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Sample records for disk properties distinguish

  1. PROPERTIES OF GRAVITOTURBULENT ACCRETION DISKS

    SciTech Connect

    Rafikov, Roman R.

    2009-10-10

    We explore the properties of cold gravitoturbulent accretion disks-non-fragmenting disks hovering on the verge of gravitational instability (GI)-using a realistic prescription for the effective viscosity caused by gravitational torques. This prescription is based on a direct relationship between the angular momentum transport in a thin accretion disk and the disk cooling in a steady state. Assuming that opacity is dominated by dust we are able to self-consistently derive disk properties for a given M-dot assuming marginal gravitational stability. We also allow external irradiation of the disk and account for a non-zero background viscosity, which can be due to the magneto-rotational instability. Spatial transitions between different co-existing disk states (e.g., between irradiated and self-luminous or between gravitoturbulent and viscous) are described and the location of the boundary at which the disk must fragment is determined in a variety of situations. We demonstrate in particular that at low enough M-dot external irradiation stabilizes the gravitoturbulent disk against fragmentation to very large distances thus providing means of steady mass transport to the central object. Implications of our results for the possibility of planet formation by GI in protoplanetary disks and star formation in the Galactic center and for the problem of feeding supermassive black holes in galactic nuclei are discussed.

  2. HERSCHEL OBSERVATIONS OF THE T CHA TRANSITION DISK: CONSTRAINING THE OUTER DISK PROPERTIES

    SciTech Connect

    Cieza, Lucas A.; Olofsson, Johan; Henning, Thomas; Harvey, Paul M.; Evans II, Neal J.; Pinte, Christophe; Augereau, Jean-Charles; Menard, Francois; Najita, Joan

    2011-11-10

    T Cha is a nearby (d {approx} 100 pc) transition disk known to have an optically thin gap separating optically thick inner and outer disk components. Huelamo et al. recently reported the presence of a low-mass object candidate within the gap of the T Cha disk, giving credence to the suspected planetary origin of this gap. Here we present the Herschel photometry (70, 160, 250, 350, and 500 {mu}m) of T Cha from the 'Dust, Ice, and Gas in Time' Key Program, which bridges the wavelength range between existing Spitzer and millimeter data and provide important constraints on the outer disk properties of this extraordinary system. We model the entire optical to millimeter wavelength spectral energy distribution (SED) of T Cha (19 data points between 0.36 and 3300 {mu}m without any major gaps in wavelength coverage). T Cha shows a steep spectral slope in the far-IR, which we find clearly favors models with outer disks containing little or no dust beyond {approx}40 AU. The full SED can be modeled equally well with either an outer disk that is very compact (only a few AU wide) or a much larger one that has a very steep surface density profile. That is, T Cha's outer disk seems to be either very small or very tenuous. Both scenarios suggest a highly unusual outer disk and have important but different implications for the nature of T Cha. Spatially resolved images are needed to distinguish between the two scenarios.

  3. Essential Properties of New Debris Disks

    NASA Astrophysics Data System (ADS)

    Weinberger, Alycia

    We propose to use HAWC+ at 53 microns to measure fundamental attributes of newly discovered debris disks - their temperatures (and hence sizes) and dust contents. Circumstellar debris disks are generated by the collisions and evaporation of planetesimals, the leftover building blocks of planets. Their structures and compositions provide clues to planet formation and planetary system architectures. Their dust may also impede our ability to detect Earth-sized planets. Our 33 A and F-type targets are drawn from recent studies that have used the Wide-field Infrared Survey Explorer (WISE) catalog to detected hundreds of hitherto unknown disks. It's amazing and exciting that despite years of work with IRAS, Spitzer, and Herschel space telescopes, our knowledge of debris disks within the solar neighborhood (<100 pc) was still vastly incomplete. While exciting, the detection of excess at a single wavelength reveals very little about a disk's basic properties. While a detection with WISE's longest wavelength band (22 micron) is sufficient to find a disk, it reveals nothing about the disk's temperature or total dust content. Most of the dust in debris disks is cold, <70 K, which is why the 60 micron band of IRAS was essential to discovering them. So, WISE's 22 micron is likely the Wien side of the iceberg. These disks around luminous stars could be ideal targets for follow-up studies to learn about their dust composition (scattered light observations with HST and JWST, infrared spectroscopy with JWST) and in which to search for planets with adaptive optics on large telescopes. The first step upon which all future work will depend is to characterize these disks in the far-infrared with SOFIA.

  4. Properties of isolated disk galaxies

    NASA Astrophysics Data System (ADS)

    Varela, J.; Moles, M.; Márquez, I.; Galletta, G.; Masegosa, J.; Bettoni, D.

    2004-06-01

    We present a new sample of northern isolated galaxies, which are defined by the physical criterion that they were not affected by other galaxies in their evolution during the last few Gyr. To find them we used the logarithmic ratio, f, between inner and tidal forces acting upon the candidate galaxy by a possible perturber. The analysis of the distribution of the f-values for the galaxies in the Coma cluster lead us to adopt the criterion f ≤ -4.5 for isolated galaxies. The candidates were chosen from the CfA catalog of galaxies within the volume defined by cz ≤5000 km s-1, galactic latitude higher than 40o and declination ≥-2.5o. The selection of the sample, based on redshift values (when available), magnitudes and sizes of the candidate galaxies and possible perturbers present in the same field is discussed. The final list of selected isolated galaxies includes 203 objects from the initial 1706. The list contains only truly isolated galaxies in the sense defined, but it is by no means complete, since all the galaxies with possible companions under the f-criterion but with unknown redshift were discarded. We also selected a sample of perturbed galaxies comprised of all the disk galaxies from the initial list with companions (with known redshift) satisfying f ≥ -2 and \\Delta(cz) ≤500 km s-1; a total of 130 objects. The statistical comparison of both samples shows significant differences in morphology, sizes, masses, luminosities and color indices. Confirming previous results, we found that late spiral, Sc-type galaxies are, in particular, more frequent among isolated galaxies, whereas Lenticular galaxies are more abundant among perturbed galaxies. Isolated systems appear to be smaller, less luminous and bluer than interacting objects. We also found that bars are twice as frequent among perturbed galaxies compared to isolated galaxies, in particular for early Spirals and Lenticulars. The perturbed galaxies have higher LFIR/LB and Mmol/LB ratios, but the

  5. Observational Properties of Protoplanetary Disk Gaps

    NASA Astrophysics Data System (ADS)

    Varnière, Peggy; Bjorkman, J. E.; Frank, Adam; Quillen, Alice C.; Carciofi, A. C.; Whitney, Barbara A.; Wood, Kenneth

    2006-02-01

    We study the effects of an annular gap induced by an embedded protoplanet on disk scattered light images and the infrared spectral energy distribution (SED). We find that the outer edge of a gap is brighter in the scattered light images than a similar location in a gap-free disk. The stellar radiation that would have been scattered by material within the gap is instead scattered by the disk wall at the outer edge of the gap, producing a bright ring surrounding the dark gap in the images. Given sufficient resolution, such gaps can be detected by the presence of this bright ring in scattered light images. A gap in a disk also changes the shape of the SED. Radiation that would have been absorbed by material in the gap is instead reprocessed by the outer gap wall. This leads to a decrease in the SED at wavelengths corresponding to the temperature at the radius of the missing gap material, and to a corresponding flux increase at longer wavelengths corresponding to the temperature of the outer wall. We note, however, that the presence of an annular gap does not change the bolometric IR flux; it simply redistributes the radiation previously produced by material within the gap to longer wavelengths. Although it will be difficult on the basis of the SED alone to distinguish between the presence of a gap and other physical effects, the level of changes can be sufficiently large to be measurable with current instruments (e.g., Spitzer).

  6. Distinguishing internal property from external property in kidney transplantation.

    PubMed

    Prasad, G V Ramesh

    2016-08-01

    What determines the ownership of human body parts? In this paper, I argue that this question can be informed by an exploration of the cognitive distinction between property external to the human body such as houses, cars or land, and internal property such as organs that are located within anatomical body confines. Each type of property has distinct brain representations and possibly different effects on the sense of self. This distinction may help explain the divergence in post-donation outcomes seen in different kidney donor populations. Poor outcomes in some types of kidney donors may be due not only to a failure in their proper selection by standard medical testing or post-donation care but may also be a manifestation of differing effects on sense of self resulting from transfer of their internal property. Because a kidney is internal property, a hypothesis worth exploring is that those who experience good outcomes post-donation experience dopaminergic activation and a feeling of reward, while those experiencing bad outcomes are instead overcoming cortisol or adrenergic-based stress or fear responses without a corresponding feeling of reward, disrupting of their sense of self. Discussions about the rules for internal property transfer must be based not only on values and laws designed to govern external property but also on cognitive science-based facts, values and judgments that discussions of external property do not presently accommodate. Any future system of rules for governing organ distribution requires a framework different from that of external property to prevent harm to living kidney donors. © 2016 John Wiley & Sons, Ltd.

  7. New Approach to Diagnosing Properties of Protoplanetary Disks

    NASA Technical Reports Server (NTRS)

    Stepinski, Tomasz F.

    1998-01-01

    In this paper we suggest that subjecting the observationally derived properties of protoplanetary disks to the evolutionary interpretation yields new insights into the working of those disks, and offers valuable constraints on their models. We propose that the global properties of individual disks, such as their accretion rates and disk masses, sorted by the mass of the central star, can be indexed by the age of the star to simulate the evolution of a single disk. Using data from published surveys of T Tauri stars, we show that accretion rate data, and disk mass data for the lowest mass stars, form well-defined evolutionary tracks. The higher mass stars show a definitive negative correlation between accretion rates and star ages. We use the time-dependent alpha-disk model of the viscous protoplanetary disk to link the theory to observations. The data are consistent with the standard theoretical paradigm, but not with the layered accretion model. The best fits to the data are obtained for the standard models that start with disks that are about one-third of the mass of the central star and have their angular momenta, j, and alpha-coefficients linked by the relationship j varies as Solar mass(exp 3/2)alpha(exp 1/3). The proportionality constant in this relationship, when derived from the accretion rate data, differs from the constant derived from the disk mass data. We argue that the accretion rate data are more reliable. Taking into account typical values of the specific angular momentum of disk-forming matter, we obtain alpha is greater than or equal to 10(exp -2). A complete time-dependent standard disk model, built on the parameters determined from the best-fit procedure, is presented. Such a model constitutes a good point of departure for various theoretical studies aimed at the issue of formation of planetary systems and the character of protoplanetary disks.

  8. Influence of luminosity bursts on properties of protostellar disks

    NASA Astrophysics Data System (ADS)

    Vorobyov, E. I.; Pavlyuchenkov, Ya. N.; Trinkl, P.

    2014-08-01

    A (2+ 1)-dimensional numerical model for the formation and evolution of young stellar objects with sub-solar masses is presented. The numerical hydrodynamicall code describing the formation and evolution of a protostellar disk in a two-dimensional approximation is supplemented by one-dimensional code for the evolution of the star and an algorithm for establishing the vertical structure of the disk. This code is used to investigate the influence of luminosity bursts with intensities similar to those observed in FU Orionis objects (FUors) on the properties and thermal balance of protostellar disks. A model with gravitational instability and fragmentation of the disk, with subsequent migration of the fragments onto the protostar, is used as a basic model for FUors. Typical FUor bursts ( L ˜ 100 L ⊙) can appreciably influence the thermal balance of their disks and parent envelopes, leading to an increase in the disk temperature by more than a factor of two. On the other hand, massive fragments in the disk are only weakly perturbed by such bursts, partially due to screening by the disk and partially due to their high temperature brought about by adiabatic heating. Apart from massive fragments, the characteristic thermal time scales are appreciably shorter than the dynamical time scales throughout the radial extent of the disk and envelope; this enables the use of a stationary radiative-transfer equation when determining the vertical structure of the disk.

  9. The occurrence and properties of disks around young stars

    NASA Technical Reports Server (NTRS)

    Beckwith, Steven V. W.; Sargent, Anneila I.

    1993-01-01

    The paper discusses the occurrence and properties of disks around young stars, emphasizing in particular how these may relate to planet formation and the evolution of the solar system. The global properties of such disks often resemble those attributed to the primitive solar nebula, suggesting that conditions appropriate for planet formation commonly accompany the birth of low-mass stars. Disk masses, between 0.001 and 1 solar mass, are generally lower than those of the stars, and may represent only a fraction (less than about 10 percent) of the total system mass. From the paucity of near-IR radiation from some disks it is inferred that the inner regions there are gaps where the opacity from small particles becomes vanishingly small. Evidence is presented to the effect that gaps in the inner disks develop preferentially in the oldest objects, suggesting that, with time, matter is lost or accumulates into large particles such as planetesimals, which cannot yet be detected.

  10. The Evolving Properties of Water in a Dynamic Protoplanetary Disk

    NASA Astrophysics Data System (ADS)

    Ciesla, Fred

    2015-08-01

    Protoplanetary disks are dynamic objects, through which mass and angular momentum are transported as part of the final stages of pre-main sequence evolution of their central stars. These disks are also rich chemical factories, in which materials inherited from the interstellar medium are transformed through a series of reactions (involving, gases, solids, ions, and photons) to the eventual building blocks of the planets.The chemical and physical evolution of a protoplanetary disk are intimately connected. Both solids and gases are subjected to large-scale motions associated with disk evolution and diffusion within the gas. Solids also settle toward the disk midplane and migrate inwards due to gravity and gas drag. This dynamical evolution exposes primitive materials to a range of physical conditions (pressure, temperature, radiation environment) within the disk. It is the integrated effects of these environments that define the physical and chemical properties of a solid grain prior to its incorporation into a planetesimal or planet.Water serves as an interesting tracer of this evolution, as it would be processed in a variety of ways within a protoplanetary disk. I will discuss new methods that allow us to trace the dynamical movement of water vapor and ice throughout the lifetime of a protoplanetary disk and to determine the physical environments to which the water would be exposed. In particular, I will show how the early evolution of a protoplanetary disk impacts the D/H ratio of the water inherited by planetary materials. I will also explore how photodesorption of water by UV photons can lead to the formation of amorphous ice and thus the trapping of noble gases and other volatiles at levels that are much greater than predicted by equilibrium chemistry models. These effects combine to lead to constantly evolving properties of water during the early stages of planet formation. I will also discuss how the observed properties of Solar System bodies constrain these

  11. Inner polar ionized-gas disks and properties of their host galaxies

    NASA Astrophysics Data System (ADS)

    Sil'chenko, Olga K.

    2015-02-01

    I have analyzed line-of-sight velocity fields of the stellar and ionized-gas components for the volume-limited sample of nearby lenticular galaxies by using the raw data of the ATLAS-3D survey undertaken with the integral-field spectrograph SAURON. Among 200 nearby lenticular galaxies, I distinguish 20 cases of nearly orthogonal rotation of the inner ionized gas with respect to the central stellar components; so I estimate a frequency of the inner polar disks in nearby S0 galaxies as 10%. Properties of the central stellar populations - mean ages, metallicities, magnesium-to-iron ratios - are derived through the Lick indices. The typical stellar population properties of the polar-disk host galaxies are exactly the same as the stellar population properties of the complete sample.

  12. Properties of Planet-Forming Prostellar Disks

    NASA Technical Reports Server (NTRS)

    Lindstrom, David (Technical Monitor); Lubow, Stephen

    2005-01-01

    The proposal achieved many of its objectives. The main area of investigation was the interaction of young planets with surrounding protostellar disks. The grant funds were used to support visits by CoIs and visitors: Gordon Ogilvie, Gennaro D Angelo, and Matthew Bate. Funds were used for travel and partial salary support for Lubow. We made important progress in two areas described in the original proposal: secular resonances (Section 3) and nonlinear waves in three dimensions (Section 5). In addition, we investigated several new areas: planet migration, orbital distribution of planets, and noncoorbital corotation resonances.

  13. Thermophysical Properties of Automotive Metallic Brake Disk Materials

    NASA Astrophysics Data System (ADS)

    Kim, S. W.; Park, K.; Lee, S. H.; Kang, K. H.; Lim, K. T.

    2008-12-01

    The temperature distribution, the thermal deformation, and the thermal stress of automotive brake disks have quite close relations with car safety; therefore, much research in this field has been performed. However, successful and satisfactory results have not been obtained because the temperature-dependent thermophysical properties of brake disk materials are not sufficiently known. In this study, the thermophysical properties (thermal diffusivity, the specific heat, and the coefficient of thermal expansion) of three kinds of iron alloy series brake disk materials, FC250, FC170, and FCD50, and two kinds of aluminum alloy series brake disk materials, Al MMC and A356, were measured in the temperature range from room temperature to 500 °C, and the thermal conductivity was calculated using the measured thermal diffusivity, specific heat capacity, and density. As expected, the results show that the two series have significant differences in respect of the thermophysical properties, and to reduce the thermal deformation of the brake disk, the aluminum alloys with a high thermal conductivity and the iron alloys with low thermal expansion are recommended.

  14. Supermassive Black Hole Masses and Global Properties of Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Castillo, Y. S.; Funes, J. G.; Díaz, R. J.

    2006-06-01

    Different scaling laws are known for the mass of supermassive black holes (M_{BH}): M_{BH}-σ M_{BH}-M_{Bulge}; M_{BH}-M_{DM}. We have reviewed these correlations for 17 disk galaxies and tried to find any correlation between M_{BH} and other disk properties (HI and H_2 masses, far infrared luminosity, star formation rate, etc.). The sample was taken from Marconi and Hunt (2003). For these galaxies we have done a search in the literature for the following properties: A) in the nucleus: star formation rates, and luminosities in Hα ; B) in the bulge: luminosity in B-band; C) in the disk: HI and H_2 total masses, total luminosities in X-ray, B band and far infrared, and total star formation rate. In this work we present the compiled data from the literature and the plots of M_{BH} against galaxy HI total mass, M_{BH} against galaxy H_2 total mass, and M_{BH} against disk blue luminosity. We did not find any evident correlation between the M_{BH} and the properties of the disk.

  15. GLOBAL PROPERTIES OF FULLY CONVECTIVE ACCRETION DISKS FROM LOCAL SIMULATIONS

    SciTech Connect

    Bodo, G.; Ponzo, F.; Rossi, P.; Cattaneo, F.; Mignone, A.

    2015-08-01

    We present an approach to deriving global properties of accretion disks from the knowledge of local solutions derived from numerical simulations based on the shearing box approximation. The approach consists of a two-step procedure. First, a local solution valid for all values of the disk height is constructed by piecing together an interior solution obtained numerically with an analytical exterior radiative solution. The matching is obtained by assuming hydrostatic balance and radiative equilibrium. Although in principle the procedure can be carried out in general, it simplifies considerably when the interior solution is fully convective. In these cases, the construction is analogous to the derivation of the Hayashi tracks for protostars. The second step consists of piecing together the local solutions at different radii to obtain a global solution. Here we use the symmetry of the solutions with respect to the defining dimensionless numbers—in a way similar to the use of homology relations in stellar structure theory—to obtain the scaling properties of the various disk quantities with radius.

  16. Properties and Distribution of Current Sheets in Accretion Disk Coronae

    NASA Astrophysics Data System (ADS)

    Salvesen, Greg; Begelman, M. C.; Simon, J. B.; Beckwith, K.

    2013-04-01

    Theoretical models involving the interplay of a geometrically thin, optically thick accretion disk embedded in an extended coronal atmosphere may describe black hole X-ray binaries across all spectral states. Buoyant magnetic field generated in the accretion disk is continuously supplied to the corona by a dynamo process driven by the magnetorotational instability. This rising field leads to the formation of a magnetic pressure-dominated, low-density, geometrically thick corona where substantial accretion energy is dissipated, likely by collisionless magnetic reconnection, perhaps even generating outflows. Despite the potential importance of magnetic reconnection in shaping the energetics and kinematics of the corona, studies of multiple reconnection sites in a large volume are currently prohibited by the computational expense required to properly treat the microphysical nature of reconnection. Under the assumption that coronal structure is determined by ideal magnetohydrodynamics, we analyze local simulations of accretion disks (i.e., shearing boxes) performed with the ATHENA code, where the spatial domains are extended to capture 'mesoscale' structures that are dynamically important in accretion disk evolution. We employ a location routine to identify zones of enhanced current density, which trace likely sites of magnetic reconnection. We describe the positions, orientations, sizes, shapes, strengths, and kinematics of these regions and correlate them with the spatial distribution of numerical dissipation. Statistical distributions of these various properties of current density zones are presented to determine the heights within the corona that contribute most to the dissipation rate, the flow properties associated with reconnection sites, and representative parameters for future large volume reconnection simulations.

  17. Mechanical Properties of a Superalloy Disk with a Dual Grain Structure

    NASA Technical Reports Server (NTRS)

    Gayda, John; Gabb, Timothy; Kantzos, Peter

    2003-01-01

    Mechanical properties from an advanced, nickel-base superalloy disk, with a dual grain structure consisting of a fine grain bore and coarse grain rim, were evaluated. The dual grain structure was produced using NASA's low cost Dual Microstructure Heat Treatment (DMHT) process. The results showed the DMHT disk to have a high strength, fatigue resistant bore comparable to a subsolvus (fine grain) heat treated disk, and a creep resistant rim comparable to a supersolvus (coarse grain) heat treated disk. Additional work on subsolvus solutioning before or after the DMHT conversion appears to be a viable avenue for further improvement in disk properties.

  18. Testing Horava-Lifshitz gravity using thin accretion disk properties

    SciTech Connect

    Harko, Tiberiu; Kovacs, Zoltan; Lobo, Francisco S. N.

    2009-08-15

    Recently, a renormalizable gravity theory with higher spatial derivatives in four dimensions was proposed by Horava. The theory reduces to Einstein gravity with a nonvanishing cosmological constant in IR, but it has improved UV behaviors. The spherically symmetric black hole solutions for an arbitrary cosmological constant, which represent the generalization of the standard Schwarzschild-(anti) de Sitter solution, have also been obtained for the Horava-Lifshitz theory. The exact asymptotically flat Schwarzschild-type solution of the gravitational field equations in Horava gravity contains a quadratic increasing term, as well as the square root of a fourth order polynomial in the radial coordinate, and it depends on one arbitrary integration constant. The IR-modified Horava gravity seems to be consistent with the current observational data, but in order to test its viability more observational constraints are necessary. In the present paper we consider the possibility of observationally testing Horava gravity by using the accretion disk properties around black holes. The energy flux, the temperature distribution, the emission spectrum, as well as the energy conversion efficiency are obtained, and compared to the standard general relativistic case. Particular signatures can appear in the electromagnetic spectrum, thus leading to the possibility of directly testing Horava gravity models by using astrophysical observations of the emission spectra from accretion disks.

  19. The dust properties of the Beta Pictoris disk

    NASA Astrophysics Data System (ADS)

    Augereau, J.-C.

    2014-09-01

    The dust grains in orbit around Beta Pictoris are an essential source of information about its planetary system. Their spatial distribution and properties tell us about the dynamics and composition of their parent, km-sized bodies, and how they interact with the planet(s). Since its discovery, thirty years ago, the Beta Pictoris disk has been intensively observed with a wealth of technics that probed the dust grains at different spatial scales and different wavelengths: broad-band photometry, (infrared) spectroscopy, scattered light and thermal emission direct imaging, polarimetry, optical and millimeter interferometry... In this talk, I will try to take stock of the knowledge accumulated over the last thirty years on dust in the planetary system of Beta Pictoris. Specific emphasis will be placed on the numerous remaining uncertainties.

  20. Research to Develop Process Models for Producing a Dual Property Titanium Alloy Compressor Disk.

    DTIC Science & Technology

    1981-10-01

    81 -4130 - RESEARCH TO DEVELOP PROCESS MODELS FOR PRODUCING A DUAL PROPERTY TITANIUM ALLOY COMPRESSOR DISK G. D. Lahoti T. Altan Battelle’s Columbus...COVERED INTERIM ANNUAL TECHNICAL RESEARCH TO DEVELOP PROCESS MODELS FOR PRODUCING A DUAL PROPERTY TITANIUM ALLOY REPORT, 8/1/80 to 7/31/81 COMPRESSOR DISK...validity and application of this approach will be demonstrated by developing forging process for a compressor disk from Ti-6242 alloy, as an example. VD

  1. ORIGIN OF CHEMICAL AND DYNAMICAL PROPERTIES OF THE GALACTIC THICK DISK

    SciTech Connect

    Bekki, Kenji; Tsujimoto, Takuji

    2011-09-01

    We adopt a scenario in which the Galactic thick disk was formed by minor merging between the first generation of the Galactic thin disk (FGTD) and a dwarf galaxy about {approx}9 Gyr ago and thereby investigate chemical and dynamical properties of the Galactic thick disk. In this scenario, the dynamical properties of the thick disk have long been influenced both by the mass growth of the second generation of the Galactic thin disk (i.e., the present thin disk) and by its non-axisymmetric structures. On the other hand, the early star formation history and chemical evolution of the thin disk was influenced by the remaining gas of the thick disk. Based on N-body simulations and chemical evolution models, we investigate the radial metallicity gradient, structural and kinematical properties, and detailed chemical abundance patterns of the thick disk. Our numerical simulations show that the ancient minor merger event can significantly flatten the original radial metallicity gradient of the FGTD, in particular, in the outer part, and also can be responsible for migration of inner metal-rich stars into the outer part (R > 10 kpc). The simulations show that the central region of the thick disk can develop a bar due to dynamical effects of a separate bar in the thin disk. Whether or not rotational velocities (V{sub {phi}}) can correlate with metallicities ([Fe/H]) for the simulated thick disks depends on the initial metallicity gradients of the FGTDs. The simulated orbital eccentricity distributions in the thick disk for models with higher mass ratios ({approx}0.2) and lower orbital eccentricities ({approx}0.5) of minor mergers are in good agreement with the corresponding observations. The simulated V{sub {phi}}-|z| relation of the thick disk in models with low orbital inclination angles of mergers are also in good agreement with the latest observational results. The vertical metallicity gradient of the simulated thick disk is rather flat or very weakly negative in the solar

  2. Debris disks as signposts of terrestrial planet formation. II. Dependence of exoplanet architectures on giant planet and disk properties

    NASA Astrophysics Data System (ADS)

    Raymond, S. N.; Armitage, P. J.; Moro-Martín, A.; Booth, M.; Wyatt, M. C.; Armstrong, J. C.; Mandell, A. M.; Selsis, F.; West, A. A.

    2012-05-01

    plausible initial conditions for planetary systems. However, among the configurations explored, the best candidates for hosting terrestrial planets at ~1 AU are stars older than 0.1-1 Gyr with bright debris disks at 70 μm but with no currently-known giant planets. These systems combine evidence for the presence of ample rocky building blocks, with giant planet properties that are least likely to undergo destructive dynamical evolution. Thus, we predict two correlations that should be detected by upcoming surveys: an anti-correlation between debris disks and eccentric giant planets and a positive correlation between debris disks and terrestrial planets. Three movies associated to Figs. 1, 3, and 7 are available in electronic form at http://www.aanda.org

  3. Properties of Circumstelar Disks of Three Northern Galactic Be Stars

    NASA Astrophysics Data System (ADS)

    Ubaque Brito, K. Y.; Sabogal Martínez, B. E.; García-Varela, A.; Salas, L.; álvarez, M.

    2017-07-01

    Be stars have a very rapid rotation that leads, along with other mechanisms, to the generation of circumstellar decretion disks. Spectroscopic analysis of their Hydrogen emission lines in the infrared can be useful to understand the disk evolution. This is possible through characterizing the dependency with wavelenght of physical parameters of the lines, such as integrated flux and full width at half maximum. In this work, we obtained integrated fluxes for Humphreys, Pfund and Brackett spectral lines of a sample of 3 Be stars: γ Cas, φ Per and 28 Tau. With these data, we analized changes in optical depth and density of the disks. We found that the circumstellar disks of these stars are optically thin, based on a flux ratio diagram and from a qualitative description of the morphology found in the infrared spectra. We studied also the optical spectra of BeSS database of these stars and found that the variability of the Hα profile is correlated with the evolution and stages of stability in Be star disks. In our case, we could say that γ Cas and φ Per have circumstellar disks stable with a high density, which have remained almost constant. By contrast the remarkable variability of Hα profile for star 28 Tau lead us to believe that its disk has had episodes of dissipation and slight changes in density. All these results are in agreement with previous studies for different Be stars, confirming the mentioned aspects as general indicators of density changes suffered by circumstellar disks of Be stars.

  4. Thermal and Mechanical Property Characterization of the Advanced Disk Alloy LSHR

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P.; Gayda, John; Telesman, Jack; Kantzos, Peter T.

    2005-01-01

    A low solvus, high refractory (LSHR) powder metallurgy disk alloy was recently designed using experimental screening and statistical modeling of composition and processing variables on sub-scale disks to have versatile processing-property capabilities for advanced disk applications. The objective of the present study was to produce a scaled-up disk and apply varied heat treat processes to enable full-scale demonstration of LSHR properties. Scaled-up disks were produced, heat treated, sectioned, and then machined into specimens for mechanical testing. Results indicate the LSHR alloy can be processed to produce fine and coarse grain microstructures with differing combinations of strength and time-dependent mechanical properties, for application at temperatures exceeding 1300 F.

  5. Properties of Be Star Disks at High Spatial Resolution Invited Review

    NASA Astrophysics Data System (ADS)

    Schaefer, G. H.

    2016-11-01

    This paper presents an observational overview of the properties of Be star disks. The presence of circumstellar gas around Be stars can be inferred from observations of the double-peaked emission line profiles, infrared excesses, and linear polarization. High spatial resolution interferometric observations have confirmed that the gas exists in a flattened disk. The geometry and angular size of the disks at different wavelengths can be used to probe the density structure. The combination of spectroscopy and interferometry can be used to study the kinematics of the rotating disks and investigate asymmetries that arise from one-armed density waves in the circumstellar material.

  6. Dust properties across the CO snowline in the HD 163296 disk from ALMA and VLA observations

    NASA Astrophysics Data System (ADS)

    Guidi, G.; Tazzari, M.; Testi, L.; de Gregorio-Monsalvo, I.; Chandler, C. J.; Pérez, L.; Isella, A.; Natta, A.; Ortolani, S.; Henning, Th.; Corder, S.; Linz, H.; Andrews, S.; Wilner, D.; Ricci, L.; Carpenter, J.; Sargent, A.; Mundy, L.; Storm, S.; Calvet, N.; Dullemond, C.; Greaves, J.; Lazio, J.; Deller, A.; Kwon, W.

    2016-04-01

    Context. To characterize the mechanisms of planet formation it is crucial to investigate the properties and evolution of protoplanetary disks around young stars, where the initial conditions for the growth of planets are set. The high spatial resolution of Atacama Large Millimeter/submillimeter Array (ALMA) and Karl G. Jansky Very Large Array (VLA) observations now allows the study of radial variations of dust properties in nearby resolved disks and the investigation of the early stages of grain growth in disk midplanes. Aims: Our goal is to study grain growth in the well-studied disk of the young, intermediate-mass star HD 163296 where dust processing has already been observed and to look for evidence of growth by ice condensation across the CO snowline, which has already been identified in this disk with ALMA. Methods: Under the hypothesis of optically thin emission, we compare images at different wavelengths from ALMA and VLA to measure the opacity spectral index across the disk and thus the maximum grain size. We also use a Bayesian tool based on a two-layer disk model to fit the observations and constrain the dust surface density. Results: The measurements of the opacity spectral index indicate the presence of large grains and pebbles (≥1 cm) in the inner regions of the disk (inside ~50 AU) and smaller grains, consistent with ISM sizes, in the outer disk (beyond 150 AU). Re-analyzing ALMA Band 7 science verification data, we find (radially) unresolved excess continuum emission centered near the location of the CO snowline at ~90 AU. Conclusions: Our analysis suggests a grain size distribution consistent with an enhanced production of large grains at the CO snowline and consequent transport to the inner regions. Our results combined with the excess in infrared scattered light suggests there is a structure at 90 AU involving the whole vertical extent of the disk. This could be evidence of small scale processing of dust at the CO snowline.

  7. The Tensile Properties of Advanced Nickel-Base Disk Superalloys During Quenching Heat Treatments

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P.; Gayda, John; Kantzos, Pete T.; Biles, Tiffany; Konkel, William

    2001-01-01

    There is a need to increase the temperature capabilities of superalloy turbine disks. This would allow full utilization of higher temperature combustor and airfoil concepts under development. One approach to meet this goal is to modify the processing and chemistry of advanced alloys, while preserving the ability to use rapid cooling supersolvus heat treatments to achieve coarse grain, fine gamma prime microstructures. An important step in this effort is to understand the key high temperature tensile properties of advanced alloys as they exist during supersolvus heat treatments. This could help in projecting cracking tendencies of disks during quenches from supersolvus heat treatments. The objective of this study was to examine the tensile properties of two advanced disk superalloys during simulated quenching heat treatments. Specimens were cooled from the solution heat treatment temperatures at controlled rates, interrupted, and immediately tensile tested at various temperatures. The responses and failure modes were compared and related to the quench cracking tendencies of disk forgings.

  8. Properties of the remnant clockwise disk of young stars in the galactic center

    SciTech Connect

    Yelda, S.; Ghez, A. M.; Meyer, L.; Morris, M. R.; Lu, J. R.; Do, T.; Matthews, K. E-mail: ghez@astro.ucla.edu E-mail: morris@astro.ucla.edu E-mail: do@di.utoronto.ca

    2014-03-10

    We present new kinematic measurements and modeling of a sample of 116 young stars in the central parsec of the Galaxy in order to investigate the properties of the young stellar disk. The measurements were derived from a combination of speckle and laser guide star adaptive optics imaging and integral field spectroscopy from the Keck telescopes. Compared to earlier disk studies, the most important kinematic measurement improvement is in the precision of the accelerations in the plane of the sky, which have a factor of six smaller uncertainties (σ ∼ 10 μas yr{sup –2}). We have also added the first radial velocity measurements for eight young stars, increasing the sample at the largest radii (6''-12'') by 25%. We derive the ensemble properties of the observed stars using Monte Carlo simulations of mock data. There is one highly significant kinematic feature (∼20σ), corresponding to the well-known clockwise disk, and no significant feature is detected at the location of the previously claimed counterclockwise disk. The true disk fraction is estimated to be ∼20%, a factor of ∼2.5 lower than previous claims, suggesting that we may be observing the remnant of what used to be a more densely populated stellar disk. The similarity in the kinematic properties of the B stars and the O/WR stars suggests a common star formation event. The intrinsic eccentricity distribution of the disk stars is unimodal, with an average value of (e) = 0.27 ± 0.07, which we show can be achieved through dynamical relaxation in an initially circular disk with a moderately top-heavy mass function.

  9. The Mechanical Properties of Candidate Superalloys for a Hybrid Turbine Disk

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P.; MacKay, Rebecca A.; Draper, Susan L.; Sudbrack, Chantal K.; Nathal, Michael V.

    2013-01-01

    The mechanical properties of several cast blade superalloys and one powder metallurgy disk superalloy were assessed for potential use in a dual alloy hybrid disk concept of joined dissimilar bore and web materials. Grain size was varied for each superalloy class. Tensile, creep, fatigue, and notch fatigue tests were performed at 704 to 815 degC. Typical microstructures and failure modes were determined. Preferred materials were then selected for future study as the bore and rim alloys in this hybrid disk concept. Powder metallurgy superalloy LSHR at 15 micron grain size and single crystal superalloy LDS-1101+Hf were selected for further study, and future work is recommended to develop the hybrid disk concept.

  10. A FEM-based method to determine the complex material properties of piezoelectric disks.

    PubMed

    Pérez, N; Carbonari, R C; Andrade, M A B; Buiochi, F; Adamowski, J C

    2014-08-01

    Numerical simulations allow modeling piezoelectric devices and ultrasonic transducers. However, the accuracy in the results is limited by the precise knowledge of the elastic, dielectric and piezoelectric properties of the piezoelectric material. To introduce the energy losses, these properties can be represented by complex numbers, where the real part of the model essentially determines the resonance frequencies and the imaginary part determines the amplitude of each resonant mode. In this work, a method based on the Finite Element Method (FEM) is modified to obtain the imaginary material properties of piezoelectric disks. The material properties are determined from the electrical impedance curve of the disk, which is measured by an impedance analyzer. The method consists in obtaining the material properties that minimize the error between experimental and numerical impedance curves over a wide range of frequencies. The proposed methodology starts with a sensitivity analysis of each parameter, determining the influence of each parameter over a set of resonant modes. Sensitivity results are used to implement a preliminary algorithm approaching the solution in order to avoid the search to be trapped into a local minimum. The method is applied to determine the material properties of a Pz27 disk sample from Ferroperm. The obtained properties are used to calculate the electrical impedance curve of the disk with a Finite Element algorithm, which is compared with the experimental electrical impedance curve. Additionally, the results were validated by comparing the numerical displacement profile with the displacements measured by a laser Doppler vibrometer. The comparison between the numerical and experimental results shows excellent agreement for both electrical impedance curve and for the displacement profile over the disk surface. The agreement between numerical and experimental displacement profiles shows that, although only the electrical impedance curve is

  11. Evolutionary stages and disk properties of young stellar objects in the Perseus cloud

    NASA Astrophysics Data System (ADS)

    Zhang, Hong-Xin; Gao, Yu; Fang, Min; Yuan, Hai-Bo; Zhao, Ying-He; Chang, Rui-Xiang; Jiang, Xue-Jian; Liu, Xiao-Wei; Luo, A.-Li; Ma, Hong-Jun; Shao, Zheng-Yi; Wang, Xiao-Long

    2015-08-01

    We investigated the evolutionary stages and disk properties of 211 young stellar objects (YSOs) across the Perseus cloud by modeling their broadband optical to mid-infrared (IR) spectral energy distribution (SED). Our optical gri photometry data were obtained from the recently finished Purple Mountain Observatory Xuyi Schmidt Telescope Photometric Survey of the Galactic Anti-center (XSTPS-GAC). About 81% of our sample fall into the Stage II phase which is characterized by having optically thick disks, while 14% into the Stage I phase characterized by having significant infalling envelopes, and the remaining 5% into the Stage III phase characterized by having optically thin disks. The median stellar age and mass of the Perseus YSOs are 3.1 Myr and 0.3 M⊙ respectively. By exploring the relationships among the turnoff wave bands λturnoff (longward of which significant IR excesses above the stellar photosphere are observed), the excess spectral index αexcess as determined for λ > λturnoff, and the disk inner radius Rin (determined from SED modeling) for YSOs at different evolutionary stages, we found that the median and standard deviation of αexcess for YSOs with optically thick disks tend to increase with λturnoff, especially at λturnoff ≥5.8 μm, whereas the median fractional dust luminosities Ldust/L★ tend to decrease with increasing λturnoff. This points to an inside-out process of disk clearing for small dust grains. Moreover, a positive correlation between αexcess and Rin was found at αexcess ≳ 0 and Rin ≳ 10 × the dust sublimation radius Rsub, irrespective of λturnoff, Ldust/L★ and disk flaring. This suggests that the outer disk flaring either does not evolve synchronously with the inside-out disk clearing of small dust grains or has little appreciable influence on the spectral slopes at λ ≲ 24 μm. About 23% of our YSO disks are classified as transitional disks, which have λturnoff ≥ 5.8 μm and Ldust/L★ > 10-3. The transitional

  12. Circumnuclear Disks in Early-type Galaxies: 12CO(2-1) and Continuum Properties

    NASA Astrophysics Data System (ADS)

    Boizelle, Benjamin; Barth, Aaron J.; Baker, Andrew J.; Darling, Jeremiah K.; Ho, Luis; Walsh, Jonelle; Buote, David A.

    2017-01-01

    Black hole masses in early-type galaxies (ETGs) can be precisely measured using the kinematics of circumnuclear gas. About 10% of nearby ETGs possess round, morphologically regular nuclear dust disks. The accompanying molecular gas is expected to be in uniform, circular rotation and therefore be a good dynamical tracer of the inner galaxy potential. Using ALMA, we have obtained 0.3”-resolution observations of thirteen ETGs which were selected based on the presence of nuclear dust disks seen in HST images. Most are detected in CO(2-1), and we find that these molecular gas disks are in dynamically cold rotation with a few showing clear evidence of rapid central rotation. We present the gas distributions and kinematics of these molecular disks, as well as the continuum properties of the dusty disks and the prevalence of low-luminosity active galactic nuclei at their centers. We discuss the suitability of molecular gas disks in ETGs for making precision measurements of black hole masses.

  13. The Effects of Heat Treatment and Microstructure Variations on Disk Superalloy Properties at High Temperature

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P.; Gayda, John; Telesman, Jack; Garg, Anita

    2008-01-01

    The effects of heat treatment and resulting microstructure variations on high temperature mechanical properties were assessed for a powder metallurgy disk superalloy LSHR. Blanks were consistently supersolvus solution heat treated and quenched at two cooling rates, than aged at varying temperatures and times. Tensile, creep, and dwell fatigue crack growth tests were then performed at 704 C. Gamma' precipitate microstructures were quantified. Relationships between heat treatment-microstructure, heat treatment-mechanical properties, and microstructure-mechanical properties were assessed.

  14. Realistic Subscale Evaluations of the Mechanical Properties of Advanced Disk Superalloys

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P.; Gayda, John; Telesman, Jack; Kantzos, Peter T.; Konkel, William A.

    2003-01-01

    A series of experimental powder metallurgy disk alloys were evaluated for their processing characteristics and high temperature mechanical properties. Powder of each alloy was hot compacted, extruded, and isothermally forged into subscale disks. Disks were subsolvus and supersolvus heat treated, then quenched using procedures designed to reproduce the cooling paths expected in large-scale disks. Mechanical tests were then performed at 538, 704, and 815 C. Several alloys had superior tensile and creep properties at 704 C and higher temperatures, but were difficult to process and prone to quench cracking, chiefly due to their high gamma prime solvus temperature. Several other alloys had more favorable processing characteristics due to their lower gamma prime solvus temperature and balanced time-dependent properties at 704 C. Results indicate an experimental low solvus, high refractory alloy can build upon the best attributes of all these alloys, giving exceptional tensile and creep properties at high temperatures with good processing characteristics due to a low gamma prime solvus.

  15. Multiwavelength analysis for interferometric (sub-)mm observations of protoplanetary disks. Radial constraints on the dust properties and the disk structure

    NASA Astrophysics Data System (ADS)

    Tazzari, M.; Testi, L.; Ercolano, B.; Natta, A.; Isella, A.; Chandler, C. J.; Pérez, L. M.; Andrews, S.; Wilner, D. J.; Ricci, L.; Henning, T.; Linz, H.; Kwon, W.; Corder, S. A.; Dullemond, C. P.; Carpenter, J. M.; Sargent, A. I.; Mundy, L.; Storm, S.; Calvet, N.; Greaves, J. A.; Lazio, J.; Deller, A. T.

    2016-04-01

    Context. The growth of dust grains from sub-μm to mm and cm sizes is the first step towards the formation of planetesimals. Theoretical models of grain growth predict that dust properties change as a function of disk radius, mass, age, and other physical conditions. High angular resolution observations at several (sub-)mm wavelengths constitute the ideal tool with which to directly probe the bulk of dust grains and to investigate the radial distribution of their properties. Aims: We lay down the methodology for a multiwavelength analysis of (sub-)mm and cm continuum interferometric observations to self-consistently constrain the disk structure and the radial variation of the dust properties. The computational architecture is massively parallel and highly modular. Methods: The analysis is based on the simultaneous fit in the uv-plane of observations at several wavelengths with a model for the disk thermal emission and for the dust opacity. The observed flux density at the different wavelengths is fitted by posing constraints on the disk structure and on the radial variation of the grain size distribution. Results: We apply the analysis to observations of three protoplanetary disks (AS 209, FT Tau, DR Tau) for which a combination of spatially resolved observations in the range ~0.88 mm to ~10 mm is available from SMA, CARMA, and VLA. In these disks we find evidence of a decrease in the maximum dust grain size, amax, with radius. We derive large amax values up to 1 cm in the inner disk 15 AU ≤ R ≤ 30 AU and smaller grains with amax ~ 1 mm in the outer disk (R ≳ 80 AU). Our analysis of the AS 209 protoplanetary disk confirms previous literature results showing amax decreasing with radius. Conclusions: Theoretical studies of planetary formation through grain growth are plagued by the lack of direct information on the radial distribution of the dust grain size. In this paper we develop a multiwavelength analysis that will allow this missing quantity to be

  16. Conduction Properties Distinguish Unmyelinated Sympathetic Efferent Fibers and Unmyelinated Primary Afferent Fibers in the Monkey

    PubMed Central

    Ringkamp, Matthias; Johanek, Lisa M.; Borzan, Jasenka; Hartke, Timothy V.; Wu, Gang; Pogatzki-Zahn, Esther M.; Campbell, James N.; Shim, Beom; Schepers, Raf J.; Meyer, Richard A.

    2010-01-01

    Background Different classes of unmyelinated nerve fibers appear to exhibit distinct conductive properties. We sought a criterion based on conduction properties for distinguishing sympathetic efferents and unmyelinated, primary afferents in peripheral nerves. Methodology/Principal Findings In anesthetized monkey, centrifugal or centripetal recordings were made from single unmyelinated nerve fibers in the peroneal or sural nerve, and electrical stimuli were applied to either the sciatic nerve or the cutaneous nerve endings, respectively. In centrifugal recordings, electrical stimulation at the sympathetic chain and dorsal root was used to determine the fiber's origin. In centrifugal recordings, sympathetic fibers exhibited absolute speeding of conduction to a single pair of electrical stimuli separated by 50 ms; the second action potential was conducted faster (0.61 0.16%) than the first unconditioned action potential. This was never observed in primary afferents. Following 2 Hz stimulation (3 min), activity-dependent slowing of conduction in the sympathetics (8.6 0.5%) was greater than in one afferent group (6.7 0.5%) but substantially less than in a second afferent group (29.4 1.9%). In centripetal recordings, most mechanically-insensitive fibers also exhibited absolute speeding to twin pulse stimulation. The subset that did not show this absolute speeding was responsive to chemical stimuli (histamine, capsaicin) and likely consists of mechanically-insensitive afferents. During repetitive twin pulse stimulation, mechanosensitive afferents developed speeding, and speeding in sympathetic fibers increased. Conclusions/Significance The presence of absolute speeding provides a criterion by which sympathetic efferents can be differentiated from primary afferents. The differences in conduction properties between sympathetics and afferents likely reflect differential expression of voltage-sensitive ion channels. PMID:20140089

  17. Catalytic properties of the retinal rod outer segment disk ADP-ribosyl cyclase.

    PubMed

    Fabiano, Andrea; Panfoli, Isabella; Calzia, Daniela; Bruschi, Maurizio; Ravera, Silvia; Bachi, Angela; Cattaneo, Angela; Morelli, Alessandro; Candiano, Giovanni

    2011-03-01

    Cyclic ADP-ribose (cADPR) is a second messenger modulating intracellular calcium levels. We have previously described a cADPR-dependent calcium signaling pathway in bovine rod outer segments (ROS), where calcium ions play a pivotal role. ROS ADP-ribosyl cyclase (ADPR-cyclase) was localized in the membrane fraction. In the present work, we examined the properties of the disk ADPR-cyclase through the production of cyclic GDP-ribose from the NAD(+) analogue NGD(+). The enzyme displayed an estimated K(m) for NGD(+) of 12.5 ± 0.3 μM, a V(max) of 26.50 ± 0.70 pmol cyclic GDP-ribose synthesized/min/mg, and optimal pH of 6.5. The effect of divalent cations (Zn(2+), Cu(2+), and Ca(2+)) was also tested. Micromolar Zn(2+) and Cu(2+) inhibited the disk ADPR-cyclase activity (half maximal inhibitory concentration, IC50=1.1 and 3.6 μM, respectively). By contrast, Ca(2+) ions had no effect. Interestingly, the properties of the intracellular membrane-associated ROS disk ADPR-cyclase are more similar to those of the ADPR-cyclase found in CD38-deficient mouse brain, than to those of CD38 or CD157. The novel intracellular mammalian ADPR-cyclase would elicit Ca(2+) release from the disks at various rates in response to change in free Ca(2+) concentrations, caused by light versus dark adaptation, in fact there was no difference in disk ADPR-cyclase activity in light or dark conditions. Data suggest that disk ADPR-cyclase may be a potential target of retinal toxicity of Zn(2+) and may shed light to the role of Cu(2+) and Zn(2+) deficiency in retina. Copyright © Cambridge University Press, 2011

  18. Circumstellar Structure Properties of Young Stellar Objects: Envelopes, Bipolar Outflows, and Disks

    NASA Astrophysics Data System (ADS)

    Kwon, Woojin

    2009-12-01

    Physical properties of the three main structures in young stellar objects (YSOs), envelopes, bipolar outflows, and circumstellar disks, have been studied using radio interferometers: the Berkeley-Illinois-Maryland Association (BIMA) array and the Combined Array for Research in Millimeter-wave Astronomy (CARMA). (1) Envelopes. Three Class 0 YSOs (L1448 IRS 2, L1448 IRS 3, and L1157) have been observed by CARMA at λ = 1.3 mm and 2.7 mm continuum. Through visibility modeling to fit the two wavelength continuum data simultaneously, we found that the dust opacity spectral index (β) of Class 0 YSOs is around unity, which implies that dust grains have significantly grown already at the earliest stage. In addition, we discussed the radial dependence of β detected in L1448 IRS 3B and also estimated the density distribution of the three targets. (2) Bipolar outflows. Polarimetric observations in the λ = 1.3 mm continuum and CO, as well as spectral line observations in 13CO and C18O have been carried out toward L1448 IRS 3, which has three Class 0 YSOs, using BIMA. We clearly identified two interacting bipolar outflows from the "binary system" of IRS 3A and 3B and estimated the velocity, inclination, and opening angle of the 3B bipolar outflow, using Bayesian inference. Also, we showed that the "binary system" can be bound gravitationally and we estimated the specific angular momentum, which is between those of binary stars and molecular cloud cores. In addition, we marginally detected linear polarizations at the center of IRS 3B (implying a toroidal magnetic field) in continuum and at the bipolar outflow region in CO. (3) Circumstellar disks. We present the results of 6 objects (CI Tau, DL Tau, DO Tau, FT Tau, Haro 6-13, and HL Tau) in our T Tauri disk survey using CARMA. The data consist of λ = 1.3 mm and 2.7 mm continuum with an angular resolution up to 0.13". Through visibility modeling of two disk models (power-law disk with a Gaussian edge and viscous accretion

  19. A Multiple Impact Hypothesis for Moon Formation: Target Spin and Disk Properties

    NASA Astrophysics Data System (ADS)

    Rufu, R.; Aharonson, O.

    2015-12-01

    We investigate aspects of the multiple impact hypothesis for Moon's formation, whereby the proto-Earth suffers successive collisions, each forming a debris disk that accretes to form a moonlet. The moonlets tidally advance outward, and potentially coalesce to form the Moon. In addressing the fundamental problem of the Moon's formation, we consider smaller impactors than previously studied, and investigate the effect of new geometries using a Smoothed Particles Hydrodynamics (SPH) code. For impacts within the equatorial plane, we find multiple impactors are effective in draining angular momentum from the target's initial spin due to the often-neglected angular momentum carried by escaping mass. Our simulations reveal new consequences of non-equatorial inclination of the impactor, also previously neglected. We note relationships with the resulting disks of corresponding equatorial cases, but find that the target's axis of rotation can now be tilted by a significant amount (10's of degrees) with sub-Mars size impactors. Importantly for distinguishing among competing Moon formation hypotheses, our results imply that (i) the rotational acceleration of the proto-Earth by successive impacts may be limited by angular momentum drain if the impacting population contains multiple members of medium size, and (ii) impacts onto such a non-rapidly rotation proto-Earth (well below break-up speed) can produce disks compatible with sub-Moon fragments in mass, momentum, and composition.

  20. Physical Properties of the Be Star Disks in h and χ Persei

    NASA Astrophysics Data System (ADS)

    Boyer, A. N.; McSwain, M. V.

    2016-11-01

    We present new results in our on-going analysis of the B-type and Be star populations of the double open clusters h and χ Persei. As these clusters are rich in massive B-type and Be stars, they present an optimal location for studying the physical properties and variability of these disk structures. In previous analysis we have established physical properties, including V sin i, Teff, log gpolar, M★, and R★, for each B-type and Be star in our sample. In this work we continue our study of the cluster Be stars by examining the disk spectral energy distributions (SEDs) via observations from WEBDA, 2MASS, Spitzer, AKARI, and WISE. We also present multiple observations of Hα taken between 2009-2012 with the KPNO Coudé Feed, KPNO 2.1m, and WIRO telescopes. We use the Hα equivalent width model of Grundstrom & Gies and the infrared flux model of Touhami et al. to constrain the disk radii and densities for our Be star sample. Our results show a systematic, order of magnitude discrepancy between the disk densities predicted by the Grundstrom & Gies models, and those which appear to match with the observed infrared flux excess.

  1. Effects of temperature distribution and elastic properties of materials on gas-turbine-disk stresses

    NASA Technical Reports Server (NTRS)

    Holms, Arthur G; Faldetta, Richard D

    1947-01-01

    Calculations were made to determine the influence of changes in temperature distribution and in elastic material properties on calculated elastic stresses for a typical gas-turbine disk. Severe temperature gradients caused thermal stresses of sufficient magnitude to reduce the operating safety of the disk. Small temperature gradients were found to be desirable because they produced thermal stresses that subtracted from the centrifugal stresses in the region of the rim. The thermal gradients produced a tendency for a severe stress condition to exist near the rim but this stress condition could be shifted away from the region of blade attachment by altering the temperature distribution. The investigation of elastic material properties showed that centrifugal stresses are slightly affected by changes in modulus of elasticity, but that thermal stresses are approximately proportional to modulus of elasticity and to coefficient of thermal expansion.

  2. Noncontact thermophysical property measurement by levitation of a thin liquid disk.

    PubMed

    Lee, Sungho; Ohsaka, Kenichi; Rednikov, Alexei; Sadhal, Satwindar Singh

    2006-09-01

    The purpose of the current research program is to develop techniques for noncontact measurement of thermophysical properties of highly viscous liquids. The application would be for undercooled liquids that remain liquid even below the freezing point when suspended without a container. The approach being used here consists of carrying out thermocapillary flow and temperature measurements in a horizontally levitated, laser-heated thin glycerin disk. In a levitated state, the disk is flattened by an intense acoustic field. Such a disk has the advantage of a relatively low gravitational potential over the thickness, thus mitigating the buoyancy effects, and helping isolate the thermocapillary-driven flows. For the purpose of predicting the thermal properties from these measurements, it is necessary to develop a theoretical model of the thermal processes. Such a model has been developed, and, on the basis of the observed shape, the thickness is taken to be a minimum at the center with a gentle parabolic profile at both the top and the bottom surfaces. This minimum thickness is much smaller than the radius of disk drop and the ratio of thickness to radius becomes much less than unity. It is heated by laser beam in normal direction to the edge. A general three-dimensional momentum equation is transformed into a two-variable vorticity equation. For the highly viscous liquid, a few millimeters in size, Stokes equations adequately describe the flow. Additional approximations are made by considering average flow properties over the disk thickness in a manner similar to lubrication theory. In the same way, the three-dimensional energy equation is averaged over the disk thickness. With convection boundary condition at the surfaces, we integrate a general three-dimensional energy equation to get an averaged two-dimensional energy equation that has convection terms, conduction terms, and additional source terms corresponding to a Biot number. A finite-difference numerical

  3. Properties of the Closest Young Binaries. I. DF Tau’s Unequal Circumstellar Disk Evolution

    NASA Astrophysics Data System (ADS)

    Allen, T. S.; Prato, L.; Wright-Garba, N.; Schaefer, G.; Biddle, L. I.; Skiff, B.; Avilez, I.; Muzzio, R.; Simon, M.

    2017-08-01

    We present high-resolution, spatially resolved, near-infrared spectroscopy and imaging of the two components of DF Tau, a young, low-mass, visual binary in the Taurus star-forming region. With these data, we provide a more precise orbital solution for the system, determine component spectral types, radial velocity, veiling and v\\sin i values, and construct individual spectral energy distributions. We estimate the masses of both stars to be ∼ 0.6 {M}ȯ . We find markedly different circumstellar properties for DF Tau A and B: evidence for a disk, such as near-infrared excess and accretion signatures, is clearly present for the primary, while it is absent for the secondary. Additionally, the v\\sin i and rotation period measurements show that the secondary is rotating significantly more rapidly than the primary. We interpret these results in the framework of disk-locking and argue that DF Tau A is an example of disk-modulated rotation in a young system. The DF Tau system raises fundamental questions about our assumptions of universal disk formation and evolution.

  4. VARIATIONS ON DEBRIS DISKS. II. ICY PLANET FORMATION AS A FUNCTION OF THE BULK PROPERTIES AND INITIAL SIZES OF PLANETESIMALS

    SciTech Connect

    Kenyon, Scott J.; Bromley, Benjamin C. E-mail: bromley@physics.utah.ed

    2010-05-15

    We describe comprehensive calculations of the formation of icy planets and debris disks at 30-150 AU around 1-3 M {sub sun} stars. Disks composed of large, strong planetesimals produce more massive planets than disks composed of small, weak planetesimals. The maximum radius of icy planets ranges from {approx}1500 km to 11,500 km. The formation rate of 1000 km objects-{sup P}lutos{sup -}is a useful proxy for the efficiency of icy planet formation. Plutos form more efficiently in massive disks, in disks with small planetesimals, and in disks with a range of planetesimal sizes. Although Plutos form throughout massive disks, Pluto production is usually concentrated in the inner disk. Despite the large number of Plutos produced in many calculations, icy planet formation is inefficient. At the end of the main sequence lifetime of the central star, Plutos contain less than 10% of the initial mass in solid material. This conclusion is independent of the initial mass in the disk or the properties of the planetesimals. Debris disk formation coincides with the formation of planetary systems containing Plutos. As Plutos form, they stir leftover planetesimals to large velocities. A cascade of collisions then grinds the leftovers to dust, forming an observable debris disk. In disks with small ({approx}<1-10 km) planetesimals, collisional cascades produce luminous debris disks with maximum luminosity {approx}10{sup -2} times the stellar luminosity. Disks with larger planetesimals produce debris disks with maximum luminosity {approx}5 x 10{sup -4} (10 km) to 5 x 10{sup -5} (100 km) times the stellar luminosity. Following peak luminosity, the evolution of the debris disk emission is roughly a power law, f {proportional_to} t {sup -n} with n{approx} 0.6-0.8. Observations of debris disks around A-type and G-type stars strongly favor models with small planetesimals. In these models, our predictions for the time evolution and detection frequency of debris disks agree with published

  5. General-relativistic magnetohydrodynamics simulations of black hole accretion disks: Dynamics and radiative properties

    NASA Astrophysics Data System (ADS)

    Shiokawa, Hotaka

    The goal of the series of studies in this thesis is to understand the black hole accretion process and predict its observational properties. The highly non-linear process involves a turbulent magnetized plasma in a general relativistic regime, thus making it hard to study analytically. We use numerical simulations, specifically general relativistic magnetohydrodynamics (GRMHD), to construct a realistic dynamical and radiation model of accretion disks. Our simulations are for black holes in low luminous regimes that probably possesses a hot and thick accretion disk. Flows in this regime are called radiatively inefficient accretion flows (RIAF). The most plausible mechanism for transporting angular momentum is turbulence induced by magnetorotational instability (MRI). The RIAF model has been used to model the supermassive black hole at the center of our Milky Way galaxy, Sagittarius A* (Sgr A*). Owing to its proximity, rich observational data of Sgr A* is available to compare with the simulation results. We focus mainly on four topics. First, we analyse numerical convergence of 3D GRMHD global disk simulations. Convergence is one of the essential factors in deciding quantitative outcomes of the simulations. We analyzed dimensionless shell-averaged quantities such as plasma beta, the azimuthal correlation length (angle) of fluid variables, and spectra of the source for four different resolutions. We found that all the variables converged with the highest resolution (384x384x256 in radial, poloidal, and azimuthal directions) except the magnetic field correlation length. It probably requires another factor of 2 in resolution to achieve convergence. Second, we studied the effect of equation of state on dynamics of GRMHD simulation and radiative transfer. Temperature of RIAF gas is high, and all the electrons are relativistic, but not the ions. In addition, the dynamical time scale of the accretion disk is shorter than the collisional time scale of electrons and ions

  6. Disk Evolution, Element Abundances and Cloud Properties of Young Gas Giant Planets

    PubMed Central

    Helling, Christiane; Woitke, Peter; Rimmer, Paul B.; Kamp, Inga; Thi, Wing-Fai; Meijerink, Rowin

    2014-01-01

    We discuss the chemical pre-conditions for planet formation, in terms of gas and ice abundances in a protoplanetary disk, as function of time and position, and the resulting chemical composition and cloud properties in the atmosphere when young gas giant planets form, in particular discussing the effects of unusual, non-solar carbon and oxygen abundances. Large deviations between the abundances of the host star and its gas giants seem likely to occur if the planet formation follows the core-accretion scenario. These deviations stem from the separate evolution of gas and dust in the disk, where the dust forms the planet cores, followed by the final run-away accretion of the left-over gas. This gas will contain only traces of elements like C, N and O, because those elements have frozen out as ices. ProDiMo protoplanetary disk models are used to predict the chemical evolution of gas and ice in the midplane. We find that cosmic rays play a crucial role in slowly un-blocking the CO, where the liberated oxygen forms water, which then freezes out quickly. Therefore, the C/O ratio in the gas phase is found to gradually increase with time, in a region bracketed by the water and CO ice-lines. In this regions, C/O is found to approach unity after about 5 Myrs, scaling with the cosmic ray ionization rate assumed. We then explore how the atmospheric chemistry and cloud properties in young gas giants are affected when the non-solar C/O ratios predicted by the disk models are assumed. The Drift cloud formation model is applied to study the formation of atmospheric clouds under the influence of varying premordial element abundances and its feedback onto the local gas. We demonstrate that element depletion by cloud formation plays a crucial role in converting an oxygen-rich atmosphere gas into carbon-rich gas when non-solar, premordial element abundances are considered as suggested by disk models. PMID:25370190

  7. Disk evolution, element abundances and cloud properties of young gas giant planets.

    PubMed

    Helling, Christiane; Woitke, Peter; Rimmer, Paul B; Kamp, Inga; Thi, Wing-Fai; Meijerink, Rowin

    2014-04-14

    We discuss the chemical pre-conditions for planet formation, in terms of gas and ice abundances in a protoplanetary disk, as function of time and position, and the resulting chemical composition and cloud properties in the atmosphere when young gas giant planets form, in particular discussing the effects of unusual, non-solar carbon and oxygen abundances. Large deviations between the abundances of the host star and its gas giants seem likely to occur if the planet formation follows the core-accretion scenario. These deviations stem from the separate evolution of gas and dust in the disk, where the dust forms the planet cores, followed by the final run-away accretion of the left-over gas. This gas will contain only traces of elements like C, N and O, because those elements have frozen out as ices. PRODIMO protoplanetary disk models are used to predict the chemical evolution of gas and ice in the midplane. We find that cosmic rays play a crucial role in slowly un-blocking the CO, where the liberated oxygen forms water, which then freezes out quickly. Therefore, the C/O ratio in the gas phase is found to gradually increase with time, in a region bracketed by the water and CO ice-lines. In this regions, C/O is found to approach unity after about 5 Myrs, scaling with the cosmic ray ionization rate assumed. We then explore how the atmospheric chemistry and cloud properties in young gas giants are affected when the non-solar C/O ratios predicted by the disk models are assumed. The DRIFT cloud formation model is applied to study the formation of atmospheric clouds under the influence of varying premordial element abundances and its feedback onto the local gas. We demonstrate that element depletion by cloud formation plays a crucial role in converting an oxygen-rich atmosphere gas into carbon-rich gas when non-solar, premordial element abundances are considered as suggested by disk models.

  8. OBSERVATIONAL PROPERTIES OF THE METAL-POOR THICK DISK OF THE MILKY WAY AND INSIGHTS INTO ITS ORIGINS

    SciTech Connect

    Ruchti, Gregory R.; Fulbright, Jon P.; Wyse, Rosemary F. G.; Gilmore, Gerard F.; Bienayme, Olivier; Siebert, Arnaud; Bland-Hawthorn, Joss; Gibson, Brad K.; Grebel, Eva K.; Helmi, Amina; Munari, Ulisse; Navarro, Julio F.; Parker, Quentin A.; Reid, Warren; Seabroke, George M.; Siviero, Alessandro; Steinmetz, Matthias; Williams, Mary; Watson, Fred G.; Zwitter, Tomaz

    2011-08-10

    We have undertaken the study of the elemental abundances and kinematic properties of a metal-poor sample of candidate thick-disk stars selected from the Radial Velocity Experiment spectroscopic survey of bright stars to differentiate among the present scenarios of the formation of the thick disk. In this paper, we report on a sample of 214 red giant branch, 31 red clump/horizontal branch, and 74 main-sequence/sub-giant branch metal-poor stars, which serves to augment our previous sample of only giant stars. We find that the thick disk [{alpha}/Fe] ratios are enhanced and have little variation (<0.1 dex), in agreement with our previous study. The augmented sample further allows, for the first time, investigation of the gradients in the metal-poor thick disk. For stars with [Fe/H] < -1.2, the thick disk shows very small gradients, <0.03 {+-} 0.02 dex kpc{sup -1}, in {alpha}-enhancement, while we find a +0.01 {+-} 0.04 dex kpc{sup -1} radial gradient and a -0.09 {+-} 0.05 dex kpc{sup -1} vertical gradient in iron abundance. In addition, we show that the peak of the distribution of orbital eccentricities for our sample agrees better with models in which the stars that comprise the thick disk were formed primarily in the Galaxy, with direct accretion of stars contributing little. Our results thus disfavor direct accretion of stars from dwarf galaxies into the thick disk as a major contributor to the thick-disk population, but cannot discriminate between alternative models for the thick disk, such as those that invoke high-redshift (gas-rich) mergers, heating of a pre-existing thin stellar disk by a minor merger, or efficient radial migration of stars.

  9. Body and Soul: Do Children Distinguish between Foods When Generalizing Biological and Psychological Properties?

    ERIC Educational Resources Information Center

    Thibaut, Jean-Pierre; Nguyen, Simone P.; Murphy, Gregory L.

    2016-01-01

    Research Findings: In 2 experiments, we tested whether children generalize psychological and biological properties to novel foods. We used an induction task in which a property (either biological or psychological) was associated with a target food. Children were then asked whether a taxonomically related and a script-related food would also have…

  10. Body and Soul: Do Children Distinguish between Foods When Generalizing Biological and Psychological Properties?

    ERIC Educational Resources Information Center

    Thibaut, Jean-Pierre; Nguyen, Simone P.; Murphy, Gregory L.

    2016-01-01

    Research Findings: In 2 experiments, we tested whether children generalize psychological and biological properties to novel foods. We used an induction task in which a property (either biological or psychological) was associated with a target food. Children were then asked whether a taxonomically related and a script-related food would also have…

  11. Herniated disk

    MedlinePlus

    ... the disk. This may place pressure on nearby nerves or the spinal cord. ... Lumbar radiculopathy; Cervical radiculopathy; Herniated ... LBP - herniated disk; Sciatica - herniated disk; Herniated disk

  12. Disk Alloy Development

    NASA Technical Reports Server (NTRS)

    Gabb, Tim; Gayda, John; Telesman, Jack

    2001-01-01

    The advanced powder metallurgy disk alloy ME3 was designed using statistical screening and optimization of composition and processing variables in the NASA HSR/EPM disk program to have extended durability at 1150 to 1250 "Fin large disks. Scaled-up disks of this alloy were produced at the conclusion of this program to demonstrate these properties in realistic disk shapes. The objective of the UEET disk program was to assess the mechanical properties of these ME3 disks as functions of temperature, in order to estimate the maximum temperature capabilities of this advanced alloy. Scaled-up disks processed in the HSR/EPM Compressor / Turbine Disk program were sectioned, machined into specimens, and tested in tensile, creep, fatigue, and fatigue crack growth tests by NASA Glenn Research Center, in cooperation with General Electric Engine Company and Pratt & Whitney Aircraft Engines. Additional sub-scale disks and blanks were processed and tested to explore the effects of several processing variations on mechanical properties. Scaled-up disks of an advanced regional disk alloy, Alloy 10, were used to evaluate dual microstructure heat treatments. This allowed demonstration of an improved balance of properties in disks with higher strength and fatigue resistance in the bores and higher creep and dwell fatigue crack growth resistance in the rims. Results indicate the baseline ME3 alloy and process has 1300 to 1350 O F temperature capabilities, dependent on detailed disk and engine design property requirements. Chemistry and process enhancements show promise for further increasing temperature capabilities.

  13. Measuring and distinguishing compositional and maturity properties of lunar soils by remote VIS-NIR spectroscopy

    NASA Technical Reports Server (NTRS)

    Fischer, Erich M.; Pieters, Carle M.

    1993-01-01

    Space weathering on the lunar surface affects the spectra/optical character of an exposed lunar soil in three ways: the reflectance is reduced, absorption band depths are reduced, and a red-sloped continuum is created and increased with exposure. As a result, the spectrum of a lunar soil is dependent upon both the degree of exposure at the lunar surface and the original composition. It is critical to the remote analysis of lunar soils to differentiate between the optical effects of maturity and the effects of composition. In the laboratory, it is possible to determine and consequently distinguish the degree of exposure, or soil maturity, as measured by parameters such as I(sub s)/FeO (e.g., 1; mature defined as I(sub s)/FeO greater than or equal to 60), and the composition, as measured by various chemical and petrographical techniques. Lunar soils returned by the Apollo missions provide important ground truth for developing methods for remotely measuring the maturity and the concentration of Fe-bearing minerals in lunar soil. The ground truth spectral data analyzed are from the John Adams lunar soil spectra collection. Soils collected from or near highland terrains are emphasized in the discussion. The mineralogical makeup of mare soils results in behavior somewhat different from highland soils.

  14. Measuring and distinguishing compositional and maturity properties of lunar soils by remote VIS-NIR spectroscopy

    NASA Astrophysics Data System (ADS)

    Fischer, Erich M.; Pieters, Carle M.

    1993-03-01

    Space weathering on the lunar surface affects the spectra/optical character of an exposed lunar soil in three ways: the reflectance is reduced, absorption band depths are reduced, and a red-sloped continuum is created and increased with exposure. As a result, the spectrum of a lunar soil is dependent upon both the degree of exposure at the lunar surface and the original composition. It is critical to the remote analysis of lunar soils to differentiate between the optical effects of maturity and the effects of composition. In the laboratory, it is possible to determine and consequently distinguish the degree of exposure, or soil maturity, as measured by parameters such as Is/FeO (e.g., 1; mature defined as Is/FeO greater than or equal to 60), and the composition, as measured by various chemical and petrographical techniques. Lunar soils returned by the Apollo missions provide important ground truth for developing methods for remotely measuring the maturity and the concentration of Fe-bearing minerals in lunar soil. The ground truth spectral data analyzed are from the John Adams lunar soil spectra collection. Soils collected from or near highland terrains are emphasized in the discussion. The mineralogical makeup of mare soils results in behavior somewhat different from highland soils.

  15. Measuring and distinguishing compositional and maturity properties of lunar soils by remote VIS-NIR spectroscopy

    NASA Technical Reports Server (NTRS)

    Fischer, Erich M.; Pieters, Carle M.

    1993-01-01

    Space weathering on the lunar surface affects the spectra/optical character of an exposed lunar soil in three ways: the reflectance is reduced, absorption band depths are reduced, and a red-sloped continuum is created and increased with exposure. As a result, the spectrum of a lunar soil is dependent upon both the degree of exposure at the lunar surface and the original composition. It is critical to the remote analysis of lunar soils to differentiate between the optical effects of maturity and the effects of composition. In the laboratory, it is possible to determine and consequently distinguish the degree of exposure, or soil maturity, as measured by parameters such as I(sub s)/FeO (e.g., 1; mature defined as I(sub s)/FeO greater than or equal to 60), and the composition, as measured by various chemical and petrographical techniques. Lunar soils returned by the Apollo missions provide important ground truth for developing methods for remotely measuring the maturity and the concentration of Fe-bearing minerals in lunar soil. The ground truth spectral data analyzed are from the John Adams lunar soil spectra collection. Soils collected from or near highland terrains are emphasized in the discussion. The mineralogical makeup of mare soils results in behavior somewhat different from highland soils.

