On the practicality of group dynamic assessment: A seminal enterprise deserving closer scrutiny

This is the final version of the article. Available from the publisher via the DOI in this record.This paper is a preliminary study designed to scrutinize the way Group Dynamic Assessment (G-DA), suggested by Poehner (2009), has been implemented in L2 classrooms regarding its basic premise: moving the group forward in its ZPD while benefiting individuals as well. Since the one-to-one interaction that characterizes DA framework represents an unrealistic model for classroom teachers who must manage classes of 15 to 30 learners, Poehner (2009) suggests the use of DA with groups of L2 learners rather than individuals and offers examples of two approaches to G-DA: concurrent and cumulative. However, the development of group ZPD cannot be easily traced in the presented approaches, and the process of shifting the activity from the individual to the group is not clarified either. To present a more realistic model of G-DA, this paper suggests the application of small group DA to L2 classrooms. To this end, it has initially delved into the concepts of 'group learning', 'group ZPD', and 'group DA'. Next, the areas of ambiguity in the two suggested approaches to G-DA have been identified. Finally, a less complicated model of classroom DA, namely small group DA is presented

Particle Image Velocimetry and Heat Transfer Measurements of a Disk at High Rotational Speeds

Abstract Flow field and local heat transfer measurements were conducted on a rotating disk in an open environment for a variety of rotational speeds ranging from 1500 to 5500 rpm. Two-dimensional particle image velocimetry (PIV) measurements were conducted on the flow field above the surface of the rotating disk. Experiments were made on a rotating disk twice as large as a computer hard disk drive and therefore, the flow conditions may be comparable with a computer disk rotating with a speed up to 20,000 rpm. Velocity field, local heat transfer, and temperature distribution are presented as the result of this investigation. Transient liquid crystal technique was employed for heat transfer measurements, while a back calculation scheme was used to obtain the temperature distributions. Heat transfer measurements were made for r/R > 0.4 which excludes the central hub holding the disk assembly. Results reveals that heat transfer increases with a smaller slope near the corner of the hub, while it increases sharply near the outside edge of the disk

Calculating and Comparison of Different Vegetation Indices by Using Landsat ETM+ Images to Study Vegetation Cover in Neyshabour Area

Abstract Understanding plant cover performance in a region is one of the most important factors in controlling soil fertility and its management. In studying plant cover by using of traditional field data collection methods are difficult and time consuming. Using of GIS data in vegetation cover studies satellite images can be helpful in reducing of time and obtaining more precise information. In this study different aspects were considered to obtain the best composite of different indices and identifying the most suitable parameters. The related bands obtained from tasseled cap, principal components analysis and the calculated indices were also used to evaluate the role and effects of different filters on Landsat ETM+ of Neyshabour region. Regression equation and regression coefficients of different parameters were analyzed and evaluated. Finally the most applicable indices were compared with the classes obtained from image classification. The results showed that mean filter of 3×3 has higher correlation coefficients when digital numbers were compared with field collected data. The indices of MSR,VI5, VI6, VI1, RI, BI1, SI, NDVI,TVI ,NDSI ,SAVI,MND, MSAVI, Complex multiratoو COSRI and also PCA1 and the PCA3 obtained from principal components analyses, brightness and greenness bands received from tasseled cap conversion are providing better recognition and evaluation of plant cover in the region. Keywords: Vegetation indices, Principal components analysis, Tasseled cap, Image classification, Landsa

Comparison of two purified toxic fractions from Mesobuthus eupeus scorpion venom

Iranian scorpions belong mainly to the Buthidae and Scorpionidae families, distributed into 16 genera and 25 species. In Iran, similar to other parts of the world, there are a few known species of scorpions responsible for severe envenoming; amongst which Mesobuthus eupeus is the most common. Its venom contains several toxin fractions that may affect the ion channel. In the present study purification, labeling and biological evaluation of M. eupeus venom are described. For separation, soluble venom was loaded on a chromatography column packed with Sephadex G-50 gel. Subsequently, the fractions were collected according to UV absorption at a wavelength of 280 nm. Toxic fraction (F3) was loaded on an anionic ion exchanger resin and then on a cationic resin. Finally, toxic subfractions F3.1.6 and F3.1.9 were labeled with 99mTc and injected into normal mice to distinguish excretion pathway. The venom toxic fraction was successfully obtained in its purified form. Radiolabeling of toxic fractions was performed at high specific activity with radiochemical purity of more than 97 and 95% respectively for F3.1.6 and F3.1.9. Biodistribution studies in normal mice with two toxic fractions usually show rapid clearance of the compounds from blood and tissue except for kidneys. Since tissue distribution studies are very important for clinical purpose, the present findings suggest that 99mTc labeling of venom is a useful tool for in vivo studies and comprises an excellent approach to monitoring the process of biodistribution and kinetics of toxins