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Sample records for radial velocity gradient

  1. Photoelectric Radial Velocities, Paper XIX Additional Spectroscopic ...

    Indian Academy of Sciences (India)

    ian velocity curve that does justice to the measurements, but it cannot be expected to have much predictive power. Key words. Stars: late-type—stars: radial velocities—spectroscopic binaries—orbits. 0. Preamble. The 'Redman K stars' are a lot of seventh-magnitude K stars whose radial velocities were first observed by ...

  2. Radial velocities of RR Lyrae stars

    International Nuclear Information System (INIS)

    Hawley, S.L.; Barnes, T.G. III

    1985-01-01

    283 spectra of 57 RR Lyrae stars have been obtained using the 2.1-m telescope at McDonald Observatory. Radial velocities were determined using a software cross-correlation technique. New mean radial velocities were determined for 46 of the stars. 11 references

  3. Radial velocity observations of VB10

    Science.gov (United States)

    Deshpande, R.; Martin, E.; Zapatero Osorio, M. R.; Del Burgo, C.; Rodler, F.; Montgomery, M. M.

    2011-07-01

    VB 10 is the smallest star known to harbor a planet according to the recent astrometric study of Pravdo & Shaklan [1]. Here we present near-infrared (J-band) radial velocity of VB 10 performed from high resolution (R~20,000) spectroscopy (NIRSPEC/KECK II). Our results [2] suggest radial velocity variability with amplitude of ~1 km/s, a result that is consistent with the presence of a massive planet companion around VB10 as found via long-term astrometric monitoring of the star by Pravdo & Shaklan. Employing an entirely different technique we verify the results of Pravdo & Shaklan.

  4. Radial oxygen gradients over rat cortex arterioles

    OpenAIRE

    Galler, Michael

    2011-01-01

    Purpose: We present the results of the visualisation of radial oxygen gradients in rats’ cortices and their use in neurocritical management. Methods: PO2 maps of the cortex of 10 wistar rats were obtained with a camera (SensiMOD, PCO, Kehlheim, Germany). Those pictures were analyzed and edited by a custom-made software. We chose a vessel for examination. A matrix, designed to evaluate the cortical O2 partial pressure, was placed vertically to the artery and afterwards multiple regio...

  5. Radial velocity asymmetries from jets with variable velocity profiles

    International Nuclear Information System (INIS)

    Cerqueira, A. H.; Vasconcelos, M. J.; Velazquez, P. F.; Raga, A. C.; De Colle, F.

    2006-01-01

    We have computed a set of 3-D numerical simulations of radiatively cooling jets including variabilities in both the ejection direction (precession) and the jet velocity (intermittence), using the Yguazu-a code. In order to investigate the effects of jet rotation on the shape of the line profiles, we also introduce an initial toroidal rotation velocity profile. Since the Yguazu-a code includes an atomic/ionic network, we are able to compute the emission coefficients for several emission lines, and we generate line profiles for the Hα, [O I]λ6300, [S II]λ6716 and [N II]λ6548 lines. Using initial parameters that are suitable for the DG Tau microjet, we show that the computed radial velocity shift for the medium-velocity component of the line profile as a function of distance from the jet axis is strikingly similar for rotating and non-rotating jet models

  6. The radial velocity variations in IC 418

    International Nuclear Information System (INIS)

    Mendez, R.H.; Verga, A.D.

    1981-01-01

    The observations presented are part of a search for spectral and radial velocity variations among central stars of planetary nebulae and include the following new data: 1) Weak, previously undetected C III emissions are visible at 4056, 4186, 4516, 5270 and 5826 A. The famous unidentified emissions at 4485 and 4503 A were also found. 2) The He I absorptions at 4471 and 5875 A are blue-shifted relative to the nebular emissions. The same happens with Hsub(delta) and Hsub(γ), although in this case the shift can be at least partly attributed to blends with the strong He II absorptions, which are estimated to contribute about one half of the equivalent width at Hsub(delta) and Hsub(γ). 3) O III 5592 and C IV 5801, 5811 are also found in absorption. (Auth.)

  7. THE NIRSPEC ULTRACOOL DWARF RADIAL VELOCITY SURVEY

    International Nuclear Information System (INIS)

    Blake, Cullen H.; Charbonneau, David; White, Russel J.

    2010-01-01

    We report the results of an infrared Doppler survey designed to detect brown dwarf and giant planetary companions to a magnitude-limited sample of ultracool dwarfs. Using the NIRSPEC spectrograph on the Keck II telescope, we obtained approximately 600 radial velocity (RV) measurements over a period of six years of a sample of 59 late-M and L dwarfs spanning spectral types M8/L0 to L6. A subsample of 46 of our targets has been observed on three or more epochs. We rely on telluric CH 4 absorption features in Earth's atmosphere as a simultaneous wavelength reference and exploit the rich set of CO absorption features found in the K-band spectra of cool stars and brown dwarfs to measure RVs and projected rotational velocities. For a bright, slowly rotating M dwarf standard we demonstrate an RV precision of 50 m s -1 and for slowly rotating L dwarfs we achieve a typical RV precision of approximately 200 m s -1 . This precision is sufficient for the detection of close-in giant planetary companions to mid-L dwarfs as well as more equal mass spectroscopic binary systems with small separations (a +0.7 -0.6 Gyr, similar to that of nearby sun-like stars. We simulate the efficiency with which we detect spectroscopic binaries and find that the rate of tight (a +8.6 -1.6 %, consistent with recent estimates in the literature of a tight binary fraction of 3%-4%.

  8. A New Filtering Algorithm Utilizing Radial Velocity Measurement

    Institute of Scientific and Technical Information of China (English)

    LIU Yan-feng; DU Zi-cheng; PAN Quan

    2005-01-01

    Pulse Doppler radar measurements consist of range, azimuth, elevation and radial velocity. Most of the radar tracking algorithms in engineering only utilize position measurement. The extended Kalman filter with radial velocity measureneut is presented, then a new filtering algorithm utilizing radial velocity measurement is proposed to improve tracking results and the theoretical analysis is also given. Simulation results of the new algorithm, converted measurement Kalman filter, extended Kalman filter are compared. The effectiveness of the new algorithm is verified by simulation results.

  9. Radial Velocities of 41 Kepler Eclipsing Binaries

    Science.gov (United States)

    Matson, Rachel A.; Gies, Douglas R.; Guo, Zhao; Williams, Stephen J.

    2017-12-01

    Eclipsing binaries are vital for directly determining stellar parameters without reliance on models or scaling relations. Spectroscopically derived parameters of detached and semi-detached binaries allow us to determine component masses that can inform theories of stellar and binary evolution. Here we present moderate resolution ground-based spectra of stars in close binary systems with and without (detected) tertiary companions observed by NASA’s Kepler mission and analyzed for eclipse timing variations. We obtain radial velocities and spectroscopic orbits for five single-lined and 35 double-lined systems, and confirm one false positive eclipsing binary. For the double-lined spectroscopic binaries, we also determine individual component masses and examine the mass ratio {M}2/{M}1 distribution, which is dominated by binaries with like-mass pairs and semi-detached classical Algol systems that have undergone mass transfer. Finally, we constrain the mass of the tertiary component for five double-lined binaries with previously detected companions.

  10. The effect of non-zero radial velocity on the impulse and circulation of starting jets

    Science.gov (United States)

    Krieg, Michael; Mohseni, Kamran

    2011-11-01

    Vortex ring formation dynamics are generally studied using two basic types of vortex generators. Piston cylinder vortex generators eject fluid through a long tube which ensures a purely axial jet; whereas, vortex ring generators which expel fluid through a flat plate with a circular orifice produce 2-D jets (non-zero radial velocity). At the nozzle exit plane of the orifice type vortex generator the radial component of velocity is linearly proportional to the radial distance from the axis of symmetry, reaching a maximum at the edge of the orifice with a magnitude around 10 % of the piston velocity (the ratio of the volume flux and the nozzle area). As the jet advances downstream the radial velocity quickly dissipates, and becomes purely axial less than a diameter away from the nozzle exit plane. The radial velocity gradient in the axial direction plays a key role in the rate at which circulation and impulse are ejected from the vortex generator. Though the radial component of velocity is small compared to the axial velocity, it has a significant effect on both the circulation and impulse of the starting jet because of this gradient. The extent of circulation and impulse enhancement is investigated through experimental DPIV data showing that the orifice device produces nearly double both circulation and energy (with identical piston velocity and stroke ratios).

  11. RADIAL VELOCITY MONITORING OF KEPLER HEARTBEAT STARS

    Energy Technology Data Exchange (ETDEWEB)

    Shporer, Avi [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Fuller, Jim [TAPIR, Walter Burke Institute for Theoretical Physics, Mailcode 350-17, Caltech, Pasadena, CA 91125 (United States); Isaacson, Howard [Department of Astronomy, University of California, Berkeley CA 94720 (United States); Hambleton, Kelly; Prša, Andrej [Department of Astrophysics and Planetary Science, Villanova University, 800 East Lancaster Avenue, Villanova, PA 19085 (United States); Thompson, Susan E. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Kurtz, Donald W. [Jeremiah Horrocks Institute, University of Central Lancashire, Preston, PR1 2HE (United Kingdom); Howard, Andrew W. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); O’Leary, Ryan M. [JILA, University of Colorado and NIST, 440 UCB, Boulder, 80309-0440 (United States)

    2016-09-20

    Heartbeat stars (HB stars) are a class of eccentric binary stars with close periastron passages. The characteristic photometric HB signal evident in their light curves is produced by a combination of tidal distortion, heating, and Doppler boosting near orbital periastron. Many HB stars continue to oscillate after periastron and along the entire orbit, indicative of the tidal excitation of oscillation modes within one or both stars. These systems are among the most eccentric binaries known, and they constitute astrophysical laboratories for the study of tidal effects. We have undertaken a radial velocity (RV) monitoring campaign of Kepler HB stars in order to measure their orbits. We present our first results here, including a sample of 22 Kepler HB systems, where for 19 of them we obtained the Keplerian orbit and for 3 other systems we did not detect a statistically significant RV variability. Results presented here are based on 218 spectra obtained with the Keck/HIRES spectrograph during the 2015 Kepler observing season, and they have allowed us to obtain the largest sample of HB stars with orbits measured using a single instrument, which roughly doubles the number of HB stars with an RV measured orbit. The 19 systems measured here have orbital periods from 7 to 90 days and eccentricities from 0.2 to 0.9. We show that HB stars draw the upper envelope of the eccentricity–period distribution. Therefore, HB stars likely represent a population of stars currently undergoing high eccentricity migration via tidal orbital circularization, and they will allow for new tests of high eccentricity migration theories.

  12. RADIAL VELOCITY MONITORING OF KEPLER HEARTBEAT STARS

    International Nuclear Information System (INIS)

    Shporer, Avi; Fuller, Jim; Isaacson, Howard; Hambleton, Kelly; Prša, Andrej; Thompson, Susan E.; Kurtz, Donald W.; Howard, Andrew W.; O’Leary, Ryan M.

    2016-01-01

    Heartbeat stars (HB stars) are a class of eccentric binary stars with close periastron passages. The characteristic photometric HB signal evident in their light curves is produced by a combination of tidal distortion, heating, and Doppler boosting near orbital periastron. Many HB stars continue to oscillate after periastron and along the entire orbit, indicative of the tidal excitation of oscillation modes within one or both stars. These systems are among the most eccentric binaries known, and they constitute astrophysical laboratories for the study of tidal effects. We have undertaken a radial velocity (RV) monitoring campaign of Kepler HB stars in order to measure their orbits. We present our first results here, including a sample of 22 Kepler HB systems, where for 19 of them we obtained the Keplerian orbit and for 3 other systems we did not detect a statistically significant RV variability. Results presented here are based on 218 spectra obtained with the Keck/HIRES spectrograph during the 2015 Kepler observing season, and they have allowed us to obtain the largest sample of HB stars with orbits measured using a single instrument, which roughly doubles the number of HB stars with an RV measured orbit. The 19 systems measured here have orbital periods from 7 to 90 days and eccentricities from 0.2 to 0.9. We show that HB stars draw the upper envelope of the eccentricity–period distribution. Therefore, HB stars likely represent a population of stars currently undergoing high eccentricity migration via tidal orbital circularization, and they will allow for new tests of high eccentricity migration theories.

  13. What velocities and eccentricities tell us about radial migration

    Directory of Open Access Journals (Sweden)

    Schönrich R.

    2012-02-01

    Full Text Available This note attempts to interpret some of the recent findings about a downtrend in the mean azimuthal velocity of low [α/Fe] thin disc stars with increasing metallicity. The presence of such a trend was predicted in the model of [19], albeit with a slightly steeper slope. We show that in a simple picture a Galactic disc without mixing in angular momenta would display an exceedingly steep trend, while in the case of complete mixing of all stars the trend has to vanish. The difference between model and observational data can hence be interpreted as the consequence of the radial abundance gradient in the model being too high resulting in an underestimate of the migration strength. We shortly discuss the value of eccentricity distributions in constraining structure and history of the Galactic disc.

  14. Radial extension of drift waves in presence of velocity profiles

    International Nuclear Information System (INIS)

    Sen, S.; Weiland, J.

    1994-01-01

    The effect of a radially varying poloidal velocity field on the recently found radially extended toroidal drift waves is investigated analytically. The role of velocity curvature (υ φ '') is found to have robust effects on the radial model structure of the mode. For a positive value of the curvature (Usually found in the H-mode edges) the radial model envelope, similar to the sheared slab case, becomes fully outgoing. The mode is therefore stable. On the other hand, for a negative value of the curvature (usually observed in the L-mode edges) all the characteristics of conventional drift waves return back. The radial mode envelope reduces to a localized Gaussian shape and the mode is therefore unstable again for typical (magnetic) shear values in tokamaks. Velocity shear (υ φ ??) on the other hand is found to have rather insignificant role both in determining the radial model structure and stability

  15. Radial Color Gradient in a Globular Cluster 1. M68

    Directory of Open Access Journals (Sweden)

    Sukyoung Yi

    1990-12-01

    Full Text Available Stars in M68 from the observed color-magnitude diagrams with CCD were integrated to find any radial gradient. The result shows that M68 has a slightly bluer core. The main cause of these calculated radial color variations seems to come from the random distribution of giants.

  16. Photoelectric Radial Velocities, Paper XVIII Spectroscopic Orbits for ...

    Indian Academy of Sciences (India)

    The fundamental origin of the work presented here rests with the radial-velocity spectrometer that .... surfaces inevitably degrade rather rapidly in the environment in which they are called ...... are not safe to incorporate in the data set here.

  17. Variational method for integrating radial gradient field

    Science.gov (United States)

    Legarda-Saenz, Ricardo; Brito-Loeza, Carlos; Rivera, Mariano; Espinosa-Romero, Arturo

    2014-12-01

    We propose a variational method for integrating information obtained from circular fringe pattern. The proposed method is a suitable choice for objects with radial symmetry. First, we analyze the information contained in the fringe pattern captured by the experimental setup and then move to formulate the problem of recovering the wavefront using techniques from calculus of variations. The performance of the method is demonstrated by numerical experiments with both synthetic and real data.

  18. Illumination Profile & Dispersion Variation Effects on Radial Velocity Measurements

    Science.gov (United States)

    Grieves, Nolan; Ge, Jian; Thomas, Neil B.; Ma, Bo; Li, Rui; SDSS-III

    2015-01-01

    The Multi-object APO Radial-Velocity Exoplanet Large-Area Survey (MARVELS) measures radial velocities using a fiber-fed dispersed fixed-delay interferometer (DFDI) with a moderate dispersion spectrograph. This setup allows a unique insight into the 2D illumination profile from the fiber on to the dispersion grating. Illumination profile investigations show large changes in the profile over time and fiber location. These profile changes are correlated with dispersion changes and long-term radial velocity offsets, a major problem within the MARVELS radial velocity data. Characterizing illumination profiles creates a method to both detect and correct radial velocity offsets, allowing for better planet detection. Here we report our early results from this study including improvement of radial velocity data points from detected giant planet candidates. We also report an illumination profile experiment conducted at the Kitt Peak National Observatory using the EXPERT instrument, which has a DFDI mode similar to MARVELS. Using profile controlling octagonal-shaped fibers, long term offsets over a 3 month time period were reduced from ~50 m/s to within the photon limit of ~4 m/s.

  19. THE RADIAL VELOCITY EXPERIMENT (RAVE): THIRD DATA RELEASE

    International Nuclear Information System (INIS)

    Siebert, A.; Williams, M. E. K.; Siviero, A.; Boeche, C.; Steinmetz, M.; De Jong, R. S.; Enke, H.; Anguiano, B.; Reid, W.; Ritter, A.; Fulbright, J.; Wyse, R. F. G.; Munari, U.; Zwitter, T.; Watson, F. G.; Burton, D.; Cass, C. J. P.; Fiegert, K.; Hartley, M.; Russel, K. S.

    2011-01-01

    We present the third data release of the RAdial Velocity Experiment (RAVE) which is the first milestone of the RAVE project, releasing the full pilot survey. The catalog contains 83,072 radial velocity measurements for 77,461 stars in the southern celestial hemisphere, as well as stellar parameters for 39,833 stars. This paper describes the content of the new release, the new processing pipeline, as well as an updated calibration for the metallicity based upon the observation of additional standard stars. Spectra will be made available in a future release. The data release can be accessed via the RAVE Web site.

  20. Rainbow refractometry on particles with radial refractive index gradients

    Energy Technology Data Exchange (ETDEWEB)

    Saengkaew, Sawitree [CNRS/Universite et INSA de Rouen, UMR 6614/CORIA, BP12, 76 800, Saint Etienne du Rouvray CEDEX (France); Chulalongkorn University, Center of Excellence in Particle Technology, Faculty of Engineering, Bangkok (Thailand); Charinpanitkul, Tawatchai; Vanisri, Hathaichanok; Tanthapanichakoon, Wiwut [Chulalongkorn University, Center of Excellence in Particle Technology, Faculty of Engineering, Bangkok (Thailand); Biscos, Yves; Garcia, Nicolas; Lavergne, Gerard [ONERA/DMAE, Toulouse (France); Mees, Loic; Gouesbet, Gerard; Grehan, Gerard [CNRS/Universite et INSA de Rouen, UMR 6614/CORIA, BP12, 76 800, Saint Etienne du Rouvray CEDEX (France)

    2007-10-15

    The rainbow refractrometry, under its different configurations (classical and global), is an attractive technique to extract information from droplets in evaporation such as diameter and temperature. Recently a new processing strategy has been developed which increases dramatically the size and refractive index measurements accuracy for homogeneous droplets. Nevertheless, for mono component as well as for multicomponent droplets, the presence of temperature and/or of concentration gradients induce the presence of a gradient of refractive index which affects the interpretation of the recorded signals. In this publication, the effect of radial gradient on rainbow measurements with a high accuracy never reached previously is quantified. (orig.)

  1. A radial velocity survey of extremely hydrogen-deficient stars

    International Nuclear Information System (INIS)

    Jeffery, C.S.; Kiel Univ.; Drilling, J.S.; Heber, U.

    1987-01-01

    A radial velocity survey of hot extremely hydrogen-deficient stars has been carried out in order to search for possible binaries. The survey found three stars to have large velocity variations. Of these, two are known hydrogen-deficient binaries and one, HDE 320156 (= LSS 4300), is a suspected binary. HDE 320156 (= LSS 4300) is therefore confirmed to be a single-lined spectroscopic hydrogen-deficient binary. The hydrogen-deficient binary stars all show weak C-lines. The remaining stars in the sample are C-strong extreme-helium (EHe) stars and did not show large-amplitude velocity variations. Small-amplitude radial velocity variations known to be present amongst the EHe stars are largely undetected. Evidence for variability is, however, present in the known variable V2076 Oph (HD 160641) and in LS IV - 1 0 2 with amplitudes between 10 and 20 km s -1 . (author)

  2. Additional radial velocities of supergiants in the Small Magellanic Cloud

    International Nuclear Information System (INIS)

    Thackeray, A.D.

    1978-01-01

    Additional radial velocities of 28 SMC supergiants determined in the years 1959-69 at the Radcliffe Observatory are presented. These and other measures from ESO and elsewhere are intercompared. The mean Radcliffe velocities have an internal standard error of +- 4.7 km/s and a systematic error exceeding 4 km/s is regarded as unlikely. Eight stars in the SMC core have a corrected velocity dispersion of only 6.9 km/s, similar to Feast's values for H II regions in the core. But the core H II regions have a velocity differential of -20 km/s relative to these stars. The velocity dispersion for stars in other parts of the Cloud is of the order 15 km/s as previously found. Two possibly variable-velocity stars are discussed, without reaching a satisfactory conclusion. (author)

  3. Accelerated radial Fourier-velocity encoding using compressed sensing

    International Nuclear Information System (INIS)

    Hilbert, Fabian; Han, Dietbert

    2014-01-01

    Purpose:Phase Contrast Magnetic Resonance Imaging (MRI) is a tool for non-invasive determination of flow velocities inside blood vessels. Because Phase Contrast MRI only measures a single mean velocity per voxel, it is only applicable to vessels significantly larger than the voxel size. In contrast, Fourier Velocity Encoding measures the entire velocity distribution inside a voxel, but requires a much longer acquisition time. For accurate diagnosis of stenosis in vessels on the scale of spatial resolution, it is important to know the velocity distribution of a voxel. Our aim was to determine velocity distributions with accelerated Fourier Velocity Encoding in an acquisition time required for a conventional Phase Contrast image. Materials and Methods:We imaged the femoral artery of healthy volunteers with ECG - triggered, radial CINE acquisition. Data acquisition was accelerated by undersampling, while missing data were reconstructed by Compressed Sensing. Velocity spectra of the vessel were evaluated by high resolution Phase Contrast images and compared to spectra from fully sampled and undersampled Fourier Velocity Encoding. By means of undersampling, it was possible to reduce the scan time for Fourier Velocity Encoding to the duration required for a conventional Phase Contrast image. Results:Acquisition time for a fully sampled data set with 12 different Velocity Encodings was 40 min. By applying a 12.6 - fold retrospective undersampling, a data set was generated equal to 3:10 min acquisition time, which is similar to a conventional Phase Contrast measurement. Velocity spectra from fully sampled and undersampled Fourier Velocity Encoded images are in good agreement and show the same maximum velocities as compared to velocity maps from Phase Contrast measurements. Conclusion: Compressed Sensing proved to reliably reconstruct Fourier Velocity Encoded data. Our results indicate that Fourier Velocity Encoding allows an accurate determination of the velocity

  4. Accelerated radial Fourier-velocity encoding using compressed sensing

    Energy Technology Data Exchange (ETDEWEB)

    Hilbert, Fabian; Han, Dietbert [Wuerzburg Univ. (Germany). Inst. of Radiology; Wech, Tobias; Koestler, Herbert [Wuerzburg Univ. (Germany). Inst. of Radiology; Wuerzburg Univ. (Germany). Comprehensive Heart Failure Center (CHFC)

    2014-10-01

    Purpose:Phase Contrast Magnetic Resonance Imaging (MRI) is a tool for non-invasive determination of flow velocities inside blood vessels. Because Phase Contrast MRI only measures a single mean velocity per voxel, it is only applicable to vessels significantly larger than the voxel size. In contrast, Fourier Velocity Encoding measures the entire velocity distribution inside a voxel, but requires a much longer acquisition time. For accurate diagnosis of stenosis in vessels on the scale of spatial resolution, it is important to know the velocity distribution of a voxel. Our aim was to determine velocity distributions with accelerated Fourier Velocity Encoding in an acquisition time required for a conventional Phase Contrast image. Materials and Methods:We imaged the femoral artery of healthy volunteers with ECG - triggered, radial CINE acquisition. Data acquisition was accelerated by undersampling, while missing data were reconstructed by Compressed Sensing. Velocity spectra of the vessel were evaluated by high resolution Phase Contrast images and compared to spectra from fully sampled and undersampled Fourier Velocity Encoding. By means of undersampling, it was possible to reduce the scan time for Fourier Velocity Encoding to the duration required for a conventional Phase Contrast image. Results:Acquisition time for a fully sampled data set with 12 different Velocity Encodings was 40 min. By applying a 12.6 - fold retrospective undersampling, a data set was generated equal to 3:10 min acquisition time, which is similar to a conventional Phase Contrast measurement. Velocity spectra from fully sampled and undersampled Fourier Velocity Encoded images are in good agreement and show the same maximum velocities as compared to velocity maps from Phase Contrast measurements. Conclusion: Compressed Sensing proved to reliably reconstruct Fourier Velocity Encoded data. Our results indicate that Fourier Velocity Encoding allows an accurate determination of the velocity

  5. Accelerated radial Fourier-velocity encoding using compressed sensing.

    Science.gov (United States)

    Hilbert, Fabian; Wech, Tobias; Hahn, Dietbert; Köstler, Herbert

    2014-09-01

    Phase Contrast Magnetic Resonance Imaging (MRI) is a tool for non-invasive determination of flow velocities inside blood vessels. Because Phase Contrast MRI only measures a single mean velocity per voxel, it is only applicable to vessels significantly larger than the voxel size. In contrast, Fourier Velocity Encoding measures the entire velocity distribution inside a voxel, but requires a much longer acquisition time. For accurate diagnosis of stenosis in vessels on the scale of spatial resolution, it is important to know the velocity distribution of a voxel. Our aim was to determine velocity distributions with accelerated Fourier Velocity Encoding in an acquisition time required for a conventional Phase Contrast image. We imaged the femoral artery of healthy volunteers with ECG-triggered, radial CINE acquisition. Data acquisition was accelerated by undersampling, while missing data were reconstructed by Compressed Sensing. Velocity spectra of the vessel were evaluated by high resolution Phase Contrast images and compared to spectra from fully sampled and undersampled Fourier Velocity Encoding. By means of undersampling, it was possible to reduce the scan time for Fourier Velocity Encoding to the duration required for a conventional Phase Contrast image. Acquisition time for a fully sampled data set with 12 different Velocity Encodings was 40 min. By applying a 12.6-fold retrospective undersampling, a data set was generated equal to 3:10 min acquisition time, which is similar to a conventional Phase Contrast measurement. Velocity spectra from fully sampled and undersampled Fourier Velocity Encoded images are in good agreement and show the same maximum velocities as compared to velocity maps from Phase Contrast measurements. Compressed Sensing proved to reliably reconstruct Fourier Velocity Encoded data. Our results indicate that Fourier Velocity Encoding allows an accurate determination of the velocity distribution in vessels in the order of the voxel size. Thus

  6. Formulating viscous hydrodynamics for large velocity gradients

    International Nuclear Information System (INIS)

    Pratt, Scott

    2008-01-01

    Viscous corrections to relativistic hydrodynamics, which are usually formulated for small velocity gradients, have recently been extended from Navier-Stokes formulations to a class of treatments based on Israel-Stewart equations. Israel-Stewart treatments, which treat the spatial components of the stress-energy tensor τ ij as dynamical objects, introduce new parameters, such as the relaxation times describing nonequilibrium behavior of the elements τ ij . By considering linear response theory and entropy constraints, we show how the additional parameters are related to fluctuations of τ ij . Furthermore, the Israel-Stewart parameters are analyzed for their ability to provide stable and physical solutions for sound waves. Finally, it is shown how these parameters, which are naturally described by correlation functions in real time, might be constrained by lattice calculations, which are based on path-integral formulations in imaginary time

  7. Radial Velocity Detection of Extra-Solar Planetary Systems

    Science.gov (United States)

    Cochran, William D.

    2004-01-01

    This NASA Origins Program grant supported four closely related research programs at The University of Texas at Austin: 1) The McDonald Observatory Planetary Search (MOPS) Program, using the McDonald Observatory 2.7m Harlan Smith telescope and its 2dcoude spectrometer, 2) A high-precision radial-velocity survey of Hyades dwarfs, using the Keck telescope and its HIRES spectrograph, 3) A program at McDonald Observatory to obtain spectra of the parent stars of planetary systems at R = 210,000, and 4) the start of high precision radial velocity surveys using the Hobby-Eberly Telescope. The most important results from NASA support of these research programs are described. A list of all papers published under support of this grant is included at the end.

  8. The innate origin of radial and vertical gradients in a simulated galaxy disc

    Science.gov (United States)

    Navarro, Julio F.; Yozin, Cameron; Loewen, Nic; Benítez-Llambay, Alejandro; Fattahi, Azadeh; Frenk, Carlos S.; Oman, Kyle A.; Schaye, Joop; Theuns, Tom

    2018-05-01

    We examine the origin of radial and vertical gradients in the age/metallicity of the stellar component of a galaxy disc formed in the APOSTLE cosmological hydrodynamical simulations. Some of these gradients resemble those in the Milky Way, where they have sometimes been interpreted as due to internal evolution, such as scattering off giant molecular clouds, radial migration driven by spiral patterns, or orbital resonances with a bar. Secular processes play a minor role in the simulated galaxy, which lacks strong spiral or bar patterns, and where such gradients arise as a result of the gradual enrichment of a gaseous disc that is born thick but thins as it turns into stars and settles into centrifugal equilibrium. The settling is controlled by the feedback of young stars; which links the star formation, enrichment, and equilibration time-scales, inducing radial and vertical gradients in the gaseous disc and its descendent stars. The kinematics of coeval stars evolve little after birth and provide a faithful snapshot of the gaseous disc structure at the time of their formation. In this interpretation, the age-velocity dispersion relation would reflect the gradual thinning of the disc rather than the importance of secular orbit scattering; the outward flaring of stars would result from the gas disc flare rather than from radial migration; and vertical gradients would arise because the gas disc gradually thinned as it enriched. Such radial and vertical trends might just reflect the evolving properties of the parent gaseous disc, and are not necessarily the result of secular evolutionary processes.

  9. The radial velocities of planetary nebulae in NGC 3379

    Science.gov (United States)

    Ciardullo, Robin; Jacoby, George H.; Dejonghe, Herwig B.

    1993-09-01

    We present the results of a radial velocity survey of planetary nebulae (PNs) in the normal elliptical galaxy NGC 3379 performed with the Kitt Peak 4 m telescope and the NESSIE multifiber spectrograph. In two half-nights, we measured 29 PNs with projected galactocentric distances between 0.4 and 3.8 effective radii with an observational uncertainty of about 7 km/s. These data extend three times farther into the halo than any previous absorption-line velocity study. The velocity dispersion and photometric profile of the galaxy agrees extremely well with that expected from a constant mass-to-light ratio, isotropic orbit Jaffe model with M/L(B) about 7; the best-fitting anisotropic models from a quadratic programming algorithm also give M/L(B) about 7. The data are consistent with models that contain no dark matter within 3.5 effective radii of the galaxy's nucleus.

  10. Identifying Clusters with Mixture Models that Include Radial Velocity Observations

    Science.gov (United States)

    Czarnatowicz, Alexis; Ybarra, Jason E.

    2018-01-01

    The study of stellar clusters plays an integral role in the study of star formation. We present a cluster mixture model that considers radial velocity data in addition to spatial data. Maximum likelihood estimation through the Expectation-Maximization (EM) algorithm is used for parameter estimation. Our mixture model analysis can be used to distinguish adjacent or overlapping clusters, and estimate properties for each cluster.Work supported by awards from the Virginia Foundation for Independent Colleges (VFIC) Undergraduate Science Research Fellowship and The Research Experience @Bridgewater (TREB).

  11. NEW RADIAL ABUNDANCE GRADIENTS FOR NGC 628 AND NGC 2403

    Energy Technology Data Exchange (ETDEWEB)

    Berg, Danielle A.; Skillman, Evan D. [Department of Astronomy, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55455 (United States); Croxall, Kevin V. [Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Marble, Andrew R. [National Solar Observatory, 950 N Cherry Avenue, Tucson, AZ 85719 (United States); Smith, J. D. [Ritter Astrophysical Observatory, University of Toledo, Toledo, OH 43606 (United States); Gordon, Karl [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Kennicutt, Robert C. Jr. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Garnett, Donald R., E-mail: berg@astro.umn.edu, E-mail: skillman@astro.umn.edu, E-mail: croxall.5@osu.edu, E-mail: amarble@nso.edu, E-mail: jd.smith@utoledo.edu, E-mail: kgordon@stsci.edu, E-mail: robk@ast.cam.ac.uk

    2013-10-01

    Motivated by recent interstellar medium studies, we present high quality MMT and Gemini spectroscopic observations of H II regions in the nearby spiral galaxies NGC 628 and NGC 2403 in order to measure their chemical abundance gradients. Using long-slit and multi-object mask optical spectroscopy, we obtained measurements of the temperature sensitive auroral lines [O III] λ4363 and/or [N II] λ5755 at a strength of 4σ or greater in 11 H II regions in NGC 628 and 7 regions in NGC 2403. These observations allow us, for the first time, to derive an oxygen abundance gradient in NGC 628 based solely on 'direct' oxygen abundances of H II regions: 12 + log(O/H) = (8.43 ± 0.03) + (–0.017 ± 0.002) × R{sub g} (dex kpc{sup –1}), with a dispersion in log(O/H) of σ = 0.10 dex, from 14 regions with a radial coverage of ∼2-19 kpc. This is a significantly shallower slope than found by previous 'strong-line' abundance studies. In NGC 2403, we derive an oxygen abundance gradient of 12 + log(O/H) = (8.48 ± 0.04) + (–0.032 ± 0.007)× R{sub g} (dex kpc{sup –1}), with a dispersion in log(O/H) of σ = 0.07 dex, from seven H II with a radial coverage of ∼1-10 kpc. Additionally, we measure the N, S, Ne, and Ar abundances. We find the N/O ratio decreases with increasing radius for the inner disk, but reaches a plateau past R{sub 25} in NGC 628. NGC 2403 also has a negative N/O gradient with radius, but we do not sample the outer disk of the galaxy past R{sub 25} and so do not see evidence for a plateau. This bi-modal pattern measured for NGC 628 indicates dominant contributions from secondary nitrogen inside of the R{sub 25} transition and dominantly primary nitrogen farther out. As expected for α-process elements, S/O, Ne/O, and Ar/O are consistent with constant values over a range in oxygen abundance.

  12. The radial velocity, velocity dispersion, and mass-to-light ratio of the Sculptor dwarf galaxy

    Science.gov (United States)

    Armandroff, T. E.; Da Costa, G. S.

    1986-01-01

    The radial velocity, velocity dispersion, and mass-to-light ratio for 16 K giants in the Sculptor dwarf galaxy are calculated. Spectra at the Ca II triplet are analyzed using cross-correlation techniques in order to obtain the mean velocity of + 107.4 + or - 2.0 km/s. The dimensional velocity dispersion estimated as 6.3 (+1.1, -1.3) km/s is combined with the calculated core radius and observed central surface brightness to produce a mass-to-light ratio of 6.0 in solar units. It is noted that the data indicate that the Sculptor contains a large amount of mass not found in globular clusters, and the mass is either in the form of remnant stars or low-mass dwarfs.

  13. RadVel: The Radial Velocity Modeling Toolkit

    Science.gov (United States)

    Fulton, Benjamin J.; Petigura, Erik A.; Blunt, Sarah; Sinukoff, Evan

    2018-04-01

    RadVel is an open-source Python package for modeling Keplerian orbits in radial velocity (RV) timeseries. RadVel provides a convenient framework to fit RVs using maximum a posteriori optimization and to compute robust confidence intervals by sampling the posterior probability density via Markov Chain Monte Carlo (MCMC). RadVel allows users to float or fix parameters, impose priors, and perform Bayesian model comparison. We have implemented real-time MCMC convergence tests to ensure adequate sampling of the posterior. RadVel can output a number of publication-quality plots and tables. Users may interface with RadVel through a convenient command-line interface or directly from Python. The code is object-oriented and thus naturally extensible. We encourage contributions from the community. Documentation is available at http://radvel.readthedocs.io.

  14. Activity-induced radial velocity variation of M dwarf stars

    DEFF Research Database (Denmark)

    Andersen, Jan Marie; Korhonen, Heidi Helena

    2012-01-01

    that can drown out a planetary signature. Cool, low-mass M dwarf stars can be highly active, which can make detection of potentially habitable planets around these stars difficult. We investigate radial velocity variations caused by different activity (spot) patterns on M dwarf stars in order to determine...... the limits of detectability for small planets orbiting active M dwarfs. We report on our progress toward the aim of answering the following questions: What types of spot patterns are realistic for M dwarf stars? What effect will spots have on M dwarf RV measurements? Can jitter from M dwarf spots mimic...... planetary signals? What is the ideal observing wavelength to reduce M dwarf jitter?...

  15. MARVELS Radial Velocity Solutions to Seven Kepler Eclipsing Binaries

    Science.gov (United States)

    Heslar, Michael Francis; Thomas, Neil B.; Ge, Jian; Ma, Bo; Herczeg, Alec; Reyes, Alan; SDSS-III MARVELS Team

    2016-01-01

    Eclipsing binaries serve momentous purposes to improve the basis of understanding aspects of stellar astrophysics, such as the accurate calculation of the physical parameters of stars and the enigmatic mass-radius relationship of M and K dwarfs. We report the investigation results of 7 eclipsing binary candidates, initially identified by the Kepler mission, overlapped with the radial velocity observations from the SDSS-III Multi-Object APO Radial-Velocity Exoplanet Large-Area Survey (MARVELS). The RV extractions and spectroscopic solutions of these eclipsing binaries were generated by the University of Florida's 1D data pipeline with a median RV precision of ~60-100 m/s, which was utilized for the DR12 data release. We performed the cross-reference fitting of the MARVELS RV data and the Kepler photometric fluxes obtained from the Kepler Eclipsing Binary Catalog (V2) and modelled the 7 eclipsing binaries in the BinaryMaker3 and PHOEBE programs. This analysis accurately determined the absolute physical and orbital parameters of each binary. Most of the companion stars were determined to have masses of K and M dwarf stars (0.3-0.8 M⊙), and allowed for an investigation into the mass-radius relationship of M and K dwarfs. Among the cases are KIC 9163796, a 122.2 day period "heartbeat star", a recently-discovered class of eccentric binaries known for tidal distortions and pulsations, with a high eccentricity (e~0.75) and KIC 11244501, a 0.29 day period, contact binary with a double-lined spectrum and mass ratio (q~0.45). We also report on the possible reclassification of 2 Kepler eclipsing binary candidates as background eclipsing binaries based on the analysis of the flux measurements, flux ratios of the spectroscopic and photometric solutions, the differences in the FOVs, the image processing of Kepler, and RV and spectral analysis of MARVELS.

  16. KECK NIRSPEC RADIAL VELOCITY OBSERVATIONS OF LATE-M DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Tanner, Angelle; White, Russel [Department of Astronomy, Georgia State University, One Park Place, Atlanta, GA 30303 (United States); Bailey, John [Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109-1042 (United States); Blake, Cullen [Department of Astrophysical Sciences, Princeton University, Peyton Hall, Ivy Lane, Princeton, NJ 08544 (United States); Blake, Geoffrey [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Cruz, Kelle [Department of Physics and Astronomy, Hunter College, 695 Park Avenue, New York, NY 10065 (United States); Burgasser, Adam J. [Center for Astrophysics and Space Science, University of California San Diego, La Jolla, CA 92093 (United States); Kraus, Adam [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)

    2012-11-15

    We present the results of an infrared spectroscopic survey of 23 late-M dwarfs with the NIRSPEC echelle spectrometer on the Keck II telescope. Using telluric lines for wavelength calibration, we are able to achieve measurement precisions of down to 45 m s{sup -1} for our late-M dwarfs over a one- to four-year long baseline. Our sample contains two stars with radial velocity (RV) variations of >1000 m s{sup -1}. While we require more measurements to determine whether these RV variations are due to unseen planetary or stellar companions or are the result of starspots known to plague the surface of M dwarfs, we can place upper limits of <40 M{sub J} sin i on the masses of any companions around those two M dwarfs with RV variations of <160 m s{sup -1} at orbital periods of 10-100 days. We have also measured the rotational velocities for all the stars in our late-M dwarf sample and offer our multi-order, high-resolution spectra over 2.0-2.4 {mu}m to the atmospheric modeling community to better understand the atmospheres of late-M dwarfs.

  17. An analysis of the variable radial velocity of alpha cygni

    International Nuclear Information System (INIS)

    Lucy, L.B.

    1976-01-01

    On the basis of 447 radial velocities obtained at the Lick Observatory by Paddock in the years 1927--1935, an attempt is made to discover the nature of the semiregular variability of α Cygni (A2 Ia). Harmonic analysis of the 144 velocities obtained in 1931 suggests that this variability is due to the simultaneous excitation of many discrete pulsation modes. The amplitudes and periods of these modes are then determined by least-squares fitting to all the data, and a final solution is obtained that comprises 16 terms with periods from 6.9 to 100.8 days. All terms are found to have highly significant amplitudes, and most terms also pass a test of the stability of their amplitudes and phases. Reasons are given for believing that most terms represent nonradial oscillations, and this leads to the suggestion that the resulting surface motions are to be identified with macroturbulence. An argument is also given for believing that the pulsational instability persists down to periods at which atmospheric oscillations become progressive, and this leads to the suggestion that such waves are observed as microturbulence and give rise to the observed mass loss. The importance of further monitoring of the variability of supergiants is stressed

  18. KECK NIRSPEC RADIAL VELOCITY OBSERVATIONS OF LATE-M DWARFS

    International Nuclear Information System (INIS)

    Tanner, Angelle; White, Russel; Bailey, John; Blake, Cullen; Blake, Geoffrey; Cruz, Kelle; Burgasser, Adam J.; Kraus, Adam

    2012-01-01

    We present the results of an infrared spectroscopic survey of 23 late-M dwarfs with the NIRSPEC echelle spectrometer on the Keck II telescope. Using telluric lines for wavelength calibration, we are able to achieve measurement precisions of down to 45 m s –1 for our late-M dwarfs over a one- to four-year long baseline. Our sample contains two stars with radial velocity (RV) variations of >1000 m s –1 . While we require more measurements to determine whether these RV variations are due to unseen planetary or stellar companions or are the result of starspots known to plague the surface of M dwarfs, we can place upper limits of J sin i on the masses of any companions around those two M dwarfs with RV variations of –1 at orbital periods of 10-100 days. We have also measured the rotational velocities for all the stars in our late-M dwarf sample and offer our multi-order, high-resolution spectra over 2.0-2.4 μm to the atmospheric modeling community to better understand the atmospheres of late-M dwarfs.

  19. Multicore fibre photonic lanterns for precision radial velocity Science

    Science.gov (United States)

    Gris-Sánchez, Itandehui; Haynes, Dionne M.; Ehrlich, Katjana; Haynes, Roger; Birks, Tim A.

    2018-04-01

    Incomplete fibre scrambling and fibre modal noise can degrade high-precision spectroscopic applications (typically high spectral resolution and high signal to noise). For example, it can be the dominating error source for exoplanet finding spectrographs, limiting the maximum measurement precision possible with such facilities. This limitation is exacerbated in the next generation of infra-red based systems, as the number of modes supported by the fibre scales inversely with the wavelength squared and more modes typically equates to better scrambling. Substantial effort has been made by major research groups in this area to improve the fibre link performance by employing non-circular fibres, double scramblers, fibre shakers, and fibre stretchers. We present an original design of a multicore fibre (MCF) terminated with multimode photonic lantern ports. It is designed to act as a relay fibre with the coupling efficiency of a multimode fibre (MMF), modal stability similar to a single-mode fibre and low loss in a wide range of wavelengths (380 nm to 860 nm). It provides phase and amplitude scrambling to achieve a stable near field and far-field output illumination pattern despite input coupling variations, and low modal noise for increased stability for high signal-to-noise applications such as precision radial velocity (PRV) science. Preliminary results are presented for a 511-core MCF and compared with current state of the art octagonal fibre.

  20. RADIAL VELOCITY STUDIES OF CLOSE BINARY STARS. XIV

    International Nuclear Information System (INIS)

    Pribulla, Theodor; Rucinski, Slavek M.; DeBond, Heide; De Ridder, Archie; Karmo, Toomas; Thomson, J. R.; Croll, Bryce; Ogloza, Waldemar; Pilecki, Bogumil; Siwak, Michal

    2009-01-01

    Radial velocity (RV) measurements and sine curve fits to the orbital RV variations are presented for 10 close binary systems: TZ Boo, VW Boo, EL Boo, VZ CVn, GK Cep, RW Com, V2610 Oph, V1387 Ori, AU Ser, and FT UMa. Our spectroscopy revealed two quadruple systems, TZ Boo and V2610 Oph, while three stars showing small photometric amplitudes, EL Boo, V1387 Ori, and FT UMa, were found to be triple systems. GK Cep is a close binary with a faint third component. While most of the studied eclipsing systems are contact binaries, VZ CVn and GK Cep are detached or semidetached double-lined binaries, and EL Boo, V1387 Ori, and FT UMa are close binaries of uncertain binary type. The large fraction of triple and quadruple systems found in this sample supports the hypothesis of formation of close binaries in multiple stellar systems; it also demonstrates that low photometric amplitude binaries are a fertile ground for further discoveries of multiple systems.

  1. Stellar Radial Velocities with IGRINS at McDonald Observatory

    Science.gov (United States)

    Mace, Gregory; Jaffe, Daniel; Park, Chan; Lee, Jae-Joon

    2016-06-01

    Exoplanet searches with dedicated instrumentation have made 1 m/s radial velocity (RV) precision routine.Yet, RVs for large samples of stars generally remain at the 1km/s level.TheImmersion Grating Infrared Spectrometer (IGRINS) is a revolutionary instrument that exploits broad spectral coverage at high-resolution in the near-infrared.IGRINS on the 2.7 meter Harlan J. Smith Telescope at McDonald Observatory is nearly as sensitive as CRIRES at the 8 meter Very Large Telescope. However, IGRINS at R=45,000 has more than 30 times the spectral grasp of CRIRES.The use of a silicon immersion grating facilitates a compact cryostat while providing simultaneous wavelength coverage from 1.45 - 2.45 microns. Wehave developed a pipeline to cross-correlate the more than 20,000 resolution elements in two IGRINS exposures and provide relative RVs with uncertainties of 50m/s (product for multi-epoch studies of low-mass, stellar and substellar multiplicity.

  2. High Velocity Spectroscopic Binary Orbits from Photoelectric Radial Velocities: BD+20 5152, a Possible Triple System

    Directory of Open Access Journals (Sweden)

    Sperauskas J.

    2010-12-01

    Full Text Available The spectroscopic orbit of a high proper motion star, BD+20 5152, is calculated from 34 CORAVEL-type radial velocity measurements. The star has a slightly eccentric orbit with a period of 5.70613 d, half-amplitude of 47.7 km/s and eccentricity of 0.049. The center-of-mass velocity of the system is -24.3 km/s. BD+20 5152 seems to be a triple system consisting of a G8 dwarf as a primary component and of two K6-M0 dwarfs as secondary and tertiary components. This model is based on the analysis of its UBVRI and JHK magnitudes. According to the SuperWASP photometry, spots on the surface of the primary are suspected. The excessive brightness in the Galex FUV and NUV magnitudes and a non-zero eccentricity suggest the age of this system to be less than 1 Gyr.

  3. VizieR Online Data Catalog: HD20794 HARPS radial velocities (Feng+, 2017)

    Science.gov (United States)

    Feng, F.; Tuomi, M.; Jones, H. R. A.

    2017-05-01

    HARPS radial velocities, activity indices and differential radial velocities for HD 20794. The HARPS spectra are available in the European Southern Observatory archive, and are processed using the TERRA algorithm (Anglada-Escude and Butler, 2012, Cat. J/ApJS/200/15). (1 data file).

  4. Dispersion of acoustic surface waves by velocity gradients

    Science.gov (United States)

    Kwon, S. D.; Kim, H. C.

    1987-10-01

    The perturbation theory of Auld [Acoustic Fields and Waves in Solids (Wiley, New York, 1973), Vol. II, p. 294], which describes the effect of a subsurface gradient on the velocity dispersion of surface waves, has been modified to a simpler form by an approximation using a newly defined velocity gradient for the case of isotropic materials. The modified theory is applied to nitrogen implantation in AISI 4140 steel with a velocity gradient of Gaussian profile, and compared with dispersion data obtained by the ultrasonic right-angle technique in the frequency range from 2.4 to 14.8 MHz. The good agreement between experiments and our theory suggests that the compound layer in the subsurface region plays a dominant role in causing the dispersion of acoustic surface waves.

  5. Instability of shallow open channel flow with lateral velocity gradients

    Energy Technology Data Exchange (ETDEWEB)

    Lima, A C; Izumi, N, E-mail: adriano@eng.hokudai.ac.jp, E-mail: nizumi@eng.hokudai.ac.jp [River and Watershed Engineering Laboratory, Hokkaido University, Sapporo, 060-8628 (Japan)

    2011-12-22

    The turbulent flow in a wide rectangular open channel partially covered with vegetation is studied using linear stability analysis. In the base state normal flow condition, the water depth is constant and the transverse velocity vanishes, while there is a lateral gradient in the streamwise velocity with an inflexion point at the boundary between the vegetated zone and the main channel. The Reynolds stress is expressed by introducing the eddy viscosity, which is obtained from assuming a logarithmic distribution of the velocity near the bed. Perturbation expansions are introduced to the streamwise and transverse velocities, as well as to the water depth. The system of governing equations was solved in order to determine the maximum growth rate of the perturbations as a function of parameters which describe physical characteristics of the channel and the flow.

  6. Acoustic beam control in biomimetic projector via velocity gradient

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Xiaowei; Dong, Erqian; Song, Zhongchang [Key Laboratory of Underwater Acoustic Communication and Marine Information Technology of the Ministry of Education, Xiamen University, Xiamen 361005 (China); Zhang, Yu, E-mail: yuzhang@xmu.edu.cn, E-mail: dzk@psu.edu; Tang, Liguo [Key Laboratory of Underwater Acoustic Communication and Marine Information Technology of the Ministry of Education, Xiamen University, Xiamen 361005 (China); State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005 (China); Cao, Wenwu, E-mail: yuzhang@xmu.edu.cn, E-mail: dzk@psu.edu [Department of Mathematics and Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Li, Songhai [Sanya Key Laboratory of Marin Mammal and Marine Bioacoustics, Sanya Institute of Deep-Sea Science and Engineering, Chinese Academy of Science, Sanya 57200 (China); Zhang, Sai [Faculty of Science, Jiangsu University, Zhenjiang 212013 (China)

    2016-07-04

    A biomimetic projector (BioP) based on computerized tomography of pygmy sperm whale's biosonar system has been designed using gradient-index (GRIN) material. The directivity of this BioP device was investigated as function of frequency and the velocity gradient of the GRIN material. A strong beam control over a broad bandwidth at the subwavelength scale has been achieved. Compared with a bare subwavelength source, the main lobe pressure of the BioP is about five times as high and the angular resolution is one order of magnitude better. Our results indicate that this BioP has excellent application potential in miniaturized underwater sonars.

  7. Transit and radial velocity survey efficiency comparison for a habitable zone Earth

    International Nuclear Information System (INIS)

    Burke, Christopher J.; McCullough, P. R.

    2014-01-01

    Transit and radial velocity searches are two techniques for identifying nearby extrasolar planets to Earth that transit bright stars. Identifying a robust sample of these exoplanets around bright stars for detailed atmospheric characterization is a major observational undertaking. In this study we describe a framework that answers the question of whether a transit or radial velocity survey is more efficient at finding transiting exoplanets given the same amount of observing time. Within the framework we show that a transit survey's window function can be approximated using the hypergeometric probability distribution. We estimate the observing time required for a transit survey to find a transiting Earth-sized exoplanet in the habitable zone (HZ) with an emphasis on late-type stars. We also estimate the radial velocity precision necessary to detect the equivalent HZ Earth-mass exoplanet that also transits when using an equal amount of observing time as the transit survey. We find that a radial velocity survey with σ rv ∼ 0.6 m s –1 precision has comparable efficiency in terms of observing time to a transit survey with the requisite photometric precision σ phot ∼ 300 ppm to find a transiting Earth-sized exoplanet in the HZ of late M dwarfs. For super-Earths, a σ rv ∼ 2.0 m s –1 precision radial velocity survey has comparable efficiency to a transit survey with σ phot ∼ 2300 ppm.

  8. Radial velocity curves of ellipsoidal red giant binaries in the Large Magellanic Cloud

    International Nuclear Information System (INIS)

    Nie, J. D.; Wood, P. R.

    2014-01-01

    Ellipsoidal red giant binaries are close binary systems where an unseen, relatively close companion distorts the red giant, leading to light variations as the red giant moves around its orbit. These binaries are likely to be the immediate evolutionary precursors of close binary planetary nebula and post-asymptotic giant branch and post-red giant branch stars. Due to the MACHO and OGLE photometric monitoring projects, the light variability nature of these ellipsoidal variables has been well studied. However, due to the lack of radial velocity curves, the nature of their masses, separations, and other orbital details has so far remained largely unknown. In order to improve this situation, we have carried out spectral monitoring observations of a large sample of 80 ellipsoidal variables in the Large Magellanic Cloud and we have derived radial velocity curves. At least 12 radial velocity points with good quality were obtained for most of the ellipsoidal variables. The radial velocity data are provided with this paper. Combining the photometric and radial velocity data, we present some statistical results related to the binary properties of these ellipsoidal variables.

  9. A radial velocity survey of the Carina Nebula's O-type stars

    Science.gov (United States)

    Kiminki, Megan M.; Smith, Nathan

    2018-03-01

    We have obtained multi-epoch observations of 31 O-type stars in the Carina Nebula using the CHIRON spectrograph on the CTIO/SMARTS 1.5-m telescope. We measure their radial velocities to 1-2 km s-1 precision and present new or updated orbital solutions for the binary systems HD 92607, HD 93576, HDE 303312, and HDE 305536. We also compile radial velocities from the literature for 32 additional O-type and evolved massive stars in the region. The combined data set shows a mean heliocentric radial velocity of 0.6 km s-1. We calculate a velocity dispersion of ≤9.1 km s-1, consistent with an unbound, substructured OB association. The Tr 14 cluster shows a marginally significant 5 km s-1 radial velocity offset from its neighbor Tr 16, but there are otherwise no correlations between stellar position and velocity. The O-type stars in Cr 228 and the South Pillars region have a lower velocity dispersion than the region as a whole, supporting a model of distributed massive-star formation rather than migration from the central clusters. We compare our stellar velocities to the Carina Nebula's molecular gas and find that Tr 14 shows a close kinematic association with the Northern Cloud. In contrast, Tr 16 has accelerated the Southern Cloud by 10-15 km s-1, possibly triggering further massive-star formation. The expansion of the surrounding H II region is not symmetric about the O-type stars in radial velocity space, indicating that the ionized gas is constrained by denser material on the far side.

  10. A radial velocity survey of the Carina Nebula's O-type stars

    Science.gov (United States)

    Kiminki, Megan M.; Smith, Nathan

    2018-06-01

    We have obtained multi-epoch observations of 31 O-type stars in the Carina Nebula using the CHIRON spectrograph on the CTIO/SMARTS 1.5-m telescope. We measure their radial velocities to 1-2 km s-1 precision and present new or updated orbital solutions for the binary systems HD 92607, HD 93576, HDE 303312, and HDE 305536. We also compile radial velocities from the literature for 32 additional O-type and evolved massive stars in the region. The combined data set shows a mean heliocentric radial velocity of 0.6 km s-1. We calculate a velocity dispersion of ≤9.1 km s-1, consistent with an unbound, substructured OB association. The Tr 14 cluster shows a marginally significant 5 km s-1 radial velocity offset from its neighbour Tr 16, but there are otherwise no correlations between stellar position and velocity. The O-type stars in Cr 228 and the South Pillars region have a lower velocity dispersion than the region as a whole, supporting a model of distributed massive star formation rather than migration from the central clusters. We compare our stellar velocities to the Carina Nebula's molecular gas and find that Tr 14 shows a close kinematic association with the Northern Cloud. In contrast, Tr 16 has accelerated the Southern Cloud by 10-15 km s-1, possibly triggering further massive star formation. The expansion of the surrounding H II region is not symmetric about the O-type stars in radial velocity space, indicating that the ionized gas is constrained by denser material on the far side.

  11. Long-term radial-velocity variations of the Sun as a star: The HARPS view

    Science.gov (United States)

    Lanza, A. F.; Molaro, P.; Monaco, L.; Haywood, R. D.

    2016-03-01

    Context. Stellar radial velocities play a fundamental role in the discovery of extrasolar planets and the measurement of their physical parameters as well as in the study of stellar physical properties. Aims: We investigate the impact of the solar activity on the radial velocity of the Sun using the HARPS spectrograph to obtain measurements that can be directly compared with those acquired in the extrasolar planet search programmes. Methods: We used the Moon, the Galilean satellites, and several asteroids as reflectors to measure the radial velocity of the Sun as a star and correlated this velocity with disc-integrated chromospheric and magnetic indexes of solar activity that are similar to stellar activity indexes. We discuss in detail the systematic effects that affect our measurements and the methods to account for them. Results: We find that the radial velocity of the Sun as a star is positively correlated with the level of its chromospheric activity at ~95 percent significance level. The amplitude of the long-term variation measured in the 2006-2014 period is 4.98 ± 1.44 m/s, which is in good agreement with model predictions. The standard deviation of the residuals obtained by subtracting a linear best fit is 2.82 m/s and is due to the rotation of the reflecting bodies and the intrinsic variability of the Sun on timescales shorter than the activity cycle. A correlation with a lower significance is detected between the radial velocity and the mean absolute value of the line-of-sight photospheric magnetic field flux density. Conclusions: Our results confirm similar correlations found in other late-type main-sequence stars and provide support to the predictions of radial velocity variations induced by stellar activity based on current models.

  12. Experimental estimation of fluctuating velocity and scalar gradients in turbulence

    Energy Technology Data Exchange (ETDEWEB)

    Hearst, R.J.; Lavoie, P. [University of Toronto, Institute for Aerospace Studies, Toronto, ON (Canada); Buxton, O.R.H. [The University of Texas at Austin, Center for Aeromechanics Research, Austin, TX (United States); Ganapathisubramani, B. [University of Southampton, Aerodynamics and Flight Mechanics Research Group, Southampton (United Kingdom)

    2012-10-15

    The effect of numerical differentiation is investigated in the context of evaluating fluctuating velocity and scalar quantities in turbulent flows. In particular, 2-point forward-difference and 3-, 5-, 7-, and 9-point centred-difference schemes are investigated. The spectral technique introduced by Wyngaard (in J Sci Instr 1(2):1105-1108, 1968) for homogeneous turbulence is used to quantify the effects of the schemes. Numerical differentiation is shown to attenuate gradient spectra over a range of wavenumbers. The spectral attenuation, which varies with the order of the scheme, results in a reduction in the measured mean-squared gradients. High-order schemes (e.g. 7- or 9-point) are shown to significantly decrease the attenuation at all wavenumbers and as a result produce more accurate gradients. Hot-wire measurements and direct numerical simulations of decaying homogeneous, isotropic turbulence are found to be in good agreement with the predictions of the analysis, which suggests that high-order schemes can be used to improve empirical gradient estimates. The shape of the probability density functions is also found to be sensitive to the choice of numerical differentiation scheme. The effect of numerical differentiation is also discussed with respect to particle image velocimetry (PIV) measurements of a nominally two-dimensional planar mixing layer. It is found that the relatively low signal-to-noise ratio inherent in typical PIV measurements necessitates the use of low-order schemes to prevent excessive noise amplification, which increases with the order of the scheme. The results of the present work demonstrate that high-order numerical differentiation schemes can be employed to more accurately resolve gradients measured at a given resolution provided the measurements have an adequate signal-to-noise ratio. (orig.)

  13. Frequentist and Bayesian Orbital Parameter Estimaton from Radial Velocity Data Using RVLIN, BOOTTRAN, and RUN DMC

    Science.gov (United States)

    Nelson, Benjamin Earl; Wright, Jason Thomas; Wang, Sharon

    2015-08-01

    For this hack session, we will present three tools used in analyses of radial velocity exoplanet systems. RVLIN is a set of IDL routines used to quickly fit an arbitrary number of Keplerian curves to radial velocity data to find adequate parameter point estimates. BOOTTRAN is an IDL-based extension of RVLIN to provide orbital parameter uncertainties using bootstrap based on a Keplerian model. RUN DMC is a highly parallelized Markov chain Monte Carlo algorithm that employs an n-body model, primarily used for dynamically complex or poorly constrained exoplanet systems. We will compare the performance of these tools and their applications to various exoplanet systems.

  14. Axial and radial velocities in the creeping flow in a pipe

    Directory of Open Access Journals (Sweden)

    Zuykov Andrey L'vovich

    2014-05-01

    Full Text Available The article is devoted to analytical study of transformation fields of axial and radial velocities in uneven steady creeping flow of a Newtonian fluid in the initial portion of the cylindrical channel. It is shown that the velocity field of the flow is two-dimensional and determined by the stream function. The article is a continuation of a series of papers, where normalized analytic functions of radial axial distributions in uneven steady creeping flow in a cylindrical tube with azimuthal vorticity and stream function were obtained. There is Poiseuille profile for the axial velocity in the uniform motion of a fluid at an infinite distance from the entrance of the pipe (at x = ∞, here taken equal to zero radial velocity. There is uniform distribution of the axial velocity in the cross section at the tube inlet at x = 0, at which the axial velocity is constant along the current radius. Due to the axial symmetry of the flow on the axis of the pipe (at r = 0, the radial velocities and the partial derivative of the axial velocity along the radius, corresponding to the condition of the soft function extremum, are equal to zero. The authors stated vanishing of the velocity of the fluid on the walls of the pipe (at r = R , where R - radius of the tube due to its viscous sticking and tightness of the walls. The condition of conservation of volume flow along the tube was also accepted. All the solutions are obtained in the form of the Fourier - Bessel. It is shown that the hydraulic losses at uniform creeping flow of a Newtonian fluid correspond to Poiseuille - Hagen formula.

  15. Radial-Velocity Signatures of Magnetic Features on the Sun Observed as a Star

    Science.gov (United States)

    Palumbo, M. L., III; Haywood, R. D.; Saar, S. H.; Dupree, A. K.; Milbourne, T. W.

    2017-12-01

    In recent years, the search for Earth-mass planets using radial-velocity measurements has become increasingly limited by signals arising from stellar activity. Individual magnetic features induce localized changes in intensity and velocity, which combine to change the apparent radial velocity of the star. Therefore it is critical to identify an indicator of activity-driven radial-velocity variations on the timescale of stellar rotation periods. We use 617.3 nm photospheric filtergrams, magnetograms, and dopplergrams from SDO/HMI and 170.0 nm chromospheric filtergrams from AIA to identify magnetically-driven solar features and reconstruct the integrated solar radial velocity with six samples per day over the course of 2014. Breaking the solar image up into regions of umbrae, penumbrae, quiet Sun, network, and plages, we find a distinct variation in the center-to-limb intensity-weighted velocity for each region. In agreement with past studies, we find that the suppression of convective blueshift is dominated by plages and network, rather than dark photospheric features. In the future, this work will be highly useful for identifying indicators which correlate with rotationally modulated radial-velocity variations. This will allow us to break the activity barrier that currently precludes the precise characterization of exoplanet properties at the lowest masses. This work was supported by the NSF-REU solar physics program at SAO, grant number AGS-1560313. This work was performed in part under contract with the California Institute of Technology (Caltech)/Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute.

  16. Radial Velocity Survey of T Tauri Stars in Taurus-Auriga

    Science.gov (United States)

    Crockett, Christopher; Mahmud, N.; Huerta, M.; Prato, L.; Johns-Krull, C.; Hartigan, P.; Jaffe, D.

    2009-01-01

    Is the frequency of giant planet companions to young stars similar to that seen around old stars? Is the "brown dwarf desert" a product of how low-mass companion objects form, or of how they evolve? Some models indicate that both giant planets and brown dwarfs should be common at young ages within 3 AU of a primary star, but migration induced by massive disks drive brown dwarfs into the parent stars, leaving behind proportionally more giant planets. Our radial velocity survey of young stars will provide a census of the young giant planet and brown dwarf population in Taurus-Auriga. In this poster we present our progress in quantifying how spurious radial velocity signatures are caused by stellar activity and in developing models to help distinguish between companion induced and spot induced radial velocity variations. Early results stress the importance of complementary observations in both visible light and NIR. We present our technique to determine radial velocities by fitting telluric features and model stellar features to our observed spectra. Finally, we discuss ongoing observations at McDonald Observatory, KPNO, and the IRTF, and several new exoplanet host candidates.

  17. Comparison of CME radial velocities from a flux rope model and an ice cream cone model

    Science.gov (United States)

    Kim, T.; Moon, Y.; Na, H.

    2011-12-01

    Coronal Mass Ejections (CMEs) on the Sun are the largest energy release process in the solar system and act as the primary driver of geomagnetic storms and other space weather phenomena on the Earth. So it is very important to infer their directions, velocities and three-dimensional structures. In this study, we choose two different models to infer radial velocities of halo CMEs since 2008 : (1) an ice cream cone model by Xue et al (2005) using SOHO/LASCO data, (2) a flux rope model by Thernisien et al. (2009) using the STEREO/SECCHI data. In addition, we use another flux rope model in which the separation angle of flux rope is zero, which is morphologically similar to the ice cream cone model. The comparison shows that the CME radial velocities from among each model have very good correlations (R>0.9). We will extending this comparison to other partial CMEs observed by STEREO and SOHO.

  18. Radial-velocity variations in Alpha Ori, Alpha Sco, and Alpha Her

    International Nuclear Information System (INIS)

    Smith, M.A.; Patten, B.M.; Goldberg, L.

    1989-01-01

    Radial-velocity observations of Alpha Ori, Alpha Sco A, and Alpha Her A are used to study radial-velocity periodicities in M supergiants. The data refer to several metallic lines in the H-alpha region and to H-alpha itself. It is shown that Alpha Ori and Alpha Sco A have cycle lengths of about 1 yr and semiamplitudes of 2 km/s. It is suggested that many semiregular red supergiant varibles such as Alpha Ori may be heading toward chaos. All three stars show short-term stochastic flucutations with an amplitude of 1-2 km/s. It is found that the long-term variability of H-alpha velocities may be a consequence of intermittent failed ejections. 58 refs

  19. Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project

    Science.gov (United States)

    de Bruijne, J. H. J.; Eilers, A.-C.

    2012-10-01

    Context. The Hundred-Thousand-Proper-Motion (HTPM) project will determine the proper motions of ~113 500 stars using a ~23-year baseline. The proper motions will be based on space-based measurements exclusively, with the Hipparcos data, with epoch 1991.25, as first epoch and with the first intermediate-release Gaia astrometry, with epoch ~2014.5, as second epoch. The expected HTPM proper-motion standard errors are 30-190 μas yr-1, depending on stellar magnitude. Aims: Depending on the astrometric characteristics of an object, in particular its distance and velocity, its radial velocity can have a significant impact on the determination of its proper motion. The impact of this perspective acceleration is largest for fast-moving, nearby stars. Our goal is to determine, for each star in the Hipparcos catalogue, the radial-velocity standard error that is required to guarantee a negligible contribution of perspective acceleration to the HTPM proper-motion precision. Methods: We employ two evaluation criteria, both based on Monte-Carlo simulations, with which we determine which stars need to be spectroscopically (re-)measured. Both criteria take the Hipparcos measurement errors into account. The first criterion, the Gaussian criterion, is applicable to nearby stars. For distant stars, this criterion works but returns overly pessimistic results. We therefore use a second criterion, the robust criterion, which is equivalent to the Gaussian criterion for nearby stars but avoids biases for distant stars and/or objects without literature radial velocity. The robust criterion is hence our prefered choice for all stars, regardless of distance. Results: For each star in the Hipparcos catalogue, we determine the confidence level with which the available radial velocity and its standard error, taken from the XHIP compilation catalogue, are acceptable. We find that for 97 stars, the radial velocities available in the literature are insufficiently precise for a 68.27% confidence

  20. RADIAL VELOCITIES FROM VLT-KMOS SPECTRA OF GIANT STARS IN THE GLOBULAR CLUSTER NGC 6388

    International Nuclear Information System (INIS)

    Lapenna, E.; Mucciarelli, A.; Lanzoni, B.; Ferraro, F. R.; Dalessandro, E.; Origlia, L.; Valenti, E.; Cirasuolo, M.

    2015-01-01

    We present new radial velocity measurements for 82 stars, members of the Galactic globular cluster (GC) NGC 6388, obtained from ESO-VLT K-band Multi Object Spectrograph (KMOS) spectra acquired during the instrument Science Verification. The accuracy of the wavelength calibration is discussed and a number of tests of the KMOS response are presented. The cluster systemic velocity obtained (81.3 ± 1.5 km s –1 ) is in very good agreement with previous determinations. While a hint of ordered rotation is found between 9'' and 20'' from the cluster center, where the distribution of radial velocities is clearly bimodal, more data are needed before drawing any firm conclusions. The acquired sample of radial velocities has also been used to determine the cluster velocity dispersion (VD) profile between ∼9'' and 70'', supplementing previous measurements at r < 2'' and r > 60'' obtained with ESO-SINFONI and ESO-FLAMES spectroscopy, respectively. The new portion of the VD profile nicely matches the previous ones, better defining the knee of the distribution. The present work clearly shows the effectiveness of a deployable integral field unit in measuring the radial velocities of individual stars for determining the VD profile of Galactic GCs. It represents the pilot project for an ongoing large program with KMOS and FLAMES at the ESO-VLT, aimed at determining the next generation of VD and rotation profiles for a representative sample of GCs

  1. The VLT-FLAMES Tarantula Survey. XVIII. Classifications and radial velocities of the B-type stars

    NARCIS (Netherlands)

    Evans, C.J.; Kennedy, M.B.; Dufton, P.L.; Howarth, I.D.; Walborn, N.R.; Markova, N.; Clark, J.S.; de Mink, S.E.; de Koter, A.; Dunstall, P.R.; Hénault-Brunet, V.; Maíz Apellániz, J.; McEvoy, C.M.; Sana, H.; Simón-Díaz, S.; Taylor, W.D.; Vink, J.S.

    2015-01-01

    We present spectral classifications for 438 B-type stars observed as part of the VLT-FLAMES Tarantula Survey (VFTS) in the 30 Doradus region of the Large Magellanic Cloud. Radial velocities are provided for 307 apparently single stars, and for 99 targets with radial-velocity variations which are

  2. The Pioneer 9 electric field experiment. III - Radial gradients and storm observations.

    Science.gov (United States)

    Scarf, F. L.; Green, I. M.; Burgess, J. S.

    1973-01-01

    We present a detailed analysis of the Pioneer 9 VLF electric field observations for 20 selected storm periods covering a heliocentric range extending from 0.754 AU to 0.99 AU. Although data from only two low frequency channels are available, the results of the present study tend to confirm the preliminary speculation by Scarf and Siscoe (1971) that the turbulent E-field spectrum in the disturbed solar wind has a significant radial gradient.

  3. Revisiting the radial abundance gradients of nitrogen and oxygen of the Milky Way

    Science.gov (United States)

    Esteban, C.; García-Rojas, J.

    2018-05-01

    We present spectra obtained with the 10.4 m Gran Telescopio Canarias telescope of 13 Galactic H II regions, most of them of very low ionisation degree. The objects are located along the Galactic disc, with RG from 5.7 to 16.1 kpc. We determine Te([N II]) for all of them. We obtain - for the first time - a radial abundance gradient of N that is independent on the ionisation correction factor. The radial distribution of the N/O ratio is almost flat, indicating that the bulk of N is not formed by standard secondary processes. We have made a reassessment of the radial O abundance gradient combining our results with previous similar ones by Esteban et al. (2017); producing a homogeneous dataset of 35 H II regions with direct determinations of the electron temperature. We report the possible presence of a flattening or drop of the O abundance in the inner part of the Galactic disc. This result confirms previous findings from metallicity distributions based on Cepheids and red giants. Finally, we find that the scatter of the N and O abundances of H II regions with respect to the gradient fittings is not substantially larger than the observational uncertainties, indicating that both chemical elements seem to be well mixed in the interstellar gas at a given distance along the Galactic disc

  4. Constraining fault interpretation through tomographic velocity gradients: application to northern Cascadia

    Directory of Open Access Journals (Sweden)

    K. Ramachandran

    2012-02-01

    Full Text Available Spatial gradients of tomographic velocities are seldom used in interpretation of subsurface fault structures. This study shows that spatial velocity gradients can be used effectively in identifying subsurface discontinuities in the horizontal and vertical directions. Three-dimensional velocity models constructed through tomographic inversion of active source and/or earthquake traveltime data are generally built from an initial 1-D velocity model that varies only with depth. Regularized tomographic inversion algorithms impose constraints on the roughness of the model that help to stabilize the inversion process. Final velocity models obtained from regularized tomographic inversions have smooth three-dimensional structures that are required by the data. Final velocity models are usually analyzed and interpreted either as a perturbation velocity model or as an absolute velocity model. Compared to perturbation velocity model, absolute velocity models have an advantage of providing constraints on lithology. Both velocity models lack the ability to provide sharp constraints on subsurface faults. An interpretational approach utilizing spatial velocity gradients applied to northern Cascadia shows that subsurface faults that are not clearly interpretable from velocity model plots can be identified by sharp contrasts in velocity gradient plots. This interpretation resulted in inferring the locations of the Tacoma, Seattle, Southern Whidbey Island, and Darrington Devil's Mountain faults much more clearly. The Coast Range Boundary fault, previously hypothesized on the basis of sedimentological and tectonic observations, is inferred clearly from the gradient plots. Many of the fault locations imaged from gradient data correlate with earthquake hypocenters, indicating their seismogenic nature.

