Home About us Contact
|
Home About us Contact | ||
|
|
||
Geometric Similarity (geometric + similarity)
Selected AbstractsPolyhedral azaborane chemistry, 6-(C5H5N)- arachno -4-NB8H11ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2000Caroline Price The title compound, 6-pyridyl-4-aza- arachno -nonaborane(11), C5H16B8N2, has an arachno nine-vertex {4-NB8H11} cluster structure with a pyridine ligand in the exo -6-position. The cluster has close geometric similarities to the thiaborane and carbaborane analogues. [source] Close range digital photogrammetric analysis of experimental drainage basin evolutionEARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2003J. Brasington Abstract Despite the difficulties of establishing formal hydraulic and geometric similarity, small-scale models of drainage basins have often been used to investigate the evolution and dynamics of larger-scale landforms. Historically, this analysis has been restricted to planform basin characteristics and only in the last decade has the topographic similarity of experimental landscapes been explored through explicitly three-dimensional parameters such as the distributions of cumulative drainage area, area,slope and catchment elevation. The current emphasis on three-dimensional morphometry reflects a growing awareness of the descriptive paucity of planform data and the need for more robust analysis of spatial scaling relationships. This paradigm shift has been significantly facilitated by technological developments in topographic survey and digital elevation modelling (DEM) which now present the opportunity to acquire and analyse high-resolution, distributed elevation data. Few studies have, however, attempted to use topographic modelling to provide information on the changing pattern and rate of sediment transport though an evolving landscape directly by using multitemporal DEM differencing techniques. This paper reports a laboratory study in which digital photogrammetry was employed to derive high-resolution DEMs of a simulated landscape in declining equilibrium at 15 minute frequency through a 240 minute simulation. Detailed evaluation of the DEMs revealed a vertical precision of 1·2 mm and threshold level of change detection between surfaces of ±3 mm at the 95 per cent confidence level. This quality assurance set the limits for determining the volumetric change between surfaces, which was used to recover the sediment budget through the experiment and to examine local - and basin-scale rates of sediment transport. A comparison of directly observed and morphometric estimates of sediment yield at the basin outlet was used to quantify the closure of the sediment budget over the simulation, and revealed an encouragingly small 6·2 per cent error. The application of this dynamic morphological approach has the potential to offer new insights into the controls on landform development, as demonstrated here by an analysis of the changing pattern of the basin sediment delivery ratio during network growth. Copyright © 2003 John Wiley & Sons, Ltd. [source] Adjusting Bone Mass for Differences in Projected Bone Area and Other Confounding Variables: An Allometric Perspective,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 4 2002Alan M. Nevill B.Sc., Ph.D. Abstract The traditional method of assessing bone mineral density (BMD; given by bone mineral content [BMC] divided by projected bone area [Ap], BMD = BMC/Ap) has come under strong criticism by various authors. Their criticism being that the projected bone "area" (Ap) will systematically underestimate the skeletal bone "volume" of taller subjects. To reduce the confounding effects of bone size, an alternative ratio has been proposed called bone mineral apparent density [BMAD = BMC/(Ap)3/2]. However, bone size is not the only confounding variable associated with BMC. Others include age, sex, body size, and maturation. To assess the dimensional relationship between BMC and projected bone area, independent of other confounding variables, we proposed and fitted a proportional allometric model to the BMC data of the L2-L4 vertebrae from a previously published study. The projected bone area exponents were greater than unity for both boys (1.43) and girls (1.02), but only the boy's fitted exponent was not different from that predicted by geometric similarity (1.5). Based on these exponents, it is not clear whether bone mass acquisition increases in proportion to the projected bone area (Ap) or an estimate of projected bone volume (Ap)3/2. However, by adopting the proposed methods, the analysis will automatically adjust BMC for differences in projected bone size and other confounding variables for the particular population being studied. Hence, the necessity to speculate as to the theoretical value of the exponent of Ap, although interesting, becomes redundant. [source] Scaling of plantar pressures in mammalsJOURNAL OF ZOOLOGY, Issue 3 2009F. Michilsens Abstract The interaction of the limbs with the substrate can teach a lot about an animal's gait mechanics. Unlike ground-reaction forces, plantar pressure distributions are rarely studied in animals, but they may provide more detailed information about the loading patterns and locomotor function of specific anatomical structures. With this study, we aim to describe pressures for a large and diverse sample of mammalian species, focusing on scaling effects. We collected dynamic plantar pressure distributions during voluntary walking in 28 mammal species. A dynamic classification of foot use was made, which distinguished between plantiportal, digitiportal and unguliportal animals. Analysis focused on scaling effects of peak pressures, peak forces and foot contact areas. Peak pressure for the complete mammal sample was found to scale to (mass)1/2, higher than predicted assuming geometric similarity, and we found no difference between the different types of foot use. Only the scaling of peak force is dependent on the dynamic foot use. We conclude that plantar peak pressure rises faster with mass than expected, regardless of the type of foot use, and scales higher than in limb bones. These results might explain some anatomical and behavioural adaptations in graviportal animals. [source] Using cluster analysis to study transition-metal geometries: four-coordinate complexes with two salicylaldiminato or related ligandsACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2007Andrew Parkin Cluster analysis is shown to be an effective method to analyse and classify metal coordination geometry in a very large number of four-coordinate bis -salicylaldimato (or bis- ,-iminoketonate) transition-metal complexes available in the Cambridge Structural Database. The methods described require no prior knowledge of chemistry to be input; retrieved structures are automatically clustered into groups based purely on the geometric similarity of the fragments and these groupings can then be interpreted by the structural chemist. [source] The structural mechanics and evolution of aquaflying birdsBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2010MICHAEL HABIB Mass-specific bone strength was examined in the forelimb and hindlimb of 64 species of birds to determine if aquaflying birds (which utilize the wings for propulsion underwater) differ in their skeletal strength compared with other avian taxa. Long bone strengths were estimated from cross-sectional measurements. Compared with the expectation from geometric similarity, humeral section modulus in volant birds scales nearly isometrically, while femoral strength scales with significant positive allometry. Penguin mass-specific humeral strength is greatly elevated, but the average humeral strength in species that are propelled by the wings in both air and water do not differ from the values calculated in non-diving taxa. However, amphibious flyers have gracile femora. Comparative analyses using independent contrasts were utilized to examine the impact of phylogenetic signal. The residual measured for the penguin,procellariiform humeral strength contrast was larger in magnitude (residual of 2.14) than at any other node in the phylogeny. The data strongly indicate that the transition from an amphibious flight condition to a fully aquatic condition involves greater changes in mechanical factors than the transition from purely aerial locomotion to amphibious wing use. There remains the possibility that a historical effect, such as ancestral body size, has impacted the mechanical scaling of penguins. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99, 687,698. [source] | |||||||||||||