Library

Notes: Rayleigh scattering (λ=488 nm) is observed in single-crystal Sr0.61Ba0.39Nb2O6 (SBN:61). In particular, the scattered intensity is measured as a function of temperature across the ferroelectric–paraelectric phase transition. The results show that the scattered intensity can vary by as much as two orders of magnitude in passing through the transition. The particular form of the intensity-vs-temperature curve is found to depend on the poling history of the crystal. The unpoled crystal exhibits a rapid change from strong scattering below the transition (ferroelectric state) to weak scattering above the transition (paraelectric state). The measured inflection point is near 63 °C upon heating and near 58 °C upon cooling. In this case the scattering is predominantly attributed to the presence of high-density ferroelectric domains, which vanish above the transition. If the crystal is thermally poled (by cooling through the transition with an electric field applied), it shows no measurable domain scattering but does exhibit strong central-peak behavior at 65 °C upon heating and 59 °C upon cooling. Despite repeated cycling through the transition, the previously thermally poled crystal consistently displays central-peak behavior. The results suggest that thermal poling in SBN followed by thermal depoling produces a significant increase in the average ferroelectric domain size when compared to the unpoled crystal.

Notes: We have studied, both in theory and experiment, the operational behavior of continuous wave CO2 lasers by monitoring the ro-vibrational state manifold of the pumping gas N2 by coherent antiStokes Raman scattering (CARS). Detailed information has been gained about the interaction between cavity photons and vibrationally excited N2(X) states for two types of sealed-off and diffusion-cooled CO2 lasers: a radiofrequency excited waveguide laser and a conventional, direct current excited version. CARS spectroscopy permits for the first time an impressive demonstration of the cooling effect of the intracavity photon flux on the vibrationally coupled v=1 state of N2 and the upper laser level involving the asymmetric stretching mode of the CO2 molecule. The kinetic model calculations indicate that the electron number density and electron temperature in the CO2 waveguide laser are higher than usually assumed in the literature.

Notes: Supersonic fluid flow and the interaction of strong shock waves to produce jets of material are ubiquitous features of inertial confinement fusion (ICF), astrophysics, and other fields of high energy-density science. The availability of large laser systems provides an opportunity to investigate such hydrodynamic systems in the laboratory, and to test their modeling by radiation hydrocodes. We describe experiments to investigate the propagation of a structured shock front within a radiation-driven target assembly, the formation of a supersonic jet of material, and the subsequent interaction of this jet with an ambient medium in which a second, ablatively driven shock wave is propagating. The density distribution within the jet, the Kelvin–Helmholz roll-up at the tip of the jet, and the jet's interaction with the counterpropagating shock are investigated by x-ray backlighting. The experiments were designed and modeled using radiation hydrocodes developed by Los Alamos National Laboratory, AWE, and Lawrence Livermore National Laboratory. The same hydrocodes are being used to model a large number of other ICF and high energy-density physics experiments. Excellent agreement between the different simulations and the experimental data is obtained, but only when the full geometry of the experiment, including both laser-heated hohlraum targets (driving the jet and counter-propagating shock), is included. The experiments were carried out at the University of Rochester's Omega laser [J. M. Soures et al., Phys. Plasmas 3, 2108 (1996)]. © 2002 American Institute of Physics.

Notes: A rotating piezoelectric device, which uses the so-called slip-stick mechanism for micropositioning is presented. The device is especially designed for use in point-contact experiments at very low temperatures in high magnetic fields. Two typical applications are presented.

Notes: The Fuping Complex and the adjoining Wutai and Hengshan Complexes are located in the central zone of the North China craton. The dominant rock types in the Fuping Complex are high-grade tonalitic–trondhjemitic–granodioritic (TTG) gneisses, with minor amounts of mafic granulites, syntectonic granitic rocks and supracrustal rocks. The petrological evidence from the mafic granulites indicates three stages of metamorphic evolution. The M1 stage is represented by garnet porphyroblasts and matrix plagioclase, quartz, orthopyroxene, clinopyroxene and hornblende. Orthopyroxene+plagioclase symplectites and clinopyroxene+plagioclase±orthopyroxene coronas formed in response to decompression during M2 following the peak metamorphism at M1. Hornblende+plagioclase symplectites formed as a result of further isobaric cooling and retrograde metamorphism during M3. The P–T  estimates using TWQ thermobarometry are: 900–950 °C and 8.0–8.5 kbar for the peak assemblage (M1), based on the core compositions of garnet, matrix pyroxene and plagioclase; 700–800 °C and 6.0–7.0 kbar for the pyroxene+plagioclase symplectites or coronas (M2); and 550–650 °C and 5.3–6.3 kbar for the hornblende+plagioclase symplectites (M3), based on garnet rim and corresponding symplectic mineral compositions. These P–T  estimates define a clockwise P–T  path involving near-isothermal decompression for the Fuping Complex, similar to the P–T  path estimated for the metapelitic gneisses. The inferred P–T  path suggests that the Fuping Complex underwent initial crustal thickening, subsequent exhumation, and finally cooling and retrogression. This tectonothermal path is similar to P–T  paths inferred for the Wutai and Hengshan Complexes and other tectonic units in the central zone of the North China craton, but different from anti-clockwise P–T paths estimated for the basement rocks in the eastern and western zones of the craton. Based on lithological, structural, metamorphic and geochronological data, the eastern and western zones of the craton are considered to represent two different Archean to Paleoproterozoic continental blocks that amalgamated along the central zone at the end of Paleoproterozoic. The P–T paths of the Fuping Complex and other tectonic units in the central zone record the collision between the eastern and western zones that led to the final assembly of the North China craton at c. 1800 Ma.

Notes: Abstract  A nursing clinic for homeless men was developed by a faculty member and her senior community health nursing students in a city mission over a 2.5-year period. The development of this clinic and a conceptualization of their nursing roles are described. Nursing care focused on promoting access to primary care through screening and referral and through nursing interventions of education, counseling, advocacy, and collaboration. Because the Student Nurses' Clinic was instrumental in clarifying and conceptualizing what nurses can do to promote primary care, mission administrators and staff gained insights about nursing and are better prepared to plan programs for the health care needs of the homeless men—the “guests” at the mission.