  5. VizieR Online Data Catalog: l Car radial velocity curves (Anderson, 2016)

    Science.gov (United States)

    Anderson, R. I.

    2018-02-01

    Line-of-sight (radial) velocities of the long-period classical Cepheid l Carinae were measured from 925 high-quality optical spectra recorded using the fiber-fed high-resolution (R~60,000) Coralie spectrograph located at the Euler telescope at La Silla Observatory, Chile. The data were taken between 2014 and 2016. This is the full version of Tab. 2 presented partially in the paper. Line shape parameters (depth, width, asymmetry) are listed for the computed cross-correlation profiles (CCFs). Radial velocities were determined using different techniques (Gaussian, bi-Gaussian) and measured on CCFs computed using three different numerical masks (G2, weak lines, strong lines). (1 data file).

  6. Radial velocity follow-up of CoRoT transiting exoplanets

    Directory of Open Access Journals (Sweden)

    Deleuil M.

    2011-02-01

    Full Text Available We report on the results from the radial-velocity follow-up program performed to establish the planetary nature and to characterize the transiting candidates discovered by the space mission CoRoT. We use the SOPHIE at OHP, HARPS at ESO and the HIRES at Keck spectrographs to collect spectra and high-precision radial velocity (RV measurements for several dozens different candidates from CoRoT. We have measured the Rossiter-McLaughlin effect of several confirmed planets, especially CoRoT-1b which revealed that it is another highly inclined system. Such high-precision RV data are necessary for the discovery of new transiting planets. Furthermore, several low mass planet candidates have emerged from our Keck and HARPS data.

  7. Radial-velocity measures and the existence of astrophysical binaries in late-type dwarf stars

    Science.gov (United States)

    Bopp, B. W.; Meredith, R.

    1986-01-01

    Radial velocities with errors of 1-2 km/s are presented based on CCD scans obtained with the Kitt Peak National Observatory coude feed telescope between 1982 and 1985 of 48 dK-M stars that lack Balmer emission. Comparison with Gliese's (1969) values shows only two stars to be spectroscopic binary candidates with small velocity amplitudes. No evidence for any short period (less than 10 days) binaries is found, supporting the conclusions of Young et al. (1986) that there are no astrophysical binaries among these chromosherically inactive dM stars.

  8. AD Leonis: Radial Velocity Signal of Stellar Rotation or Spin–Orbit Resonance?

    Science.gov (United States)

    Tuomi, Mikko; Jones, Hugh R. A.; Barnes, John R.; Anglada-Escudé, Guillem; Butler, R. Paul; Kiraga, Marcin; Vogt, Steven S.

    2018-05-01

    AD Leonis is a nearby magnetically active M dwarf. We find Doppler variability with a period of 2.23 days, as well as photometric signals: (1) a short-period signal, which is similar to the radial velocity signal, albeit with considerable variability; and (2) a long-term activity cycle of 4070 ± 120 days. We examine the short-term photometric signal in the available All-Sky Automated Survey and Microvariability and Oscillations of STars (MOST) photometry and find that the signal is not consistently present and varies considerably as a function of time. This signal undergoes a phase change of roughly 0.8 rad when considering the first and second halves of the MOST data set, which are separated in median time by 3.38 days. In contrast, the Doppler signal is stable in the combined High-Accuracy Radial velocity Planet Searcher and High Resolution Echelle Spectrometer radial velocities for over 4700 days and does not appear to vary in time in amplitude, phase, period, or as a function of extracted wavelength. We consider a variety of starspot scenarios and find it challenging to simultaneously explain the rapidly varying photometric signal and the stable radial velocity signal as being caused by starspots corotating on the stellar surface. This suggests that the origin of the Doppler periodicity might be the gravitational tug of a planet orbiting the star in spin–orbit resonance. For such a scenario and no spin–orbit misalignment, the measured v\\sin i indicates an inclination angle of 15.°5 ± 2.°5 and a planetary companion mass of 0.237 ± 0.047 M Jup.

  9. AN AFFINE-INVARIANT SAMPLER FOR EXOPLANET FITTING AND DISCOVERY IN RADIAL VELOCITY DATA

    International Nuclear Information System (INIS)

    Hou Fengji; Hogg, David W.; Goodman, Jonathan; Weare, Jonathan; Schwab, Christian

    2012-01-01

    Markov chain Monte Carlo (MCMC) proves to be powerful for Bayesian inference and in particular for exoplanet radial velocity fitting because MCMC provides more statistical information and makes better use of data than common approaches like chi-square fitting. However, the nonlinear density functions encountered in these problems can make MCMC time-consuming. In this paper, we apply an ensemble sampler respecting affine invariance to orbital parameter extraction from radial velocity data. This new sampler has only one free parameter, and does not require much tuning for good performance, which is important for automatization. The autocorrelation time of this sampler is approximately the same for all parameters and far smaller than Metropolis-Hastings, which means it requires many fewer function calls to produce the same number of independent samples. The affine-invariant sampler speeds up MCMC by hundreds of times compared with Metropolis-Hastings in the same computing situation. This novel sampler would be ideal for projects involving large data sets such as statistical investigations of planet distribution. The biggest obstacle to ensemble samplers is the existence of multiple local optima; we present a clustering technique to deal with local optima by clustering based on the likelihood of the walkers in the ensemble. We demonstrate the effectiveness of the sampler on real radial velocity data.

  10. Disentangling Time-series Spectra with Gaussian Processes: Applications to Radial Velocity Analysis

    Energy Technology Data Exchange (ETDEWEB)

    Czekala, Ian [Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA 94305 (United States); Mandel, Kaisey S.; Andrews, Sean M.; Dittmann, Jason A. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Ghosh, Sujit K. [Department of Statistics, NC State University, 2311 Stinson Drive, Raleigh, NC 27695 (United States); Montet, Benjamin T. [Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Avenue, Chicago, IL 60637 (United States); Newton, Elisabeth R., E-mail: iczekala@stanford.edu [Massachusetts Institute of Technology, Cambridge, MA 02138 (United States)

    2017-05-01

    Measurements of radial velocity variations from the spectroscopic monitoring of stars and their companions are essential for a broad swath of astrophysics; these measurements provide access to the fundamental physical properties that dictate all phases of stellar evolution and facilitate the quantitative study of planetary systems. The conversion of those measurements into both constraints on the orbital architecture and individual component spectra can be a serious challenge, however, especially for extreme flux ratio systems and observations with relatively low sensitivity. Gaussian processes define sampling distributions of flexible, continuous functions that are well-motivated for modeling stellar spectra, enabling proficient searches for companion lines in time-series spectra. We introduce a new technique for spectral disentangling, where the posterior distributions of the orbital parameters and intrinsic, rest-frame stellar spectra are explored simultaneously without needing to invoke cross-correlation templates. To demonstrate its potential, this technique is deployed on red-optical time-series spectra of the mid-M-dwarf binary LP661-13. We report orbital parameters with improved precision compared to traditional radial velocity analysis and successfully reconstruct the primary and secondary spectra. We discuss potential applications for other stellar and exoplanet radial velocity techniques and extensions to time-variable spectra. The code used in this analysis is freely available as an open-source Python package.

  11. Removing Activity-Related Radial Velocity Noise to Improve Extrasolar Planet Searches

    Science.gov (United States)

    Saar, Steven; Lindstrom, David M. (Technical Monitor)

    2004-01-01

    We have made significant progress towards the proposal goals of understanding the causes and effects of magnetic activity-induced radial velocity (v_r) jitter and developing methods for correcting it. In the process, we have also made some significant discoveries in the fields of planet-induced stellar activity, planet detection methods, M dwarf convection, starspot properties, and magnetic dynamo cycles. We have obtained super high resolution (R approximately 200,000), high S / N (greater than 300) echelle study of joint line bisector and radial velocity variations using the McDonald 2-D coude. A long observing run in October 2002 in particular was quite successful (8 clear nights). We now have close to three years of data, which begins to sample a good fraction of the magnetic cycle timescales for some of our targets (e.g., kappa Ceti; P_cyc = 5.6 yrs). This will be very helpful in unraveling the complex relationships between plage and radial velocity (v-r) changes which we have uncovered. Preliminary analysis (Saar et al. 2003) of the data in hand, reveals correlations between median line bisector displacement and v_r. The correlation appears to be specific the the particular star being considered, probably since it is a function of both spectral type and rotation rate. Further analysis and interpretation will be in the context of evolving plage models and is in progress.

  12. Evolution of the Radial Abundance Gradient and Cold Gas along the Milky Way Disk

    Science.gov (United States)

    Chen, Q. S.; Chang, R. X.; Yin, J.

    2014-03-01

    We have constructed a phenomenological model of the chemical evolution of the Milky Way disk, and treated the molecular and atomic gas separately. Using this model, we explore the radial profiles of oxygen abundance, the surface density of cold gas, and their time evolutions. It is shown that the model predictions are very sensitive to the adopted infall time-scale. By comparing the model predictions with the observations, we find that the model adopting the star formation law based on H_2 can properly predict the observed radial distributions of cold gas and oxygen abundance gradient along the disk. We also compare the model results with the predictions of the model which adopts the instantaneous recycling approximation (IRA), and find that the IRA assumption has little influence on the model results, especially in the low-density gas region.

  13. RADIAL VELOCITIES OF GALACTIC O-TYPE STARS. II. SINGLE-LINED SPECTROSCOPIC BINARIES

    International Nuclear Information System (INIS)

    Williams, S. J.; Gies, D. R.; Hillwig, T. C.; McSwain, M. V.; Huang, W.

    2013-01-01

    We report on new radial velocity measurements of massive stars that are either suspected binaries or lacking prior observations. This is part of a survey to identify and characterize spectroscopic binaries among O-type stars with the goal of comparing the binary fraction of field and runaway stars with those in clusters and associations. We present orbits for HDE 308813, HD 152147, HD 164536, BD–16°4826, and HDE 229232, Galactic O-type stars exhibiting single-lined spectroscopic variation. By fitting model spectra to our observed spectra, we obtain estimates for effective temperature, surface gravity, and rotational velocity. We compute orbital periods and velocity semiamplitudes for each system and note the lack of photometric variation for any system. These binaries probably appear single-lined because the companions are faint and because their orbital Doppler shifts are small compared to the width of the rotationally broadened lines of the primary.

  14. Solar cycle dependence of the radial gradient of cosmic ray intensity

    International Nuclear Information System (INIS)

    Allen, J.A.V.

    1988-01-01

    Observation of the interplanetary intensity of cosmic rays (E/sub p/>80 MeV) by Pioneers 10 and 11 now spans a sixteen-year time period 1972--1988 and heliocentric radial distances, r/sub 10/ and r/sub 11/, out to 43.7 AU for Pioneer 10 and 25.8 AU for Pioneer 11. Solar modulation continues to be present at the current distances of both spacecraft. The radial gradient of intensity is measured continuously over the slowly varying, outward moving radial segment Δr = r/sub 10/--r/sub 11/. The 50-day mean values of the gradient G vary systematically and cyclically in phase with solar activity as measured by sunspot number, with a maximum value of about 2.1 percent (AU)/sup -1/ at sunspot maximum and a miminum value of about 1.2 percent (AU)/sup -1/ at sunspot minimum. Thus, the apparent scale size of the heliospheric modulation region as measured by 1/G is about 48 AU at solar max and about 83 AU at solar min: a result that is the inverse of the conjectural inference of Randall and Van Allen [1986] using most of the same body of data but a different analytical point of view. There is persuasive evidence that G is independent of radial distance over the range 2.5 to 34 AU in the mid-point of the segment Δr. No dependence of G on heliographic latitude is evident, but this result does not lend itself to a quantitative statement. copyright American Geophysical Union 1988

  15. CHARACTERIZING THE GALACTIC WHITE DWARF BINARY POPULATION WITH SPARSELY SAMPLED RADIAL VELOCITY DATA

    International Nuclear Information System (INIS)

    Maoz, Dan; Badenes, Carles; Bickerton, Steven J.

    2012-01-01

    We present a method to characterize statistically the parameters of a detached binary sample—binary fraction, separation distribution, and mass-ratio distribution—using noisy radial velocity data with as few as two, randomly spaced, epochs per object. To do this, we analyze the distribution of ΔRV max , the maximum radial velocity difference between any two epochs for the same object. At low values, the core of this distribution is dominated by measurement errors, but for large enough samples there is a high-velocity tail that can effectively constrain the parameters of the binary population. We discuss our approach for the case of a population of detached white dwarf (WD) binaries with separations that are decaying via gravitational wave emission. We derive analytic expressions for the present-day distribution of separations, integrated over the star formation history of the Galaxy, for parameterized initial WD separation distributions at the end of the common-envelope phase. We use Monte Carlo techniques to produce grids of simulated ΔRV max distributions with specific binary population parameters, and the same sampling cadences and radial velocity errors as the observations, and we compare them to the real ΔRV max distribution to constrain the properties of the binary population. We illustrate the sensitivity of the method to both the model and observational parameters. In the particular case of binary WDs, every model population predicts a merger rate per star which can easily be compared to specific Type Ia supernova rates. In a companion paper, we apply the method to a sample of ∼4000 WDs from the Sloan Digital Sky Survey. The binary fractions and separation distribution parameters allowed by the data indicate a rate of WD-WD mergers per unit stellar mass in the Galactic disk, ∼1 × 10 –13 mergers yr –1 M –1 ☉ , remarkably similar to the rate per unit mass of Type Ia supernovae in Milky Way like galaxies.

  16. WIYN Open Cluster Study. XXXII. Stellar Radial Velocities in the Old Open Cluster NGC 188

    Science.gov (United States)

    Geller, Aaron M.; Mathieu, Robert D.; Harris, Hugh C.; McClure, Robert D.

    2008-06-01

    We present the results of our ongoing radial-velocity (RV) survey of the old (7 Gyr) open cluster NGC 188. Our WIYN 3.5 m data set spans a time baseline of 11 years, a magnitude range of 12 =3 measurements, finding 473 to be likely cluster members. We detect 124 velocity-variable cluster members, all of which are likely to be dynamically hard-binary stars. Using our single member stars, we find an average cluster radial velocity of -42.36 ± 0.04 km s-1. We use our precise RV and proper-motion membership data to greatly reduce field-star contamination in our cleaned color-magnitude diagram, from which we identify six stars of note that lie far from a standard single-star isochrone. We present a detailed study of the spatial distribution of cluster-member populations, and find the binaries to be centrally concentrated, providing evidence for the presence of mass segregation in NGC 188. We observe the BSs to populate a bimodal spatial distribution that is not centrally concentrated, suggesting that we may be observing two populations of BSs in NGC 188, including a centrally concentrated distribution as well as a halo population. Finally, we find NGC 188 to have a global RV dispersion of 0.64 ± 0.04 km s-1, which may be inflated by up to 0.23 km s-1 from unresolved binaries. When corrected for unresolved binaries, the NGC 188 RV dispersion has a nearly isothermal radial distribution. We use this mean-corrected velocity dispersion to derive a virial mass of 2300 ± 460 M sun .

  17. [The radial velocity measurement accuracy of different spectral type low resolution stellar spectra at different signal-to-noise ratio].

    Science.gov (United States)

    Wang, Feng-Fei; Luo, A-Li; Zhao, Yong-Heng

    2014-02-01

    The radial velocity of the star is very important for the study of the dynamics structure and chemistry evolution of the Milky Way, is also an useful tool for looking for variable or special objects. In the present work, we focus on calculating the radial velocity of different spectral types of low-resolution stellar spectra by adopting a template matching method, so as to provide effective and reliable reference to the different aspects of scientific research We choose high signal-to-noise ratio (SNR) spectra of different spectral type stellar from the Sloan Digital Sky Survey (SDSS), and add different noise to simulate the stellar spectra with different SNR. Then we obtain theradial velocity measurement accuracy of different spectral type stellar spectra at different SNR by employing a template matching method. Meanwhile, the radial velocity measurement accuracy of white dwarf stars is analyzed as well. We concluded that the accuracy of radial velocity measurements of early-type stars is much higher than late-type ones. For example, the 1-sigma standard error of radial velocity measurements of A-type stars is 5-8 times as large as K-type and M-type stars. We discuss the reason and suggest that the very narrow lines of late-type stars ensure the accuracy of measurement of radial velocities, while the early-type stars with very wide Balmer lines, such as A-type stars, become sensitive to noise and obtain low accuracy of radial velocities. For the spectra of white dwarfs stars, the standard error of radial velocity measurement could be over 50 km x s(-1) because of their extremely wide Balmer lines. The above conclusion will provide a good reference for stellar scientific study.

  18. Stellar Parameters and Radial Velocities of Hot Stars in the Carina Nebula

    Science.gov (United States)

    Hanes, Richard J.; McSwain, M. Virginia; Povich, Matthew S.

    2018-05-01

    The Carina Nebula is an active star-forming region in the southern sky that is of particular interest due to the presence of a large number of massive stars in a wide array of evolutionary stages. Here, we present the results of the spectroscopic analysis of 82 B-type stars and 33 O-type stars that were observed in 2013 and 2014. For 82 B-type stars without line blending, we fit model spectra from the Tlusty BSTAR2006 grid to the observed profiles of Hγ and He λλ4026, 4388, and 4471 to measure the effective temperatures, surface gravities, and projected rotational velocities. We also measure the masses, ages, radii, bolometric luminosities, and distances of these stars. From the radial velocities measured in our sample, we find 31 single lined spectroscopic binary candidates. We find a high dispersion of radial velocities among our sample stars, and we argue that the Carina Nebula stellar population has not yet relaxed and become virialized.

  19. Near-infrared metallicities, radial velocities, and spectral types for 447 nearby M dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    Newton, Elisabeth R.; Charbonneau, David; Irwin, Jonathan; Berta-Thompson, Zachory K. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Rojas-Ayala, Barbara [Centro de Astrofsica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Covey, Kevin [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Lloyd, James P., E-mail: enewton@cfa.harvard.edu [Department of Astronomy, Cornell University, 226 Space Sciences Building, Ithaca, NY 14853 (United States)

    2014-01-01

    We present metallicities, radial velocities, and near-infrared (NIR) spectral types for 447 M dwarfs determined from moderate resolution (R ≈ 2000) NIR spectra obtained with the NASA Infrared Telescope Facility (IRTF)/SpeX. These M dwarfs are primarily targets of the MEarth Survey, a transiting planet survey searching for super Earths around mid-to-late M dwarfs within 33 pc. We present NIR spectral types for each star and new spectral templates for the IRTF in the Y, J, H, and K-bands, created using M dwarfs with near-solar metallicities. We developed two spectroscopic distance calibrations that use NIR spectral type or an index based on the curvature of the K-band continuum. Our distance calibration has a scatter of 14%. We searched 27 NIR spectral lines and 10 spectral indices for metallicity sensitive features, taking into account correlated noise in our estimates of the errors on these parameters. We calibrated our relation using 36 M dwarfs in common proper pairs with an F-, G-, or K-type star of known metallicity. We validated the physical association of these pairs using proper motions, radial velocities, and spectroscopic distance estimates. Our resulting metallicity calibration uses the sodium doublet at 2.2 μm as the sole indicator for metallicity. It has an accuracy of 0.12 dex inferred from the scatter between the metallicities of the primaries and the estimated metallicities of the secondaries. Our relation is valid for NIR spectral types from M1V to M5V and for –1.0 dex < [Fe/H] < +0.35 dex. We present a new color-color metallicity relation using J – H and J – K colors that directly relates two observables: the distance from the M dwarf main sequence and equivalent width of the sodium line at 2.2 μm. We used radial velocities of M dwarf binaries, observations at different epochs, and comparison between our measurements and precisely measured radial velocities to demonstrate a 4 km s{sup –1} accuracy.

  20. Observations of the radial velocity of the Sun as measured with the novel SONG spectrograph

    DEFF Research Database (Denmark)

    Pallé, P. L.; Grundahl, F.; Hage, A. Triviño

    2013-01-01

    Deployment of the prototype node of the SONG project took place in April 2012 at Observatorio del Teide (Canary Islands). Its key instrument (echelle spectrograph) was installed and operational a few weeks later while its 1 m feeding telescope suffered a considerable delay to meet the required...... specifications. Using a fibre-feed, solar light could be fed to the spectrograph and we carried out a 1-week observing campaign in June 2012 to evaluate its performance for measuring precision radial velocities. In this work we present the first results of this campaign by comparing the sensitivity of the SONG...

  1. Determination of radial peculiar velocities of galaxy clusters by means of the submillimeter spectrophotometry

    International Nuclear Information System (INIS)

    Sholomitskij, G.B.

    1984-01-01

    The possibility is considered to obtain from the extraatmospheric submillimeter spectrophotometry of galaxy clusters the ratios vsub(r)/Tsub(e) for clusters intergalactic gas that permits, together with the X-ray measurements of electronic temperature Tsub(e) in the case of hot scattering gas to determine absolute radial peculiar velocities vsub(r) of galaxy clusters relative to the relic radiation. By simulating such peculiar velocities as an example for the system of bandpass filters in the wavelength range 300 μm - 2 mm the accuracy of vsub(r) estimates is proved to be about 300 km/s (not taking into account the errors in Tsub(e)) the sensitivity of deeply cooled submillimeter bolometers being 1x10 -15 W/Hzsup(1/2)

  2. Inversion of Surface Wave Phase Velocities for Radial Anisotropy to an Depth of 1200 km

    Science.gov (United States)

    Xing, Z.; Beghein, C.; Yuan, K.

    2012-12-01

    This study aims to evaluate three dimensional radial anisotropy to an depth of 1200 km. Radial anisotropy describes the difference in velocity between horizontally polarized Rayleigh waves and vertically polarized Love waves. Its presence in the uppermost 200 km mantle has well been documented by different groups, and has been regarded as an indicator of mantle convection which aligns the intrinsically anisotropic minerals, largely olivine, to form large scale anisotropy. However, there is no global agreement on whether anisotropy exists in the region below 200 km. Recent models also associate a fast vertically polarized shear wave with vertical upwelling mantle flow. The data used in this study is the globally isotropic phase velocity models of fundamental and higher mode Love and Rayleigh waves (Visser, 2008). The inclusion of higher mode surface wave phase velocity provides sensitivities to structure at depth that extends to below the transition zone. While the data is the same as used by Visser (2008), a quite different parameterization is applied. All the six parameters - five elastic parameters A, C, F, L, N and density - are now regarded as independent, which rules out possible biased conclusions induced by scaling relation method used in several previous studies to reduce the number of parameters partly due to limited computing resources. The data need to be modified by crustal corrections (Crust2.0) as we want to look at the mantle structure only. We do this by eliminating the perturbation in surface wave phase velocity caused by the difference in crustal structure with respect to the referent model PREM. Sambridge's Neighborhood Algorithm is used to search the parameter space. The introduction of such a direct search technique pales the traditional inversion method, which requires regularization or some unnecessary priori restriction on the model space. On the contrary, the new method will search the full model space, providing probability density

  3. SOAP. A tool for the fast computation of photometry and radial velocity induced by stellar spots

    Science.gov (United States)

    Boisse, I.; Bonfils, X.; Santos, N. C.

    2012-09-01

    We define and put at the disposal of the community SOAP, Spot Oscillation And Planet, a software tool that simulates the effect of stellar spots and plages on radial velocimetry and photometry. This paper describes the tool release and provides instructions for its use. We present detailed tests with previous computations and real data to assess the code's performance and to validate its suitability. We characterize the variations of the radial velocity, line bisector, and photometric amplitude as a function of the main variables: projected stellar rotational velocity, filling factor of the spot, resolution of the spectrograph, linear limb-darkening coefficient, latitude of the spot, and inclination of the star. Finally, we model the spot distributions on the active stars HD 166435, TW Hya and HD 189733, which reproduce the observations. We show that the software is remarkably fast, allowing several evolutions in its capabilities that could be performed to study the next challenges in the exoplanetary field connected with the stellar variability. The tool is available at http://www.astro.up.pt/soap

  4. A Refined Radial Velocity Curve for the L Dwarf Donor of WZ Sagittae

    Science.gov (United States)

    Harrison, Thomas E.

    2017-12-01

    We have obtained a radial velocity curve for the L dwarf donor in WZ Sagittae using phase-resolved J-band spectra obtained with GNIRS on Gemini-north. We find a radial velocity semi-amplitude of {K}2=525+/- 11 {km} {{{s}}}-1. This result reduces the error bar by a factor of three over previous attempts. A relatively strong, unidentified emission line centered near 1.177 μm, corrupts the blue K i doublet in these data. While an H i emission feature near 1.2527 μm distorts the depth of the red K i doublet. In addition, a weak H i emission line at 1.1969 μm falls in the middle of the strongest FeH feature in these spectra. The combination of these contaminants prevents us from precisely constraining the spectral type of the donor. The strength of the absorption features remains consistent with an early L spectral type. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil).

  5. Origins of Solar Systems: Removing Activity-Related Radial Velocity Noise to Improve Extrasolar Planet Searches

    Science.gov (United States)

    Saar, Steven; Lindstrom, David (Technical Monitor)

    2003-01-01

    We have continued the super high resolution (R is approximately 200,000), high S/N (> 300) echelle study of joint line bisector and radial velocity variations using the McDonald 2-D coude. A long observing run in October 2002 was quite successful (8 clear nights). We now have close to three years of data, which begins to sample a good fraction of the magnetic cycle timescales for some of our targets (e.g., K Ceti; P(sub cyc)=5.6 yrs). This will be very helpful in unraveling the complex relationships between plage and v(sub r), changes which we have uncovered. A preliminary analysis of the limited data in hand, and find some tantalizing evidence for correlations between median line bisector displacement and radial velocity v(sub r). The correlation appears to be specific to the particular star being considered, probably since it is a function of both spectral type and rotation rate. Additional information regarding progress on the grant is included.

  6. Searching for habitable exoplanets by using combined microlensing and radial velocity facilities

    International Nuclear Information System (INIS)

    Joergensen, Uffe Graae

    2008-01-01

    The habitable planetary regime, where life as we know it from the Earth in principle can exist, has long been among the technically most difficult to search for the existence of exoplanets. It spans the inner and outer orbital range, where liquid water in principle can exist on a planetary surface (the habitable zone), and the planetary mass range from the lowest mass where an atmosphere is bound over biological timescales to the upper mass limit where a nebula gas-collapse transforms a solid planet into a gas planet. With a prober equipment, microlensing is sensitive to this regime for most stellar types, including solar-type stars, while the radial velocity technique complements the detection regime by being sensitive to such planets around the lowest mass stars. By combining microlensing with radial velocity measurements, it is possible to cover the complete habitable region from the ground. I outline here the theory that in principle will make it possible to perform an efficient survey throughout the habitable regime of the most common types of stars in our galaxy over the next few years, and describe how it can be done in practise for a relatively low cost

  7. Twenty Years of Precise Radial Velocities at Keck and Lick Observatories

    Science.gov (United States)

    Wright, J. T.

    2015-10-01

    The precise radial velocity survey at Keck Observatory began over 20 years ago. Its survey of thousands of stars now has the time baseline to be sensitive to planets with decade-long orbits, including Jupiter analogs. I present several newly-finished orbital solutions for long-period giant planets. Although hot Jupiters are generally ``lonely'' (i.e. they are not part of multiplanet systems), those that are not appear to often have giant companions at 5 AU or beyond. I present two of the highest period-ratios among planets in a two-planet system, and some of the longest orbital periods ever measured for exoplanets. In many cases, combining Keck radial velocities from those from other long-term surveys at Lick Observatory, McDonald Observatory, HARPS, and, of course, OHP spectrographs, produces superior orbital fits, constraining both period and eccentricity better than could be possible with any single set alone. Stellar magnetic activity cycles can masquerade as long-period planets. In most cases this effect is very small, but a loud minority of stars, including, apparently, HD 154345, show very strong RV-activity correlations.

  8. Radial gradient and radial deviation radiomic features from pre-surgical CT scans are associated with survival among lung adenocarcinoma patients.

    Science.gov (United States)

    Tunali, Ilke; Stringfield, Olya; Guvenis, Albert; Wang, Hua; Liu, Ying; Balagurunathan, Yoganand; Lambin, Philippe; Gillies, Robert J; Schabath, Matthew B

    2017-11-10

    The goal of this study was to extract features from radial deviation and radial gradient maps which were derived from thoracic CT scans of patients diagnosed with lung adenocarcinoma and assess whether these features are associated with overall survival. We used two independent cohorts from different institutions for training (n= 61) and test (n= 47) and focused our analyses on features that were non-redundant and highly reproducible. To reduce the number of features and covariates into a single parsimonious model, a backward elimination approach was applied. Out of 48 features that were extracted, 31 were eliminated because they were not reproducible or were redundant. We considered 17 features for statistical analysis and identified a final model containing the two most highly informative features that were associated with lung cancer survival. One of the two features, radial deviation outside-border separation standard deviation, was replicated in a test cohort exhibiting a statistically significant association with lung cancer survival (multivariable hazard ratio = 0.40; 95% confidence interval 0.17-0.97). Additionally, we explored the biological underpinnings of these features and found radial gradient and radial deviation image features were significantly associated with semantic radiological features.

  9. WIYN OPEN CLUSTER STUDY. XXIV. STELLAR RADIAL-VELOCITY MEASUREMENTS IN NGC 6819

    International Nuclear Information System (INIS)

    Tabetha Hole, K.; Geller, Aaron M.; Mathieu, Robert D.; Meibom, Soeren; Platais, Imants; Latham, David W.

    2009-01-01

    We present the current results from our ongoing radial-velocity (RV) survey of the intermediate-age (2.4 Gyr) open cluster NGC 6819. Using both newly observed and other available photometry and astrometry, we define a primary target sample of 1454 stars that includes main-sequence, subgiant, giant, and blue straggler stars, spanning a magnitude range of 11 ≤V≤ 16.5 and an approximate mass range of 1.1-1.6 M sun . Our sample covers a 23 arcminute (13 pc) square field of view centered on the cluster. We have measured 6571 radial velocities for an unbiased sample of 1207 stars in the direction of the open cluster NGC 6819, with a single-measurement precision of 0.4 km s -1 for most narrow-lined stars. We use our RV data to calculate membership probabilities for stars with ≥3 measurements, providing the first comprehensive membership study of the cluster core that includes stars from the giant branch through the upper main sequence. We identify 480 cluster members. Additionally, we identify velocity-variable systems, all of which are likely hard binaries that dynamically power the cluster. Using our single cluster members, we find a cluster average RV of 2.34 ± 0.05 km s -1 . We use our kinematic cluster members to construct a cleaned color-magnitude diagram from which we identify rich giant, subgiant, and blue straggler populations and a well defined red clump. The cluster displays a morphology near the cluster turnoff clearly indicative of core convective overshoot. Finally, we discuss a few stars of note, one of which is a short-period red-clump binary that we suggest may be the product of a dynamical encounter.

  10. Theoretical and Experimental Study of Radial Velocity Generation for Extending Bandwidth of Magnetohydrodynamic Angular Rate Sensor at Low Frequency

    Directory of Open Access Journals (Sweden)

    Yue Ji

    2015-12-01

    Full Text Available The magnetohydrodynamics angular rate sensor (MHD ARS has received much attention for its ultra-low noise in ultra-broad bandwidth and its impact resistance in harsh environments; however, its poor performance at low frequency hinders its work in long time duration. The paper presents a modified MHD ARS combining Coriolis with MHD effect to extend the measurement scope throughout the whole bandwidth, in which an appropriate radial flow velocity should be provided to satisfy simplified model of the modified MHD ARS. A method that can generate radial velocity by an MHD pump in MHD ARS is proposed. A device is designed to study the radial flow velocity generated by the MHD pump. The influence of structure and physical parameters are studied by numerical simulation and experiment of the device. The analytic expression of the velocity generated by the energized current drawn from simulation and experiment are consistent, which demonstrates the effectiveness of the method generating radial velocity. The study can be applied to generate and control radial velocity in modified MHD ARS, which is essential for the two effects combination throughout the whole bandwidth.

  11. Sensitivities of surface wave velocities to the medium parameters in a radially anisotropic spherical Earth and inversion strategies

    Directory of Open Access Journals (Sweden)

    Sankar N. Bhattacharya

    2015-11-01

    Full Text Available Sensitivity kernels or partial derivatives of phase velocity (c and group velocity (U with respect to medium parameters are useful to interpret a given set of observed surface wave velocity data. In addition to phase velocities, group velocities are also being observed to find the radial anisotropy of the crust and mantle. However, sensitivities of group velocity for a radially anisotropic Earth have rarely been studied. Here we show sensitivities of group velocity along with those of phase velocity to the medium parameters VSV, VSH , VPV, VPH , h and density in a radially anisotropic spherical Earth. The peak sensitivities for U are generally twice of those for c; thus U is more efficient than c to explore anisotropic nature of the medium. Love waves mainly depends on VSH while Rayleigh waves is nearly independent of VSH . The sensitivities show that there are trade-offs among these parameters during inversion and there is a need to reduce the number of parameters to be evaluated independently. It is suggested to use a nonlinear inversion jointly for Rayleigh and Love waves; in such a nonlinear inversion best solutions are obtained among the model parameters within prescribed limits for each parameter. We first choose VSH, VSV and VPH within their corresponding limits; VPV and h can be evaluated from empirical relations among the parameters. The density has small effect on surface wave velocities and it can be considered from other studies or from empirical relation of density to average P-wave velocity.

  12. Gravitation is a Gradient in the Velocity of Light

    Science.gov (United States)

    Froedge, Dt

    2017-01-01

    It is well known that a photon moving in a gravitational field has a trajectory that can be defined by Fermat's principle with a variable speed of light and no other gravitational influence. If it can be shown that a particle composed of speed of light sub-particles has the same acceleration in a variable index of refraction as a particle in a gravitational field, then there is no need to ascribe any other mechanism to gravitation than a gradient in c. This makes gravitation an electromagnetic phenomenon, and if QFT can illustrate a gradient in c can be produced by the internal motion of lightspeed sub-particles then the unification of QM and gravitation becomes more straightforward. http://www.arxdtf.org/css/GravAPS.pdf.

  13. VizieR Online Data Catalog: Radial velocity curve of 51 Peg (Birkby+, 2017)

    Science.gov (United States)

    Birkby, J. L.; de Kok, R. J.; Brogi, M.; Schwarz, H.; Snellen, I. A. G.

    2017-07-01

    We observed the bright star 51 Peg (G2.5V, V=5.46mag, K=3.91mag) for 3.7hr during the night beginning 2010 October 21, using the CRyogenic InfraRed Echelle Spectrograph (CRIRES) mounted at Nasmyth A at the VLT (8.2 m UT1/Antu), Cerro Paranal, Chile. The observations were collected as part of the ESO large program 186.C-0289. The instrument setup consisted of a 0.2 arcsec slit centred on 3236nm (order 17), in combination with the Multi-Application Curvature Adaptive Optic system (MACAO). The CRIRES infrared detector is comprised of four Aladdin III InSb-arrays, each with 1024*512 pixels, and separated by a gap of 280 pixels. The resulting wavelength coverage of the observations was 3.1806R{approx}100000 per resolution element. We observed 51 Peg continuously while its hot Jupiter companion passed through orbital phases 0.55data are given in Table 1 and span observing dates from 1994 September 15 to 2014 July 9, resulting in 639 radial velocity measurements over 20 years. The table includes the discovery measurements from the ELODIE spectrograph at Observatoire Haute Provence and subsequent additional monitoring. We took these radial velocity measurements from the Naef et al. 2004 (Cat. J/A+A/414/351) compilation. We also included the legacy data set from Lick Observatory observed with the Hamilton spectrograph, taking measurements from the self-consistent reprocessing of all the Lick spectra presented by Fischer et al. 2014 (Cat. J/ApJS/210/5). Finally, we included more recent additional monitoring from the High Resolution Echelle Spectrometer (HIRES) at the Keck Observatory, and extracted RVs from observations with the High Accuracy Radial velocity Planet Searcher (HARPS) at the ESO-3.6m telescope in 2013 (ESO program ID 091.C-0271, PI: Santos). The reduced HARPS spectra were obtained from the ESO Science Archive (http://archive.eso.org/wdb/wdb/adp/phase3_spectral/query). (1 data file).

  14. Softverski model estimatora radijalne brzine ciljeva / Software model of a radial velocity estimator

    Directory of Open Access Journals (Sweden)

    Dejan S. Ivković

    2010-04-01

    Full Text Available U radu je softverski modelovan novi blok u delu za obradu signala softverskog radarskog prijemnika, koji je nazvan estimator radijalne brzine. Detaljno je opisan način procene Doplerove frekvencije na osnovu MUSIC algoritma i ukratko prikazan način rada pri merenju. Svi parametri pri merenju klatera i detekcije simuliranih i realnih ciljeva dati su tabelarno, a rezultati grafički. Na osnovu analize prikazanih rezultata može se zaključiti da se pomoću projektovanog estimatora radijalne brzine može precizno proceniti Doplerov pomak u reflektovanom signalu od pokretnog cilja, a samim tim može se precizno odrediti njegova brzina. / In all analyses the MUSIC method has given better results than the FFT method. The MUSIC method proved to be better at estimation precision as well as at resolving two adjacent Doppler frequencies. On the basis of the obtained results, the designed estimator of radial velocity can be said to estimate Doppler frequency in the reflected signal from a moving target precisely, and, consequently, the target velocity. It is thus possible to improve the performances of the current radar as far as a precise estimation of velocity of detected moving targets is concerned.

  15. SDSS-IV MaNGA: modelling the metallicity gradients of gas and stars - radially dependent metal outflow versus IMF

    Science.gov (United States)

    Lian, Jianhui; Thomas, Daniel; Maraston, Claudia; Goddard, Daniel; Parikh, Taniya; Fernández-Trincado, J. G.; Roman-Lopes, Alexandre; Rong, Yu; Tang, Baitian; Yan, Renbin

    2018-05-01

    In our previous work, we found that only two scenarios are capable of reproducing the observed integrated mass-metallicity relations for the gas and stellar components of local star-forming galaxies simultaneously. One scenario invokes a time-dependent metal outflow loading factor with stronger outflows at early times. The other scenario uses a time-dependent initial mass function (IMF) slope with a steeper IMF at early times. In this work, we extend our study to investigate the radial profile of gas and stellar metallicity in local star-forming galaxies using spatially resolved spectroscopic data from the SDSS-IV MaNGA survey. We find that most galaxies show negative gradients in both gas and stellar metallicity with steeper gradients in stellar metallicity. The stellar metallicity gradients tend to be mass dependent with steeper gradients in more massive galaxies while no clear mass dependence is found for the gas metallicity gradient. Then we compare the observations with the predictions from a chemical evolution model of the radial profiles of gas and stellar metallicities. We confirm that the two scenarios proposed in our previous work are also required to explain the metallicity gradients. Based on these two scenarios, we successfully reproduce the radial profiles of gas metallicity, stellar metallicity, stellar mass surface density, and star formation rate surface density simultaneously. The origin of the negative gradient in stellar metallicity turns out to be driven by either radially dependent metal outflow or IMF slope. In contrast, the radial dependence of the gas metallicity is less constrained because of the degeneracy in model parameters.

  16. Radial velocities of very low mass stars and candidate brown dwarf members of the Hyades and Pleiades

    Science.gov (United States)

    Stauffer, John R.; Liebert, James; Giampapa, Mark; Macintosh, Bruce; Reid, Neill; Hamilton, Donald

    1994-01-01

    We have determined H alpha equivalent widths and radial velocities with 1 sigma accuracies of approximately 5 km s(exp -1) for approximately 20 candidate very low mass members of the Hyades and Pleiades clusters. The radial velocities for the Hyades sample suggest that nearly all of these stars are indeed highly probable members of the Hyades. The faintest stars in the Hyades sample have masses of order 0.1 solar mass. We also obtained radial velocities for four candidate very low mass members of the Pleiades and two objects that are candidate BD Pleiads. All of these stars have apparent V magnitudes fainter than the Hyades stars we observed, and the resultant radial velocity accuracy is worse. We believe that the three brighter stars are indeed likely very low mass stellar members of the Pleiades, whereas the status of the two brown dwarf candidates is uncertain. The Hyades stars we have observed and the three Pleiades very low mass stars are the lowest mass members of any open cluster whose membership has been confirmed by radial velocities and whose chromospheric activity has been measured. We see no change in chromospheric activity at the boundary where stars are expected to become fully convective (M approximately equals 0.3 solar mass) in either cluster. In the Pleiades, however, there may be a decrease in chromospheric activity for stars with (V-I)(sub K) greater than 3.5 (M less than or equal to 0.1 solar mass).

  17. Red Optical Planet Survey: A radial velocity search for low mass M dwarf planets

    Directory of Open Access Journals (Sweden)

    Minniti D.

    2013-04-01

    Full Text Available We present radial velocity results from our Red Optical Planet Survey (ROPS, aimed at detecting low-mass planets orbiting mid-late M dwarfs. The ∼10 ms−1 precision achieved over 2 consecutive nights with the MIKE spectrograph at Magellan Clay is also found on week long timescales with UVES at VLT. Since we find that UVES is expected to attain photon limited precision of order 2 ms−1 using our novel deconvolution technique, we are limited only by the (≤10 ms−1 stability of atmospheric lines. Rocky planet frequencies of η⊕ = 0.3−0.7 lead us to expect high planet yields, enabling determination of η⊕ for the uncharted mid-late M dwarfs with modest surveys.

  18. Extracting kinetic freeze-out temperature and radial flow velocity from an improved Tsallis distribution

    Energy Technology Data Exchange (ETDEWEB)

    Lao, Hai-Ling; Liu, Fu-Hu [Shanxi University, Institute of Theoretical Physics, Shanxi (China); Lacey, Roy A. [Stony Brook University, Departments of Chemistry and Physics, Stony Brook, NY (United States)

    2017-03-15

    We analyze the transverse-momentum (p{sub T}) spectra of identified particles (π{sup ±}, K{sup ±}, p, and anti p) produced in gold-gold (Au-Au) and lead-lead (Pb-Pb) collisions over a √(s{sub NN}) (center-of-mass energy per nucleon pair) range from 14.5 GeV (one of the Relativistic Heavy Ion Collider (RHIC) energies) to 2.76 TeV (one of the Large Hadron Collider (LHC) energies). For the spectra with a narrow p{sub T} range, an improved Tsallis distribution which is in fact the Tsallis distribution with radial flow is used. For the spectra with a wide p{sub T} range, a superposition of the improved Tsallis distribution and an inverse power law is used. Both the extracted kinetic freeze-out temperature (T{sub 0}) and radial flow velocity (β{sub T}) increase with the increase of √(s{sub NN}), which indicates a higher excitation and larger expansion of the interesting system at the LHC. Both the values of T{sub 0} and β{sub T} in central collisions are slightly larger than those in peripheral collisions, and they are independent of isospin and slightly dependent on mass. (orig.)

  19. CHROMOSPHERICALLY ACTIVE STARS IN THE RADIAL VELOCITY EXPERIMENT (RAVE) SURVEY. I. THE CATALOG

    International Nuclear Information System (INIS)

    Žerjal, M.; Zwitter, T.; Matijevič, G.; Strassmeier, K. G.; Siviero, A.; Steinmetz, M.; Bienaymé, O.; Bland-Hawthorn, J.; Boeche, C.; Grebel, E. K.; Freeman, K. C.; Kordopatis, G.; Munari, U.; Navarro, J. F.; Parker, Q. A.; Reid, W.; Seabroke, G.; Wyse, R. F. G.

    2013-01-01

    RAVE, the unbiased magnitude limited survey of southern sky stars, contained 456,676 medium-resolution spectra at the time of our analysis. Spectra cover the Ca II infrared triplet (IRT) range, which is a known indicator of chromospheric activity. Our previous work classified all spectra using locally linear embedding. It identified 53,347 cases with a suggested emission component in calcium lines. Here, we use a spectral subtraction technique to measure the properties of this emission. Synthetic templates are replaced by the observed spectra of non-active stars to bypass the difficult computations of non-local thermal equilibrium profiles of the line cores and stellar parameter dependence. We derive both the equivalent width of the excess emission for each calcium line on a 5 Å wide interval and their sum EW IRT for ∼44,000 candidate active dwarf stars with signal-to-noise ratio >20, with no cuts on the basis of the source of their emission flux. From these, ∼14,000 show a detectable chromospheric flux with at least a 2σ confidence level. Our set of active stars vastly enlarges previously known samples. Atmospheric parameters and, in some cases, radial velocities of active stars derived from automatic pipelines suffer from systematic shifts due to their shallower calcium lines. We re-estimate the effective temperature, metallicity, and radial velocities for candidate active stars. The overall distribution of activity levels shows a bimodal shape, with the first peak coinciding with non-active stars and the second with the pre-main-sequence cases. The catalog will be made publicly available with the next RAVE public data releases

  20. A Low-cost Environmental Control System for Precise Radial Velocity Spectrometers

    Science.gov (United States)

    Sliski, David H.; Blake, Cullen H.; Halverson, Samuel

    2017-12-01

    We present an environmental control system (ECS) designed to achieve milliKelvin (mK) level temperature stability for small-scale astronomical instruments. This ECS is inexpensive and is primarily built from commercially available components. The primary application for our ECS is the high-precision Doppler spectrometer MINERVA-Red, where the thermal variations of the optical components within the instrument represent a major source of systematic error. We demonstrate ±2 mK temperature stability within a 0.5 m3 thermal enclosure using resistive heaters in conjunction with a commercially available PID controller and off-the-shelf thermal sensors. The enclosure is maintained above ambient temperature, enabling rapid cooling through heat dissipation into the surrounding environment. We demonstrate peak-to-valley (PV) temperature stability of better than 5 mK within the MINERVA-Red vacuum chamber, which is located inside the thermal enclosure, despite large temperature swings in the ambient laboratory environment. During periods of stable laboratory conditions, the PV variations within the vacuum chamber are less than 3 mK. This temperature stability is comparable to the best stability demonstrated for Doppler spectrometers currently achieving m s-1 radial velocity precision. We discuss the challenges of using commercially available thermoelectrically cooled CCD cameras in a temperature-stabilized environment, and demonstrate that the effects of variable heat output from the CCD camera body can be mitigated using PID-controlled chilled water systems. The ECS presented here could potentially provide the stable operating environment required for future compact “astrophotonic” precise radial velocity (PRV) spectrometers to achieve high Doppler measurement precision with a modest budget.

  1. The SDSS-III APOGEE radial velocity survey of M dwarfs. I. Description of the survey and science goals

    Energy Technology Data Exchange (ETDEWEB)

    Deshpande, R.; Bender, C. F.; Mahadevan, S.; Terrien, R. C.; Schneider, D. P.; Fleming, S. W. [Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park, PA 16802 (United States); Blake, C. H. [Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104 (United States); Carlberg, J. K. [Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015 (United States); Zasowski, G.; Hearty, F. [University of Virginia, 530 McCormick Road, Charlottesville, VA 22904 (United States); Crepp, J. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Rajpurohit, A. S.; Reylé, C. [Institut UTINAM, CNRS UMR 6213, Observatoire des Sciences de l' Univers THETA Franche-Comt é-Bourgogne, Université de Franche Comté, Observatoire de Besançon, BP 1615, F-25010 Besançon Cedex (France); Nidever, D. L. [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States); Prieto, C. Allende; Hernández, J. [Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife (Spain); Bizyaev, D. [Apache Point Observatory, P.O. Box 59, Sunspot, NM 88349-0059 (United States); Ebelke, G. [Department of Physics and Astronomy, Texas Christian University, TCU Box 298840, Fort Worth, TX 76129 (United States); Frinchaboy, P. M. [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611-2055 (United States); Ge, J. [Department of Astronomy, Ohio State University, Columbus, OH 43210 (United States); and others

    2013-12-01

    We are carrying out a large ancillary program with the Sloan Digital Sky Survey, SDSS-III, using the fiber-fed multi-object near-infrared APOGEE spectrograph, to obtain high-resolution H-band spectra of more than 1200 M dwarfs. These observations will be used to measure spectroscopic rotational velocities, radial velocities, physical stellar parameters, and variability of the target stars. Here, we describe the target selection for this survey, as well as results from the first year of scientific observations based on spectra that will be publicly available in the SDSS-III DR10 data release. As part of this paper we present radial velocities and rotational velocities of over 200 M dwarfs, with a vsin i precision of ∼2 km s{sup –1} and a measurement floor at vsin i = 4 km s{sup –1}. This survey significantly increases the number of M dwarfs studied for rotational velocities and radial velocity variability (at ∼100-200 m s{sup –1}), and will inform and advance the target selection for planned radial velocity and photometric searches for low-mass exoplanets around M dwarfs, such as the Habitable Zone Planet Finder, CARMENES, and TESS. Multiple epochs of radial velocity observations enable us to identify short period binaries, and adaptive optics imaging of a subset of stars enables the detection of possible stellar companions at larger separations. The high-resolution APOGEE spectra, covering the entire H band, provide the opportunity to measure physical stellar parameters such as effective temperatures and metallicities for many of these stars. At the culmination of this survey, we will have obtained multi-epoch spectra and radial velocities for over 1400 stars spanning the spectral range M0-L0, providing the largest set of near-infrared M dwarf spectra at high resolution, and more than doubling the number of known spectroscopic vsin i values for M dwarfs. Furthermore, by modeling telluric lines to correct for small instrumental radial velocity shifts, we

  2. A new method of measuring centre-of-mass velocities of radially pulsating stars from high-resolution spectroscopy

    Science.gov (United States)

    Britavskiy, N.; Pancino, E.; Tsymbal, V.; Romano, D.; Fossati, L.

    2018-03-01

    We present a radial velocity analysis of 20 solar neighbourhood RR Lyrae and three Population II Cepheid variables. We obtained high-resolution, moderate-to-high signal-to-noise ratio spectra for most stars; these spectra covered different pulsation phases for each star. To estimate the gamma (centre-of-mass) velocities of the programme stars, we use two independent methods. The first, `classic' method is based on RR Lyrae radial velocity curve templates. The second method is based on the analysis of absorption-line profile asymmetry to determine both pulsational and gamma velocities. This second method is based on the least-squares deconvolution (LSD) technique applied to analyse the line asymmetry that occurs in the spectra. We obtain measurements of the pulsation component of the radial velocity with an accuracy of ±3.5 km s-1. The gamma velocity was determined with an accuracy of ±10 km s-1, even for those stars having a small number of spectra. The main advantage of this method is the possibility of obtaining an estimation of gamma velocity even from one spectroscopic observation with uncertain pulsation phase. A detailed investigation of LSD profile asymmetry shows that the projection factor p varies as a function of the pulsation phase - this is a key parameter, which converts observed spectral line radial velocity variations into photospheric pulsation velocities. As a by-product of our study, we present 41 densely spaced synthetic grids of LSD profile bisectors based on atmospheric models of RR Lyr covering all pulsation phases.

  3. Astrometry, radial velocity, and photometry: the HD 128311 system remixed with data from HST, HET, and APT

    International Nuclear Information System (INIS)

    McArthur, Barbara E.; Benedict, G. Fritz.; Cochran, William D.; Henry, Gregory W.; Hatzes, Artie; Harrison, Tom E.; Johns-Krull, Chris; Nelan, Ed

    2014-01-01

    We have used high-cadence radial velocity measurements from the Hobby-Eberly Telescope with published velocities from the Lick 3 m Shane Telescope, combined with astrometric data from the Hubble Space Telescope (HST) Fine Guidance Sensors to refine the orbital parameters of the HD 128311 system, and determine an inclination of 55.°95 ± 14.°55 and true mass of 3.789 −0.432 +0.924 M JUP for HD 128311 c. The combined radial velocity data also reveal a short period signal which could indicate a third planet in the system with an Msin i of 0.133 ± 0.005 M JUP or stellar phenomena. Photometry from the T12 0.8 m automatic photometric telescope at the Fairborn Observatory and HST are used to determine a photometric period close to, but not within the errors of the radial velocity signal. We performed a cross-correlation bisector analysis of the radial velocity data to look for correlations with the photometric period and found none. Dynamical integrations of the proposed system show long-term stability with the new orbital parameters of over 10 million years. Our new orbital elements do not support the claims of HD 128311 b and c being in mean motion resonance.

  4. radial

    Directory of Open Access Journals (Sweden)

    JOHN WILLIAM BRANCH

    2007-01-01

    Full Text Available La creación de modelos de objetos reales es una tarea compleja para la cual se ha visto que el uso de técnicas tradicionales de modelamiento tiene restricciones. Para resolver algunos de estos problemas, los sensores de rango basados en láser se usan con frecuencia para muestrear la superficie de un objeto desde varios puntos de vista, lo que resulta en un conjunto de imágenes de rango que son registradas e integradas en un modelo final triangulado. En la práctica, debido a las propiedades reflectivas de la superficie, las oclusiones, y limitaciones de acceso, ciertas áreas de la superficie del objeto usualmente no son muestreadas, dejando huecos que pueden crear efectos indeseables en el modelo integrado. En este trabajo, presentamos un nuevo algoritmo para el llenado de huecos a partir de modelos triangulados. El algoritmo comienza localizando la frontera de las regiones donde están los huecos. Un hueco consiste de un camino cerrado de bordes de los triángulos en la frontera que tienen al menos un borde que no es compartido con ningún otro triangulo. El borde del hueco es entonces adaptado mediante un B-Spline donde la variación promedio de la torsión del la aproximación del B-spline es calculada. Utilizando un simple umbral de la variación promedio a lo largo del borde, se puede clasificar automáticamente, entre huecos reales o generados por intervención humana. Siguiendo este proceso de clasificación, se usa entonces una versión automatizada del interpolador de funciones de base radial para llenar el interior del hueco usando los bordes vecinos.

  5. The VMC survey. XI. Radial stellar population gradients in the galactic globular cluster 47 Tucanae

    Energy Technology Data Exchange (ETDEWEB)

    Li, Chengyuan; De Grijs, Richard [Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Hai Dian District, Beijing 100871 (China); Deng, Licai [Key Laboratory for Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012 (China); Rubele, Stefano; Girardi, Leo; Gullieuszik, Marco [INAF-Osservatorio Astronomico di Padova, vicolo dell' Osservatorio 5, I-35122 Padova (Italy); Wang, Chuchu [Department of Astronomy, Peking University, Yi He Yuan Lu 5, Hai Dian District, Beijing 100871 (China); Bekki, Kenji; For, Bi-Qing [ICRAR M468, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia); Cioni, Maria-Rosa L. [Department of Physics, Astronomy, and Mathematics, University of Hertfordshire, Hatfield AL10 9AB (United Kingdom); Clementini, Gisella [INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna (Italy); Emerson, Jim [Astronomy Unit, School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London E1 4NS (United Kingdom); Groenewegen, Martin A. T. [Royal Observatory of Belgium, Ringlaan 3, 1180 Ukkel (Belgium); Guandalini, Roald [Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D 2401, 3001 Leuven (Belgium); Marconi, Marcella; Ripepi, Vincenzo [INAF-Osservatorio Astronomico di Capodimonte, via Moiariello 16, I-80131 Naples (Italy); Piatti, Andrés E. [Observatorio Astrońomico, Universidad Nacional de Córdoba, Laprida 854, 5000 Córdoba (Argentina); Van Loon, Jacco Th., E-mail: joshuali@pku.edu.cn, E-mail: grijs@pku.edu.cn [Astrophysics Group, Lennard-Jones Laboratories, Keele University, Staffordshire ST5 5BG (United Kingdom)

    2014-07-20

    We present a deep near-infrared color-magnitude diagram of the Galactic globular cluster 47 Tucanae, obtained with the Visible and Infrared Survey Telescope for Astronomy (VISTA) as part of the VISTA near-infrared Y, J, K{sub s} survey of the Magellanic System (VMC). The cluster stars comprising both the subgiant and red giant branches exhibit apparent, continuous variations in color-magnitude space as a function of radius. Subgiant branch stars at larger radii are systematically brighter than their counterparts closer to the cluster core; similarly, red-giant-branch stars in the cluster's periphery are bluer than their more centrally located cousins. The observations can very well be described by adopting an age spread of ∼0.5 Gyr as well as radial gradients in both the cluster's helium abundance (Y) and metallicity (Z), which change gradually from (Y = 0.28, Z = 0.005) in the cluster core to (Y = 0.25, Z = 0.003) in its periphery. We conclude that the cluster's inner regions host a significant fraction of second-generation stars, which decreases with increasing radius; the stellar population in the 47 Tuc periphery is well approximated by a simple stellar population.

  6. Application of velocity imaging and gradient-recalled echo in neuroimaging

    International Nuclear Information System (INIS)

    Boyko, O.B.; Pelc, N.J.; Shimakawa, A.

    1990-01-01

    This paper describes the initial clinical experience with imaging blood flow at 1.5 T by means of a phase-sensitive gradient refocused pulse sequence. A spin-echo flow-encoding technique was modified to a gradient recalled acquisition in a steady state sequence, producing a velocity imaging and gradient recalled echo (VIGRE) sequence (TR = 24 msec, TE = 13 msec, flip angle = 45 degrees, 24-cm field of view, 7 mm contiguous sections). Two views per phase-encoding step are acquired; one using the first-moment flow-compensation gradient waveform and the second having a (selectable) nonzero first moment. A phase subtraction image is obtained where the signal is dependent on the direction and velocity of flow. The sequence was done following routine spin-echo imaging in 35 patients

  7. Calculation of pressure gradients from MR velocity data in a laminar flow model

    International Nuclear Information System (INIS)

    Adler, R.S.; Chenevert, T.L.; Fowlkes, J.B.; Pipe, J.G.; Rubin, J.M.

    1990-01-01

    This paper reports on the ability of current imaging modalities to provide velocity-distribution data that offers the possibility of noninvasive pressure-gradient determination from an appropriate rheologic model of flow. A simple laminar flow model is considered at low Reynolds number, RE calc = 0.59 + (1.13 x (dp/dz) meas ), R 2 = .994, in units of dyne/cm 2 /cm for the range of flows considered. The authors' results indicate the potential usefulness of noninvasive pressure-gradient determinations from quantitative analysis of imaging-derived velocity data

  8. SOAP: A Tool for the Fast Computation of Photometry and Radial Velocity Induced by Stellar Spots

    Science.gov (United States)

    Boisse, I.; Bonfils, X.; Santos, N. C.; Figueira, P.

    2013-04-01

    Dark spots and bright plages are present on the surface of dwarf stars from spectral types F to M, even in their low-active phase (like the Sun). Their appearance and disappearance on the stellar photosphere, combined with the stellar rotation, may lead to errors and uncertainties in the characterization of planets both in radial velocity (RV) and photometry. Spot Oscillation and Planet (SOAP) is a tool offered to the community that enables to simulate spots and plages on rotating stars and computes their impact on RV and photometric measurements. This tool will help to understand the challenges related to the knowledge of stellar activity for the next decade: detect telluric planets in the habitable zone of their stars (from G to M dwarfs), understand the activity in the low-mass end of M dwarf (on which future projects, like SPIRou or CARMENES, will focus), limitation to the characterization of the exoplanetary atmosphere (from the ground or with Spitzer, JWST), search for planets around young stars. These can be simulated with SOAP in order to search for indices and corrections to the effect of activity.

  9. Forecasting the detectability of known radial velocity planets with the upcoming CHEOPS mission

    Science.gov (United States)

    Yi, Joo Sung; Chen, Jingjing; Kipping, David

    2018-04-01

    The CHaracterizing ExOPlanets Satellite (CHEOPS) mission is planned for launch next year with a major objective being to search for transits of known radial velocity (RV) planets, particularly those orbiting bright stars. Since the RV method is only sensitive to planetary mass, the radii, transit depths and transit signal-to-noise values of each RV planet are, a priori, unknown. Using an empirically calibrated probabilistic mass-radius relation, forecaster, we address this by predicting a catalogue of homogeneous credible intervals for these three keys terms for 468 planets discovered via RVs. Of these, we find that the vast majority should be detectable with CHEOPS, including terrestrial bodies, if they have the correct geometric alignment. In particular, we predict that 22 mini-Neptunes and 82 Neptune-sized planets would be suitable for detection and that more than 80 per cent of these will have apparent magnitude of V work. Our work aims to assist the CHEOPS team in scheduling efforts and highlights the great value of quantifiable, statistically robust estimates for upcoming exoplanetary missions.

  10. On the Feasibility of Intense Radial Velocity Surveys for Earth-twin Discoveries

    Science.gov (United States)

    Hall, Richard D.; Thompson, Samantha J.; Handley, Will; Queloz, Didier

    2018-06-01

    This work assesses the potential capability of the next generation of high-precision Radial Velocity (RV) instruments for Earth-twin exoplanet detection. From the perspective of the importance of data sampling, the Terra Hunting Experiment aims to do this through an intense series of nightly RV observations over a long baseline on a carefully selected target list, via the brand-new instrument HARPS3. This paper describes an end-to-end simulation of generating and processing such data to help us better understand the impact of uncharacterised stellar noise in the recovery of Earth-mass planets with orbital periods of the order of many months. We consider full Keplerian systems, realistic simulated stellar noise, instrument white noise, and location-specific weather patterns for our observation schedules. We use Bayesian statistics to assess various planetary models fitted to the synthetic data, and compare the successful planet recovery of the Terra Hunting Experiment schedule with a typical reference survey. We find that the Terra Hunting Experiment can detect Earth-twins in the habitable zones of solar-type stars, in single and multi-planet systems, and in the presence of stellar signals. Also that it out-performs a typical reference survey on accuracy of recovered parameters, and that it performs comparably to an uninterrupted space-based schedule.

  11. AN EFFICIENT, COMPACT, AND VERSATILE FIBER DOUBLE SCRAMBLER FOR HIGH PRECISION RADIAL VELOCITY INSTRUMENTS

    Energy Technology Data Exchange (ETDEWEB)

    Halverson, Samuel; Roy, Arpita; Mahadevan, Suvrath; Ramsey, Lawrence; Levi, Eric; Schwab, Christian; Hearty, Fred [Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States); MacDonald, Nick, E-mail: shalverson@psu.edu, E-mail: aur17@psu.edu [Department of Astronomy, University of Washington, Seattle, WA 98195 (United States)

    2015-06-10

    We present the design and test results of a compact optical fiber double-scrambler for high-resolution Doppler radial velocity instruments. This device consists of a single optic: a high-index n ∼ 2 ball lens that exchanges the near and far fields between two fibers. When used in conjunction with octagonal fibers, this device yields very high scrambling gains (SGs) and greatly desensitizes the fiber output from any input illumination variations, thereby stabilizing the instrument profile of the spectrograph and improving the Doppler measurement precision. The system is also highly insensitive to input pupil variations, isolating the spectrograph from telescope illumination variations and seeing changes. By selecting the appropriate glass and lens diameter the highest efficiency is achieved when the fibers are practically in contact with the lens surface, greatly simplifying the alignment process when compared to classical double-scrambler systems. This prototype double-scrambler has demonstrated significant performance gains over previous systems, achieving SGs in excess of 10,000 with a throughput of ∼87% using uncoated Polymicro octagonal fibers. Adding a circular fiber to the fiber train further increases the SG to >20,000, limited by laboratory measurement error. While this fiber system is designed for the Habitable-zone Planet Finder spectrograph, it is more generally applicable to other instruments in the visible and near-infrared. Given the simplicity and low cost, this fiber scrambler could also easily be multiplexed for large multi-object instruments.

  12. A Comprehensive Radial Velocity Error Budget for Next Generation Doppler Spectrometers

    Science.gov (United States)

    Halverson, Samuel; Ryan, Terrien; Mahadevan, Suvrath; Roy, Arpita; Bender, Chad; Stefansson, Guomundur Kari; Monson, Andrew; Levi, Eric; Hearty, Fred; Blake, Cullen; hide

    2016-01-01

    We describe a detailed radial velocity error budget for the NASA-NSF Extreme Precision Doppler Spectrometer instrument concept NEID (NN-explore Exoplanet Investigations with Doppler spectroscopy). Such an instrument performance budget is a necessity for both identifying the variety of noise sources currently limiting Doppler measurements, and estimating the achievable performance of next generation exoplanet hunting Doppler spectrometers. For these instruments, no single source of instrumental error is expected to set the overall measurement floor. Rather, the overall instrumental measurement precision is set by the contribution of many individual error sources. We use a combination of numerical simulations, educated estimates based on published materials, extrapolations of physical models, results from laboratory measurements of spectroscopic subsystems, and informed upper limits for a variety of error sources to identify likely sources of systematic error and construct our global instrument performance error budget. While natively focused on the performance of the NEID instrument, this modular performance budget is immediately adaptable to a number of current and future instruments. Such an approach is an important step in charting a path towards improving Doppler measurement precisions to the levels necessary for discovering Earth-like planets.

  13. Radial Velocities of Subgiant Stars and New Astrophysical Insights into RV Jitter

    Science.gov (United States)

    Luhn, Jacob; Bastien, Fabienne; Wright, Jason T.

    2018-01-01

    For nearly 20 years, the California Planet Search (CPS) has simultaneously monitored precise radial velocities and chromospheric activity levels of stars from Keck observatory to search for exoplanets. This sample provides a useful set of stars to better determine the dependence of RV jitter on flicker (which traces surface gravity) first shown in Bastien et al. (2014). We expand upon this initial work by examining a much larger sample of stars covering a much wider range of stellar parameters (effective temperature, surface gravity, and activity, among others). For more than 600 stars, there are enough RV measurements to distinguish this astrophysical jitter from accelerations due to orbital companions. To properly isolate RV jitter from these effects, we must first remove the RV signal due to these companions, including several previously unannounced giant planets around subgiant stars. We highlight some new results from our analysis of the CPS data. A more thorough understanding of the various sources of RV jitter and the underlying stellar phenomena that drive these intrinsic RV variations will enable more precise jitter estimates for RV follow-up targets such as those from K2 or the upcoming TESS mission.

  14. Diffusive Promotion by Velocity Gradient of Cytoplasmic Streaming (CPS in Nitella Internodal Cells.

    Directory of Open Access Journals (Sweden)

    Kenji Kikuchi

    Full Text Available Cytoplasmic streaming (CPS is well known to assist the movement of nutrients, organelles and genetic material by transporting all of the cytoplasmic contents of a cell. CPS is generated by motility organelles that are driven by motor proteins near a membrane surface, where the CPS has been found to have a flat velocity profile in the flow field according to the sliding theory. There is a consistent mixing of contents inside the cell by CPS if the velocity gradient profile is flattened, which is not assisted by advection diffusion but is only supported by Brownian diffusion. Although the precise flow structure of the cytoplasm has an important role for cellular metabolism, the hydrodynamic mechanism of its convection has not been clarified. We conducted an experiment to visualise the flow of cytoplasm in Nitella cells by injecting tracer fluorescent nanoparticles and using a flow visualisation system in order to understand how the flow profile affects their metabolic system. We determined that the velocity field in the cytosol has an obvious velocity gradient, not a flattened gradient, which suggests that the gradient assists cytosolic mixing by Taylor-Aris dispersion more than by Brownian diffusion.

  15. Numerical simulation of bubble behavior in subcooled flow boiling under velocity and temperature gradient

    International Nuclear Information System (INIS)

    Bahreini, Mohammad; Ramiar, Abas; Ranjbar, Ali Akbar

    2015-01-01

    Highlights: • Condensing bubble is numerically investigated using VOF model in OpenFOAM package. • Bubble mass reduces as it goes through condensation and achieves higher velocities. • At a certain time the slope of changing bubble diameter with time, varies suddenly. • Larger bubbles experience more lateral migration to higher velocity regions. • Bubbles migrate back to a lower velocity region for higher liquid subcooling rates. - Abstract: In this paper, numerical simulation of the bubble condensation in the subcooled boiling flow is performed. The interface between two-phase is tracked via the volume of fluid (VOF) method with continuous surface force (CSF) model, implemented in the open source OpenFOAM CFD package. In order to simulate the condensing bubble with the OpenFOAM code, the original energy equation and mass transfer model for phase change have been modified and a new solver is developed. The Newtonian flow is solved using the finite volume scheme based on the pressure implicit with splitting of operators (PISO) algorithm. Comparison of the simulation results with previous experimental data revealed that the model predicted well the behavior of the actual condensing bubble. The bubble lifetime is almost proportional to bubble initial size and is prolonged by increasing the system pressure. In addition, the initial bubble size, subcooling of liquid and velocity gradient play an important role in the bubble deformation behavior. Velocity gradient makes the bubble move to the higher velocity region and the subcooling rate makes it to move back to the lower velocity region.

  16. Numerical simulation of bubble behavior in subcooled flow boiling under velocity and temperature gradient

    Energy Technology Data Exchange (ETDEWEB)

    Bahreini, Mohammad, E-mail: m.bahreini1990@gmail.com; Ramiar, Abas, E-mail: aramiar@nit.ac.ir; Ranjbar, Ali Akbar, E-mail: ranjbar@nit.ac.ir

    2015-11-15

    Highlights: • Condensing bubble is numerically investigated using VOF model in OpenFOAM package. • Bubble mass reduces as it goes through condensation and achieves higher velocities. • At a certain time the slope of changing bubble diameter with time, varies suddenly. • Larger bubbles experience more lateral migration to higher velocity regions. • Bubbles migrate back to a lower velocity region for higher liquid subcooling rates. - Abstract: In this paper, numerical simulation of the bubble condensation in the subcooled boiling flow is performed. The interface between two-phase is tracked via the volume of fluid (VOF) method with continuous surface force (CSF) model, implemented in the open source OpenFOAM CFD package. In order to simulate the condensing bubble with the OpenFOAM code, the original energy equation and mass transfer model for phase change have been modified and a new solver is developed. The Newtonian flow is solved using the finite volume scheme based on the pressure implicit with splitting of operators (PISO) algorithm. Comparison of the simulation results with previous experimental data revealed that the model predicted well the behavior of the actual condensing bubble. The bubble lifetime is almost proportional to bubble initial size and is prolonged by increasing the system pressure. In addition, the initial bubble size, subcooling of liquid and velocity gradient play an important role in the bubble deformation behavior. Velocity gradient makes the bubble move to the higher velocity region and the subcooling rate makes it to move back to the lower velocity region.

  17. THEORY OF DISPERSED FIXED-DELAY INTERFEROMETRY FOR RADIAL VELOCITY EXOPLANET SEARCHES

    International Nuclear Information System (INIS)

    Van Eyken, Julian C.; Ge Jian; Mahadevan, Suvrath

    2010-01-01

    The dispersed fixed-delay interferometer (DFDI) represents a new instrument concept for high-precision radial velocity (RV) surveys for extrasolar planets. A combination of a Michelson interferometer and a medium-resolution spectrograph, it has the potential for performing multi-object surveys, where most previous RV techniques have been limited to observing only one target at a time. Because of the large sample of extrasolar planets needed to better understand planetary formation, evolution, and prevalence, this new technique represents a logical next step in instrumentation for RV extrasolar planet searches, and has been proven with the single-object Exoplanet Tracker (ET) at Kitt Peak National Observatory, and the multi-object W. M. Keck/MARVELS Exoplanet Tracker at Apache Point Observatory. The development of the ET instruments has necessitated fleshing out a detailed understanding of the physical principles of the DFDI technique. Here we summarize the fundamental theoretical material needed to understand the technique and provide an overview of the physics underlying the instrument's working. We also derive some useful analytical formulae that can be used to estimate the level of various sources of error generic to the technique, such as photon shot noise when using a fiducial reference spectrum, contamination by secondary spectra (e.g., crowded sources, spectroscopic binaries, or moonlight contamination), residual interferometer comb, and reference cross-talk error. Following this, we show that the use of a traditional gas absorption fiducial reference with a DFDI can incur significant systematic errors that must be taken into account at the precision levels required to detect extrasolar planets.

  18. The impact of red noise in radial velocity planet searches: only three planets orbiting GJ 581?

    Science.gov (United States)

    Baluev, Roman V.

    2013-03-01

    We perform a detailed analysis of the latest HARPS and Keck radial velocity data for the planet-hosting red dwarf GJ 581, which attracted a lot of attention in recent time. We show that these data contain important correlated noise component (`red noise') with the correlation time-scale of the order of 10 d. This red noise imposes a lot of misleading effects while we work in the traditional white-noise model. To eliminate these misleading effects, we propose a maximum-likelihood algorithm equipped by an extended model of the noise structure. We treat the red noise as a Gaussian random process with an exponentially decaying correlation function. Using this method we prove that (i) planets b and c do exist in this system, since they can be independently detected in the HARPS and Keck data, and regardless of the assumed noise models; (ii) planet e can also be confirmed independently by both the data sets, although to reveal it in the Keck data it is mandatory to take the red noise into account; (iii) the recently announced putative planets f and g are likely just illusions of the red noise; (iv) the reality of the planet candidate GJ 581 d is questionable, because it cannot be detected from the Keck data, and its statistical significance in the HARPS data (as well as in the combined data set) drops to a marginal level of ˜2σ, when the red noise is taken into account. Therefore, the current data for GJ 581 really support the existence of no more than four (or maybe even only three) orbiting exoplanets. The planet candidate GJ 581 d requests serious observational verification.

