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Structures Alone (structure + alone)
Selected AbstractsAssessing the influence of environmental heterogeneity on bird spacing patterns: a case study with two raptorsECOGRAPHY, Issue 2 2006Thomas Cornulier Testing for aggregation or regularity in point patterns is difficult in the presence of spatial variation in abundance due to environmental heterogeneity. Using a recently developed method generalizing Ripley's K function for non homogeneous point patterns, we test the aggregation of the nests in two species of birds (little owl and Montagu's harrier) exhibiting heterogeneous distributions in response to landscape structure. We compare the results obtained under different null models accounting for environmental heterogeneity at large and/or small spatial scales. Whereas both species were initially found to form clusters at some scale, taking spatial heterogeneity into account revealed that 1) territorial little owls showed no clustering of territories when habitat availability was considered; 2) semi-colonial harriers still formed significant clusters, but part of the aggregation in this species could be explained by landscape structure alone. Our results highlight that it is feasible and highly recommended to account for non-stationarity when testing for aggregation. Further, provided that sufficient knowledge of the study system is available, this approach helps to identify behavioural and environmental components of spatial variation in abundance. Additionally, we demonstrate that accounting for large or small-scale heterogeneity affects the perception of spacing behaviours differently, so that both need to be considered. [source] Sc3+,Lu3+ -Doped ,-SiAlONsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2008Feng Ye Sc3+ and dual Sc3+,Lu3+ -doped ,-SiAlON compositions were sintered by hot pressing, and the formation behavior, microstructure, and mechanical properties were assessed. It was found that the small cation Sc3+ could not be accommodated into the ,-SiAlON structure alone. The addition of Lu2O3 in the composition induces the Sc3+ cation to enter the ,-SiAlON structure, and leads to the production of ,-SiAlON with an elongated-grain microstructure. Transmission electron microscopy analysis shows that ,-SiAlON grains always contain an ,-Si3N4 core, implicating heterogeneous nucleation to be in present in a mixed lutetium/scandium-doped ,-SiAlON system. [source] Experimental evidence of habitat provision by aggregations of Riftia pachyptila at hydrothermal vents on the East Pacific RiseMARINE ECOLOGY, Issue 1 2007Breea Govenar Abstract Habitat created or modified by the physical architecture of large or spatially dominant species plays an important role in structuring communities in a variety of terrestrial, aquatic, and marine habitats. At hydrothermal vents, the giant tubeworm Riftia pachyptila forms large and dense aggregations in a spatially and temporally variable environment. The density and diversity of smaller invertebrates is higher in association with aggregations of R. pachyptila than on the surrounding basalt rock seafloor. Artificial substrata designed to mimic R. pachyptila aggregations were deployed along a gradient of productivity to test the hypothesis that high local species diversity is maintained by the provision of complex physical structure in areas of diffuse hydrothermal flow. After 1 year, species assemblages were compared among artificial aggregations in low-, intermediate-, and high-productivity zones and compared to natural aggregations of R. pachyptila from the same site. Hydrothermal vent fauna colonized every artificial aggregation, and both epifaunal density and species richness were highest in areas of high chemosynthetic primary production. The species richness was also similar between natural aggregations of R. pachyptila and artificial aggregations in intermediate- and high-productivity zones, suggesting that complex physical structure alone can support local species diversity in areas of chemosynthetic primary production. Differences in the community composition between natural and artificial aggregations reflect the variability in microhabitat conditions and biological interactions associated with hydrothermal fluid flux at low-temperature hydrothermal vents. Moreover, these local ecological factors may further contribute to the maintenance of regional species diversity in hydrothermal vent communities on the East Pacific Rise. [source] Helical- and ahelical-dependent chiral recognition mechanisms in capillary electrophoresis using amylose as the selectorELECTROPHORESIS, Issue 8 2009Weili Wei Abstract The present study discovered that helical structures of amylose were not always responsible for its chiral recognition abilities in CE. Several enantiomers with different structures were selected as models. Based on ultraviolet,visible spectroscopy and 13C NMR measurements, it was found that helical structures were gradually destroyed by temperature elevation and almost entirely transformed to extended ahelical structures above 60°C. Then, CE and 1H NMR chiral recognitions were investigated at different temperatures; chiral selectivity of the enantiomers varied in two different ways. Summarily, helical structures were necessary only for chiral separations of the enantiomers with small (<0.78,nm) and flexible molecular structures. However, for the gauche enantiomers (>0.78,nm) with high steric hindrances over their chiral centers, ahelical structures alone can realize chiral recognitions. By using iodine as a helix including competitor, it was further proved that helical structures functioned through the inclusive complexations only in the chiral separations of small enantiomers and had no effect