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Sample records for accretion rate decreases

  1. Low Accretion Rate Expected From G2 Gas Cloud

    NASA Astrophysics Data System (ADS)

    Gracey, Brandon; Morsony, Brian; Workman, Jared

    2015-08-01

    We present high-resolution simulations of the encounter of the G2 gas cloud with Sag A*, focusing on the mass that can be accreted onto the supermassive black hole. Even assuming G2 is a gas cloud of a few time the mass of Earth, we find that very little material should be expected to be accreted. From 5 years before to 5 years after pericenter passage, at most 0.1% of the cloud mass is accreted. The total amount of material accreted by Sag A* increases by at most 20% over this period, and in many cases actually decreases due to the passage of G2. Even over very long timescales, out to 30 years after pericenter passage, only a few 10th's of a percent of the cloud will be accreted, with no significant increase in the overall mass accretion rate of Sag A*.We find that the size of the accretion radius in our simulations has a large effect on the accretion rate, with a smaller accretion radius having a smaller accretion rate. Changing the size of the accretion radius has a larger effect than changing the density profile of the cloud or changing the structure of the background material around Sag A*.

  2. Accretion Rate: An Axis Of Agn Unification

    NASA Astrophysics Data System (ADS)

    Trump, Jonathan R.; Impey, C. D.; Kelly, B. C.

    2011-01-01

    We show how accretion rate governs the physical properties of broad-line, narrow-line, and lineless active galactic nuclei (AGNs). We avoid the systematic errors plaguing previous studies of AGN accretion rate by using accurate accretion luminosities from well-sampled multiwavelength SEDs from the Cosmic Evolution Survey (COSMOS), and accurate black hole masses derived from virial scaling relations (for broad-line AGNs) or host-AGN relations (for narrow-line and lineless AGNs). In general, broad emission lines are present only at the highest accretion rates (L/L_Edd>0.01), and these rapidly accreting AGNs are observed as broad-line AGNs or possibly as obscured narrow-line AGNs. Narrow-line and lineless AGNs at lower specific accretion rates (L/L_Edd<0.01) are unobscured and yet lack a broad line region. The disappearance of the broad emission lines is caused by an expanding radiatively inefficient accretion flow (RIAF) at the inner radius of the accretion disk. The presence of the RIAF also drives L/L_Edd<0.01 narrow-line and lineless AGNs to be 10-100 times more radio-luminous than broad-line AGNs, since the unbound nature of the RIAF means it is easier to form a radio outflow. The IR torus signature also tends to become weaker or disappear from L/L_Edd<0.01 AGNs, although there may be additional mid-IR synchrotron emission associated with the RIAF. Together these results suggest that specific accretion rate is an important physical "axis" of AGN unification, described by a simple model.

  3. ACCRETION RATES OF MOONLETS EMBEDDED IN CIRCUMPLANETARY PARTICLE DISKS

    SciTech Connect

    Ohtsuki, Keiji; Yasui, Yuki; Daisaka, Hiroshi

    2013-08-01

    We examine the gravitational capture probability of colliding particles in circumplanetary particle disks and accretion rates of small particles onto an embedded moonlet, using analytic calculation, three-body orbital integrations, and N-body simulations. Expanding our previous work, we take into account the Rayleigh distribution of particles' orbital eccentricities and inclinations in our analytic calculation and orbital integration and confirm agreement between them when the particle velocity dispersion is comparable to or larger than their mutual escape velocity and the ratio of the sum of the physical radii of colliding particles to their mutual Hill radius (r-tilde{sub p}) is much smaller than unity. As shown by our previous work, the capture probability decreases significantly when the velocity dispersion is larger than the escape velocity and/or r-tilde{sub p}{approx}>0.7. Rough surfaces of particles can enhance the capture probability. We compare the results of three-body calculations with N-body simulations for accretion of small particles by an embedded moonlet and find agreement at the initial stage of accretion. However, when particles forming an aggregate on the moonlet surface nearly fill the Hill sphere, the aggregate reaches a quasi-steady state with a nearly constant number of particles covering the moonlet, and the accretion rate is significantly reduced compared to the three-body results.

  4. Mass Accretion Rate of Very Low Luminosity Objects

    NASA Astrophysics Data System (ADS)

    Sung, Ren-Shiang; Lai, Shih-Ping; Hsieh, Tien-Hao

    2013-08-01

    We propose to measure the mass accretion rate of six Very Low Luminosity Objects (VeLLOs) using Near-infrared Integral Spectrometer (NIFS). The extremely low luminosity of VeLLOs, L_int ≤ 0.1 L_⊙, was previously thought not existing in the nature because the typical accretion rate gives much larger accretion luminosity even for the lowest mass star (``Luminosity Problem''). The commonly accepted solution is that the accretion rate is not constant but episodic. Thus, VeLLOs could be interpreted as protostars being in the quiescent phase of accretion activities. However, there is no observational data directly measuring the mass accretion rate of VeLLOs. The main goal of this proposal is to examine such theory and directly measure the mass accretion rate of VeLLOs for the first time. We propose to measure the blue continuum excess (veiling) of the stellar spectrum, which is the most reliable method for measuring the accretion rate. The measurements have to be made in infrared due to the very high extinction for highly embedded protostars. Our proposal provide a first opportunity to explain the long time ``Luminosity Problem'' through the observational aspects, and Gemini is the only instrument that can provide accurate and high sensitivity infrared spectroscopy measurements within reasonably short time scale.

  5. The Accretion Rate Dependence of Burst Oscillation Amplitude

    NASA Astrophysics Data System (ADS)

    Ootes, Laura S.; Watts, Anna L.; Galloway, Duncan K.; Wijnands, Rudy

    2017-01-01

    Neutron stars in low-mass X-ray binaries exhibit oscillations during thermonuclear bursts, attributed to asymmetric brightness patterns on the burning surfaces. All models that have been proposed to explain the origin of these asymmetries (spreading hotspots, surface waves, and cooling wakes) depend on the accretion rate. By analysis of archival RXTE data of six oscillation sources, we investigate the accretion rate dependence of the amplitude of burst oscillations. This more than doubles the size of the sample analyzed previously by Muno et al., who found indications for a relationship between accretion rate and oscillation amplitudes. We find that burst oscillation signals can be detected at all observed accretion rates. Moreover, oscillations at low accretion rates are found to have relatively small amplitudes ({A}{{rms}}≤slant 0.10) while oscillations detected in bursts observed at high accretion rates cover a broad spread in amplitudes (0.05≤slant {A}{{rms}}≤slant 0.20). In this paper we present the results of our analysis and discuss these in the light of current burst oscillation models. Additionally, we investigate the bursts of two sources without previously detected oscillations. Despite the fact that these sources have been observed at accretion rates where burst oscillations might be expected, we find their behavior not to be anomalous compared to oscillation sources.

  6. Variable protostellar mass accretion rates in cloud cores

    NASA Astrophysics Data System (ADS)

    Gao, Yang; Lou, Yu-Qing

    2017-03-01

    Spherical hydrodynamic models with a polytropic equation of state (EoS) for forming protostars are revisited in order to investigate the so-called luminosity conundrum highlighted by observations. For a molecular cloud (MC) core with such an EoS with polytropic index γ > 1, the central mass accretion rate (MAR) decreases with increasing time as a protostar emerges, offering a sensible solution to this luminosity problem. As the MAR decreases, the protostellar luminosity also decreases, meaning that it is invalid to infer the star formation time from the currently observed luminosity using an isothermal model. Furthermore, observations of radial density profiles and the radio continua of numerous MC cores evolving towards protostars also suggest that polytropic dynamic spheres of γ > 1 should be used in physical models.

  7. Binary accretion rates: dependence on temperature and mass ratio

    NASA Astrophysics Data System (ADS)

    Young, M. D.; Clarke, C. J.

    2015-09-01

    We perform a series of 2D smoothed particle hydrodynamics simulations of gas accretion on to binaries via a circumbinary disc, for a range of gas temperatures and binary mass ratios (q). We show that increasing the gas temperature increases the accretion rate on to the primary for all values of the binary mass ratio: for example, for q = 0.1 and a fixed binary separation, an increase of normalized sound speed by a factor of 5 (from our `cold' to `hot' simulations) changes the fraction of the accreted gas that flows on to the primary from 10 to ˜40 per cent. We present a simple parametrization for the average accretion rate of each binary component accurate to within a few per cent and argue that this parametrization (rather than those in the literature based on warmer simulations) is relevant to supermassive black hole accretion and all but the widest stellar binaries. We present trajectories for the growth of q during circumbinary disc accretion and argue that the period distribution of stellar `twin' binaries is strong evidence for the importance of circumbinary accretion. We also show that our parametrization of binary accretion increases the minimum mass ratio needed for spin alignment of supermassive black holes to q ˜ 0.4, with potentially important implications for the magnitude of velocity kicks acquired during black hole mergers.

  8. Reaction rate and composition dependence of the stability of thermonuclear burning on accreting neutron stars

    SciTech Connect

    Keek, L.; Cyburt, R. H.; Heger, A.

    2014-06-01

    The stability of thermonuclear burning of hydrogen and helium accreted onto neutron stars is strongly dependent on the mass accretion rate. The burning behavior is observed to change from Type I X-ray bursts to stable burning, with oscillatory burning occurring at the transition. Simulations predict the transition at a 10 times higher mass accretion rate than observed. Using numerical models we investigate how the transition depends on the hydrogen, helium, and CNO mass fractions of the accreted material, as well as on the nuclear reaction rates of 3α and the hot-CNO breakout reactions {sup 15}O(α, γ){sup 19}Ne and {sup 18}Ne(α, p){sup 21}Na. For a lower hydrogen content the transition is at higher accretion rates. Furthermore, most experimentally allowed reaction rate variations change the transition accretion rate by at most 10%. A factor 10 decrease of the {sup 15}O(α, γ){sup 19}Ne rate, however, produces an increase of the transition accretion rate of 35%. None of our models reproduce the transition at the observed rate, and depending on the true {sup 15}O(α, γ){sup 19}Ne reaction rate, the actual discrepancy may be substantially larger. We find that the width of the interval of accretion rates with marginally stable burning depends strongly on both composition and reaction rates. Furthermore, close to the stability transition, our models predict that X-ray bursts have extended tails where freshly accreted fuel prolongs nuclear burning.

  9. MEASURING TINY MASS ACCRETION RATES ONTO YOUNG BROWN DWARFS

    SciTech Connect

    Herczeg, Gregory J.; Cruz, Kelle L.; Hillenbrand, Lynne A.

    2009-05-10

    We present low-resolution Keck I/LRIS spectra spanning from 3200 to 9000 A of nine young brown dwarfs and three low-mass stars in the TW Hya Association and in Upper Sco. The optical spectral types of the brown dwarfs range from M5.5 to M8.75, though two have near-IR spectral types of early L dwarfs. We report new accretion rates derived from excess Balmer continuum emission for the low-mass stars TW Hya and Hen 3-600A and the brown dwarfs 2MASS J12073347-3932540, UScoCTIO 128, SSSPM J1102-3431, USco J160606.29-233513.3, DENIS-P J160603.9-205644, and Oph J162225-240515B, and upper limits on accretion for the low-mass star Hen 3-600B and the brown dwarfs UScoCTIO 112, Oph J162225-240515A, and USco J160723.82-221102.0. For the six brown dwarfs in our sample that are faintest at short wavelengths, the accretion luminosity or upper limit is measurable only when the image is binned over large wavelength intervals. This method extends our sensitivity to accretion rate down to {approx}10{sup -13} M{sub sun}yr{sup -1} for brown dwarfs. Since the ability to measure an accretion rate from excess Balmer continuum emission depends on the contrast between excess continuum emission and the underlying photosphere, for objects with earlier spectral types the upper limit on accretion rate is much higher. Absolute uncertainties in our accretion rate measurements of {approx}3-5 include uncertainty in accretion models, brown dwarf masses, and distance. The accretion rate of 2 x 10{sup -12} M {sub sun} yr{sup -1} onto 2MASS J12073347-3932540 is within 15% of two previous measurements, despite large changes in the H{alpha} flux.

  10. ACCRETION RATE AND THE PHYSICAL NATURE OF UNOBSCURED ACTIVE GALAXIES

    SciTech Connect

    Trump, Jonathan R.; Impey, Christopher D.; Gabor, Jared M.; Diamond-Stanic, Aleksandar M.; Kelly, Brandon C.; Civano, Francesca; Hao, Heng; Lanzuisi, Giorgio; Merloni, Andrea; Salvato, Mara; Urry, C. Megan; Jahnke, Knud; Nagao, Tohru; Taniguchi, Yoshi; Koekemoer, Anton M.; Liu, Charles; Mainieri, Vincenzo; Scoville, Nick Z.

    2011-05-20

    We show how accretion rate governs the physical properties of a sample of unobscured broad-line, narrow-line, and lineless active galactic nuclei (AGNs). We avoid the systematic errors plaguing previous studies of AGN accretion rates by using accurate intrinsic accretion luminosities (L{sub int}) from well-sampled multiwavelength spectral energy distributions from the Cosmic Evolution Survey, and accurate black hole masses derived from virial scaling relations (for broad-line AGNs) or host-AGN relations (for narrow-line and lineless AGNs). In general, broad emission lines are present only at the highest accretion rates (L{sub int}/L{sub Edd} > 10{sup -2}), and these rapidly accreting AGNs are observed as broad-line AGNs or possibly as obscured narrow-line AGNs. Narrow-line and lineless AGNs at lower specific accretion rates (L{sub int}/L{sub Edd} < 10{sup -2}) are unobscured and yet lack a broad-line region. The disappearance of the broad emission lines is caused by an expanding radiatively inefficient accretion flow (RIAF) at the inner radius of the accretion disk. The presence of the RIAF also drives L{sub int}/L{sub Edd} < 10{sup -2} narrow-line and lineless AGNs to have ratios of radio-to-optical/UV emission that are 10 times higher than L{sub int}/L{sub Edd} > 10{sup -2} broad-line AGNs, since the unbound nature of the RIAF means it is easier to form a radio outflow. The IR torus signature also tends to become weaker or disappear from L{sub int}/L{sub Edd} < 10{sup -2} AGNs, although there may be additional mid-IR synchrotron emission associated with the RIAF. Together, these results suggest that specific accretion rate is an important physical 'axis' of AGN unification, as described by a simple model.

  11. Binary interactions with high accretion rates onto main sequence stars

    NASA Astrophysics Data System (ADS)

    Shiber, Sagiv; Schreier, Ron; Soker, Noam

    2016-07-01

    Energetic outflows from main sequence stars accreting mass at very high rates might account for the powering of some eruptive objects, such as merging main sequence stars, major eruptions of luminous blue variables, e.g., the Great Eruption of Eta Carinae, and other intermediate luminosity optical transients (ILOTs; red novae; red transients). These powerful outflows could potentially also supply the extra energy required in the common envelope process and in the grazing envelope evolution of binary systems. We propose that a massive outflow/jets mediated by magnetic fields might remove energy and angular momentum from the accretion disk to allow such high accretion rate flows. By examining the possible activity of the magnetic fields of accretion disks, we conclude that indeed main sequence stars might accrete mass at very high rates, up to ≈ 10-2 M ⊙ yr-1 for solar type stars, and up to ≈ 1 M ⊙ yr-1 for very massive stars. We speculate that magnetic fields amplified in such extreme conditions might lead to the formation of massive bipolar outflows that can remove most of the disk's energy and angular momentum. It is this energy and angular momentum removal that allows the very high mass accretion rate onto main sequence stars.

  12. Accretion Rate and the Physical Nature of Unobscured Active Galaxies

    NASA Astrophysics Data System (ADS)

    Trump, Jonathan R.; Impey, Christopher D.; Kelly, Brandon C.; Civano, Francesca; Gabor, Jared M.; Diamond-Stanic, Aleksandar M.; Merloni, Andrea; Urry, C. Megan; Hao, Heng; Jahnke, Knud; Nagao, Tohru; Taniguchi, Yoshi; Koekemoer, Anton M.; Lanzuisi, Giorgio; Liu, Charles; Mainieri, Vincenzo; Salvato, Mara; Scoville, Nick Z.

    2011-05-01

    We show how accretion rate governs the physical properties of a sample of unobscured broad-line, narrow-line, and lineless active galactic nuclei (AGNs). We avoid the systematic errors plaguing previous studies of AGN accretion rates by using accurate intrinsic accretion luminosities (L int) from well-sampled multiwavelength spectral energy distributions from the Cosmic Evolution Survey, and accurate black hole masses derived from virial scaling relations (for broad-line AGNs) or host-AGN relations (for narrow-line and lineless AGNs). In general, broad emission lines are present only at the highest accretion rates (L int/L Edd > 10-2), and these rapidly accreting AGNs are observed as broad-line AGNs or possibly as obscured narrow-line AGNs. Narrow-line and lineless AGNs at lower specific accretion rates (L int/L Edd < 10-2) are unobscured and yet lack a broad-line region. The disappearance of the broad emission lines is caused by an expanding radiatively inefficient accretion flow (RIAF) at the inner radius of the accretion disk. The presence of the RIAF also drives L int/L Edd < 10-2 narrow-line and lineless AGNs to have ratios of radio-to-optical/UV emission that are 10 times higher than L int/L Edd > 10-2 broad-line AGNs, since the unbound nature of the RIAF means it is easier to form a radio outflow. The IR torus signature also tends to become weaker or disappear from L int/L Edd < 10-2 AGNs, although there may be additional mid-IR synchrotron emission associated with the RIAF. Together, these results suggest that specific accretion rate is an important physical "axis" of AGN unification, as described by a simple model. Based on observations with the XMM-Newton satellite, an ESA science mission with instruments and contributions directly funded by ESA member states and NASA; the Magellan telescope, operated by the Carnegie Observatories; the ESO Very Large Telescope; and the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian

  13. Smearing of mass accretion rate variation by viscous processes in accretion disks in compact binary systems

    NASA Astrophysics Data System (ADS)

    Ghosh, A.; Chakrabarti, Sandip K.

    2016-09-01

    Variation of mass supply rate from the companion can be smeared out by viscous processes inside an accretion disk. Hence, by the time the flow reaches the inner edge, the variation in X-rays need not reflect the true variation of the mass supply rate at the outer edge. However, if the viscosity fluctuates around a mean value, one would expect the viscous time scale t_{{visc}} also to spread around a mean value. In high mass X-ray binaries, which are thought to be primarily wind-fed, the size of the viscous Keplerian disk is smaller and thus such a spread could be lower as compared to the low mass X-ray binaries which are primarily fed by Roche lobe overflow. If there is an increasing or decreasing trend in viscosity, the interval between enhanced emission would be modified systematically. In the absence of a detailed knowledge about the variation of mass supply rates at the outer edge, we study ideal circumstances where modulation must take place exactly in orbital time scales, such as when there is an ellipticity in the orbit. We study a few compact binaries using long term All Sky monitor (ASM) data (1.5-12 keV) of Rossi X-ray Timing Explorer (RXTE) and all sky survey data (15-50 keV) of Swift satellites by different methods to look for such smearing effects and to infer what these results can tell us about the viscous processes inside the respective disks. We employ three different methods to seek imprints of periodicity on the X-ray variation and found that in all the cases, the location of the peak in the power density spectra is consistent with the orbital frequencies. Interestingly, in high mass X-ray binaries the peaks are sharp with high rms values, consistent with a small Keplerian disk in a wind fed system. However, in low mass X-ray binaries with larger Keplerian disk component, the peaks are spreaded out with much lower rms values. X-ray reflections, or superhump phenomena which may also cause such X-ray modulations would not be affected by the size of

  14. Accretion rate of extraterrestrial 41Ca in Antarctic snow samples

    NASA Astrophysics Data System (ADS)

    Gómez-Guzmán, J. M.; Bishop, S.; Faestermann, T.; Famulok, N.; Fimiani, L.; Hain, K.; Jahn, S.; Korschinek, G.; Ludwig, P.; Rodrigues, D.

    2015-10-01

    Interplanetary Dust Particles (IDPs) are small grains, generally less than a few hundred micrometers in size. Their main source is the Asteroid Belt, located at 3 AU from the Sun, between Mars and Jupiter. During their flight from the Asteroid Belt to the Earth they are irradiated by galactic and solar cosmic rays (GCR and SCR), thus radionuclides are formed, like 41Ca and 53Mn. Therefore, 41Ca (T1/2 = 1.03 × 105 yr) can be used as a key tracer to determine the accretion rate of IDPs onto the Earth because there are no significant terrestrial sources for this radionuclide. The first step of this study consisted to calculate the production rate of 41Ca in IDPs accreted by the Earth during their travel from the Asteroid Belt. This production rate, used in accordance with the 41Ca/40Ca ratios that will be measured in snow samples from the Antarctica will be used to calculate the amount of extraterrestrial material accreted by the Earth per year. There challenges for this project are, at first, the much longer time for the flight needed by the IDPs to travel from the Asteroid Belt to the Earth in comparison with the 41Ca half-life yields an early saturation for the 41Ca/40Ca ratio, and second, the importance of selecting the correct sampling site to avoid a high influx of natural 40Ca, preventing dilution of the 41Ca/40Ca ratio, the quantity measured by AMS.

  15. ACCRETION RATES OF RED QUASARS FROM THE HYDROGEN Pβ LINE

    SciTech Connect

    Kim, Dohyeong; Im, Myungshin; Glikman, Eilat; Woo, Jong-Hak; Urrutia, Tanya E-mail: mim@astro.snu.ac.kr

    2015-10-10

    Red quasars are thought to be an intermediate population between merger-driven star-forming galaxies in dust-enshrouded phase and normal quasars. If so, they are expected to have high accretion ratios, but their intrinsic dust extinction hampers reliable determination of Eddington ratios. Here, we compare the accretion rates of 16 red quasars at z ∼ 0.7 to those of normal type 1 quasars at the same redshift range. The red quasars are selected by their red colors in optical through near-infrared (NIR) and radio detection. The accretion rates of the red quasars are derived from the Pβ line in NIR spectra, which is obtained by the SpeX on the Infrared Telescope Facility in order to avoid the effects of dust extinction. We find that the measured Eddington ratios (L{sub bol}/L{sub Edd} ≃ 0.69) of red quasars are significantly higher than those of normal type 1 quasars, which is consistent with a scenario in which red quasars are the intermediate population and the black holes of red quasars grow very rapidly during such a stage.

  16. Estimation of mass outflow rates from viscous relativistic accretion discs around black holes

    NASA Astrophysics Data System (ADS)

    Chattopadhyay, Indranil; Kumar, Rajiv

    2016-07-01

    We investigated flow in Schwarzschild metric, around a non-rotating black hole and obtained self-consistent accretion-ejection solution in full general relativity. We covered the whole of parameter space in the advective regime to obtain shocked, as well as, shock-free accretion solution. We computed the jet streamline using von Zeipel surfaces and projected the jet equations of motion on to the streamline and solved them simultaneously with the accretion disc equations of motion. We found that steady shock cannot exist beyond α ≳ 0.06 in the general relativistic prescription, but is lower if mass-loss is considered too. We showed that for fixed outer boundary, the shock moves closer to the horizon with increasing viscosity parameter. The mass outflow rate increases as the shock moves closer to the black hole, but eventually decreases, maximizing at some intermediate value of shock location. The jet terminal speed increases with stronger shocks; quantitatively speaking, the terminal speed of jets vj∞ > 0.1 if rsh < 20rg. The maximum of the outflow rate obtained in the general relativistic regime is less than 6 per cent of the mass accretion rate.

  17. Does the mass of a black hole decrease due to the accretion of phantom energy?

    SciTech Connect

    Gao Changjun; Chen Xuelei; Faraoni, Valerio; Shen Yougen

    2008-07-15

    According to Babichev et al., the accretion of a phantom test fluid onto a Schwarzschild black hole will induce the mass of the black hole to decrease, however the backreaction was ignored in their calculation. Using new exact solutions describing black holes in a background Friedmann-Robertson-Walker universe, we find that the physical black hole mass may instead increase due to the accretion of phantom energy. If this is the case, and the future universe is dominated by phantom dark energy, the black hole apparent horizon and the cosmic apparent horizon will eventually coincide and, after that, the black hole singularity will become naked in finite comoving time before the big rip occurs, violating the cosmic censorship conjecture.

  18. Planetary Population Synthesis: the importance of the solids accretion rate

    NASA Astrophysics Data System (ADS)

    Fortier, A.; Alibert, Y.; Carron, F.; Mordasini, C.; Benz, W.

    2011-10-01

    In the framework of the nucleated instability model, the formation time-scale of giant planets is very sensitive to the time it takes to build the solid core. The accretion of solids can be described by two different, consecutive regimes: it first proceeds in a very fast fashion, known as runaway growth, and later on in a much slower regime, the so-called oligarchic growth. The transition between the runaway and the oligarchic growth depends on many parameters (e.g. the isolation mass and the size of the accreted planetesimals), but as a general rule we can assume that an embryo of a Lunar mass is already an oligarch. Then, the timescale to build a 10 Earth masses (M⊙) core is regulated by the oligarchic regime, as the previous runaway stage proceeds in a negligible amount of time compared to the oligarchic timescale. In this work we show the results of adopting the oligarchic growth for the core in planetary population synthesis calculations. In previous works (see [1], [2]) a fast solids accretion rate was prescribed, leading to a very fast formation of massive solid embryos. Here we show that when considering the oligarchic growth, the formation of giant planets is more difficult, especially in the outer parts of the disk, where the formation of big planets is almost impossible under these hypothesis. On the other hand, many Earth to Super- Earth sized planets are found in the very innermost parts of the disk. However, if the size of the accreted planetesimals is reduced, the formation of giant planets is more likely, preserving also a large amount of smaller planets. We also consider the formation of planetary systems, including the N-body interaction between the forming planets and the collisions that may occur among them during their migration. In the case of many planets forming in the same disk, we find that the final masses of the planets are smaller (but not too small) than in the case of a single planet per star.

  19. OBSERVATIONAL LIMITS ON TYPE 1 ACTIVE GALACTIC NUCLEUS ACCRETION RATE IN COSMOS

    SciTech Connect

    Trump, Jonathan R.; Impey, Chris D.; Gabor, Jared; Kelly, Brandon C.; Elvis, Martin; Hao Heng; Huchra, John P.; Merloni, Andrea; Bongiorno, Angela; Brusa, Marcella; Cappelluti, Nico; McCarthy, Patrick J.; Koekemoer, Anton; Nagao, Tohru; Salvato, Mara; Scoville, Nick Z.

    2009-07-20

    We present black hole masses and accretion rates for 182 Type 1 active galactic nuclei (AGNs) in COSMOS. We estimate masses using the scaling relations for the broad H {beta}, Mg II, and C IV emission lines in the redshift ranges 0.16 < z < 0.88, 1 < z < 2.4, and 2.7 < z < 4.9. We estimate the accretion rate using an Eddington ratio L{sub I}/L{sub Edd} estimated from optical and X-ray data. We find that very few Type 1 AGNs accrete below L{sub I} /L{sub Edd} {approx} 0.01, despite simulations of synthetic spectra which show that the survey is sensitive to such Type 1 AGNs. At lower accretion rates the broad-line region may become obscured, diluted, or nonexistent. We find evidence that Type 1 AGNs at higher accretion rates have higher optical luminosities, as more of their emission comes from the cool (optical) accretion disk with respect to shorter wavelengths. We measure a larger range in accretion rate than previous works, suggesting that COSMOS is more efficient at finding low accretion rate Type 1 AGNs. However, the measured range in accretion rate is still comparable to the intrinsic scatter from the scaling relations, suggesting that Type 1 AGNs accrete at a narrow range of Eddington ratio, with L{sub I} /L{sub Edd} {approx} 0.1.

  20. ACCRETION ONTO BLACK HOLES FROM LARGE SCALES REGULATED BY RADIATIVE FEEDBACK. II. GROWTH RATE AND DUTY CYCLE

    SciTech Connect

    Park, Kwang Ho; Ricotti, Massimo E-mail: ricotti@astro.umd.edu

    2012-03-01

    This paper, the second in a series on radiation-regulated accretion onto black holes (BHs) from galactic scales, focuses on the effects of radiation pressure and angular momentum of the accreting gas. We simulate accretion onto intermediate-mass black holes, but we derive general scaling relationships that are solutions of the Bondi problem with radiation feedback valid for any mass of the BH M{sub bh}. Thermal pressure of the ionized sphere around the BH regulates the accretion rate, producing periodic and short-lived luminosity bursts. We find that for ambient gas densities exceeding n{sup cr}{sub H,{infinity}}{proportional_to}M{sup -1}{sub bh}, the period of the oscillations decreases rapidly and the duty cycle increases from 6%, in agreement with observations of the fraction of active galactic nuclei at z {approx} 3, to 50%. The mean accretion rate becomes Eddington limited for n{sub H,{infinity}} > n{sup Edd}{sub H,{infinity}} {approx_equal} n{sup cr}{sub H,{infinity}} T{sub {infinity},4}{sup -1} where T{sub {infinity},4} is the gas temperature in units of 10{sup 4} K. In the sub-Eddington regime, the mean accretion rate onto BHs is about 1%T{sup 2.5}{sub {infinity},4} of the Bondi rate, and thus is proportional to the thermal pressure of the ambient medium. The period of the oscillations coincides with the depletion timescale of the gas inside the ionized bubble surrounding the BH. Gas depletion is dominated by a pressure gradient pushing the gas outward if n{sub H,{infinity}} < n{sup cr}{sub H,{infinity}} and by accretion onto the BH otherwise. Generally, for n{sub H,{infinity}} < n{sup cr}{sub H,{infinity}} angular momentum does not significantly affect the accretion rate and period of the oscillations.

  1. Pyrazinoic acid decreases peritoneal transfer rates.

    PubMed

    Grzegorzewska, A E; Czyzewska, K; Szary, B

    1995-01-01

    It was shown elsewhere that in a peritoneally dialyzed woman with pulmonary tuberculosis, oral treatment with rifampicin and pyrazinamide (11 and 25 mg/kg/day, respectively) caused a decrease in the peritoneal transport of sodium, potassium, urea, uric acid, protein, and ultrafiltration rate by 48% to 75% compared to the pretreatment values. Pyrazinoic acid (PA), a metabolite of pyrazinamide, may account for these changes, because rifampicin was also previously used in this patient without peritoneal function impairment. Thus in the present study the influence of PA on the human peritoneum is examined using the modified Ussing-type chamber. PA (1 mg/dL) was introduced into the medium on the interstitial side of the membrane. After the introduction of PA, uric acid transfer from the interstitial to the mesothelial side decreased by about 50%. There were no significant changes in the urea and albumin transfer rates. In conclusion, PA induces changes in uric acid transfer acting directly on mesothelial cells, whereas a decrease in the peritoneal transfer of other solutes may be caused by a decrease in convective transfer rates due to impaired ultrafiltration.

  2. Black hole accretion versus star formation rate: theory confronts observations

    NASA Astrophysics Data System (ADS)

    Volonteri, Marta; Capelo, Pedro R.; Netzer, Hagai; Bellovary, Jillian; Dotti, Massimo; Governato, Fabio

    2015-09-01

    We use a suite of hydrodynamical simulations of galaxy mergers to compare star formation rate (SFR) and black hole accretion rate (BHAR) for galaxies before the interaction (`stochastic' phase), during the `merger' proper, lasting ˜0.2-0.3 Gyr, and in the `remnant' phase. We calculate the bivariate distribution of SFR and BHAR and define the regions in the SFR-BHAR plane that the three phases occupy. No strong correlation between BHAR and galaxy-wide SFR is found. A possible exception are galaxies with the highest SFR and the highest BHAR. We also bin the data in the same way used in several observational studies, by either measuring the mean SFR for AGN in different luminosity bins, or the mean BHAR for galaxies in bins of SFR. We find that the apparent contradiction or SFR versus BHAR for observed samples of AGN and star-forming galaxies is actually caused by binning effects. The two types of samples use different projections of the full bivariate distribution, and the full information would lead to unambiguous interpretation. We also find that a galaxy can be classified as AGN-dominated up to 1.5 Gyr after the merger-driven starburst took place. Our study is consistent with the suggestion that most low-luminosity AGN hosts do not show morphological disturbances.

  3. LAUNCHING AND QUENCHING OF BLACK HOLE RELATIVISTIC JETS AT LOW ACCRETION RATE

    SciTech Connect

    Pu, Hung-Yi; Chang, Hsiang-Kuang; Hirotani, Kouichi

    2012-10-20

    Relativistic jets are launched from black hole (BH) X-ray binaries and active galactic nuclei when the disk accretion rate is below a certain limit (i.e., when the ratio of the accretion rate to the Eddingtion accretion rate, m-dot , is below about 0.01) but quenched when above. We propose a new paradigm to explain this observed coupling between the jet and the accretion disk by investigating the extraction of the rotational energy of a BH when it is surrounded by different types of accretion disk. At low accretion rates (e.g., when m-dot {approx}<0.1), the accretion near the event horizon is quasi-spherical. The accreting plasmas fall onto the event horizon in a wide range of latitudes, breaking down the force-free approximation near the horizon. To incorporate the plasma inertia effect, we consider the magnetohydrodynamical (MHD) extraction of the rotational energy from BHs by the accreting MHD fluid, as described by the MHD Penrose process. It is found that the energy extraction operates, and hence a relativistic jet is launched, preferentially when the accretion disk consists of an outer Shakura-Sunyaev disk (SSD) and an inner advection-dominated accretion flow. When the entire accretion disk type changes into an SSD, the jet is quenched because the plasmas bring more rest-mass energy than what is extracted from the hole electromagnetically to stop the extraction. Several other issues related to observed BH disk-jet couplings, such as why the radio luminosity increases with increasing X-ray luminosity until the radio emission drops, are also explained.

  4. Elliptical Accretion and Low Luminosity from High Accretion Rate Stellar Tidal Disruption Events

    NASA Astrophysics Data System (ADS)

    Svirski, Gilad; Piran, Tsvi; Krolik, Julian

    2017-01-01

    Models for tidal disruption events (TDEs) in which a supermassive black hole disrupts a star commonly assume that the highly eccentric streams of bound stellar debris promptly form a circular accretion disk at the pericenter scale. However, the bolometric peak luminosity of most TDE candidates, ˜ 10^{44} {erg s^{-1}}, implies that we observe only ˜1% of the energy expected from radiatively efficient accretion. Even the energy that must be lost to circularize the returning tidal flow is larger than the observed energy. Recently, Piran et al. (2015) suggested that the observed optical TDE emission is powered by shocks at the apocenter between freshly infalling material and earlier arriving matter. This model explains the small radiated energy, the low temperature, and the large radius implied by the observations as well as the t-5/3 light curve. However the question of the system's low bolometric efficiency remains unanswered. We suggest that the high orbital energy and low angular momentum of the flow make it possible for magnetic stresses to reduce the matter's already small angular momentum to the point at which it can fall ballistically into the SMBH before circularization. As a result, the efficiency is only ˜1-10% of a standard accretion disk's efficiency. Thus, the intrinsically high eccentricity of the tidal debris naturally explains why most TDE candidates are fainter than expected.

  5. THE RATE OF GAS ACCRETION ONTO BLACK HOLES DRIVES JET VELOCITY

    SciTech Connect

    King, Ashley L.; Miller, Jon M.; Gültekin, Kayhan; Reynolds, Mark; Bietenholz, Michael; Bartel, Norbert; Mioduszewski, Amy; Rupen, Michael

    2015-01-20

    Accreting black holes are observed to launch relativistic, collimated jets of matter and radiation. In some sources, discrete ejections have been detected with highly relativistic velocities. These particular sources typically have very high mass accretion rates, while sources lower knot velocities are predominantly associated with black holes with relatively low mass accretion rates. We quantify this behavior by examining knot velocity with respect to X-ray luminosity, a proxy for mass accretion rate onto the black hole. We find a positive correlation between the mass-scaled X-ray luminosity and jet knot velocity. In addition, we find evidence that the jet velocity is also a function of polar angle, supporting the ''spine-sheath'' model of jet production. Our results reveal a fundamental aspect of how accretion shapes mechanical feedback from black holes into their host environments.

  6. Star-disc interaction in galactic nuclei: orbits and rates of accreted stars

    NASA Astrophysics Data System (ADS)

    Kennedy, Gareth F.; Meiron, Yohai; Shukirgaliyev, Bekdaulet; Panamarev, Taras; Berczik, Peter; Just, Andreas; Spurzem, Rainer

    2016-07-01

    We examine the effect of an accretion disc on the orbits of stars in the central star cluster surrounding a central massive black hole by performing a suite of 39 high-accuracy direct N-body simulations using state-of-the art software and accelerator hardware, with particle numbers up to 128k. The primary focus is on the accretion rate of stars by the black hole (equivalent to their tidal disruption rate for black holes in the small to medium mass range) and the eccentricity distribution of these stars. Our simulations vary not only the particle number, but disc model (two models examined), spatial resolution at the centre (characterized by the numerical accretion radius) and softening length. The large parameter range and physically realistic modelling allow us for the first time to confidently extrapolate these results to real galactic centres. While in a real galactic centre both particle number and accretion radius differ by a few orders of magnitude from our models, which are constrained by numerical capability, we find that the stellar accretion rate converges for models with N ≥ 32k. The eccentricity distribution of accreted stars, however, does not converge. We find that there are two competing effects at work when improving the resolution: larger particle number leads to a smaller fraction of stars accreted on nearly circular orbits, while higher spatial resolution increases this fraction. We scale our simulations to some nearby galaxies and find that the expected boost in stellar accretion (or tidal disruption, which could be observed as X-ray flares) in the presence of a gas disc is about a factor of 10. Even with this boost, the accretion of mass from stars is still a factor of ˜100 slower than the accretion of gas from the disc. Thus, it seems accretion of stars is not a major contributor to black hole mass growth.

  7. ACCRETION RATES FOR T TAURI STARS USING NEARLY SIMULTANEOUS ULTRAVIOLET AND OPTICAL SPECTRA

    SciTech Connect

    Ingleby, Laura; Calvet, Nuria; Blaty, Alex; Herczeg, Gregory; Walter, Frederick; Ardila, David; Alexander, Richard; Edwards, Suzan; Espaillat, Catherine; Gregory, Scott G.; Hillenbrand, Lynne; Brown, Alexander E-mail: ncalvet@umich.edu

    2013-04-20

    We analyze the accretion properties of 21 low-mass T Tauri stars using a data set of contemporaneous near-UV (NUV) through optical observations obtained with the Hubble Space Telescope Imaging Spectrograph and the ground-based Small and Medium Aperture Research Telescope System, a unique data set because of the nearly simultaneous broad wavelength coverage. Our data set includes accreting T Tauri stars in Taurus, Chamaeleon I, {eta} Chamaeleon, and the TW Hydra Association. For each source we calculate the accretion rate (M-dot ) by fitting the NUV and optical excesses above the photosphere, produced in the accretion shock, introducing multiple accretion components characterized by a range in energy flux (or density) for the first time. This treatment is motivated by models of the magnetospheric geometry and accretion footprints, which predict that high-density, low filling factor accretion spots coexist with low-density, high filling factor spots. By fitting the UV and optical spectra with multiple accretion components, we can explain excesses which have been observed in the near-IR. Comparing our estimates of M-dot to previous estimates, we find some discrepancies; however, they may be accounted for when considering assumptions for the amount of extinction and variability in optical spectra. Therefore, we confirm many previous estimates of the accretion rate. Finally, we measure emission line luminosities from the same spectra used for the M-dot estimates, to produce correlations between accretion indicators (H{beta}, Ca II K, C II], and Mg II) and accretion properties obtained simultaneously.

  8. Accretion Rates for T Tauri Stars Using Nearly Simultaneous Ultraviolet and Optical Spectra

    NASA Astrophysics Data System (ADS)

    Ingleby, Laura; Calvet, Nuria; Herczeg, Gregory; Blaty, Alex; Walter, Frederick; Ardila, David; Alexander, Richard; Edwards, Suzan; Espaillat, Catherine; Gregory, Scott G.; Hillenbrand, Lynne; Brown, Alexander

    2013-04-01

    We analyze the accretion properties of 21 low-mass T Tauri stars using a data set of contemporaneous near-UV (NUV) through optical observations obtained with the Hubble Space Telescope Imaging Spectrograph and the ground-based Small and Medium Aperture Research Telescope System, a unique data set because of the nearly simultaneous broad wavelength coverage. Our data set includes accreting T Tauri stars in Taurus, Chamaeleon I, η Chamaeleon, and the TW Hydra Association. For each source we calculate the accretion rate (\\dot{M}) by fitting the NUV and optical excesses above the photosphere, produced in the accretion shock, introducing multiple accretion components characterized by a range in energy flux (or density) for the first time. This treatment is motivated by models of the magnetospheric geometry and accretion footprints, which predict that high-density, low filling factor accretion spots coexist with low-density, high filling factor spots. By fitting the UV and optical spectra with multiple accretion components, we can explain excesses which have been observed in the near-IR. Comparing our estimates of \\dot{M} to previous estimates, we find some discrepancies; however, they may be accounted for when considering assumptions for the amount of extinction and variability in optical spectra. Therefore, we confirm many previous estimates of the accretion rate. Finally, we measure emission line luminosities from the same spectra used for the \\dot{M} estimates, to produce correlations between accretion indicators (Hβ, Ca II K, C II], and Mg II) and accretion properties obtained simultaneously.

  9. MEASURING THE STELLAR ACCRETION RATES OF HERBIG Ae/Be STARS

    SciTech Connect

    Donehew, Brian; Brittain, Sean E-mail: sbritt@clemson.edu

    2011-02-15

    The accretion rate of young stars is a fundamental characteristic of these systems. While accretion onto T Tauri stars has been studied extensively, little work has been done on measuring the accretion rate of their intermediate-mass analogs, the Herbig Ae/Be stars. Measuring the stellar accretion rate of Herbig Ae/Bes is not straightforward both because of the dearth of metal absorption lines available for veiling measurements and the intrinsic brightness of Herbig Ae/Be stars at ultraviolet wavelengths where the brightness of the accretion shock peaks. Alternative approaches to measuring the accretion rate of young stars by measuring the luminosity of proxies such as the Br {gamma} emission line have not been calibrated. A promising approach is the measurement of the veiling of the Balmer discontinuity. We present measurements of this veiling as well as the luminosity of Br {gamma}. We show that the relationship between the luminosity of Br {gamma} and the stellar accretion rate for classical T Tauri stars is consistent with Herbig Ae stars but not Herbig Be stars. We discuss the implications of this finding for understanding the interaction of the star and disk for Herbig Ae/Be stars.

  10. Baseline Assessment of Net Calcium Carbonate Accretion Rates on U.S. Pacific Reefs

    PubMed Central

    Vargas-Ángel, Bernardo; Richards, Cristi L.; Vroom, Peter S.; Price, Nichole N.; Schils, Tom; Young, Charles W.; Smith, Jennifer; Johnson, Maggie D.; Brainard, Russell E.

    2015-01-01

    This paper presents a comprehensive quantitative baseline assessment of in situ net calcium carbonate accretion rates (g CaCO3 cm-2 yr-1) of early successional recruitment communities on Calcification Accretion Unit (CAU) plates deployed on coral reefs at 78 discrete sites, across 11 islands in the central and south Pacific Oceans. Accretion rates varied substantially within and between islands, reef zones, levels of wave exposure, and island geomorphology. For forereef sites, mean accretion rates were the highest at Rose Atoll, Jarvis, and Swains Islands, and the lowest at Johnston Atoll and Tutuila. A comparison between reef zones showed higher accretion rates on forereefs compared to lagoon sites; mean accretion rates were also higher on windward than leeward sites but only for a subset of islands. High levels of spatial variability in net carbonate accretion rates reported herein draw attention to the heterogeneity of the community assemblages. Percent cover of key early successional taxa on CAU plates did not reflect that of the mature communities present on surrounding benthos, possibly due to the short deployment period (2 years) of the experimental units. Yet, net CaCO3 accretion rates were positively correlated with crustose coralline algae (CCA) percent cover on the surrounding benthos and on the CAU plates, which on average represented >70% of the accreted material. For foreeefs and lagoon sites combined CaCO3 accretion rates were statistically correlated with total alkalinity and Chlorophyll-a; a GAM analysis indicated that SiOH and Halimeda were the best predictor variables of accretion rates on lagoon sites, and total alkalinity and Chlorophyll-a for forereef sites, demonstrating the utility of CAUs as a tool to monitor changes in reef accretion rates as they relate to ocean acidification. This study underscores the pivotal role CCA play as a key benthic component and supporting actively calcifying reefs; high Mg-calcite exoskeletons makes CCA

  11. Baseline Assessment of Net Calcium Carbonate Accretion Rates on U.S. Pacific Reefs.

    PubMed

    Vargas-Ángel, Bernardo; Richards, Cristi L; Vroom, Peter S; Price, Nichole N; Schils, Tom; Young, Charles W; Smith, Jennifer; Johnson, Maggie D; Brainard, Russell E

    2015-01-01

    This paper presents a comprehensive quantitative baseline assessment of in situ net calcium carbonate accretion rates (g CaCO3 cm(-2) yr(-1)) of early successional recruitment communities on Calcification Accretion Unit (CAU) plates deployed on coral reefs at 78 discrete sites, across 11 islands in the central and south Pacific Oceans. Accretion rates varied substantially within and between islands, reef zones, levels of wave exposure, and island geomorphology. For forereef sites, mean accretion rates were the highest at Rose Atoll, Jarvis, and Swains Islands, and the lowest at Johnston Atoll and Tutuila. A comparison between reef zones showed higher accretion rates on forereefs compared to lagoon sites; mean accretion rates were also higher on windward than leeward sites but only for a subset of islands. High levels of spatial variability in net carbonate accretion rates reported herein draw attention to the heterogeneity of the community assemblages. Percent cover of key early successional taxa on CAU plates did not reflect that of the mature communities present on surrounding benthos, possibly due to the short deployment period (2 years) of the experimental units. Yet, net CaCO3 accretion rates were positively correlated with crustose coralline algae (CCA) percent cover on the surrounding benthos and on the CAU plates, which on average represented >70% of the accreted material. For foreeefs and lagoon sites combined CaCO3 accretion rates were statistically correlated with total alkalinity and Chlorophyll-a; a GAM analysis indicated that SiOH and Halimeda were the best predictor variables of accretion rates on lagoon sites, and total alkalinity and Chlorophyll-a for forereef sites, demonstrating the utility of CAUs as a tool to monitor changes in reef accretion rates as they relate to ocean acidification. This study underscores the pivotal role CCA play as a key benthic component and supporting actively calcifying reefs; high Mg-calcite exoskeletons makes CCA

  12. The Influence of Accretion Rate and Metallicity on Thermonuclear Bursts: Predictions from KEPLER Models

    NASA Astrophysics Data System (ADS)

    Lampe, Nathanael; Heger, Alexander; Galloway, Duncan K.

    2016-03-01

    Using the KEPLER hydrodynamics code, 464 models of thermonuclear X-ray bursters were performed across a range of accretion rates and compositions. We present the library of simulated burst profiles from this sample, and examine variations in the simulated light curve for different model conditions. We find that the recurrence time varies as a power law against accretion rate, and measure its slope while mixed H/He burning is occurring for a range of metallicities, finding the power law gradient to vary from η =1.1 to 1.24. We identify the accretion rates at which mixed H/He burning stops and a transition occurs to different burning regimes. We explore how varying the accretion rate and metallicity affects burst morphology in both the rise and tail.

  13. X-RAY DETERMINATION OF THE VARIABLE RATE OF MASS ACCRETION ONTO TW HYDRAE

    SciTech Connect

    Brickhouse, N. S.; Cranmer, S. R.; Dupree, A. K.; Guenther, H. M.; Wolk, S. J.; Luna, G. J. M.

    2012-12-01

    Diagnostics of electron temperature (T{sub e} ), electron density (n{sub e} ), and hydrogen column density (N{sub H}) from the Chandra High Energy Transmission Grating spectrum of He-like Ne IX in TW Hydrae (TW Hya), in conjunction with a classical accretion model, allow us to infer the accretion rate onto the star directly from measurements of the accreting material. The new method introduces the use of the absorption of Ne IX lines as a measure of the column density of the intervening, accreting material. On average, the derived mass accretion rate for TW Hya is 1.5 Multiplication-Sign 10{sup -9} M{sub Sun} yr{sup -1}, for a stellar magnetic field strength of 600 G and a filling factor of 3.5%. Three individual Chandra exposures show statistically significant differences in the Ne IX line ratios, indicating changes in N{sub H}, T{sub e} , and n{sub e} by factors of 0.28, 1.6, and 1.3, respectively. In exposures separated by 2.7 days, the observations reported here suggest a five-fold reduction in the accretion rate. This powerful new technique promises to substantially improve our understanding of the accretion process in young stars.

  14. Perturbation of mass accretion rate, associated acoustic geometry and stability analysis

    NASA Astrophysics Data System (ADS)

    Bollimpalli, Deepika A.; Bhattacharya, Sourav; Das, Tapas K.

    2017-02-01

    We investigate the stability of stationary integral solutions of an ideal irrotational fluid in a general static and spherically symmetric background, by studying the profile of the perturbation of the mass accretion rate. We consider low angular momentum axisymmetric accretion flows for three different accretion disk models and consider time dependent and radial linear perturbation of the mass accretion rate. First we show that the propagation of such perturbation can be determined by an effective 2 × 2 matrix, which has qualitatively similar acoustic causal properties as one obtains via the perturbation of the velocity potential. Next, using this matrix we analytically address the stability issues, for both standing and travelling wave configurations generated by the perturbation. Finally, based on this general formalism we briefly discuss the explicit example of the Schwarzschild spacetime and compare our results of stability with the existing literature, which instead address this problem via the perturbation of the velocity potential.

  15. Sediment accretion rates and sediment composition in Prairie Pothole wetlands under varying land use practices, Montana, United States

    USGS Publications Warehouse

    Preston, T.M.; Sojda, R.S.; Gleason, R.A.

    2013-01-01

    Increased sedimentation and nutrient cycle changes in Prairie Pothole Region wetlands associated with agriculture threaten the permanence and ecological functionality of these important resources. To determine the effects of land use on sedimentation and nutrient cycling, soil cores were analyzed for cesium-137 (137Cs), lead-210 (210Pb), and potassium-40 (40K) activities; textural composition; organic and inorganic carbon (C); and total nitrogen (N) from twelve wetlands surrounded by cropland, Conservation Reserve Program (CRP) lands, or native prairie uplands. Separate soil cores from nine of these wetlands were also analyzed for phosphorus (P), nitrate (NO3), and ammonium (NH4) concentrations. Wetlands surrounded by cropland had significantly greater linear sediment accretion rates than wetlands surrounded by CRP or native prairie. Linear sediment accretion rates from wetlands surrounded by cropland were 2.7 and 6 times greater than wetlands surrounded by native prairie when calculated from the initial and peak occurrence of 137Cs, respectively, and 0.15 cm y−1 (0.06 in yr−1) greater when calculated from 210Pb. Relative to wetlands surrounded by CRP, linear sediment accretion rates for wetlands surrounded by cropland were 4.4 times greater when calculated from the peak occurrence of 137Cs. No significant differences existed between the linear sediment accretion rates between wetlands surrounded by native prairie or CRP uplands. Wetlands surrounded by cropland had increased clay, P, NO3, and NH4, and decreased total C and N concentrations compared to wetlands surrounded by native prairie. Wetlands surrounded by CRP had the lowest P and NO3 concentrations and had clay, NH4, C, and N concentrations between those of cropland and native prairie wetlands. We documented increased linear sediment accretion rates and changes in the textural and chemical properties of sediments in wetlands with cultivated uplands relative to wetlands with native prairie uplands. These

  16. Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. IV. Hβ Time Lags and Implications for Super-Eddington Accretion

    NASA Astrophysics Data System (ADS)

    Du, Pu; Hu, Chen; Lu, Kai-Xing; Huang, Ying-Ke; Cheng, Cheng; Qiu, Jie; Li, Yan-Rong; Zhang, Yang-Wei; Fan, Xu-Liang; Bai, Jin-Ming; Bian, Wei-Hao; Yuan, Ye-Fei; Kaspi, Shai; Ho, Luis C.; Netzer, Hagai; Wang, Jian-Min; SEAMBH Collaboration

    2015-06-01

    We have completed two years of photometric and spectroscopic monitoring of a large number of active galactic nuclei (AGNs) with very high accretion rates. In this paper, we report on the result of the second phase of the campaign, during 2013-2014, and the measurements of five new Hβ time lags out of eight monitored AGNs. All five objects were identified as super-Eddington accreting massive black holes (SEAMBHs). The highest measured accretion rates for the objects in this campaign are \\mathscr{\\dot{M}} {\\mkern 1mu} ≳ 200, where \\mathscr{\\dot{M}} {\\mkern 1mu} ={{\\dot{M}}\\bullet }/{{L}Edd}{{c}-2}, {{\\dot{M}}\\bullet } is the mass accretion rates, {{L}Edd} is the Eddington luminosity and c is the speed of light. We find that the Hβ time lags in SEAMBHs are significantly shorter than those measured in sub-Eddington AGNs, and the deviations increase with increasing accretion rates. Thus, the relationship between broad-line region size ({{R}_{Hβ }}) and optical luminosity at 5100 Å, {{R}_{Hβ }}-{{L}5100}, requires accretion rate as an additional parameter. We propose that much of the effect may be due to the strong anisotropy of the emitted slim-disk radiation. Scaling {{R}_{Hβ }} by the gravitational radius of the black hole (BH), we define a new radius-mass parameter (Y) and show that it saturates at a critical accretion rate of \\mathscr{\\dot{M}} {\\mkern 1mu} {{}c}=6˜ 30, indicating a transition from thin to slim accretion disk and a saturated luminosity of the slim disks. The parameter Y is a very useful probe for understanding the various types of accretion onto massive BHs. We briefly comment on implications to the general population of super-Eddington AGNs in the universe and applications to cosmology.

  17. Accretion rate of cosmic spherules measured at the South Pole

    NASA Astrophysics Data System (ADS)

    Taylor, Susan; Lever, James H.; Harvey, Ralph P.

    1998-04-01

    Micrometeorites are terrestrially collected, extraterrestrial particles smaller than about 1mm, which account for most of the mass being accreted to the Earth,. Compared with meteorites, micrometeorites more completely represent the Earth-crossing meteoroid complex, and should include fragments of asteroids, comets, Mars and our Moon, as well as pre-solar and interstellar grains,. Previous measurements of the flux of micrometeoroids that survive to the Earth's surface have large uncertainties owing to the destruction of particles by weathering, inefficiencies in magnetic collection or separation techniques, low particle counts,, poor age constraint,, or highly variable concentrating processes,. Here we describe an attempt to circumvent these problems through the collection of thousands of well preserved and dated micrometeorites from the bottom of the South Pole water well, which supplies drinking water for the Scott-Amundsen station. Using this collection, we have determined precise estimates of the flux and mass distribution for 50-700-µm cosmic spherules (melted micrometeorites). Allowing for the expected abundance of unmelted micrometeorites in the samples, our results indicate that about 90% of the incoming mass of submillimetre particles evaporates during atmospheric entry. Our data indicate the loss of glass-rich and small stony spherules from deep-sea deposits,, and they provide constraints for models describing the survival probability of micrometeoroids,.

  18. Effects of livestock species and stocking density on accretion rates in grazed salt marshes

    NASA Astrophysics Data System (ADS)

    Nolte, Stefanie; Esselink, Peter; Bakker, Jan P.; Smit, Christian

    2015-01-01

    Coastal ecosystems, such as salt marshes, are threatened by accelerated sea-level rise (SLR). Salt marshes deliver valuable ecosystem services such as coastal protection and the provision of habitat for a unique flora and fauna. Whether salt marshes in the Wadden Sea area are able to survive accelerated SLR depends on sufficient deposition of sediments which add to vertical marsh accretion. Accretion rate is influenced by a number of factors, and livestock grazing was recently included. Livestock grazing is assumed to reduce accretion rates in two ways: (a) directly by increasing soil compaction through trampling, and (b) indirectly by affecting the vegetation structure, which may lower the sediment deposition. For four years, we studied the impact of two livestock species (horse and cattle) at two stocking densities (0.5 and 1.0 animal ha-1) on accretion in a large-scale grazing experiment using sedimentation plates. We found lower cumulative accretion rates in high stocking densities, probably because more animals cause more compaction and create a lower canopy. Furthermore, a trend towards lower accretion rates in horse-compared to cattle-grazed treatments was found, most likely because (1) horses are more active and thus cause more compaction, and (2) herbage intake by horses is higher than by cattle, which causes a higher biomass removal and shorter canopy. During summer periods, negative accretion rates were found. When the grazing and non-grazing seasons were separated, the impact of grazing differed among years. In summer, we only found an effect of different treatments if soil moisture (precipitation) was relatively low. In winter, a sufficiently high inundation frequency was necessary to create differences between grazing treatments. We conclude that stocking densities, and to a certain extent also livestock species, affect accretion rates in salt marshes. Both stocking densities and livestock species should thus be taken into account in management

  19. Chernobyl {sup 137}Cs used to determine sediment accretion rates at selected northern European coastal wetlands

    SciTech Connect

    Callaway, J.C.; DeLaune, R.D.; Patrick, W.H. Jr.

    1996-05-01

    Sediment cores were collected form five coastal wetlands along the North Sea (England and Netherlands) and Baltic Sea (Poland). {sup 137}Cs dating was used to assess sediment accretion rates, including rates based on the {sup 137}Cs peak from the 1986 accident at Chernobyl. Peaks form the Chernobyl fallout were found in cores from the Oder and Vistula Rivers in Poland, from the Eastern Scheldt in the Netherlands, and in one of the two cores from Stiffkey Marsh, UK. No evidence of Chernobyl fallout was found in cores from Dengie Marsh, UK. The Chernobyl {sup 137}Cs peak serves as an excellent marker for short-term accretion rates because of its high activity. Vertical accretion rates (cm yr{sup {minus}1}) based on 1963 and 1986 peaks were similar at most sites; differences may be due to large inputs of sediment from storms or recent accumulation of organic matter. Large differences in sediment characteristics and accretion rates were found between samples from Poland and western Europe. Vertical accretion rates over the period 1963-1986 ranged from 0.26 to 0.85 cm{sup {minus}1} and from 0.30 to 1.90 cm yr{sup {minus}1} over the 1986-1991 period. Vertical accretion rates for the period these sites are in imminent danger of excessive flooding. The Chernobyl {sup 137}Cs peak will be especially useful for studies of short-term (i.e. very recent) sedimentation in the near future and for comparisons of sediment processes over different time scales. 33 refs., 4 figs., 4 tabs.

  20. Prehistorical and historical declines in Caribbean coral reef accretion rates driven by loss of parrotfish

    NASA Astrophysics Data System (ADS)

    Cramer, Katie L.; O'Dea, Aaron; Clark, Tara R.; Zhao, Jian-Xin; Norris, Richard D.

    2017-01-01

    Caribbean coral reefs have transformed into algal-dominated habitats over recent decades, but the mechanisms of change are unresolved due to a lack of quantitative ecological data before large-scale human impacts. To understand the role of reduced herbivory in recent coral declines, we produce a high-resolution 3,000 year record of reef accretion rate and herbivore (parrotfish and urchin) abundance from the analysis of sediments and fish, coral and urchin subfossils within cores from Caribbean Panama. At each site, declines in accretion rates and parrotfish abundance were initiated in the prehistorical or historical period. Statistical tests of direct cause and effect relationships using convergent cross mapping reveal that accretion rates are driven by parrotfish abundance (but not vice versa) but are not affected by total urchin abundance. These results confirm the critical role of parrotfish in maintaining coral-dominated reef habitat and the urgent need for restoration of parrotfish populations to enable reef persistence.

  1. Prehistorical and historical declines in Caribbean coral reef accretion rates driven by loss of parrotfish

    PubMed Central

    Cramer, Katie L.; O'Dea, Aaron; Clark, Tara R.; Zhao, Jian-xin; Norris, Richard D.

    2017-01-01

    Caribbean coral reefs have transformed into algal-dominated habitats over recent decades, but the mechanisms of change are unresolved due to a lack of quantitative ecological data before large-scale human impacts. To understand the role of reduced herbivory in recent coral declines, we produce a high-resolution 3,000 year record of reef accretion rate and herbivore (parrotfish and urchin) abundance from the analysis of sediments and fish, coral and urchin subfossils within cores from Caribbean Panama. At each site, declines in accretion rates and parrotfish abundance were initiated in the prehistorical or historical period. Statistical tests of direct cause and effect relationships using convergent cross mapping reveal that accretion rates are driven by parrotfish abundance (but not vice versa) but are not affected by total urchin abundance. These results confirm the critical role of parrotfish in maintaining coral-dominated reef habitat and the urgent need for restoration of parrotfish populations to enable reef persistence. PMID:28112169

  2. Prehistorical and historical declines in Caribbean coral reef accretion rates driven by loss of parrotfish.

    PubMed

    Cramer, Katie L; O'Dea, Aaron; Clark, Tara R; Zhao, Jian-Xin; Norris, Richard D

    2017-01-23

    Caribbean coral reefs have transformed into algal-dominated habitats over recent decades, but the mechanisms of change are unresolved due to a lack of quantitative ecological data before large-scale human impacts. To understand the role of reduced herbivory in recent coral declines, we produce a high-resolution 3,000 year record of reef accretion rate and herbivore (parrotfish and urchin) abundance from the analysis of sediments and fish, coral and urchin subfossils within cores from Caribbean Panama. At each site, declines in accretion rates and parrotfish abundance were initiated in the prehistorical or historical period. Statistical tests of direct cause and effect relationships using convergent cross mapping reveal that accretion rates are driven by parrotfish abundance (but not vice versa) but are not affected by total urchin abundance. These results confirm the critical role of parrotfish in maintaining coral-dominated reef habitat and the urgent need for restoration of parrotfish populations to enable reef persistence.

  3. THE LINK BETWEEN THE HIDDEN BROAD LINE REGION AND THE ACCRETION RATE IN SEYFERT 2 GALAXIES

    SciTech Connect

    Marinucci, Andrea; Bianchi, Stefano; Matt, Giorgio; Nicastro, Fabrizio; Goulding, Andy D.

    2012-04-01

    In the past few years, more and more pieces of evidence have been presented for a revision of the widely accepted unified model of active galactic nuclei. A model based solely on orientation cannot explain all the observed phenomenology. In the following, we will present evidence that accretion rate is also a key parameter for the presence of hidden broad line regions (HBLRs) in Seyfert 2 galaxies. Our sample consists of 21 sources with polarized hidden broad lines and 18 sources without hidden broad lines. We use stellar velocity dispersions from several studies on the Ca II and Mg b triplets in Seyfert 2 galaxies to estimate the mass of the central black holes via the M{sub BH}-{sigma}{sub *} relation. The ratio between the bolometric luminosity, derived from the intrinsic (i.e., unabsorbed) X-ray luminosity, and the Eddington luminosity is a measure of the rate at which matter accretes onto the central supermassive black hole. A separation between Compton-thin HBLR and non-HBLR sources is clear, both in accretion rate (log L{sub bol}/L{sub Edd} = -1.9) and in luminosity (log L{sub bol} = 43.90). When properly luminosity-corrected Compton-thick sources are included, the separation between HBLR and non-HBLR is less sharp but no HBLR source falls below the Eddington ratio threshold. We speculate that non-HBLR Compton-thick sources with accretion rate higher than the threshold do possess a BLR, but something, probably related to their heavy absorption, is preventing us from observing it even in polarized light. Our results for Compton-thin sources support theoretical expectations. In a model presented by Nicastro, the presence of broad emission lines is intrinsically connected with disk instabilities occurring in proximity of a transition radius, which is a function of the accretion rate, becoming smaller than the innermost stable orbit for very low accretion rates and therefore luminosities.

  4. The Link between the Hidden Broad Line Region and the Accretion Rate in Seyfert 2 Galaxies

    NASA Astrophysics Data System (ADS)

    Marinucci, Andrea; Bianchi, Stefano; Nicastro, Fabrizio; Matt, Giorgio; Goulding, Andy D.

    2012-04-01

    In the past few years, more and more pieces of evidence have been presented for a revision of the widely accepted unified model of active galactic nuclei. A model based solely on orientation cannot explain all the observed phenomenology. In the following, we will present evidence that accretion rate is also a key parameter for the presence of hidden broad line regions (HBLRs) in Seyfert 2 galaxies. Our sample consists of 21 sources with polarized hidden broad lines and 18 sources without hidden broad lines. We use stellar velocity dispersions from several studies on the Ca II and Mg b triplets in Seyfert 2 galaxies to estimate the mass of the central black holes via the M BH-σsstarf relation. The ratio between the bolometric luminosity, derived from the intrinsic (i.e., unabsorbed) X-ray luminosity, and the Eddington luminosity is a measure of the rate at which matter accretes onto the central supermassive black hole. A separation between Compton-thin HBLR and non-HBLR sources is clear, both in accretion rate (log L bol/L Edd = -1.9) and in luminosity (log L bol = 43.90). When properly luminosity-corrected Compton-thick sources are included, the separation between HBLR and non-HBLR is less sharp but no HBLR source falls below the Eddington ratio threshold. We speculate that non-HBLR Compton-thick sources with accretion rate higher than the threshold do possess a BLR, but something, probably related to their heavy absorption, is preventing us from observing it even in polarized light. Our results for Compton-thin sources support theoretical expectations. In a model presented by Nicastro, the presence of broad emission lines is intrinsically connected with disk instabilities occurring in proximity of a transition radius, which is a function of the accretion rate, becoming smaller than the innermost stable orbit for very low accretion rates and therefore luminosities.

  5. ACCRETION RATES ON PRE-MAIN-SEQUENCE STARS IN THE YOUNG OPEN CLUSTER NGC 6530

    SciTech Connect

    Gallardo, Jose; Del Valle, Luciano; Ruiz, Maria Teresa E-mail: ldelvall@das.uchile.cl

    2012-01-15

    It is well accepted that during the star formation process, material from a protoplanetary disk is accreted onto the central object during the first {approx}1-5 Myr. Different authors have published measurements of accretion rates for young low- and intermediate-mass stars in several nearby star-forming regions (SFRs). Due to its somewhat larger distance, the SFR M8 (the Lagoon Nebula) has not been studied to the same extent, despite its abundant population of young stellar objects. We have obtained optical band low-resolution spectra of a sample of pre-main-sequence stars in the open cluster NGC 6530 located in the aforementioned nebulae using the Gemini Multi Object Spectrograph at Gemini-South in multi-object mode. Spectra cover the H{sub {alpha}} emission line used to measure the accretion rate, following the method presented by Natta et al. The observed spectral characteristics are fully consistent with pre-main-sequence stars, showing lithium absorption lines, which are very common in young stellar objects, as well as prominent and broad H{sub {alpha}} emission lines, indicating a T Tauri evolutionary stage. This work presents the first determinations of mass accretion rates of young stellar objects in the open cluster NGC 6530, confirming that they are classical T Tauri stars going through the accretion phase. These observations contribute to a better understanding of the stellar content and evolutionary phase of the very active Lagoon Nebula SFR.

  6. Effects of long-term grazing on sediment deposition and salt-marsh accretion rates

    NASA Astrophysics Data System (ADS)

    Elschot, Kelly; Bouma, Tjeerd J.; Temmerman, Stijn; Bakker, Jan P.

    2013-11-01

    Many studies have attempted to predict whether coastal marshes will be able to keep up with future acceleration of sea-level rise by estimating marsh accretion rates. However, there are few studies focussing on the long-term effects of herbivores on vegetation structure and subsequent effects on marsh accretion. Deposition of fine-grained, mineral sediment during tidal inundations, together with organic matter accumulation from the local vegetation, positively affects accretion rates of marsh surfaces. Tall vegetation can enhance sediment deposition by reducing current flow and wave action. Herbivores shorten vegetation height and this could potentially reduce sediment deposition. This study estimated the effects of herbivores on 1) vegetation height, 2) sediment deposition and 3) resulting marsh accretion after long-term (at least 16 years) herbivore exclusion of both small (i.e. hare and goose) and large grazers (i.e. cattle) for marshes of different ages. Our results firstly showed that both small and large herbivores can have a major impact on vegetation height. Secondly, grazing processes did not affect sediment deposition. Finally, trampling by large grazers affected marsh accretion rates by compacting the soil. In many European marshes, grazing is used as a tool in nature management as well as for agricultural purposes. Thus, we propose that soil compaction by large grazers should be taken in account when estimating the ability of coastal systems to cope with an accelerating sea-level rise.

  7. Suppression of the accretion rate in thin discs around binary black holes

    NASA Astrophysics Data System (ADS)

    Ragusa, Enrico; Lodato, Giuseppe; Price, Daniel J.

    2016-08-01

    We present three-dimensional Smoothed Particle Hydrodynamics (SPH) simulations investigating the dependence of the accretion rate on the disc thickness around an equal-mass, circular black hole binary system. We find that for thick/hot discs, with H/R ≳ 0.1, the binary torque does not prevent the gas from penetrating the cavity formed in the disc by the binary (in line with previous investigations). The situation drastically changes for thinner discs; in this case the mass accretion rate is suppressed, such that only a fraction (linearly dependent on H/R) of the available gas is able to flow within the cavity and accrete on to the binary. Extrapolating this result to the cold and thin accretion discs expected around supermassive black hole binary systems implies that this kind of system accretes less material than predicted so far, with consequences not only for the electromagnetic and gravitational waves emissions during the late inspiral phase but also for the recoil speed of the black hole formed after binary coalescence, thus influencing also the evolutionary path both of the binary and of the host galaxy. Our results, being scale-free, are also applicable to equal-mass, circular binaries of stellar mass black holes, such as the progenitor of the recently discovered gravitational wave source GW150914.

  8. Formation of a proto-Jovian envelope for various planetary accretion rates

    NASA Astrophysics Data System (ADS)

    Ikoma, M.; Emori, H.; Nakazawa, K.

    1998-12-01

    The formation of a proto-Jovian envelope has been simulated on the basis of a core accretion model and the maximum mass that a proto-Jovian planet can have while keeping its envelope gravitationally stable, called the critical core mass, has also been investigated extensively over a wide range of the core accretion rate. The value of the critical core mass has been found to depend strongly on the core accretion rate; for example, it is less than or equal to 0953-8984/10/49/040/img1 for the typical accretion rates for Uranus and Neptune. Furthermore, through simulations of the quasi-static evolution of the envelope beyond the critical core mass, we have found that the characteristic times of envelope contraction are 0953-8984/10/49/040/img2 and 0953-8984/10/49/040/img3 for the cases where the core accretion rates are 0953-8984/10/49/040/img4 per year, 0953-8984/10/49/040/img5 per year and 0953-8984/10/49/040/img6 per year, respectively. Also, in the last case, the core mass of the Jovian planet can be estimated to be about 0953-8984/10/49/040/img7. We conclude that if a given one of the Jovian planets of our solar system has a core smaller than about 0953-8984/10/49/040/img8, it is very hard to see how the core could have attracted a gaseous envelope from our solar nebula and formed the Jovian envelope. Determination of the sizes of the cores in our Jovian planets should give fruitful information for the theory of the formation of our solar system.

  9. The Relation Between Accretion Rate And Jet Power in X-Ray Luminous Elliptical Galaxies

    SciTech Connect

    Allen, Steven W.; Dunn, R.J.H.; Fabian, A.C.; Taylor, G.B.; Reynolds, C.S.; /Maryland U.

    2006-03-10

    Using Chandra X-ray observations of nine nearby, X-ray luminous elliptical galaxies with good optical velocity dispersion measurements, we show that a tight correlation exists between the Bondi accretion rates calculated from the observed gas temperature and density profiles and estimated black hole masses, and the power emerging from these systems in relativistic jets. The jet powers, which are inferred from the energies and timescales required to inflate cavities observed in the surrounding X-ray emitting gas, can be related to the accretion rates using a power law model of the form log (P{sub Bondi}/10{sup 43} erg s{sup -1}) = A + B log (P{sub jet}/10{sup 43} erg s{sup -1}), with A = 0.62 {+-} 0.15 and B = 0.77 {+-} 0.18. Our results show that a significant fraction of the energy associated with the rest mass of material entering the Bondi accretion radius (2.4{sub -0.7}{sup +1.0} per cent, for P{sub jet} = 10{sup 43} erg s{sup -1}) eventually emerges in the relativistic jets. Our results have significant implications for studies of accretion, jet formation and galaxy formation. The observed tight correlation suggests that the Bondi formulae provide a reasonable description of the accretion process in these systems, despite the likely presence of magnetic pressure and angular momentum in the accreting gas. The similarity of the P{sub Bondi} and P{sub jet} values argues that a significant fraction of the matter entering the accretion radius flows down to regions close to the black holes, where the jets are presumably formed. The tight correlation between P{sub Bondi} and P{sub jet} also suggests that the accretion flows are approximately stable over timescales of a few million years. Our results show that the black hole ''engines'' at the hearts of large elliptical galaxies and groups feed back sufficient energy to stem cooling and star formation, leading naturally to the observed exponential cut off at the bright end of the galaxy luminosity function.

  10. Numerical model of crustal accretion and cooling rates of fast-spreading mid-ocean ridges

    NASA Astrophysics Data System (ADS)

    Machetel, P.; Garrido, C. J.

    2013-10-01

    We designed a thermo-mechanical numerical model for fast-spreading mid-ocean ridge with variable viscosity, hydrothermal cooling, latent heat release, sheeted dyke layer, and variable melt intrusion possibilities. The model allows for modulating several accretion possibilities such as the "gabbro glacier" (G), the "sheeted sills" (S) or the "mixed shallow and MTZ lenses" (M). These three crustal accretion modes have been explored assuming viscosity contrasts of 2 to 3 orders of magnitude between strong and weak phases and various hydrothermal cooling conditions depending on the cracking temperatures value. Mass conservation (stream-function), momentum (vorticity) and temperature equations are solved in 2-D cartesian geometry using 2-D, alternate direction, implicit and semi-implicit finite-difference scheme. In a first step, an Eulerian approach is used solving iteratively the motion and temperature equations until reaching steady states. With this procedure, the temperature patterns and motions that are obtained for the various crustal intrusion modes and hydrothermal cooling hypotheses display significant differences near the mid-ocean ridge axis. In a second step, a Lagrangian approach is used, recording the thermal histories and cooling rates of tracers travelling from the ridge axis to their final emplacements in the crust far from the mid-ocean ridge axis. The results show that the tracer's thermal histories are depending on the temperature patterns and the crustal accretion modes near the mid-ocean ridge axis. The instantaneous cooling rates obtained from these thermal histories betray these discrepancies and might therefore be used to characterize the crustal accretion mode at the ridge axis. These deciphering effects are even more pronounced if we consider the average cooling rates occurring over a prescribed temperature range. Two situations were tested at 1275-1125 °C and 1050-850 °C. The first temperature range covers mainly the crystallization range

  11. Accretion Rates on Pre-main-sequence Stars in the Young Open Cluster NGC 6530

    NASA Astrophysics Data System (ADS)

    Gallardo, José; del Valle, Luciano; Ruiz, María Teresa

    2012-01-01

    It is well accepted that during the star formation process, material from a protoplanetary disk is accreted onto the central object during the first ~1-5 Myr. Different authors have published measurements of accretion rates for young low- and intermediate-mass stars in several nearby star-forming regions (SFRs). Due to its somewhat larger distance, the SFR M8 (the Lagoon Nebula) has not been studied to the same extent, despite its abundant population of young stellar objects. We have obtained optical band low-resolution spectra of a sample of pre-main-sequence stars in the open cluster NGC 6530 located in the aforementioned nebulae using the Gemini Multi Object Spectrograph at Gemini-South in multi-object mode. Spectra cover the Hα emission line used to measure the accretion rate, following the method presented by Natta et al. The observed spectral characteristics are fully consistent with pre-main-sequence stars, showing lithium absorption lines, which are very common in young stellar objects, as well as prominent and broad Hα emission lines, indicating a T Tauri evolutionary stage. This work presents the first determinations of mass accretion rates of young stellar objects in the open cluster NGC 6530, confirming that they are classical T Tauri stars going through the accretion phase. These observations contribute to a better understanding of the stellar content and evolutionary phase of the very active Lagoon Nebula SFR. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciencia e Tecnologia (Brazil), and Ministerio de Ciencia, Tecnología e Innovación Productiva

  12. MEASURING MASS ACCRETION RATE ONTO THE SUPERMASSIVE BLACK HOLE IN M87 USING FARADAY ROTATION MEASURE WITH THE SUBMILLIMETER ARRAY

    SciTech Connect

    Kuo, C. Y.; Asada, K.; Rao, R.; Nakamura, M.; Algaba, J. C.; Liu, H. B.; Inoue, M.; Koch, P. M.; Ho, P. T. P.; Matsushita, S.; Pu, H.-Y.; Nishioka, H.; Pradel, N.; Akiyama, K.