  19. Synthesizing exoplanet demographics from radial velocity and microlensing surveys. I. Methodology

    International Nuclear Information System (INIS)

    Clanton, Christian; Gaudi, B. Scott

    2014-01-01

    Motivated by the order of magnitude difference in the frequency of giant planets orbiting M dwarfs inferred by microlensing and radial velocity (RV) surveys, we present a method for comparing the statistical constraints on exoplanet demographics inferred from these methods. We first derive the mapping from the observable parameters of a microlensing-detected planet to those of an analogous planet orbiting an RV-monitored star. Using this mapping, we predict the distribution of RV observables for the planet population inferred from microlensing surveys, taking care to adopt reasonable priors for, and properly marginalize over, the unknown physical parameters of microlensing-detected systems. Finally, we use simple estimates of the detection limits for a fiducial RV survey to predict the number and properties of analogs of the microlensing planet population such an RV survey should detect. We find that RV and microlensing surveys have some overlap, specifically for super-Jupiter mass planets (m p ≳ 1 M Jup ) with periods between ∼3-10 yr. However, the steeply falling planetary mass function inferred from microlensing implies that, in this region of overlap, RV surveys should infer a much smaller frequency than the overall giant planet frequency (m p ≳ 0.1 M Jup ) inferred by microlensing. Our analysis demonstrates that it is possible to statistically compare and synthesize data sets from multiple exoplanet detection techniques in order to infer exoplanet demographics over wider regions of parameter space than are accessible to individual methods. In a companion paper, we apply our methodology to several representative microlensing and RV surveys to derive the frequency of planets around M dwarfs with orbits of ≲ 30 yr.

  20. A Spitzer search for transits of radial velocity detected super-Earths

    Energy Technology Data Exchange (ETDEWEB)

    Kammer, J. A.; Knutson, H. A.; Desert, J.-M. [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Howard, A. W. [Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 (United States); Laughlin, G. P.; Fortney, J. J. [Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064 (United States); Deming, D. [Department of Astronomy, University of Maryland at College Park, College Park, MD 20742 (United States); Todorov, K. O. [Institute for Astronomy, ETH Zürich, CH-8093 Zürich (Switzerland); Agol, E. [Department of Astronomy, University of Washington, Seattle, WA 98195 (United States); Burrows, A. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Showman, A. P. [Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721 (United States); Lewis, N. K., E-mail: jkammer@caltech.edu [Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)

    2014-02-01

    Unlike hot Jupiters or other gas giants, super-Earths are expected to have a wide variety of compositions, ranging from terrestrial bodies like our own to more gaseous planets like Neptune. Observations of transiting systems, which allow us to directly measure planet masses and radii and constrain atmospheric properties, are key to understanding the compositional diversity of the planets in this mass range. Although Kepler has discovered hundreds of transiting super-Earth candidates over the past 4 yr, the majority of these planets orbit stars that are too far away and too faint to allow for detailed atmospheric characterization and reliable mass estimates. Ground-based transit surveys focus on much brighter stars, but most lack the sensitivity to detect planets in this size range. One way to get around the difficulty of finding these smaller planets in transit is to start by choosing targets that are already known to host super-Earth sized bodies detected using the radial velocity (RV) technique. Here we present results from a Spitzer program to observe six of the most favorable RV-detected super-Earth systems, including HD 1461, HD 7924, HD 156668, HIP 57274, and GJ 876. We find no evidence for transits in any of their 4.5 μm flux light curves, and place limits on the allowed transit depths and corresponding planet radii that rule out even the most dense and iron-rich compositions for these objects. We also observed HD 97658, but the observation window was based on a possible ground-based transit detection that was later ruled out; thus the window did not include the predicted time for the transit detection recently made by the Microvariability and Oscillations of Stars space telescope.

  1. Relationship between velocity gradients and magnetic turbulence in the solar wind

    International Nuclear Information System (INIS)

    Garrett, H.B.

    1974-01-01

    The correlations among the time derivative of the solar-wind velocity, the magnitude of the interplanetary magnetic field (IMF), and the IMF turbulence level are examined to test the idea that interaction between two colliding solar-wind streams can generate turbulence in the solar wind and the IMF. Data obtained by Explorer 33 on the solar wind and IMF are described, and the analysis techniques are outlined. The results indicate that the IMF turbulence level, as measured by the variance, is correlated with the existence of positive velocity gradients in the solar wind. It is noted that while the variance is an increasing function of the field magnitude, it is also independently correlated with the solar-wind velocity gradient

  2. Astrometry, Radial Velocity, and Photometry: The HD 128311 System Remixed with Data from HST, HET, and APT

    Science.gov (United States)

    McArthur, Barbara. E.; Benedict, G. Fritz; Henry, Gregory W.; Hatzes, Artie; Cochran, William D.; Harrison, Tom E.; Johns-Krull, Chris; Nelan, Ed

    2014-11-01

    We have used high-cadence radial velocity measurements from the Hobby-Eberly Telescope with published velocities from the Lick 3 m Shane Telescope, combined with astrometric data from the Hubble Space Telescope (HST) Fine Guidance Sensors to refine the orbital parameters of the HD 128311 system, and determine an inclination of 55.°95 ± 14.°55 and true mass of 3.789 +0.924 -0.432 M JUP for HD 128311 c. The combined radial velocity data also reveal a short period signal which could indicate a third planet in the system with an Msin i of 0.133 ± 0.005 M JUP or stellar phenomena. Photometry from the T12 0.8 m automatic photometric telescope at the Fairborn Observatory and HST are used to determine a photometric period close to, but not within the errors of the radial velocity signal. We performed a cross-correlation bisector analysis of the radial velocity data to look for correlations with the photometric period and found none. Dynamical integrations of the proposed system show long-term stability with the new orbital parameters of over 10 million years. Our new orbital elements do not support the claims of HD 128311 b and c being in mean motion resonance. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen, and observations with T12 0.8 m automatic photoelectric telescope (APT) at Fairborn Observatory.

  3. Radial variation in sap velocity as a function of stem diameter and sapwood thickness in yellow-poplar trees.

    Science.gov (United States)

    Wullschleger, Stan D.; King, Anthony W.

    2000-04-01

    Canopy transpiration and forest water use are frequently estimated as the product of sap velocity and cross-sectional sapwood area. Few studies, however, have considered whether radial variation in sap velocity and the proportion of sapwood active in water transport are significant sources of uncertainty in the extrapolation process. Therefore, radial profiles of sap velocity were examined as a function of stem diameter and sapwood thickness for yellow-poplar (Liriodendron tulipifera L.) trees growing on two adjacent watersheds in eastern Tennessee. The compensation heat pulse velocity technique was used to quantify sap velocity at four equal-area depths in 20 trees that ranged in stem diameter from 15 to 69 cm, and in sapwood thickness from 2.1 to 14.8 cm. Sap velocity was highly dependent on the depth of probe insertion into the sapwood. Rates of sap velocity were greatest for probes located in the two outer sapwood annuli (P1 and P2) and lowest for probes in closest proximity to the heartwood (P3 and P4). Relative sap velocities averaged 0.98 at P1, 0.66 at P2, 0.41 at P3 and 0.35 at P4. Tree-specific sap velocities measured at each of the four probe positions, divided by the maximum sap velocity measured (usually at P1 or P2), indicated that the fraction of sapwood functional in water transport (f(S)) varied between 0.49 and 0.96. There was no relationship between f(S) and sapwood thickness, or between f(S) and stem diameter. The fraction of functional sapwood averaged 0.66 +/- 0.13 for trees on which radial profiles were determined. No significant depth-related differences were observed for sapwood density, which averaged 469 kg m(-3) across all four probe positions. There was, however, a significant decline in sapwood water content between the two outer probe positions (1.04 versus 0.89 kg kg(-1)). This difference was not sufficient to account for the observed radial variation in sap velocity. A Monte-Carlo analysis indicated that the standard error in

  4. Gradiente radial de [Mg/Fe] em duas galáxias elípticas

    Science.gov (United States)

    Milone, A.; Capelato, H.

    2003-08-01

    Basicamente, são propostos dois cenários de evolução quí mio-dinâmico para os sistemas esferoidais: (i) o hierárquico através da fusão e/ou acresção de sub-sistemas com ou sem surtos de formação estelar, e (ii) o colapso monolí tico dissipativo com formação estelar interrompida por um vento galáctico. Ambos, dentro de certos limites, conseguem explicar os gradientes internos de metalicidade estelar presentes nas galáxias elí pticas bem como a relação observada entre a metalicidade central e a massa (Mg20 vs. log sv0). No entanto, nenhum prevê uma variação interna para a razão de abundâncias Mg/Fe que indiretamente define a escala temporal da formação estelar. Empregamos a espectroscopia óptica de fenda longa com a finalidade de recuperar as histórias de formação estelar, de enriquecimento quí mico e da dinâmica dentro de determinadas regiões das galáxias. Os espectros de média resolução (FWHM = 7,1 Å) e escala angular de 1,092 arcsec/pixel foram coletados com o telescópio 1,60m do OPD/LNA. Comparamos nossas medidas de linhas de absorção com resultados espectrofotométricos de modelos de populações estelares simples - mais especificamente os í ndices do Sistema Lick como Mg2, Mg b, e Hb - a fim de se investigar as variações internas de [Fe/H], [Mg/Fe] e idade. Para duas galáxias elí pticas, NGC 1052 e NGC 7796, pertencentes a ambientes de baixa densidade, encontramos uma variação radial da razão Mg/Fe decrescente do centro para fora em regiões de 0,6 e 1 raio efetivo respectivamente. Discutimos alguns cenários de enriquecimento quí mico para estas duas galáxias.

  5. ASTEROSEISMOLOGY OF THE NEARBY SN-II PROGENITOR: RIGEL. I. THE MOST HIGH-PRECISION PHOTOMETRY AND RADIAL VELOCITY MONITORING

    International Nuclear Information System (INIS)

    Moravveji, Ehsan; Guinan, Edward F.; Shultz, Matt; Williamson, Michael H.; Moya, Andres

    2012-01-01

    Rigel (β Ori, B8 Ia) is a nearby blue supergiant displaying α Cyg type variability, and is one of the nearest Type II supernova progenitors. As such it is an excellent test bed to study the internal structure of pre-core-collapse stars. In this study, for the first time, we present 28 days of high-precision MOST photometry and over six years of spectroscopic monitoring. We report 19 significant pulsation modes of signal-to-noise ratio, S/N ∼> 4.6 from radial velocities, with variability timescales ranging from 1.21 to 74.7 days, which are associated with high-order low-degree gravity modes. While the radial velocity variations show a degree of correlation with the flux changes, there is no clear interplay between the equivalent widths of different metallic and Hα lines.

  6. ASTEROSEISMOLOGY OF THE NEARBY SN-II PROGENITOR: RIGEL. I. THE MOST HIGH-PRECISION PHOTOMETRY AND RADIAL VELOCITY MONITORING

    Energy Technology Data Exchange (ETDEWEB)

    Moravveji, Ehsan [Department of Physics, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731 (Iran, Islamic Republic of); Guinan, Edward F. [Department of Astronomy, Villanova University, 800 Lancaster Avenue, Villanova, PA 19085 (United States); Shultz, Matt [Royal Military College of Canada, PO Box 17000, Station Forces, Kingston, ON K7K 4B4 (Canada); Williamson, Michael H. [Center of Excellence in Information Systems, Tennessee State University, Nashville, TN (United States); Moya, Andres, E-mail: moravveji@iasbs.ac.ir [Departamento de Astrofisica, Centro de Astrobiologia (INTA-CSIC), PO BOX 78, 28691 Villanueva de la Canada, Madrid (Spain)

    2012-03-10

    Rigel ({beta} Ori, B8 Ia) is a nearby blue supergiant displaying {alpha} Cyg type variability, and is one of the nearest Type II supernova progenitors. As such it is an excellent test bed to study the internal structure of pre-core-collapse stars. In this study, for the first time, we present 28 days of high-precision MOST photometry and over six years of spectroscopic monitoring. We report 19 significant pulsation modes of signal-to-noise ratio, S/N {approx}> 4.6 from radial velocities, with variability timescales ranging from 1.21 to 74.7 days, which are associated with high-order low-degree gravity modes. While the radial velocity variations show a degree of correlation with the flux changes, there is no clear interplay between the equivalent widths of different metallic and H{alpha} lines.

  7. On the effect of velocity gradients on the depth of correlation in μPIV

    Science.gov (United States)

    Mustin, B.; Stoeber, B.

    2016-03-01

    The present work revisits the effect of velocity gradients on the depth of the measurement volume (depth of correlation) in microscopic particle image velocimetry (μPIV). General relations between the μPIV weighting functions and the local correlation function are derived from the original definition of the weighting functions. These relations are used to investigate under which circumstances the weighting functions are related to the curvature of the local correlation function. Furthermore, this work proposes a modified definition of the depth of correlation that leads to more realistic results than previous definitions for the case when flow gradients are taken into account. Dimensionless parameters suitable to describe the effect of velocity gradients on μPIV cross correlation are derived and visual interpretations of these parameters are proposed. We then investigate the effect of the dimensionless parameters on the weighting functions and the depth of correlation for different flow fields with spatially constant flow gradients and with spatially varying gradients. Finally this work demonstrates that the results and dimensionless parameters are not strictly bound to a certain model for particle image intensity distributions but are also meaningful when other models for particle images are used.

  8. On the effect of velocity gradients on the depth of correlation in μPIV

    International Nuclear Information System (INIS)

    Mustin, B; Stoeber, B

    2016-01-01

    The present work revisits the effect of velocity gradients on the depth of the measurement volume (depth of correlation) in microscopic particle image velocimetry (μPIV). General relations between the μPIV weighting functions and the local correlation function are derived from the original definition of the weighting functions. These relations are used to investigate under which circumstances the weighting functions are related to the curvature of the local correlation function. Furthermore, this work proposes a modified definition of the depth of correlation that leads to more realistic results than previous definitions for the case when flow gradients are taken into account. Dimensionless parameters suitable to describe the effect of velocity gradients on μPIV cross correlation are derived and visual interpretations of these parameters are proposed. We then investigate the effect of the dimensionless parameters on the weighting functions and the depth of correlation for different flow fields with spatially constant flow gradients and with spatially varying gradients. Finally this work demonstrates that the results and dimensionless parameters are not strictly bound to a certain model for particle image intensity distributions but are also meaningful when other models for particle images are used. (paper)

  9. McDonald Observatory Planetary Search - A high precision stellar radial velocity survey for other planetary systems

    Science.gov (United States)

    Cochran, William D.; Hatzes, Artie P.

    1993-01-01

    The McDonald Observatory Planetary Search program surveyed a sample of 33 nearby F, G, and K stars since September 1987 to search for substellar companion objects. Measurements of stellar radial velocity variations to a precision of better than 10 m/s were performed as routine observations to detect Jovian planets in orbit around solar type stars. Results confirm the detection of a companion object to HD114762.

  10. Detection of Stellar Pulsations in the Planet Host Star γ Cephei A by High Precision Radial Velocity Measurements

    International Nuclear Information System (INIS)

    Endl, Michael; Castanheira, Barbara G.; Cochran, William D.; Bean, Jacob L.; Wittenmyer, Robert A.; Hatzes, Artie P.

    2009-01-01

    We present a first analysis of our asteroseismology campaign on the planet host star γ Cep A. We used seven consecutive nights at the Harlan J. Smith 2.7 m telescope at McDonald Observatory to obtain 1200 highly precise radial velocity measurements. We find the star to be a multi-periodic pulsator with a frequency spacing of 15 μHz.

  11. An assimilation test of Doppler radar reflectivity and radial velocity from different height layers in improving the WRF rainfall forecasts

    Science.gov (United States)

    Tian, Jiyang; Liu, Jia; Yan, Denghua; Li, Chuanzhe; Chu, Zhigang; Yu, Fuliang

    2017-12-01

    Hydrological forecasts require high-resolution and accurate rainfall information, which is one of the most difficult variables to be captured by the mesoscale Numerical Weather Prediction (NWP) systems. Radar data assimilation is an effective method for improving rainfall forecasts by correcting the initial and lateral boundary conditions of the NWP system. The aim of this study is to explore an efficient way of utilizing the Doppler radar observations for data assimilation, which is implemented by exploring the effect of assimilating radar data from different height layers on the improvement of the NWP rainfall accuracy. The Weather Research and Forecasting (WRF) model is used for numerical rainfall forecast in the Zijingguan catchment located in the ;Jing-Jin-Ji; (Beijing-Tianjin-Hebei) Region of Northern China, and the three-dimensional variational data assimilation (3-DVar) technique is adopted to assimilate the radar data. Radar reflectivity and radial velocity are assimilated separately and jointly. Each type of radar data is divided into seven data sets according to the height layers: (1) 2000 m, and (7) all layers. The results show that radar reflectivity assimilation leads to better results than radial velocity assimilation. The accuracy of the forecasted rainfall deteriorates with the rise of the height of the assimilated radar reflectivity. The same results can be found when assimilating radar reflectivity and radial velocity at the same time. The conclusions of this study provide a reference for efficient assimilation of the radar data in improving the NWP rainfall products.

  12. VizieR Online Data Catalog: Radial velocities of 35 cataclysmic variables (Thorstensen+, 2016)

    Science.gov (United States)

    Thorstensen, J. R.; Alper, E. H.; Weil, K. E.

    2017-02-01

    We present spectroscopic follow-up observations of 35 newly discovered cataclysmic variables (CVs), 32 of which were found by the Catalina Real Time Transient Surveys (CRTS; Drake et al. 2009, Cat. J/ApJ/696/870; Drake et al. 2014, Cat. J/MNRAS/441/1186; Breedt et al. 2014, Cat. J/MNRAS/443/3174), ASAS-SN (Shappee et al. 2014ApJ...788...48S), and/or MASTER (Lipunov et al. 2010AdAst2010E..30L). All our observations are from Michigan-Dartmouth-MIT (MDM) Observatory on Kitt Peak, Arizona. For nearly all the spectra, we used the "modspec" spectrograph (a description of the modspec can be found at http://mdm.kpno.noao.edu/Manuals/ModSpec/modspec_man.html) with a 600line/mm grating. We mostly used a SITe 20482 CCD detector, which yielded 2Å/pixel from 4210 to 7500Å, with declining throughput toward the ends of the spectral range. When this detector was unavailable, we used a very similar 10242 SITe detector ("Templeton"), which covered 4660 to 6730Å. The modspec was mounted mostly on the 2.4m Hiltner telescope, but for some of the brighter objects, we used the 1.3m McGraw-Hill telescope. For a few of the 1.3m spectra, we used the Mark III grism spectrograph, which covered 4580 to 6850Å at 2.3Å/pixel. On both telescopes and with both spectrographs, we used an Andor Ikon camera to view the reflective slit jaws through a microscope and guided the telescope with a separate off-axis guider. With this arrangement we could place any object that was bright enough for a usable spectrum in the slit and track it accurately even if the portion of the light spilling onto the slit jaws was invisible. Our emission-line radial velocities are almost entirely of Hα, since it almost always gives the best signal-to-noise ratio with our instrument. (3 data files).

  13. K-KIDS: K Dwarfs and Their Companions. First Results from Radial Velocity Survey with CHIRON Spectrograph

    Science.gov (United States)

    Paredes, Leonardo; Henry, Todd; Nusdeo, Daniel; Winters, J.; Dincer, Tolga

    2018-01-01

    We present the K-KIDS project, an effort to survey a large sample of K dwarfs and their companions, the KIDS. We are observing a carefully vetted equatorial sample (DEC = -30 to +30) of more than 1000 K dwarfs within 50 pc to make a comprehensive assessment of stellar, substellar and planetary companions with separations of 0.1 to 10,000 AU.The initial sample of 1048 stars has been compiled using astrometric data from Hipparcos and photometric data from Tycho-2 and 2MASS. Four different imaging and spectroscopic surveys are underway. Here we present the strategy and initial results for our high-precision radial velocity survey for the closest companions using the CHIRON spectrograph on the CTIO/SMARTS 1.5m telescope. Individual measurements with CHIRON at R = 80,000 using ThAr wavelength calibration, indicate that for K dwarf radial velocity standards with V = 5.8, 7.0 and 8.0 yield precisions over 6 weeks of observing of 7.4 m/s, 9.8 m/s and 5.7 m/s. In the first two months, a core sample of 42 K dwarfs, including carefully selected calibration systems as well as previously unobserved stars, was observed every few nights to detect the radial velocity signals of close companions. In our calibration stellar systems, we have confirmed the suitability of CHIRON for our studies, by having found periodic radial velocity perturbations consistent with hot Jupiter and stellar companions previously detected. This set forms the foundation of our one-year survey of 100 K dwarfs with magnitudes as faint as V = 11.5, for which we should detect companions with masses as low as Jupiter.In light of the promising performance and efficiency of the CHIRON spectrograph for a long-term radial velocity survey, we have expanded our initial sample using Gaia Data Release 1 to 1824 K dwarfs within 50 pc. Ultimately, the combination of all four surveys will provide an unprecedented portrait of K dwarfs and their kids.This effort has been supported by the NSF through grant AST-1517413, and

  14. The influence of velocity gradient on properties and filterability of suspension formed during water treatment

    Czech Academy of Sciences Publication Activity Database

    Bubáková, Petra; Pivokonský, Martin

    2012-01-01

    Roč. 92, May (2012), s. 161-167 ISSN 1383-5866. [European Conference on Fluid-Particle Separation (FPS 2010). Lyon, 05.10.2010-07.10.2010] R&D Projects: GA ČR GAP105/11/0247 Institutional research plan: CEZ:AV0Z20600510 Keywords : aggregation * fractal dimension * filtration * particle size distribution * velocity gradient Subject RIV: BK - Fluid Dynamics Impact factor: 2.894, year: 2012

  15. Velocity gradient induced line splitting in x-ray emission accompanying plasma-wall interaction

    Czech Academy of Sciences Publication Activity Database

    Šmíd, Michal; Renner, Oldřich; Liska, R.

    2013-01-01

    Roč. 125, Aug (2013), s. 38-44 ISSN 0022-4073 R&D Projects: GA ČR GAP205/10/0814; GA ČR GAP205/11/0571 Institutional support: RVO:68378271 Keywords : laser-produced plasmas * x-ray spectroscopy * plasma-wall interaction * spectral line profiles * Doppler shift * ion velocity gradients Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 2.288, year: 2013

  16. MUSE observations of M87: radial gradients for the stellar initial-mass function and the abundance of Sodium

    Science.gov (United States)

    Sarzi, Marc; Spiniello, Chiara; Barbera, Francesco La; Krajnović, Davor; Bosch, Remco van den

    2018-05-01

    Based on MUSE integral-field data we present evidence for a radial variation at the low-mass end of the stellar initial-mass function (IMF) in the central regions of the giant early-type galaxy NGC 4486 (M87). We used state-of-the-art stellar population models and the observed strength of various IMF-sensitive absorption-line features to solve for the best low-mass tapered "bimodal" form of the IMF, while accounting also for variations in stellar metallicity, the overall α-elements abundance and the abundance of individual elements such as Ti, O, Na and Ca. Our analysis reveals a strong negative IMF gradient corresponding to an exceeding fraction of low-mass stars compared to the case of the Milky Way toward the center of M87, which drops to nearly Milky-way levels by 0.4 Re. Such IMF variations correspond to over a factor two increase in stellar mass-to-light M/L ratio compared to the case of a Milky-way IMF, consistent with independent constraints on M/L radial variations in M87 from dynamical models. We also looked into the abundance of Sodium in M87, which turned up to be super-Solar over the entire radial range of our MUSE observations and to exhibit a considerable negative gradient. These findings suggest an additional role of metallicity in boosting the Na-yields in the central, metal-rich regions of M87 during its early and brief star-formation history. Our work adds M87 to the few objects that presently have radial constraints on their IMF or [Na/Fe] abundance, while also illustrating the accuracy that MUSE could bring to this kind of investigations.

  17. BREATHING FIRE: HOW STELLAR FEEDBACK DRIVES RADIAL MIGRATION, RAPID SIZE FLUCTUATIONS, AND POPULATION GRADIENTS IN LOW-MASS GALAXIES

    International Nuclear Information System (INIS)

    El-Badry, Kareem; Geha, Marla; Wetzel, Andrew; Hopkins, Philip F.; Kereš, Dusan; Chan, T. K.; Faucher-Giguère, Claude-André

    2016-01-01

    We examine the effects of stellar feedback and bursty star formation on low-mass galaxies (M star  = 2 × 10 6  − 5 × 10 10 M ⊙ ) using the Feedback in Realistic Environments (FIRE) simulations. While previous studies emphasized the impact of feedback on dark matter profiles, we investigate the impact on the stellar component: kinematics, radial migration, size evolution, and population gradients. Feedback-driven outflows/inflows drive significant radial stellar migration over both short and long timescales via two processes: (1) outflowing/infalling gas can remain star-forming, producing young stars that migrate ∼1 kpc within their first 100 Myr, and (2) gas outflows/inflows drive strong fluctuations in the global potential, transferring energy to all stars. These processes produce several dramatic effects. First, galaxies’ effective radii can fluctuate by factors of >2 over ∼200 Myr, and these rapid size fluctuations can account for much of the observed scatter in the radius at fixed M star . Second, the cumulative effects of many outflow/infall episodes steadily heat stellar orbits, causing old stars to migrate outward most strongly. This age-dependent radial migration mixes—and even inverts—intrinsic age and metallicity gradients. Thus, the galactic-archaeology approach of calculating radial star formation histories from stellar populations at z = 0 can be severely biased. These effects are strongest at M star  ≈ 10 7–9.6 M ⊙ , the same regime where feedback most efficiently cores galaxies. Thus, detailed measurements of stellar kinematics in low-mass galaxies can strongly constrain feedback models and test baryonic solutions to small-scale problems in ΛCDM

  18. BREATHING FIRE: HOW STELLAR FEEDBACK DRIVES RADIAL MIGRATION, RAPID SIZE FLUCTUATIONS, AND POPULATION GRADIENTS IN LOW-MASS GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    El-Badry, Kareem; Geha, Marla [Department of Astronomy, Yale University, New Haven, CT (United States); Wetzel, Andrew; Hopkins, Philip F. [TAPIR, California Institute of Technology, Pasadena, CA USA (United States); Kereš, Dusan; Chan, T. K. [Department of Physics, Center for Astrophysics and Space Sciences, University of California at San Diego, La Jolla (United States); Faucher-Giguère, Claude-André, E-mail: kareem.el-badry@yale.edu [Department of Physics and Astronomy and CIERA, Northwestern University, Evanston, IL (United States)

    2016-04-01

    We examine the effects of stellar feedback and bursty star formation on low-mass galaxies (M{sub star} = 2 × 10{sup 6} − 5 × 10{sup 10} M{sub ⊙}) using the Feedback in Realistic Environments (FIRE) simulations. While previous studies emphasized the impact of feedback on dark matter profiles, we investigate the impact on the stellar component: kinematics, radial migration, size evolution, and population gradients. Feedback-driven outflows/inflows drive significant radial stellar migration over both short and long timescales via two processes: (1) outflowing/infalling gas can remain star-forming, producing young stars that migrate ∼1 kpc within their first 100 Myr, and (2) gas outflows/inflows drive strong fluctuations in the global potential, transferring energy to all stars. These processes produce several dramatic effects. First, galaxies’ effective radii can fluctuate by factors of >2 over ∼200 Myr, and these rapid size fluctuations can account for much of the observed scatter in the radius at fixed M{sub star}. Second, the cumulative effects of many outflow/infall episodes steadily heat stellar orbits, causing old stars to migrate outward most strongly. This age-dependent radial migration mixes—and even inverts—intrinsic age and metallicity gradients. Thus, the galactic-archaeology approach of calculating radial star formation histories from stellar populations at z = 0 can be severely biased. These effects are strongest at M{sub star} ≈ 10{sup 7–9.6} M{sub ⊙}, the same regime where feedback most efficiently cores galaxies. Thus, detailed measurements of stellar kinematics in low-mass galaxies can strongly constrain feedback models and test baryonic solutions to small-scale problems in ΛCDM.

  19. THE BROWN DWARF KINEMATICS PROJECT (BDKP). IV. RADIAL VELOCITIES OF 85 LATE-M AND L DWARFS WITH MagE

    Energy Technology Data Exchange (ETDEWEB)

    Burgasser, Adam J. [Center for Astrophysics and Space Science, University of California San Diego, La Jolla, CA 92093 (United States); Logsdon, Sarah E. [Department of Physics and Astronomy, UCLA, 430 Portola Plaza, Box 951547, Los Angeles, CA 90095-1547 (United States); Gagné, Jonathan [Institute for Research on Exoplanets (iREx), Université de Montréal, Département de Physique, C.P. 6128 Succ. Centre-ville, Montréal, QC H3C 3J7 (Canada); Bochanski, John J. [Rider University, 2083 Lawrenceville Road, Lawrenceville, NJ 08648 (United States); Faherty, Jaqueline K. [Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015 (United States); West, Andrew A. [Department of Astronomy, Boston University, 725 Commonwealth Avenue Boston, MA 02215 (United States); Mamajek, Eric E. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Schmidt, Sarah J. [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Cruz, Kelle L., E-mail: aburgasser@ucsd.edu [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10034 (United States)

    2015-09-15

    Radial velocity measurements are presented for 85 late M- and L-type very low-mass stars and brown dwarfs obtained with the Magellan Echellette spectrograph. Targets primarily have distances within 20 pc of the Sun, with more distant sources selected for their unusual spectral energy distributions. We achieved precisions of 2–3 km s{sup −1}, and combined these with astrometric and spectrophotometric data to calculate UVW velocities. Most are members of the thin disk of the Galaxy, and velocity dispersions indicate a mean age of 5.2 ± 0.2 Gyr for sources within 20 pc. We find signficantly different kinematic ages between late-M dwarfs (4.0 ± 0.2 Gyr) and L dwarfs (6.5 ± 0.4 Gyr) in our sample that are contrary to predictions from prior simulations. This difference appears to be driven by a dispersed population of unusually blue L dwarfs which may be more prevalent in our local volume-limited sample than in deeper magnitude-limited surveys. The L dwarfs exhibit an asymmetric U velocity distribution with a net inward flow, similar to gradients recently detected in local stellar samples. Simulations incorporating brown dwarf evolution and Galactic orbital dynamics are unable to reproduce the velocity asymmetry, suggesting non-axisymmetric perturbations or two distinct L dwarf populations. We also find the L dwarfs to have a kinematic age-activity correlation similar to more massive stars. We identify several sources with low surface gravities, and two new substellar candidate members of nearby young moving groups: the astrometric binary DENIS J08230313–4912012AB, a low-probability member of the β Pictoris Moving Group; and 2MASS J15104786–2818174, a moderate-probability member of the 30–50 Myr Argus Association.

  20. Time Variations of the Radial Velocity of H2O Masers in the Semi-Regular Variable R Crt

    Science.gov (United States)

    Sudou, Hiroshi; Shiga, Motoki; Omodaka, Toshihiro; Nakai, Chihiro; Ueda, Kazuki; Takaba, Hiroshi

    2017-12-01

    H2O maser emission {at 22 GHz} in the circumstellar envelope is one of the good tracers of detailed physics and inematics in the mass loss process of asymptotic giant branch stars. Long-term monitoring of an H2O maser spectrum with high time resolution enables us to clarify acceleration processes of the expanding shell in the stellar atmosphere. We monitored the H2O maser emission of the semi-regular variable R Crt with the Kagoshima 6-m telescope, and obtained a large data set of over 180 maser spectra over a period of 1.3 years with an observational span of a few days. Using an automatic peak detection method based on least-squares fitting, we exhaustively detected peaks as significant velocity components with the radial velocity on a 0.1 km s^{-1} scale. This analysis result shows that the radial velocity of red-shifted and blue-shifted components exhibits a change between acceleration and deceleration on the time scale of a few hundred days. These velocity variations are likely to correlate with intensity variations, in particular during flaring state of H2O masers. It seems reasonable to consider that the velocity variation of the maser source is caused by shock propagation in the envelope due to stellar pulsation.However, it is difficult to explain the relationship between the velocity variation and the intensity variation only from shock propagation effects. We found that a time delay of the integrated maser intensity with respect to the optical light curve is about 150 days.

  1. Using radial metallicity gradients in dwarf galaxies to study environmental processing

    NARCIS (Netherlands)

    Leaman, R.; Venn, K.; Brooks, A.; Battaglia, G.; Cole, A.; Ibata, R.; Irwin, M.; McConnachie, A.; Mendel, T.; Tolstoy, E.; Starkenburg, E.

    2014-01-01

    The observed morphology-density relation in the Local Group suggests that some amount of environmental processing has occurred, however the nature and efficiency of tidal and ram pressure stripping is not well constrained. A possible avenue to test these processes is to study the radial distribution

  2. Stress wave velocity patterns in the longitudinal-radial plane of trees for defect diagnosis

    Science.gov (United States)

    Guanghui Li; Xiang Weng; Xiaocheng Du; Xiping Wang; Hailin Feng

    2016-01-01

    Acoustic tomography for urban tree inspection typically uses stress wave data to reconstruct tomographic images for the trunk cross section using interpolation algorithm. This traditional technique does not take into account the stress wave velocity patterns along tree height. In this study, we proposed an analytical model for the wave velocity in the longitudinal–...

  3. A-type central stars of planetary nebulae. 1. A radial-velocity study of the central stars of NGC2346 and NGC3132

    Energy Technology Data Exchange (ETDEWEB)

    Mendez, R H; Niemela, V S [Instituto de Astronomia y Fisica del Espacio, Succuoa, Buenos Aires (Argentina); Lee, P

    1978-08-01

    Radial-velocity measurements of the A-type central stars of NGC2346 and NGC3132 are presented. The first one is almost certainly a spectroscopic binary; no definite statement can be made about the second.

  4. Stellar magnetometry and Zeeman-Doppler imaging in exo-planets research using the radial velocity method

    International Nuclear Information System (INIS)

    Hebrard, Elodie

    2015-01-01

    Forthcoming instruments dedicated to exo-planets detection through the radial velocity method are numerous, and increasingly more accurate. However this method is indirect: orbiting planets are detected and characterised from variations on the spectrum of the host star. We are therefore sensitive to all activity phenomena impacting the spectrum and producing a radial velocity signal (pulsation, granulation, spots, magnetic cycle...). The detection of rocky Earth-like planets around main-sequence stars, and of hot Jupiters into young systems, are currently limited by the intrinsic magnetic activity of the host stars. The radial velocity fluctuations caused by activity (activity jitter) can easily mimic and hide signals from such planets, whose amplitude is of a few m/s and hundreds of m/s, respectively. As a result, the detection threshold of exo-planets is largely set by the stellar activity level. Currently, efforts are invested to overcome this intrinsic limitation. During my PhD, I studied how to take advantage of imaging tomographic techniques (Zeeman-Doppler imaging, ZDI) to characterize stellar activity and magnetic field topologies, ultimately allowing us to filter out the activity jitter. My work is based on spectro-polarimetric observations of a sample of weakly-active M-dwarfs, and young active T Tauri stars. Using a modified version of ZDI, we are able to reconstruct the distribution of active regions, and then model the induced stellar signal allowing us to clean RV curves from the activity jitter. First tests demonstrate that this technique can be efficient enough to recover the planet signal, especially for the more active ones. (author)

  5. New Models for Velocity/Pressure-Gradient Correlations in Turbulent Boundary Layers

    Science.gov (United States)

    Poroseva, Svetlana; Murman, Scott

    2014-11-01

    To improve the performance of Reynolds-Averaged Navier-Stokes (RANS) turbulence models, one has to improve the accuracy of models for three physical processes: turbulent diffusion, interaction of turbulent pressure and velocity fluctuation fields, and dissipative processes. The accuracy of modeling the turbulent diffusion depends on the order of a statistical closure chosen as a basis for a RANS model. When the Gram-Charlier series expansions for the velocity correlations are used to close the set of RANS equations, no assumption on Gaussian turbulence is invoked and no unknown model coefficients are introduced into the modeled equations. In such a way, this closure procedure reduces the modeling uncertainty of fourth-order RANS (FORANS) closures. Experimental and direct numerical simulation data confirmed the validity of using the Gram-Charlier series expansions in various flows including boundary layers. We will address modeling the velocity/pressure-gradient correlations. New linear models will be introduced for the second- and higher-order correlations applicable to two-dimensional incompressible wall-bounded flows. Results of models' validation with DNS data in a channel flow and in a zero-pressure gradient boundary layer over a flat plate will be demonstrated. A part of the material is based upon work supported by NASA under award NNX12AJ61A.

  6. Southern Milky Way carbon stars - New candidates, JHK photometry, and radial velocities

    International Nuclear Information System (INIS)

    Blanco, V.M.; Cook, K.H.; Schechter, P.L.; Aaronson, M.

    1989-01-01

    Data are presented for low-latitude southern Milky Way carbon stars. Coordinates and cross identifications are given for carbon stars (67 of which are confirmed new discoveries) in seven fields deemed to be unusually transparent. JHK photometry is presented for 520 stars. Velocities are presented for 393 stars. Improved coordinates are presented for selected stars in Westerlund's catalog. Averaged photometry and velocities are presented for a sample of 336 stars. 26 refs

  7. Least squares inversion of Stokes profiles in the presence of velocity gradients

    International Nuclear Information System (INIS)

    Skumanich, A.; Rees, D.E.; Lites, B.W.; Sacramento Peak Observatory, Sunspot, NM)

    1985-01-01

    The Auer, Heasley and House Stokes inversion procedure in use at High Altitude Observatory is based on the analytic solution of the equation of transfer for polarized light where the representation of the thermodynamic and magnetic structure of the atmosphere is assumed to have a high degree of invariance, namely, a Milne-Eddington (ME) structure with a constant magnetic field. In the presence of invariance breaking gradients the resultant Stokes profiles are represented only approximately, if at all, by analytic forms. The accuracy of the inversion parameters and their significance as measures of actual structure are explored for the ME and the Landman-Finn sunspot models under the effects of velocity gradients. The resulting field parameters are good to a few percent and prove to be insensitive to the errors committed by the use of a ME-representation, but the resulting ME parameters yield a less precise measure of thermal structure

  8. Velocity ratio predicts outcomes in patients with low gradient severe aortic stenosis and preserved EF

    DEFF Research Database (Denmark)

    Jander, Nikolaus; Hochholzer, Willibald; Kaufmann, Beat A

    2014-01-01

    OBJECTIVE: To evaluate the usefulness of velocity ratio (VR) in patients with low gradient severe aortic stenosis (LGSAS) and preserved EF. BACKGROUND: LGSAS despite preserved EF represents a clinically challenging entity. Reliance on mean pressure gradient (MPG) may underestimate stenosis severity...... for severe stenosis. We hypothesised that VR may have conceptual advantages over MPG and AVA, predict clinical outcomes and thereby be useful in the management of patients with LGSAS. METHODS: Patients from the prospective Simvastatin and Ezetimibe in Aortic Stenosis (SEAS) study with an AVA...≤40 mm Hg and EF≥55% and asymptomatic at baseline were stratified according to VR with a cut-off value of 0.25. Outcomes were evaluated according to aortic valve-related events and cardiovascular death. RESULTS: Of 435 patients with LGSAS, 197 (45%) had VRVR≥0...

  9. Multiscale analysis of the invariants of the velocity gradient tensor in isotropic turbulence

    Science.gov (United States)

    Danish, Mohammad; Meneveau, Charles

    2018-04-01

    Knowledge of local flow-topology, the patterns of streamlines around a moving fluid element as described by the velocity-gradient tensor, is useful for developing insights into turbulence processes, such as energy cascade, material element deformation, or scalar mixing. Much has been learned in the recent past about flow topology at the smallest (viscous) scales of turbulence. However, less is known at larger scales, for instance, at the inertial scales of turbulence. In this work, we present a detailed study on the scale dependence of various quantities of interest, such as the population fraction of different types of flow-topologies, the joint probability distribution of the second and third invariants of the velocity gradient tensor, and the geometrical alignment of vorticity with strain-rate eigenvectors. We perform the analysis on a simulation dataset of isotropic turbulence at Reλ=433 . While quantities appear close to scale invariant in the inertial range, we observe a "bump" in several quantities at length scales between the inertial and viscous ranges. For instance, the population fraction of unstable node-saddle-saddle flow topology shows an increase when reducing the scale from the inertial entering the viscous range. A similar bump is observed for the vorticity-strain-rate alignment. In order to document possible dynamical causes for the different trends in the viscous and inertial ranges, we examine the probability fluxes appearing in the Fokker-Plank equation governing the velocity gradient invariants. Specifically, we aim to understand whether the differences observed between the viscous and inertial range statistics are due to effects caused by pressure, subgrid-scale, or viscous stresses or various combinations of these terms. To decompose the flow into small and large scales, we mainly use a spectrally compact non-negative filter with good spatial localization properties (Eyink-Aluie filter). The analysis shows that when going from the inertial

  10. Data reduction, radial velocities and stellar parameters from spectra in the very low signal-to-noise domain

    Science.gov (United States)

    Malavolta, Luca

    2013-10-01

    Large astronomical facilities usually provide data reduction pipeline designed to deliver ready-to-use scientific data, and too often as- tronomers are relying on this to avoid the most difficult part of an astronomer job Standard data reduction pipelines however are usu- ally designed and tested to have good performance on data with av- erage Signal to Noise Ratio (SNR) data, and the issues that are related with the reduction of data in the very low SNR domain are not taken int account properly. As a result, informations in data with low SNR are not optimally exploited. During the last decade our group has collected thousands of spec- tra using the GIRAFFE spectrograph at Very Large Telescope (Chile) of the European Southern Observatory (ESO) to determine the ge- ometrical distance and dynamical state of several Galactic Globular Clusters but ultimately the analysis has been hampered by system- atics in data reduction, calibration and radial velocity measurements. Moreover these data has never been exploited to get other informa- tions like temperature and metallicity of stars, because considered too noisy for these kind of analyses. In this thesis we focus our attention on data reduction and analysis of spectra with very low SNR. The dataset we analyze in this thesis comprises 7250 spectra for 2771 stars of the Globular Cluster M 4 (NGC 6121) in the wavelength region 5145-5360Å obtained with GIRAFFE. Stars from the upper Red Giant Branch down to the Main Sequence have been observed in very different conditions, including nights close to full moon, and reaching SNR - 10 for many spectra in the dataset. We will first review the basic steps of data reduction and spec- tral extraction, adapting techniques well tested in other field (like photometry) but still under-developed in spectroscopy. We improve the wavelength dispersion solution and the correction of radial veloc- ity shift between day-time calibrations and science observations by following a completely

  11. VizieR Online Data Catalog: Radial velocities in M67. I. 1278 candidate members (Geller+, 2015)

    Science.gov (United States)

    Geller, A. M.; Latham, D. W.; Mathieu, R. D.

    2015-10-01

    This is the first in a series of papers studying the dynamical state of the old open cluster M67 through precise radial velocities. This is also the paper LXVII of the WIYN Open Cluster Study. Our radial velocity survey of M67 began as part of the dissertation work of Mathieu (1983PhDT.........8M), taking advantage of the CfA Digital Speedometers (DS). Three nearly identical instruments were used, initially on the MMT (from HJD2445337 to HJD2450830) and 1.5m Tillinghast Reflector (from HJD2444184 to HJD2454958) at the Fred Lawrence Whipple Observatory on Mount Hopins, Arizona, and then later on the 1.5m Wyeth Reflector (from HJD2445722 to HJD2453433) at the Oak Ridge Observatory in the Town of Harvard, Massachusetts. Subsequently the M67 target samples were expanded several times. Radial velocities measurements from other programs were integrated into the database, and our observational facilities were extended to include Hydra Multi-Object Spectrograph (MOS) at the WIYN Observatory (from HJD2453386 to HJD2456709) and the new Tillinghast Reflector Echelle Spectrograph (TRES) on the Tillinghast Reflector (from HJD2455143 to HJD2456801). Details about the telescopes, observing procedures, and data reductions of spectra obtained with the CfA DS can be found in Latham (1985srv..conf...21L, 1992ASPC...32..110L). The corresponding information for spectra obtained with Hydra at the WIYN Observatory can be found in Geller et al. 2008 (cat. J/AJ/135/2264), Geller et al. 2010 (cat. J/AJ/139/1383) and Hole et al. (2009). TRES is a stabilized fiber-fed echelle spectrograph with a CCD detector and resolution of 44000. The initial CfA sample was defined in 1982. The last surviving CfA Digital Speedometer, on the 1.5m Tillinghast Reflector, was retired in the summer of 2009. Over the following five observing seasons, TRES was used to continue the radial velocity observations of targets (mostly binaries) from both the CfA and the WIYN samples. Importantly, Roger Griffin and James

  12. Where are the Binaries? Results of a Long-term Search for Radial Velocity Binaries in Proto-planetary Nebulae

    Energy Technology Data Exchange (ETDEWEB)

    Hrivnak, Bruce J.; Lu, Wenxian [Department of Physics and Astronomy, Valparaiso University, Valparaiso, IN 46383 (United States); Steene, Griet Van de [Royal Observatory of Belgium, Astronomy and Astrophysics, Ringlaan 3, Brussels (Belgium); Winckel, Hans Van [Instituut voor Sterrenkunde, K.U. Leuven University, Celestijnenlaan 200 D, B-3001 Leuven (Belgium); Sperauskas, Julius [Vilnius University Observatory, Ciurlionio 29 Vilnius 2009 (Lithuania); Bohlender, David, E-mail: bruce.hrivnak@valpo.edu, E-mail: wen.lu@valpo.edu, E-mail: g.vandesteene@oma.be, E-mail: Hans.VanWinckel@ster.kuleuven.be, E-mail: julius.sperauskas@ff.vu.lt, E-mail: David.Bohlender@nrc-cnrc.gc.ca [National Research Council of Canada, Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)

    2017-09-10

    We present the results of an expanded, long-term radial velocity search (25 years) for evidence of binarity in a sample of seven bright proto-planetary nebulae (PPNe). The goal is to investigate the widely held view that the bipolar or point-symmetric shapes of planetary nebulae (PNe) and PPNe are due to binary interactions. Observations from three observatories were combined from 2007 to 2015 to search for variations on the order of a few years and then combined with earlier observations from 1991 to 1995 to search for variations on the order of decades. All seven show velocity variations due to periodic pulsation in the range of 35–135 days. However, in only one PPN, IRAS 22272+5435, did we find even marginal evidence for multi-year variations that might be due to a binary companion. This object shows marginally significant evidence of a two-year period of low semi-amplitude, which could be due to a low-mass companion, and it also displays some evidence of a much longer period of >30 years. The absence of evidence in the other six objects for long-period radial velocity variations due to a binary companion sets significant constraints on the properties of any undetected binary companions: they must be of low mass, ≤0.2 M {sub ⊙}, or long period, >30 years. Thus the present observations do not provide direct support for the binary hypothesis to explain the shapes of PNe and PPNe and severely constrains the properties of any such undetected companions.

  13. Radial profiles of velocity and pressure for condensation-induced hurricanes

    International Nuclear Information System (INIS)

    Makarieva, A.M.; Gorshkov, V.G.

    2011-01-01

    The Bernoulli integral in the form of an algebraic equation is obtained for the hurricane air flow as the sum of the kinetic energy of wind and the condensational potential energy. With an account for the eye rotation energy and the decrease of angular momentum towards the hurricane center it is shown that the theoretical profiles of pressure and velocity agree well with observations for intense hurricanes. The previous order of magnitude estimates obtained in pole approximation are confirmed.

  14. Radial profiles of velocity and pressure for condensation-induced hurricanes

    Science.gov (United States)

    Makarieva, A. M.; Gorshkov, V. G.

    2011-02-01

    The Bernoulli integral in the form of an algebraic equation is obtained for the hurricane air flow as the sum of the kinetic energy of wind and the condensational potential energy. With an account for the eye rotation energy and the decrease of angular momentum towards the hurricane center it is shown that the theoretical profiles of pressure and velocity agree well with observations for intense hurricanes. The previous order of magnitude estimates obtained in pole approximation are confirmed.

  15. Radial profiles of velocity and pressure for condensation-induced hurricanes

    Energy Technology Data Exchange (ETDEWEB)

    Makarieva, A.M., E-mail: ammakarieva@gmail.co [Theoretical Physics Division, Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg (Russian Federation); Gorshkov, V.G. [Theoretical Physics Division, Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg (Russian Federation)

    2011-02-14

    The Bernoulli integral in the form of an algebraic equation is obtained for the hurricane air flow as the sum of the kinetic energy of wind and the condensational potential energy. With an account for the eye rotation energy and the decrease of angular momentum towards the hurricane center it is shown that the theoretical profiles of pressure and velocity agree well with observations for intense hurricanes. The previous order of magnitude estimates obtained in pole approximation are confirmed.

  16. The orthogonal gradients method: A radial basis functions method for solving partial differential equations on arbitrary surfaces

    KAUST Repository

    Piret, Cécile

    2012-05-01

    Much work has been done on reconstructing arbitrary surfaces using the radial basis function (RBF) method, but one can hardly find any work done on the use of RBFs to solve partial differential equations (PDEs) on arbitrary surfaces. In this paper, we investigate methods to solve PDEs on arbitrary stationary surfaces embedded in . R3 using the RBF method. We present three RBF-based methods that easily discretize surface differential operators. We take advantage of the meshfree character of RBFs, which give us a high accuracy and the flexibility to represent the most complex geometries in any dimension. Two out of the three methods, which we call the orthogonal gradients (OGr) methods are the result of our work and are hereby presented for the first time. © 2012 Elsevier Inc.

  17. Sudden Intensity Increases and Radial Gradient Changes of Cosmic Ray Mev Electrons and Protons Observed at Voyager 1 Beyond 111 AU in the Heliosheath

    Science.gov (United States)

    Webber, W. R.; Mcdonald, F. B.; Cummings, A. C.; Stone, E. C.; Heikkila, B.; Lal, N.

    2012-01-01

    Voyager 1 has entered regions of different propagation conditions for energetic cosmic rays in the outer heliosheathat a distance of about 111 AU from the Sun. The low energy 614 MeV galactic electron intensity increased by 20over a time period 10 days and the electron radial intensity gradient abruptly decreased from 19AU to 8AU at2009.7 at a radial distance of 111.2 AU. At about 2011.2 at a distance of 116.6 AU a second abrupt intensity increase of25 was observed for electrons. After the second sudden electron increase the radial intensity gradient increased to18AU. This large positive gradient and the 13 day periodic variations of 200 MeV particles observed near theend of 2011 indicate that V1 is still within the overall heliospheric modulating region. The implications of these resultsregarding the proximity of the heliopause are discussed.

  18. A new phase coding method using a slice selection gradient for high speed flow velocity meaurements in NMR tomography

    International Nuclear Information System (INIS)

    Oh, C.H.; Cho, Z.H.; California Univ., Irvine

    1986-01-01

    A new phase coding method using a selection gradient for high speed NMR flow velocity measurements is introduced and discussed. To establish a phase-velocity relationship of flow under the slice selection gradient and spin-echo RF pulse, the Bloch equation was numerically solved under the assumption that only one directional flow exists, i.e. in the direction of slice selection. Details of the numerical solution of the Bloch equation and techniques related to the numerical computations are also given. Finally, using the numerical calculation, high speed flow velocity measurement was attempted and found to be in good agreement with other complementary controlled measurements. (author)

  19. Self-calibrated multiple-echo acquisition with radial trajectories using the conjugate gradient method (SMART-CG).

    Science.gov (United States)

    Jung, Youngkyoo; Samsonov, Alexey A; Bydder, Mark; Block, Walter F

    2011-04-01

    To remove phase inconsistencies between multiple echoes, an algorithm using a radial acquisition to provide inherent phase and magnitude information for self correction was developed. The information also allows simultaneous support for parallel imaging for multiple coil acquisitions. Without a separate field map acquisition, a phase estimate from each echo in multiple echo train was generated. When using a multiple channel coil, magnitude and phase estimates from each echo provide in vivo coil sensitivities. An algorithm based on the conjugate gradient method uses these estimates to simultaneously remove phase inconsistencies between echoes, and in the case of multiple coil acquisition, simultaneously provides parallel imaging benefits. The algorithm is demonstrated on single channel, multiple channel, and undersampled data. Substantial image quality improvements were demonstrated. Signal dropouts were completely removed and undersampling artifacts were well suppressed. The suggested algorithm is able to remove phase cancellation and undersampling artifacts simultaneously and to improve image quality of multiecho radial imaging, the important technique for fast three-dimensional MRI data acquisition. Copyright © 2011 Wiley-Liss, Inc.

  20. Free-breathing contrast-enhanced T1-weighted gradient-echo imaging with radial k-space sampling for paediatric abdominopelvic MRI

    Energy Technology Data Exchange (ETDEWEB)

    Chandarana, Hersh; Block, Kai T.; Winfeld, Matthew J.; Lala, Shailee V.; Mazori, Daniel; Giuffrida, Emalyn; Babb, James S.; Milla, Sarah S. [New York University Langone Medical Center, Department of Radiology, New York, NY (United States)

    2014-02-15

    To compare the image quality of contrast-enhanced abdominopelvic 3D fat-suppressed T1-weighted gradient-echo imaging with radial and conventional Cartesian k-space acquisition schemes in paediatric patients. Seventy-three consecutive paediatric patients were imaged at 1.5 T with sequential contrast-enhanced T1-weighted Cartesian (VIBE) and radial gradient echo (GRE) acquisition schemes with matching parameters when possible. Cartesian VIBE was acquired as a breath-hold or as free breathing in patients who could not suspend respiration, followed by free-breathing radial GRE in all patients. Two paediatric radiologists blinded to the acquisition schemes evaluated multiple parameters of image quality on a five-point scale, with higher score indicating a more optimal examination. Lesion presence or absence, conspicuity and edge sharpness were also evaluated. Mixed-model analysis of variance was performed to compare radial GRE and Cartesian VIBE. Radial GRE had significantly (all P < 0.001) higher scores for overall image quality, hepatic edge sharpness, hepatic vessel clarity and respiratory motion robustness than Cartesian VIBE. More lesions were detected on radial GRE by both readers than on Cartesian VIBE, with significantly higher scores for lesion conspicuity and edge sharpness (all P < 0.001). Radial GRE has better image quality and lesion conspicuity than conventional Cartesian VIBE in paediatric patients undergoing contrast-enhanced abdominopelvic MRI. (orig.)

  1. The photometric and radial velocity variations of the central star of the planetary nebula 1C 418

    International Nuclear Information System (INIS)

    Mendez, R.H.; Verga, A.D.; Kriner, A.

    1983-01-01

    This paper brings spectrographic (1979-82) and photometric (January 1983) observations of the central star of the planetary nebula IC 418. We include an improved description of the stellar spectrum. We have found a variable photospheric velocity field, which would imply a fluctuating mass outflow, probably mixed with orbital motion in a close binary system with a period of about 0.2 days. We have also found light variations, on a time scale of one or two hours, with an amplitude of 0.1 mag, which do not appear to be periodic. Our observations are not yet sufficient to rule out definetely the existence of non-radial pulsations; further observations are suggested. (author)

  2. Predicted space motions for hypervelocity and runaway stars: proper motions and radial velocities for the Gaia Era

    Energy Technology Data Exchange (ETDEWEB)

    Kenyon, Scott J.; Brown, Warren R.; Geller, Margaret J. [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Bromley, Benjamin C., E-mail: skenyon@cfa.harvard.edu, E-mail: wbrown@cfa.harvard.edu, E-mail: mgeller@cfa.harvard.edu, E-mail: bromley@physics.utah.edu [Department of Physics, University of Utah, 115 S 1400 E, Rm 201, Salt Lake City, UT 84112 (United States)

    2014-10-01

    We predict the distinctive three-dimensional space motions of hypervelocity stars (HVSs) and runaway stars moving in a realistic Galactic potential. For nearby stars with distances less than 10 kpc, unbound stars are rare; proper motions alone rarely isolate bound HVSs and runaways from indigenous halo stars. At large distances of 20-100 kpc, unbound HVSs are much more common than runaways; radial velocities easily distinguish both from indigenous halo stars. Comparisons of the predictions with existing observations are encouraging. Although the models fail to match observations of solar-type HVS candidates from SEGUE, they agree well with data for B-type HVS and runaways from other surveys. Complete samples of g ≲ 20 stars with Gaia should provide clear tests of formation models for HVSs and runaways and will enable accurate probes of the shape of the Galactic potential.

  3. “MODAL NOISE” IN SINGLE-MODE FIBERS: A CAUTIONARY NOTE FOR HIGH PRECISION RADIAL VELOCITY INSTRUMENTS

    Energy Technology Data Exchange (ETDEWEB)

    Halverson, Samuel; Roy, Arpita; Mahadevan, Suvrath [Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States); Schwab, Christian, E-mail: shalverson@psu.edu [Macquarie University, Sydney, NSW 2109 (Australia)

    2015-12-01

    Exploring the use of single-mode fibers (SMFs) in high precision Doppler spectrometers has become increasingly attractive since the advent of diffraction-limited adaptive optics systems on large-aperture telescopes. Spectrometers fed with these fibers can be made significantly smaller than typical “seeing-limited” instruments, greatly reducing cost and overall complexity. Importantly, classical mode interference and speckle issues associated with multi-mode fibers, also known as “modal noise,” are mitigated when using SMFs, which also provide perfect radial and azimuthal image scrambling. However, SMFs do support multiple polarization modes, an issue that is generally ignored for larger-core fibers given the large number of propagation modes. Since diffraction gratings used in most high resolution astronomical instruments have dispersive properties that are sensitive to incident polarization changes, any birefringence variations in the fiber can cause variations in the efficiency profile, degrading illumination stability. Here we present a cautionary note outlining how the polarization properties of SMFs can affect the radial velocity (RV) measurement precision of high resolution spectrographs. This work is immediately relevant to the rapidly expanding field of diffraction-limited, extreme precision RV spectrographs that are currently being designed and built by a number of groups.

  4. Correlated Radial Velocity and X-Ray Variations in HD 154791/4U 1700+24

    Science.gov (United States)

    Galloway, Duncan K.; Sokoloski, J. L.; Kenyon, Scott J.

    2002-12-01

    We present evidence for approximately 400 day variations in the radial velocity of HD 154791 (V934 Her), the suggested optical counterpart of 4U 1700+24. The variations are correlated with the previously reported ~400 day variations in the X-ray flux of 4U 1700+24, which supports the association of these two objects, as well as the identification of this system as the second known X-ray binary in which a neutron star accretes from the wind of a red giant. The HD 154791 radial velocity variations can be fitted with an eccentric orbit with period 404+/-3 days, amplitude K=0.75+/-0.12kms-1, and eccentricity e=0.26+/-0.15. There are also indications of variations on longer timescales >~2000 days. We have reexamined all available All-Sky Monitor (ASM) data following an unusually large X-ray outburst in 1997-1998 and confirm that the 1 day averaged 2-10 keV X-ray flux from 4U 1700+24 is modulated with a period of 400+/-20 days. The mean profile of the persistent X-ray variations was approximately sinusoidal, with an amplitude of 0.108+/-0.012 ASM counts s-1 (corresponding to 31% rms). The epoch of X-ray maximum was approximately 40 days after the time of periastron, according to the eccentric orbital fit. If the 400 day oscillations from HD 154791/4U 1700+24 are due to orbital motion, then the system parameters are probably close to those of the only other neutron star symbiotic-like binary, GX 1+4. We discuss the similarities and differences between these two systems.

  5. RADIAL VELOCITY PLANETS DE-ALIASED: A NEW, SHORT PERIOD FOR SUPER-EARTH 55 Cnc e

    International Nuclear Information System (INIS)

    Dawson, Rebekah I.; Fabrycky, Daniel C.

    2010-01-01

    Radial velocity measurements of stellar reflex motion have revealed many extrasolar planets, but gaps in the observations produce aliases, spurious frequencies that are frequently confused with the planets' orbital frequencies. In the case of Gl 581 d, the distinction between an alias and the true frequency was the distinction between a frozen, dead planet and a planet possibly hospitable to life. To improve the characterization of planetary systems, we describe how aliases originate and present a new approach for distinguishing between orbital frequencies and their aliases. Our approach harnesses features in the spectral window function to compare the amplitude and phase of predicted aliases with peaks present in the data. We apply it to confirm prior alias distinctions for the planets GJ 876 d and HD 75898 b. We find that the true periods of Gl 581 d and HD 73526 b/c remain ambiguous. We revise the periods of HD 156668 b and 55 Cnc e, which were afflicted by daily aliases. For HD 156668 b, the correct period is 1.2699 days and the minimum mass is (3.1 ± 0.4) M + . For 55 Cnc e, the correct period is 0.7365 days-the shortest of any known planet-and the minimum mass is (8.3 ± 0.3) M + . This revision produces a significantly improved five-planet Keplerian fit for 55 Cnc, and a self-consistent dynamical fit describes the data just as well. As radial velocity techniques push to ever-smaller planets, often found in systems of multiple planets, distinguishing true periods from aliases will become increasingly important.

  6. Alignment of stress, mean wind, and vertical gradient of the velocity vector

    DEFF Research Database (Denmark)

    Berg, Jacob; Mann, Jakob; Patton, E.G.

    2012-01-01

    In many applications in the atmospheric surface layer the turbulent-viscosity hypothesis is applied, i.e. the stress vector can be described through the vertical gradient of velocity. In the atmospheric surface layer, where the Coriolis force and baroclinic effects are considered negligible......, this is supposedly a good approximation. High resolution large-eddy simulation (LES) data show that it is indeed the case. Through analysis of WindCube lidar measurements accompanied by sonic measurements we show that this is, on the other hand, rarely the case in the real atmosphere. This might indicate that large...... of atmospheric boundary layer modeling. The measurements are from the Danish wind turbine test sites at Høvsøre. With theWindCube lidar we are able to reach heights of 250 meters and hence capture the entire atmospheric surface layer both in terms of wind speed and the direction of the mean stress vector....

  7. IN-SYNC VI. Identification and Radial Velocity Extraction for 100+ Double-Lined Spectroscopic Binaries in the APOGEE/IN-SYNC Fields

    Science.gov (United States)

    Fernandez, M. A.; Covey, Kevin R.; De Lee, Nathan; Chojnowski, S. Drew; Nidever, David; Ballantyne, Richard; Cottaar, Michiel; Da Rio, Nicola; Foster, Jonathan B.; Majewski, Steven R.; Meyer, Michael R.; Reyna, A. M.; Roberts, G. W.; Skinner, Jacob; Stassun, Keivan; Tan, Jonathan C.; Troup, Nicholas; Zasowski, Gail

    2017-08-01

    We present radial velocity measurements for 70 high confidence, and 34 potential binary systems in fields containing the Perseus Molecular Cloud, Pleiades, NGC 2264, and the Orion A star-forming region. Eighteen of these systems have been previously identified as binaries in the literature. Candidate double-lined spectroscopic binaries (SB2s) are identified by analyzing the cross-correlation functions (CCFs) computed during the reduction of each APOGEE spectrum. We identify sources whose CCFs are well fit as the sum of two Lorentzians as likely binaries, and provide an initial characterization of the system based on the radial velocities indicated by that dual fit. For systems observed over several epochs, we present mass ratios and systemic velocities; for two systems with observations on eight or more epochs, and which meet our criteria for robust orbital coverage, we derive initial orbital parameters. The distribution of mass ratios for multi-epoch sources in our sample peaks at q = 1, but with a significant tail toward lower q values. Tables reporting radial velocities, systemic velocities, and mass ratios are provided online. We discuss future improvements to the radial velocity extraction method we employ, as well as limitations imposed by the number of epochs currently available in the APOGEE database. The Appendix contains brief notes from the literature on each system in the sample, and more extensive notes for select sources of interest.

  8. Rotational and radial velocities of 1.3-2.2 M {sub ☉} red giants in open clusters

    Energy Technology Data Exchange (ETDEWEB)

    Carlberg, Joleen K., E-mail: jcarlberg@dtm.ciw.edu [Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015 (United States)

    2014-06-01

    This study presents the rotational distribution of red giant (RG) stars in 11 old to intermediate age open clusters. The masses of these stars are all above the Kraft break, so they lose negligible amounts of their birth angular momentum (AM) during the main-sequence (MS) evolution. However, they do span a mass range with quite different AM distributions imparted during formation, with the stars less massive than ∼1.6M {sub ☉} arriving on the MS with lower rotation rates than the more massive stars. The majority of RGs in this study are slow rotators across the entire red giant branch regardless of mass, supporting the picture that intermediate-mass stars rapidly spin down when they evolve off the MS and develop convection zones capable of driving a magnetic dynamo. Nevertheless, a small fraction of RGs in open clusters show some level of enhanced rotation, and faster rotators are as common in these clusters as in the field RG population. Most of these enhanced rotators appear to be red clump stars, which is also true of the underlying stellar sample, while others are clearly RGs that are above or below the clump. In addition to rotational velocities, the radial velocities (RVs) and membership probabilities of individual stars are also presented. Cluster heliocentric RVs for NGC 6005 and Pismis 18 are reported for the first time.

  9. The Role of the Velocity Gradient in Laminar Convective Heat Transfer through a Tube with a Uniform Wall Heat Flux

    Science.gov (United States)

    Wang, Liang-Bi; Zhang, Qiang; Li, Xiao-Xia

    2009-01-01

    This paper aims to contribute to a better understanding of convective heat transfer. For this purpose, the reason why thermal diffusivity should be placed before the Laplacian operator of the heat flux, and the role of the velocity gradient in convective heat transfer are analysed. The background to these analyses is that, when the energy…

  10. Vorticity and helicity decompositions and dynamics with real Schur form of the velocity gradient

    Science.gov (United States)

    Zhu, Jian-Zhou

    2018-03-01

    The real Schur form (RSF) of a generic velocity gradient field ∇u is exploited to expose the structures of flows, in particular, our field decomposition resulting in two vorticities with only mutual linkage as the topological content of the global helicity (accordingly decomposed into two equal parts). The local transformation to the RSF may indicate alternative (co)rotating frame(s) for specifying the objective argument(s) of the constitutive equation. When ∇u is uniformly of RSF in a fixed Cartesian coordinate frame, i.e., ux = ux(x, y) and uy = uy(x, y), but uz = uz(x, y, z), the model, with the decomposed vorticities both frozen-in to u, is for two-component-two-dimensional-coupled-with-one-component-three-dimensional flows in between two-dimensional-three-component (2D3C) and fully three-dimensional-three-component ones and may help curing the pathology in the helical 2D3C absolute equilibrium, making the latter effectively work in more realistic situations.

  11. SEVEN NEW BINARIES DISCOVERED IN THE KEPLER LIGHT CURVES THROUGH THE BEER METHOD CONFIRMED BY RADIAL-VELOCITY OBSERVATIONS

    International Nuclear Information System (INIS)

    Faigler, S.; Mazeh, T.; Tal-Or, L.; Quinn, S. N.; Latham, D. W.

    2012-01-01

    We present seven newly discovered non-eclipsing short-period binary systems with low-mass companions, identified by the recently introduced BEER algorithm, applied to the publicly available 138-day photometric light curves obtained by the Kepler mission. The detection is based on the beaming effect (sometimes called Doppler boosting), which increases (decreases) the brightness of any light source approaching (receding from) the observer, enabling a prediction of the stellar Doppler radial-velocity (RV) modulation from its precise photometry. The BEER algorithm identifies the BEaming periodic modulation, with a combination of the well-known Ellipsoidal and Reflection/heating periodic effects, induced by short-period companions. The seven detections were confirmed by spectroscopic RV follow-up observations, indicating minimum secondary masses in the range 0.07-0.4 M ☉ . The binaries discovered establish for the first time the feasibility of the BEER algorithm as a new detection method for short-period non-eclipsing binaries, with the potential to detect in the near future non-transiting brown-dwarf secondaries, or even massive planets.

  12. Optical and Near-infrared Radial Velocity Content of M Dwarfs: Testing Models with Barnard’s Star

    Science.gov (United States)

    Artigau, Étienne; Malo, Lison; Doyon, René; Figueira, Pedro; Delfosse, Xavier; Astudillo-Defru, Nicola

    2018-05-01

    High-precision radial velocity (RV) measurements have been central in the study of exoplanets during the last two decades, from the early discovery of hot Jupiters, to the recent mass measurements of Earth-sized planets uncovered by transit surveys. While optical RV is now a mature field, there is currently a strong effort to push the technique into the near-infrared domain (chiefly Y, J, H, and K bandpasses) to probe planetary systems around late-type stars. The combined lower mass and luminosity of M dwarfs leads to an increased reflex RV signal for planets in the habitable zone compared to Sun-like stars. The estimates on the detectability of planets rely on various instrumental characteristics but also on a prior knowledge of the stellar spectrum. While the overall properties of M dwarf spectra have been extensively tested against observations, the same is not true for their detailed line profiles, which leads to significant uncertainties when converting a given signal-to-noise ratio to a corresponding RV precision as attainable on a given spectrograph. By combining archival CRIRES and HARPS data with ESPaDOnS data of Barnard’s star, we show that state-of-the-art atmosphere models over-predict the Y- and J-band RV content by more than a factor of ∼2, while under-predicting the H- and K-band content by half.

  13. A laser frequency comb that enables radial velocity measurements with a precision of 1 cm s(-1).

    Science.gov (United States)

    Li, Chih-Hao; Benedick, Andrew J; Fendel, Peter; Glenday, Alexander G; Kärtner, Franz X; Phillips, David F; Sasselov, Dimitar; Szentgyorgyi, Andrew; Walsworth, Ronald L

    2008-04-03

    Searches for extrasolar planets using the periodic Doppler shift of stellar spectral lines have recently achieved a precision of 60 cm s(-1) (ref. 1), which is sufficient to find a 5-Earth-mass planet in a Mercury-like orbit around a Sun-like star. To find a 1-Earth-mass planet in an Earth-like orbit, a precision of approximately 5 cm s(-1) is necessary. The combination of a laser frequency comb with a Fabry-Pérot filtering cavity has been suggested as a promising approach to achieve such Doppler shift resolution via improved spectrograph wavelength calibration, with recent encouraging results. Here we report the fabrication of such a filtered laser comb with up to 40-GHz (approximately 1-A) line spacing, generated from a 1-GHz repetition-rate source, without compromising long-term stability, reproducibility or spectral resolution. This wide-line-spacing comb, or 'astro-comb', is well matched to the resolving power of high-resolution astrophysical spectrographs. The astro-comb should allow a precision as high as 1 cm s(-1) in astronomical radial velocity measurements.

  14. THE MASS OF HD 38529c FROM HUBBLE SPACE TELESCOPE ASTROMETRY AND HIGH-PRECISION RADIAL VELOCITIES

    International Nuclear Information System (INIS)

    Benedict, G. Fritz; McArthur, Barbara E.; Bean, Jacob L.; Barnes, Rory; Harrison, Thomas E.; Hatzes, Artie; Martioli, Eder; Nelan, Edmund P.

    2010-01-01

    Hubble Space Telescope Fine Guidance Sensor astrometric observations of the G4 IV star HD 38529 are combined with the results of the analysis of extensive ground-based radial velocity (RV) data to determine the mass of the outermost of two previously known companions. Our new RVs obtained with the Hobby-Eberly Telescope and velocities from the Carnegie-California group now span over 11 yr. With these data we obtain improved RV orbital elements for both the inner companion, HD 38529b, and the outer companion, HD 38529c. We identify a rotational period of HD 38529 (P rot = 31.65 ± 0fd17) with Fine Guidance Sensor photometry. The inferred star spot fraction is consistent with the remaining scatter in velocities being caused by spot-related stellar activity. We then model the combined astrometric and RV measurements to obtain the parallax, proper motion, perturbation period, perturbation inclination, and perturbation size due to HD 38529c. For HD 38529c we find P = 2136.1 ± 0.3 d, perturbation semimajor axis α = 1.05 ± 0.06 mas, and inclination i = 48. 0 3 ± 3. 0 7. Assuming a primary mass M * = 1.48 M sun , we obtain a companion mass M c = 17.6 +1.5 -1.2 M Jup , 3σ above a 13 M Jup deuterium burning, brown dwarf lower limit. Dynamical simulations incorporating this accurate mass for HD 38529c indicate that a near-Saturn mass planet could exist between the two known companions. We find weak evidence of an additional low amplitude signal that can be modeled as a planetary-mass (∼0.17 M Jup ) companion at P ∼194 days. Including this component in our modeling lowers the error of the mass determined for HD 38529c. Additional observations (RVs and/or Gaia astrometry) are required to validate an interpretation of HD 38529d as a planetary-mass companion. If confirmed, the resulting HD 38529 planetary system may be an example of a 'Packed Planetary System'.

