Contrails reduce daily temperature range

The potential of condensation trails (contrails) from jet aircraft to affect regional-scale surface temperatures has been debated for years, but was difficult to verify until an opportunity arose as a result of the three-day grounding of all commercial aircraft in the United States in the aftermath of the terrorist attacks on 11 September 2001. Here we show that there was an anomalous increase in the average diurnal temperature range (that is, the difference between the daytime maximum and night-time minimum temperatures) for the period 11-14 September 2001. Because persisting contrails can reduce the transfer of both incoming solar and outgoing infrared radiation and so reduce the daily temperature range, we attribute at least a portion of this anomaly to the absence of contrails over this period.     

Sexual selection for sensory exploitation in the frog Physalaemus pustulosus

The sensory bases of species and population mate preferences are well known; in frogs properties of the female auditory system influence such preferences. By contrast, there is little understanding of how sensory characteristics could result in sexual selection within a population. One possible mechanism is that females are more sensitive to male courtship signals that deviate from the population mean. We document this mechanism in the frog Physalaemus pustulosus. Female basilar papilla tuning is biased toward lower-than-average frequencies in the 'chuck' portion of the male's call, explaining female preference for the lower-frequency chucks produced by larger males. The tuning does not differ between P. pustulosus and its close relative P. coloradorum, a species in which males never evolved the ability to produce chucks; thus the female tuning evolved before the chuck and therefore the chuck played no role in the evolution of the preference. This allows us to reject two popular hypotheses for the evolution of this female preference (runaway sexual selection and natural selection) in favour of a third: sexual selection for sensory exploitation.     

Studies on the hydrolysis of bradykinin by angiotensin-converting enzyme (kininase II)

Summary Arg-Pro-Pro-Gly-Phe, the N-terminal pentapeptide of bradykinin, is not an inhibitor of angiotensin-converting enzyme and is not hydrolyzed by the enzyme. Arg-Pro-Pro, the N-terminal tripeptide is a relatively potent (IC₅₀=2.3×10⁶ M) inhibitor but its higher homolog, Gly-Arg-Met-Lys-Arg-Pro-Pro is not an inhibitor of angiotensin-converting enzyme.This work was supported in part by grants from the US Public Health Service (HL 18415, HL 15691, HL 19764) and the John A. Hartford Foundation, Inc., and by the Medical Research Service of the Veterans Administration.     

The size of motor units in laryngeal muscles of the rat

Summary The size of motor units in rat laryngeal muscles was determined by correlating the number of neurons labeled by i.m. injections of horseradish peroxidase with the number of motor end plates stained for acetylcholinesterase. The cricothyroid has a motor unit size of 8 muscle fibers per motor neuron and the posterior cricoarytenoid 4–5 muscle fibers per motor neuron.     

Presence of modified fibroblasts in granulation tissue and their possible role in wound contraction

Résumé Au cours de la contraction du tissu de granulation, de nombreux fibroblastes acquièrent des caractéristiques ultrastructurelles qui les rendent semblables à des cellules musculaires lisses. Il est probable que ces éléments modifiés jouent un rôle dans le processus de contraction des plaies.

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This work was supported by the Fonds National Suisse de la Recherche Scientifique (grants No. 5338.3 and No. 3.356.70).     

Nucleosynthetic signatures of the first stars

The chemically most primitive stars provide constraints on the nature of the first stellar objects that formed in the Universe; elements other than hydrogen, helium and traces of lithium present within these objects were generated by nucleosynthesis in the very first stars. The relative abundances of elements in the surviving primitive stars reflect the masses of the first stars, because the pathways of nucleosynthesis are quite sensitive to stellar masses. Several models have been suggested to explain the origin of the abundance pattern of the giant star HE0107-5240, which hitherto exhibited the highest deficiency of heavy elements known. Here we report the discovery of HE1327-2326, a subgiant or main-sequence star with an iron abundance about a factor of two lower than that of HE0107-5240. Both stars show extreme overabundances of carbon and nitrogen with respect to iron, suggesting a similar origin of the abundance patterns. The unexpectedly low Li and high Sr abundances of HE1327-2326, however, challenge existing theoretical understanding: no model predicts the high Sr abundance or provides a Li depletion mechanism consistent with data available for the most metal-poor stars.