for the others. The underlying mechanisms of the functions of helical and ahelical structures in molecular level were discussed as well. [source] Studies on the quantitative relationship between the olfactory thresholds of pyrazine derivatives and their molecular structuresFLAVOUR AND FRAGRANCE JOURNAL, Issue 2 2009Feng Luan Abstract Quantitative structure,property relationship (QSPR) investigation was performed for the study of olfactory thresholds of pyrazine derivatives. Descriptors calculated from the molecular structures alone were used to represent the characteristics of the compounds. The six molecular descriptors selected by the best mutilinear regression (BMLR) in CODESSA were used as inputs for support vector machine (SVM) and radial basis function neural networks (RNFNN). The root mean squared errors (RMS) of logarithm of olfactory thresholds (p.p.m.) for the training, predicted and overall datasets were 0.5674, 0.6601 and 0.5860 for BMLR, 0.4720, 0.6861 and 0.5194 for RBFNN, and 0.5242, 0.6466 and 0.5495 for SVM, respectively. The prediction results were in agreement with the experimental values. The QSPR models provide a rapid, simple and valid way to predict the odour threshold of pyrazine derivatives. Copyright © 2009 John Wiley & Sons, Ltd. [source] Prediction of Volatile Components Retention Time in Blackstrap Molasses by Least-Squares Support Vector MachineMOLECULAR INFORMATICS, Issue 5 2008Yongna Yuan Abstract House flies are pestiferous insects that have the potential to spread many diseases to humans and livestock, so it is very significant for us to manage house fly populations. Many commercial types of bait are available to attract house flies, but most are designed for outdoor or limited indoor use, due to their malodorous components. This study sought to identify compounds present in blackstrap molasses that might be attractive to house flies. An effective Quantitative Structure-Property Relationship (QSPR) model between the Retention Time (RT) and five molecular descriptors of the volatile compounds in blackstrap molasses, was built using a modified algorithm of Least-Squares Support Vector Machine (LS-SVM). Descriptors calculated from the molecular structures alone were used to represent the characteristics of compounds. The five molecular descriptors selected by the Heuristic Method (HM) in CODESSA were used as inputs for LS-SVM. The results obtained by LS-SVM were compared with those obtained by the HM. The LS-SVM model gives better results with the predicted correlation coefficient () 0.919 and Root Mean-Square Errors (RMSE) 2.193 for the test set, as well as that 0.824 and 2.728 in the MLR model. The prediction results of log RT are in very good agreement with the experimental values. This paper provided a new and effective method for predicting the chromatography retention index. [source] Tropical Montane Forest Restoration in Costa Rica: Overcoming Barriers to Dispersal and EstablishmentRESTORATION ECOLOGY, Issue 4 2000Karen D. Holl Abstract Tropical forests are being cleared at an alarming rate although our understanding of their ecology is limited. It is therefore essential to design restoration experiments that both further our basic knowledge of tropical ecology and inform management strategies to facilitate recovery of these ecosystems. Here we synthesize the results of research on tropical montane forest recovery in abandoned pasture in Costa Rica to address the following questions: (1) What factors limit tropical forest recovery in abandoned pasture? and (2) How can we use this information to design strategies to facilitate ecosystem recovery? Our results indicate that a number of factors impede tropical forest recovery in abandoned pasture land. The most important barriers are lack of dispersal of forest seeds and seedling competition with pasture grasses. High seed predation, low seed germination, lack of nutrients, high light intensity, and rabbit herbivory also affect recovery. Successful strategies to facilitate recovery in abandoned pastures must simultaneously overcome numerous obstacles. Our research shows that establishment of woody species, either native tree seedlings or early-successional shrubs, can be successful in facilitating recovery, by enhancing seed dispersal and shading out pasture grasses. On the contrary, bird perching structures alone are not an effective strategy, because they only serve to enhance seed dispersal but do not reduce grass cover. Remnant pasture trees can serve as foci of natural recovery and may enhance growth of planted seedlings. Our results highlight the importance of: (1) understanding the basic biology of an ecosystem to design effective restoration strategies; (2) comparing results across a range of sites to determine which restoration strategies are most generally useful; and (3) considering where best to allocate efforts in large-scale restoration projects. [source] The Study of Protein Folding and Dynamics by Determination of Intramolecular Distance Distributions and Their Fluctuations Using Ensemble and Single-Molecule FRET Measurements,CHEMPHYSCHEM, Issue 5 2005Elisha Haas Prof. Abstract The folding and dynamics of globular proteins is a multidimensional problem. The structures of the heterogeneous population of refolding protein molecules are characterized by multiple distances and time constants. Deciphering the mechanism of folding depends on studies of the processes rather than the folded structures alone. Spectroscopy is indispensable for these sorts of studies. Herein, it is shown that the determination of intramolecular distance distributions by ensemble and single-molecule FRET experiments enable the exploration of partially folded states of refolding protein molecules. [source] | |||||||||||||