences in 002/200 lattice strain to the flattening of the free-energy near the tetragonal-orthorhombic phase boundary, where the flattening of the energy landscape promotes a polarization rotation response during the application of electric fields at room temperature

Stress asymmetry in cyclic deformation of b.c.c. metals

Asymmetric slip in b.c.c. metals is related to both the symmetry about screw dislocations and elastic anisotropy. The elastic anisotropy differs quite substantially from one b.c.c. metal to the next and this anisotropy has been observed in measurements of asymmetric stresses in plastic deformation experiments. In this paper, data from cyclic deformation of b.c.c. metals, with special emphasis on tungsten which is elastically isotropic, are used to demonstrate the role of screw dislocation geometry and elastic anisotropy on stress asymmetry. The interaction of dislocation geometry and thermal activation of screw dislocation motion is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30320/1/0000722.pd

Surface film effects during cyclic deformation of dislocation-mobility-limited materials

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30047/1/0000415.pd

Texture development in Si3N4/BN fibrous monolithic ceramics

Preferred orientation was measured in Si 3 N 4 /BN fibrous monolithic ceramics using x-ray diffraction. The materials were manufactured by co-extrusion of polymer binder/ceramic blends which were subsequently pyrolized and then hot-pressed to produced a fully dense ceramic composite. A very strong modified wire texture was present in the BN with the basal planes aligned parallel to the axis of extrusion due to shear-induced reorientation of the platelet-shaped BN particles during co-extrusion. Texture was also observed in the Si 3 N 4 and was attributed to a combination of co-extrusion and hot-pressing. After hot pressing, the basal planes of the rod-shaped β-Si 3 N 4 were observed to be preferentially aligned perpendicular to the extrusion direction. Measurements prior to hot-pressing revealed that a small amount (≈5%) of β-Si 3 N 4 was present in the α-Si 3 N 4 starting powder. Although texturing of the predominant α-Si 3 N 4 did not occur during co-extrusion, significant texturing of the β-Si 3 N 4 was observed. During subsequent hot-pressing, the pre-existing textured β-Si 3 N 4 particles appeared to act as seeds for transformation and preferred growth of rod-shaped β grains parallel to the axis of extrusion.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44762/1/10853_2004_Article_268427.pd

Observation of a large parity nonconserving analyzing power in Xe

A large parity nonconserving longitudinal analyzing power was discovered in polarized-neutron transmission through Xe. An analyzing power of 4.3±0.2% was observed in a p-wave resonance at En=3.2 eV. The measurement was performed with a liquid Xe target of natural isotopic abundance that was placed in the polarized epithermal neutron beam, flight path 2, at the Manuel Lujan Neutron Science Center. This apparatus was constructed by the TRIPLE Collaboration, and has been used for studies of parity symmetry in compound nuclear resonances. Part of the motivation of the experiment was to discover a nucleus appropriate for a sensitive test of time-reversal invariance in polarized-neutron transmission. The large analyzing power of the observed resonance may make it possible to design a test of time reversal invariance using a polarized-Xe target

The Kepler Smear Campaign: Light curves for 102 Very Bright Stars

We present the first data release of the Kepler Smear Campaign, using collateral 'smear' data obtained in the Kepler four-year mission to reconstruct light curves of 102 stars too bright to have been otherwise targeted. We describe the pipeline developed to extract and calibrate these light curves, and show that we attain photometric precision comparable to stars analyzed by the standard pipeline in the nominal Kepler mission. In this paper, aside from publishing the light curves of these stars, we focus on 66 red giants for which we detect solar-like oscillations, characterizing 33 of these in detail with spectroscopic chemical abundances and asteroseismic masses as benchmark stars. We also classify the whole sample, finding nearly all to be variable, with classical pulsations and binary effects. All source code, light curves, TRES spectra, and asteroseismic and stellar parameters are publicly available as a Kepler legacy sample.Comment: 35 pages, accepted ApJ

In-Space Structural Assembly: Applications and Technology

As NASA exploration moves beyond earth's orbit, the need exists for long duration space systems that are resilient to events that compromise safety and performance. Fortunately, technology advances in autonomy, robotic manipulators, and modular plug-and-play architectures over the past two decades have made in-space vehicle assembly and servicing possible at acceptable cost and risk. This study evaluates future space systems needed to support scientific observatories and human/robotic Mars exploration to assess key structural design considerations. The impact of in-space assembly is discussed to identify gaps in structural technology and opportunities for new vehicle designs to support NASA's future long duration missions

Structure and phase transitions in 0.5(Ba0.7Ca0.3TiO3)-0.5(BaZr0.2Ti0.8O3) from −100°C to 150°C

The solid solution of (x)Ba0.7Ca0.3TiO3-(1-x)BaZr0.2Ti0.8O3 is known to exhibit high piezoelectric constants. Discrepancies in the reported phase transitions and structure around room temperature, however, have complicated the understanding of the enhanced properties. Rietveld refinement of high-resolution X-ray diffraction is employed here to establish and refine the crystallographic structure at temperatures from -100 degrees C to 150 degrees C for x = 0.5. A combination of rhombohedral R3m and tetragonal P4mm is found to coexist at temperatures of 20 degrees C and -25 degrees C, bordered by single phase rhombohedral and tetragonal regions at lower (i.e., -100 degrees C) and higher (i.e., 70 degrees C) temperatures, respectively. The diffractograms also show signs of strain and domain wall scattering that are linked to the sample history. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4772741

Cyclic deformation of tungsten single crystals

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26038/1/0000111.pd