  15. The 2011 Tohoku-oki Earthquake related to a large velocity gradient within the Pacific plate

    Science.gov (United States)

    Matsubara, Makoto; Obara, Kazushige

    2015-04-01

    rays from the hypocenter around the coseismic region of the Tohoku-oki earthquake take off downward and pass through the Pacific plate. The landward low-V zone with a large anomaly corresponds to the western edge of the coseismic slip zone of the 2011 Tohoku-oki earthquake. The initial break point (hypocenter) is associated with the edge of a slightly low-V and low-Vp/Vs zone corresponding to the boundary of the low- and high-V zone. The trenchward low-V and low-Vp/Vs zone extending southwestward from the hypocenter may indicate the existence of a subducted seamount. The high-V zone and low-Vp/Vs zone might have accumulated the strain and resulted in the huge coseismic slip zone of the 2011 Tohoku earthquake. The low-V and low-Vp/Vs zone is a slight fluctuation within the high-V zone and might have acted as the initial break point of the 2011 Tohoku earthquake. Reference Matsubara, M. and K. Obara (2011) The 2011 Off the Pacific Coast of Tohoku earthquake related to a strong velocity gradient with the Pacific plate, Earth Planets Space, 63, 663-667. Okada, Y., K. Kasahara, S. Hori, K. Obara, S. Sekiguchi, H. Fujiwara, and A. Yamamoto (2004) Recent progress of seismic observation networks in Japan-Hi-net, F-net, K-NET and KiK-net, Research News Earth Planets Space, 56, xv-xxviii.

  16. Radial Velocity Fiber-Fed Spectrographs Towards the Discovery of Compact Planets and Pulsations on M Stars

    Science.gov (United States)

    Berdiñas, Zaira M.

    2016-11-01

    This thesis is developed in the framework of the paradigm that seeks for the discovery of an Earth analog. Nowadays, low mass stars, and in particular M dwarf stars, are key targets towards achieving this goal. In this thesis, I focus on the study of the short-time domain of M dwarf stars with the aim of searching for short period planets, but also for the first detection of stellar pulsations on this spectral type. Both science goals are the primary objectives of the “Cool Tiny Beats” (CTB) survey, which has produced most of the data used in this thesis. CTB data consist in high resolution and high-cadence spectroscopic Doppler measurements taken either with HARPS or HARPS-N spectrographs. First of all, a thorough understanding of the spectrographs response in the short time domain was performed to characterize the sources of noise in our range of study. Our first approach to the goals of this thesis consisted in the design of an observational experiment to delve into the HARPS-N sub-night performance. Results unveiled variability of the spectra continuum correlated with instabilities of the spectrograph illumination associated to the airmass. Such distortions, which are wavelength and time dependent, are also present in at least one of the data-products given by the HARPS-N reduction software: the width of the mean-line profiles (i.e. the so-called FWHM index), an index commonly used as a proxy of the stellar activity. As a consequence, we searched for an alternative approach to measure the width index. In particular, we calculated the mean-line profile of the spectrum with a least-squares-deconvolution technique and we obtained the profile indices as the moments of the profile distribution. As part of this study, we also corroborated that the radial velocities calculated with our template matching algorithm TERRA are not affected by the illumination stability. This work unveiled a possible failure of the HARPS-N atmospheric dispersion corrector (or ADC) and

  17. SOAP 2.0: a tool to estimate the photometric and radial velocity variations induced by stellar spots and plages

    International Nuclear Information System (INIS)

    Dumusque, X.; Boisse, I.; Santos, N. C.

    2014-01-01

    This paper presents SOAP 2.0, a new version of the Spot Oscillation And Planet (SOAP) code that estimates in a simple way the photometric and radial velocity (RV) variations induced by active regions. The inhibition of the convective blueshift (CB) inside active regions is considered, as well as the limb brightening effect of plages, a quadratic limb darkening law, and a realistic spot and plage contrast ratio. SOAP 2.0 shows that the activity-induced variation of plages is dominated by the inhibition of the CB effect. For spots, this effect becomes significant only for slow rotators. In addition, in the case of a major active region dominating the activity-induced signal, the ratio between the FWHM and the RV peak-to-peak amplitudes of the cross correlation function can be used to infer the type of active region responsible for the signal for stars with v sin i ≤8 km s –1 . A ratio smaller than three implies a spot, while a larger ratio implies a plage. Using the observation of HD 189733, we show that SOAP 2.0 manages to reproduce the activity variation as well as previous simulations when a spot is dominating the activity-induced variation. In addition, SOAP 2.0 also reproduces the activity variation induced by a plage on the slowly rotating star α Cen B, which is not possible using previous simulations. Following these results, SOAP 2.0 can be used to estimate the signal induced by spots and plages, but also to correct for it when a major active region is dominating the RV variation.

  18. New Insights on Planet Formation in WASP-47 from a Simultaneous Analysis of Radial Velocities and Transit Timing Variations

    Science.gov (United States)

    Weiss, Lauren M.; Deck, Katherine M.; Sinukoff, Evan; Petigura, Erik A.; Agol, Eric; Lee, Eve J.; Becker, Juliette C.; Howard, Andrew W.; Isaacson, Howard; Crossfield, Ian J. M.; Fulton, Benjamin J.; Hirsch, Lea; Benneke, Björn

    2017-06-01

    Measuring precise planet masses, densities, and orbital dynamics in individual planetary systems is an important pathway toward understanding planet formation. The WASP-47 system has an unusual architecture that motivates a complex formation theory. The system includes a hot Jupiter (“b”) neighbored by interior (“e”) and exterior (“d”) sub-Neptunes, and a long-period eccentric giant planet (“c”). We simultaneously modeled transit times from the Kepler K2 mission and 118 radial velocities to determine the precise masses, densities, and Keplerian orbital elements of the WASP-47 planets. Combining RVs and TTVs provides a better estimate of the mass of planet d (13.6+/- 2.0 {M}\\oplus ) than that obtained with only RVs (12.75+/- 2.70 {M}\\oplus ) or TTVs (16.1+/- 3.8 {M}\\oplus ). Planets e and d have high densities for their size, consistent with a history of photoevaporation and/or formation in a volatile-poor environment. Through our RV and TTV analysis, we find that the planetary orbits have eccentricities similar to the solar system planets. The WASP-47 system has three similarities to our own solar system: (1) the planetary orbits are nearly circular and coplanar, (2) the planets are not trapped in mean motion resonances, and (3) the planets have diverse compositions. None of the current single-process exoplanet formation theories adequately reproduce these three characteristics of the WASP-47 system (or our solar system). We propose that WASP-47, like the solar system, formed in two stages: first, the giant planets formed in a gas-rich disk and migrated to their present locations, and second, the high-density sub-Neptunes formed in situ in a gas-poor environment.

  19. SOAP 2.0: A Tool to Estimate the Photometric and Radial Velocity Variations Induced by Stellar Spots and Plages

    Science.gov (United States)

    Dumusque, X.; Boisse, I.; Santos, N. C.

    2014-12-01

    This paper presents SOAP 2.0, a new version of the Spot Oscillation And Planet (SOAP) code that estimates in a simple way the photometric and radial velocity (RV) variations induced by active regions. The inhibition of the convective blueshift (CB) inside active regions is considered, as well as the limb brightening effect of plages, a quadratic limb darkening law, and a realistic spot and plage contrast ratio. SOAP 2.0 shows that the activity-induced variation of plages is dominated by the inhibition of the CB effect. For spots, this effect becomes significant only for slow rotators. In addition, in the case of a major active region dominating the activity-induced signal, the ratio between the FWHM and the RV peak-to-peak amplitudes of the cross correlation function can be used to infer the type of active region responsible for the signal for stars with v sin i SOAP 2.0 manages to reproduce the activity variation as well as previous simulations when a spot is dominating the activity-induced variation. In addition, SOAP 2.0 also reproduces the activity variation induced by a plage on the slowly rotating star α Cen B, which is not possible using previous simulations. Following these results, SOAP 2.0 can be used to estimate the signal induced by spots and plages, but also to correct for it when a major active region is dominating the RV variation. . The work in this paper is based on observations made with the MOST satellite, the HARPS instrument on the ESO 3.6 m telescope at La Silla Observatory (Chile), and the SOPHIE instrument at the Observatoire de Haute Provence (France).

  20. A RADIAL VELOCITY STUDY OF COMPOSITE-SPECTRA HOT SUBDWARF STARS WITH THE HOBBY-EBERLY TELESCOPE

    Energy Technology Data Exchange (ETDEWEB)

    Barlow, Brad N.; Wade, Richard A.; Liss, Sandra E. [Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States); Ostensen, Roy H.; Van Winckel, Hans [Instituut voor Sterrenkunde, K.U. Leuven, B-3001 Leuven (Belgium)

    2012-10-10

    Many hot subdwarf stars show composite spectral energy distributions indicative of cool main-sequence (MS) companions. Binary population synthesis (BPS) models demonstrate such systems can be formed via Roche lobe overflow or common envelope evolution but disagree on whether the resulting orbital periods will be long (years) or short (days). Few studies have been carried out to assess the orbital parameters of these spectroscopic composite binaries; current observations suggest the periods are long. To help address this problem, we selected 15 moderately bright (V {approx} 13) hot subdwarfs with F-K dwarf companions and monitored their radial velocities from 2005 January to 2008 July using the bench-mounted Medium Resolution Spectrograph on the Hobby-Eberly Telescope (HET). Here we describe the details of our observing, reduction, and analysis techniques, and present preliminary results for all targets. By combining the HET data with recent observations from the Mercator Telescope, we are able to calculate precise orbital solutions for three systems using more than six years of observations. We also present an up-to-date period histogram for all known hot subdwarf binaries, which suggests those with F-K MS companions tend to have orbital periods on the order of several years. Such long periods challenge the predictions of conventional BPS models, although a larger sample is needed for a thorough assessment of the models' predictive success. Lastly, one of our targets has an eccentric orbit, implying some composite-spectrum systems might have formerly been hierarchical triple systems, in which the inner binary merged to create the hot subdwarf.

  1. Bayesian analysis of radial velocity data of GJ667C with correlated noise: evidence for only two planets

    Science.gov (United States)

    Feroz, F.; Hobson, M. P.

    2014-02-01

    GJ667C is the least massive component of a triple star system which lies at a distance of about 6.8 pc (22.1 light-year) from the Earth. GJ667C has received much attention recently due to the claims that it hosts up to seven planets including three super-Earths inside the habitable zone. We present a Bayesian technique for the analysis of radial velocity (RV) data sets in the presence of correlated noise component (`red noise'), with unknown parameters. We also introduce hyper-parameters in our model in order to deal statistically with under- or overestimated error bars on measured RVs as well as inconsistencies between different data sets. By applying this method to the RV data set of GJ667C, we show that this data set contains a significant correlated (red) noise component with correlation time-scale for HARPS data of the order of 9 d. Our analysis shows that the data only provide strong evidence for the presence of two planets: GJ667Cb and c with periods 7.19 and 28.13 d, respectively, with some hints towards the presence of a third signal with period 91 d. The planetary nature of this third signal is not clear and additional RV observations are required for its confirmation. Previous claims of the detection of additional planets in this system are due the erroneous assumption of white noise. Using the standard white noise assumption, our method leads to the detection of up to five signals in this system. We also find that with the red noise model, the measurement uncertainties from HARPS for this system are underestimated at the level of ˜50 per cent.

  2. SOAP 2.0: a tool to estimate the photometric and radial velocity variations induced by stellar spots and plages

    Energy Technology Data Exchange (ETDEWEB)

    Dumusque, X. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Boisse, I. [Laboratoire d' Astrophysique de Marseille (UMR 6110), Technopole de Château-Gombert, 38 rue Frédéric Joliot-Curie, F-13388 Marseille Cedex 13 (France); Santos, N. C., E-mail: xdumusque@cfa.harvard.edu [Centro de Astrofìsica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal)

    2014-12-01

    This paper presents SOAP 2.0, a new version of the Spot Oscillation And Planet (SOAP) code that estimates in a simple way the photometric and radial velocity (RV) variations induced by active regions. The inhibition of the convective blueshift (CB) inside active regions is considered, as well as the limb brightening effect of plages, a quadratic limb darkening law, and a realistic spot and plage contrast ratio. SOAP 2.0 shows that the activity-induced variation of plages is dominated by the inhibition of the CB effect. For spots, this effect becomes significant only for slow rotators. In addition, in the case of a major active region dominating the activity-induced signal, the ratio between the FWHM and the RV peak-to-peak amplitudes of the cross correlation function can be used to infer the type of active region responsible for the signal for stars with v sin i ≤8 km s{sup –1}. A ratio smaller than three implies a spot, while a larger ratio implies a plage. Using the observation of HD 189733, we show that SOAP 2.0 manages to reproduce the activity variation as well as previous simulations when a spot is dominating the activity-induced variation. In addition, SOAP 2.0 also reproduces the activity variation induced by a plage on the slowly rotating star α Cen B, which is not possible using previous simulations. Following these results, SOAP 2.0 can be used to estimate the signal induced by spots and plages, but also to correct for it when a major active region is dominating the RV variation.

  3. Radial velocity variations of photometrically quiet, chromospherically inactive Kepler stars: A link between RV jitter and photometric flicker

    Energy Technology Data Exchange (ETDEWEB)

    Bastien, Fabienne A.; Stassun, Keivan G.; Pepper, Joshua [Physics and Astronomy Department, Vanderbilt University, 1807 Station B, Nashville, TN 37235 (United States); Wright, Jason T. [Center for Exoplanets and Habitable Worlds, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA 16803 (United States); Aigrain, Suzanne [Sub-department of Astrophysics, Department of Physics, University of Oxford, Oxford OX1 3RH (United Kingdom); Basri, Gibor [Astronomy Department, University of California, Berkeley, CA 94720 (United States); Johnson, John A. [Department of Astrophysics, California Institute of Technology, MC 249-17, Pasadena, CA 91125 (United States); Howard, Andrew W. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Walkowicz, Lucianne M. [Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544 (United States)

    2014-02-01

    We compare stellar photometric variability, as measured from Kepler light curves by Basri et al., with measurements of radial velocity (RV) rms variations of all California Planet Search overlap stars. We newly derive rotation periods from the Kepler light curves for all of the stars in our study sample. The RV variations reported herein range from less than 4 to 135 m s{sup –1}, yet the stars all have amplitudes of photometric variability less than 3 mmag, reflecting the preference of the RV program for chromospherically 'quiet' stars. Despite the small size of our sample, we find with high statistical significance that the RV rms manifests strongly in the Fourier power spectrum of the light curve: stars that are noisier in RV have a greater number of frequency components in the light curve. We also find that spot models of the observed light curves systematically underpredict the observed RV variations by factors of ∼2-1000, likely because the low-level photometric variations in our sample are driven by processes not included in simple spot models. The stars best fit by these models tend to have simpler light curves, dominated by a single relatively high-amplitude component of variability. Finally, we demonstrate that the RV rms behavior of our sample can be explained in the context of the photometric variability evolutionary diagram introduced by Bastien et al. We use this diagram to derive the surface gravities of the stars in our sample, revealing many of them to have moved off the main sequence. More generally, we find that the stars with the largest RV rms are those that have evolved onto the 'flicker floor' sequence in that diagram, characterized by relatively low amplitude but highly complex photometric variations which grow as the stars evolve to become subgiants.

  4. Radial velocities of very low mass stars and candidate brown dwarf members of the Hyades and Pleiades, 2

    Science.gov (United States)

    Stauffer, John R.; Liebert, James; Giampapa, Mark

    1995-01-01

    We have determined H alpha equivalent widths and radial velocities with 1 sigma accuracies of approximately 5 km/s for approximately 20 candidate very low mass members of the Pleiades cluster and for a few proposed very low mass members of the Hyades. Most of the Pleiades targets were selected from the recent Hambly, Hawkins, and Jameson proper motion survey, where they were identified as probable Pleiades brown dwarfs with an age spread from 3 to 70 Myr. Our spectroscopic data and a reinterpretation of the photometric data confirm that these objects are indeed likely Pleiades members; however, we believe that they more likely have masses slightly above the hydrogen burning mass limit and that there is no firm evidence for an age spread amongst these stars. All of the very low mass Pleiades and Hyades members show H alpha in emission. However, the ratio of H alpha flux to biometric flux in the Pleiades shows a maximum near M(sub Bol) approximately equal to 9.5 (M approximately equal to 0.3 solar mass) and a sharp decrease to lower masses. This break occurs at the approximate mass where low mass stars are expected to become fully convective, and it is tempting to assume that the decrease in H alpha flux is caused by some change in the behavior of stellar dynamos at this mass. We do not see a similar break in activity at this mass in the Hyades. We discuss possible evolutionary explanations for this difference in the H alpha activity between the two clusters.

  5. Radial velocities and metallicities from infrared Ca ii triplet spectroscopy of open clusters. II. Berkeley 23, King 1, NGC 559, NGC 6603, and NGC 7245

    Science.gov (United States)

    Carrera, R.; Casamiquela, L.; Ospina, N.; Balaguer-Núñez, L.; Jordi, C.; Monteagudo, L.

    2015-06-01

    Context. Open clusters are key to studying the formation and evolution of the Galactic disc. However, there is a deficiency of radial velocity and chemical abundance determinations for open clusters in the literature. Aims: We intend to increase the number of determinations of radial velocities and metallicities from spectroscopy for open clusters. Methods: We acquired medium-resolution spectra (R ~ 8000) in the infrared region Ca ii triplet lines (~8500 Å) for several stars in five open clusters with the long-slit IDS spectrograph on the 2.5 m Isaac Newton Telescope (Roque de los Muchachos Observatory, Spain). Radial velocities were obtained by cross-correlation fitting techniques. The relationships available in the literature between the strength of infrared Ca ii lines and metallicity were also used to derive the metallicity for each cluster. Results: We obtain ⟨Vr⟩ = 48.6 ± 3.4, -58.4 ± 6.8, 26.0 ± 4.3, and -65.3 ± 3.2 km s-1 for Berkeley 23, NGC 559, NGC 6603, and NGC 7245, respectively. We found [ Fe/H ] = -0.25 ± 0.14 and -0.15 ± 0.18 for NGC 559 and NGC 7245, respectively. Berkeley 23 has low metallicity, [ Fe/H ] = -0.42 ± 0.13, which is similar to other open clusters in the outskirts of the Galactic disc. In contrast, we derived high metallicity ([ Fe/H ] = +0.43 ± 0.15) for NGC 6603, which places this system among the most metal-rich known open clusters. To our knowledge, this is the first determination of radial velocities and metallicities from spectroscopy for these clusters, except NGC 6603, for which radial velocities had been previously determined. We have also analysed ten stars in the line of sight to King 1. Because of the large dispersion obtained in both radial velocity and metallicity, we cannot be sure that we have sampled true cluster members. Based on observations made with the 2.5 m Isaac Newton Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the

  6. Peak negative myocardial velocity gradient in early diastole as a noninvasive indicator of left ventricular diastolic function: comparison with transmitral flow velocity indices.

    Science.gov (United States)

    Shimizu, Y; Uematsu, M; Shimizu, H; Nakamura, K; Yamagishi, M; Miyatake, K

    1998-11-01

    We sought to assess the clinical significance of peak negative myocardial velocity gradient (MVG) in early diastole as a noninvasive indicator of left ventricular (LV) diastolic function. Peak systolic MVG has been shown useful for the quantitative assessment of regional wall motion abnormalities, but limited data exist regarding the diastolic MVG as an indicator of LV diastolic function. Peak negative MVG was obtained from M-mode tissue Doppler imaging (TDI) in 43 subjects with or without impairment of systolic and diastolic performance: 12 normal subjects, 12 patients with hypertensive heart disease (HHD) with normal systolic performance and 19 patients with dilated cardiomyopathy (DCM), and was compared with standard Doppler transmitral flow velocity indices. In a subgroup of 30 patients, effects of preload increase on these indices were assessed by performing passive leg lifting. In an additional 11 patients with congestive heart failure at the initial examination, the measurements were repeated after 26+/-16 days of volume-reducing therapy. Peak negative MVG was significantly depressed both in HHD (-3.9+/-1.3/s, p indices failed to distinguish DCM from normal due to the pseudonormalization. Transmitral flow velocity indices were significantly altered (peak early/late diastolic filling velocity [E/A]=1.1+/-0.5 to 1.5+/-0.7, p indicator of LV diastolic function that is less affected by preload alterations than the transmitral flow velocity indices, and thereby could be used for the follow-up of patients with nonischemic LV dysfunction presenting congestive heart failure.

  7. Field estimates of floc dynamics and settling velocities in a tidal creek with significant along-channel gradients in velocity and SPM

    Science.gov (United States)

    Schwarz, C.; Cox, T.; van Engeland, T.; van Oevelen, D.; van Belzen, J.; van de Koppel, J.; Soetaert, K.; Bouma, T. J.; Meire, P.; Temmerman, S.

    2017-10-01

    A short-term intensive measurement campaign focused on flow, turbulence, suspended particle concentration, floc dynamics and settling velocities were carried out in a brackish intertidal creek draining into the main channel of the Scheldt estuary. We compare in situ estimates of settling velocities between a laser diffraction (LISST) and an acoustic Doppler technique (ADV) at 20 and 40 cm above bottom (cmab). The temporal variation in settling velocity estimated were compared over one tidal cycle, with a maximum flood velocity of 0.46 m s-1, a maximum horizontal ebb velocity of 0.35 m s-1 and a maximum water depth at high water slack of 2.41 m. Results suggest that flocculation processes play an important role in controlling sediment transport processes in the measured intertidal creek. During high-water slack, particles flocculated to sizes up to 190 μm, whereas at maximum flood and maximum ebb tidal stage floc sizes only reached up to 55 μm and 71 μm respectively. These large differences indicate that flocculation processes are mainly governed by turbulence-induced shear rate. In this study, we specifically recognize the importance of along-channel gradients that places constraints on the application of the acoustic Doppler technique due to conflicts with the underlying assumptions. Along-channel gradients were assessed by additional measurements at a second location and scaling arguments which could be used as an indication whether the Reynolds-flux method is applicable. We further show the potential impact of along-channel advection of flocs out of equilibrium with local hydrodynamics influencing overall floc sizes.

  8. Effect of ion orbit loss on the structure in the H-mode tokamak edge pedestal profiles of rotation velocity, radial electric field, density, and temperature

    International Nuclear Information System (INIS)

    Stacey, Weston M.

    2013-01-01

    An investigation of the effect of ion orbit loss of thermal ions and the compensating return ion current directly on the radial ion flux flowing in the plasma, and thereby indirectly on the toroidal and poloidal rotation velocity profiles, the radial electric field, density, and temperature profiles, and the interpretation of diffusive and non-diffusive transport coefficients in the plasma edge, is described. Illustrative calculations for a high-confinement H-mode DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] plasma are presented and compared with experimental results. Taking into account, ion orbit loss of thermal ions and the compensating return ion current is found to have a significant effect on the structure of the radial profiles of these quantities in the edge plasma, indicating the necessity of taking ion orbit loss effects into account in interpreting or predicting these quantities

  9. Comparative study of the temperature and velocity gradients for the interphases obtained during directional solidification of Al-Cu alloys

    International Nuclear Information System (INIS)

    Ares, Alicia Esther; Gueijman, Sergio Fabian; Schvezov, Carlos E

    2004-01-01

    Previous studies determined that in directionally solidified lead-tin alloys, the position in which the transition occurs from columnar to equiaxial structure depending on the distribution of temperatures in the system, occurs when a minimum and critical thermal gradient value is attained in the liquid before the interphase that separates the (liquid) phase from the (solid + liquid) phase and this critical gradient value is independent from the solute concentration, natural convection, degree of overheating, the mold geometry and the number of columnar and equiaxial grains that form. The study now includes aluminum-copper alloys, for which the temperature gradient test values in the liquid before the (liquid)/(solid + liquid) interphase and the speeds of the (liquid)/(solid+liquid)/(solid) interphases are determined. The values of interphase gradients and velocities contrast with the values predicted by the Hunt model for the same alloy system. The velocities of the interphases are also compared with those calculated with the Lipton equation and used in the Wang and Beckermann model for dendritic equiaxial growth. The results are compared with those obtained previously in the lead-tin system (CW)

  10. A peculiar distribution of radial velocities of faint radio-galaxies with 13.0<=msub(corr)<=15.5

    International Nuclear Information System (INIS)

    Karoji, H.; Nottale, L.; Vigier, J.-P.

    1976-01-01

    A sample of 41 radio-galaxies with 13.0<=msub(corr)<=15.5 has been analyzed to test the angular redshift anisotropy discovered on Sc I galaxies by Rubin, Rubin and Ford (1973). The sample does not present their anisotropy but contains an even more curious distribution of radial velocities which suggests that the Rubin-Ford effect results from an anomalous redshift of light when it travels through clusters of galaxies. (Auth.)

  11. The white dwarf binary pathways survey - II. Radial velocities of 1453 FGK stars with white dwarf companions from LAMOST DR 4

    Science.gov (United States)

    Rebassa-Mansergas, A.; Ren, J. J.; Irawati, P.; García-Berro, E.; Parsons, S. G.; Schreiber, M. R.; Gänsicke, B. T.; Rodríguez-Gil, P.; Liu, X.; Manser, C.; Nevado, S. P.; Jiménez-Ibarra, F.; Costero, R.; Echevarría, J.; Michel, R.; Zorotovic, M.; Hollands, M.; Han, Z.; Luo, A.; Villaver, E.; Kong, X.

    2017-12-01

    We present the second paper of a series of publications aiming at obtaining a better understanding regarding the nature of type Ia supernovae (SN Ia) progenitors by studying a large sample of detached F, G and K main-sequence stars in close orbits with white dwarf companions (i.e. WD+FGK binaries). We employ the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) data release 4 spectroscopic data base together with Galaxy Evolution Explorer (GALEX) ultraviolet fluxes to identify 1549 WD+FGK binary candidates (1057 of which are new), thus doubling the number of known sources. We measure the radial velocities of 1453 of these binaries from the available LAMOST spectra and/or from spectra obtained by us at a wide variety of different telescopes around the globe. The analysis of the radial velocity data allows us to identify 24 systems displaying more than 3σ radial velocity variation that we classify as close binaries. We also discuss the fraction of close binaries among WD+FGK systems, which we find to be ∼10 per cent, and demonstrate that high-resolution spectroscopy is required to efficiently identify double-degenerate SN Ia progenitor candidates.

  12. Reconstruction of Typhoon Structure Using 3-Dimensional Doppler Radar Radial Velocity Data with the Multigrid Analysis: A Case Study in an Idealized Simulation Context

    Directory of Open Access Journals (Sweden)

    Hongli Fu

    2016-01-01

    Full Text Available Extracting multiple-scale observational information is critical for accurately reconstructing the structure of mesoscale circulation systems such as typhoon. The Space and Time Mesoscale Analysis System (STMAS with multigrid data assimilation developed in Earth System Research Laboratory (ESRL in National Oceanic and Atmospheric Administration (NOAA has addressed this issue. Previous studies have shown the capability of STMAS to retrieve multiscale information in 2-dimensional Doppler radar radial velocity observations. This study explores the application of 3-dimensional (3D Doppler radar radial velocities with STMAS for reconstructing a 3D typhoon structure. As for the first step, here, we use an idealized simulation framework. A two-scale simulated “typhoon” field is constructed and referred to as “truth,” from which randomly distributed conventional wind data and 3D Doppler radar radial wind data are generated. These data are used to reconstruct the synthetic 3D “typhoon” structure by the STMAS and the traditional 3D variational (3D-Var analysis. The degree by which the “truth” 3D typhoon structure is recovered is an assessment of the impact of the data type or analysis scheme being evaluated. We also examine the effects of weak constraint and strong constraint on STMAS analyses. Results show that while the STMAS is superior to the traditional 3D-Var for reconstructing the 3D typhoon structure, the strong constraint STMAS can produce better analyses on both horizontal and vertical velocities.

  13. The TROY project: Searching for co-orbital bodies to known planets. I. Project goals and first results from archival radial velocity

    Science.gov (United States)

    Lillo-Box, J.; Barrado, D.; Figueira, P.; Leleu, A.; Santos, N. C.; Correia, A. C. M.; Robutel, P.; Faria, J. P.

    2018-01-01

    Context. The detection of Earth-like planets, exocomets or Kuiper belts show that the different components found in the solar system should also be present in other planetary systems. Trojans are one of these components and can be considered fossils of the first stages in the life of planetary systems. Their detection in extrasolar systems would open a new scientific window to investigate formation and migration processes. Aims: In this context, the main goal of the TROY project is to detect exotrojans for the first time and to measure their occurrence rate (η-Trojan). In this first paper, we describe the goals and methodology of the project. Additionally, we used archival radial velocity data of 46 planetary systems to place upper limits on the mass of possible trojans and investigate the presence of co-orbital planets down to several tens of Earth masses. Methods: We used archival radial velocity data of 46 close-in (P 1σ evidence for a mass imbalance between L4 and L5. Two of these systems provide >2σ detection, but no significant detection is found among our sample. We also report upper limits to the masses at L4/L5 in all studied systems and discuss the results in the context of previous findings. Radial velocity data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/609/A96

  14. THE POSTERIOR DISTRIBUTION OF sin(i) VALUES FOR EXOPLANETS WITH MT sin(i) DETERMINED FROM RADIAL VELOCITY DATA

    International Nuclear Information System (INIS)

    Ho, Shirley; Turner, Edwin L.

    2011-01-01

    Radial velocity (RV) observations of an exoplanet system giving a value of M T sin(i) condition (i.e., give information about) not only the planet's true mass M T but also the value of sin(i) for that system (where i is the orbital inclination angle). Thus, the value of sin(i) for a system with any particular observed value of M T sin(i) cannot be assumed to be drawn randomly from a distribution corresponding to an isotropic i distribution, i.e., the presumptive prior distribution. Rather, the posterior distribution from which it is drawn depends on the intrinsic distribution of M T for the exoplanet population being studied. We give a simple Bayesian derivation of this relationship and apply it to several 'toy models' for the intrinsic distribution of M T , on which we have significant information from available RV data in some mass ranges but little or none in others. The results show that the effect can be an important one. For example, even for simple power-law distributions of M T , the median value of sin(i) in an observed RV sample can vary between 0.860 and 0.023 (as compared to the 0.866 value for an isotropic i distribution) for indices of the power law in the range between -2 and +1, respectively. Over the same range of indices, the 95% confidence interval on M T varies from 1.0001-2.405 (α = -2) to 1.13-94.34 (α = +2) times larger than M T sin(i) due to sin(i) uncertainty alone. More complex, but still simple and plausible, distributions of M T yield more complicated and somewhat unintuitive posterior sin(i) distributions. In particular, if the M T distribution contains any characteristic mass scale M c , the posterior sin(i) distribution will depend on the ratio of M T sin(i) to M c , often in a non-trivial way. Our qualitative conclusion is that RV studies of exoplanets, both individual objects and statistical samples, should regard the sin(i) factor as more than a 'numerical constant of order unity' with simple and well-understood statistical

  15. Metal Abundances, Radial Velocities, and Other Physical Characteristics for the RR Lyrae Stars in The Kepler Field

    Science.gov (United States)

    Nemec, James M.; Cohen, Judith G.; Ripepi, Vincenzo; Derekas, Aliz; Moskalik, Pawel; Sesar, Branimir; Chadid, Merieme; Bruntt, Hans

    2013-08-01

    Spectroscopic iron-to-hydrogen ratios, radial velocities, atmospheric parameters, and new photometric analyses are presented for 41 RR Lyrae stars (and one probable high-amplitude δ Sct star) located in the field-of-view of the Kepler space telescope. Thirty-seven of the RR Lyrae stars are fundamental-mode pulsators (i.e., RRab stars) of which sixteen exhibit the Blazhko effect. Four of the stars are multiperiodic RRc pulsators oscillating primarily in the first-overtone mode. Spectroscopic [Fe/H] values for the 34 stars for which we were able to derive estimates range from -2.54 ± 0.13 (NR Lyr) to -0.05 ± 0.13 dex (V784 Cyg), and for the 19 Kepler-field non-Blazhko stars studied by Nemec et al. the abundances agree will with their photometric [Fe/H] values. Four non-Blazhko RR Lyrae stars that they identified as metal-rich (KIC 6100702, V2470 Cyg, V782 Cyg and V784 Cyg) are confirmed as such, and four additional stars (V839 Cyg, KIC 5520878, KIC 8832417, KIC 3868420) are also shown here to be metal-rich. Five of the non-Blazhko RRab stars are found to be more metal-rich than [Fe/H] ~-0.9 dex while all of the 16 Blazhko stars are more metal-poor than this value. New P-\\phi _31^s-[Fe/H] relationships are derived based on ~970 days of quasi-continuous high-precision Q0-Q11 long- and short-cadence Kepler photometry. With the exception of some Blazhko stars, the spectroscopic and photometric [Fe/H] values are in good agreement. Several stars with unique photometric characteristics are identified, including a Blazhko variable with the smallest known amplitude and frequency modulations (V838 Cyg). Based in part on observations made at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Keck Observatory was made possible by the generous financial support of the W.M. Keck Foundation. Also, based in part on

  16. Predictions of Planet Detections with Near-infrared Radial Velocities in the Upcoming SPIRou Legacy Survey-planet Search

    Science.gov (United States)

    Cloutier, Ryan; Artigau, Étienne; Delfosse, Xavier; Malo, Lison; Moutou, Claire; Doyon, René; Donati, Jean-Francois; Cumming, Andrew; Dumusque, Xavier; Hébrard, Élodie; Menou, Kristen

    2018-02-01

    The SPIRou near-infrared spectropolarimeter is destined to begin science operations at the Canada–France–Hawaii Telescope in mid-2018. One of the instrument’s primary science goals is to discover the closest exoplanets to the solar system by conducting a three- to five-year long radial velocity survey of nearby M dwarfs at an expected precision of ∼1 m s‑1, the SPIRou Legacy Survey-Planet Search (SLS-PS). In this study, we conduct a detailed Monte Carlo simulation of the SLS-PS using our current understanding of the occurrence rate of M dwarf planetary systems and physical models of stellar activity. From simultaneous modeling of planetary signals and activity, we predict the population of planets to be detected in the SLS-PS. With our fiducial survey strategy and expected instrument performance over a nominal survey length of ∼3 years, we expect SPIRou to detect {85.3}-12.4+29.3 planets including {20.0}-7.2+16.8 habitable-zone planets and {8.1}-3.2+7.6 Earth-like planets from a sample of 100 M1–M8.5 dwarfs out to 11 pc. By studying mid-to-late M dwarfs previously inaccessible to existing optical velocimeters, SPIRou will put meaningful constraints on the occurrence rate of planets around those stars including the value of {η }\\oplus at an expected level of precision of ≲ 45 % . We also predict that a subset of {46.7}-6.0+16.0 planets may be accessible with dedicated high-contrast imagers on the next generation of extremely large telescopes including {4.9}-2.0+4.7 potentially imagable Earth-like planets. Lastly, we compare the results of our fiducial survey strategy to other foreseeable survey versions to quantify which strategy is optimized to reach the SLS-PS science goals. The results of our simulations are made available to the community on GitHub (https://github.com/r-cloutier/SLSPS_Simulations).

  17. Velocity Gradient Across the San Andreas Fault and Changes in Slip Behavior as Outlined by Full non Linear Tomography

    Science.gov (United States)

    Chiarabba, C.; Giacomuzzi, G.; Piana Agostinetti, N.

    2017-12-01

    The San Andreas Fault (SAF) near Parkfield is the best known fault section which exhibit a clear transition in slip behavior from stable to unstable. Intensive monitoring and decades of studies permit to identify details of these processes with a good definition of fault structure and subsurface models. Tomographic models computed so far revealed the existence of large velocity contrasts, yielding physical insight on fault rheology. In this study, we applied a recently developed full non-linear tomography method to compute Vp and Vs models which focus on the section of the fault that exhibit fault slip transition. The new tomographic code allows not to impose a vertical seismic discontinuity at the fault position, as routinely done in linearized codes. Any lateral velocity contrast found is directly dictated by the data themselves and not imposed by subjective choices. The use of the same dataset of previous tomographic studies allows a proper comparison of results. We use a total of 861 earthquakes, 72 blasts and 82 shots and the overall arrival time dataset consists of 43948 P- and 29158 S-wave arrival times, accurately selected to take care of seismic anisotropy. Computed Vp and Vp/Vs models, which by-pass the main problems related to linarized LET algorithms, excellently match independent available constraints and show crustal heterogeneities with a high resolution. The high resolution obtained in the fault surroundings permits to infer lateral changes of Vp and Vp/Vs across the fault (velocity gradient). We observe that stable and unstable sliding sections of the SAF have different velocity gradients, small and negligible in the stable slip segment, but larger than 15 % in the unstable slip segment. Our results suggest that Vp and Vp/Vs gradients across the fault control fault rheology and the attitude of fault slip behavior.

  18. An ML-Based Radial Velocity Estimation Algorithm for Moving Targets in Spaceborne High-Resolution and Wide-Swath SAR Systems

    Directory of Open Access Journals (Sweden)

    Tingting Jin

    2017-04-01

    Full Text Available Multichannel synthetic aperture radar (SAR is a significant breakthrough to the inherent limitation between high-resolution and wide-swath (HRWS compared with conventional SAR. Moving target indication (MTI is an important application of spaceborne HRWS SAR systems. In contrast to previous studies of SAR MTI, the HRWS SAR mainly faces the problem of under-sampled data of each channel, causing single-channel imaging and processing to be infeasible. In this study, the estimation of velocity is equivalent to the estimation of the cone angle according to their relationship. The maximum likelihood (ML based algorithm is proposed to estimate the radial velocity in the existence of Doppler ambiguities. After that, the signal reconstruction and compensation for the phase offset caused by radial velocity are processed for a moving target. Finally, the traditional imaging algorithm is applied to obtain a focused moving target image. Experiments are conducted to evaluate the accuracy and effectiveness of the estimator under different signal-to-noise ratios (SNR. Furthermore, the performance is analyzed with respect to the motion ship that experiences interference due to different distributions of sea clutter. The results verify that the proposed algorithm is accurate and efficient with low computational complexity. This paper aims at providing a solution to the velocity estimation problem in the future HRWS SAR systems with multiple receive channels.

  19. Performance of a high-work, low-aspect-ratio turbine stator tested with a realistic inlet radial temperature gradient

    Science.gov (United States)

    Stabe, Roy G.; Schwab, John R.

    1991-01-01

    A 0.767-scale model of a turbine stator designed for the core of a high-bypass-ratio aircraft engine was tested with uniform inlet conditions and with an inlet radial temperature profile simulating engine conditions. The principal measurements were radial and circumferential surveys of stator-exit total temperature, total pressure, and flow angle. The stator-exit flow field was also computed by using a three-dimensional Navier-Stokes solver. Other than temperature, there were no apparent differences in performance due to the inlet conditions. The computed results compared quite well with the experimental results.

  20. Ion temperature gradient driven mode in presence of transverse velocity shear in magnetized plasmas

    DEFF Research Database (Denmark)

    Chakrabarti, N.; Juul Rasmussen, J.; Michelsen, Poul

    2005-01-01

    The effect of sheared poloidal flow on the toroidal branch of the ion temperature gradient driven mode of magnetized nonuniform plasma is studied. A novel "nonmodal" calculation is used to analyze the problem. It is shown that the transverse shear flow considerably reduced the growth...

  1. The Mass of the Candidate Exoplanet Companion to HD 33636 from Hubble Space Telescope Astrometry and High-Precision Radial Velocities

    Science.gov (United States)

    Bean, Jacob L.; McArthur, Barbara E.; Benedict, G. Fritz; Harrison, Thomas E.; Bizyaev, Dmitry; Nelan, Edmund; Smith, Verne V.

    2007-08-01

    We have determined a dynamical mass for the companion to HD 33636 that indicates it is a low-mass star instead of an exoplanet. Our result is based on an analysis of Hubble Space Telescope (HST) astrometry and ground-based radial velocity data. We have obtained high-cadence radial velocity measurements spanning 1.3 yr of HD 33636 with the Hobby-Eberly Telescope at McDonald Observatory. We combined these data with previously published velocities to create a data set that spans 9 yr. We used this data set to search for, and place mass limits on, the existence of additional companions in the HD 33636 system. Our high-precision astrometric observations of the system with the HST Fine Guidance Sensor 1r span 1.2 yr. We simultaneously modeled the radial velocity and astrometry data to determine the parallax, proper motion, and perturbation orbit parameters of HD 33636. Our derived parallax, πabs=35.6+/-0.2 mas, agrees within the uncertainties with the Hipparcos value. We find a perturbation period P=2117.3+/-0.8 days, semimajor axis aA=14.2+/-0.2 mas, and system inclination i=4.1deg+/-0.1deg. Assuming the mass of the primary star to be MA=1.02+/-0.03 Msolar, we obtain a companion mass MB=142+/-11 MJup=0.14+/-0.01 Msolar. The much larger true mass of the companion relative to its minimum mass estimated from the spectroscopic orbit parameters (Msini=9.3 MJup) is due to the nearly face-on orbit orientation. This result demonstrates the value of follow-up astrometric observations to determine the true masses of exoplanet candidates detected with the radial velocity method. Based on data obtained with the NASA/ESA Hubble Space Telescope (HST) and the Hobby-Eberly Telescope (HET). The HST observations were obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. The HET is a joint project of the University of Texas at Austin, Pennsylvania State University, Stanford

  2. The orthogonal gradients method: A radial basis functions method for solving partial differential equations on arbitrary surfaces

    KAUST Repository

    Piret, Cé cile

    2012-01-01

    Much work has been done on reconstructing arbitrary surfaces using the radial basis function (RBF) method, but one can hardly find any work done on the use of RBFs to solve partial differential equations (PDEs) on arbitrary surfaces. In this paper

  3. Statistical properties of the coarse-grained velocity gradient tensor in turbulence: Monte-Carlo simulations of the tetrad model

    International Nuclear Information System (INIS)

    Pumir, Alain; Naso, Aurore

    2010-01-01

    A proper description of the velocity gradient tensor is crucial for understanding the dynamics of turbulent flows, in particular the energy transfer from large to small scales. Insight into the statistical properties of the velocity gradient tensor and into its coarse-grained generalization can be obtained with the help of a stochastic 'tetrad model' that describes the coarse-grained velocity gradient tensor based on the evolution of four points. Although the solution of the stochastic model can be formally expressed in terms of path integrals, its numerical determination in terms of the Monte-Carlo method is very challenging, as very few configurations contribute effectively to the statistical weight. Here, we discuss a strategy that allows us to solve the tetrad model numerically. The algorithm is based on the importance sampling method, which consists here of identifying and sampling preferentially the configurations that are likely to correspond to a large statistical weight, and selectively rejecting configurations with a small statistical weight. The algorithm leads to an efficient numerical determination of the solutions of the model and allows us to determine their qualitative behavior as a function of scale. We find that the moments of order n≤4 of the solutions of the model scale with the coarse-graining scale and that the scaling exponents are very close to the predictions of the Kolmogorov theory. The model qualitatively reproduces quite well the statistics concerning the local structure of the flow. However, we find that the model generally tends to predict an excess of strain compared to vorticity. Thus, our results show that while some physical aspects are not fully captured by the model, our approach leads to a very good description of several important qualitative properties of real turbulent flows.

  4. Friends of hot Jupiters. I. A radial velocity search for massive, long-period companions to close-in gas giant planets

    Energy Technology Data Exchange (ETDEWEB)

    Knutson, Heather A.; Ngo, Henry; Johnson, John Asher [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Fulton, Benjamin J.; Howard, Andrew W. [Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI (United States); Montet, Benjamin T.; Kao, Melodie; Hinkley, Sasha; Morton, Timothy D.; Muirhead, Philip S. [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, 1200 East California Boulevard, MC 249-17, Pasadena, CA 91125 (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, Notre Dame, IN (United States); Bakos, Gaspar Á. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ (United States); Batygin, Konstantin, E-mail: hknutson@caltech.edu [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)

    2014-04-20

    In this paper we search for distant massive companions to known transiting gas giant planets that may have influenced the dynamical evolution of these systems. We present new radial velocity observations for a sample of 51 planets obtained using the Keck HIRES instrument, and find statistically significant accelerations in fifteen systems. Six of these systems have no previously reported accelerations in the published literature: HAT-P-10, HAT-P-22, HAT-P-29, HAT-P-32, WASP-10, and XO-2. We combine our radial velocity fits with Keck NIRC2 adaptive optics (AO) imaging data to place constraints on the allowed masses and orbital periods of the companions responsible for the detected accelerations. The estimated masses of the companions range between 1-500 M {sub Jup}, with orbital semi-major axes typically between 1-75 AU. A significant majority of the companions detected by our survey are constrained to have minimum masses comparable to or larger than those of the transiting planets in these systems, making them candidates for influencing the orbital evolution of the inner gas giant. We estimate a total occurrence rate of 51% ± 10% for companions with masses between 1-13 M {sub Jup} and orbital semi-major axes between 1-20 AU in our sample. We find no statistically significant difference between the frequency of companions to transiting planets with misaligned or eccentric orbits and those with well-aligned, circular orbits. We combine our expanded sample of radial velocity measurements with constraints from transit and secondary eclipse observations to provide improved measurements of the physical and orbital characteristics of all of the planets included in our survey.

  5. EnKF OSSE Experiments Assessing the Impact of HIRAD Wind Speed and HIWRAP Radial Velocity Data on Analysis of Hurricane Karl (2010)

    Science.gov (United States)

    Albers, Cerese; Sippel, Jason A.; Braun, Scott A.; Miller, Timothy

    2012-01-01

    Previous studies (e.g., Zhang et al. 2009, Weng et al. 2011) have shown that radial velocity data from airborne and ground-based radars can be assimilated into ensemble Kalman filter (EnKF) systems to produce accurate analyses of tropical cyclone vortices, which can reduce forecast intensity error. Recently, wind speed data from SFMR technology has also been assimilated into the same types of systems and has been shown to improve the forecast intensity of mature tropical cyclones. Two instruments that measure these properties were present during the NASA Genesis and Rapid Intensification Processes (GRIP) field experiment in 2010 which sampled Hurricane Karl, and will next be co-located on the same aircraft for the subsequent NASA HS3 experiment. The High Altitude Wind and Rain Profiling Radar (HIWRAP) is a conically scanning Doppler radar mounted upon NASAs Global Hawk unmanned aerial vehicle, and the usefulness of its radial velocity data for assimilation has not been previously examined. Since the radar scans from above with a fairly large fixed elevation angle, it observes a large component of the vertical wind, which could degrade EnKF analyses compared to analyses with data taken from lesser elevation angles. The NASA Hurricane Imaging Radiometer (HIRAD) is a passive microwave radiometer similar to SFMR, and measures emissivity and retrieves hurricane surface wind speeds and rain rates over a much wider swath. Thus, this study examines the impact of assimilating simulated HIWRAP radial velocity data into an EnKF system, simulated HIRAD wind speed, and HIWRAP+HIRAD with the Weather Research and Forecasting (WRF) model and compares the results to no data assimilation and also to the Truth from which the data was simulated for both instruments.

  6. Aortic-Brachial Pulse Wave Velocity Ratio: A Measure of Arterial Stiffness Gradient Not Affected by Mean Arterial Pressure.

    Science.gov (United States)

    Fortier, Catherine; Desjardins, Marie-Pier; Agharazii, Mohsen

    2018-03-01

    Aortic stiffness, measured by carotid-femoral pulse wave velocity (cf-PWV), is used for the prediction of cardiovascular risk. This mini-review describes the nonlinear relationship between cf-PWV and operational blood pressure, presents the proposed methods to adjust for this relationship, and discusses a potential place for aortic-brachial PWV ratio (a measure of arterial stiffness gradient) as a blood pressure-independent measure of vascular aging. PWV is inherently dependent on the operational blood pressure. In cross-sectional studies, PWV adjustment for mean arterial pressure (MAP) is preferred, but still remains a nonoptimal approach, as the relationship between PWV and blood pressure is nonlinear and varies considerably among individuals due to heterogeneity in genetic background, vascular tone, and vascular remodeling. Extrapolations from the blood pressure-independent stiffness parameter β (β 0 ) have led to the creation of stiffness index β, which can be used for local stiffness. A similar approach has been used for cardio-ankle PWV to generate a blood pressure-independent cardio-ankle vascular index (CAVI). It was recently demonstrated that stiffness index β and CAVI remain slightly blood pressure-dependent, and a more appropriate formula has been proposed to make the proper adjustments. On the other hand, the negative impact of aortic stiffness on clinical outcomes is thought to be mediated through attenuation or reversal of the arterial stiffness gradient, which can also be influenced by a reduction in peripheral medium-sized muscular arteries in conditions that predispose to accelerate vascular aging. Arterial stiffness gradient, assessed by aortic-brachial PWV ratio, is emerging to be at least as good as cf-PWV for risk prediction, but has the advantage of not being affected by operating MAP. The negative impacts of aortic stiffness on clinical outcomes are proposed to be mediated through attenuation or reversal of arterial stiffness gradient

  7. Development of tool for simulating the effect of radial electric fields on Ion-Temperature-Gradient modes in 3D configurations

    International Nuclear Information System (INIS)

    Eriksson, Lars

    2003-03-01

    The heat flux level observed in magnetic plasma confinement experiments such as tokamaks is much higher than what can be explained from neoclassical theory. There is a strong interest in the controlled nuclear fusion community to fully understand this phenomenon, called anomalous transport. One idea is that radial electric fields play a key role in the stabilization process of the electrostatic instabilities called micro instabilities that are considered responsible for the anomalous heat flux. This work studies the effect of a static ad-hoc radial electric field on microinstabilities, especially the ion temperature gradient (ITG) driven mode, within the frame of a global 3D gyrokinetic model. This will make it possible to extend the simulations done in tokamaks and helically symmetric systems to fully 313 magnetic configurations. Technically the work consists of extending the 3D gyrokinetic code Euterpe to also include the effect of the drifts induced by an imposed radial electrostatic potential. Simulations are performed in tokamak and helically symmetric configurations. The results indicate that this modified version of Euterpe can be used in studying more complex 3D fusion devices

  8. The role of the velocity gradient in laminar convective heat transfer through a tube with a uniform wall heat flux

    International Nuclear Information System (INIS)

    Wang Liangbi; Zhang Qiang; Li Xiaoxia

    2009-01-01

    This paper aims to contribute to a better understanding of convective heat transfer. For this purpose, the reason why thermal diffusivity should be placed before the Laplacian operator of the heat flux, and the role of the velocity gradient in convective heat transfer are analysed. The background to these analyses is that, when the energy conservation equation of convective heat transfer is used to explain convective heat transfer there are two points that are difficult for teachers to explain and for undergraduates to understand: thermal diffusivity is placed before the Laplacian operator of temperature; on the wall surface (the fluid side) the velocity is zero, a diffusion equation of temperature is gained from energy conservation equation, however, temperature cannot be transported. Consequently, the real physical meaning of thermal diffusivity is not clearly reflected in the energy conservation equation, and whether heat transfer occurs through a diffusion process or a convection process on the wall surface is not clear. Through a simple convective heat transfer case: laminar convective heat transfer in a tube with a uniform wall heat flux on the tube wall, this paper explains these points more clearly. The results declare that it is easier for teachers to explain and for undergraduates to understand these points when a description of heat transfer in terms of the heat flux is used. In this description, thermal diffusivity is placed before the Laplacian operator of the heat flux; the role of the velocity gradient in convective heat transfer appears, on the wall surface, the fact whether heat transfer occurs through a diffusion process or a convection process can be explained and understood easily. The results are not only essential for teachers to improve the efficiency of university-level physics education regarding heat transfer, but they also enrich the theories for understanding heat transfer

  9. The SDSS-III DR12 MARVELS radial velocity data release: the first data release from the multiple object Doppler exoplanet survey

    Science.gov (United States)

    Ge, Jian; Thomas, Neil B.; Li, Rui; Senan Seieroe Grieves, Nolan; Ma, Bo; de Lee, Nathan M.; Lee, Brian C.; Liu, Jian; Bolton, Adam S.; Thakar, Aniruddha R.; Weaver, Benjamin; SDSS-Iii Marvels Team

    2015-01-01

    We present the first data release from the SDSS-III Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS) through the SDSS-III DR12. The data include 181,198 radial velocity (RV) measurements for a total of 5520 different FGK stars with V~7.6-12, of which more than 80% are dwarfs and subdwarfs while remainders are GK giants, among a total of 92 fields nearly randomly spread out over the entire northern sky taken with a 60-object MARVELS dispersed fixed-delay interferometer instrument over four years (2008-2012). There were 55 fields with a total of 3300 FGK stars which had 14 or more observations over about 2-year survey window. The median number of observations for these plates is 27 RV measurements. This represents the largest homogeneous sample of precision RV measurements of relatively bright stars. In this first released data, a total of 18 giant planet candidates, 16 brown dwarfs, and over 500 binaries with additional 96 targets having RV variability indicative of a giant planet companion are reported. The released data were produced by the MARVELS finalized 1D pipeline. We will also report preliminary statistical results from the MARVELS 2D data pipeline which has produced a median RV precision of ~30 m/s for stable stars.

  10. RADIAL VELOCITY OBSERVATIONS AND LIGHT CURVE NOISE MODELING CONFIRM THAT KEPLER-91b IS A GIANT PLANET ORBITING A GIANT STAR

    International Nuclear Information System (INIS)

    Barclay, Thomas; Huber, Daniel; Rowe, Jason F.; Quintana, Elisa V.; Endl, Michael; Cochran, William D.; MacQueen, Phillip J.; Foreman-Mackey, Daniel

    2015-01-01

    Kepler-91b is a rare example of a transiting hot Jupiter around a red giant star, providing the possibility to study the formation and composition of hot Jupiters under different conditions compared to main-sequence stars. However, the planetary nature of Kepler-91b, which was confirmed using phase-curve variations by Lillo-Box et al., was recently called into question based on a re-analysis of Kepler data. We have obtained ground-based radial velocity observations from the Hobby-Eberly Telescope and unambiguously confirm the planetary nature of Kepler-91b by simultaneously modeling the Kepler and radial velocity data. The star exhibits temporally correlated noise due to stellar granulation which we model as a Gaussian Process. We hypothesize that it is this noise component that led previous studies to suspect Kepler-91b to be a false positive. Our work confirms the conclusions presented by Lillo-Box et al. that Kepler-91b is a 0.73 ± 0.13 M Jup planet orbiting a red giant star

  11. A RADIAL VELOCITY TEST FOR SUPERMASSIVE BLACK HOLE BINARIES AS AN EXPLANATION FOR BROAD, DOUBLE-PEAKED EMISSION LINES IN ACTIVE GALACTIC NUCLEI

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Jia; Halpern, Jules P. [Astronomy Department, Columbia University, 550 West 120th Street, New York, NY 10027 (United States); Eracleous, Michael [Department of Astronomy and Institute for Gravitation and The Cosmos, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States)

    2016-01-20

    One of the proposed explanations for the broad, double-peaked Balmer emission lines observed in the spectra of some active galactic nuclei (AGNs) is that they are associated with sub-parsec supermassive black hole (SMBH) binaries. Here, we test the binary broad-line region hypothesis through several decades of monitoring of the velocity structure of double-peaked Hα emission lines in 13 low-redshift, mostly radio-loud AGNs. This is a much larger set of objects compared to an earlier test by Eracleous et al. and we use much longer time series for the three objects studied in that paper. Although systematic changes in radial velocity can be traced in many of their lines, they are demonstrably not like those of a spectroscopic binary in a circular orbit. Any spectroscopic binary period must therefore be much longer than the span of the monitoring (assuming a circular orbit), which in turn would require black hole masses that exceed by 1–2 orders of magnitude the values obtained for these objects using techniques such as reverberation mapping and stellar velocity dispersion. Moreover, the response of the double-peaked Balmer line profiles to fluctuations of the ionizing continuum and the shape of the Lyα profiles are incompatible with an SMBH binary. The binary broad-line region hypothesis is therefore disfavored. Other processes evidently shape these line profiles and cause the long-term velocity variations of the double peaks.

  12. Estimación de la velocidad de propagación aórtica basada en el análisis de la onda de pulso radial Velocity estimation of aortic propagation based on radial pulse wave analysis

    Directory of Open Access Journals (Sweden)

    Fernando Clara

    2011-06-01

    Full Text Available Se exploró la posibilidad de utilizar la morfología del registro de onda de pulso radial obtenida mediante un transductor de movimiento para evaluar la velocidad de propagación aórtica. Se efectuó el registro de onda de pulso en arteria radial mediante un transductor apoyado sobre la zona de palpación del pulso, sobre un conjunto de 167 voluntarios varones sanos normotensos de edades comprendidas entre la 2ª y la 7ª década. Se identificó en los registros la onda reflejada y se definió un coeficiente de velocidad como el cociente entre la talla del individuo y el tiempo transcurrido entre el máximo de la onda sistólica y el instante de llegada de dicha onda. Se halló que en los normotensos el coeficiente mencionado aumentó en forma lineal con la edad, en una proporción similar al aumento de velocidad de propagación aórtica medido con otros métodos. Se repitió el procedimiento en otro conjunto de 125 varones hipertensos sin otros factores de riesgo, de edades entre la 3ª y la 7ª década, hallándose valores similares a los normotensos solamente en la 3ª década, a partir de la cual se registró un incremento significativo de dicho índice. Tales hallazgos sustentan la factibilidad de utilizar tal tipo de registros para evaluar indirectamente la velocidad de propagación junto con el índice de aumentación, un parámetro habitualmente utilizado en el análisis de onda de pulso.We analyzed the possibility of using the radial pulse wave morphology, obtained by a movement transducer, to evaluate the aortic pulse wave velocity. The radial pulse wave signals were obtained by using a transducer, located on the pulse palpation area, in 167 healthy normotensive male volunteers, ages 20 to 70. The reflected wave was identified in every case. Also, a speed coefficient was defined as the ratio between the individual's height and the time between the maximum systolic wave and the arrival time of the reflected wave. We found that the

  13. BANYAN. III. Radial velocity, rotation, and X-ray emission of low-mass star candidates in nearby young kinematic groups

    Energy Technology Data Exchange (ETDEWEB)

    Malo, Lison; Artigau, Étienne; Doyon, René; Lafrenière, David; Albert, Loïc; Gagné, Jonathan, E-mail: malo@astro.umontreal.ca, E-mail: doyon@astro.umontreal.ca [Département de physique and Observatoire du Mont-Mégantic, Université de Montréal, Montréal, QC H3C 3J7 (Canada)

    2014-06-10

    Based on high-resolution spectra obtained with PHOENIX at Gemini-South, CRIRES at VLT-UT1, and ESPaDOnS at the Canada-France-Hawaii Telescope, we present new measurements of the radial and projected rotational velocities of 219 low-mass stars. The target likely membership was initially established using the Bayesian analysis tool recently presented in Malo et al., taking into account only the position, proper motion, and photometry of the stars to assess their membership probability. In the present study, we include radial velocity as an additional input to our analysis, and in doing so we confirm the high membership probability for 130 candidates: 27 in β Pictoris, 22 in Tucana-Horologium, 25 in Columba, 7 in Carina, 18 in Argus and 18 in AB Doradus, and 13 with an ambiguous membership. Our analysis also confirms the membership of 57 stars proposed in the literature. A subsample of 16 candidates was observed at 3 or more epochs, allowing us to discover 6 new spectroscopic binaries. The fraction of binaries in our sample is 25%, consistent with values in the literature. Of the stars in our sample, 20% show projected rotational velocities (vsin i) higher than 30 km s{sup –1} and therefore are considered as fast rotators. A parallax and other youth indicators are still needed to fully confirm the 130 highly probable candidates identified here as new bona fide members. Finally, based on the X-ray emission of bona fide and highly probable group members, we show that for low-mass stars in the 12-120 Myr age range, the X-ray luminosity is an excellent indicator of youth and better than the more traditionally used R {sub X} parameter, the ratio of X-ray to bolometric luminosity.

  14. Radial electric field at the plasma edge on the FT-2 Tokamak in regimes with large gradients

    International Nuclear Information System (INIS)

    Lashkul, S.; Popov, A.

    2001-01-01

    The transport barrier formation is widely believed to be the fundamental element of transition into improved confinement regimes (H-mode). Experiments on many tokamaks demonstrate that transport barrier formation is connected with the suppression of turbulent transport by shear of E x B drift. Therefore, the calculation of radial electric field is of great importance. Our work is devoted to progress the neoclassical theory by taking into account electron viscosity and non-linear effects (ion inertia), presented results being valuable for interpretation transition into H-mode at the plasma edge in small tokamaks. Calculations of the electric field profile for FT-2 tokamak (a=8cm, R 0 =55cm, Ioffe Institute, Russia) according found expressions are in the good agreement with experimental results obtained. (orig.)

  15. On protecting the planet against cosmic attack: Ultrafast real-time estimate of the asteroid's radial velocity

    Science.gov (United States)

    Zakharchenko, V. D.; Kovalenko, I. G.

    2014-05-01

    A new method for the line-of-sight velocity estimation of a high-speed near-Earth object (asteroid, meteorite) is suggested. The method is based on the use of fractional, one-half order derivative of a Doppler signal. The algorithm suggested is much simpler and more economical than the classical one, and it appears preferable for use in orbital weapon systems of threat response. Application of fractional differentiation to quick evaluation of mean frequency location of the reflected Doppler signal is justified. The method allows an assessment of the mean frequency in the time domain without spectral analysis. An algorithm structure for the real-time estimation is presented. The velocity resolution estimates are made for typical asteroids in the X-band. It is shown that the wait time can be shortened by orders of magnitude compared with similar value in the case of a standard spectral processing.

  16. Solvent micro-evaporation and concentration gradient synergistically induced crystallization of poly(L-lactide) and ring banded supra-structures with radial periodic variation of thickness

    DEFF Research Database (Denmark)

    Huang, Shaoyong; Li, Hongfei; Wen, Huiying

    2014-01-01

    The crystalline morphology and structure of poly(L-lactide) (PLLA) in a PLLA film-chloroform system were investigated by means of wide angle X-ray diffraction (WAXD), polarized optical microscopy (POM) and atomic force microscopy (AFM). Birefringent and nonbirefringent ring banded supra-structure......The crystalline morphology and structure of poly(L-lactide) (PLLA) in a PLLA film-chloroform system were investigated by means of wide angle X-ray diffraction (WAXD), polarized optical microscopy (POM) and atomic force microscopy (AFM). Birefringent and nonbirefringent ring banded supra......-structures with radial periodic variation of thickness were obtained, which were induced by micro-evaporation of solvents and concentration gradient of PLLA. The ring banded morphologies consisted of multilayer lamellar crystals, which is a manifestation of alternating ridge and valley bands of periodic variation...

  17. Box Tomography: first application to the imaging of upper-mantle shear velocity and radial anisotropy structure beneath the North American continent

    Science.gov (United States)

    Clouzet, P.; Masson, Y.; Romanowicz, B.

    2018-06-01

    The EarthScope Transpotable Array (TA) deployment provides dense array coverage throughout the continental United States and with it, the opportunity for high-resolution 3-D seismic velocity imaging of the stable part of the North American (NA) upper mantle. Building upon our previous long-period waveform tomographic modeling, we present a higher resolution 3-D isotropic and radially anisotropic shear wave velocity model of the NA lithosphere and asthenosphere. The model is constructed using a combination of teleseismic and regional waveforms down to 40 s period and wavefield computations are performed using the spectral element method both for regional and teleseismic data. Our study is the first tomographic application of `Box Tomography', which allows us to include teleseismic events in our inversion, while computing the teleseismic wavefield only once, thus significantly reducing the numerical computational cost of several iterations of the regional inversion. We confirm the presence of high-velocity roots beneath the Archean part of the continent, reaching 200-250 km in some areas, however the thickness of these roots is not everywhere correlated to the crustal age of the corresponding cratonic province. In particular, the lithosphere is thick (˜250 km) in the western part of the Superior craton, while it is much thinner (˜150 km) in its eastern part. This may be related to a thermomechanical erosion of the cratonic root due to the passage of the NA plate over the Great Meteor hotspot during the opening of the Atlantic ocean 200-110 Ma. Below the lithosphere, an upper-mantle low-velocity zone (LVZ) is present everywhere under the NA continent, even under the thickest parts of the craton, although it is less developed there. The depth of the minimum in shear velocity has strong lateral variations, whereas the bottom of the LVZ is everywhere relatively flat around 270-300 km depth, with minor undulations of maximum 30 km that show upwarping under the thickest

  18. Experimental determination of the radial dose distribution in high gradient regions around 192Ir wires: Comparison of electron paramagnetic resonance imaging, films, and Monte Carlo simulations

    International Nuclear Information System (INIS)

    Kolbun, N.; Leveque, Ph.; Abboud, F.; Bol, A.; Vynckier, S.; Gallez, B.

    2010-01-01

    Purpose: The experimental determination of doses at proximal distances from radioactive sources is difficult because of the steepness of the dose gradient. The goal of this study was to determine the relative radial dose distribution for a low dose rate 192 Ir wire source using electron paramagnetic resonance imaging (EPRI) and to compare the results to those obtained using Gafchromic EBT film dosimetry and Monte Carlo (MC) simulations. Methods: Lithium formate and ammonium formate were chosen as the EPR dosimetric materials and were used to form cylindrical phantoms. The dose distribution of the stable radiation-induced free radicals in the lithium formate and ammonium formate phantoms was assessed by EPRI. EBT films were also inserted inside in ammonium formate phantoms for comparison. MC simulation was performed using the MCNP4C2 software code. Results: The radical signal in irradiated ammonium formate is contained in a single narrow EPR line, with an EPR peak-to-peak linewidth narrower than that of lithium formate (∼0.64 and 1.4 mT, respectively). The spatial resolution of EPR images was enhanced by a factor of 2.3 using ammonium formate compared to lithium formate because its linewidth is about 0.75 mT narrower than that of lithium formate. The EPRI results were consistent to within 1% with those of Gafchromic EBT films and MC simulations at distances from 1.0 to 2.9 mm. The radial dose values obtained by EPRI were about 4% lower at distances from 2.9 to 4.0 mm than those determined by MC simulation and EBT film dosimetry. Conclusions: Ammonium formate is a suitable material under certain conditions for use in brachytherapy dosimetry using EPRI. In this study, the authors demonstrated that the EPRI technique allows the estimation of the relative radial dose distribution at short distances for a 192 Ir wire source.

  19. A SITELLE view of M31's central region - I. Calibrations and radial velocity catalogue of nearly 800 emission-line point-like sources

    Science.gov (United States)

    Martin, Thomas B.; Drissen, Laurent; Melchior, Anne-Laure

    2018-01-01

    We present a detailed description of the wavelength, astrometric and photometric calibration plan for SITELLE, the imaging Fourier transform spectrometer attached to the Canada-France-Hawaii telescope, based on observations of a red (647-685 nm) data cube of the central region (11 arcmin × 11 arcmin) of M 31. The first application, presented in this paper is a radial-velocity catalogue (with uncertainties of ∼2-6 km s-1) of nearly 800 emission-line point-like sources, including ∼450 new discoveries. Most of the sources are likely planetary nebulae, although we also detect five novae (having erupted in the first eight months of 2016) and one new supernova remnant candidate.

  20. SOAP-T: a tool to study the light curve and radial velocity of a system with a transiting planet and a rotating spotted star

    Science.gov (United States)

    Oshagh, M.; Boisse, I.; Boué, G.; Montalto, M.; Santos, N. C.; Bonfils, X.; Haghighipour, N.

    2013-01-01

    We present an improved version of SOAP named "SOAP-T", which can generate the radial velocity variations and light curves for systems consisting of a rotating spotted star with a transiting planet. This tool can be used to study the anomalies inside transit light curves and the Rossiter-McLaughlin effect, to better constrain the orbital configuration and properties of planetary systems and the active zones of their host stars. Tests of the code are presented to illustrate its performance and to validate its capability when compared with analytical models and real data. Finally, we apply SOAP-T to the active star, HAT-P-11, observed by the NASA Kepler space telescope and use this system to discuss the capability of this tool in analyzing light curves for the cases where the transiting planet overlaps with the star's spots. The tool's public interface is available at http://www.astro.up.pt/resources/soap-t/

  1. The Kepler-19 System: A Thick-envelope Super-Earth with Two Neptune-mass Companions Characterized Using Radial Velocities and Transit Timing Variations

    Energy Technology Data Exchange (ETDEWEB)

    Malavolta, Luca; Borsato, Luca; Granata, Valentina; Piotto, Giampaolo; Nascimbeni, Valerio [Dipartimento di Fisica e Astronomia “Galileo Galilei”, Universita’di Padova, Vicolo dell’Osservatorio 3, I-35122 Padova (Italy); Lopez, Eric [SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh, EH93HJ (United Kingdom); Vanderburg, Andrew; Charbonneau, David [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138 (United States); Figueira, Pedro [Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, PT4150-762 Porto (Portugal); Mortier, Annelies; Cameron, Andrew Collier [Centre for Exoplanet Science, SUPA, School of Physics and Astronomy, University of St. Andrews, St. Andrews KY16 9SS (United Kingdom); Affer, Laura [INAF—Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, I-90124 Palermo (Italy); Bonomo, Aldo S. [INAF—Osservatorio Astrofisico di Torino, via Osservatorio 20, I-10025 Pino Torinese (Italy); Bouchy, Francois [Observatoire Astronomique de l’Université de Genève, 51 ch. des Maillettes, 1290 Versoix (Switzerland); Buchhave, Lars A. [Centre for Star and Planet Formation, Natural History Museum of Denmark and Niels Bohr Institute, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K (Denmark); Cosentino, Rosario, E-mail: luca.malavolta@unipd.it [INAF—Fundación Galileo Galilei, Rambla José Ana Fernandez Pérez 7, E-38712 Breña Baja (Spain); and others

    2017-05-01

    We report a detailed characterization of the Kepler-19 system. This star was previously known to host a transiting planet with a period of 9.29 days, a radius of 2.2 R {sub ⊕}, and an upper limit on the mass of 20 M {sub ⊕}. The presence of a second, non-transiting planet was inferred from the transit time variations (TTVs) of Kepler-19b over eight quarters of Kepler photometry, although neither the mass nor period could be determined. By combining new TTVs measurements from all the Kepler quarters and 91 high-precision radial velocities obtained with the HARPS-N spectrograph, using dynamical simulations we obtained a mass of 8.4 ± 1.6 M {sub ⊕} for Kepler-19b. From the same data, assuming system coplanarity, we determined an orbital period of 28.7 days and a mass of 13.1 ± 2.7 M {sub ⊕} for Kepler-19c and discovered a Neptune-like planet with a mass of 20.3 ± 3.4 M {sub ⊕} on a 63-day orbit. By comparing dynamical simulations with non-interacting Keplerian orbits, we concluded that neglecting interactions between planets may lead to systematic errors that can hamper the precision in the orbital parameters when the data set spans several years. With a density of 4.32 ± 0.87 g cm{sup −3} (0.78 ± 0.16 ρ {sub ⊕}) Kepler-19b belongs to the group of planets with a rocky core and a significant fraction of volatiles, in opposition to low-density planets characterized only by transit time variations and an increasing number of rocky planets with Earth-like density. Kepler-19 joins the small number of systems that reconcile transit timing variation and radial velocity measurements.

  2. TOWARD COMPLETE STATISTICS OF MASSIVE BINARY STARS: PENULTIMATE RESULTS FROM THE CYGNUS OB2 RADIAL VELOCITY SURVEY

    Energy Technology Data Exchange (ETDEWEB)

    Kobulnicky, Henry A.; Lundquist, Michael J.; Burke, Jamison; Chapman, James; Keller, Erica; Lester, Kathryn; Rolen, Emily K.; Topel, Eric; Bhattacharjee, Anirban; Smullen, Rachel A.; Álvarez, Carlos A. Vargas; Runnoe, Jessie C.; Dale, Daniel A.; Brotherton, Michael M. [Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82070 (United States); Kiminki, Daniel C., E-mail: chipk@uwyo.edu, E-mail: jburke2@swarthmore.edu, E-mail: jc6380@mcla.edu, E-mail: kelle22e@mtholyoke.edu, E-mail: kvl214@lehigh.edu, E-mail: emily.k.rolen@vanderbilt.edu, E-mail: topel@stolaf.edu [Department of Astronomy, University of Arizona, Tucson, AZ 85721 (United States)

    2014-08-01

    We analyze orbital solutions for 48 massive multiple-star systems in the Cygnus OB2 association, 23 of which are newly presented here, to find that the observed distribution of orbital periods is approximately uniform in log P for P < 45 days, but it is not scale-free. Inflections in the cumulative distribution near 6 days, 14 days, and 45 days suggest key physical scales of ≅0.2, ≅0.4, and ≅1 A.U. where yet-to-be-identified phenomena create distinct features. No single power law provides a statistically compelling prescription, but if features are ignored, a power law with exponent β ≅ –0.22 provides a crude approximation over P = 1.4-2000 days, as does a piece-wise linear function with a break near 45 days. The cumulative period distribution flattens at P > 45 days, even after correction for completeness, indicating either a lower binary fraction or a shift toward low-mass companions. A high degree of similarity (91% likelihood) between the Cyg OB2 period distribution and that of other surveys suggests that the binary properties at P ≲ 25 days are determined by local physics of disk/clump fragmentation and are relatively insensitive to environmental and evolutionary factors. Fully 30% of the unbiased parent sample is a binary with period P < 45 days. Completeness corrections imply a binary fraction near 55% for P < 5000 days. The observed distribution of mass ratios 0.2 < q < 1 is consistent with uniform, while the observed distribution of eccentricities 0.1 < e < 0.6 is consistent with uniform plus an excess of e ≅ 0 systems. We identify six stars, all supergiants, that exhibit aperiodic velocity variations of ∼30 km s{sup –1} attributed to atmospheric fluctuations.

