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Plate 5 is incorrect. Instead of representing all cases of electron acceleration events above l erg/cm 2 s as intended and as described in the text, Plate 5 actually presents instances of electron acceleration where both the electron and ion fluxes exceed this threshold. The correct Plate 5, consisting of the probability of observing electron acceleration events above the 1 erg/cm 2 s level for southward interplanetary magnetic field independent of the ion precipitation level, is given below. Plates 1-4 and most conclusions in the paper are not affected. In particular, the observation that weak events are more widely distributed in local time than are intense events is still correct. However, the absolute probabilities of observing intense events are much higher than the incorrect version of Plate 5 indicated, and the restriction of electron acceleration events to the night-side becomes pronounced only at higher-energy flux levels (such as 5 erg/cm 2 s). Start: 12/83 End' 11/92 12 15 09 ... , ..,•. '..:• • ,, 6h e3 BX Range-99.0' 99.0 •" BY Range-99.0 ß 99.0 60 ' BZ Range-99.0 ß-1.0 00 Plate 5. The same as Plate 3, except for events with energy flux above 1.0 erg/cm 2 s.

A B S T R A C TCarbon fibers have been processed from gel spun polyacrylonitrile copolymer on a continuous carbonization line at Georgia Tech (GT) with a tensile strength in the range of 5.5-5.8 GPa, and tensile modulus in the range of 354-375 GPa. This combination of strength and modulus is the highest for any continuous fiber reported to date, and the gel spinning route provides a pathway for further improvements in strength and modulus for mass production of carbon fibers. At short gauge length, fiber tensile strength was as high as 12.1 GPa, which is the highest value ever reported for a PAN based carbon fiber. Structure analysis shows random flaws of about 2 nm size, which results in limiting tensile strength of higher than 20 GPa. Inter-planar turbostratic graphite shear modulus in high strength carbon fibers is 30 GPa, while in graphite the corresponding value is only 4 GPa.

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Polyacrylonitrile (PAN) and PAN/carbon nanotube (CNT) based carbon fibers at various CNT content have been processed and their structural development was investigated using high resolution transmission electron microscope (HR-TEM). For CNT containing carbon fibers, the CNTs act as templating agents for the graphitic carbon structure development in their vicinity at the carbonization temperature of 1450 o C, which is far below the graphitization temperature of PAN based carbon fiber (>2200 o C). The addition of 1 wt% CNT in the gel spun precursor fiber results in carbon fibers with a 68% higher thermal conductivity when compared to the control gel spun PAN based carbon fiber, and a 103% and 146% increase over commercially available IM7 and T300 carbon fibers, respectively. The electrical conductivity of the gel spun PAN/CNT based carbon fibers also showed improvement over the investigated commercially available carbon fibers. Increases in thermal and electrical conductivities are attributed to the formation of the highly ordered graphitic structure observed in the HR-TEM images. Direct observation of the graphitic structure, along with improved transport properties in the PAN/CNT based carbon fiber suggest new applications for these materials.