Constraining Dark Matter Substructure With Gaia Wide Binaries

We use a catalogue of stellar binaries with wide separations (up to 1 pc) identified by the Gaia satellite to constrain the presence of extended substructure within the Milky Way galaxy. Heating of the binaries through repeated encounters with substructure results in a characteristic distribution of binary separations, allowing constraints to be placed independent of the formation mechanism of wide binaries. Across a wide range of subhalo density profiles, we show that subhalos with masses $\gtrsim 65 \ M_\odot$ and characteristic length scales similar to the separation of these wide binaries cannot make up 100% of the Galaxy's dark matter. Constraints weaken for subhalos with larger length scales and are dependent on their density profiles. For such large subhalos, higher central densities lead to stronger constraints. Subhalos with density profiles similar to those expected from cold dark matter must be at least $\sim 5,000$ times denser than predicted by simulation to be constrained by the wide binary catalogue.Comment: 21 pages, 23 figure

Meta-analysis of primary producer amino acid δ\u3csup\u3e15\u3c/sup\u3eN values and their influence on trophic position estimation

Compound-specific stable isotope analysis of individual amino acids (CSIA-AA) has emerged as a transformative approach to estimate consumer trophic positions (TPCSIA) that are internally indexed to primary producer nitrogen isotope baselines. Central to accurate TPCSIA estimation is an understanding of beta (β) values—the differences between trophic and source AA δ15N values in the primary producers at the base of a consumers’ food web. Growing evidence suggests higher taxonomic and tissue-specific β value variability than typically appreciated. This meta-analysis fulfills a pressing need to comprehensively evaluate relevant sources of β value variability and its contribution to TPCSIA uncertainty. We first synthesized all published primary producer AA δ15N data to investigate ecologically relevant sources of variability (e.g., taxonomy, tissue type, habitat type, mode of photosynthesis). We then reviewed the biogeochemical mechanisms underpinning AA δ15N and β value variability. Lastly, we evaluated the sensitivity of TPCSIA estimates to uncertainty in mean βGlx-Phe values and Glx-Phe trophic discrimination factors (TDFGlx-Phe). We show that variation in βGlx-Phe values is two times greater than previously considered, with degree of vascularization, not habitat type (terrestrial vs. aquatic), providing the greatest source of variability (vascular autotroph = –6.6 ± 3.4‰; non-vascular autotroph = +3.3 ± 1.8‰). Within vascular plants, tissue type secondarily contributed to βGlx-Phe value variability, but we found no clear distinction among C3, C4, and CAM plant βGlx-Phe values. Notably, we found that vascular plant βGlx-Lysvalues (+2.5 ± 1.6‰) are considerably less variable than βGlx-Phe values, making Lys a useful AA tracer of primary production sources in terrestrial systems. Our multi-trophic level sensitivity analyses demonstrate that TPCSIA estimates are highly sensitive to changes in both βGlx-Phe and TDFGlx-Phe values but that the relative influence of β values dissipates at higher trophic levels. Our results highlight that primary producer β values are integral to accurate trophic position estimation. We outline four key recommendations for identifying, constraining, and accounting for β value variability to improve TPCSIA estimation accuracy and precision moving forward. We must ultimately expand libraries of primary producer AA δ15N values to better understand mechanistic drivers of β value variation

Sequential isotopic analysis to characterize ontogenetic shifts and growth dynamics of loggerhead sea turtles (Caretta caretta)

