On the existence of a second scale of convection in the upper mantle

Summary. This paper is concerned with an examination of the possibility that there might exist a small scale of convective circulation beneath the oceanic lithosphere. Recent suggestions that this might be the case have been made in an effort to understand why the bathymetry of the sea-floor deviates from the prediction of boundary layer theory for ages in excess of about 100 Ma. The energy source which sustains the secondary motion is supposed to be found in the steep temperature gradient near the planetary surface which is itself presumably maintained by the large-scale convective circulation associated with plate creation and destruction. Here we investigate the extent to which the temperature dependence of viscosity may act so as to stabilize the upper boundary layer against disruption by such secondary instability. If the viscosity profile is monotonie and the asymptotic upper mantle viscosity is about 10²²poise, as suggested by post-glacial rebound data, then the existence of the second scale is extremely unlikely. On the other hand, if a sufficiently pronounced low viscosity zone does exist under old sea-floor then the development of such a second scale cannot be ruled out completely. Some recently obtained geophysical evidence is reviewed which suggests that this is unlikely to be the case.     

Density and conductivity properties of Na−CO3−Cl−SO4 brine from Mono Lake, California, USA

Relationships among conductivity, temperature, total dissolved solids (TDS), and density were determined for hypersaline brine (TDS, 83 g kg⁻¹) from Mono Lake. A theoretical estimate of density based on ionic composition and calculated partial molar volumes compared well with actual measurements (difference, 390 ppm). However, an empirically derived equation of state based on temperature and conductivity provides the most accurate density estimates (residual errors, 190 ppm) and can be used with data collected with CTD profilers.     

The impact of binary-star yields on the spectra of galaxies

One of the complexities in modelling integrated spectra of stellar populations is the effect of interacting binary stars besides Type Ia supernovae (SNeIa). These include common envelope systems, cataclysmic variables, novae, and are usually ignored in models predicting the chemistry and spectral absorption line strengths in galaxies. In this paper, predictions of chemical yields from populations of single and binary stars are incorporated into a galactic chemical evolution model to explore the significance of the effects of these other binary yields. Effects on spectral line strengths from different progenitor channels of SNeIa are also explored. Small systematic effects are found when the yields from binaries, other than SNeIa, are included, for a given star formation history. These effects are, at present, within the observational uncertainties on the line strengths. More serious differences can arise in considering different types of SNIa models, their rates and contributions.     

Configurations of community in flood risk management

ABSTRACT

Despite a notable increase in the literature on community resilience, the notion of ‘community’ remains underproblematised. This is evident within flood risk management (FRM) literature, in which the understanding and roles of communities may be acknowledged but seldom discussed in any detail. The purpose of the article is to demonstrate how community networks are configured by different actors, whose roles and responsibilities span spatial scales within the context of FRM. Accordingly, the authors analyse findings from semi-structured interviews, policy documents, and household surveys from two flood prone areas in Finnish Lapland. The analysis reveals that the ways in which authorities, civil society, and informal actors take on multiple roles are intertwined and form different types of networks. By implication, the configuration of community is fuzzy, elusive and situated, and not confined to a fixed spatiality. The authors discuss the implications of the complex nature of community for FRM specifically, and for community resilience more broadly. They conclude that an analysis of different actors across scales contributes to an understanding of the configuration of community, including community resilience, and how the meaning of community takes shape according to the differing aims of FRM in combination with differing geographical settings.     

UBV photometry of lapetus: Results from five apparitions

Measurements of the brightness and B-V color index of the leading and trailing hemispheres of Iapetus during the past five apparitions of Saturn are presented. The dependence of brightness on solar phase angle is determined for the two faces of the satellite. After correction for solar phase angle and distance effects, the brighter trailing hemisphere of Iapetus was found to be constant in brightness and color index throughout the interval covered by the observations. The brightness of the dark leading hemisphere, however, decreased by about 0.2 mag over the same period, and its B-V color index reddened by 0.05 mag. These changes are interpreted as evidence for the existence of a bright southern pole cap on Iapetus.