  16. Static and dynamical properties of a hard-disk fluid confined to a narrow channel.

    PubMed

    Godfrey, M J; Moore, M A

    2014-03-01

    The thermodynamic properties of disks moving in a channel sufficiently narrow that they can collide only with their nearest neighbors can be solved exactly by determining the eigenvalues and eigenfunctions of an integral equation. Using it, we have determined the correlation length ξ of this system. We have developed an approximate solution which becomes exact in the high-density limit. It describes the system in terms of defects in the regular zigzag arrangement of disks found in the high-density limit. The correlation length is then effectively the spacing between the defects. The time scales for defect creation and annihilation are determined with the help of transition-state theory, as is the diffusion coefficient of the defects, and these results are found to be in good agreement with molecular dynamics simulations. On compressing the system with the Lubachevsky-Stillinger procedure, jammed states are obtained whose packing fractions ϕJ are a function of the compression rate γ. We find a quantitative explanation of this dependence by making use of the Kibble-Zurek hypothesis. We have also determined the point-to-set length scale ξPS for this system. At a packing fraction ϕ close to its largest value ϕmax, ξPS has a simple power law divergence, ξPS∼1/(1-ϕ/ϕmax), while ξ diverges much faster, ln(ξ)∼1/(1-ϕ/ϕmax).

  17. One step forward toward characterization: some important material properties to distinguish biochars.

    PubMed

    Schimmelpfennig, Sonja; Glaser, Bruno

    2012-01-01

    Terra Preta research gave evidence for the positive influence of charred organic material (biochar) on infertile tropical soils. Facing global challenges such as land degradation, fossil energy decline, water shortage, and climate change, the use of biochar as a soil amendment embedded into regional matter cycles seems to provide an all-round solution. However, little is known about biochar effects on individual ecosystem processes. Besides, the term is used for a variety of charred products. Therefore, the aim of this study was to investigate principal material properties of different chars to establish a minimum set of analytical properties and thresholds for biochar identification. For this purpose, chars from different production processes (traditional charcoal stack, rotary kiln, Pyreg reactor, wood gasifier, and hydrothermal carbonization) were analyzed for physical and chemical properties such as surface area, black carbon, polycyclic aromatic hydrocarbons, and elemental composition. Our results showed a significant influence of production processes on biochar properties. Based on our results, to identify biochar suitable for soil amendment and carbon sequestration, we recommend using variables with the following thresholds: O/C ratio <0.4, H/C ratio <0.6, black carbon >15% C, polyaromatic hydrocarbons lower than soil background values, and a surface area >100 m g. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

  18. Distinguishing dissolved organic matter at its origin: size and optical properties of leaf-litter leachates.

    PubMed

    Cuss, C W; Guéguen, C

    2013-09-01

    Dissolved organic matter (DOM) was leached from eight distinct samples of leaves taken from six distinct trees (red maple, bur oak at three times of the year, two sugar maple and two white spruce trees from disparate soil types). Multiple samples were taken over 72-96h of leaching. The size and optical properties of leachates were assessed using asymmetrical flow field-flow fractionation (AF4) coupled to diode-array ultraviolet/visible absorbance and excitation-emission matrix fluorescence detectors (EEM). The fluorescence of unfractionated samples was also analyzed. EEMs were analyzed using parallel factor analysis (PARAFAC) and principal component analysis (PCA) of proportional component loadings. Both the unfractionated and AF4-fractionated leachates had distinct size and optical properties. The 95% confidence ranges for molecular weight distributions were determined as: 210-440Da for spruce, 540-920Da for sugar maple, 630-800Da for spring oak leaves, 930-950Da for senescent oak, 1490-1670 for senescent red maple, and 3430-4270Da for oak leaves that were collected from the ground after spring thaw. In most cases the fluorescence properties of leachates were different for individuals from different soil types and across seasons; however, PCA of PARAFAC loadings revealed that the observed distinctiveness was chiefly species-based. Strong correlations were found between the molecular weight distribution of both unfractionated and fractionated leachates and their principal component loadings (R(2)=0.85 and 0.95, respectively). It is concluded that results support a species-based origin for differences in optical properties. Copyright © 2013 Elsevier Ltd. All rights reserved.

  19. Binary mixtures of disks and elongated particles: Texture and mechanical properties

    NASA Astrophysics Data System (ADS)

    Azéma, Emilien; Preechawuttipong, Itthichai; Radjai, Farhang

    2016-10-01

    We analyze the shear strength and microstructure of binary granular mixtures consisting of disks and elongated particles by varying systematically both the mixture ratio and degree of homogeneity (from homogeneous to fully segregated). The contact dynamics method is used for numerical simulations with rigid particles interacting by frictional contacts. A counterintuitive finding of this work is that the shear strength, packing fraction, and, at the microscopic scale, the fabric, force, and friction anisotropies of the contact network are all nearly independent of the degree of homogeneity. In other words, homogeneous mixtures have the same strength properties as segregated packings of the two particle shapes. In contrast, the shear strength increases with the proportion of elongated particles correlatively with the increase of the corresponding force and fabric anisotropies. By a detailed analysis of the contact network topology, we show that various contact types contribute differently to force transmission and friction mobilization.

  20. Parameter estimations for measurements of thermal transport properties with the hot disk thermal constants analyzer

    NASA Astrophysics Data System (ADS)

    Bohac, Vlastimil; Gustavsson, Mattias K.; Kubicar, Ludovit; Gustafsson, Silas E.

    2000-06-01

    The objective of this work is to improve measurements of transport properties using the hot disk thermal constants analyzer. The principle of this method is based on the transient heating of a plane double spiral sandwiched between two pieces of the investigated material. From the temperature increase of the heat source, it is possible to derive both the thermal conductivity and the thermal diffusivity from one single transient recording, provided the total time of the measurement is chosen within a correct time window defined by the theory and the experimental situation. Based on a theory of sensitivity coefficients, it is demonstrated how the experimental time window should be selected under different experimental situations. In addition to the theoretical work, measurements on two different materials: poly(methylmethacrylate) and Stainless Steel A 310, with thermal conductivity of 0.2 and 14 W/mK, respectively, have been performed and analyzed based on the developed theory.

  1. Comparison between infrared Martian disk spectra and optical properties of terrestrial analogs

    NASA Technical Reports Server (NTRS)

    Egan, W. G.; Hilgeman, T.; Smith, L. L.

    1978-01-01

    Medium spectral resolution (20 kaysers) infrared measurements of the Martian disk made between 2900 and 5600 kaysers from the NASA Lear Airborne Observatory have been successfully compared with predictions derived from a model of the Martian soil and atmosphere. Modeling of the Martian atmosphere permitted the extraction of Martian soil reflectance in the CO2 bands centered at 3657 kaysers. Three Martian soil analogs previously considered acceptable - limonite, montmorillonite, and basalt - were analyzed to determine the optical complex indices of refraction in the same range as the airborne observations, for mathematical modeling. A characteristic surface particle size approximately 1 to 3 microns diameter is indicated. It is concluded that the Martian soil surface near-infrared optical properties are consistent with a soil composition similar to montmorillonite or limonite, mixed with a basalt.

  2. Complement-fixing properties of antinuclear antibodies distinguish drug-induced lupus from systemic lupus erythematosus.

    PubMed

    Rubin, R L; Teodorescu, M; Beutner, E H; Plunkett, R W

    2004-01-01

    The immunofluorescence antinuclear antibody (ANA) test has been widely used to monitor autoimmune disease, but its value for diagnostic purposes is compromised by low specificity and high prevalence in disease-free individuals. The capacity of autoantibodies to fix serum complement proteins when bound to antigen is an important effector function because this property is associated with acute and chronic inflammatory processes. The current study evaluates the complement-fixing properties of antinuclear antibodies (CANA) in three well-defined and clinically-related patient groups: systemic lupus erythematosus (SLE), drug-induced lupus (DIL) and drug-induced autoimmunity (DIA). Of 20 patients diagnosed with SLE, 90% displayed complement-fixing ANA while this feature was present in only two of 18 patients with DIL and no patients with DIA without associated disease even though the mean ANA titres were similar among these patient groups. CANA was significantly correlated with anti-Sm activity. Because SLE but not DIL or DIA can be a life-threatening disease associated with complement consumption in vivo, these results demonstrate that measurement of CANA is a diagnostically useful tool and may have immunopathologic implications.

  3. Novel strain properties distinguishing sporadic prion diseases sharing prion protein genotype and prion type

    PubMed Central

    Cracco, Laura; Notari, Silvio; Cali, Ignazio; Sy, Man-Sun; Chen, Shu G.; Cohen, Mark L.; Ghetti, Bernardino; Appleby, Brian S.; Zou, Wen-Quan; Caughey, Byron; Safar, Jiri G.; Gambetti, Pierluigi

    2017-01-01

    In most human sporadic prion diseases the phenotype is consistently associated with specific pairings of the genotype at codon 129 of the prion protein gene and conformational properties of the scrapie PrP (PrPSc) grossly identified types 1 and 2. This association suggests that the 129 genotype favours the selection of a distinct strain that in turn determines the phenotype. However, this mechanism cannot play a role in the phenotype determination of sporadic fatal insomnia (sFI) and a subtype of sporadic Creutzfeldt-Jakob disease (sCJD) identified as sCJDMM2, which share 129 MM genotype and PrPSc type 2 but are associated with quite distinct phenotypes. Our detailed comparative study of the PrPSc conformers has revealed major differences between the two diseases, which preferentially involve the PrPSc component that is sensitive to digestion with proteases (senPrPSc) and to a lesser extent the resistant component (resPrPSc). We conclude that these variations are consistent with two distinct strains in sFI and sCJDMM2, and that the rarer sFI is the result of a variant strain selection pathway that might be favoured by a different brain site of initial PrPSc formation in the two diseases. PMID:28091514

  4. Psychometric Properties of Creative Self-Efficacy Inventory Among Distinguished Students in Saudi Arabian Universities.

    PubMed

    Alotaibi, Khaled N

    2016-06-01

    This study examined the psychometric properties of the Arabic version of Abbott's Creative Self-Efficacy inventory. Saudi honors students (157 men vs. 163 women) participated. These students are undergraduates (M age = 19.5 year, SD = 1.9) who complete 30 credit hours with a grade point average of no less than 4.5 out of 5. The results showed that the internal consistency (α = .87) and the test-retest reliabilities (r = .73) were satisfactory. The study sample was separated into two subsamples. The data from the first subsample (n = 60) were used to conduct an exploratory factor analysis, whereas the data from the second subsample (n = 260) were used to perform a confirmatory factor analysis. The results of exploratory factor analysis and confirmatory factor analysis indicated that creative self-efficacy was not a unidimensional construct but consisted of two factors labeled "creative thinking self-efficacy" and "creative performance self-efficacy." As expected, this two-factor model fit the data adequately, supporting prior research that treated creative self-efficacy as multidimensional construct.

  5. Distinguished Books.

    ERIC Educational Resources Information Center

    Marles, Daisy; Ink, Gary

    1999-01-01

    Presents the following lists of distinguished books: "Best Books of 1998"; "Best Young Adult Books"; "Notable Children's Videos"; "Best Children's Books"; "Notable Recordings for Children"; "Notable Software and Web Sites for Children"; "Quick Picks for Reluctant Young Adult…

  6. A test of star formation laws in disk galaxies. II. Dependence on dynamical properties

    SciTech Connect

    Suwannajak, Chutipong; Tan, Jonathan C.; Leroy, Adam K.

    2014-05-20

    We use the observed radial profiles of the mass surface densities of total, Σ {sub g}, and molecular, Σ{sub H2}, gas, rotation velocity, and star formation rate (SFR) surface density, Σ{sub sfr}, of the molecular-rich (Σ{sub H2} ≥ Σ{sub HI}/2) regions of 16 nearby disk galaxies to test several star formation (SF) laws: a 'Kennicutt-Schmidt (K-S)' law, Σ{sub sfr}=A{sub g}Σ{sub g,2}{sup 1.5}; a 'Constant Molecular' law, Σ{sub sfr} = A {sub H2}Σ{sub H2,2}; the turbulence-regulated laws of Krumholz and McKee (KM05) and Krumholz, McKee, and Tumlinson (KMT09); a 'Gas-Ω' law, Σ{sub sfr}=B{sub Ω}Σ{sub g}Ω; and a shear-driven 'giant molecular cloud (GMC) Collision' law, Σ{sub sfr} = B {sub CC}Σ {sub g}Ω(1-0.7β), where β ≡ d ln v {sub circ}/d ln r. If allowed one free normalization parameter for each galaxy, these laws predict the SFR with rms errors of factors of 1.4-1.8. If a single normalization parameter is used by each law for the entire galaxy sample, then rms errors range from factors of 1.5-2.1. Although the Constant Molecular law gives the smallest rms errors, the improvement over the KMT, K-S, and GMC Collision laws is not especially significant, particularly given the different observational inputs that the laws utilize and the scope of included physics, which ranges from empirical relations to detailed treatment of interstellar medium processes. We next search for systematic variation of SF law parameters with local and global galactic dynamical properties of disk shear rate (related to β), rotation speed, and presence of a bar. We demonstrate with high significance that higher shear rates enhance SF efficiency per local orbital time. Such a trend is expected if GMC collisions play an important role in SF, while an opposite trend would be expected if the development of disk gravitational instabilities is the controlling physics.

  7. A Test of Star Formation Laws in Disk Galaxies. II. Dependence on Dynamical Properties

    NASA Astrophysics Data System (ADS)

    Suwannajak, Chutipong; Tan, Jonathan C.; Leroy, Adam K.

    2014-05-01

    We use the observed radial profiles of the mass surface densities of total, Σ g , and molecular, ΣH2, gas, rotation velocity, and star formation rate (SFR) surface density, Σsfr, of the molecular-rich (ΣH2 >= ΣHI/2) regions of 16 nearby disk galaxies to test several star formation (SF) laws: a "Kennicutt-Schmidt (K-S)" law, \\Sigma _{sfr}=A_g\\Sigma _{g,2}^{1.5}; a "Constant Molecular" law, Σsfr = A H2ΣH2, 2; the turbulence-regulated laws of Krumholz & McKee (KM05) and Krumholz, McKee, & Tumlinson (KMT09); a "Gas-Ω" law, \\Sigma _{sfr}=B_\\Omega \\Sigma _g\\Omega; and a shear-driven "giant molecular cloud (GMC) Collision" law, Σsfr = B CCΣ g Ω(1-0.7β), where β ≡ d ln v circ/d ln r. If allowed one free normalization parameter for each galaxy, these laws predict the SFR with rms errors of factors of 1.4-1.8. If a single normalization parameter is used by each law for the entire galaxy sample, then rms errors range from factors of 1.5-2.1. Although the Constant Molecular law gives the smallest rms errors, the improvement over the KMT, K-S, and GMC Collision laws is not especially significant, particularly given the different observational inputs that the laws utilize and the scope of included physics, which ranges from empirical relations to detailed treatment of interstellar medium processes. We next search for systematic variation of SF law parameters with local and global galactic dynamical properties of disk shear rate (related to β), rotation speed, and presence of a bar. We demonstrate with high significance that higher shear rates enhance SF efficiency per local orbital time. Such a trend is expected if GMC collisions play an important role in SF, while an opposite trend would be expected if the development of disk gravitational instabilities is the controlling physics.

  8. MILKY WAY DISK-HALO TRANSITION IN H I: PROPERTIES OF THE CLOUD POPULATION

    SciTech Connect

    Ford, H. Alyson; Lockman, Felix J.; McClure-Griffiths, N. M.

    2010-10-10

    Using 21 cm H I observations from the Parkes Radio Telescope's Galactic All-Sky Survey, we measure 255 H I clouds in the lower Galactic halo that are located near the tangent points at 16.{sup 0}9 {<=} l {<=} 35.{sup 0}3 and |b| {approx}< 20{sup 0}. The clouds have a median mass of 700 M{sub sun} and a median distance from the Galactic plane of 660 pc. This first Galactic quadrant (QI) region is symmetric to a region of the fourth quadrant (QIV) studied previously using the same data set and measurement criteria. The properties of the individual clouds in the two quadrants are quite similar suggesting that they belong to the same population, and both populations have a line-of-sight (LOS) cloud-cloud velocity dispersion of {sigma}{sub cc} {approx} 16 km s{sup -1}. However, there are three times as many disk-halo clouds at the QI tangent points and their scale height, at h = 800 pc, is twice as large as in QIV. Thus, the observed LOS random cloud motions are not connected to the cloud scale height or its variation around the Galaxy. The surface density of clouds is nearly constant over the QI tangent point region but is peaked near R {approx} 4 kpc in QIV. We ascribe all of these differences to the coincidental location of the QI region at the tip of the Milky Way's bar, where it merges with a major spiral arm. The QIV tangent point region, in contrast, covers only a segment of a minor spiral arm. The disk-halo H I cloud population is thus likely tied to and driven by large-scale star formation processes, possibly through the mechanism of supershells and feedback.

  9. Milky Way Disk-Halo Transition in H I: Properties of the Cloud Population

    NASA Astrophysics Data System (ADS)

    Ford, H. Alyson; Lockman, Felix J.; McClure-Griffiths, N. M.

    2010-10-01

    Using 21 cm H I observations from the Parkes Radio Telescope's Galactic All-Sky Survey, we measure 255 H I clouds in the lower Galactic halo that are located near the tangent points at 16fdg9 <= l <= 35fdg3 and |b| <~ 20°. The clouds have a median mass of 700 M sun and a median distance from the Galactic plane of 660 pc. This first Galactic quadrant (QI) region is symmetric to a region of the fourth quadrant (QIV) studied previously using the same data set and measurement criteria. The properties of the individual clouds in the two quadrants are quite similar suggesting that they belong to the same population, and both populations have a line-of-sight (LOS) cloud-cloud velocity dispersion of σcc ≈ 16 km s-1. However, there are three times as many disk-halo clouds at the QI tangent points and their scale height, at h = 800 pc, is twice as large as in QIV. Thus, the observed LOS random cloud motions are not connected to the cloud scale height or its variation around the Galaxy. The surface density of clouds is nearly constant over the QI tangent point region but is peaked near R ~ 4 kpc in QIV. We ascribe all of these differences to the coincidental location of the QI region at the tip of the Milky Way's bar, where it merges with a major spiral arm. The QIV tangent point region, in contrast, covers only a segment of a minor spiral arm. The disk-halo H I cloud population is thus likely tied to and driven by large-scale star formation processes, possibly through the mechanism of supershells and feedback.

  10. Self Containment, a Property of Modular RNA Structures, Distinguishes microRNAs

    PubMed Central

    Lee, Miler T.; Kim, Junhyong

    2008-01-01

    RNA molecules will tend to adopt a folded conformation through the pairing of bases on a single strand; the resulting so-called secondary structure is critical to the function of many types of RNA. The secondary structure of a particular substring of functional RNA may depend on its surrounding sequence. Yet, some RNAs such as microRNAs retain their specific structures during biogenesis, which involves extraction of the substructure from a larger structural context, while other functional RNAs may be composed of a fusion of independent substructures. Such observations raise the question of whether particular functional RNA substructures may be selected for invariance of secondary structure to their surrounding nucleotide context. We define the property of self containment to be the tendency for an RNA sequence to robustly adopt the same optimal secondary structure regardless of whether it exists in isolation or is a substring of a longer sequence of arbitrary nucleotide content. We measured degree of self containment using a scoring method we call the self-containment index and found that miRNA stem loops exhibit high self containment, consistent with the requirement for structural invariance imposed by the miRNA biogenesis pathway, while most other structured RNAs do not. Further analysis revealed a trend toward higher self containment among clustered and conserved miRNAs, suggesting that high self containment may be a characteristic of novel miRNAs acquiring new genomic contexts. We found that miRNAs display significantly enhanced self containment compared to other functional RNAs, but we also found a trend toward natural selection for self containment in most functional RNA classes. We suggest that self containment arises out of selection for robustness against perturbations, invariance during biogenesis, and modular composition of structural function. Analysis of self containment will be important for both annotation and design of functional RNAs. A Python

  11. Physical properties and evolutionary time scales of disks around solar-type and intermediate mass stars

    NASA Technical Reports Server (NTRS)

    Strom, Stephen E.; Edwards, Suzan

    1993-01-01

    Recent observations of circumstellar disks and their evolutionary timescales are reviewed. It is concluded that disks appear to be a natural outcome of the star-formation process. The disks surrounding young stars initially are massive, with optically thick structures comprised of gas and micron-sized grains. Disk masses are found to range from 0.01 to 0.2 solar masses for solar-type PMS stars, and from 0.01 to 6 solar masses for young, intermediate mass stars. Massive, optically thick accretion disks have accretion rates between 10 exp -8 and 10 exp -6 solar masses/yr for solar type PMS stars and between 10 exp -6 and 10 exp -4 solar masses/yr for intermediate stars. The results suggest that a significant fraction of the mass comprising the star may have passed through a circumstellar accretion disk.

  12. Surface properties of magnetic rigid disks for high-density data storage

    NASA Astrophysics Data System (ADS)

    Tsai, Hsiao-chu; Eltoukhy, Atef

    1990-05-01

    The chemical toughened glass is shown to be very safe for the disk-drive application based upon Weibull analyses of spin-to-break test data. Investigations revealed that frictional performance of glass disks can be correlated with two parameters (zero crossing and peak to valley) of the surface profile as measured by phase-shift interferometry. To compare the surface characteristics of glass with a conventional Al disk, the piezoelectrical baseline signals were measured by a glide head while flying steadily over a disk without asperity hits. The results showed that the glass disk caused less disturbance to the slider than the Al disk and can thus provide an intrinsically better surface for low-fly-height, high-density application.

  13. The Dust Properties of the Beta Pictoris Debris Disk from an Analysis of its Thermal Emission and Scattered Light

    NASA Astrophysics Data System (ADS)

    Ballering, Nicholas; Rieke, George; Su, Kate Y. L.; Gaspar, Andras

    2016-01-01

    Although hundreds of debris disks have been characterized from their infrared spectral energy distributions, the composition of the dust comprising these disks has, in general, not been determined because it is degenerate with the size of the dust grains and their orbital location. Spatially resolved images at multiple wavelengths—including both scattered light and thermal emission—are required to break this degeneracy. The relatively nearby A6 star Beta Pictoris hosts a large, bright, edge-on debris disk that is amenable to a detailed characterization of its composition. We constrain the optical properties (and thus composition) of the dust in this system by simultaneously modelling images in the visible (HST/STIS), near-infrared (HST/WFC3), mid-infrared (Spitzer/MIPS), far-infrared (Herschel/PACS), and sub-mm (ALMA). The HST/WFC3 and Spitzer/MIPS data that we present have not been previously published. We find that a mixture of silicates and organic refractory material can fit this suite of data well. High amounts of water ice and highly porous grains are not favored, which is in agreement with a recent study of the debris disk around HR4796A that also combined thermal and scattered light constraints, but is in contrast with studies of other debris disks that did not include scattered light data. We also find that a model disk composed entirely of silicates will over-predict the scattered light brightness when fit to the thermal data—a discrepancy seen in the modelling attempts of other debris disks that assumed a purely silicate composition.

  14. The facts that the physical-chemical properties of modern tablets distinguish them from natural food lumps

    NASA Astrophysics Data System (ADS)

    Urakov, A.; Urakova, N.; Reshetnikov, A.; Kopylov, M.; Kasatkin, A.; Baymurzin, D.; Gabdrafikov, R.

    2017-02-01

    It was found that pharmaceutical companies produce drugs in tablet form, physical or physical-chemical properties that are radically different from those of the properties of natural food lumps, in that adult converts food in our mouth before swallowing. It was shown that the conventional shape, color, size, volume, specific gravity, hardness, osmotic and acid activity of modern tablets impair the physical and physicochemical properties of the liquid contents of the stomach is much stronger than such “building” materials, such as chalk, clay, sand, river pebbles and gravel. The results showed, that the value of the specific hardness, deforming tablets, can distinguish modern tablets from each other by more than 5000 times. Therefore, introduction tablets inside without information of ability injuring their action leads to the fact that soft and “unsalted” tablets almost nothing damage, and too “salty” and solid tablets damage the gums, lips, tongue, teeth and dental structures. To reduce the traumatic action tablets offered standardize osmoticity, corrosion and hardness within the range of safe values for soft and hard tissues of the oral cavity and improve standard introduction of tablets in the mouth.

  15. Ultrasonic properties of low solvus high refractory (LSHR) super alloy disk material

    SciTech Connect

    Na, Jeong K.; Blodgett, Mark

    2011-06-23

    Measurements are made for ultrasonic linear and nonlinear properties of the powder metallurgy disk alloy LSHR material designed with a relatively low {gamma}' precipitate solvus temperature and high refractory element content. This allows versatile heat treatment processing which results in high tensile, creep and fatigue properties depending on the grain size controlled through proper selection of solution heat treatment temperatures relative to the {gamma}' precipitate solvus temperature. Sound velocity and attenuation for both longitudinal and shear modes at various frequencies from 5 to 20 MHz help to identify and quantify the size of transition zone nondestructively between the small grain ({approx}10 {mu}m) and the large grain ({approx}100 {mu}m) zones. The shear wave velocity measurements taken by aligning the transducer polarization direction parallel and perpendicular to the grain transition direction reveal some results that we do not fully understand at this time and will be the basis of future research. Similarly, measurements of the acoustic nonlinearity parameter show some variations that may originate from uncertain sources.

  16. Localization properties of covariant Lyapunov vectors for quasi-one-dimensional hard disks.

    PubMed

    Morriss, G P

    2012-05-01

    The Lyapunov exponent spectrum and covariant Lyapunov vectors are studied for a quasi-one-dimensional system of hard disks as a function of density and system size. We characterize the system using the angle distributions between covariant vectors and the localization properties of both Gram-Schmidt and covariant vectors. At low density there is a kinetic regime that has simple scaling properties for the Lyapunov exponents and the average localization for part of the spectrum. This regime shows strong localization in a proportion of the first Gram-Schmidt and covariant vectors and this can be understood as highly localized configurations dominating the vector. The distribution of angles between neighboring covariant vectors has characteristic shapes depending upon the difference in vector number, which vary over the continuous region of the spectrum. At dense gas- or liquid-like densities the behavior of the covariant vectors are quite different. The possibility of tangencies between different components of the unstable manifold and between the stable and unstable manifolds is explored but it appears that exact tangencies do not occur for a generic chaotic trajectory.

  17. Gap Opening as a Probe of Circumsolar and Circumplanetary Gas Disk Properties

    NASA Astrophysics Data System (ADS)

    Estrada, P. R.; Mosqueira, I.

    2002-09-01

    We expect that the largest objects forming in the solar nebula and giant-planet subnebulae truncated the gas disks in which they were formed, thus preventing gas outside their orbits from accreting onto the primary (Mosqueira and Estrada 2002a,b). The criterion for gap opening depends on two uncertain parameters; namely, the turbulent viscosity of the gas, and the damping length of the waves launched by the secondary in the neighborhood of resonant locations in the disk. In light of the difficulty of maintaining gas turbulence in disks with a positive radial gradient in specific angular momentum in the absence of a source of ``stirring'' (Ryu and Goodman 1992; Balbus et al. 1996), we adopt an inviscid disk. Regarding the second issue, there has been recent progress in characterizing the damping length of acoustic waves under several disk conditions. In a 2-D isothermal disk, wave steepening is likely to result in wave dissipation in a lengthscale of order ~ rL, where rL is the radial location of a Lindblad resonance and this distance has a weak dependence on the mass of the secondary (Goodman and Rafikov 2001). In an optically thick, vertically thermally stratified, disk the radial lengthscale for ``wave-channeling'' and wave dissipation is ~ rL/m, where m is the azimuthal wavenumber (Lubow and Ogilvie 1998; Bate et al. 2002). In a 3-D vertically isothermal gas disk, a significant fraction of the angular momentum flux may be transported by waves with non-zero vertical group velocity and possible radial damping lengths of the order ~ H, where H is the nebula scale-height (Bate et al. 2002; Mosqueira and Houben, this conference). The above can be used to compute the inertial mass (Ward and Hourigan 1989) and constrain the surface density of the disk at the time of gap opening. Here we do so for Jupiter in the solar disk (M2/M_1 = 9.5 x 10-4), Ganymede in the jovian disk (M2/M_1 = 7.8 x 10-5), Titan in the saturnian disk (M2/M_1 = 2.4 x 10-4), and Titania in the

  18. Results for the structural properties of random heaps of hard disks

    SciTech Connect

    Bonnier, B. )

    1995-01-01

    The average angle of repose and the packing density of random planar heaps of hard disks falling ballistically onto a sticky base line, where the first layer of disks is quenched in random positions, are computed for heaps with a small fixed number of gaps in the base layer. The results we find appear to be almost independent of the size of the heap and they agree with those obtained from computer simulations of large systems.

  19. Electrical Properties and Physical Characteristics of Polycrystalline Diamond Films Deposited in a Microwave Plasma Disk Reactor

    NASA Astrophysics Data System (ADS)

    Huang, Bohr-Ran

    1992-01-01

    This work experimentally investigates techniques for high quality diamond synthesis and develops means for electrical and physical characterization of the films. The films are deposited by plasma assisted chemical vapor deposition using a methane/hydrogen plasma in a microwave plasma disk reactor system. Both a diamond past nucleation method and a diamond powder nucleation method are studied in this research. Although as indicated by Raman spectroscopy both methods produced similar quality diamond films, the powder nucleation method produced fine grain, sub-micron sized crystallite, films whereas the past nucleation method produced large grain, several-micrometer size crystallite, films. For powder polished films, all metallic contacts were ohmic. These samples were used to explore the high electric field properties of diamond. It was discovered that for fields larger than approximately 1 times 10^5 V/cm the electrical properties are dominated by defects, where defect is used generically for either an impurity or a structural defect. For low electric fields, the electrical conductivity was constant which resulted in ohmic behavior. But for high fields, the conductivity was field activated according to Poole's law. This behavior was modeled as being due to ionizable defects and indicates that there is approximately one ionizable defect per 10,000 host atoms. As a result of such defects, the breakdown field for these films was somewhat less than 1 times 10^6 V/cm. A large concentration of defects is compatible with the observation of ohmic contact behavior regardless of metallic work function since contact space charge layers would be sufficiently thin to allow tunneling. Non-ohmic, Schottky barrier contacts were achievable on the past polished films. For Al/diamond/silicon structures diode characteristics were observed. These I-V characteristics were modeled as an ideal Schottky barrier diode in series with bulk diamond, for which the property of the bulk diamond

  20. Debris Disks: An Overview

    NASA Astrophysics Data System (ADS)

    Backman, D.

    2004-12-01

    An overview regarding planetary debris disks: First, more history to complement Low and Aumann's summary appearing elsewhere in this volume. Then, commentary on the nature of debris disks and what we've learned from them: properties of the original ``Fabulous Four" archetypes, results from surveys showing that a large fraction of ordinary stars may be hosts for debris disks, and relatively detailed discussion of β Pictoris, the most prominent disk. Finally, discussion of the connection between debris disks, our solar system's Kuiper Belt, and the zodiacal dust cloud. Open questions about these objects will be highlighted which can lead on to the remainder of the proceedings.

  1. Electrical properties and gustatory responses of various taste disk cells of frog fungiform papillae.

    PubMed

    Sato, Toshihide; Nishishita, Kazuhisa; Okada, Yukio; Toda, Kazuo

    2008-04-01

    We compared the electrical properties and gustatory response profiles of types Ia cell (mucus cell), Ib cell (wing cell), and II/III cell (receptor cell) in the taste disks of the frog fungiform papillae. The large depolarizing responses of all types of cell induced by 1 M NaCl were accompanied by a large decrease in the membrane resistance and had the same reversal potential of approximately +5 mV. The large depolarizing responses of all cell types for 1 mM acetic acid were accompanied by a small decrease in the membrane resistance. The small depolarizing responses of all cell types for 10 mM quinine-HCl (Q-HCl) were accompanied by an increase in the membrane resistance, but those for 1 M sucrose were accompanied by a decrease in the membrane resistance. The reversal potential of sucrose responses in all cell types were approximately +12 mV. Taken together, depolarizing responses of Ia, Ib, and II/III cells for each taste stimulus are likely to be generated by the same mechanisms. Gustatory depolarizing response profiles indicated that 1) each of Ia, Ib, and II/III cells responded 100% to 1 M NaCl and 1 mM acetic acid with depolarizing responses, 2) approximately 50% of each cell type responded to 10 mM Q-HCl with depolarizations, and 3) each approximately 40% of Ia and Ib cells and approximately 90% of II/III cells responded to 1 M sucrose with depolarizations. These results suggest that the receptor molecules for NaCl, acid, and Q-HCl stimuli are equivalently distributed on all cell types, but the receptor molecules for sugar stimuli are richer on II/III cells than on Ia and Ib cells. Type III cells having afferent synapses may play a main role in gustatory transduction and transmission.

  2. ALMA Observations of Circumnuclear Disks in Early-type Galaxies: 12CO(2-1) and Continuum Properties

    NASA Astrophysics Data System (ADS)

    Boizelle, Benjamin D.; Barth, Aaron J.; Darling, Jeremy; Baker, Andrew J.; Buote, David A.; Ho, Luis C.; Walsh, Jonelle L.

    2017-08-01

    We present results from an Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 2 program to map CO(2-1) emission in nearby early-type galaxies (ETGs) that host circumnuclear gas disks. We obtained ˜0.″3 resolution Band 6 observations of seven ETGs selected on the basis of dust disks in Hubble Space Telescope images. We detect CO emission in five at high signal-to-noise ratio with the remaining two only faintly detected. All CO emission is coincident with the dust and is in dynamically cold rotation. Four ETGs show evidence of rapid central rotation; these are prime candidates for higher-resolution ALMA observations to measure the black hole masses. In this paper, we focus on the molecular gas and continuum properties. Total gas masses and H2 column densities for our five CO-bright galaxies are on average ˜108 M ⊙ and ˜ {10}22.5 cm-2 over the ˜kpc-scale disks, and analysis suggests that these disks are stabilized against gravitational fragmentation. The continuum emission of all seven galaxies is dominated by a central unresolved source, and in five we also detect a spatially extended component. The ˜230 GHz nuclear continua are modeled as power laws ranging from {S}ν ˜ {ν }-0.4 to {ν }1.6 within the observed frequency band. The extended continuum profiles of the two radio-bright (and CO-faint) galaxies are roughly aligned with their radio jet and suggest resolved synchrotron jets. The extended continua of the CO-bright disks are coincident with optically thick dust absorption and have spectral slopes that are consistent with thermal dust emission.

  3. A study of circumstellar disk properties in low-mass stars and brown dwarfs

    NASA Astrophysics Data System (ADS)

    Riaz, Basmah

    We present Spitzer Space Telescope IRAC and MIPS observations for a sample of eight M dwarfs: six dMe, one dM, and one sdMe star. All of our targets are found to have Spectral Energy Distributions (SEDs) which are fitted within the error bars by a purely photospheric spectrum out to 24m m . The estimated ages for all are >10 Myr, suggesting that enough disk dissipation has occurred within the inner several AU of the star. Scaling from Houdebine's model of the AU Mic chromosphere, we have computed the free-free infrared excesses for a range of densities. Our Spitzer 24m m data shows that the chromospheres in two of our targets are less dense than in AU Mic by a factor of 10 or more. Our models also indicate that the chromospheric contribution to the observed AU Mic emission at submillimeter wavelengths is only about 2%. We present Spitzer IRAC, MIPS and IRS observations for three sub-stellar members of the TW Hydrae Association (TWA): 2MASSW J1207334-393254 (2M1207), SSSPM J1102-3431 (SSSPM 1102), and 2MASS J1139511-315921 (2M1139). The near- to mid-infrared SEDs indicate the presence of flat optically thick disks around 2M1207 and SSSPM 1102, and a transition disk around 2M1139. 2M1207 shows absorption in the 10 m m silicate feature, with a peak near 11.3 m m due to crystalline forsterite. The absorption can be attributed to a close to edge-on disk. No silicate absorption/emission is observed towards SSSPM 1102. We have performed detailed modeling of these two brown dwarf disks. The best-fits have been obtained using a flat disk of mass 10 -4 [Special characters omitted.] , M of 10 -10 [Special characters omitted.] /yr, and an inclination angle of 75=B0 for 2M1207, whereas a disk mass of 10 -5 [Special characters omitted.] , M of 10 -11 [Special characters omitted.] /yr, and an inclination angle of 63° provides a good fit to SSSPM 1102. Modeling of the 10 m m silicate feature requires the presence of large (>50 m m ) grains in the disk midplane, which indicates

  4. The inner-disk and stellar properties of the young stellar object WL 16

    NASA Technical Reports Server (NTRS)

    Carr, John S.; Tokunaga, Alan T.; Najita, Joan; Shu, Frank H.; Glassgold, Alfred E.

    1993-01-01

    We present kinematic evidence for a rapidly rotating circumstellar disk around the young stellar object WL 16, based on new high-velocity-resolution data of the v = 2-0 CO bandhead emission. A Keplerian disk provides an excellent fit to the observed profile and requires a projected velocity for the CO-emitting region of roughly 250 km/s at the inner radius and 140 km/s at the outer radius, giving a ratio of the inner to the outer radius of about 0.3. We show that satisfying the constraints imposed by the gas kinematics, the observed CO flux, and the total source luminosity requires the mass of WL 16 to lie between 1.4 and 2.5 solar mass. The inner disk radius for the CO emission must be less than 8 solar radii.

  5. Properties of the outer regions of spiral disks: abundances, colors and ages

    NASA Astrophysics Data System (ADS)

    Mollá, Mercedes; Díaz, Angeles I.; Gibson, Brad K.; Cavichia, Oscar; López-Sánchez, Ángel-R.

    2017-03-01

    We summarize the results obtained from our suite of chemical evolution models for spiral disks, computed for different total masses and star formation efficiencies. Once the gas, stars and star formation radial distributions are reproduced, we analyze the Oxygen abundances radial profiles for gas and stars, in addition to stellar averaged ages and global metallicity. We examine scenarios for the potential origin of the apparent flattening of abundance gradients in the outskirts of disk galaxies, in particular the role of molecular gas formation prescriptions.

  6. Herniated Disk

    MedlinePlus

    ... to pain if the back is stressed. A herniated disk is a disk that ruptures. This allows the ... or back pain. Your doctor will diagnose a herniated disk with a physical exam and, sometimes, imaging tests. ...

  7. Correlation analysis of radio properties and accretion-disk luminosity for low luminosity AGNs

    NASA Astrophysics Data System (ADS)

    Su, Renzhi; Liu, Xiang; Zhang, Zhen

    2017-01-01

    The correlation between the jet power and accretion disk luminosity is investigated and analyzed with our model for 7 samples of low luminosity active galactic nuclei (LLAGNs). The main results are: (1) the power-law correlation index (P_{jet} ∝ L_{disk} ^{μ}) typically ranges μ=0.4-0.7 for the LLAGN samples, and there is a hint of steep index for the LLAGN sample which hosted by a high fraction of elliptical galaxies, and there are no significant correlation between the μ and the LLAGN types (Seyfert, LINER); (2) for μ≈1, as noted in Liu et al., the accretion disk dominates the jet power and the black hole (BH) spin is not important, for the LLAGN samples studied in this paper we find that the μ is significantly less than unity, implying that BH spin may play a significant role in the jet power of LLAGNs; (3) the BH spin-jet power is negatively correlated with the BH mass in our model, which means a high spin-jet efficiency in the `low' BH-mass LLAGNs; (4) an anti-correlation between radio loudness and disk luminosity is found, which is apparently due to the flatter power-law index in the jet-disk correlation of the LLAGNs, and the radio loudness can be higher in the LLAGNs than in luminous AGNs/quasars when the BH spin-jet power is comparable to or dominate over the accretion-jet power in the LLAGNs. The high radio-core dominance of the LLAGNs is also discussed.

  8. On the Relative Relevance of Subject-Specific Geometries and Degeneration-Specific Mechanical Properties for the Study of Cell Death in Human Intervertebral Disk Models

    PubMed Central

    Malandrino, Andrea; Pozo, José M.; Castro-Mateos, Isaac; Frangi, Alejandro F.; van Rijsbergen, Marc M.; Ito, Keita; Wilke, Hans-Joachim; Dao, Tien Tuan; Ho Ba Tho, Marie-Christine; Noailly, Jérôme

    2015-01-01

    Capturing patient- or condition-specific intervertebral disk (IVD) properties in finite element models is outmost important in order to explore how biomechanical and biophysical processes may interact in spine diseases. However, disk degenerative changes are often modeled through equations similar to those employed for healthy organs, which might not be valid. As for the simulated effects of degenerative changes, they likely depend on specific disk geometries. Accordingly, we explored the ability of continuum tissue models to simulate disk degenerative changes. We further used the results in order to assess the interplay between these simulated changes and particular IVD morphologies, in relation to disk cell nutrition, a potentially important factor in disk tissue regulation. A protocol to derive patient-specific computational models from clinical images was applied to different spine specimens. In vitro, IVD creep tests were used to optimize poro-hyperelastic input material parameters in these models, in function of the IVD degeneration grade. The use of condition-specific tissue model parameters in the specimen-specific geometrical models was validated against independent kinematic measurements in vitro. Then, models were coupled to a transport-cell viability model in order to assess the respective effects of tissue degeneration and disk geometry on cell viability. While classic disk poro-mechanical models failed in representing known degenerative changes, additional simulation of tissue damage allowed model validation and gave degeneration-dependent material properties related to osmotic pressure and water loss, and to increased fibrosis. Surprisingly, nutrition-induced cell death was independent of the grade-dependent material properties, but was favored by increased diffusion distances in large IVDs. Our results suggest that in situ geometrical screening of IVD morphology might help to anticipate particular mechanisms of disk degeneration. PMID:25717471

  9. On the relative relevance of subject-specific geometries and degeneration-specific mechanical properties for the study of cell death in human intervertebral disk models.

    PubMed

    Malandrino, Andrea; Pozo, José M; Castro-Mateos, Isaac; Frangi, Alejandro F; van Rijsbergen, Marc M; Ito, Keita; Wilke, Hans-Joachim; Dao, Tien Tuan; Ho Ba Tho, Marie-Christine; Noailly, Jérôme

    2015-01-01

    Capturing patient- or condition-specific intervertebral disk (IVD) properties in finite element models is outmost important in order to explore how biomechanical and biophysical processes may interact in spine diseases. However, disk degenerative changes are often modeled through equations similar to those employed for healthy organs, which might not be valid. As for the simulated effects of degenerative changes, they likely depend on specific disk geometries. Accordingly, we explored the ability of continuum tissue models to simulate disk degenerative changes. We further used the results in order to assess the interplay between these simulated changes and particular IVD morphologies, in relation to disk cell nutrition, a potentially important factor in disk tissue regulation. A protocol to derive patient-specific computational models from clinical images was applied to different spine specimens. In vitro, IVD creep tests were used to optimize poro-hyperelastic input material parameters in these models, in function of the IVD degeneration grade. The use of condition-specific tissue model parameters in the specimen-specific geometrical models was validated against independent kinematic measurements in vitro. Then, models were coupled to a transport-cell viability model in order to assess the respective effects of tissue degeneration and disk geometry on cell viability. While classic disk poro-mechanical models failed in representing known degenerative changes, additional simulation of tissue damage allowed model validation and gave degeneration-dependent material properties related to osmotic pressure and water loss, and to increased fibrosis. Surprisingly, nutrition-induced cell death was independent of the grade-dependent material properties, but was favored by increased diffusion distances in large IVDs. Our results suggest that in situ geometrical screening of IVD morphology might help to anticipate particular mechanisms of disk degeneration.

  10. DUST PROPERTIES AND DISK STRUCTURE OF EVOLVED PROTOPLANETARY DISKS IN Cep OB2: GRAIN GROWTH, SETTLING, GAS AND DUST MASS, AND INSIDE-OUT EVOLUTION

    SciTech Connect

    Sicilia-Aguilar, Aurora; Henning, Thomas; Dullemond, Cornelis P.; Bouwman, Jeroen; Sturm, Bernhard; Patel, Nimesh; Juhasz, Attila E-mail: aurora.sicilia@uam.es

    2011-11-20

    We present Spitzer/Infrared Spectrograph spectra of 31 T Tauri stars (TTS) and IRAM/1.3 mm observations for 34 low- and intermediate-mass stars in the Cep OB2 region. Including our previously published data, we analyze 56 TTS and 3 intermediate-mass stars with silicate features in Tr 37 ({approx}4 Myr) and NGC 7160 ({approx}12 Myr). The silicate emission features are well reproduced with a mixture of amorphous (with olivine, forsterite, and silica stoichiometry) and crystalline grains (forsterite, enstatite). We explore grain size and disk structure using radiative transfer disk models, finding that most objects have suffered substantial evolution (grain growth, settling). About half of the disks show inside-out evolution, with either dust-cleared inner holes or a radially dependent dust distribution, typically with larger grains and more settling in the innermost disk. The typical strong silicate features nevertheless require the presence of small dust grains, and could be explained by differential settling according to grain size, anomalous dust distributions, and/or optically thin dust populations within disk gaps. M-type stars tend to have weaker silicate emission and steeper spectral energy distributions than K-type objects. The inferred low dust masses are in a strong contrast with the relatively high gas accretion rates, suggesting global grain growth and/or an anomalous gas-to-dust ratio. Transition disks in the Cep OB2 region display strongly processed grains, suggesting that they are dominated by dust evolution and settling. Finally, the presence of rare but remarkable disks with strong accretion at old ages reveals that some very massive disks may still survive to grain growth, gravitational instabilities, and planet formation.

  11. Comparison of Mechanical Properties of TMW Alloys, New Generation of Cast-and-Wrought Superalloys for Disk Applications

    NASA Astrophysics Data System (ADS)

    Gu, Y. F.; Fukuda, T.; Cui, C.; Harada, H.; Mitsuhashi, A.; Yokokawa, T.; Fujioka, J.; Koizumi, Y.; Kobayashi, T.

    2009-12-01

    A new kind of Ni-Co-base disk alloys, named TMW alloys, has been developed on the basis of our innovative concept. Full-scale pancakes (440 mm in diameter and 65 mm in thickness) with an average grain size of about 10 μm were successfully manufactured from TMW alloys by a conventional cast-and-wrought (C&W) processing route. The property assessments of the pancakes indicate that TMW alloys are superior to C&W U720Li alloys in tensile strength and in creep resistance, while the performances of low-cycle fatigue (LCF) and fatigue crack growth (FCG) are comparative.

  12. Disk instability and outburst properties of the intermediate polar GK Persei

    NASA Technical Reports Server (NTRS)

    Kim, Soon-Wook; Wheeler, J. C.; Mineshige, Shin

    1992-01-01

    The present study reproduces the observed recurrence time scales and duration of the 1981-1989 dwarf nova-type outbursts of the intermediate polar GK Per with a model based on the time-dependent disk instability model. The model gives approximately symmetric (type B, inside-out) outbursts, as observed. This agreement suggests that the outbursts cannot result from a mass transfer instability. A modest variation of the mass transfer rate from the companion is sufficient to account for the variable outburst recurrence time scale. Contamination from the companion and the hot spot dominate the light from the disk except during a bright outburst. An intermediate temperature stagnation wave followed by a full heating wave is consistent with the observed rapid rise and double-peaked structure in the UV and optical light curves. It is argued that the hard X-ray efficiency is dime-dependent, and it is found to be much smaller in outburst than in quiescence.

  13. Disk instability and outburst properties of the intermediate polar GK Persei

    NASA Technical Reports Server (NTRS)

    Kim, Soon-Wook; Wheeler, J. C.; Mineshige, Shin

    1992-01-01

    The present study reproduces the observed recurrence time scales and duration of the 1981-1989 dwarf nova-type outbursts of the intermediate polar GK Per with a model based on the time-dependent disk instability model. The model gives approximately symmetric (type B, inside-out) outbursts, as observed. This agreement suggests that the outbursts cannot result from a mass transfer instability. A modest variation of the mass transfer rate from the companion is sufficient to account for the variable outburst recurrence time scale. Contamination from the companion and the hot spot dominate the light from the disk except during a bright outburst. An intermediate temperature stagnation wave followed by a full heating wave is consistent with the observed rapid rise and double-peaked structure in the UV and optical light curves. It is argued that the hard X-ray efficiency is dime-dependent, and it is found to be much smaller in outburst than in quiescence.

  14. Disks in elliptical galaxies

    SciTech Connect

    Rix, H.; White, S.D.M. )

    1990-10-01

    The abundance and strength of disk components in elliptical galaxies are investigated by studying the photometric properties of models containing a spheroidal r exp 1/4-law bulge and a weak exponential disk. Pointed isophotes are observed in a substantial fraction of elliptical galaxies. If these isophote distortions are interpreted in the framework of the present models, then the statistics of observed samples suggest that almost all radio-weak ellipticals could have disks containing roughly 20 percent of the light. It is shown that the E5 galaxy NGC 4660 has the photometric signatures of a disk containing a third of the light. 30 refs.

  15. Glass rupture disk

    DOEpatents

    Glass, S. Jill; Nicolaysen, Scott D.; Beauchamp, Edwin K.

    2002-01-01

    A frangible rupture disk and mounting apparatus for use in blocking fluid flow, generally in a fluid conducting conduit such as a well casing, a well tubing string or other conduits within subterranean boreholes. The disk can also be utilized in above-surface pipes or tanks where temporary and controllable fluid blockage is required. The frangible rupture disk is made from a pre-stressed glass with controllable rupture properties wherein the strength distribution has a standard deviation less than approximately 5% from the mean strength. The frangible rupture disk has controllable operating pressures and rupture pressures.

  16. The Properties of Hypervelocity Stars and S-stars Originating from an Eccentric Disk around a Supermassive Black Hole

    NASA Astrophysics Data System (ADS)

    Šubr, Ladislav; Haas, Jaroslav

    2016-09-01

    Hypervelocity stars (HVSs), which are observed in the Galactic halo, are believed to be accelerated to large velocities by a process of tidal disruption of binary stars passing close to the supermassive black hole (SMBH) which resides in the center of the Galaxy. It is, however, still unclear where these relatively young stars were born and what dynamical process pushed them to nearly radial orbits around the SMBH. In this paper we investigate the possibility that the young binaries originated from a thin eccentric disk, similar to the one currently observed in the Galactic center. By means of direct N-body simulations, we follow the dynamical evolution of an initially thin and eccentric disk of stars with a 100% binary fraction orbiting around the SMBH. Such a configuration leads to Kozai-Lidov oscillations of orbital elements, bringing a considerable number of binaries to the close vicinity of the black hole. Subsequent tidal disruption of these binaries accelerates one of their components to velocities well above the escape velocity from the SMBH, while the second component becomes tightly bound to the SMBH. We describe the main kinematic properties of the escaping and tightly bound stars within our model, and compare them qualitatively to the properties of the observed HVSs and S-stars, respectively. The most prominent feature is strong anisotropy in the directions of the escaping stars, which is observed for Galactic HVSs but has not yet been explained.

  17. Diversity of Debris Disks - Constraining the Disk Outer Radii

    NASA Astrophysics Data System (ADS)

    Rieke, George; Smith, Paul; Su, Kate

    2008-03-01

    Existing Spitzer observations of debris disks show a wide range of diversity in disk morphologies and spectral energy distributions (SEDs). The majority of debris disks observed with Spitzer are not resolved, resulting in very few direct constraints on disk extent. In general, SEDs alone have little diagnostic power beyond some basic statistics. However, as demonstrated by some Spitzer observations of nearby systems (beta Leo and gamma Oph), the spectra of the excess emission in the IRS and MIPS-SED wavelength range can help to put tighter constraints on disk properties such as minimum/maximum grain sizes and inner/outer disk radii. The dust continuum slopes are very useful to differentiate between various disk structures and constrain the dust mass. We need to study sufficient numbers of disks to explore their characteristics systematically. Therefore, we propose to obtain MIPS-SED observations of 27 debris disks that already have IRS-LL spectra and MIPS 24 and 70 micron photometry.

  18. Effect of laser radiation on optical properties of disk shaped quantum dot in magnetic fields

    NASA Astrophysics Data System (ADS)

    Prasad, Vinod; Silotia, Poonam

    2011-10-01

    The optical absorption coefficients and changes in the refractive index in GaAs/AlGaAs, disk shaped quantum dots (DSQD) with simultaneously applied laser and magnetic field are studied in detail. The use of the density matrix formalism is made to study the variations in linear and non-linear polarizability with the frequency of the electric field. It is found that the absorption coefficient and the refractive index changes depend not only on the optical wave but also on the strength of the static magnetic field.

  19. ON THE MISALIGNMENT OF THE DIRECTLY IMAGED PLANET {beta} PICTORIS b WITH THE SYSTEM'S WARPED INNER DISK

    SciTech Connect

    Dawson, Rebekah I.; Murray-Clay, Ruth A.; Fabrycky, Daniel C.

    2011-12-10

    The vertical warp in the debris disk {beta} Pictoris-an inclined inner disk extending into a flat outer disk-has long been interpreted as the signpost of a planet on an inclined orbit. Direct images spanning 2004-2010 have revealed {beta} Pictoris b, a planet with a mass and orbital distance consistent with this picture. However, it was recently reported that the orbit of planet b is aligned with the flat outer disk, not the inclined inner disk, and thus lacks the inclination to warp the disk. We explore three scenarios for reconciling the apparent misalignment of the directly imaged planet {beta} Pictoris b with the warped inner disk of {beta} Pictoris: observational uncertainty, an additional planet, and damping of planet b's inclination. We find that, at the extremes of the uncertainties, the orbit of {beta} Pictoris b has the inclination necessary to produce the observed warp. We also find that if planet b were aligned with the flat outer disk, it would prevent another planet from creating a warp with the observed properties; therefore planet b itself must be responsible for the warp. Finally, planet b's inclination could have been damped by dynamical friction and still produce the observed disk morphology, but the feasibility of damping depends on disk properties and the presence of other planets. More precise observations of the orbit of planet b and the position angle of the outer disk will allow us to distinguish between the first and third scenarios.

  20. Transition circumnstellar disks in Lupus

    NASA Astrophysics Data System (ADS)

    Romero, G. A.; Schreiber, M. R.; Cieza, L. A.; Rebassa-Manssergas, A.; Williams, J. P.; Merin, B.; Smith-Castelli, A.; Orellana, M.

    2011-10-01

    Based on Spitzer selected YSOs, we present a study of transition disks located in Lupus. Several mechanisms have been proposed to explain their defining characteristic: an inner opacity hole and an optically thick outer disk. These processes are: planet formation, grain growth, photoevaporation, tidal truncation in close binaries. We have carried out Adaptive Optics (AO) imaging, submillimeter photometry, and echelle spectroscopy in order to observationally characterize our transition disk sample. With the analyzed data we can distinguish the four scenarios and identify candidate transition disk systems that are currently forming planets. Such objects are excellent targets to be followed-up with Herschel and ALMA.

  1. Exploring Disks Around Planets

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2017-07-01

    Giant planets are thought to form in circumstellar disks surrounding young stars, but material may also accrete into a smaller disk around the planet. Weve never detected one of these circumplanetary disks before but thanks to new simulations, we now have a better idea of what to look for.Image from previous work simulating a Jupiter-mass planet forming inside a circumstellar disk. The planet has its own circumplanetary disk of accreted material. [Frdric Masset]Elusive DisksIn the formation of giant planets, we think the final phase consists of accretion onto the planet from a disk that surrounds it. This circumplanetary disk is important to understand, since it both regulates the late gas accretion and forms the birthplace of future satellites of the planet.Weve yet to detect a circumplanetary disk thus far, because the resolution needed to spot one has been out of reach. Now, however, were entering an era where the disk and its kinematics may be observable with high-powered telescopes (like the Atacama Large Millimeter Array).To prepare for such observations, we need models that predict the basic characteristics of these disks like the mass, temperature, and kinematic properties. Now a researcher at the ETH Zrich Institute for Astronomy in Switzerland, Judit Szulgyi, has worked toward this goal.Simulating CoolingSzulgyi performs a series of 3D global radiative hydrodynamic simulations of 1, 3, 5, and 10 Jupiter-mass (MJ) giant planets and their surrounding circumplanetary disks, embedded within the larger circumstellar disk around the central star.Density (left column), temperature (center), and normalized angular momentum (right) for a 1 MJ planet over temperatures cooling from 10,000 K (top) to 1,000 K (bottom). At high temperatures, a spherical circumplanetary envelope surrounds the planet, but as the planet cools, the envelope transitions around 64,000 K to a flattened disk. [Szulgyi 2017]This work explores the effects of different planet temperatures and

  2. Electromagnetic signatures of thin accretion disks in wormhole geometries

    SciTech Connect

    Harko, Tiberiu; Kovacs, Zoltan; Lobo, Francisco S. N.

    2008-10-15

    In this paper, we study the physical properties and characteristics of matter forming thin accretion disks in static and spherically symmetric wormhole spacetimes. In particular, the time averaged energy flux, the disk temperature, and the emission spectra of the accretion disks are obtained for these exotic geometries and are compared with the Schwarzschild solution. It is shown that more energy is emitted from the disk in a wormhole geometry than in the case of the Schwarzschild potential and the conversion efficiency of the accreted mass into radiation is more than a factor of 2 higher for the wormholes than for static black holes. These effects in the disk radiation are confirmed in the radial profiles of temperature corresponding to theses flux distributions, and in the emission spectrum {omega}L({omega}) of the accretion disks. We conclude that specific signatures appear in the electromagnetic spectrum, thus leading to the possibility of distinguishing wormhole geometries by using astrophysical observations of the emission spectra from accretion disks.

  3. Effect of random surface inhomogeneities on spectral properties of dielectric-disk microresonators: Theory and modeling at millimeter wave range

    NASA Astrophysics Data System (ADS)

    Ganapolskii, E. M.; Eremenko, Z. E.; Tarasov, Yu. V.

    2009-04-01

    The influence of random axially homogeneous surface roughness on spectral properties of dielectric resonators of circular disk form is studied both theoretically and experimentally. To solve the equations governing the dynamics of electromagnetic fields, the method of eigenmode separation is applied previously developed with reference to inhomogeneous systems subject to arbitrary external static potential. We prove theoretically that it is the gradient mechanism of wave-surface scattering that is highly responsible for nondissipative loss in the resonator. The influence of side-boundary inhomogeneities on the resonator spectrum is shown to be described in terms of effective renormalization of mode wave numbers jointly with azimuth indices in the characteristic equation. To study experimentally the effect of inhomogeneities on the resonator spectrum, the method of modeling in the millimeter wave range is applied. As a model object, we use a dielectric disk resonator (DDR) fitted with external inhomogeneities randomly arranged at its side boundary. Experimental results show good agreement with theoretical predictions as regards the predominance of the gradient scattering mechanism. It is shown theoretically and confirmed in the experiment that TM oscillations in the DDR are less affected by surface inhomogeneities than TE oscillations with the same azimuth indices. The DDR model chosen for our study as well as characteristic equations obtained thereupon enable one to calculate both the eigenfrequencies and the Q factors of resonance spectral lines to fairly good accuracy. The results of calculations agree well with obtained experimental data.

  4. Effect of random surface inhomogeneities on spectral properties of dielectric-disk microresonators: theory and modeling at millimeter wave range.

    PubMed

    Ganapolskii, E M; Eremenko, Z E; Tarasov, Yu V

    2009-04-01

    The influence of random axially homogeneous surface roughness on spectral properties of dielectric resonators of circular disk form is studied both theoretically and experimentally. To solve the equations governing the dynamics of electromagnetic fields, the method of eigenmode separation is applied previously developed with reference to inhomogeneous systems subject to arbitrary external static potential. We prove theoretically that it is the gradient mechanism of wave-surface scattering that is highly responsible for nondissipative loss in the resonator. The influence of side-boundary inhomogeneities on the resonator spectrum is shown to be described in terms of effective renormalization of mode wave numbers jointly with azimuth indices in the characteristic equation. To study experimentally the effect of inhomogeneities on the resonator spectrum, the method of modeling in the millimeter wave range is applied. As a model object, we use a dielectric disk resonator (DDR) fitted with external inhomogeneities randomly arranged at its side boundary. Experimental results show good agreement with theoretical predictions as regards the predominance of the gradient scattering mechanism. It is shown theoretically and confirmed in the experiment that TM oscillations in the DDR are less affected by surface inhomogeneities than TE oscillations with the same azimuth indices. The DDR model chosen for our study as well as characteristic equations obtained thereupon enable one to calculate both the eigenfrequencies and the Q factors of resonance spectral lines to fairly good accuracy. The results of calculations agree well with obtained experimental data.

  5. The Milky Way disk

    NASA Astrophysics Data System (ADS)

    Carraro, G.

    2015-08-01

    This review summarises the invited presentation I gave on the Milky Way disc. The idea underneath was to touch those topics that can be considered hot nowadays in the Galactic disk research: the reality of the thick disk, the spiral structure of the Milky Way, and the properties of the outer Galactic disk. A lot of work has been done in recent years on these topics, but a coherent and clear picture is still missing. Detailed studies with high quality spectroscopic data seem to support a dual Galactic disk, with a clear separation into a thin and a thick component. Much confusion and very discrepant ideas still exist concerning the spiral structure of the Milky Way. Our location in the disk makes it impossible to observe it, and we can only infer it. This process of inference is still far from being mature, and depends a lot on the selected tracers, the adopted models and their limitations, which in many cases are neither properly accounted for, nor pondered enough. Finally, there are very different opinions on the size (scale length, truncation radius) of the Galactic disk, and on the interpretation of the observed outer disk stellar populations in terms either of external entities (Monoceros, Triangulus-Andromeda, Canis Major), or as manifestations of genuine disk properties (e.g., warp and flare).

  6. Properties of stability, bifurcation, and chaos of the tangential motion disk brake

    NASA Astrophysics Data System (ADS)

    Wei, Daogao; Ruan, Jingyu; Zhu, Weiwei; Kang, Zuheng

    2016-08-01

    This study proposes a new dynamic model of a brake system that combines pad tangential motion and disk torsional motion to reduce the vibration and noise of the brake system. The stability analysis of this system with a smoothed Stribeck friction model verified its instability, which is caused by Hopf bifurcation. Moreover, numerical simulation showed several phenomena of the system vibration changing with angular velocity: (1) the system vibration maintains in the stable limit cycle after Hopf bifurcation within a relatively wide range of low angular velocity and (2) period-doubling bifurcation and chaos will occur only by decreasing the angular velocity. This study further discusses the effects of friction parameter on stick-slip vibration within a common range of brake pressure under "low" and "lower" angular velocities; the result shows that a decrease of both μs -μk and decay factor can effectively reduce the range of chaotic vibration region.

  7. Physical Properties of Molecular Clouds for the Entire Milky Way Disk

    NASA Astrophysics Data System (ADS)

    Miville-Deschênes, Marc-Antoine; Murray, Norman; Lee, Eve J.

    2017-01-01

    This study presents a catalog of 8107 molecular clouds that covers the entire Galactic plane and includes 98% of the 12CO emission observed within b+/- 5^\\circ . The catalog was produced using a hierarchical cluster identification method applied to the result of a Gaussian decomposition of the Dame et al. data. The total H2 mass in the catalog is 1.2× {10}9 {M}ȯ , in agreement with previous estimates. We find that 30% of the sight lines intersect only a single cloud, with another 25% intersecting only two clouds. The most probable cloud size is R∼ 30 pc. We find that M\\propto {R}2.2+/- 0.2, with no correlation between the cloud surface density, Σ, and R. In contrast with the general idea, we find a rather large range of values of Σ, from 2 to 300 M⊙ pc‑2, and a systematic decrease with increasing Galactic radius, {R}{gal}. The cloud velocity dispersion and the normalization {σ }0={σ }v/{R}1/2 both decrease systematically with {R}{gal}. When studied over the whole Galactic disk, there is a large dispersion in the line width–size relation and a significantly better correlation between {σ }v and {{Σ }} R. The normalization of this correlation is constant to better than a factor of two for {R}{gal}< 20 {kpc}. This relation is used to disentangle the ambiguity between near and far kinematic distances. We report a strong variation of the turbulent energy injection rate. In the outer Galaxy it may be maintained by accretion through the disk and/or onto the clouds, but neither source can drive the 100 times higher cloud-averaged injection rate in the inner Galaxy.

  8. Mechanical Properties Anisotropy of Isothermally Forged and Precipitation Hardened Inconel 718 Disk

    NASA Astrophysics Data System (ADS)

    Khaja, Shaik; Mehta, K. K.; Veera Babu, R.; Sri Rama Devi, R.; Singh, A. K.

    2015-03-01

    The present work describes the tensile and cyclic flow behavior of the as-received disk of Inconel 718 in solution treated and precipitation hardened condition at different locations and orientations. The disk shows moderately high values of anisotropy index indicating significant difference in uniform true strain along radial and tangential orientations. The tensile true stress-plastic strain curves exhibit two slopes defined by Ludwigson relation []. The low-strain regime during tensile test is associated with low-strain localization between broad annealing twins and slips, while high-strain regime is related to the presence of large volume fraction of deformation twins and high-strain localization between narrow deformation twins. It appears that both the γ' and γ″ play a critical role during low deformation regime while the role of γ″ precipitates becomes significant in high-strain regime. The stabilized cyclic true stress-plastic strain curves follow Ludwik relationship ( σ = Kɛ n ) similar to that of high-strain regime of two-slope tensile curves. The true stress-strain curves show softening during cyclic test in comparison to that of monotonic condition and are independent of sample orientations and locations. The lower degree of cyclic softening associated with radial-oriented sample can be attributed to the alignment of δ-phase precipitates normal to the loading direction. The low ductility and low work-hardening exponent of radial-oriented sample in web region have been explained based on the dislocation storage capacity and dynamic recovery coefficient using Kock-Mecking-Estrin analysis.

  9. Stochastic Local Distinguishability

    NASA Astrophysics Data System (ADS)

    Bandyopadhyay, Somshubhro; Roy, Anirban; Walgate, Jonathan

    2007-03-01

    We pose the question, ``when is globally available information is also locally available?'', formally as the problem of local state discrimination, and show that the deep qualitative link between local distinguishability and entanglement lies at the level of stochastic rather than deterministic local protocols. We restrict our attention to sets of mutually orthogonal pure quantum states. We define a set of states |ψi> as beingstochastically locally distinguishable if and only if there is a LOCC protocol whereby the parties can conclusively identify a member of the set with some nonzero probability. If a set is stochastically locally distinguishable, then the complete global information is potentially locally available. If not, the physical information encoded by the system can never be completely locally exposed. Our results are proved true for all orthogonal quantum states regardless of their dimensionality or multipartiality. First, we prove that entanglement is a necessary property of any system whose total global information can never be locally accessed. Second, entangled states that form part of an orthogonal basis can never be locally singled out. Completely entangled bases are, always stochastically locally indistinguishable. Third, we prove that any set of three orthogonal states, is stochastically locally distinguishable.

  10. DIRECT DETECTION OF A FLARED DISK AROUND A YOUNG MASSIVE STAR HD200775 AND ITS 10 TO 1000 AU SCALE PROPERTIES

    SciTech Connect

    Okamoto, Yoshiko Kataza; Momose, M.; Kataza, Hirokazu; Honda, M.; Fujiwara, H.; Sakon, I.; Onaka, T.; Ohashi, N.; Fujiyoshi, T.; Sako, S.; Miyata, T.; Yamashita, T.

    2009-11-20

    We made mid-infrared (MIR) observations of the 10 M{sub sun} Herbig Be star HD200775 with the Cooled Mid-Infrared Camera and Spectrometer on the 8.2 m Subaru Telescope. We discovered diffuse emission of an elliptical shape extended in the north-south direction in an approx1000 AU radius around unresolved excess emission. The diffuse emission is perpendicular to the cavity wall formed by the past outflow activity and is parallel to the projected major axis of the central close binary orbit. The centers of the ellipse contours of the diffuse emission are shifted from the stellar position, and the amount of the shift increases as the contour brightness level decreases. The diffuse emission is well explained in all of geometry (the shape and the shift), size, and configuration by an inclined flared disk where only its surface emits the MIR photons. Our results give the first well-resolved infrared disk images around a massive star and strongly support that HD200775 is formed through the disk accretion. The disk survives the main accretion phase and shows a structure similar to that around lower mass stars with 'disk atmosphere'. At the same time, the disk also shows properties characteristic of massive stars such as photoevaporation traced by the 3.4 mm free-free emission and unusual silicate emission with a peak at 9.2 mum, which is shorter than that of many astronomical objects. It provides a good place to compare the disk properties between massive and lower mass stars.

  11. Theories of X-ray Emission from thin disks, slim disks, and ADAFs

    NASA Astrophysics Data System (ADS)

    Mineshige, S.; Watarai, K.; Manmoto, T.

    2001-05-01

    The observational properties of relativistic slim disks (or optically thick ADAFs; advection-dominated accretion flows) are discussed in comparison with those of thin disks and optically thin ADAFs. We first solve a transonic, slim disk structure in a general relativistic potential, and then calculate radiation spectra, taking into account photon redshift, Doppler boosting, gravitational lensing, and photon shielding by the inflated inner disk structure. The calculated spectra are fitted with multi-color blackbody model with fitting parameters of T in, the maximum temperature of the blackbody, r in, the (apparent) size of the innermost, hot region, and p, the power-law index of the radial temperature profile. We find that (i) for the disk around a Schwarzschild black hole r in decreases from 3r S to ~ 1.5 r S (with r S being the Schwarzschild radius) as mass-accretion rate increases beyond a critical value of ~ 30 L E/c2; (ii) for the disk around a Kerr hole, conversely, r in increases from < r S to ~ 1.5 r S as mass-accretion rate increases; (iii) at accretion rate above the critical value, therefore, disks around a Schwarzschild and Kerr BHs look quite similar and are hard to distinguish; and (iv) in both cases the temperature distribution gets flatter, from r-3/4 at low luminosity to r-1/2 at large luminosity. Implications on intermediate-mass black holes are briefly discussed. Interestingly, IC342 source 1 was observed to move along the line of decreasing r in line as luminosity increases. This provides a firm evidence that at least some of intermediate luminosity sources are shining at ⪆ L E and containing black holes with M ~= 10-100 Msun.

  12. ON THE PROPERTIES OF THERMAL DISK WINDS IN X-RAY TRANSIENT SOURCES: A CASE STUDY OF GRO J1655-40

    SciTech Connect

    Luketic, S.; Proga, D.; Kallman, T. R.; Raymond, J. C.; Miller, J. M. E-mail: dproga@physics.unlv.ed

    2010-08-10

    We present the results of hydrodynamical simulations of the disk photosphere irradiated by strong X-rays produced in the innermost part of the disk of an accreting black hole. As expected, the irradiation heats the photosphere and drives a thermal wind. To apply our results to the well-studied X-ray transient source GRO J1655-40, we adopted the observed mass of its black hole and the observed properties of its X-ray radiation. To compare the results with the observations, we also computed transmitted X-ray spectra based on the wind solution. Our main finding is that the density of the fast-moving part of the wind is more than 1 order of magnitude lower than that inferred from the observations. Consequently, the model fails to predict spectra with line absorption as strong and as blueshifted as those observed. However, despite the thermal wind being weak and Compton thin, the ratio between the mass-loss rate and the mass-accretion rate is about seven. This high ratio is insensitive to the accretion luminosity, in the limit of lower luminosities. Most of the mass is lost from the disk between 0.07 and 0.2 of the Compton radius. We discovered that beyond this range the wind solution is self-similar. In particular, soon after it leaves the disk, the wind flows at a constant angle with respect to the disk. Overall, the thermal winds generated in our comprehensive simulations do not match the wind spectra observed in GRO J1655-40. This supports the conclusion of Miller et al. and Kallman et al. that the wind in GRO J1655-40, and possibly in other X-ray transients, may be driven by magnetic processes. This in turn implies that the disk wind carries even more material than our simulations predict and as such has a very significant impact on the accretion disk structure and dynamics.

