A method for estimating the bremsstrahlung dose into spacecraft from incident electrons

An approximate procedure is proposed for finding the dose from radiation belt electron-induced bremsstrahlung inside spacecraft. A good agreement (to within 10%) with the direct three-dimensional Monte-Carlo calculation is attained when the spacecraft material is homogenized. If a homogeneous slab of material is used to estimate absorbed dose inside a spacecraft, the resultant estimate proves to be up to five times as low as the result obtained using a randomly inhomogeneous distribution of spacecraft material for an electron spectrum in a geosynchronous orbit.     

Random replicators with high-order interactions

We use tools of the equilibrium statistical mechanics of disordered systems to study analytically the statistical properties of an ecosystem composed of N species interacting via random mutual interactions, as well as via deterministic self-interactions of order p>/=2. We show that the main effect of increasing the order of the interactions among the species is to make the system less competitive, in the sense that the fraction of extinct species is greatly reduced. In addition, we find that for p>2 there is a threshold value which gives a lower bound to the concentration of the surviving species, preventing then the existence of rare species and, consequently, increasing the robustness of the ecosystem to external perturbations.     

A spacecraft shielding model for calculating exposures to radiation

A spacecraft shielding model for calculating exposure to radiation is proposed. This model is based on the concept of the randomly inhomogeneous character of the material thickness distribution both in separate equipment units and the spacecraft as a whole. This concept has made it possible to obtain the shielding function of an arbitrary point in a spacecraft necessary to calculate the radiation exposure using its mean density, geometry and the ratio of the shielding function dispersion to its mean. This is constant for the spacecraft. This conclusion was verified for several Soviet and U.S.A. spacecraft, including the Space Shuttle.     

Maturation of auditory temporal integration and inhibition assessed with event-related potentials (ERPs)

Background

We examined development of auditory temporal integration and inhibition by assessing electrophysiological responses to tone pairs separated by interstimulus intervals (ISIs) of 25, 50, 100, 200, 400, and 800 ms in 28 children aged 7 to 9 years, and 15 adults.

Results

In adults a distinct neural response was elicited to tones presented at ISIs of 25 ms or longer, whereas in children this was only seen in response to tones presented at ISIs above 100 ms. In adults, late N1 amplitude was larger for the second tone of the tone pair when separated by ISIs as short as 100 ms, consistent with the perceptual integration of successive stimuli within the temporal window of integration. In contrast, children showed enhanced negativity only when tone pairs were separated by ISIs of 200 ms. In children, the amplitude of the P1 component was attenuated at ISIs below 200 ms, consistent with a refractory process.

Conclusions

These results indicate that adults integrate sequential auditory information into smaller temporal segments than children. These results suggest that there are marked maturational changes from childhood to adulthood in the perceptual processes underpinning the grouping of incoming auditory sensory information, and that electrophysiological measures provide a sensitive, non-invasive method allowing further examination of these changes.