Removal of mercury from solutions of mercuric nitrate by mercuric sulfide

The removal of mercury from dilute solutions of mercuric nitrate by mercuric sulfide is indicative of an adsorption process. The relation of log $\text{x}\text{m}$ vs. log C shows that the Freundlich adsorption isotherm exists.At higher concentrations of mercuric nitrate a reaction takes place with the mercuric sulfide forming a compound of the possible formula 2HgS·Hg(NO₃)₂ mercuric nitratodisulfide.     

Probability Learning: Changes in Behavior Across Time and Development

Individuals track probabilities, such as associations between events in their environments, but less is known about the degree to which experience—within a learning session and over development—influences people's use of incoming probabilistic information to guide behavior in real time. In two experiments, children (4–11 years) and adults searched for rewards hidden in locations with predetermined probabilities. In Experiment 1, children (n = 42) and adults (n = 32) changed strategies to maximize reward receipt over time. However, adults demonstrated greater strategy change efficiency. Making the predetermined probabilities more difficult to learn (Experiment 2) delayed effective strategy change for children (n = 39) and adults (n = 33). Taken together, these data characterize how children and adults alike react flexibly and change behavior according to incoming information.     

Effect of intertrial interval on variable-interval discrete-trial barpressing

In seven experiments, an effect of the intertriai interval (ITI) duration on barpressing by rats was studied. A stimulus signaled a 15-sec variable-interval trial. The first response after the interval elapsed turned the stimulus off and was rewarded with food. Trials were separated by long (about 300 sec) or short (about 10 sec) ITIs. A within-subjects design established that response rate on trials after long ITIs was lower than that after short ITIs (Experiments 1 and 3–7). The effect was not cumulative (the effect of one and five consecutive short ITIs was the same). Response rate after short and long ITIs was the same when a between-subjects design was used (Experiment 2). Response rate was higher after 160-sec ITIs than after 300-sec ITIs, suggesting that the ITI duration at which all longer ITIs are treated the same (i.e., the upper limit) is greater than 160 sec (Experiment 3). When food, the trial stimulus, a novel stimulus, or a familiar stimulus never paired with food, was presented 10 sec before the next trial during some of the long ITIs, response rate on the next trial was similar to that found after 10-sec ITIs (Experiments 4–6). This similarity suggested that these events could mark the start of the ITI. However, the familiar stimulus did so only when it reliably predicted that the next trial would occur after a short interval. The effect of ITI duration on responding was apparently attributable to response latency. Response latency was greater after long ITIs, but once responding began, it was similar after long and short ITIs (Experiment 7).     

Cognitive Brain Event-Related Potentials and Emotion Processing in Maltreated Children

Cognitive event-related potentials (ERPs) were recorded from 23 maltreated and 21 nonmaltreated children. Children were presented with slides of Ekman photographs of asingle model posing an angry (25%), a happy (25%), or a neutral (50%) facial expression. In 1 of 2 counterbalanced target conditions, children were asked to press a button in response to the angry face; in the other target condition, they responded to the happy face. Both samples, as expected, exhibited the largest amplitude of the P300 component of the ERP to target stimuli and the smallest amplitude to nontargets. For nonmaltreated children, the average amplitude of P300 across slides was comparable for the 2 target conditions. In contrast, maltreated children displaed larger P300 ampltude to stimuli when they were directed to attend to angry, as opposd children displayed larger p300 amplitude to stimuli whe they were directed to attend to angry, as opposed to happy, targets. These reaults suggest different cognitive processing for positive versus negative affective expressions by children with histories of atypical emotiaonal exotional experiences.     

Is Response to Intervention Good Policy for Specific Learning Disability?

Abstract The reauthorized Individuals with Disabilities Education Improvement Act ( IDEA ) established new provisions for specific learning disability (SLD) identification, including: (a) no longer requiring consideration of IQ–achievement discrepancy and (b) permitting response to intervention (RTI) as part of SLD evaluation procedures. We discuss several policy implications of these new regulations by considering the original construct of SLD, the still “experimental” status and implementation of RTI, the closer alignment of RTI objectives with No Child Left Behind than former IDEA regulations, and the shift in focus from serving as a special education identification procedure to a general education instructional procedure. We conclude by proposing several recommendations for the appropriate inclusion of both RTI and psychometric evaluation within the continuum of SLD identification procedures.     

PLAYGROUND: preparing students for the cyber battleground

Attempting to educate practitioners of computer security can be difficult if for no other reason than the breadth of knowledge required today. The security profession includes widely diverse subfields including cryptography, network architectures, programming, programming languages, design, coding practices, software testing, pattern recognition, economic analysis, and even human psychology. While an individual may choose to specialize in one of these more narrow elements, there is a pressing need for practitioners that have a solid understanding of the unifying principles of the whole. We created the Playground network simulation tool and used it in the instruction of a network security course to graduate students. This tool was created for three specific purposes. First, it provides simulation sufficiently powerful to permit rigorous study of desired principles while simultaneously reducing or eliminating unnecessary and distracting complexities. Second, it permitted the students to rapidly prototype a suite of security protocols and mechanisms. Finally, with equal rapidity, the students were able to develop attacks against the protocols that they themselves had created. Based on our own observations and student reviews, we believe that these three features combine to create a powerful pedagogical tool that provides students with a significant amount of breadth and intense emotional connection to computer security in a single semester.     

Effects of Context on Students’ Molecular‐Level Ideas

In the studies reported here, we investigate the effects of context on students’ molecular‐level ideas regarding aqueous solutions. During one‐on‐one interviews, 19 general chemistry students recruited from a two‐year community college and a research university in the United States were asked to describe their molecular‐level ideas about various aqueous solutions in the contexts of conductivity and boiling‐point (BP) elevation. Results indicate that context is important for determining the molecular‐level ideas that students express. Specifically, students were significantly more likely to draw pictures of aqueous NaCl as separated ions in the conductivity context compared with the BP elevation context, for which they more often drew “molecular” NaCl. This phenomenon was particularly striking because the students drew molecular‐level NaCl(aq) pictures in the BP elevation context just minutes after completing the identical task in the context of conductivity. Additional data from laboratory assignments and course examinations further indicate that, even if students are able to correctly represent the molecular level in some contexts, their knowledge may remain inert in slightly different contexts. The results emphasise the importance of the context dependence of molecular‐level ideas and have implications for designing instruction in which students develop robust, coherent understandings that they can apply appropriately in new contexts.