• Local solutions of the Landau equation with rough, slowly decaying initial data

      Henderson, Christopher; Snelson, Stanley; Tarfulea, Andrei; Univ Arizona, Dept Math (Elsevier Masson SAS, 2020-05)
      We consider the Cauchy problem for the spatially inhomogeneous Landau equation with soft potentials in the case of large (i.e. non-perturbative) initial data. We construct a solution for any bounded, measurable initial data with uniform polynomial decay in the velocity variable, and that satisfies a technical lower bound assumption (but can have vacuum regions). For uniqueness in this weak class, we have to make the additional assumption that the initial data is Hölder continuous. Our hypotheses are much weaker, in terms of regularity and decay, than previous large-data well-posedness results in the literature. We also derive a continuation criterion for our solutions that is, for the case of very soft potentials, an improvement over the previous state of the art.
    • Temporal Variability in Hot Jupiter Atmospheres

      Komacek, Thaddeus D.; Showman, Adam P.; Univ Arizona, Lunar & Planetary Lab; Univ Arizona, Dept Planetary Sci (IOP PUBLISHING LTD, 2020-01-01)
      Hot Jupiters receive intense incident stellar light on their daysides, which drives vigorous atmospheric circulation that attempts to erase their large dayside-to-nightside flux contrasts. Propagating waves and instabilities in hot Jupiter atmospheres can cause emergent properties of the atmosphere to be time-variable. In this work, we study such weather in hot Jupiter atmospheres using idealized cloud-free general circulation models with double-gray radiative transfer. We find that hot Jupiter atmospheres can be time-variable at the similar to 0.1%-1% level in globally averaged temperature and at the similar to 1%-10% level in globally averaged wind speeds. As a result, we find that observable quantities are also time-variable: the secondary eclipse depth can be variable at the.2% level, the phase-curve amplitude can change by.1%, the phase-curve offset can shift by.5 degrees, and terminator-averaged wind speeds can vary by. 2.km.s-1. Additionally, we calculate how the eastern and western limb-averaged wind speeds vary with incident stellar flux and the strength of an imposed drag that parameterizes Lorentz forces in partially ionized atmospheres. We find that the eastern limb is blueshifted in models over a wide range of equilibrium temperature and drag strength, while the western limb is only redshifted if equilibrium temperatures are.1500.K and drag is weak. Lastly, we show that temporal variability may be observationally detectable in the infrared through secondary eclipse observations with the James Webb Space Telescope, phase-curve observations with future space telescopes (e.g., ARIEL), and/or Doppler wind speed measurements with high-resolution spectrographs.
    • High-resolution Near-infrared Polarimetry and Submillimeter Imaging of FS Tau A: Possible Streamers in Misaligned Circumbinary Disk System

      Yang, Yi; Akiyama, Eiji; Currie, Thayne; Dong, Ruobing; Hashimoto, Jun; Hayashi, Saeko S.; Grady, Carol A.; Janson, Markus; Jovanovic, Nemanja; Uyama, Taichi; et al. (IOP PUBLISHING LTD, 2020-02-03)
      We analyzed the young (2.8 Myr-old) binary system FS Tau A using near-infrared (H-band) high -contrast polarimetry data from Subaru/HiCIAO and submillimeter CO (J = 2-1) line emission data from Atacama Large Millimeter/submillimeter Array (ALMA). Both the near-infrared and submillimeter observations reveal several clear structures extending to similar to 240 au from the stars. Based on these observations at different wavelengths, we report the following discoveries. One arm-like structure detected in the near-infrared band initially extends from the south of the binary with a subsequent turn to the northeast, corresponding to two bar-like structures detected in ALMA observations with an local standard of rest kinematic (LSRK) velocity of 1.19-5.64 km s(-1). Another feature detected in the near-infrared band extends initially from the north of the binary, relating to an arm-like structure detected in ALMA observations with an LSRK velocity of 8.17-16.43 km s(-1). From their shapes and velocities, we suggest that these structures can mostly be explained by two streamers that connect the outer circumbinary disk and the central binary components. These discoveries will be helpful for understanding the evolution of streamers and circumstellar disks in young binary systems.
    • Probing the Full CO Spectral Line Energy Distribution (SLED) in the Nuclear Region of a Quasar-starburst System at z = 6.003

