A comparative analysis of thermophysical properties correlations for n-paraffins to be used in wax precipitation modeling

The performance of a thermodynamic wax precipitation model strongly depends upon the n-paraffin thermophysical properties used. In order to estimate them, several correlations have been proposed, and their values have a great impact on both calculated wax disappearance temperature (WDT) and amount of wax precipitated at each temperature (WPC). The main goal of this work is to evaluate the correlations available for the relevant thermophysical properties aiming at achieving a reliable wax precipitation modeling. The methodology used involves the direct comparison of the correlations with the values of pure n-paraffin properties, and indirect evaluation by their use in the estimation of wax disappearance temperatures, the amount of wax precipitated at each temperature, and DSC experimental curves. This study contemplates two thermodynamic approaches for paraffin precipitation: the solid solution (SS), which considers the formation of one solid solution; and the multisolid phase model (MS), that assumes that each solid phase consists of a pure component.publishe

Opting out increases HIV testing in a large sexually transmitted infections outpatient clinic

In January 2007, opt-out HIV testing replaced provider-initiated testing at the sexually transmitted infections (STI) outpatient clinic in Amsterdam, The Netherlands. The effect of the opt-out strategy on the uptake of HIV testing was studied and factors associated with refusal of HIV testing were identified. Data routinely collected at the STI clinic were analysed separately for men who have sex with men (MSM) and heterosexuals. Logistic regression analysis was used to identify factors associated with opting out. In 2007, 12% of MSM and 4% of heterosexuals with (presumed) negative or unknown HIV serostatus declined HIV testing. Refusals gradually decreased to 7% and 2% by the year end. In 2006, before the introduction of opt-out, 38% of MSM and 27% of heterosexuals declined testing. The proportion of HIV-positive results remained stable among MSM, 3.4% in 2007 versus 3.7% in 2006, and among heterosexuals, 0.2% in 2007 versus 0.3% in 2006. In both groups factors associated with opting out were: age >or=30 years, no previous HIV test, the presence of STI-related complaints and no risky anal/vaginal intercourse. Among heterosexuals, men and non-Dutch visitors refused more often; among MSM, those warned of STI exposure by sexual partners and those diagnosed with gonorrhoea or syphilis refused more often. An opt-out strategy increased the uptake of HIV testing. A sharp increase in testing preceeded a more gradual increase, suggesting time must pass to optimise the new strategy. A small group of visitors, especially MSM, still opt out. Counselling will focus on barriers such as fear and low risk perception among high-risk visitors considering opting ou