A dense ring of the trans-Neptunian object Quaoar outside its Roche limit.

Planetary rings are observed not only around giant planets1, but also around small bodies such as the Centaur Chariklo2 and the dwarf planet Haumea3. Up to now, all known dense rings were located close enough to their parent bodies, being inside the Roche limit, where tidal forces prevent material with reasonable densities from aggregating into a satellite. Here we report observations of an inhomogeneous ring around the trans-Neptunian body (50000) Quaoar. This trans-Neptunian object has an estimated radius4 of 555 km and possesses a roughly 80-km satellite5 (Weywot) that orbits at 24 Quaoar radii6,7. The detected ring orbits at 7.4 radii from the central body, which is well outside Quaoar's classical Roche limit, thus indicating that this limit does not always determine where ring material can survive. Our local collisional simulations show that elastic collisions, based on laboratory experiments8, can maintain a ring far away from the body. Moreover, Quaoar's ring orbits close to the 1/3 spin-orbit resonance9 with Quaoar, a property shared by Chariklo's2,10,11 and Haumea's3 rings, suggesting that this resonance plays a key role in ring confinement for small bodies.

Assessment of intraradicular bacterial composition by terminal restriction fragment length polymorphism analysis.

BACKGROUND: The aim of the study was to assess the bacterial community structures associated with endodontic infections using terminal restriction fragment length polymorphism (T-RFLP), and to investigate the correlation of whole community profiles with the manifestation of particular clinical features. METHODS: Intraradicular samples were collected from 34 subjects and classified into three study groups based on the observed clinical symptoms: acute (n = 16), sub-acute (n = 8), and asymptomatic (n = 10). Genomic DNA was extracted from each sample, submitted to polymerase chain reaction using a fluorescently labeled 16S ribosomal DNA forward primer, and digested with two tetrameric endonucleases (HhaI and MspI). The terminal restriction fragments (T-RFs) were subsequently discriminated in an automated DNA sequencer, and the results were filtered using a statistics-based criterion. RESULTS: Totals of 138 (HhaI) and 145 (MspI) unique T-RFs were detected (means 13.1 and 11.9) and there was high inter-subject variability in the bacterial assemblages. Odds-ratio analysis unveiled the existence of higher order groups of positively associated T-RFs, restating the concept that intricate ecological relationships may take place in the root canal space. A significantly greater T-RF prevalence was detected in acute cases, suggesting a straight correlation between species richness and spontaneous pain. CONCLUSION: Overall, no T-RFLP profile representing a specific bacterial consortium could be associated with the manifestation of symptoms of endodontic origin.

Role of delayed feeding and of feeding increments in necrotizing enterocolitis.

In spite of a number of studies on necrotizing enterocolitis, there remains controversy concerning prevention regimens, especially with regard to enteral alimentation. This report is of a matched case-control study of the relationship of necrotizing enterocolitis to timing of first feeding, size of feeding volumes and increments, and a risk factor index in 59 case patients with necrotizing enterocolitis and 59 matched control patients. Comparison with control patients showed that case patients were fed earlier, received full-strength formula sooner, and received larger feeding volumes and increments. More highly stressed infants, as measured by the risk index, were more vulnerable to larger feeding increments. Among case patients there was significant correlation of age at first feeding and age at diagnosis (p < 0.0001) even after control for birth weight and risk index score, indicating that delayed feeding was related to delayed onset of disease. These analyses support the theory that earlier, more rapid feeding places stressed infants at greater risk for the development of necrotizing enterocolitis, and that infants with more severe respiratory problems are more vulnerable to such feeding practices.