A typology of undergraduate students' conceptions of size and scale: Identifying and characterizing conceptual variation

The importance of “size and scale” in nanoscience and engineering has been recognized by both scientists and science educators. A solid understanding of this concept is key to the learning of nanoscience. Students, however, have been reported to have considerable difficulty grasping this concept; yet little is known regarding their state of understanding. To address this knowledge gap, we conducted a series of studies that were aimed at exploring the different ways students conceive of “size and scale” in the context of undergraduate nanoscience and engineering courses. Informed by Variation Theory of Learning (Marton and Booth, 1997), we identified four major categories (with two sub‐categories within each) of student conception—fragmented, linear, proportional, and logarithmic. These conception categories, together with the aspects of variation that characterize and distinguish them, are summarized in a typology. In addition to serving as a diagnostic tool to describe students' understanding, this typology can also be used to guide the development of instructional interventions that facilitate students to move toward a more sophisticated understanding of “size and scale.” © 2011 Wiley Periodicals, Inc., Inc. J Res Sci Teach 48: 512–533, 2011     

Returning to school for higher returns

On the basis of those respondents in the National Longitudinal Survey of Youth (NLSY) who change jobs with an intervening period of education reinvestment, the conventional assumption of linearity of log wages in years of schooling is strongly rejected: a typical reinvestment for the 1980 through 1993 period is associated with a rise of about 3.5 percentage points in the estimated return to an additional year of schooling. The estimated marginal rate of return generally rises in the former education level, and reaches the maximum at 15 years of the former level (therefore 16 years of education after reinvestment), where an additional year of investment is associated with a rise in real hourly rate of pay by approximately 20%. Evidence also shows that, while the level of individuals’ risk tolerance affects significantly the probability of returning to school, correcting for sample selectivity makes little difference in the results. Findings in the current paper survive a variety of robustness tests. The current cohort-based evidence is more helpful than existing evidence from cross-sectional data to individuals making schooling decisions.     

Click-based evidence for decaying weight distributions in search effectiveness metrics

Search effectiveness metrics are used to evaluate the quality of the answer lists returned by search services, usually based on a set of relevance judgments. One plausible way of calculating an effectiveness score for a system run is to compute the inner-product of the run’s relevance vector and a “utility” vector, where the ith element in the utility vector represents the relative benefit obtained by the user of the system if they encounter a relevant document at depth i in the ranking. This paper uses such a framework to examine the user behavior patterns—and hence utility weightings—that can be inferred from a web query log. We describe a process for extrapolating user observations from query log clickthroughs, and employ this user model to measure the quality of effectiveness weighting distributions. Our results show that for measures with static distributions (that is, utility weighting schemes for which the weight vector is independent of the relevance vector), the geometric weighting model employed in the rank-biased precision effectiveness metric offers the closest fit to the user observation model. In addition, using past TREC data as to indicate likelihood of relevance, we also show that the distributions employed in the BPref and MRR metrics are the best fit out of the measures for which static distributions do not exist.     

Noninvasive geotechnical site investigation for stability of Cheomseongdae

Architectural heritages are exposed to natural and man-made disasters so that the need for research to prevent disasters has arisen. Cheomseongdae, known as the oldest astronomical observatory in East Asia, displays separation between the members and is tilted to the north-northeast. To diagnose the present conditions and to resolve problems, site investigations are performed. Boring is conducted in the surrounding ground of Cheomseongdae, and noninvasive investigations such as seismic tests and electrical resistivity surveys are conducted as well. The present study proposes a geotechnical engineering approach focused on noninvasive site surveys, and through this, relates current tilted condition of structure and provides information on the stability of Cheomseongdae.     

Reductive surface synthesis of gold nanoparticles on silicate glass and their biochemical sensor applications

Gold nanoparticles (Au NPs) were directly synthesized on the surface of polyvinylsilazane (PVSZ, -[(vinyl)SiH-NH₂]-) without use of extra reductive additives. The reductive Si-H functional groups on the surface of cured PVSZ acted as surface bound reducing agents to form gold metal when contacted with an aqueous Au precursor (HAuCl₄) solution, leading to formation of Au NPs adhered to silicate glass surface. The Au NPs-silicate platforms were preliminarily tested to detect Rhodamine B (1 μM) by surface enhanced Raman scattering. Furthermore, gold microelectrode obtained by post-chemical plating was used as an integrated amperometric detection element in the polydimethylsilane-glass hybrid microfluidic chip.     

Fast and reliable droplet transport on single-plate electrowetting on dielectrics using nonfloating switching method

In a droplet transport based on electrowetting on dielectrics, the parallel-plate configuration is more popular than the single-plate one because the droplet transport becomes increasingly difficult without cover plate. In spite of the improved transport performance, the parallel-plate configuration often limits the access to the peripheral components, requesting the removal of the cover plate, the single-plate configuration. We investigated the fundamental features of droplet transport for the single-plate configuration. We compared the performance of several switching methods with respect to maximum speed of successive transport without failure and suggested nonfloating switching method which is inherently free from the charge-residue problem and exerts greater force on a droplet than conventional switching methods. A simple theory is provided to understand the different results for the switching methods.     

The independence of response structure and element production in timing sequences

In three experiments, participants were asked to produce a prescribed temporal sequence of key presses. The number of elements in a key press sequence, the movement time of the elements, and uniformity of the timing elements comprising the sequence were manipulated. If the processing of the sequence structure was independent of the processing of elements comprising the sequence, increasing the number of the elements in the sequence should affect the production of the sequence but not the proficiency with which the individual elements are, produced. Increasing the movement time of the elements, however, should affect the production of the elements but have little, if any, effect on the integrity of the sequence. The findings indicated that increasing the number of elements negatively affected sequence production when the elements were nonuniform but had little or no effect when elements were uniform. Alternatively, element production was affected by movement time but not number of elements. The results of these experiments appear to confirm the independence of sequence and element production. However, Experiment 3, in which the uniformity of the elements was directly contrasted, found strong evidence for coarticulatory influences in the learning processes, whereby the longer and shorter than average elements in the sequence negatively affected the sequence integrity and the production of the individual elements. When faced with a nonuniformn timing pattern, participants appear to elongate or shrink individual elements of a uniform timing pattern to fit the desired sequence requirements. The result is that the longer or shorter than average elements require more practice to produce correctly, tend to regress across retention intervals, and are generally less stable than the elements nearer the average.