A quantitative assay for assessing allelic proportions by iterative gap ligation

PURPOSE: We compared gastrointestinal toxicity of single vs. fractionated total body irradiation (TBI) administered at dose rates ranging from 0.021 to 0.75 Gy/min in a canine model of marrow transplantation. METHODS AND MATERIALS: Dogs were given otherwise marrow-lethal single or fractionated TBI from dual 60Co sources at total doses ranging from 8-18 Gy and delivered at dose rates of 0.021, 0.05, 0.10, 0.20, 0.40, and 0.75 Gy/min, respectively. They were protected from marrow death by infusion of previously stored autologous marrow cells and they were given intensive supportive care posttransplant. The study endpoint was 10-day mortality from gastrointestinal toxicity. Logistic regression analyses were used to jointly evaluate the effects of dose rate, total dose, and delivery regimen on toxicity. RESULTS AND CONCLUSION: With increasing dose rates, mortality increased for either mode of delivery of TBI. With dose rates through 0.10 Gy/min, mortality among dogs given single vs. fractionated TBI appeared comparable. Beginning at 0.20 Gy/min, fractionation appeared protective for the gastrointestinal tract. Results in dogs given TBI at 0.40 and 0.75 Gy/min, respectively, were comparable, and dose fractionation permitted the administration of considerably higher total doses of TBI than were possible after single doses, an increment that was on the order of 4.00 Gy. The data indicate that the impact of fractionating the total dose at high dose rates differs from the effect of fractionation at low dose rates.     

Processing and Electrical Properties of 0.5Pb(Yb1/2Nb1/2)O3-0.5PbTiO3 Ceramics

Pb(Yb_1/2Nb_1/2)O₃-PbTiO₃ ceramics at the morphotropic phase boundary (50:50) were sintered by conventional and reactive methods to 95% theoretical density and grain sizes <10 m. Excess PbO, added to enhance the densification, resulted in PbO-based non-ferroelectric phases that degraded the electrical properties. Volatilization of excess PbO by annealing the samples after sintering resulted in dense, perovskite samples and excellent electrical properties. The best electrical properties, obtained via reactive sintering, were a remanent polarization, P _r, of 0.36 C/m², a maximum dielectric constant of 31,000 (at the T _c = 371°C and 1 kHz), a piezoelectric charge coefficient, d ₃₃, of 508 pC/N, and an electromechanical coupling coefficient, k ₃₃, of 0.61.     

Constrained Densification of Alumina/Zirconia Hybrid Laminates, II: Viscoelastic Stress Computation

To analyze the inhibited densification during sintering and differential shrinkage during cooling of Al₂O₃/ZrO₂symmetric and asymmetric laminates, viscoelastic formulations, in which the viscosity and elastic modulus vary with time, have been developed. The viscoelastic mismatch stresses have been numerically computed over the entire processing cycle, including the heating period, the isothermal period, and the cooling period. The viscosity and free sintering rates that are needed for stress computation have been obtained by modifying the parameters that are measured for a normal isotropic densifying compact using cyclic loading dilatometry. The modification is based on the available sintering models to account for the effect of strain history on compact viscosity and sintering rates. The stress calculation shows that, with the exception of the initial heating period, the viscoelastic stress is identical to the viscous stress that is calculated solely from the strain rate mismatch. Sintering damage in the laminates is shown to occur during densification under conditions where the differential sintering stress is smaller than the intrinsic sintering pressure. The magnitude of residual stress in hybrid laminates on cooling is dependent on the cooling rate, and slower cooling rates are capable of almost completely relaxing the expansion mismatch stress at temperatures of >1200°C.     

Critical Factors in the Templated Grain Growth of Textured Reaction-Bonded Alumina

The Templated Grain Growth (TGG) of Al₂O₃ occurs in three stages: densification, radial growth of individual template grains until template impingement, and template grain thickening. Significant template growth occurs only after densification to ∼90% density. Template loading determines the inter-template spacing and, subsequently, the degree of growth. The spacing distance can be predicted from the initial template concentration and template dimensions. Thermodynamic conditions favorable for template growth occur when the size ratio between the template thickness and matrix grains is ≥1.5. The initial template concentration should be less than a critical template concentration, V _T,C, to achieve textured ceramics with a narrow orientation distribution. For this system, which uses 20 ± 5 μm × 2 μm template particles and uniaxial pressing as a forming technique, V _T,C is between 5 and 10 vol%.     

