The proper motion VS redshift relation for superluminal radio sources

Two models for superluminal radio sources predict sharp lower bounds for the apparent velocities of separation. The light echo model predicts a minimum velocityv _min=2c, and the dipole field model predictsv _min=4.446c. Yahil (1979) has suggested that, if either of these models is correct, thenv _min provides a standard velocity which can be used to determine the cosmological parametersH andq ₀. This is accomplished by estimating a lower envelope for the proper motion vs redshift relation. Yahil also argued that the procedure could easily be generalized to include a nonzero cosmical constant . We derive the formulas relating the proper motion to the redshiftz in a Friedmann universe with a nonzero . We show that the determination of a lower envelope for a given sample of measured points yields an estimate of the angle of inclination _i for each source in the sample. We formulate the estimation of the lower envelope as a constrained maximum likelihood problem with the constraints specified by the expected value of the largest order statistic for the estimated _i . We solve this problem numerically using an off-the-shelf nonlinearly constrained nonlinear optimization program from the NAg library. Assuming =0, we apply the estimation procedure to a sample of 27 sources with measured values , using both the light echo and the dipole field models. The fits giveH=103 km s^–1 Mpc^–1 for the light echo model andH=46 km s^–1 Mpc^–1 for the dipole field model. In both cases the fits giveq ₀=0.4, but the uncertainty in this result is too large to rule out the possibility thatq ₀>0.5. When is allowed to be a free parameter, we obtainH=105 km s^–1 Mpc^–1 for the light echo model andH=47 km s^–1 Mpc^–1 for the dipole field model. In both cases the fits giveq ₀=–1 and /H ₀ ² =6.7, but no significance can be attached to these results because of the paucity of measured data at hight redshifts. For all of the fits, we compute the corresponding estimates of the _i and compare the cumulative distribution of these values with that expected from a sample of randomly oriented sources. In all cases we find a large excess of sources at low-inclination angles (high apparent velocities). The expected selection effect would produce such an excess, but the excess is large enough to suggest a strong contamination of the sample by relativistic beam sources which would only be seen at low inclination angles.Applied Research Corporation     

Scenarios in Global Environmental Assessments: Key characteristics and lessons for future use

Over the last 10 years a large set of global environmental assessment studies has been published that include scenario projections. Comparison of these studies shows that there is actually a limited set of scenario families that form the basis of many scenarios used in different environmental assessments. Mapping these scenario families allow a simpler comparison across the different assessments. The fact that many assessments can be positioned within these families gives some confidence of their relevance. It is also noticeable that several recent assessments have been focusing on more focussed policy-scenarios as variant to a single baseline. This is partly a response to a different stage in the policy-making process. While there are clear advantages of both categories of scenarios (explorative scenarios and baseline/policy variants), it might be important to test the robustness of scenario outcomes of the policy-scenario approach against the different storyline scenario-families identified in this paper.     

Enhancing accessibility to web mapping systems with technology-aligned adaptive profiles

Web-based geographic information systems have advanced rapidly on the back of web-based technologies, increased bandwidths and access to Digital Earth imagery and functionality. However, these advances are causing its capabilities to slowly overtake those of end-users. Additionally, the introduction of non-desktop devices such as smartphones, tablets and netbooks is starting to undo progress made towards standardisation of web-based technology. Large variations in screen sizes, computational power, bandwidth, and operating environments are once again introducing the need to ensure software remains functional across different platforms, standards-compliant or not. These two issues highlight the need for a mechanism to tune content and capability to end-users and their environment, to prevent information and complexity overload in a field already troubled by poor usability, while promoting cross-platform compatibility. This paper proposes the use of adaptivity to accommodate for users from different backgrounds accessing web mapping systems in different technical environments. It describes adaptive profiles aligned to the finite number of states a system can adopt, rather than the limitless range of user or environment characteristics that cannot be adapted to. Each profile consists of a combination of adaptive states comprising functionality, information detail, or technical demands to optimise for individual users or technical environments.     

Pollen‐based biome reconstructions for Colombia at 3000, 6000, 9000, 12 000, 15 000 and 18 000 14C yr ago: Late Quaternary tropical vegetation dynamics

