Controlling silver nanoparticle exposure in algal toxicity testing - A matter of timing

The aquatic ecotoxicity testing of nanoparticles is complicated by unstable exposure conditions resulting from various transformation processes of nanoparticles in aqueous suspensions. In this study, we investigated the influence of exposure timing on the algal test response to silver nanoparticles (AgNPs), by reducing the incubation time and by aging the AgNPs in algal medium prior to testing. The freshwater green algae Pseudokirchneriella subcapitata were exposed to AgNO(3), NM-300 K (a representative AgNP) and citrate stabilized AgNPs from two different manufacturers (AgNP1 and AgNP2) in a standard algal growth inhibition test (ISO 8692:2004) for 48 h and a short-term (2 h) (14)C-assimilation test. For AgNO(3), similar responses were obtained in the two tests, whereas freshly prepared suspensions of citrate stabilized AgNPs were less toxic in the 2-h tests compared to the 48-h tests. The 2-h test was found applicable for dissolved silver, but yielded non-monotonous concentration–response relationships and poor reproducibility for freshly prepared AgNP suspensions. However, when aging AgNPs in algal medium 24 h prior to testing, clear concentration–response patterns emerged and reproducibility increased. Prolonged aging to 48 h increased toxicity in the 2-h tests whereas aging beyond 48 h reduced toxicity. Our results demonstrate that the outcome of algal toxicity testing of AgNPs is highly influenced not only by the test duration, but also by the time passed from the moment AgNPs are added to the test medium. This time-dependency should be considered when nanomaterial dispersion protocols for ecotoxicity testing are developed

Publisher Correction: On the issue of transparency and reproducibility in nanomedicine

© 2019, Springer Nature Limited. In the version of this Correspondence originally published, Christine Dufès was incorrectly written as Christine Dufés. This has been corrected in the online versions of the Correspondence

Influence of band width on the scattered ion yield spectra of a He + Ion by resonant or quasi-resonant charge exchange neutralization

The influence of the band structure, especially the bandwidth, on the scattered ion yield spectra of a He+ ion by the resonant or quasi-resonant neutralization was theoretically examined using quantum rate equations. When calculating the scattered ion yield spectra of He+ to simulate the experimental data, we observed that the band structure, especially the bandwidth, had a strong influence on the spectra at relatively low incident He+ ion energies of less than several hundred eV. Through many simulations, it was determined that theoretical calculations that include bandwidth calculation can simulate or reproduce the experimentally observed spectra of He+-In, He+-Ga, and He+-Sn systems. In contrast, simulations not including bandwidth simulation could neither reproduce nor account for such spectra. Furthermore, the calculated ion survival probability (ISP) at low incident ion energies tended to decrease with increasing bandwidth. This decrease in ISP probably corresponds to the relatively small scattered ion yield usually observed at low incident ion energies. Theoretically, such a decrease indicates that a He+ ion with a low incident energy can be easily neutralized on the surface when the bandwidth is large

Uneven Power and the Pursuit of Peace: How Regional Power Transitions Motivate Integration. CES Working Paper, no. 150, 2007

This paper addresses two related puzzles confronting students of regional and international integration: Why do states willingly pool and delegate sovereignty within international institutions? What accounts for the timing and content of regional integration agreements? Most theories of integration suggest that states integrate in order to solve problems of incomplete information and reduce transaction costs and other barriers to economic growth. In contrast I argue that integration can serve to establish a credible commitment that rules out the risk of future conflict among states of unequal power. Specifically, I suggest that integration presents an alternative to preventive war as a means to preclude a rising revisionist power from establishing a regional hegemony. The implication is that it is not countries enjoying stable and peaceful relations that are most likely to pursue integration, but rather countries that find themselves caught in a regional security dilemma, which they hope to break out of by means of institutionalized cooperation. I evaluate this proposition against evidence from two historical cases of regional integration: the German Zollverein and the European Communities

Sensing and data acquisition

Occupant sensing and data acquisition are essential elements for occupant behavior research. A wid