  13. PROPERTIES OF M31. II. A CEPHEID DISK SAMPLE DERIVED FROM THE FIRST YEAR OF PS1 PANDROMEDA DATA

    SciTech Connect

    Kodric, Mihael; Riffeser, Arno; Hopp, Ulrich; Seitz, Stella; Koppenhoefer, Johannes; Bender, Ralf; Goessl, Claus; Snigula, Jan; Lee, Chien-Hsiu; Ngeow, Chow-Choong; Chambers, K. C.; Magnier, E. A.; Price, P. A.; Burgett, W. S.; Hodapp, K. W.; Kaiser, N.; Kudritzki, R.-P.

    2013-04-15

    We present a sample of Cepheid variable stars toward M31 based on the first year of regular M31 observations of the PS1 survey in the r{sub P1} and i{sub P1} filters. We describe the selection procedure for Cepheid variable stars from the overall variable source sample and develop an automatic classification scheme using Fourier decomposition and the location of the instability strip. We find 1440 fundamental mode (classical {delta}) Cep stars, 126 Cepheids in the first overtone mode, and 147 belonging to the Population II types. Two hundred ninety-six Cepheids could not be assigned to one of these classes and three hundred fifty-four Cepheids were found in other surveys. These 2009 Cepheids constitute the largest Cepheid sample in M31 known so far and the full catalog is presented in this paper. We briefly describe the properties of our sample in its spatial distribution throughout the M31 galaxy, in its age properties, and we derive an apparent period-luminosity relation (PLR) in our two bands. The Population I Cepheids nicely follow the dust pattern of the M31 disk, whereas the 147 Type II Cepheids are distributed throughout the halo of M31. We outline the time evolution of the star formation in the major ring found previously and find an age gradient. A comparison of our PLR to previous results indicates a curvature term in the PLR.

  14. JET PROPERTIES OF GeV-SELECTED RADIO-LOUD NARROW-LINE SEYFERT 1 GALAXIES AND POSSIBLE CONNECTION TO THEIR DISK AND CORONA

    SciTech Connect

    Sun, Xiao-Na; Lin, Da-Bin; Liang, En-Wei; Zhang, Jin; Xue, Zi-Wei; Zhang, Shuang-Nan

    2015-01-01

    The observed spectral energy distributions of five GeV-selected narrow-line Seyfert 1 (NLS1) galaxies are fitted with a model including the radiation ingredients from the relativistic jet, the accretion disk, and the corona. We compare the properties of these GeV NLS1 galaxies with flat spectrum radio quasars (FSRQs), BL Lacertae objects (BL Lacs), and radio-quiet (RQ) Seyfert galaxies, and explore possible hints for jet-disk/corona connection. Our results show that the radiation physics and the jet properties of the GeV NLS1 galaxies resemble that of FSRQs. The luminosity variations of PMN J0948+0022 and 1H 0323+342 at the GeV band is tightly correlated with the beaming factor (δ), similar to that observed in FSRQ 3C 279. The accretion disk luminosities and the jet powers of the GeV NLS1 galaxies cover both the ranges of FSRQs and BL Lacs. With the detection of bright corona emission in 1H 0323+342, we show that the ratio of the corona luminosity (L {sub corona}) to the accretion disk luminosity (L {sub d}) is marginally within the high end of this ratio distribution for an RQ Seyfert galaxy sample, and the variation of jet luminosity may connect with L {sub corona}. However, it is still unclear whether a system with a high L {sub corona}/L {sub d} ratio prefers to power a jet.

  15. Jet Properties of GeV-Selected Radio-Loud Narrow-line Seyfert 1 Galaxies and Possible Connection to Their Disk and Corona

    NASA Astrophysics Data System (ADS)

    Zhang, Jin

    2015-08-01

    The observed spectral energy distributions of five GeV-selected narrow-line Seyfert 1 (NLS1) galaxies are fitted with a model including the radiation ingredients from the relativistic jet, the accretion disk, and the corona. We compare the properties of these GeV NLS1 galaxies with flat spectrum radio quasars (FSRQs), BL Lacertae objects (BL Lacs), and radio-quiet (RQ) Seyfert galaxies, and explore possible hints for jet-disk/corona connection. Our results show that the radiation physics and the jet properties of the GeV NLS1 galaxies resemble that of FSRQs. The luminosity variations of PMN J0948+0022 and 1H 0323+342 at the GeV band is tightly correlated with the beaming factor (δ), similar to that observed in FSRQ 3C 279. The accretion disk luminosities and the jet powers of the GeV NLS1 galaxies cover both the ranges of FSRQs and BL Lacs. With the detection of bright corona emission in 1H 0323+342, we show that the ratio of the corona luminosity (Lcorona) to the accretion disk luminosity (Ld) is marginally within the high end of this ratio distribution for an RQ Seyfert galaxy sample, and the variation of jet luminosity may connect with Lcorona. However, it is still unclear whether a system with a high Lcorona/Ld ratio prefers to power a jet.

  16. Jet Properties of GeV-selected Radio-loud Narrow-line Seyfert 1 Galaxies and Possible Connection to Their Disk and Corona

    NASA Astrophysics Data System (ADS)

    Sun, Xiao-Na; Zhang, Jin; Lin, Da-Bin; Xue, Zi-Wei; Liang, En-Wei; Zhang, Shuang-Nan

    2015-01-01

    The observed spectral energy distributions of five GeV-selected narrow-line Seyfert 1 (NLS1) galaxies are fitted with a model including the radiation ingredients from the relativistic jet, the accretion disk, and the corona. We compare the properties of these GeV NLS1 galaxies with flat spectrum radio quasars (FSRQs), BL Lacertae objects (BL Lacs), and radio-quiet (RQ) Seyfert galaxies, and explore possible hints for jet-disk/corona connection. Our results show that the radiation physics and the jet properties of the GeV NLS1 galaxies resemble that of FSRQs. The luminosity variations of PMN J0948+0022 and 1H 0323+342 at the GeV band is tightly correlated with the beaming factor (δ), similar to that observed in FSRQ 3C 279. The accretion disk luminosities and the jet powers of the GeV NLS1 galaxies cover both the ranges of FSRQs and BL Lacs. With the detection of bright corona emission in 1H 0323+342, we show that the ratio of the corona luminosity (L corona) to the accretion disk luminosity (L d) is marginally within the high end of this ratio distribution for an RQ Seyfert galaxy sample, and the variation of jet luminosity may connect with L corona. However, it is still unclear whether a system with a high L corona/L d ratio prefers to power a jet.

  17. Optical Disks.

    ERIC Educational Resources Information Center

    Gale, John C.; And Others

    1985-01-01

    This four-article section focuses on information storage capacity of the optical disk covering the information workstation (uses microcomputer, optical disk, compact disc to provide reference information, information content, work product support); use of laser videodisc technology for dissemination of agricultural information; encoding databases…

  18. Herniated Disk

    MedlinePlus

    ... forearm, or fingers.A slipped disk in the lumbar part of your spine can cause pain in the back and legs. It is often referred to as sciatica. This is because the disk pushes on the sciatic nerve, which runs down your leg. Symptoms include:Pain ...

  19. Polarization disks in near-infrared high-resolution imaging

    NASA Astrophysics Data System (ADS)

    Murakawa, K.

    2010-07-01

    A polarization disk is a characteristic feature of optical and near-infrared (NIR) polarimetric images of young stellar objects (YSOs) and is regarded as convincing evidence that a dust disk is present. We analyze high-resolution linear polarization maps of a sample of low-mass YSO disk models by means of radiative transfer calculations to investigate the effects of the disk geometry and grain sizes on polarization properties. Our modeling assumes spherical grains with a power-law size distribution of n(a)∝ a-3.5; 0.005 μm ≤ a ≤ a_max and with a fixed a_max of 0.25 μm for the outer envelope and a different a_max for the disk. The parameters to examine are the disk height (i.e. the ratio of the disk height to the outer disk radius H of 0.1 to 1.0) and the dust sizes in the disk (i.e. a_max of 0.25 to 1000.0 μm). In a near pole-on view, the polarization vectors are centro-symmetrically aligned even towards the disk, but the degree of polarization can be different from the envelope. We predict that the pole-on disk can be distinguished from the envelope. In contrast, the model images show a bipolar nebulosity and a polarization disk with a vector alignment in edge-on view. The polarization is low (<10%) for large grains or low H values and high (up to ~80%) for small grains and high H values. In contrast, comparably constant polarizations (20-40%) are obtained in the optical. The wavelength dependence in low NIR polarization cases is often detected in many T Tauri stars, suggesting that grain growth or an advanced disk accretion is expected in these objects. The opposite trend in high NIR polarization cases, which is found in some low-mass protostars, is reproduced with spherical grain models. To understand our results, we developed a generalized scattering model, which is an extension of the vector alignment mechanism. In the low-mass star disk case, multiple-scattered light behaves as if it chooses paths of comparably low optical density region (e.g. the

  20. Spontaneous formation of spiral-like patterns with distinct periodic physical properties by confined electrodeposition of Co-In disks

    PubMed Central

    Golvano-Escobal, Irati; Gonzalez-Rosillo, Juan Carlos; Domingo, Neus; Illa, Xavi; López-Barberá, José Francisco; Fornell, Jordina; Solsona, Pau; Aballe, Lucia; Foerster, Michael; Suriñach, Santiago; Baró, Maria Dolors; Puig, Teresa; Pané, Salvador; Nogués, Josep; Pellicer, Eva; Sort, Jordi

    2016-01-01

    Spatio-temporal patterns are ubiquitous in different areas of materials science and biological systems. However, typically the motifs in these types of systems present a random distribution with many possible different structures. Herein, we demonstrate that controlled spatio-temporal patterns, with reproducible spiral-like shapes, can be obtained by electrodeposition of Co-In alloys inside a confined circular geometry (i.e., in disks that are commensurate with the typical size of the spatio-temporal features). These patterns are mainly of compositional nature, i.e., with virtually no topographic features. Interestingly, the local changes in composition lead to a periodic modulation of the physical (electric, magnetic and mechanical) properties. Namely, the Co-rich areas show higher saturation magnetization and electrical conductivity and are mechanically harder than the In-rich ones. Thus, this work reveals that confined electrodeposition of this binary system constitutes an effective procedure to attain template-free magnetic, electric and mechanical surface patterning with specific and reproducible shapes. PMID:27462025

  1. Spontaneous formation of spiral-like patterns with distinct periodic physical properties by confined electrodeposition of Co-In disks

    NASA Astrophysics Data System (ADS)

    Golvano-Escobal, Irati; Gonzalez-Rosillo, Juan Carlos; Domingo, Neus; Illa, Xavi; López-Barberá, José Francisco; Fornell, Jordina; Solsona, Pau; Aballe, Lucia; Foerster, Michael; Suriñach, Santiago; Baró, Maria Dolors; Puig, Teresa; Pané, Salvador; Nogués, Josep; Pellicer, Eva; Sort, Jordi

    2016-07-01

    Spatio-temporal patterns are ubiquitous in different areas of materials science and biological systems. However, typically the motifs in these types of systems present a random distribution with many possible different structures. Herein, we demonstrate that controlled spatio-temporal patterns, with reproducible spiral-like shapes, can be obtained by electrodeposition of Co-In alloys inside a confined circular geometry (i.e., in disks that are commensurate with the typical size of the spatio-temporal features). These patterns are mainly of compositional nature, i.e., with virtually no topographic features. Interestingly, the local changes in composition lead to a periodic modulation of the physical (electric, magnetic and mechanical) properties. Namely, the Co-rich areas show higher saturation magnetization and electrical conductivity and are mechanically harder than the In-rich ones. Thus, this work reveals that confined electrodeposition of this binary system constitutes an effective procedure to attain template-free magnetic, electric and mechanical surface patterning with specific and reproducible shapes.

  2. Spontaneous formation of spiral-like patterns with distinct periodic physical properties by confined electrodeposition of Co-In disks.

    PubMed

    Golvano-Escobal, Irati; Gonzalez-Rosillo, Juan Carlos; Domingo, Neus; Illa, Xavi; López-Barberá, José Francisco; Fornell, Jordina; Solsona, Pau; Aballe, Lucia; Foerster, Michael; Suriñach, Santiago; Baró, Maria Dolors; Puig, Teresa; Pané, Salvador; Nogués, Josep; Pellicer, Eva; Sort, Jordi

    2016-07-27

    Spatio-temporal patterns are ubiquitous in different areas of materials science and biological systems. However, typically the motifs in these types of systems present a random distribution with many possible different structures. Herein, we demonstrate that controlled spatio-temporal patterns, with reproducible spiral-like shapes, can be obtained by electrodeposition of Co-In alloys inside a confined circular geometry (i.e., in disks that are commensurate with the typical size of the spatio-temporal features). These patterns are mainly of compositional nature, i.e., with virtually no topographic features. Interestingly, the local changes in composition lead to a periodic modulation of the physical (electric, magnetic and mechanical) properties. Namely, the Co-rich areas show higher saturation magnetization and electrical conductivity and are mechanically harder than the In-rich ones. Thus, this work reveals that confined electrodeposition of this binary system constitutes an effective procedure to attain template-free magnetic, electric and mechanical surface patterning with specific and reproducible shapes.

  3. Are herb-pairs of traditional Chinese medicine distinguishable from others? Pattern analysis and artificial intelligence classification study of traditionally defined herbal properties.

    PubMed

    Ung, Choong Yong; Li, Hu; Cao, Zhi Wei; Li, Yi Xue; Chen, Yu Zong

    2007-05-04

    Multi-herb prescriptions of traditional Chinese medicine (TCM) often include special herb-pairs for mutual enhancement, assistance, and restraint. These TCM herb-pairs have been assembled and interpreted based on traditionally defined herbal properties (TCM-HPs) without knowledge of mechanism of their assumed synergy. While these mechanisms are yet to be determined, properties of TCM herb-pairs can be investigated to determine if they exhibit features consistent with their claimed unique synergistic combinations. We analyzed distribution patterns of TCM-HPs of TCM herb-pairs to detect signs indicative of possible synergy and used artificial intelligence (AI) methods to examine whether combination of their TCM-HPs are distinguishable from those of non-TCM herb-pairs assembled by random combinations and by modification of known TCM herb-pairs. Patterns of the majority of 394 known TCM herb-pairs were found to exhibit signs of herb-pair correlation. Three AI systems, trained and tested by using 394 TCM herb-pairs and 2470 non-TCM herb-pairs, correctly classified 72.1-87.9% of TCM herb-pairs and 91.6-97.6% of the non-TCM herb-pairs. The best AI system predicted 96.3% of the 27 known non-TCM herb-pairs and 99.7% of the other 1,065,100 possible herb-pairs as non-TCM herb-pairs. Our studies suggest that TCM-HPs of known TCM herb-pairs contain features distinguishable from those of non-TCM herb-pairs consistent with their claimed synergistic or modulating combinations.

  4. Disks around Main Sequence Stars

    NASA Astrophysics Data System (ADS)

    Trauger, John

    1995-07-01

    About 30 other nearby stars have been shown (Aumann 1985,1988 Sadakane and Nishida 1986) to emit excess infrared flux relative to that expected from their photospheres. It is believed that such emission is the rule rather than the exception and that the limited number is caused by the IRAS detection limits. We propose to observe the prototypical objects Alpha Lyrae. If an optical counterpart to the infrared emission is observed, then the same analysis as that performed on the Beta Pictoris disk will be possible. If not, because of the low scattered light levels in the wings of the HST PSF, stringent limits on the albedo of the disk should be obtained. Only one circumstellar disk has been directly observed around a main sequence star. On the other hand, it is believed that disks are typical byproducts of star formation, and that these disks are the sites where planetary systems are formed. Both of these hypotheses will be tested with the observations proposed here. Firstly, the observations, if they detect the material will constrain its spatial distribution, and test the disk hypothesis. The material surrounding the target stars is presumed but not known to be distributed in a disk. There is not significant extinction towards these targets, but a shell of optically thin material can also fit the existing IRAS observations. The observations also only loosely constrain the radial distribution of the particles. Given a detection, it should be possible to distinguish a disk from

  5. Disk Drives

    NASA Technical Reports Server (NTRS)

    1994-01-01

    A new material known as AlBeMet, developed by Brush Wellman for research applications in the National Aero-Space Plane (NASP) program, is now used for high performance disk drives. AlBeMet is a compression of aluminum, beryllium metal matrix composite. It reduces system weight and its high thermal conductivity can effectively remove heat and increase an electrical system's lifetime. The lighter, stiffer AlBeMet (AlBeMet 160) used in the disk drive means heads can be moved faster, improving disk performance.

  6. Nebra Disk

    NASA Astrophysics Data System (ADS)

    Pásztor, Emília

    An important archaeological find from the Bronze Age has come to light in Germany. It is a round bronze disk adorned with gold figures that might be interpreted as symbols for stars, the sun, and the moon, making the disk the oldest known surviving depiction of celestial objects in Europe. By comparing the iconography and ideography of the disk with archaeological finds, ethnographic material, and historical notes of different cultures and periods, the conclusion has been reached that the compositional elements might be understood as the depiction of a traditional folk worldview.

  7. Magnetic disk

    NASA Technical Reports Server (NTRS)

    Mallinson, John C.

    1992-01-01

    Magnetic disk recording was invented in 1953 and has undergone intensive development ever since. As a result of this 38 years of development, the cost per byte and the areal density have halved and doubled respectively every 2-2 1/2 years. Today, the cost per byte is lower than 10(exp -6) dollars per byte and area densities exceed 100 10(exp 6) bits per square inch. In this talk, the recent achievements in magnetic disk recording are first surveyed briefly. Then, the principal areas of current technical development are outlined. Finally, some comments are made about the future of magnetic disk recording.

  8. Screening for cephalosporin-resistant Streptococcus pneumoniae with the Kirby-Bauer disk susceptibility test.

    PubMed

    Friedland, I R; Shelton, S; McCracken, G H

    1993-06-01

    Kirby-Bauer disk susceptibility tests with five standard cephalosporin disks were performed on 23 penicillin-resistant Streptococcus pneumoniae isolates for which ceftriaxone MICs were 0.125 to 4 micrograms/ml. Cefuroxime disk inhibition zone diameters distinguished clearly isolates for which ceftriaxone MICs were > or = 2 micrograms/ml from more susceptible strains, whereas cephalothin, ceftizoxime, cefotaxime, and ceftriaxone disks distinguished these isolates less clearly than the cefuroxime disk did.

  9. Star formation activity in spiral galaxy disks and the properties of radio halos: Observational evidence for a direct dependence

    NASA Technical Reports Server (NTRS)

    Dahlem, Michael; Lisenfeld, Ute; Golla, Gotz

    1995-01-01

    In this article we address observationally the questions: how does star formation (SF) in the disks of galaxies lead to the creation of radio halos, and what minimum energy input into the interstellar medium (ISM) is needed to facilitate this? For the investigation we use a sample of five edge-on galaxies exhibiting radio continuum emmission in their halos and enhanced SF spread over large parts of their disks. In a detailed study of the two galaxies in our sample for which we have the best data, NGC 891 and NGC 4631, we show that the radio halos cut off abruptly at galactocentric radii smaller than those of the underlying thin radio disks. Our most important result is that the halo cutoffs are spatially coincident with the radii where the SF activity in the underlying disks drops sharply. The difference in radius of the emission distributions tracing ongoing SF in the disks (IRAS 50 micrometers, H alpha) versus that of the nonthermal radio continuum thin disks (tracing the distribution of cosmic-ray (CR) electrons) is typically a few kpc. This difference in extent is caused by CR diffusion. We have measured the CR diffusion coefficients in the thin disks of both NGC 891 and NGC 4631. For radial diffusion of CR electrons within the galactic disks the values are D(sub r) = 1.1-2.5 x 10 (exp 29) sq cm/s (NGC 4631) and D(sub r) = 1.2 x 10(exp 29) sq cm/s (NGC 891). For motions in the z-direction in areas within the thin disks where no outflows occur, we derive a firm upper limit of D(sub z) less than or equal to 0.2 x 10(exp 28) sq cm/s for NGC 891. The value for NGC 4631 is D(sub z = 1.4 x 10 (exp 28) sq cm/s. The other three galaxies in our sample, NGC 3044, NGC 4666, and NGC 5775 show (at the sensitivity of our data) less extended, more filamentary radio halos. Isolates spurs or filaments of nonthermal radio continuum emission in their halos are traced only above the most actively star-forming regions in the disks. This, in conjuction with the results obtained for

  10. DIAGNOSING CIRCUMSTELLAR DEBRIS DISKS

    SciTech Connect

    Hahn, Joseph M.

    2010-08-20

    A numerical model of a circumstellar debris disk is developed and applied to observations of the circumstellar dust orbiting {beta} Pictoris. The model accounts for the rates at which dust is produced by collisions among unseen planetesimals, and the rate at which dust grains are destroyed due to collisions. The model also accounts for the effects of radiation pressure, which is the dominant perturbation on the disk's smaller but abundant dust grains. Solving the resulting system of rate equations then provides the dust abundances versus grain size and dust abundances over time. Those solutions also provide the dust grains' collisional lifetime versus grain size, and the debris disk's optical depth and surface brightness versus distance from the star. Comparison to observations then yields estimates of the unseen planetesimal disk's radius, and the rate at which the disk sheds mass due to planetesimal grinding. The model can also be used to measure or else constrain the dust grain's physical and optical properties, such as the dust grains' strength, their light-scattering asymmetry parameter, and the grains' efficiency of light scattering Q{sub s}. The model is then applied to optical observations of the edge-on dust disk orbiting {beta} Pictoris, and good agreement is achieved when the unseen planetesimal disk is broad, with 75 {approx}< r {approx}< 150 AU. If it is assumed that the dust grains are bright like Saturn's icy rings (Q{sub s} = 0.7), then the cross section of dust in the disk is A{sub d} {approx_equal} 2 x 10{sup 20} km{sup 2} and its mass is M{sub d} {approx_equal} 11 lunar masses. In this case, the planetesimal disk's dust-production rate is quite heavy, M-dot {sub d{approx}}9 M {sub +} Myr{sup -1}, implying that there is or was a substantial amount of planetesimal mass there, at least 110 Earth masses. If the dust grains are darker than assumed, then the planetesimal disk's mass-loss rate and its total mass are heavier. In fact, the apparent dearth

  11. Self-Consistent Thermal Accretion Disk Corona Models for Compact Objects. I: Properties of the Corona and the Spectrum of Escaping Radiation

    NASA Technical Reports Server (NTRS)

    Dove, James B.; Wilms, Jorn; Begelman, Mitchell C.

    1997-01-01

    We present the properties of accretion disk corona (ADC) models in which the radiation field, the temperature, and the total opacity of the corona are determined self-consistently. We use a nonlinear Monte Carlo code to perform the calculations. As an example, we discuss models in which the corona is situated above and below a cold accretion disk with a plane-parallel (slab) geometry, similar to the model of Haardt & Maraschi. By Comptonizing the soft radiation emitted by the accretion disk, the corona is responsible for producing the high-energy component of the escaping radiation. Our models include the reprocessing of radiation in the accretion disk. Here the photons either are Compton-reflected or photoabsorbed, giving rise to fluorescent line emission and thermal emission. The self- consistent coronal temperature is determined by balancing heating (due to viscous energy dissipation) with Compton cooling, determined using the fully relativistic, angle-dependent cross sections. The total opacity is found by balancing pair productions with annihilations. We find that, for a disk temperature kT(sub BB) approx. less than 200 eV, these coronae are unable to have a self-consistent temperature higher than approx. 140 keV if the total optical depth is approx. less than 0.2, regardless of the compactness parameter of the corona and the seed opacity. This limitation corresponds to the angle-averaged spectrum of escaping radiation having a photon index approx. greater than 1.8 within the 5-30 keV band. Finally, all models that have reprocessing features also predict a large thermal excess at lower energies. These constraints make explaining the X-ray spectra of persistent black hole candidates with ADC models very problematic.

  12. Observations of T Tauri Disks at Sub-AU Radii: Implications for Magnetospheric Accretion and Planet Formation

    NASA Astrophysics Data System (ADS)

    Eisner, J. A.; Hillenbrand, L. A.; White, R. J.; Akeson, R. L.; Sargent, A. I.

    2005-04-01

    We determine inner disk sizes and temperatures for four solar-type (1-2 Msolar) classical T Tauri stars, AS 207A, V2508 Oph, AS 205A, and PX Vul, using 2.2 μm observations from the Keck Interferometer. Nearly contemporaneous near-IR adaptive optics imaging photometry, optical photometry, and high-dispersion optical spectroscopy are used to distinguish contributions from the inner disks and central stars in the interferometric observations. In addition, the spectroscopic and photometric data provide estimates of stellar properties, mass accretion rates, and disk corotation radii. We model our interferometric and photometric data in the context of geometrically flat accretion disk models with inner holes, and flared disks with puffed-up inner walls. Models incorporating puffed-up inner disk walls generally provide better fits to the data, similar to previous results for higher mass Herbig Ae stars. Our measured inner disk sizes are larger than disk truncation radii predicted by magnetospheric accretion models, with larger discrepancies for sources with higher mass accretion rates. We suggest that our measured sizes correspond to dust sublimation radii, and that optically thin gaseous material may extend farther inward to the magnetospheric truncation radii. Finally, our inner disk measurements constrain the location of terrestrial planet formation as well as potential mechanisms for halting giant planet migration.

  13. Old open clusters in the outer Galactic disk

    NASA Astrophysics Data System (ADS)

    Carraro, G.; Geisler, D.; Villanova, S.; Frinchaboy, P. M.; Majewski, S. R.

    2007-12-01

    Context: The outer parts of the Milky Way disk are believed to be one of the main arenas where the accretion of external material in the form of dwarf galaxies and subsequent formation of streams is taking place. The Monoceros stream and the Canis Major and Argo over-densities are notorious examples. Understanding whether what we detect is the signature of accretion or, more conservatively, simply the intrinsic nature of the disk, represents one of the major goals of modern Galactic astronomy. Aims: We try to shed more light on the properties of the outer disk by exploring the properties of distant anti-center old open clusters. We want to verify whether distant clusters follow the chemical and dynamical behavior of the solar vicinity disk, or whether their properties can be better explained in terms of an extra-galactic population. Methods: VLT high resolution spectra have been acquired for five distant open clusters: Ruprecht 4, Ruprecht 7, Berkeley 25, Berkeley 73 and Berkeley 75. We derive accurate radial velocities to distinguish field interlopers and cluster members. For the latter we perform a detailed abundance analysis and derive the iron abundance [Fe/H] and the abundance ratios of several α elements. Results: Our analysis confirms previous indications that the radial abundance gradient in the outer Galactic disk does not follow the expectations extrapolated from the solar vicinity, but exhibits a shallower slope. By combining the metallicity of the five program clusters with eight more clusters for which high resolution spectroscopy is available, we find that the mean metallicity in the outer disk between 12 and 21 kpc from the Galactic center is [Fe/H] ≈ -0.35, with only marginal indications for a radial variation. In addition, all the program clusters exhibit solar scaled or slightly enhanced α elements, similar to open clusters in the solar vicinity and thin disk stars. Conclusions: We investigate whether this outer disk cluster sample might

  14. Molecular beam epitaxial growth and optical properties of red-emitting (λ = 650 nm) InGaN/GaN disks-in-nanowires on silicon

    NASA Astrophysics Data System (ADS)

    Jahangir, S.; Mandl, M.; Strassburg, M.; Bhattacharya, P.

    2013-02-01

    We have investigated the radiative properties of InGaN disks in GaN nanowires grown by plasma enhanced molecular beam epitaxy on (001) silicon substrates. The growth of the nanowire heterostructures has been optimized to maximize the radiative efficiency, or internal quantum efficiency (IQE), for photoluminescence emission at λ = 650 nm. It is found that the IQE increases significantly (by ˜10%) to 52%, when post-growth passivation of nanowire surface with silicon nitride or parylene is applied. The increase in efficiency is supported by radiative- and nonradiative lifetimes derived from data obtained from temperature dependent- and time-resolved photoluminescence measurements. Light emitting diodes with p-i-n disk-in-nanowire heterostructures passivated with parylene have been fabricated and characterized.

  15. Molecular beam epitaxial growth and optical properties of red-emitting ({lambda} = 650 nm) InGaN/GaN disks-in-nanowires on silicon

    SciTech Connect

    Jahangir, S.; Bhattacharya, P.; Mandl, M.; Strassburg, M.

    2013-02-18

    We have investigated the radiative properties of InGaN disks in GaN nanowires grown by plasma enhanced molecular beam epitaxy on (001) silicon substrates. The growth of the nanowire heterostructures has been optimized to maximize the radiative efficiency, or internal quantum efficiency (IQE), for photoluminescence emission at {lambda} = 650 nm. It is found that the IQE increases significantly (by {approx}10%) to 52%, when post-growth passivation of nanowire surface with silicon nitride or parylene is applied. The increase in efficiency is supported by radiative- and nonradiative lifetimes derived from data obtained from temperature dependent- and time-resolved photoluminescence measurements. Light emitting diodes with p-i-n disk-in-nanowire heterostructures passivated with parylene have been fabricated and characterized.

  16. PLANETESIMAL DISK MICROLENSING

    SciTech Connect

    Heng, Kevin; Keeton, Charles R. E-mail: keeton@physics.rutgers.ed

    2009-12-10

    Motivated by debris disk studies, we investigate the gravitational microlensing of background starlight by a planetesimal disk around a foreground star. We use dynamical survival models to construct a plausible example of a planetesimal disk and study its microlensing properties using established ideas of microlensing by small bodies. When a solar-type source star passes behind a planetesimal disk, the microlensing light curve may exhibit short-term, low-amplitude residuals caused by planetesimals several orders of magnitude below Earth mass. The minimum planetesimal mass probed depends on the photometric sensitivity and the size of the source star, and is lower when the planetesimal lens is located closer to us. Planetesimal lenses may be found more nearby than stellar lenses because the steepness of the planetesimal mass distribution changes how the microlensing signal depends on the lens/source distance ratio. Microlensing searches for planetesimals require essentially continuous monitoring programs that are already feasible and can potentially set constraints on models of debris disks, the progeny of the supposed extrasolar analogues of Kuiper Belts.

  17. Recognition of lumbar disk herniation with NMR

    SciTech Connect

    Chafetz, N.I.; Genant, H.K.; Moon, K.L.; Helms, C.A.; Morris, J.M.

    1983-12-01

    Fifteen nuclear magnetic resonance (NMR) studies of 14 patients with herniated lumbar intervertebral disks were performed on the UCSF NMR imager. Computed tomographic (CT) scans done on a GE CT/T 8800 or comparable scanner were available at the time of NMR scan interpretation. Of the 16 posterior disk ruptures seen at CT, 12 were recognized on NMR. Diminished nucleus pulposus signal intensity was present in all ruptured disks. In one patient, NMR scans before and after chymopapain injection showed retraction of the protruding part of the disk and loss of signal intensity after chemonucleolysis. Postoperative fibrosis demonstrated by CT in one patient and at surgery in another showed intermediate to high signal intensity on NMR, easily distinguishing it from nearby thecal sac and disk. While CT remains the method of choice for evaluation of the patient with suspected lumbar disk rupture, the results of this study suggest that NMR may play a role in evaluating this common clinical problem.

  18. Mechanical properties of nanocrystalline metals, intermetalics and multiphase materials determined by tension, compression and disk-bend techniques

    SciTech Connect

    Eastman, J.A.; Thompson, L.J.; DiMelfi, R.J.; Choudry, M. Dollar, M.; Weertman, J.R.; Rittner, M.N.; Youngdahl, C.J. /

    1997-02-01

    The mechanical behavior of nanocrystalline metallic, intermetallic, and multiphase materials was investigated using tension, compression, and disk-bend techniques. Nanocrystalline NiAl, Al-Al{sub 3}Zr, and Cu were synthesized by gas condensation and either resistive or electron beam heating followed by high temperature vacuum compaction. Disk- bend tests of nanocrystalline NiAl show evidence of improved ductility at room temperature in this normally extremely brittle material. In contrast, tension tests of multiphase nanocrystalline Al- Al{sub 3}Zr samples show significant increases in strength by substantial reductions in ductility with decreasing grain size. Compression tests of nanocrystalline copper result in substantially higher yield stress and total elongation values than those measured in tensile tests. Implications for operative deformation mechanisms in these materials are discussed.

  19. FIRST SCIENCE OBSERVATIONS WITH SOFIA/FORCAST: PROPERTIES OF INTERMEDIATE-LUMINOSITY PROTOSTARS AND CIRCUMSTELLAR DISKS IN OMC-2

    SciTech Connect

    Adams, Joseph D.; Herter, Terry L.; Gull, George E.; Henderson, Charles P.; Schoenwald, Justin; Stacey, Gordon; Osorio, Mayra; Macias, Enrique; Thomas Megeath, S.; Fischer, William J.; Ali, Babar; D'Alessio, Paola; De Buizer, James M.; Shuping, Ralph Y.; Keller, Luke D.; Morris, Mark R.; Remming, Ian S.; Stanke, Thomas; Stutz, Amelia; and others

    2012-04-20

    We examine eight young stellar objects in the OMC-2 star-forming region based on observations from the SOFIA/FORCAST early science phase, the Spitzer Space Telescope, the Herschel Space Observatory, Two Micron All Sky Survey, Atacama Pathfinder Experiment, and other results in the literature. We show the spectral energy distributions (SED) of these objects from near-infrared to millimeter wavelengths, and compare the SEDs with those of sheet collapse models of protostars and circumstellar disks. Four of the objects can be modeled as protostars with infalling envelopes, two as young stars surrounded by disks, and the remaining two objects have double-peaked SEDs. We model the double-peaked sources as binaries containing a young star with a disk and a protostar. The six most luminous sources are found in a dense group within a 0.15 Multiplication-Sign 0.25 pc region; these sources have luminosities ranging from 300 L{sub Sun} to 20 L{sub Sun }. The most embedded source (OMC-2 FIR 4) can be fit by a class 0 protostar model having a luminosity of {approx}50 L{sub Sun} and mass infall rate of {approx}10{sup -4} M{sub Sun} yr{sup -1}.

  20. Herschel evidence for disk flattening or gas depletion in transitional disks

    SciTech Connect

    Keane, J. T.; Pascucci, I.; Espaillat, C.; Woitke, P.; Andrews, S.; Kamp, I.; Thi, W.-F.; Meeus, G.; Dent, W. R. F.

    2014-06-01

    Transitional disks are protoplanetary disks characterized by reduced near- and mid-infrared emission, with respect to full disks. This characteristic spectral energy distribution indicates the presence of an optically thin inner cavity within the dust disk believed to mark the disappearance of the primordial massive disk. We present new Herschel Space Observatory PACS spectra of [O I] 63.18 μm for 21 transitional disks. Our survey complements the larger Herschel GASPS program ({sup G}as in Protoplanetary Systems{sup )} by quadrupling the number of transitional disks observed with PACS in this wavelength. [O I] 63.18 μm traces material in the outer regions of the disk, beyond the inner cavity of most transitional disks. We find that transitional disks have [O I] 63.18 μm line luminosities ∼2 times fainter than their full disk counterparts. We self-consistently determine various stellar properties (e.g., bolometric luminosity, FUV excess, etc.) and disk properties (e.g., disk dust mass, etc.) that could influence the [O I] 63.18 μm line luminosity, and we find no correlations that can explain the lower [O I] 63.18 μm line luminosities in transitional disks. Using a grid of thermo-chemical protoplanetary disk models, we conclude that either transitional disks are less flared than full disks or they possess lower gas-to-dust ratios due to a depletion of gas mass. This result suggests that transitional disks are more evolved than their full disk counterparts, possibly even at large radii.

  1. Molecular Gas In Young Debris Disks

    NASA Astrophysics Data System (ADS)

    Moór, Attila

    2016-07-01

    Debris disks are generally thought to be the gas poor descendants of protoplanetary disks. While this characteristic may be true for most debris systems, recent surveys in rotational transitions of carbon monoxide led to a growing sample of debris disks where gas has been detected. The origin of gas in these disks is unclear yet. It may be secondary, i.e., similarly to dust grains it is continuously replenished via erosion of larger bodies. However, because of their youth, one cannot exclude that some disks may be hybrid in the sense that they retain their residual primordial gas, while the dust component may predominantly be second generation. The first observations of gaseous debris disks with ALMA provided examples of both types. This talk will review the currently known CO-rich debris disks with special emphasis on the origin of gas and on the commonly shared disk/host star properties.

  2. THE DEBRIS DISK AROUND HR 8799

    SciTech Connect

    Su, K. Y. L.; Rieke, G. H.; Smith, P. S.; Misselt, K. A.; Stapelfeldt, K. R.; Bryden, G.; Moro-Martin, A.; Williams, J. P.

    2009-11-01

    We have obtained a full suite of Spitzer observations to characterize the debris disk around HR 8799 and to explore how its properties are related to the recently discovered set of three massive planets orbiting the star. We distinguish three components to the debris system: (1) warm dust (T approx 150 K) orbiting within the innermost planet; (2) a broad zone of cold dust (T approx 45 K) with a sharp inner edge orbiting just outside the outermost planet and presumably sculpted by it; and (3) a dramatic halo of small grains originating in the cold dust component. The high level of dynamical activity implied by this halo may arise due to enhanced gravitational stirring by the massive planets. The relatively young age of HR 8799 places it in an important early stage of development and may provide some help in understanding the interaction of planets and planetary debris, an important process in the evolution of our own solar system.

  3. Multiwavelength search for protoplanetary disks

    NASA Technical Reports Server (NTRS)

    Neuhaeuser, Ralph; Schmidt-Kaler, Theodor

    1994-01-01

    Infrared emission of circumstellar dust was observed for almost one hundred T Tauri stars. This dust is interpreted to be part of a protoplanetary disk orbiting the central star. T Tauri stars are young stellar objects and evolve into solar type stars. Planets are believed to form in these disks. The spectral energy distribution of a disk depends on its temperature profile. Different disk regions emit at different wavelengths. The disk-star boundary layer is hot and emits H(alpha) radiation. Inner disk regions at around 1 AU with a temperature of a few hundred Kelvin can be probed in near infrared wavelength regimes. Outer disk regions at around 100 AU distance from the star are colder and emit far infrared and sub-millimeter radiation. Also, X-ray emission from the stellar surface can reveal information on disk properties. Emission from the stellar surface and the boundary layer may be shielded by circumstellar gas and dust. T Tauri stars with low H(alpha) emission, i.e. no boundary layer, show stronger X-ray emission than classical T Tauri stars, because the inner disk regions of weak emission-line T Tauri stars may be clear of material. In this paper, first ROSAT all sky survey results on the X-ray emission of T Tauri stars and correlations between X-ray luminosity and properties of T Tauri disks are presented. Due to atmospheric absorption, X-ray and most infrared observations cannot be carried out on Earth, but from Earth orbiting satellites (e.g. IRAS, ROSAT, ISO) or from lunar based observatories, which would have special advantages such as a stable environment.

  4. The properties of the Malin 1 galaxy giant disk. A panchromatic view from the NGVS and GUViCS surveys

    NASA Astrophysics Data System (ADS)

    Boissier, S.; Boselli, A.; Ferrarese, L.; Côté, P.; Roehlly, Y.; Gwyn, S. D. J.; Cuillandre, J.-C.; Roediger, J.; Koda, J.; Muños Mateos, J. C.; Gil de Paz, A.; Madore, B. F.

    2016-10-01

    Context. Low surface brightness galaxies (LSBGs) represent a significant percentage of local galaxies but their formation and evolution remain elusive. They may hold crucial information for our understanding of many key issues (i.e., census of baryonic and dark matter, star formation in the low density regime, mass function). The most massive examples - the so called giant LSBGs - can be as massive as the Milky Way, but with this mass being distributed in a much larger disk. Aims: Malin 1 is an iconic giant LSBG - perhaps the largest disk galaxy known. We attempt to bring new insights on its structure and evolution on the basis of new images covering a wide range in wavelength. Methods: We have computed surface brightness profiles (and average surface brightnesses in 16 regions of interest), in six photometric bands (FUV, NUV, u, g, i, z). We compared these data to various models, testing a variety of assumptions concerning the formation and evolution of Malin 1. Results: We find that the surface brightness and color profiles can be reproduced by a long and quiet star-formation history due to the low surface density; no significant event, such as a collision, is necessary. Such quiet star formation across the giant disk is obtained in a disk model calibrated for the Milky Way, but with an angular momentum approximately 20 times larger. Signs of small variations of the star-formation history are indicated by the diversity of ages found when different regions within the galaxy are intercompared. Conclusions: For the first time, panchromatic images of Malin 1 are used to constrain the stellar populations and the history of this iconic example among giant LSBGs. Based on our model, the extreme disk of Malin 1 is found to have a long history of relatively low star formation (about 2 M⊙ yr-1). Our model allows us to make predictions on its stellar mass and metallicity. The Appendix images (FITS files) are available at the CDS via anonymous ftp to http

  5. RINGED ACCRETION DISKS: EQUILIBRIUM CONFIGURATIONS

    SciTech Connect

    Pugliese, D.; Stuchlík, Z. E-mail: zdenek.stuchlik@physics.cz

    2015-12-15

    We investigate a model of a ringed accretion disk, made up by several rings rotating around a supermassive Kerr black hole attractor. Each toroid of the ringed disk is governed by the general relativity hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. Properties of the tori can then be determined by an appropriately defined effective potential reflecting the background Kerr geometry and the centrifugal effects. The ringed disks could be created in various regimes during the evolution of matter configurations around supermassive black holes. Therefore, both corotating and counterrotating rings have to be considered as being a constituent of the ringed disk. We provide constraints on the model parameters for the existence and stability of various ringed configurations and discuss occurrence of accretion onto the Kerr black hole and possible launching of jets from the ringed disk. We demonstrate that various ringed disks can be characterized by a maximum number of rings. We present also a perturbation analysis based on evolution of the oscillating components of the ringed disk. The dynamics of the unstable phases of the ringed disk evolution seems to be promising in relation to high-energy phenomena demonstrated in active galactic nuclei.

  6. Scattering from Thin Dielectric Disks

    NASA Technical Reports Server (NTRS)

    Levine, D. M.; Schneider, A.; Lang, R. H.; Carter, H. G.

    1984-01-01

    A solution was obtained for scattering from thin dielectric disks by approximating the currents induced inside the disk with the currents which would exist inside a dielectric slab of the same thickness, orientation and dielectric properties. This approximation reduces to an electrostatic approximation when the disk thickness, T, is small compared to the wavelength of the incident radiation and the approximation yields a conventional physical optics solution when the dimension, A, characteristic of the geometrical cross section of the disk (e.g., the diameter of a circular disk) is large compared to wavelength. When the ratio A/T is sufficiently large the disk will always be in one or the other of these regimes (T lambda or kA1. Consequently, when A/T is large this solution provides a conventional approximation for the scattered fields which can be applied at all frequencies. As a check on this conclusion, a comparison was made between the theoretical and measured radar cross section of thin dielectric disks. Agreement was found for thin disks with both large and small values of kA.

  7. Scattering from thin dielectric disks

    NASA Technical Reports Server (NTRS)

    Le Vine, D. M.; Schneider, A.; Lang, R. H.; Carter, H. G.

    1985-01-01

    A solution was obtained for scattering from thin dielectric disks by approximating the currents induced inside the disk with the currents which would exist inside a dielectric slab of the same thickness, orientation and dielectic properties. This approximation reduces to an electrostatic approximation when the disk thickness, T, is small compared to the wavelength of the incident radiation and the approximation yields a conventional physical optics solution when the dimension, A, characteristic of the geometrical cross section of the disk (e.g., the diameter of a circular disk) is large compared to wavelength. When the ratio A/T sufficiently large the disk will always be in one or the other of these regimes, T lambda or kA1. Consequently, when A/T is large this solution provides a conventional approximation for the scattered fields which can be applied at all frequencies. As a check on this conclusion, a comparison was made between the theoretical and measured radar cross section of thin dielectric disks. Agreement was found for thin disks with both large and small values of kA.

  8. Disk filter

    DOEpatents

    Bergman, W.

    1985-01-09

    An electric disk filter provides a high efficiency at high temperature. A hollow outer filter of fibrous stainless steel forms the ground electrode. A refractory filter material is placed between the outer electrode and the inner electrically isolated high voltage electrode. Air flows through the outer filter surfaces through the electrified refractory filter media and between the high voltage electrodes and is removed from a space in the high voltage electrode.

  9. Optical disks

    NASA Technical Reports Server (NTRS)

    Lopez-Swafford, B.

    1986-01-01

    A comprehensive overview of the different types of optical storage technology is presented. Research efforts to integrate this technology into the VAX/VMS environment are discussed. In addition, plans for future applications of optical disk technology are described. The applications should prove to be beneficial to the NSSDC user community as a whole. Of particular interest is the concentration on the collaboration with the Dynamics Explorer project.

  10. Disk filter

    DOEpatents

    Bergman, Werner

    1986-01-01

    An electric disk filter provides a high efficiency at high temperature. A hollow outer filter of fibrous stainless steel forms the ground electrode. A refractory filter material is placed between the outer electrode and the inner electrically isolated high voltage electrode. Air flows through the outer filter surfaces through the electrified refractory filter media and between the high voltage electrodes and is removed from a space in the high voltage electrode.

  11. The physical and chemical evolution of protostellar disks. The growth of protostellar disks: Progress to date

    NASA Technical Reports Server (NTRS)

    Stahler, Steven W.

    1993-01-01

    This study constitutes one part of our multi-disciplinary approach to the evolution of planet-forming disks. The goal is to establish the disks' thermal and mechanical properties as they grow by the infall of their parent interstellar clouds. Thus far, significant advances toward establishing the evolving surface density of such disks was made.

  12. Study of the properties and the choice of alloys for bladed disks (blisks) and a method for their joining

    NASA Astrophysics Data System (ADS)

    Povarova, K. B.; Valitov, V. A.; Obsepyan, S. V.; Drozdov, A. A.; Bazyleva, O. A.; Valitova, E. V.

    2014-09-01

    The choice of materials for the bladed disks (blisks) that are intended for next-generation aviation gas turbine engines is grounded. As blade materials, single crystals of light heterophase γ' + γ VKNA-type alloys based on the γ'(Ni3Al) intermetallic compound with an ordered structure are proposed. The choice of novel deformable EP975-type nickel superalloys, which are intended for operation at 800-850°C, as the disk material is grounded. It is shown that the most effective method for forming one-piece joints of an Ni3Al-based alloy and a high-alloy EP975-type nickel superalloy is the new process of solid-phase pressure welding under conditions of high-temperature superplasticity. Solid-phase joints are formed for heterophase Ni3Al-based alloy single crystals and deformable EK61 and EP975 nickel alloys. The gradient structures in the zone of the solid-phase joints that form under the conditions of low- and high-temperature superplasticity at homologous temperatures of ˜0.6 T m and 0.9 T m are studied. The character and direction of the diffusion processes at the joint of an intermetallic alloy single crystal and a deformable polycrystalline alloy are determined.

  13. TM01-mode microwave propagation property analysis for plasmas with disk-plate windows by a finite-difference time-domain method

    SciTech Connect

    Okamura, Yoshimasa; Yamamoto, Yoshito; Fujita, Kazuhiro; Miyoshi, Taiki; Teramoto, Koji; Kawaguchi, Hideki; Kagami, Shin; Furukawa, Masakazu

    2007-07-15

    Numerical studies of microwave propagation properties in a conical horn and an adjustable waveguides, and for plasmas generated under disk-plate windows of a 220 mm diameter and in a vacuum chamber are studied by a finite-difference time-domain (FDTD) method including plasma equations. In the numerical studies, a TM01-mode microwave of 2.45 GHz at a power of 1 kW is supplied from the top of the conical horn waveguide. In addition, numerical results by the FDTD method are compared with experimental results, and a validity of the numerical results is investigated. From the numerical results, it is found that the TM01-mode microwave changes its field shape and propagates along inner surfaces of the conical horn and the adjustable waveguides. Then electromagnetic fields of the TM01-mode microwave concentrate at the center surfaces of the disk-plate windows [quartz ({epsilon}{sub r}=3.8), alumina ({epsilon}{sub r}=9.7), and WG20 ({epsilon}{sub r}=20.0)]. A diameter of higher concentration is within 80 mm, and the orientation of electric field is almost vertical to the disk-plate window. The diameters within 80 mm are equivalent to a diameter at a higher electron density in an oxygen plasma experiment in the volume mode at 1 kW and 133 Pa with a quartz window. When heights of the adjustable waveguide are changed from 64 to 244 mm, peaks of electric fields in the heights, where microwave power is estimated to be strongly absorbed into the plasmas, appear and peak positions of the electric fields are observed periodically in surface-wave mode plasmas as well as the volume mode plasmas. Heights of the peaks increase with increasing dielectric constant and peak-to-peak distances of the peak positions decrease with increasing dielectric constant. The peak positions agree to the minimum microwave power reflections tuned by a combination of an autotuning unit and adjustable waveguide heights in experiments. Furthermore, peak positions of relatively absorbed microwave powers in

  14. 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.

  15. Magnetically Torqued Thin Accretion Disks

    NASA Astrophysics Data System (ADS)

    Kluźniak, W.; Rappaport, S.

    2007-12-01

    We compute the properties of a geometrically thin, steady accretion disk surrounding a central rotating, magnetized star. The magnetosphere is assumed to entrain the disk over a wide range of radii. The model is simplified in that we adopt two (alternate) ad hoc, but plausible, expressions for the azimuthal component of the magnetic field as a function of radial distance. We find a solution for the angular velocity profile tending to corotation close to the central star and smoothly matching a Keplerian curve at a radius where the viscous stress vanishes. The value of this ``transition'' radius is nearly the same for both of our adopted B-field models. We then solve analytically for the torques on the central star and for the disk luminosity due to gravity and magnetic torques. When expressed in a dimensionless form, the resulting quantities depend on one parameter alone, the ratio of the transition radius to the corotation radius. For rapid rotators, the accretion disk may be powered mostly by spin-down of the central star. These results are independent of the viscosity prescription in the disk. We also solve for the disk structure for the special case of an optically thick alpha disk. Our results are applicable to a range of astrophysical systems including accreting neutron stars, intermediate polar cataclysmic variables, and T Tauri systems.

  16. Distinguished Cooperating Teacher Program.

    ERIC Educational Resources Information Center

    Chicago State Univ., IL.

    The Distinguished Cooperating Teacher Program at Chicago State University was developed to train cooperating teachers to supervise student teachers. The program departs from traditional practice by changing the roles of the classroom teacher and the university field supervisor. The supervisor's role becomes that of coordinator while the teacher…

  17. Accretion disks around a mass with quadrupole

    NASA Astrophysics Data System (ADS)

    Abishev, M.; Boshkayev, K.; Quevedo, H.; Toktarbay, S.

    We consider the stability properties of circular orbits of test particles moving around a mass with quadrupole. We show that the quadrupole modifies drastically the properties of an accretion disk made of such test particles.

  18. Saturn's icy satellites investigated by Cassini-VIMS. I. Full-disk properties: 350-5100 nm reflectance spectra and phase curves

    USGS Publications Warehouse

    Filacchione, G.; Capaccioni, F.; McCord, T.B.; Coradini, A.; Cerroni, P.; Bellucci, G.; Tosi, F.; D'Aversa, E.; Formisano, V.; Brown, R.H.; Baines, K.H.; Bibring, J.-P.; Buratti, B.J.; Clark, R.N.; Combes, M.; Cruikshank, D.P.; Drossart, P.; Jaumann, R.; Langevin, Y.; Matson, D.L.; Mennella, V.; Nelson, R.M.; Nicholson, P.D.; Sicardy, B.; Sotin, C.; Hansen, G.; Hibbitts, K.; Showalter, M.; Newman, S.

    2007-01-01

    Saturn's icy satellites are among the main scientific objectives of the Cassini-VIMS (Visual and Infrared Mapping Spectrometer) experiment. This paper contains a first systematic and comparative analysis of the full-disk spectral properties of Dione, Enceladus, Epimetheus, Hyperion, Iapetus, Mimas, Phoebe, Rhea and Tethys as observed by VIMS from July 2004 to June 2005. The disk integrated properties (350-5100 nm reflectance spectra and phase curves at 550-2232 nm) and images of satellites are reported and discussed in detail together with the observed geometry. In general, the spectra in the visible spectral range are almost featureless and can be classified according to the spectral slopes: from the bluish Enceladus and Phoebe to the redder Iapetus, Hyperion and Epimetheus. In the 1000-1300 nm range the spectra of Enceladus, Tethys, Mimas and Rhea are characterized by a negative slope, consistent with a surface largely dominated by water ice, while the spectra of Iapetus, Hyperion and Phoebe show a considerable reddening pointing out the relevant role played by darkening materials present on the surface. In between these two classes are Dione and Epimetheus, which have a flat spectrum in this range. The main absorption bands identified in the infrared are the 1520, 2020, 3000 nm H2O/OH bands (for all satellites), although Iapetus dark terrains show mostly a deep 3000 nm band while the 1520 and 2020 nm bands are very faint. In this spectral range, the Iapetus spectrum is characterized by a strong reddening. The CO2 band at 4260 nm and the Fresnel ice peak around 3100 nm are evident only on Hyperion, Phoebe and Iapetus. The phase curves at 550 and at 2232 nm are reported for all the available observations in the 0??-144?? range; Rhea shows an opposition surge at visible wavelengths in the 0.5??-1.17?? interval. The improvement on the retrieval of the full-disk reflectance spectra can be appreciated by a direct comparison with ground-based telescopic data available

  19. The VLA Nascent Disk and Multiplicity Survey (VANDAM): Resolved Candidate Disks around Class 0 and I Protostars

    NASA Astrophysics Data System (ADS)

    Segura-Cox, Dominique; Harris, Robert J.; Tobin, John J.; Looney, Leslie; Li, Zhi-Yun; Chandler, Claire J.; Kratter, Kaitlin M.; Dunham, Michael; Sadavoy, Sarah; Perez, Laura M.; Melis, Carl

    2016-01-01

    The properties of young protostellar disks, particularly Class 0 disks, are not well studied observationally, and their expected properties are controversial. In particular, there is debate about whether or not the earliest disks are large and massive and about when and how disks form. To characterize the properties of the youngest disks and binaries we are conducting the VLA Nascent Disk and Multiplicity survey (VANDAM) toward all known protostars in the Perseus molecular cloud (d ~ 230 pc). The survey is the largest and most complete high-resolution millimeter/centimeter wavelength survey of protostellar disks and binaries. We present the dust emission results toward a sample of ~15 protostellar disk candidates around Class 0 and I sources in the Perseus molecular cloud from the VANDAM survey with ~0.05'' or 12 AU resolution. We have begun to confirm the disk candidacy of these sources by fitting the Ka-band 8 mm dust-continuum data in the uv-plane to a simple, parametrized model based on the Shakura-Sunyaev disk model. The seven candidate disks this analysis has been performed on are well-fit by the disk shaped model, and have estimated masses from the measured flux in agreement with masses of previously known disks. The inner-disk surface densities of the VANDAM candidate disks have shallower density profiles compared to disks around more evolved Class II systems. The best-fit model radii of the seven early-result candidate disks are R > 10 AU; at 8 mm, the radii reflect lower limits on the disk size since dust continuum emission is tied to grain size and large grains radially drift inwards. These disks, if confirmed kinematically, are inconsistent with theoretical models where the disk size is limited by strong magnetic braking to < 10 AU at early times.

  20. Structural and Chemical Modification to Improve Adhesive and Material Properties of Fibrin-Genipin for Repair of Annulus Fibrosus Defects in Intervertebral Disks.

    PubMed

    Cruz, Michelle A; McAnany, Steven; Gupta, Nikita; Long, Rose G; Nasser, Philip; Eglin, David; Hecht, Andrew C; Illien-Junger, Svenja; Iatridis, James C

    2017-08-01

    Annulus fibrosus (AF) defects from intervertebral disk (IVD) herniation and degeneration are commonly associated with back pain. Genipin-crosslinked fibrin hydrogel (FibGen) is an injectable, space-filling AF sealant that was optimized to match AF shear properties and partially restored IVD biomechanics. This study aimed to enhance mechanical behaviors of FibGen to more closely match AF compressive, tensile, and shear properties by adjusting genipin crosslink density and by creating a composite formulation by adding Poly(D,L-lactide-co-glycolide) (PDLGA). This study also evaluated effects of thrombin concentration and injection technique on gelation kinetics and adhesive strength. Increasing FibGen genipin concentration from 1 to 36 mg/mL significantly increased adhesive strength (∼5 to 35 kPa), shear moduli (∼10 to 110 kPa), and compressive moduli (∼25 to 150 kPa) with concentration-dependent effects, and spanning native AF properties. Adding PDLGA to FibGen altered the material microstructure on electron microscopy and nearly tripled adhesive strength, but did not increase tensile moduli, which remained nearly 5× below native AF, and had a small increase in shear moduli and significantly decreased compressive moduli. Increased thrombin concentration decreased gelation rate to < 5 min and injection methods providing a structural FibGen cap increased pushout strength by ∼40%. We conclude that FibGen is highly modifiable with tunable mechanical properties that can be formulated to be compatible with human AF compressive and shear properties and gelation kinetics and injection techniques compatible with clinical discectomy procedures. However, further innovations, perhaps with more efficient fiber reinforcement, will be required to enable FibGen to match AF tensile properties.

  1. Evaluation of powder metallurgy superalloy disk materials

    NASA Technical Reports Server (NTRS)

    Evans, D. J.

    1975-01-01

    A program was conducted to develop nickel-base superalloy disk material using prealloyed powder metallurgy techniques. The program included fabrication of test specimens and subscale turbine disks from four different prealloyed powders (NASA-TRW-VIA, AF2-1DA, Mar-M-432 and MERL 80). Based on evaluation of these specimens and disks, two alloys (AF2-1DA and Mar-M-432) were selected for scale-up evaluation. Using fabricating experience gained in the subscale turbine disk effort, test specimens and full scale turbine disks were formed from the selected alloys. These specimens and disks were then subjected to a rigorous test program to evaluate their physical properties and determine their suitability for use in advanced performance turbine engines. A major objective of the program was to develop processes which would yield alloy properties that would be repeatable in producing jet engine disks from the same powder metallurgy alloys. The feasibility of manufacturing full scale gas turbine engine disks by thermomechanical processing of pre-alloyed metal powders was demonstrated. AF2-1DA was shown to possess tensile and creep-rupture properties in excess of those of Astroloy, one of the highest temperature capability disk alloys now in production. It was determined that metallographic evaluation after post-HIP elevated temperature exposure should be used to verify the effectiveness of consolidation of hot isostatically pressed billets.

  2. Accretion Disks around Young Stars

    NASA Astrophysics Data System (ADS)

    D'Alessio, Paola

    1996-04-01

    intensity distribution is calculated on the plane of the sky, integrating the radiative transfer equation along rays parallel to the line of sight. To this end, monochromatic opacities are used, which also allow us to construct tables of the Rosseland and Planck Mean Opacities. The disk structure and brightness distribution thus obtained are self-consistent with respect to the abundances and optical properties of the gas and the dust. With the disk intensity distribution, its spectrum is constructed and its colors are calculated in different spectral ranges. These are compared to observations of low mass young stars reported in the literature, for which the disk parameters are then inferred. It is found that the observed properties of a large fraction of classical T Tauri stars can be explained as emission from viscous disks irradiated by the central star or by a thin envelope and that the emission in the long wavelength range from a flat spectrum source like HL Tau is consistent with the predictions of a model in which a viscous disk is irradiated by an optically thick infalling envelope.

  3. Photometric properties of Comet 67P/CG as seen by VIRTIS-M onboard Rosetta: light curves and disk-integrated phase curves

    NASA Astrophysics Data System (ADS)

    Ciarniello, M.; Capaccioni, F.; Filacchione, G.; Raponi, A.; De Sanctis, M. C.; Tosi, F.; Capria, M. T.; Piccioni, G.; Cerroni, P.; Palomba, E.; Longobardo, A.; Migliorini, A.; Rosetta VIRTIS Team

    VIRTIS-M is the Visible InfraRed Thermal Imaging Spectrometer onboard the Rosetta Mission orbiter \\citep{Coradini_2007} devoted to investigate the spectrophotometric properties of the comet 67P/Churyumov-Gerasimenko in the 0.25-5.1 μm spectral range. Here we present data acquired during the first observations of the comet, starting from mid-July 2014, when the spacecraft-target distance was approximately 13000 km and the comet nucleus as seen by the instrument was pixel-size, up to more recent acquisitions in which the surface was resolved \\citep{Ciarniello_2015}. The far-approach data have allowed us to produce both light curves of the nucleus at different solar phase angles and disk-integrated phase curves over the entire instrument spectral range within the 1.2°-14.9° phase angle interval. The light curve is characterized by two asymmetric peaks due to the elongated, e.g. double-lobed, shape of the nucleus. The disk-integrated phase curves exhibit a back -scattering behavior and a well defined surge at low phase angle due to the Shadow Hiding Opposition Effect. The derived geometric albedo at 0.55 μm is Ageo = 0.062 ± 0.002. Dependence of color ratios on rotational phase and phase angle will be discussed in order to exploit large scale surface compositional variations. We also present a retrieval of the main photometric parameters by means of Hapke model \\citep{Hapke_1993} from analysis of disk-resolved images. The derived single scattering albedo at 0.55 μm is w=0.052 while the asymmetry parameter of the single particle phase function is b=-0.42. These values indicate a very dark and back-scattering surface, common also to other comets \\citep{Li_2007a, Li_2007b, Li_2009, Li_2013}. Hapke photometric parameters have been used to perform the photometric correction of the whole investigated dataset and albedo maps of the nucleus have been produced in the visible and infrared range. Albedo appears fairly ho mogeneous across the surface with Api and Imothep

  4. Wootters' distance revisited: a new distinguishability criterium

    NASA Astrophysics Data System (ADS)

    Majtey, A.; Lamberti, P. W.; Martin, M. T.; Plastino, A.

    2005-03-01

    The notion of distinguishability between quantum states has shown to be fundamental in the frame of quantum information theory. In this paper we present a new distinguishability criterium by using a information theoretic quantity: the Jensen-Shannon divergence (JSD). This quantity has several interesting properties, both from a conceptual and a formal point of view. Previous to define this distinguishability criterium, we review some of the most frequently used distances defined over quantum mechanics’ Hilbert space. In this point our main claim is that the JSD can be taken as a unifying distance between quantum states.

  5. Radiative Transfer in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Graziani, L.; Aiello, S.; Belleni-Morante, A.; Cecchi-Pestellini, C.

    2008-09-01

    Abstract Protoplanetary disks are the precursors of planetary systems. All building materials needed to assembly the planetary systems are supplied by these reservoirs, including many organic molecules [1,2]. Thus, the physical and chemical properties in Protoplanetary disks set the boundary conditions for the formation and evolution of planets and other solar system bodies. In standard radiative scenario structure and chemistry of protoplanetary disks depend strongly on the nature of central star around which they formed. The dust temperature is manly set by the stellar luminosity, while the chemistry of the whole disk depends on the UV and X ray fluxes [3,4,6,8]. Therefore, a knowledge as accurate as possible of the radiative transfer (RT) inside disks is a prerequisite for their modelling. Actually, real disks are complex, stratified and inhomogeneous environments requiring a detailed dust mixture modelling and the ability to follow the radiation transfer across radial and vertical gradients. Different energetic processes as the mass accretion processes onto the star surface, the viscous dissipative heating dominating the midplane region, and the flared atmospheres radiation reprocessing, have a significant role in the disk structuring [4,5,8]. During the last 10 years many authors suggested various numerical and analytical techniques to resolve the disk temperature structure providing vertical temperature profiles and disk SED databases [4,6]. In this work we present the results of our semi analytical and numerical model solving the radiative transfer problem in two separate interesting disk regions: 1) Disk atmospheres at large radius, r > 10 AU. 2) Vertical disk structure over 1 < r < 10 AU and 10 < r < 100 AU. A simplified analytical approach based on P-N approximation [7] for a rectified disk surface (suitable for limited range of r) is compared and contrasted with a more accurate Monte Carlo integration [5]. Our code can handle arbitrary dust

  6. VERY LARGE TELESCOPE/NACO POLARIMETRIC DIFFERENTIAL IMAGING OF HD100546-DISK STRUCTURE AND DUST GRAIN PROPERTIES BETWEEN 10 AND 140 AU

    SciTech Connect

    Quanz, Sascha P.; Schmid, Hans Martin; Meyer, Michael R.; Geissler, Kerstin; Henning, Thomas; Brandner, Wolfgang; Wolf, Sebastian

    2011-09-01

    We present polarimetric differential imaging (PDI) data of the circumstellar disk around the Herbig Ae/Be star HD100546 obtained with Very Large Telescope/NACO. We resolve the disk in polarized light in the H and K{sub s} filter between {approx}0.''1 and 1.''4 (i.e., {approx}10-140 AU). The innermost disk regions are directly imaged for the first time and the mean apparent disk inclination and position angle are derived. The surface brightness along the disk major axis drops off roughly with S(r){proportional_to}r {sup -3} but has a maximum around 0.''15 suggesting a marginal detection of the main disk inner rim at {approx}15 AU. We find a significant brightness asymmetry along the disk minor axis in both filters with the far side of the disk appearing brighter than the near side. This enhanced backward scattering and a low total polarization degree of the scattered disk flux of 14{sup +19}{sub -8}% suggest that the dust grains on the disk surface are larger than typical interstellar medium grains. Empirical scattering functions reveal the backward scattering peak at the largest scattering angles and a second maximum for the smallest scattering angles. This indicates a second dust grain population preferably forward scattering and smaller in size. It shows that, relatively, in the inner disk regions (40-50 AU) a higher fraction of larger grains is found compared to the outer disk regions (100-110 AU). Finally, our images reveal distinct substructures between 25 and 35 AU physical separation from the star and we discuss the possible origin for the two features in the context of ongoing planet formation.

  7. Disk Galaxies : Building Blocks Of The Universe?

    NASA Astrophysics Data System (ADS)

    Bower, Richard

    2016-10-01

    In my talk I look at the origin of disk galaxies from the theoretical perspective. In particular I look at simple ways to use the properties of disk galaxies, and their evolution, to test our current paradigm for galaxy formation within the CDM scenario.

  8. Polarization-sensitive OCT of bovine intervertebral disk

    NASA Astrophysics Data System (ADS)

    Matcher, Stephen J.; Winlove, C. Peter; Gangnus, Sergei V.

    2003-10-01

    Polarization-sensitive optical coherence tomography (PSOCT) is a powerful new optical imaging modality that is sensitive to the birefringence properties of tissues. It thus has potential applications in studying the large-scale ordering of collagen fibers within connective tissues and changes related to pathology. As a tissue for study by PSOCT, intervertebral disk represents an interesting system as the collagen organisation is believed to show pronounced variations with depth, on a spatial scale of about 100 microns .We have used a polarisation-sensitive optical coherence tomography system to measure the birefringence properties of bovine caudal intervertebral disk and compared this with equine flexor tendon. The result for equine tendon, Δn = (4.4 +/- 0.15) x 10-3 at 1.3μm, is somewhat larger than values reported for bovine tendon. The annulus fibrosus of freshly excised intact bovine intervertebral disk displays an identical value of birefringence, Δn = (4.4 +/- 0.4) x 10-3 at 1.3μm. However the retardance does not increase uniformly with depth into the tissue but displays a pronounced discontinuity at a depth of around 300 microns. This is believed to be related to the lamellar structure of this tissue, in which the collagen fiber orientation alternates between successive lamellae as depth into the tissue increases. The nucleus pulposus displays polarization conversion equivalent to a birefringence an order of magnitude smaller than these values i.e. Delta;n = (0.278 +/- 0.007) x 10-3. Our measurement protocol cannot distinguish this from the effects of depolarization due to multiple scattering. These results imply that PSOCT could be a useful tool to study collagen organisation within intervertebral disk in vivo and its variation with applied load and disease.

  9. Distinguishing Radiculopathies from Mononeuropathies

    PubMed Central

    Robblee, Jennifer; Katzberg, Hans

    2016-01-01

    Identifying “where is the lesion” is particularly important in the approach to the patient with focal dysfunction where a peripheral localization is suspected. This article outlines a methodical approach to the neuromuscular patient in distinguishing focal neuropathies versus radiculopathies, both of which are common presentations to the neurology clinic. This approach begins with evaluation of the sensory examination to determine whether there are irritative or negative sensory signs in a peripheral nerve or dermatomal distribution. This is followed by evaluation of deep tendon reflexes to evaluate if differential hyporeflexia can assist in the two localizations. Finally, identification of weak muscle groups unique to a nerve or myotomal pattern in the proximal and distal extremities can most reliably assist in a precise localization. The article concludes with an application of the described method to the common scenario of distinguishing radial neuropathy versus C7 radiculopathy in the setting of a wrist drop and provides additional examples for self-evaluation and reference. PMID:27468275

  10. Gas content of transitional disks: a VLT/X-Shooter study of accretion and winds

    NASA Astrophysics Data System (ADS)

    Manara, C. F.; Testi, L.; Natta, A.; Rosotti, G.; Benisty, M.; Ercolano, B.; Ricci, L.

    2014-08-01

    Context. Transitional disks are thought to be a late evolutionary stage of protoplanetary disks whose inner regions have been depleted of dust. The mechanism responsible for this depletion is still under debate. To constrain the various models it is mandatory to have a good understanding of the properties of the gas content in the inner part of the disk. Aims: Using X-Shooter broad band - UV to near-infrared - medium-resolution spectroscopy, we derive the stellar, accretion, and wind properties of a sample of 22 transitional disks. The analysis of these properties allows us to place strong constraints on the gas content in a region very close to the star (≲0.2 AU) that is not accessible with any other observational technique. Methods: We fitted the spectra with a self-consistent procedure to simultaneously derive spectral type, extinction, and accretion properties of the targets. From the continuum excess at near-infrared wavelength we distinguished whether our targets have dust free inner holes. By analyzing forbidden emission lines, we derived the wind properties of the targets. We then compared our findings with results for classical T Tauri stars. Results: The accretion rates and wind properties of 80% of the transitional disks in our sample, which is strongly biased toward stongly accreting objects, are comparable to those of classical T Tauri stars. Thus, there are (at least) some transitional disks with accretion properties compatible with those of classical T Tauri stars, irrespective of the size of the dust inner hole. Only in two cases are the mass accretion rates much lower, while the wind properties remain similar. We detected no strong trend of the mass accretion rates with the size of the dust-depleted cavity or with the presence of a dusty optically thick disk very close to the star. These results suggest that, close to the central star, there is a gas-rich inner disk with a density similar to that of classical T Tauri star disks. Conclusions: The

  11. Disk Detective Follow-Up Program

    NASA Astrophysics Data System (ADS)

    Kuchner, Marc

    As new data on exoplanets and young stellar associations arrive, we will want to know: which of these planetary systems and young stars have circumstellar disks? The vast allsky database of 747 million infrared sources from NASA's Wide-field Infrared Survey Explorer (WISE) mission can supply answers. WISE is a discovery tool intended to find targets for JWST, sensitive enough to detect circumstellar disks as far away as 3000 light years. The vast WISE archive already serves us as a roadmap to guide exoplanet searches, provide information on disk properties as new planets are discovered, and teach us about the many hotly debated connections between disks and exoplanets. However, because of the challenges of utilizing the WISE data, this resource remains underutilized as a tool for disk and planet hunters. Attempts to use WISE to find disks around Kepler planet hosts were nearly scuttled by confusion noise. Moreover, since most of the stars with WISE infrared excesses were too red for Hipparcos photometry, most of the disks sensed by WISE remain obscure, orbiting stars unlisted in the usual star databases. To remedy the confusion noise problem, we have begun a massive project to scour the WISE data archive for new circumstellar disks. The Disk Detective project (Kuchner et al. 2016) engages layperson volunteers to examine images from WISE, NASA's Two Micron All-Sky Survey (2MASS) and optical surveys to search for new circumstellar disk candidates via the citizen science website DiskDetective.org. Fueled by the efforts of > 28,000 citizen scientists, Disk Detective is the largest survey for debris disks with WISE. It has already uncovered 4000 disk candidates worthy of follow-up. However, most host stars of the new Disk Detective disk candidates have no known spectral type or distance, especially those with red colors: K and M stars and Young Stellar Objects. Others require further observations to check for false positives. The Disk Detective project is supported by

  12. Generalized Similarity for Accretion/Decretion Disks

    NASA Astrophysics Data System (ADS)

    Rafikov, Roman R.

