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At least 163 records · Page 9Linked to original sources
PubMed1999

Corresponding-states approach to small-angle scattering from polydisperse ionic colloidal fluids.

Approximate scattering functions for polydisperse ionic colloidal fluids are obtained by a corresponding-states approach. This assumes that all pair correlation functions g(alpha beta)(r) of a polydisperse fluid are conformal to those of an appropriate monodisperse binary fluid (reference system) and can be generated from them by scaling transformations. The correspondence law extends to ionic fluids a scaling approximation (SA) successfully proposed for nonionic colloids in a recent paper. For the primitive model of charged hard spheres in a continuum solvent, the partial structure factors of the monodisperse binary reference system are evaluated by solving the Orstein-Zernike (OZ) integral equations coupled with an approximate closure. The SA is first tested within the mean spherical approximation (MSA) closure, which allows analytical solutions. The results are found in good overall agreement with exact MSA predictions up to relevant polidispersity. The SA is shown to be an improvement over the "decoupling approximation" extended to the ionic case. The simplicity of the SA scheme allows its application also when the OZ equations can be solved only numerically. An example is then given by using the hypernetted chain closure. Shortcomings of the SA approach, its possible use in the analysis of experimental scattering data and other related points are also briefly addressed.

Journal Article↗
PubMed2002

The asymptotic leading term of anisotropic small-angle scattering intensities. II. Non-convex particles.

For anisotropic particulate samples with scattering contrast (delta n)(2), the leading asymptotic term of the scattering intensity, along a direction q (q/q) of reciprocal space, is [4 pi(2)(delta n)(2)/q(4)]sigmaj [1/kappaG.j(+/-q)]. Here, kappaG.j(+/-q)denotes the Gaussian curvature value at the points (labelled by j) of the interphase surface where the normal is either parallel or antiparallel to q. If the Gaussian curvature vanishes at, say, the jth of these points, the corresponding contribution takes the form Cj/qalpha with 2< or = alphaj<4, Cj and alphaj being determined by the local behaviour of the surface. However, the intensity detected by a counter pixel, with opening solid angle deltaomega(q0) along (mean) direction q0, asymptotically still behaves as 4pi(2) (delta n)(2)(deltaomega(q0))/q(4), where S(deltaomega(q0)) is the area of that part of the interface that has its normals inside deltaomega(q0).

Journal Article↗
PubMed1979

Some comments on the article: 'The Structure of Human-Plasma Low-Density Lipoprotein B. An X-Ray Small-Angle Scattering Study' by K. Muller, P. Laggner, O. Glatter, and G. Kostner [Eur. J. Biochem. 82, 73--90 (1978)].

In their paper, K. Muller, P. Laggner, O. Glatter and G. Kostner report X-ray scattering and density experiments on human plasma low-density lipoprotein B, performed at different solvent densities (i.e. contrast variation method). The interpretation of the experimental data lead those authors to question the use of that method and particularly the use of the characteristic scattering functions in the study of serum lipoproteins. In the present paper it is shown that several aspects of their analysis are in fact highly questionable and that the objections raised are therefore unfounded.

Chemical Phenomena↗
PubMedDate not supplied

On the significance of very small angle scattered radiation to radiographic imaging at low energies.

We have studied the angular distribution of scattered radiation at low energies for angles between 2 degrees and 15 degrees from the outward normal to the exit surface of several phantoms, with 1 degree resolution. A cryogenically cooled germanium detector was used to measure the spectra of the scattered radiation. The differential scattering fluences, or numbers of photons per unit solid angle per unit surface area, exhibit distinct peaks at angles in the vicinity of 5 degrees, with the angular position being only slightly energy dependent but very material dependent. The scattered spectra show large changes as a function of angle, in some cases actually becoming harder than the exit unscattered beam. The significance of this behavior relative to the imaging of targets in mammography examinations is discussed.

Humans↗