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We have earlier shown that linear poly(ethylene imine) (LPEI) is an efficient growth modifier for calcium phosphate mineralization from aqueous solution (Shkilnyy et al., Langmuir, 2008, 24 (5), 2102). The current study addresses the growth process and the reason why LPEI is such an effective additive. To that end, the solution pH and the calcium and phosphate concentrations were monitored vs. reaction time using potentiometric, complexometric, and photometric methods. The phase transformations in the precipitates and particle morphogenesis were analyzed by X-ray diffraction and transmission electron microscopy, respectively. All measurements reveal steep decreases of the pH, calcium, and phosphate concentrations along with a rapid precipitation of brushite nanoparticles early on in the reaction. Brushite transforms into hydroxyapatite (HAP) within the first 2 h, which is much faster than what is reported, for example, for calcium phosphate precipitated with poly(acrylic acid). We propose that poly(ethylene imine) acts as a proton acceptor (weak buffer), which accelerates the transformation from brushite to HAP by taking up the protons that are released from the calcium phosphate precipitate during the phase transformation.
The voice gives it away
(2021)
Two experiments examined the impact of voice pitch on gender stereotyping. Participants listened to a text read by a female (Study 1; N = 171) or male (Study 2, N = 151) speaker, whose voice pitch was manipulated to be high or low. They rated the speaker on positive and negative facets of masculinity and femininity, competence, and likability. They also indicated their own gendered self-concept. High pitch was associated with the ascription of more feminine traits and greater likability. The high-pitch female speaker was rated as less competent, and the high-pitch male speaker was perceived as less masculine. Text content and participants' gendered self-concept did not moderate the pitch effect. The findings underline the importance of voice pitch for impression formation.