Graphs with second largest eigenvalue less than 1/21/2

We characterize the simple connected graphs with the second largest eigenvalue less than 1/2, which consists of 13 classes of specific graphs. These 13 classes hint that $c_{2}\in [1/2, \sqrt{2+\sqrt{5}}]$, where $c_2$ is the minimum real number $c$ for which every real number greater than $c$ is a limit point in the set of the second largest eigenvalues of the simple connected graphs. We leave it as a problem.Comment: 36 pages, 2 table

Eightfold Fermionic Excitation in a Charge Density Wave Compound

Unconventional quasiparticle excitations in condensed matter systems have become one of the most important research frontiers. Beyond two- and fourfold degenerate Weyl and Dirac fermions, three-, six- and eightfold symmetry protected degeneracies have been predicted however remain challenging to realize in solid state materials. Here, charge density wave compound TaTe4 is proposed to hold eightfold fermionic excitation and Dirac point in energy bands. High quality TaTe4 single crystals are prepared, where the charge density wave is revealed by directly imaging the atomic structure and a pseudogap of about 45 meV on the surface. Shubnikov de-Haas oscillations of TaTe4 are consistent with band structure calculation. Scanning tunneling microscopy reveals atomic step edge states on the surface of TaTe4. This work uncovers that charge density wave is able to induce new topological phases and sheds new light on the novel excitations in condensed matter materials.Comment: Accepted by PRB: https://journals.aps.org/prb/accepted/7907cK4eW0b1ee0b93fd67c1b42942bbb08eafc3

DATA for Peng et al.

The Excel file includes 10 datasets associated with the manuscript

Domesticated honeybees facilitate interspecific hybridization between two Taraxacum congeners

Interspecific hybridization is common in plants under natural conditions, but the ecological mechanisms underlying when and how it happens have not fully been understood.Taraxacum calanthodium and Taraxacum lugubre are two herbaceous annals co-occurring in alpine meadows of the eastern Tibetan Plateau that share the same pollinators including domestic honeybees during their overlapping flowering times. Because honeybees tend to visit flowers less discriminatively when bee densities are high, we hypothesized that intense apiculture would facilitate hybridization between these two congeneric species. We tested this hypothesis by examining the frequencies of the two parent species occurrence and the hybrid (based on morphological and genetic differences) along three transects radiating from well-established apiaries. Experiments show that both T.calanthodium and T.lugubre produce seeds sexually and asexually, and that they can hybridize via pollen transfer. Bee visitation rates and the frequency of the hybrid were significantly higher in the sites nearest to apiaries compared to distant site along each of the three transects. The hybrids were consistently genetically intermediate between the two species, as indicated by simple sequence repeat-based analyses.Synthesis. These data indicate that domestic honeybees foster interspecific hybridization between the two Taraxacum species and that anthropogenic effects on pollen vectors can significantly influence species hybridization in nature. We suggest that more effort should be made to quantify the effects of environmental change on pollinators and their effects on species evolution

Data from: Domesticated honeybees facilitate interspecific hybridization between two Taraxacum congeners

1. Interspecific hybridization is common in plants under natural conditions, but the ecological mechanisms underlying when and how it happens have not fully been understood. 2. Taraxacum calanthodium and T. lugubre are two herbaceous annals co-occurring in alpine meadows of the eastern Tibetan Plateau that share the same pollinators including domestic honeybees during their overlapping flowering times. Because honeybees tend to visit flowers less discriminatively when bee densities are high, we hypothesized that intense apiculture would facilitate hybridization between these two congeneric species. 3. We tested this hypothesis by examining the frequencies of the two parent species occurrence and the hybrid (based on morphological and genetic differences) along three transects radiating from well-established apiaries. 4. Experiments show that both Taraxacum calanthodium and T. lugubre produce seeds sexually and asexually, and that they can hybridize via pollen transfer. Bee visitation rates and the frequency of the hybrid were significantly higher in the sites nearest to apiaries compared to distant site along each of the three transects. The hybrids were consistently genetically intermediate between the two species, as indicated by Simple Sequence Repeat- based analyses. 5. Synthesis. These data indicate that domestic honeybees foster interspecific hybridization between the two Taraxacum species and that anthropogenic effects on pollen vectors can significantly influence species hybridization in nature. We suggest that more effort should be made to quantify the effects of environmental change on pollinators and their effects on species evolution

