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Nearest Neighbours (nearest + neighbour)
Terms modified by Nearest Neighbours Selected AbstractsComplex networks: two ways to be robust?ECOLOGY LETTERS, Issue 6 2002Carlos J. Melián Abstract Recent studies of biological networks have focused on the distribution of the number of links per node. However, the connectivity distribution does not uncover all the complexity of their topology. Here, we analyse the relation between the connectivity of a species and the average connectivity of its nearest neighbours in three of the most resolved community food webs. We compare the pattern arising with the one recently reported for protein networks and for a simple null model of a random network. Whereas two highly connected nodes are unlikely to be connected between each other in protein networks, the reverse happens in food webs. We discuss this difference in organization in relation to the robustness of biological networks to different types of perturbation. [source] Temporal coherence of two alpine lake basins of the Colorado Front Range, U.S.A.FRESHWATER BIOLOGY, Issue 3 2000J. I. L. L. S. Baron 1. Knowledge of synchrony in trends is important to determining regional responses of lakes to disturbances such as atmospheric deposition and climate change. We explored the temporal coherence of physical and chemical characteristics of two series of mostly alpine lakes in nearby basins of the Colorado Rocky Mountains. Using year-to-year variation over a 10-year period, we asked whether lakes more similar in exposure to the atmosphere be-haved more similarly than those with greater influence of catchment or in-lake processes. 2. The Green Lakes Valley and Loch Vale Watershed are steeply incised basins with strong altitudinal gradients. There are glaciers at the heads of each catchment. The eight lakes studied are small, shallow and typically ice-covered for more than half the year. Snowmelt is the dominant hydrological event each year, flushing about 70% of the annual discharge from each lake between April and mid-July. The lakes do not thermally stratify during the period of open water. Data from these lakes included surface water temper-ature, sulphate, nitrate, calcium, silica, bicarbonate alkalinity and conductivity. 3. Coherence was estimated by Pearson's correlation coefficient between lake pairs for each of the different variables. Despite close geographical proximity, there was not a strong direct signal from climatic or atmospheric conditions across all lakes in the study. Individual lake characteristics overwhelmed regional responses. Temporal coherence was higher for lakes within each basin than between basins and was highest for nearest neighbours. 4. Among the Green Lakes, conductivity, alkalinity and temperature were temporally coherent, suggesting that these lakes were sensitive to climate fluctuations. Water tem-perature is indicative of air temperature, and conductivity and alkalinity concentrations are indicative of dilution from the amount of precipitation flushed through by snowmelt. 5. In Loch Vale, calcium, conductivity, nitrate, sulphate and alkalinity were temporally coherent, while silica and temperature were not. This suggests that external influences are attenuated by internal catchment and lake processes in Loch Vale lakes. Calcium and sulphate are primarily weathering products, but sulphate derives both from deposition and from mineral weathering. Different proportions of snowmelt versus groundwater in different years could influence summer lake concentrations. Nitrate is elevated in lake waters from atmospheric deposition, but the internal dynamics of nitrate and silica may be controlled by lake food webs. Temperature is attenuated by inconsistently different climates across altitude and glacial meltwaters. 6. It appears that, while the lakes in the two basins are topographically close, geologically and morphologically similar, and often connected by streams, only some attributes are temporally coherent. Catchment and in-lake processes influenced temporal patterns, especially for temperature, alkalinity and silica. Montane lakes with high altitudinal gradients may be particularly prone to local controls compared to systems where coherence is more obvious. [source] Trends in aquatic macrophyte species turnover in Northern Ireland , which factors determine the spatial distribution of local species turnover?GLOBAL ECOLOGY, Issue 5 2004Einar Heegaard ABSTRACT Aim, The study examined qualitative predictions of ecological theories in relation to the spatial distribution of species turnover of aquatic macrophytes, through the following parameters: (1) distance between lakes (2) chemical conditions of the lakes (3) chemical differences between the lakes, and (4) the lake size. Location, 562 lakes dispersed throughout Northern Ireland were analysed. Methods, To obtain species turnover estimates independent of richness, the average distance between focal lakes and their five nearest neighbours in ordination space (DCA) was standardized by the species richness in a Generalized Additive Model (GAM). The relationships between species turnover and ecological (chemical condition, chemical difference, distance between lakes, and lake-size) and geographical parameters (latitude, longitude, and altitude) were analysed using GAM. Results, The results indicate that the pattern in species turnover is a combination of the chemical conditions and the distance between the lakes, including the interaction term. The effects of chemical heterogeneity and lake size parameters were both positive but weak. In general, increased distance and decreased ionic concentration contribute to increased turnover. The influence of distance on species turnover is strongest at low and high altitude, and at mid-elevation the species turnover is mainly driven by the chemical conditions. Towards