Search NASA⌕ Search

Engineering topics

Wasserman, I.

Publications and source records attributed to Wasserman, I..

6 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Signal detection amid noise with known statistics

Conventional methods of signal detection are based on the comparison of a local signal-to-noise ratio S/N to some threshold value. We present a new method that compares instead the histogram of the data with the one expected for background noise alone. Signals are detected from discrepancies between the two. We expect it to be applicable in the detection of signals from any data whose background statistics is known. To illustrate the method, we apply it to the case of photon-limited imaging data where the underlying background is Poissonian. Numerical simulations are used to check the efficiency of our method, finding that for signals with low S/N (less than 5), it detects signals with a higher degree of reliability than the conventional method.

Zepka, A. F.↗
NASA NTRS1991

A relativistic model of pulsar polarization

The rotating vector model of pulsar polarization of Radhakrishnan and Cooke (1969) is extended here to include first-order special relativistic effects. The model predicts that the centroid of the position angle curve arrives later than the centroid of the intensity profile by 4r/c, where r is the emission radius. Application of the model to pulsars with well ordered position-angle swings and periods between 0.06 and 3.7 s give emission radii of not more than 2000 km for 0.43 and 1.4 GHz. Symmetry-breaking effects of the corotation velocity may help explain a general asymmetry found in pulsar intensity profiles and may strongly affect the intensity profiles of short-period pulsars.

Blaskiewicz, M.↗
NASA NTRS1990

Polarization of the binary radio pulsar 1913 + 16 - Constraints on geodetic precession

Using polarization data, the relative orientations of the line of sight and the pulsar's spin axis and magnetic moment are determined. The data are sensitive enough to allow detection of spin-orbit geodetic precession in a few years if the spin axis is misaligned from the orbital angular momentum vector by more than a few degrees. From the secular pulse shape changes measured by Weisberg, et al. (1989) it is concluded that the misalignment angle is no more than 15 deg but is probably more than 1 deg. A specific beaming model is proposed to account for the pulse shape changes.

Cordes, J. M.↗
NASA NTRS1989

Cyclotron resonant scattering in the spectra of gamma-ray bursts

Data on the GB880205 gamma-ray bursts are presented that have implications for the nature of gamma-ray burst sources. It is shown that cyclotron resonant scattering and Raman scattering account well for the positions, strengths, and shapes of the relative strengths of the first and second harmonics and their narrow widths. These results imply the existence of a superstrong (B of about 2 x 10 to the 12th G) magnetic field in the vicinity of the X-ray emission region of GB880205. Such a superstrong magnetic field points to a strongly magnetic neutron star as the origin of gamma-ray bursts, and to the fact that the gamma-ray sources belong to the Galaxy.

Lamb, D. Q.↗
NASA NTRS1987

Deceleration of infalling plasma in the atmospheres of accreting neutron stars. I - Isothermal atmospheres

The stopping of infalling protons in a strong magnetic field is studied in detail using linear response theory and a Monte Carlo code. The calculations include both Coulomb collisions with atmospheric electrons and collective forces due to the resonant excitation of the atmospheric electron plasma modes by the impinging protons. Graphs are presented showing how both energy and momentum are deposited in the atmosphere by the flow. A striking dependence of the deceleration on the temperature is found which distinguishes the magnetic from the nonmagnetic process.

Miller, G. S.↗