We consider the electronic structure near vacancies in the half-filled honeycomb lattice. It is shown that vacancies induce the formation of localized states. When particle-hole symmetry is broken, ...localized states become resonances close to the Fermi level. We also study the problem of a finite density of vacancies, obtaining the electronic density of states, and discussing the issue of electronic localization in these systems. Our results also have relevance for the problem of disorder in d-wave superconductors.
Five experiments were conducted on commercial farms in Brazil aiming to develop a fixed-time artificial insemination (TAI) protocol that achieved pregnancy rates between 40% and 55% in
Bos indicus ...cows. These studies resulted in the development of the following protocol: insertion of an intravaginal device containing 1.9
g of progesterone (CIDR) plus 2.0
mg im estradiol benzoate on Day 0; 12.5
mg im dinoprost tromethamine on Day 7 in cycling cows or on Day 9 in anestrous cows; CIDR withdrawal plus 0.5
mg im estradiol cypionate plus temporary calf removal on Day 9; TAI (48
h after CIDR withdrawal) plus reuniting of calves with their dams on Day 11. Reduced dose of prostaglandin F
2α (PGF
2α; 12.5
mg im dinoprost tromethamine) effectively caused luteolysis. In cycling cows, fertility was greater when the treatment with PGF
2α was administered on Day 7 than on Day 9, but in anestrous cows, no effects of time of the PGF
2α treatment were found. Estradiol cypionate effectively replaced estradiol benzoate or gonadotropin-releasing hormone as the ovulatory stimulus, reducing labor and cost. In this protocol, CIDR inserts were successfully used four times (9 d each use) with no detrimental effects on fertility.
Question: The community-weighted mean (CWM) approach is an easy way of analysing trait–environment association by regressing (or correlating) the mean trait per plot against an environmental variable ...and assessing the statistical significance of the slope or the associated correlation coefficient. However, the CWM approach does not yield valid tests, as random traits (or random indicator values) are far too often judged significantly related to the environmental variable, even when the trait and environmental variable are extrinsic to (not derived from) the community data. Existing solutions are the ZS (Zelený & Schaffers) modified test and the max (or sequential) test based on the fourth-corner correlation. Both tests are based on permutations which become cumbersome when many tests need to be carried out and many permutations are required, as in methods that correct for multiple testing. The main goal of this study was to compare these existing permutation-based solutions and to develop a quick and easy parametric test that can replace them. Methods: This study decomposes the fourth-corner correlation in two ways, which suggests a simple parametric approach consisting of assessing the significances of two linear regressions, one plot-level test as in the CWM approach and one species-level test, the reverse of the CWM approach, that regresses the environmental mean per species (i.e. the species niche centroid) on to the trait. The tests are combined by taking the maximum p-value. The type I error rates and power of this parametric max test are examined by simulation of one- and two-dimensional Gaussian models and log-linear models. Results: The ZS-modified test and the fourth-corner max test are conservative in different scenarios, the ZS-modified test being even more conservative than the fourth-corner. The new parametric max test is shown to control the type I error and has equal or even higher power than permutation tests based on the fourth-corner, the ZS-modified test and variants thereof. A weighted version of the new test showed inflated type I error. Conclusion: The combination of two simple regressions is a good alternative to the fourth-corner and the ZS-modified test. This combination is also applicable when multiple trait measurements are made per plot.
We analyze the propagation of electromagnetic waves along the surface of a nonlinear dielectric medium covered by a graphene layer. We reveal that this system can support and stabilize nonlinear ...transverse electric (TE) plasmon polaritons. We demonstrate that these nonlinear TE modes have a subwavelength localization in the direction perpendicular to the surface, with the intensity much higher than that of an incident wave which excites the polariton.
Climatic conditions vary in spatial frequency globally. Spatially rare climatic conditions provide fewer suitable environments than common ones and should impose constraints on the types of species ...present locally and regionally. We used data on 467 North American angiosperms to test the effects of the spatial frequency of climatic conditions on ecological niche specialisation and functional diversity. We predicted that rare climates should favour generalist species that are able to inhabit a broader range of climatic conditions. Our results show that climate frequency filters species that differ in niche breadths and rare environments host species combinations with greater functional diversity. The proposed analytical approaches and hypotheses can be adapted to investigate different aspects of ecological assemblies and their biodiversity. We discuss different mechanisms regarding how spatial frequency of environments can affect niche composition and functional diversity. These should be useful while developing theoretical frameworks for generating a deeper understanding of its underpinnings.
Climatic conditions vary in spatial frequency globally. Spatially rare climatic conditions provide fewer suitable environments than common ones and should thus impose constraints on the types of species that are present in local communities and regional pools. Our results provide evidence that climate frequency and local climate heterogeneity filter species that differ in their niche breadths and that rare environments host combinations of species with greater functional diversity.
Spatial variation of communities composition (metacommunities) results from multiple assembly mechanisms, including environmental filtering and dispersal; however, whether and why the relative ...importance of the assembly mechanisms in shaping bacterial metacommunity changes through time in marine pelagic systems remains poorly studied. Here, we applied the elements of metacommunity structure framework and the variation partitioning framework to examine whether temporal variation of hydrographic conditions influences bacterioplankton metacommunity dynamics in the southern East China Sea (ECS). The spatiotemporal variation of bacterial communities composition was revealed using 454 pyrosequencing of 16S rDNA. In addition to the whole bacterial community, we analyzed four dominant taxonomic groups (Cyanobacteria, Alphaproteobacteria, Gammaproteobacteria, and Actinobacteria) separately. Our analyses indicate that, considering the whole community level, the determinism of metacommunity structure varied among seasons. When the degree of connectivity was low (December), the metacommunity exhibited random distribution and was explained mainly by the environmental component. However, Clementsian metacommunity was found at intermediate connectivity (May), during which the environmental and spatial predictors were both significant. When connectivity was high (August), a random distribution pattern was found and no significant effect of environmental filtering or dispersal limitation was detected. Nevertheless, when considering different taxonomic groups, the differences in metacommunity dynamics among groups were found. Our results suggest that the driving forces of metacommunity dynamics varied depending on hydrography, as the degrees of environmental heterogeneity and connectivity among habitat patches were determined by circulation pattern. Moreover, mechanisms varied among different taxonomic groups, suggesting that differential dispersal capacity among taxonomic groups should be integrated into community assembly studies.
We call for journals to commit to requiring open data be archived in a format that will be simple and clear for readers to understand and use. If applied consistently, these requirements will allow ...contributors to be acknowledged for their work through citation of open data, and facilitate scientific progress.
Patterns in biodiversity and species coexistence are the result of multiple interacting processes including evolutionary history, trait variation, species interactions, dispersal, environmental ...variation, and landscape heterogeneity. Exploring patterns of biodiversity across space is perhaps the best integrative method (in contrast to the scarcity of temporal data) to interpret the influence of these multiple and interactive effects in determining community assembly, but it is still underdeveloped. Two emerging fields, metacommunity ecology and community phylogenetics, have been making relevant, though rather independent, progress toward understanding how communities are assembled in space. Our main goals were twofold. First, we described a heuristical framework to merge these two fields into "metacommunity phylogenetics." The main goal of this framework is to provide a way to think about how niche properties of species arranged across the environment and different spatial scales influence the process of community assembly. Second, we developed an analytical framework to link niche properties based on trait and phylogenetics to environmental and spatial variation. In order to assess the performance of the framework, we used extensive computer simulations of community assembly to show that the procedure is robust under a variety of scenarios.
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