    2016-10-01

    Decretion (or external) disks are gas disks freely expanding to large radii due to their internal stresses. They are expected to naturally arise in tidal disruption events, around Be stars, in mass-losing post-main-sequence binaries, as a result of supernova fallback, etc. Their evolution is theoretically understood in two regimes: when the central object does not exert torque on the disk (a standard assumption for conventional accretion disks) or when no mass inflow (or outflow) occurs at the disk center. However, many astrophysical objects—circumbinary disks, Be stars, neutron stars accreting in a propeller regime, etc.—feature non-zero torque simultaneously with the non-zero accretion (or ejection of mass) at the disk center. We provide a general description for the evolution of such disks (both linear and nonlinear) in the self-similar regime, to which the disk should asymptotically converge with time. We identify a similarity parameter λ, which is uniquely related to the degree, to which the central mass accretion is suppressed by the non-zero central torque. The known decretion disk solutions correspond to the two discrete values of λ, while our new solutions cover a continuum of its physically allowed values, corresponding to either accretion or mass ejection by the central object. A direct relationship between λ and central \\dot{M} and torque is also established. We describe the time evolution of the various disk characteristics for different λ, and show that the observable properties (spectrum and luminosity evolution) of the decretion disks, in general, are different from the standard accretion disks with no central torque.

  13. Magneto-thermal Disk Winds from Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Bai, Xue-Ning; Ye, Jiani; Goodman, Jeremy; Yuan, Feng

    2016-02-01

    The global evolution and dispersal of protoplanetary disks (PPDs) are governed by disk angular-momentum transport and mass-loss processes. Recent numerical studies suggest that angular-momentum transport in the inner region of PPDs is largely driven by magnetized disk wind, yet the wind mass-loss rate remains unconstrained. On the other hand, disk mass loss has conventionally been attributed to photoevaporation, where external heating on the disk surface drives a thermal wind. We unify the two scenarios by developing a one-dimensional model of magnetized disk winds with a simple treatment of thermodynamics as a proxy for external heating. The wind properties largely depend on (1) the magnetic field strength at the wind base, characterized by the poloidal Alfvén speed vAp, (2) the sound speed cs near the wind base, and (3) how rapidly poloidal field lines diverge (achieve {R}-2 scaling). When {v}{Ap}\\gg {c}{{s}}, corotation is enforced near the wind base, resulting in centrifugal acceleration. Otherwise, the wind is accelerated mainly by the pressure of the toroidal magnetic field. In both cases, the dominant role played by magnetic forces likely yields wind outflow rates that exceed purely hydrodynamical mechanisms. For typical PPD accretion-rate and wind-launching conditions, we expect vAp to be comparable to cs at the wind base. The resulting wind is heavily loaded, with a total wind mass-loss rate likely reaching a considerable fraction of the wind-driven accretion rate. Implications for modeling global disk evolution and planet formation are also discussed.

  14. Distinguishing the Effects of Bond-Length Alternation versus Bond-Order Alternation on the Nonlinear Optical Properties of π-Conjugated Chromophores.

    PubMed

    Gieseking, Rebecca L; Risko, Chad; Brédas, Jean-Luc

    2015-06-18

    Understanding the relationships between the molecular nonlinear optical (NLO) properties and the bond-length alternation (BLA) or π-bond-order alternation (BOA) along the molecular backbone of linear π-conjugated systems has proven widely useful in the development of NLO organic chromophores and materials. Here, we examine model polymethines to elucidate the reliability of these relationships. While BLA is solely a measure of molecular geometric structure, BOA includes information pertaining to the electronic structure. As a result, BLA is found to be a good predictor of NLO properties only when optimized geometries are considered, whereas BOA is more broadly applicable. Proper understanding of the distinction between BLA and BOA is critical when designing computational studies of NLO properties, especially for molecules in complex environments or in nonequilibrium geometries.

  15. Exclusion of cosmic rays in protoplanetary disks. II. Chemical gradients and observational signatures

    SciTech Connect

    Cleeves, L. Ilsedore; Bergin, Edwin A.; Adams, Fred C.

    2014-10-20

    The chemical properties of protoplanetary disks are especially sensitive to their ionization environment. Sources of molecular gas ionization include cosmic rays (CRs), stellar X-rays, and short-lived radionuclides, each of which varies with location in the disk. This behavior leads to a significant amount of chemical structure, especially in molecular ion abundances, which is imprinted in their submillimeter rotational line emission. Using an observationally motivated disk model, we make predictions for the dependence of chemical abundances on the assumed properties of the ionizing field. We calculate the emergent line intensity for abundant molecular ions and simulate sensitive observations with the Atacama Large Millimeter/Sub-millimeter Array (ALMA) for a disk at D = 100 pc. The models readily distinguish between high ionization rates (ζ ≳ 10{sup –17} s{sup –1} per H{sub 2}) and below, but it becomes difficult to distinguish between low ionization models when ζ ≲ 10{sup –19} s{sup –1}. We find that H{sub 2}D{sup +} emission is not detectable for sub-interstellar CR rates with ALMA (6h integration), and that N{sub 2}D{sup +} emission may be a more sensitive tracer of midplane ionization. HCO{sup +} traces X-rays and high CR rates (ζ{sub CR} ≳ 10{sup –17} s{sup –1}), and provides a handle on the warm molecular ionization properties where CO is present in the gas. Furthermore, species like HCO{sup +}, which emits from a wide radial region and samples a large gradient in temperature, can exhibit ring-like emission as a consequence of low-lying rotational level de-excitation near the star. This finding highlights a scenario where rings are not necessarily structural or chemical in nature, but simply a result of the underlying line excitation properties.

  16. On some unexpected properties of radial and symmetric eigenvalues and eigenfunctions of the p-Laplacian on a disk

    NASA Astrophysics Data System (ADS)

    Bobkov, Vladimir; Drábek, Pavel

    2017-08-01

    We discuss several properties of eigenvalues and eigenfunctions of the p-Laplacian on a ball subject to zero Dirichlet boundary conditions. Among main results, in two dimensions, we show the existence of nonradial eigenfunctions which correspond to the radial eigenvalues. Also we prove the existence of eigenfunctions whose shape of the nodal set cannot occur in the linear case p = 2. Moreover, the limit behavior of some eigenvalues as p → 1 + and p → + ∞ is studied.

  17. Expanding the principle of local distinguishability

    NASA Astrophysics Data System (ADS)

    Carmeli, Claudio; Heinosaari, Teiko; Schultz, Jussi; Toigo, Alessandro

    2015-04-01

    The principle of local distinguishability states that an arbitrary physical state of a bipartite system can be determined by the combined statistics of local measurements performed on the subsystems. A necessary and sufficient requirement for the local measurements is that each one must be able to distinguish between all pairs of states of the respective subsystems. We show that, if the task is changed into the determination of an arbitrary bipartite pure state, then at least in certain cases it is possible to restrict to local measurements which can distinguish all pure states but not all states. Moreover, we show that, if the local measurements are such that the purity of the bipartite state can be verified from the statistics without any prior assumption, then in these special cases also this property is carried over to the composite measurement. These surprising facts give evidence that the principle of local distinguishability may be expanded beyond its usual applicability.

  18. Design Requirements for Annulus Fibrosus Repair: Review of Forces, Displacements, and Material Properties of the Intervertebral Disk and a Summary of Candidate Hydrogels for Repair.

    PubMed

    Long, Rose G; Torre, Olivia M; Hom, Warren W; Assael, Dylan J; Iatridis, James C

    2016-02-01

    There is currently a lack of clinically available solutions to restore functionality to the intervertebral disk (IVD) following herniation injury to the annulus fibrosus (AF). Microdiscectomy is a commonly performed surgical procedure to alleviate pain caused by herniation; however, AF defects remain and can lead to accelerated degeneration and painful conditions. Currently available AF closure techniques do not restore mechanical functionality or promote tissue regeneration, and have risk of reherniation. This review determined quantitative design requirements for AF repair materials and summarized currently available hydrogels capable of meeting these design requirements by using a series of systematic PubMed database searches to yield 1500+ papers that were screened and analyzed for relevance to human lumbar in vivo measurements, motion segment behaviors, and tissue level properties. We propose a testing paradigm involving screening tests as well as more involved in situ and in vivo validation tests to efficiently identify promising biomaterials for AF repair. We suggest that successful materials must have high adhesion strength (∼0.2 MPa), match as many AF material properties as possible (e.g., approximately 1 MPa, 0. 3 MPa, and 30 MPa for compressive, shear, and tensile moduli, respectively), and have high tensile failure strain (∼65%) to advance to in situ and in vivo validation tests. While many biomaterials exist for AF repair, few undergo extensive mechanical characterization. A few hydrogels show promise for AF repair since they can match at least one material property of the AF while also adhering to AF tissue and are capable of easy implantation during surgical procedures to warrant additional optimization and validation.

  19. Design Requirements for Annulus Fibrosus Repair: Review of Forces, Displacements, and Material Properties of the Intervertebral Disk and a Summary of Candidate Hydrogels for Repair

    PubMed Central

    Long, Rose G.; Torre, Olivia M.; Hom, Warren W.; Assael, Dylan J.; Iatridis, James C.

    2016-01-01

    There is currently a lack of clinically available solutions to restore functionality to the intervertebral disk (IVD) following herniation injury to the annulus fibrosus (AF). Microdiscectomy is a commonly performed surgical procedure to alleviate pain caused by herniation; however, AF defects remain and can lead to accelerated degeneration and painful conditions. Currently available AF closure techniques do not restore mechanical functionality or promote tissue regeneration, and have risk of reherniation. This review determined quantitative design requirements for AF repair materials and summarized currently available hydrogels capable of meeting these design requirements by using a series of systematic PubMed database searches to yield 1500+ papers that were screened and analyzed for relevance to human lumbar in vivo measurements, motion segment behaviors, and tissue level properties. We propose a testing paradigm involving screening tests as well as more involved in situ and in vivo validation tests to efficiently identify promising biomaterials for AF repair. We suggest that successful materials must have high adhesion strength (∼0.2 MPa), match as many AF material properties as possible (e.g., approximately 1 MPa, 0. 3 MPa, and 30 MPa for compressive, shear, and tensile moduli, respectively), and have high tensile failure strain (∼65%) to advance to in situ and in vivo validation tests. While many biomaterials exist for AF repair, few undergo extensive mechanical characterization. A few hydrogels show promise for AF repair since they can match at least one material property of the AF while also adhering to AF tissue and are capable of easy implantation during surgical procedures to warrant additional optimization and validation. PMID:26720265

  20. DISKS AROUND BROWN DWARFS IN THE EJECTION SCENARIO. I. DISK COLLISIONS IN TRIPLE SYSTEMS

    SciTech Connect

    Umbreit, Stefan; Henning, Thomas; Klahr, Hubert; Spurzem, Rainer; Mikkola, Seppo E-mail: henning@mpia.de E-mail: spurzem@ari.uni-heidelberg.de

    2011-12-20

    We investigate the fate of disks around brown dwarfs in the ejection scenario and the implications on their observable properties. For that purpose, a parameter study of close triple approaches leading to escape is carried out where the ejected body is surrounded by a low-mass disk. We analyze the recircularized radial surface density profile of the post-encounter disk in dependence of the minimum two-body distances between the escaper and the perturbing bodies. Our results show that the general appearance of the disks is rather similar to disks after two-body encounters in as much as there is also an exponential drop in surface density for the outer disk regions as well as an enhancement of surface density for the innermost region relative to the initial disk profile. However, the disks after close triple approaches are mostly less massive, have generally flatter recircularized surface density disk profiles, and have radii that are similar or larger compared to disks after two-body encounters. From our results, we construct a simple scale-free model only depending on the minimum encounter distances of the two perturbers. Such a model is especially useful for statistical studies of disk collisions in triple systems that must cover a large range of encounter distances.

  1. Grain Growth in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Perez Munoz, Laura Maria

    The majority of young, low-mass stars are surrounded by optically thick accretion disks. These circumstellar disks provide large reservoirs of gas and dust that will eventually be transformed into planetary systems. Theory and observations suggest that the earliest stage toward planet formation in a protoplanetary disk is the growth of particles, from sub-micron-sized grains to centimeter- sized pebbles. Theory indicates that small interstellar grains are well coupled into the gas and are incorporated to the disk during the proto-stellar collapse. These dust particles settle toward the disk mid-plane and simultaneously grow through collisional coagulation in a very short timescale. Observationally, grain growth can be inferred by measuring the spectral energy distribution at long wavelengths, which traces the continuum dust emission spectrum and hence the dust opacity. Several observational studies have indicated that the dust component in protoplanetary disks has evolved as compared to interstellar medium dust particles, suggesting at least 4 orders of magnitude in particle-size growth. However, the limited angular resolution and poor sensitivity of previous observations has not allowed for further exploration of this astrophysical process. As part of my thesis, I embarked in an observational program to search for evidence of radial variations in the dust properties across a protoplanetary disk, which may be indicative of grain growth. By making use of high angular resolution observations obtained with CARMA, VLA, and SMA, I searched for radial variations in the dust opacity inside protoplanetary disks. These observations span more than an order of magnitude in wavelength (from sub-millimeter to centimeter wavelengths) and attain spatial resolutions down to 20 AU. I characterized the radial distribution of the circumstellar material and constrained radial variations of the dust opacity spectral index, which may originate from particle growth in these circumstellar

  2. GIANT PLANET MIGRATION, DISK EVOLUTION, AND THE ORIGIN OF TRANSITIONAL DISKS

    SciTech Connect

    Alexander, Richard D.; Armitage, Philip J.

    2009-10-20

    We present models of giant planet migration in evolving protoplanetary disks. Our disks evolve subject to viscous transport of angular momentum and photoevaporation, while planets undergo Type II migration. We use a Monte Carlo approach, running large numbers of models with a range in initial conditions. We find that relatively simple models can reproduce both the observed radial distribution of extrasolar giant planets, and the lifetimes and accretion histories of protoplanetary disks. The use of state-of-the-art photoevaporation models results in a degree of coupling between planet formation and disk clearing, which has not been found previously. Some accretion across planetary orbits is necessary if planets are to survive at radii approx<1.5 AU, and if planets of Jupiter mass or greater are to survive in our models they must be able to form at late times, when the disk surface density in the formation region is low. Our model forms two different types of 'transitional' disks, embedded planets and clearing disks, which show markedly different properties. We find that the observable properties of these systems are broadly consistent with current observations, and highlight useful observational diagnostics. We predict that young transition disks are more likely to contain embedded giant planets, while older transition disks are more likely to be undergoing disk clearing.

  3. Secchi disk theory: a reexamination

    NASA Astrophysics Data System (ADS)

    Levin, Iosif M.; Radomyslskaya, Tamara M.

    2007-04-01

    The possibility of the retrieval of the water's inherent optical properties (IOP) from Secchi disk observations is discussed. The paper directly addresses objections to the use of Secchi disks raised by Preisendorfer in 1986. A new version of Secchi depth theory is given, which in contrast to conventional Secchi disk theories includes the effects of light reflection from the sea surface and treats measurements from both the sunny and shaded sides of a vessel. Empirical correlations between different IOP are used to estimate not only the attenuation coefficient, but also the single scattering albedo and the backscattering probability at 550 nm from Secchi depth data. The theory is compared with measurements made in the Black Sea.

  4. Galaxy Mergers and Disk Formation

    NASA Astrophysics Data System (ADS)

    Naab, Thorsten; Burkert, Andreas

    We present results from high resolution N-body/SPH simulations of merging gas-rich disk galaxies. The simulations were performed using a newly developed parallel TREE-algorithm in combination with the special purpose hardware GRAPE-5. We find that the presence of gas changes the kinematical properties of the resulting merger remnants, resulting in shapes of the velocity profiles that are in good agreement with observed boxy, non-rotating and disky, fast-rotating elltiptical galaxies. We find large scale disk-like components in unequal mass merger remnants which form by late gas infall. In addition we explore limits on gas infall and the starformation rate during the merging epoch as a function of the mass ratio and the geometry of the merging disk galaxies.

  5. Statistical Properties of the Stokes V-Parameter Spatial Distribution of Some Spectral Lines Across the Solar DisK

    NASA Astrophysics Data System (ADS)

    Peshcherov, V. S.; Demidov, M. L.; Zhigalov, V. V.; Grigoryev, V. M.

    The measurements of the Stokes parameters distribution in spectral lines (the more number of lines, the better) is the most powerful and promising tool of magnetic fields and termodynamical conditions diagnostics in solar plasma. Sometimes [1] it is very important to know such mean values of V-parameter distribution over the line profile as amplitude and area asymmetries, and what is espicially valuable, - on the different positions on the solar disc. At the present paper, using the CCD stokesmeter of the Sayan observatory [2], we study the properties of these parameters as a function of center-to-limb distance and the strength of magnetic fields. A great number of data (dozens of stokesgrames of the whole solar disc) with low-spatial resolution observation (two arc minutes) are used in the investigation. Some questions of theoretical interpretation of the founded properties are discussed. References 1. O.Steiner. Flux Tube Dynamic. - 3rd Advances in Solar Physics Euroconference: Magnetic Fields and Oscillations. (Eds. B.Schmieder, A.Hofmann, J,Staude). ASP Confernce Series. Vol.184, 1999, p.38-54. 2. V.S.Peshcherov, V.V.Zhigalov, M.L.Demidov, V.M. Grigoryev. Large -Scale Solar Magnetic Fields: the Stokes V-Parameter Distribution in the Line FeI 525.0 nm. - JOSO Annual Report, 1998, p.87-88.

  6. Stellar Multiplicity in the DEBRIS disk sample

    NASA Astrophysics Data System (ADS)

    Rodriguez, David R.; Duchene, Gaspard; Tom, Henry; Kennedy, Grant; Matthews, Brenda C.; Butner, Harold M.

    2015-01-01

    Circumstellar disks around young stars serve as the sites of planet formation. A common outcome of the star formation process is that of stellar binary systems. How does the presence of multiple stars affect the properties of disks, and thus of planet formation? To examine the frequency of disks around stellar binaries we carried out a multiplicity survey on stars in the DEBRIS sample. This sample consists of 451 stars of spectral types A-M observed with the Herschel Space Telescope. We have examined the stellar multiplicity of this sample by gathering information from the literature and performing an adaptive optics imaging survey at Lick Observatory. We identify 189 (42%) binary or multiple star systems.In our sample, we find that debris disks are less common around binaries than single stars, though the disk detection frequency is comparable among A stars regardless of multiplicity. Nevertheless, the period distribution of disk-bearing binaries is consistent with that of non-disk binaries and with comparison field samples. Although the frequency of disk-bearing binaries may be lower than in single star systems, the processes behind disk formation are comparable among both single and multiple-star populations.This work is supported in part by a Chile Fondecy grant #3130520.

  7. Gaps in Protoplanetary Disks as Signatures of Planets. III. Polarization

    NASA Astrophysics Data System (ADS)

    Jang-Condell, Hannah

    2017-01-01

    Polarimetric observations of T Tauri and Herbig Ae/Be stars are a powerful way to image protoplanetary disks. However, interpretation of these images is difficult because the degree of polarization is highly sensitive to the angle of scattering of stellar light off the disk surface. We examine how disks with and without gaps created by planets appear in scattered polarized light as a function of inclination angle. Isophotes of inclined disks without gaps are distorted in polarized light, giving the appearance that the disks are more eccentric or more highly inclined than they truly are. Apparent gap locations are unaffected by polarization, but the gap contrast changes. In face-on disks with gaps, we find that the brightened far edge of the gap scatters less polarized light than the rest of the disk, resulting in slightly decreased contrast between the gap trough and the brightened far edge. In inclined disks, gaps can take on the appearance of being localized “holes” in brightness rather than full axisymmetric structures. Photocenter offsets along the minor axis of the disk in both total intensity and polarized intensity images can be readily explained by the finite thickness of the disk. Alone, polarized scattered light images of disks do not necessarily reveal intrinsic disk structure. However, when combined with total intensity images, the orientation of the disk can be deduced and much can be learned about disk structure and dust properties.

  8. Magnetically Induced Disk Winds and Transport in the HL Tau Disk

    NASA Astrophysics Data System (ADS)

    Hasegawa, Yasuhiro; Okuzumi, Satoshi; Flock, Mario; Turner, Neal J.

    2017-08-01

    The mechanism of angular momentum transport in protoplanetary disks is fundamental to understanding the distributions of gas and dust in the disks. The unprecedented ALMA observations taken toward HL Tau at high spatial resolution and subsequent radiative transfer modeling reveal that a high degree of dust settling is currently achieved in the outer part of the HL Tau disk. Previous observations, however, suggest a high disk accretion rate onto the central star. This configuration is not necessarily intuitive in the framework of the conventional viscous disk model, since efficient accretion generally requires a high level of turbulence, which can suppress dust settling considerably. We develop a simplified, semi-analytical disk model to examine under what condition these two properties can be realized in a single model. Recent, non-ideal MHD simulations are utilized to realistically model the angular momentum transport both radially via MHD turbulence and vertically via magnetically induced disk winds. We find that the HL Tau disk configuration can be reproduced well when disk winds are properly taken into account. While the resulting disk properties are likely consistent with other observational results, such an ideal situation can be established only if the plasma β at the disk midplane is β 0 ≃ 2 × 104 under the assumption of steady accretion. Equivalently, the vertical magnetic flux at 100 au is about 0.2 mG. More detailed modeling is needed to fully identify the origin of the disk accretion and quantitatively examine plausible mechanisms behind the observed gap structures in the HL Tau disk.

  9. Circumstellar disks around binary stars in Taurus

    SciTech Connect

    Akeson, R. L.

    2014-03-20

    We have conducted a survey of 17 wide (>100 AU) young binary systems in Taurus with the Atacama Large Millimeter Array (ALMA) at two wavelengths. The observations were designed to measure the masses of circumstellar disks in these systems as an aid to understanding the role of multiplicity in star and planet formation. The ALMA observations had sufficient resolution to localize emission within the binary system. Disk emission was detected around all primaries and 10 secondaries, with disk masses as low as 10{sup –4} M {sub ☉}. We compare the properties of our sample to the population of known disks in Taurus and find that the disks from this binary sample match the scaling between stellar mass and millimeter flux of F{sub mm}∝M{sub ∗}{sup 1.5--2.0} to within the scatter found in previous studies. We also compare the properties of the primaries to those of the secondaries and find that the secondary/primary stellar and disk mass ratios are not correlated; in three systems, the circumsecondary disk is more massive than the circumprimary disk, counter to some theoretical predictions.

  10. Supersized Disk Artist Concept

    NASA Image and Video Library

    2006-02-08

    This illustration compares the size of a gargantuan star and its surrounding dusty disk top to that of our solar system. Monstrous disks like this one were discovered around two hypergiant stars by NASA Spitzer Space Telescope.

  11. 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.

  12. DISK PUMP FEASIBILITY INVESTIGATION,

    DTIC Science & Technology

    The disk pump was investigated at the Air Force Rocket Propulsion Laboratory (AFRPL) to determine the feasibility of using a novel viscous pumping... pump primarily for application as an inducer. The disk pump differs drastically from conventional pumps because of the following major factors: (1) The...The pump inlet relative velocity is equal only to the through flow velocity between the disks. Therefore, there is good indication that the disk pump will

  13. Imaging protoplanets: observing transition disks with non-redundant masking

    NASA Astrophysics Data System (ADS)

    Sallum, Steph; Eisner, Josh; Close, Laird M.; Hinz, Philip M.; Follette, Katherine B.; Kratter, Kaitlin; Skemer, Andrew J.; Bailey, Vanessa P.; Briguglio, Runa; Defrere, Denis; Macintosh, Bruce A.; Males, Jared R.; Morzinski, Katie M.; Puglisi, Alfio T.; Rodigas, Timothy J.; Spalding, Eckhart; Tuthill, Peter G.; Vaz, Amali; Weinberger, Alycia; Xomperio, Marco

    2016-08-01

    Transition disks, protoplanetary disks with inner clearings, are promising objects in which to directly image forming planets. The high contrast imaging technique of non-redundant masking is well posed to detect planetary mass companions at several to tens of AU in nearby transition disks. We present non-redundant masking observations of the T Cha and LkCa 15 transition disks, both of which host posited sub-stellar mass companions. However, due to a loss of information intrinsic to the technique, observations of extended sources (e.g. scattered light from disks) can be misinterpreted as moving companions. We discuss tests to distinguish between these two scenarios, with applications to the T Cha and LkCa 15 observations. We argue that a static, forward-scattering disk can explain the T Cha data, while LkCa 15 is best explained by multiple orbiting companions.

  14. Understanding Floppy Disks.

    ERIC Educational Resources Information Center

    Valentine, Pamela

    1980-01-01

    The author describes the floppy disk with an analogy to the phonograph record, and discusses the advantages, disadvantages, and capabilities of hard-sectored and soft-sectored floppy disks. She concludes that, at present, the floppy disk will continue to be the primary choice of personal computer manufacturers and their customers. (KC)

  15. Herniated lumbar disk (image)

    MedlinePlus

    Herniated lumbar disk is a condition in which part or all of the soft, gelatinous central portion of an intervertebral disk (the nucleus pulposus) is forced through a weakened part of the disk, resulting in back pain and nerve root irritation.

  16. Optical Disk Technology.

    ERIC Educational Resources Information Center

    Abbott, George L.; And Others

    1987-01-01

    This special feature focuses on recent developments in optical disk technology. Nine articles discuss current trends, large scale image processing, data structures for optical disks, the use of computer simulators to create optical disks, videodisk use in training, interactive audio video systems, impacts on federal information policy, and…

  17. Understanding Floppy Disks.

    ERIC Educational Resources Information Center

    Valentine, Pamela

    1980-01-01

    The author describes the floppy disk with an analogy to the phonograph record, and discusses the advantages, disadvantages, and capabilities of hard-sectored and soft-sectored floppy disks. She concludes that, at present, the floppy disk will continue to be the primary choice of personal computer manufacturers and their customers. (KC)

  18. Distinguishing cell type using epigenotype

    NASA Astrophysics Data System (ADS)

    Wytock, Thomas; Motter, Adilson E.

    Recently, researchers have proposed that unique cell types are attractors of their epigenetic dynamics including gene expression and chromatin conformation patterns. Traditionally, cell types have been classified by their function, morphology, cytochemistry, and other macroscopically observable properties. Because these properties are the result of many proteins working together, it should be possible to predict cell types from gene expression or chromatin conformation profiles. In this talk, I present a maximum entropy approach to identify and distinguish cell type attractors on the basis of correlations within these profiles. I will demonstrate the flexibility of this method through its separate application to gene expression and chromatin conformation datasets. I show that our method out-performs other machine-learning techniques and uncorrelated benchmarks. We adapt our method to predict growth rate from gene expression in E. coli and S. cerevisiae and compare our predictions with those from metabolic models. In addition, our method identifies a nearly convex region of state-space associated with each cell type attractor basin. Estimates of the growth rate and attractor basin make it possible to rationally control gene regulatory networks independent of a model. This research was supported by NSF-GRFP, NSF-GK12, GAANN, and Northwestern's NIH-NIGMS Molecular Biophysics Training Grant.

  19. ALMA observations of the nearby AGB star L2 Puppis. II. Gas disk properties derived from 12CO and 13CO J = 3-2 emission

    NASA Astrophysics Data System (ADS)

    Homan, Ward; Richards, Anita; Decin, Leen; Kervella, Pierre; de Koter, Alex; McDonald, Iain; Ohnaka, Keiichi

    2017-05-01

    The circumstellar environment of the AGB star L2 Puppis was observed with ALMA in cycle 3, with a resolution of 15 × 18 mas. The molecular emission shows a differentially rotating disk, inclined to a nearly edge-on position. In the first paper in this series (Paper I) the molecular emission was analysed to accurately deduce the motion of the gas in the equatorial regions of the disk. In this work we model the optically thick 12CO J = 3-2 and the optically thin 13CO J = 3-2 rotational transition to constrain the physical conditions in the disk. To realise this effort we make use of the 3D NLTE radiative transfer code LIME. The temperature structure and velocity structure show a high degree of complexity, both radially and vertically. The radial H2 density profile in the disk plane is characterised by a power law with a slope of -3.1. We find a 12CO over 13CO abundance ratio of 10 inside the disk. Finally, estimations of the angular momentum in the disk surpass the expected available angular momentum of the star, strongly supporting the indirect detection of a compact binary companion reported in Paper I. We estimate the mass of the companion to be around 1 Jupiter mass.

  20. Floppy disk utility user's guide

    NASA Technical Reports Server (NTRS)

    Akers, J. W.

    1980-01-01

    A floppy disk utility program is described which transfers programs between files on a hard disk and floppy disk. It also copies the data on one floppy disk onto another floppy disk and compares the data. The program operates on the Data General NOVA-4X under the Real Time Disk Operating System. Sample operations are given.

  1. Floppy disk utility user's guide

    NASA Technical Reports Server (NTRS)

    Akers, J. W.

    1981-01-01

    The Floppy Disk Utility Program transfers programs between files on the hard disk and floppy disk. It also copies the data on one floppy disk onto another floppy disk and compares the data. The program operates on the Data General NOVA-4X under the Real Time Disk Operating System (RDOS).

  2. Molecular components of dissolved organic matter distinguished by optical properties and HPLC in the sediments of Lake Tõugjärv, Southern Estonia

    NASA Astrophysics Data System (ADS)

    Lepane, V.; Makarõtševa, N.; Alliksaar, T.

    2009-04-01

    Sedimentary organic matter (OM) plays an important role in many geochemical and biochemical processes in aquatic environments. Sedimentary OM is an extremely complex and heterogenous mixture of humic substances (HS), proteins, lipids, carbohydrates, and other biomolecules. OM is formed during the degradation process of higher plant detritus and the composition of microbial cellular material. It is distributed in both particulate and dissolved phases. The investigation of aquatic OM gives an overview of the processes going on in the studied media (polymerization, degradation, etc). The types and amounts of OM in lake sediments present a paleolimnological record of past conditions in the lake and its catchment area. Thus, there is a genuine interest in investigation and characterization of sedimentary OM from lakes as it allows to predict and evaluate temporal changes in the studied ecosystem. Since OM is a very complex mixture, it is impossible to identify its exact chemical composition. As a result, only detailed chemical characterization using various analytical methods could be provided. A fraction of dissolved organic matter (DOM) is optically active and, thus, methods based on UV absorption properties could be used for the characterization of DOM types. Another means of DOM analysis is the measurement of molecular weight distribution. Humic substances compose the main part of DOM. HS are formed by the association of components of the humification process. The source of aquatic HS is thought to be the formation from phytoplankton in the water or they might be washed into waters from terrestrial and soil deposits. Lake Rőuge Tőugjärv (Estonia) is a startified hard-water eutrophic lake. It is a small (4.2 ha) and 17 m deep lake with annually laminated lake sediments (8.3 m) situated in a dense prehistoric setting. Annually laminated (varved) lake sediments possess continuous and independent records with calendar year chronology and will deliver changes in lake

  3. Star-Planet-Disk Interactions

    NASA Astrophysics Data System (ADS)

    Lai, Dong

    Observations of exoplanetary systems containing hot Jupiters have revealed a number of outstanding puzzles that beg for theoretical understanding. Magnetic interactions between young stars and proto-planetary disks and tidal interactions between stars and planets play an important role in shaping the observed properties of planets and planetary systems. We propose a multifaceted theoretical/computational program devoted to understanding these interactions. (1) We will study a novel “magnetic misalignment” effect in protostar-disk systems. Our recent work shows that magnetic star-disk interactions can produce secular changes in the stellar spin direction through magnetic torques, so that the stellar spin may not always be perpendicular to the disk. Our proposed research will consider more realistic models of star-disk interactions, including 3D numerical simulations. We will examine how spin- disk misalignment may explain the small (7 degree) spin-orbit misalignment in the Solar System and contribute to the recently observed spin-orbit misalignments in exoplanetary systems. (2) We will study dynamical tides (including thermal forcing) in hot Jupiters and explore how they may contribute to the observed planetary radius “anomaly”. We will also study dynamical tides in the host star raised by a hot Jupiter in an inclined orbit to understand how tidal dissipations may affect the spin-orbit misalignment angles and planetary orbital decay. This proposal is highly relevant to several goals of the Origins of Solar Systems program, including (a) characterization of other planetary systems, (b) interpretation of observations related to the formation and evolution of planetary systems, and (c) theoretical investigations related to the formation and evolution of planetary systems. The proposed research will contribute to the NASA vision statement and goal to “Advance scientific knowledge of the origin and history of the solar system ...”.

  4. The Stability of Galaxy Disks

    NASA Astrophysics Data System (ADS)

    Westfall, Kyle B.; Andersen, D. R.; Bershady, M. A.; Martinsson, T.; Swaters, R. A.; Verheijen, M. A.

    2013-01-01

    Using measurements of velocity dispersion and mass surface density for both the gas and stellar components, we calculate the multi-component stability (Q) for 30 galaxy disks observed by the DiskMass Survey. Despite their sub-maximality (Bershady et al. 2011, ApJL, 739, 47), we find all disks to be stable with roughly 85% falling in the range 1disk stability and other galaxy properties such as star-formation rate, gas mass fraction, disk maximality, and Hubble type to understand their interdependencies within the context of the secular evolution of galaxy disks. We acknowledge support for this work from the National Science Foundation (AST-0307417, AST-0607516, OISE-0754437, AST-1009491), The Netherlands Organisation for Scientific Research (grant 614.000.807), the UW Graduate School (PRJ13SL, 050167, and the Vilas Associate award), the Leids Kerkhoven-Bosscha Fonds, and NASA/JPL/Spitzer (GO-30894).

  5. Brown dwarf disks with ALMA: Evidence for truncated dust disks in Ophiuchus

    NASA Astrophysics Data System (ADS)

    Testi, L.; Natta, A.; Scholz, A.; Tazzari, M.; Ricci, L.; de Gregorio Monsalvo, I.

    2016-10-01

    Context. The study of the properties of disks around young brown dwarfs can provide important clues on the formation of these very low-mass objects and on the possibility of forming planetary systems around them. The presence of warm dusty disks around brown dwarfs is well known, based on near- and mid-infrared studies. Aims: High angular resolution observations of the cold outer disk are limited; we used ALMA to attempt a first survey of young brown dwarfs in the ρ Oph star-forming region. Methods: All 17 young brown dwarfs in our sample were observed at 890 μm in the continuum at 0.̋5 angular resolution. The sensitivity of our observations was chosen to detect ~0.5 M⊕ of dust. Results: We detect continuum emission in 11 disks (~65% of the total), and the estimated mass of dust in the detected disks ranges from ~0.5 to ~6 M⊕. These disk masses imply that planet formation around brown dwarfs may be relatively rare and that the supra-Jupiter mass companions found around some brown dwarfs are probably the result of a binary system formation. We find evidence that the two brightest disks in ρ Oph have sharp outer edges at R ≲ 25 AU, in contrast to disks around Taurus brown dwarfs. This difference may suggest that the different environment in ρ Oph may lead to significant differences in disk properties. A comparison of the Mdisk/M∗ ratio for brown dwarf and solar-mass systems also shows a possible deficit of mass in brown dwarfs, which could support the evidence for dynamical truncation of disks in the substellar regime. These findings are still tentative and need to be put on firmer grounds by studying the gaseous disks around brown dwarfs and by performing a more systematic and unbiased survey of the disk population around the more massive stars.

  6. HNC IN PROTOPLANETARY DISKS

    SciTech Connect

    Graninger, Dawn; Öberg, Karin I.; Qi, Chunhua; Kastner, Joel

    2015-07-01

    The distributions and abundances of small organics in protoplanetary disks are potentially powerful probes of disk physics and chemistry. HNC is a common probe of dense interstellar regions and the target of this study. We use the Submillimeter Array (SMA) to observe HNC 3–2 toward the protoplanetary disks around the T Tauri star TW Hya and the Herbig Ae star HD 163296. HNC is detected toward both disks, constituting the first spatially resolved observations of HNC in disks. We also present SMA observations of HCN 3–2 and IRAM 30 m observations of HCN and HNC 1–0 toward HD 163296. The disk-averaged HNC/HCN emission ratio is 0.1–0.2 toward both disks. Toward TW Hya, the HNC emission is confined to a ring. The varying HNC abundance in the TW Hya disk demonstrates that HNC chemistry is strongly linked to the disk physical structure. In particular, the inner rim of the HNC ring can be explained by efficient destruction of HNC at elevated temperatures, similar to what is observed in the ISM. However, to realize the full potential of HNC as a disk tracer requires a combination of high SNR spatially resolved observations of HNC and HCN and disk-specific HNC chemical modeling.

  7. Detailed Microstructural Characterization of the Disk Alloy ME3

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P.; Garg, Anita; Ellis, David L.; O'Connor, Kenneth M.

    2004-01-01

    The advanced powder metallurgy disk alloy ME3 was designed using statistical screening and optimization of composition and processing variables in the NASA/General Electric/Pratt & Whitney HSR/EPM disk program to have extended durability for large disks at maximum temperatures of 600 to 700 C. Scaled-up disks of this alloy were then produced at the conclusion of that program to demonstrate these properties in realistic disk shapes. The objective of the present study was to assess the microstructural characteristics of these ME3 disks at two consistent locations, in order to enable estimation of the variations in microstructure across each disk and across several disks of this advanced alloy. Scaled-up disks processed in the HSR/EPM Compressor/Turbine Disk program had been sectioned, machined into specimens, and tested in tensile, creep, fatigue, and fatigue crack growth tests by NASA Glenn Research Center, in cooperation with General Electric Engine Company and Pratt & Whitney Aircraft Engines. For this study, microstructures of grip sections from tensile specimens in the bore and rim were evaluated from these disks. The major and minor phases were identified and quantified using transmission electron microscopy (TEM). Particular attention was directed to the .' precipitates, which along with grain size can predominantly control the mechanical properties of superalloy disks.

  8. Zombie Vortex Instability. II. Thresholds to Trigger Instability and the Properties of Zombie Turbulence in the Dead Zones of Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Marcus, Philip S.; Pei, Suyang; Jiang, Chung-Hsiang; Barranco, Joseph A.

    2016-12-01

    In Zombie Vortex Instability (ZVI), perturbations excite critical layers in stratified, rotating shear flow (as in protoplanetary disks (PPDs)), causing them to generate vortex layers, which roll up into anticyclonic zombie vortices and cyclonic vortex sheets. The process is self-sustaining as zombie vortices perturb new critical layers, spawning a next generation of zombie vortices. Here, we focus on two issues: the minimum threshold of perturbations that trigger self-sustaining vortex generation, and the properties of the late-time zombie turbulence on large and small scales. The critical parameter that determines whether ZVI is triggered is the magnitude of the vorticity on the small scales (and not velocity); the minimum Rossby number needed for instability is {{Ro}}{crit}˜ 0.2 for β \\equiv N/{{Ω }}=2, where N is the Brunt-Väisälä frequency. While the threshold is set by vorticity, it is useful to infer a criterion on the Mach number; for Kolmogorov noise, the critical Mach number scales with Reynolds number: {{Ma}}{crit}˜ {{Ro}}{crit}{{Re}}-1/2. In PPDs, this is {{Ma}}{crit}˜ {10}-6. On large scales, zombie turbulence is characterized by anticyclones and cyclonic sheets with typical Rossby number ˜0.3. The spacing of the cyclonic sheets and anticyclones appears to have a “memory” of the spacing of the critical layers. On small scales, zombie turbulence has no memory of the initial conditions and has a Kolmogorov-like energy spectrum. While our earlier work was in the limit of uniform stratification, we have demonstrated that ZVI works for non-uniform Brunt-Väisälä frequency profiles that may be found in PPDs.

  9. Mass Flow through Gaps in Circumbinary Disks

    NASA Astrophysics Data System (ADS)

    Artymowicz, Pawel; Lubow, Stephen H.

    1996-08-01

    We demonstrate through smoothed particle hydrodynamics simulations that a circumbinary disk can supply mass to the central binary through gas streams that penetrate the disk gap without closing it. The conditions for an efficient flow typically require the disk thickness-to-radius ratio z/r >~ 0.05, if the turbulent viscosity parameter alpha is greater than 0.01. This mass flow may be important for both the individual systems and their statistics. It occurs preferentially onto the lower mass object and acts toward equalization of component masses. The less massive component may be more luminous and easier to detect, owing to its larger accretion luminosity. For eccentric binaries, the mass flow is strongly modulated in time, providing diagnostics for both the disk and the binary. In the protostellar disks, the flow could be detected as shock emission phased with the binary orbit, resulting from stream impact with the circumstellar disks and/or the young stars. In the (super)massive black hole binaries in nuclei of galaxies, the flow may result from the surrounding interstellar medium and produce nearly periodic emission, as observed in quasar OJ 287. For star-planet-disk systems, our results show that the opening of a gap around a planet is not always sufficient for the termination of its growth. This suggests that planets supplied by gas streams from protoplanetary disks may outgrow Jupiter to become "superplanets" with properties heretofore reserved for stars.

  10. The nature and origin of the Solar system scale disk in the Helix Nebula

    NASA Astrophysics Data System (ADS)

    Ertel, Steve

    We aim to determine the nature and origin of the Solar system scale, dusty disk around the central star of the Helix nebula, the closest planetary nebula (PN, d=152 to 219pc). There are three scenarios for its origin: a Kuiper belt that survived the stellar post-main sequence (post-MS) evolution, a large cloud of eccentric comets resulting from a disrupted Kuiper belt, or a remnant post-Asymptotic Giant Branch (pAGB) disk that formed from material ejected by the star during that phase. Our SOFIA observations will pinpoint the peak location of the spectral energy distribution (SED) of the dust, characterize its shape, and determine the slope of the SED toward longer wavelentghs. We will combine our SOFIA data with our scheduled ALMA observations that will resolve the disk and measure its flux at 1.3mm. The grain properties (dominating size, size distribution) derived from the well sampled SED will be critical to distinguish between the three scenarios. The primordial Kuiper belt case: This will be the first Kuiper belt confirmed around a star that went through the post-MS evolution and critical, direct evidence that planetary systems survive this phase. We will investigate the effects of this phase on planetary/planetesimal systems for the first time through observations. The comet cloud: This will be the first direct evidence of the fate of a planetary system during the stellar post-MS phase. The remnant post-AGB disk case: We will measure the grain size and thus constrain grain growth in the pAGB disk. We will investigate whether second-generation planet(esimal) formation is possible there. The Helix is a bipolar PN (almost seen pole-on) but no binary companion is known to its central star. Thus, our observations will provite great insight into the evolution of post-MS stars and their disks and on the binary hypothesis of PN formation.

  11. PSOCT studies of intervertebral disk

    NASA Astrophysics Data System (ADS)

    Matcher, Stephen J.; Winlove, Peter C.; Gangnus, Sergey V.

    2004-07-01

    Polarization-sensitive optical coherence tomography (PSOCT) is an emerging optical imaging technique that is sensitive to the birefringence properties of tissues. It thus has applications in studying the large-scale ordering of collagen fibers within connective tissues. This ordering not only provides useful insights into the relationship between structure and function for various anatomical structures but also is an indicator of pathology. Intervertebral disk is an elastic tissue of the spine and possesses a 3-D collagen structure well suited to study using PSOCT. Since the outer layer of the disk has a lamellar structure with collagen fibers oriented in a trellis-like arrangement between lamellae, the birefringence fast-axis shows pronounced variations with depth, on a spatial scale of about 100 μm. The lamellar thickness varies with age and possibly with disease. We have used a polarisation-sensitive optical coherence tomography system to measure the birefringence properties of freshly excised, hydrated bovine caudal intervertebral disk and compared this with equine flexor tendon. Our results clearly demonstrate the ability of PSOCT to detect the outer three lamellae, down to a depth of at least 700 μm, via discontinuities in the depth-resolved retardance. We have applied a simple semi-empirical model based on Jones calculus to quantify the variation in the fast-axis orientation with depth. Our data and modeling is in broad agreement with previous studies using x-ray diffraction and polarization microscopy applied to histological sections of dehydrated disk. Our results imply that PSOCT may prove a useful tool to study collagen organisation within intervertebral disk in vitro and possibly in vivo and its variation with age and disease.

  12. Alloy 10: A 1300F Disk Alloy

    NASA Technical Reports Server (NTRS)

    Gayda, John

    2000-01-01

    Gas turbine engines for future subsonic transports will probably have higher pressure ratios which will require nickel-base superalloy disks with 13000 to 1400 F temperature capability. Several advanced disk alloys are being developed to fill this need. One of these, Allied Signal's Alloy 10, is a promising candidate for gas turbine engines to be used on smaller, regional aircraft. For this application, compressor/turbine disks must withstand temperatures of 1300 F for several hundred hours over the life of the engine. In this paper, three key properties of Alloy 10--tensile, 0.2% creep, and fatigue crack growth--will be assessed at 1300 F.

  13. Distinguishability of generic quantum states

    NASA Astrophysics Data System (ADS)

    Puchała, Zbigniew; Pawela, Łukasz; Życzkowski, Karol

    2016-06-01

    Properties of random mixed states of dimension N distributed uniformly with respect to the Hilbert-Schmidt measure are investigated. We show that for large N , due to the concentration of measure, the trace distance between two random states tends to a fixed number D ˜=1 /4 +1 /π , which yields the Helstrom bound on their distinguishability. To arrive at this result, we apply free random calculus and derive the symmetrized Marchenko-Pastur distribution, which is shown to describe numerical data for the model of coupled quantum kicked tops. Asymptotic value for the root fidelity between two random states, √{F }=3/4 , can serve as a universal reference value for further theoretical and experimental studies. Analogous results for quantum relative entropy and Chernoff quantity provide other bounds on the distinguishablity of both states in a multiple measurement setup due to the quantum Sanov theorem. We study also mean entropy of coherence of random pure and mixed states and entanglement of a generic mixed state of a bipartite system.

  14. Tatooine Nurseries: Structure and Evolution of Circumbinary Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Vartanyan, David; Garmilla, José A.; Rafikov, Roman R.

    2016-01-01

    Recent discoveries of circumbinary planets by the Kepler mission provide motivation for understanding their birthplaces—protoplanetary disks around stellar binaries with separations ≲ 1 {{AU}}. We explore properties and evolution of such circumbinary disks focusing on modification of their structure caused by tidal coupling to the binary. We develop a set of analytical scaling relations describing viscous evolution of the disk properties, which are verified and calibrated using 1D numerical calculations with realistic inputs. Injection of angular momentum by the central binary suppresses mass accretion onto the binary and causes radial distribution of the viscous angular momentum flux {F}J to be different from that in a standard accretion disk around a single star with no torque at the center. Disks with no mass accretion at the center develop an {F}J profile that is flat in radius. Radial profiles of temperature and surface density are also quite different from those in disks around single stars. Damping of the density waves driven by the binary and viscous dissipation dominates heating of the inner disk (within 1-2 AU), pushing the ice line beyond 3-5 AU, depending on disk mass and age. Irradiation by the binary governs disk thermodynamics beyond ˜10 AU. However, self-shadowing by the hot inner disk may render central illumination irrelevant out to ˜20 AU. Spectral energy distribution of a circumbinary disk exhibits a distinctive bump around 10 μm, which may facilitate identification of such disks around unresolved binaries. Efficient tidal coupling to the disk drives orbital inspiral of the binary and may cause low-mass and relatively compact binaries to merge into a single star within the disk lifetime. We generally find that circumbinary disks present favorable sites for planet formation (despite their wider zone of volatile depletion), in agreement with the statistics of Kepler circumbinary planets.

  15. High Frequency Scattering from Arbitrarily Oriented Dielectric Disks

    NASA Technical Reports Server (NTRS)

    Levine, D. M.; Meneghini, R.; Lang, R. H.; Seker, S. S.

    1982-01-01

    Calculations have been made of electromagnetic wave scattering from dielectric disks of arbitrary shape and orientation in the high frequency (physical optics) regime. The solution is obtained by approximating the fields inside the disk with the fields induced inside an identically oriented slab (i.e. infinite parallel planes) with the same thickness and dielectric properties. The fields inside the disk excite conduction and polarization currents which are used to calculate the scattered fields by integrating the radiation from these sources over the volume of the disk. This computation has been executed for observers in the far field of the disk in the case of disks with arbitrary orientation and for arbitrary polarization of the incident radiation. The results have been expressed in the form of a dyadic scattering amplitude for the disk. The results apply to disks whose diameter is large compared to wavelength and whose thickness is small compared to diameter, but the thickness need not be small compared to wavelength. Examples of the dependence of the scattering amplitude on frequency, dielectric properties of the disk and disk orientation are presented for disks of circular cross section.

  16. Astounding Jumping Disk.

    ERIC Educational Resources Information Center

    Guzdziol, Edward S.

    1991-01-01

    Activities involving concave rubber disks are utilized to illustrate the scientific principles of kinetic and potential energy. Provides teacher instructions and questions related to the activity. (MDH)

  17. Astounding Jumping Disk.

    ERIC Educational Resources Information Center

    Guzdziol, Edward S.

    1991-01-01

    Activities involving concave rubber disks are utilized to illustrate the scientific principles of kinetic and potential energy. Provides teacher instructions and questions related to the activity. (MDH)

  18. Turbine disks for improved reliability

    NASA Technical Reports Server (NTRS)

    Kaufman, A.

    1977-01-01

    Advanced disk structural concepts were employed to improve the cyclic lives and reliability of turbine disks. Analytical studies were conducted to evaluate bore-entry disks as potential replacements for the existing first-stage turbine disks in the CF6-50 and JT8D-17 engines. Results of low cycle fatigue, burst, fracture mechanics, and fragment energy analyses are summarized for the advanced disk designs and the existing disk designs, with both conventional and advanced disk materials. Other disk concepts such as composite, laminated, link, multibore, multidisk, and spline disks were also evaluated for the CF6-50 engine.

  19. Distinguishability of black hole microstates

    NASA Astrophysics Data System (ADS)

    Bao, Ning; Ooguri, Hirosi

    2017-09-01

    We use the Holevo information to estimate distinguishability of microstates of a black hole in anti-de Sitter space by measurements one can perform on a subregion of a Cauchy surface of the dual conformal field theory. We find that microstates are not distinguishable at all until the subregion reaches a certain size and that perfect distinguishability can be achieved before the subregion covers the entire Cauchy surface. We will compare our results with expectations from the entanglement wedge reconstruction, tensor network models, and the bit threads interpretation of the Ryu-Takayanagi formula.

  20. Stability of general-relativistic accretion disks

    NASA Astrophysics Data System (ADS)

    Korobkin, Oleg; Abdikamalov, Ernazar B.; Schnetter, Erik; Stergioulas, Nikolaos; Zink, Burkhard

    2011-02-01

    Self-gravitating relativistic disks around black holes can form as transient structures in a number of astrophysical scenarios such as binary neutron star and black hole-neutron star coalescences, as well as the core collapse of massive stars. We explore the stability of such disks against runaway and nonaxisymmetric instabilities using three-dimensional hydrodynamics simulations in full general relativity using the Thor code. We model the disk matter using the ideal fluid approximation with a Γ-law equation of state with Γ=4/3. We explore three disk models around nonrotating black holes with disk-to-black hole mass ratios of 0.24, 0.17, and 0.11. Because of metric blending in our initial data, all of our initial models contain an initial axisymmetric perturbation which induces radial disk oscillations. Despite these oscillations, our models do not develop the runaway instability during the first several orbital periods. Instead, all of the models develop unstable nonaxisymmetric modes on a dynamical time scale. We observe two distinct types of instabilities: the Papaloizou-Pringle and the so-called intermediate type instabilities. The development of the nonaxisymmetric mode with azimuthal number m=1 is accompanied by an outspiraling motion of the black hole, which significantly amplifies the growth rate of the m=1 mode in some cases. Overall, our simulations show that the properties of the unstable nonaxisymmetric modes in our disk models are qualitatively similar to those in the Newtonian theory.

  1. On the Dynamical Foundations of α Disks

    NASA Astrophysics Data System (ADS)

    Balbus, Steven A.; Papaloizou, John C. B.

    1999-08-01

    The dynamical foundations of α disk models are described. At the heart of the viscous formalism of accretion disk models are correlations in the fluctuating components of the disk velocity, magnetic field, and gravitational potential. We relate these correlations to the large-scale mean flow dynamics used in phenomenological viscous disk models. MHD turbulence readily lends itself to the α formalism, but transport by self-gravity does not. Nonlocal transport is an intrinsic property of turbulent self-gravitating disks, which in general cannot be captured by an α model. Local energy dissipation and α-like behavior can be reestablished if the pattern speeds associated with the amplitudes of an azimuthal Fourier decomposition of the turbulence are everywhere close to the local rotation frequency. In this situation, global wave transport must be absent. Shearing box simulations, which employ boundary conditions forcing local behavior, are probably not an adequate tool for modeling the behavior of self-gravitating disks. As a matter of principle, it is possible that disks that hover near the edge of gravitational stability may behave in accord with a local α model, but global simulations performed to date suggest matters are not this simple.

  2. Stability of general-relativistic accretion disks

    SciTech Connect

    Korobkin, Oleg; Abdikamalov, Ernazar B.; Schnetter, Erik; Stergioulas, Nikolaos; Zink, Burkhard

    2011-02-15

    Self-gravitating relativistic disks around black holes can form as transient structures in a number of astrophysical scenarios such as binary neutron star and black hole-neutron star coalescences, as well as the core collapse of massive stars. We explore the stability of such disks against runaway and nonaxisymmetric instabilities using three-dimensional hydrodynamics simulations in full general relativity using the Thor code. We model the disk matter using the ideal fluid approximation with a {Gamma}-law equation of state with {Gamma}=4/3. We explore three disk models around nonrotating black holes with disk-to-black hole mass ratios of 0.24, 0.17, and 0.11. Because of metric blending in our initial data, all of our initial models contain an initial axisymmetric perturbation which induces radial disk oscillations. Despite these oscillations, our models do not develop the runaway instability during the first several orbital periods. Instead, all of the models develop unstable nonaxisymmetric modes on a dynamical time scale. We observe two distinct types of instabilities: the Papaloizou-Pringle and the so-called intermediate type instabilities. The development of the nonaxisymmetric mode with azimuthal number m=1 is accompanied by an outspiraling motion of the black hole, which significantly amplifies the growth rate of the m=1 mode in some cases. Overall, our simulations show that the properties of the unstable nonaxisymmetric modes in our disk models are qualitatively similar to those in the Newtonian theory.

  3. Reprocessing in Luminous Disks

    NASA Technical Reports Server (NTRS)

    Bell, K. Robbins; DeVincenzi, Donald L. (Technical Monitor)

    1999-01-01

    We develop and investigate a procedure that accounts for disk reprocessing of photons that originate in the disk itself. Surface temperatures and simple, black body spectral energy distributions (SEDs) of protostellar disks are calculated. In disks that flare with radius, reprocessing of stellar photons results in temperature profiles considerably shallower than r(sup -3/4). Including the disk as a radiation source (as in the case of actively secreting disks) along with the stellar source further flattens the temperature profile. Disks that flare strongly near the star and then smoothly curve over and become shadowed at some distance ("decreasing curvature" disks) exhibit nearly power-law temperature profiles which result in power-law infrared SEDs with slopes in agreement with typical observations of young stellar objects. Disk models in which the photospheric thickness is controlled by the local opacity and in which the temperature decreases with radius naturally show this shape. Uniformly flaring models do not match observations as well; progressively stronger reprocessing at larger radii leads to SEDs that flatten toward the infrared or even have a second peak at the wavelength corresponding (through the Wien law) to the temperature of the outer edge of the disk. In FU Orionis outbursting systems, the dominant source of energy is the disk itself. The details of the reprocessing depend sensitively on the assumed disk shape and emitted temperature profile. The thermal instability outburst models of Bell Lin reproduce trends in the observed SEDs of Fuors with T varies as r(sup -3/4) in the inner disk (r approx. less than 0.25au corresponding to lambda approx. less than 10 microns) and T varies as r(sup -1/2) in the outer disk. Surface irradiation during outburst and quiescence is compared in the region of planet formation (1 - 10 au). The contrast between the two phases is diminished by the importance of the reprocessing of photons from the relatively high mass

  4. Reprocessing in Luminous Disks

    NASA Technical Reports Server (NTRS)

    Bell, K. Robbins; DeVincenzi, Donald L. (Technical Monitor)

    1999-01-01

    We develop and investigate a procedure that accounts for disk reprocessing of photons that originate in the disk itself. Surface temperatures and simple, black body spectral energy distributions (SEDs) of protostellar disks are calculated. In disks that flare with radius, reprocessing of stellar photons results in temperature profiles considerably shallower than r(sup -3/4). Including the disk as a radiation source (as in the case of actively secreting disks) along with the stellar source further flattens the temperature profile. Disks that flare strongly near the star and then smoothly curve over and become shadowed at some distance ("decreasing curvature" disks) exhibit nearly power-law temperature profiles which result in power-law infrared SEDs with slopes in agreement with typical observations of young stellar objects. Disk models in which the photospheric thickness is controlled by the local opacity and in which the temperature decreases with radius naturally show this shape. Uniformly flaring models do not match observations as well; progressively stronger reprocessing at larger radii leads to SEDs that flatten toward the infrared or even have a second peak at the wavelength corresponding (through the Wien law) to the temperature of the outer edge of the disk. In FU Orionis outbursting systems, the dominant source of energy is the disk itself. The details of the reprocessing depend sensitively on the assumed disk shape and emitted temperature profile. The thermal instability outburst models of Bell Lin reproduce trends in the observed SEDs of Fuors with T varies as r(sup -3/4) in the inner disk (r approx. less than 0.25au corresponding to lambda approx. less than 10 microns) and T varies as r(sup -1/2) in the outer disk. Surface irradiation during outburst and quiescence is compared in the region of planet formation (1 - 10 au). The contrast between the two phases is diminished by the importance of the reprocessing of photons from the relatively high mass

  5. Protoplanetary Disks as (Possibly) Viscous Disks

    NASA Astrophysics Data System (ADS)

    Rafikov, Roman R.

    2017-03-01

    Protoplanetary disks are believed to evolve on megayear timescales in a diffusive (viscous) manner as a result of angular momentum transport driven by internal stresses. Here we use a sample of 26 protoplanetary disks resolved by ALMA with measured (dust-based) masses and stellar accretion rates to derive the dimensionless α-viscosity values for individual objects, with the goal of constraining the angular momentum transport mechanism. We find that the inferred values of α do not cluster around a single value, but instead have a broad distribution extending from 10‑4 to 0.04. Moreover, they correlate with neither the global disk parameters (mass, size, surface density) nor the stellar characteristics (mass, luminosity, radius). However, we do find a strong linear correlation between α and the central mass accretion rate \\dot{M}. This correlation is unlikely to result from the direct physical effect of \\dot{M} on internal stress on global scales. Instead, we suggest that it is caused by the decoupling of stellar \\dot{M} from the global disk characteristics in one of the following ways: (1) The behavior (and range) of α is controlled by a yet-unidentified parameter (e.g., ionization fraction, magnetic field strength, or geometry), ultimately driving the variation of \\dot{M}. (2) The central \\dot{M} is decoupled from the global accretion rate as a result of an instability, or mass accumulation (or loss in a wind or planetary accretion) in the inner disk. (3) Perhaps the most intriguing possibility is that angular momentum in protoplanetary disks is transported nonviscously, e.g., via magnetohydrodynamic winds or spiral density waves.

  6. Growth and shape control of disks by bending and extension

    NASA Astrophysics Data System (ADS)

    Seffen, Keith A.; Maurini, Corrado

    2013-01-01

    Differential growth of thin elastic bodies furnishes a surprisingly simple explanation of the complex and intriguing shapes of many biological systems, such as plant leaves and organs. Similarly, inelastic strains induced by thermal effects or active materials in layered plates are extensively used to control the curvature of thin engineering structures. Such behaviour inspires us to distinguish and to compare two possible modes of differential growth not normally compared to each other, in order to reveal the full range of out-of-plane shapes of an initially flat disk. The first growth mode, frequently employed by engineers, is characterised by direct bending strains through the thickness, and the second mode, mainly apparent in biological systems, is driven by extensional strains of the middle surface. When each mode is considered separately, it is shown that buckling is common to both modes, leading to bistable shapes: growth from bending strains results in a double-curvature limit at buckling, followed by almost developable deformation in which the Gaussian curvature at buckling is conserved; during extensional growth, out-of-plane distortions occur only when the buckling condition is reached, and the Gaussian curvature continues to increase. When both growth modes are present, it is shown that, generally, larger displacements are obtained under in-plane growth when the disk is relatively thick and growth strains are small, and vice versa. It is also shown that shapes can be mono-, bi-, tri- or neutrally stable, depending on the growth strain levels and the material properties: furthermore, it is shown that certain combinations of growth modes result in a free, or natural, response in which the doubly curved shape of disk exactly matches the imposed strains. Such diverse behaviour, in general, may help to realise more effective actuation schemes for engineering structures.

  7. Are all flaring Herbig disks transitional?

    NASA Astrophysics Data System (ADS)

    Maaskant, K. M.; Honda, M.; Waters, L. B. F. M.; Tielens, A. G. G. M.; Dominik, Carsten; Min, M.; Verhoeff, A.; Meeus, G.; Ancker, M. E.

    2013-07-01

    Context: The evolution of young massive protoplanetary disks toward planetary systems is expected to correspond to structural changes in observational appearance, which includes the formation of gaps and the depletion of dust and gas. Aims. A special group of disks around Herbig Ae/Be stars do not show prominent silicate emission features, although they still bear signs of flaring disks, the presence of gas, and small grains. We focus our attention on four key Herbig Ae/Be stars to understand the structural properties responsible for the absence of silicate feature emission. Methods: We investigate Q- and N-band images taken with Subaru/COMICS, Gemini South/T-ReCS, and VLT/VISIR. We perform radiative transfer modeling to examine the radial distribution of dust and polycyclic aromatic hydrocarbons (PAHs). Our solutions require a separation of inner- and outer- disks by a large gap. From this, we characterize the radial density structure of dust and PAHs in the disk. Results: The inner edge of the outer disk has a high surface brightness and a typical temperature between ˜100-150 K and therefore, dominates the emission in the Q-band. All four disks are characterized by large gaps. We derive radii of the inner edge of the outer disk of 34+4 , 23+3 , 30+5 and 63+4 AU for HD 97048, HD 169142, HD 135344 B, and Oph IRS 48, respectively. For HD 97048 this is the first -4 -5 -3 -4 detection of a disk gap. The large gaps deplete the entire population of silicate particles with temperatures suitable for prominent mid- infrared feature emission, while small carbonaceous grains and PAHs can still show prominent emission at mid-infrared wavelengths. The continuum emission in the N-band is not due to emission in the wings of PAHs. This continuum emission can be due to very small grains or to thermal emission from the inner disk. We find that PAH emission is not always dominated by PAHs on the surface of the outer disk. Conclusions: The absence of silicate emission features is

  8. Scattered light mapping of protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Stolker, T.; Dominik, C.; Min, M.; Garufi, A.; Mulders, G. D.; Avenhaus, H.

    2016-12-01

    Context. High-contrast scattered light observations have revealed the surface morphology of several dozen protoplanetary disks at optical and near-infrared wavelengths. Inclined disks offer the opportunity to measure part of the phase function of the dust grains that reside in the disk surface which is essential for our understanding of protoplanetary dust properties and the early stages of planet formation. Aims: We aim to construct a method which takes into account how the flaring shape of the scattering surface of an optically thick protoplanetary disk projects onto the image plane of the observer. This allows us to map physical quantities (e.g., scattering radius and scattering angle) onto scattered light images and retrieve stellar irradiation corrected images (r2-scaled) and dust phase functions. Methods: The scattered light mapping method projects a power law shaped disk surface onto the detector plane after which the observed scattered light image is interpolated backward onto the disk surface. We apply the method on archival polarized intensity images of the protoplanetary disk around HD 100546 that were obtained with VLT/SPHERE in the R' band and VLT/NACO in the H and Ks bands. Results: The brightest side of the r2-scaled R' band polarized intensity image of HD 100546 changes from the far to the near side of the disk when a flaring instead of a geometrically flat disk surface is used for the r2-scaling. The decrease in polarized surface brightness in the scattering angle range of 40°-70° is likely a result of the dust phase function and degree of polarization which peak in different scattering angle regimes. The derived phase functions show part of a forward scattering peak, which indicates that large, aggregate dust grains dominate the scattering opacity in the disk surface. Conclusions: Projection effects of a protoplanetary disk surface need to be taken into account to correctly interpret scattered light images. Applying the correct scaling for the

  9. Structure of force networks in tapped particulate systems of disks and pentagons. II. Persistence analysis.

    PubMed

    Kondic, L; Kramár, M; Pugnaloni, Luis A; Carlevaro, C Manuel; Mischaikow, K

    2016-06-01

    In the companion paper [Pugnaloni et al., Phys. Rev. E 93, 062902 (2016)10.1103/PhysRevE.93.062902], we use classical measures based on force probability density functions (PDFs), as well as Betti numbers (quantifying the number of components, related to force chains, and loops), to describe the force networks in tapped systems of disks and pentagons. In the present work, we focus on the use of persistence analysis, which allows us to describe these networks in much more detail. This approach allows us not only to describe but also to quantify the differences between the force networks in different realizations of a system, in different parts of the considered domain, or in different systems. We show that persistence analysis clearly distinguishes the systems that are very difficult or impossible to differentiate using other means. One important finding is that the differences in force networks between disks and pentagons are most apparent when loops are considered: the quantities describing properties of the loops may differ significantly even if other measures (properties of components, Betti numbers, force PDFs, or the stress tensor) do not distinguish clearly or at all the investigated systems.

  10. Entanglement of distinguishable quantum memories

    NASA Astrophysics Data System (ADS)

    Vittorini, G.; Hucul, D.; Inlek, I. V.; Crocker, C.; Monroe, C.

    2014-10-01

    Time-resolved photon detection can be used to generate entanglement between distinguishable photons. This technique can be extended to entangle quantum memories that emit photons with different frequencies and identical temporal profiles without the loss of entanglement rate or fidelity. We experimentally realize this process using remotely trapped 171Yb+ ions where heralded entanglement is generated by interfering distinguishable photons. This technique may be necessary for future modular quantum systems and networks that are composed of heterogeneous qubits.

  11. CIRCUMPLANETARY DISK FORMATION

    SciTech Connect

    Ward, William R.; Canup, Robin M.

    2010-11-15

    The development and evolution of a circumplanetary disk during the accretion of a giant planet is examined. The planet gains mass and angular momentum from infalling solar nebula material while simultaneously contracting due to luminosity losses. When the planet becomes rotationally unstable it begins to shed material into a circumplanetary disk. Viscosity causes the disk to spread to a moderate fraction of the Hill radius where it is assumed that a small fraction of the material escapes back into heliocentric orbit, carrying away most of the excess angular momentum. As the planet's contraction continues, its radius can become smaller than the spatial range of the inflow and material begins to fall directly onto the disk, which switches from a spin-out disk to an accretion disk as the planet completes its growth. We here develop a description of the circumplanetary disk, which is combined with models of the planet's contraction and the inflow rate including its angular momentum content to yield a solution for the time evolution of a planet-disk system.

  12. Repetitive sequence environment distinguishes housekeeping genes

    PubMed Central

    Eller, C. Daniel; Regelson, Moira; Merriman, Barry; Nelson, Stan; Horvath, Steve; Marahrens, York

    2007-01-01

    Housekeeping genes are expressed across a wide variety of tissues. Since repetitive sequences have been reported to influence the expression of individual genes, we employed a novel approach to determine whether housekeeping genes can be distinguished from tissue-specific genes their repetitive sequence context. We show that Alu elements are more highly concentrated around housekeeping genes while various longer (>400-bp) repetitive sequences ("repeats"), including Long Interspersed Nuclear Element 1 (LINE-1) elements, are excluded from these regions. We further show that isochore membership does not distinguish housekeeping genes from tissue-specific genes and that repetitive sequence environment distinguishes housekeeping genes from tissue-specific genes in every isochore. The distinct repetitive sequence environment, in combination with other previously published sequence properties of housekeeping genes, were used to develop a method of predicting housekeeping genes on the basis of DNA sequence alone. Using expression across tissue types as a measure of success, we demonstrate that repetitive sequence environment is by far the most important sequence feature identified to date for distinguishing housekeeping genes. PMID:17141428

  13. An MCMC Circumstellar Disks Modeling Tool

    NASA Astrophysics Data System (ADS)

    Wolff, Schuyler; Perrin, Marshall D.; Mazoyer, Johan; Choquet, Elodie; Soummer, Remi; Ren, Bin; Pueyo, Laurent; Debes, John H.; Duchene, Gaspard; Pinte, Christophe; Menard, Francois

    2016-01-01

    We present an enhanced software framework for the Monte Carlo Markov Chain modeling of circumstellar disk observations, including spectral energy distributions and multi wavelength images from a variety of instruments (e.g. GPI, NICI, HST, WFIRST). The goal is to self-consistently and simultaneously fit a wide variety of observables in order to place constraints on the physical properties of a given disk, while also rigorously assessing the uncertainties in the derived properties. This modular code is designed to work with a collection of existing modeling tools, ranging from simple scripts to define the geometry for optically thin debris disks, to full radiative transfer modeling of complex grain structures in protoplanetary disks (using the MCFOST radiative transfer modeling code). The MCMC chain relies on direct chi squared comparison of model images/spectra to observations. We will include a discussion of how best to weight different observations in the modeling of a single disk and how to incorporate forward modeling from PCA PSF subtraction techniques. The code is open source, python, and available from github. Results for several disks at various evolutionary stages will be discussed.

  14. Radio pulsar disk electrodynamics

    NASA Technical Reports Server (NTRS)

    Michel, F. C.

    1983-01-01

    Macroscopic physics are discussed for the case of a disk close to an isolated, magnetized, rotating neutron star that acts as a Faraday disk dynamo, while the disk acts as both a load and a neutral sheet. This sheet allows the polar cap current to return to the neutron star, splitting a dipolar field into two monopolar halves. The dominant energy loss is from the stellar wind torque, and the next contribution is dissipation in the auroral zones, where the current returns to the star in a 5 cm-thick sheet. The disk itself may be a source of visible radiation comparable to that in pulsed radio frequency emission. As the pulsar ages, the disk expands and narrows into a ring which, it is suggested, may lead to a cessation of pulsed emission at periods of a few sec.

  15. Protostellar Disk L1157

    NASA Technical Reports Server (NTRS)

    1999-01-01

    These observations of interstellar dark cloud L1157, located in the Cepheus constellation, were made using Caltech's Owens Valley Millimeter Array near Bishop, California.

    The multi-colored area shows a dust disk surrounding a newborn star. The red-orange area at the center represents the brightest region, which contains the young star. It is surrounded by the cooler, dusty disk, which appears as yellow, green and blue. The diameter of the disk is about 20 times larger than our entire solar system.

    The white lines trace the radio wave emission of methanol. Note that the methanol emission comes only from the outer parts of the disk. That is the zone where a warm shock occurs when the cloud material moves in toward the star and meets up with the outer surface of the disk.

  16. Radio pulsar disk electrodynamics

    NASA Technical Reports Server (NTRS)

    Michel, F. C.

    1983-01-01

    Macroscopic physics are discussed for the case of a disk close to an isolated, magnetized, rotating neutron star that acts as a Faraday disk dynamo, while the disk acts as both a load and a neutral sheet. This sheet allows the polar cap current to return to the neutron star, splitting a dipolar field into two monopolar halves. The dominant energy loss is from the stellar wind torque, and the next contribution is dissipation in the auroral zones, where the current returns to the star in a 5 cm-thick sheet. The disk itself may be a source of visible radiation comparable to that in pulsed radio frequency emission. As the pulsar ages, the disk expands and narrows into a ring which, it is suggested, may lead to a cessation of pulsed emission at periods of a few sec.