    2014-03-10

    We present the first constraint on the Faraday rotation measure (RM) at submillimeter wavelengths for the nucleus of M87. By fitting the polarization position angles (χ) observed with the Submillimeter Array at four independent frequencies around ∼230 GHz and interpreting the change in χ as a result of external Faraday rotation associated with accretion flow, we determine the RM of the M87 core to be between –7.5 × 10{sup 5} and 3.4 × 10{sup 5} rad m{sup –2}. Assuming a density profile of the accretion flow that follows a power-law distribution and a magnetic field that is ordered, radial, and has equipartition strength, the limit on the RM constrains the mass accretion rate M-dot to be below 9.2 × 10{sup –4} M {sub ☉} yr{sup –1} at a distance of 21 Schwarzschild radii from the central black hole. This value is at least two orders of magnitude smaller than the Bondi accretion rate, suggesting significant suppression of the accretion rate in the inner region of the accretion flow. Consequently, our result disfavors the classical advection-dominated accretion flow and prefers the adiabatic inflow-outflow solution or convection-dominated accretion flow for the hot accretion flow in M87.

  13. Helium Ignition on Accreting Neutron Stars with a New Triple-α Reaction Rate

    NASA Astrophysics Data System (ADS)

    Peng, Fang; Ott, Christian D.

    2010-12-01

    We investigate the effect of a new triple-α reaction rate from Ogata et al. on helium ignition conditions on accreting neutron stars and on the properties of the subsequent type I X-ray burst. We find that the new rate leads to significantly lower ignition column density for accreting neutron stars at low accretion rates. We compare the results of our ignition models for a pure helium accretor to observations of bursts in ultracompact X-ray binaries (UCXBs), which are believed to have nearly pure helium donors. For \\dot{m}> 0.001 \\dot{m}_{{Edd}}, the new triple-α reaction rate from Ogata et al. predicts a maximum helium ignition column of ~3 × 109 g cm-2, corresponding to a burst energy of ~4 × 1040 erg. For \\dot{m}˜ 0.01 \\dot{m}_{{Edd}} at which intermediate long bursts occur, the predicted burst energies are at least a factor of 10 too low to explain the observed energies of such bursts in UCXBs. This finding adds to the doubts cast on the triple-α reaction rate of Ogata et al. by the low-mass stellar evolution results of Dotter & Paxton.

  14. The role of angular momentum transport in establishing the accretion rate-protostellar mass correlation

    NASA Astrophysics Data System (ADS)

    DeSouza, Alexander L.; Basu, Shantanu

    2017-02-01

    We model the mass accretion rate M˙ to stellar mass M* correlation that has been inferred from observations of intermediate to upper mass T Tauri stars-that is M˙ ∝ M*1.3±0.3. We explain this correlation within the framework of quiescent disk evolution, in which accretion is driven largely by gravitational torques acting in the bulk of the mass and volume of the disk. Stresses within the disk arise from the action of gravitationally driven torques parameterized in our 1D model in terms of Toomre's Q criterion. We do not model the hot inner sub-AU scale region of the disk that is likely stable according to this criterion, and appeal to other mechanisms to remove or redistribute angular momentum and allow accretion onto the star. Our model has the advantage of agreeing with large-scale angle-averaged values from more complex nonaxisymmetric calculations. The model disk transitions from an early phase (dominated by initial conditions inherited from the burst mode of accretion) into a later self-similar mode characterized by a steeper temporal decline in M˙. The models effectively reproduce the spread in mass accretion rates that have been observed for protostellar objects of 0.2 M⊙ ≤ M* ≤ 3.0 M⊙, such as those found in the ρ Ophiuchus and Taurus star forming regions. We then compare realistically sampled populations of young stellar objects produced by our model to their observational counterparts. We find these populations to be statistically coincident, which we argue is evidence for the role of gravitational torques in the late time evolution of quiescent protostellar disks.

  15. Mass accretion rates from multiband photometry in the Carina Nebula: the case of Trumpler 14

    NASA Astrophysics Data System (ADS)

    Beccari, G.; De Marchi, G.; Panagia, N.; Valenti, E.; Carraro, G.; Romaniello, M.; Zoccali, M.; Weidner, C.

    2015-01-01

    Context. We present a study of the mass accretion rates of pre-main sequence (PMS) stars in the cluster Trumpler 14 (Tr 14) in the Carina Nebula. Using optical multiband photometry we were able to identify 356 PMS stars showing Hα excess emission with equivalent width EW(Hα) > 20 Å. We interpret this observational feature as an indication that these objects are still actively accreting gas from their circumstellar medium. From a comparison of the HR diagram with PMS evolutionary models we derive ages and masses of the PMS stars. We find that most of the PMS objects are younger than 10 Myr with a median age of ~3 Myr. Surprisingly, we also find that ~20% of the mass accreting objects are older than 10 Myr. For each PMS star in Trumpler 14 we determine the mass accretion rate (Ṁacc) and discuss its dependence on mass and age. We finally combine the optical photometry with near-IR observations to build the spectral energy distribution (SED) for each PMS star in Tr 14. The analysis of the SEDs suggests the presence of transitional discs in which a large amount of gas is still present and sustains accretion onto the PMS object at ages older than 10 Myr. Our results, discussed in light of recent recent discoveries with Herschel of transitional discs containing a massive gas component around the relatively old PMS stars TW Hydrae, 49 Ceti, and HD 95086, support a new scenario n which old and evolved debris discs still host a significant amount of gas. Aims: Methods: Results:

  16. On the Accretion Rates and Radiative Efficiencies of the Highest-redshift Quasars

    NASA Astrophysics Data System (ADS)

    Trakhtenbrot, Benny; Volonteri, Marta; Natarajan, Priyamvada

    2017-02-01

    We estimate the accretion rates onto the supermassive black holes that power 20 of the highest-redshift quasars, at z≳ 5.8, including the quasar with the highest redshift known to date—ULAS J1120 at z = 7.09. The analysis is based on the observed (rest-frame) optical luminosities and reliable “virial” estimates of the BH masses of the quasars, and utilizes scaling relations derived from thin accretion disk theory. The mass accretion rates through the postulated disks cover a wide range, {\\dot{M}}{disk}≃ 4{--}190 {M}ȯ {{yr}}-1, with most of the objects (80%) having {\\dot{M}}{disk}≃ 10{--}65 {M}ȯ {{yr}}-1, confirming the Eddington-limited nature of the accretion flows. By combining our estimates of {\\dot{M}}{disk} with conservative, lower limits on the bolometric luminosities of the quasars, we investigate which alternative values of η best account for all the available data. We find that the vast majority of quasars (∼85%) can be explained with radiative efficiencies in the range η ≃ 0.03{--}0.3, with a median value close to the commonly assumed η = 0.1. Within this range, we obtain conservative estimates of η ≳ 0.14 for ULAS J1120 and SDSS J0100 (at z = 6.3), and of ≳ 0.19 for SDSS J1148 (at z=6.41; assuming their BH masses are accurate). The implied accretion timescales are generally in the range {t}{acc}\\equiv {M}{BH}/{\\dot{M}}{BH}≃ 0.1{--}1 {Gyr}, suggesting that most quasars could have had ∼ 1{--}10 mass e-foldings since BH seed formation. Our analysis therefore demonstrates that the available luminosities and masses for the highest-redshift quasars can be explained self-consistently within the thin, radiatively efficient accretion disk paradigm. Episodes of radiatively inefficient, “super-critical” accretion may have occurred at significantly earlier epochs (i.e., z≳ 10).

  17. Variations in the accretion rate and luminosity in gravitationally unstable protostellar disks

    NASA Astrophysics Data System (ADS)

    Elbakyan, V. G.; Vorobyov, E. I.; Glebova, G. M.

    2016-10-01

    Self-consistent modeling of a protostar and protostellar disk is carried out for early stages of their evolution. The accretion rate at distances of sevral astronomical units from the protostar is appreciably variable, which is reflected in the protostar's luminosity. The amplitude of the variations in the accretion rate and luminosity grows together with the sampling period, as a consequence of the nature of gravitationally unstable protostellar disks. A comparison of model luminosity variations with those derived from observations of nearby sites of star formation shows that the model variations are appreciably lower than the observed values for sampling periods of less than 10 years, indicating the presence of additional sources of variability on small dynamical distances from the protostar.

  18. NOVAE WITH LONG-LASTING SUPERSOFT EMISSION THAT DRIVE A HIGH ACCRETION RATE

    SciTech Connect

    Schaefer, Bradley E.; Collazzi, Andrew C.

    2010-05-15

    We identify a new class of novae characterized by the post-eruption quiescent light curve being more than roughly a factor of 10 brighter than the pre-eruption light curve. Eight novae (V723 Cas, V1500 Cyg, V1974 Cyg, GQ Mus, CP Pup, T Pyx, V4633 Sgr, and RW UMi) are separated out as being significantly distinct from other novae. This group shares a suite of uncommon properties, characterized by the post-eruption magnitude being much brighter than before eruption, short orbital periods, long-lasting supersoft emission following the eruption, a highly magnetized white dwarf (WD), and secular declines during the post-eruption quiescence. We present a basic physical picture which shows why all five uncommon properties are causally connected. In general, novae show supersoft emission due to hydrogen burning on the WD in the final portion of the eruption, and this hydrogen burning will be long-lasting if new hydrogen is poured onto the surface at a sufficient rate. Most novae do not have adequate accretion for continuous hydrogen burning, but some can achieve this if the companion star is nearby (with short orbital period) and a magnetic field channels the matter onto a small area on the WD so as to produce a locally high accretion rate. The resultant supersoft flux irradiates the companion star and drives a higher accretion rate (with a brighter post-eruption phase), which serves to keep the hydrogen burning and the supersoft flux going. The feedback loop cannot be perfectly self-sustaining, so the supersoft flux will decline over time, forcing a decline in the accretion rate and the system brightness. We name this new group after the prototype, V1500 Cyg. V1500 Cyg stars are definitely not progenitors of Type Ia supernovae. The V1500 Cyg stars have similar physical mechanisms and appearances as predicted for nova by the hibernation model, but with this group accounting for only 14% of novae.

  19. On the stream-accretion disk interaction - Response to increased mass transfer rate

    NASA Technical Reports Server (NTRS)

    Dgani, Ruth; Livio, Mario; Soker, Noam

    1989-01-01

    The time-dependent interaction between the stream of mass from the inner Lagrangian point and the accretion disk, resulting from an increasing mass transfer rate is calculated. The calculation is fully three-dimensional, using a pseudoparticle description of the hydrodynamics. It is demonstrated that the results of such calculations, when combined with specific observations, have the potential of both determining essential parameters, such as the viscosity parameter alpha, and can distinguish between different models of dwarf nova eruptions.

  20. Critical temperature and accretion rate of outbursts in long-period dwarf novae

    NASA Astrophysics Data System (ADS)

    Kim, Soon-Wook

    2015-11-01

    Dwarf nova outbursts are nonlinear phenomena, and a time-dependent disk model is necessary to account for observations in detail. However, it is also necessary to elaborate a simpler steady-state fit to interpret observations. To know in what condition the outburst is initiated, understanding of the dwarf nova outburst is important. The parameterized, steady-state fitting formulae are suggested by Smak (Acta Astron. 52, 429 (2002); ibid 60, 83 (2010)) for the critical disk temperature and mass accretion rate above which the disk becomes thermally unstable. The fits give a single-valued temperature and accretion rate and are radius-independent whereas the observations show that the outbursts are radius-dependent phenomena of the ionizaton propagating in the disk. The fits have been tested to account for the observed outbursts only for systems with orbital periods shorter than a half day. Therefore, we examine the fits for orbital period as long as 2 days and compare the fits to the time-dependent model of a long-period dwarf nova GK Per. The fits are not much different from the time-dependent result for the critical temperature. However, the fits for the critical mass accretion rate above which the disk enters the hot state overestimate the time-dependent model for a long-period system like GK Per. The critical mass accretion rate in the intermediate state is consistent with that from the time-dependent disk model. However, the fit value should be treated as a maximum possible value below which the disk maintains the intermediate state, which is consistent with an interpretation for the observations of the Z Cam stars.

  1. Conditions for circumstellar disc formation - II. Effects of initial cloud stability and mass accretion rate

    NASA Astrophysics Data System (ADS)

    Machida, Masahiro N.; Matsumoto, Tomoaki; Inutsuka, Shu-ichiro

    2016-12-01

    Disc formation in strongly magnetized cloud cores is investigated using a three-dimensional magnetohydrodynamic simulation with a focus on the effects of the initial cloud stability and the mass accretion rate. The initial cloud stability greatly alters the disc formation process even for prestellar clouds with the same mass-to-flux ratio. A high mass accretion rate on to the disc-forming region is realized in initially unstable clouds, and a large angular momentum is introduced into the circumstellar region in a short time. The region around the protostar has both a thin infalling envelope and a weak magnetic field, which both weaken the effect of magnetic braking. The growth of the rotation-supported disc is promoted in such unstable clouds. Conversely, clouds in an initially near-equilibrium state show lower accretion rates of mass and angular momentum. The angular momentum is transported to the outer envelope before protostar formation. After protostar formation, the circumstellar region has a thick infalling envelope and a strong magnetic field that effectively brakes the disc. As a result, disc formation is suppressed when the initial cloud is in a nearly stable state. The density distribution of the initial cloud also affects the disc formation process. Disc growth strongly depends on the initial conditions when the prestellar cloud has a uniform density, whereas there is no significant difference in the disc formation process in prestellar clouds with non-uniform densities.

  2. The radial dependence of pebble accretion rates: A source of diversity in planetary systems. I. Analytical formulation

    NASA Astrophysics Data System (ADS)

    Ida, S.; Guillot, T.; Morbidelli, A.

    2016-06-01

    Context. The classical planetesimal accretion scenario for the formation of planets has recently evolved with the idea that pebbles, centimeter- to meter-sized icy grains migrating in protoplanetary disks, can control planetesimal and/or planetary growth. Aims: We investigate how pebble accretion depends on disk properties and affects the formation of planetary systems. Methods: We construct analytical models of pebble accretion onto planetary embryos that consistently account for the mass and orbital evolution of the pebble flow and reflect disk structure. Results: We derive simple formulas for pebble accretion rates in the so-called settling regime for planetary embryos that are more than 100 km in size. For relatively smaller embryos or in outer disk regions, the accretion mode is three-dimensional (3D), meaning that the thickness of the pebble flow must be taken into account, and resulting in an accretion rate that is independent of the embryo mass. For larger embryos or in inner regions, the accretion is in a two-dimensional (2D) mode, i.e., the pebble disk may be considered infinitely thin. We show that the radial dependence of the pebble accretion rate is different (even the sign of the power-law exponent changes) for different disk conditions such as the disk heating source (viscous heating or stellar irradiation), drag law (Stokes or Epstein, and weak or strong coupling), and in the 2D or 3D accretion modes. We also discuss the effect of the sublimation and destruction of icy pebbles inside the snow line. Conclusions: Pebble accretion easily produces a large diversity of planetary systems. In other words, to infer the results of planet formation through pebble accretion correctly, detailed prescriptions of disk evolution and pebble growth, sublimation, destruction and migration are required.

  3. Massive star formation by accretion. I. Disc accretion

    NASA Astrophysics Data System (ADS)

    Haemmerlé, L.; Eggenberger, P.; Meynet, G.; Maeder, A.; Charbonnel, C.

    2016-01-01

    Context. Massive stars likely form by accretion and the evolutionary track of an accreting forming star corresponds to what is called the birthline in the Hertzsprung-Russell (HR) diagram. The shape of this birthline is quite sensitive to the evolution of the entropy in the accreting star. Aims: We first study the reasons why some birthlines published in past years present different behaviours for a given accretion rate. We then revisit the question of the accretion rate, which allows us to understand the distribution of the observed pre-main-sequence (pre-MS) stars in the HR diagram. Finally, we identify the conditions needed to obtain a large inflation of the star along its pre-MS evolution that may push the birthline towards the Hayashi line in the upper part of the HR diagram. Methods: We present new pre-MS models including accretion at various rates and for different initial structures of the accreting core. We compare them with previously published equivalent models. From the observed upper envelope of pre-MS stars in the HR diagram, we deduce the accretion law that best matches the accretion history of most of the intermediate-mass stars. Results: In the numerical computation of the time derivative of the entropy, some treatment leads to an artificial loss of entropy and thus reduces the inflation that the accreting star undergoes along the birthline. In the case of cold disc accretion, the existence of a significant swelling during the accretion phase, which leads to radii ≳ 100 R⊙ and brings the star back to the red part of the HR diagram, depends sensitively on the initial conditions. For an accretion rate of 10-3M⊙ yr-1, only models starting from a core with a significant radiative region evolve back to the red part of the HR diagram. We also obtain that, in order to reproduce the observed upper envelope of pre-MS stars in the HR diagram with an accretion law deduced from the observed mass outflows in ultra-compact HII regions, the fraction of the

  4. Evidence for a correlation between mass accretion rates onto young stars and the mass of their protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Manara, C. F.; Rosotti, G.; Testi, L.; Natta, A.; Alcalá, J. M.; Williams, J. P.; Ansdell, M.; Miotello, A.; van der Marel, N.; Tazzari, M.; Carpenter, J.; Guidi, G.; Mathews, G. S.; Oliveira, I.; Prusti, T.; van Dishoeck, E. F.

    2016-06-01

    A relation between the mass accretion rate onto the central young star and the mass of the surrounding protoplanetary disk has long been theoretically predicted and observationally sought. For the first time, we have accurately and homogeneously determined the photospheric parameters, mass accretion rate, and disk mass for an essentially complete sample of young stars with disks in the Lupus clouds. Our work combines the results of surveys conducted with VLT/X-Shooter and ALMA. With this dataset we are able to test a basic prediction of viscous accretion theory, the existence of a linear relation between the mass accretion rate onto the central star and the total disk mass. We find a correlation between the mass accretion rate and the disk dust mass, with a ratio that is roughly consistent with the expected viscous timescale when assuming an interstellar medium gas-to-dust ratio. This confirms that mass accretion rates are related to the properties of the outer disk. We find no correlation between mass accretion rates and the disk mass measured by CO isotopologues emission lines, possibly owing to the small number of measured disk gas masses. This suggests that the mm-sized dust mass better traces the total disk mass and that masses derived from CO may be underestimated, at least in some cases.

  5. An upper limit on the contribution of accreting white dwarfs to the type Ia supernova rate.

    PubMed

    Gilfanov, Marat; Bogdán, Akos

    2010-02-18

    There is wide agreement that type Ia supernovae (used as standard candles for cosmology) are associated with the thermonuclear explosions of white dwarf stars. The nuclear runaway that leads to the explosion could start in a white dwarf gradually accumulating matter from a companion star until it reaches the Chandrasekhar limit, or could be triggered by the merger of two white dwarfs in a compact binary system. The X-ray signatures of these two possible paths are very different. Whereas no strong electromagnetic emission is expected in the merger scenario until shortly before the supernova, the white dwarf accreting material from the normal star becomes a source of copious X-rays for about 10(7) years before the explosion. This offers a means of determining which path dominates. Here we report that the observed X-ray flux from six nearby elliptical galaxies and galaxy bulges is a factor of approximately 30-50 less than predicted in the accretion scenario, based upon an estimate of the supernova rate from their K-band luminosities. We conclude that no more than about five per cent of type Ia supernovae in early-type galaxies can be produced by white dwarfs in accreting binary systems, unless their progenitors are much younger than the bulk of the stellar population in these galaxies, or explosions of sub-Chandrasekhar white dwarfs make a significant contribution to the supernova rate.

  6. Stellar parameters and accretion rate of the transition disk star HD 142527 from X-shooter

    SciTech Connect

    Mendigutía, I.; Fairlamb, J.; Oudmaijer, R. D.; Montesinos, B.; Najita, J. R.; Brittain, S. D.; Van den Ancker, M. E.

    2014-07-20

    HD 142527 is a young pre-main-sequence star with properties indicative of the presence of a giant planet and/or a low-mass stellar companion. We have analyzed an X-Shooter/Very Large Telescope spectrum to provide accurate stellar parameters and accretion rate. The analysis of the spectrum, together with constraints provided by the spectral energy distribution fitting, the distance to the star (140 ± 20 pc), and the use of evolutionary tracks and isochrones, led to the following set of parameters: T{sub eff} = 6550 ± 100 K, log g = 3.75 ± 0.10, L{sub *}/L{sub ☉} = 16.3 ± 4.5, M{sub *}/M{sub ☉} = 2.0 ± 0.3, and an age of 5.0 ± 1.5 Myr. This stellar age provides further constraints to the mass of the possible companion estimated by Biller et al., being between 0.20 and 0.35 M{sub ☉}. Stellar accretion rates obtained from UV Balmer excess modeling and optical photospheric line veiling, and from the correlations with several emission lines spanning from the UV to the near-IR, are consistent with each other. The mean value from all previous tracers is 2 (±1) × 10{sup –7} M{sub ☉} yr{sup –1}, which is within the upper limit gas flow rate from the outer to the inner disk recently provided by Cassasus et al.. This suggests that almost all gas transferred between both components of the disk is not trapped by the possible planet(s) in between but fall onto the central star, although it is discussed how the gap flow rate could be larger than previously suggested. In addition, we provide evidence showing that the stellar accretion rate of HD 142527 has increased by a factor ∼7 on a timescale of 2 to 5 yr.

  7. PHOTOMETRIC DETERMINATION OF THE MASS ACCRETION RATES OF PRE-MAIN-SEQUENCE STARS. IV. RECENT STAR FORMATION IN NGC 602

    SciTech Connect

    De Marchi, Guido; Beccari, Giacomo; Panagia, Nino E-mail: gbeccari@eso.org

    2013-09-20

    We have studied the young stellar populations in NGC 602, in the Small Magellanic Cloud, using a novel method that we have developed to combine Hubble Space Telescope photometry in the V, I, and Hα bands. We have identified about 300 pre-main-sequence (PMS) stars, all of which are still undergoing active mass accretion, and have determined their physical parameters (effective temperature, luminosity, age, mass, and mass accretion rate). Our analysis shows that star formation has been present in this field over the last 60 Myr. In addition, we can recognize at least two clear, distinct, and prominent episodes in the recent past: one about 2 Myr ago, but still ongoing in regions of higher nebulosity, and one (or more) older than 30 Myr, encompassing both stars dispersed in the field and two smaller clusters located about 100'' north of the center of NGC 602. The relative locations of younger and older PMS stars do not imply a causal effect or triggering of one generation on the other. The strength of the two episodes appears to be comparable, but the episodes occurring more than 30 Myr ago might have been even stronger than the current one. We have investigated the evolution of the mass accretion rate, M-dot{sub acc}, as a function of the stellar parameters finding that log M-dot{sub acc}≅-0.6 log t + log m + c, where t is the age of the star, m is its mass, and c is a decreasing function of the metallicity.

  8. 78 FR 24979 - Olives Grown in California; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-04-29

    ... Service 7 CFR Part 932 Olives Grown in California; Decreased Assessment Rate AGENCY: Agricultural... assessment rate established for the California Olive Committee (Committee) for the 2013 and subsequent fiscal years from $31.32 to $21.16 per ton of assessable olives handled. The Committee locally administers...

  9. 78 FR 45841 - Olives Grown in California; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-07-30

    ... Service 7 CFR Part 932 Olives Grown in California; Decreased Assessment Rate AGENCY: Agricultural... rate established for the California Olive Committee (Committee) for the 2013 and subsequent fiscal years from $31.32 to $21.16 per ton of assessable olives handled. The Committee locally administers...

  10. 76 FR 35957 - Olives Grown in California; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-06-21

    ... Agricultural Marketing Service 7 CFR Part 932 Olives Grown in California; Decreased Assessment Rate AGENCY... the assessment rate established for the California Olive Committee (Committee) for 2011 and subsequent fiscal years from $44.72 to $16.61 per ton of olives handled. The Committee locally administers...

  11. 76 FR 11937 - Olives Grown in California; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-03-04

    ... Service 7 CFR Part 932 Olives Grown in California; Decreased Assessment Rate AGENCY: Agricultural... assessment rate established for the California Olive Committee (Committee) for 2011 and subsequent fiscal years from $44.72 to $16.61 per ton of olives handled. The Committee locally administers the...

  12. 78 FR 62959 - Kiwifruit Grown in California; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-10-23

    ... Service 7 CFR Part 920 Kiwifruit Grown in California; Decreased Assessment Rate AGENCY: Agricultural... assessment rate established for the Kiwifruit Administrative Committee (Committee) for the 2013-14 and subsequent fiscal periods from $0.035 to $0.025 per 9-kilo volume-fill container or equivalent of...

  13. GX 3+1: The Stability of Spectral Index as a Function of Mass Accretion Rate

    NASA Technical Reports Server (NTRS)

    Seifana, Elena; Titarchuk, Lev

    2012-01-01

    We present an analysis of the spectral and timing properties observed in X-rays from neutron star (NS) binary GX 3+1 (4U 1744-26) during long-term transitions between the faint and bright phases superimposed on short-term transitions between lower banana (LB) and upper banana (UB) branches in terms of its color-color diagram, We analyze all observations of this source obtained with the Rossi X-ray Timing Explorer and BeppoSAX satellites, We find that the X-ray broadband energy spectra during these spectral transitions can be adequately reproduced by a composition of a low-temperature blackbody component, a Comptonized component (COMPTB), and Gaussian component We argue that the electron temperature kTe of the Compton cloud monotonically increases from 2.3 keY to 4.5 keY, when GX 3+1 makes a transition from UB to LB. We also detect an evolution of noise components (a very low frequency noise and a high-frequency noise) during these LB-UB transitions. Using a disk seed photon normalization of COMPTB, which is proportional to the mass accretion rate, we find that the photon power-law index Gamma is almost constant (Gamma = 2.00 +/- 0.02) when mass accretion rate changes by factor four. In addition, we find that the emergent spectrum is dominated by the strong Comptonized component We interpret this quasi-stability of the index Gamma and a particular form of the spectrum in the framework of a model in which the energy release in the transition layer located between the accretion disk and NS surface dominates that in the disk. Moreover, this index stability effect now established for GX 3+ I was previously found in the atoll source 4U 1728-34 and suggested for a number of other low-mass X-ray NS binaries. This intrinsic behavior of NSs, in particular for atoll sources, is fundamentally different from that seen in black hole binary sources where the index monotonically increases during spectral transition from the low state to the high state and then finally saturates at

  14. POISSON project. III. Investigating the evolution of the mass accretion rate

    NASA Astrophysics Data System (ADS)

    Antoniucci, S.; García López, R.; Nisini, B.; Caratti o Garatti, A.; Giannini, T.; Lorenzetti, D.

    2014-12-01

    Context. As part of the Protostellar Optical-Infrared Spectral Survey On NTT (POISSON) project, we present the results of the analysis of low-resolution near-IR spectroscopic data (0.9-2.4 μm) of two samples of young stellar objects in the Lupus (52 objects) and Serpens (17 objects) star-forming clouds, with masses in the range of 0.1 to 2.0 M⊙ and ages spanning from 105 to a few 107 yr. Aims: After determining the accretion parameters of the targets by analysing their H i near-IR emission features, we added the results from the Lupus and Serpens clouds to those from previous regions (investigated in POISSON with the same methodology) to obtain a final catalogue (143 objects) of mass accretion rate values (Ṁacc) derived in a homogeneous and consistent fashion. Our final goal is to analyse how Ṁacc correlates with the stellar mass (M∗) and how it evolves in time in the whole POISSON sample. Methods: We derived the accretion luminosity (Lacc) and Ṁacc for Lupus and Serpens objects from the Brγ (Paβ in a few cases) line by using relevant empirical relationships available in the literature that connect the H i line luminosity and Lacc. To minimise the biases that arise from adopting literature data that are based on different evolutionary models and also for self-consistency, we re-derived mass and age for each source of the POISSON samples using the same set of evolutionary tracks. Results: We observe a correlation Ṁacc~M*2.2 between mass accretion rate and stellar mass, similarly to what has previously been observed in several star-forming regions. We find that the time variation of Ṁacc is roughly consistent with the expected evolution of the accretion rate in viscous disks, with an asymptotic decay that behaves as t-1.6. However, Ṁacc values are characterised by a large scatter at similar ages and are on average higher than the predictions of viscous models. Conclusions: Although part of the scattering may be related to systematics due to the

  15. A New Paradigm for Gamma Ray Bursts: Long Term Accretion Rate Modulation by an External Accretion Disk

    NASA Technical Reports Server (NTRS)

    Cannizzo, John; Gehrels, Neil

    2009-01-01

    We present a new way of looking at the very long term evolution of GRBs in which the disk of material surrounding the putative black hole powering the GRB jet modulates the mass flow, and hence the efficacy of the process that extracts rotational energy from the black hole and inner accretion disk. The pre-Swift paradigm of achromatic, shallow-to-steep "breaks" in the long term GRB light curves has not been borne out by detailed Swift data amassed in the past several years. We argue that, given the initial existence of a fall-back disk near the progenitor, an unavoidable consequence will be the formation of an "external disk" whose outer edge continually moves to larger radii due to angular momentum transport and lack of a confining torque. The mass reservoir at large radii moves outward with time and gives a natural power law decay to the GRB light curves. In this model, the different canonical power law decay segments in the GRB identified by Zhang et al. and Nousek et al. represent different physical states of the accretion disk. We identify a physical disk state with each power law segment.

  16. 76 FR 8871 - Walnuts Grown in California; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-02-16

    ... From the Federal Register Online via the Government Publishing Office #0; #0;Rules and Regulations... Marketing Service 7 CFR Part 984 Walnuts Grown in California; Decreased Assessment Rate AGENCY: Agricultural Marketing Service, USDA. ACTION: Affirmation of interim rule as final rule. SUMMARY: The Department...

  17. 78 FR 28120 - Tomatoes Grown in Florida; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-05-14

    ... Agricultural Marketing Service 7 CFR Part 966 Tomatoes Grown in Florida; Decreased Assessment Rate AGENCY: Agricultural Marketing Service, USDA. ACTION: Affirmation of interim rule as final rule. SUMMARY: The... locally administers the marketing order which regulates the handling of tomatoes grown in Florida....

  18. Differential rates of vertical accretion and elevation change among aerial root types in Micronesian mangrove forests

    USGS Publications Warehouse

    Krauss, K.W.; Allen, J.A.; Cahoon, D.R.

    2003-01-01

    Root systems in mangrove swamps have captured the attention of scientists for decades. Among the postulated roles of root structures include a contribution to the geomorphological stability of mangrove soils through sediment trapping and binding. In this study, we used feldspar marker horizons and sediment pins to investigate the influence of three different functional root types - prop roots in Rhizophora spp., root knees in Bruguiera gymnorrhiza, and pneumatophores in Sonneratia alba - on vertical accretion and elevation change in three mangrove forests in the Federated States of Micronesia. Prop roots facilitated vertical accretion (11.0 mm year-1) more than pneumatophores or bare soil controls (mean, 8.3 mm year-1). Sediment elevation, on the other hand, increased at an average rate of only 1.3 mm year-1 across all root types, with rate differences by root type, ranging from -0.2 to 3.4 mm year-1, being detected within river basins. This investigation demonstrates that prop roots can assist in the settling of suspended sediments from estuarine waters, yet prop root structures are not as successful as pneumatophores in maintaining sediment elevation over 2.5 years. As root densities increase over time, an increase in turbulence-induced erosion and in shallow subsidence as organic peat layers form is expected in Micronesian mangrove forests. ?? 2003 Elsevier Science B.V. All rights reserved.

  19. Differential rates of vertical accretion and elevation change among aerial root types in Micronesian mangrove forests

    NASA Astrophysics Data System (ADS)

    Krauss, K. W.; Allen, J. A.; Cahoon, D. R.

    2003-02-01

    Root systems in mangrove swamps have captured the attention of scientists for decades. Among the postulated roles of root structures include a contribution to the geomorphological stability of mangrove soils through sediment trapping and binding. In this study, we used feldspar marker horizons and sediment pins to investigate the influence of three different functional root types—prop roots in Rhizophora spp., root knees in Bruguiera gymnorrhiza, and pneumatophores in Sonneratia alba—on vertical accretion and elevation change in three mangrove forests in the Federated States of Micronesia. Prop roots facilitated vertical accretion (11.0 mm year -1) more than pneumatophores or bare soil controls (mean, 8.3 mm year -1). Sediment elevation, on the other hand, increased at an average rate of only 1.3 mm year 1 across all root types, with rate differences by root type, ranging from -0.2 to 3.4 mm year -1, being detected within river basins. This investigation demonstrates that prop roots can assist in the settling of suspended sediments from estuarine waters, yet prop root structures are not as successful as pneumatophores in maintaining sediment elevation over 2.5 years. As root densities increase over time, an increase in turbulence-induced erosion and in shallow subsidence as organic peat layers form is expected in Micronesian mangrove forests.

  20. Ocean Zircon - constraints on cooling histories, spreading rate, and modes of crustal accretion

    NASA Astrophysics Data System (ADS)

    John, B. E.; Cheadle, M. J.; Baines, G.; Grimes, C. B.; Wooden, J.

    2009-12-01

    Igneous zircon is an ubiquitous component of evolved gabbroic rocks (including gabbro norite, Fe-Ti oxide and/or amphibole-bearing gabbro, quartz diorite, and tonalite) found in oceanic lithosphere. Ion microprobe analysis by SHRIMP-RG has allowed characterization of a large set of trace elements from these zircon, which help define a robust method for discriminating source in provenance studies. U/Yb and Th/Yb vs. Hf, Y, or other HREE reveal distinct chemical fields discriminating between ocean and continental-derived zircon in ancient environments. Decreasing Ti correlates with enrichment in Hf and U, suggesting growth from fractionating melt. Ti-in-zircon temperatures range from ~1000-600°C (corrected for aTiO2=0.7,aSiO2=1.0,P=2 kbar), with intra-sample variation typically ~60-180°C. Individual grains show up to 120°C temperature variation, corresponding to concentric CL zoning, but not to sector zoning. Individual zircons from a single sample can have differing Ti concentrations, suggesting that each zircon may record different parts of the crystallization history over a temperature range of up to ~200°C. This observation is consistent with previous single-grain TIMS dating of zircon from five samples recording an age range up to 90-235ka (Lissenberg et al, 2009). Combining SIMS Ti-in-zircon temperatures with TIMS U-Pb zircon ages can constrain cooling rates over the temperature interval of ~900-700°C. Rare single zircon crystals show distinct cores and rims that record up to 2.5 m.y. of inheritance, testifying to the complexity of crustal growth at slow spreading mid-ocean ridges. U/Pb SHRIMP dating of zircon collected from in-situ ocean lithosphere also constrain plate spreading rates, helps calibrate marine magnetic anomalies, provides constraints on the timing of both magmatism and denudation, and contributes to knowledge of the rates and duration of crustal growth at mid-ocean ridges. Spreading rate estimates based on zircon geochronology from

  1. Experience with dynamic reinforcement rates decreases resistance to extinction.

    PubMed

    Craig, Andrew R; Shahan, Timothy A

    2016-03-01

    The ability of organisms to detect reinforcer-rate changes in choice preparations is positively related to two factors: the magnitude of the change in rate and the frequency with which rates change. Gallistel (2012) suggested similar rate-detection processes are responsible for decreases in responding during operant extinction. Although effects of magnitude of change in reinforcer rate on resistance to extinction are well known (e.g., the partial-reinforcement-extinction effect), effects of frequency of changes in rate prior to extinction are unknown. Thus, the present experiments examined whether frequency of changes in baseline reinforcer rates impacts resistance to extinction. Pigeons pecked keys for variable-interval food under conditions where reinforcer rates were stable and where they changed within and between sessions. Overall reinforcer rates between conditions were controlled. In Experiment 1, resistance to extinction was lower following exposure to dynamic reinforcement schedules than to static schedules. Experiment 2 showed that resistance to presession feeding, a disruptor that should not involve change-detection processes, was unaffected by baseline-schedule dynamics. These findings are consistent with the suggestion that change detection contributes to extinction. We discuss implications of change-detection processes for extinction of simple and discriminated operant behavior and relate these processes to the behavioral-momentum based approach to understanding extinction.

  2. Genetic risk factors for decreased bone mineral accretion in children with asthma receiving multiple oral corticosteroid bursts

    PubMed Central

    Park, Heung-Woo; Ge, Bing; Tse, Szeman; Grundberg, Elin; Pastinen, Tomi; Kelly, H. William; Tantisira, Kelan G.

    2015-01-01

    Introduction Long-term, intermittent oral corticosteroid (OCS) use in children with asthma leads to significant decrements in bone mineral accretion (BMA). We aimed to identify genetic factors influencing OCS dose effects on BMA in children with asthma. Methods We first performed a gene by OCS interaction genome-wide association study (GWAS) of BMA in 489 white participants in the Childhood Asthma Management Program trial, who took short-term oral prednisone bursts when they experienced acute asthma exacerbations. We selected the top-ranked 2,000 single nucleotide polymorphisms (SNPs) in the GWAS and determined whether these SNPs also had cis-regulatory effects on dexamethasone-induced gene expression in osteoblast cells. Results We identified two SNPs (rs9896933 and rs2074439) associated with decreased BMA and related to the tubulin γ pathway. Rs9896933 met criteria for genome-wide significance (P = 3.15 ×10−8 in GWAS) and is located on the intron of tubulin folding cofactor D gene. Rs2074439 (P = 2.74 × 10−4 in GWAS) showed strong cis-regulatory effects on dexamethasone-induced tubulin γ gene expression in osteoblast cells (P = 8.64 × 10−4). Interestingly, we found that BMA worsened with increased dose of prednisone as the number of mutant alleles of the two SNPs increased. Conclusions We have identified two novel tubulin γ pathway SNPs, rs9896933 and rs2074439, showing independent interactive effects with cumulative corticosteroid dose on BMA in children with asthma receiving multiple OCS bursts. PMID:26025128

  3. High monetary reward rates and caloric rewards decrease temporal persistence

    PubMed Central

    Bode, Stefan; Murawski, Carsten

    2017-01-01

    Temporal persistence refers to an individual's capacity to wait for future rewards, while forgoing possible alternatives. This requires a trade-off between the potential value of delayed rewards and opportunity costs, and is relevant to many real-world decisions, such as dieting. Theoretical models have previously suggested that high monetary reward rates, or positive energy balance, may result in decreased temporal persistence. In our study, 50 fasted participants engaged in a temporal persistence task, incentivised with monetary rewards. In alternating blocks of this task, rewards were delivered at delays drawn randomly from distributions with either a lower or higher maximum reward rate. During some blocks participants received either a caloric drink or water. We used survival analysis to estimate participants' probability of quitting conditional on the delay distribution and the consumed liquid. Participants had a higher probability of quitting in blocks with the higher reward rate. Furthermore, participants who consumed the caloric drink had a higher probability of quitting than those who consumed water. Our results support the predictions from the theoretical models, and importantly, suggest that both higher monetary reward rates and physiologically relevant rewards can decrease temporal persistence, which is a crucial determinant for survival in many species. PMID:28228517

  4. PHOTOMETRIC DETERMINATION OF THE MASS ACCRETION RATES OF PRE-MAIN-SEQUENCE STARS. II. NGC 346 IN THE SMALL MAGELLANIC CLOUD

    SciTech Connect

    De Marchi, Guido; Sirianni, Marco; Panagia, Nino; Sabbi, Elena; Romaniello, Martino; Prada Moroni, Pier Giorgio; Degl'Innocenti, Scilla E-mail: panagia@stsci.edu

    2011-10-10

    We have studied the properties of the stellar populations in the field of the NGC 346 cluster in the Small Magellanic Cloud, using a novel self-consistent method that allows us to reliably identify pre-main-sequence (PMS) objects actively undergoing mass accretion, regardless of their age. The method does not require spectroscopy and combines broadband V and I photometry with narrowband H{alpha} imaging to identify all stars with excess H{alpha} emission and derive the accretion luminosity L{sub acc} and mass accretion rate M-dot{sub acc} for all of them. The application of this method to existing Hubble Space Telescope (HST)/Advanced Camera for Surveys photometry of the NGC 346 field has allowed us to identify and study 680 bona fide PMS stars with masses from {approx}0.4 M{sub sun} to {approx}4 M{sub sun} and ages in the range from {approx}1 Myr to {approx}30 Myr. Previous investigations of this region, based on the same data, had identified young ({approx}3 Myr old) candidate PMS stars on the basis of their broadband colors. In this study, we show that there are at least two, almost equally numerous, young populations with distinct ages of, respectively, {approx}1 and {approx}20 Myr. We provide accurate physical parameters for all of them. We take advantage of the unprecedented size of our PMS sample and of its spread in mass and age to study the evolution of the mass accretion rate as a function of stellar parameters. We find that, regardless of stellar mass, the mass accretion rate decreases with roughly the square root of the age, or about three times slower than predicted by current models of viscous disk evolution, and that more massive stars systematically have a higher mass accretion rate in proportion to their mass. A multivariate linear regression fit reveals that log M-dot{sub acc}{approx_equal}-0.6 log t + log m + c, where t is the age of the star, m is its mass, and c is a quantity that is higher at lower metallicity. This result is consistent with

  5. Tracing the incidence of X-ray AGN and their distribution of accretion rates across the galaxy population

    NASA Astrophysics Data System (ADS)

    Aird, James; Coil, Alison; Georgakakis, Antonis; Nandra, Kirpal

    2016-08-01

    X-ray selection provides a powerful method of identifying AGN across a variety of host galaxies and with a wide range of accretion rates. However, careful consideration of the underlying selection biases are vital to reveal the true underlying distribution of accretion rates and determine how the incidence of AGN is related to the properties of the galaxies that host them. I will present new measurements of the distribution of specific accretion rates (scaled relative to the total host galaxy mass, roughly tracing the Eddington ratio) within both star-forming and quiescent galaxy populations. We combine near-infrared selected samples of galaxies from the CANDELS/3D-HST and UltraVISTA surveys with deep Chandra X-ray data and use an advanced Bayesian technique to constrain the underlying distribution of specific accretion rates as a function of stellar mass and redshift. Our results reveal a broad distribution of accretion rates (reflecting long-term variability in the level of AGN fuelling) in both galaxy types. The probability of a star-forming galaxy hosting an AGN (above a fixed specific accretion rate) has a strong stellar mass dependence - revealing an intrinsically higher incidence of AGN in massive star-forming galaxies - and undergoes a stellar-mass-dependent evolution with redshift. The probability of a quiescent galaxy hosting an AGN is generally lower but does not depend on stellar mass and evolves differently with redshift. These results provide vital insights into the relationship between the growth of black hole and the physical properties of their host galaxies.

  6. Wetland Accretion Rate Model of Ecosystem Resilience (WARMER) and its application to habitat sustainability for endangered species in the San Francisco Estuary

    USGS Publications Warehouse

    Swanson, Kathleen M.; Drexler, Judith Z.; Schoellhamer, David H.; Thorne, Karen M.; Casazza, Michael L.; Overton, Cory T.; Callaway, John C.; Takekawa, John Y.

    2014-01-01

    Salt marsh faunas are constrained by specific habitat requirements for marsh elevation relative to sea level and tidal range. As sea level rises, changes in relative elevation of the marsh plain will have differing impacts on the availability of habitat for marsh obligate species. The Wetland Accretion Rate Model for Ecosystem Resilience (WARMER) is a 1-D model of elevation that incorporates both biological and physical processes of vertical marsh accretion. Here, we use WARMER to evaluate changes in marsh surface elevation and the impact of these elevation changes on marsh habitat for specific species of concern. Model results were compared to elevation-based habitat criteria developed for marsh vegetation, the endangered California clapper rail (Rallus longirostris obsoletus), and the endangered salt marsh harvest mouse (Reithrodontomys raviventris) to determine the response of marsh habitat for each species to predicted >1-m sea-level rise by 2100. Feedback between vertical accretion mechanisms and elevation reduced the effect of initial elevation in the modeled scenarios. Elevation decreased nonlinearly with larger changes in elevation during the latter half of the century when the rate of sea-level rise increased. Model scenarios indicated that changes in elevation will degrade habitat quality within salt marshes in the San Francisco Estuary, and degradation will accelerate in the latter half of the century as the rate of sea-level rise accelerates. A sensitivity analysis of the model results showed that inorganic sediment accumulation and the rate of sea-level rise had the greatest influence over salt marsh sustainability.

  7. Decreased glomerular filtration rate in solderers exposed to cadmium.

    PubMed Central

    Järup, L; Persson, B; Elinder, C G

    1995-01-01

    OBJECTIVES--to evaluate the degree of cadmium induced glomerular impairment and to assess the dose-response relation between cadmium dose and the prevalence of glomerular dysfunction. METHODS--A comparison of glomerular filtration rates (GFR) assessed by Cr-EDTA clearance was made in 42 solderers previously exposed to cadmium for at least five years. Blood and urine data were collected at health examinations in 1984, 1989, and 1993. Individual doses of cadmium were estimated by analysing cadmium in blood. RESULTS--Glomerular lesions induced by cadmium are irreversible and the GFR decreases with the degree of tubular damage. The GFR also decreases with cadmium dose and there is a dose-response relation between blood cadmium and prevalence of glomerular damage with 3.4% prevalence at blood cadmium concentrations below 50 nmol/l, 33% at blood cadmium concentrations between 50 and 75 nmol/l and 100% prevalence of glomerular damage when cadmium in blood exceeds 75 nmol/l. CONCLUSIONS--The kidney lesions induced by cadmium are irreversible and the prevalence of those lesions are dose dependent. There is also evidence of a dose related decrease in GFR even a long time after the end of exposure. Exposure to cadmium should therefore be minimised and workers exposed to cadmium should be examined regularly for many years after the end of exposure. PMID:8563845

  8. Whole body synthesis rates of DHA from α-linolenic acid are greater than brain DHA accretion and uptake rates in adult rats[S

    PubMed Central

    Domenichiello, Anthony F.; Chen, Chuck T.; Trepanier, Marc-Olivier; Stavro, P. Mark; Bazinet, Richard P.

    2014-01-01

    Docosahexaenoic acid (DHA) is important for brain function, however, the exact amount required for the brain is not agreed upon. While it is believed that the synthesis rate of DHA from α-linolenic acid (ALA) is low, how this synthesis rate compares with the amount of DHA required to maintain brain DHA levels is unknown. The objective of this work was to assess whether DHA synthesis from ALA is sufficient for the brain. To test this, rats consumed a diet low in n-3 PUFAs, or a diet containing ALA or DHA for 15 weeks. Over the 15 weeks, whole body and brain DHA accretion was measured, while at the end of the study, whole body DHA synthesis rates, brain gene expression, and DHA uptake rates were measured. Despite large differences in body DHA accretion, there was no difference in brain DHA accretion between rats fed ALA and DHA. In rats fed ALA, DHA synthesis and accretion was 100-fold higher than brain DHA accretion of rats fed DHA. Also, ALA-fed rats synthesized approximately 3-fold more DHA than the DHA uptake rate into the brain. This work indicates that DHA synthesis from ALA may be sufficient to supply the brain. PMID:24212299

  9. Decreased identification rate of sentinel lymph node after neoadjuvant chemotherapy.

    PubMed

    Kang, Seok Hyung; Kim, Seok-Ki; Kwon, Youngmee; Kang, Han-Sung; Kang, Jae Hee; Ro, Jungsil; Lee, Eun Sook

    2004-10-01

    We prospectively studied the feasibility of sentinel lymph node biopsy (SLNB) after neoadjuvant chemotherapy by comparing the identification rate and the false-negative rate (FNR) with the results obtained from the patients without chemotherapy. From October 2001 to March 2003, a total of 284 consecutive patients who underwent SLNB and axillary lymph node dissection (ALND) at the Center for Breast Cancer, National Cancer Center were enrolled. Of the 284 patients, 54 underwent neoadjuvant chemotherapy prior to operation. The sentinel lymph node (SLN) was mapped by radioactive colloid alone or in combination with blue dye. All SLNs were evaluated by 2 mm serial sections after hematoxylin-eosin staining. The overall SLN identification rate was 91.9% (261/284): 72.2% (39/54) of the patients after chemotherapy and 96.5% (222/230) of the patients without chemotherapy. These results suggest that preoperative chemotherapy significantly affects lymphatic mapping ( p< 0.001). Among the patients with chemotherapy, there were 3 false negatives in 39 successfully mapped tumors, yielding an FNR of 11.1% (3/27), a negative prediction value (NPV) of 80.0% (12/15), and an accuracy of 92.3% (36/39). There were 10 false negatives among 222 successfully detected patients without chemotherapy, yielding an FNR of 9.9% (10/101), an NPV of 92.4% (121/131), and an accuracy of 95.5% (212/222). These results were not statistically different when compared ( p > 0.05). Although the SLN identification rate significantly decreased after neoadjuvant chemotherapy, SLNB could accurately predict axillary status. Thus SLNB can be an alternative to ALND even after neoadjuvant chemotherapy in cases of successful identification of the SLN.

  10. Building bones in babies: can and should we exceed the human milk-fed infant's rate of bone calcium accretion?

    PubMed

    Abrams, Steven A

    2006-11-01

    Increasing calcium absorption and bone calcium accretion to levels above those achieved by human milk-fed, full-term infants is possible with infant formulas. However, no data support such a goal or suggest that it is beneficial to short- or long-term bone health. Small differences in the bioavailability of calcium between infant formulas are unlikely to have long-term consequences. Long-term studies of the effects of infant feeding type on ultimate bone mass are needed. For now, the vitamin-replete breast-fed infant's rate of calcium accretion during the first year of life should be the standard targeted for infant formulas.

  11. A CORRELATION BETWEEN STAR FORMATION RATE AND AVERAGE BLACK HOLE ACCRETION IN STAR-FORMING GALAXIES

    SciTech Connect

    Chen, Chien-Ting J.; Hickox, Ryan C.; Alberts, Stacey; Pope, Alexandra; Brodwin, Mark; Jones, Christine; Forman, William R.; Goulding, Andrew D.; Murray, Stephen S.; Alexander, David M.; Mullaney, James R.; Assef, Roberto J.; Gorjian, Varoujan; Brown, Michael J. I.; Dey, Arjun; Jannuzi, Buell T.; Le Floc'h, Emeric

    2013-08-10

    We present a measurement of the average supermassive black hole accretion rate (BHAR) as a function of the star formation rate (SFR) for galaxies in the redshift range 0.25 < z < 0.8. We study a sample of 1767 far-IR-selected star-forming galaxies in the 9 deg{sup 2} Booetes multi-wavelength survey field. The SFR is estimated using 250 {mu}m observations from the Herschel Space Observatory, for which the contribution from the active galactic nucleus (AGN) is minimal. In this sample, 121 AGNs are directly identified using X-ray or mid-IR selection criteria. We combined these detected AGNs and an X-ray stacking analysis for undetected sources to study the average BHAR for all of the star-forming galaxies in our sample. We find an almost linear relation between the average BHAR (in M{sub Sun} yr{sup -1}) and the SFR (in M{sub Sun} yr{sup -1}) for galaxies across a wide SFR range 0.85 < log SFR < 2.56: log BHAR = (- 3.72 {+-} 0.52) + (1.05 {+-} 0.33)log SFR. This global correlation between SFR and average BHAR is consistent with a simple picture in which SFR and AGN activity are tightly linked over galaxy evolution timescales.

  12. Colorectal cancer incidence rates have decreased in central Italy.

    PubMed

    Crocetti, Emanuele; Buzzoni, Carlotta; Zappa, Marco

    2010-11-01

    We analyzed colorectal cancer incidence data from the Tuscany Cancer Registry, central Italy, for the period 1985-2005. We carried out a trend analysis through a Joinpoint regression analysis, and summarized trends as annual percent change (APC) of the standardized (European standard) rates. Colorectal incidence rates increased until 1996 (APC=+1.4, 95% CI: 0.8-1.9), then decreased significantly (APC=-1.1, 95% CI: -0.8 to -0.4). The change was detected as statistically significant in the age group of 54+ years. Among younger individuals, we observed an increasing incidence until 2003. In the same geographical area, a colorectal screening programme has been active from 1982; it was initially based on guaiac faecal occult blood testing (GFOBT) and on immunological testing (IFOBT) since the mid 1990s. The decline in colorectal cancer incidence since 1996, in the whole population and especially among individuals older than 54 years, may suggest the effect of FOBT screening in terms of precancerous polyps removal.

  13. Accretion rate of extraterrestrial matter: Iridium deposited over the last 70 million years

    NASA Technical Reports Server (NTRS)

    Kyte, Frank T.

    1988-01-01

    In order to quantify the accretion rate of extraterrestrial matter during the Cenozoic, Ir concentrations were measured in a continuous series of 450 samples across most of the length of piston core LL44-GPC3. LL44-GPC3 is a 25-meter-long, large-diameter piston core of abyssal clay from the central North Pacific. This core contains a nearly continuous record of sedimentation over the last 70 Ma, as this site migrated from a region near the Equator in the late Cretaceous to its present position north of Hawaii. The first-cut survey across the core is nearing completion, and all of the conclusions of the earlier study, in which was reported the concentrations of Ir, Co, and Sb across 9 meters of this core, remain unchanged. The only strongly enhanced Ir concentrations occur at the Cretaceous-Tertiary (K-T) boundary and outside the K-T boundary Ir correlates well with Co, a terrestrial element which is largely present in hydrogenous ferromanganese oxide precipitates from seawater. Concentrations of both elements appear to be inversely correlated with the sedimentation rate. Although the K-T Ir anomaly is unique in magnitude in this core, there are several small bumps in the Ir profile which may reflect smaller accretionary events. The most promising Ir enhancement was observed in a 30 cm section approximately 1 m below the K-T boundary. Preliminary data suggest deposition of an excess across this interval at a time estimate to be approximate 1 Ma before the K-T impact event, but there is insufficient evidence at present to prove that this reflects enhanced accretion of extraterrestrial matter. A detailed model is being prepared of the chemical record of sedimentation in this core using a combined database of 39 elements in approximately 450 samples across the Cenozoic. Preliminary working model indicates that the only sedimentary sources which contribute significantly to the Ir budget in this core are the hydrogenous precipitates and extraterrestrial particulates.

  14. Weak Line Quasars at High Redshift: Extremely High Accretion Rates or Anemic Broad-line Regions?

    NASA Astrophysics Data System (ADS)

    Shemmer, Ohad; Trakhtenbrot, Benny; Anderson, Scott F.; Brandt, W. N.; Diamond-Stanic, Aleksandar M.; Fan, Xiaohui; Lira, Paulina; Netzer, Hagai; Plotkin, Richard M.; Richards, Gordon T.; Schneider, Donald P.; Strauss, Michael A.

    2010-10-01

    We present Gemini-North K-band spectra of two representative members of the class of high-redshift quasars with exceptionally weak rest-frame ultraviolet emission lines (WLQs), SDSS J114153.34+021924.3 at z = 3.55 and SDSS J123743.08+630144.9 at z = 3.49. In both sources, we detect an unusually weak broad Hβ line and place tight upper limits on the strengths of their [O III] lines. Virial, Hβ-based black hole mass determinations indicate normalized accretion rates of L/L Edd=0.4 for these sources, which is well within the range observed for typical quasars with similar luminosities and redshifts. We also present high-quality XMM-Newton imaging spectroscopy of SDSS J114153.34+021924.3 and find a hard-X-ray photon index of Γ = 1.91+0.24 -0.22, which supports the virial L/L Edd determination in this source. Our results suggest that the weakness of the broad emission lines in WLQs is not a consequence of an extreme continuum-emission source but instead due to abnormal broad emission line region properties.

  15. Estimation of calcium and phosphorus content in growing and finishing pigs: whole empty body components and relative accretion rates.

    PubMed

    Pettey, L A; Cromwell, G L; Jang, Y D; Lindemann, M D

    2015-01-01

    Two comparative serial-slaughter experiments were conducted to determine whole empty body (WEB) composition and accretion rates of Ca and P in 18 to 109 kg BW pigs to provide information for modeling of these nutrients for growth. Both studies were conducted with 5 sets of 5 littermate barrows which were allotted to 5 slaughter groups in each study (Exp. 1: 18, 27, 36, 45, and 54 kg BW; Exp. 2: 36, 54, 73, 91, and 109 kg BW). Pigs were fed corn-soybean meal-based diets fortified with minerals and vitamins in 2 dietary phases in Exp. 1 (Phase 1: 18 to 36 kg BW; Phase 2: 36 to 54 kg BW) and 3 dietary phases in Exp. 2 (Phase 2: 36 to 54 kg BW; Phase 3: 54 to 78 kg BW; and Phase 4: 78 to 109 kg BW). At the predetermined BW, pigs were slaughtered and separated into body components of hair, hooves, blood, head, viscera, and carcass. The carcass was split along the dorsal midline and the left carcass side was ground for chemical analysis. Whole empty body weight averaged 93.6% and 94.0% of live BW in Exp. 1 and Exp. 2, respectively. As WEB weight increased in both experiments, the percentage carcass of the WEB linearly (P < 0.05) increased, the percentage viscera linearly (P < 0.05) decreased, and the mass (g) of N, ash, Ca, and P in the WEB increased linearly (R(2) = 0.98). The concentration (g/kg) of P in the WEB of 18 to 54 kg pigs increased from 4.30 to 4.57 (linear; P < 0.05) and for Ca increased from 5.13 to 5.66 (linear; P < 0.05). In Exp. 2, P concentration was not related to WEB weight and Ca concentration increased quadratically (P < 0.05). The relative accretion rate of N to P was 1.00 (R(2) = 0.99) in the pigs from 18 to 54 kg. In conclusion, these results indicate that compositional changes as BW increases are strongly related to P retention and that the quantification of WEB P and relationships of WEB P to other chemical components in the body may be useful for modeling purposes in growing and finishing pigs.

  16. ENHANCED ACCRETION RATES OF STARS ON SUPERMASSIVE BLACK HOLES BY STAR-DISK INTERACTIONS IN GALACTIC NUCLEI

    SciTech Connect

    Just, Andreas; Yurin, Denis; Makukov, Maxim; Berczik, Peter; Omarov, Chingis; Spurzem, Rainer; Vilkoviskij, Emmanuil Y.

    2012-10-10

    We investigate the dynamical interaction of a central star cluster surrounding a supermassive black hole (SMBH) and a central accretion disk (AD). The dissipative force acting on stars in the disk leads to an enhanced mass flow toward the SMBH and to an asymmetry in the phase space distribution due to the rotating AD. The AD is considered as a stationary Keplerian rotating disk, which is vertically extended in order to employ a fully self-consistent treatment of stellar dynamics including the dissipative force originating from star-gas ram pressure effects. The stellar system is treated with a direct high-accuracy N-body integration code. A star-by-star representation, desirable in N-body simulations, cannot be extended to real particle numbers yet. Hence, we carefully discuss the scaling behavior of our model with regard to particle number and tidal accretion radius. The main idea is to find a family of models for which the ratio of two-body relaxation time and dissipation time (for kinetic energy of stellar orbits) is constant, which then allows us to extrapolate our results to real parameters of galactic nuclei. Our model is derived from basic physical principles and as such it provides insight into the role of physical processes in galactic nuclei, but it should be regarded as a first step toward more realistic and more comprehensive simulations. Nevertheless, the following conclusions appear to be robust: the star accretion rate onto the AD and subsequently onto the SMBH is enhanced by a significant factor compared to purely stellar dynamical systems neglecting the disk. This process leads to enhanced fueling of central disks in active galactic nuclei (AGNs) and to an enhanced rate of tidal stellar disruptions. Such disruptions may produce electromagnetic counterparts in the form of observable X-ray flares. Our models improve predictions for their rates in quiescent galactic nuclei. We do not yet model direct stellar collisions in the gravitational potential

  17. Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. I. First Results from a New Reverberation Mapping Campaign

    NASA Astrophysics Data System (ADS)

    Du, Pu; Hu, Chen; Lu, Kai-Xing; Wang, Fang; Qiu, Jie; Li, Yan-Rong; Bai, Jin-Ming; Kaspi, Shai; Netzer, Hagai; Wang, Jian-Min; SEAMBH Collaboration

    2014-02-01

    We report first results from a large project to measure black hole (BH) mass in high accretion rate active galactic nuclei (AGNs). Such objects may be different from other AGNs in being powered by slim accretion disks and showing saturated accretion luminosities, but both are not yet fully understood. The results are part of a large reverberation mapping (RM) campaign using the 2.4 m Shangri-La telescope at the Yunnan Observatory in China. The goals are to investigate the gas distribution near the BH and the properties of the central accretion disks, to measure BH mass and Eddington ratios, and to test the feasibility of using such objects as a new type of cosmological candles. The paper presents results for three objects, Mrk 335, Mrk 142, and IRAS F12397+3333, with Hβ time lags relative to the 5100 Å continuum of 10.6^{+1.7}_{-2.9}, 6.4^{+0.8}_{-2.2} and 11.4^{+2.9}_{-1.9} days, respectively. The corresponding BH masses are (8.3_{-3.2}^{+2.6})\\times 10^6\\,M_{\\odot }, (3.4_{-1.2}^{+0.5})\\times 10^6\\,M_{\\odot }, and (7.5_{-4.1}^{+4.3})\\times 10^6\\,M_{\\odot }, and the lower limits on the Eddington ratios are 0.6, 2.3, and 4.6 for the minimal radiative efficiency of 0.038. Mrk 142 and IRAS F12397+333 (extinction corrected) clearly deviate from the currently known relation between Hβ lag and continuum luminosity. The three Eddington ratios are beyond the values expected in thin accretion disks and two of them are the largest measured so far among objects with RM-based BH masses. We briefly discuss implications for slim disks, BH growth, and cosmology.

  18. Crossing the Eddington Limit: Examining Disk Spectra at High Accretion Rates

    NASA Astrophysics Data System (ADS)

    Sutton, Andrew D.; Swartz, Douglas A.; Roberts, Timothy P.; Middleton, Matthew J.; Soria, Roberto; Done, Chris

    2017-02-01

    The faintest ultraluminous X-ray sources (ULXs), those with 0.3–10 keV luminosities 1< {L}{{X}}/{10}39< 3 {erg} {{{s}}}-1, tend to have X-ray spectra that are disk-like but broader than expected for thin accretion disks. These “broadened disk (BD)” spectra are thought to indicate near- or mildly super-Eddington accretion onto stellar remnant black holes. Here we report that a sample of bright thermal-dominant black hole binaries, which have Eddington ratios constrained to moderate values, also show BD spectra in the 0.3–10 keV band at an order of magnitude lower luminosities. This broadening would be missed in studies that only look above ∼ 2 {keV}. While this may suggest that BD ULXs could be powered by accretion onto massive stellar remnant black holes with close to maximal spin, we argue in favor of a scenario where they are at close to the Eddington luminosity, such that radiation pressure would be expected to result in geometrically slim, advective accretion disks. However, this implies that an additional physical mechanism is required to produce the observed broad spectra at low Eddington ratios.

  19. Decreased reproductive rates in sheep fed a high selenium diet

    Technology Transfer Automated Retrieval System (TEKTRAN)

    High Se-containing forages grow on seleniferous soils in many parts of the United States and throughout the world. Selenium is an essential trace element that is required for many physiological processes but can also be either acutely or chronically toxic to livestock. Anecdotal reports of decrease...

  20. Vaccination of influenza a virus decreases transmission rates in pigs.

    PubMed

    Romagosa, Anna; Allerson, Matt; Gramer, Marie; Joo, Han Soo; Deen, John; Detmer, Susan; Torremorell, Montserrat

    2011-12-20

    Limited information is available on the transmission and spread of influenza virus in pig populations with differing immune statuses. In this study we assessed differences in transmission patterns and quantified the spread of a triple reassortant H1N1 influenza virus in naïve and vaccinated pig populations by estimating the reproduction ratio (R) of infection (i.e. the number of secondary infections caused by an infectious individual) using a deterministic Susceptible-Infectious-Recovered (SIR) model, fitted on experimental data. One hundred and ten pigs were distributed in ten isolated rooms as follows: (i) non-vaccinated (NV), (ii) vaccinated with a heterologous vaccine (HE), and (iii) vaccinated with a homologous inactivated vaccine (HO). The study was run with multiple replicates and for each replicate, an infected non-vaccinated pig was placed with 10 contact pigs for two weeks and transmission of influenza evaluated daily by analyzing individual nasal swabs by RT-PCR. A statistically significant difference between R estimates was observed between vaccinated and non-vaccinated pigs (p < 0.05). A statistically significant reduction in transmission was observed in the vaccinated groups where R (95%CI) was 1 (0.39-2.09) and 0 for the HE and the HO groups respectively, compared to an Ro value of 10.66 (6.57-16.46) in NV pigs (p < 0.05). Transmission in the HE group was delayed and variable when compared to the NV group and transmission could not be detected in the HO group. Results from this study indicate that influenza vaccines can be used to decrease susceptibility to influenza infection and decrease influenza transmission.

  1. Models of the hard X-ray spectrum of AM Herculis and implications for the accretion rate

    NASA Technical Reports Server (NTRS)

    Swank, J. H.; Fabian, A. C.; Ross, R. R.

    1983-01-01

    Phenomenological fits to the hard X-ray spectrum of AM Herculis left unexplained the high equivalent width (0.8 + or - 0.1 keV) of Fe K alpha emission. A purely thermal origin implies a much steeper spectrum than was observed. With Monte Carlo calculations, scattering and fluorescent line production in a cold or partially ionized accretion column of hard X-rays emitted at the base were investigated. The strength of the iron emission and the flat spectral continuum can be explained by the effects of fluorescence and absorption within the accretion column and the surface of the white dwarf on a thermal X-ray spectrum. Thomson optical depths across the column in the range 0.2 to 0.7 are acceptable. The accretion rate and gravitational power can be deduced from the optical depth across the column, if the column size is known, and, together with the observed hard X-ray and polarized light luminosities, imply a lower limit for the luminosity in the UV to soft X-ray range, for which the observations give model-dependent values. Estimates of the column size differ by a factor of 40. Small spot sizes and low luminosities would be consistent with the soft component being the expected reprocessed bremsstrahlung and cyclotron radiation, although the constraint of matching the spectrum confines one to solutions with fluxes exceeding 20% the Eddington limits.

  2. UNLEASHING POSITIVE FEEDBACK: LINKING THE RATES OF STAR FORMATION, SUPERMASSIVE BLACK HOLE ACCRETION, AND OUTFLOWS IN DISTANT GALAXIES

    SciTech Connect

    Silk, Joseph

    2013-08-01

    Pressure-regulated star formation is a simple variant on the usual supernova-regulated star formation efficiency that controls the global star formation rate as a function of cold gas content in star-forming galaxies, and accounts for the Schmidt-Kennicutt law in both nearby and distant galaxies. Inclusion of active galactic nucleus (AGN) induced pressure, by jets and/or winds that flow back onto a gas-rich disk, can lead, under some circumstances, to significantly enhanced star formation rates, especially at high redshift and most likely followed by the more widely accepted phase of star formation quenching. Simple expressions are derived that relate supermassive black hole growth, star formation, and outflow rates. The ratios of black hole to spheroid mass and of both black hole accretion and outflow rates to star formation rate are predicted as a function of time. I suggest various tests of the AGN-triggered star formation hypothesis.

  3. VizieR Online Data Catalog: RM AGNs accretion rates and BH masses (Du+, 2016)

    NASA Astrophysics Data System (ADS)

    Du, P.; Wang, J.-M.; Hu, C.; Ho, L. C.; Li, Y.-R.; Bai, J.-M.

    2016-05-01

    We select all AGNs with reverberation mapping (RM) data (here only broad Hβ line), which yield robust BH mass estimates needed for our analysis. All RM AGNs before 2013 are summarized by Bentz et al. (2013ApJ...767..149B). Our project to search for super-Eddington accreting massive black holes (SEAMBHs) has monitored about 25 candidates and successfully measured Hβ lags ({tau}Hβ) in 14 AGNs to date (Du et al. 2015, J/ApJ/806/22) and other five objects monitored between 2014 and 2015 (to be submitted). See section 2 for further explanations. (2 data files).

  4. 2500 years of changing shoreline accretion rates at the mouths of the Mekong River delta

    NASA Astrophysics Data System (ADS)

    Besset, Manon; Tamura, Toru; Anthony, Edward; Brunier, Guillaume; Saito, Yoshiki; Dussouillez, Philippe; Lap Nguyen, Van; Ta, Oahn

    2016-04-01

    The Mekong River delta prograded rapidly in a relatively sheltered bight in the South China Sea under the influence of high fluvial sediment supply 5300 to 3500 years ago, developing from an estuary into a delta. This >200 km seaward growth resulted in increasing exposure of the delta to ocean waves that led to a more wave-influenced mode of progradation characterized by the construction of numerous sets of beach ridges in the eastern sector of the delta, which shows a system of multiple distributary mouths. The growth pattern of this river-mouth sector over the last 2500 years has been determined from OSL dating of these beach-ridge deposits, while the most up-to-date trends (1950-2014) have been highlighted from the analysis of maps and satellite images. The OSL ages show that the area of the delta in the mouths sector remained nearly constant till about 500 yr BP, following which significant accretion occurred, possibly in response to changes in catchment land-use and monsoon rainfall and attendant river water and sediment discharge. A fine-tuned analysis of changes since 1950 shows dominant but fluctuating accretion, with two periods of erosion. The first (1965-1973) occurred in the course of the second Indochina war, and the second more recently from 2003 to 2011, followed by mild recovery between 2011 and 2014. These fluctuations most likely reflect changes in sediment supply caused by the vicissitudes of war and its effect on vegetation cover, as well as variations in monsoon rainfall and discharge, and, for the most recent period, massive sand mining in the river and deltaic channels. Accretion of the mouths sector has gone apace, over the same recent multi-decadal period, with large-scale erosion of the muddy shores of the delta in the western South China Sea and the Gulf of Thailand, thus suggesting that the mouths sector may be increasingly sequestering sediment to the detriment of the rest of the delta shoreline. The accretion in the mouths sector is

  5. To accrete or not accrete, that is the question

    USGS Publications Warehouse

    von, Huene R.

    1986-01-01

    Along modern convergent margins tectonic processes span a spectrum from accretion to erosion. The process of accretion is generally recognized because it leaves a geologic record, whereas the process of erosion is generally hypothetical because it produces a geologic hiatus. Major conditions that determine the dominance of accretion or erosion at modern convergent margins are: 1) rate and direction of plate convergence, 2) sediment supply and type in the trench, and 3) topography of the subducting ocean floor. Most change in structure has been ascribed to plate motion, but both erosion and accretion are observed along the same convergence margin. Thus sediment supply and topography are probably of equivalent importance to plate motion because both erosion and accretion are observed under constant conditions of plate convergence. The dominance of accretion or erosion at a margin varies with the thickness of trench sediment. In a sediment flooded trench, the proportions of subducted and accreted sediment are commonly established by the position of a decollement along a weak horizon in the sediment section. Thus, the vertical variation of sediment strength and the distribution of horizontal stress are important factors. Once deformation begins, the original sediment strength is decreased by sediment remolding and where sediment thickens rapidly, increases in pore fluid pressure can be pronounced. In sediment-starved trenches, where the relief of the subducting ocean floor is not smoothed over, the front of the margin must respond to the topography subducted as well as that accreted. The hypothesized erosion by the drag of positive features against the underside of the upper plate (a high stress environment) may alternate with erosion due to the collapse of a margin front into voids such as graben (a low stress environment). ?? 1986 Ferdinand Enke Verlag Stuttgart.

  6. Supermassive black holes with high accretion rates in active galactic nuclei. I. First results from a new reverberation mapping campaign

    SciTech Connect

    Du, Pu; Hu, Chen; Qiu, Jie; Li, Yan-Rong; Wang, Jian-Min; Lu, Kai-Xing; Wang, Fang; Bai, Jin-Ming; Kaspi, Shai; Netzer, Hagai; Collaboration: SEAMBH collaboration

    2014-02-10

    We report first results from a large project to measure black hole (BH) mass in high accretion rate active galactic nuclei (AGNs). Such objects may be different from other AGNs in being powered by slim accretion disks and showing saturated accretion luminosities, but both are not yet fully understood. The results are part of a large reverberation mapping (RM) campaign using the 2.4 m Shangri-La telescope at the Yunnan Observatory in China. The goals are to investigate the gas distribution near the BH and the properties of the central accretion disks, to measure BH mass and Eddington ratios, and to test the feasibility of using such objects as a new type of cosmological candles. The paper presents results for three objects, Mrk 335, Mrk 142, and IRAS F12397+3333, with Hβ time lags relative to the 5100 Å continuum of 10.6{sub −2.9}{sup +1.7}, 6.4{sub −2.2}{sup +0.8} and 11.4{sub −1.9}{sup +2.9} days, respectively. The corresponding BH masses are (8.3{sub −3.2}{sup +2.6})×10{sup 6} M{sub ⊙}, (3.4{sub −1.2}{sup +0.5})×10{sup 6} M{sub ⊙}, and (7.5{sub −4.1}{sup +4.3})×10{sup 6} M{sub ⊙}, and the lower limits on the Eddington ratios are 0.6, 2.3, and 4.6 for the minimal radiative efficiency of 0.038. Mrk 142 and IRAS F12397+333 (extinction corrected) clearly deviate from the currently known relation between Hβ lag and continuum luminosity. The three Eddington ratios are beyond the values expected in thin accretion disks and two of them are the largest measured so far among objects with RM-based BH masses. We briefly discuss implications for slim disks, BH growth, and cosmology.

  7. Influence of Sea-Level Rise and Storms on Soil Accretion Rates in the Mangrove Forests of Everglades National Park, USA

    NASA Astrophysics Data System (ADS)

    Smoak, J. M.; Breithaupt, J.; Smith, T., III; Sanders, C. J.; Peterson, L. C.

    2014-12-01

    Mangrove forests provide a range of valuable ecosystem services including sequestering large quantities of organic carbon (OC) in their soils at rates higher than other forests. Whether or not mangrove soils continue to be a sink for OC will be determined by the mangrove ecosystems' response to climate change-induced stressors. The threats of rising sea level outpacing mangrove forest soil accretion and increased wave energy associated with this rise may become the primary climate change-induced stressors on mangrove ecosystems. The threat from wave energy is amplified during storm events, which could increasingly damage mangrove forests along the coastline. However, storms may enhance accretion rates at some sites due to delivery of storm surge material, which could increase the system's ability to keep pace with sea-level rise (SLR). To investigate these processes we measure soil accretion rates over the last 100 years (via 210Pb dating) within the mangrove forests of Everglades National Park, which are situated within the largest contiguous mangrove forest in North America. Accretion rates range from 2 to 2.8 mm per year for sites within 10 km of the Gulf of Mexico. These rates match (within error) or exceed SLR over the last 100 years. Sites farther inland than 10 km have slightly lower accretion rates. Throughout the system organic matter accumulation is the most important source material contributing to accretion. The more seaward sites also show an important contribution from carbonate material. Soil cores from the most seaward sites exhibited visual laminations and Ca peaks (determined via x-ray fluorescence). These are indicators of storm surge deposits. While higher sea level might produce more damage and loss of mangrove forest along open water (e.g., Gulf of Mexico), our findings suggest some sites will have enhanced accretion rates due to supplementation with storm surge material.

