Detection of pre-main-sequence binaries using spectro-astrometry

The technique of spectro-astrometry (measuring the wavelength dependence of the position of an object) has been used to observe a number of pre-main-sequence stars. Several previously known binaries with separations down to 100 milliarcseconds (mas) were easily detected in these observations by the presence of a broad feature in the position spectrum on the Hα line. The observations show that T CrA is a pre-main-sequence binary with a PA of 275°, and a separation of at least 140 mas. The binary period may be short enough for orbital motion to be detectable. The technique has the potential to find new binaries with smaller separations than have been possible by other methods. The observations can also reveal small-scale structure associated with the outflows in these systems as is clearly seen by the detection of structure corresponding to the jet in Z CMa.     

The paleomagnetic record from deep-sea sediment cores

The paleomagnetic record of deep-sea sediment cores is compared with that which would be expected from our knowledge of the Earth's magnetic field. It is found that some of the scatter in directions of magnetization obtained from deep-sea cores is removed in cores with very low sedimentation rate, the cause being that the secular variation of the Earth's magnetic field is more completely averaged out over the finite size of each sample, when these samples comprise a longer time span of sedimentation. Corrections have been applied to the results from a series of cores in order to obtain the inclination of the average direction of magnetization from the average inclination and the scatter of inclination. These corrected inclination values confirm the hypothesis that the average Earth's field over the past few million years has been similar to an axial dipole displaced towards the North Pole. The amount of displacement obtained was 168 km. The record of short-period polarity intervals within the Brunhes, the Matuyama and the Gauss epochs was studied. It was shown that these intervals are very scattered in position. It is thought that some hitherto undiscovered short-period polarity intervals may be responsible for part of the scatter, but it is also highly likely that many samples give spurious reversals (i.e., ones not caused by the Earth's magnetic field).The possible correlation between climatic changes and the Earth's magnetic field is examined. It is concluded that the cores which show correlations between direction and/or intensity of magnetization and climatic indicators, thus suggesting the possible correlation between climate and the Earth's magnetic field, are not accurately recording the relevant parameters of the Earth's magnetic field. The correlation must be caused by climatic effects which have a direct influence on the magnetization of the sediments.Very little is known about the mechanisms of magnetization in deep-sea sediment cores, and there are several unexplained phenomena, such as the fact that many cores have maximum susceptibilities which are vertical, and the fact that cores differ widely in their ability to record accurately the Earth's magnetic field.     

Heat exchanges in muddy intertidal sediments: Chichester Harbour,West Sussex,England

Temperature observations made from a lightweight tower assembly in Chichester Harbour, West Sussex, demonstrate that marked changes in temperature at intertidal mud surfaces occur on a flow tide. The magnitude and direction of these changes are dependent on the external atmospheric and marine conditions, and on the timing of tidal inundation. Calculated heat exchange values for the 3h prior to high water fall into four distinct timing zones. There is a relationship between thermal stress, measured as rate of change of temperature with time, and time of high water. Mud surfaces are net receivers of heat energy from inundating water layers.     

Synergistic feedbacks between ocean and vegetation on mid- and high-latitude climates during the mid-Holocene

Simulations with the IPSL atmosphere–ocean model asynchronously coupled with the BIOME1 vegetation model show the impact of ocean and vegetation feedbacks, and their synergy, on mid- and high-latitude (>40°N) climate in response to orbitally-induced changes in mid-Holocene insolation. The atmospheric response to orbital forcing produces a +1.2 °C warming over the continents in summer and a cooling during the rest of the year. Ocean feedback reinforces the cooling in spring but counteracts the autumn and winter cooling. Vegetation feedback produces warming in all seasons, with largest changes (+1 °C) in spring. Synergy between ocean and vegetation feedbacks leads to further warming, which can be as large as the independent impact of these feedbacks. The combination of these effects causes the high northern latitudes to be warmer throughout the year in the ocean–atmosphere-vegetation simulation. Simulated vegetation changes resulting from this year-round warming are consistent with observed mid-Holocene vegetation patterns. Feedbacks also impact on precipitation. The atmospheric response to orbital-forcing reduces precipitation throughout the year; the most marked changes occur in the mid-latitudes in summer. Ocean feedback reduces aridity during autumn, winter and spring, but does not affect summer precipitation. Vegetation feedback increases spring precipitation but amplifies summer drying. Synergy between the feedbacks increases precipitation in autumn, winter and spring, and reduces precipitation in summer. The combined changes amplify the seasonal contrast in precipitation in the ocean–atmosphere-vegetation simulation. Enhanced summer drought produces an unrealistically large expansion of temperate grasslands, particularly in mid-latitude Eurasia.     

Temporal variability of disturbances: is this important for diversity and structure of marine fouling assemblages?

Natural communities are constantly changing due to a variety of interacting external processes and the temporal occurrence and intensity of these processes can have important implications for the diversity and structure of marine sessile assemblages. In this study, we investigated the effects of temporal variation in a disturbance regime, as well as the specific timing of events within different regimes, on the composition and diversity of marine subtidal fouling assemblages. We did this in a multi‐factorial experiment using artificial settlement tiles deployed at two sites on the North East coast of England. We found that although there were significant effects of disturbances on the composition of assemblages, there were no effects of either the variation in the disturbance regime or the specific timing of events on the diversity or assemblage composition at either site. In contrast to recent implications we conclude that in marine fouling assemblages, the variability in disturbance regimes (as a driving force) is unimportant, while disturbance itself is an important force for structuring robust ecosystems.     

Assessing the Potential of Low-Impact Development Techniques on Runoff and Streamflow in the Templeton Gap Watershed,Colorado

This study examines how the impact of impervious surface in the Templeton Gap watershed (Colorado) could be reduced through the use of low-impact development (LID) strategies. LID is a sustainable stormwater approach to land management that retains runoff close to the source by preserving natural landscape features and limiting imperviousness. Our research indicates that LID techniques could reduce peak flows generated by stormwater runoff, allow city engineers to restore the stream channel to a more natural state, and improve the safety of residents and the security of property below the levee. This study developed a model of the Templeton Gap watershed and its associated stormwater infrastructure using the Stormwater Management Model (SWMM) developed by the U.S. Environmental Protection Agency (EPA). Specifically designed for small urban watersheds, SWMM allows users to accurately represent stormwater runoff dynamics and project the impact of hypothetical LID features such as porous pavement, rain gardens, and infiltration trenches on runoff and streamflow.     

Seeing ghosts: parsing China’s “ghost city” controversy

Controversy has arisen in recent years over the creation of so-called “ghost cities” across China. The ghost city term tends to describe large-scale urban areas, sometimes planned as new towns, featuring an abundance of new built space and appearing to also have extremely low tenancy. This article examines key questions related to the ghost city phenomenon, such as: what is a ghost city? Are ghost cities driven by a tendency toward over-supply in housing? How are local-level political incentives aligned to foster the production of ghost cities? Are ghost cities temporary anomalies or structural features of China’s urban-led economic growth model? We discuss recent scholarly research into ghost cities and present original findings to show how an excess of urban space may plague certain Chinese cities.