  17. THE EXTENDED OPTICAL DISK OF M101

    SciTech Connect

    Mihos, J. Christopher; Harding, Paul; Spengler, Chelsea E.; Rudick, Craig S.; Feldmeier, John J. E-mail: paul.harding@case.edu E-mail: craig.rudick@phys.ethz.ch

    2013-01-10

    We have used deep, wide-field optical imaging to study the faint outskirts of the luminous spiral galaxy M101 (NGC 5457) as well as its surrounding environment. Over 6 deg{sup 2}, our imaging has a limiting surface brightness of {mu} {sub B} {approx} 29.5 mag arcsec{sup -2}, and has revealed the stellar structure of M101's disk out to nearly 25' (50 kpc), 3 times our measured R {sub 25} isophotal size of the optical disk. At these radii, the well-known asymmetry of the inner disk slews 180 Degree-Sign , resulting in an asymmetric plume of light at large radius which follows the very extended H I disk to the northeast of M101. This plume has very blue colors (B - V {approx} 0.2), suggesting that it is the somewhat more evolved (few hundred Myr to {approx}1 Gyr) counterpart of the young far-ultraviolet emitting population traced by Galaxy Evolution Explorer imaging. We also detect another, redder spur of extended light to the east of the disk, and both structures are reminiscent of features produced during fly-by galaxy interactions. However, we see no evidence of very extended tidal tails around M101 or any of its companions which might be expected from a recent encounter with a massive companion. We consider the properties of M101's outer disk in light of possible past interactions with the nearby companion galaxies NGC 5477 and NGC 5474. The detection of optical starlight at such large radii gives us the ability to study star formation histories and stellar populations in outer disks over longer timescales than those traced by the UV or H{alpha} emitting populations. Our data suggest an ongoing buildup of M101's outer disk due to encounters in the group environment triggering extended star formation and tidal heating of existing disk populations.

  18. Investigation of selected disk systems

    NASA Technical Reports Server (NTRS)

    1976-01-01

    The large disk systems offered by IBM, UNIVAC, Digital Equipment Corporation, and Data General were examined. In particular, these disk systems were analyzed in terms of how well available operating systems take advantage of the respective disk controller's transfer rates, and to what degree all available data for optimizing disk usage is effectively employed. In the course of this analysis, generic functions and components of disk systems were defined and the capabilities of the surveyed disk system were investigated.

  19. Static property and current-driven precession of 2π-vortex in nano-disk with Dzyaloshinskii-Moriya interaction

    SciTech Connect

    Liu, Xianyin; Zhu, Qiyuan; Zhang, Senfu; Liu, Qingfang E-mail: wangjb@lzu.edu.cn; Wang, Jianbo E-mail: wangjb@lzu.edu.cn

    2015-08-15

    An interesting type of skyrmion-like spin texture, 2π-vortex, is obtained in a thin nano-disk with Dzyaloshinskii-Moriya interaction. We have simulated the existence of 2π-vortex by micromagnetic method. Furthermore, the spin polarized current is introduced in order to drive the motion of 2π-vortex in a nano-disk with diameter 2 R = 140 nm. When the current density matches with the current injection area, 2π-vortex soon reaches a stable precession (3∼4 ns). The relationship between the precession frequency of 2π-vortex and the current density is almost linear. It may have potential use in spin torque nano-oscillators.

  20. Effect of hall current on MHD flow of a nanofluid with variable properties due to a rotating disk with viscous dissipation and nonlinear thermal radiation

    NASA Astrophysics Data System (ADS)

    Abdel-Wahed, Mohamed; Akl, Mohamed

    2016-09-01

    Analysis of the MHD Nanofluid boundary layer flow over a rotating disk with a constant velocity in the presence of hall current and non-linear thermal radiation has been covered in this work. The variation of viscosity and thermal conductivity of the fluid due to temperature and nanoparticles concentration and size is considered. The problem described by a system of P.D.E that converted to a system of ordinary differential equations by the similarity transformation technique, the obtained system solved analytically using Optimal Homotopy Asymptotic Method (OHAM) with association of mathematica program. The velocity profiles and temperature profiles of the boundary layer over the disk are plotted and investigated in details. Moreover, the surface shear stress, rate of heat transfer explained in details.

  1. Non-local Thermodynamic Equilibrium Stellar Spectroscopy with 1D and >3D< Models. II. Chemical Properties of the Galactic Metal-poor Disk and the Halo

    NASA Astrophysics Data System (ADS)

    Bergemann, Maria; Collet, Remo; Schönrich, Ralph; Andrae, Rene; Kovalev, Mikhail; Ruchti, Greg; Hansen, Camilla Juul; Magic, Zazralt

    2017-09-01

    From exploratory studies and theoretical expectations it is known that simplifying approximations in spectroscopic analysis (local thermodynamic equilibrium (LTE), 1D) lead to systematic biases of stellar parameters and abundances. These biases depend strongly on surface gravity, temperature and, in particular, for LTE versus non-LTE (NLTE), on metallicity of the stars. Here we analyze the [Mg/Fe] and [Fe/H] plane of a sample of 326 stars, comparing LTE and NLTE results obtained using 1D hydrostatic models and averaged <3D> models. We show that compared to the <3D> NLTE benchmark, the other three methods display increasing biases toward lower metallicities, resulting in false trends of [Mg/Fe] against [Fe/H], which have profound implications for interpretations by chemical evolution models. In our best <3D> NLTE model, the halo and disk stars show a clearer behavior in the [Mg/Fe]–[Fe/H] plane, from the knee in abundance space down to the lowest metallicities. Our sample has a large fraction of thick disk stars and this population extends down to at least [Fe/H] ∼ ‑1.6 dex, further than previously proven. The thick disk stars display a constant [Mg/Fe] ≈ 0.3 dex, with a small intrinsic dispersion in [Mg/Fe] that suggests that a fast SN Ia channel is not relevant for the disk formation. The halo stars reach higher [Mg/Fe] ratios and display a net trend of [Mg/Fe] at low metallicities, paired with a large dispersion in [Mg/Fe]. These indicate the diverse origin of halo stars from accreted low-mass systems to stochastic/inhomogeneous chemical evolution in the Galactic halo.

  2. Elemental Abundances in the Galactic Disk

    NASA Astrophysics Data System (ADS)

    Reddy, B. E.; Tomkin, J.; Lambert, D. L.; Allende Prieto, C.

    Here, we discussed our recent results of elemental abundance survey of Galactic disk based on 181 F- and G-type dwarfs (published by Reddy et al. 2003, MNRAS, 340, 304). Using high-resolution and high signal-to-noise spectra we obtained quantitative abundances for 27 elements: C, N, O, Na, Mg, Al, Si, S, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd, and Eu. For the entire sample we have determined kinematic (U,V,W) and the orbital parameters (peri- and apo- Galactic distances). The alpha-elements -- O, Mg, Si, Ca, and Ti -- show [α/Fe] to increase slightly with decreasing [Fe/H]. Heavy elements with dominant contributions at solar metallicity from the s-process show [s/Fe] to decrease slightly with decreasing [Fe/H]. Scatter in [X/Fe] at a fixed [Fe/H] is entirely attributable to the small measurement errors, after excluding the few thick disk stars and the s-process enriched CH subgiants. Tight limits are set on `cosmic' scatter. If a weak trend with [Fe/H] is taken into account, the composition of a thin disk star expressed as [X/Fe] is independent of the star's age and birthplace for elements contributed in different proportions by massive stars (Type II SN), exploding white dwarfs (Type Ia SN), and asymptotic red giant branch stars. By combining our sample with published studies, we deduced properties of thin and thick disk stars. Thick disk stars are primarily identified by their VLSR in the range - 40 to -100 km s-1. These are very old stars with origins in the inner Galaxy and metallicities [Fe/H] <˜-0.4. At the same [Fe/H], the sampled thin disk stars have VLSR ˜0 km s-1, and are generally younger with a birthplace at about the Sun's Galactocentric distance. In the range -0.35 ≥ [Fe/H] ≥ -0.70, well represented by present thin and thick disk samples, [X/Fe] of the thick disk stars is greater than that of thin disk stars for Mg, Al, Si, Ca, Ti, and Eu. [X/Fe] is very similar for the thin and thick disk for -- notably -- Na, and iron

  3. Modeling Observable Signatures of Protoplanetary Disks: Combining Hydrodynamic Simulations with Radiative Transfer Methods

    NASA Astrophysics Data System (ADS)

    Kloster, Dylan; Jang-Condell, Hannah; Kasper, David

    2016-01-01

    New high resolution images of protoplanetary disks from facilities like ALMA are revealing complex disk structures, possibly due to interactions between the disk and newly forming planets within that disk. Analysis of what the structures in these images reveal about the evolution of protoplanetary disks requires detailed models of disk/planet interaction combined with radiative transfer techniques to calculate observable signatures of these disks. We model this disk-planet interaction as hydrodynamic and magnetohydrodynamic numerical simulations using the PLUTO code. We then apply a modified version of the radiative transfer code PaRTY (Parallel Radiative Transfer in YSOs) to these HD/MHD simulations to calculate the observed intensity of these disks via thermal emission and scattering from the host star. Using a wide variety of stellar properties, disk structures, and planet masses, our goal is to produce a robust set of models that will be essential in analyzing the images taken with this new generation of telescopes.

  4. Distinguishing Recent Admixture from Ancestral Population Structure

    PubMed Central

    Slatkin, Montgomery

    2017-01-01

    We develop and test two methods for distinguishing between recent admixture and ancestral population structure as explanations for greater similarity of one of two populations to an outgroup population. This problem arose when Neanderthals were found to be slightly more similar to nonAfrican than to African populations. The excess similarity is consistent with both recent admixture from Neanderthals into the ancestors of nonAfricans and subdivision in the ancestral population. Although later studies showed that there had been recent admixture, distinguishing between these two classes of models will be important in other situations, particularly when high-coverage genomes cannot be obtained for all populations. One of our two methods is based on the properties of the doubly conditioned frequency spectrum combined with the unconditional frequency spectrum. This method does not require a linkage map and can be used when there is relatively low coverage. The second method uses the extent of linkage disequilibrium among closely linked markers. PMID:28186554

  5. Simple and accurate determination of sol-gel phase transition point using disk-type electromagnetically spinning viscosity measurement system

    NASA Astrophysics Data System (ADS)

    Hirano, Taichi; Sakai, Keiji

    2017-07-01

    We performed viscosity measurements with ultrahigh sensitivity by combining our original electromagnetically spinning technique and a newly developed floating disk probe. This system is, in principle, a torque-control-type viscometer with a noncontact function that can apply an arbitrary low torque, and therefore, enables us to clearly distinguish between liquids and solids from the viewpoint of the mechanical property of materials. In our measurements, we examined the difference in the thermoreversible sol-gel transition of a methylcellulose solution to determine the precise transition points, and successfully observed the hysteresis behavior of the gelation and solation processes.

  6. Fallback Disks, Magnetars and Other Neutron Stars

    NASA Astrophysics Data System (ADS)

    Alpar, M. Ali; Çalışkan, Ş.; Ertan, Ü.

    2013-02-01

    The presence of matter with angular momentum, in the form of a fallback disk around a young isolated neutron star will determine its evolution. This leads to an understanding of many properties of different classes of young neutron stars, in particular a natural explanation for the period clustering of AXPs, SGRs and XDINs. The spindown or spinup properties of a neutron star are determined by the dipole component of the magnetic field. The natural possibility that magnetars and other neutron stars may have different strengths of the dipole and higher multipole components of the magnetic field is now actually required by observations on the spindown rates of some magnetars. This talk gives a broad overview and some applications of the fallback disk model to particular neutron stars. Salient points are: (i) A fallback disk has already been observed around the AXP 4U 0142+61 some years ago. (ii) The low observed spindown rate of the SGR 0418+5729 provides direct evidence that the dipole component of the field is in the 1012 G range. All properties of the SGR 0418+5729 at its present age can be explained by spindown under torques from a fallback disk. (iii) The anomalous braking index of PSR J1734-3333 can also be explained by the fallback disk model which gives the luminosity, period, period derivative and the period second derivative at the present age. (iv) These and all applications to a variety of other sources employ the same disk physics and evolution, differing only in the initial conditions of the disk.

  7. Exact general relativistic disks with magnetic fields

    NASA Astrophysics Data System (ADS)

    Letelier, Patricio S.

    1999-11-01

    The well-known ``displace, cut, and reflect'' method used to generate cold disks from given solutions of Einstein equations is extended to solutions of Einstein-Maxwell equations. Four exact solutions of the these last equations are used to construct models of hot disks with surface density, azimuthal pressure, and azimuthal current. The solutions are closely related to Kerr, Taub-NUT, Lynden-Bell-Pinault, and to a one-soliton solution. We find that the presence of the magnetic field can change in a nontrivial way the different properties of the disks. In particular, the pure general relativistic instability studied by Bic̆ák, Lynden-Bell, and Katz [Phys. Rev. D 47, 4334 (1993)] can be enhanced or cured by different distributions of currents inside the disk. These currents, outside the disk, generate a variety of axial symmetric magnetic fields. As far as we know these are the first models of hot disks studied in the context of general relativity.

  8. Signatures Of Secular Evolution In Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Díaz-García, Simón

    2016-09-01

    In this thesis we shed light on the formation and evolution of disk galaxies, which often host a stellar bar (about 2/3 of cases). In particular, we address the bar-driven secular evolution, that is, the steady redistribution of stellar and gaseous material through the disk induced by the bar torques and resonances. We characterize the mass distribution of the disks in the Spitzer Survey of Stellar Structure in Galaxies (S4G, Sheth et al. 2010) and study the properties of the different stellar structure components and the interplay between them.We use 3.6 μm photometry for ˜1300 face-on and moderately inclined disk galaxies to analyze the frequency, dimensions, orientations and shapes of stellar bars, spiral arms, rings, (ring)lenses, and barlenses (i.e. lens-like structures embedded in the bars). We calculate the strength of the bars in the S4G via ellipse fitting, Fourier decomposition of the galaxy images, and from the gravitational tangential-to-radial forces. We also estimate the stellar contribution to the circular velocity, allowing us to analyze the coupling between non-baryonic and stellar matter within the optical disk. We average stellar density profiles (1D), the disk(+bulge) component of the rotation curve, and stellar bars (2D) as a function of fundamental galaxy parameters.We complement the study with integral-field unit kinematic data from Seidel et al. (2015b) for a subsample of 16 S4G barred galaxies. We quantify the bar-induced perturbation strengths in the stellar and gaseous disk from the kinematics, and show that they agree with the estimates obtained from the images. We also use Hα Fabry-Perot observations from Erroz-Ferrer et al. (2015) for 29 S4G disk galaxies to study the inner slope of the rotation curves.We provide possible observational evidence for the growth of bars in a Hubble time. We demonstrate the role of bars causing the spreading of the disk and the enhancement of the central stellar concentration. Our observations support

  9. Organizing Your Hard Disk.

    ERIC Educational Resources Information Center

    Stocker, H. Robert; Hilton, Thomas S. E.

    1991-01-01

    Suggests strategies that make hard disk organization easy and efficient, such as making, changing, and removing directories; grouping files by subject; naming files effectively; backing up efficiently; and using PATH. (JOW)

  10. Organizing Your Hard Disk.

    ERIC Educational Resources Information Center

    Stocker, H. Robert; Hilton, Thomas S. E.

    1991-01-01

    Suggests strategies that make hard disk organization easy and efficient, such as making, changing, and removing directories; grouping files by subject; naming files effectively; backing up efficiently; and using PATH. (JOW)

  11. Planet Forming Protostellar Disks

    NASA Technical Reports Server (NTRS)

    Lubow, Stephen

    1998-01-01

    The project achieved many of its objectives. The main area of investigation was the interaction of young binary stars with surrounding protostellar disks. A secondary objective was the interaction of young planets with their central stars and surrounding disks. The grant funds were used to support visits by coinvestigators and visitors: Pawel Artymowicz, James Pringle, and Gordon Ogilvie. Funds were also used to support travel to meetings by Lubow and to provide partial salary support.

  12. Protostars and Disks

    NASA Technical Reports Server (NTRS)

    Ho, Paul

    1997-01-01

    The research concentrated on high angular resolution (arc-second scale) studies of molecular cloud cores associated with very young star formation. New ways to study disks and protoplanetary systems were explored. Findings from the areas studied are briefly summarized: (1) molecular clouds; (2) gravitational contraction; (3) jets, winds, and outflows; (4) Circumstellar Disks (5) Extrasolar Planetary Systems. A bibliography of publications and submitted papers produced during the grant period is included.

  13. Be Star Disks from a Polarimetric Perspective

    NASA Astrophysics Data System (ADS)

    Jones, C. E.; Halonen, R. J.; Demers, Z. T.

    2016-11-01

    The intrinsic linearly polarized light arising from electron scattering of stellar radiation in a non-spherically symmetric distribution of gas is a characterizing feature of classical Be stars. The spectropolarimetric signature provides a means for directly probing the physical and geometric properties of the gaseous material enveloping these rapidly rotating massive stars. Using a Monte Carlo radiative transfer computation and a self-consistent radiative equilibrium solution for the circumstellar gas, we explore the role of this observable property in investigating the dynamic nature of classical Be star disks. In particular, we focus on the potential for providing polarimetric diagnostics of mass-loss events and for tracing the evolution of the gas in a circumstellar disk. This context for interpreting the observed linear polarization signature can play an important role in identifying the physical process(es) which govern the formation and dissipation of these disks.

  14. Optic disk drusen.

    PubMed

    Auw-Haedrich, Claudia; Staubach, Flemming; Witschel, Heinrich

    2002-01-01

    Optic disk drusen occur in 3.4 to 24 per 1,000 population and are bilateral in approximately 75%. Disturbance in the axonal metabolism in the presence of a small scleral canal--regardless of eyelength--is considered responsible for the development. The drusen increase in size, becoming more visible with age due to continuing calcium apposition, and they are associated with visual field defects in a considerable number of patients. Patients do not usually notice these defects, despite their progressive nature over the years, and this indicates an insidious course. A correct diagnosis of optic disk drusen is mandatory, although effective treatment is not yet available. It is most important to differentiate optic disk drusen from papilledema in order to avoid unnecessary neurological examinations, but also to avoid overlooking genuine neurologic disorders. Because optic disk drusen can cause severe visual field defects, patients require individual consultation regarding work issues and whether or not to drive. Optic disk drusen can be accompanied by vascular complications as well. In some cases these vascular changes--for example, choroidal neovascularization--are treatable. Patients with optic disk drusen should undergo regular visual field, IOP, and nerve fiber layer examinations. In patients with deteriorating visual field and borderline IOP, we recommend antiglaucomatous therapy.

  15. Disk Precession in Pleione

    NASA Astrophysics Data System (ADS)

    Hirata, R.

    2007-03-01

    From the polarimetric observation of Pleione, we found that the intrinsic polarization angle varied from 60° to 130° in 1974-2003. The Hα profile also changed dramatically from the edge-on type (shell-line profile) to the surface-on type (wine-bottle profile). These facts clearly indicate the spatial motion of the disk axis. We interpret these variations in terms of the disk precession, caused by the secondary of this spectroscopic binary with a period of 218d. We performed the χ^2 minimization for the polarization angle, assuming uniform precession with an imposed condition that the shell maximum occurred at edge-on view. The resulting precession angle is 59° with a period of 81 years. Then, we can describe chronologically the spatial motion of disk axis. We also derived the Hα disk radius from the peak separation, assuming the Keplerian disk. The precession of the disk gives natural explanation of the mysterious long-term spectroscopic behaviors of this star.

  16. Star formation rates and abundance gradients in disk galaxies

    NASA Technical Reports Server (NTRS)

    Wyse, Rosemary F. G.; Silk, Joseph

    1989-01-01

    Analytic models for the evolution of disk galaxies are presented, placing special emphasis on the radial properties. These models are straightforward extensions of the original Schmidt (1959, 1963) models, with a dependence of star formation rate on gas density. The models provide successful descriptions of several measures of galactic disk evolution, including solar neighborhood chemical evolution, the presence and amplitude of metallicity and color gradients in disk galaxies, and the global rates of star formation in disk galaxies, and aid in the understanding of the apparent connection between young and old stellar populations in spiral galaxies.

  17. Tracking debris disks within the Beta Pictoris Moving Group

    NASA Astrophysics Data System (ADS)

    Debes, J.

    2014-09-01

    Beta Pictoris represents a stunning example of a young planetary system with a debris disk, moving through local space with a host of other co-eval companion stars. These fellow travelers provide additional understanding for placing the Beta Pictoris disk into a proper context with regards to planet formation throughout the galaxy and our own Solar System. I will review the members of the Beta Pictoris moving group and catalog the latest results regarding the presence and understanding of debris disks around these other systems. Since these stars are close and very young, they represent an excellent opportunity for understanding the structure, composition, and grain properties of debris disks.

  18. Microlensing and the structure of active galactic nucleus accretion disks

    NASA Technical Reports Server (NTRS)

    Rauch, Kevin P.; Blandford, Roger D.

    1991-01-01

    Rapid variability has been reported in two of the four gravitationally lensed images of Q2237 + 0305, and this is attributed to microlensing caused by the intervening stars. The associated constraints on the source size and properties are studied and compared with a variety of stationary accretion disk models. The reported microlensing variation in Q2237 + 0305 requires the disk size to be over 3 times smaller than a blackbody disk of similar luminosity, implying that the optical emission is either nonthermal or optically tin. An exploration of nonstationary disk models including orbiting, transient hot spots leads to a similar conclusion. Implications for models of active galactic nucleus optical continua are briefly discussed.

  19. Modeling Protostar Envelopes and Disks Seen With ALMA

    NASA Astrophysics Data System (ADS)

    Terebey, Susan; Flores-Rivera, Lizxandra; Willacy, Karen

    2017-01-01

    Thermal continuum emission from protostars comes from both the envelope and circumstellar disk. The dust emits on a variety of spatial scales, ranging from sub-arcseconds for disks to roughly 10 arcseconds for envelopes for nearby protostars. We present models of what ALMA should detect that incorporate a self-consistent collapse solution, radiative transfer, and realistic dust properties.

  20. The MAD View on the Outskirts of Disks

    NASA Astrophysics Data System (ADS)

    Carollo, C. M.; Erroz-Ferrer, S.; den Brok, M.; Fagioli, M.; Onodera, M.; Tacchella, S. MAD Collaboration

    2017-03-01

    We present the MUSE Atlas of Disks (MAD), a GTO program with the MUSE spectrograph on the ESO/VLT that is dedicated to the study of the optical spectroscopic properties of z = 0 disk galaxies on the star-forming `Main Sequence' at < 100 pc physical resolution. MUSE pointings on the MAD galaxies extend out to ~ 2 disk scale lengths, enabling to investigate the bulge and inner disk properties of galaxies with different outer disks. Here we specifically compare, at constant stellar-mass, the stellar population properties of the inner components in disks with down-bending (Type II) and up-bending (Type III) outer profiles. We highlight similarities in the inner stellar properties of such different hosts, which point at a universal inside-out growth of disks, as well as differences which suggest an additional role of stellar migration and/or gas accretion in the growth of disk galaxies with an outer up-bending profile, as expected from theoretical models.

  1. A disk of scattered icy objects and the origin of Jupiter-family comets.

    PubMed

    Duncan, M J; Levison, H F

    1997-06-13

    Orbital integrations carried out for 4 billion years produced a disk of scattered objects beyond the orbit of Neptune. Objects in this disk can be distinguished from Kuiper belt objects by a greater range of eccentricities and inclinations. This disk was formed in the simulations by encounters with Neptune during the early evolution of the outer solar system. After particles first encountered Neptune, the simulations show that about 1 percent of the particles survive in this disk for the age of the solar system. A disk currently containing as few as approximately 6 x 10(8) objects could supply all of the observed Jupiter-family comets. Two recently discovered objects, 1996 RQ20 and 1996 TL66, have orbital elements similar to those predicted for objects in this disk, suggesting that they are thus far the only members of this disk to be identified.

  2. DEEP MIPS OBSERVATIONS OF THE IC 348 NEBULA: CONSTRAINTS ON THE EVOLUTIONARY STATE OF ANEMIC CIRCUMSTELLAR DISKS AND THE PRIMORDIAL-TO-DEBRIS DISK TRANSITION

    SciTech Connect

    Currie, Thayne; Kenyon, Scott J. E-mail: skenyon@cfa.harvard.edu

    2009-09-15

    We describe new, deep MIPS photometry and new high signal-to-noise optical spectroscopy of the 2.5 Myr old IC 348 Nebula. To probe the properties of the IC 348 disk population, we combine these data with previous optical/infrared photometry and spectroscopy to identify stars with gas accretion, to examine their mid-IR colors, and to model their spectral energy distributions. IC 348 contains many sources in different evolutionary states, including protostars and stars surrounded by primordial disks, two kinds of transitional disks, and debris disks. Most disks surrounding early/intermediate spectral-type stars (>1.4 M {sub sun} at 2.5 Myr) are debris disks; most disks surrounding solar and subsolar-mass stars are primordial disks. At the 1-2 {sigma} level, more massive stars also have a smaller frequency of gas accretion and smaller mid-IR luminosities than lower-mass stars. These trends are suggestive of a stellar mass-dependent evolution of disks, where most disks around high/intermediate-mass stars shed their primordial disks on rapid, 2.5 Myr timescales. The frequency of MIPS-detected transitional disks is {approx}15%-35% for stars plausibly more massive than 0.5 M {sub sun}. The relative frequency of transitional disks in IC 348 compared to that for 1 Myr old Taurus and 5 Myr old NGC 2362 is consistent with a transition timescale that is a significant fraction of the total primordial disk lifetime.

  3. Deep MIPS Observations of the IC 348 Nebula: Constraints on the Evolutionary State of Anemic Circumstellar Disks and the Primordial-to-Debris Disk Transition

    NASA Astrophysics Data System (ADS)

    Currie, Thayne; Kenyon, Scott J.

    2009-09-01

    We describe new, deep MIPS photometry and new high signal-to-noise optical spectroscopy of the 2.5 Myr old IC 348 Nebula. To probe the properties of the IC 348 disk population, we combine these data with previous optical/infrared photometry and spectroscopy to identify stars with gas accretion, to examine their mid-IR colors, and to model their spectral energy distributions. IC 348 contains many sources in different evolutionary states, including protostars and stars surrounded by primordial disks, two kinds of transitional disks, and debris disks. Most disks surrounding early/intermediate spectral-type stars (>1.4 M sun at 2.5 Myr) are debris disks; most disks surrounding solar and subsolar-mass stars are primordial disks. At the 1-2 σ level, more massive stars also have a smaller frequency of gas accretion and smaller mid-IR luminosities than lower-mass stars. These trends are suggestive of a stellar mass-dependent evolution of disks, where most disks around high/intermediate-mass stars shed their primordial disks on rapid, 2.5 Myr timescales. The frequency of MIPS-detected transitional disks is ≈15%-35% for stars plausibly more massive than 0.5 M sun. The relative frequency of transitional disks in IC 348 compared to that for 1 Myr old Taurus and 5 Myr old NGC 2362 is consistent with a transition timescale that is a significant fraction of the total primordial disk lifetime.

  4. Structure of force networks in tapped particulate systems of disks and pentagons. I. Clusters and loops.

    PubMed

    Pugnaloni, Luis A; Carlevaro, C Manuel; Kramár, M; Mischaikow, K; Kondic, L

    2016-06-01

    The force network of a granular assembly, defined by the contact network and the corresponding contact forces, carries valuable information about the state of the packing. Simple analysis of these networks based on the distribution of force strengths is rather insensitive to the changes in preparation protocols or to the types of particles. In this and the companion paper [Kondic et al., Phys. Rev. E 93, 062903 (2016)10.1103/PhysRevE.93.062903], we consider two-dimensional simulations of tapped systems built from frictional disks and pentagons, and study the structure of the force networks of granular packings by considering network's topology as force thresholds are varied. We show that the number of clusters and loops observed in the force networks as a function of the force threshold are markedly different for disks and pentagons if the tangential contact forces are considered, whereas they are surprisingly similar for the network defined by the normal forces. In particular, the results indicate that, overall, the force network is more heterogeneous for disks than for pentagons. Such differences in network properties are expected to lead to different macroscale response of the considered systems, despite the fact that averaged measures (such as force probability density function) do not show any obvious differences. Additionally, we show that the states obtained by tapping with different intensities that display similar packing fraction are difficult to distinguish based on simple topological invariants.

  5. Secular Evolution in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Kormendy, John

    2013-10-01

    Self-gravitating systems evolve toward the most tightly bound configuration that is reachable via the evolution processes that are available to them. They do this by spreading -- the inner parts shrink while the outer parts expand -- provided that some physical process efficiently transports energy or angular momentum outward. The reason is that self-gravitating systems have negative specific heats. As a result, the evolution of stars, star clusters, protostellar and protoplanetary disks, black hole accretion disks and galaxy disks are fundamentally similar. How evolution proceeds then depends on the evolution processes that are available to each kind of self-gravitating system. These processes and their consequences for galaxy disks are the subjects of my lectures and of this Canary Islands Winter School. I begin with a review of the formation, growth and death of bars. Then I review the slow (`secular') rearrangement of energy, angular momentum, and mass that results from interactions between stars or gas clouds and collective phenomena such as bars, oval disks, spiral structure and triaxial dark haloes. The `existence-proof' phase of this work is largely over: we have a good heuristic understanding of how nonaxisymmetric structures rearrange disk gas into outer rings, inner rings and stuff dumped onto the centre. The results of simulations correspond closely to the morphology of barred and oval galaxies. Gas that is transported to small radii reaches high densities. Observations confirm that many barred and oval galaxies have dense central concentrations of gas and star formation. The result is to grow, on timescales of a few Gyr, dense central components that are frequently mistaken for classical (elliptical-galaxy-like) bulges but that were grown slowly out of the disk (not made rapidly by major mergers). The resulting picture of secular galaxy evolution accounts for the richness observed in galaxy structure. We can distinguish between classical and pseudo

  6. Fast, Capacious Disk Memory Device

    NASA Technical Reports Server (NTRS)

    Muller, Ronald M.

    1990-01-01

    Device for recording digital data on, and playing back data from, memory disks has high recording or playback rate and utilizes available recording area more fully. Two disks, each with own reading/writing head, used to record data at same time. Head on disk A operates on one of tracks numbered from outside in; head on disk B operates on track of same number in sequence from inside out. Underlying concept of device applicable to magnetic or optical disks.

  7. Chemistry in disks. X. The molecular content of protoplanetary disks in Taurus

    NASA Astrophysics Data System (ADS)

    Guilloteau, S.; Reboussin, L.; Dutrey, A.; Chapillon, E.; Wakelam, V.; Piétu, V.; Di Folco, E.; Semenov, D.; Henning, Th.

    2016-08-01

    Aims: We attempt to determine the molecular composition of disks around young low-mass stars. Methods: We used the IRAM 30 m radio telescope to perform a sensitive wideband survey of 30 stars in the Taurus Auriga region known to be surrounded by gaseous circumstellar disks. We simultaneously observed HCO+(3-2), HCN(3-2), C2H(3-2), CS(5-4), and two transitions of SO. We combined the results with a previous survey that observed 13CO (2-1), CN(2-1), two o-H2CO lines, and another transition of SO. We used available interferometric data to derive excitation temperatures of CN and C2H in several sources. We determined characteristic sizes of the gas disks and column densities of all molecules using a parametric power-law disk model. Our study is mostly sensitive to molecules at 200-400 au from the stars. We compared the derived column densities to the predictions of an extensive gas-grain chemical disk model under conditions representative of T Tauri disks. Results: This survey provides 20 new detections of HCO+ in disks, 18 in HCN, 11 in C2H, 8 in CS, and 4 in SO. HCO+ is detected in almost all sources and its J = 3-2 line is essentially optically thick, providing good estimates of the disk radii. The other transitions are (at least partially) optically thin. Large variations of the column density ratios are observed, but do not correlate with any specific property of the star or disk. Disks around Herbig Ae stars appear less rich in molecules than those around T Tauri stars, although the sample remains small. SO is only found in the (presumably younger) embedded objects, perhaps reflecting an evolution of the S chemistry due to increasing depletion with time. Overall, the molecular column densities, and in particular the CN/HCN and CN/C2H ratios, are well reproduced by gas-grain chemistry in cold disks. Conclusions: This study provides a comprehensive census of simple molecules in disks of radii >200-300 au. Extending that to smaller disks, or searching for less

  8. Lupus disks with faint CO isotopologues: low gas/dust or high carbon depletion?

    NASA Astrophysics Data System (ADS)

    Miotello, A.; van Dishoeck, E. F.; Williams, J. P.; Ansdell, M.; Guidi, G.; Hogerheijde, M.; Manara, C. F.; Tazzari, M.; Testi, L.; van der Marel, N.; van Terwisga, S.

    2017-03-01

    Context. An era has started in which gas and dust can be observed independently in protoplanetary disks, thanks to the recent surveys with the Atacama Large Millimeter/sub-millimeter Array (ALMA). The first near-complete high-resolution disk survey in both dust and gas in a single star-forming region has been carried out in Lupus, finding surprisingly low gas-to-dust ratios. Aims: The goal of this work is to fully exploit CO isotopologue observations in Lupus, comparing them with physical-chemical model results, in order to obtain gas masses for a large number of disks and compare gas and dust properties. Methods: We have employed the grid of physical-chemical models presented previously to analyze continuum and CO isotopologue (13CO J = 3-2 and C18O J = 3-2) observations of Lupus disks, including isotope-selective processes and freeze-out. We also employed the ALMA 13CO-only detections to calculate disk gas masses for a total of 34 sources, which expands the sample of 10 disks reported earlier, where C18O was also detected. Results: We confirm that overall gas-masses are very low, often lower than 1MJ, when volatile carbon is not depleted. Accordingly, global gas-to-dust ratios are much lower than the expected interstellar-medium value of 100, which is predominantly between 1 and 10. Low CO-based gas masses and gas-to-dust ratios may indicate rapid loss of gas, or alternatively chemical evolution, for example, through sequestering of carbon from CO to more complex molecules, or carbon locked up in larger bodies. Conclusions: Current ALMA observations of 13CO and continuum emission cannot distinguish between these two hypotheses. We have simulated both scenarios, but chemical model results do not allow us to rule out one of the two, pointing to the need to calibrate CO-based masses with other tracers. Assuming that all Lupus disks have evolved mainly as a result of viscous processes over the past few Myr, the previously observed correlation between the current mass

  9. Mixing of dust in protoplanetary disks and the solar nebula

    NASA Astrophysics Data System (ADS)

    Hughes, Anna Louise Haugsjaa

    Understanding the small-dust component of protoplanetary disks is key to understanding the conditions for planet formation. Small dust grains, particularly at large distances, provide our primary observational window into the physics of protoplanetary disks, being much more easily observed than the gas component. Furthermore, the distribution of these grains must ultimately control the timing and locations for planetesimal formation, the first major step toward planet formation. For my thesis work, I have used numerical simulations to model the radial distribution of dust grains as they are acted upon by the gas disk, including the evolution of the disk (outward expansion and inward accretion), radial and azimuthal drag of the gas flow on the particle orbits, and turbulent mixing of the particle ensemble radially within the disk. I have run simulations using a range of particle sizes and disk-model parameters and consider primarily two phenomena: the radial diffusion of hot, inner disk particles outward to large AU, relevant to the compositional makeup of bodies within our own solar system, and the time evolution of the global dust-to-gas ratio, which dictates the supply of solid material to the planetesimal- and planet-forming regions. I find that, while the degree out outward mixing depends sensitively on a number of disk-model parameters, the behavior of the global dust-to-gas distribution is relatively uniform between different disk-model simulations, suggesting that, while still mysterious, the conditions for planetesimal formation are commonly met across a range of disk configurations. Observed disk compositions correlate poorly with most observable disk parameters. However, my simulations suggest compositional properties are most-strongly controll= ed by the initial conditions of young disk systems.

  10. Epsilon Aurigae: a Laboratory for Understanding Circumstellar Disk Physics

    NASA Astrophysics Data System (ADS)

    Stencel, Robert; Ake, Thomas; Backman, Dana; Guinan, Edward

    2005-06-01

    Circumstellar disks are now known to be common around young stellar objects. However, their dimensions and compositions are measured only with difficulty. Models suffer from lack of key constraints. The disk around the secondary in the epsilon Aurigae binary, in contrast, has some well-determined properties. A disk is inferred from eclipse circumstances to be a 20 AU diameter, viewed edge-on & partially covers the F0 supergiant primary star for 2 full years during the 27 year binary period. This disk was discovered to be a strong thermal IR source during the 1982-84 eclipse, in part by IRAS. We seek IRS & MIPS SED data to clarify the nature and evolutionary status of this large protoplanetary-like disk & help to better constrain a class of disk models. This is among the most massive stellar systems with a disk. Its dimensions are well-known from the eclipse light curve. Temperature of the disk facing us during eclipse is known from its IR SED; the composition & velocities of gas from the secondary are known from absorption lines detected in the last eclipse. The mass of the system & proximity of the disk to the luminous primary star let us explore extremes of circumstellar disk physics. The secondary now is near quadrature, the time of most rapidly changing geometric aspect, so that measurements now give best resolution of temperature versus azimuth angle around the disk. Our goals include: More precisely defining temperature & projected size of the disk-shaped IR-emitting secondary object via IRS and MIPS measurements; Searching with IRS for emission and absorption features, against the cool secondary; Determining grain composition & properties via the full range of SST spectroscopy coverage [IRS & MIPS SED]; Seeking evidence for mass-loss history in extended material around the system [MIPS]; Establishing baselines of these & other measures for comparison during forthcoming eclipse campaigns (2009). It is only with SST that these science goals can be accomplished.

  11. A Pulsar and a Disk

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-07-01

    V appeared.Hong and collaborators were then left with the task of piecing together this strange behavior into a picture of what was happening with this binary system.The authors proposed model for SXP 214. Here the binary has a ~30-day orbit tilted at 15 to the circumstellar disk. The pulsar passes through the circumstellar disk of its companion once per orbit. The interval marked A (orange line) is suggested as the period of time corresponding to the Chandra observations in this study: just as the neutron star is emerging from the disk after passing through it. [Hong et al. 2016]Passing Through a DiskIn the model the authors propose, the pulsar is on a ~30-day eccentric orbit that takes it through the circumstellar disk of its companion once per orbit.In this picture, the authors Chandra detections must have been made just as the pulsar was emerging from the circumstellar disk. The disk had initially hidden the soft X-ray emission from the pulsar, but as the pulsar emerged, that component became brighter, causing both the overall rise in X-ray counts and the shift in the spectrum to lower energies.Since the pulsars accretion is fueled by material picked up as it passes through the circumstellar disk, the accretion from a recent passage through the disk likely also caused the observed spin-up to the shorter period.If the authors model is correct, this series of observations of the pulsar as it emerges from the disk provides a rare opportunity to examine what happens to X-ray emission during this passage. More observations of this intriguing system can help us learn about the properties of the disk and the emission geometry of the neutron star surface.CitationJaeSub Hong et al 2016 ApJ 826 4. doi:10.3847/0004-637X/826/1/4

  12. Distinguishing cellulitis from its mimics.

    PubMed

    Keller, Emily C; Tomecki, Kenneth J; Alraies, M Chadi

    2012-08-01

    Distinguishing true cellulitis from its many imitators is challenging but critical if we are to avoid unnecessary use of antibiotics and delays in treatment. Common imitators of cellulitis are stasis dermatitis, lipodermatosclerosis, contact dermatitis, lymphedema, eosinophilic cellulitis, and papular urticaria. Specific criteria do not exist for the diagnosis of cellulitis, but the alert physician can find clues in the history and physical examination that point toward cellulitis.

  13. Characterizing Debris Disks Around Young Suns

    NASA Astrophysics Data System (ADS)

    Rieke, George; Gorlova, Nadya; Muzerolle, James; Rebull, Luisa; Siegler, Nick; Stauffer, John; Su, Kate; Young, Erick

    2006-05-01

    There is geological evidence that in the first few hundred Myr of the birth of the Solar System there was an epoch of strong bombardment caused by the collisions between growing planetesimals. Spitzer has the capability to probe that epoch in other stars by observing dust emission from debris disks around young solar system analogs. The MIPS GTO and FEPS Legacy teams have carried out a 24 micron survey of debris disks in a number of rich open clusters, with ages ranging from a few to 100 Myr. However, only a few of these clusters are close enough to detect fluxes in the MIPS bands to photospheric levels in solar mass stars; even fewer are close enough (<160 pc) to study disk properties by means of IRS spectroscopy. This proposal consists of two parts. 1) We will build on our previous investigation of the Pleiades core where we discovered a few solar analogs with MIPS excesses signaling debris disks. The excess fraction is tentatively bigger than among older field stars. To confirm this conclusion, we propose to observe the remaining F-G stars that are situated in the Pleiades corona and thus less affected by interstellar cirrus. 2) We will obtain IRS spectra for debris candidates in the Pleiades (100 Myr) as well as in two other intermediate-age clusters -- IC 2391 (50 Myr) and M47 (80 Myr). Disk spectra will allow us to constrain the disk geometry and other properties of debris dust, and to search for correlations of theses properties with the spectral type/mass of the host star. The IRS sample includes a range of spectral types from A to G stars. This program will provide the first representative sample of dust emission spectra at the intermediate age of 50-100 Myr, which likely corresponds to the final stages of terrestrial planet formation.

  14. Bimodality of Circumstellar Disk Evolution Induced by the Hall Current

    NASA Astrophysics Data System (ADS)

    Tsukamoto, Y.; Iwasaki, K.; Okuzumi, S.; Machida, M. N.; Inutsuka, S.

    2015-09-01

    The formation process of circumstellar disks is still controversial because of the interplay of complex physical processes that occurs during the gravitational collapse of prestellar cores. In this study, we investigate the effect of the Hall current term on the formation of the circumstellar disk using three-dimensional simulations. In our simulations, all non-ideal effects, as well as the radiation transfer, are considered. The size of the disk is significantly affected by a simple difference in the inherent properties of the prestellar core, namely whether the rotation vector and the magnetic field are parallel or anti-parallel. In the former case, only a very small disk (\\lt 1 {AU}) is formed. On the other hand, in the latter case, a massive and large (\\gt 20 {AU}) disk is formed in the early phase of protostar formation. Since the parallel and anti-parallel properties do not readily change, we expect that the parallel and anti-parallel properties are also important in the subsequent disk evolution and the difference between the two cases is maintained or enhanced. This result suggests that the disk size distribution of the Class 0 young stellar objects is bimodal. Thus, the disk evolution can be categorized into two cases and we may call the parallel and anti-parallel systems Ortho-disk and Para-disk, respectively. We also show that the anti-rotating envelopes against the disk rotation appear with a size of ≳ 200 {AU}. We predict that the anti-rotating envelope will be found in the future observations.

  15. EMERGENT SPECTRA FROM DISKS SURROUNDING KERR BLACK HOLES: EFFECT OF PHOTON TRAPPING AND DISK SELF-SHADOWING

    SciTech Connect

    Li Guangxing; Yuan Yefei; Cao Xinwu E-mail: yfyuan@ustc.edu.c

    2010-05-20

    Based on a new estimation of their thickness, the global properties of relativistic slim accretion disks are investigated in this work. The resulting emergent spectra are calculated using the relativistic ray-tracing method, in which we neglect the self-irradiation of the accretion disk. The angular dependence of the disk luminosity, the effects of the heat advection, and the disk thickness on the estimation of the black hole spin are discussed. Compared with the previous works, our improvements are that we use the self-consistent disk equations and we consider the disk self-shadowing effect. We find that at the moderate accretion rate, the radiation trapped in the outer region of the accretion disks will escape in the inner region of the accretion disk and contribute to the emergent spectra. At the high accretion rate, for the large inclination and large black hole spin, both the disk thickness and the heat advection have significant influence on the emergent spectra. Consequently, these effects will influence the measurement of the black hole spin based on the spectra fitting and influence the angular dependence of the luminosity. For the disks around Kerr black holes with a = 0.98, if the disk inclination is greater than 60{sup 0}, and their luminosity is beyond 0.2 Eddington luminosity, the spectral model which is based on the relativistic standard accretion disk is no longer applicable for the spectra fitting. We also confirm that the effect of the self-shadowing is significantly enhanced by the light bending, which implies that the non-relativistic treatment of the self-shadowing is inaccurate. According to our results, the observed luminosity dependence of the measured spin suggests that the disk self-shadowing significantly shapes the spectra of GRS 1915+105, which might lead to the underestimation of the black hole spin for the high luminosity states.

  16. Winds from disks in compact binaries

    SciTech Connect

    Mauche, C.W.

    1993-10-27

    We herein present an observational and theoretical review of the winds of compact binaries. After a brief consideration of the accretion disk coronae and winds of X-ray binaries, the review concentrates on the winds of cataclysmic variables (CVs). Specifically, we consider the related problems of the geometry and mass-loss rate of the winds of CVs, their ionization state and variability, and the results from studies of eclipsing CVs. Finally, the properties of bona fide accretion disk wind models are reviewed.

  17. Terrestrial Planet Growth in Circumbinary Disks

    NASA Technical Reports Server (NTRS)

    Lissauer, J. J.; Quintana, E. V.

    2006-01-01

    We examine the accuulation of terrestrial from circumbinary disks surrounding pairs of stars with masses of either 0.5 solar masses each or 0.8 and 0.2 solar masses and orbital separations of 0.05 AU to 0.4 AU by performing numerical simulations of the late stages of planetary growth. Initial disks contain about 2.6 Earth masses of lunar to Mars-sized bodies orbiting within 2 AU of the center of mass of the system, plus giant planets with masses and orbits analogous to those of Jupiter and Saturn. We also performed simulations using analogous disks orbiting single 1 solar mass stars. The dynamics of planetary growth is quite chaotic because the gravitational perturbations resulting from close approaches greatly amplify differences in orbits. Thus, several simulations of each configuration were run with very slightly different initial conditions to enable us to distinguish systematic effects resulting from differences in the binary orbit (or differences of the initial orbits of the bodies within the disk) from pseudo-random variability in outcomes resulting from chaos. Most runs simulated 200 million years of evolution. At least one terrestrial planet remained at the end of each run; one simulation produced 6 terrestrial planets in a configuration that appears to be quite stable. The systems that formed around stars with binary apastron separations of less than 0.2 AU contained on average slightly more planets than those that formed around single stars, with the outermost planet typically orbiting at a greater distance from the system barycenter. Greater stellar separations tended to result in fewer planets, with the inner planet orbiting farther from the stars. More eccentric binaries have a more pronounced effect for the same apastron distance. The statistical distribution of final systems is not sensitive to moderate differences in the initial eccentricities of the bodies in the disk.

  18. Terrestrial Planet Growth in Circumbinary Disks

    NASA Technical Reports Server (NTRS)

    Lissauer, J. J.; Quintana, E. V.

    2006-01-01

    We examine the accuulation of terrestrial from circumbinary disks surrounding pairs of stars with masses of either 0.5 solar masses each or 0.8 and 0.2 solar masses and orbital separations of 0.05 AU to 0.4 AU by performing numerical simulations of the late stages of planetary growth. Initial disks contain about 2.6 Earth masses of lunar to Mars-sized bodies orbiting within 2 AU of the center of mass of the system, plus giant planets with masses and orbits analogous to those of Jupiter and Saturn. We also performed simulations using analogous disks orbiting single 1 solar mass stars. The dynamics of planetary growth is quite chaotic because the gravitational perturbations resulting from close approaches greatly amplify differences in orbits. Thus, several simulations of each configuration were run with very slightly different initial conditions to enable us to distinguish systematic effects resulting from differences in the binary orbit (or differences of the initial orbits of the bodies within the disk) from pseudo-random variability in outcomes resulting from chaos. Most runs simulated 200 million years of evolution. At least one terrestrial planet remained at the end of each run; one simulation produced 6 terrestrial planets in a configuration that appears to be quite stable. The systems that formed around stars with binary apastron separations of less than 0.2 AU contained on average slightly more planets than those that formed around single stars, with the outermost planet typically orbiting at a greater distance from the system barycenter. Greater stellar separations tended to result in fewer planets, with the inner planet orbiting farther from the stars. More eccentric binaries have a more pronounced effect for the same apastron distance. The statistical distribution of final systems is not sensitive to moderate differences in the initial eccentricities of the bodies in the disk.

  19. THE OUTER DISKS OF DWARF IRREGULAR GALAXIES

    SciTech Connect

    Hunter, Deidre A.; Massey, Philip; Wilsey, Nick; Riabokin, Malanka; Elmegreen, Bruce G.; Oh, Se-Heon; Anderson, Ed; Nordgren, Tyler E. E-mail: phil.massey@lowell.edu E-mail: riabokin@msu.edu E-mail: seheon-oh@ast.uct.ac.za E-mail: tyler_nordgren@redlands.edu

    2011-10-15

    In order to explore the properties of extreme outer stellar disks, we obtained ultra-deep V and GALEX ultraviolet (UV) images of four dwarf irregular galaxies and one blue compact dwarf galaxy, and ultra-deep B images of three of these. Our V-band surface photometry extends to 29.5 mag arcsec{sup -2}. We convert the FUV and V-band photometry, along with H{alpha} photometry obtained in a larger survey, into radial star formation rate profiles that are sensitive to timescales from 10 Myr to the lifetime of the galaxy. We also obtained H I-line emission data and compare the stellar distributions, surface brightness profiles, and star formation rate profiles to H I-line emission maps, gas surface density profiles, and gas kinematics. Our data lead us to two general observations. First, the exponential disks in these irregular galaxies are extraordinarily regular. We observe that the stellar disks continue to decline exponentially as far as our measurements extend. In spite of lumpiness in the distribution of young stars and H I distributions and kinematics that have significant unordered motions, sporadic processes that have built the disks-star formation, radial movement of stars, and perhaps even perturbations from the outside-have, nevertheless, conspired to produce standard disk profiles. Second, there is a remarkable continuity of star formation throughout these disks over time. In four out of five of our galaxies the star formation rate in the outer disk measured from the FUV tracks that determined from the V-band, to within factors of five, requiring star formation at a fairly steady rate over the galaxy's lifetime. Yet, the H I surface density profiles generally decline with radius more shallowly than the stellar light, and the gas is marginally gravitationally stable against collapse into clouds. Outer stellar disks are challenging our concepts of star formation and disk growth and provide a critical environment in which to understand processes that mold

  20. Porous dust grains in circumstellar disks

    NASA Astrophysics Data System (ADS)

    Kirchschlager, Florian; Wolf, Sebastian

    2013-07-01

    We investigate the impact of porous dust grains on the structure and observable appearance of circumstellar disks (Kirchschlager & Wolf 2013). Our study is motivated by observations and laboratory studies which indicate that dust grains in various astrophysical environments are porous. In addition, the modeling of the spatial structure and grain size distribution of debris disks reveals that under the assumption of spherical compact grains the resulting minimum grain size is often significantly larger than the blowout size, which might be a hint for porosity. Using the discrete dipole approximation, we compute the optical properties of spherical, porous grains (Draine & Flatau 1994, 2010). Subsequently, we calculate the blowout sizes for various debris disk systems and grain porosities. We find that the blowout size increases with particle porosity and stellar temperature. In addition, the lower dust equilibrium temperature of porous particles results in a shift of the maximum of the thermal reemission of debris disks towards longer wavelengths. For our studies of the impact of dust grain porosity in protoplanetary disks we use the radiative transfer software MC3D, which is based on the Monte-Carlo method and solves the radiative transfer problem self-consistently (Wolf et al. 1999, Wolf 2003). We find that the spectral energy distribution of protoplanetary disks shows significant differences between the cases of porous and compact grains. In particular, the flux in the optical wavelength range is increased for porous grains. Furthermore, the silicate peak at ~9.8 microns exhibits a strong dependence on the degree of grain porosity. We also investigate the temperature distribution in the disk. In the midplane no influence of porosity is detectable, but in the vertical direction minor changes of a few Kelvin are found. To complete our study we outline the differences between the two grain types in maps of the linear polarization. We detect a polarization reversal in

  1. Radiative ablation of disks around massive stars

    NASA Astrophysics Data System (ADS)

    Kee, Nathaniel Dylan

    Hot, massive stars (spectral types O and B) have extreme luminosities (10. 4 -10. 6 L?) that drive strong stellar winds through UV line-scattering.Some massive stars also have disks, formed by either decretion from the star (as in the rapidly rotating "Classical Be stars"), or accretion during the star's formation. This dissertation examines the role of stellar radiation in driving (ablating) material away from these circumstellar disks. A key result is that the observed month to year decay of Classical Be disks can be explained by line-driven ablation without, as previously done, appealing to anomalously strong viscous diffusion. Moreover, the higher luminosity of O stars leads to ablation of optically thin disks on dynamical timescales of order a day, providing a natural explanation for the lack of observed Oe stars. In addition to the destruction of Be disks, this dissertation also introduces a model for their formation by coupling observationally inferred non-radial pulsation modes and rapid stellar rotation to launch material into orbiting Keplerian disks of Be-like densities. In contrast to such Be decretion disks, star-forming accretion disks are much denser and so are generally optically thick to continuum processes. To circumvent the computational challenges associated with radiation hydrodynamics through optically thick media, we develop an approximate method for treating continuum absorption in the limit of geometrically thin disks. The comparison of ablation with and without continuum absorption shows that accounting for disk optical thickness leads to less than a 50% reduction in ablation rate, implying that ablation rate depends mainly on stellar properties like luminosity. Finally, we discuss the role of "thin-shell mixing" in reducing X-rays from colliding wind binaries. Laminar, adiabatic shocks produce well understood X-ray emission, but the emission from radiatively cooled shocks is more complex due to thin-shell instabilities. The parameter

  2. Thermal Test on Target with Pressed Disks

    SciTech Connect

    Woloshun, Keith Albert; Dale, Gregory E.; Olivas, Eric Richard; Romero, Frank Patrick; Dalmas, Dale Allen; Chemerisov, Sergey; Gromov, Roman; Lowden, Rick

    2016-05-27

    A thorough test of the thermal performance of a target for Mo99 production using solid Mo100 target to produce the Mo99 via a gamma-n reaction has previously been conducted at Argonne National Laboratory (ANL). The results are reported in “Zero Degree Line Mo Target Thermal Test Results and Analysis,” LANL report Number LA-UR-15-23134 dated 3/27/15. This target was comprised of 25 disks 1 mm thick and 12 mm in diameter, separated by helium coolant gaps 0.5 mm wide. The test reported in the above referenced report was conducted with natural Mo disks all cut from commercial rod. The production plant will have Mo100 disks pressed and sintered using a process being developed at Oak Ridge National Laboratory (ORNL). The structural integrity of press-and-sinter disks is of some concern. The test reported herein included 4 disks made by the ORNL process and placed in the high heat, and therefore high thermal stress, region of the target. The electron beam energy was 23 MeV for these tests. Beam spot size was 3.5 mm horizontal and 3 mm vertical, FWHM. The thermal stress test of pressed-and-sintered disks resulted in no mechanical failures. The induced thermal stresses were below yield stress for natural Mo, indicating that up to that stress state no inherent deficiencies in the mechanical properties of the fabricated disks were evident.

  3. Premixed direct injection disk

    SciTech Connect

    York, William David; Ziminsky, Willy Steve; Johnson, Thomas Edward; Lacy, Benjamin; Zuo, Baifang; Uhm, Jong Ho

    2013-04-23

    A fuel/air mixing disk for use in a fuel/air mixing combustor assembly is provided. The disk includes a first face, a second face, and at least one fuel plenum disposed therebetween. A plurality of fuel/air mixing tubes extend through the pre-mixing disk, each mixing tube including an outer tube wall extending axially along a tube axis and in fluid communication with the at least one fuel plenum. At least a portion of the plurality of fuel/air mixing tubes further includes at least one fuel injection hole have a fuel injection hole diameter extending through said outer tube wall, the fuel injection hole having an injection angle relative to the tube axis. The invention provides good fuel air mixing with low combustion generated NOx and low flow pressure loss translating to a high gas turbine efficiency, that is durable, and resistant to flame holding and flash back.

  4. Supersized Disk (Artist's Concept)

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Annotated ImageData Graph

    This illustration compares the size of a gargantuan star and its surrounding dusty disk (top) to that of our solar system. Monstrous disks like this one were discovered around two 'hypergiant' stars by NASA's Spitzer Space Telescope. Astronomers believe these disks might contain the early 'seeds' of planets, or possibly leftover debris from planets that already formed.

    The hypergiant stars, called R 66 and R 126, are located about 170,000 light-years away in our Milky Way's nearest neighbor galaxy, the Large Magellanic Cloud. The stars are about 100 times wider than the sun, or big enough to encompass an orbit equivalent to Earth's. The plump stars are heavy, at 30 and 70 times the mass of the sun, respectively. They are the most massive stars known to sport disks.

    The disks themselves are also bloated, with masses equal to several Jupiters. The disks begin at a distance approximately 120 times greater than that between Earth and the sun, or 120 astronomical units, and terminate at a distance of about 2,500 astronomical units.

    Hypergiant stars are the puffed-up, aging descendants of the most massive class of stars, called 'O' stars. The stars are so massive that their cores ultimately collapse under their own weight, triggering incredible explosions called supernovae. If any planets circled near the stars during one of these blasts, they would most likely be destroyed.

    The orbital distances in this picture are plotted on a logarithmic scale. This means that a given distance shown here represents proportionally larger actual distances as you move to the right. The sun and planets in our solar system have been scaled up in size for better viewing. Little Dust Grains in Giant Stellar Disks The graph above of data from NASA's Spitzer Space Telescope shows the composition of a monstrous disk of what may be planet-forming dust circling the colossal 'hypergiant' star

  5. Spiral disk packings

    NASA Astrophysics Data System (ADS)

    Yamagishi, Yoshikazu; Sushida, Takamichi

    2017-04-01

    It is shown that van Iterson's metric for disk packings, proposed in 1907 in the study of a centric model of spiral phyllotaxis, defines a bounded distance function in the plane. This metric is also related to the bifurcation of Voronoi tilings for logarithmic spiral lattices, through the continued fraction expansion of the divergence angle. The phase diagrams of disk packings and Voronoi tilings for logarithmic spirals are dual graphs to each other. This gives a rigorous proof that van Iterson's diagram in the centric model is connected and simply connected. It is a nonlinear analog of the duality between the phase diagrams for disk packings and Voronoi tilings on the linear lattices, having the modular group symmetry.

  6. Supersized Disk (Artist's Concept)

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Annotated ImageData Graph

    This illustration compares the size of a gargantuan star and its surrounding dusty disk (top) to that of our solar system. Monstrous disks like this one were discovered around two 'hypergiant' stars by NASA's Spitzer Space Telescope. Astronomers believe these disks might contain the early 'seeds' of planets, or possibly leftover debris from planets that already formed.

    The hypergiant stars, called R 66 and R 126, are located about 170,000 light-years away in our Milky Way's nearest neighbor galaxy, the Large Magellanic Cloud. The stars are about 100 times wider than the sun, or big enough to encompass an orbit equivalent to Earth's. The plump stars are heavy, at 30 and 70 times the mass of the sun, respectively. They are the most massive stars known to sport disks.

    The disks themselves are also bloated, with masses equal to several Jupiters. The disks begin at a distance approximately 120 times greater than that between Earth and the sun, or 120 astronomical units, and terminate at a distance of about 2,500 astronomical units.

    Hypergiant stars are the puffed-up, aging descendants of the most massive class of stars, called 'O' stars. The stars are so massive that their cores ultimately collapse under their own weight, triggering incredible explosions called supernovae. If any planets circled near the stars during one of these blasts, they would most likely be destroyed.

    The orbital distances in this picture are plotted on a logarithmic scale. This means that a given distance shown here represents proportionally larger actual distances as you move to the right. The sun and planets in our solar system have been scaled up in size for better viewing. Little Dust Grains in Giant Stellar Disks The graph above of data from NASA's Spitzer Space Telescope shows the composition of a monstrous disk of what may be planet-forming dust circling the colossal 'hypergiant' star

  7. Triaxiality in disk galaxies

    SciTech Connect

    Bertola, F.; Vietri, M.; Zeilinger, W.W. Roma, Osservatorio Astronomico, Rome European Southern Observatory, Garching )

    1991-06-01

    Thirty-two bulges of nearby spirals have been observed, to detect misalignment between disk and bulge apparent major axes. Such misalignment is unequivocally present in the majority of observed objects. This may be due to the triaxiality of disks, bulges, or both. The probability distribution function for the axial ratios is derived under the two extreme hypotheses, i.e., that either only disks (case I) or only bulges (case II) are triaxial: the observational data are equally well fitted by either one. Since dynamical evidence and the internal twisting of isophotes show that bulges are triaxial, case I is unlikely, but an intermediate case cannot be ruled out. These distribution functions are compared with available constraints; in particular, that of case II is projected and compared with the distribution of apparent ellipticities of minor-axis dust-lane ellipticals and of all ellipticals. Both tests show that the observed and derived distributions are consistent. 34 refs.

  8. Theory of protostellar accretion disks

    NASA Technical Reports Server (NTRS)

    Ruden, S.

    1994-01-01

    I will present an overview of the current paradigm for the theory of gaseous accretion disks around young stars. Protostellar disks form from the collapse of rotating molecular cloud cores. The disks evolve via outward angular momentum transport provided by several mechanisms: gravitational instabilities, thermal convective turbulence, and magnetic stresses. I will review the conditions under which these mechanisms are efficient and consistent with the observed disk evolutionary timescales of several million years. Time permitting, I will discuss outbursts in protostellar disks (FU Orionis variables), the effect of planet formation on disk structure, and the dispersal of remnant gas.

  9. Debris disks: a theorist's view

    NASA Astrophysics Data System (ADS)

    Krivov, A. V.

    2007-08-01

    Debris disks are roughly solar system-sized, optically thin, gas-poor dust disks that encircle a notable fraction of main-sequence stars at ages ranging from about 10 Myr to several Gyr. They are thought to be continuously replenished by collisions between "exoasteroids" and activity of "exocomets", small bodies left over from the planet formation process. I will first outline main physical mechanisms operating in debris disks and compare them with other dusty systems: protoplanetary disks, dusty planetary rings, and classical Saturn's rings. I will then review basic methods and essential results of debris disks modeling, covering both steady-state and stochastic models of axisymmetric and structured disks.

  10. The Evolution of FU Orionis Disks

    NASA Astrophysics Data System (ADS)

    Green, Joel D.

    2016-06-01

    Do protoplanetary disks undergo regular (or irregular) bursts of accretion? FU Orionis objects (FUors) are the strongest direct evidence for episodic accretion in low mass young stellar objects. FUors exhibit rapid changes in disk chemistry, both because they are temporarily bright IR sources relative to their core mass, and vary on day, month, year, and decade timescales. With improved spatial and spectral resolution from FORCAST, and a ten year time baseline compared with Spitzer-IRS data, we can observe and constrain the properties of silicate dust, and disk profiles, as they are altered by the outburst. We also consider the occurrence of binarity and whether any connection exists between multiplicity and evidence of recent outburst behavior.

  11. Lupus Alma Disk Survey

    NASA Astrophysics Data System (ADS)

    Ansdell, Megan

    2016-07-01

    We present the first unbiased ALMA survey of both dust and gas in a large sample of protoplanetary disks. We surveyed 100 sources in the nearby (150-200 pc), young (1-2 Myr) Lupus region to constrain M_dust to 2 M_Mars and M_gas to 1 M_Jup. Most disks have masses < MMSN and gas-to-dust ratios < ISM. Such rapid gas depletion may explain the prevalence of super-Earths in the exoplanet population.

  12. MPP disk subsystem

    NASA Technical Reports Server (NTRS)

    Hudgins, W. A.

    1984-01-01

    A disk subsystem for the Massively Parallel processor (MPP) is designed to the block diagram level. The subsystem is capable of storing 4,992 megabytes of data, expandable to 39,936 megabytes. The subsystem is capable of transferring data to the MPP Staging Memory at a rate of 25 megabytes/second, expandable to 100 megabytes/second. A lower cost disk subsystem is also presented. This alternate subsystem is capable of storing 3,744 megabytes with a transfer rate of 10.6 megabyte/second.

  13. From Disks to Planets

    NASA Astrophysics Data System (ADS)

    Youdin, Andrew N.; Kenyon, Scott J.

    This pedagogical chapter covers the theory of planet formation, with an emphasis on the physical processes relevant to current research. After summarizing empirical constraints from astronomical and geophysical data, we describe the structure and evolution of protoplanetary disks. We consider the growth of planetesimals and of larger solid protoplanets, followed by the accretion of planetary atmospheres, including the core accretion instability. We also examine the possibility that gas disks fragment directly into giant planets and/or brown dwarfs. We defer a detailed description of planet migration and dynamical evolution to other work, such as the complementary chapter in this series by Morbidelli.

  14. Secondary Disks and Disk Regrowth in S0 Galaxies

    NASA Astrophysics Data System (ADS)

    Moffett, Amanda; Kannappan, Sheila; Norris, Mark; Khochfar, Sadegh; Berlind, Andreas

    2010-08-01

    Early-type galaxies are predicted to regrow late-type disks in hierarchical models of galaxy formation, but the observational confirmation of this process remains largely indirect. We seek to approach this problem kinematically by searching for evidence of disk regrowth in the form of extended secondary disks in S0s (distinct from the small-scale KDCs identified in SAURON). In order to address the possible contribution of secondary disks not indicative of true disk regrowth and the expected variations of secondary disk frequency with mass, color, and environment, we propose deep spectroscopy of a broad sample of 60 S0 galaxies located in the RESOLVE Survey volume. With these data and similar data in hand for ~12 additional S0s, we aim both to resolve conflicting measurements of the frequency of secondary disks in early-type galaxies and to determine the incidence of disk regrowth.

  15. The hybrid disks: a search and study to better understand evolution of disks

    NASA Astrophysics Data System (ADS)

    Péricaud, J.; Di Folco, E.; Dutrey, A.; Guilloteau, S.; Piétu, V.

    2017-04-01

    Context. The increased sensitivity of millimeter-wave facilities now makes possible the detection of low amounts of gas in debris disks. Some of the gas-rich debris disks harbor peculiar properties, with possible pristine gas and secondary generated dust. The origin of the gas in these hybrid disks is strongly debated and the current sample is too sparse to understand this phenomenon. Aims: More detections are necessary to increase the statistics on this population. Lying at the final stages of evolution of proto-planetary disks and at the beginning of the debris disk phase, these objects could provide new insight into the processes involved in the making of planetary systems. Methods: We carried out a deep survey of the CO J = 2 → 1 and CO J = 3 → 2 lines with the APEX and IRAM radiotelescopes in young debris disks selected according to hybrid disk properties. The survey is complemented with a bibliographic study of the ratio between the emission of the gas and the continuum (SCO/Fcont) in CTTS, Herbig Ae, WTTS, hybrid, and debris disks. Results: Our sub-mm survey comprises 25 stars, including 17 new targets, and we increase the sensitivity limit by a factor 2 on eight sources compared to similar published studies. We report a 4σ tentative detection of a double-peaked CO J = 2 → 1 line around HD 23642; an eclipsing binary located in the Pleiades. We also reveal a correlation between the emission of the CO gas and the dust continuum from CTTS, Herbig Ae and few debris disks. The observed trend of the gas to dust flux ratio suggests a concurrent dissipation of the dust and gas components. Hybrid disks systematically lie above this trend, suggesting that these systems may witness a transient phase, when the dust has evolved more rapidly than the gas, with a flux ratio SCO/Fcont enhanced by a factor of between 10 and 100 compared to standard (proto-)planetary disks. Reduced data used in the paper (FITS) are only available at the CDS via anonymous ftp to http

  16. Childhood to adolescence: dust and gas clearing in protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Brown, Joanna Margaret

    Disks are ubiquitous around young stars. Over time, disks dissipate, revealing planets that formed hidden by their natal dust. Since direct detection of young planets at small orbital radii is currently impossible, other tracers of planet formation must be found. One sign of disk evolution, potentially linked to planet formation, is the opening of a gap or inner hole in the disk. In this thesis, I have identified and characterized several cold disks with large inner gaps but retaining massive primordial outer disks. While cold disks are not common, with ~5% of disks showing signs of inner gaps, they provide proof that at least some disks evolve from the inside-out. These large gaps are equivalent to dust clearing from inside the Earth's orbit to Neptune's orbit or even the inner Kuiper belt. Unlike more evolved systems like our own, the central star is often still accreting and a large outer disk remains. I identified four cold disks in Spitzer 5-40 μm spectra and modeled these disks using a 2-D radiative transfer code to determine the gap properties. Outer gap radii of 20-45 AU were derived. However, spectrophotometric identification is indirect and model-dependent. To validate this interpretation, I observed three disks with a submillimeter interferometer and obtained the first direct images of the central holes. The images agree well with the gap sizes derived from the spectrophotometry. One system, LkH&alpha 330, has a very steep outer gap edge which seems more consistent with gravitational perturbation rather than gradual processes, such as grain growth and settling. Roughly 70% of cold disks show CO v=1&rarr 0 gas emission from the inner 1 AU and therefore are unlikely to have evolved due to photoevaporation. The derived rotation temperatures are significantly lower for the cold disks than disks without gaps. Unresolved (sub)millimeter photometry shows that cold disks have steeper colors, indicating that they are optically thin at these wavelengths, unlike

  17. Radiative-Thermal Winds from an Accretion Disk

    NASA Astrophysics Data System (ADS)

    Fukue, Jun

    2002-06-01

    We examine a hydrodynamical wind, which emanates from an accretion disk and is driven by thermal and radiation pressures, under a one-dimensional approximation along supposed streamlines. Such a disk wind is characterized by the disk gravitational and radiation fields, whose behavior is rather different from the spherical case. Along the streamline of winds, the gravitational field produced by the central object generally has a peak at some height, unlike the spherical case where it decreases monotonically. The radiation field produced by the disk, on the other hand, is almost constant near to the disk surface and decreases far from the disk, again unlike the spherical case. Due to these characteristic properties of force fields, disk winds are classified into three patterns: in the cold less-luminous case no wind can blow, in the warm luminous case transonic winds are established, and beyond some critical luminosity disk winds are always supersonic. We found that transonic winds can blow for the parameter range of a0 + 2Γeff >~ 0.8, where a0 is the initial sound speed in units of the Keplerian speed at the wind base and Γeff the normalized disk luminosity at the wind base. Furthermore, supersonic winds blow for Γeff >~ 0.4. We derive the terminal speed as a function of Γeff A radial extension of the flow is also discussed and applie d to mass outflow from several active objects.

  18. Radiative-Thermal Winds from an Accretion Disk

    NASA Astrophysics Data System (ADS)

    Fukue, J.

    We examine a hydrodynamical wind, which emanates from an accretion disk and is driven by thermal and radiation pressures, under a one-dimensional approximation along supposed streamlines. Such a disk wind is characterized by the disk gravitational and radiation fields, whose behavior is rather different from the spherical case. Along the streamline of winds, the gravitational field produced by the central object generally has a peak at some height. The radiation field produced by the disk, on the other hand, is almost constant near to the disk surface and decreases far from the disk. As a result of these characteristic properties of force fields, disk winds are classified into three patterns; in the cold less-luminous case no wind can blow, in the warm luminous case transonic winds are established, and beyond some critical luminosity disk winds are always supersonic. We found that transonic winds can blow for the parameter range of a0 + 2Γeff > 0.8, where a0 is the initial sound speed in units of the Keplerian speed at the wind base and Γeff the normalized disk luminosity at the wind base. Furthermore, supersonic winds blow for Γeff > 0.4.

  19. Sharp Eccentric Rings in Planetless Hydrodynamical Models of Debris Disks

    NASA Technical Reports Server (NTRS)

    Lyra, W.; Kuchner, M. J.