Ontogenetic niche theory predicts that as organisms grow they make size-specific changes in habitat use and diet to optimize growth and survival. A variety of factors contribute to growth and survival in different habitats, ultimately leading to variation in life history that can affect population dynamics. An understanding of the variation in timing of habitat shifts and fidelity to those habitats is critical for population dynamics modeling and evaluation of conservation strategies, especially for species whose population vital rates are sensitive to changes in growth and survival of critical life stages, such as the loggerhead sea turtle (Caretta caretta). Isotopic analysis of sequentially deposited structures, such as sea turtle humerus bone, provides a means of studying intraspecific life history variation. I sequentially analyzed the annual humerus bone growth increments of 84 juvenile loggerhead sea turtles for stable isotopes (δ¹³C, δ¹⁵N) to reconstruct the diet and habitat use histories of turtles undergoing an oceanic-to-neritic ontogenetic shift. I also used skeletochronological methods to evaluate the growth dynamics surrounding this transition. Generated isotopic transects were used to classify individuals into alternative life history pattern groups and were combined with body size and growth data obtained from skeletal analyses to evaluate differences in the duration, timing, and growth dynamics of ontogenetic shifts. Sea turtles that displayed increases in nitrogen stable isotope ratios (δ¹⁵N) greater than 3.0‰ over one or more years were presumed to have transitioned from oceanic to neritic diets and/or habitats based on oceanic and neritic prey isotopic information collected from the literature, and were classified into one of two life history pattern groups: discrete shifters (n = 23) completed this transition within year, while facultative shifters (n = 16) completed this transition in up to eight years. As differences in isotopic values between neritic and oceanic prey are most likely driven by differences in isotopic baselines, I propose the gradual increases in δ¹⁵N values within facultative shifters over multiple years is indicative of foraging in both oceanic and neritic habitats within growth years. Size-at-transition between habitats was similar between discrete shifters (55.1 ± 7.6 cm straightline carapace length, SCL) and facultative shifters (52.8 ± 6.9 cm SCL). Growth variance was higher for facultative shifters versus discrete shifters. Yet, mean size at transition, size-at-age relationships, and mean increment-specific growth rates were similar between turtles with alternative life history patterns. Annual growth rates generally peaked within one year of transition (31/38 of turtles), providing support for a short-term (i.e., 1-2 year) ontogenetic shift-associated growth advantage. However, there was considerable variation in the timing of maximal growth rate among turtles with some individuals exhibiting maximal growth in years prior to the ontogenetic shift (14/38 turtles). The lack of substantial differences in the timing of transition and growth dynamics between discrete and facultative shifters likely limits the influence of these alternative life history patterns on time to sexual maturity in this species, though differences in habitat-specific survival probabilities could affect loggerhead population dynamics. This study demonstrates the value of paired isotopic and skeletal analyses to the study of long-term sea turtle life history variation and its affect on growth.Keywords: stable isotope analysis, nitrogen isotopes, growth dynamics, life history pattern, facultative shift, ontogenetic shift, discrete shift, skeletochronology, loggerhead sea turtl

It’s in Their Bones: Ecological Drivers of Kemp’s Ridley Sea Turtle (Lepidochelys kempii) Somatic Growth and Population Dynamics

