Ground-Truthing Maxent in East Texas Rivers

Unionid mussels are a guild of freshwater, sedentary filter-feeders, which play a critical role in freshwater systems. Mussels are currently experiencing a global decline in both species richness and abundance, due to invasive species, human alteration of water systems, and climate change. In North America, which is considered to have the highest global diversity of bivalve species, native mussels are currently declining rapidly with at least 37 species considered to already be extinct. If extant mussel species are to be preserved, then it is vital that conservation efforts be prioritized towards areas in which they are likely to be found. This is often done through ecological niche models. Maxent for example uses the principle of maximum entropy on presence data and environmental variables to create a suitability score for a particular area, and is one of the most widely used of the ecological niche modeling programs. It has been used to make maps predicting the suitability scores for multiple species but very little ground-truthing to see if the maps are assigning the correct scores has been conducted. We ground-truthed the Maxent program’s suitability score from 30 samples for six threatened mussel species in the rivers of East Texas by visiting differently scored sites to determine if the Maxent suitability scores were reflective of actual abundances. Ground-truthing was done by sampling at 138 sites throughout East Texas. These sites had been assigned suitability scores from a previous study, and the mussels found at the site were compared to those that were predicted to be there by Maxent. The new maps created by Maxent were compared to the original maps to see if new occurrence points added to the predictive ability of the maps by looking at the test AUC and test gain values. The influences of new data on Maxent’s predictive ability for finding a particular mussel species at a site, and the number of mussels found at a site were also investigated by linear and logistic regression. Additional occurrence points were found to significantly improve the predictive maps for the Triangle Pigtoe, the Texas Heelsplitter, and the Southern Hickorynut, and all maps were found to accurately predict locations for mussels. Maxent’s predictive ability via their suitability scores was improved for all species with additional occurrence points. However, for almost all of the species looked at, there was a data cap, which was a point at which additional data no longer improved the models. This suggests that the amount of data necessary to make accurate maps may not be as large as originally thought, and when trying to conserve an organism this could be important

Bayesian Methods for Analysis and Adaptive Scheduling of Exoplanet Observations

We describe work in progress by a collaboration of astronomers and statisticians developing a suite of Bayesian data analysis tools for extrasolar planet (exoplanet) detection, planetary orbit estimation, and adaptive scheduling of observations. Our work addresses analysis of stellar reflex motion data, where a planet is detected by observing the "wobble" of its host star as it responds to the gravitational tug of the orbiting planet. Newtonian mechanics specifies an analytical model for the resulting time series, but it is strongly nonlinear, yielding complex, multimodal likelihood functions; it is even more complex when multiple planets are present. The parameter spaces range in size from few-dimensional to dozens of dimensions, depending on the number of planets in the system, and the type of motion measured (line-of-sight velocity, or position on the sky). Since orbits are periodic, Bayesian generalizations of periodogram methods facilitate the analysis. This relies on the model being linearly separable, enabling partial analytical marginalization, reducing the dimension of the parameter space. Subsequent analysis uses adaptive Markov chain Monte Carlo methods and adaptive importance sampling to perform the integrals required for both inference (planet detection and orbit measurement), and information-maximizing sequential design (for adaptive scheduling of observations). We present an overview of our current techniques and highlight directions being explored by ongoing research.Comment: 29 pages, 11 figures. An abridged version is accepted for publication in Statistical Methodology for a special issue on astrostatistics, with selected (refereed) papers presented at the Astronomical Data Analysis Conference (ADA VI) held in Monastir, Tunisia, in May 2010. Update corrects equation (3

Random tree growth by vertex splitting

We study a model of growing planar tree graphs where in each time step we separate the tree into two components by splitting a vertex and then connect the two pieces by inserting a new link between the daughter vertices. This model generalises the preferential attachment model and Ford's $\alpha$-model for phylogenetic trees. We develop a mean field theory for the vertex degree distribution, prove that the mean field theory is exact in some special cases and check that it agrees with numerical simulations in general. We calculate various correlation functions and show that the intrinsic Hausdorff dimension can vary from one to infinity, depending on the parameters of the model.Comment: 47 page