      Li, Jianan; Wang, Ran; Riechers, Dominik; Walter, Fabian; Decarli, Roberto; Venamans, Bram P.; Neri, Roberto; Shao, Yali; Fan, Xiaohui; Gao, Yu; et al. (IOP PUBLISHING LTD, 2020-02-04)
      We report Atacama Large Millimeter/submillimeter Array observations of CO(8-7), (9-8), H2O(2(0,2)-1(1,1)), and OH+(1(1)-0(1)) and NOrthern Extended Millimeter Array observations of CO(5-4), (6-5), (12-11), and (13-12) toward the z.=.6.003 quasar SDSS J231038.88+185519.7, aiming to probe the physical conditions of the molecular gas content of this source. We present the best sampled CO spectral line energy distribution (SLED) at z.=.6.003, and analyzed it with the radiative transfer code MOLPOP-CEP. Fitting the CO SLED to a one-component model indicates a kinetic temperature T-kin=.228 K, molecular gas density log(n(H-2) cm(-3)).=.4.75, and CO column density log(N (CO) cm(-2)) = 17.5; although, a two-component model better fits the data. In either case, the CO SLED is dominated by a "warm" and "dense" component. Compared to samples of local (Ultra) Luminous Infrared Galaxies, starburst galaxies, and high-redshift submillimeter galaxies, J2310+1855 exhibits higher CO excitation at (J >= 8), like other high-redshift quasars. The high CO excitation, together with the enhanced L-H2O/L-IR, L-H2O/L-CO, and LOH+/L-H2O ratios, suggests that besides the UV radiation from young massive stars, other mechanisms such as shocks, cosmic-rays, and X-rays might also be responsible for the heating and ionization of the molecular gas. In the nuclear region probed by the molecular emissions lines, any of these mechanisms might be present due to the powerful quasar and the starburst activity.
    • A Classification Algorithm for Time-domain Novelties in Preparation for LSST Alerts. Application to Variable Stars and Transients Detected with DECam in the Galactic Bulge

      Soraisam, Monika D.; Saha, Abhijit; Matheson, Thomas; Lee, Chien-Hsiu; Narayan, Gautham; Vivas, A. Katherina; Scheidegger, Carlos; Oppermann, Niels; Olszewski, Edward W.; Sinha, Sukriti; et al. (IOP PUBLISHING LTD, 2020-04-03)
      With the advent of the Legacy Survey of Space and Time, time-domain astronomy will be faced with an unprecedented volume and rate of data. Real-time processing of variables and transients detected by such large-scale surveys is critical to identifying the more unusual events and allocating scarce follow-up resources efficiently. We develop an algorithm to identify these novel events within a given population of variable sources. We determine the distributions of magnitude changes (dm) over time intervals (dt) for a given passband f, , and use these distributions to compute the likelihood of a test source being consistent with the population or being an outlier. We demonstrate our algorithm by applying it to the DECam multiband time-series data of more than 2000 variable stars identified by Saha et al. in the Galactic Bulge that are largely dominated by long-period variables and pulsating stars. Our algorithm discovers 18 outlier sources in the sample, including a microlensing event, a dwarf nova, and two chromospherically active RS CVn stars, as well as sources in the blue horizontal branch region of the color-magnitude diagram without any known counterparts. We compare the performance of our algorithm for novelty detection with the multivariate Kernel Density Estimator and Isolation Forest on the simulated PLAsTiCC data set. We find that our algorithm yields comparable results despite its simplicity. Our method provides an efficient way for flagging the most unusual events in a real-time alert-broker system.
    • Birds of a Feather? Magellan/IMACS Spectroscopy of the Ultra-faint Satellites Grus II, Tucana IV, and Tucana V

