Lehigh University

About: Lehigh University is a education organization based out in Bethlehem, Pennsylvania, United States. It is known for research contribution in the topics: Catalysis & Fracture mechanics. The organization has 12684 authors who have published 26550 publications receiving 770061 citations.

The Effects of Instruction in Solving Mathematical Word Problems for Students with Learning Problems A Meta-Analysis

Abstract: This article provides a synthesis of word-problem-solving intervention research with samples of students with learning problems (i.e., mild disabilities and at risk for mathematics failure). The effectiveness of word-problem-solving instruction in 25 outcome studies was examined across student characteristics (e.g., grade, IQ); instructional features (e.g., intervention approach, treatment length); methodological features; skill maintenance; and generalization components. Separate analyses were performed for group-design studies and single-subject studies using standardized mean change and percentage of nonoverlapping data (PND), respectively. The overall mean weighted effect size (d) and PND for word-problem-solving instruction were positive across the group-design studies (ES = +.89) and single-subject studies (PND = 89%). In addition, positive effects for skill maintenance and generalization were found for group design (ES = +.78 and +.84, respectively) and single-subject studies (PND = 100%). Computer...

Dissociation of the Tubulin-sequestering and Microtubule Catastrophe-promoting Activities of Oncoprotein 18/Stathmin

Abstract: Oncoprotein 18/stathmin (Op18) has been identified recently as a protein that destabilizes microtubules, but the mechanism of destabilization is currently controversial Based on in vitro microtubule assembly assays, evidence has been presented supporting conflicting destabilization models of either tubulin sequestration or promotion of microtubule catastrophes We found that Op18 can destabilize microtubules by both of these mechanisms and that these activities can be dissociated by changing pH At pH 68, Op18 slowed microtubule elongation and increased catastrophes at both plus and minus ends, consistent with a tubulin-sequestering activity In contrast, at pH 75, Op18 promoted microtubule catastrophes, particularly at plus ends, with little effect on elongation rates at either microtubule end Dissociation of tubulin-sequestering and catastrophe-promoting activities of Op18 was further demonstrated by analysis of truncated Op18 derivatives Lack of a C-terminal region of Op18 (aa 100‐147) resulted in a truncated protein that lost sequestering activity at pH 68 but retained catastrophe-promoting activity In contrast, lack of an N-terminal region of Op18 (aa 5‐25) resulted in a truncated protein that still sequestered tubulin at pH 68 but was unable to promote catastrophes at pH 75 At pH 68, both the full length and the N-terminal‐ truncated Op18 bound tubulin, whereas truncation at the C-terminus resulted in a pronounced decrease in tubulin binding Based on these results, and a previous study documenting a pH-dependent change in binding affinity between Op18 and tubulin, it is likely that tubulin sequestering observed at lower pH resulted from the relatively tight interaction between Op18 and tubulin and that this tight binding requires the C-terminus of Op18; however, under conditions in which Op18 binds weakly to tubulin (pH 75), Op18 stimulated catastrophes without altering tubulin subunit association or dissociation rates, and Op18 did not depolymerize microtubules capped with guanylyl (a, b)-methylene diphosphonate‐ tubulin subunits We hypothesize that weak binding between Op18 and tubulin results in free Op18, which is available to interact with microtubule ends and thereby promote catastrophes by a mechanism that likely involves GTP hydrolysis

Net impact of a plant invasion on nitrogen-cycling processes within a brackish tidal marsh

Abstract: Using comparative analysis of the rates of key processes, we have documented the net effect of a shift in plant species composition on nitrogen cycles with the example of the rapid expansion of Phragmites australis (common reed) and its replacement of short grasses (e.g., Spartina patens) in coastal marshes of the eastern United States. In this study, we measured nitrogen (N) uptake by marsh plants, N adsorption from the water column by litter, changes in N content of litter, sediment N mineralization, nitrification, and nitrate consumption in adjacent plots dominated either by P. australis or by historically dominant S. patens. Rates of individual processes were generally greater in P. australis than in S. patens, but the magnitude of difference varied greatly among processes. Seasonal measurements of standing stock nitrogen in plant tissue indicate that P. australis took up ∼60% more N than did S. patens, and annual rates of N immobilization were nearly 300% greater in P. australis litter than in S. pat...