  8. Supermassive black holes with high accretion rates in active galactic nuclei. II. The most luminous standard candles in the universe

    SciTech Connect

    Wang, Jian-Min; Du, Pu; Hu, Chen; Qiu, Jie; Li, Yan-Rong; Netzer, Hagai; Kaspi, Shai; Bai, Jin-Ming; Wang, Fang; Lu, Kai-Xing; Collaboration: SEAMBH collaboration

    2014-10-01

    This is the second in a series of papers reporting on a large reverberation mapping (RM) campaign to measure black hole (BH) mass in high accretion rate active galactic nuclei (AGNs). The goal is to identify super-Eddington accreting massive black holes (SEAMBHs) and to use their unique properties to construct a new method for measuring cosmological distances. Based on theoretical models, the saturated bolometric luminosity of such sources is proportional to the BH mass, which can be used to obtain their distance. Here we report on five new RM measurements and show that in four of the cases, we can measure the BH mass and three of these sources are SEAMBHs. Together with the three sources from our earlier work, we now have six new sources of this type. We use a novel method based on a minimal radiation efficiency to identify nine additional SEAMBHs from earlier RM-based mass measurements. We use a Bayesian analysis to determine the parameters of the new distance expression and the method uncertainties from the observed properties of the objects in the sample. The ratio of the newly measured distances to the standard cosmological ones has a mean scatter of 0.14 dex, indicating that SEAMBHs can be use as cosmological distance probes. With their high luminosity, long period of activity, and large numbers at high redshifts, SEAMBHs have a potential to extend the cosmic distance ladder beyond the range now explored by Type Ia supernovae.

  9. Using Multiwavelength Observations to Determine the Black Hole Mass and Accretion Rate in the Type 1 Seyfert Galaxy NGC 5548

    NASA Technical Reports Server (NTRS)

    Chiang, James; Blaes, Omer

    2002-01-01

    We model the spectral energy distribution of the type 1 Seyfert galaxy NGC 5548, fitting data from simultaneous optical, UV, and X-ray monitoring observations. We assume a geometry consisting of a hot central Comptonizing region surrounded by a thin accretion disk. The properties of the disk and the hot central region are determined by the feedback occurring between the hot Comptonizing region and thermal reprocessing in the disk that, along with viscous dissipation, provides the seed photons for the Comptonization process. The constraints imposed upon this model by the multiwavelength data allow us to derive limits on the central black hole mass, Mu is approximately or less than 2x10(exp 7) solar mass, the accretion rate, Mu is approximately or less than 2.5x10(exp 5) sq solar mass per year/Mu, and the radius of the transition region between the thin outer disk and the geometrically thick, hot inner region, is approximately 2-5x10(exp 14) cm.

  10. The Long-term Centimeter Variability of Active Galactic Nuclei: A New Relation between Variability Timescale and Accretion Rate

    NASA Astrophysics Data System (ADS)

    Park, Jongho; Trippe, Sascha

    2017-01-01

    We study the long-term (≈ 30 years) radio variability of 43 radio-bright active galactic nuclei (AGNs) by exploiting the database of the University of Michigan Radio Astronomy Observatory monitoring program. We model the periodograms (temporal power spectra) of the observed light curves as simple power-law noise (red noise, spectral power P(f)\\propto {f}-β ) using Monte Carlo simulations, taking into account windowing effects (red-noise leak, aliasing). The power spectra of 39 (out of 43) sources are in good agreement with the models, yielding a range in power spectral index (β) from ≈1 to ≈3. We fit a Gaussian function to each flare in a given light curve to obtain the flare duration. We discover a correlation between β and the median duration of the flares. We use the derivative of a light curve to obtain a characteristic variability timescale, which does not depend on the assumed functional form of the flares, incomplete fitting, and so on. We find that, once the effects of relativistic Doppler boosting are corrected for, the variability timescales of our sources are proportional to the accretion rate to the power of 0.25 ± 0.03 over five orders of magnitude in accretion rate, regardless of source type. We further find that modeling the periodograms of four of our sources requires the assumption of broken power-law spectra. From simulating light curves as superpositions of exponential flares, we conclude that strong overlap of flares leads to featureless simple power-law periodograms of AGNs at radio wavelengths in most cases. Based on observations obtained by the University of Michigan Radio Astronomy Observatory (UMRAO).

  11. Mapping the average AGN accretion rate in the SFR-M* plane for Herschel-selected galaxies at 0 < z ≤ 2.5

    NASA Astrophysics Data System (ADS)

    Delvecchio, I.; Lutz, D.; Berta, S.; Rosario, D. J.; Zamorani, G.; Pozzi, F.; Gruppioni, C.; Vignali, C.; Brusa, M.; Cimatti, A.; Clements, D. L.; Cooray, A.; Farrah, D.; Lanzuisi, G.; Oliver, S.; Rodighiero, G.; Santini, P.; Symeonidis, M.

    2015-05-01

    We study the relation of AGN accretion, star formation rate (SFR) and stellar mass (M*) using a sample of ≈8600 star-forming galaxies up to z = 2.5 selected with Herschel imaging in the GOODS and COSMOS fields. For each of them we derive SFR and M*, both corrected, when necessary, for emission from an active galactic nucleus (AGN), through the decomposition of their spectral energy distributions (SEDs). About 10 per cent of the sample are detected individually in Chandra observations of the fields. For the rest of the sample, we stack the X-ray maps to get average X-ray properties. After subtracting the X-ray luminosity expected from star formation and correcting for nuclear obscuration, we derive the average AGN accretion rate for both detected sources and stacks, as a function of M*, SFR and redshift. The average accretion rate correlates with SFR and with M*. The dependence on SFR becomes progressively more significant at z > 0.8. This may suggest that SFR is the original driver of these correlations. We find that average AGN accretion and star formation increase in a similar fashion with offset from the star-forming `main-sequence'. Our interpretation is that accretion on to the central black hole and star formation broadly trace each other, irrespective of whether the galaxy is evolving steadily on the main-sequence or bursting.

  12. Macro- and micromineral composition of fetal pigs and their accretion rates during fetal development.

    PubMed

    Mahan, D C; Watts, M R; St-Pierre, N

    2009-09-01

    be an increasing sow mineral requirement particularly with high-producing sows having larger litter sizes. Regression equations developed on an individual fetus basis for each macro- and micromineral from 45 d postcoitum to parturition could be used to model mineral accretions.

  13. 78 FR 48285 - Irish Potatoes Grown in Washington; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-08-08

    ... Agricultural Marketing Service 7 CFR Part 946 Irish Potatoes Grown in Washington; Decreased Assessment Rate... decreased the assessment rate established for the State of Washington Potato Committee (Committee) for the... potatoes handled. The Committee locally administers the marketing order for Irish potatoes grown...

  14. 77 FR 39150 - Avocados Grown in South Florida; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-07-02

    ... Agricultural Marketing Service 7 CFR Part 915 Avocados Grown in South Florida; Decreased Assessment Rate AGENCY... decreases the assessment rate established for the Avocado Administrative Committee (Committee) for the 2012... avocados handled. The Committee locally administers the marketing order which regulates the handling...

  15. 77 FR 21623 - Pears Grown in Oregon and Washington; Assessment Rate Decrease for Fresh Pears

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-04-11

    ... Service 7 CFR Part 927 Pears Grown in Oregon and Washington; Assessment Rate Decrease for Fresh Pears... decreased the assessment rate established for the Fresh Pear Committee (Committee) for the 2011-2012 and subsequent fiscal periods from $0.501 to $0.471 per standard box or equivalent of fresh winter pears...

  16. 76 FR 53811 - Pears Grown in Oregon and Washington; Assessment Rate Decrease for Processed Pears

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-08-30

    ... Service 7 CFR Part 927 Pears Grown in Oregon and Washington; Assessment Rate Decrease for Processed Pears...: This rule decreases the assessment rate established for the Processed Pear Committee (Committee) for the 2011-2012 and subsequent fiscal periods from $8.41 to $7.73 per ton of summer/fall processed...

  17. 77 FR 21624 - Pears Grown in Oregon and Washington; Assessment Rate Decrease for Processed Pears

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-04-11

    ... Agricultural Marketing Service 7 CFR Part 927 Pears Grown in Oregon and Washington; Assessment Rate Decrease for Processed Pears AGENCY: Agricultural Marketing Service, USDA. ACTION: Affirmation of interim rule..., an interim rule that decreased the assessment rate established for the Processed Pear...

  18. 76 FR 54075 - Pears Grown in Oregon and Washington; Assessment Rate Decrease for Fresh Pears

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-08-31

    ... Agricultural Marketing Service 7 CFR Part 927 Pears Grown in Oregon and Washington; Assessment Rate Decrease for Fresh Pears AGENCY: Agricultural Marketing Service, USDA. ACTION: Interim rule with request for comments. SUMMARY: This rule decreases the assessment rate established for the Fresh Pear...

  19. 78 FR 21521 - Pears Grown in Oregon and Washington; Assessment Rate Decrease for Processed Pears

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-04-11

    ... Agricultural Marketing Service 7 CFR Part 927 Pears Grown in Oregon and Washington; Assessment Rate Decrease for Processed Pears AGENCY: Agricultural Marketing Service, USDA. ACTION: Affirmation of interim rule..., an interim rule that decreased the assessment rate established for the Processed Pear...

  20. 77 FR 72197 - Pears Grown in Oregon and Washington; Assessment Rate Decrease for Processed Pears

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-12-05

    ... Service 7 CFR Part 927 Pears Grown in Oregon and Washington; Assessment Rate Decrease for Processed Pears...: This rule decreases the assessment rate established for the Processed Pear Committee (Committee) for the 2012-2013 and subsequent fiscal periods from $7.73 to $7.00 per ton of summer/fall processed...

  1. Sedimentation, accretion, and subsidence in marshes of Barataria Basin, Louisiana

    SciTech Connect

    Hatton, R.S.; DeLaune, R.D.; Patrick, W.H. Jr.

    1983-05-01

    Vertical accretion and sediment accumulation rates were determined from the distribution of /sup 137/Cs in cores collected from fresh water, intermediate, brackish, and salt marshes in the Barataria Basin, Louisiana. Vertical accretion rates vary from about 1.3 cm.yr/sup -1/ in levee areas to 0.7 in backmarshes. Mineral sediment content of the marsh soil profile decreased with distance from the coast. Except in natural levee areas, marsh accretion rates are less than subsidence measured by water level data, however this alone cannot account for observed land-loss patterns in the basin area.

  2. Lung cancer death rates fall, helping drive decrease in overall cancer death rates

    Cancer.gov

    The Annual Report to the Nation on the Status of Cancer, covering the period 1975–2010, showed death rates for lung cancer, which accounts for more than one in four cancer deaths, dropping at a faster pace than in previous years.

  3. PHOTOMETRIC DETERMINATION OF THE MASS ACCRETION RATES OF PRE-MAIN-SEQUENCE STARS. I. METHOD AND APPLICATION TO THE SN 1987A FIELD

    SciTech Connect

    De Marchi, Guido; Panagia, Nino; Romaniello, Martino E-mail: panagia@stsci.ed

    2010-05-20

    We have developed and successfully tested a new self-consistent method to reliably identify pre-main-sequence (PMS) objects actively undergoing mass accretion in a resolved stellar population, regardless of their age. The method does not require spectroscopy and combines broadband V and I photometry with narrowband H{alpha} imaging to (1) identify all stars with excess H{alpha} emission, (2) convert the excess H{alpha} magnitude into H{alpha} luminosity L(H{alpha}), (3) estimate the H{alpha} emission equivalent width, (4) derive the accretion luminosity L{sub acc} from L(H{alpha}), and finally (5) obtain the mass accretion rate M-dot{sub acc} from L{sub acc} and the stellar parameters (mass and radius). By selecting stars with an accuracy of 15% or better in the H{alpha} photometry, the statistical uncertainty on the derived M-dot{sub acc} is typically {approx_lt}17% and is dictated by the precision of the H{alpha} photometry. Systematic uncertainties, of up to a factor of 3 on the value of M-dot{sub acc}, are caused by our incomplete understanding of the physics of the accretion process and affect all determinations of the mass accretion rate, including those based on a spectroscopic H{alpha} line analysis. As an application of our method, we study the accretion process in a field of 9.16 arcmin{sup 2} around SN 1987A, using existing Hubble Space Telescope photometry. We identify as bona fide PMS stars a total of 133 objects with a H{alpha} excess above the 4{sigma} level and a median age of 13.5 Myr. Their median mass accretion rate of 2.6 x 10{sup -8} M{sub sun} yr{sup -1} is in excellent agreement with previous determinations based on the U-band excess of the stars in the same field, as well as with the value measured for G-type PMS stars in the Milky Way. The accretion luminosity of these PMS objects shows a strong dependence on their distance from a group of hot massive stars in the field and suggests that the ultraviolet radiation of the latter is rapidly

  4. Interpreting the γ Statistic in Phylogenetic Diversification Rate Studies: A Rate Decrease Does Not Necessarily Indicate an Early Burst

    PubMed Central

    Fordyce, James A.

    2010-01-01

    Background Phylogenetic hypotheses are increasingly being used to elucidate historical patterns of diversification rate-variation. Hypothesis testing is often conducted by comparing the observed vector of branching times to a null, pure-birth expectation. A popular method for inferring a decrease in speciation rate, which might suggest an early burst of diversification followed by a decrease in diversification rate is the γ statistic. Methodology Using simulations under varying conditions, I examine the sensitivity of γ to the distribution of the most recent branching times. Using an exploratory data analysis tool for lineages through time plots, tree deviation, I identified trees with a significant γ statistic that do not appear to have the characteristic early accumulation of lineages consistent with an early, rapid rate of cladogenesis. I further investigated the sensitivity of the γ statistic to recent diversification by examining the consequences of failing to simulate the full time interval following the most recent cladogenic event. The power of γ to detect rate decrease at varying times was assessed for simulated trees with an initial high rate of diversification followed by a relatively low rate. Conclusions The γ statistic is extraordinarily sensitive to recent diversification rates, and does not necessarily detect early bursts of diversification. This was true for trees of various sizes and completeness of taxon sampling. The γ statistic had greater power to detect recent diversification rate decreases compared to early bursts of diversification. Caution should be exercised when interpreting the γ statistic as an indication of early, rapid diversification. PMID:20668707

  5. Combining Hf-W Ages, Cooling Rates, and Thermal Models to Estimate the Accretion Time of Iron Meteorite Parent Bodies

    NASA Astrophysics Data System (ADS)

    Qin, L.; Dauphas, N.; Wadhwa, M.; Masarik, J.; Janney, P. E.

    2007-12-01

    The 182Hf-182W short-lived chronometer has been widely used to date metal-silicate differentiation processes in the early Solar System. However the presence of cosmogenic effects from exposure to GCR can potentially hamper the use of this system for chronology purposes (e.g. [1,2]). These effects must be corrected for in order to calculate metal-silicate differentiation ages. In this study, high-precision W isotope measurements are presented for 32 iron meteorites from 8 magmatic and 2 non-magmatic groups. Exposure ages and pre- atmospheric size estimates are available for most of these samples [3]. Our precision is better than or comparable to the currently most precise literature data and our results agree with previous work [4]. All magmatic irons have ɛ182W equal within error to or more negative than the Solar System initial derived from a CAI isochron [5]. Iron meteorites from the same magmatic groups show variations in ɛ182W. These are most easily explained by exposure to cosmic rays in space. A correction method was developed to estimate pre-exposure ɛ182W for individual iron meteorite groups. Metal-silicate differentiation in most iron meteorite parent bodies must have occurred within 2 Myr of formation of refractory inclusions. For the first time, we combine 182Hf-182W ages with parent body sizes inferred from metallographic cooling rates in a thermal model to constrain the accretion time of iron meteorite parent bodies. The estimated accretion ages are within 1.5 Myr for most magmatic groups, and could be as early as 0.2 Myr after CAI formation. This is consistent with the study of Bottke et al. [6] who argued that iron meteorite parent bodies could represent an early generation of planetesimals formed in the inner region of the Solar System. [1] Masarik J. (1997) EPSL 152, 181-185. [2] Markowski A. et al. (2006) EPSL 250,104-115. [3] Voshage H. (1984) EPSL 71, 181-194. [4] Markowski A. et al. (2006) EPSL 242, 1-15. [5] Kleine T. et al. (2005) GCA 69

  6. Weak-Line Quasars at High Redshift: Extremely High Accretion Rates or Anemic Broad-Line Regions?

    NASA Astrophysics Data System (ADS)

    Shemmer, Ohad; Trakhtenbrot, B.; Anderson, S. F.; Brandt, W. N.; Diamond-Stanic, A. M.; Fan, X.; Lira, P.; Netzer, H.; Plotkin, R. M.; Richards, G. T.; Schneider, D. P.; Strauss, M. A.

    2011-01-01

    We present Gemini-North K-band spectra of two representative members of the class of high-redshift quasars with exceptionally weak rest-frame ultraviolet emission lines (WLQs), SDSS J114153.34+021924.3 at z=3.55 and SDSS J123743.08+630144.9 at z=3.49. In both sources we detect an unusually weak broad Hβ line and we place tight upper limits on the strengths of their [O III] lines. Virial, Hβ-based black-hole mass determinations indicate normalized accretion rates of L/LEdd=0.4 for these sources, which is well within the range observed for typical quasars with similar luminosities and redshifts. We also present high-quality XMM-Newton imaging spectroscopy of SDSS J114153.34+021924.3 and find a hard-X-ray photon index of Γ=1.91+0.24-0.22which supports the virial L/LEdd determination in this source. Our results suggest that the weakness of the broad-emission lines in WLQs is not a consequence of an extreme continuum-emission source but instead due to abnormal broad-emission line region properties.

  7. Decreased neonatal jaundice readmission rate after implementing hyperbilirubinemia guidelines and universal screening for bilirubin.

    PubMed

    Alkalay, Arie L; Bresee, Catherine J; Simmons, Charles F

    2010-09-01

    Readmission rate for neonatal jaundice approximate 10 per 1000 live births. After applying hyperbilirubinemia guidelines and universal screening for bilirubin in term and near-term newborns, the readmission rate declined significantly from 24 to 3.7 per 1000 live births. Decreased readmission rate for neonatal jaundice may reduce kernicterus rate and health care costs. Further studies are necessary to explore these potential benefits.

  8. An in-depth study of a neutron star accreting at low Eddington rate: on the possibility of a truncated disc and an outflow

    NASA Astrophysics Data System (ADS)

    Degenaar, N.; Pinto, C.; Miller, J. M.; Wijnands, R.; Altamirano, D.; Paerels, F.; Fabian, A. C.; Chakrabarty, D.

    2017-01-01

    Due to observational challenges, our knowledge of low-level accretion flows around neutron stars is limited. We present NuSTAR, Swift and Chandra observations of the low-mass X-ray binary IGR J17062-6143, which has been persistently accreting at ≃0.1 per cent of the Eddington limit since 2006. Our simultaneous NuSTAR/Swift observations show that the 0.5-79 keV spectrum can be described by a combination of a power law with a photon index of Γ ≃ 2, a blackbody with a temperature of kTbb ≃ 0.5 keV (presumably arising from the neutron star surface) and disc reflection. Modelling the reflection spectrum suggests that the inner accretion disc was located at Rin ≳ 100 GM/c2 (≳225 km) from the neutron star. The apparent truncation may be due to evaporation of the inner disc into a radiatively-inefficient accretion flow, or due to the pressure of the neutron star magnetic field. Our Chandra gratings data reveal possible narrow emission lines near 1 keV that can be modelled as reflection or collisionally ionized gas, and possible low-energy absorption features that could point to the presence of an outflow. We consider a scenario in which this neutron star has been able to sustain its low accretion rate through magnetic inhibition of the accretion flow, which gives some constraints on its magnetic field strength and spin period. In this configuration, IGR J17062-6143 could exhibit a strong radio jet as well as a (propeller-driven) wind-like outflow.

  9. Magnetized accretion

    NASA Astrophysics Data System (ADS)

    Heyvaerts, J.

    This lecture reviews in simple terms the general subject of large scale magnetic field coupling to plasma flows in the vicinity of accreting compact stars. The relevant astrophysical phenomenology is summarized. Disk interaction with the magnetosphere of accreting stars is first discussed, in particular the structure of the magnetopause, its stability and plasma ejection in so-called propeller systems. The physics of accretion/ejection is then considered. Acceleration and focusing mechanisms of jets from accretion disks around compact stars or black holes and the question of the self-consistency of accretion and ejection are described. By contrast, small scale MHD turbulence in disks is not discussed, neither are accretion columns near the polar caps of neutron stars or white dwarfs. The reader is only assumed to have some basic knowledge of astrophysics and of fluid mechanics and electromagnetism.

  10. 77 FR 21842 - Dried Prunes Produced in California; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-04-12

    ... wage and salary expenses. The current excess funds carried forward along with the estimated interest... its assessment rate because of a substantial decrease in wage and salary expenses. The current...

  11. 78 FR 21518 - Apricots Grown in Designated Counties in Washington; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-04-11

    ... reduction in the manager's salary and the Committee's operating expenditures. DATES: Effective April 12... handled under the order. The decrease in the assessment rate reflects a reduction in the manager's...

  12. Constrains on Crustal Accretion Obtained from Cooling Rate Calculations with a Thermo-Mechanical Model of Fast-Spreading Mid-Ocean Ridges

    NASA Astrophysics Data System (ADS)

    Garrido, C. J.; Machetel, P.

    2012-12-01

    We have used a thermo-mechanical model designed to find steady-state solutions of motion and temperature with variable viscosity, heat diffusion, heat advection, hydrothermal cooling and latent heat release. Cases analogous to the "gabbro glacier" (G accretion structure), "sheeted sills" (S structure) and "mixed shallow and MTZ lenses" (M structure) were computed with and without sheeted dyke level modeling. The results show that thermal patterns near the ridge mainly depend on hydrothermal cooling. Several hydrothermal cooling cracking temperature have been used in order to illustrate the present scientific debate on the penetration depth and efficiency of hydrothermal flows. Second, higher cooling rates are obtained for the G structures. Third, whereas the subsolidus cooling rates, SCR, decrease monotonically with depth, the igneous cooling rates, ICR, display local minima at the merging levels of the upper and lower lenses. It appears that ICR reveal the near-ridge thermal and mechanical structures, whereas the lower value of the initial-to-closure temperature ranges used for SCR cause shifts farther from the ridge that reduces the ability of SCR to discriminate the ridge thermo-mechanical configuration. It also indicates that the common assumption that ICR and SCR should be similar is probably over-simplified. Finally, the cooling rates obtained bears the clear signature of the three intrusion hypothesis. The results show that numerical modeling of the lower crust's thermo-mechanical properties may provide new insights to discriminate among hypotheses related to G, M and S structures for fast-spreading ridges.; Thermal history obtained for the Gabro Glacier (top panels), Mixed shallow and MTZ zone (middle panels) and Sheeted Sills hypothesis (bottom panels)for the magma intrusion at ridge. Columns corresponds to various hydrothermal cooling and viscosity hypothesis.

  13. 78 FR 76031 - Sweet Cherries Grown in Designated Counties in Washington; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-12-16

    ... Marketing Service 7 CFR Part 923 Sweet Cherries Grown in Designated Counties in Washington; Decreased... rule that decreased the assessment rate established for the Washington Cherry Marketing Committee (Committee) for the 2013-2014 and subsequent fiscal periods from $0.18 to $0.15 per ton of sweet...

  14. 76 FR 41589 - Irish Potatoes Grown in Washington; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-07-15

    ... Service 7 CFR Part 946 Irish Potatoes Grown in Washington; Decreased Assessment Rate AGENCY: Agricultural... rate established for the State of Washington Potato Committee (Committee) for the 2011-2012 and subsequent fiscal periods from $0.0035 to $0.003 per hundredweight of potatoes handled. The Committee...

  15. 77 FR 71688 - Avocados Grown in South Florida; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-12-04

    ... Agricultural Marketing Service 7 CFR Part 915 Avocados Grown in South Florida; Decreased Assessment Rate AGENCY... the assessment rate established for the Avocado Administrative Committee (Committee) for the 2012-13 and subsequent fiscal periods from $0.37 to $0.25 per 55-pound bushel container of Florida...

  16. Magnetospheric accretion in EX Lupi

    NASA Astrophysics Data System (ADS)

    Abraham, Peter; Kospal, Agnes; Bouvier, Jerome

    2016-08-01

    We propose to observe EX Lup, the prototype of the EXor class of young eruptive stars, in order to understand how the accretion process works in the quiescent system. Here, we request 2.6 hours of telescope time on Spitzer, to carry out a mid-infrared photometric monitoring, which we will supplement with simultaneous ground-based optical and near-infrared data. The multi-wavelength light curves will allow us to reliably separate the effects of fluctuating accretion rate from the rotation of the star. By analyzing the variations of the accretion rate we will determine whether EX Lup accretes through a few stable accretion columns or several short-lived random accretion streams. With this campaign, EX Lup will become one of the T Tauri systems where the accretion process is best understood.

  17. Turbulent Distortion of Condensate Accretion

    NASA Technical Reports Server (NTRS)

    Hazoume, R.; Orou Chabi, J.; Johnson, J. A., III

    1997-01-01

    When a simple model for the relationship between the density-temperature fluctuation correlation and mean values is used, we determine that the rate of change of turbulent intensity can influence directly the accretion rate of droplets. Considerable interest exists in the accretion rate for condensates in nonequilibrium flow with icing and the potential role which reactant accretion can play in nonequilibrium exothermic reactant processes. Turbulence is thought to play an important role in such flows. It has already been experimentally determined that turbulence influences the sizes of droplets in the heterogeneous nucleation of supersaturated vapors. This paper addresses the issue of the possible influence of turbulence on the accretion rate of droplets.

  18. When can decreasing diversification rates be detected with molecular phylogenies and the fossil record?

    PubMed

    Liow, Lee Hsiang; Quental, Tiago B; Marshall, Charles R

    2010-12-01

    Traditionally, patterns and processes of diversification could only be inferred from the fossil record. However, there are an increasing number of tools that enable diversification dynamics to be inferred from molecular phylogenies. The application of these tools to new data sets has renewed interest in the question of the prevalence of diversity-dependent diversification. However, there is growing recognition that the absence of extinct species in molecular phylogenies may prevent accurate inferences about the underlying diversification dynamics. On the other hand, even though the fossil record provides direct data on extinct species, its incompleteness can also mask true diversification processes. Here, using computer-generated diversity-dependent phylogenies, we mimicked molecular phylogenies by eliminating extinct lineages. We also simulated the fossil record by converting the temporal axis into discrete intervals and imposing a variety of preservation processes on the lineages. Given the lack of reliable phylogenies for many fossil marine taxa, we also stripped away phylogenetic information from the computer-generated phylogenies. For the simulated molecular phylogenies, we examined the efficacy of the standard metric (the γ statistic) for identifying decreasing rates of diversification. We find that the underlying decreasing rate of diversification is detected only when the rate of change in the diversification rate is high, and if the molecular phylogeny happens to capture the diversification process as the equilibrium diversity is first reached or shortly thereafter. In contrast, estimating rates of diversification from the simulated fossil record captures the expected zero rate of diversification after equilibrium is reached under a wide range of preservation scenarios. The ability to detect the initial decreasing rate of diversification is lost as the temporal resolution of the fossil record drops and with a decreased quality of preservation. When the

  19. Chandra and MMT observations of low-mass black hole active galactic nuclei accreting at low rates in dwarf galaxies

    SciTech Connect

    Yuan, W.; Zhou, H.; Dou, L.; Dong, X.-B.; Wang, T.-G.; Fan, X.

    2014-02-10

    We report on Chandra X-ray observations of four candidate low-mass black hole (M {sub bh} ≲ 10{sup 6} M {sub ☉}) active galactic nuclei (AGNs) that have the estimated Eddington ratios among the lowest (∼10{sup –2}) found for this class. The aims are to validate the nature of their AGNs and to confirm the low Eddington ratios that are derived from the broad Hα line, and to explore this poorly studied regime in the AGN parameter space. Among them, two objects with the lowest significance of the broad lines are also observed with the Multi-Mirror Telescope, and the high-quality optical spectra taken confirm them as Seyfert 1 AGNs and as having small black hole masses. X-ray emission is detected from the nuclei of two of the galaxies, which is variable on timescales of ∼10{sup 3} s, whereas no significant (or only marginal at best) detection is found for the remaining two. The X-ray luminosities are on the order of 10{sup 41} erg s{sup –1} or even lower, on the order of 10{sup 40} erg s{sup –1} for non-detections, which are among the lowest regimes ever probed for Seyfert galaxies. The low X-ray luminosities, compared to their black hole masses derived from Hα, confirm their low accretion rates assuming typical bolometric corrections. Our results hint at the existence of a possibly large population of under-luminous low-mass black holes in the local universe. An off-nucleus ultra-luminous X-ray source in one of the dwarf galaxies is detected serendipitously, with a luminosity (6-9)× 10{sup 39} erg s{sup –1} in 2-10 keV.

  20. Clump Accretion in Supergiant Fast X-Ray Transients

    NASA Astrophysics Data System (ADS)

    Chase, Eve; Raymer, E.; Blondin, J. M.

    2014-01-01

    Supergiant Fast X-Ray Transients (SFXTs) are a subclass of High-Mass X-Ray Binaries that consist of a neutron star and OB supergiant donor star. These systems display short, bright x-ray flares lasting a few minutes to a few hours with luminosities reaching 1036 erg/s, several orders of magnitude larger than the quiescent luminosities of 1032 erg/s. The clumpy wind hypothesis has been proposed as a possible mechanism for these transient flares; in this model, a portion of the stellar wind from the donor star forms into clumps and is accreted onto the neutron star, inducing flares. We use high-resolution 3D hydrodynamic simulations to test the clumpy wind hypothesis, tracking the mass and angular momentum accretion rates to infer properties of the resulting x-ray flare and secular evolution of the neutron star rotation. Our results are significantly different from the predictions of Hoyle-Lyttleton Accretion (HLA) theory, which assume steady, laminar, axisymmetric flow. For example, an off-axis clump initiated with an impact parameter greater than the clump radius (for which HLA predicts no effect) produces a small spike in mass accretion and induces a long period of disk-like flow that dramatically reduces the accretion rate below the steady HLA value. The result is a brief, weak flare with a net decrease in total accreted mass compared with steady wind accretion accompanied by a substantial accretion of angular momentum.

  1. A mid-Holocene record of sediment dynamics and high resolution accretion rates in a coastal salt marsh from Northern California

    NASA Astrophysics Data System (ADS)

    Brown, L. N.; Holmquist, J. R.; MacDonald, G. M.

    2013-12-01

    Sediment accretion rates in coastal salt marshes are the critical determining factor in terms of ecosystem stability in the face of accelerated sea level rise (SLR), projected to rise by up to 1.4 m by 2100 in Southern California (National Research Council, 2012). However, high resolution studies of accretion rates in coastal salt marshes over the past several millennia have not yet been conducted for most of the US west coast. We collected multiple sediment records from small salt marshes surrounding Humboldt Bay, California. Due to this unique tectonic setting, many suspect cores from these marshes have evidence of coastal subsidence due to earthquake activity or large tsunami deposits (Jacoby et al., 1995). These records therefore are one of the best proxy measures for how salt marshes in California may respond to accelerated SLR. We analyzed all cores for magnetic susceptibility, % organic matter, and select cores for particle size. High resolution, millennial and centennial scale, radiocarbon dating for these sediment records reveals a detailed history of marsh accretion rates.

  2. Building bones in babies: can and should we exceed the human milk-fed infant's rate of bone calcium accretion?

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Increasing calcium absorption and bone calcium accretion to levels above those achieved by human milk-fed, full-term infants is possible with infant formulas. However, no data support such a goal or suggest that it is beneficial to short- or long-term bone health. Small differences in the bioavailab...

  3. Evolution of the luminosity function of quasar accretion disks

    NASA Technical Reports Server (NTRS)

    Caditz, David M.; Petrosian, Vahe; Wandel, Amri

    1991-01-01

    Using an accretion-disk model, accretion disk luminosities are calculated for a grid of black hole masses and accretion rates. It is shown that, as the black-hole mass increases with time, the monochromatic luminosity at a given frequency first increases and then decreases rapidly as this frequency is crossed by the Wien cutoff. The upper limit on the monochromatic luminosity, which is characteristic for a given epoch, constrains the evolution of quasar luminosities and determines the evolultion of the quasar luminosity function.

  4. JWH-018 in rhesus monkeys: differential antagonism of discriminative stimulus, rate-decreasing, and hypothermic effects.

    PubMed

    Rodriguez, Jesse S; McMahon, Lance R

    2014-10-05

    Several effects of the abused synthetic cannabinoid JWH-018 were compared to those of Δ9-tetrahydrocannabinol (Δ9-THC) in rhesus monkeys. JWH-018 (0.1 mg/kg i.v.) was established as a discriminative stimulus and rimonabant was used to examine mechanisms responsible for discrimination as well as operant response rate-decreasing and hypothermic effects. JWH-018 dose-dependently increased drug-lever responding (ED50=0.01 mg/kg) and decreased response rate (ED50=0.064 mg/kg). Among various cannabinoids, the relative potency for producing discriminative stimulus and rate-decreasing effects was the same: CP-55940=JWH-018>Δ9-THC=WIN-55212-2=JWH-073. The benzodiazepine agonist midazolam and the NMDA antagonist ketamine did not exert JWH-018 like discriminative stimulus effects up to doses that disrupted responding. JWH-018 and Δ9-THC decreased rectal temperature by 2.2 and 2.8°C, respectively; the doses decreasing temperature by 2°C were 0.21 and 1.14 mg/kg, respectively. Antagonism did not differ between JWH-018 and Δ9-THC, but did differ among effects. The apparent affinities of rimonabant calculated in the presence of JWH-018 and Δ9-THC were not different from each other for antagonism of discriminative stimulus effects (6.58 and 6.59, respectively) or hypothermic effects (7.08 and 7.19, respectively). Apparent affinity estimates are consistent with the same receptors mediating the discriminative stimulus and hypothermic effects of both JWH-018 and Δ9-THC. However, there was more limited and less orderly antagonism of rate-decreasing effects, suggesting that an additional receptor mechanism is involved in mediating the effects of cannabinoids on response rate. Overall, these results strongly suggest that JWH-018 and Δ9-THC act at the same receptors to produce several of their shared psychopharmacological effects.

  5. SUPERMASSIVE BLACK HOLES WITH HIGH ACCRETION RATES IN ACTIVE GALACTIC NUCLEI. VI. VELOCITY-RESOLVED REVERBERATION MAPPING OF THE Hβ LINE

    SciTech Connect

    Du, Pu; Lu, Kai-Xing; Hu, Chen; Qiu, Jie; Li, Yan-Rong; Huang, Ying-Ke; Wang, Jian-Min; Wang, Fang; Bai, Jin-Ming; Bian, Wei-Hao; Yuan, Ye-Fei; Ho, Luis C. E-mail: wangjm@ihep.ac.cn; Collaboration: SEAMBH Collaboration

    2016-03-20

    In the sixth of a series of papers reporting on a large reverberation mapping (RM) campaign of active galactic nuclei (AGNs) with high accretion rates, we present velocity-resolved time lags of Hβ emission lines for nine objects observed in the campaign during 2012–2013. In order to correct the line broadening caused by seeing and instruments before analyzing the velocity-resolved RM, we adopt the Richardson–Lucy deconvolution to reconstruct their Hβ profiles. The validity and effectiveness of the deconvolution are checked using Monte Carlo simulation. Five among the nine objects show clear dependence of the time delay on velocity. Mrk 335 and Mrk 486 show signatures of gas inflow whereas the clouds in the broad-line regions (BLRs) of Mrk 142 and MCG +06-26-012 tend to be radial outflowing. Mrk 1044 is consistent with having virialized motions. The lags of the remaining four are not velocity-resolvable. The velocity-resolved RM of super-Eddington accreting massive black holes (SEAMBHs) shows that they have diverse kinematics in their BLRs. Comparing with the AGNs with sub-Eddington accretion rates, we do not find significant differences in the BLR kinematics of SEAMBHs.

  6. Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. VI. Velocity-resolved Reverberation Mapping of the Hβ Line

    NASA Astrophysics Data System (ADS)

    Du, Pu; Lu, Kai-Xing; Hu, Chen; Qiu, Jie; Li, Yan-Rong; Huang, Ying-Ke; Wang, Fang; Bai, Jin-Ming; Bian, Wei-Hao; Yuan, Ye-Fei; Ho, Luis C.; Wang, Jian-Min; SEAMBH Collaboration

    2016-03-01

    In the sixth of a series of papers reporting on a large reverberation mapping (RM) campaign of active galactic nuclei (AGNs) with high accretion rates, we present velocity-resolved time lags of Hβ emission lines for nine objects observed in the campaign during 2012-2013. In order to correct the line broadening caused by seeing and instruments before analyzing the velocity-resolved RM, we adopt the Richardson-Lucy deconvolution to reconstruct their Hβ profiles. The validity and effectiveness of the deconvolution are checked using Monte Carlo simulation. Five among the nine objects show clear dependence of the time delay on velocity. Mrk 335 and Mrk 486 show signatures of gas inflow whereas the clouds in the broad-line regions (BLRs) of Mrk 142 and MCG +06-26-012 tend to be radial outflowing. Mrk 1044 is consistent with having virialized motions. The lags of the remaining four are not velocity-resolvable. The velocity-resolved RM of super-Eddington accreting massive black holes (SEAMBHs) shows that they have diverse kinematics in their BLRs. Comparing with the AGNs with sub-Eddington accretion rates, we do not find significant differences in the BLR kinematics of SEAMBHs.

  7. 77 FR 21841 - Pistachios Grown in California, Arizona, and New Mexico; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-04-12

    ... / Thursday, April 12, 2012 / Rules and Regulations#0;#0; ] DEPARTMENT OF AGRICULTURE Agricultural Marketing Service 7 CFR Part 983 Pistachios Grown in California, Arizona, and New Mexico; Decreased Assessment Rate...: The Department of Agriculture (USDA) is adopting, as a final rule, without change, an interim...

  8. 76 FR 60361 - Pistachios Grown in California, Arizona, and New Mexico; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-09-29

    ... Agricultural Marketing Service 7 CFR Part 983 Pistachios Grown in California, Arizona, and New Mexico; Decreased Assessment Rate AGENCY: Agricultural Marketing Service, USDA. ACTION: Interim rule with request... per pound of assessed weight pistachios. The Committee locally administers the marketing order...

  9. Similar rates of decrease of persistent, hydrophobic and particle-reactive contaminants in riverine systems

    USGS Publications Warehouse

    Van Metre, Peter C.; Wilson, Jennifer T.; Callender, Edward; Fuller, Christopher C.

    1998-01-01

    Although it is well-known that concentrations of anthropogenic radionuclides and organochlorine compounds in aquatic systems have decreased since their widespread release has stopped in the United States, the magnitude and variability of rates of decrease are not well-known. Paleolimnological studies of reservoirs provide a tool for evaluating these long-term trends in riverine systems. Rates of decrease from the 1960s to the 1990s of 137Cs, PCBs, and total DDT in dated sediment cores from 11 reservoirs in the eastern and central United States were modeled using first-order rate models. Mean half-times of 10.0 (±2.5), 9.5 (±2.2), and 13 (±5.8) yr for decay-corrected 137Cs, PCBs, and total DDT, respectively, are surprisingly similar. Similar rates of decrease in a few reservoirs are also demonstrated for chlordane and lead. Conceptual and simple mathematical models relating two soil distributions of 137Cs to trends in the cores provide insight into differences in trends between watersheds with different land uses and suggest that trends are controlled by erosion, transport, mixing, and deposition of sediments. These results, supported by similar trends reported for other settings and environmental media, could provide an estimate of the decadal response time of riverine systems to changes in the regulation of other persistent hydrophobic or particle-reactive contaminants.

  10. 78 FR 1130 - Domestic Dates Produced or Packed in Riverside County, CA; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-01-08

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF AGRICULTURE Agricultural Marketing Service 7 CFR Part 987 Domestic Dates Produced or Packed in Riverside County, CA; Decreased Assessment Rate AGENCY: Agricultural Marketing Service, USDA. ACTION: Interim rule with...

  11. 78 FR 54147 - Domestic Dates Produced or Packed in Riverside County, California; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-09-03

    ...; Decreased Assessment Rate AGENCY: Agricultural Marketing Service, USDA. ACTION: Interim rule with request... as the ``order.'' The order is effective under the Agricultural Marketing Agreement Act of 1937, as... Regulatory Flexibility Act (RFA) (5 U.S.C. 601-612), the Agricultural Marketing Service (AMS) has...

  12. 76 FR 53813 - Dried Prunes Produced in California; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-08-30

    ... Agricultural Marketing Service 7 CFR Part 993 Dried Prunes Produced in California; Decreased Assessment Rate AGENCY: Agricultural Marketing Service, USDA. ACTION: Interim rule with request for comments. SUMMARY... order is effective under the Agricultural Marketing Agreement Act of 1937, as amended (7 U.S.C....

  13. 78 FR 21520 - Sweet Cherries Grown in Designated Counties in Washington; Decreased Assessment Rate

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-04-11

    ... Agricultural Marketing Service 7 CFR Part 923 Sweet Cherries Grown in Designated Counties in Washington..., an interim rule that decreased the assessment rate established for the Washington Cherry Marketing... cherries handled. The Committee locally administers the marketing order for sweet cherries grown...

  14. Accretion rate of extraterrestrial particles determined from osmium isotope systematics of pacific pelagic clay and manganese nodules

    SciTech Connect

    Esser, B.K.; Turekian, K.K. )

    1988-06-01

    Pelagic clay and Mn nodules from DOMES sites in the North Pacific and a varved glacial lake deposit from Connecticut were analyzed for Os concentration and isotopic composition by isotope-dilution secondary ion mass spectrometry after treatment by NiS fusion of oxalic acid leaching. Bulk pelagic clay from DOMES site C has {sup 187}Os/{sup 186}Os = 6.5 and Os = 0.14 ng/g. Oxalic acid leaches of this same sediment and of Mn nodules for DOMES sites A and C have more radiogenic {sup 187}Os/{sup 186}Os ratios which average 8.3. Bulk glacial Lake Hitchcock sediment has {sup 187}Os/{sup 186}Os = 12.5 and Os = 0.06 ng/g. The total Os flux to North Pacific pelagic clay is 7 to 10 ng Os/cm{sup 2}/10{sup 6} y. Lake Hitchcock sediment provides an integrated value for the local crustal {sup 187}Os/{sup 186}Os ratio. The oxalic acid leaches are assumed to attack hydrogenous phases selectively. A simple model in which the only sources of Os to the ocean are continental crust with the isotopic composition of Lake Hitchcock and extraterrestrial particles with {sup 187}Os/{sup 186}Os = 1.1 results in a cosmic flux of osmium to the sediment of 4.9 ng Os/cm{sup 2}/10{sub 6} y of which 20% is hydrogenous. A model in which the sources of Os to the ocean are continental crust with an {sup 187}Os/{sup 186}Os ratio of 30, oceanic mantle or crust with {sup 187}Os/{sup 186}Os = 1.04 and extraterrestrial particles with {sup 187}Os/{sup 186}Os = 1.1 results in a cosmic flux of Os to the sediment of 5.7 ng Os/cm{sup 2}/10{sup 6} y of which none is hydrogenous. These extraterrestrial Os fluxes correspond to maximum C-1 chondrite accretion rates of between 4.9 {times} 10{sub 4} and 5.6 {times}10{sub 4} tonnes/y.

  15. A decreased metabolic clearance rate of aldosterone in benign essential hypertension

    PubMed Central

    Nowaczynski, W.; Kuchel, O.; Genest, J.

    1971-01-01

    Aldosterone secretion rate, metabolic clearance rate, and/or plasma concentration were determined in 16 patients with benign, uncomplicated essential hypertension and compared with those of control subjects. The mean metabolic clearance rate of aldosterone in 10 patients was significantly (P < 0.001) lower (mean 867 liters of plasma/day per m2 ±270 SD) than in a group of 7 healthy subjects (mean 1480 liters/day per m2 ±265 SD). Secretion rates in 13 patients (including the 10 already mentioned) tended to be low (83 ±43 vs. 109 ±54 μg/day) and plasma concentrations tended to be high (13.6 ±4.6 vs. 7.5 ±4.8 ng/100 ml), but neither of these differences was statistically significant. The lower metabolic clearance rate could account for elevated plasma concentrations of aldosterone even when the secretion rate is normal or low. Measurement of secretion rate or urinary excretion only is therefore insufficient to establish the presence and/or mode of evolution of hyperaldosteronism. Failure of the aldosterone secretion to adapt fully to a decreased aldosterone metabolic clearance rate (MCR) could explain the state of relative hyperaldosteronism in patients with benign essential hypertension, even when the secretion rate and the urinary excretion rate are in the normal range. PMID:5116208

  16. Decreased growth rate of P. falciparum blood stage parasitemia with age in a holoendemic population.

    PubMed

    Pinkevych, Mykola; Petravic, Janka; Chelimo, Kiprotich; Vulule, John; Kazura, James W; Moormann, Ann M; Davenport, Miles P

    2014-04-01

    In malaria holoendemic settings, decreased parasitemia and clinical disease is associated with age and cumulative exposure. The relative contribution of acquired immunity against various stages of the parasite life cycle is not well understood. In particular, it is not known whether changes in infection dynamics can be best explained by decreasing rates of infection, or by decreased growth rates of parasites in blood. Here, we analyze the dynamics of Plasmodium falciparum infection after treatment in a cohort of 197 healthy study participants of different ages. We use both polymerase chain reaction (PCR) and microscopy detection of parasitemia in order to understand parasite growth rates and infection rates over time. The more sensitive PCR assay detects parasites earlier than microscopy, and demonstrates a higher overall prevalence of infection than microscopy alone. The delay between PCR and microscopy detection is significantly longer in adults compared with children, consistent with slower parasite growth with age. We estimated the parasite multiplication rate from delay to PCR and microscopy detections of parasitemia. We find that both the delay between PCR and microscopy infection as well as the differing reinfection dynamics in different age groups are best explained by a slowing of parasite growth with age.

  17. Leptin decreases heart rate associated with increased ventricular repolarization via its receptor.

    PubMed

    Lin, Yen-Chang; Huang, Jianying; Hileman, Stan; Martin, Karen H; Hull, Robert; Davis, Mary; Yu, Han-Gang

    2015-11-15

    Leptin has been proposed to modulate cardiac electrical properties via β-adrenergic receptor activation. The presence of leptin receptors and adipocytes in myocardium raised a question as to whether leptin can directly modulate cardiac electrical properties such as heart rate and QT interval via its receptor. In this work, the role of local direct actions of leptin on heart rate and ventricular repolarization was investigated. We identified the protein expression of leptin receptors at cell surface of sinus node, atrial, and ventricular myocytes isolated from rat heart. Leptin at low doses (0.1-30 μg/kg) decreased resting heart rate; at high doses (150-300 μg/kg), leptin induced a biphasic effect (decrease and then increase) on heart rate. In the presence of high-dose propranolol (30 mg/kg), high-dose leptin only reduced heart rate and sometimes caused sinus pauses and ventricular tachycardia. The leptin-induced inhibition of resting heart rate was fully reversed by leptin antagonist. Leptin also increased heart rate-corrected QT interval (QTc), and leptin antagonist did not. In isolated ventricular myocytes, leptin (0.03-0.3 μg/ml) reversibly increased the action potential duration. These results supported our hypothesis that in addition to indirect pathway via sympathetic tone, leptin can directly decrease heart rate and increase QT interval via its receptor independent of β-adrenergic receptor stimulation. During inhibition of β-adrenergic receptor activity, high concentration of leptin in myocardium can cause deep bradycardia, prolonged QT interval, and ventricular arrhythmias.

  18. Prostate cancer incidence rates have started to decrease in central Italy.

    PubMed

    Crocetti, Emanuele; Ciatto, Stefano; Buzzoni, Carlotta; Zappa, Marco

    2010-01-01

    The widespread use of prostate-specific antigen (PSA) testing has dramatically changed the epidemiology of prostate cancer. Growing incidence rates have been documented in almost all western countries following the increased usage of PSA screening. In the United States after a period of huge increase in incidence, rates have decreased to values lower than those of the pre-PSA era. Similar changes have been documented also in the area of the Tuscany Cancer Registry, central Italy, where prostate cancer incidence rates doubled from the early 1990s to 2003 and afterwards decreased. This is the first evidence, to our knowledge, of a decline in prostate cancer incidence in Italy following the screening-related increase.

  19. Lacustrine responses to decreasing wet mercury deposition rates: results from a case study in northern Minnesota

    USGS Publications Warehouse

    Brigham, Mark E.; Sandheinrich, Mark B.; Gay, David A.; Maki, Ryan P.; Krabbenhoft, David P.; Wiener, James G.

    2014-01-01

    We present a case study comparing metrics of methylmercury (MeHg) contamination for four undeveloped lakes in Voyageurs National Park to wet atmospheric deposition of mercury (Hg), sulfate (SO4–2), and hydrogen ion (H+) in northern Minnesota. Annual wet Hg, SO4–2, and H+ deposition rates at two nearby precipitation monitoring sites indicate considerable decreases from 1998 to 2012 (mean decreases of 32, 48, and 66%, respectively). Consistent with decreases in the atmospheric pollutants, epilimnetic aqueous methylmercury (MeHgaq) and mercury in small yellow perch (Hgfish) decreased in two of four lakes (mean decreases of 46.5% and 34.5%, respectively, between 2001 and 2012). Counter to decreases in the atmospheric pollutants, MeHgaq increased by 85% in a third lake, whereas Hgfish increased by 80%. The fourth lake had two disturbances in its watershed during the study period (forest fire; changes in shoreline inundation due to beaver activity); this lake lacked overall trends in MeHgaq and Hgfish. The diverging responses among the study lakes exemplify the complexity of ecosystem responses to decreased loads of atmospheric pollutants.

  20. Diversity of burial rates in convergent settings decreased as Earth aged.

    PubMed

    Nicoli, Gautier; Moyen, Jean-François; Stevens, Gary

    2016-05-24

    The evolution and the growth of the continental crust is inextricably linked to the evolution of Earth's geodynamic processes. The detrital zircon record within the continental crust, as well as the isotopic composition of this crust, indicates that the amount of juvenile felsic material decreased with time and that in geologically recent times, the generation of new crust is balanced by recycling of the crust back into the mantle within subduction zones. However it cannot always have been so; yet the nature of the crust and the processes of crustal reworking in the Precambrian Earth are not well constrained. Here we use both detrital zircon ages and metamorphic pressure-temperature-time (P-T-t) information from metasedimentary units deposited in proposed convergent settings from Archaean, Proterozoic and Phanerozoic terrains to characterize the evolution of minimum estimates of burial rate (km.Ma(-1)) as a function of the age of the rocks. The demonstrated decrease in burial rate correlates positively with a progressive decrease in the production of juvenile felsic crust in the Archaean and Proterozoic. Burial rates are also more diverse in the Archaean than in modern times. We interpret these features to reflect a progressive decrease in the diversity of tectonic processes from Archaean to present, coupled with the emergence of the uniquely Phanerozoic modern-style collision.

  1. Diversity of burial rates in convergent settings decreased as Earth aged

    PubMed Central

    Nicoli, Gautier; Moyen, Jean-François; Stevens, Gary

    2016-01-01

    The evolution and the growth of the continental crust is inextricably linked to the evolution of Earth’s geodynamic processes. The detrital zircon record within the continental crust, as well as the isotopic composition of this crust, indicates that the amount of juvenile felsic material decreased with time and that in geologically recent times, the generation of new crust is balanced by recycling of the crust back into the mantle within subduction zones. However it cannot always have been so; yet the nature of the crust and the processes of crustal reworking in the Precambrian Earth are not well constrained. Here we use both detrital zircon ages and metamorphic pressure-temperature-time (P-T-t) information from metasedimentary units deposited in proposed convergent settings from Archaean, Proterozoic and Phanerozoic terrains to characterize the evolution of minimum estimates of burial rate (km.Ma−1) as a function of the age of the rocks. The demonstrated decrease in burial rate correlates positively with a progressive decrease in the production of juvenile felsic crust in the Archaean and Proterozoic. Burial rates are also more diverse in the Archaean than in modern times. We interpret these features to reflect a progressive decrease in the diversity of tectonic processes from Archaean to present, coupled with the emergence of the uniquely Phanerozoic modern-style collision. PMID:27216133

  2. Diversity of burial rates in convergent settings decreased as Earth aged

    NASA Astrophysics Data System (ADS)

    Nicoli, Gautier; Moyen, Jean-François; Stevens, Gary

    2016-05-01

    The evolution and the growth of the continental crust is inextricably linked to the evolution of Earth’s geodynamic processes. The detrital zircon record within the continental crust, as well as the isotopic composition of this crust, indicates that the amount of juvenile felsic material decreased with time and that in geologically recent times, the generation of new crust is balanced by recycling of the crust back into the mantle within subduction zones. However it cannot always have been so; yet the nature of the crust and the processes of crustal reworking in the Precambrian Earth are not well constrained. Here we use both detrital zircon ages and metamorphic pressure-temperature-time (P-T-t) information from metasedimentary units deposited in proposed convergent settings from Archaean, Proterozoic and Phanerozoic terrains to characterize the evolution of minimum estimates of burial rate (km.Ma‑1) as a function of the age of the rocks. The demonstrated decrease in burial rate correlates positively with a progressive decrease in the production of juvenile felsic crust in the Archaean and Proterozoic. Burial rates are also more diverse in the Archaean than in modern times. We interpret these features to reflect a progressive decrease in the diversity of tectonic processes from Archaean to present, coupled with the emergence of the uniquely Phanerozoic modern-style collision.

  3. Interleukin-6 impairs chronotropic responsiveness to cholinergic stimulation and decreases heart rate variability in mice.

    PubMed

    Hajiasgharzadeh, Khalil; Mirnajafi-Zadeh, Javad; Mani, Ali R

    2011-12-30

    Heart rate variability is reduced in several clinical settings associated with systemic inflammation. The underlying mechanism of decreased heart rate variability during systemic inflammation is unknown. It appears that the inflammatory cytokines might play a role, since epidemiologic studies has shown that circulating levels of interleukine-6 (IL-6) correlate significantly with indexes of depressed heart rate variability in various clinical conditions. The present investigation was carried out to study the peripheral and central effects of IL-6 on heart rate dynamic in mice. Adult male BALB/c mice were used in the study. RT-PCR was performed to study the expression of IL-6 receptor in mouse atrial and the results showed that gp130 mRNA was detectable in the atrium. The effect of IL-6 was also studies on chronotropic responsiveness of isolated atria to adrenergic and cholinergic stimulations. Incubation of isolated atria with 10 ng/ml of IL-6 was associated with a significant hypo-responsiveness to cholinergic stimulation (log IC₅₀ of carbacholine changed from -6.26±0.10 in controls to -5.59±0.19 following incubation with IL-6, P<0.05). The chronotropic responsiveness to adrenergic stimulation was identical with or without incubation with IL-6. Intraperitoneal injection of IL-6 (200 ng/mouse) was associated with a significant decrease in heart rate variability parameters (SDNN, SD1, and SD2). While intracerebroventricular injection of IL-6 (50 ng/mouse) had no significant effect on heart rate variability parameters. These data are in line with a peripheral role for IL-6 in the genesis of decreased heart rate variability during systemic inflammation.

  4. Temporal and Spatial Variations in Volcanic Accretion Over the Past Few 100 Years on the EPR Axis at Superfast Spreading rates at 17 to 18 deg S

    NASA Astrophysics Data System (ADS)

    Rubin, K. H.; Sinton, J. M.; Bergmanis, E. C.

    2008-12-01

    Ridges at fast to superfast spreading rates are excellent locations to study temporal and spatial variations in volcanic construction because magma supply and eruption rates are high, and because much of the volcanic accretion occurs within a narrow (≤1-2 km) zone at the rise axis. This presentation will summarize temporal and spatial variations in volcanic accretion over the past few hundred years at 17.5° to 18.5°S on the East Pacific Rise using geological observations made by submersible and other methods, as well shore-based petrological, geochemical and radiometric analyses of samples recovered from mapped lava flow fields along the ridge axis. Collectively they demonstrate that the styles and rates of volcanic accretion can vary substantially both within and between volcanic segments over relatively short timescales. Mapped lavas indicate that single eruptions can span small structural discontinuities (ridge axis offsets). Compositional shifts accompany these offsets, indicating segmentation or zonation of the magma chamber that fed them. Similar observations have been made in analogous eruption sequences at subaerial rift zone volcanoes. U-series disequilibria, radiogenic isotopes and major and trace element compositions within and between single mapped lava flows indicate that magma chambers are open and poorly mixed over the timescale of volcanic repose (decades to ~1 century). Within flow compositional variations along axis can be used to test for magma emplacement by lateral injection from a central reservoir near inflated segment centers versus near vertical emplacement from magma bodies distributed along the axis. The latter best describes observations of lava flows at both 17.5°S and 18.5°S. Volcanic accretion occurs along a volcanically robust, inflated ridge segment at 17.5°S, whereas at 18.5°S the most recent eruptions have formed small, discontinuous lava shields and pillow mounds on the floor of a deep, few hundred year old graben that

  5. RADIATIVELY EFFICIENT MAGNETIZED BONDI ACCRETION

    SciTech Connect

    Cunningham, Andrew J.; Klein, Richard I.; McKee, Christopher F.; Krumholz, Mark R.; Teyssier, Romain

    2012-01-10

    We have carried out a numerical study of the effect of large-scale magnetic fields on the rate of accretion from a uniform, isothermal gas onto a resistive, stationary point mass. Only mass, not magnetic flux, accretes onto the point mass. The simulations for this study avoid complications arising from boundary conditions by keeping the boundaries far from the accreting object. Our simulations leverage adaptive refinement methodology to attain high spatial fidelity close to the accreting object. Our results are particularly relevant to the problem of star formation from a magnetized molecular cloud in which thermal energy is radiated away on timescales much shorter than the dynamical timescale. Contrary to the adiabatic case, our simulations show convergence toward a finite accretion rate in the limit in which the radius of the accreting object vanishes, regardless of magnetic field strength. For very weak magnetic fields, the accretion rate first approaches the Bondi value and then drops by a factor of {approx}2 as magnetic flux builds up near the point mass. For strong magnetic fields, the steady-state accretion rate is reduced by a factor of {approx}0.2 {beta}{sup 1/2} compared to the Bondi value, where {beta} is the ratio of the gas pressure to the magnetic pressure. We give a simple expression for the accretion rate as a function of the magnetic field strength. Approximate analytic results are given in the Appendices for both time-dependent accretion in the limit of weak magnetic fields and steady-state accretion for the case of strong magnetic fields.

  6. Asian ethnicity is associated with decreased pregnancy rates following intrauterine insemination.

    PubMed

    Lamb, Julie D; Huddleston, Heather G; Purcell, Karen J; Modan, Aisha; Farsani, Taraneh T; Dingeldein, Margaret A; Vittinghoff, Eric; Fujimoto, Victor Y

    2009-08-01

    Asian ethnicity has been associated with decreased pregnancy outcomes in patients undergoing IVF. The objective of this study was to determine if a difference exists in pregnancy rates between Asian and Caucasian patients undergoing intrauterine insemination (IUI). A retrospective cohort of Asian and Caucasian patients treated with IUI between December 2002 and 2006 was analysed, including 2327 IUI cycles among 814 patients. Baseline characteristics were similar between Asian and Caucasian women. A significantly greater proportion of Asians (43.9%) presented for treatment after more than 2 years of infertility compared with Caucasians (24.6%) (P < 0.0001). Unadjusted analysis showed a trend towards decreased pregnancy rates associated with Asian ethnicity (odds ratio (OR) 0.71, 95% CI 0.50-1.01, not significant). Age, stimulation protocol, differences in gravity and parity, and duration of infertility did not account for this difference (adjusted OR 0.68, 95% CI 0.47-0.98, P = 0.039). Asian ethnicity is associated with lower pregnancy rates in IUI treatment. The increased duration of infertility in Asians does not explain the reduced pregnancy rates.

  7. Does obtaining an initial magnetic resonance imaging decrease the reamputation rates in the diabetic foot?

    PubMed Central

    Jbara, Marlena; Gokli, Ami; Beshai, Sally; Lesser, Martin L.; Hanna, Shirley; Lin, Cheryl; Zeb, Annie

    2016-01-01

    Objective Diabetes mellitus (DM) through its over glycosylation of neurovascular structures and resultant peripheral neuropathy continues to be the major risk factor for pedal amputation. Repetitive trauma to the insensate foot results in diabetic foot ulcers, which are at high risk to develop osteomyelitis. Many patients who present with diabetic foot complications will undergo one or more pedal amputations during the course of their disease. The purpose of this study was to determine if obtaining an initial magnetic resonance imaging (MRI), prior to the first amputation, is associated with a decreased rate of reamputation in the diabetic foot. Our hypothesis was that the rate of reamputation may be associated with underutilization of obtaining an initial MRI, useful in presurgical planning. This study was designed to determine whether there was an association between the reamputation rate in diabetic patients and utilization of MRI in the presurgical planning and prior to initial forefoot amputations. Methods Following approval by our institutional review board, our study design consisted of a retrospective cohort analysis of 413 patients at Staten Island University Hospital, a 700-bed tertiary referral center between 2008 and 2013 who underwent an initial great toe (hallux) amputation. Of the 413 patients with a hallux amputation, there were 368 eligible patients who had a history of DM with documented hemoglobin A1c (HbA1c) within 3 months of the initial first ray (hallux and first metatarsal) amputation and available radiographic data. Statistical analysis compared the incidence rates of reamputation between patients who underwent initial MRI and those who did not obtain an initial MRI prior to their first amputation. The reamputation rate was compared after adjustment for age, gender, ethnicity, HbA1c, cardiovascular disease, hypoalbuminemia, smoking, body mass index, and prior antibiotic treatment. Results The results of our statistical analysis failed to

  8. How will induced seismicity in Oklahoma respond to decreased saltwater injection rates?

    PubMed

    Langenbruch, Cornelius; Zoback, Mark D

    2016-11-01

    In response to the marked number of injection-induced earthquakes in north-central Oklahoma, regulators recently called for a 40% reduction in the volume of saltwater being injected in the seismically active areas. We present a calibrated statistical model that predicts that widely felt M ≥ 3 earthquakes in the affected areas, as well as the probability of potentially damaging larger events, should significantly decrease by the end of 2016 and approach historic levels within a few years. Aftershock sequences associated with relatively large magnitude earthquakes that occurred in the Fairview, Cherokee, and Pawnee areas in north-central Oklahoma in late 2015 and 2016 will delay the rate of seismicity decrease in those areas.

  9. How will induced seismicity in Oklahoma respond to decreased saltwater injection rates?

    PubMed Central

    Langenbruch, Cornelius; Zoback, Mark D.

    2016-01-01

    In response to the marked number of injection-induced earthquakes in north-central Oklahoma, regulators recently called for a 40% reduction in the volume of saltwater being injected in the seismically active areas. We present a calibrated statistical model that predicts that widely felt M ≥ 3 earthquakes in the affected areas, as well as the probability of potentially damaging larger events, should significantly decrease by the end of 2016 and approach historic levels within a few years. Aftershock sequences associated with relatively large magnitude earthquakes that occurred in the Fairview, Cherokee, and Pawnee areas in north-central Oklahoma in late 2015 and 2016 will delay the rate of seismicity decrease in those areas. PMID:28138533

  10. Using Shoulder Straps Decreases Heart Rate Variability and Salivary Cortisol Concentration in Swedish Ambulance Personnel

    PubMed Central

    Karlsson, Kåre J.; Niemelä, Patrik H.; Jonsson, Anders R.; Törnhage, Carl-Johan A.

    2015-01-01

    Background Previous research has shown that paramedics are exposed to risks in the form of injuries to the musculoskeletal system. In addition, there are studies showing that they are also at increased risk of cardiovascular disease, cancer, and psychiatric diseases, which can partly be explained by their constant exposure to stress. The aim of this study is to evaluate whether the use of shoulder straps decreases physical effort in the form of decreased heart rate and cortisol concentration. Methods A stretcher with a dummy was carried by 20 participants for 400 m on two occasions, one with and one without the shoulder straps. Heart rate was monitored continuously and cortisol samples were taken at intervals of 0 minutes, 15 minutes, 30 minutes, 45 minutes, and 60 minutes. Each participant was her or his own control. Results A significant decrease in heart rate and cortisol concentration was seen when shoulder straps were used. The median values for men (with shoulder straps) at 0 minutes was 78 bpm/21.1 nmol/L (heart rate/cortisol concentration), at 15 minutes was 85 bpm/16.9 nmol/L, and at 60 minutes was 76 bpm/15.7 nmol/L; for men without shoulder straps, these values were 78 bpm/21.9 nmol/L, 93 bpm/21.9 nmol/L, and 73 bpm/20.5 nmol/L. For women, the values were 85 bpm/23.3 nmol/L, 92 bpm/20.8 nmol/L, and 70 bpm/18.4 nmol/L and 84 bpm/32.4 nmol/L, 100 bpm/32.5 nmol/L, and 75 bpm/25.2 nmol/L, respectively. Conclusion The use of shoulder straps decreases measurable physical stress and should therefore be implemented when heavy equipment or a stretcher needs to be carried. An easy way to ensure that staff use these or similar lifting aids is to provide them with personalized, well-adapted shoulder straps. Another better option would be to routinely sewn these straps into the staff's personal alarm jackets so they are always in place and ready to be used. PMID:27014488

  11. Igneous Cooling Rate constraints on the Accretion of the lower Oceanic Crust in Mid-ocean Ridges: Insights from a new Thermo-mechanical Model

    NASA Astrophysics Data System (ADS)

    Garrido, C. J.; Machetel, P.

    2005-12-01

    We report the results of a new thermo-mechanical model of crustal flow beneath fast spreading mid-ocean ridges to investigate both the effect of deep, near off-axis hydrothermal convection on the thermal structure of the magma chamber and the role of variable number of melt intrusions on the accretion of the oceanic crust. In our model the melt is injected at the center of the axial magma chamber with a 'needle' with adjustable porosity at different depths allowing the simulation of different arrangements of melt injection and supply within the magma chamber. Conversely to previous models, the shape of the magma chamber -defined as the isotherm where 95% solidification of the melt occurs- is not imposed but computed from the steady state reached by the thermal field considering the heat diffusion and advection and the latent heat of crystallization. The motion equation is solved for a temperature and phase dependent viscosity. The thermal diffusivity is also dependent on temperature and depth, with a higher diffusivity in the upper plutonic crust to account for more efficient hydrothermal cooling at these crustal levels. In agreement with previous non-dynamic thermal models, our results show that near, deep off-axis hydrothermal circulation strongly affects the shape of the axial magma by tightening isotherms in the upper half of the plutonic oceanic crust where hydrothermal cooling is more efficient. Different accretion modes have however little effect on the shape of the magma chamber, but result in variable arrangements of flow lines ranging from tent-shape in a single-lens accretion scenario to sub-horizontal in "sheeted-sill" intrusion models. For different intrusion models, we computed the average Igneous Cooling Rates (ICR) of gabbros by dividing the crystallization temperature interval of gabbros by the integrated time, from the initial intrusion to the point where it crossed the 950 °C isotherm where total solidification of gabbro occurs, along individual

  12. In vitro thrombogenesis resulting from decreased shear rate and blood coagulability.

    PubMed

    Maruyama, Osamu; Kosaka, Ryo; Nishida, Masahiro; Yamane, Takashi; Tatsumi, Eisuke; Taenaka, Yoshiyuki

    2016-06-15

    In vitro antithrombogenic testing with mock circulation is a useful type of pre-evaluation in ex vivo testing of mechanical assist devices. For effective in vitro testing, we have been developing a clear quantitative thrombogenesis model based on shear stress and blood coagulability. Bovine blood was used as the test medium. The activating clotting time (ACT) was adjusted with trisodium citrate and calcium chloride from 200 to 1,000 seconds. The blood was then applied to a rheometer and subjected to shear at 50 to 2,880 s-1. Blood coagulation time and degree of thrombogenesis were measured by the torque sensor of the rheometer. Prothrombin time (PT) and activated partial thromboplastin time (APTT) of the test blood were also measured after the application of shear. Blood coagulation time increased, and the degree of thrombogenesis decreased, with increases in shear rate to between 50 and 2,880 s-1. for test bloods with ACTs of 200 to 250 seconds. An ACT of 200 to 250 seconds is thus appropriate for in vitro antithrombogenic testing under a shear rate of 2,880 s-1. APTT was prolonged, whereas PT did not change, with increasing shear rate: that is, increasing the shear rate reduced thrombogenesis related to the intrinsic clotting pathway. An ACT of 200 to 250 seconds was suitable for in vitro antithrombogenic testing, and increasing the shear stress generated in the mechanical assist device reduced thrombogenesis via the intrinsic clotting pathway.

  13. Modelling the cross-spectral variability of the black hole binary MAXI J1659-152 with propagating accretion rate fluctuations

    NASA Astrophysics Data System (ADS)

    Rapisarda, S.; Ingram, A.; Kalamkar, M.; van der Klis, M.

    2016-11-01

    The power spectrum of the X-ray fluctuations of accreting black holes often consists of two broad humps. We quantitatively investigate the hypothesis that the lower frequency hump originates from variability in a truncated thin accretion disc, propagating into a large scaleheight inner hot flow which, in turn, itself is the origin of the higher frequency hump. We extend the propagating mass accretion rate fluctuations model PROPFLUC to accommodate double-hump power spectra in this way. Furthermore, we extend the model to predict the cross-spectrum between two energy bands in addition to their power spectra, allowing us to constrain the model using the observed time lags, which in the model result from both propagation of fluctuations from the disc to the hot flow, and inside the hot flow. We jointly fit soft and hard power spectrum, and the cross-spectrum between the two bands using this model for five Swift X-ray Telescope observations of MAXI J1659-152. The new double-hump model provides a better fit to the data than the old single-hump model for most of our observations. The data show only a small phase lag associated with the low-frequency hump. We demonstrate quantitatively that this is consistent with the model. We compare the truncation radius measured from our fits with that measured purely by spectral fitting and find agreement within a factor of two. This analysis encompasses the first joint fits of stellar-mass black hole cross-spectra and power spectra with a single self-consistent physical model.

  14. Decrease in Suicide Rates after a Change of Policy Reducing Access to Firearms in Adolescents: A Naturalistic Epidemiological Study

    ERIC Educational Resources Information Center

    Lubin, Gad; Werbeloff, Nomi; Halperin, Demian; Shmushkevitch, Mordechai; Weiser, Mark; Knobler, Haim Y.

    2010-01-01

    The use of firearms is a common means of suicide. We examined the effect of a policy change in the Israeli Defense Forces reducing adolescents' access to firearms on rates of suicide. Following the policy change, suicide rates decreased significantly by 40%. Most of this decrease was due to decrease in suicide using firearms over the weekend.…

  15. Decreased beating rate variability of spontaneously contracting cardiomyocytes after co-incubation with endotoxin.

    PubMed

    Schmidt, Hendrik; Saworski, Jana; Werdan, Karl; Müller-Werdan, Ursula

    2007-01-01

    Decreased heart rate variability (HRV) in critically ill patients indicates a poor prognosis. In heart failure patients, there is an elevated sympathetic tone, reflected by a dominance of sympathetic parameters in HRV, whereas in critically ill patients sympathetic and parasympathetic modulation of heart rate is attenuated despite increased catecholamine blood levels. Thus, autonomic dysfunction in the critically ill cannot be causally related to an impairment at the level of neural transmission, but may be due to a derangement of signal transduction at the effector cell level. On the basis of our working hypothesis that endotoxin may be involved in this blunting of effector cell response to nerval input, we studied the spontaneous beating of cardiomyocytes under the influence of endotoxin. Applying the clinically established indices of HRV to the analysis of beating rate variability (BRV) of neonatal rat cardiomyocytes in serum-free medium, a narrowing of their BRV by endotoxin is demonstrated. We propose that the narrowing of HRV in critically ill patients does not only reflect the altered input from the central or peripheral neurons, but rather a remodeling of the cardiac pacemaker cells by endotoxin and inflammatory mediators.

  16. Onshore-offshore decrease in genus origination rate in Recent tropical bivalves (Red Sea)

    NASA Astrophysics Data System (ADS)

    Tomasovych, Adam; Zuschin, Martin

    2014-05-01

    Broad-scale macroevolutionary and macroecological studies show significant effects of latitude on diversification rates and the clustering of range limits, with temperature being one of the most important correlates of macroecological attributes in marine environments. Temperature, however, also varies predictably with depth, but variation in diversification along bathymetric gradients remains much less explored. Here we assess bathymetric gradients in range configuration (and thus in the clustering of range limits), in taxonomic structure and in age structure of bivalve communities in the Red Sea. We find that depth minima of bivalve species and genera do not cluster along bathymetric gradients while depth maxima significantly cluster at ~50 and 700 m. Therefore, bivalve species and genera show a marked nestedness of their bathymetric ranges: taxa restricted to shallow environments are nested within generalistic taxa that have broad bathymetric distribution. Nested ranges imply that extinction, origination and dispersal processes that structure bivalve metacommunities in the Red Sea change significantly with depth. In accord with this, bivalve genera show (1) a significant increase in median age towards deeper environments, implying that genus origination rate decreases with depth, and (2) a significant decrease in the proportion of monotypic genera and increase in the per-genus species richness towards deeper environments, implying that per-species genus origination and in species extinction rates decrease with depth. These patterns suggest that genera preferentially originated onshore and then expanded offshore in the Red Sea, but still kept their presence in onshore (i.e., offshore specialists are rare). The unique configuration of bathymetric ranges in the Red Sea with rarity of taxa restricted to deeper waters can be related to the lack of temperature stratification. Our analyses, however, indicate that bivalve metacommunities in tropical and warm

  17. On the application of the auto mutual information rate of decrease to biomedical signals.

    PubMed

    Escudero, Javier; Hornero, Roberto; Abasolo, Daniel; Lopez, Miguel

    2008-01-01

    The auto mutual information function (AMIF) evaluates the signal predictability by assessing linear and non-linear dependencies between two measurements taken from a single time series. Furthermore, the AMIF rate of decrease (AMIFRD) is correlated with signal entropy. This metric has been used to analyze biomedical data, including cardiac and brain activity recordings. Hence, the AMIFRD can be a relevant parameter in the context of biomedical signal analysis. Thus, in this pilot study, we have analyzed a synthetic sequence (a Lorenz system) and real biosignals (electroencephalograms recorded with eyes open and closed) with the AMIFRD. We aimed at illustrating the application of this parameter to biomedical time series. Our results show that the AMIFRD can detect changes in the non-linear dynamics of a sequence and that it can distinguish different physiological conditions.

