Using the System Schema Representational Tool to Promote Student Understanding of Newton's Third Law

The Modeling Instruction program at Arizona State University has developed a representational tool, called a system schema, to help students make a first level of abstraction of an actual physical situation [1]. A system schema consists of identifying and labeling all objects of interest from a given physical situation, as well as all the different types of interactions between the objects. Given all the relevant objects and their interactions, students can explicitly identify which are part of their system and which are not, and then go on to model the interactions affecting their choice of system as either (i) mechanisms for energy transfer, or (ii) forces being exerted. In this paper, I describe the system schema tool, give examples of its use in the context of forces, and present some evidence on its effectiveness in helping students understand Newton's Third Law

The influence of rifle carriage on the kinetics of human gait

The influence that rifle carriage has on human gait has received little attention in the published literature. Rifle carriage has two main effects, to add load to the anterior of the body and to restrict natural arm swing patterns. Kinetic data were collected from 15 male participants, with 10 trials in each of four experimental conditions. The conditions were: walking without a load (used as a control condition); carrying a lightweight rifle simulator, which restricted arm movements but applied no additional load; wearing a 4.4 kg diving belt, which allowed arms to move freely; carrying a weighted (4.4 kg) replica SA80 rifle. Walking speed was fixed at 1.5 m/s (+5%) and data were sampled at 400 Hz. Results showed that rifle carriage significantly alters the ground reaction forces produced during walking, the most important effects being an increase in the impact peak and mediolateral forces. This study suggests that these effects are due to the increased range of motion of the body’s centre of mass caused by the impeding of natural arm swing patterns. The subsequent effect on the potential development of injuries in rifle carriers is unknown

Volume 2 - Literature review of adsorption on metal surfaces Final report, 1 May 1966 - 2 Jul. 1967

Atom and ion desorption energy, chemisorption theory and surface bonds, work functions and potential energy in literature review of adsorption on metal surface

Stratify or adjust? Dealing with multiple populations when evaluating rare variants

The unrelated individuals sample from Genetic Analysis Workshop 17 consists of a small number of subjects from eight population samples and genetic data composed mostly of rare variants. We compare two simple approaches to collapsing rare variants within genes for their utility in identifying genes that affect phenotype. We also compare results from stratified analyses to those from a pooled analysis that uses ethnicity as a covariate. We found that the two collapsing approaches were similarly effective in identifying genes that contain causative variants in these data. However, including population as a covariate was not an effective substitute for analyzing the subpopulations separately when only one subpopulation contained a rare variant linked to the phenotype

A note on Makeev's conjectures

A counterexample is given for the Knaster-like conjecture of Makeev for functions on $S^2$. Some particular cases of another conjecture of Makeev, on inscribing a quadrangle into a smooth simple closed curve, are solved positively

A novel reversed phase high performance liquid chromatography method to accurately determine low concentrations of curcumin in rat plasma

Due to its lipophilic nature, curcumin levels in plasma are very low after oral administration, and therefore hard to detect. A number of chromatographic methods, including LC/MS have been developed. Although the LC/MS method is sensitive, the matrix effect can be difficult to handle. Furthermore, LC/MS equipment is relatively expensive compared to the conventional RP-HPLC. Therefore, the aim of this study was to develop a sensitive and reliable method for the determination of curcumin concentration in plasma using an RP-HPLC. Curcuma longa extract was used which contains three curcuminoids. The method started by selection of mobile phase to optimally separate the curcuminoids. The best mobile phase composition was used to analyze the plasma samples. Rat plasma was spiked with curcumin and processed for protein precipitation followed by liquid-liquid extraction of curcuminoids and an internal standard, emodin. Chromatogaphic separation of curcuminoids and emodin was achieved using a Knauer C-18 column (250 x 4.6 mm; particle size: 5µm) and a gradient program of mobile phase of three solvents, methanol -acetonitrile-1% acetic acid. A gradient elution was applied with increasing the ratio of the volume percentages of acetonitrile to acetic acid from 50/45 to 53/42 during 5 minute and thereafter elution was isocratic for 15 minute. The methanol concentration was kept constant at 5 vol-% during the whole run. The method was validated according to the FDA guidelines.The method was selective, with an excellent resolution (Rs value > 2.5). The peak shape of both curcumin and emodin were symmetric with a tailing factor of 0.9-1.1. The method linearity (correlation coefficient of 0.999) was demonstrated at 6 to 200 ng/mL. The intra and inter-day precision was 5.90-8.50% and 5.37-11.26%, respectively; the intra- and inter-day accuracy was 92.47-103.61% and 96.17-105.70%, respectively. In conclusion, the RP-HPLC method meets the validation requirements as described in the FDA guidelines and is applicable to accurately quantify curcumin concentrations as low as 6 ng/mL in rat plasma samples