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Fixed Distance (fixed + distance)

Distribution by Scientific Domains

Life Sciences	50%

Selected Abstracts

The Fixed Slope Rule: An Inter-Specific Study

ETHOLOGY, Issue 11 2006
Dana Gulbransen
There are two broad mechanisms by which animals can assess risk when deciding whether to flee: temporally and spatially. Animals that employ temporal mechanisms use predator speed to gauge threat. In contrast, those that use spatial mechanisms use the distance to the predator as an indication of danger. Traditionally, this was viewed as a fixed distance. Recently, a new type of spatial mechanism was proposed that focused on animals initiating flight at a fixed ratio of the distance at which they first responded to the threat. Our study investigated the consistency of this slope among three species: the Eastern gray kangaroo (Macropus giganteus), the Australian wood duck (Chenonetta jubata), and the Australian magpie (Gymnorhina tibicen). We found that these species exhibited statistically indistinguishable slopes from each other and the 0.44 slope that was initially reported in another species. Our results further support the assumption that escape decisions are dynamic. Future studies should determine the ubiquity of this fixed ratio. [source]

Raman spectroscopy for spinline crystallinity measurements.

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008

Abstract Online Raman spectra, obtained at different points along the spinline during the melt spinning of polypropylene homopolymer (hPP) fibers, are presented. The percentage crystallinity corresponding to each spectrum was determined from the normalized intensity of the 809-cm,1 Raman band. A calibration curve for propylene crystallinity was established offline with compression-molded films and fibers spun under different processing conditions. Several hPPs and propylene,ethylene copolymers (with 5,15% ethylene) were used to cover a wide calibration range for propylene crystallinity (9.5,60.9%) with an R2 value of 0.989. This calibration curve was subsequently used to predict the polypropylene crystallinity in the spinline as a function of distance from the spinneret. Under identical conditions of quench and throughput, at a fixed point along the spinline, the overall crystallinity developed in the fiber was found to increase with an increase in the spinning speed. As the spinning speed increased, the point of the onset of crystallization moved closer to the spinneret. The rise in crystallinity was more gradual, at 750 m/min as opposed to 1500 m/min. Increasing the throughput at constant spinning speed was found to decrease the rate of crystallization because of a decrease in the spinline stress. At a fixed distance from the spinneret under identical conditions of quench and spinning speed, fibers spun at a higher throughput showed less overall crystallinity. The onset and rate of crystallization was found to be faster in the lower melt index H502-25RG resin as compared to the 5D49 resin under the spinning conditions explored. The experimental data presented here were used to validate fundamental fiber-spinning models (see part II of this series of articles). The validated models and experimental observations can be used to guide the fiber spinning of isotactic polypropylene for rapid product development. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Hydrodynamic simulation (computational fluid dynamics) of asymmetrically positioned tablets in the paddle dissolution apparatus: impact on dissolution rate and variability

JOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 10 2005
D. M. D'Arcy
The aim of this work was to investigate the dissolution rate from both the curved and planar surfaces of cylindrical compacts of benzoic acid, which were placed centrally and non-centrally at the base of the vessel of the paddle dissolution apparatus. The effect of fixing the compacts to a particular position on the variability of dissolution results was also examined. In addition, computational fluid dynamics (CFD) was used to simulate fluid flow around compacts in the different positions in the vessel, and the relationship between the local hydrodynamics in the region of the compacts and the dissolution rate determined. The dissolution rate was found to increase from the centre position to the off-centre positions for each surface examined. There was a corresponding increase in maximum fluid velocities calculated from the CFD fluid flow simulations at a fixed distance from the compact. There was less variability in dissolution from compacts fixed to any of the positions compared with those that were not fixed. Fluid flow around compacts in different positions could be successfully modelled, and hydrodynamic variability examined, using CFD. The effect of asymmetric fluid flow was evident visually from the change in shape of the eroded compacts. [source]

Population substructures in the soil invertebrate Orchesella cincta, as revealed by microsatellite and TE-AFLP markers

MOLECULAR ECOLOGY, Issue 6 2003
A. W. G. Van Der Wurff
Abstract Microsatellite and three enzyme,amplified fragment length polymorphism (TE-AFLP) DNA markers were used to describe the population genetic structure in the soil dwelling collembolan Orchesella cincta (L.). Two forests were sampled according to a three-level nested hierarchical design, with fixed distances among samples within a parcel and among parcels within a forest. The largest component of variation was found at the smallest scale, within parcels (77,97%), while the smallest component of variation was found between forests. The two different methods to study population structure indicated a similar allocation of variance. Population genetic substructuring was revealed between samples on a scale of 50 m; the degree of substructuring however, varied between parcels and forests. One forest showed a high degree of structure as revealed by microsatellites, while another showed a low degree of structure. A significant deviation from random-mating (average FIS = 0.23) over the two forests was detected. Two of 18 samples showed a difference in population genetic structure between males and females. We discuss the fact that the population genetic structure of O. cincta is significantly affected by long-range dispersal, even though it is a small and wingless insect. This interpretation is supported by observations on tree-climbing behaviour in this species that may facilitate air dispersal. As a consequence, the assumption that migration a priori may be neglected in demographic analysis of O. cincta is incorrect. [source]