Comments on alternative calculations of the broadening of spectral lines of neutral sodium by H-atom collisions

With the exception of the sodium D-lines recent calculations of line broadening cross-sections for several multiplets of sodium by Leininger et al (2000) are in substantial disagreement with cross-sections interpolated from the tables of Anstee and O'Mara (1995) and Barklem and O'Mara (1997). The discrepancy is as large as a factor of three for the 3p-4d multiplet. The two theories are tested by using the results of each to synthesize lines in the solar spectrum. It is found that generally the data from the theory of Anstee, Barklem and O'Mara produce the best match to the observed solar spectrum. It is found, using a simple model for reflection of the optical electron by the potential barrier between the two atoms, that the reflection coefficient is too large for avoided crossings with the upper states of subordinate lines to contribute to line broadening, supporting the neglect of avoided ionic crossings by Anstee, Barklem and O'Mara for these lines. The large discrepancies between the two sets of calculations is a result of an approximate treatment of avoided ionic crossings for these lines by Leininger et al (2000).Comment: 18 pages, 5 ps figures included, to appear in J Phys B: At. Mol. Opt. Phy

Nestedness of Ectoparasite-Vertebrate Host Networks

Determining the structure of ectoparasite-host networks will enable disease ecologists to better understand and predict the spread of vector-borne diseases. If these networks have consistent properties, then studying the structure of well-understood networks could lead to extrapolation of these properties to others, including those that support emerging pathogens. Borrowing a quantitative measure of network structure from studies of mutualistic relationships between plants and their pollinators, we analyzed 29 ectoparasite-vertebrate host networks—including three derived from molecular bloodmeal analysis of mosquito feeding patterns—using measures of nestedness to identify non-random interactions among species. We found significant nestedness in ectoparasite-vertebrate host lists for habitats ranging from tropical rainforests to polar environments. These networks showed non-random patterns of nesting, and did not differ significantly from published estimates of nestedness from mutualistic networks. Mutualistic and antagonistic networks appear to be organized similarly, with generalized ectoparasites interacting with hosts that attract many ectoparasites and more specialized ectoparasites usually interacting with these same “generalized” hosts. This finding has implications for understanding the network dynamics of vector-born pathogens. We suggest that nestedness (rather than random ectoparasite-host associations) can allow rapid transfer of pathogens throughout a network, and expand upon such concepts as the dilution effect, bridge vectors, and host switching in the context of nested ectoparasite-vertebrate host networks

Novel combinations of aquifer thermal energy storage with solar collectors, soil remediation and other types of geothermal energy systems

Aquifer Thermal Energy Storage (ATES) system make use of the groundwater to exchange energy with the building: in winter, groundwater is pumped from the warm well to the buildings heat exchanger and the building extracts heat from the groundwater as energy source for the heat pumps, while the groundwater will be injected in the cold well at lower temperature; in summer, the direction will be reversed and groundwater will be pumped out of the cold well to the heat exchanger, where the building will gather cold from the groundwater. ATES combined with solar collectors at two sites in Belgium and the Netherlands proved to allow for additional efficiencies and energy savings. Pilot sites showed promising results for combining ATES with groundwater remediation by enhanced natural attenuation for chlorinated solvents. Pilot sites were also realized in two countries with a less mature ATES market, Spain and Italy. In Spain an innovative hybrid technology between a closed loop and an open loop system has been tested, allowing ATES to be used also in water scarcity conditions. In Italy, a small scale integration with a cold low temperature district heating system has been realized. Technical and economic performances of the pilots are briefly described. The lessons learnt in the pilots provide useful insights for the replication of these solutions