      Simon, J. D.; Li, T. S.; Erkal, D.; Pace, A. B.; Drlica-Wagner, A.; James, D. J.; Marshall, J. L.; Bechtol, K.; Hansen, T.; Kuehn, K.; et al. (IOP PUBLISHING LTD, 2020-04-07)
      We present Magellan/IMACS spectroscopy of three recently discovered ultra-faint Milky Way satellites, Grus.II, Tucana.IV, and Tucana.V. We measure systemic velocities of vhel = -110.0. 0.5 km s-1, = v 15.9+ hel 1.71.8 km s-1, and = - v 36.2+ hel 2.22.5 km s-1 for the three objects, respectively. Their large relative velocities demonstrate that the satellites are unrelated despite their close physical proximity. We determine a velocity dispersion for Tuc.IV of s = 4.3+ 1.01.7 km s-1, but we cannot resolve the velocity dispersions of the other two systems. For Gru.II, we place an upper limit (90%.confidence) on the dispersion of s.<.1.9 km s-1, and for Tuc.V, we do not obtain any useful limits. All three satellites have metallicities below[Fe H] = -2.1, but none has a detectable metallicity spread. We determine proper motions for each satellite based on Gaia astrometry and compute their orbits around the Milky Way. Gru.II is on a tightly bound orbit with a pericenter of 25+ 76 kpc and orbital eccentricity of 0.45+ 0.050.08. Tuc.V likely has an apocenter beyond 100.kpc and could be approaching the Milky Way for the first time. The current orbit of Tuc.IV is similar to that of Gru.II, with a pericenter of 25+ 811 kpc and an eccentricity of 0.36+ 0.060.13. However, a backward integration of the position of Tuc.IV demonstrates that it collided with the Large Magellanic Cloud at an impact parameter of 4. kpc 120.Myr ago, deflecting its trajectory and possibly altering its internal kinematics. Based on their sizes, masses, and metallicities, we classify Gru.II and Tuc.IV as likely dwarf galaxies, but the nature of Tuc.V remains uncertain.
    • Evaluation of the Impact of School Garden Exposure on Youth Outlook and Behaviors toward Vegetables in Southern Arizona

      Lohr, Abby M; Henry, Nick; Roe, Denise; Rodriguez, Claudio; Romero, Rosalva; Ingram, Maia; Univ Arizona, Arizona Prevent Res Ctr, Mel & Enid Zuckerman Coll Publ Hlth (WILEY, 2020-05-06)
      BACKGROUND Our objective was to evaluate the effect of garden-based learning on outlook and behaviors toward vegetables among primarily Latinx students. An educational strategy, garden-based learning is a teaching tool that complements other disciplines. METHODS Third- and fourth-grade students at 4 elementary schools with different garden programs completed a bingo survey and participated in class discussions to measure outlook and behaviors toward vegetables. RESULTS Students in schools with more garden exposure were more likely to answer "Yes" to survey questions reflecting a positive attitude and behaviors toward vegetables. In class discussions, students most often mentioned vegetables grown in the school garden as their favorite vegetables. CONCLUSION For third- and fourth-grade students, the length of exposure to a school garden appears to have a positive impact on both perceptions of and desire to consume vegetables. Other studies have shown that positive outlook and behaviors toward vegetables can change vegetable consumption habits in children. Integrating garden-based learning into the school curriculum may positively influence eating behaviors over the long-term future.
    • Dusty Stellar Birth and Death in the Metal-poor Galaxy NGC 6822

      Hirschauer, Alec S.; Gray, Laurin; Meixner, Margaret; Jones, Olivia C.; Srinivasan, Sundar; Boyer, Martha L.; Sargent, B. A.; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2020-04-01)
      The nearby (similar to 500 kpc) metal-poor ([Fe/H] -1.2; Z 30% Z) star-forming galaxy NGC 6822 has a metallicity similar to systems at the epoch of peak star formation. Through identification and study of dusty and dust-producing stars, it is therefore a useful laboratory to shed light on the dust life cycle in the early universe. We present a catalog of sources combining near- and mid-IR photometry from the United Kingdom Infrared Telescope (J, H, and K) and the Spitzer Space Telescope (IRAC 3.6, 4.5, 5.8, and 8.0 mu m and MIPS 24 mu m). This catalog is employed to identify dusty and evolved stars in NGC 6822 utilizing three color-magnitude diagrams (CMDs). With diagnostic CMDs covering a wavelength range spanning the near- and mid-IR, we develop color cuts using kernel density estimate (KDE) techniques to identify dust-producing evolved stars, including red supergiant (RSG) and thermally pulsing asymptotic giant branch (TP-AGB) star candidates. In total, we report 1292 RSG candidates, 1050 oxygen-rich AGB star candidates, and 560 carbon-rich AGB star candidates with high confidence in NGC 6822. Our analysis of the AGB stars suggests a robust population inhabiting the central stellar bar of the galaxy, with a measured global stellar metallicity of [Fe/H] = -1.286 0.095, consistent with previous studies. In addition, we identify 277 young stellar object (YSO) candidates. The detection of a large number of YSO candidates within a centrally located, compact cluster reveals the existence of an embedded, high-mass star formation region that has eluded previous detailed study. Spitzer I appears to be younger and more active than the other prominent star-forming regions in the galaxy.
    • Simulating JWST/NIRCam Color Selection of High-redshift Galaxies