  18. Do efforts to decrease door-to-needle time risk increasing stroke mimic treatment rates?

    PubMed Central

    Liberman, Ava L.; Liotta, Eric M.; Caprio, Fan Z.; Ruff, Ilana; Maas, Matthew B.; Bernstein, Richard A.; Khare, Rahul; Bergman, Deborah

    2015-01-01

    Summary An unintended consequence of rapid thrombolysis may be more frequent treatment of stroke mimics, nonvascular conditions that simulate stroke. We explored the relationship between door-to-needle (DTN) times and thrombolysis of stroke mimics at a single academic center by analyzing consecutive quartiles of patients who were treated with IV tissue plasminogen activator for suspected stroke from January 1, 2010 to February 28, 2014. An increase in the proportion of stroke mimic patients (6.7% in each of the 1st and 2nd, 12.9% in the 3rd, and 30% in the last consecutive case quartile; p = 0.03) and a decrease in median DTN time from 89 to 56 minutes (p < 0.01) was found. As more centers reduce DTN times, the rates of stroke mimic treatment should be carefully monitored. PMID:26124982

  19. Endomorphins decrease heart rate and blood pressure possibly by activating vagal afferents in anesthetized rats.

    PubMed

    Kwok, E H; Dun, N J

    1998-08-24

    Endomorphin 1 (10, 30, 100 nmol/kg) administered intravenously (i.v. ) to urethane-anesthetized rats consistently and dose-dependently lowered heart rate (HR) and mean arterial pressure (MAP); the decrease in blood pressure recovered faster as compared to the HR. The effects of endomorphin 2 were qualitatively similar. Naloxone (2 mg/kg, i.v.) completely antagonized the bradycardia and hypotension caused by endomorphin 1. Pretreatment of the rats with atropine methylnitrate, atropine sulfate (2 mg/kg, i.v.) or bilateral vagotomy nearly abolished the bradycardia and attenuated the hypotensive effect of endomorphin 1. Our studies suggest that the bradycardia effect following systemic administration of the new opioid peptide may be explained by activation of vagal afferents and the hypotensive effect may be secondary to a reduction of cardiac output and/or a direct vasodilation.

  20. Gopher mounds decrease nutrient cycling rates and increase adjacent vegetation in volcanic primary succession.

    PubMed

    Yurkewycz, Raymond P; Bishop, John G; Crisafulli, Charles M; Harrison, John A; Gill, Richard A

    2014-12-01

    Fossorial mammals may affect nutrient dynamics and vegetation in recently initiated primary successional ecosystems differently than in more developed systems because of strong C and N limitation to primary productivity and microbial communities. We investigated northern pocket gopher (Thomomys talpoides) effects on soil nutrient dynamics, soil physical properties, and plant communities on surfaces created by Mount St. Helens' 1980 eruption. For comparison to later successional systems, we summarized published studies on gopher effects on soil C and N and plant communities. In 2010, 18 years after gopher colonization, we found that gophers were active in ~2.5% of the study area and formed ~328 mounds ha(-1). Mounds exhibited decreased species density compared to undisturbed areas, while plant abundance on mound margins increased 77%. Plant burial increased total soil carbon (TC) by 13% and nitrogen (TN) by 11%, compared to undisturbed soils. Mound crusts decreased water infiltration, likely explaining the lack of detectable increases in rates of NO3-N, NH4-N or PO4-P leaching out of the rooting zone or in CO2 flux rates. We concluded that plant burial and reduced infiltration on gopher mounds may accelerate soil carbon accumulation, facilitate vegetation development at mound edges through resource concentration and competitive release, and increase small-scale heterogeneity of soils and communities across substantial sections of the primary successional landscape. Our review indicated that increases in TC, TN and plant density at mound margins contrasted with later successional systems, likely due to differences in physical effects and microbial resources between primary successional and older systems.

  1. Hemodynamic Response to Hemodialysis With Ultrafiltration Rate Profiles Either Gradually Decreasing or Gradually Increasing.

    PubMed

    Morales-Alvarez, Ricardo; Martínez-Memije, Raúl; Becerra-Luna, Brayans; García-Paz, Paola; Infante, Oscar; Palma-Ramírez, Alfredo; Caviedes-Aramburu, Amaya; Vargas-Barrón, Jesús; Lerma, Claudia; Pérez-Grovas, Héctor

    2016-07-01

    Hemodialysis (HD) is usually performed with the gradually decreasing ultrafiltration rate (UFR) profile (dUFR). The aim of the present study was to compare the hemodynamic response to HD with the dUFR to that of HD with the gradually increasing UFR profile (iUFR). The study population included 10 patients (three women, mean age: 28 ± 8 years) undergoing maintenance HD who had reached dry weight without taking antihypertensive medications. Each patient received (in random order) one HD session with the dUFR and another with the iUFR (both with 3 h total UFR = 2200 mL). Hemodynamic response was evaluated with a brachial blood pressure (BP) monitor, echocardiogram and Portapres to measure digital BP, heart rate, cardiac output, stroke volume, and peripheral resistance. Mean values were compared at each HD hour during the first 3 h of a 4-h HD session. The HD characteristics, including Kt/V, were similar for both UFR profiles. Relative blood volume decreased more gradually and linearly with the iUFR. Hemodynamic variables were not significantly different between the two profiles, but brachial BP was more stable with the iUFR. Digital diastolic BP increased with both profiles. Peripheral resistance increased with both profiles, and tended to increase more with the iUFR. Echocardiographic variables changed similarly during the HD session with both profiles. In conclusion, these two UFR profiles are similar in most hemodynamic variables. The statistical equivalence of both profiles suggests that either could be prescribed based on the clinical characteristics of the patient.

  2. ACCRETION OUTBURSTS IN CIRCUMPLANETARY DISKS

    SciTech Connect

    Lubow, S. H.; Martin, R. G.

    2012-04-20

    We describe a model for the long-term evolution of a circumplanetary disk that is fed mass from a circumstellar disk and contains regions of low turbulence (dead zones). We show that such disks can be subject to accretion-driven outbursts, analogous to outbursts previously modeled in the context of circumstellar disks to explain FU Ori phenomena. Circumplanetary disks around a proto-Jupiter can undergo outbursts for infall accretion rates onto the disks in the range M-dot{sub infall} approx. 10{sup -9} to 10{sup -7} M{sub Sun} yr{sup -1}, typical of accretion rates in the T Tauri phase. During outbursts, the accretion rate and disk luminosity increases by several orders of magnitude. Most of the planet mass growth during planetary gas accretion may occur via disk outbursts involving gas that is considerably hotter than predicted by steady state models. For low infall accretion rates M-dot{sub infall} {approx}< 10{sup -10} M{sub sun} yr{sup -1} that occur in late stages of disk accretion, disk outbursts are unlikely to occur, even if dead zones are present. Such conditions are favorable for the formation of icy satellites.

  3. Experimental sources of variation in avian energetics: estimated basal metabolic rate decreases with successive measurements.

    PubMed

    Jacobs, Paul J; McKechnie, Andrew E

    2014-01-01

    Basal metabolic rate (BMR) is one of the most widely used metabolic variables in endotherm ecological and evolutionary physiology. Surprisingly few studies have investigated how BMR is influenced by experimental and analytical variables over and above the standardized conditions required for minimum normothermic resting metabolism. We tested whether avian BMR is affected by habituation to the conditions experienced during laboratory gas exchange measurements by measuring BMR five times in succession in budgerigars (Melopsittacus undulatus) housed under constant temperature and photoperiod. Both the magnitude and the variability of BMR decreased significantly with repeated measurements, from 0.410 ± 0.092 W (n = 9) during the first measurement to 0.285 ± 0.042 W (n = 9) during the fifth measurement. Thus, estimated BMR decreased by ∼30% within individuals solely on account of the number of times they had previously experienced the experimental conditions. The most likely explanation for these results is an attenuation with repeated exposure of the acute stress response induced by birds being handled and placed in respirometry chambers. Our data suggest that habituation to experimental conditions is potentially an important determinant of observed BMR, and this source of variation needs to be taken into account in future studies of metabolic variation among individuals, populations, and species.

  4. Surgical proficiency decreases the rate of healing abnormalities using anterior transobturator mesh in cystocele women

    PubMed Central

    Yuk, Jin-Sung; Kim, Yong Jin; Yi, Kyong Wook; Hur, Jun-Young; Shin, Jung-Ho

    2016-01-01

    Aims: The objective of this study is to report the outcomes of cystocele repair with anterior transobutrator mesh kits.  Methods: 119 consecutive women with cystoceles were treated between January 2006 and November 2010 by a single surgeon at a university hospital using the anterior transobturator mesh kit procedure. Postoperative follow-up visits were scheduled at 1, 6, and 12 months after surgery. Results: A total of 114 women who were operated on with the anterior transobturator mesh kit completed 12 months of follow-up. The population had a mean age of 65.8 ± 7.0, a body mass index of 25.1 ± 3.0, and a parity average of 4.0 ± 1.7. An overall anatomic cure was reported for 108 patients (94.7%). The Ba point of the POP-Q exam used for grading cystoceles decreased significantly from 2.5 ± 1.6 cm to -2.8 ± 0.8 cm after 12 months (P < 0.01). One patient (0.9%) presented with bladder perforation, and five patients (4.4%) showed with healing abnormalities. Surgical case volume was negatively correlated with healing abnormalities after adjusting for age, body mass index, operation time, and parity (P = 0.15).  Conclusion: The surgeon’s experience decreases the incidence of healing abnormalities using anterior transobturator mesh in cystocele women. The anatomical cure rate of anterior transobturator mesh is quite good. PMID:28003880

  5. The ultraluminous X-ray source NGC 5643 ULX1: a large stellar mass black hole accreting at super-Eddington rates?

    NASA Astrophysics Data System (ADS)

    Pintore, Fabio; Zampieri, Luca; Sutton, Andrew D.; Roberts, Timothy P.; Middleton, Matthew J.; Gladstone, Jeanette C.

    2016-06-01

    A sub-set of the brightest ultraluminous X-ray sources (ULXs), with X-ray luminosities well above 1040 erg s-1, typically have energy spectra which can be well described as hard power laws, and short-term variability in excess of ˜10 per cent. This combination of properties suggests that these ULXs may be some of the best candidates to host intermediate-mass black holes (IMBHs), which would be accreting at sub-Eddington rates in the hard state seen in Galactic X-ray binaries. In this work, we present a temporal and spectral analysis of all of the available XMM-Newton data from one such ULX, the previously poorly studied 2XMM J143242.1-440939, located in NGC 5643. We report that its high-quality EPIC spectra can be better described by a broad, thermal component, such as an advection-dominated disc or an optically thick Comptonizing corona. In addition, we find a hint of a marginal change in the short-term variability which does not appear to be clearly related to the source unabsorbed luminosity. We discuss the implications of these results, excluding the possibility that the source may be host an IMBH in a low state, and favouring an interpretation in terms of super-Eddington accretion on to a black hole of stellar origin. The properties of NGC 5643 ULX1 allow us to associate this source to the population of the hard/ultraluminous ULX class.

  6. Decrease in the growth rates of atmospheric chlorofluorocarbons 11 and 12

    NASA Astrophysics Data System (ADS)

    Elkins, J. W.; Thompson, T. M.; Swanson, T. H.; Butler, J. H.; Hall, B. D.; Cummings, S. O.; Fishers, D. A.; Raffo, A. G.

    1993-08-01

    THE discovery of the Antarctic ozone hole1 in 1985 led to international efforts to reduce emissions of ozone-destroying chlorofluorocarbons2. These efforts culminated in the Montreal Protocol3 and its subsequent amendments, which called for the elimination of CFC production by 1996. Here we focus on CFC-11 (CC13F) and CFC-12 (CC12F2), which are used for refrigeration, air conditioning and the production of aerosols and foams4, and which together make up about half of the total abundance of stratospheric organic chlorine5. We report a significant recent decrease in the atmospheric growth rates of these two species, based on measurements spanning the past 15 years and latitudes ranging from 83° N to 90° S. This is consistent with CFC-producers' own estimates of reduced emissions6,7. If the atmospheric growth rates of these two species continue to slow in line with predicted changes in industrial emissions, global atmospheric mixing ratios will reach a maximum before the turn of the century, and then begin to decline.

  7. Role of hydraulic diffusivity in the decrease of weathering rates over time

    NASA Astrophysics Data System (ADS)

    Pacheco, Fernando A. L.; Van der Weijden, Cornelis H.

    2014-05-01

    Springs emerging within massifs of crystalline rocks were monitored for discharge rate (Q), and the Q values combined with geomorphic and hydrographic parameters in a hydrologic model to calculate hydraulic conductivity (K) and effective porosity (ne) of the spring watersheds. The spring waters, several borehole waters and rain water were analyzed for major dissolved compounds, strontium and isotopes (δ18O, δ2H, δ13C and 87Sr/86Sr). With a shift to less negative values, δ18O and δ2H were fitted by a line approximately parallel to the GMWL, but no significant dependence on altitude was found. The δ18O and δ2H values correlate better with those of precipitation amount. The 87Sr/86Sr ratios in drilled well waters correlate positively with the depth of water circulation reported in the borehole logs. The corresponding regression equations were used to extrapolate the depth of hydraulic circuits within the spring watersheds. The previous data, together with groundwater travel times calculated by a water balance model, and with reactions of granite/metassediment plagioclase and biotite precipitating halloysite, gibbsite and vermiculite, were assembled in a mass balance model to calculate solute-flux weathering rates of plagioclase (WPl). The WPl's were described as a function of √{D}∝√{K/n}, where D is the hydraulic diffusivity. The discrepancies between the WPl values and solid-state rates, based on the differences between elemental, isotopic and mineral compositions measured in present-day regoliths and in the assumed protolith, were assigned to a decrease in D over time, from values in the protolith to values in the weathered aquifer.

  8. Leptin Administration Favors Muscle Mass Accretion by Decreasing FoxO3a and Increasing PGC-1α in ob/ob Mice

    PubMed Central

    Sáinz, Neira; Rodríguez, Amaia; Catalán, Victoria; Becerril, Sara; Ramírez, Beatriz; Gómez-Ambrosi, Javier; Frühbeck, Gema

    2009-01-01

    Absence of leptin has been associated with reduced skeletal muscle mass in leptin-deficient ob/ob mice. The aim of our study was to examine the effect of leptin on the catabolic and anabolic pathways regulating muscle mass. Gastrocnemius, extensor digitorum longus and soleus muscle mass as well as fiber size were significantly lower in ob/ob mice compared to wild type littermates, being significantly increased by leptin administration (P<0.001). This effect was associated with an inactivation of the muscle atrophy-related transcription factor forkhead box class O3 (FoxO3a) (P<0.05), and with a decrease in the protein expression levels of the E3 ubiquitin-ligases muscle atrophy F-box (MAFbx) (P<0.05) and muscle RING finger 1 (MuRF1) (P<0.05). Moreover, leptin increased (P<0.01) protein expression levels of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), a regulator of muscle fiber type, and decreased (P<0.05) myostatin protein, a negative regulator of muscle growth. Leptin administration also activated (P<0.01) the regulators of cell cycle progression proliferating cell nuclear antigen (PCNA) and cyclin D1, and increased (P<0.01) myofibrillar protein troponin T. The present study provides evidence that leptin treatment may increase muscle mass of ob/ob mice by inhibiting myofibrillar protein degradation as well as enhancing muscle cell proliferation. PMID:19730740

  9. Periodontal treatment during pregnancy decreases the rate of adverse pregnancy outcome: a controlled clinical trial

    PubMed Central

    SANT’ANA, Adriana Campos Passanezi; de CAMPOS, Marinele R.; PASSANEZI, Selma Campos; de REZENDE, Maria Lúcia Rubo; GREGHI, Sebastião Luiz Aguiar; PASSANEZI, Euloir

    2011-01-01

    Objectives The aim of this study was to evaluate the effects of non-surgical treatment of periodontal disease during the second trimester of gestation on adverse pregnancy outcomes. Material and Methods Pregnant patients during the 1st and 2nd trimesters at antenatal care in a Public Health Center were divided into 2 groups: NIG – "no intervention" (n=17) or IG- "intervention" (n=16). IG patients were submitted to a non-surgical periodontal treatment performed by a single periodontist consisting of scaling and root planning (SRP), professional prophylaxis (PROPH) and oral hygiene instruction (OHI). NIG received PROPH and OHI during pregnancy and were referred for treatment after delivery. Periodontal evaluation was performed by a single trained examiner, blinded to periodontal treatment, according to probing depth (PD), clinical attachment level (CAL), plaque index (PI) and sulcular bleeding index (SBI) at baseline and 35 gestational weeks-28 days post-partum. Primary adverse pregnancy outcomes were preterm birth (<37 weeks), low birth weight (<2.5 kg), late abortion (14-24 weeks) or abortion (<14 weeks). The results obtained were statistically evaluated according to OR, unpaired t test and paired t test at 5% significance level. Results No significant differences were observed between groups at baseline examination. Periodontal treatment resulted in stabilization of CAL and PI (p>0.05) at IG and worsening of all periodontal parameters at NIG (p<0.0001), except for PI. Significant differences in periodontal conditions of IG and NIG were observed at 2nd examination (p<0.001). The rate of adverse pregnancy outcomes was 47.05% in NIG and 6.25% in IG. Periodontal treatment during pregnancy was associated to a decreased risk of developing adverse pregnancy outcomes [OR=13.50; CI: 1.47-123.45; p=0.02]. Conclusions Periodontal treatment during the second trimester of gestation contributes to decrease adverse pregnancy outcomes. PMID:21552714

  10. PS1-10jh CONTINUES TO FOLLOW THE FALLBACK ACCRETION RATE OF A TIDALLY DISRUPTED STAR

    SciTech Connect

    Gezari, S.; Chornock, R.; Lawrence, A.; Rest, A.; Jones, D. O.; Berger, E.; Challis, P. M.; Narayan, G.

    2015-12-10

    We present late-time observations of the tidal disruption event candidate PS1-10jh. UV and optical imaging with Hubble Space Telescope/WFC3 localize the transient to be coincident with the host galaxy nucleus to an accuracy of 0.023 arcsec, corresponding to 66 pc. The UV flux in the F225W filter, measured 3.35 rest-frame years after the peak of the nuclear flare, is consistent with a decline that continues to follow a t{sup −5/3} power-law with no spectral evolution. Late epochs of optical spectroscopy obtained with MMT ∼ 2 and 4 years after the peak, enable a clean subtraction of the host galaxy from the early spectra, revealing broad helium emission lines on top of a hot continuum, and placing stringent upper limits on the presence of hydrogen line emission. We do not measure Balmer Hδ absorption in the host galaxy that is strong enough to be indicative of a rare, post-starburst “E+A” galaxy as reported by Arcavi et al. The light curve of PS1-10jh over a baseline of 3.5 years is best modeled by fallback accretion of a tidally disrupted star. Its strong broad helium emission relative to hydrogen (He iiλ4686/Hα > 5) could be indicative of either the hydrogen-poor chemical composition of the disrupted star, or certain conditions in the tidal debris of a solar-composition star in the presence of an optically thick, extended reprocessing envelope.

  11. Temporary Increases in Problem Behavior and Sleep Disruption Following Decreases in Medication: A Descriptive Analysis of Conditional Rates

    ERIC Educational Resources Information Center

    Rapp, John T.; Swanson, Greg; Dornbusch, Kaitlin

    2007-01-01

    Conditional rates of problem behavior for weeks that followed medication decreases and no medication changes were compared for 12 individuals who exhibited severe problem behavior (e.g., self-injury, aggression). The results indicate that conditional rates of problem behavior were higher following medication decreases than following no changes in…

  12. Glutamate induces series of action potentials and a decrease in circumnutation rate in Helianthus annuus.

    PubMed

    Stolarz, Maria; Król, Elzbieta; Dziubińska, Halina; Kurenda, Andrzej

    2010-03-01

    Reports concerning the function of glutamate (Glu) in the electrical and movement phenomena in plants are scarce. Using the method of extracellular measurement, we recorded electrical potential changes in the stem of 3-week-old Helianthus annuus L. plants after injection of Glu solution. Simultaneously, circumnutation movements of the stem were measured with the use of time-lapse images. Injection of Glu solution at millimolar (200, 50, 5 mM) concentrations in the basal part of the stem evoked a series of action potentials (APs). The APs appeared in the site of injection and in different parts of the stem and were propagated acropetally and/or basipetally along the stem. Glu injection also resulted in a transient, approximately 5-h-long decrease in the stem circumnutation rate. The APs initiated and propagating in the sunflower stem after Glu injection testify the existence of a Glu perception system in vascular plants and suggest its involvement in electrical, long-distance signaling. Our experiments also demonstrated that Glu is a factor affecting circumnutation movements.

  13. Relationship between star formation rate and black hole accretion at z=3: the different contributions in quiescent, normal, and starburst galaxies

    SciTech Connect

    Rodighiero, G.; Franceschini, A.; Baronchelli, I.; Brusa, M.; Delvecchio, I.; Pozzi, F.; Cimatti, A.; Mullaney, J. R.; Lutz, D.; Gruppioni, C.; Silverman, J.

    2015-02-10

    We investigate the co-evolution of the black hole accretion rate (BHAR) and the star formation rate (SFR) in 1.5accretion density of the universe at z∼2 is associated with normal star-forming systems, with only ∼6(±1)% and ∼11(±1)% associated with starburst and quiescent galaxies, respectively.

  14. Planetary migration, accretion, and atmospheres

    NASA Astrophysics Data System (ADS)

    Dobbs-Dixon, Ian M.

    mechanisms for stopping this accretion involve either disk dispersal or gap formation. Although mass accretion may eventually be quenched by a global depletion of gas, as in the ease of Uranus and Neptune, such a mechanism is unlikely to have stalled the growth of some known planetary systems which contain relatively low-mass and close-in planets along with more massive and longer period companions. Similarly, the formation of a gap cannot fully explain the decrease in mass accretion. Several groups have shown that, even in the presence of a gap, diffusion allows rapid gas accretion to continue. Here I explore the effect of the growing tidal barrier on the flow within the protoplanetary disk. Using both analytic and numerical approaches I show that accretion rates increases rapidly with the ratio of the protoplanet's Roche to Bondi radii or equivalently to the disk thickness. Mass accretion timescales become comparable to observed disk lifetimes. In regions with loco geometric aspect ratios gas accretion is efficiently quenched with relatively low protoplanetary masses. This mechanism is important for determining the gas- giant planets' mass function, the distribution of their masses within multiple planet systems around solar type stars, and for suppressing the emergence of gas-giants around low mass stars. The final section explores the atmospheric dynamics of short-period gas-giant planets. Ubiquitous among currently observed extrasolar planetary systems these planets receive intense irradiation from their host stars that dominates the energy input into their atmospheres. Characterization of several of these planets through transit observations have revealed information on temperature, structure, and composition. Here we present three-dimensional radiative hydrodynamical simulations of atmospheric circulation on close-in gas giant planets. In contrast to previous Global Climate Models and shallow water algorithms, this method does not assume quasi hydrostatic equilibrium

  15. Impact of initial models and variable accretion rates on the pre-main-sequence evolution of massive and intermediate-mass stars and the early evolution of H II regions

    NASA Astrophysics Data System (ADS)

    Haemmerlé, Lionel; Peters, Thomas

    2016-05-01

    Massive star formation requires the accretion of gas at high rate while the star is already bright. Its actual luminosity depends sensitively on the stellar structure. We compute pre-main-sequence tracks for massive and intermediate-mass stars with variable accretion rates and study the evolution of stellar radius, effective temperature and ionizing luminosity, starting at 2 M⊙ with convective or radiative structures. The radiative case shows a much stronger swelling of the protostar for high accretion rates than the convective case. For radiative structures, the star is very sensitive to the accretion rate and reacts quickly to accretion bursts, leading to considerable changes in photospheric properties on time-scales as short as 100-1000 yr. The evolution for convective structures is much less influenced by the instantaneous accretion rate, and produces a monotonically increasing ionizing flux that can be many orders of magnitude smaller than in the radiative case. For massive stars, it results in a delay of the H II region expansion by up to 10 000 yr. In the radiative case, the H II region can potentially be engulfed by the star during the swelling, which never happens in the convective case. We conclude that the early stellar structure has a large impact on the radiative feedback during the pre-main-sequence evolution of massive protostars and introduces an important uncertainty that should be taken into account. Because of their lower effective temperatures, our convective models may hint at a solution to an observed discrepancy between the luminosity distribution functions of massive young stellar objects and compact H II regions.

  16. Short-term secondhand smoke exposure decreases heart rate variability and increases arrhythmia susceptibility in mice.

    PubMed

    Chen, Chao-Yin; Chow, Drin; Chiamvimonvat, Nipavan; Glatter, Kathryn A; Li, Ning; He, Yuxia; Pinkerton, Kent E; Bonham, Ann C

    2008-08-01

    Exposure to secondhand smoke (SHS), a major indoor air pollutant, is linked to increased cardiovascular morbidity and mortality, including cardiac arrhythmias. However, the mechanisms underlying the epidemiological findings are not well understood. Impaired cardiac autonomic function, indexed by reduced heart rate variability (HRV), may represent an underlying cause. The present study takes advantage of well-defined short-term SHS exposure (3 days, 6 h/day) on HRV and the susceptibility to arrhythmia in mice. With the use of electrocardiograph telemetry recordings in conscious mice, HRV parameters in the time domain were measured during the night after each day of exposure and 24 h after 3 days of exposure to either SHS or filtered air. The susceptibility to arrhythmia was determined after 3 days of exposure. Exposure to a low concentration of SHS [total suspended particle (TSP), 2.4 +/- 3.2; and nicotine, 0.3 +/- 0.1 mg/m(3)] had no significant effect on HRV parameters. In contrast, the exposure to a higher but still environmentally relevant concentration of SHS (TSP, 30 +/- 1; and nicotine, 5 +/- 1 mg/m(3)) significantly reduced HRV starting after the first day of exposure and continuing 24 h after the last day of exposure. Moreover, the exposed mice showed a significant increase in ventricular arrhythmia susceptibility and atrioventricular block. The data suggest that SHS exposure decreased HRV beyond the exposure period and was associated with an increase in arrhythmia susceptibility. The data provide insights into possible mechanisms underlying documented increases in cardiovascular morbidity and mortality in humans exposed to SHS.

  17. Decreasing soil erosion rates with evolving land-use techniques in a central European catchment

    NASA Astrophysics Data System (ADS)

    Larsen, Annegret; Heckmann, Tobias; Hans-Rudolf, Bork; Alexander, Fuelling

    2015-04-01

    Agricultural societies around the world have caused accelerated soil erosion. Soil erosion and a decrease in soil fertility may also have caused the abandonment of entire landscapes and the collapse of civilizations. In central Europe, Medieval land-use is thought to have lead to the largest loss of top soil in history, which in turn lead to a malnutrition of the population and abandonment of agricultural land. However, this might be only part of the picture, as people are also able to adapt to changing environmental conditions, including the type of land-use they adopt. Within a catchment in the central European mountain belt, we were able to distinguish the evolution between three main types of land-use techniques between ~ 900 AD and 1950 AD: horticulture, agriculture and shifting cultivation. We were able to relate these techniques with different soil erosion rates, which differ by an order of magnitude, ranging from 0.83 ± 0.09 mm/yr to 1.62 ± 0.17 mm/yr. Using high-resolution surface data and chrono-stratigraphical methods in combination with soil charcoal analysis, we were able to reconstruct past land-use techniques on a local scale. This illustrates that less erosive and more sustainable techniques were developed through time, and hypothesize that people were able to adapt to the less favorable environmental conditions by changing the cultivation techniques. Although cultural adaptation to changing environmental conditions has been extensively discussed, this study is able to quantitatively demonstrate improved soil management with evolving land-use in central Europe.

  18. Migration of accreting giant planets

    NASA Astrophysics Data System (ADS)

    Crida, A.; Bitsch, B.; Raibaldi, A.

    2016-12-01

    We present the results of 2D hydro simulations of giant planets in proto-planetary discs, which accrete gas at a more or less high rate. First, starting from a solid core of 20 Earth masses, we show that as soon as the runaway accretion of gas turns on, the planet is saved from type I migration : the gap opening mass is reached before the planet is lost into its host star. Furthermore, gas accretion helps opening the gap in low mass discs. Consequently, if the accretion rate is limited to the disc supply, then the planet is already inside a gap and in type II migration. We further show that the type II migration of a Jupiter mass planet actually depends on its accretion rate. Only when the accretion is high do we retrieve the classical picture where no gas crosses the gap and the planet follows the disc spreading. These results impact our understanding of planet migration and planet population synthesis models. The e-poster presenting these results in French can be found here: L'e-poster présentant ces résultats en français est disponible à cette adresse: http://sf2a.eu/semaine-sf2a/2016/posterpdfs/156_179_49.pdf.

  19. Decreases in Smoking-Related Cancer Mortality Rates Are Associated with Birth Cohort Effects in Korean Men.

    PubMed

    Jee, Yon Ho; Shin, Aesun; Lee, Jong-Keun; Oh, Chang-Mo

    2016-12-05

    Background: This study aimed to examine trends in smoking-related cancer mortality rates and to investigate the effect birth cohort on smoking-related cancer mortality in Korean men. Methods: The number of smoking-related cancer deaths and corresponding population numbers were obtained from Statistics Korea for the period 1984-2013. Joinpoint regression analysis was used to detect changes in trends in age-standardized mortality rates. Birth-cohort specific mortality rates were illustrated by 5 year age groups. Results: The age-standardized mortality rates for oropharyngeal decreased from 2003 to 2013 (annual percent change (APC): -3.1 (95% CI, -4.6 to -1.6)) and lung cancers decreased from 2002 to 2013 (APC -2.4 (95% CI -2.7 to -2.2)). The mortality rates for esophageal declined from 1994 to 2002 (APC -2.5 (95% CI -4.1 to -0.8)) and from 2002 to 2013 (APC -5.2 (95% CI -5.7 to -4.7)) and laryngeal cancer declined from 1995 to 2013 (average annual percent change (AAPC): -3.3 (95% CI -4.7 to -1.8)). By the age group, the trends for the smoking-related cancer mortality except for oropharyngeal cancer have changed earlier to decrease in the younger age group. The birth-cohort specific mortality rates and age-period-cohort analysis consistently showed that all birth cohorts born after 1930 showed reduced mortality of smoking-related cancers. Conclusions: In Korean men, smoking-related cancer mortality rates have decreased. Our findings also indicate that current decreases in smoking-related cancer mortality rates have mainly been due to a decrease in the birth cohort effect, which suggest that decrease in smoking rates.

  20. Decreases in Smoking-Related Cancer Mortality Rates Are Associated with Birth Cohort Effects in Korean Men

    PubMed Central

    Jee, Yon Ho; Shin, Aesun; Lee, Jong-Keun; Oh, Chang-Mo

    2016-01-01

    Background: This study aimed to examine trends in smoking-related cancer mortality rates and to investigate the effect birth cohort on smoking-related cancer mortality in Korean men. Methods: The number of smoking-related cancer deaths and corresponding population numbers were obtained from Statistics Korea for the period 1984–2013. Joinpoint regression analysis was used to detect changes in trends in age-standardized mortality rates. Birth-cohort specific mortality rates were illustrated by 5 year age groups. Results: The age-standardized mortality rates for oropharyngeal decreased from 2003 to 2013 (annual percent change (APC): −3.1 (95% CI, −4.6 to −1.6)) and lung cancers decreased from 2002 to 2013 (APC −2.4 (95% CI −2.7 to −2.2)). The mortality rates for esophageal declined from 1994 to 2002 (APC −2.5 (95% CI −4.1 to −0.8)) and from 2002 to 2013 (APC −5.2 (95% CI −5.7 to −4.7)) and laryngeal cancer declined from 1995 to 2013 (average annual percent change (AAPC): −3.3 (95% CI −4.7 to −1.8)). By the age group, the trends for the smoking-related cancer mortality except for oropharyngeal cancer have changed earlier to decrease in the younger age group. The birth-cohort specific mortality rates and age-period-cohort analysis consistently showed that all birth cohorts born after 1930 showed reduced mortality of smoking-related cancers. Conclusions: In Korean men, smoking-related cancer mortality rates have decreased. Our findings also indicate that current decreases in smoking-related cancer mortality rates have mainly been due to a decrease in the birth cohort effect, which suggest that decrease in smoking rates. PMID:27929405

  1. MN Lup: X-RAYS FROM A WEAKLY ACCRETING T TAURI STAR

    SciTech Connect

    Guenther, H. M.; Wolk, S. J.; Wolter, U.; Robrade, J.

    2013-07-01

    Young T Tauri stars (TTS) are surrounded by an accretion disk, which over time disperses due to photoevaporation, accretion, and possibly planet formation. The accretion shock on the central star produces an UV/optical veiling continuum, line emission, and X-ray signatures. As the accretion rate decreases, the impact on the central star must change. In this article we study MN Lup, a young star where no indications of a disk are seen in IR observations. We present XMM-Newton and VLT/UVES observations, some of them taken simultaneously. The X-ray data show that MN Lup is an active star with L{sub X} /L{sub bol} close to the saturation limit. However, we find high densities (n{sub e} > 3 Multiplication-Sign 10{sup 10} cm{sup -3}) in the X-ray grating spectrum. This can be well fitted using an accretion shock model with an accretion rate of 2 Multiplication-Sign 10{sup -11} M{sub Sun} yr{sup -1}. Despite the simple H{alpha} line profile which has a broad component, but no absorption signatures as typically seen on accreting TTS, we find rotational modulation in Ca II K and in photospheric absorption lines. These line profile modulations do not clearly indicate the presence of a localized hot accretion spot on the star. In the H{alpha} line we see a prominence in absorption about 2R{sub *} above the stellar surface-the first of its kind on a TTS. MN Lup is also the only TTS where accretion is seen, but no dust disk is detected that could fuel it. We suggest that MN Lup presents a unique and short-lived state in the disk evolution. It may have lost its dust disk only recently and is now accreting the remaining gas at a very low rate.

  2. Glutamate transporter type 3 knockout leads to decreased heart rate possibly via parasympathetic mechanism.

    PubMed

    Deng, Jiao; Li, Jiejie; Li, Liaoliao; Feng, Chenzhuo; Xiong, Lize; Zuo, Zhiyi

    2013-08-01

    Parasympathetic tone is a dominant neural regulator for basal heart rate. Glutamate transporters (EAAT) via their glutamate uptake functions regulate glutamate neurotransmission in the central nervous system. We showed that EAAT type 3 (EAAT3) knockout mice had a slower heart rate than wild-type mice when they were anesthetized. We design this study to determine whether non-anesthetized EAAT3 knockout mice have a slower heart rate and, if so, what may be the mechanism for this effect. Young adult EAAT3 knockout mice had slower heart rates than those of their littermate wild-type mice no matter whether they were awake or anesthetized. This difference was abolished by atropine, a parasympatholytic drug. Carbamylcholine chloride, a parasympathomimetic drug, equally effectively reduced the heart rates of wild-type and EAAT3 knockout mice. Positive immunostaining for EAAT3 was found in the area of nuclei deriving fibers for vagus nerve. There was no positive staining for the EAATs in the sinoatrial node. These results suggest that EAAT3 knockout mice have a slower heart rate at rest. This effect may be caused by an increased parasympathetic tone possibly due to increased glutamate neurotransmission in the central nervous system. These findings indicate that regulation of heart rate, a vital sign, is one of the EAAT biological functions.

  3. Ubiquitous equatorial accretion disc winds in black hole soft states

    NASA Astrophysics Data System (ADS)

    Ponti, G.; Fender, R. P.; Begelman, M. C.; Dunn, R. J. H.; Neilsen, J.; Coriat, M.

    2012-05-01

    High-resolution spectra of Galactic black holes (GBHs) reveal the presence of highly ionized absorbers. In one GBH, accreting close to the Eddington limit for more than a decade, a powerful accretion disc wind is observed to be present in softer X-ray states and it has been suggested that it can carry away enough mass and energy to quench the radio jet. Here we report that these winds, which may have mass outflow rates of the order of the inner accretion rate or higher, are a ubiquitous component of the jet-free soft states of all GBHs. We furthermore demonstrate that these winds have an equatorial geometry with opening angles of few tens of degrees, and so are only observed in sources in which the disc is inclined at a large angle to the line of sight. The decrease in Fe XXV/Fe XXVI line ratio with Compton temperature, observed in the soft state, suggests a link between higher wind ionization and harder spectral shapes. Although the physical interaction between the wind, accretion flow and jet is still not fully understood, the mass flux and power of these winds and their presence ubiquitously during the soft X-ray states suggest they are fundamental components of the accretion phenomenon.

  4. Meta-stable low-level accretion rate states or neutron star crust cooling in the Be/X-ray transients V0332+53 and 4U 0115+63

    NASA Astrophysics Data System (ADS)

    Wijnands, R.; Degenaar, N.

    2016-11-01

    The Be/X-ray transients V0332+53 and 4U 0115+63 exhibited giant, type-II outbursts in 2015. Here we present Swift/XRT follow-up observations at the end of those outbursts. Surprisingly, the sources did not decay back to their known quiescent levels but stalled at a (slowly decaying) meta-stable state with luminosities a factor ˜10 above that observed in quiescence. The spectra in these states are considerably softer than the outburst spectra and appear to soften in time when the luminosity decreases. The physical mechanism behind these meta-stable states is unclear and they could be due to low-level accretion (either directly on to the neutron stars or on to their magnetospheres) or due to cooling of the accretion-heated neutron star crusts. Based on the spectra, the slowly decreasing luminosities, and the spectral softening, we favour the crust cooling hypothesis but we cannot exclude the accretion scenarios. On top of this meta-stable state, weak accretion events were observed that occurred at periastron passage and may thus be related to regular type-I outbursts.

  5. Managing broiler litter application rate and grazing to decrease watershed runoff losses.

    PubMed

    Sistani, K R; Brink, G E; Oldham, J L

    2008-01-01

    Pasture management and broiler litter application rate are critical factors influencing the magnitude of nutrients being transported by runoff from fields. We investigated the impact of pasture management and broiler litter application rate on nutrient runoff from bermudagrass (Cynodon dactylon) pastures. The experiment was conducted on a Ruston fine sandy loam with a factorial arrangement on 21 large paddocks. Runoff water was collected from natural rainfall events from 2001 to 2003. Runoff water and soil samples were analyzed for nutrients and sediments. Runoff was generally greater (29%) from grazed than hayed pastures regardless of the litter application rate. There was greater inorganic N in the runoff from grazed paddocks when litter rate was based on N rather than P. The mean total P loss per runoff event for all treatments ranged from 7 to 45 g ha(-1) and the grazed treatment with litter applied on N basis had the greatest total P loss. Total dissolved P was the dominant P fraction in the runoff, ranging from 85% to 93% of the total P. The soluble reactive P was greater for treatments with litter applied on N basis regardless of pasture management. Runoff total sediments were greater for N-based litter application compared to those which received litter on P basis. Our results indicate that litter may be applied on N basis if the pasture is hayed and the soil P is low. In contrast, litter rates should be based on a P-basis if pasture is grazed.

  6. Recent accretion in two managed marsh impoundments in coastal Louisiana

    USGS Publications Warehouse

    Cahoon, D.R.

    1994-01-01

    Recent accretion was measured by the feldspar marker horizon method in two gravity-drained, managed, marsh impoundments and unmanaged reference marshes located on the rapidly subsiding coast of Louisiana. Water level management was designed to limit hydrologic exchange to the managed marsh by regulating the direction and rate of water flows. During a drawdown-flooding water management cycle, the unmanaged reference marshes had significantly higher vertical accretion rates, higher soil bulk density and soil mineral matter content, lower soil organic matter content, and higher rates of organic matter accumulation than the managed marsh. The rate of mineral matter accumulation was higher in both reference marshes, but was significantly higher in only one. Spatial variability in accumulation rates was low when analyzed in one managed marsh site, suggesting a primarily autochthonous source of matter. In contrast, the associated reference marsh apparently received allochthonous material that settled out in a distinct spatial pattern as water velocity decreased. The impoundment marshes experienced an accretion deficit of one full order of magnitude (0.1 vs. 1.0 m/yr) based on comparison of accretion and sea level rise data, while the unmanaged reference marshes experienced a five-fold smaller deficit or no deficit. These data suggest that the gravity-drained impoundments likely have a shorter life expectancy than the reference marshes in the rapidly subsiding Louisiana coast.

  7. Expansion of inverted repeat does not decrease substitution rates in Pelargonium plastid genomes.

    PubMed

    Weng, Mao-Lun; Ruhlman, Tracey A; Jansen, Robert K

    2017-04-01

    For species with minor inverted repeat (IR) boundary changes in the plastid genome (plastome), nucleotide substitution rates were previously shown to be lower in the IR than the single copy regions (SC). However, the impact of large-scale IR expansion/contraction on plastid nucleotide substitution rates among closely related species remains unclear. We included plastomes from 22 Pelargonium species, including eight newly sequenced genomes, and used both pairwise and model-based comparisons to investigate the impact of the IR on sequence evolution in plastids. Ten types of plastome organization with different inversions or IR boundary changes were identified in Pelargonium. Inclusion in the IR was not sufficient to explain the variation of nucleotide substitution rates. Instead, the rate heterogeneity in Pelargonium plastomes was a mixture of locus-specific, lineage-specific and IR-dependent effects. Our study of Pelargonium plastomes that vary in IR length and gene content demonstrates that the evolutionary consequences of retaining these repeats are more complicated than previously suggested.

  8. Magnetron sputtering of metallic coatings onto elastomeric substrates for a decrease in fuel permeation rate

    NASA Astrophysics Data System (ADS)

    Myntti, Matthew F.

    The purpose of this research was to investigate the application of a metallic coating by magnetron sputtering onto elastomeric substrates, as an inhibiting layer to permeation transport. The metallic coatings which were deposited were aluminum, titanium, and copper. The substrates used were NBR, FVMQ, and FKM elastomers. The permeating fluids were ASTM Fuel C, isooctane, and toluene. The magnetron sputtering properties of these metallic elements were unique to each material, with the titanium sputtering rate being very low. The sputtering rates of these materials correlated well with their sublimation temperature. It was found that some of the metallic particles which were sputtered onto the substrates, implanted into the surface of the elastomeric membranes, with the total amount and distance of implantation being related to the density of the substrate material. The permeation of these solvents through the composite materials was reduced by the presence of these coatings with the reduction in permeation rate ranging from 12 to 25% for Fuel C. The pervaporation properties of these substrates were also evaluated. It was found from this analysis that for the FVMQ and NBR substrates, the permeation rate of the permeating solute molecules was proportional to the size of the permeation molecule. The substrate materials were not significantly stiffened by the addition of the thin metallic coatings. The coated materials were cohesive and well adhered, as determined by stretching of the substrate materials with the metallic layer in place. Upon stretching, there was no evidence of damage to the metallic coating.

  9. Competition between apex predators? Brown bears decrease wolf kill rate on two continents.

    PubMed

    Tallian, Aimee; Ordiz, Andrés; Metz, Matthew C; Milleret, Cyril; Wikenros, Camilla; Smith, Douglas W; Stahler, Daniel R; Kindberg, Jonas; MacNulty, Daniel R; Wabakken, Petter; Swenson, Jon E; Sand, Håkan

    2017-02-08

    Trophic interactions are a fundamental topic in ecology, but we know little about how competition between apex predators affects predation, the mechanism driving top-down forcing in ecosystems. We used long-term datasets from Scandinavia (Europe) and Yellowstone National Park (North America) to evaluate how grey wolf (Canis lupus) kill rate was affected by a sympatric apex predator, the brown bear (Ursus arctos). We used kill interval (i.e. the number of days between consecutive ungulate kills) as a proxy of kill rate. Although brown bears can monopolize wolf kills, we found no support in either study system for the common assumption that they cause wolves to kill more often. On the contrary, our results showed the opposite effect. In Scandinavia, wolf packs sympatric with brown bears killed less often than allopatric packs during both spring (after bear den emergence) and summer. Similarly, the presence of bears at wolf-killed ungulates was associated with wolves killing less often during summer in Yellowstone. The consistency in results between the two systems suggests that brown bear presence actually reduces wolf kill rate. Our results suggest that the influence of predation on lower trophic levels may depend on the composition of predator communities.

  10. Competition between apex predators? Brown bears decrease wolf kill rate on two continents

    PubMed Central

    Ordiz, Andrés; Metz, Matthew C.; Milleret, Cyril; Wikenros, Camilla; Smith, Douglas W.; Stahler, Daniel R.; Kindberg, Jonas; MacNulty, Daniel R.; Wabakken, Petter; Swenson, Jon E.; Sand, Håkan

    2017-01-01

    Trophic interactions are a fundamental topic in ecology, but we know little about how competition between apex predators affects predation, the mechanism driving top-down forcing in ecosystems. We used long-term datasets from Scandinavia (Europe) and Yellowstone National Park (North America) to evaluate how grey wolf (Canis lupus) kill rate was affected by a sympatric apex predator, the brown bear (Ursus arctos). We used kill interval (i.e. the number of days between consecutive ungulate kills) as a proxy of kill rate. Although brown bears can monopolize wolf kills, we found no support in either study system for the common assumption that they cause wolves to kill more often. On the contrary, our results showed the opposite effect. In Scandinavia, wolf packs sympatric with brown bears killed less often than allopatric packs during both spring (after bear den emergence) and summer. Similarly, the presence of bears at wolf-killed ungulates was associated with wolves killing less often during summer in Yellowstone. The consistency in results between the two systems suggests that brown bear presence actually reduces wolf kill rate. Our results suggest that the influence of predation on lower trophic levels may depend on the composition of predator communities. PMID:28179516

  11. Formation of the Giant Planets by Concurrent Accretion of Solids and Gas

    NASA Technical Reports Server (NTRS)

    Hubickyj, Olenka

    1997-01-01

    Models were developed to simulate planet formation. Three major phases are characterized in the simulations: (1) planetesimal accretion rate, which dominates that of gas, rapidly increases owing to runaway accretion, then decreases as the planet's feeding zone is depleted; (2) occurs when both solid and gas accretion rates are small and nearly independent of time; and (3) starts when the solid and gas masses are about equal and is marked by runaway gas accretion. The models applicability to planets in our Solar System are judged using two basic "yardsticks". The results suggest that the solar nebula dissipated while Uranus and Neptune were in the second phase, during which, for a relatively long time, the masses of their gaseous envelopes were small but not negligible compared to the total masses. Background information, results and a published article are included in the report.

  12. Pulsed Accretion onto Eccentric and Circular Binaries

    NASA Astrophysics Data System (ADS)

    Muñoz, Diego J.; Lai, Dong

    2016-08-01

    We present numerical simulations of circumbinary accretion onto eccentric and circular binaries using the moving-mesh code AREPO. This is the first set of simulations to tackle the problem of binary accretion using a finite-volume scheme on a freely moving mesh, which allows for accurate measurements of accretion onto individual stars for arbitrary binary eccentricity. While accretion onto a circular binary shows bursts with period of ˜ 5 times the binary period P b, accretion onto an eccentric binary is predominantly modulated at the period ˜ 1{P}{{b}}. For an equal-mass circular binary, the accretion rates onto individual stars are quite similar to each other, following the same variable pattern in time. By contrast, for eccentric binaries, one of the stars can accrete at a rate 10-20 times larger than its companion. This “symmetry breaking” between the stars, however, alternates over timescales of order 200P b and can be attributed to a slowly precessing, eccentric circumbinary disk. Over longer timescales, the net accretion rates onto individual stars are the same, reaching a quasi-steady state with the circumbinary disk. These results have important implications for the accretion behavior of binary T Tauri stars and supermassive binary black holes.

  13. Acute supplementation of amino acids increases net protein accretion in IUGR fetal sheep.

    PubMed

    Brown, Laura D; Rozance, Paul J; Thorn, Stephanie R; Friedman, Jacob E; Hay, William W

    2012-08-01

    Placental insufficiency decreases fetal amino acid uptake from the placenta, plasma insulin concentrations, and protein accretion, thus compromising normal fetal growth trajectory. We tested whether acute supplementation of amino acids or insulin into the fetus with intrauterine growth restriction (IUGR) would increase net fetal protein accretion rates. Late-gestation IUGR and control (CON) fetal sheep received acute, 3-h infusions of amino acids (with euinsulinemia), insulin (with euglycemia and euaminoacidemia), or saline. Fetal leucine metabolism was measured under steady-state conditions followed by a fetal muscle biopsy to quantify insulin signaling. In CON, increasing amino acid delivery rates to the fetus by 100% increased leucine oxidation rates by 100%. In IUGR, amino acid infusion completely suppressed fetal protein breakdown rates but increased leucine oxidation rate by only 25%, resulting in increased protein accretion rates by 150%. Acute insulin infusion, however, had very little effect on amino acid delivery rates, fetal leucine disposal rates, or fetal protein accretion rates in CON or IUGR fetuses despite robust signaling of the fetal skeletal muscle insulin-signaling cascade. These results indicate that, when amino acids are given directly into the fetal circulation independently of changes in insulin concentrations, IUGR fetal sheep have suppressed protein breakdown rates, thus increasing net fetal protein accretion.

  14. Drug eluting biliary stents to decrease stent failure rates: A review of the literature

    PubMed Central

    Shatzel, Joseph; Kim, Jisoo; Sampath, Kartik; Syed, Sharjeel; Saad, Jennifer; Hussain, Zilla H; Mody, Kabir; Pipas, J Marc; Gordon, Stuart; Gardner, Timothy; Rothstein, Richard I

    2016-01-01

    Biliary stenting is clinically effective in relieving both malignant and non-malignant obstructions. However, there are high failure rates associated with tumor ingrowth and epithelial overgrowth as well as internally from biofilm development and subsequent clogging. Within the last decade, the use of prophylactic drug eluting stents as a means to reduce stent failure has been investigated. In this review we provide an overview of the current research on drug eluting biliary stents. While there is limited human trial data regarding the clinical benefit of drug eluting biliary stents in preventing stent obstruction, recent research suggests promise regarding their safety and potential efficacy. PMID:26839648

  15. Decreased heart rate and enhanced sinus arrhythmia during interictal sleep demonstrate autonomic imbalance in generalized epilepsy

    PubMed Central

    Sivakumar, Siddharth S.; Namath, Amalia G.; Tuxhorn, Ingrid E.; Lewis, Stephen J.

    2016-01-01

    We hypothesized that epilepsy affects the activity of the autonomic nervous system even in the absence of seizures, which should manifest as differences in heart rate variability (HRV) and cardiac cycle. To test this hypothesis, we investigated ECG traces of 91 children and adolescents with generalized epilepsy and 25 neurologically normal controls during 30 min of stage 2 sleep with interictal or normal EEG. Mean heart rate (HR) and high-frequency HRV corresponding to respiratory sinus arrhythmia (RSA) were quantified and compared. Blood pressure (BP) measurements from physical exams of all subjects were also collected and analyzed. RSA was on average significantly stronger in patients with epilepsy, whereas their mean HR was significantly lower after adjusting for age, body mass index, and sex, consistent with increased parasympathetic tone in these patients. In contrast, diastolic (and systolic) BP at rest was not significantly different, indicating that the sympathetic tone is similar. Remarkably, five additional subjects, initially diagnosed as neurologically normal but with enhanced RSA and lower HR, eventually developed epilepsy, suggesting that increased parasympathetic tone precedes the onset of epilepsy in children. ECG waveforms in epilepsy also displayed significantly longer TP intervals (ventricular diastole) relative to the RR interval. The relative TP interval correlated positively with RSA and negatively with HR, suggesting that these parameters are linked through a common mechanism, which we discuss. Altogether, our results provide evidence for imbalanced autonomic function in generalized epilepsy, which may be a key contributing factor to sudden unexpected death in epilepsy. PMID:26888110

  16. Decreased rates of methionine synthesis by methylene tetrahydrofolate reductase-deficient fibroblasts and lymphoblasts.

    PubMed

    Boss, G R; Erbe, R W

    1981-06-01

    Methionine synthesis from homocysteine was measured in intact human fibroblasts and lymphoblasts using a [14C]formate label. Seven fibroblast lines and two lymphoblast lines derived from patients with 5,10-methylene tetrahydrofolate reductase deficiency had rates of methionine synthesis that were from 4 to 43% of normal. When the patients were divided by clinical status into mildly (two patients), moderately (two patients), and severely (three patients) affected, methionine biosynthesis expressed as a percent of control values was 43 and 33%, 11 and 10%, and 7, 6, and 4%, respectively, in fibroblasts. Similar data for the two lymphoblast lines were 36 and 26% for a mildly and moderately affected patient, respectively. These data are to be contrasted with the measurement of residual enzyme activity in cell extracts which agrees less precisely with the clinical status of the patients. In the presence of normal methionine synthetase activity, the rate of synthesis of methionine from homocysteine is a function of the activity of the enzyme 5,10-methylene tetrahydrofolate reductase, and measurement of the methionine biosynthetic capacity of cells deficient in this enzyme accurately reflects the clinical status of the patient from whom the cells were derived.

  17. Decreased Spontaneous Eye Blink Rates in Chronic Cannabis Users: Evidence for Striatal Cannabinoid-Dopamine Interactions

    PubMed Central

    Kowal, Mikael A.; Colzato, Lorenza S.; Hommel, Bernhard

    2011-01-01

    Chronic cannabis use has been shown to block long-term depression of GABA-glutamate synapses in the striatum, which is likely to reduce the extent to which endogenous cannabinoids modulate GABA- and glutamate-related neuronal activity. The current study aimed at investigating the effect of this process on striatal dopamine levels by studying the spontaneous eye blink rate (EBR), a clinical marker of dopamine level in the striatum. 25 adult regular cannabis users and 25 non-user controls matched for age, gender, race, and IQ were compared. Results show a significant reduction in EBR in chronic users as compared to non-users, suggesting an indirect detrimental effect of chronic cannabis use on striatal dopaminergic functioning. Additionally, EBR correlated negatively with years of cannabis exposure, monthly peak cannabis consumption, and lifetime cannabis consumption, pointing to a relationship between the degree of impairment of striatal dopaminergic transmission and cannabis consumption history. PMID:22125599

  18. Morphological Change and Decreasing Transfer Rate of Biofilm-Featured Listeria monocytogenes EGDe.

    PubMed

    Lee, Yuejia; Wang, Chinling

    2017-03-01

    Listeria monocytogenes , a lethal foodborne pathogen, has the ability to resist the hostile food processing environment and thus frequently contaminates ready-to-eat foods during processing. It is commonly accepted that the tendency of L. monocytogenes ' to generate biofilms on various surfaces enhances its resistance to the harshness of the food processing environment. However, the role of biofilm formation in the transferability of L. monocytogenes EGDe remains controversial. We examined the growth of Listeria biofilms on stainless steel surfaces and their effect on the transferability of L. monocytogenes EGDe. The experiments were a factorial 2 × 2 design with at least three biological replicates. Through scanning electron microscopy, a mature biofilm with intensive aggregates of cells was observed on the surface of stainless steel after 3 or 5 days of incubation, depending on the initial level of inoculation. During biofilm development, L. monocytogenes EGDe carried out binary fission vigorously before a mature biofilm was formed and subsequently changed its cellular morphology from rod shaped to sphere shaped. Furthermore, static biofilm, which was formed after 3 days of incubation at 25°C, significantly inhibited the transfer rate of L. monocytogenes EGDe from stainless steel blades to 15 bologna slices. During 7 days of storage at 4°C, however, bacterial growth rate was not significantly impacted by whether bacteria were transferred from biofilm and the initial concentrations of transferred bacteria on the slice. In conclusion, this study is the first to report a distinct change in morphology of L. monocytogenes EGDe at the late stage of biofilm formation. More importantly, once food is contaminated by L. monocytogenes EGDe, contamination proceeds independently of biofilm development and the initial level of contamination when food is stored at 4°C, even if contamination with L. monocytogenes EGDe was initially undetectable before storage.

  19. Decreases in human immunodeficiency virus infection rates in Kombolcha, Ethiopia: a 10-year data review

    PubMed Central

    Shiferaw, Melashu Balew; Gebregergs, Gebremedhin Berhe; Sinishaw, Mulusew Alemneh; Yesuf, Yohannes Amede

    2016-01-01

    Introduction Acquired immunodeficiency syndrome is one of the most serious public health and development challenges in sub-Saharan Africa, including Ethiopia. A particular challenge for prevention strategies has been the emergence of hotspot areas. Therefore, human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome programs should not be based on national level statistics, but need to be more focused geographically. Kombolcha is one of the high spot areas with different projects and development corridors. Hence, the aim of this study is to assess the trend of HIV infection rates among patients who visited Africa Service Committee clinic from 2005 to 2014. Methods An institutional-based cross-sectional study was conducted from January 1 to January 30, 2016. All records of new patients enrolled from February 8, 2005 to December 31, 2014 were reviewed. Data on sociodemographic information, risky sexual behavior, and HIV test result were collected from each study participant using data collection format. Data were analyzed using SPSS version 20.0. A multivariate logistic regression model was used to identify risk factors of HIV infection. Results The overall HIV infection was 10.8% (2,233/20,674). The rate of infection varied from 13.3% in 2005 to 4.5% in 2014, and its trend had significantly declined from 2008 to 2014. Urban residence (adjusted odds ratio [AOR]: 2.53; 95% confidence interval [CI]: 1.22–5.25), patients who ever had intercourse with penetration (AOR: 5.62; 95% CI: 1.11–28.57), and those who had marriage experience (AOR: 11.65; 95% CI: 4.2–32.3) were more infected with HIV. Conclusion The trend of HIV infection significantly reduced in the last 10 years in Kombolcha area. However, the HIV infection still remains high (4.5%) that needs intervention of those who had marriage experience, risky sexual behavior, and urban dwellers. PMID:27462177

  20. Star formation sustained by gas accretion

    NASA Astrophysics Data System (ADS)

    Sánchez Almeida, Jorge; Elmegreen, Bruce G.; Muñoz-Tuñón, Casiana; Elmegreen, Debra Meloy

    2014-07-01

    Numerical simulations predict that metal-poor gas accretion from the cosmic web fuels the formation of disk galaxies. This paper discusses how cosmic gas accretion controls star formation, and summarizes the physical properties expected for the cosmic gas accreted by galaxies. The paper also collects observational evidence for gas accretion sustaining star formation. It reviews evidence inferred from neutral and ionized hydrogen, as well as from stars. A number of properties characterizing large samples of star-forming galaxies can be explained by metal-poor gas accretion, in particular, the relationship among stellar mass, metallicity, and star-formation rate (the so-called fundamental metallicity relationship). They are put forward and analyzed. Theory predicts gas accretion to be particularly important at high redshift, so indications based on distant objects are reviewed, including the global star-formation history of the universe, and the gas around galaxies as inferred from absorption features in the spectra of background sources.

  1. Accretion Processes in Astrophysics

    NASA Astrophysics Data System (ADS)

    González Martínez-País, Ignacio; Shahbaz, Tariq; Casares Velázquez, Jorge

    2014-03-01

    List of contributors; List of participants; Preface; Acknowledgments; Abbreviations; 1. Accretion disks Henk Spruit; 2. The evolution of binary systems Philipp Podsiadlowski; 3. Accretion onto white dwarfs Brian Warner; 4. Accretion in X-ray binary systems Robert I. Hynes; 5. X-ray binary populations in galaxies Giuseppina Fabbiano; 6. Observational characteristics of accretion onto black holes I Chris Done; 7. Observational characteristics of accretion onto black holes II Rob Fender; 8. Computing black hole accretion John F. Hawley; Appendix: Piazzi Smyth, the Cape of Good Hope, Tenerife and the siting of large telescopes Brian Warner.

  2. The PISA Pre-Main Sequence accreting models

    NASA Astrophysics Data System (ADS)

    Tognelli, Emanuele; Prada Moroni, Pier Giorgio; Degl'Innocenti, Scilla

    2013-07-01

    The poster investigates the effect of accretion processes on the evolution of stellar models computed by means of the well tested and updated PROSECCO evolutionary code, under the hypothesis of thin-disk accretion. We analysed the effect on the evolution of the adoption of different parameters as the accretion rate, accretion history, seed mass, and the fraction of the infalling matter energy (alpha_acc) deposed in to the star (accretion energy). We confirm that the most critical parameter is the accretion energy. We show that, depending on alpha_acc the evolution of accreting and non-accreting objects can be completely different, confirming that the adoption of small alpha_acc value (i.e. small accretion energy, cold accretion) produces fainter and more compact models with respect to the ones predicted from non-accreting structures at the same mass and age, models that can not be reconciled with the data available for young objects (i.e. position in the HR diagram, lithium abundances). On the contrary, if a large part of the accretion luminosity is deposed into the star (alpha_acc = 1, hot accretion), at least during the fisrt stages of the accretion phase or during bursts episodes, large radii and luminosities are achievable, with resulting structures much more similar to the non-accreting ones.

  3. Detraining increases body fat and weight and decreases VO2peak and metabolic rate.

    PubMed

    Ormsbee, Michael J; Arciero, Paul J

    2012-08-01

    Competitive collegiate swimmers commonly take a month off from swim training after their last major competition. This abrupt cessation of intense physical training has not been well studied and may lead to physiopsychological decline. The purpose of this investigation was to examine the effects of swim detraining (DT) on body composition, aerobic fitness, resting metabolism, mood state, and blood lipids in collegiate swimmers. Eight healthy endurance-trained swimmers (V(O2)peak, 46.7 ± 10.8 ml · kg(-1) · min(-1)) performed 2 identical test days, 1 in the trained (TR) state and 1 in the detrained (~5 weeks) state (DT). Body composition and circumferences, maximal oxygen consumption (V(O2)peak), resting metabolism (RMR), blood lipids, and mood state were measured. After DT, body weight (TR, 68.9 ± 9.7 vs. DT, 69.8 ± 9.8 kg; p = 0.03), fat mass (TR, 14.7 ± 7.6 vs. DT, 16.5 ± 7.4 kg; p = 0.001), and waist circumference (TR, 72.7 ± 3.1 vs. DT, 73.8 ± 3.6 cm; p = 0.03) increased, whereas V(O2)peak (TR, 46.7 ± 10.8 vs. DT, 43.1 ± 10.3 ml · kg(-1) · min(-1); p = 0.02) and RMR (TR, 1.34 ± 0.2 vs. DT, 1.25 ± 0.17 kcal · min(-1); p = 0.008) decreased, and plasma triglycerides showed a trend to increase (p = 0.065). Our data suggest that DT after a competitive collegiate swim season adversely affects body composition, fitness, and metabolism. Athletes and coaches need to be aware of the negative consequences of detraining from swimming, and plan off-season training schedules accordingly to allow for adequate rest/recovery and prevent overuse injuries. It's equally important to mitigate the negative effects on body composition, aerobic fitness and metabolism so performance may continue to improve over the long term.

  4. Is volcanic air pollution associated with decreased heart-rate variability?

    PubMed Central

    Chow, Dominic C; Grandinetti, Andrew; Fernandez, Ed; Sutton, A J; Elias, Tamar; Brooks, Barbara; Tam, Elizabeth K

    2010-01-01

    Objectives To determine the autonomic cardiovascular control among residents of Hawaii who are exposed to varying levels of volcanic air pollution (vog), which consists largely of sulfur dioxide (SO2) and acid aerosols. Methods In a cross-sectional study between April 2006 and June 2008, the authors measured cardiovagal autonomic function by heart-rate variability (HRV) in 72 healthy individuals who lived in four exposure zones on Hawaii Island: vog-free (n=18); episodic exposure to SO2 >200 ppb and acid aerosol (n=19); chronic exposure to SO2 ≥30 ppb and acid aerosol (n=15); and chronic exposure to acid aerosols (n=20). Individuals with diabetes or heart disease, or who had smoked in the preceding month were excluded. HRV was measured in all subjects during rest, paced breathing and active standing (Ewing manoeuvre). HRV was analysed in time and frequency domains and compared between the four exposure zones. Results There were no significant differences between exposure zones in HRV, in either time or frequency domains, even after adjustment for age, gender, ethnicity and body mass index. There was no significant HRV change in three individuals in whom HRV was measured before and during an exposure to combined SO2 100–250 ppb and concentration of respirable particles of diameter ≤2.5 μ (PM2.5) >500 μg/m3. Age was significantly correlated with time-domain parameters during paced breathing and the Ewing manoeuvre. Conclusions This study of healthy individuals found no appreciable effects of vog on the autonomic nervous system. PMID:21546995

  5. Scaling of the photon index vs. mass accretion rate correlation and estimate of black hole mass in M101 ULX-1

    NASA Astrophysics Data System (ADS)

    Titarchuk, Lev; Seifina, Elena

    2016-01-01

    We report the results of Swift and Chandra observations of an ultraluminous X-ray source, ULX-1 in M101. We show strong observational evidence that M101 ULX-1 undergoes spectral transitions from the low/hard state to the high/soft state during these observations. The spectra of M101 ULX-1 are well fitted by the so-called bulk motion Comptonization (BMC) model for all spectral states. We have established the photon index (Γ) saturation level, Γsat = 2.8 ± 0.1, in the Γ versus mass accretion rate (Ṁ) correlation. This Γ-Ṁ correlation allows us to evaluate black hole (BH) mass in M101 ULX-1 to be MBH ~ (3.2-4.3) × 104 M⊙, assuming the spread in distance to M101 (from 6.4 ± 0.5 Mpc to 7.4 ± 0.6 Mpc). For this BH mass estimate we apply the scaling method, using Galactic BHs XTE J1550-564, H 1743-322 and 4U 1630-472 as reference sources. The Γ vs. Ṁ correlation revealed in M101 ULX-1 is similar to that in a number of Galactic BHs and clearly exhibits the correlation along with the strong Γ saturation at ≈ 2.8. This is robust observational evidence for the presence of a BH in M101 ULX-1. We also find that the seed (disk) photon temperatures are low, on the order of 40-100 eV, which is consistent with high BH mass in M101 ULX-1. Thus, we suggest that the central object in M101 ULX-1 has intermediate BH mass on the order of 104 solar masses.

  6. The Structure and Evolution of an Accretion Flow Interacting with the Central Star

    NASA Astrophysics Data System (ADS)

    Fujimoto, Masayuki Y.

    1995-09-01

    The mechanical and thermal structure of accretion flows interacting with the central stars via viscous stress is studied by modeling the spatial variation of dynamical viscosity with a simple one-parameter function. The latter assumption has the advantage of yielding the analytical solution of rotation laws, and the thermal balance near the disk-star interface is analyzed by means of a one-zone approximation. Based on these results, a general picture of the evolutionary changes in the accretion process is presented with the spin history of central stars taken into account. Under a constant accretion rate, there exists the maximum rotation rate of the central star which allows the structure of accretion flow in hydrostatic and thermal equilibrium; it is smaller for larger accretion rates and occurs when the inflow rate of angular momentum decreases to the critical value Jdottrn, which takes the values around zero or larger, depending on the physical conditions in the flows. The equilibrium configurations with both the positive and negative inflow rate of angular momentum, as discussed by Paczynski and by Popham & Narayan are possible, in which the stellar rotation rate is no longer accelerated, and hence, the structure of accretion flow remains the same. It is shown, however, that these configurations exchange their thermal stability at this maximum rotation rate; in particular, the structures of mass accretion with the inflow rate of angular momentum below Jdottrn is secularly unstable, and hence, they cannot be realized in the course of the evolution. The evolution of the systems differs according to the stellar response to the mass accretion; corresponding to Jdottrn, there exists the critical value, Scri (≃ -3 or larger), for the changing rate of the stellar radius 5 = d log R*(t)/d log M*(t)(M* and R* being the mass and equator radius of the central star, respectively). If the central star expands or shrinks moderately during accreting mass as 5 ≥ Scri, the

  7. Perturbation growth in accreting filaments

    NASA Astrophysics Data System (ADS)

    Clarke, S. D.; Whitworth, A. P.; Hubber, D. A.

    2016-05-01

    We use smoothed particle hydrodynamic simulations to investigate the growth of perturbations in infinitely long filaments as they form and grow by accretion. The growth of these perturbations leads to filament fragmentation and the formation of cores. Most previous work on this subject has been confined to the growth and fragmentation of equilibrium filaments and has found that there exists a preferential fragmentation length-scale which is roughly four times the filament's diameter. Our results show a more complicated dispersion relation with a series of peaks linking perturbation wavelength and growth rate. These are due to gravo-acoustic oscillations along the longitudinal axis during the sub-critical phase of growth. The positions of the peaks in growth rate have a strong dependence on both the mass accretion rate onto the filament and the temperature of the gas. When seeded with a multiwavelength density power spectrum, there exists a clear preferred core separation equal to the largest peak in the dispersion relation. Our results allow one to estimate a minimum age for a filament which is breaking up into regularly spaced fragments, as well as an average accretion rate. We apply the model to observations of filaments in Taurus by Tafalla & Hacar and find accretion rates consistent with those estimated by Palmeirim et al.

  8. Episodic Accretion in Young Stars

    NASA Astrophysics Data System (ADS)

    Audard, M.; Ábrahám, P.; Dunham, M. M.; Green, J. D.; Grosso, N.; Hamaguchi, K.; Kastner, J. H.; Kóspál, Á.; Lodato, G.; Romanova, M. M.; Skinner, S. L.; Vorobyov, E. I.; Zhu, Z.

    In the last 20 years, the topic of episodic accretion has gained significant interest in the star-formation community. It is now viewed as a common, although still poorly understood, phenomenon in low-mass star formation. The FU Orionis objects (FUors) are long-studied examples of this phenomenon. FU Orionis objects are believed to undergo accretion outbursts during which the accretion rate rapidly increases from typically 10-7 to a few 10-4 M⊙ yr-1, and remains elevated over several decades or more. EXors, a loosely defined class of pre-main-sequence stars, exhibit shorter and repetitive outbursts, associated with lower accretion rates. The relationship between the two classes, and their connection to the standard pre-main-sequence evolutionary sequence, is an open question: Do they represent two distinct classes, are they triggered by the same physical mechanism, and do they occur in the same evolutionary phases? Over the past couple of decades, many theoretical and numerical models have been developed to explain the origin of FUor and EXor outbursts. In parallel, such accretion bursts have been detected at an increasing rate, and as observing techniques improve, each individual outburst is studied in increasing detail. We summarize key observations of pre-main-sequence star outbursts, and review the latest thinking on outburst triggering mechanisms, the propagation of outbursts from star/disk to disk/jet systems, the relation between classical EXors and FUors, and newly discovered outbursting sources — all of which shed new light on episodic accretion. We finally highlight some of the most promising directions for this field in the near- and long-term.

  9. Eclipse Mapping of Accretion Discs

    NASA Astrophysics Data System (ADS)

    Baptista, R.

    The eclipse mapping method is an inversion technique that makes use of the information contained in eclipse light curves to probe the structure, the spectrum and the time evolution of accretion discs. In this review I present the basics of the method and discuss its different implementations. I summarize the most important results obtained to date and discuss how they have helped to improve our understanding of accretion physics, from testing the theoretical radial brightness temperature distribution and measuring mass accretion rates to showing the evolution of the structure of a dwarf novae disc throughout its outburst cycle, from isolating the spectrum of a disc wind to revealing the geometry of disc spiral shocks. I end with an outline of the future prospects.

  10. Accretion flows onto supermassive black holes

    NASA Technical Reports Server (NTRS)

    Begelman, Mitchell C.

    1988-01-01

    The radiative and hydrodynamic properties of an angular momentum-dominated accretion flow onto a supermassive black hole depend largely on the ratio of the accretion rate to the Eddington accretion rate. High values of this ratio favor optically thick flows which produce largely thermal radiation, while optically thin 'two-temperature' flows may be present in systems with small values of this ratio. Observations of some AGN suggest that thermal and nonthermal sources of radiation may be of comparable importance in the 'central engine'. Consideration is given to the possibilities for coexistence of different modes of accretion in a single flow. One intriguing possibility is that runaway pair production may cause an optically thick 'accretion annulus' to form at the center of a two-temperature inflow.

  11. Determination of time-dependent skin temperature decrease rates in the case of abrupt changes of environmental temperature.

    PubMed

    Mall, G; Hubig, M; Beier, G; Büttner, A; Eisenmenger, W

    2000-09-11

    The present study deals with the development of a method for determining time-dependent temperature decrease rates and its application to postmortem surface cooling. The study concentrates on evaluating skin cooling behavior since data on skin cooling in the forensic literature are scarce. Furthermore, all heat transfer mechanisms strongly depend on the temperature gradient between body surface and environment. One of the main problems in modelling postmortem cooling processes is the dependence on the environmental temperature. All models for postmortem rectal cooling essentially presuppose a constant environmental temperature. In medico-legal practice, the temperature of the surrounding of a corpse mostly varies; therefore, an approach for extending the models to variable environmental temperatures is desirable. It consists in 'localizing' them to infinitesimal small intervals of time. An extended model differential equation is obtained and solved explicitly. The approach developed is applied to the single-exponential Newtonian model of surface cooling producing the following differential equation:T(S)'(t)=-lambda(t)(T(S)(t)-T(E)(t))(with T(S)(t) the surface/skin temperature, T(E)(t) the environmental temperature, lambda(t) the temperature decrease rate and T(S)'(t) the actual change of skin temperature or first-order derivative of T(S)). The differential equation directly provides an estimator:lambda(t)=-T(S)'(t)T(S)(t)-T(E)(t)for the time-dependent temperature decrease rate. The estimator is applied to two skin cooling experiments with different types of abrupt changes of environmental temperature, peak-like and step-like; the values of the time-dependent temperature decrease rate function were calculated. By reinserting them, the measured surface temperature curve could be accurately reconstructed, indicating that the extended model is well suited for describing surface cooling in the case of abrupt changes of environmental temperature.

  12. Black Hole Advective Accretion Disks with Optical Depth Transition

    SciTech Connect

    Artemove, Y.V.; Bisnovatyi-Kogan, G.S.; Igumenshchev, I.V.; Novikov, I.D.

    2006-02-01

    We have constructed numerically global solutions of advective accretion disks around black holes that describe a continuous transition between the effectively optically thick outer and optically thin inner disk regions. We have concentrated on models of accretion flows with large mass accretion rates, and we have employed a bridging formula for radiative losses at high and low effective optical depths.

  13. Two-dimensional numerical simulations of supercritical accretion flows revisited

    SciTech Connect

    Yang, Xiao-Hong; Yuan, Feng; Bu, De-Fu; Ohsuga, Ken E-mail: fyuan@shao.ac.cn

    2014-01-01

    We study the dynamics of super-Eddington accretion flows by performing two-dimensional radiation-hydrodynamic simulations. Compared with previous works, in this paper we include the T {sub θφ} component of the viscous stress and consider various values of the viscous parameter α. We find that when T {sub θφ} is included, the rotational speed of the high-latitude flow decreases, while the density increases and decreases at the high and low latitudes, respectively. We calculate the radial profiles of inflow and outflow rates. We find that the inflow rate decreases inward, following a power law form of M-dot {sub in}∝r{sup s}. The value of s depends on the magnitude of α and is within the range of ∼0.4-1.0. Correspondingly, the radial profile of density becomes flatter compared with the case of a constant M-dot (r). We find that the density profile can be described by ρ(r)∝r {sup –p} and the value of p is almost same for a wide range of α ranging from α = 0.1 to 0.005. The inward decrease of inflow accretion rate is very similar to hot accretion flows, which is attributed to the mass loss in outflows. To study the origin of outflow, we analyze the convective stability of the slim disk. We find that depending on the value of α, the flow is marginally stable (when α is small) or unstable (when α is large). This is different from the case of hydrodynamical hot accretion flow, where radiation is dynamically unimportant and the flow is always convectively unstable. We speculate that the reason for the difference is because radiation can stabilize convection. The origin of outflow is thus likely because of the joint function of convection and radiation, but further investigation is required.

  14. Partial accretion regime of accreting millisecond pulsars

    NASA Astrophysics Data System (ADS)

    Eksi, Kazim

    2016-07-01

    The inner parts of the disks around neutron stars in low mass X-ray binaries may become geometrically thick due to inhibition of accretion at the disk mid-plane when the central object is rotating rapidly. In such a case matter inflowing through the disk may keep accreting onto the poles of the neutron star from the parts of the disk away from the disk mid-plane while the matter is propelled at the disk mid-plane. An important ingredient of the evolution of millisecond pulsars is then the fraction of the inflowing matter that can accrete onto the poles in the fast rotation regime depending on the fastness parameter. This ``soft'' propeller regime may be associated with the rapid decay stage observed in the light curves of several accreting millisecond pulsars. To date only a few studies considered the partial accretion regime. By using geometrical arguments we improve the existing studies and test the model by reproducing the lightcurves of millisecond X-ray pulsars via time dependent simulations of disk evolution. We also present analytical solutions that represent disks with partial accretion.