Transit Timing Observations from Kepler: VI. Potentially interesting candidate systems from Fourier-based statistical tests

We analyze the deviations of transit times from a linear ephemeris for the Kepler Objects of Interest (KOI) through Quarter six (Q6) of science data. We conduct two statistical tests for all KOIs and a related statistical test for all pairs of KOIs in multi-transiting systems. These tests identify several systems which show potentially interesting transit timing variations (TTVs). Strong TTV systems have been valuable for the confirmation of planets and their mass measurements. Many of the systems identified in this study should prove fruitful for detailed TTV studies.Comment: 32 pages, 6 of text and one long table, Accepted to Ap

GHOSTS I: A New Faint very Isolated Dwarf Galaxy at D = 12 +/- 2 Mpc

We report the discovery of a new faint dwarf galaxy, GHOSTS I, using HST/ACS data from one of our GHOSTS (Galaxy Halos, Outer disks, Substructure, Thick disk, and Star clusters) fields. Its detected individual stars populate an approximately one magnitude range of its luminosity function (LF). Using synthetic color-magnitude diagrams (CMDs) to compare with the galaxy's CMD, we find that the colors and magnitudes of GHOSTS I's individual stars are most consistent with being young helium-burning and asymptotic giant branch stars at a distance of 12 +/- 2 Mpc. Morphologically, GHOSTS I appears to be actively forming stars, so we tentatively classify it as a dwarf irregular (dIrr) galaxy, although future HST observations deep enough to resolve a larger magnitude range in its LF are required to make a more secure classification. GHOSTS I's absolute magnitude is $M_V = -9.85^{+ 0.40}_{- 0.33}$, making it one of the least luminous dIrr galaxies known, and its metallicity is lower than [Fe/H] =-1.5 dex. The half-light radius of GHOSTS I is 226 +/- 38 pc and its ellipticity is 0.47 +/- 0.07, similar to Milky Way and M31 dwarf satellites at comparable luminosity. There are no luminous massive galaxies or galaxy clusters within ~ 4 Mpc from GHOSTS I that could be considered as its host, making it a very isolated dwarf galaxy in the Local Universe.Comment: 8 pages, 7 figures. Accepted for publication in Ap

Childhood membranoproliferative glomerulonephritis type I: Limited steroid therapy

Childhood membranoproliferative glomerulonephritis type I: Limited steroid therapy. Nineteen patients with biopsy proven membranopro liferative glomerulonephritis type I (MPGN I) and a minimum of three years of follow-up (mean 6.5 ± 0.7 years) have been treated with an uncontrolled regimen of limited corticosteroids . Initial therapy ranged from 20 mg per os (po) every other day to 30 mg/kg/day i.v. for three consecutive days, depending on clinical disease severity. Therapy was then decreased based on each patient's improving clinical status. At diagnosis creatinine clearance (Ccr) was < 80 ml/min/l .73 m2 in 12 patients and < 50 in 2. All patients had hematuria and proteinuria, with 15 in the nephrotic range. Hypertension, present at diagnosis in 13, developed in five others following institution of prednisone, and was controlled medically. Renal biopsy was repeated after two years of therapy prior to cessation of treatment (mean total treatment duration 38 ± 3 months). Follow-up biopsy revealed decreased glomerular inflamn activity in 88% of patients. All patients have now been off prednisone for 40 ± 9 months. The mean CCr is 126 ± 5 ml/min/l.73 m2. Eight patients have normal urinalyses. These data suggest that early therapy with a limited course of corticosteroids, and control of associ ated hypertension, may forestall progressive renal insufficiency in children with MPGN type I

Searching for Trojan Asteroids in the HD 209458 System: Space-based MOST Photometry and Dynamical Modeling

