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A carbon nanotube polymer material was used to form a piezoresistive strain sensor for structural health monitoring applications. The polymer improves the interfacial bonding between the nanotubes. Previous single walled carbon nanotube buckypaper sensors produced distorted strain measurements because the van der Waals attraction force allowed axial slipping of the smooth surfaces of the nanotubes. The polymer sensor uses larger multi-walled carbon nanotubes which improve the strain transfer, repeatability and linearity of the sensor. An electrical model of the nanotube strain sensor was derived based on electrochemical impedance spectroscopy and strain testing. The model is useful for designing nanotube sensor systems. A biomimetic artificial neuron was developed by extending the length of the sensor. The neuron is a long continuous strain sensor that has a low cost, is simple to install and is lightweight. The neuron has a low bandwidth and adequate strain sensitivity. The neuron sensor is particularly useful for detecting large strains and cracking, and can reduce the number of channels of data acquisition needed for the health monitoring of large structures.

Ultrathin films of Eu 3+ doped Y2O3 were deposited onto alumina nanoparticles using a unique solution synthesis method. The surface structure, composition, and morphology of the thin films deposited were analysed using high resolution transmission electron microscopy (TEM) and high angle annular dark field scanning TEM imaging and energy dispersive x-ray measurements. The films deposited were extremely thin, on the order of 3–5 nm, and uniformly covered all the alumina nanoparticles. X-ray diffraction was used to investigate the phases and structures of the thin films deposited. At the heat treatment temperature of 600 ◦ C, cubic Y2O3 nanocrystals were found in the film while as-coated layers exhibited mainly amorphous features. As the heat treatment temperature increased to 750 ◦ C, the amorphous thin film became well crystallized. Optical properties of Eu 3+ doped Y2O3 films were characterized by fluorescence spectroscopy. Strong photoluminescence was observed in the sample annealed at 750 ◦ C, from the fluorescence of Eu 3+ ions in a well-crystallized film, consistent with the

Despite great success in the TFA methods of depositing Y Ba2Cu3Ox?(YBCO) thin films for coated conductors, critical issues involved in removing BaCO3 have not entirely been settled. There could be other possible ways of dealing with carbon that remains in the film. We have recently developed a fluorine-free sol?gel synthesis with several important advantages including precursor solution stability, improved film density, and elimination of HF during processing. With this approach, high-quality YBCO films have been developed on single crystal substrates with the transport Jc s up to 106?A?cm?2. In this study, the precursor solution stoichiometry was altered and its effects on superconducting properties were studied. The fluorine-free sol?gel-derived films on the LaAlO3?(LAO) substrate exhibited epitaxial growth with excellent in-?and out-of-plane texture. Experimental details are reported on the sol?gel synthesis chemistry and XRD and TEM characterization of the YBCO thin films. Also discussed is the underlying formation mechanism of the YBCO phase during the synthesis.

Using a fluorine-free sol–gel method, both c- and a-axis textured YBCO thin films were synthesized in low oxygen partial pressure. The experimental results of both x-ray diffraction 2θ scan and pole figure showed well epitaxial grown films on LaAlO3 (LAO) single crystal substrates. When the processing condition was altered, the scanning electron microscopy indicated a large fraction of a-axis oriented grains in the film. High-resolution transmission electron microscopy was performed on both types of films and revealed interface lattice structural characteristics. A classic nucleation and growth model was used to explain the texturing mechanism. Other possible mechanisms for the a-axis oriented grains are also discussed.

The structural and electronic properties of Eu3+-doped Y2O3 films coated on spherical alumina nanoparticles are studied using transmission electron microscope, x-ray diffraction, and laser spectroscopic techniques. It is observed that the coated films crystallize at temperatures higher than 600°C and may be completely converted into a cubic Y2O3 nanocrystalline layer at 750°C. At 900°C, phase transition occurs between the outer coating layer and the inner core, and different types of crystalline nanophase can be obtained. In the materials that we prepared and studied, all possible crystallographic phases, including two of solid-state laser media, YAlO3 (YAP), and Y3Al5O12 (YAG), may be formed in the pseudo-binary Al2O3–Y2O3 nanosystem by controlling thermal annealing procedures from 600 to 900°C, a temperature region far below the conventional solid-state reaction temperature. The spectroscopic properties of Eu3+ in all the nanophases are characterized in comparison with those of their bulk counterparts.

