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  • 1
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    Basic physics and cosmology from pulsar timing data (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: Radio pulsars provide unparalleled opportunities for making measurements of astrophysically interesting phenomena. The author concentrates on two particular applications of high precision timing observations of pulsars: tests of relativistic gravitation theory using the binary pulsar 1913+16, and tests of cosmological models using timing data from millisecond pulsars. New upper limits are presented for the energy density of a cosmic background of low frequency gravitational radiation.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 385-393
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    NASA TECHNICAL REPORTS
  • 2
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    High-precision timing of millisecond pulsars. II - Astrometry, orbital evolution, and eclipses of PSR 1957 + 20 (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Pulse time-of-arrival measurements have been acquired for PSR 1957 + 20 on 61 days over a 2.7 yr interval, including the times of 44 eclipse disappearance or reappearance events. The timing data provide a reliable measurement of the pulsar's proper motion, 29 +/- 3 mas/yr, at position angle 216 +/- 6 deg; this direction is in excellent agreement with that suggested by the cometlike shape of a surrounding optical emission nebula. The rate of change of the orbital period has been measured: a surprisingly large (-3.9 +/- 0.9) x 10 exp -11, implying that significant orbital evolution must take place on a time scale of 30 Myr. Finally, the present observations extend the eclipse measurements to higher frequencies and provide better statistics for these highly variable phenomena. The eclipse data are used to compute a column-density profile of free electrons in the outer parts of the eclipsing region, and thereby provide an important glimpse into the material being ablated from the companion star.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 380; 557-563
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    NASA TECHNICAL REPORTS
  • 3
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    The Parallax of Pulsar 0950+08 and the Local Free Electron Density (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: A parallax of 7.9 + or - 0.8 mas for PSR 0950+08, corresponding to a distance of 130 + or - 15 pc is reported. The measured pulse dispersion of this pulsar implies an average free electron density of 0.023 + or 0.002/cu cm along the line of sight. This parallax measurement is subject to systematic errors and questions of interpretation which are not yet fully explored.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 281-283
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  • 4
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    Heat transfer in the turbulent boundary layer with a step change in surface roughness (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Measurements of Stanton numbers, velocity profiles, temperature profiles, and turbulence intensity profiles are reported for turbulent flat plate boundary layer flows with a step change in surface roughness. The first 0.9 m length of the test surface is roughened with 1.27 mm diameter hemispheres spaced 2 base diameters apart in a staggered array. The remaining 1.5 m length is smooth. The experiments show that the step change from a rough to a smooth surface has a dramatic effect on the convective heat transfer. In many cases, the Stanton number drops below the smooth-wall correlation immediately downstream of the change in roughness. The Stanton number measurements are compared with predictions using the discrete element method with excellent results.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: ASME PAPER 91-GT-266
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  • 5
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    Two newly discovered millisecond pulsars (1993)
    In:  Other Sources
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    Publication Date: 2019-08-14
    Description: Two millisecond pulsars have been discovered in the course of systematic surveys being made with the Arecibo radio telescope. PSR J2019 + 2425 has a 3.935 ms period and moves in a nearly circular, 76.5 day orbit around a about 0.3 solar mass companion. PSR J2322 + 2057, with a period of 4.808 ms, is an isolated object. The two pulsars have unusually small period derivatives, corresponding to spin-down time scales of 7.5 +/- 0.5 and 11 +/- 5 Gyr, respectively. Both objects show pulse time-of-arrival residuals no larger than a few microseconds over many months, lending further support to the observation that 'recycled' pulsars have extremely stable rotational behavior. The timing results also confirm that physics related to the rotational dynamics of these strongly self-gravitating stars - in particular, the value of the gravitational coupling constant G - remains essentially constant over time scales comparable to the Hubble time. Dispersion measures of the two pulsars indicate distances of 0.8-0.9 kpc.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 402; 2; p. L49-L52.
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  • 6
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    Pulsar distances and the galactic distribution of free electrons (1993)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The present quantitative model for Galactic free electron distribution abandons the assumption of axisymmetry and explicitly incorporates spiral arms; their shapes and locations are derived from existing radio and optical observations of H II regions. The Gum Nebula's dispersion-measure contributions are also explicitly modeled. Adjustable quantities are calibrated by reference to three different types of data. The new model is estimated to furnish distance estimates to known pulsars that are accurate to about 25 percent.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal - Part 1 (ISSN 0004-637X); 411; 2; p. 674-684.
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  • 7
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    The turbulent thermal boundary layer with an abrupt change from a rough to a smooth wall (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The work reported here was motivated by concern over the use of smooth heat flux gages for heat transfer measurements on the otherwise rough turbine blades. Stanton number distributions and boundary layer profiles of mean temperature, mean velocity, and turbulence intensity are reported for a surface with a step change from a rough to a smooth surface. In most cases, the Stanton number immediately downstream of the change in roughness drops below the all-smooth-wall data at the same x-Reynolds number. The alignment of the smooth surface between the bases and crests of the roughness elements is shown to have only a weak effect on the Stanton number distribution. It is concluded that the use of smooth heat flux gages on otherwise rough surfaces can cause large errors. It is recommended that heat transfer data collected in this manner be used with caution.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal of Heat and Mass Transfer (ISSN 0017-9310); 36; 1; p. 141-146.
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  • 8
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    Investigation of the influence of a step change in surface roughness on turbulent heat transfer (1991)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The use is studied of smooth heat flux gages on the otherwise very rough SSME fuel pump turbine blades. To gain insights into behavior of such installations, fluid mechanics and heat transfer data were collected and are reported for a turbulent boundary layer over a surface with a step change from a rough surface to a smooth surface. The first 0.9 m length of the flat plate test surface was roughened with 1.27 mm hemispheres in a staggered, uniform array spaced 2 base diameters apart. The remaining 1.5 m length was smooth. The effect of the alignment of the smooth surface with respect to the rough surface was also studied by conducting experiments with the smooth surface aligned with the bases or alternatively with the crests of the roughness elements. Stanton number distributions, skin friction distributions, and boundary layer profiles of temperature and velocity are reported and are compared to previous data for both all rough and all smooth wall cases. The experiments show that the step change from rough to smooth has a dramatic effect on the convective heat transfer. It is concluded that use of smooth heat flux gages on otherwise rough surfaces could cause large errors.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-189531 , NAS 1.26:189531
    Format: application/pdf
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