    2013-01-01

    Exoplanets are often associated with disks of dust and debris, analogs of the Kuiper Belt in our solar system. These "debris disks" show a variety of non-trivial structures attributed to planetary perturbations and utilized to constrain the properties of the planets. However, analyses of these systems have largely ignored the fact that, increasingly, debris disks are found to contain small quantities of gas, a component all debris disks should contain at some level. Several debris disks have been measured with a dust-to-gas ratio around unity where the effect of hydrodynamics on the structure of the disk cannot be ignored. Here we report that dust-gas interactions can produce some of the key patterns seen in debris disks that were previously attributed to planets. Through linear and nonlinear modeling of the hydrodynamical problem, we find that a robust clumping instability exists in this configuration, organizing the dust into narrow, eccentric rings, similar to the Fomalhaut debris disk. The hypothesis that these disks might contain planets, though thrilling, is not necessarily required to explain these systems.

  20. The Warped Disk of Integral-Sign Galaxy PGC 20348

    NASA Astrophysics Data System (ADS)

    Ann, H. B.

    2007-03-01

    We examine the morphology and luminosity distribution of a strongly warped spiral galaxy PGC 20348 by conducting a detailed BVI CCD surface photometry using BOAO 1.8m telescope. The radial surface brightness shows a break at warp radius (r_{w}) with a shallow gradient in the inner disk and a steeper gradient in the outer disk. The luminosity of east side of the disk is ˜ 0.5 mag fainter than the west side at r > r_{w}. The reason for the asymmetric luminosity distribution is thought to be the asymmetric flarings that result in the formation of a large diffuse region at the edge of the east disk and a smaller diffuse region at the west disk. The vertical luminosity profiles show a thick disk component whose scale heights increase with increasing galactocentric distances. The warp of PGC 20348 seems to be made by the tidal interactions with the two massive companion galaxies since the flarings and radial increase of disk scale heights are thought to be general properties of tidally perturbed disks. According to the colors of the two clumps inside the diffuse region at the edge of the east disk, they seem to be sites of active star formation triggered by tidal forces from the companion galaxies.

  1. Accretion in Radiative Equipartition (AiRE) Disks

    NASA Astrophysics Data System (ADS)

    Yazdi, Yasaman K.; Afshordi, Niayesh

    2017-07-01

    Standard accretion disk theory predicts that the total pressure in disks at typical (sub-)Eddington accretion rates becomes radiation pressure dominated. However, radiation pressure dominated disks are thermally unstable. Since these disks are observed in approximate steady state over the instability timescale, our accretion models in the radiation-pressure-dominated regime (i.e., inner disk) need to be modified. Here, we present a modification to the Shakura & Sunyaev model, where the radiation pressure is in equipartition with the gas pressure in the inner region. We call these flows accretion in radiative equipartition (AiRE) disks. We introduce the basic features of AiRE disks and show how they modify disk properties such as the Toomre parameter and the central temperature. We then show that the accretion rate of AiRE disks is limited from above and below, by Toomre and nodal sonic point instabilities, respectively. The former leads to a strict upper limit on the mass of supermassive black holes as a function of cosmic time (and spin), while the latter could explain the transition between hard and soft states of X-ray binaries.

  2. Herschel DUNES Observations of Cold Debris Disks Around Nearby Stars

    NASA Astrophysics Data System (ADS)

    Roberge, Aki; Eiroa, C.; DUNES Team

    2011-01-01

    The DUNES (DUst discs around NEarby Stars) Open Time Key Programme for the Herschel Space Observatory is a sensitivity-limited photometric survey for faint, cold debris disks around nearby FGK stars. It takes advantage of the PACS and SPIRE instruments to detect and characterize cold disks as faint as Ldust/Lstar 10-7 - 10-6, at dust temperatures around 30 - 40 K. Such systems are extrasolar analogues of Solar System's Edgeworth-Kuiper Belt (EKB). DUNES will observe a statistically significant, volume-limited (d < 20 pc) sample, constrained only by background confusion. Stars at larger distances (d < 25 pc) with previously known exoplanets and/or Spitzer-detected faint debris disks are also included. More than one third of the DUNES sample has been observed to date. Our goal of detecting very faint, cold dust disks has been achieved; many disks are also spatially resolved. The unresolved disks show a variety of spectral energy distributions, some suggesting the presence of cold EKB-like dust rings. A number of previously unknown debris disks have been detected, including the coldest disks yet found. Preliminary results relating disk properties to the host star parameters will be shown.

  3. Water Masers in AGN Accretion Disks

    NASA Astrophysics Data System (ADS)

    Braatz, J. A.; Reid, M. J.; Greenhill, L. J.; Kuo, C.-Y.; Condon, J. J.; Lo, K.-Y.; Henkel, C.

    2009-08-01

    Water vapor masers at 22 GHz have been detected in over 100 galaxies, most of them AGNs. High resolution VLBI observations of these masers provide the only opportunity for direct imaging of sub-parsec structure in AGN accretion disks. The key science goals associated with such observations are concentrated in two areas. First, observations of nearby, bright sources, exemplified by NGC 4258, enable unique investigations of accretion disk geometry, substructure, thickness, and rotation properties. Second, when combined with spectral line monitoring, VLBI imaging and subsequent disk modeling enables the estimation of a distance to the host galaxy independent of standard candle arguments. In this contribution we present VLBI observations of two maser disk systems in galaxies well into the Hubble flow, UGC 3789 and NGC 6323. A long term goal in these studies is to measure the Hubble constant with high precision and, as a complement to CMB observations, constrain several key cosmological parameters, including the equation of state for dark energy. Observations with VSOP-2 at 22 GHz will have the resolution critical for mapping substructure in these accretion disks and will contribute to reducing systematic errors in the measurement of distances to galaxies.

  4. Ionization and Dust Charging in Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Ivlev, A. V.; Akimkin, V. V.; Caselli, P.

    2016-12-01

    Ionization-recombination balance in dense interstellar and circumstellar environments is a key factor for a variety of important physical processes, such as chemical reactions, dust charging and coagulation, coupling of the gas with magnetic field, and development of instabilities in protoplanetary disks. We determine a critical gas density above which the recombination of electrons and ions on the grain surface dominates over the gas-phase recombination. For this regime, we present a self-consistent analytical model, which allows us to calculate exactly the abundances of charged species in dusty gas, without making assumptions on the grain charge distribution. To demonstrate the importance of the proposed approach, we check whether the conventional approximation of low grain charges is valid for typical protoplanetary disks, and discuss the implications for dust coagulation and development of the “dead zone” in the disk. The presented model is applicable for arbitrary grain-size distributions and, for given dust properties and conditions of the disk, has only one free parameter—the effective mass of the ions, shown to have a small effect on the results. The model can be easily included in numerical simulations following the dust evolution in dense molecular clouds and protoplanetary disks.

  5. Observability of characteristic binary-induced structures in circumbinary disks

    NASA Astrophysics Data System (ADS)

    Avramenko, R.; Wolf, S.; Illenseer, T. F.

    2017-07-01

    Context. A substantial fraction of protoplanetary disks form around stellar binaries. The binary system generates a time-dependent non-axisymmetric gravitational potential, inducing strong tidal forces on the circumbinary disk. This leads to a change in basic physical properties of the circumbinary disk, which should in turn result in unique structures that are potentially observable with the current generation of instruments. Aims: The goal of this study is to identify these characteristic structures, constrain the physical conditions that cause them, and evaluate the feasibility of observing them in circumbinary disks. Methods: To achieve this, first we perform 2D hydrodynamic simulations. The resulting density distributions are post-processed with a 3D radiative transfer code to generate re-emission and scattered light maps. Based on these distributions, we study the influence of various parameters, such as the mass of the stellar components, mass of the disk, and binary separation on observable features in circumbinary disks. Results: We find that the Atacama Large (sub-)Millimetre Array (ALMA) as well as the European Extremely Large Telescope (E-ELT) are capable of tracing asymmetries in the inner region of circumbinary disks, which are affected most by the binary-disk interaction. Observations at submillimetre/millimetre wavelengths allow the detection of the density waves at the inner rim of the disk and inner cavity. With the E-ELT one can partially resolve the innermost parts of the disk in the infrared wavelength range, including the disk's rim, accretion arms, and potentially the expected circumstellar disks around each of the binary components.

  6. SMA Continuum Survey of Circumstellar Disks in Serpens

    NASA Astrophysics Data System (ADS)

    Law, Charles; Ricci, Luca; Andrews, Sean M.; Wilner, David J.; Qi, Chunhua

    2017-06-01

    The lifetime of disks surrounding pre-main-sequence stars is closely linked to planet formation and provides information on disk dispersal mechanisms and dissipation timescales. The potential for these optically thick, gas-rich disks to form planets is critically dependent on how much dust is available to be converted into terrestrial planets and rocky cores of giant planets. For this reason, an understanding of how dust mass varies with key properties such as stellar mass, age, and environment is critical for understanding planet formation. Millimeter wavelength observations, in which the dust emission is optically thin, are required to study the colder dust residing in the disk’s outer regions and to measure disk dust masses. Hence, we have obtained SMA 1.3 mm continuum observations of 62 Class II sources with suspected circumstellar disks in the Serpens star-forming region (SFR). Relative to the well-studied Taurus SFR, Serpens allows us to probe the distribution of dust masses for disks in a much denser and more clustered environment. Only 13 disks were detected in the continuum with the SMA. We calculate the total dust masses of these disks and compare their masses to those of disks in Taurus, Lupus, and Upper Scorpius. We do not find evidence of diminished dust masses in Serpens disks relative to those in Taurus despite the fact that disks in denser clusters may be expected to contain less dust mass due to stronger and more frequent tidal interactions that can disrupt the outer regions of disks. However, considering the low detection fraction, we likely detected only bright continuum sources and a more sensitive survey of Serpens would help clarify these results.

  7. The Gaseous Disks of Young Stellar Objects

    NASA Technical Reports Server (NTRS)

    Glassgold, A. E.

    2006-01-01

    Disks represent a crucial stage in the formation of stars and planets. They are novel astrophysical systems with attributes intermediate between the interstellar medium and stars. Their physical properties are inhomogeneous and are affected by hard stellar radiation and by dynamical evolution. Observing disk structure is difficult because of the small sizes, ranging from as little as 0.05 AU at the inner edge to 100-1000 AU at large radial distances. Nonetheless, substantial progress has been made by observing the radiation emitted by the dust from near infrared to mm wavelengths, i.e., the spectral energy distribution of an unresolved disk. Many fewer results are available for the gas, which is the main mass component of disks over much of their lifetime. The inner disk gas of young stellar objects (henceforth YSOs) have been studied using the near infrared rovibrational transitions of CO and a few other molecules, while the outer regions have been explored with the mm and sub-mm lines of CO and other species. Further progress can be expected in understanding the physical properties of disks from observations with sub-mm arrays like SMA, CARMA and ALMA, with mid infrared measurements using Spitzer, and near infrared spectroscopy with large ground-based telescopes. Intense efforts are also being made to model the observations using complex thermal-chemical models. After a brief review of the existing observations and modeling results, some of the weaknesses of the models will be discussed, including the absence of good laboratory and theoretical calculations for essential microscopic processes.

  8. Dual-Alloy Disks are Formed by Powder Metallurgy

    NASA Technical Reports Server (NTRS)

    Harf, F. H.; Miner, R. V.; Kortovich, C. S.; Marder, J. M.

    1982-01-01

    High-performance disks have widely varying properties from hub to rim. Dual property disk is fabricated using two nickel-base alloys, AF-115 for rim and Rene 95 for hub. Dual-alloy fabrication may find applications in automobiles, earth-moving equipment, and energy conversion systems as well as aircraft powerplants. There is potential for such applications as shafts, gears, and blades.

  9. GIANT PLANET FORMATION BY DISK INSTABILITY IN LOW MASS DISKS?

    SciTech Connect

    Boss, Alan P.

    2010-12-20

    Forming giant planets by disk instability requires a gaseous disk that is massive enough to become gravitationally unstable and able to cool fast enough for self-gravitating clumps to form and survive. Models with simplified disk cooling have shown the critical importance of the ratio of the cooling to the orbital timescales. Uncertainties about the proper value of this ratio can be sidestepped by including radiative transfer. Three-dimensional radiative hydrodynamics models of a disk with a mass of 0.043 M{sub sun} from 4 to 20 AU in orbit around a 1 M{sub sun} protostar show that disk instabilities are considerably less successful in producing self-gravitating clumps than in a disk with twice this mass. The results are sensitive to the assumed initial outer disk (T{sub o}) temperatures. Models with T{sub o} = 20 K are able to form a single self-gravitating clump, whereas models with T{sub o} = 25 K form clumps that are not quite self-gravitating. These models imply that disk instability requires a disk with a mass of at least {approx}0.043 M{sub sun} inside 20 AU in order to form giant planets around solar-mass protostars with realistic disk cooling rates and outer-disk temperatures. Lower mass disks around solar-mass protostars must rely upon core accretion to form inner giant planets.

  10. Instabilities of interacting vortex rings generated by an oscillating disk

    NASA Astrophysics Data System (ADS)

    Deng, Jian; Teng, Lubao; Caulfield, C. P.; Mao, Xuerui

    2016-09-01

    We propose a natural model to probe in a controlled fashion the instability of interacting vortex rings shed from the edge of an oblate spheroid disk of major diameter c , undergoing oscillations of frequency f0 and amplitude A . We perform a Floquet stability analysis to determine the characteristics of the instability modes, which depend strongly on the azimuthal (integer) wave number m . We vary two key control parameters, the Keulegan-Carpenter number KC=2 π A /c and the Stokes number β =f0c2/ν , where ν is the kinematic viscosity of the fluid. We observe two distinct flow regimes. First, for sufficiently small β , and hence low frequency of oscillation corresponding to relatively weak interaction between sequentially shedding vortex rings, symmetry breaking occurs directly to a single unstable mode with m =1 . Second, for sufficiently large yet fixed values of β , corresponding to a higher oscillation frequency and hence stronger ring-ring interaction, the onset of asymmetry is predicted to occur due to two branches of high m instabilities as the amplitude is increased, with m =1 structures being dominant only for sufficiently large values of KC. These two branches can be distinguished by the phase properties of the vortical structures above and below the disk. The region in (KC,β ) parameter space where these two high m instability branches arise can be described accurately in terms of naturally defined Reynolds numbers, using appropriately chosen characteristic length scales. We subsequently carry out direct numerical simulations of the fully three-dimensional flow to verify the principal characteristics of the Floquet analysis, in particular demonstrating that high wave-number symmetry-breaking generically occurs when vortex rings sequentially interact sufficiently strongly.

  11. The Effects of Accretion Disk Geometry on AGN Reflection Spectra

    NASA Astrophysics Data System (ADS)

    Taylor, Corbin James; Reynolds, Christopher S.

    2017-08-01

    Despite being the gravitational engines that power galactic-scale winds and mega parsec-scale jets in active galaxies, black holes are remarkably simple objects, typically being fully described by their angular momenta (spin) and masses. The modelling of AGN X-ray reflection spectra has proven fruitful in estimating the spin of AGN, as well as giving insight into their accretion histories and the properties of plasmas in the strong gravity regime. However, current models make simplifying assumptions about the geometry of the reflecting material in the accretion disk and the irradiating X-ray corona, approximating the disk as an optically thick, infinitely thin disk of material in the orbital plane. We present results from the new relativistic raytracing suite, Fenrir, that explore the effects that disk thickness may have on the reflection spectrum and the accompanying reverberation signatures. Approximating the accretion disk as an optically thick, geometrically thin, radiation pressure dominated disk (Shakura & Sunyaev 1973), one finds that the disk geometry is non-negligible in many cases, with significant changes in the broad Fe K line profile. Finally, we explore the systematic errors inherent in approximating the disk as being infinitely thin when modeling reflection spectrum, potentially biasing determinations of black hole and corona properties.

  12. Properties of the hermean regolith: iii. disk-resolved vis-NIR reflectance spectra and implications for the abundance of iron*

    NASA Astrophysics Data System (ADS)

    Warell, J.

    2003-02-01

    Disk-resolved reflectance spectra of the surface of Mercury (longitudes 240-300°), obtained in the visual (vis) and near-infrared (NIR) spectral region, are presented and analyzed. The observations were made at the 2.6-m Nordic Optical Telescope with the ALFOSC low-resolution spectrograph on 20 and 22 June 1999 in the wavelength range 520-970 nm with a footprint size of 700 km on the mid-disk of Mercury. A method which enables more accurate correction for telluric line absorptions and atmospheric extinction than that applied on previously published vis-NIR spectra of Mercury is introduced. The resulting reflectance spectra are remarkably linear, lack significant absorption features, and have optical slopes comparable to remotely sensed lunar pure anorthosites. The relation between spectral slope and photometric geometry found by Warell (2002, Icarus 156, 313-317) is confirmed and is explained as caused by strongly backscattering particles with embedded submicroscopic metallic iron in a mature regolith. With the theoretical maturation model of Hapke (2001, J. Geophys. Res. 106 (E5), 10039-10073) an abundance of 0.05-0.3 wt% submicroscopic metallic iron in the regolith for silicate grain sizes in the range 10-80 μm is determined, implying a ferrous iron content in mafic minerals intrinsically lower than that of the lunar highlands. A binary crustal composition model with anorthite linearly mixed with pyroxene provides better spectral fits than a pure anorthitic composition. Comparison with mature lunar pure anorthosite spectra yields a confident upper limit to the FeO content of 3 wt% under the assumption that the surfaces are similarly matured, but this figure probably represents a considerable overestimate. The average mercurian regolith does not seem to be substantially more weathered than the most mature lunar highland soils in terms of abundance of submicroscopic metallic iron, indicating that a steady-state maturation level has been reached. However, the

  13. Warm gas in protoplanetary disks

    NASA Astrophysics Data System (ADS)

    van der Plas, Gerrit

    2010-12-01

    This thesis presents a study of warm CO, [OI] and H2 gas coming from the disks around Herbig Ae/Be stars. These various gas tracers are each a proxy for a different radial and vertical region of the PP disk surface. Our sample consists of disks whose shape (based on modeling of the the disk dust emission) can be divided into flaring and self-shadowed (flat). We find [1] evidence for the vertical decoupling of gas and dust in one disks (Chapter 2); [2] That disk geometry has a large influence on the spatial distribution and excitation mechanism of the CO emission (chapters 3,4); [3] Near-IR H 2 emission around 2 (out of 14) HAEBE stars, probably originating from large (±50AU) radii of the disk (chapter 5). In chapter 6 we investigate the trends between CO emission and disk geometry as noted in Chapter 3 and 4.

  14. Herniated disk repair (image)

    MedlinePlus

    ... is one of the most common causes of lower back pain. The mainstay of treatment for herniated disks is an initial period of rest with pain and anti-inflammatory medications followed by physical therapy. If pain and symptoms persist, surgery to remove ...

  15. Disk Valve For Cryogenics

    NASA Technical Reports Server (NTRS)

    Calhoun, Richard B.

    1993-01-01

    Lightweight disk valve designed to have dimensions and capabilities similar to those of valve described in "Lightweight Right-Angle Valve For Cryogenics" (MSC-21889). Simple unit remains leaktight over wide range of pressures and temperatures without need for manual readjustment of packing gland. Weighs less than 60 g and made relatively inexpensively from some commercial and few simple custom-machined components.

  16. Solar disk sextant

    NASA Technical Reports Server (NTRS)

    Sofia, S.; Chiu, H.-Y.; Maier, E.; Schatten, K. H.; Minott, P.; Endal, A. S.

    1984-01-01

    This paper presents the conceptual design of an instrument, called the solar disk sextant, to be used in space to measure the shape and the size of the sun and their variations. The instrumental parameters required to produce sufficient sensitivity to address the problems of solar oblateness, solar pulsations, and global size changes of climatic importance are given.

  17. Tracking the Disk Wind Behavior of MAXI J1305-704

    NASA Astrophysics Data System (ADS)

    Sinclair, Kimberly Poppy; Miller, Jon M.

    2017-01-01

    There is still much to be understood about black hole accretion disks and their relationship to black hole disk winds. In an attempt to better understand these relationships, we have analyzed the x-ray transient black hole binary MAXI J1305-704 during its outburst in 2012 in order to draw conclusions about the parameters of its disk. The source showed strong absorption signs, as detected by Chandra, on April 21, 2012. From this date on, we analyzed SWIFT observations of the source, using XSPEC from HEASOFT, in order to find strong signals of absorption. By modeling 67 successive observations over the period of 74 days, we were able to closely track the evolution of various disk properties, from inner disk temperature, to power law index, to column density. We could also analyze various parameter relationships in order to determine if there is a statistically significant correlation between any of the properties of a disk. We found that there are strong linear relationships between disk temperature & ionization, photon index & disk temperature, and photon index & ionization. These relationships seem to imply that the corona, in addition to the disk, may be driving the wind properties. Additionally, the counterintuitive relationship between disk temperature and ionization, where disk temperature increases as ionization decreases, seems to imply that there are mechanisms at play in the disk system that are not yet fully understood.

  18. Understanding the water emission in the mid- and far-IR from protoplanetary disks around T Tauri stars

    NASA Astrophysics Data System (ADS)

    Antonellini, S.; Kamp, I.; Riviere-Marichalar, P.; Meijerink, R.; Woitke, P.; Thi, W.-F.; Spaans, M.; Aresu, G.; Lee, G.

    2015-10-01

    Aims: We investigate which properties of protoplanetary disks around T Tauri stars affect the physics and chemistry in the regions where mid- and far-IR water lines originate and their respective line fluxes. We search for diagnostics for future observations. Methods: With the code ProDiMo, we build a series of models exploring a large parameter space, computing rotational and ro-vibrational transitions of water in nonlocal thermodynamic equilibrium (non-LTE). We select a sample of transitions in the mid-IR regime and the fundamental ortho and para water transitions in the far-IR. We investigate the chemistry and the local physical conditions in the line emitting regions. We calculate Spitzer spectra for each model and compare far-IR and mid-IR lines. In addition, we use mid-IR colors to tie the water line predictions to the dust continuum. Results: Parameters affecting the water line fluxes in disks by more than a factor of three are : the disk gas mass, the dust-to-gas mass ratio, the dust maximum grain size, interstellar medium (ISM) UV radiation field, the mixing parameter of Dubrulle settling, the disk flaring parameter, and the dust size distribution. The first four parameters affect the mid-IR lines much more than the far-IR lines. Conclusions: A key driver behind water spectroscopy is the dust opacity, which sets the location of the water line emitting region. We identify three types of parameters, including those (1) affecting global disk opacity and opacity function (maximum dust size and dust size distribution); (2) affecting global disk opacity (dust-to-gas mass ratio, Dubrulle settling, disk gas mass); and (3) not affecting disk opacity (flaring parameter, ISM UV radiation field, fraction of PAHs). Parameters, such as dust-to-gas ratio, ISM radiation field, and dust size distribution, affect the mid-IR lines more, while the far-IR transitions are more affected by the flaring index. The gas mass greatly affects lines in both regimes. Higher spectral

  19. Nickel Base Superalloy Turbine Disk

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P. (Inventor); Gauda, John (Inventor); Telesman, Ignacy (Inventor); Kantzos, Pete T. (Inventor)

    2005-01-01

    A low solvus, high refractory alloy having unusually versatile processing mechanical property capabilities for advanced disks and rotors in gas turbine engines. The nickel base superalloy has a composition consisting essentially of, in weight percent, 3.0-4.0 N, 0.02-0.04 B, 0.02-0.05 C, 12.0-14.0 Cr, 19.0-22.0 Co, 2.0-3.5 Mo, greater than 1.0 to 2.1 Nb, 1.3 to 2.1 Ta,3.04.OTi,4.1 to 5.0 W, 0.03-0.06 Zr, and balance essentially Ni and incidental impurities. The superalloy combines ease of processing with high temperature capabilities to be suitable for use in various turbine engine disk, impeller, and shaft applications. The Co and Cr levels of the superalloy can provide low solvus temperature for high processing versatility. The W, Mo, Ta, and Nb refractory element levels of the superalloy can provide sustained strength, creep, and dwell crack growth resistance at high temperatures.

  20. Secular evolution in disk galaxies

    NASA Astrophysics Data System (ADS)

    Knapen, J. H.

    2013-05-01

    The detailed study of the different structural components of nearby galaxies can supply vital information about the secular, or internal, evolution of these galaxies which they may have undergone since their formation. We highlight a series of new studies based on the analysis of mid-infrared images of over 2000 local galaxies which we are collecting within the Spitzer Survey of Stellar Structure in Galaxies (S^4G). In particular, we discuss new results on the thick and thin disk components of galaxies, which turn out to be roughly equally massive, and whose properties indicate that the thick disks mostly formed in situ, and to a lesser degree as a result of galaxy-galaxy interactions and secular evolution. We then briefly review recent research into rings in galaxies, which are common and closely linked to secular evolution of galaxies. Finally, we report on the research into local galaxy morphology, kinematics and stellar populations that we will perform over the coming four years within the EU-funded initial training network DAGAL (Detailed Anatomy of GALaxies).

  1. Hydrodynamic Viscosity in Accretion Disks

    NASA Astrophysics Data System (ADS)

    Duschl, Wolfgang J.; Strittmatter, Peter A.; Biermann, Peter L.

    We propose a generalized accretion disk viscosity prescription based on hydrodynamically driven turbulence at the critical effective Reynolds number. This approach is consistent with recent re-analysis by Richard & Zahn (1999) of experimental results on turbulent Couette-Taylor flows. This new β-viscosity formulation applies to both selfgravitating and non-selfgravitating disks and is shown to yield the standard α-disk prescription in the case of shock dissipation limited, non-selfgravitating disks.

  2. Kingella kingae intervertebral disk infection.

    PubMed

    Amir, J; Shockelford, P G

    1991-05-01

    Disk inflammation in children is believed to result from infection, and Staphylococcus aureus is reported to be the organism most commonly isolated from cases of intervertebral disk infection. A case of disk inflammation caused by the unusual pathogen Kingella kingae is described. The antibiotic susceptibility of other K. kingae isolates and the clinical features of 11 other previously reported cases of disk infection caused by this microorganism are reviewed.

  3. Unveiling the X-ray/UV properties of disk winds in active galactic nuclei using broad and mini-broad absorption line quasars

    NASA Astrophysics Data System (ADS)

    Giustini, M.

    2016-05-01

    We present the results of the uniform analysis of 46 XMM-Newton observations of six BAL and seven mini-BAL QSOs belonging to the Palomar-Green Quasar catalogue. Moderate-quality X-ray spectroscopy was performed with the EPIC-pn, and allowed to characterise the general source spectral shape to be complex, significantly deviating from a power law emission. A simple power law analysis in different energy bands strongly suggests absorption to be more significant than reflection in shaping the spectra. If allowing for the absorbing gas to be either partially covering the continuum emission source or to be ionised, large column densities of the order of 1022-1024 cm-2 are inferred. When the statistics was high enough, virtually every source was found to vary in spectral shape on various time scales, from years to hours. All in all these observational results are compatible with radiation driven accretion disk winds shaping the spectra of these intriguing cosmic sources.

  4. Accretion disks in luminous young stellar objects

    NASA Astrophysics Data System (ADS)

    Beltrán, M. T.; de Wit, W. J.

    2016-01-01

    An observational review is provided of the properties of accretion disks around young stars. It concerns the primordial disks of intermediate- and high-mass young stellar objects in embedded and optically revealed phases. The properties were derived from spatially resolved observations and, therefore, predominantly obtained with interferometric means, either in the radio/(sub)millimeter or in the optical/infrared wavelength regions. We make summaries and comparisons of the physical properties, kinematics, and dynamics of these circumstellar structures and delineate trends where possible. Amongst others, we report on a quadratic trend of mass accretion rates with mass from T Tauri stars to the highest mass young stellar objects and on the systematic difference in mass infall and accretion rates.

  5. Self-consistent dynamical and thermodynamical evolutions of protoplanetary disks.

    NASA Astrophysics Data System (ADS)

    Baillie, K.; Charnoz, S.; Taillifet, E.; Piau, L.

    2012-09-01

    the disk. We present the diversity of disk evolutions depending on the star properties, and on the initial molecular cloud mass and angular momentum. In particular, we compare our results to observations and see to which extent the diversity of protoplanetary disks is reproduced from their birth to their photoevaporation. A special attention will be dedicated to the influence of the stellar type on the disk evolution in order to identify which stars are more prone to planet formation. This will help targeting future JWST observations.

  6. A High-mass Protobinary System with Spatially Resolved Circumstellar Accretion Disks and Circumbinary Disk

    NASA Astrophysics Data System (ADS)

    Kraus, S.; Kluska, J.; Kreplin, A.; Bate, M.; Harries, T. J.; Hofmann, K.-H.; Hone, E.; Monnier, J. D.; Weigelt, G.; Anugu, A.; de Wit, W. J.; Wittkowski, M.

    2017-01-01

    High-mass multiples might form via fragmentation of self-gravitational disks or alternative scenarios such as disk-assisted capture. However, only a few observational constraints exist on the architecture and disk structure of high-mass protobinaries and their accretion properties. Here, we report the discovery of a close (57.9 ± 0.2 mas = 170 au) high-mass protobinary, IRAS17216-3801, where our VLTI/GRAVITY+AMBER near-infrared interferometry allows us to image the circumstellar disks around the individual components with ∼3 mas resolution. We estimate the component masses to ∼20 and ∼18 M⊙ and find that the radial intensity profiles can be reproduced with an irradiated disk model, where the inner regions are excavated of dust, likely tracing the dust sublimation region in these disks. The circumstellar disks are strongly misaligned with respect to the binary separation vector, which indicates that the tidal forces did not have time to realign the disks, pointing toward a young dynamical age of the system. We constrain the distribution of the Brγ and CO-emitting gas using VLTI/GRAVITY spectro-interferometry and VLT/CRIRES spectro-astrometry and find that the secondary is accreting at a higher rate than the primary. VLT/NACO imaging shows L‧-band emission on (3–4)× larger scales than the binary separation, matching the expected dynamical truncation radius for the circumbinary disk. The IRAS17216-3801 system is ∼3× more massive and ∼5× more compact than other high-mass multiplies imaged at infrared wavelength and the first high-mass protobinary system where circumstellar and circumbinary dust disks could be spatially resolved. This opens exciting new opportunities for studying star–disk interactions and the role of multiplicity in high-mass star formation. Based on observations made with ESO telescopes at Paranal Observatory under program IDs 60.A-9174(A), 089.C-0819(A,C), 089.C-0959(D,E), 094.C-0153(A), 096.C-0652(A).

  7. The Newtonian potential of thin disks

    NASA Astrophysics Data System (ADS)

    Huré, J.-M.; Hersant, F.

    2011-07-01

    The one-dimensional, ordinary differential equation (ODE) that satisfies the midplane gravitational potential of truncated, flat power-law disks is extended to the whole physical space. It is shown that thickness effects (i.e. non-flatness) can be easily accounted for by implementing an appropriate "softening length" λ. The solution of this "softened ODE" has the following properties: i) it is regular at the edges (finite radial accelerations); ii) it possesses the correct long-range properties; iii) it matches the Newtonian potential of a geometrically thin disk very well; and iv) it tends continuously to the flat disk solution in the limit λ → 0. As illustrated by many examples, the ODE, subject to exact Dirichlet conditions, can be solved numerically with efficiency for any given colatitude at second-order from center to infinity using radial mapping. This approach is therefore particularly well-suited to generating grids of gravitational forces in order to study particles moving under the field of a gravitating disk as found in various contexts (active nuclei, stellar systems, young stellar objects). Extension to non-power-law surface density profiles is straightforward through superposition. Grids can be produced upon request.

  8. Partial polarization by quantum distinguishability

    NASA Astrophysics Data System (ADS)

    Lahiri, Mayukh; Hochrainer, Armin; Lapkiewicz, Radek; Lemos, Gabriela Barreto; Zeilinger, Anton

    2017-03-01

    We establish that a connection exists between wave-particle duality of photons and partial polarization of a light beam. We perform a two-path lowest-order (single photon) interference experiment and demonstrate both theoretically and experimentally that the degree of polarization of the light beam emerging from an output of the interferometer depends on path distinguishability. In our experiment, we are able to change the quantum state of the emerging photon from a pure state to a fully mixed state without any direct interaction with the photon. Although most lowest-order interference experiments can be explained by classical theory, our experiment has no genuine classical analog. Our results show that a case exists where the cause of partial polarization is beyond the scope of classical theory.

  9. Consistent dust and gas models for protoplanetary disks. I. Disk shape, dust settling, opacities, and PAHs

    NASA Astrophysics Data System (ADS)

    Woitke, P.; Min, M.; Pinte, C.; Thi, W.-F.; Kamp, I.; Rab, C.; Anthonioz, F.; Antonellini, S.; Baldovin-Saavedra, C.; Carmona, A.; Dominik, C.; Dionatos, O.; Greaves, J.; Güdel, M.; Ilee, J. D.; Liebhart, A.; Ménard, F.; Rigon, L.; Waters, L. B. F. M.; Aresu, G.; Meijerink, R.; Spaans, M.

    2016-02-01

    We propose a set of standard assumptions for the modelling of Class II and III protoplanetary disks, which includes detailed continuum radiative transfer, thermo-chemical modelling of gas and ice, and line radiative transfer from optical to cm wavelengths. The first paper of this series focuses on the assumptions about the shape of the disk, the dust opacities, dust settling, and polycyclic aromatic hydrocarbons (PAHs). In particular, we propose new standard dust opacities for disk models, we present a simplified treatment of PAHs in radiative equilibrium which is sufficient to reproduce the PAH emission features, and we suggest using a simple yet physically justified treatment of dust settling. We roughly adjust parameters to obtain a model that predicts continuum and line observations that resemble typical multi-wavelength continuum and line observations of Class II T Tauri stars. We systematically study the impact of each model parameter (disk mass, disk extension and shape, dust settling, dust size and opacity, gas/dust ratio, etc.) on all mainstream continuum and line observables, in particular on the SED, mm-slope, continuum visibilities, and emission lines including [OI] 63 μm, high-J CO lines, (sub-)mm CO isotopologue lines, and CO fundamental ro-vibrational lines. We find that evolved dust properties, i.e. large grains, often needed to fit the SED, have important consequences for disk chemistry and heating/cooling balance, leading to stronger near- to far-IR emission lines in general. Strong dust settling and missing disk flaring have similar effects on continuum observations, but opposite effects on far-IR gas emission lines. PAH molecules can efficiently shield the gas from stellar UV radiation because of their strong absorption and negligible scattering opacities in comparison to evolved dust. The observable millimetre-slope of the SED can become significantly more gentle in the case of cold disk midplanes, which we find regularly in our T Tauri models

  10. Chemical Signposts in Transition Disks

    NASA Astrophysics Data System (ADS)

    Cleeves, I.; Bergin, E. A.; Fogel, J.

    2011-05-01

    In the era of the Kepler Mission, the detection of numerous multi-planet systems has demonstrated that planet-formation appears to be a rather ubiquitous phenomenon. Such systems are believed to form from nascent protoplanetary disks, whose environment sets the stage for initial planetary chemical composition and evolution. However, disk systems typically vary by orders of magnitude in radiation field, densities and temperatures, and thus complex disk models are necessary to fully understand this unique chemical environment. Further evidence for disks as progenitors to planetary systems comes from Spitzer surveys of young disk systems, which have revealed a class of objects known as ``transition disks''. These systems appear to have inner voids and gaps in the dust opacity, possibly indicative of planet evolution and disk clearing. This physical evolution in the dust disk will significantly impact its chemical nature, and therefore these potentially planet-forming systems in ``transition'' should have unique chemical signatures. We predict one such signature to be an active chemistry at the wall interface where the conditions are such that the disk is both heated and optically thick to the photo-dissociating UV. The net result is a wide variety of gas-phase molecules, appearing in line emission as bright molecular rings far from the central star. This behavior should also reveal a wealth of information about the physical conditions in this actively evolving zone between the inner ``cleared'' disk and the massive outer disk. For this presentation I will discuss the features of our disk chemical model pipeline and select model results of transition disk systems. I will also highlight the exciting future of protoplanetary disk chemistry in the era of ALMA, which will truly revolutionize our understanding of the chemical nature of disks.

  11. Two-temperature Debris Disks: Signposts for Directly Imaged Planets?

    NASA Astrophysics Data System (ADS)

    Kennedy, Grant M.; Wyatt, Mark C.

    2016-01-01

    This work considers debris disks whose spectra can be modelled by dust emission at two different temperatures. These disks are typically assumed to be a sign of multiple belts, but only a few cases have been confirmed via high resolution observations. We derive the properties of a sample of two-temperature disks, and explore whether this emission can arise from dust in a single narrow belt. While some two-temperature disks arise from single belts, it is probable that most have multiple spatial components. These disks are plausibly similar to the outer Solar System's configuration of Asteroid and Edgeworth-Kuiper belts separated by giant planets. Alternatively, the inner component could arise from inward scattering of material from the outer belt, again due to intervening planets. For either scenario, the ratio of warm/cool component temperatures is indicative of the scale of outer planetary systems, which typically span a factor of about ten in radius.

  12. The inner disks of EXor-type eruptive stars

    NASA Astrophysics Data System (ADS)

    Sipos, Nikoletta; Kóspál, Ágnes

    2014-01-01

    EX Lupi-type young stars (EXors) show sporadic brightenings of several magnitudes, caused by the episodic increase in the accretion rate of the circumstellar matter onto the young star. As the inner disk plays a crucial role during the onset of the outburst, we examined the quiescent properties of the circumstellar environment of EXors, focusing on the inner regions. We found that in case of three EXors (VY Tau, V1143 Ori and EX Lup) the spectral energy distributions show no or weak excess above the stellar photosphere at NIR-MIR wavelengths, indicative of inner disk clearing. A detailed radiative transfer modeling of the sources revealed that the inner regions of these disks had to go through significant evolution, either the inner radius of the dusty disk is beyond the sublimation radius and/or the inner disks are flattened.

  13. THE EVOLUTION OF INNER DISK GAS IN TRANSITION DISKS

    SciTech Connect

    Hoadley, K.; France, K.; McJunkin, M.; Alexander, R. D.; Schneider, P. C.

    2015-10-10

    Investigating the molecular gas in the inner regions of protoplanetary disks (PPDs) provides insight into how the molecular disk environment changes during the transition from primordial to debris disk systems. We conduct a small survey of molecular hydrogen (H{sub 2}) fluorescent emission, using 14 well-studied Classical T Tauri stars at two distinct dust disk evolutionary stages, to explore how the structure of the inner molecular disk changes as the optically thick warm dust dissipates. We simulate the observed Hi-Lyman α-pumped H{sub 2} disk fluorescence by creating a 2D radiative transfer model that describes the radial distributions of H{sub 2} emission in the disk atmosphere and compare these to observations from the Hubble Space Telescope. We find the radial distributions that best describe the observed H{sub 2} FUV emission arising in primordial disk targets (full dust disk) are demonstrably different than those of transition disks (little-to-no warm dust observed). For each best-fit model, we estimate inner and outer disk emission boundaries (r{sub in} and r{sub out}), describing where the bulk of the observed H{sub 2} emission arises in each disk, and we examine correlations between these and several observational disk evolution indicators, such as n{sub 13–31}, r{sub in,} {sub CO}, and the mass accretion rate. We find strong, positive correlations between the H{sub 2} radial distributions and the slope of the dust spectral energy distribution, implying the behavior of the molecular disk atmosphere changes as the inner dust clears in evolving PPDs. Overall, we find that H{sub 2} inner radii are ∼4 times larger in transition systems, while the bulk of the H{sub 2} emission originates inside the dust gap radius for all transitional sources.

  14. The Peculiar Velocities of Satellites of External Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Azzaro, Marco; Zentner, Andrew R.; Prada, Francisco; Klypin, Anatoly A.

    2006-07-01

    We analyze the angular distribution and the orbital rotation directions of a sample of carefully selected satellite galaxies about disk galaxy primaries extracted from the Sloan Digital Sky Survey (SDSS). We complement this analysis with a theoretical study of these statistics in an N-body simulation of cosmological structure formation set within the ΛCDM paradigm under various assumptions for the orientations of disk angular momenta. Under the assumption that the angular momenta of the disks are aligned with the angular momenta of the inner regions of their host dark matter halos, we find that the fraction of simulated satellite halos that exhibit prograde motion is fprog~0.55-0.60, with larger satellites more likely to be prograde. In our observational sample, approximately 60% of the satellites exhibit prograde motion, a result that is broadly consistent with the simulated sample. Our observational sample of satellite galaxies shows no evidence for an anisotropic satellite distribution relative to disk primaries; however, the small sample size does not yet support a statistically significant comparison to previous studies of satellite anisotropy. Again, this result is broadly consistent with our simulated sample of satellites under the assumption that disk and halo angular momenta are aligned. However, the small size of our observational sample does not yet allow us to distinguish between various assumptions regarding the orientations of disks in their halos. Finally, we present an assessment of the importance of contamination by interlopers on the measured prograde and retrograde statistics.

  15. PLANETESIMAL AND PROTOPLANET DYNAMICS IN A TURBULENT PROTOPLANETARY DISK: IDEAL UNSTRATIFIED DISKS

    SciTech Connect

    Yang, Chao-Chin; Mac Low, Mordecai-Mark; Menou, Kristen E-mail: mordecai@amnh.or

    2009-12-20

    The dynamics of planetesimals and planetary cores may be strongly influenced by density perturbations driven by magneto-rotational turbulence in their natal protoplanetary gas disks. Using the local shearing box approximation, we perform numerical simulations of planetesimals moving as massless particles in a turbulent, magnetized, unstratified gas disk. Our fiducial disk model shows turbulent accretion characterized by a Shakura-Sunyaev viscosity parameter of alpha approx 10{sup -2}, with rms density perturbations of approx10%. We measure the statistical evolution of particle orbital properties in our simulations including mean radius, eccentricity, and velocity dispersion. We confirm random walk growth in time of all three properties, the first time that this has been done with direct orbital integration in a local model. We find that the growth rate increases with the box size used at least up to boxes of eight scale heights in horizontal size. However, even our largest boxes show velocity dispersions sufficiently low that collisional destruction of planetesimals should be unimportant in the inner disk throughout its lifetime. Our direct integrations agree with earlier torque measurements showing that type I migration dominates over diffusive migration by stochastic torques for most objects in the planetary core and terrestrial planet mass range. Diffusive migration remains important for objects in the mass range of kilometer-sized planetesimals. Discrepancies in the derived magnitude of turbulence between local and global simulations of magneto-rotationally unstable disks remains an open issue, with important consequences for planet formation scenarios.

  16. Formation and evolution of the protoplanetary disk

    NASA Technical Reports Server (NTRS)

    Ruzmaikina, Tamara V.; Makalkin, A. B.

    1991-01-01

    A disk formation model during collapse of the protosolar nebula, yielding a low-mass protoplanetary disk is presented. The following subject areas are covered: (1) circumstellar disks; (2) conditions for the formation of stars with disks; (3) early evolution of the protoplanetary disk; and (4) temperature conditions and the convection in the protoplanetary disk.

  17. Millimeter Studies of Nearby Debris Disks

    NASA Astrophysics Data System (ADS)

    MacGregor, Meredith A.

    2017-01-01

    At least 20% of nearby main sequence stars are known to be surrounded by disks of dusty material resulting from the collisional erosion of planetesimals, larger bodies similar to asteroids and comets in our own Solar System. Since the dust-producing planetesimals are expected to persist in stable regions like belts and resonances, the locations, morphologies, and physical properties of dust in these ‘debris disks’ provide probes of planet formation and subsequent dynamical evolution. Observations at millimeter wavelengths are especially critical to our understanding of these systems, since the large grains that dominate emission at these long wavelengths do not travel far from their origin and therefore reliably trace the underlying planetesimal distribution. The newly upgraded capabilities of millimeter interferometers like ALMA are providing us with the opportunity to image these disks with unprecedented sensitivity and resolution. In this dissertation talk, I will present my ongoing work, which uses observations of the angularly resolved brightness distribution and the spectral dependence of the flux density to constrain both the structure and grain size distribution of a sample of nearby debris disks. I will present constraints on the position, width, surface density gradient, and any asymmetric structure of several debris disks (including Epsilon Eridani, Tau Ceti, and Fomalhaut) determined from ALMA and SMA observations. In addition, I will present the results of a survey using the VLA and ATCA to measure the long wavelength spectral index and thus the grain size distribution of fifteen debris disks. Together these results provide a foundation to investigate the dynamical evolution of planetary systems through multi-wavelength observations of debris disks.

  18. Internal and environmental secular evolution of disk galaxies

    NASA Astrophysics Data System (ADS)

    Kormendy, John

    2015-03-01

    that are available to them. They do this by spreading - the inner parts shrink while the outer parts expand. Significant changes happen only if some process efficiently transports energy or angular momentum outward. The consequences are very general: evolution by spreading happens in stars, star clusters, protostellar and protoplanetary disks, black hole accretion disks and galaxy disks. This meeting is about disk galaxies, so the evolution most often involves the redistribution of angular momentum. We now have a good heuristic understanding of how nonaxisymmetric structures rearrange disk gas into outer rings, inner rings and stuff dumped onto the center. Numerical simulations reproduce observed morphologies very well. Gas that is transported to small radii reaches high densities that are seen in CO observations. Star formation rates measured (e.g.) in the mid-infrared show that many barred and oval galaxies grow, on timescales of a few Gyr, dense central `pseudobulges' that are frequently mistaken for classical (elliptical-galaxy-like) bulges but that were grown slowly out of the disk (not made rapidly by major mergers). Our resulting picture of secular evolution accounts for the richness observed in morphological classification schemes such as those of de Vaucouleurs (1959) and Sandage (1961). State-of-the art morphology discussions include the de Vaucouleurs Atlas of Galaxies (Buta et al. 2007) and Buta (2012, 2013). Pseudobulges as disk-grown alternatives to merger-built classical bulges are important because they impact many aspects of our understanding of galaxy evolution. For example, they are observed to contain supermassive black holes (BHs), but they do not show the well known, tight correlations between BH mass and host properties (Kormendy et al. 2011). We can distinguish between classical and pseudo bulges because the latter retain a `memory' of their disky origin. That is, they have one or more characteristics of disks: (1) flatter shapes than those of

  19. Distinguishing XY from Ising electron nematics

    NASA Astrophysics Data System (ADS)

    Basak, S.; Carlson, E. W.

    2017-08-01

    At low temperatures in ultraclean GaAs-AlGaAs heterojunctions, high Landau levels near half-integral filling break rotational symmetry, leading to increasingly anisotropic transport properties as temperature is lowered below ˜150 mK . While the onset of transport anisotropy is well described by an XY model of an electron nematic in the presence of a weak uniform symmetry-breaking term, the low-temperature behavior deviates significantly from this model. We find that inclusion of interactions between the electron nematic and the underlying crystalline lattice in the form of a fourfold symmetry-breaking term is sufficient to describe the entire temperature dependence of the transport anisotropy at ν =9 /2 . This implies that this electron nematic is in the Ising universality class. We propose new experimental tests that can distinguish whether any two-dimensional electron nematic is in the XY or Ising universality class.

  20. Experiments with the Secchi disk

    NASA Astrophysics Data System (ADS)

    Aas, E.; Høkedal, J.; Sørensen, K.

    2013-10-01

    The Secchi depth and its relationships to other properties of the sea water in the Oslofjord-Skagerrak area have been investigated. White and black disks of different sizes have been applied, and the Secchi depth has been observed with the naked eye, through colour filters and with a water telescope. Spectral luminances and illuminances have been calculated from recordings of radiance and irradiance. A theoretical expression for the Secchi depth has been tested against field observations, and statistical relationships between Secchi depths and attenuation coefficients have been determined. Effects of size, colour filters, sun glitter and ship shadow have been quantified. The possibility to estimate quanta irradiance, chlorophyll a and total suspended material has also been studied.

  1. TURBULENT LINEWIDTHS IN PROTOPLANETARY DISKS: PREDICTIONS FROM NUMERICAL SIMULATIONS

    SciTech Connect

    Simon, Jacob B.; Beckwith, Kris; Armitage, Philip J.

    2011-12-10

    Submillimeter observations of protoplanetary disks now approach the acuity needed to measure the turbulent broadening of molecular lines. These measurements constrain disk angular momentum transport, and furnish evidence of the turbulent environment within which planetesimal formation takes place. We use local magnetohydrodynamic (MHD) simulations of the magnetorotational instability (MRI) to predict the distribution of turbulent velocities in low-mass protoplanetary disks, as a function of radius and height above the mid-plane. We model both ideal MHD disks and disks in which Ohmic dissipation results in a dead zone of suppressed turbulence near the mid-plane. Under ideal conditions, the disk mid-plane is characterized by a velocity distribution that peaks near v {approx_equal} 0.1c{sub s} (where c{sub s} is the local sound speed), while supersonic velocities are reached at z > 3H (where H is the vertical pressure scale height). Residual velocities of v Almost-Equal-To 10{sup -2} c{sub s} persist near the mid-plane in dead zones, while the surface layers remain active. Anisotropic variation of the linewidth with disk inclination is modest. We compare our MHD results to hydrodynamic simulations in which large-scale forcing is used to initiate similar turbulent velocities. We show that the qualitative trend of increasing v with height, seen in the MHD case, persists for forced turbulence and is likely a generic property of disk turbulence. Percentage level determinations of v at different heights within the disk, or spatially resolved observations that probe the inner disk containing the dead zone region, are therefore needed to test whether the MRI is responsible for protoplanetary disk turbulence.

  2. Brown dwarf disks with ALMA

    SciTech Connect

    Ricci, L.; Isella, A.; Testi, L.; De Gregorio-Monsalvo, I.; Natta, A.; Scholz, A.

    2014-08-10

    We present Atacama Large Millimeter/submillimeter Array continuum and spectral line data at 0.89 mm and 3.2 mm for three disks surrounding young brown dwarfs and very low mass stars in the Taurus star forming region. Dust thermal emission is detected and spatially resolved for all the three disks, while CO(J = 3-2) emission is seen in two disks. We analyze the continuum visibilities and constrain the disks' physical structure in dust. The results of our analysis show that the disks are relatively large; the smallest one has an outer radius of about 70 AU. The inferred disk radii, radial profiles of the dust surface density, and disk to central object mass ratios lie within the ranges found for disks around more massive young stars. We derive from our observations the wavelength dependence of the millimeter dust opacity. In all the three disks, data are consistent with the presence of grains with at least millimeter sizes, as also found for disks around young stars, and confirm that the early stages of the solid growth toward planetesimals occur also around very low-mass objects. We discuss the implications of our findings on models of solids evolution in protoplanetary disks, the main mechanisms proposed for the formation of brown dwarfs and very low-mass stars, as well as the potential of finding rocky and giant planets around very low-mass objects.

  3. Dark-disk universe.

    PubMed

    Fan, JiJi; Katz, Andrey; Randall, Lisa; Reece, Matthew

    2013-05-24

    We point out that current constraints on dark matter imply only that the majority of dark matter is cold and collisionless. A subdominant fraction of dark matter could have much stronger interactions. In particular, it could interact in a manner that dissipates energy, thereby cooling into a rotationally supported disk, much as baryons do. We call this proposed new dark matter component double-disk dark matter (DDDM). We argue that DDDM could constitute a fraction of all matter roughly as large as the fraction in baryons, and that it could be detected through its gravitational effects on the motion of stars in galaxies, for example. Furthermore, if DDDM can annihilate to gamma rays, it would give rise to an indirect detection signal distributed across the sky that differs dramatically from that predicted for ordinary dark matter. DDDM and more general partially interacting dark matter scenarios provide a large unexplored space of testable new physics ideas.

  4. ON HYDROMAGNETIC STRESSES IN ACCRETION DISK BOUNDARY LAYERS

    SciTech Connect

    Pessah, Martin E.; Chan, Chi-kwan E-mail: ckch@nordita.org

    2012-05-20

    Detailed calculations of the physical structure of accretion disk boundary layers, and thus their inferred observational properties, rely on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. The standard model for turbulent shear viscosity satisfies this assumption by construction. However, this behavior is not supported by numerical simulations of turbulent magnetohydrodynamic (MHD) accretion disks, which show that angular momentum transport driven by the magnetorotational instability (MRI) is inefficient in disk regions where, as expected in boundary layers, the angular frequency increases with radius. In order to shed light on physically viable mechanisms for angular momentum transport in this inner disk region, we examine the generation of hydromagnetic stresses and energy density in differentially rotating backgrounds with angular frequencies that increase outward in the shearing-sheet framework. We isolate the modes that are unrelated to the standard MRI and provide analytic solutions for the long-term evolution of the resulting shearing MHD waves. We show that, although the energy density of these waves can be amplified significantly, their associated stresses oscillate around zero, rendering them an inefficient mechanism to transport significant angular momentum (inward). These findings are consistent with the results obtained in numerical simulations of MHD accretion disk boundary layers and challenge the standard assumption of efficient angular momentum transport in the inner disk regions. This suggests that the detailed structure of turbulent MHD accretion disk boundary layers could differ appreciably from those derived within the standard framework of turbulent shear viscosity.

  5. Dynamical Evolution of Galaxy Disks in CDM models

    NASA Astrophysics Data System (ADS)

    Font, A.; Navarro, J.; Quinn, T.; Stadel, J.

    2002-12-01

    A long lasting problem in our understanding of the evolution of disk galaxies is the question of how stellar disks respond to encounters with the numerous dark matter sub-halos predicted by the Cold Dark Matter cosmology. We address this issue through a set of high resolution numerical simulations that include a realistic distribution of satellites (with masses and orbital parameters as predicted by CDM models), orbiting around a typical stellar disk, like the Milky Way's. This is the first numerical study to account for the interactions of multiple satellites with a disk within the full cosmological context. The primary conclusion of our study is that the disk is able to survive in this violent environment for several Gyrs, thus weakening the argument calling for a revision of the CDM paradigm. The only visible adjustments made by the disk to the incoming satellites are through the (angular momentum conserving) tilting, and through changes in the kinematical properties of the stars: minor vertical disk heating, flaring and warping. Changes in the disk structure are driven mainly by a few massive satellites rather than by the cumulative effect of many minor mergers.

  6. RESOLVING THE CIRCUMSTELLAR DISK OF HL TAURI AT MILLIMETER WAVELENGTHS

    SciTech Connect

    Kwon, Woojin; Looney, Leslie W.; Mundy, Lee G.

    2011-11-01

    We present results of high-resolution imaging toward HL Tau by the Combined Array for Research in Millimeter-wave Astronomy. We have obtained {lambda} = 1.3 mm and 2.7 mm dust continua with an angular resolution down to 0.''13. Through simultaneous model fitting to the two wavelength data sets in Bayesian inference using a flared viscous accretion disk model, we estimate the physical properties of HL Tau, such as density distribution, dust opacity spectral index, disk mass, disk size, inclination angle, position angle, and disk thickness. HL Tau has a circumstellar disk mass of 0.13 M{sub sun}, a characteristic radius of 79 AU, an inclination of 40{sup 0}, and a position angle of 136{sup 0}. Although a thin disk model is preferred by our two wavelength data sets, a thick disk model is needed to explain the high mid- and far-infrared emission of the HL Tau spectral energy distribution. This could imply large dust grains settled down on the midplane with fine dust grains mixed with gas. The HL Tau disk is likely gravitationally unstable and can be fragmented between 50 and 100 AU of radius. However, we did not detect dust thermal continuum supporting the protoplanet candidate claimed by a previous study using observations of the Very Large Array at {lambda} = 1.3 cm.

  7. On Hydromagnetic Stresses in Accretion Disk Boundary Layers

    NASA Astrophysics Data System (ADS)

    Pessah, Martin E.; Chan, Chi-kwan

    2012-05-01

    Detailed calculations of the physical structure of accretion disk boundary layers, and thus their inferred observational properties, rely on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. The standard model for turbulent shear viscosity satisfies this assumption by construction. However, this behavior is not supported by numerical simulations of turbulent magnetohydrodynamic (MHD) accretion disks, which show that angular momentum transport driven by the magnetorotational instability (MRI) is inefficient in disk regions where, as expected in boundary layers, the angular frequency increases with radius. In order to shed light on physically viable mechanisms for angular momentum transport in this inner disk region, we examine the generation of hydromagnetic stresses and energy density in differentially rotating backgrounds with angular frequencies that increase outward in the shearing-sheet framework. We isolate the modes that are unrelated to the standard MRI and provide analytic solutions for the long-term evolution of the resulting shearing MHD waves. We show that, although the energy density of these waves can be amplified significantly, their associated stresses oscillate around zero, rendering them an inefficient mechanism to transport significant angular momentum (inward). These findings are consistent with the results obtained in numerical simulations of MHD accretion disk boundary layers and challenge the standard assumption of efficient angular momentum transport in the inner disk regions. This suggests that the detailed structure of turbulent MHD accretion disk boundary layers could differ appreciably from those derived within the standard framework of turbulent shear viscosity

  8. THE PHYSICAL STRUCTURE OF PROTOPLANETARY DISKS: THE SERPENS CLUSTER COMPARED WITH OTHER REGIONS

    SciTech Connect

    Oliveira, Isa; Van Dishoeck, Ewine F.; Merin, Bruno; Pontoppidan, Klaus M.

    2013-01-10

    correlation is that the processes affecting the dust within disks have short timescales, happening repeatedly, making it difficult to distinguish long-lasting evolutionary effects.

  9. Bladed disk vibration

    NASA Technical Reports Server (NTRS)

    Griffin, J. H.

    1987-01-01

    The objective was to better understand the vibratory response of bladed disk assemblies that occur in jet engines or turbopumps. Two basic problems were investigated: how friction affects flutter; and how friction, mistuning, and stage aerodynamics affect resonance. Understanding these phenomena allows a better understanding of why some stages have high vibratory stresses, how best to manage those stresses, and what to do about reducing them if they are too large.

  10. Gaseous Inner Disks

    DTIC Science & Technology

    2007-01-01

    spectral line diagnostics have been used as probes of the gas in inner disks. These include transitions of molecular hydrogen at UV, near-infrared, and...mid-infrared wavelengths (Sections 2.4, 2.5) and the fundamental ro-vibrational transitions of the OH molecule (Section 2.2). Additional potential...phase and sufficiently ex- cited to produce rovibrational features in the infrared. Com- plementary atomic transitions are likely to be good probes of

  11. Hydrodynamical processes in planet-forming accretion disks

    NASA Astrophysics Data System (ADS)

    Lin, Min-Kai

    thermodynamics, dust dynamics, disk self-gravity and three-dimensional effects. By including these effects, we go wellbeyond previous works based on idealized disk models. This effort is necessary to understand how these instabilities operate and interact in realistic protoplanetary disks. This will enable us to provide a unified picture of how various hydrodynamic activities fit together to drive global disk evolution. We will address key questions including the strength of the resulting hydrodynamic turbulence, the lifetime of large-scale vortices under realistic disk conditions, and their impact on the evolution of solids within the disk. Inclusion of these additional physics will likely uncover new, yet-unknown hydrodynamic processes. Our generalized models enables a direct link between theory and observations. For example, a self-consistent incorporation of dust dynamics into the theory of hydrodynamic instabilities is particularly important, since it is the dust component that is usually observed. We will also establish the connection between the properties of large-scale, observable structures such as vortices, to the underlying disk properties, such as disk mass, and vertical structure, which are difficult to infer directly from observations. We also propose to study, for the first time, the dynamical interaction between hydrodynamic turbulence and proto-planets, as well as the influence of largescale vortices on disk-planet interaction. This is necessary towards a realistic modeling of the orbital evolution of proto planets, and thus in predicting the final architecture of planetary systems. The proposal team's expertise and experience, ranging from mathematical analyses to state-of the-art numerical simulations in astrophysical fluid dynamics, provides a multi-method approach to these problems. This is necessary towards establishing a rigorous understanding of these fundamental hydrodynamical processes in protoplanetary accretion disks.

  12. Embedded Protostellar Disks Around (Sub-)Solar Stars. II. Disk Masses, Sizes, Densities, Temperatures, and the Planet Formation Perspective

    NASA Astrophysics Data System (ADS)

    Vorobyov, Eduard I.

    2011-03-01

    We present basic properties of protostellar disks in the embedded phase of star formation (EPSF), which is difficult to probe observationally using available observational facilities. We use numerical hydrodynamics simulations of cloud core collapse and focus on disks formed around stars in the 0.03-1.0 M sun mass range. Our obtained disk masses scale near-linearly with the stellar mass. The mean and median disk masses in the Class 0 and I phases (M mean d,C0 = 0.12 M sun, M mdn d,C0 = 0.09 M sun and M mean d,CI = 0.18 M sun, M mdn d,CI = 0.15 M sun, respectively) are greater than those inferred from observations by (at least) a factor of 2-3. We demonstrate that this disagreement may (in part) be caused by the optically thick inner regions of protostellar disks, which do not contribute to millimeter dust flux. We find that disk masses and surface densities start to systematically exceed that of the minimum mass solar nebular for objects with stellar mass as low as M * = 0.05-0.1 M sun. Concurrently, disk radii start to grow beyond 100 AU, making gravitational fragmentation in the disk outer regions possible. Large disk masses, surface densities, and sizes suggest that giant planets may start forming as early as in the EPSF, either by means of core accretion (inner disk regions) or direct gravitational instability (outer disk regions), thus breaking a longstanding stereotype that the planet formation process begins in the Class II phase.

  13. DISK-SATELLITE INTERACTION IN DISKS WITH DENSITY GAPS

    SciTech Connect

    Petrovich, Cristobal; Rafikov, Roman R.

    2012-10-10

    Gravitational coupling between a gaseous disk and an orbiting perturber leads to angular momentum exchange between them that can result in gap opening by planets in protoplanetary disks and clearing of gas by binary supermassive black holes (SMBHs) embedded in accretion disks. Understanding the co-evolution of the disk and the orbit of the perturber in these circumstances requires knowledge of the spatial distribution of the torque exerted by the latter on a highly non-uniform disk. Here we explore disk-satellite interaction in disks with gaps in linear approximation both in Fourier and in physical space, explicitly incorporating the disk non-uniformity in the fluid equations. Density gradients strongly displace the positions of Lindblad resonances in the disk (which often occur at multiple locations), and the waveforms of modes excited close to the gap edge get modified compared to the uniform disk case. The spatial distribution of the excitation torque density is found to be quite different from the existing prescriptions: most of the torque is exerted in a rather narrow region near the gap edge where Lindblad resonances accumulate, followed by an exponential falloff with the distance from the perturber. Despite these differences, for a given gap profile, the full integrated torque exerted on the disk agrees with the conventional uniform disk theory prediction at the level of {approx}10%. The nonlinearity of the density wave excited by the perturber is shown to decrease as the wave travels out of the gap, slowing down its nonlinear evolution and damping. Our results suggest that gap opening in protoplanetary disks and gas clearing around SMBH binaries can be more efficient than the existing theories predict. They pave the way for self-consistent calculations of the gap structure and the orbital evolution of the perturber using accurate prescription for the torque density behavior.

  14. Statistical Properties of the Disk Counterparts of Type II Spicules from Simultaneous Observations of Rapid Blueshifted Excursions in Ca II 8542 and Hα

    NASA Astrophysics Data System (ADS)

    Sekse, D. H.; Rouppe van der Voort, L.; De Pontieu, B.

    2012-06-01

    Spicules were recently found to exist as two different types when a new class of so-called type II spicules was discovered at the solar limb with the Solar Optical Telescope on board the Hinode spacecraft. These type II spicules have been linked with on-disk observations of rapid blueshifted excursions (RBEs) in the Hα and Ca II 8542 lines. Here we analyze observations optimized for the detection of RBEs in both Hα and Ca II 8542 lines simultaneously at a high temporal cadence taken with the Crisp Imaging Spectropolarimeter at the Swedish Solar Telescope on La Palma. In this study, we used a high-quality time sequence for RBEs at different blueshifts and employed an automated detection routine to detect a large number of RBEs in order to expand on the statistics of RBEs. We find that the number of detected RBEs is strongly dependent on the associated Doppler velocity of the images on which the search is performed. Automatic detection of RBEs at lower velocities increases the estimated number of RBEs to the same order of magnitude expected from limb spicules. This shows that RBEs and type II spicules are indeed exponents of the same phenomenon. Furthermore, we provide solid evidence that Ca II 8542 RBEs are connected to Hα RBEs and are located closer to the network regions with the Hα RBEs being a continuation of the Ca II 8542 RBEs. Our results show that RBEs have an average lifetime of 83.9 s when observed in both spectral lines and that the Doppler velocities of RBEs range from 10 to 25 km s-1 in Ca II 8542 and 30 to 50 km s-1 in Hα. In addition, we automatically determine the transverse motion of a much larger sample of RBEs than previous studies, and find that, just like type II spicules, RBEs undergo significant transverse motions of the order of 5-10 km s-1. Finally, we find that the intergranular jets discovered at Big Bear Solar Observatory are a subset of RBEs.

  15. Distinguishing ordinal and disordinal interactions.

    PubMed

    Widaman, Keith F; Helm, Jonathan L; Castro-Schilo, Laura; Pluess, Michael; Stallings, Michael C; Belsky, Jay

    2012-12-01

    Re-parameterized regression models may enable tests of crucial theoretical predictions involving interactive effects of predictors that cannot be tested directly using standard approaches. First, we present a re-parameterized regression model for the Linear × Linear interaction of 2 quantitative predictors that yields point and interval estimates of 1 key parameter-the crossover point of predicted values-and leaves certain other parameters unchanged. We explain how resulting parameter estimates provide direct evidence for distinguishing ordinal from disordinal interactions. We generalize the re-parameterized model to Linear × Qualitative interactions, where the qualitative variable may have 2 or 3 categories, and then describe how to modify the re-parameterized model to test moderating effects. To illustrate our new approach, we fit alternate models to social skills data on 438 participants in the National Institute of Child Health and Human Development Study of Early Child Care. The re-parameterized regression model had point and interval estimates of the crossover point that fell near the mean on the continuous environment measure. The disordinal form of the interaction supported 1 theoretical model-differential-susceptibility-over a competing model that predicted an ordinal interaction. PsycINFO Database Record (c) 2013 APA, all rights reserved.

  16. Disk-resolved spectral reflectance properties of Phobos from 0.3-3.2 micron: Preliminary integrated results from Phobos 2

    NASA Technical Reports Server (NTRS)

    Murchie, Scott L.; Erard, Stephane; Langevin, Yves; Britt, Daniel T.; Bibring, Jean-Pierre; Mustard, John F.; Head, James W.; Pieters, Carle M.

    1991-01-01

    The Phobos 2 mission provided multispectral observations of Phobos over a large wavelength range and with relatively high spectral resolution. Here, researchers integrate results from three multispectral detectors by determining the ultraviolet-visible near infrared spectral properties of color and brightness features recognized in VSK TV images. Researchers present evidence that there are two fundamental spectral units within the region of overlapping coverage by the detectors. They describe the units' spectral and reflectance properties and discuss the implications of these results for the composition of Phobos.

  17. Simple spark erosion device based on optical disk or hard disk drive actuators.

    PubMed

    Kamer, O

    2011-12-01

    We present the design of a compact electric discharge device incorporating hard disk or optical disk drive actuators. It is simple enough to be assembled in the absence of a mechanical workshop. The electronic circuit allows the adjustment of current, voltage, and discharge power. The system has been tested with organic dielectric liquids and deionized water and spark conditions; dynamic properties and machining characteristics were investigated. This device can be used to shape materials or to produce powdered samples with low material loss and minimal liquid consumption.

  18. Forming Gaps in Debris Disks with Migrating Planets

    NASA Astrophysics Data System (ADS)

    Morrison, Sarah J.; Kratter, Kaitlin M.

    2017-01-01

    The observed wide gaps of at least several AU in debris disks from ~10 Myr to Gyr old are suggestive of multiple planets. While two planets are likely needed for maintaining the inner and outer edges of such gaps, large gaps may require more than two if planets fully occupy the gap in dynamically packed configurations at the present day. But direct imaging surveys are not discovering enough high mass planets in these systems for giant planets to be the culprit. As an alternative to currently packed planets occupying gaps in debris disks, we investigate whether planetesimal driven planet migration could produce wide gaps with lower mass, fewer planets on relevant timescales with physically realistic planetesimal disks to be consistent with the observed properties of debris disk systems. We also assess what observational signatures we may expect in gaps cleared via migration versus more packed planetary systems. We discuss implications for the disk properties in which these mechanisms could operate within the broader evolutionary context linking planets, debris disks, and the protoplanetary disks from which they originated.

  19. DVD - digital versatile disks

    SciTech Connect

    Gaunt, R.

    1997-05-01

    An international standard has emerged for the first true multimedia format. Digital Versatile Disk (by its official name), you may know it as Digital Video Disks. DVD has applications in movies, music, games, information CD-ROMS, and many other areas where massive amounts of digital information is needed. Did I say massive amounts of data? Would you believe over 17 gigabytes on a single piece of plastic the size of an audio-CD? That`s the promise, at least, by the group of nine electronics manufacturers who have agreed to the format specification, and who hope to make this goal a reality by 1998. In this major agreement, which didn`t come easily, the manufacturers will combine Sony and Phillip`s one side double-layer NMCD format with Toshiba and Matsushita`s double sided Super-Density disk. By Spring of this year, they plan to market the first 4.7 gigabyte units. The question is: Will DVD take off? Some believe that read-only disks recorded with movies will be about as popular as video laser disks. They say that until the eraseable/writable DVD arrives, the consumer will most likely not buy it. Also, DVD has a good market for replacement of CD- Roms. Back in the early 80`s, the international committee deciding the format of the audio compact disk decided its length would be 73 minutes. This, they declared, would allow Beethoven`s 9th Symphony to be contained entirely on a single CD. Similarly, today it was agreed that playback length of a single sided, single layer DVD would be 133 minutes, long enough to hold 94% of all feature-length movies. Further, audio can be in Dolby`s AC-3 stereo or 5.1 tracks of surround sound, better than CD-quality audio (16-bits at 48kHz). In addition, there are three to five language tracks, copy protection and parental ``locks`` for R rated movies. DVD will be backwards compatible with current CD-ROM and audio CD formats. Added versatility comes by way of multiple aspect rations: 4:3 pan-scan, 4:3 letterbox, and 16:9 widescreen. MPEG

  20. Deformation and Life Analysis of Composite Flywheel Disk and Multi-disk Systems

    NASA Technical Reports Server (NTRS)

    Arnold, S. M.; Saleeb, A. F.; AlZoubi, N. R.

    2001-01-01

    In this study an attempt is made to put into perspective the problem of a rotating disk, be it a single disk or a number of concentric disks forming a unit. An analytical model capable of performing an elastic stress analysis for single/multiple, annular/solid, anisotropic/isotropic disk systems, subjected to both pressure surface tractions, body forces (in the form of temperature-changes and rotation fields) and interfacial misfits is derived and discussed. Results of an extensive parametric study are presented to clearly define the key design variables and their associated influence. In general the important parameters were identified as misfit, mean radius, thickness, material property and/or load gradation, and speed; all of which must be simultaneously optimized to achieve the "best" and most reliable design. Also, the important issue of defining proper performance/merit indices (based on the specific stored energy), in the presence of multiaxiality and material anisotropy is addressed. These merit indices are then utilized to discuss the difference between flywheels made from PMC and TMC materials with either an annular or solid geometry. Finally two major aspects of failure analysis, that is the static and cyclic limit (burst) speeds are addressed. In the case of static limit loads, upper, lower, and out-of-plane bounds for disks with constant thickness are presented for both the case of internal pressure loading (as one would see in a hydroburst test) and pure rotation (as in the case of a free spinning disk). The results (interaction diagrams) are displayed graphically in designer friendly format. For the case of fatigue, a representative fatigue/life master curve is illustrated in which the normalized limit speed versus number of applied cycles is given for a cladded TMC disk application.

  1. 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.

  2. BINARIES AMONG DEBRIS DISK STARS

    SciTech Connect

    Rodriguez, David R.; Zuckerman, B.

