Indiana University

About: Indiana University is a education organization based out in Bloomington, Indiana, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 64480 authors who have published 150058 publications receiving 6392902 citations. The organization is also known as: Indiana University system & indiana.edu.

Superior mechanical flexibility of phosphorene and few-layer black phosphorus

Abstract: Recently, fabricated two dimensional (2D) phosphorene crystal structures have demonstrated great potential in applications of electronics. Mechanical strain was demonstrated to be able to significantly modify the electronic properties of phosphorene and few-layer black phosphorus. In this work, we employed first principles density functional theory calculations to explore the mechanical properties of phosphorene, including ideal tensile strength and critical strain. It was found that a monolayer phosphorene can sustain tensile strain up to 27% and 30% in the zigzag and armchair directions, respectively. This enormous strain limit of phosphorene results from its unique puckered crystal structure. We found that the tensile strain applied in the armchair direction stretches the pucker of phosphorene, rather than significantly extending the P-P bond lengths. The compromised dihedral angles dramatically reduce the required strain energy. Compared to other 2D materials, such as graphene, phosphorene demonstrates superior flexibility with an order of magnitude smaller Young's modulus. This is especially useful in practical large-magnitude-strain engineering. Furthermore, the anisotropic nature of phosphorene was also explored. We derived a general model to calculate the Young's modulus along different directions for a 2D system.

Reanalysis suggests that genomic islands of speciation are due to reduced diversity, not reduced gene flow

Abstract: The metaphor of ‘genomic islands of speciation’ was first used to describe heterogeneous differentiation among loci between the genomes of closely related species. The biological model proposed to explain these differences was that the regions showing high levels of differentiation were resistant to gene flow between species, while the remainder of the genome was being homogenized by gene flow and consequently showed lower levels of differentiation. However, the conditions under which such differentiation can occur at multiple unlinked loci are restrictive; additionally, essentially, all previous analyses have been carried out using relative measures of divergence, which can be misleading when regions with different levels of recombination are compared. Here, we test the model of differential gene flow by asking whether absolute divergence is also higher in the previously identified ‘islands’. Using five species pairs for which full sequence data are available, we find that absolute measures of divergence are not higher in genomic islands. Instead, in all cases examined, we find reduced diversity in these regions, a consequence of which is that relative measures of divergence are abnormally high. These data therefore do not support a model of differential gene flow among loci, although islands of relative divergence may represent loci involved in local adaptation. Simulations using the program IMa2 further suggest that inferences of any gene flow may be incorrect in many comparisons. We instead present an alternative explanation for heterogeneous patterns of differentiation, one in which postspeciation selection generates patterns consistent with multiple aspects of the data.

Do Politically Connected Boards Affect Firm Value

Abstract: In countries with a weak legal system and a high level of corruption it has been shown that political connections are valuable to a corporation. This paper explores whether political connections are also important in the U.S., which has well-developed financial markets as well as a strong legal system. The paper uses an original hand-collected data set on the political connections of board members of S&P 500 companies to sort companies into those connected to the Republican Party and those connected to the Democratic Party. An analysis of the stock price response to the announcement of the board nomination of a politically connected director shows a positive abnormal stock return. The paper also analyses the stock price response to the Republican win in the 2000 Presidential Election and finds that companies connected to the Republican Party increase in value while companies connected to the Democratic Party decrease in value. The results further suggest that these effects are more pronounced for larger corporations. Finally, the paper controls for political donations by corporations prior to the 2000 election and finds that, unlike board connections, donations do not predict industry-adjusted abnormal post-election returns.