Effect Of Initial Density Research Articles

Nanocluster Formation within the Vapor Plume, Produced by Nanosecond-Laser Ablation: Effect of Initial Density and Pressure Distributions

The condensation of vapor in the expanding plume produced by ns-laser ablation is discussed within the framework of the Zeldovich and Raizer theory of condensation. The spherical plume expansion is described by a numerical solution of the hydrodynamic equations by the cubic interpolated pseudo-particle (CIP) method. This permits us to analyze the role of initial distributions of density and pressure on the size distribution function of nanoclusters. For parabolic distributions (for the plume expansion into vacuum), calculations reproduce the same results as those obtained by particular solutions of gas-dynamic equations. When initial distributions deviate from the parabolic distributions, the size distribution function varies. For the rectangular plume, the size distribution function of nanoclusters demonstrates two maximums. A similar effect is observed due to the ambient gas influence.

Possible ways of enhancing high temperature ductility in CuO doped cubic zirconia (8Y–CSZ)

The effect of initial density and rapid prestraining on superplastic ductility of 1 wt-%CuO doped cubic zirconia (8Y–CSZ) was investigated. To obtain a range of initial densities, the tensile test specimens were slip cast to net shape and pressureless sintered over a range of temperatures in air. The specimens were then superplastically tested at a temperature of 1500 K and at a constant strain rate of 1×10-4 s-1. The results showed that specimens with low initial densities had lower flow stresses and higher superplastic elongations to failure than higher density specimens. The reasons for the ductility change were discussed with reference to the presence of porosity and grain growth. For the prestraining test, a specimen with an initial density of 95% was prestrained to 30% at a temperature of 1550 K and at a prestrain rate ɛ ·1 of 1×10-3 s-1, followed by elongation to failure at a slower test strain rate ɛ ·2 of 1×10-4 s-1. It was seen that prestraining at the above test conditions considerably improved superplastic ductility. The reasons for this ductility enhancement were explained in terms of suppression of grain growth.

The effect of initial density on interactions between bryophytes at individual and community levels

Summary 1 A glasshouse experiment was conducted with seven bryophyte species to determine the effects of competition. We tested whether competitive hierarchies varied with initial abundance (density and biomass) and between two different experimental approaches. 2 Relative competition intensities were calculated based on proportional growth (G) and relative biomass (R). The standards for comparison (i.e. no interactions) were species’ performance in monocultures at one of two sowing abundances (the combined monocultures method; CM) and in a low‐density mixture of equal proportions of all species (the community density series method; CDS). 3 Proportional growth decreased with increasing initial abundance for all species. Community effects (relative biomass of each species) were generally weaker and more variable than individual effects. R increased linearly with abundance for only one species, while three species showed a quadratic response (of which two were negative). 4 Competitive hierarchies derived by the CM method differed with abundance, and we argue that the CDS method is likely to provide a more reliable comparison. 5 With CDS, competitive hierarchies were similar along the community abundance gradient, implying that non‐linear competitive effects are not likely to be a mechanism of coexistence in this community. 6 There were significant competitive effects on community composition, but not on diversity as measured by evenness. At the community level individual species tended to show either competitive or positive effects throughout the gradient of initial community abundance, with decreasing values for most species at high initial community abundance, as were the effects of interactions on community composition.

Effects of Initial Density on Soil Instability at High Pressures

A high-pressure triaxial compression and extension testing apparatus was utilized to investigate the effect of initial relative density on soil instability. Stress paths from a series of undrained tests, at confining pressures from 8 to 60 MPa, were evaluated to determine the location of the potential instability region. Experiments were performed on specimens with relative densities of 30% and 60%, and compared with previously published results for 90%. The results indicate that initial relative density has a small effect on the slope of the instability line, with the slope of the line decreasing as initial density is reduced. In addition, the conditions under which a specimen exhibits unstable behavior were confirmed by performing series of specialized instability tests. For tests with undrained conditions imposed inside the region of potential instability, instability was observed immediately. For tests with undrained conditions imposed outside, but relatively close to this region, creep effects would cause pore pressures to increase resulting eventually in instability. In general, it was found that initiation of unstable behavior depends on the relationship between the shape of the yield surface and the effective stress path followed.

INTRODUCING A “BOUNDARY-FLUX” APPROACH TO QUANTIFYING INSECT DIFFUSION RATES

Dispersal behaviors of organisms have been the subject of extensive ecological investigation at both the theoretical and experimental levels. One common framework for field studies of dispersal behavior that can be easily melded with theoretical work is the calculation of “diffusion rates.” Traditionally, this approach to studying dispersal has required (1) the tedious location of large numbers of individuals at a particular time or (2) actively tracking the movements of individuals. Here, I present a flux-based or “boundary-oriented” methodology that quantifies the passage of individuals into an absorbing boundary of known location at multiple points in time. This approach, which is the natural complement of existing methods, may make quantification of dispersal behavior more practical for time-strapped field researchers. Under the umbrella of the flux-based approach presented here, I use data from field experiments to determine the effect of initial density on dispersal rate for two sympatric species of...

One-Dimensional Compression of Sands at High Pressures

A one-dimensional testing apparatus was developed to test soils to axial stresses up to 850 MPa. The apparatus was instrumented with strain gauges such that lateral soil stresses, and therefore K0 , could be inferred from measured circumferential strains. Three different initial densities of quartz, Cambria, and gypsum sands were tested and it was found that the effect of initial density was eliminated at high stress magnitudes. This stress magnitude was higher for mineralogically harder grains than for softer grains. The inferred values of K0 for the mineralogically harder Cambria sand was found to be constant at high pressures, but slightly below that indicated by Jaky's equation. However, the softer gypsum sand indicated increasing values of K0 as the stress magnitude increased. This apparently was caused by inelastic, viscous flow during shearing.

Effect of initial density on the compaction of loess soils by heavy compactors

Effect of initial density on the compaction of loess soils by heavy compactors