A fossil pollen analysis of Fox Prairie bog, Hamilton county, Indiana

The study of post-Pleistocene vegetations and migration of forests by means of fossil pollen in peat is a comparatively recent addition to the study of paleobotany and plant geography in America and is certainly in its pioneer stage in Indiana; yet that state offers a rich field to the botanist interested in the postglacial migration of vegetation. In the northern part of the state, numerous bogs in various stages of development, ranging from the open lake stage to those completely covered by meadow or forest, are readily accessible for study. In central Indiana, bogs are less numerous, but all the more interesting, because they mark the southernmost extension of glacial bogs in Indiana

Self-Ligating vs. Conventional Brackets as Perceived by Orthodontists

Introduction: Within the past decade, significant developments, new designs, and numerous proposed advantages of self-ligating (SL) brackets have caused them to gain great popularity among practicing orthodontists. The purpose of this study was to determine if there are significant clinical differences between SL and conventional brackets on orthodontic treatment as perceived by practicing orthodontists, and more specifically, if the proposed advantages of SL brackets are evident in clinical practice. Methods: A survey was developed to evaluate how SL brackets compare to conventional brackets when perceived by practicing orthodontists (n=430). The initial series of questions focused on individual practitioner characteristics and the clinician’s experience with SL brackets, while the second part of the survey allowed the orthodontists to indicate a preference for either SL or conventional brackets in regard to a variety of treatment factors. Results: Most of the responding orthodontists (90%) had experience using SL brackets in clinical practice. SL brackets were preferred for the majority of orthodontic treatment factors, and were most significantly indicated as having shorter adjustment appointments (P \u3c0.0001), providing faster initial treatment progress (P \u3c0.0001), and were the most preferred bracket during the initial alignment stage of treatment (P \u3c0.0001). On the other hand, practitioners reported a stronger preference for conventional brackets during the finishing and detailing stages of treatment (P \u3c0.0001), and regarded conventional brackets as being significantly more cost effective than SL brackets (P \u3c0.0001). Less emergency appointments were also reported with conventional brackets compared to SL brackets (P \u3c0.0001). Despite the perceived overall preference for SL brackets, more than one-third of practitioners no longer use or are planning on discontinuing use of SL brackets. In many circumstances, the orthodontists’ bracket preference was significantly influenced by the proportion of patients they treated with SL brackets (P \u3c0.0001), the number of cases it took them to become accustomed to SL brackets (P \u3c0.0001), and their average appointment intervals for both SL brackets (P \u3c0.0001) and conventional brackets (P = 0.0002). Conclusion: Overall, the orthodontists participating in this study reported a perceived difference between SL brackets and conventional brackets on orthodontic treatment. SL brackets were found to be preferred for the majority of the treatment factors, while there were a few situations in which conventional brackets were preferred. Ultimately, due to the lack of high-quality evidence supporting SL brackets, more objective, evidence-based research is essential in order to evaluate definitively the clinical differences of SL and conventional brackets on orthodontic treatment

A novel scaling indicator of early warning signals helps anticipate tropical cyclones

Tipping events in dynamical systems have been studied in many contexts, often modelled by the decay of critical modes, system states which are tending towards bifurcation, characterised by increased return times to stable equilibria. Temporal scaling properties of time series data can be used to detect the presence of a critical mode by estimating the decay rate, and indicators of changes in these properties may therefore be used to provide an early warning signal (EWS) for an impending tipping event. The lag-1 autocorrelation function (ACF(1)) indicator and the detrended fluctuation analysis (DFA) indicator have previously been used in such a way; in this paper we introduce a novel scaling indicator based on the decay rate of the power spectrum (PS). We compare the ACF(1), DFA- and PS-indicators using artificial data; data from a model which includes a bifurcation point; and sea-level pressure data along the paths of 14 tropical cyclones. By using the PS-indicator with such data, we show that the new indicator may be used to provide an EWS in a context where the ACF(1)- and DFA-indicators fail