Sintering,microstructure and mechanical properties of Al2O3–Y2O3–ZrO2 (AYZ) eutectic composition ceramic microcomposites

We report on how the mechanical properties of sintered ceramics (i.e., a random mixture of equiaxed grains) with the Al₂O₃–Y₂O₃–ZrO₂ eutectic composition compare with those of rapidly or directionally solidified Al₂O₃–Y₂O₃–ZrO₂ eutectic melts. Ceramic microcomposites with the Al₂O₃–Y₂O₃–ZrO₂ eutectic composition were fabricated by sintering in air at 1400–1500 °C, or hot pressing at 1300–1400 °C. Fully dense, three phase composites of Al₂O₃, Y₂O₃-stabilized ZrO₂ and YAG with grain sizes ranging from 0.4 to 0.8 μm were obtained. The grain size of the three phases was controlled by the size of the initial powders. Annealing at 1500 °C for 96 h resulted in grain sizes of 0.5–1.8 μm. The finest scale microcomposite had a maximum hardness of 19 GPa and a four-point bend strength of 282 MPa. The fracture toughness, as determined by Vickers indentation and indented four-point bending methods, ranged from 2.3 to 4.7 MPa m^1/2. Although strengths and fracture toughnesses are lower than some directionally or rapidly solidified eutectic composites, the intergranular fracture patterns in the sintered ceramic suggest that ceramic microcomposites have the potential to be tailored to yield stronger, tougher composites that may be comparable with melt solidified eutectic composites.     

Kinetic Analysis of Solution-Precipitation During Liquid-Phase Sintering of Alumina

Densification controlled by solution-precipitation during liquid-phase sintering was analyzed for the aluminamagnesium aluminosilicate glass system. As a model system for liquid-phase sintering, narrowly sized alumina powders and up to 20 vol% magnesium aluminosilicate glass samples were isothermally sintered at 1550° to 1650°C. Densification rate increases with increasing liquid content and sintering temperature but decreases with increasing density. For samples with >15% grain growth, the densification rate during the solution-precipitation stage of sintering was proportional to (particle size)⁻² and thus interface reaction-controlled. Activation energies ranged from 270 to 500 kJ/mol over the relative density range of 66% to 96%, respectively. The low activation energy is attributed to densification by particle rearrangement, whereas the higher activation energy is due to densification controlled by interface-reaction-controlled solution-precipitation. Intermediate activation energies are attributed to simultaneous densification by the two mechanisms.     

Generation of size-selected gold nanoparticles by spark discharge — for growth of epitaxial nanowires

One-dimensional semiconductor nanowires are a promising candidate for future electronic devices. The epitaxial growth of nanowires is often mediated by metal seed particles, usually gold particles. In this paper the setup of a simple and robust technique to generate nanometer-sized aerosol gold particles by spark discharge is described. Furthermore we demonstrate for the first time that particles generated by spark discharge can be used to design advanced nanoelectronic structures, namely nanowires. In order to obtain compact, spherical particles suitable for nanowire growth, the sparkgenerated agglomerate particles were reshaped in a special compaction furnace. The reshaped particles were used to seed the growth of epitaxial GaP and InP nanowires, by metal organic vapor phase epitaxy, which was shown to be a reliable and reproducible method. This work indicates the possibility of using spark-discharge generated gold particles for the creation of new electronic devices even at large scale processing.     

Temperature-sensitive neuromuscular transmission in Kv1.1 null mice: role of potassium channels under the myelin sheath in young nerves

In mammalian myelinated nerves, the internodal axon that is normally concealed by the myelin sheath expresses a rich repertoire of K channel subtypes thought to be important in modulating action potential propagation. The function of myelin-covered K channels at transition zones, however, has remained unexplored. Here we show that deleting the voltage-sensitive potassium channel Kv1.1 from mice confers a marked temperature-sensitivity to neuromuscular transmission in postnatal day 14 (P14)-P21 mice. Using immunofluorescence and electrophysiology, we examined contributions of four regions of the peripheral nervous system to the mutant phenotype: the nerve trunk, the myelinated segment preceding the terminal, the presynaptic terminal membrane itself, and the muscle. We conclude that the temperature-sensitive neuromuscular transmission is accounted for solely by a deficiency in Kv1.1 normally concealed in the myelinated segments just preceding the terminal. This paper demonstrates that under certain situations of physiological stress, the functional role of myelin-covered K channels is dramatically enhanced as the transition zone at the neuromuscular junction is approached.