Ordination of the herbaceous stratum of savanna in the Nylsvley Nature Reserve, South Africa

The purpose of the study was to determine the ecological status of representative herbaceous species with respect to environmental factors and subhabitats of which the spatial and temporal pattern could be elucidated.The basal cover of the herbaceous vegetation was determined by means of the wheel-point method. Frequency data in each of 200 1 m2 contiguous quadrats were ordinated by means of detrended correspondence analysis (DECORANA).The distribution of the species along the first axis is a function of conditions representing an open habitat with full sunlight and somewhat drier conditions to the left and a denser and/or shrub habitat with more shade and wetter, more favourable conditions to the right. The gradient along the second axis is that of undisturbed conditions with more perennials at the lower end to disturbed conditions with more annuals at the upper end. From the scatter diagrams it can be concluded that the herbaceous layer is functionally homogeneous, that it represents a seral stage and that Eragrostis pallens and Digitaria eriantha, both with the highest basal cover in the study area, are representative of a seral stage rather than of the climax. The lack of pattern in the herbaceous layer can be attributed mainly to the large number of annual and perennial pioneer and disturbance-indicating species. In a similar study Whittaker et al. (in press) concluded that the woody vegetation dominates the pattern

Mechanism of Electromigration Failure in Al Thin Film Interconnects Containing Sc

In order to understand the role of Sc on electromigration (EM) failure, Al interconnects with 0.1 and 0.3 wt.% Sc sere tested as a function of post-pattern annealing time. In response to the evolution of the line structure, the statistics of lifetime evolved. While the addition of Sc greatly reduces the rate of evolution of the failure statistics because the grain growth rate decreases, the MTF variation was found to be very similar to that of pure Al. These observations seem to show that Sc has little influence on the kinetics of Al EM; however, it has some influence on the EM resistance of the line since it is an efficient grain refiner. Unlike Cu in Al, Sc does not seem to migrate, which may explain its lack of influence on the kinetics of Al EM

Polarization and Color Filtering Applied to Enhance Photogrammetric Measurements of Reflective Surfaces

Techniques for enhancing photogrammetric measurement of reflective surfaces by reducing noise were developed utilizing principles of light polarization. Signal selectivity with polarized light was also compared to signal selectivity using chromatic filters. Combining principles of linear cross polarization and color selectivity enhanced signal-to-noise ratios by as much as 800 fold. More typical improvements with combining polarization and color selectivity were about 100 fold. We review polarization-based techniques and present experimental results comparing the performance of traditional retroreflective targeting materials, cornercube targets returning depolarized light, and color selectivity

The influence of microstructure on the mechanical properties of solder

Solder joints in microelectronics devices consist of low-melting solder compositions that wet and join metal contacts and are, ordinarily, used at high homologous temperatures in the as-solidified condition. Differences in solidification rate and substrate interactions have the consequence that even solder joints of similar compositions exhibit a wide range of microstructures. The variation in microstructure causes a variation in properties; in particular, the high-temperature creep properties that govern much of the mechanical behavior of the solder may differ significantly from joint to joint. The present paper reviews the varieties of microstructure that are found in common solder joints, and describes some of the ways in which microstructural changes affect mechanical properties and joint reliability

Thermodynamics of non-local materials: extra fluxes and internal powers

The most usual formulation of the Laws of Thermodynamics turns out to be suitable for local or simple materials, while for non-local systems there are two different ways: either modify this usual formulation by introducing suitable extra fluxes or express the Laws of Thermodynamics in terms of internal powers directly, as we propose in this paper. The first choice is subject to the criticism that the vector fluxes must be introduced a posteriori in order to obtain the compatibility with the Laws of Thermodynamics. On the contrary, the formulation in terms of internal powers is more general, because it is a priori defined on the basis of the constitutive equations. Besides it allows to highlight, without ambiguity, the contribution of the internal powers in the variation of the thermodynamic potentials. Finally, in this paper, we consider some examples of non-local materials and derive the proper expressions of their internal powers from the power balance laws.Comment: 16 pages, in press on Continuum Mechanics and Thermodynamic