Centrality dependence of charged hadron and strange hadron elliptic flow from sqrt(s_NN) = 200 GeV Au+Au collisions

We present STAR results on the elliptic flow v_2 of charged hadrons, strange and multi-strange particles from sqrt(s_NN) = 200 GeV Au+Au collisions at RHIC. The detailed study of the centrality dependence of v_2 over a broad transverse momentum range is presented. Comparison of different analysis methods are made in order to estimate systematic uncertainties. In order to discuss the non-flow effect, we have performed the first analysis of v_2 with the Lee-Yang Zero method for K_s^0 and Lambda. In the relatively low p_T region, p_T <= 2 GeV/c, a scaling with m_T - m is observed for identified hadrons in each centrality bin studied. However, we do not observe v_2(p_T) scaled by the participant eccentricity to be independent of centrality. At higher p_T, 2 GeV/c <= p_T <= 6 GeV/c, v_2 scales with quark number for all hadrons studied. For the multi-strange hadron Omega, which does not suffer appreciable hadronic interactions, the values of v_2 are consistent with both m_T -m scaling at low p_T and number-of-quark scaling at intermediate p_T. As a function of collision centrality, an increase of p_T-integrated v_2 scaled by the participant eccentricity has been observed, indicating a stronger collective flow in more central Au+Au collisions.Comment: 25 pages, as accepted for Phys. Rev. C. The data tables are at http://drupal.star.bnl.gov/STAR/files/starpublications/108/data.htm

A spatial analysis of pit latrine density and groundwater source contamination

This study aims to assess the relationship between chemical and microbial contamination of groundwater sources and a range of potential hazards in two peri-urban areas of Kisumu, Kenya where shallow wells and pit latrines are widely used. From 1998-2004, 263 samples were taken from 61 groundwater sources and tested for thermotolerant coliforms. 18 of these sources were also tested for chemical contaminants, including nitrate, chloride and fluoride. The locations of all water sources, buildings, and pit latrines in the study area were surveyed. Local pit latrine densities were calculated using a Geographic Information System (GIS). 10 out 18 samples were above World Health Organization guideline values for nitrate, 236 out of 263 were positive for thermotolerant coliforms, and all were above guideline values for fluoride. There was no relationship between thermotolerant coliform levels and daily rainfall patterns, nor with sanitary risk inspection scores for samples from shallow wells (r=0.01, p=0.91, n=191). The density of pit latrines within a 100 metre radius was significantly correlated with nitrate and chloride levels (r=0.64, p=0.004 and r=0.46, p=0.05 respectively) but not with TTC (r=0.22, p=0.11). These results illustrate both the public health risks associated with shallow groundwater sources, onsite sanitation, and high population density. These findings have implications for current policies that promote latrine construction, especially in peri-urban areas of high population density. More comprehensive studies of larger communities should be commissioned to extend this analysis of the links between latrine density and groundwater contamination and so identify the contingent policy risks