Continuous synthesis of YBa2Cu3O6+x by thermal explosion in a rotary kiln

Continuous synthesis of YBa₂Cu₃O_6+x superconductor was conducted in a rotary kiln. Dense pellets or loose powder of a stoichiometric mixture of copper, barium peroxide, and yttrium oxide were fed into a heated rotary kiln causing ignition on the whole outer surface followed by an inward movement of a combustion front. Following this thermal explosion, the pellet was post-treated (sintered) at 900 to 985°C as it moved along the kiln, and a product containing about 95 wt% YBa₂Cu₃O_6+x was obtained. The impact of the thermal-explosion temperature, the post-treatment temperature, the pellet density, and the total residence time in the kiln on the product quality were studied. The best thermal-explosion temperature was found to be 800°C, the best post-treatment temperature was 985°C, and the total residence time in the kiln of 100 minutes was sufficient for the pellet to reach equilibrium.     

Symmetry breaking and branching patterns in equivariant bifurcation theory II

Communicated by M. Golubitsky     

Reactions of bowhead whales, Balaena mysticetus, to seismic exploration in the Canadian Beaufort Sea

The behavioral reactions of bowhead whales to distant seismic vessels not under our control, a controlled approach by a seismic vessel, and controlled tests with a single airgun were observed. On 21 occasions in the summers of 1980-84, general activities of bowheads exposed to pulses of underwater noise (107-158 dB re: 1 mu Pa) from seismic vessels 6-99 km away were observed. Activities were indistinguishable from those without seismic noise; there was no detectable avoidance. Hints of subtle changes in surfacing, respiration, and diving behavior were unconfirmed, but were consistent with reactions to stronger noise pulses from closer seismic boats. In a test with a full-scale seismic boat (30 airguns totaling 471, source level 248 dB re: 1 mu Pa, closest point of approach = 1 1/2 km), bowheads began to orient away when the airgun array began to fire 7 1/2 km away. However, some whales continued apparent near-bottom feeding until the vessel was 3 km away. Whales were displaced by about 2 km. Reactions were not much stronger than those to any conventional vessel. Tests with one 0.66-1 airgun showed that some bowheads move away from sources of strong seismic impulses even in the absence of boat noise, and that bowheads can detect the direction from which seismic impulses arrive. In general, bowheads exhibit avoidance reactions when they receive seismic pulses stronger than about 160 dB re: 1 mu Pa. Evidence of reactions to lower received levels remains inconclusive.     

Control of traveling waves in the Mammalian cortex

We experimentally confirmed predictions that modulation of the neuronal threshold with electrical fields can speed up, slow down, and even block traveling waves in neocortical slices. The predictions are based on a Wilson-Cowan-type integro-differential equation model of propagating neocortical activity. Wave propagation could be modified quickly and reversibly within targeted regions of the network. To the best of our knowledge, this is the first example of direct modulation of the threshold to control wave propagation in a neural system.     

P-Regular Convergence Spaces

A generalized notion of regularity is introduced which enables one to study locally compact spaces, sequential spaces, ω-regular spaces, and other diverse types of spaces as special wises of p-regular spaces.     

Conjugation of poor inhibitors with surface binding groups: a strategy to improve inhibition

Conjugation of surface binding groups with inhibitors for carbonic anhydrase leads to the conversion of weak inhibitors to strong inhibitors.     

Determination of fat in dairy products using pressurized solvent extraction

Gravimetric fat data were obtained for a wide range of dairy products with fat contents ranging from 0.5 to 83% using pressurized solvent extraction at elevated temperatures and pressure (80-120 degrees C; 10.3 MPa). Extraction performance was sensitive to solvent composition, temperature, and sample matrix. By optimizing solvent mixtures, sample-solvent contact times of 8-10 min were sufficient for high recoveries from all products tested. The most successful solvents with regard to speed of extraction, selectivity, and recovery (average recovery, %) were various mixtures of hexane (or petroleum ether)-dichloromethane-methanol for dried cream (99.8%), dried whole milk (99.6%), dried buttermilk (98.2%), dried skim milk (97.0%), dried whey protein concentrate (97.5%), casein (95.0%), and caseinate (102.1%); petroleum ether-acetone-ethanol or petroleum ether-acetone-isopropanol for cheddar-type cheese (99.4%); petroleum ether-acetone for butter (99.9%); petroleum ether-acetone-isopropanol for cream (100.3%); and petroleum ether-isopropanol for liquid milks (99.0%). Relative standard deviations for repeatability were obtained for dried whole milk (0.2%), dried whey protein concentrate (0.7%), cheese (0.3%), butter (0.1%), and ultraheat treated (UHT) milk (0.7%). Solvent removal and drying of extracts with a heated block evaporator saved time compared with conventional drying ovens. Estimated savings in labor (50-75%) and solvents (80%) were substantial compared with the manual Mojonnier methods.     

Approximation of Planar Convex Sets from Hyperplane Probes

This paper studies a geometric probing problem. Suppose that an unknown convex set in R ² can be probed by an oracle which, when given a unit vector, will return the position of the supporting hyperplane of the convex set that has the given vector as an outward normal. We present an on-line algorithm for choosing probing directions so that, after n probes, an inner and an outer estimate of the convex set are obtained that are within of each other in Hausdorff distance. This is optimal since there exist convex sets that, even if visible, cannot be approximated better than with n-sided polygons, for example, a circle. Received April 18, 1995, and in revised form March 28, 1996.