Somatic growth variation manifests from the cumulative effects of a suite of biological, ecological, and environmental processes and can have profound effects on individual fitness and species population dynamics. As ectotherms whose growth dynamics are greatly influenced by environmental factors, sea turtles display considerable variation in somatic growth within and among individuals, populations, and species. Given the sensitivity of sea turtle population dynamics to small changes in demographic rates, identifying the proximate drivers of somatic growth variation, and subsequent influences on population dynamics, is of high importance to sea turtle conservation and management. This is particularly true for the critically endangered Kemp’s ridley sea turtle (Lepidochelys kempii), which displays regional differences in somatic growth rates and whose recovery is now uncertain given recent changes in population growth. Through the integration of multiple skeletal, geochemical, and quantitative analyses, my dissertation aims to identify ecological factors influential to Kemp’s ridley sea turtle somatic growth variation and the potential influence of life history variation on their population dynamics. In Chapter 2, I used a 20+ year dataset of Kemp’s ridley sea turtle somatic growth rates generated through skeletochronology to quantify the influence of the Deepwater Horizon oil spill, climate change, and changing population density on age- and region-specific somatic growth rates. These analyses revealed a significant reduction in mean somatic growth rates in 2012–2015 for Age 0 and Age 2–5 turtles that stranded in the U.S. Gulf of Mexico and Atlantic Coasts. Additionally, Age 0 and Age 2–5 growth rates were related to regional climate indices and population abundance estimates, respectively. Integrative analysis determined that the 2012 growth shift explained the greatest variation in somatic growth rates, which I hypothesize may be related to long-term deleterious effects of the Deepwater Horizon oil spill. Continued evaluation of growth rates is needed to distinguish the effects of population density and climate indices as drivers of somatic growth variation in this species. In Chapter 3, I sampled bones processed in Chapter 2 for stable isotope ratios (δ13C, δ15N) to characterize regional variation in diet composition and quantify relationships between diet composition and somatic growth rates. Turtle bone stable isotope date were combined with prey stable isotope data collated from the literature into a Bayesian stable isotope mixing model to estimate the proportional contribution of crustaceans, bivalves, gastropods, fish, and seagrass/macroalgae to turtle diets. I found distinct regional differences in model-derived estimates of diet composition that largely follow known diet patterns. My mixing models indicated that northern GoM and Atlantic turtles primarily consumed invertebrates, western GoM turtles consumed equal amounts of invertebrates and fish, and eastern GoM turtles consumed equal amounts of invertebrates and basal resources. Growth rates were poorly correlated with δ15N values and diet composition estimates, suggesting that higher trophic level diets do not cause higher Kemp’s ridley growth rates and that diet composition does not drive the apparent regional differences in somatic growth evident in this species. In Chapter 4, I investigated the ability of complementary lead (Pb) stable isotope, trace element, and growth rate analyses to discriminate regional (GoM vs. Atlantic) Kemp’s ridley sea turtle habitat use. Through multiple quadratic discriminant function analyses, I found that 208Pb:206Pb could be used to classify turtles to stranding region with exceptional accuracy (94.1 %), whereas somatic growth rates in conjunction with Sr:Ca, Cu:Ca, Ba:Ca, Mg:Ca, and Zn:Ca had a correct classification success rate of 79.5 %. These results suggest that Pb stable isotopes, and possibly somatic growth rates, may provide a useful tool for studying Atlantic-to-GoM ontogenetic shifts in this and other sea turtle species in the future. In Chapter 5, I used a spatially explicit, age-structured matrix population model to evaluate the relative contribution of Atlantic Kemp’s ridley sea turtles to population growth and recovery prior to 2010. I specifically evaluated sensitivity to changes in key transition probabilities that describe the movement of turtles among habitats and life stages within the western North Atlantic Ocean. My model simulations suggest that Atlantic turtles were a strong contributor to Kemp’s ridley population growth during the species’ pre-2010 recovery and are unlikely to influence recovery time, even under the most extreme scenarios evaluated. Future work will include simulations under stable or declining population growth rate indicators, as have been observed in the species since 2010. Taken together, this study filled some critical knowledge gaps in our understanding of the relationship between multiple ecological and environmental factors (oil spills, climate, population density, foraging ecology, habitat use) and Kemp’s ridley sea turtle somatic growth and population dynamics. This research also highlighted the importance of continued collection and study of stranded turtle tissues as they provide a means to investigate otherwise intractable research questions in sea turtle ecology

Robotic partial nephrectomy for posterior tumors through a retroperitoneal approach offers decreased length of stay compared with the transperitoneal approach: A propensity-matched analysis