      Hainline, Kevin N.; Hviding, Raphael E.; Rieke, Marcia; Shivaei, Irene; Endsley, Ryan; Curtis-Lake, Emma; Smit, Renske; Williams, Christina C.; Alberts, Stacey; K Boyett, Kristan N.; et al. (IOP PUBLISHING LTD, 2020-04-06)
      The Near Infrared Camera (NIRCam) instrument on the upcoming James Webb Space Telescope will offer an unprecedented view of the most distant galaxies. In preparation for future deep NIRCam extragalactic surveys, it is crucial to understand the color selection of high-redshift galaxies using the Lyman dropout technique. To that end, we have used the JAdes extraGalactic Ultradeep Artificial Realizations mock catalog to simulate a series of extragalactic surveys with realistic noise estimates. This enables us to explore different color selections and their impact on the number density of recovered high-redshift galaxies and lower-redshift interlopers. We explore how survey depth, detection signal-to-noise ratio, color selection method, detection filter choice, and the presence of the Ly alpha emission line affects the resulting dropout selected samples. We find that redder selection colors reduce the number of recovered high-redshift galaxies, but the overall accuracy of the final sample is higher. In addition, we find that methods that utilize two or three color cuts have higher accuracy because of their ability to select against low-redshift quiescent and faint dusty interloper galaxies. We also explore the near-IR colors of brown dwarfs and demonstrate that, while they are predicted to have low on-sky densities, they are most likely to be recovered in F090W dropout selection, but there are color cuts that help to mitigate this contamination. Overall, our results provide NIRCam selection methods to aid in the creation of large, pure samples of ultra-high-redshift galaxies from photometry alone.
    • Enhanced adsorption of tetrabromobisphenol a (TBBPA) on cosmetic-derived plastic microbeads and combined effects on zebrafish

      Yu, Yunjiang; Ma, Ruixue; Qu, Han; Zuo, You; Yu, Ziling; Hu, Guocheng; Li, Zongrui; Chen, Haibo; Lin, Bigui; Wang, Bin; et al. (PERGAMON-ELSEVIER SCIENCE LTD, 2020-06-20)
      Microplastics (MPs) pollution and its potential environmental risks have drawn increasing concerns in recent years. Among which, microbeads in personal care and cosmetic products has becoming an emerging issue for their abundance as well as the knowledge gaps in their precise environmental behaviors in freshwater. The present study investigated the sorption process of tetrabromobisphenol A (TBBPA), the most widely applied and frequently encountered flame retardant in aquatic environments, on two sources of polyethylene (PE) particles (pristine PE particles and microbeads isolated from personal care and cosmetic products). Significantly enhanced adsorption capacity of microbeads was observed with up to 5-folds higher than the pristine PE particles. The sorption efficiency was also governed by solution pH, especially for the cosmetic-derived microbeads, indicating the strong adsorption of TBBPA on PE was dominated by both hydrophobic and electrostatic interactions. Additionally, combined effects on redox status of zebrafish were evaluated with two environmental relevant concentrations of PE particles (0.5 and 5 mg L-1) using integrated biomarker response (IBR) index through a 14-d exposure. Co-exposure induced significant antioxidative stress than either PE or TBBPA alone when exposed to 0.5 mg L-1 of MPs. After 7-d depuration, the IBR value for combination treatments [TBBPA + PE (L)] was 3-fold compared with that in MP-free groups, indicating the coexistence might exert a prolonged adverse effects on aquatic organisms. These results highlight the probability of risk from microbead pollution in freshwater, where toxic compounds can be adsorbed on microbeads in a considerable amount resulting in potential adverse effects towards aquatic organisms.
    • Students’ struggles with temporal order in the limit definition: uncovering resources using knowledge in pieces

