Biomedical subjects

E G Mullen

Publications and source records attributed to E G Mullen.

5 recordsLinked to original sources

PubMed1998

Low altitude dose measurements from APEX, CRRES and DMSP.

Dosimeter data taken on the APEX (1994-1996), CRRES (1990-1991) and DMSP (1984-1987) satellites have been used to study the low altitude (down to 350 km) radiation environment. Of special concern has been the inner edge of the inner radiation belt due to its steep gradient. We have constructed dose models of the inner edge of the belt from all three spacecraft and put them into a personal computer utility, called APEXRAD, that calculates dose for user-selected orbits. The variation of dose for low altitude, circular orbits is given as a function of altitude, inclination and particle type. Dose-depth curves show that shielding greater than approximately 1/4 in Al is largely ineffectual for low altitude orbits. The contribution of outer zone electrons to low altitude dose is shown to be important only for thin shields and to have significant variation with magnetic activity and solar cycle.

Altitude↗

PubMed1994

Solar particle events as seen on CRRES.

High energy proton detectors on the Combined Release and Radiation Effects Satellite (CRRES) were used to measure near-Earth solar protons in an 18 degrees inclination orbit between 350 km and 36000 km from July 1990 to October 1991. CRRES data from the major solar particle event on 23-25 March 1991 show conclusively that MeV solar protons can penetrate deep inside the magnetosphere (to an L-shell of 2.5 RE) when a large shock-induced Sudden Storm Commencement (SSC) occurs and significant solar particle populations are present at geosynchronous altitudes. The penetration of solar particles well inside boundaries predicted by Stormer theory occurred during every large solar event of the CRRES mission, as well as many of the smaller ones. Often the deep penetrations occurred simultaneously with the formation of new trapped radiation populations which peak at L-values between 2.3 and 4 RE (depending on particle energy) and which last from days to months.

Earth, Planet↗

PubMed1994

Microelectronics effects as seen on CRRES.

A MicroElectronics Test Package (MEP) measured total dose degradation and single event upsets (SEUs) on 60 device types on the Combined Release and Radiation Effects Satellite (CRRES) in an 18 degrees inclination orbit between 350 km and 36000 km from July 1990 to October 1991. Simultaneous measurements of the high energy particle environment were used to make a direct cause and effect comparison of the energetic particle backgrounds and microelectronic performance characteristics. The galactic cosmic ray background for the period of the CRRES mission was at a minimum. The SEUs experienced from the cosmic ray background were correspondingly few in number, but surprisingly produced an equal probability of upset over an L-shell range of 8.5 Earth radii (RE) down to less than 3.0 RE. Cosmic ray induced upset frequencies in proton sensitive chips were over 2 orders of magnitude lower than those produced by protons in the heart of the inner proton radiation belts. Multiple upsets, those produced when a single particle upsets more than one memory location, were just as common from protons as from cosmic rays.

Cosmic Radiation↗

PubMed1994

Near-Earth radiation model deficiencies as seen on CRRES.

The Space Radiation (SPACERAD) experiments on the Combined Release and Radiation Effects Satellite (CRRES) gathered 14 months of radiation particle data in an 18 degrees inclination orbit between 350 km and 36000 km from July 1990 to October 1991. When compared to the NASA radiation belt models AP8 and AE8, the data show the proton model (AP8) does not take into account a second belt formed after major solar flare/shock injection events, and the electron model (AE8) is misleading, at best, in calculating dose in near-Earth orbits. The second proton belt, although softer in energy than the main proton belt, can produce upsets in proton sensitive chips and would produce significant dose in satellites orbiting in it. The MeV electrons observed on CRRES show a significant particle population above 5 MeV (not in the AE8 model) which must be included in any meaningful dose predictions for satellites operating between L-shells of 1.7 and 3.0 RE.

Aluminum↗

PubMed1986

Placental lesions in maternal autoimmune diseases.

We have investigated the presence and clinical implications of maternal vascular lesions and chronic villitis of unknown etiology (CVUE) in 18 placentas of 15 mothers with several autoimmune diseases (AD), including, for the first time, idiopathic thrombocytopenic purpura, autoimmune thyroid diseases, and multiple sclerosis. The group with AD had significantly more maternal vascular lesions and CVUE than the control group. We did not find lesions that could be attributed to any of the diseases in particular. The histopathologic picture was similar in these diseases, although there appears to be a spectrum in severity. Placental vascular damage with deposits of IgM, C3, and C1q was more prominent in systemic lupus erythematosus and in a patient with systemic sclerosis. In both of these diseases but not in the other conditions, these lesions were related to poor fetal outcome. Although the precise role of each of these autoimmune diseases in pregnancy and fetal outcome remains to be established, there appears to be at least one link between them represented by the presence of severe acute atherosis and heavy granular vascular deposits of IgM, C3, and C1q associated in some with poor fetal outcome. The role of CVUE remains speculative.

Adult↗