ABSTRACT
Interstellar dust plays a crucial role in the evolution of the Universe by assisting the formation of molecules, by triggering the formation of the first low-mass stars, and by absorbing stellar ultraviolet-optical light and subsequently re-emitting it at infrared/millimetre wavelengths. Dust is thought to be produced predominantly in the envelopes of evolved (age >1 Gyr), low-mass stars. This picture has, however, recently been brought into question by the discovery of large masses of dust in the host galaxies of quasars at redshift z > 6, when the age of the Universe was less than 1 Gyr. Theoretical studies, corroborated by observations of nearby supernova remnants, have suggested that supernovae provide a fast and efficient dust formation environment in the early Universe. Here we report infrared observations of a quasar at redshift 6.2, which are used to obtain directly its dust extinction curve. We then show that such a curve is in excellent agreement with supernova dust models. This result demonstrates a supernova origin for dust in this high-redshift quasar, from which we infer that most of the dust at high redshifts probably has the same origin.
ABSTRACT
Gastrin has a trophic effect on the mucosa of the gastrointestinal tract and seems to have the potential for promoting colonic cancerogenesis through a chronic stimulation of the epithelial proliferation. Plasma gastrin has been reported to be elevated in patients with colorectal neoplasms. The aim of the present study was to verify this observation. Presurgical serum levels of gastrin were compared between 49 patients with colorectal neoplasms and 47 controls hospitalized for other surgical lesions. Results show significantly higher gastrin levels of case group than controls: 72.72 + 85.41 vs. 46.79 + 24.09 pg/ml (p < 0.05), and provide support for the hypothesis of a gastrin-stimulated neoplastic growth enhancing at the same time the potential therapeutic role of reducing gastrin secretion.