350 research outputs found
Space charge enhanced plasma gradient effects on satellite electric field measurements
It has been recognized that plasma gradients can cause error in magnetospheric electric field measurements made by double probes. Space charge enhanced Plasma Gradient Induced Error (PGIE) is discussed in general terms, presenting the results of a laboratory experiment designed to demonstrate this error, and deriving a simple expression that quantifies this error. Experimental conditions were not identical to magnetospheric conditions, although efforts were made to insure the relevant physics applied to both cases. The experimental data demonstrate some of the possible errors in electric field measurements made by strongly emitting probes due to space charge effects in the presence of plasma gradients. Probe errors in space and laboratory conditions are discussed, as well as experimental error. In the final section, theoretical aspects are examined and an expression is derived for the maximum steady state space charge enhanced PGIE taken by two identical current biased probes
Communications Biophysics
Contains reports on five research projects.National Institutes of Health (Grant 1 P01 GM-14940-01)Joint Services Electronics Program under Contract DA 28-043-AMC-02536(E
Experimental Limit to Interstellar 244Pu Abundance
Short-lived nuclides, now extinct in the solar system, are expected to be
present in the interstellar medium (ISM). Grains of ISM origin were recently
discovered in the inner solar system and at Earth orbit and may accrete onto
Earth after ablation in the atmosphere. A favorable matrix for detection of
such extraterrestrial material is presented by deep open-sea sediments with
very low sedimentation rates (0.8-3 mm/kyr). We report here on the measurement
of Pu isotopic abundances in a 1-kg deep-sea dry sediment collected in 1992 in
the North Pacific. Our measured value of (3+-3)x10^5 244Pu atoms in the
Pu-separated fraction of the sample shows no excess over the expected
stratospheric nuclear fallout content and under reasonable assumptions we
derive a limit of 2x10^-11 g-244Pu/g-ISM for the abundance of 244Pu in ISM.Comment: 10 p, 1 fig, LateX(AASTeX) Accepted for publication in ApJL, aug 2,
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