Engineering topics

Bennett, Charles L.

Publications and source records attributed to Bennett, Charles L..

25 records · Page 2

NASA NTRS1996

Report on 3 and 4-point correlation statistics in the COBE DMR anisotrophy maps

As part of the work performed under NASA contract # NAS5-32648, we have computed the 3-point and 4-point correlation functions of the COBE-DNIR 2-year and 4-year anisotropy maps. The motivation for this study was to search for evidence of non-Gaussian statistical fluctuations in the temperature maps: skewness or asymmetry in the case of the 3-point function, kurtosis in the case of the 4-point function. Such behavior would have very significant implications for our understanding of the processes of galaxy formation, because our current models of galaxy formation predict that non-Gaussian features should not be present in the DMR maps. The results of our work showed that the 3-point correlation function is consistent with zero and that the 4-point function is not a very sensitive probe of non-Gaussian behavior in the COBE-DMR data. Our computation and analysis of 3-point correlations in the 2-year DMR maps was published in the Astrophysical Journal Letters, volume 446, page L67, 1995. Our computation and analysis of 3-point correlations in the 4-year DMR maps will be published, together with some additional tests, in the June 10, 1996 issue of the Astrophysical Journal Letters. Copies of both of these papers are attached as an appendix to this report.

Hinshaw, Gary↗

NASA NTRS1996

Report on 3- and 4-Point Correlation Statistics in COBE DMR Anisotropy Maps

As part of the work performed under this contract, we have computed the 3- and 4-point correlation functions of the COBE-DMR 2-year and 4-year anisotropy maps. The results of our work showed that the 3-point correlation function is consistent with zero and that the 4-point function is not a very sensitive probe of non-Gaussian behavior in the COBE-DMR data.

Hinshaw, Gary↗

NASA NTRS1993

Design and Results of Differential Microwave Radiometers (DMR) on COBE

The Differential Microwave Radiometer (DMR) experiment on the Cosmic Background Explorer is in the final year of a scheduled four years of operation to measure large- and intermediate-scale anisotropies in the Cosmic Microwave Background (CMB). The DMR instrument comprises two independent radiometers at each of three frequencies, 31.5 53, and 90 GHz, where the frequencies were chosen to best separate the CMB from the foreground emissions from galactic dust and electrons...

Kogut, Alan J.↗

NASA NTRS1991

A search for vibrationally excited H2O at 68 GHz

Water vapor may be one of the most abundant constituents of shocked molecular clouds. The nonequilibrium distribution of population among its rotational energy states requires the observation of a multiplicity of transitions to constrain its abundance and excitation state. Flux limits are presented for emission due to the (010) 4(14) - 3(21) rotational transition of ortho-H2O at 67.804 GHz in several nebular and stellar sources. Upper limits for a beam-averaged column density of H2O in its nu2 vibrational manifold are derived for Orion BN-KL. Constraints placed by these observations on an internal source of infrared radiation in the Orion shock are discussed.

Petuchowski, Sam J.↗

NASA NTRS1991

After the first three minutes; Proceedings of the 1st Astrophysics Workshop, Univ. of Maryland, College Park, Oct. 15-17, 1990

Various papers on cosmology are presented. The general topics addressed include: spectrum and isotropy of the cosmic microwave background; the IR background: early star and galaxy formation; large scale structure from galaxy distributions; large scale structure and the intergalactic medium; velocity-dependent and velocity-independent evidence for dark matter; dark matter candidates and alternatives.

Holt, Stephen S.↗

NASA NTRS1989

The COBE cosmic 3 K anisotropy experiment: A gravity wave and cosmic string probe

Among the experiments to be carried into orbit next year, by the COBE satellite, are differential microwave radiometers. They will make sensitive all-sky maps of the temperature of the cosmic microwave background radiation at three frequencies, giving dipole, quadrupole, and higher order multipole measurements of the background radiation. The experiment will either detect, or place significant constraints on, the existence of cosmic strings and long wavelength gravity waves.

Bennett, Charles L.↗

NASA NTRS1989

Measurements of very low-sidelobe conical horn antennas

A description is given of conical corrugated-horn antennas that were designed for millimeter-wave radiometers with a 7 degree field of view, namely the Differential Microwave Radiometers (DMRs) that will measure the large-angular-scale anisotropy of the cosmic background radiation that is generally thought to be the remnant of the primeval explosion, the Big Bang. The DMRs will be part of the Cosmic Background Explorer (COBE) satellite. Measured test results for three radiometers at 31.4, 53, and 90 GHz are reported along with those of a circular polarization orthomode transducer designed and characterized at 31.4 GHz. The measurement techniques and facilities are described, including an outdoor far-field facility where measurements down to levels 90 dB below the main beam maximum were achieved. The goal of achieving very low-sidelobe antennas with good symmetry has been demonstrated.

Toral, Marco A.↗