Renal arteriovenous fistulas

Sinusoidal variations of CO2 were applied to anesthetized White Leghorn cockerels enclosed in a body plethysmograph. Waveforms were 2.5% mean plus 2.5% peak sine wave CO2 in air, at frequencies of 0.011 to 0.467 rad/s. Reflex variation in tidal volume and respiratory interval in response to the inputs of sinusoidally varying fractional content of inhaled CO2 for nine points within the above range of driving frequencies were recorded breath-by-breath. A least squares best-fit procedure was used to estimate mathematical input-output relationships (transfer functions) between the outputs, tidal volume (VT) and respiratory interval (1/f), and the single input, inspired CO2 fraction. For VT, a three time constant model most closely fitted the data. Two time constants, 80 s and 3.9 s, were associated with negligible delay; the third, 14 s, has a 0.35 s time delay. Dynamics of VT and interval reflex responses differed significantly suggesting that they are regulated by separate mechanisms.     

Alpha-adrenergic reactivity of the microcirculation in conscious spontaneously hypertensive rats

The goal of this study was to determine the functional distribution of alpha 1- and alpha 2-adrenoceptors in the striated muscle microcirculation. Experiments were performed in intact conscious spontaneously hypertensive rats (SHR) that were provided with a dorsal microcirculatory chamber to allow microvascular diameter measurements. Administration of selective alpha 1- and alpha 2-agonists, phenylephrine and azepexole, respectively, induced different patterns of microvascular constriction. alpha 1-Adrenoceptor stimulation showed a preferential constriction of large arteries and venules. The entire arteriolar microvasculature was sensitive to alpha 2-adrenoceptor stimulation, whereas the venular vessels did not respond to azepexole. The selective alpha 1- and alpha 2-antagonists prazosin and yohimbine showed patterns of vasodilator activity comparable to those of the corresponding agonists. The specificity of the drug-induced effects was verified by comparing their effects with those of graded hemorrhage, a non-pharmacological method for blood pressure lowering. In the range of blood pressure decreases comparable to that obtained by alpha-adrenoceptor antagonists, graded hemorrhage did not influence microvascular diameters. These results show a differential functional distribution of alpha 1- and alpha 2-adrenoceptors along the microvascular tree in striated muscle of conscious SHR.     

A Method for Preparation of Unsupported Sol–Gel Thin Films

Unsupported gel films 1 to 3 μm thick may be prepared from colloidal sol–gel systems by spin-coating onto a camphor substrate. Sublimation of the camphor surface allows the film to separate and be freely sintered, giving a rapid indication of sintering behavior and microstructural development.     

Industrielle Kristallisation – Moderne großtechnische Anlagen und Fallstudien

Industrial crystallization – Modern industrial plants and case studies . In the field of mass crystallization a number of advanced plant designs have been implemented in the past decade, and are exemplified in the crystallization of adipic acid and common salt, and in evaporation of aluminate liquor which is susceptible to encrustation. Assessment criteria are, inter alia, product qualities such as the purity achieved and the crystal size distribution, and operation parameters such as the duration of process flow and control behaviour. The significant increase in quality is largely attributable to the crystallizers, which have been optimized above all with regard to the crystal-size distribution and the duration of product flow.     

Electric field induced splitting of the preferred orientation in PMN-PT textured ceramics

We have performed studies of the orientation distribution in <001>_C textured, 0.03(Na_1/2Bi_1/2)TiO₃ - 0.97[0.715Pb(Mg_1/3Nb_2/3)TiO₃ - 0.285PbTiO₃] (0.03NBT-0.97[PMN-28.5PT]) ceramics by a pole figure method, comparing the results to those for PMN-PT single crystal and polycrystal samples. The pole figures about the (001) zone are found to have monoclinic, Ma, phase for textured ceramics in the annealed condition and were similar to those for electrically poled single crystals. However, electrical poling of the textured ceramics resulted in a doublet splitting of the orientation distribution about the direction that defined the original grain texturing. Studies of pole figures about other high-symmetry zones also revealed the development of some degree of preferred orientation along the in-plane directions after poling. Our findings demonstrate that E-field induced phase transformation and domain textures superimpose with that of preferred grain orientations, giving rise to a unique texture symmetry for PMN-PT. The texture symmetry changes are driven by minimization of the elastic strain energy, and have an important effect upon the piezoelectric properties.     

Direct writing of textured ceramics using anisotropic nozzles

Direct writing is a unique means to align anisotropic particles for the fabrication of textured ceramics by templated grain growth (TGG). We show that alignment of tabular barium titanate (BT) template particles (20–40 μm width and 0.5–2 μm thickness) in a PIN-PMN-PT matrix powder (d₅₀ = 280 nm) is significantly improved during direct writing using anisotropic nozzles at high printing rates. The particle orientation distribution in as-printed filaments, and the texture orientation distribution in sintered ceramic filaments are shown to directly correlate with COMSOL Multiphysics-predicted torque distributions for direct writing with aspect ratio 2, 3 and 5 oval nozzles. Electromechanical strain properties of the textured piezoelectric ceramics significantly improved relative to random ceramics when printed with anisotropic nozzles. Simulations of aspect ratio 20 nozzles and nozzles with interior baffles demonstrate significantly increased torque and near elimination of constant shear stress cores (i.e. plug flow).     

Processing and electromechanical properties of high-coercive field ZnO-doped PIN-PZN-PT ceramics

This study explores sintering and piezoelectricity of ZnO-doped perovskite Pb(In_1/2Nb_1/2)O₃-Pb(Zn_1/3Nb_2/3)O₃-PbTiO₃ (PIN-PZN-PT) ceramics. The enhanced densification of ZnO-doped PIN-PZN-PT is attributed to the formation of oxygen vacancies by the incorporation of Zn²⁺ into the perovskite B-site and increased rate of bulk diffusion relative to undoped PIN-PZN-PT. Incorporation of Zn²⁺ into the perovskite lattice increased the tetragonal character of PIN-PZN-PT as demonstrated by tetragonal peak splitting and increased Curie temperature. Sintering in flowing oxygen reduced the solubility of Zn²⁺ in the perovskite lattice and resulted in rhombohedral PIN-PZN-PT. Sintering in oxygen prevented secondary phase formation which resulted in a high-piezoelectric coefficient (d₃₃ – 550 pC/N), high-coercive field (E_c – 13 kV/cm), and high-rhombohedral to tetragonal phase transition temperature (T_r-t – 165°C). We conclude that ZnO-doped PIN-PZN-PT ceramics are excellent candidates for high-power transducer applications.     

Kinetic Analysis of Combustion Synthesis of Lead Magnesium Niobate from Metal Carboxylate Gels

A combustion synthesis route was developed for direct crystallization of perovskite lead magnesium niobate (PMN) from metal carboxylate gels. Direct PMN formation is attributed to a homogeneous cation distribution in the gel and the rapid heating during exothermic gel decomposition in oxidizing atmospheres. The maximum bed temperature and gel decomposition rate are determined by the combined influence of chemical kinetics, heat, and mass transfer. It is shown that there is a temperature window between 700° and 750°C which favors direct PMN formation, whereas pyrochlore formation is favored below 650°C and PbO volatilization occurs above 800°C. The effects of kinetic and transport parameters including oxygen partial pressure, gas flow rate, and bed geometry on PMN formation are discussed on the basis of a thermal ignition model for heterogeneous reactions.