Effect of track structure and radioprotectors on the induction of oncogenic transformation in murine fibroblasts by heavy ions

The oncogenic potential of high-energy ⁵⁶Fe particles (1 GeV/nucleon) accelerated with the Alternating Gradient Synchrotron at the Brookhaven National Laboratory was examined utilizing the mouse C3H 10T1/2 cell model. The dose-averaged LET for high-energy ⁵⁶Fe is estimated to be 143 keV/μm with the exposure conditions used in this study. For ⁵⁶Fe ions, the maximum relative biological effectiveness (RBE_max) values for cell survival and oncogenic transformation were 7.71 and 16.5 respectively. Compared to 150 keV/μm ⁴He nuclei, high-energy ⁵⁶Fe nuclei were significantly less effective in cell killing and oncogenic induction. The prostaglandin E₁ analog misoprostol, an effective oncoprotector of C3H 10T1/2 cells exposed to X rays, was evaluated for its potential as a radioprotector of oncogenic transformation with high-energy ⁵⁶Fe. Exposure of cells to misoprostol did not alter ⁵⁶Fe cytotoxicity or the rate of ⁵⁶Fe-induced oncogenic transformation.     

Clinorotation reduces number, but not size, of cartilaginous nodules formed in micromass cultures of mouse limbbud cells.

In previous studies we used a ground based model to investigate the cellular responses to microgravity by exposing micromass cultures of embryonic limb cells to simulated weightlessness on a clinostat. Cultures set up in T-flasks and rotated at 30 rpm showed that clinostatted cultures had less chondrocyte differentiation than stationary or rotation controls, as assessed by number of nodules/culture stained with cartilage specific Alcian blue. In the current study, nodule size and shape of these nodules was assessed by interactive measurement of area, perimeter, circularity, and equivalent diameters, using the Optimas imaging software. Results show no significant difference in any of the measurements, indicating that clinorotation has no effect on expansion of the nodules either by differentiation of cells within the nodule, or by recruitment of cells into the nodule. The reduction in number of nodules without an alteration in size and shape indicates that the effect of simulated microgravity is to reduce the cell interactions required for the initial condensation of cells into a nodule, probably by interference with cell adhesion molecules.     

EXOSAT LE-CMA observations of the Vela supernova remnant

Presented here are Exosat LE1-CMA images of fields in the Vela SNR. Soft X-ray emission is observed in the north of the remnant indicating a filamentry structure. No X-ray emission was seen in two fields to the west and south-west which have optical filaments but were not studied by Einstein. The Vela pulsar is observed and is significantly broader than a point source indicating the presence of a small nebula as seen by the Einstein HRI. The flux seen from the point source in the CMA is consistent with blackbody radiation from a 10⁶ degree neutron star of approx. 10 km radius. A bright ridge of emission is seen north of the pulsar which may be part of the extended synchroton nebula seen in the 2–10 keV range.     

New evidence for strong non-thermal effects in Tycho’s supernova remnant

For the case of Tycho’s supernova remnant (SNR), we present the relation between the blast wave and contact discontinuity radii calculated within the nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs. It is demonstrated that these radii are confirmed by recently published Chandra measurements which show that the observed contact discontinuity radius is very close to the shock radius. Therefore a consistent explanation of these observations can be given in terms of efficient CR acceleration which makes the medium more compressible.     

Tissue responses to low protracted doses of high LET radiations or photons: early and late damage relevant to radio-protective countermeasures.

Early and late murine tissue responses to single or fractionated low doses of heavy charged particles, fission-spectrum neutrons or gamma rays are considered. Damage to the hematopoietic system is emphasized, but results on acute lethality, host response to challenge with transplanted leukemia cells and life-shortening are presented. Low dose rates per fraction were used in some neutron experiments. Split-dose lethality studies (LD 50/30) with fission neutrons indicated greater accumulation of injury during a 9 fraction course (over 17 days) than was the case for gamma-radiation. When total doses of 96 or 247 cGy of neutrons or gamma rays were given as a single dose or in 9 fractions, a significant sparing effect on femur CFU-S depression was observed for both radiation qualities during the first 11 days, but there was not an earlier return to normal with dose fractionation. During the 9 fraction sequence, a significant sparing effect of low dose rate on CFU-S depression was observed in both neutron and gamma-irradiated mice. CFU-S content at the end of the fractionation sequence did not correlate with measured LD 50/30. Sustained depression of femur and spleen CFU-S and a significant thrombocytopenia were observed when a total neutron dose of 240 cGy was given in 72 fractions over 24 weeks at low dose rates. The temporal aspects of CFU-S repopulation were different after a single versus fractionated neutron doses. The sustained reduction in the size of the CFU-S population was accompanied by an increase in the fraction in DNA synthesis. The proliferation characteristics and effects of age were different for radial CFU-S population closely associated with bone, compared with the axial population that can be readily aspirated from the femur. In aged irradiated animals, the CFU-S proliferation/redistribution response to typhoid vaccine showed both an age and radiation effect. After high single doses of neutrons or gamma rays, a significant age- and radiation-related deficiency in host defense mechanisms was detected by a shorter mean survival time following challenge with transplantable leukemia cells. Comparison of dose-response curves for life shortening after irradiation with fission-spectrum neutrons or high energy silicon particles indicated high initial slopes for both radiation qualities at low doses, but for higher doses of silicon, the effect per Gy decreased to a value similar to that for gamma rays. The two component life-shortening curve for silicon particles has implications for the potential efficacy of radioprotectants. Recent studies on protection against early and late effects by aminothiols, prostaglandins, and other compounds are discussed.     

A Simple Real-Time Incoherent Optical Correlator

The Theory and experimental results of a simple optical correlator are given. The optical components consist only of an incoherent source, condensing, collimating, and transforming lenses, and a photodetector. For real-time operation, a reference signal on a photographic transparency is correlated with an unknown signal on an ultrasonic light modulator. The output is a function of time proportional to the correlation function's amplitude rather than the squared amplitude generated by other optical correlators. When used for correlation in radar signal processing, the optical processor may be used for both pulse coding and decoding (pulse expansion and compression) and the decoded signal is shown to be described by Woodward's ambiguity function. The experimental results demonstrated the validity of the theory in both real and scaled time. However, developmental work is still required to improve the operation.     

On the Radar Echo from Aircraft

The nonstationarity of the low-frequency radar echo envelope observed from an aircraft is shown and a simple model of the echo is suggested. This model, devised specifically for simulation studies using computers, reproduces the characteristics of the observed envelope, demonstrating the correlation between the observed nonstationarity and aircraft motion relative to the receiver.     

Plasma observations in the auroral and polar cap region

The last decade has seen a period of rapid growth in our understanding of the processes which occur in the auroral regions. Much of our understanding is based on the copious new observations which have been made available in the auroral community. The present work is a short overview of the plasma conditions which obtain throughout much of the auroral region. It covers the diffuse and discrete auroral electron precipitation in the morning and evening oval, cusp, and polar cap. The ionospheric ion outflow throughout the high latitude regime is also described and related to the electron observations.