  15. How to Decrease Suicide Rates in Both Genders? An Effectiveness Study of a Community-Based Intervention (EAAD)

    PubMed Central

    Székely, András; Konkolÿ Thege, Barna; Mergl, Roland; Birkás, Emma; Rózsa, Sándor

    2013-01-01

    Background The suicide rate in Hungary is high in international comparison. The two-year community-based four-level intervention programme of the European Alliance Against Depression (EAAD) is designed to improve the care of depression and to prevent suicidal behaviour. Our aim was to evaluate the effectiveness of a regional community-based four-level suicide prevention programme on suicide rates. Method The EAAD programme was implemented in Szolnok (population 76,311), a town in a region of Hungary with an exceptionally high suicide rate. Effectiveness was assessed by comparing changes in suicide rates in the intervention region after the intervention started with changes in national suicide rates and those in a control region (Szeged) in the corresponding period. Results For the duration of the programme and the follow-up year, suicide rates in Szolnok were significantly lower than the average of the previous three years (p = .0076). The suicide rate thus went down from 30.1 per 100,000 in 2004 to 13.2 in 2005 (−56.1 %), 14.6 in 2006 (−51.4 %) and 12.0 in 2007 (−60.1 %). This decrease of annual suicide rates in Szolnok after the onset of the intervention was significantly stronger than that observed in the whole country (p = .017) and in the control region (p = .0015). Men had the same decrease in suicide rates as women. As secondary outcome, an increase of emergency calls to the hotline service (200%) and outpatient visits at the local psychiatry clinic (76%) was found. Conclusions These results seem to provide further support for the effectiveness of the EAAD concept. Whilst the majority of suicide prevention programs mainly affect female suicidal behaviour, this programme seems to be beneficial for both sexes. The sustainability and the role of the mediating factors (social service and health care utilization, community attitudes about suicide) should be key points in future research. PMID:24086443

  16. Increased plasma clearance rate of thyroxine despite decreased 5'-monodeiodination: study with a peroxisome proliferator in the rat

    SciTech Connect

    Kaiser, C.A.; Seydoux, J.; Giacobino, J.P.; Girardier, L.; Burger, A.G.

    1988-03-01

    In euthyroid rats a 17-day treatment with nafenopin, a hypolipidemic agent and peroxisome proliferator, decreased serum total and free T4 concentrations to 32 +/- 5% and 62 +/- 8% (mean +/- SEM; n = 10), respectively, with no change in serum T3 and TSH concentrations. In methimazole-treated rats infused with 3 nmol T4/day/100 g BW, the nafenopin inhibitory effect was not significantly different from that in euthyroid rats. Nafenopin treatment had the following effects on peripheral T4 and T3 metabolism in euthyroid rats. The plasma clearance rate of T4 (PCR), which was measured by Alzet minipump infusion of tracer, was increased 2-fold (1.58 +/- 0.09 vs. 0.82 +/- 0.06 ml/h.100 g BW; P less than 0.001; n = 5), while the PCR of T3 was decreased (37.5 +/- 1.3 vs. 53.8 +/- 1.8; P less than 0.001; n = 5). The fecal clearance rate of radioactivity derived from T4 was increased 2-fold (1.93 +/- 0.10 vs. 0.77 +/- 0.07 ml/h.100 g BW), whereas the urinary clearance rate was not significantly modified. The 5'-deiodinase (5'D) activity, measured by deiodination of labeled rT3, was strongly inhibited in liver and kidney, not modified in brown fat and anterior pituitary, and increased in cerebral cortex. In methimazole-treated rats substituted with isopropyl-diiodothyronine only hepatic 5'D activity was decreased. It is concluded that the decrease in serum total and free T4, without alteration in serum T3 and TSH concentrations, resulting from nafenopin treatment is mainly due to changes in peripheral T4 and T3 metabolism, since it is also observed in T4-substituted animals. The increased PCR of T4 cannot be explained by an increase in deiodination activity, since the major 5'D pathways are inhibited after nafenopin treatment, and the urinary clearance rate is not modified. It can partly be explained by an increase in the fecal clearance rate of T4, which could be due to an increase in glucoronoconjugation.

  17. Differences in rates of decrease of environmental radiation dose rates by ground surface property in Fukushima City after the Fukushima Daiichi nuclear power plant accident.

    PubMed

    Kakamu, Takeyasu; Kanda, Hideyuki; Tsuji, Masayoshi; Kobayashi, Daisuke; Miyake, Masao; Hayakawa, Takehito; Katsuda, Shin-ichiro; Mori, Yayoi; Okouchi, Toshiyasu; Hazama, Akihiro; Fukushima, Tetsuhito

    2013-01-01

    After the Great East Japan Earthquake on 11 March 2011, the environmental radiation dose in Fukushima City increased. On 11 April, 1 mo after the earthquake, the environmental radiation dose rate at various surfaces in the same area differed greatly by surface property. Environmental radiation measurements continue in order to determine the estimated time to 50% reduction in environmental radiation dose rates by surface property in order to make suggestions for decontamination in Fukushima. The measurements were carried out from 11 April to 11 November 2011. Forty-eight (48) measurement points were selected, including four kinds of ground surface properties: grass (13), soil (5), artificial turf (7), and asphalt (23). Environmental radiation dose rate was measured at heights of 100 cm above the ground surface. Time to 50% reduction of environmental radiation dose rates was estimated for each ground surface property. Radiation dose rates on 11 November had decreased significantly compared with those on 11 April for all surface properties. Artificial turf showed the longest time to 50% reduction (544.32 d, standard error: 96.86), and soil showed the shortest (213.20 d, standard error: 35.88). The authors found the environmental radiation dose rate on artificial materials to have a longer 50% reduction time than that on natural materials. These results contribute to determining an order of priority for decontamination after nuclear disasters.

  18. Pulsed accretion in a variable protostar

    NASA Astrophysics Data System (ADS)

    Muzerolle, James; Furlan, Elise; Flaherty, Kevin; Balog, Zoltan; Gutermuth, Robert

    2013-01-01

    Periodic increases in luminosity arising from variable accretion rates have been predicted for some pre-main-sequence close binary stars as they grow from circumbinary disks. The phenomenon is known as pulsed accretion and can affect the orbital evolution and mass distribution of young binaries, as well as the potential for planet formation. Accretion variability is a common feature of young stars, with a large range of amplitudes and timescales as measured from multi-epoch observations at optical and infrared wavelengths. Periodic variations consistent with pulsed accretion have been seen in only a few young binaries via optical accretion tracers, albeit intermittently with accretion luminosity variations ranging from zero to 50 per cent from orbit to orbit. Here we report that the infrared luminosity of a young protostar (of age about 105 years) increases by a factor of ten in roughly one week every 25.34 days. We attribute this to pulsed accretion associated with an unseen binary companion. The strength and regularity of this accretion signal is surprising; it may be related to the very young age of the system, which is a factor of ten younger than the other pulsed accretors previously studied.

  19. Pulsed accretion in a variable protostar.

    PubMed

    Muzerolle, James; Furlan, Elise; Flaherty, Kevin; Balog, Zoltan; Gutermuth, Robert

    2013-01-17

    Periodic increases in luminosity arising from variable accretion rates have been predicted for some pre-main-sequence close binary stars as they grow from circumbinary disks. The phenomenon is known as pulsed accretion and can affect the orbital evolution and mass distribution of young binaries, as well as the potential for planet formation. Accretion variability is a common feature of young stars, with a large range of amplitudes and timescales as measured from multi-epoch observations at optical and infrared wavelengths. Periodic variations consistent with pulsed accretion have been seen in only a few young binaries via optical accretion tracers, albeit intermittently with accretion luminosity variations ranging from zero to 50 per cent from orbit to orbit. Here we report that the infrared luminosity of a young protostar (of age about 10(5) years) increases by a factor of ten in roughly one week every 25.34 days. We attribute this to pulsed accretion associated with an unseen binary companion. The strength and regularity of this accretion signal is surprising; it may be related to the very young age of the system, which is a factor of ten younger than the other pulsed accretors previously studied.

  20. Microwave ice accretion meter

    NASA Technical Reports Server (NTRS)

    Magenheim, Bertram (Inventor); Rocks, James K. (Inventor)

    1984-01-01

    A system for indicating ice thickness and rate of ice thickness growth on surfaces is disclosed. The region to be monitored for ice accretion is provided with a resonant surface waveguide which is mounted flush, below the surface being monitored. A controlled oscillator provides microwave energy via a feed point at a controllable frequency. A detector is coupled to the surface waveguide and is responsive to electrical energy. A measuring device indicates the frequency deviation of the controlled oscillator from a quiescent frequency. A control means is provided to control the frequency of oscillation of the controlled oscillator. In a first, open-loop embodiment, the control means is a shaft operated by an operator. In a second, closed-loop embodiment, the control means is a processor which effects automatic control.

  1. Diagnostic significance of a mild decrease of baroreflex sensitivity with respect to heart rate in type 1 diabetes mellitus.

    PubMed

    Svačinová, J; Honzíková, N; Krtička, A; Tonhajzerová, I; Javorka, K; Javorka, M

    2013-01-01

    Decreased baroreflex sensitivity is an early sign of autonomic dysfunction in patients with type-1 diabetes mellitus. We evaluated the repeatability of a mild baroreflex sensitivity decrease in diabetics with respect to their heart rate. Finger blood pressure was continuously recorded in 14 young diabetics without clinical signs of autonomic dysfunction and in 14 age-matched controls for 42 min. The recordings were divided into 3-min segments, and the mean inter-beat interval (IBI), baroreflex sensitivity in ms/mm Hg (BRS) and mHz/mm Hg (BRSf) were determined in each segment. These values fluctuated in each subject within 42 min and therefore coefficients of repeatability were calculated for all subjects. Diabetics compared with controls had a decreased mean BRS (p=0.05), a tendency to a shortened IBI (p=0.08), and a decreased BRSf (p=0.17). IBI correlated with BRS in diabetics (p=0.03); this correlation was at p=0.12 in the controls. BRSf was IBI independent (controls: p=0.81, diabetics: p=0.29). We conclude that BRS is partially dependent on mean IBI. Thus, BRS reflects not only an impairment of the quick baroreflex responses of IBI to blood pressure changes, but also a change of the tonic sympathetic and parasympathetic heart rate control. This is of significance during mild changes of BRS. Therefore, an examination of the BRSf index is highly recommended, because this examination improves the diagnostic value of the measurement, particularly in cases of early signs of autonomic dysfunction.

  2. Delivery by Cesarean Section is not Associated With Decreased at-Birth Fracture Rates in Osteogenesis Imperfecta

    PubMed Central

    Bellur, S; Jain, M; Cuthbertson, D; Krakow, D; Shapiro, JR; Steiner, RD; Smith, PA; Bober, MB; Hart, T; Krischer, J; Mullins, M; Byers, PH; Pepin, M; Durigova, M; Glorieux, FH; Rauch, F; Sutton, VR; Lee, B; Nagamani, SC

    2015-01-01

    Purpose Osteogenesis imperfecta (OI) predisposes to recurrent fractures. The moderate-to-severe forms of OI present with antenatal fractures and the mode of delivery that would be safest for the fetus is not known. Methods We conducted systematic analyses on the largest cohort of individuals (n=540) with OI enrolled to-date in the OI Linked Clinical Research Centers. Self-reported at-birth fracture rates were compared in individuals with OI types I, III, and IV. Multivariate analyses utilizing backward-elimination logistic regression model building were performed to assess the effect of multiple covariates including method of delivery on fracture-related outcomes. Results When accounting for other covariates, at-birth fracture rates did not differ based on whether delivery was by vaginal route or by cesarean section (CS). Increased birth weight conferred higher risk for fractures irrespective of the delivery method. In utero fracture, maternal history of OI, and breech presentation were strong predictors for choosing CS for delivery. Conclusion Our study, the largest to analyze the effect of various factors on at-birth fracture rates in OI shows that delivery by CS is not associated with decreased fracture rate. With the limitation that the fracture data were self-reported in this cohort, these results suggest that CS should be performed only for other maternal or fetal indications, but not for the sole purpose of fracture prevention in OI. PMID:26426884

  3. Does Breast Magnetic Resonance Imaging Combined With Conventional Imaging Modalities Decrease the Rates of Surgical Margin Involvement and Reoperation?

    PubMed Central

    Lai, Hung-Wen; Chen, Chih-Jung; Lin, Ying-Jen; Chen, Shu-Ling; Wu, Hwa-Koon; Wu, Yu-Ting; Kuo, Shou-Jen; Chen, Shou-Tung; Chen, Dar-Ren

    2016-01-01

    Abstract The objective of this study was to assess whether preoperative breast magnetic resonance imaging (MRI) combined with conventional breast imaging techniques decreases the rates of margin involvement and reexcision. Data on patients who underwent surgery for primary operable breast cancer were obtained from the Changhua Christian Hospital (CCH) breast cancer database. The rate of surgical margin involvement and the rate of reoperation were compared between patients who underwent conventional breast imaging modalities (Group A: mammography and sonography) and those who received breast MRI in addition to conventional imaging (Group B: mammography, sonography, and MRI). A total of 1468 patients were enrolled in this study. Among the 733 patients in Group A, 377 (51.4%) received breast-conserving surgery (BCS) and 356 (48.6%) received mastectomy. Among the 735 patients in Group B, 348 (47.3%) received BCS and 387 (52.7%) received mastectomy. There were no significant differences in operative method between patients who received conventional imaging alone and those that received MRI and conventional imaging (P = 0.13). The rate of detection of pathological multifocal/multicentric breast cancer was markedly higher in patients who received preoperative MRI than in those who underwent conventional imaging alone (14.3% vs 8.6%, P < 0.01). The overall rate of surgical margin involvement was significantly lower in patients who received MRI (5.0%) than in those who received conventional imaging alone (9.0%) (P < 0.01). However, a significant reduction in rate of surgical margin positivity was only observed in patients who received BCS (Group A, 14.6%; Group B, 6.6%, P < 0.01). The overall BCS reoperation rates were 11.7% in the conventional imaging group and 3.2% in the combined MRI group (P < 0.01). There were no significant differences in rate of residual cancer in specimens obtained during reoperation between the 2 preoperative imaging groups

  4. No evidence for a decrease of nuclear decay rates with increasing heliocentric distance based on radiochronology of meteorites

    NASA Astrophysics Data System (ADS)

    Meier, Matthias M. M.; Wieler, Rainer

    2014-03-01

    . Moreover, the oldest U-Pb ages of meteorites agree with the main-sequence age of the sun derived from helioseismology within the formal ˜1% uncertainty of the latter. Meteorite ages also provide no evidence for a decrease of decay rates with heliocentric distance for nuclides such as 87Rb (decay mode β-) 40K (β- and electron capture), and 147Sm (α).

  5. The Criterion of Supernova Explosion Revisited: The Mass Accretion History

    NASA Astrophysics Data System (ADS)

    Suwa, Yudai; Yamada, Shoichi; Takiwaki, Tomoya; Kotake, Kei

    2016-01-01

    By performing neutrino-radiation hydrodynamic simulations in spherical symmetry (1D) and axial symmetry (2D) with different progenitor models by Woosley & Heger from 12 to 100 M⊙, we find that all 1D runs fail to produce an explosion and several 2D runs succeed. The difference in the shock evolutions for different progenitors can be interpreted by the difference in their mass accretion histories, which are in turn determined by the density structures of progenitors. The mass accretion history has two phases in the majority of the models: the earlier phase, in which the mass accretion rate is high and rapidly decreasing, and the later phase, with a low and almost constant accretion rate. They are separated by the so-called turning point, the origin of which is a change of the accreting layer. We argue that shock revival will most likely occur around the turning point and hence that its location in the \\dot{M}{--}{L}ν plane will be a good measure for the possibility of shock revival: if the turning point lies above the critical curve and the system stays there for a long time, shock revival will obtain. In addition, we develop a phenomenological model to approximately evaluate the trajectories in the \\dot{M}{--}{L}ν plane, which, after calibrating free parameters by a small number of 1D simulations, reproduces the location of the turning point reasonably well by using the initial density structure of progenitor alone. We suggest the application of the phenomenological model to a large collection of progenitors in order to infer without simulations which ones are more likely to explode.

  6. The Use of a Computerized Provider Order Entry Alert to Decrease Rates of Clostridium difficile Testing in Young Pediatric Patients.

    PubMed

    Nicholson, Maribeth R; Freswick, Peter N; Di Pentima, M Cecilia; Wang, Li; Edwards, Kathryn M; Wilson, Gregory J; Talbot, Thomas R

    2017-02-21

    BACKGROUND Infants and young children are frequently colonized with C. difficile but rarely have symptomatic disease. However, C. difficile testing remains prevalent in this age group. OBJECTIVE To design a computerized provider order entry (CPOE) alert to decrease testing for C. difficile in young children and infants. DESIGN An interventional age-targeted before-after trial with comparison group SETTING Monroe Carell Jr. Children's Hospital at Vanderbilt University, Nashville, Tennessee. PATIENTS All children seen in the inpatient or emergency room settings from July 2012 through July 2013 (pre-CPOE alert) and September 2013 through September 2014 (post-CPOE alert) INTERVENTION In August of 2013, we implemented a CPOE alert advising against testing in infants and young children based on the American Academy of Pediatrics recommendations with an optional override. We further offered healthcare providers educational seminars regarding recommended C. difficile testing. RESULTS The average monthly testing rate significantly decreased after the CPOE alert for children 0-11 months old (11.5 pre-alert vs 0 post-alert per 10,000 patient days; P<.001) and 12-35 months old (61.6 pre-alert vs 30.1 post-alert per 10,000 patients days; P<.001), but not for those children ≥36 months old (50.9 pre-alert vs 46.4 post-alert per 10,000 patient days; P=.3) who were not targeted with a CPOE alert. There were no complications in those children who testing positive for C. difficile. CONCLUSIONS The average monthly testing rate for C. difficile for children <35 months old decreased without complication after the use of a CPOE alert in those who tested positive for C. difficile. Infect Control Hosp Epidemiol 2017;1-5.

  7. Rates of cortisol increase and decrease in channel catfish and sunshine bass exposed to an acute confinement stressor.

    PubMed

    Davis, Kenneth B; Small, Brian C

    2006-05-01

    Channel catfish and sunshine bass were exposed to a low-water stress event and allowed to recover in fresh water or a solution of metomidate (dl-1-(1-phenylethyl)-5-(metoxycarbonyl) imidazole hydrochloride), which inhibits the synthesis of cortisol. Change in time of plasma cortisol was used as an index of cortisol secretion and clearance. Plasma cortisol and glucose increased during the exposure to low-water stress in both fish, but the changes of both plasma components were more dramatic in sunshine bass. Exposure to metomidate during recovery resulted in a short-term increase in plasma glucose but differences between controls and metomidate-exposed fish were relatively minor thereafter. Cortisol began to decrease in catfish immediately after the removal of the stress but continued to increase for 15 min in sunshine bass recovering in fresh water and for 5 min in bass recovering in metomidate. Catfish recovering in fresh water had a cortisol elimination rate of -1.28 ng/mL/min compared with -2.45 ng/mL/min for fish recovering in metomidate (P>0.05) while sunshine bass recovering in fresh water had an elimination rate of -6.96 ng/mL/min compared with -4.50 ng/mL/min for fish recovering in metomidate (P>0.05). These data indicate that the rapid decrease of plasma cortisol after removal of the stressor is due to an almost immediate decrease of secretion, tissue uptake and a rapid renal loss due to the absence of a plasma binding protein.

  8. Holocene reef accretion: southwest Molokai, Hawaii, U.S.A.

    USGS Publications Warehouse

    Engels, Mary S.; Fletcher, Charles H.; Field, Michael E.; Storlazzi, Curt D.; Grossman, Eric E.; Rooney, John J.B.; Conger, Christopher L.; Glenn, Craig

    2004-01-01

    Two reef systems off south Molokai, Hale O Lono and Hikauhi (separated by only 10 km), show strong and fundamental differences in modern ecosystem structure and Holocene accretion history that reflect the influence of wave-induced near-bed shear stresses on reef development in Hawaii. Both sites are exposed to similar impacts from south, Kona, and trade-wind swell. However, the Hale O Lono site is exposed to north swell and the Hikuahi site is not. As a result, the reef at Hale O Lono records no late Holocene net accretion while the reef at Hikauhi records consistent and robust accretion over late Holocene time. Analysis and dating of 24 cores from Hale O Lono and Hikauhi reveal the presence of five major lithofacies that reflect paleo-environmental conditions. In order of decreasing depositional energy they are: (1) coral-algal bindstone; (2) mixed skeletal rudstone; (3) massive coral framestone; (4) unconsolidated floatstone; and (5) branching coral framestone-bafflestone. At Hale O Lono, 10 cores document a backstepping reef ranging from ∼ 8,100 cal yr BP (offshore) to ∼ 4,800 cal yr BP (nearshore). A depauperate community of modern coral diminishes shoreward and seaward of ∼ 15 m depth due to wave energy, disrupted recruitment activities, and physical abrasion. Evidence suggests a change from conditions conducive to accretion during the early Holocene to conditions detrimental to accretion in the late Holocene. Reef structure at Hikauhi, reconstructed from 14 cores, reveals a thick, rapidly accreting and young reef (maximum age ∼ 900 cal yr BP). Living coral cover on this reef increases seaward with distance from the reef crest but terminates at a depth of ∼ 20 m where the reef ends in a large sand field. The primary limitation on vertical reef growth is accommodation space under wave base, not recruitment activities or energy conditions. Interpretations of cored lithofacies suggest that modern reef growth on the southwest corner of Molokai, and by

  9. Myosin MgADP release rate decreases at longer sarcomere length to prolong myosin attachment time in skinned rat myocardium.

    PubMed

    Tanner, Bertrand C W; Breithaupt, Jason J; Awinda, Peter O

    2015-12-15

    Cardiac contractility increases as sarcomere length increases, suggesting that intrinsic molecular mechanisms underlie the Frank-Starling relationship to confer increased cardiac output with greater ventricular filling. The capacity of myosin to bind with actin and generate force in a muscle cell is Ca(2+) regulated by thin-filament proteins and spatially regulated by sarcomere length as thick-to-thin filament overlap varies. One mechanism underlying greater cardiac contractility as sarcomere length increases could involve longer myosin attachment time (ton) due to slowed myosin kinetics at longer sarcomere length. To test this idea, we used stochastic length-perturbation analysis in skinned rat papillary muscle strips to measure ton as [MgATP] varied (0.05-5 mM) at 1.9 and 2.2 μm sarcomere lengths. From this ton-MgATP relationship, we calculated cross-bridge MgADP release rate and MgATP binding rates. As MgATP increased, ton decreased for both sarcomere lengths, but ton was roughly 70% longer for 2.2 vs. 1.9 μm sarcomere length at maximally activated conditions. These ton differences were driven by a slower MgADP release rate at 2.2 μm sarcomere length (41 ± 3 vs. 74 ± 7 s(-1)), since MgATP binding rate was not different between the two sarcomere lengths. At submaximal activation levels near the pCa50 value of the tension-pCa relationship for each sarcomere length, length-dependent increases in ton were roughly 15% longer for 2.2 vs. 1.9 μm sarcomere length. These changes in cross-bridge kinetics could amplify cooperative cross-bridge contributions to force production and thin-filament activation at longer sarcomere length and suggest that length-dependent changes in myosin MgADP release rate may contribute to the Frank-Starling relationship in the heart.

  10. Lipid transfer between phosphatidylcholine vesicles and human erythrocytes: exponential decrease in rate with increasing acyl chain length.

    PubMed

    Ferrell, J E; Lee, K J; Huestis, W H

    1985-06-04

    The rate of phospholipid transfer from sonicated phospholipid vesicles to human erythrocytes has been studied as a function of membrane concentration and lipid acyl chain composition. Phospholipid transfer exhibits saturable first-order kinetics with respect to both cell and vesicle membrane concentrations. This kinetic behavior is consistent either with transfer during transient contact between cell and vesicle surfaces (but only if the fraction of the cell surface susceptible to such interaction is small) or with transfer of monomers through the aqueous phase. The acyl chain composition of the transferred phospholipid affects the transfer kinetics profoundly; for homologous saturated phosphatidylcholines, the rate of transfer decreases exponentially with increasing acyl chain length. This behavior is consistent with passage of phospholipid monomers through a polar phase, which might be the bulk aqueous phase( as in the monomer transfer model) or the hydrated head-group regions of a cell-vesicle complex (transient collision model). Collisional transfer also predicts that intercell transfer of phospholipids should be slow compared to cell-vesicle transfer, as surface charge and steric effects should prevent close apposition of donor and acceptor membranes. This is not found; dilauroylphosphatidylcholine transfers rapidly between red cells. Thus, the observed relationship between acyl chain length and intermembrane phospholipid transfer rates likely reflects the energetics of monomer transfer through the aqueous phase.

  11. Swings between rotation and accretion power in a binary millisecond pulsar.

    PubMed

    Papitto, A; Ferrigno, C; Bozzo, E; Rea, N; Pavan, L; Burderi, L; Burgay, M; Campana, S; Di Salvo, T; Falanga, M; Filipović, M D; Freire, P C C; Hessels, J W T; Possenti, A; Ransom, S M; Riggio, A; Romano, P; Sarkissian, J M; Stairs, I H; Stella, L; Torres, D F; Wieringa, M H; Wong, G F

    2013-09-26

    It is thought that neutron stars in low-mass binary systems can accrete matter and angular momentum from the companion star and be spun-up to millisecond rotational periods. During the accretion stage, the system is called a low-mass X-ray binary, and bright X-ray emission is observed. When the rate of mass transfer decreases in the later evolutionary stages, these binaries host a radio millisecond pulsar whose emission is powered by the neutron star's rotating magnetic field. This evolutionary model is supported by the detection of millisecond X-ray pulsations from several accreting neutron stars and also by the evidence for a past accretion disc in a rotation-powered millisecond pulsar. It has been proposed that a rotation-powered pulsar may temporarily switch on during periods of low mass inflow in some such systems. Only indirect evidence for this transition has hitherto been observed. Here we report observations of accretion-powered, millisecond X-ray pulsations from a neutron star previously seen as a rotation-powered radio pulsar. Within a few days after a month-long X-ray outburst, radio pulses were again detected. This not only shows the evolutionary link between accretion and rotation-powered millisecond pulsars, but also that some systems can swing between the two states on very short timescales.

  12. Consciously controlled breathing decreases the high-frequency component of heart rate variability by inhibiting cardiac parasympathetic nerve activity.

    PubMed

    Sasaki, Konosuke; Maruyama, Ryoko

    2014-01-01

    Heart rate variability (HRV), the beat-to-beat alterations in heart rate, comprises sympathetic and parasympathetic nerve activities of the heart. HRV analysis is used to quantify cardiac autonomic regulation. Since respiration could be a confounding factor in HRV evaluation, some studies recommend consciously controlled breathing to standardize the method. However, it remains unclear whether controlled breathing affects HRV measurement. We compared the effects of controlled breathing on HRV with those of spontaneous breathing. In 20 healthy volunteers, we measured respiratory frequency (f), tidal volume, and blood pressure (BP) and recorded electrocardiograms during spontaneous breathing (14.8 ± 0.7 breaths/min) and controlled breathing at 15 (0.25 Hz) and 6 (0.10 Hz) breaths/min. Compared to spontaneous breathing, controlled breathing at 0.25 Hz showed a higher heart rate and a lower high-frequency (HF) component, an index of parasympathetic nerve activity, although the f was the same. During controlled breathing at 0.10 Hz, the ratio of the low frequency (LF) to HF components (LF/HF), an index of sympathetic nerve activity, increased greatly and HF decreased, while heart rate and BP remained almost unchanged. Thus, controlled breathing at 0.25 Hz, which requires mental concentration, might inhibit parasympathetic nerve activity. During controlled breathing at 0.10 Hz, LF/HF increases because some HF subcomponents are synchronized with f and probably move into the LF band. This increment leads to misinterpretation of the true autonomic nervous regulation. We recommend that the respiratory pattern of participants should be evaluated before spectral HRV analysis to correctly understand changes in autonomic nervous regulation.

  13. Plastic Deformation of Accreted Planetesimals

    NASA Astrophysics Data System (ADS)

    Kadish, J.

    2005-08-01

    The early stages of planetesimal growth follow an accretion model (Weidenschilling, Icarus 2000), which influences the intrinsic strength of a body and may control how its shape evolves after growth. In previous work we have determined the stress field of an accreted planetesimal accounting for possible variation in the object's spin as it accretes (Kadish et al., IJSS In Press) At the end of growth, these objects are subject to transport mechanisms that can distribute them throughout the solar system. As they are transported these objects can be spun-up by tidal forces (Scheeres et al, Icarus 2000), YORP (Bottke et al., Asteroids III 2002), and collisions (Binzel et al., Asteroids II 1989). Such an increase of spin will cause perturbations to the initial stress field and may lead to failure. We are able to show analytically that failure is initiated on the object's surface and a plastic zone propagates inward as the object's spin is increased. If we model an accreted body as a conglomeration of rocks similar to a gravel or sand, the deformation in the region of failure is characterized using a Mohr-Coulomb failure criterion with negligible cohesion and zero hardening(e.g. Holsapple, Icarus 2001). Such a response is highly non-linear and must be solved using finite elements and iterative methods (Simo and Hughes, Computational Inelasticity 1998). Using the commercial finite element code ABAQUS, we present the shape deformation resulting from an elasto-plastic analysis of a spinning, self-gravitating accreted sphere that is spun-up after growth is complete. The methodology can be extended to model plastic deformation due to local failure for more complex planetesimal shapes, such as for the asteroid Kleopatra. This work has implications for the evolution of planetesimal shapes, the creation of binary and contact binary asteroids, and for the maximum spin rate of small planetary bodies.

  14. Central exogenous nitric oxide decreases cardiac sympathetic drive and improves baroreflex control of heart rate in ovine heart failure.

    PubMed

    Ramchandra, Rohit; Hood, Sally G; May, Clive N

    2014-08-01

    Heart failure (HF) is associated with increased cardiac and renal sympathetic drive, which are both independent predictors of poor prognosis. A candidate mechanism for the centrally mediated sympathoexcitation in HF is reduced synthesis of the inhibitory neuromodulator nitric oxide (NO), resulting from downregulation of neuronal NO synthase (nNOS). Therefore, we investigated the effects of increasing the levels of NO in the brain, or selectively in the paraventricular nucleus of the hypothalamus (PVN), on cardiac sympathetic nerve activity (CSNA) and baroreflex control of CSNA and heart rate in ovine pacing-induced HF. The resting level of CSNA was significantly higher in the HF than in the normal group, but the resting level of RSNA was unchanged. Intracerebroventricular infusion of the NO donor sodium nitroprusside (SNP; 500 μg · ml(-1)· h(-1)) in conscious normal sheep and sheep in HF inhibited CSNA and restored baroreflex control of heart rate, but there was no change in RSNA. Microinjection of SNP into the PVN did not cause a similar cardiac sympathoinhibition in either group, although the number of nNOS-positive cells was decreased in the PVN of sheep in HF. Reduction of endogenous NO with intracerebroventricular infusion of N(ω)-nitro-l-arginine methyl ester decreased CSNA in normal but not in HF sheep and caused no change in RSNA in either group. These findings indicate that endogenous NO in the brain provides tonic excitatory drive to increase resting CSNA in the normal state, but not in HF. In contrast, exogenously administered NO inhibited CSNA in both the normal and HF groups via an action on sites other than the PVN.

  15. Increased classical endoplasmic reticulum stress is sufficient to reduce chondrocyte proliferation rate in the growth plate and decrease bone growth.

    PubMed

    Kung, Louise H W; Rajpar, M Helen; Preziosi, Richard; Briggs, Michael D; Boot-Handford, Raymond P

    2015-01-01

    Mutations in genes encoding cartilage oligomeric matrix protein and matrilin-3 cause a spectrum of chondrodysplasias called multiple epiphyseal dysplasia (MED) and pseudoachondroplasia (PSACH). The majority of these diseases feature classical endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR) as a result of misfolding of the mutant protein. However, the importance and the pathological contribution of ER stress in the disease pathogenesis are unknown. The aim of this study was to investigate the generic role of ER stress and the UPR in the pathogenesis of these diseases. A transgenic mouse line (ColIITgcog) was generated using the collagen II promoter to drive expression of an ER stress-inducing protein (Tgcog) in chondrocytes. The skeletal and histological phenotypes of these ColIITgcog mice were characterised. The expression and intracellular retention of Tgcog induced ER stress and activated the UPR as characterised by increased BiP expression, phosphorylation of eIF2α and spliced Xbp1. ColIITgcog mice exhibited decreased long bone growth and decreased chondrocyte proliferation rate. However, there was no disruption of chondrocyte morphology or growth plate architecture and perturbations in apoptosis were not apparent. Our data demonstrate that the targeted induction of ER stress in chondrocytes was sufficient to reduce the rate of bone growth, a key clinical feature associated with MED and PSACH, in the absence of any growth plate dysplasia. This study establishes that classical ER stress is a pathogenic factor that contributes to the disease mechanism of MED and PSACH. However, not all the pathological features of MED and PSACH were recapitulated, suggesting that a combination of intra- and extra-cellular factors are likely to be responsible for the disease pathology as a whole.

  16. Stable SREBP-1a knockdown decreases the cell proliferation rate in human preadipocyte cells without inducing senescence

    SciTech Connect

    Alvarez, María Soledad; Fernandez-Alvarez, Ana; Cucarella, Carme; Casado, Marta

    2014-04-25

    Highlights: • SGBS cells mostly expressed SREBP-1a variant. • SREBP-1a knockdown decreased the proliferation of SGBS cells without inducing senescence. • We have identified RBBP8 and CDKN3 genes as potential SREBP-1a targets. - Abstract: Sterol regulatory element binding proteins (SREBP), encoded by the Srebf1 and Srebf2 genes, are important regulators of genes involved in cholesterol and fatty acid metabolism. Whereas SREBP-2 controls the cholesterol synthesis, SREBP-1 proteins (-1a and -1c) function as the central hubs in lipid metabolism. Despite the key function of these transcription factors to promote adipocyte differentiation, the roles of SREBP-1 proteins during the preadipocyte state remain unknown. Here, we evaluate the role of SREBP-1 in preadipocyte proliferation using RNA interference technology. Knockdown of the SREBP-1a gene decreased the proliferation rate in human SGBS preadipocyte cell strain without inducing senescence. Furthermore, our data identified retinoblastoma binding protein 8 and cyclin-dependent kinase inhibitor 3 genes as new potential SREBP-1 targets, in addition to cyclin-dependent kinase inhibitor 1A which had already been described as a gene regulated by SREBP-1a. These data suggested a new role of SREBP-1 in adipogenesis via regulation of preadipocyte proliferation.

  17. Flumazenil decreases surface expression of α4β2δ GABAA receptors by increasing the rate of receptor internalization

    PubMed Central

    Kuver, Aarti; Smith, Sheryl S.

    2015-01-01

    Increases in expression of α4βδ GABAA receptors (GABARs), triggered by fluctuations in the neurosteroid THP (3α-OH-5α[β]-pregnan-20-one), are associated with changes in mood and cognition. We tested whether α4βδ trafficking and surface expression would be altered by in vitro exposure to flumazenil, a benzodiazepine ligand which reduces α4βδ expression in vivo. We first determined that flumazenil (100 nM – 100 μM, IC50=~1 μM) acted as a negative modulator, reducing GABA (10 μM)-gated current in the presence of 100 nM THP (to increase receptor efficacy), assessed with whole cell patch clamp recordings of recombinant α4β2δ expressed in HEK-293 cells. Surface expression of recombinant α4β2δ receptors was detected using a 3XFLAG reporter at the C-terminus of α4 (α4F) using confocal immunocytochemical techniques following 48 h exposure of cells to GABA (10 μM) + THP (100 nM). Flumazenil (10 μM) decreased surface expression of α4F by ~60%, while increasing its intracellular accumulation, after 48 h. Reduced surface expression of α4β2δ after flumazenil treatment was confirmed by decreases in the current responses to 100 nM of the GABA agonist gaboxadol. Flumazenil-induced decreases in surface expression of α4β2δ were prevented by the dynamin blocker, dynasore, and by leupeptin, which blocks lysosomal enzymes, suggesting that flumazenil is acting to increase endocytosis and lysosomal degradation of the receptor. Flumazenil increased the rate of receptor removal from the cell surface by 2-fold, assessed using botulinum toxin B to block insertion of new receptors. These findings may suggest new therapeutic strategies for regulation of α4β2δ expression using flumazenil. PMID:26592470

  18. Meta-analytic evidence for decreased heart rate variability in chronic pain implicating parasympathetic nervous system dysregulation.

    PubMed

    Tracy, Lincoln M; Ioannou, Liane; Baker, Katharine S; Gibson, Stephen J; Georgiou-Karistianis, Nellie; Giummarra, Melita J

    2016-01-01

    Both sympathetic and parasympathetic nervous systems are involved in regulating pain states. The activity of these systems seems to become disturbed in states of chronic pain. This disruption in autonomic balance can be measured through the assessment of heart rate variability (HRV), that is, the variability of the interval between consecutive heart beats. However, there is yet to be a systematic evaluation of the body of literature concerning HRV across several chronic pain conditions. Moreover, modern meta-analytical techniques have never been used to validate and consolidate the extent to which HRV may be decreased in chronic pain. Following the preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement guidelines, this study systematically evaluated and critically appraised the literature concerning HRV in people living with chronic pain. After screening 17,350 sources, 51 studies evaluating HRV in a chronic pain group met the inclusion criteria. Twenty-six moderate-high quality studies were included in quantitative meta-analyses. On average, the quality of studies was moderate. There were 6 frequency-domain and time-domain measures of HRV across a broad range of chronic pain conditions. High heterogeneity aside, pooled results from the meta-analyses reflected a consistent, moderate-to-large effect of decreased high-frequency HRV in chronic pain, implicating a decrease in parasympathetic activation. These effects were heavily influenced by fibromyalgia studies. Future research would benefit from wider use of standardised definitions of measurement, and also investigating the synergistic changes in pain state and HRV throughout the development and implementation of mechanism-based treatments for chronic pain.

  19. Looking Māori Predicts Decreased Rates of Home Ownership: Institutional Racism in Housing Based on Perceived Appearance

    PubMed Central

    2015-01-01

    This study examined differences in rates of home ownership among Māori (the indigenous peoples of New Zealand). We identified systematic factors that predicted why some Māori were more likely to own their own home (partially or fully) relative to other Māori. Data were drawn from a large national postal sample of 561 self-identified Māori collected as part of the New Zealand Attitudes and Values Study. As predicted, our analyses indicated that self-reported appearance as Māori, or the extent to which people thought they personally displayed features which visibly identified them as Māori to others, significantly predicted decreased rates of home ownership. This association held when adjusting for numerous demographic covariates, such as education, level of deprivation of the immediate area, household income, age, relationship status, region of residence, and so forth. Our analyses suggest there is, or at least has been in the recent past, institutional racism against Māori in New Zealand’s home lending industry based on merely appearing more Māori. PMID:25738961

  20. Looking Māori predicts decreased rates of home ownership: institutional racism in housing based on perceived appearance.

    PubMed

    Houkamau, Carla A; Sibley, Chris G

    2015-01-01

    This study examined differences in rates of home ownership among Māori (the indigenous peoples of New Zealand). We identified systematic factors that predicted why some Māori were more likely to own their own home (partially or fully) relative to other Māori. Data were drawn from a large national postal sample of 561 self-identified Māori collected as part of the New Zealand Attitudes and Values Study. As predicted, our analyses indicated that self-reported appearance as Māori, or the extent to which people thought they personally displayed features which visibly identified them as Māori to others, significantly predicted decreased rates of home ownership. This association held when adjusting for numerous demographic covariates, such as education, level of deprivation of the immediate area, household income, age, relationship status, region of residence, and so forth. Our analyses suggest there is, or at least has been in the recent past, institutional racism against Māori in New Zealand's home lending industry based on merely appearing more Māori.

  1. Fat oxidation rate and the exercise intensity that elicits maximal fat oxidation decreases with pubertal status in young male subjects.

    PubMed

    Riddell, M C; Jamnik, V K; Iscoe, K E; Timmons, Brian W; Gledhill, N

    2008-08-01

    The range of exercise intensities that elicit high fat oxidation rates (FOR) in youth and the influence of pubertal status on peak FOR are unknown. In a longitudinal design, we compared FOR over a range of exercise intensities in a small cohort of developing prepubertal male subjects. Five boys all at Tanner stage 1 (ages 11-12 yr) and nine men (ages 20-26 yr) underwent an incremental cycle ergometry test to volitional exhaustion. FOR curves were determined from indirect calorimetry during the final 30 s of each increment. The same protocol was duplicated annually in the boys as they progressed through puberty. The peak FOR was considerably higher (P<0.05) in boys at Tanner 1 (8.6+/-1.5 mg.kg lean body mass(-1).min(-1)) (mean+/-SD) compared with men (4.2+/-1.1 mg.kg lean body mass(-1).min(-1)). FOR dropped as boys developed through puberty (Tanner 2/3 peak rate=7.6+/-0.6 mg.kg lean body mass(-1).min(-1); Tanner 4 peak rate=5.4+/-1.8 mg.kg lean body mass(-1).min(-1), main effect of Tanner stage; P<0.05) to the levels found in men (not significant). The exercise intensity that elicited peak FOR was higher in the boys at Tanner 1 [56+/-6% peak aerobic power (VO2 peak)] than in men (31+/-4% VO2 peak) (P<0.001). This value tended to decrease by Tanner stage 4 (45+/-10% VO2 peak, main effect of Tanner stage; P=0.06). We conclude that, compared with men, prepubertal boys have higher relative FOR throughout a wide range of exercise intensities and that FOR drops as boys develop through puberty.

  2. Variable accretion processes in the young binary-star system UY Aur

    SciTech Connect

    Stone, Jordan M.; Eisner, J. A.; Kulesa, Craig; McCarthy, Don; Salyk, Colette E-mail: jeisner@as.arizona.edu E-mail: dmccarthy@as.arizona.edu

    2014-09-01

    We present new K-band spectroscopy of the UY Aur binary star system. Our data are the first to show H{sub 2} emission in the spectrum of UY Aur A and the first to spectrally resolve the Brγ line in the spectrum of UY Aur B. We see an increase in the strength of the Brγ line in UY Aur A and a decrease in Brγ and H{sub 2} line luminosity for UY Aur B compared to previous studies. Converting Brγ line luminosity to accretion rate, we infer that the accretion rate onto UY Aur A has increased by 2 × 10{sup –9} M {sub ☉} yr{sup –1} per year since a rate of zero was observed in 1994. The Brγ line strength for UY Aur B has decreased by a factor of 0.54 since 1994, but the K-band flux has increased by 0.9 mag since 1998. The veiling of UY Aur B has also increased significantly. These data evince a much more luminous disk around UY Aur B. If the lower Brγ luminosity observed in the spectrum of UY Aur B indicates an intrinsically smaller accretion rate onto the star, then UY Aur A now accretes at a higher rate than UY Aur B. However, extinction at small radii or mass pile-up in the circumstellar disk could explain decreased Brγ emission around UY Aur B even when the disk luminosity implies an increased accretion rate. In addition to our scientific results for the UY Aur system, we discuss a dedicated pipeline we have developed for the reduction of echelle-mode data from the ARIES spectrograph.

  3. ASYMMETRIC ACCRETION FLOWS WITHIN A COMMON ENVELOPE

    SciTech Connect

    MacLeod, Morgan; Ramirez-Ruiz, Enrico

    2015-04-10

    This paper examines flows in the immediate vicinity of stars and compact objects dynamically inspiralling within a common envelope (CE). Flow in the vicinity of the embedded object is gravitationally focused, leading to drag and potentially to gas accretion. This process has been studied numerically and analytically in the context of Hoyle–Lyttleton accretion (HLA). Yet, within a CE, accretion structures may span a large fraction of the envelope radius, and in so doing sweep across a substantial radial gradient of density. We quantify these gradients using detailed stellar evolution models for a range of CE encounters. We provide estimates of typical scales in CE encounters that involve main sequence stars, white dwarfs, neutron stars, and black holes with giant-branch companions of a wide range of masses. We apply these typical scales to hydrodynamic simulations of three-dimensional HLA with an upstream density gradient. This density gradient breaks the symmetry that defines HLA flow, and imposes an angular momentum barrier to accretion. Material that is focused into the vicinity of the embedded object thus may not be able to accrete. As a result, accretion rates drop dramatically, by one to two orders of magnitude, while drag rates are only mildly affected. We provide fitting formulae to the numerically derived rates of drag and accretion as a function of the density gradient. The reduced ratio of accretion to drag suggests that objects that can efficiently gain mass during CE evolution, such as black holes and neutron stars, may grow less than implied by the HLA formalism.

  4. The Eddington limit and supercritical accretion. I - Time-independent calculations. [on neutron star

    NASA Technical Reports Server (NTRS)

    Burger, H. L.; Katz, J. I.

    1980-01-01

    Spherically symmetric, steady state accretion of an ionized hydrogen plasma onto a neutron star is considered for accretion rates which exceed a critical rate at which the Eddington limiting luminosity is produced. The coupled hydrodynamic and frequency integrated, radiative transfer equations are solved for accretion rates up to 10 times the nominal limit. Steady state solutions are presented that imply a multiplicity of different luminosity solutions for a single accretion rate in this 'supercritical' regime.

  5. Climate Change at Northern Latitudes: Rising Atmospheric Humidity Decreases Transpiration, N-Uptake and Growth Rate of Hybrid Aspen

    PubMed Central

    Tullus, Arvo; Kupper, Priit; Sellin, Arne; Parts, Leopold; Sõber, Jaak; Tullus, Tea; Lõhmus, Krista; Sõber, Anu; Tullus, Hardi

    2012-01-01

    At northern latitudes a rise in atmospheric humidity and precipitation is predicted as a consequence of global climate change. We studied several growth and functional traits of hybrid aspen (Populus tremula L.×P. tremuloides Michx.) in response to elevated atmospheric humidity (on average 7% over the ambient level) in a free air experimental facility during three growing seasons (2008–2010) in Estonia, which represents northern temperate climate (boreo-nemoral zone). Data were collected from three humidified (H) and three control (C) plots, and analysed using nested linear models. Elevated air humidity significantly reduced height, stem diameter and stem volume increments and transpiration of the trees whereas these effects remained highly significant also after considering the side effects from soil-related confounders within the 2.7 ha study area. Tree leaves were smaller, lighter and had lower leaf mass per area (LMA) in H plots. The magnitude and significance of the humidity treatment effect – inhibition of above-ground growth rate – was more pronounced in larger trees. The lower growth rate in the humidified plots can be partly explained by a decrease in transpiration-driven mass flow of NO3− in soil, resulting in a significant reduction in the measured uptake of N to foliage in the H plots. The results suggest that the potential growth improvement of fast-growing trees like aspens, due to increasing temperature and atmospheric CO2 concentration, might be smaller than expected at high latitudes if a rise in atmospheric humidity simultaneously takes place. PMID:22880067

  6. Multifaceted intervention to decrease the rate of severe postpartum haemorrhage: the PITHAGORE6 cluster-randomised controlled trial

    PubMed Central

    Deneux-Tharaux, Catherine; Dupont, Corinne; Colin, C.; Rabilloud, Muriel; Touzet, S.; Lansac, Jacques; Harvey, Thierry; Tessier, Véronique; Chauleur, C.; Pennehouat, G.; Morin, X.; Bouvier-Colle, Marie-Hélène; Rudigoz, René

    2010-01-01

    Objective Decreasing the prevalence of severe postpartum haemorrhages (PPH) is a major obstetrical challenge. These are often considered to be associated with substandard initial care. Strategies to increase the appropriateness of early management of PPH must be assessed. We tested the hypothesis that a multifaceted intervention aimed at increasing the translation into practice of a protocol for early management of PPH, would reduce the incidence of severe PPH. Design Cluster-randomised trial Population 106 maternity units in 6 French regions Methods Maternity units were randomly assigned to receive the intervention, or to have the protocol passively disseminated. The intervention combined outreach visits to discuss the protocol in each local context, reminders, and peer reviews of severe cases, and was implemented in each maternity hospital by a team pairing an obstetrician and a midwife. Main outcome measures The primary outcome was the incidence of severe PPH, defined as a composite of one or more of: transfusion, embolisation, surgical procedure, transfer to intensive care, peripartum haemoglobin delta of 4 g/dl or more, death. The main secondary outcomes were PPH management practices. Results The mean rate of severe PPH was 1.64% (SD0.80) in the intervention units and 1.65% (SD0.96) in control units; difference not significant. Some elements of PPH management were applied more frequently in intervention units –help from senior staff (p=0.005)-, or tended to – second line pharmacological treatment (p=0.06), timely blood test (p=0.09). Conclusion This educational intervention did not affect the rate of severe PPH as compared to control units, although it improved some practices. Trial registration: ClinicalTrials.gov NCT 00344929 PMID:20573150

  7. Anodal Stimulation of the Left DLPFC Increases IGT Scores and Decreases Delay Discounting Rate in Healthy Males

    PubMed Central

    He, Qinghua; Chen, Mei; Chen, Chuansheng; Xue, Gui; Feng, Tingyong; Bechara, Antoine

    2016-01-01

    Previous correlational imaging studies have implicated the dorsolateral prefrontal cortex (DLPFC) in decision making. Using High-Definition Transcranial Direct Current Stimulation (HD-tDCS), the present study directly investigated the causal role of the DLPFC in performing the Iowa Gambling Task (IGT) and the Inter-Temporal Choice (ITC) task. Three experiments were conducted: Experiment 1 (N = 41) to study the left DLPFC, Experiment 2 (N = 49) to study the right DLPFC, and Experiment 3 (N = 20, a subset of those in Experiment 1) to switch the experimental and control conditions. All participants were healthy male college students. For Experiments 1 and 2, participants were randomly assigned to either the HD-tDCS or the sham stimulation condition. For Experiment 3, participants were assigned to the condition they were not in during Experiment 1. Results showed that HD-tDCS over the left DLPFC increased IGT score, decreased the recency parameter in IGT, and lowered delay discounting rate (k) in the ITC task. We discussed the potential roles of impulse control and time perception in mediating the effect of tDCS stimulation of left DLPFC on decision making. Our results have clinical implications for the treatment of disorders involving poor decision-making, such as addictions. PMID:27703440

  8. Pseudomembranous Type of Oral Candidiasis is Associated with Decreased Salivary Flow Rate and Secretory Immunoglobulin A Levels.

    PubMed

    Mahajan, Bela; Bagul, Neeta; Desai, Rajiv; Reddy, Mamatha; Mahajan, Amit; Shete, Ashwini; Risbud, Arun; Mane, Arati

    2015-08-01

    Saliva plays an important role in maintaining microbial homeostasis in the oral cavity, while salivary gland hypofunction predisposes the oral mucosa to pathologic alteration and increases the risk for oral candidiasis. This study sought to determine the salivary flow rate (SFR) and secretory immunoglobulin A (SIgA) levels in HIV-positive and HIV-negative individuals and evaluate their relationship with the determinants of oral candidiasis. Sixty HIV-positive (30 with and 30 without oral candidiasis) and 30 healthy HIV-negative individuals were enrolled. Cotton pellet was weighed pre- and post-saliva collection for the assessment of SFR, while SIgA levels were estimated by commercial ELISA (Diametra, Italy) kit. The mean ± SD, SFR and SIgA levels in HIV-positive individuals with candidiasis, without candidiasis and HIV-negative controls were 0.396 ± 0.290, 0.546 ± 0.355 and 0.534 ± 0.214 ml/min and 115.891 ± 37.621, 136.024 ± 51.075 and 149.418 ± 31.765 µg/ml, respectively. A positive correlation between low CD4 counts (indicator of immunodeficiency) and SIgA was observed in HIV-positive individuals with candidiasis (r = 0.373, p = 0.045). We also report here for the first time the significant decrease in SFR and SIgA levels in individuals presenting with pseudomembranous type of oral candidiasis and Candida albicans infection.

  9. Giant planet formation via pebble accretion

    NASA Astrophysics Data System (ADS)

    Guilera, O. M.

    2016-08-01

    In the standard model of core accretion, the formation of giant planets occurs by two main processes: first, a massive core is formed by the accretion of solid material; then, when this core exceeds a critical value (typically greater than ) a gaseous runaway growth is triggered and the planet accretes big quantities of gas in a short period of time until the planet achieves its final mass. Thus, the formation of a massive core has to occur when the nebular gas is still available in the disk. This phenomenon imposes a strong time-scale constraint in the giant planet formation due to the fact that the lifetimes of the observed protoplanetary disks are in general lower than 10 Myr. The formation of massive cores before 10 Myr by accretion of big planetesimals (with radii 10 km) in the oligarchic growth regime is only possible in massive disks. However, planetesimal accretion rates significantly increase for small bodies, especially for pebbles, particles of sizes between mm and cm, which are strongly coupled with the gas. In this work, we study the formation of giant planets incorporating pebble accretion rates in our global model of planet formation.

  10. Magnetized Accretion and Dead Zones in Protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Dzyurkevich, Natalia; Turner, Neal J.; Henning, Thomas; Kley, Wilhelm

    2013-07-01

    The edges of magnetically-dead zones in protostellar disks have been proposed as locations where density bumps may arise, trapping planetesimals and helping form planets. Magneto-rotational turbulence in magnetically-active zones provides both accretion of gas on the star and transport of mass to the dead zone. We investigate the location of the magnetically-active regions in a protostellar disk around a solar-type star, varying the parameters like dust-to-gas ratio. The dead zone is in most cases defined by the ambipolar diffusion. In our maps, the dead zone takes a variety of shapes, including a fish-tail pointing away from the star and islands located on and off the midplane. The corresponding accretion rates vary with radius, indicating locations where the surface density will increase over time, and others where it will decrease. We show that density bumps do not readily grow near the dead zone's outer edge, independently of the disk parameters and the dust properties. Instead, the accretion rate peaks at the radius where the gas-phase metals freeze out. This could lead to clearing a valley in the surface density, and to a trap for pebbles located just outside the metal freeze-out line. Here, we provide the fitting formula for the metal line and consider the cojoint impact of metal ans snow lines on the shape of the dead zone.

  11. ACCRETION ONTO PLANETARY MASS COMPANIONS OF LOW-MASS YOUNG STARS

    SciTech Connect

    Zhou, Yifan; Herczeg, Gregory J.; Kraus, Adam L.; Metchev, Stanimir; Cruz, Kelle L. E-mail: zhouyifan1012@gmail.com

    2014-03-01

    Measurements of accretion rates onto planetary mass objects may distinguish between different planet formation mechanisms, which predict different accretion histories. In this Letter, we use Hubble Space Telescope (HST)/WFC3 UVIS optical photometry to measure accretion rates onto three accreting objects, GSC 06214–00210 b, GQ Lup b, and DH Tau b, that are at the planet/brown dwarf boundary and are companions to solar mass stars. The excess optical emission in the excess accretion continuum yields mass accretion rates of 10{sup –9}-10{sup –11} M {sub ☉} yr{sup –1} for these three objects. Their accretion rates are an order of magnitude higher than expected from the correlation between mass and accretion rates measured from the UV excess, which is applicable if these wide planetary mass companions formed by protostellar core fragmentation. The high accretion rates and large separation from the central star demonstrate the presence of massive disks around these objects. Models for the formation and evolution of wide planetary mass companions should account for their large accretion rates. High ratios of Hα luminosity over accretion luminosity for objects with low accretion rates suggest that searches for Hα emission may be an efficient way to find accreting planets.

  12. Accretion onto Planetary Mass Companions of Low-mass Young Stars

    NASA Astrophysics Data System (ADS)

    Zhou, Yifan; Herczeg, Gregory J.; Kraus, Adam L.; Metchev, Stanimir; Cruz, Kelle L.

    2014-03-01

    Measurements of accretion rates onto planetary mass objects may distinguish between different planet formation mechanisms, which predict different accretion histories. In this Letter, we use Hubble Space Telescope (HST)/WFC3 UVIS optical photometry to measure accretion rates onto three accreting objects, GSC 06214-00210 b, GQ Lup b, and DH Tau b, that are at the planet/brown dwarf boundary and are companions to solar mass stars. The excess optical emission in the excess accretion continuum yields mass accretion rates of 10-9-10-11 M ⊙ yr-1 for these three objects. Their accretion rates are an order of magnitude higher than expected from the correlation between mass and accretion rates measured from the UV excess, which is applicable if these wide planetary mass companions formed by protostellar core fragmentation. The high accretion rates and large separation from the central star demonstrate the presence of massive disks around these objects. Models for the formation and evolution of wide planetary mass companions should account for their large accretion rates. High ratios of Hα luminosity over accretion luminosity for objects with low accretion rates suggest that searches for Hα emission may be an efficient way to find accreting planets.

  13. Jet production in super-Eddington accretion disks

    NASA Technical Reports Server (NTRS)

    Eggum, G. E.; Coroniti, F. V.; Katz, J. I.

    1985-01-01

    A two-dimensional, radiation-coupled, Newtonian hydrodynamic simulation is reported for a super-Eddington, mass accretion rate, M = 4 M(E) disk accretion flow onto a 3-solar mass pseudoblack hole. Near the disk midplane, convection cells effectively block the accretion flow, even though viscous heating maximizes there. Accretion predominantly occurs in a supersonic inflow which follows streamlines of approximately constant angular momentum. The optically thick inflow traps radiation so that 80 percent of the luminosity is absorbed by the black hole; the emergent power is sub-Eddington. An axial jet self consistently forms just outside a conical photosphere which bounds the accretion zone; radiation pressure accelerates the jet to about 10 to the 10th cm/s. The jet's mass efflux is only 0.4 percent of the total mass accretion rate.

  14. Short-term variability of X-rays from accreting neutron star Vela X-1. II. Monte Carlo modeling

    SciTech Connect

    Odaka, Hirokazu; Khangulyan, Dmitry; Watanabe, Shin; Takahashi, Tadayuki; Tanaka, Yasuyuki T.; Makishima, Kazuo

    2014-01-01

    We develop a Monte Carlo Comptonization model for the X-ray spectrum of accretion-powered pulsars. Simple, spherical, thermal Comptonization models give harder spectra for higher optical depth, while the observational data from Vela X-1 show that the spectra are harder at higher luminosity. This suggests a physical interpretation where the optical depth of the accreting plasma increases with the mass accretion rate. We develop a detailed Monte Carlo model of the accretion flow, including the effects of the strong magnetic field (∼10{sup 12} G), both in geometrically constraining the flow into an accretion column and in reducing the cross section. We treat bulk-motion Comptonization of the infalling material as well as thermal Comptonization. These model spectra can match the observed broadband Suzaku data from Vela X-1 over a wide range of mass accretion rates. The model can also explain the so-called 'low state' in which the luminosity decreases by an order of magnitude. Here, thermal Comptonization should be negligible, so the spectrum is instead dominated by bulk-motion Comptonization.

  15. A Wind Accretion Model for HLX-1

    NASA Astrophysics Data System (ADS)

    Miller, M. Coleman; Farrell, Sean A.; Maccarone, Thomas J.

    2014-06-01

    The brightest ultraluminous X-ray source currently known, HLX-1, has been observed to undergo five outburst cycles. The periodicity of these outbursts, and their high inferred maximum accretion rates of ~few × 10-4 M ⊙ yr-1, naturally suggest Roche lobe overflow at the pericenter of an eccentric orbit. It is, however, difficult for the Roche lobe overflow model to explain the apparent trend of decreasing decay times over the different outbursts while the integrated luminosity also drops. Thus, if the trend is real rather than simply being a reflection of the complex physics of accretion disks, a different scenario may be necessary. We present a speculative model in which, within the last decade, a high-mass giant star had most of its envelope tidally stripped by the ~104 - 5 M ⊙ black hole in HLX-1, and the remaining core plus low-mass hydrogen envelope now feeds the hole with a strong wind. This model can explain the short decay time of the disk, and could explain the fast decrease in decay time if the wind speed changes with time. A key prediction of this model is that there will be excess line absorption due to the wind; our analysis does in fact find a flux deficit in the ~0.9-1.1 keV range that is consistent with predictions, albeit at low significance. If this idea is correct, we also expect that within years to dacades the bound material from the original disruption will return and will make HLX-1 a persistently bright source.

  16. Promises and Problems of Pebble Accretion

    NASA Astrophysics Data System (ADS)

    Kretke, Katherine A.; Levison, H. F.

    2013-10-01

    Despite the large number of exoplanets indicating that giant planets are a common outcome of the star formation process, theoretical models still struggle to explain how ~10 Earth mass rocky/icy embryos can form within the lifetimes of gaseous circumstellar disks. In recent years, aerodynamic-aided accretion of ``pebbles,'' particles ranging from millimeters to decimeters in size, has been suggested as a potential solution to this long-standing problem. Local simulations, simulations which look at the detailed behavior of these pebbles in the vicinity of a planetary embryo, have shown that the potential planetary growth rates can be surprisingly fast. If one assumes that most of the mass in a protoplanetary disk resides in these pebble-sized particles, a Mars mass core could grow to 10 Earth masses in only a few thousand years. However, these local studies cannot investigate how this accretion process behaves in the more complicated, multi-planet environment. We have incorporated the local accretion physics into LIPAD, a Lagrangian code which can follow the collisional / accretional / dynamical evolution of a planetary system, to investigate the how this pebble accretion will manifest itself in the larger planet formation picture. We present how these more comprehensive models raise challenges to using pebble accretion to form observed planetary systems.

  17. Problems and Promises of Pebble Accretion

    NASA Astrophysics Data System (ADS)

    Kretke, Katherine A.; Levison, H. F.

    2013-05-01

    Abstract (2,250 Maximum Characters): Despite the large number of exoplanets indicating that planets are a common outcome of the star formation process, theoretical models still struggle to explain how ~10 Earth mass rocky/icy embryos can form within the lifetimes of gaseous circumstellar disks. Recently, aerodynamic-aided accretion of ``pebbles,'' particles ranging from millimeters to decimeters in size, has been suggested as a potential solution to this long-standing problem. Local simulations, simulations which look at the detailed behavior of these pebbles in the vicinity of a planetary embryo, have shown that the potential planetary growth rates can be surprisingly fast. If one assumes that most of the mass in a protoplanetary disk resides in these pebble-sized particles, a Mars mass core could grow to 10 Earth masses in only a few thousand years. However, these local studies cannot investigate how this accretion process behaves in the more complicated, multi-planet environment. We have incorporated a prescription of this pebble accretion into LIPAD, a Lagrangian code which can follow the collisional/accretional/dynamical evolution of a planetary system, to investigate the how this pebble accretion will manifest itself in the larger planet formation picture. We discuss how these more comprehensive models present challenges for using pebble accretion to form observed planetary systems.

  18. Accretion onto Fast X-Ray Pulsars

    NASA Technical Reports Server (NTRS)

    Rappaport, S. A.; Fregeau, J. M.; Spruit, H.

    2004-01-01

    The recent emergence of a new class of accretion-powered, transient, millisecond X-ray pulsars presents some difficulties for the conventional picture of accretion onto rapidly rotating magnetized neutron stars and their spin behavior during outbursts. In particular, it is not clear that the standard paradigm can accommodate the wide range in M(i.e., approx. greater than a factor of 50) over which these systems manage to accrete and the high rate of spindown that the neutron stars exhibit in at least a number of cases. When the accretion rate drops sufficiently, the X-ray pulsar is said to become a "fast rotator," and in the conventional view, this is accompanied by a transition from accretion to "propellering," in which accretion ceases and the matter is ejected from the system. On the theoretical side, we note that this scenario for the onset of propellering cannot be entirely correct because it is not energetically self-consistent. We show that, instead, the transition is likely to take place through disks that combine accretion with spindown and terminate at the corotation radius. We demonstrate the existence of such disk solutions by modifying the Shakura-Sunyaev equations with a simple magnetic torque prescription. The solutions are completely analytic and have the same dependence on M and a (the viscosity parameter) as the original Shakura-Sunyaev solutions, but the radial profiles can be considerably modified, depending on the degree of fastness. We apply these results to compute the torques expected during the outbursts of the transient millisecond pulsars and find that we can explain the large spin-down rates that are observed for quite plausible surface magnetic fields of approx. 10(exp 90 G.

  19. Decreased Heart Rate Variability in HIV Positive Patients Receiving Antiretroviral Therapy: Importance of Blood Glucose and Cholesterol

    PubMed Central

    Askgaard, Gro; Kristoffersen, Ulrik Sloth; Mehlsen, Jesper; Kronborg, Gitte; Kjaer, Andreas; Lebech, Anne-Mette

    2011-01-01

    The presence of autonomic dysfunction in HIV patients is largely unknown. Early studies found autonomic dysfunction in patients with AIDS. Antiretroviral combination therapy (ART) has dramatically changed the course of the disease and improved prognosis and decreased morbidity. Aim To evaluate whether autonomic dysfunction is present in an ART treated HIV population and if so to identify factors of importance. Methods HIV patients receiving ART for at least 12 months (n = 97) and an age-matched control group of healthy volunteers (n = 52) were included. All were non-diabetic and had never received medication for hypertension. Following a 10 min resting period a 15 min ECG recording was performed. Heart-rate variability (HRV) analysis was performed in accordance with current guidelines and data reported as mean [interquartile range]. Results Mean normal-to-normal (NN) and total HRV measured as standard deviation of normal-to-normal (SDNN) was lower in HIV patients compared to controls (905 vs. 982 ms; p<0.001 and 48 vs. 54 ms; p = 0.028, respectively). No differences were found between the groups in parasympathetic activity measured as square root of the mean squared difference of successive NN-intervals (RMSSD) or the percent of differences between adjacent NN intervals greater than 50 ms (pNN50). In the HIV positives, haemoglobin A1c correlated inversely with SDNN, RMSSD and pNN50 (p<0.05). Total cholesterol and LDL-C correlated inversely with RMSSD and pNN50 (p<0.05). Neither HIV duration, HIV-RNA, CD4 cell count nor CD4 nadir correlated with time or phase domain HRV variables. Conclusions Moderate autonomic dysfunction is present in HIV positives patients even with suppressed viral load due to ART. The dysfunction is correlated with HbA1c and hypercholesterolemia but not to duration of HIV or whether the patients were receiving protease inhibitors as part of the ART regime. PMID:21655281

  20. The Burst Mode of Protostellar Accretion

    NASA Astrophysics Data System (ADS)

    Vorobyov, E. I.; Basu, Shantanu

    2006-10-01

    We present new numerical simulations in the thin disk approximation that characterize the burst mode of protostellar accretion. The burst mode begins upon the formation of a centrifugally balanced disk around a newly formed protostar. It comprises prolonged quiescent periods of low accretion rate (typically <~10-7 Msolar yr-1) that are punctuated by intense bursts of accretion (typically >~10-4 Msolar yr-1, with duration <~100 yr) during which most of the protostellar mass is accumulated. The accretion bursts are associated with the formation of dense protostellar/protoplanetary embryos, which are later driven onto the protostar by the gravitational torques that develop in the disk. Gravitational instability in the disk, driven by continuing infall from the envelope, is shown to be an effective means of transporting angular momentum outward and mass inward to the protostar. We show that the disk mass always remains significantly less than the central protostar's mass throughout this process. The burst phenomenon is robust enough to occur for a variety of initial values of rotation rate and frozen-in (supercritical) magnetic field and a variety of density-temperature relations. Even in cases where the bursts are nearly entirely suppressed, a moderate increase in cloud size or rotation rate can lead to vigorous burst activity. We conclude that most (if not all) protostars undergo a burst mode of evolution during their early accretion history, as inferred empirically from observations of FU Orionis variables.

  1. The Eddington limit and supercritical accretion. II - Time-dependent calculations

    NASA Technical Reports Server (NTRS)

    Burger, H. L.; Katz, J. I.

    1983-01-01

    Spherically symmetric, time-dependent accretion of an ionized hydrogen plasma onto a neutron star is calculated for accretion rates in excess of the Eddington limit. The coupled hydrodynamic and frequency integrated radiative transfer equations are solved on an Eulerian grid for these supercritical accretion flows. Our results indicate that steady state flows are limited to rates at or below the critical rate, with emergent luminosities equal to or less than the Eddington luminosity. Initially supercritical accretion rates generate a large pulse of radiation which reduces the accretion rate to the critical value and produces an extended quasi-static envelope.

  2. Multi-dimensional structure of accreting young stars

    NASA Astrophysics Data System (ADS)

    Geroux, C.; Baraffe, I.; Viallet, M.; Goffrey, T.; Pratt, J.; Constantino, T.; Folini, D.; Popov, M. V.; Walder, R.

    2016-04-01

    This work is the first attempt to describe the multi-dimensional structure of accreting young stars based on fully compressible time implicit multi-dimensional hydrodynamics simulations. One major motivation is to analyse the validity of accretion treatment used in previous 1D stellar evolution studies. We analyse the effect of accretion on the structure of a realistic stellar model of the young Sun. Our work is inspired by the numerical work of Kley & Lin (1996, ApJ, 461, 933) devoted to the structure of the boundary layer in accretion disks, which provides the outer boundary conditions for our simulations. We analyse the redistribution of accreted material with a range of values of specific entropy relative to the bulk specific entropy of the material in the accreting object's convective envelope. Low specific entropy accreted material characterises the so-called cold accretion process, whereas high specific entropy is relevant to hot accretion. A primary goal is to understand whether and how accreted energy deposited onto a stellar surface is redistributed in the interior. This study focusses on the high accretion rates characteristic of FU Ori systems. We find that the highest entropy cases produce a distinctive behaviour in the mass redistribution, rms velocities, and enthalpy flux in the convective envelope. This change in behaviour is characterised by the formation of a hot layer on the surface of the accreting object, which tends to suppress convection in the envelope. We analyse the long-term effect of such a hot buffer zone on the structure and evolution of the accreting object with 1D stellar evolution calculations. We study the relevance of the assumption of redistribution of accreted energy into the stellar interior used in the literature. We compare results obtained with the latter treatment and those obtained with a more physical accretion boundary condition based on the formation of a hot surface layer suggested by present multi

  3. He-accreting WDs: AM CVn stars with WD donors

    NASA Astrophysics Data System (ADS)

    Piersanti, L.; Yungelson, L. R.; Tornambé, A.

    2015-09-01

    We study the physical and evolutionary properties of the `white dwarf (WD) family' of AM CVn stars by computing realistic models of interacting double-degenerate systems. We evaluate self-consistently both the mass-transfer rate from the donor, as determined by gravitational wave emission and interaction with the binary companion, and the thermal response of the accretor to mass deposition. We find that, after the onset of mass transfer, all the considered systems undergo a strong non-dynamical He-flash. However, due to the compactness of these systems, the expanding accretors fill their Roche lobe very soon, thus preventing the efficient heating of the external layers of the accreted CO WDs. Moreover, due to the loss of matter from the systems, the orbital separations enlarge and mass transfer comes to a halt. The further evolution depends on the value of dot{M} after the donors fill again their lobe. On one hand, if the accretion rate, as determined by the actual value of (Mdon, Macc), is high enough, the accretors experience several He-flashes of decreasing strength and then quiescent He-burning sets in. Later on, since the mass-transfer rate in IDD is a permanently decreasing function of time, accretors experience several recurrent strong flashes. On the other hand, for intermediate and low values of dot{M} the accretors enter directly the strong flashes accretion regime. As expected, in all the considered systems the last He-flash is the strongest one, even if the physical conditions suitable for a dynamical event are never attained. When the mass accretion rate decreases below (2-3) × 10-8 M⊙ yr-1, the compressional heating of the He-shell becomes less efficient than the neutrino cooling, so that all the accretors in the considered systems evolve into massive degenerate objects. Our results suggest that SNe .Ia or Type Ia Supernovae due to Edge-Lit Detonation in the WD family of AM CVn stars should be much more rare than previously expected.

  4. Gamma-burst emission from neutron-star accretion

    NASA Technical Reports Server (NTRS)

    Colgate, S. A.; Petschek, A. G.; Sarracino, R.

    1983-01-01

    A model for emission of the hard photons of gamma bursts is presented. The model assumes accretion at nearly the Eddington limited rate onto a neutron star without a magnetic field. Initially soft photons are heated as they are compressed between the accreting matter and the star. A large electric field due to relatively small charge separation is required to drag electrons into the star with the nuclei against the flux of photons leaking out through the accreting matter. The photon number is not increased substantially by Bremsstrahlung or any other process. It is suggested that instability in an accretion disc might provide the infalling matter required.

  5. NUMERICAL SIMULATION OF HOT ACCRETION FLOWS. II. NATURE, ORIGIN, AND PROPERTIES OF OUTFLOWS AND THEIR POSSIBLE OBSERVATIONAL APPLICATIONS

    SciTech Connect

    Yuan Feng; Bu Defu; Wu Maochun E-mail: dfbu@shao.ac.cn

    2012-12-20

    Hydrodynamical (HD) and magnetohydrodynamical (MHD) numerical simulations of hot accretion flows have indicated that the inflow accretion rate decreases inward. Two models have been proposed to explain this result. In the adiabatic inflow-outflow solution (ADIOS), this is because of the loss of gas in the outflow. In the alternative convection-dominated accretion flow model, it is thought that the flow is convectively unstable and gas is locked in convective eddies. We investigate the nature of the inward decrease of the accretion rate using HD and MHD simulations. We calculate various properties of the inflow and outflow such as temperature and rotational velocity. Systematic and significant differences are found. These results suggest that the inflow and outflow are not simply convective turbulence; instead, systematic inward and outward motion (i.e., real outflow) must exist. We have also analyzed the convective stability of MHD accretion flows and found that they are stable. These results favor the ADIOS scenario. We suggest that the mechanisms of producing outflow in HD and MHD flows are the buoyancy associated with the convection and the centrifugal force associated with the angular momentum transport mediated by the magnetic field, respectively. The latter is similar to the Blandford and Payne mechanism but no large-scale open magnetic field is required. We discuss some possible observational applications, including the Fermi bubble in the Galactic center and winds in active galactic nuclei and black hole X-ray binaries.

  6. Strong Role of Non-stationary Accretion in Spectral Transitions of X-ray Binaries and Implications for Revealing the Accretion Geometry and Broadband Radiation Mechanisms

    NASA Astrophysics Data System (ADS)

    Yu, Wenfei; Yan, Zhen; Tang, Jing; Wu, Yuxiang

    Observations of spectral transitions from the hard state to the soft state in bright X-ray binaries show strong evidence that the rate-of-change of the mass accretion rate plays a dominant role in determining the luminosity at which the spectral transition occurs. This indicates that in many cases, especially accretion in transients during outbursts, the rate-of-change of the mass accretion rate is the primary parameter driving high energy phenomena. Although this goes beyond the scope of current stationary model of disk and jet, it tells us that it is the rate-of-change of the mass accretion rate that we need to trace observationally. Since state transition is a broadband phenomenon, multi-wavelength observations of spectral transitions of different rate-of-changes of mass accretion rate are expect to reveal the accretion geometry and broadband radiation mechanisms.