  3. The CARMENES search for exoplanets around M dwarfs . First visual-channel radial-velocity measurements and orbital parameter updates of seven M-dwarf planetary systems

    Science.gov (United States)

    Trifonov, T.; Kürster, M.; Zechmeister, M.; Tal-Or, L.; Caballero, J. A.; Quirrenbach, A.; Amado, P. J.; Ribas, I.; Reiners, A.; Reffert, S.; Dreizler, S.; Hatzes, A. P.; Kaminski, A.; Launhardt, R.; Henning, Th.; Montes, D.; Béjar, V. J. S.; Mundt, R.; Pavlov, A.; Schmitt, J. H. M. M.; Seifert, W.; Morales, J. C.; Nowak, G.; Jeffers, S. V.; Rodríguez-López, C.; del Burgo, C.; Anglada-Escudé, G.; López-Santiago, J.; Mathar, R. J.; Ammler-von Eiff, M.; Guenther, E. W.; Barrado, D.; González Hernández, J. I.; Mancini, L.; Stürmer, J.; Abril, M.; Aceituno, J.; Alonso-Floriano, F. J.; Antona, R.; Anwand-Heerwart, H.; Arroyo-Torres, B.; Azzaro, M.; Baroch, D.; Bauer, F. F.; Becerril, S.; Benítez, D.; Berdiñas, Z. M.; Bergond, G.; Blümcke, M.; Brinkmöller, M.; Cano, J.; Cárdenas Vázquez, M. C.; Casal, E.; Cifuentes, C.; Claret, A.; Colomé, J.; Cortés-Contreras, M.; Czesla, S.; Díez-Alonso, E.; Feiz, C.; Fernández, M.; Ferro, I. M.; Fuhrmeister, B.; Galadí-Enríquez, D.; Garcia-Piquer, A.; García Vargas, M. L.; Gesa, L.; Gómez Galera, V.; González-Peinado, R.; Grözinger, U.; Grohnert, S.; Guàrdia, J.; Guijarro, A.; de Guindos, E.; Gutiérrez-Soto, J.; Hagen, H.-J.; Hauschildt, P. H.; Hedrosa, R. P.; Helmling, J.; Hermelo, I.; Hernández Arabí, R.; Hernández Castaño, L.; Hernández Hernando, F.; Herrero, E.; Huber, A.; Huke, P.; Johnson, E.; de Juan, E.; Kim, M.; Klein, R.; Klüter, J.; Klutsch, A.; Lafarga, M.; Lampón, M.; Lara, L. M.; Laun, W.; Lemke, U.; Lenzen, R.; López del Fresno, M.; López-González, M. J.; López-Puertas, M.; López Salas, J. F.; Luque, R.; Magán Madinabeitia, H.; Mall, U.; Mandel, H.; Marfil, E.; Marín Molina, J. A.; Maroto Fernández, D.; Martín, E. L.; Martín-Ruiz, S.; Marvin, C. J.; Mirabet, E.; Moya, A.; Moreno-Raya, M. E.; Nagel, E.; Naranjo, V.; Nortmann, L.; Ofir, A.; Oreiro, R.; Pallé, E.; Panduro, J.; Pascual, J.; Passegger, V. M.; Pedraz, S.; Pérez-Calpena, A.; Pérez Medialdea, D.; Perger, M.; Perryman, M. A. C.; Pluto, M.; Rabaza, O.; Ramón, A.; Rebolo, R.; Redondo, P.; Reinhardt, S.; Rhode, P.; Rix, H.-W.; Rodler, F.; Rodríguez, E.; Rodríguez Trinidad, A.; Rohloff, R.-R.; Rosich, A.; Sadegi, S.; Sánchez-Blanco, E.; Sánchez Carrasco, M. A.; Sánchez-López, A.; Sanz-Forcada, J.; Sarkis, P.; Sarmiento, L. F.; Schäfer, S.; Schiller, J.; Schöfer, P.; Schweitzer, A.; Solano, E.; Stahl, O.; Strachan, J. B. P.; Suárez, J. C.; Tabernero, H. M.; Tala, M.; Tulloch, S. M.; Veredas, G.; Vico Linares, J. I.; Vilardell, F.; Wagner, K.; Winkler, J.; Wolthoff, V.; Xu, W.; Yan, F.; Zapatero Osorio, M. R.

    2018-02-01

    Context. The main goal of the CARMENES survey is to find Earth-mass planets around nearby M-dwarf stars. Seven M dwarfs included in the CARMENES sample had been observed before with HIRES and HARPS and either were reported to have one short period planetary companion (GJ 15 A, GJ 176, GJ 436, GJ 536 and GJ 1148) or are multiple planetary systems (GJ 581 and GJ 876). Aims: We aim to report new precise optical radial velocity measurements for these planet hosts and test the overall capabilities of CARMENES. Methods: We combined our CARMENES precise Doppler measurements with those available from HIRES and HARPS and derived new orbital parameters for the systems. Bona-fide single planet systems were fitted with a Keplerian model. The multiple planet systems were analyzed using a self-consistent dynamical model and their best fit orbits were tested for long-term stability. Results: We confirm or provide supportive arguments for planets around all the investigated stars except for GJ 15 A, for which we find that the post-discovery HIRES data and our CARMENES data do not show a signal at 11.4 days. Although we cannot confirm the super-Earth planet GJ 15 Ab, we show evidence for a possible long-period (Pc = 7030-630+970 d) Saturn-mass (mcsini = 51.8M⊕) planet around GJ 15 A. In addition, based on our CARMENES and HIRES data we discover a second planet around GJ 1148, for which we estimate a period Pc = 532.6 days, eccentricity ec = 0.342 and minimum mass mcsini = 68.1M⊕. Conclusions: The CARMENES optical radial velocities have similar precision and overall scatter when compared to the Doppler measurements conducted with HARPS and HIRES. We conclude that CARMENES is an instrument that is up to the challenge of discovering rocky planets around low-mass stars. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 072.C-0488, 072.C-0513, 074.C-0012, 074.C-0364, 075.D-0614, 076.C-0878, 077.C

  4. High-resolution H -band Spectroscopy of Be Stars with SDSS-III/APOGEE. II. Line Profile and Radial Velocity Variability

    International Nuclear Information System (INIS)

    Chojnowski, S. Drew; Holtzman, Jon A.; Wisniewski, John P.; Whelan, David G.; Labadie-Bartz, Jonathan; Pepper, Joshua; Fernandes, Marcelo Borges; Lin, Chien-Cheng; Majewski, Steven R.; Stringfellow, Guy S.; Mennickent, Ronald E.; Tang, Baitian; Roman-Lopes, Alexandre; Hearty, Fred R.; Zasowski, Gail

    2017-01-01

    We report on the H -band spectral variability of classical Be stars observed over the course of the Apache Point Galactic Evolution Experiment (APOGEE), one of four subsurveys comprising SDSS-III. As described in the first paper of this series, the APOGEE B-type emission-line (ABE) star sample was culled from the large number of blue stars observed as telluric standards during APOGEE observations. In this paper, we explore the multi-epoch ABE sample, consisting of 1100 spectra for 213 stars. These “snapshots” of the circumstellar disk activity have revealed a wealth of temporal variability including, but not limited to, gradual disappearance of the line emission and vice versa over both short and long timescales. Other forms of variability include variation in emission strength, emission peak intensity ratios, and emission peak separations. We also analyze radial velocities (RVs) of the emission lines for a subsample of 162 stars with sufficiently strong features, and we discuss on a case-by-case basis whether the RV variability exhibited by some stars is caused by binary motion versus dynamical processes in the circumstellar disks. Ten systems are identified as convincing candidates for binary Be stars with as of yet undetected companions.

  5. High-resolution H -band Spectroscopy of Be Stars with SDSS-III/APOGEE. II. Line Profile and Radial Velocity Variability

    Energy Technology Data Exchange (ETDEWEB)

    Chojnowski, S. Drew; Holtzman, Jon A. [Apache Point Observatory and New Mexico State University, P.O. Box 59, Sunspot, NM, 88349-0059 (United States); Wisniewski, John P. [Department of Physics and Astronomy, The University of Oklahoma, 440 W. Brooks Street, Norman, OK 73019 (United States); Whelan, David G. [Department of Physics, Austin College, 900 N. Grand Avenue, Sherman, TX 75090 (United States); Labadie-Bartz, Jonathan; Pepper, Joshua [Department of Physics, Lehigh University, Bethlehem, PA 18015 (United States); Fernandes, Marcelo Borges [Observatório Nacional, Rua General José Cristino 77, 20921-400, São Cristovão, Rio de Janeiro (Brazil); Lin, Chien-Cheng [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road Shanghai 200030 (China); Majewski, Steven R. [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States); Stringfellow, Guy S. [Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Sciences, University of Colorado, 389 UCB, Boulder, Colorado 80309-0389 (United States); Mennickent, Ronald E.; Tang, Baitian [Departamento de Astronomía, Universidad de Concepción, Concepción (Chile); Roman-Lopes, Alexandre [Departamento de Física, Facultad de Ciencias, Universidad de La Serena, Cisternas 1200, La Serena (Chile); Hearty, Fred R. [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Zasowski, Gail [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218 (United States)

    2017-04-01

    We report on the H -band spectral variability of classical Be stars observed over the course of the Apache Point Galactic Evolution Experiment (APOGEE), one of four subsurveys comprising SDSS-III. As described in the first paper of this series, the APOGEE B-type emission-line (ABE) star sample was culled from the large number of blue stars observed as telluric standards during APOGEE observations. In this paper, we explore the multi-epoch ABE sample, consisting of 1100 spectra for 213 stars. These “snapshots” of the circumstellar disk activity have revealed a wealth of temporal variability including, but not limited to, gradual disappearance of the line emission and vice versa over both short and long timescales. Other forms of variability include variation in emission strength, emission peak intensity ratios, and emission peak separations. We also analyze radial velocities (RVs) of the emission lines for a subsample of 162 stars with sufficiently strong features, and we discuss on a case-by-case basis whether the RV variability exhibited by some stars is caused by binary motion versus dynamical processes in the circumstellar disks. Ten systems are identified as convincing candidates for binary Be stars with as of yet undetected companions.

  6. Determinations of its Absolute Dimensions and Distance by the Analyses of Light and Radial-Velocity Curves of the Contact Binary -I. V417 Aquilae

    Directory of Open Access Journals (Sweden)

    Jae Woo Lee

    2004-06-01

    Full Text Available New photometric and spectroscopic solutions of W-type overcontact binary V417 Aql were obtained by solving the UBV light curves of Samec et al. (1997 and radial-velocity ones of Lu & Rucinski (1999 with the 2003 version of the Wilson-Devinney binary code. In the light curve synthesis the light of a third-body, which Qian (2003 proposed, was considered and obtained about 2.7%, 2.2%, and 0.4% for U, B, and V bandpasses, respectively. The model with third-light is better fitted to eclipse parts than that with no third-light. Absolute dimensions of V417 Aql are determined from our solution as M1=0.53 M⊙, M2=1.45 M⊙, R1=0.84 R⊙ and R2=1.31 M⊙, and the distance to it is deduced as about 216pc. Our distance is well consistent with that (204pc derived from Rucinski & Duerbeck's (1997 relation, MV=MV(log P, B-V, but is more distant than that (131±40pc determined by the Hipparcos trigonometric parallax. The difference may result from the relatively large error of Hipparcos parallax for V417 Aql.

  7. Influence of velocity gradient on optimisation of the aggregation process and physical properties of formed aggregates. Part 1. Inline high density suspension (IHDS) aggregation process

    Czech Academy of Sciences Publication Activity Database

    Polášek, Pavel

    2011-01-01

    Roč. 59, č. 2 (2011), s. 107-117 ISSN 0042-790X R&D Projects: GA ČR GA103/07/1016 Institutional research plan: CEZ:AV0Z20600510 Keywords : flocculation optimum * inline high density suspension (IHDS) formation process * properties of aggregates * intensity of agitation * velocity gradient G Subject RIV: BK - Fluid Dynamics Impact factor: 0.340, year: 2011

  8. Phenomena accompanying gradient-B drift injection of energetic ions into Tokamak plasmas

    International Nuclear Information System (INIS)

    Goldston, R.J.; Jassby, D.L.

    1976-01-01

    The application of vertically asymmetric toroidal-field ripple, in order to permit the gradient B-drift injection and subsequent capture of energetic ions, results in a new radial diffusion of banana orbits. The nearly mono-kinetic velocity distribution of gradient B-drifting ions in the outer plasma region represents a large source of free energy; and the nonambipolar inward drift of these ions modifies the radial electric field

  9. MARVELS-1: A FACE-ON DOUBLE-LINED BINARY STAR MASQUERADING AS A RESONANT PLANETARY SYSTEM AND CONSIDERATION OF RARE FALSE POSITIVES IN RADIAL VELOCITY PLANET SEARCHES

    International Nuclear Information System (INIS)

    Wright, Jason T.; Roy, Arpita; Mahadevan, Suvrath; Wang, Sharon X.; Fleming, Scott W.; Ford, Eric B.; Payne, Matt; Lee, Brian L.; Ge, Jian; Wang, Ji; Crepp, Justin R.; Gaudi, B. Scott; Eastman, Jason; Pepper, Joshua; Cargile, Phillip; Stassun, Keivan G.; Ghezzi, Luan; González-Hernández, Jonay I.; Wisniewski, John; Dutra-Ferreira, Leticia

    2013-01-01

    We have analyzed new and previously published radial velocity (RV) observations of MARVELS-1, known to have an ostensibly substellar companion in a ∼6 day orbit. We find significant (∼100 m s –1 ) residuals to the best-fit model for the companion, and these residuals are naïvely consistent with an interior giant planet with a P = 1.965 days in a nearly perfect 3:1 period commensurability (|P b /P c – 3| –4 ). We have performed several tests for the reality of such a companion, including a dynamical analysis, a search for photometric variability, and a hunt for contaminating stellar spectra. We find many reasons to be critical of a planetary interpretation, including the fact that most of the three-body dynamical solutions are unstable. We find no evidence for transits, and no evidence of stellar photometric variability. We have discovered two apparent companions to MARVELS-1 with adaptive optics imaging at Keck; both are M dwarfs, one is likely bound, and the other is likely a foreground object. We explore false-alarm scenarios inspired by various curiosities in the data. Ultimately, a line profile and bisector analysis lead us to conclude that the ∼100 m s –1 residuals are an artifact of spectral contamination from a stellar companion contributing ∼15%-30% of the optical light in the system. We conclude that origin of this contamination is the previously detected RV companion to MARVELS-1, which is not, as previously reported, a brown dwarf, but in fact a G dwarf in a face-on orbit.

  10. A HIGH-PRECISION NEAR-INFRARED SURVEY FOR RADIAL VELOCITY VARIABLE LOW-MASS STARS USING CSHELL AND A METHANE GAS CELL

    Energy Technology Data Exchange (ETDEWEB)

    Gagné, Jonathan [Carnegie Institution of Washington DTM, 5241 Broad Branch Road NW, Washington, DC 20015 (United States); Plavchan, Peter [Department of Physics, Missouri State University, 901 S National Ave, Springfield, MO 65897 (United States); Gao, Peter [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Anglada-Escude, Guillem [School of Physics and Astronomy, Queen Mary University of London, 327 Mile End Rd, E1 4NS, London (United Kingdom); Furlan, Elise; Brinkworth, Carolyn; Ciardi, David R. [NASA Exoplanet Science Institute, California Institute of Technology, 770 S. Wilson Ave., Pasadena, CA 91125 (United States); Davison, Cassy; Henry, Todd J.; White, Russel [Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303 (United States); Tanner, Angelle [Mississippi State University, Department of Physics and Astronomy, Hilbun Hall, Starkville, MS 39762 (United States); Riedel, Adric R. [Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States); Latham, David; Johnson, John A. [Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States); Bottom, Michael [Department of Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States); Mills, Sean [Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Ave, Chicago, IL 60637 (United States); Beichman, Chas [NASA Exoplanet Science Institute, California Institute of Technology, Pasadena, CA 91125 (United States); Wallace, Kent; Mennesson, Bertrand [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr, Pasadena, CA 91125 (United States); Von Braun, Kaspar, E-mail: jgagne@carnegiescience.edu [Lowell Observatory, West Mars Hill Road, Flagstaff, AZ 86001 (United States); and others

    2016-05-01

    We present the results of a precise near-infrared (NIR) radial velocity (RV) survey of 32 low-mass stars with spectral types K2–M4 using CSHELL at the NASA InfraRed Telescope Facility in the K band with an isotopologue methane gas cell to achieve wavelength calibration and a novel, iterative RV extraction method. We surveyed 14 members of young (≈25–150 Myr) moving groups, the young field star ε Eridani, and 18 nearby (<25 pc) low-mass stars and achieved typical single-measurement precisions of 8–15 m s{sup −1}with a long-term stability of 15–50 m s{sup −1} over longer baselines. We obtain the best NIR RV constraints to date on 27 targets in our sample, 19 of which were never followed by high-precision RV surveys. Our results indicate that very active stars can display long-term RV variations as low as ∼25–50 m s{sup −1} at ≈2.3125 μ m, thus constraining the effect of jitter at these wavelengths. We provide the first multiwavelength confirmation of GJ 876 bc and independently retrieve orbital parameters consistent with previous studies. We recovered RV variabilities for HD 160934 AB and GJ 725 AB that are consistent with their known binary orbits, and nine other targets are candidate RV variables with a statistical significance of 3 σ –5 σ . Our method, combined with the new iSHELL spectrograph, will yield long-term RV precisions of ≲5 m s{sup −1} in the NIR, which will allow the detection of super-Earths near the habitable zone of mid-M dwarfs.

  11. ASTROMETRY AND RADIAL VELOCITIES OF THE PLANET HOST M DWARF GJ 317: NEW TRIGONOMETRIC DISTANCE, METALLICITY, AND UPPER LIMIT TO THE MASS OF GJ 317b

    International Nuclear Information System (INIS)

    Anglada-Escudé, Guillem; Boss, Alan P.; Weinberger, Alycia J.; Butler, R. Paul; Thompson, Ian B.; Vogt, Steven S.; Rivera, Eugenio J.

    2012-01-01

    We have obtained precision astrometry of the planet host M dwarf GJ 317 in the framework of the Carnegie Astrometric Planet Search project. The new astrometric measurements give a distance determination of 15.3 pc, 65% further than previous estimates. The resulting absolute magnitudes suggest that it is metal-rich and more massive than previously assumed. This result strengthens the correlation between high metallicity and the presence of gas giants around low-mass stars. At 15.3 pc, the minimal astrometric amplitude for planet candidate GJ 317b is 0.3 mas (edge-on orbit), just below our astrometric sensitivity. However, given the relatively large number of observations and good astrometric precision, a Bayesian Monte Carlo Markov Chain analysis indicates that the mass of planet b has to be smaller than twice the minimum mass with a 99% confidence level, with a most likely value of 2.5 M Jup . Additional radial velocity (RV) measurements obtained with Keck by the Lick-Carnegie Planet search program confirm the presence of an additional very long period planet candidate, with a period of 20 years or more. Even though such an object will imprint a large astrometric wobble on the star, its curvature is yet not evident in the astrometry. Given high metallicity, and the trend indicating that multiple systems are rich in low-mass companions, this system is likely to host additional low-mass planets in its habitable zone that can be readily detected with state-of-the-art optical and near-infrared RV measurements.

  12. A HIGH-PRECISION NEAR-INFRARED SURVEY FOR RADIAL VELOCITY VARIABLE LOW-MASS STARS USING CSHELL AND A METHANE GAS CELL

    International Nuclear Information System (INIS)

    Gagné, Jonathan; Plavchan, Peter; Gao, Peter; Anglada-Escude, Guillem; Furlan, Elise; Brinkworth, Carolyn; Ciardi, David R.; Davison, Cassy; Henry, Todd J.; White, Russel; Tanner, Angelle; Riedel, Adric R.; Latham, David; Johnson, John A.; Bottom, Michael; Mills, Sean; Beichman, Chas; Wallace, Kent; Mennesson, Bertrand; Von Braun, Kaspar

    2016-01-01

    We present the results of a precise near-infrared (NIR) radial velocity (RV) survey of 32 low-mass stars with spectral types K2–M4 using CSHELL at the NASA InfraRed Telescope Facility in the K band with an isotopologue methane gas cell to achieve wavelength calibration and a novel, iterative RV extraction method. We surveyed 14 members of young (≈25–150 Myr) moving groups, the young field star ε Eridani, and 18 nearby (<25 pc) low-mass stars and achieved typical single-measurement precisions of 8–15 m s −1 with a long-term stability of 15–50 m s −1 over longer baselines. We obtain the best NIR RV constraints to date on 27 targets in our sample, 19 of which were never followed by high-precision RV surveys. Our results indicate that very active stars can display long-term RV variations as low as ∼25–50 m s −1 at ≈2.3125 μ m, thus constraining the effect of jitter at these wavelengths. We provide the first multiwavelength confirmation of GJ 876 bc and independently retrieve orbital parameters consistent with previous studies. We recovered RV variabilities for HD 160934 AB and GJ 725 AB that are consistent with their known binary orbits, and nine other targets are candidate RV variables with a statistical significance of 3 σ –5 σ . Our method, combined with the new iSHELL spectrograph, will yield long-term RV precisions of ≲5 m s −1 in the NIR, which will allow the detection of super-Earths near the habitable zone of mid-M dwarfs.

  13. ASTROMETRY AND RADIAL VELOCITIES OF THE PLANET HOST M DWARF GJ 317: NEW TRIGONOMETRIC DISTANCE, METALLICITY, AND UPPER LIMIT TO THE MASS OF GJ 317b

    Energy Technology Data Exchange (ETDEWEB)

    Anglada-Escude, Guillem; Boss, Alan P.; Weinberger, Alycia J.; Butler, R. Paul [Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Road NW, Washington, DC 20015 (United States); Thompson, Ian B. [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Vogt, Steven S.; Rivera, Eugenio J., E-mail: anglada@dtm.ciw.edu [UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States)

    2012-02-10

    We have obtained precision astrometry of the planet host M dwarf GJ 317 in the framework of the Carnegie Astrometric Planet Search project. The new astrometric measurements give a distance determination of 15.3 pc, 65% further than previous estimates. The resulting absolute magnitudes suggest that it is metal-rich and more massive than previously assumed. This result strengthens the correlation between high metallicity and the presence of gas giants around low-mass stars. At 15.3 pc, the minimal astrometric amplitude for planet candidate GJ 317b is 0.3 mas (edge-on orbit), just below our astrometric sensitivity. However, given the relatively large number of observations and good astrometric precision, a Bayesian Monte Carlo Markov Chain analysis indicates that the mass of planet b has to be smaller than twice the minimum mass with a 99% confidence level, with a most likely value of 2.5 M{sub Jup}. Additional radial velocity (RV) measurements obtained with Keck by the Lick-Carnegie Planet search program confirm the presence of an additional very long period planet candidate, with a period of 20 years or more. Even though such an object will imprint a large astrometric wobble on the star, its curvature is yet not evident in the astrometry. Given high metallicity, and the trend indicating that multiple systems are rich in low-mass companions, this system is likely to host additional low-mass planets in its habitable zone that can be readily detected with state-of-the-art optical and near-infrared RV measurements.

  14. Search for Exoplanets around Northern Circumpolar Stars. II. The Detection of Radial Velocity Variations in M Giant Stars HD 36384, HD 52030, and HD 208742

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Byeong-Cheol; Jeong, Gwanghui; Han, Inwoo; Lee, Sang-Min; Kim, Kang-Min [Korea Astronomy and Space Science Institute 776, Daedeokdae-ro, Yuseong-gu, Daejeon 305-348 (Korea, Republic of); Park, Myeong-Gu; Oh, Hyeong-Il [Department of Astronomy and Atmospheric Sciences, Kyungpook National University, Daegu 702-701 (Korea, Republic of); Mkrtichian, David E. [National Astronomical Research Institute of Thailand, Chiang Mai 50200 (Thailand); Hatzes, Artie P. [Thüringer Landessternwarte Tautenburg (TLS), Sternwarte 5, D-07778 Tautenburg (Germany); Gu, Shenghong; Bai, Jinming, E-mail: bclee@kasi.re.kr [Yunnan Observatories, Chinese Academy of Sciences, Kunming 650011 (China)

    2017-07-20

    We present the detection of long-period RV variations in HD 36384, HD 52030, and HD 208742 by using the high-resolution, fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) for the precise radial velocity (RV) survey of about 200 northern circumpolar stars. Analyses of RV data, chromospheric activity indicators, and bisector variations spanning about five years suggest that the RV variations are compatible with planet or brown dwarf companions in Keplerian motion. However, HD 36384 shows photometric variations with a period very close to that of RV variations as well as amplitude variations in the weighted wavelet Z-transform (WWZ) analysis, which argues that the RV variations in HD 36384 are from the stellar pulsations. Assuming that the companion hypothesis is correct, HD 52030 hosts a companion with minimum mass 13.3 M {sub Jup} orbiting in 484 days at a distance of 1.2 au. HD 208742 hosts a companion of 14.0 M {sub Jup} at 1.5 au with a period of 602 days. All stars are located at the asymptotic giant branch (AGB) stage on the H–R diagram after undergoing the helium flash and leaving the giant clump.With stellar radii of 53.0 R {sub ⊙} and 57.2 R {sub ⊙} for HD 52030 and HD 208742, respectively, these stars may be the largest yet, in terms of stellar radius, found to host substellar companions. However, given possible RV amplitude variations and the fact that these are highly evolved stars, the planet hypothesis is not yet certain.

  15. Magellan/PFS Radial Velocities of GJ 9827, a Late K dwarf at 30 pc with Three Transiting Super-Earths

    Science.gov (United States)

    Teske, Johanna K.; Wang, Sharon; Wolfgang, Angie; Dai, Fei; Shectman, Stephen A.; Butler, R. Paul; Crane, Jeffrey D.; Thompson, Ian B.

    2018-04-01

    The Kepler mission showed us that planets with sizes between that of Earth and Neptune appear to be the most common type in our Galaxy. These “super-Earths” continue to be of great interest for exoplanet formation, evolution, and composition studies. However, the number of super-Earths with well-constrained mass and radius measurements remains small (40 planets with σ mass Earth planets were detected by the K2 mission around the nearby star GJ 9827/HIP 115752, at only 30 pc away. The radii of the planets span the “radius gap” detected by Fulton et al. (2017), and all orbit within ∼6.5 days, easing follow-up observations. Here, we report radial velocity (RV) observations of GJ 9827, taken between 2010 and 2016 with the Planet Finder Spectrograph on the Magellan II Telescope. We employ two different RV analysis packages, SYSTEMIC and RADVEL, to derive masses and thus densities of the GJ 9827 planets. We also test a Gaussian Process regression analysis but find the correlated stellar noise is not well constrained by the PFS data and that the GP tends to over-fit the RV semi-amplitudes resulting in a lower K value. Our RV observations are not able to place strong mass constraints on the two outer planets (c and d) but do indicate that planet b, at 1.64 R ⊕ and ∼8 M ⊕, is one of the most massive (and dense) super-Earth planets detected to date.

  16. Electron velocity distribution function in a plasma with temperature gradient and in the presence of suprathermal electrons: application to incoherent-scatter plasma lines

    Directory of Open Access Journals (Sweden)

    P. Guio

    Full Text Available The plasma dispersion function and the reduced velocity distribution function are calculated numerically for any arbitrary velocity distribution function with cylindrical symmetry along the magnetic field. The electron velocity distribution is separated into two distributions representing the distribution of the ambient electrons and the suprathermal electrons. The velocity distribution function of the ambient electrons is modelled by a near-Maxwellian distribution function in presence of a temperature gradient and a potential electric field. The velocity distribution function of the suprathermal electrons is derived from a numerical model of the angular energy flux spectrum obtained by solving the transport equation of electrons. The numerical method used to calculate the plasma dispersion function and the reduced velocity distribution is described. The numerical code is used with simulated data to evaluate the Doppler frequency asymmetry between the up- and downshifted plasma lines of the incoherent-scatter plasma lines at different wave vectors. It is shown that the observed Doppler asymmetry is more dependent on deviation from the Maxwellian through the thermal part for high-frequency radars, while for low-frequency radars the Doppler asymmetry depends more on the presence of a suprathermal population. It is also seen that the full evaluation of the plasma dispersion function gives larger Doppler asymmetry than the heat flow approximation for Langmuir waves with phase velocity about three to six times the mean thermal velocity. For such waves the moment expansion of the dispersion function is not fully valid and the full calculation of the dispersion function is needed.

    Key words. Non-Maxwellian electron velocity distribution · Incoherent scatter plasma lines · EISCAT · Dielectric response function

  17. Electron velocity distribution function in a plasma with temperature gradient and in the presence of suprathermal electrons: application to incoherent-scatter plasma lines

    Directory of Open Access Journals (Sweden)

    P. Guio

    1998-10-01

    Full Text Available The plasma dispersion function and the reduced velocity distribution function are calculated numerically for any arbitrary velocity distribution function with cylindrical symmetry along the magnetic field. The electron velocity distribution is separated into two distributions representing the distribution of the ambient electrons and the suprathermal electrons. The velocity distribution function of the ambient electrons is modelled by a near-Maxwellian distribution function in presence of a temperature gradient and a potential electric field. The velocity distribution function of the suprathermal electrons is derived from a numerical model of the angular energy flux spectrum obtained by solving the transport equation of electrons. The numerical method used to calculate the plasma dispersion function and the reduced velocity distribution is described. The numerical code is used with simulated data to evaluate the Doppler frequency asymmetry between the up- and downshifted plasma lines of the incoherent-scatter plasma lines at different wave vectors. It is shown that the observed Doppler asymmetry is more dependent on deviation from the Maxwellian through the thermal part for high-frequency radars, while for low-frequency radars the Doppler asymmetry depends more on the presence of a suprathermal population. It is also seen that the full evaluation of the plasma dispersion function gives larger Doppler asymmetry than the heat flow approximation for Langmuir waves with phase velocity about three to six times the mean thermal velocity. For such waves the moment expansion of the dispersion function is not fully valid and the full calculation of the dispersion function is needed.Key words. Non-Maxwellian electron velocity distribution · Incoherent scatter plasma lines · EISCAT · Dielectric response function

  18. The three-dimensional distributions of tangential velocity and total- temperature in vortex tubes

    DEFF Research Database (Denmark)

    Linderstrøm-Lang, C.U.

    1971-01-01

    The axial and radial gradients of the tangential velocity distribution are calculated from prescribed secondary flow functions on the basis of a zero-order approximation to the momentum equations developed by Lewellen. It is shown that secondary flow functions may be devised which meet pertinent...... physical requirements and which at the same time lead to realistic tangential velocity gradients. The total-temperature distribution in both the axial and radial directions is calculated from such secondary flow functions and corresponding tangential velocity results on the basis of an approximate...

  19. Monitoring of the spatio-temporal change in the interplate coupling at northeastern Japan subduction zone based on the spatial gradients of surface velocity field

    Science.gov (United States)

    Iinuma, Takeshi

    2018-04-01

    A monitoring method to grasp the spatio-temporal change in the interplate coupling in a subduction zone based on the spatial gradients of surface displacement rate fields is proposed. I estimated the spatio-temporal change in the interplate coupling along the plate boundary in northeastern (NE) Japan by applying the proposed method to the surface displacement rates based on global positioning system observations. The gradient of the surface velocities is calculated in each swath configured along the direction normal to the Japan Trench for time windows such as 0.5, 1, 2, 3 and 5 yr being shifted by one week during the period of 1997-2016. The gradient of the horizontal velocities is negative and has a large magnitude when the interplate coupling at the shallow part (less than approximately 50 km in depth) beneath the profile is strong, and the sign of the gradient of the vertical velocity is sensitive to the existence of the coupling at the deep part (greater than approximately 50 km in depth). The trench-parallel variation of the spatial gradients of a displacement rate field clearly corresponds to the trench-parallel variation of the amplitude of the interplate coupling on the plate interface, as well as the rupture areas of previous interplate earthquakes. Temporal changes in the trench-parallel variation of the spatial gradient of the displacement rate correspond to the strengthening or weakening of the interplate coupling. We can monitor the temporal change in the interplate coupling state by calculating the spatial gradients of the surface displacement rate field to some extent without performing inversion analyses with applying certain constraint conditions that sometimes cause over- and/or underestimation at areas of limited spatial resolution far from the observation network. The results of the calculation confirm known interplate events in the NE Japan subduction zone, such as the post-seismic slip of the 2003 M8.0 Tokachi-oki and 2005 M7.2 Miyagi

  20. A Versatile Technique to Enable Sub-milli-Kelvin Instrument Stability for Precise Radial Velocity Measurements: Tests with the Habitable-zone Planet Finder

    Science.gov (United States)

    Stefansson, Gudmundur; Hearty, Frederick; Robertson, Paul; Mahadevan, Suvrath; Anderson, Tyler; Levi, Eric; Bender, Chad; Nelson, Matthew; Monson, Andrew; Blank, Basil; Halverson, Samuel; Henderson, Chuck; Ramsey, Lawrence; Roy, Arpita; Schwab, Christian; Terrien, Ryan

    2016-12-01

    Insufficient instrument thermomechanical stability is one of the many roadblocks for achieving 10 cm s-1 Doppler radial velocity precision, the precision needed to detect Earth-twins orbiting solar-type stars. Highly temperature and pressure stabilized spectrographs allow us to better calibrate out instrumental drifts, thereby helping in distinguishing instrumental noise from astrophysical stellar signals. We present the design and performance of the Environmental Control System (ECS) for the Habitable-zone Planet Finder (HPF), a high-resolution (R = 50,000) fiber-fed near-infrared (NIR) spectrograph for the 10 {{m}} Hobby-Eberly Telescope at McDonald Observatory. HPF will operate at 180 {{K}}, driven by the choice of an H2RG NIR detector array with a 1.7 μ {{m}} cutoff. This ECS has demonstrated 0.6 {mK} rms stability over 15 days at both 180 and 300 {{K}}, and maintained high-quality vacuum (\\lt {10}-7 {Torr}) over months, during long-term stability tests conducted without a planned passive thermal enclosure surrounding the vacuum chamber. This control scheme is versatile and can be applied as a blueprint to stabilize future NIR and optical high-precision Doppler instruments over a wide temperature range from ˜77 {{K}} to elevated room temperatures. A similar ECS is being implemented to stabilize NEID, the NASA/NSF NN-EXPLORE spectrograph for the 3.5 {{m}} WIYN telescope at Kitt Peak, operating at 300 {{K}}. A [full SolidWorks 3D-CAD model] and a comprehensive parts list of the HPF ECS are included with this manuscript to facilitate the adaptation of this versatile environmental control scheme in the broader astronomical community. Certain commercial equipment, instruments, or materials are identified in this paper in order to specify the experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the materials or equipment

  1. Free-breathing dynamic liver examination using a radial 3D T1-weighted gradient echo sequence with moderate undersampling for patients with limited breath-holding capacity

    Energy Technology Data Exchange (ETDEWEB)

    Kaltenbach, Benjamin, E-mail: benjamin.kaltenbach@kgu.de [Department of Diagnostic and Interventional Radiology, University Hospital Frankfurt am Main (Germany); Roman, Andrei; Polkowski, Christoph; Gruber-Rouh, Tatjana [Department of Diagnostic and Interventional Radiology, University Hospital Frankfurt am Main (Germany); Bauer, Ralf W. [Department of Diagnostic and Interventional Radiology, University Hospital Frankfurt am Main (Germany); Divison of Radiology and Nuclear Medicine, Kantonsspital, St. Gallen (Switzerland); Hammerstingl, Renate; Vogl, Thomas J.; Zangos, Stephan [Department of Diagnostic and Interventional Radiology, University Hospital Frankfurt am Main (Germany)

    2017-01-15

    Highlights: • Respiratory artifacts are a frequent problem in abdominal MR imaging. • Non-diagnostic examinations could be reduced using free-breathing us-radial-VIBE for dynamic liver examination in challenging patients. • Streak artifacts are characteristic for an undersampled radial acquisition but do not affect diagnostic validity. - Abstract: Purpose: To compare free-breathing radial VIBE with moderate undersampling (us-radial-VIBE) with a standard breathhold T1-weighted volumetric interpolated sequence (3D GRE VIBE) in patients unable to suspend respiration during dynamic liver examination. Material and methods: 23 consecutive patients underwent dynamic liver MR examination using the free-breathing us-radial-VIBE sequence as part of their oncologic follow-up. All patients were eligible for the free-breathing protocol due to severe respiratory artifacts at the planning or precontrast sequences. The us-radial-VIBE acquisitions were compared to the patientś last staging liver MRI including a standard breathhold 3D GRE VIBE. For an objective image evaluation, signal intensity (SI), image noise (IN), signal-to-noise ratio (SNR) and contrast-enhancement ratio (CER) were compared. Representative image quality parameters, including typical artifacts were independently, retrospectively and blindly scored by four readers. Results: Us-radial-VIBE had significant lower SNR (p < 0.0001) and higher IN (p < 0.0001), whereas SI did not differ (p = 0.62). Temporal resolution assessed with CER in the arterial phase showed higher values for us-radial-VIBE (p = 0.028). Subjective image quality parameters received generally slightly higher scores for 3D GRE VIBE. In a smaller subgroup comprising patients with severe respiratory artifacts also at reference breathhold 3D GRE VIBE examination, us-radial-VIBE showed significantly higher image quality scores. Furthermore, there were generally more severe respiratory artifacts in 3D GRE VIBE, whereas streaking was characteristic

  2. Local topology via the invariants of the velocity gradient tensor within vortex clusters and intense Reynolds stress structures in turbulent channel flow

    International Nuclear Information System (INIS)

    Buchner, Abel-John; Kitsios, Vassili; Atkinson, Callum; Soria, Julio; Lozano-Durán, Adrián

    2016-01-01

    Previous works have shown that momentum transfer in the wall–normal direction within turbulent wall–bounded flows occurs primarily within coherent structures defined by regions of intense Reynolds stress [1]. Such structures may be classified into wall–attached and wall–detached structures with the latter being typically weak, small–scale, and isotropically oriented, while the former are larger and carry most of the Reynolds stresses. The mean velocity fluctuation within each structure may also be used to separate structures by their dynamic properties. This study aims to extract information regarding the scales, kinematics and dynamics of these structures within the topological framework of the invariants of the velocity gradient tensor (VGT). The local topological characteristics of these intense Reynolds stress structures are compared to the topological characteristics of vortex clusters defined by the discriminant of the velocity gradient tensor. The alignment of vorticity with the principal strain directions within these structures is also determined, and the implications of these findings are discussed. (paper)

  3. Recent TAURUS results on Hα velocities in M83

    International Nuclear Information System (INIS)

    Allen, R.J.; Atherton, P.D.; Oosterloo, T.A.

    1983-01-01

    Preliminary Hα observations with the TAURUS imaging spectrometer confirm a pattern of systematic radial motions in a section of spiral arm in M83. The velocity gradients are not consistent with those predicted for the neutral gas. Non-circular motions have also been discovered in the central regions of the galaxy. (Auth.)

  4. Shear-Velocity Structure and Azimuthal and Radial Anisotropy Beneath the Kaapvaal Craton From Bayesian Inversion of Surface-Wave Data: Inferences for the Architecture and Early Evolution of Cratons

    Science.gov (United States)

    Lebedev, S.; Ravenna, M.; Adam, J.

    2017-12-01

    Seismic anisotropy provides essential information on the deformation of the lithosphere. Knowledge of anisotropy also allows us to isolate the isotropic-average seismic velocities, relatable to the lithospheric temperature and composition. We use Rayleigh and Love-wave phase velocities and their azimuthal anisotropy measured in broad period ranges across the footprint of the Southern Africa Seismic Experiment (SASE), from the Kaapvaal Craton to the Limpopo Belt. We invert the data using our recently developed, fully non-linear Markov Chain Monte Carlo method and determine, for the first time, both the isotropic-average S velocity and its radial and azimuthal anisotropy as a function of depth from the upper crust down to the asthenosphere. The probabilistic inversion provides a way to quantify non-uniqueness, using direct parameter-space sampling, and assess model uncertainties. The high-velocity anomaly indicative of the cold cratonic lithosphere bottoms at 200-250 km beneath the central and western Kaapvaal Craton, underlain by a low-velocity zone. Beneath northern Kaapvaal and Limpopo, by contrast, high velocities extend down to 300-350 km. Although this does not require a lithosphere that has maintained this thickness over a geologically long time, the data does require the mantle to be anomalously cold down to 300-350 km. Interestingly, topography correlates with the thickness of this high-velocity layer, with lower elevations where the lid is thicker. Radial shear-wave anisotropy is in the 2-5 percent range (Vsh > Vsv) from the lower crust down to 200 km, below which depth it decreases gradually. Radial variations in the amplitude of radial anisotropy show no clear relationship with those in the amplitude of azimuthal anisotropy or isotropic-average Vs anomalies. Azimuthal anisotropy changes the fast-propagation direction near the base of the lithosphere (200-300 km depth), from the laterally varying fast azimuths in the lower lithosphere to a spatially

  5. GICLAS 112-29 (=NLTT 18149), A VERY WIDE COMPANION TO GJ 282 AB WITH COMMON PROPER MOTION, COMMON PARALLAX, COMMON RADIAL VELOCITY AND COMMON AGE

    OpenAIRE

    A. Poveda; A. Hernández-Alcántara; R. Costero; J. Echevarría

    2008-01-01

    En una búsqueda de compa~neras con movimiento propio común para las binarias separadas de la vecindad solar encontramos que GJ 282AB tiene una compañera distante (NLTT 18149), a una separaci on de s = 1:09°. Las paralajes trigonométricas (Hipparcos), velocidades radiales y edades son similares, y sugieren que éste es un sistema físico.

  6. Metallicity gradient of the thick disc progenitor at high redshift

    Science.gov (United States)

    Kawata, Daisuke; Allende Prieto, Carlos; Brook, Chris B.; Casagrande, Luca; Ciucă, Ioana; Gibson, Brad K.; Grand, Robert J. J.; Hayden, Michael R.; Hunt, Jason A. S.

    2018-01-01

    We have developed a novel Markov Chain Monte Carlo chemical 'painting' technique to explore possible radial and vertical metallicity gradients for the thick disc progenitor. In our analysis, we match an N-body simulation to the data from the Apache Point Observatory Galactic Evolution Experiment survey. We assume that the thick disc has a constant scaleheight and has completed its formation at an early epoch, after which time radial mixing of its stars has taken place. Under these assumptions, we find that the initial radial metallicity gradient of the thick disc progenitor should not be negative, but either flat or even positive, to explain the current negative vertical metallicity gradient of the thick disc. Our study suggests that the thick disc was built-up in an inside-out and upside-down fashion, and older, smaller and thicker populations are more metal poor. In this case, star-forming discs at different epochs of the thick disc formation are allowed to have different radial metallicity gradients, including a negative one, which helps to explain a variety of slopes observed in high-redshift disc galaxies. This scenario helps to explain the positive slope of the metallicity-rotation velocity relation observed for the Galactic thick disc. On the other hand, radial mixing flattens the slope of an existing gradient.

  7. Measurement of the radial electric field in the ASDEX tokamak

    International Nuclear Information System (INIS)

    Field, A.R.; Fussmann, G.; Hofmann, J.V.

    1990-12-01

    The radial electric field (E Τ ) at the plasma periphery is determined by measuring the drift velocities of low-Z impurities ions (BIV, CIII and HeII). The measurements are performed with a scannable mirror system which allows the determination of the poloidal, perpendicular (to B vector) and toroidal components of the drift velocities from the differential Doppler shift of visible line emission observed along opposing viewing directions. The principle of the measurement is investigated in detail. In particular, it is shown that for radially localised emission shells there exits a line of sight oriented perpendicular to B vector along which E Τ may be inferred directly from the observed Doppler shift of the line emission. Along such a line of sight the net contribution to the shift from the diamagnetic drift and the radial gradient of the excitation probability is negligible. During the Ohmic- and L-phases the perpendicular drift velocity of the BIV ions measured approximately 2 cm inside the separatrix is small (≤ 2 kms -1 ) and in the ion diamagnetic drift direction. However, at the L → H-Mode transition it changes sign and begins to increase on the time-scale of the edge pressure gradients reaching the highest values at the end of the H * -phase. From these high perpendicular drift velocities it is infered that, in the H-mode, there exists a strong negative radial electric field (vertical strokeE τ vertical stroke ≤ kVm -1 ) just inside the separatrix. The dependence of the drift velocity of the BIV ions and E Τ on the NBI-heating power and the magnitude and direction of the plasma current and the magnetic field is investigated. (orig.)

  8. Variação temporal do gradiente radial de o/h a partir de uma amostra de nebulosas planetárias

    Science.gov (United States)

    Maciel, W. J.; Costa, R. D. D.; Uchida, M. M. M.

    2003-08-01

    Gradientes radiais de abundância são observados no disco de nossa Galáxia e também em outras galáxias espirais. No caso da Galáxia, o principal problema relativo aos gradientes é sua variação temporal, que constitui um dos principais vínculos aos modelos de evolução química da Galáxia. As nebulosas planetárias são particularmente interessantes no estudo dos gradientes e suas variações, tanto espaciais como temporais. São objetos brilhantes, podendo ser observadas a grandes distâncias, e têm abundâncias relativamente precisas de diversos elementos químicos. Além disso, sendo originadas de estrelas com massas entre 0.8 e 8 massas solares na sequência principal, incluem objetos com idades e populações diferentes, o que as torna especialmente interessantes ao estudo da variação temporal dos gradientes. Neste trabalho, apresentamos resultados recentes sobre a variação temporal do gradiente de O/H a partir de uma amostra contendo cerca de 200 nebulosas, para as quais obtivemos distâncias por métodos estatísticos. As abundâncias foram parcialmente obtidas a partir de observações em Itajubá e La Silla, sendo as restantes obtidas da literatura. Os resultados mostram, pela primeira vez, evidências de um achatamento do gradiente de O/H, de -0.11 dex/kpc para -0.06 dex/kpc nos últimos 9 giga-anos ou de -0.08 dex/kpc para -0.06 dex/kpc nos últimos 5 giga-anos. Esses valores apresentam um bom acordo com alguns modelos recentes para a evolução química da Galáxia. (FAPESP/CNPq)

  9. THE EFFECTS OF GRADIENT VELOCITY AND DETENTION TIME TO COAGULATION – FLOCCULATION OF DYES AND ORGANIC COMPOUND IN DEEP WELL WATER

    Directory of Open Access Journals (Sweden)

    Muhamad Lindu

    2010-06-01

    Full Text Available The treatment of deep well water of Trisakti University by coagulation and flocculation using baffle channel system has been conducted. The detention time of hydrolic were varied. The coagulant dose was varied as 50, 100, 150, 200, 300, 350, 400, 450 and 500 ppm. Water of well sampel was added by coagulant with rotation velocity 200 rpm for 1 minute. The optimal coagulant dose was determined by measuring turbidity, colour, total suspended solids and organic compound. The result showed that the organic compound and colour of deep well water of Trisakti University could be reduced by coagulation and flocculation process by hydrolyc system. The optimal dose of the coagulant was 250 ppm. The removal efficiency of colour and organic compound using optimal dose for continuous flow reactor reached after water flow passed the reactor for 3 - 5 times detention time in the reactor. The optimal gradient velocity (G was 30 - 35 sec-1 and collision energy (GT was 65.000 - 79.000 to get optimal flocculation. With this condition, the removal efficiency of turbidity, colour and organic was more than 90%.   Keywords: coagulation, flocculation, colour, organic compound, deep well

  10. Wood formation from the base to the crown in Pinus radiata: gradients of tracheid wall thickness, wood density, radial growth rate and gene expression

    Science.gov (United States)

    Sheree Cato; Lisa McMillan; Lloyd Donaldson; Thomas Richardson; Craig Echt; Richard Gardner

    2006-01-01

    Wood formation was investigated at five heights along the bole for two unrelated trees of Pinus radiataBoth trees showed clear gradients in wood properties from the base to the crown. Cambial cells at the base of the tree were dividing 3.3-fold slower than those at the crown, while the average thickness of cell walls in wood was highest at the base....

  11. Radial k-t SPIRiT: autocalibrated parallel imaging for generalized phase-contrast MRI.

    Science.gov (United States)

    Santelli, Claudio; Schaeffter, Tobias; Kozerke, Sebastian

    2014-11-01

    To extend SPIRiT to additionally exploit temporal correlations for highly accelerated generalized phase-contrast MRI and to compare the performance of the proposed radial k-t SPIRiT method relative to frame-by-frame SPIRiT and radial k-t GRAPPA reconstruction for velocity and turbulence mapping in the aortic arch. Free-breathing navigator-gated two-dimensional radial cine imaging with three-directional multi-point velocity encoding was implemented and fully sampled data were obtained in the aortic arch of healthy volunteers. Velocities were encoded with three different first gradient moments per axis to permit quantification of mean velocity and turbulent kinetic energy. Velocity and turbulent kinetic energy maps from up to 14-fold undersampled data were compared for k-t SPIRiT, frame-by-frame SPIRiT, and k-t GRAPPA relative to the fully sampled reference. Using k-t SPIRiT, improvements in magnitude and velocity reconstruction accuracy were found. Temporally resolved magnitude profiles revealed a reduction in spatial blurring with k-t SPIRiT compared with frame-by-frame SPIRiT and k-t GRAPPA for all velocity encodings, leading to improved estimates of turbulent kinetic energy. k-t SPIRiT offers improved reconstruction accuracy at high radial undersampling factors and hence facilitates the use of generalized phase-contrast MRI for routine use. Copyright © 2013 Wiley Periodicals, Inc.

  12. Effect of Doppler Radial Velocity Data Assimilation on the Simulation of a Typhoon Approaching Taiwan: A Case Study of Typhoon Aere (2004

    Directory of Open Access Journals (Sweden)

    Hsin-Hung Lin

    2011-01-01

    Full Text Available Compared to conventional data, radar observations have an advantage of high spatial and temporal resolutions, and Doppler radars are capable of capturing detailed characteristics of flow fields, including typhoon circulation. In this study, the possible improvement of short-term typhoon predictions near Taiwan, particularly with regard to related rainfall forecasts over the mountainous island, using Doppler radial wind observations is explored. The case of Typhoon Aere (2004 was chosen for study, and a series of experiments were carried out using the Penn State University/National Center for Atmospheric Research (PSU/NCAR Mesoscale Model Version 5 (MM5 with its three-dimensional variational (3D-VAR data assimilation system.

  13. Atmospheric kinematics of high velocity long period variables

    International Nuclear Information System (INIS)

    Willson, L.A.

    1982-01-01

    Radial velocities of atomic absorption lines of three long period variables, RT Cyg, Z Oph and S Car, have been analysed in order to understand velocity gradients and discontinuities in their atmospheres. Phase coverage is from five days before maximum to 73 days after maximum for RT Cyg, from 17 days before to 44 days after maximum for Z Oph, and at 9 days before maximum for S Car. On a few spectrograms double lines were seen. All spectrograms were analysed by a four-parameter regression programme to yield the dependence of the radial velocity on the excitation potential, first ionization potential, wavelength and line strength, as indicators of the depth of line formation. The data were analysed to yield the velocity discontinuity across shock waves and velocity gradients between shock waves. Near maximum light the radial velocities cannot be understood by the presence of one shock only but rather require two shocks. The lower shock becomes apparent at the longer wavelengths. Consistent parameters are obtained if these stars are fundamental mode pulsators with total masses in the range of 0.5 to 1.0 solar mass and effective radii in the range of 0.85 to 1.5 x 10 13 cm. (author)

  14. The influence of collisional and anomalous radial diffusion on parallel ion transport in edge plasmas

    International Nuclear Information System (INIS)

    Helander, P.; Hazeltine, R.D.; Catto, P.J.

    1996-01-01

    The orderings in the kinetic equations commonly used to study the plasma core of a tokamak do not allow a balance between parallel ion streaming and radial diffusion, and are, therefore, inappropriate in the plasma edge. Different orderings are required in the edge region where radial transport across the steep gradients associated with the scrape-off layer is large enough to balance the rapid parallel flow caused by conditions close to collecting surfaces (such as the Bohm sheath condition). In the present work, we derive and solve novel kinetic equations, allowing for such a balance, and construct distinctive transport laws for impure, collisional, edge plasmas in which the perpendicular transport is (i) due to Coulomb collisions of ions with heavy impurities, or (ii) governed by anomalous diffusion driven by electrostatic turbulence. In both the collisional and anomalous radial transport cases, we find that one single diffusion coefficient determines the radial transport of particles, momentum and heat. The parallel transport laws and parallel thermal force in the scrape-off layer assume an unconventional form, in which the relative ion-impurity flow is driven by a combination of the conventional parallel gradients, and new (i) collisional or (ii) anomalous terms involving products of radial derivatives of the temperature and density with the radial shear of the parallel velocity. Thus, in the presence of anomalous radial diffusion, the parallel ion transport cannot be entirely classical, as usually assumed in numerical edge computations. The underlying physical reason is the appearance of a novel type of parallel thermal force resulting from the combined action of anomalous diffusion and radial temperature and velocity gradients. In highly sheared flows the new terms can modify impurity penetration into the core plasma

  15. Deconstructing Disk Velocity Distribution Functions in the Disk-Mass Survey

    NARCIS (Netherlands)

    Westfall, K. B.; Bershady, M. A.; Verheijen, M. A. W.; Andersen, D. R.; Swaters, R. A.

    2008-01-01

    We analyze integral-field ionized gas and stellar line-of-sight kinematics in the context of determining the stellar velocity ellipsoid for spiral galaxies observed by the Disk-Mass Survey. Our new methodology enables us to measure, for the first time, a radial gradient in the ellipsoid ratio

  16. Stability of radial swirl flows

    International Nuclear Information System (INIS)

    Dou, H S; Khoo, B C

    2012-01-01

    The energy gradient theory is used to examine the stability of radial swirl flows. It is found that the flow of free vortex is always stable, while the introduction of a radial flow will induce the flow to be unstable. It is also shown that the pure radial flow is stable. Thus, there is a flow angle between the pure circumferential flow and the pure radial flow at which the flow is most unstable. It is demonstrated that the magnitude of this flow angle is related to the Re number based on the radial flow rate, and it is near the pure circumferential flow. The result obtained in this study is useful for the design of vaneless diffusers of centrifugal compressors and pumps as well as other industrial devices.

  17. Neoclassical rotation velocities in multispecies plasmas

    International Nuclear Information System (INIS)

    Houlberg, W.A.; Hirshman, S.P.; Shaing, K.C.

    1996-01-01

    We examine the relationships between the poloidal, toroidal and parallel rotation velocities for typical plasma conditions in existing tokamak experiments. The radial force balance, neoclassical solution to the poloidal flow from the parallel force balance, and anomalous toroidal rotation axe included. A full multispecies formulation of the neoclassical transport theory is implemented in the NCLASS code (which includes arbitrary axisymmetric geometries and plasma collisionalities) to determine the poloidal rotation velocities. Comparisons are made with analytic relationships derived from a single impurity formulation of the problem. The roles of the radial electric field and species density and pressure gradients are evaluated. The determination of the radial electric field using the NCLASS solution for poloidal rotation and a local measurement of the toroidal rotation in conjunction with measured plasma profiles is discussed; it has been used in analysis of TFTR enhanced reverse shear plasmas. The ordering of banana orbit size small relative to local minor radius and gradients (as incorporated into initial versions of NCLASS) are examined for typical negative shear plasmas. We show the degree to which these constraints axe violated and demonstrate that finite orbit corrections axe required for better determination of the bootstrap current, particle fluxes and ion heat fluxes, i.e., the conditions r much-lt Δ b much-lt r n , r T , r E are significantly violated. Progress in relaxing these constraints is discussed

  18. EarthFinder: A Precise Radial Velocity Survey Probe Mission of our Nearest Stellar Neighbors for Earth-Mass Habitable Zone Analogs Using High-Resolution UV-Vis-NIR Echelle Spectroscopy on a Space Platform

    Science.gov (United States)

    Plavchan, Peter; EarthFinder Team

    2018-01-01

    We are investigating the science case for a 1.0-1.4 meter space telescope to survey the closest, brightest FGKM main sequence stars to search for Habitable Zone (HZ) Earth analogs using the precise radial velocity (PRV) technique at a precision of 1-10 cm/s. Our baseline instrument concept uses two diffraction-limited spectrographs operating in the 0.4-1.0 microns and 1.0-2.4 microns spectral regions each with a spectral resolution of R=150,000~200,000, with the possibility of a third UV arm. Because the instrument utilizes a diffraction-limited input beam, the spectrograph would be extremely compact, less than 50 cm on a side, and illumination can be stabilized with the coupling of starlight into single mode fibers. With two octaves of wavelength coverage and a cadence unimpeded by any diurnal, seasonal, and atmospheric effects, EarthFinder will offer a unique platform for recovering stellar activity signals from starspots, plages, granulation, etc. to detect exoplanets at velocity semi-amplitudes currently not obtainable from the ground. Variable telluric absorption and emission lines may potentially preclude achieving PRV measurements at or below 10 cm/s in the visible and advantage compared to an annual ~3-6 month observing season from the ground for mitigating stellar activity and detecting the orbital periods of HZ Earth-mass analogs (e.g. ~6-months to ~2 years). Finally, we are compiling a list of ancillary science cases for the observatory, ranging from asteroseismology to the direct measurement of the expansion of the Universe.

  19. Aortic-Radial Pulse Wave Velocity Ratio in End-stage Renal Disease Patients: Association with Age, Body Tissue Hydration Status, Renal Failure Etiology and Five Years of Hemodialysis.

    Science.gov (United States)

    Bia, Daniel; Valtuille, Rodolfo; Galli, Cintia; Wray, Sandra; Armentano, Ricardo; Zócalo, Yanina; Cabrera-Fischer, Edmundo

    2017-03-01

    The etiology of the end-stage renal disease (ESRD) and the hydration status may be involved in the arterial stiffening process observed in hemodialyzed patients. The ratio between carotid-femoral and carotid-radial pulse wave velocity (PWV ratio) was recently proposed to characterize the patient-specific stiffening process. to analyze: (1) the PWV-ratio in healthy and hemodialyzed subjects, analyzing potential changes associated to etiologies of the ESRD, (2) the PWV-ratio and hydration status using multiple-frequency bioimpedance and, (3) the effects of hemodialysis on PWV-ratio in a 5-year follow-up. PWV-ratio was evaluated in 151 patients differentiated by the pathology determining their ESRD. Total body fluid (TBF), intra and extra cellular fluid (ICF, ECF) were measured in 65 of these patients using bioelectrical-impedance. The association between arterial, hemodynamic or fluid parameters was analyzed. PWV-ratio was evaluated in a group of patients (n = 25) 5 years later (follow-up study). PWV-ratio increased in the ESRD cohort with respect to the control group (1.03 ± 0.23 vs. 1.31 ± 0.37; p hydration status, but not with the blood pressure. PWV-ratio could be considered a blood pressure-independent parameter, associated with the age and hydration status of the patient.

  20. Improved Holistic Analysis of Rayleigh Waves for Single- and Multi-Offset Data: Joint Inversion of Rayleigh-Wave Particle Motion and Vertical- and Radial-Component Velocity Spectra

    Science.gov (United States)

    Dal Moro, Giancarlo; Moustafa, Sayed S. R.; Al-Arifi, Nassir S.

    2018-01-01

    Rayleigh waves often propagate according to complex mode excitation so that the proper identification and separation of specific modes can be quite difficult or, in some cases, just impossible. Furthermore, the analysis of a single component (i.e., an inversion procedure based on just one objective function) necessarily prevents solving the problems related to the non-uniqueness of the solution. To overcome these issues and define a holistic analysis of Rayleigh waves, we implemented a procedure to acquire data that are useful to define and efficiently invert the three objective functions defined from the three following "objects": the velocity spectra of the vertical- and radial-components and the Rayleigh-wave particle motion (RPM) frequency-offset data. Two possible implementations are presented. In the first case we consider classical multi-offset (and multi-component) data, while in a second possible approach we exploit the data recorded by a single three-component geophone at a fixed offset from the source. Given the simple field procedures, the method could be particularly useful for the unambiguous geotechnical exploration of large areas, where more complex acquisition procedures, based on the joint acquisition of Rayleigh and Love waves, would not be economically viable. After illustrating the different kinds of data acquisition and the data processing, the results of the proposed methodology are illustrated in a case study. Finally, a series of theoretical and practical aspects are discussed to clarify some issues involved in the overall procedure (data acquisition and processing).

  1. Development of vortex model with realistic axial velocity distribution

    International Nuclear Information System (INIS)

    Ito, Kei; Ezure, Toshiki; Ohshima, Hiroyuki

    2014-01-01

    A vortex is considered as one of significant phenomena which may cause gas entrainment (GE) and/or vortex cavitation in sodium-cooled fast reactors. In our past studies, the vortex is assumed to be approximated by the well-known Burgers vortex model. However, the Burgers vortex model has a simple but unreal assumption that the axial velocity component is horizontally constant, while in real the free surface vortex has the axial velocity distribution which shows large gradient in radial direction near the vortex center. In this study, a new vortex model with realistic axial velocity distribution is proposed. This model is derived from the steady axisymmetric Navier-Stokes equation as well as the Burgers vortex model, but the realistic axial velocity distribution in radial direction is considered, which is defined to be zero at the vortex center and to approach asymptotically to zero at infinity. As the verification, the new vortex model is applied to the evaluation of a simple vortex experiment, and shows good agreements with the experimental data in terms of the circumferential velocity distribution and the free surface shape. In addition, it is confirmed that the Burgers vortex model fails to calculate accurate velocity distribution with the assumption of uniform axial velocity. However, the calculation accuracy of the Burgers vortex model can be enhanced close to that of the new vortex model in consideration of the effective axial velocity which is calculated as the average value only in the vicinity of the vortex center. (author)

  2. Stirling Engine With Radial Flow Heat Exchangers

    Science.gov (United States)

    Vitale, N.; Yarr, George

    1993-01-01

    Conflict between thermodynamical and structural requirements resolved. In Stirling engine of new cylindrical configuration, regenerator and acceptor and rejector heat exchangers channel flow of working gas in radial direction. Isotherms in regenerator ideally concentric cylinders, and gradient of temperature across regenerator radial rather than axial. Acceptor and rejector heat exchangers located radially inward and outward of regenerator, respectively. Enables substantial increase in power of engine without corresponding increase in diameter of pressure vessel.

  3. Radial electric field in JET advanced tokamak scenarios with toroidal field ripple

    Energy Technology Data Exchange (ETDEWEB)

    Crombe, K [Postdoctoral Fellow of the Research Foundation - Flanders (FWO), Department of Applied Physics, Ghent University, Rozier 44, B-9000 Gent (Belgium); Andrew, Y; De Vries, P C; Giroud, C; Hawkes, N C; Meigs, A; Zastrow, K-D [EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon, OX14 3DB (United Kingdom); Biewer, T M [Oak Ridge National Laboratory, Oak Ridge, TN 37831-6169, TN (United States); Blanco, E [Laboratorio Nacional de Fusion, Asociacion EURATOM-CIEMAT, Madrid (Spain); Tala, T [VTT Technical Research Centre of Finland, Association EURATOM-Tekes, PO Box 1000, FIN-02044 VTT (Finland); Von Hellermann, M [FOM Institute for Plasma Physics Rijnhuizen, Association EURATOM-FOM, Trilateral Euregio Cluster, PO Box 1207, 3430 BE Nieuwegein (Netherlands)], E-mail: Kristel.Crombe@jet.uk

    2009-05-15

    A dedicated campaign has been run on JET to study the effect of toroidal field (TF) ripple on plasma performance. Radial electric field measurements from experiments on a series of plasmas with internal transport barriers (ITBs) and different levels of ripple amplitude are presented. They have been calculated from charge exchange measurements of impurity ion temperature, density and rotation velocity profiles, using the force balance equation. The ion temperature and the toroidal and poloidal rotation velocities are compared in plasmas with both reversed and optimized magnetic shear profiles. Poloidal rotation velocity (v{sub {theta}}) in the ITB region is measured to be of the order of a few tens of km s{sup -1}, significantly larger than the neoclassical predictions. Increasing levels of the TF ripple are found to decrease the ion temperature gradient in the ITB region, a measure for the quality of the ITB, and the maximum value of v{sub {theta}} is reduced. The poloidal rotation term dominates in the calculations of the total radial electric field (E{sub r}), with the largest gradient in E{sub r} measured in the radial region coinciding with the ITB.

  4. Spectrum of resistivity gradient driven turbulence

    International Nuclear Information System (INIS)

    Terry, P.W.; Diamond, P.H.; Shaing, K.C.; Garcia, L.; Carreras, B.A.

    1986-01-01

    The resistivity fluctuation correlation function and electrostatic potential spectrum of resistivity gradient driven turbulence are calculated analytically and compared to the results of three dimensional numerical calculations. Resistivity gradient driven turbulence is characterized by effective Reynolds' numbers of order unity. Steady-state solution of the renormalized spectrum equations yields an electrostatic potential spectrum (circumflex phi 2 )/sub ktheta/ approx. k/sub theta//sup -3.25/. Agreement of the analytically calculated potential spectrum and mean-square radial velocity with the results of multiple helicity numerical calculations is excellent. This comparison constitutes a quantitative test of the analytical turbulence theory used. The spectrum of magnetic fluctuations is also calculated, and agrees well with that obtained from the numerical computations. 13 refs., 8 figs

  5. The ATLAS3D project - XXI. Correlations between gradients of local escape velocity and stellar populations in early-type galaxies

    NARCIS (Netherlands)

    Scott, Nicholas; Cappellari, Michele; Davies, Roger L.; Kleijn, Gijs Verdoes; Bois, Maxime; Alatalo, Katherine; Blitz, Leo; Bournaud, Frédéric; Bureau, Martin; Crocker, Alison; Davis, Timothy A.; de Zeeuw, P. T.; Duc, Pierre-Alain; Emsellem, Eric; Khochfar, Sadegh; Krajnović, Davor; Kuntschner, Harald; McDermid, Richard M.; Morganti, Raffaella; Naab, Thorsten; Oosterloo, Tom; Sarzi, Marc; Serra, Paolo; Weijmans, Anne-Marie; Young, Lisa M.

    We explore the connection between the local escape velocity, Vesc, and the stellar population properties in the ATLAS3D survey, a complete, volume-limited sample of nearby early-type galaxies. We make use of ugriz photometry to construct Multi-Gaussian Expansion models of the surface brightnesses of

  6. The ATLAS(3D) project : XXI. Correlations between gradients of local escape velocity and stellar populations in early-type galaxies

    NARCIS (Netherlands)

    Scott, Nicholas; Cappellari, Michele; Davies, Roger L.; Kleijn, Gijs Verdoes; Bois, Maxime; Alatalo, Katherine; Blitz, Leo; Bournaud, Frederic; Bureau, Martin; Crocker, Alison; Davis, Timothy A.; de Zeeuw, P. T.; Duc, Pierre-Alain; Emsellem, Eric; Khochfar, Sadegh; Krajnovic, Davor; Kuntschner, Harald; McDermid, Richard M.; Morganti, Raffaella; Naab, Thorsten; Oosterloo, Tom; Sarzi, Marc; Serra, Paolo; Weijmans, Anne-Marie; Young, Lisa M.

    2013-01-01

    We explore the connection between the local escape velocity, V-esc, and the stellar population properties in the ATLAS(3D) survey, a complete, volume-limited sample of nearby early-type galaxies. We make use of ugriz photometry to construct Multi-Gaussian Expansion models of the surface brightnesses

  7. Radial nerve dysfunction

    Science.gov (United States)

    Neuropathy - radial nerve; Radial nerve palsy; Mononeuropathy ... Damage to one nerve group, such as the radial nerve, is called mononeuropathy . Mononeuropathy means there is damage to a single nerve. Both ...

  8. The effect of magnetic field configuration on particle pinch velocity in compact helical system (CHS)

    International Nuclear Information System (INIS)

    Iguchi, H.; Ida, K.; Yamada, H.

    1994-01-01

    Radial particle transport has been experimentally studied in the low-aspect-ratio heliotron/torsatron device CHS. A non-diffusive outward particle flow (inverse pinch) is observed in the magnetic configuration with the magnetic axis shifted outward, while an inward pinch, like in tokamaks, is observed with the magnetic axis shifted inward. This change in the direction of anomalous particle flow is not due to the reversal of temperature gradient nor the radial electric field. The observation suggests that the particle pinch velocity is sensitive to the magnetic field structure. (author)

  9. NEW MASER EMISSION FROM NONMETASTABLE AMMONIA IN NGC 7538. III. DETECTION OF THE (10,6) TRANSITION AND A VELOCITY GRADIENT

    Energy Technology Data Exchange (ETDEWEB)

    Hoffman, Ian M., E-mail: ihoffman@wittenberg.edu [Physics Department Wittenberg University, Springfield, OH 45501 (United States)

    2012-11-01

    We present the first astronomical detection of the {sup 14}NH{sub 3} (J, K) = (10, 6) line: nonthermal emission at several velocities in the Galactic star-forming region NGC 7538. Using the Very Large Array we have imaged the (10,6) and (9,6) ammonia masers at several positions within NGC 7538 IRS 1. The individual sources have angular sizes {approx}< 0.1 arcsec corresponding to brightness temperatures T{sub B} {approx}> 10{sup 6} K. We apply the pumping model of Brown and Cragg, confirming the conjecture that multiple ortho-ammonia masers can occur with the same value of K. The positions and velocities of the (10,6) and (9,6) masers are modeled as motion in a possible disk or torus and are discussed in the context of recent models of the region.

  10. A theory of self-organized zonal flow with fine radial structure in tokamak

    Science.gov (United States)

    Zhang, Y. Z.; Liu, Z. Y.; Xie, T.; Mahajan, S. M.; Liu, J.

    2017-12-01

    The (low frequency) zonal flow-ion temperature gradient (ITG) wave system, constructed on Braginskii's fluid model in tokamak, is shown to be a reaction-diffusion-advection system; it is derived by making use of a multiple spatiotemporal scale technique and two-dimensional (2D) ballooning theory. For real regular group velocities of ITG waves, two distinct temporal processes, sharing a very similar meso-scale radial structure, are identified in the nonlinear self-organized stage. The stationary and quasi-stationary structures reflect a particular feature of the poloidal group velocity. The equation set posed to be an initial value problem is numerically solved for JET low mode parameters; the results are presented in several figures and two movies that show the spatiotemporal evolutions as well as the spectrum analysis—frequency-wave number spectrum, auto power spectrum, and Lissajous diagram. This approach reveals that the zonal flow in tokamak is a local traveling wave. For the quasi-stationary process, the cycle of ITG wave energy is composed of two consecutive phases in distinct spatiotemporal structures: a pair of Cavitons growing and breathing slowly without long range propagation, followed by a sudden decay into many Instantons that carry negative wave energy rapidly into infinity. A spotlight onto the motion of Instantons for a given radial position reproduces a Blob-Hole temporal structure; the occurrence as well as the rapid decay of Caviton into Instantons is triggered by zero-crossing of radial group velocity. A sample of the radial profile of zonal flow contributed from 31 nonlinearly coupled rational surfaces near plasma edge is found to be very similar to that observed in the JET Ohmic phase [J. C. Hillesheim et al., Phys. Rev. Lett. 116, 165002 (2016)]. The theory predicts an interior asymmetric dipole structure associated with the zonal flow that is driven by the gradients of ITG turbulence intensity.