    2012-02-01

    We have gathered a sample of 112 main-sequence stars with known debris disks. We collected published information and performed adaptive optics observations at Lick Observatory to determine if these debris disks are associated with binary or multiple stars. We discovered a previously unknown M-star companion to HD 1051 at a projected separation of 628 AU. We found that 25% {+-} 4% of our debris disk systems are binary or triple star systems, substantially less than the expected {approx}50%. The period distribution for these suggests a relative lack of systems with 1-100 AU separations. Only a few systems have blackbody disk radii comparable to the binary/triple separation. Together, these two characteristics suggest that binaries with intermediate separations of 1-100 AU readily clear out their disks. We find that the fractional disk luminosity, as a proxy for disk mass, is generally lower for multiple systems than for single stars at any given age. Hence, for a binary to possess a disk (or form planets) it must either be a very widely separated binary with disk particles orbiting a single star or it must be a small separation binary with a circumbinary disk.

  3. THE TRANSITIONAL PROTOPLANETARY DISK FREQUENCY AS A FUNCTION OF AGE: DISK EVOLUTION IN THE CORONET CLUSTER, TAURUS, AND OTHER 1-8 Myr OLD REGIONS

    SciTech Connect

    Currie, Thayne; Sicilia-Aguilar, Aurora

    2011-05-01

    We present Spitzer 3.6-24 {mu}m photometry and spectroscopy for stars in the 1-3 Myr old Coronet Cluster, expanding upon the survey of Sicilia-Aguilar et al. Using sophisticated radiative transfer models, we analyze these new data and those from Sicilia-Aguilar et al. to identify disks with evidence for substantial dust evolution consistent with disk clearing: transitional disks. We then analyze data in Taurus and others young clusters-IC 348, NGC 2362, and {eta} Cha-to constrain the transitional disk frequency as a function of time. Our analysis confirms previous results finding evidence for two types of transitional disks-those with inner holes and those that are homologously depleted. The percentage of disks in the transitional phase increases from {approx}15%-20% at 1-2 Myr to {>=}50% at 5-8 Myr; the mean transitional disk lifetime is closer to {approx}1 Myr than 0.1-0.5 Myr, consistent with previous studies by Currie et al. and Sicilia-Aguilar et al. In the Coronet Cluster and IC 348, transitional disks are more numerous for very low mass M3-M6 stars than for more massive K5-M2 stars, while Taurus lacks a strong spectral-type-dependent frequency. Assuming standard values for the gas-to-dust ratio and other disk properties, the lower limit for the masses of optically thick primordial disks is M{sub disk} {approx} 0.001-0.003 M{sub *}. We find that single color-color diagrams do not by themselves uniquely identify transitional disks or primordial disks. Full spectral energy distribution modeling is required to accurately assess disk evolution for individual sources and inform statistical estimates of the transitional disk population in large samples using mid-IR colors.

  4. Multifunctional ferromagnetic disks for modulating cell function

    PubMed Central

    Vitol, Elina A.; Novosad, Valentyn; Rozhkova, Elena A.

    2013-01-01

    In this work, we focus on the methods for controlling cell function with ferromagnetic disk-shaped particles. We will first review the history of magnetically assisted modulation of cell behavior and applications of magnetic particles for studying physical properties of a cell. Then, we consider the biological applications of the microdisks such as the method for induction of cancer cell apoptosis, controlled drug release, hyperthermia and MRI imaging. PMID:23766544

  5. Flow of a magnetic fluid between eccentric rotating disks

    NASA Astrophysics Data System (ADS)

    Kaloni, P. N.; Venkatasubramanian, S.

    We discuss the flow of a magnetic fluid between two parallel disks rotating about non-coincident axes, normal to the disks, but with same angular velocity. This device is known as an orthogonal rheometer and has been used to measure the rheological properties of polymer melts and viscoelastic fluids. For a certain range of effective relaxation times, we obtain an exact solution of this three-dimensional problem in a magnetic fluid and determine the forces exerted by the fluid on one of the rotating disks.

  6. Erosion of circumstellar particle disks by interstellar dust

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.; Griffith, Caitlin A.

    1989-01-01

    Circumstellar particle disks appear to be a common phenomenon; however, their properties vary greatly. Models of the evolution of such systems focus on internal mechanisms such as interparticle collisions and Poynting-Robertson drag. Herein it is shown that 'sandblasting' by interstellar dust can be an important and even dominant contributor to the evolution of circumstellar particle disks. Stars spend up to about 3 percent of their main-sequence lifetimes within atomic clouds. Among an IRAS sample of 21 nearby main-sequence A stars, beta Pictoris has the brightest disk; it also possesses the smallest random velocity and therefore the slowest predicted erosion rate.

  7. Disk accretion onto magnetic T Tauri stars

    SciTech Connect

    Koenigl, A. )

    1991-03-01

    The dynamical and radiative consequences of disk accretion onto magnetic T Tauri stars (TTS) are examined using the Ghosh and Lamb model. It is shown that a prolonged disk accretion phase is compatible with the low rotation rates measured in these stars if they possess a kilogauss strength field that disrupts the disk at a distance of a few stellar radii from the center. It is estimated that a steady state in which the net torque exerted on the star is zero can be attained on a time scale that is shorter than the age of the youngest visible TTS. Although the disk does not develop an ordinary shear boundary layer in this case, one can account for the observed UV excess and Balmer emission in terms of the shocks that form at the bottom of the high-latitude magnetic accretion columns on the stellar surface. This picture also provides a natural explanation of some of the puzzling variability properties of stars like DF Tau and RY Lup. YY Ori stars are interpreted as magnetic TTS in which the observer's line of sight is roughly parallel to an accretion column. 37 refs.

  8. Exoplanets and debris disk imaging with JWST

    NASA Astrophysics Data System (ADS)

    Pueyo, Laurent; Soummer, Remi; Perrin, Marshall D.

    2017-06-01

    Dramatic progress in exoplanetary systems imaging has occurred since the first generation of space coronagraphs on HST (NICMOS, STIS, ACS). While HST remains at forefront of both exoplanetary and circumstellar disk science, ground-based instruments have improved by three orders of magnitudes over the past decade. JWST will extend the current state of the art with a larger set of superior coronagraphs and greater sensitivity across more than a factor of 10 in wavelength, making it extraordinarily capable for detailed imaging characterization of planets and disks. We will address specific questions about nearby exoplanetary systems, while also optimizing observing strategies across the breadth of JWST’s high-contrast imaging modes, as follows: (a) Deep, multi-wavelength observations of selected nearby stars hosting known debris disks & planets. We will use the NIRCam and MIRI coronagraphs across the full range of JWST wavelengths, and perhaps MIRI MRS spatially resolved spectroscopy. Each comprehensive dataset will support a variety of investigations addressing both disk characterization and exoplanet detection & characterization. (b) Characterization of Planetary Systems around Cool M Stars. We will observe young and dusty M dwarfs, to complement observations of the closer but older M dwarf samples under consideration by other GTO groups. JWST observations will dramatically exceed HST images in their ability to address questions about the properties of dust rings, while the more favorable contrast ratios of planets relative to M dwarf hosts will enable sensitivity to relatively low mass planetary companions.

  9. Task 8.4 - High Temperature Turbine Disk Development

    SciTech Connect

    1997-02-27

    The goal of this task is to demonstrate a bonding technique to produce a dual-alloy turbine disk concept which will satisfy the diverse property requirements of the rim and hub areas of the disk. The program examines methods of attaching a cast superalloy rim with sufficient rupture strength to a fine grain hub materials with the required LCF properties. The goals of the program were established in the context of a preliminary turbine design by Solar Turbines, Inc. designated ATS 5. The initial target for the ATS 5 application was to allow rim operating temperatures in the 1350-1400 {degrees} F range. The life goal of the Dual-Alloy Disk was envisioned to maintain Solar`s standard turbine disk philosophy of 1000,000 hours.

  10. Generation of dynamo magnetic fields in protoplanetary and other astrophysical accretion disks

    NASA Technical Reports Server (NTRS)

    Stepinski, T. F.; Levy, E. H.

    1988-01-01

    A computational method for treating the generation of dynamo magnetic fields in astrophysical disks is presented. The numerical difficulty of handling the boundary condition at infinity in the cylindrical disk geometry is overcome by embedding the disk in a spherical computational space and matching the solutions to analytically tractable spherical functions in the surrounding space. The lowest lying dynamo normal modes for a 'thick' astrophysical disk are calculated. The generated modes found are all oscillatory and spatially localized. Tha potential implications of the results for the properties of dynamo magnetic fields in real astrophysical disks are discussed.

  11. Planetesimal and Protoplanet Dynamics in a Turbulent Protoplanetary Disk: Ideal Stratified Disks

    NASA Astrophysics Data System (ADS)

    Yang, Chao-Chin; Mac Low, Mordecai-Mark; Menou, Kristen

    2012-04-01

    Due to the gravitational influence of density fluctuations driven by magneto-rotational instability in the gas disk, planetesimals and protoplanets undergo diffusive radial migration as well as changes in other orbital properties. The magnitude of the effect on particle orbits can have important consequences for planet formation scenarios. We use the local-shearing-box approximation to simulate an ideal, isothermal, magnetized gas disk with vertical density stratification and simultaneously evolve numerous massless particles moving under the gravitational field of the gas and the host star. We measure the evolution of the particle orbital properties, including mean radius, eccentricity, inclination, and velocity dispersion, and its dependence on the disk properties and the particle initial conditions. Although the results converge with resolution for fixed box dimensions, we find the response of the particles to the gravity of the turbulent gas correlates with the horizontal box size, up to 16 disk scale heights. This correlation indicates that caution should be exercised when interpreting local-shearing-box models involving gravitational physics of magneto-rotational turbulence. Based on heuristic arguments, nevertheless, the criterion Lh /R ~ O(1), where Lh is the horizontal box size and R is the distance to the host star, is proposed to possibly circumvent this conundrum. If this criterion holds, we can still conclude that magneto-rotational turbulence seems likely to be ineffective at driving either diffusive migration or collisional erosion under most circumstances.

  12. PLANETESIMAL AND PROTOPLANET DYNAMICS IN A TURBULENT PROTOPLANETARY DISK: IDEAL STRATIFIED DISKS

    SciTech Connect

    Yang, Chao-Chin; Mac Low, Mordecai-Mark; Menou, Kristen E-mail: mordecai@amnh.org

    2012-04-01

    Due to the gravitational influence of density fluctuations driven by magneto-rotational instability in the gas disk, planetesimals and protoplanets undergo diffusive radial migration as well as changes in other orbital properties. The magnitude of the effect on particle orbits can have important consequences for planet formation scenarios. We use the local-shearing-box approximation to simulate an ideal, isothermal, magnetized gas disk with vertical density stratification and simultaneously evolve numerous massless particles moving under the gravitational field of the gas and the host star. We measure the evolution of the particle orbital properties, including mean radius, eccentricity, inclination, and velocity dispersion, and its dependence on the disk properties and the particle initial conditions. Although the results converge with resolution for fixed box dimensions, we find the response of the particles to the gravity of the turbulent gas correlates with the horizontal box size, up to 16 disk scale heights. This correlation indicates that caution should be exercised when interpreting local-shearing-box models involving gravitational physics of magneto-rotational turbulence. Based on heuristic arguments, nevertheless, the criterion L{sub h} /R {approx} O(1), where L{sub h} is the horizontal box size and R is the distance to the host star, is proposed to possibly circumvent this conundrum. If this criterion holds, we can still conclude that magneto-rotational turbulence seems likely to be ineffective at driving either diffusive migration or collisional erosion under most circumstances.

  13. Characterization of the Temperature Capabilities of Advanced Disk Alloy ME3

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P.; Telesman, Jack; Kantzos, Peter T.; OConnor, Kenneth

    2002-01-01

    The successful development of an advanced powder metallurgy disk alloy, ME3, was initiated in the NASA High Speed Research/Enabling Propulsion Materials (HSR/EPM) Compressor/Turbine Disk program in cooperation with General Electric Engine Company and Pratt & Whitney Aircraft Engines. This alloy was designed using statistical screening and optimization of composition and processing variables to have extended durability at 1200 F in large disks. Disks of this alloy were produced at the conclusion of the program using a realistic scaled-up disk shape and processing to enable demonstration of these properties. The objective of the Ultra-Efficient Engine Technologies disk program was to assess the mechanical properties of these ME3 disks as functions of temperature in order to estimate the maximum temperature capabilities of this advanced alloy. These disks were sectioned, machined into specimens, and extensively tested. Additional sub-scale disks and blanks were processed and selectively tested to explore the effects of several processing variations on mechanical properties. Results indicate the baseline ME3 alloy and process can produce 1300 to 1350 F temperature capabilities, dependent on detailed disk and engine design property requirements.

  14. Debris disks as seen by Herschel: statistics and modeling

    NASA Astrophysics Data System (ADS)

    Lebreton, J.; Marshall, J. P.; Augereau, J. C.; Eiroa, C.

    2011-10-01

    As leftovers of planet formation, debris disks represent an essential component of planetary systems. We first introduce the latest statistics obtained by the DUNES consortium, who are taking a census of extrasolar analogues to the Edgeworth-Kuiper Belt using the Herschel Space Observatory. Then we present a detailed study of the much younger debris disk surrounding the F5.5 star HD 181327. We derive strong constraints on the properties of its dust and we discuss its possible gaseous counterpart.

  15. THE IMPORTANCE OF DISK STRUCTURE IN STALLING TYPE I MIGRATION

    SciTech Connect

    Kretke, Katherine A.; Lin, D. N. C.

    2012-08-10

    As planets form they tidally interact with their natal disks. Though the tidal perturbation induced by Earth and super-Earth mass planets is generally too weak to significantly modify the structure of the disk, the interaction is potentially strong enough to cause the planets to undergo rapid type I migration. This physical process may provide a source of short-period super-Earths, though it may also pose a challenge to the emergence and retention of cores on long-period orbits with sufficient mass to evolve into gas giants. Previous numerical simulations have shown that the type I migration rate sensitively depends upon the circumstellar disk's properties, particularly the temperature and surface density gradients. Here, we derive these structure parameters for (1) a self-consistent viscous-disk model based on a constant {alpha} prescription, (2) an irradiated disk model that takes into account heating due to the absorption of stellar photons, and (3) a layered accretion disk model with variable {alpha} parameter. We show that in the inner viscously heated regions of typical protostellar disks, the horseshoe and corotation torques of super-Earths can exceed their differential Lindblad torque and cause them to undergo outward migration. However, the temperature profile due to passive stellar irradiation causes type I migration to be inward throughout much of the disk. For disks in which there is outward migration, we show that location and the mass range of the 'planet traps' depend on some uncertain assumptions adopted for these disk models. Competing physical effects may lead to dispersion in super-Earths' mass-period distribution.

  16. The Long-term Evolution of Photoevaporating Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Bae, Jaehan; Hartmann, Lee; Zhu, Zhaohuan; Gammie, Charles

    2013-09-01

    We perform calculations of our one-dimensional, two-zone disk model to study the long-term evolution of the circumstellar disk. In particular, we adopt published photoevaporation prescriptions and examine whether the photoevaporative loss alone, coupled with a range of initial angular momenta of the protostellar cloud, can explain the observed decline of the frequency of optically thick dusty disks with increasing age. In the parameter space we explore, disks have accreting and/or non-accreting transitional phases lasting for <~ 20% of their lifetime, which is in reasonable agreement with observed statistics. Assuming that photoevaporation controls disk clearing, we find that the initial angular momentum distribution of clouds needs to be weighted in favor of slowly rotating protostellar cloud cores. Again, assuming inner disk dispersal by photoevaporation, we conjecture that this skewed angular momentum distribution is a result of fragmentation into binary or multiple stellar systems in rapidly rotating cores. Accreting and non-accreting transitional disks show different evolutionary paths on the \\dot{M}{--}R_wall plane, which possibly explains the different observed properties between the two populations. However, we further find that scaling the photoevaporation rates downward by a factor of 10 makes it difficult to clear the disks on the observed timescales, showing that the precise value of the photoevaporative loss is crucial to setting the clearing times. While our results apply only to pure photoevaporative loss (plus disk accretion), there may be implications for models in which planets clear disks preferentially at radii of the order of 10 AU.

  17. THE LONG-TERM EVOLUTION OF PHOTOEVAPORATING PROTOPLANETARY DISKS

    SciTech Connect

    Bae, Jaehan; Hartmann, Lee; Zhu Zhaohuan; Gammie, Charles E-mail: lhartm@umich.edu E-mail: gammie@illinois.edu

    2013-09-01

    We perform calculations of our one-dimensional, two-zone disk model to study the long-term evolution of the circumstellar disk. In particular, we adopt published photoevaporation prescriptions and examine whether the photoevaporative loss alone, coupled with a range of initial angular momenta of the protostellar cloud, can explain the observed decline of the frequency of optically thick dusty disks with increasing age. In the parameter space we explore, disks have accreting and/or non-accreting transitional phases lasting for {approx}< 20% of their lifetime, which is in reasonable agreement with observed statistics. Assuming that photoevaporation controls disk clearing, we find that the initial angular momentum distribution of clouds needs to be weighted in favor of slowly rotating protostellar cloud cores. Again, assuming inner disk dispersal by photoevaporation, we conjecture that this skewed angular momentum distribution is a result of fragmentation into binary or multiple stellar systems in rapidly rotating cores. Accreting and non-accreting transitional disks show different evolutionary paths on the M-dot-R{sub wall} plane, which possibly explains the different observed properties between the two populations. However, we further find that scaling the photoevaporation rates downward by a factor of 10 makes it difficult to clear the disks on the observed timescales, showing that the precise value of the photoevaporative loss is crucial to setting the clearing times. While our results apply only to pure photoevaporative loss (plus disk accretion), there may be implications for models in which planets clear disks preferentially at radii of the order of 10 AU.

  18. Distinguishing quasiperiodic dynamics from chaos in short-time series.

    PubMed

    Zou, Y; Pazó, D; Romano, M C; Thiel, M; Kurths, J

    2007-07-01

    We propose a procedure to distinguish quasiperiodic from chaotic orbits in short-time series, which is based on the recurrence properties in phase space. The histogram of the return times in a recurrence plot is introduced to disclose the recurrence property consisting of only three peaks imposed by Slater's theorem. Noise effects on the statistics are studied. Our approach is demonstrated to be efficient in recognizing regular and chaotic trajectories of a Hamiltonian system with mixed phase space.

  19. Imaging Debris Disks with CCAT

    NASA Astrophysics Data System (ADS)

    Carpenter, John M.; Bryden, G.; Matthews, B. C.; Isella, A.; Ricci, L.; Swift, J.

    2013-01-01

    Debris disks are sustained by the collisional grinding of planetesimals down to micron-sized particles. The mechanisms by which the planetesimals are perturbed include stirring by planetary mass bodies, which interact gravitationally to sculpt the disk by scattering dust particles out of the disk, and capturing dust in mean motion resonances as particles drift inwards from Poynting-Robertson drag or as planets migrate. Thus the location of the debris dust can trace where planetesimals have formed, as well as the dynamical history of the disk. With high angular resolution and high sensitivity at submillimeter wavelengths, CCAT will be a powerful telescope to discover and image the structure of debris disks around nearby stars. This poster will describe various surveys that CCAT will conduct to search for new debris disks.

  20. A search for debris disks in the Herschel-ATLAS

    NASA Astrophysics Data System (ADS)

    Thompson, M. A.; Smith, D. J. B.; Stevens, J. A.; Jarvis, M. J.; Vidal Perez, E.; Marshall, J.; Dunne, L.; Eales, S.; White, G. J.; Leeuw, L.; Sibthorpe, B.; Baes, M.; González-Solares, E.; Scott, D.; Vieiria, J.; Amblard, A.; Auld, R.; Bonfield, D. G.; Burgarella, D.; Buttiglione, S.; Cava, A.; Clements, D. L.; Cooray, A.; Dariush, A.; de Zotti, G.; Dye, S.; Eales, S.; Frayer, D.; Fritz, J.; Gonzalez-Nuevo, J.; Herranz, D.; Ibar, E.; Ivison, R. J.; Lagache, G.; Lopez-Caniego, M.; Maddox, S.; Negrello, M.; Pascale, E.; Pohlen, M.; Rigby, E.; Rodighiero, G.; Samui, S.; Serjeant, S.; Temi, P.; Valtchanov, I.; Verma, A.

    2010-07-01

    Aims: We aim to demonstrate that the Herschel-ATLAS (H-ATLAS) is suitable for a blind and unbiased survey for debris disks by identifying candidate debris disks associated with main sequence stars in the initial science demonstration field of the survey. We show that H-ATLAS reveals a population of far-infrared/sub-mm sources that are associated with stars or star-like objects on the SDSS main-sequence locus. We validate our approach by comparing the properties of the most likely candidate disks to those of the known population. Methods: We use a photometric selection technique to identify main sequence stars in the SDSS DR7 catalogue and a Bayesian Likelihood Ratio method to identify H-ATLAS catalogue sources associated with these main sequence stars. Following this photometric selection we apply distance cuts to identify the most likely candidate debris disks and rule out the presence of contaminating galaxies using UKIDSS LAS K-band images. Results: We identify 78 H-ATLAS sources associated with SDSS point sources on the main-sequence locus, of which two are the most likely debris disk candidates: H-ATLAS J090315.8 and H-ATLAS J090240.2. We show that they are plausible candidates by comparing their properties to the known population of debris disks. Our initial results indicate that bright debris disks are rare, with only 2 candidates identified in a search sample of 851 stars. We also show that H-ATLAS can derive useful upper limits for debris disks associated with Hipparcos stars in the field and outline the future prospects for our debris disk search programme. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

  1. Evolution of Planetary Disks: Observations, Modeling and Instrumental Prospect

    NASA Astrophysics Data System (ADS)

    Augereau, Jean-Charles

    2000-11-01

    The recently discovered extrasolar planets have formed in gaseous and dusty disks possibily analogous to those observed around stars close to the Main Sequence, such as β Pictoris. This thesis deals with the dust in circumstellar environments around such stars and combines: high angular resolution observations, the modeling of grains' physical and chemical properties to deduce their optical behaviour, the modeling of optically thin disks, and the dynamics of planetesimals that release the dust grains observed. Our images obtained with the Hubble Space Telescope reveal two new circumstellar disks around HD 141569 and HD 100546, two stars sometimes classified as Herbig-like stars. Whereas the two systems have almost the same age (~10 million years), their morphologies differ. These observations highlight the difficulties to ellaborate a single scenario that would describe the all evolution of protoplanetary systems. The dust ring surrounding HR 4796 A, a star with an age similar to the two previous stars, is marginaly resolved from the ground. The full modeling of this disk allows to reproduce all the available observations. These results imply that, whereas the star is still quite young, planetesimals should be present to supply the disk in porous and amorphous dust grains which are afterwards blown away by radiation pressure. A dynamical model for the prototypical disk around β Pictoris is proposed. Assuming realistic optical grain properties, this approach allows to reproduce the main caracteristics of the disk and in particular the fine asymmetries that are observed. This model assumes the presence of a planetary companion which perturbes a disk of planetesimals and takes into account the differential effect of the radiation pressure on the grains. Finally, the disk model I developped during the thesis is used in order to optimize the use of future observationnal instruments.

  2. Lightweight Disk Alloy Development

    DTIC Science & Technology

    1991-04-01

    2001 (1982). 45. K C. Russell and J. W Eddington , JI Mat. Sci., 6, 20 (1972). 46. M. J. Lequeux, Ph.D. Thesis, Univ. de Paris-Sud (1979). 47. P S ...AD-A237 064 UGHTWEIGHT DISK ALLOY DEVELOPMENT S . M. Russel, C. C. Law and M. J. Blackburn Uted Te lowkles Corpoaton Prat & Whtney Govnment Enes...Space Propulo P. 0. Box 109600 West Palm Beach, FL 33410-9600 P. C. Clapp and D. M. Pease Istitute of Materials Science 9 ELECT Fg AW 11il S E Final

  3. Upper lumbar disk herniations.

    PubMed

    Cedoz, M E; Larbre, J P; Lequin, C; Fischer, G; Llorca, G

    1996-06-01

    Specific features of upper lumbar disk herniations are reviewed based on data from the literature and from a retrospective study of 24 cases treated surgically between 1982 and 1994 (seven at L1-L2 and 17 at L2-L3). Clinical manifestations are polymorphic, misleading (abdominogenital pain suggestive of a visceral or psychogenic condition, meralgia paresthetica, isolated sciatica; femoral neuralgia is uncommon) and sometimes severe (five cases of cauda equina syndrome in our study group). The diagnostic usefulness of imaging studies (radiography, myelography, computed tomography, magnetic resonance imaging) and results of surgery are discussed. The risk of misdiagnosis and the encouraging results of surgery are emphasized.

  4. Disk Evolution: Testing The Foundations

    NASA Astrophysics Data System (ADS)

    Armitage, Phil

    2016-07-01

    Models for planet formation and observable large-scale structure in protoplanetary disks are built on a foundation of gas-phase physics. In the simplest telling, it is assumed that the disk evolves due to turbulence, and that photoevaporation is the dominant driver of mass loss. How secure is this foundation to our understanding? I will review recent results from magnetohydrodynamic simulations of protoplanetary disks, which suggest a modified picture in which MHD winds and fossil magnetic flux play a critical role. I will discuss what these theoretical results may imply for observations of disks.

  5. Gravitational Instability in Planetesimal Disks

    NASA Astrophysics Data System (ADS)

    Bolin, Bryce T.; Lithwick, Yoram; Pan, Margaret; Rein, Hanno; Wu, Yanqin

    2014-11-01

    Gravitational instability (GI) has been proposed as a method of forming giant gas planets enhanced by disk thermodynamics in a protoplanetary disk (Boss, 1997, Science 276; Durisen et al., 2007, Protostars and Planets V) and as a method of forming planetesimals through the focusing of boulders by the interaction between solids and gases in a turbulent circumstellar disk (Johansen et al., 2007, Nature 448; Youdin & Goodman, 2005, Astrophys. J. 620). GI is mediated through a gaseous circumstellar disk in each each of these scenarios. We explore the possibility of GI occurring in a planetesimal disk devoid of gas. In this regime, mutual collisions between planetesimals are required to dissipate their orbital shear and velocity dispersion enough for collapse to occur as described by the Toomre stability criterion (Toomre, 1964, Astrophys. J. 139; Toomre, 1981, Structure and Evolution of Normal Galaxies). How frequent must collisions be between planetesimals in a gravitationally stable planetesimal disk for GI to occur? Are there collisional rates where GI is postponed indefinitely in an equilibrium state between gravitational stirring and collisional cooling? We present 3D shearing sheet simulations using the REBOUND N-body code with the symplectic epicyclic integrator (Rein & Liu, 2011, A&A 537; Rein & Tremaine, 2011, MNRAS 415) in which the candidate collision rates are within a few orders of magnitude of the disk dynamical lifetime. Our simulations suggest that collisions rate directly controls disk cooling. The shape of the disk cooling curve is independent of the collision rate when scaled to the collision time.

  6. Signatures of planets in circumstellar debris disks

    NASA Astrophysics Data System (ADS)

    Moro-Martin, Maria Amaya

    2004-12-01

    Main sequence stars are commonly surrounded by debris disks, composed of cold dust continuously replenished by a reservoir of undetected dust-producing planetesimals. In the outer Solar System, Kuiper Belt (KB) objects produce dust by mutual or interstellar grain collisions. The orbital evolution of KB dust has been numerically modeled. Its equilibrium radial density distribution can be accurately estimated even though there are inherent uncertainties in the prediction of structure, owing to the chaotic dynamics of dust orbital evolution imposed by resonant gravitational perturbations of the planets. The particle size distribution of dust is greatly changed from the distribution at production, as a result of radiation forces and the perturbations of the planets. The contribution of KB dust to the population of interplanetary dust particles collected at Earth may be as low as a few percent. Gravitational scattering by giant planets creates an outflow of large grains. We quantify the characteristics of this large-particle outflow in different planetary architectures, discuss its implications for exo-planetary debris disks, and for the interpretation of in-situ dust detection experiments in space probes traveling in the outer Solar System. These outflows may contribute to the clearing of circumstellar debris in planetary systems, affecting the particle size distribution of their local ISM. In anticipation of future observations of unresolved debris disks with Spitzer , we are interested in studying how the structure carved by planets affects the shape of the disk's spectral energy distribution (SED), and consequently if the SED can be used to infer the presence of planets. We numerically calculate the equilibrium spatial density distributions and SEDs of dust disks originated by an outer belt of planetesimals (35-50 AU) in the presence of different planetary configurations, and for a representative sample of chemical compositions. The dynamical models are needed to

  7. Concepts for improving turbine disk integrity

    NASA Technical Reports Server (NTRS)

    Kaufman, A.

    1976-01-01

    Advanced disk structural concepts are used to improve the cyclic lives and reliability of turbine disks. Analytical studies were conducted to evaluate bore-entry disks as potential replacements for the existing first-stage turbine disks in the CF6-50 and JT8D-17 engines. Results of low-cycle fatigue, burst, fracture mechanics, and fragment energy analyses are summarized for the advanced disk designs and the existing disk designs with both conventional and advanced disk materials. Other disk concepts such as composite, laminated, link, multibore, multidisk, and spline disks were also evaluated for the CF6-50 engine.

  8. STRUCTURE AND EVOLUTION OF PRE-MAIN-SEQUENCE CIRCUMSTELLAR DISKS

    SciTech Connect

    Isella, Andrea; Carpenter, John M.; Sargent, Anneila I.

    2009-08-10

    mass are conserved in the formation of the star/disk system. We demonstrate that the similarity solution for the surface density for {gamma} < 0 can explain the properties of some 'transitional disks' without requiring discontinuities in the disk surface density. In the case of LkCa 15, a smooth distribution of material from few stellar radii to about 240 AU can produce both the observed spectral energy distribution and the spatially resolved continuum emission at millimeter wavelengths. Finally we show that among the observed sample, TW Hya is the only object that has a disk radius comparable with the early solar nebula.

  9. Directly detecting exozodiacal dust and disk variability

    NASA Astrophysics Data System (ADS)

    Scott, Nicholas J.

    2015-01-01

    Dust is common throughout stellar systems. The architecture of stellar systems may be typically comprised of a distant cold debris disk, a warm exozodiacal disk, and a hot inner disk. Dust in this exozodiacal region confounds exoplanet detections by scattering light or mimicking planetary emission. This environment must be well-modelled in order to find Earth-sized exoplanets. Interferometry at the Center for High Resolution Astronomy (CHARA) Array provides the angular resolution to directly detect near-infrared (NIR) excesses originating from warm and hot dust close to the host star. The recently upgraded Fiber-Linked Unit for Optical Recombination (JouFLU) is capable of measuring interferometric visibility contrasts to a precision of <0.1% and dust disk fluxes equal to 1% of the host star. There is likely a connection between these hot interferometrically detected dust disks and the harder-to-detect warm zodiacal dust analogues. In this way interferometric studies can observe the tip-of-the-iceberg of stellar system dust, providing details such as composition and grain size of dust, as well as statistics on the correlation of dust populations and stellar properties. These inner dust regions may exhibit a high degree of variability which should also be characterized and may give hint to the dust origin and replenishment mechanisms. JouFLU is currently involved in a large survey of exozodiacal dust stars of spectral types A through K with the aim to provide statistics about dust disk occurrence in relation to their host stars and the presence of cold dust reservoirs. Complementing this survey is a project of re-observing the earliest excess detections in order to determine their variability. In addition, NASA's InfraRed Telescope Facility (IRTF) provides a method for spectrophotometric detections of excess stellar flux corresponding to the presence of hot/warm exozodiacal dust. Multiple NIR interferometric instruments as well as medium resolution spectroscopy are a

  10. THE COLLISIONAL EVOLUTION OF DEBRIS DISKS

    SciTech Connect

    Gaspar, Andras; Rieke, George H.; Balog, Zoltan E-mail: grieke@as.arizona.edu

    2013-05-01

    We explore the collisional decay of disk mass and infrared emission in debris disks. With models, we show that the rate of the decay varies throughout the evolution of the disks, increasing its rate up to a certain point, which is followed by a leveling off to a slower value. The total disk mass falls off {proportional_to}t {sup -0.35} at its fastest point (where t is time) for our reference model, while the dust mass and its proxy-the infrared excess emission-fades significantly faster ({proportional_to}t {sup -0.8}). These later level off to a decay rate of M{sub tot}(t){proportional_to}t {sup -0.08} and M{sub dust}(t) or L{sub ir}(t){proportional_to}t {sup -0.6}. This is slower than the {proportional_to}t {sup -1} decay given for all three system parameters by traditional analytic models. We also compile an extensive catalog of Spitzer and Herschel 24, 70, and 100 {mu}m observations. Assuming a log-normal distribution of initial disk masses, we generate model population decay curves for the fraction of stars harboring debris disks detected at 24 {mu}m. We also model the distribution of measured excesses at the far-IR wavelengths (70-100 {mu}m) at certain age regimes. We show general agreement at 24 {mu}m between the decay of our numerical collisional population synthesis model and observations up to a Gyr. We associate offsets above a Gyr to stochastic events in a few select systems. We cannot fit the decay in the far-infrared convincingly with grain strength properties appropriate for silicates, but those of water ice give fits more consistent with the observations (other relatively weak grain materials would presumably also be successful). The oldest disks have a higher incidence of large excesses than predicted by the model; again, a plausible explanation is very late phases of high dynamical activity around a small number of stars. Finally, we constrain the variables of our numerical model by comparing the evolutionary trends generated from the exploration

  11. Disk MHD generator study

    NASA Technical Reports Server (NTRS)

    Retallick, F. D.

    1980-01-01

    Directly-fired, separately-fired, and oxygen-augmented MHD power plants incorporating a disk geometry for the MHD generator were studied. The base parameters defined for four near-optimum-performance MHD steam power systems of various types are presented. The finally selected systems consisted of (1) two directly fired cases, one at 1920 K (2996F) preheat and the other at 1650 K (2500 F) preheat, (2) a separately-fired case where the air is preheated to the same level as the higher temperature directly-fired cases, and (3) an oxygen augmented case with the same generator inlet temperature of 2839 (4650F) as the high temperature directly-fired and separately-fired cases. Supersonic Mach numbers at the generator inlet, gas inlet swirl, and constant Hall field operation were specified based on disk generator optimization. System pressures were based on optimization of MHD net power. Supercritical reheat stream plants were used in all cases. Open and closed cycle component costs are summarized and compared.

  12. Disk storage at CERN

    NASA Astrophysics Data System (ADS)

    Mascetti, L.; Cano, E.; Chan, B.; Espinal, X.; Fiorot, A.; González Labrador, H.; Iven, J.; Lamanna, M.; Lo Presti, G.; Mościcki, JT; Peters, AJ; Ponce, S.; Rousseau, H.; van der Ster, D.

    2015-12-01

    CERN IT DSS operates the main storage resources for data taking and physics analysis mainly via three system: AFS, CASTOR and EOS. The total usable space available on disk for users is about 100 PB (with relative ratios 1:20:120). EOS actively uses the two CERN Tier0 centres (Meyrin and Wigner) with 50:50 ratio. IT DSS also provide sizeable on-demand resources for IT services most notably OpenStack and NFS-based clients: this is provided by a Ceph infrastructure (3 PB) and few proprietary servers (NetApp). We will describe our operational experience and recent changes to these systems with special emphasis to the present usages for LHC data taking, the convergence to commodity hardware (nodes with 200-TB each with optional SSD) shared across all services. We also describe our experience in coupling commodity and home-grown solution (e.g. CERNBox integration in EOS, Ceph disk pools for AFS, CASTOR and NFS) and finally the future evolution of these systems for WLCG and beyond.

  13. The disk(s) of the Milky Way

    NASA Astrophysics Data System (ADS)

    Concejo, J.; Stanchev, O.; Georgiev, Ts. B.

    2013-09-01

    We present a review of formation of the Milky Way's disk(s). We discuss the most recent disk formation and evolution scenarios that can be probed by the orbital eccentricities of stellar populations. These scenarios are included in two different frames, namely violent origin and secular evolution. They are also arranged in four main models: (i) accretion and disruption of satellites, (ii) disk heating by a minor merger, (iii) in situ formation during/after a gas-rich merger, and (iv) stellar migration (radial and vertical). The majority of the models have been developed according to the Lambda Cold Dark Matter (ΛCDM) cosmogony and are based on advanced numerical simulations. They aim to explain the observational data- chemical (e.g., abundances gradients and the [α/Fe] ratio) and kinematic/dynamical (e.g., rotational velocities and velocity dispersions). Models reproduce only some aspects of the Galaxy disk system because all of them are limited by numerous preliminary assumptions, inevitable numerical artifacts, etc. Here, we concentrate on the importance of stellar migration (radial and vertical), which definitively plays an essential role in the formation of the Galaxy's thick disk and gives different interpretation on the structure of the Galaxy's disk(s).

  14. The Transitional Protoplanetary Disk Frequency as a Function of Age: Disk Evolution in the Coronet Cluster, Taurus, and Other 1--8 Myr-old Regions

    NASA Technical Reports Server (NTRS)

    Currie, Thayne; Sicilia-Aguilar, Auora

    2011-01-01

    We present Spitzer 3.6-24 micron photometry and spectroscopy for stars in the 1-3 Myr-old Coronet Cluster, expanding upon the survey of Sicilia-Aguilar et al. (2008). Using sophisticated radiative transfer models, we analyze these new data and those from Sicilia-Aguilar et al. (2008) to identify disks with evidence for substantial dust evolution consistent with disk clearing: transitional disks. We then analyze data in Taurus and others young clusters - IC 348, NGC 2362, and eta Cha -- to constrain the transitional disk frequency as a function of time. Our analysis confirms previous results finding evidence for two types of transitional disks -- those with inner holes and those that are homologously depleted. The percentage of disks in the transitional phase increases from approx.15-20% at 1-2 Myr to > 50% at 5-8 Myr; the mean transitional disk lifetime is closer to approx. 1 Myr than 0.1-0.5 Myr, consistent with previous studies by Currie et al. (2009) and Sicilia-Aguilar et al. (2009). In the Coronet Cluster and IC 348, transitional disks are more numerous for very low-mass M3--M6 stars than for more massive K5-M2 stars, while Taurus lacks a strong spectral type-dependent frequency. Assuming standard values for the gas-to-dust ratio and other disk properties, the lower limit for the masses of optically-thick primordial disks is Mdisk approx. 0.001-0.003 M*. We find that single color-color diagrams do not by themselves uniquely identify transitional disks or primordial disks. Full SED modeling is required to accurately assess disk evolution for individual sources and inform statistical estimates of the transitional disk population in large samples using mid-IR colors.

  15. The disk around the brown dwarf KPNO Tau 3

    SciTech Connect

    Broekhoven-Fiene, Hannah; Matthews, Brenda; Di Francesco, James; Duchêne, Gaspard; Scholz, Aleks; Chrysostomou, Antonio; Jayawardhana, Ray

    2014-07-10

    We present submillimeter observations of the young brown dwarfs KPNO Tau 1, KPNO Tau 3, and KPNO Tau 6 at 450 μm and 850 μm taken with the Submillimetre Common-User Bolometer Array on the James Clerk Maxwell Telescope. KPNO Tau 3 and KPNO Tau 6 have been previously identified as Class II objects hosting accretion disks, whereas KPNO Tau 1 has been identified as a Class III object and shows no evidence of circumsubstellar material. Our 3σ detection of cold dust around KPNO Tau 3 implies a total disk mass of (4.0 ± 1.1) × 10{sup –4} M{sub ☉} (assuming a gas to dust ratio of 100:1). We place tight constraints on any disks around KPNO Tau 1 or KPNO Tau 6 of <2.1 × 10{sup –4} M{sub ☉} and <2.7 × 10{sup –4} M{sub ☉}, respectively. Modeling the spectral energy distribution of KPNO Tau 3 and its disk suggests the disk properties (geometry, dust mass, and grain size distribution) are consistent with observations of other brown dwarf disks and low-mass T-Tauri stars. In particular, the disk-to-host mass ratio for KPNO Tau 3 is congruent with the scenario that at least some brown dwarfs form via the same mechanism as low-mass stars.

  16. Comets as collisional fragments of a primordial planetesimal disk

    NASA Astrophysics Data System (ADS)

    Morbidelli, A.; Rickman, H.

    2015-11-01

    Context. The Rosetta mission and its exquisite measurements have revived the debate on whether comets are pristine planetesimals or collisionally evolved objects. Aims: We investigate the collisional evolution experienced by the precursors of current comet nuclei during the early stages of the solar system in the context of the so-called Nice model. Methods: We considered two environments for the collisional evolution: (1) the transplanetary planetesimal disk, from the time of gas removal until the disk was dispersed by the migration of the ice giants; and (2) the dispersing disk during the time that the scattered disk was formed. We performed simulations using different methods in the two cases to determine the number of destructive collisions typically experienced by a comet nucleus of 2 km radius. Results: In the widely accepted scenario, where the dispersal of the planetesimal disk occurred at the time of the Late Heavy Bombardment about 4 Gy ago, comet-sized planetesimals have a very low probability of surviving destructive collisions in the disk. On the extreme assumption that the disk was dispersed directly upon gas removal, a significant fraction of the planetesimals might have remained intact. However, these survivors would still bear the marks of many nondestructive impacts. Conclusions: The Nice model of solar system evolution predicts that typical km-sized comet nuclei are predominantly fragments resulting from collisions experienced by larger parent bodies. An important goal for future research is to investigate whether the observed properties of comet nuclei are compatible with such a collisional origin.

  17. Are cosmic rays effective for ionization of protoplanetary disks?

    NASA Technical Reports Server (NTRS)

    Dolginov, Arkady Z.; Stepinski, Tomasz F.

    1994-01-01

    The principal uncertainty in studying the magnetic properties of protoplanetary disks concerns the ionization levels of the disk's gas. The low gas temperature precludes thermal ionization, leaving cosmic rays as the dominant source of ionization. It has been shown that the resulting electrical conductivity is just high enough for a MHD dynamo to produce contemporaneously a magnetic field in most of the extended parts of a turbulent protoplanetary disk. Here we argue that the effectiveness of cosmic rays to ionize the bulk of the gas is impaired by the influence of the generated magnetic field on the propagation of cosmic rays within a disk. Cosmic rays scatter on magnetic inhomogeneities, and, as a result, their penetration depth decreases to only a fraction of the disk half-thickness, resulting in a severe depletion of free charge from the midplane regions of a disk. That, in turn, undercuts the dynamo mechanism, so extended parts of the disk are free from a dynamically significant magnetic field. We also point out that any additional, even small, in situ source of ionization, such as radioactive Al-26, may again make a dynamo a viable regeneration process capable of producing a dynamically important magnetic field.

  18. The origin of Jovian and Saturnian satellites in accretion disks

    NASA Astrophysics Data System (ADS)

    Ruskol, E. L.

    2006-12-01

    The properties of gas-dust disks that surrounded Jupiter and Saturn during the final stage of their formation are analyzed. The sizes of the disks are determined by the total planetocentric angular momentum of the matter accreted by planets and correspond to the sizes of the orbits of their largest satellites. The mass of the solid component of disks is limited from below by the total mass of the Galilean satellites of Jupiter (no less than 4 × 1026 g) and the mass of the largest Saturnian satellites (1.4 × 1026 g), whereas the mass of the gaseous component is limited from above by the amount of hydrogen and helium that could have been later lost by the disks. Our analysis of the known mechanisms of dissipation of gas showed that its simultaneous content in the disks relative to the solid component was much lower than the corresponding gas-to-solid ratio in the Sun. A certain amount of solid compounds (including ice) could have been brought into the disks with planetesimals, which had undergone mutual collisions in the neighborhood of giant planets and served as germs of satellites. The bulk of solid matter appears to have been captured into disks when the latter were crossed by smaller and intermediate-sized planetesimals, which then became parts of the satellites.

  19. ACCRETION DISKS AROUND KICKED BLACK HOLES: POST-KICK DYNAMICS

    SciTech Connect

    Ponce, Marcelo; Faber, Joshua A.; Lombardi, James C. E-mail: jafsma@rit.edu

    2012-01-20

    Numerical calculations of merging black hole binaries indicate that asymmetric emission of gravitational radiation can kick the merged black hole at up to thousands of km s{sup -1}, and a number of systems have been observed recently whose properties are consistent with an active galactic nucleus containing a supermassive black hole moving with substantial velocity with respect to its broader accretion disk. We study here the effect of an impulsive kick delivered to a black hole on the dynamical evolution of its accretion disk using a smoothed particle hydrodynamics code, focusing attention on the role played by the kick angle with respect to the orbital angular momentum vector of the pre-kicked disk. We find that for more vertical kicks, for which the angle between the kick and the normal vector to the disk {theta} {approx}< 30 Degree-Sign , a gap remains present in the inner disk, in accordance with the prediction from an analytic collisionless Keplerian disk model, while for more oblique kicks with {theta} {approx}> 45 Degree-Sign , matter rapidly accretes toward the black hole. There is a systematic trend for higher potential luminosities for more oblique kick angles for a given black hole mass, disk mass, and kick velocity, and we find large amplitude oscillations in time in the case of a kick oriented 60 Degree-Sign from the vertical.

  20. Serendipitous detection of a debris disk near the Sun

    NASA Astrophysics Data System (ADS)

    Kalas, Paul

    2004-07-01

    We report the unexpected detection of the Fomalhaut debris disk in scattered light during one orbit of observation for our Cycle 12 program GO9862. This is a major discovery because Fomalhaut is now the closest {7.7 pc} and oldest { 200 Myr} debris disk detected in reflected light. We would like to request Director's Discretionary Time to further study the Fomalhaut disk. The goals are to image the disk around its entire perimeter, increase the signal-to-noise of the detection, and to obtain data at a second wavelength. We will perform a high-resolution study of radial and azimuthal disk asymmetries that are thought to arise from perturbations by planet-mass companions, and we will constrain the physical properties of grain material by obtaining the color of the disk. Because our original Cycle 12 program was designed to study point sources in the field, and the ACS/HRC coronagraph is a limited lifetime resource, it is necessary to acquire these additional data via Director's Discretionary Time during Cycle 13. The observational challenge of high contrast cannot be met by other observatories, and these data will complement new Spitzer results on the Fomalhaut disk at mid and far-infared wavelengths.

  1. Effect of nanoparticles on the structure and properties of an aluminum alloy poured into a mould with the use of a magnetohydrodynamic disk pump

    NASA Astrophysics Data System (ADS)

    Katsnelson, S. S.; Pozdnyakov, G. A.; Cherepanov, A. N.

    2015-09-01

    The influence of two nanomodifiers with different compositions during their homogenization in the AL7 aluminum melt and moulding on the properties of the modified aluminum alloy is studied. Experiments are performed with the use of a centrifugal conductive magnetohydrodynamic pump. The melt is poured into a graphite mould with three cylindrical channels 38 mm in diameter and 160 mm long, which are designed for a metal mass of 500 g. Two compositions are used as modifying agents: nano-scale particles of the aluminum nitride powder 40-100 nm in size and metallized carbon nanotubes smaller than 25 nm, which are clad with aluminum to improve wetting of their surface. The analysis of the structure of the experimental and reference samples shows that the use of modifiers leads to refinement of the grain structure of the cast metal. According to the Hall-Petch theory, this effect may result in improvement of mechanical characteristics of the cast metal.

  2. ON THE ROLE OF THE ACCRETION DISK IN BLACK HOLE DISK-JET CONNECTIONS

    SciTech Connect

    Miller, J. M.; Reis, R. C.; Pooley, G. G.; Fabian, A. C.; Cackett, E. M.; Nowak, M. A.; Pottschmidt, K.; Wilms, J.

    2012-09-20

    Models of jet production in black hole systems suggest that the properties of the accretion disk-such as its mass accretion rate, inner radius, and emergent magnetic field-should drive and modulate the production of relativistic jets. Stellar-mass black holes in the 'low/hard' state are an excellent laboratory in which to study disk-jet connections, but few coordinated observations are made using spectrometers that can incisively probe the inner disk. We report on a series of 20 Suzaku observations of Cygnus X-1 made in the jet-producing low/hard state. Contemporaneous radio monitoring was done using the Arcminute MicroKelvin Array radio telescope. Two important and simple results are obtained: (1) the jet (as traced by radio flux) does not appear to be modulated by changes in the inner radius of the accretion disk and (2) the jet is sensitive to disk properties, including its flux, temperature, and ionization. Some more complex results may reveal aspects of a coupled disk-corona-jet system. A positive correlation between the reflected X-ray flux and radio flux may represent specific support for a plasma ejection model of the corona, wherein the base of a jet produces hard X-ray emission. Within the framework of the plasma ejection model, the spectra suggest a jet base with v/c {approx_equal} 0.3 or the escape velocity for a vertical height of z {approx_equal} 20 GM/c {sup 2} above the black hole. The detailed results of X-ray disk continuum and reflection modeling also suggest a height of z {approx_equal} 20 GM/c {sup 2} for hard X-ray production above a black hole, with a spin in the range 0.6 {<=} a {<=} 0.99. This height agrees with X-ray time lags recently found in Cygnus X-1. The overall picture that emerges from this study is broadly consistent with some jet-focused models for black hole spectral energy distributions in which a relativistic plasma is accelerated at z = 10-100 GM/c {sup 2}. We discuss these results in the context of disk-jet connections

  3. Distinguishing quantum operations: LOCC versus separable operators

    NASA Astrophysics Data System (ADS)

    Chattopadhyay, Indrani; Sarkar, Debasis

    2016-08-01

    In this paper, we discuss the issue of distinguishing a pair of quantum operation in general. We use Krause theorem for representing the operations in unitary form. This supports the existence of pair of quantum operations that are not locally distinguishable, but distinguishable in asymptotic sense in some higher dimensional system. The process can even be successful without any use of the entangled initial state.

  4. A twisted disk equation that describes warped galaxy disks

    NASA Technical Reports Server (NTRS)

    Barker, K.

    1994-01-01

    Warped H1 gas layers in the outer regions of spiral galaxies usually display a noticeably twisted structure. This structure is thought to arise primarily as a result of differential precession in the H1 disk as it settles toward a 'preferred orientation' in an underlying dark halo potential well that is not spherically symmetric. In an attempt to better understand the structure and evolution of these twisted, warped disk structures, we have utilized the 'twist-equation' formalism. Specifically, we have generalized the twist equation to allow the treatment of non-Keplerian disks and from it have derived the steady-state structure of twisted disks that develop from free precession in a nonspherical, logarithmic halo potential. This generalized equation can also be used to examine the time-evolutionary behavior of warped galaxy disks.

  5. Herschel Observations of Dusty Debris Disks

    NASA Astrophysics Data System (ADS)

    Vican, Laura; Schneider, Adam; Bryden, Geoff; Melis, Carl; Zuckerman, B.; Rhee, Joseph; Song, Inseok

    2016-12-01

    We present results from two Herschel observing programs using the Photodetector Array Camera and Spectrometer. During three separate campaigns, we obtained Herschel data for 24 stars at 70, 100, and 160 μm. We chose stars that were already known or suspected to have circumstellar dust based on excess infrared (IR) emission previously measured with the InfraRed Astronomical Satellite (IRAS) or Spitzer and used Herschel to examine long-wavelength properties of the dust. Fifteen stars were found to be uncontaminated by background sources and possess IR emission most likely due to a circumstellar debris disk. We analyzed the properties of these debris disks to better understand the physical mechanisms responsible for dust production and removal. Seven targets were spatially resolved in the Herschel images. Based on fits to their spectral energy distributions, nine disks appear to have two temperature components. Of these nine, in three cases, the warmer dust component is likely the result of a transient process rather than a steady-state collisional cascade. The dust belts at four stars are likely stirred by an unseen planet and merit further investigation.

  6. Full-disk view of Titania

    NASA Technical Reports Server (NTRS)

    1986-01-01

    Voyager 2 obtained this full-disk view of Uranus' moon Titania in the early morning hours of Jan. 24, 1986, from a distance of about 500,000 kilometers (300,000 miles). Many circular depressions -- probably impact craters -- are visible in this clear-filter image returned by the Voyager narrow-angle camera. Other bright spots are distinguished by radiating rays and are probably halo craters that mark relatively more recent impacts. Even more interesting are linear troughs (right) that are probably fault canyons. The troughs break the crust in two directions, an indication of some tectonic extension of Titania's crust. These features indicate that this icy satellite has a dynamic, active interior. Titania is about 1,600 km (1,000 mi) in diameter; the resolution of this image is about 9 km (6 mi). The Voyager project is managed for NASA by the Jet Propulsion Laboratory.

  7. Full-disk view of Titania

    NASA Technical Reports Server (NTRS)

    1986-01-01

    Voyager 2 obtained this full-disk view of Uranus' moon Titania in the early morning hours of Jan. 24, 1986, from a distance of about 500,000 kilometers (300,000 miles). Many circular depressions -- probably impact craters -- are visible in this clear-filter image returned by the Voyager narrow-angle camera. Other bright spots are distinguished by radiating rays and are probably halo craters that mark relatively more recent impacts. Even more interesting are linear troughs (right) that are probably fault canyons. The troughs break the crust in two directions, an indication of some tectonic extension of Titania's crust. These features indicate that this icy satellite has a dynamic, active interior. Titania is about 1,600 km (1,000 mi) in diameter; the resolution of this image is about 9 km (6 mi). The Voyager project is managed for NASA by the Jet Propulsion Laboratory.

  8. Formation of sharp eccentric rings in debris disks with gas but without planets.

    PubMed

    Lyra, W; Kuchner, M

    2013-07-11

    'Debris disks' around young stars (analogues of the Kuiper Belt in our Solar System) show a variety of non-trivial structures attributed to planetary perturbations and used to constrain the properties of those planets. However, these analyses have largely ignored the fact that some debris disks are found to contain small quantities of gas, a component that all such disks should contain at some level. Several debris disks have been measured with a dust-to-gas ratio of about unity, at which the effect of hydrodynamics on the structure of the disk cannot be ignored. Here we report linear and nonlinear modelling that shows that dust-gas interactions can produce some of the key patterns attributed to planets. We find a robust clumping instability that organizes the dust into narrow, eccentric rings, similar to the Fomalhaut debris disk. The conclusion that such disks might contain planets is not necessarily required to explain these systems.

  9. Formation of Sharp Eccentric Rings in Debris Disks with Gas but Without Planets

    NASA Technical Reports Server (NTRS)

    Lyra, W.; Kuchner, M.

    2013-01-01

    'Debris disks' around young stars (analogues of the Kuiper Belt in our Solar System) show a variety of non-trivial structures attributed to planetary perturbations and used to constrain the properties of those planets. However, these analyses have largely ignored the fact that some debris disks are found to contain small quantities of gas, a component that all such disks should contain at some level. Several debris disks have been measured with a dust-to-gas ratio of about unity, at which the effect of hydrodynamics on the structure of the disk cannot be ignored. Here we report linear and nonlinear modelling that shows that dust-gas interactions can produce some of the key patterns attributed to planets. We find a robust clumping instability that organizes the dust into narrow, eccentric rings, similar to the Fomalhaut debris disk. The conclusion that such disks might contain planets is not necessarily required to explain these systems.

  10. Herschel survey of brown dwarf disks in ρ Ophiuchi

    NASA Astrophysics Data System (ADS)

    Alves de Oliveira, C.; Ábrahám, P.; Marton, G.; Pinte, C.; Kiss, Cs.; Kun, M.; Kóspál, Á.; André, P.; Könyves, V.

    2013-11-01

    Context. Young brown dwarfs are known to possess circumstellar disks, a characteristic that is fundamental to the understanding of their formation process, and raises the possibility that these objects harbour planets. Aims: We want to characterise the far-IR emission of disks around the young brown dwarf population of the ρ Ophiuchi cluster in LDN 1688. Methods: Recent observations of the ρ Ophiuchi cluster with the Herschel Space Observatory allow us to probe the spectral energy distribution (SED) of the brown dwarf population in the far-IR, where the disk emission peaks. We performed aperture photometry at 70, 100, and 160 μm, and constructed SEDs for all previously known brown dwarfs detected. These were complemented with ancillary photometry at shorter wavelengths. We compared the observed SEDs to a grid of synthetic disks produced with the radiative transfer code MCFOST, and used the relative figure of merit estimated from the Bayesian inference of each disk parameter to analyse the structural properties. Results: We detected 12 Class II brown dwarfs with Herschel, which corresponds to one-third of all currently known brown dwarf members of ρ Ophiuchi. We did not detect any of the known Class III brown dwarfs. Comparison to models reveals that the disks are best described by an inner radius between 0.01 and 0.07 AU, and a flared disk geometry with a flaring index between 1.05 and 1.2. Furthermore, we can exclude values of the disk scale-height lower than 10 AU (measured at a fiducial radius of 100 AU). We combined the Herschel data with recent ALMA observations of the brown dwarf GY92 204 (ISO-Oph 102), and by comparing its SED to the same grid of disk models, we derived an inner disk radius of 0.035 AU, a scale height of 15 AU with a flaring index of β ~ 1.15, an exponent for dust settling of -1.5, and a disk mass of 0.001 M⊙. This corresponds to a disk-to-central object mass ratio of ~1%. Conclusions: The structural parameters constrained by the

  11. Selected Papers on Protoplanetary Disks

    NASA Technical Reports Server (NTRS)

    Bell, K. R.; Cassen, P. M.; Wasson, J. T.; Woolum, D. S.; Klahr, H. H.; Henning, Th.

    2004-01-01

    Three papers present studies of thermal balances, dynamics, and electromagnetic spectra of protoplanetary disks, which comprise gas and dust orbiting young stars. One paper addresses the reprocessing, in a disk, of photons that originate in the disk itself in addition to photons that originate in the stellar object at the center. The shape of the disk is found to strongly affect the redistribution of energy. Another of the three papers reviews an increase in the optical luminosity of the young star FU Orionis. The increase began in the year 1936 and similar increases have since been observed in other stars. The paper summarizes astronomical, meteoric, and theoretical evidence that these increases are caused by increases in mass fluxes through the inner portions of the protoplanetary disks of these stars. The remaining paper presents a mathematical-modeling study of the structures of protostellar accretion disks, with emphasis on limits on disk flaring. Among the conclusions reached in the study are that (1) the radius at which a disk becomes shadowed from its central stellar object depends on radial mass flow and (2) most planet formation has occurred in environments unheated by stellar radiation.

  12. Circumstellar disks and planetary formation

    NASA Astrophysics Data System (ADS)

    Huélamo, N.

    2017-03-01

    Circumstellar disks are very common around young intermediate-, low-mass stars, and brown dwarfs. They are the cradle of planetary systems, although the mechanism to form planets is still unknown. In this text I review some advances in the field of circumstellar disks and planetary formation coming from observations.

  13. The Evolution of FU Orionis Disks

    NASA Astrophysics Data System (ADS)

    Green, Joel

    2015-10-01

    Mid-IR dust features occasionally vary dramatically in T Tauri stars, but are typically consistent over multiple epochs. Most T Tauri silicate features indicate both grain growth and high crystallinity fractions. In contrast, outbursting sources (FUors) exhibit some grain growth but pristine silicate emission features, hinting at modification of their protoplanetary disk chemistry, with resulting implications for planet formation. FUors are the best candidates to observe rapid changes in disks, both because they are unusually bright IR sources relative to their core mass, and vary on day, month, year, and decadal timescales. With improved spatial and spectral resolution from FORCAST, we can combine with Spitzer-IRS to observe and constrain the properties of silicate dust, and disk profiles, as they are altered by the outburst. We propose to observe five FU Orionis objects (FU Ori, V1057 Cyg, V1515 Cyg, V1735 Cyg, and V2775 Ori) in order to determine whether the outburst influences the dust feature or in- stead highlights a larger dust radius where processing has not yet occurred. This sample includes every FUor observed with Spitzer-IRS in 2005-8 that is detectable with FORCAST at sufficient S/N to sample the silicate feature. They represent a spread of FUor subtypes, and have declined in overall brightness at different rates, providing several different case studies. Their bright continuum provides the perfect opportunity for FORCAST spectroscopy, with a 7-10 year baseline to probe changes in their mid-IR properties. This will be the first mid-IR spectroscopic variability study of multi-year processes in FUors, producing calibrated spectra at better spectral and spatial resolution than previous epoch Spitzer-IRS data. We will search for changes in crystallinity fraction, grain growth, and continuum. We expect to observe signposts of dust processing and evolution providing time constraints on disk evolution, and input to planet formation models.

  14. Constraining Galaxy Evolution With Bulge+Disk+Bar Decomposition

    NASA Astrophysics Data System (ADS)

    Weinzirl, Tim; Jogee, S.; Barazza, F.

    2007-12-01

    Structural decomposition of galaxies into bulge, disk, and bar components is important to address a number of scientific problems. Measuring bulge, disk, and bar structural parameters will set constraints on the violent and secular processes of galaxy assembly and recurrent bar formation and dissolution models. It can also help to quantify the fraction and properties of bulgeless galaxies (those systems having no bulge or only a relatively insignificant disky-pseudobulges), which defy galaxy formation paradigms requiring almost every disk galaxy to have a classical bulge at its core. We demonstrate three-component bulge+disk+bar decomposition of NIR images for a sample of 200+ galaxies, with Hubble types S0 to Sm, from the Ohio State University Bright Spiral Galaxy Survey (OSUBSGS) and the UKIRT Infrared Deep Sky Survey (UKIDSS). Unlike most early studies, which attempt two-component bulge+disk decomposition, we perform three-component bulge+disk+bar decomposition with GALFIT. We show that it is important to include the bar component, as this can lower the bulge fractional luminosity ratio (B/T), often by a factor of two or more, and effectively change the Hubble type of a galaxy from early to late. We investigate how the structure of bulges and B/T vary across the Hubble sequence for barred and unbarred galaxies. We also identify the fraction of bulgeless galaxies in our sample and characterize their properties.

  15. Disk Density Tuning of a Maximal Random Packing

    PubMed Central

    Ebeida, Mohamed S.; Rushdi, Ahmad A.; Awad, Muhammad A.; Mahmoud, Ahmed H.; Yan, Dong-Ming; English, Shawn A.; Owens, John D.; Bajaj, Chandrajit L.; Mitchell, Scott A.

    2016-01-01

    We introduce an algorithmic framework for tuning the spatial density of disks in a maximal random packing, without changing the sizing function or radii of disks. Starting from any maximal random packing such as a Maximal Poisson-disk Sampling (MPS), we iteratively relocate, inject (add), or eject (remove) disks, using a set of three successively more-aggressive local operations. We may achieve a user-defined density, either more dense or more sparse, almost up to the theoretical structured limits. The tuned samples are conflict-free, retain coverage maximality, and, except in the extremes, retain the blue noise randomness properties of the input. We change the density of the packing one disk at a time, maintaining the minimum disk separation distance and the maximum domain coverage distance required of any maximal packing. These properties are local, and we can handle spatially-varying sizing functions. Using fewer points to satisfy a sizing function improves the efficiency of some applications. We apply the framework to improve the quality of meshes, removing non-obtuse angles; and to more accurately model fiber reinforced polymers for elastic and failure simulations. PMID:27563162

  16. Mass distributions in disk galaxies

    NASA Astrophysics Data System (ADS)

    Martinsson, Thomas; Verheijen, Marc; Bershady, Matthew; Westfall, Kyle; Andersen, David; Swaters, Rob

    2017-03-01

    We present results on luminous and dark matter mass distributions in disk galaxies from the DiskMass Survey. As expected for normal disk galaxies, stars dominate the baryonic mass budget in the inner region of the disk; however, at about four optical scale lengths (hR ) the atomic gas starts to become the dominant contributor. Unexpectedly, we find the total baryon to dark-matter fraction within a galaxy stays nearly constant with radius from 1hR out to at least 6hR , with a baryon fraction of 15-50% among galaxies. On average, only one third of the mass within 2.2hR in a disk galaxy is baryonic and these baryons appear to have had only a minor effect on the distribution of the dark matter.

  17. Debris Disks and Hidden Planets

    NASA Technical Reports Server (NTRS)

    Kuchner, Marc

    2008-01-01

    When a planet orbits inside a debris disk like the disk around Vega or Beta Pictoris, the planet may be invisible, but the patterns it creates in the disk may give it away. Observing and decoding these patterns may be the only way we can detect exo-Neptunes orbiting more than 20 AU from their stars, and the only way we can spot planets in systems undergoing the late stages of planet formation. Fortunately, every few months, a new image of a debris disk appears with curious structures begging for explanation. I'll describe some new ideas in the theory of these planet-disk interactions and provide a buyers guide to the latest models (and the planets they predict).

  18. Generation of dynamo magnetic fields in thin Keplerian disks

    NASA Technical Reports Server (NTRS)

    Stepinski, T. F.; Levy, E. H.

    1990-01-01

    The combined action of nonuniform rotation and helical convection in protoplanetary disks, in the Galaxy, or in accretion disks surrounding black holes and other compact objects, enables an alpha-omega dynamo to generate a large-scale magnetic field. In this paper, the properties of such magnetic fields are investigated using a two-dimensional, partially numerical method. The structures of the lowest-order steady state and oscillatory modes are calculated for two kinds of external boundary conditions. A quadruple, steady state, highly localized mode is the most easily excited for low values of the dynamo number. The results indicate that, except under special conditions, disk dynamo modes tend to consist of relatively localized rings structures. For large values of the dynamo number, the magnetic field consists of a number of quasi-independent, spatially localized modes generated in various concentric rings filling the disk inward of a dynamo generation 'front'.

  19. A re-examination of the disk flow regulator*

    PubMed Central

    Weathers, D. B.; Taylor, J. W.; Jensen, J. A.

    1971-01-01

    It is important in residual spraying programmes for malaria eradication that a uniform deposit of insecticide should be applied to the walls of dwellings. The uniformity of application with hand compression sprayers is greatly enhanced if a disk flow regulator is used, but this device has not been popular for field use as its properties alter after a few days' use. This study explains the mode of action of the device and discloses that swelling of the disk caused by the DDT formulation is the primary cause of the gradual reduction of output. The need for proper mating of the disk with the nozzle tip is explained, and the 9504E-type tip is described as best suited for the desired spray output. Use of the disk flow regulator is recommended because it permits uniform spray application and reduces nozzle-tip erosion. PMID:5317451

  20. The Upside Down Construction of a Simulated Disk Galaxy

    NASA Astrophysics Data System (ADS)

    Bird, J. C.; Kazantzidis, S.; Weinberg, D. H.; Guedes, J.; Callegari, S.; Mayer, L.; Madau, P.

    2014-03-01

    We analyze the dynamical evolution of stellar age cohorts, groups of stars with similar formation times, to determine the detailed structure formation history of the cosmological simulation of the formation of a disk galaxy similar to the Milky Way (the “Eris” simulation). There is a remarkably smooth correlation between structure and stellar age at z = 0, going from spheroidal distributions for the oldest stars to long, thin disks for the youngest populations. We find the velocity dispersion of a cohort increases monotonically with age. The smooth relationships between stellar age, structure, and dynamics seen at z = 0, which agree nicely with the observed properties of mono-abundance populations in the Milky Way, are largely established by the disk formation process. Stars continuously form as the initially spheroidal gas reservoir cools and contracts, increasing its rotational support and becomingly progressively longer and vertically thinner. Thus, the stellar disk forms “inside-out” radially and “upside-down” vertically.

  1. TRANSITIONAL DISKS AND THEIR ORIGINS: AN INFRARED SPECTROSCOPIC SURVEY OF ORION A

    SciTech Connect

    Kim, K. H.; Watson, Dan M.; Manoj, P.; Forrest, W. J.; Arnold, Laura; Najita, Joan; Furlan, Elise; Sargent, Benjamin; Espaillat, Catherine; Muzerolle, James; Megeath, S. T.; Calvet, Nuria; Green, Joel D.

    2013-06-01

    Transitional disks are protoplanetary disks around young stars, with inner holes or gaps which are surrounded by optically thick outer, and often inner, disks. Here we present observations of 62 new transitional disks in the Orion A star-forming region. These were identified using the Spitzer Space Telescope's Infrared Spectrograph and followed up with determinations of stellar and accretion parameters using the Infrared Telescope Facility's SpeX. We combine these new observations with our previous results on transitional disks in Taurus, Chamaeleon I, Ophiuchus, and Perseus, and with archival X-ray observations. This produces a sample of 105 transitional disks of ''cluster'' age 3 Myr or less, by far the largest hitherto assembled. We use this sample to search for trends between the radial structure in the disks and many other system properties, in order to place constraints on the possible origins of transitional disks. We see a clear progression of host-star accretion rate and the different disk morphologies. We confirm that transitional disks with complete central clearings have median accretion rates an order of magnitude smaller than radially continuous disks of the same population. Pre-transitional disks-those objects with gaps that separate inner and outer disks-have median accretion rates intermediate between the two. Our results from the search for statistically significant trends, especially related to M-dot , strongly support that in both cases the gaps are far more likely to be due to the gravitational influence of Jovian planets or brown dwarfs orbiting within the gaps, than to any of the photoevaporative, turbulent, or grain-growth processes that can lead to disk dissipation. We also find that the fraction of Class II YSOs which are transitional disks is large, 0.1-0.2, especially in the youngest associations.

  2. THE NATURE OF TRANSITION CIRCUMSTELLAR DISKS. III. PERSEUS, TAURUS, AND AURIGA

    SciTech Connect

    Cieza, Lucas A.; Williams, Jonathan P.; Schreiber, Matthias R.; Romero, Gisela A.; Rebassa-Mansergas, Alberto; Merin, Bruno

    2012-05-10

    As part of an ongoing program aiming to characterize a large number of Spitzer-selected transition disks (disks with reduced levels of near-IR and/or mid-IR excess emission), we have obtained (sub)millimeter wavelength photometry, high-resolution optical spectroscopy, and adaptive optics near-infrared imaging for a sample of 31 transition objects located in the Perseus, Taurus, and Auriga molecular clouds. We use these ground-based data to estimate disk masses, multiplicity, and accretion rates in order to investigate the mechanisms potentially responsible for their inner holes. Following our previous studies in other regions, we combine disk masses, accretion rates, and multiplicity data with other information, such as spectral energy distribution morphology and fractional disk luminosity, to classify the disks as strong candidates for the following categories: grain-growth-dominated disks (seven objects), giant planet-forming disks (six objects), photoevaporating disks (seven objects), debris disks (11 objects), and cicumbinary disks (one object, which was also classified as a photoevaporating disk). Combining our sample of 31 transition disks with those from our previous studies results in a sample of 74 transition objects that have been selected, characterized, and classified in a homogenous way. We discuss this combined high-quality sample in the context of the current paradigm of the evolution and dissipation of protoplanetary disks and use its properties to constrain different aspects of the key processes driving their evolution. We find that the age distribution of disks that are likely to harbor recently formed giant planets favors core accretion as the main planet formation mechanism and a {approx}2-3 Myr formation timescale.

  3. VISCOUS EVOLUTION AND PHOTOEVAPORATION OF CIRCUMSTELLAR DISKS DUE TO EXTERNAL FAR ULTRAVIOLET RADIATION FIELDS

    SciTech Connect

    Anderson, Kassandra R.; Adams, Fred C.; Calvet, Nuria

    2013-09-01

    This paper explores the effects of FUV radiation fields from external stars on circumstellar disk evolution. Disks residing in young clusters can be exposed to extreme levels of FUV flux from nearby OB stars, and observations show that disks in such environments are being actively photoevaporated. Typical FUV flux levels can be factors of {approx}10{sup 2}-10{sup 4} higher than the interstellar value. These fields are effective in driving mass loss from circumstellar disks because they act at large radial distance from the host star, i.e., where most of the disk mass is located, and where the gravitational potential well is shallow. We combine viscous evolution (an {alpha}-disk model) with an existing FUV photoevaporation model to derive constraints on disk lifetimes, and to determine disk properties as functions of time, including mass-loss rates, disk masses, and radii. We also consider the effects of X-ray photoevaporation from the host star using an existing model, and show that for disks around solar-mass stars, externally generated FUV fields are often the dominant mechanism in depleting disk material. For sufficiently large viscosities, FUV fields can efficiently photoevaporate disks over the entire range of parameter space. Disks with viscosity parameter {alpha} = 10{sup -3} are effectively dispersed within 1-3 Myr; for higher viscosities ({alpha} = 10{sup -2}) disks are dispersed within {approx}0.25-0.5 Myr. Furthermore, disk radii are truncated to less than {approx}100 AU, which can possibly affect the formation of planets. Our model predictions are consistent with the range of observed masses and radii of proplyds in the Orion Nebula Cluster.

