Plasma-Treated Microplates with Enhanced Protein Recoveries and Minimized Extractables.

SiO2 Medical Products, Inc. (SiO) has developed a proprietary technology that greatly enhances protein recoveries and reduces extractables from commercial microplates used for bioanalytical assays and storage of biologics. SiO technology is based on plasma treatment that chemically modifies the surface of polypropylene with predominantly hydrogen-bond-acceptor uncharged polar groups. The resultant surface resists nonspecific protein adsorption over a wide range of protein concentrations, thereby eliminating the need to passivate (and hence potentially contaminate) the microplates with blocking proteins. High shelf-life stability and cleanliness of the plasma-treated microplates have been demonstrated using five different proteins for two common microplate formats. The protein recovery performance of plasma-treated microplates is found to be higher compared with commercial low-protein-binding microplates.

Premarital first births: The influence of the timing of sexual onset versus post-onset risks in the United States.

Motivated by long-standing debates between abstinence proponents and sceptics, we examine how socio-economic factors influence premarital first births via: (i) age at first sexual intercourse and (ii) the risk of a premarital first birth following the onset of sexual activity. Factors associated with an earlier age at first intercourse will imply more premarital first births owing to increased exposure to risk, but many of these same factors will also be associated with higher risks of a premarital first birth following onset. Our analyses confirm previous findings that women from disadvantaged backgrounds are younger at first intercourse and have higher premarital first-birth risks than women from more advantaged backgrounds. However, differences in onset timing have a strikingly smaller influence on premarital first-birth probabilities than do differences in post-onset risks. Our findings thus suggest that premarital first births result primarily from differences in post-onset risk behaviours as opposed to differences in onset timing.

EFFECTS OF EXPOSURE ON PREVALENCE AND CUMULATIVE RELATIVE RISK: DIRECT AND INDIRECT EFFECTS IN A RECURSIVE HAZARD MODEL.

This paper outlines decomposition methods for assessing how exposure affects prevalence and cumulative relative risk. Let x denote a vector of exogenous covariates and suppose that a single dimension of time t governs two event processes T(1) and T(2). If the occurrence of the event T(1) determines entry into the risk of the event T(2), then subgroup variation in T(1) will affect the prevalence T(2), even if subgroups in the population are otherwise identical. Although researchers often acknowledge this phenomenon, the literature has not provided procedures to assess the magnitude of an exposure effect of T(1) on the prevalence of T(2). We derive decompositions that assess how variation in exposure generated by direct and indirect effects of the covariates x affect measures of absolute and relative prevalence of T(2). We employ a parametric but highly flexible specification for baseline hazard for the T(1) and T(2) processes and use the resulting parametric proportional hazard model to illustrate the direct and indirect effects of family structure when T(1) is age at first sexual intercourse and T(2) is age at a premarital first birth for data on a cohort of nonhispanic white U.S. women.