Investigation into effect of grain sizes on deformation behavior of AZ31 alloys in different loading conditions

The AZ31 magnesium alloy with different grain sizes was prepared by adjusting the heat treatment process, and then the tension and compression tests were carried out to explore the effect of grain sizes and loading conditions on the microstructures and properties of the magnesium alloy. The Hall-Petch slope presented dramatic anisotropy under tension (181 Mpa· μm1∕2) and compression (115 Mpa· μm1∕2), the geometric compatibility factor (m′) and the difference in activation stress between the initiated deformation modes of two neighboring grains (σd) were calculated to analyze the anisotropy quantitatively. In compression, it was found that the elongation increased with further grain coarsening, which was attributed to the fact that more twins were initiated in the coarse grains and the preferred initiation of twinning to inhibit competitive crack initiation

Determinants of Mammal and Bird Species Richness in China Based on Habitat Groups.

Understanding the spatial patterns in species richness is a central issue in macroecology and biogeography. Analyses that have traditionally focused on overall species richness limit the generality and depth of inference. Spatial patterns of species richness and the mechanisms that underpin them in China remain poorly documented. We created a database of the distribution of 580 mammal species and 849 resident bird species from 2376 counties in China and established spatial linear models to identify the determinants of species richness and test the roles of five hypotheses for overall mammals and resident birds and the 11 habitat groups among the two taxa. Our result showed that elevation variability was the most important determinant of species richness of overall mammal and bird species. It is indicated that the most prominent predictors of species richness varied among different habitat groups: elevation variability for forest and shrub mammals and birds, temperature annual range for grassland and desert mammals and wetland birds, net primary productivity for farmland mammals, maximum temperature of the warmest month for cave mammals, and precipitation of the driest quarter for grassland and desert birds. Noteworthily, main land cover type was also found to obviously influence mammal and bird species richness in forests, shrubs and wetlands under the disturbance of intensified human activities. Our findings revealed a substantial divergence in the species richness patterns among different habitat groups and highlighted the group-specific and disparate environmental associations that underpin them. As we demonstrate, a focus on overall species richness alone might lead to incomplete or misguided understanding of spatial patterns. Conservation priorities that consider a broad spectrum of habitat groups will be more successful in safeguarding the multiple services of biodiversity

Low ecological representation in the protected area network of China

Protected areas are considered as an essential strategy to halt the decline of biodiversity. Ecological representation in protected areas is crucial for assessment on the progress toward conservation targets. Although China has established a large number of protected areas since the 1950s, ecological representation of protected areas is poorly understood. Here, we performed the complementarity analysis to evaluate ecological representation of protected areas in China. We used a database of the geographical distribution for 10,396 woody plant species, 2,305 fern species, 406 amphibian species, 460 reptile species, 1,364 bird species, and 590 mammal species from 2,376 counties across China. We identified complementary sets of counties for all species or threatened species of plant and vertebrate species using a complementarity algorithm. We evaluated ecological representation of 3,627 protected areas and discerned conservation gaps by comparing the distribution of protected areas with complementary sets. The results show that the spatially representative and complementary sites for biodiversity are poorly covered, and a fairly large proportion of protected areas is not designed to efficiently represent biodiversity at the national scale. Our methodology can serve as a generic framework for assessment on ecological representation of protected areas at the national scale

SLM multivariate models for the residuals of species richness of all mammals and its habitat groups.

<p>Six variables that explained most of the variance of the residuals of species richness were selected based on univariate regression models and hierarchical partitioning. We established the best multivariate model using multivariable GLM regression. To avoid inflation of type I errors and invalid parameter estimate owning to spatial autocorrelation, we then performed SLM multivariate regression (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0143996#sec002" target="_blank">Methods</a>). All continuous variables were log10-transformed (n = 2376; *: Pr(>|z|)<0.05; **: Pr(>|z|)<0.01; ***: Pr(>|z|)<0.001).</p><p>SLM multivariate models for the residuals of species richness of all mammals and its habitat groups.</p