In our previous work, we have shown that a single-domain YBa2Cu3Ox (YBCO) exhibits a low surface resistance. However, the second phase Y2BaCuO5 (211) precipitates inevitably as a result of peritectic reaction. These 211 particles are potential sources of RF losses, which need to be eliminated. In this study, a non-fluorine sol–gel synthesis was developed to deposit a YBCO thin film on the surface of single-domain YBCO. The deposited YBCO thin film entirely covered the 211 particles. The interface structure was studied by high-resolution transmission electron microscopy. The experimental results on sol–gel synthesis and thin film characterization are reported. Also discussed is the underlying mechanism of film growth on single-domain YBCO.

Efficient delivery of small interfering RNAs (siRNAs) to the targeted cells has remained a significant challenge in clinical applications. In the present study, we developed a novel aptamer-siRNA chimera delivery system mediated by cationic Au-Fe3O4 nanoparticles (NPs). The chimera constructed by VEGF RNA aptamer and Notch3 siRNA was bonded with heterogeneous Au-Fe3O4 nanoparticles by electrostatic interaction. The obtained complex exhibited much higher silencing efficiency against Notch3 gene compared with chimera alone and lipofectamine-siRNA complex, and improved the antitumor effects of the loaded chimera. Moreover, the efficient delivery of the chimera by Au-Fe3O4 NPs could reverse multi-drug resistance (MDR) of ovarian cancer cells against the chemotherapeutic drug cisplatin, indicating its potential capability for future targeted cancer therapy while overcoming MDR.

To develop high-quality rf components for wireless telecommunications, we have processed single-domain YBCO of various dimensions and geometry for the device applications including high-Q resonators and filters. In this development, a critical parameter, the surface resistance, Rs, of single-domain YBCO has been measured in wide ranges of temperature and magnetic field. We have found that the Pippard model can best describe the well oxygenated crystal, indicating the high-quality of single-domain YBCO. However, such scaling breaks down when the oxygen structural disorders are introduced into the sample. A fundamentally different scaling behaviour is observed, which is closely related to the structural defects of oxygen. We report such a behaviour and discuss the possible underlying mechanism.

The authors measured magnetic irreversibility, H*(T), in liquid-quenched Bi-Sr-Ca-Cu-O samples with various microstructures at high applied field (up to 7 T). We found that H*(T) is considerably increased in the Bi2Sr2Ca3Cu4Ox (2234) sample with a large number of crystal defects, including severe lattice distortion and calcium and copper rich precipitates. They argue that the lattice distortion may affect the degree of anisotropy and the Josephson coupling between the Cu-O layers, which in turn enhance the irreversibility in the Bi-Sr-Ca-Cu-O system. A critical-current density, Jc, of 8*104 A cm-2 at 8 kG and 40 K was obtained in the 2234 sample with many defects, while the Jc dropped significantly at the same temperature and field in the near stoichiometry Bi2Sr2Ca2Cu3Ox (2223) sample with a uniform microstructure.

Transmission electron microscopy data of crystal defects have been taken in as-sintered and zone-melted YBa2Cu3Ox samples to correlate with the corresponding critical current density properties. The origins and microstructural characteristics of the typical defects, including twin boundaries, grain boundaries, precipitates and dislocations are discussed. A new model is proposed to interpret the effect of twinning on the transport current density. High resolution electron microscopy data of dislocations observed in the zone-melted sample are presented, which indicate the possibility of these dislocations acting as strong pinning centers. Also discussed are the effects of these microstructural changes on transport and magnetization critical current density.

