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Studies have investigated various aspects of the use of questions in science lessons, but there is still a lack of research that demonstrates how, during peer reflection, teachers learn through identifying and overcoming obstacles to their own questioning in their professional development process. The present study is aimed at analyzing the types of obstacles identified by science teachers who participated in a Teacher Reflection Workshop (TRW) on the formulation and use of questions in their lessons. The workshop consisted of stage 1 (7 sessions), stage 2 (video recordings in school classrooms), and stage 3 (3 sessions). The discourses of 8 participating teachers in the areas of chemistry, biology, physics, and natural science at different educational institutions in the city of Santiago, Chile, were analyzed in this case study. The analysis was carried out by the professors participating in the workshop, based on the participants' identification, initial attempts to address, and proposals to overcome, their obstacles. In the earlier stages of the process, the identified obstacles had procedural characteristics, but as the process advanced, they took on a more epistemological nature. One of the main differences between the initial and final identification of obstacles by the participating teachers is that the latter were more precise and critical, and the teachers increasingly demonstrated the ability to propose specific solutions to teaching problems. Engagement with the obstacles does not take place uniformly but depends on the types of obstacles that the teachers identify in their practice. Proposals for overcoming the obstacles require the teachers to have time for reflecting and validating their ideas in their practice. [ABSTRACT FROM AUTHOR]

A field study was performed to evaluate the accuracy of six pesticide screening leaching indexes for herbicide movement. Adsorption, dissipation and soil movement were studied in a vineyard in a sandy loam soil during 2005 season. Simazine, diuron, pendimethalin, oxyfluorfen and flumioxazin were applied to bare soil at rates commonly used, and their soil concentrations throughout soil profile were determined at 0, 10, 20, 40 and 90 days after application (DAA). Herbicides were subjected to two pluviometric regimens, natural field condition and modified conditions (plus natural rainfall 180 mm). Leaching indexes utilized were: Briggs's Rf, Hamaker's Rf, LEACH, LPI, GUS and LIX. Simazine reached 120 cm, diuron 90 cm, flumioxazin 30 cm soil depth respectively. Pendimethalin and oxyfluorfen were retained up to 5 cm. None of the herbicides leaching was affected by rainfall regimen. Only flumioxazin field dissipation was clearly affected by pluviometric condition. The best representation of the herbicide soil depth movement and leaching below 15 cm soil depth were: Hamaker's Rf < Briggs's Rf < GUS < LPI, < LEACH < LIX. Field results showed a good correlation between herbicides Kd and their soil depth movement and mass leached below 15 cm soil depth. [ABSTRACT FROM AUTHOR]

L-Arginine transport by the fetal side of human placenta was investigated through the characterization of L-[3H]arginine uptake in isolated perfused cotyledon. Competitive inhibition experiments suggest the presence of at least two transport systems: a Na+-independent, pH-insensitive system inhibitable by cationic amino acids, similar to system y+, and a Na+-dependent system which recognizes both cationic and neutral amino acids only in the presence of Na+, i.e. a Bo,+-like system. The kinetic analysis of L-arginine uptake in the presence of Na+ revealed that the process is mediated by saturable components: a high-affinity system (Km = 167 +/- 18.0 microM; Vmax = 0.174 +/- 0.012 micromol min-1) and a low-affinity carrier (Km = 980 +/- 112 microM; Vmax = 1.60 +/- 0.12 micromol min-1). In the absence of Na+, L-arginine uptake was fitted by one model with a Michaelis-Menten constant of 200 +/- 24.8 microM. These results suggest that the high-affinity component corresponds to the Na+-independent system y+, whilst the low-affinity system may represent the activity of the Na+-dependent Bo,+ transporter. Kinetic studies in placentae taken from aspirin-treated pregnancies showed that L-arginine is transported with a significantly higher affinity (Km = 42.5 +/- 5.7 microM), but with a lower capacity (Vmax = 0.064 +/- 0.003 micromol min-1) than in the non-treated group. The latter finding suggests that aspirin would facilitate the uptake of the NO precursor only at very low arginine concentrations.