Instability of radially spreading extensional flows. Part 2. Theoretical analysis

The interface of a strain-rate-softening fluid that displaces a low-viscosity fluid in a circular geometry with negligible drag can develop finger-like patterns separated by regions in which the fluid appears to be torn apart. Such patterns were observed and explored experimentally in Part 1 using polymeric solutions. They do not occur when the viscosity of the displacing fluid is constant, or when the displacing fluid has no-slip conditions along its boundaries. We investigate theoretically the formation of tongues at the interface of an axisymmetric initial state. We show that finger-like patterns can emerge when circular interfaces of strain-rate-softening fluids displace low-viscosity fluids between stress-free boundaries. The instability, which is fundamentally different from the classical Saffman–Taylor viscous fingering, is driven by the tension that builds up along the circular front of the propagating fluid. That destabilising tension is a geometrical consequence and is present independently of the nonlinear properties of the fluid. Shear stresses stabilise the growth either along extended circumferential streamlines or through a street of vortices. However, such stabilising processes become weaker, thereby allowing the instability to develop, the more strain-rate-softening the fluid is. The theoretical model that we present predicts the main experimental observations made in Part 1. In particular, the patterns we predict using linear-stability theory are consistent with the strongly nonlinear experimental patterns. Our model depends on a single dimensionless number representing the power-law exponent, which implies that the instability we describe could arise in any extensional flow of strain-rate-softening material, ranging from suspensions that rupture in squeeze experiments to rifts formed in ice shelves.Israel Science Foundation (grant No. 1368/16

Tidal controls on the flow of ice streams

The flow of many Antarctic ice streams is known to be significantly influenced by tides. In the past, modeling studies have implemented the tidal forces acting on a coupled ice stream/ice shelf system in a number of different ways, but the consequences that this has on the modeled response of ice streams to tides have, until now, not been considered. Here we investigate for the first time differences in model response that are only due to differences in the way tidal forcings are implemented. We find that attempts to simplify the problem by neglecting flexural stresses are generally not valid and forcing models with only changes in ocean back pressure will not capture either the correct amplitudes or length scale

Sea ice dynamics across the Mid-Pleistocene transition in the Bering Sea.

Sea ice and associated feedback mechanisms play an important role for both long- and short-term climate change. Our ability to predict future sea ice extent, however, hinges on a greater understanding of past sea ice dynamics. Here we investigate sea ice changes in the eastern Bering Sea prior to, across, and after the Mid-Pleistocene transition (MPT). The sea ice record, based on the Arctic sea ice biomarker IP25 and related open water proxies from the International Ocean Discovery Program Site U1343, shows a substantial increase in sea ice extent across the MPT. The occurrence of late-glacial/deglacial sea ice maxima are consistent with sea ice/land ice hysteresis and land-glacier retreat via the temperature-precipitation feedback. We also identify interactions of sea ice with phytoplankton growth and ocean circulation patterns, which have important implications for glacial North Pacific Intermediate Water formation and potentially North Pacific abyssal carbon storage

Paying is believing: the effect of costly information on Bayesian updating

The supposed irrelevance of historical costs for rational decision making has been the subject of much interest in the economic literature. In this paper we explore whether individual decision making under risk is affected by the cost of information. To do so one must distinguish the effect of cost from self selection by individuals who value information the most. Outside of the laboratory it is difficult to disentangle these two effects. We thus create an experimental environment where subjects are o¤ered additional, useful and identical information on the state of the world across treatments. We find a systematic effect of sunk costs on the manner in which subjects update their beliefs. Subjects over-weigh costly information relatively to free information, which results in a ‘push’of beliefs towards the extremes. This shift does not necessarily lead to behavior more attuned with Bayesian updating. We find that an intensification of representativeness bias due to cost is the most likely explanation of our results

Information at a cost

The supposed irrelevance of historical costs for rational decision making has been the subject of much interest in the economic literature. In this paper we explore whether individual decision making under risk is affected by the cost of the supplied information. Outside of the lab, it is difficult to disentangle the effect of the cost of information itself from the effect of self-selection by individuals who tend to gain the most from this information. We thus create an environment in the lab where subjects are offered additional, useful and identical information on the state of the world across treatments. By varying the cost of information we can distinguish between selection and sunk cost effects. We find a systematic effect of sunk costs on the manner in which subjects update their beliefs on the state of the world. Subjects over-weigh costly information relatively to free information, which results in a 'push' of beliefs towards the extremes. This shift does not necessarily lead to behavior more attuned with Bayesian updating

Changes in population structure and body dimensions of two xanthid crabs: A long-term study in a single boulder-shore

Abstract Two xanthid crab species were studied during 29 months over a period of 14 years between 1986 and 1999 all in exactly the same boulder shore. One of the crab species studied was the xanthid, Eriphia verrucosa (Forskåll, 1775) with 60 specimens, the other species, Xantho poressa (Olivi, 1792), with 155 specimens. A significant change in numbers of both males and females of E. verrucosa was noticeable between 1986 and 1996 with a marked drop in numbers between these years. In 1997 male numbers increased again to almost their previous numbers in the population during 1986. The population of X. poressa declined significantly towards the end of the study period. Numbers of both genders peaked in spring and again, in summer. There was generally a decline in numbers of both crab species during autumn and winter. Thus, the average capture during the seasons was highest in spring for males of both E. verrucosa, and X. poressa. The body dimensions: mass, carapace length (CL) and width (CW) were measured in both xanthids. The aim of this long-term study was to determine whether temporal changes in the population structure and allometric changes in the dimensions of these crabs took place. Only such long-term observations could reveal these changes in population