Methane bubbling from Siberian thaw lakes as a positive feedback to climate warming

Large uncertainties in the budget of atmospheric methane, an important greenhouse gas, limit the accuracy of climate change projections. Thaw lakes in North Siberia are known to emit methane, but the magnitude of these emissions remains uncertain because most methane is released through ebullition (bubbling), which is spatially and temporally variable. Here we report a new method of measuring ebullition and use it to quantify methane emissions from two thaw lakes in North Siberia. We show that ebullition accounts for 95 per cent of methane emissions from these lakes, and that methane flux from thaw lakes in our study region may be five times higher than previously estimated. Extrapolation of these fluxes indicates that thaw lakes in North Siberia emit 3.8 teragrams of methane per year, which increases present estimates of methane emissions from northern wetlands (< 6-40 teragrams per year; refs 1, 2, 4-6) by between 10 and 63 per cent. We find that thawing permafrost along lake margins accounts for most of the methane released from the lakes, and estimate that an expansion of thaw lakes between 1974 and 2000, which was concurrent with regional warming, increased methane emissions in our study region by 58 per cent. Furthermore, the Pleistocene age (35,260-42,900 years) of methane emitted from hotspots along thawing lake margins indicates that this positive feedback to climate warming has led to the release of old carbon stocks previously stored in permafrost.     

The intense starburst HDF 850.1 in a galaxy overdensity at z ≈ 5.2 in the Hubble Deep Field

The Hubble Deep Field provides one of the deepest multiwavelength views of the distant Universe and has led to the detection of thousands of galaxies seen throughout cosmic time. An early map of the Hubble Deep Field at a wavelength of 850?micrometres, which is sensitive to dust emission powered by star formation, revealed the brightest source in the field, dubbed HDF?850.1 (ref. 2). For more than a decade, and despite significant efforts, no counterpart was found at shorter wavelengths, and it was not possible to determine its redshift, size or mass. Here we report a redshift of z = 5.183 for HDF?850.1, from a millimetre-wave molecular line scan. This places HDF?850.1 in a galaxy overdensity at z?≈?5.2, corresponding to a cosmic age of only 1.1?billion years after the Big Bang. This redshift is significantly higher than earlier estimates and higher than those of most of the hundreds of submillimetre-bright galaxies identified so far. The source has a star-formation rate of 850 solar masses per year and is spatially resolved on scales of 5 kiloparsecs, with an implied dynamical mass of about 1.3?×?10(11) solar masses, a significant fraction of which is present in the form of molecular gas. Despite our accurate determination of redshift and position, a counterpart emitting starlight remains elusive.     

Impact of corrections for dynamic selection bias on forecasts of retention behavior

We investigate the impact of corrections for dynamic selection bias on forecasting accuracy in a multi‐period stay/leave model. While corrections for selection bias are needed for consistent coefficient estimates, they do not necessarily produce more accurate forecasts than uncorrected techniques. Theorem 1 shows that, apart from estimation errors, a shrinkage principle applies: the heterogeneity restriction imposed by uncorrected and combination techniques improves accuracy for forecasting individuals that leave, and hurts accuracy for forecasting individuals that stay. This has important implications for decision making because of the potential for asymmetric losses. We also present an illustrative empirical application and results from Monte Carlo experiments. We find that differences in relative accuracy vary directly with the degree of selection bias and inversely with the percentage of the initial population that stays. Copyright © 2007 John Wiley & Sons, Ltd.     

Comparison of the mode of action of oxytocin and lysine-vasopressin on the isolated rat uterus

Zusammenfassung Ein der Rezeptorentheorie zugrunde liegender Vergleich der Dosis-Wirkungs-Beziehung zwischen Oxytocin und Lysine-vasopressin an der isolierten Rattengebärmutter hat gezeigt, dass während der Evolution die Oktapeptide der Neurohypophyse sowohl ihre Affinität für den Rezeptor als auch ihre maximale Aktivität bei Absättigung des Rezeptors, «intrinsic activity», verändert haben. Weiterhin wurde gefunden, dass Magnesium-Ionen in einer Konzentration von 0.5 mM nicht nur, wie bisher angenommen, die Affinität der Hormone, sondern auch ihre maximale Aktivität bei Absättigung des Rezeptors beeinflussen.     

Inactivation studies of angiotensin II by purified enzymes

Zusammenfassung Die hochgereinigte Arylamidase vom Schweinehirn spaltet, im Gegensatz zur ebenfalls isolierten Säureprotease und Aminopeptidase, Ile⁵-Angiotensin II, wobei die ersten 5 N-terminalen Aminosäuren von hydrolytischen Enzymen freigesetzt werden.