Ecological Invasion, Roughened Fronts, and a Competitor's Extreme Advance: Integrating Stochastic Spatial-Growth Models

Both community ecology and conservation biology seek further understanding of factors governing the advance of an invasive species. We model biological invasion as an individual-based, stochastic process on a two-dimensional landscape. An ecologically superior invader and a resident species compete for space preemptively. Our general model includes the basic contact process and a variant of the Eden model as special cases. We employ the concept of a "roughened" front to quantify effects of discreteness and stochasticity on invasion; we emphasize the probability distribution of the front-runner's relative position. That is, we analyze the location of the most advanced invader as the extreme deviation about the front's mean position. We find that a class of models with different assumptions about neighborhood interactions exhibit universal characteristics. That is, key features of the invasion dynamics span a class of models, independently of locally detailed demographic rules. Our results integrate theories of invasive spatial growth and generate novel hypotheses linking habitat or landscape size (length of the invading front) to invasion velocity, and to the relative position of the most advanced invader.Comment: The original publication is available at www.springerlink.com/content/8528v8563r7u2742

Stiffness, strength and interwall sliding in aligned and continuous multi-walled carbon nanotube/glass composite microcantilevers

Individual perfect multi-wall carbon nanotubes (MWCNT) can exhibit exceptional properties, such as an elastic modulus of 1 TPa. However, integration of carbon nanotubes (CNTs) in bulk ceramic composites has not yet resulted in the significant improvements in mechanical properties that such data suggest to be achievable. Composites with aligned and continuous CNTs and with high CNT volume fractions might be expected to maximise the improvements. We have produced aligned MWCNT preforms by chemical vapour deposition and fabricated dense, aligned and continuous 20% MWCNT/glass composites. This was achieved by infiltration of a ceramic precursor sol into the interstices of a MWCNT preform and consolidation by hot-pressing. The elastic modulus was measured using microcantilever tests and showed a 32% improvement over that of glass. The Young’s modulus inferred for the MWCNTs in the composite was 200 ± 20 GPa. The load–displacement curves showed a non-linear and hysteretic behaviour which was attributed to interwall sliding within the MWCNTs. Apparent bridging of the cracks by the MWCNTs and a load maximum preceding failure were observed in the composite, indicating progressive toughening with crack growth. The results are discussed in terms of the microstructures of the MWCNTs and composites

The role of gender stereotypes in perceptions of entrepreneurs and intentions to become an entrepreneur

In this study we examine the role of socially constructed gender stereotypes in entrepreneurship and their influence on men and women's entrepreneurial intentions. Data on characteristics of males, females, and entrepreneurs were collected from young adults in three countries. As hypothesized, entrepreneurs were perceived to have predominantly masculine characteristics. Additional results revealed that although both men and women perceive entrepreneurs to have characteristics similar to those of males (masculine gender-role stereotype), only women also perceived entrepreneurs and females as having similar characteristics (feminine gender-role stereotype). Further, though men and women did not differ in their entrepreneurial intentions, those who perceived themselves as more similar to males (high on male gender identification) had higher entrepreneurial intentions than those who saw themselves as less similar to males (low male gender identification). No such difference was found for people who saw themselves as more or less similar to females (female gender identification). The results were consistent across the three countries. Practical implications and directions for future research are discussed