Diffraction Symmetry in Crystalline, Close-Packed C60

We have grown crystals of the carbon structure C60 by sublimation. In contrast to solution-grown crystals, the sublimed crystals have long range order with no evidence of solvent inclusions. Sublimed C60 forms three dimensional, faceted crystals with a close-packed, face-centered cubic unit cell. We have refined a crystal structure using the “soccer ball” model of the C60 molecule. The results indicate that the C60 molecule has the expected spherical shape, however the data are not sufficiently accurate to unambiguously determine atomic positions.

Overview and initial results of the very long baseline interferometry space observatory programme

High angular resolution images of extragalactic radio sources are being made with the Highly Advanced Laboratory for Communications and Astronomy (HALCA) satellite and ground-based radio telescopes as part of the Very Long Baseline Interferometry (VLBI) Space Observatory Programme (VSOP). VSOP observations at 1.6 and 5 gigahertz of the milli-arc-second-scale structure of radio quasars enable the quasar core size and the corresponding brightness temperature to be determined, and they enable the motions of jet components that are close to the core to be studied. Here, VSOP images of the gamma-ray source 1156+295, the quasar 1548+056, the ultraluminous quasar 0014+813, and the superluminal quasar 0212+735 are presented and discussed.

Subparsec-scale structure and evolution of Centaurus A (NGC5128)

We present a series of 8.4-GHz very-long-baseline radio interferometry images of the nucleus of Centaurus A (NGC5128) made with a Southern Hemisphere array, representing a 3.3-year monitoring effort. The nuclear radio jet is approximately 50 milliarcseconds in extent, or at the 3.5-megaparsec distance of NGC5128, approximately 1 parsec in length. Subluminal motion is seen and structural changes are observed on time scales shorter than 4 months. High-resolution observations at 4.8 and 8.4 GHz made in November 1992 reveal a complex morphology and allow us to unambiguously identify the self-absorbed core located at the southwestern end of the jet.

Defects in Carbon Nanostructures

Previous high-resolution electron microscopy (HREM) observations of the carbon nanotubes have led to a "Russian doll" structural model that is based on hollow concentric cylinders capped at both ends. The structures of the carbon nanotubes and particles were characterized here by bulk physical and chemical property measurements. The individual nanostructure is as compressible as graphite in the c axis, and such nanostructures can be intercalated with potassium and rubidium, leading to a saturation composition of "MC(8)." These results are counter to expectations that are based on a Russian doll structure. HREM after intercalation with potassium and deintercalation indicates that individual nanoparticles are a "paper-mache" of smaller graphite layers. Direct current magnetization and electron spin resonance measurements indicate that the electronic properties of the nanostructures are distinctly different from those of graphite. Although the nanostructures have distinct morphologies and electronic properties, they are highly defective and have a local structure similar to turbostratic graphite.

13 C NMR Spectroscopy of K x C 60 : Phase Separation, Molecular Dynamics, and Metallic Properties

The results of (13)C nuclear magnetic resonance (NMR) measurements on alkali fullerides KxC(60) are reported. The NMR spectra demonstrate that material with 0 < x < 3 is in fact a two-phase system at equilibrium, with x = 0 and x = 3. NMR lineshapes indicate that C(3-)(60) ions rotate rapidly in the K(3)C(60) phase at 300 K, while C(6)-(60) ions in the insulating K(6)C(60) phase are static on the time scale of the lineshape measurement. The temperature dependence of the (13)C spin-lattice relaxation rate in the normal state of K(3)C(60) is found to be characteristic of a metal, indicating the important role of the C(3-)(60) ions in the conductivity. From the relaxation measurements, an estimate of the density of electronic states at the Fermi level is derived.

Microscopic lesions of naturally occurring and experimental "spiking mortality" in young broiler chickens

Tissues from five chickens from each of 44 flocks affected with "spiking mortality" were examined histologically. Tissues from these chickens were characterized by: multifocal necrosis of hepatocytes with congestion and blood lake formation; severe lymphocyte necrosis in the bursal medulla, thymic cortex, and gut-associated lymphoid tissues; acute necrotic vasculitis in the alimentary serosa and liver; rickets; and air-sac disease in survivors. No specific etiology was identified in sections examined.