  11. Radial gas turbine design

    Energy Technology Data Exchange (ETDEWEB)

    Krausche, S.; Ohlsson, Johan

    1998-04-01

    The objective of this work was to develop a program dealing with design point calculations of radial turbine machinery, including both compressor and turbine, with as few input data as possible. Some simple stress calculations and turbine metal blade temperatures were also included. This program was then implanted in a German thermodynamics program, Gasturb, a program calculating design and off-design performance of gas turbines. The calculations proceed with a lot of assumptions, necessary to finish the task, concerning pressure losses, velocity distribution, blockage, etc., and have been correlated with empirical data from VAT. Most of these values could have been input data, but to prevent the user of the program from drowning in input values, they are set as default values in the program code. The output data consist of geometry, Mach numbers, predicted component efficiency etc., and a number of graphical plots of geometry and velocity triangles. For the cases examined, the error in predicted efficiency level was within {+-} 1-2% points, and quite satisfactory errors in geometrical and thermodynamic conditions were obtained Examination paper. 18 refs, 36 figs

  12. Radial MR images of the knee

    International Nuclear Information System (INIS)

    Hewes, R.C.; Miller, T.R.

    1988-01-01

    To profile optimally each portion of the meniscus, the authors use the multiangle, multisection feature of a General Electric SIGNA 1.5-T imager to produce radial images centered on each meniscus. A total of 12-15 sections are imaged at 10 0 -15 0 intervals of each meniscus, yielding perpendicular images of the entire meniscus, comparable with the arthrographic tangential views. The authors review their technique and demonstrate correlation cases between the radial gradient recalled acquisition in a steady state sequences, sagittal and coronal MR images, and arthrograms. Radial images should be a routine part of knee MR imaging

  13. Radial evolution of the solar wind from IMP 8 to Voyager 2

    Science.gov (United States)

    Richardson, John D.; Paularena, Karolen I.; Lazarus, Alan J.; Belcher, John W.

    1995-01-01

    Voyager 2 and Interplanetary Monitoring Platform (IMP) 8 data from 1977 through 1994 are presented and compared. Radial velocity and temperature structures remain intact over the distance from 1 to 43 AU, but density structures do not. Temperature and velocity changes are correlated and nearly in phase at 1 AU, but in the outer heliosphere temperature changes lead velocity changes by tens of days. Solar cycle variations are detected by both spacecraft, with minima in flux density and dynamic pressure near solar maxima. Differences between Voyager 2 and IMP 8 observations near the solar minimum in 1986-1987 are attributed to latitudinal gradients in solar wind properties. Solar rotation variations are often present even at 40 AU. The Voyager 2 temperature profile is best fit with a R(exp -0.49 +/- 0.01) decrease, much less steep than an adiabatic profile.

  14. Southern high-velocity stars

    International Nuclear Information System (INIS)

    Augensen, H.J.; Buscombe, W.

    1978-01-01

    Using the model of the Galaxy presented by Eggen, Lynden-Bell and Sandage (1962), plane galactic orbits have been calculated for 800 southern high-velocity stars which possess parallax, proper motion, and radial velocity data. The stars with trigonometric parallaxes were selected from Buscombe and Morris (1958), supplemented by more recent spectroscopic data. Photometric parallaxes from infrared color indices were used for bright red giants studied by Eggen (1970), and for red dwarfs for which Rodgers and Eggen (1974) determined radial velocities. A color-color diagram based on published values of (U-B) and (B-V) for most of these stars is shown. (Auth.)

  15. Calculation method and influencing factors of the fragmental radial velocities of PELE after penetrating thin target%PELE贯穿薄靶后外壳破片径向速度计算方法与影响因素分析

    Institute of Scientific and Technical Information of China (English)

    樊自建; 冉宪文; 汤文辉; 于国栋; 陈为科; 任才清

    2017-01-01

    基于横向效应增强型弹丸(PELE)侵彻金属薄靶板过程分析,将弹体前端在撞击作用下的变形过程分解为轴向一维压缩和径向自由膨胀两个变形阶段;依据冲击波理论,给出了弹体前端的冲击波压缩势能,由功能转化原理,给出了PELE前端外壳在靶后形成破片的最大径向飞散速度计算公式.计算结果在多种工况下均与文献的实验结果较为一致.计算结果表明:PELE靶后外壳破片的最大径向飞散速度与外壳和内芯材料的体积模量和泊松比有关,且随二者的增大而增大;PELE外壳破片的最大径向飞散速度是壳体和内芯在冲击波压缩作用下共同径向膨胀的结果,且外壳膨胀能在弹体整体膨胀能中所占比例较大,计算中应当同时考虑弹体外壳和内芯材料的横向膨胀效应对弹体破片径向飞散速度的影响.%Based on an analysis of the PELE (penetrator with enhanced lateral efficiency) penetrating thin metal targets,the deformation process of the front-end projectile was divided into two distinct phases.one-dimensional decomposition in the axial direction and the free conversion in the radial direction,for experimental study.Based on the shock wave theory,we obtained the shock wave compression energy of the front end of the projectile and,on the basis of the conservation of energy and the assumption of two-stage deformation,presented a method for determining the scattered radial velocity of the PELE jacket fragments behind the target.The calculated results in a variety of conditions are fairly consistent with the experimental results.The theoretical analysis showed that the maximum radial velocity of the PELE jacket fragments depends on the radial expansion of both the jacket and the filling part under the shock compression,the former playing a major role in the overall expansion of the projectile whereas the maximum radial velocity of the PELE jacket fragments increasing with the bulk modulus

  16. Gradient computation for VTI acoustic wavefield tomography

    KAUST Repository

    Li, Vladimir; Wang, Hui; Tsvankin, Ilya; Diaz, Esteban; Alkhalifah, Tariq Ali

    2016-01-01

    -power objective functions. We also obtain the gradient expressions for the data-domain objective function, which can incorporate borehole information necessary for stable VTI velocity analysis. These gradients are compared to the ones obtained with a space

  17. Three-dimensional inviscid analysis of radial turbine flow and a limited comparison with experimental data

    Science.gov (United States)

    Choo, Y. K.; Civinskas, K. C.

    1985-01-01

    The three-dimensional inviscid DENTON code is used to analyze flow through a radial-inflow turbine rotor. Experimental data from the rotor are compared with analytical results obtained by using the code. The experimental data available for comparison are the radial distributions of circumferentially averaged values of absolute flow angle and total pressure downstream of the rotor exit. The computed rotor-exit flow angles are generally underturned relative to the experimental values, which reflect the boundary-layer separation at the trailing edge and the development of wakes downstream of the rotor. The experimental rotor is designed for a higher-than-optimum work factor of 1.126 resulting in a nonoptimum positive incidence and causing a region of rapid flow adjustment and large velocity gradients. For this experimental rotor, the computed radial distribution of rotor-exit to turbine-inlet total pressure ratios are underpredicted due to the errors in the finite-difference approximations in the regions of rapid flow adjustment, and due to using the relatively coarser grids in the middle of the blade region where the flow passage is highly three-dimensional. Additional results obtained from the three-dimensional inviscid computation are also presented, but without comparison due to the lack of experimental data. These include quasi-secondary velocity vectors on cross-channel surfaces, velocity components on the meridional and blade-to-blade surfaces, and blade surface loading diagrams. Computed results show the evolution of a passage vortex and large streamline deviations from the computational streamwise grid lines. Experience gained from applying the code to a radial turbine geometry is also discussed.

  18. An axially averaged-radial transport model of tokamak edge plasmas

    International Nuclear Information System (INIS)

    Prinja, A.K.; Conn, R.W.

    1984-01-01

    A two-zone axially averaged-radial transport model for edge plasmas is described that incorporates parallel electron and ion conduction, localized recycling, parallel electron pressure gradient effects and sheath losses. Results for high recycling show that the radial electron temperature profile is determined by parallel electron conduction over short radial distances (proportional 3 cm). At larger radius where Tsub(e) has fallen appreciably, convective transport becomes equally important. The downstream density and ion temperature profiles are very flat over the region where electron conduction dominates. This is seen to result from a sharply decaying velocity profile that follows the radial electron temperature. A one-dimensional analytical recycling model shows that at high neutral pumping rates, the plasma density at the plate, nsub(ia), scales linearly with the unperturbed background density, nsub(io). When ionization dominates nsub(ia)/nsub(io) proportional exp(nsub(io)) while in the intermediate regime nsub(ia)/nsub(io) proportional exp(proportional nsub(io)). Such behavior is qualitatively in accord with experimental observations. (orig.)

  19. The role of radial particle pinches in ELM suppression by resonant magnetic perturbations

    International Nuclear Information System (INIS)

    Stacey, W.M.; Evans, T.E.

    2011-01-01

    The force balance in the plasma edge in a matched pair of DIII-D (Luxon 2002 Nucl. Fusion 42 6149) tokamak discharges with and without resonant magnetic perturbations (RMPs) is evaluated in order to investigate the effects on particle transport of RMP applied for the purpose of suppressing edge-localized modes (ELMs). Experimental data are used to evaluate the radial and toroidal force balances, which may be written as a pinch-diffusion relation for the radial ion flux to facilitate investigation of transport effects. The radial electric field in the H-mode plasma had a sharp negative dip in the steep gradient region of the edge pedestal, associated with which was a large inward pinch velocity. The main effect of RMP was to make the edge electric field less negative or more positive, reducing this strong negative dip in the radial electric field (even reversing it from negative to positive over some regions), thereby reducing the strong inward particle pinch in the edge of an H-mode discharge, thus causing a reduction in edge density below the ELM threshold.

  20. Physical mechanism determining the radial electric field and its radial structure in a toroidal plasma

    International Nuclear Information System (INIS)

    Ida, Katsumi; Miura, Yukitoshi; Itoh, Sanae

    1994-10-01

    Radial structures of plasma rotation and radial electric field are experimentally studied in tokamak, heliotron/torsatron and stellarator devices. The perpendicular and parallel viscosities are measured. The parallel viscosity, which is dominant in determining the toroidal velocity in heliotron/torsatron and stellarator devices, is found to be neoclassical. On the other hand, the perpendicular viscosity, which is dominant in dictating the toroidal rotation in tokamaks, is anomalous. Even without external momentum input, both a plasma rotation and a radial electric field exist in tokamaks and heliotrons/torsatrons. The observed profiles of the radial electric field do not agree with the theoretical prediction based on neoclassical transport. This is mainly due to the existence of anomalous perpendicular viscosity. The shear of the radial electric field improves particle and heat transport both in bulk and edge plasma regimes of tokamaks. (author) 95 refs

  1. Design of gamma radiation equipment for studying a bubbling gas fluidized bed. Determination of a radial void fraction profile and bubble velocities in a 0.40 m column

    Energy Technology Data Exchange (ETDEWEB)

    Hoogeveen, M O [Technische Univ. Delft (Netherlands). Lab. voor Fysische Technologie

    1993-12-01

    In this work the possibility of the use of gamma radiation in investigating bubbles in a large three dimensional gas-fluidised bed was examined. A measuring system was designed based upon the absorption of gamma radiation. As high energy (>100 keV) gamma radiation penetrates deeply into matter, it can be used to scan through a gas-solid fluidised bed. The attenuation of a beam of mono-energetic photons is related to the amount of solid particles in the path of the beam. With the gamma absorption technique two parameters can be determined: The void fraction and the bubble velocity. With one narrow beam of gamma radiation a chordal void fraction can be measured in the homogeneous part of the bed. An optimalisation procedure for the void fraction determination led to the choice of Cs-137 as radiation source. This optimalisation procedure concerned minimizing of the standard deviation in the determined chordal void fraction as a function of the energy of gamma radiation. With two narrow parallel beams placed at a distance of 12 cm above each other a bubble velocity can be obtained. A cross-correlation between the two detector responses gives the time shift between the two responses. The system was designed for velocity measurements in the non-homogeneous part of the column. A simulation of the two beam measurement method for an air fluidized bed, 0.40 m in diameter, of polystyrene particles led to the choice of 100 mCi for the source strength for each of the two Cs-137 sources. For a 100 mCi Cs-137 source a shielding of 8 cm of lead is necessary to comply with safety regulations, concerning the use of radioactive materials. A source holder was designed, containing two encapsulated 100 mCi Cs-137 sources, in accordance with the regulations in the licence of the Delft University of Technology for the use of encapsulated sources. (orig.).

  2. Design of gamma radiation equipment for studying a bubbling gas fluidized bed. Determination of a radial void fraction profile and bubble velocities in a 0.40 m column

    International Nuclear Information System (INIS)

    Hoogeveen, M.O.

    1993-12-01

    In this work the possibility of the use of gamma radiation in investigating bubbles in a large three dimensional gas-fluidised bed was examined. A measuring system was designed based upon the absorption of gamma radiation. As high energy (>100 keV) gamma radiation penetrates deeply into matter, it can be used to scan through a gas-solid fluidised bed. The attenuation of a beam of mono-energetic photons is related to the amount of solid particles in the path of the beam. With the gamma absorption technique two parameters can be determined: The void fraction and the bubble velocity. With one narrow beam of gamma radiation a chordal void fraction can be measured in the homogeneous part of the bed. An optimalisation procedure for the void fraction determination led to the choice of Cs-137 as radiation source. This optimalisation procedure concerned minimizing of the standard deviation in the determined chordal void fraction as a function of the energy of gamma radiation. With two narrow parallel beams placed at a distance of 12 cm above each other a bubble velocity can be obtained. A cross-correlation between the two detector responses gives the time shift between the two responses. The system was designed for velocity measurements in the non-homogeneous part of the column. A simulation of the two beam measurement method for an air fluidized bed, 0.40 m in diameter, of polystyrene particles led to the choice of 100 mCi for the source strength for each of the two Cs-137 sources. For a 100 mCi Cs-137 source a shielding of 8 cm of lead is necessary to comply with safety regulations, concerning the use of radioactive materials. A source holder was designed, containing two encapsulated 100 mCi Cs-137 sources, in accordance with the regulations in the licence of the Delft University of Technology for the use of encapsulated sources. (orig.)

  3. Condition of damping of anomalous radial transport, determined by ordered convective electron dynamics

    International Nuclear Information System (INIS)

    Maslov, V.I.; Barchuk, S.V.; Lapshin, V.I.; Volkov, E.D.; Melentsov, Yu.V.

    2006-01-01

    It is shown, that at development of instability due to a radial gradient of density in the crossed electric and magnetic fields in nuclear fusion installations ordering convective cells can be excited. It provides anomalous particle transport. The spatial structures of these convective cells have been constructed. The radial dimensions of these convective cells depend on their amplitudes and on a radial gradient of density. The convective-diffusion equation for radial dynamics of the electrons has been derived. At the certain value of the universal controlling parameter, the convective cell excitation and the anomalous radial transport are suppressed. (author)

  4. Color gradients in elliptical galaxies

    International Nuclear Information System (INIS)

    Franx, M.; Illingworth, G.

    1990-01-01

    The relationship of the color gradients within ellipticals and the color differences between them are studied. It is found that the local color appears to be strongly related to the escape velocity. This suggests that the local escape velocity is the primary factor that determines the metallicity of the stellar population. Models with and without dark halos give comparable results. 27 refs

  5. Role of impurity dynamics in resistivity-gradient-driven turbulence and tokamak edge plasma phenomena

    International Nuclear Information System (INIS)

    Hahm, T.S.; Diamond, P.H.; Terry, P.W.; Garcia, L.; Carreras, B.A.

    1986-03-01

    The role of impurity dynamics in resistivity gradient driven turbulence is investigated in the context of modeling tokamak edge plasma phenomena. The effects of impurity concentration fluctuations and gradients on the linear behavior of rippling instabilities and on the nonlinear evolution and saturation of resistivity gradient driven turbulence are studied both analytically and computationally. At saturation, fluctuation levels and particle and thermal diffusivities are calculated. In particular, the mean-square turbulent radial velocity is given by 2 > = (E 0 L/sub s/B/sub z/) 2 (L/sub/eta/ -1 + L/sub z -1 ) 2 . Thus, edged peaked impurity concentrations tend to enhance the turbulence, while axially peaked concentrations tend to quench it. The theoretical predictions are in semi-quantitative agreement with experimental results from the TEXT, Caltech, and Tosca tokamaks. Finally, a theory of the density clamp observed during CO-NBI on the ISX-B tokamak is proposed

  6. Stellar Angular Momentum Distributions and Preferential Radial Migration

    Science.gov (United States)

    Wyse, Rosemary; Daniel, Kathryne J.

    2018-04-01

    I will present some results from our recent investigations into the efficiency of radial migration in stellar disks of differing angular momentum distributions, within a given adopted 2D spiral disk potential. We apply to our models an analytic criterion that determines whether or not individual stars are in orbits that could lead to radial migration around the corotation resonance. We couch our results in terms of the local stellar velocity dispersion and find that the fraction of stars that could migrate radially decreases as the velocity dispersion increases. I will discuss implications and comparisons with the results of other approaches.

  7. Poloidal rotation dynamics, radial electric field, and neoclassical theory in the jet internal-transport-barrier region.

    Science.gov (United States)

    Crombé, K; Andrew, Y; Brix, M; Giroud, C; Hacquin, S; Hawkes, N C; Murari, A; Nave, M F F; Ongena, J; Parail, V; Van Oost, G; Voitsekhovitch, I; Zastrow, K-D

    2005-10-07

    Results from the first measurements of a core plasma poloidal rotation velocity (upsilontheta) across internal transport barriers (ITB) on JET are presented. The spatial and temporal evolution of the ITB can be followed along with the upsilontheta radial profiles, providing a very clear link between the location of the steepest region of the ion temperature gradient and localized spin-up of upsilontheta. The upsilontheta measurements are an order of magnitude higher than the neoclassical predictions for thermal particles in the ITB region, contrary to the close agreement found between the determined and predicted particle and heat transport coefficients [K.-D. Zastrow, Plasma Phys. Controlled Fusion 46, B255 (2004)]. These results have significant implications for the understanding of transport barrier dynamics due to their large impact on the measured radial electric field profile.

  8. Effect of electric field and temperature gradient on orientational dynamics of nematics encapsulated in a hallow cylindrical cavity

    Science.gov (United States)

    Zakharov, A. V.; Maslennikov, P. V.

    2018-05-01

    We have considered a homogeneously oriented liquid crystal (HOLC) microvolume, confined between two infinitely long horizontal coaxial cylinders subjected to both a temperature gradient ∇T and a radially applied electric field E . We have investigated dynamic field pumping, i.e. studied the interactions between director, velocity, electric fields, as well as a radially applied temperature gradient, where the inner cylinder is kept at a lower temperature than the outer one. In order to elucidate the role of ∇T and E in producing hydrodynamic flow, we have carried out a numerical study of a system of hydrodynamic equations including director reorientation, fluid flow, and temperature redistribution across the HOLC cavity. Calculations show that, under the effect of the named perturbations and at high curvature of the inner cylinder, the HOLC microvolume settles down to a nonstandard pumping regime with maximum flow in the vicinity of the cooler inner cylinder.

  9. Interactions between Radial Electric Field, Transport and Structure in Helical Plasmas

    International Nuclear Information System (INIS)

    Ida, Katsumi and others

    2006-01-01

    Control of the radial electric field is considered to be important in helical plasmas, because the radial electric field and its shear are expected to reduce neoclassical and anomalous transport, respectively. Particle and heat transport, that determines the radial structure of density and electron profiles, sensitive to the structure of radial electric field. On the other hand, the radial electric field itself is determined by the plasma parameters. In general, the sign of the radial electric field is determined by the plasma collisionality, while the magnitude of the radial electric field is determined by the temperature and/or density gradients. Therefore the structure of radial electric field and temperature and density are strongly coupled through the particle and heat transport and formation mechanism of radial electric field. Interactions between radial electric field, transport and structure in helical plasmas is discussed based on the experiments on Large Helical Device

  10. Radial nerve dysfunction (image)

    Science.gov (United States)

    The radial nerve travels down the arm and supplies movement to the triceps muscle at the back of the upper arm. ... the wrist and hand. The usual causes of nerve dysfunction are direct trauma, prolonged pressure on the ...

  11. Observation of E×B Flow Velocity Profile Change Using Doppler Reflectometry in HL-2A

    Institute of Scientific and Technical Information of China (English)

    XIAO Wei-Wen; ZOU Xiao-Lan; DING Xuan-Tong; DONG Jia-Qi; LIU Ze-Tian; SONG Shao-Dong; GAO Ya-Dong; YAO Liang-Hua; FENG Bei-Bin; SONG Xian-Ming; CHEN Cheng-Yuan; SUN Hong-Juan; LI Yong-Gao; YANG Qing-Wei; YAN Long-Wen; LIU Yi; DUAN Xu-Ru; PAN Chuan-Hong; LIU Yong

    2009-01-01

    A broadband,O-mode sweeping Doppler reflectometry designed for measuring plasma E×B flow velocity profiles is operated in HL-2A.The main feature of the Doppler reflectometry is its capability to be tuned to any selected frequency in total waveband from 26-40 GHz.This property enables us to probe several plasma layers within a short time interval during a discharge,permitting the characterization of the radial distribution of plasma fluctuations.The system allows us to extract important information about the velocity change layer,namely its spatial localization.In purely Ohmic discharge a change of the E×B flow velocity profiles has been observed in the region for 28 < r < 30cm if only the line average density exceeds 2.2×1019 m-3.The density gradient change is measured in the same region,too.

  12. Comparison between gradient-dependent hydraulic conductivities of roots using the root pressure probe: the role of pressure propagations and implications for the relative roles of parallel radial pathways.

    Science.gov (United States)

    Bramley, Helen; Turner, Neil C; Turner, David W; Tyerman, Stephen D

    2007-07-01

    Hydrostatic pressure relaxations with the root pressure probe are commonly used for measuring the hydraulic conductivity (Lp(r)) of roots. We compared the Lp(r) of roots from species with different root hydraulic properties (Lupinus angustifolius L. 'Merrit', Lupinus luteus L. 'Wodjil', Triticum aestivum L. 'Kulin' and Zea mays L. 'Pacific DK 477') using pressure relaxations, a pressure clamp and osmotic gradients to induce water flow across the root. Only the pressure clamp measures water flow under steady-state conditions. Lp(r) determined by pressure relaxations was two- to threefold greater than Lp(r) from pressure clamps and was independent of the direction of water flow. Lp(r) (pressure clamp) was two- to fourfold higher than for Lp(r) (osmotic) for all species except Triticum aestivum where Lp(r) (pressure clamp) and Lp(r) (osmotic) were not significantly different. A novel technique was developed to measure the propagation of pressure through roots to investigate the cause of the differences in Lp(r). Root segments were connected between two pressure probes so that when root pressure (P(r)) was manipulated by one probe, the other probe recorded changes in P(r). Pressure relaxations did not induce the expected kinetics in pressure in the probe at the other end of the root when axial hydraulic conductance, and probe and root capacitances were accounted for. An electric circuit model of the root was constructed that included an additional capacitance in the root loaded by a series of resistances. This accounted for the double exponential kinetics for intact roots in pressure relaxation experiments as well as the reduced response observed with the double probe experiments. Although there were potential errors with all the techniques, we considered that the measurement of Lp(r) using the pressure clamp was the most unambiguous for small pressure changes, and provided that sufficient time was allowed for pressure propagation through the root. The differences in

  13. Experimental feasibility study of radial injection cooling of three-pad radial air foil bearings

    Science.gov (United States)

    Shrestha, Suman K.

    Air foil bearings use ambient air as a lubricant allowing environment-friendly operation. When they are designed, installed, and operated properly, air foil bearings are very cost effective and reliable solution to oil-free turbomachinery. Because air is used as a lubricant, there are no mechanical contacts between the rotor and bearings and when the rotor is lifted off the bearing, near frictionless quiet operation is possible. However, due to the high speed operation, thermal management is one of the very important design factors to consider. Most widely accepted practice of the cooling method is axial cooling, which uses cooling air passing through heat exchange channels formed underneath the bearing pad. Advantage is no hardware modification to implement the axial cooling because elastic foundation structure of foil bearing serves as a heat exchange channels. Disadvantage is axial temperature gradient on the journal shaft and bearing. This work presents the experimental feasibility study of alternative cooling method using radial injection of cooling air directly on the rotor shaft. The injection speeds, number of nozzles, location of nozzles, total air flow rate are important factors determining the effectiveness of the radial injection cooling method. Effectiveness of the radial injection cooling was compared with traditional axial cooling method. A previously constructed test rig was modified to accommodate a new motor with higher torque and radial injection cooling. The radial injection cooling utilizes the direct air injection to the inlet region of air film from three locations at 120° from one another with each location having three axially separated holes. In axial cooling, a certain axial pressure gradient is applied across the bearing to induce axial cooling air through bump foil channels. For the comparison of the two methods, the same amount of cooling air flow rate was used for both axial cooling and radial injection. Cooling air flow rate was

  14. Theory of neoclassical ion temperature-gradient-driven turbulence

    Science.gov (United States)

    Kim, Y. B.; Diamond, P. H.; Biglari, H.; Callen, J. D.

    1991-02-01

    The theory of collisionless fluid ion temperature-gradient-driven turbulence is extended to the collisional banana-plateau regime. Neoclassical ion fluid evolution equations are developed and utilized to investigate linear and nonlinear dynamics of negative compressibility ηi modes (ηi≡d ln Ti/d ln ni). In the low-frequency limit (ωB2p. As a result of these modifications, growth rates are dissipative, rather than sonic, and radial mode widths are broadened [i.e., γ˜k2∥c2s(ηi -(2)/(3) )/μi, Δx˜ρs(Bt/Bp) (1+ηi)1/2, where k∥, cs, and ρs are the parallel wave number, sound velocity, and ion gyroradius, respectively]. In the limit of weak viscous damping, enhanced neoclassical polarization persists and broadens radial mode widths. Linear mixing length estimates and renormalized turbulence theory are used to determine the ion thermal diffusivity in both cases. In both cases, a strong favorable dependence of ion thermal diffusivity on Bp (and hence plasma current) is exhibited. Furthermore, the ion thermal diffusivity for long wavelength modes exhibits favorable density scaling. The possible role of neoclassical ion temperature-gradient-driven modes in edge fluctuations and transport in L-phase discharges and the L to H transition is discussed.

  15. Radial electric field studies in the plasma edge of ASDEX upgrade

    International Nuclear Information System (INIS)

    Viezzer, Eleonora

    2012-01-01

    In magnetically confined fusion plasmas, edge transport barriers (ETBs) are formed during the transition from a highly turbulent state (low confinement regime, L-mode) to a high energy confinement regime (H-mode) with reduced turbulence and transport. The performance of an H-mode fusion plasma is highly dependent on the strength of the ETB which extends typically over the outermost 5% of the confined plasma. The formation of the ETB is strongly connected to the existence of a sheared plasma flow perpendicular to the magnetic field caused by a local radial electric field E r . The gradients in E r and the accompanying E x B velocity shear play a fundamental role in edge turbulence suppression, transport barrier formation and the transition to H-mode. Thus, the interplay between macroscopic flows and transport at the plasma edge is of crucial importance to understanding plasma confinement and stability. The work presented in this thesis is based on charge exchange recombination spectroscopy (CXRS) measurements performed at the plasma edge of the ASDEX Upgrade (AUG) tokamak. During this thesis new high-resolution CXRS diagnostics were installed at the outboard and inboard miplane of AUG, which provide measurements of the temperature, density and flows of the observed species. From these measurements the radial electric field can be directly determined via the radial force balance equation. The new CXRS measurements, combined with the other edge diagnostics available at AUG, allow for an unprecedented, high-accuracy localization (2-3 mm) of the E r profile. The radial electric field has been derived from charge exchange spectra measured on different impurity species including He 2+ , B 5+ , C 6+ and Ne 10+ . The resulting E r profiles are found to be identical within the uncertainties regardless of the impurity species used, thus demonstrating the validity of the diagnostic technique. Inside the ETB the E r profile forms a deep, negative (i.e. directed towards the

  16. Measuring surface current velocities in the Agulhas region with ASAR

    CSIR Research Space (South Africa)

    Rouault, MJ

    2010-01-01

    Full Text Available is known to perform well. Although radial velocities derived from ASAR are on occasion able to represent the measured flow with incredible accuracy, the overall performance of the ASAR radial velocity product is negatively impacted by a few very large...

  17. On radial flow between parallel disks

    International Nuclear Information System (INIS)

    Wee, A Y L; Gorin, A

    2015-01-01

    Approximate analytical solutions are presented for converging flow in between two parallel non rotating disks. The static pressure distribution and radial component of the velocity are developed by averaging the inertial term across the gap in between parallel disks. The predicted results from the first approximation are favourable to experimental results as well as results presented by other authors. The second approximation shows that as the fluid approaches the center, the velocity at the mid channel slows down which is due to the struggle between the inertial term and the flowrate. (paper)

  18. Three-dimensional inviscid analysis of radial-turbine flow and a limited comparison with experimental data

    Science.gov (United States)

    Choo, Y. K.; Civinskas, K. C.

    1985-01-01

    The three-dimensional inviscid DENTON code is used to analyze flow through a radial-inflow turbine rotor. Experimental data from the rotor are compared with analytical results obtained by using the code. The experimental data available for comparison are the radial distributions of circumferentially averaged values of absolute flow angle and total pressure downstream of the rotor exit. The computed rotor-exit flow angles are generally underturned relative to the experimental values, which reflect the boundary-layer separation at the trailing edge and the development of wakes downstream of the rotor. The experimental rotor is designed for a higher-than-optimum work factor of 1.126 resulting in a nonoptimum positive incidence and causing a region of rapid flow adjustment and large velocity gradients. For this experimental rotor, the computed radial distribution of rotor-exit to turbine-inlet total pressure ratios are underpredicted due to the errors in the finite-difference approximations in the regions of rapid flow adjustment, and due to using the relatively coarser grids in the middle of the blade region where the flow passage is highly three-dimensional. Additional results obtained from the three-dimensional inviscid computation are also presented, but without comparison due to the lack of experimental data. These include quasi-secondary velocity vectors on cross-channel surfaces, velocity components on the meridional and blade-to-blade surfaces, and blade surface loading diagrams. Computed results show the evolution of a passage vortex and large streamline deviations from the computational streamwise grid lines. Experience gained from applying the code to a radial turbine geometry is also discussed.

  19. Radial wedge flange clamp

    Science.gov (United States)

    Smith, Karl H.

    2002-01-01

    A radial wedge flange clamp comprising a pair of flanges each comprising a plurality of peripheral flat wedge facets having flat wedge surfaces and opposed and mating flat surfaces attached to or otherwise engaged with two elements to be joined and including a series of generally U-shaped wedge clamps each having flat wedge interior surfaces and engaging one pair of said peripheral flat wedge facets. Each of said generally U-shaped wedge clamps has in its opposing extremities apertures for the tangential insertion of bolts to apply uniform radial force to said wedge clamps when assembled about said wedge segments.

  20. Radially global δf computation of neoclassical phenomena in a tokamak pedestal

    International Nuclear Information System (INIS)

    Landreman, Matt; Parra, Felix I; Catto, Peter J; Ernst, Darin R; Pusztai, Istvan

    2014-01-01

    Conventional radially-local neoclassical calculations become inadequate if the radial gradient scale lengths of the H-mode pedestal become as small as the poloidal ion gyroradius. Here, we describe a radially global δf continuum code that generalizes neoclassical calculations to allow for stronger gradients. As with conventional neoclassical calculations, the formulation is time-independent and requires only the solution of a single sparse linear system. We demonstrate precise agreement with an asymptotic analytic solution of the radially global kinetic equation in the appropriate limits of aspect ratio and collisionality. This agreement depends crucially on accurate treatment of finite orbit width effects. (paper)

  1. Sirenomelia with radial dysplasia.

    Science.gov (United States)

    Kulkarni, M L; Abdul Manaf, K M; Prasannakumar, D G; Kulkarni, Preethi M

    2004-05-01

    Sirenomelia is a rare anomaly usually associated with other multiple malformations. In this communication the authors report a case of sirenomelia associated with multiple malformations, which include radial hypoplasia also. Though several theories have been proposed regarding the etiology of multiple malformation syndromes in the past, the recent theory of primary developmental defect during blastogenesis holds good in this case.

  2. Radially truncated galactic discs

    NARCIS (Netherlands)

    Grijs, R. de; Kregel, M.; Wesson, K H

    2000-01-01

    Abstract: We present the first results of a systematic analysis of radially truncatedexponential discs for four galaxies of a sample of disc-dominated edge-onspiral galaxies. Edge-on galaxies are very useful for the study of truncatedgalactic discs, since we can follow their light distributions out

  3. Neoclassical transport, poloidal rotation and radial electric field at the L-H transition

    International Nuclear Information System (INIS)

    Minardi, E.; Gervasini, G.; Lazzaro, E.

    1993-01-01

    The transition to a high confinement regime in tokamaks operating with a magnetic divertor configuration is accompanied by the strong steepening of the edge temperature profile and the onset of a large positive poloidal mass rotation associated with a negative radial electric field. The latter phenomena are signatures of a neoclassical transport mechanism. We address the question of establishing whether neoclassical transport is indeed sufficient to establish high edge gradients and drive poloidal rotation under strong auxiliary heating. The heat transport equation is solved numerically in a narrow edge layer interfaced to the plasma body through heat flux continuity, but allowing for heat conductivity discontinuity. The results compared with recent experimental measurements support the assumption that a highly sheared neoclassical poloidal velocity profile can suppress the anomalous part of the heat transport, and that the neoclassical residual transport, characterizes the plasma behaviour at the edge during H modes. (author) 3 refs., 4 figs

  4. Photoelectric Radial Velocities, Paper XX 45 Years' Monitoring of ...

    Indian Academy of Sciences (India)

    ... through the 'Open Horizons' schol- arship programme. She is also grateful to the Institute of Astronomy, Cambridge, for a summer studentship kindly funded personally by Prof. D. Lynden-Bell, to whom also R.F.G. is much indebted for the provision in that way of technical computing skills well beyond his own. References.

  5. Interpolation of the Radial Velocity Data from Coastal HF Radars

    Science.gov (United States)

    2013-01-01

    effectiveness of such DA approach. In a similar manner, a 3d covariance matrix for the Princeton Ocean model model has been constructed by Breivik ...1839-1856. [8] Bennett, A.F., 2002: Inverse modeling of the ocean and atmosphere. Cambridge Uni- versity Press, 256 pp [9] Breivik , O., and O

  6. A survey of radial velocities in the zodiacal dust cloud

    CERN Document Server

    May, Brian Harold

    2008-01-01

    The Zodiacal Light, that misty diffuse cone of light seen in the West after Sunset and the East before Sunrise, is a beautiful and intriguing phenomenon. Even though everyone can enjoy the sight from a suitably dark location, it is poorly understood, and has been the subject of relatively little research. Brian May began his research into the subject in 1970, and was finally awarded his PhD in 2007, after a hiatus of more than 30 years pursuing his other career as guitarist with his rock band Queen. This book is Brian 's thesis, and as such presents the results of his research for astronomers.

  7. Possible Relativistic Definitions of Parallax, Proper Motion and Radial Velocity

    National Research Council Canada - National Science Library

    Klioner, S

    2000-01-01

    .... In this paper, the authors briefly describe a relativistic model of space-based optical positional observations valid at a high level of accuracy, and suggest definitions of parallax, proper motion...

  8. Variable stator radial turbine

    Science.gov (United States)

    Rogo, C.; Hajek, T.; Chen, A. G.

    1984-01-01

    A radial turbine stage with a variable area nozzle was investigated. A high work capacity turbine design with a known high performance base was modified to accept a fixed vane stagger angle moveable sidewall nozzle. The nozzle area was varied by moving the forward and rearward sidewalls. Diffusing and accelerating rotor inlet ramps were evaluated in combinations with hub and shroud rotor exit rings. Performance of contoured sidewalls and the location of the sidewall split line with respect to the rotor inlet was compared to the baseline. Performance and rotor exit survey data are presented for 31 different geometries. Detail survey data at the nozzle exit are given in contour plot format for five configurations. A data base is provided for a variable geometry concept that is a viable alternative to the more common pivoted vane variable geometry radial turbine.

  9. Estimation of Radial Runout

    OpenAIRE

    Nilsson, Martin

    2007-01-01

    The demands for ride comfort quality in today's long haulage trucks are constantly growing. A part of the ride comfort problems are represented by internal vibrations caused by rotating mechanical parts. This thesis work focus on the vibrations generated from radial runout on the wheels. These long haulage trucks travel long distances on smooth highways, with a constant speed of 90 km/h resulting in a 7 Hz oscillation. This frequency creates vibrations in the cab, which can be found annoying....

  10. Radial Fuzzy Systems

    Czech Academy of Sciences Publication Activity Database

    Coufal, David

    2017-01-01

    Roč. 319, 15 July (2017), s. 1-27 ISSN 0165-0114 R&D Projects: GA MŠk(CZ) LD13002 Institutional support: RVO:67985807 Keywords : fuzzy systems * radial functions * coherence Subject RIV: BA - General Mathematics OBOR OECD: Computer sciences, information science, bioinformathics (hardware development to be 2.2, social aspect to be 5.8) Impact factor: 2.718, year: 2016

  11. Radial transfer effects for poloidal rotation

    Science.gov (United States)

    Hallatschek, Klaus

    2010-11-01

    Radial transfer of energy or momentum is the principal agent responsible for radial structures of Geodesic Acoustic Modes (GAMs) or stationary Zonal Flows (ZF) generated by the turbulence. For the GAM, following a physical approach, it is possible to find useful expressions for the individual components of the Poynting flux or radial group velocity allowing predictions where a mathematical full analysis is unfeasible. Striking differences between up-down symmetric flux surfaces and asymmetric ones have been found. For divertor geometries, e.g., the direction of the propagation depends on the sign of the ion grad-B drift with respect to the X-point, reminiscent of a sensitive determinant of the H-mode threshold. In nonlocal turbulence computations it becomes obvious that the linear energy transfer terms can be completely overwhelmed by the action of the turbulence. In contrast, stationary ZFs are governed by the turbulent radial transfer of momentum. For sufficiently large systems, the Reynolds stress becomes a deterministic functional of the flows, which can be empirically determined from the stress response in computational turbulence studies. The functional allows predictions even on flow/turbulence states not readily obtainable from small amplitude noise, such as certain transport bifurcations or meta-stable states.

  12. Radial Field Piezoelectric Diaphragms

    Science.gov (United States)

    Bryant, R. G.; Effinger, R. T., IV; Copeland, B. M., Jr.

    2002-01-01

    A series of active piezoelectric diaphragms were fabricated and patterned with several geometrically defined Inter-Circulating Electrodes "ICE" and Interdigitated Ring Electrodes "ICE". When a voltage potential is applied to the electrodes, the result is a radially distributed electric field that mechanically strains the piezoceramic along the Z-axis (perpendicular to the applied electric field). Unlike other piezoelectric bender actuators, these Radial Field Diaphragms (RFDs) strain concentrically yet afford high displacements (several times that of the equivalent Unimorph) while maintaining a constant circumference. One of the more intriguing aspects is that the radial strain field reverses itself along the radius of the RFD while the tangential strain remains relatively constant. The result is a Z-deflection that has a conical profile. This paper covers the fabrication and characterization of the 5 cm. (2 in.) diaphragms as a function of poling field strength, ceramic thickness, electrode type and line spacing, as well as the surface topography, the resulting strain field and displacement as a function of applied voltage at low frequencies. The unique features of these RFDs include the ability to be clamped about their perimeter with little or no change in displacement, the environmentally insulated packaging, and a highly repeatable fabrication process that uses commodity materials.

  13. The effect of gradational velocities and anisotropy on fault-zone trapped waves

    Science.gov (United States)

    Gulley, A. K.; Eccles, J. D.; Kaipio, J. P.; Malin, P. E.

    2017-08-01

    Synthetic fault-zone trapped wave (FZTW) dispersion curves and amplitude responses for FL (Love) and FR (Rayleigh) type phases are analysed in transversely isotropic 1-D elastic models. We explore the effects of velocity gradients, anisotropy, source location and mechanism. These experiments suggest: (i) A smooth exponentially decaying velocity model produces a significantly different dispersion curve to that of a three-layer model, with the main difference being that Airy phases are not produced. (ii) The FZTW dispersion and amplitude information of a waveguide with transverse-isotropy depends mostly on the Shear wave velocities in the direction parallel with the fault, particularly if the fault zone to country-rock velocity contrast is small. In this low velocity contrast situation, fully isotropic approximations to a transversely isotropic velocity model can be made. (iii) Fault-aligned fractures and/or bedding in the fault zone that cause transverse-isotropy enhance the amplitude and wave-train length of the FR type FZTW. (iv) Moving the source and/or receiver away from the fault zone removes the higher frequencies first, similar to attenuation. (v) In most physically realistic cases, the radial component of the FR type FZTW is significantly smaller in amplitude than the transverse.

  14. Perceived radial translation during centrifugation

    NARCIS (Netherlands)

    Bos, J.E.; Correia Grácio, B.J.

    2015-01-01

    BACKGROUND: Linear acceleration generally gives rise to translation perception. Centripetal acceleration during centrifugation, however, has never been reported giving rise to a radial, inward translation perception. OBJECTIVE: To study whether centrifugation can induce a radial translation

  15. Models of disk chemical evolution focusing the pure dynamical radial mixing

    Directory of Open Access Journals (Sweden)

    Re Fiorentin P.

    2012-02-01

    Full Text Available We performed N-body simulations to study the dynamical evolution of a stellar disk inside a Dark Matter (DM halo. Our results evidence how a standard -radially decreasing- metallicity gradient produces a negative vϕ vs. [Fe/H] correlation, similar to that shown by the thin disk stars, while an inverse radial gradient generates a positive rotation-metallicity correlation, as that observed in the old thick population.

  16. Radial reflection diffraction tomography

    Science.gov (United States)

    Lehman, Sean K.

    2012-12-18

    A wave-based tomographic imaging method and apparatus based upon one or more rotating radially outward oriented transmitting and receiving elements have been developed for non-destructive evaluation. At successive angular locations at a fixed radius, a predetermined transmitting element can launch a primary field and one or more predetermined receiving elements can collect the backscattered field in a "pitch/catch" operation. A Hilbert space inverse wave (HSIW) algorithm can construct images of the received scattered energy waves using operating modes chosen for a particular application. Applications include, improved intravascular imaging, bore hole tomography, and non-destructive evaluation (NDE) of parts having existing access holes.

  17. Sodium Velocity Maps on Mercury

    Science.gov (United States)

    Potter, A. E.; Killen, R. M.

    2011-01-01

    The objective of the current work was to measure two-dimensional maps of sodium velocities on the Mercury surface and examine the maps for evidence of sources or sinks of sodium on the surface. The McMath-Pierce Solar Telescope and the Stellar Spectrograph were used to measure Mercury spectra that were sampled at 7 milliAngstrom intervals. Observations were made each day during the period October 5-9, 2010. The dawn terminator was in view during that time. The velocity shift of the centroid of the Mercury emission line was measured relative to the solar sodium Fraunhofer line corrected for radial velocity of the Earth. The difference between the observed and calculated velocity shift was taken to be the velocity vector of the sodium relative to Earth. For each position of the spectrograph slit, a line of velocities across the planet was measured. Then, the spectrograph slit was stepped over the surface of Mercury at 1 arc second intervals. The position of Mercury was stabilized by an adaptive optics system. The collection of lines were assembled into an images of surface reflection, sodium emission intensities, and Earthward velocities over the surface of Mercury. The velocity map shows patches of higher velocity in the southern hemisphere, suggesting the existence of sodium sources there. The peak earthward velocity occurs in the equatorial region, and extends to the terminator. Since this was a dawn terminator, this might be an indication of dawn evaporation of sodium. Leblanc et al. (2008) have published a velocity map that is similar.

  18. Thermal conduction down steep temperature gradients

    International Nuclear Information System (INIS)

    Bell, A.R.; Evans, R.G.; Nicholas, D.J.

    1980-08-01

    The Fokker-Planck equation has been solved numerically in one spatial and two velocity dimensions in order to study thermal conduction in large temperature gradients. An initially cold plasma is heated at one end of the spatial grid producing temperature gradients with scale lengths of a few times the electron mean free path. The heat flow is an order of magnitude smaller than that predicted by the classical theory which is valid in the limit of small temperature gradients. (author)

  19. Control rod velocity limiter

    International Nuclear Information System (INIS)

    Cearley, J.E.; Carruth, J.C.; Dixon, R.C.; Spencer, S.S.; Zuloaga, J.A. Jr.

    1986-01-01

    This patent describes a velocity control arrangement for a reciprocable, vertically oriented control rod for use in a nuclear reactor in a fluid medium, the control rod including a drive hub secured to and extending from one end therefrom. The control device comprises: a toroidally shaped control member spaced from and coaxially positioned around the hub and secured thereto by a plurality of spaced radial webs thereby providing an annular passage for fluid intermediate the hub and the toroidal member spaced therefrom in coaxial position. The side of the control member toward the control rod has a smooth generally conical surface. The side of the control member away from the control rod is formed with a concave surface constituting a single annular groove. The device also comprises inner and outer annular vanes radially spaced from one another and spaced from the side of the control member away from the control rod and positioned coaxially around and spaced from the hub and secured thereto by spaced radial webs thereby providing an annular passage for fluid intermediate the hub and the vanes. The vanes are angled toward the control member, the outer edge of the inner vane being closer to the control member and the inner edge of the outer vane being closer to the control member. When the control rod moves in the fluid in the direction toward the drive hub the vanes direct a flow of fluid turbulence which provides greater resistance to movement of the control rod in the direction toward the drive hub than in the other direction

  20. Rayleigh-Taylor instability of cylindrical jets with radial motion

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Xiang M. [GE Nuclear, Wilmington, NC (United States); Schrock, V.E.; Peterson, P.F. [Univ. of California, Berkeley, CA (United States)

    1995-09-01

    Rayleigh-Taylor instability of an interface between fluids with different densities subjected to accelleration normal to itself has interested researchers for almost a century. The classic analyses of a flat interface by Rayleigh and Taylor have shown that this type of instability depends on the direction of acceleration and the density differences of the two fluids. Plesset later analyzed the stability of a spherically symmetric flows (and a spherical interface) and concluded that the instability also depends on the velocity of the interface as well as the direction and magnitude of radial acceleration. The instability induced by radial motion in cylindrical systems seems to have been neglected by previous researchers. This paper analyzes the Rayleigh-Taylor type of the spherical case, the radial velocity also plays an important role. As an application, the example of a liquid jet surface in an Inertial Confinement Fusion (ICF) reactor design is analyzed.

  1. Irradiance gradients

    International Nuclear Information System (INIS)

    Ward, G.J.; Heckbert, P.S.; Technische Hogeschool Delft

    1992-04-01

    A new method for improving the accuracy of a diffuse interreflection calculation is introduced in a ray tracing context. The information from a hemispherical sampling of the luminous environment is interpreted in a new way to predict the change in irradiance as a function of position and surface orientation. The additional computation involved is modest and the benefit is substantial. An improved interpolation of irradiance resulting from the gradient calculation produces smoother, more accurate renderings. This result is achieved through better utilization of ray samples rather than additional samples or alternate sampling strategies. Thus, the technique is applicable to a variety of global illumination algorithms that use hemicubes or Monte Carlo sampling techniques

  2. Radial semiconductor drift chambers

    International Nuclear Information System (INIS)

    Rawlings, K.J.

    1987-01-01

    The conditions under which the energy resolution of a radial semiconductor drift chamber based detector system becomes dominated by the step noise from the detector dark current have been investigated. To minimise the drift chamber dark current attention should be paid to carrier generation at Si/SiO 2 interfaces. This consideration conflicts with the desire to reduce the signal risetime: a higher drift field for shorter signal pulses requires a larger area of SiO 2 . Calculations for the single shaping and pseudo Gaussian passive filters indicate that for the same degree of signal risetime sensitivity in a system dominated by the step noise from the detector dark current, the pseudo Gaussian filter gives only a 3% improvement in signal/noise and 12% improvement in rate capability compared with the single shaper performance. (orig.)

  3. ISR Radial Field Magnet

    CERN Multimedia

    1983-01-01

    There were 37 (normal) + 3 (special) Radial Field magnets in the ISR to adjust vertically the closed orbit. Gap heights and strengths were 200 mm and .12 Tm in the normal magnets, 220 mm and .18 Tm in the special ones. The core length was 430 mm in both types. Due to their small length as compared to the gap heights the end fringe field errors were very important and had to be compensated by suitably shaping the poles. In order to save on cables, as these magnets were located very far from their power supplies, the coils of the normal type magnets were formed by many turns of solid cpper conductor with some interleaved layers of hollow conductor directly cooled by circulating water

  4. The ARCS radial collimator

    International Nuclear Information System (INIS)

    Stone, M.B.; Abernathy, D.L.; Niedziela, J.L.; Overbay, M.A.

    2015-01-01

    We have designed, installed, and commissioned a scattered beam radial collimator for use at the ARCS Wide Angular Range Chopper Spectrometer at the Spallation Neutron Source. The collimator has been designed to work effectively for thermal and epithermal neutrons and with a range of sample environments. Other design considerations include the accommodation of working within a high vacuum environment and having the ability to quickly install and remove the collimator from the scattered beam. The collimator is composed of collimating blades (or septa). The septa are 12 micron thick Kapton foils coated on each side with 39 microns of enriched boron carbide ( 10 B 4 C with 10 B > 96%) in an ultra-high vacuum compatible binder. The collimator blades represent an additional 22 m 2 of surface area. In the article we present collimator's design and performance and methodologies for its effective use

  5. Hydraulic gradients in rock aquifers

    International Nuclear Information System (INIS)

    Dahlblom, P.

    1992-05-01

    This report deals with fractured rock as a host for deposits of hazardous waste. In this context the rock, with its fractures containing moving groundwater, is called the geological barrier. The desired properties of the geological barrier are low permeability to water, low hydraulic gradients and ability to retain matter dissolved in the water. The hydraulic gradient together with the permeability and the porosity determines the migration velocity. Mathematical modelling of the migration involves calculation of the water flow and the hydrodynamic dispersion of the contaminant. The porous medium approach can be used to calculate mean flow velocities and hydrodynamic dispersion of a large number of fractures are connected, which means that a large volume have to be considered. It is assumed that the porous medium approach can be applied, and a number of idealized examples are shown. It is assumed that the groundwater table is replenished by percolation at a constant rate. One-dimensional analytical calculations show that zero hydraulic gradients may exist at relatively large distance from the coast. Two-dimensional numerical calculations show that it may be possible to find areas with low hydraulic gradients and flow velocities within blocks surrounded by areas with high hydraulic conductivity. (au)

  6. Antiproton compression and radial measurements

    CERN Document Server

    Andresen, G B; Bowe, P D; Bray, C C; Butler, E; Cesar, C L; Chapman, S; Charlton, M; Fajans, J; Fujiwara, M C; Funakoshi, R; Gill, D R; Hangst, J S; Hardy, W N; Hayano, R S; Hayden, M E; Humphries, A J; Hydomako, R; Jenkins, M J; Jorgensen, L V; Kurchaninov, L; Lambo, R; Madsen, N; Nolan, P; Olchanski, K; Olin, A; Page R D; Povilus, A; Pusa, P; Robicheaux, F; Sarid, E; Seif El Nasr, S; Silveira, D M; Storey, J W; Thompson, R I; Van der Werf, D P; Wurtele, J S; Yamazaki, Y

    2008-01-01

    Control of the radial profile of trapped antiproton clouds is critical to trapping antihydrogen. We report detailed measurements of the radial manipulation of antiproton clouds, including areal density compressions by factors as large as ten, achieved by manipulating spatially overlapped electron plasmas. We show detailed measurements of the near-axis antiproton radial profile, and its relation to that of the electron plasma. We also measure the outer radial profile by ejecting antiprotons to the trap wall using an octupole magnet.

  7. Parameters determining maximum wind velocity in a tropical cyclone

    International Nuclear Information System (INIS)

    Choudhury, A.M.

    1984-09-01

    The spiral structure of a tropical cyclone was earlier explained by a tangential velocity distribution which varies inversely as the distance from the cyclone centre outside the circle of maximum wind speed. The case has been extended in the present paper by adding a radial velocity. It has been found that a suitable combination of radial and tangential velocities can account for the spiral structure of a cyclone. This enables parametrization of the cyclone. Finally a formula has been derived relating maximum velocity in a tropical cyclone with angular momentum, radius of maximum wind speed and the spiral angle. The shapes of the spirals have been computed for various spiral angles. (author)

  8. METALLICITY GRADIENTS OF THICK DISK DWARF STARS

    Energy Technology Data Exchange (ETDEWEB)

    Carrell, Kenneth; Chen Yuqin; Zhao Gang, E-mail: carrell@nao.cas.cn [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

    2012-12-01

    We examine the metallicity distribution of the Galactic thick disk using F, G, and K dwarf stars selected from the Sloan Digital Sky Survey, Data Release 8. Using the large sample of dwarf stars with proper motions and spectroscopically determined stellar parameters, metallicity gradients in the radial direction for various heights above the Galactic plane and in the vertical direction for various radial distances from the Galaxy center have been found. In particular, we find a vertical metallicity gradient of -0.113 {+-} 0.010 (-0.125 {+-} 0.008) dex kpc{sup -1} using an isochrone (photometric) distance determination in the range 1 kpc <|Z| < 3 kpc, which is the vertical height range most consistent with the thick disk of our Galaxy. In the radial direction, we find metallicity gradients between +0.02 and +0.03 dex kpc{sup -1} for bins in the vertical direction between 1 kpc <|Z| < 3 kpc. Both of these results agree with similar values determined from other populations of stars, but this is the first time a radial metallicity gradient for the thick disk has been found at these vertical heights. We are also able to separate thin and thick disk stars based on kinematic and spatial probabilities in the vertical height range where there is significant overlap of these two populations. This should aid further studies of the metallicity gradients of the disk for vertical heights lower than those studied here but above the solar neighborhood. Metallicity gradients in the thin and thick disks are important probes into possible formation scenarios for our Galaxy and a consistent picture is beginning to emerge from results using large spectroscopic surveys, such as the ones presented here.

  9. Radially sheared azimuthal flows and turbulent transport in a cylindrical helicon plasma device

    International Nuclear Information System (INIS)

    Tynan, G R; Burin, M J; Holland, C; Antar, G; Diamond, P H

    2004-01-01

    A radially sheared azimuthal flow is observed in a cylindrical helicon plasma device. The shear flow is roughly azimuthally symmetric and contains both time-stationary and slowly varying components. The turbulent radial particle flux is found to peak near the density gradient maximum and vanishes at the shear layer location. The shape of the radial plasma potential profile associated with the azimuthal E x B flow is predicted accurately by theory. The existence of the mean shear flow in a plasma with finite flow damping from ion-neutral collisions and no external momentum input implies the existence of radial angular momentum transport from the turbulent Reynolds-stress

  10. Radial expansion and multifragmentation

    International Nuclear Information System (INIS)

    Angelique, J.C.; Bizard, G.; Bougault, R.; Brou, R.; Buta, A.; Colin, J.; Cussol, D.; Durand, D.; Kerambrun, A.; Le Brun, C.; Lecolley, J.F.; Lopez, O.; Louvel, M.; Meslin, C.; Nakagawa, T.; Patry, J.P.; Peter, J.; Popescu, R.; Regimbart, R.; Steckmeyer, J.C.; Tamain, B.; Vient, E.; Yuasa-Nakagawa, K.; Wieloch, A.

    1998-01-01

    The light systems 36 Ar + 27 Al and 64 Zn + nat Ti were measured at several bombarding energies between ∼ 35 and 95 MeV/nucleon. It was found that the predominant part of the cross section is due to binary collisions. In this paper the focus is placed on the properties of the quasi-projectile nuclei. In the central collisions the excitation energies of the quasi-projectile reach values exceeding largely 10 MeV/nucleon. The slope of the high energy part of the distribution can give only an upper limit of the apparent temperature (the average temperature along the decay chain). The highly excited quasi-projectile may get rapidly fragmented rather than sequentially. The heavy fragments are excited and can emit light particles (n, p, d, t, 3 He, α,...) what perturbs additionally the spectrum of these particles. Concerning the expansion energy, one can determine the average kinetic energies of the product (in the quasi-projectile-framework) and compare with simulation values. To fit the experimental data an additional radial expansion energy is to be considered. The average expansion energy depends slightly on the impact parameter but it increases with E * / A, ranging from 0.4 to 1,2 MeV/nucleon for an excitation energy increasing from 7 to 10.5 MeV/nucleon. This collective radial energy seems to be independent of the fragment mass, what is possibly valid for the case of larger quasi-projectile masses. The origin of the expansion is to be determined. It may be due to a compression in the interaction zone at the initial stage of the collision, which propagates in the quasi-projectile and quasi-target, or else, may be due, simply, to the increase of thermal energy leading to a rapid fragment emission. The sequential de-excitation calculation overestimates light particle emission and consequently heavy residues, particularly, at higher excitation energies. This disagreement indicates that a sequential process can not account for the di-excitation of very hot nuclei

  11. The role of fluctuation-induced transport in a toroidal plasma with strong radial electric fields

    Science.gov (United States)

    Roth, J. R.; Krawczonek, W. M.; Powers, E. J.; Hong, J. Y.; Kim, Y. C.

    1981-01-01

    Previous work employing digitally implemented spectral analysis techniques is extended to demonstrate that radial fluctuation-induced transport is the dominant ion transport mechanism in an electric field dominated toroidal plasma. Such transport can be made to occur against a density gradient, and hence may have a very beneficial effect on confinement in toroidal plasmas of fusion interest. It is shown that Bohm or classical diffusion down a density gradient, the collisional Pedersen-current mechanism, and the collisionless electric field gradient mechanism described by Cole (1976) all played a minor role, if any, in the radial transport of this plasma.

  12. Radial flow heat exchanger

    Science.gov (United States)

    Valenzuela, Javier

    2001-01-01

    A radial flow heat exchanger (20) having a plurality of first passages (24) for transporting a first fluid (25) and a plurality of second passages (26) for transporting a second fluid (27). The first and second passages are arranged in stacked, alternating relationship, are separated from one another by relatively thin plates (30) and (32), and surround a central axis (22). The thickness of the first and second passages are selected so that the first and second fluids, respectively, are transported with laminar flow through the passages. To enhance thermal energy transfer between first and second passages, the latter are arranged so each first passage is in thermal communication with an associated second passage along substantially its entire length, and vice versa with respect to the second passages. The heat exchangers may be stacked to achieve a modular heat exchange assembly (300). Certain heat exchangers in the assembly may be designed slightly differently than other heat exchangers to address changes in fluid properties during transport through the heat exchanger, so as to enhance overall thermal effectiveness of the assembly.

  13. The effect of radial migration on galactic disks

    International Nuclear Information System (INIS)

    Vera-Ciro, Carlos; D'Onghia, Elena; Navarro, Julio; Abadi, Mario

    2014-01-01

    We study the radial migration of stars driven by recurring multi-arm spiral features in an exponential disk embedded in a dark matter halo. The spiral perturbations redistribute angular momentum within the disk and lead to substantial radial displacements of individual stars, in a manner that largely preserves the circularity of their orbits and that results, after 5 Gyr (∼40 full rotations at the disk scale length), in little radial heating and no appreciable changes to the vertical or radial structure of the disk. Our results clarify a number of issues related to the spatial distribution and kinematics of migrators. In particular, we find that migrators are a heavily biased subset of stars with preferentially low vertical velocity dispersions. This 'provenance bias' for migrators is not surprising in hindsight, for stars with small vertical excursions spend more time near the disk plane, and thus respond more readily to non-axisymmetric perturbations. We also find that the vertical velocity dispersion of outward migrators always decreases, whereas the opposite holds for inward migrators. To first order, newly arrived migrators simply replace stars that have migrated off to other radii, thus inheriting the vertical bias of the latter. Extreme migrators might therefore be recognized, if present, by the unexpectedly small amplitude of their vertical excursions. Our results show that migration, understood as changes in angular momentum that preserve circularity, can strongly affect the thin disk, but cast doubts on models that envision the Galactic thick disk as a relic of radial migration.

  14. Temperature dynamics and velocity scaling laws for interchange driven, warm ion plasma filaments

    DEFF Research Database (Denmark)

    Olsen, Jeppe Miki Busk; Madsen, Jens; Nielsen, Anders Henry

    2016-01-01

    The influence of electron and ion temperature dynamics on the radial convection of isolated structures in magnetically confined plasmas is investigated by means of numerical simulations. It is demonstrated that the maximum radial velocity of these plasma blobs roughly follows the inertial velocity...

  15. Radial mixing of material in the asterodial zone

    International Nuclear Information System (INIS)

    Ruzmaikina, T.V.; Safronov, V.S.; Weidenschilling, S.J.

    1989-01-01

    The asteroid belt shows radial zoning of compositional structure. The most abundant types are successively S, C and P types from the inner to the outer parts of the main belt, and D type in the Trojan clouds. Boundaries between compositional zones are not sharp, but gradual transitions over scales ∼1 AU in semimajor axis. The authors examine processes for producing this structure before, during and after the accretion of asteroids. The initial structure is established by temperature and composition gradients in the turbulent solar nebula during the collapse of the presolar cloud. The radial scale of the zoning, comparable to the disk thickness, favors disk models with relatively low turbulent viscosity. Radial decay of solid bodies due to gas drag during settling to the central plane and planetesimal formation probably causes only a small degree of mixing, due to the systematic nature of drag-induced motions

  16. Simulation of High-Speed Droplet Impact Against Dry Substrates with Partial Velocity Slip

    Science.gov (United States)

    Kondo, Tomoki; Ando, Keita

    2017-11-01

    High-speed droplet impact can be used to clean substrates such as silicon wafers. Radially spreading shear flow after the impact may allow for mechanically removing contaminant particles at substrate surfaces. Since it is a big challenge to experimentally explore such complicated flow that exhibits contact line motion and water hammer, its flow feature is not well understood. Here, we aim to numerically evaluate shear flow caused by the impact of a spherical water droplet (of submillimeter sizes) at high speed (up to 50 m/s) against a dry rigid wall. We model the flow based on compressible Navier-Stokes equations with Stokes' hypothesis and solve them by a high-order-accurate finite volume method equipped with shock and interface capturing. To treat the motion of a contact line between the three phases (the droplet, the rigid wall, and the ambient air) in a robust manner, we permit velocity slip at the wall with Navier's model, for wall slip is known to come into play under steep velocity gradients that can arise from high-speed droplet impact. In our presentation, we will examine radially spreading flow after the droplet impact and the resulting wall shear stress generation from the simulation. This work was supported by JSPS KAKENHI Grant Number JP17J02211.

  17. Comparison of Poloidal Velocity Meassurements to Neoclassical Theory on the National Spherical Torus Experiment

    International Nuclear Information System (INIS)

    Bell, R.E.; Andre, R.; Kaye, S.M.; Kolesnikov, R.A.; LeBlance, B.P.; Rewolldt, G.; Wang, W.X.; Sabbagh, S.A.

    2010-01-01

    Knowledge of poloidal velocity is necessary for the determination of the radial electric field, Er, which along with its gradient is linked to turbulence suppression and transport barrier formation. Recent measurements of poloidal flow on conventional tokamaks have been reported to be an order of magnitude larger than expected from neoclassical theory. In contrast, recent poloidal velocity measurements on the NSTX spherical torus (S. M. Kaye et al., Phys. Plasmas 8, 1977 (2001)) are near or below neoclassical estimates. A novel charge exchange recombination spectroscopy diagnostic is used, which features active and passive sets of up/down symmetric views to produce line-integrated poloidal velocity measurements that do not need atomic physics corrections. Local profiles are obtained with an inversion. Poloidal velocity measurements are compared with neoclassical values computed with the codes NCLASS (W. A. Houlberg et al., Phys. Plasmas 4, 3230 (1997)) and GTC-Neo (W. X. Wang, et al., Phys. Plasmas 13, 082501 (2006)), which has been updated to handle impurities.

  18. On-line learning in radial basis functions networks

    OpenAIRE

    Freeman, Jason; Saad, David

    1997-01-01

    An analytic investigation of the average case learning and generalization properties of Radial Basis Function Networks (RBFs) is presented, utilising on-line gradient descent as the learning rule. The analytic method employed allows both the calculation of generalization error and the examination of the internal dynamics of the network. The generalization error and internal dynamics are then used to examine the role of the learning rate and the specialization of the hidden units, which gives ...

  19. THE INFLUENCE OF RADIAL STELLAR MIGRATION ON THE CHEMICAL EVOLUTION OF THE MILKY WAY

    Energy Technology Data Exchange (ETDEWEB)

    Wang Yue; Zhao Gang, E-mail: gzhao@nao.cas.cn [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

    2013-05-20

    Stellar migration is an important dynamical process in the Galactic disk. Here we model radial stellar migration in the Galactic disk with an analytical method, then add it to a detailed Galactic chemical evolution model to study the influence of radial stellar migration on the chemical evolution of the Milky Way, especially for the abundance gradients. We found that the radial stellar migration in the Galactic disk can make the profile of the G-dwarf metallicity distribution of the solar neighborhood taller and narrower, and thus it becomes another solution to the ''G-dwarf problem''. It can also scatter the age-metallicity relation. However, after migration, the abundance distributions along the Galactic radius do not change much; namely, the abundance gradients would not be flattened by the radial stellar migration, which is different from the predictions of many theoretical works. However, it can flatten the radial gradients of the mean chemical abundance of stars, and older stars possess flatter abundance gradients than younger stars. The most significant effect of radial stellar migration on the chemical abundance is that at a certain position it scatters the abundance of stars from a relatively concentrated value to a range.

  20. Hybrid simulations of radial transport driven by the Rayleigh-Taylor instability

    Science.gov (United States)

    Delamere, P. A.; Stauffer, B. H.; Ma, X.

    2017-12-01

    Plasma transport in the rapidly rotating giant magnetospheres is thought to involve a centrifugally-driven flux tube interchange instability, similar to the Rayleigh-Taylor (RT) instability. In three dimensions, the convective flow patterns associated with the RT instability can produce strong guide field reconnection, allowing plasma mass to move radially outward while conserving magnetic flux (Ma et al., 2016). We present a set of hybrid (kinetic ion / fluid electron) plasma simulations of the RT instability using high plasma beta conditions appropriate for Jupiter's inner and middle magnetosphere. A density gradient, combined with a centrifugal force, provide appropriate RT onset conditions. Pressure balance is achieved by initializing two ion populations: one with fixed temperature, but varying density, and the other with fixed density, but a temperature gradient that offsets the density gradient from the first population and the centrifugal force (effective gravity). We first analyze two-dimensional results for the plane perpendicular to the magnetic field by comparing growth rates as a function of wave vector following Huba et al. (1998). Prescribed perpendicular wave modes are seeded with an initial velocity perturbation. We then extend the model to three dimensions, introducing a stabilizing parallel wave vector. Boundary conditions in the parallel direction prohibit motion of the magnetic field line footprints to model the eigenmodes of the magnetodisc's resonant cavity. We again compare growth rates based on perpendicular wave number, but also on the parallel extent of the resonant cavity, which fixes the size of the largest parallel wavelength. Finally, we search for evidence of strong guide field magnetic reconnection within the domain by identifying areas with large parallel electric fields or changes in magnetic field topology.

  1. Observational hints of radial migration in disc galaxies from CALIFA

    Science.gov (United States)

    Ruiz-Lara, T.; Pérez, I.; Florido, E.; Sánchez-Blázquez, P.; Méndez-Abreu, J.; Sánchez-Menguiano, L.; Sánchez, S. F.; Lyubenova, M.; Falcón-Barroso, J.; van de Ven, G.; Marino, R. A.; de Lorenzo-Cáceres, A.; Catalán-Torrecilla, C.; Costantin, L.; Bland-Hawthorn, J.; Galbany, L.; García-Benito, R.; Husemann, B.; Kehrig, C.; Márquez, I.; Mast, D.; Walcher, C. J.; Zibetti, S.; Ziegler, B.; Califa Team

    2017-07-01

    Context. According to numerical simulations, stars are not always kept at their birth galactocentric distances but they have a tendency to migrate. The importance of this radial migration in shaping galactic light distributions is still unclear. However, if radial migration is indeed important, galaxies with different surface brightness (SB) profiles must display differences in their stellar population properties. Aims: We investigate the role of radial migration in the light distribution and radial stellar content by comparing the inner colour, age, and metallicity gradients for galaxies with different SB profiles. We define these inner parts, avoiding the bulge and bar regions and up to around three disc scale lengths (type I, pure exponential) or the break radius (type II, downbending; type III, upbending). Methods: We analysed 214 spiral galaxies from the CALIFA survey covering different SB profiles. We made use of GASP2D and SDSS data to characterise the light distribution and obtain colour profiles of these spiral galaxies. The stellar age and metallicity profiles were computed using a methodology based on full-spectrum fitting techniques (pPXF, GANDALF, and STECKMAP) to the Integral Field Spectroscopic CALIFA data. Results: The distributions of the colour, stellar age, and stellar metallicity gradients in the inner parts for galaxies displaying different SB profiles are unalike as suggested by Kolmogorov-Smirnov and Anderson-Darling tests. We find a trend in which type II galaxies show the steepest profiles of all, type III show the shallowest, and type I display an intermediate behaviour. Conclusions: These results are consistent with a scenario in which radial migration is more efficient for type III galaxies than for type I systems, where type II galaxies present the lowest radial migration efficiency. In such a scenario, radial migration mixes the stellar content, thereby flattening the radial stellar properties and shaping different SB profiles. However

  2. Color Gradient in the King Type Globular Cluster NGC 7089

    Directory of Open Access Journals (Sweden)

    Young-Jong Sohn

    1999-12-01

    Full Text Available We use BV CCD images to investigate the reality of the color gradient within a King type globular cluster NGC 7089. Surface photometry shows that there is a strong radial color gradient in the central region of the cluster in the sense of bluer center with the amplitude of -0.39 +/- 0.07 mag/arcsec2 in (B - V. In the outer region of the cluster, however, the radial color gradient shows a reverse case, i.e., redder toward the center. (B - V color profile which was derived from resolved stars in VGC 7089 field also shows a significant color gradient in the central region of the clusters, indicating that lights from the combination of red giant stars and blue horizontal branch stars cause the radial color gradient. Color gradient of the outer region of NGC 7089 may be due to the unresolved background of the cluster. Similar color gradients in the central area of clusters have been previously observed exserved exclusively in highly concentrated systems classified as post core collapse clusters. We caution, however, to confirm the reality of the color gradient from resolved stars, we need more accurate imaging data of the cluster with exceptional seeing condition because the effect of completeness correlates with local density of stars.

  3. Radial retinotomy in the macula.

    Science.gov (United States)

    Bovino, J A; Marcus, D F

    1984-01-01

    Radial retinotomy is an operative procedure usually performed in the peripheral or equatorial retina. To facilitate retinal attachment, the authors used intraocular scissors to perform radial retinotomy in the macula of two patients during vitrectomy surgery. In the first patient, a retinal detachment complicated by periretinal proliferation and macula hole formation was successfully reoperated with the aid of three radial cuts in the retina at the edges of the macular hole. In the second patient, an intraoperative retinal tear in the macula during diabetic vitrectomy was also successfully repaired with the aid of radial retinotomy. In both patients, retinotomy in the macula was required because epiretinal membranes, which could not be easily delaminated, were hindering retinal reattachment.

  4. Detonation in supersonic radial outflow

    KAUST Repository

    Kasimov, Aslan R.; Korneev, Svyatoslav

    2014-01-01

    We report on the structure and dynamics of gaseous detonation stabilized in a supersonic flow emanating radially from a central source. The steady-state solutions are computed and their range of existence is investigated. Two-dimensional simulations

  5. Dedicated radial ventriculography pigtail catheter

    Energy Technology Data Exchange (ETDEWEB)

    Vidovich, Mladen I., E-mail: miv@uic.edu

    2013-05-15

    A new dedicated cardiac ventriculography catheter was specifically designed for radial and upper arm arterial access approach. Two catheter configurations have been developed to facilitate retrograde crossing of the aortic valve and to conform to various subclavian, ascending aortic and left ventricular anatomies. The “short” dedicated radial ventriculography catheter is suited for horizontal ascending aortas, obese body habitus, short stature and small ventricular cavities. The “long” dedicated radial ventriculography catheter is suited for vertical ascending aortas, thin body habitus, tall stature and larger ventricular cavities. This new design allows for improved performance, faster and simpler insertion in the left ventricle which can reduce procedure time, radiation exposure and propensity for radial artery spasm due to excessive catheter manipulation. Two different catheter configurations allow for optimal catheter selection in a broad range of patient anatomies. The catheter is exceptionally stable during contrast power injection and provides equivalent cavity opacification to traditional femoral ventriculography catheter designs.

  6. Transition from resistive ballooning to neoclassical magnetohydrodynamic pressure-gradient-driven instability

    International Nuclear Information System (INIS)

    Spong, D.A.; Shaing, K.C.; Carreras, B.A.; Charlton, L.A.; Callen, J.D.; Garcia, L.