the north there is an increasing influence of distance, whereas in the south the chemical conditions have their strongest influence. Conclusions, There is a need for components from several established ecological theories to explain the spatial trends in species turnover within Northern Ireland. Central theories in this particular study are the population/metapopulation dynamics, the continuum concept, and the species-pool concept. [source] A comparison of nearest neighbours, discriminant and logit models for auditing decisionsINTELLIGENT SYSTEMS IN ACCOUNTING, FINANCE & MANAGEMENT, Issue 1-2 2007Chrysovalantis Gaganis This study investigates the efficiency of k -nearest neighbours (k -NN) in developing models for estimating auditors' opinions, as opposed to models developed with discriminant and logit analyses. The sample consists of 5276 financial statements, out of which 980 received a qualified audit opinion, obtained from 1455 private and public UK companies operating in the manufacturing and trade sectors. We develop two industry-specific models and a general one using data from the period 1998,2001, which are then tested over the period 2002,2003. In each case, two versions of the models are developed. The first includes only financial variables. The second includes both financial and non-financial variables. The results indicate that the inclusion of credit rating in the models results in a considerable increase both in terms of goodness of fit and classification accuracies. The comparison of the methods reveals that the k -NN models can be more efficient, in terms of average classification accuracy, than the discriminant and logit models. Finally, the results are mixed concerning the development of industry-specific models, as opposed to general models. Copyright © 2007 John Wiley & Sons, Ltd. [source] Location of Mn sites in ferromagnetic Ga1,xMnxAs studied by means of X-ray diffuse scattering holographyJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2006M. Kopecký A three-dimensional image of the local neighbourhood of Mn atoms in a Ga1,xMnxAs (x = 0.02) layer has been obtained by using X-ray diffuse scattering holography. The first and second nearest neighbours of the Mn atoms correspond to the local structure around Ga atoms in the zinc-blende GaAs structure. Accordingly, the Mn atoms are situated in substitutional positions. [source] Non-adiabatic small polaron hopping conduction in sodium borate tungstate glassesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2003A. Al-Shahrani Abstract The dc electrical conductivity of (100,x)Na2B4O7,xWO3 (x = 5, 15, 20 and 30 mol%) glasses is reported in the temperature range 323,473 K. The density and molar volume for these glasses are consistent with the ionic size, atomic weight and amount of different elements in the glasses. At high temperatures the Mott model of phonon-assisted small polaron hopping between nearest neighbours is consistent with conductivity data, while at intermediate temperatures the Greaves variable-range hopping model is found to be appropriate. The estimated model parameters such as number of ions per unit volume, hopping distance, polaron radius and activation energy are found to be consistent with the formation of localized states in these glasses. The electrical conduction of these glasses is confirmed to be that of non-adiabatic small polaron hopping. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The C,C pair in the vicinity of a bcc Fe bulk vacancy: electronic structure and bondingPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2007S. Simonetti Abstract C,Fe and C,C interactions near a bcc Fe vacancy were analysed using DFT calculations. A cell containing 14 atoms was used to simulate the local environment of the Fe vacancy. Carbon atoms were positioned in their local energy minimum configurations. The most stable positions for the C atoms in the vacancy region were found at about 1.23 Ĺ from the vacancy centre and near the first nearest-neighbour octahedral sites. Changes in the electronic structure of Fe atoms near a vacancy were analysed. Fe,Fe bonds surrounding the vacancy weaken their bond when the C atoms are present. This bond weakening is a consequence of C,Fe bond formation. The Fe,C interactions occur mainly via Fe 4s orbitals with a lesser participation of Fe 3p orbitals. There is an electron transfer to the C atoms from their Fe nearest neighbours. The C,C interaction was also analysed. For the C,C distance of 1.462 Ĺ, there is a bonding between the C atoms. The C,C interaction is stronger than the C,Fe interactions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Surface and interface investigations using radioactive atomsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2004K. Potzger Abstract The magnetic behavior of isolated nonmagnetic probe atoms (Cd) at ferromagnetic Ni surfaces and interfaces have been studied using perturbed angular correlation (PAC) spectroscopy. Atomic resolution is achieved making it possible to distinguish between probe atoms at various surface sites, i.e., in/at terraces, atomic steps, kinks. These different atomic surface sites have differing Ni coordination numbers, (i.e., the number of Ni nearest neighbours). With decreasing coordination number, a continuous nonlinear dependent correlation was found with increasing magnetic hyperfine fields (Bhf). Furthermore, experimental evidence is presented, that the induced s-moments on the Cd isolated impurity is independent of the details of the surface symmetry but essentially determined only by the coordination number. Finally, it has been observed that monolayers of Pd on Ni form large unit cells, which offer selected sites to the Cd impurity. We discuss this finding as basic research towards future applications with self-organizing patterned structures. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||