A comprehensive taxonomy of algorithm animation languages

In this paper, we present a taxonomy of algorithm animation languages that augments Price's well-known taxonomy of software visualization. Whereas Price's taxonomy is directed to classifying features and characteristics of visualization systems, the new taxonomy focuses on evaluating current animation languages. The taxonomy can be used by algorithm visualization system designers as a tool to compare visualization system languages with each other as well as for designing and implementing new systems and language features. In addition, the taxonomy provides guidelines to the features that are needed for transferring animations between systems. This is an ongoing project that elaborates upon the work reported on in a briefer version of the taxonomy.     

Downstream Hydrological Impacts of Hydropower Development in the Upper Mekong Basin

The Mekong River Basin in Southeast Asia is experiencing extensive hydropower development. Concerns have been raised about the consequences of the development for the ecosystems, livelihoods and food security in the region. The largest planned hydropower dam cascade in the basin, the Lancang-Jiang cascade, is currently under construction and already partly built into the Upper Mekong Basin, China. In this paper we assess the impact of the Lancang-Jiang cascade on downstream hydrology by using a combination of a hydrological model and a reservoir cascade optimization model. The hydrological changes were quantified in detail at the Chiang Saen gauging station in Thailand, the first gauge station downstream from the cascade, and in lesser detail at four other downstream locations in the Mekong mainstream. We found that on average the Lancang-Jiang cascade increased the December?CMay discharge by 34?C155?% and decreased the July?CSeptember discharge by 29?C36?% at Chiang Saen. Furthermore, the Lancang-Jiang cascade reduced (increased) the range of hydrological variability during the wet season (dry season) months. The dry season hydrological changes were significant also in all downstream gauging stations, even as far as Kratie in Cambodia. Thus the Mekong??s hydrological regime has been significantly altered by the Lancang-Jiang cascade, but what the consequences are for ecosystems and livelihoods, needs further study.     

Performance of different spectral and textural aerial photograph features in multi-source forest inventory

Most multi-source forest inventory (MSFI) applications have thus far been based on the use of medium resolution satellite imagery, such as Landsat TM. The high plot and stand level estimation errors of these applications have, however, restricted their use in forest management planning. One reason suggested for the high estimation errors has been the coarse spatial resolution of the imagery employed. Therefore, very high spatial resolution (VHR) imagery sources provide interesting data for stand-level inventory applications. However, digital interpretation of VHR imagery, such as aerial photographs, is more complicated than the use of traditional satellite imagery. Pixel-by-pixel analysis is not applicable to VHR imagery because a single pixel is small in relation to the object of interest, i.e. a forest stand, and therefore it does not adequately represent the spectral properties of a stand. Additionally in aerial photographs, the spectral properties of the objects are dependent on their location in the image. Therefore, MSFI applications based on aerial imagery must employ features that are less sensitive to their location in the image and that have been derived using the spatial neighborhood of each pixel, e.g. a square-shaped window of pixels. In this experiment several spectral and textural features were extracted from color-infrared aerial photographs and employed in estimation of forest attributes. The features were extracted from original, normalized difference vegetation index and channel ratio images. The correlations between the extracted image features and forest attributes measured from sample plots were examined. Additionally, the spectral and textural features were used for estimating the forest attributes of sample plots, applying the k nearest neighbor estimation method. The results show that several spectral and textural image features that are moderately or well correlated with the forest attributes. Furthermore, the accuracy of forest attribute estimation can be significantly improved by a careful selection of image features.     

Local radiometric correction of digital aerial photographs for multi source forest inventory

Digitized colour infrared images are a potential information source for multi-source forest inventory applications and particularly for estimating the forest characteristics of relatively small areas. The main problem in computer-aided image analysis of aerial photographs is the presence of bidirectional reflectance, which causes the spectral values of the image pixels to depend on their location in the image. Because of this, and the lack of operational methods for radiometric correction, the full potential of aerial photographs has not been utilised. This paper presents a local radiometric correction method that can be used for reducing the effect of bidirectional reflectance. The method employs satellite images that are less affected by the bidirectional reflectance for the local adjustment of the registered pixel values of aerial photographs. Because of the different spatial resolution of the aerial and satellite imagery, the local correction coefficients are computed for units that are larger than a single aerial photo pixel. In this way, the general level of brightness of the correction units can be determined on the basis of the satellite imagery while retaining the finer spatial resolution of the original aerial photo. The main advantage of the suggested method is that it does not require complex mathematical models for simulating the effect of bidirectional reflectance, neither does it require a priori knowledge of the actual forest attributes in the inventory area, but relies only on the image data.     

How undergraduate students meet a new learning environment?

We evaluated if the theory of planned behavior explains students‘ activity in a web-based learning environment. Two of the considerations of the theory, attitude toward the behavior (behavioral beliefs and outcome evaluations) and perceived behavioral control (computer self-efficacy), were evaluated. The scope was also widened to students' approaches to learning and anxiety in computer using situations as well as their interpretations of the environment and the learning situation. Forty-two undergraduate medical and sociology students completed the questionnaire assessing attitudes, self-efficacy, anxiety and approaches to learning before and after the web-based courses. The attitude toward the behavior, efficacy beliefs, approaches to learning and anxiety in computer using situations did not predict the activity in the learning environment, but students interpreted the environment and the learning situation more negatively after the courses. Students' anxiety and approaches to learning also affect some of their expectations and experiences after the courses.     

Parallel computation of three-dimensional nonlinear magnetostatic problems

We describe a general-purpose parallel code for computing accurate solutions to large computationally demanding, 3D, nonlinear magnetostatic problems. The code, CORAL, is based on a volume integral equation formulation. Using an IBM SP parallel computer and iterative solution methods, we successfully solved the dense linear systems inherent in such formulations. A key component of our work was the use of the PETSc library, which provides parallel portability and access to the latest linear algebra solution technology. Copyright © 1999 John Wiley & Sons, Ltd.     

Interactive Dynamics of Cell Volume and Cell Death in Human Erythrocytes Exposed to α-Hemolysin from Escherichia coli

α-hemolysin (HlyA) of E. coli binds irreversibly to human erythrocytes and induces cell swelling, ultimately leading to hemolysis. We characterized the mechanism involved in water transport induced by HlyA and analyzed how swelling and hemolysis might be coupled. Osmotic water permeability (P_f) was assessed by stopped-flow light scattering. Preincubation with HlyA strongly reduced P_f in control- and aquaporin 1-null red blood cells, although the relative P_f decrease was similar in both cell types. The dynamics of cell volume and hemolysis on RBCs was assessed by electrical impedance, light dispersion and hemoglobin release. Results show that HlyA induced erythrocyte swelling, which is enhanced by purinergic signaling, and is coupled to osmotic hemolysis. We propose a mathematical model of HlyA activity where the kinetics of cell volume and hemolysis in human erythrocytes depend on the flux of osmolytes across the membrane, and on the maximum volume that these cells can tolerate. Our results provide new insights for understanding signaling and cytotoxicity mediated by HlyA in erythrocytes.