INTRODUCTION: We sought to compare surgical outcomes between transperitoneal and retroperitoneal robotic partial nephrectomy (RPN) for posterior tumors. PATIENTS AND METHODS: Using our multi-institutional RPN database, we reviewed 610 consecutive cases for posterior renal masses treated between 2007 and 2015. Primary outcomes were complications, operative time, length of stay (LOS), surgical margin status, and estimated glomerular filtration rate (eGFR) preservation. Secondary outcomes were estimated blood loss, warm ischemia time (WIT), disease recurrence, and disease-specific mortality. Due to significant differences in treatment year and tumor size between approaches, retroperitoneal cases were matched 1:4 to transperitoneal cases based on propensity scores using the greedy algorithm. Outcomes were compared between approaches using the chi-square and Mann-Whitney U tests. RESULTS: After matching, 296 transperitoneal and 74 retroperitoneal cases were available for analysis, and matched groups were well balanced in terms of treatment year, age, gender, race, American Society of Anesthesiologists physical status classification (ASA) score, body mass index, tumor laterality, tumor size, R.E.N.A.L. (radius, exophytic/endophytic properties, nearness of tumor to the collecting system or sinus, anterior/posterior, location relative to polar lines) score, and hilar location. Compared with transperitoneal, the retroperitoneal approach was associated with significantly shorter mean LOS (2.2 vs 2.6 days, p = 0.01), but longer mean WIT (21 vs 19 minutes, p = 0.01). Intraoperative (p = 0.35) and postoperative complications (p = 0.65), operative time (p = 0.93), positive margins (p = 1.0), and latest eGFR preservation (p = 0.25) were not significantly different between approaches. No differences were detected in the other outcomes. CONCLUSIONS: Among high-volume surgeons, transperitoneal and retroperitoneal RPN achieved similar outcomes for posterior renal masses, although with slight differences in LOS and WIT. Retroperitoneal RPN may be an effective option for the treatment of certain small posterior renal masses

Characterization of designed, synthetically accessible bryostatin analog HIV latency reversing agents.

HIV latency in resting CD4+ T cell represents a key barrier preventing cure of the infection with antiretroviral drugs alone. Latency reversing agents (LRAs) can activate HIV expression in latently infected cells, potentially leading to their elimination through virus-mediated cytopathic effects, host immune responses, and/or therapeutic strategies targeting cells actively expressing virus. We have recently described several structurally simplified analogs of the PKC modulator LRA bryostatin (termed bryologs) designed to improve synthetic accessibility, tolerability in vivo, and efficacy in inducing HIV latency reversal. Here we report the comparative performance of lead bryologs, including their effects in reducing cell surface expression of HIV entry receptors, inducing proinflammatory cytokines, inhibiting short-term HIV replication, and synergizing with histone deacetylase inhibitors to reverse HIV latency. These data provide unique insights into structure-function relationships between A- and B-ring bryolog modifications and activities in primary cells, and suggest that bryologs represent promising leads for preclinical advancement

A Neutron Star Binary Merger Model for GW170817/GRB170817a/SSS17a

The merging neutron star gravitational wave event GW170817 has been observed throughout the entire electromagnetic spectrum from radio waves to $\gamma$-rays. The resulting energetics, variability, and light curves are shown to be consistent with GW170817 originating from the merger of two neutron stars, in all likelihood followed by the prompt gravitational collapse of the massive remnant. The available $\gamma$-ray, X-ray and radio data provide a clear probe for the nature of the relativistic ejecta and the non-thermal processes occurring within, while the ultraviolet, optical and infrared emission are shown to probe material torn during the merger and subsequently heated by the decay of freshly synthesized $r$-process material. The simplest hypothesis that the non-thermal emission is due to a low-luminosity short $\gamma$-ray burst (sGRB) seems to agree with the present data. While low luminosity sGRBs might be common, we show here that the collective prompt and multi-wavelength observations are also consistent with a typical, powerful sGRB seen off-axis. Detailed follow-up observations are thus essential before we can place stringent constraints on the nature of the relativistic ejecta in GW170817.Comment: 9 pages, 5 figures, accepted to ApJ Letter

Theory of paramagnetic scattering in highly frustrated magnets with long-range dipole-dipole interactions: The case of the Tb2Ti2O7, pyrochlore antiferromagnet

