The Relationship Between the Photopic Negative Response and Retinal Ganglion Cell Topography

Purpose: To assess the topographic relationship between the photopic negative response (PhNR) and retinal ganglion cell distribution in healthy individuals. Method: Data was recorded from 16 healthy participants. The amplitude of PhNRs obtained in response to focal long duration (250 ms) and brief flash (5 ms), red (660 nm) on blue (469 nm) stimuli of increasing size (5° - full field) were measured. The number of retinal ganglion cell receptive fields (RGCf) in each stimulus area was established from the literature and regression analysis used to determine the relationships between: PhNR amplitude and number of RGCfs stimulated, PhNR density and the RGCf density and response per RGCf as a function of eccentricity. Results: The overall amplitude of the PhNR increased with stimulus size and the response density declined from ∼0.1 μV/deg in the macular region to ∼0.003 μV/deg approximately 45° from the fovea. Contrary to expectations, the relationship between the PhNR and number of RGCf was nonlinear, the response from more eccentric neurons being about three times greater than those in the macular region. Conclusions: Although the amplitude of the PhNR broadly maps on to the topographic distribution of RGCf the increase in PhNR amplitude with increasing eccentricity is only partly explained by RGCf numbers. Increases in the PhNR amplitude may be due to topographic variations in the contributions from other non-RGC neurons, as well as eccentricity-related morphologic and physiologic differences in RGCs

Cosmic Ray Abundances of Sn, Te, Xe, and Ba Nuclei Measured on HEAO 3

Elements with even atomic number ( Z) in the interval 50 ~ Z ~ 56 have been resolved in the cosmic radiation using the Heavy Nuclei Experiment on the HEAO 3 satellite. The observation that 50Sn and 56Ba are more abundant than 52Te Elements with even atomic number ( Z) in the interval 50 ~ Z ~ 56 have been resolved in the cosmic radiation using the Heavy Nuclei Experiment on the HEAO 3 satellite. The observation that 50Sn and 56Ba are more abundant than 52Te and 54Xe is inconsistent with a purer-process cosmic-ray source. Adjustment of source abundances for an enhancement of those elements with a low first ionization potential does not change this conclusion and 54Xe is inconsistent with a purer-process cosmic-ray source. Adjustment of source abundances for an enhancement of those elements with a low first ionization potential does not change this conclusion

Applications of Abundance Data and Requirements for Cosmochemical Modeling

Understanding the evolution of the universe from Big Bang to its present state requires an understanding of the evolution of the abundances of the elements and isotopes in galaxies, stars, the interstellar medium, the Sun and the heliosphere, planets and meteorites. Processes that change the state of the universe include Big Bang nucleosynthesis, star formation and stellar nucleosynthesis, galactic chemical evolution, propagation of cosmic rays, spallation, ionization and particle transport of interstellar material, formation of the solar system, solar wind emission and its fractionation (FIP/FIT effect), mixing processes in stellar interiors, condensation of material and subsequent geochemical fractionation. Here, we attempt to compile some major issues in cosmochemistry that can be addressed with a better knowledge of the respective element or isotope abundances. Present and future missions such as Genesis, Stardust, Interstellar Pathfinder, and Interstellar Probe, improvements of remote sensing instrumentation and experiments on extraterrestrial material such as meteorites, presolar grains, and lunar or returned planetary or cometary samples will result in an improved database of elemental and isotopic abundances. This includes the primordial abundances of D, ^3He, ^4He, and ^7Li, abundances of the heavier elements in stars and galaxies, the composition of the interstellar medium, solar wind and comets as well as the (highly) volatile elements in the solar system such as helium, nitrogen, oxygen or xenon

Galactic Cosmic Ray Origins and OB Associations: Evidence from SuperTIGER Observations of Elements 26_{26}Fe through 40_{40}Zr

We report abundances of elements from $_{26}$Fe to $_{40}$Zr in the cosmic radiation measured by the SuperTIGER (Trans-Iron Galactic Element Recorder) instrument during 55 days of exposure on a long-duration balloon flight over Antarctica. These observations resolve elemental abundances in this charge range with single-element resolution and good statistics. These results support a model of cosmic-ray origin in which the source material consists of a mixture of 19$^{+11}_{-6}$\% material from massive stars and $\sim$81\% normal interstellar medium (ISM) material with solar system abundances. The results also show a preferential acceleration of refractory elements (found in interstellar dust grains) by a factor of $\sim$4 over volatile elements (found in interstellar gas) ordered by atomic mass (A). Both the refractory and volatile elements show a mass-dependent enhancement with similar slopes.Comment: 9 pages, 12 figures, 2 tables, accepted by Ap

Implications of Ultraheavy Cosmic-Ray Source Composition Derived from Observations by the HEAO-3 Heavy Nuclei Experiment

We have derived the contribution of r-process and s-process nucleosynthesis to the Cameron (1980) solar system (SS) abundances for Z~33. In the interval 34 ~Zs; 40 our HEA0-3 data extrapolated to the cosmic-ray source (CRS) fit the solar system mix better than r-process. In the interval 26 < Z < 40 the HEA0-3 results for CRS/SS follow the same general correlation with first ionization potential as for the lighter eiements although there are deviations in detail

Abundances of Cosmic Ray Nuclei for 26 ≤ Z ≤ 40 From HEAO-3 Heavy Nuclei Experiment

Individual elements in the cosmic radiation of even atomic number (Z)in the interval 26≤ Z ≤ 40 have been resolved and their relative abundances measured. The results are inconsistent with a cosmic-ray source whose composition in this charge interval is dominated by r-process nucleosynthesis

Cosmic-ray abundances of elements with atomic number 26 ≤ Z ≤ 40 measured on HEAO 3

Individual elements in the cosmic radiation of even atomic number (Z) in the interval 26 ≤ Z ≤ 40 have been resolved and their relative abundances measured. The results are inconsistent with a cosmic-ray source whose composition in this charge interval is dominated by r-process nucleosynthests. The ratios of cosmic-ray source abundances to solar system abundances in this interval follow the same general correlation with first ionization potential as for the lighter elements although there are deviations in detail

Energy Spectra of Ultraheavy Cosmic Rays Results from HEAO-3

The HEAO-3 Heavy Nuclei Experiment measures cosmic-ray energy directly in the interval 400 to ~1200 MeV/amu. Geomagnetic cutoffs can also be derived up to ~15 GV. We present preliminary rigidity spectra of various ultraheavy cosmic-ray elements relative to iron