      Adiredja, Aditya P.; Univ Arizona, Dept Math (TAYLOR & FRANCIS LTD, 2020-04-29)
      A few case studies have suggested students' struggles with the temporal order of epsilon and delta in the formal limit definition. This study problematizes this hypothesis by exploring students' claims in different contexts and uncovering productive resources from students to make sense of the critical relationship between epsilon and delta. A three-step analysis supports these aims. The analysis starts by investigating the generalizability and specificity of the struggle with the temporal order. Then, analysing students' justifications reveals dominant ideas supporting students' claims. Finally, attending to the foci of the justifications reveals the potential resources to make sense of the temporal order. This study illustrates the productivity of the principles context sensitivity, cueing priority, and reliability priority from Knowledge in Pieces in understanding students' struggles. The study offers the three-step analysis as a method to approach students' understanding from an anti-deficit perspective.
    • Exploring everyday examples to explain basis: insights into student understanding from students in Germany

      Zandieh, Michelle; Adiredja, Aditya; Knapp, Jessica; Univ Arizona, Dept Math (SPRINGER HEIDELBERG, 2019-12)
      There is relatively little research specifically about student understanding of basis. Our ongoing work addresses student understanding of basis from an anti-deficit perspective, which focuses on the resources that students have to make sense of basis using everyday ideas. Using data from a group of women of color in the United States, we previously developed an analytical framework to describe student understanding about basis, including codes related to characteristics of basis vectors and roles of basis vectors in the vector space. In this paper, we utilize the methods of the previous study to further enrich our findings about student understanding of basis. By analyzing interview data from students in Germany, we found that this group of students most often used ideas that we describe by the roles generating, structuring, and traveling, and the characteristics different and essential. Some of the themes that emerged from the data illustrate common pairings of these ideas, students' flexibility in interpreting multiple roles within one everyday example, and the ways that the roles and characteristics motivate students to create additional examples. We also discuss two ways that differences between the German and English languages were pointed out by students in the interviews.
    • 13,000 years of sociocultural plant use in the Atacama Desert of northern Chile

      Ugalde, Paula C.; McRostie, Virginia; Gayo, Eugenia M.; García, Magdalena; Latorre, Claudio; Santoro, Calogero M.; Univ Arizona, Sch Anthropol (SPRINGER, 2020-05-06)
      Throughout Earth's most extreme environments, such as the Kalahari Desert or the Arctic, hunter-gatherers found ingenious ways to obtain proteins and sugars provided by plants for dietary requirements. In the hyperarid Atacama Desert, wild plant resources are scarce and unevenly distributed due to limited water availability. This study brings together all available archaeobotanical evidence gathered in the Atacama Desert from the Late Pleistocene (ca. 13,000 cal bp) until the Inka epoch (ca. 450 cal bp) to help us comprehend when these populations acquired and managed useful plants from the coastal zone, Intermediate Depression, High Andes, as well as tropical and subtropical ecosystems. Widespread introduction of farming crops, water control techniques and cultivation of diverse plants by 3,000 cal bp ended not only a chronic food shortage, but also led to the establishment of a set of staple foods for the Atacama Desert dwellers, a legacy that remains visible today. By contrasting these trends with major sociocultural changes, together with palaeodemographic and climatic fluctuations, we note that humans adapted to, and transformed this hyperarid landscape and oscillating climate, with plants being a key factor in their success. This long-term process, which we term the "Green Revolution", coincided with an exponential increase in the number of social groups inhabiting the Atacama Desert during the Late Holocene.
    • Mitochondria-Targeted Therapeutics for Alzheimer's Disease: The Good, the Bad, the Potential

