Some effects of small-scale metallicity variations in cooling flows

In an attempt to reconcile recent spectral data with predictions of the standard cooling flow model, it has been suggested that the metals in the intracluster medium (ICM) might be distributed inhomogeneously on small scales. We investigate the possible consequences of such a situation within the framework of the cooling flow scenario. Using the standard isobaric cooling flow model, we study the ability of such metallicity variations to preferentially suppress low-temperature line emission in cooling flow spectra. We then use simple numerical simulations to investigate the temporal and spatial evolution of the ICM when the metals are distributed in such a fashion. Simulated observations are used to study the constraints real data can place on conditions in the ICM. The difficulty of ruling out abundance variations on small spatial scales with current observational limits is emphasized. We find that a bimodal distribution of metals may give rise to interesting effects in the observed abundance profile, in that apparent abundance gradients with central abundance drops and off-centre peaks, similar to those seen recently in some clusters, are produced. Different elements behave in different fashion as governed by the temperature dependence of their equivalent widths. Our overall conclusion is that, whilst this process alone seems unlikely to be able to account for the sharp reduction in low temperature emission lines seen in current spectral data, a contribution at some level is possible and difficult to rule out. The possibility of small-scale metallicity variations should be considered when analysing high resolution cluster X-ray spectra.Comment: 14 pages, 10 figures. Accepted for publication in MNRA

Ranking the Risks: The 10 Pathogen-Food Combinations With the Greatest Burden on Public Health

Examines food-borne pathogens with the highest disease burdens and the top ten foods most commonly contaminated by them, such as salmonella in poultry, toxoplasma in pork, and listeria in deli meats. Makes policy recommendations for improving prevention

Adjacent habitat distribution and management of the lone star tick in Tennessee

A six-year treatment program involving the administration of ivermectin to whitetailed deer to manage a population of lone star ticks (LST) implicated in the transmission of Ehrlichia chaffeensis Anderson, Dawson, Jones & Wilson to humans in 1993 was performed in Fairfield Glade, TN, on the Cumberland Plateau from 1994 to 1999. Ehrlichia chaffeensis is the causative agent of human monocytic ehrlichiosis (HME). Two concentrations of ivermectin, 250 mg and 500 mg / 22.7 kg whole kernel corn, were administered from 1994 to 1996 and 1997 to 1999, respectively. Treatment was typically initiated in March and ended in July of each year in compliance with Food and Dmg Administration guidelines. All free-living LST stages were sampled in the first treatment area (FTA) and non-treatment area (NonTA) from 1994 to 1999. These sites and an additional treatment area (NTA) were sampled from 1997 to 1999. In each of the three areas, three sites were selected, and wooded and open, grassy areas were sampled at each site. Cloth flags (1 m X 1 m were used to sample all free-living LST stages. In addition CO2 traps (1 m x 1 m) were used to sample adult and nymphal LSTs. Reductions in all stages of the LST population were observed in the FTA from 1994 to 1996 and the NTA from 1997 to 1999 relative to the NonTA. The effect of the two concentrations of ivermectin was equivalent on male and female LSTs. Natural fluctuations in the LST population and absence of 1999 larval mass data at the time of this publication make this estimate for LST nymphs and larval masses inconclusive. Comparison of two sampling methods revealed that CO2 traps placed in wooded habitats during spring captured LST males and females more frequently. Nymphal LSTs were captured more frequently by cloth flags in wooded habitats during summer and early fall. No comparison was possible for larval masses of LSTs, because CO2 traps were not used to sample them. Adjacent habitats of woods, ecotone and open, grassy areas were sampled to determine the most likely area one would encounter LSTs. Three sites were selected on the golf course that was the focus of the 1993 HME epidemic and three additional roadside sites were selected in the same area. Lone star tick larval masses were most abundant 5 and 10 m into the woods and nymphs were most abundant 10 m into the woods. No differences were found for LST nymphs and larval masses between golf and roadside sites. Few adults were captured on the six sites which prevented thorough statistical analysis. Fisher\u27s exact test (FET) suggested that males were most abundant in the ecotone of both golf and roadside sites. Females appeared most abundant in the ecotone and 10 m into the woods on golf course sites, but in roadside sites they were most abundant 10 m into the woods

Cholera—Modern Pandemic Disease of Ancient Lineage

Environmental triggers may lead to increases in Vibrio cholerae in environmental reservoirs, with spillover into human populations