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Studies of the interaction of polarized light or particles (including electrons, e-, or positrons, e+) with asymmetric forms of matter has been of interest to scientists since the discovery of chirality and the subsequent development of particle physics. Researchers have been interested in e+ interactions with chiral molecules for decades, but with mixed and indecisive results. After reviewing the field, we speculated that the e+ or positronium (Ps) might interact differently with chiral pairs of large single crystals, i.e., the left-handed or right-handed asymmetric forms of the crystals -- and subsequently observed significant differences in "free positron" annihilation and intensities in the evaluation of left-handed or right-handed quartz single crystals. This result may be understood to be a "particle stereorecognition" phenomenon. To extend this line of inquiry we crystallized mm scale L- or D-alanine crystals and performed positron annihilation lifetime spectroscopy measurements using a 22Na positron source. Alanine crystals were obtained via slow evaporation of water in a Dewar, or from water/acetone solvent in a temperature-controlled environment. These methods resulted in small (≈ 0:5 cm/side) or large (≥ 1:0 cm/side) crystals, respectively. While some intensity (I2) results from left-handed and right-handed crystals varied in positron annihilation lifetime spectroscopy analysis, the errors associated with the measurements do not indicate a stereorecognition of alanine via positron interactions. [ABSTRACT FROM AUTHOR]

Fluorine atom incorporation into polymers typically yields a low refractive index and dielectric constant. Two effects contribute to this: the decreased electronic polarizability of the C-F bond relative to C-H, and the introduction of additional fractional free volume due to less dense polymer chain packing. Here, it is reported that the change in fractional free volume contributes an average of 49% of the observed decrease in refractive index and 64% of the 1 kHz dielectric constant for symmetric structures. This surprisingly large magnitude is found comparing exact fluorine/hydrogen analogous pairs of polyimides using positron annihilation lifetime (PAL) spectroscopy and the application of a Lorenz-Lorentz normalization. [ABSTRACT FROM AUTHOR]

Positron annihilation spectroscopy(PAS) is a novel method thatprovides molecular-level information about complex macromolecularstructure in a manner different from, but complementary to, conventionalphysical and chemical methodology. This paper presents a perspectiveof PAS in polymeric systems covering 12 aspects: historical, spacial,spherical quantum model, anisotropic structure, voids, positroniumchemistry, time, positron annihilation lifetime spectroscopy and dataanalysis, variable monoenergetic slow positron beam techniques anddepth profiling, elemental analysis, multidimensional instrumentationadvances in PAS, and free volume and free-volume theories. [ABSTRACT FROM AUTHOR]

Atomic force microscopy (AFM) has been used to study the morphology and microstructure of an amine-cured epoxy before and after outdoor exposure. Measurements were made from samples prepared in an essentially CO2-free, H2O-free glove box and from samples prepared in ambient conditions. For those prepared in a CO2-free glove box, AFM imaging was conducted on (1) an unexposed air/coating surface, (2) an unexposed coating bulk, (3) an unexposed coating/substrate interface, and (4) a field exposed air/coating surface. For samples prepared in ambient conditions, only the unexposed air/coating surface was investigated. The same regions of the exposed samples were scanned periodically by the AFM to monitor changes in the surface morphology of the coating as UV exposure progressed. Small angle neutron scattering and Fourier transform infrared spectroscopy (FTIR) studies were performed to verify the microstructure and to follow chemical changes during outdoor exposure, respectively. The results have shown that amine blushing, which occurs only under ambient conditions, had a significant effect on the surface morphology and microstructure of the epoxy. The surface morphology of the samples prepared under CO2-free, dry conditions was generally smooth and homogeneous. However, the interface and the bulk samples clearly revealed a two-phase structure consisting of bright nodular domains and dark interstitial regions, indicating an inhomogeneous microstructure. Such heterogeneous structure of the bulk was in good agreement with results obtained by small angle neutron scattering of unexposed samples and by AFM phase imaging of the degraded sample surface. The relationship between submicrometer physical changes and molecular chemical degradation is discussed. [ABSTRACT FROM AUTHOR]

Surface properties of a polymeric coating system have a strong influence on its performance and service life. However, the surface of a polymer coating may have different chemical, physical, and mechanical properties from the bulk. In order to monitor the coating property changes with environmental exposures from the early stages of degradation, nondestructive techniques with the ability to characterize surface properties with micro- to nanoscale spatial resolution are required. In this article, atomic force microscopy has been applied to study surface microstructure and morphological changes during degradation in polymer coatings. Additionally, the use of AFM with a controlled tip-sample environment to study nanochemical heterogeneity and the application of nanoindentation to characterize mechanical properties of coatings surfaces are demonstrated. The results obtained from these nanometer characterization techniques will provide a better understanding of the degradation mechanisms and a fundamental basis for predicting the service life of polymer coatings. [ABSTRACT FROM AUTHOR]

Examines the action of bone morphogenetic proteins (BMP) in the stages of folliculogenesis. Regulation of ovulation by the type 1 BMP receptor (BmprIB); Exhibition of estrous cycles in mice deficient with BmprIB; Decrease of aromatase production in granulosa cells.

The intrinsic oxygen-vacancies and the extrinsic dopants are two major fundamental free-carrier sources for the extrinsic conducting oxides, such as Sn-doped In2O3. Yet, the individual contributions of the above two free-carrier sources to the total carrier concentrations have never been unraveled. A carrier-concentration separation model is derived in this work, which can define the individual contributions to the total carrier concentration from the intrinsic oxygen-vacancies and the extrinsic dopants, separately. The individual contributions obtained from the present carrier-concentration separation model are verified by the two-state trapping model, photoluminescence, and positron annihilation lifetime (PAL) spectroscopy. In addition, the oxygen-vacancy formation energy of the Sn:In2O3 thin film is determined to be 0.25 eV by PAL spectroscopy. [ABSTRACT FROM AUTHOR]

Describes the design and construction of three x-ray beamlines extracted out from one 25-pole 1.8 T wiggler insertion device at the Synchrotron Radiation Research Center in Taiwan. Design of the front end for the wiggler x-ray beamlines; Features of the A, B, and C beamlines and the photon energies they cover.