Free-volume hole relaxation in molecularly oriented glassy polymers.

The free-volume hole relaxation in polycarbonate and poly(methyl methacrylate) with different levels of molecular orientation was studied by positron annihilation lifetime spectroscopy at variable pressures. The molecular orientation was achieved through a simple shear process performed at different temperatures and extrusion rates. It has been demonstrated that the β relaxation is largely responsible for the free-volume hole anisotropy after simple shear orientation.

Annealing effect reversal by water sorption-desorption and heating above the glass transition temperature-comparison of properties.

Our objective is to compare the physical properties of materials obtained from two different methods of annealing reversal, that is, water sorption-desorption (WSD) and heating above glass transition temperature (HAT). Trehalose was annealed by storing at 100 °C for 120 h. The annealing effect was reversed either by WSD or HAT, and the resulting materials were characterized by differential scanning calorimetry (DSC), water sorption studies, and positron annihilation spectroscopy (PAS).

Decoupling free-carriers contributions from oxygen-vacancy and cation-substitution in extrinsic conducting oxides.

The intrinsic oxygen-vacancies and the extrinsic dopants are two major fundamental free-carrier sources for the extrinsic conducting oxides, such as Sn-doped In(2)O(3). 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.

Correlation between free-volume properties and pervaporative flux of polyurethane-zeolite composites on organic solvent mixtures.

Micron-sized zeolite particles were incorporated into a polyurethane (PU) matrix to prepare ethylbenzene-selective membranes. The resulting composite membranes were used in the pervaporation (PV) of ethylbenzene/styrene (EB/ST) mixtures. The sorption, diffusion, and PV permeation behaviors as a result of zeolite addition were elucidated.

Solving the charging effect in insulating materials probed by a variable monoenergy slow positron beam.

A variable monoenergy slow positron beam (VMSPB) operating at a high vacuum on insulating materials encounters a problem of significant surface charging effect with time. As a result, positronium formation is inhibited, and the positron annihilation radiation counting rate is reduced; these consequently distorted the experimental positron annihilation and results. To solve such problems, a technique of depositing an ultrathin layer of sputtering noble metals on insulators is developed.

Subsurface characterization of carbon nanotubes in polymer composites via quantitative electric force microscopy.

Subsurface characterization of carbon nanotubes (CNTs) dispersed in free-standing polymer composite films was achieved via quantitative electric force microscopy (EFM). The effects of relative humidity, EFM probe geometry, tip-sample distance and bias voltage on the EFM contrast were studied. Non-parabolic voltage dependence of the EFM signal of subsurface CNTs in polymer composites was observed and a new mechanism was proposed taking consideration of capacitive coupling as well as coulombic coupling.

Amplified potentiometric determination of pK(00), pK(0), pK(l), and pK(2) of hydrogen sulfides with Ag(2)S ISE.

The chemical capacitor theory has been applied to accurately determine dissociation constants of H(2)S with the Ag(2)S ion-selective electrode (ISE). The theory's principle is based on the measurement of the change in electrode charge density as a result of protonated or unprotonated sulfide adsorbed on the electrode surface. This charge density is related to the potential.

Positron annihilation spectroscopy for surface and interface studies in nanoscale polymeric films.

Positron annihilation spectroscopy (PAS), coupled with a variable mono-energetic positron beam, has been used to investigate surface and interfacial properties in thin polymeric films. Free-volume properties have been measured from ortho-Positronium (o-Ps) lifetime and the S parameter of Doppler broadening of energy spectra from annihilation radiation as a function of the depth and of the temperature in thin polymeric films. Depth profiles of glass transition temperature and nanoscale layered structures in polystyrene (PS) thin films on the Si substrate are presented.

Lattice deformation and thermal stability of crystals in spider silk.

The X-ray diffraction of dragline silks, produced by Nephila and Cyrtophora spiders, were measured by synchrotron radiation in their original states or in situ during stretching and heating. Nephila pilipes spiders construct a two-dimensional orb web that must be rebuilt in one or 2 days, but Cyrtophora spiders form a three-dimensional tent web that can exist for several weeks in a tropical forest. Diffraction patterns of N.

Depth profile of free volume in a mixture and copolymers of poly(N-vinyl-pyrrolidone) and poly(ethylene glycol) studied by positron annihilation spectroscopy.

Effect of hydrogen bonding on the depth profile of the free-volume in a mixture (weight ratio of 65:35) of poly(N-vinyl-pyrrolidone) (PVP) and poly(ethylene glycol) (PEG) and the copolymers of vinyl pyrrolidone with poly(ethylene glycol) diacrylate (PVP-PEGDA) and monomethacrylate (PVP-PEGMMA) was studied using positron annihilation spectroscopy. Doppler broadening energy spectra of annihilation radiation and positron annihilation lifetime were measured as a function of positron incident energy (0-30 keV). Significant variations of the free-volume depth profile in terms of the S parameter, ortho-positronium lifetime, intensity, and lifetime distribution are observed as a result of the hydrogen-bonding replacement of covalent bonds.

Multiple diffraction data analysis for macromolecular crystals in stereoscopic multibeam imaging.

A detailed analysis of multiple diffraction data collected by the stereoscopic multibeam imaging technique from a tetragonal lysozyme crystal is reported. Calculations based on the dynamical theory are employed to account for diffraction profiles obtained with Bragg-angle scan in stereoscopic imaging and the conventional azimuthal scan in Renninger arrangement. The formation of a multibeam intensity profile and the relationship and mutual influence between the two scans are investigated.

Quantitative phase determination for macromolecular crystals using stereoscopic multibeam imaging.

Without invoking anomalous dispersion and heavy-atom derivatives, it is demonstrated that it is possible to directly determine the phases of a large number of reflections collected in a short time from macromolecular crystals using a stereoscopic oscillation-crystal imaging technique, in a multibeam diffraction geometry, where two crystallographic axes in opposite directions are employed as the rotation axes. The intensity profiles (distributions) of the diffraction spots versus the varying tilt Bragg angle of the rotation axis in the two stereoscopically related images yield quantitative phase information. Many multiple diffraction profiles of tetragonal lysozyme and an unknown protein structure are obtained at the rate of 100 profiles per 30 min of X-ray exposure.

Traumatic spinal cord injuries in the rural region of Taiwan: an epidemiological study in Hualien county, 1986-1990.

In order to survey the epidemiological characteristics of traumatic spinal cord injuries (SCI) in Hualien county, a retrospective study was conducted from January 1986 to December 1990 in four local general hospitals. During this period, 135 traumatic SCI patients were identified and 99 of them were residents of Hualien county. The estimated annual incidence of traumatic SCI in Hualien county was 56.

Z-DNA structure of a modified DNA hexamer at 1.4-A resolution: aminohexyl-5'-d(pCpGp[br5C]pGpCpG).

Oligonucleotides with modification at the 5'-end have been used for various biochemical applications. As a first step to better assess the effects of those modifications on DNA conformation, we determined at 1.4-A resolution the left-handed Z-DNA structure of a DNA hexamer, aminohexyl-5'-d(pCpGp[br5C]pGpCpG), by X-ray diffraction analysis.