  7. Chaotic cold accretion on to black holes

    NASA Astrophysics Data System (ADS)

    Gaspari, M.; Ruszkowski, M.; Oh, S. Peng

    2013-07-01

    Bondi theory is often assumed to adequately describe the mode of accretion in astrophysical environments. However, the Bondi flow must be adiabatic, spherically symmetric, steady, unperturbed, with constant boundary conditions. Using 3D adaptive mesh refinement simulations, linking the 50 kpc to the sub-parsec (sub-pc) scales over the course of 40 Myr, we systematically relax the classic assumptions in a typical galaxy hosting a supermassive black hole. In the more realistic scenario, where the hot gas is cooling, while heated and stirred on large scales, the accretion rate is boosted up to two orders of magnitude compared with the Bondi prediction. The cause is the non-linear growth of thermal instabilities, leading to the condensation of cold clouds and filaments when tcool/tff ≲ 10. The clouds decouple from the hot gas, `raining' on to the centre. Subsonic turbulence of just over 100 km s-1 (M > 0.2) induces the formation of thermal instabilities, even in the absence of heating, while in the transonic regime turbulent dissipation inhibits their growth (tturb/tcool ≲ 1). When heating restores global thermodynamic balance, the formation of the multiphase medium is violent, and the mode of accretion is fully cold and chaotic. The recurrent collisions and tidal forces between clouds, filaments and the central clumpy torus promote angular momentum cancellation, hence boosting accretion. On sub-pc scales the clouds are channelled to the very centre via a funnel. In this study, we do not inject a fixed initial angular momentum, though vorticity is later seeded by turbulence. A good approximation to the accretion rate is the cooling rate, which can be used as subgrid model, physically reproducing the boost factor of 100 required by cosmological simulations, while accounting for the frequent fluctuations. Since our modelling is fairly general (turbulence/heating due to AGN feedback, galaxy motions, mergers, stellar evolution), chaotic cold accretion may be common in

  8. The Correlation of Decreased Heart Rate Recovery and Chronotropic Incompetence with Exercise Capacity in Idiopathic Pulmonary Arterial Hypertension Patients

    PubMed Central

    Wu, Changwei; Guo, Jian; Liu, Hui; Pudasaini, Bigyan; Yang, Wenlan; Zhao, Qinhua; Wang, Lan

    2017-01-01

    We show by this study that a decrease in HRR1 in IPAH patients is associated with severe limitation of exercise capacity. HRR1 < 16 beats and CI just after completion of a CPET could be an indicator of poor prognosis. PMID:28286762

  9. Modeling the optical-X-ray accretion lag in LMC X-3: Insights into black-hole accretion physics

    SciTech Connect

    Steiner, James F.; McClintock, Jeffrey E.; Orosz, Jerome A.; Buxton, Michelle M.; Bailyn, Charles D.; Remillard, Ronald A.; Kara, Erin

    2014-03-10

    The X-ray persistence and characteristically soft spectrum of the black hole X-ray binary LMC X-3 make this source a touchstone for penetrating studies of accretion physics. We analyze a rich, ten-year collection of optical/infrared (OIR) time-series data in conjunction with all available contemporaneous X-ray data collected by the All-Sky Monitor and Proportional Counter Array detectors aboard the Rossi X-ray Timing Explorer. A cross-correlation analysis reveals an X-ray lag of ≈2 weeks. Motivated by this result, we develop a model that reproduces the complex OIR light curves of LMC X-3. The model is comprised of three components of emission: stellar light, accretion luminosity from the outer disk inferred from the time-lagged X-ray emission, and light from the X-ray-heated star and outer disk. Using the model, we filter a strong noise component out of the ellipsoidal light curves and derive an improved orbital period for the system. Concerning accretion physics, we find that the local viscous timescale in the disk increases with the local mass accretion rate; this in turn implies that the viscosity parameter α decreases with increasing luminosity. Finally, we find that X-ray heating is a strong function of X-ray luminosity below ≈50% of the Eddington limit, while above this limit X-ray heating is heavily suppressed. We ascribe this behavior to the strong dependence of the flaring in the disk upon X-ray luminosity, concluding that for luminosities above ≈50% of Eddington, the star lies fully in the shadow of the disk.

  10. Accretion onto Pre-Main-Sequence Stars

    NASA Astrophysics Data System (ADS)

    Hartmann, Lee; Herczeg, Gregory; Calvet, Nuria

    2016-09-01

    Accretion through circumstellar disks plays an important role in star formation and in establishing the properties of the regions in which planets form and migrate. The mechanisms by which protostellar and protoplanetary disks accrete onto low-mass stars are not clear; angular momentum transport by magnetic fields is thought to be involved, but the low-ionization conditions in major regions of protoplanetary disks lead to a variety of complex nonideal magnetohydrodynamic effects whose implications are not fully understood. Accretion in pre-main-sequence stars of masses ≲1M⊙ (and in at least some 2-3-M⊙ systems) is generally funneled by the stellar magnetic field, which disrupts the disk at scales typically of order a few stellar radii. Matter moving at near free-fall velocities shocks at the stellar surface; the resulting accretion luminosities from the dissipation of kinetic energy indicate that mass addition during the T Tauri phase over the typical disk lifetime ˜3 Myr is modest in terms of stellar evolution, but is comparable to total disk reservoirs as estimated from millimeter-wave dust emission (˜10-2 M⊙). Pre-main-sequence accretion is not steady, encompassing timescales ranging from approximately hours to a century, with longer-timescale variations tending to be the largest. Accretion during the protostellar phase—while the protostellar envelope is still falling onto the disk—is much less well understood, mostly because the properties of the central obscured protostar are difficult to estimate. Kinematic measurements of protostellar masses with new interfometric facilities should improve estimates of accretion rates during the earliest phases of star formation.

  11. Accretion dynamics of EX Lupi in quiescence. The star, the spot, and the accretion column

    NASA Astrophysics Data System (ADS)

    Sicilia-Aguilar, Aurora; Fang, Min; Roccatagliata, Veronica; Collier Cameron, Andrew; Kóspál, Ágnes; Henning, Thomas; Ábrahám, Peter; Sipos, Nikoletta

    2015-08-01

    Context. EX Lupi is a young, accreting M0 star and the prototype of EXor variable stars. Its spectrum is very rich in emission lines, including many metallic lines with narrow and broad components. The presence of a close companion has also been proposed, based on radial velocity signatures. Aims: We use the metallic emission lines to study the accretion structures and to test the companion hypothesis. Methods: We analyse 54 spectra obtained during five years of quiescence time. We study the line profile variability and the radial velocity of the narrow and broad metallic emission lines. We use the velocity signatures of different species with various excitation conditions and their time dependency to track the dynamics associated with accretion. Results: We observe periodic velocity variations in the broad and the narrow line components, consistent with rotational modulation. The modulation is stronger for lines with higher excitation potentials (e.g. He II), which are likely produced in a confined area very close to the accretion shock. Conclusions: We propose that the narrow line components are produced in the post-shock region, while the broad components originate in the more extended, pre-shock material in the accretion column. All the emission lines suffer velocity modulation due to the rotation of the star. The broad components are responsible for the line-dependent veiling observed in EX Lupi. We demonstrate that a rotationally modulated line-dependent veiling can explain the radial velocity signature of the photospheric absorption lines, making the close-in companion hypothesis unnecessary. The accretion structure is locked to the star and very stable during the five years of observations. Not all stars with similar spectral types and accretion rates show the same metallic emission lines, which could be related to differences in temperature and density in their accretion structure(s). The contamination of photospheric signatures by accretion

  12. Tidal marsh accretion processes in the San Francisco Bay-Delta - are our models underestimating the historic and future importance of plant-mediated organic accretion?

    NASA Astrophysics Data System (ADS)

    Windham-Myers, L.; Drexler, J. Z.; Byrd, K. B.; Schile, L. M.

    2012-12-01

    Peat-accreting coastal wetlands have the potential to keep elevational pace with sea-level rise, thus providing both adaptation and mitigation for expected rises in atmospheric concentrations of greenhouse gases (GHGs). Due to oxidation and sedimentation processes, marsh elevations are generally constrained by sea level rise (1-2 mm yr-1). However, the relative importance of mineral vs. organic accretion remain poorly understood. At least four lines of evidence from the brackish-fresh region of California's SFBay-Delta suggest that potential rates of organic accretion may be underestimated in calibration datasets of the last century. First, tidal marsh elevations have been maintained with changing rates of SLR over the past 6700 years even during periods of low sediment availability. Second, the presence of fibric remnants in historic peat cores suggests that millennial preservation of autochtonous material may be greater in the absence of mineral inputs. Third, an experimental restoration of emergent marsh on subsided peat soil has generated new "proto-peat" at average rates of 4 cm y-1, nearly 40-times mean sea level rise, storing an average of 1 kg C m-2 yr-1 since 1997. Fourth, annual measurements of root production of the dominant fresh-brackish marsh species tule (Schoenoplectus acutus) show high productivity and minimal sensitivity to variable tidal range elevations and fresh-brackish salinities. Separating the relative importance of belowground productivity from decomposition in driving rates of organic accretion may be possible by assessment of fibric remnants, as an index of organic "preservation". Using three distinct peat cores from a larger study with calibrated dating and geochemistry data, fibric remnants (particles >2mm) were assessed at 10 cm intervals and compared with physical and associated geochemical down-core variability (n=230 segments). The presence of fibric remnants was reduced in the presence of sediment, as indicated by mineral content

  13. The accretion of migrating giant planets

    NASA Astrophysics Data System (ADS)

    Dürmann, Christoph; Kley, Wilhelm

    2017-02-01

    Aims: Most studies concerning the growth and evolution of massive planets focus either on their accretion or their migration only. In this work we study both processes concurrently to investigate how they might mutually affect one another. Methods: We modeled a two-dimensional disk with a steady accretion flow onto the central star and embedded a Jupiter mass planet at 5.2 au. The disk is locally isothermal and viscosity is modeled using a constant α. The planet is held on a fixed orbit for a few hundred orbits to allow the disk to adapt and carve a gap. After this period, the planet is released and free to move according to the gravitational interaction with the gas disk. The mass accretion onto the planet is modeled by removing a fraction of gas from the inner Hill sphere, and the removed mass and momentum can be added to the planet. Results: Our results show that a fast migrating planet is able to accrete more gas than a slower migrating planet. Utilizing a tracer fluid we analyzed the origin of the accreted gas originating predominantly from the inner disk for a fast migrating planet. In the case of slower migration, the fraction of gas from the outer disk increases. We also found that even for very high accretion rates, in some cases gas crosses the planetary gap from the inner to the outer disk. Our simulations show that the crossing of gas changes during the migration process as the migration rate slows down. Therefore, classical type II migration where the planet migrates with the viscous drift rate and no gas crosses the gap is no general process but may only occur for special parameters and at a certain time during the orbital evolution of the planet.

  14. Face-on accretion onto a protoplanetary disc

    NASA Astrophysics Data System (ADS)

    Wijnen, T. P. G.; Pols, O. R.; Pelupessy, F. I.; Portegies Zwart, S.

    2016-10-01

    ) accretion of material with no azimuthal angular momentum. Our study, as well as previous work, suggests that the former, dominant process is mainly caused by numerical, rather than physical effects, while the latter is not. The latter process, as expected theoretically, causes the disc to become more compact and increases the surface density profile considerably at smaller radii. Conclusions: The disc size is determined in the first place by the ram pressure exerted by the flow when it first hits the disc. Further evolution is governed by the decrease in the specific angular momentum of the disc as it accretes material with no azimuthal angular momentum. Even taking into account the uncertainties in our simulations and the result that the loading rate is within a factor two of a simple geometric estimate, the size and lifetime of the disc are probably not sufficient to accrete the amount of mass required in the early disc accretion scenario. An animation of the simulation is available at http://www.aanda.org

  15. Analytical Investigation of the Decrease in the Size of the Habitable Zone Due to a Limited CO2 Outgassing Rate

    NASA Astrophysics Data System (ADS)

    Abbot, Dorian S.

    2016-08-01

    The habitable zone concept is important because it focuses the scientific search for extraterrestrial life and aids the planning of future telescopes. Recent work has shown that planets near the outer edge of the habitable zone might not actually be able to stay warm and habitable if CO2 outgassing rates are not large enough to maintain high CO2 partial pressures against removal by silicate weathering. In this paper, I use simple equations for the climate and CO2 budget of a planet in the habitable zone that can capture the qualitative behavior of the system. With these equations I derive an analytical formula for an effective outer edge of the habitable zone, including limitations imposed by the CO2 outgassing rate. I then show that climate cycles between a snowball state and a warm climate are only possible beyond this limit if the weathering rate in the snowball climate is smaller than the CO2 outgassing rate (otherwise stable snowball states result). I derive an analytical solution for the climate cycles including a formula for their period in this limit. This work allows us to explore the qualitative effects of weathering processes on the effective outer edge of the habitable zone, which is important because weathering parameterizations are uncertain.

  16. A Decrease in Suicide Rates in Japanese Rural Towns after Community-Based Intervention by the Health Promotion Approach

    ERIC Educational Resources Information Center

    Motohashi, Yutaka; Kaneko, Yoshihiro; Sasaki, Hisanaga

    2007-01-01

    A community-based intervention study for suicide prevention was conducted in six towns (total population 43,964) in Akita Prefecture of Japan according to a quasi-experimental design to reduce suicide rates in rural towns. Public awareness raising activities using a health promotion approach emphasizing the empowerment of residents and civic…

  17. Magnetohydrodynamic Origin of Jets from Accretion Disks

    NASA Technical Reports Server (NTRS)

    Lovelace, R. V. E.; Romanova, M. M.

    1998-01-01

    A review is made of magnetohydrodynamic (MHD) theory and simulation of outflows from disks for different distributions of magnetic field threading the disk. In one limit of a relatively weak, initially diverging magnetic field, both thermal and magnetic pressure gradients act to drive matter to an outflow, while a toroidal magnetic field develops which strongly collimates the outflow. The collimation greatly reduces the field divergence and the mass outflow rate decreases after an initial peak. In a second limit of a strong magnetic field, the initial field configuration was taken with the field strength on the disk decreasing outwards to small values so that collimation was reduced. As a result, a family of stationary solutions was discovered where matter is driven mainly by the strong magnetic pressure gradient force. The collimation in this case depends on the pressure of an external medium. These flows are qualitatively similar to the analytic solutions for magnetically driven outflows. The problem of the opening of a closed field line configuration linking a magnetized star and an accretion disk is also discussed.

  18. The Final Fates of Accreting Supermassive Stars

    NASA Astrophysics Data System (ADS)

    Umeda, Hideyuki; Hosokawa, Takashi; Omukai, Kazuyuki; Yoshida, Naoki

    2016-10-01

    The formation of supermassive stars (SMSs) via rapid mass accretion and their direct collapse into black holes (BHs) is a promising pathway for sowing seeds of supermassive BHs in the early universe. We calculate the evolution of rapidly accreting SMSs by solving the stellar structure equations including nuclear burning as well as general relativistic (GR) effects up to the onset of the collapse. We find that such SMSs have a less concentrated structure than a fully convective counterpart, which is often postulated for non-accreting ones. This effect stabilizes the stars against GR instability even above the classical upper mass limit ≳105 M ⊙ derived for the fully convective stars. The accreting SMS begins to collapse at the higher mass with the higher accretion rate. The collapse occurs when the nuclear fuel is exhausted only for cases with \\dot{M}≲ 0.1 {M}⊙ {{{yr}}}-1. With \\dot{M}≃ 0.3{--}1 {M}⊙ {{{yr}}}-1, the star becomes GR unstable during the helium-burning stage at M ≃ 2-3.5 × 105 M ⊙. In an extreme case with 10 {M}⊙ {{{yr}}}-1, the star does not collapse until the mass reaches ≃8.0 × 105 M ⊙, where it is still in the hydrogen-burning stage. We expect that BHs with roughly the same mass will be left behind after the collapse in all the cases.

  19. Episodic Accretion among the Orion Protostars

    NASA Astrophysics Data System (ADS)

    Fischer, William J.; Safron, Emily; Megeath, S. Thomas

    2016-06-01

    Episodic accretion, where a young stellar object undergoes stochastic spikes in its disk-to-star accretion rate one or more times over its formation period, may be a crucial process in the formation of low-mass stars. These spikes result in a factor of 10 to 100 increase in the source luminosity over the course of several months that may persist for years. Six years after the Spitzer survey of the Orion molecular clouds, the WISE telescope mapped Orion with similar wavelength coverage. Thus, the two surveys can be used to explore the mid-infrared variability of young stars on this timescale, which is suitable for discovering episodic accretion events. Out of 319 Orion protostars that were targets of the Herschel Orion Protostar Survey, we identified two examples of episodic accretion with this method. One of them, HOPS 223, was previously known. The other, HOPS 383, is the first known example of episodic accretion in a Class 0 protostar (age < 0.2 Myr). With these and one other outburst that began early in the Spitzer mission, we estimate that the most likely interval between protostellar outbursts is 740 years, with a 90% confidence interval of 470 to 6200 years. These outbursts are weaker than the optically revealed FU Ori events. We will update the mid-infrared light curves of HOPS 223 and HOPS 383 with recent data from FORCAST aboard SOFIA; HOPS 223 shows signs of fading.

  20. Association of apneic oxygenation with decreased desaturation rates during rapid sequence intubation by a Chinese emergency medicine service.

    PubMed

    Mao, Yong; Qin, Zong-He

    2015-01-01

    Rapid and safe airway management has always been of paramount importance in successful management of critically ill and injured patients in the emergency department. The achievement rate of emergency medicine inhabitants in airway management improved enhanced essentially subsequent to finishing anaesthesiology turn. There was a slightly higher rate of quick sequence intubation in the postapneic oxygenation groups (preapneic oxygenation 6.4%; postapneic oxygenation 9.1%). The majority of patients intubated in both groups were men (preapneic oxygenation 72.3%; postapneic oxygenation 63.5%). A higher percentage of patients in the preapneic oxygenation group had a Cormack-Lehane grade III or worse view (23.2% versus 11.8%). Anaesthesiology turns should be considered as an essential component of emergency medicine training programs. A collateral curriculum of this nature should also focus on the acquisition of skills in airway management.

  1. Decreasing salinity of seawater moderates immune response and increases survival rate of giant groupers post betanodavirus infection.

    PubMed

    Chen, Tz-Shiang; Wu, Yu-Chi; Chi, Shau-Chi

    2016-10-01

    Giant groupers (Epinephelus lanceolatus), an important aquaculture fish in Asia, are attacked by nervous necrosis virus (NNV), belonging to betanodavirus. Environmental salinity can affect fish immunity and physiology. We examined whether decreasing salinity from 30 to 15 ppt during acclimation of groupers could affect survival with NNV infection and the associated factors. Although NNV infection decreased muscle moisture, up-regulated the gene expression of Na(+)-K(+)-2Cl(-) cotransporter isoform 2, and elevated plasma cortisol level in groupers, these factors were not related to the higher mortality of groupers reared at 30-ppt salinity (S30-groupers), compared to 15-ppt reared groupers (S15-groupers). Infected S30-groupers exhibited high leukocyte count and innate immune gene expression level. Moreover, NNV-infected dead S30-groupers showed high IL-1β gene expression level but low NNV load in the brain. The high or excess IL-1β gene expression levels in the brain of NNV-infected S30-groupers may be the factor in high mortality.

  2. Accretions of dark matter and dark energy onto (n+2)-dimensional Schwarzschild black hole and Morris-Thorne wormhole

    NASA Astrophysics Data System (ADS)

    Debnath, Ujjal

    2015-12-01

    In this work, we have studied accretion of the dark matter and dark energy onto of (n+2)-dimensional Schwarzschild black hole and Morris-Thorne wormhole. The mass and the rate of change of mass for (n+2)-dimensional Schwarzschild black hole and Morris-Thorne wormhole have been found. We have assumed some candidates of dark energy like holographic dark energy, new agegraphic dark energy, quintessence, tachyon, DBI-essence, etc. The black hole mass and the wormhole mass have been calculated in term of redshift when dark matter and above types of dark energies accrete onto them separately. We have shown that the black hole mass increases and wormhole mass decreases for holographic dark energy, new agegraphic dark energy, quintessence, tachyon accretion and the slope of increasing/decreasing of mass sensitively depends on the dimension. But for DBI-essence accretion, the black hole mass first increases and then decreases and the wormhole mass first decreases and then increases and the slope of increasing/decreasing of mass not sensitively depends on the dimension.

  3. Do high progesterone concentrations decrease pregnancy rates in embryo recipients synchronized with PGF2alpha and eCG?

    PubMed

    Nogueira, Marcelo F Gouveia; Melo, Danilas S; Carvalho, Luciano M; Fuck, Egon J; Trinca, Luzia A; Barros, Ciro Moraes

    2004-05-01

    The objective of this study was to evaluate the effects of equine chorionic gonadotropin (eCG) treatment on the number of induced accessory corpora lutea (CL), plasma progesterone concentrations and pregnancy rate in cross-bred heifers after transfer of frozen-thawed (1.5M ethylene glycol) embryos. All recipients received 500 microg PGF2alpha (dl-cloprostenol, i.m.) at random stages of the estrous cycle (Day 0) and were observed for estrus for 7 days. On Day 14, heifers detected in estrus between 2 and 7 days after PGF2alpha treatment were randomly allocated to four groups ( n=83 per group) and given 0 (control), 200, 400, or 600 IU of eCG. Two days later (Day 16), these recipients were given PGF2alpha and observed for estrus. Six to eight days after detection of estrus, plasma samples were collected to determine progesterone concentration and ultrasonography was performed to observe ovarian structures. Heifers with multiple CL or a single CL >15 mm in diameter received an embryo by direct transfer. Embryos of excellent and good quality were thawed and transferred to the recipients by the same veterinarian. Pregnancy was diagnosed by ultrasonography and confirmed by transrectal palpation 21 and 83 days after embryo transfer (ET), respectively. Plasma progesterone concentrations on the day of transfer (Day 7 of the estrous cycle) were 3.9+/-0.7, 4.2+/-0.4,6.0+/-0.4 and 7.8+/-0.6 ng/ml for groups Control, 200, 400, and 600, respectively (Control versus treated groups P=0.009; 200 versus 400 and 600 groups P=0.0001; and 400 versus 600 P=0.012 ). Conception rates 83 days after ET were 41.9, 50.0, 25.0, and 20.9% for groups Control, 200, 400, and 600, respectively (200 versus 400 and 600 groups P=0.0036 ). In conclusion, an increase in progesterone concentration, induced by eCG treatment, did not improve pregnancy rates in ET recipients. Conversely, there was a decline in conception rates in the animals with the highest plasma progesterone concentrations.

  4. Reduced snow cover alters root-microbe interactions and decreases nitrification rates in a northern hardwood forest.

    PubMed

    Sorensen, Patrick O; Templer, Pamela H; Christenson, Lynn; Duran, Jorge; Fahey, Timothy; Fisk, Melany C; Groffman, Peter M; Morse, Jennifer L; Finzi, Adrien C

    2016-12-01

    Snow cover is projected to decline during the next century in many ecosystems that currently experience a seasonal snowpack. Because snow insulates soils from frigid winter air temperatures, soils are expected to become colder and experience more winter soil freeze-thaw cycles as snow cover continues to decline. Tree roots are adversely affected by snowpack reduction, but whether loss of snow will affect root-microbe interactions remains largely unknown. The objective of this study was to distinguish and attribute direct (e.g., winter snow- and/or soil frost-mediated) vs. indirect (e.g., root-mediated) effects of winter climate change on microbial biomass, the potential activity of microbial exoenzymes, and net N mineralization and nitrification rates. Soil cores were incubated in situ in nylon mesh that either allowed roots to grow into the soil core (2 mm pore size) or excluded root ingrowth (50 μm pore size) for up to 29 months along a natural winter climate gradient at Hubbard Brook Experimental Forest, NH (USA). Microbial biomass did not differ among ingrowth or exclusion cores. Across sampling dates, the potential activities of cellobiohydrolase, phenol oxidase, and peroxidase, and net N mineralization rates were more strongly related to soil volumetric water content (P < 0.05; R(2 ) = 0.25-0.46) than to root biomass, snow or soil frost, or winter soil temperature (R(2 ) < 0.10). Root ingrowth was positively related to soil frost (P < 0.01; R(2)  = 0.28), suggesting that trees compensate for overwinter root mortality caused by soil freezing by re-allocating resources towards root production. At the sites with the deepest snow cover, root ingrowth reduced nitrification rates by 30% (P < 0.01), showing that tree roots exert significant influence over nitrification, which declines with reduced snow cover. If soil freezing intensifies over time, then greater compensatory root growth may reduce nitrification rates directly via plant-microbe N

  5. Stretch of contracting cardiac muscle abruptly decreases the rate of phosphate release at high and low calcium.

    PubMed

    Mansfield, Catherine; West, Tim G; Curtin, Nancy A; Ferenczi, Michael A

    2012-07-27

    The contractile performance of the heart is linked to the energy that is available to it. Yet, the heart needs to respond quickly to changing demands. During diastole, the heart fills with blood and the heart chambers expand. Upon activation, contraction of cardiac muscle expels blood into the circulation. Early in systole, parts of the left ventricle are being stretched by incoming blood, before contraction causes shrinking of the ventricle. We explore here the effect of stretch of contracting permeabilized cardiac trabeculae of the rat on the rate of inorganic phosphate (P(i)) release resulting from ATP hydrolysis, using a fluorescent sensor for P(i) with millisecond time resolution. Stretch immediately reduces the rate of P(i) release, an effect observed both at full calcium activation (32 μmol/liter of Ca(2+)), and at a physiological activation level of 1 μmol/liter of Ca(2+). The results suggest that stretch redistributes the actomyosin cross-bridges toward their P(i)-containing state. The redistribution means that a greater fraction of cross-bridges will be poised to rapidly produce a force-generating transition and movement, compared with cross-bridges that have not been subjected to stretch. At the same time stretch modifies the P(i) balance in the cytoplasm, which may act as a cytoplasmic signal for energy turnover.

  6. High Emergency Lung Transplantation: dramatic decrease of waiting list death rate without relevant higher post-transplant mortality.

    PubMed

    Roux, Antoine; Beaumont-Azuar, Laurence; Hamid, Abdul Monem; De Miranda, Sandra; Grenet, Dominique; Briend, Guillaume; Bonnette, Pierre; Puyo, Philippe; Parquin, François; Devaquet, Jerome; Trebbia, Gregoire; Cuquemelle, Elise; Douvry, Benoit; Picard, Clément; Le Guen, Morgan; Chapelier, Alain; Stern, Marc; Sage, Edouard

    2015-09-01

    Many candidates for lung transplantation (LT) die on the waiting list, raising the question of graft availability and strategy for organ allocation. We report the experience of the new organ allocation program, "High Emergency Lung Transplantation" (HELT), since its implementation in our center in 2007. Retrospective analysis of 201 lung transplant patients, of whom 37 received HELT from 1st July 2007 to 31th May 2012. HELT candidates had a higher impairment grade on respiratory status and higher Lung Allocation Score (LAS). HELT patients had increased incidence of perioperative complications (e.g., perioperative bleeding) and extracorporeal circulatory assistance (75% vs. 36.6%, P = 0.0005). No significant difference was observed between HELT and non-HELT patients in mechanical ventilation duration (15.5 days vs. 11 days, P = 0.27), intensive care unit length of stay (15 days vs. 10 days, P = 0.22) or survival rate at 12 (81% vs. 80%), and 24 months post-LT (72.9% vs. 75.0%). Lastly, mortality on the waiting list was spectacularly reduced from 19% to 2% when compared to the non-HELT 2004-2007 group. Despite a more severe clinical status of patients on the waiting list, HELT provided similar results to conventional LT. These results were associated with a dramatic reduction in the mortality rate of patients on the waiting list.

  7. Bondi-Hoyle Accretion in an Isothermal Magnetized Plasma

    NASA Astrophysics Data System (ADS)

    Lee, Aaron T.; Cunningham, Andrew J.; McKee, Christopher F.; Klein, Richard I.

    2014-03-01

    In regions of star formation, protostars and newborn stars will accrete mass from their natal clouds. These clouds are threaded by magnetic fields with a strength characterized by the plasma β—the ratio of thermal and magnetic pressures. Observations show that molecular clouds have β <~ 1, so magnetic fields have the potential to play a significant role in the accretion process. We have carried out a numerical study of the effect of large-scale magnetic fields on the rate of accretion onto a uniformly moving point particle from a uniform, non-self-gravitating, isothermal gas. We consider gas moving with sonic Mach numbers of up to {\\cal M}\\approx 45; magnetic fields that are either parallel, perpendicular, or oriented 45° to the flow; and β as low as 0.01. Our simulations utilize adaptive mesh refinement in order to obtain high spatial resolution where it is needed; this also allows the boundaries to be far from the accreting object to avoid unphysical effects arising from boundary conditions. Additionally, we show that our results are independent of our exact prescription for accreting mass in the sink particle. We give simple expressions for the steady-state accretion rate as a function of β and {\\cal M} for the parallel and perpendicular orientations. Using typical molecular cloud values of {\\cal M}\\sim 5 and β ~ 0.04 from the literature, our fits suggest that a 0.4 M ⊙ star accretes ~4 × 10-9 M ⊙ yr-1, almost a factor of two less than accretion rates predicted by hydrodynamic models. This disparity can grow to orders of magnitude for stronger fields and lower Mach numbers. We also discuss the applicability of these accretion rates versus accretion rates expected from gravitational collapse, and under what conditions a steady state is possible. The reduction in the accretion rate in a magnetized medium leads to an increase in the time required to form stars in competitive accretion models, making such models less efficient than predicted by

  8. Bondi-Hoyle accretion in an isothermal magnetized plasma

    SciTech Connect

    Lee, Aaron T.; McKee, Christopher F.; Klein, Richard I.; Cunningham, Andrew J.

    2014-03-01

    In regions of star formation, protostars and newborn stars will accrete mass from their natal clouds. These clouds are threaded by magnetic fields with a strength characterized by the plasma β—the ratio of thermal and magnetic pressures. Observations show that molecular clouds have β ≲ 1, so magnetic fields have the potential to play a significant role in the accretion process. We have carried out a numerical study of the effect of large-scale magnetic fields on the rate of accretion onto a uniformly moving point particle from a uniform, non-self-gravitating, isothermal gas. We consider gas moving with sonic Mach numbers of up to M≈45; magnetic fields that are either parallel, perpendicular, or oriented 45° to the flow; and β as low as 0.01. Our simulations utilize adaptive mesh refinement in order to obtain high spatial resolution where it is needed; this also allows the boundaries to be far from the accreting object to avoid unphysical effects arising from boundary conditions. Additionally, we show that our results are independent of our exact prescription for accreting mass in the sink particle. We give simple expressions for the steady-state accretion rate as a function of β and M for the parallel and perpendicular orientations. Using typical molecular cloud values of M∼5 and β ∼ 0.04 from the literature, our fits suggest that a 0.4 M {sub ☉} star accretes ∼4 × 10{sup –9} M {sub ☉} yr{sup –1}, almost a factor of two less than accretion rates predicted by hydrodynamic models. This disparity can grow to orders of magnitude for stronger fields and lower Mach numbers. We also discuss the applicability of these accretion rates versus accretion rates expected from gravitational collapse, and under what conditions a steady state is possible. The reduction in the accretion rate in a magnetized medium leads to an increase in the time required to form stars in competitive accretion models, making such models less efficient than predicted by

  9. Human carotid atherosclerotic lesion protein components decrease cholesterol biosynthesis rate in macrophages through 3-hydroxy-3-methylglutaryl-CoA reductase regulation.

    PubMed

    Cohen, Elad; Aviram, Michael; Khatib, Soliman; Rosenblat, Mira; Vaya, Jacob

    2015-01-01

    Atherosclerosis is characterized by the formation of cholesterol-loaded macrophages, which are turned into foam cells, the hallmark of early atherogenesis. As part of ongoing research on the interactions among human carotid lesion components and blood elements, the effect of plaque homogenate on macrophage cholesterol biosynthesis rate was examined. Human carotid plaques were ground, extracted with phosphate-buffered saline (homogenate), and then added to the macrophage medium. This extract decreased macrophage cholesterol biosynthesis rate up to 50% in a dose-dependent manner. Cholesterol or lipoproteins were separated from the homogenate and added to the MQ medium. Unlike the homogenate, neither free cholesterol nor the lipoproteins were able to inhibit cholesterol biosynthesis rate under the above experimental concentration, suggesting that the homogenate-induced cholesterol biosynthesis inhibition in our experimental system was not owing to the feedback inhibition of cholesterol. Furthermore, the homogenate remaining after lipoprotein removal (lipoprotein-deficient homogenate) also decreased cholesterol biosynthesis rate, whereas boiled homogenate or phospholipids extracted from the homogenate decreased macrophage cholesterol biosynthesis rate only partially. Finally, cholesterol biosynthesis inhibition was achieved only upon using the precursor [(3)H]acetate, but not [(14)C]mevalonate, suggesting that 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCoA Reductase), the rate-limiting enzyme in the cholesterol biosynthesis pathway, is involved in the above antiatherogenic effect of the homogenate, whereas the treatment with homogenate decreased HMGCoA Reductase mRNA. Proteins and phospholipids from human carotid lesion homogenate decrease cholesterol biosynthesis rate in macrophages secondary to HMGCoA Reductase feedback regulation. Such an effect may delay foam cell formation and atherosclerosis progression.

  10. Non-expert listeners show decreased heart rate and increased blood pressure (fear bradycardia) in response to atonal music

    PubMed Central

    Proverbio, Alice M.; Manfrin, Luigi; Arcari, Laura A.; De Benedetto, Francesco; Gazzola, Martina; Guardamagna, Matteo; Lozano Nasi, Valentina; Zani, Alberto

    2015-01-01

    Previous studies suggested that listening to different types of music may modulate differently psychological mood and physiological responses associated with the induced emotions. In this study the effect of listening to instrumental classical vs. atonal contemporary music was examined in a group of 50 non-expert listeners. The subjects’ heart rate and diastolic and systolic blood pressure values were measured while they listened to music of different style and emotional typologies. Pieces were selected by asking a group of composers and conservatory professors to suggest a list of the most emotional music pieces (from Renaissance to present time). A total of 214 suggestions from 20 respondents were received. Then it was asked them to identify which pieces best induced in the listener feelings of agitation, joy or pathos and the number of suggested pieces per style was computed. Atonal pieces were more frequently indicated as agitating, and tonal pieces as joyful. The presence/absence of tonality in a musical piece did not affect the affective dimension of pathos (being touching). Among the most frequently cited six pieces were selected that were comparable for structure and style, to represent each emotion and style. They were equally evaluated as unfamiliar by an independent group of 10 students of the same cohort) and were then used as stimuli for the experimental session in which autonomic parameters were recorded. Overall, listening to atonal music (independent of the pieces’ emotional characteristics) was associated with a reduced heart rate (fear bradycardia) and increased blood pressure (both diastolic and systolic), possibly reflecting an increase in alertness and attention, psychological tension, and anxiety. This evidence fits with the results of the esthetical assessment showing how, overall, atonal music is perceived as more agitating and less joyful than tonal one. PMID:26579029

  11. Non-expert listeners show decreased heart rate and increased blood pressure (fear bradycardia) in response to atonal music.

    PubMed

    Proverbio, Alice M; Manfrin, Luigi; Arcari, Laura A; De Benedetto, Francesco; Gazzola, Martina; Guardamagna, Matteo; Lozano Nasi, Valentina; Zani, Alberto

    2015-01-01

    Previous studies suggested that listening to different types of music may modulate differently psychological mood and physiological responses associated with the induced emotions. In this study the effect of listening to instrumental classical vs. atonal contemporary music was examined in a group of 50 non-expert listeners. The subjects' heart rate and diastolic and systolic blood pressure values were measured while they listened to music of different style and emotional typologies. Pieces were selected by asking a group of composers and conservatory professors to suggest a list of the most emotional music pieces (from Renaissance to present time). A total of 214 suggestions from 20 respondents were received. Then it was asked them to identify which pieces best induced in the listener feelings of agitation, joy or pathos and the number of suggested pieces per style was computed. Atonal pieces were more frequently indicated as agitating, and tonal pieces as joyful. The presence/absence of tonality in a musical piece did not affect the affective dimension of pathos (being touching). Among the most frequently cited six pieces were selected that were comparable for structure and style, to represent each emotion and style. They were equally evaluated as unfamiliar by an independent group of 10 students of the same cohort) and were then used as stimuli for the experimental session in which autonomic parameters were recorded. Overall, listening to atonal music (independent of the pieces' emotional characteristics) was associated with a reduced heart rate (fear bradycardia) and increased blood pressure (both diastolic and systolic), possibly reflecting an increase in alertness and attention, psychological tension, and anxiety. This evidence fits with the results of the esthetical assessment showing how, overall, atonal music is perceived as more agitating and less joyful than tonal one.

  12. Fungi in a changing world: growth rates will be elevated, but spore production may decrease in future climates

    NASA Astrophysics Data System (ADS)

    Damialis, Athanasios; Mohammad, Aqilah B.; Halley, John M.; Gange, Alan C.

    2015-09-01

    Very little is known about the impact of climate change on fungi and especially on spore production. Fungal spores can be allergenic, thus being important for human health. The aim of this study was to investigate how climate change influences the responsive ability of fungi by simulating differing environmental regimes. Fungal species with high spore allergenic potential and atmospheric abundance were grown and experimentally examined under a variety of temperatures and different nutrient availability. Each represented the average decadal air temperature of the 1980s, 1990s and 2000s in the UK, along with an Intergovernmental Panel on Climate Change (IPCC) climate change scenario for 2100. All tests were run on six fungal species: Alternaria alternata, Aspergillus niger, Botrytis cinerea, Cladosporium cladosporioides, Cladosporium oxysporum and Epicoccum purpurascens. Mycelium growth rate and spore production were examined on each single species and competitive capacity among species combinations in pairs. All fungal species grew faster at higher temperatures, and this was more pronounced for the temperature projection in 2100. Most species grew faster when there was lower nutrient availability. Exceptions were the species with the highest growth rate ( E. purpurascens) and with the highest competition capacity ( A. alternata). Most species (except for E. purpurascens) produced more spores in the richer nutrient medium but fewer as temperature increased. C. cladosporioides was an exception, exponentially increasing its spore production in the temperature of the 2100 scenario. Regarding competitive capacity, no species displayed any significant alterations within the environmental range checked. It is suggested that in future climates, fungi will display dramatic growth responses, with faster mycelium growth and lower spore production, with questions risen on relevant allergen potential.

  13. Effect of Mass Stool Examination and Mass Treatment For Decreasing Intestinal Helminth and Protozoan Infection Rates in Bolivian Children: A Cross-Sectional Study.

    PubMed

    Asai, Takao; Còrdova Vidal, Claudia; Strauss, Wilma; Ikoma, Toshikazu; Endoh, Kazuo; Yamamoto, Masaharu

    2016-12-01

    Bolivia is one of the countries with a high intestinal helminth and protozoan infection rate. Despite the high prevalence of the parasitic infection, nationwide preventive measures for Bolivian children have not yet been implemented. We evaluated the effect of mass stool examination and treatment as a strategy for decreasing the infection rate. This study was conducted between 2013 and 2015 in children aged 2-18 years. A total of 2,033 stool samples (575 in 2013, 815 in 2014 and 642 in 2015) were collected and examined using the formalin-ether medical sedimentation method. As an anthelminthic medicine, nitazoxanide was given to all infected children within 2 months post-examination, each year. The effect of mass stool examination and treatment was evaluated based on the changes in the overall or individual parasitic infection rates during the study period. The overall parasitic infection rate decreased significantly from 65.2% in 2013 to 43.0% in 2015; a 22.2 percentage point decrease (P<0.001). Protozoan infection accounted for a large portion of the parasitic infections, in the following rates: 62.4% in 2013, 49.3% in 2014, and 41.0% in 2015. The rate of the most common helminth infection, Hymenolepis nana, decreased significantly from 9.0% in 2013 to 6.4% in 2014 to 3.4% in 2015 (P<0.001). Prevalence of the most common pathogenic protozoan infection, Entamoeba histolytica, decreased significantly from 19.0% in 2013 to 3.0% in 2015 (P<0.001). Conversely, the rate of Giardia intestinalis increased significantly from 16.5% in 2013 to 21.2% in 2015 (P<0.01). Mass stool examination and treatment for intestinal helminth and protozoan infections was effective for decreasing the overall parasitic infection rate in the study population, excluding Giardia intestinalis. Further studies on the long-term effect of mass stool examination and treatment for decreasing all intestinal parasitic infection rates in Bolivian children are needed.

  14. Effect of Mass Stool Examination and Mass Treatment For Decreasing Intestinal Helminth and Protozoan Infection Rates in Bolivian Children: A Cross-Sectional Study

    PubMed Central

    Còrdova Vidal, Claudia; Strauss, Wilma; Ikoma, Toshikazu; Endoh, Kazuo; Yamamoto, Masaharu

    2016-01-01

    Bolivia is one of the countries with a high intestinal helminth and protozoan infection rate. Despite the high prevalence of the parasitic infection, nationwide preventive measures for Bolivian children have not yet been implemented. We evaluated the effect of mass stool examination and treatment as a strategy for decreasing the infection rate. This study was conducted between 2013 and 2015 in children aged 2–18 years. A total of 2,033 stool samples (575 in 2013, 815 in 2014 and 642 in 2015) were collected and examined using the formalin-ether medical sedimentation method. As an anthelminthic medicine, nitazoxanide was given to all infected children within 2 months post-examination, each year. The effect of mass stool examination and treatment was evaluated based on the changes in the overall or individual parasitic infection rates during the study period. The overall parasitic infection rate decreased significantly from 65.2% in 2013 to 43.0% in 2015; a 22.2 percentage point decrease (P<0.001). Protozoan infection accounted for a large portion of the parasitic infections, in the following rates: 62.4% in 2013, 49.3% in 2014, and 41.0% in 2015. The rate of the most common helminth infection, Hymenolepis nana, decreased significantly from 9.0% in 2013 to 6.4% in 2014 to 3.4% in 2015 (P<0.001). Prevalence of the most common pathogenic protozoan infection, Entamoeba histolytica, decreased significantly from 19.0% in 2013 to 3.0% in 2015 (P<0.001). Conversely, the rate of Giardia intestinalis increased significantly from 16.5% in 2013 to 21.2% in 2015 (P<0.01). Mass stool examination and treatment for intestinal helminth and protozoan infections was effective for decreasing the overall parasitic infection rate in the study population, excluding Giardia intestinalis. Further studies on the long-term effect of mass stool examination and treatment for decreasing all intestinal parasitic infection rates in Bolivian children are needed. PMID:27923058

  15. Accretion of southern Alaska

    USGS Publications Warehouse

    Hillhouse, J.W.

    1987-01-01

    Paleomagnetic data from southern Alaska indicate that the Wrangellia and Peninsular terranes collided with central Alaska probably by 65 Ma ago and certainly no later than 55 Ma ago. The accretion of these terranes to the mainland was followed by the arrival of the Ghost Rocks volcanic assemblage at the southern margin of Kodiak Island. Poleward movement of these terranes can be explained by rapid motion of the Kula oceanic plate, mainly from 85 to 43 Ma ago, according to recent reconstructions derived from the hot-spot reference frame. After accretion, much of southwestern Alaska underwent a counterclockwise rotation of about 50 ?? as indicated by paleomagnetic poles from volcanic rocks of Late Cretaceous and Early Tertiary age. Compression between North America and Asia during opening of the North Atlantic (68-44 Ma ago) may account for the rotation. ?? 1987.

  16. Matter accreting neutron stars

    NASA Technical Reports Server (NTRS)

    Meszaros, P.

    1981-01-01

    Some of the fundamental neutron star parameters, such as the mass and the magnetic field strength, were experimentally determined in accreting neutron star systems. Some of the relevant data and the models used to derive useful information from them, are reviewed concentrating mainly on X-ray pulsars. The latest advances in our understanding of the radiation mechanisms and the transfer in the strongly magnetized polar cap regions are discussed.

  17. Accretion disk electrodynamics

    NASA Technical Reports Server (NTRS)

    Coroniti, F. V.

    1985-01-01

    Accretion disk electrodynamic phenomena are separable into two classes: (1) disks and coronas with turbulent magnetic fields; (2) disks and black holes which are connected to a large-scale external magnetic field. Turbulent fields may originate in an alpha-omega dynamo, provide anomalous viscous transport, and sustain an active corona by magnetic buoyancy. The large-scale field can extract energy and angular momentum from the disk and black hole, and be dynamically configured into a collimated relativistic jet.

  18. Synergistic decrease of DNA single-strand break repair rates in mouse neural cells lacking both Tdp1 and aprataxin

    PubMed Central

    El-Khamisy, Sherif F.; Katyal, Sachin; Patel, Poorvi; Ju, Limei; McKinnon, Peter J.; Caldecott, Keith W.

    2009-01-01

    Ataxia oculomotor apraxia-1 (AOA1) is an autosomal recessive neurodegenerative disease that results from mutations of aprataxin (APTX). APTX associates with the DNA single- and double-strand break repair machinery and is able to remove AMP from 5′-termini at DNA strand breaks in vitro. However, attempts to establish a DNA strand break repair defect in APTX-defective cells have proved conflicting and unclear. We reasoned that this may reflect that DNA strand breaks with 5′-AMP represent only a minor subset of breaks induced in cells, and/or the availability of alternative mechanisms for removing AMP from 5′-termini. Here, we have attempted to increase the dependency of chromosomal single- and double-strand break repair on aprataxin activity by slowing the rate of repair of 3′-termini in aprataxin-defective neural cells, thereby increasing the likelihood that the 5′-termini at such breaks become adenylated and/or block alternative repair mechanisms. To do this, we generated a mouse model in which APTX is deleted together with tyrosyl DNA phosphodiesterase (TDP1), an enzyme that repairs 3′-termini at a subset of single-strand breaks (SSBs), including those with 3′-topoisomerase-1 (Top1) peptide. Notably, the global rate of repair of oxidative and alkylation-induced SSBs was significantly slower in Tdp1−/−/Aptx−/− double knockout quiescent mouse astrocytes compared with Tdp1−/− or Aptx−/− single knockouts. In contrast, camptothecin-induced Top1-SSBs accumulated to similar levels in Tdp1−/− and Tdp1−/−/Aptx−/− double knockout astrocytes. Finally, we failed to identify a measurable defect in double-strand break repair in Tdp1−/−, Aptx−/− or Tdp1−/−/Aptx−/− astrocytes. These data provide direct evidence for a requirement for aprataxin during chromosomal single-strand break repair in primary neural cells lacking Tdp1. PMID:19303373

  19. Accretion of the Earth.

    PubMed

    Canup, Robin M

    2008-11-28

    The origin of the Earth and its Moon has been the focus of an enormous body of research. In this paper I review some of the current models of terrestrial planet accretion, and discuss assumptions common to most works that may require re-examination. Density-wave interactions between growing planets and the gas nebula may help to explain the current near-circular orbits of the Earth and Venus, and may result in large-scale radial migration of proto-planetary embryos. Migration would weaken the link between the present locations of the planets and the original provenance of the material that formed them. Fragmentation can potentially lead to faster accretion and could also damp final planet orbital eccentricities. The Moon-forming impact is believed to be the final major event in the Earth's accretion. Successful simulations of lunar-forming impacts involve a differentiated impactor containing between 0.1 and 0.2 Earth masses, an impact angle near 45 degrees and an impact speed within 10 per cent of the Earth's escape velocity. All successful impacts-with or without pre-impact rotation-imply that the Moon formed primarily from material originating from the impactor rather than from the proto-Earth. This must ultimately be reconciled with compositional similarities between the Earth and the Moon.

  20. Nitrogen deficiency inhibits leaf blade growth in Lolium perenne by increasing cell cycle duration and decreasing mitotic and post-mitotic growth rates.

    PubMed

    Kavanová, Monika; Lattanzi, Fernando Alfredo; Schnyder, Hans

    2008-06-01

    Nitrogen deficiency severely inhibits leaf growth. This response was analysed at the cellular level by growing Lolium perenne L. under 7.5 mM (high) or 1 mM (low) nitrate supply, and performing a kinematic analysis to assess the effect of nitrogen status on cell proliferation and cell growth in the leaf blade epidermis. Low nitrogen supply reduced leaf elongation rate (LER) by 43% through a similar decrease in the cell production rate and final cell length. The former was entirely because of a decreased average cell division rate (0.023 versus 0.032 h(-1)) and thus longer cell cycle duration (30 versus 22 h). Nitrogen status did not affect the number of division cycles of the initial cell's progeny (5.7), and accordingly the meristematic cell number (53). Meristematic cell length was unaffected by nitrogen deficiency, implying that the division and mitotic growth rates were equally impaired. The shorter mature cell length arose from a considerably reduced post-mitotic growth rate (0.033 versus 0.049 h(-1)). But, nitrogen stress did not affect the position where elongation stopped, and increased cell elongation duration. In conclusion, nitrogen deficiency limited leaf growth by increasing the cell cycle duration and decreasing mitotic and post-mitotic elongation rates, delaying cell maturation.

  1. Decrease in sensitisation rate and intestinal anaphylactic response after nitric oxide synthase inhibition in a food hypersensitivity model.

    PubMed Central

    Fargeas, M J; Theodorou, V; Weirich, B; Fioramonti, J; Buéno, L

    1996-01-01

    BACKGROUND--Although nitric oxide (NO) has been found to have a role in gut inflammation and to modulate immunoglobulin production, little is known about its part in food hypersensitivities. AIM--This study aimed to evaluate the role of NO through the inhibition of constitutive and inducible NO synthase (cNOS and iNOS respectively) on the sensitisation process (antibody titres) and on intestinal anaphylactic responses (colonic hypersecretion upon antigen challenge). ANIMALS AND METHODS--Guinea pigs sensitised to cow's milk proteins were treated either during the sensitisation period or before antigen challenge by N-nitro-L-arginine methyl ester (L-NAME) (inhibiting both cNOS and iNOS) or amino-guanidine (selective iNOS inhibitor). RESULTS--Chronic treatment by L-NAME or aminoguanidine reduced antibody titres and the secretory response to antigen challenge. In contrast, only L-NAME administered before challenge was able to antagonise the hypersecretion induced by the challenge. CONCLUSIONS--NO generated by iNOS has a role in the sensitisation process: iNOS inhibition results in lower rates of antibodies leading to a reduced secretory response upon challenge. In contrast, blockade of colonic hypersecretion by L-NAME but not by aminoguanidine suggests that NO via cNOS is a key mediator in intestinal anaphylactic reactions. PMID:8707095

  2. Hoyle-Lyttleton Accretion from a Planar Wind

    NASA Astrophysics Data System (ADS)

    Raymer, Eric

    2014-01-01

    Two-dimensional hydrodynamic simulations of Hoyle-Lyttleton accretion have informed predictions about the evolution of wind-driven accretion systems for over two decades. These simulations frequently exhibit dramatic nonlinear behavior such as the flip-flop instability and the formation of transient accretion disks. During disk accretion, the mass accretion rate is suppressed and angular momentum accretion occurs at quasi-Keplerian rates. These results have been used to interpret neutron star accretion from the equatorially enhanced wind of a Be star in Be/X-ray Binaries. We employ large-scale hydrodynamic simulations to investigate whether the flip-flop instability is possible in three dimensions or is simply a consequence of the restrictions on a 2D flow. We do not observe the flip-flop instability in 3D for any values of the wind scale height or density. Moreover, the angular momentum vector of the accreting gas is typically found to be in the plane of the disk wind rather than perpendicular to it as one might expect based on the results of 2D planar simulations. We measure large-scale asymmetries about the plane of the disk wind that arise due to rotational flow near the accretor. Gas is driven above and below the plane, where it interacts with the bow shock and results in a time-varying shock structure. Winds with scale heights of 0.25 Ra enter locked rotation modes that remain stable for the duration of our computational runs. During this phase, the mass accretion rate is suppressed by up to two orders of magnitude below the analytical prediction and angular momentum accretion occurs at sub-Keplerian values.

  3. Fingering Convection and its Consequences for Accreting White Dwarfs

    NASA Astrophysics Data System (ADS)

    Vauclair, Sylvie; Vauclair, Gérard; Deal, Morgan; Wachlin, F. C.

    2015-06-01

    A number of white dwarf stars show absoption lines of heavy elements in their spectra. Many of them also exhibit infra-red excess in their spectral energy distribution. These observations prove that these white dwarfs are surrounded by an orbiting debris disk resulting from the disruption of rocky planetesimals, remnants of the primordial planetary system. Part of the material from the debris disk is accreted onto the white dwarfs, explaining the presence of heavy elements in their outer layers. Previous attempts to estimate the accretion rates have overlooked the importance of the fingering convection. The fingering convection is an instability triggered by the accumulation in the white dwarf outer layers of material heavier than the underlying H-rich (for the DA) or the He-rich (for the DB) composition. The fingering convection induces a deep mixing of the accreted material. Our preliminary simulations of the fingering convection show that the effect may be important in DA white dwarfs. The accretion rates needed in order to reproduce the observed heavy element abundances exceed by order of magnitudes the accretion rates estimated when this extra-mixing is ignored. By contrast, in the cases of the DB white dwarfs that we have considered in our simulations the fingering convection either does not occur or has very little effects on the derived accretion rates. We have undertaken a systematic exploration of the consequences of the fingering convection in accreting white dwarfs.

  4. Decreased rate of protein synthesis, caspase-3 activity, and ubiquitin-proteasome proteolysis in soleus muscles from growing rats fed a low-protein, high-carbohydrate diet.

    PubMed

    Batistela, Emanuele; Pereira, Mayara Peron; Siqueira, Juliany Torres; Paula-Gomes, Silvia; Zanon, Neusa Maria; Oliveira, Eduardo Brandt; Navegantes, Luiz Carlos Carvalho; Kettelhut, Isis C; Andrade, Claudia Marlise Balbinotti; Kawashita, Nair Honda; Baviera, Amanda Martins

    2014-06-01

    The aim of this study was to investigate the changes in the rates of both protein synthesis and breakdown, and the activation of intracellular effectors that control these processes in soleus muscles from growing rats fed a low-protein, high-carbohydrate (LPHC) diet for 15 days. The mass and the protein content, as well as the rate of protein synthesis, were decreased in the soleus from LPHC-fed rats. The availability of amino acids was diminished, since the levels of various essential amino acids were decreased in the plasma of LPHC-fed rats. Overall rate of proteolysis was also decreased, explained by reductions in the mRNA levels of atrogin-1 and MuRF-1, ubiquitin conjugates, proteasome activity, and in the activity of caspase-3. Soleus muscles from LPHC-fed rats showed increased insulin sensitivity, with increased levels of insulin receptor and phosphorylation levels of AKT, which probably explains the inhibition of both the caspase-3 activity and the ubiquitin-proteasome system. The fall of muscle proteolysis seems to represent an adaptive response that contributes to spare proteins in a condition of diminished availability of dietary amino acids. Furthermore, the decreased rate of protein synthesis may be the driving factor to the lower muscle mass gain in growing rats fed the LPHC diet.

  5. Bone density and amenorrhea in ballet dancers are related to a decreased resting metabolic rate and lower leptin levels.

    PubMed

    Kaufman, Becky A; Warren, Michelle P; Dominguez, Jennifer E; Wang, Jack; Heymsfield, Steven B; Pierson, Richard N

    2002-06-01

    Osteopenia, which is correlated with amenorrhea and poor nutritional habits, has been well documented in elite ballet dancers. Estrogen replacement therapy and recovery from amenorrhea have not been associated with normalization of bone density. Thus, the osteopenia may be related to changes brought about by chronic dieting or other factors, such as a hypometabolic state induced by poor nutrition. The purpose of this study was to investigate the relationship of chronic dieting and resting metabolic rate (RMR) to amenorrhea and bone density. RMR, bone density, eating disorder assessments, leptin levels, and complete menstrual and medical histories were determined in 21 elite ballet dancers and in 27 nondancers (age, 20-30 yr). No significant correlations were found between high EAT26 scores, a measure of disordered eating, and RMR, bone densities, body weight, body fat, or fat-free mass. However, when RMR was adjusted for fat-free mass (FFM), a significant positive correlation was found between RMR/FFM and bone density in both the arms (P < 0.001) and spine (P < 0.05) in ballet dancers, but not in the normal controls. The dancers also demonstrated significantly higher EAT scores (22.9 +/- 10.3 vs. 4.1 +/- 2.4; P < 0.001) and lower RMR/FFM ratios (30.0 +/- 2.2 vs. 32.05 +/- 2.8; P < 0.01). The only variable to predict lower RMR/FFM in the entire sample was ever having had amenorrhea; this group had significantly higher EAT scores (18.0 +/- 13.5 vs. 10.3 +/- 10.2; P < 0.05), lower leptin levels (4.03 +/- 0.625 vs. 7.10 +/- 4.052; P < 0.05), and lower bone mineral density in the spine (0.984 +/- 0.11 vs. 1.10 +/- 0.13; P < 0.05) and arm (0.773 +/- 0.99 vs. 0.818 +/- 0.01; P < 0.05). We hypothesize that the correlation between low RMR and lower leptin levels and bone density may be more strongly related to nutritional habits in ballet dancers, causing significant depression of RMR, particularly for those with a history of amenorrhea.

  6. Early Pan-African evolution of the basement around Elat, Israel, and the Sinai Peninsula revealed by single-zircon evaporation dating, and implications for crustal accretion rates

    SciTech Connect

    Kroener, A. ); Eyal, M.; Eyal, Y. )

    1990-06-01

    The authors report {sup 207}Pb/{sup 206}Pb single-zircon evaporation ages for early Pan-African rocks from southern Israel and the northeastern Sinai Peninsula, the northernmost extension of the Arabian-Nubian shield. The oldest rocks are metamorphic schists of presumed island-arc derivation; detrital zircons date the source terrain at ca. 800-820 Ma. A major phase of tonalite-trondhjemite plutonism occurred at ca. 760-780 Ma; more evolved granitic rocks were emplaced at about 745 Ma. A metagabbro-metadiorite complex reflects the youngest igneous phase at ca. 640 Ma. We find no evidence for pre-Pan-African crust, and our data document important crust-forming events that correlate with similar episodes elsewhere in the shield. The widespread presence of early Pan-African juvenile rocks (i.e., ca. 760-850 Ma) in many parts of the Arabian-Nubian shield makes this period the most important in the magmatic history of the shield and supports earlier suggestions for unusually high crust-production rates.

  7. Magnetized Accretion and Dead Zones in Protostellar Disks

    NASA Astrophysics Data System (ADS)

    Dzyurkevich, Natalia; Turner, Neal J.; Henning, Thomas; Kley, Wilhelm

    2013-03-01

    The edges of magnetically dead zones in protostellar disks have been proposed as locations where density bumps may arise, trapping planetesimals and helping form planets. Magneto-rotational turbulence in magnetically active zones provides both accretion of gas on the star and transport of mass to the dead zone. We investigate the location of the magnetically active regions in a protostellar disk around a solar-type star, varying the disk temperature, surface density profile, and dust-to-gas ratio. We also consider stellar masses between 0.4 and 2 M ⊙, with corresponding adjustments in the disk mass and temperature. The dead zone's size and shape are found using the Elsasser number criterion with conductivities including the contributions from ions, electrons, and charged fractal dust aggregates. The charged species' abundances are found using the approach proposed by Okuzumi. The dead zone is in most cases defined by the ambipolar diffusion. In our maps, the dead zone takes a variety of shapes, including a fish tail pointing away from the star and islands located on and off the midplane. The corresponding accretion rates vary with radius, indicating locations where the surface density will increase over time, and others where it will decrease. We show that density bumps do not readily grow near the dead zone's outer edge, independently of the disk parameters and the dust properties. Instead, the accretion rate peaks at the radius where the gas-phase metals freeze out. This could lead to clearing a valley in the surface density, and to a trap for pebbles located just outside the metal freezeout line.

  8. MAGNETIZED ACCRETION AND DEAD ZONES IN PROTOSTELLAR DISKS

    SciTech Connect

    Dzyurkevich, Natalia; Henning, Thomas; Turner, Neal J.; Kley, Wilhelm

    2013-03-10

    The edges of magnetically dead zones in protostellar disks have been proposed as locations where density bumps may arise, trapping planetesimals and helping form planets. Magneto-rotational turbulence in magnetically active zones provides both accretion of gas on the star and transport of mass to the dead zone. We investigate the location of the magnetically active regions in a protostellar disk around a solar-type star, varying the disk temperature, surface density profile, and dust-to-gas ratio. We also consider stellar masses between 0.4 and 2 M{sub Sun }, with corresponding adjustments in the disk mass and temperature. The dead zone's size and shape are found using the Elsasser number criterion with conductivities including the contributions from ions, electrons, and charged fractal dust aggregates. The charged species' abundances are found using the approach proposed by Okuzumi. The dead zone is in most cases defined by the ambipolar diffusion. In our maps, the dead zone takes a variety of shapes, including a fish tail pointing away from the star and islands located on and off the midplane. The corresponding accretion rates vary with radius, indicating locations where the surface density will increase over time, and others where it will decrease. We show that density bumps do not readily grow near the dead zone's outer edge, independently of the disk parameters and the dust properties. Instead, the accretion rate peaks at the radius where the gas-phase metals freeze out. This could lead to clearing a valley in the surface density, and to a trap for pebbles located just outside the metal freezeout line.

  9. Inception of ice accretion by ice crystal impact

    NASA Astrophysics Data System (ADS)

    Löwe, Jens; Kintea, Daniel; Baumert, Arne; Bansmer, Stephan; Roisman, Ilia V.; Tropea, Cameron

    2016-09-01

    In this experimental and theoretical study the ice accretion phenomena on a heated cylinder in Braunschweig Icing Wind Tunnel are investigated. The ice crystal size, velocity, the liquid-to-total mass ratio are accurately controlled. The evolution of the cylinder temperature, the time required for the inception of the ice accretion, and the ice accretion rate are measured for various operating conditions. The surface temperature of the solid target is determined by balancing the heating power in the wall and the cooling effect of the stream of ice particles. We have discovered that the inception of the ice crystal accretion is determined by the instant when the surface temperature of the heated target reduces to the freezing temperature. This result will help to model the phenomena of ice crystal accretion.

  10. Site-Specific Polymer Attachment to HR2 Peptide Fusion Inhibitors against HIV-1 Decreases Binding Association Rates and Dissociation Rates Rather Than Binding Affinity.

    PubMed

    Danial, Maarten; Stauffer, Angela N; Wurm, Frederik R; Root, Michael J; Klok, Harm-Anton

    2017-03-15

    A popular strategy for overcoming the limited plasma half-life of peptide heptad repeat 2 (HR2) fusion inhibitors against HIV-1 is conjugation with biocompatible polymers such as poly(ethylene glycol) (PEG). However, despite improved resistance to proteolysis and reduced renal elimination, covalent attachment of polymers often causes a loss in therapeutic potency. In this study, we investigated the molecular origins of the loss in potency upon conjugation of linear, midfunctional, and hyperbranched PEG-like polymers to peptides that inhibit HIV-1-host cell membrane fusion. Fluorescence binding assays revealed that polymer conjugation imparted mass transport limitations that manifested as coexistent slower association and dissociation rates from the gp41 target on HIV-1. Furthermore, reduced association kinetics rather than affinity disruption was responsible for the loss in antiviral potency. Finally, the binding assays indicated that the unmodified HR2-derived peptide demonstrated diffusion-limited binding. The observed high potency of the unmodified peptide in HIV-1 inhibition assays was therefore attributed to rapid peptide conformational changes upon binding to the gp41 prehairpin structure. This study emphasizes that the view in which polymer ligation to therapeutic peptides inadvertently leads to loss in potency due to a loss in binding affinity requires scientific verification on a case-by-case basis and that high peptide potency may be due to rapid target-binding events.

  11. Formation Of the Giant Planets By Concurrent Accretion Of Solids And Gas

    NASA Technical Reports Server (NTRS)

    Pollack, James B.; Hubickyj, Olenka; Bodenheimer, Peter; Lissauer, Jack J.; Podolak, Morris; Greenzweig, Yuval; Cuzzi, Jeffery N. (Technical Monitor)

    1995-01-01

    New numerical simulations of the formation of the giant planets are presented, in which for the first time both the gas and planetesimal accretion rates are calculated in a self-consistent, interactive fashion. The simulations combine three elements: 1) three-body accretion cross-sections of solids onto an isolated planetary embryo, 2) a stellar evolution code for the planet's gaseous envelope, and 3) a planetesimal dissolution code within the envelope, used to evaluate the planet's effective capture radius and the energy deposition profile of accreted material. Major assumptions include: The planet is embedded in a disk of gas and small planetesimals with locally uniform initial surface mass density, and planetesimals are not allowed to migrate into or out of the planet's feeding zone. All simulations are characterized by three major phases. During the first phase, the planet's mass consists primarily of solid material. The planetesimal accretion rate, which dominates that of gas, rapidly increases owing to runaway accretion, then decreases as the planet's feeding zone is depleted. During the second phase, both solid and gas accretion rates are small and nearly independent of time. The third phase, marked by runaway gas accretion, starts when the solid and gas masses are about equal. It is engendered by a strong positive feedback on the gas accretion rates, driven by the rapid contraction of the gaseous envelope and the rapid expansion of the outer boundary, which depends on the planet's total mass. The overall evolutionary time scale is generally determined by the length of the second phase. The actual rates at which the giant planets accreted small planetesimals is probably intermediate between the constant rates assumed in most previous studies and the highly variable rates that we have used. Within the context, of the adopted model of planetesimal accretion, the joint constraints of the time scale for dissipation of the solar nebula and the current high

  12. Spiral-driven accretion in protoplanetary discs . III. Tridimensional simulations

    NASA Astrophysics Data System (ADS)

    Hennebelle, Patrick; Lesur, Geoffroy; Fromang, Sébastien

    2017-03-01

    Context. Understanding how accretion proceeds in proto-planetary discs, and more generally, understanding their dynamics, is a crucial questions that needs to be answered to explain the conditions in which planets form. Aims: The role that accretion of gas from the surrounding molecular cloud onto the disc may have on its structure needs to be quantified. Methods: We performed tridimensional simulations using the Cartesian AMR code RAMSES of an accretion disc that is subject to infalling material. Results: For the aspect ratio of H/R ≃ 0.15 and disc mass Md ≃ 10-2M⊙ used in our study, we find that for typical accretion rates of the order of a few 10-7M⊙ yr-1, values of the α parameter as high as a few 10-3 are inferred. The mass that is accreted in the inner part of the disc is typically at least 50% of the total mass that has been accreted onto the disc. Conclusions: Our results suggest that external accretion of gas at moderate values onto circumstellar discs may trigger prominent spiral arms that are reminiscent of recent observations made with various instruments, and may lead to significant transport through the disc. If confirmed from observational studies, such accretion may therefore influence disc evolution.

  13. Time-dependent Models of Magnetospheric Accretion onto Young Stars

    NASA Astrophysics Data System (ADS)

    Robinson, C. E.; Owen, J. E.; Espaillat, C. C.; Adams, F. C.

    2017-04-01

    Accretion onto Classical T Tauri stars is thought to take place through the action of magnetospheric processes, with gas in the inner disk being channeled onto the star’s surface by the stellar magnetic field lines. Young stars are known to accrete material in a time-variable manner, and the source of this variability remains an open problem, particularly on the shortest (∼day) timescales. Using one-dimensional time-dependent numerical simulations that follow the field line geometry, we find that for plausibly realistic young stars, steady-state transonic accretion occurs naturally in the absence of any other source of variability. However, we show that if the density in the inner disk varies smoothly in time with ∼day-long timescales (e.g., due to turbulence), this complication can lead to the development of shocks in the accretion column. These shocks propagate along the accretion column and ultimately hit the star, leading to rapid, large amplitude changes in the accretion rate. We argue that when these shocks hit the star, the observed time dependence will be a rapid increase in accretion luminosity, followed by a slower decline, and could be an explanation for some of the short-period variability observed in accreting young stars. Our one-dimensional approach bridges previous analytic work to more complicated multi-dimensional simulations and observations.

  14. Long-term suicide mortality rates decrease in men and increase in women after the Niigata-Chuetsu earthquake in Japan.

    PubMed

    Hyodo, Keiko; Nakamura, Kazutoshi; Oyama, Mari; Yamazaki, Osamu; Nakagawa, Izumi; Ishigami, Kazuo; Tsuchiya, Yasuo; Yamamoto, Masaharu

    2010-02-01

    A devastating earthquake causes psychological distress, and may increase suicide mortality thereafter, yet previous studies have made inconsistent conclusions regarding this issue. The purpose of the present study was to determine whether the 2004 Niigata-Chuetsu earthquake in Japan affected long-term mortality from suicide. We conducted a comparative study of suicide mortality rates during the 5-year period preceding and the 3-year period following the earthquake in the disaster area and a control area in Niigata Prefecture, by analyzing death certificate data from October 1, 1999, to September 30, 2007. In men, baseline suicide mortality rates (5 years preceding the earthquake) were 48.4 per 100,000 person-years in the disaster area and 46.1 in the control area, and suicide mortality rates during the 3-year period following the earthquake were 46.0 and 45.1, respectively. In women, baseline suicide mortality rates were 22.3 in the disaster area and 18.7 in the control area, and post-earthquake suicide mortality rates were 20.2 and 15.3, respectively. In consequence, the decrease in suicide mortality rate during the 3 years post-earthquake was significantly higher in the disaster area (2.5) than in the control area (1.0) (p = 0.0013) in men, whereas the decrease in suicide mortality rate was 2.1 in the disaster area and 3.0 in the control area (p = 0.1246) in women. We have concluded that the long-term mortality from suicide after the earthquake decreases in men and increases in women, suggesting that post-earthquake suicide mortality is sex-dependent. Post-earthquake suicide prevention strategies should more aggressively target women.

  15. Cr(VI) induces the decrease of ATP level and the increase of apoptosis rate mediated by ROS or VDAC1 in L-02 hepatocytes.

    PubMed

    Yuan, Yang; Ming, Zen; Gong-Hua, Hu; Lan, Guan; Lu, Dai; Peng, Li; Feng, Jing; Cai-Gao, Zhong

    2012-09-01

    The present study explored the ability of the voltage-dependent anion channel 1 (VDAC1) mRNA and ROS levels to modulate the effects of hexavalent chromium Cr(VI) on the adenosine triphosphate (ATP) level and the rate of apoptotic cell death. Cultured L-02 cells were pretreated with 20mM N-acetyl-cysteine (NAC) for 24h or transiently transfected with small interfering RNAs targeting VDAC1 (siVDAC1) for 48h; cells that were not pretreated were used as the control. The cells were subsequently treated with 0, 2, 8, or 32μM Cr(VI) for 24h. Then, levels of VDAC1 mRNA, ROS, and ATP and the apoptosis rate were measured by reverse-transcription quantitative PCR, fluorometry, a bioluminescence assay, and flow cytometry, respectively. The results showed that Cr(VI) at 32μM led to increase in the ROS level, VDAC1 mRNA expression, and the apoptosis rate and a decrease in the ATP level; pretreatment with NAC led to the down-regulation in the levels of ROS, VDAC1 mRNA and apoptosis and the significant up-regulation in the ATP levels. Interestingly, after the pretreatment with siVDAC1 to inhibit VDAC1 mRNA expression, the increased apoptosis rates and decreased ATP levels were reversed as well. These results suggested that changes in the ROS or VDAC1 mRNA levels were associated with changes in the ATP level and apoptosis rate. Furthermore, correlation analysis confirmed the association between both the ROS and VDAC1 levels and both the ATP level and the apoptosis rate. In conclusion, Cr(VI) induced ROS- and VDAC1-mediated decreases in ATP levels and increases in the apoptosis rate.

  16. Accretion in the galactic halo

    NASA Astrophysics Data System (ADS)

    Stephens, Alex Courtney

    2000-10-01

    The Milky Way disk is enveloped in a diffuse, dynamically-hot collection of stars and star clusters collectively known as the ``stellar halo''. Photometric and chemical analyses suggest that these stars are ancient fossils of the galaxy formation epoch. Yet, little is known about the origin of this trace population. Is this system merely a vestige of the initial burst of star formation within the decoupled proto-Galaxy, or is it the detritus of cannibalized satellite galaxies? In an attempt to unravel the history of the Milky Way's stellar halo, I performed a detailed spectroscopic analysis of 55 metal-poor stars possessing ``extreme'' kinematic properties. It is thought that stars on orbits that either penetrate the remote halo or exhibit large retrograde velocities could have been associated with assimilated (or ``accreted'') dwarf galaxies. The hallmark of an accreted halo star is presumed to be a deficiency (compared with normal stars) of the α-elements (O, Mg, Si, Ca, Ti) with respect to iron, a consequence of sporadic bursts of star formation within the diminutive galaxies. Abundances for a select group of light metals (Li, Na, Mg, Si, Ca, Ti), iron-peak nuclides (Cr, Fe, Ni), and neutron-capture elements (Y, Ba) were calculated using line-strengths measured from high-resolution, high signal-to-noise spectral observations collected with the Keck I 10-m and KPNO 4-m telescopes. The abundances extracted from the spectra reveal: (1)The vast majority of outer halo stars possess supersolar [α/Fe] > 0.0) ratios. (2)The [α/Fe] ratio appears to decrease with increasing metallicity. (3)The outer halo stars have lower ratios of [α/Fe] than inner halo stars at a given metallicity. (4)At the largest metallicities, there is a large spread in the observed [α/Fe] ratios. (5)[α/Fe] anti-correlates with RAPO. (6)Only one star (BD+80° 245) exhibits the peculiar abundances expected of an assimilated star. The general conclusion extracted from these data is that the

  17. Comment on `A dramatic decrease in the growth rate of atmospheric methane in the Northern Hemisphere during 1992` by E. J. Dlugokencky et al.

    SciTech Connect

    Hogan, K.B.; Harriss, R.C. |

    1994-11-01

    The carefully measured decrease in the growth rate of atmospheric methane (CH4) in 1992 reported by Dlugokencky et al. (1994) is an impressive accomplishment, and testimony for the importance of maintaining high-quality, long-term monitoring of atmospheric composition. The changing growth rate of atmospheric CH4 has important implications for assessing and understanding the potential magnitude and rates of a future greenhouse gas-induced climate change. Furthermore, the CH4 data from the current Climate Monitoring and Diagnostics Laboratory (CMDL) globally-distributed network of cooperative air sampling sites are clearly the best record of global CH4 trends and distribution currently available. However, we argue briefly here that the speculation by Dlugokencky et al. (1994) on possible mechanisms for the decreased growth rate in 1992 is only one scenario of many that could possibly fit with the constraints imposed by the reported data. Our comments are to (1) illustrate the difficulties of deducing small changes in complex, poorly understood, geographically diverse natural and anthropogenic sources of CH4 from measurements at the remotely-located CMDL sampling sites and (2) emphasize that detailed bottoms-up analyses are necessary to really advance the understanding of changes in source strengths; we are not promoting alternative mechanisms to explain the 1992 decrease in atmospheric CH4.

