Atmospheric monitoring with a spectrographic imager

A compact airborne spectrographic imager (CASI) mounted on top of an attitude stabilizing platform inside a Cessna 207T was used to monitor changes in and around a lake near Berlin for 4 months in 1993-1994. The radiance was recorded at three different altitudes in the wavelength range 0.4-0.9 mu m. The observed radiances were found to be different from 1 month to another due to the variability of phytoplankton and suspended solids in the lake. The observed radiance was similar when measured at three different altitudes during the same month, whereas the effect of altitude was seen when comparing the radiances from month to month. The radiances in the month of May 1994 have been found to be anomalous when comparing the radiances measured at the altitudes 1500 and 2000 m in the months of July and September 1993 and February 1994. This anomaly was found to be associated with aerosol concentration around an altitude of 1500-2000 m in the atmosphere as compared with LOWTRAN modelling.     

MICROSTRUCTURAL EVOLUTION AND CONTROL IN SUPERALLOY FORGINGS

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Admixture of an s-Wave Component to the d-Wave Gap Symmetry in High-Temperature Superconductors

Neutron crystal-field spectroscopy experiments in the Y- and La-type high-temperature superconductors HoBa₂Cu₃O_6.56, HoBa₂Cu₄O₈, and La_1.81Sr_0.15Ho_0.04- CuO₄ are reviewed. By this bulk-sensitive technique, information on the gap function is obtained from the relaxation behavior of crystal-field transitions associated with the Ho³⁺ ions which sit as local probes close to the superconducting copper-oxide planes. The relaxation data exhibit a peculiar change from a convex to a concave shape between the superconducting transition temperature T _c and the pseudogap temperature T ^* which can only be modeled satisfactorily if the gap function of predominantly d-wave symmetry includes an s-wave component of the order of 20–25%, independent of the doping level. Moreover, our results are compatible with an unusual temperature dependence of the gap function in the pseudogap region (T _c≤T≤T ^*), i.e., a break up of the Fermi surface into disconnected arcs.     

Real and Marginal Isotope Effects in Cuprate Superconductors

We critically review recent and earlier results on isotope effects in cuprate superconductors and emphasize that the sample preparation and the isotope exchange and back exchange are crucial in understanding and interpreting the data. Only extremely careful preparation techniques yield reliable results and permit differentiation between real isotope effects and marginal ones. The former are substantial and highlight the lattice vibrational importance in cuprate superconductors.     

Aldosterone and renin in liver cirrhosis with ascites

Supine plasma aldosterone and plasma renin activity were determined in patients with cirrhosis of the liver and ascites (n = 10). Most of the patients initially showed an increase in plasma aldosterone and plasma renin activity. However, values within the normal range were observed (plasma aldosterone, n = 3; plasma renin activity, n = 4). In the ascitic fluid renin activity could not be detected, whereas aldosterone concentrations correlated significantly with the respective plasma levels (r = 0.8, p less than 0.01). During therapy with spironolactone alone (n =2) or in combination with furosemide (n = 4), diuresis and natriuresis showed no correlation with changes in plasma aldosterone and/or plasma renin activity. Our results suggest that other factors than renin and aldosterone secretion may be important in the formation of ascites in patients with cirrhosis of the liver. In addition, the inverse correlation between mean arterial blood pressure and plasma renin activity (r = -0.65, p less than 0.05) found in our patients supports the assumption that the increase in renin secretion is probably induced by changes in (renal) hemodynamics.     

Optimizing the heat treatment of Ni-based superalloy turbine discs

The heat-treatment processes for nickel-based superalloys continue to change due to the development of new alloys, new requirements, and subsequent new manufacturing facilities. Nickel-based superalloys are continuing to evolve to meet emerging applications, while new alloys are also being introduced for advanced applications. These new materials are also being optimized for numerous mechanical and physical properties, making the selection of heat-treatment parameters increasingly challenging. New processing facilities and methods are also being implemented to allow tailoring of heat-treating parameters to meet these new challenges. For example, the Ladish SuperCooler technology allows engineering and control of all aspects of the heat-treatment process for nickel-based components, resulting in never-before possible disc properties. For more information, contact D.U. Furrer, Ladish Company, P.O. Box 8902, Cudahy, WI 53110-8902; (414) 747-3063; e-mail dfurrer@ladishco.com.     

Frustrated Phase Separation in the Overdoped Regime of “123” High-T c Superconductors

Recent inelastic neutron scattering measurements revealed the crystal-field (CF) spectra of the overdoped R_{1 ? y} Ca_yBa₂Cu₃O_≈7 (R = Ho, Er; 0 < y < 0.25) high-T _c superconductors to consist of two spectral components associated with the optimally doped and the overdoped domains. Increase of the Ca concentration does not affect the local charge density of domains, but changes the spectral weight of the components. In the sense of this “two-phase” picture, which was established earlier for the underdoped region, there is a smooth crossover between the under- and overdoped parts of the phase diagram. The charge origin of the observed superposition effect is confirmed by the systematic analysis of the concentration dependences of the CF parameters for both Ho- and Er-based compounds. Therefore, the local charge inhomogeneity in the CuO₂ planes of high-T _c cuprates is a characteristic feature of the doping process, which depends neither on the way to introduce doping nor on the doping level.