The Dynamical Environment of Dawn at Vesta

Dawn is the first NASA mission to operate in the vicinity of the two most massive asteroids in the main belt, Ceres and Vesta. This double-rendezvous mission is enabled by the use of low-thrust solar electric propulsion. Dawn will arrive at Vesta in 2011 and will operate in its vicinity for approximately one year. Vesta's mass and non-spherical shape, coupled with its rotational period, presents very interesting challenges to a spacecraft that depends principally upon low-thrust propulsion for trajectory-changing maneuvers. The details of Vesta's high-order gravitational terms will not be determined until after Dawn's arrival at Vesta, but it is clear that their effect on Dawn operations creates the most complex operational environment for a NASA mission to date. Gravitational perturbations give rise to oscillations in Dawn's orbital radius, and it is found that trapping of the spacecraft is possible near the 1:1 resonance between Dawn's orbital period and Vesta's rotational period, located approximately between 520 and 580 km orbital radius.This resonant trapping can be escaped by thrusting at the appropriate orbital phase. Having passed through the 1:1 resonance, gravitational perturbations ultimately limit the minimum radius for low-altitude operations to about 400 km,in order to safely prevent surface impact. The lowest practical orbit is desirable in order to maximize signal-to-noise and spatial resolution of the Gamma-Ray and Neutron Detector and to provide the highest spatial resolution observations by Dawn's Framing Camera and Visible InfraRed mapping spectrometer. Dawn dynamical behavior is modeled in the context of a wide range of Vesta gravity models. Many of these models are distinguishable during Dawn's High Altitude Mapping Orbit and the remainder are resolved during Dawn's Low Altitude Mapping Orbit, providing insight into Vesta's interior structure.Comment: Corrected normalization coefficients; updated table text and reference

The contamination of the surface of Vesta by impacts and the delivery of the dark material

The Dawn spacecraft observed the presence of dark material, which in turn proved to be associated with OH and H-rich material, on the surface of Vesta. The source of this dark material has been identified with the low albedo asteroids, but it is still a matter of debate whether the delivery of the dark material is associated with a few large impact events, to micrometeorites or to the continuous, secular flux of impactors on Vesta. The continuous flux scenario predicts that a significant fraction of the exogenous material accreted by Vesta should be due to non-dark impactors likely analogous to ordinary chondrites, which instead represent only a minor contaminant in the HED meteorites. We explored the continuous flux scenario and its implications for the composition of the vestan regolith, taking advantage of the data from the Dawn mission and the HED meteorites. We used our model to show that the stochastic events scenario and the micrometeoritic flux scenario are natural consequences of the continuous flux scenario. We then used the model to estimate the amounts of dark and hydroxylate materials delivered on Vesta since the LHB and we showed how our results match well with the values estimated by the Dawn mission. We used our model to assess the amount of Fe and siderophile elements that the continuous flux of impactors would mix in the vestan regolith: concerning the siderophile elements, we focused our attention on the role of Ni. The results are in agreement with the data available on the Fe and Ni content of the HED meteorites and can be used as a reference frame in future studies of the data from the Dawn mission and of the HED meteorites. Our model cannot yet provide an answer to the fate of the missing non-carbonaceous contaminants, but we discuss possible reasons for this discrepancy.Comment: 31 pages, 7 figures, 4 tables. Accepted for publication on the journal ICARUS, "Dark and Bright Materials on Vesta" special issu

Radioelements on Vesta: An Update

The main-belt asteroid 4 Vesta is the putative parent body of the howardite, eucrite, and diogenite (HED) meteorites. Because these achondrites have similar petrology, geochemistry, chronology, and O-isotope compositions, it is thought that most HEDs originated from a single parent body. The connection to Vesta is supported by a close spectroscopic match between Vesta and the HEDs and a credible mechanism for their delivery to Earth. Studies of the HEDs show that Vesta underwent igneous differentiation, forming a Fe-rich core, ultramafic mantle, and basaltic crust. Here we present the results of peak analyses applied to a gamma ray difference spectrum to determine the absolute abundances of K and Th. Data are compared to meteorite whole-rock compositions and other inner solar system bodies. The results, while preliminary, represent our present best estimates for these elements. Because the element signatures are near detection limits and not fully resolved, further analysis (e.g. using spectral unmixing) will be required for improved accuracy and to characterize systematic errors

Olivine or Impact Melt: Nature of the "Orange" Material on Vesta from Dawn

NASA's Dawn mission observed a great variety of colored terrains on asteroid (4) Vesta during its survey with the Framing Camera (FC). Here we present a detailed study of the orange material on Vesta, which was first observed in color ratio images obtained by the FC and presents a red spectral slope. The orange material deposits can be classified into three types, a) diffuse ejecta deposited by recent medium-size impact craters (such as Oppia), b) lobate patches with well-defined edges, and c) ejecta rays from fresh-looking impact craters. The location of the orange diffuse ejecta from Oppia corresponds to the olivine spot nicknamed "Leslie feature" first identified by Gaffey (1997) from ground-based spectral observations. The distribution of the orange material in the FC mosaic is concentrated on the equatorial region and almost exclusively outside the Rheasilvia basin. Our in-depth analysis of the composition of this material uses complementary observations from FC, the visible and infrared spectrometer (VIR), and the Gamma Ray and Neutron Detector (GRaND). Combining the interpretations from the topography, geomorphology, color and spectral parameters, and elemental abundances, the most probable analog for the orange material on Vesta is impact melt