    1988-10-01

    The linearized neoclassical magnetohydrodynamic equations, including perturbed neoclassical flows and currents, have been solved for parameter regimes where the neoclassical pressure-gradient-driven instability becomes important. This instability is driven by the fluctuating bootstrap current term in Ohm's law. It begins to dominate the conventional resistive ballooning mode in the banana-plateau collisionality regime [μ/sub e//ν/sub e/ /approximately/ √ε/(1 + ν/sub *e/) > ε 2 ] and is characterized by a larger radial mode width and higher growth rate. The neoclassical instability persists in the absence of the usual magnetic field curvature drive and is not significantly affected by compressibility. Scalings with respect to β, n (toroidal mode number), and μ (neoclassical viscosity) are examined using a large-aspect-ratio, three-dimensional initial-value code that solves linearized equations for the magnetic flux, fluid vorticity, density, and parallel ion flow velocity in axisymmetric toroidal geometry. 13 refs., 10 figs

  7. Radial propagation of microturbulence in tokamaks

    International Nuclear Information System (INIS)

    Garbet, X.; Laurent, L.; Roubin, J.P.; Samain, A.

    1992-01-01

    Energy confinement time in tokamaks exhibits a clear dependence on global plasma parameters. This is not the case for transport coefficients; their dependence on local plasma parameters cannot be precisely established. The aim of the present paper is to give a possible explanation of this behaviour; turbulence propagates radially because of departure from cylindrical geometry. This implies that the turbulence level at a given point and hence transport coefficients are not only functions of local plasma parameters. A quantitative estimate of the propagation velocity is derived from a Lagrangian formalism. Two cases are considered: the effect of toroidicity and the effect of non linear mode-mode coupling. The consequences of this model are discussed. This process does not depend on the type of instability. For the sake of simplicity only electrostatic perturbations are considered

  8. Composition gradients across spiral galaxies II. The stellar mass limit

    International Nuclear Information System (INIS)

    Shields, G.A.; Tinsley, B.M.

    1976-01-01

    The equivalent width of the Hβ emission from H ii regions in spiral galaxies increases with distance from the nucleus. This W (Hβ) gradient is interpreted in terms of a radial gradient in the temperature of the hottest exciting stars. (T/subu/). From Searle's observations of M101, an increase Δ log T/subu/=0.02--0.13 from the intermediate to outermost spiral arms of M101 is inferred. There is also a radial decrease in the metal abundance (Z) across M101, and the T/subu/ gradient is consistent with the prediction of Kahn's recent theory that the upper mass limit for star formation should be smaller in regions of high Z. It is noted also that, even in the absence of changes in the upper mass limit, a T/subu/ gradient is expected because metal-rich stars of given mass have smaller effective temperatures. Several observational and theoretical improvements are needed before firm conclusions can be drawn, but it is clear that the presence of a T/subu/ gradient may lead to several important systematic changes in the interpretation of gradients in the properties of H ii regions across galaxies. A T/subu/ gradient reduces the Z gradient that is inferred from emission-line ratios, and it may help to explain why O ii is strong in the innermost regions where O iii is weak. A T/subu/ gradient may also partly camouflage a helium abundance gradient

  9. ROTATIONAL VELOCITIES FOR M DWARFS

    International Nuclear Information System (INIS)

    Jenkins, J. S.; Ramsey, L. W.; Jones, H. R. A.; Pavlenko, Y.; Barnes, J. R.; Pinfield, D. J.; Gallardo, J.

    2009-01-01

    We present spectroscopic rotation velocities (v sin i) for 56 M dwarf stars using high-resolution Hobby-Eberly Telescope High Resolution Spectrograph red spectroscopy. In addition, we have also determined photometric effective temperatures, masses, and metallicities ([Fe/H]) for some stars observed here and in the literature where we could acquire accurate parallax measurements and relevant photometry. We have increased the number of known v sin i values for mid M stars by around 80% and can confirm a weakly increasing rotation velocity with decreasing effective temperature. Our sample of v sin is peak at low velocities (∼3 km s -1 ). We find a change in the rotational velocity distribution between early M and late M stars, which is likely due to the changing field topology between partially and fully convective stars. There is also a possible further change in the rotational distribution toward the late M dwarfs where dust begins to play a role in the stellar atmospheres. We also link v sin i to age and show how it can be used to provide mid-M star age limits. When all literature velocities for M dwarfs are added to our sample, there are 198 with v sin i ≤ 10 km s -1 and 124 in the mid-to-late M star regime (M3.0-M9.5) where measuring precision optical radial velocities is difficult. In addition, we also search the spectra for any significant Hα emission or absorption. Forty three percent were found to exhibit such emission and could represent young, active objects with high levels of radial-velocity noise. We acquired two epochs of spectra for the star GJ1253 spread by almost one month and the Hα profile changed from showing no clear signs of emission, to exhibiting a clear emission peak. Four stars in our sample appear to be low-mass binaries (GJ1080, GJ3129, Gl802, and LHS3080), with both GJ3129 and Gl802 exhibiting double Hα emission features. The tables presented here will aid any future M star planet search target selection to extract stars with low v

  10. Anomalous cross-field velocities in a CIV laboratory experiment

    International Nuclear Information System (INIS)

    Axnaes, I.

    1988-10-01

    The axial and radial ion velocities and the electron radial velocity are determined in coaxial plasma gun operated under critical velocity conditions. The particle celocities are determined from probe measurement together with He I 3889 AA absolute intensity measurements and the consideration of the total momentum balance of the current sheet. The ions are found move axially and the electrons radially much faster than predicted by the E/B drift in the macroscopic fields. These results agree with what can be expected from the instability processes, which has earlier been proposed to operate in these experiments. It is therefore a direct experimental demonstration that instability processes have to be invoked not only for the electron heating, but also to explain the macroscopic velocities and currents. (author)

  11. Destabilization of drift waves due to nonuniform density gradient

    International Nuclear Information System (INIS)

    Hirose, A.; Ishihara, O.

    1985-01-01

    It is shown that the conventional mode differential equation for low frequency electrostatic waves in a tokamak does not contain full ion dynamics. Both electrons and ions contribute to the ballooning term, which is subject to finite ion Larmor radius effects. Also, both fluid ion approximation and kinetic ion model yield the same correction. Reexamined are the density gradient universal mode and ion temperature gradient instability employing the lowest order Pearlstein-Berk type radial eigenfunctions. No unstable, bounded, energy outgoing eigenfunctions have been found. In particular, a large ion temperature gradient (eta/sub i/) tends to further stabilize the temperature gradient driven mode

  12. Collisional transport in a plasma with steep gradients

    International Nuclear Information System (INIS)

    Wang, W.; Okamoto, M.; Nakajima, N.; Murakami, S.

    1999-06-01

    The validity is given to the newly proposed two δf method for neoclassical transport calculation, which can be solve the drift kinetic equation considering effects of steep plasma gradients, large radial electric field, finite banana width, and an orbit topology near the axis. The new method is applied to the study of ion transport with steep plasma gradients. It is found that the ion thermal diffusivity decreases as the scale length of density gradient decreases, while the ion particle flux due to ion-ion self collisions increases with increasing gradient. (author)

  13. Radial Flow in a Multiphase Transport Model at FAIR Energies

    Directory of Open Access Journals (Sweden)

    Soumya Sarkar

    2018-01-01

    Full Text Available Azimuthal distributions of radial velocities of charged hadrons produced in nucleus-nucleus (AB collisions are compared with the corresponding azimuthal distribution of charged hadron multiplicity in the framework of a multiphase transport (AMPT model at two different collision energies. The mean radial velocity seems to be a good probe for studying radial expansion. While the anisotropic parts of the distributions indicate a kind of collective nature in the radial expansion of the intermediate “fireball,” their isotropic parts characterize a thermal motion. The present investigation is carried out keeping the upcoming Compressed Baryonic Matter (CBM experiment to be held at the Facility for Antiproton and Ion Research (FAIR in mind. As far as high-energy heavy-ion interactions are concerned, CBM will supplement the Relativistic Heavy-Ion Collider (RHIC and Large Hadron Collider (LHC experiments. In this context our simulation results at high baryochemical potential would be interesting, when scrutinized from the perspective of an almost baryon-free environment achieved at RHIC and LHC.

  14. Rayleigh-Taylor instability of cylindrical jets with radial motion

    International Nuclear Information System (INIS)

    Chen, X.M.; Schrock, V.E.; Peterson, P.F.

    1997-01-01

    Rayleigh-Taylor instability of an interface between fluids with different densities subjected to acceleration normal to itself has interested researchers for almost a century. The classic analyses of a flat interface by Rayleigh and Taylor have shown that this type of instability depends on the direction of acceleration and the density differences of the two fluids. Plesset later analyzed the stability of a spherically symmetric flows (and a spherical interface) and concluded that the instability also depends on the velocity of the interface as well as the direction and magnitude of radial acceleration. The instability induced by radial motion in cylindrical systems seems to have been neglected by previous researchers. This paper analyzes the Rayleigh-Taylor type of instability for a cylindrical surface with radial motions. The results of the analysis show that, like the spherical case, the radial velocity also plays an important role. As an application, the example of a liquid jet surface in an Inertial Confinement Fusion (ICF) reactor design is analyzed. (orig.)

  15. Planetesimal formation by an axisymmetric radial bump of the column density of the gas in a protoplanetary disk

    Science.gov (United States)

    Onishi, Isamu K.; Sekiya, Minoru

    2017-04-01

    We investigate the effect of a radial pressure bump in a protoplanetary disk on planetesimal formation. We performed the two-dimensional numerical simulation of the dynamical interaction of solid particles and gas with an initially defined pressure bump under the assumption of axisymmetry. The aim of this work is to elucidate the effects of the stellar vertical gravity that were omitted in a previous study. Our results are very different from the previous study, which omitted the vertical gravity. Because dust particles settle toward the midplane because of the vertical gravity to form a thin dust layer, the regions outside of the dust layer are scarcely affected by the back-reaction of the dust. Hence, the gas column density keeps its initial profile with a bump, and dust particles migrate toward the bump. In addition, the turbulence due to the Kelvin-Helmholtz instability caused by the difference of the azimuthal velocities between the inside and outside of the dust layer is suppressed where the radial pressure gradient is reduced by the pressure bump. The dust settling proceeds further where the turbulence is weak, and a number of dust clumps are formed. The dust density in some clumps exceeds the Roche density. Planetesimals are considered to be formed from these clumps owing to the self-gravity.[Figure not available: see fulltext.

  16. Atomistic simulations of void migration under thermal gradient in UO2

    International Nuclear Information System (INIS)

    Desai, Tapan G.; Millett, Paul; Tonks, Michael; Wolf, Dieter

    2010-01-01

    It is well known that within a few hours after startup of a nuclear reactor, the temperature gradient within a fuel element causes migration of voids/bubbles radially inwards to form a central hole. To understand the atomic processes that control this migration of voids, we performed molecular dynamics (MD) simulations on single crystal UO 2 with voids of diameter 2.2 nm. An external temperature gradient was applied across the simulation cell. At the end of the simulation run, it was observed that the voids had moved towards the hot end of the simulation cell. The void migration velocity obtained from the simulations was compared with the available phenomenological equations for void migration due to different transport mechanisms. Surface diffusion of the slowest moving specie, i.e. uranium, was found to be the dominant mechanism for void migration. The contribution from lattice diffusion and the thermal stress gradient to the void migration was analyzed and found to be negligible. By extrapolation, a crossover from the surface-diffusion-controlled mechanism to the lattice-diffusion-controlled mechanism was found to occur for voids with sizes in the μm range.

  17. Latitudinal Dependence of the Radial IMF Component: Coronal Imprint

    Science.gov (United States)

    Suess, S. T.; Smith, E. J.

    1996-01-01

    Measurements by Ulysses have confirmed that there is no significant gradient with respect to heliomagnetic latitude in the radial component, B(sub r,) of the interplanetary magnetic field. In the corona, the plasma, beta is much less than 1, except directly above streamers, so longitudinal and latitudinal gradients in field strength will relax due to the transverse magnetic pressure gradient force as the solar wind carries magnetic flux away from the Sun. This happens quickly enough so that the field is essentially uniform by 5 - 10 solar radius, apparently remaining so as it is carried to beyond 1 AU. Here, we illustrate the coronal relaxation with a qualitative physical argument and by reference to a detailed Magneto HydroDynamics (MHD) simulation.

  18. Radial electric field studies in the plasma edge of ASDEX upgrade

    Energy Technology Data Exchange (ETDEWEB)

    Viezzer, Eleonora

    2012-12-18

    In magnetically confined fusion plasmas, edge transport barriers (ETBs) are formed during the transition from a highly turbulent state (low confinement regime, L-mode) to a high energy confinement regime (H-mode) with reduced turbulence and transport. The performance of an H-mode fusion plasma is highly dependent on the strength of the ETB which extends typically over the outermost 5% of the confined plasma. The formation of the ETB is strongly connected to the existence of a sheared plasma flow perpendicular to the magnetic field caused by a local radial electric field E{sub r}. The gradients in E{sub r} and the accompanying E x B velocity shear play a fundamental role in edge turbulence suppression, transport barrier formation and the transition to H-mode. Thus, the interplay between macroscopic flows and transport at the plasma edge is of crucial importance to understanding plasma confinement and stability. The work presented in this thesis is based on charge exchange recombination spectroscopy (CXRS) measurements performed at the plasma edge of the ASDEX Upgrade (AUG) tokamak. During this thesis new high-resolution CXRS diagnostics were installed at the outboard and inboard miplane of AUG, which provide measurements of the temperature, density and flows of the observed species. From these measurements the radial electric field can be directly determined via the radial force balance equation. The new CXRS measurements, combined with the other edge diagnostics available at AUG, allow for an unprecedented, high-accuracy localization (2-3 mm) of the E{sub r} profile. The radial electric field has been derived from charge exchange spectra measured on different impurity species including He{sup 2+}, B{sup 5+}, C{sup 6+} and Ne{sup 10+}. The resulting E{sub r} profiles are found to be identical within the uncertainties regardless of the impurity species used, thus demonstrating the validity of the diagnostic technique. Inside the ETB the E{sub r} profile forms a deep

  19. Radial lean direct injection burner

    Science.gov (United States)

    Khan, Abdul Rafey; Kraemer, Gilbert Otto; Stevenson, Christian Xavier

    2012-09-04

    A burner for use in a gas turbine engine includes a burner tube having an inlet end and an outlet end; a plurality of air passages extending axially in the burner tube configured to convey air flows from the inlet end to the outlet end; a plurality of fuel passages extending axially along the burner tube and spaced around the plurality of air passage configured to convey fuel from the inlet end to the outlet end; and a radial air swirler provided at the outlet end configured to direct the air flows radially toward the outlet end and impart swirl to the air flows. The radial air swirler includes a plurality of vanes to direct and swirl the air flows and an end plate. The end plate includes a plurality of fuel injection holes to inject the fuel radially into the swirling air flows. A method of mixing air and fuel in a burner of a gas turbine is also provided. The burner includes a burner tube including an inlet end, an outlet end, a plurality of axial air passages, and a plurality of axial fuel passages. The method includes introducing an air flow into the air passages at the inlet end; introducing a fuel into fuel passages; swirling the air flow at the outlet end; and radially injecting the fuel into the swirling air flow.

  20. Three-dimensional flow field measurements in a radial inflow turbine scroll using LDV

    Science.gov (United States)

    Malak, M. F.; Hamed, A.; Tabakoff, W.

    1986-01-01

    The results of an experimental study of the three-dimensional flow field in a radial inflow turbine scroll are presented. A two-color LDV system was used in the measurement of three orthogonal velocity components at 758 points located throughout the scroll and the unvaned portion of the nozzle. The cold flow experimental results are presented for through-flow velocity contours and the cross velocity vectors.

  1. Self-consistent radial sheath

    International Nuclear Information System (INIS)

    Hazeltine, R.D.

    1988-12-01

    The boundary layer arising in the radial vicinity of a tokamak limiter is examined, with special reference to the TEXT tokamak. It is shown that sheath structure depends upon the self-consistent effects of ion guiding-center orbit modification, as well as the radial variation of E /times/ B-induced toroidal rotation. Reasonable agreement with experiment is obtained from an idealized model which, however simplified, preserves such self-consistent effects. It is argued that the radial sheath, which occurs whenever confining magnetic field-lines lie in the plasma boundary surface, is an object of some intrinsic interest. It differs from the more familiar axial sheath because magnetized charges respond very differently to parallel and perpendicular electric fields. 11 refs., 1 fig

  2. Direct evidence of stationary zonal flows and critical gradient behavior for Er during formation of the edge pedestal in JET

    Science.gov (United States)

    Hillesheim, Jon

    2015-11-01

    High spatial resolution measurements with Doppler backscattering in JET have provided new insights into the development of the edge radial electric field during pedestal formation. The characteristics of Er have been studied as a function of density at 2.5 MA plasma current and 3 T toroidal magnetic field. We observe fine-scale spatial structure in the edge Er well prior to the LH transition, consistent with stationary zonal flows. Zonal flows are a fundamental mechanism for the saturation of turbulence and this is the first direct evidence of stationary zonal flows in a tokamak. The radial wavelength of the zonal flows systematically decreases with density. The zonal flows are clearest in Ohmic conditions, weaker in L-mode, and absent in H-mode. Measurements also show that after neutral beam heating is applied, the edge Er builds up at a constant gradient into the core during L-mode, at radii where Er is mainly due to toroidal velocity. The local stability of velocity shear driven turbulence, such as the parallel velocity gradient mode, will be assessed with gyrokinetic simulations. This critical Er shear persists across the LH transition into H-mode. Surprisingly, a reduction in the apparent magnitude of the Er well depth is observed directly following the LH transition at high densities. Establishing the physics basis for the LH transition is important for projecting scalings to ITER and these observations challenge existing models based on increased Er shear or strong zonal flows as the trigger for the transition. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

  3. Nonlinear radial propagation of drift wave turbulence

    International Nuclear Information System (INIS)

    Prakash, M.

    1985-01-01

    We study the linear and the nonlinear radial propagation of drift wave energy in an inhomogeneous plasma. The drift mode excited in such a plasma is dispersive in nature. The drift wave energy spreads out symmetrically along the direction of inhomogeneity with a finite group velocity. To study the effect of the nonlinear coupling on the propagation of energy in a collision free plasma, we solve the Hasegawa-Mima equation as a mixed initial boundary-value problem. The solutions of the linearized equation are used to check the reliability of our numerical calculations. Additional checks are also performed on the invariants of the system. Our results reveal that a pulse gets distorted as it propagates through the medium. The peak of the pulse propagates with a finite velocity that depends on the amplitude of the initial pulse. The polarity of propagation depends on the initial parameters of the pulse. We have also studied drift wave propagation in a resistive plasma. The Hasegawa-Wakatani equations are used to investigate this problem

  4. Vortex Ring Dynamics in Radially Confined Domains

    Science.gov (United States)

    Stewart, Kelley; Niebel, Casandra; Jung, Sunghwan; Vlachos, Pavlos

    2010-11-01

    Vortex ring dynamics have been studied extensively in semi-infinite quiescent volumes. However, very little is known about vortex-ring formation in wall-bounded domains where vortex wall interaction will affect both the vortex ring pinch-off and propagation velocity. This study addresses this limitation and studies vortex formation in radially confined domains to analyze the affect of vortex-ring wall interaction on the formation and propagation of the vortex ring. Vortex rings were produced using a pneumatically driven piston cylinder arrangement and were ejected into a long cylindrical tube which defined the confined downstream domain. A range of confinement domains were studied with varying confinement diameters Velocity field measurements were performed using planar Time Resolved Digital Particle Image Velocimetry (TRDPIV) and were processed using an in-house developed cross-correlation PIV algorithm. The experimental analysis was used to facilitate the development of a theoretical model to predict the variations in vortex ring circulation over time within confined domains.

  5. Detonation in supersonic radial outflow

    KAUST Repository

    Kasimov, Aslan R.

    2014-11-07

    We report on the structure and dynamics of gaseous detonation stabilized in a supersonic flow emanating radially from a central source. The steady-state solutions are computed and their range of existence is investigated. Two-dimensional simulations are carried out in order to explore the stability of the steady-state solutions. It is found that both collapsing and expanding two-dimensional cellular detonations exist. The latter can be stabilized by putting several rigid obstacles in the flow downstream of the steady-state sonic locus. The problem of initiation of standing detonation stabilized in the radial flow is also investigated numerically. © 2014 Cambridge University Press.

  6. Revealing the velocity structure of the filamentary nebula in NGC 1275 in its entirety

    Science.gov (United States)

    Gendron-Marsolais, M.; Hlavacek-Larrondo, J.; Martin, T. B.; Drissen, L.; McDonald, M.; Fabian, A. C.; Edge, A. C.; Hamer, S. L.; McNamara, B.; Morrison, G.

    2018-05-01

    We have produced for the first time a detailed velocity map of the giant filamentary nebula surrounding NGC 1275, the Perseus cluster's brightest galaxy, and revealed a previously unknown rich velocity structure across the entire nebula. These new observations were obtained with the optical imaging Fourier transform spectrometer SITELLE at CFHT. With its wide field of view (˜11'×11'), SITELLE is the only integral field unit spectroscopy instrument able to cover the 80 kpc×55 kpc (3.8'×2.6') large nebula in NGC 1275. Our analysis of these observations shows a smooth radial gradient of the [N II]λ6583/Hα line ratio, suggesting a change in the ionization mechanism and source across the nebula. The velocity map shows no visible general trend or rotation, indicating that filaments are not falling uniformly onto the galaxy, nor being uniformly pulled out from it. Comparison between the physical properties of the filaments and Hitomi measurements of the X-ray gas dynamics in Perseus are also explored.

  7. The Three-Dimensional Velocity Distribution of Wide Gap Taylor-Couette Flow Modelled by CFD

    Directory of Open Access Journals (Sweden)

    David Shina Adebayo

    2016-01-01

    Full Text Available A numerical investigation is conducted for the flow between two concentric cylinders with a wide gap, relevant to bearing chamber applications. This wide gap configuration has received comparatively less attention than narrow gap journal bearing type geometries. The flow in the gap between an inner rotating cylinder and an outer stationary cylinder has been modelled as an incompressible flow using an implicit finite volume RANS scheme with the realisable k-ε model. The model flow is above the critical Taylor number at which axisymmetric counterrotating Taylor vortices are formed. The tangential velocity profiles at all axial locations are different from typical journal bearing applications, where the velocity profiles are quasilinear. The predicted results led to two significant findings of impact in rotating machinery operations. Firstly, the axial variation of the tangential velocity gradient induces an axially varying shear stress, resulting in local bands of enhanced work input to the working fluid. This is likely to cause unwanted heat transfer on the surface in high torque turbomachinery applications. Secondly, the radial inflow at the axial end-wall boundaries is likely to promote the transport of debris to the junction between the end-collar and the rotating cylinder, causing the build-up of fouling in the seal.

  8. Blade bowing effects on radial equilibrium of inlet flow in axial compressor cascades

    Directory of Open Access Journals (Sweden)

    Han XU

    2017-10-01

    Full Text Available The circumferentially averaged equation of the inlet flow radial equilibrium in axial compressor was deduced. It indicates that the blade inlet radial pressure gradient is closely related to the radial component of the circumferential fluctuation (CF source item. Several simplified cascades with/without aerodynamic loading were numerically studied to investigate the effects of blade bowing on the inlet flow radial equilibrium. A data reduction program was conducted to obtain the CF source from three-dimensional (3D simulation results. Flow parameters at the passage inlet were focused on and each term in the radial equilibrium equation was discussed quantitatively. Results indicate that the inviscid blade force is the inducement of the inlet CF due to geometrical asymmetry. Blade bowing induces variation of the inlet CF, thus changes the radial pressure gradient and leads to flow migration before leading edge (LE in the cascades. Positive bowing drives the inlet flow to migrate from end walls to mid-span and negative bowing turns it to the reverse direction to build a new equilibrium. In addition, comparative studies indicate that the inlet Mach number and blade loading can efficiently impact the effectiveness of blade bowing on radial equilibrium in compressor design.

  9. Computational Strain Gradient Crystal Plasticity

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Kysar, Jeffrey W.

    2011-01-01

    A model for strain gradient crystal visco-plasticity is formulated along the lines proposed by Fleck andWillis (2009) for isotropic plasticity. Size-effects are included in the model due to the addition of gradient terms in both the free energy as well as through a dissipation potential. A finite...... element solution method is presented, which delivers the slip-rate field and the velocity-field based on two minimum principles. Some plane deformation problems relevant for certain specific orientations of a face centered cubic crystal under plane loading conditions are studied, and effective in......-plane parameters are developed based on the crystallographic properties of the material. The problem of cyclic shear of a single crystal between rigid platens is studied as well as void growth of a cylindrical void....

  10. Vortex Whistle in Radial Intake

    National Research Council Canada - National Science Library

    Tse, Man-Chun

    2004-01-01

    In a radial-to-axial intake with inlet guide vanes (IGV) at the entry, a strong flow circulation Gamma can be generated from the tangential flow components created by the IGVs when their setting exceed about halfclosing (approx. 45 deg...

  11. Consolidation by Prefabricated Vertical Drains with a Threshold Gradient

    OpenAIRE

    Xiao Guo; Kang-He Xie; Yue-Bao Deng

    2014-01-01

    This paper shows the development of an approximate analytical solution of radial consolidation by prefabricated vertical drains with a threshold gradient. To understand the effect of the threshold gradient on consolidation, a parametric analysis was performed using the present solution. The applicability of the present solution was demonstrated in two cases, wherein the comparisons with Hansbo’s results and observed data were conducted. It was found that (1) the flow with the threshold gradie...

  12. Effect of Wall Friction and Vortex Generation on Radial Void Distribution The Wall - Vortex Effect

    Energy Technology Data Exchange (ETDEWEB)

    Rouhani, Zia

    1974-09-15

    Arguments are presented to prove the existence of rolling vortices in two-phase flow. In liquid phase they will appear in a boundary layer near the walls while in the continuous vapor phase they will occur near the interface with a liquid film. The intensity and size of these vortices are expected to depend on the local velocity gradients normal to the walls. A discussion is given of the interaction between the rotational field associated with such vortices and bubbles in liquid flow or droplets in vapor-flow. This interaction is called the wall-vortex effect. It appears that several, apparently unrelated, phenomena observed in two-phase flow systems may be interpreted in terms of this mechanism. Among these are: Radial void peaking near the walls; Slip ratios less than unity observed even in vertical upward flow; Reduced droplet diffusion near the liquid film; Reduced vapor mixing between subchannels at low steam qualities; and Accelerated flashing process in flow of depressurized liquid. Finally, a comparison with the well-known Magnus effect is also included

  13. Electron velocity and momentum density

    International Nuclear Information System (INIS)

    Perkins, G.A.

    1978-01-01

    A null 4-vector eta + sigma/sub μ/based on Dirac's relativistic electron equation, is shown explicitly for a plane wave and various Coulomb states. This 4-vector constitutes a mechanical ''model'' for the electron in those staes, and expresses the important spinor quantities represented conventionally by n, f, g, m, j, kappa, l, and s. The model for a plane wave agrees precisely with the relation between velocity and phase gradient customarily used in quantum theory, but the models for Coulomb states contradict that relation

  14. Role of the vertical pressure gradient in wave boundary layers

    DEFF Research Database (Denmark)

    Jensen, Karsten Lindegård; Sumer, B. Mutlu; Vittori, Giovanna

    2014-01-01

    By direct numerical simulation (DNS) of the flow in an oscillatory boundary layer, it is possible to obtain the pressure field. From the latter, the vertical pressure gradient is determined. Turbulent spots are detected by a criterion involving the vertical pressure gradient. The vertical pressure...... gradient is also treated as any other turbulence quantity like velocity fluctuations and statistical properties of the vertical pressure gradient are calculated from the DNS data. The presence of a vertical pressure gradient in the near bed region has significant implications for sediment transport....

  15. Estimation of the magnetic field gradient tensor using the Swarm constellation

    DEFF Research Database (Denmark)

    Kotsiaros, Stavros; Finlay, Chris; Olsen, Nils

    2014-01-01

    For the first time, part of the magnetic field gradient tensor is estimated in space by the Swarm mission. We investigate the possibility of a more complete estimation of the gradient tensor exploiting the Swarm constellation. The East-West gradients can be approximated by observations from...... deviations compared to conventional vector observations at almost all latitudes. Analytical and numerical analysis of the spectral properties of the gradient tensor shows that specific combinations of the East-West and North-South gradients have almost identical signal content to the radial gradient...

  16. Measurement of Poloidal Velocity on the National Spherical Torus Experiment

    Energy Technology Data Exchange (ETDEWEB)

    Ronald E. Bell and Russell Feder

    2010-06-04

    A diagnostic suite has been developed to measure impurity poloidal flow using charge exchange recombination spectroscopy on the National Spherical Torus Experiment. Toroidal and poloidal viewing systems measure all quantities required to determine the radial electric field. Two sets of up/down symmetric poloidal views are used to measure both active emission in the plane of the neutral heating beams and background emission in a radial plane away from the neutral beams. Differential velocity measurements isolate the line-integrated poloidal velocity from apparent flows due to the energy-dependent chargeexchange cross section. Six f/1.8 spectrometers measure 276 spectra to obtain 75 active and 63 background channels every 10 ms. Local measurements from a similar midplane toroidal viewing system are mapped into two dimensions to allow the inversion of poloidal line-integrated measurements to obtain local poloidal velocity profiles. Radial resolution after inversion is 0.6-1.8 cm from the plasma edge to the center.

  17. Measurement of Poloidal Velocity on the National Spherical Torus Experiment

    International Nuclear Information System (INIS)

    Bell, Ronald E.; Feder, Russell

    2010-01-01

    A diagnostic suite has been developed to measure impurity poloidal flow using charge exchange recombination spectroscopy on the National Spherical Torus Experiment. Toroidal and poloidal viewing systems measure all quantities required to determine the radial electric field. Two sets of up/down symmetric poloidal views are used to measure both active emission in the plane of the neutral heating beams and background emission in a radial plane away from the neutral beams. Differential velocity measurements isolate the line-integrated poloidal velocity from apparent flows due to the energy-dependent chargeexchange cross section. Six f/1.8 spectrometers measure 276 spectra to obtain 75 active and 63 background channels every 10 ms. Local measurements from a similar midplane toroidal viewing system are mapped into two dimensions to allow the inversion of poloidal line-integrated measurements to obtain local poloidal velocity profiles. Radial resolution after inversion is 0.6-1.8 cm from the plasma edge to the center.

  18. Radial head dislocation during proximal radial shaft osteotomy.

    Science.gov (United States)

    Hazel, Antony; Bindra, Randy R

    2014-03-01

    The following case report describes a 48-year-old female patient with a longstanding both-bone forearm malunion, who underwent osteotomies of both the radius and ulna to improve symptoms of pain and lack of rotation at the wrist. The osteotomies were templated preoperatively. During surgery, after performing the planned radial shaft osteotomy, the authors recognized that the radial head was subluxated. The osteotomy was then revised from an opening wedge to a closing wedge with improvement of alignment and rotation. The case report discusses the details of the operation, as well as ways in which to avoid similar shortcomings in the future. Copyright © 2014 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.

  19. Planetary nebula velocities in the disc and bulge of M31

    NARCIS (Netherlands)

    Halliday, C.; Carter, D.; Bridges, T. J.; Jackson, Z. C.; Wilkinson, M. I.; Quinn, D. P.; Evans, N. W.; Douglas, N. G.; Merrett, H. R.; Merrifield, M. R.; Romanowsky, A. J.; Kuijken, K.; Irwin, M. J.

    2006-01-01

    We present radial velocities for a sample of 723 planetary nebulae in the disc and bulge of M31, measured using the WYFFOS fibre spectrograph on the William Herschel Telescope. Velocities are determined using the [OIII] lambda 5007 emission line. Rotation and velocity dispersion are measured to a

  20. Latitudinal Dependence of the Radial IMF Component - Interplanetary Imprint

    Science.gov (United States)

    Suess, S. T.; Smith, E. J.; Phillips, J.; Goldstein, B. E.; Nerney, S.

    1996-01-01

    Ulysses measurements have confirmed that there is no significant gradient with respect to heliomagnetic latitude in the radial component, B(sub r,), of the interplanetary magnetic field. There are two processes responsible for this observation. In the corona, the plasma beta is much less than 1, except directly above streamers, so both longitudinal and latitudinal (meridional) gradients in field strength will relax, due to the transverse magnetic pressure gradient force, as the solar wind carries magnetic flux away from the Sun. This happens so quickly that the field is essentially uniform by 5 solar radius. Beyond 10 solar radius, beta is greater than 1 and it is possible for a meridional thermal pressure gradient to redistribute magnetic flux - an effect apparently absent in Ulysses and earlier ICE and Interplanetary Magnetic Physics (IMP) data. We discuss this second effect here, showing that its absence is mainly due to the perpendicular part of the anisotropic thermal pressure gradient in the interplanetary medium being too small to drive significant meridional transport between the Sun and approx. 4 AU. This is done using a linear analytic estimate of meridional transport. The first effect was discussed in an earlier paper.

  1. Manipulation of viscous fingering in a radially tapered cell geometry

    Science.gov (United States)

    Bongrand, Grégoire; Tsai, Peichun Amy

    2018-06-01

    When a more mobile fluid displaces another immiscible one in a porous medium, viscous fingering propagates with a partial sweep, which hinders oil recovery and soil remedy. We experimentally investigate the feasibility of tuning such fingering propagation in a nonuniform narrow passage with a radial injection, which is widely used in various applications. We show that a radially converging cell can suppress the common viscous fingering observed in a uniform passage, and a full sweep of the displaced fluid is then achieved. The injection flow rate Q can be further exploited to manipulate the viscous fingering instability. For a fixed gap gradient α , our experimental results show a full sweep at a small Q but partial displacement with fingering at a sufficient Q . Finally, by varying α , we identify and characterize the variation of the critical threshold between stable and unstable displacements. Our experimental results reveal good agreement with theoretical predictions by a linear stability analysis.

  2. Shallow crustal radial anisotropy beneath the Tehran basin of Iran from seismic ambient noise tomography

    Science.gov (United States)

    Shirzad, Taghi; Shomali, Z. Hossein

    2014-06-01

    We studied the shear wave velocity structure and radial anisotropy beneath the Tehran basin by analyzing the Rayleigh wave and Love wave empirical Green's functions obtained from cross-correlation of seismic ambient noise. Approximately 199 inter-station Rayleigh and Love wave empirical Green's functions with sufficient signal-to-noise ratios extracted from 30 stations with various sensor types were used for phase velocity dispersion analysis of periods ranging from 1 to 7 s using an image transformation analysis technique. Dispersion curves extracted from the phase velocity maps were inverted based on non-linear damped least squares inversion method to obtain a quasi-3D model of crustal shear wave velocities. The data used in this study provide an unprecedented opportunity to resolve the spatial distribution of radial anisotropy within the uppermost crust beneath the Tehran basin. The quasi-3D shear wave velocity model obtained in this analysis delineates several distinct low- and high-velocity zones that are generally separated by geological boundaries. High-shear-velocity zones are located primarily around the mountain ranges and extend to depths of 2.0 km, while the low-shear-velocity zone is located near regions with sedimentary layers. In the shallow subsurface, our results indicate strong radial anisotropy with negative magnitude (VSV > VSH) primarily associated with thick sedimentary deposits, reflecting vertical alignment of cracks. With increasing depth, the magnitude of the radial anisotropy shifts from predominantly negative (less than -10%) to predominantly positive (greater than 5%). Our results show a distinct change in radial anisotropy between the uppermost sedimentary layer and the bedrock.

  3. Turbulent flow velocity distribution at rough walls

    International Nuclear Information System (INIS)

    Baumann, W.

    1978-08-01

    Following extensive measurements of the velocity profile in a plate channel with artificial roughness geometries specific investigations were carried out to verify the results obtained. The wall geometry used was formed by high transverse square ribs having a large pitch. The measuring position relative to the ribs was varied as a parameter thus providing a statement on the local influence of roughness ribs on the values measured. As a fundamental result it was found that the gradient of the logarithmic rough wall velocity profiles, which differs widely from the value 2.5, depends but slightly on the measuring position relative to the ribs. The gradients of the smooth wall velocity profiles deviate from 2.5 near the ribs, only. This fact can be explained by the smooth wall shear stress varying with the pitch of the ribs. (orig.) 891 GL [de

  4. RADIAL STABILITY IN STRATIFIED STARS

    International Nuclear Information System (INIS)

    Pereira, Jonas P.; Rueda, Jorge A.

    2015-01-01

    We formulate within a generalized distributional approach the treatment of the stability against radial perturbations for both neutral and charged stratified stars in Newtonian and Einstein's gravity. We obtain from this approach the boundary conditions connecting any two phases within a star and underline its relevance for realistic models of compact stars with phase transitions, owing to the modification of the star's set of eigenmodes with respect to the continuous case

  5. Velocidades radiales en Collinder 121

    Science.gov (United States)

    Arnal, M.; Morrell, N.

    Se han llevado a cabo observaciones espectroscópicas de unas treinta estrellas que son posibles miembros del cúmulo abierto Collinder 121. Las mismas fueron realizadas con el telescopio de 2.15m del Complejo Astronómico El Leoncito (CASLEO). El análisis de las velocidades radiales derivadas del material obtenido, confirma la realidad de Collinder 121, al menos desde el punto de vista cinemático. La velocidad radial baricentral (LSR) del cúmulo es de +17 ± 3 km.s-1. Esta velocidad coincide, dentro de los errores, con la velocidad radial (LSR) de la nebulosa anillo S308, la cual es de ~20 ± 10 km.s-1. Como S308 se encuentra físicamente asociada a la estrella Wolf-Rayet HD~50896, es muy probable que esta última sea un miembro de Collinder 121. Desde un punto de vista cinemático, la supergigante roja HD~50877 (K3Iab) también pertenecería a Collinder 121. Basándonos en la pertenencia de HD~50896 a Collinder 121, y en la interacción encontrada entre el viento de esta estrella y el medio interestelar circundante a la misma, se estima para este cúmulo una distancia del orden de 1 kpc.

  6. Liquid velocity in upward and downward air-water flows

    International Nuclear Information System (INIS)

    Sun Xiaodong; Paranjape, Sidharth; Kim, Seungjin; Ozar, Basar; Ishii, Mamoru

    2004-01-01

    Local characteristics of the liquid phase in upward and downward air-water two-phase flows were experimentally investigated in a 50.8-mm inner-diameter round pipe. An integral laser Doppler anemometry (LDA) system was used to measure the axial liquid velocity and its fluctuations. No effect of the flow direction on the liquid velocity radial profile was observed in single-phase liquid benchmark experiments. Local multi-sensor conductivity probes were used to measure the radial profiles of the bubble velocity and the void fraction. The measurement results in the upward and downward two-phase flows are compared and discussed. The results in the downward flow demonstrated that the presence of the bubbles tended to flatten the liquid velocity radial profile, and the maximum liquid velocity could occur off the pipe centerline, in particular at relatively low flow rates. However, the maximum liquid velocity always occurred at the pipe center in the upward flow. Also, noticeable turbulence enhancement due to the bubbles in the two-phase flows was observed in the current experimental flow conditions. Furthermore, the distribution parameter and the void-weighted area-averaged drift velocity were obtained based on the definitions

  7. UNVEILING THE DETAILED DENSITY AND VELOCITY STRUCTURES OF THE PROTOSTELLAR CORE B335

    Energy Technology Data Exchange (ETDEWEB)

    Kurono, Yasutaka; Saito, Masao; Kamazaki, Takeshi; Morita, Koh-Ichiro; Kawabe, Ryohei, E-mail: yasutaka.kurono@nao.ac.jp [Chile Observatory, National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588 (Japan)

    2013-03-10

    We present an observational study of the protostellar core B335 harboring a low-mass Class 0 source. The observations of the H{sup 13}CO{sup +}(J = 1-0) line emission were carried out using the Nobeyama 45 m telescope and Nobeyama Millimeter Array. Our combined image of the interferometer and single-dish data depicts detailed structures of the dense envelope within the core. We found that the core has a radial density profile of n(r){proportional_to}r {sup -p} and a reliable difference in the power-law indices between the outer and inner regions of the core: p Almost-Equal-To 2 for r {approx}> 4000 AU and p Almost-Equal-To 1.5 for r {approx}< 4000 AU. The dense core shows a slight overall velocity gradient of {approx}1.0 km s{sup -1} over the scale of 20, 000 AU across the outflow axis. We believe that this velocity gradient represents a solid-body-like rotation of the core. The dense envelope has a quite symmetrical velocity structure with a remarkable line broadening toward the core center, which is especially prominent in the position-velocity diagram across the outflow axis. The model calculations of position-velocity diagrams do a good job of reproducing observational results using the collapse model of an isothermal sphere in which the core has an inner free-fall region and an outer region conserving the conditions at the formation stage of a central stellar object. We derived a central stellar mass of {approx}0.1 M{sub Sun }, and suggest a small inward velocity, v{sub r{>=}r{sub i{sub n{sub f}}}}{approx}0 km s{sup -1} in the outer core at {approx}> 4000 AU. We concluded that our data can be well explained by gravitational collapse with a quasi-static initial condition, such as Shu's model, or by the isothermal collapse of a marginally critical Bonnor-Ebert sphere.

  8. Pressure anisotropy and radial stress balance in the Jovian neutral sheet

    Science.gov (United States)

    Paranicas, C. P.; Mauk, B. H.; Krimigis, S. M.

    1991-01-01

    By examining particle and magnetic field data from the Voyager 1 and 2 spacecraft, signatures were found indicating that the (greater than about 28 keV) particle pressure parallel to the magnetic field is greater than the pressure perpendicular to the field within the nightside neutral sheet (three nightside neutral sheet crossings, with favorable experimental conditions, were used). By incorporating the pressure anisotropy into the calculation of radial forces within the hightside neutral sheet, it is found that (1) force balance is approximately achieved and (2) the anisotropy force term provides the largest contribution of the other particle forces considered (pressure gradients and the corotation centrifugal force). With regard to the problem of understanding the balance of radial forces within the dayside neutral sheet (McNutt, 1984; Mauk and Krimigis, 1987), the nightside pressure anisotropy force is larger than the dayside pressure gradient forces at equivalent radial distances; however, a full accounting of the dayside regions remains to be achieved.

  9. The geostrophic velocity field in shallow water over topography

    Science.gov (United States)

    Charnock, Henry; Killworth, Peter D.

    1998-01-01

    A recent note (Hopkins, T.S., 1996. A note on the geostrophic velocity field referenced to a point. Continental Shelf Research 16, 1621-1630) suggests a method for evaluating absolute pressure gradients in stratified water over topography. We demonstrate that this method requires no along-slope bottom velocity, in contradiction to what is usually observed, and that mass is not conserved.

  10. The role of the radial electric field in confinement and transport in H-mode and VH-mode discharges in the DIII-D tokamak

    International Nuclear Information System (INIS)

    Gohil, P.; Burrell, K.H.; Groebner, R.J.; Osborne, T.H.; Doyle, E.J.; Rettig, C.L.

    1993-08-01

    Measurements of the radial electric field, E r , with high spatial and high time resolution in H-mode and VH-mode discharges in the DIII-D tokamak have revealed the significant influence of the shear in E r on confinement and transport in these discharges. These measurements are made using the DIII-D Charge Exchange Recombination (CER) System. At the L-H transition in DIII-D plasmas, a negative well-like E r profile develops just within the magnetic separatrix. A region of shear in E r results, which extends 1 to 2 cm into the plasma from the separatrix. At the transition, this region of sheared E r exhibits the greatest increase in impurity ion poloidal rotation velocity and the greatest reduction in plasma fluctuations. A transport barrier is formed in this same region of E x B velocity shear as is signified by large increases in the observed gradients of the ion temperature, the carbon density, the electron temperature and electron density. The development of the region of sheared E r , the increase in impurity ion poloidal rotation, the reduction in plasma turbulence, and the transport barrier all occur simultaneously at the L-H transition. Measurements of the radial electric field, plasma turbulence, thermal transport, and energy confinement have been performed for a wide range of plasma conditions and configurations. The results support the supposition that the progression of improving confinement at the L-H transition, into the H-mode and then into the VH-mode can be explained by the hypothesis of the suppression of plasma turbulence by the increasing penetration of the region of sheared E x B velocity into the plasma interior

  11. Analysis of magnetic gradients to study gravitropism.

    Science.gov (United States)

    Hasenstein, Karl H; John, Susan; Scherp, Peter; Povinelli, Daniel; Mopper, Susan

    2013-01-01

    Gravitropism typically is generated by dense particles that respond to gravity. Experimental stimulation by high-gradient magnetic fields provides a new approach to selectively manipulate the gravisensing system. The movement of corn, wheat, and potato starch grains in suspension was examined with videomicroscopy during parabolic flights that generated 20 to 25 s of weightlessness. During weightlessness, a magnetic gradient was generated by inserting a wedge into a uniform, external magnetic field that caused repulsion of starch grains. The resultant velocity of movement was compared with the velocity of sedimentation under 1 g conditions. The high-gradient magnetic fields repelled the starch grains and generated a force of at least 0.6 g. Different wedge shapes significantly affected starch velocity and directionality of movement. Magnetic gradients are able to move diamagnetic compounds under weightless or microgravity conditions and serve as directional stimulus during seed germination in low-gravity environments. Further work can determine whether gravity sensing is based on force or contact between amyloplasts and statocyte membrane system.

  12. Solar updraft power generator with radial and curved vanes

    Science.gov (United States)

    Hafizh, Hadyan; Hamsan, Raziff; Zamri, Aidil Azlan Ahmad; Keprawi, Mohamad Fairuz Mohamad; Shirato, Hiromichi

    2018-02-01

    Solar radiation is the largest source of energy available on earth and the solar updraft power generator (SUPG) is a renewable energy facility capable of harnessing its abundant power. Unlike the conventional wind turbines that harness natural wind in the atmosphere and often encounter with the intermittent issue or even complete cut-off from airflow, the SUPG creates artificial wind as a result of solar-induced convective flows. However, the SUPG has an inherent low total efficiency due to the conversion of thermal energy into pressure energy. Acknowledging the low efficiency and considering its potential as a renewable energy facility, the current work aims to increase the total efficiency by installing a series of guide walls inside the collector. Two types of guide walls were used i.e. radial and curved vanes. The result with curved vanes showed that the updraft velocity is higher compare to those without vanes. About 18% and 64% improvement of updraft velocity and mechanical power were attained respectively. Furthermore, it was observed that the role of radial vanes configuration was more to produce a smooth updraft velocity profile rather than increasing the total efficiency.

  13. Seismic Linear Noise Attenuation with Use of Radial Transform

    Science.gov (United States)

    Szymańska-Małysa, Żaneta

    2018-03-01

    One of the goals of seismic data processing is to attenuate the recorded noise in order to enable correct interpretation of the image. Radial transform has been used as a very effective tool in the attenuation of various types of linear noise, both numerical and real (such as ground roll, direct waves, head waves, guided waves etc). The result of transformation from offset - time (X - T) domain into apparent velocity - time (R - T) domain is frequency separation between reflections and linear events. In this article synthetic and real seismic shot gathers were examined. One example was targeted at far offset area of dataset where reflections and noise had similar apparent velocities and frequency bands. Another example was a result of elastic modelling where linear artefacts were produced. Bandpass filtering and scaling operation executed in radial domain attenuated all discussed types of linear noise very effectively. After noise reduction all further processing steps reveal better results, especially velocity analysis, migration and stacking. In all presented cases signal-to-noise ratio was significantly increased and reflections covered previously by noise were revealed. Power spectra of filtered seismic records preserved real dynamics of reflections.

  14. A new method for measurement of granular velocities

    International Nuclear Information System (INIS)

    Nyborg Andersen, B.

    1984-01-01

    A new, supplementary method to measure granular velocities is presented. The method utilizes the Doppler shift caused by the line of sight component of the solar rotation to cause a wavelength shift through spectral lines as function of heliocentric angle. By measuring the center-to-limb variation of the granular intensity fluctations at different wavelength positions in the lines, the velocities are found. To do this, assumptions regarding the geometrical structure of the velocity and intensity fields have to be made. Preliminary application of the method results in a steep velocity gradient suggesting zero velocity at a hight of 200 km above tau 500 = 1. Possible causes are discussed

  15. A comparative study for the estimation of geodetic point velocity by ...

    Indian Academy of Sciences (India)

    Geodetic point velocity; artificial neural networks; back propagation; radial basis function; Kriging. J. Earth Syst. Sci. ...... The employment of BPANN is an alternative tool to KRIG for .... Computational Intelligence and Multimedia Applications.

  16. Velocity dispersion profiles of clusters of galaxies

    International Nuclear Information System (INIS)

    Struble, M.F.

    1979-01-01

    Velocity dispersion as a function of radius, called sigma/sub ls/ profiles, is presented for 13 clusters of galaxies having > or =30 radial velocities from both published and unpublished lists. A list of probable new members and possible outlying members for these clusters is also given. chi 2 and Kolmogoroff--Smirnoff one-sample tests for the goodness of fit of power laws to portions of the profiles indicate two significant structures in some profiles: (1) a local minimum corresponding to the local minimum noted in surface density or surface brightness profiles, and (2) a decrease in sigma/sub ls/ toward the cores. Both of these features are discussed in terms of a comparison with Wielen's N-body simulations. The sigma/sub ls/ profiles are placed in a new classification scheme which lends itself to interpreting clusters in a dynamical age sequence. The velocity field of galaxies at large distances from cluster centers is also discussed

  17. Exceptional circles of radial potentials

    International Nuclear Information System (INIS)

    Music, M; Perry, P; Siltanen, S

    2013-01-01

    A nonlinear scattering transform is studied for the two-dimensional Schrödinger equation at zero energy with a radial potential. Explicit examples are presented, both theoretically and computationally, of potentials with nontrivial singularities in the scattering transform. The singularities arise from non-uniqueness of the complex geometric optics solutions that define the scattering transform. The values of the complex spectral parameter at which the singularities appear are called exceptional points. The singularity formation is closely related to the fact that potentials of conductivity type are ‘critical’ in the sense of Murata. (paper)

  18. Abundance gradients in disc galaxies and chemical evolution models

    International Nuclear Information System (INIS)

    Diaz, A.I.

    1989-01-01

    The present state of abundance gradients and chemical evolution models of spiral galaxies is reviewed. An up to date compilation of abundance data in the literature concerning HII regions over galactic discs is presented. From these data Oxygen and Nitrogen radial gradients are computed. The slope of the Oxygen gradient is shown to have a break at a radius between 1.5 and 1.75 times the value of the effective radius of the disc, i.e. the radius containing half of the light of the disc. The gradient is steeper in the central parts of the disc and becomes flatter in the outer parts. N/O gradients are shown to be rather different from galaxy to galaxy and only a weak trend of N/O with O/H is found. The existing chemical evolution models for spiral galaxies are reviewed with special emphasis in the interpretation of numerical models having a large number of parameters. (author)

  19. Influence of radial magnetic field on the peristaltic flow of Williamson fluid in a curved complaint walls channel

    Directory of Open Access Journals (Sweden)

    Tasawar Hayat

    Full Text Available Peristaltic transport of Williamson fluid in a curved geometry is modeled. Problem formulation is completed by complaint walls of channel. Radial magnetic field in the analysis is taken into account. Resulting problem formulation is simplified using long wavelength and low Reynolds number approximations. Series solution is obtained for small Weissenberg number. Influences of different embedded parameters on the axial velocity and stream function are examined. As expected the velocity in curved channel is not symmetric. Axial velocity is noticed decreasing for Hartman number. Trapped bolus increases for Hartman and curvature parameters. Keywords: Williamson fluid, Curved channel, Radial magnetic field, Complaint walls

  20. Evaluation for the effects of a ring plate device to eliminate free surface gradients in liquid metal fast breeder reactor vessel using multi-dimensional thermohydraulics computer code

    International Nuclear Information System (INIS)

    Gao Ming Qing.

    1997-02-01

    There is a free surface at the upper plenum in a reactor vessel of LMFBR. The free surface has spatial gradient caused by the internal coolant flow. This is a disadvantageous factor to engineering from the view point of gas entrainment into coolant. To eliminate the free surface gradients, ring plates about 20 cm wide are fitted at about 1 meter under the free surface. They interfere fluid flow, and decrease the component velocity in vertical direction. To investigate the efficiency of the ring plates, analyses with the AQUA-VOF code were carried out. For contrast, three conditions were given: Case-1: Without ring plates. Case-2: Ring plates, fitted at 1.125 m under the free surface. Case-3: Ring plates, fitted at 1.5 m under the free surface. The results shown that the ring plates have a sufficiently high potential to eliminate the free surface gradients due to disperse the momentum along reactor vessel axis to radial direction. In the calculations with ring plate (Cases-2 and -3), the maximum free surface height differences and the maximum gradients of free surface were decreased to less than 15% and 64% compared with the case without ring plates, respectively. (author)

  1. Nerve conduction velocity

    Science.gov (United States)

    ... this page: //medlineplus.gov/ency/article/003927.htm Nerve conduction velocity To use the sharing features on this page, please enable JavaScript. Nerve conduction velocity (NCV) is a test to see ...

  2. Axial and Radial Gas Holdup in Bubble Column Reactor

    International Nuclear Information System (INIS)

    Wagh, Sameer M.; Ansari, Mohashin E Alan; Kene, Pragati T.

    2014-01-01

    Bubble column reactors are considered the reactor of choice for numerous applications including oxidation, hydrogenation, waste water treatment, and Fischer-Tropsch (FT) synthesis. They are widely used in a variety of industrial applications for carrying out gas-liquid and gas-liquid-solid reactions. In this paper, the computational fluid dynamics (CFD) model is used for predicting the gas holdup and its distribution along radial and axial direction are presented. Gas holdup increases linearly with increase in gas velocity. Gas bubbles tends to concentrate more towards the center of the column and follows a wavy path

  3. Ray transference of a system with radial gradi- ent index

    Directory of Open Access Journals (Sweden)

    W. F. Harris

    2012-12-01

    Full Text Available The ray transference is central to the understanding of the first-order optical character of an optical system including the visual optical system of the eye.  It can be calculated for dioptric and catadioptric systems from a knowledge of curvatures, tilts and spacing of surfaces in the system provided the material between successive surfaces has a uniform index of refraction.  However the index of the natural lens of the eye is not uniform but varies with position.  There is a need, therefore, for a method of calculating the transference of systems containing such gradient-index elements.  As a first step this paper shows that the transference of elements in which the index varies radially can be obtained directly from published formulae.  The transferences of radial-gradient systems are examined.  Expressions are derived for several properties including the power, the front- and back-surface powers and the locations of the cardinal points.  Equations are obtained for rays through such systems and for the locations of images of object points through them.  Numerical examples are presented in the appen-dix. (S Afr Optom 2012 71(2 57-63

  4. The velocity of sound

    International Nuclear Information System (INIS)

    Beyer, R.T.

    1985-01-01

    The paper reviews the work carried out on the velocity of sound in liquid alkali metals. The experimental methods to determine the velocity measurements are described. Tables are presented of reported data on the velocity of sound in lithium, sodium, potassium, rubidium and caesium. A formula is given for alkali metals, in which the sound velocity is a function of shear viscosity, atomic mass and atomic volume. (U.K.)

  5. A measurement of the local ion temperature gradient in the PLT tokamak

    International Nuclear Information System (INIS)

    Lovberg, J.A.; Strachan, J.D.; Princeton Univ., NJ

    1989-12-01

    Local ion temperature gradients were measured at two radial positions in the PLT tokamak by counting escaping d(d,p)t protons on orbits at closely spaced intervals. A single surface barrier detector was used to make each gradient measurement, eliminating relative calibration uncertainties. The ion thermal diffusivities inferred through ion energy balance with the measured temperature gradients are within a factor of two of Chang-Hinton neoclassical values for the 3 He-minority ICRH plasmas. 12 refs., 8 figs

  6. A contrastive study on the influences of radial and three-dimensional satellite gravity gradiometry on the accuracy of the Earth's gravitational field recovery

    International Nuclear Information System (INIS)

    Zheng Wei; Hsu Hou-Tse; Zhong Min; Yun Mei-Juan

    2012-01-01

    The accuracy of the Earth's gravitational field measured from the gravity field and steady-state ocean circulation explorer (GOCE), up to 250 degrees, influenced by the radial gravity gradient V zz and three-dimensional gravity gradient V ij from the satellite gravity gradiometry (SGG) are contrastively demonstrated based on the analytical error model and numerical simulation, respectively. Firstly, the new analytical error model of the cumulative geoid height, influenced by the radial gravity gradient V zz and three-dimensional gravity gradient V ij are established, respectively. In 250 degrees, the GOCE cumulative geoid height error measured by the radial gravity gradient V zz is about 2 ½ times higher than that measured by the three-dimensional gravity gradient V ij . Secondly, the Earth's gravitational field from GOCE completely up to 250 degrees is recovered using the radial gravity gradient V zz and three-dimensional gravity gradient V ij by numerical simulation, respectively. The study results show that when the measurement error of the gravity gradient is 3 × 10 −12 /s 2 , the cumulative geoid height errors using the radial gravity gradient V zz and three-dimensional gravity gradient V ij are 12.319 cm and 9.295 cm at 250 degrees, respectively. The accuracy of the cumulative geoid height using the three-dimensional gravity gradient V ij is improved by 30%–40% on average compared with that using the radial gravity gradient V zz in 250 degrees. Finally, by mutual verification of the analytical error model and numerical simulation, the orders of magnitude from the accuracies of the Earth's gravitational field recovery make no substantial differences based on the radial and three-dimensional gravity gradients, respectively. Therefore, it is feasible to develop in advance a radial cold-atom interferometric gradiometer with a measurement accuracy of 10 −13 /s 2 −10 −15 /s 2 for precisely producing the next-generation GOCE Follow-On Earth gravity field

  7. $L_{0}$ Gradient Projection.

    Science.gov (United States)

    Ono, Shunsuke

    2017-04-01

    Minimizing L 0 gradient, the number of the non-zero gradients of an image, together with a quadratic data-fidelity to an input image has been recognized as a powerful edge-preserving filtering method. However, the L 0 gradient minimization has an inherent difficulty: a user-given parameter controlling the degree of flatness does not have a physical meaning since the parameter just balances the relative importance of the L 0 gradient term to the quadratic data-fidelity term. As a result, the setting of the parameter is a troublesome work in the L 0 gradient minimization. To circumvent the difficulty, we propose a new edge-preserving filtering method with a novel use of the L 0 gradient. Our method is formulated as the minimization of the quadratic data-fidelity subject to the hard constraint that the L 0 gradient is less than a user-given parameter α . This strategy is much more intuitive than the L 0 gradient minimization because the parameter α has a clear meaning: the L 0 gradient value of the output image itself, so that one can directly impose a desired degree of flatness by α . We also provide an efficient algorithm based on the so-called alternating direction method of multipliers for computing an approximate solution of the nonconvex problem, where we decompose it into two subproblems and derive closed-form solutions to them. The advantages of our method are demonstrated through extensive experiments.

  8. Walker-type velocity oscillations of magnetic domain walls

    International Nuclear Information System (INIS)

    Vella-Coleiro, G.P.

    1976-01-01

    We report stroboscopic observations of the radial motion of a magnetic bubble domain wall in an epitaxial LuGdAl iron garnet film. At high drive fields, initial velocities up to 9500 cm/sec were measured, and the domain wall was observed to move backwards during the field pulse, in agreement with calculations based on the Walker model

  9. Designing optimal nanofocusing with a gradient hyperlens

    Directory of Open Access Journals (Sweden)

    Shen Lian

    2017-11-01

    Full Text Available We report the design of a high-throughput gradient hyperbolic lenslet built with real-life materials and capable of focusing a beam into a deep sub-wavelength spot of λ/23. This efficient design is achieved through high-order transformation optics and circular effective-medium theory (CEMT, which are used to engineer the radially varying anisotropic artificial material based on the thin alternating cylindrical metal and dielectric layers. The radial gradient of the effective anisotropic optical constants allows for matching the impedances at the input and output interfaces, drastically improving the throughput of the lenslet. However, it is the use of the zeroth-order CEMT that enables the practical realization of a gradient hyperlens with realistic materials. To illustrate the importance of using the CEMT versus the conventional planar effective-medium theory (PEMT for cylindrical anisotropic systems, such as our hyperlens, both the CEMT and PEMT are adopted to design gradient hyperlenses with the same materials and order of elemental layers. The CEMT- and PEMT-based designs show similar performance if the number of metal-dielectric binary layers is sufficiently large (9+ pairs and if the layers are sufficiently thin. However, for the manufacturable lenses with realistic numbers of layers (e.g. five pairs and thicknesses, the performance of the CEMT design continues to be practical, whereas the PEMT-based design stops working altogether. The accurate design of transformation optics-based layered cylindrical devices enabled by CEMT allow for a new class of robustly manufacturable nanophotonic systems, even with relatively thick layers of real-life materials.

  10. The Gaussian radial basis function method for plasma kinetic theory

    Energy Technology Data Exchange (ETDEWEB)

    Hirvijoki, E., E-mail: eero.hirvijoki@chalmers.se [Department of Applied Physics, Chalmers University of Technology, SE-41296 Gothenburg (Sweden); Candy, J.; Belli, E. [General Atomics, PO Box 85608, San Diego, CA 92186-5608 (United States); Embréus, O. [Department of Applied Physics, Chalmers University of Technology, SE-41296 Gothenburg (Sweden)

    2015-10-30

    Description of a magnetized plasma involves the Vlasov equation supplemented with the non-linear Fokker–Planck collision operator. For non-Maxwellian distributions, the collision operator, however, is difficult to compute. In this Letter, we introduce Gaussian Radial Basis Functions (RBFs) to discretize the velocity space of the entire kinetic system, and give the corresponding analytical expressions for the Vlasov and collision operator. Outlining the general theory, we also highlight the connection to plasma fluid theories, and give 2D and 3D numerical solutions of the non-linear Fokker–Planck equation. Applications are anticipated in both astrophysical and laboratory plasmas. - Highlights: • A radically new method to address the velocity space discretization of the non-linear kinetic equation of plasmas. • Elegant and physically intuitive, flexible and mesh-free. • Demonstration of numerical solution of both 2-D and 3-D non-linear Fokker–Planck relaxation problem.

  11. Revisiting Earth's radial seismic structure using a Bayesian neural network approach

    NARCIS (Netherlands)

    de Wit, R.W.L.

    2015-01-01

    The gross features of seismic observations can be explained by relatively simple spherically symmetric (1-D) models of wave velocities, density and attenuation, which describe the Earth's average(radial) structure. 1-D earth models are often used as a reference for studies on Earth's thermo-chemical

  12. HD 101065, the Most Peculiar Star: First Results from Precise Radial ...

    Indian Academy of Sciences (India)

    Abstract. In this paper we discuss the prospects for asteroseismology with spatial resolution and motivate studies of the most chemically peculiar. roAp star HD 101065. We present the first results from a high-precision radial velocity (RV) study of HD 101065 based on data spanning four nights that were acquired using the ...

  13. Experimental research on time-resolved evolution of cathode plasma expansion velocity in a long pulsed magnetically insulated coaxial diode

    Science.gov (United States)

    Zhu, Danni; Zhang, Jun; Zhong, Huihuang; Ge, Xingjun; Gao, Jingming

    2018-02-01

    Unlike planar diodes, separate research of the axial and radial plasma expansion velocities is difficult for magnetically insulated coaxial diodes. Time-resolved electrical diagnostic which is based on the voltage-ampere characteristics has been employed to study the temporal evolution of the axial and radial cathode plasma expansion velocities in a long pulsed magnetically insulated coaxial diode. Different from a planar diode with a "U" shaped profile of temporal velocity evolution, the temporal evolution trend of the axial expansion velocity is proved to be a "V" shaped profile. Apart from the suppression on the radial expansion velocity, the strong magnetic field is also conducive to slowing down the axial expansion velocity. Compared with the ordinary graphite cathode, the carbon velvet and graphite composite cathode showed superior characteristics as judged by the low plasma expansion velocity and long-term electrical stability as a promising result for applications where long-pulsed and reliable operation at high power is required.

  14. Bayesian inversion of surface-wave data for radial and azimuthal shear-wave anisotropy, with applications to central Mongolia and west-central Italy

    Science.gov (United States)

    Ravenna, Matteo; Lebedev, Sergei

    2018-04-01

    Seismic anisotropy provides important information on the deformation history of the Earth's interior. Rayleigh and Love surface-waves are sensitive to and can be used to determine both radial and azimuthal shear-wave anisotropies at depth, but parameter trade-offs give rise to substantial model non-uniqueness. Here, we explore the trade-offs between isotropic and anisotropic structure parameters and present a suite of methods for the inversion of surface-wave, phase-velocity curves for radial and azimuthal anisotropies. One Markov chain Monte Carlo (McMC) implementation inverts Rayleigh and Love dispersion curves for a radially anisotropic shear velocity profile of the crust and upper mantle. Another McMC implementation inverts Rayleigh phase velocities and their azimuthal anisotropy for profiles of vertically polarized shear velocity and its depth-dependent azimuthal anisotropy. The azimuthal anisotropy inversion is fully non-linear, with the forward problem solved numerically at different azimuths for every model realization, which ensures that any linearization biases are avoided. The computations are performed in parallel, in order to reduce the computing time. The often challenging issue of data noise estimation is addressed by means of a Hierarchical Bayesian approach, with the variance of the noise treated as an unknown during the radial anisotropy inversion. In addition to the McMC inversions, we also present faster, non-linear gradient-search inversions for the same anisotropic structure. The results of the two approaches are mutually consistent; the advantage of the McMC inversions is that they provide a measure of uncertainty of the models. Applying the method to broad-band data from the Baikal-central Mongolia region, we determine radial anisotropy from the crust down to the transition-zone depths. Robust negative anisotropy (Vsh < Vsv) in the asthenosphere, at 100-300 km depths, presents strong new evidence for a vertical component of asthenospheric

  15. Radial growth of two dominant montane conifer tree species in response to climate change in North-Central China.

    Science.gov (United States)

    Jiang, Yuan; Zhang, Wentao; Wang, Mingchang; Kang, Muyi; Dong, Manyu

    2014-01-01

    North-Central China is a region in which the air temperature has clearly increased for several decades. Picea meyeri and Larix principis-rupprechtii are the most dominant co-occurring tree species within the cold coniferous forest belt ranging vertically from 1800 m to 2800 m a.s.l. in this region. Based on a tree-ring analysis of 292 increment cores sampled from 146 trees at different elevations, this study aimed to examine if the radial growth of the two species in response to climate is similar, whether the responses are consistent along altitudinal gradients and which species might be favored in the future driven by the changing climate. The results indicated the following: (1) The two species grew in different rhythms at low and high elevation respectively; (2) Both species displayed inconsistent relationships between radial growth and climate data along altitudinal gradients. The correlation between radial growth and the monthly mean temperature in the spring or summer changed from negative at low elevation into positive at high elevation, whereas those between the radial growth and the total monthly precipitation displayed a change from positive into negative along the elevation gradient. These indicate the different influences of the horizontal climate and vertical mountainous climate on the radial growth of the two species; (3) The species-dependent different response to climate in radial growth appeared mainly in autumn of the previous year. The radial growth of L. principis-rupprechtii displayed negative responses both to temperature and to precipitation in the previous September, October or November, which was not observed in the radial growth of P. meyeri. (4) The radial growth of both species will tend to be increased at high elevation and limited at low elevation, and L. principis-rupprechtii might be more favored in the future, if the temperature keeps rising.

  16. Radial growth of two dominant montane conifer tree species in response to climate change in North-Central China.

    Directory of Open Access Journals (Sweden)

    Yuan Jiang

    Full Text Available North-Central China is a region in which the air temperature has clearly increased for several decades. Picea meyeri and Larix principis-rupprechtii are the most dominant co-occurring tree species within the cold coniferous forest belt ranging vertically from 1800 m to 2800 m a.s.l. in this region. Based on a tree-ring analysis of 292 increment cores sampled from 146 trees at different elevations, this study aimed to examine if the radial growth of the two species in response to climate is similar, whether the responses are consistent along altitudinal gradients and which species might be favored in the future driven by the changing climate. The results indicated the following: (1 The two species grew in different rhythms at low and high elevation respectively; (2 Both species displayed inconsistent relationships between radial growth and climate data along altitudinal gradients. The correlation between radial growth and the monthly mean temperature in the spring or summer changed from negative at low elevation into positive at high elevation, whereas those between the radial growth and the total monthly precipitation displayed a change from positive into negative along the elevation gradient. These indicate the different influences of the horizontal climate and vertical mountainous climate on the radial growth of the two species; (3 The species-dependent different response to climate in radial growth appeared mainly in autumn of the previous year. The radial growth of L. principis-rupprechtii displayed negative responses both to temperature and to precipitation in the previous September, October or November, which was not observed in the radial growth of P. meyeri. (4 The radial growth of both species will tend to be increased at high elevation and limited at low elevation, and L. principis-rupprechtii might be more favored in the future, if the temperature keeps rising.

  17. Radial smoothing and closed orbit

    International Nuclear Information System (INIS)

    Burnod, L.; Cornacchia, M.; Wilson, E.

    1983-11-01

    A complete simulation leading to a description of one of the error curves must involve four phases: (1) random drawing of the six set-up points within a normal population having a standard deviation of 1.3 mm; (b) random drawing of the six vertices of the curve in the sextant mode within a normal population having a standard deviation of 1.2 mm. These vertices are to be set with respect to the axis of the error lunes, while this axis has as its origins the positions defined by the preceding drawing; (c) mathematical definition of six parabolic curves and their junctions. These latter may be curves with very slight curvatures, or segments of a straight line passing through the set-up point and having lengths no longer than one LSS. Thus one gets a mean curve for the absolute errors; (d) plotting of the actually observed radial positions with respect to the mean curve (results of smoothing)

  18. Waves on radial film flows

    Science.gov (United States)

    Cholemari, Murali R.; Arakeri, Jaywant H.

    2005-08-01

    We study the stability of surface waves on the radial film flow created by a vertical cylindrical water jet striking a horizontal plate. In such flows, surface waves have been found to be unstable and can cause transition to turbulence. This surface-wave-induced transition is different from the well-known Tollmien-Schlichting wave-induced transition. The present study aims at understanding the instability and the transition process. We do a temporal stability analysis by assuming the flow to be locally two-dimensional but including spatial variations to first order in the basic flow. The waves are found to be dispersive, mostly unstable, and faster than the mean flow. Spatial variation is the major destabilizing factor. Experiments are done to test the results of the linear stability analysis and to document the wave breakup and transition. Comparison between theory and experiments is fairly good and indicates the adequacy of the model.

  19. Radial flow gas dynamic laser

    International Nuclear Information System (INIS)

    Damm, F.C.

    1975-01-01

    The unique gas dynamic laser provides outward radial supersonic flow from a toroidal shaped stacked array of a plurality of nozzles, through a diffuser having ring shaped and/or linear shaped vanes, and through a cavity which is cylindrical and concentric with the stacked array, with the resultant laser beam passing through the housing parallel to the central axis of the diffuser which is coincident with the axis of the gas dynamic laser. Therefore, greater beam extraction flexibility is attainable, because of fewer flow shock disturbances, as compared to the conventional unidirectional flow gas dynamic laser in which unidirectional supersonic flow sweeps through a rectangular cavity and is exhausted through a two-dimensional diffuser. (auth)

  20. Ulnar nerve entrapment complicating radial head excision

    Directory of Open Access Journals (Sweden)

    Kevin Parfait Bienvenu Bouhelo-Pam

    Full Text Available Introduction: Several mechanisms are involved in ischemia or mechanical compression of ulnar nerve at the elbow. Presentation of case: We hereby present the case of a road accident victim, who received a radial head excision for an isolated fracture of the radial head and complicated by onset of cubital tunnel syndrome. This outcome could be the consequence of an iatrogenic valgus of the elbow due to excision of the radial head. Hitherto the surgical treatment of choice it is gradually been abandoned due to development of radial head implant arthroplasty. However, this management option is still being performed in some rural centers with low resources. Discussion: The radial head plays an important role in the stability of the elbow and his iatrogenic deformity can be complicated by cubital tunnel syndrome. Conclusion: An ulnar nerve release was performed with favorable outcome. Keywords: Cubital tunnel syndrome, Peripheral nerve palsy, Radial head excision, Elbow valgus

  1. Inversion gradients for acoustic VTI wavefield tomography

    KAUST Repository

    Li, Vladimir; Wang, Hui; Tsvankin, Ilya; Dí az, Esteban; Alkhalifah, Tariq Ali

    2017-01-01

    Wavefield tomography can handle complex subsurface geology better than ray-based techniques and, ultimately, provide a higher resolution. Here, we implement forward and adjoint wavefield extrapolation for VTI (transversely isotropic with a vertical symmetry axis) media using a generalized pseudospectral operator based on a separable approximation for the P-wave dispersion relation. This operator is employed to derive the gradients of the differential semblance optimization (DSO) and modified image-power objective functions. We also obtain the gradient expressions for a data-domain objective function that can more easily incorporate borehole information necessary for stable VTI velocity analysis. These gradients are similar to the ones obtained with a space-time finite-difference (FD) scheme for a system of coupled wave equations but the pseudospectral method is not hampered by the imprint of the shear-wave artifact. Numerical examples also show the potential advantages of the modified image-power objective function in estimating the anellipticity parameter η.