Colombian biomes are reconstructed at 45 sites from the modern period extending to the Last Glacial Maximum (LGM). The basis for our reconstruction is pollen data assigned to plant functional types and biomes at six 3000‐yr intervals. A reconstruction of modern biomes is used to check the treatment of the modern pollen data set against a map of potential vegetation. This allows the biomes reconstructed at past periods to be assessed relative to the modern situation. This process also provides a check on the a priori assignment of pollen taxa to plant functional types and biomes. For the majority of the sites, the pollen data accurately reflect the potential vegetation, even though much of the original vegetation has been transformed by agricultural practices. At 18 000 ¹⁴C yr BP, a generally cool and dry environment is reflected in biome, assignments of cold mixed forests, cool evergreen forests and cool grassland–shrub; the latter extending to lower altitudes than presently recorded. This signal is strongly recorded at 15 000 and 12 000 ¹⁴C yr BP, the vegetation at these times also reflecting a relatively cool and dry environment. At 9000 ¹⁴C yr BP there is a shift to biomes thought to result from slightly cooler environmental conditions. This trend is reversed by 6000 ¹⁴C yr BP; most sites, within a range of different environmental settings, recording a shift to more xeric biome types. There is an expansion of steppe and cool mixed‐forest biomes, replacing tropical dry forest and cool grassland–shrub biomes, respectively. These changes in biome assignments from the modern situation can be interpreted as a biotic response to mid‐Holocene climatic aridity. At 3000 ¹⁴C yr BP the shift is mainly to biomes characteristic of slightly more mesic environmental conditions. There are a number of sites that do not change biome assignment relative to the modern reconstruction, although the affinities that these sites have to a specific biome do change. These ‘anomalies’ are interpreted on a site‐by‐site basis. Spatially constant, but differential response of the vegetation to climatic shifts are related to changes in moisture sources and the importance of edaphic controls on the vegetation. The Late Quaternary reconstruction of large‐scale vegetation dynamics in Colombia allows an understanding of the environmental controls on these to be developed. In particular, shifts in the character of the main climatic systems that influence Colombian vegetation are described. Copyright © 2002 John Wiley & Sons, Ltd.     

Coastal morphometry as regulator of water exchange—a Swedish example

This is a paper from the Swedish research project ‘The coastal zone—scientific criteria for planners’. The goal has been to establish simple, general scientific methods for management of Swedish coastal waters. In this paper the focus is on a set of empirical data from 21 so-called type areas and on the exchange of surface water. The working hypothesis has been that the water retention (or residence) time is regulated by the morphometry. The theory has been verified. It has been shown that the water retention time can be determined from a formula based on only two key morphometric parameters, the exposure and the mean coastal width. It provides an 86% degree of explanation (r²=0·86) of the variation in empirically determined retention times and can be physically linked to the basic mass balance equation. The formula is valid for the bioproductive season (May–Oct.) and for small (1–100 km²) Swedish coastal areas. It cannot be directly applied to areas affected by heavy tides.     

Modern and early Holocene mollusc fauna of the Ounianga lakes (northern Chad): implications for the palaeohydrology of the central Sahara

The fresh and saline lakes of Ounianga Kebir and Serir in northeastern Chad are among the very few permanent aquatic ecosystems currently existing in the hyper‐arid core of the Sahara desert. The confirmed modern fauna of aquatic molluscs at Ounianga comprises three widespread species (Melanoides tuberculata, Biomphalaria pfeifferi and Lymnaea natalensis), of which only the first appears to maintain a thriving population. We recovered seven more species of gastropods, among which one is new to science (Gabbiella ouniangaensis), and one bivalve species from early Holocene outcrops of diatomaceous limestone at Ounianga Serir. All species except one are known to be commonly spread between lake and river systems by birds, and in its entirety this species‐rich fossil mollusc fauna of Ounianga Serir resembles that of other Saharan lake sites known to have been hydrologically isolated during the early Holocene. The impoverished modern mollusc fauna, which lacks even the widespread and opportunistic species Bulinus truncatus, may have become established relatively recently through new colonisation events, following eradication of the early Holocene mollusc fauna during a later episode of high salinity or desiccation. Copyright © 2011 John Wiley & Sons, Ltd.     

The subsurface of tidal-flat sediments as a model for the deep biosphere

Subsurface sediments of tidal flats and the marine deep biosphere share several features. Although on different scales in time and space, geochemical profiles and microbial successions follow the same trends. Microbial activities are governed by the availability of electron acceptors and the quality of electron donors. Two deep-biosphere sites and a shallow site from a German North Sea tidal flat were exemplarily chosen to compare geochemical settings and microbiological features. At all sites, microbial abundance was elevated at sulfate–methane transition zones. The known discrepancy between cultivation-based and molecular diversity assessments is observed, but similar microbial community compositions are found with each of the approaches at deep and shallow sites. These findings lead to the conclusion that we are presently unable to draw a cutting line between the shallow and the deep subsurface. Rather, there appears to exist only one “subsurface biosphere” with gradual differences. Therefore, tidal flats serve as an excellent model to perform microbiological experiments and to test novel techniques before applying them to much deeper and older samples. Responsible editor: Meinhard Simon