      Mi, Yashi; Qi, Guoyuan; Brinton, Roberta Diaz; Yin, Fei; Univ Arizona Hlth Sci, Ctr Innovat Brain Sci; Univ Arizona, Coll Med Tucson, Dept Pharmacol; Univ Arizona, Coll Med Tucson, Dept Neurol; Univ Arizona, Grad Interdisciplinary Program Neurosci (MARY ANN LIEBERT, INC, 2020-04-21)
      Significance: Alzheimer's disease (AD) is the leading cause of dementia. Thus far, 99.6% of clinical trials, including those targeting energy metabolism, have failed to exert disease-modifying efficacy. Altered mitochondrial function and disruption to the brain bioenergetic system have long-been documented as early events during the pathological progression of AD. Recent Advances: While therapeutic approaches that directly promote mitochondrial bioenergetic machinery or eliminate reactive oxygen species have exhibited limited translatability, emerging strategies targeting nonenergetic aspects of mitochondria provide novel therapeutic targets with the potential to modify AD risk and progression. Growing evidence also reveals a critical link between mitochondrial phenotype and neuroinflammation via metabolic reprogramming of glial cells. Critical Issues: Herein, we summarize major classes of mitochondrion-centered AD therapeutic strategies. In addition, the discrepancy in their efficacy when translated from preclinical models to clinical trials is addressed. Key factors that differentiate the responsiveness to bioenergetic interventions, including sex, apolipoprotein E genotype, and cellular diversity in the brain, are discussed. Future Directions: We propose that the future development of mitochondria-targeted AD therapeutics should consider the interactions between bioenergetics and other disease mechanisms, which may require cell-type-specific targeting to distinguish neurons and non-neuronal cells. Moreover, a successful strategy will likely include stratification by metabolic phenotype, which varies by sex and genetic risk profile and dynamically changes throughout the course of disease. As the network of mitochondrial integration expands across intracellular and systems level biology, assessment of intended, the good, versus unintended consequences, the bad, will be required to reach the potential of mitochondrial therapeutics.
    • Warming and precipitation addition interact to affect plant spring phenology in alpine meadows on the central Qinghai-Tibetan Plateau

      Ganjurjav, Hasbagan; Gornish, Elise S.; Hu, Guozheng; Schwartz, Mark W.; Wan, Yunfan; Li, Yue; Gao, Qingzhu; Univ Arizona, Sch Nat Resources & Environm (ELSEVIER, 2020-06-15)
      Temperature and precipitation are primary regulators of plant phenology. However, our knowledge of how these factors might interact to affect plant phenology is incomplete. The Qinghai-Tibetan Plateau, a cold and high region, has experienced no consistent changes in spring phenology, despite a significant warming trend. We conducted a manipulative experiment of warming and precipitation addition in an alpine meadow on the Qinghai-Tibetan Plateau in 2015 (cold and wet), 2016 (warm and dry) and 2017 (mild and very wet). We found that warming increased annual variability of plant spring phenology. Warming delayed green up of all monitored species in 2016, advanced green up of early flowering species in 2015, and did not alter green up in 2017. For example, green up of the shallow rooted Kobresia pygmaea advanced 8 (+/- 2) days in 2015 and was delayed by 23 (+/- 3) days in a dry year (2016) under warming compared with control. Early spring precipitation addition can offset the delaying effects of warming in a dry year on the Qinghai-Tibetan Plateau. Under warming plus precipitation addition, community average green up advanced compared to control plots in 2015 and 2016, and community average flowering advanced for all three years. In 2016, flowering of K. pygmaea (an early flowering species) advanced under warming plus precipitation addition compared to control while flowering of other species did not change. Our results highlight that annual variation of soil moisture condition plays a critical role in determining the magnitude and direction of spring phenology response to warming. We provide insights in how plant spring phenology might change in a warmer future in the presence or absence of precipitation increase.
    • Buffelgrass invasion and glyphosate effects on desert soil microbiome communities

      Gornish, Elise S.; Franklin, Kim; Rowe, Julia; Barberán, Albert; Univ Arizona, Sch Nat Resources & Environm; Univ Arizona, Dept Environm Sci (SPRINGER, 2020-05-04)
      Buffelgrass (Cenchus ciliaris) is a drought-tolerant invasive grass in the Americas and Australia that significantly impacts native plant communities and ecosystems. Despite the clear need to develop a comprehensive understanding of how buffelgrass is able to invade and rapidly establish in arid ecosystems, there is still a lack of knowledge as to if and how this weed might change the soil microbiome in a way that affects its dominance in the presence of management. We investigated the effect of buffelgrass on soil microbial communities in areas that have either been exposed to or not exposed to glyphosate in Saguaro National Park, Arizona USA. We found that buffelgrass roots in invaded areas are surrounded by a distinct soil community that includes a greater number of nitrifiers than in uninvaded soil. We also observed increases in arbuscular mycorrhizal fungi, ectomycorrhizal fungi and methanotrophs with buffelgrass invasion compared to uninvaded soil. Finally, we found no evidence of glyphosate effects on the soil microbiome. Overall, our study results suggest that buffelgrass can escape the limitation of nutrient availability in arid ecosystems by directly or indirectly modifying the soil microbiome. The competitive dominance of buffelgrass in arid systems might be indirectly enhanced by nitrifiers and fungal symbionts, which are often involved in rapid biomass accumulation. This work highlights the importance of soil microbiome considerations in weed science research.
    • Nucleation seed size determines amyloid clearance and establishes a barrier to prion appearance in yeast

