Catálogo de publicaciones - revistas

<jats:p> Variations in dielectric constant and patterns of microwave loss have been imaged in a yttrium-doped LiNbO <jats:sub>3</jats:sub> crystal with periodic ferroelectric domains with the use of a scanning-tip near-field microwave microscope. Periodic profiles of dielectric constant and images of ferroelectric domain boundaries were observed at submicrometer resolution. The combination of these images showed a growth-instability–induced defect of periodic domain structure. Evidence of a lattice-edge dislocation has also been observed through a stress-induced variation in dielectric constant. </jats:p>

<jats:p> Magnetic domain behavior was imaged in calcium-doped lanthanum manganese trioxide films. Magnetic domains behave differently at temperatures that are well below and near the Curie temperature <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> . At low temperatures the domains are very stable. As temperature rises toward <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> , domain-domain interactions become weaker and domains become highly mobile and subject to merging and splitting, yet the domains are still traceable. The contrast (which is a measure of magnetization) and size of domains continuously reduce to zero. The temperature at which the domains disappear agrees with the <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> obtained by a macroscopic magnetization measurement. Sample defects such as scratches tend to attract magnetic domains. </jats:p>

<jats:p>An independently controlled, three-color, organic light-emitting device was constructed with a vertically stacked pixel architecture that allows for independent tuning of color, gray scale, and intensity. The 12-layer device structure consists of sequentially stacked layers of metal oxide, amorphous organic, crystalline organic, and metal thin films deposited by a combination of thermal evaporation and radio-frequency sputtering. Each of the three addressable colors is sufficiently bright for flat panel video display applications. A novel inverted structure is used for the middle device in the stack to lower the maximum drive voltage of the compound pixel.</jats:p>

<jats:p>The fluorescence of individual nitrogen-vacancy defect centers in diamond was observed with room-temperature scanning confocal optical microscopy. The centers were photostable, showing no detectable change in their fluorescence emission spectrum as a function of time. Magnetic resonance on single centers at room temperature was shown to be feasible. The magnetic resonance spectra revealed marked changes in zero-field splitting parameters among different centers. These changes were attributed to strain-induced differences in the symmetry of the centers.</jats:p>

<jats:p>In 1996, an 18-millimeter creep event, the largest ever observed on the Hayward fault, occurred between surveys 63 days apart. This event marked the end of a period of severely reduced creep on the southern part of the fault that began after the 1989 Loma Prieta, California, earthquake. The reduction in creep was consistent with elastic models for earthquake-induced static stress changes on the Hayward fault. These data suggest that creep observations can indicate regional stress changes of about 1 bar or less.</jats:p>

<jats:p>The stretching of individual polymers in a spatially homogeneous velocity gradient was observed through use of fluorescently labeled DNA molecules. The probability distribution of molecular extension was determined as a function of time and strain rate. Although some molecules reached steady state, the average extension did not, even after a ∼300-fold distortion of the underlying fluid element. At the highest strain rates, distinct conformational shapes with differing dynamics were observed. There was considerable variation in the onset of stretching, and chains with a dumbbell shape stretched more rapidly than folded ones. As the strain rate was increased, chains did not deform with the fluid element. The steady-state extension can be described by a model consisting of two beads connected by a spring representing the entropic elasticity of a worm-like chain, but the average dynamics cannot.</jats:p>

<jats:p>Surface stress changes and kinetics were measured in situ during the self-assembly of alkanethiols on gold by means of a micromechanical sensor. Self-assembly caused compressive surface stress that closely followed Langmuir-type adsorption kinetics up to monolayer coverage. The surface stress at monolayer coverage increased linearly with the length of the alkyl chain of the molecule. These observations were interpreted in terms of differences in surface potential. This highly sensitive sensor technique has a broad range of applicability to specific chemical and biological interactions.</jats:p>

<jats:p>Neutralizing antibodies are necessary and sufficient for protection against infection with vesicular stomatitis virus (VSV). The in vitro neutralization capacities and in vivo protective capacities of a panel of immunoglobulin G monoclonal antibodies to the glycoprotein of VSV were evaluated. In vitro, neutralizing activity correlated with avidity and with neutralization rate constant, a measure of on-rate. However, in vivo, protection was independent of immunoglobulin subclass, avidity, neutralization rate constant, and in vitro neutralizing activity; above a minimal avidity threshold, protection depended simply on a minimum serum concentration. These two biologically defined thresholds of antibody specificity offer hope for the development of adoptive therapy with neutralizing antibodies.</jats:p>

<jats:p> The synthesis of virulence factors and other extracellular proteins by <jats:italic>Staphylococcus aureus</jats:italic> is globally controlled by the <jats:italic>agr</jats:italic> locus, which encodes a two-component signaling pathway whose activating ligand is an <jats:italic>agr</jats:italic> -encoded autoinducing peptide. The cognate peptides produced by some strains inhibit the expression of <jats:italic>agr</jats:italic> in other strains, and the amino acid sequences of peptide and receptor are markedly different between such strains, suggesting a hypervariability-generating mechanism. Cross-inhibition of gene expression represents a type of bacterial interference that could be correlated with the ability of one strain to exclude others from infection or colonization sites, or both. </jats:p>