Assessment of accuracy of intraesophageal pH probe in a dog model

We performed an experiment in dogs in order to assess the accuracy of an intraesophageal pH probe and to examine possible mechanisms for any lack of accuracy. Two pH probes were placed in the esophagus of supine anesthetized dogs and acid was infused in small serial volumes from an infusion tube placed at the gastroesophageal junction. Two general patterns of pH probe responses were seen: (1) neither probe recorded a fall in pH with acid infusion, and (2) both probes recorded a fall in pH, but in a nonsynchronous manner. Changing the relationship of the tips of the probes with respect to the adjacent mucosa caused a fall in the pH recorded by each probe to the pH of the intraesophageal infusate. This and other evidence seen in the pH tracings suggest that mucosal abutment of the probe tips causes a falsely negative pH recording and raises the question of whether such a phenomenon occurs in human studies.

Does the intraesophageal pH probe accurately detect acid reflux? Simultaneous recording with two pH probes in humans

Little is known about the accuracy of intraesophageal pH monitoring, ie, do false negatives occur? This study was designed based on the assumption that if two pH probes are placed equidistant from a distal acid source, and the probes measure different values, then one probe might miss acid if it were there alone. We performed 24-hr intraesophageal pH monitoring in 10 patients with gastroesophageal reflux disease, simultaneously placing two pediatric pH probes (probes A and B) 5 cm proximal to the LES in such close proximity that one would expect only small differences in the acid exposure measured by the probes. However, the amount of acid exposure measured by probes A and B differed greatly in some instances. Individual probe performance does not alone account for these differences, since, when pH recordings were reviewed, one probe was as likely to miss acid exposure as the other. These differences would result in a change in the clinical diagnosis in two of 10 patients. Variability in the number of episodes was great and occurred even when there was concordance in percent acid exposure. These data raise questions about the absolute accuracy of the pH probe as the gold standard in the measurement of gastroesophageal reflux.

Processing Techniques for the 93 K Superconductor Ba 2 YCu 3 O 7

Superconductivity above the temperature of liquid nitrogen in copper oxide-based systems has led to optimism that superconductors may at last find wide application. The critical temperature, however, is just one of the required parameters. The materials must be made into usable forms such as wire, thick films, thin films, and bulk ceramics. In addition, the critical current in these various forms is a crucial test of their utility. This article reviews the processing techniques used to fabricate potentially useful forms and assesses remaining problems. Considerable improvement in critical current density is necessary in bulk materials, and thin films need to be made compatible with other thin-film technology.

Chocolate and heartburn: evidence of increased esophageal acid exposure after chocolate ingestion

Chocolate has been shown to decrease mean basal lower esophageal sphincter (LES) pressure, providing a rationale for the pathogenesis of chocolate-induced reflux symptoms. We assessed the relationship between chocolate ingestion and increased esophageal acid exposure using intraesophageal pH monitoring. Compared with ingestion of a dextrose control solution of similar volume, osmolality, and calories, postprandial ingestion of chocolate resulted in a significant increase in acid exposure in the first postprandial hour in patients with esophagitis. We conclude that this finding supports recommendations that patients with reflux esophagitis abstain from chocolate.

Toxicology of 85Kr: chronic exposure studies

Male and female Wistar rats were exposed chronically to graded doses of 85Kr to determine long-term biological effects of simulated environmental exposure. Rats were exposed in 4 groups, including room air-exposed controls and 3 groups exposed to 85Kr concentrations equivalent to 10(2), 10(3) and 10(4) times the maximum permissible concentration (MPC) for the general population (3 X 10(-7) microCi/ml). Exposures continued 24 hr/day, 7 days/week for 808 days, until only approximately 10% of the original 400 rats were alive. No effect of 85Kr exposure was observed on weight gain or tumor incidence, including leukemias. The results support the adequacy of established 85Kr exposure limits for the general population in light of the absence of evidence of build-up in tissues after chronic exposure and the lack of exposure-related biological effects in rats after near-lifespan exposure to concentrations equivalent to 10,000 times the MPC.

Toxicology of 85Kr: tissue distribution and retention in the rat

Wistar rats were exposed to 85Kr gas atmospheres to determine saturation/desaturation kinetics in major tissues. Tissue partition coefficients [concentration 85Kr in tissue (muCi/g)/concentration of 85Kr in the atmosphere (muCi/cc)] were determined following equilibration with 85Kr gas. Tissue partition coefficients were highest for adrenals and fat; lowest for bone, heart and brain. Tissue partition coefficients for immature rats, 1-12 days of age, and for adults, were not significantly different. The highest concentrations of 85Kr were found in fatty tissues and in gas pockets in the intestinal lumen.