Despite the fact that needle exchange was introduced in Vancouver as early as 1988, needle sharing remains common. An analysis was conducted to identify determinants of borrowing used needles among subjects participating in a case-control study. IDUs had a documented HIV seroconversion after 1 January, 1994 (n = 89), or repeatedly tested HIV-seronegative after this date (n = 192). Interviewer-administered questionnaires focused on drug use, sexual behaviours, source of needles and depression. Subjects were asked if they had "ever been forced to have sex" as a child, youth or adult. Logistic regression identified determinants of borrowing needles. After controlling for HIV serostatus, factors independently associated with borrowing were injecting > 4 times/day, polydrug use, and ever experiencing non-consensual sex (AOR = 3.4, 95% CI: 1.8, 6.5). Depression was associated with borrowing, although not independently so. Homosexual activity was independently associated with borrowing among males, whereas living with a sexual partner was an independent predictor for females. Access or barriers to clean needle use were not associated with borrowing. Social determinants, particularly a history of sexual abuse, are among the most significant predictors of needle borrowing among Vancouver's IDUs. Early identification of these factors should be a component of HIV prevention programmes.
We generalize the de nition of the symmetric algebra of a vector space in order to de ne noncommutative symmetric algebras of two-sided vector spaces. Not all two-sided vector spaces have noncommutative symmetric algebras; the ones that do are called admissible, and conditions for admissibility are given. Further, for some classes of admissible two-sided vector spaces, the skew elds of fractions of their noncommutative symmetric algebras are computed. The 0-degree components of these skew elds correspond to function elds of certain noncommutative ruled surfaces, and hence allow us to determine birational equivalence classes for such surfaces. P X (E), where E is a rank 2 locally free O X -bimodule (in the sense of Artin and Van den Bergh AV], V]), and the projectivization P X (E) is de ned as Proj S(E), where S(E) is a noncommutative analog of the sheaf of symmetric algebras of E.Unfortunately, this sheaf is di cult to work with, as it does not have a nice local structure (for instance, in general the sections S(E)(U) over an open set U do not
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