Nearly space-filling fractal networks of carbon nanopores

Small-angle x-ray scattering, nitrogen adsorption, and scanning tunneling microscopy show that a series of activated carbons host an extended fractal network of channels with dimension D(p) = 2.8-3.0 (pore fractal), channel width 15-20 A (lower end of scaling), network diameter 3000-3400 A (upper end of scaling), and porosity of 0.3-0.6. We interpret the network as a stack of quasiplanar invasion percolation clusters, formed by oxidative removal of walls between closed voids of diameter of approximately 10 A and held in registry by fibrils of the biological precursor, and point out unique applications.

Conversion factors for the estimation of effective dose in paediatric cardiac angiography

Conversion factors, which relate the kerma-area product to effective dose, have been estimated for paediatric cardiac x-ray angiography. Monte Carlo techniques have been used to calculate the conversion factors for a wide range of projection angles for children of five ages and for adults. Correction factors are provided so that the conversion factors can be adjusted for different tube potentials and filtrations.

The sampling theorem and small-angle scattering

All information about the scattering sample obtainable from small-angle scattering data is shown to be contained in the discrete measured points of a scattering curve distorted by arbitrary collimation conditions, provided that the interval Δh between adjacent measured points fulfils the condition Δh ≤ π/L, where L is the largest correlation distance in the sample; h = 4πλ −1sinθ; λ is the scattered wavelength; and 2θ is the scattering angle. A simple technique has been developed for separation of part of the noise. It is shown that if the total time for measuring a scattering curve is held constant, a scattering curve recorded with Δh equal to the sampling-point interval π/L gives results like those obtained for a scattering curve recorded with a measured point distance smaller than that sampling-point interval. Therefore, Δh should be chosen to be small enough to guarantee that Δh ≤ π/L. Furthermore, a technique has been developed to calculate missing data points from the measured intensities. The condition Δh ≤ π/L has been found to be important for this calculation.

Small-angle X-ray scattering from helical macromolecules

An earlier calculation of the intensity of small-angle X-ray scattering from helical filaments is extended to give an expression for the intensity from helical macromolecules with a finite cross section. The results are in quite good agreement with an experimental scattering curve for a solution of DNA molecules.