  4. IMAGING DISCOVERY OF THE DEBRIS DISK AROUND HIP 79977

    SciTech Connect

    Thalmann, C.; Dominik, C.; Janson, M.; Brandt, T. D.; Knapp, G. R.; Buenzli, E.; Wisniewski, J. P.; Carson, J.; McElwain, M. W.; Currie, T.; Moro-Martin, A.; Abe, L.; Brandner, W.; Feldt, M.; Goto, M.; Hashimoto, J.; and others

    2013-02-01

    We present Subaru/HiCIAO H-band high-contrast images of the debris disk around HIP 79977, whose presence was recently inferred from an infrared excess. Our images resolve the disk for the first time, allowing characterization of its shape, size, and dust grain properties. We use angular differential imaging (ADI) to reveal the disk geometry in unpolarized light out to a radius of {approx}2'', as well as polarized differential imaging to measure the degree of scattering polarization out to {approx}1.''5. In order to strike a favorable balance between suppression of the stellar halo and conservation of disk flux, we explore the application of principal component analysis to both ADI and reference star subtraction. This allows accurate forward modeling of the effects of data reduction on simulated disk images, and thus direct comparison with the imaged disk. The resulting best-fit values and well-fitting intervals for the model parameters are a surface brightness power-law slope of S{sub out} = -3.2[ - 3.6, -2.9], an inclination of i = 84 Degree-Sign [81 Degree-Sign , 86 Degree-Sign ], a high Henyey-Greenstein forward-scattering parameter of g = 0.45[0.35, 0.60], and a non-significant disk-star offset of u = 3.0[ - 1.5, 7.5] AU = 24[ - 13, 61] mas along the line of nodes. Furthermore, the tangential linear polarization along the disk rises from {approx}10% at 0.''5 to {approx}45% at 1.''5. These measurements paint a consistent picture of a disk of dust grains produced by collisional cascades and blown out to larger radii by stellar radiation pressure.

  5. The Red and Featureless Outer Disks of Nearby Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Watkins, Aaron E.; Mihos, J. Christopher; Harding, Paul

    2016-07-01

    We present results from deep, wide-field surface photometry of three nearby (D = 4-7 Mpc) spiral galaxies: M94 (NGC 4736), M64 (NGC 4826), and M106 (NGC 4258). Our imaging reaches a limiting surface brightness of {μ }B ˜ 28-30 mag arcsec-2 and probes colors down to {μ }B ˜ 27.5 mag arcsec-2. We compare our broadband optical data to available ultraviolet and high column density H i data to better constrain the star-forming history and stellar populations of the outermost parts of each galaxy’s disk. Each galaxy has a well-defined radius beyond which little star formation occurs and the disk light appears both azimuthally smooth and red in color, suggestive of old, well-mixed stellar populations. Given the lack of ongoing star formation or blue stellar populations in these galaxies’ outer disks, the most likely mechanisms for their formation are dynamical processes such as disk heating or radial migration, rather than inside-out growth of the disks. This is also implied by the similarity in outer disk properties despite each galaxy showing distinct levels of environmental influence, from a purely isolated galaxy (M94) to one experiencing weak tidal perturbations from its satellite galaxies (M106) to a galaxy recovering from a recent merger (M64), suggesting that a variety of evolutionary histories can yield similar outer disk structure. While this suggests a common secular mechanism for outer disk formation, the large extent of these smooth, red stellar populations—which reach several disk scale lengths beyond the galaxies’ spiral structure—may challenge models of radial migration given the lack of any nonaxisymmetric forcing at such large radii.

  6. Non-LTE Infrared Emission from Protoplanetary Disk Surfaces

    NASA Astrophysics Data System (ADS)

    Lockwood, A.; Blake, G.

    2011-05-01

    Accurately characterizing protoplanetary disks (proplyds) is integral to understanding the formation and evolution of planetary systems. The chemical reactions and physical processes within a disk determine the abundances and variety of molecular building blocks available for planet formation. Observations at infrared to millimeter wavelengths confirm a plethora of organic molecules exist in proplyds, including H2O, OH, HCN, C2H2, CO, and CO2 (Carr & Najita, 2008; Pontoppidan et al., 2010). These molecules not only provide the solid material for ice+rock planetary cores, their line emission dominates the thermal balance in the disk and provides robust signatures to examine the dynamical evolution of protoplanetary environments. Thus, it is critical to understand molecular abundance profiles in disks and the processes that affect them. We aim to model molecular excitation in a sample of proplyds and thereby verify certain disk properties. Densities in the warm molecular layers of a disk are insufficient to ensure the conditions for local thermodynamic equilibrium (LTE), so the state of the gas must be computed precisely. We utilize a radiative transfer code to model the radiation field in the disk, coupled with an escape probability code to determine the excitation of a given molecule, to derive the non-LTE level populations. We then utilize a raytracer to generate spectral image cubes covering the entire disk. We will present results for CO, whose relatively stable abundance and strong emission features provide a good foundation from which we can further constrain the parameters of a disk. Using infrared spectra from the NIRSPEC instrument on the Keck Telescope, we constrain column densities, temperatures, and emitting radii for a suite of nearby proplyds.

  7. An Incipient Debris Disk in the Chamaeleon I Cloud

    NASA Astrophysics Data System (ADS)

    Espaillat, C. C.; Ribas, Á.; McClure, M. K.; Hernández, J.; Owen, J. E.; Avish, N.; Calvet, N.; Franco-Hernández, R.

    2017-07-01

    The point at which a protoplanetary disk becomes a debris disk is difficult to identify. To better understand this, here we study the ∼40 au separation binary T 54 in the Chamaeleon I cloud. We derive a K5 spectral type for T 54 A (which dominates the emission of the system) and an age of ∼2 Myr. However, the dust disk properties of T 54 are consistent with those of debris disks seen around older- and earlier-type stars. At the same time, T 54 has evidence of gas remaining in the disk, as indicated by [Ne ii], [Ne iii], and [O i] line detections. We model the spectral energy distribution of T 54 and estimate that ∼ 3× {10}-3 {M}\\oplus of small dust grains (<0.25 μm) are present in an optically thin circumbinary disk along with at least ∼ 3× {10}-7 {M}\\oplus of larger (>10 μm) grains within a circumprimary disk. Assuming a solar-like mixture, we use Ne line luminosities to place a minimum limit on the gas mass of the disk (∼ 3× {10}-4 {M}\\oplus ) and derive a gas-to-dust mass ratio of ∼0.1. We do not detect substantial accretion, but we do see Hα in emission in one epoch, which is suggestive that there may be intermittent dumping of small amounts of matter onto the star. Considering the low dust mass, the presence of gas, and young age of T 54, we conclude that this system is on the bridge between the protoplanetary and debris disk stages.

  8. Evolution of magnetized protoplanetary disks

    NASA Technical Reports Server (NTRS)

    Reyes-Ruiz, Mauricio; Stepinski, Tomasz F.

    1995-01-01

    We investigate the global evolution of a turbulent protoplanetary disk in its viscous stage, incorporating the effects of Maxwell stress due to a large-scale magnetic field permeating disk. We assume that the viscous stress is given by an alpha model. A magnetic field is produced contemporaneously by an alpha omega dynamo mechanism and the resultant Maxwell stress assists the viscous stress in providing the means for disk evolution. The aim of this work is to compare the evolution of magnetized and nonmagnetized disks driven by turbulent viscosity of the same magnitude and thus assess the effects of a self-generated magnetic field on the structure and dynamical evolution of protoplanetary disks. Two illustrative examples corresponding to two different initial conditions are considered: a high-mass case that starts with a disk of 0.245 solar mass and angular momentum of 5.6 x 10(exp 52)g sq cm/s, and a low-mass that case starts with a disk of 0.11 solar mass and angular momentum of 1.8 x 10(exp 52)g sq cm/s. For each of these two cases the radial development of a disk is calculated numerically assuming a fiducial value of the dimensionless viscosity parameter alpha(sub ss) = 0.01, as well as alpha(sub ss) = 2 x 10(exp -3). In all cases the central star has a mass equal to 1 solar mass. The most striking feature of magnetized disk evolution is the presence of the surface density bulge located in the region of the disk where the dynamo mechanism cannot support a magnetic field. The bulge persists for a time of the order of 10(exp 5)-10(exp 6) yr. The presence and persistence of the surface density bulge may have important implications for the process of planet formation and the overall characteristics of resultant planetary systems.

  9. Evolution of magnetized protoplanetary disks

    NASA Technical Reports Server (NTRS)

    Reyes-Ruiz, Mauricio; Stepinski, Tomasz F.

    1995-01-01

    We investigate the global evolution of a turbulent protoplanetary disk in its viscous stage, incorporating the effects of Maxwell stress due to a large-scale magnetic field permeating disk. We assume that the viscous stress is given by an alpha model. A magnetic field is produced contemporaneously by an alpha omega dynamo mechanism and the resultant Maxwell stress assists the viscous stress in providing the means for disk evolution. The aim of this work is to compare the evolution of magnetized and nonmagnetized disks driven by turbulent viscosity of the same magnitude and thus assess the effects of a self-generated magnetic field on the structure and dynamical evolution of protoplanetary disks. Two illustrative examples corresponding to two different initial conditions are considered: a high-mass case that starts with a disk of 0.245 solar mass and angular momentum of 5.6 x 10(exp 52)g sq cm/s, and a low-mass that case starts with a disk of 0.11 solar mass and angular momentum of 1.8 x 10(exp 52)g sq cm/s. For each of these two cases the radial development of a disk is calculated numerically assuming a fiducial value of the dimensionless viscosity parameter alpha(sub ss) = 0.01, as well as alpha(sub ss) = 2 x 10(exp -3). In all cases the central star has a mass equal to 1 solar mass. The most striking feature of magnetized disk evolution is the presence of the surface density bulge located in the region of the disk where the dynamo mechanism cannot support a magnetic field. The bulge persists for a time of the order of 10(exp 5)-10(exp 6) yr. The presence and persistence of the surface density bulge may have important implications for the process of planet formation and the overall characteristics of resultant planetary systems.

  10. Stochastic disks that roll.

    PubMed

    Holmes-Cerfon, Miranda

    2016-11-01

    We study a model of rolling particles subject to stochastic fluctuations, which may be relevant in systems of nano- or microscale particles where rolling is an approximation for strong static friction. We consider the simplest possible nontrivial system: a linear polymer of three disks constrained to remain in contact and immersed in an equilibrium heat bath so the internal angle of the polymer changes due to stochastic fluctuations. We compare two cases: one where the disks can slide relative to each other and the other where they are constrained to roll, like gears. Starting from the Langevin equations with arbitrary linear velocity constraints, we use formal homogenization theory to derive the overdamped equations that describe the process in configuration space only. The resulting dynamics have the formal structure of a Brownian motion on a Riemannian or sub-Riemannian manifold, depending on if the velocity constraints are holonomic or nonholonomic. We use this to compute the trimer's equilibrium distribution with and without the rolling constraints. Surprisingly, the two distributions are different. We suggest two possible interpretations of this result: either (i) dry friction (or other dissipative, nonequilibrium forces) changes basic thermodynamic quantities like the free energy of a system, a statement that could be tested experimentally, or (ii) as a lesson in modeling rolling or friction more generally as a velocity constraint when stochastic fluctuations are present. In the latter case, we speculate there could be a "roughness" entropy whose inclusion as an effective force could compensate the constraint and preserve classical Boltzmann statistics. Regardless of the interpretation, our calculation shows the word "rolling" must be used with care when stochastic fluctuations are present.

  11. RAID 7 disk array

    NASA Technical Reports Server (NTRS)

    Stout, Lloyd

    1993-01-01

    Each RAID level reflects a different design architecture. Associated with each is a backdrop of imposed limitations, as well as possibilities which may be exploited within the architectural constraints of that level. There are three unique features that differentiate RAID 7 from all other levels. RAID 7 is asynchronous with respect to usage of I/O data paths. Each I/O drive (includes all data and one parity drives) as well as each host interface (there may be multiple host interfaces) has independent control and data paths. This means that each can be accessed completely, independently, of the other. This is facilitated by a separate device cache for each device/interface as well. RAID 7 is asynchronous with respect to device hierarchy and data bus utilization. Each drive and each interface is connected to a high speed data bus controlled by the embedded operating system to make independent transfers to and from central cache. RAID 7 is asynchronous with respect to the operation of an embedded real time process oriented operating system. This means that exclusive and independent of the host, or multiple host paths, the embedded OS manages all I/O transfers asynchronously across the data and parity drives. A key factor to consider is that of the RAID 7's ability to anticipate and match host I/O usage patterns. This yields the following benefits over RAID's built around micro-code based architectures. RAID 7 appears to the host as a normally connected Big Fast Disk (BFD). RAID 7 appears, from the perspective of the individual disk devices, to minimize the total number of accesses and optimize read/write transfer requests. RAID 7 smoothly integrates the random demands of independent users with the principles of spatial and temporal locality. This optimizes small, large, and time sequenced I/O requests which results in users having an I/O performance which approaches performance to that of main memory.

  12. Stochastic disks that roll

    NASA Astrophysics Data System (ADS)

    Holmes-Cerfon, Miranda

    2016-11-01

    We study a model of rolling particles subject to stochastic fluctuations, which may be relevant in systems of nano- or microscale particles where rolling is an approximation for strong static friction. We consider the simplest possible nontrivial system: a linear polymer of three disks constrained to remain in contact and immersed in an equilibrium heat bath so the internal angle of the polymer changes due to stochastic fluctuations. We compare two cases: one where the disks can slide relative to each other and the other where they are constrained to roll, like gears. Starting from the Langevin equations with arbitrary linear velocity constraints, we use formal homogenization theory to derive the overdamped equations that describe the process in configuration space only. The resulting dynamics have the formal structure of a Brownian motion on a Riemannian or sub-Riemannian manifold, depending on if the velocity constraints are holonomic or nonholonomic. We use this to compute the trimer's equilibrium distribution with and without the rolling constraints. Surprisingly, the two distributions are different. We suggest two possible interpretations of this result: either (i) dry friction (or other dissipative, nonequilibrium forces) changes basic thermodynamic quantities like the free energy of a system, a statement that could be tested experimentally, or (ii) as a lesson in modeling rolling or friction more generally as a velocity constraint when stochastic fluctuations are present. In the latter case, we speculate there could be a "roughness" entropy whose inclusion as an effective force could compensate the constraint and preserve classical Boltzmann statistics. Regardless of the interpretation, our calculation shows the word "rolling" must be used with care when stochastic fluctuations are present.

  13. Comparison of Thin Disk and Thick Disk Chemical Evolution

    NASA Astrophysics Data System (ADS)

    Brewer, M. M.; Carney, B. W.

    2003-12-01

    If the Milky Way's thick disk is the antecedent of the thin disk, there should be continuity in the chemical and dynamical evolution. Also, there should be continuity in the chemical evolution as showed through element-to-iron ratios compared to [Fe/H]. Previous results (i.e. Prochaska et al. 2000) suggest that the thick and thin disks do not share a common chemical history. Prior results have compared abundance analyses of thick disk stars with literature values for thin disk stars. We have selected two dozen stars, half from each population, based on kinematics and obtained high-resolution blue and red spectra for stars with similar temperatures. The stars are cool enough that their life expectancies exceed the age of the Galaxy. The stellar metallicities range from solar to one-tenth solar. The stars are analyzed using the same sets of absorption lines so that direct comparision can be made between the thick and thin disks. Abundances of alpha elements as well as s- and r- process elements confirm that the thick and thin disks appear to have experienced independent chemical histories.

  14. N18, Powder metallurgy superalloy for disks: Development and applications

    NASA Astrophysics Data System (ADS)

    Guedou, J. Y.; Lautridou, J. C.; Honnorat, Y.

    1993-08-01

    The preliminary industrial development of a powder metallurgy (PM) superalloy, designated N18, for disk applications has been completed. This alloy exhibits good overall mechanical properties after appro-priate processing of the material. These properties have been measured on both isothermally forged and extruded billets, as well as on specimens cut from actual parts. The temperature capability of the alloy is about 700 °C for long-term applications and approximately 750 °C for short-term use because of micro-structural instability. Further improvements in creep and crack propagation properties, without signifi-cant reduction in tensile strength, are possible through appropriate thermomechanical processing, which results in a large controlled grain size. Spin pit tests on subscale disks have confirmed that the N18 alloy has a higher resistance than PM Astroloy and is therefore an excellent alloy for modern turbine disk ap-plications.

  15. N18, powder metallurgy superalloy for disks: Development and applications

    SciTech Connect

    Guedou, J.Y.; Lautridou, J.C.; Honnorat, Y. . Materials and Processes Dept.)

    1993-08-01

    The preliminary industrial development of a powder metallurgy (PM) superalloy, designated N18, for disk applications has been completed. This alloy exhibits good overall mechanical properties after appropriate processing of the material. These properties have been measured on both isothermally forged and extruded billets, as well as on specimens cut from actual parts. The temperature capability of the alloy is about 700 C for long-term applications and approximately 750 C for short-term use because of microstructural instability. Further improvements in creep and crack propagation properties, without significant reduction in tensile strength, are possible through appropriate thermomechanical processing, which results in a large controlled grain size. Spin pit tests on subscale disks have confirmed that the N18 alloy has a higher resistance than PM Astrology and is therefore an excellent alloy for modern turbine disk applications.

  16. Strengthening Precipitate Morphologies Fully Quantified in Advanced Disk Superalloys

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P.

    1998-01-01

    Advanced aviation gas turbine engines will require disk superalloys that can operate at higher temperatures and stresses than current conditions. Such applications will be limited by the tensile, creep, and fatigue mechanical properties of these alloys. These mechanical properties vary with the size, shape, and quantity of the gamma precipitates that strengthen disk superalloys. It is therefore important to quantify these precipitate parameters and relate them to mechanical properties to improve disk superalloys. Favorable precipitate morphologies and practical processing approaches to achieve them can then be determined. A methodology has been developed at the NASA Lewis Research Center to allow the comprehensive quantification of the size, shape, and quantity of all types of gamma precipitates.

  17. Self-regulating galaxy formation. I - H II disk and Lyman-alpha pressure

    NASA Technical Reports Server (NTRS)

    Cox, D. P.

    1985-01-01

    The nascent interstellar medium and star formation model are incorporated into a scenario for the formation epoch of spiral galaxies. The structure, star formation time scale, and luminosity of a self-gravitating isothermal disk are evaluated as functions of the disk surface density. The importance of radiation pressure, particularly that of Lyman-alpha, in maintaining an inflated disk and halting infall is discussed. The Lyman-alpha pressure also supports a considerable halo of material in the vicinity of the disk. A first-order infall scenario and the time-dependent properties of the system it constructs are presented. Disk properties are evaluated at the epoch at which further material is supportable against infall by Lyman-alpha pressure. The two-dimensional family of disk galaxies whose scales and surface density are expressible in terms of fundamental constants and which arise from the three parameter sets of perturbations in the Hubble flow are determined.

  18. Apocenter Glow in Eccentric Debris Disks: Implications for Fomalhaut and Epsilon Eridani

    NASA Technical Reports Server (NTRS)

    Pan, Margaret; Nesvold, Erika R.; Kuchner, Marc J.

    2016-01-01

    Debris disks often take the form of eccentric rings with azimuthal asymmetries in surface brightness. Such disks are often described as showing pericenter glow, an enhancement of the disk brightness in regions nearest the central star. At long wavelengths, however, the disk apocenters should appear brighter than their pericenters: in the long-wavelength limit, we find that the apocenter pericenter flux ratio scales as 1 + e for disk eccentricity e. We produce new models of this apocenter glow to explore its causes and wavelength dependence and study its potential as a probe of dust grain properties. Based on our models, we argue that several far-infrared and (sub)millimeter images of the Fomalhaut and Epsilon Eridani debris rings obtained with Herschel, JCMT, SHARC II, ALMA, and ATCA should be reinterpreted as suggestions or examples of apocenter glow. This reinterpretation yields new constraints on the disks dust grain properties and size distributions.

  19. Forming Gaps in Debris Disks with Fewer Planets via Planet Migration

    NASA Astrophysics Data System (ADS)

    Morrison, Sarah J.; Kratter, Kaitlin M.

    2016-10-01

    Debris disks across a wide range of ages can possess wide gaps of several AU or more; these gaps have been attributed to the presence of multiple planets. While at least two planets are likely needed for maintaining the edges of such gaps, large gaps may require more than two in more dynamically packed configurations to be able to have cleared material within the gap in the present day. As an alternative to currently packed planets occupying gaps in debris disks, we assess whether planetesimal and dynamical instability-driven planet migration could produce wide gaps with lower mass, fewer planets on relevant timescales to be consistent with the observed properties of debris disk systems. We also discuss implications for the disk properties in which these mechanisms could operate within the broader evolutionary context linking planets, debris disks, and the protoplanetary disks from which they originated.

  20. Low-state disks and low-beta disks

    NASA Technical Reports Server (NTRS)

    Mineshige, Shin; Kusnose, Masaaki; Matsumoto, Ryoji

    1995-01-01

    Stellar black hole candidates (BHCs) exhibit bimodal spectral states. We calculate nonthermal disk spectra, demonstrating that a large photon index (alpha (sub x) approximately 2-3) observed in the soft (high) state is due to a copious soft photon supply, whereas soft photon starvation leads to a smaller index (alpha (sub x) approximately 1.5-2) in the hard (low) state. Thus, the absence of the soft component flux in the low state cannot be due to obscuration. A possible disk configuration during the low state is discussed. We proposed that a low-state disk may be a low-beta disk in which magnetic pressure may exceed gas pressure becuase of the suppression of field escape by a strong shear. As a result, disk material will take the form of blobs constricted by mainly toroidal magnetic fields. Fields are dissipated mainly by occasional reconnection events with a huge energy release. This will account for large-amplitude, aperiodic X-ray variations (flickering) and high-energy radiation with small alpha(sub x) from hard state BHCs and possibly from active galactic nuclei. Further, we propose a hysteretic relation between the mass-flow rate and plasma-beta, a ratio of gas pressure to magnetic pressure, for the spectral evolution of transient BHCs. The disk is in the low-beta state in quiescence and early rise. The low-beta disk is optically thin and affected by advection. A hard-to-soft transition occurs before the peak luminosity, since there is no advection-dominated branch at higher luminosities. An optically thick, high-beta disk appears at small radii. In the decay phase of the light curve, the standard-type disk becomes effectively optically thin, when a soft-hard transition is triggered. High-beta plasmas in the main body shrink to form minute blobs, and low-beta coronal plasma fills interblob space.

  1. Low-state disks and low-beta disks

    NASA Technical Reports Server (NTRS)

    Mineshige, Shin; Kusnose, Masaaki; Matsumoto, Ryoji

    1995-01-01

    Stellar black hole candidates (BHCs) exhibit bimodal spectral states. We calculate nonthermal disk spectra, demonstrating that a large photon index (alpha (sub x) approximately 2-3) observed in the soft (high) state is due to a copious soft photon supply, whereas soft photon starvation leads to a smaller index (alpha (sub x) approximately 1.5-2) in the hard (low) state. Thus, the absence of the soft component flux in the low state cannot be due to obscuration. A possible disk configuration during the low state is discussed. We proposed that a low-state disk may be a low-beta disk in which magnetic pressure may exceed gas pressure becuase of the suppression of field escape by a strong shear. As a result, disk material will take the form of blobs constricted by mainly toroidal magnetic fields. Fields are dissipated mainly by occasional reconnection events with a huge energy release. This will account for large-amplitude, aperiodic X-ray variations (flickering) and high-energy radiation with small alpha(sub x) from hard state BHCs and possibly from active galactic nuclei. Further, we propose a hysteretic relation between the mass-flow rate and plasma-beta, a ratio of gas pressure to magnetic pressure, for the spectral evolution of transient BHCs. The disk is in the low-beta state in quiescence and early rise. The low-beta disk is optically thin and affected by advection. A hard-to-soft transition occurs before the peak luminosity, since there is no advection-dominated branch at higher luminosities. An optically thick, high-beta disk appears at small radii. In the decay phase of the light curve, the standard-type disk becomes effectively optically thin, when a soft-hard transition is triggered. High-beta plasmas in the main body shrink to form minute blobs, and low-beta coronal plasma fills interblob space.

  2. SERS of Gold/C 60 (/C 70) nano-clusters deposited on floppy disk and hard disk

    NASA Astrophysics Data System (ADS)

    Luo, Zhixun; Fang, Yan

    2006-01-01

    It is important to apply the surface enhanced Raman scattering (SERS) spectra to study the interfacial properties of films and the adsorption behavior of molecules on substrates. In this paper, SERS spectra of good quality of gold/C 60 (/C 70) nano-clusters deposited on floppy disk and hard disk were reported with the pyridine as a kind of solvent intermediate. The floppy disk or hard disk, as a new and effective substrate for SERS, provides a plank for C 60/C 70 molecules to adsorb on the gold nano-particles. The number of vibrational modes was greatly increased, especially some modes that were forbidden in Raman spectrum, appeared and even split as prediction of group theory. The enhancement factor is estimated to over 10 6. It provides convenience for probing the C 60/C 70 vibrational structure and the physical properties with the high sensitivity, as well as the adsorption behavior, the interaction of fullerene with gold surface and the SERS mechanism of molecules adsorbed on substrates. What's more, the SERS sensitivity of the magnetism is demonstrated by comparing the SERS of gold/C 60 (/C 70) nano-clusters deposited on floppy disk and hard disk.

  3. The wealth of distinguished doctors: retrospective survey.

    PubMed

    McManus, I C

    2005-12-24

    To assess changes in the wealth of distinguished doctors in the United Kingdom between 1860 and 2001. Retrospective survey. The UK. 980 doctors of sufficient distinction to be included in the Oxford Dictionary of National Biography and who died between 1860 and 2001. Wealth at death, based on probate records and adjusted relative to average earnings in 2002. The wealth of distinguished doctors declined substantially between 1860 and 2001, and paralleled a decline in the relative income of doctors in general. The wealth of distinguished doctors also declined relative to other groups of distinguished individuals. In the 19th century, distinction in doctors was accompanied by substantial wealth, whereas by the end of the 20th century, the most distinguished doctors were less wealthy than their contemporaries who had achieved national distinction in other areas.

  4. The wealth of distinguished doctors: retrospective survey

    PubMed Central

    McManus, I C

    2005-01-01

    Objective To assess changes in the wealth of distinguished doctors in the United Kingdom between 1860 and 2001. Design Retrospective survey. Setting The UK. Participants 980 doctors of sufficient distinction to be included in the Oxford Dictionary of National Biography and who died between 1860 and 2001. Main outcome measures Wealth at death, based on probate records and adjusted relative to average earnings in 2002. Results The wealth of distinguished doctors declined substantially between 1860 and 2001, and paralleled a decline in the relative income of doctors in general. The wealth of distinguished doctors also declined relative to other groups of distinguished individuals. Conclusions In the 19th century, distinction in doctors was accompanied by substantial wealth, whereas by the end of the 20th century, the most distinguished doctors were less wealthy than their contemporaries who had achieved national distinction in other areas. PMID:16373738

  5. The Gas Disk: Evolution and Chemistry

    NASA Astrophysics Data System (ADS)

    Rab, Christian; Baldovin-Saavedra, Carla; Dionatos, Odysseas; Vorobyov, Eduard; Güdel, Manuel

    2016-12-01

    Protoplanetary disks are the birthplaces of planetary systems. The evolution of the star-disk system and the disk chemical composition determines the initial conditions for planet formation. Therefore a comprehensive understanding of the main physical and chemical processes in disks is crucial for our understanding of planet formation. We give an overview of the early evolution of disks, discuss the importance of the stellar high-energy radiation for disk evolution and describe the general thermal and chemical structure of disks. Finally we provide an overview of observational tracers of the gas component and disk winds.

  6. Protoplanetary and Debris Disk Morphologies

    NASA Astrophysics Data System (ADS)

    Lomax, Jamie R.; Wisniewski, John P.; Grady, Carol A.; McElwain, Michael W.; Hashimoto, Jun; Donaldson, Jessica; Debes, John H.; Malumuth, Eliot; Roberge, Aki; Weinberger, Alycia J.; SEEDS Team

    2016-01-01

    The types of planets that form around other stars are highly dependent on their natal disk conditions. Therefore, the composition, morphology, and distribution of material in protoplanetary and debris disks are important for planet formation. Here we present the results of studies of two disk systems: AB Aur and AU Mic.The circumstellar disk around the Herbig Ae star AB Aur has many interesting features, including spirals, asymmetries, and non-uniformities. However, comparatively little is known about the envelope surrounding the system. Recent work by Tang et al (2012) has suggested that the observed spiral armss may not in fact be in the disk, but instead are due to areas of increased density in the envelope and projection effects. Using Monte Carlo modeling, we find that it is unlikely that the envelope holds enough material to be responsible for such features and that it is more plausible that they form from disk material. Given the likelihood that gravitational perturbations from planets cause the observed spiral morphology, we use archival H band observations of AB Aur with a baseline of 5.5 years to determine the locations of possible planets.The AU Mic debris disk also has many interesting morphological features. Because its disk is edge on, the system is an ideal candidate for color studies using coronagraphic spectroscopy. Spectra of the system were taken by placing a HST/STIS long slit parallel to and overlapping the disk while blocking out the central star with an occulting fiducial bar. Color gradients may reveal the chemical processing that is occuring within the disk. In addition, it may trace the potential composition and architecture of any planetary bodies in the system because collisional break up of planetesimals produces the observed dust in the system. We present the resulting optical reflected spectra (5200 to 10,200 angstroms) from this procedure at several disk locations. We find that the disk is bluest at the innermost locations of the

  7. Transitional Disks Associated with Intermediate-Mass Stars: Results of the SEEDS YSO Survey

    NASA Technical Reports Server (NTRS)

    Grady, C.; Fukagawa, M.; Maruta, Y.; Ohta, Y.; Wisniewski, J.; Hashimoto, J.; Okamoto, Y.; Momose, M.; Currie, T.; McElwain, M.; Muto, T.; Kotani, T.; Kusakabe, N. B.; Follette, K.; Bonnefoy, M.; Feldt, M.; Sitko, M.; Takami, M.; Karr, J.; Tamura, M.

    2014-01-01

    Protoplanetary disks are where planets form, grow, and migrate to produce the diversity of exoplanet systems we observe in mature systems. Disks where this process has advanced to the stage of gap opening, and in some cases central cavity formation, have been termed pre-transitional and transitional disks in the hope that they represent intermediate steps toward planetary system formation. Recent reviews have focussed on disks where the star is of solar or sub-solar mass. In contrast to the sub-millimeter where cleared central cavities predominate, at H-band some T Tauri star transitional disks resemble primordial disks in having no indication of clearing, some show a break in the radial surface brightness profile at the inner edge of the outer disk, while others have partially to fully cleared gaps or central cavities. Recently, the Meeus Group I Herbig stars, intermediate-mass PMS stars with IR spectral energy distributions often interpreted as flared disks, have been proposed to have transitional and pre-transitional disks similar to those associated with solar-mass PMS stars, based on thermal-IR imaging, and sub-millimeter interferometry. We have investigated their appearance in scattered light as part of the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS), obtaining H-band polarimetric imagery of 10 intermediate-mass stars with Meeus Group I disks. Augmented by other disks with imagery in the literature, the sample is now sufficiently large to explore how these disks are similar to and differ from T Tauri star disks. The disk morphologies seen in the Tauri disks are also found for the intermediate-mass star disks, but additional phenomena are found; a hallmark of these disks is remarkable individuality and diversity which does not simply correlate with disk mass or stellar properties, including age, including spiral arms in remnant envelopes, arms in the disk, asymmetrically and potentially variably shadowed outer disks, gaps, and one disk

  8. Megamaser Disks in Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Kartje, John F.; Königl, Arieh; Elitzur, Moshe

    1999-03-01

    observed maser distribution and whose mass is dominated by the clumped, high-density gas component. The shielding of the high-energy continuum, which is required in order that the gas remain molecular, can be provided in this case by the dusty clouds themselves. We show that even the simplest version of this model, in which the disk is flat and the continuum radiation reaches the masing clouds through the plane of the disk, can account for the maser observations in NGC 1068. We point out the striking similarities between the maser ring properties as interpreted with this model and the inferred characteristics of the circumnuclear disk in the Galactic center, and we briefly discuss the implications of such rings for the AGN accretion disk paradigm. Our second scenario is motivated by the apparent warps observed in some of the imaged megamaser disks and by our finding that the flat-disk version of the irradiated ring scenario could apply to a source like NGC 4258 only if the water abundance in the masing clouds were higher than the value implied by equilibrium photoionization-driven chemistry. This scenario is based on the disk-driven hydromagnetic wind model originally proposed to account for the molecular ``tori'' in Seyfert 2-like galaxies and for several other observed phenomena in AGNs. In this picture, the wind uplifts (by its ram pressure) and confines (by its magnetic pressure) dense clouds fragmented from the disk, which mase after they become exposed to the central radiation field. Much of the requisite continuum shielding can be provided in this case by the dusty portions of the wind. We show that comparatively massive clouds that move in low-altitude, nearly circular orbits could be shielded in this way, and we suggest that an apparent warp in the maser distribution might arise under these circumstances from an observational selection effect induced by the strong vertical density stratification that characterizes a centrifugally driven wind. We construct a self

  9. Frictional contact of two rotating elastic disks

    NASA Astrophysics Data System (ADS)

    Ostrik, V. I.; Ulitko, A. F.

    2007-10-01

    We study the problem of constrained uniform rotation of two precompressed elastic disks made of different materials with friction forces in the contact region taken into account. The exact solution of the problem is obtained by the Wiener-Hopf method. An important stage in the study of rolling of elastic bodies is the Hertz theory [1] of contact interaction of elastic bodies with smoothly varying curvature in the contact region under normal compression. Friction in the contact region is assumed to be negligible. If there are tangential forces and the friction in the contact region is taken into account, then the picture of contact interaction of elastic bodies changes significantly. Although the normal contact stress distribution strictly follows the Hertz theory for bodies with identical elastic properties and apparently slightly differs from the Hertz diagram for bodies made of different materials, the presence of tangential stresses results in the splitting of the contact region into the adhesion region and the slip region. This phenomenon was first established by Reynolds [2], who experimentally discovered slip regions near points of material entry in and exit from the contact region under constrained rolling of an aluminum cylinder on a rubber base. The theoretical justification of the partial slip phenomenon in the contact region, discovered by Reynolds [2], can be found in Carter [3] and Fromm [4]. Moreover, Fromm presents a complete solution of the problem of constrained uniform rotation of two identical disks. Apparently, Fromm was the first to consider the so-called "clamped" strain and postulated that slip is absent at the point at which the disk materials enter the contact region. Ishlinskii [5, 6] gave an engineering solution of the problem on slip in the contact region under rolling friction. Considering the problem on a rigid disk rolling on an elastic half-plane, we model this problem by an infinite set of elastic vertical rods using Winkler

  10. Millimeter observations of the disk around GW Orionis

    NASA Astrophysics Data System (ADS)

    Fang, M.; Sicilia-Aguilar, A.; Wilner, D.; Wang, Y.; Roccatagliata, V.; Fedele, D.; Wang, J. Z.

    2017-07-01

    The GW Ori system is a pre-main sequence triple system (GW Ori A/B/C) with companions (GW Ori B/C) at 1 AU and 8 AU, respectively, from the primary (GW Ori A). The primary of the system has a mass of 3.9 M⊙, but shows a spectral type of G8. Thus, GW Ori A could be a precursor of a B star, but it is still at an earlier evolutionary stage than Herbig Be stars. GW Ori provides an ideal target for experiments and observations (being a "blown-up" solar system with a very massive sun and at least two upscaled planets). We present the first spatially resolved millimeter interferometric observations of the disk around the triple pre-main sequence system GW Ori, obtained with the Submillimeter Array, both in continuum and in the 12CO J = 2-1, 13CO J = 2-1, and C18O J = 2-1 lines. These new data reveal a huge, massive, and bright disk in the GW Ori system. The dust continuum emission suggests a disk radius of around 400 AU, but the 12CO J = 2-1 emission shows a much more extended disk with a size around 1300 AU. Owing to the spatial resolution ( 1''), we cannot detect the gap in the disk that is inferred from spectral energy distribution (SED) modeling. We characterize the dust and gas properties in the disk by comparing the observations with the predictions from the disk models with various parameters calculated with a Monte Carlo radiative transfer code RADMC-3D. The disk mass is around0.12 M⊙, and the disk inclination with respect to the line of sight is around 35°. The kinematics in the disk traced by the CO line emission strongly suggest that the circumstellar material in the disk is in Keplerian rotation around GW Ori.Tentatively substantial C18O depletion in gas phase is required to explain the characteristics of the line emission from the disk.

  11. Disk Dispersal Around Young Stars

    NASA Technical Reports Server (NTRS)

    Hollenbach, David; Yorke, Harold W.; Johnstone, Doug; DeVincenzi, Donald L. (Technical Monitor)

    1999-01-01

    We review the evidence pertaining to the lifetimes of planet-forming disks and discuss possible disk dispersal mechanisms: 1) viscous accretion of material onto the central source, 2) close stellar encounters, 3) stellar winds, and 4) by ultraviolet radiation. We focus on 3) and 4) and describe the quasi-steady state appearance and the overall evolution of disks under the influence of winds and radiation from the central star and of radiation from external OB stars. Viscous accretion likely dominates disk dispersal in the, inner disk (r approx. less than A 10 AU), while photoevaporation is the principal process of disk dispersal outside of r approximately greater than 10 AU. Disk dispersed timescales are compared and discussed in relation to theoretical estimates for planet formation timescales. Photoevaporation may explain the large differences in the hydrogen content of the giant planets in the solar system. The commonly held belief that our early sun's stellar wind dispersed the solar nebula is called into question.

  12. Formation of warped disks by galactic flyby encounters. I. Stellar disks

    SciTech Connect

    Kim, Jeonghwan H.; An, Sung-Ho; Yoon, Suk-Jin; Peirani, Sebastien; Kim, Sungsoo; Ann, Hong Bae

    2014-07-01

    Warped disks are almost ubiquitous among spiral galaxies. Here we revisit and test the 'flyby scenario' of warp formation, in which impulsive encounters between galaxies are responsible for warped disks. Based on N-body simulations, we investigate the morphological and kinematical evolution of the stellar component of disks when galaxies undergo flyby interactions with adjacent dark matter halos. We find that the so-called 'S'-shaped warps can be excited by flybys and sustained for even up to a few billion years, and that this scenario provides a cohesive explanation for several key observations. We show that disk warp properties are governed primarily by the following three parameters: (1) the impact parameter, i.e., the minimum distance between two halos; (2) the mass ratio between two halos; and (3) the incident angle of the flyby perturber. The warp angle is tied up with all three parameters, yet the warp lifetime is particularly sensitive to the incident angle of the perturber. Interestingly, the modeled S-shaped warps are often non-symmetric depending on the incident angle. We speculate that the puzzling U- and L-shaped warps are geometrically superimposed S-types produced by successive flybys with different incident angles, including multiple interactions with a satellite on a highly elongated orbit.

  13. Evolution of Protoplanetary Disks in the Orion A Star-Forming Region

    NASA Astrophysics Data System (ADS)

    Kim, Kyoung Hee

    2014-01-01

    We present our investigation of the characteristics of Class II protoplanetary disks in Orion A star-forming region. Our major goal is to analyze a large sample of protoplanetary disks with near- and mid-IR spectra, by statistical approaches, to understand protoplanetary disk evolution in Orion A. For this work, 303 protoplanetary disks in Orion A region observed by IRS/Spitzer and the follow-up observation of 120 objects from SpeX/IRTF are used to reveal the characteristics of Class II disks in Orion A. For clues on environmental effects on disk evolution and planet formation, we compare the disk properties and dust properties of Orion A disks to that of Taurus disks and examine trends with respect to position within Orion A. We extract spectral indices, equivalent widths, and integrated fluxes from IRS spectra of Class II objects in Orion A which pertain to disk structure and dust composition. We measure mass accretion rates using hydrogen recombination lines in SpeX spectra of our targets. Utilizing the properties, we analyze the general distribution of properties of disks in ONC, L1641, and Taurus from their histograms. Our main findings are as follows. (1) From the high frequency (>20%) of transitional disks and the similar vertical structure of the Orion A disks to those of Taurus, we infer that giant planet formation and dust sedimentation is well under way, if not complete, even in the youngest Class II objects. (2) Less grain processing - crystallization and growth of grains to diameter of 1-10 μm - has occurred among the dust grains in the Orion A disks than in Taurus. The time scales for dust processing must therefore lie in the range of ages of the nearby clouds like Orion, NGC 1333, Taurus, Ophiuchus and Chamaeleon. (3) We detected PAH emission at 6-14 μm from disks around low-mass and low-luminosity young stars, excited externally by UV from the Trapezium stars. (4) As others have found for the Trapezium region of Orion, the disks of the surrounding

  14. STUDIES ON NATURAL IMMUNITY TO PNEUMOCOCCUS TYPE III : II. CERTAIN DISTINGUISHING PROPERTIES OF TWO STRAINS OF PNEUMOCOCCUS TYPE III VARYING IN THEIR VIRULENCE FOR RABBITS, AND THE REAPPEARANCE OF THESE PROPERTIES FOLLOWING R-->S RECONVERSION OF THEIR RESPECTIVE ROUGH DERIVATIVES.

    PubMed

    Shaffer, M F; Enders, J F; Wu, C J

    1936-07-31

    The results which have been presented show that under the conditions of artificial cultivation at 37 degrees C. definite differences exist between two smooth strains of Pneumococcus Type III both of which are highly virulent for mice by the intraperitoneal route, but which may be sharply distinguished in their virulence for rabbits. These differences consist in the size of the fully developed intact capsule and the interval of time required for its loss. The somewhat smaller capsule of the avirulent strain, well formed and easily demonstrable during the early period of growth, diminishes quickly, while the large capsule of the strain virulent for rabbits is retained for a considerably longer period. Closely correlated with the time at which this reduction of capsule occurs is the appearance of changes in the surface properties of the bacteria which are revealed by a shifting of the range of acid agglutination, susceptibility to clumping in anti-R serum and ingestion by normal adult human polymorphonuclear leucocytes and serum. Since it has been shown that these alterations as growth continues, result in a loss of characteristics which distinguish the strictly type specific, fully capsulated pneumococcus and ultimately lead to a state temporarily approximating that of the completely avirulent R form, and since under the experimental conditions they are inaugurated sooner, advance more rapidly and are more complete in the rabbit avirulent organism, we believe that they may partly account for difference in rabbit virulence of the two strains. In the following paper an attempt has therefore been made to correlate this behavior in vitro with the events attendant upon inoculation into the animal body. The studies of Clark and Ruehl (16), Henrici (17), Bayne-Jones and Adolph (18) and others have demonstrated a marked increase in the size of the bacterial cell associated with the early phases of growth. These authors have dealt chiefly with noncapsulated rod forms and even

  15. Rotating flexible disk under shaft temperature increment

    NASA Astrophysics Data System (ADS)

    Pei, Yong-Chen; He, Ling; Wang, Ji-Xin

    2010-08-01

    A rotating flexible annular thin disk subjected to the temperature increment of the shaft clamping the disk was modeled in this paper. At disk top and bottom surfaces and free outer edge, the heat convection boundaries were assumed. Disk transverse deflection was considered as a function of both disk radial and circumferential coordinates, and temperature distribution was solved along disk thickness and radial directions simultaneously. As a result, the shaft temperature increment causes thermo-elastic instability of some disk modes. Effects of the shaft temperature increment, ratio of disk convective heat transfer coefficient to thermal conductivity, disk thickness, nodal circle and diameter numbers of disk mode on the natural frequencies, thermo-elastic instability and critical angular speed of the disk were discussed.

  16. Disk-averaged synthetic spectra of Mars.

    PubMed

    Tinetti, Giovanna; Meadows, Victoria S; Crisp, David; Fong, William; Velusamy, Thangasamy; Snively, Heather

    2005-08-01

    The principal goal of the NASA Terrestrial Planet Finder (TPF) and European Space Agency's Darwin mission concepts is to directly detect and characterize extrasolar terrestrial (Earthsized) planets. This first generation of instruments is expected to provide disk-averaged spectra with modest spectral resolution and signal-to-noise. Here we use a spatially and spectrally resolved model of a Mars-like planet to study the detectability of a planet's surface and atmospheric properties from disk-averaged spectra. We explore the detectability as a function of spectral resolution and wavelength range, for both the proposed visible coronograph (TPFC) and mid-infrared interferometer (TPF-I/Darwin) architectures. At the core of our model is a spectrum-resolving (line-by-line) atmospheric/surface radiative transfer model. This model uses observational data as input to generate a database of spatially resolved synthetic spectra for a range of illumination conditions and viewing geometries. The model was validated against spectra recorded by the Mars Global Surveyor-Thermal Emission Spectrometer and the Mariner 9-Infrared Interferometer Spectrometer. Results presented here include disk-averaged synthetic spectra, light curves, and the spectral variability at visible and mid-infrared wavelengths for Mars as a function of viewing angle, illumination, and season. We also considered the differences in the spectral appearance of an increasingly ice-covered Mars, as a function of spectral resolution, signal-to-noise and integration time for both TPF-C and TPFI/ Darwin.

  17. Disk-averaged synthetic spectra of Mars

    NASA Technical Reports Server (NTRS)

    Tinetti, Giovanna; Meadows, Victoria S.; Crisp, David; Fong, William; Velusamy, Thangasamy; Snively, Heather

    2005-01-01

    The principal goal of the NASA Terrestrial Planet Finder (TPF) and European Space Agency's Darwin mission concepts is to directly detect and characterize extrasolar terrestrial (Earthsized) planets. This first generation of instruments is expected to provide disk-averaged spectra with modest spectral resolution and signal-to-noise. Here we use a spatially and spectrally resolved model of a Mars-like planet to study the detectability of a planet's surface and atmospheric properties from disk-averaged spectra. We explore the detectability as a function of spectral resolution and wavelength range, for both the proposed visible coronograph (TPFC) and mid-infrared interferometer (TPF-I/Darwin) architectures. At the core of our model is a spectrum-resolving (line-by-line) atmospheric/surface radiative transfer model. This model uses observational data as input to generate a database of spatially resolved synthetic spectra for a range of illumination conditions and viewing geometries. The model was validated against spectra recorded by the Mars Global Surveyor-Thermal Emission Spectrometer and the Mariner 9-Infrared Interferometer Spectrometer. Results presented here include disk-averaged synthetic spectra, light curves, and the spectral variability at visible and mid-infrared wavelengths for Mars as a function of viewing angle, illumination, and season. We also considered the differences in the spectral appearance of an increasingly ice-covered Mars, as a function of spectral resolution, signal-to-noise and integration time for both TPF-C and TPFI/ Darwin.

  18. Disk-Averaged Synthetic Spectra of Mars

    NASA Astrophysics Data System (ADS)

    Tinetti, Giovanna; Meadows, Victoria S.; Crisp, David; Fong ,William; Velusamy, Thangasamy; Snively, Heather

    2005-08-01

    The principal goal of the NASA Terrestrial Planet Finder (TPF) and European Space Agency's Darwin mission concepts is to directly detect and characterize extrasolar terrestrial (Earthsized) planets. This first generation of instruments is expected to provide disk-averaged spectra with modest spectral resolution and signal-to-noise. Here we use a spatially and spectrally resolved model of a Mars-like planet to study the detectability of a planet's surface and atmospheric properties from disk-averaged spectra. We explore the detectability as a function of spectral resolution and wavelength range, for both the proposed visible coronograph (TPFC) and mid-infrared interferometer (TPF-I/Darwin) architectures. At the core of our model is a spectrum-resolving (line-by-line) atmospheric/surface radiative transfer model. This model uses observational data as input to generate a database of spatially resolved synthetic spectra for a range of illumination conditions and viewing geometries. The model was validated against spectra recorded by the Mars Global Surveyor-Thermal Emission Spectrometer and the Mariner 9-Infrared Interferometer Spectrometer. Results presented here include disk-averaged synthetic spectra, light curves, and the spectral variability at visible and mid-infrared wavelengths for Mars as a function of viewing angle, illumination, and season. We also considered the differences in the spectral appearance of an increasingly ice-covered Mars, as a function of spectral resolution, signal-to-noise and integration time for both TPF-C and TPFI/ Darwin.

  19. Disk-averaged synthetic spectra of Mars

    NASA Technical Reports Server (NTRS)

    Tinetti, Giovanna; Meadows, Victoria S.; Crisp, David; Fong, William; Velusamy, Thangasamy; Snively, Heather

    2005-01-01

    The principal goal of the NASA Terrestrial Planet Finder (TPF) and European Space Agency's Darwin mission concepts is to directly detect and characterize extrasolar terrestrial (Earthsized) planets. This first generation of instruments is expected to provide disk-averaged spectra with modest spectral resolution and signal-to-noise. Here we use a spatially and spectrally resolved model of a Mars-like planet to study the detectability of a planet's surface and atmospheric properties from disk-averaged spectra. We explore the detectability as a function of spectral resolution and wavelength range, for both the proposed visible coronograph (TPFC) and mid-infrared interferometer (TPF-I/Darwin) architectures. At the core of our model is a spectrum-resolving (line-by-line) atmospheric/surface radiative transfer model. This model uses observational data as input to generate a database of spatially resolved synthetic spectra for a range of illumination conditions and viewing geometries. The model was validated against spectra recorded by the Mars Global Surveyor-Thermal Emission Spectrometer and the Mariner 9-Infrared Interferometer Spectrometer. Results presented here include disk-averaged synthetic spectra, light curves, and the spectral variability at visible and mid-infrared wavelengths for Mars as a function of viewing angle, illumination, and season. We also considered the differences in the spectral appearance of an increasingly ice-covered Mars, as a function of spectral resolution, signal-to-noise and integration time for both TPF-C and TPFI/ Darwin.

  20. Molecular Line Emission from Massive Protostellar Disks: Predictions for ALMA and EVLA

    NASA Astrophysics Data System (ADS)

    Krumholz, Mark R.; Klein, Richard I.; McKee, Christopher F.

    2007-08-01

    We compute the molecular line emission of massive protostellar disks by solving the equation of radiative transfer through the cores and disks produced by the recent radiation-hydrodynamic simulations of Krumholz, Klein, & McKee. We find that in several representative lines the disks show brightness temperatures of hundreds of kelvins over velocity channels ~10 km s-1 wide, extending over regions hundreds of AU in size. We process the computed intensities to model the performance of next-generation radio and submillimeter telescopes. Our calculations show that observations using facilities such as the Expanded Very Large Array (EVLA) and Atacama Large Millimeter Array (ALMA) should be able to detect massive protostellar disks and measure their rotation curves, at least in the nearest massive star-forming regions. They should also detect significant substructure and nonaxisymmetry in the disks, and in some cases may be able to detect star-disk velocity offsets of a few km s-1, both of which are the result of strong gravitational instability in massive disks. We use our simulations to explore the strengths and weaknesses of different observational techniques, and we also discuss how observations of massive protostellar disks may be used to distinguish between alternative models of massive star formation.

  1. Molecular Line Emission from Massive Protostellar Disks: Predictions for ALMA and the EVLA

    SciTech Connect

    Krumholz, M R; Klein, R I; McKee, C F

    2007-05-07

    We compute the molecular line emission of massive protostellar disks by solving the equation of radiative transfer through the cores and disks produced by the recent radiation-hydrodynamic simulations of Krumholz, Klein, & McKee. We find that in several representative lines the disks show brightness temperatures of hundreds of Kelvin over velocity channels {approx} 10 km s{sup -1} wide, extending over regions hundreds of AU in size. We process the computed intensities to model the performance of next-generation radio and submillimeter telescopes. Our calculations show that observations using facilities such as the EVLA and ALMA should be able to detect massive protostellar disks and measure their rotation curves, at least in the nearest massive star-forming regions. They should also detect significant sub-structure and non-axisymmetry in the disks, and in some cases may be able to detect star-disk velocity offsets of a few km s{sup -1}, both of which are the result of strong gravitational instability in massive disks. We use our simulations to explore the strengths and weaknesses of different observational techniques, and we also discuss how observations of massive protostellar disks may be used to distinguish between alternative models of massive star formation.

  2. DiskJockey: Protoplanetary disk modeling for dynamical mass derivation

    NASA Astrophysics Data System (ADS)

    Czekala, Ian

    2016-03-01

    DiskJockey derives dynamical masses for T Tauri stars using the Keplerian motion of their circumstellar disks, applied to radio interferometric data from the Atacama Large Millimeter Array (ALMA) and the Submillimeter Array (SMA). The package relies on RADMC-3D (ascl:1202.015) to perform the radiative transfer of the disk model. DiskJockey is designed to work in a parallel environment where the calculations for each frequency channel can be distributed to independent processors. Due to the computationally expensive nature of the radiative synthesis, fitting sizable datasets (e.g., SMA and ALMA) will require a substantial amount of CPU cores to explore a posterior distribution in a reasonable timeframe.

  3. Spread of the dust temperature distribution in circumstellar disks

    NASA Astrophysics Data System (ADS)

    Heese, S.; Wolf, S.; Dutrey, A.; Guilloteau, S.

    2017-07-01

    Context. Accurate temperature calculations for circumstellar disks are particularly important for their chemical evolution. Their temperature distribution is determined by the optical properties of the dust grains, which, among other parameters, depend on their radius. However, in most disk studies, only average optical properties and thus an average temperature is assumed to account for an ensemble of grains with different radii. Aims: We investigate the impact of subdividing the grain radius distribution into multiple sub-intervals on the resulting dust temperature distribution and spectral energy distribution (SED). Methods: The temperature distribution, the relative grain surface below a certain temperature, the freeze-out radius, and the SED were computed for two different scenarios: (1) Radius distribution represented by 16 logarithmically distributed radius intervals, and (2) radius distribution represented by a single grain species with averaged optical properties (reference). Results: Within the considered parameter range, i.e., of grain radii between 5 nm and 1 mm and an optically thin and thick disk with a parameterized density distribution, we obtain the following results: in optically thin disk regions, the temperature spread can be as large as 63% and the relative grain surface below a certain temperature is lower than in the reference disk. With increasing optical depth, the difference in the midplane temperature and the relative grain surface below a certain temperature decreases. Furthermore, below 20 K, this fraction is higher for the reference disk than for the case of multiple grain radii, while it shows the opposite behavior for temperatures above this threshold. The thermal emission in the case of multiple grain radii at short wavelengths is stronger than for the reference disk. The freeze-out radius (snowline) is a function of grain radius, spanning a radial range between the coldest and warmest grain species of 30 AU.

  4. Future hard disk drive systems

    NASA Astrophysics Data System (ADS)

    Wood, Roger

    2009-03-01

    This paper briefly reviews the evolution of today's hard disk drive with the additional intention of orienting the reader to the overall mechanical and electrical architecture. The modern hard disk drive is a miracle of storage capacity and function together with remarkable economy of design. This paper presents a personal view of future customer requirements and the anticipated design evolution of the components. There are critical decisions and great challenges ahead for the key technologies of heads, media, head-disk interface, mechanics, and electronics.

  5. Disk tides and accretion runaway

    NASA Technical Reports Server (NTRS)

    Ward, William R.; Hahn, Joseph M.

    1995-01-01

    It is suggested that tidal interaction of an accreting planetary embryo with the gaseous preplanetary disk may provide a mechanism to breach the so-called runaway limit during the formation of the giant planet cores. The disk tidal torque converts a would-be shepherding object into a 'predator,' which can continue to cannibalize the planetesimal disk. This is more likely to occur in the giant planet region than in the terrestrial zone, providing a natural cause for Jupiter to predate the inner planets and form within the O(10(exp 7) yr) lifetime of the nebula.

  6. Cold Dark Matter Substructure and Galactic Disks I: Morphological Signatures of Hierarchical SatelliteAccretion

    SciTech Connect

    Kazantzidis, Stelios; Bullock, James S.; Zentner, Andrew R.; Kravtsov, Andrey V.; Moustakas, Leonidas A.

    2007-12-03

    primarily as a result of the interaction with the most massive subhalo. We conclude that satellite-disk encounters of the kind expected in {Lambda}CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way, M31, and in other nearby and distant disk galaxies. These results highlight the significant role of CDM substructure in setting the structure of disk galaxies and driving galaxy evolution. Upcoming galactic structure surveys and astrometric satellites may be able to distinguish between competing cosmological models by testing whether the detailed structure of galactic disks is as excited as predicted by the CDM paradigm.

  7. Hints for Small Disks around Very Low Mass Stars and Brown Dwarfs

    NASA Astrophysics Data System (ADS)

    Hendler, Nathanial P.; Mulders, Gijs D.; Pascucci, Ilaria; Greenwood, Aaron; Kamp, Inga; Henning, Thomas; Ménard, François; Dent, William R. F.; Evans, Neal J., II

    2017-06-01

    The properties of disks around brown dwarfs and very low mass stars (hereafter VLMOs) provide important boundary conditions on the process of planet formation and inform us about the numbers and masses of planets than can form in this regime. We use the Herschel Space Observatory PACS spectrometer to measure the continuum and [O i] 63 μm line emission toward 11 VLMOs with known disks in the Taurus and Chamaeleon I star-forming regions. We fit radiative transfer models to the spectral energy distributions of these sources. Additionally, we carry out a grid of radiative transfer models run in a regime that connects the luminosity of our sources with brighter T Tauri stars. We find that VLMO disks with sizes 1.3-78 au, smaller than typical T Tauri disks, fit well the spectral energy distributions assuming that disk geometry and dust properties are stellar mass independent. Reducing the disk size increases the disk temperature, and we show that VLMOs do not follow previously derived disk temperature-stellar luminosity relationships if the disk outer radius scales with stellar mass. Only 2 out of 11 sources are detected in [O i] despite a better sensitivity than was achieved for T Tauri stars, suggesting that VLMO disks are underluminous. Using thermochemical models, we show that smaller disks can lead to the unexpected [O i] 63 μm nondetections in our sample. The disk outer radius is an important factor in determining the gas and dust observables. Hence, spatially resolved observations with ALMA—to establish if and how disk radii scale with stellar mass—should be pursued further. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

  8. A SPITZER c2d LEGACY SURVEY TO IDENTIFY AND CHARACTERIZE DISKS WITH INNER DUST HOLES

    SciTech Connect

    Merin, Bruno; Brown, Joanna M.; Herczeg, Gregory J.; Van Dishoeck, Ewine F.; Oliveira, Isa; Lahuis, Fred; Bottinelli, Sandrine; Augereau, Jean-Charles; Olofsson, Johan; Evans, Neal J.; Harvey, Paul M.; Cieza, Lucas; Spezzi, Loredana; Prusti, Timo; Alcala, Juan M.; Blake, Geoffrey A.; Bayo, Amelia; Geers, Vincent G.; Walter, Frederick M.; Chiu, Kuenley

    2010-08-01

    Understanding how disks dissipate is essential to studies of planet formation. However, identifying exactly how dust and gas dissipate is complicated due to the difficulty of finding objects that are clearly in the transition phase of losing their surrounding material. We use Spitzer Infrared Spectrograph (IRS) spectra to examine 35 photometrically selected candidate cold disks (disks with large inner dust holes). The infrared spectra are supplemented with optical spectra to determine stellar and accretion properties and 1.3 mm photometry to measure disk masses. Based on detailed spectral energy distribution modeling, we identify 15 new cold disks. The remaining 20 objects have IRS spectra that are consistent with disks without holes, disks that are observed close to edge-on, or stars with background emission. Based on these results, we determine reliable criteria to identify disks with inner holes from Spitzer photometry, and examine criteria already in the literature. Applying these criteria to the c2d surveyed star-forming regions gives a frequency of such objects of at least 4% and most likely of order 12% of the young stellar object population identified by Spitzer. We also examine the properties of these new cold disks in combination with cold disks from the literature. Hole sizes in this sample are generally smaller than in previously discovered disks and reflect a distribution in better agreement with exoplanet orbit radii. We find correlations between hole size and both disk and stellar masses. Silicate features, including crystalline features, are present in the overwhelming majority of the sample, although the 10 {mu}m feature strength above the continuum declines for holes with radii larger than {approx}7 AU. In contrast, polycyclic aromatic hydrocarbons are only detected in 2 out of 15 sources. Only a quarter of the cold disk sample shows no signs of accretion, making it unlikely that photoevaporation is the dominant hole-forming process in most cases.

  9. MHD Modelling of Protostellar Disk Winds and Jets

    NASA Astrophysics Data System (ADS)

    Nolan, Christopher; Sutherland, Ralph; Salmeron, Raquel; Bicknell, Geoff

    2013-07-01

    One of the outstanding challenges in star formation is the angular momentum problem. Angular momentum transport is required to allow a cloud core to collapse to form a star. Angular momentum in the initial collapsing cloud prevents the majority of material falling directly onto the protostar, instead settling into a circumstellar disk around it. It is from this point that the angular momentum must be redistributed to allow material to accrete. Radial transport of angular momentum is accomplished via the magnetorotational instability (MRI). Vertical angular momentum transport has generally been attributed to centrifugally driven winds (CDWs) from the disk surface. Both modes of transport depend on the strength of the local magnetic field, parametrised by the ratio of the vertical Alfven speed to the isothermal sound speed, a0. MRI is expected to dominate in the presence of weak fields (a0 ≪ 1), whereas CDWs require a strong field (a0 ≲ 1). Here we present calculations of the structure of minimum-mass solar nebula protostellar disks in strong fields (a0 = 1) around a solar mass star, focusing on the regions of these disks that may launch a CDW from their surface. These results have implications for disk-driven models of protostellar jet launching including the connection between disk properties and large scale features of jets.

  10. Shaping Disk Galaxy Stellar Populations via Internal and External Processes

    NASA Astrophysics Data System (ADS)

    Roškar, Rok

    2015-03-01

    In recent years, effects such as the radial migration of stars in disks have been recognized as important drivers of the properties of stellar populations. Radial migration arises due to perturbative effects of disk structures such as bars and spiral arms, and can deposit stars formed in disks to regions far from their birthplaces. Migrant stars can significantly affect the demographics of their new locales, especially in low-density regions such as in the outer disks. However, in the cosmological environment, other effects such as mergers and filamentary gas accretion also influence the disk formation process. Understanding the relative importance of these processes on the detailed evolution of stellar population signatures is crucial for reconstructing the history of the Milky Way and other nearby galaxies. In the Milky Way disk in particular, the formation of the thickened component has recently attracted much attention due to its potential to serve as a diagnostic of the galaxy's early history. Some recent work suggests, however, that the vertical structure of Milky Way stellar populations is consistent with models that build up the thickened component through migration. I discuss these developments in the context of cosmological galaxy formation.

  11. Modeling Mid-Infrared Polarization from Protoplanetary Disks and YSOs

    NASA Astrophysics Data System (ADS)

    Zhang, Han; Pantin, Eric; Li, Dan; Telesco, Charles M.

    2017-01-01

    Imaging polarimetry has demonstrated its potential to map magnetic fields in star formation regions. To interpret high-resolution, mid-infrared (mid-IR) observations obtained with present or forthcoming instruments, such as GTC/CanariCam and SOFIA/HAWC+, we have developed a new package of codes to model mid-IR polarization from protoplanetary disks and YSOs. Based on RADMC-3D and DDSCAT, our package is the first of its kind that takes into account all polarization mechanisms known to be present in the mid-IR, including dichroic absorption, dichroic emission, and scattering. Mid-IR polarization arising from a disk or YSO depends on dust properties (e.g., the size distribution, shape, and composition), magnetic field configurations, and the geometry of the disk and/or envelope, all of which can be customized in our model. We have created synthetic maps of mid-IR linear polarization for a series of fiducial disk and YSO models to compare with observations. In general, we find 1) that emissive polarization arising from aligned dust grains in disk magnetic fields is at the level of a few percent and lower than previous expectations, and 2) that micron-sized dust particles are required to reproduce the observed level of polarization from dust scattering in the mid-IR for a typical Herbig Ae/Be disk. The research was support in part by NSF awards AST -0903672, AST-0908624, and AST-1515331 to CMT.

  12. Connecting Clump Sizes in Turbulent Disk Galaxies to Instability Theory

    NASA Astrophysics Data System (ADS)

    Fisher, David B.; Glazebrook, Karl; Abraham, Roberto G.; Damjanov, Ivana; White, Heidi A.; Obreschkow, Danail; Basset, Robert; Bekiaris, Georgios; Wisnioski, Emily; Green, Andy; Bolatto, Alberto D.

    2017-04-01

    In this letter we study the mean sizes of Hα clumps in turbulent disk galaxies relative to kinematics, gas fractions, and Toomre Q. We use ∼100 pc resolution HST images, IFU kinematics, and gas fractions of a sample of rare, nearby turbulent disks with properties closely matched to z∼ 1.5{--}2 main-sequence galaxies (the DYNAMO sample). We find linear correlations of normalized mean clump sizes with both the gas fraction and the velocity dispersion-to-rotation velocity ratio of the host galaxy. We show that these correlations are consistent with predictions derived from a model of instabilities in a self-gravitating disk (the so-called “violent disk instability model”). We also observe, using a two-fluid model for Q, a correlation between the size of clumps and self-gravity-driven unstable regions. These results are most consistent with the hypothesis that massive star-forming clumps in turbulent disks are the result of instabilities in self-gravitating gas-rich disks, and therefore provide a direct connection between resolved clump sizes and this in situ mechanism.

  13. FORMING DOUBLE-BARRED GALAXIES FROM DYNAMICALLY COOL INNER DISKS

    SciTech Connect

    Du, Min; Shen, Juntai; Debattista, Victor P.

    2015-05-10

    About one-third of early-type barred galaxies host small-scale secondary bars. The formation and evolution of such double-barred (S2B) galaxies remain far from being well understood. In order to understand the formation of such systems, we explore a large parameter space of isolated pure-disk simulations. We show that a dynamically cool inner disk embedded in a hotter outer disk can naturally generate a steady secondary bar while the outer disk forms a large-scale primary bar. The independent bar instabilities of inner and outer disks result in long-lived double-barred structures whose dynamical properties are comparable to those in observations. This formation scenario indicates that the secondary bar might form from the general bar instability, the same as the primary bar. Under some circumstances, the interaction of the bars and the disk leads to the two bars aligning or single, nuclear, bars only. Simulations that are cool enough of the center to experience clump instabilities may also generate steady S2B galaxies. In this case, the secondary bars are “fast,” i.e., the bar length is close to the co-rotation radius. This is the first time that S2B galaxies containing a fast secondary bar are reported. Previous orbit-based studies had suggested that fast secondary bars were not dynamically possible.

  14. Constraining Galaxy Evolution With Bulge-Disk-Bar Decomposition

    NASA Astrophysics Data System (ADS)

    Weinzirl, T.; Jogee, S.; Barazza, F. D.

    2008-08-01

    Structural decomposition of galaxies into bulge, disk, and bar components is important to address a number of scientific problems. Measuring bulge, disk, and bar structural parameters will set constraints on the violent and secular processes of galaxy assembly and recurrent bar formation and dissolution models. It can also help to quantify the fraction and properties of bulgeless galaxies (those systems having no bulge or only a relatively insignificant disky-pseudobulges), which defy galaxy formation paradigms requiring almost every disk galaxy to have a classical bulge at its core. We demonstrate a proof of concept and show early results of our ongoing three-component bulge-disk-bar decomposition of NIR images for samples spanning different environments (field and cluster). In contrast to most early studies, which only attempt two-component bulge-disk decomposition, we fit three components using GALFIT: a bulge, a disk, and a bar. We show that it is important to include the bar component, as this can significantly lower the bulge-to-total luminosity ratio (B/T), in many cases by a factor of two or more, thus effectively changing the Hubble type of a galaxy from early to late.

  15. DUST EVOLUTION CAN PRODUCE SCATTERED LIGHT GAPS IN PROTOPLANETARY DISKS

    SciTech Connect

    Birnstiel, Tilman; Andrews, Sean M.; Pinilla, Paola; Kama, Mihkel E-mail: sandrews@cfa.harvard.edu E-mail: mkama@strw.leidenuniv.nl

    2015-11-01

    Recent imaging of protoplanetary disks with high resolution and contrast have revealed a striking variety of substructure. Of particular interest are cases where near-infrared scattered light images show evidence for low-intensity annular “gaps.” The origins of such structures are still uncertain, but the interaction of the gas disk with planets is a common interpretation. We study the impact that the evolution of the solid material can have on the observable properties of disks in a simple scenario without any gravitational or hydrodynamical disturbances to the gas disk structure. Even with a smooth and continuous gas density profile, we find that the scattered light emission produced by small dust grains can exhibit ring-like depressions similar to those presented in recent observations. The physical mechanisms responsible for these features rely on the inefficient fragmentation of dust particles. The occurrence and position of the proposed “gap” features depend most strongly on the dust-to-gas ratio, the fragmentation threshold velocity, the strength of the turbulence, and the age of the disk, and should be generic (at some radius) for typically adopted disk parameters. The same physical processes can affect the thermal emission at optically thin wavelengths (∼1 mm), although the behavior can be more complex; unlike for disk–planet interactions, a “gap” should not be present at these longer wavelengths.

  16. Magnetized Black Hole Accretion Disks with Poloidal Flux

    NASA Astrophysics Data System (ADS)

    Salvesen, Greg; Simon, Jacob B.; Armitage, Philip J.; Begelman, Mitchell C.

    2017-08-01

    Observations of blueshifted absorption lines associated with black hole X-ray binary accretion disk winds sometimes imply a magnetic driving mechansim. To study the properties of magnetized disks, we performed shearing box simulations (stratified, isothermal, ideal MHD) with different amounts of net vertical magnetic flux, spanning essentially the entire range over which the MRI is linearly unstable. This net vertical flux sets the strength of the dominant toroidal field that is generated by the MRI-dynamo. Given sufficiently large net vertical flux, magnetic pressure support against gravity dominates throughout the vertical column of the disk. Without net poloidal flux, a strongly magnetized state cannot persist because the toroidal field buoyantly escapes faster than it can be replenished. With increasing disk magnetization: (1) toroidal field reversals characteristic of the MRI-dynamo become less frequent and more sporadic and (2) gas density becomes more inhomogeneous, with field concentrating in low-density regions. We are currently investigating whether magnetic pressure support in the disk atmosphere alters the disk continuum spectrum, which would bring the robustness of black hole spin measurements into question.

  17. STRUCTURE AND EVOLUTION OF CIRCUMBINARY DISKS AROUND SUPERMASSIVE BLACK HOLE BINARIES

    SciTech Connect

    Rafikov, Roman R.

    2013-09-10

    We explore properties of circumbinary disks around supermassive black hole (SMBH) binaries in centers of galaxies by reformulating standard viscous disk evolution in terms of the viscous angular momentum flux F{sub J}. If the binary stops gas inflow and opens a cavity in the disk, then the inner disk evolves toward a constant-F{sub J} (rather than a constant M-dot ) state. We compute disk properties in different physical regimes relevant for SMBH binaries, focusing on the gas-assisted evolution of systems starting at separations 10{sup -4} - 10{sup -2} pc, and find the following. (1) Mass pileup at the inner disk edge caused by the tidal barrier accelerates binary inspiral. (2) Binaries can be forced to merge even by a disk with a mass below that of the secondary. (3) Torque on the binary is set non-locally, at radii far larger than the binary semi-major axis; its magnitude does not reflect disk properties in the vicinity of the binary. (4) Binary inspiral exhibits hysteresis-it depends on the past evolution of the disk. (5) The Eddington limit can be important for circumbinary disks even if they accrete at sub-Eddington rates, but only at late stages of the inspiral. (6) Gas overflow across the orbit of the secondary can be important for low secondary mass, high- M-dot systems, but mainly during the inspiral phase dominated by the gravitational wave emission. (7) Circumbinary disks emit more power and have harder spectra than constant M-dot disks; their spectra are very sensitive to the amount of overflow across the secondary orbit.

  18. Young stars in ɛ Cha