The flux-creep activation energy Uo has been obtained by using Arrhenius plots for polycrystalline YBa2Cu3Ox for various oxygen stoichiometries. An exponential relationship between Uo and x has been established for different applied magnetic fields. This relationship can be used to explain the resistive transition broadening for samples with different oxygen concentrations. The observed field dependence of Uo suggests the existence of 90 K and 60 K superconductors.

The resistivity has been measured as a function of temperature in magnetic fields up to 12 T for a typical Tl2Ca2Ba2Cu3Ox sample. The resistive transition width has been observed to broaden with increasing field while the transition onset remains unchanged. This broadening can be explained by the flux-creep model. The flux-creep activation energy at the applied field values has been estimated from the slopes of Arrhenius plots of log rho against 1/T. The flux-creep activation energy has been found to be weakly field-dependent (H12/) in high-field regions (>2 T). The upper critical field of the Tl-based superconductor has also been estimated to be 133 T.

The microstructures of polycrystalline YBa2Cu3Ox samples were varied through different sintering mechanisms to study transport-current characteristics in magnetic fields. TEM experimental results indicate that the transport critical current in polycrystalline YBa2Cu3Ox is closely correlated with grain boundary microstructures. Specifically, the Jc(H) is severely suppressed as the grain boundaries are contaminated with the second phases. The field required for the Jc(H) values to decrease to zero is also strongly affected by the grain boundary microstructure. The critical-current behaviour and closely related microstructural changes are explained with Josephson weak-link and flux-flow models.

Hydroxylapatite (HA) nanoparticles were conjugated with quantum dots (QDs) for in vivo imaging. The surface structures of HA nanoparticles with conjugated quantum dots (HA-QD) were studied by transmission electron microscopy (TEM) and laser fluorescent spectroscopy. The TEM data showed that the quantum dots were well conjugated on the HA nanoparticle surfaces. The laser fluorescent spectroscopy results indicated that the HA-QD exhibited promising luminescent emission in vitro. The initial in vivo experiments revealed clear images of HA-QD from the hypodermic injected area at the emission of 600 nm. Furthermore, the optimized in vivo images of HA-QD with near-infrared emission at 800 nm were visualized after intravenous injection. These luminescent HA-QD nanoparticles may find important applications as biodegradable substrates for biomarkers and in drug delivery.

The (110) twin boundary separation d has been varied from 1500 AA to 300 AA by annealing polycrystalline samples in air at different temperatures ranging from 400 to 700 degrees C. The intragrain critical current density Jc and its in-field behaviour are strongly affected by the variation of the superconducting properties and the microstructures. Jc(H) has been found to drop more rapidly with increasing field as the d value decreases. This decrease in Jc with increasing field may be associated with the weak link effects created by the twin boundaries and a corresponding decrease in pinning effectiveness. The corresponding pinning mechanisms are discussed.

YBa2Cu3O7-x powders, made at Argonne National Laboratory by solid-state reaction or supplied by Rhone-Poulenc, were sintered in oxygen at 910 or 950 degrees C. Heating rates to the sintering temperature were varied from 0.5 to 5 degrees C min-1. Sintered specimens were characterised by differential thermal analysis, X-ray diffraction, optical and scanning electron microscopy, and measurement of electrical resistivity, superconducting transition temperature and critical current density. It was found that the heating rate affected only the properties of specimens which were heated to a temperature at which second phases present could react. Slower heating improved electrical properties as a consequence of inducing greater reaction to desired phases such as YBa2Cu3O7-x.

The composition TlCa3BaCu3Oy has been reacted to form the high-temperature superconducting phase Tl2Ca2Ba2Cu3Ox. Compacts were sintered in sealed containers from 870 to 925 degrees C in various oxygen partial pressures. Zero-resistance temperatures (T0) reached 118 K; the highest values were obtained from sintering in pure oxygen at 915 to 920 degrees C for 2 to 4 h. Critical current densities (Jc) at 77 K in zero field reached about 700 A cm-2; no correlation was found between T0 and Jc.