The Red-Cockaded Woodpecker Cavity Tree: A Very Special Pine

The adaptation of red-cockaded woodpeckers (Picoides borealis) to fire-maintained southern pine ecosystems has included the development of behaviors that permit the species to use living pines for their cavity trees. Their adaptation to pine ecosystems has also involved a major adjustment in the species\u27 breeding system to cooperative breeding, probably in response to the extended time period required to excavate a completed cavity in a living pine and the relative rarity of completed cavities for nesting. The characteristics of live pines make them variable in their suitability as cavity trees, leading to the evolution of selection behavior among woodpeckers. Red-cockaded woodpeckers require a very special type of pine for their cavity tree. Potential cavity trees must be sufficiently old because only older pines have heartwood of sufficient diameter to physically house a woodpecker cavity without breaching the resin producing sapwood. Older pines also have a larger diameter of heartwood higher in the pine, permitting higher cavity placement, well away from frequent fires. Older pines also have a higher occurrence rate of red heart fungus (Phellinus pini), which decays the heartwood allowing cavity excavation to proceed more quickly. The potential cavity tree also needs to have relatively thin sapwood, which reduces the time the woodpecker must spend excavating through living xylem tissue that exudes sticky pine resin when pecked. Red-cockaded woodpeckers scale loose bark from the bole of their cavity trees and excavate resin wells above and below cavity entrances. These behaviors create a resin barrier that is very effective in deterring predation by rat snakes (Elaphe spp.). Thus, the ability of pines to produce adequate resin is also important to the woodpecker. Red-cockaded wood- peckers can detect the pine\u27s ability to produce resin and select pines that are high producers. Higher yields of resin likely create better barriers against rat snakes. The socially dominant breeding male red-cockaded woodpecker selects the cavity tree that produces the most resin for its roost tree, which during spring becomes the group\u27s nest tree. Our recent research suggests that red-cockaded woodpeckers also select pines with particular resin chemistries. High concentrations of diterpenes may increase resin viscosity, stickiness, irritability, or other factors that may be important for creating a barrier against rat snakes

Fragment-to-Lead Medicinal Chemistry Publications in 2018

This Perspective, the fourth in an annual series, summarizes fragment-to-lead (F2L) success stories published during 2018. Topics such as target class, screening methods, physicochemical properties, and ligand efficiency are discussed for the 2018 examples as well as for the combined 111 F2L examples covering 2015-2018. While the overall properties of fragments and leads have remained constant, a number of new trends are noted, for example, broadening of target class coverage and application of FBDD to covalent inhibitors. Moreover, several studies make use of fragment hits that were previously described in the literature, illustrating that fragments are versatile starting points that can be optimized to structurally diverse leads. By focusing on success stories, the hope is that this Perspective will identify and inform best practices in fragment-based drug discovery.</p

Performance of a Monocular Vision-aided Inertial Navigation System for a Small UAV

DOI: http://dx.doi.org/10.2514/6.2013-4699The use of optical sensors for navigation on aircraft has receive much attention recently. Optical sensors provide a wealth of information about the environment and are standard payloads for many unmanned aerial vehicles (UAVs). Simultaneous localization and map- ping (SLAM) algorithms using optical sensors have become computationally feasible in real time in the last ten years. However, implementations of visual SLAM navigation systems on aerial vehicles are still new and consequently are often limited to restrictive environ- ments or idealized conditions. One example of a ight condition which can dramatically a ect navigation performance is altitude. This paper seeks to examine the performance of monocular extended Kalman lter based SLAM (EKF-SLAM) navigation over a large altitude change. Simulation data is collected which illustrates the behavior of the naviga- tion system over the altitude range. Navigation and control system parameters values are speci ed which improve vehicle performance across the ight conditions. Additionally, a detailed presentation of the monocular EKF-SLAM navigation system is given. Flight test results are presented on a quadrotor

Dynamic communities in multichannel data: An application to the foreign exchange market during the 2007--2008 credit crisis

We study the cluster dynamics of multichannel (multivariate) time series by representing their correlations as time-dependent networks and investigating the evolution of network communities. We employ a node-centric approach that allows us to track the effects of the community evolution on the functional roles of individual nodes without having to track entire communities. As an example, we consider a foreign exchange market network in which each node represents an exchange rate and each edge represents a time-dependent correlation between the rates. We study the period 2005-2008, which includes the recent credit and liquidity crisis. Using dynamical community detection, we find that exchange rates that are strongly attached to their community are persistently grouped with the same set of rates, whereas exchange rates that are important for the transfer of information tend to be positioned on the edges of communities. Our analysis successfully uncovers major trading changes that occurred in the market during the credit crisis.Comment: 8 pages, 6 figures, accepted for publication in Chao