We have searched Microvariability and Oscillations of STars (MOST) satellite photometry obtained in 2004, 2005, and 2007 of the solar-type star HD 209458 for Trojan asteroid swarms dynamically coupled with the system's transiting "hot Jupiter" HD 209458b. Observations of the presence and nature of asteroids around other stars would provide unique constraints on migration models of exoplanetary systems. Our results set an upper limit on the optical depth of Trojans in the HD 209458 system that can be used to guide current and future searches of similar systems by upcoming missions. Using cross-correlation methods with artificial signals implanted in the data, we find that our detection limit corresponds to a relative Trojan transit depth of 1\times10-4, equivalent to ~1 lunar mass of asteroids, assuming power-law Trojan size distributions similar to Jupiter's Trojans in our solar system. We confirm with dynamical interpretations that some asteroids could have migrated inward with the planet to its current orbit at 0.045 AU, and that the Yarkovsky effect is ineffective at eliminating objects of > 1 m in size. However, using numerical models of collisional evolution we find that, due to high relative speeds in this confined Trojan environment, collisions destroy the vast majority of the asteroids in <10 Myr. Our modeling indicates that the best candidates to search for exoTrojan swarms in 1:1 mean resonance orbits with "hot Jupiters" are young systems (ages of about 1 Myr or less). Years of Kepler satellite monitoring of such a system could detect an asteroid swarm with a predicted transit depth of 3\times10-7.Comment: 32 pages, 8 figure

On the poverty of a priorism: technology, surveillance in the workplace and employee responses

Many debates about surveillance at work are framed by a set of a priori assumptions about the nature of the employment relationship that inhibits efforts to understand the complexity of employee responses to the spread of new technology at work. In particular, the debate about the prevalence of resistance is hamstrung from the outset by the assumption that all apparently non-compliant acts, whether intentional or not, are to be counted as acts of resistance. Against this background this paper seeks to redress the balance by reviewing results from an ethnographic study of surveillance-capable technologies in a number of British workplaces. It argues for greater attention to be paid to the empirical character of the social relations at work in and through which technologies are deployed and in the context of which employee responses are played out

The absence of myocardial calcium-independent phospholipase a2γ results in impaired prostaglandin e2 production and decreased survival in mice with acute trypanosoma cruzi infection

Cardiomyopathy is a serious complication of Chagas' disease, caused by the protozoan parasite Trypanosoma cruzi. The parasite often infects cardiac myocytes, causing the release of inflammatory mediators, including eicosanoids. A recent study from our laboratory demonstrated that calcium-independent phospholipase A(2)γ (iPLA(2)γ) accounts for the majority of PLA(2) activity in rabbit ventricular myocytes and is responsible for arachidonic acid (AA) and prostaglandin E(2) (PGE(2)) release. Thus, we hypothesized that cardiac iPLA(2)γ contributes to eicosanoid production in T. cruzi infection. Inhibition of the isoform iPLA(2)γ or iPLA(2)β, with the R or S enantiomer of bromoenol lactone (BEL), respectively, demonstrated that iPLA(2)γ is the predominant isoform in immortalized mouse cardiac myocytes (HL-1 cells). Stimulation of HL-1 cells with thrombin, a serine protease associated with microthrombus formation in Chagas' disease and a known activator of iPLA(2), increased AA and PGE(2) release, accompanied by platelet-activating factor (PAF) production. Similarly, T. cruzi infection resulted in increased AA and PGE(2) release over time that was inhibited by pretreatment with (R)-BEL. Further, T. cruzi-infected iPLA(2)γ-knockout (KO) mice had lower survival rates and increased tissue parasitism compared to wild-type (WT) mice, suggesting that iPLA(2)γ-KO mice were more susceptible to infection than WT mice. A significant increase in iPLA(2) activity was observed in WT mice following infection, whereas iPLA(2)γ-KO mice showed no alteration in cardiac iPLA(2) activity and produced less PGE(2). In summary, these studies demonstrate that T. cruzi infection activates cardiac myocyte iPLA(2)γ, resulting in increased AA and PGE(2) release, mediators that may be essential for host survival during acute infection. Thus, these studies suggest that iPLA(2)γ plays a cardioprotective role during the acute stage of Chagas' disease