Highly frustrated antiferromagnets composed of magnetic rare-earth moments are currently attracting much experimental and theoretical interest. Rare-earth ions generally have small exchange interactions and large magnetic moments. This makes it necessary to understand in detail the role of long-range magnetic dipole-dipole interactions in these systems, in particular in the context of spin-spin correlations that develop in the paramagnetic phase, but are often unable to condense into a conventional long-range magnetic ordered phase. This scenario is most dramatically emphasized in the frustrated pyrochlore antiferromagnet material Tb2Ti207 which does not order down to 50 mK despite an antiferromagnetic Curie-Weiss temperature Tcw ~ -20 K. In this paper we report results from mean-field theory calculations of the paramagnetic elastic neutron-scattering in highly frustrated magnetic systems with long-range dipole-dipole interactions, focusing on the Tb2Ti207 system. Modeling Tb2Ti207 as an antiferromagnetic Ising pyrochlore, we find that the mean-field paramagnetic scattering is inconsistent with the experimentally observed results. Through simple symmetry arguments we demonstrate that the observed paramagnetic correlations in Tb2Ti207 are precluded from being generated by any spin Hamiltonian that considers only Ising spins, but are qualitatively consistent with Heisenberg-like moments. Explicit calculations of the paramagnetic scattering pattern for both Ising and Heisenberg models, which include finite single-ion anisotropy, support these claims. We offer suggestions for reconciling the need to restore spin isotropy with the Ising like structure suggested by the single-ion properties of Tb3+.Comment: Revtex4, 18 pages, 3 eps figures (2 color figures). Change in title and emphasis on Tb2Ti2O7 only. Spin-ice material removed, to appear in a later publicatio

Electromagnetic Evidence that SSS17a is the Result of a Binary Neutron Star Merger

11 hours after the detection of gravitational wave source GW170817 by the Laser Interferometer Gravitational-Wave Observatory and Virgo Interferometers, an associated optical transient SSS17a was discovered in the galaxy NGC 4993. While the gravitational wave data indicate GW170817 is consistent with the merger of two compact objects, the electromagnetic observations provide independent constraints of the nature of that system. Here we synthesize all optical and near-infrared photometry and spectroscopy of SSS17a collected by the One-Meter Two-Hemisphere collaboration. We find that SSS17a is unlike other known transients. The source is best described by theoretical models of a kilonova consisting of radioactive elements produced by rapid neutron capture (the r-process). We find that SSS17a was the result of a binary neutron star merger, reinforcing the gravitational wave result.Comment: 21 pages, 4 figures, accepted to Scienc

Late-time post-merger modeling of a compact binary: effects of relativity, r-process heating, and treatment of transport effects

Detectable electromagnetic counterparts to gravitational waves from compact binary mergers can be produced by outflows from the black hole-accretion disk remnant during the first ten seconds after the merger. Two-dimensional axisymmetric simulations with effective viscosity remain an efficient and informative way to model this late-time post-merger evolution. In addition to the inherent approximations of axisymmetry and modeling turbulent angular momentum transport by a viscosity, previous simulations often make other simplifications related to the treatment of the equation of state and turbulent transport effects. In this paper, we test the effect of these modeling choices. By evolving with the same viscosity the exact post-merger initial configuration previously evolved in Newtonian viscous hydrodynamics, we find that the Newtonian treatment provides a good estimate of the disk ejecta mass but underestimates the outflow velocity. We find that the inclusion of heavy nuclei causes a notable increase in ejecta mass. An approximate inclusion of r-process effects has a comparatively smaller effect, except for its designed effect on the composition. Diffusion of composition and entropy, modeling turbulent transport effects, has the overall effect of reducing ejecta mass and giving it a speed with lower average and more tightly-peaked distribution. Also, we find significant acceleration of outflow even at distances beyond 10,000\,km, so that thermal wind velocities only asymptote beyond this radius and at somewhat higher values than previously reported.Comment: 19 pages, 7 figures, submitted to Classical and Quantum Gravit