  2. Inversion gradients for acoustic VTI wavefield tomography

    KAUST Repository

    Li, Vladimir

    2017-03-21

    Wavefield tomography can handle complex subsurface geology better than ray-based techniques and, ultimately, provide a higher resolution. Here, we implement forward and adjoint wavefield extrapolation for VTI (transversely isotropic with a vertical symmetry axis) media using a generalized pseudospectral operator based on a separable approximation for the P-wave dispersion relation. This operator is employed to derive the gradients of the differential semblance optimization (DSO) and modified image-power objective functions. We also obtain the gradient expressions for a data-domain objective function that can more easily incorporate borehole information necessary for stable VTI velocity analysis. These gradients are similar to the ones obtained with a space-time finite-difference (FD) scheme for a system of coupled wave equations but the pseudospectral method is not hampered by the imprint of the shear-wave artifact. Numerical examples also show the potential advantages of the modified image-power objective function in estimating the anellipticity parameter η.

  3. Ca II TRIPLET SPECTROSCOPY OF SMALL MAGELLANIC CLOUD RED GIANTS. I. ABUNDANCES AND VELOCITIES FOR A SAMPLE OF CLUSTERS

    International Nuclear Information System (INIS)

    Parisi, M. C.; Claria, J. J.; Grocholski, A. J.; Geisler, D.; Sarajedini, A.

    2009-01-01

    We have obtained near-infrared spectra covering the Ca II triplet lines for a large number of stars associated with 16 Small Magellanic Cloud (SMC) clusters using the VLT + FORS2. These data compose the largest available sample of SMC clusters with spectroscopically derived abundances and velocities. Our clusters span a wide range of ages and provide good areal coverage of the galaxy. Cluster members are selected using a combination of their positions relative to the cluster center as well as their location in the color-magnitude diagram, abundances, and radial velocities (RVs). We determine mean cluster velocities to typically 2.7 km s -1 and metallicities to 0.05 dex (random errors), from an average of 6.4 members per cluster. By combining our clusters with previously published results, we compile a sample of 25 clusters on a homogeneous metallicity scale and with relatively small metallicity errors, and thereby investigate the metallicity distribution, metallicity gradient, and age-metallicity relation (AMR) of the SMC cluster system. For all 25 clusters in our expanded sample, the mean metallicity [Fe/H] = -0.96 with σ = 0.19. The metallicity distribution may possibly be bimodal, with peaks at ∼-0.9 dex and -1.15 dex. Similar to the Large Magellanic Cloud (LMC), the SMC cluster system gives no indication of a radial metallicity gradient. However, intermediate age SMC clusters are both significantly more metal-poor and have a larger metallicity spread than their LMC counterparts. Our AMR shows evidence for three phases: a very early (>11 Gyr) phase in which the metallicity reached ∼-1.2 dex, a long intermediate phase from ∼10 to 3 Gyr in which the metallicity only slightly increased, and a final phase from 3 to 1 Gyr ago in which the rate of enrichment was substantially faster. We find good overall agreement with the model of Pagel and Tautvaisiene, which assumes a burst of star formation at 4 Gyr. Finally, we find that the mean RV of the cluster system

  4. Scaling laws for radial foil bearings

    Science.gov (United States)

    Honavara Prasad, Srikanth

    The effects of fluid pressurization, structural deformation of the compliant members and heat generation in foil bearings make the design and analysis of foil bearings very complicated. The complex fluid-structural-thermal interactions in foil bearings also make modeling efforts challenging because these phenomena are governed by highly non-linear partial differential equations. Consequently, comparison of various bearing designs require detailed calculation of the flow fields (velocities, pressures), bump deflections (structural compliance) and heat transfer phenomena (viscous dissipation in the fluid, frictional heating, temperature profile etc.,) resulting in extensive computational effort (time/hardware). To obviate rigorous computations and aid in feasibility assessments of foil bearings of various sizes, NASA developed the "rule of thumb" design guidelines for estimation of journal bearing load capacity. The guidelines are based on extensive experimental data. The goal of the current work is the development of scaling laws for radial foil bearings to establish an analytical "rule of thumb" for bearing clearance and bump stiffness. The use of scale invariant Reynolds equation and experimentally observed NASA "rule of thumb" yield scale factors which can be deduced from first principles. Power-law relationships between: a. Bearing clearance and bearing radius, and b. bump stiffness and bearing radius, are obtained. The clearance and bump stiffness values obtained from scaling laws are used as inputs for Orbit simulation to study various cases. As the clearance of the bearing reaches the dimensions of the material surface roughness, asperity contact breaks the fluid film which results in wear. Similarly, as the rotor diameter increases (requiring larger bearing diameters), the load capacity of the fluid film should increase to prevent dry rubbing. This imposes limits on the size of the rotor diameter and consequently bearing diameter. Therefore, this thesis aims

  5. Oxygen distribution in packed-bed membrane reactors for partial oxidations: effect of the radial porosity profiles on the product selectivity

    NARCIS (Netherlands)

    Kurten, U.; van Sint Annaland, M.; Kuipers, J.A.M.

    2004-01-01

    A two-dimensional, pseudohomogeneous reactor model was presented to describe the radial and axial concentration profiles in a packed-bed membrane reactor and the local velocity field while accounting for the influences due to the distributive membrane flow and the radial porosity profile. The effect

  6. Copernicus observations of Iota Herculis velocity variations

    Science.gov (United States)

    Rogerson, J. B., Jr.

    1984-01-01

    Observations of Iota Her at 109.61-109.67 nm obtained with the U1 channel of the Copernicus spectrophotometer at resolution 5 pm during 3.6 days in May, 1979, are reported. Radial-velocity variations are detected and analyzed as the sum of two sinusoids with frequencies 0.660 and 0.618 cycles/day and amplitudes 9.18 and 8.11 km/s, respectively. Weak evidence supporting the 13.9-h periodicity seen in line-profile variations by Smith (1978) is found.

  7. Analysis of the cross flow in a radial inflow turbine scroll

    Science.gov (United States)

    Hamed, A.; Abdallah, S.; Tabakoff, W.

    1977-01-01

    Equations of motion were derived, and a computational procedure is presented, for determining the nonviscous flow characteristics in the cross-sectional planes of a curved channel due to continuous mass discharge or mass addition. An analysis was applied to the radial inflow turbine scroll to study the effects of scroll geometry and the through flow velocity profile on the flow behavior. The computed flow velocity component in the scroll cross-sectional plane, together with the through flow velocity profile which can be determined in a separate analysis, provide a complete description of the three dimensional flow in the scroll.

  8. The Limit Deposit Velocity model, a new approach

    Directory of Open Access Journals (Sweden)

    Miedema Sape A.

    2015-12-01

    Full Text Available In slurry transport of settling slurries in Newtonian fluids, it is often stated that one should apply a line speed above a critical velocity, because blow this critical velocity there is the danger of plugging the line. There are many definitions and names for this critical velocity. It is referred to as the velocity where a bed starts sliding or the velocity above which there is no stationary bed or sliding bed. Others use the velocity where the hydraulic gradient is at a minimum, because of the minimum energy consumption. Most models from literature are one term one equation models, based on the idea that the critical velocity can be explained that way.

  9. Radial head button holing: a cause of irreducible anterior radial head dislocation

    Energy Technology Data Exchange (ETDEWEB)

    Shin, Su-Mi; Chai, Jee Won; You, Ja Yeon; Park, Jina [Seoul National University Seoul Metropolitan Government Boramae Medical Center, Department of Radiology, Seoul (Korea, Republic of); Bae, Kee Jeong [Seoul National University Seoul Metropolitan Government Boramae Medical Center, Department of Orthopedic Surgery, Seoul (Korea, Republic of)

    2016-10-15

    ''Buttonholing'' of the radial head through the anterior joint capsule is a known cause of irreducible anterior radial head dislocation associated with Monteggia injuries in pediatric patients. To the best of our knowledge, no report has described an injury consisting of buttonholing of the radial head through the annular ligament and a simultaneous radial head fracture in an adolescent. In the present case, the radiographic findings were a radial head fracture with anterior dislocation and lack of the anterior fat pad sign. Magnetic resonance imaging (MRI) clearly demonstrated anterior dislocation of the fractured radial head through the torn annular ligament. The anterior joint capsule and proximal portion of the annular ligament were interposed between the radial head and capitellum, preventing closed reduction of the radial head. Familiarity with this condition and imaging findings will aid clinicians to make a proper diagnosis and fast decision to perform an open reduction. (orig.)

  10. Radial Domany-Kinzel models with mutation and selection

    Science.gov (United States)

    Lavrentovich, Maxim O.; Korolev, Kirill S.; Nelson, David R.

    2013-01-01

    We study the effect of spatial structure, genetic drift, mutation, and selective pressure on the evolutionary dynamics in a simplified model of asexual organisms colonizing a new territory. Under an appropriate coarse-graining, the evolutionary dynamics is related to the directed percolation processes that arise in voter models, the Domany-Kinzel (DK) model, contact process, and so on. We explore the differences between linear (flat front) expansions and the much less familiar radial (curved front) range expansions. For the radial expansion, we develop a generalized, off-lattice DK model that minimizes otherwise persistent lattice artifacts. With both simulations and analytical techniques, we study the survival probability of advantageous mutants, the spatial correlations between domains of neutral strains, and the dynamics of populations with deleterious mutations. “Inflation” at the frontier leads to striking differences between radial and linear expansions. For a colony with initial radius R0 expanding at velocity v, significant genetic demixing, caused by local genetic drift, occurs only up to a finite time t*=R0/v, after which portions of the colony become causally disconnected due to the inflating perimeter of the expanding front. As a result, the effect of a selective advantage is amplified relative to genetic drift, increasing the survival probability of advantageous mutants. Inflation also modifies the underlying directed percolation transition, introducing novel scaling functions and modifications similar to a finite-size effect. Finally, we consider radial range expansions with deflating perimeters, as might arise from colonization initiated along the shores of an island.

  11. Ponderomotive force effects on temperature-gradient-driven instabilities

    International Nuclear Information System (INIS)

    Sundaram, A.K.; Hershkowitz, N.

    1992-01-01

    The modification of temperature-gradient-driven instabilities due to the presence of nonuniform radio-frequency fields near the ion cyclotron frequency is investigated in the linear regime. Employing the fluid theory, it is shown that the induced field line compression caused by ion cyclotron range of frequencies (ICRF) fields makes the net parallel compressibility positive, and thus provides a stabilizing influence on the ion-temperature-gradient-driven mode for an appropriately tailored profile of radio-frequency (rf) pressure. Concomitantly, the radial ponderomotive force generates an additional contribution via coupling between the perturbed fluid motion and the equilibrium ponderomotive force and this effect plays the role of dissipation to enhance or decrease the growth of temperature-gradient-driven modes depending upon the sign of rf pressure gradients. For decreased growth of temperature-gradient-driven instabilities, the plasma density gradients and rf pressure gradients must have opposite signs while enhancement in growth arises when both gradients have the same sign. Finally, the kinetic effects associated with these modes are briefly discussed

  12. Gradients estimation from random points with volumetric tensor in turbulence

    Science.gov (United States)

    Watanabe, Tomoaki; Nagata, Koji

    2017-12-01

    We present an estimation method of fully-resolved/coarse-grained gradients from randomly distributed points in turbulence. The method is based on a linear approximation of spatial gradients expressed with the volumetric tensor, which is a 3 × 3 matrix determined by a geometric distribution of the points. The coarse grained gradient can be considered as a low pass filtered gradient, whose cutoff is estimated with the eigenvalues of the volumetric tensor. The present method, the volumetric tensor approximation, is tested for velocity and passive scalar gradients in incompressible planar jet and mixing layer. Comparison with a finite difference approximation on a Cartesian grid shows that the volumetric tensor approximation computes the coarse grained gradients fairly well at a moderate computational cost under various conditions of spatial distributions of points. We also show that imposing the solenoidal condition improves the accuracy of the present method for solenoidal vectors, such as a velocity vector in incompressible flows, especially when the number of the points is not large. The volumetric tensor approximation with 4 points poorly estimates the gradient because of anisotropic distribution of the points. Increasing the number of points from 4 significantly improves the accuracy. Although the coarse grained gradient changes with the cutoff length, the volumetric tensor approximation yields the coarse grained gradient whose magnitude is close to the one obtained by the finite difference. We also show that the velocity gradient estimated with the present method well captures the turbulence characteristics such as local flow topology, amplification of enstrophy and strain, and energy transfer across scales.

  13. MULTI-COMPONENT ANALYSIS OF POSITION-VELOCITY CUBES OF THE HH 34 JET

    International Nuclear Information System (INIS)

    Rodríguez-González, A.; Esquivel, A.; Raga, A. C.; Cantó, J.; Curiel, S.; Riera, A.; Beck, T. L.

    2012-01-01

    We present an analysis of Hα spectra of the HH 34 jet with two-dimensional spectral resolution. We carry out multi-Gaussian fits to the spatially resolved line profiles and derive maps of the intensity, radial velocity, and velocity width of each of the components. We find that close to the outflow source we have three components: a high (negative) radial velocity component with a well-collimated, jet-like morphology; an intermediate velocity component with a broader morphology; and a positive radial velocity component with a non-collimated morphology and large linewidth. We suggest that this positive velocity component is associated with jet emission scattered in stationary dust present in the circumstellar environment. Farther away from the outflow source, we find only two components (a high, negative radial velocity component, which has a narrower spatial distribution than an intermediate velocity component). The fitting procedure was carried out with the new AGA-V1 code, which is available online and is described in detail in this paper.

  14. Acoustic and streaming velocity components in a resonant waveguide at high acoustic levels.

    Science.gov (United States)

    Daru, Virginie; Reyt, Ida; Bailliet, Hélène; Weisman, Catherine; Baltean-Carlès, Diana

    2017-01-01

    Rayleigh streaming is a steady flow generated by the interaction between an acoustic wave and a solid wall, generally assumed to be second order in a Mach number expansion. Acoustic streaming is well known in the case of a stationary plane wave at low amplitude: it has a half-wavelength spatial periodicity and the maximum axial streaming velocity is a quadratic function of the acoustic velocity amplitude at antinode. For higher acoustic levels, additional streaming cells have been observed. Results of laser Doppler velocimetry measurements are here compared to direct numerical simulations. The evolution of axial and radial velocity components for both acoustic and streaming velocities is studied from low to high acoustic amplitudes. Two streaming flow regimes are pointed out, the axial streaming dependency on acoustics going from quadratic to linear. The evolution of streaming flow is different for outer cells and for inner cells. Also, the hypothesis of radial streaming velocity being of second order in a Mach number expansion, is not valid at high amplitudes. The change of regime occurs when the radial streaming velocity amplitude becomes larger than the radial acoustic velocity amplitude, high levels being therefore characterized by nonlinear interaction of the different velocity components.

  15. Concepts of radial and angular kinetic energies

    DEFF Research Database (Denmark)

    Dahl, Jens Peder; Schleich, W.P.

    2002-01-01

    We consider a general central-field system in D dimensions and show that the division of the kinetic energy into radial and angular parts proceeds differently in the wave-function picture and the Weyl-Wigner phase-space picture, Thus, the radial and angular kinetic energies are different quantities...

  16. From Boltzmann equations to steady wall velocities

    International Nuclear Information System (INIS)

    Konstandin, Thomas; Rues, Ingo; Nardini, Germano; California Univ., Santa Barbara, CA

    2014-07-01

    By means of a relativistic microscopic approach we calculate the expansion velocity of bubbles generated during a first-order electroweak phase transition. In particular, we use the gradient expansion of the Kadanoff-Baym equations to set up the fluid system. This turns out to be equivalent to the one found in the semi-classical approach in the non-relativistic limit. Finally, by including hydrodynamic deflagration effects and solving the Higgs equations of motion in the fluid, we determine velocity and thickness of the bubble walls. Our findings are compared with phenomenological models of wall velocities. As illustrative examples, we apply these results to three theories providing first-order phase transitions with a particle content in the thermal plasma that resembles the Standard Model.

  17. Pulsar velocity observations: Correlations, interpretations, and discussion

    International Nuclear Information System (INIS)

    Helfand, D.J.; Tademaru, E.

    1977-01-01

    From an examination of the current sample of 12 pulsars with measured proper motions and the z-distribution of the much larger group of over 80 sources with measured period derivatives, we develop a self-consistent picture of pulsar evolution. The apparent tendency of pulsars to move parallel to the galactic plane is explained as the result of various selection effects. A method for calculating the unmeasurable radial velocity of a pulsar is presented; it is shown that the total space velocities thus obtained are consistent with the assumption of an extreme Population I origin for pulsars which subsequently move away from the plane with a large range of velocities. The time scale for pulsar magnetic field decay is derived from dynamical considerations. A strong correlation of the original pulsar field strength with the magnitude of pulsar velocity is discussed. This results in the division of pulsars into two classes: Class A sources characterized by low space velocities, a small scale height, and low values of P 0 P 0 ; and Class B sources with a large range of velocities (up to 1000 km s -1 ), a much greater scale height, and larger values of initial field strength. It is postulated that Class A sources originate in tight binaries where their impulse acceleration at birth is insufficient to remove them from the system, while the Class B sources arise from single stars or loosely bound binaries and are accelerated to high velocities by their asymmetric radiation force. The evolutionary picture which is developed is shown to be consistent with a number of constraints imposed by supernova rates, the relative frequency of massive binaries and Class A sources, theoretical field-decay times, and the overall pulsar galactic distribution

  18. Migration of inclusions in solids in stress gradients

    International Nuclear Information System (INIS)

    Olander, D.R.

    1980-01-01

    A theoretical method of assessing the influence of stress and temperature gradients on the motion of inclusions in solids is developed. In nonuniform stress fields, the stress distribution on the surface of the cavity must be calculated and transformed to a potential gradient for driving a surface atom flux. The bubble migration velocity is the first Legendre coefficient of the surface flux. Higher order components represent distortion. The stress gradient effect appears only in small-magnitude terms in the surface chemical potential, specifically in the stress effect on the solid atomic volume and in the elastic energy density. The migration velocities of spherical and faceted bubbles in solids are computed and the extent of distortion of a spherical bubble is estimated. The role of vacancy exchange with the bulk solid on the migration velocity is assessed. (author)

  19. Travelling gradient thermocouple calibration

    International Nuclear Information System (INIS)

    Broomfield, G.H.

    1975-01-01

    A short discussion of the origins of the thermocouple EMF is used to re-introduce the idea that the Peltier and Thompson effects are indistinguishable from one another. Thermocouples may be viewed as devices which generate an EMF at junctions or as integrators of EMF's developed in thermal gradients. The thermal gradient view is considered the more appropriate, because of its better accord with theory and behaviour, the correct approach to calibration, and investigation of service effects is immediately obvious. Inhomogeneities arise in thermocouples during manufacture and in service. The results of travelling gradient measurements are used to show that such effects are revealed with a resolution which depends on the length of the gradient although they may be masked during simple immersion calibration. Proposed tests on thermocouples irradiated in a nuclear reactor are discussed

  20. Quaternion Gradient and Hessian

    OpenAIRE

    Xu, Dongpo; Mandic, Danilo P.

    2014-01-01

    The optimization of real scalar functions of quaternion variables, such as the mean square error or array output power, underpins many practical applications. Solutions typically require the calculation of the gradient and Hessian. However, real functions of quaternion variables are essentially nonanalytic, which are prohibitive to the development of quaternion-valued learning systems. To address this issue, we propose new definitions of quaternion gradient and Hessian, based on the novel gen...

  1. Color Gradients Within Globular Clusters: Restricted Numerical Simulation

    Directory of Open Access Journals (Sweden)

    Young-Jong Sohn

    1997-06-01

    Full Text Available The results of a restricted numerical simulation for the color gradients within globular clusters have been presented. The standard luminosity function of M3 and Salpeter's initial mass functions were used to generate model clusters as a fundamental population. Color gradients with the sample clusters for both King and power law cusp models of surface brightness distributions are discussed in the case of using the standard luminosity function. The dependence of color gradients on several parameters for the simulations with Salpeter's initial mass functions, such as slope of initial mass functions, cluster ages, metallicities, concentration parameters of King model, and slopes of power law, are also discussed. No significant radial color gradients are shown to the sample clusters which are regenerated by a random number generation technique with various parameters in both of King and power law cusp models of surface brightness distributions. Dynamical mass segregation and stellar evolution of horizontal branch stars and blue stragglers should be included for the general case of model simulations to show the observed radial color gradients within globular clusters.

  2. Water velocity meter

    Science.gov (United States)

    Roberts, C. W.; Smith, D. L.

    1970-01-01

    Simple, inexpensive drag sphere velocity meter with a zero to 6 ft/sec range measures steady-state flow. When combined with appropriate data acquisition system, it is suited to applications where large numbers of simultaneous measurements are needed for current mapping or velocity profile determination.

  3. Estimation of vector velocity

    DEFF Research Database (Denmark)

    2000-01-01

    Using a pulsed ultrasound field, the two-dimensional velocity vector can be determined with the invention. The method uses a transversally modulated ultrasound field for probing the moving medium under investigation. A modified autocorrelation approach is used in the velocity estimation. The new...

  4. Current density and polarization curves for radial flow field patterns applied to PEMFCs (Proton Exchange Membrane Fuel Cells)

    International Nuclear Information System (INIS)

    Cano-Andrade, S.; Hernandez-Guerrero, A.; Spakovsky, M.R. von; Damian-Ascencio, C.E.; Rubio-Arana, J.C.

    2010-01-01

    A numerical solution of the current density and velocity fields of a 3-D PEM radial configuration fuel cell is presented. The energy, momentum and electrochemical equations are solved using a computational fluid dynamics (CFD) code based on a finite volume scheme. There are three cases of principal interest for this radial model: four channels, eight channels and twelve channels placed in a symmetrical path over the flow field plate. The figures for the current-voltage curves for the three models proposed are presented, and the main factors that affect the behavior of each of the curves are discussed. Velocity contours are presented for the three different models, showing how the fuel cell behavior is affected by the velocity variations in the radial configuration. All these results are presented for the case of high relative humidity. The favorable results obtained for this unconventional geometry seems to indicate that this geometry could replace the conventional commercial geometries currently in use.

  5. The causal relation between turbulent particle flux and density gradient

    Energy Technology Data Exchange (ETDEWEB)

    Milligen, B. Ph. van; Martín de Aguilera, A.; Hidalgo, C. [CIEMAT - Laboratorio Nacional de Fusión, Avda. Complutense 40, 28040 Madrid (Spain); Carreras, B. A. [BACV Solutions, 110 Mohawk Road, Oak Ridge, Tennessee 37830 (United States); García, L.; Nicolau, J. H. [Universidad Carlos III, 28911 Leganés, Madrid (Spain)

    2016-07-15

    A technique for detecting the causal relationship between fluctuating signals is used to investigate the relation between flux and gradient in fusion plasmas. Both a resistive pressure gradient driven turbulence model and experimental Langmuir probe data from the TJ-II stellarator are studied. It is found that the maximum influence occurs at a finite time lag (non-instantaneous response) and that quasi-periodicities exist. Furthermore, the model results show very long range radial influences, extending over most of the investigated regions, possibly related to coupling effects associated with plasma self-organization. These results clearly show that transport in fusion plasmas is not local and instantaneous, as is sometimes assumed.

  6. Computational Fluid Dynamics Simulations of Gas-Phase Radial Dispersion in Fixed Beds with Wall Effects

    Directory of Open Access Journals (Sweden)

    Anthony G. Dixon

    2017-10-01

    Full Text Available The effective medium approach to radial fixed bed dispersion models, in which radial dispersion of mass is superimposed on axial plug flow, is based on a constant effective dispersion coefficient, DT. For packed beds of a small tube-to-particle diameter ratio (N, the experimentally-observed decrease in this parameter near the tube wall is accounted for by a lumped resistance located at the tube wall, the wall mass transfer coefficient km. This work presents validated computational fluid dynamics (CFD simulations to obtain detailed radial velocity and concentration profiles for eight different computer-generated packed tubes of spheres in the range 5.04 ≤ N ≤ 9.3 and over a range of flow rates 87 ≤ Re ≤ 870 where Re is based on superficial velocity and the particle diameter dp. Initial runs with pure air gave axial velocity profiles vz(r averaged over the length of the packing. Then, simulations with the tube wall coated with methane yielded radial concentration profiles. A model with only DT could not describe the radial concentration profiles. The two-parameter model with DT and km agreed better with the bed-center concentration profiles, but not with the sharp decreases in concentration close to the tube wall. A three-parameter model based on classical two-layer mixing length theory, with a wall-function for the decrease in transverse radial convective transport in the near-wall region, showed greatly improved ability to reproduce the near-wall concentration profiles.

  7. MIGHT WE EVENTUALLY UNDERSTAND THE ORIGIN OF THE DARK MATTER VELOCITY ANISOTROPY?

    International Nuclear Information System (INIS)

    Hansen, Steen H.

    2009-01-01

    The density profile of simulated dark matter structures is fairly well-established, and several explanations for its characteristics have been put forward. In contrast, the radial variation of the velocity anisotropy has still not been explained. We suggest a very simple origin, based on the shapes of the velocity distribution functions, which are shown to differ between the radial and tangential directions. This allows us to derive a radial variation of the anisotropy profile which is in good agreement with both simulations and observations. One of the consequences of this suggestion is that the velocity anisotropy is entirely determined once the density profile is known. We demonstrate how this explains the origin of the γ-β relation, which is the connection between the slope of the density profile and the velocity anisotropy. These findings provide us with a powerful tool, which allows us to close the Jeans equations.

  8. Gradient Alloy for Optical Packaging

    Data.gov (United States)

    National Aeronautics and Space Administration — Advances in additive manufacturing, such as Laser Engineered Net Shaping (LENS), enables the fabrication of compositionally gradient microstructures, i.e. gradient...

  9. High-precision MoSi multilayer coatings for radial and 2D designs on curved optics

    Science.gov (United States)

    Kriese, Michael D.; Li, Yang; Platonov, Yuriy Y.

    2017-10-01

    The development of industrial infrastructure for EUV lithography requires a wide array of optics beyond the mask and the scanner optics, which include optics for critical instruments such as exposure testing and actinic inspection. This paper will detail recent results in the production of a variety of high-precision multilayer coatings achieved to support this development. It is critical that the optical designs factor in the capabilities of the achievable multilayer gradients and the associated achievable precision, including impact to surface distortion from the added figure error of the multilayer coating, which adds additional requirements of a specific shape to the period distribution. For example, two different coatings may achieve a ±0.2% variation in multilayer period, but have considerably different added figure error. Part I of the paper will focus on radially-symmetric spherical and aspherical optics. Typical azimuthal uniformity (variation at a fixed radius) achieved is less than ±0.005nm total variation, including measurement precision, on concave optics up to 200mm diameter. For highly curved convex optics (radius of curvature less than 50mm), precision is more challenging and the total variation increases to ±0.01nm total variation for optics 10-30mm in diameter. Total added figure error achieved has been as low as 0.05nm. Part II of the paper will focus on multilayer designs graded in two directions, rather than radially, in order to accommodate the increased complexity of elliptical, toroidal and hyperbolic surfaces. In most cases, the symmetry of the required multilayer gradient does not match the symmetry of the optical surface, and this interaction must be countered via the process design. Achieving such results requires additional flexibility in the design of the deposition equipment, and will be discussed with several examples in the paper, such as the use of variable velocity of an inline substrate carrier in conjunction with a shaped

  10. Transitionless Enhanced Confinement and the Role of Radial Electric Field Shear

    International Nuclear Information System (INIS)

    Coppi, B.; Ernst, D.R.; Bell, M.G.; Bell, R.E.; Budny, R.V.

    1999-01-01

    Evidence for the role of radial electric field shear in enhanced confinement regimes attained without sharp bifurcations or transitions is presented. Temperature scans at constant density, created in the reheat phase following deuterium pellet injection into supershot plasmas in the Tokamak Fusion Test Reactor [J.D. Strachan, et al., Phys. Rev. Lett. 58 (1987) 1004] are simulated using a first-principles transport model. The slow reheat of the ion temperature profile, during which the temperature nearly doubles, is not explained by relatively comprehensive models of transport due to Ion Temperature Gradient Driven Turbulence (ITGDT), which depends primarily on the (unchanging) electron density gradient. An extended model, including the suppression of toroidal ITGDT by self-consistent radial electric field shear, does reproduce the reheat phase

  11. Numerical study of ion thermal gradient driven modes

    International Nuclear Information System (INIS)

    Garbet, X.; Laurent, L.; Mourgues, F.; Samain, A.

    1987-01-01

    Anomalous ion thermal confinement has been observed in tokamaks (1). The ion temperature gradient driven modes could provide a possible explanation of this fact. The goal of this paper is to examine the stability of such modes by a linear, analytical and numerical study. The value of the threshold parameter and the radial profiles of the modes are computed. The effects of the particles vertical drift due to the field curvature are discussed

  12. Temperature Gradients on the Cell Wall in the Critical Viscosity Experiment

    Science.gov (United States)

    Berg, Robert F.; Moldover, Michael R.

    1993-01-01

    Because of the diverging susceptibility delta rho/delta Tau near the liquid-vapor critical point, temperature gradients must be kept small to maintain adequate sample homogeneity. In our Science Requirements Document we paid particular attention to radial density gradients caused by equilibration of the xenon sample. Axial density gradients were addressed through the requirement that the cell's copper wall have a gradient less than 22 microK/m. This report re-examines the cell wall's temperature distribution in more detail by estimating all known significant contributions to temperature differences on the cell's wall.

  13. Axial magnetic field produced by axially and radially magnetized permanent rings

    International Nuclear Information System (INIS)

    Peng, Q.L.; McMurry, S.M.; Coey, J.M.D.

    2004-01-01

    Axial magnetic fields produced by axially and radially magnetized permanent magnet rings were studied. First, the axial magnetic field produced by a current loop is introduced, from which the axial field generated by an infinitely thin solenoid and by an infinitely thin current disk can be derived. Then the axial fields produced by axially and by radially magnetized permanent magnet rings can be obtained. An analytic formula for the axial fields produced by two axially magnetized rings is given. A permanent magnet with a high axial gradient field is fabricated, the measured results agree with the theoretical calculation very well. As an example, the axial periodic field produced by an arrangement of alternating axially and radially magnetized rings has been discussed

  14. A parametric study of adverse pressure gradient turbulent boundary layers

    International Nuclear Information System (INIS)

    Monty, J.P.; Harun, Z.; Marusic, I.

    2011-01-01

    There are many open questions regarding the behaviour of turbulent boundary layers subjected to pressure gradients and this is confounded by the large parameter space that may affect these flows. While there have been many valuable investigations conducted within this parameter space, there are still insufficient data to attempt to reduce this parameter space. Here, we consider a parametric study of adverse pressure gradient turbulent boundary layers where we restrict our attention to the pressure gradient parameter, β, the Reynolds number and the acceleration parameter, K. The statistics analyzed are limited to the streamwise fluctuating velocity. The data show that the mean velocity profile in strong pressure gradient boundary layers does not conform to the classical logarithmic law. Moreover, there appears to be no measurable logarithmic region in these cases. It is also found that the large-scale motions scaling with outer variables are energised by the pressure gradient. These increasingly strong large-scale motions are found to be the dominant contributor to the increase in turbulence intensity (scaled with friction velocity) with increasing pressure gradient across the boundary layer.

  15. Gyrokinetic full f analysis of electric field dynamics and poloidal velocity in the FT2-tokamak configuration

    International Nuclear Information System (INIS)

    Leerink, S.; Heikkinen, J. A.; Janhunen, S. J.; Kiviniemi, T. P.; Nora, M.; Ogando, F.

    2008-01-01

    The ELMFIRE gyrokinetic simulation code has been used to perform full f simulations of the FT-2 tokamak. The dynamics of the radial electric field and the creation of poloidal velocity in the presence of turbulence are presented.

  16. Growth trends and climate responses of Norway spruce along elevational gradients in East-Central Europe

    Czech Academy of Sciences Publication Activity Database

    Ponočná, T.; Spyt, B.; Kaczka, R. J.; Büntgen, Ulf; Treml, V.

    2016-01-01

    Roč. 30, č. 5 (2016), s. 1633-1646 ISSN 0931-1890 R&D Projects: GA MŠk(CZ) EE2.3.20.0248 Institutional support: RVO:67179843 Keywords : abies l. karst. * tree-ring chronologies * basal area increment * radial growth * forest growth * altitudinal gradient * sudetes mountains * northern europe * tatra mountains * alps * climate change * mountain forests * picea abies * radial growth * rree rings * trend preservation Subject RIV: GK - Forestry Impact factor: 1.842, year: 2016

  17. A model for radial cesium transport in a fuel pellet

    International Nuclear Information System (INIS)

    Imoto, Shosuke

    1989-01-01

    In order to explain the radial redistribution of cesium in an irradiated pellet, a two-step release model is proposed. The first step involves the migration of cesium by atomic diffusion to some channels, such as grain boundaries and cracks, and the second step assumes a thermomigration down along the temperature gradient. Distribution profiles of cesium are obtained by numerical calculation with the present model assuming a constant and spatially uniform birth rate of cesium in the pellet. The result agrees well with the profile observed by micro-gamma scanning for the LWR fuel in the outer region of the pellet but diverges from it at the inner region. Discussion is made on the steady-state model hitherto generally utilized. (orig.)

  18. Effect of Phase Transformations on Seismic Velocities

    Science.gov (United States)

    Weidner, D. J.; Li, L.; Whitaker, M.; Triplett, R.

    2017-12-01

    The radial velocity structure of the Earth consists of smooth variations of velocities with depth punctuated by abrupt changes of velocity, which are typically due to multivariant phase transformations, where high - low pressure phases can coexist. In this mixed phase region, both the effective shear and bulk moduli will be significantly reduced by the dynamic interaction of the propagating wave and the phase transition if the period of the wave is long enough relative to the kinetic time so that some of the transition can take place. In this presentation, we will give examples from both laboratory studies of phases transitions of Earth minerals and the calculated velocity profile based on our models. We focus on understanding the time limiting factor of the phase transformation in order to extrapolate laboratory results to Earth observations. Both the olivine to ringwoodite transition and KLB-1 partial melting are explored. We find that when the transformation requires diffusion, the kinetics are often slowed down considerably and as a result the diffusivity of atoms become the limiting factor of characteristic time. Specifically Fe-Mg exchange rate in the olivine-ringwoodite phase transition becomes the limiting factor that seismic waves are likely to sample. On the other hand, partial melting is an extremely fast phase transformation at seismic wave periods. We present evidence that ultrasonic waves, with a period of a few tens of nanoseconds, are slowed by the reduction of the effective elastic moduli in this case.

  19. Measurement bias of fluid velocity in molecular simulations

    International Nuclear Information System (INIS)

    Tysanner, Martin W.; Garcia, Alejandro L.

    2004-01-01

    In molecular simulations of fluid flow, the measurement of mean fluid velocity is considered to be a straightforward computation, yet there is some ambiguity in its definition. We show that in systems far from equilibrium, such as those with large temperature or velocity gradients, two commonly used definitions give slightly different results. Specifically, a bias can arise when computing the mean fluid velocity by measuring the mean particle velocity in a cell and averaging this mean over samples. We show that this bias comes from the correlation of momentum and density fluctuations in non-equilibrium fluids, obtain an analytical expression for predicting it, and discuss what system characteristics (e.g., number of particles per cell, temperature gradients) reduce or magnify the error. The bias has a physical origin so although we demonstrate it by direct simulation Monte Carlo (DSMC) computations, the same effect will be observed with other particle-based simulation methods, such as molecular dynamics and lattice gases

  20. Vacuum laser acceleration using a radially polarized CO sub 2 laser beam

    CERN Document Server

    Liu, Y; He, P

    1999-01-01

    Utilizing the high-power, radially polarized CO sub 2 laser and high-quality electron beam at the Brookhaven Accelerator Test Facility, a vacuum laser acceleration scheme is proposed. In this scheme, optics configuration is simple, a small focused beam spot size can be easily maintained, and optical damage becomes less important. At least 0.5 GeV/m acceleration gradient is achievable by 1 TW laser power.

  1. Modified echo peak correction for radial acquisition regime (RADAR).

    Science.gov (United States)

    Takizawa, Masahiro; Ito, Taeko; Itagaki, Hiroyuki; Takahashi, Tetsuhiko; Shimizu, Kanichirou; Harada, Junta

    2009-01-01

    Because radial sampling imposes many limitations on magnetic resonance (MR) imaging hardware, such as on the accuracy of the gradient magnetic field or the homogeneity of B(0), some correction of the echo signal is usually needed before image reconstruction. In our previous study, we developed an echo-peak-shift correction (EPSC) algorithm not easily affected by hardware performance. However, some artifacts remained in lung imaging, where tissue is almost absent, or in cardiac imaging, which is affected by blood flow. In this study, we modified the EPSC algorithm to improve the image quality of the radial aquisition regime (RADAR) and expand its application sequences. We assumed the artifacts were mainly caused by errors in the phase map for EPSC and used a phantom on a 1.5-tesla (T) MR scanner to investigate whether to modify the EPSC algorithm. To evaluate the effectiveness of EPSC, we compared results from T(1)- and T(2)-weighted images of a volunteer's lung region using the current and modified EPSC. We then applied the modified EPSC to RADAR spin echo (SE) and RADAR balanced steady-state acquisition with rewound gradient echo (BASG) sequence. The modified EPSC reduced phase discontinuity in the reference data used for EPSC and improved visualization of blood vessels in the lungs. Motion and blood flow caused no visible artifacts in the resulting images in either RADAR SE or RADAR BASG sequence. Use of the modified EPSC eliminated artifacts caused by signal loss in the reference data for EPSC. In addition, the modified EPSC was applied to RADAR SE and RADAR BASG sequences.

  2. Modified echo peak correction for radial acquisition regime (RADAR)

    International Nuclear Information System (INIS)

    Takizawa, Masahiro; Ito, Taeko; Itagaki, Hiroyuki; Takahashi, Tetsuhiko; Shimizu, Kanichirou; Harada, Junta

    2009-01-01

    Because radial sampling imposes many limitations on magnetic resonance (MR) imaging hardware, such as on the accuracy of the gradient magnetic field or the homogeneity of B 0 , some correction of the echo signal is usually needed before image reconstruction. In our previous study, we developed an echo-peak-shift correction (EPSC) algorithm not easily affected by hardware performance. However, some artifacts remained in lung imaging, where tissue is almost absent, or in cardiac imaging, which is affected by blood flow. In this study, we modified the EPSC algorithm to improve the image quality of the radial acquisition regime (RADAR) and expand its application sequences. We assumed the artifacts were mainly caused by errors in the phase map for EPSC and used a phantom on a 1.5-tesla (T) MR scanner to investigate whether to modify the EPSC algorithm. To evaluate the effectiveness of EPSC, we compared results from T 1 -and T 2 -weighted images of a volunteer's lung region using the current and modified EPSC. We then applied the modified EPSC to RADAR spin echo (SE) and RADAR balanced steady-state acquisition with rewound gradient echo (BASG) sequence. The modified EPSC reduced phase discontinuity in the reference data used for EPSC and improved visualization of blood vessels in the lungs. Motion and blood flow caused no visible artifacts in the resulting images in either RADAR SE or RADAR BASG sequence. Use of the modified EPSC eliminated artifacts caused by signal loss in the reference data for EPSC. In addition, the modified EPSC was applied to RADAR SE and RADAR BASG sequences. (author)

  3. Radial electric fields for improved tokamak performance

    International Nuclear Information System (INIS)

    Downum, W.B.

    1981-01-01

    The influence of externally-imposed radial electric fields on the fusion energy output, energy multiplication, and alpha-particle ash build-up in a TFTR-sized, fusing tokamak plasma is explored. In an idealized tokamak plasma, an externally-imposed radial electric field leads to plasma rotation, but no charge current flows across the magnetic fields. However, a realistically-low neutral density profile generates a non-zero cross-field conductivity and the species dependence of this conductivity allows the electric field to selectively alter radial particle transport

  4. Radial pattern of nuclear decay processes

    International Nuclear Information System (INIS)

    Iskra, W.; Mueller, M.; Rotter, I.; Technische Univ. Dresden

    1994-05-01

    At high level density of nuclear states, a separation of different time scales is observed (trapping effect). We calculate the radial profile of partial widths in the framework of the continuum shell model for some 1 - resonances with 2p-2h nuclear structure in 16 O as a function of the coupling strength to the continuum. A correlation between the lifetime of a nuclear state and the radial profile of the corresponding decay process is observed. We conclude from our numerical results that the trapping effect creates structures in space and time characterized by a small radial extension and a short lifetime. (orig.)

  5. Radial profiles of temperature and viscosity in the Earth's mantle inferred from the geoid and lateral seismic structure

    NARCIS (Netherlands)

    Cadek, O.; Berg, A.P. van den

    1998-01-01

    In the framework of dynamical modelling of the geoid, we have estimated basic features of the radial profile of temperature in the mantle. The applied parameterization of the geotherm directly characterizes thermal boundary layers and values of the thermal gradient in the upper and lower mantle.

  6. Propagation of the Semidiurnal Internal Tide: Phase Velocity Versus Group Velocity

    Science.gov (United States)

    Zhao, Zhongxiang

    2017-12-01

    The superposition of two waves of slightly different wavelengths has long been used to illustrate the distinction between phase velocity and group velocity. The first-mode M2 and S2 internal tides exemplify such a two-wave model in the natural ocean. The M2 and S2 tidal frequencies are 1.932 and 2 cycles per day, respectively, and their superposition forms a spring-neap cycle in the semidiurnal band. The spring-neap cycle acts like a wave, with its frequency, wave number, and phase being the differences of the M2 and S2 internal tides. The spring-neap cycle and energy of the semidiurnal internal tide propagate at the group velocity. Long-range propagation of M2 and S2 internal tides in the North Pacific is observed by satellite altimetry. Along a 3,400 km beam spanning 24°-54°N, the M2 and S2 travel times are 10.9 and 11.2 days, respectively. For comparison, it takes the spring-neap cycle 21.1 days to travel over this distance. Spatial maps of the M2 phase velocity, the S2 phase velocity, and the group velocity are determined from phase gradients of the corresponding satellite observed internal tide fields. The observed phase and group velocities agree with theoretical values estimated using the World Ocean Atlas 2013 annual-mean ocean stratification.

  7. High Gradient Accelerator Research

    International Nuclear Information System (INIS)

    Temkin, Richard

    2016-01-01

    The goal of the MIT program of research on high gradient acceleration is the development of advanced acceleration concepts that lead to a practical and affordable next generation linear collider at the TeV energy level. Other applications, which are more near-term, include accelerators for materials processing; medicine; defense; mining; security; and inspection. The specific goals of the MIT program are: • Pioneering theoretical research on advanced structures for high gradient acceleration, including photonic structures and metamaterial structures; evaluation of the wakefields in these advanced structures • Experimental research to demonstrate the properties of advanced structures both in low-power microwave cold test and high-power, high-gradient test at megawatt power levels • Experimental research on microwave breakdown at high gradient including studies of breakdown phenomena induced by RF electric fields and RF magnetic fields; development of new diagnostics of the breakdown process • Theoretical research on the physics and engineering features of RF vacuum breakdown • Maintaining and improving the Haimson / MIT 17 GHz accelerator, the highest frequency operational accelerator in the world, a unique facility for accelerator research • Providing the Haimson / MIT 17 GHz accelerator facility as a facility for outside users • Active participation in the US DOE program of High Gradient Collaboration, including joint work with SLAC and with Los Alamos National Laboratory; participation of MIT students in research at the national laboratories • Training the next generation of Ph. D. students in the field of accelerator physics.

  8. Evolution of a Planar Wake in Adverse Pressure Gradient

    Science.gov (United States)

    Driver, David M.; Mateer, George G.

    2016-01-01

    In the interest of improving the predictability of high-lift systems at maximum lift conditions, a series of fundamental experiments were conducted to study the effects of adverse pressure gradient on a wake flow. Mean and fluctuating velocities were measured with a two-component laser-Doppler velocimeter. Data were obtained for several cases of adverse pressure gradient, producing flows ranging from no reversed flow to massively reversed flow. While the turbulent Reynolds stresses increase with increasing size of the reversed flow region, the gradient of Reynolds stress does not. Computations using various turbulence models were unable to reproduce the reversed flow.

  9. Velocity Feedback Experiments

    Directory of Open Access Journals (Sweden)

    Chiu Choi

    2017-02-01

    Full Text Available Transient response such as ringing in a control system can be reduced or removed by velocity feedback. It is a useful control technique that should be covered in the relevant engineering laboratory courses. We developed velocity feedback experiments using two different low cost technologies, viz., operational amplifiers and microcontrollers. These experiments can be easily integrated into laboratory courses on feedback control systems or microcontroller applications. The intent of developing these experiments was to illustrate the ringing problem and to offer effective, low cost solutions for removing such problem. In this paper the pedagogical approach for these velocity feedback experiments was described. The advantages and disadvantages of the two different implementation of velocity feedback were discussed also.

  10. The critical ionization velocity

    International Nuclear Information System (INIS)

    Raadu, M.A.

    1980-06-01

    The critical ionization velocity effect was first proposed in the context of space plasmas. This effect occurs for a neutral gas moving through a magnetized plasma and leads to rapid ionization and braking of the relative motion when a marginal velocity, 'the critical velocity', is exceeded. Laboratory experiments have clearly established the significance of the critical velocity and have provided evidence for an underlying mechanism which relies on the combined action of electron impact ionization and a collective plasma interaction heating electrons. There is experimental support for such a mechanism based on the heating of electrons by the modified two-stream instability as part of a feedback process. Several applications to space plasmas have been proposed and the possibility of space experiments has been discussed. (author)

  11. High Velocity Gas Gun

    Science.gov (United States)

    1988-01-01

    A video tape related to orbital debris research is presented. The video tape covers the process of loading a High Velocity Gas Gun and firing it into a mounted metal plate. The process is then repeated in slow motion.

  12. Stability of boundary layer flow based on energy gradient theory

    Science.gov (United States)

    Dou, Hua-Shu; Xu, Wenqian; Khoo, Boo Cheong

    2018-05-01

    The flow of the laminar boundary layer on a flat plate is studied with the simulation of Navier-Stokes equations. The mechanisms of flow instability at external edge of the boundary layer and near the wall are analyzed using the energy gradient theory. The simulation results show that there is an overshoot on the velocity profile at the external edge of the boundary layer. At this overshoot, the energy gradient function is very large which results in instability according to the energy gradient theory. It is found that the transverse gradient of the total mechanical energy is responsible for the instability at the external edge of the boundary layer, which induces the entrainment of external flow into the boundary layer. Within the boundary layer, there is a maximum of the energy gradient function near the wall, which leads to intensive flow instability near the wall and contributes to the generation of turbulence.

  13. Is the temperature gradient or the derivative of the density gradient responsible for drift solitons?

    International Nuclear Information System (INIS)

    Salat, A.

    1990-01-01

    In conventional drift wave theory the density gradient κ n =d lnn/dχ determines the linear phase velocity, and the (electron) temperature gradient κ T =d lnT/dχ gives rise to a nonlinear term which leads to the existence of soliton-type solutions and solitary waves. LAKHIN, MIKHAILOVSKI and ONISHCHENKO, Phys. Lett. A 119, 348 (1987) and Plasma Phys. and Contr. Fus. 30, 457 (1988), recently claimed that it is not κ T but essentially the derivative of the density gradient, dκ n /dχ, that is relevant. This claim is refuted by means of an expansion scheme in ε=eΦ/T≤1, where Φ is the drift wave potential. (orig.)

  14. Radial pseudoaneurysm following diagnostic coronary angiography

    Directory of Open Access Journals (Sweden)

    Shankar Laudari

    2015-06-01

    Full Text Available The radial artery access has gained popularity as a method of diagnostic coronary catheterization compared to femoral artery puncture in terms of vascular complications and early ambulation. However, very rare complication like radial artery pseudoaneurysm may occur following cardiac catheterization which may give rise to serious consequences. Here, we report a patient with radial pseudoaneurysm following diagnostic coronary angiography. Adequate and correct methodology of compression of radial artery following puncture for maintaining hemostasis is the key to prevention.DOI: http://dx.doi.org/10.3126/jcmsn.v10i3.12776 Journal of College of Medical Sciences-Nepal, 2014, Vol-10, No-3, 48-50

  15. Uniform gradient expansions

    CERN Document Server

    Giovannini, Massimo

    2015-01-01

    Cosmological singularities are often discussed by means of a gradient expansion that can also describe, during a quasi-de Sitter phase, the progressive suppression of curvature inhomogeneities. While the inflationary event horizon is being formed the two mentioned regimes coexist and a uniform expansion can be conceived and applied to the evolution of spatial gradients across the protoinflationary boundary. It is argued that conventional arguments addressing the preinflationary initial conditions are necessary but generally not sufficient to guarantee a homogeneous onset of the conventional inflationary stage.

  16. High gradient superconducting quadrupoles

    International Nuclear Information System (INIS)

    Lundy, R.A.; Brown, B.C.; Carson, J.A.; Fisk, H.E.; Hanft, R.H.; Mantsch, P.M.; McInturff, A.D.; Remsbottom, R.H.

    1987-07-01

    Prototype superconducting quadrupoles with a 5 cm aperture and gradient of 16 kG/cm have been built and tested as candidate magnets for the final focus at SLC. The magnets are made from NbTi Tevatron style cable with 10 inner and 14 outer turns per quadrant. Quench performance and multipole data are presented. Design and data for a low current, high gradient quadrupole, similar in cross section but wound with a cable consisting of five insulated conductors are also discussed

  17. Radial transport with perturbed magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Hazeltine, R. D. [Institute for Fusion Studies, University of Texas at Austin, Austin, Texas 78712 (United States)

    2015-05-15

    It is pointed out that the viscosity coefficient describing radial transport of toroidal angular momentum is proportional to the second power of the gyro-radius—like the corresponding coefficients for particle and heat transport—regardless of any geometrical symmetry. The observation is widely appreciated, but worth emphasizing because some literature gives the misleading impression that asymmetry can allow radial moment transport in first-order.

  18. Radial transport with perturbed magnetic field

    International Nuclear Information System (INIS)

    Hazeltine, R. D.

    2015-01-01

    It is pointed out that the viscosity coefficient describing radial transport of toroidal angular momentum is proportional to the second power of the gyro-radius—like the corresponding coefficients for particle and heat transport—regardless of any geometrical symmetry. The observation is widely appreciated, but worth emphasizing because some literature gives the misleading impression that asymmetry can allow radial moment transport in first-order

  19. Thermal-gradient migration of brine inclusions in salt crystals

    International Nuclear Information System (INIS)

    Yagnik, S.K.

    1982-09-01

    It has been proposed that high-level nuclear waste be disposed in a geologic repository. Natural-salt deposits, which are being considered for this purpose, contain a small volume fraction of water in the form of brine inclusions distributed throughout the salt. Radioactive-decay heating of the nuclear wastes will impose a temperature gradient on the surrounding salt which mobilizes the brine inclusions. Inclusions filled completely with brine migrate up the temperature gradient and eventually accumulate brine near the buried waste forms. The brine may slowly corrode or degrade the waste forms which is undesirable. In this work, thermal gradient migration of both all-liquid and gas-liquid inclusions was experimentally studied in synthetic single crystals of NaCl and KCl using a hot-stage attachment to an optical microscope which was capable of imposing temperature gradients and axial compressive loads on the crystals. The migration velocities of the inclusions were found to be dependent on temperature, temperature gradient, and inclusion shape and size. The velocities were also dictated by the interfacial mass transfer resistance at brine/solid interface. This interfacial resistance depends on the dislocation density in the crystal, which in turn, depends on the axial compressive loading of the crystal. At low axial loads, the dependence between the velocity and temperature gradient is non-linear.At high axial loads, however, the interfacial resistance is reduced and the migration velocity depends linearly on the temperature gradient. All-liquid inclusions filled with mixed brines were also studied. For gas-liquid inclusions, three different gas phases (helium, air and argon) were compared. Migration studies were also conducted on single crystallites of natural salt as well as in polycrystalline natural salt samples. The behavior of the inclusions at large angle grain boundaries was observed. 35 figures, 3 tables

  20. Thermal gradient migration of brine inclusions in salt crystals

    International Nuclear Information System (INIS)

    Yagnik, S.K.

    1982-01-01

    Natural salt deposits, which are being considered for high-level nuclear wastes repositories, contain a small volume fraction of water in the form of brine inclusions distributed throughout the salt. Radioactive decay heating of the nuclear wastes will impose a temperature gradient on the surrounding salt which mobilizes the brine inclusions. Inclusions filled completely with brine (the all-liquid inclusions) migrate up the temperature gradient and eventually accumulate brine near the buried waste forms. The brine may slowly corrode or degrade the waste forms which is undesirable. In the present work, thermal gradient migration of both all-liquid and gas-liquid inclusions was experimentally studied in synthetic single crystals of NaCl and KCl using a hot-stage attachment to an optical microscope which was capable of imposing temperature gradients and axial compressive loads on the crystals. The migration velocities of the inclusions were found to be dependent on temperature, temperature gradient, and inclusion shape and size. The velocities were also dictated by the interfacial mass transfer resistance at brine/solid interface. This interfacial resistance depends on the dislocation density in the crystal, which in turn, depends on the axial compressive loading of the crystal. At low axial loads, the dependence between the velocity and temperature gradient is nonlinear. At high axial loads, however, the interfacial resistance is reduced and the migration velocity depends linearly on the temperature gradient. All-liquid inclusions filled with mixed brines were also studied. For gas-liquid inclusions, three different gas phases (helium, air and argon) were compared. Migration studies were also conducted on single crystallites of natural salt as well as in polycrystalline natural salt samples. The behavior of the inclusions at large angle grain boudaries was observed

  1. Structure, Kinematics and Origin of Radial Faults: 3D Seismic Observations from the Santos Basin, offshore Brazil

    Science.gov (United States)

    Coleman, Alexander; Jackson, Christopher A.-L.

    2017-04-01

    Salt stock growth is typically accompanied by the development of geometrically and kinematically complex fault networks in the surrounding country rock. The most common networks comprise radial faults; these are characterised by low displacement (stock into flanking strata. Radial faults are commonly observed in an arched, unpierced roof developed above a rising salt stock; in these cases, the faults are typically well-imaged seismically and likely form due to outer-arc extension during overburden stretching. Radial faults are also found at deeper structural levels, in strata flanking the diapir stem; in these cases, they are typically less well-imaged, thus their structure, kinematics and origin are less well understood. Furthermore, understanding the growth of radial faults may provide insights into hydrocarbon reservoir compartmentalisation and the evolution of neighbouring salt stocks. Here, we use high-quality 3D seismic reflection data from the Santos Basin, offshore Brazil to determine the structure and kinematics, and infer the likely origin of exceptionally well-imaged radial faults overlying and flanking a mature salt stock. Furthermore, we compare the geometric (e.g. throw, geometry, spacing, distribution etc.) and kinematic (e.g. timing of formation and duration of activity) characteristics of radial faults at both structural levels, allowing us to infer their temporal relationship and likely origins. We show that radial faults regardless of their structural level typically have aspect ratios of c. 1.8 - 2, are laterally-restricted in the vicinity of the salt, and have lengths of indices of c. 1, with low throw gradients of 0.05 - 0.1 at the upper tip indicate that radial faults were likely blind. Throws range from 5 - 80 ms, with throw-maxima within 1 - 2 radii of the salt diapir. However, we note that the position of the throw maxima is not at the same level for all radial faults. We propose that radial faults nucleate and initially grow as blind

  2. Stability of radial and non-radial pulsation modes of massive ZAMS models

    International Nuclear Information System (INIS)

    Odell, A.P.; Pausenwein, A.; Weiss, W.W.; Hajek, A.

    1987-01-01

    The authors have computed non-adiabatic eigenvalues for radial and non-radial pulsation modes of star models between 80 and 120 M solar with composition of chi=0.70 and Z=0.02. The radial fundamental mode is unstable in models with mass greater than 95 M solar , but the first overtone mode is always stable. The non-radial modes are all stable for all models, but the iota=2 f-mode is the closest to being driven. The non-radial modes are progressively more stable with higher iota and with higher n (for both rho- and g-modes). Thus, their results indicate that radial pulsation limits the upper mass of a star

  3. Evaluation of the friction coefficient, the radial stress, and the damage work during needle insertions into agarose gels.

    Science.gov (United States)

    Urrea, Fabián A; Casanova, Fernando; Orozco, Gustavo A; García, José J

    2016-03-01

    Agarose hydrogels have been extensively used as a phantom material to mimic the mechanical behavior of soft biological tissues, e.g. in studies aimed to analyze needle insertions into the organs producing tissue damage. To better predict the radial stress and damage during needle insertions, this study was aimed to determine the friction coefficient between the material of commercial catheters and hydrogels. The friction coefficient, the tissue damage and the radial stress were evaluated at 0.2, 1.8, and 10mm/s velocities for 28, 30, and 32 gauge needles of outer diameters equal to 0.36, 0.31, and 0.23mm, respectively. Force measurements during needle insertions and retractions on agarose gel samples were used to analyze damage and radial stress. The static friction coefficient (0.295±0.056) was significantly higher than the dynamic (0.255±0.086). The static and dynamic friction coefficients were significantly smaller for the 0.2mm/s velocity compared to those for the other two velocities, and there was no significant difference between the friction coefficients for 1.8 and 10mm/s. Radial stress averages were 131.2±54.1, 248.3±64.2, and 804.9±164.3Pa for the insertion velocity of 0.2, 1.8, and 10mm/s, respectively. The radial stress presented a tendency to increase at higher insertion velocities and needle size, which is consistent with other studies. However, the damage work did not show to be a good predictor of tissue damage, which appears to be due to simplifications in the analytical model. Differently to other approaches, the method proposed here based on radial stress may be extended in future studies to quantity tissue damage in vivo along the entire needle track. Copyright © 2015 Elsevier Ltd. All rights reserved.

  4. 21 CFR 866.4800 - Radial immunodiffusion plate.

    Science.gov (United States)

    2010-04-01

    ...) MEDICAL DEVICES IMMUNOLOGY AND MICROBIOLOGY DEVICES Immunology Laboratory Equipment and Reagents § 866.4800 Radial immunodiffusion plate. (a) Identification. A radial immunodiffusion plate for clinical use...

  5. Gradient computation for VTI acoustic wavefield tomography

    KAUST Repository

    Li, Vladimir

    2016-09-06

    Wavefield tomography can handle complex subsurface geology better than ray-based techniques and, ultimately, provide a higher resolution. Here, we implement forward and adjoint wavefield extrapolation for VTI (transversely isotropic with a vertical symmetry axis) media using a pseudospectral operator that employes a separable approximation of the P-wave dispersion relation. This operator is employed to derive the gradients of the differential semblance optimization (DSO) and modified stack-power objective functions. We also obtain the gradient expressions for the data-domain objective function, which can incorporate borehole information necessary for stable VTI velocity analysis. These gradients are compared to the ones obtained with a space-time finite-difference (FD) scheme for a system of coupled wave equations. Whereas the kernels computed with the two wave-equation operators are similar, the pseudospectral method is not hampered by the imprint of the shear-wave artifact. Numerical examples also show that the modified stack-power objective function produces cleaner gradients than the more conventional DSO operator.

  6. Ion confinement and transport in a toroidal plasma with externally imposed radial electric fields

    Science.gov (United States)

    Roth, J. R.; Krawczonek, W. M.; Powers, E. J.; Kim, Y. C.; Hong, H. Y.

    1979-01-01

    Strong electric fields were imposed along the minor radius of the toroidal plasma by biasing it with electrodes maintained at kilovolt potentials. Coherent, low-frequency disturbances characteristic of various magnetohydrodynamic instabilities were absent in the high-density, well-confined regime. High, direct-current radial electric fields with magnitudes up to 135 volts per centimeter penetrated inward to at least one-half the plasma radius. When the electric field pointed radially toward, the ion transport was inward against a strong local density gradient; and the plasma density and confinement time were significantly enhanced. The radial transport along the electric field appeared to be consistent with fluctuation-induced transport. With negative electrode polarity the particle confinement was consistent with a balance of two processes: a radial infusion of ions, in those sectors of the plasma not containing electrodes, that resulted from the radially inward fields; and ion losses to the electrodes, each of the which acted as a sink and drew ions out of the plasma. A simple model of particle confinement was proposed in which the particle confinement time is proportional to the plasma volume. The scaling predicted by this model was consistent with experimental measurements.

  7. Structure of the radial electric field and toroidal/poloidal flow in high temperature toroidal plasma

    International Nuclear Information System (INIS)

    Ida, Katsumi

    2001-01-01

    The structure of the radial electric field and toroidal/poloidal flow is discussed for the high temperature plasma in toroidal systems, tokamak and Heliotron type magnetic configurations. The spontaneous toroidal and poloidal flows are observed in the plasma with improved confinement. The radial electric field is mainly determined by the poloidal flow, because the contribution of toroidal flow to the radial electric field is small. The jump of radial electric field and poloidal flow are commonly observed near the plasma edge in the so-called high confinement mode (H-mode) plasmas in tokamaks and electron root plasma in stellarators including Heliotrons. In general the toroidal flow is driven by the momentum input from neutral beam injected toroidally. There is toroidal flow not driven by neutral beam in the plasma and it will be more significant in the plasma with large electric field. The direction of these spontaneous toroidal flows depends on the symmetry of magnetic field. The spontaneous toroidal flow driven by the ion temperature gradient is in the direction to increase the negative radial electric field in tokamak. The direction of spontaneous toroidal flow in Heliotron plasmas is opposite to that in tokamak plasma because of the helicity of symmetry of the magnetic field configuration. (author)

  8. A physical process of the radial acceleration of disc galaxies

    Science.gov (United States)

    Wilhelm, Klaus; Dwivedi, Bhola N.

    2018-03-01

    An impact model of gravity designed to emulate Newton's law of gravitation is applied to the radial acceleration of disc galaxies. Based on this model (Wilhelm et al. 2013), the rotation velocity curves can be understood without the need to postulate any dark matter contribution. The increased acceleration in the plane of the disc is a consequence of multiple interactions of gravitons (called `quadrupoles' in the original paper) and the subsequent propagation in this plane and not in three-dimensional space. The concept provides a physical process that relates the fit parameter of the acceleration scale defined by McGaugh et al. (2016) to the mean free path length of gravitons in the discs of galaxies. It may also explain the gravitational interaction at low acceleration levels in MOdification of the Newtonian Dynamics (MOND, Milgrom 1983, 1994, 2015, 2016). Three examples are discussed in some detail: the spiral galaxies NGC 7814, NGC 6503 and M 33.

  9. Feasibility tests of a high resolution sampling radial drift chamber

    International Nuclear Information System (INIS)

    Huth, J.

    1985-01-01

    The design concept and results of feasibility tests for a vertex detector intended for use in the TPC-PEP4/9 experiment are presented. The detector is based on a slow radial drift in dimethyl ether. High resolution localization of the avalanches at the sense wire is accomplished with nearby pickup wires and the utilization of waveform sampling electronics. The avalanche angular coordinate measurements, combined with knowledge of the electric field distribution and drift velocity permit reconstruction of the trajectory using essentially all track information. Measurements with a test chamber constructed to study characteristics of avalanche localization indicate that the recoverable track information in one centimeter of dimethyl ether at 1.5 atm is equivalent to 30 measurements of 40 μm accuracy. (orig.)

  10. Manipulating the Gradient

    Science.gov (United States)

    Gaze, Eric C.

    2005-01-01

    We introduce a cooperative learning, group lab for a Calculus III course to facilitate comprehension of the gradient vector and directional derivative concepts. The lab is a hands-on experience allowing students to manipulate a tangent plane and empirically measure the effect of partial derivatives on the direction of optimal ascent. (Contains 7…

  11. Effects of the radial electric field in a quasisymmetric stellarator

    International Nuclear Information System (INIS)

    Landreman, Matt; Catto, Peter J

    2011-01-01

    Recent calculations have shown that a radial electric field can significantly alter the neoclassical ion heat flux, ion flow, bootstrap current and residual zonal flow in a tokamak, even when the E x B drift is much smaller than the ion thermal speed. Here we show the novel analytical methods used in these calculations can be adapted to a quasisymmetric stellarator. The methods are based on using the conserved helical momentum ψ * instead of the poloidal or toroidal flux as a radial coordinate in the kinetic equation. The banana-regime calculations also employ a model collision operator that keeps only the velocity-space derivatives normal to the trapped-passing boundary, even as this boundary is shifted and deformed by the E x B drift. We prove the isomorphism between quasisymmetric stellarators and tokamaks extends to the finite-E x B generalizations of both banana-regime and plateau-regime neoclassical theory and the residual zonal flow. The plateau-regime results may be relevant to the HSX stellarator, and both the plateau- and banana-regime results can be used to validate stellarator transport codes.

  12. New perspectives in hydrodynamic radial polishing techniques for optical surfaces

    Science.gov (United States)

    Ruiz, Elfego; Sohn, Erika; Luna, Esteban; Salas, Luis; Cordero, Alberto; González, Jorge; Núñez, Manuel; Salinas, Javier; Cruz-González, Irene; Valdés, Jorge; Cabrera, Victor; Martínez, Benjamín

    2004-09-01

    In order to overcome classic polishing techniques, a novel hydrodynamic radial polishing tool (HyDRa) is presented; it is useful for the corrective lapping and fine polishing of diverse materials by means of a low-cost abrasive flux and a hydrostatic suspension system that avoids contact of the tool with the working surface. This tool enables the work on flat or curved surfaces of currently up to two and a half meters in diameter. It has the advantage of avoiding fallen edges during the polishing process as well as reducing tool wear out and deformation. The functioning principle is based on the generation of a high-velocity, high-pressure, abrasive emulsion flux with radial geometry. The polishing process is repeatable by means of the control of the tool operational parameters, achieving high degrees of precision and accuracy on optical and semiconductor surfaces, with removal rates of up to 9 mm3/hour and promising excellent surface polishing qualities. An additional advantage of this new tool is the possibility to perform interferometric measurements during the polishing process without the need of dismounting the working surface. A series of advantages of this method, numerical simulations and experimental results are described.

  13. Light and velocity curve bumps for BW Vulpeculae

    International Nuclear Information System (INIS)

    Pesnell, W.D.; Cox, A.N.

    1980-01-01

    Bumps in the light and radial velocity curves of the Beta Cephei star BW Vulpeculae were modeled. Two mechanisms, a resonance phenomena and non-linear pulsations, were investigated. The resonance condition was clearly not fulfilled, the calculated period ratio being approximately 0.60, where a value of 0.50 L +- 0.03 is required for resonance. In the non-linear calculation, the bump appears, with the correct phase, but was found at an amplitude that is too large. Further, the light curve does not show any bump-like feature. The cause of the bump is the large spurious boost given the star's velocity field by the solution methods. The calculated periods of the stellar models are shorter than those of previous calculations, enhancing the possibility that these stars pulsate in a radial fundamental mode

  14. The Open Cluster Chemical Abundances and Mapping (OCCAM) Survey: Galactic Neutron CaptureAbundance Gradients

    Science.gov (United States)

    O'Connell, Julia; Frinchaboy, Peter M.; Shetrone, Matthew D.; Melendez, Matthew; Cunha, Katia; Majewski, Steven R.; Zasowski, Gail; APOGEE Team

    2017-06-01

    The evolution of elements, as a function or age, throughout the Milky Way disk provides a key constraint for galaxy evolution models. In an effort to provide these constraints, we have conducted an investigation into the r- and s- process elemental abundances for a large sample of open clusters as part of an optical follow-up to the SDSS-III/APOGEE-1 survey. Stars were identified as cluster members by the Open Cluster Chemical Abundance & Mapping (OCCAM) survey, which culls member candidates by radial velocity, metallicity and proper motion from the observed APOGEE sample. To obtain data for neutron capture elements in these clusters, we conducted a long-term observing campaign covering three years (2013-2016) using the McDonald Observatory Otto Struve 2.1-m telescope and Sandiford Cass Echelle Spectrograph (R ~ 60,000). We present Galactic neutron capture abundance gradients using 30+ clusters, within 6 kpc of the Sun, covering a range of ages from ~80 Myr to ~10 Gyr .

  15. Analytical approximations of diving-wave imaging in constant-gradient medium

    KAUST Repository

    Stovas, Alexey; Alkhalifah, Tariq Ali

    2014-01-01

    behavior and traveltime in a constant-gradient medium to develop insights into the traveltime moveout of diving waves and the image (model) point dispersal (residual) when the wrong velocity is used. The explicit formulations that describe these phenomena

  16. Patterns of radial and shoot growth of five tree species in a gamma-irradiated northern Wisconsin forest

    International Nuclear Information System (INIS)

    Zavitkovski, J.; Buech, R.R.; Rudolph, T.D.; Bauer, E.O.

    1977-01-01

    Patterns of radial and shoot growth of Abies balsamea, Acer rubrum, A. saccharum, Betula papyrifera, and Populus tremuloides were observed before (1970) and during (1972) gamma-irradiation of forest communities in the Enterprise Radiation Forest. Measurements were made during the growing season along the radiation gradient, and year days (YD) of 10, 25, 50, 75, and 90 percent of total growth were obtained by interpolation. The experimental area was divided into an ''affected'' and a ''no-effect'' zone. The boundary of the affected zone coincided with radiation exposures that effectively reduced the 1972 radial growth of a given species in comparison to the preirradiation growth. In 1970 and in the no-effect zone in 1972, shoot growth of the four broadleaved species started and terminated earlier than the radial growth. In A. balsamea the radial growth started earlier and terminated later than the shoot growth. In all five species, duration of radial growth was significantly longer than that of shoot growth. Radial growth of A. rubrum, A. saccharum, and B. papyrifera started significantly earlier in 1972 than in 1970, but no difference between years was found in the early-starting A. balsamea and P. tremuloides. In contrast, shoot growth of all five species started earlier in 1970 than in 1972. It is suggested that temperature regimes during the early developmental stages were probably responsible for the difference. In the affected zone in 1972, the radiation depressed radial growth and changed its normal pattern in all five species

  17. A study on the velocity characteristics of the spray formed by two impinging jets

    International Nuclear Information System (INIS)

    Choo, Yeon Jun; Seo, Kwi Hyun; Kang, Bo Seon

    2001-01-01

    In this study, the velocity characteristics of liquid elements formed by two impinging jets is analysed using double pulse image capturing technique. For the droplets formed by low speed impinging jets, the droplet velocities are higher with smaller azimuthal and impingement angle. The maximum droplet velocities are about 25% lower than jet velocity. With an increase of azimuthal angle, the shedding angles increases but remains lower than azimuthal angle. The velocities of ligaments formed by high speed impinging jets gradually decreases with an increase of azimuthal angle. The maximum ligament velocities are about 40% lower than jet velocity. Higher impingement angles produce lower ligament velocities. The shedding angles of ligament almost increases with the same value of azimuthal angle, which implies that the moving direction of ligaments is radial from the origin as the impingement point

  18. Velocity and turbulence at a wing-wall abutment

    Indian Academy of Sciences (India)

    Experimental investigation of the 3D turbulent flow field around a 45° wing-wall abutment, resting on a rough rigid bed, is reported. The experiment was conducted ... The shear stresses acting on the bed around the abutment are estimated from the Reynolds stresses and velocity gradients. The data presented in this study ...

  19. Modified circular velocity law

    Science.gov (United States)

    Djeghloul, Nazim

    2018-05-01

    A modified circular velocity law is presented for a test body orbiting around a spherically symmetric mass. This law exhibits a distance scale parameter and allows to recover both usual Newtonian behaviour for lower distances and a constant velocity limit at large scale. Application to the Galaxy predicts the known behaviour and also leads to a galactic mass in accordance with the measured visible stellar mass so that additional dark matter inside the Galaxy can be avoided. It is also shown that this circular velocity law can be embedded in a geometrical description of spacetime within the standard general relativity framework upon relaxing the usual asymptotic flatness condition. This formulation allows to redefine the introduced Newtonian scale limit in term of the central mass exclusively. Moreover, a satisfactory answer to the galactic escape speed problem can be provided indicating the possibility that one can also get rid of dark matter halo outside the Galaxy.

  20. Three dimensional LDV flow measurements and theoretical investigation in a radial inflow turbine scroll

    Science.gov (United States)

    Malak, Malak Fouad; Hamed, Awatef; Tabakoff, Widen

    1990-01-01

    A two-color LDV system was used in the measurement of three orthogonal velocity components at 758 points located throughout the scroll and the unvaned portion of the nozzle of a radial inflow turbine scroll. The cold flow experimental results are presented for the velocity field at the scroll tongue. In addition, a total pressure loss of 3.5 percent for the scroll is revealed from the velocity measurements combined with the static pressure readings. Moreover, the measurement of the three normal stresses of the turbulence has showed that the flow is anisotropic. Furthermore, the mean velocity components are compared with a numerical solution of the potential flow field using the finite element technique. The theoretical prediction of the exit flow angle variation agrees well with the experimental results. This variation leads to a higher scroll pattern factor which can be avoided by controlling the scroll cross sectional area distribution.