  18. Causes of decreased photosynthetic rate and metabolic capacity in water-deficient leaf cells: a critical evaluation of mechanisms and integration of processes

    PubMed Central

    Lawlor, David W.; Tezara, Wilmer

    2009-01-01

    Background Water deficit (WD) decreases photosynthetic rate (A) via decreased stomatal conductance to CO2 (gs) and photosynthetic metabolic potential (Apot). The relative importance of gs and Apot, and how they are affected by WD, are reviewed with respect to light intensity and to experimental approaches. Scope and Conclusions With progressive WD, A decreases as gs falls. Under low light during growth and WD, A is stimulated by elevated CO2, showing that metabolism (Apot) is not impaired, but at high light A is not stimulated, showing inhibition. At a given intercellular CO2 concentration (Ci) A decreases, showing impaired metabolism (Apot). The Ci and probably chloroplast CO2 concentration (Cc), decreases and then increases, together with the equilibrium CO2 concentration, with greater WD. Estimation of Cc and internal (mesophyll) conductance (gi) is considered uncertain. Photosystem activity is unaffected until very severe WD, maintaining electron (e−) transport (ET) and reductant content. Low A, together with photorespiration (PR), which is maintained or decreased, provides a smaller sink for e−, causing over-energization of energy transduction. Despite increased non-photochemical quenching (NPQ), excess energy and e− result in generation of reactive oxygen species (ROS). Evidence is considered that ROS damages ATP synthase so that ATP content decreases progressively with WD. Decreased ATP limits RuBP production by the Calvin cycle and thus Apot. Rubisco activity is unlikely to determine Apot. Sucrose synthesis is limited by lack of substrate and impaired enzyme regulation. With WD, PR decreases relative to light respiration (RL), and mitochondria consume reductant and synthesise ATP. With progressing WD at low A, RL increases Ci and Cc. This review emphasises the effects of light intensity, considers techniques, and develops a qualitative model of photosynthetic metabolism under WD that explains many observations: testable hypotheses are suggested. PMID

  19. Revealing the accretion disc corona in Mrk 335 with multi-epoch X-ray spectroscopy

    NASA Astrophysics Data System (ADS)

    Keek, L.; Ballantyne, D. R.

    2016-03-01

    Active galactic nuclei host an accretion disc with an X-ray producing corona around a supermassive black hole. In bright sources, such as the Seyfert 1 galaxy Mrk 335, reflection of the coronal emission off the accretion disc has been observed. Reflection produces spectral features such as an Fe Kα emission line, which allow for properties of the inner accretion disc and the corona to be constrained. We perform a multi-epoch spectral analysis of all XMM-Newton, Suzaku, and NuSTAR observations of Mrk 335, and we optimize our fitting procedure to unveil correlations between the Eddington ratio and the spectral parameters. We find that the disc's ionization parameter correlates strongly with the Eddington ratio: the inner disc is more strongly ionized at higher flux. The slope of the correlation is less steep than previously predicted. Furthermore, the cut-off of the power-law spectrum increases in energy with the Eddington ratio, whereas the reflection fraction exhibits a decrease. We interpret this behaviour as geometrical changes of the corona as a function of the accretion rate. Below ˜10 per cent of the Eddington limit, the compact and optically thick corona is located close to the inner disc, whereas at higher accretion rates the corona is likely optically thin and extends vertically further away from the disc surface. Furthermore, we find a soft excess that consists of two components. In addition to a contribution from reflection in low ionization states, a second component is present that traces the overall flux.

  20. A GENERAL RELATIVISTIC MODEL OF ACCRETION DISKS WITH CORONAE SURROUNDING KERR BLACK HOLES

    SciTech Connect

    You Bei; Cao Xinwu; Yuan Yefei E-mail: cxw@shao.ac.cn

    2012-12-20

    We calculate the structure of a standard accretion disk with a corona surrounding a massive Kerr black hole in the general relativistic frame, in which the corona is assumed to be heated by the reconnection of the strongly buoyant magnetic fields generated in the cold accretion disk. The emergent spectra of accretion disk-corona systems are calculated by using the relativistic ray-tracing method. We propose a new method to calculate the emergent Comptonized spectra from the coronae. The spectra of disk-corona systems with a modified {alpha}-magnetic stress show that both the hard X-ray spectral index and the hard X-ray bolometric correction factor L{sub bol}/L{sub X,2-10keV} increase with the dimensionless mass accretion rate, which is qualitatively consistent with the observations of active galactic nuclei. The fraction of the power dissipated in the corona decreases with increasing black hole spin parameter a, which leads to lower electron temperatures of the coronae for rapidly spinning black holes. The X-ray emission from the coronae surrounding rapidly spinning black holes becomes weak and soft. The ratio of the X-ray luminosity to the optical/UV luminosity increases with the viewing angle, while the spectral shape in the X-ray band is insensitive to the viewing angle. We find that the spectral index in the infrared waveband depends on the mass accretion rate and the black hole spin a, which deviates from the f{sub {nu}}{proportional_to}{nu}{sup 1/3} relation expected by the standard thin disk model.

  1. Coronal Neutrino Emission in Hypercritical Accretion Flows

    NASA Astrophysics Data System (ADS)

    Kawabata, R.; Mineshige, S.; Kawanaka, N.

    2008-03-01

    Hypercritical accretion flows onto stellar mass black holes (BHs) are commonly believed to be as a promising model of central engines of gamma-ray bursts (GRBs). In this model a certain fraction of the gravitational binding energy of accreting matter is deposited to the energy of relativistic jets via neutrino annihilation and/or magnetic fields. However, some recent studies have indicated that the energy deposition rate by neutrino annihilation is somewhat smaller than that needed to power a GRB. To overcome this difficulty, Ramirez-Ruiz and Socrates proposed that high-energy neutrinos from the hot corona above the accretion disk might enhance the efficiency of the energy deposition. We elucidate the disk corona model in the context of hypercritical accretion flows. From the energy balance in the disk and the corona, we can calculate the disk and coronal temperature, Td and Tc, and neutrino spectra, taking into account the neutrino cooling processes by neutrino-electron scatterings and neutrino pair productions. The calculated neutrino spectra consist of two peaks: one by the neutrino emission from the disk and the other by that from the corona. We find that the disk corona can enhance the efficiency of energy release but only by a factor of 1.5 or so, unless the height of the corona is very small, Hll r. This is because the neutrino emission is very sensitive to the temperature of the emitting region, and then the ratio Tc/Td cannot be very large.

  2. Accretion and star formation in RQQs

    NASA Astrophysics Data System (ADS)

    White, Sarah; Jarvis, Matt; Häußler, Boris; Maddox, Natasha; Kalfountzou, Eleni; Hardcastle, Martin

    2016-06-01

    Active Galactic Nuclei (AGN) and star-forming galaxies are well-traced in the radio part of the electromagnetic spectrum, due to emission at these wavelengths being unaffected by dust obscuration. The key processes involved in producing the radio emission are black-hole accretion and star formation, both of which are thought to be crucial in determining how galaxies evolve. Disentangling the two contributions requires multi-wavelength data, and this is the approach we use for our work on radio-quiet quasars (RQQs). In contrast to previous studies, we find that accretion-connected radio emission dominates over that due to star formation, even at very low radio flux-densities. The first sample we describe is selected from the VISTA Deep Extragalactic Observations (VIDEO) survey, whose depth allows the study of very low accretion rates and/or lower-mass black holes. A second sample is obtained from the Spitzer-Herschel Active Galaxy Survey, spanning a factor of ~100 in optical luminosity over a narrow redshift range at z ~ 1. This enables evolutionary effects to be decoupled when comparisons are made with the VIDEO sample. Using radio data from the Karl G. Jansky Very Large Array (JVLA), we find further support that the AGN makes a significant contribution to the radio emission in RQQs. In addition, the levels of accretion and star formation appear to be weakly correlated with each other, and with optical luminosity.

  3. Accreting neutron stars by QFT

    NASA Astrophysics Data System (ADS)

    Chen, Shao-Guang

    layer with thickness of 1 km then q = 1 (N1S1), the gravity from N1S1 inside and exterior will be completely shielded. Because of net nuν _{0} flux is the medium to produce and transmit gravity, q obstructed by the shielding layer lie on the density of layer matter and the section of single nucleon to electronic neutrino obtained by nuclear physics experiments is about 1.1*10 ({-) 43} cm (2) . The mass inside N1S1 for exterior has not gravity interaction, it equivalent to has not inertia as the mass vanish. The neutron star is as a empty shell thereby may rapidly rotating and has not upper limit of mass and radii by the gravity accretion of N1S1, which will influence the mechanisms of pulsars, quasars and X-rays generated. At N1S1 interior the mass for exterior has not gravity which is just we searching dark matter. The mass each part will each other shielding and gravity decrease to less than the pressure of the degenerate neutron gas. The neutron star cannot collapse into a singular point with infinite density, i.e., the black hole with infinite gravity cannot be formed or the neutron star is jest the black hole in observational meaning. By the gravity accrete of N1S1 the neutron star may enlarge its shell radii but thickness keep. Only a shell gravity may be not less than any a observed value which to be deemed as black hole. The neutron star has powerful gravity certainly accompany with great surface negative charge and it may rapidly to rotate, so that there is a powerful magnetic field surround it. The accreting neutron star is as a slowly expand empty shell with fixed thickness of 1 km, its spin period depend on its radii or total accretion mass.

  4. The environmental dependence of gas accretion on to galaxies: quenching satellites through starvation

    NASA Astrophysics Data System (ADS)

    van de Voort, Freeke; Bahé, Yannick M.; Bower, Richard G.; Correa, Camila A.; Crain, Robert A.; Schaye, Joop; Theuns, Tom

    2017-04-01

    Galaxies that have fallen into massive haloes may no longer be able to accrete gas from their surroundings: a process referred to as 'starvation' or 'strangulation' of satellites. We study the environmental dependence of gas accretion on to galaxies using the cosmological, hydrodynamical EAGLE simulation. We quantify the dependence of gas accretion on stellar mass, redshift, and environment, using halo mass and galaxy overdensity as environmental indicators. We find a strong suppression, of many orders of magnitude, of the gas accretion rate in dense environments, primarily for satellite galaxies. This suppression becomes stronger at lower redshift. However, the scatter in accretion rates is very large for satellites. This is (at least in part) due to the variation in the halocentric radius, since gas accretion is more suppressed at smaller radii. Central galaxies are influenced less strongly by their environment and exhibit less scatter in their gas accretion rates. The star formation rates of both centrals and satellites show similar behaviour to their gas accretion rates. The relatively small differences between gas accretion and star formation rates demonstrate that galaxies generally exhaust their gas reservoir somewhat faster at higher stellar mass, lower redshift, and in denser environments. We conclude that the environmental suppression of gas accretion could directly result in the quenching of star formation.

  5. Mergers of accreting stellar-mass black holes

    NASA Astrophysics Data System (ADS)

    Tagawa, H.; Umemura, M.; Gouda, N.

    2016-11-01

    We present post-Newtonian N-body simulations on mergers of accreting stellar-mass black holes (BHs), where such general relativistic effects as the pericentre shift and gravitational wave (GW) emission are taken into consideration. The attention is concentrated on the effects of the dynamical friction and the Hoyle-Lyttleton mass accretion by ambient gas. We consider a system composed of 10 BHs with initial mass of 30 M⊙. As a result, we show that mergers of accreting stellar-mass BHs are classified into four types: a gas drag-driven, an interplay-driven, a three-body-driven, or an accretion-driven merger. We find that BH mergers proceed before significant mass accretion, even if the accretion rate is ˜10 Eddington accretion rate, and then all BHs can merge into one heavy BH. Using the simulation results for a wide range of parameters, we derive a critical accretion rate (dot{m}_c), below which the BH growth is promoted faster by mergers. Also, it is found that the effect of the recoil by the GW emission can reduce dot{m}_c especially in gas number density higher than 108 cm-3, and enhance the escape probability of merged BHs. Very recently, a gravitational wave event, GW150914, as a result of the merger of a ˜30 M⊙ BH binary has been detected. Based on the present simulations, the BH merger in GW150914 is likely to be driven by three-body encounters accompanied by a few M⊙ of gas accretion, in high-density environments like dense interstellar clouds or galactic nuclei.

  6. Counterturns initiated by decrease in rate of increase of concentration : Possible mechanism of chemotaxis by walking femaleIps paraconfusus bark beetles.

    PubMed

    Patrick Akers, R

    1989-01-01

    The position of beetles were marked at 1-sec intervals after they were released in still air 16-18 cm from point sources of pheromone. Characteristics of the tracks were quantified and compared to those that might be produced by counterturning schemakinesis, tropotaxis, klinotaxis, zigzagging, look-and-leap, or steepest-ascent schemakinesis mechanisms. The beetles' movements were highly irregular, but they turned almost continually and never fixed on a heading near 0° (=straight towards the source). Turn angle sizes increased slightly with absolute size of heading but had the opposite sign, thus compensating slightly for heading. Their distribution was centered about 0° and was unimodal. Heading decreased gradually as the source was neared, but the decrease became steeper within 1-5 cm of the source. Histograms showed that the maximum headings between occurrences when the beetle was headed directly towards the source (0°) were centered around 0° and most of them were less than 90°. However, maximum headings between 90° and 180° were not uncommon. Turn radius decreased as the source was neared. The counterturning mechanism was the most consistent with these observations. An analysis of rate of change of concentration with respect to heading and distance to the source further demonstrated that the counterturning mechanism could explain the form of the decrease in heading as the source was neared, if the major cue used to initiate counterturns was a decrease in the rate of increase of concentration. The tropotaxis could not recreate the form of the decrease, under any form of stimulus processing.

  7. ACCRETION DISK TEMPERATURES OF QSOs: CONSTRAINTS FROM THE EMISSION LINES

    SciTech Connect

    Bonning, E. W.; Shields, G. A.; Stevens, A. C.; Salviander, S. E-mail: shields@astro.as.utexas.edu E-mail: triples@astro.as.utexas.edu

    2013-06-10

    We compare QSO emission-line spectra to predictions based on theoretical ionizing continua of accretion disks. The observed line intensities do not show the expected trend of higher ionization with theoretical accretion disk temperature as predicted from the black hole mass and accretion rate. Consistent with earlier studies, this suggests that the inner disk does not reach temperatures as high as expected from standard disk theory. Modified radial temperature profiles, taking account of winds or advection in the inner disk, achieve better agreement with observation. The emission lines of radio-detected and radio-undetected sources show different trends as a function of the theoretically predicted disk temperature.

  8. LAMBDA BOO ABUNDANCE PATTERNS: ACCRETION FROM ORBITING SOURCES

    SciTech Connect

    Jura, M.

    2015-12-15

    The abundance anomalies in λ Boo stars are popularly explained by element-specific mass inflows at rates that are much greater than empirically inferred bounds for interstellar accretion. Therefore, a λ Boo star’s thin outer envelope must derive from a companion star, planet, analogs to Kuiper Belt objects or a circumstellar disk. Because radiation pressure on gas-phase ions might selectively allow the accretion of carbon, nitrogen, and oxygen and inhibit the inflow of elements such as iron, the source of the acquired matter need not contain dust. We propose that at least some λ Boo stars accrete from the winds of hot Jupiters.

  9. Accretion tori and cones of ionizing radiation in Seyfert galaxies

    NASA Technical Reports Server (NTRS)

    Acosta-Pulido, Jose A.; Perez-Fournon, Ismael; Calvani, Massimo; Wilson, Andrew S.

    1990-01-01

    The photoionization of extended narrow-line regions in Seyfert galaxies by the radiation produced in a thick accretion disk is studied. The emission-line spectrum is calculated for a range of black hole masses, varying the values of the ionization parameter and the disk size. It is found that models with a million solar masses fit observations of very large accretion disk sizes, while models with 10 million solar masses fit them better with smaller disks. The latter models are preferable since they have lower super-Eddington accretion rates.

  10. Recent Observational Progress on Accretion Disks Around Compact Objects

    NASA Astrophysics Data System (ADS)

    Miller, Jon M.

    2016-04-01

    Studies of accretion disks around black holes and neutron stars over the last ten years have made remarkable progress. Our understanding of disk evolution as a function of mass accretion rate is pushing toward a consensus on thin/thick disk transitions; an apparent switching between disk-driven outflow modes has emerged; and monitoring observations have revealed complex spectral energy distributions wherein disk reprocessing must be important. Detailed studies of disk winds, in particular, have the potential to reveal the basic physical processes that mediate disk accretion, and to connect with numerical simulations. This talk will review these developments and look ahead to the potential of Astro-H.

  11. Accretion Disk Emission Around Kerr Black Holes

    NASA Astrophysics Data System (ADS)

    Campitiello, Samuele; Sbarrato, T.; Ghisellini, G.

    2016-10-01

    Measuring the spin of supermassive Black holes in Active Galactic Nuclei is a further step towards a better understanding of the evolution of their physics. We proposed a new method to estimate the Black hole spin, based on data-fitting. We consider a numerical model called KERRBB, including all relativistic effects (i.e. light-bending, gravitational redshift and Doppler beaming). We found that the same spectrum can be produced by different masses, accretion rates and spins, but that these three quantities are related. In other words, having a robust indipendent estimate on one of these three quantities fixes the other two. By using the Black hole mass, estimated by the virial method, we can pinpoint a narrow range of possible spins and accretion rates for the 32 blazars we have studied. For these objects, we found a lower limit of the spin, that must be a/M > 0.6-0.7

  12. Adenosine mediates decreased cerebral metabolic rate and increased cerebral blood flow during acute moderate hypoxia in the near-term fetal sheep.

    PubMed

    Blood, Arlin B; Hunter, Christian J; Power, Gordon G

    2003-12-15

    Exposure of the fetal sheep to moderate to severe hypoxic stress results in both increased cortical blood flow and decreased metabolic rate. Using intravenous infusion of 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), a selective adenosine A1 receptor antagonist that is permeable to the blood brain barrier, we examine the role of adenosine A1 receptors in mediating cortical blood flow and metabolic responses to moderate hypoxia. The effects of DPCPX blockade are compared to controls as well as animals receiving intravenous 8-(p-sulfophenyl)-theophylline) (8-SPT), a non-selective adenosine receptor antagonist which has been found to be blood brain barrier impermeable. Laser Doppler flow probes, tissue PO2, and thermocouples were implanted in the cerebral cortices of near-term fetal sheep. Catheters were placed in the brachial artery and sagittal sinus vein for collection of samples for blood gas analysis. Three to seven days later responses to a 30-min period of fetal hypoxemia (arterial PO2 10-12 mmHg) were studied with administration of 8-SPT, DPCPX, or vehicle. Cerebral metabolic rate was determined by calculation of both brain heat production and oxygen consumption. In response to hypoxia, control experiments demonstrated a 42 +/- 7 % decrease in cortical heat production and a 35 +/- 10 % reduction in oxygen consumption. In contrast, DPCPX infusion during hypoxia resulted in no significant change in brain heat production or oxygen consumption, suggesting the adenosine A1 receptor is involved in lowering metabolic rate during hypoxia. The decrease in cerebral metabolic rate was not altered by 8-SPT infusion, suggesting that the response is not mediated by adenosine receptors located outside the blood brain barrier. In response to hypoxia, control experiments demonstrated a 35 +/- 7 % increase in cortical blood flow. DPCPX infusion did not change this increase in cortical blood flow, however 8-SPT infusion attenuated increases in flow, indicating that hypoxic

  13. EARTH, MOON, SUN, AND CV ACCRETION DISKS

    SciTech Connect

    Montgomery, M. M.

    2009-11-01

    accretion disks are present or not. Our results suggest that the accretion disk's geometric shape directly affects the disk's precession rate.

  14. Accreting planets as dust dams in 'transition' disks

    SciTech Connect

    Owen, James E.

    2014-07-01

    We investigate under what circumstances an embedded planet in a protoplanetary disk may sculpt the dust distribution such that it observationally presents as a 'transition' disk. We concern ourselves with 'transition' disks that have large holes (≳ 10 AU) and high accretion rates (∼10{sup –9}-10{sup –8} M {sub ☉} yr{sup –1}), particularly, those disks which photoevaporative models struggle to explain. Adopting the observed accretion rates in 'transition' disks, we find that the accretion luminosity from the forming planet is significant, and can dominate over the stellar luminosity at the gap edge. This planetary accretion luminosity can apply a significant radiation pressure to small (s ≲ 1 μm) dust particles provided they are suitably decoupled from the gas. Secular evolution calculations that account for the evolution of the gas and dust components in a disk with an embedded, accreting planet, show that only with the addition of the radiation pressure can we explain the full observed characteristics of a 'transition' disk (NIR dip in the spectral energy distribution (SED), millimeter cavity, and high accretion rate). At suitably high planet masses (≳ 3-4 M{sub J} ), radiation pressure from the accreting planet is able to hold back the small dust particles, producing a heavily dust-depleted inner disk that is optically thin to infrared radiation. The planet-disk system will present as a 'transition' disk with a dip in the SED only when the planet mass and planetary accretion rate are high enough. At other times, it will present as a disk with a primordial SED, but with a cavity in the millimeter, as observed in a handful of protoplanetary disks.

  15. Decreased Sperm Motility Retarded ICSI Fertilization Rate in Severe Oligozoospermia but Good-Quality Embryo Transfer Had Achieved the Prospective Clinical Outcomes

    PubMed Central

    Zheng, Jufeng; Lu, Yongning; Qu, Xianqin; Wang, Peng; Zhao, Luiwen; Gao, Minzhi; Shi, Huijuan; Jin, Xingliang

    2016-01-01

    Introduction Spermatozoa motility is the critical parameter to affect the treatment outcomes during assisted reproductive technologies (ART), but its reproductive capability remains a little informed in condition of severe male factor infertility. This retrospective cohort study aimed to evaluate the effects of reduced sperm motility on the embryological and clinical outcomes in intra-cytoplasmic sperm injection (ICSI) treatment of severe oligozoospermia. Patients and Methods 966 cycles (812 couples) of severe oligozoospermia diagnosed by spermatozoa count ≤ 5 × 106/mL and motile spermatozoa ≤ 2 × 106/mL were divided into four groups in according to the number of motile spermatozoa in one ejaculate on the day of oocyte retrieval (Group B—E). The control (Group A) was 188 cycles of moderate oligozoospermia with spermatozoa count > 5 × 106/mL and motile spermatozoa > 2 × 106/mL. All female partners were younger than 35 years of age. Logistic regression analyzed embryological outcomes (the rates of fertilization, cleavage and good-quality embryo) and clinical outcomes (the rates of pregnancy, implantation, early miscarriage and live birth). Quality of embryo transfer (ET) was divided into three classes as continuous factor to test the effects of embryo quality on clinical outcomes. Results The reduction in the number of motile sperm in four groups of severe oligozoospermia gave rise to comparable inability of the fertilization (p < 0.001) and a decreased rate of good-quality embryo at Day 3 (p < 0.001) by compared to the control. The cleavage rate of the derived zygotes was similar to the control. ET classes significantly affected the clinical outcomes (p < 0.001). Class I ET gave rise to similar rates of clinical outcomes between five groups, but Class II and Class III ET retarded the rates of pregnancy, implantation and live birth and this particularly occurred in Group C, D and E. The rate of early miscarriage was not comparably different between groups

  16. Chaotic cold accretion on to black holes in rotating atmospheres

    NASA Astrophysics Data System (ADS)

    Gaspari, M.; Brighenti, F.; Temi, P.

    2015-07-01

    The fueling of black holes is one key problem in the evolution of baryons in the universe. Chaotic cold accretion (CCA) profoundly differs from classic accretion models, as Bondi and thin disc theories. Using 3D high-resolution hydrodynamic simulations, we now probe the impact of rotation on the hot and cold accretion flow in a typical massive galaxy. In the hot mode, with or without turbulence, the pressure-dominated flow forms a geometrically thick rotational barrier, suppressing the black hole accretion rate to ~1/3 of the spherical case value. When radiative cooling is dominant, the gas loses pressure support and quickly circularizes in a cold thin disk; the accretion rate is decoupled from the cooling rate, although it is higher than that of the hot mode. In the more common state of a turbulent and heated atmosphere, CCA drives the dynamics if the gas velocity dispersion exceeds the rotational velocity, i.e., turbulent Taylor number Tat< 1. Extended multiphase filaments condense out of the hot phase via thermal instability (TI) and rain toward the black hole, boosting the accretion rate up to 100 times the Bondi rate (Ṁ• ~ Ṁcool). Initially, turbulence broadens the angular momentum distribution of the hot gas, allowing the cold phase to condense with prograde or retrograde motion. Subsequent chaotic collisions between the cold filaments, clouds, and a clumpy variable torus promote the cancellation of angular momentum, leading to high accretion rates. As turbulence weakens (Tat > 1), the broadening of the distribution and the efficiency of collisions diminish, damping the accretion rate ∝ Tat-1, until the cold disk drives the dynamics. This is exacerbated by the increased difficulty to grow TI in a rotating halo. The simulated sub-Eddington accretion rates cover the range inferred from AGN cavity observations. CCA predicts inner flat X-ray temperature and r-1 density profiles, as recently discovered in M 87 and NGC 3115. The synthetic Hα images

  17. Vegetation change on a northeast tidal marsh: Interaction of sea-level rise and marsh accretion

    SciTech Connect

    Warren, R.S.; Niering, W.A. )

    1993-01-01

    Increasing rates of relative sea-level rise (RSL) have been linked to coastal wetland losses along the Gulf of Mexico and elsewhere. Rapidly rising RSL may be affecting New England tidal marshes. Studies of the Wequetequock-Pawcatuck tidal marshes over four decades have documented dramatic changes in vegetation apparently related primarily to differential rates of marsh accretion and sea-level rise though sediment supply and anthropogenic modifications of the system may also be involved. When initially studied in 1947-1948 the high marsh supported a Juncus gerardi-Spartina patens belting pattern typical of many New England salt marshes. On most of the marsh complex the former Juncus belt has now been replaced by forbs, primarily Triglochin maritima, while the former S. patens high marsh is now a complex of vegetation types-stunted Spartina alterniflora, Distichlis spicata, forbs, and relic stands of S. patens. The mean surface elevation of areas where the vegetation has changed is significantly lower than that of areas still supporting the earlier pattern (4.6 vs. 13.9 cm above mean tide level). The differences in surface elevation reflect differences in accretion of marsh peat. Stable areas have been accreting at the rate of local sea-level rise, 2.0-2.5 mm/yr at least since 1938; changed areas have accreted at about one half that rate. Lower surface elevations result in greater frequency and duration of tidal flooding, and thus in increased peat saturation, salinity, and sulfide concentrations, and in decreased redox potential, as directly measured over the growing season at both changed and stable sites. These edaphic changes may have combined to favor establishment of a wetter, more open vegetation type. Similar changes have been observed on other Long Island Sound marshes and may be a model for the potential effects of sea-level rise on New England tidal salt marshes. 39 refs., 4 figs., 1 tab.

  18. Accretion Effects on Disks Around Non-Magnetic Compact Objects

    NASA Astrophysics Data System (ADS)

    Montgomery, Michele M.

    2013-02-01

    Accretion disks in compact binaries are thought to sometimes tilt and precess in the retrograde direction as indicated by modulations in light curves and/or signals. Using 3D Smoothed Particle Hydrodynamics and a low mass transfer rate, Montgomery (2012) shows the disk in non-magnetic Cataclysmic Variables tilts naturally after enough time has passed. In that work, twice the fundamental negative superhump signal 2ν_ is associated with disk tilt around the line of nodes, gas stream overflow approximately twice per orbital period, and retrograde precession. In this work, we show that after enough additional time has passed in the same simulation, the 4ν_ harmonic appears. The decrease in the 2ν_ amplitude approximately equals the amplitude of the 4ν_ harmonic. We discuss the implications.

  19. Azimuthal Stress and Heat Flux In Radiatively Inefficient Accretion Flows

    NASA Astrophysics Data System (ADS)

    Devlen, Ebru

    2016-07-01

    Radiatively Inefficient Accretion Flows (RIAFs) have low radiative efficiencies and/or low accretion rates. The accreting gas may retain most of its binding energy in the form of heat. This lost energy for hot RIAFs is one of the problems heavily worked on in the literature. RIAF observations on the accretion to super massive black holes (e.g., Sagittarius A* in the center of our Galaxy) have shown that the observational data are not consistent with either advection-dominated accretion flow (ADAF) or Bondi models. For this reason, it is very important to theoretically comprehend the physical properties of RIAFs derived from observations with a new disk/flow model. One of the most probable candidates for definition of mass accretion and the source of excess heat energy in RIAFs is the gyroviscous modified magnetorotational instability (GvMRI). Dispersion relation is derived by using MHD equations containing heat flux term based on viscosity in the energy equation. Numerical solutions of the disk equations are done and the growth rates of the instability are calculated. This additional heat flux plays an important role in dissipation of energy. The rates of the angular momentum and heat flux which are obtained from numerical calculations of the turbulence brought about by the GVMRI are also discussed.

  20. X-Shooter study of accretion in Chamaeleon I

    NASA Astrophysics Data System (ADS)

    Manara, C. F.; Fedele, D.; Herczeg, G. J.; Teixeira, P. S.

    2016-01-01

    We present the analysis of 34 new VLT/X-Shooter spectra of young stellar objects in the Chamaeleon I star-forming region, together with four more spectra of stars in Taurus and two in Chamaeleon II. The broad wavelength coverage and accurate flux calibration of our spectra allow us to estimate stellar and accretion parameters for our targets by fitting the photospheric and accretion continuum emission from the Balmer continuum down to ~700 nm. The dependence of accretion on stellar properties for this sample is consistent with previous results from the literature. The accretion rates for transitional disks are consistent with those of full disks in the same region. The spread of mass accretion rates at any given stellar mass is found to be smaller than in many studies, but is larger than that derived in the Lupus clouds using similar data and techniques. Differences in the stellar mass range and in the environmental conditions between our sample and that of Lupus may account for the discrepancy in scatter between Chamaeleon I and Lupus. Complete samples in Chamaeleon I and Lupus are needed to determine whether the difference in scatter of accretion rates and the lack of evolutionary trends are not influenced by sample selection. This work is based on observations made with ESO Telescopes at the Paranal Observatory under programme ID 084.C-1095 and 094.C-0913.

  1. Modeling Anomalous Crustal Accretion at Spreading Zones

    NASA Astrophysics Data System (ADS)

    Schmeling, H.; Marquart, G.

    2003-12-01

    The thermal and seismic structure of normal oceanic crust or anomalous crust such as Iceland depends on the mode of melt extraction from the mantle and its emplacement within or on top of the crust. We model crustal accretion by a two fold approach. In a 2D spreading model with anomalous mantle temperature beneath the ridge we solve the Navier-Stokes-, the heat tansport, the mass conservation and the melting equations to determine the enhanced melt production beneath the ridge. This melt is extracted and emplaced on top of the model to form the crust. Two cases are distinguished: a) Extruded crustal material is taken out of the model and is only advected according to the spreading of the plate, b) extruded material is fed back into the model from the top to mimic isostatic subsidence of extruded crust. We find that the feed back of case b) is only moderate. For example, if extruded crustal material as thick as 40 km is fed back into the model, the melting region is depressed downward only by as much as 10km, and the total amount of generated melt is reduced by about 20 %. On the other hand, the upper 30 km of the model is cooled considerably by several 100 degrees. A second set of models focuses on the details of crustal accretion without explicitly solving for the melting and extraction. Knowing the spreading rate, the rate of crustal production can be estimated, but the site of emplacement is not obvious. For an anomalous crust such as Iceland we define four source regions of crustal accretion: surface extrusion, intrusion in fissure swarms at shallow depth connected to volcanic centres, magma chambers at shallow to mid-crustal level, and a deep accretion zone, where crust is produced by widespread dyke and sill emplacement and underplating. We solve the Navier-Stokes-, the heat tansport and the mass conservation equations and prescribe different functions in space and time for crustal production in the four defined regions. The temperature of the imposed

  2. TARP vaccination is associated with slowing in PSA velocity and decreasing tumor growth rates in patients with Stage D0 prostate cancer.

    PubMed

    Wood, Lauren V; Fojo, Antonio; Roberson, Brenda D; Hughes, Meghan S B; Dahut, William; Gulley, James L; Madan, Ravi A; Arlen, Philip M; Sabatino, Marianna; Stroncek, David F; Castiello, Luciano; Trepel, Jane B; Lee, Min-Jung; Parnes, Howard L; Steinberg, Seth M; Terabe, Masaki; Wilkerson, Julia; Pastan, Ira; Berzofsky, Jay A

    2016-08-01

    T-cell receptor alternate reading frame protein (TARP) is a 58-residue protein over-expressed in prostate and breast cancer. We investigated TARP peptide vaccination's impact on the rise in PSA (expressed as Slope Log(PSA) or PSA Doubling Time (PSADT)), validated tumor growth measures, and tumor growth rate in men with Stage D0 prostate cancer. HLA-A*0201 positive men were randomized to receive epitope-enhanced (29-37-9V) and wild-type (27-35) TARP peptides administered as a Montanide/GM-CSF peptide emulsion or as an autologous peptide-pulsed dendritic cell vaccine every 3 weeks for a total of five vaccinations with an optional 6th dose of vaccine at 36 weeks based on immune response or PSADT criteria with a booster dose of vaccine for all patients at 48 and 96 weeks. 41 patients enrolled with median on-study duration of 75 weeks at the time of this analysis. Seventy-two percent of patients reaching 24 weeks and 74% reaching 48 weeks had a decreased Slope Log(PSA) compared to their pre-vaccination baseline (p = 0.0012 and p = 0.0004 for comparison of overall changes in Slope Log(PSA), respectively). TARP vaccination also resulted in a 50% decrease in median tumor growth rate (g): pre-vaccine g = 0.0042/day, post-vaccine g = 0.0021/day (p = 0.003). 80% of subjects exhibited new vaccine-induced TARP-specific IFNγ ELISPOT responses but they did not correlate with decreases in Slope Log(PSA). Thus, vaccination with TARP peptides resulted in significant slowing in PSA velocity and reduction in tumor growth rate in a majority of patients with PSA biochemical recurrence.

  3. X-ray Measurements of Variable Accretion onto the Young Star TW Hydrae

    NASA Astrophysics Data System (ADS)

    Brickhouse, Nancy S.; Cranmer, S. R.; Dupree, A. K.; Wolk, S. J.; Guenther, H. M.

    2013-06-01

    We report X-ray line ratio diagnostics of the electron temperature, electron density and hydrogen column density observed from the classical T Tauri star (CTTS) TW Hydrae using the High Energy Transmission Grating (HETG) spectrometer onboard Chandra. Applying a classical model of magnetically channeled flow from an accretion disk onto the stellar surface, and making the assumption that the absorber of the X-ray shock is the accreting stream itself, we are able to determine all the properties of the accretion, namely the mass accretion rate, stellar magnetic field strength, disk truncation radius, and surface filling factor. We find that the diagnostic ratios, and thus the accretion parameters, are variable, lending support to the absorption assumption. We also report X-ray and optical signatures that respond to the variable accretion, with timescales suggesting the response of the stellar atmosphere to the impact of accretion.

  4. Wind-accretion Disks in Wide Binaries, Second-generation Protoplanetary Disks, and Accretion onto White Dwarfs

    NASA Astrophysics Data System (ADS)

    Perets, Hagai B.; Kenyon, Scott J.

    2013-02-01

    Mass transfer from an evolved donor star to its binary companion is a standard feature of stellar evolution in binaries. In wide binaries, the companion star captures some of the mass ejected in a wind by the primary star. The captured material forms an accretion disk. Here, we study the evolution of wind-accretion disks, using a numerical approach which allows us to follow the long-term evolution. For a broad range of initial conditions, we derive the radial density and temperature profiles of the disk. In most cases, wind accretion leads to long-lived stable disks over the lifetime of the asymptotic giant branch donor star. The disks have masses of a few times 10-5-10-3 M ⊙, with surface density and temperature profiles that follow broken power laws. The total mass in the disk scales approximately linearly with the viscosity parameter used. Roughly, 50%-80% of the mass falling into the disk accretes onto the central star; the rest flows out through the outer edge of the disk into the stellar wind of the primary. For systems with large accretion rates, the secondary accretes as much as 0.1 M ⊙. When the secondary is a white dwarf, accretion naturally leads to nova and supernova eruptions. For all types of secondary star, the surface density and temperature profiles of massive disks resemble structures observed in protoplanetary disks, suggesting that coordinated observational programs might improve our understanding of uncertain disk physics.

  5. AGN Accretion Physics: Insights from K2

    NASA Astrophysics Data System (ADS)

    Vogeley, Michael

    We propose to use Kepler K2 mission observations of 1800 supermassive black holes at the centers of galaxies (Active Galactic Nuclei; AGN) to test models for accretion physics, to study the relationship between variability and other AGN properties such as accretion rate, and to guide methods for detecting and classifying AGN in future time-domain surveys. AGN exhibit optical brightness fluctuations on timescales from below an hour up to many years. These fluctuations are determined by the physics of accretion of matter onto black holes from their galactic environment. By observing variability on timescales down to below an hour, Kepler probes the accretion region on length scales that are too small to be directly imaged using conventional telescopes. These data allow us to test competing models for accretion physics that make different predictions for the statistics of variability. Our previous work provides strong evidence that models of AGN variability that work on long timescale data are not adequate to describe the full range of fluctuation timescales probed by Kepler. We will analyze the light curves of 1800 AGN that have been monitored by Kepler during recent and ongoing K2 campaigns. These objects span a large range of luminosity and AGN type, thus allowing study of the relationship between variability and other physical properties. We will characterize the statistics of AGN variability using state-of-the-art methods of time series analysis that are appropriate for quantifying the stochastic behavior of AGN. This analysis builds on our previous work in which we developed and tested new analysis software that extracts the full information content of these light curves and will enable several key outcomes: (1) Measurement of the relationship between types of AGN and their variability. (2) Tests for dependence of variability on accretion rate. (3) Investigation of changes in variability behavior that point to changes in the mode of accretion. (4) Correlations

  6. An investigation of quality improvement initiatives in decreasing the rate of avoidable 30-day, skilled nursing facility-to-hospital readmissions: a systematic review

    PubMed Central

    Mileski, Michael; Topinka, Joseph Baar; Lee, Kimberly; Brooks, Matthew; McNeil, Christopher; Jackson, Jenna

    2017-01-01

    Objectives The main objective was to investigate the applicability and effectiveness of quality improvement initiatives in decreasing the rate of avoidable 30-day, skilled nursing facility (SNF)-to-hospital readmissions. Problem The rate of rehospitalizations from SNF within 30 days of original discharge has increased within the last decade. Setting The research team participants conducted a literature review via Cumulative Index of Nursing and Allied Health Literature and PubMed to collect data about quality improvement implemented in SNFs. Results The most common facilitator was the incorporation of specialized staff. The most cited barriers were quality improvement tracking and implementation. Conclusion These strategy examples can be useful to acute care hospitals attempting to lower bounce back from subacute care providers and long-term care facilities seeking quality improvement initiatives to reduce hospital readmissions. PMID:28182162

  7. FITDisk: Cataclysmic Variable Accretion Disk Demonstration Tool

    NASA Astrophysics Data System (ADS)

    Wood, Matthew A.; Dolence, J.

    2013-05-01

    FITDisk models accretion disk phenomena using a fully three-dimensional hydrodynamics calculation, and data can either be visualized as they are computed or stored to hard drive for later playback at a fast frame rate. Simulations are visualized using OpenGL graphics and the viewing angle can be changed interactively. Pseudo light curves of simulated systems can be plotted along with the associated Fourier amplitude spectrum. It provides an easy to use graphical user interface as well as 3-D interactive graphics. The code computes the evolution of a CV accretion disk, visualizes results in real time, records and plays back simulations, and generates and plots pseudo light curves and associated power spectra.

  8. Depletion of Molecular Gas by an Accretion Outburst in a Protoplanetary Disk

    NASA Astrophysics Data System (ADS)

    Banzatti, A.; Pontoppidan, K. M.; Bruderer, S.; Muzerolle, J.; Meyer, M. R.

    2015-01-01

    We investigate new and archival 3-5 μm high-resolution (~3 km s-1) spectroscopy of molecular gas in the inner disk of the young solar-mass star EX Lupi, taken during and after the strong accretion outburst of 2008. The data were obtained using the CRIRES spectrometer at the European Southern Observatory Very Large Telescope in 2008 and 2014. In 2008, emission lines from CO, H2O, and OH were detected with broad profiles tracing gas near and within the corotation radius (0.02-0.3 AU). In 2014, the spectra display marked differences. The CO lines, while still detected, are much weaker, and the H2O and OH lines have disappeared altogether. At 3 μm a veiled stellar photospheric spectrum is observed. Our analysis finds that the molecular gas mass in the inner disk has decreased by an order of magnitude since the outburst, matching a similar decrease in the accretion rate onto the star. We discuss these findings in the context of a rapid depletion of material accumulated beyond the disk corotation radius during quiescent periods, as proposed by models of episodic accretion in EXor-type young stars.

  9. DEPLETION OF MOLECULAR GAS BY AN ACCRETION OUTBURST IN A PROTOPLANETARY DISK

    SciTech Connect

    Banzatti, A.; Pontoppidan, K. M.; Muzerolle, J.; Bruderer, S.; Meyer, M. R.

    2015-01-01

    We investigate new and archival 3-5 μm high-resolution (∼3 km s{sup –1}) spectroscopy of molecular gas in the inner disk of the young solar-mass star EX Lupi, taken during and after the strong accretion outburst of 2008. The data were obtained using the CRIRES spectrometer at the European Southern Observatory Very Large Telescope in 2008 and 2014. In 2008, emission lines from CO, H{sub 2}O, and OH were detected with broad profiles tracing gas near and within the corotation radius (0.02-0.3 AU). In 2014, the spectra display marked differences. The CO lines, while still detected, are much weaker, and the H{sub 2}O and OH lines have disappeared altogether. At 3 μm a veiled stellar photospheric spectrum is observed. Our analysis finds that the molecular gas mass in the inner disk has decreased by an order of magnitude since the outburst, matching a similar decrease in the accretion rate onto the star. We discuss these findings in the context of a rapid depletion of material accumulated beyond the disk corotation radius during quiescent periods, as proposed by models of episodic accretion in EXor-type young stars.

  10. Dynamics of core accretion

    DOE PAGES

    Nelson, Andrew F.; Ruffert, Maximilian

    2012-12-21

    In this paper, we perform three-dimensional hydrodynamic simulations of gas flowing around a planetary core of mass Mpl = 10M⊕ embedded in a near Keplerian background flow, using a modified shearing box approximation. We assume an ideal gas behaviour following an equation of state with a fixed ratio of the specific heats, γ = 1.42, consistent with the conditions of a moderate-temperature background disc with solar composition. No radiative heating or cooling is included in the models. We employ a nested grid hydrodynamic code implementing the ‘Piecewise Parabolic Method’ with as many as six fixed nested grids, providing spatial resolutionmore » on the finest grid comparable to the present-day diameters of Neptune and Uranus. We find that a strongly dynamically active flow develops such that no static envelope can form. The activity is not sensitive to plausible variations in the rotation curve of the underlying disc. It is sensitive to the thermodynamic treatment of the gas, as modelled by prescribed equations of state (either ‘locally isothermal’ or ‘locally isentropic’) and the temperature of the background disc material. The activity is also sensitive to the shape and depth of the core's gravitational potential, through its mass and gravitational softening coefficient. Each of these factors influences the magnitude and character of hydrodynamic feedback of the small-scale flow on the background, and we conclude that accurate modelling of such feedback is critical to a complete understanding of the core accretion process. The varying flow pattern gives rise to large, irregular eruptions of matter from the region around the core which return matter to the background flow: mass in the envelope at one time may not be found in the envelope at any later time. No net mass accretion into the envelope is observed over the course of the simulation and none is expected, due to our neglect of cooling. Except in cases of very rapid cooling however, as

  11. Dynamics of core accretion

    SciTech Connect

    Nelson, Andrew F.; Ruffert, Maximilian

    2012-12-21

    In this paper, we perform three-dimensional hydrodynamic simulations of gas flowing around a planetary core of mass Mpl = 10M embedded in a near Keplerian background flow, using a modified shearing box approximation. We assume an ideal gas behaviour following an equation of state with a fixed ratio of the specific heats, γ = 1.42, consistent with the conditions of a moderate-temperature background disc with solar composition. No radiative heating or cooling is included in the models. We employ a nested grid hydrodynamic code implementing the ‘Piecewise Parabolic Method’ with as many as six fixed nested grids, providing spatial resolution on the finest grid comparable to the present-day diameters of Neptune and Uranus. We find that a strongly dynamically active flow develops such that no static envelope can form. The activity is not sensitive to plausible variations in the rotation curve of the underlying disc. It is sensitive to the thermodynamic treatment of the gas, as modelled by prescribed equations of state (either ‘locally isothermal’ or ‘locally isentropic’) and the temperature of the background disc material. The activity is also sensitive to the shape and depth of the core's gravitational potential, through its mass and gravitational softening coefficient. Each of these factors influences the magnitude and character of hydrodynamic feedback of the small-scale flow on the background, and we conclude that accurate modelling of such feedback is critical to a complete understanding of the core accretion process. The varying flow pattern gives rise to large, irregular eruptions of matter from the region around the core which return matter to the background flow: mass in the envelope at one time may not be found in the envelope at any later time. No net mass accretion into the envelope is observed over the course of the simulation and none is expected, due to our neglect of cooling. Except in cases of very rapid cooling

  12. Does Breast Magnetic Resonance Imaging Combined With Conventional Imaging Modalities Decrease the Rates of Surgical Margin Involvement and Reoperation?: A Case-Control Comparative Analysis.

    PubMed

    Lai, Hung-Wen; Chen, Chih-Jung; Lin, Ying-Jen; Chen, Shu-Ling; Wu, Hwa-Koon; Wu, Yu-Ting; Kuo, Shou-Jen; Chen, Shou-Tung; Chen, Dar-Ren

    2016-05-01

    The objective of this study was to assess whether preoperative breast magnetic resonance imaging (MRI) combined with conventional breast imaging techniques decreases the rates of margin involvement and reexcision.Data on patients who underwent surgery for primary operable breast cancer were obtained from the Changhua Christian Hospital (CCH) breast cancer database. The rate of surgical margin involvement and the rate of reoperation were compared between patients who underwent conventional breast imaging modalities (Group A: mammography and sonography) and those who received breast MRI in addition to conventional imaging (Group B: mammography, sonography, and MRI).A total of 1468 patients were enrolled in this study. Among the 733 patients in Group A, 377 (51.4%) received breast-conserving surgery (BCS) and 356 (48.6%) received mastectomy. Among the 735 patients in Group B, 348 (47.3%) received BCS and 387 (52.7%) received mastectomy. There were no significant differences in operative method between patients who received conventional imaging alone and those that received MRI and conventional imaging (P = 0.13). The rate of detection of pathological multifocal/multicentric breast cancer was markedly higher in patients who received preoperative MRI than in those who underwent conventional imaging alone (14.3% vs 8.6%, P < 0.01). The overall rate of surgical margin involvement was significantly lower in patients who received MRI (5.0%) than in those who received conventional imaging alone (9.0%) (P < 0.01). However, a significant reduction in rate of surgical margin positivity was only observed in patients who received BCS (Group A, 14.6%; Group B, 6.6%, P < 0.01). The overall BCS reoperation rates were 11.7% in the conventional imaging group and 3.2% in the combined MRI group (P < 0.01). There were no significant differences in rate of residual cancer in specimens obtained during reoperation between the 2 preoperative imaging groups (Group A, 50

  13. Gas accretion from halos to disks: observations, curiosities, and problems

    NASA Astrophysics Data System (ADS)

    Elmegreen, Bruce G.

    2016-08-01

    Accretion of gas from the cosmic web to galaxy halos and ultimately their disks is a prediction of modern cosmological models but is rarely observed directly or at the full rate expected from star formation. Here we illustrate possible large-scale cosmic HI accretion onto the nearby dwarf starburst galaxy IC10, observed with the VLA and GBT. We also suggest that cosmic accretion is the origin of sharp metallicity drops in the starburst regions of other dwarf galaxies, as observed with the 10-m GTC. Finally, we question the importance of cosmic accretion in normal dwarf irregulars, for which a recent study of their far-outer regions sees no need for, or evidence of, continuing gas buildup.

  14. Fate of accreting white dwarfs: Type I supernovae vs collapse

    SciTech Connect

    Nomoto, Ken'ichi

    1986-01-01

    The final fate of accreting C + O white dwarfs is either thermonuclear explosion or collapse, if the white dwarf mass grows to the Chandrasekhar mass. We discuss how the fate depends on the initial mass, age, composition of the white dwarf and the mass accretion rate. Relatively fast accretion leads to a carbon deflagration at low central density that gives rise to a Type Ia supernova. Slower accretion induces a helium detonation that could be observed as a Type Ib supernova. If the initial mass of the C + O white dwarf is larger than 1.2 Msub solar, a carbon deflagration starts at high central density and induces a collapse of the white dwarf to form a neutron star. We examine the critical condition for which a carbon deflagration leads to collapse, not explosion. For the case of explosion, we discuss to what extent the nucleosynthesis models are consistent with spectra of Type Ia and Ib supernovae. 61 refs., 18 figs.

  15. Mass-loss from advective accretion disc around rotating black holes

    NASA Astrophysics Data System (ADS)

    Aktar, Ramiz; Das, Santabrata; Nandi, Anuj

    2015-11-01

    We examine the properties of the outflowing matter from an advective accretion disc around a spinning black hole. During accretion, rotating matter experiences centrifugal pressure-supported shock transition that effectively produces a virtual barrier around the black hole in the form of post-shock corona (hereafter PSC). Due to shock compression, PSC becomes hot and dense that eventually deflects a part of the inflowing matter as bipolar outflows because of the presence of extra thermal gradient force. In our approach, we study the outflow properties in terms of the inflow parameters, namely specific energy (E) and specific angular momentum (λ) considering the realistic outflow geometry around the rotating black holes. We find that spin of the black hole (ak) plays an important role in deciding the outflow rate R_{dot{m}} (ratio of mass flux of outflow to inflow); in particular, R_{dot{m}} is directly correlated with ak for the same set of inflow parameters. It is found that a large range of the inflow parameters allows global accretion-ejection solutions, and the effective area of the parameter space (E, λ) with and without outflow decreases with black hole spin (ak). We compute the maximum outflow rate (R^{max}_{dot{m}}) as a function of black hole spin (ak) and observe that R^{max}_{dot{m}} weakly depends on ak that lies in the range ˜10-18 per cent of the inflow rate for the adiabatic index (γ) with 1.5 ≥ γ ≥ 4/3. We present the observational implication of our approach while studying the steady/persistent jet activities based on the accretion states of black holes. We discuss that our formalism seems to have the potential to explain the observed jet kinetic power for several Galactic black hole sources and active galactic nuclei.

  16. Nebular gas drag and planetary accretion. II. Planet on an eccentric orbit.

    NASA Astrophysics Data System (ADS)

    Kary, David M.; Lissauer, Jack J.

    1995-09-01

    avoiding accretion while migrating past the planet can be described as the probability of not being accreted in a single conjunction to the power of the number of conjunctions that a planetesimal has with the planet while passing through its feeding zone. In the nongravitating planet limit (which is valid for a low mean density planet on a highly eccentric orbit), the accretion probability increases with planetary eccentricity due to the growth of the planet's feeding zone. When the planet's gravity is considered using the 2+2-body approximation (which is valid for a dense planet on a moderately eccentric orbit), the accretion rate is nearly independent of planetary eccentricity. Numerical simulations show that at small planetary eccentricities, the 2+2-body approximation breaks down, and the accretion probability gradually increases with decreasing eccentricity in this regime.

  17. Temperature Shift Experiments Suggest That Metabolic Impairment and Enhanced Rates of Photorespiration Decrease Organic Acid Levels in Soybean Leaflets Exposed to Supra-Optimal Growth Temperatures.

    PubMed

    Sicher, Richard C

    2015-08-05

    Elevated growth temperatures are known to affect foliar organic acid concentrations in various plant species. In the current study, citrate, malate, malonate, fumarate and succinate decreased 40 to 80% in soybean leaflets when plants were grown continuously in controlled environment chambers at 36/28 compared to 28/20 °C. Temperature effects on the above mentioned organic acids were partially reversed three days after plants were transferred among optimal and supra-optimal growth temperatures. In addition, CO2 enrichment increased foliar malate, malonate and fumarate concentrations in the supra-optimal temperature treatment, thereby mitigating effects of high temperature on respiratory metabolism. Glycerate, which functions in the photorespiratory pathway, decreased in response to CO2 enrichment at both growth temperatures. The above findings suggested that diminished levels of organic acids in soybean leaflets upon exposure to high growth temperatures were attributable to metabolic impairment and to changes of photorespiratory flux. Leaf development rates differed among temperature and CO2 treatments, which affected foliar organic acid levels. Additionally, we report that large decreases of foliar organic acids in response to elevated growth temperatures were observed in legume species.

  18. The Dripping Handrail Model: Transient Chaos in Accretion Systems

    NASA Technical Reports Server (NTRS)

    Young, Karl; Scargle, Jeffrey D.; Cuzzi, Jeffrey (Technical Monitor)

    1995-01-01

    We define and study a simple dynamical model for accretion systems, the "dripping handrail" (DHR). The time evolution of this spatially extended system is a mixture of periodic and apparently random (but actually deterministic) behavior. The nature of this mixture depends on the values of its physical parameters - the accretion rate, diffusion coefficient, and density threshold. The aperiodic component is a special kind of deterministic chaos called transient chaos. The model can simultaneously exhibit both the quasiperiodic oscillations (QPO) and very low frequency noise (VLFN) that characterize the power spectra of fluctuations of several classes of accretion systems in astronomy. For this reason, our model may be relevant to many such astrophysical systems, including binary stars with accretion onto a compact object - white dwarf, neutron star, or black hole - as well as active galactic nuclei. We describe the systematics of the DHR's temporal behavior, by exploring its physical parameter space using several diagnostics: power spectra, wavelet "scalegrams," and Lyapunov exponents. In addition, we note that for large accretion rates the DHR has periodic modes; the effective pulse shapes for these modes - evaluated by folding the time series at the known period - bear a resemblance to the similarly- determined shapes for some x-ray pulsars. The pulsing observed in some of these systems may be such periodic-mode accretion, and not due to pure rotation as in the standard pulsar model.

  19. Freddi: Fast Rise Exponential Decay accretion Disk model Implementation

    NASA Astrophysics Data System (ADS)

    Malanchev, K. L.; Lipunova, G. V.

    2016-10-01

    Freddi (Fast Rise Exponential Decay: accretion Disk model Implementation) solves 1-D evolution equations of the Shakura-Sunyaev accretion disk. It simulates fast rise exponential decay (FRED) light curves of low mass X-ray binaries (LMXBs). The basic equation of the viscous evolution relates the surface density and viscous stresses and is of diffusion type; evolution of the accretion rate can be found on solving the equation. The distribution of viscous stresses defines the emission from the source. The standard model for the accretion disk is implied; the inner boundary of the disk is at the ISCO or can be explicitely set. The boundary conditions in the disk are the zero stress at the inner boundary and the zero accretion rate at the outer boundary. The conditions are suitable during the outbursts in X-ray binary transients with black holes. In a binary system, the accretion disk is radially confined. In Freddi, the outer radius of the disk can be set explicitely or calculated as the position of the tidal truncation radius.

  20. TURBULENT MIXING ON HELIUM-ACCRETING WHITE DWARFS

    SciTech Connect

    Piro, Anthony L.

    2015-03-10

    An attractive scenario for producing Type Ia supernovae (SNe Ia) is a double detonation, where detonation of an accreted helium layer triggers ignition of a C/O core. Whether or not such a mechanism can explain some or most SNe Ia depends on the properties of the helium burning, which in turn is set by the composition of the surface material. Using a combination of semi-analytic and simple numerical models, I explore when turbulent mixing due to hydrodynamic instabilities during the accretion process can mix C/O core material up into the accreted helium. Mixing is strongest at high accretion rates, large white dwarf (WD) masses, and slow spin rates. The mixing would result in subsequent helium burning that better matches the observed properties of SNe Ia. In some cases, there is considerable mixing that can lead to more than 50% C/O in the accreted layer at the time of ignition. These results will hopefully motivate future theoretical studies of such strongly mixed conditions. Mixing also has implications for other types of WD surface explosions, including the so-called .Ia supernovae, the calcium-rich transients (if they arise from accreting WDs), and metal-enriched classical novae.

  1. Observational Tests of the Picture of Disk Accretion

    NASA Astrophysics Data System (ADS)

    Maccarone, Thomas J.

    2014-09-01

    In this chapter, I present a summary of observational tests of the basic picture of disk accretion. An emphasis is placed on tests relevant to black holes, but many of the fundamental results are drawn from studies of other classes of systems. Evidence is discussed for the basic structures of accretion flows. The cases of systems with and without accretion disks are discussed, as is the evidence that disks actually form. Also discussed are the hot spots where accretion streams impact the disks, and the boundary layers in the inner parts of systems where the accretors are not black holes. The nature of slow, large amplitude variability is discussed. It is shown that some of the key predictions of the classical thermal-viscous ionization instability model for producing outbursts are in excellent agreement with observational results. It is also show that there are systems whose outbursts are extremely difficult to explain without invoking variations in the rate of mass transfer from the donor star into the outer accretion disk, or tidally induced variations in the mass transfer rates. Finally, I briefly discuss recent quasar microlensing measurements which give truly independent constraints on the inner accretion geometry around black holes.

  2. X-Ray Spectra from MHD Simulations of Accreting Black Holes

    NASA Technical Reports Server (NTRS)

    Schnittman, Jeremy D.; Krolik, Julian H.; Noble, Scott C.

    2012-01-01

    We present the results of a new global radiation transport code coupled to a general relativistic magneto-hydrodynamic simulation of an accreting, nonrotating black hole. For the first time, we are able to explain from first principles in a self-consistent way the X-ray spectra observed from stellar-mass black holes, including a thermal peak, Compton reflection hump, power-law tail, and broad iron line. Varying only the mass accretion rate, we are able to reproduce the low/hard, steep power-law, and thermal-dominant states seen in most galactic black hole sources. The temperature in the corona is T(sub e) 10 keV in a boundary layer near the disk and rises smoothly to T(sub e) greater than or approximately 100 keV in low-density regions far above the disk. Even as the disk's reflection edge varies from the horizon out to approximately equal to 6M as the accretion rate decreases, we find that the shape of the Fe Ka line is remarkably constant. This is because photons emitted from the plunging region are strongly beamed into the horizon and never reach the observer. We have also carried out a basic timing analysis of the spectra and find that the fractional variability increases with photon energy and viewer inclination angle, consistent with the coronal hot spot model for X-ray fluctuations.

  3. Magnetic field evolution of accreting neutron stars

    NASA Astrophysics Data System (ADS)

    Istomin, Y. N.; Semerikov, I. A.

    2016-01-01

    The flow of a matter, accreting on to a magnetized neutron star, is accompanied by an electric current. The closing of the electric current occurs in the crust of a neutron stars in the polar region across the magnetic field. But the conductivity of the crust along the magnetic field greatly exceeds the conductivity across the field, so the current penetrates deep into the crust down up to the superconducting core. The magnetic field, generated by the accretion current, increases greatly with the depth of penetration due to the Hall conductivity of the crust is also much larger than the transverse conductivity. As a result, the current begins to flow mainly in the toroidal direction, creating a strong longitudinal magnetic field, far exceeding an initial dipole field. This field exists only in the narrow polar tube of r width, narrowing with the depth, i.e. with increasing of the crust density ρ, r ∝ ρ-1/4. Accordingly, the magnetic field B in the tube increases with the depth, B∝ρ1/2, and reaches the value of about 1017 Gauss in the core. It destroys superconducting vortices in the core of a star in the narrow region of the size of the order of 10 cm. Because of generated density gradient of vortices, they constantly flow into this dead zone and the number of vortices decreases, the magnetic field of a star decreases as well. The attenuation of the magnetic field is exponential, B = B0(1 + t/τ)-1. The characteristic time of decreasing of the magnetic field τ is equal to τ ≃ 103 yr. Thus, the magnetic field of accreted neutron stars decreases to values of 108-109 Gauss during 107-106 yr.

  4. CIRCUMBINARY MAGNETOHYDRODYNAMIC ACCRETION INTO INSPIRALING BINARY BLACK HOLES

    SciTech Connect

    Noble, Scott C.; Mundim, Bruno C.; Nakano, Hiroyuki; Campanelli, Manuela; Zlochower, Yosef; Krolik, Julian H.; Yunes, Nicolas

    2012-08-10

    We have simulated the magnetohydrodynamic evolution of a circumbinary disk surrounding an equal-mass binary comprising two non-spinning black holes during the period in which the disk inflow time is comparable to the binary evolution time due to gravitational radiation. Both the changing spacetime and the binary orbital evolution are described by an innovative technique utilizing high-order post-Newtonian approximations. Prior to the beginning of the inspiral, the structure of the circumbinary disk is predicted well by extrapolation from Newtonian results: a gap of roughly two binary separation radii is cleared, and matter piles up at the outer edge of this gap as inflow is retarded by torques exerted by the binary; the accretion rate is roughly half its value at large radius. During inspiral, the inner edge of the disk initially moves inward in coordination with the shrinking binary, but-as the orbital evolution accelerates-the inward motion of the disk edge falls behind the rate of binary compression. In this stage, the binary torque falls substantially, but the accretion rate decreases by only 10%-20%. When the binary separation is tens of gravitational radii, the rest-mass efficiency of disk radiation is a few percent, suggesting that supermassive binary black holes could be very luminous at this stage of their evolution. Inner disk heating is modulated at a beat frequency comparable to the binary orbital frequency. However, a disk with sufficient surface density to be luminous may be optically thick, suppressing periodic modulation of the luminosity.

  5. Accretion onto Black Holes from Large Scales Regulated by Radiative Feedback. III. Enhanced Luminosity of Intermediate-mass Black Holes Moving at Supersonic Speeds

    NASA Astrophysics Data System (ADS)

    Park, KwangHo; Ricotti, Massimo

    2013-04-01

    In this third paper of a series, we study the growth and luminosity of black holes (BHs) in motion with respect to their surrounding medium. We run a large set of two-dimensional axis-symmetric simulations to explore a large parameter space of initial conditions and formulate an analytical model for the accretion. Contrary to the case without radiation feedback, the accretion rate increases with increasing BH velocity v bh reaching a maximum value at v bh = 2c s, in ~ 50 km s-1, where c s, in is the sound speed inside the "cometary-shaped" H II region around the BH, before decreasing as v_bh^{-3} when the ionization front (I-front) becomes R-type (rarefied) and the accretion rate approaches the classical Bondi-Hoyle-Lyttleton solution. The increase of the accretion rate with v bh is produced by the formation of a D-type (dense) I-front preceded by a standing bow shock that reduces the downstream gas velocity to transonic values. There is a range of densities and velocities where the dense shell is unstable producing periodic accretion rate peaks which can significantly increase the detectability of intermediate-mass BHs. We find that the mean accretion rate for a moving BH is larger than that of a stationary BH of the same mass if the medium temperature is T ∞ < 104 K. This result could be important for the growth of seed BHs in the multi-phase medium of the first galaxies and for building an early X-ray background that may affect the formation of the first galaxies and the reionization process.

  6. Giant planet formation with pebble accretion

    NASA Astrophysics Data System (ADS)

    Chambers, J. E.

    2014-05-01

    In the core accretion model for giant planet formation, a solid core forms by coagulation of dust grains in a protoplanetary disk and then accretes gas from the disk when the core reaches a critical mass. Both stages must be completed in a few million years before the disk gas disperses. The slowest stage of this process may be oligarchic growth in which a giant-planet core grows by sweeping up smaller, asteroid-size planetesimals. Here, we describe new numerical simulations of oligarchic growth using a particle-in-a-box model. The simulations include several processes that can effect oligarchic growth: (i) planetesimal fragmentation due to mutual collisions, (ii) the modified capture rate of planetesimals due to a core’s atmosphere, (iii) drag with the disk gas during encounters with the core (so-called “pebble accretion”), (iv) modification of particle velocities by turbulence and drift caused by gas drag, (v) the presence of a population of mm-to-m size “pebbles” that represent the transition point between disruptive collisions between larger particles, and mergers between dust grains, and (vi) radial drift of small objects due to gas drag. Collisions between planetesimals rapidly generate a population of pebbles. The rate at which a core sweeps up pebbles is controlled by pebble accretion dynamics. Metre-size pebbles lose energy during an encounter with a core due to drag, and settle towards the core, greatly increasing the capture probability during a single encounter. Millimetre-size pebbles are tightly coupled to the gas and most are swept past the core during an encounter rather than being captured. Accretion efficiency per encounter increases with pebble size in this size range. However, radial drift rates also increase with size, so metre-size objects encounter a core on many fewer occasions than mm-size pebbles before they drift out of a region. The net result is that core growth rates vary weakly with pebble size, with the optimal diameter

  7. The Effect of Transient Accretion on the Spin-up of Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Sudip; Chakrabarty, Deepto

    2017-01-01

    A millisecond pulsar is a neutron star that has been substantially spun up by accretion from a binary companion. A previously unrecognized factor governing the spin evolution of such pulsars is the crucial effect of nonsteady or transient accretion. We numerically compute the evolution of accreting neutron stars through a series of outburst and quiescent phases, considering the drastic variation of the accretion rate and the standard disk–magnetosphere interaction. We find that, for the same long-term average accretion rate, X-ray transients can spin up pulsars to rates several times higher than can persistent accretors, even when the spin-down due to electromagnetic radiation during quiescence is included. We also compute an analytical expression for the equilibrium spin frequency in transients, by taking spin equilibrium to mean that no net angular momentum is transferred to the neutron star in each outburst cycle. We find that the equilibrium spin rate for transients, which depends on the peak accretion rate during outbursts, can be much higher than that for persistent sources. This explains our numerical finding. This finding implies that any meaningful study of neutron star spin and magnetic field distributions requires the inclusion of the transient accretion effect, since most accreting neutron star sources are transients. Our finding also implies the existence of a submillisecond pulsar population, which is not observed. This may point to the need for a competing spin-down mechanism for the fastest-rotating accreting pulsars, such as gravitational radiation.

  8. Dynamics of continental accretion.

    PubMed

    Moresi, L; Betts, P G; Miller, M S; Cayley, R A

    2014-04-10

    Subduction zones become congested when they try to consume buoyant, exotic crust. The accretionary mountain belts (orogens) that form at these convergent plate margins have been the principal sites of lateral continental growth through Earth's history. Modern examples of accretionary margins are the North American Cordilleras and southwest Pacific subduction zones. The geologic record contains abundant accretionary orogens, such as the Tasmanides, along the eastern margin of the supercontinent Gondwana, and the Altaïdes, which formed on the southern margin of Laurasia. In modern and ancient examples of long-lived accretionary orogens, the overriding plate is subjected to episodes of crustal extension and back-arc basin development, often related to subduction rollback and transient episodes of orogenesis and crustal shortening, coincident with accretion of exotic crust. Here we present three-dimensional dynamic models that show how accretionary margins evolve from the initial collision, through a period of plate margin instability, to re-establishment of a stable convergent margin. The models illustrate how significant curvature of the orogenic system develops, as well as the mechanism for tectonic escape of the back-arc region. The complexity of the morphology and the evolution of the system are caused by lateral rollback of a tightly arcuate trench migrating parallel to the plate boundary and orthogonally to the convergence direction. We find geological and geophysical evidence for this process in the Tasmanides of eastern Australia, and infer that this is a recurrent and global phenomenon.

  9. Dynamics of continental accretion

    NASA Astrophysics Data System (ADS)

    Moresi, L.; Betts, P. G.; Miller, M. S.; Cayley, R. A.

    2014-04-01

    Subduction zones become congested when they try to consume buoyant, exotic crust. The accretionary mountain belts (orogens) that form at these convergent plate margins have been the principal sites of lateral continental growth through Earth's history. Modern examples of accretionary margins are the North American Cordilleras and southwest Pacific subduction zones. The geologic record contains abundant accretionary orogens, such as the Tasmanides, along the eastern margin of the supercontinent Gondwana, and the Altaïdes, which formed on the southern margin of Laurasia. In modern and ancient examples of long-lived accretionary orogens, the overriding plate is subjected to episodes of crustal extension and back-arc basin development, often related to subduction rollback and transient episodes of orogenesis and crustal shortening, coincident with accretion of exotic crust. Here we present three-dimensional dynamic models that show how accretionary margins evolve from the initial collision, through a period of plate margin instability, to re-establishment of a stable convergent margin. The models illustrate how significant curvature of the orogenic system develops, as well as the mechanism for tectonic escape of the back-arc region. The complexity of the morphology and the evolution of the system are caused by lateral rollback of a tightly arcuate trench migrating parallel to the plate boundary and orthogonally to the convergence direction. We find geological and geophysical evidence for this process in the Tasmanides of eastern Australia, and infer that this is a recurrent and global phenomenon.

  10. FILAMENTARY ACCRETION FLOWS IN THE EMBEDDED SERPENS SOUTH PROTOCLUSTER

    SciTech Connect

    Kirk, Helen; Myers, Philip C.; Bourke, Tyler L.; Gutermuth, Robert A.; Wilson, Grant W.; Hedden, Abigail

    2013-04-01

    One puzzle in understanding how stars form in clusters is the source of mass-is all of the mass in place before the first stars are born, or is there an extended period when the cluster accretes material which can continuously fuel the star formation process? We use a multi-line spectral survey of the southern filament associated with the Serpens South embedded cluster-forming region in order to determine if mass is accreting from the filament onto the cluster, and whether the accretion rate is significant. Our analysis suggests that material is flowing along the filament's long axis at a rate of {approx}30 M{sub Sun} Myr{sup -1} (inferred from the N{sub 2}H{sup +} velocity gradient along the filament), and radially contracting onto the filament at {approx}130 M{sub Sun} Myr{sup -1} (inferred from HNC self-absorption). These accretion rates are sufficient to supply mass to the central cluster at a similar rate to the current star formation rate in the cluster. Filamentary accretion flows may therefore be very important in the ongoing evolution of this cluster.

  11. [The mechanism of phenoptosis: I. Age-dependent decrease of the overall rate of protein synthesis is caused by the programmed attenuation of bio-energetics].

    PubMed

    Trubitsyn, A G

    2009-01-01

    The age-dependent degradation of all vital processes of an organism can be result of influences of destructive factors (the stochastic mechanism of aging), or effect of realizations of the genetic program (phenoptosis). The stochastic free-radical theory of aging dominating now contradicts the set of empirical data, and the semicentenial attempts to create the means to slow down aging did not give any practical results. It makes obvious that the stochastic mechanism of aging is incorrect. At the same time, the alternative mechanism of the programmed aging is not developed yet but preconditions for it development have already been created. It is shown that the genes controlling process of aging exist (contrary to the customary opinion) and the increase in the level of damaged macromolecules (basic postulate of the free-radical theory) can be explained by programmed attenuation of bio-energetics. As the bio-energetics is a driving force of all vital processes, decrease of its level is capable to cause degradation of all functions of an organism. However to transform this postulate into a basis of the theory of phenoptosis it is necessary to show, that attenuation of bio-energetics predetermines such fundamental processes accompanying aging as decrease of the overall rate of protein biosynthesis, restriction of cellular proliferations (Hayflick limit), loss of telomeres etc. This article is the first step in this direction: the natural mechanism of interaction of overall rate of protein synthesis with a level of cellular bio-energetics is shown. This is built-in into the translation machine and based on dependence of recirculation rate of eukaryotic initiation factor 2 (elF2) from ATP/ADP value that is created by mitochondrial bio-energetic machine.

  12. Rethinking Black Hole Accretion Discs

    NASA Astrophysics Data System (ADS)

    Salvesen, Greg

    Accretion discs are staples of astrophysics. Tapping into the gravitational potential energy of the accreting material, these discs are highly efficient machines that produce copious radiation and extreme outflows. While interesting in their own right, accretion discs also act as tools to study black holes and directly influence the properties of the Universe. Black hole X-ray binaries are fantastic natural laboratories for studying accretion disc physics and black hole phenomena. Among many of the curious behaviors exhibited by these systems are black hole state transitions -- complicated cycles of dramatic brightening and dimming. Using X-ray observations with high temporal cadence, we show that the evolution of the accretion disc spectrum during black hole state transitions can be described by a variable disc atmospheric structure without invoking a radially truncated disc geometry. The accretion disc spectrum can be a powerful diagnostic for measuring black hole spin if the effects of the disc atmosphere on the emergent spectrum are well-understood; however, properties of the disc atmosphere are largely unconstrained. Using statistical methods, we decompose this black hole spin measurement technique and show that modest uncertainties regarding the disc atmosphere can lead to erroneous spin measurements. The vertical structure of the disc is difficult to constrain due to our ignorance of the contribution to hydrostatic balance by magnetic fields, which are fundamental to the accretion process. Observations of black hole X-ray binaries and the accretion environments near supermassive black holes provide mounting evidence for strong magnetization. Performing numerical simulations of accretion discs in the shearing box approximation, we impose a net vertical magnetic flux that allows us to effectively control the level of disc magnetization. We study how dynamo activity and the properties of turbulence driven by the magnetorotational instability depend on the

  13. ACCRETING CIRCUMPLANETARY DISKS: OBSERVATIONAL SIGNATURES

    SciTech Connect

    Zhu, Zhaohuan

    2015-01-20

    I calculate the spectral energy distributions of accreting circumplanetary disks using atmospheric radiative transfer models. Circumplanetary disks only accreting at 10{sup –10} M {sub ☉} yr{sup –1} around a 1 M{sub J} planet can be brighter than the planet itself. A moderately accreting circumplanetary disk ( M-dot ∼10{sup −8} M{sub ⊙} yr{sup −1}; enough to form a 10 M{sub J} planet within 1 Myr) around a 1 M{sub J} planet has a maximum temperature of ∼2000 K, and at near-infrared wavelengths (J, H, K bands), this disk is as bright as a late-M-type brown dwarf or a 10 M{sub J} planet with a ''hot start''. To use direct imaging to find the accretion disks around low-mass planets (e.g., 1 M{sub J} ) and distinguish them from brown dwarfs or hot high-mass planets, it is crucial to obtain photometry at mid-infrared bands (L', M, N bands) because the emission from circumplanetary disks falls off more slowly toward longer wavelengths than those of brown dwarfs or planets. If young planets have strong magnetic fields (≳100 G), fields may truncate slowly accreting circumplanetary disks ( M-dot ≲10{sup −9} M{sub ⊙} yr{sup −1}) and lead to magnetospheric accretion, which can provide additional accretion signatures, such as UV/optical excess from the accretion shock and line emission.

  14. Diskoseismology: Probing relativistic accretion disks

    NASA Astrophysics Data System (ADS)

    Nowak, Michael Allen

    1992-08-01

    Helioseismology has provided a wealth of information about the structure of the solar atmosphere. Little is known, however, about the structure of accretion disks that are thought to exist around black holes and neutron stars. In this thesis we present calculations of modes that are trapped in thin Keplerian accretion disks. We hope to use observations of thes modes to elucidate the structure of the inner relativistic regions of accretion disks. Our calculations assume that the thin disk is terminated by an innermost stable orbit, as would occur around a slowly rotating black hole or weakly magnetized compact neutron star. The dominant relativistic effects, which allow modes to be trapped within the inner region of the disk, are approximated via a modified Newtonian potential. Using the Lagrangian formulation of Friedman and Schutz, we develop a general formalism for investigating the adiabatic oscillations of arbitrary unperturbed disk models. First we consider the special case of acoustic waves in disks with isothermal atmospheres. Next we describe the Lagrangian perturbation vectors in terms of the derivatives of a scalar potential, as has been done by Ipser and Lindblom. Using this potential, we derive a single partial differential equation governing the oscillations of a disk. The eigenfunctions and eigenfrequencies of a variety of disk models are found to fall into two main classes which are analogous to the p-modes and g-modes in the sun. Specifically we use the potential formalism to compute the g-modes for disks with isothermal atmospheres. Physical arguments show that both the p-modes and g-modes belong to the same family of modes as the p-modes and g-modes in the sun, just viewed in a different parameter regime. With the aid of the Lagrangian formalism we consider possible growth or damping mechanisms and compute the (assumed) relatively small rates of growth or damping of the modes. Specifically, we consider gravitational radiation reaction and

  15. The Standing Accretion Shock Instability: Enhanced Growth in Rotating Progenitors

    NASA Astrophysics Data System (ADS)

    Blondin, John M.; Gipson, Emily; Harris, Sawyer; Mezzacappa, Anthony

    2017-02-01

    We investigate the effect of progenitor rotation on the standing accretion shock instability (SASI) using two- and three-dimensional hydrodynamic simulations. We find that the growth rate of the SASI is a near-linearly increasing function of the specific angular momentum in the accreting gas. Both the growth rate and the angular frequency in the two-dimensional model with cylindrical geometry agree well with previous linear stability analyses. When excited by very small random perturbations, a one-armed spiral mode dominates the small rotation rates predicted by current stellar evolution models, while progressively higher-order modes are seen as the specific angular momentum increases.

