No abstract

No abstract

Titanium dioxide nanoparticles (nano-TiO(2)) are now widely applied in consumer products, and the dispersion of nano-TiO(2) may adsorb metals and modify their behavior and bioavailability in the aquatic environment. In the present study, the aqueous uptake, dietary assimilation efficiency (AE), and efflux rate constant (k(e)) of two toxic metals (cadmium-Cd, and zinc-Zn) adsorbed on nano-TiO(2) in a freshwater zooplankton Daphnia magna were quantified. The biokinetics was then compared to daphnids that were exposed only to dissolved metals as controls. The aqueous uptake of Cd and Zn involved an initial rapid uptake and then an apparent saturation, and the uptake of metals was accompanied by an ingestion of nano-TiO(2). The AEs of Cd and Zn adsorbed on nano-TiO(2) were 24.6 ± 2.4-44.5 ± 3.7% and 30.4 ± 3.4-51.8 ± 5.0%, respectively, and decreased with increasing concentrations of nano-TiO(2). Furthermore, the difference between the AEs of Cd and Zn indicated that the desorption of Cd and Zn from nano-TiO(2) may have occurred within the gut of daphnids. With the use of algae as carrier, the AEs of Cd and Zn adsorbed on nano-TiO(2) were significantly higher than those of Cd and Zn directly from nano-TiO(2). The efflux rate constants of Cd and Zn adsorbed on nano-TiO(2) in the zooplankton were significantly lower than those of Cd and Zn not adsorbed on nano-TiO(2). Our study shows that the uptake and retention of toxic metals is enhanced when they are adsorbed on nano-TiO(2), and suggests more attention be paid to the potential influences of nano-TiO(2) on the bioavailability and toxicity of other contaminants.

The present study addresses the issue of how different forms of cultural capital may influence children's mathematics achievement in economies with different socioeconomic gradients. Data from 73,178 parent-child dyads from 10 economies with different socioeconomic gradients who participated in the Programme for International Student Assessment (PISA) 2012 were analysed using hierarchical linear modelling. The cultural capital variables examined comprised the availability of home educational resources and parental educational expectations of their children. Results showed that after controlling for parent education, student gender and student history of repeating grades in the past, there were statistically significant main and interaction effects (home educational resources 9 parent education and parental educational expectations 9 parent education) of cultural capital on student achievement. Furthermore, these effects explained more student achievement variance in high than in medium socioeconomic gradient economies (7.45% vs 2.82% respectively). In particular, the main effects for parental educational expectations, and interaction effect between parental educational expectations and parent education were more pronounced in high as compared with medium socioeconomic gradient economies. Overall, the results underscore the challenges confronting low socioeconomic status (SES) parents who aspire for social mobility for their children and the need for high SES parents to strategically 'activate' their cultural capital advantages to benefit their children's achievement maximally.*Room 330, Hui Oi Chow Science Building,

The present study examined indirect effects of principal leadership on the mathematics achievement of 254,475 15-year-old students from 10,313 schools in 32 OECD economies. Results showed that the students could be divided into three categories (Disadvantaged, Average, and Privileged) differing in levels of student SES and prior achievement, parental academic expectations, and access to school resources. Results also showed that principal leadership effects accounted for a greater proportion of between-school achievement variance for Disadvantaged vis-a-vis Privileged or Average students. In particular, instructional leadership had the largest positive effect on Disadvantaged vis-a-vis other students' achievement via the mediating variables of teacher autonomy and morale. Distributed leadership negatively affected the achievement of Disadvantaged but not other students. The negative effects of principal goal-setting were the largest while those of principal problem-solving were the smallest for Disadvantaged students. The study contributes to the literature by examining contextual influences on the leadership-achievement relationship.

A key element (one is tempted to say the heart) of most digital systems is the clock. Its period determines the rate at which data is processed, and so should be made as small as possible, consistent with reliable operation. B~ed on a worst-case analysis, clocking schemes for high-performance systems are analyzed. These are 1-and 2-phase systems using simple clocked latches, and I-pha.se systems using edge-triggered D-flip-flops. Within these categories (any of which may be preferable in a given situation), it is shown how optimal trade-oUs can be made by appropriately choosing the parameters of the clocking system as a function of the technology parameters. The trade-oUs involve the clock period (which of course determines the data rate) and the tolerances that must be enforced on the propagation delays through the logic. Clock-pulse edge tolerances are shown to be an important factor. It is shown tlra.t, for systems using latches, their detrimental effects on the clock period can be converted to tighter bounds on the short-path delays by allowing D-changes to lag behind the leading edges of the clock pulses a.nd by using wider clock pulses or, in the ca.se of 2-pha.se systems, by overlapping the clock pulses.

, where he is involved in a major system-wide research project on school leadership led by Prof Clive Dimmock and funded by the Singapore Government.

The traditional discourse in the scholarship on cultural capital theory has focused on how exclusive participation in elite status culture by students from higher socioeconomic status families benefits their learning in schools, the effects of which are most evident in linguistic subject areas such as reading achievement. However, some scholars have argued that cultural capital is not restricted to elite status culture but could include parental familiarity with school evaluation standards and job market requirements, and that the effects could transcend languages to include performance domains with more objective evaluation that are susceptible to school influences (e.g. mathematics and science). The present study systematically examines this position using data involving 96,591 15‐year‐old students from 3602 schools in eight countries who participated in the Programme for International Student Assessment 2012. Results of three‐level hierarchical linear modelling showed positive relationships between seven cultural capital variables and student mathematics achievement. The cultural variables comprised: home educational resources; parental educational attainment and occupational status; parental expectations of their children's educational attainment, future career in mathematics and school; and parental valuing of mathematics. In particular, the three parental expectations variables had substantively larger effect sizes on student achievement than the other cultural capital variables. The results demonstrated that parental familiarity with school evaluation standards and future job requirements, especially as measured by parental expectations, may constitute cultural capital that privileges student mathematics achievement in schools.