Purdue University

About: Purdue University is a education organization based out in West Lafayette, Indiana, United States. It is known for research contribution in the topics: Population & Heat transfer. The organization has 73219 authors who have published 163563 publications receiving 5775236 citations. The organization is also known as: Purdue & Purdue-West Lafayette.

The Selaginella genome identifies genetic changes associated with the evolution of vascular plants.

Abstract: Vascular plants appeared ~410 million years ago, then diverged into several lineages of which only two survive: the euphyllophytes (ferns and seed plants) and the lycophytes. We report here the genome sequence of the lycophyte Selaginella moellendorffii (Selaginella), the first nonseed vascular plant genome reported. By comparing gene content in evolutionarily diverse taxa, we found that the transition from a gametophyte- to a sporophyte-dominated life cycle required far fewer new genes than the transition from a nonseed vascular to a flowering plant, whereas secondary metabolic genes expanded extensively and in parallel in the lycophyte and angiosperm lineages. Selaginella differs in posttranscriptional gene regulation, including small RNA regulation of repetitive elements, an absence of the trans-acting small interfering RNA pathway, and extensive RNA editing of organellar genes.

Hyperbolic metamaterials

Abstract: Metamaterials with hyperbolic dispersion (where two eigenvalues of the dielectric permittivity tensor have opposite signs) exhibit a broad bandwidth singularity in the photonic density of states, with resulting manifestations in a variety of phenomena, from spontaneous emission to light propagation and scattering. In this tutorial, I will review some of the recent developments in this field.

Monetary and Non-Monetary Punishment in the Voluntary Contributions Mechanism

Abstract: A demand for behavioral norms arises when members of a group have individual incentives to take actions that reduce the group's overall welfare (James S. Coleman, 1990). Norms require enforcement with a system of sanctions that penalize deviations from acceptable behavior (George C. Homans, 1961). Formal sanctions include fines or restrictions implemented by a legal system or private individuals that impose costs of money and time on the offender. However, informal sanctions such as peer pressure, gossip, or social ostracism might in some cases also be effective deterrents, and expressions of social acceptance might be effective in encouraging group-oriented behavior (Peter M. Blau, 1964). Indeed, the fact that expressions of approval and disapproval are commonly observed in human interaction suggests that they must influence the behavior of at least some individuals. In recognition of the importance of informal sanctions, economists have integrated phenomena such as peer pressure (Eugene Kandel and Edward P. Lazear, 1992; John M. Barron and Kathy Paulson-Gjerde, 1997), and the avoidance of social disapproval (George A. Akerlof, 1980; Heinz Hollander, 1990; Assar Lindbeck et al., 1999) into theoretical models. Social pressures are thought to be a major factor behind high voter participation (Carol-Jean Uhlaner, 1989; Stephen Knack, 1992) and compliance with the law (Tom R. Tyler, 1990).

Interference by clustered regularly interspaced short palindromic repeat (CRISPR) RNA is governed by a seed sequence

Abstract: Prokaryotic clustered regularly interspaced short palindromic repeat (CRISPR)/Cas (CRISPR-associated sequences) systems provide adaptive immunity against viruses when a spacer sequence of small CRISPR RNA (crRNA) matches a protospacer sequence in the viral genome. Viruses that escape CRISPR/Cas resistance carry point mutations in protospacers, though not all protospacer mutations lead to escape. Here, we show that in the case of Escherichia coli subtype CRISPR/Cas system, the requirements for crRNA matching are strict only for a seven-nucleotide seed region of a protospacer immediately following the essential protospacer-adjacent motif. Mutations in the seed region abolish CRISPR/Cas mediated immunity by reducing the binding affinity of the crRNA-guided Cascade complex to protospacer DNA. We propose that the crRNA seed sequence plays a role in the initial scanning of invader DNA for a match, before base pairing of the full-length spacer occurs, which may enhance the protospacer locating efficiency of the E. coli Cascade complex. In agreement with this proposal, single or multiple mutations within the protospacer but outside the seed region do not lead to escape. The relaxed specificity of the CRISPR/Cas system limits escape possibilities and allows a single crRNA to effectively target numerous related viruses.