  16. How do accretion discs break?

    NASA Astrophysics Data System (ADS)

    Dogan, Suzan

    2016-07-01

    Accretion discs are common in binary systems, and they are often found to be misaligned with respect to the binary orbit. The gravitational torque from a companion induces nodal precession in misaligned disc orbits. In this study, we first calculate whether this precession is strong enough to overcome the internal disc torques communicating angular momentum. We compare the disc precession torque with the disc viscous torque to determine whether the disc should warp or break. For typical parameters precession wins: the disc breaks into distinct planes that precess effectively independently. To check our analytical findings, we perform 3D hydrodynamical numerical simulations using the PHANTOM smoothed particle hydrodynamics code, and confirm that disc breaking is widespread and enhances accretion on to the central object. For some inclinations, the disc goes through strong Kozai cycles. Disc breaking promotes markedly enhanced and variable accretion and potentially produces high-energy particles or radiation through shocks. This would have significant implications for all binary systems: e.g. accretion outbursts in X-ray binaries and fuelling supermassive black hole (SMBH) binaries. The behaviour we have discussed in this work is relevant to a variety of astrophysical systems, for example X-ray binaries, where the disc plane may be tilted by radiation warping, SMBH binaries, where accretion of misaligned gas can create effectively random inclinations and protostellar binaries, where a disc may be misaligned by a variety of effects such as binary capture/exchange, accretion after binary formation.

  17. A pure hydrodynamic origin of accretion disk turbulence

    NASA Astrophysics Data System (ADS)

    Nath, Sujit Kumar; Mukhopadhyay, Banibrata

    2016-07-01

    Accretion disks consist of flows for which angular velocity decreases but specific angular momentum increases with increasing radial coordinate. Such flows are Rayleigh stable, but must be turbulent in order to explain observed data. Since molecular viscosity is negligible in these systems, scientists have argued for turbulent viscosity for energy dissipation and hence to explain infall of matter. However, so far, the success to explain the origin of turbulence in accretion disks is done with caveats. Here we investigate the evolution of pure hydrodynamic perturbations in stochastically driven accretion disks. We show that the accretion flows, which are inevitably driven by stochastic noise, are hydrodynamically unstable under linear perturbations. We also argue that in accretion disks, stochastic forcing appears generically due to the presence of shear between different annuli of the disk. This work resolves the turbulence problem of accretion disks from pure hydrodynamics and explains the infall of matter for both hot and cold disks. This would help in explaining the origin of timing and spectral features in the disk flows generically.

  18. Selective logging: do rates of forest turnover in stems, species composition and functional traits decrease with time since disturbance? - A 45 year perspective.

    PubMed

    Osazuwa-Peters, Oyomoare L; Jiménez, Iván; Oberle, Brad; Chapman, Colin A; Zanne, Amy E

    2015-12-01

    Selective logging, the targeted harvesting of timber trees in a single cutting cycle, is globally rising in extent and intensity. Short-term impacts of selective logging on tropical forests have been widely investigated, but long-term effects on temporal dynamics of forest structure and composition are largely unknown. Understanding these long-term dynamics will help determine whether tropical forests are resilient to selective logging and inform choices between competing demands of anthropogenic use versus conservation of tropical forests. Forest dynamics can be studied within the framework of succession theory, which predicts that temporal turnover rates should decline with time since disturbance. Here, we investigated the temporal dynamics of a tropical forest in Kibale National Park, Uganda over 45 years following selective logging. We estimated turnover rates in stems, species composition, and functional traits (wood density and diameter at breast height), using observations from four censuses in 1989, 1999, 2006, and 2013, of stems ≥ 10 cm diameter within 17 unlogged and 9 logged 200 × 10 m vegetation plots. We used null models to account for interdependencies among turnover rates in stems, species composition, and functional traits. We tested predictions that turnover rates should be higher and decrease with increasing time since the selective logging event in logged forest, but should be less temporally variable in unlogged forest. Overall, we found higher turnover rates in logged forest for all three attributes, but turnover rates did not decline through time in logged forest and was not less temporally variable in unlogged forest. These results indicate that successional models that assume recovery to pre-disturbance conditions are inadequate for predicting the effects of selective logging on the dynamics of the tropical forest in Kibale. Selective logging resulted in persistently higher turnover rates, which may compromise the carbon storage capacity

  19. Selective logging: do rates of forest turnover in stems, species composition and functional traits decrease with time since disturbance? – A 45 year perspective

    PubMed Central

    Osazuwa-Peters, Oyomoare L.; Jiménez, Iván; Oberle, Brad; Chapman, Colin A.; Zanne, Amy E.

    2015-01-01

    Selective logging, the targeted harvesting of timber trees in a single cutting cycle, is globally rising in extent and intensity. Short-term impacts of selective logging on tropical forests have been widely investigated, but long-term effects on temporal dynamics of forest structure and composition are largely unknown. Understanding these long-term dynamics will help determine whether tropical forests are resilient to selective logging and inform choices between competing demands of anthropogenic use versus conservation of tropical forests. Forest dynamics can be studied within the framework of succession theory, which predicts that temporal turnover rates should decline with time since disturbance. Here, we investigated the temporal dynamics of a tropical forest in Kibale National Park, Uganda over 45 years following selective logging. We estimated turnover rates in stems, species composition, and functional traits (wood density and diameter at breast height), using observations from four censuses in 1989, 1999, 2006, and 2013, of stems ≥ 10 cm diameter within 17 unlogged and 9 logged 200 × 10 m vegetation plots. We used null models to account for interdependencies among turnover rates in stems, species composition, and functional traits. We tested predictions that turnover rates should be higher and decrease with increasing time since the selective logging event in logged forest, but should be less temporally variable in unlogged forest. Overall, we found higher turnover rates in logged forest for all three attributes, but turnover rates did not decline through time in logged forest and was not less temporally variable in unlogged forest. These results indicate that successional models that assume recovery to pre-disturbance conditions are inadequate for predicting the effects of selective logging on the dynamics of the tropical forest in Kibale. Selective logging resulted in persistently higher turnover rates, which may compromise the carbon storage capacity

  20. X-ray and UV radiation from accreting nonmagnetic degenerate dwarfs. II

    NASA Technical Reports Server (NTRS)

    Kylafis, N. D.; Lamb, D. Q.

    1982-01-01

    Numerical calculations of X-ray and UV emission from accreting nonmagnetic degenerate dwarfs are reported, which span the entire range of accretion rates and stellar masses. Calculations include the effects of bremsstrahlung, Compton cooling, radiation pressure, albedo of the stellar surface, Compton degradation and free-free abscription of the X-ray spectrum by the accreting matter. Maximum X-ray luminosity for degenerate dwarfs undergoing spherical accretion is found to be 2.2 x 10 to the 36th ergs/s, which is little changed if accretion occurs radially over only a fraction of the stellar surface, so that the emitted radiation escapes without significant scattering. The temperature characterizing the X-ray spectra produced by degenerate dwarfs strongly depends on the stellar mass and the accretion rate, and it is suggested that the correlation between spectral temperature and luminosity is an important signature of degenerate X-ray sources.

  1. Modifying two-body relaxation in N-body systems by gas accretion

    NASA Astrophysics Data System (ADS)

    Leigh, Nathan; Sills, Alison; Böker, Torsten

    2013-08-01

    We consider the effects that accretion from the interstellar medium on to the particles of an N-body system has on the rate of two-body relaxation. To this end, we derive an accretion-modified relaxation time by adapting Spitzer's two-component model to include the damping effects of accretion. We consider several different mass- dependences and efficiency factors for the accretion rate, as well as different mass ratios for the two components of the model. The net effect of accretion is to accelerate mass segregation by increasing the average mass bar{m}, since the relaxation time is inversely proportional to bar{m}. Under the assumption that the accretion rate increases with the accretor mass, there are two additional effects that accelerate mass segregation. First, accretion acts to increase the range of any initial mass spectrum, quickly driving the heaviest members to even higher masses. Secondly, accretion acts to reduce the velocities of the accretors due to conservation of momentum, and it is the heaviest members that are affected the most. Using our two-component model, we quantify these effects as a function of the accretion rate, the total cluster mass and the component masses. We conclude by discussing the implications of our results for the dynamical evolution of primordial globular clusters, primarily in the context of black holes formed from the most massive stellar progenitors.

  2. MODELING THE ACCRETION STRUCTURE OF AU Mon

    SciTech Connect

    Atwood-Stone, Corwin; Miller, Brendan P.; Richards, Mercedes T.; Budaj, Jan; Peters, Geraldine J. E-mail: mbrendan@umich.edu E-mail: budaj@ta3.sk

    2012-12-01

    AU Mon is a long-period (11.113 days) Algol-type binary system with a persistent accretion disk that is apparent as double-peaked H{alpha} emission. We present previously unpublished optical spectra of AU Mon which were obtained over 20 years from 1991-2011 with dense orbital phase coverage. We utilize these data, along with archival UV spectra, to model the temperature and structure of the accretion disk and the gas stream. Synthetic spectral profiles for lines including H{alpha}, H{beta}, and the Al III and Si IV doublets were computed with the Shellspec program. The best match between the model spectra and the observations is obtained for an accretion disk of inner/outer radius 5.1/23 R {sub Sun }, thickness of 5.2 R {sub Sun }, density of 1.0 Multiplication-Sign 10{sup -13} g cm{sup -3}, and maximum temperature of 14,000 K, along with a gas stream at a temperature of {approx}8000 K transferring {approx}2.4 Multiplication-Sign 10{sup -9} M {sub Sun} yr{sup -1}. We show H{alpha} Doppler tomograms of the velocity structure of the gas, constructed from difference profiles calculated through sequentially subtracting contributions from the stars and accretion structures. The tomograms provide independent support for the Shellspec modeling, while also illustrating that residual emission at sub-Keplerian velocities persists even after subtracting the disk and stream emission. Spectral variability in the H{alpha} profile beyond that expected from either the orbital or the long-period cycle is present on both multi-week and multi-year timescales, and may reflect quasi-random changes in the mass transfer rate or the disk structure. Finally, a transient UV spectral absorption feature may be modeled as an occasional outflow launched from the vicinity of the disk-stream interaction region.

  3. ELECTROMAGNETIC SPINDOWN OF A TRANSIENT ACCRETING MILLISECOND PULSAR DURING QUIESCENCE

    SciTech Connect

    Melatos, A.; Mastrano, A. E-mail: alpham@unimelb.edu.au

    2016-02-10

    The measured spindown rates in quiescence of the transient accreting millisecond pulsars IGR J00291+5934, XTE J1751–305, SAX J1808.4–3658, and Swift J1756.9–2508 have been used to estimate the magnetic moments of these objects assuming standard magnetic dipole braking. It is shown that this approach leads to an overestimate if the amount of residual accretion is enough to distort the magnetosphere away from a force-free configuration through magnetospheric mass loading or crushing, so that the lever arm of the braking torque migrates inside the light cylinder. We derive an alternative spindown formula and calculate the residual accretion rates where the formula is applicable. As a demonstration we apply the alternative spindown formula to produce updated magnetic moment estimates for the four objects above. We note that based on current uncertain observations of quiescent accretion rates, magnetospheric mass loading and crushing are neither firmly indicated nor ruled out in these four objects. Because quiescent accretion rates are not measured directly (only upper limits are placed), without more data it is impossible to be confident about whether the thresholds for magnetospheric mass loading or crushing are reached or not.

  4. Electromagnetic Spindown of a Transient Accreting Millisecond Pulsar During Quiescence

    NASA Astrophysics Data System (ADS)

    Melatos, A.; Mastrano, A.

    2016-02-01

    The measured spindown rates in quiescence of the transient accreting millisecond pulsars IGR J00291+5934, XTE J1751-305, SAX J1808.4-3658, and Swift J1756.9-2508 have been used to estimate the magnetic moments of these objects assuming standard magnetic dipole braking. It is shown that this approach leads to an overestimate if the amount of residual accretion is enough to distort the magnetosphere away from a force-free configuration through magnetospheric mass loading or crushing, so that the lever arm of the braking torque migrates inside the light cylinder. We derive an alternative spindown formula and calculate the residual accretion rates where the formula is applicable. As a demonstration we apply the alternative spindown formula to produce updated magnetic moment estimates for the four objects above. We note that based on current uncertain observations of quiescent accretion rates, magnetospheric mass loading and crushing are neither firmly indicated nor ruled out in these four objects. Because quiescent accretion rates are not measured directly (only upper limits are placed), without more data it is impossible to be confident about whether the thresholds for magnetospheric mass loading or crushing are reached or not.

  5. Terrestrial Planets Accreted Dry

    NASA Astrophysics Data System (ADS)

    Albarede, F.; Blichert-Toft, J.

    2007-12-01

    Plate tectonics shaped the Earth, whereas the Moon is a dry and inactive desert. Mars probably came to rest within the first billion years of its history, and Venus, although internally very active, has a dry inferno for its surface. The strong gravity field of a large planet allows for an enormous amount of gravitational energy to be released, causing the outer part of the planetary body to melt (magma ocean), helps retain water on the planet, and increases the pressure gradient. The weak gravity field and anhydrous conditions prevailing on the Moon stabilized, on top of its magma ocean, a thick buoyant plagioclase lithosphere, which insulated the molten interior. On Earth, the buoyant hydrous phases (serpentines) produced by reactions between the terrestrial magma ocean and the wet impactors received from the outer Solar System isolated the magma and kept it molten for some few tens of million years. The elemental distributions and the range of condensation temperatures show that the planets from the inner Solar System accreted dry. The interior of planets that lost up to 95% of their K cannot contain much water. Foundering of their wet surface material softened the terrestrial mantle and set the scene for the onset of plate tectonics. This very same process may have removed all the water from the surface of Venus 500 My ago and added enough water to its mantle to make its internal dynamics very strong and keep the surface very young. Because of a radius smaller than that of the Earth, not enough water could be drawn into the Martian mantle before it was lost to space and Martian plate tectonics never began. The radius of a planet therefore is the key parameter controlling most of its evolutional features.

  6. Evolution of accretion disks in tidal disruption events

    SciTech Connect

    Shen, Rong-Feng; Matzner, Christopher D. E-mail: matzner@astro.utoronto.ca

    2014-04-01

    During a stellar tidal disruption event (TDE), an accretion disk forms as stellar debris returns to the disruption site and circularizes. Rather than being confined within the circularizing radius, the disk can spread to larger radii to conserve angular momentum. A spreading disk is a source of matter for re-accretion at rates that may exceed the later stellar fallback rate, although a disk wind can suppress its contribution to the central black hole accretion rate. A spreading disk is detectible through a break in the central accretion rate history or, at longer wavelengths, by its own emission. We model the evolution of TDE disk size and accretion rate by accounting for the time-dependent fallback rate, for the influence of wind losses in the early advective stage, and for the possibility of thermal instability for accretion rates intermediate between the advection-dominated and gas-pressure-dominated states. The model provides a dynamic basis for modeling TDE light curves. All or part of a young TDE disk will precess as a solid body because of the Lense-Thirring effect, and precession may manifest itself as a quasi-periodic modulation of the light curve. The precession period increases with time. Applying our results to the jetted TDE candidate Swift J1644+57, whose X-ray light curve shows numerous quasi-periodic dips, we argue that the data best fit a scenario in which a main-sequence star was fully disrupted by an intermediate mass black hole on an orbit significantly inclined from the black hole equator, with the apparent jet shutoff at t = 500 days corresponding to a disk transition from the advective state to the gas-pressure-dominated state.

  7. Evolution of Accretion Disks in Tidal Disruption Events

    NASA Astrophysics Data System (ADS)

    Shen, Rong-Feng; Matzner, Christopher D.

    2014-04-01

    During a stellar tidal disruption event (TDE), an accretion disk forms as stellar debris returns to the disruption site and circularizes. Rather than being confined within the circularizing radius, the disk can spread to larger radii to conserve angular momentum. A spreading disk is a source of matter for re-accretion at rates that may exceed the later stellar fallback rate, although a disk wind can suppress its contribution to the central black hole accretion rate. A spreading disk is detectible through a break in the central accretion rate history or, at longer wavelengths, by its own emission. We model the evolution of TDE disk size and accretion rate by accounting for the time-dependent fallback rate, for the influence of wind losses in the early advective stage, and for the possibility of thermal instability for accretion rates intermediate between the advection-dominated and gas-pressure-dominated states. The model provides a dynamic basis for modeling TDE light curves. All or part of a young TDE disk will precess as a solid body because of the Lense-Thirring effect, and precession may manifest itself as a quasi-periodic modulation of the light curve. The precession period increases with time. Applying our results to the jetted TDE candidate Swift J1644+57, whose X-ray light curve shows numerous quasi-periodic dips, we argue that the data best fit a scenario in which a main-sequence star was fully disrupted by an intermediate mass black hole on an orbit significantly inclined from the black hole equator, with the apparent jet shutoff at t = 500 days corresponding to a disk transition from the advective state to the gas-pressure-dominated state.

  8. Stent type used does not impact complication rate or placement time but can decrease treatment cost for benign and malignant esophageal lesions

    PubMed Central

    McGaw, Camille; Alkaddour, Ahmad; Vega, Kenneth J; Munoz, Juan Carlos

    2016-01-01

    AIM: To evaluate if differences exist between self-expanding esophageal metal stents (SEMS) and self-expanding esophageal plastic stents (SEPS) when used for benign or malignant esophageal disorders with regard to safety, efficacy, clinical outcomes, placement ease and cost. METHODS: A retrospective analysis was performed to evaluate outcome in patients having SEPS/SEMS placed for malignant or benign esophageal conditions from January 2005 to April 2012. Inclusion criteria was completed SEMS/SEPS placement. Outcomes assessed included technical success of and time required for stent placement, procedure-related complications, need for repeat intervention, hospital stay, mortality and costs. RESULTS: Forty-three patients underwent stent placement for either benign/malignant esophageal disease during the study period. Thirty patients had SEMS (25 male, mean age 59.6 years old) and 13 patients had SEPS (10 male, mean age 61.7 years old). Placement outcome as well as complication rate (SEPS 23.1%, SEMS 25.2%) and in-hospital mortality (SEPS 7.7%, SEMS 6.7%) after placement did not differ between stent types. Migration was the most frequent complication reported occurring equally between types (SEPS 66.7%, SEMS 57.1%). SEPS was less costly than SEMS, decreasing institutional cost by $255/stent. CONCLUSION: SEPS and SEMS have similar outcomes when used for benign or malignant esophageal conditions. However, SEPS use results in decreased costs without impacting care. PMID:27076872

  9. Salicylic acid treatment via the rooting medium interferes with stomatal response, CO2 fixation rate and carbohydrate metabolism in tomato, and decreases harmful effects of subsequent salt stress.

    PubMed

    Poór, P; Gémes, K; Horváth, F; Szepesi, A; Simon, M L; Tari, I

    2011-01-01

    Salicylic acid (SA) applied at 10(-3) m in hydroponic culture decreased stomatal conductance (g(s)), maximal CO(2) fixation rate (A(max) ) and initial slopes of the CO(2) (A/C(i)) and light response (A/PPFD) curves, carboxylation efficiency of Rubisco (CE) and photosynthetic quantum efficiency (Q), resulting in the death of tomato plants. However, plants could acclimate to lower concentrations of SA (10(-7) -10(-4) m) and, after 3 weeks, returned to control levels of g(s), photosynthetic performance and soluble sugar content. In response to high salinity (100 mm NaCl), the pre-treated plants exhibited higher A(max) as a function of internal CO(2) concentration (C(i) ) or photosynthetic photon flux density (PPFD), and higher CE and Q values than salt-treated controls, suggesting more effective photosynthesis after SA treatment. Growth in 10(-7) or 10(-4) m SA-containing solution led to accumulation of soluble sugars in both leaf and root tissues, which remained higher in both plant parts during salt stress at 10(-4) m SA. The activity of hexokinase (HXK) with glucose, but not fructose, as substrate was reduced by SA treatment in leaf and root samples, leading to accumulation of glucose and fructose in leaf tissues. HXK activity decreased further under high salinity in both plant organs. The accumulation of soluble sugars and sucrose in roots of plants growing in the presence of 10(-4) m SA contributed to osmotic adjustment and improved tolerance to subsequent salt stress. Apart from its putative role in delaying senescence, decreased HXK activity may divert hexoses from catabolic reactions to osmotic adaptation.

  10. Quasispherical subsonic accretion in X-ray pulsars

    NASA Astrophysics Data System (ADS)

    Shakura, Nikolai I.; Postnov, Konstantin A.; Kochetkova, A. Yu; Hjalmarsdotter, L.

    2013-04-01

    A theoretical model is considered for quasispherical subsonic accretion onto slowly rotating magnetized neutron stars. In this regime, the accreting matter settles down subsonically onto the rotating magnetosphere, forming an extended quasistatic shell. Angular momentum transfer in the shell occurs via large-scale convective motions resulting, for observed pulsars, in an almost iso-angular-momentum \\omega \\sim 1/R^2 rotation law inside the shell. The accretion rate through the shell is determined by the ability of the plasma to enter the magnetosphere due to Rayleigh-Taylor instabilities, with allowance for cooling. A settling accretion regime is possible for moderate accretion rates \\dot M \\lesssim \\dot M_* \\simeq 4\\times 10^{16} g s ^{-1}. At higher accretion rates, a free-fall gap above the neutron star magnetosphere appears due to rapid Compton cooling, and the accretion becomes highly nonstationary. Observations of spin-up/spin-down rates of quasispherically wind accreting equilibrium X-ray pulsars with known orbital periods (e.g., GX 301-2 and Vela X-1) enable us to determine the main dimensionless parameters of the model, as well as to estimate surface magnetic field of the neutron star. For equilibrium pulsars, the independent measurements of the neutron star magnetic field allow for an estimate of the stellar wind velocity of the optical companion without using complicated spectroscopic measurements. For nonequilibrium pulsars, a maximum value is shown to exist for the spin-down rate of the accreting neutron star. From observations of the spin-down rate and the X-ray luminosity in such pulsars (e.g., GX 1+4, SXP 1062, and 4U 2206+54), a lower limit can be put on the neutron star magnetic field, which in all cases turns out to be close to the standard value and which agrees with cyclotron line measurements. Furthermore, both explains the spin-up/spin-down of the pulsar frequency on large time-scales and also accounts for the irregular short

  11. Black hole growth and AGN feedback under clumpy accretion

    NASA Astrophysics Data System (ADS)

    DeGraf, C.; Dekel, A.; Gabor, J.; Bournaud, F.

    2017-04-01

    High-resolution simulations of supermassive black holes in isolated galaxies have suggested the importance of short (∼10 Myr) episodes of rapid accretion caused by interactions between the black hole and massive dense clouds within the host. Accretion of such clouds could potentially provide the dominant source for black hole growth in high-z galaxies, but it remains unresolved in cosmological simulations. Using a stochastic subgrid model calibrated by high-resolution isolated galaxy simulations, we investigate the impact that variability in black hole accretion rates has on black hole growth and the evolution of the host galaxy. We find this clumpy accretion to more efficiently fuel high-redshift black hole growth. This increased mass allows for more rapid accretion even in the absence of high-density clumps, compounding the effect and resulting in substantially faster overall black hole growth. This increased growth allows the black hole to efficiently evacuate gas from the central region of the galaxy, driving strong winds up to ∼2500 km s-1, producing outflows ∼10 × stronger than the smooth accretion case, suppressing the inflow of gas on to the host galaxy, and suppressing the star formation within the galaxy by as much as a factor of 2. This suggests that the proper incorporation of variability is a key factor in the co-evolution between black holes and their hosts.

  12. A Systems-Level Perspective on Engine Ice Accretion

    NASA Technical Reports Server (NTRS)

    May, Ryan D.; Guo, Ten-Huei; Simon, Donald L.

    2013-01-01

    The accretion of ice in the compression system of commercial gas turbine engines operating in high ice water content conditions is a safety issue being studied by the aviation sector. While most of the research focuses on the underlying physics of ice accretion and the meteorological conditions in which accretion can occur, a systems-level perspective on the topic lends itself to potential near-term operational improvements. This work focuses on developing an accurate and reliable algorithm for detecting the accretion of ice in the low pressure compressor of a generic 40,000 lbf thrust class engine. The algorithm uses only the two shaft speed sensors and works regardless of engine age, operating condition, and power level. In a 10,000-case Monte Carlo simulation, the detection approach was found to have excellent capability at determining ice accretion from sensor noise with detection occurring when ice blocks an average of 6.8% of the low pressure compressor area. Finally, an initial study highlights a potential mitigation strategy that uses the existing engine actuators to raise the temperature in the low pressure compressor in an effort to reduce the rate at which ice accretes.

  13. TW Hya: SPECTRAL VARIABILITY, X-RAYS, AND ACCRETION DIAGNOSTICS

    SciTech Connect

    Dupree, A. K.; Brickhouse, N. S.; Cranmer, S. R.; Luna, G. J. M.; Schneider, E. E.; Bessell, M. S.; Bonanos, A.; Crause, L. A.; Lawson, W. A.; Mallik, S. V.; Schuler, S. C.

    2012-05-01

    The nearest accreting T Tauri star, TW Hya was intensively and continuously observed over {approx}17 days with spectroscopic and photometric measurements from four continents simultaneous with a long segmented exposure using the Chandra satellite. Contemporaneous optical photometry from WASP-S indicates a 4.74 day period was present during this time. The absence of a similar periodicity in the H{alpha} flux and the total X-ray flux which are dominated by accretion processes and the stellar corona, respectively, points to a different source of photometric variations. The H{alpha} emission line appears intrinsically broad and symmetric, and both the profile and its variability suggest an origin in the post-shock cooling region. An accretion event, signaled by soft X-rays, is traced spectroscopically for the first time through the optical emission line profiles. After the accretion event, downflowing turbulent material observed in the H{alpha} and H{beta} lines is followed by He I ({lambda}5876) broadening near the photosphere. Optical veiling resulting from the heated photosphere increases with a delay of {approx}2 hr after the X-ray accretion event. The response of the stellar coronal emission to an increase in the veiling follows {approx}2.4 hr later, giving direct evidence that the stellar corona is heated in part by accretion. Subsequently, the stellar wind becomes re-established. We suggest a model that incorporates the dynamics of this sequential series of events: an accretion shock, a cooling downflow in a supersonically turbulent region, followed by photospheric and later, coronal heating. This model naturally explains the presence of broad optical and ultraviolet lines, and affects the mass accretion rates determined from emission line profiles.

  14. Lunar Accretion and the Moon’s Initial Thermal State

    NASA Astrophysics Data System (ADS)

    Salmon, Julien; Canup, R. M.

    2012-10-01

    Previous models of lunar formation from an impact-generated disk predict the Moon accretes in less than a year (Ida et al. 1997, Kokubo et al. 2000). Such a rapid accretion implies a fully molten initial Moon (e.g., Pritchard & Stevenson 2000). However, the lack of global faults on the Moon has been interpreted as constraining the depth of initial melting to the Moon’s outer few hundred kilometers (Solomon & Chaiken 1976). Depth estimates for the lunar magma ocean (250 to 1000 km; e.g., Shearer et al. 2006) are also typically less than the Moon’s full radius (1738 km). Taken at face value, such observations appear most consistent with a partially molten initial Moon. We have developed a new lunar accretion model that includes a more accurate description of the inner protolunar disk, taking into account thermal processes that limit the disk’s evolution rate (Salmon and Canup 2012). Our model predicts a 3-phase accretion of the Moon, in which material initially orbiting in the outer disk accumulates rapidly, followed by a much slower evolution of the vapor/fluid inner disk and a final phase of accretion of inner disk material onto the Moon. The Moon’s total accretion then occurs over about 100 years, which could be compatible with partial cooling of protolunar material. We have coupled our accretion model to a simple model for the Moon’s initial thermal state. We use a 3D spherical grid to model the forming Moon. We estimate heating due to each accretionary event using the impactor properties predicted by our accretion model, assuming that a fixed fraction ("h") of each impactor’s kinetic energy is retained locally within the Moon’s interior, and include cooling from the Moon’s surface. We use this model to estimate the Moon’s initial thermal state as a function of h and specific accretionary histories.

  15. Accretion and Structure in the SW Sextantis Stars

    NASA Astrophysics Data System (ADS)

    Hoard, Donald Wayne

    1998-09-01

    The SW Sextantis stars are cataclysmic variables (CVs) sharing properties that set them apart from other CVs. These include: strong He II λ4686 emission, velocity curves implying asymmetric disk emission, and variable line profiles displaying a transient absorption feature at specific orbital phases. A number of mechanisms have been proposed to explain these characteristics including (non-disk) circumstellar material, a bipolar disk wind, a white dwarf magnetic field, and coherent accretion stream overflow across the disk, but none has been completely satisfying. I present the results of new photometric and spectroscopic observations of seven SW Sex stars, including Doppler tomogram mapping of emission regions in these systems. These observations, along with recent advances in simulations of accretion disks, suggest a scenario in which the accretion stream undergoes a violent impact with the disk edge. Depending on the mass transfer rate in the stream, the impact site will either cool efficiently (low M) and allow substantial material to flow directly over the disk, or will cool inefficiently (high M) and form a prominent bright spot at the impact site with hot stream material swept 'downstream' along the disk edge. In the former case, non-axisymmetric vertical structure develops in the disk at the terminus of the stream overflow (accounting for absorption seen at φapprox0.5), while in the latter case vertical structure is built up along the disk edge (accounting for absorption at φapprox0.8). The absorption feature phasing in different SW Sex stars implies M decreases as P orb decreases (as expected during CV evolution), but it is not clear whether normal CV evolution can drive changes in M rapidly enough to generate the onset of the SW Sex phenomenon in the narrow range of orbital period they occupy (P orb=3[-]4 hr). I present a gallery of new and archived IUE spectra of the SW Sex stars that display the typically strong UV resonant scattering lines seen in

  16. Core Accretion - Gas Capture Model for Gas Giant Planet Formation

    NASA Astrophysics Data System (ADS)

    Hubickyj, O.; Bodenheimer, P.; Lissauer, J. J.

    2005-12-01

    The core accretion - gas capture model is generally accepted as the standard formation model for gas giant planets. This model proposes that a solid core grows via the accretion of planetesimals and then captures a massive envelope from the solar nebula gas. Simulations based on this model (Pollack et al. 1996, Bodenheimer et al. 2000) have been successful in explaining many features of giant planets. We have computed simulations (Hubickyj et al. 2005) of the growth of Jupiter using various values for the opacity produced by grains in the protoplanet's atmosphere and for the initial planetesimal surface density in the protoplanetary disk. We also explore the implications of halting the solid accretion at selected core mass values during the protoplanet's growth. Halting planetesimal accretion at low core mass simulates the presence of a competing embryo, and decreasing the atmospheric opacity due to grains emulates the settling and coagulation of grains within the protoplanet's atmosphere. We examine the effects of adjusting these parameters to determine whether or not gas runaway can occur for small mass cores on a reasonable timescale. Our results demonstrate that reducing grain opacities results in formation times less than half of those for models computed with full interstellar grain opacity values. The reduction of opacity due to grains in the upper portion of the envelope with T ≤ 500 K has the largest effect on the lowering of the formation time. If the accretion of planetesimals is not cut off prior to the accretion of gas, then decreasing the surface density of planetesimals lowers the final core mass of the protoplanet, but increases the formation timescale considerably. Finally, a core mass cutoff results in a reduction of the time needed for a protoplanet to evolve to the stage of runaway gas accretion, provided the cutoff mass is sufficiently large. The overall results indicate that, with reasonable parameters, it is possible that Jupiter formed at

  17. Appetite - decreased

    MedlinePlus

    ... cancer Ovarian cancer Stomach cancer Pancreatic cancer Other causes of decreased appetite include: Chronic liver disease Chronic kidney disease Chronic obstructive pulmonary disease (COPD) Dementia Heart failure ...

  18. Decreasing population selection rates of resistance mutation K65R over time in HIV-1 patients receiving combination therapy including tenofovir

    PubMed Central

    Theys, K.; Snoeck, J.; Vercauteren, J.; Abecasis, A. B.; Vandamme, A.-M.; Camacho, R. J.

    2013-01-01

    Objectives The use of tenofovir is highly associated with the emergence of mutation K65R, which confers broad resistance to nucleoside/nucleotide analogue reverse transcriptase inhibitors (NRTIs), especially when tenofovir is combined with other NRTIs also selecting for K65R. Although recent HIV-1 treatment guidelines discouraging these combinations resulted in reduced K65R selection with tenofovir, updated information on the impact of currently recommended regimens on the population selection rate of K65R is presently lacking. Methods In this study, we evaluated changes over time in the selection rate of resistance mutation K65R in a large population of 2736 HIV-1-infected patients failing combination antiretroviral treatment between 2002 and 2010. Results The K65R resistance mutation was detected in 144 patients, a prevalence of 5.3%. A large majority of observed K65R cases were explained by the use of tenofovir, reflecting its wide use in clinical practice. However, changing patterns over time in NRTIs accompanying tenofovir resulted in a persistent decreasing probability of K65R selection by tenofovir-based therapy. The currently recommended NRTI combination tenofovir/emtricitabine was associated with a low probability of K65R emergence. For any given dual NRTI combination including tenofovir, higher selection rates of K65R were consistently observed with a non-nucleoside reverse transcriptase inhibitor than with a protease inhibitor as the third agent. Discussion Our finding of a stable time trend of K65R despite elevated use of tenofovir illustrates increased potency of current HIV-1 therapy including tenofovir. PMID:23027713

  19. Warm gas accretion onto the Galaxy

    NASA Astrophysics Data System (ADS)

    Bland-Hawthorn, J.

    2009-03-01

    We present evidence that the accretion of warm gas onto the Galaxy today is at least as important as cold gas accretion. For more than a decade, the source of the bright Hα emission (up to 750 mR†) along the Magellanic Stream has remained a mystery. We present a hydrodynamical model that explains the known properties of the Hα emission and provides new insights on the lifetime of the Stream clouds. The upstream clouds are gradually disrupted due to their interaction with the hot halo gas. The clouds that follow plough into gas ablated from the upstream clouds, leading to shock ionisation at the leading edges of the downstream clouds. Since the following clouds also experience ablation, and weaker Hα (100-200 mR) is quite extensive, a disruptive cascade must be operating along much of the Stream. In order to light up much of the Stream as observed, it must have a small angle of attack (≈ 20°) to the halo, and this may already find support in new Hi observations. Another prediction is that the Balmer ratio (Hα/Hβ) will be substantially enhanced due to the slow shock; this will soon be tested by upcoming WHAM observations in Chile. We find that the clouds are evolving on timescales of 100-200 Myr, such that the Stream must be replenished by the Magellanic Clouds at a fairly constant rate (≳ 0.1 M⊙ yr-1). The ablated material falls onto the Galaxy as a warm drizzle; diffuse ionized gas at 104 K is an important constituent of galactic accretion. The observed Hα emission provides a new constraint on the rate of disruption of the Stream and, consequently, the infall rate of metal-poor gas onto the Galaxy. We consider the stability of Hi clouds falling towards the Galactic disk and show that most of these must break down into smaller fragments that become partially ionized. The Galactic halo is expected to have huge numbers of smaller neutral and ionized fragments. When the ionized component of the infalling gas is accounted for, the rate of gas accretion is

  20. Hyper-Eddington accretion flows on to massive black holes

    NASA Astrophysics Data System (ADS)

    Inayoshi, Kohei; Haiman, Zoltán; Ostriker, Jeremiah P.

    2016-07-01

    We study very high rate, spherically symmetric accretion flows on to massive black holes (BHs; 102 ≲ MBH ≲ 106 M⊙) embedded in dense metal-poor clouds, performing one-dimensional radiation hydrodynamical simulations. We find solutions from outside the Bondi radius at hyper-Eddington rates, unimpeded by radiation feedback when (n∞/105 cm-3) > (MBH/104 M⊙)-1(T∞/104 K)3/2, where n∞ and T∞ are the density and temperature of ambient gas. Accretion rates in this regime are steady, and larger than 5000LEdd/c2, where LEdd is the Eddington luminosity. At lower Bondi rates, the accretion is episodic due to radiative feedback and the average rate is below the Eddington rate. In the hyper-Eddington case, the solution consists of a radiation-dominated central core, where photon trapping due to electron scattering is important, and an accreting envelope which follows a Bondi profile with T ≃ 8000 K. When the emergent luminosity is limited to ≲ LEdd because of photon trapping, radiation from the central region does not affect the gas dynamics at larger scales. We apply our result to the rapid formation of massive BHs in protogalaxies with a virial temperature of Tvir ≳ 104K. Once a seed BH forms at the centre of the galaxy, it can grow to a maximum ˜105(Tvir/104 K) M⊙ via gas accretion independent of the initial BH mass. Finally, we discuss possible observational signatures of rapidly accreting BHs with/without allowance for dust. We suggest that these systems could explain Lyα emitters without X-rays and nearby luminous infrared sources with hot dust emission, respectively.

  1. Numerical and experimental study of magnetized accretion phenomena in young stars

    NASA Astrophysics Data System (ADS)

    Khiar, Benjamin; Ciardi, Andrea; Revet, Guilhem; Vinci, Tommaso; Fuchs, Julien; Orlando, Salvatore; Inaf Team; Luli Team; Lerma Team

    2016-10-01

    Newly formed stars accrete mass from the circumstellar disc via magnetized accretion funnels that connect the inner disc regions to the star. The ensuing impact of this free-falling plasma onto the stellar surface generates a strong shock, whose emission is used as a proxy to determine the accretion rates. Observations show that the X-ray luminosity arising from the shock heated plasma at the base of accretion columns is largelybelow the value expected on the basis of optical/UV observations. As a result, current 2D numerical simulations matching X-ray accretion rates cannot reproduce optical accretion rates. To understand the impact of accretion flows on the stellar surface in the presence of a strong magnetic field we have developed laboratory experiments reproducing crucial aspects of the accretion dynamics in Young Stellar Objects. As a model of accretion columns, we use laser-produced super-Alfvenic magnetically confined jets to collide them on solid targets. Here we present results from these experiments and from multi-dimensional MHD simulations. The authors acknowledge the support from the Ile-de-France DIM ACAV, from the LABEX Plas@par and from the ANR Grant SILAMPA.

  2. Influence of hydrodynamic energy on Holocene reef flat accretion, Great Barrier Reef

    NASA Astrophysics Data System (ADS)

    Dechnik, Belinda; Webster, Jody M.; Nothdurft, Luke; Webb, Gregory E.; Zhao, Jian-xin; Duce, Stephanie; Braga, Juan C.; Harris, Daniel L.; Vila-Concejo, Ana; Puotinen, Marji

    2016-01-01

    The response of platform reefs to sea-level stabilization over the past 6 ka is well established for the Great Barrier Reef (GBR), with reefs typically accreting laterally from windward to leeward. However, these observations are based on few cores spread across reef zones and may not accurately reflect a reef's true accretional response to the Holocene stillstand. We present a new record of reef accretion based on 49 U/Th ages from Heron and One Tree reefs in conjunction with re-analyzed data from 14 reefs across the GBR. We demonstrate that hydrodynamic energy is the main driver of accretional direction; exposed reefs accreted primarily lagoon-ward while protected reefs accreted seawards, contrary to the traditional growth model in the GBR. Lateral accretion rates varied from 86.3 m/ka-42.4 m/ka on the exposed One Tree windward reef and 68.35 m/ka-15.7 m/ka on the protected leeward Heron reef, suggesting that wind/wave energy is not a dominant control on lateral accretion rates. This represents the most comprehensive statement of lateral accretion direction and rates from the mid-outer platform reefs of the GBR, confirming great variability in reef flat growth both within and between reef margins over the last 6 ka, and highlighting the need for closely-spaced transects.

  3. Detection of a Cool, Accretion-Shock-Generated X-Ray Plasma in EX Lupi During the 2008 Optical Eruption

    NASA Technical Reports Server (NTRS)

    Teets, William K.; Weintraub, David A.; Kastner, Joel H.; Grosso, Nicholas; Hamaguchi, Kenji; Richmond, Michael

    2012-01-01

    EX Lupi is the prototype for a class of young, pre-main-sequence stars which are observed to undergo irregular, presumably accretion-generated, optical outbursts that result in a several magnitude rise of the optical flux. EX Lupi was observed to optically erupt in 2008 January, triggering Chandra ACIS Target of Opportunity observations shortly thereafter. We find very strong evidence that most of the X-ray emission in the first few months after the optical outburst is generated by accretion of circumstellar material onto the stellar photosphere. Specifically, we find a strong correlation between the decreasing optical and X-ray fluxes following the peak of the outburst in the optical, which suggests that these observed declines in both the optical and X-ray fluxes are the result of declining accretion rate. In addition, in our models of the X-ray spectrum, we find strong evidence for an approx 0.4 keV plasma component, as expected for accretion shocks on low-mass, pre-main-sequence stars. From 2008 March through October, this cool plasma component appeared to fade as EX Lupi returned to its quiescent level in the optical, consistent with a decrease in the overall emission measure of accretion-shock-generated plasma. The overall small increase of the X-ray flux during the optical outburst of EX Lupi is similar to what was observed in previous X-ray observations of the 2005 optical outburst of the EX Lupi-type star V1118 Ori but contrasts with the large increase of the X-ray flux from the erupting young star V1647 Ori during its 2003 and 2008 optical outbursts.

  4. Use and abuse of crustal accretion calculations

    NASA Astrophysics Data System (ADS)

    Pallister, John S.; Cole, James C.; Stoeser, Douglas B.; Quick, James E.

    1990-01-01

    Recent attempts to calculate the average growth rate of continental crust for the Late Proterozoic shield of Arabia and Nubia are subject to large geological uncertainties, and widely contrasting conclusions result from dissimilar boundary conditions. The four greatest sources of divergence are (1) the extent of 620-920 Ma arc-terrane crust beneath Phanerozoic cover; (2) the extent of pre-920 Ma continental crust within the arc terranes; (3) the amount of postaccretion magmatic addition and erosion; and (4) the aggregate length and average life span of Late Proterozoic magmatic-arc systems that formed the Arabian-Nubian Shield. Calculations restricted to the relatively well known Arabian segment of the Arabian-Nubian Shield result in average crustal growth rates and arc accretion rates comparable to rates for modern arc systems, but we recognize substantial uncertainty in such results. Critical review of available geochemical, isotopic, and geochronological evidence contradicts the often stated notion that intact, pre-920 Ma crust is widespread in the eastern Arabian Shield. Instead, the arc terranes of the region apparently were "contaminated" with sediments derived, in part, from pre-920 Ma crust. Available geologic and radiometric data indicate that the Arabian-Nubian Shield and its "Pan-African" extensions constitute the greatest known volume of arc-accreted crust on Earth that formed in the period 920-620 Ma. Thus, the region may truly represent a disproportionate share of Earth's crustal growth budget for this time period.

  5. Magnetic fields in primordial accretion disks

    NASA Astrophysics Data System (ADS)

    Latif, M. A.; Schleicher, D. R. G.

    2016-01-01

    Magnetic fields are considered a vital ingredient of contemporary star formation and may have been important during the formation of the first stars in the presence of an efficient amplification mechanism. Initial seed fields are provided via plasma fluctuations and are subsequently amplified by the small-scale dynamo, leading to a strong, tangled magnetic field. We explore how the magnetic field provided by the small-scale dynamo is further amplified via the α-Ω dynamo in a protostellar disk and assess its implications. For this purpose, we consider two characteristic cases, a typical Pop. III star with 10M⊙ and an accretion rate of 10-3M⊙ yr-1, and a supermassive star with 105M⊙ and an accretion rate of 10-1M⊙ yr-1. For the 10M⊙ Pop. III star, we find that coherent magnetic fields can be produced on scales of at least 100 AU, which are sufficient to drive a jet with a luminosity of 100L⊙ and a mass outflow rate of 10-3.7M⊙ yr-1. For the supermassive star, the dynamical timescales in its environment are even shorter, implying smaller orbital timescales and an efficient magnetization out to at least 1000 AU. The jet luminosity corresponds to ~106.0L⊙ and a mass outflow rate of 10-2.1M⊙ yr-1. We expect that the feedback from the supermassive star can have a relevant impact on its host galaxy.

  6. Accretion and canal impacts in a rapidly subsiding wetland II: Feldspar marker horizon technique

    USGS Publications Warehouse

    Cahoon, D.R.; Turner, R.E.

    1989-01-01

    Recent (6-12 months) marsh sediment accretion and accumulation rates were measured with feldspar marker horizons in the vicinity of natural waterways and man-made canals with spoil banks in the rapidly subsiding environment of coastal Louisiana. Annual accretion rates in a Spartina alterniflora salt marsh in the Mississippi deltaic plain averaged 6 mm in marsh adjacent to canals compared to 10 mm in marsh adjacent to natural waterways. The rates, however, were not statistically significantly different. The average rate of sediment accretion in the same salt marsh region for a transect perpendicular to a canal (13 mm yr-1) was significantly greater than the rate measured for a transect perpendicular to a natural waterway (7 mm yr-1). Measurements of soil bulk density and organic matter content from the two transects were also different. This spatial variability in accretion rates is probably related to (1) spoil bank influences on local hydrology; and (2) a locally high rate of sediment input from lateral erosion associated with pond enlargement. In a brackish Spatina patens marsh on Louisiana's chenier plain, vertical accretion rates were the same along natural and canal waterways (3-4 mm yr-1) in a hydrologically restricted marsh region. However, the accretion rates for both waterways were significantly lower than the rates along a nonhydrologically restricted natural waterway nearby (11 mm yr-1). The vertical accretion of matter displayed semi-annual differences in the brackish marsh environment.

  7. Growth of asteroids, planetary embryos, and Kuiper belt objects by chondrule accretion

    PubMed Central

    Johansen, Anders; Low, Mordecai-Mark Mac; Lacerda, Pedro; Bizzarro, Martin

    2015-01-01

    Chondrules are millimeter-sized spherules that dominate primitive meteorites (chondrites) originating from the asteroid belt. The incorporation of chondrules into asteroidal bodies must be an important step in planet formation, but the mechanism is not understood. We show that the main growth of asteroids can result from gas drag–assisted accretion of chondrules. The largest planetesimals of a population with a characteristic radius of 100 km undergo runaway accretion of chondrules within ~3 My, forming planetary embryos up to Mars’s size along with smaller asteroids whose size distribution matches that of main belt asteroids. The aerodynamical accretion leads to size sorting of chondrules consistent with chondrites. Accretion of millimeter-sized chondrules and ice particles drives the growth of planetesimals beyond the ice line as well, but the growth time increases above the disc lifetime outside of 25 AU. The contribution of direct planetesimal accretion to the growth of both asteroids and Kuiper belt objects is minor. In contrast, planetesimal accretion and chondrule accretion play more equal roles in the formation of Moon-sized embryos in the terrestrial planet formation region. These embryos are isolated from each other and accrete planetesimals only at a low rate. However, the continued accretion of chondrules destabilizes the oligarchic configuration and leads to the formation of Mars-sized embryos and terrestrial planets by a combination of direct chondrule accretion and giant impacts. PMID:26601169

  8. Growth of asteroids, planetary embryos, and Kuiper belt objects by chondrule accretion.

    PubMed

    Johansen, Anders; Low, Mordecai-Mark Mac; Lacerda, Pedro; Bizzarro, Martin

    2015-04-01

    Chondrules are millimeter-sized spherules that dominate primitive meteorites (chondrites) originating from the asteroid belt. The incorporation of chondrules into asteroidal bodies must be an important step in planet formation, but the mechanism is not understood. We show that the main growth of asteroids can result from gas drag-assisted accretion of chondrules. The largest planetesimals of a population with a characteristic radius of 100 km undergo runaway accretion of chondrules within ~3 My, forming planetary embryos up to Mars's size along with smaller asteroids whose size distribution matches that of main belt asteroids. The aerodynamical accretion leads to size sorting of chondrules consistent with chondrites. Accretion of millimeter-sized chondrules and ice particles drives the growth of planetesimals beyond the ice line as well, but the growth time increases above the disc lifetime outside of 25 AU. The contribution of direct planetesimal accretion to the growth of both asteroids and Kuiper belt objects is minor. In contrast, planetesimal accretion and chondrule accretion play more equal roles in the formation of Moon-sized embryos in the terrestrial planet formation region. These embryos are isolated from each other and accrete planetesimals only at a low rate. However, the continued accretion of chondrules destabilizes the oligarchic configuration and leads to the formation of Mars-sized embryos and terrestrial planets by a combination of direct chondrule accretion and giant impacts.

  9. Self-consistent evolution of accreting low-mass stars and brown dwarfs

    NASA Astrophysics Data System (ADS)

    Baraffe, I.; Elbakyan, V. G.; Vorobyov, E. I.; Chabrier, G.

    2017-01-01

    We present self-consistent calculations coupling numerical hydrodynamics simulations of collapsing pre-stellar cores and stellar evolution models of accreting objects. We analyse the main impact of consistent accretion history on the evolution and lithium depletion of young low-mass stars and brown dwarfs. These consistent models confirm the generation of a luminosity spread in Herzsprung-Russell diagrams at ages 1-10 Myr. They also confirm that early accretion can produce objects with abnormal Li depletion, as found in a previous study that was based on arbitrary accretion rates. The results strengthen that objects with anomalously high level of Li depletion in young clusters should be extremely rare. We also find that early phases of burst accretion can produce coeval models of similar mass with a range of different Li surface abundances, and in particular with Li-excess compared to the predictions of non-accreting counterparts. This result is due to a subtle competition between the effect of burst accretion and its impact on the central stellar temperature, the growth of the stellar radiative core and the accretion of fresh Li from the accretion disk. Only consistent models could reveal such a subtle combination of effects. This new result could explain the recent, puzzling observations of Li-excess of fast rotators in the young cluster NGC 2264. Present self-consistent accreting models are available in electronic form.

  10. Characterizing Accreting White Dwarf Pulsators

    NASA Astrophysics Data System (ADS)

    Szkody, Paula; Mukadam, Anjum

    2014-02-01

    Understanding the population, mass distribution, and evolution of accreting white dwarfs impacts the entire realm of binary interaction, including the creation of Type Ia supernovae. We are concentrating on accreting white dwarf pulsators, as the pulsation properties allow us a view of how the accretion affects the interior of the star. Our ground- based photometry on 11 accreting pulsators with corresponding temperatures from HST UV spectra suggest a broad instability strip in the range of 10500 to 16000K. Additionally, tracking a post-outburst heated white dwarf as it cools and crosses the blue edge and resumes pulsation provides an independent method to locate the empirical instability strip. Determining a post-outburst cooling curve yields an estimate of the amount of heating and the accreted mass during the outburst. We request additional photometry of 2 objects that present unique properties: GW Lib which has not yet returned to its pre-outburst pulsation spectrum after 6 yrs, and EQ Lyn which returned to its pre- outburst pulsation after 3 yrs but is now turning on and off without ongoing outbursts. Following the pulsation spectrum changes over stretches of several nights in a row will provide specific knowledge of the stability of the observed modes.

  11. Classical Accreting Pulsars with NICER

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.

    2014-01-01

    Soft excesses are very common center dot Lx > 1038 erg/s - reprocessing by optically thick material at the inner edge of the accretion disk center dot Lx < 1036 erg/s - photoionized or collisionally heated diffuse gas or thermal emission from the NS surface center dot Lx 1037 erg/s - either or both types of emission center dot NICER observations of soft excesses in bright X-ray pulsars combined with reflection modeling will constrain the ionization state, metalicity and dynamics of the inner edge of the magnetically truncated accretion disk Reflection models of an accretion disk for a hard power law - Strong soft excess below 3 keV from hot X-ray heated disk - For weakly ionized case: strong recombination lines - Are we seeing changes in the disk ionization in 4U1626-26? 13 years of weekly monitoring with RXTE PCA center dot Revealed an unexpectedly large population of Be/X-ray binaries compared to the Milky Way center dot Plotted luminosities are typical of "normal" outbursts (once per orbit) center dot The SMC provides an excellent opportunity to study a homogenous population of HMXBs with low interstellar absorption for accretion disk studies. Monitoring with NICER will enable studies of accretion disk physics in X-ray pulsars center dot The SMC provides a potential homogeneous low-absorption population for this study center dot NICER monitoring and TOO observations will also provide measurements of spinfrequencies, QPOs, pulsed fluxes, and energy spectra.

  12. Efficacy of intraoperative cell salvage in decreasing perioperative blood transfusion rates in first-time cardiac surgery patients: a retrospective study

    PubMed Central

    Côté, Claudia L.; Yip, Alexandra M.; MacLeod, Jeffrey B.; O’Reilly, Bill; Murray, Joshua; Ouzounian, Maral; Brown, Craig D.; Forgie, Rand; Pelletier, Marc P.; Hassan, Ansar

    2016-01-01

    Background Evidence regarding the safety and efficacy of intraoperative cell salvage (ICS) in transfusion reduction during cardiac surgery remains conflicting. We sought to evaluate the impact of routine ICS on outcomes following cardiac surgery. Methods We conducted a retrospective analysis of patients who underwent nonemergent, first-time cardiac surgery 18 months before and 18 months after the implementation of routine ICS. Perioperative transfusion rates, postoperative bleeding, clinical and hematological outcomes, and overall cost were examined. We used multivariable logistic regression modelling to determine the risk-adjusted effect of ICS on likelihood of perioperative transfusion. Results A total of 389 patients formed the final study population (186 undergoing ICS and 203 controls). Patients undergoing ICS had significantly lower perioperative transfusion rates of packed red blood cells (pRBCs; 33.9% v. 45.3% p = 0.021), coagulation products (16.7% v. 32.5% p < 0.001) and any blood product (38.2% v. 52.7%, p = 0.004). Patients receiving ICS had decreased mediastinal drainage at 12 h (mean 320 [range 230–550] mL v. mean 400 [range 260–690] mL, p = 0.011) and increased postoperative hemoglobin (mean 104.7 ± 13.2 g/L v. 95.0 ± 11.9 g/L, p < 0.001). Following adjustment for other baseline and intraoperative covariates, ICS emerged as an independent predictor of lower perioperative transfusion rates of pRBCs (odds ratio [OR] 0.52, 95% confidence interval [CI] 0.31–0.87), coagulation products (OR 0.41, 95% CI 0.24–0.71) and any blood product (OR 0.47, 95% CI 0.29–0.77). Additionally, ICS was associated with a cost benefit of $116 per patient. Conclusion Intraoperative cell salvage could represent a clinically cost-effective way of reducing transfusion rates in patients undergoing cardiac surgery. Further research on systematic ICS is required before recommending it for routine use. PMID:27668331

  13. Winds and accretion in delta Sagittae

    NASA Astrophysics Data System (ADS)

    Eaton, Joel A.; Hartkopf, William I.; McAlister, Harold A.; Mason, Brian D.

    1995-04-01

    The ten-year binary delta Sge (M2 Ib-II+B9.5 V) is a zeta Aur binary containing an abnormally cool component. Combining our analysis of the system as a visual binary with Batten's radial-velocity solution leads to the following properties: i = 40 deg, a = 51 mas = 8.83 A.U. = 1893 solar radius, hence d = 173 pc; MB = 2.9 solar mass and MM = 3.8 solar mass; and RB = 2.6 solar radius and RM = 152 solar radius. This interpretation of the orbit places the M supergiant on the asymptotic giant branch. We have collected ultraviolet spectra throughout the star's 1980-90 orbit, concentrated around the conjuction of 1990. The wind of the M giant appears in these as narrow shell lines of singly ionized metals, chiefly Fe II, with P-Cyg profiles at many phases, which show the slow variation in strength expected for the orbit but no pronounced atmospheric eclipse. The terminal velocity of the wind is 16-18 km/s, and its excitation temperature is approximately 10,000 K. Most of the broadening of the wind lines is caused by differential expansion of the atmosphere, with (unmeasurably) low turbulent velocities. Nontheless, the mass loss rate (1.1 +/- 0.4 X 10 -8 solar mas/yr) is almost the same as found previously by Reimers and Schroder for very different assumptions about the velocity structure. Also seen in the spectrum throughout the orbit are the effects of a variable, high-speed wind as well as evidence for accretion onto the B9.5 star. This high-speed wind absorbs in species of all ionization stages observed, e. g., C II, Mg II, Al III, SI IV, C IV, and has a terminaal velocity in the range 200-450 km/s. We presume this wind originates at the B dwarf, not the M supergiant, and speculate that it comes from an accretion disk, as suggested by recent models of magnetically moderated accretion. Evidence for accretion is redshifted absorption in the same transitions formed in the high-speed wind, as well as broad emission lines of singly ionized metals. This emission seems to be

  14. Lessons from accretion disks in cataclysmic variables

    NASA Astrophysics Data System (ADS)

    Horne, Keith

    1998-04-01

    We survey recent progress in the interpretation of observations of cataclysmic variables, whose accretion disks are heated by viscous dissipation rather than irradiation. Many features of standard viscous accretion disk models are confirmed by tomographic imaging studies of dwarf novae. Eclipse maps indicate that steady disk temperature structures are established during outbursts. Doppler maps of double-peaked emission lines suggest disk chromospheres heated by magnetic activity. Gas streams impacting on the disk rim leave expected signatures both in the eclipses and emission lines. Doppler maps of dwarf nova IP Peg at the beginning of an outburst show evidence for tidally-induced spiral shocks. While enjoying these successes, we must still face up to the dreaded ``SW Sex syndrome'' which afflicts most if not all cataclysmic variables in high accretion states. The anomalies include single-peaked emission lines with skewed kinematics, flat temperature-radius profiles, shallow offset line eclipses, and narrow low-ionization absorption lines at phase 0.5. The enigmatic behavior of AE Aqr is now largely understood in terms of a magnetic propeller model in which the rapidly spinning white dwarf magnetosphere expels the gas stream out of the system before an accretion disk can form. A final piece in this puzzle is the realization that an internal shock zone occurs in the exit stream at just the right place to explain the anomalous kinematics and violent flaring of the single-peaked emission lines. Encouraged by this success, we propose that disk-anchored magnetic propellers operate in the high accretion rate systems afflicted by the SW Sex syndrome. Magnetic fields anchored in the Keplerian disk sweep forward and apply a boost that expels gas stream material flowing above the disk plane. This working hypothesis offers a framework on which we can hang all the SW Sex anomalies. The lesson for theorists is that magnetic links appear to be transporting energy and angular

  15. Chondrule formation in the radiative accretional shock

    NASA Technical Reports Server (NTRS)

    Ruzmaikina, T. V.; Ip, W.

    1994-01-01

    The physical, mineralogical, and isotopic properties of chondrules strongly indicate that they were formed by the rapid melting and resolidification of preexisting solids composed of primitive material. The chondrule precursors were heated to temperatures of about 1800 K in short high-temperature events, followed by cooling with a rate of 10(exp 2)-10(exp 3) K/hr. A heat input of about 1500 J/g is required to heat chondrule precursors to such a temperature and melt them. Lightning discharges and flares in the solar nebula, and heating of the chondrule precursors by friction with gas decelerated in the accretional shock or in a shock (of unspecified origin) within the solar nebula, have been discussed as possible mechanisms for chondrule formation. One advantage of chondrule formation in large-scale shocks is that a lot of dust material can be processed. An accretional shock, which is produced by infalling gas of the presolar cloud when it collides with the solar nebula, belongs to this type of shock. In 1984 Wood considered the possibility of chondrule formation in the accretional shock by heating of chondrule precursors by gas drag. He concluded that the density in the accreting material is much lower than needed to melt silicates at the distance of the asteroid belt if the accreting matter had the cosmic ratio of dust to gas, and the mass of the solar nebula did not exceed 2 solar mass units. Melting of chondrule precursors is difficult because of their effective cooling by thermal radiation. Suppression of the radiative cooling of individual grains in dust swarms, which are opaque to thermal emission, was considered to be the only possible means of chondrule formation in solar nebula shocks. Previous models of solid grain melting in solar nebula shocks have neglected gas cooling behind the shock front, i.e., they considered adiabatic shocks. In this paper we show that large dust grains could be heated much stronger than was supposed by these authors, because of

  16. Hamsters chewing betel quid or areca nut directly show a decrease in body weight and survival rates with concomitant epithelial hyperplasia of cheek pouch.

    PubMed

    Chiang, Chun-Pin; Chang, Mei-Chi; Lee, Jang-Jaer; Chang, Julia Yu-Fong; Lee, Po-Hsuen; Hahn, Liang-Jiunn; Jeng, Jiiang-Huei

    2004-08-01

    Betel quid (BQ) chewing is strongly associated with the occurrence of oral leukoplakia, oral submucous fibrosis, and oral cancer. There are about 200-600 million BQ chewers in the world. Previous animal studies support the potential carcinogenicity of BQ in different test systems. However, little animal experiment has let hamsters or rats to chew BQ directly, similar to that in humans. In the present study, we established a hamster model of chewing BQ or areca nut (AN). A total of 81 2-week-old hamsters were randomly divided into three groups: 25 for control group, 28 for BQ-chewing group, and 28 for AN-chewing group. These animals were fed with powdered diet with/without BQ or AN for 18 months. Although the consumption of BQ or AN showed some variations, hamsters fed with powdered diet could chew and grind AN or BQ into small pieces of coarse fibers during the entire experimental period. The survival rate of AN-chewing hamsters decreased significantly after 6 months of exposure. The mean survival time was 15.6 +/- 0.9 months for control animals, 13.6 +/- 0.98 months for AN-chewing animals, and 15.7 +/- 0.55 months for BQ-chewing animals. The body weight of BQ- or AN-chewing animals also decreased after 4-13 months. Hamsters fed with AN for 18 months showed hyperkeratosis in 80% and acanthosis in 50% of cheek pouches. Animals fed with BQ for 18 months also showed hyperkeratosis in 93% and acanthosis in 14% of cheek pouches. These results indicate that AN and BQ components may induce alterations in proliferation and differentiation of oral epithelial cells. Animal model of chewing BQ or AN can be useful for future tumor initiation, promotion and chemoprevention experiments simulating the condition of BQ chewing in humans.

  17. Detectable MeV neutrinos from black hole neutrino-dominated accretion flows

    NASA Astrophysics Data System (ADS)

    Liu, Tong; Zhang, Bing; Li, Ye; Ma, Ren-Yi; Xue, Li

    2016-06-01

    Neutrino-dominated accretion flows (NDAFs) around rotating stellar-mass black holes (BHs) have been theorized as the central engine of relativistic jets launched in massive star core collapse events or compact star mergers. In this work, we calculate the electron neutrino/antineutrino spectra of NDAFs by fully taking into account the general relativistic effects, and investigate the effects of viewing angle, BH spin, and mass accretion rate on the results. We show that even though a typical NDAF has a neutrino luminosity lower than that of a typical supernova (SN), it can reach 1050- 1051 erg s-1 peaking at ˜10 MeV , making NDAFs potentially detectable with the upcoming sensitive MeV neutrino detectors if they are close enough to Earth. Based on the observed gamma-ray burst (GRB) event rate in the local universe and requiring that at least three neutrinos are detected to claim a detection, we estimate a detection rate up to ˜(0.10 - 0.25 ) per century for GRB-related NDAFs by the Hyper-Kamiokande (Hyper-K) detector if one neglects neutrino oscillation. If one assumes that all type Ib/c SNe have an engine-driven NDAF, the Hyper-K detection rate would be ˜(1 - 3 ) per century. By considering neutrino oscillations, the detection rate may decrease by a factor of 2-3. Detecting one such event would establish the observational evidence of NDAFs in the Universe.

  18. Polymorphisms of the UCP2 Gene Are Associated with Glomerular Filtration Rate in Type 2 Diabetic Patients and with Decreased UCP2 Gene Expression in Human Kidney

    PubMed Central

    de Souza, Bianca Marmontel; Michels, Marcus; Sortica, Denise Alves; Bouças, Ana Paula; Rheinheimer, Jakeline; Buffon, Marjoriê Piuco; Bauer, Andrea Carla; Canani, Luís Henrique; Crispim, Daisy

    2015-01-01

    Introduction Uncoupling protein 2 (UCP2) reduces production of reactive oxygen species (ROS) by mitochondria. ROS overproduction is one of the major contributors to the pathogenesis of chronic diabetic complications, such as diabetic kidney disease (DKD). Thus, deleterious polymorphisms in the UCP2 gene are candidate risk factors for DKD. In this study, we investigated whether UCP2 -866G/A, Ala55Val and Ins/Del polymorphisms were associated with DKD in patients with type 2 diabetes mellitus (T2DM), and whether they had an effect on UCP2 gene expression in human kidney tissue biopsies. Materials and Methods In a case-control study, frequencies of the UCP2 -866G/A, Ala55Val and Ins/Del polymorphisms as well as frequencies of the haplotypes constituted by them were analyzed in 287 T2DM patients with DKD and 281 T2DM patients without this complication. In a cross-sectional study, UCP2 gene expression was evaluated in 42 kidney biopsy samples stratified according to the presence of the UCP2 mutated -866A/55Val/Ins haplotype. Results In the T2DM group, multivariate logistic regression analysis showed that the -866A/55Val/Ins haplotype was an independent risk factor for DKD (OR = 2.136, 95% CI 1.036–4.404), although neither genotype nor allele frequencies of the individual polymorphisms differed between case and control groups. Interestingly, T2DM patients carrying the mutated haplotype showed decreased estimated glomerular filtration rate (eGFR) when compared to subjects with the reference haplotype (adjusted P= 0.035). In kidney biopsy samples, UCP2 expression was significantly decreased in UCP2 mutated haplotype carriers when compared to kidneys from patients with the reference haplotype (0.32 ± 1.20 vs. 1.85 ± 1.16 n fold change; adjusted P< 0.000001). Discussion Data reported here suggest that the UCP2 -866A/55Val/Ins haplotype is associated with an increased risk for DKD and with a lower eGFR in T2DM patients. Furthermore, this mutated haplotype was associated

  19. Accretion-driven star formation in central dominant galaxies in X-ray clusters

    NASA Astrophysics Data System (ADS)

    Sarazin, C. L.; Oconnell, R. W.

    1983-05-01

    Analytical and observational evidence for the formation of low-mass stars in the gas accreting in the central dominant galaxies in clusters is presented. Observations of the (U-V) and (K-V) color gradients in accreting galaxies are suggested to reveal colors altered by the appearance of young stars, e.g., the excess blue and the A star spectrum detected in NGC 1275. Low-temperature X ray line emissions from accreting galaxies have been partially surveyed with the result that 10 pct of the brightest cluster galaxies in a magnitude-limited sample show evidence of significant accretion. Photometric data from the quasar 3C 48, located in a galaxy with a very blue population, also suggests low-mass star formation, especially when compared to measurements of NGC 1275, which has the highest accretion rate among observed central dominant cluster galaxies. The quasar, however, would not be accreting interstellar gas.

  20. Swept wing ice accretion modeling

    NASA Technical Reports Server (NTRS)

    Potapczuk, M. G.; Bidwell, C. S.

    1990-01-01

    An effort to develop a three-dimensional ice accretion modeling method is initiated. This first step toward creation of a complete aircraft icing simulation code builds on previously developed methods for calculating three-dimensional flowfields and particle trajectories combined with a two-dimensional ice accretion calculation along coordinate locations corresponding to streamlines. This work is intended as a demonstration of the types of calculations necessary to predict a three-dimensional ice accretion. Results of calculations using the 3D method for a MS-317 swept wing geometry are projected onto a 2D plane normal to the wing leading edge and compared to 2D results for the same geometry. These results indicate that the flowfield over the surface and the particle trajectories differed for the two calculations. This led to lower collection efficiencies, convective heat transfer coefficients, freezing fractions, and ultimately ice accumulation for the 3D calculation.

  1. Radiative efficiency of hot accretion flow and the radio/X-ray correlation in X-ray binaries

    NASA Astrophysics Data System (ADS)

    Xie, Fu-Guo

    2016-02-01

    Significant progresses have been made since the discovery of hot accretion flow, a theory successfully applied to the low-luminosity active galactic nuclei (LLAGNs) and black hole (BH) X-ray binaries (BHBs) in their hard states. Motivated by these updates, we re-investigate the radiative efficiency of hot accretion flow. We find that, the brightest regime of hot accretion flow shows a distinctive property, i.e. it has a constant efficiency independent of accretion rates, similar to the standard thin disk. For less bright regime, the efficiency has a steep positive correlation with the accretion rate, while for faint regime typical of advection-dominated accretion flow, the correlation is shadower. This result can naturally explain the observed two distinctive correlations between radio and X-ray luminosities in black hole X-ray binaries. The key difference in systems with distinctive correlations could be the viscous parameter, which determines the critical luminosity of different accretion modes.

  2. The Influence of Outflow in Supercritical Accretion Flows

    NASA Astrophysics Data System (ADS)

    Zahra Zeraatgari, Fatemeh; Abbassi, Shahram; Mosallanezhad, Amin

    2016-06-01

    We solve the radiation-hydrodynamic equations of supercritical accretion flows in the presence of radiation force and outflow by using self-similar solutions. Similar to the pioneering works, in this paper we consider a power-law function for mass inflow rate as \\dot{M}\\propto {r}s. We found that s = 1 when the radiative cooling term is included in the energy equation. Correspondingly, the effective temperature profile with respect to the radius was obtained as {T}{eff}\\propto {r}-1/2. In addition, we investigated the influence of the outflow on the dynamics of the accretion flow. We also calculated the continuum spectrum emitted from the disk surface as well as the bolometric luminosity of the accretion flow. Furthermore, our results show that the advection parameter, f, depends strongly on mass inflow rate.

  3. Accretion disk emission from a BL Lacertae object

    NASA Technical Reports Server (NTRS)

    Wandel, Amri; Urry, C. Megan

    1991-01-01

    It is suggested here that the UV and X-ray emission of BL Lac objects may originate in an accretion disk. Using detailed calculations of accretion disk spectra, the best-measured ultraviolet and soft X-ray spectra of the BL Lac object PKS 2155-304 are fitted, and the mass and accretion rate required is determined. The ultraviolet through soft X-ray continuum is well fitted by the spectrum of an accretion disk, but near-Eddington accretion rates are required to produce the soft X-ray excess. A hot disk or corona could Comptonize soft photons from the cool disk and produce the observed power-law spectrum in the 1-10 keV range. The dynamic time scale in the disk regions that contribute most of the observed ultraviolet and soft X-ray photons are consistent with the respective time scales for intensity variations observed in these two wave bands; the mass derived from fitting the continuum spectrum is consistent with the limit derived from the fastest hard X-ray variability.

  4. The Evolution of Gas Giant Entropy During Formation by Runaway Accretion

    NASA Astrophysics Data System (ADS)

    Berardo, David; Cumming, Andrew; Marleau, Gabriel-Dominique

    2017-01-01

    We calculate the evolution of gas giant planets during the runaway gas accretion phase of formation, to understand how the luminosity of young giant planets depends on the accretion conditions. We construct steady-state envelope models, and run time-dependent simulations of accreting planets with the code Modules for Experiments in Stellar Astrophysics. We show that the evolution of the internal entropy depends on the contrast between the internal adiabat and the entropy of the accreted material, parametrized by the shock temperature T0 and pressure P0. At low temperatures ({T}0≲ 300–1000 {{K}}, depending on model parameters), the accreted material has a lower entropy than the interior. The convection zone extends to the surface and can drive a high luminosity, leading to rapid cooling and cold starts. For higher temperatures, the accreted material has a higher entropy than the interior, giving a radiative zone that stalls cooling. For {T}0≳ 2000 {{K}}, the surface–interior entropy contrast cannot be accommodated by the radiative envelope, and the accreted matter accumulates with high entropy, forming a hot start. The final state of the planet depends on the shock temperature, accretion rate, and starting entropy at the onset of runaway accretion. Cold starts with L≲ 5× {10}-6 {L}ȯ require low accretion rates and starting entropy, and the temperature of the accreting material needs to be maintained close to the nebula temperature. If instead the temperature is near the value required to radiate the accretion luminosity, 4π {R}2σ {T}04∼ ({GM}\\dot{M}/R), as suggested by previous work on radiative shocks in the context of star formation, gas giant planets form in a hot start with L∼ {10}-4 {L}ȯ .

  5. Migration of accreting planets in radiative discs from dynamical torques

    NASA Astrophysics Data System (ADS)

    Pierens, A.; Raymond, S. N.

    2016-11-01

    We present the results of hydrodynamical simulations of the orbital evolution of planets undergoing runaway gas accretion in radiative discs. We consider accreting disc models with constant mass flux through the disc, and where radiative cooling balances the effect of viscous heating and stellar irradiation. We assume that 20-30 M⊕ giant planet cores are formed in the region where viscous heating dominates and migrate outward under the action of a strong entropy-related corotation torque. In the case where gas accretion is neglected and for an α viscous stress parameter α = 2 × 10-3, we find evidence for strong dynamical torques in accreting discs with accretion rates {dot{M}}≳ 7× 10^{-8} M_{⊙} yr{}^{-1}. Their main effect is to increase outward migration rates by a factor of ˜2 typically. In the presence of gas accretion, however, runaway outward migration is observed with the planet passing through the zero-torque radius and the transition between the viscous heating and stellar heating dominated regimes. The ability for an accreting planet to enter a fast migration regime is found to depend strongly on the planet growth rate, but can occur for values of the mass flux through the disc of {dot{M}}≳ 5× 10^{-8} M_{⊙} yr{}^{-1}. We find that an episode of runaway outward migration can cause an accreting planet formed in the 5-10 au region to temporarily orbit at star-planet separations as large as ˜60-70 au. However, increase in the amplitude of the Lindblad torque associated with planet growth plus change in the streamline topology near the planet systematically cause the direction of migration to be reversed. Subsequent evolution corresponds to the planet migrating inward rapidly until it becomes massive enough to open a gap in the disc and migrate in the type II regime. Our results indicate that a planet can reach large orbital distances under the combined effect of dynamical torques and gas accretion, but an alternative mechanism is required to

  6. Accretion Disks around Young Stars

    NASA Astrophysics Data System (ADS)

    D'Alessio, Paola

    1996-04-01

    A method to calculate the structure and brightness distribution of accretion disks surrounding low and intermediate mass young stars is introduced and discussed. The method includes a realistic treatment of the energy transport mechanisms and disk heating by radiation from external sources. The disk is assumed steady, geometrically thin and in vertical hydrostatic equilibrium. The turbulent viscosity coefficient is expressed using the α prescription and the α parameter and the mass accretion rate are assumed to be constant through the disk. Energy is transported in the vertical direction by: (a) a turbulent flux, computed self-consistently with the viscosity coefficient used to describe the viscous energy dissipation, (b) radiation, using the first moments of the transfer equation, the Eddington approximation, and the Rosseland and Planck Mean Opacities, and (c) convection, taking into account that the convective elements, not necessarily optically thick, lose energy by radiation and turbulent flux. This treatment of the energy transport mechanisms differs from previous work in this field, allowing one to extend, with confidence, the calculation of the disk structure to optically thin regimes. The heating mechanisms considered, which affect the disk's structure and emission, are stellar radiation and a circumstellar envelope which reprocesses and scatters radiation from the star and from the disk itself. In addition to a detailed numerical calculation, an analytical self-consistent formulation of the irradiation of the disk is given. This analytical formulation allows one to understand and extend the numerical results. To evaluate the potential of the method presented in this thesis, a set of models of viscous non-irradiated and irradiated disks are computed. Their predictions are compared with observations of young stellar sources likely to have disks. Given the disk structure and specifying its orient