In Pursuit of Knowledge: Preschoolers Expect Agents to Weigh Information Gain and Information Cost When Deciding Whether to Explore.

When deciding whether to explore, agents must consider both their need for information and its cost. Do children recognize that exploration reflects a trade-off between action costs and expected information gain, inferring epistemic states accordingly? In two experiments, 4- and 5-year-olds (N = 144; of diverse race and ethnicity) judge that an agent who refuses to obtain low-cost information must have already known it, and an agent who incurs a greater cost to gain information must have a greater epistemic desire. Two control studies suggest that these findings cannot be explained by low-level associations between competence and knowledge. Our results suggest that preschoolers' theory of mind includes expectations about how costs interact with epistemic desires and states to produce exploratory action.

Enhanced hydrogen storage kinetics of an Mg-Pr-Al composite by in situ formed Pr3Al11 nanoparticles.

Slow hydrogen sorption kinetics is one of the challenges facing practical applications of MgH2. To improve the hydrogen sorption kinetics, an Mg-Pr-Al composite is prepared by ball milling of a 14MgH2 + Pr + Al powder mixture. During hydrogenation and dehydrogenation processes of the Mg-Pr-Al composite, two reversible side reactions, i.e. 2PrH2 + H2 = 2PrH3 and Mg17Al12 + 17H2 = 17MgH2 + 12Al, occur accompanying hydrogen adsorption and desorption of the Mg-H2 system. The in situ formed Pr3Al11 phase in the activated Mg-Pr-Al composite is stable during further hydrogen adsorption and desorption processes, which plays a role in inhibiting growth of Mg crystallites. Hence, the improvement of hydrogen sorption kinetics for the Mg-Pr-Al composite is ascribed to the inhibiting role of Pr3Al11 in crystallite growth as well as the catalytic effect of PrH3/PrH2 on hydrogen sorption. These findings provide an important guidance for developing new Mg-based materials with superior hydrogen storage properties.

Protective effects of antioxidant vitamins on Aroclor 1254-induced toxicity in cultured chicken embryo hepatocytes.

Primary culture of chicken embryo hepatocytes (CEHs) was established to reveal toxicity of polychlorinated biphenyls (PCBs) and attenuating effects of antioxidants vitamin E (VE), vitamin C (VC) and vitamin A (VA) on PCBs-induced cytotoxicity. CEHs were dispersed from 14-day-old chicken embryo livers and exposed to Aroclor 1254 (A1254) in the range of 0.1-10 microg/ml, A1254 (10 microg/ml) and each vitamin (10 microg/ml) for 24 h. Cell viability was evaluated by determinations of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) reduction and lactate dehydrogenase (LDH) leakage. The antioxidant status, namely cellular lipid peroxidation, was evaluated by measuring the thiobarbituric acid reactive substances (TBARS) and glutathion (GSH) levels and superoxide dismutase (SOD) activities. The cultured CEHs maintained normal polygonal cell shape and formed confluent monolayer after 24-h culture. A1254 (10 microg/ml) caused irreversible damage to cell membrane integrity and induced cell death in a dose-dependent manner. It induced increased TBARS production, decreased SOD activity and GSH concentration. VE, VC and VA alone or combinations of VE+VC and VE+VA significantly attenuated A1254-induced toxic effects, which suggested that lipid peroxidation was involved in the sequence of events leading to A1254-induced damage or death of the cultured CEHs. These results indicated that CEHs in serum-free culture represented a suitable model for rapid toxicity assessment of environmental pollutants such as PCBs in a visible manner. Antioxidant vitamins displayed protective effects on CEHs from A1254-induced damage through preventing lipid peroxidation.