      Villali, Janice; Dark, Jason; Brechtel, Teal M; Pei, Fen; Sindi, Suzanne S; Serio, Tricia R; Univ Arizona, Dept Mol & Cellular Biol (NATURE PUBLISHING GROUP, 2020-05-04)
      Amyloid appearance is a rare event that is promoted in the presence of other aggregated proteins. These aggregates were thought to act by templating the formation of an assembly-competent nucleation seed, but we find an unanticipated role for them in enhancing the persistence of amyloid after it arises. Specifically, Saccharomyces cerevisiae Rnq1 amyloid reduces chaperone-mediated disassembly of Sup35 amyloid, promoting its persistence in yeast. Mathematical modeling and corresponding in vivo experiments link amyloid persistence to the conformationally defined size of the Sup35 nucleation seed and suggest that amyloid is actively cleared by disassembly below this threshold to suppress appearance of the [PSI+] prion in vivo. Remarkably, this framework resolves multiple known inconsistencies in the appearance and curing of yeast prions. Thus, our observations establish the size of the nucleation seed as a previously unappreciated characteristic of prion variants that is key to understanding transitions between prion states.
    • Debt and Bargaining Outcomes: Evidence from U.S. Hospitals

      Towner, Mitch; Univ Arizona, Eller Coll Management (INFORMS, 2020-05)
      Using the healthcare industry as a novel laboratory, I study whether a firm's use of debt enhances its bargaining power during negotiations with nonfinancial stakeholders. I find that reimbursement rates negotiated between a hospital and insurers for two homogeneous procedures are higher when the hospital has more debt. This relation is stronger among hospitals with less bargaining power relative to insurers ex ante. The evidence is consistent with the idea that debt improves a firm's bargaining power.
    • On the arithmetic of a family of twisted constant elliptic curves

      Griffon, Richard; Ulmer, Douglas; Univ Arizona, Dept Math (PACIFIC JOURNAL MATHEMATICS, 2020-04-29)
      Let F-r be a finite field of characteristic p > 3. For any power q of p, consider the elliptic curve E = E-q,E-r defined by y(2) = x(3) + t(q) - t over K = F-r (t). We describe several arithmetic invariants of E such as the rank of its Mordell-Weil group E(K), the size of its Neron-Tate regulator Reg(E), and the order of its Tate-Shafarevich group III(E) (which we prove is finite). These invariants have radically different behaviors depending on the congruence class of p modulo 6. For instance III(E) either has trivial p-part or is a p-group. On the other hand, we show that the product III(E) Reg(E) has size comparable to r(q/6) as q -> infinity, regardless of p (mod 6). Our approach relies on the BSD conjecture, an explicit expression for the L -function of E, and a geometric analysis of the Neron model of E.
    • Simplified method to quantify valve back-leak uncovers severe mesenteric lymphatic valve dysfunction in mice deficient in connexins 43 and 37

      Castorena-Gonzalez, Jorge A; Srinivasan, R Sathish; King, Philip D; Simon, Alexander M; Davis, Michael J; Univ Arizona, Dept Physiol (WILEY, 2020-04-08)
      Lymphatic valve defects are one of the major causes of lymph transport dysfunction; however, there are no accessible methods for quantitatively assessing valve function. This report describes a novel technique for quantifying lymphatic valve back-leak. Postnatal endothelial-specific deletion of connexin 43 (Cx43) in connexin 37 null (Cx37-/- ) mice results in rapid regression of valve leaflets and severe valve dysfunction. This method can also be used for assessing the function of venous and lymphatic valves from various species, including humans.