Gas-injection valve operates at high speed

Fast acting gas valve is used for injecting a short pulse of gas into a vacuum chamber during plasma acceleration experiments. It contains a lightweight closure disk that is forced away from the valve seat when an electromagnetic coil is momentarily energized and immediately rebounds from a stop back onto the seat

Watching My Mind Unfold versus Yours: An fMRI Study Using a Novel Camera Technology to Examine Neural Differences in Self-projection of Self versus Other Perspectives

Self-projection, the capacity to re-experience the personal past and to mentally infer another person's perspective, has been linked to medial prefrontal cortex (mPFC). In particular, ventral mPFC is associated with inferences about one's own self, whereas dorsal mPFC is associated with inferences about another individual. In the present fMRI study, we examined self-projection using a novel camera technology, which employs a sensor and timer to automatically take hundreds of photographs when worn, in order to create dynamic visuospatial cues taken from a first-person perspective. This allowed us to ask participants to self-project into the personal past or into the life of another person. We predicted that self-projection to the personal past would elicit greater activity in ventral mPFC, whereas self-projection of another perspective would rely on dorsal mPFC. There were three main findings supporting this prediction. First, we found that self-projection to the personal past recruited greater ventral mPFC, whereas observing another person's perspective recruited dorsal mPFC. Second, activity in ventral versus dorsal mPFC was sensitive to parametric modulation on each trial by the ability to relive the personal past or to understand another's perspective, respectively. Third, task-related functional connectivity analysis revealed that ventral mPFC contributed to the medial temporal lobe network linked to memory processes, whereas dorsal mPFC contributed to the fronto-parietal network linked to controlled processes. In sum, these results suggest that ventral–dorsal subregions of the anterior midline are functionally dissociable and may differentially contribute to self-projection of self versus other

Plasmas and Controlled Nuclear Fusion

Contains reports on two research projects.U. S. Atomic Energy Commission (Contract AT(11-1)-3070

Plasmas and Controlled Nuclear Fusion

Contains reports on three research projects.U. S. Atomic Energy Commission (Contract AT(30-1)-3980

Strangelets: Who is Looking, and How?

It has been over 30 years since the first suggestion that the true ground state of cold hadronic matter might be not nuclear matter but rather strange quark matter (SQM). Ever since, searches for stable SQM have been proceeding in various forms and have observed a handful of interesting events but have neither been able to find compelling evidence for stable strangelets nor to rule out their existence. I will survey the current status and near future of such searches with particular emphasis on the idea of SQM from strange star collisions as part of the cosmic ray flux.Comment: Talk given at International Conference on Strangeness in Quark Matter, 2006. 8 pages. 1 figur

Test of Antiproton Apparatus

This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440

Plasmas and Controlled Nuclear Fusion

Contains reports on three research projects.U. S. Atomic Energy Commission (Contract AT(11-1)-3070

The Energy Spectra and Relative Abundances of Electrons and Positrons in the Galactic Cosmic Radiation

Observations of cosmic-ray electrons and positrons have been made with a new balloon-borne detector, HEAT (the "High-Energy Antimatter Telescope"), first flown in 1994 May from Fort Sumner, NM. We describe the instrumental approach and the data analysis procedures, and we present results from this flight. The measurement has provided a new determination of the individual energy spectra of electrons and positrons from 5 GeV to about 50 GeV, and of the combined "all-electron" intensity (e+ + e-) up to about 100 GeV. The single power-law spectral indices for electrons and positrons are alpha = 3.09 +/- 0.08 and 3.3 +/- 0.2, respectively. We find that a contribution from primary sources to the positron intensity in this energy region, if it exists, must be quite small.Comment: latex2e file, 30 pages, 15 figures, aas2pp4.sty and epsf.tex needed. To appear in May 10, 1998 issue of Ap.

Development of an Electrostatic Precipitator to Remove Martian Atmospheric Dust from ISRU Gas Intakes During Planetary Exploration Missions

Manned exploration missions to Mars will need dependable in situ resource utilization (ISRU) for the production of oxygen and other commodities. One of these resources is the Martian atmosphere itself, which is composed of carbon dioxide (95.3%), nitrogen (2.7%), argon (1.6%), oxygen (0.13%), carbon monoxide (0.07%), and water vapor (0.03%), as well as other trace gases. However, the Martian atmosphere also contains relatively large amounts of dust, uploaded by frequent dust devils and high Winds. To make this gas usable for oxygen extraction in specialized chambers requires the removal of most of the dust. An electrostatic precipitator (ESP) system is an obvious choice. But with an atmospheric pressure just one-hundredth of Earth's, electrical breakdown at low voltages makes the implementation of the electrostatic precipitator technology very challenging. Ion mobility, drag forces, dust particle charging, and migration velocity are also affected because the low gas pressure results in molecular mean free paths that are approximately one hundred times longer than those at Earth .atmospheric pressure. We report here on our efforts to develop this technology at the Kennedy Space Center, using gases with approximately the same composition as the Martian atmosphere in a vacuum chamber at 9 mbars, the atmospheric pressure on Mars. We also present I-V curves and large particle charging data for various versions of wire-cylinder and rod-cylinder geometry ESPs. Preliminary results suggest that use of an ESP for dust collection on Mars may be feasible, but further testing with Martian dust simulant is required

Optical Properties of Deep Ice at the South Pole - Absorption

We discuss recent measurements of the wavelength-dependent absorption coefficients in deep South Pole ice. The method uses transit time distributions of pulses from a variable-frequency laser sent between emitters and receivers embedded in the ice. At depths of 800 to 1000 m scattering is dominated by residual air bubbles, whereas absorption occurs both in ice itself and in insoluble impurities. The absorption coefficient increases approximately exponentially with wavelength in the measured interval 410 to 610 nm. At the shortest wavelength our value is about a factor 20 below previous values obtained for laboratory ice and lake ice; with increasing wavelength the discrepancy with previous measurements decreases. At around 415 to 500 nm the experimental uncertainties are small enough for us to resolve an extrinsic contribution to absorption in ice: submicron dust particles contribute by an amount that increases with depth and corresponds well with the expected increase seen near the Last Glacial Maximum in Vostok and Dome C ice cores. The laser pulse method allows remote mapping of gross structure in dust concentration as a function of depth in glacial ice.Comment: 26 pages, LaTex, Accepted for publication in Applied Optics. 9 figures, not included, available on request from [email protected]