Strategies towards statistically robust interpretations of in situ U–Pb zircon geochronology

Zircon U–Pb geochronology has become a keystone tool across Earth science, arguably providing the gold standard in resolving deep geological time. The development of rapid in situ analysis of zircon (via laser ablation and secondary ionization mass spectrometry) has allowed for large amounts of data to be generated in a relatively short amount of time and such large volume datasets offer the ability to address a range of geological questions that would otherwise remain intractable (e.g. detrital zircons as a sediment fingerprinting method). The ease of acquisition, while bringing benefit to the Earth science community, has also led to diverse interpretations of geochronological data. In this work we seek to refocus U–Pb zircon geochronology toward best practice by providing a robust statistically coherent workflow. We discuss a range of data filtering approaches and their inherent limitations (e.g. discordance and the reduced chi-squared; MSWD). We evaluate appropriate mechanisms to calculate the most geologically appropriate age from both 238U/206Pb and 207Pb/206Pb ratios and demonstrate the cross over position when chronometric power swaps between these ratios. As our in situ analytical techniques become progressively more precise, appropriate statistical handing of U–Pb datasets will become increasingly pertinent

Vegetation Structure of Mangrove Ecosystems in Panama

Mangroves provide important habitat for terrestrial and marine wildlife. They buffer shorelines from flooding and sequester excess nutrients and pollutants in runoff before reaching rivers and oceans. Mangroves provide a wintering habitat for migratory bird species. These habitats are being rapidly lost to coastal development. This research focused on assessing the vegetation structure of mangrove ecosystems in Panama

Signal distortion from microelectrodes in clinical EEG acquisition systems

Many centers are now using high-density microelectrodes during traditional intracranial electroencephalography (iEEG) both for research and clinical purposes. These microelectrodes are FDA-approved and integrate into clinical EEG acquisition systems. However, the electrical characteristics of these electrodes are poorly described and clinical systems were not designed to use them; thus, it is possible that this shift into clinical practice could have unintended consequences. In this study, we characterized the impedance of over 100 commercial macro- and microelectrodes using electrochemical impedance spectroscopy (EIS) to determine how electrode properties could affect signal acquisition and interpretation. The EIS data were combined with the published specifications of several commercial EEG systems to design digital filters that mimic the behavior of the electrodes and amplifiers. These filters were used to analyze simulated brain signals that contain a mixture of characteristic features commonly observed in iEEG. Each output was then processed with several common quantitative EEG measurements. Our results show that traditional macroelectrodes had low impedances and produced negligible distortion of the original signal. Brain tissue and electrical wiring also had negligible filtering effects. However, microelectrode impedances were much higher and more variable than the macroelectrodes. When connected to clinical amplifiers, higher impedance electrodes produced considerable distortion of the signal at low frequencies (<60 Hz), which caused significant changes in amplitude, phase, variance and spectral band power. In contrast, there were only minimal changes to the signal content for frequencies above 100 Hz. In order to minimize distortion with microelectrodes, we determined that an acquisition system should have an input impedance of at least 1 GΩ, which is much higher than most clinical systems. These results show that it is critical to account for variations in impedance when analyzing EEG from different-sized electrodes. Data from microelectrodes may yield misleading results unless recorded with high-impedance amplifiers.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98632/1/1741-2552_9_5_056007.pd

Chopping skyrmions from magnetic chiral domains with uniaxial stress in magnetic nanowire

<p>Results from log-linear models comparing visits to patches by <i>Notomys alexis</i> in different habitats and with and without predator odors.</p

How many clones need to be sequenced from a single forensic or ancient DNA sample in order to determine a reliable consensus sequence?

Forensic and ancient DNA (aDNA) extracts are mixtures of endogenous aDNA, existing in more or less damaged state, and contaminant DNA. To obtain the true aDNA sequence, it is not sufficient to generate a single direct sequence of the mixture, even where the authentic aDNA is the most abundant (e.g. 25% or more) in the component mixture. Only bacterial cloning can elucidate the components of this mixture. We calculate the number of clones that need to be sampled (for various mixture ratios) in order to be confident (at various levels of confidence) to have identified the major component. We demonstrate that to be >95% confident of identifying the most abundant sequence present at 70% in the ancient sample, 20 clones must be sampled. We make recommendations and offer a free-access web-based program, which constructs the most reliable consensus sequence from the user's input clone sequences and analyses the confidence limits for each nucleotide position and for the whole consensus sequence. Accepted authentication methods must be employed in order to assess the authenticity and endogeneity of the resulting consensus sequences (e.g. quantification and replication by another laboratory, blind testing, amelogenin sex versus morphological sex, the effective use of controls, etc.) and determine whether they are indeed aDNA

Land Conservation in the Northeastern United States: An Assessment of Historic Trends and Current Conditions

This article discusses the evolution of land conservation efforts and outcomes in the Northeast, examine major drivers of landscape change, and review key conservation tools that have been used to protect public values at the local and landscape levels. We then assess the current status of land conservation, and draw lessons for other regions facing conservation challenges across mixed ownership landscapes under varying development and land-use pressures. Finally, we explore new and emerging trends in the factors driving land development and conservation activities in an effort to assess the challenges that lie ahead